Numerical correction of anti-symmetric aberrations in single HRTEM images of weakly scattering 2D-objects

Here, we present a numerical post-processing method for removing the effect of anti-symmetric residual aberrations in high-resolution transmission electron microscopy (HRTEM) images of weakly scattering 2D-objects. The method is based on applying the same aberrations with the opposite phase to the Fourier transform of the recorded image intensity and subsequently inverting the Fourier transform. We present the theoretical justification of the method and its verification based on simulated images in the case of low-order anti-symmetric aberrations. Ultimately the method is applied to experimental hardware aberration-corrected HRTEM images of single-layer graphene and MoSe2 resulting in images with strongly reduced residual low-order aberrations, and consequently improved interpretability. Alternatively, this method can be used to estimate by trial and error the residual anti-symmetric aberrations in HRTEM images of weakly scattering objects

Sodiophilic Current Collectors Based on MOF‐Derived Nanocomposites for Anode‐Less Na‐Metal Batteries

“Anode-less” sodium metal batteries (SMBs) with high energy may become the next-generation batteries due to the abundant resources. However, their cycling performance is still insufficient for practical uses. Herein, a metal organic frameworks (MOF)-derived copper-carbon (Cu@C) composite is developed as a sodiophilic layer to improve the Coulombic efficiency (CE) and cycle life. The Cu particles can provide abundant nucleation sites to spatially guide Na deposition and the carbon framework offer void volume to avoid volume changes during the plating/stripping process. As a result, Cu@C-coated copper and aluminum foils (denoted as Cu-Cu@C and Al-Cu@C foil) can be used as efficient current collectors for sodium plating/stripping, achieving, nearly 1600 and 240 h operation upon cycling at 0.5 mA cm$^{-2}$ and 1 mA h cm$^{-2}$, respectively. In situ dilatometry measurements demonstrate that Cu@C promotes the formation of dense Na deposits, thereby inhibiting side reactions, dendrite growth, and accumulation of dead Na. Such current collectors are employed in Na metal cells using carbon-coated Na$_{3}$V$_{2}$(PO$_{4}$)$_{3}$ (NVP/C) and copper selenides (Cu$_{2-x}$Se@C) cathodes, achieving outstanding rate capability and improved cycling performance. Most noticeably, “anode-less” Na batteries using Al-Cu@C as anode and NVP/C as cathode demonstrate promising CE as high as 99.5%, and long-term cycling life

Elucidating the Effect of Iron Doping on the Electrochemical Performance of Cobalt‐Free Lithium‐Rich Layered Cathode Materials

The eco‐friendly and low‐cost Co‐free Li1.2Mn0.585Ni0.185Fe0.03O2 is investigated as a positive material for Li‐ion batteries. The electrochemical performance of the 3 at% Fe‐doped material exhibits an optimal performance with a capacity and voltage retention of 70 and 95%, respectively, after 200 cycles at 1C. The effect of iron doping on the electrochemical properties of lithium‐rich layered materials is investigated by means of in situ X‐ray diffraction spectroscopy and galvanostatic intermittent titration technique during the first charge–discharge cycle while high‐resolution transmission electron microscopy is used to follow the structural and chemical change of the electrode material upon long‐term cycling. By means of these characterizations it is concluded that iron doping is a suitable approach for replacing cobalt while mitigating the voltage and capacity degradation of lithium‐rich layered materials. Finally, complete lithium‐ion cells employing Li1.2Mn0.585Ni0.185Fe0.03O2 and graphite show a specific energy of 361 Wh kg−1 at 0.1C rate and very stable performance upon cycling, retaining more than 80% of their initial capacity after 200 cycles at 1C rate. These results highlight the bright prospects of this material to meet the high energy density requirements for electric vehicles

Evaluation of Sn0.9_{0.9}Fe0.1_{0.1}O2‐δ_{2‐ δ} as Potential Anode Material for Sodium‐Ion Batteries

The introduction of transition metals such as iron in oxides of alloying elements as, for instance, SnO$_2$ has been proven to enable higher capacities and superior charge storage performance when used as lithium-ion electrode materials. Herein, we report the evaluation of such electrode materials, precisely (carbon-coated) Sn$_{0.9}$Fe$_{0.1}$O$_{2−δ}$(−C), for sodium-ion battery applications. The comparison with SnO$_2$ as reference material reveals the beneficial impact of the presence of iron in the tin oxide lattice, enabling higher specific capacities and a greater reversibility of the de-/sodiation process – just like for lithium-ion battery applications. The overall achievable capacity, however, remains relatively low with about 300 mAh g$^{−1}$ and up to more than 400 mAh g$^{−1}$ for Sn$_{0.9}$Fe$_{0.1}$O$_{2-δ}$ and Sn$_{0.9}$Fe$_{0.1}$O$_{2−δ}$-C, respectively, compared to the theoretical specific capacity of more than 1,300 mAh g$^{−1}$ when assuming a completely reversible alloying and conversion reaction. The subsequently performed ex situ/operando XRD and ex situ TEM/EDX analysis unveils that this limited capacity results from an incomplete de-/sodiation reaction, thus, providing valuable insights towards an enhanced understanding of alternative reaction mechanisms for sodium-ion anode material candidates

Reversible Copper Sulfide Conversion in Nonflammable Trimethyl Phosphate Electrolytes for Safe Sodium‐Ion Batteries

Rechargeable sodium-ion batteries are considered promising candidates for low-cost and large-scale energy storage systems. However, the limited energy density, cyclability, and safety issues remain challenges for practical applications. Herein, investigation of the Cu1.8S/C composite material as the negative electrode active (conversion) material in combination with a concentrated electrolyte composed of a 3.3 m solution of sodium bis(fluorosulfonyl)imide (NaFSI) in trymethyl phosphate and fluoroethylene carbonate (FEC) as the additive is reported on. Such a combination enables the stable cycling of the conversion-type Cu1.8S/C electrode material for hundreds of cycles with high capacity (380 mAh g−1). Both the salt (NaFSI) and the additive (FEC) contribute to the formation of a stable NaF-rich solid electrolyte interphase (SEI) on the anode surface. A full cell using the Na3V2(PO4)3/C cathode also demonstrates stable cycling performance for 200 cycles with a promising Coulombic efficiency (CE) (99.3%). These findings open new opportunities for the development of safer rechargeable sodium-ion batteries

Tailoring the Charge/Discharge Potentials and Electrochemical Performance of SnO₂ Lithium‐Ion Anodes by Transition Metal Co‐Doping

It has been shown that the introduction of several transition metal (TM) dopants into SnO2 lithium‐ion battery anodes can overcome the issues associated with the irreversible capacity loss from the conversion reaction of SnO2 and the aggregation of the metallic Sn particles formed upon lithiation. As the choice of the single dopant, however, plays a decisive role for the achievable energy density – precisely its redox potential – we investigate herein TM co‐doped SnO2, prepared by using a readily scalable continuous hydrothermal flow synthesis (CHFS) process, to tailor the dis‐/charge profile and by this the energy density. It is shown that the judicious choice of different elemental doping combinations in samples made via CHFS simultaneously improves the cycling performance and the full‐cell energy density. To support these findings, we realized a lithium‐ion full‐cell incorporating the best performing co‐doped SnO2 as negative electrode and high‐voltage LiNi0.5Mn1.5O4 (LNMO) as positive electrode–to the best of our knowledge, the first full‐cell based on such anode material in combination with LNMO as cathode active material

Superior Lithium Storage Capacity of α‐MnS Nanoparticles Embedded in S‐Doped Carbonaceous Mesoporous Frameworks

Herein, a Mn‐based metal–organic framework is used as a precursor to obtain well‐defined α‐MnS/S‐doped C microrod composites. Ultrasmall α‐MnS nanoparticles (3–5 nm) uniformly embedded in S‐doped carbonaceous mesoporous frameworks (α‐MnS/SCMFs) are obtained in a simple sulfidation reaction. As‐obtained α‐MnS/SCMFs shows outstanding lithium storage performance, with a specific capacity of 1383 mAh g−1 in the 300th cycle or 1500 mAh g−1 in the 120th cycle (at 200 mA g−1) using copper or nickel foil as the current collector, respectively. The significant (pseudo)capacitive contribution and the stable composite structure of the electrodes result in impressive rate capabilities and outstanding long‐term cycling stability. Importantly, in situ X‐ray diffraction measurements studies on electrodes employing various metal foils/disks as current collector reveal the occurrence of the conversion reaction of CuS at (de)lithiation process when using copper foil as the current collector. This constitutes the first report of the reaction mechanism for α‐MnS, eventually forming metallic Mn and Li2S. In situ dilatometry measurements demonstrate that the peculiar structure of α‐MnS/SCMFs effectively restrains the electrode volume variation upon repeated (dis)charge processes. Finally, α‐MnS/SCMFs electrodes present an impressive performance when coupled in a full cell with commercial LiMn1/3Co1/3Ni1/3O2 cathodes

Impact of the Transition Metal Dopant in Zinc Oxide Lithium-Ion Anodes on the Solid Electrolyte Interphase Formation

Conversion/alloying materials (CAMs) provide substantially higher specific capacities than graphite, the state‐of‐the‐art lithium‐ion battery anode material. The ability to host much more lithium per unit weight and volume is, however, accompanied by significant volume changes, which challenges the realization of a stable solid electrolyte interphase (SEI). Herein, the comprehensive characterization of the composition and evolution of the SEI on transition metal (TM) doped zinc oxide as CAM model compound, is reported, with a particular focus on the impact of the TM dopant (Fe or Co). The results unveil that the presence of iron specifically triggers the electrolyte decomposition. However, this detrimental effect can be avoided by stabilizing the interface with the electrolyte by a carbonaceous coating. These findings provide a great leap forward toward the enhanced understanding of such doped materials and (transition) metal oxide active materials in general

Iron-Doped ZnO for Lithium-Ion Anodes: Impact of the Dopant Ratio and Carbon Coating Content

Herein, an investigation of the impact of the dopant and carbon content in iron-doped zinc oxide/carbon composites is presented. For this purpose, a comprehensive morphological, structural, and electrochemical characterization of a series of different compounds is reported, including techniques like X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma optical emission spectroscopy (ICP-OES), thermogravimetric analysis (TGA), specific surface area using the Brunauer-Emmett-Teller (BET) algorithm, pycnometry, small-angle X-ray scattering (SAXS), cyclic voltammetry (CV), and galvanostatic cycling. The obtained results reveal an impact of the iron-dopant content on the crystallite and particle size as well as the detailed de-/lithiation mechanism. The effect on the cycling stability, however, appears to be rather minor. The carbon coating content, on the contrary, has a significant influence on the cycling stability and rate capability. According to these results, a carbon content of about 10 wt% is sufficient to achieve stable cycling at lower current densities, while a carbon content of 15–20 wt% allows for specific capacities of 425–500 mAh g−1, when applying a specific current of 1 A g−1, for instance