Researchers at the Ulsan National Institute of Science and Technology (UNIST) in Korea have developed an innovative electrolyte additive that enables a high-energy-density Li-ion battery to retain more than 80% of its initial capacity even after hundreds of cycles.
When this additive was added to a large-capacity battery composed of a high-nickel anode and a silicon mixed anode, the initial capacity was maintained at 81.5% even after 400 charging and discharging cycles—10% to 30% better than commercial additives such as FEC (fluoroethylene carbonate) or VC (vinylene carbonate).
An open-access paper on their work is published in Nature Communications.
Solid electrolyte interphases generated using electrolyte additives are key for anode-electrolyte interactions and for enhancing the lithium-ion battery lifespan. Classical solid electrolyte interphase additives, such as vinylene carbonate and fluoroethylene carbonate, have limited potential for simultaneously achieving a long lifespan and fast chargeability in high-energy-density lithium-ion batteries (LIBs).
Here we report a next-generation synthetic additive approach that allows to form a highly stable electrode-electrolyte interface architecture from fluorinated and silylated electrolyte additives; it endures the lithiation-induced volume expansion of Si-embedded anodes and provides ion channels for facile Li-ion transport while protecting the Ni-rich LiNi0.8Co0.1Mn0.1O2 cathodes. The retrosynthetically designed solid electrolyte interphase-forming additives, 5-methyl-4-((trifluoromethoxy)methyl)-1,3-dioxol-2-one and 5-methyl-4-((trimethylsilyloxy)methyl)-1,3-dioxol-2-one, provide spatial flexibility to the vinylene carbonate-derived solid electrolyte interphase via polymeric propagation with the vinyl group of vinylene carbonate.
The interface architecture from the synthesized vinylene carbonate-type additive enables high-energy-density LIBs with 81.5% capacity retention after 400 cycles at 1 C and fast charging capability (1.9% capacity fading after 100 cycles at 3 C).—Park et al.
As the demand for large-capacity batteries for uses including electric vehicles increases, research to replace electrodes in commercial lithium-ion batteries with high-capacity materials such as silicon and high nickel is active. However, the volume of silicon anodes is increased by three times or more during charging and discharging, so mechanical durability is weak, and high nickel anodes are also chemically unstable.
The protective film made by the new dioxolone additives on the surface of the silicon mixed anode is flexible like a rubber band and has good elasticity, as well as excellent lithium ion permeability (mobility). This enables high-speed charging and reduces the mechanical overload caused by repeated volume changes of silicon.
Incorporation of DMVC-OCF3 and DMVC-OTMS in the VC scaffold leads to the creation of a flexible and robust SEI on the Si–C anode. DMVC-OTMS scavenges HF and deactivates PF5, resulting in compositional and structural stability of the interfacial layers on the electrodes. The Me (−CH3) moiety bonded to the VC scaffold provides ion channels, providing space for Li-ion transport in the SEI. Park et al.
In addition, the additive removes hydrofluoric acid (HF) from the electrolyte to prevent the metal (nickel) inside the high nickel anode from leaking out. The amount of metal inside the anode determines the battery capacity.
This achievement is the result of the collaboration of material structure design, experiment, simulation, and synthesis method research to actually make this material structure that can compensate for the shortcomings of existing additives (VC). It suggested a new direction for development.—Prof. Nam-soon Choi, co-corresponding author
The research was conducted with the support of the Korea Institute of Energy Technology Evaluation and Planning’s energy technology development project and the Korea Research Foundation’s climate change response technology development project.
Park, S., Jeong, S.Y., Lee, T.K. et al. (2021) “Replacing conventional battery electrolyte additives with dioxolone derivatives for high-energy-density lithium-ion batteries.” Nat Commun 12, 838 doi: 10.1038/s41467-021-21106-6