Photo: DICP
Aqueous batteries are much safer than traditional Li-ion cells but generally have a lower energy density. However, a team of researchers in China invented a new water-based battery that is almost twice as energy-dense as traditional Li-ion cells.
Advances in lithium-ion batteries have allowed carmakers to offer competitive electric vehicles. Although electric vehicles are more than a century old, it wasn't until Tesla used Li-ion cells in the Roadster that they became a viable alternative to combustion cars. Li-ion batteries have become ubiquitous, powering almost everything that works on electricity, thanks to their high energy density and relatively affordable prices.
However, current Li-ion cells use flammable electrolytes, which makes them extremely dangerous when they overheat or catch fire. Because these organic electrolytes generate their own oxygen during a thermal runaway reaction, a Li-ion battery fire is very difficult to extinguish. For this reason, scientists have been working hard to find better alternatives to lithium-ion batteries currently used in electric vehicles and other mobile devices.
Among the lesser-known battery types that researchers think can replace traditional Li-ion cells are those that use water as a solvent for electrolytes. These are inherently safe since water is not flammable but have a lower energy density due to the limited solubility of the electrolyte and low battery voltage. However, Chinese researchers discovered a way to improve electron transfer and boost energy density.
A research group from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) developed a multi-electron transfer cathode based on bromine and iodine. Their study proved that this type of cathode can achieve a specific capacity of more than 840 Ah/L and an energy density of up to 1,200 Wh/L. Researchers used a mixed halogen solution of iodide ions (I-) and bromide ions (Br-) as the electrolyte to improve the energy density. This leads to a multi-electron transfer reaction, transferring I- to iodine element (I2) and then to iodate (IO3-).
During the charging process, iodide ions (I-) were oxidized to iodate (IO3-) on the positive side, and the generated hydrogen cations (H+) were conducted to the negative side in the form of a supporting electrolyte. Hydrogen cations were conducted from the positive side during the discharge process, and iodate was reduced to iodide ions. According to the researchers, the bromide ions (Br-) added to the electrolyte could generate polar iodine bromide (IBr) during the charging process, facilitating the reaction with H2O to form iodate.
The bromide intermediate formed during the charge and discharge process optimized the reaction process, effectively improving the kinetic and reversibility of the electrochemical reaction. When the researchers tested their aqueous electrolyte with a vanadium anode, they discovered that the resulting battery was impressively stable, exceeding 1,000 cycles. The energy density is higher than that of some solid electrolyte materials, while costs are comparable to those of traditional Li-ion batteries.
However, current Li-ion cells use flammable electrolytes, which makes them extremely dangerous when they overheat or catch fire. Because these organic electrolytes generate their own oxygen during a thermal runaway reaction, a Li-ion battery fire is very difficult to extinguish. For this reason, scientists have been working hard to find better alternatives to lithium-ion batteries currently used in electric vehicles and other mobile devices.
Among the lesser-known battery types that researchers think can replace traditional Li-ion cells are those that use water as a solvent for electrolytes. These are inherently safe since water is not flammable but have a lower energy density due to the limited solubility of the electrolyte and low battery voltage. However, Chinese researchers discovered a way to improve electron transfer and boost energy density.
A research group from the Dalian Institute of Chemical Physics (DICP) of the Chinese Academy of Sciences (CAS) developed a multi-electron transfer cathode based on bromine and iodine. Their study proved that this type of cathode can achieve a specific capacity of more than 840 Ah/L and an energy density of up to 1,200 Wh/L. Researchers used a mixed halogen solution of iodide ions (I-) and bromide ions (Br-) as the electrolyte to improve the energy density. This leads to a multi-electron transfer reaction, transferring I- to iodine element (I2) and then to iodate (IO3-).
During the charging process, iodide ions (I-) were oxidized to iodate (IO3-) on the positive side, and the generated hydrogen cations (H+) were conducted to the negative side in the form of a supporting electrolyte. Hydrogen cations were conducted from the positive side during the discharge process, and iodate was reduced to iodide ions. According to the researchers, the bromide ions (Br-) added to the electrolyte could generate polar iodine bromide (IBr) during the charging process, facilitating the reaction with H2O to form iodate.
The bromide intermediate formed during the charge and discharge process optimized the reaction process, effectively improving the kinetic and reversibility of the electrochemical reaction. When the researchers tested their aqueous electrolyte with a vanadium anode, they discovered that the resulting battery was impressively stable, exceeding 1,000 cycles. The energy density is higher than that of some solid electrolyte materials, while costs are comparable to those of traditional Li-ion batteries.
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