In situ defect characterization of LiFePO4 cathodes with positron annihilation spectroscopy PAS

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Today lithium ion batteries (LIB) are one of the most promising candidates for energy storage. The aim of this project is to get further insight into the generation of defects and their properties in cathodes during cycling. The positron annihilation spectroscopy (PAS) is used to establish the technique as analyzing tool for in situ defect characterization of LIBs. The investigation focusses on LiFePO4 as cathode material.Based on the highly used Swagelok type cell system the design of an in situ cell is intended which will satisfy both the requirements to PAS-Method and to battery technology. The objective is to observe the cathode processes on atomic scale during cycling. The focus is on the behavior of defects like lattice vacancies or boundaries due to phase changes. Understanding and optimizing the ongoing processes in the cathode material is the objective. Dynamic PALS measurements with previously unrealized time resolution were developed by the proposer (Banhart, 2011) and will be employed here.The investigation of material parameters in respect to the PAS signal is substantial for the use of the PAS-technique in the field of LIB-technology. The parameters of interest are grain size, type of reaction and defects like anti site defects and grain or sub lattice boundaries. Simultaneously ex situ measurements on pure LiFePO4 are planned to use them as starting parameters for the more complex cathode system consisting of LiFePO4, Carbon Black and Binder. The PAS results will give new insight into the phase reactions of LiFePO4 during cycling. This unique in situ measurement method will allow a correlation between the development of defects and efficiency decay of cycled LIBs.Successful completion of the applied project in the above mentioned aspects will immensely improve the comprehension of the processes in LiFePO4.