Natural Activation of CuO to CuCl₂ as a Cathode Material for Dual-Ion Lithium Metal Batteries

To meet the rising energy demand for rapidly advancing battery-driven devices, a novel Li/Cl dual-ion battery chemistry based on non-flammable SO₂-in-salt electrolyte is receiving significant attention. Herein, we propose a natural-activable CuO hollow nanocube (HNC) cathode material for dual-ion Li metal batteries using SO₂-in-salt electrolyte. Natural activation is achieved via spontaneous chlorination of CuO HNCs into an electrochemically active CuCl₂ phase upon immersed in a SO₂-in-salt electrolyte. The on-site conversion reactions are proposed with the support of thermodynamic calculations; the phase transformations of active materials are confirmed through X-ray diffraction, X-ray photoelectron spectroscopy, and field emission scanning electron microscopy. As a solution to alleviate the volume expansion after chlorination, the HNC structure of CuO allows the resulting CuCl₂ cathode material to deliver a reversible capacity up to 262.2 mAh g⁻¹ (894.2 Wh kg_CuO⁻¹) with stable cycle performance over 150 cycles. The Li-CuO battery system presented here demonstrates the feasibility of non-flammable, high-energy density Li/Cl dual-ion Li metal batteries as a potential alternative to currently used lithium ion batteries.