| Lithium ion battery has small volume, light quality, big specific capacity, long cycle life, low self-discharge, no memory effect after many times charging, etc, so it has been widely used in portable tools, digital products and other fields. In recent years, it has been gradually used in electric vehicles and military equipment, and other fields. In recent years, the mainstream of commercial cathode material LiCoO2 has gradually exposed its shortcomings, due to the expensive price of cobalt resources and the constraints of electric supply. Since the lamellar structure LiNi1/3Co1/3Mn1/3O2 was developed for the first time by T.Ohzuku, the material quickly caught the attention for its high reversible capacity [5], and has a tendency to replace LiCoO2 positive materials. The reversible specific capacity can reach 160 and 200 mAh/g within the range of voltage from 2.5 V to 4.4 V, 2.8 to 4.2 V; LiNi1/3Co1/3Mn1/3O2 has the layered structure of ɑ- NaFeO2, the genus R3 m space group. Ni has the valence of +2, Co has the valence of +3, Mn mainly has the valence of +4, and there is a small amount of Ni3+ and Mn3+ ions. The ion radius of Ni2+ is close to Li+ ion, leading to LiNi1/3Co1/3Mn1/3O2 prone to "cationic mixed" phenomenon, which destroy the structure stability of crystal materials, thus make its electrochemical performance becomes poor. In the process of battery charge and discharge reaction, only Ni2+ / Ni3+, Ni3+ / Ni4+, Co3+ / Co4+ participate in the reaction, Mn4+ plays the role as stable structure material, replacing Mn4+ will not reduce the amount of active substance in the material.The researchers found that the metal cation Al, Mg, Ti, Fe doping can maintain the structural stability of materials, improve the properties of materials. The study of Sn4+ ion doping is very rare, mainly because of the high melting point of SnO2, and it is difficult to dissolve and Sn4+ is hard to dope into the phase structure of anode material by solid phase method, SnO2 takes shape of coating in surface of particles. This experiment studied the influence of the structure and electrochemical properties by doping Sn4+ into the body phase structure of LiNi1/3Co1/3Mn1/3O2, rather than the normal doping Mn4+. The sample was prepared by coprecipitation method using SnCl2 ? 2H2 O as raw doping materials. The structure, morphology and electrochemical properties of LiNi1/3Co1/3Mn1/3O2 were characterized with X-ray diffraction(XRD), scanning electron microscope(SEM) and charge-discharge test.The results show that:(1) The anode materials LiNi1/3Co1/3Mn1/3O2 were prepared by coprecipitation method, Sn4+ can dope into the phase structure of anode materials LiNi1/3Co1/3Mn1/3O2 effectively by replacing of Mn4+. The appropriate doping content is x = 0.04 by electrochemical performance analysis.(2) Sn4+ doping can improve the electrochemical properties of materials. The first time discharge specific capacity and discharge efficiency of LiNi1/3Co1/3Mn1/3O2 are 138.5 mAh/g and 83% respectively, in the range of voltage from 2.5 V to 4.4 V and 0.2 C. The capacity remains at a rate of 96.96% after 30 cycles. The first time discharge specific capacity and discharge efficiency are improved remarkable compared with none doping materials. |
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