Critical Role of Potential-Driven Charge Effects in Hard Carbon Anodes for Sodium Storage.

Sodium (Na) storage in hard carbon (HC) is a fundamental electrochemical process for sodium-ion batteries, where adsorption energy critically influences charge/discharge rates and storage capacity. Accurate prediction of this energy is essential for designing of high-performance HC. Traditional quantum mechanical simulations often neglect charge effects from electrochemical potentials, leading to inaccurate adsorption energies and discrepancies with experiments. Here, we demonstrate that potential-driven charge effects play a pivotal role in governing Na storage under realistic conditions. To address this, we develop a charge-dependent computational model (CDM) that explicitly incorporates potential-induced charge dynamics. Using flat carbon layers as a model, we show that charge effects significantly influence the identification of active Na-storage sites and induce sodiation/desodiation voltage shifts exceeding 1.1 V relative to conventional charge-neutral models. These effects originate from distinct chemical reactivities between neutral and charged carbon. When extended to curved and defect-rich carbon-hallmarks of HC-CDM accurately predicts storage sites and voltage-capacity profiles that closely match experimental data. This work resolves long-standing theory-experiment inconsistencies and provides a powerful framework for designing next-generation sodium-ion batteries.