Neutron-Induced Enhancement of Ion Transport Through Lithium-Ion Battery Materials

Abstract

Polycrystalline solid-state ionic conductors (SSICs) are essential energy materials for all-solid-state Li-ion batteries. To date, achieving a room-temperature ionic conductivity of solid electrolytes comparable to that of their liquid counterparts remains a critical challenge. Here, we experimentally demonstrate that thermal neutron irradiation can offer an innovative strategy in that neutron-induced modification in an SSIC model (LiBO${}_2$ as an effective cathode coating) can facilitate ion transport through the material, enhancing its ionic conductivity. The central concept is that high-flux ($\sim 10^9\text{ neutrons}\cdot {\text{cm}}^{-2}\cdot {\text{s}}^{-1}$) thermal neutrons ($\sim \text{25 meV}$) selectively transmute strong neutron absorbers [which are ${}^{10}$B (3840 barns) and ${}^6$Li (940 barns) isotopes and present in their natural abundances of $\sim 19.9\%$ and $\sim 7.5\%$, respectively, in polycrystalline grains of LiBO${}_2$] to generate lattice vacancies without compromising their crystallographic long-range order. In addition, by-product gamma photons emitted from ${}^{10}$B transmutation free electrons to stop atomic displacement and simultaneously neutralize the space charge built up by positively-charged oxygen vacancies at grain boundaries. As a result, the ionic conductivity is increased by nearly 20\% for the grains and more than 80\% for the grain boundaries. This study validates theoretical predictions and highlights a vital strategy for boosting ion transport in ionic solids. Overall, this novel approach establishes a new revenue for broader applications and greater enhancements of advanced functional materials in their related solid-state ionic devices, including all-solid-state lithium-ion batteries.

41 pages, 10 figures,2 tables