Positive electrode active substance for secondary cell and method for producing same

Abstract

A positive electrode active substance for a secondary cell, where the positive electrode active substance is capable of suppressing adsorption of water effectively in order to obtain a high-performance lithium ion secondary cell or sodium ion secondary cell. The positive electrode active substance contains 0.3 to 5 mass % of graphite, 0.1 to 4 mass % of carbon obtained by carbonizing a water-soluble carbon material, or 0.1 to 5 mass % of a metal fluoride is supported on a composite containing a compound which contains at least iron or manganese, where the compound is represented by formula (A) LiFe.sub.aMn.sub.bM.sub.cPO.sub.4, formula (B) Li.sub.2Fe.sub.dMn.sub.eN.sub.fSiO.sub.4, or formula (C) NaFe.sub.gMn.sub.hQ.sub.iPO.sub.4, and carbon obtained by carbonizing a cellulose nanofiber.

Claims

1. A positive electrode active substance, comprising: a pyrolyzed composite of a compound of formula (A), (B), or (C); carbon obtained by carbonizing a cellulose nanofiber; and one material selected from the group consisting of 0.3 to 5 mass % of graphite, 0.1 to 4 mass % of carbon obtained by carbonizing a water-soluble carbon material, and 0.1 to 5 mass % of a metal fluoride:
LiFe.sub.aMn.sub.bM.sup.1.sub.cPO.sub.4  (A) wherein M.sup.1 represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd, and a, b, and c each represent a number satisfying 0.1≤a≤0.9, 0.1≤b≤0.9, 0<c≤0.1, 2a+2b+(valence of M.sup.1)×c=2;
Li.sub.2Fe.sub.dMn.sub.eM.sup.2.sub.fSiO.sub.4  (B) wherein M.sup.2 represents Al, Zn, V, or Zr, and d, e, and f each represent a number satisfying 0.1≤d≤0.6, 0.1≤e≤0.6, 0.05≤f≤0.4, 2d+2e+(valence of M.sup.2)×f=2; and
NaFe.sub.gMn.sub.hQ.sub.iPO.sub.4  (C) wherein Q represents Mg, Ca, Co, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd, and g, h, and i each represent a number satisfying 0<g≤1, 0.5≤h<1, 0<i≤0.3, 2g+2h+(valence of Q)×i=2; wherein the compound of formula (A), (B) or (C) has an olivine-type structure, and a surface of the compound of formula (A), (B), or (C) is completely covered by the carbon obtained by carbonizing a cellulose nanofiber and the graphite, carbonized product of the water-soluble carbon material or metal fluoride.

2. The positive electrode active substance according to claim 1, wherein an amount of the carbon obtained by carbonizing a cellulose nanofiber is 0.5 to 15 mass % expressed in terms of carbon atoms.

3. The positive electrode active substance according to claim 1, which comprises 0.3 to 5 mass % of graphite and is obtained by adding the graphite to the compound of formula (A), (B), or (C); and carbon obtained by carbonizing a cellulose nanofiber and conducting mixing treatment for 6 to 90 minutes while applying compressive force and shear force, wherein a mass ratio of an amount of the graphite added to an amount of the cellulose nanofiber expressed in terms of carbon atoms, (graphite/cellulose nanofiber), is 0.08 to 6.

4. The positive electrode active substance according to claim 1, which comprises 0.1 to 4 mass % of carbon obtained by carbonizing a water-soluble carbon material and the water-soluble carbon material is supported on the composite as carbon obtained by subjecting the water-soluble carbon material and the compound of formula (A), (B), or (C); and carbon obtained by carbonizing a cellulose nanofiber to wet mixing and then carbonizing the resulting mixture.

5. The positive electrode active substance according to claim 4, wherein the water-soluble carbon material is at least one selected from the group consisting of saccharides, polyols, polyethers, and organic acids.

6. The positive electrode active substance according to claim 1, which comprises 0.1 to 5 mass % of a metal fluoride and the metal fluoride is supported on the composite by subjecting the compound of formula (A), (B), or (C); and carbon obtained by carbonizing a cellulose nanofiber and a precursor of the metal fluoride to wet mixing.

7. The positive electrode active substance according to claim 6, wherein: a metal of the metal fluoride is selected from the group consisting of lithium, sodium, magnesium, calcium, and aluminum; and a precursor of the metal fluoride comprises: a fluorine compound selected from the group consisting of ammonium fluoride, hydrofluoric acid, and hypofluorous acid; and a metal compound selected from the group consisting of metal acetates, metal nitrates, metal lactates, metal oxalates, metal hydroxides, metal ethoxides, metal isopropoxides, and metal butoxides.

8. The positive electrode active substance according to claim 1, wherein the composite comprising the compound and the carbon obtained by carbonizing a cellulose nanofiber is obtained by subjecting a slurry comprising: a lithium compound or a sodium compound; a compound comprising M.sup.1, M.sup.2 or Q.sub.i; a phosphoric acid compound or a silicic acid compound; an iron compound and a manganese compound; and a cellulose nanofiber to hydrothermal reaction.

9. A method for producing a positive electrode active substance, the positive electrode active substance comprising 0.3 to 5 mass % of graphite supported on a composite comprising: a compound of formula (A), (B), or (C):
LiFe.sub.aMn.sub.bM.sup.1.sub.cPO.sub.4  (A) wherein M.sup.1 represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd, and a, b, c each represent a number satisfying 0.1≤a<0.9, 0.1≤b≤0.9, 0<c≤0.1, 2a+2b+(valence of M.sup.1)×c=2;
Li.sub.2Fe.sub.dMn.sub.eM.sup.2.sub.fSiO.sub.4  (B) wherein M.sup.2 represents Al, Zn, V, or Zr, and d, e, and f each represent a number satisfying 0.1≤d≤0.6, 0.1≤e≤0.6, 0.05≤f≤0.4, 2d+2e+(valence of M.sup.2)×f=2; and
NaFe.sub.gMn.sub.hQ.sub.iPO.sub.4  (C) wherein Q represents Mg, Ca, Co, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd, and g, h, and i each represent a number satisfying 0<g≤1, 0.5≤h<1, 0<i≤0.3, 2g+2h+(valence of Q)×i=2; wherein the compound of formula (A), (B) or (C) has an olivine-type structure; and carbon obtained by carbonizing a cellulose nanofiber, the method comprising: (I-1) mixing a phosphoric acid compound or a silicic acid compound with a mixture (X-1) comprising: a lithium compound or a sodium compound; a compound comprising M.sup.1, M.sup.2 or Q.sub.i and a cellulose nanofiber, thereby obtaining a composite (X-1); (II-1) subjecting slurry (Y-1) comprising: the obtained composite (X-1); and a metal salt comprising an iron compound and a manganese compound to hydrothermal reaction, thereby obtaining a composite (Y-1); (III-1) adding the graphite to the obtained composite (Y-1) to conduct mixing for 6 to 90 minutes while applying compressive force and shear force, thereby obtaining a composite (Z-1); and (IV-1) pyrolyzing the obtained composite (Z-1) in a reducing atmosphere or an inert atmosphere.

10. A method for producing a positive electrode active substance, the positive electrode active substance comprising 0.1 to 4 mass % of carbon obtained by carbonizing a water-soluble carbon material, or 0.1 to 5 mass % of a metal fluoride supported on a composite comprising a compound of formula (A), (B), or (C):
LiFe.sub.aMn.sub.bM.sup.1.sub.cPO.sub.4  (A) wherein M.sup.1 represents Mg, Ca, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd, and a, b, c each represent a number satisfying 0.1≤a<0.9, 0.1≤b≤0.9, 0<c≤0.1, 2a+2b+(valence of M.sup.1)×c=2;
Li.sub.2Fe.sub.dMn.sub.eM.sup.2.sub.fSiO.sub.4  (B) wherein M.sup.2 represents Al, Zn, V, or Zr, and d, e, and f each represent a number satisfying 0.1≤d≤0.6, 0.1≤e≤0.6, 0.05≤f≤0.4, 2d+2e+(valence of M.sup.2)×2; and
NaFe.sub.gMn.sub.hQ.sub.iPO.sub.4  (C) wherein Q represents Mg, Ca, Co, Sr, Y, Zr, Mo, Ba, Pb, Bi, La, Ce, Nd, or Gd, and g, h, and i each represent a number satisfying 0<g≤1, 0.5≤h<1, 0<i≤0.3, 2g+2h+(valence of Q)×i=2; wherein the compound of formula (A), (B) or (C) has an olivine-type structure; and carbon obtained by carbonizing a cellulose nanofiber, the method comprising: (I-2) mixing a phosphoric acid compound or a silicic acid compound with a mixture (X-2) comprising: a lithium compound or a sodium compound; a compound comprising M.sup.1, M.sup.2 or Q.sub.i and a cellulose nanofiber, thereby obtaining a composite (X-2); (II-2) subjecting slurry (Y-2) comprising: the obtained composite (X-2); and a metal salt comprising an iron compound and a manganese compound to hydrothermal reaction, thereby obtaining a composite (Y-2); and (III-2) adding 0.1 to 16 mass parts of a water-soluble organic compound to the obtained composite (Y-2) based on 100 mass parts of the composite (Y-2) or adding 0.1 to 40 mass parts of a precursor of the metal fluoride to the obtained composite (Y-2) based on 100 mass parts of the composite (Y-2) and conducting wet mixing, and then pyrolyzing.

11. The positive electrode active substance according to claim 1, wherein when water is adsorbed at a temperature of 20° C. and a relative humidity of 50% until an equilibrium is achieved, when the compound comprising iron and manganese is of formula (A) or (C), the amount of the absorbed water in the positive electrode active substance is 1,200 ppm or less and when the compound comprising iron and manganese is of formula (B), the amount of the absorbed water in the positive electrode active substance is 2,500 ppm or less.

Description

EXAMPLES

(1) Hereinafter, the present invention will be described specifically based on Examples; however, the present invention is not limited to the Examples.

Example 1-1

(2) Slurry was obtained by mixing 12.72 g of LiOH.H.sub.2O, 90 mL of water, and 5.10 g of a cellulose nanofiber (CELISH KY-100G, manufactured by Daicel FineChem Ltd., fiber diameter of 4 to 100 nm, CNF for short). Subsequently, 11.53 g of an 85% phosphoric acid aqueous solution was added dropwise to the obtained slurry at 35 mL/min while the obtained slurry was stirred for 5 minutes, during which the temperature was kept at 25° C., and subsequently, the resultant mixture was stirred at a speed of 400 rpm for 12 hours under a nitrogen gas purge to obtain slurry (X.sup.11-1) (dissolved oxygen concentration of 0.5 mg/L) comprising a composite (X.sup.11-1). The slurry (X.sup.11-1) comprised 2.97 mol of lithium based on 1 mol of phosphorus.

(3) Subsequently, 4.17 g of FeSO.sub.4.7H.sub.2O and 19.29 g of MnSO.sub.4.5H.sub.2O were added to 119.4 g of the obtained slurry (X.sup.11-1), and the resultant mixture was mixed to obtain slurry (Y.sup.11-1). Subsequently, the obtained slurry (Y.sup.11-1) was put into an autoclave purged with a nitrogen gas to conduct hydrothermal reaction at 170° C. for 1 hour. The pressure in the autoclave was 0.8 MPa. A produced crystal was filtered and then washed with 12 mass parts of water based on 1 mass part of the crystal. The washed crystal was freeze-dried at −50° C. for 12 hours to obtain a composite (Y.sup.11-1) (chemical composition of compound represented by formula (A): LiFe.sub.0.2Mn.sub.0.8PO.sub.4, BET specific surface area of 21 m.sup.2/g, average particle diameter of 60 nm, amount of carbon derived from CNF of 1.5 mass %).

(4) A mixture (Y.sup.11-1) was obtained by mixing 98.0 g of the obtained composite (Y.sup.11-1) and 2.0 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance) of graphite (high-purity graphite powder, manufactured by Nippon Graphite Industries, Co., Ltd., BET specific surface area of 5 m.sup.2/g, average particle diameter of 6.1 μm) in advance. The obtained mixture (Y.sup.11-1) was put into a particle composing machine, Nobilta (NOB-130, manufactured by Hosokawa Micron Corporation, output of 5.5 kw) and was mixed under the condition of the treatment temperature at 25 to 35° C., the circumferential speed of the impeller at 30 m/s, and the treatment time for 15 minutes to obtain a preliminary particle (Y.sup.11-1) for a composite.

(5) Subsequently, the obtained preliminary particle (Y.sup.11-1) for a composite was pyrolyzed at a temperature of 750° C. for 90 minutes using an electric furnace purged with a nitrogen gas to obtain a positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=3.5 mass %) for a lithium ion secondary cell as a composite (Z.sup.11-1).

Example 1-2

(6) Slurry (X.sup.12-1) was obtained in the same manner as the slurry (X.sup.11-1) obtained in Example 1-1 except that the amount of the CNF was changed to 1.70 g, and a composite (Y.sup.12-1) (BET specific surface area of 22 m.sup.2/g, average particle diameter of 58 nm, amount of carbon derived from CNF of 0.5 mass %) was then obtained in the same manner as the composite (Y.sup.11-1) obtained in Example 1-1. Subsequently, a positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.5 mass %) for a lithium ion secondary cell was obtained using the obtained composite (Y.sup.12-1) in the same manner as in Example 1-1 except that 98.0 g of the composite (Y.sup.12-1) and 2.0 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance) of the graphite were mixed.

Example 1-3

(7) Slurry (X.sup.13-1) was obtained in the same manner as the slurry (X.sup.11-1) obtained in Example 1-1 except that the amount of the CNF was changed to 3.40 g, and a composite (Y.sup.13-1) (BET specific surface area of 21 m.sup.2/g, average particle diameter of 55 nm, amount of carbon derived from CNF of 1.0 mass %) was then obtained in the same manner as the composite (Y.sup.11-1) obtained in Example 1-1. Subsequently, a positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=3.0 mass %) for a lithium ion secondary cell was obtained using the obtained composite (Y.sup.13-1) in the same manner as in Example 1-1 except that 98.0 g of the composite (Y.sup.13-1) and 2.0 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance) of the graphite were mixed.

Example 1-4

(8) A positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=3.5 mass %) for a lithium ion secondary cell was obtained using the composite (Y.sup.11-1) obtained in Example 1-1 in the same manner as in Example 1-1 except that 98.0 g of the composite (Y.sup.11-1) and 2.0 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance) of flake graphite (manufactured by Ito Graphite Co., Ltd., BET specific surface area of 13.2 m.sup.2/g, average particle diameter of 8.6 μm) were mixed.

Example 1-5

(9) A positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.0 mass %) for a lithium ion secondary cell was obtained using the composite (Y.sup.11-1) obtained in Example 1-1 in the same manner as in Example 1-1 except that 99.5 g of the composite (Y.sup.11-1) and 0.5 g (corresponding to 0.5 mass % expressed in terms of carbon atoms in active substance) of the graphite were mixed.

Example 1-6

(10) A positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=4.5 mass %) for a lithium ion secondary cell was obtained using the composite (Y.sup.11-1) obtained in Example 1-1 in the same manner as in Example 1-1 except that 97.0 g of the composite (Y.sup.11-1) and 3.0 g (corresponding to 3.0 mass % expressed in terms of carbon atoms in active substance) of the graphite were mixed.

Example 1-7

(11) A composite (Y.sup.17-1) (chemical composition of compound represented by formula (A): LiFe.sub.0.18Mn.sub.0.80Mg.sub.0.02PO.sub.4, BET specific surface area of 21 m.sup.2/g, average particle diameter of 56 nm) was obtained using the slurry (X.sup.11-1) obtained in Example 1-1 in the same manner as in Example 1-1 except that 0.50 g of MgSO.sub.4.7H.sub.2O was added to the slurry (X.sup.11-1) in addition to 5.00 g of FeSO.sub.4.7H.sub.2O and 19.29 g of MnSO.sub.4.5H.sub.2O.

(12) Subsequently, a positive electrode active substance (LiFe.sub.0.18Mn.sub.0.80Mg.sub.0.02PO.sub.4, amount of carbon=3.5 mass %) for a lithium ion secondary cell was obtained using the obtained composite (Y.sup.17-1) in the same manner as in Example 1-1 except that 98.0 g of the composite (Y.sup.17-1) and 2.0 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance) of the graphite were mixed.

Example 1-8

(13) A composite (Y.sup.18-1) (chemical composition of compound represented by formula (A): LiFe.sub.0.18Mn.sub.0.80Zr.sub.0.01PO.sub.4, BET specific surface area of 21 m.sup.2/g, average particle diameter of 60 nm, amount of carbon derived from CNF of 1.5 mass %) was obtained using the slurry (X.sup.11-1) obtained in Example 1-1 in the same manner as in Example 1-1 except that 0.36 g of Zr(SO.sub.4).sub.2.4H.sub.2O was added to the slurry (X.sup.11-1) in addition to 5.00 g of FeSO.sub.4.7H.sub.2O and 19.29 g of MnSO.sub.4.5H.sub.2O.

(14) Subsequently, a positive electrode active substance (LiFe.sub.0.18Mn.sub.0.80Zr.sub.0.01PO.sub.4, amount of carbon=3.5 mass %) for a lithium ion secondary cell was obtained using the obtained composite (Y.sup.18-1) in the same manner as in Example 1-1 except that 98.0 g of the composite (Y.sup.18-1) and 2.0 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance) of the graphite were mixed.

Comparative Example 1-1

(15) A positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=1.5 mass %) for a lithium ion secondary cell was obtained using the composite (Y.sup.11-1) obtained in Example 1-1 in the same manner as in Example 1-1 except that the carbon source, such as graphite, other than the cellulose nanofiber was not added to the composite (Y.sup.11-1).

Comparative Example 1-2

(16) A positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=3.5 mass %) for a lithium ion secondary cell was obtained using the composite (Y.sup.11-1) obtained in Example 1-1 in the same manner as in Example 1-1 except that 98.0 g of the composite (Y.sup.11-1) and 2.0 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance) of Ketjen black (manufactured by Lion Corporation, BET specific surface area of 800 m.sup.2/g, average particle diameter of 30.0 μm) were mixed.

Comparative Example 1-3

(17) Slurry (Xc.sup.13-1) was obtained in the same manner as the slurry (X.sup.11-1) obtained in Example 1-1 except that the CNF was not used, and a composite (Y.sup.c13-1) (chemical composition of compound represented by formula (A): LiFe.sub.0.2Mn.sub.0.8PO.sub.4, BET specific surface area of 21 m.sup.2/g, average particle diameter of 60 nm, amount of carbon derived from CNF of 0.0 mass %) was then obtained in the same manner as the composite (Y.sup.11-1) obtained in Example 1-1. Subsequently, a positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.0 mass %) for a lithium ion secondary cell was obtained using the obtained primary particle (Y.sup.c13-1) in the same manner as in Example 1-1 except that 98.0 g of the composite (Y.sup.c13-1) and 2.0 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance) of the graphite were mixed.

Comparative Example 1-4

(18) A composite (Y.sup.14-1) (chemical composition of compound represented by formula (A): LiFePO.sub.4, BET specific surface area of 19 m.sup.2/g, average particle diameter of 85 nm, amount of carbon derived from CNF of 1.5 mass %) was obtained using the slurry (X.sup.11-1) obtained in Example 1-1 in the same manner as in Example 1-1 except that 27.80 g of FeSO.sub.4.7H.sub.2O was only added to the slurry (X.sup.11-1).

(19) Subsequently, a positive electrode active substance (LiFePO.sub.4, amount of carbon=3.5 mass %) for a lithium ion secondary cell was obtained using the obtained composite (Y.sup.14-1) in the same manner as in Example 1-1 except that 98.0 g of the composite (Y.sup.14-1) and 2.0 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance) of the Ketjen black were mixed.

Example 2-1

(20) Slurry (X.sup.21-1) was obtained by mixing 3.75 L of ultrapure water with 0.428 kg of LiOH.H.sub.2O and 1.40 kg of Na.sub.4SiO.sub.4.nH.sub.2O. Subsequently, the nitrogen gas purge was conducted to the obtained slurry (X.sup.21-1) to adjust the dissolved oxygen concentration to 0.5 mg/L, 1.49 kg of the CNF, 0.39 kg of FeSO.sub.4.7H.sub.2O, 0.79 kg of MnSO.sub.4.5H.sub.2O, and 0.053 kg of Zr(SO.sub.4).sub.2.4H.sub.2O were then added to the slurry (X.sup.21-1), and the resultant mixture was mixed to obtain slurry (Y.sup.21-1). Subsequently, the obtained slurry (Y.sup.21-1) was put into the autoclave purged with a nitrogen gas to conduct hydrothermal reaction at 150° C. for 12 hours. The pressure in the autoclave was 0.4 MPa. A produced crystal was filtered and then washed with 12 mass parts of water based on 1 mass part of the crystal. The washed crystal was freeze-dried at −50° C. for 12 hours to obtain a composite (Y.sup.21-1) (powder, chemical composition represented by formula (B): Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, amount of carbon derived from CNF of 7.0 mass %).

(21) The obtained composite (Y.sup.21-1) in an amount of 98.0 g was taken out and was then dry-mixed with 2.0 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance) of the graphite with a ball mill to obtain a mixture (Y.sup.21-1). Mixing treatment was conducted to the obtained mixture (Y.sup.21-1) using Nobilta (NOB-130, manufactured by Hosokawa Micron Corporation, output of 5.5 kw) at a circumferential speed of the impeller of 30 m/s for 15 minutes to obtain a preliminary particle (Y.sup.21-1) for a composite. The obtained preliminary particle (Y.sup.21-1) for a composite was pyrolyzed at 650° C. for 1 hour under a reducing atmosphere to obtain a positive electrode active substance (Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, amount of carbon=9.0 mass %) for a lithium ion secondary cell as a composite (Z.sup.21-1).

Example 2-2

(22) A positive electrode active substance (Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, amount of carbon=10.0 mass %) for a lithium ion secondary cell was obtained using the composite (Y.sup.21-1) obtained in Example 2-1 in the same manner as in Example 2-1 except that 97.0 g of the composite (Y.sup.21-1) and 3.0 g (corresponding to 3.0 mass % expressed in terms of carbon atoms in active substance) of the graphite were mixed.

Comparative Example 2-1

(23) A positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=7.0 mass %) for a lithium ion secondary cell was obtained using the composite (Y.sup.21-1) obtained in Example 2-1 in the same manner as in Example 2-1 except that the carbon source, such as graphite, other than the cellulose nanofiber was not added to the composite (Y.sup.21-1).

Example 3-1

(24) Slurry was obtained by mixing 0.60 kg of NaOH, 9.0 L of water, and 0.51 g of the CNF. Subsequently, 0.577 kg of the 85% phosphoric acid aqueous solution was added dropwise to the obtained slurry at 35 mL/min while the obtained slurry was stirred for 5 minutes, during which the temperature was kept at 25° C., and subsequently, the resultant mixture was stirred at a speed of 400 rpm for 12 hours to obtain slurry (X.sup.31-1) comprising a composite (X.sup.31-1). The slurry (X.sup.31-1) comprised 3.00 mol of sodium based on 1 mol of phosphorus. Subsequently, the obtained slurry (X.sup.31-1) was purged with the nitrogen gas to adjust the dissolved oxygen concentration to 0.5 mg/L, 0.139 kg of FeSO.sub.4.7H.sub.2O, 0.964 kg of MnSO.sub.4.5H.sub.2O, and 0.124 kg of MgSO.sub.4.7H.sub.2O were then added to the slurry (X.sup.31-1), and the resultant mixture was mixed to obtain slurry (Y.sup.31-1). Subsequently, the obtained slurry (Y.sup.31-1) was put into the autoclave purged with a nitrogen gas to conduct hydrothermal reaction at 200° C. for 3 hours. The pressure in the autoclave was 1.4 MPa. A produced crystal was filtered and then washed with 12 mass parts of water based on 1 mass part of the crystal. The washed crystal was freeze-dried at −50° C. for 12 hours to obtain a composite (Y.sup.31-1) (powder, chemical composition represented by formula (C): NaFe.sub.0.1Mn.sub.0.8Mg.sub.0.1PO.sub.4, amount of carbon derived from CNF of 1.5 mass %).

(25) The obtained composite (Y.sup.31-1) in an amount of 98.0 g was taken out and was then dry-mixed with 2.0 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance) of the graphite with the ball mill to obtain a mixture (Y.sup.31-1). Mixing treatment was conducted to the obtained mixture (Y.sup.31-1) using Nobilta (NOB-130, manufactured by Hosokawa Micron Corporation, output of 5.5 kw) at a circumferential speed of the impeller of 30 m/s for 15 minutes to obtain a preliminary particle (Y.sup.31-1) for a composite.

(26) Subsequently, the obtained preliminary particle (Y.sup.31-1) for a composite was pyrolyzed at a temperature of 700° C. for 1 hour using the electric furnace purged with a nitrogen gas to obtain a positive electrode active substance (NaFe.sub.0.1Mn.sub.0.8Mg.sub.0.1PO.sub.4, amount of carbon=3.5 mass %) for a sodium ion secondary cell.

Example 3-2

(27) A positive electrode active substance (NaFe.sub.0.1Mn.sub.0.9Mg.sub.0.1PO.sub.4, amount of carbon=4.5 mass %) for a sodium ion secondary cell was obtained using the composite (Y.sup.31-1) obtained in Example 3-1 in the same manner as in Example 3-1 except that 97.0 g of the composite (Y.sup.31-1) and 3.0 g (corresponding to 3.0 mass % expressed in terms of carbon atoms in active substance) of the graphite were mixed.

Comparative Example 3-1

(28) A positive electrode active substance (NaFe.sub.0.1Mn.sub.0.8Mg.sub.0.1PO.sub.4, amount of carbon=1.6 mass %) for a sodium ion secondary cell was obtained using the composite (Y.sup.31-1) obtained in Example 3-1 in the same manner as in Example 3-1 except that 99.9 g of the composite (Y.sup.31-1) and 0.1 g (corresponding to 0.1 mass % expressed in terms of carbon atoms in active substance) of the Ketjen black were mixed.

Comparative Example 3-2

(29) A positive electrode active substance (NaFe.sub.0.1Mn.sub.0.8Mg.sub.0.1PO.sub.4, amount of carbon=1.5 mass %) for a sodium ion secondary cell was obtained using the composite (Y.sup.31-1) obtained in Example 3-1 in the same manner as in Example 3-1 except that the carbon source, such as graphite, other than the cellulose nanofiber was not added to such composite (Y.sup.31-1).

(30) <<Measurement of Amount of Adsorbed Water>>

(31) The amount of the adsorbed water for each positive electrode active substance obtained in Examples 1-1 to 3-2 and Comparative Examples 1-1 to 3-2 was measured according to the following method.

(32) The amount of water volatilized from a start point to an end point, wherein when the positive electrode active substance (composite particle) was left to stand in an environment of a temperature of 20° C. and a relative humidity of 50% for one day to adsorb water until an equilibrium was achieved, the temperature was then raised to 150° C. where the temperature was kept for 20 minutes, and the temperature was then further raised to 250° C. where the temperature was kept for 20 minutes, the start point is defined as the time when raising the temperature was restarted from 150° C., and the end point is defined as the time when the state of the constant temperature at 250° C. was completed, was measured with a Karl Fischer moisture titrator (MKC-610, manufactured by Kyoto Electronics Manufacturing Co., Ltd.) to determine the amount of the adsorbed water in the positive electrode active substance.

(33) The results are shown in Tables 1 to 3.

(34) <<Evaluation of Charge and Discharge Properties Using Secondary Cells>>

(35) Positive electrodes for a lithium ion secondary cell or a sodium ion secondary cell were prepared using each positive electrode active substance obtained in Examples 1-1 to 3-2 and Comparative Examples 1-1 to 3-2. Specifically, the obtained positive electrode active substance, the Ketjen black, and polyvinylidene fluoride were mixed in a blending ratio of 90:3:7 in terms of a weight ratio, N-methyl-2-pyrrolidone was then added thereto, and the resultant mixture was kneaded sufficiently to prepare a positive electrode slurry. The positive electrode slurry was applied on a current collector made of aluminum foil having a thickness of 20 μm using a coating machine to conduct vacuum drying at 80° C. for 12 hours. Thereafter, it was punched in a ϕ 14 mm disk shape and was pressed using a hand press at 16 MPa for 2 minutes to produce a positive electrode.

(36) Subsequently, a coin type secondary cell was assembled using the positive electrode. As a negative electrode, lithium foil punched in a ϕ 15 mm disk shape was used. As an electrolytic solution, a solution obtained by dissolving LiPF.sub.6 (in the case of lithium ion secondary cell) or NaPF.sub.6 (in the case of sodium ion secondary cell) in a mixed solvent obtained by mixing ethylene carbonate and ethyl methyl carbonate in a volume ratio of 1:1 so that the concentration of LiPF.sub.6 or NaPF.sub.6 might be 1 mol/L was used. As a separator, a known separator such as a porous polymer film such as polypropylene was used. These cell parts were incorporated and accommodated under an atmosphere in which the dew point thereof is −50° C. or less by an ordinary method to produce the coin type secondary cell (CR-2032).

(37) Charge and discharge tests were conducted using the produced secondary cells. In the case of the lithium ion cell, the discharge capacity at 1 CA was determined setting the discharge conditions to constant current and constant voltage discharge at a current of 1 CA (330 mA/g) and a voltage of 4.5 V and setting the discharge conditions to constant current discharge at 1 CA (330 mA/g) and a final voltage of 1.5 V. In the case of the sodium ion cell, the discharge capacity at 1CA was determined setting the charge conditions to constant current and constant voltage discharge at a current of 1 CA (154 mA/g) and a voltage of 4.5 V and setting the discharge conditions to constant current discharge at 1 CA (154 mA/g) and a final voltage of 2.0 V. Further, repeated tests of 50 cycles were conducted under the similar charge-discharge conditions to determine capacity retention rates (%) according to the following formula (2). It is to be noted that all the charge and discharge tests were conducted at 30° C.
Capacity retention rate (%)=(discharge capacity after 50 cycles)/(discharge capacity after 2 cycles)×100  (2)

(38) The results are shown in Tables 1 to 3.

(39) TABLE-US-00001 TABLE 1 Example 1-1 Example 1-2 Example 1-3 Example 1-4 Example 1-5 Composite X Chemical composition of LiFe.sub.0.2Mn.sub.0.8PO.sub.4 LiFe.sub.0.2Mn.sub.0.8PO.sub.4 LiFe.sub.0.2Mn.sub.0.8PO.sub.4 LiFe.sub.0.2Mn.sub.0.8PO.sub.4 LiFe.sub.0.2Mn.sub.0.8PO.sub.4 olivine type positive electrode material Amount added to positive 98.0 98.0 98.0 98.0 99.5 electrode active substance (mass parts) Carbon source Kind Graphite*.sup.1 Graphite*.sup.1 Graphite*.sup.1 Flake graphite*.sup.2 Graphite*.sup.1 added to Specific surface area (m.sup.2/g) 5.0 5.0 5.0 13.2 5.0 composite X Amount added (mass parts) 2.0 2.0 2.0 2.0 0.5 Mechanofusion Circumferential speed of 30 30 30 30 30 treatment impeller (m/s) conditions Treatment time (min) 15 15 15 15 15 Pyrolyzing Temperature (° C.) 750 750 750 750 750 conditions Time (min) 90 90 90 90 90 Positive Oxide (mass %) 96.5 97.5 97.0 96.5 98 electrode Amount of cellulose 1.5 0.5 1.0 1.5 1.5 active nanofiber expressed in terms substance of carbon atoms (mass %) Amount of carbon source 2.0 2.0 2.0 2.0 0.5 added to composite X (mass %) Graphite/cellulose nanofiber 1.3 4.0 2.0 1.3 0.3 Tap density (g/cm.sup.3) 1.40 1.38 1.41 1.42 1.46 Amount of adsorbed water 356 384 366 372 512 (ppm) Cell 0.1 C Discharge capacity 159 153 156 157 161 (mAh/g) Capacity retention rate (%) 94 95 96 94 93 Example 1-6 Example 1-7 Example 1-8 Composite X Chemical composition of LiFe.sub.0.2Mn.sub.0.8PO.sub.4 LiFe.sub.0.18Mn.sub.0.80Mg.sub.0.02PO.sub.4 LiFe.sub.0.18Mn.sub.0.80Zr.sub.0.01PO.sub.4 olivine type positive electrode material Amount added to positive 97.0 98.0 98.0 electrode active substance (mass parts) Carbon source Kind Graphite*.sup.1 Graphite*.sup.1 Graphite*.sup.1 added to Specific surface area (m.sup.2/g) 5.0 5.0 5.0 composite X Amount added (mass parts) 3.0 2.0 2.0 Mechanofusion Circumferential speed of 30 30 30 treatment impeller (m/s) conditions Treatment time (min) 15 15 15 Pyrolyzing Temperature (° C.) 750 750 750 conditions Time (min) 90 90 90 Positive Oxide (mass %) 95.5 96.5 96.5 electrode Amount of cellulose 1.5 1.5 1.5 active nanofiber expressed in terms substance of carbon atoms (mass %) Amount of carbon source 3.0 2.0 2.0 added to composite X (mass %) Graphite/cellulose nanofiber 2.0 1.3 1.3 Tap density (g/cm.sup.3) 1.39 1.41 1.43 Amount of adsorbed water 347 361 387 (ppm) Cell 0.1 C Discharge capacity 156 157 158 (mAh/g) Capacity retention rate (%) 94 96 93 *.sup.1UP-5N manufactured by Nippon Graphite Industries, Co., Ltd. Average particle diameter of 6.1 μm *.sup.2SG-BH8 manufactured by Ito Graphite Co., Ltd. Average particle diameter of 8.6 μm

(40) TABLE-US-00002 TABLE 2 Comparative Comparative Comparative Comparative Example 1-1 Example 1-2 Example 1-3 Example 1-4 Composite X Chemical composition of olivine type LiFe.sub.0.2Mn.sub.0.8PO.sub.4 LiFe.sub.0.2Mn.sub.0.8PO.sub.4 LiFe.sub.0.2Mn.sub.0.8PO.sub.4 LiFePO.sub.4 positive electrode material Amount added to positive electrode 100.0 98.0 98.0 98.0 active substance (mass parts) Carbon source Kind None Ketjen black*.sup.3 Graphite*.sup.1 Ketjen black*.sup.3 added to Specific surface area (m.sup.2/g) 800 5.0 800 composite X Amount added (mass parts) 2.0 2.0 2.0 Mechanofusion Circumferential speed of impeller (m/s) 0 30 30 30 treatment Treatment time (min) 0 15 15 15 conditions Pyrolyzing Temperature (° C.) 750 750 750 750 conditions Time (min) 90 90 90 90 Positive Oxide (mass %) 98.5 96.5 98 96.5 electrode Amount of cellulose nanofiber expressed 1.5 1.5 0.0 1.5 active in terms of carbon atoms (mass %) substance Amount of carbon source added to 0.0 2.0 2.0 2.0 composite X (mass %) Graphite/cellulose nanofiber 0.0 1.3 — 1.3 Tap density (g/cm.sup.3) 1.16 1.38 1.4 13.6 Amount of adsorbed water (ppm) 3870 2960 391 3060 Cell 0.1 C Discharge capacity (mAh/g) 156 157 46 135 Capacity retention rate (%) 84 86 83 82 *.sup.1UP-5N manufactured by Nippon Graphite Industries, Co., Ltd. Average particle diameter of 6.1 μm *.sup.3Manufactured by Lion Corporation Average particle diameter of 30 μm

(41) TABLE-US-00003 TABLE 3 Comparative Example Example 2-1 Example 2-2 2-1 Composite X Chemical composition of olivine Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4 Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4 Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4 type positive electrode material Amount added to positive electrode 98.0 97.0 100.0 active substance (mass parts) Carbon source Kind Graphite*.sup.1 Graphite*.sup.1 None added to Specific surface area (m.sup.2/g) 5.0 5.0 composite X Amount added (mass parts) 2.0 2.0 Mechanofusion Circumferential speed of impeller 30 30 0 treatment (m/s) conditions Treatment time (min) 15 15 0 Pyrolyzing Temperature (° C.) 650 650 650 conditions Time (min) 60 60 60 Positive Oxide (mass %) 91.0 90.0 93.0 electrode active Amount of cellulose nanofiber 7.0 7.0 7.0 substance expressed in terms of carbon atoms (mass %) Amount of carbon source added to 2.0 3.0 0.0 composite X (mass %) Graphite/cellulose nanofiber 0.3 0.4 0.0 Tap density (g/cm.sup.3) 1.33 1.32 0.99 Amount of adsorbed water (ppm) 720 700 3000 Cell 0.1 C Discharge capacity (mAh/g) 214 216 201 Capacity retention rate (%) 34 35 23 Example 3-1 Example 3-2 Composite X Chemical composition of olivine NaFe.sub.0.1Mn.sub.0.8Mg.sub.0.1PO.sub.4 NaFe.sub.0.1Mn.sub.0.8Mg.sub.0.1PO.sub.4 type positive electrode material Amount added to positive electrode 98.0 97.0 active substance (mass parts) Carbon source Kind Graphite*.sup.1 Graphite*.sup.1 added to Specific surface area (m.sup.2/g) 5.0 5.0 composite X Amount added (mass parts) 2.0 3.0 Mechanofusion Circumferential speed of impeller 30 30 treatment (m/s) conditions Treatment time (min) 15 15 Pyrolyzing Temperature (° C.) 700 700 conditions Time (min) 60 60 Positive Oxide (mass %) 96.5 95.5 electrode active Amount of cellulose nanofiber 1.5 1.5 substance expressed in terms of carbon atoms (mass %) Amount of carbon source added to 2.0 3.0 composite X (mass %) Graphite/cellulose nanofiber 1.3 2.0 Tap density (g/cm.sup.3) 1.41 1.40 Amount of adsorbed water (ppm) 320 240 Cell 0.1 C Discharge capacity (mAh/g) 120 127 Capacity retention rate (%) 94 95 Comparative Example Comparative Example 3-1 3-2 Composite X Chemical composition of olivine NaFe.sub.0.1Mn.sub.0.8Mg.sub.0.1PO.sub.4 NaFe.sub.0.1Mn.sub.0.8Mg.sub.0.1PO.sub.4 type positive electrode material Amount added to positive electrode 99.9 100.0 active substance (mass parts) Carbon source Kind Ketjen black*.sup.3 None added to Specific surface area (m.sup.2/g) 800 composite X Amount added (mass parts) 0.1 Mechanofusion Circumferential speed of impeller 30 0 treatment (m/s) conditions Treatment time (min) 15 0 Pyrolyzing Temperature (° C.) 700 700 conditions Time (min) 60 60 Positive Oxide (mass %) 98.4 98.5 electrode active Amount of cellulose nanofiber 1.5 1.5 substance expressed in terms of carbon atoms (mass %) Amount of carbon source added to 0.1 0.0 composite X (mass %) Graphite/cellulose nanofiber 0.07 0.0 Tap density (g/cm.sup.3) 1.22 1.12 Amount of adsorbed water (ppm) 1650 1820 Cell 0.1 C Discharge capacity (mAh/g) 115 115 Capacity retention rate (%) 89 89 *.sup.1UP-5N manufactured by Nippon Graphite Industries, Co., Ltd. Average particle diameter of 6.1 μm *.sup.3Manufactured by Lion Corporation Average particle diameter of 30 μm

Example 4-1

(42) Slurry was obtained by mixing 12.72 g of LiOH.H.sub.2O, 90 mL of water, and 6.8 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance) of the cellulose nanofiber (CELISH KY-100G, manufactured by Daicel FineChem Ltd., fiber diameter of 4 to 100 nm, CNF for short). Subsequently, 11.53 g of the 85% phosphoric acid aqueous solution was added dropwise to the obtained slurry at 35 mL/min while the obtained slurry was stirred for 5 minutes, during which the temperature was kept at 25° C., and subsequently, the resultant mixture was stirred at a speed of 400 rpm for 12 hours under the nitrogen gas purge to obtain a mixture (X.sup.41-2a) (slurry (X.sup.41-2a), dissolved oxygen concentration of 0.5 mg/L) comprising a composite (X.sup.41-2a). The slurry (X.sup.41-2a) comprised 2.97 mol of lithium based on 1 mol of phosphorus.

(43) Subsequently, 5.56 g of FeSO.sub.4.7H.sub.2O and 19.29 g of MnSO.sub.4.5H.sub.2O were added to 121.0 g of the obtained slurry (X.sup.41-2a), and the resultant mixture was mixed to obtain slurry (Y.sup.41-2a). Subsequently, the obtained slurry (Y.sup.41-2a) was put into an autoclave to conduct hydrothermal reaction at 170° C. for 1 hour. The pressure in the autoclave was 0.8 MPa. A produced crystal was filtered and then washed with 12 mass parts of water based on 1 mass part of the crystal. The washed crystal was freeze-dried at −50° C. for 12 hours to obtain a composite (Y.sup.41-2a) (chemical composition of compound represented by formula (A): LiMn.sub.0.8Fe.sub.0.2PO.sub.4, BET specific surface area of 21 m.sup.2/g, average particle diameter of 60 nm).

(44) The obtained composite (Y.sup.41-2a) in an amount of 10 g was taken out, 0.25 g (corresponding to 1.0 mass % expressed in terms of carbon atoms in active substance) of glucose and 10 mL of water were then added thereto, and the resultant mixture was mixed, then dried at 80° C. for 12 hours, and then pyrolyzed at 700° C. for 1 hour under the reducing atmosphere to obtain a positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=3.0 mass %) for a lithium secondary cell.

Example 4-2

(45) A positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=4.0 mass %) for a lithium secondary cell was obtained in the same manner as in Example 4-1 except that the amount of glucose added to the composite (Y.sup.41-2a) was changed to 0.5 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance).

Example 4-3

(46) A positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=4.9 mass %) for a lithium secondary cell was obtained in the same manner as in Example 4-1 except that the amount of glucose added to the composite (Y.sup.41-2a) was changed to 0.75 g (corresponding to 2.9 mass % expressed in terms of carbon atoms in active substance).

Comparative Example 4-1

(47) A positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.0 mass %) for a lithium secondary cell was obtained in the same manner as in Example 4-1 except that glucose was not added.

Example 5-1

(48) Slurry was obtained by mixing 37.5 mL of ultrapure water with 4.28 g of LiOH.H.sub.2O and 13.97 g of Na.sub.4SiO.sub.4.nH.sub.2O. To the slurry, 14.9 g (corresponding to 8.0 mass % expressed in terms of carbon atoms in active substance) of the cellulose nanofiber (CELISH KY-100G, manufactured by Daicel FineChem Ltd., fiber diameter of 4 to 100 nm, CNF for short), 3.92 g of FeSO.sub.4.7H.sub.2O, 7.93 g of MnSO.sub.4.5H.sub.2O, and 0.53 g of Zr(SO.sub.4).sub.2.4H.sub.2O were added, and the resultant mixture was stirred at a speed of 400 rpm for 30 minutes, during which the temperature was kept at 25° C., to obtain slurry (Y.sup.51-2a).

(49) Subsequently, the obtained slurry (Y.sup.51-2a) was put into a synthesis container installed in a steam heating type autoclave. After the slurry was put into the synthesis container, the slurry was heated while being stirred at 150° C. for 12 hours using saturated steam obtained by heating water (dissolved oxygen concentration of less than 0.5 mg/L) with a diaphragm separation apparatus. The pressure in the autoclave was 0.4 MPa. A produced crystal was filtered and then washed with 12 mass parts of water based on 1 mass part of the crystal. The washed crystal was freeze-dried at −50° C. for 12 hours to obtain a composite (Y.sup.51-2a) (chemical composition of compound represented by formula (B): Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, BET specific surface area of 35 m.sup.2/g, average particle diameter of 50 nm).

(50) The obtained composite (Y.sup.51-2a) in an amount of 5.0 g was taken out, 0.125 g (corresponding to 1.0 mass % expressed in terms of carbon atoms in active substance) of glucose and 5 mL of water were then added thereto, and the resultant mixture was mixed, then dried at 80° C. for 12 hours, and then pyrolyzed at 650° C. for 1 hour under the reducing atmosphere to obtain a positive electrode active substance (Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, amount of carbon=9.0 mass %) for a lithium secondary cell.

Example 5-2

(51) A positive electrode active substance (Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, amount of carbon=10.0 mass %) for a lithium secondary cell was obtained in the same manner as in Example 5-1 except that the amount of glucose added to the composite (Y.sup.51-2a) was changed to 0.25 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance).

Example 5-3

(52) A positive electrode active substance (Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, amount of carbon=10.9 mass %) for a lithium secondary cell was obtained in the same manner as in Example 5-1 except that the amount of glucose added to the composite (Y.sup.51-2a) was changed to 0.375 g (corresponding to 2.9 mass % expressed in terms of carbon atoms in active substance).

Comparative Example 5-1

(53) A positive electrode active substance (Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, amount of carbon=13.7 mass %) for a lithium secondary cell was obtained in the same manner as in Example 5-1 except that the amount of glucose added to the composite (Y.sup.51-2a) was changed to 0.75 g (corresponding to 5.7 mass % expressed in terms of carbon atoms in active substance).

Comparative Example 5-2

(54) A positive electrode active substance (Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, amount of carbon=8.0 mass %) for a lithium secondary cell was obtained in the same manner as in Example 5-1 except that glucose was not added.

Example 6-1

(55) Slurry was obtained by mixing 6.00 of NaOH, 90 mL of water, and 5.10 g (corresponding to 1.3 mass % expressed in terms of carbon atoms in active substance) of the cellulose nanofiber. Subsequently, 5.77 g of the 85% phosphoric acid aqueous solution was added dropwise to the obtained slurry at 35 mL/min while the obtained slurry was stirred for 5 minutes, during which the temperature was kept at 25° C., and subsequently, the resultant mixture was stirred at a speed of 400 rpm for 12 hours to obtain slurry (X.sup.61-2a) comprising a composite (X.sup.61-2a). The slurry (X.sup.61-2a) comprised 3.00 mol of sodium based on 1 mol of phosphorus. The obtained slurry was purged with the nitrogen gas to adjust the dissolved oxygen concentration to 0.5 mg/L, and 1.39 g of FeSO.sub.4.7H.sub.2O, 9.64 g of MnSO.sub.4.5H.sub.2O, and 1.24 g of MgSO.sub.4.7H.sub.2O were then added to the slurry to obtain slurry (Y.sup.61-2a). Subsequently, the obtained slurry (Y.sup.61-2a) was put into a synthesis container which was installed in a steam heating type autoclave and which was purged with a nitrogen gas. After the slurry was put into the synthesis container, the slurry was heated while being stirred at 200° C. for 3 hours using saturated steam obtained by heating water (dissolved oxygen concentration of less than 0.5 mg/L) with the diaphragm separation apparatus. The pressure in the autoclave was 1.4 MPa. A produced crystal was filtered and then washed with 12 mass parts of water based on 1 mass part of the crystal. The washed crystal was freeze-dried at −50° C. for 12 hours to obtain a composite (Y.sup.61-2a) (chemical composition of compound represented by formula (C): NaFe.sub.0.1Mn.sub.0.8Mg.sub.0.1PO.sub.4, BET specific surface area of 15 m.sup.2/g, average particle diameter of 100 nm).

(56) The obtained composite (Y.sup.61-2a) in an amount of 5.0 g was taken out, 0.125 g (corresponding to 1.0 mass % expressed in terms of carbon atoms in active substance) of glucose and 5 mL of water were then added thereto, and the resultant mixture was mixed, then dried at 80° C. for 12 hours, and then pyrolyzed at 700° C. for 1 hour under the reducing atmosphere to obtain a positive electrode active substance (NaFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.3 mass %) for a sodium secondary cell.

Example 6-2

(57) A positive electrode active substance (NaFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=3.3 mass %) for a sodium secondary cell was obtained in the same manner as in Example 6-1 except that the amount of glucose added to the composite (Y.sup.61-2a) was changed to 0.25 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance).

Example 6-3

(58) A positive electrode active substance (NaFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=4.2 mass %) for a sodium secondary cell was obtained in the same manner as in Example 6-1 except that the amount of glucose added to the composite (Y.sup.61-2a) was changed to 0.375 g (corresponding to 2.9 mass % expressed in terms of carbon atoms in active substance).

Comparative Example 6-1

(59) A positive electrode active substance (NaFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=1.3 mass %) for a sodium secondary cell was obtained in the same manner as in Example 6-1 except that glucose was not added.

(60) <<Measurement of Amount of Adsorbed Water and Evaluation of Charge and Discharge Properties Using Secondary Cells>>

(61) The measurement of the amount of the adsorbed water and the evaluation of the charge and discharge properties using secondary cells were conducted for each positive electrode active substance obtained in Examples 4-1 to 6-3 and Comparative Examples 4-1 to 6-1 in the same manner as in Examples 1-1 to 3-2 and Comparative Examples 1-1 to 3-2.

(62) The results are shown in Tables 4 to 5.

(63) TABLE-US-00004 TABLE 4 Amount supported in 100 mass % of active substance (mass %) Water-soluble Cellulose nanofiber carbon material 250° C. (expressed in terms (expressed in terms Amount of of carbon atoms) of carbon atoms) water (ppm) Example 4-1 2.0 1.0 426 Example 4-2 2.0 2.0 356 Example 4-3 2.0 2.9 458 Comparative 2.0 0.0 2157 Example 4-1 Example 5-1 8.0 1.0 2070 Example 5-2 8.0 2.0 1570 Example 5-3 8.0 2.9 2150 Comparative 8.0 5.7 2750 Example 5-1 Comparative 8.0 0.0 3000 Example 5-2 Example 6-1 1.3 1.0 360 Example 6-2 1.3 2.0 290 Example 6-3 1.3 2.9 400 Comparative 1.3 0.0 1820 Example 6-1

(64) TABLE-US-00005 TABLE 5 Initial discharge capacity Capacity retention at 1 C (mAh/g) rate (%) Example 4-1 153 94 Example 4-2 156 95 Example 4-3 153 94 Comparative Example 4-1 151 91 Example 5-1 205 31 Example 5-2 216 33 Example 5-3 203 30 Comparative Example 5-1 188 22 Comparative Example 5-2 201 23 Example 6-1 119 93 Example 6-2 126 95 Example 6-3 118 93 Comparative Example 6-1 115 88

Example 7-1

(65) Slurry was obtained by mixing 12.72 g of LiOH.H.sub.2O, 90 mL of water, and 6.8 g (corresponding to 2.0 mass % expressed in terms of carbon atoms in active substance) of the cellulose nanofiber (CELISH KY-100G, manufactured by Daicel FineChem Ltd., fiber diameter of 4 to 100 nm, CNF for short). Subsequently, 11.53 g of the 85% phosphoric acid aqueous solution was added dropwise to the obtained slurry at 35 mL/min while the obtained slurry was stirred for 5 minutes, during which the temperature was kept at 25° C., and subsequently, the resultant mixture was stirred at a speed of 400 rpm for 12 hours under the nitrogen gas purge to obtain a mixture (X.sup.71-2b) (slurry (X.sup.71-2b), dissolved oxygen concentration of 0.5 mg/L) comprising a composite (X.sup.71-2b).

(66) The slurry (X.sup.71-2b) comprised 2.97 mol of lithium based on 1 mol of phosphorus.

(67) Subsequently, 5.56 g of FeSO.sub.4.7H.sub.2O and 19.29 g of MnSO.sub.4.5H.sub.2O were added to 121.0 g of the obtained slurry (X.sup.71-2b), and the resultant mixture was mixed to obtain slurry (Y.sup.71-2b). Subsequently, the obtained slurry (Y.sup.71-2b) was put into an autoclave to conduct hydrothermal reaction at 170° C. for 1 hour. The pressure in the autoclave was 0.8 MPa. A produced crystal was filtered and then washed with 12 mass parts of water based on 1 mass part of the crystal. The washed crystal was freeze-dried at −50° C. for 12 hours to obtain a composite (Y.sup.71-2b) (chemical composition of compound represented by formula (A): LiMn.sub.0.8Fe.sub.0.2PO.sub.4, BET specific surface area of 21 m.sup.2/g, average particle diameter of 60 nm).

(68) A composite (Y.sup.71-2b) supporting LiF was obtained by mixing 4.0 g of the obtained composite (Y.sup.71-2b), 0.033 g of LiOH, and 0.029 g (corresponding to 0.5 mass % expressed in terms of amount of LiF supported in positive electrode active substance for lithium ion secondary cell) with 5 ml of water and then stirring the resultant mixture for 1 hour. Subsequently, the composite (Y.sup.71-2b) was pyrolyzed at 700° C. for 1 hour under the reducing atmosphere to obtain a positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.0 mass %, amount of LiF=0.5 mass %) for a lithium ion secondary cell.

Example 7-2

(69) A positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.0 mass %, amount of LiF=1.0 mass %) for a lithium ion secondary cell was obtained in the same manner as in Example 7-1 except that the amount of LiOH added to the composite (Y.sup.71-2b) was changed to 0.066 g, and the amount of ammonium fluoride added to the composite (Y.sup.71-2b) was changed to 0.059 g (corresponding to 1.0 mass % expressed in terms of amount of LiF supported in positive electrode active substance for lithium ion secondary cell).

Example 7-3

(70) A positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.0 mass %, amount of LiF=2.0 mass %) for a lithium ion secondary cell was obtained in the same manner as in Example 7-1 except that the amount of LiOH added to the composite (Y.sup.71-2b) was changed to 0.132 g, and the amount of ammonium fluoride added to the composite (Y.sup.71-2b) was changed to 0.118 g (corresponding to 2.0 mass % expressed in terms of amount of LiF supported in positive electrode active substance for lithium ion secondary cell).

Example 7-4

(71) A positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.0 mass %, amount of AlF.sub.3=2.0 mass %) for a lithium ion secondary cell was obtained in the same manner as in Example 7-1 except that 0.078 g of Al(OH).sub.3 in place of LiOH added to the composite (Y.sup.71-2b) was added, and the amount of ammonium fluoride added to the composite (Y.sup.71-2b) was changed to 0.353 g (corresponding to 2.0 mass % expressed in terms of amount of AlF.sub.3 supported in positive electrode active substance for lithium ion secondary cell).

Example 7-5

(72) A positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.0 mass %, amount of MgF.sub.3=2.0 mass %) for a lithium ion secondary cell was obtained in the same manner as in Example 7-1 except that 0.277 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O in place of LiOH added to the composite (Y.sup.71-2b) was added, and the amount of ammonium fluoride added to the composite (Y.sup.71-2b) was changed to 0.236 g (corresponding to 2.0 mass % expressed in terms of amount of MgF.sub.2 supported in positive electrode active substance for lithium ion secondary cell).

Comparative Example 7-1

(73) A positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.0 mass %, amount of LiF=6.0 mass %) for a lithium ion secondary cell was obtained in the same manner as in Example 7-1 except that the amount of LiOH added to the composite (Y.sup.71-2b) was changed to 0.396 g, and the amount of ammonium fluoride added to the composite (Y.sup.71-2b) was changed to 0.353 g (corresponding to 6.0 mass % expressed in terms of amount of LiF supported in positive electrode active substance for lithium ion secondary cell).

Comparative Example 7-2

(74) A positive electrode active substance (LiFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.0 mass %, amount of metal fluoride=0.0 mass %) for a lithium ion secondary cell was obtained in the same manner as in Example 7-1 except that the metal fluoride was not added.

Example 8-1

(75) Slurry (X.sup.81-2b) was obtained by mixing 37.5 mL of ultrapure water with 4.28 g of LiOH.H.sub.2O and 13.97 g of Na.sub.4SiO.sub.4.nH.sub.2O. To the slurry (X.sup.81-2b), 14.9 g (corresponding to 7.2 mass % expressed in terms of carbon atoms in active substance) of the cellulose nanofiber (CELISH KY-100G, manufactured by Daicel FineChem Ltd., fiber diameter of 4 to 100 nm, CNF for short), 3.92 g of FeSO.sub.4.7H.sub.2O, 7.93 g of MnSO.sub.4.5H.sub.2O, and 0.53 g of Zr(SO.sub.4).sub.2.4H.sub.2O were added, and the resultant mixture was stirred at a speed of 400 rpm for 30 minutes, during which the temperature was kept at 25° C., to obtain slurry (X.sup.81-2b).

(76) Subsequently, the obtained slurry (X.sup.81-2b) was put into the synthesis container installed in the steam heating type autoclave. After the slurry was put into the synthesis container, the slurry was heated while being stirred at 150° C. for 12 hours using saturated steam obtained by heating water (dissolved oxygen concentration of less than 0.5 mg/L) with the diaphragm separation apparatus. The pressure in the autoclave was 0.4 MPa. A produced crystal was filtered and then washed with 12 mass parts of water based on 1 mass part of the crystal. The washed crystal was freeze-dried at −50° C. for 12 hours to obtain a composite (Y.sup.81-2b) (chemical composition of compound represented by formula (B): Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, BET specific surface area of 35 m.sup.2/g, average particle diameter of 50 nm).

(77) The obtained composite (Y.sup.81-2b) in an amount of 4.0 g was taken out, 0.033 g of LiOH and 0.029 g (corresponding to 0.5 mass % expressed in terms of amount of LiF supported in positive electrode active substance for lithium ion secondary cell) of ammonium fluoride, and 5 mL of water were then mixed therewith, and the resultant mixture was stirred for 1 hour and then pyrolyzed at 650° C. for 1 hour under the reducing atmosphere to obtain a positive electrode active substance (Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, amount of carbon=7.2 mass %, amount of LiF=0.5 mass %) for a lithium ion secondary cell.

Example 8-2

(78) A positive electrode active substance (Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, amount of carbon=7.2 mass %, amount of LiF=1.0 mass %) for a lithium ion secondary cell was obtained in the same manner as in Example 8-1 except that the amount of LiOH added to the composite (Y.sup.81-2b) was changed to 0.066 g, and the amount of ammonium fluoride added to the composite (Y.sup.81-2b) was changed to 0.059 g (corresponding to 1.0 mass % expressed in terms of amount of LiF supported in positive electrode active substance for lithium ion secondary cell).

Example 8-3

(79) A positive electrode active substance (Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, amount of carbon=7.2 mass %, amount of LiF=2.0 mass %) for a lithium ion secondary cell was obtained in the same manner as in Example 8-1 except that the amount of LiOH added to the composite (Y.sup.81-2b) was changed to 0.132 g, and the amount of ammonium fluoride added to the composite (Y.sup.81-2b) was changed to 0.118 g (corresponding to 2.0 mass expressed in terms of amount of LiF supported in positive electrode active substance for lithium ion secondary cell).

Example 8-4

(80) A positive electrode active substance (Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, amount of carbon=7.2 mass %, amount of AlF.sub.2=2.0 mass %) for a lithium ion secondary cell was obtained in the same manner as in Example 8-1 except that 0.078 g of Al(OH).sub.3 in place of LiOH added to the composite (Y.sup.81-2b) was added, and the amount of ammonium fluoride added to the composite (Y.sup.81-2b) was changed to 0.353 g (corresponding to 2.0 mass % expressed in terms of amount of AlF.sub.2 supported in positive electrode active substance for lithium ion secondary cell).

Example 8-5

(81) A positive electrode active substance (Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, amount of carbon=7.2 mass %, amount of MgF.sub.2=2.0 mass %) for a lithium ion secondary cell was obtained in the same manner as in Example 8-1 except that 0.277 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O in place of LiOH added to the composite (Y.sup.81-2b) was added, and the amount of ammonium fluoride added to the composite (Y.sup.81-2b) was changed to 0.236 g (corresponding to 2.0 mass % expressed in terms of amount of MgF.sub.2 supported in positive electrode active substance for lithium ion secondary cell).

Comparative Example 8-1

(82) A positive electrode active substance (Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, amount of carbon=7.2 mass %, amount of LiF=6.0 mass %) for a lithium ion secondary cell was obtained in the same manner as in Example 8-1 except that the amount of LiOH added to the composite (Y.sup.81-2b) was changed to 0.396 g, and the amount of ammonium fluoride added to the composite (Y.sup.81-2b) was changed to 0.353 g (corresponding to 6.0 mass % expressed in terms of amount of LiF supported in positive electrode active substance for lithium ion secondary cell).

Comparative Example 8-21

(83) A positive electrode active substance (Li.sub.2Fe.sub.0.28Mn.sub.0.66Zr.sub.0.03SiO.sub.4, amount of carbon=7.2 mass %, amount of metal fluoride=0.0 mass %) for a lithium ion secondary cell was obtained in the same manner as in Example 8-1 except that the metal fluoride was not added.

Example 9-1

(84) Slurry was obtained by mixing 6.00 g of NaOH, 90 mL of water, and 5.10 g (corresponding to 2.4 mass % expressed in terms of carbon atoms in active substance) of the cellulose nanofiber. Subsequently, 5.77 g of the 85% phosphoric acid aqueous solution was added dropwise to the obtained slurry at 35 mL/min while the obtained slurry was stirred for 5 minutes, during which the temperature was kept at 25° C., and subsequently, the resultant mixture was stirred at a speed of 400 rpm for 12 hours to obtain slurry (X.sup.91-2b) comprising a composite (X.sup.91-2b). The slurry (X.sup.91-2b) comprised 3.00 mol of sodium based on 1 mol of phosphorus. The obtained slurry (X.sup.91-2b) was purged with the nitrogen gas to adjust the dissolved oxygen concentration to 0.5 mg/L, and 1.39 g of FeSO.sub.4.7H.sub.2O, 9.64 g of MnSO.sub.4.5H.sub.2O, and 1.24 g of MgSO.sub.4.7H.sub.2O were then added to the slurry to obtain slurry (Y.sup.91-2b). Subsequently, the obtained slurry (Y.sup.91-2b) was put into the synthesis container which was installed in the steam heating type autoclave and which was purged with a nitrogen gas. After the slurry was put into the synthesis container, the slurry was heated while being stirred at 200° C. for 3 hours using saturated steam obtained by heating water (dissolved oxygen concentration of less than 0.5 mg/L) with the diaphragm separation apparatus. The pressure in the autoclave was 1.4 MPa. A produced crystal was filtered and then washed with 12 mass parts of water based on 1 mass part of the crystal. The washed crystal was freeze-dried at −50° C. for 12 hours to obtain a composite (Y.sup.91-2b) (chemical composition of compound represented by formula (C): NaFe.sub.0.1Mn.sub.0.8Mg.sub.0.1PO.sub.4, BET specific surface area of 15 m.sup.2/g, average particle diameter of 100 nm).

(85) The obtained composite (Y.sup.91-2b) in an amount of 4.0 g was taken out, 0.033 g of LiOH and 0.029 g (corresponding to 0.5 mass % expressed in terms of amount of LiF supported in positive electrode active substance for sodium ion secondary cell) of ammonium fluoride, and 5 mL of water were then mixed therewith, and the resultant mixture was stirred for 1 hour and then pyrolyzed at 700° C. for 1 hour under the reducing atmosphere to obtain a positive electrode active substance (NaFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.4 mass %, amount of LiF=0.5 mass %) for a sodium ion secondary cell.

Example 9-2

(86) A positive electrode active substance (NaFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.4 mass %, amount of LiF=1.0 mass %) for a sodium ion secondary cell was obtained in the same manner as in Example 9-1 except that the amount of LiOH added to the composite (Y.sup.91-2b) was changed to 0.066 g, and the amount of ammonium fluoride added to the composite (Y.sup.91-2b) was changed to 0.059 g (corresponding to 1.0 mass % expressed in terms of amount of LiF supported in positive electrode active substance for sodium ion secondary cell).

Example 9-3

(87) A positive electrode active substance (NaFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.4 mass %, amount of LiF=2.0 mass %) for a sodium ion secondary cell was obtained in the same manner as in Example 9-1 except that the amount of LiOH added to the composite (Y.sup.91-2b) was changed to 0.132 g, and the amount of ammonium fluoride added to the composite (Y.sup.91-2b) was changed to 0.118 g (corresponding to 2.0 mass % expressed in terms of amount of LiF supported in positive electrode active substance for sodium ion secondary cell).

Example 9-4

(88) A positive electrode active substance (NaFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.4 mass %, amount of AlF.sub.3=2.0 mass %) for a sodium ion secondary cell was obtained in the same manner as in Example 9-1 except that 0.078 g of Al(OH).sub.3 in place of LiOH added to the composite (Y.sup.91-2b) was added, and the amount of ammonium fluoride added to the composite (Y.sup.91-2b) was changed to 0.353 g (corresponding to 2.0 mass % expressed in terms of amount of AlF.sub.3 supported in positive electrode active substance for sodium ion secondary cell).

Example 9-5

(89) A positive electrode active substance (NaFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.4 mass %, amount of MgF.sub.3=2.0 mass %) for a sodium ion secondary cell was obtained in the same manner as in Example 9-1 except that 0.277 g of Mg(CH.sub.3COO).sub.2.4H.sub.2O in place of LiOH added to the composite (Y.sup.91-2b) was added, and the amount of ammonium fluoride added to the composite (Y.sup.91-2b) was changed to 0.236 g (corresponding to 2.0 mass % expressed in terms of amount of MgF.sub.3 supported in positive electrode active substance for sodium ion secondary cell).

Comparative Example 9-1

(90) A positive electrode active substance (NaFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.4 mass %, amount of LiF=6.0 mass %) for a sodium ion secondary cell was obtained in the same manner as in Example 9-1 except that the amount of LiOH added to the composite (Y.sup.91-2b) was changed to 0.396 g, and the amount of ammonium fluoride added to the composite (Y.sup.91-2b) was changed to 0.353 g (corresponding to 6.0 mass % expressed in terms of amount of LiF supported in positive electrode active substance for sodium ion secondary cell).

Comparative Example 9-2

(91) A positive electrode active substance (NaFe.sub.0.2Mn.sub.0.8PO.sub.4, amount of carbon=2.4 mass %, amount of metal fluoride=0.0 mass %) for a sodium ion secondary cell was obtained in the same manner as in Example 9-1 except that the metal fluoride was not added.

(92) <<Measurement of Amount of Adsorbed Water and Evaluation of Charge and Discharge Properties Using Secondary Cells>>

(93) The measurement of the amount of the adsorbed water and the evaluation of the charge and discharge properties using the secondary cells were conducted for each positive electrode active substance obtained in Examples 7-1 to 9-5 and Comparative Examples 7-1 to 9-2 in the same manner as in Examples 1-1 to 3-2 and Comparative Examples 1-1 to 3-2.

(94) The results are shown in Tables 6 to 7.

(95) TABLE-US-00006 TABLE 6 Amount supported in 100 mass % of active substance (mass %) Cellulose nanofiber 250° C. (expressed in terms Metal Amount of of carbon atoms) fluoride water (ppm) Example 7-1 2.0 LiF 0.5 928 Example 7-2 2.0 LiF 1.0 285 Example 7-3 2.0 LiF 2.0 262 Example 7-4 2.0 AlF.sub.3 2.0 321 Example 7-5 2.0 MgF.sub.2 2.0 283 Comparative 2.0 LiF 6.0 359 Example 7-1 Comparative 2.0 0.0% 2157 Example 7-2 Example 8-1 7.2 LiF 0.5 980 Example 8-2 7.2 LiF 1.0 620 Example 8-3 7.2 LiF 2.0 480 Example 8-4 7.2 AlF.sub.3 2.0 620 Example 8-5 7.2 MgF.sub.2 2.0 480 Comparative 7.2 LiF 6.0 590 Example 8-1 Comparative 7.2 0.0 3000 Example 8-2 Example 9-1 2.4 LiF 0.5 860 Example 9-2 2.4 LiF 1.0 240 Example 9-3 2.4 LiF 2.0 210 Example 9-4 2.4 AlF.sub.3 2.0 290 Example 9-5 2.4 MgF.sub.2 2.0 220 Comparative 2.4 LiF 6.0 340 Example 9-1 Comparative 2.4 0.0 1820 Example 9-2

(96) TABLE-US-00007 TABLE 7 Initial discharge capacity Capacity retention at 1 C (mAh/g) rate (%) Example 7-1 152 93 Example 7-2 150 95 Example 7-3 150 94 Example 7-4 151 94 Example 7-5 151 95 Comparative Example 7-1 110 83 Comparative Example 7-2 151 91 Example 8-1 202 34 Example 8-2 205 35 Example 8-3 210 38 Example 8-4 205 36 Example 8-5 208 38 Comparative Example 8-1 190 20 Comparative Example 8-2 201 23 Example 9-1 118 92 Example 9-2 126 95 Example 9-3 128 96 Example 9-4 126 95 Example 9-5 128 96 Comparative Example 9-1 114 88 Comparative Example 9-2 115 89

(97) From the above-mentioned results, it found that the positive electrode active substances of Examples can reduce the amount of the adsorbed water more surely and can exhibit more excellent performance in the obtained cells than the positive electrode active substances of Comparative Examples.