Regulating B-N moieties in carbon anode toward stable and fast potassium-storage

Boron (B) and nitrogen (N) co-doped hard carbons usually tend to deliver an excellent rate and ultra-long cycle lifespan, because of the formed B-N moieties can accelerate both ion/electron transfer. However, the rational regulation of B-N moieties content is rarely mentioned, and correlating rate and reversible capacity with B-N moieties content is still lacking yet. Hence, a series of B/N co-doped hard carbons are designed based on varied carbonization temperatures. Systematic characterizations prove that the introduced B-heteroatoms can create more defects and form well-developed pore channels. Besides, with increasing carbonization temperatures, B-N moieties content first increases and then decreases, which is in accordance with the evolution of defect degree of carbon matrix. Therefore, rich B-N moieties can induce more defect sites to greatly improve capacitive contribution, and as a result both rate and reversible capacity are strongly correlated with B-N moieties content. Based on this, the electrode with the highest B-N moieties content (79.6%) realizes an excellent rate (220.9 mAh g(-1) at 2 A g(-1)) and cycling stability (over 2000 cycles). Note that the storage of B-N moieties on K+ only occurs in a high potential region (>0.5 V), and this process is highly reversible.