An Investigation Of Performance Of Nano Lithium-rich Materials Coated Lithium-ion Battery Separator

Lithium-ion batteries are widely used because of high energy density,high output voltage and capacity of fast charge and discharge.As one of the most important components of lithium-ion battery,separator is required not only to have high electrolyte uptake,but also to have high thermal stability to protect battery safety.Therefore,most separators are coated with a layer of inorganic material on the surface to improve the electrochemical performance and thermal stability.Solid Electrolyte Interface（SEI）was formed during the lithium battery first charge,LiF and Li₂CO₃ are two inorganic components of SEI.In this paper,LiF and Li₂CO₃,the main inorganic components in SEI with appropriate particle size,are prepared as coating materials.They are coated on both sides of the separator by dip-coating to prepare the coated separators.The thermal stability,porosity,electrolyte uptake and contact Angle of the coated separator are characterized,and the electrochemical performance of the coated separators are tested.The experimental results are as follows:（1）Size-tunable LiF nanoparticles are prepared by various volume ratios of the ethanol and reactants.The batteries with various sizes LiF nanoparticles coated separator was tested and appropriate LiF nanoparticles size was chosen for study of different size LiF loaded on separator.The test results shown:158 nm LiF coated separator has higher porosity and electrolyte uptake than pristine PE separator,and with highest capacity.The initial capacity of LiF coated separator was improved,which was attributed to that LiF as the main inorganic component of SEI,induced the formation of SEI during formation and further reaction between electrolyte and electrode material.With loading increasing on the separator,both of higher porosity and electrolyte uptake were improved.The thermal shrinkage of LFCoated-8 is only 1.4%at 120℃.（2）Li₂CO₃ with particle size of 330 nm were prepared by controlling the content of ethanol in precipitation reaction.The physical and electrochemical properties of Li₂CO₃separators with different loading were investigated.The experimental results show that the thermal stability and hydrophilicity of Li₂CO₃ separators gradually improve with the increase of coating amount.The initial capacity of the battery increases gradually,and the Coulombic efficiency of batteries with Li₂CO₃ separators is more stable in 100 cycles.This is attributed to the earlier appearance of the electrochemical reaction platform during the formation because of presence of Li₂CO₃,the formation of SEI in advance and the formation of more dense SEI structure.（3）The synergistic effect of LiF and Li₂CO₃ on battery performance was studied.By electrochemical performance test,LiF/Li₂CO₃ modified separator has better rate performance and cycling performance than LiF and Li₂CO₃ alone.After 100 cycles,the battery capacity is 82.69%of initial capacity.The presence of LiF and Li₂CO₃ can make SEI grow rapidly with LiF and Li₂CO₃ as skeleton at different sites and components on the electrode surface,and increase the content of LiF and Li₂CO₃ in SEI.Thus,the Coulombic efficiency of the batteries are increased at first cycles of battery cycle test.