The available capacity of Mg hybrid batteries is closely related to the number of charge carriers within electrolyte solutions. Therefore, in this study, a dual-salt composition capable of supplying high Li+ concentration was prepared. A dual-salt electrolyte consisting of a LiAlCl4 complex (LACC) and LiN­(SO2CF3)2 (LiTFSI) was found to be an excellent candidate, providing 2.2 M Li+ concentration along with anodic stability up to 3 V (vs Mg/Mg2+). However, the LACC moiety of the above composition first had to undergo a two-step modification procedure comprising “Mg powder treatment” and “conditioning process” to properly implement Mg deposition and stripping at the Mg anode. Spontaneous substitutions of oxidation states between the anionic Al3+ complex and metallic Mg induced by these processes resulted in the generation of Mg2+ complex species within the LACC solutions. The modified LACC was compatible even with 2 M of LiTFSI, the concentration with which we achieved 150 mA h g–1 capacity of a FePO4 cathode at 1.5 mg cm–2 loading density, when using an electrolyte volume of only 25.5 μL cm–2.

Lithium aluminum chloride complexes (LACCs) are excellent electrolyte candidates for Mg−Li hybrid batteries (MgHBs) because they can simultaneously conduct electrochemical reactions both at Mg anodes and Li +insertion cathodes. However, to ensure compatibility with Mg anodes, LACCs must first undergo a cumbersome conditioning process; this severely lowers their productivity and limits any improvement in the electrolyte performance. To resolve this issue, we employed a conditioning-free process for the facile modification of LACCs. The conditioning-free process was conducted by reacting LACCs and metallic Mg powder with a small amount of CrCl 3 that promotes the rapid and high-degree substitution of oxidation states between anionic Al 3+ complexes and Mg. The newly generated Mg 2+ ions in the conditioning-free LACC (cf-LACC) reached a high concentration of up to 1.2 M and formed anionic complexes that function as charge carriers for Mg anodes. Moreover, the cf-LACC electrolyte successfully demonstrated its applicability to the MgHB system, which used a high voltage cathode material LiFePO 4 , by exhibiting excellent rate capability and cyclability.