Structural Modulation And Electrochemical Performance Of Lithium Ion Battery Cathode Materials

Due to high thermal stability,environmental benignity,long cycling life and the natural abundance of raw materials,lithium iron phosphate has been extensively developed.However,the key barrier to wide applications was its intrinsically low electrical conductivity and low Li ion diffusion rate.For the obstacles,controling LiFePO₄ particle size,metal ion doping and surface carbon coating were the effective methods.In this paper,LiFePO₄ cathode materials were prepared by solvothermal method,and some works have been done as the follows:?1?Water,ethanol and ethylene glycol were used as the solvent,seperately,and the effects of synthesis parameters such as reaction temperature and synthesis time on the particle size,phase and electrochemical performance of LiFePO₄ were studied.The results showed that when using ethylene glycol as a solvent,the reaction temperature was 180°C and the holding time was 10 h,the synthesized particles were uniform.The obtained material was pure phase LiFePO₄,the grain size was about 400nm,and the discharge specific capacity at 0.1 C is 148.6 mAh·g^-1.?2?Ethylene glycol as the solvent,and in the synthesis process,Na⁺and Al³⁺were doped respectively,and the effects of doping with different metal ions and different doping content on the morphology,size,and electrochemical performance of LiFePO₄particles were investigated.The results showed that compared with Al³⁺,Na⁺doping improved the LiFePO₄ cathode material more significantly.Among them,the Li_0.99Na_0.01FePO₄ was the best,the particle size was 200-500 nm,the discharge capacity at 0.1 C was 156 mAh·g^-1,and the capacity retention rate was 86.7%after500 cycles at 10 C rate.?3?In the synthesis process,LiFePO₄/C composites were synthesized using biomass material cotton as carbon source and template,and the effects of cotton on the morphology,size and electrochemical performance of LiFePO₄ particles were studied.The results showed that the addition of cotton has little effect on the phase and surface morphology of the synthesized materials.The particle size was 200-300nm,and the improvement of electrochemical performance is significant.Among them,the rate performance and cycling stability of the LiFePO₄/C sample synthesized by adding 0.1 mol·L^-1 LiOH pretreated cotton performed best.The specific discharge capacity at 0.1 C rate was 160.4 mAh·g^-1 and the capacity retention rate after 500cycles at 2 C rate was 92.2%.