Surface Analysis of Thermal Neutron Irradiated LiBO₂: Implication for Use as Cathode Coating of Li-ion Batteries

Lithium metaborate (LiBO₂) is a material of high interest due to its important applications such as conformal coating of the cathode surface in high-voltage lithium-ion batteries to passivate electrochemical side reactions between the cathode surface and the liquid electrolyte. However, its poor lithium-ion conductivity limits its practical application. Here, we present preliminary experimental results showing that thermal neutron irradiation is a promising strategy to improve the lithium diffusion in LiBO₂. LiBO₂ contains both ⁶Li (~ 7.5% of Li) and ¹⁰B (~19.9% of B) isotopes with large cross sections for thermal neutron capture leading to nuclear reactions ⁶Li + ¹n —> ³H + ⁴He + 4.78 MeV and ¹⁰B + ¹n —> ⁷Li + ⁴He + 2.79 MeV, which lead to defects in the crystalline structure. In this initial proof-of-concept investigation, we employed experimental surface-analysis tools such as scanning electron microscopy (SEM) and x-ray photoelectron spectroscopy (XPS) to characterize the surface of our LiBO₂ samples as a function of the neutron dose. Both SEM and XPS showed a systematic dose-dependent modification of surface microstructure and chemistry resulting from the formation of neutron-induced defects. Further comprehensive investigations using high-resolution tools such as synchrotron x-ray total scattering and high-resolution transmission electron microscopy (HRTEM) in combination with electrochemical impedance spectroscopy will be performed to obtain quantitative insights into the neutron-induced surface physics and chemistry of LiBO₂. The induction of defects in the crystalline structure is promising due to the potential to increase ionic conductivity [1] leading to improved performance in coatings and solid-state electrolytes in lithium-ion batteries.

[1] Ziemke et al., Formation of Lattice Vacancies and their Effects on Lithium-ion Transport in LiBO2 Crystals: Comparative Ab Initio Studies, J. Mat. Chem. A (under review, preprint: https://doi.org/10.48550/arXiv.2410.06284).