Composite utilization of solid-state electrolytes in all-solid-state batteries

Developing novel sustainable energy sources and exploring safe and efficient chemical energy storage systems are of significant importance for the development of the new energy industry. Currently, lithium-ion batteries (LIBs), leveraging their relatively highest energy density and mature large-scale manufacturing processes, dominate the markets for portable electronic devices and electric vehicles. However, their performance bottlenecks are becoming increasingly apparent. The traditional liquid organic electrolyte system they rely upon suffers from a series of inherent defects that severely limit their expansion towards higher energy densities and broader, safer application scenarios. These defects are primarily manifested as follows: flammability and explosiveness (low flash point, poor thermal stability) leading to severe safety hazards batteries under abusive conditions are highly prone to thermal runaway, even fire or explosion; Electrolyte leakage risk, which not only pollutes the environment but also causes battery failure; Limited ability of the liquid system to suppress lithium dendrite growth; at high current densities or in later cycles, lithium dendrites easily penetrate the separator, causing short circuits. The aforementioned safety issues, compounded by the poor compatibility of liquid electrolytes with high-voltage cathodes or highly reactive lithium metal anodes (manifested as numerous side reactions and unstable interfaces), severely constrain the further enhancement of battery energy density and the expansion into broader, safer application scenarios. All-solid-state batteries (ASSBs), as next-generation energy storage devices offering high specific energy, high safety, and long cycle life, have garnered significant attention and are a current research hotspot in chemical energy storage. Their core innovation lies in completely abandoning traditional liquid organic electrolytes in favor of entirely solid electrolyte materials. The solid electrolyte itself is non-flammable and leakage-proof, significantly enhancing the battery’s intrinsic safety. Simultaneously, its wide electrochemical stability window enables compatibility with higher-voltage cathode materials (such as lithium-rich manganese-based and high-nickel materials) and the most promising high-capacity lithium metal anode (theoretical specific capacity: 3860 mAh/g). This provides the most viable technological pathway for constructing battery systems with energy densities far exceeding current levels (targeting breakthroughs beyond 500 Wh/kg). As the core component of ASSBs, the solid electrolyte must first possess high room-temperature ionic conductivity approaching or even surpassing that of existing liquid electrolytes (typically ​>10−3 S/cm) to ensure usable rate capability and power output. Secondly, it requires excellent chemical and electrochemical interfacial stability with both cathode and anode active materials, forming low-impedance interfaces that remain stable over long-term cycling, thereby avoiding detrimental side reactions and interfacial degradation. Thirdly, it demands outstanding mechanical strength, particularly a sufficiently high shear modulus, to physically block and suppress lithium dendrite penetration, ensuring long-term safe operation. Finally, it must exhibit a sufficiently wide electrochemical stability window to simultaneously withstand the strong oxidizing environment at the high-voltage cathode and the strong reducing environment at the lithium metal anode without decomposing. Among the numerous solid electrolyte material systems, two categories of composite solid electrolytes-layered structures and framework/filler structures-demonstrate significant advantages and immense potential for engineered applications. Leveraging their unique crystal configurations and designable ion transport channels, along with tunable interfacial properties and potential high chemical/electrochemical stability achievable through composite strategies (such as introducing polymers or inorganic fillers), they show great promise in synergistically optimizing key performance indicators: ionic conductivity, interfacial compatibility, mechanical strength, and electrochemical window. Consequently, they have become the paramount focus and a fiercely competitive frontier in current ASSB material development and fundamental mechanism research. Deeply understanding the structure-property relationships, ion transport mechanisms, and interfacial formation and evolution processes within these two special structural categories, and conducting precise structural design and performance optimization based on this understanding, is undoubtedly the key to unlocking the high performance, intrinsic safety, and ultra-long cycle life potential promised by ASSBs. It is also the essential pathway to propel them from the laboratory towards large-scale commercial application.