Analysis of Charged State Stability for Monoclinic LiMnBO₃ Cathode

The stability of the charged state of monoclinic LiMnBO 3 has been analyzed to better understand its electrochemical cycling behavior in this work. First-principles calculations indicate that delithiated monoclinic Li 1– x MnBO 3 becomes unstable for x ≥ 0.625. Results obtained from ex-situ X-ray diffraction on charged electrodes and chemically oxidized powder confirm the phase decomposition of the LiMnBO 3 phase when a significant amount of Li is extracted. Energy-dispersive X-ray spectroscopy and X-ray diffraction analysis also reveal Mn dissolution from the cycled LiMnBO 3 cathodes and chemically delithiated LiMnBO 3 specimen. Based on these results, we consider the cycling performance of monoclinic LiMnBO 3 to be primarily limited by its charged state instability. To overcome this limitation, we partially substituted Mn with Mg to maintain structural integrity of the phase and reduce capacity fading over multiple cycles.