Constructing Composite Solid Electrolytes for Commercial All-Solid-State Lithium Batteries

The rapid advancement of electric vehicles has increasing demands on the energy density of power batteries(i.e., 400 (W·h)/kg in 2025, and 500 (W·h)/kg in 2030). However, the existing lithium-ion batteries have their theoretical energy capacity limits primarily due to the constraints of graphite anodes. Also, the use of flammable electrolytes in lithium-ion batteries poses significant safety risks, making the development of safer and higher-energy-density batteries an urgent necessity. All-solid-state lithium batteries (ASSLBs), which replace liquid electrolytes with non-flammable solid electrolytes, offer a promising solution to these challenges. The use of solid-state electrolytes can enhance battery safety, extend service life, and enable the use of lithium metal anodes, thus increasing energy density via eliminating dendrite growth. Moreover, solid-state electrolytes allow for a wider operational temperature range, reducing a need for complex thermal management systems and further improving energy density.

Solid-state electrolytes are central to the performance of ASSLBs, impacting key metrics such as power density, energy density, and cycle life. The success of ASSLBs large-scale production hinges on the selection of appropriate solid-state electrolyte materials. These electrolytes are generally classified into inorganic and organic polymer types. The inorganic group is further subdivided into oxides, sulfides, and halides. Despite significant progress in each of these types, no single electrolyte material meets all the industrial requirements for ASSLB production. The primary challenge lies in balancing high ionic conductivity at room temperature, low cost, good chemical and electrochemical stability, high thermal stability, high mechanical strength, and ease of processing.

In response, composite solid electrolytes with both inorganic and polymer electrolytes emerge as a promising strategy. These materials offer improved performance characteristics via leveraging the benefits of both components. However, the challenge remains in selecting and optimizing the right inorganic and polymer combination to achieve the desired balance of properties. This review introduces a concept of SHOP-type composite solid electrolytes, where "S," "H," "O," and "P" represent sulfides, halides, oxides, and polymers, respectively. SHOP-type electrolytes can overcome the limitations of individual materials via utilizing synergistic effects between multiple components. The review also explores the potential advantages of SHOP-type composite electrolytes for the industrialization of ASSLBs, highlighting some promising development directions for future research.

This review addresses some challenges faced by four major types of single-phase solid-state electrolytes, i.e., oxides, sulfides, halides, and polymers, in large-scale production and application. These challenges stem from the difficulty of balancing the various performance requirements for commercial feasibility. Oxides offer excellent thermal stability and electrochemical windows but suffer from low ionic conductivity and complex processing requirements. Sulfides provide high ionic conductivity but are prone to air sensitivity and narrow electrochemical windows. Halides, while offering high ionic conductivity and electrochemical stability, face high production costs and poor interface stability with lithium metal anodes. Polymers, known for their flexibility and processability, are limited by low ionic conductivity and poor high-voltage stability.

A concept of SHOP-type composite solid electrolytes is proposed to address these challenges. SHOP-type electrolytes provide a balanced solution that meets the demanding requirements for ASSLBs via combining the benefits of polymer electrolytes (i.e., processing flexibility and low cost) with the advantages of inorganic electrolytes (i.e., high ionic conductivity, thermal stability, and mechanical strength). These materials offer a potential for improved safety, performance, and scalability in large-scale production, making them highly promising for future energy storage systems.

Despite their numerous advantages, the development of SHOP-type electrolytes still faces several key challenges. Future research should focus on optimizing the composition and structure of composite solid electrolytes. Understanding the interactions between inorganic and polymer components will be crucial to achieving the ideal performance characteristics. Also, the compatibility of SHOP electrolytes with lithium metal anodes and high-voltage cathodes must be further explored to improve battery efficiency and longevity. Another critical area of research is the reduction of production costs, which is achieved via selecting sustainable materials and optimizing processing methods. Innovations in fabrication techniques that can lower costs and improve scalability are essential for the widespread adoption of ASSLBs.

Interdisciplinary collaborations also play a vital role in advancing the development of ASSLB technologies. Researchers can overcome the existing barriers and accelerate the transition of ASSLBs from lab-scale to industrial-scale production via integrating insights from materials science, electrochemistry, and engineering. Through continuous innovation and optimization, SHOP-type composite solid electrolytes hold a great promise for enabling the widespread adoption of ASSLBs, driving forward the development of high-energy-density, safe, and long-lasting energy storage systems in the future.

Some significant strides are made in the development of solid-state electrolytes, the challenges remain considerable. SHOP-type composite electrolytes with their potential for balanced performance offer a promising path toward the commercial realization of ASSLBs. With further research and development, these materials can significantly contribute to the advancement of next-generation energy storage technologies.