Light-battery interactions for enhanced energy storage and operando spectroscopy

Energy storage systems can play a pivotal role in reducing greenhouse gas emissions by electrifying transport networks and enabling the integration of intermittent renewable energy sources into the grid. Over the past two decades, lithium-ion batteries (LIBs) have emerged as the main energy storage solution due to their high energy density. However, current electric cars cannot match the range of their fossil fuel-powered counterparts due to limitations in the capacities of modern LIB materials. Moreover, improvements in LIB capacities have plateaued over the last decade, suggesting that alternate solutions are required. Finally, lithium-ion batteries degrade with continuous use, limiting their lifespan. Understanding the causes of degradation is key to building better batteries, but current methods to do this are expensive and difficult. This thesis aims to address these challenges through two different routes - photobatteries and a new operando method called diffuse reflectance spectroscopy (DRS). Photobatteries are a new class of devices that aim to combine the properties of energy harvesting and storage within the same device architecture. These devices have been reported to offer much higher capacities under illumination (photoenhanced batteries), providing a pathway for higher energy densities, along with the ability to be charged solely by light (photorechargeable batteries). Here, we attempt to unravel the mechanisms behind this light-induced behaviour. First, a cell design that allows for the interaction of light with batteries is developed. An optical window is introduced within the cell and a range of current collectors that allow for robust electrochemical behaviour are tested. Next, the physical conditions for photocharging to be possible are established. It is shown that only when the quasi-Fermi level of the photoabsorber is higher than the intercalation potential of the anode, is photocharging possible. This is contrary to most reported mechanisms in literature, indicating the need for alternate mechanisms to explain this apparent ‘photocharging’ behaviour. Next, the origins of photo-enhanced behaviour are investigated. Operando diffuse reflection spectroscopy (DRS) is used to show that the band gap of V2O5 - a popular photobattery cathode, disappears after zinc ion intercalation, suggesting that other effects are at play. Through a series of control experiments, it is shown that the thermal effects of irradiation are mainly responsible for the enhanced capacities seen, rather than light itself. Finally, the DRS technique developed earlier is used along with optical coin cells to study processes within lithium-ion batteries. By correlating the state-of-charge of the battery with its reflectance a variety of electrochemical phenomena can be optically reconstructed. This enables the study of electrode heterogeneity and solid-state diffusion, as well as tracking the origin of first-cycle losses within LIBs. These results will help establish DRS as a simple, inexpensive technique to study LIBs. Overall, this thesis highlights the complex interplay between light and batteries. It is shown that meticulous control experiments must be performed to understand whether light can truly improve battery performance. On the other hand, the simplicity and cost-effectiveness of optical techniques such as DRS can help democratize battery research worldwide.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2024

Author dc:creator

• Pujari, Arvind

Advisors dc:contributor.advisor

• Greenham, Neil
• De Volder, Michael

• Batteries
• Photobatteries
• Spectroscopy

Licence

• https://www.repository.cam.ac.uk/bitstreams/017a79bd-d0d5-4a8c-a759-5fef08a70ead/download
• https://creativecommons.org/licenses/by-nd/4.0/

Language dc:language

eng

Author Identifier

0000-0002-5415-3411

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/391279