JP3017847B2 - Non-aqueous solvent secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a positive electrode active material of a non-aqueous solvent secondary battery using a carbonaceous material as a negative electrode carrier.

[0002]

2. Description of the Related Art In recent years, with the development of electronic equipment, there has been a demand for the development of a secondary battery that is small, lightweight, has a high energy density, and can be charged and discharged repeatedly. As this type of secondary battery, those using lithium or a lithium alloy as a negative electrode active material, and using oxides such as molybdenum, vanadium, titanium, and niobium, sulfides, and selenides as a positive electrode active material are known. I have. In recent years, studies have been actively conducted on spinel-type LiMn ₂ O ₄ having improved and improved cycle characteristics of a manganese oxide having a high energy density and other lithium manganese composite oxides.

In a battery system using these lithium manganese oxide as a positive electrode active material and lithium as a negative electrode active material, a cycle of repeating the dissolution / precipitation reaction of lithium, which is a negative electrode active material, is repeated. The problem of forming needle-like lithium dendrite deposits on top arises. Therefore, in the battery system,
The battery life is regulated by the dendrite generation and the solvent decomposition reaction on the negative electrode side with the collapse of the crystal structure gradually progressing in the positive electrode active material, and the production of a battery having a life of 500 cycles or more and long-term reliability is required. Very difficult.

On the other hand, an electrode active material utilizing intercalation or doping of a layered compound having a different reaction form from these manganese oxides has attracted attention.
Since these electrode active materials do not cause a complicated chemical reaction during charge and discharge reactions, they are expected to have an extremely excellent charge / discharge cycle. Above all, those using a carbonaceous material as a support have attracted attention. This carbonaceous material was used as a negative electrode carrier, and LiCoO ₂ /
LiNiO ₂ system has been proposed.

[0005]

However, when a carbonaceous material is used as a negative electrode active material, when a metal chalcogen compound such as TiS ₂ or MoS ₂ is used as a positive electrode active material, the electromotive force is small, and LiCoO ₂ , LiNiO ₂ When the positive electrode active material is used as the positive electrode active material, the operating voltage range is as large as about 3.0 to 4.3 V. However, the charge curve of this active material is 4.
It rises almost linearly to 3 V, and it is difficult to detect and set the termination of charging, and there is a possibility that decomposition of the electrolytic solution and dissolution of the electrode base material due to overcharging may occur.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and it is intended to prevent decomposition of a solvent and dissolution of a base material on a positive electrode side when a carbonaceous negative electrode active material is used, and to charge and discharge a battery in a positive electrode. An object is to obtain a positive electrode active material containing a sometimes movable Li ion.

[0007]

A non-aqueous solvent secondary battery according to the present invention comprises a negative electrode containing a carbonaceous material ; a composition formula of LiM _1-X V _X
O ₂ (where M is at least one selected from Co and Ni, and the atomic ratio X represents 0 <X ≦ 0.5), a lithium-containing composite oxide, a conductive agent and a binder.
And a substrate on which the positive electrode mixture layer is carried.
It is characterized in that comprising a; positive for.

[0008] LiM _1-X V _X O ₂ used in the present invention
Is generally synthesized by the following method. That is, starting from one or two kinds of carbonates, nitrates, hydroxides and the like selected from lithium and Co and Ni,
It is obtained by adding ammonium vanadate as a compound, mixing them in a stoichiometric ratio and heating. Note that carbonate is the most common starting material.
The heating temperature varies slightly depending on the starting material, but is usually 6
In the temperature range of 00 to 1000 ° C, preferably 600 to 8
00 ° C. The amount of vanadium added is 0 <X ≦
0.5 is preferable, and particularly preferably 0 <X ≦ 0.
It is one. This is because if the added amount of vanadium is more than 0.5, the high voltage portion of 4.2 V or more with respect to Li ⁺ / Li increases during charging, and the voltage range is 3.0 ← → 4.3.
This is because the reversible charge / discharge capacity between V becomes small.

As the carbonaceous material as the negative electrode carrier, a carbonaceous material obtained by firing an organic compound is preferably used in order to improve battery characteristics. The organic compound serving as a raw material of the carbonaceous material is not particularly limited as long as it is a commonly used organic compound. For example, a phenol resin, particularly a novolak resin, and polyacrylonitrile can be used. As the carbonaceous material, a material having the characteristics of an organic compound fired body as shown in Japanese Patent Application No. 1-283086 is particularly preferable.

In the non-aqueous solvent secondary battery of the present invention, a binder may be used to form a positive electrode and a negative electrode. Examples of the binder include a terpolymer of ethylene-propylene-cyclic diene, polytetrafluoroethylene, polyacrylic acid, and polyacrylates.

The electrolyte of the non-aqueous electrolyte used in the non-aqueous solvent secondary battery of the present invention includes LiPF ₆ , LiCl
Lithium salts such as O ₄ , LiBF ₄ , and LiCF ₃ SO ₃ are exemplified. As the solvent for the electrolytic solution, propylene carbonate (PC), ethylene carbonate (E
C), tetrahydrofuran, 2-methyltetrahydrofuran, γ-butyrolactone, 1.2-dimethoxyethane (DME). These solvents can be used alone or in a mixture of two or more. In particular, from the viewpoint of extending the charge / discharge cycle life, a mixed solvent of propylene carbonate and 1,2-dimethoxyethane, ethylene carbonate and 2-methyltetrahydrofuran. , A mixed solvent of ethylene carbonate and 1,2-dimethoxyethane, and a mixed solvent of propylene carbonate and ethylene carbonate.

[0012]

The charge curve of the cathode active material of the present invention is expressed by Li ⁺ / L
For i, the charge rises almost linearly from 3.9 V to 4.1 V, rises sharply from 4.1 V to 4.2 V, and when charging is further performed, the charge voltage rises almost linearly. On the other hand, the charging curve of the conventional LiCoO ₂ rises almost linearly from 3.9V to 4.3V. As described above, the positive electrode active material of the present invention has a two-stage charging curve, which makes it possible to easily confirm the termination of charging in the battery from 4.1 V to 4.2 V, to take measures against overcharging of the battery, The decomposition of the solvent and the dissolution of the substrate due to the voltage can be suppressed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the drawings by way of examples and comparative examples. Example 1 Commercially available lithium carbonate, cobalt carbonate, and ammonium vanadate were prepared using Li: Co: V = 1: 0.9:
It was weighed out at a 0.1 molar ratio and mixed well in a mortar.
This mixture was placed in an alumina crucible and heat-treated at 800 ° C. for 6 hours in an electric furnace. The obtained fired product was cooled and pulverized again, and was similarly heated at 800 ° C. for 6 hours, and then sufficiently washed with distilled water to wash away unreacted alkali components. Was identified the product by powder X-ray method, it is shown in Figure 2, which is consistent with Li C oO ₂ diffraction peaks, other compounds such as vanadium bronze (lithium vanadium compound) was not confirmed.

90% by weight of this product, 7% by weight of acetylene black as a conductive material and 3% by weight of a terpolymer of ethylene-propylene-cyclic diene as a binder are kneaded in hexane to form a slurry-like positive electrode. A mixture was prepared, and this positive electrode mixture was applied on a titanium substrate having a thickness of 15 μm, air-dried, and then pressurized to a constant thickness.
By heating and drying under the condition of time, a plate-shaped positive electrode having a positive electrode mixture layer having a thickness of 0.26 mm was manufactured.

On the other hand, the carbonaceous material as the negative electrode carrier is obtained by firing a novolak resin at 950 ° C. in a nitrogen atmosphere.
It was further manufactured by heating to 2,000 ° C. to carbonize and pulverized to a powder having an average particle size of 10 μm.

A ternary copolymer of ethylene-propylene-cyclic diene as a binder is dissolved in hexane and dispersed so that the carbonaceous material: the binder = 97: 3. Prepared. This slurry was applied on a stainless steel substrate having a thickness of 10 μm and dried to form a negative electrode mixture layer having a thickness of 0.2 mm.

Using the positive and negative electrodes thus obtained, a non-aqueous solvent secondary battery of AA size as shown in FIG. 1 was assembled. That is, the non-aqueous solvent secondary battery 1
An insulator 2 is disposed at the bottom, and has a bottomed cylindrical stainless steel container 3 also serving as a negative electrode terminal. The container 3 contains an electrode group 4. The electrode group 4 has a structure in which a strip formed by laminating a negative electrode 5, a separator 6, and a positive electrode 7 in this order is spirally wound so that the negative electrode 5 is located outside. The separator 6 is formed of a polypropylene porous film impregnated with an electrolytic solution.
The electrolytic solution was prepared by adding lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte in a mixed solvent of propylene carbonate and 1.2 dimethoxyethane (volume ratio: 50:50).
Contains 5 molar concentration. Above the electrode group 4 in the container 3, an insulating plate 8 having an opening at the center is arranged. At the upper opening of the container 3, an insulating sealing body 9 is provided.
It is caulked tightly and fixed. A positive electrode terminal 10 is fitted into a central opening of the insulating sealing plate 8. The positive terminal 10 is connected to the positive electrode 7 via a positive electrode lead 11. The negative electrode 5 is connected to the container 3 as a negative terminal via a negative lead (not shown).

Example 2 Commercially available lithium carbonate, cobalt carbonate, nickel carbonate and ammonium vanadate were prepared by adding L
i: Co: Ni: V = 1.0: 0.7: 0.25: 0.
The mixture was weighed at a molar ratio of 05 and mixed well in a mortar. Thereafter, the same operation as in Example 1 was performed to manufacture a battery of the same type.

Comparative Example: Lithium carbonate and cobalt carbonate were L
i: Co = 1: 1 was mixed, and the other operations were performed in the same manner as in the example to produce the same type of battery.

FIG. 3 shows the initial charging curves of the three types of non-aqueous solvent secondary batteries prepared in this manner, up to 4.3 V, at a constant temperature of 20 ° C. and a constant current of 100 mA. Shown in In the figure, A is the charging curve of the battery of Example 1, B is the battery of Example 2, and C is the charging curve of the battery of Comparative Example. As is clear from FIG. 3, the non-aqueous solvent secondary batteries of Examples 1 and 2 have a feature that the charging voltage sharply increases near a battery voltage of 4.0 V. In the initial charge, the charge curve is almost the same as that of the conventional LiCoO ₂ up to around 4.0 V. It is considered that the charge voltage rises stepwise due to an increase in energy caused by distortion of the crystal structure due to the addition of vanadium. This makes it easier to detect the end of charging in the battery, and suppresses decomposition of the solvent, dissolution of the base material, and the like.

FIG. 4 is a graph showing the discharge capacity retention rates of these three types of batteries. The evaluation conditions of each battery were as follows: the batteries of Examples 1 and 2 were in a range of 2.7 V to 4.0 V at a constant current of 100 mA, and the batteries of Comparative Examples were 3.0 V to 4.0 at a constant current of 100 mA. Charge / discharge was performed in the range of 3V. As is clear from FIG. 4, in Examples 1 and 2, the capacity deterioration due to the sakuru hardly changed.
It turns out that it has good cycle characteristics.

[0022]

According to the non-aqueous solvent secondary battery of the present invention, the composition voltage LiM _1-X V _X O 2 is used as the positive electrode active material and the carbon material is used for the negative electrode support. ← → Excellent charge / discharge reversibility around 4.0V,
It can be used without decomposing the solvent. Further, when charging is further performed, the voltage suddenly rises by 0.1 V, which makes it easier to detect the end of charging.

[Brief description of the drawings]

FIG. 1 is a half-mounted sectional view of a non-aqueous solvent secondary battery according to Embodiment 1 of the present invention.

FIG. 2 is an X-ray diffraction diagram of a powder of a positive electrode active material manufactured according to Example 1 of the present invention and a comparative example.

FIG. 3 is a charge curve diagram of non-aqueous solvent secondary batteries of Examples 1 and 2 of the present invention and a comparative example.

FIG. 4 is a characteristic diagram showing a change in a discharge capacity retention ratio with respect to the number of charge / discharge cycles of the nonaqueous solvent secondary batteries of Examples 1 and 2 and Comparative Example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Non-aqueous solvent secondary battery 4 Electrode group 7 Positive electrode A Example 1 of this invention B Example 2 of this invention C Comparative example

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-256371 (JP, A) JP-A-2-265167 (JP, A) JP-A-1-265456 (JP, A) JP-A-62-256 90863 (JP, A) JP-A-4-22066 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/58 H01M 4/02 H01M 10/40

Claims (1)

(57) [Claims] 1. A negative electrode containing a carbonaceous material ; a composition formula LiM _{1 -X} V _X O ₂ (where M is at least one selected from Co and Ni, and an atomic ratio X is 0 <X ≦
0.5), a lithium-containing composite oxide represented by the following formula :
The positive electrode mixture layer comprising an electric agent and a binder and the positive electrode mixture layer
A non-aqueous solvent secondary battery , comprising : a positive electrode having a supported substrate ;