Operando Characterization of Volume Changes in Lithium-Ion Battery Electrodes during Cycling using Isotope Multilayers

TL;DR

This paper introduces an operando neutron reflectometry method using isotope multilayers to measure real-time volume changes in lithium-ion battery electrodes, specifically germanium, during cycling.

Contribution

The study presents a novel isotope multilayer technique to track electrode volume changes in real time, excluding side reactions and simplifying data analysis.

Findings

Reversible volume change of amorphous germanium up to 250% for x=3.

Volume change largely independent of current density, cycle number, and layer thickness.

Crystallization and re-amorphization do not significantly affect volume change.

Abstract

This study reports on advancements in operando characterization of volume changes in lithium-ion battery (LIB) electrode materials during electrochemical cycling. Volume changes are crucial for LIB operation because they are related to the amount of stored energy as well as LIB integrity, performance, and safety. The study introduces a method based on isotope multilayers as active material to track the intrinsic modification of electrode volume in real time under operating conditions with operando neutron reflectometry. A natGe-73Ge multilayer film is used as a model system to measure the volume change of amorphous germanium electrodes during charging and discharging. Isotope modulation produces a Bragg peak in the neutron reflectivity pattern, sensitive only to the modification of volume within the active material of the electrode. Battery side reactions, such as the growth and reduction of the solid-electrolyte interphase is excluded. Using this method, the volume modification as a function of Li content x in LixGe can easily be derived from the scattering vector position of the Bragg peak without fitting numerous complex reflectivity patterns. The experiments show a reversible volume change of amorphous germanium of up to 250 percent for x = 3, which appears to be largely independent of current density, cycle number, and the thickness of the individual Ge layers. Also, there are tentative indications that the crystallization and re-amorphization of LixGe are not influencing the volume change.