Surface Of Active Material Research Articles

3D Microstructure Modeling of Lithium Ion Batteries during Rapid Charging

Battery models can be used to predict conditions ripe for lithium metal plating in the anode during rapid charging. One common procedure is to simulate a rapid charge using a pseudo-two-dimensional (P2D) model and determine if and when the minimum local potential reaches 0.0 V with respect to metallic lithium in the anode. This normally occurs at higher states of charge during a DC fast charging or rapid regenerative charging event. However, we have recently determined that three-dimensional (3D) models, while broadly agreeing with P2D results, demonstrate much variation in the in-plane and through plane direction, which P2D models cannot resolve. Because P2D models employ effective medium approximations, any “local” value in the P2D space along the through-plane coordinate represents an average across a slice of the domain. Therefore, it may be insufficient to use minimum anode potentials from P2D models as indicators of local plating and may only be representative of global lithium plating onset.In this work, the results of rapid-charge 3D microstructure simulations are compared to P2D results. This allows us to verify whether rapid charging induces negative local potentials at the anode active material surface that are left undetected in a P2D model. The expected result implies that the 3D microstructure model is necessary to predict the onset of lithium plating.

Oxygen vacancy-enriched bilayer flower-like structure of ZnO&NiO@C-ZnO nanorod arrays on carbon cloth with improved eletrochemical performance

Herein, flower-like ZnO&NiO@C-coated ZnO nanorod arrays based on carbon cloth (ZnO&NiO@C-ZnO NRs/CC) is designed based on ZnO&NiO nanosheets epitaxially grown on C-ZnO nanorod arrays by electrochemical deposition and chemical reaction method. Notably, the ZnO&NiO@C-ZnO NRs/CC possess significant synergistic effect of ZnO and NiO, 3-dimension scaffolding of C-ZnO NRs, and importantly, abundant oxygen vacancy defects, thus rendering them deliver a specific capacity of 1001.5 F g−1 at 3 A g−1 current density and maintains 92.33 % retention after 20,000 cycles in 1 M KOH electrolyte. Further, theoretical calculation certifies that the abundant oxygen vacancies in interface model of ZnO and NiO are favor of rapid electron transfer, ion diffusion, and adsorption/desorption between electrolyte ions and the surface of active material. Moreover, an all-solid symmetric supercapacitor is also fabricated using the ZnO&NiO@C-ZnO NRs/CC and gel electrolyte, which shows the energy density of 27.5 Wh kg−1 at the power density of 4.5 kW kg−1, and ultrahigh capacitance retention of 102.83 % after 10,000 cycles. These research results demonstrate that the design of nanomaterials with numerous oxygen vacancies, unique flower-like structure, and synergistic effect of ZnO and NiO may open up new opportunities for the development of high-performance supercapacitors.

Roll-to-roll solvent-free manufactured electrodes for fast-charging batteries

Roll-to-roll solvent-free manufactured electrodes for fast-charging batteries

Elucidation of intercalation-pseudocapacitor mechanism in Binder-free Bi2S3@Ni foam electrodes towards high-performance supercapattery

Pseudocapacitance has been commonly correlated with surface or near-surface reversible redox reactions of active electrode material in the electrolyte. However, we recently demonstrated an intercalated pseudocapacitor mechanism into the mesoporous 2-D orthorhombic Bi2S3 nanomaterial over nickel foam for supercapattery application. Such a mechanism effectively reduces the gap between a battery and a supercapacitor for achieving both high energy and power densities. A facile binder-free electrode has been architectured by a coating of Bi2S3 nanoflakes over the Nickel (Ni) foam at a constant 80 °C temperature and pressure resulting in better adhesion and electrochemical functioning. The process-controlled morphologies led to an enhanced electrochemical activity obtained due to enhanced surface area (149.698 m2/g) and high binding of Bi2S3 and Ni foam. The electrochemical supercapacitor studies revealed its battery-type characteristics which show a semi-infinite diffusion-controlled faradaic process that occurs in the bulk of the nanomaterial. The material exhibits an enhanced capacity of 1906 A h g − 1 at a constant high-discharging current density of 5 Ag−1. Furthermore, it provides a very high capacitive retention up to 97.22% till 2000 cycles owing to its unique structural and morphological stability. The principal interest realized from the intercalation mechanism is that high charge storage is achieved within a short period because of the negligible solid-state diffusion. The novel method of electrode design and its morphological changes have enabled it to surpass the electrochemical performance of many other previously reported Bi2S3-related materials.

Correlation between Surface Reactions and Electrochemical Performance of Al2O3‐ and CeO2‐Coated NCM Thin Film Cathodes

AbstractDepositing ultrathin oxide coatings has been proven a successful approach to stabilize the surface of LiNixCoyMnzO2active cathode material in lithium‐ion batteries (LIB). The beneficial effect of Al2O3coatings arises at least partly from spontaneous reactions between coating and liquid electrolyte. However, it remains unclear if comparable surface reactions occur for other oxide coatings. One difficulty is the characterization of reaction products at the cathode–electrolyte interface due to the multi‐phase properties of composite cathodes. Here, thin films are utilized as model systems to correlate surface reactions with the performance of Al2O3‐ and CeO2‐coated nickel cobalt manganese oxides (NCM). Electrochemical characterization confirms that an Al2O3coating improves long‐term cycling stability, while CeO2‐coated thin films perform even worse than uncoated counterparts. The analysis of the surface reaction products using X‐ray photoelectron spectroscopy shows that both coatings are fluorinated upon contact with liquid electrolyte in agreement with thermodynamic considerations. The fluorinated Al2O3coating is stable during cycling, resulting in the improved cell performance. In contrast, the fluorinated CeO2coating changes chemical composition, facilitating corrosion of the NCM surface. The results demonstrate the importance of a detailed analysis of surface reactions to evaluate the suitability of ultrathin oxide layers as protective coatings for LIBs.

Substrate-dependent fractal growth and wettability of N+ ion implanted V2O5 thin films

Wettability of active material surface affects the electrolyte and electrode-material interaction in electrochemical applications. An increase in the V2O5 electrode's wetting behaviour allows for better contact with the electrolyte. The surface properties of the V2O5 sample were examined in order to evaluate its wettability. In this work, the surface growth of V2O5 thin films on three different substrates (glass, silicon, and sapphire) after 16 keV N+ ion implantation is presented as a function of ion dose. Thin films of 500 nm V2O5 deposited on different substrates show the formation of the nanocrystalline structure over the surface after thermal annealing. Silicon substrate shows the formation of V2O5 nanorods over the surface. Surface morphology shows the growth dynamics of the surface in terms of roughness (α) and growth (β) exponents. Lateral growth of surface features has been quantified in terms of co-relation length (ξ) and fractal dimensions (Df). The scaling laws studies of the surfaces in terms of exponents and co-relation length shows the role of N+ implantation in structural modifications. Furthermore, wetting dynamics have been co-related with fractal growth of the films under ion implantation. The contact angle of V2O5 thin films is found to be higher for V2O5 nanorods on silicon substrate as compared to crystallite grains on sapphire. The present study showed that the surface morphology and wettability of V2O5 are mainly substrate-dependent and can be controlled by surface fractal parameters.

Understanding Interfacial Chemistry Interactions in Energy-Dense Lithium-Ion Electrodes

ConspectusFor the past two decades, conversion and alloying-type materials have been heralded as the natural heir to commercially available graphite anodes due to their ability to deliver high gravimetric/volumetric power. Commercialization of batteries with these high-energy-density active materials could impact a variety of sectors including electric vehicles, grid storage, and consumer electronics and contribute toward an ever-increasing electrified world. However, the various failure mechanisms from inherent interfacial chemical instabilities associated with these materials make them unable to be merely substituted into currently available electrode fabrication and formulation processing techniques. As a result, realizing the high theoretical capacity and achieving commercial viability of these materials will rely on the careful manipulation of interfacial chemical interactions that dictate and control various kinetic and transport processes across multiple scales of the composite electrode. This has led to a plethora of research that has focused on systematically understanding properties of the different electrode components and designing carefully constructed electrode formulations to achieve composite electrodes with increased chemical stability, enhanced local mixed conductivities, or improved mechanical resilience.This Account relates recent progress in the understanding of synergetic opportunities for energy-dense, resilient composite anodes. By understanding the interplay between components of the composite electrode, we can construct enhanced well-integrated electrodes with performance metrics that surpass empirically derived architectures. Due to the increased complexity of high-volume-expanding electrodes, performance is more than the cumulative contributions of the individual components, and therefore energy and compatibility matching are important for robust electrochemical performance across cycling, rate capability, facile lithium-ion transport, and stability. In this Account, synergistic opportunities are framed from a chemistry perspective as we focus on examining interfacial interactions that span all electrode components: the active material surface, conductive agent linkage, and polymeric binder mesoscale. Control of key interfacial chemistry can be achieved through chemical functionalization, physical interactions, and other types of linkages and thereby lead to utilization of high-energy-density active materials in robust composite electrodes. Leveraging several techniques such as the Hanson solubility parameter (HSP) analysis, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FT-IR) spectroscopy among others can be important in gaining mechanistic insights for key kinetic and transport phenomena that occur across multiple interface length scales. Importantly, understanding the underlying effect of interfacial manipulation on the mechanisms of transport and kinetic processes leads to the development of experimental toolsets and design frameworks applicable to not just current material classes but to forward-looking chemistries that can be applied to next-generation battery materials. Herein, we discuss interfacial control of the composite electrodes via chemical modification techniques toward the creation of reliable, long-lasting, energy-dense lithium-ion batteries.

Coating versus Doping: Understanding the Enhanced Performance of High‐Voltage Batteries by the Coating of Spinel LiNi0.5Mn1.5O4 with Li0.35La0.55TiO3

AbstractLi0.35La0.55TiO3 (LLTO) coated spinel LiNi0.5Mn1.5O4 (LNMO) as cathode material is fabricated by a new method using hydrogen‐peroxide as activating agent. The structure of the obtained active materials is investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray diffraction (XRD), and X‐ray photoelectron spectroscopy (XPS), and the electrochemical properties of the prepared cathodes are probed by the charge–discharge studies. The morphology of the coating material on the surface and the degree of coverage of the coated particles is investigated by the SEM, which shows a fully dense and homogeneous coating (thickness ≈ 7 nm, determined by TEM) on the surface of active material. XRD studies of the coated active materials treated at different temperatures (between 300 °C and 1000 °C) reveal expansion or contraction of the unit cell in dependence of the coating concentration and degree of Ti diffusion. It is concluded, that for the LNMO particles calcined at low temperatures, the LLTO coating layer is still intact and protects the active material from the interaction with the electrolyte. However, for the coated particles treated at high temperatures, Ti ions migrate into the structure of LNMO during the modification process between 500 °C and 800 °C, resulting in “naked” and unprotected particles.

Insights into Enhancing Electrochemical Performance of Li-Ion Battery Anodes via Polymer Coating

Due to the ever-growing importance of rechargeable lithium-ion batteries, the development of electrode materials and their processing techniques remains a hot topic in academia and industry. Even the well-developed and widely utilized active materials present issues, such as surface reactivity, irreversible capacity in the first cycle, and ageing. Thus, there have been many efforts to modify the surface of active materials to enhance the electrochemical performance of the resulting electrodes and cells. Herein, we review the attempts to use polymer coatings on the anode active materials. This type of coating stands out because of the possibility of acting as an artificial solid electrolyte interphase (SEI), serving as an anode protective layer. We discuss the prominent examples of anodes with different mechanisms: intercalation (graphite and titanium oxides), alloy (silicon, tin, and germanium), and conversion (transition metal oxides) anodes. Finally, we give our perspective on the future developments in this field.

Resolving Chemical and Spatial Heterogeneities at Complex Electrochemical Interfaces in Li Ion Batteries

The development of cheap, high energy density electrode materials for Li ion batteries (LIBs) is critical to reaching net zero emissions targets and mitigating climate change. To this end, Ni- and Mn-rich transition metal oxide cathodes simultaneously offer high energy densities as well as cost effective solutions for LIBs. Despite the immense potential of these materials, both Ni- and Mn-rich cathodes suffer from severe interfacial instabilities that lead to crystallographic rearrangement of the active material surface, transition metal dissolution, and the formation of a cathode electrolyte interphase (CEI) layer on the composite surface during electrochemical cycling. While changes in the crystallographic structure of these materials are readily detected with diffraction-based methods, probing the chemistry associated with transition metal dissolution and characterizing the disordered, heterogeneous CEI layer have proven to be substantially more challenging. In this talk, I will discuss our efforts to use a combination of solid-state nuclear magnetic resonance (SSNMR) spectroscopy and X-ray photoemission electron microscopy (XPEEM) to provide information on the CEI deposited on composite cathode films with high chemical and spatial resolution (on the order of nanometers). In situ and operando magnetic resonance spectroscopies are used to correlate specific cathode degradation modes with electrolyte oxidation events. The final properties of the resulting CEI architectures are evaluated in the context of battery performance, where poor capacity retention and high interfacial resistance in LIBs is related to specific surface moieties on the cathode composite.

Amylopectin-Assisted Fabrication of In Situ Carbon-Coated Na3V2(PO4)2F3 Nanosheets for Ultra-Fast Sodium Storage.

Na3V2(PO4)2F3 is one of the most studied polyanion type cathode materials for sodium-ion batteries (SIBs) and offers great promises. However, the inferior rate capability induced by its sluggish diffusion of electrons and ions greatly limits the practical application of electrode materials in SIBs. Herein, we develop an efficient method to fabricate in situ carbon-coated Na3V2(PO4)2F3 nanosheets by using cost-effective amylopectin. The amylopectin not only could induce the nucleation of Na3V2(PO4)2F3 along its backbone to form a 2D nanostructure, but also act as a source of amorphous carbon for in situ coating on the active material surface. The composite exhibits extraordinary rate capability (104 mA h g-1 at 40 C, 51 mA h g-1 at 150 C) and desirable cycling stability. Such satisfactory achievements, especially the superior rate performance, should be ascribed to its unique 2D nanostructure which shortens the Na+ diffusion length, and the in situ carbon coating endows the composites with effective electron transport. Even applied to full cells, the obtained devices still display an exceptionally high energy density (94.8 W h kg-1), high power density (7295 W kg-1), and excellent cyclic stability.

Recent Progress on Graphene-Based Nanocomposites for Electrochemical Sodium-Ion Storage.

In advancing battery technologies, primary attention is paid to developing and optimizing low-cost electrode materials capable of fast reversible ion insertion and extraction with good cycling ability. Sodium-ion batteries stand out due to their inexpensive price and comparable operating principle to lithium-ion batteries. To achieve this target, various graphene-based nanocomposites fabricate strategies have been proposed to help realize the nanostructured electrode for high electrochemical performance sodium-ion batteries. In this review, the graphene-based nanocomposites were introduced according to the following main categories: graphene surface modification and doping, three-dimensional structured graphene, graphene coated on the surface of active materials, and the intercalation layer stacked graphene. Through one or more of the above strategies, graphene is compounded with active substances to prepare the nanocomposite electrode, which is applied as the anode or cathode to sodium-ion batteries. The recent research progress of graphene-based nanocomposites for SIBs is also summarized in this study based on the above categories, especially for nanocomposite fabricate methods, the structural characteristics of electrodes as well as the influence of graphene on the performance of the SIBs. In addition, the relevant mechanism is also within the scope of this discussion, such as synergistic effect of graphene with active substances, the insertion/deintercalation process of sodium ions in different kinds of nanocomposites, and electrochemical reaction mechanism in the energy storage. At the end of this study, a series of strategies are summarized to address the challenges of graphene-based nanocomposites and several critical research prospects of SIBs that provide insights for future investigations.

Improving Fundamental Understanding of Si-Based Anodes Using Carboxymethyl Cellulose (CMC) and Styrene-Butadiene Rubber (SBR) Binder for High Energy Lithium Ion Battery Applications

With increasing demand of high energy density lithium ion batteries, silicon (Si) based anodes are an obvious substitute of graphite based systems due to their high capacity. However, large volume changes of Si during lithiation and delithiation processes causes pulverization of silicon particles. The resulting reduction in electrical continuity and solid electrolyte interphase (SEI) growth within the anode leads to a fast depletion of lithium reservoirs and an accelerates battery failure. High energy lithium ion battery applications such as electrical vehicles and electronic devices require high capacity retention over extended cycling, so improving performance of Si-based anodes is a critical need for many applications.Commonly, a combination of sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) is used as a binder for waterborne Si anode slurries. In these systems, carboxyl (-COOH) groups on CMC form chemical bonding with hydroxyl (-OH) groups on Si active material surface and SBR addition provides enhanced flexibility in the anode layer. Several reports on electrode integrity improvement through adhesion promoters, increased crosslinking, different binding groups, etc. are available in the literature. Delving deeper into the weak mechanical integrity of Si based anodes, and understanding the parameters influencing the fabrication process and subsequent properties, is important. This presentation will focus on several variations in Si based anode slurries and electrodes using CMC-SBR binders. Physical, mechanical, and electrochemical properties are extensively studied as a function of these parameters and will be discussed.

Transmembrane transport characterization across ionic redox transistors using surface-tracked scanning ion conductance microscopy

A fundamental understanding of ion transport at the nanoscale is critical to the development of efficient chemical separation membranes, catalysts, ionic/bio-inspired materials, and its scale up into multi-functional ionic devices. Electrochemical imaging using scanning probe microscopy hardware has provided a method to visualize and understand processes that occur at the surface of ionic active materials. The suite of scanning probe microscopy techniques developed over the last few years are limited to imaging surface-level phenomena and have not been applied to investigate transmembrane properties of synthetic and natural membranes with high spatial and temporal resolution. In this article, we demonstrate the application our recently developed ‘surface-tracked scanning ion conductance microscopy’ technique to characterize voltage-regulated ion transport in an ionic redox transistor. The ionic redox transistor exhibits controlled transmembrane ion transport as a function of its electrochemical redox state. The technique presented in this article uses shear force measured between the nanopipette and ionic substrate to image topography of the porous substrate and simultaneously characterize topography-correlated transmembrane transport through the ionic redox transistor. The transmembrane conductance measured across an array of pores within the ionic redox transistor varies from 0.004 μS/cm (OFF state) to 0.015 μS/cm (ON state). We anticipate that the spatial correlation of transmembrane ion transport in the ionic redox transistor would result in a scale up into smart membrane separators for energy storage, neuromorphic circuits, and desalination membranes.

Graphene Quantum Dot Surface Coating for Improving the Electrochemical Performance of Li-Rich Li1.2Mn0.54Ni0.13Co0.13O2

Lithium-rich Li-ion battery cathode materials possess the virtues of high specific capacities and high working potential, but the severe decay of discharge potential and capacity during repeated cycling hinders the practical applications. Herein, a Li-rich Li1.2Mn0.54Ni0.13Co0.13O2 (LMNCO) material is synthesized by a carbonate co-precipitation method, and then three graphene quantum dots (GQDs)-coated LMNCO materials with different contents of GQDs are fabricated by a solvent evaporation method, in which the GQDs are prepared by a solvothermal method. The GQDs-coated LMNCO material with 3 wt % GQDs demonstrates the best electrochemical performance. For instance, the discharge specific capacity at 0.2C rate is 270.3 mAh g–1. When the charge/discharge current rate increases from 0.2C to 5C, the capacity retention is 47.1%. After 150 cycles at 1C rate, the discharge capacity decreases from 184.2 to 159.4 mAh g–1, with the capacity retained at 86.5%. Surface coating with an appropriate amount of highly conductive GQDs can effectively enhance the electrical conductivity of the LMNCO material and promote the electron transport and charge transfer process and thereby improve the specific capacity and rate performance. Moreover, the GQDs coating layer can impede the side reactions of the active material surface with the electrolyte as well as the surface structure phase transition and therefore boost the cycle stability.

Transformation and migration mechanism of fluorine-containing pollutants in the pyrolysis process of spent lithium-ion battery

Pyrolysis is an effective method to remove organics (e.g. electrolytes and binders) from spent lithium-ion battery (LIB). In this study, the co-pyrolysis characteristics of fluorine-containing substances and active materials from LIB were investigated using thermogravimetric-differential scanning calorimetry (TG-DSC), infrared spectroscopy (IR), and mass spectrometry (MS) analysis. Associated with the pyrolysis, active materials adsorb the residues of electrolyte on the surface and into the pores (20–200 °C), while polyvinylidene fluoride (PVDF) forms a liquid film to cover the local surface of active materials (400–500 °C). These interactions prevent deep removal of organics, leaving fluorine-containing contaminants in active materials. The barrier effect of PVDF liquid mesophase on the removal of organics with secondary liquidous phase formation during pyrolysis was confirmed by in situ optical observation. The migration behavior of fluorine element during the pyrolysis of black mass (BM) from spent LIB was also investigated. With pyrolysis temperature increasing from 100 °C to 600 °C, the dissociable fluorine content in pyrolyzed BM increased from 1.4 wt% to 3.7 wt%. The fluorine-containing contaminants in BM cannot be removed completely by simply increasing pyrolysis temperature. This study provides a better understanding on the transformation of fluorine-containing pollutants during the pyrolysis of BM.

Manipulating Nanoparticle Aggregates Regulates Receptor-Ligand Binding in Macrophages.

The receptor-ligand interactions in cells are dynamically regulated by modulation of the ligand accessibility. In this study, we utilize size-tunable magnetic nanoparticle aggregates ordered at both nanometer and atomic scales. We flexibly anchor magnetic nanoparticle aggregates of tunable sizes over the cell-adhesive RGD ligand (Arg-Gly-Asp)-active material surface while maintaining the density of dispersed ligands accessible to macrophages at constant. Lowering the accessible ligand dispersity by increasing the aggregate size at constant accessible ligand density facilitates the binding of integrin receptors to the accessible ligands, which promotes the adhesion of macrophages. In high ligand dispersity, distant magnetic manipulation to lift the aggregates (which increases ligand accessibility) stimulates the binding of integrin receptors to the accessible ligands available under the aggregates to augment macrophage adhesion-mediated pro-healing polarization both in vitro and in vivo. In low ligand dispersity, distant control to drop the aggregates (which decreases ligand accessibility) repels integrin receptors away from the aggregates, thereby suppressing integrin receptor-ligand binding and macrophage adhesion, which promotes inflammatory polarization. Here, we present "accessible ligand dispersity" as a novel fundamental parameter that regulates receptor-ligand binding, which can be reversibly manipulated by increasing and decreasing the ligand accessibility. Limitless tuning of nanoparticle aggregate dimensions and morphology can offer further insight into the regulation of receptor-ligand binding in host cells.

Unveiling the impact of Mg doping and in-situ Li reactive coating on the Ni-rich cathode material for LIBs

The LiNi0.91Co0.06Mn0.03O2 Ni-rich cathode material is modified with Mg doping and Li3PO4 coating through an efficient and single-step method. The samples are characterized by XPS, XRD, FESEM and FETEM. Cycling results demonstrate that, 1 mol% MgHPO4 modified NCM (MgP-1) exhibits 73.5% capacity retention while pristine sample shows only 50.6% at 4.3 V cycling. The presence of Mg2+ inside the crystal lattice provides pillaring effect during delithiation which screen O2− — O2− repulsion that inhibits the phase transition in the modified samples. These results are confirmed by cyclic voltammetry test. Besides that, transforming the surface residual lithium into lithium phosphate (Li3PO4) coating on the active material surface is facilitating the Li+ diffusion during cycling. In addition, this coating acted as a protective layer against hostile attack of electrolyte. The lower Rct of MgP-1 is due to the Li3PO4 coating which contributes to the highest discharge capacity at high current rate (160.8 mAh g−1 at 2C and 124.6 mAh g−1 3C) as compared to pristine (157.2 mAh g−1 at 2C and 107.2 mAh g−1 at 3C). These results confirm that Mg doping along with Li-ion conductor Li3PO4 coating is a promising technique to control the surface residual lithium and enhance the electrochemical performance of cathode electrode.

Impact of Surface Layer Formation during Cycling on the Thermal Stability of the LiNi0.8Co0.1Mn0.1O2 Cathode

In this study, the effects of charge/discharge cycling on the thermal stability of LiNi0.8Co0.1Mn0.1O2, a high-Ni cathode material, are systematically investigated. X-ray diffraction measurements show that there is almost no change in the bulk structure of the cathode after cycling. However, X-ray absorption fine structure measurements indicate that Ni in the surface layer is reduced and stable rock-salt structures are formed. Differential scanning calorimetry (DSC) measurements show that the heat generation at the lowest temperature, which can trigger thermal runaway in batteries that use high-Ni cathodes, decreases significantly with the formation of rock-salt structures on the active material surface. This finding indicates that the rock-salt layer on the surface enhances the thermal stability of a high-Ni cathode. The change in the total heat generation with degradation, indicated by DSC measurements, is similar to that in the K-edge of Ni (i.e., the Ni valency), suggesting a strong correlation between the heat generation and crystal structure changes during cycling.

Resolving Chemical and Spatial Heterogeneities at Complex Electrochemical Interfaces in Li-Ion Batteries

The high specific capacities of Ni-rich transition-metal oxides have garnered immense interest for improving the energy density of Li-ion batteries (LIBs). Despite the potential of these materials, Ni-rich cathodes suffer from interfacial instabilities that lead to crystallographic rearrangement of the active material surface as well as the formation of a cathode electrolyte interphase (CEI) layer on the composite surface during electrochemical cycling. While changes in crystallographic structure can be detected with diffraction-based methods, probing the chemistry of the disordered, heterogeneous CEI layer is challenging. In this work, we use a combination of ex situ solid-state nuclear magnetic resonance (SSNMR) spectroscopy and X-ray photoemission electron microscopy (XPEEM) to provide chemical and spatial information, on the nanometer length scale, on the CEI deposited on LiNi0.8Mn0.1Co0.1O2 (NMC811) composite cathode films. XPEEM elemental maps offer insight into the lateral arrangement of the electrolyte decomposition products that comprise the CEI and paramagnetic interactions (assessed with electron paramagnetic resonance (EPR) and relaxation measurements) in 13C SSNMR provide information on the radial arrangement of the CEI from the NMC811 particles outward. Using this approach, we find that LiF, Li2CO3, and carboxy-containing structures are directly appended to NMC811 active particles, whereas soluble species detected during in situ 1H and 19F solution NMR experiments (e.g., alkyl carbonates, HF, and vinyl compounds) are randomly deposited on the composite surface. We show that the combined approach of ex situ SSNMR and XPEEM, in conjunction with in situ solution NMR, allows spatially resolved, molecular-level characterization of paramagnetic surfaces and new insights into electrolyte oxidation mechanisms in porous electrode films.