Study On Polyacrylic Acid As Binder Of Cathode In Lithium Ion Battery

Abstract:Among the components of lithium ion battery, binder is an essential part. Although the amount of binder for using is not much, it plays an important role in the battery, such as forming stable electrode structure and good conducting web. As well as buffering the volume changing of active material powders while lithiated and delithated. There is no doubt that a kind of perfect binder can ensure good electrochemical performances of the lithium ion battery.In this article, we made a research of a new kind of battery binder, polyacrylic acid (PAA) binder. First of all, physical and chemical properties of pristine PAA polymer are investigated, including functional group analysis, crystallinity, morphology, thermal properties, electrochemical stable properties and solubility in the electro hyte. Then LiFePO4and LiMn2O4cathode are prepared by using PAA as binder, some physical properties of the two electrodes such as peel tests, swelling properties and surface morphologies are tested. In the end, cycle performances of the two kinds of cathodes are tested both at room temperature and at elevated temperature. The results are presented as follows:1. PAA is a kind of amorphous state polymer, there are long carbon chains&carboxylic groups exist in the molecule. Results of the thermal properties show that comparing with PVDF and CMC, the PAA polymer have a better stability, lower thermal expansion rate and larger thermal diffusion coefficient. Also, it shows stable electrochemical properties in the normal use rang of the battery voltages, and there is no side reaction happen. PAA is insoluble in the electrolyte. All in all, all the physical properities of PAA polymer are good, and it can be researched as a lithium ion battery binder.2. Both the room temperature and elevated temperature electrochemical performances of the LiFePO4cathodes are improved by using PAA as a binder. The capacity retention at room temperature and high temperature are99.3%for200cycles and97.7%for100cycles, respectively. It can be seen from the cyclic vottammetry curves that the PAA binder cathode has a smaller polarization than the PVDF binder cathode. EIS of the different cycles reveal that, as the proceeding of cycle, the diversity of electrochemical performances between the PAA and PVDF binder cathode is caused by the different changing trends of Rcell. After testing the physical and chemical properties of the electrodes, we know that the LiFePO4cathode with PAA binder has well binding strength and appropriate swelling prosperity, which ensure good electrical performances.3. After comparing the electro performances of LiMn2O4cathodes with PAA/NMP, PAA/H2O, CMC and PVDF binder systems, we know that both the room temperature and elevated temperature electrochemical performances of the LiMn2O4cathodes are improved by using PAA/NMP binder system. The capacity retention at room temperature and high temperature are85.7%for200cycles and74.8%for100cycles, respectively. Physical and chemical properties of the four different electrodes reveal that the LiMn2O4cathode with PAA/NMP binder system has well binding strength, appropriate swelling prosperity as well as good dispersibility, which ensure good electrical performances. There are38pictures,9tables and100references.