A solid-state battery (SSB) is a type of electrical battery that uses a solid material to move ions between its parts, called electrodes. This is different from traditional batteries, which use liquid or gel-like materials to do the same job. Solid-state batteries can store more energy than common lithium-ion or lithium polymer batteries.

Solid electrolytes were first discovered in the 1800s, but early problems made it hard to use them widely. Later, in the late 1900s and early 2000s, new discoveries sparked interest in this technology, especially for use in electric vehicles. As of 2026, solid-state batteries are still being studied and are not yet widely available for mass use.

These batteries often use metal lithium as the negative electrode and materials like oxides or sulfides as the positive electrode. This helps them store more energy. The solid electrolyte acts as a barrier that only allows lithium ions to pass through. Because of this, solid-state batteries may help solve issues found in traditional batteries, such as the risk of catching fire, limited voltage, unstable interfaces, poor performance over time, and weak structure.

Materials being tested for use in solid-state batteries include ceramics (such as oxides, sulfides, and phosphates) and solid polymers. These batteries are already used in medical devices like pacemakers and in small electronics like RFID tags and wearable gadgets. They are safer and can store more energy than traditional batteries. However, challenges remain, including how much energy they can store, how long they last, the cost of materials, their sensitivity to conditions, and their overall stability.

History

Between 1831 and 1834, Michael Faraday discovered two solid electrolytes: silver sulfide and lead(II) fluoride. These discoveries helped start the field of solid-state ionics. Faraday observed that these materials changed from not conducting electricity to conducting electricity when heated. This idea was not widely recognized until 1976, when Michael O'Keeffe noted it. Faraday’s work marked the first recorded example of a solid-state battery with both ionic and electronic conduction.

By the late 1950s, some systems used solid electrolytes that conducted silver ions. However, these systems had problems, such as low energy storage, low voltage, and high resistance. In 1967, scientists discovered a material called β-alumina that could conduct many types of ions quickly. This discovery helped create solid-state electrochemical devices with better energy storage. Soon after, companies like Ford Motor Company in the United States and NGK in Japan developed batteries using β-alumina. Researchers also found new materials, such as poly(ethylene) oxide (PEO) and NASICON. However, many of these materials required high temperatures or were expensive to make, which limited their use.

In the 1990s, scientists at Oak Ridge National Laboratory created a new solid electrolyte called lithium–phosphorus oxynitride (LiPON). LiPON was used to make thin-film lithium-ion batteries, but these batteries had limited capacity and were costly to produce.

In 2011, Kamaya and others discovered a solid electrolyte called Li₁₀GeP₂S₁₂ (LGPS). This material could conduct ions as well as liquid electrolytes at room temperature. This breakthrough allowed solid-state batteries to compete with traditional lithium-ion batteries.

During the 2010s, automotive companies studied solid-state battery technology. In 2011, Bolloré introduced cars with lithium metal polymer (LMP) batteries that used a polymeric electrolyte. Toyota began researching solid-state batteries in 2012, and Volkswagen partnered with technology companies. In 2013, researchers at the University of Colorado Boulder developed a solid-state battery with a lithium-sulfur cathode. Toyota continued working with Panasonic on solid-state batteries and held the most patents related to solid-state batteries by 2019. Other companies, including BMW, Honda, Hyundai, and Nissan, also announced research efforts.

Outside of the automotive industry, researchers in the 2010s explored solid-state batteries for electronics and other uses. In 2017, John Goodenough, who co-invented lithium-ion batteries, introduced a solid-state glass battery with a glass electrolyte and an alkali-metal anode. In 2018, Qing Tao announced solid-state batteries for electronics.

In the 2020s, many companies claimed they could produce solid-state batteries on a large scale. Examples include ProLogium (2022), QuantumScape (2024), Qing Tao (2020), and others. However, as of January 2026, few companies had successfully commercialized their products, and the market had not reached large-scale production.

In 2026, Donut Lab, a company that started as a spinoff of Verge, announced it had developed a solid-state battery ready for commercial production. Tests on the battery showed results similar to current Li-NMC batteries. However, experts said the initial tests by VTT did not prove the battery’s long-term performance or how well it would work in real-world conditions.

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 of the four SSEs compared to Li is in the order of LAGP < LATP < LLTO < LLZO. Chloride superionic conductors have been proposed as another promising solid electrolyte. They conduct ions well and are flexible like sulfides, but they are not affected by the poor oxidation stability of sulfides. Their cost is considered lower than oxide and sulfide SSEs. Current 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 and depend on the type of electrolyte. Examples include In, Si, GeₓSi₁−ₓ, SnO–B₂O₃, SnS–P₂S₅, Li₂FeS₂, FeS, NiP₂, and Li₂SiS₃.

Lithium-ceramic batteries may improve with the use of single-walled carbon nanotubes (SWCNTs). SWCNTs create strong, long conductive pathways between electrode particles, reducing resistance and increasing 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 is unsuitable as a cathode in liquid electrolyte applications because it dissolves in most liquid electrolytes, greatly reducing battery lifespan. Sulfur is studied for use in solid-state applications.

Another encouraging cathode is NCM662 (LiNi₀.₆Co₀.₂Mn₀.₂O₂), especially when coated with NiCo₂S₄ using a resonant acoustic mixing process. This creates a material with a capacity retention of 60.6%, with few side reactions.

Li–O₂ batteries also have high theoretical capacity. The main challenge is that the anode must be sealed from the environment, while the cathode must be exposed to it.

A Li/LiFePO₄ battery shows promise for use in solid-state electric vehicles. A 2010 study presented this material as a safe alternative to rechargeable batteries for electric vehicles 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 (99.9 wt% purity), solid-state electrolyte (SSE), and lithium–nickel–cobalt–manganese oxide (NCM811) cathode. This solid-state battery demonstrated a high current density up to 5 mA/cm², a wide working temperature range (-20 °C and 80 °C), and an anode areal capacity of up to 11 mAh/cm² (2,890 mAh/g). After 500 cycles at 5 mA/cm², the batteries retained 80% of their capacity, the best performance reported for μSi all-solid-state batteries.

Chloride solid electrolytes also show promise over conventional oxide solid electrolytes because they have higher theoretical ionic conductivity and better formability. Their high oxidation stability and ductility improve performance. A lithium mixed-metal chloride family of solid electrolytes, Li₂InₓSc₀.₆₆₆₋ₓCl₄ developed by Zhou et al., shows high ionic conductivity (2.0 mS/cm) across a wide range of compositions. This is because chloride solid electrolytes can be used with uncoated cathode materials and have low electronic conductivity. Cheaper chloride solid electrolytes, such as Li₂ZrCl₆, also show impressive ionic conductivity (0.81 mS/cm), deformability, and high humidity tolerance.

Perovskite materials also have great potential for use in solid-state batteries. To improve the low efficiency and pollution of traditional fossil fuels, researchers are developing solid-state batteries that last longer and work more efficiently. However, solid-state batteries still have safety concerns and drawbacks, so researchers are using new materials like perovskite to solve these problems. Perovskite materials have excellent ionic conductivity, good charge storage capacity, and strong electrochemical activity, making them promising for energy storage and conversion. They are used in solid-state batteries and solar cells. Their general formula is ABX₃. In ABX₃, the B ion is surrounded by X ions in an octahedron, and the A ion is at the center of a cube. Transition metal perovskite fluoride, as a perovskite-type electrode material, has a high voltage window, specific capacity, and stability. Its structure helps ions move easily, and its pseudocapacitance-controlled kinetic features allow fast charge transport, giving it good electrochemical properties. Shan et al. showed that lithium ions can be inserted into perovskite oxides, and perovskite oxides with high ionic conductivity can be used as electrode materials. Transition metal perovskite fluoride has a fast charge transport rate, high

Uses

Solid-state batteries may be used in pacemakers, RFIDs, wearable devices, and electric vehicles. Hybrid and plug-in electric vehicles have used many types of batteries, such as lead–acid, nickel–metal hydride (NiMH), lithium ion (Li-ion), and electric double-layer capacitors (ultracapacitors). Li-ion batteries are most common because they store more energy. Solid-state batteries are preferred because they are lighter and have higher energy storage than batteries with liquid electrolytes. This can help increase a vehicle’s range, lower costs, and reduce weight, which are important issues for current electric vehicles.

In 2022, Honda announced plans to begin testing a production line for all-solid-state batteries in early 2024. Nissan stated in 2022 that it plans to launch an electric vehicle with all-solid-state batteries by FY2028. In June 2023, Toyota said it would not use commercial solid-state batteries until at least 2027.

In January 2022, Mercedes-Benz invested in ProLogium to work together on developing new ceramic solid-state battery cells. The company also partners on solid-state technology and plans to build eight gigafactories with others. By December 2023, Mercedes-Benz had invested in Factorial Energy, a U.S. company, to improve its solid-state battery projects.

Solid-state batteries have high energy storage and can perform well in extreme conditions. These features may help create smaller and more reliable wearable devices. In March 2021, Hitachi Zosen Corporation announced a solid-state battery with one of the highest energy capacities in the industry. It can operate in a wide range of temperatures, making it suitable for harsh environments like space. In February 2022, a test mission was launched, and in August 2023, Japan’s space agency confirmed the batteries worked properly in space, powering equipment on the International Space Station.

Solid-state batteries are lighter and more powerful than traditional lithium-ion batteries. This makes them useful for commercial drones. Vayu Aerospace, a drone company, reported longer flight times after using solid-state batteries in its G1 long flight drone. Another benefit is that solid-state batteries can be charged quickly. In September 2023, Panasonic introduced a prototype all-solid-state battery that can be charged from 10% to 80% in 3 minutes.

All-solid-state batteries last a long time and resist heat well. Because of this, they are expected to be used in harsh environments. Production of Maxell’s all-solid-state batteries for industrial machinery has already started.

In 2023, Yoshino became the first company to produce solid-state portable solar generators. These generators have 2.5 times higher energy storage and double the rated and surge AC output power compared to non-solid-state lithium generators.

Challenges

Thin-film solid-state batteries are expensive to make. They use manufacturing processes that are hard to scale up, which requires costly vacuum equipment. Because of this, thin-film solid-state batteries are too expensive for use in consumer products. In 2012, it was estimated that a 20 Ah solid-state battery cell would cost US$100,000. A high-range electric car would need between 800 and 1,000 of these cells. High costs have also limited the use of thin-film solid-state batteries in other areas, such as smartphones.

Operating at low temperatures can be difficult. Solid-state batteries have historically performed poorly in these conditions.

Solid-state batteries with ceramic electrolytes need high pressure to keep the electrodes in contact. Solid-state batteries with ceramic separators may break because of mechanical stress.

In November 2022, a Japanese research group, including Kyoto University, Tottori University, and Sumitomo Chemical, announced they successfully operated solid-state batteries without applying pressure. These batteries had a capacity of 230 Wh/kg using new copolymerized materials for the electrolyte.

In June 2023, a Japanese research group from Osaka Metropolitan University announced they stabilized the high-temperature phase of Li₃PS₄ (α-Li₃PS₄) at room temperature. They achieved this by rapidly heating the material to crystallize the Li₃PS₄ glass.

High interfacial resistance between the cathode and solid electrolyte has long been a problem for all-solid-state batteries. Traditional methods used in Li-ion battery production, such as hot-rolling and uniaxial pressing, create uneven pressure and porosity in the solid electrolyte. Modern equipment designed for solid-state batteries, like warm isostatic pressing, applies nearly uniform pressure, leading to more even densification and lower resistance.

To study degradation at interfaces and within materials, advanced imaging techniques are used. Atomic force microscopy (AFM) maps the surface of solid-state battery materials at the nanometer scale, revealing features like cracks or dendrite growth. Kelvin probe force microscopy (KPFM) maps surface potential, helping to visualize charge buildup and instability. Conductive AFM (C-AFM) maps electrical conductivity, identifying failure zones and evaluating ion pathways.

Interfacial instability between the electrode and electrolyte is a serious issue in solid-state batteries. When the solid electrolyte contacts the electrode, chemical or electrochemical reactions at the interface often form a passivated layer, blocking lithium movement. At high voltages, some solid electrolytes may degrade.

Solid lithium metal anodes are being considered as replacements for traditional Li-ion batteries because they offer higher energy density, better safety, and faster recharging. However, these anodes can form lithium dendrites—uneven metal growths that pierce the electrolyte, causing short circuits. Short circuits can lead to energy discharge, overheating, and even fires or explosions due to thermal runaway. Dendrites also reduce battery efficiency.

The exact reasons for dendrite growth are still being studied. Research on dendrites began with studies of molten sodium/sodium-β-alumina/sulfur cells at high temperatures. In these systems, dendrites sometimes grow due to pressure from plating at the sodium-solid electrolyte interface. Dendrites can also form from chemical breakdown of the solid electrolyte. Uneven pressure from hot-rolling creates cracks where dendrites may start.

In solid electrolytes stable to lithium metal, dendrites grow mainly due to pressure buildup at the electrode-electrolyte interface, causing cracks. In electrolytes chemically unstable with their metal, interphase growth and cracking often prevent dendrites from forming.

Dendrite growth in solid-state Li-ion cells can be reduced by operating at higher temperatures, which delays short circuits. Aluminum-based interphases between the solid electrolyte and lithium anode have also been shown to stop dendrite growth.

A common failure in solid-state batteries is mechanical failure caused by volume changes in the anode and cathode during charging and discharging. Lithium ions entering or leaving the host structures cause expansion or contraction.

Cathodes usually mix active particles with solid electrolyte particles to help ions move. During charging/discharging, cathode particles change volume by a few percent. This creates gaps between particles, worsening contact and reducing ion transport, which lowers battery capacity.

One solution is to use cathode materials that expand only along certain crystal directions. If secondary particles grow along directions with minimal expansion, volume changes can be reduced. Another solution is to mix cathode materials with opposite expansion trends in the right ratio. For example, LiCoO₂ (LCO) expands when discharged, while LiNi₀.₉Mn₀.₀₅Co₀.₀₅O₂ (NMC) contracts. A mix of LCO and NMC at the correct ratio could minimize overall volume change.

Ideally, solid-state batteries would use pure lithium metal anodes because of their high energy capacity. However, lithium expands greatly during charging, increasing pressure in porous electrolytes. This can cause lithium to creep through pores, leading to short circuits. Lithium has a low melting point (453K) and low activation energy for self-diffusion (50 kJ/mol), making it prone to creep at room temperature. At room temperature, lithium undergoes power-law creep, where dislocations move to avoid obstacles. The creep stress is given by:

σ_cree = (ε̇_A_c)^{1/m} exp(Q_c/(mRT))

Advantages

Solid-state batteries can store much more energy than traditional lithium-ion batteries. This is because they use lithium metal anodes, which can hold more charge than the graphite anodes in lithium-ion batteries. In general, lithium-ion batteries have energy densities below 300Wh/kg, while solid-state batteries can reach over 350Wh/kg. This increased energy storage is helpful for uses that need long-lasting and small batteries, like electric vehicles.

A major benefit of solid-state batteries is their better safety. Solid electrolytes lower the risk of thermal runaway, which is a main reason batteries catch fire. Since most solid electrolytes do not burn, solid-state batteries are less likely to catch fire and need fewer safety systems. This can also increase energy storage in battery packs. Research shows that heat produced during thermal runaway in solid-state batteries is about 20-30% of what happens in traditional batteries with liquid electrolytes.

Solid electrolytes allow batteries to work in a wider range of temperatures and voltages, which is important for high-performance uses. Solid-state batteries can function at temperatures above 60°C, while traditional batteries usually work between -20°C and 60°C.

Solid-state batteries can use high-voltage cathode materials, such as lithium nickel manganese oxide, lithium nickel phosphate, and lithium cobalt phosphate. This allows voltages to reach over 5V (compared to a Li/Li reference electrode), while traditional lithium-ion cathodes cannot go above 4.5V (compared to a Li/Li reference electrode).

The combination of solid electrolytes and lithium metal anodes allows ions to move faster, which can reduce charging times compared to lithium-ion batteries. Also, cells can be stacked in a bipolar arrangement, which makes batteries smaller and more compact. This improves overall energy efficiency and allows for flexible battery designs in different applications.

Thin-film solid-state batteries

In 1986, Keiichi Kanehori discovered the earliest thin-film solid-state batteries. These batteries use a Li electrolyte. The technology was not advanced enough to power larger electronic devices, so it was not fully developed. In 2018, "polyamorphism" was observed in thin-film Li-garnet solid-state batteries, which exist in addition to crystalline states. In 2021, Moran showed that ceramic films with sizes ranging from 1–20 μm could be manufactured.

Anode materials: Lithium is preferred because of its ability to store energy. Alloys of Al, Si, and Sn are also suitable for use as anodes.

Cathode materials: These materials must be lightweight, have good cycle life, and high energy density. Common cathode materials include LiCoO₂, LiFePO₄, TiS₂, V₂O₅, and LiMnO₂.

Some methods for producing thin-film solid-state batteries are listed below:

• Physical methods: Magnetron sputtering (MS) is a widely used process for thin-film manufacturing. It relies on physical vapor deposition. Ion-beam deposition (IBD) is similar to MS, but no bias is applied, and no plasma forms between the target and the substrate. Pulsed laser deposition (PLD) uses a high-power laser, up to about 10 W/cm². Vacuum evaporation (VE) is a method to create alpha-Si thin films. During this process, Si evaporates and deposits onto a metallic surface.
• Chemical methods: Electrodeposition (ED) is used to make Si films. It is a convenient and cost-effective technique. Chemical vapor deposition (CVD) is a method that produces high-quality and pure thin films. Glow discharge plasma deposition (GDPD) combines physical and chemical processes. This method increases synthesis temperature to reduce hydrogen content in the films.

• Lithium–oxygen and nitrogen-based polymer thin-film electrolytes are now fully used in solid-state batteries.
• Non-Li-based thin-film solid-state batteries have been studied. Examples include Ag-doped germanium chalcogenide systems and barium-doped systems, which can be as thin as 2 μm. Nickel can also be used in thin-film systems.
• Other methods for making electrolytes include: 1) electrostatic-spray deposition, 2) the DSM-Soulfill process, and 3) using MoO₃ nanobelts to improve the performance of lithium-based thin-film solid-state batteries.

• Compared to other batteries, thin-film batteries have high gravimetric and volumetric energy densities. These are key measures of battery performance.
• Thin-film solid-state batteries also have long lifetimes, excellent flexibility, and low weight. These features make them useful in applications such as electric vehicles, military equipment, and medical devices.

• The performance and efficiency of thin-film batteries depend on their geometry. The amount of current a thin-film battery can provide depends on the shape and interface between the electrolyte and the cathode or anode.
• Thin electrolyte layers and high resistance at the electrode-electrolyte interface can affect the output and integration of thin-film systems.
• During charging and discharging, significant volume changes in materials can cause material loss.

Innovation and IP protection

The patent situation for solid-state batteries has changed since 2010, showing how countries and companies are working to create safer and better energy storage. Large companies, especially those in the car and electronics industries, have been applying for patents to protect their new ideas in this area. Toyota has the most patents granted for solid-state batteries, followed by LG, Samsung, Murata, and Panasonic. Between 2020 and 2023, Toyota was given 8,274 patents for solid-state batteries.

A 2024 WIPO Technology Trends report on the future of transportation says that research and patent activity for solid-state batteries has increased greatly from 2010 to 2023. This area is an important part of battery technology. A method called isostatic pressing has become more popular for making solid-state batteries. From 2017 to 2024, patents related to combining solid-state batteries with isostatic pressing grew by an average of 22% each year. By November 2025, there were 2,110 patents connected to this combination.