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Polar topological structures in ferroelectric materials have attracted significant interest due to their fascinating physical properties and promising applications in high‐density, nonvolatile memories. Currently, most polar topological patterns are only observed in the bulky perovskite superlattices. In this work, a discovery of tunable ferroelectric polar topological structures is reported, designed, and achieved using topological strain engineering in two‐dimensional (2D) PbX (X = S, Se, and Te) materials via integrating first‐principles calculations, machine learning molecular dynamics simulations, and continuum modeling. First‐principles calculations discover the strain‐induced reversible ferroelectric phase transition with diverse polarization directions strongly correlated to the straining conditions. Taking advantage of the mechanical flexibility of 2D PbX, using molecular dynamics (MD) simulations, it is successfully demonstrated that the complex strain fields of 2D topological surfaces under mechanical indentation can generate unique skyrmion‐like polar topological vortex patterns. Further continuum simulations for experimentally accessible larger‐scale 2D topological surfaces uncover multiple skyrmion‐like structures (i.e., vortex, anti‐vortex, and flux‐closure) and transition between them by adopting/designing different types of mechanical loadings (such as out‐of‐plane indention and air blowing). Topological surfaces with various designable reversible polar topological structures can be tailored by complex straining flexible 2D materials, which provides excellent opportunities for next‐generation nanoelectronics and sensor devices. [ABSTRACT FROM AUTHOR]

Combined with the inherent spin-orbital coupling effect, the elemental ferroelectricity of monolayer Bi (bismuthene) is the critical property that renders this system a 2D ferroelectric topological insulator. Here, using first-principles calculations, we systematically investigate the ferroelectric polarization in bismuthene nanoribbons and discover the width size limiting effect arising from the edge effects. The decreasing width led to the spontaneous transformation of the zigzag (ZZ) and armchair (AC) paired Bi nanoribbons into newly discovered high-symmetric nonpolarized nanoribbons. For ZZ-paired nanoribbons, the driving force of the phase transition is attributed to the depolarization field, similar to the conventional perovskite ferroelectric thin films. Instead, edge stress as a novel mechanism played a major role in the phase transition of AC-paired nanoribbons. Inspired by such a revealed mechanism, the phase transition and related ultrahigh piezoelectricity can be achieved by strain engineering in Bi nanoribbons, which could enable new applications for 2D ferroelectric devices.

Lithium (Li) metal, a promising anode for high-energy-density rechargeable batteries, typically grows along the low-surface energy (110) plane in the plating process, resulting in uncontrollable dendrite growth and unstable interface. Herein, an unexpected Li growth behavior by lanthanum (La) doping is reported: the preferred orientation turns to (200) from (110) plane, enabling 2D nuclei rather than the usual 1D nuclei upon Li deposition and thus forming a dense and dendrite-free morphology even at an ultrahigh areal capacity of 10 mAh cm -2 . Noticeably, La doping further decreases the reactivity of Li metal toward electrolytes, thereby establishing a stable interface. The dendrite-free, stable Li anode enables a high average Coulombic efficiency of 99.30% at 8 mAh cm -2 for asymmetric Li||LaF 3 -Cu cells. A 3.1 Ah LaF 3 -Li||LiNi 0.8 Co 0.1 Mn 0.1 O 2 pouch cell at a high energy density (425.73 Wh kg -1 ) with impressive cycling stability (0.0989% decay per cycle) under lean electrolyte (1.76 g Ah -1 ) and high cathode loading (5.77 mAh cm -2 ) using this doped Li anode is further demonstrated., (© 2023 Wiley-VCH GmbH.)