Electrochemical Noise Analysis applied to new generation Li-ion batteries

International audienceThis work aims to assess the possibility for Electrochemical Noise Analysis (ENA) to be used as a diagnosis method for new generation Li-ion cells (LNMO, LTO, TNO). Since it is only based on electrical fluctuations generated by the system, this method has the undisputed advantage of being non-invasive, operando and low cost. Plus, the implementation of this method into the current systems would not require any additional hardware, since cell voltage measurements is mandatory in a battery pack. The latter point is critical for economical and practical concerns. Nevertheless, the very low level of voltage fluctuations (<μV) provided by the batteries renders a proper measurement challenging. That may explain why the literature is still poor on this application. In this work, an ultra low noise instrumentation has been purposely designed and realized to extract the voltage noise signature of four Li-ion coin cells with different electrode materials. The noise of the developed conditioning circuit has been characterized, and demonstrates the ability to perform measurements with an ultra-low background noise compatible with the targeted requirements for the ENA application. The estimation of the power spectral density of the signal allows a statistical description of the cells voltage fluctuations under different operating conditions. It is shown that the noise signature has a 1/f flicker nature, regardless the cell type. The noise level apparently depends on electrode materials (figure 1). It is also found out that the voltage noise intensity is proportional to the DC current load (figure 2). Finally, overcharging of a Li/LNMO cell seems to induce sharp transient in the voltage signal. This work demonstrates the high sensitivity of the ENA method to operating conditions, and thus its great potential for new generation Li-ion batteries diagnosis

Electrochemical Noise Analysis applied to new generation Li-ion batteries

International audienceThis work aims to assess the possibility for Electrochemical Noise Analysis (ENA) to be used as a diagnosis method for new generation Li-ion cells (LNMO, LTO, TNO). Since it is only based on electrical fluctuations generated by the system, this method has the undisputed advantage of being non-invasive, operando and low cost. Plus, the implementation of this method into the current systems would not require any additional hardware, since cell voltage measurements is mandatory in a battery pack. The latter point is critical for economical and practical concerns. Nevertheless, the very low level of voltage fluctuations (<μV) provided by the batteries renders a proper measurement challenging. That may explain why the literature is still poor on this application. In this work, an ultra low noise instrumentation has been purposely designed and realized to extract the voltage noise signature of four Li-ion coin cells with different electrode materials. The noise of the developed conditioning circuit has been characterized, and demonstrates the ability to perform measurements with an ultra-low background noise compatible with the targeted requirements for the ENA application. The estimation of the power spectral density of the signal allows a statistical description of the cells voltage fluctuations under different operating conditions. It is shown that the noise signature has a 1/f flicker nature, regardless the cell type. The noise level apparently depends on electrode materials (figure 1). It is also found out that the voltage noise intensity is proportional to the DC current load (figure 2). Finally, overcharging of a Li/LNMO cell seems to induce sharp transient in the voltage signal. This work demonstrates the high sensitivity of the ENA method to operating conditions, and thus its great potential for new generation Li-ion batteries diagnosis

Electrochemical noise diagnostics of PEM fuel cell stack for micro-cogeneration application

International audienceElectrochemical noise (EN) generated by a 3500 W PEM fuel cell stack (50 cells) has been measured during micro-cogeneration durability tests. The experiments have been provided during long term campaign of measurements (more than 1200 h and 100 h have been analyzed) in well controlled operational conditions following The U.S. Department of Energy (DOE) recommendations. The micro-cogeneration operation mode involves two different regimes, one at 5 A (0.02 A.cm-²) and the other 99 A (0.45 A.cm-²). Thus, recorded signals are non-stationary, under dynamic load and specific data treatment procedure has been developed to overcome this difficulty. For both currents robust and stable statistical noise descriptors have been obtained based on Power Spectral Density (PSD) in the frequency range 0.01 Hz < f < 103 Hz. The noise signature of these currents involves two fractional noises (1 / f α) with different slopes α and pronounced peaks, at the characteristic frequency f = 1.6 Hz. The obtained noise signature is similar to the one obtained previously with the same type of the stack under stationary operation mode. It was demonstrated that noise signature varies slightly during stack operation. It seems that the observed evolution of the noise signature is related with reversible phenomena because after sudden interruption of the stack operation the PSD spectra return back to its initial shape. The proposed methodology of data treatment demonstrates that EN can be used as a tool for diagnostics of possible faults in long-term operation of electrochemical sources of energy under non-stationary conditions

Non-precious metal catalysts for Anion Exchange Membrane Fuel Cell

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Non-Precious Hydrogen Oxidation Catalysts for Anion Exchange Membrane Fuel Cells

International audienceGreen hydrogen as an energy carrier has the potential to dramatically reduce our greenhouse gas emissions and meet the net-zero emissions targets set by the Paris Agreement countries by 2050. This hydrogen can be produced by electrolysis using water and renewable electricity, and be converted into electricity on demand in a fuel cell. Proton exchange membrane fuel cells (PEMFC) are already commercialized, but due to their acidic environment, these devices require precious metal catalysts, in particular platinum, which is an obstacle to their large-scale deployment. In contrast, anion exchange membrane fuel cells (AEMFCs) operate at high pH, facilitating the use of cost-effective and sustainable precious metal free catalysts.To catalyze the hydrogen oxidation reaction (HOR) in alkaline media, nickel has shown interesting performances to replace precious metal catalysts at the anode of AEMFCs [1]. In order to improve the intrinsic activity of nickel-based materials and reach the performance of precious metals catalysts, two approaches are studied in the literature: optimization of intrinsic properties by alloying Ni with other earth abundant elements, or core@shell nanostructuration of Ni by a protective carbon shell. We are focused on this second approach through the mechanochemical synthesis of a nickel-based Metal-Organic Framework (MOF) from a Ni2+ salt and BTC (1,3,5-benzenetricarboxylic acid), followed by pyrolysis under different atmospheres (Figure 1.a). As already shown in the literature [2], there is a significant effect of the pyrolysis atmospheres (NH3, H2, N2, in various ratios) on the electrochemical performance of the catalysts (Figure 1.b). In this study, we employed ex situ and operando studies approaches to investigate the influence of these different atmospheres on the nanoparticles structuration and to relate them to the electrochemical performances obtained.Our Ni-based anode materials were characterized by X-ray diffraction, electron microscopy, nitrogen adsorption, and electrochemical techniques, including AEMFC tests. Furthermore, the transformation of the MOF into an active catalyst was followed with in-situ X-ray absorption spectroscopy.[1] Zhao, J. Chen, W. Sun, H. Pan, «Non-Platinum Group Metal Electrocatalysts toward Efficient Hydrogen Oxidation Reaction», Adv. Funct. Mater., vol. 31, no 20, 2021, p. 2010633.[2] Ni et al., « An efficient nickel hydrogen oxidation catalyst for hydroxide exchange membrane fuel cells », Nat. Mater., vol. 21, no 7, 2022, p. 804