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Electrochemical Quartz Crystal Microbalance

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Basics of EQCM-D

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Electrochemical Quartz Crystal Microbalance

  1. 1. In situ hydrodynamic spectroscopy for structure characterization of porous energy storage electrodes Saurav Chandra Sarma Under the guidance of DR. SEBASTIAN C. PETER SOLID STATE AND INORGANIC CHEMISTRY LAB NCU, JNCASR 1
  2. 2. In situ hydrodynamic spectroscopy for structure characterization of porous energy storage electrodes 2 Netanel Shpigel, Mikhael D. Levi, Sergey Sigalov, Olga Girshevitz, Doron Aurbach, Leonid Daikhin, Piret Pikma, Margus Marandi, Alar Jänes, Enn Lust, Nicolas Jäckel & Volker Presser
  3. 3. Introduction Novelty of the Paper EQCM technique Some common terms Factors affecting resonance frequency and resonance width Experimental Section Results and Discussions Conclusion 3 Sketch of my talkSketch of my Talk
  4. 4. Introduction 4
  5. 5. Lithium insertion/deinsertion in Li Ion battery Repeated ion insertion/deinsertion affects the electrode porous structure, dimensions and mechanical integrity, and is a major cause of deterioration in the long-term cycling performance. 5Source: http://www.eco-aesc-lb.com/en/about_liion/
  6. 6. Electrode deterioration during cycling 6Source: Song, B. et al., J. Mat. Chem. A 3, 18171-18179 (2015)
  7. 7. Novelty of the paper 7Source: Wang, C. M. et al., Nano Letters 11, 1874-1880 (2011)
  8. 8. Disadvantage of conventional technique The 2D microstructure in (a) could be generated by aligned ellipses (b), by non-aligned cylinders (c), or by myriad other 3D structures. Although additional 2D sections can rule out some possibilities, they cannot resolve all ambiguities. 8 It has a high vertical strain resolution (<10 nm) but it is less informative for investigating lateral changes at mesoscopic scale. Atomic Force Microscopy (AFM)
  9. 9. Novelty of the paper • In this paper they introduced a new comprehensive methodology, to track the in situ electrode changes during charging/discharging process. • It uses EQCM technique to probe the change in electrode morphology. • It is a non-destructible technique. • Both vertical and lateral changes can be probed using this technique. • Rigidity, roughness, porosity, specific capacity, dimensions of the electrode material can be easily tracked using this technique. 9
  10. 10. EQCM is an acronym for Electrochemical Quartz Crystal Microbalance It is a extremely sensitive label-free technique that is capable of measuring the mass in the nanogram to sub-monolayer range while simultaneously probing the electrical properties of the system EQCM was first introduced by Kanazawa et. al. in 1990 This technique makes use of the piezoelectric effect of quartz to induce an oscillation at the fundamental frequency (4-10 MHz) of the quartz crystal EQCM - An analytical method 10
  11. 11. Quartz is used in clocks and watches to keep time. If a charge is passed through a special shaped quartz crystal, it will vibrate at an exact number of time per second (around 33000). These vibrations remain constant provide the crystal is connected to a battery The circuit inside a timepiece detects vibration from the crystal and will know how many times it should vibrate within a second. This means that everytime the circuit detects a fixed number of vibrations, it will send an electric pulse to add 1 second to a digital or analogue counter. Quartz as a Piezoelectric material 11
  12. 12. Quartz crystal cut and Vibration mode 12
  13. 13. The electrochemical quartz crystal microbalance (EQCM) can be used to study a variety of interfacial phenomena. These phenomena can include: • Li+ Intercalation • Electrodeposition • Corrosion Studies • Electropolymerization • Ion/Solvent Adsorption and Transport • Binding Events All of these processes result in mass changes to the surface being studied. The EQCM utilizes quartz crystals that resonate at specific frequencies upon the application of an AC signal. These resonant frequencies will change as mass is lost or added to the electrode on the face of the quartz crystal. Applications of EQCM 13
  14. 14. EQCM Schematic 14
  15. 15. Piezoelectric effect: a mechanical deformation (on the order of 10-100nm) is produced when an electric field is applied [or vice versa] This oscillation creates an acoustic shear wave that penetrations into the media above the crystal. This wave is sensitive to changes in the viscosity of the media or physical adsorption of materials onto the crystal, which is typically shown by a decrease in frequency ~ Eac Mechanism of EQCM 15 Source: King. W. H., Anal. Chem. 36, 1735-39 (1964) Q. Xie, Q. et. al., J. Chem. Ed. 84, 681-4 (2007)
  16. 16. 2 2 o q q f f m A f C m           Sauerbrey Equation: off m where is the change in frequency, is the fundamental frequency of quartz crystal, , , are the area, density and shear modulus of the quartz crystal, respectively, and is the change in mass on the crystal surface A q q 0 100 200 300 400 500 0.00 -1.25 -2.50 -3.75 -5.00 -6.25 -7.50 0 25 50 75 100 125 150 m/ng f/Hz Time / s Mechanism of EQCM 16
  17. 17. Some common terminologies 17
  18. 18. Resonance frequency and resonance width Resonance frequency, f, corresponds to the conductance peak, whereas the full- width at half-maximum (W) characterizes the dissipation of oscillation energy. 18 Admittance= 1/ Impedance= X + iY
  19. 19. Factors affecting Resonance Freq. and Resonance Width Liquids trapped in the narrow pores contribute only to the frequency shift, whereas movement of liquid in wider pores results in shifts in both the frequency and resonance width 19 • Pore Size
  20. 20. 20 It shows the case of metal deposition. The QCM act as a true microbalance. The resonance frequency is shifted to lower values with increasing mass, but the shape of the spectrum remains altered. The resonance frequency is shifted to lower values with increasing viscosity, and the resonance width changes dramatically. Resonance frequency is shifted to lower values with increasing electrode roughness, and the resonance width changes dramatically. Factors affecting Resonance Freq. and Resonance Width • Mass Deposition • Density and viscosity of electrolyte medium • Roughness of the electrode surface Source: Q. Xie, Q. et. al., J. Chem. Ed. 84, 681-4 (2007)
  21. 21. Penetration depth as hydrodynamic probe Penetration depth is a characteristic depth of decaying of the transverse wave coming from the oscillating quartz crystal surface towards liquid environment. The equation shows that the penetration depth decreases with the frequency of the wave (that is, with n) and the density of the liquid, ρ, but increases with its dynamic viscosity, η. Ex-situ measurement: Changing η and ρ In-situ measurement: Changing n 21
  22. 22. Experiment 1: 22 Purpose: 1) To compare the in situ and ex situ hydrodynamic spectroscopy 2) To characterize the nature and roughness of the electrode surface
  23. 23. Validation of hydrodynamic model for multiple harmonics 23 Plane Surface Rough Surface Au covered quartz crystal Lithographically fabricated polymeric photoresist Two limiting cases
  24. 24. Validation of hydrodynamic model for multiple harmonics Ideally flat gold covered quartz crystal immersed in water and water-glycerol mixtures. 24
  25. 25. Equations for hydrodynamic modelling 25 q= fraction of crystal surface coverage by electrodes, h= average thickness of the hydrodynamic porous boundary layer, ξ= permeability length of hydrodynamic porous layer, r= average radius of non-porous aggregates, m = surface density
  26. 26. Validation of hydrodynamic model for multiple harmonics Ideally flat gold covered quartz crystal immered in water and water-glycerol mixtures. 26
  27. 27. Validation of hydrodynamic model for multiple harmonics Artificially rough surface composed of lithographically fabricated polymeric photoresist semi-spheres in contact with water. 27 Average radius of semi-spheres= 1.78 μm Surface density occupation= 0.002 μm-2
  28. 28. Conclusion from Experiment 1 • Ex-situ technique can now be extended to in-situ technique and hence lot more information on electrode changes can be obtained. • Fitting experimental patterns through hydrodynamic equation, the extent of roughness can easily be inferred. • Output parameters such as average radius of bumps on electrodes and their surface density can be obtained. 28
  29. 29. Experiment 2: 29 Purpose: 1) To know the effect of loading of electrode material of different amount.
  30. 30. Fabrication of LiMn2O4 coatings on quartz crystal Spray Pyrolysis Technique: 0.025 M CH3COOLi + 0.05 M Mn(NO3)2 in Ethanol  Spray Pyrolysed at 300 oC 30
  31. 31. Fabrication of LiMn2O4 coatings on quartz crystal Spray Pyrolysis Technique: 0.025 M CH3COOLi + 0.05 M Mn(NO3)2 in Ethanol  Spray Pyrolysed at 300 oC 31 Loading 1 Δf=0.16 kHz Loading 2 Δf=0.9 kHz Loading 3 Δf=2.7 kHz Loading 4 Δf=3.3 kHz
  32. 32. Behaviour of spray-pyrolysed LiMn2O4 electrodes Electrochemical properties of spray-pyrolysed LiMn2O4 electrode coatings of different loading masses Slope of the straight line gives the specific capacity of 144 mAhg-1 which matches well with that of 148 mAhg-1 Integration of the differential capacity curve is proportional to the charge Four electrode were coated with different mass of LiMn2O4 Δfn /n = −Cm Δm, Sauerbrey’s equation 32
  33. 33. Complex porous electrode structures Thin Dense Layer Thicker porous layer Non-porous asperities • Increase in the thickness of layer 1 affects Δfn /n rather than ΔW/n • Layer 2 having characteristic pore size d>> penetration depth contributes to both Δfn /n and ΔW/n • Layer 3 contributes significantly to the hydrodynamic spectroscopic curves at OCV, appear electrochemically inactive, with no contribution to the potential-dependent changes Δfn /n and ΔW/n. 33
  34. 34. Characterization of the electrodes in air 34 To make sure that there are no substantial dissipation of oscillation energy inside these electrodes, i.e. that they are rigid. Ideally, in the case of rigid electrode, W /n for all overtone orders should be exactly the same as that on neat (uncovered crystal). For, 3.3 kHz coating, W/n is not fixed as a function of higher overtones. So, the coated material is not rigid and thus neglected.
  35. 35. Conclusion from Experiment 2 • Amount of loading of dry mass can easily be obtained by using Sauerbrey’s equation • Total charge storage capability of this dry mass can be obtained from the differential capacity curve • Specific capacity of the material can be obtained quite accurately • Nature of each of the layer can be understood from their electrochemical and hydrodynamic interaction • Deformation in the electrodes can be monitored and optimal loading for the electrochemical process can be finalized 35
  36. 36. Experiment 3: 36 Purpose: 1) To know the effect on electrode surface at open circuit voltage (OCV) and during charging/discharging process.
  37. 37. Equations for hydrodynamic modelling 37 q= fraction of crystal surface coverage by electrodes, h= average thickness of the hydrodynamic porous boundary layer, ξ= permeability length of hydrodynamic porous layer, r= average radius of non-porous aggregates, m = surface density
  38. 38. In situ hydrodynamic spectroscopy of LiMn2O4 electrodes • A large deviation of Δfn /n and ΔW/n from the straight lines of the ideally flat surface is observed as a function of higher electrode mass. 38 For 0.9 kHz coating, q= 0.24 h= 100 nm ξ= 53 nm For 2.7 kHz coating, q= 1 h= 240 nm ξ= 80 nm m= 0.0004 μm-2 r= 3.05 μm For 0.16 kHz coating, q= 0.24 h= 90 nm ξ= 57 nm At OCV
  39. 39. Raw EQCM data 39 For 0.9 kHz coating, q= 0.24 h= 102.7 nm ξ= 51.2 nm For 2.7 kHz coating, q= 1 h= 260 nm ξ= 71 nm m= 0.0004 μm-2 r= 3.05 μm 0.16 kHz coating is the gravimetric case During Charging/Discharging
  40. 40. Comparison of OCV data with charging/discharging 40 For 0.9 kHz coating, q= 0.24 h= 102.7 nm ξ= 51.2 nm For 2.7 kHz coating, q= 1 h= 260 nm ξ= 71 nm m= 0.0004 μm-2 r= 3.05 μm For 0.9 kHz coating, q= 0.24 h= 100 nm ξ= 53 nm For 2.7 kHz coating, q= 1 h= 240 nm ξ= 80 nm m= 0.0004 μm-2 r= 3.05 μm At OCV During Charging h increases Electrode layer swollen Due to insertion of solvent molecules within the micropores Li deintercalates Pore Size decreases ξ decreases
  41. 41. Conclusion from Experiment 3 • Electrode deformation during charging/discharging can be monitored using following output parameters  Fraction of the total surface covered.  Height of the porous layer  Mean pore size diameter  Radius of non-porous species  Surface density of such non-porous species. 41
  42. 42. Conclusion • Based on easy assessment of high overtone orders by EQCM, a new method have been developed for in situ hydrodynamic spectroscopy of porous/rough battery electrodes with penetration depth n as the hydrodynamic probe. • It enables a much better and more comprehensive understanding of how ion insertion/extraction affects the structure of the porous electrode in contact with solutions on a mesoscopic scale of penetration depth. • It has the potential to become a primary tool for selecting better electrode coating for batteries and supercapacitors. 42
  43. 43. 43
  44. 44. 44
  45. 45. Series RLC resonance circuit 45 Inductive Reactance, XL= Lω Capacitive Reactance, Xc= 1/ Cω Resonance Frequency = 𝟏 𝑳𝑪 So, resonance freq. is completely determined by ‘L’ and ‘C’ At Resonance Frequency, XL=XC Total Impedance, Z= 𝑹 𝟐 + 𝑿 𝑳 − 𝑿𝑪 𝟐 Z=R So. Total impedance or energy loss is completely determined by change in resistance
  46. 46. • The surface charge can affect adsorption of molecules (i.e. SiO2 layer carriers negative charge inhibiting adsorption of anionic species) • It can be difficult to model since we lack control outside of the sample preparation (solutions cannot be to complicated) Problems with QCM: Solution – Couple with electrochemistry: Mechanism of EQCM • Thus, by adding electrochemical techniques, we can alter the charge on the surface to adsorb/desorb a wide range of molecules and we can two independent data sets (i.e. frequency shifts with EC data) to allow for modeling of more complex reactions 46
  47. 47. Shift/Damping of Frequency The top diagram illustrates how the frequency of the oscillating sensor crystal (quartz) changes when the mass is increased by addition of a molecular layer. The bottom diagram illustrates the difference in dissipation signal generated by a rigid (red) and soft (green) molecular layer on the sensor crystal. 47
  48. 48. Advantage of EQCM-D measurements M.D. Levi et al. / Electrochemistry Communications 67 (2016) 16–21 • It enables probing a wide range of penetration depths, δn Two methods: • In-situ gravimetric sensing: a) One necessary condition to fulfill this requirement is that the electrode coating is rigidly attached to the quartz crystal surface and retains its rigidity both in air and in contact with solutions under open-circuit potential (OCP) and during polarization. This excludes the appearance of dissipation inside the solid matrix of the electrode. b) The next necessary condition is the absence of potential dependence of the electrode volume/porosity changes since such dependences modify the hydrodynamic solid–liquid interactions resulting in changes of the dissipation factor within the boundary hydrodynamic layer. When these two conditions are fulfilled, the electrodes loading can be considered as entirely inertial. Consequently, the mass changes of electrodes in EQCM measurements can be related to change in frequency, Δf, in accordance with the Sauerbrey's equation: Δm = −C∙Δf/n, where C is the mass sensitivity constant and n is the overtone order 48
  49. 49. When an external polarization is applied to an electrode coating on a crystal surface, the resonance peak may behave in two principally different modes. The polarization results in changes of the electrode mass due to insertion/extraction or adsorption/desorption of ions in a way that resonance peak shifts without change of its width; thus the change of the electrode mass occurs without change in the dissipation factor. Significant changes of the dissipation factor occur in addition to the change of the resonance frequency, which generally indicate that in addition to mass change, the electrode layer is subjected to deformation (expansion/contraction). This should modify the solid-liquid hydrodynamic interactions, and or accompanied by changes of the elastic properties of composite electrodes (e.g. electrodes containing ions inserting particles and polymeric binder). 49
  50. 50. Advantage of EQCM-D measurements M.D. Levi et al. / Electrochemistry Communications 67 (2016) 16–21 • It enables probing a wide range of penetration depths, δn Two methods: • In-situ hydrodynamic sensing: 50
  51. 51. 51
  52. 52. Although traditional in situ height-sensing techniques (atomic force microscopy or electrochemical dilatometry) are able to sense electrode thickness changes at a nanometre scale, they are much less informative concerning intercalation-induced changes of the porous electrode structure at a mesoscopic scale. 52

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