Method for producing active material for lithium secondary battery and method of using lithium secondary battery

Abstract

A lithium secondary battery is produced by employing a charging method where a positive electrode upon charging has a maximum achieved potential of 4.3 V (vs. Li/Li.sup.+) or lower. The lithium secondary battery contains an active material including a solid solution of a lithium transition metal composite oxide having an α-NaFeO.sub.2-type crystal structure. The solid solution has a diffraction peak observed near 20 to 30° in X-ray diffractometry using CuKα radiation for a monoclinic Li[Li.sub.1/3Mn.sub.2/3]O.sub.2-type before charge-discharge. The lithium secondary battery is charged to reach at least a region with substantially flat fluctuation of potential appearing in a positive electrode potential region exceeding 4.3 V (vs. Li/Li.sup.+) and 4.8 V (vs. Li/Li.sup.+) or lower. A dischargeable electric quantity in a potential region of 4.3 V (vs. Li/Li.sup.+) or lower is 177 mAh/g or higher.

Claims

1. A method for producing a lithium secondary battery, comprising: producing a hydroxide precursor by coprecipitation of a compound containing Co, Ni, and Mn in a solvent, wherein a hydroxide in the hydroxide precursor is expressed by M(OH).sub.2 where M is a transition metal, mixing the hydroxide precursor and a lithium compound, and calcining the mixture, thereby producing a solid solution of a lithium transition metal composite oxide, preparing the lithium secondary battery including a positive electrode having an active material comprising the solid solution of a lithium transition metal composite oxide having an α-NaFeO.sub.2 crystal structure, said solid solution having a diffraction peak observed near 20 to 30° in X-ray diffractometry using CuKα radiation for a monoclinic Li[Li.sub.1/3Mn.sub.2/3]O.sub.2 before an initial charge-discharge process, and charging the positive electrode of the lithium secondary battery in said initial charge-discharge process after preparing the lithium secondary battery and before an actual usage, the positive electrode of the lithium secondary battery being charged in said initial charge-discharge process to reach at least a region with relatively flat fluctuation of potential appearing relative to a charging electric amount in a positive electrode potential region, and exceeding 4.3 V (vs. Li/Li.sup.+) but lower than 4.8 V (vs. Li/Li.sup.+), wherein in charging the battery in the actual usage after said initial charge-discharge process, the positive electrode of the lithium secondary battery is always charged at a maximum achieved potential of 4.3V (vs. Li/Li.sup.+) or lower, and the lithium secondary battery has a dischargeable electric quantity, after being charged at 4.3 V (vs. Li/Li.sup.+) or lower, of 177 mAh/g or higher.

2. A method for producing a lithium secondary battery according to claim 1, wherein the charging to reach at least the region with substantially flat fluctuation of potential appearing in the positive electrode potential region exceeding 4.3 V (vs. Li/Li.sup.+) but lower than 4.8 V (vs. Li/Li.sup.+) to a charging electric quantity, is the initial charge-discharge process.

3. A method for producing a lithium secondary battery according to claim 1, wherein the solid solution of the lithium-transition metal composite oxide having the diffraction peak near 20 to 30° in the X-ray diffractometry using CuKα radiation for the monoclinic Li[Li.sub.1/3Mn.sub.2/3]O.sub.2 before the initial charge-discharge process has an intensity of the diffraction peak about 7% or lower relative to the diffraction peak of a (003) plane.

4. A method for producing a lithium secondary battery according to claim 3, wherein the solid solution of the lithium-transition metal composite oxide having the diffraction peak near 20 to 30° in the X-ray diffractometry using CuKα radiation for the monoclinic Li[Li.sub.1/3Mn.sub.2/3]O.sub.2 before the initial charge-discharge process has the intensity of the diffraction peak about 4 to 7% of the intensity of the diffraction peak of the (003) plane.

5. A method for producing a lithium secondary battery according to claim 1, wherein the solid solution of the lithium-transition metal composite oxide has an intensity ratio between the diffraction peaks on a (003) plane and a (104) plane measured by the X-ray diffractometry using CuKα radiation, which is I.sub.(003)/I.sub.(104)≧1.56 before the charge-discharge process and I.sub.(003)/I.sub.(104)>1 at an end of discharge.

6. A method for producing a lithium secondary battery according to claim 1, wherein the solid solution of the lithium-transition metal composite oxide has an intensity ratio between the diffraction peaks on a (003) plane and a (104) plane measured by the X-ray diffractometry using CuKα radiation, the intensity ratio at the end of discharge relative to before the initial charge-discharge step is 70% or higher.

7. A method for producing a lithium secondary battery according to claim 1, wherein the lithium secondary battery has a dischargeable electric quantity, after being charged at 4.3 V (vs. Li/Li.sup.+) or lower, of 200 mAh/g or higher.

8. A method of using a lithium secondary battery, comprising: producing a hydroxide precursor by coprecipitation of a compound containing Co, Ni, and Mn in a solvent, wherein a hydroxide in the hydroxide precursor is expressed by M(OH).sub.2 where M is a transition metal, mixing the hydroxide precursor and a lithium compound, and calcining the mixture, thereby producing a solid solution of a lithium transition metal composite oxide, preparing the lithium secondary battery to contain an active material including the solid solution of a lithium transition metal composite oxide having an α-NaFeO.sub.2 crystal structure, said solid solution having a diffraction peak observed near 20 to 30° in X-ray diffractometry using CuKα radiation for a monoclinic Li[Li.sub.1/3Mn.sub.2/3]O.sub.2 before an initial charge-discharge process, charging initially a positive electrode of the lithium secondary battery in the initial charge-discharge process after preparing the lithium secondary battery and before an actual usage, the positive electrode of the lithium secondary battery being charged in said initial charge-discharge process to reach at least a region with relatively flat fluctuation of potential appearing relative to a charging electric amount in a positive electrode potential region, and exceeding 4.3 V (vs. Li/Li.sup.+) but lower than 4.8 V (vs. Li/Li.sup.+), and in the actual usage after the initial charge-discharge process, charging the positive electrode with a maximum achieved potential of 4.3 V (vs. Li/Li.sup.+) or lower, and discharging the positive electrode with a minimum achievable potential of 2.0 V(vs. Li/Li.sup.+), wherein the lithium secondary battery has a dischargeable electric quantity, after being charged at 4.3 V (vs. Li/Li.sup.+) or lower, of 177 mAh/g or higher.

9. A method of using a lithium secondary battery according to claim 8, wherein the solid solution of the lithium-transition metal composite oxide having the diffraction peak near 20 to 30° in the X-ray diffractometry using CuKα radiation for the monoclinic Li[Li.sub.1/3Mn.sub.2/3]O.sub.2 before the initial charge-discharge process has an intensity of a diffraction peak about 7% or lower relative to the diffraction peak of a (003) plane.

10. A method of using a lithium secondary battery according to claim 8, wherein the solid solution of the lithium-transition metal composite oxide having the diffraction peak near 20 to 30° in the X-ray diffractometry using CuKα radiation for the monoclinic Li[Li.sub.1/3Mn.sub.2/3]O.sub.2 before the initial charge-discharge process has an intensity of a diffraction peak about 4 to 7% of the intensity of the diffraction peak of the (003) plane.

11. A method of using a lithium secondary battery according to claim 8, wherein the solid solution of the lithium-transition metal composite oxide has an intensity ratio between the diffraction peaks on a (003) plane and a (104) plane measured by the X-ray diffractometry using CuKα radiation, which is I.sub.(003)/I.sub.(104)≧1.56 before the initial charge-discharge process and I.sub.(003)/I.sub.(104)>1 at an end of discharge.

12. A method of using a lithium secondary battery according to claim 8, wherein the solid solution of the lithium-transition metal composite oxide has an intensity ratio between the diffraction peaks on a (003) plane and a (104) plane measured by the X-ray diffractometry using CuKα radiation, and the intensity ratio at the end of discharge relative to before the initial charge-discharge process is 70% or higher.

13. A method of using a lithium secondary battery according to claim 8, wherein the lithium secondary battery has a dischargeable electric quantity, after being charged at 4.3 V (vs. Li/Li.sup.+) or lower, of 200 mAh/g or higher.

14. A method of using a lithium secondary battery according to claim 8, wherein the charging to reach at least the region with substantially flat fluctuation of potential appearing in the positive electrode potential region exceeding 4.3 V (vs. Li/Li.sup.+) but lower than 4.8 V (vs. Li/Li.sup.+) to a charging electric quantity, is the initial charge-discharge process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: A diagram showing the technical idea and the technical scope of the present invention.

(2) FIG. 2: A diagram for explaining the technical idea of a conventional technique.

(3) FIG. 3: A view showing the crystal structure of an active material having a composition formula: Li.sub.1+(1/3)xCo.sub.1−x−yNi.sub.(1/2)yMn.sub.(2/3)x+(1/2)y (x+y≦1 and 0≦y).

(4) FIG. 4A: An X-ray diffraction pattern of an active material assumed to be LiNiO.sub.2 (simulation result close to the measurement result of the present invention).

(5) FIG. 4B: An X-ray diffraction pattern of an active material assumed to be (Li.sub.0.8Ni.sub.0.2)[Ni.sub.0.8Li.sub.0.2]O.sub.2 (simulation result close to the description of a document).

(6) FIG. 5: X-ray diffraction patterns of conventional active materials made of LiNi.sub.0.20Li.sub.0.20Mn.sub.0.60O.sub.2 and LiCo.sub.0.20Li.sub.0.27Mn.sub.0.53O.sub.2 before charge-discharge, after charge, and after discharge.

(7) FIG. 6: An X-ray diffraction pattern of the active material of Example 1 (AT06).

(8) FIG. 7: A view showing the XAFS measurement results of active materials of Examples 1 to 4 and Comparative Example 41.

(9) FIG. 8: An X-ray diffraction pattern of the active material of Comparative Example 3 (AT09).

(10) FIG. 9: A view showing the potential behaviors at the time of initial charge-discharge carried out in the lithium secondary battery production method using the active materials of Example 6 (AT17) and Comparative Example 4 (AT11).

(11) FIG. 10: A view showing the potential behaviors of lithium secondary batteries using the active materials of Example 6, Comparative Example 4, and Comparative Example 42.

(12) FIG. 11: X-ray diffraction patterns of the active material of Example 7 (AT18) before charge-discharge (synthesized sample), after charge, and after discharge.

(13) FIG. 12: X-ray diffraction patterns of the active material of Example 16 (AT33) before charge-discharge (synthesized sample), after charge, and after discharge.

(14) FIG. 13: An Li[Li.sub.1/3Mn.sub.2/3]O.sub.2(x)-LiNi.sub.1/2Mn.sub.1/2O.sub.2(y)-LiCoO.sub.2(z) type ternary phase diagram in which the discharge capacity values of active materials of Examples 1 to 44 and Comparative Examples 1 to 40 are plotted.

BEST MODE FOR CARRYING OUT THE INVENTION

(15) As described above, in the active material for a lithium secondary battery of the present invention is characterized in that in an Li[Li.sub.1/3Mn.sub.2/3]O.sub.2(x)-LiNi.sub.1/2Mn.sub.1/2O.sub.2(y)-LiCoO.sub.2(z) type ternary phase diagram, (x, y, z) is represented by values in a range present on or within a line of a heptagon (ABCDEFG) defined by the vertexes; point A(0.45, 0.55, 0), point B(0.63, 0.37, 0), point C(0.7, 0.25, 0.05), point D(0.67, 0.18, 0.15), point E(0.75, 0, 0.25), point F(0.55, 0, 0.45), and point G(0.45, 0.2, 0.35), and that the intensity ratio between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry before charge-discharge is I.sub.(003)/I.sub.(104)≧1.56 and at the end of discharge is I.sub.(003)/I.sub.(104)>1.

(16) As shown in FIG. 13 and following Table 1 and Table 2, in a case where (x, y, z) is a value in the above-mentioned range, the discharge capacity in a potential rang of 4.3 V or lower becomes 177 mAh/g or higher; however if it is out of the range, only a discharge capacity of 176 mAh/g or lower is obtained and in order to obtain an active material capable of increasing the discharge capacity, (x, y, z) needs to be in the specified range.

(17) Further, it is found that within the heptagon ABCDEFG, if (x, y, z) is in a range present on or within a line of a tetragon HIJK defined by the vertexes; point H(0.6, 0.4, 0), point I(0.67, 0.13, 0.2), point J(0.7, 0, 0.3), and point K(0.55, 0.05, 0.4), a particularly high discharge capacity (198 mAh/g or higher) can be obtained.

(18) Furthermore, with respect to the intensity ratio I.sub.(003)/I.sub.(104) between the diffraction peaks on (003) plane and (104) plane measured by X-ray diffractometry, the following can be assumed.

(19) The active material with a composition formula: Li.sub.1+(1/3)xCo.sub.1−x−yNi.sub.(1/2)yMn.sub.(2/3)x+(1/2)y (x+y≦1 and 0≦y) has a layered structure as shown in FIG. 3 and the Me.sup.3+ layer is configured by Li.sup.+, Co.sup.3+, Ni.sup.2+, and Mn.sup.4+. Further, with respect to the active material having a layered structure as shown in FIG. 3, if Ni.sup.3+ is contaminated in a portion of the Li.sup.+ layer and Li.sup.+ is contaminated in a portion of the Ni.sup.3+ layer, the intensity of I.sub.(104) is supposed to be higher. Therefore, taking up a representative layered oxide, LiNiO.sub.2 (Me.sup.3+ layer is only Ni.sup.3+), and assuming that so-called disorder phase (Li.sub.0.8Ni.sub.0.2)[Ni.sub.0.8Li.sub.0.2]O.sub.2 in which Ni.sup.3+ is contaminated in a portion of the Li.sup.+ layer and Li.sup.+ is contaminated in a portion of the Ni.sup.3+ layer is formed, the X-ray diffraction pattern is simulated by theoretical calculation and the result is shown in FIG. 4.

(20) As shown in FIG. 4A, LiNiO.sub.2 has a intensity ratio I.sub.(003)/I.sub.(104)=1.10 and the (003) diffraction peak is sufficiently high; however as shown in FIG. 4B, the intensity ratio of both is considerably changed to be I.sub.(003)/I.sub.(104)≦1 since the disorder phase in which a transition metal (Co, Ni, Mn) is contaminated in the Li layer is formed.

(21) In a conventional active material, it is supposed that such disorder phase is formed to inhibit smooth transfer of Li ion and it affects the reversible capacity.

(22) On the other hand, in the active material of the present invention, it is supposed that since I.sub.(003)/I.sub.(104)≧1.56, formation of the disorder phase is extremely slight and an excellent discharge capacity can be obtained.

(23) The following can be assumed regarding the change of the intensity ratio I.sub.(003)/I.sub.(104) of the diffraction peaks before charge-discharge and that of the diffraction peaks after charge-discharge after the active material production.

(24) Even if the intensity ratio of the diffraction peaks before charge-discharge satisfies I.sub.(003)/I.sub.(104)≧1.56, in a case where contamination of the transition metals in the Li layer occurs during discharge, the diffraction peak on (003) plane becomes broad and at the same time, the intensity ratio I.sub.(003)/I.sub.(104) becomes significantly small and in a conventional active material, as shown in FIG. 5, transcription of a view described in Non-patent Document 6, the diffraction peak on (104) plane and its intensity may be sometimes reversed.

(25) On the other hand, with respect to the active material of the present invention, as shown in Table 1, FIG. 11 and FIG. 12, I.sub.(003)/I.sub.(104)≧1.56 before charge-discharge and I.sub.(003)/I.sub.(104)>1 (I.sub.(003)/I.sub.(104)>1.3 in Examples) at the end of discharge and since the intensity of the diffraction peak on (003) plane does not reverse to that of the diffraction peak on (104) plane, it is indicated that contamination of the transition metals in the Li layer during charge-discharge does not occur and accordingly, it is supposed that a stable and high reversible capacity can be obtained. At the end of discharge, the intensity ratio I.sub.(003)/I.sub.(104) may be higher than that before charge-discharge. In a case where the intensity ratio I.sub.(003)/I.sub.(104) becomes smaller at the end of discharge than before charge-discharge, the change of the intensity ratio is preferably slight and it is more preferably within 30% of that before charge-discharge, and it is within 26% in Examples.

(26) Next, a method for producing the active material for a lithium secondary battery of the present invention will be described.

(27) Basically, the active material for a lithium secondary battery of the invention is obtained by preparing raw materials containing the metal elements (Li, Mn, Co, Ni) constituting the active material as those in the composition of the active material (oxide) of interest and calcining them. However, the amount of a Li raw material is preferable to be in excess by about 1 to 5% corresponding to the elimination of a portion of the Li raw material during calcining.

(28) In order to produce the oxide in the composition of interest, methods known are a so-called “solid-state method” involving mixing and calcining respective salts of Li, Co, Ni, and Mn, and a “coprecipitation method” involving previously preparing a coprecipitated precursor in which Co, Ni, and Mn are made to be present in each single particle and then mixing and calcining a Li salt with the precursor. In the synthesis process by the “solid-state method”, since Mn is particularly hard to uniformly form an solid solution with Co and Ni, it is difficult to obtain a sample of which the respective elements are uniformly distributed in each single particle. So far, many trials for forming a solid solution of Mn with a portion of Ni or Co by the solid-phase method have been performed and reported in documents (e.g. LiNi.sub.1−xMn.sub.xO.sub.2), it is easy to obtain a uniform phase in the atomic level by selecting the “coprecipitation method”. Therefore, in Examples described below, the “coprecipitation method” is employed.

(29) In order to produce a coprecipitated precursor, it is extremely important to make a solution from which the coprecipitated precursor is to be obtained inert atmosphere. It is because Mn tends to be oxidized among Co, Ni, and Mn and thus production of a coprecipitated hydroxide in which Co, Ni, and Mn are uniformly distributed in divalent state is not easy and consequently, uniform mixing of Co, Ni, and Mn in the atomic level tends to be insufficient. Particularly, in the composition range of the present invention, since the Mn ratio is high as compared with the Co and Ni ratios, it is moreover important to make the solution inert atmosphere. In Examples described below, bubbling of an inert gas is carried out in aqueous solutions to remove dissolved oxygen and further a reducing agent is simultaneously dropwise added.

(30) A preparation method of the above-mentioned precursor to be subjected to calcining is not particularly limited. A Li compound, a Mn compound, a Ni compound, and a Co compound may be simply mixed, or a hydroxide containing the transition metal elements may be coprecipitated in a solution and then mixed with a Li compound. In order to produce a uniform composite oxide, a method of mixing a coprecipitated hydroxide of Mn, Ni, and Co and a Li compound and calcining the mixture is preferable.

(31) Production of the above-mentioned coprecipitated hydroxide precursor is preferable to give a compound in which Mn, Ni, and Co are uniformly mixed. However, the precursor is not limited to the hydroxide but other than the hydroxide, any compound such as carbonate and citrate may be similarly employed, if the compounds are hardly soluble salts in which the elements are present uniformly in atomic level. Further, a crystallization reaction using a complexing agent may be employed to produce a precursor with a higher bulk density. At that time, since an active material with a high density and a small specific surface area can be obtained by mixing and calcining the precursor with a Li source, the energy density per electrode area can be improved.

(32) Examples of raw materials for the above-mentioned coprecipitated hydroxide precursor include, as a Mn compound, manganese oxide, manganese carbonate, manganese sulfate, manganese nitrate, and manganese acetate; as a Ni compound, nickel hydroxide, nickel carbonate, nickel sulfate, nickel nitrate, and nickel acetate; and as a Co compound, cobalt sulfate, cobalt nitrate, and cobalt acetate.

(33) As the raw materials to be used for the production of the above-mentioned coprecipitated hydroxide precursor, those in any state may be employed if they can cause precipitation reaction with an aqueous alkaline solution and preferably metal salts with high solubility.

(34) The active material for a lithium secondary battery of the present invention can be produced preferably by mixing the coprecipitated hydroxide precursor with a Li compound and thereafter carrying out heat treatment for the mixture. Use of lithium hydroxide, lithium carbonate, lithium nitrate, or lithium acetate as the Li compound makes it possible to preferably carry out the production.

(35) In the case of obtaining an active material with a high reversible capacity, selection of the calcining temperature is extremely important.

(36) If the calcining temperature is too high, the obtained active material corrupts while being accompanied with oxygen releasing reaction and in addition to the hexagonal main phase, a phase defined as monoclinic Li[Li.sub.1/3Mn.sub.2/3]O.sub.2 tends to be observed as a separate phase but not as a solid phase and such a material is undesirable since the reversible capacity of the active material is considerably decreased. With respect to such a material, impurity peaks are observed near 35° and 45° in the X-ray diffraction pattern. Accordingly, it is important that the calcining temperature is adjusted lower than the temperature which affects the oxygen releasing reaction of the active material. In the composition range of the present invention, the oxygen releasing temperature of the active material is around 1000° C. or higher; however, the oxygen releasing temperature slightly differs based on the composition of the active material and therefore it is preferable to previously confirm the oxygen releasing temperature of the active material. Particularly, it is confirmed that the oxygen releasing temperature of a precursor is shifted to the lower temperature side as the Co amount contained in a sample is higher and therefore, it should be considered carefully. As a method for confirming the oxygen releasing temperature of the active material, a mixture of a coprecipitated precursor and LiOH.H.sub.2O may be subjected to thermogravimetry (DTA-TG measurement) in order to simulate the calcining reaction process; however in this method, platinum employed for a sample chamber of a measurement instrument may be possibly corroded with an evaporated Li component to break the instrument and therefore, a composition of which crystallization is promoted to a certain extent by employing a calcining temperature of about 500° C. is preferable to be subjected to thermogravimetry.

(37) On the other hand, if the calcining temperature is too low, the crystallization is not carried out sufficiently and the electrode property is also considerably lowered and it is thus not preferable. The calcining temperature is required to be at least 800° C. or higher. Sufficient crystallization is important to lower the resistance of grain boundaries and promote smooth lithium ion transfer. A method for careful evaluation of the crystallization may be visible observation using a scanning electron microscope. When the scanning electron microscopic observation is carried out for the positive active materials of the present invention, at the sample synthesis temperature of 800° C. or lower, there are those made of primary particles in nano-order and some are crystallized to a sub-micron extent by further increasing the sample synthesis temperature and large primary particles which lead to improvement of the electrode property can be obtained.

(38) On the other hand, as another factor for showing crystallization, there is a half width of the X-ray diffraction peak described above. However, merely selection of the synthesis temperature at which the half width of the diffraction peak of the main phase is not necessarily adequate to obtain an active material with a high reversible capacity. It is because the half width of the diffraction peak is dominated by two factors; one is the quantity of strain showing the extent of mismatch of the crystal lattice and the other is the size of crystallite, which is the minimum domain and therefore, in order to carefully evaluate the extent of crystallinity from the half width, these factors need to be separately measured. The present inventors have confirmed that strains remain in the lattice in a sample which is synthesized at a temperature up to 800° C. by analysis in detail of the half width of the active material of the invention and synthesis of the temperature or higher makes it possible to fairly remove the strains. Further, the size of the crystallite becomes large in proportional to the increase of the synthesis temperature. Consequently, with respect to the composition of the active material of the invention, a desirable discharge capacity is obtained by forming particles sufficiently grown in the crystallite size with scarce strains in the lattice of the system. More concretely, it is found preferable to employ a synthesis temperature (a calcining temperature) at which the strain degree affecting the lattice constant is 1% or lower and the crystallite size is grown to 150 nm or larger. Although a change due to expansion and contraction is observed by molding the active materials into electrodes and carrying out charge-discharge, it is preferable to keep the crystallite size 130 nm or higher also in the charge-discharge process as a good effect to be obtained. That is, it is made at first possible to obtain an active material with a remarkably high reversible capacity by selecting the calcining temperature to be as near as possible to the oxygen releasing temperature of the active material.

(39) As described above, although it is difficult to set a definitely preferable range of the calcining temperature since it differs depending on the oxygen releasing temperature of an active material, it is preferably 900 to 1100° C., more preferably 950 to 1050° C. since excellent properties can be exhibited.

(40) An nonaqueous electrolyte to be used for the lithium secondary battery of the present invention is not particularly limited and those generally proposed for use for lithium batteries and the like can be used. Examples of nonaqueous solvents to be used for the nonaqueous electrolyte can include, but are not limited to, one compound or a mixture of two or more of compounds of cyclic carbonic acid esters such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonates; chain esters such as methyl formate, methyl acetate, and methyl butyrate; tetrahydrofuran and derivatives thereof; ethers such as 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, and methyl diglyme; nitriles such as acetonitrile and benzonitrile; dioxolan and derivatives thereof; and ethylene sulfide, sulfolane, sulfone and derivatives thereof.

(41) Examples of electrolytic salts to be used for the nonaqueous electrolyte include inorganic ionic salts containing one of lithium (Li), sodium (Na), and potassium (K) such as LiClO.sub.4, LiBF.sub.4, LiAsF.sub.6, LiPF.sub.6, LiSCN, LiBr, LiI, Li.sub.2SO.sub.4, Li.sub.2B.sub.10Cl.sub.10, NaClO.sub.4, NaI, NaSCN, NaBr, KClO.sub.4, and KSCN; and organic ionic salts such as LiCF.sub.3SO.sub.3, LiN(CF.sub.3SO.sub.2).sub.2, LiN(C.sub.2F.sub.5SO.sub.2).sub.2, LiN(CF.sub.3SO.sub.2)(C.sub.4F.sub.9SO.sub.2), LiC(CF.sub.3SO.sub.2).sub.3, LiC(C.sub.2F.sub.5SO.sub.2).sub.3, (CH.sub.3).sub.4NBF.sub.4, (CH.sub.3).sub.4NBr, (C.sub.2H.sub.5).sub.4NClO.sub.4, (C.sub.2H.sub.5).sub.4NI, (C.sub.3H.sub.7).sub.4NBr, (n-C.sub.4H.sub.9).sub.4NClO.sub.4, (n-C.sub.4H.sub.9).sub.4NI, (C.sub.2H.sub.5).sub.4N-maleate, (C.sub.2H.sub.5).sub.4N-benzoate, (C.sub.2H.sub.5).sub.4N-phthalate, lithium stearylsulfonate, lithium octylsulfonate, and lithium dodecylbenzenesulfonate and these ionic compounds may be used alone or in combination of two or more of them.

(42) Further, if a lithium salt having a perfluoroalkyl group such as LiBF.sub.4 and LiN(C.sub.2F.sub.5SO.sub.2).sub.2 is added to be used, the viscosity of the electrolyte can be lowered and therefore the low temperature properties can be further improved and self-discharge can be suppressed and therefore, it is preferable.

(43) Further, a normal temperature molten salt or ionic liquid may be used as the nonaqueous electrolyte.

(44) The concentration of the electrolytic salt in the nonaqueous electrolyte is preferably 0.1 mold to 5 mol/l and more preferably 0.5 mol/l to 2 mol/l to reliably obtain a nonaqueous electrolyte battery having high battery properties.

(45) A negative electrode material is not particularly limited and may be any if it can precipitate or absorb lithium ions. Examples thereof include a titanium type materials such as lithium titanate having a spinel type crystal structure typified by Li[Li.sub.1/3Ti.sub.5/3]O.sub.4; alloy type lithium metal and lithium alloys of Si and Sb and Sn (lithium metal-containing alloy such as lithium-silicon, lithium-aluminum, lithium-lead, lithium-tin, lithium-aluminum-tin, lithium-gallium, and Wood' alloy), lithium composite oxide (lithium-titanium), silicon oxide as wells as alloys capable of absorbing and releasing lithium, and carbon materials (e.g. graphite, hard carbon, low temperature calcined carbon, amorphous carbon).

(46) A powder of the positive active material and a powder of the negative active material preferably have an average particle size of 100 μm or smaller. Particularly, the powder of the positive active material is desirable to be 10 μm or smaller in order to improve the high output performance of the nonaqueous electrolyte battery. In order to obtain a powder in a prescribed shape, a pulverizer or a classifier may be used. For example, usable are mortars, ball mills, sand mills, vibration ball mills, planet ball mills, jet mills, counter jet mills, swirling current type jet mill, and sieves. At the time of pulverization, wet pulverization in co-presence of water or an organic solvent such as hexane can also be employed. A classification method is not particularly limited and sieves, pneumatic classifiers and the like may be employed in both dry and wet manner if necessary.

(47) The positive active material and the negative active material, which are main constituent components of a positive electrode and a negative electrode are described in detail, and the positive electrode and the negative electrode may contain an electric conductive agent, a binder, a thickener, a filler and the like as other constituent components besides the above-mentioned main constituent components.

(48) The electric conductive agent is not particularly limited if it is an electron conductive material causing no adverse effect on the battery performance and it may be, in general, electric conductive materials such as natural graphite (scaly graphite, flaky graphite, earthy graphite), artificial graphite, carbon black, acetylene black, Ketjen black, carbon whisker, carbon fibers, powders of metals (copper, nickel, aluminum, silver, gold, etc.), metal fibers and electric conductive ceramic materials, and one or a mixture of these materials may be used.

(49) As an electric conductive agent among them, acetylene black is preferable form the viewpoints of electron conductivity and coatability. The addition amount of the electric conductive agent is preferably 0.1% by weight to 50% by weight and particularly preferably 0.5% by weight to 30% by weight based on the total weight of the positive electrode or the negative electrode. Particularly, if acetylene black is used while being pulverized into ultrafine particles of 0.1 to 0.5 μm, the carbon amount to be needed can be saved and therefore it is preferable. A mixing method of them may be physical mixing and ideally, it is uniform mixing. For this reason, powder mixers such as V-shaped mixers, S-shaped mixers, attriters, ball mills, and planet ball mills may be used to carry out dry or wet mixing.

(50) As the binder, in general, thermoplastic resins such as polytetrafluoroethylene (PTFE), poly(vinylidene fluoride) (PVDF), polyethylene, and polypropylene; and polymers having rubber elasticity such as ethylene-propylene-diene-terpolymers (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluoro rubber can be used alone or in combination of two or more of them. The addition amount of the binder is preferably 1 to 50% by weight and particularly preferably 2 to 30% by weight based on the total weight of the positive electrode or the negative electrode.

(51) The filler is not particularly limited if it is a material causing no adverse effect on the battery performance. In general, usable may be olefin type polymers such as polypropylene and polyethylene; amorphous silica, alumina, zeolite, glass, carbon and the like. The addition amount of the filler is preferably 30% by weight or less based on the total weight of the positive electrode or the negative electrode.

(52) The positive electrode and the negative electrode can be preferably produced by mixing the main constituent components (the positive active material in the positive electrode and the negative active material in the negative electrode) and other materials to obtain composites, then mixing the composites with an organic solvent such as N-methylpyrrolidone, toluene, or the like, applying the obtained mixed solutions onto current collectors described below or bonding the solution with pressure, and carrying out heat treatment at a temperature of about 50° C. or 250° C. for about 2 hours. The application method is preferably carried out to give an arbitrary thickness and an arbitrary shape by using means such as roller coating such as applicator rolls, screen coating, doctor blade coating manner, spin coating, and bar coaters; however it is not limited to thereto.

(53) As a separator, porous membranes and nonwoven fabrics having excellent high rate discharge performance may be used preferably alone or in combination. Examples of materials constituting a separator for a nonaqueous electrolyte battery can include polyolefin type resins typified by polyethylene and polypropylene; polyester type resins typified by poly(ethylene terephthalate) and poly(butylene terephthalate); poly(vinylidene fluoride), vinylidene fluoride-hexafluoropropylene copolymers, vinylidene fluoride-perfluorovinyl ether copolymers, vinylidene fluoride-tetrafluoroethylene copolymers, vinylidene fluoride-trifluoroethylene copolymers, vinylidene fluoride-fluoroethylene copolymers, vinylidene fluoride-hexafluoroacetone copolymers, vinylidene fluoride-ethylene copolymers, vinylidene fluoride-propylene copolymers, vinylidene fluoride-trifluoropropylene copolymers, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymers, and vinylidene fluoride-ethylene-tetrafluoroethylene copolymers.

(54) The porosity of the separator is preferable 98% by volume or less from the viewpoint of strength. Further, from the viewpoint of charge-discharge property, the porosity is preferably 20% by volume or higher.

(55) The separator may be a polymer gel configured by, for example, a polymer of acrylonitrile, ethylene oxide, propylene oxide, methyl methacrylate, vinyl acetate, vinylpyrrolidone, and poly(vinylidene fluoride) and an electrolyte. If the nonaqueous electrolyte is used in a gel state as described above, it is preferable since it is effective to prevent liquid leakage.

(56) Further, in the separator, the above-mentioned porous membranes or nonwoven fabrics are used in combination with the polymer gel, it is preferable since the electrolyte retention property is improved. That is, a film is obtained by coating the surface and fine pore wall surfaces of a polyethylene fine porous membrane with a solvophilic polymer in a thickness of several μm or less and making the fine pores of the film keep the electrolyte, so that the solvophilic polymer can be formed into gel.

(57) Examples of the solvophilic polymer include poly(vinylidene fluoride) and also polymers crosslinked by acrylate monomers having ethylene oxide groups or ester groups, epoxy monomers, and monomers having isocyanato groups. Crosslinking reaction of the monomers may be carried out by heating or using ultraviolet rays (UV) with a radical initiator in combination or using activation beam such as electron beam.

(58) The configuration of the lithium secondary battery is not particularly limited and examples thereof include cylindrical batteries, prismatic batteries, and flat type batteries including the positive electrode, negative electrode, and roll type separator.

EXAMPLES

(59) The compositions of positive active materials used for lithium secondary batteries of Examples and Comparative Examples are shown in Table 1. The compositions of Examples 1 to 44 satisfy the composition formula: Li.sub.1+(1/3)xCo.sub.1−x−yNi.sub.(1/2)yMn.sub.(2/3)x+(1/2)y (x+y≦1, 0≦y, 1−x−y=z) and also satisfy the range disclosed in claim 1: although Comparative Examples 1 to 40 satisfy the above-mentioned composition formula, the value of (x, y, z) is out of the range disclosed in claim 1: and Comparative Examples 41 to 43 do not satisfy even the composition formula. That is, in FIG. 1, the compositions of Examples 1 to 44 are present on or within a line of a heptagon ABCDEFG and the compositions of Comparative Examples 1 to 40 are present outside of the heptagon ABCDEFG.

Example 1

(60) An aqueous mixed solution was produced by dissolving manganese sulfate pentahydrate, nickel sulfate hexahydrate, and cobalt sulfate heptahydrate at a ratio of 0.25:0.17:0.45 of the respective elements Co, Ni, and Mn in ion-exchanged water. At that time, the total concentration was adjusted to 0.667 M and the volume to 180 ml. Next, 600 ml of ion exchanged water was made available in a 1 L beaker and using a hot bath to keep the temperature at 50° C., 8N NaOH was dropwise added to adjust the pH 11.5. In such a state, bubbling with Ar gas was carried out for 30 min to sufficiently remove dissolved oxygen in the solution. The content in the beaker was stirred at 700 rpm, the prepared sulfates-mixed aqueous solution was added dropwise at a speed of 3 ml/min. During the time, the temperature was kept constant by the hot bath and pH was kept constant by intermittently adding 8 N NaOH dropwise. Simultaneously, 50 ml of an aqueous 2.0 M hydrazine solution as a reducing agent was added dropwise at a speed of 0.83 ml/min. On the completion of the dropwise addition of both, the stirring was stopped and the solution was kept still for 12 hours or longer to sufficiently grow particles of a coprecipitated hydroxide.

(61) Herein, in the above-mentioned procedure, if the dropwise addition speed of each solution was too high, it became impossible to obtain a uniform precursor in atomic level. For example, in a case where the dropwise addition speed was increased 10 times as fast as that described above, the fact that the element distribution in the precursor was apparently ununiform was made clear from the results of EPMA measurement. Further, it was also confirmed that in a case where an active material was synthesize using such ununiform precursor, the distribution of elements after calcining also became ununiform and it resulted in impossibility of exhibiting sufficient electrode properties. In this connection, in the case of using LiOH.H.sub.2O, Co(OH).sub.2, Ni(OH).sub.2, and MnOOH as raw material powders in a solid-phase method, further ununiformity was proved by the results of EPMA measurement.

(62) Next, the coprecipitation product was taken out by suction filtration and dried at 100° C. in atmospheric air and normal pressure in an oven. After drying, in order to adjust particle diameter, the product was pulverized for several minutes by a mortar with a diameter of about 120 mmφ to obtain a dried powder.

(63) By X-ray diffractometry, the dried powder was confirmed to have a β-Ni(OH).sub.2 type single phase. Further, Co, Ni, and Mn were confirmed to be present uniformly by EPMA measurement.

(64) A lithium hydroxide monohydrate salt powder (LiOH.H.sub.2O) was weighed to make the Li amount to the transition metals (Ni+Mn+Co) satisfy the composition formula of Example 1 in Table 1 and mixed to obtain a mixed powder.

(65) Next, the mixed powder was pellet-molded at a pressure of 6 MPa. The amount of the precursor powder supplied to the pellet molding was determined by calculation for controlling the mass as a product after synthesis to be 3 g. As a result, the pellets after molding had a diameter of 25 mmφ, thickness about 10 to 12 mm. The pellets were put on an alumina boat with a whole length of about 100 mm, and then set in a box type electric furnace and calcined at 1000° C. for 12 hours in atmospheric air under normal pressure. The inside size of the boxy type electric furnace was 10 cm height, 20 cm width, and 30 cm depth and heating wires were set at 20 cm intervals in the width direction. After calcination, a switch of the heater was turned off and the alumina boat was left in the furnace as it was to carry out spontaneous cooling. As a result, the temperature of the furnace was lowered to about 200° C. after 5 hours; however the rate of the temperature decrease thereafter was slightly slow. After overnight, the temperature of the furnace was confirmed to be 100° C. or lower and thereafter the pellets were taken out and pulverized to make the particle diameter uniform by using a mortar.

(66) The crystal structure of the obtained active material was confirmed to contain an α-NaFeO.sub.2 type hexagonal structure as a main phase according to the results of powder X-ray diffractometry using a Cu(Kα) radiation and at the same time was observed to have a diffraction peak around 20 to 30° which is obtained partially for a monoclinic Li[Li.sub.1/3Mn.sub.2/3]O.sub.2. FIG. 6 shows the X-ray diffraction pattern of the active material (AT06) of Example 1. The intensity ratio I.sub.(003)/I.sub.(104) between the diffraction peaks on (003) plane and (104) plane before charge-discharge was 1.69. Further, the count number of the diffraction peak at 21° which is observed for the monoclinic Li[Li.sub.1/3Mn.sub.2/3]O.sub.2 was 7 in a case where the count number of the peaks near 18° showing the maximum intensity was assumed to be 100.

(67) Further, XAFS measurement was carried out for valence evaluation of the transition metal elements. When the spectrometric analysis was carried out for the XANES region, it was confirmed that Co.sup.3+, Ni.sup.2+, and Mn.sup.4+ were in electron state. The results of XANES measurement are shown in FIG. 7.

Examples 2 to 44

(68) The active materials of the present invention were synthesize in the same manner as Example 1, except that the compositions of the transition metal elements contained in the coprecipitated hydroxide precursors and the amount of lithium hydroxide to be mixed was changed according to the composition formulas shown in Examples 2 to 44 shown in Table 1.

(69) As a result of X-ray diffractometry, similarly to Example 1, the α-NaFeO.sub.2 type hexagonal structure was confirmed to be a main phase and also a diffraction peak around 20 to 30° which is obtained partially for monoclinic Li[Li.sub.1/3Mn.sub.2/3]O.sub.2 was observed. Further, as shown in Table 1, the intensity ratio I.sub.(003)/I.sub.(104) between the diffraction peaks on (003) plane and (104) plane before charge-discharge was all 1.56 or higher.

Comparative Examples 1 to 40

(70) The active materials of Comparative Examples were synthesize in the same manner as Example 1, except that the compositions of the transition metal elements contained in the coprecipitated hydroxide precursors and the amount of lithium hydroxide to be mixed was changed according to the composition formulas shown in Comparative Examples 1 to 40 shown in Table 1.

(71) FIG. 8 shows the X-ray diffraction pattern of the active material of Comparative Example 3 (AT09) as representative. With respect to Comparative Examples 12 to 18 and 33 to 40 in which the x value is ⅔ or more, similarly to Example 1, the α-NaFeO.sub.2 type hexagonal structure was confirmed to be a main phase and also a diffraction peak around 20 to 30° which is obtained partially for monoclinic Li[Li.sub.1/3Mn.sub.2/3]O.sub.2 was observed. However, with respect to Comparative Examples 1 to 11 and 19 to 32 in which the x value is ⅓ or less, although the α-NaFeO.sub.2 type hexagonal structure was confirmed, no diffraction peak observed for monoclinic Li[Li.sub.1/3Mn.sub.2/3]O.sub.2 was clearly observed as long as the peak height of the maximum intensity in the X-ray diffraction pattern was enlarged to the full scale. Further, as shown in Table 1, the intensity ratios I.sub.(003)/I.sub.(104) between the diffraction peaks on (003) plane and (104) plane of the active materials before charge-discharge were 1.43 or higher, however some were 1.56 or lower.

Comparative Examples 41 and 42

(72) The active materials of Comparative Examples 41 and 42 were synthesize in the same manner as Example 1, except that the compositions of the transition metal elements contained in the coprecipitated hydroxide precursors and the amount of lithium hydroxide to be mixed was changed according to the composition formula: LiCo.sub.1/3Ni.sub.1/3Mn.sub.1/3O.sub.2.

(73) Herein, Comparative Examples 41 and 42 were different from each other in the set values of the charging voltage in the test condition described below (Comparative Example 41: 4.6 V, Comparative Example 42: 4.3 V) and were identical with each other as the active material.

Comparative Example 43

(74) The active material of Comparative Example 43 was synthesize in the same manner as Example 1, except that a powder obtained by mixing respective powders of LiOH.H.sub.2O, Co(OH).sub.2, Ni(OH).sub.2, and MnOOH at element ratio of Li:Co:Ni:Co=1:0.33:0.33:0.33 was used in place of the coprecipitated hydroxide precursor powder. The X-ray diffraction pattern could not be discriminated from those of Comparative Examples 1 and 42. However, from the results of EPMA observation, Co, Ni, and Mn were not uniformly distributed in the material.

(75) (Production and Evaluation of Lithium Secondary Batteries)

(76) Using the respective active materials of Examples 1 to 44 and Comparative Examples 1 to 43 as a positive active material for a lithium secondary battery, lithium secondary batteries were produced in the following procedure and the battery properties were evaluated.

(77) Each coating solution was prepared by mixing each active material, acetylene black (AB), and poly(vinylidene fluoride) (PVdF) at a weight ratio of 85:87 and adding N-methylpyrrolidone as a dispersion medium and mixing and dispersing these compounds. As PVdF, a liquid in which solid matter was dissolved and dispersed was used and solid matter weight conversion was carried out. The coating solution was applied to an aluminum foil current collector with a thickness of 20 μm to produce each positive electrode plate. In all batteries, the electrode weight and thickness were standardized to make the same test conditions for all of the batteries.

(78) As a counter electrode, lithium metal was used for a negative electrode to observe the behavior of each positive electrode alone. The lithium metal was closely attached to a nickel foil current collector. However, it was prepared in such a manner that the capacity of each lithium secondary battery was controlled sufficiently by the positive electrode.

(79) As an electrolyte, a solution was used which was obtained by dissolving LiPF.sub.6 in a solvent mixture of EC/EMC/DMC at a ratio of 6:7:7 by volume to give a concentration of 1 mol/L. As a separator, a finely porous film made of polypropylene was used which was provided with improved electrolyte retention property by surface modification with polyacrylate. Further, an electrode obtained by sticking a lithium metal foil to a nickel plate was used as a reference electrode. As an outer casing, a metal resin composite film was used which was made of poly(ethylene terephthalate) (15 μm)/aluminum foil (50 μm)/metal-adhesive polypropylene film (50 μm) and the electrodes were housed in such a manner that the opened terminal parts of the positive electrode terminal, negative electrode terminal, and reference electrode terminal were exposed to the outside and fusion-melting margins where the inner surfaces of the metal resin composite films were mutually encountered were tightly sealed except the portion where an injection hole was to be formed.

(80) Each lithium secondary battery produced in the above-mentioned manner was subjected to the initial charge-discharge process of 5 cycles at 20° C. The voltage control was all carried out for the positive electrode potential. Charge was carried out at constant current and constant voltage charge for 0.1 ItA and 4.5 V and the condition of ending the charge was set to be the time point when the electric current value was decreased to ⅙. Discharge was carried out at constant current for 0.1 ItA and 2.0 V at the end. In all cycles, a 30 minute-rest was set after charge and after discharge. The behavior of the first two cycles in the initial charge-discharge process is shown in FIG. 9. FIG. 9A and FIG. 9B correspond to Example 6 (AT17) and Comparative Example 4 (AT11), respectively.

(81) Successively, a charge-discharge cycle test was carried out. The voltage control was carried out all for the positive electrode potential. The conditions of the charge-discharge cycle test were the same as those in the above-mentioned initial charge-discharge process, except that the charge voltage was set to 4.3 V (vs. Li/Li.sup.+) (4.6 V only for Comparative Example 41). In all cycles, a 30 minute-pause was set after charge and after discharge. The discharge electric quantity at 5.sup.th cycle was recorded as “discharge capacity (mAh/g)”. FIG. 10 shows a representative charge-discharge curve of the 5.sup.th cycle in this charge-discharge cycle test.

(82) Further, percentage of the discharge electric quantity at 10.sup.th cycle in the charge-discharge cycle test to the above-mentioned “discharge capacity (mAh/g)” was measured and defined as “capacity retention ratio (%)”.

(83) Similarly to the measurement before charge-discharge, after charge-discharge, the active materials of Examples 1 to 44 and Comparative Examples 1 to 40 were subjected to powder X-ray diffractometry using a Cu(Kα) radiation. Charge was constant current and constant voltage charge at 0.1 ItA current and 4.5 V voltage and the ending of the charge was set to be the time point when the electric current value was decreased to ⅙. Thereafter, charging was carried out to 4.3 V (vs. Li/Li.sup.+) and then constant current discharge at 0.1 ItA current was carried out and the time point when the voltage at the end became 2.0 V was defined as the end of the discharge. The X-ray diffraction patterns of the active material of Example 7 (AT18) and the active material of Example 16 (AT33) before charge-discharge (synthesized samples), at end of charge, and at end of discharge are shown respectively in FIG. 11 and FIG. 12.

(84) With respect to the active materials of Examples 1 to 44 and Comparative Examples 1 to 40, the results of the battery test (excluding the capacity retention ratio) are show in Table 1 and Table 2. FIG. 13 shows the values of the discharge capacities by plotting them in a Li[Li.sub.1/3Mn.sub.2/3]O.sub.2(x)-LiNi.sub.1/2Mn.sub.1/2O.sub.2(y)-LiCoO.sub.2(z) type ternary phase diagram.

(85) TABLE-US-00001 TABLE 1 Discharge Before At end of capacity Li[Li.sub.1/3Mn.sub.2/3]O.sub.2 LiNi.sub.0.5Mn.sub.0.5O.sub.2 LiCoO.sub.2 Example No. Experiment No. charge-discharge I.sub.(0.03)/I.sub.(104) charge I.sub.(0.03)/I.sub.(104) (mAh/g) (x) (y) (z) Example 1 AT06 1.69 1.43 189 0.50 0.25 0.25 Example 2 AT14 1.77 1.68 186 0.45 0.20 0.35 Example 3 AT15 1.79 1.44 182 0.45 0.40 0.15 Example 4 AT16 1.65 1.39 180 0.45 0.50 0.05 Example 5 AT22 1.84 1.63 220 0.60 0.10 0.30 Example 6 AT17 1.77 1.67 225 0.60 0.20 0.20 Example 7 AT18 1.68 1.61 224 0.60 0.30 0.10 Example 8 AT19 1.61 1.43 219 0.60 0.40 0.00 Example 9 AT25 2.00 1.42 177 0.70 0.10 0.20 Example 10 AT27 1.64 1.60 180 0.67 0.23 0.10 Example 11 AT28 1.68 1.53 223 0.67 0.13 0.20 Example 12 AT29 1.78 1.50 207 0.67 0.03 0.30 Example 13 AT30 1.63 1.50 187 0.67 0.18 0.15 Example 14 AT31 1.62 1.56 185 0.67 0.00 0.33 Example 15 AT32 1.66 1.31 187 0.70 0.05 0.25 Example 16 AT33 1.78 1.31 198 0.70 0.00 0.30 Example 17 AT51 1.94 2.08 179 0.50 0.10 0.40 Example 18 AT53 2.07 2.18 183 0.60 0.00 0.40 Example 19 AT54 1.57 1.47 185 0.50 0.50 0.00 Example 20 AT55 1.91 1.75 185 0.50 0.40 0.10 Example 21 AT56 2.06 1.79 185 0.50 0.30 0.20 Example 22 AT57 2.13 2.40 185 0.50 0.20 0.30 Example 23 AT58 1.61 1.90 190 0.63 0.37 0.00 Example 24 AT59 1.66 1.46 191 0.63 0.32 0.05 Example 25 AT60 1.85 2.10 206 0.63 0.27 0.10 Example 26 AT61 1.93 1.81 200 0.63 0.22 0.15 Example 27 AT62 1.94 1.78 206 0.63 0.17 0.20 Example 28 AT63 2.17 1.79 200 0.63 0.07 0.30 Example 29 AT64 2.19 2.21 203 0.60 0.05 0.35 Example 30 AT65 2.16 1.61 200 0.67 0.08 0.25 Example 31 AT66 1.56 1.54 182 0.45 0.55 0.00 Example 32 AT67 1.83 1.99 177 0.45 0.30 0.25 Example 33 AT68 1.96 2.22 179 0.45 0.10 0.45 Example 34 AT69 2.11 2.27 186 0.50 0.15 0.35 Example 35 AT70 2.17 2.35 197 0.55 0.10 0.35 Example 36 AT71 2.22 2.06 199 0.55 0.05 0.40 Example 37 AT72 2.15 2.08 189 0.75 0.05 0.20 Example 38 AT73 1.81 1.59 180 0.75 0.00 0.25 Example 39 AT75 1.87 2.08 178 0.55 0.35 0.10 Example 40 AT76 2.02 1.97 185 0.55 0.25 0.20 Example 41 AT77 2.25 2.28 188 0.55 0.15 0.30 Example 42 AT78 2.08 2.44 183 0.55 0.00 0.45 Example 43 AT79 1.72 1.77 182 0.67 0.28 0.05 Example 44 AT81 1.67 1.70 190 0.70 0.25 0.05

(86) TABLE-US-00002 TABLE 2 Discharge Before capacity Li[Li.sub.1/3Mn.sub.2/3]O.sub.2 LiNi.sub.0.5Mn.sub.0.5O.sub.2 LiCoO.sub.2 Example No. Experiment No. charge-discharge I.sub.(0.03)/I.sub.(104) (mAh/g) (x) (y) (z) Comparative AT04 1.65 158 0.33 0.33 0.33 Example 1 Comparative AT05 1.54 149 0.25 0.50 0.25 Example 2 Comparative AT09 1.56 148 0.15 0.60 0.25 Example 3 Comparative AT11 1.52 152 0.30 0.40 0.30 Example 4 Comparative AT20 2.07 143 0.15 0.20 0.65 Example 5 Comparative AT08 1.75 145 0.15 0.40 0.45 Example 6 Comparative AT10 1.89 145 0.15 0.80 0.05 Example 7 Comparative AT21 1.95 152 0.30 0.20 0.50 Example 8 Comparative AT12 1.83 154 0.30 0.60 0.10 Example 9 Comparative AT13 1.60 154 0.30 0.70 0.00 Example 10 Comparative AT07 1.76 145 0.25 0.25 0.50 Example 11 Comparative AT23 1.72 176 0.70 0.20 0.10 Example 12 Comparative AT24 1.70 147 0.80 0.10 0.10 Example 13 Comparative AT26 1.43 175 0.67 0.33 0.00 Example 14 Comparative AT34 1.75 166 0.80 0.05 0.15 Example 15 Comparative AT35 1.84 171 0.80 0.00 0.20 Example 16 Comparative AT36 1.61 164 0.90 0.05 0.05 Example 17 Comparative AT37 1.54 173 0.90 0.00 0.10 Example 18 Comparative AT38 1.61 172 0.33 0.60 0.07 Example 19 Comparative AT39 1.63 170 0.33 0.47 0.20 Example 20 Comparative AT40 1.96 157 0.33 0.20 0.47 Example 21 Comparative AT41 2.27 156 0.33 0.07 0.60 Example 22 Comparative AT42 2.62 141 0.30 0.10 0.60 Example 23 Comparative AT43 2.12 130 0.30 0.00 0.70 Example 24 Comparative AT44 2.50 159 0.40 0.10 0.50 Example 25 Comparative AT45 2.46 156 0.40 0.00 0.60 Example 26 Comparative AT46 1.55 167 0.40 0.60 0.00 Example 27 Comparative AT47 1.72 162 0.40 0.50 0.10 Example 28 Comparative AT48 1.69 158 0.40 0.40 0.20 Example 29 Comparative AT49 1.73 170 0.40 0.30 0.30 Example 30 Comparative AT50 2.33 152 0.40 0.20 0.40 Example 31 Comparative AT52 2.09 173 0.50 0.00 0.50 Example 32 Comparative AT80 1.61 139 0.70 0.30 0.00 Example 33 Comparative AT82 2.02 172 0.70 0.15 0.15 Example 34 Comparative AT83 1.67 147 0.75 0.25 0.00 Example 35 Comparative AT84 1.76 172 0.75 0.20 0.05 Example 36 Comparative AT85 2.12 160 0.75 0.15 0.10 Example 37 Comparative AT86 2.11 155 0.75 0.10 0.15 Example 38 Comparative AT87 1.67 147 0.80 0.20 0.00 Example 39 Comparative AT88 1.71 149 0.80 0.15 0.05 Example 40

(87) As being understood from Table 1, Table 2, and FIG. 13, use of the active materials of Examples 1 to 44 having values of (x, y, z) in a range present on or within a line of a heptagon (ABCDEFG) defined by the vertexes; point A(0.45, 0.55, 0: corresponding to the composition of AT66), point B(0.63, 0.37, 0: corresponding to the composition of AT58), point C(0.7, 0.25, 0.05: corresponding to the composition of AT81), point D(0.67, 0.18, 0.15: corresponding to the composition of AT30), point E(0.75, 0, 0.25: corresponding to the composition of AT73), point F(0.55, 0, 0.45: corresponding to the composition of AT78), and point G(0.45, 0.2, 0.35: corresponding to the composition of AT14) made it possible to obtain lithium secondary batteries with discharge capacities as high as 177 mAh/g or higher in a potential region of 4.3 V or lower. Those using the active materials of Comparative Examples 1 to 40 out of the above-mentioned range had discharge capacities of 176 mAh/g or lower. Especially, in the case of using active materials having particularly specified values (x, y, z) in a range present on or within a line of a tetragon (HIJK) defined by the vertexes; point H(0.6, 0.4, 0: corresponding to the composition of AT19), point I(0.67, 0.13, 0.2: corresponding to the composition of AT28), point J(0.7, 0, 0.3; corresponding to the composition of AT33), and point K(0.55, 0.05, 0.4: corresponding to the composition of AT71) (Examples 5 to 8, Examples 11, 12, 16, 25 to 30, and 36), lithium secondary batteries with discharge capacities as high as 198 mAh/g or higher in a potential region of 4.3 V or lower could be obtained.

(88) Further, with respect to LiCo.sub.1/3Ni.sub.1/3Mn.sub.1/3O.sub.2, in a case where the discharge potential was adjusted to 4.6 V as in Comparative Example 41, the discharge capacity was 181 mAh/g; however, in a case where the discharge potential was adjusted to 4.3 V as in Comparative Example 42, the discharge capacity was 149 mAh/g and therefore, the value of the discharge capacity of the active material of the present invention exceeds that of Li[Co.sub.1−2xNi.sub.xMn.sub.x]O.sub.2 (0≦x≦½) or LiNiO.sub.2 type, which is regarded as representative of high capacity.

(89) As shown in Table 1, the active material of the present invention had the intensity ratio of the diffraction peaks satisfying I.sub.(003)/I.sub.(104)≧1.56 before charge-discharge and I.sub.(003)/I.sub.(104)>1.3 exceeding I.sub.(003)/I.sub.(104)>1 at the end of discharge and moreover, since the change of the intensity ratio at the end of discharge was within 26% of that before charge-discharge, it is indicated that no contamination of the transition metals to the Li layer during charge-discharge was generated and at this point, the active material is apparently distinguished from the conventional Li[Li.sub.1/3Mn.sub.2/3]O.sub.2(x)-LiNi.sub.1/2Mn.sub.1/2O.sub.2(y)-LiCoO.sub.2(z) type active material.

(90) Furthermore, with respect to the capacity retention, the lithium secondary batteries using the active materials of Examples 1 to 44 kept 100%, whereas the lithium secondary batteries using the active materials of Comparative Examples 41, 42, and 43 kept only 89%, 98%, and 80%, respectively, and therefore, the lithium secondary battery of the present invention is found excellent also in the charge/discharge cycle performance.