A new understanding of the role oxygen plays could revolutionise battery development
Diamond Light Source stands as one of the leading research facilities globally, driving scientific advancements. The 14,000th paper published as a result of innovative experiments undertaken at the UK’s national synchrotron highlights the profound impact science can have in addressing the world’s most urgent challenges. A team of researchers from WMG at the University of Warwick, in collaboration with academic partners in the Faraday Institution’s Degradation and FutureCat projects, has conducted a ground-breaking study that bridges the gap between academic models and real-world battery performance.
Their work, recently published in Joule, used a trio of synchrotron techniques – Resonant Inelastic soft X-ray Scattering (RIXS), hard and soft X-ray absorption spectroscopy (XAS) – to investigate the charge compensation mechanism of lithium-ion (Li-ion) battery cathodes during high-voltage operation. This study demonstrates that oxygen plays a significant role through a metal-ligand redox process, emphasising the importance of focusing on surface passivation strategies to mitigate oxygen reactivity with electrolytes, reducing degradation and enhancing safety. By using pilot-line fabricated pouch cells, this work aligns fundamental research with commercial applications and offers crucial insights to improve energy density and cycling stability.
Challenges and Opportunities for High-Energy-Density Batteries
The global transition to a low-carbon future requires the development of low-cost, reliable and long-range electric vehicles, with Li-ion batteries playing a crucial role. However, traditional models of the electronic charge compensation mechanism in layered metal oxide cathodes are insufficient for developing next-generation batteries with increased energy density through high-voltage operation.
Prof Louis Piper explained:
When we talk about trying to increase the energy density of a battery, what that means is being able to remove as many electrons as possible, In a lithium-ion battery, Li-ions move between the anode and a cathode, releasing an equal number of electrons as current. In a commercial layered metal oxide battery, we can pull out about two-thirds of the accessible lithium ions, and therefore, two-thirds of the available electrons. That means the battery is always below its theoretical capacity, but it’s engineered that way to prevent the degradation that occurs when you pull more out. Replacing cobalt with nickel increases the practical capacity of the battery, but it pushes it closer to the point where you see accelerated degradation. Traditional models attribute charge compensation solely to transition metal oxidation, but if that’s true then why does replacing cobalt with nickel change things, and why do we have more problems with safety and oxygen loss as we increase the energy density? We need a better understanding of the metal-ligand redox process to develop safe, stable, higher performance Li-ion cells.
Innovating Battery Research with Real-World Testing
WMG is home to a Battery Scale-Up pilot facility, a suite of cell production equipment covering the full production process cell assembly and testing. It allows researchers to manufacture battery cells in a variety of different formats.
Read more on Diamond website
Image: Graphical abstract of the publication