High Temperature Testing of NMC/Graphite Cells for Rapid Cell Performance Screening and Studies of Electrolyte Degradation

Abstract

LiNi0.5Mn0.3Co0.2O2/graphite cells with two different electrolytes underwent charge-discharge cycling at 70ºC. The 70ºC condition reduced the time it took for cells to lose significant capacity. Studies of the changes to the electrolyte after cycling by gas chromatography/mass spectrometry (GC/MS) and by Nuclear Magnetic Resonance spectroscopy (NMR) suggest that the same processes which cause cell failure and electrolyte degradation at 40ºC and 55ºC occur at 70ºC, only at an accelerated rate. Transition metal dissolution from the positive electrode was tracked using X-ray fluorescence studies of the negative electrode after testing. Based on the confidence obtained that the same degradation processes were occurring; advanced graphites were screened in NMC811/graphite cells at 70ºC. Differences in cell lifetime were apparent in weeks at 70ºC while the same differences took much longer to observe at 40ºC. It is our opinion that elevated temperature testing of Li-ion cells at 70oC is a viable rapid screening technique for advanced electrolytes and advanced electrode materials.

Identification of Redox Shuttle Generated in LFP/Graphite and NMC811/Graphite Cells

“…If both, EC and DMC, are present in the electrolyte molecules like dimethyl-2,5-dioxahexane carboxylate (DMOHC) can be formed, which makes the search for the shuttle molecule more difficult. 6,28,29 Redox shuttle identification in GC-MS spectra of extracted electrolytes.-Figure 9 shows the GC-MS spectra of electrolytes extracted from LFP/AG (see. Figure 9b shows clear peaks for DMC at 5.5 min, TMP at 11.8 min, EC at 12.2 min and DMT at 18.2 min retention time for the electrolyte extracted from an LFP/AG cell after formation at T F = 70 °C (red line).…”

Low-Voltage Operation and Lithium Bis(fluorosulfonyl)imide Electrolyte Salt Enable Long Li-Ion Cell Lifetimes at 85 °C

“…Prior work has shown that cell degradation follows Arrhenius kinetics, therefore cell lifetime can be estimated as a function of temperature using the accelerated failure data obtained at higher temperatures. [4][5][6][7][8][9][10] Another important factor to consider for high-temperature operations is the selection of lithium salt. Increasingly, the salt lithium bis(trifluoromethanesulfonyl)imide (LiFSI) is used for its ability to improve cycle life by promoting the stability of the graphite (or silicon) negative electrode/electrolyte interface.…”

Understanding the Mechanism of Secondary Cation Release from the (001) Surface of Li(Ni1/3Mn1/3Co1/3)O2: Insights from First-Principles

“…All calculations are spin-polarized, with NMC modeled as ferrimagnetic, as in previous work. , Experimental studies on the magnetism of NMC have shown that between 100 and 300 K the magnetic ordering is paramagnetic . This, among other studies, − also suggests that there is random structural ordering of metals in the M–O layers. While it is challenging to experimentally characterize the details of cation ordering, the alternating pattern is consistent with Monte Carlo and simulated-annealing-based modeling for 333-NMC .…”