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. A solid state battery shown at 2020's Consumer Electronics Show suggested an overall energy density 29% to 56% higher than current lithium-ion batteries in use in electric vehicles at the time.
One challenge to the widespread use of solid-state batteries is the buildup of dendrites. Dendrites are branching networks of lithium which grow through the solid, ceramic electrolyte during charging of the battery, causing a short circuit. The dendrites build during the charging and discharging of the solid-state battery when voids are created at the anode of solid-state cells.
Solid electrolyte candidate materials include ceramics, glass and sulfides. The cathodes are lithium based with variants including LiCoO2, LiNi1/3Co1/3Mn1/3O2, LiMn2O4, and LiNi0.8Co0.15Al0.05O2. Anode materials vary more and are affected by the type of electrolyte.
Michael Faraday discovered the solid electrolytes silver sulfide and lead(II) flouride between 1831 and 1834 and laid the foundation for solid-state ionics. In the late 1950s several electrochemical systems employed solid electrolytes using a silver ion, but with low energy density and cell voltages and high internal resistance. It was not until the 1990's that Oak Ridge National Laboratory created a new class of solid-state electrolyte which developed into thin film lithium-ion batteries.
In 2011, French transportation company Bolloré launched BlueCar with a 30kWh lithium metal polymer batter and a polymeric electrolyte created by dissolving a lithium salt in a co-polymer. In 2013, researchers at the University of Colorado Boulder developed a solid-state lithium battery with a solid composite cathode based on iron-sulfur that promised higher energy capacity.
Researchers at Sakti3 announced a solid-state lithium-ion battery in 2014. They claimed their battery had higher energy density for lower cost and in 2015 Sakti3 was acquired by Dyson who planned at the time to develop an electric vehicle using solid-state battery technology.
In 2017, John Goodenough, one of the inventors of the lithium-ion battery, announced a solid-state battery using a glass electrolyte and an alkali-metal anode consisting of lithium, sodium or potassium.
In February of 2020, researchers out of the Massachusetts Institute of Technology announced a new solid-state battery architecture aimed at solving the problem of voids and dendrites in solid state lithium batteries. The architecture involves a combination of mixed ionic-electronic conductors and electron and lithium-ion insulators built into a honeycomb-shaped architecture. The tubes are then infused with solid lithium metal to form the battery's anode. Spare room is built into each of these tubes, allowing the lithium metal to expand and shrink during charging and discharging.
The advantages of solid-state batteries for electric vehicles, if production cost could be reduced, would be greater driving range, lighter battery packs, and greater stability. The stability would mean electric automakers would be able to reduce the cooling they have in place for current lithium-ion batteries, which can become unstable at higher heat and explode.
Toyota announced in 2014 their development efforts for a solid-state battery to power their electric vehicles, for which they hold the most related patents. They expect to implement the solid-state technology in 2020, and aim to increase the current solid-state batteries energy density, around 400 watts-hour per liter, to between 600 and 700 watt-hour per liter by 2025. They also announced a deepening of their partnership with Panasonic which includes a collaboration on solid-state batteries.
Other automakers following Toyota include BMW, Honda, Hyundai Motor Company, Nissan, Volkswagen and Mercedes-Benz.
Companies involved in the research, development and manufacturing of solid-state batteries include CATL, Tesla, Nissan, SolidEnergy Systems, BMW, Samsung Electronics, Fisker Automotive, A123 Systems, Toyota, Volkswagen, Honda, Applied Materials, Toshiba, Panasonic, Hitachi, Enphase Energy, Johnson Controls, Bollore, Solvay, Albemarle Corporation, QuantumScape, Dyson, STMicroelectronics, TDK, Mercedes-Benz, Energizer, Seeo, Sakti3, LG Chem, BYD Electronics, Infinite Power Solutions, NGK, Solid Power and BrightVolt.
The anode in today's lithium batteries is made from a mix of copper and graphite, but if it were made of pure lithium instead, it could break the "energy-density bottleneck of current Li-ion chemistry," according to a recent study published in Trends in Chemistry.
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