A Joint DFT and Experimental Study of an Imidazolidinone Additive in Lithium-Ion Cells

Abstract

Electrolyte additives are a practical route to improving the lifetime and performance of lithium-ion cells. It is not well understood what makes a good additive; thus, the discovery of new additives poses a significant challenge. Computational methods have the potential to streamline the search for new additives, but it is important to compare predicted additive behavior with experimentally measured results. A new electrolyte additive, 1,3-dimethyl-2-imidazolidinone (DMI), has been evaluated in LiNi 1-x-y Mn x Co y O 2 (NMC)/graphite pouch cells as a single additive and with the co-additive vinylene carbonate (VC). This work compares the density functional theory (DFT)-predicted behavior of DMI with experimental results, including differential capacity analysis (dQ/dV), electrochemical impedance spectroscopy (EIS), high-temperature storage, gas chromatography-mass spectrometry (GC-MS) and long-term cycling tests. The DFT-calculated reduction potential of DMI is −0.63 V vs Li/Li + , consistent with the experimental observation that it reduces at a lower potential than ethylene carbonate (EC), ∼0.80 V vs Li/Li + . Although DMI turns out not to be a competitively useful additive, the good match between many aspects of the experimental results and theoretical predictions is a good indication that it is possible to understand aspects of the behavior of additives. This can guide future researchers.

Impact of Functionalization and Co-Additives on Dioxazolone Electrolyte Additives

“…The cell voltages corresponding to the standard reduction potentials were calculated as described before. 62 The cell voltages at which pFDO and PDO reduce are very similar (2.25 V and 2.24 V), while it is larger for pMODO (2.42 V) and much smaller for pNDO (0.78 V). As an example, the reduction product of PDO is shown in Fig.…”

Understanding the Outstanding High‐Voltage Performance of NCM523||Graphite Lithium Ion Cells after Elimination of Ethylene Carbonate Solvent from Conventional Electrolyte

“…[ 20 ] The mechanistic difference of EC‐free electrolyte compared to EC‐based electrolyte (Scheme 1) is schematically illustrated in Scheme 2. Absence of the highly reductive EC [ 25,59,60 ] promotes reduction of LiPF 6 at graphite side resulting in more Li x PF y species. [ 61,62 ] The contact with oxygen species (LiOH, Li 2 CO 3 , water traces, oxygen release from cathode, etc.)…”

Compatibility of Various Electrolytes with Cation Disordered Rocksalt Cathodes in Lithium Ion Batteries

“…Dahn et al 28 have successfully tracked in situ gas volume change in a cell after various cycles using the Archimedean principle. Thereby, inspired by that work, the buoyant force of the cell suspended in water [MilliQ water, Merck Millipore Milli-Q Advantage A10, resistivity at 25 °C = 18.2 MΩ cm, total organic carbon ≤ 5 ppb] was measured with a Archimedes' in situ gas analyzer 29 using a small-scale thin film load cell (KD45 2 N, ME-Meßsysteme). Volume changes of the pouch cell influence the mass of the water that is replaced and therefore also the load detected by strain gauges in the measuring device.…”