Research On Lithium Titanate As Anode Material For New Energy Storage Battery System

Spinel Li4Ti5O12(FD3m,LTO)is used as a new energy storage material due to its excellent stability and safety Compared with traditional carbon-based materials,the volume expansion of Li4Ti5O12 battery is almost zero during the working process,the cycle performance is very stable,and the material life is long,can reach more than 10 000 cycles.The discharge platform of Li4Ti5O12 is higher than that of graphite,which can inhibit the lithium dendrites and loss of lithium in the electrolyte,thereby improving the safety of the battery system.Spinel Li4Ti5O12 has a relatively fixed position space during lithium insertion/delithiation,so reversibility and stability are very good.However,L14Ti5O12 has many intermediate phases during the synthesis process,and it is difficult to obtain high-purity Li4Ti5O12.Moreover,its low electrical conductivity(～10-13 S/cm)and specific discharge capacity(175 mAh/g)lead to poor fast charge-discharge and energy density,which limits its commercialization.In response to above problems,this thesis can control the synthesis of high-purity Li4Ti5O12 materials,and through morphology control,nanomaterials,doping to further improve the electrical conductivity of the material,shorten the Li+diffusion path,thereby improving its electrochemical performance.In this thesis,Li4Ti5O12 materials were synthesized by hydrothermal/solvothermal and solid-state reaction.Different precursors were used to explore the reaction during the formation of Li4Ti5O12.And through XRD and electrochemical methods,the raw material ratio,reaction temperature,precursor material and final product are optimized and the purity is determined.High-purity Li4Ti5O12 materials can be obtained under optimized reaction conditions.In this paper,LiOH·H2O is used for lithium source,anatase(Aeroxide P25,HOMBIKAT-8602)and amorphous TiO2 are used for titanium source,and the optimal conditions for hydrothermal synthesis of high-purity Li4Ti5O12 are finally determined:the molar ratio of lithium source to titanium source is 4.4/5.Hydrothermal reaction at 120℃for 12 h,calcination at 700℃ for 4 h.The pure phase Li4Ti5O12 synthesized with P25 as the titanium source has a capacity of 136.7 mAh/g after 1000 cycles at 1C.In order to further study the full-cell system,commercial LiFePO4 was used as the positive electrode,and Li4Ti5O12 synthesized from different titanium sources was used as the negative electrode.The whole battery system was prepared and tested for its electrochemical performance.The capacity of first cycle at 1C were 166.2,154.0 and 138.5 mAh/g,respectively,and the capacity retention rate after 1000 cycles was 87.4%,99.2%and 99.8%,respectively.Further study the Li4ZTi5O12 material,form materials with different morphologies in different reaction methods,and conduct charge-discharge tests on them.In order to improve the electrical conductivity and high rate performance of Li4Ti5O12 Nb and Al were doped at Ti3+/4+site or Li+site of Li4Ti5O12 to study the influence of doping elements on the morphology and lithium insertion/extraction.Experiments show that element doping can increase the discharge platform,and it is also conducive to improve rate performance.