Solid-state battery

A solid-state battery is a battery technology that uses solid electrodes and a solid electrolyte, instead of the liquid or polymer gel electrolytes found in lithium-ion or lithium polymer batteries. Materials proposed for use as solid electrolytes in solid-state batteries include ceramics (e.g. oxides, sulfides, phosphates), and solid polymers. Solid-state batteries have found use in pacemakers, RFID and wearable devices. They are potentially safer, with higher energy densities, but at a much higher cost.

Challenges to widespread adoption include energy and power density, durability, material costs, sensitivity and stability.

History
Between 1831 and 1834, Michael Faraday discovered the solid electrolytes silver sulfide and lead(II) fluoride, which laid the foundation for solid-state ionics.

In the late 1950s, several electrochemical systems employed solid electrolytes. They used a silver ion, but had low energy density and cell voltages, and high internal resistance. A new class of solid-state electrolyte, developed by the Oak Ridge National Laboratory in the 1990s, was used to make thin film lithium-ion batteries.

In 2011, Bolloré launched BlueCar with a 30kWh lithium metal polymer (LMP) battery with a polymeric electrolyte created by dissolving a lithium salt in a co-polymer (polyoxyethylene).

In 2012, Toyota began experimental research in solid-state batteries.

In 2013, researchers at University of Colorado Boulder announced the development of a solid-state lithium battery, with a solid composite cathode based upon an iron-sulfur chemistry that promised higher energy capacity.

In 2014, researchers at Sakti3 announced a solid-state lithium-ion battery, claiming higher energy density for lower cost, and in 2015, Sakti3 was acquired by Dyson.

In 2017, John Goodenough, the co-inventor of Li-ion batteries, unveiled a solid-state battery, using a glass electrolyte and an alkali-metal anode consisting of lithium, sodium or potassium. Toyota announced the deepening of its decades-long partnership with Panasonic, including a collaboration on solid-state batteries. Toyota also holds the most SSB-related patents. Other car makers developing solid-state battery technologies include BMW, Honda, Hyundai Motor Company and Nissan. Household appliance maker Dyson announced and then abandoned a plan to build an electric car. Fisker Inc. claimed that its solid-state battery technology would be ready for "automotive-grade production" in 2023. Spark plug maker NGK is developing ceramic-based solid state batteries.

In 2018, Solid Power, spun off from CU Boulder research, received $20 million in funding for a small manufacturing line to produce all-solid-state, rechargeable lithium-metal batteries, with a predicted 10 megawatt hours of capacity per year. Volkswagen announced a $100 million investment in QuantumScape, a solid-state battery startup that spun out of Stanford. Chinese company Qing Tao started a production line of solid-state batteries.

In 2021, Toyota will unveil a prototype electric vehicle powered by solid-state batteries, with further plans to be the first automaker to sell an electric vehicle with solid state batteries.

Materials
Solid-state electrolytes candidate materials include ceramics such as lithium orthosilicate, glass and sulfides. 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, GexSi1−x, SnO–B2O3, SnS –P2S5, Li2FeS2, FeS, NiP2, and Li2SiS3.

One promising cathode material is Li-S, which (as part of a solid lithium anode/Li2S cell) has a theoretical specific capacity of 1670 mAh g−1, "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. Recently, a ceramic textile was developed that showed promise in a LI-S solid state battery. This textile facilitated ion transmission while also handling sulfur loading, although it did not reach the projected energy density. The result "with a 500-μm-thick electrolyte support and 63% utilization of electrolyte area" was "71 Wh/kg." while the projected energy density was 500 Wh/kg.

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".

Uses
Solid-state batteries have found potential use in pacemakers, RFID and wearable devices.

Electric vehicles
Hybrid and plug-in electric cars use a variety of battery technologies, including Li-ion, Nickel–metal hydride (NiMH), Lead–acid, and electric double-layer capacitor (or ultracapacitor), led by Li-ion.

Cost
Solid-state batteries are traditionally expensive to make and employs manufacturing processes thought to be difficult to scale, requiring expensive vacuum deposition equipment. 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 800 to 1,000 of such cells. Cost has impeded the adoption of solid-state batteries in other areas, such as smartphones.

Temperature and pressure sensitivity
Low temperature operations may be challenging. Solid-state batteries historically 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.

Dendrites
Solid lithium (Li) metal anodes in solid-state batteries are replacement candidates in lithium-ion batteries for higher energy densities, safety, and faster recharging times. Such anodes tend to suffer from the formation and the growth of Li dendrites.

Dendrites penetrate the separator between the anode and the cathode causing short circuits. This causes overheating, which may result in fire and maybe even explosion from thermal runaway. Li dendrites reduce coulombic efficiency.

Dendrites commonly form during electrodeposition during charge and discharge. Li ions in combine with electrons at the anode surface as the battery charges - forming a layer of lithium metal. Ideally, the lithium deposition occurs evenly on the anode. However, if the growth is uneven, dendrites form.

Stable solid electrolyte interphase (SEI) was found to be the most effective strategy for inhibiting dendrite growth and increasing cycling performance. solid-state electrolytes (SSEs) may prevent dendrite growth, although this remains speculative. A 2018 study identified nanoporous ceramic separators that block Li dendrite growth up to critical current densities.

Advantages
Solid-state battery technology is believed to deliver higher energy density (2.5x), by enabling lithium metal anodes.

They may avoid the use of dangerous or toxic materials found in commercial batteries, such as organic electrolytes.

Because most liquid electrolytes are flammable and solid electrolytes are nonflammable, solid-state batteries are believed to have lower risk of catching fire. Fewer safety systems are needed, further increasing energy density. Recent studies show that heat generation inside is only ~20-30% of conventional batteries with liquid electrolyte under thermal runaway.

Solid-state battery technology is believed to allow for faster charging. Higher voltage and longer cycle life is also possible.