Surface structure optimization of hard carbon to improve its initial coulomb efficiency for sodium-ion storage

Hard carbon is one of the most prospective anode materials for sodium-ion batteries (SIBs). It has high capacity, low operating potential and low cost, but its low initial Coulomb efficiency (ICE) and poor rate performance seriously hinder the further application of hard carbon materials. This paper reports a method of regulating defects and residual oxygen atoms on the surface of commercial hard carbon by using methane molecules, which improves its low ICE materials due to the influence of surface and defect structure. By simply post-heat treating commercial hard carbon in an argon atmosphere containing 5% methane, the ICE increased from 80% to 90%, the reversible capacity increased from 270 mA h g- 1 to 310 mA h g-1, and the rate performance and cycle stability were also significantly improved in sodium-ion half cells. The effectiveness of the hard carbon modification strategy was further verified in the sodium-ion full cell. This work provides an effective method for the engineering of hard carbon heteroatoms and defects and a new idea and insight for the realization of high performance commercial hard carbon.