Research On High Voltage Electrolytes For Lithium Batteries

Energy density of lithium-ion batteries is one of most important factor which influences the mileage of electric vehicles.Enhance the voltage of electrolyte can effectively improve the energy density.In the conventional electrolytes,the highest cut-off voltage of is only 4.35 V due to the unstable carbonate solvent decomposed at 4.5 V,which lead to an oxidation reaction occurred in charge state with high oxidation state metal surface and cause the electrolyte decomposition.Furthermore,a large amount of combustible gas will be produced in this process which affecting the rate performance and the safety of lithium-ion battery.Research and development of high voltage electrolyte with stability is of great significance to accelerate the development of electric vehicles.The mainly innovative achievements of this research are as follows,(1)A high voltage electrolyte(1 mol/L LiPF6+0.1 mol/L LiDFOB-FEC/PC/DMC)with an electrochemical window of 5.5 V was obtained which can effective passivate aluminum foil.Battery test demonstrated that initial reversible discharge capacity of LiNi0.5Mn1.5O4 was up to 128.7 mAh/g with 99%coulombic efficiency,and a specific capacity of 108.2 mAh/g and 85.3%capacity retention is still remained in 200 cycles.The results from CV and SEM showed better compatibility and lithium ion reversibility between the electrolyte and LiNi0.5Mn1.5O4.The positive interfacial membrane is formed on the cathode surface,which inhibits the decomposition of the electrolyte and improves the cycle performances of the battery.(2)The systematical research on compatibility and cyclicity among Li4Ti5O12,silica and graphite in electrolyte was performed.The results from the semi-cell tests with three kinds of negative electrode materials showed that the electrolyte exhibit good cycles performance.When charging and discharging rate is less than 1 C,lithium titanate electrode can be released more than 157.2 mAh/g of specific capacity.The specific capacity can reach up to 74%with coulomb efficiency more than 99.5%after 520 charge discharge cycles at room temperature,yet its high temperature performance and large multiplier performance was unsatisfactory.In the CV test,the oxidation peak and the reduction peak form the center symmetric closed loop curve,and the electrode has good de-intercalation lithium reversibility.The initial discharge capacity of silicon/carbon composite is 707 mAh/g at a current density of 0.33 mAh/cm2.However,the cycle performance of the battery was not good,and the discharge capacity reduced to 550 mAh/g in 100 cycles.Graphite electrode has the very good specific capacity,coulomb efficiency and cycle stability.The discharge capacity was 323.3 mAh/g after 100 discharge cycles at a current density of 0.33 mAh/cm2.The battery capacity shows no obvious attenuation.