Study of Electrolyte and Electrode Composition Changes vs Time in Aged Li-Ion Cells

Abstract

Many studies of Li-ion cells examine compositional changes to electrolyte and electrodes to determine desirable or undesirable reactions that affect cell performance. Cells involved in these studies typically have a limited test lifetime due to the resource intensive and time-consuming nature of these experiments. Here, electrolyte and electrode analyses were performed on a large matrix of cells tested at various conditions and with various cycle lifetimes. The matrix included LiNi0.5Mn0.3Co0.2O2 (NMC532)/graphite and LiNi0.6Mn0.2Co0.2O2 (NMC622)/graphite pouch cells with excellent performing electrolyte mixtures, both cycling and storage protocols at 40 °C and 55 °C with both 4.3 V and 4.4 V upper cutoff potentials. This study presents post-test analysis (electrochemical impedance spectroscopy, differential voltage analysis, differential thermal analysis), electrolyte analysis (gas chromatography, quantitative nuclear magnetic resonance), and electrode analysis (micro X-ray fluorescence) for these cells after 3, 6, 9, and 12 months of testing. Many products and reactants, such as fraction of transesterification, gas production, transition metal dissolution appeared to have a constant rate of increase in this 12-month observation period. In most cases, results from cells after 3 to 6 months of testing could be used to reasonably estimate the status of the cells (electrolyte composition, gas production, transition metal dissolution) at 12 months.

Solution NMR of Battery Electrolytes: Assessing and Mitigating Spectral Broadening Caused by Transition Metal Dissolution

“…NMR investigation of degradation species in lithium-ion battery electrolyte solutions is typically performed ex situ (i.e., samples are from model experiments or from post-mortem cells). These experiments are generally performed by (i) mixing electrolyte solutions with (or extracting them into) deuterated solvents including dimethyl sulfoxide- d 6 (DMSO), − CD 3 CN, − CDCl 3 , − tetrahydrofuran- d 8 , − and acetone- d 6 ; or (ii) using electrolyte solutions neat ,− or diluted with/extracted into dimethyl carbonate − or ethyl methyl carbonate (EMC) . In case (ii), deuterated solvents are incorporated into, but are physically separated from, the sample (e.g., via use of a solvent capillary).…”

Improving Lithium-ion Cells by Replacing Polyethylene Terephthalate Jellyroll Tape

“…Interestingly, ethylene glycol bis-(methyl carbonate) (DMOHC) is produced from the in situ generated EC reacting with DMC (Scheme S3). 12 Like the PET depolymerization, this dimerization reaction is also catalyzed by lithium methoxide. DMOHC formation consumes EC, which explains why there is less EC than DMT in Fig.…”

Aging‐Driven Composition and Distribution Changes of Electrolyte and Graphite Anode in 18650‐Type Li‐Ion Batteries

“…[19] The method has been successfully validated and found well suited for non-invasive investigations of the electrolyte in lithium-ion batteries. [41] In the current work, an adapted calorimetry measurement utilizing a closed-cycle refrigerator filled with 1 bar He (class 4 purity) as a calorimeter was applied for studies of parts of the variously aged lithium-ion cells described above. An illustration of the data reduction procedure is given in Figure S6 (Supporting Information).…”