A fully parameterized microscale model for lithium ion cells is presented in which the solid and pores (filled by electrolyte) are spatially resolved, and the mass and charge transport equations describing diffusion and migration in each phase are solved separately. Such a model allows: (1) the correlation of structure-scale, non-homogeneous material properties with macroscopic battery performance, and (2) the correlation of geometrical electrode morphology with macroscopic battery performance (electrode design). The micro-model approach discussed here allows for a simpler parameterization as fewer constitutive relations are needed in contrast to the macro-homogenous physical-based approaches. Input parameters were measured experimentally on lithium manganese oxide electrodes and LiPF 6 in 3:7 EC:DMC. Verification and validation for the model is also reported.

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Dissolution of active material is one of the primary reasons for capacity fade in lithium-ion batteries, particularly at elevated temperatures. The effects of the volume fraction changes due to dissolution in both the active and inert material phases in composite Li-ion electrodes are investigated by a thermal-electrochemical coupled model. The study reveals that the changes in effective transport properties result in a reduction in the electrochemical reaction rate and an increase in the cell resistance, reducing capacity. The simulation results are also used to map the nature of the effects of dissolution of the active particles on the capacity decrease during cycling with different conditions, including temperature and voltage range.Capacity fade in Li-ion batteries is one of the critical problems that must be resolved to realize practical power sources for electrical vehicles. Capacity fade is linked to a number of processes and their interactions, including electrochemical, chemical, and mechanical degradations, in both cathodes and anodes. The lithium manganese oxide spinel is a particularly promising cathode material because of its high voltage, low cost, and low environmental impact, but the material is apparently more vulnerable to cathode dissolution in an electrolyte 1-4 than other cathode materials. For example, weights of dissolved metal ions measured by atomic absorption spectroscopy ͑AAS͒ have been reported for LiCoO 2 , LiFePO 4 , and LiMn 2 O 4 as 0.8, 0.5, and 3.2%. 5 Also, the amount of cobalt and nickel in the electrolyte was below the limit of detection after four week storage of lithium-nickel-cobalt mixed oxide in 1 M LiPF 6 with ͑ethylene carbonate/dimethyl carbonate͒ ͑EC/DMC͒ at 40°C. 6 Thus, study of cathode dissolution in LiMn 2 O 4 is warranted in order to better mitigate the cathode dissolution and take better advantage of this high voltage, low-cost material. Figure 1 shows a schematic diagram of the dissolution of manganese into the electrolyte, with associated mechanisms. The dissolution process occurs according to the disproportional reaction: 2,3,7,8 2Mn 3+ → Mn 4+ + Mn 2+ . The sequencing of these phenomena is as follows. Spinel particles begin dissolving, losing their intimate contact with conductive additive particles and increasing contact resistance. Electrode reaction resistance is increased due to the presence of dissolved Mn 2+ ions in the electrolyte. The dissolved Mn 2+ ions may be transported through the electrolyte to be deposited on the anode side. This phenomenon can deplete the anode by the reduction of Mn, which would oxidize Li in the anode. 9 This would also accelerate the capacity fade of Li-ion batteries.The three main factors determining the dissolution rate are temperature, particle size, and operating voltage. The amount of the dissolved manganese ions has been observed to markedly increase with increasing temperature. 5,10 Particle size also plays an important role in determining the dissolution process. As the surface area increases for small particles, d...

The extension of Li-ion batteries, from portable electronics to hybrid and electric vehicles, is significant. Developing a better understanding of the role of material properties and manipulating the morphology of the particle clusters comprising Li-ion electrodes could lead to potential opportunities for attaining higher performance goals, for which the effect of both material properties and morphology needs to be considered in a physics-based model. In this work, different particle packing arrangements are analyzed for the calculation of effective transport properties and reaction density that appear in the porous-electrode formulation due to the volume-averaging process. Surrogate-based analysis is used to systematically construct and validate reduced-order models for species transport at the particle-electrolyte interface. The low effective solid transport predicted through microscale modeling indicates the effect of packing arrangement and tortuosity, an aspect not captured by the Bruggeman's relation. Particle cluster simulations reveal a Li-ion flux quantitatively different than that predicted by the porous-electrode model due to the variation of overpotential at the microscale. The present study offers a first-step towards integration of the effect of microstructure into a macroscale simulation.The extension of Li-ion batteries, from portable electronics to hybrid and electric vehicles, is significant. Typically, optimizing the design and performance of a battery-pack begins from the material to the cell level. However, this process can be expensive, both in time and monetary terms, since a design that may be optimum at the cell level may not be the best choice at the pack-scale. In addition, battery performance is directly related to the selection of chemistry, topology of the electrodes, and their tortuosity.At the battery-scale, the number of variables governing performance increases enormously and can only be analyzed at a reasonable cost in an appropriate mathematical framework. Recent work has shown that performance of Li-ion technology can be improved through emphasis on engineering the microstructural architecture of the electrodes. In such a scenario, developing a better understanding of the role of material properties and manipulating the morphology of the particle clusters comprising Li-ion electrodes could potentially lead to attainment of higher performance goals.Interrogation of cell performance can be achieved through either experimental or numerical investigations. 1-28 However, numerical simulations provide an advantage over their experimental counterparts since they are able to quantify the effects of several variables in a systematic fashion. As a result, the past two decades has seen a steady incline in the modeling of Li-ion cells. These analyses have separately utilized the equivalent circuit models, 7,8 single-particle model, 9,10 porous-electrode formulation, 11-13 capacity-fade models 14 and microscopic simulations. 15-22 While such analyses have proved successful in predicting th...

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