Unstructured Self-Assembled Molecular Lamella Induces Ultrafast Thermal Transfer through a Cathode/Separator Interphase in Lithium-Ion Batteries

Thermal issues associated with lithium-ion batteries (LIBs) can dramatically affect their life cycle and overall performance. However, the effective heat transfer is deeply restrained by the high thermal resistance across the cathode (lithium cobalt oxide, LCO)-separator (polyethylene, PE) interface. This work presents a new approach to tailoring the interfacial thermal resistance, namely, unstructured self-assembled lamella (USAL). Compared to the popular self-assembled monolayers, although the USAL gives a redundant interface and amorphous molecule patterns, it can also provide many benefits, including easy assembly, more thermal bridges, and ready pressurization. Three small organic molecules (SOMs) were assembled into an LCO-PE interface, providing unique functional groups, -NH2, -SH, and -CH3, to illustrate its energy conversion efficiency. Through molecular dynamics simulations, our results show that the USAL can facilitate interfacial heat transfer remarkably. A 3-aminopropyl trimethoxysilane (APTMS)-coated LCO-PE system with 11.4 Å thickness demonstrates the maximum enhancement of thermal conductance, about 320% of the pristine system. Such enhancement is attributed to the developed double heat passages by strong non-bonded interactions across LCO-SOM and PE-SOM interfaces, a tuned temperature field, and high compatibility between SOMs and PE. Importantly, due to SOMs' amorphous morphology, the pressure can be imposed and further enhance the interfacial heat transfer. Results show the improved thermal conductance rises the most for the APTMS-coated LCO-PE system with 11.4 Å thickness at 10 GPa, almost 685% higher than that of the pristine system. The high efficiency of heat transfer comes as a result of the enhanced binding strength across the LCO-SOM and SOM-PE interface, the reduced phonon scattering in PE and SOMs, and the high LCO stiffness. These investigations are expected to provide a new perspective for modulating the heat transfer across the interphase of LIBs and achieve more effective thermal management for the multi-material system.