Evaluating the Effects of Carbon Physicochemistry on the Rate Capability of Polyaniline and Phytic Acid-Derived Sodium-Ion Battery Anodes

As inexpensive anodes for sodium-ion batteries (SIBs), hard carbons are a highly tunable class of materials that hold promise to alleviate societal reliance on traditional lithium-based battery chemistries. However, the combination of sodium storage mechanisms, ranging from surface adsorption to pore-filling, has led to convoluted structure-function relationships and debate toward optimal desired material properties. To this end, a suite of nitrogen and phosphorus codoped carbons (NPCs) derived from phytic acid cross-linked polyaniline precursors were systematically evaluated as SIB anodes at practical cycling rates. The addition of calcium or zinc salts to the cross-linked polymerization process before pyrolysis ultimately led to nanoporous hard carbons with varied physicochemical properties and subsequent electrochemical performances. A majority of sodium storage capacity in these polyaniline-derived NPCs occurred in a higher-voltage, sloping region and primarily stemmed from sodium-ion adsorption at defective sites. This storage mechanism was also associated with increased stability compared to lower-voltage mechanisms related to bulk sodium insertion, both in cycle life and rate capability. Best-performing NPCs demonstrated an initial capacity of 212.1 mAh g(-1) with approximately 77% capacity retention over 300 cycles at a cycling rate of similar to 1 C, and high-rate testing revealed a considerable fast charge capacity of 117.8 mAh g(-1) (similar to 8 C, 7.5 min charge time). The superior rate performance and stability of certain NPCs were strongly correlated to the lateral nanocrystalline domain sizes (L-a). Overall, this study outlines a simple and tunable synthetic method for the production of high-performance NPCs for SIBs and sheds light on important considerations for the design of carbon anodes for practical SIBs.

Automated summary

Hard carbons are promising and tunable anode materials for sodium-ion batteries. This study evaluated nitrogen and phosphorus codoped carbons derived from phytic acid cross-linked polyaniline precursors as anodes for sodium-ion batteries. The addition of calcium or zinc salts during the synthesis process resulted in nanoporous hard carbons with varied physicochemical properties. The best-performing carbons exhibited excellent rate performance and stability, which were strongly correlated to the lateral nanocrystalline domain sizes.