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CO partial current densities of 144 [6g] and 147 mA cm −2 , [7a] respectively.Here, we investigate the electrocatalytic performance and stability of a GDE design for the electrocatalytic reduction of gaseous CO 2 employing earth-abundant tin/copper (Sn/Cu) catalysts. Sn-decorated Cu surfaces were shown previously to provide high selectivity for CO 2 to CO conversion in aqueous electrolyte and achieve CO partial current densities of up to 11.5 mA cm −2 . [8] However, at higher current densities, the hydrogen evolution reaction (HER) starts to dominate due to insufficient CO 2 supply. [8b] To enhance CO 2 mass transport, we develop a process to fabricate electrospun polyvinylidene fluoride (PVDF) nanofibers with uniform Cu coating, and employ electrochemical underpotential deposition (UPD) of Sn to decorate the Cu surface. We demonstrate that Sn/Cu-coated PVDF (Sn/Cu-PVDF) nanofiber GDEs have CO faradaic efficiencies (FEs) above 80%, and achieve high CO partial current densities of up to 104 mA cm −2 , representing the highest reported current density for a Sn/Cu-based catalyst for CO 2 RR to CO.We employ electrospun PVDF nanofiber membranes as templates for fabricating freestanding Cu-nanofiber electrodes (Figure 1; Figure S1, Supporting Information). The PVDF surface is activated by grafting a self-assembled polydopamine (pDA) layer. [9] The pDA layer provides nuclei for electroless Cu deposition from a precursor consisting of 50 × 10 −3 m Cu(II) ethylenediaminetetraacetate (Cu-EDTA) and 0.1 m borane dimethylamine complex. After a reaction at 35 °C for 2 h, conformally Cu-coated PVDF (Cu-PVDF) nanofibers form a conductive network with a sheet resistivity lower than 2.41 Ω. UPD, providing 2D deposition control, is employed to decorate the Cu-PVDF nanofibers with Sn. Control over the exact amount of Sn is critical to obtain high selectivity for CO 2 RR to CO. [8a,b] On CO-selective Sn/Cu catalysts, the initial intermediate of the CO 2 RR is proposed to bind to the surface via the carbon (*COOH). [8g,10] When the amount of Sn on the Cu surface exceeds the optimal value, CO 2 binds to the surface preferentially via the oxygen forming a bidentate *OCHO intermediate, [8g,10] and behaves similarly to a Sn electrode which is selective for HCOO − . [8c-g,11] To quantify the coverage of deposited Sn by UPD, we make use of a polycrystalline Cu rotating disk electrode with an electrochemical surface area of 0.686 cm 2 . Sn UPD from an Ar-saturated 1 × 10 −3 m SnSO 4 + 0.1 m H 2 SO 4 solution correlates to the reduction peak tailing to Earth-abundant Sn/Cu catalysts are highly selective for the electrocatalytic reduction of CO 2 to CO in aqueous electrolytes. However, CO 2 mass transport limitations, resulting from the low solubility of CO 2 in water, so far limit the CO partial current density for Sn/Cu catalysts to about 10 mA cm −2 . Here, a freestanding gas diffusion electrode design based on Sn-decorated Cu-coated electrospun polyvinylidene fluoride nanofibers is demonstrated. The use of gaseous CO 2 as a feedst...

Developing high-energy-density cathodes with prolonged cycling life is crucial to the continuing success of lithium-ion batteries. In particular, nickel-rich layered LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) cathodes are receiving growing interest due to their high reversible capacities in the range of 160−200 mAh/g and reduced content of critical and expensive cobalt. Nevertheless, nickel-rich NMC materials still encounter several challenges limiting their long-term cyclability, such as irreversible structural rearrangements, transitionmetal dissolution, high surface reactivity, and parasitic oxidation of organic electrolyte at the surface of delithiated Li 1−z Ni x Mn y Co 1−x−y O 2 at high voltages. Here, we investigate the use of several electrolyte additives that can alleviate capacity fading through the formation of a protective layer passivating the surface of nickel-rich NMC811. Film-forming cathode additives should decompose prior to the solvents and cover the electrode surface with a protection layer which prevents further oxidative decomposition of the electrolyte and minimizes surface side reactions. We find that the addition of 1 vol. % tris(trimethylsilyl)phosphite (TMSPi) in combination with 1 vol. % vinylene carbonate (VC) to a standard electrolyte consisting of 1 M LiPF 6 in ethylene carbonate (EC):dimethyl carbonate (DMC) (1:1 vol.) significantly enhances the capacity retention of NMC811/graphite full cells. Remarkably, a discharge capacity retention of 91% is achieved after 200 cycles at C/3. KEYWORDS: LiNi 0.8 Mn 0.1 Co 0.1 O 2 cathodes, electrolyte additives, tris(trimethylsilyl)phosphite, vinylene carbonate, lithium-ion batteries

Lithium‐ion batteries based on single‐crystal LiNi1−x−yCoxMnyO2 (NCM, 1−x−y ≥ 0.6) cathode materials are gaining increasing attention due to their improved structural stability resulting in superior cycle life compared to batteries based on polycrystalline NCM. However, an in‐depth understanding of the less pronounced degradation mechanism of single‐crystal NCM is still lacking. Here, a detailed postmortem study is presented, comparing pouch cells with single‐crystal versus polycrystalline LiNi0.60Co0.20Mn0.20O2 (NCM622) cathodes after 1375 dis‐/charge cycles against graphite anodes. The thickness of the cation‐disordered layer forming in the near‐surface region of the cathode particles does not differ significantly between single‐crystal and polycrystalline particles, while cracking is pronounced for polycrystalline particles, but practically absent for single‐crystal particles. Transition metal dissolution as quantified by time‐of‐flight mass spectrometry on the surface of the cycled graphite anode is much reduced for single‐crystal NCM622. Similarly, CO2 gas evolution during the first two cycles as quantified by electrochemical mass spectrometry is much reduced for single‐crystal NCM622. Benefitting from these advantages, graphite/single‐crystal NMC622 pouch cells are demonstrated with a cathode areal capacity of 6 mAh cm−2 with an excellent capacity retention of 83% after 3000 cycles to 4.2 V, emphasizing the potential of single‐crystalline NCM622 as cathode material for next‐generation lithium‐ion batteries.

Using an epitaxial thin-film model system deposited by pulsed laser deposition (PLD), we study the Li-ion conductivity in Li4Ti5O12, a common anode material for Li-ion batteries. Epitaxy, phase purity, and film composition across the film thickness are verified employing out-of-plane and in-plane X-ray diffraction, transmission electron microscopy, time-of-flight mass spectrometry, and elastic recoil detection analysis. We find that epitaxial Li4Ti5O12 behaves like an ideal ionic conductor that is well described by a parallel RC equivalent circuit, with an ionic conductivity of 2.5 × 10–5 S/cm at 230 °C and an activation energy of 0.79 eV in the measured temperature range of 205 to 350 °C. Differently, in a co-deposited polycrystalline Li4Ti5O12 thin film with an average in-plane grain size of <10 nm, a more complex behavior with contributions from two distinct processes is observed. Ultimately, epitaxial Li4Ti5O12 thin films can be grown by PLD and reveal suitable transport properties for further implementation as zero-strain and grain boundary free anodes in future solid-state microbattery designs.