A full physics stack model combined with a detailed thermal model are applied to simulate voltage and temperature profiles of 26700 sized commercial Li-ion power cells. A wide range of currents (3A → 40A) and a wide range of temperatures (−20 • C → 40 • C) are considered. The conventional stack model is augmented to include pseudo-capacitance effects in order to get a reasonable agreement with the measured data. Least squares refinement of 21 data sets is used to determine a number of material properties and their temperature dependence. Practical guidelines are described for choosing input material properties and for using the least squares method. All 21 data sets are successfully simulated using one set of input parameters. Key features in the voltage and temperature profiles are explained by looking at the simulated state inside the stack.Li-ion cells are now well established for use in applications which require high currents, such as power tools, e-bikes and various varieties of the HEV. For these applications, the cell design engineer must pay careful attention to the cell impedance for any proposed cell design. However, the estimation of cell impedance is a vastly more complex issue than is the calculation of cell capacity. In fact, the notion of cell impedance is not even a well defined concept. What is really required is the calculation of voltage curves at high currents in the presence of self heating.Accurately predicting the dynamic cell response for a wide range of applied currents, ambient temperatures and cell designs is nontrivial. The original work in this direction 1 achieved good results up to about a 2C rate, at ambient temperature, for a graphite/Li Mn 2 O 4 Li-ion cell. More recent work 2 focused on simultaneous simulation of three cell designs with various electrode thicknesses, and numerous electrolyte salt concentrations. Again, the simulation results deviate significantly from the cell data for discharge rates > 2C. These authors found it necessary to modify the salt or solid phase diffusion coefficients, as a function of discharge rate, in order to accurately reproduce the observed voltage profiles. Further studies which include self heating effects 3,4 have similar issues with high currents. None of these researchers had access to recently measured 5-8 electrolyte transport properties and salt activity. At a minimum, the temperature and concentration dependence of the salt diffusion must play an important role when self heating takes place. Other work has shown simulations of HEV pulse profiles 9 with 4C pulses lasting 18 seconds wherein the short duration of the pulses did enable a rather good agreement with experiment using the isothermal model. Pulses up to 10C were simulated using a full electro-thermal coupled model in reference 10 including some comparisons with experimental data at 0 • C. The authors observed some disagreement at 5C and 10C rates at 0 • C, but obtained remarkably good results for full 10C discharges at 25 • C without optimizing the model parameters. Reference 1...
PurposeThe purpose of this paper is to describe how Barnardo's, a large children's charity, has developed a system for measuring and reporting on service user outcomes as part of its performance management approach. The challenges that confront third sector organisations when adopting this approach are summarised, as are the benefits that can accrue.Design/methodology/approachThe paper's approach is to describe the development of an outcome monitoring tool (OMT) and to explore some of the benefits of and challenges to embedding this tool across Barnardo's services.FindingsThird sector organisations operate in competitive, resource‐constrained environments, where funding arrangements are often short‐term and piecemeal. The ability to evidence the effectiveness of services through demonstrating positive outcomes for service users is becoming an increasingly important factor in the process of securing and sustaining funding. An outcome‐focused approach contributes to the development of excellent services by helping to ensure that services are making a difference to the people that use them. Barnardo's OMT offers a model for evidencing the impact of services on the people who use them, thus contributing to the organisation's competitive edge.Originality/valueThis paper is informed by current thinking on outcomes and evidence‐based practice and offers a practical example of how to implement an outcome‐focused approach in a third sector organisation.
NASA continues to have an interest in developing high specific energy and high power rechargeable batteries that can operate well over a wide temperature range. Concepts for applications that could be enabled or enhanced by such technology include: (i) future Mars landers, (ii) future Mars rovers, including a possible Mars Sample Return mission, and (iii) future planetary aerial vehicles, where high specific energy, high power and wide operating temperature range is desired. Future missions to some of the distant icy moons of Jupiter and Saturn are also anticipated to benefit from improved ultra-low temperature rechargeable batteries with high specific energy.1 To meet these needs, the Electrochemical Technologies Group (ETG) at the Jet Propulsion Laboratory (JPL) has developed a number of low temperature Li-ion electrolytes utilizing various approaches. In general, the performance targets of this work is to provide operation over the temperature range of +40oC to -60oC (delivering up to 150 Wh/kg at -40oC at reasonable rates). In addition, continuous operation at low temperatures is desired, so the cells should possess good charge characteristics without undesirable lithium plating. In previous collaborative work with E-One Moli Energy Ltd.1, we have demonstrated excellent specific energy at -40oC (> 150 Wh/kg) at low rates (C/100) in custom 18650-sized Li-ion cells containing JPL- developed electrolytes. The electrolytes investigated included all-carbonate-based low EC-content electrolyte formulations, as well as solutions containing ester co-solvents with various additives. 2-6 In an extention of this work, we have investigated the performance of a number of Li-ion electrolytes optimized for low temperature performance in custom high specific energy cells as well high power prototype 18650-size cells manufactured by E-One Moli. The electrolytes evaluated included blends which contain elements of various approaches, including (i) ester co-solvents (such as methyl propionate, methyl butyrate, and propyl butyrate), (ii) the use of electrolyte additives (such as VC and FEC), and (ii) the use of mixed lithium electrolyte salts. In contrast to the previous work that was focused on low rate operation at high temperature, emphasis was placed on characterizing the cells using more aggressive discharge rates over a range of temperatures. To evaluate the high specific energy and high power 18650-size cells, extensive discharge rate characterization was performed over a wide temperature range (down to -80oC). Emphasis was also devoted to establishing the charge acceptance characteristics of the cells at very low temperatures, especially at -40oC. Given that lithium plating when charging at low temperatures is a known degradation mode of Li-ion cells in general, attention was focused upon characterizing the conditions in which its likelihood may be more pronounced and attempting to detect its occurrence indirectly. These results will be compared to baseline commercial off the shelf (COTS) cells. DC current interrupt impedance measurements have also been performed as a function of temperature in an attempt to more fully understand the impact of electrolyte type upon the low temperature performance for the cells. ACKNOWLEDGEMENT The work described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA) and supported by an internal JPL Research and Technology Development (R&TD) Fund. The information in this document is pre-decisional and is provided for planning and discussion only. 1. M. C. Smart, F. C. Krause, J. –P. Jones, L. D. Whitcanack, , B. V. Ratnakumar, E. J. Brandon, and M. Shoesmith, 2016 Prime Pacific Rim Meeting on Electrochemical and Solid-State Science, Honolulu, HI, October 2-7, 2016. 2. M. C. Smart, B. V. Ratnakumar, K. B. Chin, and L. D. Whitcanack, J. Electrochem. Soc., 157(12), A1361-A1374 (2010). 3. M. C. Smart, B. L. Lucht, S. Dalavi, F. C. Krause, and B. V. Ratnakumar, J. Electrochem. Soc., 159 (6), A739-A751 (2012). 4. M. C. Smart, B. V. Ratnakumar, F. C. Krause, L. D. Whitcanack, E. A. Dewell, S. F. Dawson, R. B. Shaw, S. Santee, F. J. Puglia, A. Buonanno, C. Deroy, and R. Gitzendanner, NASA Aerospace Battery Workshop, Huntsville, Alabama, November 17-19, 2015. 5. M. C. Smart, et. al., 2010 Power Sources Conference, Las Vegas, NV, June 16, 2010, Pages 191-194. 6. (a) M. C. Smart, et. al., 214th Meeting of the Electrochemical Society, Honolulu, HI, Oct. 12-17, 2008. (b) M. C. Smart, A. S. Gozdz, L. D. Whitcanack, and B. V. Ratnakumar, 220th Meeting of the Electrochemical Society, Boston, MA, October 11, 2011.
NASA continues to have an interest in developing robust, high specific energy, rechargeable batteries that can operate well at low temperatures. Improvements in battery specific energy translates into reduced launch costs and/or enhanced mission capability. Improved low temperature performance results in reduced thermal management complexity and reduced allocation of energy to heaters. There is current interest in exploring some of the distant icy moons of Jupiter and Saturn, since these bodies are believed to have liquid oceans beneath the icy surface that may harbor life. In particular, NASA is considering surface missions to Europa, which would benefit from improved high specific energy, low temperature batteries. To address these mission needs, the Electrochemical Technologies Group (ETG) at the Jet Propulsion Laboratory (JPL) is engaged in developing ultra-low temperature rechargeable batteries with high specific energy and enhanced low temperature capability for icy moon surface missions.1 The performance goals of this program include operation over the temperature range of +40oC to -60oC (delivering up to 100 Wh/kg at -40oC and 75 Wh/kg at -60oC). In addition, continuous operation at low temperatures is desired, so the cells should possess good charge characteristics without undesirable lithium plating. E-One Moli Energy Ltd.’s commercially available 18650-size lithium-ion cells have been identified to be especially attractive, due to their high specific energy (>200 Wh/kg at ambient temperatures) and reasonably wide temperature range of operation. 1 Given the desire for enhanced performance at low temperatures, E-One Moli has fabricated advanced prototype cells containing JPL-developed low temperature electrolytes. These electrolytes have been developed under previous programs and included all-carbonate-based low EC-content electrolytes formulations, as well as methyl propionate (MP)-based electrolytes with various additives. 2-5 To assess the performance of these cells, we have performed discharge rate characterization over a wide temperature range (down to -70oC). In addition, we have evaluated the cells during long term cycling continuously at very low temperatures, especially at -40oC. These results have been compared to baseline commercial off the shelf (COTS) cells.In an attempt to characterize the likelihood of lithium plating when charging at low temperatures, the charge current and charge voltage has been systematically studied. Impedance measurements have also been performed as a function of temperature in an attempt to more fully understand the impact of electrolyte type upon the low temperature performance. ACKNOWLEDGEMENT The work described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA) and supported by the NASA Game Changing Development Program. REFERENCES 1. F. C. Krause, A. Lawrence, M. C. Smart, S. F. Dawson, A. Ulloa-Severino, and B. V. Ratnakumar, “Evaluation of Commercial High Energy Lithium-Ion Cells for Aerospace Applications”, 227thMeeting of the Electrochemical Society, Chicago, Illinois, May 25-29, 2015 (Abstract #47580). 2. M. C. Smart, B. V. Ratnakumar, K. B. Chin, and L. D. Whitcanack, J. Electrochem. Soc., 157(12), A1361-A1374 (2010). 3. M. C. Smart, B. V. Ratnakumar, F. C. Krause, L. D. Whitcanack, E. A. Dewell, S. F. Dawson, R. B. Shaw, S. Santee, F. J. Puglia, A. Buonanno, C. Deroy, and R. Gitzendanner, NASA Aerospace Battery Workshop, Huntsville, Alabama, November 17-19, 2015. 4.M. C. Smart, B. V. Ratnakumar, M. R. Tomcsi, M. Nagata, V. Visco, and H. Tsukamoto, 2010 Power Sources Conference, Las Vegas, NV, June 16, 2010, Pages 191-194. 5. (a) M. C. Smart, B.V. Ratnakumar, A. S. Gozdz, and S. Mani, 214th Meeting of the Electrochemical Society, Honolulu, HI, Oct. 12-17, 2008. (b) M. C. Smart, A. S. Gozdz, L. D. Whitcanack, and B. V. Ratnakumar, 220thMeeting of the Electrochemical Society, Boston, MA, October 11, 2011.
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