Engineers improve battery life by coating anodes with metal particles

Silicon however can be problematic.

“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 said.

This SEI can irreversibly deplete the battery’s lithium reserve.

“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 on the study. “We want this layer to remain stable throughout the battery’s later charge and discharge cycles.”

The researchers have now conceived of a prelithiation method that improves SEI layer stability, resulting in fewer lithium ions being depleted.

“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.”

None of these elements are new but the Biswal lab improved the process.

“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.”

The researchers also highlighted the importance of controlling the cycling capacity of the cell.

“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 in the statement. “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.”

The study is published in ACS Applied Energy Materials.

Study abstract:

Silicon (Si) has been considered as one of the most promising replacements for graphite anodes in next-generation lithium-ion batteries due to its superior specific capacity. However, the irreversible consumption of lithium (Li) ions in Si-based anodes, which is associated with a large volume expansion upon lithiation and the continuous formation of the solid electrolyte interphase (SEI), is especially detrimental to full-cell batteries, whose Li-ion reserve is limited. This study demonstrates the application of stabilized lithium metal particles (SLMPs) as a prelithiation method for Si anodes that can be readily incorporated into large-scale industrial battery manufacturing. Particularly, a surfactant-stabilized SLMP dispersion was designed to be spray-coated onto prefabricated Si composite anodes, forming a uniformly distributed and well-adhered SLMP layer for in situ prelithiation. In full-cells with lithium iron phosphate (LFP) cathodes, the Si-based anodes demonstrated an improved 1st cycle Coulombic efficiency and cycle life with SLMP prelithiation using capacity-control cycling. However, when cycling over the full potential range, prelithiation with high SLMP loading was found to initially increase battery capacity while inducing accelerated fading in later cycles. This phenomenon was caused by Li trapping in the Li–Si alloy associated with higher SLMP-enabled Li diffusion kinetics. Additionally, cycled Si anodes from full-cells were also examined by surface analysis techniques, X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS), demonstrating SLMP effects in modifying the SEI by increasing the inorganic content, particularly LiF, which had been widely credited with improving SEI morphology and Li-ion diffusion through the interphase. Our findings provide valuable insights into the design of prelithiation and cycling strategies for high-capacity Si-based full-cell batteries to utilize the benefits of SLMP while avoiding the Li trapping phenomenon.