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A copper fluoride with small size and high purity is very important to present its ability as a cathode material for lithium thermal batteries (LTBs). In this paper, we investigate the effect of the heat treatment temperature of the precursor ammonium copper fluoride on the preparation of a high-performance copper fluoride cathode. The color of CuF2 gradually changes from white to dark brown as the heat treatment temperature of the ammonium copper fluoride precursor is increased due to the change in dimensions and morphology. The CuF2-250 prepared at the heat treatment temperature of 250 ℃ has a small D50 particle size of 1.838 µm (agglomeration of particles from 50 to 100 nm), high purity, large BET surface area of 16.3649 m2/g, and excellent working properties. Its operating voltage reached as high as 3.5 V in the initial activation stage at a discharge current density of 500 mA/g, which is attributed to the better conductivity caused by its small size favorable shortened Li+ diffusion path, and its specific capacity and discharge time at the cut-off voltage of 1.5 V were 498 mAh/g close to 94% of the theoretical specific capacity (528 mAh/g) and ultralong 3585 s, respectively. This study provides a guideline for the development of high-performance cathode materials for LTBs. [ABSTRACT FROM AUTHOR]

Manufacturing thin‐film components is crucial for achieving high‐efficiency and high‐power thermal batteries (TBs). However, developing binders with low‐gas production at the operating temperature range of TBs (400–550 °C) has proven to be a significant challenge. Here, we report the use of acrylic acid derivative terpolymer (LA136D) as a low‐volatile binder for thin‐film cathode fabrication and studied the chain scission and chemical bond‐breaking mechanisms in pyrolysis. It is shown LA136D defers to random‐chain scission and cross‐linking chain scission mechanisms, which gifts it with a low proportion of volatile products (ψ, ψ = 39.2 wt%) at even up to 550 °C, well below those of the conventional PVDF (77.6 wt%) and SBR (99.2 wt%) binders. Surprisingly, LA136D contributes to constructing a thermal shock‐resistant cathode due to the step‐by‐step bond‐breaking process. This is beneficial for the overall performance of TBs. In discharging test, the thin‐film cathodes exhibited a remarkable 440% reduction in polarization and 300% enhancement in the utilization efficiency of cathode materials, while with just a slight increase of 0.05 MPa in gas pressure compared with traditional "thick‐film" cathode. Our work highlights the potential of LA136D as a low‐volatile binder for thin‐film cathodes and shows the feasibility of manufacturing high‐efficiency and high‐power TBs through polymer molecule engineering. [ABSTRACT FROM AUTHOR]

• 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]

CoS 2 cathode has been extensively adopted for application in thermal batteries due to its excellent electrochemical performance. However, CoS 2 undergoes rapid discharge degradation at high-rates or low working temperatures because of its high polarization resistance. This is ascribed to the kinetically slow rate of Li+ inset in the CoS 2 cathode. With the aim of accelerating charge carrier exchange at the cathode-electrolyte interface, the construction of a heterostructure with an engineered electronic structure at the surface of CoS 2 is described in this present work. The results show that the specific discharge capacity (V ≥ 1.75 V) of heterostructured CoS 2 increases 23% at 500 °C and 42.3% at 450 °C with discharge currents of 300 and 100 mA cm−2, respectively. Electrochemistry measurements and density functional theory (DFT) analysis decipher that N modification alters the surface structure of CoS 2 , resulting in beneficial "defect" formation, that further enhances surface exchange density and the adsorption capability of Li+. [Display omitted] • Specific discharge capacity (V ≥ 1.75 V) of heterostructured CoS 2 increases 23% at 500 °C and 42.3% at 450 °C. • Electrochemical behaviors of heterostructured CoS 2 in molten salt are discussed and verified. • Influence mechanisms of heterostructured CoS 2 are studied by the DFT calculation. [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 route is proposed to load nanoparticles and electrolyte into ceramic paper separator. • The proposed route is efficient and safe, which can be promoted to used in large scales. • Electrochemical performance of thermal batteries can be obviously improved with ceramic paper as separator. Composites consisted of ceramic paper, nanoparticles as well as molten salt electrolyte, are developed as the new electrolyte separators to substitute the traditional ones in thermal batteries, due to their flexible manufacture and good exhibition in electrochemical performance. However, the existed methods for fabricating the composites by roughly dip-coating with aqueous solutions, are suffering from drawbacks such as inefficiency, low consistence, or high temperature risk. Therefore, a new approach based on a melting-absorption-diffusion process, by using precursors without solvent, is developed. Firstly, the salts are accurately weighted. Then they melt on surfaces of ceramic papers and diffuse inside. After being treated at appropriate temperature for hours, high quality electrolyte separators based on ceramic papers are achieved. Compared to the traditional approaches, the new method can obviously increase and accurately control the amount of loaded nanoparticles and molten salts for each time. The achieved electrolyte separators also exhibit good electrochemical performance in single cells of thermal batteries compared with the traditional ones. With advantages like easy operation, high efficiency, and improved performance, this melting and in situ loading method holds broad prospect in preparing electrolyte separators at large scale. [ABSTRACT FROM AUTHOR]

Thermal batteries are widely used as the power sources in the field of aerospace and military applications, due to their high-power density and long storage life. Compared to the cubic transition metal disulfides, another hexagonal metal disulfide SnS 2 , is studied as a new cathode of thermal batteries. SnS 2 exhibits good environmental and thermal stability, high electronic conductivity, good wettability, as well as high discharge voltage and rate capability. Its working voltage reaches 2.23 V under discharge current of 100 mA cm−2. During the discharge process, three distinct discharge steps are existed at a cut-off voltage of 1.5 V, as described followed: 1) 2 S n S 2 + 2 L i + + 2 e − = S n 2 S 3 + L i 2 S ; 2) S n 2 S 3 + 2 L i + + 2 e − = 2 S n S + L i 2 S ; 3) SnS + 2 L i + + 2 e − = S n + L i 2 S. In conclusions, SnS 2 is proved a most promising cathode material for thermal batteries, and can be widely used. [Display omitted] • SnS 2 with good stable and wettability is used as cathode of thermal batteries. • Electrochemical behaviors of SnS 2 in molten salt are discussed and verified. • Further application of SnS 2 in thermal batteries is defined. [ABSTRACT FROM AUTHOR]

As the most investigated cathode of thermal batteries, the electrochemical performance of CoS 2 is limited by a big polarization at high current density and low working temperature, which is ascribed to the poor wettability of molten salt on CoS 2 surface and low exchange current density. In this contribution, Al 2 O 3 is selected as a modifier to improve the wettability of molten salt on CoS 2 surface and exchange current density at the same time, by adjusting the dielectric polarization field of CoS 2 surface. The discharge capacity (V ≥ 1.7 V) of CoS 2 increases by ~11% at 500 °C with a discharge current of 300 mA cm−2, and 55% at 450 °C with a discharge current of 100 mA cm−2, by the decoration of Al 2 O 3 nanoparticles. Moreover, the influence of decorated Al 2 O 3 nanoparticles on the electrochemical performance of CoS 2 are discussed. • CoS 2 decorated with Al 2 O 3 nanoparticles can be synthesized via a simple way. • Optimized interface is able to boost the discharge ability of thermal batteries. • Influence mechanisms of Al 2 O 3 on electrochemical behavior of CoS 2 are studied. [ABSTRACT FROM AUTHOR]

The discharge performance of thermal batteries with long-life is mainly limited by the decrease of working temperature, due to the continuous heat release during the work process. In this contribution, we firstly propose a slow heat-supply component (SHSC) with layer structure, composed of reducers (Li–Si), oxidizers (CuO) and "lithium" permeation membrane (LPM), to compensate the released heat in thermal batteries. The LPM is composed of electronic conductor (CeO 2) and high Li+ molten salt conductor (LiCl–LiBr–KBr), which can modify the permeation rate of "lithium" by changing the electric conductivity. The results confirm that thereaction rates between Li–Si and CuO can be adjusted by changing the weights or compositions of LPM, and the heat supply rate of SHSC can be regulated. By using SHSC, the inner temperature of thermal batteries can be maintained properly. Moreover, the discharge capacity of thermal batteries with long working life, can achieve 10% increase at least, with SHSC as the heat supplied component, which are measured and confirmed in the real thermal batteries. [Display omitted] • A slow heat supply component (SHSC) with layer structure is constructed based on a composite membrane. • Inner temperature of thermal batteries is maintained properly. • Electrochemical performance of thermal batteries is improved by using SHSC as heat sources. [ABSTRACT FROM AUTHOR]