Modification Of Lithium Titanate And Preparation Of Polymer Composite Electrolyte

Lithium titanate(Li₄Ti₅O₁₂)is a kind of lithium ion battery anode material.The advantages of small volume strain,high cyclic stability,high voltage platform,no SEI layer on the surface make its safety performance higher than other negative electrode materials.The platform of Li₄Ti₅O₁₂?LTO?material is 1.55 V?vs.Li⁺/Li?,and the diffusion coefficient of Li⁺in Li₄Ti₅O₁₂ is about 2×10^-8cm²/s?25^oC?.Compared with graphite negative electrode,the diffusion coefficient is greater,but the polarization phenomenon is serious.This is mainly caused by lower intrinsic conductivity of Li₄Ti₅O₁₂ material(?10^-9S/cm),the capacity loss is serious in the large rate charging and discharging cycle,resulting in the serious decrease of the cyclic stability.In this paper,Li₄Ti₅O₁₂ composites with new nano structure,high power density,high safety and long life were prepared with metal ion doping and carbon coating.At the same time,based on the industrial production of Li₄Ti₅O₁₂ with"flatulence"problem,we improve the comprehensive performance of lithium titanate battery from two aspects:the modification of lithium titanate conductivity and the design of new polymer electrolytes.The main contents and results are as follows:?1?Li_4-xMg_xT_i5O₁₂?0?x?0.2?anode material was synthesized by a solid-state method using Li₂CO₃,MgO and anatase TiO₂.The effects of Mg element doping on the crystal structure,phase composition,morphology and electrochemical properties of Li_4-xMg_xTi₅O₁₂were investigated by XRD,SEM and EDX.The electrochemical properties of Li_4-x-x Mg_xT_i5O₁₂ were characterized through cyclic voltammetry and AC impedance experiments.The results indicated that,when x=0.10,the resultants show better on electrochemical performance of higher rates cycle stability and the polarization degree.The initial discharge capacity reaches 122.5 mAh/g at 2 C,and the discharge capacity still remains 119.3 mAh/g after 100 cycles.?2?In order to further improve the properties of Li_3.9Mg_0.1Ti₅O₁₂ materials,carbon coated Li_3.9Mg_0.1Ti₅O₁₂ composites were prepared from polyvinyl alcohol?PVA?.The effects of different coating amounts on the properties of Li_3.9Mg_0.1Ti₅O₁₂2 composites were studied.The results show that,when the coating amount is 8%,the composite material has better comprehensive performance than Li_3.9Mg_0.1Ti₅O₁₂.When the coating amount is 8%,the composite material has better comprehensive performance than Li_3.9Mg_0.1Ti₅O₁₂.Carbon coating greatly improves the electronic conductivity of materials,and also reduces the side reaction between electrode materials and electrolyte.?3?We synthesized a new polymer electrolyte NCN500 instead of the traditional carbonate electrolyte.The experimental results show that the NCN500 mechanics of the polymer electrolyte has good mechanical strain,thermal stability and electrochemical stability.At the same time,the electrochemical performance of LCO/NCN500/LTO was investigated,and the effect of NCN500 inhibited by polymer electrolyte was also explored.The polymer electrolyte NCN500 can solve the problem of flatulence and improve battery safety.