Real-time Observations of Structural Changes in a Commercial Li-ion Battery

Authors

Neeraj Sharma and Vanessa Peterson (ANSTO), Hui-Chia Su (National Synchrotron Radiation Research Center, Taiwan), Chih-Wei Hu and Chih-Hao Lee (National Tsing Hua University, Taiwan)

Introduction

Li-ion batteries are currently found in laptop computers and mobile phones, providing portable power for today's needs. Scaling up these batteries to provide more power for use in hybrid electric vehicles, or electric vehicles, requires a number of scientific and engineering hurdles to be overcome.

These include synthesising new materials for various components used in batteries, controlling the synthesis of these components to produce uniform particle sizes and shapes, designing methods to extract energy to power these batteries, investigating at the environmental impact of Li-ion batteries and, most importantly, the safety of consumers. Neutron diffraction is an ideal tool to use to study Li-ion batteries, because we can effectively see what the crystalline components inside the battery do.

In particular, in this experiment conducted with users from Taiwan, we were able to see how the structure of the anode and cathode of a Li-ion battery changed, as the battery was charged and discharged - an in-situ neutron diffraction experiment.

Using our high-intensity powder diffractometer, WOMBAT, we observed real-time structural changes in the graphite anode and LiFePO4 cathode of a commercial Li-ion battery manufactured in Taiwan.

Figure 1 shows the changes in the (002) graphite reflection as the battery is cycled. In the charged state, there is evidence of two phases being formed, while near the discharged state the peak position shifts to higher angles suggesting a reduction in the unit cell size.

This behaviour can be correlated to Li being inserted and extracted from the graphite structure, since it is the transport of Li from the anode to the cathode that constitutes the discharging process and vice versa for charging. This level of detail can be used to give valuable insight into the inner workings of the battery. From which we can speculate on how to improve these materials and make better batteries.