Exploring Classes of Co-Solvents for Fast-Charging Lithium-Ion Cells

Abstract

Fast-charging lithium-ion cells require electrolyte solutions that balance high ionic conductivity and chemical stability. The introduction of an organic ester co-solvent is one route that can improve the rate capability of a cell. Several new co-solvent candidates were identified based on viscosity, permittivity (dielectric constant), and DFT-calculated electrochemical stability windows. Several formate, nitrile, ketone, and amide co-solvents are shown to increase the ionic conductivity of lithium hexafluorophosphate in conventional organic-carbonate-based solutions. Based on gas production during the first formation cycle in Li[Ni 1-x-y Co x Al y ]O 2 /graphite-SiO pouch cells, five candidates were identified: methyl formate (MF), ethyl formate (EF), propionitrile (PN), isobutyronitrile (iBN), and dimethyl formamide (DMF). High temperature storage (60 • C), long-term cycling, and ultrahigh-precision coulometry results indicate that MF offers the greatest balance between conductivity increase and cell lifetime. Future work is encouraged to develop more stable solution chemistries that incorporate MF. PN may prove useful for low temperature (< 40 • C) applications.

A Review of Existing and Emerging Methods for Lithium Detection and Characterization in Li‐Ion and Li‐Metal Batteries

“…Developing an accurate and computationally efficient lithium plating/stripping sub-model within the standard Newman pseudo 2D (P2D) electrochemical model is a key step in optimizing fast charging for EV batteries and developing robust, practical techniques for on-board Li detection. Numerous strategies have been reported in the literature for mitigating Li plating during fast charging of high energy density cells such as: improved electrolytes, [149,150] elevated temperature operation, [151][152][153] advanced electrode architectures, [154][155][156] electrode coatings, [157,158] and modifying active graphite material. [159,160] A well-parameterized P2D model with accurate Li sub-model enables understanding of limitations resulting in Li plating such as amount resulting from insufficient lithiation kinetics, solid-phase ion transport, and ion transport within the electrolyte phase.…”

Challenges and Strategies for Fast Charge of Li‐Ion Batteries

“…Li plating is thought to be the primary origin for performance degradation, which often occurs when the batteries are charged at low temperatures and high rates, especially in high energy batteries and in high SOC regions . Due to the high reactivity of Li metal, the plated Li reacts with electrolyte solvents, which not only reduces coulombic efficiency of the charging process but also depletes electrolyte leading to impedance growth and volumetric swelling of the battery . On the other hand, the plated Li can chemically re‐intercalate into graphite via micro‐galvanic cells as long as they are in contact with graphite and in the presence of electrolyte .…”

“…Employing an electrolyte with high ionic conductivity is always the first choice for enhancing the fast‐charging capability of Li‐ion batteries. The strategies for increasing ionic conductivity of the electrolytes are either or both modifying the existing solvent blend and using an alternative Li salt with a high dissociating ability . The solvent blends are commonly modified by introducing a co‐solvent that has the combined merits of viscosity, polarity (dielectric constant), and boiling point.…”

Advanced Materials for Sodium‐Ion Capacitors with Superior Energy–Power Properties: Progress and Perspectives

“…The majority of electrolytes used for NIBs and NICs rely on sodium salts, such as NaClO 4 and NaPF 6 , dissolved in a carbonate‐based organic solvent. Commonly used ester‐based solvents include ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) . These carbonates are used alone or in a combination by forming a mixture.…”