Technical Analysis of Three Mainstream Solid-State Battery Electrolyte Routes

There are three mainstream technical routes for solid-state batteries: polymer solid-state batteries, oxide solid-state batteries, and sulfide solid-state batteries. Different technical routes of solid-state batteries are mainly differentiated by distinct solid electrolytes. Classified by solid electrolyte types, there are three primary categories of solid electrolytes:
polymer electrolytes, oxide electrolytes, and sulfide electrolytes. Among them, polymer electrolytes are organic electrolytes, while oxide and sulfide electrolytes fall under inorganic electrolytes. An ideal solid electrolyte material should feature high ionic conductivity, chemical and electrochemical stability against lithium metal, effective suppression of lithium dendrite formation, low manufacturing costs, and no reliance on rare metals. However, each of the three major technical routes has its own strengths and drawbacks, and none can satisfy all the above criteria simultaneously, leaving certain obstacles to technological breakthroughs. Overall, sulfide electrolytes hold promising development prospects for all-solid-state batteries.
Polymer Electrolytes
Advantages of polymers include easy processability, good compatibility with existing liquid electrolyte production equipment and processes, and favorable mechanical properties. Their disadvantages are as follows:
Extremely low ionic conductivity, requiring heating up to 60 °C for normal charging and discharging;
Poor chemical stability, incompatible with high-voltage cathode materials, and prone to fire and combustion under high temperatures;
Narrow electrochemical window. When the potential difference exceeds 4 V, the electrolyte is susceptible to electrolysis, resulting in a low performance ceiling for polymer electrolytes.
Oxide Electrolytes
Oxide electrolytes deliver decent conductivity and stability, with higher ionic conductivity than polymer counterparts and outstanding thermal stability up to 1000 °C, alongside reliable mechanical and electrochemical stability. Their drawbacks include:
Lower ionic conductivity compared with sulfide electrolytes, which restricts capacity and rate performance during performance optimization of oxide solid-state batteries;
Extreme hardness of oxides leads to rigid interfacial contact issues in solid-state batteries. Simple cold pressing at room temperature results in excessively high porosity within cells, which may render the batteries inoperable.
Sulfide Electrolytes
Sulfide electrolytes boast the highest ionic conductivity, excellent mechanical properties, and a wide electrochemical stability window (above 5 V), delivering superior overall performance and the greatest development potential among all-solid-state battery technologies. Their disadvantages are listed below:
Unstable interfaces that readily trigger side reactions with cathode and anode materials, generating high interfacial impedance and increasing internal resistance;
Complicated manufacturing processes for sulfide solid-state batteries. In addition, sulfides react readily with moisture and oxygen in air to produce highly toxic hydrogen sulfide gas.
Among the three categories, polymer electrolytes have seen the fastest development and relatively mature technology. They were the first to advance toward commercialization and have achieved small-scale mass production. Nevertheless, plagued by low conductivity and a low performance ceiling, they have not yet achieved large-scale market adoption. Oxide electrolytes exhibit balanced performance across all indicators and are advancing at a rapid pace currently. Sulfide electrolytes feature high conductivity and outstanding performance, making them ideal for electric vehicles with vast commercial potential, yet they pose significant research challenges—maintaining high stability remains an unsolved critical issue. Technological breakthroughs addressing core bottlenecks of solid electrolytes are expected to accelerate the industrialization of solid-state batteries.