Analytical Study of Insulation Characteristics of Thermal Batteries with Vacuum Insulation

In this study, a thermal battery is designed with vacuum insulation to improve its thermal insulation. Thermal insulation is one of the many factors that determine the stability and operation of the battery. The battery’s operating time as well as the improvement in its thermal insulation performance were analyzed. The location of the vacuum insulation was set as a variable in the analysis models. The thermal battery was subjected to unsteady heat transfer analysis until the electrolyte temperature reached 450°C. Vacuum insulation was applied to the part of the base thermal battery to fabricate three model batteries. Compared with the base model B, the operating time increased by 48% for the model BS, 76% for the model BSB, and 179% for the model BSBT. Due to the large area of the side, a large amount of heat was transferred; the quantity of heat transfer was in the order B>BS>BSB>BSBT. In the model BSBT, the heat loss per unit area was reduced by 93% at the side, top, bottom compared with the base model. The results of this study will serve as basic data for the design of thermal batteries with vacuum insulation and for improvement in insulation performance.

Co-harvesting Solar Energy with Ambient Heat and On-Demand Release of Thermal Energy Below 0 oC Through Visible-Light-Controlled Photochemical Phase Transitions of Azopyrazoles

Photochemical crystal-to-liquid transition generally needs UV light as a stimulus and it is even more challenging to carry out below 0 oC. Here, we design a series of 4-alkylthioarylazopyrazoles as molecular solar thermal batteries, which show bidirectional visible-light-triggered photochemical trans-crystal ↔ cis-liquid transitions below ice point (-1 oC). Through co-harvesting visible-light energy and low-temperature ambient heat, high energy density (0.25 MJ kg-1) is achieved. Further, the rechargeable solar thermal batteries devices are fabricated, which can be charged by blue light (400 nm) at -1 oC. Then, the charged devices can release energy on demand in the form of high-temperature heat. Under green light (532 nm) irradiation, the temperature difference between the charged devices and the ice-cold surrounding is up to 13.5 oC. This study paves the way for the design of advanced molecular solar thermal batteries that store both natural sunlight and ambient heat over a wide temperature range.

A new method for thermal conductivity measurement: application to complex heterogeneous materials used in thermal batteries

The thermal conductivity of heterogeneous materials used in thermal batteries is difficult to measure. These materials must be handled under controlled atmosphere with methods adapted to their porous nature. The method presented in this work uses heating plates to send a sinusoidal thermal signal to the tested sample. The whole setup is confined in a glovebox to ensure the composition and hygrometry of the atmosphere. Parametric computer simulations with varying thermal conductivity (λ) of the sample and thermal resistance (h) of the contacts as inputs were performed to calculate the phase shifts associated with two thicknesses of the sample. Experimental measurements of phase shifts on these two configurations allowed the identification of the only couple (λ,h) which matches the phase shifts on the respective thicknesses. This method is validated using the reference material BK7 at different temperatures. Thermal conductivities of a heterogeneous cathode used in thermal batteries is also given using this method.

Electrochemical Properties of a Lithium-Impregnated Metal Foam Anode (LIMFA Fecral) for Molten Salt Thermal Batteries

Although numerous cathode materials with excellent properties have been developed for use in molten salt thermal batteries, similar progress is yet to be made with anode materials. Herein, a high-performance lithium-impregnated metal foam anode (LIMFA) is fabricated by impregnating molten lithium into a gold-coated iron–chrome–aluminum (FeCrAl) foam at 400°C. A test cell employing the LIMFA FeCrAl anode exhibited a specific capacity of 2,627 As·g−1. For comparison, a cell with a conventional Li(Si) anode was also discharged, demonstrating a specific capacity of 982 As·g−1. This significant improvement in performance can be attributed to the large amount (18 wt.%) of lithium incorporated into the FeCrAl foam and the ability of the FeCrAl foam to absorb and immobilize molten lithium without adopting a cup system. For thermal batteries without a cup, the LIMFA FeCrAl provides the highest-reported specific capacity and a flat discharge voltage curve of molten lithium. After cell discharge, the FeCrAl foam exhibited no lithium leakage, surface damage, or structural collapse. Given these advantageous properties, in addition to its high specific capacity, LIMFA FeCrAl is expected to aid the development of thermal batteries with enhanced performance.