The use of graphite as a negative electrode in lithium ion (LIBs) is due to the high specific capacities, good cycling performances, and stable properties. Due to the growing demand for LIBs it's important to promote responsible graphite sourcing and recycling in order reduce dependency on foreign sources and guarantee adequate supplies. Graphite has a unique structure that allows it to be easily recycled to regain its original high specific capacitance. Graphite's initial capacity loss can however be caused by the formation of solid electrolyte (SEI) interfaces during charging and discharge, which can result in microcracks. SEI formation is a result of repeated interactions between the graphite and lithium intercalation/deintercalation. Many researchers are focusing on increasing the initial performance of graphite by using various methods, including surface modification, coating, capping, and doping.
The carbonization process and laser structuring techniques are both promising methods to enhance the anode properties of graphite. The carbonization of graphite, through heat treatment and conversion into solid material, can increase its ability to store charge reversibly. Meanwhile, laser-structuring graphite results in the formation of a 3-dimensional network with improved conductivity and surface area. Both processes can also mitigate the effect of SEI on graphite anode performance by preventing the propagation of faradaic currents, thus maintaining high electrochemical efficiency.
Another technique for graphite modifcation is to add other materials like tin in order to enhance its electrochemical property and make use of tin's higher specific capacitance. For example, Zhu et al. [134] fabricated nano-tin oxide/graphite composites by first using SnCl2 as a reducing agent to form tin ions and then mixing these with bitumen to produce carbon coated tin graphite. These composites showed a high CE of 85.1 % and high capacity retention after 500 cycles with a specific capacitance of 607.6 mAh/g.
It is also possible to use composites of Si/G to increase the anode thickness in LIBs. Although silicon has higher capacity per unit volume than graphite it is subject to severe volume growth during cycling, which can result in mechanical breakdown and significant capacity loss. A team from Sandia National Laboratory has developed a method for synthesizing self-supported, multi-walled carbon nanotube (MWCNT) embedded silicon that alleviates this issue by shielding the silicon against expansion, thereby preserving its large capacitance and cycle stability. They also conduct electrons through the graphite/silicon surface and improve overall material performance. It is an important step in developing high-performance graphite for lithium battery anodes. Further research is required to create other combinations of graphite and silica that provide better performance. The results have so far been promising, even though we have a ways to go until the goal of recycling waste graphite is reached.
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