Lithium Distribution in Structured Graphite Anodes Investigated by Laser-Induced Breakdown Spectroscopy

Yijing Zheng,Hans Jürgen Seifert,Lisa Pfäffl,Wilhelm Pfleging

doi:10.3390/app9204218

Abstract

For the development of thick film graphite electrodes, a 3D battery concept is applied, which significantly improves lithium-ion diffusion kinetics, high-rate capability, and cell lifetime and reduces mechanical tensions. Our current research indicates that 3D architectures of anode materials can prevent cells from capacity fading at high C-rates and improve cell lifespan. For the further research and development of 3D battery concepts, it is important to scientifically understand the influence of laser-generated 3D anode architectures on lithium distribution during charging and discharging at elevated C-rates. Laser-induced breakdown spectroscopy (LIBS) is applied post-mortem for quantitatively studying the lithium concentration profiles within the entire structured and unstructured graphite electrodes. Space-resolved LIBS measurements revealed that less lithium-ion content could be detected in structured electrodes at delithiated state in comparison to unstructured electrodes. This result indicates that 3D architectures established on anode electrodes can accelerate the lithium-ion extraction process and reduce the formation of inactive materials during electrochemical cycling. Furthermore, LIBS measurements showed that at high C-rates, lithium-ion concentration is increased along the contour of laser-generated structures indicating enhanced lithium-ion diffusion kinetics for 3D anode materials. This result is correlated with significantly increased capacity retention. Moreover, the lithium-ion distribution profiles provide meaningful information about optimizing the electrode architecture with respect to film thickness, pitch distance, and battery usage scenario.

Highlights

During the last three decades, lithium-ion batteries (LIBs) have become the predominant energy storage for electric vehicles, portable devices, and secondary energy storage due to the high energy density
Line structures with a pitch distance of 200 μm were generated for electrochemical measurements and subsequent laser-induced breakdown spectroscopy (LIBS) measurements
200 μm line structures can deliver improved high-rate capability. This improvement is associated with an increased electrochemical reactivity as well as an improved lithium-ion diffusion kinetic by means of laser-generated new diffusion pathways

Summary

Introduction

During the last three decades, lithium-ion batteries (LIBs) have become the predominant energy storage for electric vehicles, portable devices, and secondary energy storage due to the high energy density. LIBs were developed in the 1980s and commercialized by Sony Corporation (Tokyo, Japan) based on a graphite anode and lithium cobalt oxide as the cathode in 1991. Different cathode materials were proposed and developed in order to improve energy density and power density. To date, more than twenty years later, carbon-based materials are still used as the commercial anode material while the requirements for anode materials have been changed. In addition to demands of high capacities, the duration of the charging process plays an important role. In mobile applications, the ratio of battery charging time to its operation range has become a deciding factor for

Methods

Results

Conclusion