Salt water battery
In 2008 Carnegie Mellon professor Jay Whitacre founded Aquion Energy and received venture funding from Kleiner Perkins Caufield and Byers. He won the 2015 Lemelson–MIT Prize, an award worth $500,000, for inventing the company's salt water battery. They are the first and only battery manufacturer to have met all the stringent criteria to obtain Cradle-to-Cradle (Bronze) certification. The company raised $190 million in equity and debt before going bankrupt in 2017, then being acquired by a Chinese company later that year for slightly under $10 million.
Aquion Energy's batteries are classified as standard goods with no special handling required in shipment. It has no life-reducing side reactions while not in use. It is robust to any variable cycling profiles and long duration intervals while partially charged. Maintenance cycling to maintain performance/life is unnecessary. Its optimal operating temperature range is -5 °C to 40 °C and are little affected by operational temperature swings. It operates without auxiliary loads or an external power supply. Its chemistry is not susceptible to thermal runaway. Active thermal management is generally not required, except given extreme ambient temperature. Its mechanical materials can be recycled in normal recycling streams. Chemical materials can be disposed of without special equipment or containers.
Water in salt
A different design used an electrolyte that has a salt to water ratio of six to one, nearly saturated, such that it could also be called a water in salt battery.
In November 2015, researchers from the University of Maryland and the Army Research Laboratory claimed that they had induced the cell to form a Solid-electrolyte interphase (SEI), a first for an aqueous electrolyte. The SEI allows the aqueous lithium-ion battery to operate at higher voltages and self-discharge more slowly. The high salt concentration allows the interphase to form. It raised the maximum voltage for such a battery from 1.23 V to around 3 V. At 2.4V, the battery's specific energy was approximately 100 watt-hour/kg and it displayed consistent performance over 1,000 charge/discharge cycles. The device operated with nearly 100% coulombic efficiency at both low (0.15 C) and high (4.5 C) discharge and charge rates.
In May 2019, researchers published an article where the voltage increased to 4.2 volts. High specific capacity from a densely packed stage-I graphite intercalation compound of C3.5[Br0.5Cl0.5] can form reversibly in water-in-bisalt electrolyte. By coupling this cathode with a passivated graphite anode, a cell can achieve an energy density of 460 watt-hours per kilogram of total composite electrode and about 100 per cent coulombic efficiency.
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