Papers by Hugues-Yanis Amanieu
Active materials used in lithium ion batteries consist of micro-metric ceramic particles. Mechani... more Active materials used in lithium ion batteries consist of micro-metric ceramic particles. Mechanical failure can happen within these brittle particles due to large internal stresses provoked by lithium intercalating in the crystalline structure during charge and discharge. Their mechanical behavior is directly related to some key intrinsic parameters, namely the elastic modulus, the fracture toughness and lithium di usivity. This works deals with the development of new characterization techniques to quantify these parameters at the local scale. Obtaining quantitative measurements is notably challenging for this type of specimen due to the highly heterogeneous structure of battery electrodes. For this, spinel LiMn 2 O 4-based commercial cathodes are proposed as material of investigation. First, composition analysis of cathode materials at di erent states of charge was done. In general it was noticed that commercial cells are not as consistent as laboratory cells: impurities are often present (Ni, Co,...) and particles can be porous agglomerates of nanoparticles as well as large single grains. However only spinel structure was detected by X-ray di raction and Rietveld analysis showed a typical lattice expansion for higher lithium concentrations. A method using nanoindentation was developed. It consists of applying a large number of indents in cathode cross-sections and subsequently ltering the measurements depending on whether they t the set of hypotheses of the Oliver and Pharr method. It was observed that for decreasing lithium concentrations, the elastic modulus and the hardness increase from 87 GPa (0% State of Charge) to 104 GPa (100% SoC) and from 7.0 GPa (0% SoC) to 8.0 Gpa (100%SoC), respectively. With the help of contact-resonance atomic force microscopy, the elastic property could also be qualitatively mapped and it seems that the particles are homogeneous. Added to micro-raman spectroscopy, it was observed that neighboring particles can have di erent lithiation levels. The fracture toughness was estimated by measuring the crack opening displacement by atomic force microscopy and applying Irwin's near eld theory. A toughness of about 0.9 MPa•m 1/2 was found but should not be taken at face-value. Irwin's theory requires a purely elastic-brittle fracture with traction-free crack walls. Unfortunately this condition cannot be met due to the size of the particles and the toughness is surely overestimated. Associated with electron backscattered di raction, cleavage planes were also evaluated on a reference {111} wafer. It was found that cracks always propagate in the <121> direction, corresponding to {101} planes just below the surface. At higher depths (> 100 nm), the crack deviates of 30 to 40 •. The last part of this work consists of developing a model to better comprehend electrochemical strain microscopy "time spectroscopy" (ESM-TS). It is the most promising technique to quantify locally ionic di usion coe cients. An AFM cantilever is used II to measure the mechanical excitation induced by lithium ions, themselves excited by an alternative current applied to the tip. The cantilever amplitude is recorded after applying a short electric potential pulse. The change in the lithium concentration eld induced by the pulse has an impact in the change of the measured amplitude. If the physics binding these two events is better understood, this technique can be used to measure the di usivity. The model draw the attention on the origin of the signal: while the pulses can change locally the concentration, our hypothesis is that it is not the case during the AC excitation, hence the signal does not originate from Vegard's deformation as originally thought. It is suggested that the signal is dependent on the Lorentz force applied on the ions by the AC excitation. We could demonstrate that the model can t experimental data. Besides, we introduced an e ective di usion coe cient which is dependent on the lithium concentration and showed that some experimental observations can be explained with it. However we could not explain the exact physics behind ESM-TS and only pointed at some new research directions.
M. Sebastiani*1, K. E. Johanns2, Hugues-Yanis Amanieu3,4, G. M. Pharr5,6 1 Roma TRE University, E... more M. Sebastiani*1, K. E. Johanns2, Hugues-Yanis Amanieu3,4, G. M. Pharr5,6 1 Roma TRE University, Engineering Department, Italy 2 Department of Materials Science, TU Darmstadt, D-64287 Darmstadt, Germany 3 Robert Bosch GmbH, Robert-Bosch-Platz 1, 70839 Gerlingen-Schillerhoehe, Germany 4 Institute for Materials Science, Center for Nanointegration Duisburg-Essen (CENIDE), University of DuisburgEssen, Universitätsstr. 15, 45141 Essen, Germany 5 Department of Materials Science & Engineering, The University of Tennessee, Knoxville, TN, USA 6 Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, TN, USA *corresponding author: [email protected]
Scripta Materialia, 2016
Abstract An optimized nanoindentation pillar splitting technique is used for the fracture toughne... more Abstract An optimized nanoindentation pillar splitting technique is used for the fracture toughness measurement of spinel Li x Mn 2 O 4 cathode material under different states of charge (SoC), along with the high-speed nanoindentation results for nanomechanical property mapping. High-speed nanoindentation enables for a robust and efficient evaluation of elastic modulus and hardness as a function of the SoC on strongly heterogeneous materials. The fracture toughness decreases linearly upon de-lithiation, with an overall reduction of 53% from 0% to 100% SoC. Decrease in fracture toughness is associated with the volume change, increase of defect density and stresses related to diffusion of lithium upon de-lithiation.
PAMM, 2015
Atomic Force Microscopy (AFM) probes the surface features of specimens using an extremely sharp t... more Atomic Force Microscopy (AFM) probes the surface features of specimens using an extremely sharp tip scanning the sample surface while the force is applied. AFM is also widely used for investigating the electrically non-conductive materials by applying an electric potential on the tip. Piezoresponse Force Microscopy (PFM) and Electrochemical Strain Microscopy (ESM) are variants of AFM for different materials. Both PFM and ESM signals are obtained by observing the displacement of the tip when applying electric fields during the scanning process. The PFM technique is based on converse piezoelectric effect of ferroelectrics and the ESM technique is based on electrochemical coupling in solid ionic conductors. In this work, two continuum-mechanical formulations for simulation of PFM and ESM are discussed. In the first model, for PFM simulation, a phase field approach based on the Allen-Cahn equation for non-conserved order parameters is employed for ferroelectrics. Here, the polarization vector is chosen as order parameter. Since ferroelectrics have highly anisotropic properties, this model accounts for transversely isotropic symmetry using an invariant formulation. The polarization switching behavior under the electric field will be discussed with some numerical examples. In the simulation of ESM, we employ a constitutive model based on the work of Bohn et al. [8] for the modeling of lithium manganese dioxide LiMn 2 O 4 (LMO). It simulates the deformation of the LMO particle according to an applied voltage and the evolution of lithium concentration after removing a DC pulse. The modeling results are compared to experimental data.
Journal of Applied Physics, 2015
Electrochemical Strain Microscopy (ESM) can provide useful information on ionic diffusion in soli... more Electrochemical Strain Microscopy (ESM) can provide useful information on ionic diffusion in solids at the local scale. In this work, a finite element model of ESM measurements was developed and applied to commercial lithium manganese (III,IV) oxide (LiMn 2 O 4) particles. ESM time spectroscopy was used, where a direct current (DC) voltage pulse locally disturbs the spatial distribution of mobile ions. After the pulse is off, the ions return to equilibrium at a rate which depends on the Li diffusivity in the material. At each stage, Li diffusivity is monitored by measuring the ESM response to a small alternative current (AC) voltage simultaneously applied to the tip. The model separates two different mechanisms, one linked to the response to DC bias and another one related to the AC excitation. It is argued that the second one is not diffusiondriven but is rather a contribution of the sum of several mechanisms with at least one depending on the lithium ion concentration explaining the relaxation process. With proper fitting of this decay, diffusion coefficients of lithium hosts could be extracted. Additionally, the effect of phase transition in LiMn 2 O 4 is taken into account, explaining some experimental observations. V
Acta Materialia, 2015
ABSTRACT Elastic and hardness properties of LiMn2O4 particles extracted from commercially availab... more ABSTRACT Elastic and hardness properties of LiMn2O4 particles extracted from commercially available Li-ion batteries are investigated under different States of Charge (SoC). Instrumented indentation was used for quantitative measurements. It was found that the particles become stiffer for increasing SoC, ranging from 87 GPa (0% SoC) to 104 GPa (100% SoC). Nanoindentation could also detect dissimilar properties between particles of a same cathode. As its spatial resolution is limited, atomic force acoustic microscopy (AFAM) was used to generate stiffness maps. By combining it with micro-Raman spectroscopy as well as Electron Back-Scattered Diffraction (EBSD), elastic isotropy and homogeneity within single particles were found. On the other hand, different neighboring particles present different states of lithiation and stiffnesses. For reference, a {1 1 1} LiMn2O4 wafer was also synthesized and characterized.
Journal of Power Sources, 2014
We observed a coreeshell surface potential on graphite particles of an aged anode. We observed a ... more We observed a coreeshell surface potential on graphite particles of an aged anode. We observed a mosaic surface potential on graphite particles of an unaged anode. Our results corroborate "radial" and "mosaic" models of Li distribution.
Materials Science and Engineering: A, 2014
ABSTRACT Mechanical properties of composite materials for application as electrodes in batteries ... more ABSTRACT Mechanical properties of composite materials for application as electrodes in batteries have been measured by means of selective statistical nanoindentation. The sample is strongly heterogeneous, as it consists of LiMn2O4 particles, carbon black and PVDF embedded in a soft and compliant epoxy matrix. For comparison, a similar composite sample of SiO2 particles in epoxy was prepared. The difference in terms of elastic modulus between the matrix and the particles is of one order of magnitude. Structural compliance and edge effects induce inconsistent tests which in return cause spurious measurements. A 2-step filtering method has been designed to overcome this problem. This automated method consists in identifying spurious tests and withdraw them from the final statistical analysis. First, nonquadratic load versus displacement curves are filtered out. Then, the Joslin–Oliver analysis is used to filter out tests with an apparent structural compliance. The method greatly improves the noise to signal ratio. After deconvolution, the E-modulus of the silica particles was measured as 69.8 GPa (±1.2). It shows the reliability of the method. 105 GPa (±7.5) was found for the LiMn2O4 particle E-modulus. After pile-up correction, the real E-modulus of LiMn2O4 particles is estimated to be 13% smaller. The developed method has been demonstrated to be an effective tool to investigate mechanical properties of composites.
Materials
Accurate estimation of fracture behavior of commercial LiMn 2 O 4 particles is of great importanc... more Accurate estimation of fracture behavior of commercial LiMn 2 O 4 particles is of great importance to predict the performance and lifetime of a battery. The present study compares two different microscale techniques to quantify the fracture toughness of LiMn 2 O 4 particles embedded in an epoxy matrix. The first technique uses focused ion beam (FIB) milled micro pillars that are subsequently tested using the nanoindentation technique. The pillar geometry, critical load at pillar failure, and cohesive FEM simulations are then used to compute the fracture toughness. The second technique relies on the use of atomic force microscopy (AFM) to measure the crack opening displacement (COD) and subsequent application of Irwin's near field theory to measure the mode-I crack tip toughness of the material. Results show pillar splitting method provides a fracture toughness value of~0.24 MPa.m 1/2 , while COD measurements give a crack tip toughness of~0.81 MPa.m 1/2. The comparison of fracture toughness values with the estimated value on the reference LiMn 2 O 4 wafer reveals that micro pillar technique provides measurements that are more reliable than the COD method. The difference is associated with ease of experimental setup, calculation simplicity, and little or no influence of external factors as associated with the COD measurements.
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Papers by Hugues-Yanis Amanieu