A Water-Soluble NaCMC/NaPAA Binder for Exceptional Improvement of Sodium-Ion Batteries with an SnO₂-Ordered Mesoporous Carbon Anode

SnO₂@CMK-8 composite, a highly promising anode for Na-ion batteries (NIBs), was incorporated with polyvinylidene difluoride (PVDF), sodium carboxymethylcellulose (NaCMC), sodium polyacrylate (NaPAA), and NaCMC/NaPAA mixed binders to optimize the electrode sodiation/desodiation properties. Synergistic effects between NaCMC and NaPAA led to the formation of an effective protective film on the electrode. This coating layer not only increased the charge–discharge Coulombic efficiency, suppressing the accumulation of solid–electrolyte interphases, but also kept the SnO₂ nanoparticles in the CMK-8 matrix, preventing the agglomeration and removal of oxide upon cycling. The adhesion strength and stability towards the electrolyte of the binders were evaluated. In addition, the charge–transfer resistance and apparent Na⁺ diffusion of the SnO₂@CMK-8 electrodes with various binders were examined and post-mortem analyses were conducted. With NaCMC/NaPAA binder, exceptional electrode capacities of 850 and 425 mAh g⁻¹ were obtained at charge–discharge rates of 20 and 2000 mA g⁻¹, respectively. After 300 cycles, 90 % capacity retention was achieved. The thermal reactivity of the sodiated electrodes was studied by using differential scanning calorimetry. The binder effects on NIB safety, in terms of thermal runaway, are discussed.