Predicting Reactivity and Passivation of Solid-State Battery Interfaces
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The Importance of a Moving Boundary Approach for Modeling the SEI Layer Growth to Predict Capacity Fade
One of the contributing factors to the aging of lithium-ion batteries is the growth of the solid-electrolyte interphase (SEI) layer. The growth of the SEI layer leads to the irreversible loss of lithium available for cycling and increases the resistance of the battery. Physics-based models in literature model the kinetically limited or solvent diffusion-limited growth. In such models, the interface resistance is a constant, and the contribution to the overpotential of the intercalation reaction from the SEI layer is considered to be ohmic. In this study, we propose a model that describes the growth of the SEI layer on the electrode surface as a moving interface. The transport of lithium ions and the solvent in the electrolyte are affected by this moving interface. The equations that govern the species transport and the potential drop across the SEI layer are derived from dilute solution theory and solved by transforming the coordinates of the moving boundary. The ion transport induces changes in the conductivity across the SEI layer, which affects the potential drop that arises due to its growth. The effects of this potential on capacity fade are studied over cycling the battery.
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A Modified Sand’s Time Incorporating Li-Ion Transport Across the SEI: Basis for Understanding Li Dendrite Formation and Li-Metal Battery Electrolyte Selection
Abstract Understanding the initiation of lithium dendrites remains elusive, largely due to the intricate role of the solid electrolyte interphase (SEI) which forms on the Li surface during electrodeposition. Many studies have utilized the classical Sand’s equation to estimate the onset time when lithium dendrites begin to form. The Sand’s equation provides the time when the cation (Li+) concentration at the electrode-electrolyte interface approaches zero under diffusion-limited conditions in galvanostatic Li electrodeposition. However, recent experimental studies have revealed that the observed lithium dendrite onset time deviates considerably from the Sand’s time. Here, we show that this deviation from classical theory is likely due to the transport of Li+ ions through the SEI - a transport limitation that is much more dominant in controlling dendrite formation. We develop a ‘modified’ Sand's equation, incorporating the SEI layer and the diffusional transport across it to predict Li dendrite onset times. To validate this approach, we conducted Li electrodeposition experiments at various current densities using two distinct organic electrolytes. Analysis of the results demonstrates that the modified Sand's equation provides a more accurate prediction of dendrite onset times, highlighting the importance of incorporating SEI into transport models of Li plating in next-generation rechargeable Li-metal batteries.
Ma, Yuanman (ORCID:0000000200444811)↗
Nano-FTIR Spectroscopy of the Solid Electrolyte Interphase Layer on a Thin-Film Silicon Li-Ion Anode
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Chemical Challenges that the Peroxide Dianion Presents to Rechargeable Lithium–Air Batteries
Understanding the fundamental redox reactions and processes that occur in lithium–air and, more generally, metal–air batteries is important to the progress of this promising energy-storage technology. Knowledge of the chemistry of the peroxide dianion, O 2 2– , is especially crucial, as the dianion is at the nexus of the charge/discharge cycle of lithium–air batteries. The intrinsic electron transfer properties and redox chemistry of peroxide dianion are poorly defined because it is difficult to isolate the dianion free of protons and metal ions. We review the results of (i) the electron transfer kinetics and (ii) the redox reaction chemistry of isolated peroxide dianion encapsulated within the cavity of a hexacarboxamide cryptand. With regard to the former, electron transfer kinetics measurements provide fundamental Marcus parameters that will be useful for models that seek to disentangle the precise contributions of Li + ion-coupled electron transfer, electron transfer across the Li 2 O 2 solid particle interface, and charge hopping among Li 2 O 2 particles. With regard to the latter, an underappreciated chemistry of peroxide dianion with CO 2 produces peroxymonocarbonate (OOCO 2 2– ) and peroxydicarbonate (O 2 COOCO 2 2– ). An autocatalytic cycle will lead to oxidative degradation of traditional organic electrolytes and other vulnerable cell components employed in lithium–air batteries. Furthermore, this peroxycarbonate-derived chemistry, in addition to more commonly recognized solution-based oxidation chemistry, will need to be mitigated to realize the long-term cyclability of rechargeable lithium–air batteries.
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Elucidating the mechanism underlying the augmented capacity of MoO 2 as an anode material in Li-ion batteries
Transition-metal oxide anode materials have been observed to possess an intriguing surplus of capacity beyond the expected values based on conversion reaction. However, the mechanisms behind this phenomenon have remained contentious and elusive. Here, this study focuses on synthesized nanosized molybdenum dioxide and its electrochemical performance as an anode material for Li-ion batteries. Our findings reveal a substantial increase in capacity upon cycling, achieving approximately 1688 mA h g -1 , nearly double the theoretical capacity, after 700 cycles at a 1C rate. To elucidate the mechanisms underlying this augmented capacity, a comprehensive analysis employing in situ and ex situ X-ray diffraction, X-ray absorption spectroscopy, scanning electron microscopy, and transmission electron microscopy was conducted at various stages of the Li-ion cell cycling. Our results indicate that no conversion reaction occurs during the initial discharge phase, with Li 2 O and Mo remaining undetected. Instead, Li 0.98 MoO 2 is generated upon lithiation. Further materials characterization employing electron energy loss spectroscopy and energy-dispersive X-ray spectroscopy on the cycled electrode suggests the potential formation of a metallic Li-rich layer at the interface of the Li-ion intercalated phase subsequent to the formation of Li 0.98 MoO 2 , contributing to the surplus Li storage. Moreover, electrochemical impedance spectroscopy coupled with ex situ SEM and TEM analyses reveals that alterations in particle size and morphology, along with changes in the solid electrolyte interphase (SEI) resistance, are instrumental in the capacity variation observed upon cycling.
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The Chemistry, Formation and Passivation of Solid-Electrolyte Interphase (SEI) from FSI- Breakdown at Li-metal Potential
LiFSI-based liquid electrolytes are promising for realizing high Coulombic efficiency (CE) and long cycle life of next-generation high-energy Li metal battery. Nevertheless, the fundamentals of both the chemistry and formation of solid-electrolyte interphase (SEI) in these electrolytes have remained elusive. Herein, we extensively combine electrochemistry and X-ray photoelectron spectroscopy (XPS) to illustrate the reaction pathways of electrolyte decomposition, especially FSI- breakdown, as well as the dissolution trend of various inorganic SEI components. The SEI-forming reactions at Cu/electrolyte interface manifest a potential (E) dependence, driven by direct electron-transfer (ET) and Li underpotential-deposition (Li UPD) at high and low E regions, respectively. By closely correlating the XPS data obtained with and without solvent washing, we demonstrate that not all the products derived from SEI reactions are incorporated into forming a passivating surface layer, with a notable portion dissolving into liquid electrolyte instead. Importantly, high-CE electrolyte dictated by the chemical identity of solvent, is found to exhibit minimized interfacial reactivity of SEI formation enabling more effective interphasial passivation, via preferential integration of passivating ingredients such as LiF. Overall, this work formulates a systematic understating of bridging the SEI chemistry, formation and passivation while identifying key characteristics of high-performance electrolyte for guiding future design.
Bao, Zhenan [SLAC National Accelerator Laboratory ↗
Dimensionality effects on multicomponent ionic transport and surface complexation in porous media
Coulombic interactions between charged species in pore water and at surface/solution interfaces are of pivotal importance for multicomponent reactive transport in porous media. In this study, we investigate the impact of domain dimensionality on electrostatically coupled dispersion and surface-solution reactions during transport of acidic plumes and major ions in porous media. Column and quasi two-dimensional flow-through experiments were performed, with identical silica porous media and under the same advection-dominated conditions. Equal mass fluxes of different electrolyte solutions (i.e., HCl - pH ~ 2.8, NaBr - 100 mM, HCl - pH ~ 2.8 plus NaBr - 100 mM) were continuously injected in the 1-D and 2-D experiments and breakthrough curves of pH and major ions were measured at the outlet of the domains. The presence of pronounced ionic strength gradients in the transverse direction in the 2-D setup caused distinct retardation and transport behaviors of protons and major ions which were not observed in the one-dimensional column experiments. Furthermore, in the cases of salt electrolytes injection, considerably enhanced release of H + (>61%) from the quartz surface was observed in the multidimensional system compared to the one-dimensional setup. Reactive transport modeling was performed to reproduce the experimental outcomes and to analyse the coupling between transport processes, based on the Nernst-Planck formulation of diffusive/dispersive fluxes and on surface complexation reactions at the solid-solution interface. Electrostatic interactions between Na + , B – , and H + , and deprotonation of the quartz surface upon the formation of sodium outer-sphere complexes, are the primary controllers of the spatial and temporal features displayed by the pH and major ions measurements. The reactive transport simulations allowed us to interpret the experimental observations, to visualize the distribution and spatio-temporal evolution of dissolved and solid species, to identify a spatially heterogeneous zonation of Coulombic interactions with distinct behavior at the fringe and core of the injected plumes in the multidimensional setup, and to quantify the different components of the Nerst-Planck fluxes of the charged solutes. This study demonstrates that the domain dimensionality directly affects electrostatic interactions between charged aqueous species in the pore water and surface complexation reactions at the solid-solution interface. The non-trivial effects of dimensionality on multicomponent ionic transport result in a significantly different behavior in 1-D and 2-D systems.
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Localized high-concentration electrolytes get more localized through micelle-like structures
Liquid electrolytes in batteries are typically treated as macroscopically homogeneous ionic transport media despite having a complex chemical composition and atomistic solvation structures, leaving a knowledge gap of the microstructural characteristics. Here, we reveal a unique micelle-like structure in a localized high-concentration electrolyte, in which the solvent acts as a surfactant between an insoluble salt in a diluent. The miscibility of the solvent with the diluent and simultaneous solubility of the salt results in a micelle-like structure with a smeared interface and an increased salt concentration at the centre of the salt–solvent clusters that extends the salt solubility. These intermingling miscibility effects have temperature dependencies, wherein a typical localized high-concentration electrolyte peaks in localized cluster salt concentration near room temperature and is used to form a stable solid–electrolyte interphase on a Li metal anode. Importantly, these findings serve as a guide to predicting a stable ternary phase diagram and connecting the electrolyte microstructure with electrolyte formulation and formation protocols of solid–electrolyte interphases for enhanced battery cyclability.
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How Interface Evolution at the Nanoscale Dictates Protonic Ceramic Cell Behavior
Understanding the effects of heterointerfaces in nanodevices remains a challenge in interface engineering for systems applied in solid oxide fuel cells, catalysis, sensors, and memristors [1]. Previous studies have shown that the presence of interfaces in ceramic oxide nanodevices affects their impedance properties compared to bulk systems [2]. In this work, we analyze a thin-film model system designed to study the interfaces between representative electrode and electrolyte materials employed in protonic ceramic electrochemical cells for the reversible conversion of hydrogen o electricity. The investigated device features a 21-layer architecture that alternates between an electrode material PBSCF (PrBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5+ϵ ) and a proton-conducting electrolyte BZY (BaZr 0.8 Y 0.2 O 3-δ ), with uniform 20 nm thickness for each layer. Here, the device was fabricated using Pulsed Laser Deposition (PLD) and supported on a conductive Nb-doped STO (Nb-SrTiO 3 ) substrate.
dos Santos, Gabriel T. [Northwestern University, E↗
Cation Migration and LSCF/SDC Decomposition Related to Long-Term Operation Mode as Revealed by Electron Microscopy
This study utilized energy dispersive spectroscopy (EDS) in a scanning electron microscope (SEM) and a scanning transmission electron microscope (STEM) in order to track cation migration and related particle decomposition for air electrode components of solid oxide cells. The influence of a Sm-doped ceria (SDC) barrier layers was assessed for three operation modes (fuel cell, electrolysis, reversible) over long time periods (1000-1500 hours). Composition profiles across air electrode/electrolyte interfaces indicated negligible accumulation of La/Sr cations to the yttria-stabilized zirconia (YSZ) electrolyte during operation. Instead, air electrode particles composed of SDC and/or La-Sr-Co-Fe-oxides (LSCF) exhibited decomposition by Sr evaporation and Sm migration to LSCF particle edges.
Picard, Yoosuf↗
Imaging, understanding, and control of nanoscale materials transformations
The development of liquid cells for transmission electron microscopy has enabled breakthroughs in our ability to follow nanoscale structural, morphological, or chemical changes during materials growth and applications. Time-resolved high-resolution imaging and chemical analysis through liquids opened the opportunity to capture nanoscale dynamic processes of materials, including reaction intermediates and the transformation pathways. In this article, a series of work is highlighted with topics ranging from liquid cell developments to in situ studies of nanocrystal growth and transformations, dendrite formation, and suppression of lithium dendrites through in situ characterization of the solid–electrolyte interphase chemistry. The understanding garnered is expected to accelerate the discovery of novel materials for applications in energy storage, catalysis, sensors, and other functional devices.
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Ultrasmooth Epitaxial Pt Thin Films Grown by Pulsed Laser Deposition
Platinum (Pt) thin films are useful in applications requiring high-conductivity electrodes with excellent thermal and chemical stability. Ultrasmooth and epitaxial Pt thin films with single-crystalline domains have the added benefit of providing ideal templates for the subsequent growth of heteroepitaxial structures. Here, we grow epitaxial Pt (111) electrodes (ca. 30 nm thick) on sapphire (α-Al 2 O 3 (0001)) substrates with pulsed laser deposition. This versatile technique allows control of the growth process and fabrication of films with carefully tailored parameters. X-ray scattering, atomic-force microscopy, and electron microscopy provide structural characterization of the films. Various gaseous atmospheres and temperatures were explored to achieve epitaxial growth of films with low roughness. A two-step (500 °C/300 °C) growth process was developed, yielding films with improved epitaxy without compromising roughness. The resulting films possess ultrasmooth interfaces (<3 Å) and high electrical conductivity (6.9 × 10 6 S/m). Finally, Pt films were used as current collectors and templates to grow lithium manganese oxide (LiMn 2 O 4 (111)) epitaxial thin films, a cathode material used in Li-ion batteries. In conclusion, using a solid-state ionogel electrolyte, the films were highly stable when electrochemically cycled in the 3.5-4.3 V vs Li/Li + range.
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Scalable, Ultrathin, and High-Temperature-Resistant Solid Polymer Electrolytes for Energy-Dense Lithium Metal Batteries
We report all-solid-state batteries (ASSBs) demonstrate great promise, offering high energy density, good thermal stability, and safe operation compared with traditional Li-ion batteries. Among various solid-state electrolytes (SSEs), solid polymer electrolytes (SPEs) offer an attractive choice due to their thinness, low density, and good manufacturability. However, ultrathin SPEs that work with practical current densities or at high temperatures remain challenging, limiting applicable conditions of SPE-based batteries. Here, the authors report a novel scalable, ultrathin, and high-temperature-resistant SPE for ASSBs. This design includes an electrospun polyacrylonitrile (PAN) matrix and polyethylene oxide (PEO)/Li salt ionic conductor, which offers a stable LiF and Li 3 N containing SSE/Li interface. The unique interface—as well as the good mechanical strength—inhibits lithium dendrites and prevents short circuiting. As a result, symmetrical Li-Li cells deliver more than 300 h cyclability at 0.5 mA cm -2 . ASSBs fabricated with only 5 µm-thickness PAN-PEO/lithium bis(trifluoromethanesulfonyl)imide reach 300 cycles at 0.3 C rate at 60 °C. The excellent thermal stability of PAN also results in safer SPEs at high temperatures. The design extends battery operation up to temperatures of 120 and 150 °C, where it achieves 500 cycles at C/2 rate and 100 cycles at 2C rate, respectively.
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Locally developed electronic conduction in a yttria stabilized zirconia (YSZ) electrolyte for durable solid oxide fuel cells
In the present work, anode supported solid oxide fuel cells (SOFCs) based on a YSZ single layer electrolyte with locally developed electronic conduction near the anode side is fabricated to improve the cell durability under negative voltage conditions. A ceria added Ni/YSZ anode functional layer is utilized and co-sintered with the YSZ electrolyte at 1460 °C. Cerium ions are diffused into a limited region of the YSZ layer (~6 μm), establishing a ceria doped YSZ region. We successfully demonstrate that this YSZ single layer cell can operate stably for ~100 h without anode/electrolyte interface delamination, even under a negative voltage. The embedded probe technique and theoretical calculation reveal that the internal oxygen partial pressure (near the anode) is substantially reduced (stabilized) by means of local electronic conduction of ceria doped YSZ. Thus, we propose an SOFC electrolyte design comprising a YSZ single layer with a ceria added anode functional layer (locally formed ceria doped YSZ in the electrolyte) as a protection method against fuel cell stack degradation caused by negative voltage operation.
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Lithium‐Containing Hybrid SEI Layer Enabling High Mass Loading and Anode‐Less Sodium Metal Batteries
Abstract The continuous rupturing and rebuilding of unstable solid electrolyte interphase (SEI) layer during cycling would block Na + diffusion and induce Na dendrite formation, ultimately limiting the practical application of high‐energy‐density sodium metal batteries. Herein, a hybrid SEI layer containing Li‐species is dexterously constructed on the surface of sodium metal anode. Li‐containing inorganic components (Li 3 N, LiF, and Li 2 CO 3 ) are introduced to stabilize the Na/electrolyte interface and enhance the mechanical and diffusion kinetic properties of the SEI layer, which can reduce the side reactions and gas generation, regulate Na + flux during cycling and promote rapid Na + migration for uniform dendrite‐free Na deposition. As a result, the constructed Na symmetric cells achieve low overpotential and long cycle life of 5900, 1800, and 500 h at current densities of 3, 10, and 30 mA cm −2 , respectively. Furthermore, the full cells paired with the Na₃V₂(PO₄)₃ cathode demonstrate high specific capacity and excellent cycle stability, even at an ultra‐high cathode loading of 39.3 mg cm −2 and a low N/P ratio (negative/positive electrode capacity ratio of 1.21).
Xia, Li [State Key Laboratory of Physical Chemistr↗
Pore-Filling Induced Solid Electrolyte Failure of Ti-Doped Na 3 Zr 2 Si 2 PO 12 Characterized by Operando Synchrotron X-Ray Tomography
Solid-state batteries (SSBs), particularly those utilizing sodium metal, are emerging as a promising technology due to their potential for enhanced safety, higher energy density, and longer cycle life. NASICON (Na superionic conductor) materials, known for their robust crystalline structure and high ionic conductivity, are pivotal in the development of efficient sodium all-solid-state batteries. These materials exhibit high room-temperature ionic conductivity and electrochemical stability, making them ideal for various applications. Research has focused on improving NASICON's ionic conductivity and stability through doping, interface regulation, and composite anode design. Recent advancements include Ti-doped Na 3 Zr 2 Si 2 PO 12 (Ti-NZSP), which demonstrates improved surface stability, higher ionic conductivity, and increased critical current density. However, challenges such as Na dendrite formation and mechanical integrity under operational conditions persist. Advanced imaging techniques like operando synchrotron X-ray tomography have provided insights into failure mechanisms, revealing that pore-filling and dendrite growth are significant issues. Understanding these processes is essential for enhancing the performance and safety of Na-based SSBs. Here, this study underscores the need for continued research to address these challenges and develop reliable, high-performance solid-state electrolytes for future energy storage solutions.
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