Optimizing The Electrochemical Performance Of Lithium Zinc Titanate Anode Materials By Carbon For Lithium-Ion Batteries

With the development of new energy field,lithium ion battery is widely used because of its safety,environmental protection and long cycle life.Moreover,as a promoter of scientific and technological progress,materials also play a crucial role in improving the performance of lithium-ion batteries.Lithium zinc titanate,as a new anode material for lithium ion batteries,has the capacity of 229 mAh g-1(higher than lithium titanate),and has a stable crystal structure similar to lithium titanate,with a relatively good cycle life.However,compared with the commercial graphite anode,lithium zinc titanate has poor conductivity,which makes it easy to produce large polarization at large electric currents,resulting in poor electrochemical performance.In order to overcome this problem,this paper uses carbon material(with high conductivity)to cover its surface.The influence of different carbon sources such as fulvic acid and polyacrylonitrile on the electrochemical performance of lithium zinc titanate was investigated.The surface of lithium zinc titanate was coated with non-uniform or uniform carbon layer,which can improve the conductivity of lithium zinc titanate and isolate the electrolyte,prevent the further occurrence of side reactions,and further improve its long cycle stability.In short,carbon can compensate for the weakness of lithium zinc titanate to a certain extent,enabling it to have relatively higher capacity at different current densities.This paper focuses on the modification characteristics of lithium zinc titanate by different carbon sources,and the main contents are as follows:(1)The mixture of fulvic acid and lithium zinc titanate was sintered at high temperature in nitrogen atmosphere to obtain the anode material of lithium zinc titanate coated with carbon layer.The excellent performance suitable for industrial power LIBs associates with the N and S co-doped carbon coating layers,small carbon bumps and membranes on the LZTO particle surface,with the carbon material facilitating electron transfer and the less coated area maintaining the good Li-ion migration of LZTO.Experiments show that when the content of fulvic acid is 28 wt%,calcination temperature is 800?,the material has coulombic efficiency of 88%,and owes discharge capacity of 191,179.4,165.4,157.1 and 143.5 mAh g-1 at 0.1,0.2,0.4,0.8 and 1.6 A g-1,respectively.The materials can also maintain 215.3 mAh g-1 under 0.5 A g-1 after 1000 cycle loops.As can be seen,Li2ZnTi3Os has improved electrochemical performance after modified by fulvic acid.According to the research analysis,under this condition,both N and S can be co-doped,and a large number of NO3-and weak SO42-can be obtained at 800?,which is conducive to futher improve the ionic conductivity and comprehensively improve the electrochemical performance of the material.(2)The lithium zinc titanate anode with uniform carbon layer was obtained under the same sintering condition as the above work by using polyacrylonitrile.Polyacrylonitrile doped N to lithium zinc titanate while improving its conductivity.Experiments show that when the content of polyacrylonitrile is 60 wt%,calcination temperature is 800?,the material can exibit discharge capacity of 226,209.5,196.6,242.6 and 181.7 mAh g-1 under the current density of 0.1,0.2,0.4,0.8 and 1.6 A g-1 respectively,and owes 250.8 mAh g-1 under the current density of 0.5 A g-1 after 1100 loops.In short,compared to the pure zinc titanate lithium,the material has obviously improved electrochemical performance.The large number of defects brought by N doping can improve the ionic conductivity of the material,and the high electronic conductivity brought by the carbon layer can improve the electrochemical performance comprehensively.Moreover,the uniformly coated carbon layer can isolate the electrolyte,avoid the occurrence of side reactions,and improve the cyclic stability.(3)The mixture of polyacrylonitrile and lithium zinc titanate was treated by pre-oxidation process,when the content of polyacrylonitrile is 40 wt%and the maximum calcination temperature is 850?,the resulting sample has discharge capacities of 223.8,198.3,179.3,163.8 and 147.8 mAh g-1 at current densities of 0.1,0.2,0.4,0.8 and 1.6 A g-1,respectively.The appropriate carbon content increases the electronic conductivity of the material,and the pre-oxidation process increases the content of N-Zn bond,increases the doping of N to lithium zinc titanate,and boost the migration of Li+.In general,the electronic conductivity and ionic conductivity of the material are improved.Therefore,the improved electronic conductivity and ionic conductivity promote the material to have better electrochemical properties in the pre-oxidation process.