Solid-state batteries are mainly classified into three categories based on their technological approach: polymer all-solid-state batteries, oxide all-solid-state batteries, and sulfide all-solid-state batteries.
Research on polymer all-solid-state batteries began as early as 1973; oxygen-based all-solid-state batteries were researched even earlier, in 1953; and sulfur-based all-solid-state batteries were first researched in 1981.
The main advantages of polymer all-solid-state batteries are: they are easy to process, can produce large-capacity cells, have relatively soft mechanical properties, and their performance is similar to that of currently used electrolytes. Their manufacturing process is also similar to that of current lithium batteries, making them the easiest solid-state batteries to mass-produce using existing equipment through modification.
The main disadvantages of polymer all-solid-state batteries are: They have the lowest ionic conductivity, requiring heating to above 60 degrees Celsius to improve it to approximately 10⁻³ S/CM, thus necessitating high-temperature operation. Their energy density is also limited. Because polymers are organic, their electrochemical performance is poor compared to other solid-state inorganic battery materials. They have good compatibility with lithium iron phosphate batteries but poor compatibility with ternary lithium batteries, preventing improvements in energy density.
The main advantages of oxide-based all-solid-state batteries are: high voltage tolerance and higher conductivity than polymer batteries. The ionic conductivity of oxides can reach the level of 10⁻⁵⁻³ S/cm, but it is not as high as that of liquid electrolytes. Typical examples include oxides such as LAGP and LATP.
The main disadvantages of oxide-based all-solid-state batteries are: the mechanical properties of oxides are hard, making them prone to breakage if used to make electrolyte sheets; the solid-solid contact with the positive electrode active material is not good enough, causing the contact to change from surface contact to point contact, resulting in excessive interface loss; these disadvantages make it difficult to manufacture high-capacity cells. Currently, oxides can only be combined with electrolytes or polymers to make the solid-liquid hybrid batteries used today, thereby reducing the electrolyte content.
The main advantages of sulfide-based all-solid-state batteries are: good contact properties, resulting in excellent overall ionic conductivity; relatively soft particles, making it easy to form surface contacts between solid and solid components; and the fact that it is the only solid-state battery material that can exceed the ionic conductivity level of liquid electrolytes, making it the most likely future technology route for all-solid-state batteries.
The main advantages of sulfide-based all-solid-state batteries are: very high product cost and poor air stability. Sulfides are highly chemically reactive, reacting strongly with air, organic solvents, and positive and negative electrode active materials, resulting in poor interfacial stability. This makes production, transportation, and processing extremely difficult, limiting their widespread application.
