Solid-state battery

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.

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.

In the 2010s, automotive companies began researching practical application of using solid state technology. Kamaya et al. demonstrated in 2011 the first solid-electrolyte, Li10GeP2S12 (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. …

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. …

Solid-state batteries are potentially useful in pacemakers, RFIDs, wearable devices, and electric vehicles.

Hybrid and plug-in electric vehicles have used a variety of battery technologies, including lead–acid, nickel–metal hydride (NiMH), lithium ion (Li-ion) and electric double-layer capacitor (or ultracapacitor), with Li-ion batteries dominating the market due to their superior energy density. Solid state batteries are desirable due to their lighter weight and higher energy density compared to batteries with liquid electrolytes, which can potentially increase a vehicle's range, reduce cost, and reduce curb weight, all of which are major challenges with current electric vehicles.

Honda stated in 2022 that it planned to start operation of a demonstration line for the production of all-solid-state batteries in early 2024, and Nissan announced that, by FY2028, it aims to launch an electric vehicle with all-solid-state batteries that are to be developed in-house.

In June 2023, Toyota updated its strategy for battery electric vehicles, announcing that it will not use commercial solid-state batteries until at least 2027.

In January 2022, Mercedes-Benz invested significantly in ProLogium to codevelop next gen ceramic solid-state battery cell. The company also collaborates on solid-state technology and plans to construct eight gigafactories with partners. By December 2023, Mercedes-Benz had invested in US-based Factorial Energy, advancing its solid-state battery initiatives.

The characteristics of high energy density and keeping high performance even in harsh environments are expected in realization of new wearable devices that are smaller and more reliable than ever.

In March 2021, industrial manufacturer Hitachi Zosen Corporation announced a solid-state battery they claimed has one of the highest capacities in the industry and has a wider operating temperature range, potentially suitable for harsh environments like space. …

Thin-film solid-state batteries are expensive to make and employ manufacturing processes thought to be difficult to scale, requiring expensive vacuum deposition equipment. As a result, costs for thin-film solid-state batteries become prohibitive in consumer-based applications. It was estimated in 2012 that, based on then-current technology, a 20 Ah solid-state battery cell would cost US$100,000, and a high-range electric car would require between 800 and 1,000 of such cells. Likewise, cost has impeded the adoption of thin-film solid-state batteries in other areas, such as smartphones.

Low temperature operations may be challenging. Solid-state batteries historically have had poor performance.

Solid-state batteries with ceramic electrolytes require high pressure to maintain contact with the electrodes. Solid-state batteries with ceramic separators may break from mechanical stress.

In November 2022, Japanese research group, consisting of Kyoto University, Tottori University and Sumitomo Chemical, announced that they have managed to operate solid-state batteries stably without applying pressure with 230 Wh/kg capacity by using copolymerized new materials for electrolyte.

In June 2023, Japanese research group of the Graduate School of Engineering at Osaka Metropolitan University announced that they have succeeded in stabilizing the high-temperature phase of Li3PS4 (α-Li3PS4) at room temperature. This was accomplished via rapid heating to crystallize the Li3PS4 glass.

High interfacial resistance between a cathode and solid electrolyte has been a long-standing problem for all-solid-state batteries. Traditional densification techniques used in Li-ion battery production—such as hot-rolling and uniaxial pressing—produce a non-uniform pressure field and therefore non-uniform closure of porosity in the solid electrolyte. In contrast, modern equipment designed specifically for solid-state batteries, such as warm isostatic pressing, applies a nearly uniform pressure throughout the solid electrolyte, leading to more homogeneous densification and, as a consequence, reduced bulk and grain boundary resistivity.

To better understand degradation mechanisms at the interfaces and within materials, advanced nanoscale imaging techniques are often employed. …

Solid-state batteries offer the potential for significantly higher energy densities compared to traditional lithium-ion batteries. This is largely due to the use of lithium metal anodes, which have a much higher charge capacity than the graphite anodes used in lithium-ion batteries. At a cell level, lithium-ion energy densities are generally below 300Wh/kg while solid-state battery energy densities are able to exceed 350 Wh/kg. This energy density boost is especially beneficial for applications requiring longer-lasting and more compact batteries such as electric vehicles.

One significant advantage of solid-state batteries is their improved safety profile. Solid electrolytes greatly reduce the risk of thermal runaway—a primary cause of battery fires. Because most solid electrolytes are nonflammable, solid-state batteries have a much lower fire risk and do not require as many safety systems, which can further increase energy density at the cell pack level. Studies have shown that heat generation during thermal runaway is only about 20-30% of what is observed in conventional batteries with liquid electrolytes.

Solid electrolytes enable a broader range of operating temperatures and voltages, which is crucial for high performance applications. SSBs can operate at temperatures above 60 °C, where traditional are generally only able to operate from -20 to 60 °C.

Solid state batteries also support high-voltage cathode chemistries such as lithium nickel manganese oxide, lithium nickel phosphate, and lithium cobalt phosphate. This allows voltages to potentially exceed 5 V (vs. a Li/Li reference electrode) while traditional cathode chemistries in lithium-ion batteries are unable to exceed 4.5V (vs. a Li/Li reference electrode).

The solid electrolyte and lithium metal anode combination enables faster ion transfer, which can reduce charging times compared to lithium-ion batteries. Furthermore, bipolar stacking of cells can be incorporated, allowing for reduced cell size and more compact battery packs. This allows for improved overall energy efficiency and enables design flexibility for various applications.

Solid electrolyte stability reduces the rate at which solid-state batteries discharge when being stored.