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Gold nanoparticles (Au NPs) and gold-based nanomaterials combine unique properties relevant for medicine, imaging, optics, sensing, catalysis, and energy conversion. While the Turkevich-Frens and Brust-Schiffrin methods remain the state-of-the-art colloidal syntheses of Au NPs, there is a need for more sustainable and tractable synthetic strategies leading to new model systems. In particular, stabilizers are almost systematically used in colloidal syntheses, but they can be detrimental for fundamental and applied studies. Here, a surfactant-free synthesis of size-controlled colloidal Au NPs stable for months is achieved by the simple reduction of HAuCl4 at room temperature in alkaline solutions of low-viscosity mono-alcohols such as ethanol or methanol and water, without the need for any other additives. Palladium (Pd) and bimetallic AuxPdy NPs, nanocomposites and multimetallic samples, are also obtained and are readily active (electro)catalysts. The multiple benefits over the state-of-the-art syntheses that this simple synthesis bears for fundamental and applied research are highlighted.

[NH(CH3)3][CB9H10] and the solid solution [NH(CH3)3][(CB8H9)0.26(CB9H10)0.66(CB11H12)0.08] exhibit polymorphism as a function of temperature. The weakly coordinating carboranes may play an important role as electrolytes for all-solid-state-batteries.

Lithium vanadium fluorophosphate, LiVPO4F, is a promising cathode material for Li-ion batteries because of its high intercalation potential (4.24 V vs Li/Li+) and high stability. However, recent studies show that as-synthesized LiVPO4F very often contains oxygen defects on the fluoride site giving rise to a general composition of LiVPO4F1−yOy with vanadium in a mixed +III/+IV valence state. The inclusion of oxygen naturally influences the electrochemical properties greatly, and a thorough material characterization is necessary to understand the performance. In this study, we synthesize lithium vanadium fluorophosphate by two common strategies: solid-state and hydrothermal synthesis. We show that solid-state synthesis provides LiVPO4F, while the hydrothermal method, in contrast to previous reports, leads to the inclusion of ca. 35% oxygen on the fluoride site and significant disorder in the material. The different electrochemical properties were probed by operando synchrotron X-ray powder diffraction to investigate the effects of oxygen inclusion on the structural evolution during electrochemical lithiation and delithiation. This reveals that while LiVPO4F exhibits a typical biphasic phase evolution, the sample with oxygen inclusion on the fluoride site displays extended solid-solution behavior. This explains previous observations of improved capacity retention due to defects.

Commercially available 18650 Li-ion batteries are considered for high-energy-density storage and usage in mobile applications as well as to store energy from intermittent energy sources. This has triggered intense research for suitable electrode and electrolyte materials, while their current state-of-the-art, temperature-dependent performance is hardly described in detail. The fatigue process in two brands of rechargeable commercial high-energy Li-ion batteries (18650-type, 3500 mAh LiNi0.83Mn0.07Co0.11O2 (NMC-811) and LiNi0.86Co0.11Al0.03O2 (NCA)) as a function of cycling temperature has been investigated using in situ neutron powder diffraction (NPD) and electrochemical impedance spectroscopy (EIS). The batteries (∼140) were cycled at conditions specified by the manufacturer and simulated realistic user conditions with good statistics. Cycling temperature (25, 35, and 45 °C) had a significant influence on capacity fade, with 35 °C showing the highest capacity retention. The NCA cells reached the end-of-life condition of 70% of the initial capacity after only 200 cycles when cycling at 25 °C and 1/0.5C discharging/charging rates. EIS showed that the largest increase in impedance came from the charge-transfer resistance for both cell brands, while one brand also showed a sudden increase in the ohmic resistance, which coincides with a sudden capacity drop. From in situ NPD, the decrease in Li content in the cathode and the anode could be traced as a function of cycle number, and this was found to correlate well with the observed discharge capacity. In addition, Rietveld refinement allowed for the detection of changes in the lattices of the anode and cathode, which were linked to trapping of Li ions in the electrodes.

Commercial 18,650 lithium-ion batteries are cycled at different discharge current rates. It reveals that an accelerated capacity fade occurs for cells at a low discharge rate which is attributed to the loss of lithium inventory (LLI) from the differential voltage analysis (DVA). Cells using high discharge rates exhibit more kinetic loss at the same capacity retention from the analysis of impedance. Characterization techniques, i.e., post-mortem analysis including scanning electron microscopy (SEM) and ex-situ x-ray diffraction (XRD), galvanostatic tests, and in-situ XRD on half-cells made with cathodes and anodes retrieved from the 18,650 batteries, are used to further address the degradation factors. It indicates that the kinetic loss of the high discharge cells can be ascribed to the cathode where more particles are cracked and pulverized. Degradation on the anode is the primary reason for accelerated capacity fade occurring at the low discharge rate. The low discharge current deepens the discharge depth leading the graphite accessing into a higher potential over de-lithiation. Worse interphases and dense agglomerated structure are found from SEM images, which is deemed to result from the anode cycled at a high potential where large volumetric change happens as evidenced by the cycling of new anode half-cells.

18650-type cells comprising of LiNi0.5Co0.2Mn0.3O2 and LiNi0.9Co0.05Al0.05O2 as cathode blend and graphite as anode are cycled in various SoC ranges. Differing capacity fade is found, indicating that cycling in a medium SoC range results in lower capacity loss and behaves better than including high or low SoC in the cycling ranges. Cycling to low SoC tends to have nonlinear capacity fade (sudden capacity drop). Non-destructive methods, i.e. in situ neutron powder diffraction (NPD) and alternating current (AC) impedance, are employed to study the degradation mechanisms. Lithiated cathode loss and loss of lithium inventory (LLI) are calculated from crystal structure parameters refined from the in situ NPD. LLI is the dominating degradation factor for the differing capacity fade of cells. Lithiated cathode loss and solid electrolyte interphase (SEI) growth are deemed to be main fatigue reasons behind the LLI. By investigating the sensitivity of impedance parameters concerning the change in battery capacity, both ohmic resistance (R0) and SEI resistance (R1) present a linear relationship with the change of capacity for both, linear and nonlinear degradation, i.e. R0 and R1 follow the sudden capacity drop, which is ascribed to the formation of new SEI as evidenced by scanning electron microscopy (SEM) images.

18650-type cells with 2.5 Ah capacity are cycled at both 25 °C and 0 °C separately, and at 25 °C two charging protocols (constant current, and constant current-constant voltage charge) are used. Differential voltage analysis (dV/dQ) and alternating current (AC) impedance are mainly used to investigate battery degradation mechanisms quantitatively. The dV/dQ suggests that active cathode loss and loss of lithium inventory (LLI) are the dominating degradation factors. Significant microcracks are observed in the fatigued cathode particles from the scanning electron microscopy (SEM) images. Crystal structure parameters of selected fatigued batteries at fully charged state are determined by in situ high-resolution neutron powder diffraction. Obvious increases of ohmic resistance and solid electrolyte interphase (SEI) resistance occur when the battery capacity fade falls beneath 20%. Continuous charge transfer resistance and Warburg impedance coefficient (W.eff) increase are observed in the course of cycling. Correlation analysis is performed to bridge the gap between material loss as well as LLI and impedance increase. The increase of the charge transfer resistance is related to both active cathode loss and LLI, and a functional relationship is revealed between LLI and W.eff regardless of the used cycling protocols.