Cobalt-Doped NiS₂ Micro/Nanostructures with Complete Solid Solubility as High-Performance Cathode Materials for Actual High-Specific-Energy Thermal Batteries

Abstract

Transition-metal sulfides are key cathode materials for thermal batteries used in military applications. However, it is still a big challenge to prepare sulfides with good electronic conductivity and thermal stability. Herein, we rapidly synthesized a Co-doped NiS2 micro/nanostructure using a hydrothermal method. We found that the specific capacity of the Ni1–x Co x S2 micro/nanostructure increases with the amount of Co doping. Under a current density of 100 mA cm–2, the specific capacity of Ni0.5Co0.5S2 was about 1565.2 As g–1 (434.8 mAh g–1) with a cutoff voltage of 1.5 V. Owing to the small polarization impedance (5 mΩ), the pulse voltage reaches about 1.74 V under a pulse current of 2.5 A cm–2, 30 ms. Additionally, the discharge mechanism was proposed by analyzing the discharge product according to the anionic redox chemistry. Furthermore, a 3.9 kg full thermal battery is assembled based on the synthesized Ni0.5Co0.5S2 cathode materials. Notably, the full thermal battery discharges at a current density of 100 mA cm–2, with an operating time of about 4000 s, enabling a high specific energy density of around 142.5 Wh kg–1. In summary, this work presents an effective cathode material for thermal battery with high specific energy and long operating life.

Ternary Transition Metal Sulfide as High Real Energy Cathode for Lithium–Sulfur Pouch Cell Under Lean Electrolyte Conditions

“…Therefore, the crystal lattice exhibits the same spacing ( d = 0.248 nm) at the surface and in the center of FCN111 particles in HRTEM, which is exactly between FeS 2 ( d = 0.242 nm), [ 57 ] CoS 2 ( d = 0.247 nm), [ 54 ] and NiS 2 ( d = 0.254 nm), [ 54 ] indicating that FCN111 is more like a solid solution structure formed by the three elements (Fe, Co, and Ni). [ 53,55 ] The FCN111 crystals expose the (210) crystal plane, similar to some Fe‐based alloy sulfides in previous studies. [ 53 ] Figure 2e shows the EDS results of FCN111/GC without S 8 loading.…”

“…Therefore, valence of Co in both FCN111/GC and FCN111@S/GC with L 3 absorption peaks at 781.5 eV exhibit a mixed‐valence of Co 2+/3+ , which is different from previously reported Fe−Co alloy sulfides or Ni−Co alloy sulfides with only Co 2+ . [ 53,55 ] In Figure 3c, FCN111/GC and FCN111@S/GC are in full agreement with L‐edge absorption peaks of NiS 2 , indicating that Ni adopts a valence of 2+ in both samples. The same conclusion can also be drawn from the 2p orbital spectra of Fe, Co, and Ni, as shown in Figures S5–S10, Supporting Information, in XPS.…”

“…In other electrochemical fields, it was shown that polybasic sulfides, such as Fe x Co 1− x S 2 and Ni x Co 1− x S 2 exhibited better electrochemical performance compared to CoS 2 , NiS 2 , and FeS 2 . [ 52–55 ] Therefore, we postulate that ternary sulfides with a 3d orbital transition metal cation from group VIII may integrate advantages of the above materials. The surface electrically positive nature of the ternary sulfides may theoretically generate strong Lewis acid–base interactions with polysulfides, [ 42 ] thereby improving the working performance of ternary sulfides.…”

Fabrication of the Ni-NiCl2 Composite Cathode Material for Fast-Response Thermal Batteries

“…For example, the voltage decreases from 100 to 70 V under a current density of 6 A/ cm 2 in the Ni-NiCl 2 battery at 25 s. The voltage drop in the Ni-NiCl 2 system (Figure 7A) is 30 V and the corresponding internal resistance is 0.12 Ω (Figure 7B), which is significantly lower than that of the FeS 2 (70 V, 0.28 Ω) and CoS 2 (65 V, 0.26 Ω) thermal batteries. Moreover, as shown in Figure 7C, the activation time of the Ni-NiCl 2 battery is significantly lower than those of previously reported thermal batteries (Liu and Chu, 2004;Yu et al, 2018;Guo et al, 2019;Gui et al, 2020;Guo et al, 2020;Luo et al, 2020), which indicates the quick response ability of the battery. The power density of Ni-NiCl 2 (11.4 kW/kg), as shown in Figure 7D, is considerably higher than those of several previously reported electrode materials (Zhu et al, 2012;Yu et al, 2018;Guo et al, 2019;Gui et al, 2020;Guo et al, 2020;Luo et al, 2020).…”

“…Moreover, as shown in Figure 7C, the activation time of the Ni-NiCl 2 battery is significantly lower than those of previously reported thermal batteries (Liu and Chu, 2004;Yu et al, 2018;Guo et al, 2019;Gui et al, 2020;Guo et al, 2020;Luo et al, 2020), which indicates the quick response ability of the battery. The power density of Ni-NiCl 2 (11.4 kW/kg), as shown in Figure 7D, is considerably higher than those of several previously reported electrode materials (Zhu et al, 2012;Yu et al, 2018;Guo et al, 2019;Gui et al, 2020;Guo et al, 2020;Luo et al, 2020). In addition, the comparison of the power density of the present thermal batteries is summarized in Supplementary Table S2.…”