Preparation Of Niobium-Based Oxide Anode Materials And Application In Low-Temperature Lithium-ion Batteries

At low temperatures,the electrochemical performance of Lithium-ion batteries(LIBs)deteriorates rapidly,resulting in capacity degradation,charging difficulties,and life degradation,leading to serious economic losses and safety accidents.By optimizing electrode and electrolyte,the mass transfer resistance in the solid-phase electrode and liquid electrolyte and the charge transfer resistance at the solid-liquid/solid-solid interface of Li+ can be reduced,which can effectively improve the low-temperature performance of LIBs.Niobium-based oxides store lithium based on intercalated pseudocapacitance mechanism,which have low diffusion resistance and desolvation resistance of Li+,and are expected to be ideal anode materials for low-temperature LIBs.However,Niobium-based oxides are wide band-gap materials with low electronic conductivity.In addition,theirs low-temperature performance are also restricted by the electrolyte.Based on this,this paper optimizes the low-temperature lithium storage performance of niobium-based oxides by modifying the interface of anode materials and adjusting the formula of low-temperature electrolyte.The details are as follows:(1)N-doped carbon-coated Mo3Nb14O44(MNO@N-C)was synthesized using polydopamine as carbon source.Due to the high degree of graphitization and defects of carbon material in MNO@N-C,MNO@N-C has more mesopore distribution,larger specific surface area.larger diffusion coefficient and excellent structural stability.MNO@N-C composite exhibits a capacitory-controlled energy storage behavior with superior rate performance(184 mAh g-1,5C)and cycle stability(92%,500 cycles).At-20℃,MNO@N-C exhibits an excellent rate performance with specific capacities of 175 and 43 mAh g-1 at 0.1 C and 10C.Assembled LiNi0.8Co0.1Mn0.1O2‖MNO@N-C full-cell also demonstrates outstanding electrochemical performance,with a specific capacity as high as 110 mAh g-1 at 3C after 500 cycles(capacity retention of 93%).(2)With lithium bis(trifluoromethanesulfonimide)(LiTFSI)and lithium bisfluorosulfaimide(LiFSI)as lithium salts,diethyl ether(DEE)as organic solvent,DEE-based weakly solvated electrolytes with different lithium salt ratios(LiTFSI and LiFSI)were prepared,and their properties at different temperatures were tested.The relationship between electrochemical properties and temperature of T-Nb2O5 in different electrolytes and its internal mechanism were studied systematically.It is found that 0.50 M LiTFSI/0.50 M LiFSI DEE double salt electrolyte has moderate conductivity and better stability at low temperatures.Assembly of T-Nb2O5‖0.50 M LiTFSI/0.50 M LiFSI DEE‖Li half-cell has higher lithium ion apparent diffusion coefficient and lower transfer impedance interface,can adapt to a wide range of temperature.When charged and discharged at 0.5C,the half-cell provides reversible specific capacities of 180,121,100 and 54 mAh g-1 at 25℃,-20℃,-40℃ and-60℃.At the same time,the half-cell also exhibits significant rate performance and cycle stability at low temperatures.In this paper,the low-temperature performance of niobium-based oxide anode materials is improved by electrode modification and electrolyte optimization,and the feasibility of niobium-based oxide materials used in low-temperature LIBs is demonstrated,which provides a new way for the development of low-temperature LIBs.