JP3440705B2 - Manufacturing method of non-aqueous electrolyte 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 improvement of a non-aqueous electrolyte secondary battery, in particular, a negative electrode.

[0002]

2. Description of the Related Art As electronic devices have become smaller and lighter, there has been a growing demand for smaller and lighter batteries as their power sources. Above all, non-aqueous electrolyte secondary batteries using lithium metal for the negative electrode have been greatly expected because of their large theoretical energy density. However,
When lithium metal is used for the negative electrode, dendritic lithium (dendrites) is generated during charging, and during repeated charging and discharging of the battery, this dendrite grows and penetrates the separator, causing an internal short circuit of the battery. In extreme cases, there is a problem such as the battery temperature rising rapidly,
Until now, it has not been completely resolved.

As a means for solving this problem, various attempts have been made to use not a lithium metal alone but an alloy of a low melting point metal such as aluminum, lead, indium, bismuth and cadmium and a lithium as a negative electrode, but also in this case. As the battery is charged and discharged, the alloy becomes finer as it repeatedly occludes and releases lithium, and this fine alloy penetrates through the separator to cause an internal short circuit in the battery, similar to the lithium metal negative electrode, and a rapid temperature rise is resolved. It's hard to say.

On the other hand, as a solution to the above problems,
Batteries using carbon for the negative electrode have been proposed. A battery using carbon as a negative electrode of a non-aqueous electrolyte secondary battery is 1986.
Annual Meeting of the 27th Battery Symposium P. 97 or 198
7th Annual 28th Battery Symposium Summary P. 201, it is said that a method of supporting lithium ions, which is an active material, on carbon of a negative electrode is an electrochemical method outside the battery system, and a positive electrode active material is vanadium pentoxide, manganese dioxide, Alternatively, chromium oxide is used. Among them, a battery using vanadium pentoxide for the positive electrode and carbon for the negative electrode has been put into practical use as a coin-shaped battery mainly used for memory backup applications. In this battery, as a method of supporting lithium on the negative electrode, a method of electrically contacting lithium metal and carbon in the battery is adopted.

[0005] Recently, the 1993 33rd Battery Symposium Abstracts P. In 83, as a power source for electronic equipment, Li is used for the positive electrode.
A cylindrical battery using CoO ₂ and carbon for the negative electrode has been proposed, and it is reported that the capacity of 70% or more of the initial capacity was retained even after 1200 cycles in deep-depth charge / discharge. At present, this battery system is put to practical use as a 4V class lithium ion secondary battery. The features of this battery system are
It is said that the charge / discharge reaction of the negative electrode is a reaction of occluding and releasing lithium ions in the carbon of the negative electrode, so that lithium does not deposit on the negative electrode due to charging, and therefore dendrite does not occur, so that good cycle characteristics can be obtained. Another point is that carbon does not undergo miniaturization as in a lithium alloy even when lithium ion absorption and desorption reactions are repeated, and a rapid temperature rise of the battery does not occur. Another feature of this battery system is that it uses a lithium-containing composite oxide called LiCoO _{2 for} the positive electrode, and lithium ions, which are the negative electrode active material, are supplied from the positive electrode. The point is that it is not necessary to support lithium ions.

Not only the above LiCoO ₂ but also LiNi is used as the positive electrode active material of the 4V class lithium ion secondary battery.
O ₂ , LiMn ₂ O ₄ , LiFeO ₂ , or these C
The materials in which o, Ni, Mn, and Fe are partially replaced with other metal elements have been studied so far. Further, as carbon which is the negative electrode material, initially, coke, pyrolytic carbon, or low temperature fired products of various organic materials, such as so-called amorphous carbon, has been mainly studied, but the absorption of lithium ion which is the active material, Recently, highly crystalline carbon, so-called graphite-based carbon, has been attracting attention from the viewpoint of release ability.

In Japanese Patent Laid-Open No. 4-115457, it is said that a graphite material composed of easily graphitizable spherical particles as a negative electrode exhibits excellent characteristics. C ₆ Li, which is an intercalation compound of graphite and lithium ions, has been known for a long time. When electrochemically absorbing and desorbing lithium ions (intercalation, deintercalation), the theoretical capacity is 1 g of carbon. It shows a very large value of 372 mAh. Nevertheless, it was the Journal of Ele that was initially not adopted as the negative electrode of lithium-ion secondary batteries.
As reported in ctrochemical Society 117, No2 (1970) p.222, when propylene carbonate, which is widely used as one of the solvent components of the electrolytic solution in the non-aqueous electrolytic solution primary battery, is used, The solvent molecules decompose on the surface of graphite,
It was that the intercalation reaction of lithium ions into graphite was not carried out smoothly. In contrast, the 1992 59th Electrochemical Convention Abstracts P. Two
In No. 38, it is reported that this problem can be solved by using ethylene carbonate as a solvent component of the electrolytic solution. Since then, natural graphite and various artificial graphites have been studied as negative electrodes for lithium-ion secondary batteries, and at present, graphite-based negative electrodes have become the mainstream.

On the other hand, the requirements for the negative electrode of the battery include the ability of the carbon itself to occlude and release lithium ions, and the filling property of how much carbon can be loaded in the limited volume of the battery. This is not limited to carbon, but if it is powder, it greatly depends on the shape.

Considering the shape of carbon powder,
It is roughly divided into four types: block, scale, and fibrous. In a lithium-ion battery, usually, a mixed paste of carbon and a binder is applied to both sides or one side of a metal thin film which is a current collector, and the electrode plate is dried and then appropriately rolled to form an electrode.
Of the above four shapes, scale-like carbon has the best filling property. That is, in the other three types of carbon, the shape of the particles does not change even if the electrode plate is dried and then rolled, and the particles are simply densely packed, but in the scale-like carbon, the particles are oriented in the same direction by rolling. Therefore, the filling property becomes greater. Therefore, from the viewpoint of the ability to store and release lithium ions and the filling property of carbon powder, it can be said that natural or artificial graphite having a scaly powder shape is the most excellent carbon negative electrode material.

However, in the case of natural graphite, it is necessary to modify the material by variations in the material due to the difference in the place of production, or by special treatment for removing a large amount of impurities. It can be said that flake-shaped artificial graphite is the most excellent. A typical flake-shaped artificial graphite is graphitized coal pitch or petroleum pitch, and artificial graphite manufactured by Lonza Co. or Nippon Graphite Co., Ltd. can be mentioned.

[0011]

However, graphite,
Especially when flake-shaped artificial graphite is used as the negative electrode material,
The graphite is oriented by the rolling process during the production of the negative electrode, so that the filling property is increased, but conversely the filling property is too high and the pores in the electrode are limited, and the electrolyte solution inside the negative electrode when the battery is constructed. There was a problem that it did not penetrate. And for this purpose intercalation of lithium ions into graphite,
The deintercalation reaction is carried out only on the surface of the electrode, and there has been a problem that the capacity characteristic during high rate charging / discharging of the battery is not good.

Further, when this battery is rapidly charged, the diffusion of lithium ions into the electrode cannot be caught up, the concentration of lithium ions on the surface of the electrode becomes high, and the lithium ion intercalates into graphite. It becomes easier for metal lithium to deposit on the surface. During such repeated charging and discharging, lithium may deposit in the form of dendrite on the surface of the negative electrode.If the battery is placed under high temperature in this state, the chemical reaction between the lithium metal deposited on the negative electrode plate and the electrolytic solution This may cause heat generation and the battery temperature may rise rapidly.

The present invention is intended to solve the above problems, and relates to a battery using a graphite negative electrode, which has good high-rate charge / discharge characteristics and does not deposit metallic lithium on the surface of the negative electrode. The purpose is to provide a battery.

[0014]

In order to solve these problems, the non-aqueous electrolyte secondary battery of the present invention has an appropriate amount of pores of an appropriate pore size in a negative electrode mixture layer filled with graphite. As a result, the electrolytic solution sufficiently penetrates into the inside of the negative electrode, and the occlusion and release reactions of lithium ions are efficiently performed, so that the high rate charge / discharge characteristics of the battery can be improved.

In the above-mentioned method for producing a non-aqueous electrolyte secondary battery, a sublimable substance that changes from solid to gas or a substance that decomposes and evaporates by heat treatment is added to the negative electrode mixture, and then these are mixed and kneaded. Combined and coated on a metal foil for a current collector, rolled to a predetermined thickness, heated and dried to vaporize the sublimable substance, or a substance decomposed and evaporated by heat treatment to fill the negative electrode with a filling density, The porosity is adjusted.

Alternatively, a solid component soluble in an electrolytic solution is added to graphite in a negative electrode mixture, which is then mixed and kneaded, coated on a metal foil, and then rolled to a predetermined thickness to form a negative electrode. After that, the electrolyte soluble component is dissolved to adjust the packing density and porosity of the negative electrode.

[0017]

DETAILED DESCRIPTION OF THE INVENTION The present invention has the filling density graphite is not less than 1.2 g / cc in the negative electrode mixture layer, and a diameter in the negative electrode mixture layer is vacancy is 0.5μm or more It is configured so that the occupied volume occupies 80% or more of the void volume.

Further, in the above-mentioned method for manufacturing a non-aqueous electrolyte secondary battery, the negative electrode mixture may contain a sublimable substance which changes from solid to gas or a substance which decomposes and evaporates by heat treatment. 1 to 10% by weight is added to the graphite material of the negative electrode, which is then mixed and kneaded, coated on a metal foil, rolled to a predetermined thickness, and then dried by heating to obtain the sublimable substance,
Alternatively, a battery is constructed by vaporizing a substance that decomposes and evaporates by heat treatment to set the packing density and porosity of the negative electrode as described above.

Alternatively, as described in claim 2, a solid component soluble in the electrolytic solution is contained in the negative electrode mixture in an amount of 1 to 40 relative to graphite.
% By weight , then mixed and kneaded, coated on a metal foil and rolled to a predetermined thickness to form a negative electrode, and then the electrolyte-soluble component is dissolved to fill the negative electrode with a filling density and voids. The rate is as described above.

Usually, a rolling step is provided during the preparation of the negative electrode to improve the filling state of the graphite material. However, since this graphite has a state in which the hexagonal mesh plane of graphite is oriented parallel to the electrode surface by rolling, during charging / discharging. It was arranged so that lithium ions would not easily come and go, and graphite was filled in the negative electrode mixture layer without any gaps. In such a configuration, since the mixture has almost no pores, the electrolytic solution did not sufficiently penetrate into all the graphite in the mixture layer, and the charge / discharge reaction of the battery was not efficiently performed.

In the present invention, a suitable amount of a sublimable substance or a substance that decomposes and evaporates by heat treatment is included in the mixture during the preparation of the negative electrode, and these substances are vaporized or decomposed and evaporated by heat treatment to produce a proper amount of the negative electrode. A fine hole portion is provided. Alternatively, a component soluble in the electrolytic solution which is contained in the negative electrode mixture layer during the production of the negative electrode is dissolved in the electrolytic solution to provide a proper amount of pores. According to these methods, graphite has a packing density of 1.2 g / cc or more in the negative electrode mixture layer, and the volume occupied by pores having a pore size of 0.5 μm or more in the negative electrode mixture layer is 80% or more of the void volume. It can be configured to occupy, the liquid penetrates sufficiently into the inside of the electrode plate and all graphite can react, the lithium ion absorption and desorption reactions are efficiently performed, and lithium deposition is achieved even during rapid charging. It is possible to provide a non-aqueous electrolyte secondary battery that is excellent in high rate charge / discharge characteristics and safety.

[0022]

Embodiments of the present invention will be described below with reference to the drawings. In the examples, a cylindrical battery was constructed and evaluated.

FIG. 1 shows a vertical sectional view of a cylindrical battery used in this embodiment. In the figure, reference numeral 1 is a negative electrode, which is mainly composed of artificial graphite manufactured by Lonza Co., and is mixed with an acrylic binder in a weight ratio of 100: 6 and applied on both surfaces of a copper foil.
It is dried, rolled, and then cut into a predetermined size. A nickel negative electrode lead plate 2 is spot-welded to this. Reference numeral 3 denotes a positive electrode, which is an active material of LiCoO 2.
_2. Carbon black as a conductive material and an aqueous dispersion of polytetrafluoroethylene as a binder mixed in a weight ratio of 100: 3: 9 are applied to both sides of an aluminum foil, dried, and rolled. After that, it is cut into a predetermined size. A positive electrode lead plate made of titanium 4 is spot-welded to this. The mixing ratio of the aqueous dispersion of polytetrafluoroethylene as the binder is calculated based on its solid content. Reference numeral 5 denotes a separator made of a polyethylene microporous film, which is interposed between the positive electrode 1 and the negative electrode 3, and is wholly spirally wound to form an electrode plate group.
A polypropylene upper insulating plate 6 and a lower insulating plate 7 are arranged at the upper and lower ends of the electrode plate group, respectively, and are inserted into a case 8 nickel-plated with iron. Then, the positive electrode lead plate 2 is spot-welded to the titanium sealing plate 10 and the negative electrode lead plate 4 is spot-welded to the bottom of the case 8, and then a predetermined amount of electrolytic solution is injected into the case, and the battery is sealed via the gasket 9. Board 1
Seal with 0 to complete the battery. The size of this battery is 1
The height is 4 mm and 50 mm. In addition, 11 is a positive electrode terminal of the battery, and the battery case 8 also serves as a negative electrode terminal.

The electrolyte used was a solvent in which ethylene carbonate and diethyl carbonate were mixed at a volume ratio of 1: 1 and lithium hexafluorophosphate was dissolved as a solute at a concentration of 1.1 mol / l.

The packing density and thickness of the positive electrode were constant. Batteries A to D were produced by changing the packing density of the negative electrode graphite material by adjusting the pressure during rolling and the number of times of rolling while keeping the amount of the mixture coated on the copper core material constant for the negative electrode. In addition, 1,6,12% of powdery naphthalene, which is a sublimable substance, was added at the time of manufacturing the negative electrode,
After coating and rolling, the dried product was set as batteries E to G. In addition, ethylene carbonate (hereinafter abbreviated as EC) that is solid at room temperature was used as an electrolyte solution-dissolving component, and 5, 20, and 50% were added to the negative electrode mixture, and rolling was performed to manufacture batteries H to J. Batteries H to J were placed at 45 ° C. for 5 hours, and E
C was dissolved in the electrolyte.

By changing the packing density of the negative electrode mixture,
Since the thickness of the negative electrode plate changes, change the length of the positive and negative electrode plates,
The electrode plates were adjusted so that they would fit into the battery case. In this case, since the capacity of the battery is determined by the length of the positive electrode, the capacity becomes larger as the packing density of the thin negative electrode plate, that is, the negative electrode active material, becomes higher.

The above 10 kinds of batteries were subjected to constant current discharge by low rate discharge and high rate discharge, and the discharge capacities were compared. The test conditions were a charge / discharge current of 100 mA, a charge end voltage of 4.2 V, a discharge end voltage of 3.0 V, and an environmental temperature of 20 ° C., and a charge / discharge of 5
After repeating this operation, only the discharge current was changed to 500 mA, and charging / discharging was performed 100 times. After completing the above electrical characteristics test, disassemble the battery in a charged state and observe the electrode plate surface state,
The generation state of the graphite stage structure was measured by X-ray diffraction measurement of the negative electrode.

Theoretical capacity, discharge capacity at 5th cycle at low rate discharge, discharge capacity at high rate discharge, 1 by X-ray diffraction measurement
The ratio of peak intensity of st stage, 2nd stage, 3rd stage and graphite is shown in (Table 1).

[0029]

[Table 1]

The charge capacity is determined by the phenomenon that the lithium storage capacity of the negative electrode reaches the limit at the end of charging, the negative electrode potential drops sharply, and the charging ends when the potential difference between the positive and negative electrodes reaches the end-of-charge voltage. . On the other hand, the charging / discharging efficiency when discharged at a low rate is almost 100% for all batteries,
The discharge capacity is determined by the charge capacity, and the charge / discharge efficiency at high rate discharge is 100% or less, and the discharge capacity is determined by the easiness of reaction of lithium migration in the negative electrode during discharge.

A comparison of the packing densities of graphite (Table 1) shows that the lower rate discharge capacity is such that the higher the packing density is, the larger the battery capacity is, but the packing density is high and the volume of pores of 0.5 μm or more is 80. When it is less than% (Batteries C and D), the difference between the theoretical capacity and the actual discharge capacity is large. This is because the pores need to have a pore size of 0.5 μm or more for the non-aqueous electrolyte to permeate, and when the packing density is high, the volume of the pores of 0.5 μm or more is so small that the electrolyte cannot permeate sufficiently. It is considered that, since the reaction does not sufficiently occur, the state of charge becomes uneven in the thickness direction of the electrode plate, and as a result, the battery capacity becomes smaller than the theoretical capacity.

The high-rate discharge capacity is battery C, D is battery B
Smaller than. In the batteries C and D, it is not easy for lithium to move in the negative electrode during high rate discharge, but in the battery B, it is thought that almost the same capacity as in low rate discharge can be obtained because lithium in the negative electrode is easily moved. To be According to decomposition observation after the cycle, in the battery D, deposition of metallic lithium was partially observed. Looking at the X-ray diffraction peak intensity ratio (Table 1), batteries C and D had strong peak intensities at the 2nd stage, but 1st, 3
The peaks of rd and graphite were also observed, and uneven charging was performed. Batteries A, B and C have strong 1st stage peaks,
The 2nd stage was slightly observed, but the 3rd and graphite peaks were not detected at all, indicating that the charging was relatively uniform. From these facts, it was found that when the packing density is high, the weight that can be packed in the battery is large, but a uniform reaction does not occur, and the high rate discharge characteristics are particularly poor.

Similar to the battery B, the batteries E, F, H, and I had a small capacity difference between the theoretical capacity and the actual discharge capacity, and a large capacity was obtained even at a high rate discharge. However, since batteries G and J contained a large amount of the mixture in the mixture, the packing density of graphite was low and the capacity was slightly low.

Further, in comparison with the case where the packing density is adjusted by rolling, in the negative electrode plate prepared by adding the sublimable substance and the electrolyte solution component, the diameter is 0.5 μm even if the packing density is high.
A battery was obtained in which the proportion of the pore volume of m or more was large and the uniform reaction proceeded in the electrode plate, and the high rate discharge characteristics were excellent.

As a result of the above, as a comprehensive evaluation, it has a large discharge capacity at a low rate discharge and a charge / discharge of 100 at a high rate discharge.
It was the batteries B, E, F, H and I of the present invention that metal lithium was not deposited even after cycling.

Although naphthalene was used as the sublimable substance in the present embodiment, sublimable substances such as camphor and solid carbonic acid can also be used. Further, instead of the sublimable substance, an inorganic or organic substance that decomposes or evaporates by vacuum heat treatment can be used, and examples thereof include ice, polyvinylpyrrolidone, and polyvinyl butyral.

As the electrolytic solution-dissolving component, any substance that can be dissolved in the electrolytic solution can be used. For example, lithium hexafluorophosphate, lithium borofluoride, lithium perchlorate, lithium trifluoromethanesulfonate, and hexafluoride. Substances usually used as supporting salts such as lithium arsenate, sodium hexafluorophosphate, sodium perchlorate, potassium chloride and sodium chloride, and solvents having a relatively high melting point such as sulfolane and dimethyl carbonate can be used.

In order to obtain a negative electrode having the same packing density and porosity, 1 to 10% of a sublimable substance or a substance that decomposes and evaporates by heat treatment is added, and a solid component soluble in an electrolytic solution is 1 to 40%. The reason for adding is that the pores formed when the sublimable substance is vaporized are larger than the pores formed when the solid component soluble in the electrolytic solution is dissolved.

Although a composite oxide of lithium and cobalt was used as the positive electrode active material, other positive electrode active materials such as a composite oxide of lithium and nickel, a composite oxide of lithium and manganese, a composite oxide of lithium and iron were used. Almost the same effect was obtained even when a lithium-containing oxide such as the above, or a compound obtained by partially substituting cobalt, nickel, manganese, and iron of each of the above composite oxides with another transition metal was used.

In the present embodiment, lithium hexafluorophosphate was used as the solute of the electrolytic solution, but other lithium-containing salts such as lithium borofluoride, lithium perchlorate, lithium trifluoromethanesulfonate, and hexafluoride were used. Similar effects were obtained even when lithium arsenate was used.

[0041]

As is clear from the above description, according to the present invention, 1 to 10% of graphite is added to the negative electrode mixture with a sublimable substance or a substance which decomposes and evaporates by heat treatment, or the electrolytic solution. By adding 1 to 40% of a substance that dissolves in graphite to graphite, the graphite has a packing density of 1.2 g / cc or more and the pore diameter of the negative electrode mixture layer is 0.5 μm or more. The volume of the pores occupies 80% or more of the void volume, and the non-aqueous electrolyte secondary battery having excellent capacity characteristics during high-rate charge / discharge can be provided.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a cylindrical battery according to an embodiment of the present invention.

[Explanation of symbols]

1 negative electrode 2 Negative electrode lead plate 3 positive electrode 4 Positive lead plate 5 separator 6 Upper insulating plate 7 Lower insulation plate 8 cases 9 gasket 10 Seal plate 11 Positive terminal

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-6-231766 (JP, A) JP-A-7-94171 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 4/00-4/04

Claims (2)

(57) [Claims] 1. A sublimable substance that changes from solid to gas or a substance that decomposes and evaporates by heat treatment is added to graphite in an amount of 1 to 1.
Was added 10 wt%, these mixing-kneading the <br/> Ru steps to create a negative electrode mixture using what, and rolled to the negative electrode after Nurigi the negative electrode mixture on a current collector
Substances which have a step, after the rolling step, to vaporize the sublimable substance by heating and drying the negative electrode, or decomposed by heat treatment to evaporate
By decomposing and evaporating the graphite, 1.
It has a packing density of 2 g / cc or more, and the volume of the pores with a pore size of 0.5 μm or more in the negative electrode mixture is 8% of the whole void volume of the negative electrode.
To obtain a porous anode of which accounts for more than 0% non <br/> aqueous electrolyte solution preparation of the rechargeable battery that make up the battery. 2. A step of adding 1 to 40% by weight of a solid component soluble in an electrolytic solution to a negative electrode mixture with respect to graphite and mixing and kneading these components, and the negative electrode mixture on a current collector. And then roll it to the negative electrode.
A step of forming a battery using this negative electrode, and adding the solid component to an electrolytic solution.
In the negative electrode, graphite has a packing density of 1.2 g / cc or more, and the volume of pores having a pore size of 0.5 μm or more in the negative electrode mixture occupies 80% or more of the whole void volume of the negative electrode. preparation of including non-aqueous electrolyte rechargeable batteries the step of a negative electrode of.