Adding silicon (Si) to graphite (Gr) anodes is an effective approach for boosting the energy density of lithium-ion batteries, but it also triggers mechanical instability due to Si volume changes upon (de)lithiation reactions. In this work, component-specific (de)lithiation dynamics on Si-rich (30 and 70 wt.% Si) SiGr anodes at various charge/discharge C-rates are unveiled and compared to a graphite-only electrode (100Gr) via operando synchrotron X-ray diffraction coupled with differential capacity plots analysis. Results show preferential lithiation of amorphous Si above approximate to 200 mV and competing lithiation of Gr, amorphous Si, and crystalline Si below approximate to 200 mV. Discharge proceeds via sequential delithiation of Gr and amorphous lithium silicide. Si shifts the interconversion potentials of graphite intercalation compounds, lowering the Gr state of charge compared to 100Gr. In the 30% Si electrode, crystalline Si amorphization at potentials <110 mV is found to be kinetically hindered at C-rates higher than C/5, which can be key for enhancing the cycling stability of SiGr anodes. The 70% Si electrode exhibits restricted lithium diffusion in Gr, full Si amorphization, and Li15Si4 formation. These findings related to the potential- and current-dependent dynamic changes on SiGr blends are crucial for designing stable high energy density SiGr anodes.

SiO2 structures show great promise for increasing the energy density of anodes for next-generation lithium-ion batteries (LIBs). However, high control of the area, porosity, and morphology of SiO2 particles is critical to optimize anodes electrochemical performance, and the lack of sustainable methods for producing SiO2 particles with tailored properties at the nano- and microscale represents a serious challenge. Exoskeletons of diatoms (microalgae) display nanoporous structures made of SiO2, and each diatom species grows SiO2 exoskeletons with unique morphology. In this work, we show that by performing the first comparative analysis of the species-dependent electrochemical performance of diatom-based anodes, we are introducing a new concept in which single-species diatoms with preferred physical and textural properties can be carefully chosen and cultivated to develop anode materials with optimized electrochemical performance for next-generation LIBs. SiO2 anodes made using SiO2 exoskeletons from two cultured diatom species, Nitzschia sp. and Craspedostauros sp., with diatomaceous earth as the active material are presented. Pristine micron-sized frustules exhibiting areas of 85.4, 47.1, and 2.0 m2 g–1 displayed specific capacities of 811, 747, and 520 mAh g–1, respectively, after 100 cycles at 100 mA g–1 and capacity retention up to ∼97% after 200 cycles. Results show that significant improvement on specific capacity, cycle life, and rate capability of SiO2 anodes can be achieved by selecting diatom species growing desired SiO2 structures. The presented results aim to unveil the potential of the wide variability of diatom exoskeletons physical properties to optimize anode performance, opening the path for the sustainable production of outperforming Si-based anodes for next-generation LIBs.

Graphite is the most used anode material for current-generation lithium-ion batteries due to its beneficial cycle life, availability and reasonable rate capability. Still, the modest capacity of 372 mAhg -1 represents a bottleneck in the pursuit of high-energy density anodes. Enabling much higher theoretical capacities of 3600 mAhg -1 [1], silicon represents a promising candidate as anode material for next generation batteries. However, the alloying-based lithiation mechanism of silicon is accompanied by a large volumetric change of up to 300% upon cycling, leading to fast degradation due to electrode pulverization, continuous SEI formation and extensive electrolyte consumption. Even though shallow cycling of silicon anodes has been demonstrated in laboratory scale cells [2], the mixing of silicon with graphite is considered the most viable approach to lift energy density while maintaining appropriate cycle life. Due to the fundamentally different kinetics and potentials of Li insertion and extraction of both materials, the development of silicon-graphite composite electrodes is not straightforward. One of the key questions for optimization is how the incorporation of silicon impacts the (de)lithiation behavior of graphite as a function of the silicon:graphite mass ratio, operating current and electrode potential. While lithiation of graphite in composite electrodes of 15 wt% silicon has been shown to occur in a similar manner as pure graphite, higher fractions of silicon are expected to exert more stress on the graphite and represent kinetic barriers for Li diffusion. This study presents results from in-situ X-ray diffraction experiments (XRD) of silicon-graphite/Li half cells conducted at the European Synchrotron Radiation Facility (ESRF). Serving as a reference, the current-dependent (de)lithiation behavior of a pure graphite/Li half cell has been thoroughly investigated and systematically compared to the (de)lithiation behavior of two selected silicon-graphite composite anodes (silicon:graphite ratio of 30:70 and 70:30, respectively) exposed to the same formation cycle and C-rate protocol. An optimized and novel measurement setup was used, based on a perforated current collector of the anode, providing a complete picture of the graphite in-plane and interplanar structural changes as well as the evolution of semicrystalline silicon peaks which would usually be obscured by the current collector signal. By correlating the electrochemical features (voltage curve and differential capacity plot) with the in-situ diffraction data, it was possible to identify and assign the occurrence and absence of dilute-stage and ordered graphite intercalation compounds (GICs) for the respective electrodes, yielding an in-depth insight into the graphite state of charge upon (de)lithiation and how it is influenced by the silicon content and applied C-rate. As expected, the silicon is (de)lithiated within the entire potential range, whereas graphite is most electrochemically active at potentials lower than 260 mV. In both composite electrodes, graphite attains a lower lithiation degree compared to pure graphite. This is because the high theoretical capacity of silicon results in high specific currents, ultimately challenging the rate capability of graphite. Moreover, the high delithiation overpotential encountered in the composite electrodes results in a highly asymmetrical lithiation/delithiation behavior of graphite. Also, graphite lithiation is less uniform in the composite anodes, indicated by the coexistence of dilute GICs upon (de)lithiation, compared to pure graphite where dilute phases are fully consumed (formed) as (de)lithiation progresses. Surprisingly, the in-situ XRD studies did not reveal signs of structural degradation and strain of graphite as a result of mechanical interaction with silicon. Instead, the volume change of graphite is well correlated with the amorphization of crystalline, unreacted silicon and the volume evolution of silicon crystallites upon charge-discharge. To mitigate the observed effects, the work suggests nanostructuring and advanced electrode architectures towards higher utilization and more homogeneous lithiation of graphite. Overall, the study provides a demonstration of a suitable operando cell for studies of anodes for Li-based systems, and aids the rational design of silicon-graphite composite anodes. References: [1] M.N. Obrovac and L. Christensen, Electrochem. Solid State Letters (2004) vol. 7, A93-A96 [2] T. Eguchi, K. Sawada, M. Tomioka and S. Kumagi, Electrochim. Acta (2021), 394, 139115. [3] K.P. C. Yao, J. S. Okasinski, K. Kalaga, J. D. Almer, and D. P. Abraham, Adv. Energy Mater. (2019), 9, 1803380 Figure caption: A: Structure of the in-situ coin cell. B: Image of the electrode backside, showing the perforated current collector, the electrode active material and the spots of acquired diffractograms. C: In-situ XRD plot, voltage curve and differential capacity plot of a 30:70 silicon:graphite electrode operated at C/5. Five different stages of the (de)lithiation process are denoted. Figure 1

Abstract SiO2 is a promising material for developing high-capacity anodes for lithium-ion batteries (LIBs). However, degradation behavior of SiO2 anodes upon prolonged electrochemical cycling remains unexplored. In this work, the causes leading to capacity fade on SiO2 anodes are investigated and simple strategies to attenuate anode degradation are explored. Nanostructured SiO2 from diatomaceous earth was integrated into anodes containing different quantities of conductive carbon in the form of either a conductive additive or a nanometric coating layer. Galvanostatic cycling was conducted for 200 cycles and distinctive trends on capacity fade were identified. A thorough analysis of the anodes at selected cycle numbers was performed using a toolset of characterization techniques, including electrochemical impedance spectroscopy, FIB-SEM cross-sectional analysis and TEM inspections. Significant fragmentation of SiO2 particles surface and formation of filigree structures upon cycling are reported for the first time. Morphological changes are accompanied by an increase in impedance and a loss of electroactive surface area. Carbon-coating was found to restrict particle fracture and increase capacity retention to 66% compared to 47% for uncoated samples after 200 cycles. Results provide valuable insights to improve cycling stability of SiO2 anodes for next-generation LIBs.

The effect of point defects and interactions with thesubstrateare shown by density functional theory calculations to be of significantimportance for the structure and functional properties of hexagonalboron nitride (h-BN) films on highly ordered pyrolytic graphite (HOPG)and Ni(111) substrates. The structure, surface chemistry, and electronicproperties are calculated for h-BN systems with selected intrinsic,oxygen, and carbon defects and with graphene hybrid structures. Theelectronic structure of a pristine monolayer of h-BN is dependenton the type of substrate, as h-BN is decoupled electronically fromthe HOPG surface and acts as bulk-like h-BN, whereas on a Ni(111)substrate, metallic-like behavior is predicted. These different film/substratesystems therefore show different reactivities and defect chemistries.The formation energies for substitutional defects are significantlylower than for intrinsic defects regardless of the substrate, andvacancies formed during film deposition are expected to be filledby either ambient oxygen or carbon from impurities. Significantlylower formation energies for intrinsic and oxygen and carbon substitutionaldefects were predicted for h-BN on Ni(111). In-plane h-BCN hybridstructures were predicted to be terminated by N-C bonding.Substitutional carbon on the boron site imposes n-type semiconductivityin h-BN, and the n-type character increases significantly for h-BNon HOPG. The h-BN film surface becomes electronically decoupled fromthe substrate when exceeding monolayer thickness, showing that thesurface electronic properties and point defect chemistry for multilayerh-BN films should be comparable to those of a freestanding h-BN layer.

A first-principles study of the tetragonal tungsten bronze (TTB) K4Bi2Nb10O30 has suggested that the Bi 6s lone pair causes in-plane polarization (within the a-b plane), corresponding to the one found in Pb5Nb10O30 (PN), in contrast to the out-of-plane polarization (along c) found in most TTBs. Replacing PN with KBN potentially opens for a leadfree analogue to morphotropic phase boundaries known in TTBs based on PN. Here, we report on the synthesis and properties of A4Bi2Nb10O30 (ABN, A = Na, K, Rb) with the objective to determine the structure and electrical properties, paying particular attention to the role of the Bi 6s lone pair. The ABN materials were synthesized via conventional solid-state synthesis in a two-step process. Convergent-beam electron diffraction demonstrated a centrosymmetric tetragonal space group for the two compounds KBN and RBN, and ferroelectric polarization-electric field measurements confirmed the lack of hysteretic behavior in line with the observed centrosymmetric symmetry. Non-ambient powder X-ray diffraction demonstrated the signature of a phase transition for KBN and RBN, as several weak satellite reflections vanished during heating and reappeared upon cooling. Dielectric spectroscopy supported the observation of an anomaly due to the presence of a weak maximum in the electrical permittivity at temperatures corresponding to the disappearance of the satellite reflections. Possible explanations for the absence of polarization in ABN TTBs are discussed with particular attention to the suppression of the 6s2 lone pair effect of Bi and the size of A-site cations in the TTB crystal structure.

Atom probe tomography (APT) is a 3D analysis technique that offers unique chemical accuracy and sensitivity with sub-nanometer spatial resolution. Recently, there is an increasing interest in the application of APT to complex oxides materials, giving new insight into the relation between local variations in chemical composition and emergent physical properties. However, in contrast to the field of metallurgy, where APT is routinely applied to study materials at the atomic level, complex oxides and their specific field evaporation mechanisms are much less explored. Here, we perform APT measurements on the hexagonal manganite ErMnO3 and systematically study the effect of different experimental parameters on the measured composition and atomic structure. We demonstrate that both the mass resolving power (MRP) and compositional accuracy can be improved by increasing the charge-state ratio (CSR) working at low laser energy (< 5 pJ). Furthermore, we observe a substantial preferential retention of Er atoms, which is suppressed at higher CSRs. We explain our findings based on fundamental field evaporation concepts, expanding the knowledge about the impact of key experimental parameters and the field evaporation process in complex oxides in general.

Ni-rich layered oxides are proven high-energy cathode materials for Li-ion batteries, but their characteristic short cycle life remains a challenge for implementation on a wider scale. The surface reactivity of Ni-rich layered oxides is the driving force for several capacity fading mechanisms, and a common strategy to combat these issues is to apply a protective surface coating. In this work, LiNi0.88Mn0.06Co0.06O2 (NMC) is surface-modified using octadecyl phosphonic acid (OPA) as a coupling agent through a wet-chemical process. Post-treatments of the coated NMC material at 350 and 450 degrees C in an O-2 atmosphere are also evaluated. Physical characterization confirms the presence of a surface coating and confirms that the surface modification processing has a negligible effect on the bulk material structure. The bare NMC material shows an initial discharge capacity of 199 mAh/g in NMC||LTO cells. The coated NMC material shows a slightly lower initial discharge capacity of 188 mAh/g, but the capacity retention after 210 cycles improves from 86 to 95%. The coated NMC material shows higher discharge capacities than the bare NMC material beyond cycle 75. Postmortem characterizations indicate that the surface reactivity is reduced by the OPA coating as less fluorinated byproducts are formed. The high-temperature post-treatments of the coated NMC material change the surface chemistry but do not improve the electrochemical performance.

Abstract $$\hbox {SiO}_2$$ SiO 2 is a promising material for developing high-capacity anodes for lithium-ion batteries (LIBs). However, microstructural changes of $$\hbox {SiO}_2$$ SiO 2 anodes at the particle and electrode level upon prolonged cycling remains unclear. In this work, the causes leading to capacity fade on $$\hbox {SiO}_2$$ SiO 2 anodes were investigated and simple strategies to attenuate anode degradation were explored. Nanostructured $$\hbox {SiO}_2$$ SiO 2 from diatomaceous earth was integrated into anodes containing different quantities of conductive carbon in the form of either a conductive additive or a nanometric coating layer. Galvanostatic cycling was conducted for 200 cycles and distinctive trends on capacity fade were identified. A thorough analysis of the anodes at selected cycle numbers was performed using a toolset of characterization techniques, including electrochemical impedance spectroscopy, FIB-SEM cross-sectional analysis and TEM inspections. Significant fragmentation of $$\hbox {SiO}_2$$ SiO 2 particles surface and formation of filigree structures upon cycling are reported for the first time. Morphological changes are accompanied by an increase in impedance and a loss of electroactive surface area. Carbon-coating is found to restrict particle fracture and to increase capacity retention to 66%, compared to 47% for uncoated samples after 200 cycles. Results provide valuable insights to improve cycling stability of $$\hbox {SiO}_2$$ SiO 2 anodes for next-generation LIBs.

Hexagonal manganites, RMnO3 (R = Sc, Y, Ho-Lu), are potential oxygen storage materials for air separation due to their reversible oxygen storage and release properties. Their outstanding ability to absorb and release oxygen at relatively low temperatures of 250–400 °C holds promise of saving energy compared to current industrial methods. Unfortunately, the low temperature of operation also implies slow kinetics of oxygen exchange in these materials, which would make them inefficient in applications such as chemical looping air separation. Here, we show that the oxidation kinetics of RMnO3 can be improved through Ti4+-doping as well as by increasing the rare earth cation size. The rate of oxygen absorption of nanocrystalline RMn1–xTixO3 (R = Ho, Dy; x = 0, 0.15) was investigated by thermogravimetric analysis, X-ray absorption near-edge structure, and high-temperature X-ray diffraction (HT-XRD) with in situ switching of atmosphere from N2 to O2. The kinetics of oxidation increases for larger R and even more with Ti4+ donor doping, as both induce expansion of the ab-plane, which reduces the electrostatic repulsion between oxygen in the lattice upon oxygen ion migration. Surface exchange rates and activation energies of oxidation were determined from changes in lattice parameters observed through HT-XRD upon in situ switching of atmosphere.

Lithium-ion capacitors (LICs) represent promising high-power energy storage devices, most commonly composed of a lithium-ion intercalation anode (e. g., graphite or hard carbon), a supercapacitor activated carbon (AC) cathode, and an electrolyte with 1 M LiPF6 in carbonate solvents. LiPF6 is susceptible to hydrolysis, forming HF, which leads to challenges for disassembly and recycling, risks during hazardous events, and extensive energy consumption during production. Here, we report on the feasibility of replacing LiPF6 with the non-hydrolysing salt LiFSI for use with AC electrodes. Based on voltage hold measurements in a half-cell setup, good long-term stability is achieved with an upper cut-off voltage of 3.95 V vs. Li/Li+, potentially enabling cell voltages of similar to 3.8 V when combined with graphite or silicon-based anodes (operating at similar to 0.1 V vs. Li/Li+) in LIC full cells. The lower cut-off voltage was determined to be 2.15 V vs. Li/Li+. The systematic comparison of CV, leakage current analysis and capacity retention upon voltage hold highlights the importance of the latter method to provide a realistic assessment of the electrochemical stability window (ESW) of LiFSI on a commercial AC electrode. The morphological and surface-chemical post-mortem analysis of AC electrodes used with LiFSI revealed that the oxidation of the FSI anion, as evidenced by the presence of new S 2p and N 1s features in the XPS spectra, and an increasing number of oxygenated species on the AC were the main processes causing capacity fade at positive polarization.

The Front Cover shows our in-situ X-ray diffraction setup for analysing the crystallization process in oxide thin films made by chemical solution deposition. By adjusting the process parameters, the nucleation and growth conditions are changed and the degree of preferred orientation and epitaxi in the oxide films can be tailored. This change is illustrated by the change in microstructure of the polycrystalline films with random orientation (left) towards highly oriented cube-on-cube grown films (right) where the film unit cell follows that of the substrate. This effect can be observed experimentally by the appearance of spot reflection instead of full diffraction rings on the detector. More information can be found in the Full Paper by Kristine Bakken et al.

Ferroelectric properties of thin films can be enhanced by crystallographic texture. In this work, we report on how heat treatment of films can be designed to tailor the degree of preferential orientation in BaTiO3-based thin films from aqueous chemical solution deposition. In situ synchrotron X-ray diffraction in combination with Rietveld refinements was used to study the crystallization process of films from a single deposition and to give an in-depth characterization of the crystallographic texture of the films. Transmission electron microscopy was employed to evaluate the microstructure and degree of preferred orientation in thicker films from multiple depositions. Texture was induced in the multilayer films by a repeated annealing process. Cube-on-cube growth was demonstrated to occur in both single and multi-layered films provided the heating program was designed to give limited nucleation and growth below the threshold for where cube-on-cube growth is favoured, resulting in a very high degree of preferred orientation. The cube-on-cube grown films were relaxed with respect to the lattice unit cell mismatch between the film and the substrate, where the relaxation of stress depends on the film thickness. Texture and cube-on-cube growth were demonstrated on several types of single-crystal oxide substrates. Calcium and zirconium substitution did not alter the crystallization process, but zirconium slowed down the texture formation kinetics. The ferroelectric response was strongest in the films with a high degree of preferred orientation.

Gadolinium molybdate is a classical example of an improper ferroelectric and ferroelastic material. It is established that the spontaneous polarization arises as a secondary effect, induced by a structural instability in the paraelectric phase, which leads to a unit cell doubling and the formation of a polar axis. However, previous X-ray diffraction studies on gadolinium molybdate have been restricted by the limited ability to include the entire 2{\theta} range in the analysis, and thus, at atomic scale, much remains to be explored. By applying temperature dependent X-ray diffraction, we observe the transition from the paraelectric tetragonal phase to the orthorhombic ferroelectric phase. The ferroelastic strain is calculated based on the thermal evolution of the lattice parameters and Rietveld refinement of the temperature dependent data reveals that the displacement of different cations follows different critical behavior, providing new insight into the structural changes that drive the improper ferroelectricity in gadolinium molybdate.

The crystal structure of tetragonal tungsten bronzes, with the general formula A12A24C4B12B28O30, is flexible both from a chemical and structural viewpoint, resulting in a multitude of compositions. The A1 and A2 lattice sites, with different coordination environments, are usually regarded to be occupied by two different cations such as in Ba4Na2Nb10O30 with Na+ and Ba2+ occupying the A1 and A2 sites, respectively. Here, we report on a systematic study of the lattice site occupancy on the A1 and A2 sites in the series Ba4M2Nb10O30 (M = Na, K, and Rb). The three compounds were synthesized by a two-step solid-state method. The site occupancy on the A1 and A2 sites were investigated by a combination of Rietveld refinement of X-ray diffraction patterns and scanning transmission electron microscopy with simultaneous energy-dispersive spectroscopy. The two methods demonstrated consistent site occupancy of the cations on the A1 and A2 sites, rationalized by the variation in the size of the alkali cations. The cation order-disorder phenomenology in the tungsten bronzes reported is discussed using a thermodynamic model of O'Neill and Navrotsky, originally developed for cation interchange in spinels.

Ferroelectric properties of films can be tailored by strain engineering, but a wider space for property engineering can be opened by including crystal anisotropy. Here, we demonstrate a huge anisotropy in the dielectric and ferroelectric properties of BaTiO3 films. Epitaxial BaTiO3 films deposited on (100), (110), and (111) SrTiO3 substrates were fabricated by chemical solution deposition. The films were tensile-strained due to thermal strain confirmed by the enhanced Curie temperature. A massive anisotropy in the dielectric constant, dielectric tunability, and ferroelectric hysteresis loops was observed depending on the in-plane direction probed and the orientation of the films. The anisotropy was low for (111) BaTiO3, while the anisotropy was particularly strong for (110) BaTiO3, reflecting the low in-plane rotational symmetry. The anisotropy also manifested at the level of the ferroelectric domain patterns in the films, providing a microscopic explanation for the macroscopic response. This study demonstrates that the properties of ferroelectric films can be tailored not only by strain but also by crystal orientation. This is particularly interesting for multilayer stacks where the strain state is defined by the boundary conditions. We propose that other materials can be engineered in a similar manner by utilizing crystal anisotropy.

Carbonate formation is a prevailing challenge in synthesis of BaTiO3, especially through wet chemical synthesis routes. In this work, we report the phase evolution during thermal annealing of an aqueous BaTiO3 precursor solution, with a particular focus on the structures and role of intermediate phases forming prior to BaTiO3 nucleation. In situ infrared spectroscopy, in situ X-ray total scattering, and transmission electron microscopy were used to reveal the decomposition, pyrolysis, and crystallization reactions occurring during thermal processing. Our results show that the intermediate phases consist of nanosized calcite-like BaCO3 and BaTi4O9 phases and that the intimate mixing of these along with their metastability ensures complete decomposition to form BaTiO3 above 600 °C. We demonstrate that the stability of the intermediate phases is dependent on the processing atmosphere, where especially enhanced CO2 levels is detrimental for the formation of phase pure BaTiO3.