A Dilatometric Study of Graphite Electrodes during Cycling with X-Ray Computed Tomography

Abstract

Graphite is the most commonly used anode material in commercial lithium-ion batteries (LiBs). Understanding the mechanisms driving the dimensional changes of graphite can pave the way to methods for inhibiting degradation pathways and possibly predict electrochemical performance loss. In this study, correlative microscopy tools were used alongside electrochemical dilatometry (ECD) to provide new insights into the dimensional changes during galvanostatic cycling. X-ray computed tomography (CT) provided a morphological perspective of the cycled electrode so that the effects of dilation and contraction on effective diffusivity and electrode pore phase volume fraction could be examined. During the first cycle, the graphite electrode underwent thickness changes close to 9% after lithiation and, moreover, it did not return to its initial thickness after subsequent delithiation. The irreversible dilation increased over subsequent cycles. It is suggested the primary reason for this dilation is electrode delamination. This is supported by the finding that the electrode porosity remained mostly unchanged during cycling, as revealed by X-ray CT.

Synthesis of a High-Capacity α-Fe2O3@C Conversion Anode and a High-Voltage LiNi0.5Mn1.5O4 Spinel Cathode and Their Combination in a Li-Ion Battery

“… 4 , 6 Graphite uptakes Li + delivering a capacity of 372 mA h g –1 , which is limited by the amount of alkali-metal ions stored within the carbon layers, reaching a maximum of 0.16 Li-equivalents per mole of C, that is, according to the LiC 6 chemical formula. 7 , 8 Transition-metal oxides react in the cell by an electrochemical conversion pathway mainly occurring below 1.5 V versus Li + /Li and involving a multiple exchange of electrons, which ensures a higher capacity than that of graphite. 9 − 14 However, this intriguing class of materials intrinsically suffers from poor electrical conductivity and a large volume change throughout the electrochemical process, which causes the voltage hysteresis and rapid cell decay upon cycling.…”

Sensing as the key to battery lifetime and sustainability

“…Archimedes' in situ gas analysers 32 , whereby a cell is immersed in a fluid and a force sensor allows its buoyancy to be quantified as volume, have mainly been used to measure gas build-up stemming from the first charge-discharge (i.e., formation) cycles. In situ microscopy 10 , electrochemical dilatometry 33 , X-ray computed tomography 34 , and mechanical stress measurements 35 , can also probe the reversible expansion of insertion and alloy electrodes, as well as irreversible expansion concomitant with prolonged cycling. In essentially all cases, these techniques require specially designed cells to monitor expansion.…”