We present a wide range of testing results on an excellent moderate-energy-density lithium-ion pouch cell chemistry to serve as benchmarks for academics and companies developing advanced lithium-ion and other "beyond lithium-ion" cell chemistries to (hopefully) exceed. These results are far superior to those that have been used by researchers modelling cell failure mechanisms and as such, these results are more representative of modern Li-ion cells and should be adopted by modellers. Up to three years of testing has been completed for some of the tests. Tests include long-term charge-discharge cycling at 20, 40 and 55°C, long-term storage at 20, 40 and 55°C, and high precision coulometry at 40°C. Several different electrolytes are considered in this LiNi 0.5 Mn 0.3 Co 0.2 O 2 /graphite chemistry, including those that can promote fast charging. The reasons for cell performance degradation and impedance growth are examined using several methods. We conclude that cells of this type should be able to power an electric vehicle for over 1.6 million kilometers (1 million miles) and last at least two decades in grid energy storage. The authors acknowledge that other cell format-dependent loss, if any, (e.g. cylindrical vs. pouch) may not be captured in these experiments.

An ultrasonic imaging technique has been developed to investigate the internal changes of pouch cells nondestructively. The local ultrasonic transmittance of pouch cells has been measured and used for imaging with a new ultrasonic scanning machine designed and built in-house. The wetting process of the cells is clearly observed via such ultrasonic imaging techniques. Furthermore, ultrasonic transmission images of fresh cells and aged cells with different electrolytes and cycling conditions exhibit very different ultrasonic transmittance, which can be caused by electrolyte dry-out or ''unwetting'' due to cell swelling. The ultrasonic imaging technique is a very sensitive method to probe failure mechanisms in Li-ion pouch cells.

The dependence of differential capacity versus voltage (dQ/dV) of Li/NCA half cells on temperature and testing current (C-rate) was studied. Kinetic hindrance of lithium diffusion at both low (∼3.5 V vs Li/Li + ) and high states of charge (∼4.17 V) was observed. In-situ X-ray diffraction measured the volume changes of the NCA lattice versus state of charge. NCA/graphite pouch cells were cycled in various voltage ranges to explore the impacts of depth of discharge (DOD) ranges and the kinetic hindrance regions in NCA on cell failure. dV/dQ analysis, full cell impedance and symmetric cell impedance analysis as well as half-cell studies of recovered electrodes were performed after 0, ∼400 and 800 charge-discharge cycles. The contributions of active mass loss and shift loss (from loss of Li inventory) to the capacity fade of NCA/graphite cells under various testing conditions were determined. The increase in positive electrode charge transfer impedance with cycle number was proportional to the increase of positive electrode active mass loss. There was no strong correlation between positive electrode active mass loss and lattice volume change. NCA active mass loss during cycling can be minimized when the dQ/dV peaks at ∼3.5 and 4.17 V (vs. Li/Li + ), that show kinetic hindrance, are partially or completely avoided.

Lithium-ion cells produce a considerable amount of gas in their first cycle. If the gases are not removed in a degassing step, most are consumed by the cell over time. This phenomenon has never been investigated explicitly in the literature. In this paper, the evolution and subsequent consumption of gas in typical lithium-ion cells are measured by Archimedes' principle and gas chromatography. It is found that all evolved gases are subsequently consumed to some degree, except for saturated hydrocarbons. The consumption of gas occurs predominantly at the negative electrode, where the gases are reduced to form part of the solid-electrolyte interphase (SEI). Changes to the negative electrode SEI upon gas consumption are investigated using X-ray photoelectron spectroscopy. The effect of gas consumption on cell performance is studied with ultra-high precision charging and high voltage storage experiments. It is found that gas consumption does not result in measurable adverse effects to cell performance. Lithium-ion cells can produce a significant amount of gas during the first charge (in the formation cycle), as electrolyte and additives react at the surfaces of the charging electrodes to form passivating films. If lithium-ion cells are packaged in a flexible casing, these gases are normally removed by the manufacturer in a degassing step, to prevent deformation of the cell and to ensure uniform stack pressure on the electrodes. If the degassing step is omitted, a large portion of the gas evolved is consumed over time.1 The reactions that consume gas are presumably prevalent in hard-cased cylindrical cells, such as 18650 s, which are often hermetically sealed before the first charge, and therefore cannot be easily degassed. The reactions that consume gas are presumably less prevalent in pouch-type cells, which are degassed.Several authors have speculated about the fates of gases in lithiumion cells.2-5 There has been no work explicitly dedicated to understanding the phenomenon of gas consumption. There is no consensus as to whether the effects of gas consumption are beneficial or harmful to cell performance. For example, it has been argued by some that the consumption of CO 2 is beneficial to cells, as it reacts to form a passivating film on the negative electrode. 3,4,6 However it has also been argued that the consumption of CO 2 is detrimental to cells, as it may reduce at the negative electrode to form Li 2 C 2 O 4 , which causes continual self-discharge at high voltage. 2It is important for both scientists and manufacturers of lithium-ion cells to understand the causes and the effects of gas consumption. If gas consumption is quick, benign, or even beneficial to cell performance, then the time-consuming degassing step for lithium-ion pouch cells might be skipped. 7 The gases evolved in lithium-ion pouch cells could be left for consumption within the cell, perhaps leaving the pouch cell flat and rigid after several hours if all the gases were consumed. If gas consumption in a cell produces undesirable effects, such...

The effects of electrolyte additives singly or in combination on Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 (NMC)/graphite pouch cells have been systematically investigated and compared using the ultra high precision charger (UHPC) at Dalhousie University, electrochemical impedance spectroscopy (EIS), an automated storage system, gas evolution measurements and selected long-term cycling experiments. The results of testing Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 (NMC)/graphite pouch cells with different electrolyte additives singly or in combination were measured and the results for over 110 additive sets are compared. A "Figure of Merit" approach is used to rank the effectiveness of the additives and their combinations. The combination of vinylene carbonate (VC) and/or prop-1-ene-1,3 sultone (PES), a sulfur containing additive, such as methylene methane disulfonate (MMDS), as well as either tris(-trimethly-silyl)-phosphate (TTSP) and/or tris(-trimethyl-silyl)-phosphite (TTSPi) as additives in the electrolyte can give cells with extremely high coulombic efficiency, excellent storage properties, low impedance and superior long term cycling at 55 • C. Additive mixtures such as 2% PES + 1% MMDS + 1% TTSPi are especially excellent in all respects. It is hoped that this comprehensive report sets a benchmark for future studies by others and can be used as a guide and reference for the comparison of other electrolyte additives singly or in combination.