In-situ-interface-engineered mechanically robust solid polymer electrolyte for carbon fiber reinforced structural battery composites

Carbon fiber structural battery composites (SBCs), which integrate energy storage and load-bearing functions, hold significant promise for vehicle weight reduction. This work developed strategies based on interfacial engineering to design and construct a deep eutectic polymer electrolyte (EP) at the electrode/glass fiber reinforced composite polymer electrolyte (GF-CPE) interface, which effectively enhances ionic conductivity of GF-CPE and improves the stability of the electrode/electrolyte interface. Therefore, the mechanically robust EP/GF-CPE (Young's modulus of 1.5 GPa) achieved an ionic conductivity of 0.41 mS cm⁻¹ with a high ion transference number (0.77). The Li//EP/GF-CPE//Li symmetric cell also demonstrated stable cycling performance for 1500 h at 0.5 mA cm⁻². Furthermore, the in-situ interfacial engineered EP/GF-CPE enabled carbon fiber LiFePO₄//EP/GF-CPE//Li SBCs to attain a high energy density of 466.8 Wh kg⁻¹ based on active materials and 28.0 Wh kg⁻¹ based on the mass of whole device. Regarding cyclic durability, the structural battery preserves 90.5 % of its capacity after undergoing 1000 cycles. It concurrently demonstrates mechanical robustness with a flexural strength value of 348.6 MPa and a flexural modulus of 29.7 GPa. Comprehensive in-situ electrochemical-mechanical testing offers confirmatory evidence of the structural battery's capacity to preserve electrochemical functionality and structural integrity when subjected to diverse mechanical loading scenarios. A prototype solar storage charging integrated system powering a boat model further showcased the multifunctionality of the structural batteries. This work highlights that interfacial engineering is a feasible and effective strategy for developing high-performance multifunctional carbon fiber structural batteries.