We have all used some form of battery in our life, for instance in our laptops, handphones or even electric vehicles. The most prominent type of a battery is the Li-ion battery (LIB), which was first proposed in the 1970s and was commercially used in 1991. Why are we still researching on batteries if it has already been commercially available for so long?
Considerable improvements have been made over the past decades with discovery of new materials to be used in the anode, cathode and electrolyte within LIB. One of the drives behind these discoveries is to improve the amount of energy a battery can hold so that the battery can last longer in a single charge, which is very important to make a sustainable electric vehicle with adequate driving range. Furthermore, the bulk of the cost of a battery is due to its material, so finding new and cheaper materials could reduce the cost. Scientist and engineers have also been trying to charge the battery quicker and provide more power. Cathodes is the main bottleneck of LIB in terms of performance qualities and cost. The degradation mechanisms of cathodes over prolong cycling needs to be understood and it is important to be able to observe these materials at nano-scale.
Traditionally, optical microscopes have been used to observe magnified details of microstructures, but they are constrained by the resolution of visible light where the smallest resolvable distance is around 300nm. The resolution of a microscope is limited by the wavelength of the radiation used. A straightforward approach to improve the resolution would be to utilise radiation of shorter wavelength. Louis de Broglie first theorised that electron, whilst being considered as particles, had wave-like characteristics, with wavelengths substantially less than visible light. This principle led to the creation of transmission electron microscope where the maximum resolution reaches below 1 nm.
An electron microscope works by having a stream of high voltage electrons travel through a vacuum in the column of the microscope. Electrons are focused onto a series of electromagnetic lenses and then directed to the sample. The electrons can either bounce off or go through the sample, which then impact on a detector. These detectors can provide several information from nano-scale morphological to chemical features of material down to near atomic level.
For my research, I am investigating the charge transport and degradation mechanisms of cathode materials using electron microscopy techniques to understand what happens to the material during its operation. Some of the degradation that would happen to the material are material cracking, dissolution of atoms into the electrolyte, formation of a completely different crystal structure after prolong usage. This degradation not only impedes the electrochemical performance, but could be potential fire hazard too. Therefore, by using electron microscopes to gain better understanding the causes of degradation of cathodes could hopefully shed some light on ways to improve the performance and lifetime of Li-ion batteries.
NanoDTC Associate, a2021