Graphite, the unheralded hero in lithium batteries is essential to their performance and conductivity. Understanding graphite and its role in batteries is crucial as the demand for electric vehicle grows.
The fundamental research conducted on graphite, despite its important role in LIBs is much less extensive than the basic research done on other materials like silicon [1], SiOx[2], Lithium Metal [3], Sulfides and Oxides. Graphite remains the material of choice for electrodes in lithium-ion and electrolytic batteries. Graphite electrodes have many characteristics that are beneficial to batteries, like good conductivity of electricity and the ability to resist chemical side-reactions with electrolytes.
Graphite is a sphere-shaped material, and its shape makes it possible to put more particles on an electrode. This increases the electrode's electrical conductivity. This property also helps to reduce the ohm resistance inside the battery, which ultimately improves its charge and discharge efficiency and cycle life. It also has good thermal stability, and is able to withstand heat produced during charging and discharge, thus reducing the risk of thermal runningaway.
As for the electrolyte, choosing an appropriate one will also play a significant role in graphite's charge and discharge performance. Choosing the right electrolyte can increase charge capacity and life. Temperature, current density and other working conditions will have an effect on the performance. Temperatures that are too high can accelerate degradation and ageing of electrodes, while current densities which are excessive will polarize electrodes and reduce their capacity.
The authors of a recent paper show that customizing the morphology and size of the particles in graphite can significantly improve the performance during high-rate charge. In this experiment, spherical graphite particles with an average particle size of about 50 nm were used. Electrical discharge machining was used to fabricate them. For a better understanding of graphite morphology, samples were examined with an electron scanning microscope.
The study revealed that the smaller surfaces of the spherical grains allowed for an efficient packing as well as a greater electrical conductivity. They also studied the structural change in graphite after high-rate cycles of charge and discharge. Studies have previously only investigated structural changes along the stacking direction, and the in-plane arrangements haven't been studied. It was therefore not known whether changes in stage structure or in-plane arrangements were responsible for the high-rate charge.
They built coin-cells with KS6 Graphite as working electrode, Li foil fresh as the counter electrode as well as polypropylene Film as separator to tackle this problem. The cells were cycled under a galvanostatic conditions between 0.0 to 3.0V (compared with Li+/Li0), in an Ar filled glove box. The results revealed that the fluorinated SEI was conducive to improving the graphite anode's performance in fast-charging by accelerating Li+ interfacial diffusion.
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