Composite graphite material, method for producing same, negative electrode material for lithium ion secondary batteries, negative electrode for lithium ion secondary batteries, and lithium ion secondary battery

Abstract

A composite graphite material which is configured of an adhesive (A) that is formed of a carbon material and/or a graphite material having low crystallinity, a flake graphite material (B) and a spheroidized or generally spheroidized graphite material (C), and which is characterized in that: at least a part of the flake graphite material (B) is adhered to the graphite material (C) in the form of projections, with the adhesive (A) being therebetween; the content of the adhesive (A) is 0.1-20% by mass; the content of the flake graphite material (B) is 0.05% by mass or more but less than 30% by mass; the content of the graphite material (C) is 99.8-50% by mass; and the composite graphite material has no fractured surface. A method for producing the composite graphite material; a negative electrode material for lithium ion secondary batteries, which uses the composite graphite material; and a lithium ion secondary battery.

Description

technical field [0001] The invention relates to a composite graphite material, a negative electrode material for a lithium ion secondary battery using the same, and a lithium ion secondary battery using the same, in particular to a negative electrode material for a lithium ion secondary battery and a lithium ion secondary battery with excellent rapid charge and discharge characteristics and cycle characteristics. secondary battery. Background technique [0002] In recent years, along with miniaturization and higher performance of electronic equipment, expectations for higher energy density of batteries have been increasing. In particular, lithium ion secondary batteries are attracting attention due to their ability to increase their voltage and energy density (owing to their high energy density and high voltage) compared to other secondary batteries. Lithium-ion secondary batteries are mainly composed of negative electrode, positive electrode and non-aqueous electrolyte. L...

AI Technical Summary

Problems solved by technology

[0006] In the case of the negative electrode material obtained by merely mixing vapor-phase-grown carbon fibers in graphite particles described in Patent Document 2, or the negative-electrode material obtained by mixing only fibrous graphite with spherical graphite or flake graphite, the gas-phase growth of graphitization The discharge capacity and initial charge and discharge efficiency of carbon fiber itself are lower than those of the matrix mesophase graphite, so there are problems with the discharge capacity and initial charge and discharge efficiency of the negative electrode material

In addition, there are few opportunities for vapor-grown carbon fiber to contact the matrix mesophase graphite, and it often does not contribute to the improvement of electrical conductivity.

As a result, the effect of improving rapid charge-discharge characteristics and cycle characteristics is insufficient.

In addition, vapor-grown carbon fibers are expensive, and since they need to be mixed in a large amount of 3 to 20% by mass, there is also a problem of cost increase.

In addition, when manufacturing the negative electrode, the negative electrode material, solvent, and binder are mixed, the negative electrode mixture paste is prepared, and the paste is applied to the current collector. Problems such as unstable viscosity of mixture paste

[0007] In the case of the negative electrode material obtained by mixing and granulating granular graphite, petroleum pitch, and flake graphite as described in Patent Document 3, the amount of flake graphite incorporated is as large as 40% by mass. The remaining part other than the contact point between adjacent particles is oriented in the electrode, and the problem of rapid charge and discharge and degradation of cycle characteristics

In addition, there are problems of unstable viscosity of negative electrode mixture paste and insufficient electrode compression

[0008] In the case of the negative electrode material with flake graphite attached to the surface of the granular graphite described in Patent Document 4, a pulverization process is required, so that the reactive surface will be exposed and react excessively with the electrolyte, resulting in low efficiency during initial charge and discharge. Problems such as heat generation and expansion caused by gas generation during the reaction

In addition, due to pulverization, the scaly graphite attached to the graphite surface falls off, and the effect of improving cycle characteristics is not sufficient.

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