Recently, the university of Maryland, the department of energy national laboratory in collaboration with the U.S. military researchers developed a new type of lithium ion battery cathode of nano materials, the energy density of three times of existing commercial lithium-ion batteries, the results of the study are published in the journal nature communications.
As lithium ion batteries are used more and more widely, the demand for high energy density batteries is also increasing.However, in traditional commercial lithium-ion batteries, anode materials are usually good conductive materials such as graphite, but the capacity of cathode materials is very limited."Cathode materials are the bottleneck in lithium battery research, and it is very difficult to improve the battery energy density based on them," said lead author fan xiulin, a researcher at the university of Maryland.
To solve this problem, researchers from several U.S. institutions have synthesized a modified iron trifluoride (FeF3), which has a higher energy density and is environmentally friendly.
In fact, ferrotrifluoride was not previously used as a cathode material for lithium-ion batteries.When an electrode reaction occurs, ferrotrifluoride gets electrons from lithium and converts them into iron and lithium fluoride.Because this compound has a certain hysteresis effect, the reaction rate is low in the electrode reaction, and its reaction byproduct will also hinder the electrode reaction.In addition, this reaction is not completely reversible, which means that the reaction times of the ferrofluoride electrode are very limited and will greatly reduce the economic performance of the battery.
To solve these problems, the researchers found the mechanism of the electrode reaction from the microscopic level through a large number of experimental studies.Using a transmission electron microscope (TEM), the researchers determined the true size of the cathode nanomaterials and observed structural changes during charging and discharging.
Since then, the researchers have used X-ray powder diffraction (XPD) technology to observe the crystal structure in the nanorods, and found that adding other atoms can effectively improve the reaction rate.As a result, the team used chemical substitution method adding cobalt atoms and oxygen atoms into trifluoride iron nanorods, changed its reaction mechanism, so that the three iron fluoride electrode become reversible reaction, greatly increase the battery life.