An Analysis Protocol for Three-Electrode Li-Ion Battery Impedance Spectra: Part II. Analysis of a Graphite Anode Cycled vs. LNMO

Daniel Pritzl,Sophie Solchenbach,Hubert A Gasteiger,Johannes Landesfeind

doi:10.1149/2.0461810jes

Daniel Pritzl, Sophie Solchenbach + Show 2 more

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https://doi.org/10.1149/2.0461810jes

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Abstract

Lithium-Ion batteries consisting of LNMO (LiNi0.5Mn1.5O4) cathodes and graphite anodes show severe capacity fading at elevated temperatures due to a damage of the solid electrolyte interface (SEI) on the anode. Hence, a detailed investigation of the anode with electrochemical impedance spectroscopy (EIS) can provide valuable insight into the phenomenon of anode degradation. In this study, we use a modified version of our novel impedance procedure (Part I of this study), where the anode impedance is measured at non-blocking conditions (10% SOC) and blocking conditions (0% SOC) in a graphite/LNMO full-cell with a gold wire micro-reference electrode (GWRE). We show that during cycling an ionic contact resistance (RCont.Ion) at the separator/anode interface evolves, which is most likely caused by manganese dissolution from the high-voltage cathode (LNMO). By simultaneously fitting EIS spectra in blocking and non-blocking conditions, we can deconvolute the anode impedance evolving over 86 cycles at 40°C into contributions of: a) the separator resistance (RSep.), b) the true charge transfer resistance (RCT), and, c) the ionic contact resistance (RCont.Ion) evolving at the separator/anode electrode interface. We also show that the main contributor to a rising anode impedance is the ionic contact resistance (RCont.Ion).

Highlights

In view of the growing concerns with regards to cobalt supply constraints for Lithium-Ion batteries,[1] LiNi0.5Mn1.5O4 (LNMO) as cathode active material with a theoretical energy density of ≈690 Wh/kgLNMO2 is an interesting alternative for Co-free LithiumIon batteries
The impedance is recorded at different potentials during lithiation of a graphite anode and the impedance response is generally fitted with two R/C or R/Q elements connected in series, representing the charge transfer resistance and the solid electrolyte interface (SEI) resistance
To check at which potentials blocking conditions of the graphite anode can be reached in a full-cell, a graphite/LNMO cell with a gold wire micro-reference electrode (GWRE) was assembled and two formation cycles were done at C/10 at 25◦C

Summary

Introduction

In view of the growing concerns with regards to cobalt supply constraints for Lithium-Ion batteries,[1] LiNi0.5Mn1.5O4 (LNMO) as cathode active material with a theoretical energy density of ≈690 Wh/kgLNMO2 is an interesting alternative for Co-free LithiumIon batteries.

Results

Conclusion