Composite graphite negative electrode material for lithium ion secondary cell and its preparation method

Abstract

This invention discloses one lithium ion second battery compound negative materials and its process method, wherein, the materials comprise modified natural graphite and artificial graphite with quality proportion of 30í†70í½80í†20 and the process method comprises the following steps: a, the natural graphite surface is covered with organism; b, making the thermal process in temperature range of 800íµí½1500íµ for one to six hours; c, mixing the natural graphite with the artificial graphite as proportion of 30í†70í½80í†20.

Description

technical field [0001] The invention relates to a composite graphite negative electrode material for a lithium ion secondary battery and a preparation method thereof. Background technique [0002] Lithium-ion batteries are a new generation of secondary batteries after nickel-metal hydride batteries since the 1990s. Because of its advantages such as high working voltage, high energy density, long cycle life, small self-discharge, and no memory effect, it has become the preferred chemical power source for high-end electronic consumer products, and has penetrated into aerospace, military and other cutting-edge technology fields. With its ever-increasing demand, lithium-ion batteries are becoming the focus and focus of scientific and technological research and development in the new century. At present, the anode materials of commercial lithium-ion batteries are all carbon materials, mainly petroleum coke and graphite materials, among which natural graphite is widely used becau...

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Problems solved by technology

However, due to the high degree of graphitization of natural graphite, the crystal structure and other physical and chemical properties between the edge and bottom of the crystallites are quite different, and the inhomogeneity of the reaction with the electrolyte is strong, and the decomposition reaction of the electrolyte is mainly Occurs at the edge of the crystallite

Therefore, the density of the generated passivation film is poor. During the charging process, the co-intercalation of solvated lithium ions is prone to occur, which causes the expansion and collapse of the graphite layer and increases the irreversible capacity.

In addition, after natural graphite has been treated by physical or chemical methods, it has the disadvantage of poor bonding performance with the plate, and it is easy to fall off from the plate during the cycle charge and discharge process, which affects the cycle life, especially when the high current charge and discharge is reduced. cycle life

On the other hand, as the negative electrode material of lithium ion battery, natural graphite must be pulverized to increase its surface area to store more lithium. Graphite, as a lubricating material, is prone to interlayer sliding, resulting in the change and destruction of the crystal structure of graphite during the crushing process, which affects the charge-discharge capacity and high-current charge-discharge performance of graphite materials, and limits the use of natural graphite anode materials. widely used

[0003] In order to improve the electrochemical properties of natural graphite materials, people have carried out physical and chemical modification and surface modification of natural graphite through various methods, and achieved corresponding effects, such as pulverizing, grading and processing natural graphite into spherical particles, improving the Tap density, in addition, various surface modification methods are used to improve the electrochemical properties of graphite, such as Japanese Patent No. 2000-261046 discloses a thermal oxidation treatment of graphite powder to change the surface state of graphite powder, although Improved reactivity of negative electrode material with electrolyte, but lower discharge capacity than natural graphite

U.S. Pat. No. 6403259 discloses a carbon material coated on the surface of ground natural graphite or artificial graphite, which improves the high-temperature self-discharge performance and low-temperature performance of the negative electrode material, but the performance in other aspects is not satisfactory

In addition, U.S. Pat. No. 5908715 uses organic solvents to dissolve epoxy resin and poly-p-phenylene to coat pyrolytic carbon on the surface of graphite. Chinese patent CN1224251A uses ethanol to dissolve phenolic resin or urea-formaldehyde resin to coat graphite. Chinese patent CN1304187A Coating graphite with organic solvent solutions such as polyacrylonitrile, polyvinylidene fluoride, epoxy resin, etc., the above method has environmental pollution, graphite particles after coating are easy to bond, and the coating layer is easy to fall off in the subsequent pulverization process. Damaged, affecting the overall performance of the negative electrode material

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