Researchers at HZB have discovered that highly porous tin foam can alleviate mechanical stress in lithium-ion batteries, making it a promising alternative to traditional graphite electrodes. Metal-based electrodes in lithium-ion batteries have higher capacities than traditional graphite electrodes. However, they tend to degrade due to mechanical stress during charge and discharge cycles.
Researchers at HZB demonstrated that highly porous tin foam can better absorb this stress, thereby improving the stability of the electrode. This discovery makes tin foam a promising material for lithium-ion batteries.
Traditional lithium-ion batteries typically use multilayer graphite electrodes and cobalt oxide counter electrodes. During charge and discharge cycles, lithium ions migrate into the graphite with minimal volume changes, thus maintaining structural integrity. However, graphite has a limited capacity, prompting a search for alternative materials with higher energy storage potential.
Metal-based electrodes such as aluminum or tin have the potential to provide higher capacities. However, when absorbing lithium, they tend to expand significantly in volume, which is associated with structural changes and material fatigue. Tin is particularly attractive because it has almost three times the capacity per kilogram of graphite and because it is not a rare raw material but is available in large quantities. One way to achieve less "fatigued" metal electrodes is to nanostructure thin metal foils. Another approach is to use porous metal foam.
A research team at the Helmholtz Zentrum Berlin (HZB) used operational X-ray imaging to study various types of tin electrodes during discharge and charging processes and developed an innovative method to solve this problem. Some experiments were conducted in BESSYII's BAMline. The high-resolution X-ray images were taken in collaboration with HZB's imaging experts Dr. Nikolai Kardjilov and Dr. André Hilger.
"This allowed us to track the structural changes of the studied tin metal-based electrode during the charge/discharge process," said Dr. Bouchra Bouabadi, first author of the study. Together with battery expert Dr. Sebastian Risse, she explored the morphological changes of the tin electrode during operation due to the uneven absorption of lithium ions.
Dr. Francisco Garcia-Moreno created the best version of a tin electrode: a tin foam with countless micron-sized pores. "We were able to show that the mechanical stress during volume expansion of this tin foam is significantly reduced," said Dr. Risse. "This makes tin foam an interesting material for lithium batteries."
Garcia-Moreno has worked on a number of metal foams, including those used in parts for the automotive industry and aluminum foam used in battery electrodes. He said: "The tin foam we developed at TU Berlin is highly porous and is an ideal alternative to conventional electrode materials. The structure of the tin foam is crucial to minimize mechanical stress. The tin foam technology is also attractive from an economic point of view: Although tin foam is more expensive than conventional tin foil, it offers a cheaper alternative to expensive nanostructures while being able to store more lithium ions, thus increasing capacity.
Compiled from /ScitechDaily