Renewable generation, such as solar and wind, is intermittent, which causes sudden and unanticipated changes to power output and contributes to electricity grid instability. The stability and reliability of electricity grids requires a continuous balance between energy supply and demand. The aqueous lithium-ion battery (LIB) may solve both 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 including lead-acid and nickel-metal hydride systems. Aqueous LIBs have been demonstrated to be one of the most promising stationary power sources for the sustainable energy such as wind and solar power.

As early as in 2005, we developed a new concept hybrid electrochemical supercapacitor in which a Li-ion intercalated compound was used as a positive electrode in combination with an activated carbon negative electrode in a Li₂SO₄ aqueous electrolyte (ZL. 200510025269.6). A hybrid cell consisting of a spinel LiMn₂O₄ positive and an AC negative electrode shows excellent reversibility with a sloping voltage profile from 0.8 to 1.8 V at an average voltage near 1.3 V, and delivers an 8 Wh/kg of 60000 F practical cell. In order to improve the specific energy, we employed LiTi₂(PO₄)₃, but the cell shows poorer cycling stability compared with the pure AC anode. We found that, in the presence of oxygen, the discharged state of lithium-ion intercalated compounds (LIC) of all negative electrode materials will react with water and O₂ despite of the pH value of the electrolyte, which is mainly responsible for the capacity fading of aqueous lithium-ion batteries during charge/discharge cycling. By eliminating the O₂ (using a sealed cell), adjusting the pH values of the electrolyte, and using carbon-coated electrode materials; the LIB shows much cycling stability. A commercialized hybrid LIB shows a specific energy of ca. 30 Wh/kg, and exhibits a good cycling stability over 3500 cycles. In 2005, we also for the first time employed carbon coating technology to improve the electrode performance of Li₄Ti₅O_4. By optimizing the graphitization and the coated carbon layer thickness, the nano-thickness carbon layer coated LTO shows excellent rate capability and less gas generation during cycling and storage. A LMO/LTO Li-ion battery show excellent cycling stability, high power and safety as stationary power source for smart-grid systems.

References:

1. Xia et al., TiP₂O₇ and Expanded Graphite Nanocomposite as Anode Material for Aqueous Lithium-Ion Batteries. ACS Appl. Mater. Interfaces, 9, 8075-8082 (2017).
2. Xia et al., Raising the Cycling Stability of Aqueous Lithium-Ion Batteries by Eliminating O₂ in the Electrolyte ”, Nat. Chem., 2, 760-765 (2010).
3. Xia et al., Hybrid aqueous energy storage cells using activated carbon and lithium-intercalated compounds I. The C/LiMn₂O₄ system, Electrochem. Soc., 153(2): A450-A454 (2006).