Graphite Cathode and Lithium Ion Batteries
graphite cathode is the key to achieving high gravimetric energy density for lithium-ion batteries (LIBs). However, there is still much work needed to improve the capacity and cycling stability of this material.
Recent developments in the aluminium ion battery (AIB) field show promising results using graphite cathodes with high tapping densities in combination with ionic liquid electrolytes. However, a number of issues remain to be addressed, including the inability to reach high mass loadings of the active material and the understanding of the mechanism by which graphite intercalates bulky anion ions.
For example, the pristine natural graphite flakes used in the current study showed high capacities at low rates with clear discharge voltage plateaus, but cycling was limited by the formation of large polarization that limits the capacity and cyclability of the material. Moreover, there was an insufficient amount of the material available to meet industry-compatible mass loading densities.
To resolve these challenges, the authors studied the kinetics of anion intercalation in pristine natural graphite and HOPG through various electrochemical measurements including electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). Their GITT data reveal that during charging, the graphite G band split into a lower-frequency component, attributed to vibrations within bound graphite layer planes not adjacent to the intercalant layer, and a higher-frequency peak at 2.37 V associated with ions in the intercalant layers.
In addition, they observed that the GITT results for pristine graphite exhibit a gradual improvement in charge transfer resistance and mass transfer process over cycling. Specifically, the R ct of graphite decreased from several tens of Ohm to 23 O at 1000 cycles and further improved over 2000 cycles to 8 O. This indicates the self-activating effect of the graphite cathode and suggests ultrafast ion diffusion, in contrast to the slow ion transport of LFP-graphite hybrids.
