Reviewing electrochemical stability of ionic liquids-/deep eutectic solvents-based electrolytes in lithium-ion, lithium-metal and post-lithium-ion batteries for green and safe energy

Sustainable energy is the key issue for the environment protection, human activity and economic development. Ionic liquids (ILs) and deep eutectic solvents (DESs) are dogmatically regarded as green and sustainable electrolytes in lithium-ion, lithium-metal (e.g., lithium-sulphur, lithium-oxygen) and post-lithium-ion (e.g., sodium-ion, magnesium-ion, and aluminum-ion) batteries. High electrochemical stability of ILs/DESs is one of the prerequisites for green, sustainable and safe energy; while easy electrochemical decomposition of ILs/DESs would be contradictory to the concept of green chemistry by adding the cost, releasing volatile/hazardous by-products and hindering the recyclability. However, (1) are ILs/DESs-based electrolytes really electrochemically stable when they are not used in batteries? (2) are ILs/DESs-based electrolytes really electrochemically stable in real batteries? (3) how to design ILs/DESs-based electrolytes with high electrochemical stability for batteries to achieve sustainability and green development? Up to now, there is no summary on this topic, to the best of our knowledge. Here, we review the effect of chemical structure and non-structural factors on the electrochemical stability of ILs/DESs in simulated conditions. More importantly, electrochemical stability of ILs/DESs in real lithium-ion, lithium-metal and post-lithium-ion batteries is concluded and compared. Finally, the strategies to improve the electrochemical stability of ILs/DESs in lithium-ion, lithium-metal and post-lithium-ion batteries are proposed. This review would provide a guide to design ILs/DESs with high electrochemical stability for lithium-ion, lithium-metal and post-lithium-ion batteries to achieve sustainable and green energy.