Solid-state batteries: When Will "Substitutes" Become "Mainstays"?

Solid-state batteries are emerging as the next-generation power source, but hybrid solid–liquid batteries are likely to commercialize first and act as a crucial bridge between today’s liquid lithium-ion cells and future all-solid-state systems.

What solid-state batteries are

Solid-state batteries replace flammable liquid electrolytes with solid materials while enabling higher energy density and better safety performance. Their cathodes can use high-energy materials such as lithium-rich manganese-based compounds, while the anode can combine nano-silicon and graphite to push energy density toward 300–450 Wh/kg.

A solid electrolyte carries lithium ions without leakage risk and significantly reduces thermal runaway probability.

Higher-capacity anodes and high-voltage cathodes give solid-state batteries the potential for longer driving range in electric vehicles and improved endurance in drones or energy storage systems.

Hybrid solid–liquid as a transition

The article distinguishes liquid, hybrid solid–liquid, and all-solid-state lithium batteries, emphasizing that hybrid designs are an essential transition stage. Semi-solid, quasi-solid, and “solid” batteries on the market largely fall into this hybrid category, differing only in the ratio of liquid to solid electrolyte.

Hybrid solid–liquid batteries still contain some liquid electrolyte, which improves contact with active materials and eases manufacturing.

All-solid-state batteries contain only solid electrolyte, offering better intrinsic safety and higher theoretical energy density but facing more severe engineering challenges today.

Technical barriers to full solid-state

Although many companies and research institutes worldwide are investing in solid-state technology, no large-capacity solid-state power cell has yet matched liquid lithium-ion batteries on both performance and cost. The core difficulty lies at the solid–solid interface, where rigid electrolyte materials make it hard to maintain intimate contact with electrodes during cycling and volume changes.

Current routes include polymer, thin-film, sulfide, and oxide solid-state batteries, each with distinct advantages and limitations.

For example, polymer solid-state cells struggle at room temperature and with high-voltage cathodes, while sulfide systems are sensitive to air and require demanding manufacturing conditions.

In-situ solidification strategy

To overcome interface issues while leveraging existing lithium-ion infrastructure, researchers propose an in-situ solidification approach for hybrid solid–liquid electrolytes. During cell assembly, a liquid precursor ensures good wetting and contact; later, chemical or electrochemical reactions convert all or part of this liquid into a solid electrolyte inside the cell.

This method improves electrode–electrolyte contact, suppresses lithium dendrite growth, and balances safety, high voltage, and fast-charge performance.

It can also reuse much of the current liquid lithium-ion production process, helping manufacturers scale up more quickly and reduce costs.

Future development directions

Experts expect that all-solid-state lithium batteries will need roughly five more years before true large-scale commercialization, so hybrid solid–liquid power batteries remain a realistic near-term pathway. To accelerate industrialization, the article highlights the need for coordinated progress in materials, cell design, manufacturing, and standards.

Priorities include: developing solid electrolytes with balanced ionic conductivity, stability, and processability; matching high-energy electrodes such as high-nickel cathodes and silicon–carbon or lithium metal anodes; and integrating digital simulation with intelligent manufacturing.

Industry is encouraged to build robust supply chains for key materials, invest in automated equipment, refine testing and evaluation systems, and gradually evolve from hybrid solid–liquid lithium-ion batteries toward fully solid-state lithium metal batteries.