Jennifer Schaefer, Univ of Notre Dame
Christopher Soles, NIST
Jun Wang, A123 Systems LLC
Kang Xu, US Army Research Lab
Army Research Office
EC2.1: Interfaces and Impedance
Monday AM, November 28, 2016
Sheraton, 2nd Floor, Back Bay B
8:15 AM - *EC2.1.01
Simulating Diffusional Impedance Behavior of Polycrystalline Electrode Particles Using the Smoothed Boundary Method
Min-Ju Choe 1 , Hui-Chia Yu 1 , Ping-Chun Tsai 2 , Bohua Wen 2 , Yet-Ming Chiang 2 , Katsuyo Thornton 1
1 University of Michigan Ann Arbor United States, 2 Massachusetts Institute of Technology Cambridge United StatesShow Abstract
Microstructures strongly affect transport phenomena in electrode materials and their performance. However, explicit consideration of the complex structures such as the grain boundary network poses a challenge in simulations. In this work, we develop an innovative method for incorporating the surface and interface diffusion with the bulk diffusion based on the smoothed boundary method. Complex grain structures are described using multiple domain parameters, where the value of domain parameter is uniformly one inside the corresponding grain, and zero outside. As such, the grain boundaries are implicitly defined by the transition regions of domain parameters, and the diffusion equations can be straightforwardly solved on a standard Cartesian grid system. This method is applied to simulate the diffusional impedance of polycrystalline electrode materials. The simulations show that both grain boundary diffusivity and grain size affect the diffusional impedance. With high grain boundary diffusivities, the concentration of ions along the grain boundaries is similar to that at the electrode particle surfaces, such that radial diffusion within each primary particle dominates the impedance behavior. Conversely, with low grain boundary diffusivities, the overall radial diffusion in the secondary particle determines the impedance behavior. In coordination with the modeling effort, electrochemical impedance spectroscopy measurements of polycrystalline single secondary cathode particles are conducted. The simulations and experiments are combined to reveal the impact of interfacial transport on electrode materials’ performance. In turn, the insight gained through this work opens a new avenue for extracting microstructural characteristics (e.g., the grain size) from its impedance behavior.
8:45 AM - EC2.1.02
Inhomogeneous Conductivities in Li7La3Zr2O12 Ceramics Investigated by Spatially Resolved Impedance Spectroscopy and Elemental Analytics
Andreas Wachter-Welzl 1 , Julia Kirowitz 1 , Reinhard Wagner 2 , Stefan Smetaczek 1 , Maximilian Bonta 1 , Daniel Rettenwander 3 , Stefanie Taibl 1 , Georg Amthauer 2 , Andreas Limbeck 1 , Jurgen Fleig 1
1 Vienna University of Technology Vienna Austria, 2 Chemistry and Physics of Materials University of Salzburg Salzburg Austria, 3 Massachusetts Institute of Technology Cambridge United StatesShow Abstract
Current Li-ion batteries suffer from problems caused by the chemical instability of their organic electrolyte. Therefore a lot of research focuses on replacing the organic electrolyte by inorganic solid ion conductors. Cubic Li7La3Zr2O12 (LLZO) garnets and its variants are among the most promising candidates for next generation all solid state Li-ion batteries [1,2]. They provide a high Li-ion conductivity and combine chemical and electrochemical stability. One crucial aspect is the doping of the material, in order to stabilize its cubic phase but also in terms of diffusion paths and mobile defects. Different dopants have been investigated, but the specific effect of each dopant, the importance of the exact Li-ion stoichiometry, as well as degradation phenomena are still not completely understood. For nominally identical dopant content, for example, rather different conductivities were reported.
In this contribution, we present a combined study of electrochemical impedance spectroscopy (EIS) and elemental analysis (inductively coupled plasma mass spectrometry, ICP-MS) has been used to determine the effects of varying lithium and dopant content on the Li-ion conductivity. The roles of sintering temperature and preparation procedure, but also effects of the sample dimension are considered and reasons behind severe variations of effective Li-ion conductivities are discussed. Besides overall Li-ion conductivity measurements using blocking electrodes and analysis of the bulk composition, measurements on microelectrodes of different sizes (20 – 300 µm) were performed to obtain information on local Li-ion conductivities. Within one and the same sample, conductivity variations up to almost one order of magnitude were found. Laser ablation (LA) ICP-MS was employed to obtain local information on the exact composition and thus of stoichiometric variations in the samples. For example, a correlation between spatially varying Al content and local conductivities was found, with higher conductivities primarily in the outer regions of the ceramics. These studies provide a deeper understanding for the variation of Li-ion conductivity in publications on nominally similar samples. Furthermore they help in finding optimal dopant contents, Li contents and preparation procedures of LLZO.
 Murugan, R.; et al.; Angew. Chem. 2007, 119, 7925-7928
 Thangadurai, V.; et al.; Chem. Soc. Rev. 2014, 43(13), 4714-4727
8:45 AM - EC2.1.03
Electronic and Ionic Transport Properties and Interfacial Kinetics of Ordered and Disordered Li1-xMn1.5Ni0.5O4 as a Function of Lithium Content
Ruhul Amin 1
1 Qatar Environment and Energy Institute, Hamad Bin Khalifa University Education City, Doha QatarShow Abstract
LiMn1.5Ni0.5O4 is a high voltage cathode material for lithium ion batteries which has attracted great attention within the battery community due to its potential for high energy and power density. This compound can be ordered or disordered depending on the arrangement of Mn and Ni in the spinel structure. The charge-discharge behavior of ordered and disordered structures has been tested by several research groups. However still it is not clear which structural composition is suitable for a high performance battery. It is also not clearly understood if the rate performance of the material is limited by bulk transport properties or interfacial reactions. Here we report on the electronic and ionic conductivity and diffusivity of ordered (P4332) and disordered LiMn1.5Ni0.5O4 which has been determined separately by using ion and electron blocking cell configurations as a function of lithium concentration on sintered dense pellets. The disordered phase exhibits about fifteen time higher electronic conductivity than the ordered phase at room temperature in the lithiated state. The conductivities of the partially delithiated ordered phase measured at a given temperature increase monotonically with increasing delithiation at x = ~0.3 and beyond that the electronic conductivity is almost leveled up. In contrast, the electronic conductivity of disordered phase initially decreases with delithiation and comes down to the level of lithiated ordered phase. After that it exhibits almost the same electron conducting behavior as of ordered phase. The lithiated ordered and disordered phases exhibit the same order of magnitude of ionic conductivity and diffusivity. The measurements of lithium ion diffusivity (conductivity) as function of lithium content in electron-blocking cells, is found to be consistent with AC and DC technique. Chemical diffusion during electrochemical use is limited by lithium transport, but is fast enough over the entire state-of-charge range to allow charge/discharge of micron-scale particles at practical C-rates. Furthermore, measurements of exchange current density of the two phases as a function of lithium concentration are in progress. The measurements are being also performed on sintered dense pellets with a defined surface area.
9:00 AM - *EC2.1.04
Transport Phenomena in Li- or Na-Based Batteries
Joachim Maier 1
1 Max-Planck-Institute Stuttgart GermanyShow Abstract
The first part of the contribution refers to ionic and mixed ionic/electronic transport in the constituent phases of Li- or Na-based batteries. Adjusting screws for tuning mass transport in electrolyte and electrode phases are discussed using recent materials examples.
The second part of the talk addresses interfacial phenomena and the influence of interfacial resistances and capacitances. Here the job-sharing mechanism is of particular relevance as it has the potential to lead to artificial electrodes. Interfacial anomalies are not only relevant for nanostructured electrodes but also for composite electrolytes with single ion conduction.
The third part refers to the important issue of electrochemical networks and the transport therein. Such network issues that may comprise electrode and electrolyte phases, are especially important when adjusting screws to optimize transport properties of the individual phases are exhausted.
9:30 AM - EC2.1.05
Investigating the Complex Chemistry of Functional Energy Storage Systems—The Benefit of an Integrative, Multiscale (Molecular- to Meso-Scale) Perspective
Amy Marschilok 1 , Kenneth Takeuchi 1 , Esther Takeuchi 1 2
1 Stony Brook University Stony Brook United States, 2 Brookhaven National Laboratory Upton United StatesShow Abstract
A critical challenge for electric energy storage is understanding the basic science associated with the gap between the usable output of energy storage systems and their theoretical energy contents. The goal of overcoming this inefficiency is to achieve more useful work (w) and minimize the generation of waste heat (q). Minimization of inefficiency can be approached at the macro level, where bulk parameters are identified and manipulated, with optimization an ultimate goal. However, such a strategy may not provide insight towards the complexities of electric energy storage, especially the inherent heterogeneity of ion and electron flux contributing to the local resistances at numerous interfaces found at several scale lengths within a battery. Thus, the ability to predict and ultimately tune these complex systems to specific applications, both current and future, demands not just parameterization at the bulk scale, but rather specific experimentation and understanding over multiple length scales within the same battery system, from the molecular- to the meso-scale. This presentation will be structured as a case study examining the insights and implications from multiscale investigations of a prospective iron oxide based battery material.
10:15 AM - *EC2.1.06
Generation and Evolution of Materials in the Anode Solid Electrolyte Interphase (SEI) of Lithium Ion Batteries
Brett Lucht 1
1 University of Rhode Island Kingston United StatesShow Abstract
A solid electrolyte interphase is generated on the anode of lithium ion batteries during the first few charging cycles. The presence and stability of the SEI is critical to the performance of the battery. Despite thorough investigation of the SEI for over 20 years, the mechanism of formation and function are still relatively poorly understood. We have investigated the structure of the SEI on graphite and silicon electrodes along with changes which occur to the SEI upon additional cycling. In addition, we have been using the one electron reducing agent, lithium napthalenide to independently prepare the reduction products which constitute the SEI. The reduction products and their subsequent decomposition products have been thoroughly investigated via a combination of NMR, XPS, IR-ATR, TGA, and GC-MS. The investigation of SEI via different methods of generation and evolution provides significant insight into the structure and properties of the anode SEI.
10:45 AM - EC2.1.07
In Situ TEM Observations of the Formation of Solid Electrolyte Interface on Silicon Anodes in Lithium Ion Batteries
Chuan-Yu Wei 1 , Chia-Hao Yu 1 , Ahmad Fauzan Adziimaa 2 , Di-Yan Wang 3 , Fu-Ming Wang 2 , Cheng-Yen Wen 1
1 Department of Materials Science and Engineering National Taiwan University Taipei Taiwan, 2 National Taiwan University of Science and Technology Taipei Taiwan, 3 Department of Chemistry National Taiwan Normal University Taipei TaiwanShow Abstract
Electrochemical energy storage is an important issue for future technology development. For lithium ion batteries, graphite is the most popular anode material, but its theoretical capacity is only 372 mAh/g. This capacity is not high enough for future electronics. By contrast, the theoretical capacity of silicon is 4200 mAh/g. In addition, silicon anode can be charged at a higher rate with sufficient cycle stability. Silicon is therefore regarded as one of the most potential anode materials for next generation batteries. However, there is a large volume expansion (about 300%) when lithium ions are inserted into silicon; besides, the poor capacity retention due to the formation of solid electrolyte interface (SEI) makes silicon unfavorable for practical applications. In our recent TEM observations of the anode made of Si nanoparticles in lithium ion battery, the size of Si nanoparticles reduces from 100 nm to 5 nm after 20 charge/discharge cycles. The silicon nanoparticles are also wrapped by SEI. In order to understand the evolution of Si nanoparticles and the formation of SEI during lithiation, we use the electrochemical liquid cell holder for in-situ TEM analysis. The configuration of the electrochemical system includes the silicon nanoparticles as the working electrode, Pt reference electrode, LiCoO2 powder at the counter electrode to provide lithium ions. The electrolyte is LiClO4 in EC/DMC (vol% 1:1), which is stable in air. We use the Omniprobe manipulator in a focused-ion beam system to prepare the nano battery on a silicon nitride membrane window, which is pre-patterned with Pt electrodes, on a Si chip. Another Si chip with a silicon nitride membrane window covers on the system to seal the electrolyte. The cell is mounted on a TEM holder. We cycle the voltage on the cell to intercalate lithium ions into silicon nanoparticles and deintercalate the lithium ions for in-situ observations of the volume change of the silicon nanoparticles and the formation of SEI.
11:00 AM - EC2.1.08
Direct In Situ Observations of the Chemo-Mechanical Stability of the Solid Electrolyte Interphase (SEI) on Silicon Anodes
Brian Sheldon 1 , Ravi Kumar 1 , Anton Tokranov 1 , Xingcheng Xiao 2 , Ivan Yermolenko 3 , Zhuangqun Huang 3 , Chunzeng Li 3 , Thomas Mueller 3
1 Brown University Providence United States, 2 General Motors Global Ramp; D Center Warren United States, 3 Bruker Nano Surfaces Goleta United StatesShow Abstract
During initial battery cycling carbonate electrolytes undergo reduction at the negatively polarized electrode surface. This generates a passivating layer consisting of inorganic and organic electrolyte decomposition products usually referred to as the Solid Electrolyte Interphase (SEI). These passivation films undergo substantial deformations when the underlying electrode particles expand and contract during electrochemical cycling. While there has been considerable speculation about the relationships between SEI formation and mechanical failure, observing and probing these phenomena directly is extremely challenging. In this study we demonstrate a new approach for applying controlled strains to SEI films with patterned Si electrodes, in conjunction with direct observations of SEI growth and mechanical degradation using in situ atomic force microscopy (AFM). This provides an excellent platform for investigating the deformation and failure of SEI films, in response to controlled mechanical strains that are induced by lithiation and delithiation of the underlying Si. This approach enabled in operando monitoring of SEI growth, strain, and mechanical failure in SEI films during electrochemical cycling. This work provides a wealth of new information about relationships between SEI formation and the mechanical degradation of SEI films. For example, the results verify that crack formation occurs during lithiation (this has been predicted previously, but not directly observed). Additional SEI formation at low potentials did not fill these cracks, which directly contradicts prior speculation by some previous researchers. Also, analysis of these measurements make it possible to obtain the fracture toughness of the SEI, a key value which has not been previously measured..
The new methodology reported here makes it possible to obtain critical information about the chemo-mechanical stability of SEI films. These carefully controlled experiments also provide important information for chemical-mechanical degradation models that are used to predict capacity fade in Li-ion batteries. These models, combined with our direct experimental observations of key failure mechanisms will ultimately be used to design improved SEI passivation layers.
11:15 AM - EC2.1.09
Surface and Interface Properties of Li-ion Cathode Materials—A Surface Science Approach
Wolfram Jaegermann 1 , Rene Hausbrand 1 , Gennady Cherkashinin 1 , Matthias Fingerle 1
1 Technische Universität Darmstadt Darmstadt GermanyShow Abstract
Lithium-Ion batteries are important devices for present and future electric energy storage, offering high energy density and durability. Positive electrodes (cathode) materials are predominantly transition metal oxides containing exchangeable lithium. The electronic and ionic structure of these materials in the bulk as well as on their surfaces/interfaces are key factors for their properties, such as electrode potential, charge transfer intercalation reactions, as well as degradation and reactivity.
This contribution gives an overview of our surface science studies to investigate layered-oxide cathodes and Li addressing their electronic structure and cathode-electrolyte interface formation. In a surface science approach, well-defined surfaces/interfaces are prepared and analyzed with surface sensitive analytical techniques such as electron spectroscopy (XPS, UPS, XAS) using emersed electrodes after electrochemical treatment and modelling experiments by adsorbing/depositing contact materials as solvents (H2O, DEC) or solid electrolytes (LiPON). With this approach the electronic and chemical structure of surfaces and interfaces can be analysed allowing conclusions on the electronic structure of the bulk, on reactivity with other phases, and on electrochemical interface properties.
The obtained results on the interaction can be addressed to charge transfer reactions of electrons and ions and related defect formation which will be discussed on the basis of energy level diagrams extracted from the experimental data. The results indicate that presently available concepts should be improved in considering electron induced effects on bulk properties and possibly occuring electron induced side reactions.
11:30 AM - EC2.1.10
Growth and Ion Transport of SEI Layers with 6Li/7Li NMR Exchange Experiments
Andrew Ilott 1 , Alexej Jerschow 1
1 New York University New York United StatesShow Abstract
The nature of the surface electrolyte interphase (SEI) is critical to proper electrode and battery function. Characterization of this layer is difficult, especially when it is desired to do so in situ. Although Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) have been demonstrated in situ, the sensitivity typically does not allow one to measure the SEI directly. We describe here NMR methodology based on 6Li/7Li exchange, by which the formation and the properties of the SEI can be probed indirectly.
The technique involves tracking particular isotopes of lithium over time. A model based on ion diffusion and diffusion through the SEI, as well as the skin effect of the radiofrequency signals is developed. The technique provides a unique, time resolved “window” into the lithium ion dynamics at the metal-SEI-electrolyte interfaces. We will describe how this “window” can be used to extract information about the growth of the SEI layer and measure the diffusion of lithium ions through it using NMR experiments on well-designed, isotopically-enriched systems.
11:45 AM - EC2.1.11
Transport Mechanism of Li-Ions through Amorphous Al
3 Coatings—Role of Proton Concentration
Masihhur Laskar 1 , David Jackson 1 , Shenzhen Xu 1 , Laura Slaymaker 1 , Yingxin Guan 1 , Mark Dreibelbis 2 , Robert Hamers 1 , Mahesh Mahanthappa 1 , Dane Morgan 1 , Thomas Kuech 1
1 University of Wisconsin-Madison Madison United States, 2 The Dow Chemical Company Midland United StatesShow Abstract
A thin amorphous coating of Al2O3 obtained via atomic layer deposition (ALD) has demonstrated the ability to improve cycle-life for several cathode materials in rechargeable Li-ion batteries . However, due to the insulating nature of Al2O3, the coatings on cathode particles impede the transport of Li-ion and electrons during the battery cycling. Therefore, a large overpotential on the cathode surface can develop leading to significant capacity loss at higher C-rates and for thicker coatings. In this work, we describe a method to estimate the overpotential of amorphous ALD Al2O3 coatings on Li[Ni0.5Mn0.3Co0.2]O2 (NMC) cathode and can be extended to any other coating materials. At 1C-rate (2.062mA), t