A star polymer POSS-PMMA based gel electrolyte with balanced electrochemical and mechanical properties for lithium metal battery

Gel polymer electrolyte (GPE) is one of the promising candidates to overcome the defects of liquid and solid electrolyte for lithium metal batteries (LMBs). The obstacle for the practical application of GPEs lies in achieving a balance between ion transport, mechanical properties and interface stability. In this work, a star shaped polymer matrix polyhedral oligomeric silsesquioxane-polymethyl methacrylate (POSS-PMMA) is successfully synthesized with POSS as the core via atom transfer radical polymerization (ATRP) method. 1-ethyl-3-methylimidazole bis(trifluoromethanesulfon)imide ([EMIM][TFSI]) and bistrifluoromethanesulfonimide lithium salt (LiTFSI) are blended with the matrix to increase ionic conductivity. Attributed to the star structure and the lithium ion migration channel provided by POSS, the synthesized GPE possesses excellent balanced mechanical and electrochemical properties. To further stabilize the Li/GPE interface, a polymer and plastic crystalline electrolyte (PPCE) is coated as interface modification layer on both sides of GPE. Benefitting from the design, the synthesized GPE reaches a highly stable Li striping/plating cycling for 1000 h at 0.1 mA cm- 2 with ionic conductivity of 3.5 x 10-4 S cm- 1, Li+ transference number of 0.35, and electrochemical stability window of 4.9 V. Furthermore, the Li||POSS-PMMA-PPCE||LiFePO4 (LFP) full cell shows a high capacity retention of 99.5 % after 100 cycles at 0.2 C under room temperature (RT), and the high voltage Li||POSS-PMMA-PPCE||LiNi1-x-yMnxCo O2 (NCM811) cell shows a high capacity retention of 88.3 % after 50 cycles at 0.1 C under RT. This work opens up a new frontier to stabilize the Li/GPE interface and enables safe operation of room temperature lithium metal batteries.