Scale-up of thermal batteries for flight back-up power

Abstract

Thermal (thermal activated) batteries are primary batteries commonly used for their long shelf life and high-power density. This project investigates the use of casting thermal battery components to improve the electrochemical performance, form factor design and large-scale manufacture required to design thermal batteries which can power aircraft.

The FeS₂ cathode was cast with LiCl, LiClKCl, LiClKCl/MgO, carbon nanofibers (CNF) and multiwalled carbon nanotubes (MWCNT) as the casting binder. The LiCl, LiClKCl, and LiClKCl/MgO- FeS₂ systems were made at 10wt% binder with CNF and MWCNT- FeS₂ casts using only 1wt% binder with etched copper foil. FeS2- LiCl casts were prone to skin formation but was eradicated by either using a homogeniser or decreasing the LiCl content to 5wt%. FeS₂- LiClKCl and LiClKCl/MgO suffered from poor adhesion and rigidity which had been improved by either changing substrate and/or lowering the LiClKCl content to 5wt%. All cathode casts could achieve gravimetric power densities greater than an all- pellet cell (2W/ g vs 1W/g) and FeS₂- LiCl began to achieve greater areal power density to all- pellet processed cells with sufficient processing.

LiClKCl/MgO electrolyte layer was cast as a co- cast layer with a cast FeS₂- LiCl substrate or as a free- standing film using Mylar as a substrate. Although the casting was successful, the electrolyte layer has shown issues with popping (minimised by changing solvents), and self- discharge during testing.

Novel anode design using structured Li₁₃Si₄ wafers and a LAN anode using more than 20wt% Li using Ni foam were investigated. Si wafers were able to double in thickness without significant fracturing on lithiation and Ni foam was electrodeposited with lithium using ionic liquids albeit with low lithium content.

Overall, the procedures examined allow for new form factor design which can lead to alternative designs of thermal batteries with improved performance.

Date of Award	2 Jul 2026
Original language	English
Awarding Institution	University of St Andrews
Supervisor	John Irvine (Supervisor) & Thierry Brousse (Supervisor)