Talk about the reasons for the decline of lithium batteries

A few days ago, scientists studied a lithium battery with iron oxide electrodes and found that the loss of the battery after charging and discharging more than 100 times was caused by the accumulation of lithium oxide and electrolyte analysis. The iron oxide electrode used in the research is made of cheap and non-toxic magnetite. Compared with current electrode materials, conversion electrode materials such as magnetite (that is, converted into new products when reacting with lithium), can store more energy because they can hold more lithium ions. However, the energy storage capacity of these materials decays very quickly and depends on the current density. For example, our electrochemical detection of magnetite shows that the capacity of magnetite drops rapidly during the first 10 high-speed charge and discharge cycles. According to DongSu, the research leader and the leader of the Electron Microscopy Group of the Center for Functional Nanomaterials (CFN). CFN is the Office of Science User Facilities of the US Department of Energy located in Brookhaven National Laboratory. In order to find out the cause of the cycle instability, scientists tried to observe the changes in the crystal structure and chemical properties of magnetite after the battery completed 100 cycles. They combined transmission electron microscopy (TEM) and simultaneous X-ray absorption spectroscopy (XAS) to conduct research. The electron beam of TEM is transmitted through the sample, and the structure image or diffraction pattern of the characteristic substance appears. XAS uses X-rays to detect the chemical properties of the material. Scientists have used these techniques to discover that during the first discharge, magnetite is completely analyzed into metallic iron nanoparticles and lithium oxide. However, in the subsequent charging process, this conversion reaction is not completely reversible, and the residues of metallic iron and lithium oxide still exist. In addition, the original spinel structure of magnetite evolved into a rock salt structure in the charged state (the positions of iron atoms are not exactly the same in the two structures). In the subsequent charge and discharge cycles, rock salt iron oxide and lithium are used together to form a composite material of lithium oxide and metallic iron nanoparticles. Because the conversion reaction is not completely reversible, these residual products will gradually accumulate. The scientists also discovered that the electrolyte (the chemical medium that allows lithium ions to flow between the two electrodes) is analyzed in subsequent cycles. Based on the research results, scientists have proposed an explanation for the decline in energy storage capacity. Sooyeon Hwang, a scientist and co-lead author of the CFN Electron Microscopy Group, said that due to the low electronic conductivity of lithium oxide, its accumulation will form a barrier to electrons that shuttle between the positive and negative electrodes of the battery. We call it the internal passivation layer. Similarly, electrolyte analysis will also form a surface passivation layer that hinders ion conduction. These obstacles accumulate and prevent electrons and lithium ions from reaching the active electrode material where the electrochemical reaction occurs. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete.