Green Preparation Of High Performance PEO-based Solid Polymer Electrolytes And Their Applications In Solid-state Lithium Batteries

Commercial lithium batteries?LBs?normally use a flammable liquid electrolyte,which causes serious safety issues in practical use.The use of solid polymer electrolytes?SPEs?in place of liquid electrolytes is regarded as a fundamental method to solve the safety issue of LBs.Among the various SPEs,poly?ethylene oxide??PEO?-based polymer electrolytes are the most widely explored because of their inexpensive cost,flexibility and great capability of dissolving lithium salts.However,the preparation of an ideal PEO-based SPEs simultaneously possessing high thermal stability,good mechanical strength,sufficient electrochemical stability at high voltage and high ionic conductivity still remains a key challenge.For the above issues,two environmentally friendly strategies were used to prepare two kinds of novel SPEs,meanwhile the electrochemical performances of these SPEs in all solid-state lithium batteries were thoroughly studied in this work,.Firstly,we synthesized a hydroxypropyl trimethylammonium bis?trifluoromethane?sulfonimide chitosan salt?HACC-TFSI?by ion-exchange reaction,which is an amorphous poly?ionic liquid?based biomass chitosan derivative,as a modifier for PEO-based SPEs.And the hybrid SPEs using 10wt%HACC-TFSI in PEO?10%HACC-TFSI/SPEs?display the best performance.The ionic5.01×10^-4 S cm^-1 at 60 ^oC,respectively.And The transference number and electrochemical windows of the 10%HACC-TFSI/SPEs are 0.34 and 5.28 V at 60 ^oC,respectively.Because of these improvement,the assembled Li Fe PO₄/SPEs/Li full-cells with 10wt%HACC-TFSI/SPEs presents better electrochemical performances in both discharge capacities and cycling performances than that with blank SPEs at 60 ^oC and 150 ^oC.Secondly,we demonstrated a cryogenic engineering to improve PEO-based SPEs for ASSLBs operated at RT.The rapid in situ cooling process can lead to the uniform formation of PEO crystal nuclei,which can limit the PEO crystal growth in SPEs.The novel crystallization structure could simultaneously promote the ionic conductivity and the electrochemical stability of SPEs.Such improved cryogenic electrochemical stability at a high voltage of 5.58 V at RT.And the ionic conductivity of cryogenic 10%HACC-TFSI/SPEs is 3.14×10^-5 s cm^-1.A discharge capacity of154.9 m Ah g^-1 can be achieved at 0.1 C and RT when Li Fe PO₄?LFP?is used as the cathode.Notably,cryogenic SPEs can be utilized in high voltage ASSLBs.A high discharge capacity of 118 m Ah g^-1 can be achieved at 0.2 C and RT with the Li Ni_0.6Co_0.2Mn_0.2O₂?NCM622?as the cathode and can retain a 94.1%capacity even after 100 cycles.