Design And Performance Control Of Electrolyte Formulation For High-performance Lithium-ion Batteries

As we all know,alternative energy is a high-tech industry in the 21st century,and the battery industry stands out in the field of alternative energy due to its broad development prospects and has received extensive attention from researchers.At present,lithium-ion batteries have been widely used as important energy sources and play a vital role in the field of electronic communication and transportation.However,the comprehensive performance of lithium ion batteries still can not meet the needs of power battery applications.The main reasons are as follows:The low discharge capacity of lithium-ion batteries at low temperature,or even unable to discharge,seriously impedes the application of batteries.The commercial lithium ion battery electrolyte is composed of LiPF₆ and organic carbonate,but the redox decomposition of the traditional electrolyte above 4.3 V intensifies,which leads to the increase of the interface impedance between the electrode and electrolyte,thus deteriorating the battery performance.Therefore,in view of the shortcomings of conventional electrolyte,this thesis attempts to improve the performance of the battery at low temperatures and high voltages by adding different functional electrolyte additives to the electrolyte.The main contents are as follows:（1）In order to improve the electrochemical performance of the battery at a low temperature of-40-0℃,the basic electrolyte（1M LiPF₆+DMC/EMC（3:5 w/w）+PC（4%）+FEC（0.2%））is used as the research object（DMC:dimethyl carbonate;EMC:methyl ethyl carbonate;PC:Propylene Carbonate）,LiPO₂F₂（lithium difluorophosphate）as an additive,and matched with NCM-811 material to investigate the low temperature behaviors of the batteries.The experimental results show that LiPO₂F₂ can increase the ionic conductivity of the electrolyte,and has little effect on the concentration of the electrolyte,thereby improving the low-temperature discharge capacity of the battery.At a temperature of-40℃and a current density of 0.1 C for low-temperature discharge test,the battery has a specific discharge capacity of137.5 m Ah/g,which is much higher than that of the basic electrolyte battery（only 106.9 m Ah/g）,even in the case of low-temperature charge and low-temperature discharge at-40℃,the specific capacity of cyclic discharge can be stably maintained at 81.9 m Ah/g,which is much higher than that of the basic electrolyte battery（only 33.3 m Ah/g）,fully indicating that LiPO₂F₂additive exhibits excellent low-temperature performance.（2）In order to further improve the charge and discharge performance of the battery at a low temperature of-40-0℃,the electrolyte containing 2%LiPO₂F₂ additives is used as the research object,and the modified reagent EB（ethyl butyrate）is added and match the NCM-811 materia,to further investigate the low temperature behaviors of the batteries.The experimental results show that after adding the modified reagent of EB,improve the viscosity and conductivity of the electrolyte,thereby improving the low temperature performance of the battery at a temperature of-40℃,the specific discharge capacity of the battery when discharged at a current density of 0.1 C is 145.79 m Ah/g,reaching 73.6%of the discharge capacity at room temperature,which is higher than that of the basic electrolyte battery（137.5 m Ah/g,which is only reaching 70.1%of the discharge capacity at room temperature）.The results indicate taht the EB modified electrolyte battery exhibits excellent low temperature performance,which can meet the application requirements of a low temperature environment of-40℃.（3）In order to improve the performance of the battery under high voltages and obtainexcellent cycle and rate behaviors under high voltages,this thesis synthesized a new electrolyte additive（TTD）as the high voltage additive of the electrolyte,which is also matched with NCM-811 cathode material.The results show that the TTD additive significantly improves the battery capacity,cycle stability and rate cabality.After 1%TTD added to the basic electrolyte,the 0.2C capacity retention rate of the battery at 4.2 V,4.3 V,4.4 V and 4.5 V after 200 cycles increased by 42.6%,40%,50%and 31.9%,respectively.In addition,the TEM and XPS analysis results show that TTD can effectively inhibit the decomposition of the electrolyte and participate in the formation of a uniform and stable CEI film on the electrode surface,thereby effectively inhibiting the reaction between the electrolyte and the active cathode material,and finally improve the performance of batteries at different high voltages.