JP2007250469A - Negative active material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative active material made of material having both a function absorbing and releasing ions, and a function conducting electrons. <P>SOLUTION: By using the negative active material comprising carbon of porous structure having three-dimensional mutual through holes passing through amorphous carbon which is a base material, three-dimensionally spreading in a net shape, and having an average passing through width of 0.05-5 μm, the specific surface area of the negative active material is increased, and the negative active material increasing the absorbing-releasing amount of ions is provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a negative electrode active material, and more particularly to a negative electrode active material for a secondary battery.

  As a negative electrode active material of a secondary battery, an intercalator capable of reversibly occluding and releasing ions with charge and discharge is used. For example, in a lithium ion secondary battery, graphite or the like is used as an intercalator that absorbs and releases lithium ions. These carbon-based materials are used.

  When the specific surface area of the intercalator is improved, the occlusion-release rate of ions is improved and the resistance can be suppressed, so that the battery can have high output. For this reason, in the prior art, in order to improve the specific surface area, a method in which a negative electrode active material made of an intercalator is made into fine particles has been adopted. However, the negative electrode active material also plays a role of conducting electrons, and if the negative electrode active material becomes fine particles and the electronic network is easily disconnected due to the divergence between the particles, the performance of the battery is deteriorated.

In contrast, in Patent Document 1, a fibrous current collector is used in place of the film-shaped current collector that is generally used, and an intercalator attached to the surface is used as the negative electrode. Yes. In FIG. 2B of Patent Document 1, a negative electrode formed in a fiber shape is disclosed.
Japanese Laid-Open Patent Publication No. 10-312794

  However, the negative electrode described in Patent Document 1 has a problem in that the amount of occluded / released ions is limited because an intercalator is disposed on the surface of a fibrous material intended only for electron conduction. is doing. Furthermore, the negative electrode described in Patent Document 1 has a low mechanical strength because the electron conductor serving as the skeleton of the negative electrode is a fiber, and there is a possibility that the negative electrode collapses due to a change in the volume of the intercalator during ion storage and release. In the structure of the negative electrode described in Patent Document 1, when the electronic conductor collapses, the specific surface area of the intercalator may be reduced.

  In order to solve the above problems, an object of the present invention is to provide a negative electrode active material that is excellent in the amount of occlusion-release of ions.

  The present inventor has found that the above problems can be solved by using a porous structure composed only of a negative electrode active material, and has completed the present invention.

  That is, this invention solves the said subject by providing the negative electrode active material which consists of carbon which has a three-dimensional mutual through-hole.

  According to the present invention, it is possible to provide a negative electrode active material excellent in the amount of occlusion-release of ions.

  The first of the present invention is a negative electrode active material made of carbon having three-dimensional mutual through holes.

  The three-dimensional mutual through hole referred to in the present invention refers to a hole that penetrates carbon as a base material, and the hole extends in a mesh shape in the three-dimensional direction. Examples of the carbon structure having three-dimensional mutual through holes include a sponge structure. By using carbon having three-dimensional mutual through holes, the specific surface area of the negative electrode active material can be improved, and further, the electronic network is less likely to be cut than when fine particles are used.

  The negative electrode active material made of carbon having three-dimensional mutual through-holes of the present invention (hereinafter also simply referred to as “the negative electrode active material of the present invention”) may be used in the form of a film, or processed into a certain shape such as particles. You may use what you did.

  When the negative electrode active material of the present invention is used in a film form, it is preferable in that the electronic network is hardly cut. When used in a film form, the average film thickness is preferably 1 to 200 μm, more preferably 5 to 50 μm. When it is 1 μm or more, it is preferable because the occlusion amount of ions is excellent, and when it is 200 μm or less, it is preferable because it is excellent in the occlusion-release rate of ions.

  When the negative electrode active material of the present invention is used in the form of particles, it is preferable because it has an excellent ion storage-release rate. When used in the form of particles, the average particle diameter is preferably 1 to 50 μm, more preferably 5 to 25 μm. When it is 1 μm or more, it is preferable because the occlusion amount of ions is excellent, and when it is 50 μm or less, it is preferable because the occlusion-release rate of ions is excellent.

  The negative electrode active material of the present invention is preferably made of only a material having both a function of occluding and releasing ions and a function of conducting electrons. Thereby, the quantity of the electricity which can be charged / discharged per unit mass can be improved.

  The average through width of the three-dimensional mutual through holes contained in the negative electrode active material of the present invention is preferably 0.05 μm or more, more preferably 0.05 to 5 μm, still more preferably 0.2 to 2 μm. When the thickness is 0.05 μm or more, the amount of the electrolytic solution filled in the negative electrode active material is excellent, the surface protective film (SEI) can be prevented from being excessively formed, and the consumption of electricity can also be suppressed. . A thickness of 5 μm or less is preferable because the specific surface area of the negative electrode active material is excellent.

  The negative electrode active material of the present invention is made of carbon, and amorphous carbon is preferable as the carbon. Use of amorphous carbon is preferable because the amount of ions deposited on the electrode surface is suppressed. When the amount of deposited ions is suppressed, more rapid charge / discharge can be performed. For this reason, the negative electrode active material using amorphous carbon is suitable for vehicles that require rapid discharge when starting.

  In the present invention, the volume ratio between the carbon portion and the void portion of the negative electrode active material is preferably 1: 0.1 to 1:10, more preferably 1: 0.3 to 1: 3. When the volume of the carbon portion is 1 and the volume of the void portion is 0.1 or more, the amount of the electrolyte solution filled in the negative electrode active material is excellent, and when it is 10 or less, the amount of ion occlusion-release is excellent.

  As the above-mentioned ions, lithium ions are preferable.

  A second aspect of the present invention is a method for producing the above-described negative electrode active material.

  Although the manufacturing method of the negative electrode active material of this invention is not specifically limited, It is preferable to produce by carbonizing the precursor which has a three-dimensional mutual through-hole in inert atmosphere.

  The precursor is not particularly limited as long as it has three-dimensional mutual through-holes and can be carbonized, but a precursor that can retain a shape to some extent during the carbonization process is preferable. For example, a polyimide resin, a phenol resin, or a furan resin can be used.

  Examples of the method for producing a precursor having a three-dimensional mutual through hole include a method of irradiating an organic gel with ultrasonic waves, a method of exposing a polyamic acid solution to a poor solvent, and the like.

  The inert atmosphere is not particularly limited, and examples thereof include a nitrogen atmosphere, a helium atmosphere, a neon atmosphere, and an argon atmosphere.

  Examples of the carbonizing method include atmospheric pressure carbonization, reduced pressure carbonization, and pressurized carbonization.

  3rd of this invention is a negative electrode for ion batteries characterized by including the negative electrode active material mentioned above or the negative electrode active material produced by the above-mentioned method.

  In the present invention, the negative electrode for an ion battery includes a negative electrode active material and a current collector. 1A and 1B are schematic cross-sectional views of a preferred embodiment of the negative electrode of the present invention. 1A and 1B, reference numeral 35 denotes a current collector, 100 denotes a negative electrode active material, 110 denotes a carbon portion, and 120 denotes a void portion. 1A and 1B respectively show a film-like negative electrode active material and a particulate negative electrode active material described in the above-mentioned negative electrode active material section. These advantages are as described above. In the case of using a particulate negative electrode active material, it is preferable to use a binder in order to bind the particles, and examples of the binder include PVdF.

  Although patent document 1 was described in the section of background art, the negative electrode active material of this invention and the negative electrode active material of the cited reference 1 may look the same on an external appearance. However, as can be seen by comparing the schematic cross-sectional view of the negative electrode of Patent Document 1 shown in FIG. 2 with A and B in FIG. 1, they have completely different structures. In the present application, the negative electrode active material 100 having a porous structure is formed on the film-like current collector 35, whereas in the cited document 1, the negative electrode active material 200 is formed on the surface of the current collector 45 having a porous structure. Yes.

  As points superior to Patent Document 1 of the present invention, there are an excellent amount of electricity that can be charged and discharged per unit mass, a point that a structure shown in FIG. 1B can be formed, and the like.

  4th of this invention is a secondary battery characterized by including the above-mentioned negative electrode active material, the negative electrode active material produced by the above-mentioned method, or the negative electrode for ion batteries.

  By including the above-described negative electrode active material, the negative electrode active material produced by the above-described method, or the negative electrode for an ion battery, it is possible to provide a high-power-density battery that can be repeatedly charged and discharged with a large current.

  The structure of the secondary battery of this invention is not specifically limited, The structure of a conventionally well-known secondary battery is employable. For example, a structure of a bipolar secondary battery as shown in FIG. 3 may be adopted. 3, reference numeral 13 indicates a positive electrode active material layer, reference numeral 15 indicates a negative electrode active material layer, reference numeral 17 indicates an electrolyte layer, reference numeral 19 indicates a single cell layer, reference numeral 25 indicates a positive electrode tab, reference numeral 27 Indicates a negative electrode tab, reference numeral 29 indicates a laminate sheet, reference numeral 33 indicates a positive electrode current collector, and reference numeral 35 indicates a negative electrode current collector. Each constituent element other than the negative electrode active material contained in the negative electrode active material layer is not particularly limited, and a conventionally known material can be appropriately selected.

  In the present invention, the secondary battery is preferably a lithium ion secondary battery.

  According to a fifth aspect of the present invention, there is provided a vehicle including the negative electrode active material described above, the negative electrode active material prepared by the method described above, a negative electrode for an ion battery, or a secondary battery.

  Since the negative electrode active material contained in the vehicle of the present invention is excellent in output, the battery volume can also be reduced. For this reason, since the mass or volume which occupies in a vehicle can be saved, it has a big merit on vehicle design.

  EXAMPLES Next, although an Example is given and this invention is demonstrated concretely, these Examples do not restrict | limit this invention at all.

Example 1
[Production of carbon having three-dimensional mutual through holes]
When 50 g of diaminodiphenyl ether was dissolved in 800 g of dimethylacetamide, and diaminodiphenyl ether and equimolar pyromellitic acid were added to the solution and stirred for about 1 hour, the viscosity of the solution increased and a starchy polyamic acid solution was obtained. This was applied on a glass plate and immersed in water as a poor solvent for 5 minutes to dissolve dimethylacetamide, thereby obtaining a precursor having three-dimensional mutual through holes.

  The precursor was dried in a vacuum dryer at 100 ° C. for 1 hour and then imidized by heating in a vacuum vessel at 300 ° C. for 1 hour. This was heated to 1000 ° C. at a heating rate of 400 ° C./h under an ultra-high purity argon (99.9999%) atmosphere (flow at about 100 ml / min), and kept at 1000 ° C. for 1 hour for carbonization. Amorphous carbon with three-dimensional mutual through holes was prepared.

  An electron micrograph of the produced carbon is shown in FIG. It can be seen that macropores are developed. This was pulverized with an agate mortar to obtain a powder. The average particle size at that time was 19 μm.

[Production of negative electrode]
The carbon powder prepared above was weighed so that the mass ratio of PVdF was 85:15. The carbon powder prepared above, PVdF, and an appropriate amount of NMP were added to a homogenizer container, and stirred well and mixed to prepare a slurry. This slurry was applied onto a foil using a die coater and dried. Electrode layers were formed on both sides of the copper foil, and pressed to cut out 55 mm × 105 mm, leaving a lead portion without the electrode layer. The coating conditions were adjusted so that the thickness of the electrode layer was 45 μm at the time of completion.

[Production of positive electrode]
The positive electrode was produced using lithium manganate having an average particle size of 1.2 μm spinel. Each composition was made to be active material: acetylene black: PVdF = 75: 15: 10 by mass ratio. First, spinel type lithium manganate, acetylene black and PVdF were weighed, and an appropriate amount of NMP (N-methyl-2-pyrrolidone) was added thereto, followed by thorough stirring and mixing with a homogenizer. A certain amount of this slurry was applied to an aluminum foil using a die coater and dried. In this way, electrode layers were formed on both surfaces of the aluminum foil, and pressed with a roll press, and the electrode layer portion was cut out so as to be 50 mm × 100 mm, leaving a lead portion without the electrode layer. The coating conditions were adjusted so that the thickness of the electrode layer was 40 μm at the time of completion.

[Production of battery]
The battery was produced as follows. Each of the positive electrode and negative electrode cut out above was dried in a vacuum dryer at 90 ° C. for 1 day. Between the positive electrode and the negative electrode, 10 positive electrodes and 11 negative electrodes are alternately laminated so that the outermost electrode becomes a negative electrode through a 25 μm thick porous polypropylene film. Bundled and welded with lead, and the laminate was placed in an aluminum laminate film back with the positive and negative lead taken out, and the electrolyte was injected with a liquid injector and sealed under reduced pressure. A battery was produced.

(Example 2)
In the synthesis of carbon having three-dimensional interpenetrating holes in Example 1, amorphous carbon having three-dimensional interpenetrating macropores was produced in the same manner except that the poor solvent was acetone.

  Further, a battery was produced in the same manner as in Example 1.

(Example 3)
The carbon precursor used in the synthesis of the amorphous carbon having the three-dimensional interpenetrating macropores of Example 1 was synthesized according to the method described in the literature (CARBON, 43, (2005), pp. 2808 to 2811.). Carbonization was performed under the same conditions as in Example 1 to produce amorphous carbon having three-dimensional mutual through holes.

  Further, a battery was produced in the same manner as in Example 1.

(Comparative example)
A battery was fabricated in the same manner as in Example 1, except that the negative electrode active material was changed to soft carbon having an average particle size of 0.5 μm.

(Battery performance evaluation test)
Charging / discharging was performed at room temperature, and charging was performed in a constant current-constant voltage mode of 1 A up to 4.2 V for a total of 2 hours. The battery output is measured by discharging the low current after charging and calculating the product of the maximum current value and the terminal voltage at that time so that the battery terminal voltage at 10 seconds does not fall below 2.5V. The power density was taken. In Table 1, for comparison, the power density of the battery of the comparative example was set to 100, and the power density of the example was shown as a relative value.

  As can be seen from Table 1, according to the present invention, the power density of the battery can be drastically improved by using amorphous carbon having three-dimensional interpenetrating macropores as the negative electrode active material.

A is a schematic cross-sectional view of a negative electrode of the present invention having a film-like negative electrode active material, and B is a schematic cross-sectional view of a negative electrode of the present invention having a particulate negative electrode active material. 1 is a schematic cross-sectional view of a negative electrode of Patent Document 1. FIG. It is a section schematic diagram of an ion battery of one embodiment of the present invention. 2 is an electron micrograph of amorphous carbon that is a negative electrode active material of Example 1. FIG.

Explanation of symbols

13 positive electrode active material layer,
15 negative electrode active material layer,
17 electrolyte layer,
19 cell layer,
25 positive electrode tab,
27 negative electrode tab,
29 Laminate sheet,
33 positive electrode current collector,
35 negative electrode current collector,
45 Current collector,
100 negative electrode active material,
110 carbon part,
120 void part,
200 Negative electrode active material.

Claims (9)

  A negative electrode active material made of carbon having three-dimensional mutual through holes. The ability to occlude and release ions,
The ability to conduct electrons,
The negative electrode active material according to claim 1, comprising only a material having both of   3. The negative electrode active material according to claim 1, wherein an average through width of the three-dimensional mutual through holes is 0.05 to 5 μm.   The negative electrode active material according to claim 1, wherein the carbon is amorphous carbon. A precursor having three-dimensional mutual through-holes,
The method for producing a negative electrode active material according to claim 1, wherein carbonization is performed in an inert atmosphere. A negative electrode for an ion battery comprising the negative electrode active material according to claim 1 or the negative electrode active material produced by the method according to claim 5. The negative electrode active material according to claim 1,
A secondary battery comprising the negative electrode active material produced by the method according to claim 5 or the negative electrode for an ion battery according to claim 6.   A secondary battery, wherein the secondary battery is a lithium ion secondary battery. The negative electrode active material according to claim 1,
A negative electrode active material produced by the method according to claim 5,
The negative electrode for an ion battery according to claim 6, or the secondary battery according to claim 7 or 8,
Including a vehicle.