Role of Electrolyte Oxidation and Difluorophosphoric Acid Generation in Crossover and Capacity Fade in Lithium Ion Batteries

Chamithri Jayawardana,Brett L Lucht,Bharathy Parimalam,Nuwanthi Rodrigo

doi:10.1021/acsenergylett.1c01657

Chamithri Jayawardana, Brett L Lucht + Show 2 more

Open Access

https://doi.org/10.1021/acsenergylett.1c01657

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Journal: ACS Energy Letters	Publication Date: Oct 6, 2021
Citations: 42	License type: CC BY-NC-ND 4.0

Affiliation: University of Rhode Island

Abstract

Poor cycling performance for many high voltage lithium ion batteries (LIB) has been attributed to damage of the anode solid electrolyte interphase (SEI) resulting from crossover reactions. Transition-metal ion crossover has been proposed as a primary source of SEI damage and capacity loss, especially for high-voltage spinel cathodes. However, deposition of transition metals on the anode SEI may not be the primary source of SEI degradation. This investigation focuses on the oxidative decomposition of LiPF6 in ethylene carbonate (EC)-based carbonate electrolytes to generate acidic species which subsequently cross over to the anode and degrade the anode SEI components. The generation of the strong acid, difluorophosphoric acid (F2PO2H), has been quantified for both graphite || LiNi0.5Mn1.5O4 and graphite || LiMn2O4 cells. There is a correlation between the concentration F2PO2H, SEI degradation, and the capacity loss of the cells.

Highlights

Poor cycling performance for many high voltage lithium ion batteries (LIB) has been attributed to damage of the anode solid electrolyte interphase (SEI) resulting from crossover reactions
The more interesting spinel cathode material, LiNi0.5Mn1.5O4, has a higher energy density because of the higher operating potential (4.8−4.9 V vs Li), but it suffers significant capacity fade upon cycling at moderately elevated temperature. This is generally attributed to acid-mediated transition-metal ion dissolution and related shuttle or crossover reactions.[1−6] Upon dissolution, the Mn and Ni ions migrate through the electrolyte and have been reported to be reduced on the graphite surface damaging the anode solid electrolyte interphase (SEI).[7−9] The mechanism for transition-metal reductive deposition is not fully understood
OPF3.12,13 These species can be involved in crossover reactions which could facilitate the decomposition of the anode SEI components.[16]

Summary

Introduction

Poor cycling performance for many high voltage lithium ion batteries (LIB) has been attributed to damage of the anode solid electrolyte interphase (SEI) resulting from crossover reactions.

Results

Conclusion