The Effects of Acid Treatment on the Electrochemical Properties of 0.5 Li2MnO3 ∙ 0.5 LiNi0.44Co0.25Mn0.31O2 Electrodes in Lithium Cells

The electrochemical properties of 0.5 Li 2 MnO 3 ·0.5 LiNi 0.4 Co 0.25 Mn 0.31 O 2 electrodes, when preconditioned and activated with acid for 2-24 h, have been studied in lithium cells. Powder X-ray diffraction data and electrochemical measurements provide supporting evidence for an intergrown, composite electrode structure from which Li 2 O can be leached from the Li 2 MnO 3 (Li 2 O MnO 2 ) component with acid, thereby mimicking the electrochemical charge process at high potentials (>4.5 V). The MnO 2 -rich domains generated by acid treatment are reduced during electrochemical discharge at a lower potential than electrochemically generated MnO 2 -rich domains. With prolonged cycling between 4.6 and 2.0 V, dQ/dV plots of untreated and acid-treated electrodes develop similar, but not identical, character, suggesting a coalescence and redox interaction of the manganese ions in MnO 2 -rich and Ni 0.44 Co 0.25 Mn 0.31 O 2 regions of the structure. Acid treatment eliminates the first-cycle capacity loss of the electrodes, consistent with earlier reports for related systems, but it damages their cycling stability and rate capability.

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