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• The coating layer of carbon was designed for a bare CuF 2 cathode. • The carbon layer inhibits side reactions between CuF 2 and LiF–LiCl–LiBr electrolyte. • CuF 2 @C delivers ultrahigh discharge specific capacity and actual discharge time. Conversion-type compounds as cathodes for thermal batteries have recently attracted considerable attention due to their excellent specific capacities. CuF 2 has been regarded as a promising candidate owing to its high theoretical discharge voltage (3.55 V, vs Li) and theoretical capacity (528 mAh·g−1). However, mass loss caused by side-reactions from CuF 2 cathode and molten salt electrolyte leads to severe degradation of the discharge capacity of single-cells in thermal batteries. As a proof-of-concept, in this work, carbon coated CuF 2 (CuF 2 @C) is employed as the cathode to fabricate thermal batteries, in which carbon serves as a protector to inhibit the mass loss of CuF 2 in molten salt electrolyte. As a result, CuF 2 @C demonstrates obviously improved electrochemical performance with a discharge specific capacity of 462.45 mAh·g−1 at the current density of 10 mA·cm−2, which is 82.67 % higher than that of the counterpart (bare CuF 2). This can be attributed to the reduced average polarization resistance of the single-cells in CuF 2 @C composites. This work provides a new route for developing high performance CuF 2 -based cathode material for thermal batteries and promoting its further practical application. [ABSTRACT FROM AUTHOR]

• The CF 0.75 cathode has successfully modified by an ultrathin carbon layer (CF 0.75 @C). • The modified CF 0.75 @C has a high degree of disorganization. • The modified CF 0.75 @C provides additional paths for electronic transmission. • The Li/CF x primary batteries using of CF 0.75 @C cathode achieve better performance. To improve the electrochemical performance of lithium/fluorinated graphite (Li/CF x) primary batteries, the surface of fluorinated graphite cathode is modified with ultrathin carbon layer (CF 0.75 @C) by hydrothermal method. The electrochemical performance and voltage delay of the CF 0.75 @C are significantly improved compared to the pristine CF 0.75 , due to the carbon coating reducing charge transfer resistance and providing more electrons/ions transport paths. As a result, the assembled batteries can discharge at a high rate of 6C and exhibit a specific capacity of 327 mAh/g, corresponding to a high energy density of 625 Wh kg−1. In addition, the optimized batteries exhibit excellent high and low temperature performances (−20 °C ∼ 80 °C), which can be used regularly under harsh conditions. Significantly, this research provides a novel idea to achieve Li/CF x primary batteries with high discharge speed, low voltage delays and a wide temperature range. [ABSTRACT FROM AUTHOR]

• The FeS 2 cathode has successfully modified by Al 2 O 3 nanoparticles (FeS 2 @Al 2 O 3). • The modified FeS 2 @Al 2 O 3 increases the transport rate of lithium ions. • The good wettability of solid-liquid interface suppresses the overflow of electrolytes. • The thermal batteries using of FeS 2 @Al 2 O 3 cathode achieve better performance. Thermal batteries are widely employed as the primary reserve batteries due to their high energy density and long shelf lifespan. FeS 2 is the most studied and promising cathode material of thermal batteries at present because of its abundant stock and superior electrochemical performance. However, the FeS 2 cathode is limited by low discharge capacity, big polarization, and security issues during discharge process. Herein, the improved electrochemical performance is achieved by increasing the interface wettability between cathode and electrolyte, in which the FeS 2 cathode has modified by Al 2 O 3 (FeS 2 @Al 2 O 3) nanoparticles. The good wettability of the solid-liquid interface suppresses the overflow of electrolytes, and the discharge capacity of thermal batteries by using FeS 2 @Al 2 O 3 cathode is 341.3 mAh·g−1, which is higher than that of pure FeS 2 cathode (319.7 mAh·g−1). Significantly, this work provides a novel idea for modifying cathode material for comprehensive performance and safe thermal batteries in practical engineering applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel three-dimensional tremella -like FeS/C microspheres, has been prepared. • The capacitive behavior of FeS/C were investigated. • The composite performs excellent capacitive and electrochemical performance. • The special structure is helpful to develop other multiple sulfides hybrid. In this work, a simple experimental method one-step hydrothermal method is made to prepare tremella-like FeS anchored into three-dimensional carbon (FeS/C) and get substantial progress in electrochemical properties and microstructure. The unique tremella-like structure is formed by the self-assembly of layered FeS/C, which would make the contact between the active material and the electrolyte sufficient, and maintain pronounced electrochemical performance. The studies show that the FeS/C synthesized is mainly dominated by the pseudocapacitive behavior in the electrochemical reaction processes, leading to fast the electrode reaction kinetics. The FeS/C anode also exhibits a large initial capacity of 619 mAh g−1 and remains 410.5 mAh g−1 with excellent rate performances. [ABSTRACT FROM AUTHOR]