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 ($\sigma \sim {10}^{-2}-10\mathrm{S}\cdot \mathrm{c}{\mathrm{m}}^{-1}$) 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 ${}^6\mathrm{L}\mathrm{i}$ at their natural abundances ($\sim 19.9\mathrm{\%}$ and $\sim 7.5\mathrm{\%}$). 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 $20\mathrm{\%}$ in grains and more than $80\mathrm{\%}$ 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.