Effect of Cobalt Doping on Enhanced Lithium Storage Performance of Nanosilicon

Abstract

High-capacity silicon anodes are attracting more attention, owing to their high theoretical capacities and low working potentials. However, massive volume changes and low intrinsic electric conductivity remain substantial challenges that limit the practical applications of these anodes in lithium-ion batteries (LIBs). In this study, cobalt-doped silicon nanoparticles with different Co concentrations (0.1 %, 0.3 %, and 0.5 %) are prepared by using a simple low-temperature annealing process and are studied as anodes for LIBs. Compared to pure silicon, the obtained 0.5 % cobalt-doped silicon anode can serve as a promising anode and shows a high discharge capacity of 3409 mAh g À 1 (97.2 % capacity retention vs. first reversible capacity) with 98.1 % coulombic efficiency after 40 cycles, at 200 mA g À 1 . After a long 320 cycles, the electrode delivered 3029 mAh g À 1 with 86.4 % capacity retention. This cobalt-doped silicon anode also exhibits superior rate capability and a highly stable long cycle life at higher current densities as well as high mass loading. These remarkable enhancements in electrochemical properties indicate that cobalt doping yields increased conductivity, mitigates volume expansion, and provides shorter lithium transportation lengths across the silicon nanoparticles.

Facile Synthesis of Porous Hollow Cobalt‐Doped λ‐MnO2 Nano Architectures as a High‐performance Anode Material for Li‐ion Batteries and Li‐ion Hybrid Supercapacitors

“…For Li1s spectra, the broad peak at 55.02 eV can be assigned to LiOH/ Li 2 CO 3 (∼ 55.0 eV), Li 2 O (∼ 55.6 eV), and LiCOR (54.5 eV), suggests that these are observed from the composition of SEI film. [45][46][47] Another convincing piece of evidence to support Mn 3 O 4 secondary phase formation is the measured CV scans for h-CoMO shown in Figure 6b; where all three scans show a shift of single cathodic peak to higher potentials from 0.25 to 0.3 V and two anodic peaks at 1.3 and 2.2 V, which is consistent with what was observed CV peaks for Mn 3 O 4 electrode in the literature. [49] Also, comparing the CV scans of MnO 2 (h-MO) to Mn 0.95 Co 0.05 O 2 (h-CoMO), the main cathode peak shifted from 0.27 to 0.3 V after 3 CV scans indicate Co doping progress in the oxidation of MnO 2 outer surface during cycling.…”

“…It is observed that the R ct value of h-CoMO is increased where the h-MO is decreased to a small extent, and it could be due to the morphological changes that occurred during Li + reactions with the anode materials. [46,23] The summarized R s , R SEI , and R ct values are shown in Table S3 The fast Li + reactions in the electrodes are estimated by the diffusion coefficient and can be determined by the following equation,…”

“…[47] The evaluated Co chemical states represent main Co 2P 3/2 and Co 2P 1/2 peaks with binding energies at 780.4 and 798 eV which can be assigned to the Co 3 + , Co 2 + due to the formation of Co 3 O 4 and CoO phases as the possible extruded Co oxide phases after the Li-ion reaction. [46] After intensive 100 cycles, the O ads /O lat is greatly enhanced, implying that more adsorbed oxygen species are enriched on the surface obtained from the created carbonates that are generated during the formation of the SEI layer. The major O1s peak for the after analyzed sample shifts a little to the higher level, indicating the change in the coordinating configuration of (Mn, Co)À O, which could be due to the formation of (Mn 2 + , Mn 3 + )À O and CoÀ O.…”

“…The proposed circuit has the solution resistance (R s ), SEI layer resistance (R SEI ), charge transfer resistance (R ct ), two constant phase elements (CPE), and Warburg Impedance (W b ) as parameters and is simulated by ZSimpWin software. It is observed that the R ct value of h‐CoMO is increased where the h‐MO is decreased to a small extent, and it could be due to the morphological changes that occurred during Li + reactions with the anode materials [46,23] . The summarized R s , R SEI , and R ct values are shown in Table S3 The fast Li + reactions in the electrodes are estimated by the diffusion coefficient and can be determined by the following equation, …”

“…This process may shift the Mn 2p peaks to lower binding energy values that can cause a change in the Mn oxidation states, i. e., 641.3 and 653 eV, which are consistent with the binding energy of Mn(II) to Mn(III) in Mn 2+ (Mn 3+ ) 2 O 4 [47] . The evaluated Co chemical states represent main Co 2P 3/2 and Co 2P 1/2 peaks with binding energies at 780.4 and 798 eV which can be assigned to the Co 3+ , Co 2+ due to the formation of Co 3 O 4 and CoO phases as the possible extruded Co oxide phases after the Li‐ion reaction [46] . After intensive 100 cycles, the O ads /O lat is greatly enhanced, implying that more adsorbed oxygen species are enriched on the surface obtained from the created carbonates that are generated during the formation of the SEI layer.…”