JP2003257419A - Nonaqueous secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery with high cycle characteristics and high load characteristics. <P>SOLUTION: The surface of a carbon particle 221 is coated with a hydrate layer 221b of aluminum oxide. Fine roughness 221c is formed on the surface of the hydrate layer 221b of the aluminum oxide, and by the presence of the fine roughness 221c, lipophilic nature with an electrolyte is enhanced. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for improving a negative electrode active material of a non-aqueous secondary battery. 2. Description of the Related Art In recent years, the development of electronic devices and the downsizing of electronic devices brought about by the progress of semiconductor integrated technologies that have progressed to ICs, LSIs, and ULSIs have led to a demand for cordless devices. The low power consumption has spurred this, and the need for batteries as power sources for cordless electronic devices has increased. [0003] As a result of experiencing the convenience of cordless devices, cordless devices have been required even for devices with large power consumption. It is used for fully automatic cameras and portable personal computers. As the need for batteries has increased, the need for high-performance secondary batteries has never stopped. Accordingly, an object of the present invention is to provide a high performance non-aqueous secondary battery. In order to achieve the above object, a non-aqueous secondary battery according to the present invention is provided with a negative electrode in which a hydrate of aluminum oxide is present on a carbon surface. . With such a configuration, the lipophilicity of the negative electrode active material with respect to the non-aqueous electrolyte is improved, so that the liquid content of the negative electrode is improved. Accordingly, the cycle characteristics and the load characteristics are improved. The above object is also achieved by a method for manufacturing a non-aqueous secondary battery, which comprises coating a carbon surface with aluminum oxide, and then converting the coated aluminum oxide into a hydrate by hot water treatment. can do. According to this manufacturing method, a non-aqueous secondary battery having the above-described various performances and including the negative electrode having the hydrate of aluminum oxide on the carbon surface can be obtained. Hereinafter, a non-aqueous secondary battery according to an embodiment of the present invention will be described with reference to a lithium ion polymer battery as an example. <Structure of Battery> FIG. 1 is a perspective view showing a structure of a lithium ion polymer battery 1 according to an embodiment (including a cut-away portion). As shown in FIG. 1, the lithium ion polymer battery 1 has an exterior body 10, a battery body 20 housed therein, a space between the battery body and the exterior body 10, and a battery body 20. And a polymer electrolyte (not shown) filled therein. The battery body 20 includes a positive electrode plate 21 and a negative electrode plate 22.
Are wound bodies wound with the separator 23 interposed therebetween. In the battery body 20, the positive electrode plate 21 has a positive current collector plate,
A negative electrode current collector plate is attached to the negative electrode plate 22, and its ends serve as lead terminals 21 a and 22 a, which protrude from the upper edge of the outer package 10. The positive electrode plate 21 is made of a lithium-containing salt as a positive electrode active material (specific examples: LiCoO ₂ , LiNiO ₂ , LiM
A mixture of nO ₂ , LiFeO ₂ ), a carbon material (a specific example; graphite powder, coke powder) as a conductive agent, and a binder (a specific example; PVdF (polyvinylidene fluoride)) is formed into a belt shape. The negative electrode plate 22 includes a carbon material (specific examples: graphite powder, coke powder) obtained by coating the surfaces of particles as negative electrode active materials with aluminum oxide hydrate, and a binder (specific examples: PVdF).
(Polyvinylidene fluoride)) in a belt shape. This detailed configuration will be described later. The separator 23 is made of a polyolefin porous film and is generally wider than the positive electrode plate 21 and the negative electrode plate 22 (not shown in the drawing). This is for preventing an internal short circuit in the battery due to contact at both ends in the width direction of the positive electrode and the negative electrode. A polymer electrolyte is a mixture of a polymer and an electrolyte. The polymer is not limited to any kind as long as it has ionic conductivity and mediates an electrochemical oxidation / reduction reaction in a battery. Examples of the polymer include polyalkylene glycol diacrylate (specific examples: polyethylene glycol). It is possible to use a pre-gel composed mainly of diacrylate, polypropylene glycol diacrylate), polyalkylene glycol dimethacrylate (specific examples: polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate), and use a polymerized and cured product of these. it can. The electrolytic solution is prepared by adding a non-aqueous solvent such as ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane or ethoxymethoxyethane to LiPF ₆ , LiClO ₄ , It is a solution in which a lithium-containing salt such as LiCF ₃ SO ₃ is dissolved. With the above configuration, charging and discharging are performed according to the reaction formula shown in the following Chemical Formula 1. ## STR1 ## Next, the structure of the negative electrode will be described in detail. <Detailed Configuration of Negative Electrode> FIG. 2 is an enlarged schematic diagram showing a main configuration of the negative electrode. As described above, the negative electrode plate 22 is formed on the substrate by the negative electrode active material composed of the carbon particles 221 (specific examples; graphite powder, coke powder) and the binder 222 (specific examples;
(PVdF). The carbon particles 221 do not differ from the conventional ones in that they absorb and release (exit and enter) lithium during charge / discharge as in Chemical Formula 1, but the present invention provides: A significant feature is that a hydrate of a metal oxide is added to the surface of the carbon material particles. [Negative electrode active material surface structure and functions / effects] First, when the charge / discharge reaction is performed as described above, the efficient absorption and release of lithium ions from the negative electrode active material improves battery characteristics such as cycle characteristics. It is an important factor in making For this purpose, various attempts have been made to increase the lipophilicity of the negative electrode active material with respect to the electrolytic solution. For example, as the simplest method, there is a method of controlling the adhesion between carbon particles as the negative electrode active material (sparsely filling the carbon particles) and providing a large space for the electrolyte to penetrate into the negative electrode.
Another method is to increase the lipophilicity to the electrolyte by mechanically treating the surface of the carbon particles as the negative electrode active material. However, these methods have the following problems. First, in the former technique of sparsely filling carbon particles, a decrease in battery capacity cannot be avoided. In the latter method using a mechanical treatment, the crystal structure of the carbon particle material changes, so that the efficiency of occlusion / release of lithium ions may be reduced. Therefore, in the present invention, such a problem is avoided and the lipophilicity to the electrolyte is increased by adopting a structure in which the surface of the carbon material particles constituting the negative electrode active material is coated with a hydrate of aluminum oxide. That is, as shown in FIG. 2, the hydrate layer 221b of aluminum oxide exists on almost the entire surface 221a of the carbon particles 221. By making the surface state coated with the hydrate layer 221b of aluminum oxide in this manner, it is possible to increase the lipophilicity of the negative electrode active material with respect to the electrolytic solution. It has been found that this is an effect obtained by the surface state of the aluminum oxide hydrate layer 221b. That is, since it was observed by an electron microscope that fine irregularities (surface roughness Ra = 1.5 to 3) were present on the surface,
It is considered that the presence of the fine irregularities improved the lipophilicity with the electrolytic solution. Therefore, since there is no need to sparsely fill the negative electrode active material or perform a mechanical treatment, the above-described problems of a decrease in battery capacity and a change in the crystal structure of the carbon particle material do not occur. FIG. 3 is a schematic diagram showing details of this operation. As shown in this figure, an uneven portion 221c is formed on the surface of the aluminum oxide hydrate layer 221b. Therefore, it is considered that the contact area with the electrolytic solution was improved, and the lipophilicity to the electrolytic solution was improved. By coating the surface of the carbon particles with the hydrate of aluminum oxide, it is considered that the permeability of lithium between the electrolytic solution and the carbon particles is reduced by the presence of the film. As described above, the effect of improving the lipophilicity obtained by making the surface of the coating layer uneven is higher, and as a result, various battery characteristics are improved. This can be understood from the following examples. <Method for Manufacturing Negative Electrode> FIG. 4 is a process diagram showing a process for manufacturing the negative electrode plate 22. As shown in FIG. 4, the negative electrode plate 22 is produced mainly through a negative electrode active material particle (carbon particle) preparation step and a rolling step. In the rolling step, the prepared mixed paste of the negative electrode active material particles and the binder is applied on a conductive substrate, and then rolled into a strip-shaped thin plate. The negative electrode active material particle preparation step is performed through the following sub-steps. FIG. 5 is a process chart showing this negative electrode active material particle preparation step. As shown in this figure, first, carbon powder is impregnated with an alcohol solution of aluminum alkoxide (step S1). The impregnated material is heat-treated at a predetermined temperature (for example, 500 ° C.) to form a coating layer of aluminum oxide on the surface of the carbon particles (Step S2). Next, the aluminum oxide coating layer is converted into an aluminum oxide hydrate layer by immersing it in hot water at a predetermined temperature (for example, 80 ° C.) (step S3). In the step S2, processing is performed at such a high temperature that the metal oxide is melted, so that only a flat surface can be obtained. However, the crystal structure changes in the step 3 to impart irregularities to the surface. Is done. <Preparation of Battery> A negative electrode plate prepared as described above and a previously prepared positive electrode plate are wound with a separator interposed therebetween to prepare a battery element body, and then housed in an exterior body. . Then, prior to the sealing, the pre-gel is filled and a polymerization reaction is performed to produce a polymer battery provided with a polymer electrolyte. Examples of the present invention will be specifically described below. Graphite powder having a particle size of 10 μm to 35 μm was formed into a pellet, and the carbon powder was impregnated with an aluminum trisecondary butoxide solution in isopropanol (concentration: 30% by mass) as described above. Here, the amount of aluminum trisecondary butoxide was adjusted to 2% by mass of carbon in terms of boehmite (aluminum oxide monohydrate (AlOOH)). 5
By performing heat treatment at 00 ° C. for 3 hours, the surface of the graphite particles was coated with alumina. Then 8
The alumina was converted to boehmite by immersion in warm water at 0 ° C., and the surface of the graphite particles was coated with boehmite. The thus obtained boehmite-coated graphite particles are classified, mixed with PVdF at a ratio (mass ratio) of 90:10, and applied to a copper foil having a thickness of 10 μm. After drying, this was rolled to obtain a negative electrode plate having a thickness of 120 μm. Also, lithium cobaltate: graphite: PVdF = 90: 5:
5 (mass ratio) and mixed at a ratio of 20 μm
m after drying on aluminum foil
m of the positive electrode plate was obtained. A 20 μm-thick polyethylene microporous membrane is used for the separator. The electrolyte is a mixed solvent of ethylene carbonate: propylene carbonate: diethylene carbonate = 10: 10: 80 (volume ratio) and LiPF _{6 is used} as an electrolyte salt. Was adjusted to be 1.0 mol / L. Then, a pregel was prepared so that polyethylene glycol diacrylate: electrolyte solution = 10: 90 (mass ratio). The positive electrode plate and the negative electrode plate manufactured as described above are overlapped with a separator interposed therebetween, and centered in the width direction of each electrode plate, and wound by a winding machine. As a result, a battery body was produced. After inserting the battery element body thus manufactured into an exterior body configured by lamination, before sealing, the pregel was injected,
After sealing, a polymerization reaction was performed to prepare a polymer battery. Comparative Example 1 A battery was produced in the same manner as in Example 1, except that graphite powder having no surface coating applied to the negative electrode active material was used. Comparative Example 2 A battery was produced in the same manner as in Example 1, except that the negative electrode active material was coated with an alumina-based material, but was not treated with warm water, and using graphite powder not modified into boehmite. Comparative Example 3 A battery was produced in the same manner as in Example 1, except that a graphite powder whose surface was modified by mechanical treatment (mechanochemical treatment) was used as the negative electrode active material. Using the batteries of these Examples and Comparative Examples, the battery was charged to 4.2 V with a current of 600 mA, and after reaching 4.2 V, was charged at a constant voltage of 4.2 V until the charging current value became 30 mA or less, and was suspended for 10 minutes. After that, charging and discharging were repeated at a current of 600 mA until the voltage reached 2.75 V, and cycle characteristics were examined. The load characteristics were as follows: charging was performed at a current of 600 mA to 4.2 V, and after reaching 4.2 V, constant voltage charging at 4.2 V was performed until the charging current value became 30 mA or less.
After a pause of one minute, the discharge was 120 mA (0.2 It),
The discharge was performed under the condition that the discharge was performed at 2.75 V at each discharge current value of 1200 mA (2 It) and 1800 mA (3 It). The results are shown in Table 1 below. [Table 1] As is clear from the results shown in Table 1, there is a great difference in the cycle characteristics and load characteristics between the comparative example and the examples, and the batteries according to the examples have remarkably excellent cycle characteristics and load characteristics. Was. That is, in the battery of the embodiment,
The capacity retention rate after 500 cycles was 82%. Regarding the load characteristics, the capacity ratios of 2It and 3It to 0.2It were 96% and 80%, respectively. On the other hand, in the battery of Comparative Example 1, the capacity retention after 500 cycles was 77%. For load characteristics, 2It and 3I
The capacitance ratio of t to 0.2It is 94% and 72%, respectively.
%Met. In the battery of Comparative Example 2, the capacity retention after 500 cycles was 71%. 2I for load characteristics
The capacitance ratio of t and 3It to 0.2It is 9
1% and 64%. In the battery of Comparative Example 3, the capacity retention after 500 cycles was 77%. Regarding the load characteristics, the capacity ratio of 2It and 3It to 0.2It was 93% and 69%, respectively. <Modifications> The present invention is not limited to the above-described configuration, and can be modified as follows, for example. (1) In the above battery configuration, the battery body is a wound body. However, the battery body can be similarly implemented by a type in which a positive electrode plate and a negative electrode plate are alternately stacked with a separator interposed therebetween. (2) Although the battery is a polymer electrolyte, the present invention is not limited to this and can be similarly implemented using a normal electrolyte. (3) Although the above-mentioned battery is a lithium ion battery, the present invention is not limited to this, and any type of non-aqueous secondary battery can be similarly used. As described above, according to the non-aqueous secondary battery of the present invention, since the negative electrode having the aluminum oxide hydrate on the carbon surface is provided, By improving the lipophilicity of the negative electrode active material with respect to the water electrolyte, the liquid content of the negative electrode is improved. Accordingly, the cycle characteristics and the load characteristics are improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a configuration of a lithium ion polymer battery 1 according to an embodiment (including a partly cutaway portion). FIG. 2 is an enlarged schematic diagram illustrating a main configuration of a negative electrode. FIG. 3 is a schematic diagram showing details of an action of enhancing lipophilicity between the negative electrode active material particles and the electrolytic solution. FIG. 4 is a process diagram showing a process for producing a negative electrode plate. FIG. 5 is a process chart showing a negative electrode active material particle preparing step in a negative electrode plate manufacturing step. [Description of Signs] 1 Lithium ion polymer battery 22 Negative electrode plate 221 Carbon particles 221a Carbon particle surface 221b Hydrate layer of aluminum oxide 221c Irregularities existing on the surface of hydrate layer of aluminum oxide

Claims (1)

1. A non-aqueous secondary battery comprising a negative electrode having a hydrate of aluminum oxide on a carbon surface.