Preparation And Performance Study Of PEO/HEMC Composite Polymer Electrolyte

As for the most important material in all-solid-state lithium-ion batteries,electrolyte,especially for polymer electrolyte,has been attracted ever-increasing attentions.But the low ionic conductivity at ambient temperature and poor mechanical strength hinder its broad applications.Numerous researchers have tried to improve its abilities through modifying or embellishing,and much progress have been made.But it is a long road leading to the practical applications,because of the relatively dissatisfied comprehensive capabilities as well as the unclear intrinsic mechanisms.Based on the extensive literature reading and fundamental experiments,we propose Methyl 2-hydroxyethyl cellulose(HEMC)as the organic filler to enhance PEO-based polymer electrolyte.Thus we have obtained a kind of flexible and superior all-solid-state polymer electrolyte.Meanwhile,we have unveiled the improvement mechanism,and also discussed the enhancement on ionic conductivity reinforced by active inorganic fillers.We have prepared PEO/HEMC-CPEs using simple solution-cast technique,and the highest ionic conductivity of 1.30 × 10-4 S cm-1 at ambient temperature is obtained,and 1.68×10-3 S cm-1 at 60?.The remarkable conductivity improvement is mainly stemmed from the multiple functional groups of HEMC,which can act as Lewis base and boost the dissociation of LiTFSI towards much more carriers.The ethylene oxide group in HEMC can not only serve as Lewis base,but also transport Lithium ion like PEO does.In that way.additional lithium ion transfer channels are shaped.And the enhanced mechanical strength is achieved because of the forceful frameworks origin from HEMC.The best performed PEO16-LiTFSI-20HEMC exhibits excellent strength characterized by Young's modulus of 46.95 Mpa and tensile strength of 3,26 Mpa.Since HEMC can redistribute or undertake force and absorb plastic deformation energy,the rupture of PEO chains is mitigated.Therefore,the resistance to external forces is heightened.The assembled Li|PEO16-LiTFSI-20HEMC|LiFePO4 cells show terrific cycling and rate performances in the battery test(?120 mA h g-1 at 1 C-rate for at least 300 cycles and 80 mA h g-1 up to 2 C-rate).Furthermore,the wide electrochemical window(up to 5.56 V)endows high-voltage materials with potential in applications.There is a threshold in the process of reinforcing polymer electrolyte on ionic conductivity by active inorganic fillers.The conductivity is dominated by polymer base when it's below the optimal value,and vice versa.Above all,we have modified PEO-based polymer electrolyte by employing HEMC and obtained flexible and all-solid-state polymer electrolyte with high conductivity at ambient temperature,good mechanical strength,wide electrochemical window and super stability to anode lithium.Also,we have investigated the fundamental mechanism of organic/inorganic composite polymer electrolyte.It provides distinctive solutions and illumination for designing and fabrication of practical all-solid-state electrolyte.