Analysis of Charged State Stability for Monoclinic LiMnBO3 Cathode

The stability of the charged state of monoclinic LiMnBO3 has been analyzed to better understand its electrochemical cycling behavior in this work. First-principles calculations indicate that delithiated monoclinic Li1-xMnBO3 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 LiMnBO3 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 LiMnBO3 cathodes and chemically delithiated LiMnBO3 specimen. Based on these results, we consider the cycling performance of monoclinic LiMnBO3 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.