The charging and discharging process in lithium-ion batteries is a very complex reaction process. It exists in many different reaction states. Although Li-ion batteries are becoming increasingly popular and are being replaced and applied in more industries, some of their operating principles are still not well known. Continuous observation is one of the best ways to improve the performance of lithium-ion batteries, but this is not an easy task given the complexity of their structure and the limitations of microscopy.
Scientists at the Skoltech Energy Technology Center in Moscow have developed a new method to closely observe the formation of solid electrolyte intermediates (SEI) in certain lithium batteries. The researchers describe SEI as the product of a thin layer of electrolyte reduction that forms on the surface of the anode during several initial cycles of a lithium-ion battery.
The formation of this film is critical to slowing lithium battery loss and aging, the researchers said. However, in situ measurements of SEI horizons have proven difficult, and the only way to obtain results is to replace commercial battery materials with more uniform alternative materials in the lab. For the time being. This approach is very limiting and has a high degree of operational difficulty
"Since the material of the battery's electrical level is usually in a powder state, the dynamics of its surface is already given difficulty by atomic force microscopy (AFM), and in a liquid environment this difficulty will be increased even more," said Sergey Lukkin, a scientist at Skolt Technologies. Because standard cell electrodes are too rough, such measurements are simply impossible, and isolated particles are often separated from the substrate during the scanning process. To try to solve this problem, we had to embed the particles in epoxy resin and cross-sections so they could be fixed to the detection substrate."
In addition to highly oriented pyrolytic graphite, one of the more homogeneous carbon materials previously used to study SEI, the Skoltech group applied its cross-section process to electrodes of medium-carbon microbead graphite and non-graphitizable amorphous carbon, allowing the researchers to observe the thickness of the resulting SEI films and evaluate their electrical and mechanical properties.
It was found that different electrode materials have a significant effect on the conditions of SEI formation, while the adhesion of SEI is related to the surface roughness of the electrode. Since SEI can penetrate high porosity surfaces and obtain good adhesion, a rough surface can promote a lower degradation rate.
In the cross-sectional analysis of the Li-Mn-Co cathode, the presence of SEI layer was not found. Based on the scientists' findings, future studies should recognize the fundamental difference between anode and cathode stability mechanisms.
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