14 MeV Neutron Activation Analysis of Oxygen in Li-Si Alloys for Li(Si)/FeS2 Thermally Activated Batteries

Development of a Li(Si)/FeS2 thermally activated battery required establishment of a 14 MeV neutron activation procedure for the determination of total oxygen (0.1 wt % and greater) in the Li-56 wt % Si alloy anode material used in the batteries. The method developed allows the reactive samples to remain in a controlled atmosphere throughout sampling and analysis. An interference due to triple random coincidence detection of 28A1 gamma rays produced by (n, p) reaction on 28Si was observed. A simplified correction procedure, based on one by Nass1 but not requiring knowledge of the detector resolution time, has been derived and evaluated. The correction procedure should be useful in the analysis of other low O, high Si materials such as Si metal, other Si-rich alloys, SiC and Si3N4. Geologic, meteoritic and lunar silicate materials commonly analyzed for O are low enough in Si content and high enough in O content that the interference is not significant. Some results of applying the analysis and correction procedure to thermally activated battery materials are described.