Guar Gum: A Promising Aqueous Binder for Electrode Material with High Energy Density

Abstract

Eelectrode film of lithium ion-batteries is composed of active material, conductive carbon, and binder material. Binder makes up only a small part of the electrode composition (normally less than 10%), however it play an important role in affecting electrochemical performance of a battery. In comparison with the mainstream binder PVDF, that aqueous binders can sometimes are cheaper, greener, and easier to use for electrode fabrication, and make a battery perform better. Guar gum is a polysaccharide derived from the seeds of Cyamopsis tetragonolobus and consists of linear chains of (1→4)-β-D-mannopyranosyl units with α-D-galactopyranosyl units attached through (1→6) linkages. Guar gum was chosen as the aqueous binder for the Si anode and lithium-rich cathode materials, due to its high ion-conductivity and the large amounts of polar hydroxyl groups in the this molecule. Guar gum was firstly tested as the binder of Si nanoparticle (average size 100 nm) anode. Due to the large number of polar hydroxyl groups in the guar gum molecule, a robust interaction between the guar gum binder and the Si nanoparticle is achieved, resulting in a stable Si anode during cycling. More specifically, the guar gum binder can effectively transfer lithium ions to the Si surface, similarly to polyethylene oxide solid electrolytes. As a result, guar gum binder offers a better performance than the sodium alginate and PVDF binders. Si nanoparticle anode with the guar gum as the binder can deliver an initial discharge capacity as high as 3364 mAh/g, with a Coulombic efficiency of 88.3% at the current density of 2100 mA/g , and maintain a capacity of 1561 mAh/g after 300 cycles. Guar gum was then tested as the binder of lithium-rich cathode materials (Li1.14Ni0.18Mn0.62O2) to suppress the voltage fading. Compared with conventional PVDF binder, guar gum could suppress the voltage fading of lithium-rich materials. The average discharge voltage for electrodes with PVDF binder shifted from 3.45 V to 2.84 V after 200 cycles at 0.5 C, while for the electrodes with guar gum binder the average discharge voltage shifted from 3.48 V to 3.08 V. The capacity retention at 0.5 C is 62 % and 95 % for PVDF and guar gum binder, respectively. This improvement could be ascribed to the GG coated tightly on the surface of particles, hindering the side reaction and corrosion of the electrode. In a conclusion, our studies have demonstrated that the guar gum could be a low-cost, environmentally friendly and multi-functional binder for the next generation lithium-ion batteries with high energy density. REFERENCES: 1. Liu, J.; Zhang, Q.; Zhang, T.; Li, J. T.; Huang, L.; Sun, S. G., Adv. Funct. Mater. 2015, 25, 3599. 2. Zhang, T.; Li, J. T.; Liu, J.; Deng, Y. P.; Wu Z. G.; Yin, Z. W.; Guo, D.; Huang, L.; Sun, S. G., Chem. Commun. 2016, 52, 4683. ACKNOWLEDGEMENTS: This work was supported by National Natural Science Foundation of China (21373008, 21321062 and 21273184) and Natural Science Foundation of Fujian Province of China (No.2015J01063).