Cell

Abstract

The present invention provides a cell that has a high theoretical voltage and theoretical capacity, and can be discharged and recharged multiple times. The cell includes a cathode, an anode, and an electrolyte, wherein the cathode contains a cathode active material containing an alkali metal compound represented by the formula (1):
A.sub.xO.sub.y(1)
(wherein A is an alkali metal atom, x is 0.5 to 2.5, and y is 0.5 to 2.5), the anode contains an anode active material containing at least one selected from the group consisting of an alkali metal, tin, titanium, boron, nitrogen, silicon, and carbon, and the cathode, the anode, and the electrolyte are hermetically sealed in the cell.

Claims

1. A secondary cell comprising: a positive electrode; a negative electrode; and an electrolyte, wherein the positive electrode comprises: a positive electrode active material comprising an alkali metal compound represented by following formula (1):
A.sub.xO.sub.y(1) wherein A is an alkali metal atom, x is in a range from 0.5 to 2.5, and y is in a range from 0.5 to 2.5; and a catalyst for the positive electrode, wherein the catalyst for the positive electrode comprises at least one element selected from the group consisting of Ag, Au, Cu, Fe, Co, and Ni, and the catalyst for the positive electrode is in a form of a solid solution in a crystal structure of the alkali metal compound represented by the formula (1), reactions at the positive electrode include one represented by a following formula:
A.sub.2O.sub.2+2A.sup.++2e.sup.2A.sub.2O wherein A is the alkali metal atom, the negative electrode comprises a negative electrode active material comprising at least one material selected from the group consisting of an alkali metal, tin, titanium, boron, nitrogen, silicon, and carbon, and the positive electrode, the negative electrode, and the electrolyte are hermetically sealed in the secondary cell.

2. The secondary cell according to claim 1, wherein the positive electrode comprises a current collector and an active material layer, and the active material layer comprises the alkali metal compound represented by the formula (1) in an amount of 5% by mass or more relative to mass of the active material layer.

3. The secondary cell according to claim 1, wherein when the secondary cell is fully charged, the negative electrode comprises the alkali metal at a ratio, determined on a molar basis relative to an alkali metal peroxide represented by following formula (2) in the positive electrode, of not more than 100:
A.sub.2O.sub.2(2) wherein A is the alkali metal atom.

4. The secondary cell according to claim 1, wherein A is Li.

5. The secondary cell according to claim 1, wherein the negative electrode active material in the negative electrode comprises at least one material selected from the group consisting of an alkali metal and carbon.

6. The secondary cell according to claim 1, wherein the alkali metal in the negative electrode active material is Li, and the carbon in the negative electrode active material is graphite.

7. The secondary cell according to claim 1, wherein reactions at the negative electrode and overall reactions, which are combinations of reactions at the positive electrode and reactions at the negative electrode, include reactions represented by following formulas:
the reactions at the negative electrode: A A.sup.++e.sup.
the overall reactions: A+1/2A.sub.2O.sub.2A.sub.2O wherein A is the alkali metal atom.

8. The secondary cell according to claim 1, wherein the alkali metal compound is represented by A.sub.2O, or A.sub.2O.sub.2, or a combination thereof.

9. The secondary cell according to claim 1, wherein A is Li or Na.

10. A composition for forming a positive electrode comprising: a positive electrode active material; and a catalyst for a positive electrode, wherein the positive electrode active material comprises: an alkali metal compound represented by the following formula (1):
A.sub.xO.sub.y(1) wherein A is an alkali metal atom, x is in a range from 0.5 to 2.5, and y is in a range from 0.5 to 2.5, and wherein the catalyst for the positive electrode comprises at least one element selected from the group consisting of Ag, Au, Cu, Fe, Co, and Ni and the catalyst for the positive electrode is in a form of a solid solution in a crystal structure of the alkali metal compound represented by the formula (1).

11. A method for producing the coposition according to claim 10, comprising: producing the positive electrode material by mixing the alkali metal compound and the catalyst for the positive electrode using a planetary ball mill.

12. The composition according to claim 10, wherein the alkali metal compound is represented by A.sub.2O, or A.sub.2O.sub.2, or a combination thereof.

13. The composition according to claim 10, wherein A is Li or Na.

14. The composition according to claim 10, wherein A is Li.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a graph showing the results of cyclic voltammetry using a cathode prepared in Preparation 1.

(2) FIG. 2 is a graph showing the results of cyclic voltammetry using a cathode prepared in Preparation 2.

(3) FIG. 3 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 7.

(4) FIG. 4 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 8.

(5) FIG. 5 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 9.

(6) FIG. 6 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 10.

(7) FIG. 7 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 11.

(8) FIG. 8 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 12.

(9) FIG. 9 is a graph showing the results of a charge/discharge test in Example 3.

(10) FIG. 10 is a graph showing the results of a charge/discharge test in Example 4.

(11) FIG. 11 is a graph showing the results of a charge/discharge test in Example 5.

(12) FIG. 12 is a graph showing the results of a charge/discharge test in Example 6.

(13) FIG. 13 is a graph showing the results of a charge/discharge test in Example 7.

(14) FIG. 14 is a graph showing the results of a charge/discharge test in Example 8.

(15) FIG. 15 is a graph showing the results of analysis of gas generated during charge in Example 9.

(16) FIG. 16 is a graph showing the result of XRD measurement of a charged cathode in Example 10.

(17) FIG. 17 is a graph showing the results of a charge/discharge test in Example 12.

(18) FIG. 18 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 13.

(19) FIG. 19 is a graph showing the results of a charge/discharge test in Example 13.

(20) FIG. 20 is a graph showing the result of XRD measurement before and after charging in Example 14.

(21) FIG. 21 is a graph showing the results of quantification of a peroxide in Example 15.

(22) FIG. 22 is a graph showing the results of quantification of a peroxide in Example 15.

(23) FIG. 23 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 14.

(24) FIG. 24 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 15.

(25) FIG. 25 is a graph showing the results of a charge/discharge test in Example 16.

(26) FIG. 26 is a graph showing the results of a charge/discharge test in Example 17.

(27) FIG. 27 is a graph showing the results of a charge/discharge test in Example 18.

(28) FIG. 28 is a graph showing the results of a charge/discharge test in Example 19.

(29) FIG. 29 is a graph showing the results of a charge/discharge test in Example 20.

(30) FIG. 30 is a graph showing the results of a charge test in Example 21.

(31) FIG. 31 is a graph showing the results of a charge test in Example 22.

(32) FIG. 32 is a graph showing the results of a charge test in Example 23.

(33) FIG. 33 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 16.

(34) FIG. 34 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 17.

(35) FIG. 35 is a graph showing the results of a charge/discharge test in Example 24.

(36) FIG. 36 is a graph showing the results of a charge/discharge test in Example 25.

(37) FIG. 37 is a graph showing the results of a charge/discharge test in Example 26.

(38) FIG. 38 is a graph showing the results of a charge/discharge test in Example 27.

(39) FIG. 39 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 18.

(40) FIG. 40 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 19.

(41) FIG. 41 is a graph showing the results of a charge/discharge test in Example 28.

(42) FIG. 42 is a graph showing the results of a charge/discharge test in Example 29.

(43) FIG. 43 is a graph showing the results of a charge/discharge test in Example 30.

(44) FIG. 44 is a graph showing the results of a charge/discharge test in Example 31.

(45) FIG. 45 is a graph showing the results of XRD measurement before and after charging and discharging in Example 32.

(46) FIG. 46 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 20.

(47) FIG. 47 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 21.

(48) FIG. 48 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 22.

(49) FIG. 49 is a graph showing the results of XRD measurement of solid powder prepared in Preparation 23.

(50) FIG. 50 is a graph showing the results of a charge/discharge test in Example 34.

(51) FIG. 51 is a graph showing the results of a charge/discharge test in Example 35.

(52) FIG. 52 is a graph showing the results of a charge/discharge test in Example 36.

(53) FIG. 53 is a graph showing the results of a charge/discharge test in Example 37.

DESCRIPTION OF EMBODIMENTS

(54) The following examples are offered to demonstrate the present invention in more detail, but should not be construed as limiting the present invention. All parts are by mass unless otherwise specified, and all percentages are by mass unless otherwise specified.

PREPARATION 1

(55) An amount of 28 mg of lithium oxide (Li.sub.2O, produced by Strem Chemicals Inc.) as a cathode active material, 80 mg of a catalyst for an electrode (60% Ag/C, produced by Alfa Aesar), and 15 mg of polytetrafluoroethylene (PTFE) were kneaded into a cathode mix. A 14 mg portion of the cathode mix was pressed onto 80 mg of a nickel mesh, whereby a cathode was prepared.

PREPARATION 2

(56) An amount of 85 mg of a catalyst for an electrode (60% Ag/C, produced by Alfa Aesar) and 15 mg of PTFE were kneaded into a cathode mix. A 14 mg portion of the cathode mix was pressed onto 80 mg of a nickel mesh, whereby a cathode was prepared.

EXAMPLE 1

(57) A three-electrode cell was prepared in which the working electrode was the cathode prepared in Preparation 1, the counter electrode and the reference electrode were lithium metal, and the electrolyte solution was a 1 M LiClO.sub.4/propylenecarbonate (PC) electrolyte solution. The three-electrode cell was measured by cyclic voltammetry (CV) in a glove box. In the measurement, the electrode potential was changed from the open circuit voltage (OCV) 3.38 V.fwdarw.4 V.fwdarw.1.2 V.fwdarw.OCV 3.38 V at a scan rate of 0.2 mV/s.

(58) FIG. 1 shows the results. In FIG. 1, the horizontal axis represents the potential, and the vertical axis represents the current.

(59) The results shown in FIG. 1 demonstrate that the use of the cathode prepared in Preparation 1 resulted in oxidation peaks at approximately 3.05 V and approximately 3.7 V, and a reduction peak at approximately 2.25 V. Considering that the theoretical potential of the reaction 2Li.sub.2O.fwdarw.Li.sub.2O.sub.2+2Li.sup.++2e.sup. is 2.87 V, the oxidation and reduction peaks observed in this experiment were concluded as oxidation reduction peaks corresponding to the forward and reverse reactions of the formula.

COMPARATIVE EXAMPLE 1

(60) Following the same procedure as in Example 1 and using the cathode prepared in Preparation 2 as a working electrode, cyclic voltammetry (CV) was performed.

(61) FIG. 2 shows the results. The results shown in FIG. 2 demonstrate that the use of the cathode prepared in Preparation 2 which is free from Li.sub.2O resulted in no oxidation and reduction peak.

PREPARATION 3

(62) An amount of 44 mg of lithium oxide (Li.sub.2O, produced by Strem Chemicals Inc.) as a cathode active material, 84 mg of artificial graphite KS6L (produced by TIMCAL Graphite & Carbon's), and 7 mg of polytetrafluoroethylene (PTFE) were kneaded into a cathode mix. A 6 mg portion of the cathode mix was pressed onto 80 mg of a nickel mesh, whereby a cathode was prepared.

PREPARATION 4

(63) Following the same procedure as in Preparation 3 and using lithium peroxide (Li.sub.2O.sub.2, produced by Alfa Aesar) as a cathode active material instead of lithium oxide, a cathode mix was prepared. A 6 mg portion of the cathode mix was pressed onto 80 mg of a nickel mesh, whereby a cathode was prepared.

PREPARATION 5

(64) Following the same procedure as in Preparation 3 and using sodium oxide (Na.sub.2O, produced by Alfa Aesar) as a cathode active material instead of lithium oxide, a cathode mix was prepared. A 6 mg portion of the cathode mix was pressed onto 80 mg of a nickel mesh, whereby a cathode was prepared.

PREPARATION 6

(65) Following the same procedure as in Preparation 3 and using sodium peroxide (Na.sub.2O.sub.2, produced by Wako Pure Chemical Industries, Ltd.) as a cathode active material instead of lithium oxide, a cathode mix was prepared. A 6 mg portion of the cathode mix was pressed onto 80 mg of a nickel mesh, whereby a cathode was prepared.

EXAMPLE 2

(66) Three-electrode cells were prepared in which the cathodes prepared in Preparations 3 to 6 were individually used as a working electrode, the counter electrode and the reference electrode were lithium metal, and the electrolyte solution was a propylenecarbonate (PC) electrolyte solution. The three-electrode cells were subjected to a charge/discharge test in a glove box. Charging and discharging were performed under the following conditions: cut-off potential: 1.4 to 4.2 V; and current load: 0.134 A per mol of the active material. In the experiments using the cathodes prepared in Preparations 3 and 5, the cycle was started with a charge phase, and in the experiments using the cathodes prepared in Preparations 4 and 6, the cycle was started with a discharge phase. Table 1 shows the results.

(67) TABLE-US-00001 TABLE 1 (mAh/g) Preparation 3 Preparation 4 Preparation 5 Preparation 6 Discharge 79 150 146 115 capacity in first cycle Discharge 66 41 13 16 capacity in third cycle

(68) As seen in Table 1, in all the cases using the cathodes, the cells could be discharged and recharged multiple times. It was also revealed that the cathodes according to the present invention can function regardless of whether they are in a discharged state or a charged state when assembled into a cell.

PREPARATION 7 (PROCESS FOR PREPARING Li2O/Fe2O3 CATHODE)

(69) An amount of 1.99 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd.) as a cathode active material and 2.09 g of -iron oxide (produced by Wako Pure Chemical Industries, Ltd.) as a catalyst for an electrode were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm) were operated at a rate of rotation of 600 rpm for 60 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 3 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to be a mixture of Li.sub.2O and LiFeO.sub.2. A 172 mg portion of the solid powder, 200 mg of acetylene black as a conductive auxiliary agent, and 28 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

PREPARATION 8 (PROCESS FOR PREPARING Li2O/Co3O4 CATHODE)

(70) An amount of 1.43 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd.) as a cathode active material and 1.54 g of cobalt oxide (Co.sub.3O.sub.4, produced by Wako Pure Chemical Industries, Ltd.) as a catalyst for an electrode were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm) were operated at a rate of rotation of 600 rpm for 60 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 4 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to be a mixture of Li.sub.2O and Co.sub.3O.sub.4. A 126 mg portion of the solid powder, 142 mg of acetylene black as a conductive auxiliary agent, and 20 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

PREPARATION 9 (PROCESS FOR PREPARING Li2O/NiO CATHODE)

(71) An amount of 2.75 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd.) as a cathode active material and 2.74 g of nickel oxide (NiO, produced by Kanto Chemical Co., Inc.) as a catalyst for an electrode were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm) were operated at a rate of rotation of 600 rpm for 60 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 5 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to be a mixture of Li.sub.2O and NiO. A 73 mg portion of the solid powder, 89 mg of acetylene black as a conductive auxiliary agent, and 14 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

PREPARATION 10 (PROCESS FOR PREPARING Li2O/LiCoO2 CATHODE)

(72) An amount of 2.32 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd.) as a cathode active material and 3.05 g of lithium cobalt oxide (produced by Wako Pure Chemical Industries, Ltd.) as a catalyst for an electrode were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm) were operated at a rate of rotation of 600 rpm for 60 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 6 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to be a mixture of Li.sub.2O and LiCoO.sub.2. A 61 mg portion of the solid powder, 77 mg of acetylene black as a conductive auxiliary agent, and 10 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

PREPARATION 11 (PROCESS FOR PREPARING Li2O/MnO2 CATHODE)

(73) An amount of 1.90 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd.) as a cathode active material and 2.22 g of manganese dioxide (produced by Wako Pure Chemical Industries, Ltd.) as a catalyst for an electrode were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm were operated at a rate of rotation of 600 rpm for 60 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 7 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to be a mixture of Li.sub.2O and MnO.sub.2. A 113 mg portion of the solid powder, 134 mg of acetylene black as a conductive auxiliary agent, and 21 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

PREPARATION 12 (PROCESS FOR PREPARING Li2O/SrCoO2.5 CATHODE)

(74) An amount of 4.43 g of strontium carbonate (produced by Wako Pure Chemical Industries, Ltd.) and 2.41 g of cobalt oxide (Co.sub.3O.sub.4, produced by Wako Pure Chemical Industries, Ltd.) were mixed in an agate mortar, and fired under an air atmosphere at 900 C. for 12 hours, whereby an oxygen-deficient perovskite compound SrCoO.sub.2.5 was obtained.

(75) An amount of 0.98 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd.) as a cathode active material and 0.48 g of the SrCoO.sub.2.5 prepared above as a catalyst for an electrode were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm were operated at a rate of rotation of 600 rpm for 60 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 8 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to be a mixture of Li.sub.2O and amorphous SrCoO.sub.2.5. A 35 mg portion of the solid powder, 46 mg of acetylene black as a conductive auxiliary agent, and 7 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

EXAMPLE 3 (CHARGE/DISCHARGE TEST)

(76) A charge/discharge test was performed using a three-electrode cell having a conventional structure. The working electrode was the Li.sub.2O/Fe.sub.2O.sub.3 cathode mix electrode prepared in Preparation 7, the counter and reference electrodes were lithium metal, and the electrolyte solution was a 1 M LiTFSI DME electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2], DME: 1,2-dimethoxyethane). After charging at a current density of 4.5 mA/g of the cathode active material, discharging was performed at a similar current density. FIG. 9 shows the results of the charge/discharge test. As seen in FIG. 9, the use of lithium oxide as a cathode active material allows for repetition of charging and discharging.

EXAMPLE 4 (CHARGE/DISCHARGE TEST)

(77) The charge/discharge test was performed under the same conditions as in Example 3 using the Li.sub.2O/Co.sub.3O.sub.4 cathode mix electrode prepared in Preparation 8 as a working electrode. FIG. 10 shows the results of the measurement. As seen in FIG. 10, the use of lithium oxide as a cathode active material allows for charging and discharging.

EXAMPLE 5 (CHARGE/DISCHARGE TEST)

(78) The charge/discharge test was performed under the same conditions as in Example 3 using the Li.sub.2O/NiO cathode mix electrode prepared in Preparation 9 as a working electrode. FIG. 11 shows the results of the measurement. As seen in FIG. 11, the use of lithium oxide as a cathode active material allows for charging and discharging.

EXAMPLE 6 (CHARGE/DISCHARGE TEST)

(79) The charge/discharge test was performed under the same conditions as in Example 3 using the Li.sub.2O/LiCoO.sub.2 cathode mix electrode prepared in Preparation 10 as a working electrode. FIG. 12 shows the results of the measurement. As seen in FIG. 12, the use of lithium oxide as a cathode active material allows for charging and discharging.

EXAMPLE 7 (CHARGE/DISCHARGE TEST)

(80) The charge/discharge test was performed under the same conditions as in Example 3 using the Li.sub.2O/MnO.sub.2 cathode mix electrode prepared in Preparation 11 as a working electrode. FIG. 13 shows the results of the measurement. As seen in FIG. 13, the use of lithium oxide as a cathode active material allows for charging and discharging.

EXAMPLE 8 (CHARGE/DISCHARGE TEST)

(81) The charge/discharge test was performed under the same conditions as in Example 3 using the Li.sub.2O/SrCoO.sub.2.5 cathode mix electrode prepared in Preparation 12 as a working electrode. FIG. 14 shows the results of the measurement. As seen in FIG. 14, the use of lithium oxide as a cathode active material allows for charging and discharging.

EXAMPLE 9 (ANALYSIS OF GAS GENERATED DURING CHARGE)

(82) The charge test was performed under the same conditions as in Example 3, and components in the gas phase in the cell were identified and quantified using a quadrupole mass spectrometer. FIG. 15 shows the results of the measurement. As seen in FIG. 15, no noticeable gas generation was observed in the range of the capacity of oxidation up to 600 mAh/g. This demonstrates that Li.sub.2O was converted into Li.sub.2O.sub.2 without generating oxygen. The arrows in FIG. 15 indicate which scale of the right or left vertical axis to use for each line in the graph.

EXAMPLE 10 (XRD ANALYSIS OF CHARGED CATHODE)

(83) The charge test was performed under the same conditions as in Example 5. After charging to a cut-off voltage of 3.3 V, the cathode was washed with a DME (1,2-dimethoxyethane) solvent and then dried. The charged cathode was then placed on a hermetically sealed sample stage purged with argon, and subjected to XRD measurement. FIG. 16 shows the results. A Li.sub.2O signal diminishes around 33.5 with changing capacity of oxidation, and signals of Li.sub.2O.sub.2 were observed at 34.5 and 39.8. This demonstrates that Li.sub.2O was converted into Li.sub.2O.sub.2 during charge.

EXAMPLE 11 (QUANTIFICATION OF Li2O2 IN CHARGED CATHODE)

(84) The charge test was performed under the same conditions as in Example 4. A cathode was prepared by pressing 8.24 mg of the cathode mix onto 60 mg of an aluminum mesh. After charging to a cut-off voltage of 3.3 V, the cathode was washed with a DME (1,2-dimethoxyethane) solvent and then dried. The oxidized cathode prepared in a glove box under an argon atmosphere and 1 mg of manganese dioxide were dispersed in 1 ml of deoxidized water. Li.sub.2O.sub.2, which was converted from Li.sub.2O during charge, dissolved in water to form H.sub.2O.sub.2, and then the reaction (H.sub.2O.sub.2.fwdarw.H.sub.2O+0.5O.sub.2) occurred in the presence of manganese dioxide as a catalyst, thereby to generate oxygen gas. The oxygen gas was identified and quantified using a quadrupole mass spectrometer. The results confirm generation of 2.3 mol of oxygen. This demonstrates that Li.sub.2O.sub.2 was generated as a result of the charge reaction from Li.sub.2O.

EXAMPLE 12 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(85) The charge/discharge test was performed using a commercially available two-electrode cell (HS cell, produced by Hohsen Corp.). The working electrode was the Li.sub.2O/Fe.sub.2O.sub.3 cathode mix electrode prepared in Preparation 7, the counter electrode was lithium metal, and the electrolyte solution was a 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl) imide [LiN(SO.sub.2CF.sub.3).sub.2]). After charging at a current density of 4.5 mA/g of the cathode active material, discharging was performed at a similar current density. FIG. 17 shows the results of the charge/discharge test. As seen in FIG. 17, the use of lithium oxide as a cathode active material allows for charging and discharging.

(86) LiCoO.sub.2 used in Preparation 10 and Example 6 is a common compound widely known as a cathode active material. Although the charge/discharge potential of LiCoO.sub.2 is 3.8 V (vs. Li metal) the charge potential in the charge/discharge experiment in Example 6 (shown in FIG. 12) was approximately 3.2 V (vs. Li metal). From this fact, it is unlikely that LiCoO.sub.2 itself functioned as an active material in charging and discharging, and LiCoO.sub.2 is presumed to have functioned as a catalyst for an electrode in Example 6. Likewise, LiFeO.sub.2 used in Preparation 7 and Example 3 and SrCoO.sub.2.5 used in Preparation 12 and Example 8 are presumed to have functioned as a catalyst for an electrode in Example 8. Additionally, each single oxide (Co.sub.3O.sub.4, NiO, MnO.sub.2) is also presumed to have functioned as a catalyst for an electrode when used alone in the absence of Li.sub.2O because flat ranges indicating charging and discharging were not observed unlike the examples.

PREPARATION 13 (PROCESS FOR PREPARING Li2O/Fe2O3/Co3O4 CATHODE)

(87) An amount of 2.62 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd.) as a cathode active material, 1.38 g of -iron oxide (produced by Wako Pure Chemical Industries, Ltd.) as a catalyst for an electrode, and 1.36 g of cobalt oxide (Co.sub.3O.sub.4, produced by Wako Pure Chemical Industries, Ltd.) were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm) were operated at a rate of rotation of 600 rpm for 60 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 18 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to contain Li.sub.2O and LiFeO.sub.2. An 81 mg portion of the solid powder, 100 mg of acetylene black as a conductive auxiliary agent, and 15 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

EXAMPLE 13 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(88) The charge/discharge test was performed using a commercially available two-electrode cell (HS cell, produced by Hohsen Corp.). The working electrode was the Li.sub.2O/Fe.sub.2O.sub.3/Co.sub.3O.sub.4 cathode mix electrode prepared in Preparation 13, the counter electrode was lithium metal, and the electrolyte solution was a 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2]). After charging at a current density of 4.5 mA/g of the cathode active material, discharging was performed at a similar current density. FIG. 19 shows the results of the charge/discharge test. As seen in FIG. 19, the use of lithium oxide as a cathode active material allows for charging and discharging.

EXAMPLE 14 (XRD ANALYSIS OF CHARGED CATHODE)

(89) The charge test was performed under the same conditions as in Example 13. After charging to a cut-off voltage of 3.3V, the cathode was washed with an acetonitrile solvent and then dried. The charged cathode was then placed on a hermetically sealed sample stage purged with argon, and subjected to XRD measurement. FIG. 20 shows the results. A Li.sub.2O signal diminishes around 33.5 with changing capacity of oxidation. This indicates that Li.sub.2O was converted into Li.sub.2O.sub.2 during charge.

EXAMPLE 15 (QUANTIFICATION OF Li2O2 IN CATHODE AFTER CHARGING AND DISCHARGING)

(90) The charge/discharge test was performed under the same conditions as in Example 13. Quantification of lithium peroxide in the cathode was performed in the same manner as in Example 11 at different depths of charge/discharge. FIG. 21 shows the results of the detected amount of Li.sub.2O.sub.2 plotted against the charge capacity in the first charge phase. The figure also includes a solid line representing the theoretical amount of Li.sub.2O.sub.2 estimated against the charge capacity based on the reaction formula (II). As seen in FIG. 21, it was confirmed that, the charge reaction generated Li.sub.2O.sub.2 as shown in the reaction formula (II) at a theoretical efficiency based on the charge capacity of approximately 80%. FIG. 22 shows detected amounts of Li.sub.2O.sub.2 plotted against the discharge capacity in the first discharge phase after the first charge phase. The figure also includes a solid line representing the theoretical amount of Li.sub.2O.sub.2 estimated against the discharge capacity based on the reaction formula (II). As seen in FIG. 22, it was confirmed that Li.sub.2O.sub.2 was consumed as shown in the reaction formula (II) at a theoretical efficiency based on the discharge capacity of almost 100%.

PREPARATION 14 (PROCESS FOR PREPARING Li2O/Fe2O3/Co3O4 CATHODE)

(91) An amount of 2.46 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd) as a cathode active material, 0.65 g of -iron oxide (produced by Wako Pure Chemical Industries, Ltd.) as a catalyst for an electrode, and 0.67 g of cobalt oxide (CO.sub.3O.sub.4, produced by Wako Pure Chemical Industries, Ltd.) were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm) were operated at a rate of rotation of 600 rpm for 120 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 23 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to contain Li.sub.2O. A 79 mg portion of the solid powder, 83 mg of acetylene black as a conductive auxiliary agent, and 12 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

PREPARATION 15 (PROCESS FOR PREPARING Li2O/Fe2O3/Co3O4 CATHODE)

(92) An amount of 2.47 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd.) as a cathode active material, 0.33 g of -iron oxide (produced by Wako Pure Chemical Industries, Ltd.) as a catalyst for an electrode, and 0.33 g of cobalt oxide (Co.sub.3O.sub.4, produced by Wako Pure Chemical Industries, Ltd.) were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm) were operated at a rate of rotation of 600 rpm for 120 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 24 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to contain Li.sub.2O. A 66 mg portion of the solid powder, 70 mg of acetylene black as a conductive auxiliary agent, and 6 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

EXAMPLE 16 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(93) The charge/discharge test was performed under the same conditions as in Example 13 using the Li.sub.2O/Fe.sub.2O.sub.3/Co.sub.3O.sub.4 cathode mix electrode prepared in Preparation 14 as a working electrode. FIG. 25 shows the results of the charge/discharge test. As seen in FIG. 25, the use of lithium oxide as a cathode active material allows for charging and discharging.

EXAMPLE 17 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(94) The charge/discharge test was performed under the same conditions as in Example 13 using the Li.sub.2O/Fe.sub.2O.sub.3/Co.sub.3O.sub.4 cathode mix electrode prepared in Preparation 15 as a working electrode. FIG. 26 shows the results of the charge/discharge test. As seen in FIG. 26, the use of lithium oxide as a cathode active material allows for charging and discharging.

EXAMPLE 18 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(95) The charge/discharge test was performed under the same conditions as in Example 13, except that a 4.2 M LiFSI acetonitrile electrolyte solution (LiFSI: lithium bis(fluorosulfonyl)imide [LiN(SO.sub.2F).sub.2]) was used as an electrolyte solution instead of the 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2]). FIG. 27 shows the results of the charge/discharge test. As seen in FIG. 27, the use of lithium oxide as a cathode active material under the above conditions also allows for charging and discharging.

EXAMPLE 19 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(96) The charge/discharge test was performed under the same conditions as in Example 16, except that a 4.2 M LiFSI acetonitrile electrolyte solution (LiFSI: lithium bis(fluorosulfonyl)imide [LiN(SO.sub.2F).sub.2]) was used as an electrolyte solution instead of the 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2]). FIG. 28 shows the results of the charge/discharge test. As seen in FIG. 28, the use of lithium oxide as a cathode active material under the above conditions also allows for charging and discharging.

EXAMPLE 20 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(97) The charge/discharge test was performed under the same conditions as in Example 17, except that a 4.2 M LiFSI acetonitrile electrolyte solution (LiFSI: lithium bis(fluorosulfonyl)imide [LiN(SO.sub.2F).sub.2]) was used as an electrolyte solution instead of the 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2]). FIG. 29 shows the results of the charge/discharge test. As seen in FIG. 29, the use of lithium oxide as a cathode active material under the above conditions also allows for charging and discharging.

EXAMPLE 21 (CHARGE TEST USING TWO-ELECTRODE CELL)

(98) The charge test was performed using a commercially available two-electrode cell (HS cell, produced by Hohsen Corp.). The working electrode was the Li.sub.2O/Fe.sub.2O.sub.3/Co.sub.3O.sub.4 cathode mix electrode prepared in Preparation 13, the counter electrode was lithium metal, and the electrolyte solution was a 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2]). Charging was performed at a current density of 4.5 mA/g of the cathode active material. FIG. 30 shows the results of the charge test. In FIG. 30, a fast increase of the potential is observed around the theoretical charge capacity (894 mAh/g) of the charge reaction at the cathode (2Li.sub.2O.fwdarw.Li.sub.2O.sub.2+2Li.sup.++2e.sup.). This demonstrates that the charge reaction at the cathode proceeded at remarkably high efficiency.

EXAMPLE 22 (CHARGE TEST USING TWO-ELECTRODE CELL)

(99) The charge test was performed using a commercially available two-electrode cell (HS cell, produced by Hohsen Corp.). The working electrode was the Li.sub.2O/Fe.sub.2O.sub.2/Co.sub.3O.sub.4 cathode mix electrode prepared in Preparation 14, the counter electrode was lithium metal, and the electrolyte solution was a 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2]). Charging was performed at a current density of 4.5 mA/g of the cathode active material. FIG. 31 shows the results of the charge test. In FIG. 31, a fast increase of the potential is observed around the theoretical charge capacity (894 mAh/g) of the charge reaction at the cathode (2Li.sub.2O.fwdarw.Li.sub.2O.sub.2+2Li.sup.++2e.sup.). This demonstrates that the charge reaction at the cathode proceeded at remarkably high efficiency.

EXAMPLE 23 (CHARGE TEST USING TWO-ELECTRODE CELL)

(100) The charge test was performed using a commercially available two-electrode cell (HS cell, produced by Hohsen Corp.). The working electrode was the Li.sub.2O/Fe.sub.2O.sub.3/Co.sub.3O.sub.4 cathode mix electrode prepared in Preparation 15, the counter electrode was lithium metal, and the electrolyte solution was a 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2]). Charging was performed at a current density of 4.5 mA/g of the cathode active material. FIG. 32 shows the results of the charge test. In FIG. 32, a fast increase of the potential is observed around the theoretical charge capacity (894 mAh/g) of the charge reaction at the cathode (2Li.sub.2O.fwdarw.Li.sub.2O.sub.2+2Li.sup.++2e.sup.). This demonstrates that the charge reaction at the cathode proceeded at remarkably high efficiency.

PREPARATION 16 (PROCESS FOR PREPARING Li2O/Co3O4 CATHODE)

(101) An amount of 2.09 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd.) as a cathode active material and 2.23 g of cobalt oxide (Co.sub.3O.sub.4, produced by Wako Pure Chemical Industries, Ltd.) as a catalyst for an electrode were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm) were operated at a rate of rotation of 600 rpm for 180 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 33 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to contain Li.sub.2O and LiCoO.sub.2. A 57 mg portion of the solid powder, 69 mg of acetylene black as a conductive auxiliary agent, and 6 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

PREPARATION 17 (PROCESS FOR PREPARING Li2O/Co3O4 CATHODE)

(102) An amount of 2.19 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd.) as a cathode active material and 1.16 g of cobalt oxide (CO.sub.3O.sub.4, produced by Wako Pure Chemical Industries, Ltd.) as a catalyst for an electrode were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm) were operated at a rate of rotation of 600 rpm for 180 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 34 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to contain Li.sub.2O and LiCoO.sub.2. A 67 mg portion of the solid powder, 70 mg of acetylene black as a conductive auxiliary agent, and 6 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

EXAMPLE 24 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(103) The charge/discharge test was performed under the same conditions as in Example 13 using the Li.sub.2O/Co.sub.3O.sub.4 cathode mix electrode prepared in Preparation 16 as a working electrode. FIG. 35 shows the results of the charge/discharge test. As seen in FIG. 35, the use of lithium oxide as a cathode active material allows for charging and discharging.

EXAMPLE 25 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(104) The charge/discharge test was performed under the same conditions as in Example 13 using the Li.sub.2O/Co.sub.3O.sub.4 cathode mix electrode prepared in Preparation 17 as a working electrode. FIG. 36 shows the results of the charge/discharge test. As seen in FIG. 36, the use of lithium oxide as a cathode active material allows for charging and discharging.

EXAMPLE 26 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(105) The charge/discharge test was performed under the same conditions as in Example 24, except that a 4.2 M LiFSI acetonitrile electrolyte solution (LiFSI: lithium bis(fluorosulfonyl)imide [LiN(SO.sub.2F).sub.2]) was used as an electrolyte solution instead of the 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2]). FIG. 37 shows the results of the charge/discharge test. As seen in FIG. 37, the use of lithium oxide as a cathode active material under the above conditions also allows for charging and discharging.

EXAMPLE 27 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(106) The charge/discharge test was performed under the same conditions as in Example 25, except that a 4.2 M LiFSI acetonitrile electrolyte solution (LiFSI: lithium bis(fluorosulfonyl)imide [LiN(SO.sub.2F).sub.2]) was used as an electrolyte solution instead of the 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2]). FIG. 38 shows the results of the charge/discharge test. As seen in FIG. 38, the use of lithium oxide as a cathode active material under the above conditions also allows for charging and discharging.

PREPARATION 18 (PROCESS FOR PREPARING Li2O/Co3O4 CATHODE)

(107) An amount of 2.43 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd.) as a cathode active material and 0.66 g of cobalt oxide (Co.sub.3O.sub.4, produced by Wako Pure Chemical Industries, Ltd.) as a catalyst for an electrode were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm) were operated at a rate of rotation of 600 rpm for 180 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 39 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to contain Li.sub.2O. A 51 mg portion of the solid powder, 63 mg of acetylene black as a conductive auxiliary agent, and 4 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

PREPARATION 19 (PROCESS FOR PREPARING Li2O/Co3O4 CATHODE)

(108) An amount of 2.63 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd.) as a cathode active material and 0.36 g of cobalt oxide (CO.sub.3O.sub.4, produced by Wako Pure Chemical Industries, Ltd.) as a catalyst for an electrode were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm) were operated at a rate of rotation of 600 rpm for 180 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 40 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to contain Li.sub.2O. A 57 mg portion of the solid powder, 61 mg of acetylene black as a conductive auxiliary agent, and 5 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

EXAMPLE 28 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(109) The charge/discharge test was performed under the same conditions as in Example 13 using the Li.sub.2O/Co.sub.3O.sub.4 cathode mix electrode prepared in Preparation 18 as a working electrode. FIG. 41 shows the results of the charge/discharge test. As seen in FIG. 41, the use of lithium oxide as a cathode active material allows for charging and discharging.

EXAMPLE 29 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(110) The charge/discharge test was performed under the same conditions as in Example 13 using the Li.sub.2O/Co.sub.3O.sub.4 cathode mix electrode prepared in Preparation 19 as a working electrode. FIG. 42 shows the results of the charge/discharge test. As seen in FIG. 42, the use of lithium oxide as a cathode active material allows for charging and discharging.

EXAMPLE 30 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(111) The charge/discharge test was performed under the same conditions as in Example 28, except that a 4.2 M LiFSI acetonitrile electrolyte solution (LiFSI: lithium bis(fluorosulfonyl)imide [LiN(SO.sub.2F).sub.2]) was used as an electrolyte solution instead of the 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2]). FIG. 43 shows the results of the charge/discharge test. As seen in FIG. 43, the use of lithium oxide as a cathode active material under the above conditions also allows for charging and discharging.

EXAMPLE 31 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(112) The charge/discharge test was performed under the same conditions as in Example 29, except that a 4.2 M LiFSI acetonitrile electrolyte solution (LiFSI: lithium bis(fluorosulfonyl)imide [LiN(SO.sub.2F).sub.2]) was used as an electrolyte solution instead of the 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2]). FIG. 44 shows the results of the charge/discharge test. As seen in FIG. 44, the use of lithium oxide as a cathode active material under the above conditions also allows for charging and discharging.

EXAMPLE 32 (XRD ANALYSIS OF CHARGED CATHODE)

(113) The charge test was performed under the same conditions as in Example 27. After charging at 400 mAh/g, the cathode was washed with an acetonitrile solvent and then dried. The charged cathode was placed on a hermetically sealed sample stage purged with argon, and subjected to XRD measurement. FIG. 45 shows the results. A Li.sub.2O signal diminishes around 33.5 with changing capacity of oxidation. This indicates that Li.sub.2O was converted into Li.sub.2O.sub.2 during charge.

EXAMPLE 33 (QUANTIFICATION OF Li2O2 IN CATHODE AFTER CHARGING AND DISCHARGING)

(114) The charge/discharge test was performed under the same conditions as in Example 27. Quantification of lithium peroxide in the cathode was performed in the same manner as in Example 11 after each charge or discharge phase. The amount of lithium peroxide in the mix after the first charge phase was 4.17 mmol/g of lithium oxide in the mix at the beginning. The amount of lithium peroxide in the mix after the first discharge phase following the first charge phase was 0.17 mmol/g of lithium oxide in the mix at the beginning. Thus, it was confirmed that lithium peroxide was almost completely consumed through discharge. The amount of lithium peroxide after the second charge phase was 3.89 mmol/g. This demonstrates that reversible oxidation into lithium peroxide occurred again during recharge.

PREPARATION 20 (PROCESS FOR PREPARING Li2O/CoO CATHODE)

(115) An amount of 2.30 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd.) as a cathode active material and 2.31 g of cobalt oxide (CoO, produced by Wako Pure Chemical Industries, Ltd.) as a catalyst for an electrode were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm) were operated at a rate of rotation of 600 rpm for 180 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 46 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to contain Li.sub.2O. A 75 mg portion of the solid powder, 85 mg of acetylene black as a conductive auxiliary agent, and 6 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

PREPARATION 21 (PROCESS FOR PREPARING Li2O/CoO CATHODE)

(116) An amount of 2.30 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd.) as a cathode active material and 1.15 g of cobalt oxide (CoO, produced by Wako Pure Chemical Industries, Ltd.) as a catalyst for an electrode were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm) were operated at a rate of rotation of 600 rpm for 180 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 47 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to contain Li.sub.2O. A 59 mg portion of the solid powder, 66 mg of acetylene black as a conductive auxiliary agent, and 4 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

PREPARATION 22 (PROCESS FOR PREPARING Li2O/CoO CATHODE)

(117) An amount of 2.95 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd) as a cathode active material and 0.75 g of cobalt oxide (CoO, produced by Wako Pure Chemical Industries, Ltd.) as a catalyst for an electrode were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm) were operated at a rate of rotation of 600 rpm for 180 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 48 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to contain Li.sub.2O. An 89 mg portion of the solid powder, 107 mg of acetylene black as a conductive auxiliary agent, and 8 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

PREPARATION 23 (PROCESS FOR PREPARING Li2O/CoO CATHODE)

(118) An 3.09 g of lithium oxide (produced by Kojundo Chemical Laboratory Co., Ltd.) as a cathode active material and 0.39 g of cobalt oxide (CoO, produced by Wako Pure Chemical Industries, Ltd.) as a catalyst for an electrode were combined in a planetary ball mill pot, and mixed using a planetary ball mill (under conditions in which 25 zirconia balls (10 mm) were operated at a rate of rotation of 600 rpm for 180 hours). The whole procedure was performed in an argon-substituted glove box with a moisture concentration of not higher than 1 ppm. FIG. 49 shows the results of XRD measurement of the resultant solid powder. The solid powder was found to contain Li.sub.2O. An 87 mg portion of the solid powder, 94 mg of acetylene black as a conductive auxiliary agent, and 7 mg of polytetrafluoroethylene powder as a binder were mixed in an agate mortar, and processed into a clay-like mixture, whereby a cathode mix was prepared. The cathode mix was pressed onto 60 mg of an aluminum mesh, whereby a cathode was prepared.

EXAMPLE 34 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(119) The charge/discharge test was performed under the same conditions as in Example 28, except that a 4.2 M LiFSI acetonitrile electrolyte solution (LiFSI: lithium bis(fluorosulfonyl) imide [LiN(SO.sub.2F).sub.2]) was used as an electrolyte solution instead of the 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2]). FIG. 50 shows the results of the charge/discharge test. As seen in FIG. 50, the use of lithium oxide as a cathode active material under the above conditions also allows for charging and discharging.

EXAMPLE 35 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(120) The charge/discharge test was performed under the same conditions as in Example 29, except that a 4.2 M LiFSI acetonitrile electrolyte solution (LiFSI: lithium bis(fluorosulfonyl) imide [LiN(SO.sub.2F).sub.2]) was used as an electrolyte solution instead of the 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2]). FIG. 51 shows the results of the charge/discharge test. As seen in FIG. 51, the use of lithium oxide as a cathode active material under the above conditions also allows for charging and discharging.

EXAMPLE 36 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(121) The charge/discharge test was performed under the same conditions as in Example 28, except that a 4.2 M LiFSI acetonitrile electrolyte solution (LiFSI: lithium bis(fluorosulfonyl)imide [LiN(SO.sub.2F).sub.2]) was used as an electrolyte solution instead of the 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2]), and that the current density during the charge and discharge phases was 22.5 mA/g of the active material. FIG. 52 shows the results of the charge/discharge test. As seen in FIG. 52, the use of lithium oxide as a cathode active material under the above conditions also allows for charging and discharging.

EXAMPLE 37 (CHARGE/DISCHARGE TEST USING TWO-ELECTRODE CELL)

(122) The charge/discharge test was performed under the same conditions as in Example 29, except that a 4.2 M LiFSI acetonitrile electrolyte solution (LiFSI: lithium bis(fluorosulfonyl)imide [LiN(SO.sub.2F).sub.2]) was used as an electrolyte solution instead of the 4.2 M LiTFSI acetonitrile electrolyte solution (LiTFSI: lithium bis(trifluoromethanesulfonyl)imide, [LiN(SO.sub.2CF.sub.3).sub.2]), and that the current density during the charge and discharge phases was 22.5 mA/g of the active material. FIG. 53 shows the results of the charge/discharge test. As seen in FIG. 53, the use of lithium oxide as a cathode active material under the above conditions also allows for charging and discharging.

(123) The results of the examples reveal that the cells including a cathode according to the present invention have a high theoretical voltage and theoretical capacity, and can be discharged and recharged multiple times. The examples also suggest that in cells including such a cathode, the same mechanism functions to provide a high theoretical volume and theoretical capacity, and allow repetition of charging and discharging.

(124) Accordingly, the results of the examples demonstrate that all of the various embodiments of the present invention disclosed herein can be applied in the entire technical range of the present invention, and provide advantageous effects.