JPH08306353A - Nonaqueous electrolyte secondary battery and its manufacture - Google Patents

Abstract

PURPOSE: To suppress the generation of a gas generated in an initial charging and suppress the deformation of the shape of a battery and the deterioration of discharging properties by coating the surface of an anode with a macromolecular film consisting of a macromolecular material and an alkali metal salt. CONSTITUTION: The surface of an anode 4 made of a carbon material is coated with a macromolecular film consisting of a macromolecular material such as polyethylene oxide, polybutylene oxide, etc., and an alkali metal salt such as LiClO4 , LiBF4 , etc. A method involving dissolving the macromolecular material and the alkali metal salt in a solvent, applying the resulting solution to the surface of an anode, hardening, and drying and a method involving mixing an anode material powder with a macromolecular material and an alkali metal salt while using a prescribed solvent, making the mixture be a paste, applying the paste to an anode collector, hardening and drying the paste can be employed to form the coating. Consequently, the electrolytic liquid and the surface of the carbon material are prevented from being brought into direct contact mutually and gas generation by charging can be suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery having a high energy density, particularly to the negative electrode thereof.

[0002]

2. Description of the Related Art Non-aqueous electrolyte secondary batteries using lithium or a lithium compound as a negative electrode are expected to have a high voltage and a high energy density, and have been actively studied.

So far, V ₂ O ₆ , Cr ₂ O ₃ , MnO ₂ , TiS _{2 and the} like have been known as positive electrode active materials for non-aqueous electrolyte secondary batteries. 4 with higher energy density in recent years
Li as a positive electrode active material for a bolt-class non-aqueous electrolyte secondary battery
Mn ₂ O _4, such as LiCoO _2, LiNiO _2, LiFeO ₂ has been attracting attention. In particular, LiMn ₂ O ₄ and LiNiO
₂ and LiFeO ₂ are low in cost and the supply of raw materials is stable, and active research is being conducted as an active material for a large capacity non-aqueous electrolyte secondary battery.

On the other hand, as a negative electrode active material, a carbon material has been attracting attention in place of metallic lithium in terms of safety and rate characteristics. In particular, graphite powder with advanced graphitization
Since the battery has a high capacity and a discharge potential of about 0.1 V, which is higher than that of metallic lithium, and a battery having a higher energy density can be developed, active research is being conducted.

[0005]

A graphite material such as natural graphite, artificial graphite, vapor-grown graphite, mesocarbon microbeads, etc., or an amorphous material such as carbon fiber, coke, etc., is used for the negative electrode, using the positive electrode active material as described above. As a result of studying a non-aqueous electrolyte secondary battery using carbon, it was found that gas is generated from the negative electrode only during initial charging. Although a clear reaction mechanism for this gas generation is unknown, the electrolytic solution or the negative electrode constituent material (for example, the binder) at the active sites such as the surface functional groups (for example, OH groups) of the carbon material used for the negative electrode. ) Is expected to produce gas and a reactant. In particular, it has been found that the amount of generated gas changes greatly by changing the type of electrolyte solution, and that gas is generated even in the second charge when ethylene carbonate is not present in the electrolyte solution component. That is, it is considered that the gas generation is due to the interaction between the surface of the carbon material of the negative electrode and the electrolytic solution.

The generated gas species are mainly hydrogen and carbon monoxide, and trace amounts of acetylene, methane and the like are also detected. Particularly, hydrogen gas occupied 90 vol% of the whole.

As a problem caused by gas generation at the time of initial charging, there are leakage due to increase in internal pressure of the battery, deformation of the battery, increase in internal resistance caused by gaps between electrodes, and deterioration of charge / discharge performance. Conventionally, in order to solve the above-mentioned problems caused by gas generation, a method of discharging tens of percent of the battery capacity in an opened state immediately after battery assembly and performing so-called preliminary charging to release the first generated gas outside the battery However, it was not a preferable method in terms of battery manufacturing equipment and process.

[0008]

In order to solve such a problem, the present invention suppresses gas generation by avoiding direct contact between the surface of the carbon material and the electrolytic solution.

On the surface of the negative electrode made of a carbon material, a polymer material such as polyethylene oxide or polybutylene oxide and LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₅ ,
It is characterized by coating with a polymer film composed of an alkali metal salt such as LiCF ₃ SO ₃ . In addition, as a method of forming the coating on the surface of the negative electrode, a method of dissolving a polymer material and an alkali metal salt in a predetermined solvent, coating this on the surface of the negative electrode and curing and drying, or a negative electrode material powder and the polymer material There is also a method in which an alkali metal salt and an alkali metal salt are mixed and made into a paste, which is applied to a negative electrode current collector, cured, and dried to obtain a negative electrode. Curing can be performed by heating or irradiating with light.

[0010]

According to the present invention, by coating the surface of the negative electrode with the polymer film composed of the above-mentioned polymer material and alkali metal salt, the electrolytic solution which is a gas generating factor does not come into direct contact with the surface of the carbon material of the negative electrode. , No gas is generated by charging.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

(Example 1) A battery was manufactured by the following procedure.

For the positive electrode, LiCoO _{2 as the} positive electrode active material was mixed with carbon black as a conductive agent at a weight ratio of 100: 3, and distilled water and ethanol were further added and wet mixed. An aqueous dispersion of polytetrafluoroethylene was added to this as a binder, and the mixture was further mixed and dried in a hot air dryer at 100 ° C. to obtain a positive electrode mixture. This positive electrode mixture has a diameter of 1
It was press-molded into 7 mm at 2 ton / cm ² to obtain a positive electrode.

For the negative electrode, 1 mol / liter of LiClO ₄ was dissolved in a 1% aqueous solution of polyethylene oxide. Further, graphite powder was added to this solution, and then an acrylic binder was added and mixed well. This was dried with a warm air dryer at 80 ° C. to obtain a negative electrode mixture. This electrode mixture has a diameter of 17.5 m
m was press-molded at 2 ton / cm ² to obtain a negative electrode. Also,
A negative electrode similar to the above was prepared except that a solution of LiClO ₄ dissolved in an aqueous solution of polyethylene oxide was applied to the surface of the negative electrode using graphite powder. A cross-sectional view of the manufactured battery is shown in FIG. A porous polypropylene separator 3 having a diameter of 18.5 mm was placed on the positive electrode 1, and a negative electrode 4 was further placed thereon. As a non-aqueous electrolytic solution, a mixed solution of ethylene carbonate and diethyl carbonate in an equal volume ratio, in which 1 mol / liter of lithium hexafluorophosphate was dissolved, was injected and sealed with a sealing plate 5 to form a coin battery.

The batteries using the above negative electrodes were designated as batteries A and B of the present invention. These batteries have a charge / discharge current of 2 m
A, the charge / discharge test was performed in a charge / discharge voltage range of 4.1 V to 3.0 V, and the thickness change of the battery before charging and after the first cycle charging and the average discharge voltage of the battery at the 10th cycle were measured.

(Comparative Example) As a comparative example, a battery was prepared in the same manner as in (Example 1) except that the negative electrode prepared by the following method was used.

First, water and ethanol are added to graphite powder,
The mixture was thoroughly mixed, and further an acrylic binder was added and mixed, and then this was dried at 80 ° C. to obtain a negative electrode mixture.

The battery C thus produced was also tested under the above conditions. The amount of change in battery thickness before and after initial charging is shown in (Table 1). Further, FIG. 2 shows the discharge curves at the 10th cycle of the battery A of the present invention and the battery of the comparative example.

[0019]

[Table 1]

As shown in (Table 1), the comparative battery C generates gas at the first charge, and the battery thickness expands by about 0.58 mm. On the other hand, the expansion of the thickness of batteries A and B was 0.07 to 0.08 mm. When the cause of cell expansion of the batteries A and B that the LiCoO ₂ graphite itself when graphite occludes lithium during charge expands and releasing lithium, was due to the LiCoO ₂ itself is expanded. Further, as shown in FIG. 2, in the discharge curve at the 10th cycle of the battery A, the average discharge voltage is higher by about 0.05 V and the discharge capacity is about 20% higher than that of the comparative battery C.
In the comparative battery, the gas generated during the first charge is accumulated between the electrode plates, which increases the internal resistance of the battery,
Although the discharge characteristics deteriorated, it is considered that the battery A of the present invention has improved discharge characteristics because no gas is generated.

(Example 2) Next, the molecular weight of the polyethylene oxide (PEO) used was examined.
The molecular weights of PEO investigated are 1,000, 10,000, and 10
0000, 1,000,000, 4,000,000, 7,000
The battery was manufactured in the same manner as in (Example 1), and the test method was also the same. FIG. 3 shows the change in thickness of the batteries after initial charging and the average discharge voltage of the batteries. When the molecular weight is 1,000,000 or less, the initial swelling of the battery is large, and the average discharge voltage of the battery decreases as the molecular weight increases. Therefore, it was found that the optimum polymer has a molecular weight of 100,000 to 100,000,000.

Example 3 Next, the type of polymer and the type of alkali metal salt used were examined. A battery was prepared by the same method as in (Example 1) except that the type of polymer and the type of alkali metal salt were changed. The polymer was cured by heating the electrode mixture at 80 ° C. Also,
The battery test was performed in the same manner as in (Example 1).

The combinations of polymers and alkali metal salts examined are shown in (Table 2). The change in battery thickness after the first charge is also shown in (Table 2).

[0024]

[Table 2]

All the batteries shown in the results (Table 2) showed no increase in thickness and no decrease in discharge capacity after initial charging.

In this embodiment, the case where a system in which 1 mol / liter of lithium hexafluorophosphate is dissolved in an equal volume mixed solvent of ethylene carbonate and diethyl carbonate is used as the non-aqueous electrolytic solution has been described. In addition to this, carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, esters such as gamma-butyrolactone and methyl acetate are used alone or in combination of one or more selected from these,
Similar results were obtained when lithium perchlorate, lithium borofluoride, or lithium hexafluorophosphate was used as the solute.

Further, although the coin type battery is described in the embodiment, it has been confirmed that the discharge characteristic can be improved and the deformation of the battery can be prevented also in the cylindrical battery and the prismatic battery.

[0028]

As described above, by coating the negative electrode using the carbon material with the polymer film composed of the polymer material and the alkali metal salt, it is possible to suppress the gas generated from the carbon material in the first charge, It is possible to suppress changes in the shape of the battery and deterioration of discharge characteristics.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a non-aqueous electrolyte secondary battery of the present invention.

FIG. 2 is a diagram showing a discharge curve at 10th cycle of a battery of the present invention and a battery for comparison.

FIG. 3 is a diagram showing the relationship between the molecular weight of polyethylene oxide and the battery thickness.

[Explanation of symbols]

 1 Positive electrode 2 Case 3 Separator 4 Negative electrode 5 Sealing plate 6 Gasket

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hide Koshina 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Akikatsu Morita, 1006 Kadoma, Kadoma City Osaka Prefecture

Claims (5)

[Claims] 1. A positive electrode, a non-aqueous electrolytic solution, and a negative electrode containing a carbon material as a main constituent material, wherein the surface of the carbon material is coated with a polymer film composed of a polymer material and an alkali metal salt is used. Water electrolyte secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the polymer material is at least one selected from polyethylene oxide, polybutylene oxide, and polyphosazene. 3. The alkali metal salt is LiClO ₄ , LiB
The non-aqueous electrolyte secondary battery according to claim 1, which is at least one selected from F ₄ , LiPF ₆ , LiAsF ₅ , and LiCF ₃ SO ₃ . 4. A method for producing a non-aqueous electrolyte secondary battery comprising a positive electrode, a non-aqueous electrolyte and a negative electrode containing a carbon material as a main constituent material, wherein a polymer material and an alkali metal salt are dissolved in a solvent. Then, after applying this to the surface of the negative electrode, the polymer is cured to coat the surface of the negative electrode with the polymeric material. 5. A method for producing a non-aqueous electrolyte secondary battery comprising a positive electrode, a non-aqueous electrolyte and a negative electrode containing a carbon material as a main constituent material, which comprises a carbon material, a polymer material and an alkali metal salt. A method for manufacturing a non-aqueous electrolyte secondary battery, in which a negative electrode is formed by mixing a polymer and curing the polymer.