Spontaneous Lithium Transportation via LiMn2O4/Electrolyte Interface Studied by 6/7Li Solid-State Nuclear Magnetic Resonance

•Spontaneous Li+ exchange between LiMn2O4 and LiPF6-based electrolyte was studied.•6/7Li solid-state NMR techniques were developed to examine the exchange.•The exchange occurs for stoichiometric LiMn2O4 but not in Li-excess LiMn2O4.•The exchange was approximated by the 1st-order reaction with the rate of 0.024 min-1.•The suppression in Li-excess LiMn2O4 was ascribed to excess amount of Mn4+.

Lithium transportation across the interface of LiMn2O4/LiPF6-based electrolyte was studied by 6/7Li solid-state NMR with 6Li-enriched LiPF6. For almost stoichiometric LiMn2O4, we show that exchange of lithium ions occurs across an electrolyte/electrode interface just by immersing LiMn2O4 powder into LiPF6-based electrolyte, while such transportation is suppressed in Li-excess LiMn2O4. The exchange was approximated by the 1st-order reaction, and the rate was estimated from the 6Li/7Li intensities to be 0.024 min−1 at room temperature. The lithium ions penetrated into the surface of a LiMn2O4 particle reach to the core with a time scale of a few hours at room temperature. The suppression of the exchange in Li-excess LiMn2O4 was ascribed to the presence of excess amount of Mn4+.

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