An AB alternating diblock single ion conducting polymer electrolyte membrane for all-solid-state lithium metal secondary batteries

Lithium 4,4′-difluorobenzene sulfonyl imide is copolymerized with polyethylene glycol (PEG, Mw = 200, 400, 600, 800 and 1000) to synthesize a series of AB alternating diblock copolymer electrolytes (ADCE-1, 2, 3, 4, 5) for reducing the crystallinity of solid-state single ion conducting materials for applications in all-solid-state lithium metal secondary batteries. The free-standing film of ADCE-5 with the highest [EO]/[Li+] ratio (23.7:1) is found to display the lowest glass transition temperature (Tg) and the highest ionic conductivities of 6.61 × 10−6 S cm−1 at 30 °C and 2.24 × 10−4 S cm−1 at 100 °C. The alternating architecture of the polymer effectively prevents the polymer from phase separation originated from aggregation of the ionic groups as well as the ethylene oxide groups. As a result, segment motion may take place readily in the amorphous region at low temperature. Subsequently, a piece of glass fiber mat reinforced composite polymer electrolyte film is prepared for practical battery tests. The fabricated all-solid-state single ion conducting polymeric lithium metal secondary battery is able to work at a temperature as low as 40 °C with stable cycling performance. The battery delivers 102 mA h g−1 at 0.1 C and is stabilized at 94 mA h g−1 after 200 cycles.