A comprehensive review of single ion-conducting polymer electrolytes as a key component of lithium metal batteries: From structural design to applications

Lithium ion batteries have been widely used in portable electronics and electric vehicles as highly efficient energy-storage devices. However, due to the safety concerns and the relatively poor-interfacial compatibility with metals of liquid electrolytes, it is an urgent need to develop some novel electrolytes to drive the development of high energy-density metal-based battery technology. Polymer electrolytes have emerged as one of powerful contenders to replace traditional liquid electrolytes, owing to their advantages of low flammability, good flexibility, convenient processing and lightweight. Yet, most of the commonly used polymer electrolytes belong to dual-ion conductors and may generate concentration polarization, leading to the dendrite growth and degradation of battery performance. The development of single-ion conducting polymer electrolytes (SICPEs) is believed to be one of effective approaches to resolve these problems caused by dual-ion conductors. Such ion-selective polymers can significantly enhance the lithium ion transfer number and improve the electrochemical performance of the batteries. In the last two decades, sufficient energies have been dedicated to the research on SICPEs and a remarkable progress has been made. Therefore, in this review, the structural design and synthetic strategies of single Li-ion conductors, the construction of SICPEs with different functions and their applications in Li-metal batteries are relatively systematically reviewed. Finally, the current challenges and future prospects of SICPEs are outlined to pave the way for the commercial development of next-generation battery technology.