Study On Fluoride Modification Of Lithium Titanate Anode Material

Li₄Ti₅O₁₂（LTO）material is one of the candidates for the negative electrode material of power lithium-ion battery,because of its fast charging performance,long cycle life,good safety and non-flammability.However,LTO material has some drawback of low electronic conductivity,capacity degradation under high current density,low energy density and high voltage platform,which seriously hinders its commercial applications.Therefore,it will contribute to LTO commercial applications to improve the electrical conductivity of the material and make full use of the material’s capacity at low voltage.In this paper,in order to improve the rate performance and cycle performance of LTO materials in practical applications,LTO materials modified with CaF₂,Zn F₂ and LaF₃ were prepared and their structures,morphologies and electrochemical properties were studied.In the process of CaF₂ modified LTO material,F^-ion reacts with Ca²⁺ions to form CaF₂,which does not form a continuous coating on the surface of LTO,but is stacked on LTO particles.The 2 wt%CaF₂ modified LTO showed superior rate performance with smaller R_sei and R_ct values.The cycle stability of CaF₂-modified LTO was also improved.The specific discharge capacity after the 125 cycles at 3C was 187 m Ah·g^-1,and the capacity retention rate was 96.7%.In the process of Zn²⁺and F^-modified LTO materials,Zn²⁺and F^-did not form Zn F₂material on the surface of LTO,but formed Zn O and Li F on the surface of LTO,and Ti O₂was formed at the same time.The reaction mechanism of the modification process is similar to that of the Mg²⁺and F^-modified LTO materials.The 1 wt%Zn F₂ modified LTO material exhibits excellent rate performance.The Zn O material forms a coating on the surface of the LTO.The coating layer can inhibit the side reaction between the electrolyte and the LTO,thereby improving the material properties.The cycle stability of Zn F₂modified LTO is also improved.The specific capacity of the 1 wt%Zn F₂ modified LTO sample after the 200 cycles was 193.9 m Ah·g^-1,and the capacity retention rate was 96.0%.In the process of LaF₃ modified LTO material,La³⁺firstly reacts with F^-ions to form LaF₃,forming an incomplete coating layer on the surface of LTO material particles.However,the introduction of the LaF₃ cladding layer did not change the bulk structure of the LTO material,and the LTO material still retained its original spinel structure.The 1wt%LaF₃ modified LTO sample showed good stability in the cyclic voltammetry test.Compared with other samples,the side reaction between the 1 wt%LaF₃ modified LTO sample and the electrolyte got a certain degree inhibition.At the same time,1 wt%LaF₃modified LTO sample showed excellent rate performance and better cycle stability.After a certain period of activation in the cycle,the capacity can reach 175 m Ah·g^-1.The retention after the 200 cycles was 90.1%.