Solid-state battery refers to an advanced battery cell technology that replaces the liquid organic electrolyte and separator used in conventional lithium-ion batteries with a solid-state electrolyte. Based on the proportion of solid electrolyte within the system, solid-state batteries are classified into three primary categories: semi-solid-state (liquid electrolyte content of 5–10 wt%), quasi-solid-state (0–5 wt%), and all-solid-state (0 wt%), with semi-solid-state, quasi-solid-state, and all-solid-state collectively referred to as solid-state batteries. All-solid-state batteries are widely regarded by the automotive industry as the ultimate technological frontier for lithium batteries, poised to eliminate both "range anxiety" and "safety anxiety" for electric vehicle (EV) owners.
The electrochemical working principle of a solid-state battery is fundamentally identical to that of a conventional lithium-ion battery, with the defining difference lying in the physical state of the electrolyte. Conventional lithium batteries comprise a cathode, an anode, a liquid electrolyte, and a porous separator. In contrast, all-solid-state batteries utilise a solid electrolyte membrane in place of both the liquid electrolyte and separator, with lithium ions shuttling between the positive and negative electrodes through dedicated ionic channels within the solid medium. This architecture results in a far more compact structure whilst facilitating the adoption of higher-capacity electrode materials, paving the way for a substantial leap in energy density.
The core competitive strengths of solid-state batteries centre on two main pillars. Significantly enhanced safety is the standout benefit. Conventional liquid lithium-ion batteries utilise flammable organic solvents, which are prone to thermal runaway under internal short circuits or severe impact. Conversely, most inorganic solid electrolytes are non-flammable, non-volatile, and non-corrosive, with thermal decomposition thresholds exceeding 300°C, thereby eliminating fire and explosion hazards at the root. Dongfeng Motor's solid-state battery demonstrated no fire or explosion even under continuous exposure to 170°C heat, vastly outperforming the current Chinese national testing standard of 130°C.
A quantum leap in energy density represents another major breakthrough. The wide electrochemical stability window of solid electrolytes accommodates high-voltage cathode chemistry and ultra-high-capacity lithium metal anodes, unlocking theoretical energy densities exceeding 500 Wh/kg—far beyond the current ceiling of around 260 Wh/kg for liquid lithium-ion batteries. Dongfeng's production-ready solid-state battery achieves an energy density of 350 Wh/kg, delivering an EV driving range of over 1,000 km, whilst GAC's all-solid-state battery currently in development nearly doubles the energy density of prevailing battery packs.
The solid electrolyte forms the technological core of solid-state batteries, with four primary pathways being actively pursued:
Sulfide electrolytes deliver the highest ionic conductivity (on par with liquid electrolytes) and are regarded as the definitive roadmap for all-solid-state batteries, drawing heavy investment from automakers and battery giants such as Toyota, CATL, and Huawei. However, they exhibit poor atmospheric stability and react readily with moisture to generate toxic hydrogen sulfide gas, demanding exceptionally stringent manufacturing conditions.
Oxide electrolytes offer outstanding thermal stability and safety performance, but suffer from high brittleness and poor solid-to-solid interfacial contact, requiring liquid electrolytes or polymer compounding to optimise boundary performance.
Polymer electrolytes provide excellent processability and cost efficiency, but feature low room-temperature ionic conductivity, requiring elevated operating temperatures of 65–78°C to function effectively, which severely restricts their practical automotive applications.
Halide electrolytes demonstrate good chemical stability and manageable production costs, but display poor compatibility with lithium metal anodes and are prone to moisture absorption.
As no single technology route has established absolute dominance, the prevailing industry consensus leans towards hybrid composite electrolyte solutions that combine the strengths of each pathway.
Solid-state batteries are currently making the pivotal leap from research laboratories into commercial series production. The automotive industry broadly views 2026 as the milestone year for the commercial roll-out of semi-solid-state batteries. Dongfeng Motor has confirmed that its 350 Wh/kg oxide-polymer composite solid-state battery will enter series vehicle fitment in the second half of 2026, retaining over 74% of its usable capacity at sub-zero temperatures of -30°C. GAC Group plans to introduce its 400 Wh/kg quasi-solid-state battery under its Hyper brand within 2026, whilst BYD is expected to equip its semi-solid-state batteries on the facelifted Yangwang U8 and Han L models in the fourth quarter of 2026.
The full industrialisation of all-solid-state batteries will take longer to mature. In 2024, China's Ministry of Industry and Information Technology (MIIT) committed approximately RMB 6 billion to support R&D among leading battery enterprises. The projected timeline anticipates consumer electronics adoption between 2025 and 2026, automotive EV deployment from 2027 onwards, and full-scale mass production post-2030. Academician Ouyang Minggao noted that the technological roadmap for all-solid-state batteries will progress across three generations: "graphite/low-silicon anode → high-silicon anode → lithium metal anode", identifying 2027 to 2030 as the decisive commercialisation window.
Solid-state batteries must clear three major technical and commercial hurdles before achieving widespread mass adoption. Prohibitive manufacturing costs remain the primary barrier, with lithium sulfide—the core precursor for sulfide electrolytes—currently priced at millions of yuan per tonne, vastly exceeding the raw material costs of conventional liquid cells. The solid-solid interfacial challenge is the critical engineering bottleneck: rigid contact between the electrodes and the solid electrolyte is prone to escalating internal impedance and contact degradation caused by volume changes during charge-discharge cycles, severely shortening cycle life. An incomplete supply chain ecosystem also poses challenges, as bespoke manufacturing machinery (including dry electrode coating, isostatic pressing, and high-voltage formation equipment), industrial standards, and quality-testing frameworks have yet to mature, requiring coordinated breakthroughs across the entire supply chain.
Over the medium to long term, solid-state battery adoption will follow a tiered progression: moving from non-automotive sectors to premium passenger EVs, and ultimately filtering down to mainstream family cars. This phased roadmap enables the industry to refine manufacturing processes and achieve economies of scale in performance-critical, low-price-sensitivity domains like eVTOL aircraft, robotics, and specialised equipment before scaling to the mass market. Ongoing breakthroughs in solid-state battery technology are set to elevate new energy vehicles from merely functional alternatives to effortless, compromise-free daily drivers.
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