High Specific Energy Li7La3Zr2O12 Solid Electrolyte Based Thermal Battery

Garnet-type Ta-doped Li7La3Zr2O12 (LLZTO) solid electrolyte has been widely investigated for secondary Li ionic or metal batteries at ambient temperature. Because of the increasing ionic conductivity of LLZTO with temperature, we applied the LLZTO solid electrolyte to thermal battery working at 550℃. The LLZTO presents ultrahigh specific energy as the discharge specific energy and specific power is 605 W h/kg and 2.74 kW/kg at 100 mA/cm2 with a cut-off voltage of 1.8 V, respectively. This is larger than the LiF–LiCl-LiBr electrolyte which is commonly used in thermal battery with a specific energy of 514 W h/kg. The internal resistance of the single cell reaches 0.65 Ω, but the specific energy remains at about 400 W h/kg as the current density increases to 400 mA/cm2. We report the application of LLZTO in thermal battery with high specific energy, large current, and high voltage discharge for the first time, broadening the application range of solid electrolytes.

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.