An Organic‐Aqueous Miscible Electrolyte Enables High‐Voltage Magnesium Batteries With Outstanding Cycling Stability

Magnesium batteries offer a safe, high‐energy density, and cost‐effective alternative to lithium‐ion systems, recognized by Europe and the US, but are hindered in aqueous media by the narrow electrochemical window and interfacial instability. Here, we develop an organic–aqueous miscible electrolyte, SEU‐01, containing water, ethylene glycol (EG), and lactobionic acid (LBA). EG participates in the solvation structure and expands the electrochemical window, while LBA further regulates the solvation shell and enhances Mg 2+ desolvation kinetics. Their synergy forms a stable solid‐electrolyte interphase (SEI) and induces uniform Mg deposition, thus enabling efficient and stable Mg cycling. So, Mg//Mg symmetric batteries cycle for more than 400 h (0.1 mA cm −2 , 0.1 mAh cm −2 ), and the full battery with CuHCF shows a well‐maintained discharge platform at 1.9 V and long life (1000 cycles at 1 A g −1 ). These findings offer a viable pathway for the development of next‐generation magnesium batteries and related electrochemical devices.