Simplified algebraic area specific impedance (ASI) correlations have been developed for solid-state composite battery electrodes made of a single ion conducting electrolyte, conductive additive, and intercalation active material. Two ASI expressions were developed, one for short times ( i.e. , pulsed power operation) and another for the pseudo steady state operation ( i.e., sustained discharge for energy estimation). A full electrochemical model based on porous electrode theory was developed to examine the accuracy of the simplified ASI expressions. The simplified expressions agree favorably with full model results over a wide range of parameters ( i.e. , electrode thicknesses, electrolyte conductivities, solid-state diffusion coefficients, specific surface areas, etc.) and conditions ( i.e. , C-rates, states of charge, and pulse times). Under most conditions, the error between the full model and the correlations is well below 7 %. Higher errors were observed for the pseudo steady state expression at high/ low states of charge where the assumption of uniform reaction distributions loses validity. The short time ASI has higher error at low states of charge due to the nonlinearity of the open circuit voltage equation, which is assumed linear in the formulation of the simplified algebraic expression.

Lithium-ion batteries currently dominate the light-duty electric vehicle (EV) market due to their high energy density, low self-discharge, and high efficiency. Because of these advantages, Li-ion batteries are now being explored for next-generation EV applications like heavy trucks and aerial vehicles. The new applications present design challenges somewhat different from light-duty, road vehicles. For instance, aerial EVs during take-off and landing or heavy trucks on lengthy inclines/declines require high power (or regenerative) pulses for >1 minute. These long-duration, high power pulses may lead to significant temperature rise that could damage the battery and/or produce unsafe conditions resulting in thermal runaway. Accurate estimations of the temperature rise during these pulses are important for initial studies focused on assessing the validity of Li-ion batteries in these and other applications. This work starts by demonstrating how the accuracy of approximating the temperature rise using Joule heating – i.e., I2R, where I is the applied current and R is the electrochemical resistance – decays considerably for high power pulses. A 3-D thermal-electrochemical model of an NMC532-Graphite pouch cell is then used to explain the causes of the deviation. It is shown that a combination of transport in the electrolyte and self-heating cause variations in the resistance during the pulse, which invalidate the Joule heating approximation. Insights from these results are used to develop a correlation for the temperature rise during high power pulses. The correlation provides an improved estimation of the temperature using minimal experimental data for the area specific resistance of the cell.

The method of standard contact porosimetry was utilized to establish electrode and separator pore size distribution and electrolyte wetting parameters for a single layer lithium-ion pouch cell. A classical two phase flow model was developed to examine the complete cell electrolyte wetting process. The modeling indicates that reaching greater than 90% saturation of the porosity by the end of the formation protocol is easily accomplished. Completely filling all porosity is shown to be more of a challenge. Because the electrolyte tends to build up at the edges of the cell first, the process slows dramatically at high saturation levels. Further, this situation can result in possibly trapping a small amount of gas in the pores. Simulations with an electrochemical model applied to the edge of the pouch cell indicates there is a correlation between the nonuniform wetting of the pores and observed lithium plating patterns.

The temperature-dependent behaviors of five nickel-containing positive electrodes (NCA, NMC811, NMC622, NMC532, and NMC111) in lithium-ion batteries are investigated using an electrochemical protocol involving rate studies, mild aging (~100 cycles), and hybrid pulse power characterization (HPPC). Tests are conducted using coin-cells with graphite negative electrodes at -20 ???C, 0 ???C, 20 ???C, and 40 ???C. Three techniques are compared for determining the area-specific impedance (ASI): i) fits to the rate study average voltages, ii) fitting to the entire voltage curves using a regularization scheme, and iii) HPPC. When fit to an Arrhenius-type equation, all methods yield similar apparent activation energies (??2 kJ/mol) for the impedance, which range from -20 to -31 kJ/mol for the electrodes. Impedance growth increases with temperature but remains at less than 0.2% per cycle for most electrodes and temperatures. NCA and NMC811 are the exceptions, which yield 0.5% and 1.5% increases in ASI per cycle, respectively, at 40 ???C. For cells with the same electrodes, the capacities are similar at 20 and 40 ???C but reduce at lower temperatures, with up to a 52% reduction at -20 ???C and 2C. The fade in energy of the cells during C/3 cycling is attributed to decreasing capacity as opposed to increasing ASI.

Galvanostatic intermittent titration experiments were performed in three-electrode cells to characterize the effect of C/2, 2-C and 4-C charge rates on the observed lithium diffusion coefficient. As part of the data analysis process, we compared the classic Weppner-Huggins analysis of polarization data with a newer (Wang et al.) analysis method for depolarization data. At low values of x in LixC6, both analysis methods showed the same general trend in the apparent lithium diffusion coefficient, 4-C > 2-C > C/2. The two techniques differed in the magnitude of the estimated diffusion coefficient by about a factor of 100. The observed increase in diffusion coefficient does not last over a large compositional range. Since the estimates from the method of Weppner and Huggins may contain artifacts due to the use of particulate electrodes and high charge rates, the method of Wang et al. may produce better values.

This work demonstrates pathways toward affordable, fast-charging Li-ion batteries by implementing a constant-risk charging protocol with active thermal management.

In this study, we assert that the apparent lithium diffusion coefficient in graphite active particles in the negative electrodes of lithium-ion cells increases appreciably with the intercalation rate. This assertion is based on an electrochemical model analysis of a wide range of electrochemical micro-reference electrode full cell studies on a coated natural graphite and other literature results. While the mechanism for this increase is a subject of further investigation, the results of our study suggest that the lithium transport in the graphite does not limit the maximum attainable charging rate in typical lithium-ion cells for electric vehicles.

Coin cells are used extensively as test devices in battery research for evaluation of new materials and optimization of cycling protocols. In this study,in situX-ray diffraction profilometry is used to characterize spatial distribution of the active materials, lithiation, and phase distribution in electrodes of NCM523/graphite coin cells. The X-ray data indicate uneven areal compression of the electrode assembly in such cells, which we trace to a specific design feature that leads to elastic deformation of a metal spacer. Steep lithiation gradients observed in the electrodes imply radially-dependent resistivity, for which uneven compression of the separator is a likely cause. Electrochemical model calculations suggest that variable porosity of the polymer separator would account for the salient features of spatial profiles observed in these coin cells.

The charging of lithium ion batteries in a fast and safe manner is critical for promoting the mass adoption of electric vehicles. Li intercalation in graphite electrodes is known to be one of the bottlenecks during the fast charging process. The mechanism of Li diffusion in highly polarized graphite anode at high current rates remains, however, not well understood. Herein, Density Functional Theory (DFT) calculations are used to gain insights into the Li diffusion process in graphite when it is far from equilibrium under fast charging conditions. The effect of uncompensated charges on Li mobility is determined in the highly polarized regions of the anode close to the interfaces. The extra charge was found to increase the interlayer spacing in the diffusion layer and adjacent channels, increasing the diffusivity and promoting the formation of Li clusters. A concerted diffusion mechanism at the edge of high-concentration Li domains is proposed to enhance the diffusion of Li.

Increasing the charge rate of Li-ion cells over 1-2C (full charge in 30-60 min) would be highly desirable, but high currents flowing through the active materials push these cells to their endurance limits. In this article, we aim to understand how such high-current regimes affect electrochemical properties of the cells. Formation of Li metal deposits is a recognized hazard of high-rate charging, as Li plating can overtake lithium intercalation in the negative electrode. Here we demonstrate how microprobe Li/Cu reference electrodes can be used to characterize the graphite anode and layered oxide (NCM523) cathode during constant-current (<= 6C) voltage-limited (4.39 V) charging of Li-ion cells. These reference electrodes are used to monitor the onset of Li plating conditions in situ during cell charging. As the current increases over 3C, the anode potentials decrease below -40 mV causing lithium nucleation. Surprisingly, this nucleation (at least, initially) does not result in capacity fade or a higher anode impedance even in strongly polarized cells, so it appears that the nascent Li nuclei are isolated from electrolyte by the pre-existing solid electrolyte interphase. Our study shows that microprobe reference electrodes are an important diagnostic tool to characterize full-cell behavior in the high-current regimes. (C) The Author(s) 2019. Published by ECS.

In this series, Li/Cu microprobes are used to monitor potentials of individual electrodes in situ during high-rate charging of Li-ion cells. Here we focus on capacity-limited charging of these cells to 6C, and present a general treatment of polarization that allows for data reduction and accurate interpolation/extrapolation over a wide range of charge rates. We show that the anode impedance as measured both using this new treatment and the more established pulsed-current techniques is not significantly changed after high-rate aging of the cell, including the conditions under which Li plating has occurred. Our measurements suggest that the changes in cell and electrode polarization to a large extent occur through nonlinear effects that involve time-delayed processes. An electrochemical model that includes phase dynamics in lithiated graphite is shown to capture some but not all of the observed trends suggesting that important facets of the high-rate behavior need to be included in such models. (C) The Author(s) 2019. Published by ECS.

This report details the Battery Performance and Cost model (BatPaC) developed at Argonne National Laboratory for lithium-ion battery packs used in automotive transportation. The model designs the battery for a specified power, energy, and type of vehicle battery. The cost of the designed battery is then calculated by accounting for every step in the lithium-ion battery manufacturing process. The assumed annual production level directly affects each process step. The total cost to the original equipment manufacturer calculated by the model includes the materials, manufacturing, and warranty costs for a battery produced in the year 2020 (in 2010 US$). At the time this report is written, this calculation is the only publically available model that performs a bottom-up lithium-ion battery design and cost calculation. Both the model and the report have been publically peer-reviewed by battery experts assembled by the U.S. Environmental Protection Agency. This report and accompanying model include changes made in response to the comments received during the peer-review. The purpose of the report is to document the equations and assumptions from which the model has been created. A user of the model will be able to recreate the calculations and perhaps more importantly, understand the driving forces for the results. Instructions for use and an illustration of model results are also presented. Almost every variable in the calculation may be changed by the user to represent a system different from the default values pre-entered into the program. The distinct advantage of using a bottom-up cost and design model is that the entire power-to-energy space may be traversed to examine the correlation between performance and cost. The BatPaC model accounts for the physical limitations of the electrochemical processes within the battery. Thus, unrealistic designs are penalized in energy density and cost, unlike cost models based on linear extrapolations. Additionally, the consequences on cost and energy density from changes in cell capacity, parallel cell groups, and manufacturing capabilities are easily assessed with the model. New proposed materials may also be examined to translate bench-scale values to the design of full-scale battery packs providing realistic energy densities and prices to the original equipment manufacturer. The model will be openly distributed to the public in the year 2011. Currently, the calculations are based in a Microsoft{reg_sign} Office Excel spreadsheet. Instructions are provided for use; however, the format is admittedly not user-friendly. A parallel development effort has created an alternate version based on a graphical user-interface that will be more intuitive to some users. The version that is more user-friendly should allow for wider adoption of the model.

Amorphous silicon thin films having various thicknesses were investigated as a negative electrode material for lithium-ion batteries. Electrochemical characterization of the 20 nm thick thin silicon film revealed a very low first cycle Coulombic efficiency, which can be attributed to the silicon oxide layer formed on both the surface of the as-deposited Si thin film and the interface between the Si and the substrate. Among the investigated films, the 100 nm Si thin film demonstrated the best performance in terms of first cycle efficiency and cycle life. Observations from scanning electron microscopy demonstrated that the generation of cracks was inevitable in the cycled Si thin films, even as the thickness of the film was as little as 20 nm, which was not predicted by previous modeling work. However, the cycling performance of the 20 and 100 nm silicon thin films was not detrimentally affected by these cracks. The poor capacity retention of the 1 μm silicon thin film was attributed to the delamination.

In this work, we study the design aspects and process dynamics of solvent removal from Lithium-ion battery electrode coatings. For this, we use a continuum level mathematical model to describe the physical phenomenon of cathode drying involving coupled simultaneous heat and mass transfer with phase change. Our results indicate that around 90% of solvent is removed in less than half of the overall drying time. We study the effect of varying temperature and air velocity on the drying process. We show that the overall drying energy can be reduced by at least 50% by using a multi-zone drying process. Also, the peak solvent flux can be reduced by at least 40%. We further present the effect of using an aqueous solvent instead of N-Methyl-2-pyrrolidone (NMP) in electrode drying. Our results indicate that Water dries nearly 4.5 times faster as compared to NMP and requires nearly 10 times less overall drying energy per kg of solvent.

The potential for operating automotive battery packs at high upper cutoff voltages (UCV) has been explored using preliminary data on eight cathode materials. The pack level energy density, specific energy, and battery cost are calculated using the spreadsheet tool BatPaC. The tool used experimental data for some cathode materials such as the lithiated oxides of nickel manganese cobalt (NMC), nickel cobalt aluminum (NCA), layered lithium- and manganese-rich nickel manganese cobalt (LMRNMC). The half-cell data were obtained at UCVs between 4.2 and 4.7 V vs. Li/Li+. The experimental data showed LMRNMC with the highest lithiation capacity gain, increasing from 176 mAh.g(-1) at 4.2 V to 260 mAh.g(-1) at 4.7 V; this advantage is partly offset by its lower average voltage. Assuming optimized cell materials/design and an area-specific impedance of 12 Omega.cm(2) for all the materials, the BatPaC results indicate that the specific energies or energy densities of the battery electric vehicle (BEV) and plug-in hybrid electric vehicle (PHEV) battery packs with the LMRNMC and NMC cathodes can exceed 180 (BEV) and 160 (PHEV) Wh.kg(-1) at UCV > 4.6 V vs. Li/Li+. The costs of these battery packs are lowest at UCV = 4.7 V (vs. Li/Li+); estimated at 135-145 and 210-220 $.kWh(-1) for BEV and PHEV packs, respectively.

We develop three novel enhanced mixed integer-linear representations of the power limit of the battery and its efficiency as a function of the charge and discharge power and the state of charge of the battery, which can be directly implemented in large-scale power systems models and solved with commercial solvers. Using these representations, we conduct a techno-economic analysis of the performance of a 10MWh lithium-ion battery system testing the effect of a 5-min vs. a 60-min period price signal on profits using real time prices from a selected node in the MISO electricity market. Results show that models of lithium-ion batteries where the power limits and efficiency are held constant overestimate profits by 10% compared to those obtained from an enhanced representation that closely matches the real behavior of the battery. When the battery system is exposed to a 5-min price signal, the profitability from energy arbitrage improves by 60% compared to that from hourly price exposure. These results indicate that a more accurate representation of li-ion batteries as well as the market rules that govern the frequency of electricity prices can play a major role on the estimation of the value of battery technologies for power grid applications.

The price of the cathode active materials in lithium ion batteries is a key cost driver and thus significantly impacts consumer adoption of devices that utilize large energy storage contents (e.g. electric vehicles). A process model has been developed and used to study the production process of a common lithium-ion cathode material, lithiated nickel manganese cobalt oxide, using the co-precipitation method. The process was simulated for a plant producing 6500 kg day−1. The results indicate that the process will consume approximately 4 kWh kgNMC−1 of energy, 15 L kgNMC−1 of process water, and cost $23 to produce a kg of Li-NMC333. The calculations were extended to compare the production cost using two co-precipitation reactions (with Na2CO3 and NaOH), and similar cathode active materials such as lithium manganese oxide and lithium nickel cobalt aluminum oxide. A combination of cost saving opportunities show the possibility to reduce the cost of the cathode material by 19%.

In this study, parasitic side reactions in lithium- ion batteries were examined experimentally using a potentiostatic hold at high cell voltage. The experimental leakage current measured during the potentiostatic hold was compared to the Tafel expression and showed poor agreement with the expected transfer coefficient values, indicating that a more complicated expression could be needed to accurately capture the physics of this side reaction. Here we show that cross-talk between the electrodes is the primary contribution to the observed leakage current after the relaxation of concentration gradients has ceased. This cross-talk was confirmed with experiments using a lithium-ion conducting glass ceramic (LICGC) separator, which has high conductance only for lithium cations. The cells with LICGC separators showed significantly less leakage current during the potentiostatic hold test compared to cells with standard microporous separators where cross-talk is present. In addition, direct-current pulse power tests show an impedance rise for cells held at high potentials and for cells held at high temperatures, which could be attributed to film formation from the parasitic side reaction. Based on the experimental findings, a phenomenological mechanism is proposed for the parasitic side reaction which accounts for cross-talk and mass transport of the decomposition products across the separator. (C) 2017 The Electrochemical Society.