Mechanism of Na‐Ion Storage in Hard Carbon Anodes Revealed by Heteroatom Doping

Abstract

Hard carbon is the leading candidate anode for commercialization of Na-ion batteries. Hard carbon has a unique local atomic structure, which is composed of nanodomains of layered rumpled sheets that have short-range local order resembling graphene within each layer but complete disorder along the caxis between layers. A primary challenge holding back the development of Na-ion batteries is that a complete understanding of the structure-capacity correlations of Na-ion storage in hard carbon has remained elusive. This article presents two key discoveries: first that characteristics of hard carbon's structure can be modified systematically by heteroatom doping, and second, that these structural changes greatly affect Na-ion storage properties, which reveals the mechanisms for Na storage in hard carbon. Specifically, via P or S doping, the interlayer spacing is dilated, which extends the low-voltage plateau capacity, while increasing the defect concentrations with P or B doping leads to higher sloping sodiation capacity. Our combined experimental studies and first principles calculations reveal that it is the Na-ion-defect binding that corresponds to the sloping capacity, while the Na intercalation between graphenic layers causes the low-potential plateau capacity. The new understanding provides a new set of guiding principles to optimize hard carbon for Na-ion battery applications.

Nanotube-like hard carbon as high-performance anode material for sodium ion hybrid capacitors

“…Raman spectra of NTHCs as shown in Fig. 3b exhibit broad D-bands around 1350 cm −1 and G-bands around 1580 cm −1 , which could be attributed to the disorder of graphite edges and crystalline graphite [44], respectively. The ratios of the intensity of D-and G-bands could be obtained by the spectra, with I D /I G being employed to index the degree of graphitic ordering.…”

Hard Carbons for Sodium‐Ion Battery Anodes: Synthetic Strategies, Material Properties, and Storage Mechanisms

“…[36][37][38][39] Bommier et al demonstrated that the total contribution of the sloping region was not af unction of interplanar separation;r ather,i ts howedalinear dependence on the defectd ensity. It is established that sodium storage proceeds through two pathways.…”

Bimetal-organic-framework derived CoTiO3 mesoporous micro-prisms anode for superior stable power sodium ion batteries

“…As present in Table 1, the asprepared pure CoTiO 3 micro-prisms also deliver significantly higher capacity and better rate capability than typical carbon materials [9][10][11], and pure TiO 2 anode materials, meanwhile, show similar or even better electrochemical performance with N, Mo, Sn doped TiO 2 and ultra-small sized TiO 2 [13][14][15][16][17][18][19][20][21][22][23][24]. The better electrical conductivity of CoTiO 3 than NiTiO 3 , TiO 2 , because of the narrower band gap of CoTiO 3 (2.34 eV) than NiTiO 3 (3.02 eV) and TiO 2 (3.3 eV), should be one of the reason responsible for the much enhanced sodium ion storage performance [31,32].…”

“…Before this, one of the urgent research interests for materials scientists delved into next generation SIBs is developing novel low cost anode materials with higher capacity and better cycle stability at higher power state, since the migration resistance to Na + is much larger than that to Li + . Nowadays, various advanced carbon materials have been applied as high power anode materials for SIBs, but their relatively low capacity limit the future application [9][10][11]. Nanostructured transition metals (Sn, Sb, etc.)…”