Reasons for the decline of lithium batteries

A few days ago, after studying a lithium battery with iron oxide electrodes, scientists found that the loss of the battery after charging and discharging more than 100 times was caused by the accumulation of lithium oxide and the differentiation of the electrolyte. The iron oxide electrode used in the research process 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 accommodate more lithium ions. However, the energy storage of these materials decays very quickly, and it 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 leader of this research and the leader of the Electron Microscopy Group of the Center for Functional Nanodata (CFN). CFN is the Office of Scientific User Equipment of the U.S. Department of Energy located in Brookhaven National Laboratory. In order to find out the reason for the instability of the cycle, the scientists tried to investigate the changes in the crystal structure and chemical properties of magnetite after the battery has 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 to produce structural images or diffraction pictures of characteristic substances. XAS uses X-rays to detect the chemical properties of the data. Scientists have used these techniques to discover that during the first discharge, magnetite completely differentiated into metallic iron nanoparticles and lithium oxide. However, in the subsequent charging process, this conversion response 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 completely 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 transformation response is not completely reversible, these remaining products will gradually accumulate. The scientists also discovered that the electrolyte (the chemical medium that makes lithium ions move between the two electrodes) diverges in subsequent cycles. On the basis of the research results, the scientists put forward an explanation of the fading power of energy storage. Sooyeon Hwang, a scientist and co-lead author of the CFN Electron Microscopy Group, said that because lithium oxide has low electronic conductivity, its stack will form a barrier to the electrons that flow between the positive and negative electrodes of the battery. We call it the internal passivation layer. Similarly, electrolyte differentiation will also form a surface passivation layer to prevent ion conduction. These obstacles accumulate and prevent electrons and lithium ions from reaching the active electrode material that produces electrochemical reactions. Scientists pointed out that operating the battery at low current can slow down the charging speed and recover part of the capacity for electronic transmission. However, there are other ways to deal with this problem thoroughly. They believe that adding other elements and changing the electrolyte in the electrode materials can improve the capacity attenuation. Disclaimer: Some pictures and content of articles published on this site are from the Internet. If there is any infringement, please contact to delete. Previous post: What role does graphene play in lithium battery materials?