High-Performance Hard Carbon Anode: Tunable Local Structures and Sodium Storage Mechanism

Abstract

Hard carbon (HC) is one of the most promising anode materials for sodium-ion batteries (SIBs) due to its suitable potential and high reversible capacity. At the same time, the correlation between carbon local structure and sodium-ion storage behavior is not clearly understood. In this paper, the two series of HC materials with perfect spherical morphology and tailored microstructures were designed and successfully produced using resorcinol formaldehyde (RF) resin as precursor. Via hydrothermal self-assembly and controlled pyrolysis, RF is a flexible precursor for high-purity carbon with a wide range of local-structure variation. Using these processes, one series of five representative RF-based HC nanospheres with varying degrees of graphitization were obtained from an RF precursor at different carbonization temperatures. The other series of HC materials with various microscopic carbon layer lengths and shapes was achieved by carbonizing five RF precursors with different cross-linking degrees at a single carbonization condition (1300 °C and 2 h). On the basis of the microstructures, unique electrochemical characteristics, and atomic pair distribution function (PDF) analyses, we proposed a new model of “three-phase” structural for HC materials and found triregion Na-ion storage behavior: chemi-/physisorption, intercalation between carbon layers, and pore-filling, derived from the HC phases, respectively. These results enable new understanding and insight into the sodium storage mechanism in HC materials and improve the potential for carbon-based SIB anodes.

High-performance sodium-ion batteries with a hard carbon anode: transition from the half-cell to full-cell perspective

“…Generally, the primary debate is on the detailed sodiation process during the "sloping part" and "plateau part", and there are mainly four potential candidates for the two parts of the capacity: defect absorption, 29 nanopore filling, 30 interlayer intercalation, 4 and underpotential deposition. 1 Some typical speculations 3,4,29,31,32 are demonstrated in Fig. 3(B-D) but none of the models can explain all the experimental facts well.…”

Carbon Anode Materials: A Detailed Comparison between Na‐ion and K‐ion Batteries

“…[59] Pore-filling mechanism is also a kind of possible ions storage mechanism. [60][61][62][63][64][65][66] For carbon materials with abundant pores, alkali ions can fill in pores to realize ions storage. Xu and co-workers [60] provided solid evidence to demonstrate pore-filling mechanism by two comparative experiments: hard carbon materials with abundant micropores delivered a low-voltage plateau while filling S into the pores of hard carbon could remove this plateau.…”

Hard Carbon Anodes: Fundamental Understanding and Commercial Perspectives for Na‐Ion Batteries beyond Li‐Ion and K‐Ion Counterparts

“…The first region of potential slope for the sodiation at 1.0–0.1 V with high D ion may be derived from easily accessible sites such as defects, since these slope capacities decrease with increasing pyrolysis temperature which may be due to the reduction of defects during thermal treatment. [ 49 ] The second region of the potential plateaus for the sodiation at 0.1–0.03 V with decreasing D ion upon discharge, which is likely to be stemmed from the intercalation of Na + into the graphitic domains. Additionally, the D ion of the third region for the sodiation at 0.03–0 V increased during discharge which was proposed to be due to the possible pore filling with Na clusters.…”

“…e,f) Reproduced with permission. [ 49 ] Copyright 2018, American Chemical Society. g,h) Adapted with permission.…”