A cost-effective water-in-salt electrolyte enables highly stable operation of a 2.15-V aqueous lithium-ion battery

Abstract

Extensive efforts are currently underway to develop safe and cost-effective electrolytes for large-scale energy storage. In this regard, water-based electrolytes may be an attractive option, but their narrow electrochemical stability window hinders their realization. Although highly concentrated fluorinated electrolytes have been shown to be highly effective in suppression of water splitting, enabling significant widening of the applied potential range, they utilize expensive salts (e.g., lithium bis(trifluoromethane sulfonyl) imide [LiTFSI] or lithium trifluoromethane sulfonate [LiOTf]); hence, they cannot be considered for practical applications. Here, we demonstrate a cost-effective aqueous electrolyte solution combining 14 M LiCl and 4 M CsCl that allows stable operation of a 2.15-V battery comprising a TiO 2 anode and LiMn 2 O 4 cathode. Addition of CsCl to the electrolyte plays a double role in system stabilization: the added chloride anions interact with the free water molecules, whereas the chaotropic cesium cations adsorb at the electrified interface, preventing hydrogen formation. Mixed aqueous LiCl + CsCl electrolyte solution enables widely stable electrochemical window Cl − anions interact with the free H 2 O molecules and reduce their bulk activity The added chaotropic Cs + cations adsorb on the anode interface and prevent H 2 generation Long-term stable 2.15-V cell comprising TiO 2 anode and LiMn 2 O 4 cathode demonstrated The need for safe and cost-effective energy storage systems has advanced the development of aqueous batteries. Looking for a cost-effective electrolyte solution, Turgeman et al. propose saturated LiCl + 4 M CsCl. It is found that addition of CsCl significantly improves electrolyte stability and enables stable operation of a 2.15-V battery.