A new cathode material of NiF2 for thermal batteries with high specific power

Review of Transition Metal Chalcogenides and Halides as Electrode Materials for Thermal Batteries and Secondary Energy Storage Systems

Transition metal chalcogenides and halides (TMCs and TMHs) have been extensively used and reported as electrode materials in diverse primary and secondary batteries. This review summarizes the suitability of TMCs and TMHs as electrode materials focusing on thermal batteries (utilized for defense applications) and energy storage systems like mono- and multivalent rechargeable batteries. The report also identifies the specific physicochemical properties that need to be achieved for the same materials to be employed as cathode materials in thermal batteries and anode materials in monovalent rechargeable systems. For example, thermal stability of the materials plays a crucial role in delivering the performance of the thermal battery system, whereas the electrical conductivity and layered structure of similar materials play a vital role in enhancing the electrochemical performance of the mono- and multivalent rechargeable batteries. It can be summarized that nonlayered CoS2, FeS2, NiS2, and WS2 were found to be ideal as cathode materials for thermal batteries primarily due to their better thermal stability, whereas the layered structures of these materials with a coating of carbon allotrope (CNT, graphene, rGO) were found to be suitable as anode materials for monovalent alkali metal ion rechargeable batteries. On the other hand, vanadium, titanium, molybdenum, tin, and antimony based chalcogenides were found to be suitable as cathode materials for multivalent rechargeable batteries due to the high oxidation state of cathode materials which resists the stronger field produced during the interaction of di- and trivalent ions with the cathode material facilitating higher energy density with minimal structural and volume changes at a high rate of discharge.

FeF3/(Acetylene Black and Multi-Walled Carbon Nanotube) Composite for Cathode Active Material of Thermal Battery through Formation of Conductive Network Channels

Considerable research is being conducted on the use of FeF3 as a cathode replacement for FeS2 in thermal batteries. However, FeF3 alone is inefficient as a cathode active material because of its low electrical conductivity due to its wide bandgap (5.96 eV). Herein, acetylene black and multi-walled carbon nanotubes (MWCNTs) were combined with FeF3, and the ratio was optimized. When acetylene black and MWCNTs were added separately to FeF3, the electrical conductivity increased, but the mechanical strength decreased. When acetylene black and MWCNTs were both added to FeF3, the FeF3/M1AB4 sample (with 1 wt.% MWCNTs and 4% AB) afforded a discharge capacity of approximately 74% of the theoretical capacity (712 mAh/g) of FeF3. Considering the electrical conductivity and mechanical strength, this composition was confirmed to be the most suitable.

Probing Dynamic Self-Reconstruction on Perovskite Fluorides toward Ultrafast Oxygen Evolution

Exploring low cost, highly active, and durable electrocatalysts for oxygen evolution reaction (OER) is of prime importance to boost energy conversion efficiency. Perovskite fluorides are emerging as alternative electrocatalysts for OER, however, their intrinsically active sites during real operation are still elusive. Herein, the self-reconstruction on newly designed NiFe coupled perovskite fluorides during OER process is demonstrated. In situ Raman spectroscopy, ex situ X-ray absorption spectroscopy, and theoretical calculation reveal that Fe incorporation can significantly activate the self-reconstruction of perovskite fluorides and efficiently lower the energy barrier of OER. Benefiting from self-reconstruction and low energy barrier, the KNi0.8 Fe0.2 F3 @nickel foam (KNFF2@NF) electrocatalyst delivers an ultralow overpotential of 258 mV to afford 100 mA cm-2 and an excellent durability for 100 h, favorably rivaling most the state-of-the-art OER electrocatalysts. This protocol provides the fundamental understanding on OER mechanism associated with surface reconstruction for perovskite fluorides.

Recent Developments of Cathode Materials for Thermal Batteries

Big progress has been made in batteries based on an intercalation mechanism in the last 20 years, but limited capacity in batteries hinders their further increase in energy density. The demand for more energy intensity makes research communities turn to conversion-type batteries. Thermal batteries are a special kind of conversion-type battery, which are thermally activated primary batteries composed mainly of cathode, anode, separator (electrolyte), and heating mass. Such kinds of battery employ an internal pyrotechnic source to make the battery stack reach its operating temperature. Thermal batteries have a long history of research and usage in military fields because of their high specific capacity, high specific energy, high thermal stability, long shelf life, and fast activation. These experiences and knowledge are of vital importance for the development of conversion-type batteries. This review provides a comprehensive account of recent studies on cathode materials. The paper covers the preparation, characterization of various cathode materials, and the performance test of thermal batteries. These advances have significant implications for the development of high-performance, low-cost, and mass production conversion-type batteries in the near future.