Rice’s Quan Nguyen holds one of the silicon anode batteries assembled using the novel prelithiation method. Photo: Jeff Fitlow/Rice University.Silicon anode batteries have the potential to revolutionize energy-storage capabilities, which is key to meeting climate goals and unlocking the full potential of electric vehicles. However, the irreversible depletion of lithium ions in silicon anodes puts a major constraint on the development of next-generation lithium-ion batteries.
Scientists at Rice University’s George R. Brown School of Engineering have now developed a readily scalable method to optimize prelithiation, a process that helps mitigate lithium loss and improves battery life cycles by coating silicon anodes with stabilized lithium metal particles (SLMPs).
The Rice lab of chemical and biomolecular engineer Sibani Lisa Biswal found that spray-coating the anodes with a mixture of SLMPs and a surfactant improves battery life by 22% to 44%. Battery cells with a greater amount of the coating initially achieved a higher stability and cycle life. However, there was a drawback: when cycled at full capacity, a larger amount of the particle coating led to more lithium trapping, causing the battery to fade more rapidly in subsequent cycles. Biswal and her colleagues report their findings in a paper in ACS Applied Energy Materials.
Replacing graphite with silicon in the anodes of lithium-ion batteries would significantly improve their energy density ? the amount of energy stored relative to weight and size ? because graphite, which is made of carbon, can pack fewer lithium ions than silicon. Six carbon atoms are required to incorporate a single lithium ion, whereas just one silicon atom can bond with as many as four lithium ions.
“Silicon is one of those materials that has the capability to really improve the energy density for the anode side of lithium-ion batteries,” Biswal said. “That’s why there’s currently this push in battery science to replace graphite anodes with silicon ones.”
However, silicon has other properties that present challenges. “One of the major problems with silicon is that it continually forms what we call a solid-electrolyte interphase or SEI layer that actually consumes lithium,” Biswal explained.
The SEI layer is formed when the electrolyte in a battery cell reacts with electrons and lithium ions, resulting in a nanometer-scale layer of salts being deposited on the anode. Once formed, this layer insulates the anode from the electrolyte, preventing the reaction from continuing. However, the SEI can break during subsequent charge and discharge cycles, causing it to deplete the battery’s lithium reserves even further as it reforms.
“The volume of a silicon anode will vary as the battery is being cycled, which can break the SEI or otherwise make it unstable,” said Quan Nguyen, a chemical and biomolecular engineering doctoral alum and lead author of the paper. “We want this layer to remain stable throughout the battery’s later charge and discharge cycles.”
The prelithiation method developed by Biswal and her team improves the stability of the SEI layer, which means fewer lithium ions are depleted when it is formed.
“Prelithiation is a strategy designed to compensate for the lithium loss that typically occurs with silicon,” Biswal said. “You can think of it in terms of priming a surface, like when you're painting a wall and you need to first apply an undercoat to make sure your paint sticks. Prelithiation allows us to ‘prime’ the anodes so batteries can have a much more stable, longer cycle life.”
While these particles and prelithiation are not new, the Biswal lab was able to improve the process so that it can be readily incorporated into existing battery manufacturing processes.
“One aspect of the process that is definitely new and that Quan developed was the use of a surfactant to help disperse the particles,” Biswal said. “This has not been reported before, and it's what allows you to have an even dispersion. So instead of them clumping up or building up into different pockets within the battery, they can be uniformly distributed.”
Nguyen explained that mixing the particles with a solvent without the surfactant will not result in a uniform coating. Moreover, spray-coating proved better at achieving an even distribution on the anodes than other application methods.
“The spray-coating method is compatible with large-scale manufacturing,” Nguyen said.
Controlling the cycling capacity of the cell is crucial to the process. “If you do not control the capacity at which you cycle the cell, a higher amount of particles will trigger this lithium-trapping mechanism we discovered and described in the paper,” Nguyen said. “But if you cycle the cell with an even distribution of the coating, then lithium trapping won’t happen.
“If we find ways to avoid lithium-trapping by optimizing cycling strategies and the SLMP amount, that would allow us to better exploit the higher energy density of silicon-based anodes.”
This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.