Lithium isotope effects accompanying oxidation reactions in lithium ion secondary batteries

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In the electrochemical lithium release from a lithium cobalt oxide (LiCoO2) cathode to ethylene carbonate-based organic electrolyte solution containing lithium ions, it was observed that the heavier isotope, 7Li, was preferentially transferred to the electrolyte solution. Contrary to this, no lithium isotope effects were observed when the electrolyte solution contained no lithium ions. It was induced that the kind of electrolyte solution controlled the attainment of the lithium isotope exchange equilibrium between the cathode and the electrolyte solution.When lithium manganese oxide (LiMn2O4) was used as the cathode material, the lighter isotope of lithium, 6Li, was preferentially released to the electrolyte phase, irrespective of the kind of electrolyte solution. The great contrast in lithium isotope effects between LiCoO2 and LiMn2O4 cathodes seemed mostly ascribable to the structural difference between the two cathode materials.