EC Power 200 Innovation Blvd. State College, PA, 16803, USA [email protected] Phone: +1-814-861-6233 What is Different about AutoLionTM Compared to Other Li-Ion Battery Softwares? temperature and Li concentration are taken from in-built database. AutoLion’s materials database consists of validated properties for common Liion battery electrolyte, cathode materials (NCM, LFP, LMO, and LCO), and anode materials (graphite and LTO). Ambient temperature is -20oC with constant current discharge operating condition at C/3, 1C and 3C rates. Three cases are simulated. The only difference in the three cases are heat transfer boundary conditions 1) cell with natural convection (heat transfer coefficient, h, to ambient is 20 W/m2K) to ambient, mimicking experiment in an environmental chamber with no active cooling; 2) Adiabatic thermal boundary condition for cell; and 3) Isothermal simulation. Starting SOC is 100% Depth of Discharge is defined as used capacity discharged normalized by room temperature cell capacity at very low C-rate room temperature Introduction We commonly get these questions while interacting with engineers and researchers: “What is different about AutoLionTM over other Li-ion battery softwares?” and “If there is any difference between AutoLionTM and Classic Newman model?”. There are many differences in the modeling approach of AutoLion™ over other software offerings. These differences largely stem from the coupled treatment of heat and electrochemistry in AutoLionTM that is largely absent (in isothermal Newman model) or is over-simplified (derivatives of Newman model with simplified thermal treatment) in other softwares. This has a very little effect on room temperature performance simulation, but under extreme temperature (very common for automotive applications)- especially for large format cells with large surface area to volume ratio- it becomes a major distinguishing feature for AutoLion™. This case study is aimed at highlighting this very important issue.     Results Technology Used Voltage (0.33C) Voltage (1C) Voltage (3C) Temperature (0.33C) Temperature (1C) Temperature (3C) 4.5 25 4 15 3.5 3 5 2.5 2 -5 1.5 1 Temperature (oC) Constant current discharge at -20oC is simulated with AutoLionTM that has tight coupling of heat and electrochemistry. Simulations are also executed using the isothermal option in AutoLion™. Isothermal model option in AutoLionTM makes the predicted behavior is similar to common competing isothermal models. Voltage (V) Problem Statement -15 0.5 AutoLion-STM 0 -25 0 0.2 0.4 0.6 0.8 1 Depth of Discharge Setup  A 2.2 Ah NCM-Gr 18650 cell with material loading of 3.9 mAh/cm2 and 4.5 mAh/cm2 in cathode and anode, respectively.  Cell NP ratio is 1.15 with single side electrode thickness of 77 µm and 81 µm for cathode and anode, respectively.  All the material properties for NMC and graphite material as well as for electrolyte as a function of Figure 1 AutoLion™ non-isothermal simulated cell voltage and temperature as a function of cell depth of discharge with heat transfer coeff, h, to ambient as 20 W/m2K that represent natural convection. Ambient temperature is -20oC. © 2014 EC Power, LLC. All Rights Reserved. EC Power 200 Innovation Blvd. State College, PA, 16803, USA [email protected] Phone: +1-814-861-6233 anode cathode separator 0.33C 1C 3C Figure 2 Simulated cell voltage as a function of cell depth of discharge using isothermal model. Ambient temperature is -20oC. h = 0W/m2K h = 20W/m2K Isothermal Figure 3 Simulated voltage and temperature for 1C constant current discharge operation at -20oC ambient. Simulation results are for three different values of heat transfer coeff to ambient. anode cathode separator Figure 4 Simulated electrolyte concentration distribution along cell thickness for DOD of 0.2. Simulation results corresponds to 1C discharge with ambient temperature of -20oC Figure 5 Simulated Li stoichiometry at active material particle surface along cell thickness for DoD of 0.2. Simulation results corresponds to 1C discharge with ambient temperature of -20oC Benefits and Conclusions  Li-ion battery performance, especially under extreme temperature conditions, strongly depends on temperature. To correctly simulate cell performance/life under such extreme conditions, tight coupling between heat transport and cell electrochemical reaction is absolutely important.  AutoLion™ captures this important physics that common isothermal models or models with simplified heat transport treatment, commonly used in other software, cannot.  As shown in Figs. 4 and 5, under isothermal conditions, electrolyte depletion in cathode and Li stoichiometry depletion in anode particles clearly limits the cell operation at DoD ~ 0.2 (for 1C discharge). However, under more practicallyrelevant thermal conditions, the cell can continue to discharge at least 4x as long (DoD ~ 0.8 under natural convection conditions). As captured by AutoLionTM, this 4x+ increase in discharge length is due to cell internal-heating, which cannot be properly captured with isothermal and simplified models, and therefore cannot accurately guide users in optimizing cell design under automotive conditions.  AutoLion™ has capabilities of not only simulating performance over wide range of operating conditions but has demonstrated very good agreement with experimental data. Users are encouraged to refer to other case studies for more details.  One example of how an academic client has used AutoLion™ to investigate the low-temperature performance of Li-ion batteries can be found in © 2014 EC Power, LLC. All Rights Reserved. EC Power 200 Innovation Blvd. State College, PA, 16803, USA [email protected] Phone: +1-814-861-6233 reference [1]. Other papers where authors have used AutoLion™ to investigate the electrochemical-thermal coupled performance of Li-ion batteries can be found at the publications link on our website. References [1] Ji, Y., Zhang, Y., and Wang, C.Y. (2013). “Li-Ion operation at low temperatures,” Journal of the Electrochemical Society, 160(4), A636-A649. © 2014 EC Power, LLC. All Rights Reserved.