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Solid phase diffusivity D s is a key parameter in Lithium-Ion cell models because solid phase diffusion typically dominates the voltage transients. The Galvanostatic Intermittent Titration Technique (GITT) is easy to implement and universally accepted as the standard for diffusivity measurement, but the accuracy of GITT diffusivity measurement is unknown. This paper develops a Least Squares GITT (LS-GITT) that uses all of the voltage data from a GITT test to optimally tune the diffusivity in a reduced order solid phase diffusion model. The accuracies of the GITT and LS-GITT diffusivity measurements are evaluated using the RMS error between the model predicted and experimentally measured voltages. Based on experimental results from a NCM half cell, LS-GITT is more accurate than GITT, often by an order of magnitude. The GITT test overestimates D s because the underlying model neglects the effects of bulk capacity on the voltage transients. LS-GITT gives results accurate to 1 mV RMS from 15%-100% SOC where GITT provides the same level of accuracy over less than half that SOC range. Neither technique provides accurate D s measurements below 10% SOC.

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Temperature is critical to the performance, durability and safety of Li-ion batteries. This paper reports in situ measurement of the radial temperature distribution inside a cylindrical Li-ion battery cell. 18650-size cylindrical cells with multiple micro thermocouples embedded are designed and manufactured. The radial temperature distribution is obtained under various operating conditions. The effects of critical parameters, such as discharge C rate, ambient temperature, and cooling condition, are investigated. It is found that higher discharge C rate and lower ambient temperature lead to higher temperature rise and larger temperature gradient within the battery cell. Stronger cooling results in smaller temperature rise but larger temperature gradient. Correlation between relative temperature gradient and cooling coefficient suggests that the assumption of uniform temperature distribution is applicable under natural-convection conditions but not applicable under strong forced convection conditions. The present results provide valuable experimental data that can be readily used to validate electrochemical-thermal coupled (ECT) battery models.Driven by the ever-increasing applications in electric vehicles and grand challenges, 1-4 the need for Li-ion batteries with enhanced performance, durability and safety is increasing. Previous studies show that temperature is critical to the performance, durability and safety of Li-ion batteries. 5-25 On one hand, the performance is reduced at lower temperatures, 6-11 and too low temperature can even cause detrimental lithium plating during charge. 12-14 On the other hand, a Li-ion battery degrades considerably faster at higher temperatures, 15-19 and excessively high temperature can lead to breakdown of the solid electrolyte interface (SEI) layer, 20-22 electrolyte decomposition, 23-25 and even to disastrous thermal runaway. 2,26,27 The surface temperatures of Li-ion cells, batteries and battery packs are commonly monitored. 28,29 However, surface temperature is expected to be different from internal temperature due to the very low thermal conductivity (∼1 W m −1 K −1 ) of electrodes and separator in the through plane direction. 5,30-32 This spatial temperature distribution inside a Li-ion battery may exacerbate the non-uniform distribution of current density 33-35 due to complex interactions among local reaction current, state of charge (SOC) and temperature. Under extreme conditions, e.g. accidental short circuit or overcharge, substantial heat is generated internally and monitoring of surface temperature could significantly underestimate the maximum temperature. Measuring internal temperature can thus provide more accurate information and is a better indicator of the health and safety of a Li-ion battery.In addition, electrochemical-thermal coupled (ECT) modeling has been widely used in the research and development of Li-ion batteries to gain insight into internal processes, to optimize battery design and operation, as well as to improve performance, durability and safety...

The ethanol electro-oxidation at gas diffusion electrodes made of different catalysts, Pt/C, PtRu͑1:1͒/C, and PtSn͑7:3͒/C, were studied by on-line differential electrochemical mass spectrometry in a wide temperature range ͑30-90°C͒ as a function of the anode potential, the fuel concentration, and catalyst loading. The CO 2 current efficiency ͑CCE͒ of the ethanol oxidation reaction ͑EOR͒ exhibits a maximum at about 0.6 V and decreases rapidly with further increasing potentials. The CCE for the EOR goes down with the increase in concentration of ethanol. CCE for ethanol oxidation reaction shows a strong increase with increasing catalyst loading. The CCE increases with increasing temperature, exceeding 75% at 90°C, 0.1 M ethanol, and 5 mg/cm 2 Pt catalyst loading. PtSn/C shows high CCE, like Pt/C. But PtRu/C exhibits very small CCE. Of the intermediates, acetaldehyde is quite active for further oxidation. But acetic acid is fairly resistant against further oxidation. Our results indicate that the C-C bond scission observed for the EOR with CCE in excess of 50% has to proceed in parallel with ethanol oxidation to either acetaldehyde or acetic acid, and not sequentially from acetic acid further on, as acetic acid cannot be oxidized any further.

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A stable solid electrolyte interphase (SEI) has been proven to be a key enabler to most advanced battery chemistries, where the reactivity between the electrolyte and the anode operating beyond the electrolyte stability limits must be kinetically suppressed by such SEIs. The graphite anode used in state-of-the-art Li-ion batteries presents the most representative SEI example. Because of similar operation potentials between graphite and silicon (Si), a similar passivation mechanism has been thought to apply on the Si anode when using the same carbonate-based electrolytes. In this work, we found that the chemical formation process of a proto-SEI on Si is closely entangled with incessant SEI decomposition, detachment, and reparation, which lead to continuous lithium consumption. Using a special galvanostatic protocol designed to observe the SEI formation prior to Si lithiation, we were able to deconvolute the electrochemical formation of such dynamic SEI from the morphology and mechanical complexities of Si and showed that a pristine Si anode could not be fully passivated in carbonate-based electrolytes.

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