Observation of Lithium Isotope Effects Accompanying Electrochemical Release from Lithium Cobalt Oxide

Abstract

Change in the lithium isotope composition in a lithium cobalt oxide (LiCoO 2 ) cathode for lithium ion secondary batteries accompanying the electrochemical lithium release from the cathode into an organic electrolyte solution was observed. The 7 Li/ 6 Li isotopic ratios of the electrodes after the release of 37.2 to 55.4% lithium were 1.018 to 1.033 times smaller than that before the release. This means that the heavier isotope, 7 Li, is preferentially transferred to the electrolyte solution.

Lithium Isotope Effects upon Electrochemical Release from Lithium Manganese Oxide

“…The lighter isotope of lithium was preferentially fractionated to the electrolyte solution phase with the value of the isotope separation factor ranging from 0.971 to 0.989 at 25 ºC. These results are in marked contrast with experiments with the LiCoO 2 electrode [9,10] and seem ascribable mostly to the structural difference between LiMn 2 O 4 and LiCoO 2.…”

“…It is in great contrast with the LiCoO 2 -EC/EMC/LiClO 4 (Co-Li) system in our previous paper [9] in which lithium was electrochemically released form the LiCoO 2 electrode to the EC/EMC/LiClO 4 , and accompanying the release, substantial depletion of 7 Li was observed on the cathode after the electrolysis with the value of S' (expressed as S in [9]) ranging from 1.045 to 1.060. The two systems give just the opposite lithium isotope effects.…”

“…The two systems give just the opposite lithium isotope effects. In the previous paper [9], we explained the lithium isotope fractionation observed in the Co-Li system based on the equilibrium lithium isotope effects between lithium remaining in the LiCoO 2 and lithium released to the electrolyte solution. That is, we considered that the observed lithium isotope fractionation originated from the fact that the equilibrium constant of the lithium isotope exchange reaction, 7 Li A-cathode + 6 Li A-electrolyte = 6 Li A-cathode + 7 Li A-electrolyte (6) where i Li A-cathode denotes lithium-i (i = 6 or 7) in the LiCoO 2 phase and i Li A-electrolyte denotes lithium-i released to the electrolyte solution phase, is larger than unity.…”

“…So far, we have investigated only the lithium isotope effects by the charge reaction. n our previous paper [9], we studied lithium isotope effects accompanying lithium release from the lithium cobalt oxide (LiCoO 2 ) cathode into an organic electrolyte solution, a 1:2 v/v mixed solution of ethylene carbonate (EC) and ethylmethyl carbonate (EMC) containing 1 M lithium perchlorate (LiClO 4 ) (EC/EMC/LiClO 4 ). Lithium cobalt oxide, belonging to the rhombohedral system, is a stable lithium composite oxide with a layered structure and is used as the cathode material in a large majority of lithium ion secondary batteries.…”

Chitosan-graft-benzo-15-crown-5-ether/PVA Blend Membrane with Sponge-Like Pores for Lithium Isotope Adsorptive Separation

“…In the recent decades, many other techniques have been developed to separate the lithium isotope, such as electromigration, , laser, , electrochemical, , solvent extraction, − chromatography, , and membrane separation . Among them, solvent extraction and chromatography using crown ether as an extracting agent have been proven to be effective techniques for lithium isotope separation.…”