Overview
Recently, with automakers such as SAIC and GAC announcing solid-state battery products, the topic of solid-state batteries has rapidly become a focus in the Chinese new energy industry. All-solid-state batteries have been included in development strategies in China, the United States, the EU, Japan and South Korea, and they are a key area of global next-generation battery technology competition.
In January 2024, the China All-Solid-State Battery Industry-Academia-Research Collaborative Innovation Platform (CASIP) held its unveiling ceremony in Beijing. From a national perspective, China’s development of solid-state batteries is partly intended to reduce the disruptive impact of global technology breakthroughs on domestic industry; from a corporate perspective, solid-state batteries represent a next-generation technology route many Chinese new energy battery companies are pursuing.
All-solid-state batteries consist of a cathode, an anode and a solid electrolyte membrane. During charge and discharge, lithium ions are transferred between the electrodes via the solid electrolyte. In contrast, in conventional lithium batteries, lithium ions migrate through a liquid electrolyte. The all-solid-state structure improves safety by eliminating hazards caused by liquid electrolyte leakage, and it enables the use of higher-capacity silicon or lithium metal anodes to reach energy densities above 500 Wh/kg and extend cycle life.
Many companies currently promote products labeled as solid-state batteries that are actually semi-solid (hybrid solid-liquid) designs. These add solid electrolyte components to a liquid-cell architecture; their internal structure is still similar to liquid lithium-ion batteries and does not represent a disruptive technology, but rather a technical approach to improve safety. Semi-solid cells are entering trial vehicle installs, but yield, battery cost, charge rate and cycle life remain challenges.
Advantages of All-Solid-State Batteries
Compared with traditional liquid batteries, all-solid-state batteries offer several advantages:
- Solid electrolytes are less flammable and improve safety by eliminating liquid-electrolyte leak risks.
- Because the solid electrolyte cannot flow, internal series stacking is possible, reducing external series components and improving system-level volumetric energy density.
- Higher energy density is achievable because the solid electrolyte can suppress lithium dendrite growth, enabling lithium-metal anodes and significantly increasing energy density, especially volumetric energy density, which is valuable for automotive applications.
The technology is still at an early stage but has seen important progress. For example, sulfide solid electrolytes have made breakthroughs in ionic conductivity, significantly improving cell performance. Countries around the world have included all-solid-state batteries in strategic plans and invested heavily in R&D and industrialization.
In China, an innovative semi-solid route has been proposed: before full solid-state mass production is achieved, accelerate the semi-solid route that mixes solid and liquid components to enable earlier production. This differs from the international emphasis on full solid-state approaches. Many Chinese new energy companies that are about to enter mass production or already in mass production are using hybrid solid-liquid routes, combining oxide and polymer electrolytes and other approaches. The hybrid route is a transitional pathway from liquid cells to full solid-state cells, improving safety while enabling faster deployment. Major issues to resolve include yield, cost, charge rate and cycle life.
Although semi-solid cells are developing rapidly, full solid-state remains the mainstream next-generation direction. China’s solid-state battery industry may achieve industrial breakthroughs around 2030 while also serving as strategic technology reserve.
Honeycomb Energy: Research and Breakthroughs
Honeycomb Energy has reported notable progress in both semi-solid and all-solid-state battery areas. In the semi-solid field, the company introduced first- and second-generation "jelly" batteries, which it reports lead traditional liquid products on key parameters such as energy density, safety and fast charging.
The second-generation jelly battery reportedly overcomes swelling issues in high-nickel silicon-doped systems by using a second-generation jelly electrolyte and integrated composite cathode technology, which helps suppress propagation of internal short circuits. Honeycomb Energy has established a 4,800 m2 jelly battery pilot line and states the second-generation jelly battery is entering B-sample testing and has received positive feedback from an international OEM.
However, full solid-state battery development still faces many challenges. From materials development to cell manufacturing, technical difficulties include sulfide electrolyte stability, membrane fabrication complexity and insufficient insulation between electrodes.
Approaches to address these challenges include multi-element doping, specialized binders and solvent processing techniques.
With increased attention from China’s government and industry, policy support and funding for solid-state batteries have grown, which could accelerate technology maturation and commercialization.
Preferred Electrolyte Types and Technical Progress
Honeycomb Energy focuses on four main solid electrolyte types: polymers, oxides, halides and sulfides. After targeted research, the company considers sulfides to be the primary development direction currently, due to high ionic conductivity, low density and favorable processing properties. Sulfide-based all-solid-state cells with energy density above 350 Wh/kg are seen as a leading route for high energy density full solid-state batteries.
Reported recent progress in materials, membranes and cells includes:
- Electrode material: development of coated and modified cathode materials.
- Sulfide electrolyte: an independently developed sulfide electrolyte with ionic conductivity greater than 10.50 mS/cm and operability at -40°C dew point conditions.
- Electrolyte membrane: large-area membrane fabrication capability, ionic conductivity above 2.3 mS/cm and minimum membrane thickness down to 15 μm.
- Cell development: capability to manufacture 20 Ah all-solid-state cells with energy density above 380 Wh/kg.
Conclusion
All-solid-state batteries are an important technology in the energy sector and are progressing toward maturity and commercialization. Ongoing technical advances and efforts to address remaining challenges are expected to determine the timeline and extent of their adoption in automotive and other scenarios. Continued progress in materials, manufacturing and system integration will be essential for their wider deployment.
