Here I would like to share my experiences from my three-month research visit to Lawrence Berkeley National Laboratory and the University of California, Berkeley, which took place from January to April this year.

With my PhD focusing on the development and research of novel next-generation batteries, my work brought me to Berkeley. During my visit, I supported researchers and scientists in developing an electrochemical, physics-based continuum model for their experimental setup of an anode-free solid-state battery cell. The purpose of the model, and my role within the project, was to validate our theoretical understanding and assumptions regarding the physical and chemical phenomena occurring inside the experimental battery. This work will support the further design and optimisation of the real battery cell in Berkeley.

What makes an anode-free solid-state battery cell so special compared with contemporary lithium-ion cells is mainly two things: it has a solid electrolyte rather than a liquid one, reducing the risk of leakage and enabling higher energy density and it does not have a pre-formed anode, one of the three key components of a battery, the others being the cathode and the electrolyte. Instead, the anode is a physically and geometrically dynamic structure that grows during charging as lithium metal is plated onto the current collector and shrinks during discharging as lithium is stripped away. This further increases the energy density of the overall cell, meaning the same amount of energy can be stored in less material and it lowers material costs, making the cell cheaper.

Through discussions and literature review, we categorised the work into two main theories, each represented by its own model. The first model assumes adsorption and surface diffusion of lithium ions within the buffer layer. The second model describes pore filling, in which lithium metal grows through the pores towards the other side of the cell, represented by a pore-reservoir model. Currently, both models are being validated using data from the literature and will be further validated with upcoming experimental data from the laboratories at Berkeley.

Beyond the theoretical work, my personal experience at Berkeley was highly insightful. Living for three months on the west coast of the United States, close to the Pacific Ocean and far away from friends and family in the UK and Germany, was certainly a unique experience. I made many new friends and was warmly hosted by the scientists and students there. Experiencing a different academic environment, university structure, work culture, and wider cultural setting gave me a valuable new perspective. Overall, I came to realise that although countries may differ in their structures and customs, people and everyday experiences often have many similarities.

This was also the longest flight I had taken so far, from Heathrow to San Francisco. From a transport perspective, which may be of particular interest to the IAAPS community, the public transport system in Berkeley and the wider Bay Area was very convenient. Buses were the main form of transport, connecting different parts of the city and surrounding areas. As a laboratory affiliate, I also had the opportunity to use a free shuttle service directly from my accommodation to the lab, which was very helpful. From a European perspective, it was interesting to observe the differences in urban infrastructure. Many European cities have developed around walkability and older urban layouts, whereas many cities in the United States are more car-oriented. Experiencing these differences first-hand was both interesting and valuable.

I am very thankful to the AAPS CDT management for enabling this fantastic experience through the International Travel Opportunity. I would strongly recommend that any student apply for this opportunity, as it can contribute greatly to both academic and personal growth.

Eymen Kilic