A solid-state battery (SSB) is an electrical battery that uses a solid electrolyte to conduct ions between the electrodes, instead of the liquid or gel polymer electrolytes found in conventional batteries. Theoretically, solid-state batteries offer much higher energy density than the typical lithium-ion or lithium polymer batteries.
While solid electrolytes were first discovered in the 19th century, several problems prevented widespread application. Developments in the late 20th and early 21st century generated renewed interest in the technology, especially in the context of electric vehicles. As of 2026, the solid-state battery market has yet to reach scalability and commercialization.
Solid-state batteries can use metallic lithium for the anode and oxides or sulfides for the cathode, improving energy density. The solid electrolyte acts as an ideal separator that allows only lithium ions to pass through, allowing solid-state batteries to potentially solve many liquid electrolyte Li-ion battery problems including flammability, voltage range, unstable electrode interface formation, cycling performance, and mechanical strength.
Materials proposed for use as solid electrolytes include ceramics (e.g., oxides, sulfides, phosphates), and solid polymers.
Solid-state batteries are found in pacemakers and in RFID and wearable devices. These batteries offer enhanced safety and higher energy densities. To achieve to widespread adoption over lithium ion batteries, solid-state batteries need to overcome many challenges, including energy density and power density, durability, material costs, and chemical stability.
History
Origin Between 1831 and 1834, Michael Faraday discovered the solid electrolytes silver sulfide and lead(II) fluoride, which laid the foundation for solid-state ionics. Through his research, Faraday took note of these solid compounds transitioning from insulators to conductors after being heated. In 1963, over a century later, Michael O'Keeffe acknowledged the ionic/electronic conductivity of these solid electrolytes when combined with electrodes to become one of the first records of a practical solid-state battery.
By the late 1950s, several silver-conducting electrochemical systems employed solid electrolytes, at the price of low energy density and cell voltages, and high internal resistance. In 1967, the discovery of fast ionic conduction β-alumina for a broad class of ions (Li+, Na+, K+, Ag+, and Rb+) kick-started the development of solid-state electrochemical devices with increased energy density. The first were molten sodium / β-alumina / sulfur cells developed at Ford Motor Company in the US, and NGK in Japan. This excitement manifested in the discovery of new systems in both organics, i.e. poly(ethylene) oxide (PEO), and inorganics such as NASICON. However, many of these systems required operation at temperatures greater than 300 °C (or 572 °F) and were expensive to produce, limiting commercial deployment and funding towards research efforts in the space.
1990s and 2000s A new class of solid-state electrolyte developed by Oak Ridge National Laboratory, lithium–phosphorus oxynitride (LiPON), emerged in the 1990s. LiPON was successfully used to make thin-film lithium-ion batteries, although applications were limited due to the cost associated with deposition of the thin-film electrolyte, along with the small capacities that could be accessed using the thin-film format.
2010s In the 2010s, automotive companies began researching practical application of using solid state technology. Kamaya et al. demonstrated in 2011 the first solid-electrolyte, LiGePS (LGPS), capable of achieving a bulk ionic conductivity in excess of liquid electrolyte counterparts at room temperature, allowing technological competition with proven Li-ion liquid electrolytes.
In 2011, Bolloré launched a fleet of their BlueCar model cars featuring a 30kWh lithium metal polymer (LMP) battery with a polymeric electrolyte, created by dissolving lithium salt in polyoxyethylene co-polymer. In 2012, Toyota began researching automotive applications of solid-state batteries. Concurrently, Volkswagen began partnering with Quantumscape and others specializing in the technology. Researchers at the University of Colorado Boulder announced in 2013 the spinout of Solid Power and the development of a solid-state lithium battery, with a solid iron–sulfur composite cathode touting higher energy density.
In 2017, Toyota extended its decades-long partnership with Panasonic to include collaboration on solid-state batteries. As of 2019 Toyota held the most SSB-related patents. The following years similar research efforts into solid-state batteries was separately announced by BMW, Honda, Hyundai (with Solid Power and Samsung), and Nissan.
Outside of the automotive sector, other research and development in the 2010s included: solid-state batteries for electronics by Qing Tao announced in 2018; and a solid-state glass battery by John Goodenough, the co-inventor of Li-ion batteries, unveiled in 2017, featuring a glass electrolyte and an alkali-metal anode consisting of lithium, sodium or potassium.
2020s Many companies have announced readiness to commercialize solid-state batteries at the GWh scale in the 2020s, but their batteries' feasibility or technology readiness is unknown. These announcements include: ProLogium – GWh production capacity by 2022; QuantumScape – GWh production capacity by 2024; Qing Tao – GWh production capacity by 2020; Ampcera – commercial availability by 2021; Panasonic and Toyota – market maturity by 2025; Solid Power, BMW, and Ford – market maturity by end of 2020s; WeLion – GWh production capacity by 2022; StoreDot; Honda – market maturity by 2030; Ionic Materials and Hyundai – market maturity in the 2030s; Donut Lab - GWh production in January 2026; and others.
As of January 2026, many of these companies have not commercialized their products and the solid-state battery market has yet to reach scalability and commercialization..
Materials
Candidate materials for solid-state electrolytes (SSEs) include ceramics such as lithium orthosilicate, glass, sulfides and RbAg4I5. Mainstream oxide solid electrolytes include Li1.5Al0.5Ge1.5(PO4)3 (LAGP), Li1.4Al0.4Ti1.6(PO4)3 (LATP), perovskite-type Li3xLa2/3-xTiO3 (LLTO), and garnet-type Li6.4La3Zr1.4Ta0.6O12 (LLZO) with metallic Li. The thermal stability versus Li of the four SSEs was in order of LAGP < LATP < LLTO < LLZO. Chloride superionic conductors have been proposed as another promising solid electrolyte. They are ionic conductive as well as deformable sulfides, but at the same time not troubled by the poor oxidation stability of sulfides. Other than that, their cost is considered lower than oxide and sulfide SSEs. The present chloride solid electrolyte systems can be divided into two types: Li3MCl6 and Li2M2/3Cl4. M Elements include Y, Tb-Lu, Sc, and In. The cathodes are lithium-based. Variants include LiCoO2, LiNi1/3Co1/3Mn1/3O2, LiMn2O4, and LiNi0.8Co0.15Al0.05O2. The anodes vary more and are affected by the type of electrolyte. Examples include In, Si, GexSi1−x, SnO–B2O3, SnS –P2S5, Li2FeS2, FeS, NiP2, and Li2SiS3.
Lithium-ceramic batteries demonstrate potential improvements with the integration of single wall carbon nanotubes (SWCNTs). SWCNTs build durable, long-range conductive pathways between electrode particles, effectively reducing electrode resistance and enhancing energy density.
One promising cathode material is Li–S, which (as part of a solid lithium anode/Li2S cell) has a theoretical specific capacity of 1,670 mAh/g, "ten times larger than the effective value of LiCoO2". Sulfur makes an unsuitable cathode in liquid electrolyte applications because it is soluble in most liquid electrolytes, dramatically decreasing the battery's lifetime. Sulfur is studied in solid-state applications.
Another encouraging cathode is NCM662 (LiNi0.6Co0.2Mn0.2O2), especially when coated with NiCo2S4 in a resonant acoustic mixing process. This creates a material with a capacity retention of 60.6%, with minimal side reactions.
Li-O2 also have high theoretical capacity. The main issue with these devices is that the anode must be sealed from ambient atmosphere, while the cathode must be in contact with it.
A Li/LiFePO4 battery shows promise as a solid-state application for electric vehicles. A 2010 study presented this material as a safe alternative to rechargeable batteries for EV's that "surpass the USABC-DOE targets".
A cell with a pure silicon μSi||SSE||NCM811 anode was assembled by Darren H.S Tan et al. using μSi anode (purity of 99.9 wt %), solid-state electrolyte (SSE) and lithium–nickel–cobalt–manganese oxide (NCM811) cathode. This kind of solid-state battery demonstrated a high current density up to 5 mA cm−2, a wide range of working temperature (-20 °C and 80 °C), and areal capacity (for the anode) of up to 11 mAh/cm2 (2,890 mAh/g). At the same time, after 500 cycles under 5 mA cm−2, the batteries still provide 80% of capacity retention, which is the best performance of μSi all solid-state battery reported so far.
Chloride solid electrolytes also show promise over conventional oxide solid electrolytes owing to chloride solid electrolytes having theoretically higher ionic conductivity and better formability. In addition chloride solid electrolyte's exceptionally high oxidation stability and high ductility add to its performance. In particular a lithium mixed-metal chloride family of solid electrolytes, Li2InxSc0.666-xCl4 developed by Zhou et al., show high ionic conductivity (2.0 mS cm−1) over a wide range of composition. This is owing to the chloride solid electrolyte being able to be used in conjunction with bare cathode active materials as opposed to coated cathode active materials and its low electronic conductivity. Alternative cheaper chloride solid electrolyte compositions with lower, but still impressive, ionic conductivity can be found with an Li2ZrCl6 solid electrolyte. This particular chloride solid electrolyte maintains a high room temperature ionic conductivity (0.81 mS cm−1), deformability, and has a high humidity tolerance.
Perovskite-type
Meanwhile, Perovskite materials also have great potential for application in solid-state batteries. In order to improve the low efficiency and high pollution of traditional fossil-based energy sources, more and more researchers have put forward the idea of solid-state batteries, which will have a longer lifespan and higher efficiency. However, solid-state batteries still have a lot of safety concerns and drawbacks, so researchers are using a lot of new materials to solve this problem. One such material is perovskite materials.