Researchers at Mie University in Japan have developed a new protected lithium electrode for aqueous lithium/air rechargeable batteries. Lead researcher Nobuyuki Imanishi said that the system has a practical energy density of more than 300 Wh/kg, about twice that of many commercial lithium-ion batteries. They presented their work at the 247th National Meeting & Exposition of the American Chemical Society (ACS) in Dallas.
Lithium/air rechargeable batteries are attracting great attention, because of a possibility to achieve energy density which is comparable to combustion engines. Most of the studies recently reported focus on the non-aqueous system in which the reaction product Li2O2 is deposited at the surface of the air electrode. In the aqueous Li-air system, the reaction product (LiOH•H2O) is soluble into the electrolyte solution.
A key challenge of the aqueous system is the low output power of the protected lithium electrode. In 2004, a research team developed a composite lithium anode with a three-layered structure to overcome this problem. The Mie team used this approach, and adopted a lamination of NASICON-type lithium conducting solid electrolyte (LATP) and PEO-based polymer electrolyte as the protective layers which cover and isolate lithium metal from contacting directly with aqueous electrolytes.
The researchers also used ether-oligomer electrolyte additives, e.g., tetraethylene glycol dimethyl ether (TEGDME) to PEO18LiTFSI. The electrode/electrolyte interface resistance was decreased and maximum current density of 4 mA cm-2 can be applied. A Li/PEO18LiTFSI- 2TEGDME/LATP/saturated LiCl aqueous solution/Pt, air cell showed stable cyclability up to 100 cycles at 2.0 mAh cm-2 of capacity.