Single crystal Li[Ni 0.5 Mn 0.3 Co 0.2 ]O 2 materials in NMC532/artificial graphite cells have excellent long term charge-discharge cycle lifetime which greatly exceeds that of conventional NMC532 materials. There are a few patents from industry regarding the synthesis of single crystal NMC. In addition, there have only been a few reports in the academic literature showing that single crystal NMC with a grain size of ∼2-5 μm having good electrochemical performance was successfully synthesized, but these workers used complex approaches. This work systematically studies the steps required to synthesize single crystal NMC materials. The key synthesis steps including the impact of the Li to transition metal ratio, sintering temperature, precursor size and sintering time are discussed. This work provides guidance for the synthesis of single crystal NMC positive electrode materials that may be suitable for lithium-ion cells with high energy density and long lifetime. 1, the authors briefly discussed the synthesis method for single crystal materials, while the detailed information regarding the impact of the steps required to synthesize single crystal NMC materials was not discussed. In this work, the key synthesis steps including the impact of lithium to transition metal (Li/TM) ratio (molar), sintering temperature, sintering time and precursor size will be discussed. The optimization of the final synthesis conditions and evaluation of the electrochemical stability of the materials is not the main focus of this paper. However, the initial electrochemical properties, such as reversible specific capacity and irreversible specific capacity, of the best materials in this report are certainly competitive to commercial NMC532 materials. ExperimentalReagents used for the synthesis of single crystal NMC532 included nickel (II) sulfate hexahydrate (NiSO 4 • 6H 2 O, 98%, Alfa Aesar), manganese sulfate monohydrate (MnSO 4 • H 2 O, 98%, Alfa Aesar), sodium hydroxide (NaOH, 98%, Alfa Aesar), ammonium hydroxide (NH 4 OH, 28.0-30.0%, Sigma-Aldrich). All aqueous solutions used in the precursor synthesis were prepared with deionized (DI) water which was de-aerated by boiling for 10 minutes. Reagents used for coin cells included 1:2 v/v ethylene carbonate:diethyl carbonate (EC:DEC, BASF, purity 99.99%) and lithium hexafluorophosphate (LiPF 6 , BASF, purity 99.9%, water content 14 ppm).Synthesis of single crystal NMC532.-Ni 0.5 Mn 0.3 Co 0.2 (OH) 2 precursors were prepared via co-precipitation in a continuously stirred tank reactor (CSTR) (Brunswick Scientific/Eppendorf BioFlo 310). 9The details of the synthesis of similar precursors has been described by J. Li et al. 10,11 Precursors with three different sizes, labelled as large (L), medium (M) and small (S), were prepared individually by adjusting the pH and stirring rate. Unless specified, precursor L was * Electrochemical Society Fellow.z E-mail: jeff.dahn@dal.ca used for the synthesis of lithiated samples. The dried precursors were mixed with a stoichiometric equivalent of Li 2 CO ...

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...

A set of LiNi 0.5 Mn 0.3 Co 0.2 O 2 /graphite lithium-ion cells underwent 750 charge-discharge cycles during about 8 months at 55 • C to upper cutoff potentials of 4.0, 4.1, 4.2, 4.3, and 4.4 V. The electrolyte in these cells was extracted using a centrifuge method and studied using gas chromatography/mass spectrometry to determine the changes to the solvents and by inductively coupled plasma-mass spectrometry to determine the changes to the salt content in the electrolyte. The negative electrodes from the cells were harvested and studied by micro-X-ray fluorescence to quantify the amount of transition metals which migrated from the positive electrode to the negative electrode during the testing. Emphasis is given to a detailed description of the quantitative methods used in the hope that others will adopt them in similar studies of different types of aged lithium-ion cells. The cells studied here initially had 1.1 molal LiPF 6 ethylene carbonate (EC): ethyl methyl carbonate (EMC) (3:7 by weight) electrolyte. The aged cells showed increasing amounts of dimethyl carbonate and diethyl carbonate created by transesterification as the upper cutoff potential increased. Only extremely small amounts of Mn, less than 0.1% of the total Mn in the positive electrode, were found on the negative electrode after this aggressive testing. Lithium-ion batteries are currently used in a wide range of applications: cell phones, power tools, vehicles and even grid energy storage.

NMC532/artificial graphite cells using single crystal NMC532 active material can have excellent long term lifetime at 4.4 V and elevated temperature if appropriate electrolytes are used. However, electrolytes developed earlier for these cells and reported in the literature cannot support even C/2 rates during charging without unwanted lithium plating at room temperature. This work is thus focused on the development of new electrolytes for single crystal NMC532/artificial graphite cells that can yield long lifetime and support higher charging rates. Ex-situ and in-situ gas measurements, ultra-high precision coulometry, isothermal microcalorimetry, lithium plating tests and long term cycling tests were used for the screening of electrolytes. Capacity loss in lithium ion cells can be caused by the loss of lithium inventory to the solid electrolyte interphase (SEI).1-3 Active material loss due to structural degradation and due to electrical disconnection at the particle/electrode level can also lead to capacity loss. Internal impedance or polarization increase is another major contributor to capacity loss under high rate discharge conditions. Moreover, unwanted lithium plating, which can occur during high rate or low temperature charging, can also result in severe capacity fade. At high potentials, accelerated unwanted reactions in the electrolyte such as electrolyte oxidation occur and can hasten capacity loss by causing reconstruction of the positive electrode surface which can lead to impedance growth. [1][2][3][4][5] In addition the oxidized by-products can migrate to the negative electrode surface and be reduced there.6,7 Such reactions can lead to the consumption of lithium ions from the electrolyte (to maintain charge neutrality in the electrolyte), a reduction in lithium inventory, as well as a thickening of the negative electrode SEI which together ultimately cause impedance growth and capacity loss. 8,9 These processes are usually accelerated by higher charging potentials and higher temperatures.Novel electrolyte additives and modifications to positive electrode materials have been developed to improve the lifetime of Li-ion cells operated to high potential. • C, more than 88% of the original capacity was maintained after testing for one year (∼2000 cycles with C/2 rate, CCCV) and more than 82% was maintained after 18 months (3000 cycles with C/2 rate, CCCV). Figure S1 in the supplemental information shows the extended test results for the same cells shown in Figure 12 of Reference 22.Liu et al. found that additives and electrolytes that increase the negative electrode area-specific resistance lead to a decreased onset current for unwanted lithium plating.23 Such additives are often those that also increase lifetime of cells under moderate rate conditions. PES211 electrolyte usually leads to large negative electrode charge transfer resistance and therefore is not suitable for applications requiring high rates during charging. Liu et al. showed that NMC111/graphite cells with PES211 electrolyte could not be...

One goal of researchers focusing on lithium-ion batteries for electric vehicles is to decrease the time required for charging. This can be done by several methods, including increasing the electrolyte transport properties. Methyl acetate, used as a co-solvent in the electrolyte, has been shown by a number of researchers to increase cell rate capability dramatically but careful considerations of the impact of methyl acetate on cell lifetime have not been published to our knowledge. The impacts of methyl acetate as a co-solvent in NMC532/ graphite cells were systematically studied in this work. Ex-situ gas evolution measurements, electrochemical impedance spectroscopy, high rate charging tests, ultra-high precision coulometry, isothermal microcalorimetry and long term cycling at both 20 and 40 • C were used to probe the impacts of including methyl acetate as a co-solvent. This work will be of great interest to Li-ion battery scientists developing cells that can support rapid charge and still maintain long lifetime. Lithium ion cells for electric vehicles should have long lifetime, high energy density and be able to support high rate charging. If cells are charged too rapidly for a given temperature, it is possible that unwanted lithium plating on the graphite negative electrode can occur and can accelerate cell capacity loss.1 There are a number of factors that influence the ability of cells to be charged rapidly. These include the thicknesses of the electrodes and the separator, the porosity and tortuosity of the electrodes and the separator and the electrolyte transport properties. In addition, Liu et al.,2 recently highlighted the importance of the negative electrode solid electrolyte interphase (SEI) resistance on the ability of cells to be charged rapidly without unwanted lithium plating during charge.For any given cell design, the easiest change to make in Liion cell manufacturing is a change in the electrolyte. All that entails, apart from possible materials compatibility issues, is filling cells with a different fluid. Electrolytes that promote high lithiumion diffusion constants, low viscosity, high conductivity, a high lithium ion transference number and promote low resistance negative electrode SEI layers are preferred for cells designed for high rate charging. Esters are beneficial co-solvents that lower freezing points, increase ionic conductivity and lower viscosity. Esters have been applied to improve the low temperature rate capability of Liion cells and also improve rate capability at room temperature. [3][4][5][6][7][8][9][10] Li-ion batteries with esters and positive electrodes of LiCoO 2 were studied in References 4-7 while those with LiNi x Co 1-x O 2 positive electrodes were studied by Smart et al. lifetime with an electrolyte containing 2 wt% prop-1-ene-1,3 sultone (PES) + 1 wt% tris (trimethylsilyl) phosphite (TTSPi) + 1 wt % ethylene sulfate (DTD) in 1 M LiPF 6 in ethylene carbonate (EC): ethyl methyl carbonate (EMC) (3:7 by weight). More than 92% capacity was maintained after testing for ...

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.

Mixtures of metallic phosphates which are produced as by‐products of the phosphate industry have been found to have superior corrosion‐inhibiting properties in water systems while at the same time preventing scale deposition in those sections where the water has a tendency to form scales. Thus, chemical control of acidity in water systems becomes much less critical. The new technique is considered important and it is thought that metallic phosphates may in the future be applied to fields other than water treatment. The following article is based on the results of work carried out in the laboratories of the Deady Chemical Co., Kansas City, U.S.A.

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