"Solid-state batteries are about to be mass-produced" will become a hot topic in the industry almost every few months, but the actual industrialization progress is often much slower than the slogan. To understand the current situation of solid-state batteries, we need to go back to the technical route itself and see clearly the advantages and hard bones of each path.

1. Three mainstream technical routes

oxide system: Mainly based on ceramic electrolytes, it has a wide electrochemical window, good thermal stability, and relatively high compatibility with existing production lines. However, it is highly brittle and has poor interface contact, which is a typical "head-to-head" problem. Many domestic companies have chosen oxides as the transition path to semi-solid solutions.

Sulfide system: It has the highest ionic conductivity, which can be close to or even exceed that of liquid electrolyte. It is focused on by Japanese and Korean companies. However, sulfide will produce hydrogen sulfide when it comes into contact with water. The requirements for dew point control in the production environment are extremely stringent, and mass production costs remain high.

polymer system: Good processability and flexibility, but the ionic conductivity at room temperature is low, and it usually needs to be heated to above 60°C to exert its performance, which limits the application scenarios.

2. Where is the real bottleneck?

  • Solid-solid interface impedance: The liquid electrolyte can fully wet the electrode, but there is only point contact between solid and solid, and the interface impedance is large and deteriorates with circulation.
  • Lithium dendrite problem: Solid electrolytes are not omnipotent, and lithium metal anodes may still form dendrites and penetrate the electrolyte during cycling.
  • cost: The current unit cost of solid-state batteries is several times that of liquid lithium batteries, and materials, equipment and yield are all challenges.
  • Production line compatible: A large number of existing lithium battery equipment cannot be used directly and requires reinvestment.

3. A pragmatic timetable

The more consensus judgment in the industry is that from 2024 to 2027, "semi-solid" will be the main one, that is, a small amount of electrolyte is retained to improve the interface, the energy density can reach 300~360Wh/kg, and it will be the first to be applied in small batches in high-end models and special fields; from 2027 to 2030, all-solid-state batteries will enter small batch installation verification; the real large-scale popularization will most likely have to wait until after 2030.

This means that liquid lithium batteries will remain the absolute mainstream for a long time to come, and polymer lithium batteries also have solid space in consumer and special fields.

4. How should companies respond?

For battery companies, the pragmatic strategy is to "walk on two legs": on the one hand, continue to optimize the existing liquid system (high nickel, silicon carbon anode, CTP/CTC structural innovation), on the other hand, accumulate interface and process experience through semi-solid technology to prepare for the all-solid era. For downstream customers, there is no need to wait excessively for solid-state batteries. Instead, they should optimize the structure and thermal management of existing mature solutions to make good products.

5. Conclusion

Solid-state batteries are worth looking forward to, but technological evolution has its own objective laws. It is a rational attitude to see the timeline clearly and neither blindly pursue it nor ignore the layout.