Uncontrollable dendrite growth hinders the direct use of a lithium metal anode in batteries, even though it has the highest energy density of all anode materials. Achieving uniform lithium deposition ...is the key to solving this problem, but it is hard to be realized on a planar electrode surface. In this study, a thin lithiophilic layer consisting of vertically aligned CuO nanosheets directly grown on a planar Cu current collector is prepared by a simple wet chemical reaction. The lithiophilic nature of the CuO nanosheets reduces the polarization of the electrode, ensuring uniform Li nucleation and continuous smooth Li plating, which is difficult to realize on the normally used lithiophobic Cu current collector surface. The integration of the grown CuO arrays and the Cu current collector guarantees good electron transfer, and moreover, the vertically aligned channels between the CuO nanosheets guarantee fast ion diffusion and reduce the local current density. As a result, a high Columbic efficiency of 94% for 180 cycles at a current density of 1 mA cm−2 and a prolonged lifespan of a symmetrical cell (700 h at 0.5 mA cm−2) can be easily achieved, showing a simple but effective way to realize Li metal‐based anode stabilization.
The vertically aligned CuO nanosheets grown on planar Cu foil help realize steady Li nucleation and plating because of the regulation of the Li ion distribution and the increased affinity toward Li.
Lithium‐sulfur (Li‐S) batteries are considered as one of the most promising energy storage systems for next‐generation electric vehicles because of their high‐energy density. However, the poor cyclic ...stability, especially at a high sulfur loading, is the major obstacles retarding their practical use. Inspired by the nacre structure of an abalone, a similar configuration consisting of layered carbon nanotube (CNT) matrix and compactly embedded sulfur is designed as the cathode for Li‐S batteries, which are realized by a well‐designed unidirectional freeze‐drying approach. The compact and lamellar configuration with closely contacted neighboring CNT layers and the strong interaction between the highly conductive network and polysulfides have realized a high sulfur loading with significantly restrained polysulfide shuttling, resulting in a superior cyclic stability and an excellent rate performance for the produced Li‐S batteries. Typically, with a sulfur loading of 5 mg cm−2, the assembled batteries demonstrate discharge capacities of 1236 mAh g−1 at 0.1 C, 498 mAh g−1 at 2 C and moreover, when the sulfur loading is further increased to 10 mg cm−2 coupling with a carbon‐coated separator, a superhigh areal capacity of 11.0 mAh cm−2 is achieved.
Lithium–sulfur batteries are one of the most promising energy storage systems for the next‐generation electric vehicles from the high theoretical energy density. From the unidirectional freeze‐drying approach, a nacre‐like carbon nanotube sheet is prepared and used as the cathode matrix. Such a structure with compact carbon nanotube matrix–sulfur configuration enables a considerably high performance at a high areal sulfur loading.
Low-dimensional organic–inorganic halide perovskites have attracted interest for their properties in exciton dynamics, broad-band emission, magnetic spin selectivity. However, there is no ...quantitative model for predicting the structure-directing effect of organic cations on the dimensionality of these low-dimensional perovskites. Here, we report a machine learning (ML)-assisted approach to predict the dimensionality of lead iodide-based perovskites. A literature review reveals 86 reported amines that are classified into “2D”-forming and “non-2D”-forming based on the dimensionality of their perovskites. Machining learning models were trained and tested based on the classification and descriptor features of these ammonium cations. Four structural features, including steric effect index, eccentricity, largest ring size, and hydrogen-bond donor, have been identified as the key controlling factors. On the basis of these features, a quantified equation is created to calculate the probability of forming 2D perovskite for a selected amine. To further illustrate its predicting capability, the built model is applied to several untested amines, and the predicted dimensionality is verified by growing single crystals of perovskites from these amines. This work represents a step toward predicting the crystal structures of low dimensional hybrid halide perovskites using ML as a tool.
Gelation is an effective way to realize the self‐assembly of nanomaterials into different macrostructures, and in a typical use, the gelation of graphene oxide (GO) produces various graphene‐based ...carbon materials with different applications. However, the gelation of MXenes, another important type of 2D materials that have different surface chemistry from GO, is difficult to achieve. Here, the first gelation of MXenes in an aqueous dispersion that is initiated by divalent metal ions is reported, where the strong interaction between these ions and OH groups on the MXene surface plays a key role. Typically, Fe2+ ions are introduced in the MXene dispersion which destroys the electrostatic repulsion force between the MXene nanosheets in the dispersion and acts as linkers to bond the nanosheets together, forming a 3D MXene network. The obtained hydrogel effectively avoids the restacking of the MXene nanosheets and greatly improves their surface utilization, resulting in a high rate performance when used as a supercapacitor electrode (≈226 F g−1 at 1 V s−1). It is believed that the gelation of MXenes indicates a new way to build various tunable MXene‐based structures and develop different applications.
Fast gelation of Ti3C2Tx MXenes is initiated by divalent metal ions in aquesous solution. Typically, Fe2+ ions eliminate the electrostatic repulsion, networking MXene nanosheets into a 3D structured hydrogel. The wet hydrogel avoids nanosheet restacking and is ideal for applications highlighting the surface utilization, especially as freestanding electrodes for high‐rate supercapacitors.
In studies of low-dimensional hybrid organic lead halide compounds (HOLHCs), understanding the composition–structure relationship is important for controlling their optical, optoelectronic, ...spintronic, and ferroelectric properties. Prior knowledge usually considers the primary structure of organic cations to predict the dimensionality of the HOLHCs. However, with the existence of noncovalent interactions (especially hydrogen bonding), the structure-directing organic cations may form secondary structures, which change their shape and steric hindrance when the cations are packed inside the crystal structure. To the best of our knowledge, the role of secondary structures of organic cations has not been systematically investigated yet. Herein, we report a systematic investigation of the influence from the secondary structure of ammonium ions induced by hydrogen bonding. We use a series of alkoxy-ammoniums as the model system to investigate how the NH···O hydrogen bonding induces the folding of the organic cations into ring structures. The folding increases the steric hindrance around the NH3 + end and thus reduces the dimensionality of the hybrid organic lead iodide compounds. By changing the linker length between alkoxy and ammonium groups, we have determined that the seven-member ring forms the strongest intramolecular hydrogen bonding. More intriguingly, the folded secondary structures become chiral, which provides a new approach for creating symmetry-breaking chiral materials.
Lithium metal anodes with high energy density are important for further development of next‐generation batteries. However, inhomogeneous Li deposition and dendrite growth hinder their practical ...utilization. 3D current collectors are widely investigated to suppress dendrite growth, but they usually occupy a large volume and increase the weight of the system, hence decreasing the energy density. Additionally, the nonuniform distribution of Li ions results in low utilization of the porous structure. A lightweight, 3D Cu nanowire current collector with a phosphidation gradient is reported to balance the lithiophilicity with conductivity of the electrode. The phosphide gradient with good lithiophilicity and high ionic conductivity enables dense nucleation of Li and its steady deposition in the porous structure, realizing a high pore utilization. Specifically, the homogenous deposition of Li leads to the formation of an oriented texture on the electrode surface at high capacities. A high mass loading (≈44 wt%) of Li with a capacity of 3 mAh cm−2 and a high average Coulombic efficiency of 97.3% are achieved. A lifespan of 300 h in a symmetrical cell is obtained at 2 mA cm−2, implying great potential to stabilize lithium metal.
A lightweight three‐dimensional (3D) Cu nanowire network with a lithiophilic phosphidation gradient along the cross‐section is used as the current collector for a Li‐metal anode. The gradient structure and the formed Li3P‐rich surface with good ionic/electrical conductivity guide the stable deposition of Li ions inside the 3D structure, improving the Li mass loading and the energy density of the anode.
Chiral organic–inorganic metal halides (OIMHs) are attractive for their potential applications in chiral optoelectronics and spintronics, such as circular polarized light emitters, detectors, and ...chiral-induced spin selectivity. Here, we report three pairs of chiral OIMHs with great water stability constructed from chiral viologens. These OIMHs contain either 1D or 0D structures, however, with small band gaps around 2 eV. Circular dichroism (CD) spectroscopy on transparent thin films of two OIMH pairs showed a wide CD response covering most of the visible light range. Although the chiral center is not directly attached to the pyridinium in these chiral viologens, the chirality is still successfully transferred into both the band gap and the exciton absorption ranges. Liquid and solid CD studies of the chiral viologens further indicate that the chiral induction inside these OIMHs is possibly through chiral crystallization. This work demonstrated the design strategy of water-stable, small band gap chiral OIMHs through chiral viologens. These low-dimensional chiral materials may provide an interesting system to investigate chiral induction, and their broad CD response may enable their potential application as circular photodetectors with a wide detection range.
Semiconductor photoelectrochemistry (PEC) is a promising technology for solar fuels and photovoltaics. However, the application of organic–inorganic halide perovskites (OIHPs) to PEC has been limited ...by their instability in polar solvents. Here, we report the use of methylviologen lead iodide (MVPb2I6) as an unprotected photoelectrode, which is stable inside an acetonitrile-based polar electrolyte. Moreover, the charge-transfer absorption inside MVPb2I6 reduces its band gap to 2.1 eV and thus makes it a suitable solar absorber. The stability of MVPb2I6 allows the use of cyclic voltammetry to determine its energetics. A stable anodic photocurrent was observed with only 28% decay after 15 h of operation under 1 sun illumination and 0.9 V (vs normal hydrogen electrode (NHE)) applied bias toward the oxidation of I–. The degradation mechanism due to the photoreduction of MVPb2I6 was also studied using scanning electron microscopy (SEM) and a rotating ring-disk electrode (RRDE). This work illustrates the potential and challenge of using viologen-based small-band-gap one-dimensional (1D) OIHPs to achieve stable PEC inside polar solvents without protection.
A dense and stable lithium deposition process is highlighted by a snowy world, where the snowflakes represent the Li ions and the branches are like the ultralight 3D copper nanowire network with a ...phosphidation gradient employed by Wei Lv, Quan‐Hong Yang, Feiyu Kang, and co‐workers in article number 1904991. The gradient surface increases the lithiophilicity and high utilization of 3D structure, enabling a dendrite‐free lithium‐metal anode with high energy density.
PDF
