Lithium polyacrylate (LiPAA) is widely used as a binder for lithium-ion battery anodes due to its high ionic conductivity and good chemical stability. However, LiPAA has disadvantages such as low viscosity and high hardness, as a result of which the adhesive performance, flexibility and processability of the anode becomes an issue when LiPAA is used as a binder. In this paper, a composite formula was developed by integrating LiPAA with other polymers, including carboxymethyl cellulose (CMC) or Xanthan gum (XG) to tune the viscosity, sodium hyaluronate (HA) to reduce the brittleness, and benzene butadiene rubber (SBR) to improve the stripping strength. On this basis, two LiPAA-based composite binders (LiPAA-CMC-HA-SBR and LiPAA-XG-HA-SBR) were developed. Compared with the commercial anode binder (CMC-SBR), the two LiPAA-based composite binders both demonstrate well-tuned bonding strength and flexibility; more importantly, they also can significantly improve the interfacial affinity between the graphite particles, the conductive agent and the electrolyte, which hence promotes the diffusion kinetics of lithium ions at the electrode/electrolyte interface and thus improves the electrochemical performance of the graphite anode. At the current density of 0.5 C, after 150 cycles, the graphite anode prepared with our two composite binders display a capacity of 209 mAh g^-1 and 191 mAh g^-1, respectively, which was much higher than the graphite anode prepared with the commercial CMC-SBR binder (which is 108 mAh g^-1). The graphite anode prepared with our binder also demonstrate much higher rate capability and better cycling stability compared to the control. Characterizations of the cycled anode reveal that, in the anode prepared with our binders, much more homogeneous distribution of the conductive carbon and the graphite particles was observed, and a SEI with higher fraction of LiF was formed. In addition, in the commercial CMC-SBR formula, a mass fraction of SBR up to 50% is required; in comparison, in our two LiPAA-based formulations, only a small fraction of SBR is employed yet which can still maintain the integrity of the anode sheet. It is worth noting that, at a low binder content (~3%) and high active material load (~95%), the graphite anode sheet prepared by these two composite binders can still maintain remarkable mechanical strength, and it also demonstrates excellent electrochemical performance, showing the promising industrialization potential of such LiPAA-based composite binders.

Key words: Lithium-ion batteries, Graphite anode, Composite binder, Lithium polyacrylate