Designing Of Functional Separators For Lithium Batteries

Lithium-based battery(including lithium-ion battery and lithium sulfur battery)as one of the most promising energy storage systems,has been widely used in flat electronic devices,electric vehicles.However,some fatal problems of lithium battery need to be solved,such as safety,mechanical strength,and the shuttle and self-discharge of polysulfide.Therefore,optimized lithium battery components must be developed to improve the performance of lithium-based batteries.So many excellent electrode materials and new electrolytes have been reported.Developing new functional separator to replace commercial separator is an effective strategy to improve the overall performance of batteries.The development of functional separator can improve the safety performance of battery and solve the decay problem of battery performance.we aim at solving the deficiency of lithium battery separator.It is mainly divided into two parts:Chapter 2 and chapter 3 are the modification of lithium-ion battery separator;Chapter 4and chapter 5 are the modification of lithium sulfur battery separator.Through separator modification,the safety performance,ionic conductivity and electrochemical performance of lithium-ion battery were further improved.At the same time,the shuttle effect and self-discharge effect of polysulfide in lithium sulfur battery are inhibited.The research contents are summarized as follows:(1)A bi-layer separator for safe lithium-ion battery was designed.The bi-layer separator combines the advantages of MoO₃-PVDF-HFP layer and LLZTO-PVDF-HFP layer,and exhibits excellent mechanical properties,electrolyte wettability,thermal shrinkage,ionic conductivity,thermal distribution and electrochemical properties.In addition,the bi-layer also has excellent flame-retardant performance.(2)A LLZTO solid electrolyte-reinforced PVDF-HFP composite separator was prepared through electrophoretic deposition.The composite separator provides high mechanical strength,thermal stability,lithium-ion conductivity and electrochemical performances.(3)A lepidolite-modified polypropylene(C-Lepidolite@PP)separator was designed to suppress polysulfide shuttling and accelerate the transformation of polysulfides.According to the characterization,lepidolite effectively confines polysulfides by forming strong Si-S bonds to weaken the S-S bonds of polysulfides.The ultralow lithium-ion diffusion barrier of lepidolite allows for free lithium-ion migration and thus significantly facilitates polysulfide conversion to enable fast polysulfide redox for high-rate current operation.(4)A Fe-Phytate-modified polypropylene separator(C-Fe-Phytate@PP)was designed to inhibit LiPSs shuttle and accelerate LiPSs conversion.According to the characterization,Fe-Phytate can form Fe-S bond with LiPSs to confine LiPSs and accelerate its transformation.