Single-ion conducting gel polymer electrolytes: design, preparation and application

Electrolytes as pivotal components of lithium-ion batteries (LIBs) and lithium metal batteries (LMBs) influence the capacity, cycle stability, safety and operating conditions of the batteries. An ideal electrolyte should possess high ionic conductivity, enhanced safety, unity lithium ion transference number (LITN) and good electrochemical stability. Single-ion conducting solid polymer electrolytes (SIC-SPEs) have garnered considerable attention due to their unique unity LITNs. In SIC-SPEs, immobilization of anions gives rise to unity LITNs, the absences of anionic concentration polarization, low internal impedances, higher discharge voltages and suppressions of lithium dendrite growth. Single-ion conducting gel polymer electrolytes (SIC-GPEs) can be fabricated by adding plasticizers to SIC-SPEs to enhance the ionic conductivities. Meanwhile, the original feature of unity LITNs (similar to 0.98) remains. Therefore, SIC-GPEs have been widely applied in LFP cells, LTO cells, LMO cells and Li/S cells, which showed excellent cycle stabilities, good rate capabilities and high capacities at ambient temperature. Good compatibility with lithium metal anodes and suppression of lithium dendrites that benefited from immobilization of anions are also inherited for SIC-GPEs. The current status of SIC-GPEs in terms of designs, preparation methods, electrochemical performances and applications is described in this review. The development directions and future prospects of SIC-GPEs are also discussed.