With the lithium-ion (Li-ion) battery the de facto electrical energy storage device in a world increasingly turning to electrification, researchers continue to develop innovative processes and materials that increase energy density, reduce the time to charge and improve safety.
One such innovation has seen manufacturers introduce and increase the silicon (Si) content in the anode to increase energy density and performance.
However, developing a stable electrode with Si as an active material is challenging, particularly in fast-charging batteries used in EVs, due to the fact that it undergoes severe volumetric changes during the charge and discharge cycle, which can lead to mechanical stress, cracking, and pulverization of the electrode.
To combat this researchers have applied several innovative solutions to stabilize the Si-rich anode, including modifying the electrode (binder, Si morphology etc.) and/or adding an SEI-forming additive to the electrolyte solution to form a stable SEI (solid-electrolyte interphase).
The SEI is a thin, passivating layer that forms on the surface of the anode in Li-ion batteries during the initial charging cycles. The formation of a stable and protective SEI is essential for the long-term performance and safety of Li-ion batteries.
StoreDot’s invention outlines methods of producing fast-charging Li-ion batteries with electrolytes that do not react with the cells’ anodes, but instead selectively interact with the cathodes, enabling the formation of a SEI layer. By so doing these electrolytes improve the performance of the fast-charging cells, and enhance their lifetime and safety.
In Li-ion batteries with traditional graphite anodes the electrolyte solutions are designed to have high anodic stability and low cathodic stability. However, when applied to anodes containing Si, which undergo significant volumetric changes during the charging and discharging process, the formation and breakdown of the SEI on the anodes leads to reduced cycle life, increased resistance, and capacity loss.
To overcome the problem, Storedot's patent for fast-charging lithium-ion cells employs electrolyte solutions that do not react with the anodes but instead form a SEI on the cathodes. By limiting the electrolyte interactions to the cathodes or even preventing them entirely through cathode coating, the performance, lifetime, and safety of the cells are significantly improved.
Storedot’s invention also describes methods of incorporating redox couples into the electrolyte solution to further promote SEI formation on the cathode and eliminate the SEI on the anode. These redox couples consist of two pairs of oxidation and reduction reactions. The first redox pair, which is inert with respect to the anodes, ensures that SEI is not formed on the anodes. The second redox pair promotes SEI formation on the cathodes during the cell's operation.
Furthermore, the patent describes various esters, ethers, alkyl carbonates, and nitriles that can be used in the electrolyte solution, each with different decomposition potentials that align with the operational voltages of the cathode materials. Additionally, the invention is compatible with an array of lithium salts such as LiPF6, LiClO4, LiFSI, LiTFSI, LiTDI, LiBOB, and LiFOB that can be dissolved in the electrolyte solutions to enhance their performance.
By utilizing electrolytes that do not react with the anodes and promote SEI formation on the cathodes, StoreDot addresses several key limitations of Si-dominant anodes found in Li-ion batteries. The improved performance, enhanced lifetime, and increased safety of these fast-charging cells pave the way for a more sustainable and efficient energy storage future, enabling a more sustainable and rapid rollout of fast charging EVs.