Study On Electrolyte Additives For Ni-Rich/Si-C Materials Of Lithium-Ion Batteries

The electrolyte is an important part of lithium-ion batteries,and the development of new additives is still the key to improve the performance of the electrolyte.A small amount of additives has little effect on the viscosity and ionic conductivity of the electrolyte,but can significantly improve the performance of lithium-ion batteries.The purposeful use of electrolyte additives is the most economical and effective strategy.This paper mainly includes the following three aspects.It is still a big challenge to stabilize Ni-rich cathode interface at high current rate and a long-term cycle in the present Li-ion battery for electric vehicles.In the third chapter,succinic anhydride(SA)is used as an electrolyte additive to improve the performance of LiNi0.8Co0.1Mn0.1O2/Li cell.The LiNi0.8Co0.1Mn0.1O2/Li cell with 3%SA has the highest capacity retention,and shows capacity retention of 80.7%after 200 cycles at 1 C rate.From the characterization results,SA additive can react with trace water in the electrolyte,thereby inhibiting the decomposition of LiPF6,which also lesds to less LiF generated on the cathode surface.In addition,the addition of S A has a beneficial effect on the self-discharge of NCM811 electrode.In the fourth chapter,we introduce an organic N,O-Bis(trimethylsilyl)acetamide(BSA)with multifunctional groups(Si-N,Si-O and C=N bond)as a novel electrolyte additive to stabilize LiNi0.8Co0.1Mn0.1O2 cathode interface and enhance its electrochemical performances.After 200 cycles,the LiNi0.8Co0.1Mn0.1O2/Li cell at 1 C rate with 0.5%BSA shows enhanced capacity retention of 86%,while only 69.4%with the baseline electrolyte.When the discharge rate is increased to 2 C,the LiNi0.8Co0.1Mn0.1O2/Li cell with BSA additive shows improved capacity retention of 72.6%after 400 cycles,while the counterpart is only 49.5%.The experimental results show that HF、H2O can be scavenged by BSA and the hydrolysis of LiPF6 is reduced.Moreover,BSA additive can be preferentially oxidized during the charging process and form a robust,uniform electrode/electrolyte interface film on NCM811 cathode surface.Consequently,a better CEI film can suppress the electrolyte decomposition,improve cathode interface stability and alleviate transition metal ions dissolution.Electrolyte additives for silicon-carbon materials:silicon-carbon materials have serious volume expansion problems during the process of lithium insertion,so it is necessary to construct SEI film with good flexibility and mechanical strength on the interface.In the fifth chapter,we studied a variety of additives with unsaturated bonds,fluoride and ring structures.Among them,we found that 3,3,3-trifluoropropylene carbonate(TFMEC)additives with fluorinated and ring structures has a good improvement on the electrochemical performance of silicon-carbon materials,TFMEC additive also participate in the formation of an interface film with a smaller interface impedance.