A Dual Protection System for Heterostructured 3D CNT/CoSe₂/C as High Areal Capacity Anode for Sodium Storage

Abstract

TMC) based material, are very promising candidates as an anode for SIB due to their higher theoretical capacity (≈494.36 mAh g −1 for CoSe 2 ) than graphite (≈35 mAh g −1 ) [7,8] and low synthesis cost. [9,10] Nevertheless, severe volume changes during sodiation/desodiation process, slow transport of charges, and diffusion of Na + along with high intrinsic resistance resulted in capacity fading and hindered the practical application of transition metal diselenides. [9,11] Until now, a lot of efforts have been devoted to overcome these issues by synthesizing transition metal diselenides based nanostructures with various shapes, morphologies, and particle sizes. [10][11][12] Although creating voids, hollow, or porous nanostructures have improved the gravimetric capacity due to their ability to accommodate the volume expansion, shorten the diffusion path for charge transportation, optimized the electrode and electrolyte contact area, etc. [13,14] However, downsizing the materials at the nanoscale is not always in favor of rechargeable batteries for practical applications. [15] Because the nanomaterials possess low tap density that results in low areal mass loading (<1 mg cm −2 ), consequently lowering the areal and volumetric capacities which are very important metrics in practical applications. [16,17] Traditional high areal mass loadings of active material bring high electrode thicknesses which severely limits the in-depth accessibility of active materials ultimately fading the reversible capacity. [15,18] 3D electrode design is normally opted for multiple advantages, however, instability/detachment of active material causes the pulverization and degradation of the structure, and ultimately poor cyclic stability. Here, a dually protected, highly compressible, and freestanding anode is presented for sodium-ion batteries, where 3D carbon nanotube (CNT) sponge is decorated with homogeneously dispersed CoSe 2 nanoparticles (NPs) which are protected under carbon overcoat (CNT/CoSe 2 /C). The 3D CNT sponge delivers enough space for high mass loading while providing high mechanical strength and faster conduction pathway among the NPs. The outer amorphous carbon overcoat controls the formation of solid electrolyte interphase film by avoiding direct contact of CoSe 2 with electrolyte, accommodates large volume changes, and ultimately enhances the overall conductivity of cell and assists in transmitting electron to an external circuit. Moreover, the hybrid can be densified up to 11-fold without affecting its microstructure that results in ultrahigh areal mass loading of 17.4 mg cm −2 and an areal capacity of 7.03 mAh cm −2 along with a high gravimetric capacity of 531 mAh g −1 at 100 mA g −1 . Thus, compact and smart devices can be realized by this new electrode design for heavy-duty commercial applications.

In‐Situ Fabrication of Bone‐Like CoSe2 Nano‐Thorn Loaded on Porous Carbon Cloth as a Flexible Electrode for Na‐Ion Storage

“…Compared to CoSe 2 /CC, the lower initial CE of BLÀ CoSe 2 /PCC results from the nano-thorn structure and porous character with higher surface area, leading to more formation of stable SEI layer, side reaction and irreversible electrolyte decomposition in the initial cycle. [30][31][32] The cycling capabilities of the both electrodes at a current density of 0.1 A g À 1 and consistent CE are shown in Figure 5c. The BLÀ CoSe 2 /PCC electrode with mass loading of 0.50 mg cm À 2 delivers a stable reversible capacity of 360.7 mAh g À 1 (0.18 mAh cm À 2 ) after 180 cycles, and the CE of the electrode remains around 100% during cycling.…”

Core–Shell FeSe2/C Nanostructures Embedded in a Carbon Framework as a Free Standing Anode for a Sodium Ion Battery

“…According to Equation (4), the larger slope between Z re and ω −1/2 stands for a higher Na + diffusion coefficient. [10,24] In Equation (4), R is the gas constant, T is absolute temperature, S is the area of electrodes, n is the electron transfer during oxidation/reduction process, F is the Faraday constant, and C is the Na + ion concentration. The calculated outcomes of D Na specify that amorphous coated electrodes, (i.e., CNT/FeSe 2 /C-1 [1.1 × 10 −10 cm 2 s −1 ] and CNT/FeSe 2 /C-2 [5.3 × 10 −11 cm 2 s −1 ]) exhibit faster Na + ion transport than uncoated (CNT/FeSe 2 [3.28 × 10 −11 cm 2 s −1 ]).…”

“…Recently, transition metal selenides (TMSe) are found highly suitable for sodium storage due to their large theoretical capacities (>450 mAh g −1 ) and comparably high conductivities. [ 9–10 ] Moreover, TMSe did not suffer from the poly‐sulfide anion shuttle effect that is normally associated with sulfide type anodes. [ 11 ] Taking an example of TMSe, FeSe 2 is highly attractive as an anode for SIBs due to a large abundance of Fe, low toxicity, environment benignity, good chemical stability, selenium‐rich structure and high theoretical capacity (501.5 mAh g −1 ).…”

Synthesis of Porous Ni‐Doped CoSe2/C Nanospheres towards High‐Rate and Long‐Term Sodium‐Ion Half/Full Batteries

“…In the thirdw eight loss stage, CoSe furtherd ecomposes into Co 3 O 4 and SeO 2 . [36,37] Figure 3e shows al arge number of uniform nanospheres with diameters in the range 600-800nm. The surface structure of the Ni-CoSe 2 /C can be clearly seen in am agnified SEM image, as shown in Figure 3f.…”