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Lithium‐ion cells with graphite anodes and nickel–manganese–cobalt oxide (NMC622) cathodes are filled with three different amounts of electrolyte. During formation, incremental capacity analysis indicates small differences in the formation processes between cells with insufficient electrolytes to fill all pores and those with an electrolyte volume above the total pore volume of the cell. Complimentary analysis of the gases developed during formation shows that the composition of these cells differs from the cells with a sufficient electrolyte. The aging of cells under high temperature (60 °C) and high constant voltage of 4.2 V is studied. During aging, cells with higher amounts of electrolyte degrade substantially slower. Based on data available from electrical tests, a theory explaining the volume‐dependent rise of resistance and capacity decay is proposed. [ABSTRACT FROM AUTHOR]

In order to make electric transportation more accessible, the cost of lithium‐ion batteries must decrease. One way to achieve this is by increasing the production rates, especially in the time‐consuming steps of electrolyte filling and cell formation. Within this work, lithium‐ion pouch and hardcase cells are filled with electrolyte and the formation is started at varying wetting degrees. Data from the formation, stabilization, and life cycle testing are analyzed to determine the effect of an incomplete wetting degree on the cell quality. Additionally, postmortem analysis is performed to help understand the mechanisms induced when a cell with incomplete wetting is subjected to a current. The pouch cells demonstrate a linear capacity fade, regardless of the wetting degree, but feature strong lithium plating which becomes visible during postmortem analysis. In contrast, the hardcase cells display a clear correlation between the cell quality and the wetting degree in both the life cycle test and the postmortem analysis. It is shown that a wetting degree of 98% is required before starting the formation to avoid lithium plating in the cell. [ABSTRACT FROM AUTHOR]

In order to meet consumer demands for electric transportation, the energy density of lithium-ion batteries (LIB) must be improved. Therefore, a trend to increase the overall size of the individual cell and to decrease the share of inactive materials is needed. The process of electrolyte filling involves the injection of electrolyte liquid into the cell, as well as the absorption of the electrolyte into the pores of the electrodes and the separator, which is known as wetting. The trend towards larger-format LIB challenges the electrolyte filling due to an increase in wetting distance for the electrolyte as well as a decrease in the void volume of the cell. The optimization of the process via numerical simulation promises to reduce costs and ensure quality during battery production. The two models developed in this study are based on a commercial computational fluid dynamics (CFD) program to study the effect of process parameters, such as pressure and temperature, on the filling process. The results were verified with neutron radiography images of the dosing process and a feasibility study for a wetting simulation is shown. For all simulations, specific recommendations are provided to set up the electrolyte filling process, based on which factors generate the greatest improvement. [ABSTRACT FROM AUTHOR]

Herein, the effects of charge rate in coin cells containing NMC532/1506‐T graphite are investigated. The cells are cycled at room temperature using charge rates of 1‐, 2‐, 4‐, and 8‐C and discharged at the 1‐C rate for 50 cycles. The amounts of lithium and LiF are found to be highly correlated with charge time. Three decomposition products are identified in the organic electrolyte. The proposed, empirical formulae for these compounds are C14H33O15P3, C16H37O15P3, and C11H22O7PF; all are most likely organophosphates formed by the reaction of organic electrolyte decomposition products with LiPF6 or P(=O)F3. The relative concentrations of these organics do not display sensitivity to charge rate. These results imply that a new performance fade mechanism is not introduced by electrolyte decomposition. [ABSTRACT FROM AUTHOR]

The impact of the electrolyte additives methyl phenyl carbonate, ethyl phenyl carbonate, and diphenyl carbonate was evaluated in Li[Ni 0.33 Mn 0.33 Co 0.33 ]O 2 /graphite pouch cells with or without 2% vinylene carbonate. Experiments included high precision coulometry, automated storage, electrochemical impedance spectroscopy on symmetric cells and gas chromatography coupled with mass spectrometry. Gas chromatography/mass spectrometry analysis, electrochemical studies during the first charge and impedance spectroscopy on symmetric cells indicated that phenyl carbonates act as solid electrolyte interphase modifiers rather than formers. High precision coulometry showed that cells containing 1–4 wt% methyl phenyl carbonate, ethyl phenyl carbonate or diphenyl carbonate had similar coulombic efficiencies and charge-endpoint capacity slippage as cells filled with 2 wt% vinylene carbonate. Impedance spectroscopy showed that cells containing phenyl carbonates have substantially lower impedance than cells filled with 2 wt% vinylene carbonate and produced minimal volumes of gas during cell use. Results presented in the report show that phenyl carbonates are competitive additives for 4.2 V class cells and should lead to good cycle life, low polarization and low gas evolution during normal use. Phenyl carbonates can also be used as gas-producing safety agents (to trip pressure activated disconnects) in combination with vinylene carbonate in cylindrical or prismatic cells without adverse effects. [ABSTRACT FROM AUTHOR]

This work performed a comprehensive investigation on a fluorinated electrolyte (1 M LiPF 6 in a 1:9 solvent blend, by mass, of fluoroethylene carbonate (FEC) and methyl (2,2,2-trifluoroethyl) carbonate (FEMC)) proposed by Im et al. [ 1 ]. The fluorinated electrolyte addicted with 3 wt% lithium difluorophosphate (LFO), named FF19+3LFO is found to demonstrate better cycling performance in high-voltage Li(Ni 0.8 Mn 0.1 Co 0.1)O 2 lithium-ion cells over the other researched electrolytes. The improvement of cells' performance under high-voltage conditions is revealed to benefit from the robust CEI layers formed by FF19+3LFO, which can significantly enhance the electrode/electrolyte interface and restrain the side reactions between cathode materials and electrolytes. Moreover, the FF19+3LFO cells also illustrate more competitive performance than the conventional non-aqueous electrolyte based cells in the high-temperature storage tests, accelerating rate calorimetry (ARC) tests, nail tests, overcharge tests, and so on. In short, the electrochemical and safety features of high-voltage cells are effectively improved by FF19+3LFO. More concern into the fluorinated electrolyte is warranted for achieving the high-capacity and high-safety lithium-ion cells. • A robust CEI layer was formed by FF19+3LFO on the surface of cathode materials. • FF19+3LFO improves the cycling performance of NMC811 cells under high voltages. • FF19+3LFO improves the safety performance of NMC811 cells under abusive conditions. [ABSTRACT FROM AUTHOR]

Abstract: Ceramic-coated separators are prepared by coating the sides of a porous polyethylene membrane with nano-sized Al2O3 powder and hydrophilic poly(lithium 4-styrenesulfonate) binder. These separators exhibit an improved thermal stability at high temperatures without significant thermal shrinkage. Due to the high hydrophilicity of the polymer binder and large surface area of the small ceramic particles, the separators show good wettability in non-aqueous liquid electrolytes. By using the ceramic-coated separators, lithium-ion cells composed of a carbon anode and a LiCoO2 cathode are assembled and their cycling performance is evaluated. The cells are proven to have better capacity retention than for cells prepared with polyethylene membrane. It is expected that the ceramic-coated separator in this study can be potential candidate as a separator for rechargeable lithium-ion batteries that require thermal safety and good capacity retention. [Copyright &y& Elsevier]

Abstract: The fundamental electrochemical properties of lithium perfluoroalkyltrifluoroborates Li[C n F2n+1BF3] (n =1∼4) were evaluated as electrolyte salts for lithium-ion battery in comparison with LiBF4 and LiPF6. Li[C n F2n+1BF3] showed higher electrolytic conductivities than LiBF4 in aprotic solvents. In these series, the conductivities decreased with the perfluoroalkyl group being longer, and Li[C2F5BF3] exhibited a comparable conductivity to LiPF6. The relationship between the conductivity and the anion size showed that the anion with a moderate size is in favor of obtaining high conductivities. The limiting oxidation potentials determined by linear sweep voltammetry demonstrated that Li[C n F2n+1BF3] were less resistant against oxidation than LiBF4. The HOMO energies and ionization energies of [C n F2n+1BF3]− calculated by ab initio molecular orbital (MO) theory and density functional theory (DFT) supported this observation, however, there was no accuracy to explain the effect of the chain length of perfluoroalkyl groups on the limiting oxidation potentials. The cell performances of a LiC6/Li0.5CoO2 cell using Li[C2F5BF3] were comparable to those using LiPF6 at room temperature, however, it deteriorated at elevated temperature due to the reaction on the cathode. [Copyright &y& Elsevier]

Accelerating Rate Calorimetry (ARC) has been used to study the reaction between Li0FePO4 having an average particle size of 3, 7 or 15 μm with EC/DEC solvent, 1.0 M LiPF6 EC/DEC or 0.8 M lithium bis(oxalato)borate (LiBOB) EC/DEC electrolyte. LiFePO4 electrode material was charged to 3.8 V vs. Li metal to produce Li0FePO4 before analysis. In EC/DEC solvent, all the three Li0FePO4 samples show high thermal stability and their ARC onset temperature is higher than 300 °C. As the particle size of Li0FePO4 increases from 3–7 to 15 μm, the self-heating rate (SHR) with EC/DEC solvent at the same temperature becomes slightly lower. With the addition of LiPF6 to EC/DEC, self-heating exotherms begin at approximately 190 °C for all the three Li0FePO4 samples, independent of particle size. LiBOB-based electrolyte shows higher thermal stability than LiPF6-based electrolytes for all the three Li0FePO4 samples. Self-heating exotherms for the three Li0FePO4 samples in 0.8 M LiBOB EC/DEC begin at about 240 °C. [Copyright &y& Elsevier]

The electrochemical performances of composite positive electrodes including polymer materials have been investigated in lithium secondary cells with inorganic solid electrolytes. The polymer added to the electrode generally tends to enlarge the electrode impedance because of its insulating nature. Comparison of charge and discharge characteristics between some composite electrodes in this study revealed that the texture of polymer-coated on the surface of the active materials had a dominant influence on their electrochemical performance. It was found that porous polymer would be promising for the composite electrodes with high performance. [Copyright &y& Elsevier]

There has been increasing interest in developing lithium-ion electrolytes that possess enhanced safety characteristics, while still able to provide the desired stability and performance. Toward this end, our efforts have been focused on the development of lithium-ion electrolytes which contain partially and fully fluorinated carbonate solvents. The advantage of using such solvents is that they possess the requisite stability demonstrated by the hydrocarbon-based carbonates, while also possessing more desirable physical properties imparted by the presence of the fluorine substituents, such as lower melting points, increased stability toward oxidation, and favorable SEI film forming characteristics on carbon. Specifically, we have demonstrated the beneficial effect of electrolytes which contain the following fluorinated carbonate-based solvents: methyl-2,2,2-trifluoroethyl carbonate (MTFEC), ethyl-2,2,2-trifluoroethyl carbonate (ETFEC), propyl-2,2,2-trifluoroethyl carbonate (PTFEC), methyl-2,2,2,2′,2′,2′-hexafluoro-i-propyl carbonate (MHFPC), ethyl-2,2,2,2′,2′,2′-hexafluoro-i-propyl carbonate (EHFPC), and di-2,2,2-trifluoroethyl carbonate (DTFEC). These solvents have been incorporated into multi-component ternary and quaternary carbonate-based electrolytes and evaluated in lithium–carbon and carbon–LiNi0.8Co0.2O2 cells (equipped with lithium reference electrodes). In addition to determining the charge/discharge behavior of these cells, a number of electrochemical techniques were employed (i.e. Tafel polarization measurements, linear polarization measurements, and electrochemical impedance spectroscopy (EIS)) to further characterize the performance of these electrolytes, including the SEI formation characteristics and lithium intercalation/de-intercalation kinetics. [Copyright &y& Elsevier]

In order to enable future missions involving the exploration of the surface of Mars with Landers, and Rovers, NASA desires long life, high energy density rechargeable batteries which can operate well at very low temperature (down to −40 °C). Lithium-ion technology has been identified as being the most promising chemistry, due to high gravimetric and volumetric energy densities, as well as, long life characteristics. However, the state-of-art (SOA) technology is not sufficient to meet the needs of many applications that require excellent low-temperature capabilities. To further improve this technology, work at JPL has been focused upon developing electrolytes that result in lithium-ion cells with wider temperature ranges of operation. These efforts have led to the identification of a number of ternary and quaternary, all carbonate-based electrolytes that have been demonstrated to result in improved low-temperature performance in experimental three-electrode MCMB–carbon/LiNi0.8Co0.2O2 cells. A number of electrochemical characterization techniques were performed on these cells (i.e. Tafel polarization measurements, linear polarization measurements, and electrochemical impedance spectroscopy (EIS)) to further enhance our understanding of the performance limitations at low temperature. The most promising electrolyte formulations, namely 1.0 M LiPF6 EC+DEC+DMC+EMC (1:1:1:2 v/v) and 1.0 M LiPF6 EC+DEC+DMC+EMC (1:1:1:3 v/v), were incorporated into SAFT prototype DD-size (9 Ah) lithium-ion cells for evaluation. A number of electrical tests were performed on these cells, including rate characterization as a function of temperature, cycle life characterization at different temperatures, as well as, many mission specific characterization tests to determine their viability to enable future missions to Mars. Excellent performance was observed with the prototype DD-size cells over a wide temperature range (−50 to 40 °C), with high specific energy being delivered at very low temperatures (i.e. over 95 Wh/kg being delivered at −40 °C using a C/10 discharge rate). [Copyright &y& Elsevier]

• Development of an improved single-particle model for high C-rate applications. • Effect of non-linear spatial distribution of electrolyte potential, overpotential and open-circuit potential incorporated, leading to significantly improved prediction of the cell voltage. • Ease of implementation for battery management systems as a linear system of differential-algebraic equations in state-variables need to be solved. • Criteria for series-truncation of a semi-analytical model for electrode particle diffusion proposed. • Model validated against pseudo-2D and improvement to previous reduced-order models demonstrated. [Display omitted] In this work, an isothermal, reduced-order polynomial-based model is proposed for lithium-ion cells. The correction incorporated into the single-particle model considers the effect of electrolyte dynamics leading to improved model predictions at high current applications without adding any significant computational complexity. The model includes the spatial distribution of the electrode and electrolyte potentials and the electrolyte lithium concentration on the resulting cell voltage. A novel approach to account for the spatially varying overpotential and open-circuit potential is proposed. A linear system of differential-algebraic equations is obtained in the state variables and the cell voltage is computed using a non-linear expression in these states. The resulting linear state-space system makes the model easily implementable for state-estimation algorithms in battery management system applications. Additionally, a semi-analytical model is incorporated for the diffusion of lithium in electrodes and a criterion for truncating the infinite-series solution is proposed for achieving a balance between accuracy and complexity for cells subjected to fluctuating currents. The proposed model results in a decrease in error for cell voltage prediction by a factor of five when compared with existing enhanced single-particle models. [ABSTRACT FROM AUTHOR]