A Deep Eutectic Solvent Electrolyte Enables Planar Cu Deposition and High‐Temperature Cu–MnO ₂ Battery

Cu anodes exhibit a higher theoretical specific capacity (843 mAh g^-1 or 7558 mAh cm^-3) than Zn anodes (820 mAh g^-1 or 5855 mAh cm^-3), and have garnered widespread attention. However, aqueous Cu-ion batteries suffer from severe Cu dendrite growth, limited cycle life, and poor high-temperature performance. To the best of our knowledge, this is the first time that a deep eutectic solvent (DES) electrolyte is proposed to address these issues. Fourier transform infrared spectroscopy and molecular dynamics simulations confirm that the DES electrolyte coordinates with Cu²⁺, thereby modulating the Cu deposition behavior. Consequently, planar deposition and extended cycle life (6000 h versus 730 h) are achieved. Furthermore, the DES electrolyte exhibits the promising application potential under harsh conditions. A high-temperature Cu─MnO₂ full cell retains a capacity of 174.8 mAh g^-1 after 300 cycles at 2 A g^-1 under 50 °C.