Scientists from Helmholtz-Zentrum Berlin have developed new cathode materials to significantly boost the capacity of lithium batteries.
The left side of the figure shows nanotomography images of an LRTMO particle taken at the TXM of BESSY II before the first charging cycle (top) and after 10 charging cycles (bottom). In the simulation (right side), the isolated pores are highlighted in light blue. After 10 charging cycles, the number of pores and cracks has significantly increased. Image Credit: Helmholtz-Zentrum Berlin
Researchers are making exciting progress in improving lithium-ion batteries with new cathode materials. Multilayer lithium-rich transition metal oxides (LRTMOs) are particularly promising because of their high energy density, but they face a major challenge: their capacity declines over time as they undergo structural and chemical changes during use.
A team of scientists from Chinese institutions working with advanced X-ray techniques at BESSY II has taken a closer look at these changes than ever before. Using a cutting-edge X-ray microscope, they were able to observe nanoscale transformations in the material and uncover important chemical details.
Lithium-ion batteries are already widely used, but new materials like LRTMOs could make them even more powerful. These materials, however, degrade over time as lithium ions move back and forth during charging and discharging cycles. Until now, scientists have not fully understood the specific changes that caused this degradation.
The researchers were able to secure beam time at the world’s only transmission X-ray microscope (TXM) at the BESSY II storage ring to study their samples using advanced 3D tomography and nanospectroscopy.
Dr. Peter Guttmann at HZB conducted the measurements back in 2019, before the onset of the COVID-19 pandemic. These X-ray analyses were later enhanced with additional spectroscopic and microscopic techniques. After thorough analysis of the extensive data, the team has unveiled detailed insights into how the material's structure, shape, and chemical composition change during discharge cycles.
Soft X-ray transmission microscopy allows us to visualize chemical states in LRTMO particles in three dimensions with high spatial resolution and to gain insights into chemical reactions during the electrochemical cycle.
Dr. Stephan Werner, Physicist, Helmholtz-Zentrum Berlin
The study showed that slow charging can lead to phase transitions and oxygen loss, while fast charging causes lattice distortions and uneven lithium diffusion. It also revealed how nanopores form and how the oxidation states of different elements shift. These findings could help improve battery performance and durability.
Here at the TXM, we have a unique capability: we can offer energy-resolved transmission X-ray tomography. This gives us a 3D image with structural information at every element-specific energy level – energy is the fourth dimension here.
Dr. Stephan Werner, Physicist, Helmholtz-Zentrum Berlin
This research provides crucial guidance for designing long-lasting, stable cathode materials.
The TXM is excellently suited to provide new insights into morphological and chemical changes in battery materials in the future through in-operando studies – that is, during charging and discharging.
Gerd Schneider, Professor, Helmholtz-Zentrum Berlin