Chemically induced delithiation and phase change of lithium rich nickel manganese oxides

Abstract

In this study, Li[Ni.25Li.167Mn.583]O2 (LLRNMO) was exposed to acidic solutions of H3PO4, H2SO4, HCl, and HNO3 in an attempt to chemically motivated the phase transformation analogous to the that encountered during electrochemically-driven delithiation. Powder X-ray diffraction and electrochemical data provide evidence of delithiation similar to a low cell potential charge (sub 4.5 V), but the data were not consistent with the phase change induced by the initial high cell potential (>4.5 V) charge. Repeated full cycling revealed that acidic treatments reduced sample capacity and cell potential. XRF and SEM data suggest the effects of acid treatment are not universal and are dependent on the acid used. To the best of our knowledge, this study marks the first time that a lithium-excess cobalt-free cathode was exposed to acidic solutions for this purpose. Our results demonstrate that these chemically induced phase transformations are a poor substitute for the electrochemically induced phase transformation. The possible reasons and consequences of this are discussed.