JP3195175B2 - Non-aqueous solvent secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous solvent secondary battery, and more particularly to a non-aqueous solvent secondary battery having an improved positive electrode active material.

[0002]

2. Description of the Related Art In recent years, lithium batteries using lithium, a lithium alloy or a compound capable of occluding and releasing lithium ions as a negative electrode active material have attracted attention as high energy density batteries. Among them, primary batteries using manganese dioxide (MnO ₂ ), fluorocarbon [(CF) _n ], thionyl chloride (SOCl ₂ ), etc. as a positive electrode active material have already been used in calculators,
It is often used as a power source for watches and backup batteries for memories.

In recent years, as various electronic devices such as VTRs, communication devices, and personal computers have become smaller and lighter, the demand for high-energy-density secondary batteries has increased as a power source for these devices. Research on non-aqueous solvent secondary batteries has been actively conducted.

A non-aqueous solvent secondary battery uses lithium, a lithium alloy or a compound capable of absorbing and releasing lithium ions as a negative electrode, and uses propylene carbonate (P) as an electrolyte.
C), ethylene carbonate (EC), dimethyl carbonate (DMC), dimethyl carbonate (DEC),
1,2-dimethoxyethane (DME), γ-butyrolactone (γ-BL), tetrahydrofuran (THF),
LiClO ₄ , LiBF ₄ , LiAs in a non-aqueous solvent such as -methyltetrahydrofuran (2-MeTHF)
F ₆ , LiPF ₆ , LiCF ₃ SO ₃ , LiAlCl ₄
And the like in which a lithium salt (electrolyte) is dissolved. As a positive electrode, an active material utilizing intercalation or doping of a layered compound has attracted attention.

As an example utilizing the intercalation of the layered compound, chalcogenide compounds have relatively excellent charge / discharge cycle characteristics. However,
Chalcogenide compounds have a low electromotive force, and even when lithium metal is used as the negative electrode, the practical discharge voltage is at most about 2 V, which satisfies the high electromotive force which is one of the characteristics of non-aqueous solvent secondary batteries. Was not something to do.

On the other hand, V ₂ O ₅ having a similar layered structure,
Metal oxide compounds such as V ₆ O ₁₃ , LiCoO ₂ , LiNiO _2, or LiMnO ₄ using a doping phenomenon have attracted attention because of their high electromotive force characteristics.
In particular, the positive electrode made of LiCoO ₂ or LiNiO ₂ is 4 V
And the theoretical energy density has a large value of about 1000 Wh / kg per positive electrode active material.

However, the above-mentioned metal oxide-based compound changes its crystal structure due to a charge / discharge reaction, and is accompanied by volume expansion and contraction. For this reason, as the charge / discharge cycle progresses, the conductivity between the active materials or the conductivity between the active material and the electrode substrate decreases. As a result, polarization increases, and a sufficient charge / discharge capacity cannot be obtained. Also, the crystal structure collapses,
Accordingly, the resistance at the reaction interface increases, and the reversibility of the charge / discharge reaction decreases. Further, the above-mentioned metal oxide compound reacts gently with water, substitution occurs between lithium ions and protons in the compound, and the charge / discharge capacity decreases,
As a result, there is a problem that storage characteristics are deteriorated.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a non-aqueous solvent secondary battery having a high energy density and excellent charge-discharge cycle characteristics and storage characteristics.

[0009]

According to the present invention, there is provided a non-aqueous solvent secondary battery comprising a negative electrode comprising lithium or a lithium alloy or containing a compound capable of inserting and extracting lithium ions, and a positive electrode mainly comprising LiNiO _2. In a non-aqueous solvent secondary battery including a positive electrode including an active material and an electrolyte solution in which an electrolyte is dissolved in a non-aqueous solvent, the LiNiO ₂ powder includes:
Aluminum alone or aluminum at least on the surface
And two kinds of elements selected from the group consisting of boron, cobalt, iron and manganese, and the surface is covered with a layer having a higher element concentration than the inside. is there. Since the stability of the crystal structure of the LiNiO ₂ powder whose surface is covered with such a layer having a high element concentration is remarkably improved, a non-aqueous solution provided with a positive electrode containing a positive electrode active material mainly composed of the LiNiO ₂ powder is used. The solvent secondary battery has improved cycle characteristics and storage characteristics.

Hereinafter, a non-aqueous solvent secondary battery (for example, a cylindrical non-aqueous solvent secondary battery) according to the present invention will be described in detail with reference to FIG.

A bottomed cylindrical container 1 made of, for example, stainless steel has an insulator 2 disposed at the bottom. Electrode group 3
Are stored in the container 1. The electrode group 3 includes:
It has a structure in which a belt-like material in which a positive electrode 4, a separator 5 and a negative electrode 6 are laminated in this order is spirally wound so that the negative electrode 6 is located outside. The separator 5 is formed of, for example, a nonwoven fabric or a porous polypropylene film.

The container 1 contains an electrolytic solution. The insulating paper 7 having a central portion opened is placed above the electrode group 3 in the container 1. The insulating sealing plate 8
The sealing plate 8 is disposed at the upper opening of the container 1 and caulked in the vicinity of the upper opening inward.
Is fixed to the container 1 in a liquid-tight manner. The positive terminal 9 is
The insulating sealing plate 8 is fitted at the center. Positive lead
One end of the cathode 10 is connected to the positive electrode 4, and the other end is connected to the positive electrode terminal 9.
Connected to each other. The negative electrode 6 is connected to the container 1 as a negative terminal via a negative lead (not shown).

Next, the positive electrode 4, the negative electrode 6, and the electrolyte will be specifically described.

A) Positive Electrode 4 The positive electrode 4 is obtained by suspending a conductive agent and a binder in an appropriate solvent in a positive electrode active material, applying the suspension to a current collector, and drying the resultant to form a thin plate. It is made. Further, pellets formed by molding the positive electrode active material together with a conductive agent and a binder, or kneading the positive electrode active material together with a conductive agent and a binder,
The positive electrode 4 is produced by sticking the sheet formed on the current collector.

Examples of the conductive agent include acetylene black, carbon black, graphite and the like. Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVD).
E), ethylene-propylene-diene copolymer (EPD)
M), styrene-butadiene rubber (SBR) and the like can be used. The mixing ratio of the positive electrode active material, the conductive agent and the binder is 80 to 95% by weight of the positive electrode active material,
It is preferred that the content be in the range of 20% by weight and 2 to 7% by weight of the binder.

As the current collector, for example, aluminum foil, stainless steel foil, nickel foil or the like can be used.

In one embodiment of the invention, the positive electrode active material is at least on the surface
A layer containing only minium or two elements of aluminum and any one element selected from boron, cobalt, iron, and manganese, and having a surface having a higher concentration of the element than the inside thereof (hereinafter referred to as a high concentration layer) LiNi covered with)
Mainly O ₂ powder.

The LiNiO ₂ powder covered with the high concentration layer preferably has an average diameter of 2 to 20 μm.

The LiNiO ₂ powder covered with the high concentration layer contains a nickel compound such as nickel hydroxide [Ni (OH) 2], nickel carbonate (NiCO ₃ ), nickel nitrate [Ni (NO ₃ ) ₂ ] and water. Lithium oxide (LiOH, lithium oxide (Li ₂ O), lithium carbonate (Li ₂ CO
₃ ) In a mixture with lithium salt such as lithium nitrate LiNO ₃ or lithium halide, aluminum alone,
Alternatively, after mixing a compound containing two elements of aluminum and any one element selected from boron, cobalt, iron, and manganese (hereinafter, referred to as a dissimilar element compound), at least two stages of heating states are recorded. Or Li
It is manufactured by mixing NiO ₂ powder and the above-mentioned heterogeneous element compound and then heating or reacting them. Upon mixing the mixture and the heterogeneous compound, these substances are converted into an acid such as nitric acid, acetic acid, sulfuric acid, or an aqueous solution of ammonium, an aqueous solution of lithium hydroxide, or an organic solvent such as methanol, ethanol, or acetone. After dissolution, stirring and mixing may be performed.
When the two-stage heating state is recorded, it is preferable that the first-stage heating is performed at 100 to 700 ° C. in an atmosphere containing oxygen and the second-stage heating is performed at 300 to 950 ° C. in the same atmosphere. . The heating after mixing the LiNiO ₂ powder and the heterogeneous element compound is performed in an atmosphere containing oxygen at 100 ° C.
It is preferable to carry out at a temperature of up to 700 ° C.

The above-mentioned compounds of different elements have the following effects depending on the characteristics of the elements.

(1) A solid solution or substitution in the LiNiO ₂ crystal structure suppresses a crystal structure change accompanying a charge / discharge reaction and suppresses a collapse of the crystal structure.

(2) Pure Li on the surface of LiNiO ₂ powder
It forms a compound different from NiO _2, and suppresses the reaction with water and the decomposition of the electrolyte that may occur on the powder surface.

Aluminum alone or with aluminum
The two kinds of elements (heterogeneous elements) with any one element selected from boron, cobalt, iron and manganese are as described in (1) above.
The main effect can be expected. These elements are relatively easily replaced or substituted without applying a special treatment such as high-pressure / high-temperature heating to a hexacoordinate site or a vacant tetracoordinate site which is a 3b site of lithium ion, a 3a site of nickel ion, or a vacancy. Can be dissolved. However, when the 3b site is substituted, the amount of lithium ions that can be charged and discharged necessarily decreases.

Further, the different element can also expect the effect of the above (2). When this dissimilar element is added to the raw material of LiNiO ₂ , it affects the shape of the surface of the LiNiO ₂ powder and changes the surface area of the powder.

Therefore, the stability of the crystal structure is remarkably improved by forming a high concentration layer of a different element on the surface of the LiNiO ₂ powder, so that the positive electrode containing the positive electrode active material mainly composed of the LiNiO ₂ powder is used. The provided non-aqueous solvent secondary battery has improved cycle characteristics and storage characteristics. However, the high-concentration layer of the different element has at least the effect shown in the above (1) or (2), and it is necessary to take the form of substitution or solid solution by the different element, or at least one of precipitation.

As the heterogeneous element compound, boric acid (H
Borate compounds such as ₃ BO ₃ ), lithium borate (Li ₂ B ₄ O ₇ ), boron oxide (B ₂ O ₃ ), and lithium tetrahydride borate (LiBH ₄ ); aluminum hydroxide [Al (OH) ₃ ], Aluminum oxide (Al ₂ O
₃ ), aluminum nitrate [Al (NO ₃ ) ₃ ], aluminum phosphate (AlPO ₄ ), lithium tetrahydridoaluminate (LiAlH ₄ ), trienylaluminum [Al (C ₆ H ₅ ) ₃ ], diphenylaluminum hydride [ _{AlH (C 6 H 5) 2} ], phenyl aluminum dihydride _{(AlH 2 C 6 H 5)} , aluminum compounds such as triethylaluminum _{[Al (C 2 H 5)} 3]; cobalt hydroxide [Co (OH) _2] , Iron hydroxide [F
hydroxides such as e (OH) ₃ ] and manganese hydroxide [Mn (OH) ₂ ]; iron dodecacarbonyl (Fe ₃ CO ₁₂ );
Tricarbonyl nickel {[Co (CO ₃ ) ₃ ] ₄ },
Carbonyl complexes such as pentacarbonylmanganese {[Mn (CO) ₅ ] ₂ }; oxides such as iron oxide (Fe ₂ O ₃ ) and manganese oxide (MnO ₂ .H ₂ O); cobalt nitrate [Co (NO ₃ ) ₂ ], iron nitrate [Ga (NO ₃ )
₃ ] and nitrates such as manganese nitrate [Mn (NO ₃ ) ₂ ].

The concentration of the different element to which the LiNiO ₂ powder is added in the depth direction from the surface can be measured by XPS, Auger electron spectroscopy, or the like. It is desirable that the concentration of the element added at a portion from the powder surface to a depth of about 1.0 μm is 5% or more, more preferably 10% or more, based on the nickel element. The LiNiO ₂
The ratio of the additive element to the nickel atom in the depth direction from the surface of the powder is shown as a specific characteristic diagram in Examples described later.

The LiNiO ₂ powder is prepared by adding different elements, kinds of compounds, amounts to be added, and synthesis conditions (heating temperature,
It has already been mentioned that the different element can be replaced with a hexacoordinate site which is a 3b site of lithium ion, a hexacoordinate site which is a 3a site of nickel ion, or a tetracoordinate site which is vacant depending on the difference in time, atmosphere, etc.). LiNi by substitution of different elements
The unit volume of O ₂ (α-NaFeO ₂ structure) shrinks or expands. FIG. 2 is a characteristic diagram showing the relationship between the added boron element and the change in lattice constant. From FIG. 2, the a-axis length is 0.28 in proportion to the concentration of the additional element (for example, boron).
5 to 0.291 nm, c-axis length is 1.412 to 1.42
It can be seen that it changes in the range of 8 nm. There is a close relationship between the lattice constant and the ease of diffusion of lithium ions in the crystal, and it is expected that the spread of the lattice facilitates the diffusion of lithium ions. However, depending on the amount and site of the substituted element, the reaction resistance may be increased, and a sufficient charge / discharge capacity may not be obtained. Therefore, in the LiNiO ₂ powder, the concentration of the added foreign element is 1 to 10 with respect to 100 nickel atoms, and the thickness of the high-concentration layer made of the compound of the added foreign element takes into consideration the stability of the crystal structure and the reduction of the reaction resistance. 0.1-1.0 μm,
More preferably, the thickness is 0.1 to 0.5 μm. In consideration of the ease of diffusion of lithium ions, stability of crystal structure, and reduction of reaction resistance, the lattice constant is a
The axis length is 0.286 to 0.289 nm, and the c-axis length is 1.
It is preferable to set it in the range of 410 to 1.423 nm.

When the specific surface area of the surface of the LiNiO ₂ powder covered with the high-concentration layer is measured, the specific surface area has a maximum value which increases and then decreases as the amount of the added foreign element increases. As described above, the specific surface area is the above-mentioned LiNiO
_{2 It is} a measure of the state of formation of a high concentration layer of powder. The LiNiO ₂ powder covered with the high concentration layer has a specific surface area of 0.5 to
It is preferably 2 m ² / g. The specific surface area is set to 0.
If it is less than 5 m ² / g, the charge / discharge efficiency may decrease due to a decrease in the reaction area. On the other hand, the specific surface area is 2 m
If it exceeds ² / g, a decomposition reaction of the electrolytic solution is likely to occur, and the charge / discharge capacity may decrease. Further, the LiNi
Local overcharge and overdischarge reactions are likely to occur on the surface of the O ₂ powder, which may cause the crystal structure to collapse.

B) Negative Electrode 6 The negative electrode 6 is made of lithium or a lithium alloy, or contains a compound capable of inserting and extracting lithium ions.

As the lithium alloy, for example, LiA
1, LiPb, LiSn, LiBi and the like.

Examples of the compounds that occlude and release lithium ions include conductive polymers such as polyacetal, polyacetylene, and polypyrrole doped with lithium ions, and carbon materials made of organic sintered materials doped with lithium ions. Can be.

The characteristics of the carbonaceous material vary considerably depending on its raw material and firing method. Examples of the material include graphite carbon, carbon having a mixture of graphite crystal parts and non-crystal parts, and a carbon material having a disordered structure having no regularity in the crystal layer stack.

The negative electrode containing the carbon material is specifically produced by the following method. The binder is suspended in a suitable solvent in the carbon material, and the suspension is applied to a current collector and dried to form a thin plate, thereby producing the positive electrode. Also,
A pellet formed by molding the carbon material together with a binder, or a sheet obtained by kneading the carbon material together with a binder and forming a sheet is attached to the current collector to produce the negative electrode.

Examples of the binder include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDE), ethylene-propylene-diene copolymer (EPDM), styrene-butadiene rubber (SBR),
Carboxymethyl cellulose (CMC) or the like can be used.

The mixing ratio of the carbon material and the binder is preferably in the range of 90 to 98% by weight of the carbon material and 2 to 10% by weight of the binder. In particular, the carbon material is preferably in the range of 5 to ²⁰ mg / cm ^{2 when} the negative electrode 6 is manufactured.

As the current collector, for example, a copper foil, an aluminum foil, a stainless steel foil, a nickel foil or the like can be used.

C) Electrolytic Solution The electrolytic solution has a composition in which an electrolyte is dissolved in a non-aqueous solvent.

Examples of the non-aqueous solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, dimethyl carbonate, tetrahydrofuran,
2-methyltetrahydrofuran, γ-butyrolactone,
1,2-dimethoxyethane, diethoxyethane, 1,3
-Dioxolan, 1,3-dimethoxypropane, or a mixture of two or more thereof.

Examples of the electrolyte include lithium borofluoride (LiBF ₄ ) and lithium hexafluorophosphate (Li
PF ₆ ), one selected from lithium perchlorate (LiClO ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluorometasulfonic acid (LiCF ₃ SO ₃ ), lithium aluminum tetrachloride (LiAlCl ₄ ) or Two or more lithium salts can be mentioned. The amount of the electrolyte dissolved in the non-aqueous solvent is 0.5 to 1.
Preferably it is 5 mol / l.

According to the present invention described above, at least
Aluminum alone or aluminum and hoe on the surface
Any one selected from elemental, cobalt, iron and manganese
And two elements, and the surface is in front of the inside
LiNiO covered with a layer (high concentration layer) having a high element concentration
₍₂₎ By using as a positive electrode active material mainly composed of powder, it is possible to suppress the collapse of the crystal structure due to the charge / discharge reaction and suppress the reaction with water during storage, so that the energy density is large, the charge / discharge cycle characteristics, storage A non-aqueous solvent secondary battery having excellent properties can be obtained.

That is, by covering the LiNiO ₂ powder with the high-concentration layer, the crystal structure of the LiNiO ₂ powder is stabilized, so that the collapse of the crystal structure due to the charge / discharge reaction is suppressed and the increase in polarization is suppressed. In addition, the decomposition reaction of the electrolytic solution can be suppressed. As a result, the charge / discharge cycle characteristics of the non-aqueous solvent secondary battery including the positive electrode containing the LiNiO ₂ powder as the positive electrode active material can be significantly improved.

[0043] In addition, the high concentration layer will suppress the reaction with moisture LiNiO ₂ powder surface and in the air, it becomes difficult to occur is the substitution reaction between the lithium ions and protons LiNiO ₂ crystal, LiNiO ₂ during storage It is possible to eliminate a decrease in charge / discharge capacity due to formation of a high-resistance layer by replacing lithium on the crystal surface with protons.

[0044]

An embodiment of the present invention will be described below in detail with reference to FIG.

Reference Example 1 First, LiNiO ₂ powder and lithium borate (Li ₂ B ₄
O ₇ ) was mixed with B: Ni at a molar ratio of 1:20, and thoroughly mixed in a mortar.
Treated at ℃ for 1 hour. The obtained product was measured by Auger electron spectroscopy. As a result, mainly from the surface of the product particles having an average particle size of 10 μm over a depth of 0.5 μm, Li
It was confirmed that a layer of a boron compound composed of ₂ B ₄ O ₇ and B ₂ O ₃ was formed on the surface. Li ₂ B ₄ O
_In No. ₇ , since recrystallization occurs at a temperature of 350 to 400 ° C., it is expected that boron oxide was formed on the surface of the LiNiO ₂ powder. The measured ratio of nickel atoms of the additional element (boron) over the depth direction from the LiNiO ₂ powder surface, it was found that a high concentration of boron as the surface as shown by a characteristic line A in FIG. 3 . Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder. Subsequently, a mixture composed of 91% by weight of LiNiO ₂ powder, the surface of which is covered with the boron oxide layer, 3.5% by weight of acetylene black, 3.5% by weight of graphite, and 2% by weight of ethylene-propylene-diene copolymer Was made into a paste with toluene, applied to a stainless steel foil, dried, and roll-pressed to produce a positive electrode.

Further, the mesophase pitch-based carbon fiber was graphitized at 3000 ° C. in an argon gas atmosphere, and heat-treated in a chlorine gas atmosphere at 2400 ° C. to prepare a graphitized carbon powder. Subsequently, a mixture consisting of 98% by weight of the graphitized carbon powder and 2% by weight of ethylene-propylene-diene copolymer was made into a paste with toluene,
The composition was applied to a copper foil, dried, and roll-pressed to produce a negative electrode.

After laminating the positive electrode, the separator made of a porous polypropylene film, and the negative electrode in this order, they were spirally wound so that the negative electrode was located outside, thereby producing an electrode group.

Further, 1.0 mol / l of LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate and diethyl carbonate (mixing volume ratio: 50:50) to prepare an electrolytic solution.

Each of the electrode groups and the electrolytic solution was housed in a stainless steel bottomed cylindrical container, respectively, as shown in FIG.
The cylindrical non-aqueous solvent secondary battery shown in (1) was assembled.

REFERENCE EXAMPLE 2 Nickel hydroxide powder [Ni (OH) ₂ ], lithium hydroxide (LiOH) and lithium borate (Li ₂ B ₄ O ₇ ) with a molar ratio of Li: Ni: B of 1 1: Formulated to be 0.05, mixed well in a mortar, and then in an oxygen stream,
The temperature was maintained at 380 to 480 ° C. for 1 hour, and the heat treatment was performed at 700 ° C. for 5 hours. By making history of such two-stage heating states, a boron-added LiNiO ₂ powder having an average particle diameter of 10 μm was synthesized. The obtained product was measured by Auger electron spectroscopy. As a result, in the same manner as in Example 1, the surface of the LiNiO ₂ powder has a thickness of 0.1
It was confirmed that a high concentration surface layer of about 0.5 μm was formed. Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

(Example 1 ) Nickel hydroxide powder [Ni (OH) ₂ ], lithium hydroxide (LiOH) and aluminum hydroxide [Al (O
H) ₃ ] with a molar ratio of Li: Ni: Al of 1: 1: 0.
After mixing well in a mortar,
In an oxygen stream, hold at a temperature of 300 ° C. for 1 hour, 700 ° C.
At a temperature of 5 hours. The history of such two-stage heating was used to synthesize an aluminum-added LiNiO ₂ powder having an average particle size of 10 μm. The obtained product was measured by Auger electron spectroscopy. as a result,
_{On the} surface of the LiNiO ₂ powder, the aluminum concentration is higher than that inside the surface where the aluminum concentration is 0.5 μm or more.
It was confirmed that a high concentration layer of about 0.5 μm was formed. The measured ratio of nickel atoms of the additional element (aluminum) over the depth direction from the LiNiO ₂ powder surface, it was found that a high concentration of aluminum as the surface as shown by a characteristic line B in FIG. 3 . Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Reference Example 3 Nickel hydroxide powder [Ni (OH) ₂ ], lithium hydroxide (LiOH) and silicon bromide (Si ₂ Br ₅ ) were mixed with L
i: Ni: Si was mixed at a molar ratio of 1: 1: 0.05, and thoroughly mixed in a mortar.
It was kept at a temperature of 40 ° C. for 1 hour and heat-treated at a temperature of 700 ° C. for 5 hours. By storing such two-stage heating states, a silicon-added LiNi having an average particle size of 10 μm is obtained.
O ₂ powder was synthesized. The obtained product was measured by Auger electron spectroscopy. As a result, it was confirmed that a high-concentration layer having a thickness of 0.1 to 0.5 μm was formed on the surface of the LiNiO ₂ powder, in which the silicon concentration was higher than the inside of the surface of 0.5 μm or more from the surface. Further, the obtained Li
Table 1 below shows the a-axis length, c-axis length, and specific surface area of the NiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Reference Example 4 Nickel hydroxide powder [Ni (OH) ₂ ], lithium hydroxide (LiOH), and lithium phosphate (Li ₃ PO ₄ ) were mixed at a molar ratio of Li: Ni: P of 1: 1. : After mixing in a mortar and mixing well in an oxygen stream,
The temperature was maintained at a temperature of 00 to 200 ° C. for 1 hour, and a heat treatment was performed at a temperature of 700 ° C. for 5 hours. The history of such two-stage heating is used to determine the phosphorus addition L having an average particle size of 10 μm.
iNiO ₂ powder was synthesized. The obtained product was measured by Auger electron spectroscopy. As a result, it was confirmed that a high-concentration layer having a thickness of 0.1 to 0.5 μm was formed on the surface of the LiNiO ₂ powder, which had a higher phosphorus concentration than the inside of the powder having a thickness of 0.5 μm or more from the surface. Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Reference Example 5 Nickel hydroxide powder [Ni (OH) ₂ ], lithium hydroxide (LiOH) and lithium sulfate (Li ₂ SO ₄ .H)
₂ O) and a Li: Ni: S molar ratio of 1: 1: 0.05.
And mixed well in a mortar, and then kept in a stream of oxygen at a temperature of 450 to 500 ° C. for 1 hour,
Heat treatment was performed at a temperature of 0 ° C. for 5 hours. By making history of such two-stage heating states, a sulfur-added LiNiO ₂ powder having an average particle diameter of 10 μm was synthesized. The obtained product was measured by Auger electron spectroscopy. As a result, Li
The sulfur concentration on the surface of NiO ₂ powder is 0.5μ from the surface.
0.1-0.5 µm thick, higher than inside
It was confirmed that a high concentration layer was formed. Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Reference Example 6 LiNiO ₂ powder and manganese nitrate [Mn (NO ₃ ) ₂ ]
Are mixed so that the molar ratio of Mn: Ni is 1:20, and sufficiently mixed in a mortar.
Heat treatment was performed at a temperature of 400 ° C. for one hour. The obtained product was measured by Auger electron spectroscopy. As a result, a high-concentration layer having a thickness of 0.1 to 0.5 μm was formed on the surface of the LiNiO ₂ powder having an average particle diameter of 10 μm, in which the manganese concentration was higher than that inside the surface of 0.5 μm or more from the surface. confirmed. Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Reference Example 7 Nickel hydroxide powder [Ni (OH) ₂ ], lithium hydroxide (LiOH), and cobalt hydroxide [Co (OH) ₂ ] were mixed at a molar ratio of Li: Ni: Co of 1: 1: 0.05, and mixed well in a mortar, and then kept at a temperature of 700 ° C. for 1 hour in an oxygen stream, and 800-900 ° C.
At a temperature of 5 hours. The history of such two-stage heating was used to synthesize cobalt-added LiNiO ₂ powder having an average particle size of 10 μm. The obtained product was measured by Auger electron spectroscopy. As a result, Li
_{On the} surface of the NiO ₂ powder, the cobalt concentration was 0.1% from the surface.
0.1-0.5 thick, higher than inside 5 μm or more
It was confirmed that a high concentration layer of μm was formed. Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Reference Example 8 Nickel hydroxide powder [Ni (OH) ₂ ], lithium hydroxide (LiOH), and iron hydroxide [Fe (OH) ₃ ]
i: Ni: Fe was mixed at a molar ratio of 1: 1: 0.05, and mixed sufficiently in a mortar.
It was kept at a temperature of 00 ° C. for 1 hour and heat-treated at a temperature of 700 ° C. for 5 hours. The history of such a two-stage heating state allows the addition of iron-added LiNiO ₂ having an average particle size of 10 μm.
A powder was synthesized. The obtained product was measured by Auger electron spectroscopy. As a result, it was confirmed that a high-concentration layer having a thickness of 0.1 to 0.5 μm was formed on the surface of the LiNiO ₂ powder, where the iron concentration was higher than the inside of the powder having a thickness of 0.5 μm or more from the surface. The measured ratio of nickel atoms of the additional element (iron) over the depth direction from the LiNiO ₂ powder surface, it was found that high concentrations of iron as the surface as shown by the characteristic line C in FIG. 3 . Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Reference Example 9 Nickel hydroxide powder [Ni (OH) ₂ ], lithium hydroxide (LiOH) and zinc hydroxide [Zn (OH) ₂ ]
i: Ni: Zn was mixed at a molar ratio of 1: 1: 0.05, and thoroughly mixed in a mortar.
The temperature was maintained at a temperature of 00 to 200 ° C. for 1 hour, and a heat treatment was performed at a temperature of 700 ° C. for 5 hours. The history of such a two-stage heating state allows the addition of zinc-added L having an average particle size of 10 μm.
iNiO ₂ powder was synthesized. The obtained product was measured by Auger electron spectroscopy. As a result, it was confirmed that a high-concentration layer having a thickness of 0.1 to 0.5 μm was formed on the surface of the LiNiO ₂ powder where the zinc concentration was higher than the inside of the surface at 0.5 μm or more from the surface. Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Reference Example 10 Nickel hydroxide powder [Ni (OH) ₂ ], lithium hydroxide (LiOH) and gallium sulfate [Ga ₂ (SO ₄ ) ₃ ]
Are mixed so that the molar ratio of Li: Ni: Ga is 1: 1: 0.05, and after sufficiently mixed in a mortar, kept at a temperature of 500 to 550 ° C. for 1 hour in an oxygen stream, 700 ° C
At a temperature of 5 hours. A gallium-added LiNiO ₂ powder having an average particle diameter of 10 μm was synthesized by history of such two stages of heating. The obtained product was measured by Auger electron spectroscopy. As a result, Li
_{On the} surface of the NiO ₂ powder, the gallium concentration is set at 0.
0.1-0.5 thick, higher than inside 5 μm or more
It was confirmed that a high concentration layer of μm was formed. Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Example 2 Nickel hydroxide powder [Ni (OH) ₂ ], lithium hydroxide (LiOH), lithium borate (Li ₂ B ₄ O ₇ ) and aluminum hydroxide [Al (OH) ₃ ] To LiOH:
Ni (OH) ₂ : Li ₂ B ₄ O ₇ : Al (OH) ₃ The molar ratio was 1: 1: 0.02: 0.03, and the mixture was thoroughly mixed in a mortar. 300 ~
It was kept at a temperature of 480 ° C. for 1 hour and heat-treated at a temperature of 700 ° C. for 5 hours. By making history of such a two-stage heating state, a boron / aluminum-added LiNiO ₂ powder having an average particle diameter of 10 μm was synthesized. The obtained product was measured by Auger electron spectroscopy. As a result, Li
It was confirmed that a high-concentration layer having a thickness of 0.1 to 0.5 μm was formed on the surface of the NiO ₂ powder in which the concentration of boron and the concentration of aluminum were higher than the inside of the surface 0.5 μm or more from the surface. Also, when the ratio of additive elements (boron and aluminum) to nickel atoms in the depth direction from the surface of the LiNiO ₂ powder was measured,
As shown by the characteristic line D in FIG. 3 , it was found that the concentration of boron and aluminum was higher at the surface. Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Example 3 Nickel hydroxide powder [Ni (OH) ₂ ], lithium hydroxide (LiOH) and aluminum hydroxide [Al (O
H) ₃ ] and cobalt hydroxide [Co (OH) ₂ ] with Li
OH: Ni (OH) ₂ : Al (OH) ₃ : Co (OH)
₂ were mixed at a molar ratio of 1: 1: 0.02: 0.03, and thoroughly mixed in a mortar.
It was kept at a temperature of 0 ° C. for 1 hour and heat-treated at a temperature of 700 ° C. for 5 hours. The history of the two stages of heating was used to synthesize an aluminum / cobalt-added LiNiO ₂ powder having an average particle size of 10 μm. The obtained product was measured by Auger electron spectroscopy. As a result, LiN
It was confirmed that a high-concentration layer having a thickness of 0.1 to 0.5 μm was formed on the surface of the iO ₂ powder, in which the aluminum concentration and the cobalt concentration were higher than the inside of the surface of 0.5 μm or more from the surface. Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Example 4 Nickel hydroxide powder [Ni (OH) ₂ ], lithium hydroxide (LiOH) and aluminum hydroxide [Al (O
H) ₃ ] and iron hydroxide [Fe (OH) ₃ ] with Li: N
i: Al: Fe was mixed at a molar ratio of 1: 1: 0.05, and mixed sufficiently in a mortar.
The temperature was maintained at a temperature of 00 to 200 ° C. for 1 hour, and a heat treatment was performed at a temperature of 700 ° C. for 5 hours. By making history of such two-stage heating states, an aluminum / iron-added LiNiO ₂ powder having an average particle diameter of 10 μm was synthesized. The obtained product was measured by Auger electron spectroscopy. As a result, L
The aluminum concentration and the iron concentration on the surface of the iNiO ₂ powder are higher than those inside the surface 0.5 μm or more from the surface,
It was confirmed that a high concentration layer having a thickness of 0.1 to 0.5 μm was formed. Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Example 5 Nickel hydroxide powder [Ni (OH) ₂ ], lithium hydroxide (LiOH · H ₂ O) and aluminum hydroxide [Al
(OH) ₃ ] and manganese nitrate [Mn (NO ₃ ) ₂ ] in a molar ratio of Li: Ni: Al: Mn of 1: 1: 0.02:
0.03, mixed well in a mortar, and kept in a stream of oxygen at a temperature of 300 ° C. for 1 hour,
It was kept at a temperature of 0 to 500 ° C. for 1 hour, and heat-treated at a temperature of 700 ° C. for 5 hours. The history of these three heating states was used to synthesize an aluminum / manganese-added LiNiO ₂ powder having an average particle diameter of 10 μm.
The obtained product was measured by Auger electron spectroscopy.
As a result, it was confirmed that a high concentration layer having a thickness of 0.1 to 0.5 μm was formed on the surface of the LiNiO ₂ powder in which the aluminum concentration and the manganese concentration were higher than the inside of the surface of 0.5 μm or more from the surface. Was. Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Reference Example 11 Nickel hydroxide powder [Ni (OH) ₂ ], lithium hydroxide (LiOH · H ₂ O) and cobalt hydroxide [Co (O
H) ₂ ] and iron hydroxide [Fe (OH) ₃ ] with Li: N
i: Co: Fe molar ratio of 1: 1: 0.02: 0.03
After mixing well in a mortar, the mixture was kept at a temperature of 500 ° C. for 1 hour in an oxygen stream, and was heated to 700 ° C. to 9 ° C.
Heat treatment was performed at a temperature of 00 ° C. for 5 hours. The history of such two-stage heating state allows the average particle diameter to be 10 μm.
Of iron-cobalt-added LiNiO ₂ powder was synthesized. The obtained product was measured by Auger electron spectroscopy. As a result, it was confirmed that a high-concentration layer having a thickness of 0.1 to 0.5 μm was formed on the surface of the LiNiO ₂ powder in which the iron concentration and the cobalt concentration were higher than the inside of the surface of 0.5 μm or more from the surface. Was. Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Reference Example 12 LiNiO ₂ powdered water and manganese nitrate [Mn (N
O ₃ ) ₂ ] and cobalt hydroxide [Co (OH) ₂ ]
n: Co: Ni was blended so as to have a molar ratio of 0.5: 0.5: 20, and after sufficiently mixed in a mortar, kept at a temperature of 250 to 500 ° C. for 1 hour in an oxygen stream, 700 ~
Heat treatment was performed at a temperature of 900 ° C. for 5 hours. The obtained product was measured by Auger electron spectroscopy. As a result, a high-concentration layer having a thickness of 0.1 to 0.5 μm is formed on the surface of the LiNiO ₂ powder having an average particle diameter of 10 μm, in which the manganese concentration and the cobalt concentration are higher than the inside of the surface of 0.5 μm or more from the surface. It was confirmed that. Table 1 below shows the a-axis length, c-axis length and specific surface area of the obtained LiNiO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Example 6 Nickel hydroxide powder [Ni (OH) ₂ ], lithium hydroxide (LiOH · H ₂ O) and aluminum hydroxide [Al
(OH) ₃ ] and manganese nitrate [Mn (NO ₃ ) ₂ ] in a molar ratio of Li: Ni: Co: Al: Mn of 1: 1: 0.
02: 0.02, and the mixture was sufficiently mixed in a mortar, then kept at a temperature of 300 ° C. for 1 hour in an oxygen stream, and heat-treated at a temperature of 700 ° C. to 900 ° C. for 5 hours. By history of such two-stage heating state, aluminum / manganese-added Li having an average particle size of 10 μm is obtained.
NiO ₂ powder was synthesized. The obtained product was measured by Auger electron spectroscopy. As a result, on the surface of the LiNiO ₂ powder, the aluminum concentration and the manganese concentration are higher than those inside the surface of 0.5 μm or more from the surface, and the thickness is 0.1 mm.
It was confirmed that a high concentration layer of 1 to 0.5 μm was formed. The measured ratio of nickel atoms of the additional element (aluminum and manganese) over the depth direction from the LiNiO ₂ powder surface, higher concentrations of aluminum and manganese as the surface as shown by the characteristic line E in FIG. 3 I understand. Further, the obtained LiN
Table 1 below shows the a-axis length, c-axis length, and specific surface area of the iO ₂ powder.

LiN whose surface is covered with the obtained high concentration layer
The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 described above was assembled in the same manner as in Reference Example 1, except that the iO ₂ powder was used as the positive electrode active material.

Reference Example 13, Example 7, LiNi synthesized in the same manner as in Reference Example 2 and Example 1.
The O ₂ powders were each left in the air at room temperature for 6 months.
Except that these LiNiO ₂ powders were used as a positive electrode active material, two types of cylindrical nonaqueous solvent secondary batteries shown in FIG. 1 were assembled in the same manner as in Reference Example 1.

Comparative Example 1 Nickel hydroxide powder [Ni (OH) ₂ ] and lithium hydroxide (LiOH) were blended so that the molar ratio of Li: Ni was 1: 1. After mixing, a heat treatment was performed in an oxygen stream at a temperature of 700 ° C. for 5 hours. The obtained product was measured by the X-ray diffraction method. As a result, LiN
It was confirmed that an iO ₂ phase was formed. further,
Table 1 below shows the a-axis length, c-axis length, and specific surface area of the obtained LiNiO ₂ powder.

The cylindrical non-aqueous solvent secondary battery shown in FIG. 1 was assembled in the same manner as in Reference Example 1 except that the obtained LiNiO ₂ powder was used as a positive electrode active material.

Comparative Example 2 A LiNiO ₂ powder synthesized in the same manner as in Comparative Example 1 was left in the air at room temperature for 6 months. A cylindrical non-aqueous solvent secondary battery shown in FIG. 1 was assembled in the same manner as in Reference Example 1, except that this LiNiO ₂ powder was used as a positive electrode active material.

The obtained non-aqueous solvent secondary batteries of Examples 1 to 6, Reference Examples 1 to 12 and Comparative Example 1 were charged with 4.
After performing the test at a constant current of 400 mA to 1 V, the voltage was further increased to 4.1 V.
3 hours at a constant voltage of 400m to 3.0V
Charge until discharged with current of A, 400m to 3.0V
The charge and discharge in which the current A was discharged were repeated, and the number of cycles when the initial capacity was reduced by 80% was measured. The results are shown in Table 1 below.

[0089]

[Table 1]

As apparent from Table 1 above, Examples 1 to 6
It can be seen that the non-aqueous solvent secondary battery of Example 1 has better cycle characteristics than the secondary battery of Comparative Example 1.

The non-aqueous solvent secondary batteries of Reference Examples 1, 2, 13 and Examples 1, 7 and Comparative Examples 1 and 2 were charged up to 4.1 V at a constant current of 400 mA, and then further charged.
Perform a total of 3 hours at a constant voltage of 1 V, up to 3.0 V and 40
Charge until the battery is discharged with a current of 0 mA.
Charge / discharge at a current of 0 mA was repeatedly performed, and the discharge capacity of each battery in each cycle was measured. FIG. 4 shows the results.

As is apparent from FIG. 4, the non-aqueous solvent secondary battery of the present invention uses the LiNiO ₂ powder synthesized in Example 1 as a positive electrode active material and the Li-NiO ₂ powder described in Example 7
Even when the NiO ₂ powder is left in air at room temperature for 6 months as a positive electrode active material, a decrease in the discharge capacity with the progress of the charge / discharge cycle is suppressed, and the charge / discharge cycle characteristics are good and high. It turns out that it has storage performance. This is because LiN whose surface is covered with a high concentration layer
It is considered that the crystal structure of the iO ₂ powder was stable, the change in the crystal structure due to the charge / discharge cycle was suppressed, and the reactivity with moisture was also suppressed, so that the charge / discharge cycle characteristics and the storage performance were improved.

On the other hand, in the non-aqueous solvent secondary battery of Comparative Example 1, the discharge capacity was remarkably reduced with the progress of the charge / discharge cycle, and the LiNiO ₂ powder synthesized in Comparative Example 1 was cooled to room temperature in air at room temperature for 6 hours. In the secondary battery of Comparative Example 2 in which the battery left for a month was used as the positive electrode active material, the decrease in the discharge capacity with the progress of the charge / discharge cycle became more remarkable, indicating that the storage stability was poor.

[0094]

As described above, according to the present invention, it is possible to provide a non-aqueous solvent secondary battery having a high energy density and excellent charge / discharge cycle characteristics and storage characteristics.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a cylindrical non-aqueous solvent secondary battery according to the present invention.

FIG. 2 is a characteristic diagram showing the relationship between the amount of boron added and the lattice constant of LiNiO ₂ powder.

FIG. 3 Reference Example 1, Example 1, Reference Example 8, Examples 2, 6
FIG. 4 is a characteristic diagram showing a ratio of an additive element to a nickel atom in a depth direction from a surface of the LiNiO ₂ powder synthesized in Step (a).

FIG. 4 is a characteristic diagram showing a relationship between a charge / discharge cycle and a discharge capacity in the non-aqueous solvent secondary batteries of Reference Examples 1, 2, 13, Examples 1, 7 and Comparative Examples 1 and 2.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 3 ... Electrode group, 4 ... Positive electrode, 5 ... Separator, 6 ... Negative electrode, 8 ... Sealing plate, 9 ... Positive electrode terminal.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-7-192720 (JP, A) JP-A-7-288127 (JP, A) JP-A-7-235292 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01M 4/58 H01M 4/02 H01M 10/40

Claims (1)

(57) [Claims] 1. A negative electrode comprising a compound made of lithium or a lithium alloy or absorbing and releasing lithium ions, a positive electrode containing a positive electrode active material mainly composed of LiNiO ₂ , and an electrolytic solution obtained by dissolving an electrolyte in a non-aqueous solvent. in non-aqueous solvent secondary battery and a liquid, the LiNiO ₂ powder, aluminum at least on the surface
Aluminum alone, or aluminum and boron, cobalt, iron,
A non-aqueous solvent secondary battery comprising two elements of any one element selected from manganese, and a surface of which is covered with a layer having a higher element concentration than the inside.