Thermal Stability of Nanocrystalline NiS₂ as High Specific Capacity Thermal Battery Cathode Material

Abstract

Nanocrystallization can shorten the Li+ transport distance, resulting in the enhancement of electrochemical activity for cathode materials. However, nanocathode materials tend to be thermally unstable, further leading to poor electrochemical performance of a battery system. This disadvantage can be especially detrimental for thermal batteries because they are often operated at high temperatures (≥450 °C). Herein, the decomposition character of NiS2 at 500 °C is investigated. The decomposition temperatures of NiS2 are found to decrease from 510 to 350 °C with the grain size decreasing to 39 nm, due to the dramatically increased surface energy. The decomposition product is confirmed to be NiS, evidenced by a high‐temperature X‐ray diffractometer. The useful mass of the cathode will reduce once the discharging temperature is higher than 500 °C. Namely, although the small grain size shorthens the Li+ transport distance, the discharge performance of the NiS2 cathode may also decrease due to its inferior thermal stability. For the Li‐B/LiF–LiCl–LiBr/NiS2 system, the NiS2 with the grain size of 70 nm shows the highest specific capacity of 831 mAh g−1 under the discharging temperature of 500 °C, with the cut‐off voltage of 0.5 V, compared with other grain sizes from 39 to 112 nm.

In Situ Fabrication of NiS2 Nanoparticle-Coated g-C3N4 as a Cathode for Enhanced Lithium Thermal Battery Performance

“…Figure d displays a comparison diagram of specific capacity and peak voltage of various cathode materials of Li thermal batteries. This as-synthesized NiS 2 @g-C 3 N 4 cathode material exhibits superior performances with a higher specific capacity than previously reported cathode materials, such as transition metal fluorides (FeF 3 and NiF 2 ), transition metal chlorides (NiCl 2 ), transition metal oxides (CuO, Cu 2 O, and NiO), and other transition metal sulfides (CoS 2 , CoS 2 , MoS 2 , FeS 2 , ZrS 3 , WS 2 , FeS 2 , NiS 2 , and NiS 2 ).…”

“…(a) Discharge specific capacity of 2NCN and 5NCN samples at 100 mA cm –2 at 500 °C; (b) discharge capacity of the 5NCN sample at 50, 100, 300, and 500 mA cm –2 at 500 °C; (c) discharge capacity of the 5NCN sample at 100 mA cm –2 at 450, 475, 500, and 525 °C; (d) comparison of the specific capacity and peak voltage of different cathode materials for Li thermal batteries reported in the literature; ,,− (e) pulse discharge curve and internal resistance of 2NCN and 5NCN with a pulse current density of 300 mA cm –2 for 2 s every 30 s under a constant current density of 100 mA cm –2 ; (f) EIS curves of 2NCN and 5NCN electrodes.…”

“…Transition metal sulfides, such as FeS 2 , CoS 2 , , and NiS 2 , have been reported as promising cathode materials for Li thermal batteries due to their multiple valence state and high theoretical specific capacity. , Among them, NiS 2 has been attracting more and more attention owing to its earth-abundant, low-cost, and easy synthesis and is used as an emerging cathode material for Li thermal batteries. − For example, Xu et al . synthesized the micro/nano-NiS 2 cathode displaying a specific capacity of 271.2 mAh g –1 with a cut-off voltage of 1.4 V at 0.2 A cm –2 at 500 °C.…”

High‐Temperature Solid‐State Synthesis and Electrochemical Properties of Transition Metal Sulfides for Thermal Batteries

“…[24] However, due to its narrow window, it can only be synthesized by liquid-phase method with low yield and cumbersome process. [25,26] To realize the mass production of cathode materials and meet the needs of modern weapon systems, this paper adopts the high-temperature solid-phase method with simple process and high production efficiency to synthesize single-phase FeS 2 , CoS 2 and NiS 2 by adjusting the synthesis temperature. The high-temperature solid-phase method uses pure powder as raw material, which can realize complete conversion from raw material to product, and reduce waste and cost.…”

“…[ 24 ] However, due to its narrow window, it can only be synthesized by liquid‐phase method with low yield and cumbersome process. [ 25,26 ]…”