Solid-state Li-air batteries: Fundamentals, challenges, and strategies

The landmark Net Zero Emissions by 2050 Scenario requires the revolution of today's energy system for realizing nonenergy-related global economy. Advanced batteries with high energy density and safety are expected to realize the shift of end-use sectors toward renewable and clean sources of electricity. Present Li-ion technologies have dominated the modern energy market but face with looming challenges of limited theoretical specific capacity and high cost. Li-air(O-2) battery, characterized by energy-rich redox chemistry of Li stripping/plating and oxygen conversion, emerges as a promising "beyond Li-ion" strategy. In view of the superior stability and inherent safety, a solid-state Li-air battery is regarded as a more practical choice compared to the liquid-state counterpart. However, there remain many challenges that retard the development of solid-state Li-air batteries. In this review, we provide an in-depth understanding of fundamental science from both thermodynamics and kinetics of solid-state Li-air batteries and give a comprehensive assessment of the main challenges. The discussion of effective strategies along with authoritative demonstrations for achieving high-performance solid-state Li-air batteries is presented, including the improvement of cathode kinetics and durability, solid electrolyte design, Li anode optimization and protection, as well as interfacial engineering.