[technical PI] the application of mathematical model in the design of lithium battery
Publish：Sino Energy Corporation Time：2017-05-16
In the design and development of lithium ion batteries, the choice of cathode materials is critical, and it will directly determine whether the developed batteries meet the needs of the end customers. At present, mature commercial lithium-ion battery cathode materials are: lithium cobalt oxide, lithium manganese oxide, nickel, cobalt, manganese, three yuan material, and lithium iron phosphate.
These materials have different characteristics, such as lithium manganate has a good rate performance, three yuan material with high capacity, lithium iron phosphate can provide long cycle life. In order to take into account each positive material advantage, positive system of mixed material is used for the design of many battery manufacturers of power battery, for example, three yuan can be mixed materials and lithium manganate designed both capacity and power of the battery, but also because the battery system is relatively complex and difficult for its analysis.
Dr. Mao Zhiyu of the University of Waterloo in Canada established a mathematical model of the two scales used to describe a commercial battery three yuan and lithium manganese cathode materials mixed (Journal of The Electrochemical Society performance, 163 (3) A458-A469 (2016)), as the research model, select the button type battery as the research object, the physical the model includes single particle size and electrode scale (Figure 1). Figure 1. Schematic diagram of a two scale physical model of a lithium ion mixed anode system half cell.
According to the actual measurement, the model is composed of two kinds of materials with three different diameters and a size of lithium manganate material, and they are related to the capacity contribution of the battery. The physical specifications for measuring active material (such as size), design specifications (such as rolling electrode density, conductivity), the input parameters of mathematical model, all through the calculation, the performance curve fitting rate electrode can describe well the cell (Figure two).
Figure two: three yuan (a) lithium manganate mixed cathode materials (lithium manganate: three yuan mass ratio =3:7) measurement rate curve (circle) and model (solid line) of the comparison chart; and (b) comparison of the discharge capacity at different rates.
Through the quantitative analysis of the model, because of the serious agglomeration of three yuan particles caused by a wide particle size distribution, which exerted great influence on the capacity of the battery, the small particles can be fully utilized, with high capacity, large particles and reunion after the formation of the low utilization rate (Figure three).
The process engineer material suppliers and battery production has a guiding role, if the coating does not affect the normal situation, the synthesis of three yuan materials with small particle sizes and good uniformity, and was as far as possible to reduce the agglomeration of particles, the ultimate capacity of the design of this battery will be improved greatly.
Figure three: the relationship between the maximum utilization of the lithium manganate particles in the mixing electrode, and the maximum utilization ratio of three yuan material large particles (micro, group) and small particles (submicron, group)
In addition, by using this mathematical model, by adjusting other parameters, it can also detect which factors are most sensitive to the final performance of the battery, thus optimizing the design. For example, by adjusting the electrode porosity, the change is how to influence the performance of the battery, and then the process engineer by adjusting the electrode drying temperature and wind speed to optimize the porosity, then optimize the battery design.
