Recent progress in the use of polyanions as solid electrolytes

Due to the urgent need for high-safety and high-energy density energy storage devices, all-solid-state lithium batteries have become a current research focus, with a solid electrolyte being a key component that determines their performance. Compared with other solid electrolytes, polyanions have a unique three-dimensional open framework for conducting lithium ions and an ultra-stability to water and oxygen, which gives them many potential applications. However, their poor room temperature ionic conductivity, the unstable interfacial structure of the electrode/electrolyte and their processability has hindered practical applications. To address these issues, recent progress in using polyanions as solid electrolytes is reviewed. First, ion transport mechanisms within polyanionic crystals and in the electrode/electrolyte interlayer are elaborated. Then, the principles and methods to improve lithium-ion transport in polyanionic electrolytes are summarized, and various surface modification methods to improve the stability and processability of the electrode/electrolyte interfaces are discussed. Finally, the processing and equipment that need to be developed and improved for all-solid-state battery fabrication are outlined, and developing trends to achieve the practical use of polyanions in all-solid-state batteries are discussed.