The Chinese University of Hong Kong Has Developed a Molecular Crowding Electrolyte For High-voltage Aqueous Batteries

 Recently,  Yijun Lu and others from the Chinese University of Hong Kong  have developed a molecular crowding electrolyte with a wide voltage window, which is conducive to the realization of a safe, high energy density, sustainable development of lithium ion batteries. Related results were published in the recent "Nature Materials" journal.

In the research of water-based lithium-ion batteries, the use of high-salt-concentration water electrolytes, namely "water-in-salt electrolyte" (WiSE), is considered to be an effective method to extend the voltage window of water-based lithium-ion batteries, but this method is costly and causes People have paid attention to the toxicity of water-based batteries. In view of this, the researchers have inspired by "molecular crowding" and designed this new type of water-based electrolyte.

Molecular crowding is a common phenomenon in living cells where water activity is substantially suppressed by molecular crowding agents through altering the hydrogen-bonding structure.

The researchers used water-miscible polymer polyethylene glycol as a crowding agent to reduce the activity of water molecules. When the solvent contained a low content (2 mol kg-1) of bis(trifluoromethane)sulfonimide lithium salt (LiTFSi), it can completely inhibit the decomposition of water, thereby achieving a wider electrolyte working range (3.2 V)

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The researchers assembled an aqueous full-cell Li₄Ti₅O₁₂/LiMn₂O₄ based on this aqueous electrolyte, using LiMn₂O₄ as the positive electrode and Li₄Ti₅O₁₂ as the negative electrode, and tested their reversible electrochemical behavior using CV. The results of on-line electrochemical mass spectrometry indicate that the molecularly crowded aqueous electrolyte avoids the decomposition of water in the L-LTO/LMO full battery. The full battery charge-discharge curve and electrochemical stability test show that the full battery can achieve an initial energy density of 110 Wh·kg^-1 at a rate of 1C and maintain an energy density of 75 Wh·kg-1 after 300 cycles, and It can maintain high Coulomb efficiency during charging and discharging.

This research provides ideas for designing a low-cost, environmentally friendly, and wide-voltage window aqueous electrolyte.

References: Jing Xie, Zhuojian Liang, Yi-Chun Lu, Molecular crowding electrolytes for high-voltage aqueous batteries, Nature Materials, DOI: 10.1038/s41563-020-0667-y