The electrode deterioration and capacity decay caused by the dissolution of transition metal ions have been criticized for a long time. The branched polyethyleneimine (PEI) was employed as a functional binder for spinel lithium manganese oxide (LiMn2O4, LMO) and layer structure lithium cobalt oxide (LiCoO2, LCO) to resolve the problem. Due to the chelation reaction of amine groups, PEI polymer binder can effectively absorb soluble transition metal ions, which is beneficial to reduce the loss of active materials. For PEI-based cathode, the uniform distribution of key components is achieved by the rapid curing process of water, which endow PEI-based cathode with a higher Li+ diffusion coefficient and improved electrochemical reaction kinetics. In addition, the fixed binder coating is favorable to protecting the active materials from parasitic reaction with the lithium hexafluorophosphate (LiPF6)-based electrolyte. Therefore, the PEI-based cell shows superior rate capability and long-term cycle performance. Functional binders of this study provide a simple and effective strategy to achieve higher capacity and longer cycle stability for transition metal oxide electrodes.
Keywords: binder; lithium cobalt oxide; lithium manganese oxide; lithium metal battery; polyethylenimine.