Creating rich closed nanopores in anthracite-derived soft carbon enables greatly-enhanced sodium-ion storage in the low-working-voltage region

Abstract

Soft carbon, characterized by its abundant reserves, low cost, and high carbon yield, should have been an important choice for anode materials in sodium-ion batteries (SIBs), similar to hard carbon. However, traditional high-temperature synthesis tends to graphitize soft carbon, which is extremely detrimental to the adsorption and intercalation of Na⁺ ions. This raises a highly challenging scientific question: whether it is possible to suppress the graphitization of soft carbon and transform it towards closed nanopores favorable for Na⁺ storage during high-temperature treatment. Herein, we introduce flash Joule heating (FJH) technology to treat anthracite with rapid heating and quenching, obtaining metastable soft carbon (anthracite-FJH) containing a large number of short-range ordered graphitic microdomains and their assembled closed nanopores. Benefiting from the abundant closed nanopores, this kinetically-controlled soft carbon exhibits a significantly enhanced Na⁺ adsorption and pore-filling capacity of 309 mAh g⁻¹ at 0.1 C, dominantly contributed by the low-voltage plateau. Moreover, a reversible specific capacity of 256.2 mAh g⁻¹ is maintained at 0.5 C with a capacity retention of 93.2 % after 200 cycles. We experimentally and theoretically explicitly disclose the “carbon microstructure regulation-Na⁺ storage mechanism” relationship. This work paves the way for the disruptive synthesis of high-capacity soft carbon SIB anodes based on anthracite