Electrochemical Cross-Talk Leading to Gas Evolution and Capacity Fade in LiNi_0.5Mn_1.5O₄/Graphite Full-Cells

Abstract

Continuous destruction of the solid electrolyte interphase (SEI) on the graphite-based negative electrode during cycling operation is a significant degradation mechanism that raises safety concerns and limits the cycle life of LiNi0.5Mn1.5O4 (LNMO)/graphite full-cells. Herein, we report on gassing phenomena which are typically concomitant with SEI destruction processes. Abrupt H2 evolution is observed by differential electrochemical mass spectrometry and pressure measurements at the end of discharge. Using a lithium reference electrode reveals that the gassing, which intensifies with cycling, is caused by an increase in the anode potential. Lithium is irreversibly consumed upon SEI formation, but this loss is not compensated for by the intrinsic degradation of LNMO in the first cycle. When the potential of the anode on discharge increases above approximately 0.9 V, the SEI is instantly damaged, causing gas generation, and eventually capacity fade. We show that this (“mediator-free”) cross-talk phenomenon can be suppressed to various degrees by either using a precycled graphite electrode or an LNMO material having a higher initial irreversible capacity loss.

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