Li-diffusion accelerates grain growth in intercalation electrodes: a phase-field study

Grain boundary migration is driven by the boundary's curvature and external loads such as temperature and stress. In intercalation electrodes an additional driving force results from Li-diffusion. That is, Li-intercalation induces volume expansion of the host-electrode, which is stored as elastic energy in the system. This stored energy is hypothesized as an additional driving force for grain boundaries and edge dislocations. Here, we apply the 2D Cahn-Hilliard$-$phase-field-crystal (CH-PFC) model to investigate the coupled interactions between highly mobile Li-ions and host-electrode lattice structure, during an electrochemical cycle. We use a polycrystalline FePO$_{4}$/ LiFePO$_{4}$ electrode particle as a model system. We compute grain growth in the FePO$_{4}$ electrode in two parallel studies: In the first study, we electrochemically cycle the electrode and calculate Li-diffusion assisted grain growth. In the second study, we do not cycle the electrode and calculate the curvature-driven grain growth. External loads, such as temperature and stress, did not differ across studies. We find the mean grain-size increases by $\sim11\%$ in the electrochemically cycled electrode particle. By contrast, in the absence of electrochemical cycling, we find the mean grain-size increases by $\sim2\%$ in the electrode particle. These CH-PFC computations suggest that Li-intercalation accelerates grain-boundary migration in the host-electrode particle. The CH-PFC simulations provide atomistic insights on diffusion-induced grain-boundary migration, edge dislocation movement and triple-junction drag-effect in the host-electrode microstructure.Comment: 11 pages, 9 figure

Grain boundary mobility and segregation in non-stoichiometric solid solutions of magnesium aluminate spinel

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 1985.MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE.Vita.Includes bibliographical references.by Yet-Ming Chiang.Sc.D

Producing High Concentrations of Hydrogen in Palladium via Electrochemical Insertion from Aqueous and Solid Electrolytes

Metal hydrides are critical materials in numerous technologies including hydrogen storage, gas separation, and electrocatalysis. Here, using Pd-H as a model metal hydride, we perform electrochemical insertion studies of hydrogen via liquid and solid state electrolytes at 1 atm ambient pressure, and achieve H:Pd ratios near unity, the theoretical solubility limit. We show that the compositions achieved result from a dynamic balance between the rate of hydrogen insertion and evolution from the Pd lattice, the combined kinetics of which are sufficiently rapid that operando experiments are necessary to characterize instantaneous PdHx composition. We use simultaneous electrochemical insertion and X-ray diffraction measurements, combined with a new calibration of lattice parameter versus hydrogen concentration, to enable accurate quantification of the composition of electrochemically synthesized PdHx. Furthermore, we show that the achievable hydrogen concentration is severely limited by electrochemomechanical damage to the palladium and/or substrate. The understanding embodied in these results helps to establish new design rules for achieving high hydrogen concentrations in metal hydrides.Comment: 38 page

Classifying the mechanisms of electrochemical shock in ion-intercalation materials

“Electrochemical shock” – the electrochemical cycling-induced fracture of materials – contributes to impedance growth and performance degradation in ion-intercalation batteries, such as lithium-ion. Using a combination of micromechanical models and acoustic emission experiments, the mechanisms of electrochemical shock are identified, classified, and modeled in targeted model systems with different composition and microstructure. A particular emphasis is placed on mechanical degradation occurring in the first electrochemical cycle. Three distinct mechanisms of electrochemical shock are identified, and a fracture mechanics failure criterion is derived for each mechanism. In a given material system, crystal symmetry and phase-behavior determine the active mechanisms. A surprising result is that electrochemical shock in commercial lithium-storage materials occurs by mechanisms that are insensitive to the electrochemical cycling rate. This fundamental understanding of electrochemical shock leads naturally to practical design criteria for battery materials and microstructures that improve performance and energy storage efficiency. These microstructure and crystal chemical design criteria are demonstrated experimentally for spinel materials such as LiMn2O4 and LiMn1.5Ni0.5O4. A case study of LiMn1.5Ni0.5O4 is presented, in which small changes in composition that have negligible impact on electrochemical properties induce a significant change in phase behavior that allow electrochemical shock at relevant electrochemical cycling rates to be avoided. Although lithium-storage materials are used as model systems for experimental study, the physical phenomena are common to other ion-intercalation systems, including sodium- and magnesium-storage compounds

Mechanical and electrochemical response of all-solid-state lithium-ion batteries

All-solid-state rechargeable lithium-ion batteries have attracted much interest because they have features particularly favorable for large-scale application to automotive applications and to stationary load-leveling for intermittent power generation from solar or wind energy. The replacement of an organic liquid electrolyte with a nonflammable and more reliable inorganic solid electrolyte (SE) simplifies the battery design and improves safety and durability of the system [1]. However, the mechanical behavior of such electrodes will be considerably different than their liquid electrolyte counterparts. Direct stacking of solid-state cells enables the achievement of high operating voltages in a reduced volume. Furthermore, all-solid-state batteries allow the use of large-capacity electrode materials, for instance, sulfur positive electrode paired with a lithium metal negative electrode, which are difficult to employ in conventional liquid electrolyte batteries. A key development to the success of all-solid-state batteries is a SE with high Li+ ion conductivity at room Temperature [2, 3, 4]. In recent years, several SEs having the same level of conductivity as organic liquid electrolytes have been discovered and tested with many active materials. The durability of a cohering solid–solid interface between electrode and electrolyte is likely to be important practical consideration. Notwithstanding the several techniques have been investigated to increase the contact area at the interface [5], interface cohesion and its effects on the rate capability and the overall performance throughout the expected life cycles needs to be maintained. This research focuses on the development of a nonlinear continuum model able to account for the combined effects of Li diffusion and for the consequent isotropic or anisotropic volumetric expansion of the hosting material. The electrode and electrolyte are modeled as idealized as elastic-viscoplastic materials, with elastic properties varying with lithium concentration. A discrete approximation of such a model has been implemented (in the framework of finite elements) to simulate mechanical and elctrochemical response of the system. Side reactions being mostly inhibited in all-solid cells, the battery life depends in larger measure on the mechanical integrity of the composite system [6]. As physical values for the SE’s mechanical behavior are not available, our calculations indicate trends of how mechanical reliability will depend on temperature-dependent viscoelastic behavior. When mechanical properties become available, they can be used directly in our model. Of relevant practical interest is thus the prediction of stress, plastic flow, and damage within the bulk and in particular at the electrode–electrolyte interface. KEY WORDS Lithium ion batteries, All-solid-state batteries, Electrochemical–mechanical continuum model, Diffusion, Elasto-viscoplastic material REFERENCES [1] Kazunori Takada. Progress and prospective of solid-state lithium batteries. Acta Materialia. 2013, 61(3), 759–770. [2] Bates, J.B., Dudney, N.J., Neudecker, B., Ueda, A., Evans, C.D. Thin-film lithium and lithium-ion batteries. Solid State Ionics. 2000, 135(1–4), 33–45. [3] Yoshikatsu Seino, Tsuyoshi Ota, Kazunori Takada, Akitoshi Hayashi, and Masahiro Tatsumisago. A sulphide lithium super ion conductor is superior to liquid ion conductors for use in rechargeable batteries. Energy Environ. Sci. 2014, 7, 627–631. [4] Noriaki Kamaya, Kenji Homma, Yuichiro Yamakawa, Masaaki Hirayama, Ryoji Kanno, Masao Yonemura, Takashi Kamiyama, Yuki Kato, Shigenori Hama, Koji Kawamoto, Akio Mitsui. A lithium superionic conductor. Nature Mater. 2011, 10(9), 682–686. [5] Masahiro Tatsumisago, Motohiro Nagao, Akitoshi Hayashi. Recent development of sulfide solid electrolytes and interfacial modification for all-solid-state rechargeable lithium batteries. J Asian Ceram Soc. 2013, 1(1), 17–25. [6] Akitoshi Hayashi, Kousuke Noi, Atsushi Sakuda, Masahiro Tatsumisago. Superionic glass-ceramic electrolytes for room-temperature rechargeable sodium batteries. Nature Commun. 2012, 3

Ordering Control of Self-Assembled Colloidal Crystals

Colloidal crystals are 3D nanostructures formed by self assembly of nanoparticles in suspension. The interaction forces between the colloid particles are expected to affect the ordering and the defect density in the resultant crystal. Based on this insight, the effect of ionic strength on the quality of the colloidal crystal is examined. It is found that at intermediate ionic strength, it is possible to get the best ordering of the colloidal crystal. The reason for this is explained based on previous work on the structural changes in an assembling colloidal crystal. A method for reducing the defect density in colloidal crystal will also be proposed.Singapore-MIT Alliance (SMA

Design Principles for Self-forming Interfaces Enabling Stable Lithium Metal Anodes

The path toward Li-ion batteries with higher energy-densities will likely involve use of thin lithium metal (Li) anode (<50 $\mu$m in thickness), whose cyclability today remains limited by dendrite formation and low Coulombic efficiency. Previous studies have shown that the solid-electrolyte-interface (SEI) of Li metal plays a crucial role in Li electrodeposition and stripping. However, design rules for optimal SEIs on lithium metal are not well-established. Here, using integrated experimental and modeling studies on a series of structurally-similar SEI-modifying compounds as model systems, we reveal the relationship between SEI compositions, Li deposition morphology and coulombic efficiency, and identify two key descriptors (ionicity and compactness) for high performance SEIs through integrated experimental and modeling studies. Using this understanding, we design a highly ionic and compact SEI that shows excellent cycling performance in LiCoO$_2$-Li full cells at practical current densities. Our results provide guidance for the rational selection and optimization of SEI modifiers to further improve Li metal anodes.Comment: 21 pages, 6 figures and Supplementary Informatio

The Effect of Stress on Battery-Electrode Capacity

Constraint-induced stresses develop during Li-ion battery cycling, because anode and cathode materials expand and contract as they intercalate or de-intercalate Li. We show in this manuscript that these stresses, in turn, can significantly modify the maximum capacity of the device at a given cell voltage. All-solid-state batteries impose an external elastic constraint on electrode particles, promoting the development of large stresses during cycling. We employ an analytic and a finite element model to study this problem, and we predict that the electrode's capacity decreases with increasing matrix stiffness. In the case of lithiation of a silicon composite electrode, we calculate 64% of capacity loss for stresses up to 2 GPa. According to our analysis, increasing the volume ratio of Si beyond 25-30% has the effect of decreasing the total capacity, because of the interaction between neighboring particles. The stress-induced voltage shift depends on the chemical expansion of the active material and on the constraint-induced stress. However, even small voltage changes may result in very large capacity shift if the material is characterized by a nearly flat open-circuit potential curve. Keywords: Finite element modeling; Li-ion battery; Solid electrolyte; Stress-potential coupling; ThermodynamicsUnited States. Department of Energy (Grant DE-SC0002633)United States. Department of Energy. Office of Basic Energy Sciences (Contract DE-FG02-10ER46771