An apparatus was built to make accurate and precise in situ measurements of the volumes of gas evolved in Li-ion pouch cells during operation. With a thin film load cell accurately measuring the weight of a cell submerged in a fluid, the volume of a pouch cell can be precisely monitored using Archimedes' Principle. Examples showing the utility and sensitivity of the device have been selected from measurements made during the formation cycle (very first charge and discharge) of Li[Ni 1/3 Mn 1/3 Co 1/3 ]O 2 /graphite (NMC) Li-ion pouch cells. Gas production occurs at the very beginning of the formation cycle but quickly stops for cells containing a variety of electrolytes. The volume of the pouch cell then decreases with time. The testing of cells with various electrolyte additives indicated that the common additive, vinylene carbonate, is very effective at reducing the amount of gas formed during formation, but the best results among the additives reported here were obtained by using a combination of 2% vinylene carbonate and 2% prop-1-ene 1,3-sultone. The additives vinyl ethylene carbonate and ethylene sulfite were found to delay the onset of gas production during formation.

The role of two homologous cyclic sulfate electrolyte additives, trimethylene sulfate (or 1,3,2-dioxathiane-2,2-dioxide, TMS) and ethylene sulfate (or 1,3,2-dioxathiolane-2,2-dioxide, DTD), used either alone or in combination with vinylene carbonate (VC) on the lifetime of LiNi 1/3 Mn 1/3 Co 1/3 O 2 (NMC)/graphite pouch cells was studied by correlating data from gas chromatography/mass spectroscopy (GC−MS), dQ/dV analysis, ultrahigh precision coulometry, storage experiments, and X-ray photoelectron spectroscopy. For VC alone, more stable and protective SEI films were observed at the surface of both electrodes due to the formation of a polymer of VC, which results in higher capacity retention. For TMS, similar chemical SEI compositions were found compared to the TMS-free electrolytes. When VC was added to TMS, longer cell lifetime is attributed to VC. For DTD, a cell lifetime that competes with VC was explained by a preferential reduction potential and a much higher fraction of organic compounds in the SEI films. When VC was added to DTD, the contribution of both additives to the SEI films is consistent with the initial reactivity observed from dQ/dV and GC−MS analysis.

Many literature reports show that layered Li-Ni-Mn-Co oxides (NMC) have a surface reconstruction to a rocksalt (Fm3m) structure which is claimed to be responsible for the increase in cell impedance during high voltage cycling. It is important to determine if appropriate electrolyte additives can suppress the surface reconstructions of NMC materials. LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811)/Graphite pouch cells with different electrolyte additives and different upper cutoff potentials were charge-discharge cycled and the electrodes were recovered for z-contrast scanning transmission electron microscope (STEM) studies. It was found that there was no significant surface layer growth for cells cycled between 2.8 and 4.1 V. For cells with an upper cutoff voltage of 4.3 V, the electrodes from cells with control electrolyte (no additives) showed the thickest surface layer. The electrolyte additives vinylene carbonate (VC) and prop-1-ene-1,3-sultone (PES) were found to suppress the growth of the surface layer. However, cells with PES showed a more rapid capacity fade than control cells or cells with 2% VC showing that, at least for NMC811/graphite cells with PES or VC additives, failure cannot only be solely ascribed to a growing rocksalt surface layer. Other processes, for example associated with electrolyte oxidation, are believed to be responsible for failure. High energy density lithium-ion batteries that are cheaper, safer and with longer lifetimes need to be developed in order to meet the increasing demand for applications such as electric vehicles. LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) can deliver a high capacity of ∼200 mAh/g with an average discharge voltage of ∼3.8 V (vs. Li+/Li), making it a promising positive electrode material for high energy density lithium-ion batteries.1 However, electrochemical tests of NMC811 from half cells and full cells show poor cycling performance when charged to voltages above 4.2 V.2 In-situ and ex-situ X-ray diffraction showed that there are no significant irreversible structural changes in the bulk of the material during charge-discharge cycling. Instead, the parasitic reactions between the electrolyte and the surface of the positive electrode particles at high voltages were suggested to be the cause of the failure of cells cycled above 4.2 V. 2Layered NMC materials have a hexagonal layered structure (α-NaFeO 2 -type structure described in the Rm space group), where Li and transition metal atoms form alternating layers between oxygen layers and Li atoms have a 2-D diffusion path. [3][4][5] Lin et al. 6 showed that the surface of LiNi 0.42 Mn 0.42 Co 0.16 O 2 (NMC442) went through a structural reconstruction from layered (Rm) to rocksalt (Fm3m). In that transition, transition metal ions migrated to the lithium layers with a possible loss of Li and O from the surface of the structure. This was cited as one of the causes of a significant increase in cell impedance under high voltage cycling conditions. This surface reconstruction phenomenon was also observed in many other reports abou...

The trajectories, referred to as lifelines, of individual microorganisms in an industrial scale fermentor under substrate limiting conditions were studied using an Euler‐Lagrange computational fluid dynamics approach. The metabolic response to substrate concentration variations along these lifelines provides deep insight in the dynamic environment inside a large‐scale fermentor, from the point of view of the microorganisms themselves. We present a novel methodology to evaluate this metabolic response, based on transitions between metabolic “regimes” that can provide a comprehensive statistical insight in the environmental fluctuations experienced by microorganisms inside an industrial bioreactor. These statistics provide the groundwork for the design of representative scale‐down simulators, mimicking substrate variations experimentally. To focus on the methodology we use an industrial fermentation of Penicillium chrysogenum in a simplified representation, dealing with only glucose gradients, single‐phase hydrodynamics, and assuming no limitation in oxygen supply, but reasonably capturing the relevant timescales. Nevertheless, the methodology provides useful insight in the relation between flow and component fluctuation timescales that are expected to hold in physically more thorough simulations. Microorganisms experience substrate fluctuations at timescales of seconds, in the order of magnitude of the global circulation time. Such rapid fluctuations should be replicated in truly industrially representative scale‐down simulators.

When NMC/graphite Li-ion cells are operated at elevated temperature or at a cutoff potential above 4.2 V, electrolyte oxidation becomes increasingly severe leading to gaseous products and other oxidized species. These generated gas products and oxidized species can migrate to, and then interact with, the negative electrode. A variety of cell formats (pouch cells, symmetric cells and coin cells) as well as pouch bags, containing only a delithiated positive electrode or a lithiated negative electrode, were used to investigate electrode/electrode interactions. Open circuit potential measurements during high temperature storage, ex-situ measurements of gas volume produced versus time, gas chromatography-mass spectrometry (GC-MS) of the gases produced and electrochemical impedance spectroscopy (EIS) of the electrodes versus time were performed. During storage at 60 • C, pouch bags containing only a lithiated negative electrode and electrolyte produced no gas while charged full pouch cells produced some gas and pouch bags containing only a delithiated positive electrode and electrolyte produced a significant amount of gas. The predominant gas produced in the positive electrode pouch bags was CO 2 while virtually no CO 2 was detected in the gases evolved in the charged full cell, suggesting that the negative electrode in the full cell consumes CO 2 generated at the charged positive electrode. In addition, the impedance of the surface film on the charged positive electrodes in the pouch bags increased at least three times more than the positive electrodes in the charged pouch cells, even though they were both in contact with electrolyte for the same period of time. These impedance results suggest that oxidized species created at the positive electrode in the pouch bag remain in the vicinity of the positive electrode and create a high impedance film possibly a rock salt surface layer, while the same species migrate to the negative and are "consumed" in the pouch cell where the impedance of the positive electrode remains small. These interactions are apparently essential for the health of a NMC/graphite Li-ion pouch cell when operated at an elevated temperature or at a cutoff voltage above 4. Increasing evidence show that interactions between positive and negative electrodes exist in full Li-ion cells.1 A well-known example is Mn dissolution from the positive electrode and its subsequent deposition at the negative electrode. This interaction has been shown to be detrimental to cell performance.2-5 Another proposed example is CO 2 generation at the positive electrode followed by reduction at the negative electrode. This "dialog" between both electrodes was proposed as creating a "shuttle" which could damage cell performance. When NMC/graphite Li-ion cells are operated at a cutoff potential higher than 4.2 V, severe impedance increase can be the main contributor to cell failure instead of conventional mechanisms, like loss of Li inventory, that dominate in low voltage cells. [8][9][10][11][12] It is our opinion that the pr...

Li [Ni 0.4 Mn 0.4 Co 0.2 ]O 2 (NMC442)/graphite pouch cells containing various electrolyte additives, either singly or in combination, were studied using cycling experiments up to 4.4 and 4.5 V coupled with simultaneous electrochemical impedance spectroscopy (EIS) measurements. The impedance of most cells increased dramatically at 4.4 and 4.5 V, but was nearly reversible over one cycle. However, during continued cycling, the impedance of all cells slowly increased at all potentials. Electrolyte additives were found to dramatically affect this behavior. The impacts of adding prop-1-ene-1,3-sultone (PES), vinylene carbonate (VC), triallyl phosphate (TAP), methylene methane disulfonate (MMDS), ethylene sulfate (DTD) and/or tris(-trimethyl-silyl)-phosphite (TTSPi) to 1M LiPF 6 ethylene carbonate:ethyl methyl carbonate (EC:EMC) electrolyte were studied. PES-containing cells had dramatically lower impedance and better capacity retention than VC and TAP-containing cells during both 4.4 and 4.5 V experiments. When MMDS, DTD and/or TTSPi were added in combination with PES, the performance was improved further. Finally, continuous charge-discharge cycling was compared to cycling with a 24-hour hold applied at the top of charge at 4.4 V. The high voltage hold led to severe impedance growth which could be partially overcome through the use of optimal additive combinations. Lithium-ion (Li-ion) batteries are currently used in phones, laptop computers and, more recently, electric vehicles. It is well known that electrolyte additives can have a dramatic effect on the performance and lifetime of Li-ion batteries.1,2 Vinylene carbonate (VC) is perhaps the most famous and widely used additive and has been shown to improve cycle and calendar life of Li-ion cells.3 VC is less effective, however, when used in cells cycling to potentials above 4.2 V 4 or at elevated temperatures.5 Sulfur-containing additives have recently been investigated by several research groups in the hopes of overcoming the temperature sensitivity of VC and extending the usable voltage range of Li-ion cells. [6][7][8] Prop-1-ene-1,3-sultone (PES) has been shown to function as a stable solid electrolyte interphase (SEI)-forming additive that improved coulombic efficiency (CE), reduced charge end point capacity slippage and self-discharge rates. 8,9 PES nearly eliminated all gas production during storage at 4.2 V and 60• C, whereas VC did not. 9,10The work by Xia et al. 9 and Nelson et al. 10 demonstrated the superiority of PES over VC as an electrolyte additive in NMC/graphite cells. Methylene methane disulfonate (MMDS) has been shown to reduce electrolyte oxidation at the positive electrode and reduce the volume of gas produced, as well as decrease the impedance and rate of parasitic reactions when compared to cells without MMDS.6,11 The additive ethylene sulfate or 1,3,2-dioxathiolane-2,2-dioxide (DTD) has been shown to function as a film-forming additive for the SEI on the negative electrode.12,13 The additive tris-(trimethyl-silyl) phosphite (TTSPi) has bee...

Ethylene carbonate is a co-solvent used in virtually every lithium ion cell produced today because it enables operation of both the positive and negative electrodes. Most battery scientists believe ethylene carbonate is essential. Surprisingly, totally removing all ethylene carbonate from typical organic carbonate-based electrolytes and adding small amounts of electrolyte additives creates cells that are better than those containing ethylene carbonate. For example an electrolyte of only 2% vinylene carbonate and 98% ethyl methyl carbonate, with selected additives, provides excellent performance to Li[Ni 0.4 Mn 0.4 Co 0.2 ]O 2 /graphite cells cycled up to 4.4 V which increases their energy density by at least 10%. The cells have low impedance, low rates of electrolyte oxidation, good graphite passivation, low gas generation, acceptable conductivity and low cost. This discovery opens an entirely new space for electrolyte development.

Li [Ni 0.42 Mn 0.42 Co 0.16 ]O 2 (NMC442)/graphite pouch cells demonstrate superb performance at high voltage when ethylene carbonate (EC)-free electrolytes, using a solvent mixture that is >95% ethyl methyl carbonate (EMC) and between 2 and 5% of an "enabler", are used. The "enablers", required to passivate graphite during formation, can be vinylene carbonate (VC), methylene-ethylene carbonate (MEC), fluoroethylene carbonate (FEC) or difluoro ethylene carbonate (DiFEC), among others. In order to optimize the amount of "enabler" added to EMC, gas chromatography coupled with mass spectrometry (GC-MS) was used to track the consumption of "enabler" during the formation step. Storage tests, electrochemical impedance spectroscopy (EIS), ultrahigh precision coulometry (UHPC), long-term cycling, differential voltage analysis and isothermal microcalorimetry were used to determine the optimum amount of enabler to add to the cells. It was found that the graphite negative electrode cannot be fully passivated when the amount of "enabler" is too low resulting in gas production and capacity fade. Using excess "enabler" can cause large impedance and gas production in most cases. The choice of "enabler" also impacts cell performance. A solvent blend of 5% FEC with 95% EMC (by weight) provides the best combination of properties in NMC442/graphite cells operated to 4.4 V. It is our opinion that the experiments and their interpretation presented here represent a primer for the design of EC-free electrolytes. Lithium-ion batteries (LIB) are now widely used in electrified vehicles and energy storage systems.1 These applications require longer calendar and cycle lifetime as well as higher energy density. In order to increase the energy density of LIB, researchers focus on developing electrode materials with high specific capacity that may involve charging to increased upper cutoff potentials.2,3