Study On The Surface Modification Of Li₄Ti₅O₁₂ As Anode Material For Lithium Ion Batteries

The Spinel lithium titanite(Li4Ti5O12,LTO)has been considered as a promising anode material for power lithium ion batteries due to its excellent safety performance and ultralong cycle life.Unfortunately,the LTOstill has not been large-scale applied.The main obstacle is the severe interface reaction between the electrolyte and the LTOwhile using it as anode during cycles and storage age.In order to suppress the side reactions between LTOand electrolyte,the LTOwas in-situ coated with some organic and inorganic compounds through simple wet chemical approaches.All the results demonstrated that the ratio capability and cycle performance of the LTOcould be well improved because of the suppression of the interfacial reaction between LTOand electrolyte.Firstly,the microstructures and electrochemical performance of in-situ carbon coated LTOcomposites were studied,the carbon source are phenolic resin(PR)and glucose.The pristine LTOsample was synthesized from the Li2CO3 and TiO2 via a solid phase method.And the in-situ carbon coated LTOcomposite(LTO/C-PR)was synthesized via a wet chemical method from the phenolic resin coated TiO2(TiO2/PR)and Li2CO3.The LTOcoated with carbon from glucose(LTO/C-G)composite was also synthesized via a wet chemical method from Li2CO3,TiO2 as well as glucose.The results indicated that LTO/C-PR composite exhibited the best electrochemical performance for the graphitization of carbon layer was higher than LTO/C-G.It was well known that the higher graphitization of the carbon coating layer the better of the electronic conductivity,which also could better suppression the interfacial reaction between LTOand electrolyte.The discharge specific capacity retention ratio of the LTO/C-PR is 99.3%at 5.0C after100 cycles.(Frornl36mAh g-1 to 135mAh g-1)Then,the LTOwas surface modified with inorganic coating YPO4,using y(NO3)3·6H2O and NH4HPO4 as the raw materials.The results show that the YPO4 coating layer is amorphous and electrochemically inert,and the coating layer did not change the bulk structure of LTO.Experimental results indicated the 0.5wt%YPO4 in the composite was the optimum amount,which could not only well suppress the undesired interf-acial reaction but also be favorable to improve the rate capability and cyclic performance of the LTO.Finally,a kind of fluoride with well lithium ion conductivity,that is to say the LiF was selected to modify the surface of LTOto improve its electrochemical performance.The research demonstrated that the LiF coating layer also did not change the bulk structure of LTO.however,it could well suppress the interface interaction.Therefore,the LiF modified LTOalso exhibited good cycling stability and rate capability.In a conclusion,the interface reaction between LTOand electrolyte could be well suppression by in-situ coating with carbon or some inorganic compound such as YPO4 or LiF via facile wet chemically approach.The corresponding composites could exhibit excellent cycling stability and rate capability.