Research On Application Of Diatomite In Lithium-ion Battery Separator

Separator,as one of the important components of lithium-ion batteries,its performance directly affects the discharge specific capacity,cycle stability and life of the battery.Polyolefin separator is used most widely in the market currently.However,due to its low porosity,poor affinity for liquild electrolyte and poor thermal stability,the battery performance is limited and has potential safety hazards.Therefore,the development of high-performance separators that can replace polyolefin separators is of great significance for improving the performance of lithium-ion batteries.In order to improve the porosity and thermal stability of separators,in this paper,polyethylene terephthalate（PET）nonwoven with better heat resistance was used as the separator substrate,and diatomite with a porous structure as the coating material to prepare composite separators.The effects of diatomite content on the properties of composite separators and electrochemical performance of batteries were investigated.The experimental results showed that the increase in the content of diatomite in the coating was beneficial to improve the pore structure of the composite separators,and then increased the porosity,liquid electrolyte absorption rate and ionic conductivity of separators.When the diatomite content is 80 wt%,the maximum value reached 63.8%,0.866 g cm^-3,1.43 mS cm^-1,respectively.Diatomite has a good affinity with the liquid electrolyte,which can improve the wettability of the separator.Meanwhile,diatomite improved the thermal stability of the separator.After heat treatment at 160°C for 0.5 h,the composite separator shrank 1.17%merely.In addition,the battery assembled with a composite separator exhibited better cycle stability and C-rate performance.After100 cycles,its discharge specific capacity was 144.3 mAh g^-1,the capacity retention rate was 98.26%,and the coulombic efficiency reached 98.8%.The study confirmed that the unique morphology of diatomite can help the separator to build a porous structure.In order to further improve the thermal stability of the separator,the organic substrate was removed,taking advantage of the porous structure of diatomite,and LiOH was added to prepare the inorganic separator at high temperature.The effects of sintering temperature and the amount of LiOH on the composition,properties of inorganic separators and electrochemical performance of the batteries were studied.The results showed that diatomite and LiOH can produce lithium silicate at high temperature.When the content of LiOH was low,the product was Li₂Si₂O₅,which changed from amorphous to crystalline with the increasing sintering temperature,and the degree of crystallization gradually increased,which was beneficial to improve the electrochemical performance of the separator in the battery.The wettability and thermal stability of the inorganic separator were perfect,which can improve the safety of the battery effectively.When the content of LiOH in the raw material was changed,the composition of the inorganic separator changed significantly.As the content of LiOH increased,Li₂Si₂O₅,Li₂SiO₃,and Li₄SiO₄ were successively formed in the product.The porosity and liquid electrolyte absorption rate of the inorganic separator showed an increasing trend with the increasing LiOH content,and the contact angle with the liquid electrolyte gradually decreased.Lithium silicate can contribute to improve the efficiency of lithium-ion transmission,so that the ionic conductivity of the inorganic separator could reach 2.05 mS cm^-1.Among different forms of lithium silicate,Li₂SiO₃ could help to improve the discharge specific capacity of the battery.The battery assembled with an inorganic separator with a higher Li₂SiO₃ content can achieve a maximum discharge specific capacity of164 mAh g^-1 at a current density of 0.5 C,which is very close to the theoretical capacity of lithium iron phosphate(170 mAh g^-1).Li₂Si₂O₅ had a significant effect on improving the cycle stability of the battery.The battery,assembled with an inorganic separator with a higher Li₂Si₂O₅ content,after cycled for 180 cycles at a current density of 0.5 C,its capacity retention was 99.8%and the coulombic efficiency was as high as 99.8%,showed an excellent cycle stability.