Hard carbon is a non-graphitizable carbon material built from randomly oriented graphene-like nanodomains, curved or fullerene-like fragments, and internal closed pores, and it cannot be converted into graphite even after treatment above about 2500 °C [1]. It is obtained mainly by pyrolysis of biomass, sugars, resins, and polymers at 1000–1600 °C, and its structure is usually described by the interlayer spacing (0.36–0.40 nm, against 0.335 nm for graphite) together with the volume fraction of closed micropores [2]. For sodium-ion batteries the material serves as the negative electrode, where reversible capacities of roughly 250–350 mAh/g are commonly reported [3]. Two storage processes are distinguished in the galvanostatic curve: adsorption of sodium at defect sites and pore surfaces, which gives the sloping region, and insertion or pore filling, which is associated with the low-potential plateau near 0.1 V [4]. Because plateau capacity depends on closed-pore volume, the balance between the sloping and plateau regions is governed by precursor selection, pyrolysis temperature, and heteroatom doping rather than by any single synthesis parameter [5]. Initial Coulombic efficiency, typically 70–90%, and the contribution of sodium metal plating to the measured capacity remain debated [3][,4].
- non-graphitizable carbon
- sodium-ion battery
- anode material
- sodium storage mechanism
- closed pore
- pyrolysis
- initial Coulombic efficiency
Advancements in Battery Materials·Electrical and Electronic Engineering·Engineering·Physical Sciences
References
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- Wahid, M.; Puthusseri, D.; Gawli, Y.; Sharma, N.; Ogale, S. Hard Carbons for Sodium-Ion Battery Anodes: Synthetic Strategies, Material Properties, and Storage Mechanisms. ChemSusChem 2018, 11, 506-526. [CrossRef]
- Dou, X.; Hasa, I.; Saurel, D.; Vaalma, C.; Wu, L.; Buchholz, D.; Bresser, D.; Komaba, S.; Passerini, S. Hard carbons for sodium-ion batteries: Structure, analysis, sustainability, and electrochemistry. Materials Today 2019, 23, 87-104. [CrossRef]
- Liu, L.; Tian, Y.; Abdussalam, A.; Gilani, M.R.H.S.; Zhang, W.; Xu, G. Hard Carbons as Anodes in Sodium-Ion Batteries: Sodium Storage Mechanism and Optimization Strategies. Molecules 2022, 27, 6516. [CrossRef]