JPH07307165A - Lithium secondary battery - Google Patents

Abstract

PURPOSE:To enhance lithium utilization efficiency in a positive electrode by using the positive electrode with enhanced Coulomb efficiency and a negative electrode containing a specified carbon material. CONSTITUTION:As a positive electrode material capable of storing/releasing lithium, lithium nickelate having alpha-NaFeO2 type structure in which Coulomb efficiency in the initial charge/discharge is 80% or more is obtained by dispersing a nickel compound in a lithium nitrate solution, drying the mixture to mix them, then baking the mixture, and as a negative electrode material capable of storing/releasing lithium, a mixture of 70-99wt.% graphite and 30-1wt.% pseudographite carbon black is contained, and the graphite is flake natural graphite powder or flake artificial graphite powder. The pseudographite is a carbon material having a spacing in X-ray diffraction pattern of 3.38-3.46Angstrom , a crystallite thickness of 50-250Angstrom , a true specific gravity of 1.9-2.1, and a mean primary particle size of 10-100nm. Utilization efficiency of lithium in the positive electrode is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-capacity lithium battery that combines a positive electrode capable of occluding / releasing lithium excellent in initial charge / discharge characteristics and a negative electrode capable of occluding / releasing lithium excellent in initial charge / discharge characteristics. Regarding the next battery.

[0002]

2. Description of the Related Art A lithium secondary battery provided with a positive electrode capable of occluding and releasing lithium, a negative electrode capable of occluding and releasing lithium, and a non-aqueous electrolyte solution comprises a positive electrode containing lithium cobalt oxide and a negative electrode containing a carbon material. It has already been put to practical use in a battery configuration using a non-aqueous electrolyte solution. This lithium secondary battery is
It utilizes an electrochemical reversible reaction in which lithium in the positive electrode is occluded in the negative electrode via the electrolyte solution during charging, and lithium in the negative electrode is released during storage and is occluded in the positive electrode via the electrolytic solution. The characteristics required for these electrodes are that the capacity (capacity) and capacity (capacity) of lithium to be stored in the electrode are large, and the capacity deterioration during the capacity storage / release cycle is small.

[0003] The battery using the capable of absorbing and desorbing lithium electrode _{material, Li x M y O 2 (} M = Co, Ni) having a layered structure of alpha-NaCrO ₂ composed of ionic conductor having the formula Battery using the prepared electrode (Japanese Patent Publication No. 63-5)
9507), a battery using a carbon material having a specific structure obtained by carbonizing a metal chalcogen compound or an organic polymer compound as a positive electrode and a carbon material having a specific structure obtained by carbonizing an organic polymer compound as a negative electrode (special Kaisho 62-12206
No. 6), a battery using a composite oxide in which Al, In, Sn and the like are further mixed in an alkali metal and a transition metal as a positive electrode and a carbonaceous material having a specific structure as a negative electrode (JP-A-62-90863). Gazette), LiCoO as a positive electrode
Many proposals have been made such as a battery using ₂ or LiNiO ₂ and using carbon as a negative electrode (Japanese Patent Laid-Open No. 63-121260).

The cathode material for lithium secondary batteries will be described in more detail. Hexagonal α-NaFeO ₂
Lithium cobalt oxide having a type structure (hereinafter, abbreviated as lithium cobalt oxide) is a compound having a structure in which lithium ions and cobalt ions are alternately arranged in a layered pattern in the vertical direction of the oxygen ion closest packing layer. Due to the structure, diffusion of lithium ions in the layer is relatively easy, and lithium ions can be desorbed and inserted electrochemically. On the other hand, lithium nickelate having an α-NaFeO ₂ type structure (hereinafter, abbreviated as lithium nickelate) is also known as a substance having the same properties as lithium cobaltate, and has a high raw material cost and abundant resources. However, there is a problem that it is difficult to stably synthesize lithium nickelate having higher performance than lithium cobaltate.

The reason why it is difficult to synthesize lithium nickelate is a so-called rock salt type domain (hereinafter sometimes referred to as rock salt domain) in which lithium ions and nickel ions are irregularly arranged when fired at a high temperature exceeding 800 ° C. There is a point that the ratio of mixing becomes large. The rock salt domain not only contributes to charge and discharge, but also inhibits reversible structural change when lithium ions are extracted from lithium nickelate. Therefore, if the rock salt domain is mixed, a sufficient discharge capacity as a secondary battery cannot be obtained, which is not preferable.

It is known that if it is fired at a low temperature of 800 ° C. or less to avoid this, the substitution of nickel in the lithium site is likely to occur. It is considered that this is because the decomposition reaction and diffusion of a lithium compound such as lithium carbonate used as a raw material are rate-determining, and as a result, the supply of lithium is delayed. It is said that the presence of nickel at the lithium site hinders the diffusion of lithium ions and adversely affects the charge / discharge characteristics. In such a case, the Li / Ni ratio of the sample becomes smaller than 1, but
The relationship between this value and the initial discharge capacity has been investigated, and L
It has been reported that the larger the i / Ni ratio, the larger the discharge capacity [Arai et al., 33rd Battery Symposium, Lecture No. 1A11 (1
992)].

Therefore, in consideration of application as a positive electrode material for a lithium secondary battery, it does not contribute to charge and discharge, does not contain rock salt domains that inhibit reversible charge and discharge, and adversely affects diffusion of lithium ions. It is desirable to obtain lithium nickelate having a small amount of nickel present in the lithium site, that is, LiNiO ₂ having a layered structure and a stoichiometric composition.

Examples of such attempts include, for example, lithium oxide Li ₂ O [N. Bronger et al., Z. Ano, which does not require decomposition of a lithium compound prior to a lithium nickelate forming reaction.
Allg. Chem., 333, 188 (1964)] and lithium peroxide Li ₂ O ₂ [Sugano et al., Electrochemical Society 60th Convention, Lecture No. 1G20 (1993)] are known. . However, these methods have drawbacks in that they cannot be handled in air because all the starting materials are difficult to obtain and easily react with carbon dioxide gas or moisture in air.

Further, Japanese Patent Laid-Open No. 2-40861 discloses that
Mixing lithium hydroxide and nickel oxide in powder form,
By firing at 600 ° C to 800 ° C in the atmosphere, L
i _y Ni _2-y O ₂ (y is in the range of 0.84 to 1.22)
Is disclosed. However, according to the publication, Li _y Ni _2-y O ₂ obtained by this method has a maximum charge voltage Vmax = 4.25 V and a minimum discharge voltage Vmin = 3.
It is described that, when a charge / discharge test is performed at a constant current of V and 0.2 mA / cm ^2, the capacity decreases by repeating the charge / discharge cycle. That is, it can be seen from the drawings described in the publication that the cycle characteristics are not good and the discharge capacity at the 30th time is only about 60% at the 5th time. Thus, the performance as a positive electrode material for a lithium secondary battery was still insufficient.

Further, lithium nitrate was used as a lithium compound, mixed with nickel carbonate or nickel hydroxide in powder form, and baked in oxygen at 750 ° C. for 15 hours to obtain Vmax = 4.2V, Vmin = 2.5V, 0.17m
Approximately 16 when charged / discharged at constant current of A / cm ^2.
It has been reported that lithium nickel oxide having a discharge capacity of 0 mAh / g was obtained and that the Coulombic efficiency E of the second and subsequent charging / discharging shows an excellent value of 99.3%. Although it can be seen that the value is significantly lower than the second and subsequent times, there is no specific report [Otsuki et al., 33rd Battery Symposium, Lecture No. 1A07 (1992)].

Further, after the nickel hydroxide powder is dispersed in a lithium hydroxide aqueous solution, lithium hydroxide is deposited on the surface of the nickel hydroxide powder by a spray drying method, and then 6
A method of firing in air at 00 ° C. for 4 hours is known [JR Dahn et al., Solid State Ionics, 44, 87 (199).
0)]. According to this method, since the product contains a small amount of lithium hydroxide and lithium carbonate, it is necessary to wash with water. In this washing step, some of the lithium ions of lithium nickelate are replaced with hydrogen ions H ⁺ , so the hydrogen ions must be removed as water by baking in air at 600 ° C. for 1 hour. As such, it is a very complicated process and not an industrially efficient method. As described above, a positive electrode material containing lithium nickel oxide that exhibits excellent charge / discharge characteristics when applied to a lithium secondary battery using the conventional synthesis method has not been obtained yet.

Next, the negative electrode material for the lithium secondary battery will be described in more detail. A battery using a carbon material capable of inserting and extracting lithium as a negative electrode is a battery using a graphite negative electrode in which lithium is mixed in a crystal (Japanese Patent Laid-Open No. 57-208079).
Japanese Patent Laid-Open No. 4-115457), a battery using a graphitic material composed of easily graphitizable spherical particles as a negative electrode (Japanese Patent Laid-Open No. 4-115457),
A battery using as a negative electrode a carbon material having a pseudo-graphite structure obtained by carbonizing an organic polymer compound or the like (Japanese Patent Laid-Open No. 62-122066).
Japanese Patent Laid-Open No. 2-66856, a battery using a carbon material having a specific structure as a negative electrode (Japanese Patent Laid-Open No. 62-90863), a battery using a carbon material having a turbostratic structure as a negative electrode (Japanese Patent Laid-Open No. 2-66856), and many others. Has been made, and the carbon material for the negative electrode has a wide range from graphite material to turbostratic carbon material.

[0013]

As a result of experiments using a wide range of carbon powders for negative electrodes as electrodes, the present inventors have found that lithium storage capacity and release capacity are large, and that the lithium discharge voltage is higher than that of lithium batteries. It was confirmed that graphite powder, particularly flake-shaped natural graphite or flake-shaped artificial graphite, is suitable as a negative electrode material for lithium secondary batteries among carbon powders. However, it has been clarified that these carbon materials have insufficient initial charge / discharge characteristics, and batteries having a negative electrode cannot have high capacity.

A battery comprising an electrode containing a positive electrode capable of occluding and releasing lithium by charging and discharging and an electrode containing a carbon powder for negative electrode capable of occluding and releasing lithium by charging and discharging, including an electrode containing lithium nickel oxide and graphite. In the battery constructed by using the electrodes, the voltage of this battery is almost 0V at the initial stage, and a battery having a voltage of about 4V is obtained by charging the electrode containing lithium nickel oxide as the positive electrode and the electrode containing graphite as the negative electrode. Will be completed. The amount of electricity that can be discharged by the battery (called the discharge capacity) is considerably smaller than the amount of electricity at the initial charge stage (called the initial charge capacity), that is, the Coulomb efficiency in the first charge / discharge is poor and a high capacity battery is obtained. It turned out not to be possible. Here, the charge / discharge Coulombic efficiency E is defined by the following equation. E = (discharged electricity amount) / (charged electricity amount) × 100 (%) = (discharge current × discharge time) / (charge current × charge time) ×
100 (%)

In the charging step, a reaction is mainly carried out in which lithium in the positive electrode is released and occluded in the graphite of the negative electrode, and in the discharging step, mainly lithium occluded in the negative electrode is released and occluded in the positive electrode. It is considered that the reaction takes place, and the coulombic efficiencies at the positive and negative electrodes are related to each other, and as a result, the utilization efficiency of lithium in the positive electrode is reduced. on the other hand,
The charge and discharge characteristics of the positive electrode and the negative electrode are generally evaluated by forming a battery (evaluation battery) using Li metal for the counter electrode. According to this evaluation, the positive and negative electrodes each have an irreversible capacity (= charge capacity-discharge capacity), and specifically, the initial irreversible capacity of the positive electrode (= lithium release capacity from the positive electrode-lithium storage capacity to the positive electrode). ) And the initial irreversible capacity of the negative electrode (= the lithium storage capacity to the negative electrode-the lithium release capacity from the negative electrode) are complicatedly related, and it is considered that the initial Coulombic efficiency of the battery is lowered.

An object of the present invention is to combine a positive electrode for a lithium secondary battery capable of occluding and releasing lithium with an electrode having a small irreversible capacity at the time of initial charge / discharge of the negative electrode (improving the Coulombic efficiency of each electrode) to form a positive electrode. An object of the present invention is to provide a high-capacity lithium secondary battery with improved utilization efficiency of lithium.

[Means for Solving the Problems]

The inventors of the present invention have conducted intensive experiments and studies by paying attention to the capacity and initial charge / discharge characteristics, and as a result, as a positive electrode for a lithium secondary battery capable of inserting and extracting lithium, a nickel compound is dispersed in a lithium nitrate solution. The electrode containing lithium nickel oxide obtained by mixing the both by drying after drying, and then firing is 8
It has been found that it exhibits a Coulombic efficiency of 0% or more.

On the other hand, as a negative electrode for a lithium secondary battery capable of occluding and releasing lithium, a mixed electrode containing a graphite material and pseudo-graphitic carbon black has a significantly higher irreversible capacity than the case where both materials are used as the negative electrode material. We found that it can be lowered. It was also found that the irreversible capacity can be significantly reduced by treating the electrode material used for the negative electrode with a silane coupling agent. Then, by using the positive electrode and the negative electrode in combination, it was found that a high-capacity lithium secondary battery with high utilization efficiency of lithium in the positive electrode (Coulomb efficiency in the first charge and discharge) can be obtained, and the present invention is completed. Came to do.

That is, the present invention comprises the following inventions.
It (1) A positive electrode capable of inserting and extracting lithium by charging and discharging,
A negative electrode that can store and release lithium by charging and discharging, and a non-aqueous
In a lithium secondary battery including a denaturing solution, the positive electrode
Is an electrode containing the following lithium nickelate (A),
And the negative electrode is made of the following carbon material (B) or (C)
A lithium battery characterized by being an electrode containing a carbon material.
Next battery. (A) Coulomb efficiency of 80% or more in the first charge and discharge
And α-NaFeO ₂Nickel oxide having a die structure
Tium. (B) 70-99% by weight of graphite material and pseudo-graphitic carbon bra
30 to 1% by weight, and the graphite material is scaly natural
Graphite powder or scale-like artificial graphite powder, and the pseudo black
Lattice plane spacing of lead carbon black in X-ray diffraction
(D₀₀₂) Is 3.38 to 3.46Å, and the crystallite thickness is
(Lc) is 50 to 150Å and the true specific gravity is 1.9 to
2.1, and the average primary particle size is 10 to 100 nm.
Carbon material. (C) Graphite material treated with a silane coupling agent
Is a carbon material.

(2) Lithium nickelate is prepared by dispersing a nickel compound in a lithium nitrate solution and then volatilizing the solvent to obtain a mixture of lithium nitrate and a nickel compound.
The lithium secondary battery according to (1), which is lithium nickelate obtained by firing the mixture in an atmosphere containing oxygen. (3) The lithium secondary battery according to (1), wherein the carbon material (B) is treated with a silane coupling agent.

The present invention will be described in detail below. First, the positive electrode material for lithium secondary batteries will be described. When lithium nickel oxide is used as the positive electrode material for the lithium secondary battery, the Coulomb efficiency in the first charge / discharge is 10%.
It is much lower than 0%, and in the past, 80% or more has not been obtained.

The positive electrode material used in the lithium secondary battery of the present invention is a lithium nickelate having a Coulomb efficiency of 80% or more in the first charge / discharge, and preferably 85% or more. Furthermore, the positive electrode material has an efficiency of 99% after the second time.
The above is shown, and there is a feature that cycle deterioration is small.

It is preferable that lithium nitrate used as a raw material for the positive electrode material has high purity. Since the solution is once mixed, the particle size is not particularly limited.

As a solvent for dissolving lithium nitrate,
Examples thereof include water and alcohols such as ethanol. Water is particularly preferable. However, the present invention is not limited to these, and other organic solvents that dissolve lithium nitrate can also be used. When carbon dioxide gas is dissolved in the solvent, it is possible to form sparingly soluble lithium carbonate. Therefore, it is more preferable to perform decarboxylation operation prior to the preparation of the lithium nitrate solution, but it is not an essential operation.

As the nickel compound dispersed in the lithium nitrate solution, nickel oxide, nickel carbonate, nickel hydroxide or the like can be used. As nickel oxide, nickel monoxide (NiO), dinickel trioxide (N
i ₂ O ₃ ) and trinickel tetroxide (Ni ₃ O ₄ ). Note that dinickel trioxide and trinickel tetraoxide also include hydrates. The nickel compound used is preferably highly pure. Considering dispersibility and depositing lithium nitrate on the surface, the average particle size of the nickel compound used is preferably 100 μm or less, more preferably 50 μm or less. It is preferable to use a nickel compound having a specific surface area of 1 m ² / g or more. When the nickel compound is dispersed in the lithium nitrate solution, it is preferable that the nickel compound is placed in a vacuum container and evacuated, and then the lithium nitrate solution is added to carry out vacuum impregnation. The lithium nitrate solution penetrates into the pores of the nickel compound, and can be mixed more uniformly. The lithium nickelate obtained by firing in this manner has no change in discharge capacity as compared with the one not vacuum impregnated, but the variation in discharge capacity between samples is reduced.

The lithium nitrate and the nickel compound can be mixed at a stoichiometric composition ratio of Li / Ni = 1, but preferably in the range of 1.0 ≦ Li / Ni ≦ 1.1.
If this ratio is less than 1.0, there is a lithium deficiency in the obtained composite oxide when there is a loss of the lithium nitrate solution, which is not preferable. If this ratio exceeds 1.1, the proportion of unreacted lithium component that becomes lithium carbonate and remains in the sample when handled in the air after firing is unfavorable because it lowers the discharge capacity.

A rotary evaporator and a spray dryer can be used to volatilize the solvent from the lithium nitrate solution in which the nickel compound is dispersed. Further, it is possible to use a so-called spray pyrolyzer, which is a combination of a spray dryer for simultaneously drying and firing and a vertical firing furnace.

The firing atmosphere is preferably an atmosphere containing oxygen. Specifically, a mixed gas of an inert gas and oxygen,
An atmosphere containing oxygen such as air can be used. The oxygen partial pressure in the firing atmosphere is preferably high. Calcination is preferably carried out in oxygen, more preferably in a stream of oxygen. Further, it is preferable to dry the mixed powder of lithium nitrate and nickel compound before firing. However, if the temperature is higher than the melting point of lithium nitrate, phase separation may occur, which is not preferable. The discharge capacity of lithium nickel oxide obtained by firing in this manner is not different from that of the non-dried one, but variation in discharge capacity between samples is reduced, which is preferable.

The firing temperature is preferably 350 ° C. or higher and 800 ° C. or lower. More preferably, it is 600 ° C. or higher and 750 ° C. or lower. If the firing temperature exceeds 800 ° C., the mixing ratio of rock salt domains increases, which is not preferable. Further, if the firing temperature is lower than 350 ° C., the reaction for producing lithium nickelate hardly proceeds, which is not preferable. The firing time is preferably 2 hours or longer, more preferably 5 hours or longer.

A washing operation of the lithium nickel oxide powder after firing is not particularly required, but washing and subsequent heat treatment, or a single heat treatment step may be added as necessary.

Next, the carbon material (B) used for the negative electrode for the lithium secondary battery in the present invention will be described. The negative electrode for a lithium secondary battery according to the present invention is a graphite material 70 to 9
The carbon material (B) is included in an amount of 30 to 1% by weight of pseudo-graphitic carbon black with respect to 9% by weight. Preferably graphite material 8
Pseudographitic carbon black 20 to 0 to 97% by weight
~ 3 wt%, more preferably 90-96 wt% graphite material
To 10 to 4% by weight of pseudo-graphite treated carbon black
Is. When the blending amount of the pseudographitic carbon black exceeds 30% by weight, the discharge capacity of the negative electrode active material decreases, while when the blending amount is less than 1% by weight, the irreversible capacity of the negative electrode active material increases, which is not preferable.

The graphite material used in the present invention is scaly natural graphite or scaly artificial graphite. The graphite material has a lattice spacing (d ₀₀₂ ) of 3.37 in X-ray diffraction.
It is preferably Å or less and has a true specific gravity of 2.23 or more. More preferably, the lattice plane spacing (d
₀₀₂ ) is 3.36Å or less and the true specific gravity is 2.24 or more. Here, the lattice spacing (d ₀₀₂ ) is
An X-ray diffraction method using CuKα rays as X-rays and using high-purity silicon as a standard substance [Shiro Otani, carbon fiber, 733-7]
42 (1986), Modern Editing Co., Ltd.].

The ash content of the graphite material used in the present invention is preferably 0.5% by weight or less, more preferably 0.1% by weight.
It is the following. In the case of natural graphite, the content of ash varies depending on the place of production, but since the ash content is as large as several wt% or more, it is preferably treated at a high temperature of 2500 ° C. or higher, more preferably 2800 ° C. or higher, and the ash content is preferably 0.5 or more. The content is preferably not more than 0.1% by weight, more preferably not more than 0.1% by weight. Here, the ash content means a value according to JISM8812.

The particle size of the graphite material used in the present invention is not particularly limited, but the average particle size is preferably about 1 to 50 μm. More preferably, it is 2 to 20 μm.

The pseudo-graphitic carbon black used in the present invention has a lattice spacing (d ₀₀₂ ) in X-ray diffraction of 3.38 to 3.46Å and a crystallite thickness (Lc) of 5
0 to 150Å, the true specific gravity is 1.9 to 2.1,
The average primary particle diameter is 10 to 100 nm. Further, the pseudo-graphitic carbon black preferably has a specific surface area of about 10 to 300 m ² / g by a nitrogen adsorption method, and preferably has a volatile content of 0.5% by weight or less. Here, the true specific gravity is the value according to JIS R7222, and the volatile content is JIS M88.
Means a value of 12.

The pseudo-graphitic carbon black can be obtained by subjecting carbon black to so-called graphitization treatment. Specifically, the pseudo-graphitic carbon black is obtained by heat treating carbon black at a temperature of about 1500 to 3000 ° C. Particularly, the one heat-treated at about 2500 to 3000 ° C. is preferable. Carbon black is a non-graphitizable carbon that has a lattice spacing (d ₀₀₂ ) in X-ray diffraction of 3.37 Å or less and a true specific gravity of 2.23 or more, and is difficult to be a graphite material even if such a graphitization treatment is performed. It is a material.

As the pseudo-graphitic carbon black, for example, carbon black such as furnace black made of creosote oil, ethylene bottom oil, natural gas or the like, or acetylene black made of acetylene as a raw material is 2500 to 2800. The heat treatment may be performed at a high temperature of about ℃. With or without graphitization, the lattice spacing (d) in X-ray diffraction
₀₀₂ ) is more than 3.46Å, the true specific gravity is less than 1.9, and the use of carbon black having a volatile content of more than 0.5% by weight has no or little effect of reducing the irreversible capacity, and also releases lithium. The electric potential at this time is higher than the lithium electric potential, which is not preferable. Next, the carbon material (C) used in the negative electrode for a lithium secondary battery in the present invention will be described. The carbon material (C) is a silane coupling-treated graphite material, and the surface or a part of the surface of the graphite material is coated with a silane coupling agent. here,
The graphite material is the same as the graphite material used in the carbon material (B).

Further, the carbon material (B) for the negative electrode used in the present invention is preferably treated with a silane coupling agent. Examples of the silane coupling agent used in the present invention include those represented by the general formula 1.

Embedded image In the formula YSiX ₃ , Y is CH ₂ ═CH−, CH ₂ ═C (CH ₃ ) COOC ₃ H ₆ −,

[Chemical 2]

[Chemical 3] NH ₂ C ₃ H _6- , NH ₂ C ₂ H ₄ NHC ₃ H _6- , NH ₂ CONHC ₃ H _6- , CH ₃ COOC ₂ H ₄
NHC ₂ H ₄ NHC ₃ H _6- , NH ₂ C ₂ H ₄ NHC ₂ H ₄ NHC ₃ H _6- , SHC ₃ H _6- , ClC ₃
H _6- , CH _3- , C ₂ H _5- , C ₂ H ₅ OCONHC ₃ H _6- , OCNC ₃ H _6- , C ₆ H _5- , C
₆ H ₅ CH ₂ NHC ₃ H _6- , C ₆ H ₅ NHC ₃ H _6- and the like. As the X, a functional group bonded to a silicon _{atom, -OCH 3, -OC 2 H 5} , -OCOCH 3, -OC 2 H 4 OCH 3, -N (CH 3) 2, -Cl
Groups such as.

Specific examples of the silane coupling agent include vinyltriethoxysilane, vinyltrimethoxysilane, vinyltrichlorosilane, vinyltris (2-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane and γ-meta. Acryloxypropyltriethoxysilane, γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β
-(Aminoethyl) -γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropyltriethoxysilane, γ-ureidopropyltriethoxysilane, γ-ureidopropyltrimethoxysilane,
β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-mercaptopropyltrimethoxysilane, γ-mercaptopropyltriethoxysilane, γ-chloropropyltrimethoxysilane, γ-chloropropyltriethoxysilane, methyltriethoxysilane, methyltrimethoxysilane, phenyltriethoxysilane, phenyltrimethoxy Examples include silane.

Of these, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris (2-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropyltriethoxysilane and γ- are preferable. Aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropyltriethoxysilane, γ- Ureidopropyltriethoxysilane, γ-ureidopropyltrimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltrimethoxysilane, β- (3,4-epoxycyclohexyl) ethyltriethoxysilane, γ-glycidoxypropyl Trimethoxy Emissions, such as γ- glycidoxypropyl triethoxy silane.

More preferably, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris (2-
(Methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N-β- (aminoethyl) -γ-aminopropyltrimethoxysilane, γ-ureidopropyltriethoxysilane, β- Examples include (3,4-epoxycyclohexyl) ethyltrimethoxysilane and γ-glycidoxypropyltrimethoxysilane.

Although the mechanism by which the excellent effect is obtained by the treatment with the silane coupling agent is not clear, surface adsorbed water and surface functional groups which are considered to chemically react with lithium and do not contribute to the charge / discharge reaction of the battery, It is considered that this is because the water resistance (lipophilicity) is improved and the water content is reduced. Therefore, it is considered that titanate coupling agents, aluminate coupling agents, and the like, which can expect the same effects, are also applicable. Furthermore, a lithium nickel oxide powder as a positive electrode material or an auxiliary conductive material treated with a silane coupling agent can be applied to the positive electrode for a lithium secondary battery of the present invention.

Further, the carbon material (C) in the present invention, or the carbon material (B) or the positive electrode material (B), if necessary (hereinafter, these may be collectively referred to as an electrode material), is subjected to silane coupling. The method of treating with a chemical agent is not particularly limited, but if one example is shown, a silane coupling agent is reacted with water to hydrolyze a part or the whole amount thereof is added to an electrode material, mixed, and then dried. There is a method. The amount of the silane coupling agent used in the present invention is not particularly limited, but it is preferably determined in consideration of the specific surface area of the electrode material used. That is, the silane coupling agent is estimated to be able to cover an area of approximately 100 to 600 m ² per 1 g (Sm ² / g), though it depends on the type, so that the specific surface area of the electrode material used is Am ² / g. Then, A / S per 1 g of electrode material
It is preferable to use the amount of the silane coupling agent (g) as a guide. However, it has been confirmed that the irreversible capacity can be significantly reduced even if the total surface area of the electrode material cannot be covered with the silane coupling agent. More specifically, the amount of silane coupling agent is
The amount is preferably 0.01 to 20 parts by weight, more preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the electrode material used.

Next, a method for manufacturing the lithium secondary battery of the present invention will be described. For a positive electrode capable of inserting and extracting lithium, lithium nickel oxide powder and auxiliary conductive material powder used in the present invention are uniformly mixed with a binder or the like for binding the powder, and then pressure molding is performed, or a solvent or the like is used. It can be manufactured by a known method such as forming a paste by using, coating on a current collector, drying and pressing. Regarding the negative electrode capable of occluding and releasing lithium, the graphite material powder, the pseudographitic carbon black powder, and the binder for binding the powders are uniformly mixed and then pressure-molded, or an organic solvent is used. It can be manufactured by a known method similar to that for the positive electrode, such as forming a paste using the above or the like, coating on a current collector, drying and pressing.

The binder used for the positive electrode and the negative electrode is
Any material having a binding effect and resistance to the non-aqueous electrolyte solution used and to the potential of the positive electrode and the negative electrode may be used, and examples thereof include fluororesin, polyethylene, and polypropylene. The amount of the binder is 1-2 with respect to 100 parts by weight of the lithium nickel oxide powder used.
It is preferably about 0 parts by weight, and about 1 to 20 parts by weight based on 100 parts by weight of the total amount of the graphite material powder and the pseudographitic carbon black powder.

As the above-mentioned auxiliary conductive material for the positive electrode, any material may be used as long as it has a conductive effect and has resistance to the non-aqueous electrolyte solution used and to the potential at the positive electrode and the negative electrode. For example, graphite powder or carbon black, Examples thereof include conductive polymers. The amount of the auxiliary conductive material is preferably about 1 to 20 parts by weight based on 100 parts by weight of the lithium nickel oxide powder used.

The non-aqueous electrolyte solution used in the lithium secondary battery of the present invention is preferably a solution prepared by dissolving a lithium salt in an organic solvent having a high dielectric constant. The type of lithium salt is not particularly limited, and examples include LiPF ₆ and LiB.
F ₄ , LiCF ₃ SO ₃ , LiClO ₄ or the like can be used. The concentration of lithium salt is usually 0.5 mol
/ L to 1.5 mol / l. Further, the organic solvent may be any one as long as it dissolves a lithium salt to give electrical conductivity and is electrochemically stable with respect to the constituent negative electrode / positive electrode material. For example, ethylene carbonate, propylene carbonate, dimethyl carbonate,
Examples include diethyl carbonate, 1,2-dimethoxyethane, tetrahydrofuran, acetonitrile, sulfolane, γ-butyrolactone, and the like. Usually, two or more kinds are mixed and used, and preferably ethylene carbonate, dimethyl carbonate or diethyl carbonate are mixed and used.

In the lithium secondary battery of the present invention, in addition to the positive electrode, the negative electrode and the non-aqueous electrolyte solution, it generally has a function of preventing contact between the both electrodes, holding the non-aqueous electrolyte solution, and allowing passage of lithium ions. It is preferable to use a separator and a current collector having a function of holding an electrode material and collecting current in combination. Examples of the separator include porous films such as polyethylene, polypropylene, and polytetrafluoroethylene, non-woven fabrics, and woven fabrics. The thickness of the separator is preferably about 10 to 200 μm.

As the current collector, a positive / negative electrode and a conductor that is electrochemically stable with respect to the electrolytic solution can be used. For example, nickel, titanium, stainless steel, copper, aluminum and the like can be mentioned. Further, the lithium secondary battery of the present invention can be formed into various shapes such as a cylinder type, a box type, a coin type, a button type, a paper type and a card type.

[0050]

EXAMPLES Examples and comparative examples of the present invention will be described below.
The effect of the present invention will be described in detail below.
However, the present invention is not limited to this example. Example 1 A positive electrode for a lithium secondary battery was produced as follows.
Lithium nitrate (Wako Pure Chemical Industries, Ltd., reagent grade
108.6 g of water is dissolved in 150 g of water, and charcoal is added.
Nickel acid [NiCO₃・ 2Ni (OH)₂・ 4H₂O:
Wako Pure Chemical Industries, Ltd., reagent grade] 188.1 g
Add well and disperse well, then use a rotary evaporator.
Was used to evaporate the water. Agate powder obtained
After crushing lightly in a mortar, tubular using alumina core tube
Put in the furnace, oxygen flow rate 50cm³/ Min in oxygen flow
It was baked at 700 ° C. for 5 hours. Powder the obtained baked product
When crushed and subjected to powder X-ray diffraction measurement, α-NaFe
O ₂Confirmed to be lithium nickelate having a mold structure
It has been certified.

After thoroughly mixing the lithium nickel oxide powder and the artificial graphite powder as an auxiliary conductive material, a paste prepared by using polyvinylidene fluoride as a binder and N-merylpyrrolidone as a solvent is coated on both sides of an aluminum foil current collector. Application, drying and roll pressing were performed to obtain a positive electrode sheet electrode. At this time, the mixing ratio of the lithium nickel oxide, the auxiliary conductive material and the binder was 87: 10: 3 by weight.

Next, a negative electrode for a lithium secondary battery was produced as follows. Lattice plane spacing (d
₀₀₂ ) is 3.36Å, true specific gravity is 2.26, specific surface area by nitrogen adsorption method is 9 m ² / g, average particle size is 10 μm, and natural graphite (Madagascar) flaky powder, and lattice spacing in X-ray diffraction (D ₀₀₂ ) is 3.40 A, crystallite thickness (L
c) is 120Å and the specific surface area by nitrogen adsorption method is 24m ²
/ G, true specific gravity 1.98, number average primary particle size 66 nm
Pseudo-graphitic carbon black powder [Tokai Carbon Co., Ltd.
Manufactured by trade name TB3800] in a weight ratio of 95: 5 and thoroughly mixed, and then a silane coupling agent [Nippon Unicar Co., Ltd.]
Manufactured by Product Name A1100] and dried to obtain a silane coupling agent-treated mixed carbon material. The weight ratio of the carbon material and the silane coupling agent at this time was 100: 1.

A paste prepared by using the silane coupling agent-treated carbon material, polyvinylidene fluoride as a binder, and N-methylpyrrolidone as a solvent was applied to both surfaces of a copper foil current collector, dried, and roll pressed to form a negative electrode. A sheet electrode for use was obtained. The weight ratio of the carbon material and the binder at this time was 90:10.

The positive electrode and the negative electrode obtained as described above were wound up with a polypropylene separator interposed therebetween, and ethylene carbonate (EC) and dimethyl carbonate (DM
C) and diethyl carbonate (DEC) in a volume ratio of 2:
A cylindrical battery was produced by impregnating a 1: 1 mixed solvent with an electrolyte solution (concentration 1 mol / l) in which lithium hexafluorophosphate was dissolved. The initial voltage of this battery was 0.02V. Then, the battery was charged at a current of 50 mA and a constant voltage of 4.10 V for 15 hours to obtain a lithium secondary battery having an initial voltage of 4.1 V. Then, after discharging the battery at a constant current of 100 mA to a voltage of 2.75 V, a test of charging at a current of 500 mA and a constant voltage of 4.10 V for 3 hours and discharging to a voltage of 2.75 V at a constant current of 100 mA was repeated. The results are shown in Table 1.

Furthermore, the single-sided coated positive electrode sheet electrode prepared in the same manner as above was evaluated for initial charge / discharge characteristics with a lithium counter electrode (voltage range 4.2 V to 2.5 V, constant current 0.17 mA).
/ Cm ² ), the initial Coulombic efficiency was 85%. Further, the one-side coated negative electrode sheet electrode prepared in the same manner as above was evaluated for initial charge / discharge characteristics with a lithium counter electrode (voltage range 0 V to 0.6 V, constant current 0.17 mA / cm ² ).
As a result, the initial Coulombic efficiency was 88%.

COMPARATIVE EXAMPLE 1 Lithium carbonate and cobalt carbonate were used as raw materials, and 90% in air.
A sheet electrode for a positive electrode was obtained in the same manner as in Example 1 except that lithium cobalt oxide powder obtained by firing at 0 ° C., artificial graphite powder as an auxiliary conductive material, and polyvinylidene fluoride as a binder were used. On the other hand, graphitized carbon of mesocarbon microbeads having an average particle size of 6 μm [manufactured by Osaka Gas Co., Ltd., MC
MB6-28] A sheet electrode for negative electrode was obtained in the same manner as in Example 1 except that spherical powder and polyvinylidene fluoride were used as the binder.

The positive electrode and the negative electrode obtained as described above were wound up with a polypropylene separator interposed therebetween, and ethylene carbonate (EC) and dimethyl carbonate (DMC) were obtained.
An electrolyte solution (concentration: 1 mol / l) in which lithium hexafluorophosphate was dissolved was mixed in an equal volume mixed solvent of 1 to prepare a cylindrical battery. The initial voltage of this battery was 0.01V. Then, at a constant current of 50 mA and a constant voltage of 4.20 V, 15
After charging for an hour, a lithium secondary battery having an initial voltage of 4.2 V was obtained. Then, after discharging the battery at a constant current of 80 mA to a voltage of 2.75 V, a test of charging at a current of 400 mA and a constant voltage of 4.20 V for 3 hours and discharging at a constant current of 80 mA to a voltage of 2.75 V was repeated. The results are shown in Table 1.

[0058]

[Table 1]

[0059]

The lithium secondary battery of the present invention is a combination of a positive electrode and a negative electrode with improved Coulomb efficiency, and is a high-capacity lithium secondary battery with improved utilization efficiency of lithium in the positive electrode. Yes, and has great industrial value.

Front page continued (72) Inventor Yuki Nishida 6 Kitahara, Tsukuba, Ibaraki Sumitomo Chemical Co., Ltd.

Claims (3)

[Claims] 1. A positive electrode capable of inserting and extracting lithium by charging and discharging.
A negative electrode capable of inserting and extracting lithium by charging and discharging,
In a lithium secondary battery provided with a non-aqueous electrolyte solution,
The positive electrode is an electrode containing lithium nickelate (A) below.
And the negative electrode has the following (B) carbon material or
(C) An electrode containing a carbon material
Tium secondary battery. (A) Coulomb efficiency of 80% or more in the first charge and discharge
And α-NaFeO ₂Nickel oxide having a die structure
Tium. (B) 70-99% by weight of graphite material and pseudo-graphitic carbon bra
30 to 1% by weight, and the graphite material is scaly natural
Graphite powder or scale-like artificial graphite powder, and the pseudo black
Lattice plane spacing of lead carbon black in X-ray diffraction
(D₀₀₂) Is 3.38 to 3.46Å, and the crystallite thickness is
(Lc) is 50 to 150Å and the true specific gravity is 1.9 to
2.1, and the average primary particle size is 10 to 100 nm.
Carbon material. (C) Graphite material treated with a silane coupling agent
Is a carbon material. 2. Lithium nickelate is prepared by dispersing a nickel compound in a lithium nitrate solution and then volatilizing a solvent to obtain a mixture of lithium nitrate and a nickel compound, and calcining the mixture in an atmosphere containing oxygen. The lithium secondary battery according to claim 1, which is lithium nickel oxide obtained by the above. 3. The lithium secondary battery according to claim 1, wherein the carbon material (B) is treated with a silane coupling agent.