Graphite Anode and Cathode Materials for EV Batteries
With its high energy density, good electrical conductivity and affordability, graphite is the anode and cathode material of choice for electric vehicle (EV) batteries. During charging, lithium ions move from the cathode to the anode through an electrolyte buffer separating these electrodes. The anode enables the battery to store and deliver its energy by hosting the lithium ions in vacant sites in its crystal lattice, a process known as intercalation.
During discharging, the lithium ions are extracted from the anode and transferred to the cathode. The reversible transfer of lithium from the anode to the cathode is made possible by the formation of a solid electrolyte interphase (SEI) at the interface between the graphite active materials and the liquid electrolyte. This SEI layer kinetically suppresses the continuous electrolyte decomposition and inhibits solvent co-intercalation, while allowing for lithium cation conduction, thereby maximizing the reversible capacity of the anode.
As a result, EV battery makers need to use a highly porous material with adequate structural integrity to minimize the volume expansion and mechanical strain during repeated insertion/extraction of lithium ions during cycling. Despite numerous strategies to improve the anode performance and enhance the energy density of LIBs, one key limitation remains the first cycle irreversible capacity (Cirr) caused by the reductive electrolyte decomposition.
To mitigate the impact of Cirr, many researchers have explored the surface modification of the graphite particles. This can be accomplished by various treatment methods such as oxidative solutions, ceramic materials or gases, typically followed by a heat treatment.
