Chemical Bonding Interface Enables Lithium Batteries to Operate Under Near-Vacuum Conditions

The reliance on high stack pressure in lithium metal batteries (LMBs) conflicts with the requirements of lightweight design and low-pressure operating environments, motivating the development of pressure-independent battery designs. Here, a chemical bonding interfacial prototype is proposed to substitute the physical contact interface, thereby liberating LMBs from high stacking pressures. This chemical bonding interface is constructed via strong interactions between the carbonyl groups of poly(ε-caprolactone) segments and Li metal, manifesting as Li─O bonding interfaces. Benefiting from Li─O bonding, the PPE electrolyte exhibits a high adhesion energy of 22.44 J m⁻² and a high lap shear strength of 0.31 MPa, sustaining intimate electrode–electrolyte contact without external stack pressure. In addition, the Li─O bonding interface significantly reduces the thickness of the electric double layer, achieving a 120% increase in capacitance (0.20 µF cm⁻²), thus promoting efficient transport (t_Li+ = 0.7) and uniform deposition of Li⁺. As a result, the Li||Cu half-cell equipped with PPE electrolyte achieves a superior coulombic efficiency of 99.78%. A pouch cell equipped with PPE electrolyte and NCM cathode demonstrates high capacity retention of 90.12% after 40 cycles at −0.1 MPa (relative to standard atmospheric pressure). This discovery offers novel insights into material and structural design for pressure-insensitive batteries intended for high-altitude aerospace applications.