Revisiting the Low-Temperature “Stablization Process” for Starch-Derived Hard Carbon Anodes

Sodium-ion batteries are applicable in cost-sensitive fields like grid electricity storage systems due to the widely distributed of sodium reserves. Hard carbons currently stand out as the most promising anode for practical sodium-ion batteries, but their performance and economy require improvement. In this work, we successfully developed spherical hard carbons through controlled pyrolysis of starch. Starch has an attractive natural spherical morphology, but direct pyrolysis leads to the cracking of spherical structure caused by the rapid release of small molecules. To address this issue, we employed an additive-free "stablization process" to establish a stable structure prior to pyrolysis. The underlying principle of this "stablization process" has been clarified: preheating starch below its melting point prompts partial thermal decomposition, preventing structural meltdown during subsequent decomposition. The resulting hard carbon, obtained through controlled pyrolysis, exhibits a high tap density exceeding 1 g cm -3 and the optimal reversible capacity reaches 321 mAh g -1 with an outstanding initial columb efficiency of 88% at 30 mA g -1 . Furthermore, its practical application was validated via multi–layer pouch cells. When coupled with Na 2 Fe(SO 4 ) 2 cathode, the pouch cell demonstrated a cycle life approaching 1000 cycles, surpassing all starch-based hard carbons reported thus far. This work guides an efficient approach for fabricating high–performance, remarkably economical hard carbon anodes for practical application of sodium-ion batteries.