Lithium secondary battery and cathode active material for use in lithium secondary battery

Provided is a lithium secondary battery of a high energy density using a cathode active material having an excellent cycle characteristic in charging/discharging at a high capacity and a small irreversible capacity. The lithium secondary battery comprising: a cathode including a material that can be doped/undoped with lithium ions as an active material; an anode including a lithium metal, a lithium alloy, or a material that can be doped/undoped with lithium ions as an active material; and a liquid or solid electrolyte, wherein lithiated nickel dioxide containing tin is used as the cathode active material, and said lithiated nickel dioxide has a peak near 2.theta.=34.4.degree. and does not have a peak near 2.theta.=22.5.degree. in the X-ray diffraction pattern by CuK.alpha. rays, or the intensity ratio of the peak near 2.theta.=22.5.degree. to the peak near 2.theta.=34.4.degree. is 1.2 or less.

BACKGROUND OF THE INVENTION
 1. Technical Field of the Invention
 The present invention relates to a lithium secondary battery comprising a
 cathode including a material that can be doped/undoped with lithium ions
 as an active material; an anode including a lithium metal, a lithium
 alloy, or a material that can be doped/undoped with lithium ions as an
 active material; and a liquid or solid electrolyte, and to the cathode
 active material for use in the lithium secondary battery.
 2. Related Art of the Invention
 With a rapid advance of portable and cordless electronic devices, demands
 for a lithium secondary battery which can realize small size, lightweight
 and a large capacity compared to the conventional secondary batteries have
 been increasing.
 As a cathode active material in a lithium secondary battery, lithiated
 cobalt dioxide has been studied and it has already been put into practical
 use in the lithium secondary batteries as a power source for cellular
 phones and camcorders. Recently, lithiated nickel dioxide using a nickel
 compound as a raw material which is cheaper than cobalt compound and
 abundant in terms of resources has been examined actively.
 Lithiated nickel dioxide, as well as lithiated cobalt dioxide, is a
 compound having an .alpha.-NaFeO.sub.2 structure. However, it is difficult
 to synthesize lithiated nickel dioxide compared to lithiated cobalt
 dioxide, because nickel is easily substituted at a lithium site in
 lithiated nickel dioxide. Recent progress in the synthetic conditions has
 offered substantial practicability of stoichiometric composition of
 lithiated nickel dioxide presenting a high discharge capacity. However,
 the lithiated nickel dioxide still suffers capacity drop-off associated
 with repeated cycles of charging/discharging processes at high capacity,
 or in other words, a poor cycle characteristic.
 SUMMARY OF THE INVENTION
 An object of the present invention is to provide a lithium secondary
 battery of a high energy density using a cathode active material having an
 excellent cycle characteristic in charging/discharging at a high capacity
 and a small irreversible capacity.

DETAILED DESCRIPTION OF THE INVENTION
 After intensive studies, the present inventors found that a lithium
 secondary battery having an excellent cycle characteristic in
 charging/discharging at a high capacity and a high energy density, can be
 obtained by using, as a cathode active material, a lithium secondary
 battery comprising: a cathode including a material that can be
 doped/undoped with lithium ions as an active material; an anode including
 a lithium metal, a lithium alloy, or a material that can be doped/undoped
 with lithium ions as an active material; and a liquid or solid
 electrolyte, wherein lithiated nickel dioxide containing tin is used as
 the cathode active material, and said lithiated nickel dioxide has
 specific intensity ratio in the X-ray diffraction pattern by CuK.alpha.
 rays.
 That is, the present invention is:
 [1] A lithium secondary battery comprising:
 a cathode including a material that can be doped/undoped with lithium ions
 as an active material;
 an anode including a lithium metal, a lithium alloy, or a material that can
 be doped/undoped with lithium ions as an active material; and a liquid or
 solid electrolyte, wherein lithiated nickel dioxide containing tin is used
 as the cathode active material, and said lithiated nickel dioxide has a
 peak near 2.theta.=34.4.degree. and does not have a peak near
 2.theta.=22.5.degree. in the X-ray diffraction pattern by CuK.alpha. rays,
 or the intensity ratio of the peak near 2.theta.=22.5.degree. to the peak
 near 2.theta.=34.4.degree. is 1.2 or less.
 [2] A lithium secondary battery according to [1], wherein the lithiated
 nickel dioxide containing tin is obtained by firing a mixture of a lithium
 compound, a nickel compound and tin or a tin compound.
 [3] A lithium secondary battery according to [2], wherein lithium stannate
 is used as a tin compound.
 [4] A lithium secondary battery according to [2], wherein the lithiated
 nickel dioxide containing tin is obtained by the steps of dispersing a tin
 compound and a nickel compound in an aqueous solution including a
 water-soluble lithium salt, evaporating a water content of the resultant
 solution to obtain a mixture, and firing the resultant mixture in an
 atmosphere containing oxygen.
 [5] A lithium secondary battery according to [4], wherein lithium nitrate
 is used as the water-soluble lithium salt, and a basic nickel carbonate is
 used as the nickel compound.
 [6] A lithium secondary battery according to [2], wherein the firing is
 conducted at a temperature of lower than 660.degree. C.
 [7] A cathode active material for use in a lithium secondary battery,
 wherein said cathode active material is lithiated nickel dioxide
 containing tin, which has a peak near 2.theta.=34.4.degree. and does not
 have a peak near 2.theta.=22.5.degree. in the X-ray diffraction pattern by
 CuK.alpha. rays, or the intensity ratio of the peak near
 2.theta.=22.5.degree. to the peak near 2.theta.=34.4.degree. is 1.2 or
 less.
 Next, the present invention will be explained in detail. In the lithium
 secondary battery of the present invention, the cathode includes a
 material that can be doped/undoped with lithium ions as an active
 material. And as the material that can be doped/undoped with lithium ions,
 lithiated nickel dioxide containing tin is used, in which said lithiated
 nickel dioxide has a peak near 2.theta.=34.4.degree. and does not have a
 peak near 2.theta.=22.5.degree. in the X-ray diffraction pattern by
 CuK.alpha. rays, or the intensity ratio of the peak near
 2.theta.=22.5.degree. to the peak near 2.theta.=34.4.degree. is 1.2 or
 less.
 Here, the peak near 2.theta.=34.4.degree. is assigned to the diffraction
 line (200) of lithium stannate (Li.sub.2 SnO.sub.3 :JCPDS card
 No.31-0763). When this peak is not observed, improvement of the cycle
 characteristic in the charging/discharging at a high capacity is
 insufficient, and it is not preferable.
 Although the peak near 2.theta.=22.5.degree. is unassigned, when the
 relative intensity of this peak to the peak near 2.theta.=344.4.degree.
 becomes large, it is not preferable because the irreversible capacity
 (difference of charged quantity of electricity and discharged quantity of
 electricity observed in early stages) at the time of charging/discharging
 increases, even though the cycle characteristic is improved.
 Specifically, when the intensity ratio of the peak near
 2.theta.=22.5.degree. to the peak near 2.theta.=34.4.degree. is 1.2 or
 less, the irreversible capacity can be lowered below 50 mAh/g on the basis
 of the weight of cathode active material with maintaining a good cycle
 characteristic, it is preferable.
 As a process for obtaining the above-mentioned lithiated nickel dioxide
 containing tin, the process comprising the steps of mixing tin or a tin
 compound with previously synthesized lithiated nickel dioxide and firing
 the mixture can be used. However, a process comprising the steps of mixing
 a lithium compound, a nickel compound and tin or a tin compound and firing
 the mixture is preferable because the production process can be simplified
 and a small amount of tin can be added uniformly.
 Moreover, it can also be used the process comprising the steps of mixing
 first a nickel compound and tin or a tin compound and firing the mixture,
 and then further mixing a lithium compound and firing the resultant
 mixture again. Similarly, it can also be used the process comprising the
 steps of mixing first a lithium compound and tin or a tin compound and
 firing the mixture, and then further mixing a nickel compound and firing
 the resultant mixture again.
 Examples of the lithium compound used in the present invention include
 lithium carbonate, lithium nitrate, lithium hydroxide, etc.
 Examples of the nickel compound used in the present invention include
 nickel oxide, nickel hydroxide, nickel nitrate, nickel carbonate
 NiCO.sub.3.wH.sub.2 O (in the formula, w&gt;=0), basic nickel carbonate
 xNiCO.sub.3.yNi(OH).sub.2.zH.sub.2 O (in the formula, x&gt;0, y&gt;0 and z&gt;0),
 acidic nickel carbonate Ni.sub.m H.sub.2n (CO.sub.3).sub.m+n (in the
 formula, m&gt;0 and n&gt;0) etc.
 As a raw material of tin to be added, tin compounds such as metallic tin or
 oxide and its hydrate, and nitrate can be used. The valence of tin in a
 tin compound can be either divalent or tetravalent, and mixtures thereof
 can be also used. By using lithium stannate (Li.sub.2 SnO.sub.3) as a tin
 compound previously synthesized by reacting with a lithium compound, a
 material having an especially excellent cycle characteristic can be
 obtained, and it is preferable.
 As a process for mixing and firing a lithium compound, a nickel compound
 and a tin compound, it is preferred that the process comprising the steps
 of dispersing a tin compound and a nickel compound in an aqueous solution
 including a water-soluble lithium salt, evaporating a water content of the
 resultant solution to obtain a mixture, and firing the resultant mixture
 in an atmosphere containing oxygen.
 According to the above process, the water-soluble lithium salt can be mixed
 with the tin compound and the nickel compound uniformly, and a partial
 deficiency of lithium in lithiated nickel dioxide containing tin generated
 by the inhomogeneity of mixed composition can be prevented.
 The present inventors found a preferable combination of raw materials,
 namely, lithium nitrate is used as a water-soluble lithium salt and a
 basic nickel carbonate is used as a nickel compound, respectively. The
 lithium secondary battery using a resultant lithiated nickel dioxide
 containing tin obtained by this method shows a high energy density.
 The firing process preferably proceeds in an atmosphere containing oxygen,
 more preferably in an atmosphere of oxygen, and particularly preferably in
 a stream of oxygen.
 The firing temperature is preferably from 350.degree. C. to 800.degree. C.,
 and more preferably from 600.degree. C. to 750.degree. C. When the firing
 temperature is not lower than 600.degree. C. and lower than 660.degree.
 C., the irreversible capacity can be lowered below 40 mAh/g on the basis
 of the weight of cathode active material with maintaining a good cycle
 characteristic, it is preferable. When the firing temperature is higher
 than 800.degree. C., the rate of the rock salt type domain in which
 lithium ions and nickel ions are arranged irregularly in lithiated nickel
 dioxide becomes large, and reversible charging/discharging is disturbed,
 it is not preferable. When the firing temperature is lower than
 350.degree. C., the generation reaction of lithiated nickel dioxide hardly
 proceeds, and it is not preferable.
 The firing time is preferably 2 hours or more, and more preferably 5 hours
 or more. Moreover, 40 hours or less is practically preferable.
 After firing, obtained lithiated nickel dioxide can be treated or milled in
 an atmosphere including carbon dioxide, preferably in an atmosphere which
 carbon dioxide content is higher than air. According to the above process,
 the sheet-type cathode with large density can be produced.
 The cathode of the lithium secondary battery of the invention includes the
 active material of the aforementioned lithiated nickel dioxide containing
 tin, and can further include other components such as a carbonaceous
 material as a conductive substance and a thermoplastic resin as a binder.
 Examples of the carbonaceous material include natural graphite, artificial
 graphite, cokes, carbon black and the like. Such conductive substances may
 be used alone or in combination as a composite conductive substance, such
 as of artificial graphite and carbon black.
 Examples of the thermoplastic resin include poly(vinylidene fluoride)
 (which may hereinafter be referred to as "PVDF"), polytetrafluoroethylene
 (which may hereinafter be referred to as "PTFE"),
 tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride copolymer,
 hexafluoropropylene-vinylidene fluoride copolymer,
 tetrafluoroethylene-perfluorovinyl ether copolymer and the like. The above
 resins may be used alone or in combination of two or more.
 The anode of the lithium secondary battery of the invention includes a
 lithium metal, a lithium alloy or a material that can be doped/undoped
 with lithium ions. Examples of the material that can be doped/undoped with
 lithium ions include carbonaceous materials such as natural graphite,
 artificial graphite, cokes, carbon black, pyrolytic carbons, carbon
 fibers, fired products of organic polymer compounds and the like; and a
 chalcogen compound of oxide, sulfide and the like, which compound can be
 doped/undoped with lithium ions at lower potentials than in the cathode. A
 carbonaceous material including a graphite material such as natural
 graphite and artificial graphite as a main component is preferred, because
 the combination of such a carbonaceous material and a cathode provides a
 high energy density due to the flatness of their charging/discharging
 potential and low average working potential.
 As to a combination of the anode with a liquid electrolyte, in case where
 the liquid electrolyte does not contain ethylene carbonate, an anode
 containing poly(ethylene carbonate) is preferably used to improve the
 cycle characteristic and the large-current discharging characteristic of
 the battery.
 The carbonaceous material can be in any shape including a flaky shape like
 natural graphite, a spherical shape like mesocarbon micro-beads, a fibrous
 shape like graphitized carbon fiber and an agglomerate of fine powders. If
 required, a thermoplastic resin as a binder can be added to the
 carbonaceous material. Examples of a usable thermoplastic resin include
 PVDF, polyethylene, polypropylene and the like.
 Examples of the chalcogen compound of an oxide, sulfide and such, used as
 the anode, include crystalline or amorphous oxides essentially comprised
 of a group XIII element, a group XIV element and a group XV element of the
 periodic law, such as amorphous compounds essentially comprised of tin
 compounds. Similarly to the above, there can be added, as required, a
 carbonaceous material as the conductive substance, or a thermoplastic
 resin as the binder.
 The electrolyte of the lithium secondary battery of the present invention
 is a liquid or solid electrolyte. As an electrolyte of a liquid, the
 non-aqueous electrolyte which dissove a lithium salt in an organic solvent
 is exemplified, and as a solid electrolyte, so-called a solid electrolyte
 is exemplified.
 As lithium salts dissolved in a non-aqueous electrolyte, LiClO.sub.4,
 LiPF.sub.6, LiAsF.sub.6, LiSbF.sub.6, LiBF.sub.4, LiCF.sub.3 SO.sub.3,
 LiC(CF.sub.3 SO.sub.2).sub.3, LiN(CF.sub.3 SO.sub.2).sub.2, Li.sub.2
 B.sub.10 Cl.sub.10, lower aliphatic lithium carboxylate and LiAlCl.sub.4
 are mentioned, and can be used alone or in combination of two or more.
 Examples of the organic solvent include: carbonates such as propylene
 carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate,
 ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolane-2-one,
 1,2-di(methoxycarbonyloxy)ethane and the like; ethers such as
 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methyl ether,
 2,2,3,3-tetrafluoropropyl difluoromethyl ether, tetrahydrofuran, 2-methyl
 tetrahydrofuran and the like; esters such as methyl formate, methyl
 acetate, y-butyrolactone and the like; nitrites such as acetonitrile,
 butyronitrile and the like; amides such as N,N-dimethylformamide,
 N,N-dimethylacetoamide and the like; carbamates such as
 3-methyl-2-oxazolidone and the like; sulfur-containing compounds such as
 sulfolane, dimethylsulfoxide, 1,3-propane sultone and the like. Normally,
 two or more compounds of the above are used in combination. Above all, a
 mixed solvent containing a carbonate is preferred and more preferred is a
 mixed solvent of a cyclic carbonate and a non-cyclic carbonate or of a
 cyclic carbonate and an ether.
 As the mixed solvent of a cyclic carbonate and a non-cyclic carbonate,
 preferred is a mixed solvent containing ethylene carbonate, dimethyl
 carbonate and ethyl methyl carbonate, because such a mixed solvent
 provides a wide operating temperature range, an excellent drain capability
 and hardly decomposes even when the graphite material such as natural
 graphite and artificial graphite is used as an anode active material.
 Examples of a solid electrolyte include polymer electrolytes such as
 polyethylene oxide polymer compounds and polymer compounds containing at
 least one of a polyorganosiloxane branch or polyoxyalkylene branch;
 sulfide electrolytes such as of Li.sub.2 S--SiS.sub.2, Li.sub.2
 S--GeS.sub.2, Li.sub.2 S--P.sub.2 S.sub.5, Li.sub.2 S--B.sub.2 S.sub.3 and
 the like; and inorganic compound electrolytes comprising sulfides such as
 Li.sub.2 S--SiS.sub.2 --Li.sub.3 PO.sub.4, Li.sub.2 S--SiS.sub.2
 --Li.sub.2 SO.sub.4 and the like. Additionally, also included is a
 so-called gel-type electrolyte in which a nonaqueous liquid electrolyte is
 maintained by a polymer.
 The lithium secondary battery according to the invention is not
 particularly limited in shape and may have any one of the shapes such as a
 paper-sheet shape, a coin-like shape, a cylindrical shape and a
 rectangular parallelepiped shape.
 In accordance with the invention, there can be obtained a lithium secondary
 battery of a good cycle characteristic even in the charging/discharging at
 a high capacity.
 Since the irreversible capacity can be lowered by making the intensity
 ratio of the peak near 2.theta.=22.5.degree. to the peak near
 2.theta.=34.4.degree. in the X-ray diffraction pattern by CuK.alpha. rays
 below 1.2, the active material can be filled advantageously into a limited
 volume of a battery, and a high energy density can be attained.
 The reason why a battery having excellent characteristics is obtained is
 not clear, it is presumed that the added tin is incorporated into the
 crystal structure of lithiated nickel dioxide in a certain form, and
 further, excess tin exists together as lithium stannate (Li.sub.2
 SnO.sub.3), and the structure of lithiated nickel dioxide is stabilized at
 the time of charging/discharging, especially at the time of deep charging.
 EXAMPLES
 The following examples are presented to illustrate the present invention,
 but should not be construed as limiting the scope of this invention.
 Unless otherwise particularly described, electrodes for a
 charging/discharging test and plate batteries were prepared in the
 following manners.
 To a mixture of lithiated nickel dioxide or lithiated nickel dioxide
 containing tin, as the active material, and acetylene black, as the
 conductive substance, there was added a solution of PVDF, as the binder,
 dissolved in 1-methyl-2-pyrrolidone (which may hereinafter be referred to
 as "NMP") in a ratio of active material:conductive substance:binder=91:6:3
 (weight ratio). The resultant mixture was kneaded to obtain a paste. The
 paste was coated over a #200 stailess steel mesh, which was to work as a
 current collector, and the mesh bearing the paste was dried under vacuum
 at a temperature of 150.degree. C. for 8 hours. Thus, an electrode was
 obtained.
 The resultant electrode, an electrolyte comprising a mixed solution of
 ethylene carbonate (which may hereinafter be referred to as "EC"),
 dimethyl carbonate (which may hereinafter be referred to as "DMC") and
 ethyl methyl carbonate (which may hereinafter be referred to as "EMC") in
 a ratio of 30:35:35, in which mixed solution LiPF.sub.6 was dissolved in a
 concentration of 1 mol/l (which may hereinafter be represented by
 LiPF.sub.6 /EC+DMC+EMC), a polypropylene microporous membrane as the
 separator, and a lithium metal as the counter electrode (i.e., an anode)
 were assembled together to form the plate battery.
 In addition, for X-ray powder diffraction measurement of a sample, RU200
 system (manufactured by Rigaku Corporation) was used in the following
 conditions.
 X-ray: CuK.alpha.
 Voltage-Current: 40kV-30mA
 Range of measured angle: 2.theta.=15 to 90.degree.
 Slit: DS-1.degree., RS-0.3mm, SS-1.degree.
 Step: 0.02.degree.
 Counting time: 1 second
 For calculation of the peak intensity ratio, the line strength after
 removing the background was used.
 Example 1
 Lithium nitrate (manufactured by Wako Pure Chemical Industries, Ltd.,
 guaranteed graded reagent) 1.45 g, basic nickel carbonate
 [NiCO.sub.3.2Ni(OH).sub.2.4H.sub.2 O: manufactured by Wako Pure Chemical
 Industries, Ltd., graded reagent] 2.38 g and stannic oxide (SnO.sub.2 :
 manufactured by Nihon Kagaku Sangyo Co., Ltd., SH-S, purity 99%) 0.15 g
 were dry-mixed using agate mortar, and the resultant mixture was charged
 in a tubular furnace having an alumina core tube and fired in a stream of
 oxygen (50 cm.sup.3 /min) at 640.degree. C. for 30 hours. At this point,
 the molar ratio x of tin to the sum of tin and nickel was set to be 0.05.
 X-ray diffraction measurement of resultant powder was conducted, and
 besides the strong peaks assigned to lithiated nickel dioxide, peaks near
 2.theta.=22.5.degree. and 34.4.degree. were observed. The intensity ratio
 of the peak near 2.theta.=22.5.degree. to the peak near
 2.theta.=34.4.degree. was 0.1.
 By using thus obtained powder, a plate battery (electrolyte: LiPF.sub.6
 /EC+DMC+EMC) was manufactured and subjected to a charging/discharging test
 using charge by a constant current and voltage, and discharge by a
 constant current under the following conditions.
 Max. charging voltage: 4.3 V, Charging time: 8 hours,
 Charging current: 0.3 mA/cm.sup.2
 Min. discharging voltage: 3.0 V,
 Discharging current: 0.3 mA/cm.sup.2
 FIG. 1 is a graphical representation of the variations of the discharge
 capacity in 20 cycles of charging/discharging processes. Moreover
 irreversible capacity and retention rate of capacity R (=discharging
 capacity at 20th cycle/discharging capacity at 10th cycle) are shown in
 Table 1.
 Comparative Example 1
 Lithium nitrate (manufactured by Wako Pure Chemical Industries, Ltd.,
 guaranteed graded reagent) 94.1 g was dissolved in 150 g of water, and
 then basic nickel carbonate [NiCO.sub.3.2Ni(OH).sub.2.4H.sub.2 O:
 manufactured by Wako Pure Chemical Industries, Ltd., graded reagent] 163.0
 g was added and homogeneously dispersed therein. After evaporating the
 water content, the resultant mixture was charged in a tubular furnace
 having an alumina core tube and fired in a stream of oxygen (50 cm.sup.3
 /min) at 720.degree. C. for 5 hours.
 X-ray diffraction measurement of resultant powder was conducted, and the
 peaks assigned to lithiated nickel dioxide was observed but peaks near
 2.theta.=22.5.degree. and 34.4.degree. were not observed.
 By using thus obtained powder, a plate battery (electrolyte: LiPF.sub.6
 /EC+DMC+EMC) was manufactured and subjected to the charging/discharging
 test using charge by a constant current and voltage, and discharge by a
 constant current under the same conditions in Example 1.
 FIG. 1 is a graphical representation of the variations of the discharge
 capacity in 20 cycles of charging/discharging processes. Irreversible
 capacity and retention rate of capacity R (=discharging capacity at 20th
 cycle/discharging capacity at 10th cycle) are shown in Table 1.
 Example 2
 First, Lithium nitrate (manufactured by Wako Pure Chemical Industries,
 Ltd., guaranteed graded reagent) 12.07 g was dissolved in 16.7 g of water,
 and then metastannic acid (H.sub.2 SnO.sub.3 : manufactured by Nihon
 Kagaku Sangyo Co., Ltd., purity 95%) 0.28 g and basic nickel carbonate
 [NiCO.sub.3.2Ni(OH).sub.2.4H.sub.2 O: manufactured by Wako Pure Chemical
 Industries, Ltd., graded reagent] 22.06 g were added and homogeneously
 dispersed therein. After evaporating the water content, the resultant
 mixture was charged in a tubular furnace having an alumina core tube and
 fired in a stream of oxygen (50 cm.sup.3 /min) at 640.degree. C. for 20
 hours. At this point, the molar ratio x of tin to the sum of tin and
 nickel was set to be 0.01.
 X-ray diffraction measurement of the resultant powder was conducted, and
 besides the strong peaks assigned to lithiated nickel dioxide, peaks near
 2.theta.=22.5.degree. and 34.4.degree. were observed. The intensity ratio
 of the peak near 2.theta.=22.5.degree. to the peak near
 2.theta.=34.4.degree. was 0.8.
 By using thus obtained powder, a plate battery (electrolyte: LiPF.sub.6
 /EC+DMC+EMC) was manufactured and subjected to the charging/discharging
 test using charge by a constant current and voltage, and discharge by a
 constant current under the same conditions with Example 1.
 FIG. 1 is a graphical representation of the variations of the discharge
 capacity in 20 cycles of charging/discharging processes. Irreversible
 capacity and retention rate of capacity R (=discharging capacity at 20th
 cycle/discharging capacity at 10th cycle) are shown in Table 1.
 Example 3
 First, Lithium nitrate (manufactured by Wako Pure Chemical Industries,
 Ltd., guaranteed graded reagent) 12.07 g was dissolved in 16.7 g of water,
 and then metastannic acid (H.sub.2 SnO.sub.3 : manufactured by Nihon
 Kagaku Sangyo Co., Ltd., purity 95%) 0.56 g and basic nickel carbonate
 [NiCO.sub.3.2Ni(OH).sub.2.4H.sub.2 O: manufactured by Wako Pure Chemical
 Industries, Ltd., graded reagent] 21.84 g were added and homogeneously
 dispersed therein, and the water content of resultant solution was
 evaporated. At this point, the molar ratio x of tin to the sum of tin and
 nickel was set to be 0.02. The resultant mixture were devided into three
 portions, charged in a tubular furnace having an alumina core tube and
 fired at 640.degree. C. for 15 hours, at 640.degree. C. for 20 hours, and
 at 660.degree. C. for 15 hours, respectively.
 X-ray diffraction measurement of three resultant powders were conducted,
 and besides the strong peaks assigned to lithiated nickel dioxide, peaks
 near 2.theta.=22.5.degree. and 34.4.degree. were observed in all three
 powders. The intensity ratios of the peak near 2.theta.=22.5.degree. to
 the peak near 2.theta.=34.4.degree. were 0.2 (firing at 640.degree. C. for
 15 hours), 0.5 (firing at 640.degree. C. for 20 hours), and 0.8(firing at
 660.degree. C. for 15 hours).
 By using thus obtained powders, plate batteries (electrolyte: LiPF.sub.6
 /EC+DMC+EMC) were manufactured and subjected to the charging/discharging
 test using charge by a constant current and voltage, and discharge by a
 constant current under the same conditions with Example 1.
 FIG. 1 is a graphical representation of the variations of the discharge
 capacity in 20 cycles of charging/discharging processes. Irreversible
 capacity and retention rate of capacity R (=discharging capacity at 20th
 cycle/discharging capacity at 10th cycle) are shown in Table 1.
 Comparative Example 2
 The mixture of lithium nitrate, metastannic acid and basic nickel carbonate
 obtained in Example 3, was charged in a tubular furnace having an alumina
 core tube and fired in a stream of oxygen (50 cm.sup.3 /min) at
 720.degree. C. for 5 hours.
 X-ray diffraction measurement of the resultant powder was conducted, and
 besides the strong peaks assigned to lithiated nickel dioxide, peaks near
 2.theta.=22.5.degree. and 34.4.degree. were observed. The intensity ratio
 of the peak near 2.theta.=22.5.degree. to the peak near
 2.theta.=34.4.degree. was 1.3.
 By using thus obtained powder, a plate battery (electrolyte: LiPF.sub.6
 /EC+DMC+EMC) was manufactured and subjected to the charging/discharging
 test using charge by a constant current and voltage, and discharge by a
 constant current under the same conditions with Example 1.
 FIG. 2 is a graphical representation of the variations of the discharge
 capacity in 20 cycles of charging/discharging processes. Irreversible
 capacity and retention rate of capacity R (=discharging capacity at 20th
 cycle/discharging capacity at 10th cycle) are shown in Table 1.
 Comparative Example 3
 The mixture of lithium nitrate, metastannic acid and basic nickel carbonate
 obtained in Example 3, was charged in a tubular furnace having an alumina
 core tube and fired in a stream of oxygen (50 cm.sup.3 /min) at
 750.degree. C. for 5 hours.
 X-ray diffraction measurement of the resultant powder was conducted, and
 besides the strong peaks assigned to lithiated nickel dioxide, peaks near
 2.theta.=22.5.degree. and 34.4.degree. were observed. The intensity ratio
 of the peak near 2.theta.=22.5.degree. to the peak near
 2.theta.=34.4.degree. was 1.6.
 By using thus obtained powder, a plate battery (electrolyte:
 LiPF6/EC+DMC+EMC) was manufactured and subjected to the
 charging/discharging test using charge by a constant current and voltage,
 and discharge by a constant current under the same conditions with Example
 1.
 FIG. 2 is a graphical representation of the variations of the discharge
 capacity in 20 cycles of charging/discharging processes. Irreversible
 capacity and retention rate of capacity R (=discharging capacity at 20th
 cycle/discharging capacity at 10th cycle) are shown in Table 1.
 Example 4
 First, Lithium nitrate (manufactured by Wako Pure Chemical Industries,
 Ltd., guaranteed graded reagent) 12.07 g was dissolved in 16.7 g of water,
 and then metastannic acid (H.sub.2 SnO.sub.3 : manufactured by Nihon
 Kagaku Sangyo Co., Ltd., purity 95%) 0.84 g and basic nickel carbonate
 [NiCO.sub.3.2Ni(OH).sub.2.4H.sub.2 O: manufactured by Wako Pure Chemical
 Industries, Ltd., graded reagent] 21.62 g were added and homogeneously
 dispersed therein. After evaporating the water content, the resultant
 mixture was charged in a tubular furnace having an alumina core tube and
 fired in a stream of oxygen (50 cm.sup.3 /min) at 750.degree. C. for 5
 hours. At this point, the molar ratio x of tin to the sum of tin and
 nickel was set to be 0.03.
 X-ray diffraction measurement of the resultant powder was conducted, and
 besides the strong peaks assigned to lithiated nickel dioxide, peaks near
 2.theta.=22.5.degree. and 34.4.degree. were observed. The intensity ratio
 of the peak near 2.theta.=22.5.degree. to the peak near
 2.theta.=34.4.degree. was 0.4.
 By using thus obtained powder, a plate battery (electrolyte: LiPF.sub.6
 /EC+DMC+EMC) was manufactured and subjected to the charging/discharging
 test using charge by a constant current and voltage, and discharge by a
 constant current under the same conditions with Example 1.
 FIG. 2 is a graphical representation of the variations of the discharge
 capacity in 20 cycles of charging/discharging processes. Irreversible
 capacity and retention rate of capacity R (=discharging capacity at 20th
 cycle/discharging capacity at 10th cycle) are shown in Table 1.
 Example 5
 First, Lithium nitrate (manufactured by Wako Pure Chemical Industries,
 Ltd., guaranteed graded reagent) 4.26 g and metastannic acid (H.sub.2
 SnO.sub.3 : manufactured by Nihon Kagaku Sangyo Co., Ltd., purity 95%)
 5.06 g were mixed well, then the resultant mixture was charged in a
 tubular furnace having an alumina core tube and fired in a stream of
 oxygen (50 cm.sup.3 /min) at 640.degree. C. for 20 hours to produce
 lithium stannate (Li.sub.2 SnO.sub.3).
 Next, Lithium nitrate (manufactured by Wako Pure Chemical Industries, Ltd.,
 guaranteed graded reagent) 11.82 g was dissolved in 17.1 g of water, and
 then 0.60 g of lithium stannate obtained above and basic nickel carbonate
 [NiCO.sub.3.2Ni(OH).sub.2.4H.sub.2 O: manufactured by Wako Pure Chemical
 Industries, Ltd., graded reagent] 21.84 g were added and homogeneously
 dispersed therein. After evaporating the water content, the resultant
 mixture was charged in a tubular furnace having an alumina core tube and
 fired in a stream of oxygen (50 cm.sup.3 /min) at 660.degree. C. for 15
 hours. At this point, the molar ratio x of tin to the sum of tin and
 nickel was set to be 0.02.
 X-ray diffraction measurement of the resultant powder was conducted, and
 besides the strong peaks assigned to lithiated nickel dioxide, peaks near
 2.theta.=22.5.degree. and 34.4.degree. were observed. The intensity ratio
 of the peak near 2.theta.=22.5.degree. to the peak near
 2.theta.=34.4.degree. was 0.3.
 By using thus obtained powder, a plate battery (electrolyte: LiPF.sub.6
 /EC+DMC+EMC) was manufactured and subjected to the charging/discharging
 test using charge by a constant current and voltage, and discharge by a
 constant current under the same conditions with Example 1.
 FIG. 2 is a graphical representation of the variations of the discharge
 capacity in 20 cycles of charging/discharging processes. Irreversible
 capacity and retention rate of capacity R (=discharging capacity at 20th
 cycle/discharging capacity at 10th cycle) are shown in Table 1.
 Comparative Example 4
 First, Lithium nitrate (manufactured by Wako Pure Chemical Industries,
 Ltd., guaranteed graded reagent) 12.07 g was dissolved in 16.7 g of water,
 and then metastannic acid (H.sub.2 SnO.sub.3 : manufactured by Nihon
 Kagaku Sangyo Co., Ltd., purity 95%) 0.28 g and basic nickel carbonate
 [NiCO.sub.3. 2Ni(OH).sub.2.4H.sub.2 O : manufactured by Wako Pure Chemical
 Industries, Ltd., graded reagent] 22.06 g were added and homogeneously
 dispersed therein. After evaporating the water content, the resultant
 mixture was charged in a tubular furnace having an alumina core tube and
 fired in a stream of oxygen (50 cm.sup.3 /min) at 750.degree. C. for 5
 hours. At this point, the molar ratio x of tin to the sum of tin and
 nickel was set to be 0.01.
 X-ray diffraction measurement of the resultant powder was conducted, and
 the peaks assigned to lithiated nickel dioxide and the unassigned peak
 near 2.theta.=22.5.degree. were observed, but the peak near
 2.theta.=34.4.degree. was not observed.
 By using thus obtained powder, a plate battery (electrolyte: LiPF.sub.6
 /EC+DMC+EMC) was manufactured and subjected to the charging/discharging
 test using charge by a constant current and voltage, and discharge by a
 constant current under the same conditions with Example 1.
 FIG. 2 is a graphical representation of the variations of the discharge
 capacity in 20 cycles of charging/discharging processes. Irreversible
 capacity and retention rate of capacity R (=discharging capacity at 20th
 cycle/discharging capacity at 10th cycle) are shown in Table 1.
 TABLE 1