Neutron-enhanced ion transport in cathode coating of Li-ion batteries

Polycrystalline solid-state ionic conductors (PolySSICs) are key energy materials for all-solid-state Li-ion batteries (LIBs). However, achieving room-temperature ionic conductivity comparable to that of liquid electrolytes ($\sigma \sim 10^{-2}-10\,\mathrm{S\cdot cm^{-1}}$) remains a major challenge. Here, we experimentally demonstrate that thermal neutron irradiation provides an effective strategy for engineering ion transport in a model PolySSIC, LiBO$_2$, a promising electrode coating material for LIBs. High-flux ($\sim 10^{9}$ neutrons$\cdot$cm$^{-2}\cdot$s$^{-1}$) thermal neutrons ($\sim 25$ meV), delivered at Beam Port E of the University of Missouri Research Reactor (MURR), selectively transmute the strong neutron absorbers $^{10}\mathrm{B}$ and $^{6}\mathrm{Li}$ at their natural abundances ($\sim19.9\%$ and $\sim7.5\%$). This process generates lattice vacancies within polycrystalline grains while preserving long-range crystallographic order. In addition, $\gamma$ photons produced during $^{10}$B transmutation release electrons that suppress atomic displacement and partially neutralize the space charge associated with positively charged oxygen vacancies at grain boundaries. As a result, the ionic conductivity increases by nearly $20\%$ in grains and more than $80\%$ at grain boundaries. These results validate theoretical predictions and demonstrate a controllable strategy for enhancing ion transport in PolySSICs for solid ionic devices, including LIBs.