Surface Modifacation Of Nature Graphite For Anode Of Lithium-Ion Battery

Lithium-ion batteries have high voltage, specific energy, long cycle life, good safety performance, low self-discharge, fast charge and discharge. They have been widely used in the mobile phone, laptop, electric bicycles, and other areas now. With the rapid development of electric vehicles, in the 21st century, the concept of lithium-ion electric car is to be more and more concerned. The key point of lithium-ion electric vehicle batteries'development is the battery performance, and which contribute most is the battery materials.This article outlines the composition of lithium-ion secondary battery, principles and advantages, describes the status and challenges, introduce the case of the material, and explain the detail studies of natural graphite anode materials and modification methods currently. On this basis, we use four different methods to modify the natural graphite.(1) Oxidizing natural graphite by nitric acid to obtain active substance on different PH value, the oxidation graphite have a more smooth surface, more closely arrangement, and the tapped density increases by 3.5%. The electrochemical performance of natural graphite has been significantly improved by oxidation, in which the best performance sample is the PH 1.0 one. The first discharge capacity is up to 356 mAh·g^-1,which is closing to the theoretical capacity of graphite. Compared with untreated samples, discharge capacity increases 46 mAh?g-1, and remains 339 mAh·g^-1 after 20 cycles. The capacity retention rate is 95.2%. When using nitric acid solution of PH value of 0.5 to deal with natural graphite, the active material has a higher initial discharge capacity, but the cycling performance is poor. After analysis, when surface oxidation is too m, the cycle performance of materials will be affected adversely.(2) Using stannic chloride as raw material to prepare tin oxide nanometer particles. Add the tin oxide to toluene solution, and a certain amount of silicon reagents to be amination treatment. The natural graphite materials are oxidized by nitric acid in the PH value of 1.0, and react with the tin oxide which is obtained by amination treatment further, to form a stable compound key between the two materials. The distribution of composite materials are more homogeneous, the aggregation morphology can be divided into three: the distribution of tin oxide small particles on graphite surface depression fracture, the reunion and deposition of a large number of tin oxide on graphite edge area and the dispersion of small tin oxide particles on flat graphite surface area. The composites exhibit a better electrochemical performance, the first discharge capacity is up to 567 mAh·g^-1, which have greatly improved than the other methods reported in the literature, the capacity retention rate is 75 % after 20 cycles.(3)The NG/SnO₂ composite materials form a sheet coated structure after coating by ppy. As coat with SnO₂ particles and other small particles on the surface of graphite as core, a core-shell structure forms. The coating condition of SnO₂ materials is quite complete, but some areas of the surface of large graphite particles are not fully covered. The coated NG/SnO₂ materials show good electrical properties. Compare to the not coated one with 567 mAh·g^-1, the first discharge capacity decreases by 54.3 mAh·g^-1. While the irreversible capacity has also been significantly reduced,the first charge and discharge efficiency is up to 75%, and cycling performance has been significantly improved. Specific capacity remains 479.4 mAh?g-1 after 20 cycles, the capacity retention rate is 90%, which have greatly improved than the one without coating of 75%.(4) Dealing the natural graphite with high temperature and high pressure in water or glycerin solution, the structure and surface morphology of processed materials did not change much. The initial capacity of modified natural graphite increases a lot. Among them the material treated in water attenuated fast in the first few cycles. And after that the cycle properties are stable. The initial capacity of materials treated in glycerin solution (specific discharge capacity is 342.3mAh·g^-1) and cycle properties are both obviously improved. The method of high temperature and high pressure processing is very simple, the further processing is also easy, and there is no environmental pollution in the processing. The materials after treatment show a good electrochemical performance, which are expected to the further application.