Chitosan-based gel polymer electrolytes for high performance Li-ion battery

This study explores the use of glutaraldehyde-crosslinked chitosan-based gel polymer electrolytes (GPEs) in lithium-ion batteries (LIBs). GPEs are prepared by solution casting using two different molecular weights of chitosan including 150 kDa as medium and 400 kDa as high molecular weight (MMWCS and HMWCS, respectively) with varying amounts of crosslinker. Degree of crystallinity was 25.9 and 24.1 % for HMWCS and MMWCS, respectively that was decreased to 18.3 and 22.7 % by using 5 % crosslinker and 17.8 and 21.1 % by using 10 % crosslinker, and 17.2 and 17.6 % by using 20 % crosslinker. The obtained ionic conductivity for HMWCS and MMWCS was 3.1 x 10(-3) and 2.9 x 10(-3) S.cm(-1). After crosslinking by 5, 10, and 20 % crosslinker, the ionic conductivity was obtained to 0.9 x 10(-3) and 0.3 x 10(-3) S.cm(-1), 6.3 x 10(-3) and 5 x 10(-3) S.cm(-1), and 1.1 x 10(-3) and 0.5 x 10(-3) S.cm(-1) for high and medium molecular weight, respectively. Lithium-ion transfer number was obtained between 0.34 and 0.83 and the highest t(+) value was obtained for the MMWCS-GA10. Electrochemical stability window of the prepared polymer electrolytes was >5 V and samples showed no remarkable dendrite growth after cycling analyses. The symmetric cells demonstrated reliable performance, operating for over 300 h without any short-circuiting, which indicates excellent reversible cycling stability for chitosan-based lithium-ion batteries. Furthermore, the Gr/GPE cell exhibited very low voltage polarization, with the over-potential decreasing from 10 mV initially to 6 mV after 300 h at the same current density. Discharge capacity was obtained higher than 170 mAh/g at 0.2C with CE = 97 % for both HMWCS-GA(20) and HMWCS-GA(20).