In operando phase transitions and Lithium ion transport in LiFePO4

Abstract

Chemical energy storage in Li-ion batteries is a key technology for the future renewable society. Their energy and power density is largely determined by electrode materials that are able to host lithium in their crystal structure. Aiming at faster and more efficient energy storage, one of the key objectives in Li-ion batteries is to improve the charge transport through the complex heterogeneous electrode morphology. The complex transport phenomena and phase behavior are timely topics and subject of many studies and intense debates. Remarkably, our current knowledge is mostly based on ex-situ techniques or techniques that do not have sufficient time and space resolution to reveal the actual phase nucleation and growth in individual grains. On the electrode length scale the absence of experimental probes that allow direct observation of Li-ion transport in electrodes under realistic in-operando conditions hinders fundamental understanding and the development of rational strategies towards improved electrodes. For LiFePO4, a state of the art cathode material for today’s Li-ion batteries, such direct insights are of high fundamental and practical impact, potentially creating new perspectives in the working and improvements of electrode materials in general. This is the main object of this thesis, revealing the cycling rate dependent phase transition behavior and Li-ion transport throughout the electrodes in LiFePO4 under realistic in-operando conditions.