The high energy-storage performance of LIBs is largely due to their graphite negatively electrode. This layered electrode's structure allows for reversible extraction and intercalation of lithium during charge and discharge. The irreversible formation on the surface of its solid electrolyte (SEI), however, limits its cycle stability and life over a long period. The SEI is caused by uncontrolled interactions with the aqueous electrolyte, including co-intercalation of solvent molecules and reduction of the chemisorbed oxygen groups on the prismatic surface of the graphite anode.
To address this issue, many research groups have attempted to reduce the formation of SEI on graphite anodes by physical coating, chemical modification, or both. Nevertheless, results were inconsistent. For example, Shi et al. [20] uniformly coated the graphite surface with sodium maleate salt using liquid coating technique, and demonstrated a much improved cycling performance of their modified graphite electrode. Nonetheless, the SEM and TEM images showed that the graphite particles were buried under lots of reductive decomposition products in the SEI layer.
SEI layers are a complex web of pores and fissures that allow the particles to be captured during REDOX. The pores and cracks limit the flow of electrons in the graphite, thereby, preventing the battery from reaching its full capacity. Researchers have added functional groups to the surface of the graphite in order to improve the performance. Researchers have created an SEI that has better properties like cycling stability, long-term life and durability.
In addition, the layered graphite structure allows for silicon nanoparticles to be accommodated in a fairly stable fashion. To maximize silicon use in graphite, certain studies used multi-walled Carbon Nanotubes embedded with silicon particles in a matrix of graphite. Guo et al. [31] used CVD technology to make amorphous silicon shells on graphite. They also demonstrated the MWCNT/silicon particle interface significantly improved the composite's electrical conductivity.
Composite anodes made of Si/G have proven to be promising materials to use in LIBs. They are more energy dense and possess higher specific energies than graphite alone. However, the synthesis of Si/G composite anodes is still a challenge. It is difficult to obtain high-quality, sustainable, low-cost materials in order to produce SI/G Composites at large scale.
Presently, the two most important raw materials used to produce LIBs are synthetic graphite and natural graphite. The latter is made from petroleum coke. Historically, synthetic graphite was used for most commercial purposes. But natural graphite may become more popular in the future due to its higher purity and consistency. In order to maximize the utility of future lithium-ion technologies, it's important to examine strategies that can enhance natural graphite. This article provides several techniques for increasing the performance of graphite. They range from modifications in surface treatments to development of Si/G Composites, and even sustainable recycling.
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