A Promising Hard Carbon−Soft Carbon Composite Anode with Boosting Sodium Storage Performance

Abstract

Hard carbon anodes are the most promising candidates for sodium-ion batteries due to lower sodium-embedded platform and higher specific capacity. However, pure hard carbon carbons usually show very low initial coulombic efficiency, low electronic conductance, et al. Herein, hard carbon-soft carbon (HC-SC) composites composed of carbon nanotubes (CNTs) blooming on porous hard carbon, which were synthesized through thermal decomposition of zeolitic imidazolate framework-67 (ZIF-67) and polyvinyl alcohol (PVA) composite. This unique structure could greatly promote the sodium-ion diffusion and electron transport due to the increased electrode/ electrolyte contact area and enlarged pores. As expected, the HC-SC delivers a high capacity (306.8 mAh g À 1 at 500 mA g À 1), impressive cycling stability (256.8 mAh g À 1 after 1000 cycles) and enhanced rate performance (144.9 mAh g À 1 at 20 C), which are far superior to those of both individual hard carbon and soft carbon. This encouraging performance may benefit from the synergistic effect of the modified defect concentration and interlayer distance in hard carbon by soft carbon, as well as the unique hierarchical structure. This work provides an exemplary strategy to develop optimized carbon materials for sodium-ion batteries.

Directional Regulation of Surface Chemistry of Graphene Using Carbon Dots for Sodium-Ion Battery Anodes

“…The reason for the existence of a higher R SEI may be that the introduction of defects and OFGs can modulate the hydrophobicity of the electrode, which further affects the wettability of the electrolyte. 55 The values of R e are similar for all samples, while the values of R ct of CDs/rGO are higher than those of GO resulting from the defect-rich structure of CDs. 56 The 0.4 CDs/rGO displays a smaller R ct (106.8 Ω) compared with that of 0.2 CDs/rGO (111.7 Ω) and 0.6 CDs/rGO (134.2 Ω).…”

Advantageous Tubular Structure of Biomass-Derived Carbon for High-Performance Sodium Storage

“…(1) reversible absorption/desorption at the surface, edges, and defective regions of the carbon materials and the insertion/ deinsertion in graphene-like layers/turbostratic carbon domains, corresponding to the slope capacity of 0.1−1.0 V; 41 (2) the plateau below 0.1 V corresponding to the filling of Na + to the voids; 42,43 and (3) the capacity over 1.0 V owing to the Faradaic pseudocapacitance provided by heteroatomic functional groups. 9,32 Herein, no voltage platform region under 0.1 V in the GCD profiles was observed, indicating no sodium cluster fillings and Na deposition to the closed micropores/ voids in the NPF-500 storage.…”

“…It can be observed that the initial specific discharge/charge capacity in the first cycle is 523.0 and 260.0 mA h g –1 with a Coulombic efficiency of 49.7%, which is due to the irreversible reactions of SEI formation. The Na storage mechanism of carbon materials generally includes three steps: (1) reversible absorption/desorption at the surface, edges, and defective regions of the carbon materials and the insertion/deinsertion in graphene-like layers/turbostratic carbon domains, corresponding to the slope capacity of 0.1–1.0 V; (2) the plateau below 0.1 V corresponding to the filling of Na + to the voids; , and (3) the capacity over 1.0 V owing to the Faradaic pseudocapacitance provided by heteroatomic functional groups. , Herein, no voltage platform region under 0.1 V in the GCD profiles was observed, indicating no sodium cluster fillings and Na deposition to the closed micropores/voids in the NPF-500 storage . Generally, the plateau voltage is lower than 0.1 V because sodium fills the internal pores/voids, and the aggregated sodium clusters tend to deposit and generate sodium dendrites when approaching 0 V. Sodium dendrites can pierce the diaphragm and cause short circuit, posing a safety hazard to the entire battery system. , Consequently, the elimination of platform capacity is more favorable to ensure the safety and cycle stability of the battery .…”

Preparation of CoO/SnO2@NC/S composite as high-stability cathode material for lithium-sulfur batteries

“…The larger radius of the semicircle in the high frequency ranges show that the greater interface impedance between the surface of the active material and the electrolyte, and the greater the charge transfer resistance. After the charge-discharge cycle of the two materials, the semicircle of the impedance curve gradually become smaller, it found that the active material is activated after the cycle, the protective SEI layer film gradually forms, the interface impedance reduces, the electron diffusion rate and ion transfer ability are continuously enhanced, and the charge transfer ability is improved [43][44]. Comparing the impedance curves of the two materials before and after cycling, it is found that the semicircle of CoO/SnO 2 @NC/S composite is significantly smaller than the curve of precursor/S composite.…”