Aqueous lithium-ion batteries may solve the safety problem associated with lithium-ion batteries that use highly toxic and flammable organic solvents, and the poor cycling life associated with commercialized aqueous rechargeable batteries such as lead-acid and nickel-metal hydride systems. But all reported aqueous lithium-ion battery systems have shown poor stability: the capacity retention is typically less than 50% after 100 cycles. Here, the stability of electrode materials in an aqueous electrolyte was extensively analysed. The negative electrodes of aqueous lithium-ion batteries in a discharged state can react with water and oxygen, resulting in capacity fading upon cycling. By eliminating oxygen, adjusting the pH values of the electrolyte and using carbon-coated electrode materials, LiTi(2)(PO(4))(3)/Li(2)SO(4)/LiFePO(4) aqueous lithium-ion batteries exhibited excellent stability with capacity retention over 90% after 1,000 cycles when being fully charged/discharged in 10 minutes and 85% after 50 cycles even at a very low current rate of 8 hours for a full charge/discharge offering an energy storage system with high safety, low cost, long cycling life and appropriate energy density.

Based on a systematic investigation on aprotic Li-CO 2 electrochemistry, we design a flexible strategy for either CO 2 fixation or energy storage. Typically, CO 2 can be fixed into carbon species through a rechargeable/irreversible electrochemical process. Moreover, using a specific catalyst, the aprotic Li-CO 2 battery system can be realized via a reversible cycle. The proof of concept revealed in this study provides strong theoretical support for the practical design of both CO 2 fixation techniques and renewable energy storage devices.

The application of Ru nanoparticles as a cathode catalyst significantly promotes the reversibility of Li–CO2 batteries.