3D nano-rheology microscopy : Operando nanomapping of 3D mechanical nanostructure of SEI in Na-ion batteries

The Solid Electrolyte Interphase (SEI) is a nanoscale thickness passivation layer that is formed as the product of electrolyte decomposition through a combination of chemical and electrochemical reactions in the cell and defines the fundamental battery properties - its capacity, cycle stability and safety. While local mechanical properties of SEI hold a clue to its performance, their operando characterisation is difficult as one has to probe nanoscale surface features in electrochemical environment that are also dynamically changing. Here, we report novel 3D nano-rheology microscopy (3D-NRM) that uses a tiny (sub-nm to few nm) lateral dithering of the sharp SPM tip at kHz frequencies to probe the minute sample reaction forces. By mapping the increments of the real and imaginary components of these forces, while the tip penetrates the soft interfacial layers, we obtain the true 3D nanoscale structure of sub–m thick layers [1]. 3D-NRM allows to elucidate the key role of solvents in SEI formation and predict the conditions for building SEI for robust, safe and efficient Li-ion and Na-ion batteries. Here, we discuss the extension of these studies on smooth HOPG and inhomogeneous and rough copper anodes as sodium ion battery electrodes. Essentially, the new approach allows nanoscale characterisation of SEI with a few nm precision on the electrodes with 1000 nm roughness, and quantitatively evaluate the real and imaginary parts of the elastic moduli over the whole thickness of SEI layer. The observation of the change in moduli and the tip-surface distance helps to evaluate the growth of SEI as a function of the electrolyte, additives, electrode material and charge-discharge rate. We believe that such evaluation of key interfacial nanomechanical properties of SEI will allow us to develop the electrochemically and mechanically robust SEI surface passivation layer and the development of efficient and safe rechargeable batteries

Revealing the nanoscale fundamentals of batteries performance via x-sectional in-situ/operando Electrochemical SPM

Scanning Probe Microscopy (SPM) techniques have provided essential solutions for probing the nanophysical properties of battery materials, such as nano-electronic/ionic conductivity of battery materials [1] and Young's moduli of solid electrolyte interphase (SEI).[2] More significantly, in-situ/operando electrochemical (EC) SPM, operating simultaneously with the potentiometry/voltammetry in liquid electrochemical systems, has distinct advantages for observing the dynamic electrochemical processes (DEPs) happening on battery electrode/SEI-electrolyte (solid-liquid) interfaces,[3] especially the SEI formation and ion intercalation, which are critically important for lithium/sodium-ion batteries. However, so far, the direct observations of the solid-liquid interfaces using in-situ/operando SPM are hindered by the rough topography and inhomogeneity on the battery solid electrode side. In this work we introduce the Beam Exit x-section nano-polishing (BEXP) to expand the studies of the commonly used model electrode, such as HOPG, with ultra-flat carbon atomic terraces and steps, to nano-sections of commercial composite electrodes (Fig.1a), and to artificial atomic scale steps in layered battery materials (Fig.1b). This enables the studies of ion-intercalations and SEI formations in the real-life materials for lithium/sodium ion batteries by a variety of in-situ/operando EC SPM modes. Furthermore, to overcome the limitation of traditional in-situ/operando EC SPM, that limit imaging to the immediate sample surface, we adapted the Ultrasonic force microscopy (UFM) [4] and Shear Force Modulation Microscopy (SFMM) modes to operation in the liquid electrolyte environment. With these ‘tip invasive’ SPM modes, the three-dimensional (3D) nano-rheology of the SEI layers was employed to provide detailed understanding of the in-depth distribution of the organic/inorganic species in SEI across the 2D area of the electrodes. The novel 3D nanorheology approach provides a 3D map of viscoelastic (complex phase and amplitude) response of the SIE to the local in-plane (shear) and out-of-plane modulation of the SPM tip. By introducing the complementary sample preparation method and advanced SPM modes, several important DEPs, which are deeply ‘buried’ inside the operating lithium/sodium-ion battery, were observed in liquid electrolyte environment under battery operation conditions for the first time. To be specific, as shown in Fig. 1a, the dynamic CEI formations on the BEXP-polished commercial electrode surface was recorded by operando EC UFM mechanical mapping with high material sensitivity/contrast. The SEI formation on the graphite carbon atomic terraces and artificial steps were monitored and compared by operando SPM as shown in Fig. 1b, which confirmed that the SEIs formation are ‘defect-related’ at non-intercalation voltage range, while the SEIs formed on the edge sites are mainly ‘intercalation-related’ within the intercalation voltage range. Moreover, SSFM were used to study the 3D nanorheology of SEI layers formed on deep-lithiated/sodiated LTO/NTO anode surface. As shown in the torsional phase-Z approach-retract spectra in Figs. 1c, a significant phase shift can be found on the spectra C with clear transition from the viscoelastic response of the outer SEI layers to the solid-like response closer to the electrode surface. Furthermore, the 3D mechanical properties and exact geometry of the SEI layers can be reconstructed by the deconvolution of shear (torsional) amplitude and out-of-plane (vertical) deformation signals. An expansion to the lithium-ions intercalation induced cathode insulator-to-metal transition [5, 6] and the anode volume expansion/contraction [7] will also be discussed in this presentation. In each characterization example, special attention will be paid to correlate the nanoscale SPM characterization results with the macroscopic battery performance, demonstrating the significant advantages of these in-situ/operando EC SPM approaches on the studies of energy materials and micro/nano-scale processes

Synthesis, characterisation, and feasibility studies on the use of vanadium tellurate (VI) as a cathode material for aqueous rechargeable Zn-ion batteries

(NH4)4{(VO2)2[Te2O8(OH)2]}·2H2O is tested as a cathode in an aqueous Zn-ion battery for the first time, showing a discharge capacity of 283 mA h g−1 in half-cells and excellent capacity retention (91%) in concentration cells after 20 cycles

Solid-state synthesis of coordination polymers for [2+2] photoreactions by grinding

10.1071/CH09473Australian Journal of Chemistry634589-595AJCH

Synthesis of first acyclic trinuclear ruthenium(II) phenolate schiff base complex from acyclic tripodal and macrobicyclic ligands

442-450An acyclic trinuclear ruthenium(II) Schiff base complex Ru3H3L1(DMSO)6Cl6, 1, has been isolated for the first time from preformed acyclic tripodal ligands H3L1, H3L2 and also from macrobicyclic ligand H3L3 instead of the dinuclear ruthenium complex 2. The ligand H3L1 crystallizes in space group R and exhibits carry over of molecular trigonal symmetry into crystal. Trigonal network is due to intermolecular interactions of aminomethylene (N-CH2) proton and formyl (CH=O) oxygen. The CSD analysis reveals that N-C-H... O=CH interaction is unique. The complex Ru3H3L1(DMSO)6Cl6 1 crystallizes in triclinic P space group. Each ruthenium atom is coordinated by phenolic and formyl oxygens of ligand, sulphur atoms of two DMSO moieties in equitorial plane and two chloride ions in axial positions providing distorted octahedral geometry. The Ru-Ru distances in complex 1 indicate that there is no interaction between the metal centers. Further reaction of complex 1 with tren and ruthenium metal does not yield macrobicyclic complex 2 showing the inertness of the coordinated formyl group towards Schiff base condensation. The electronic spectrum of the complex shows charge transfer bands while cyclic voltammetry in dichloromethane solvent gives a single reversible redox couple at E1/2 = 0.87 V (vs Ag-AgCl) corresponding to Ru(II) to Ru(III) oxidation

High-energy NCA cells on idle:anode versus cathode driven side reactions

We report on the first year of calendar ageing of commercial high‐energy 21700 lithium‐ion cells, varying over eight state of charge (SoC) and three temperature values. Lithium‐nickel‐cobalt‐aluminium oxide (NCA) and graphite with silicon suboxide (Gr‐SiOx) form cathodes and anodes of those cells, respectively. Degradation is fastest for cells at 70–80 % SoC according to monthly electrochemical check‐up tests. Cells kept at 100 % SoC do not show the fastest capacity fade but develop internal short circuits for temperatures T≥40 °C. Degradation is slowest for cells stored close to 0 % SoC at all temperatures. Rates of capacity fade and their temperature dependencies are distinctly different for SoC values below and above 60 %, respectively. Differential voltage analyses, apparent activation energy analysis, and endpoint slippage tracking provide useful insights into the degradation mechanisms and the respective roles of anode and cathode potential. We discuss how reversible losses of lithium might play a role in alleviating the rate of irreversible losses on commercial cells

Parametrisation and use of a predictive DFN model for a high­energy NCA/Gr­SiOx battery

We demonstrate the predictive power of a parametrised Doyle­Fuller­Newman (DFN) model of a commercial cylindrical (21700) lithium­ion cell with NCA/Gr­SiOx chem­ istry. Model parameters result from the deconstruction of a fresh commercial cell to deter­ mine/confirm chemistry and micro­structure, and also from electrochemical experiments with half­cells built from electrode samples. The simulations predict voltage profiles for (i) galvanostatic discharge and (ii) drive­cycles. Predicted voltage responses deviate from measured ones by <1% throughout at least ∼95% of a full galvanostatic discharge, whilst the drive cycle discharge is matched to a ∼1­3% error throughout. All simulations are performed using the online computational tool DandeLiion, which rapidly solves the DFN model using only modest computational resource. The DFN results are used to quantify the irreversible energy losses occurring in the cell and deduce their location. In addition to demonstrating the predictive power of a properly validated DFN model, this work pro­ vides a novel simplified parametrisation workflow that can be used to accurately calibrate an electrochemical model of a cell

High‐Energy Nickel‐Cobalt‐Aluminium Oxide (NCA) Cells on Idle: Anode‐ versus Cathode‐Driven Side Reactions

International audienceWe report on the first year of calendar ageing of commercial high-energy 21700 lithium-ion cells, varying over eight state of charge (SoC) and three temperature values. Lithium-nickelcobalt-aluminium oxide (NCA) and graphite with silicon suboxide (Gr-SiO x) form cathodes and anodes of those cells, respectively. Degradation is fastest for cells at 70-80 % SoC according to monthly electrochemical checkup tests. Cells kept at 100 % SoC do not show the fastest capacity fade but develop internal short circuits for temperatures T ⩾ 40°C. Degradation is slowest for cells stored close to 0 % SoC at all temperatures. Rates of capacity fade and their temperature dependencies are distinctly different for SoC values below and above 60 %, respectively. Differential voltage analyses, apparent activation energy analysis, and endpoint slippage tracking provide useful insights into the degradation mechanisms and the respective roles of anode and cathode potential. We discuss how reversible losses of lithium might play a role in alleviating the rate of irreversible losses on commercial cells

Key design considerations for synthesis of mesoporous alpha-Li3V2(PO4)(3)/C for high power lithium batteries

10.1016/j.electacta.2021.137831ELECTROCHIMICA ACTA37

Entropy Profiling for the Diagnosis of NCA/Gr-SiOx Li-Ion Battery Health

Graphite-silicon (Gr-Si) blends have become common in commercial Li-ion battery negative electrodes, offering increased capacity over pure graphite. Lithiation/delithiation of the silicon particles results in volume changes, which may be associated with increased hysteresis of the open circuit potential (OCP). The OCP is a function of both concentration and temperature. Entropy change measurement, which probes the response of the OCP to temperature, offers a unique battery diagnostics tool. While entropy change measurements have previously been applied to study degradation, the implications of Si additives on the entropy profiles of commercial cells have not been explored. Here, we use entropy profiling to track aging markers in the same way as differential voltage analysis. In addition to lithiation/delithiation hysteresis in the OCP of Gr-Si blends, cells with Gr-Si anodes also exhibit differences in entropy profile depending on cycling direction, reflecting degradation-related morphological changes. For cycled cells, entropy change decreased during discharge, likely corresponding to graphite particles breaking and cracking. However, entropy change during charge increased with cycling, likely due to the volume change of silicon. Over a broad voltage range, these combined effects led to the observed rise in entropy hysteresis with age. Conversely, for calendar aged cells entropy hysteresis remained stable