Large-Scale Fabrication of Stable Silicon Anode in Air for Sulfide Solid State Batteries via Ionic-Electronic Dual Conductive Binder.

The construction of a continuous ionic/electronic pathway is critical for Si-based sulfide all-solid-state batteries (ASSBs) with the advantages of high-energy density and high-cycle stability. However, a significant impediment arises from the parasitic reaction occurring between the ionic sulfide solid-state electrolyte and electronic carbon additive, posing a formidable challenge. Additionally, the fabrication of electrodes necessitates stringent operational conditions, further limiting practical applicability. Herein, an ionic-electronic dual conductive binder for the fabrication of robust silicon anode under ambient air conditions in the absence of high-cost and air-sensitive sulfide solid-state electrolyte for ASSBs is reported. This binder incorporates in situ reduced silver nanoparticles into a high-strength polymer rich in ether bonds, establishing a conductive pathway for lithium ions and electrons. With the binder-composited Si anode, the half-cell exhibits a remarkable capacity of 1906.9 mAh g-1 and stable cycling for 500 cycles at a current density of 2 C (4.4 mA cm-2) under a low stack pressure of 5 MPa. The full cell using Ni0.9Co0.075Mn0.025O2 (NCM90) exhibits a remark cycling stability within 2000 cycles at 5 C (8 mA cm-2). This work presents an inspired design of functional binders for large-scale manufacture and mild operation in a low-cost way for Si anodes in ASSBs.

Synergetic regulation of SEI mechanics and crystallographic orientation for stable lithium metal pouch cells.

The advancement of Li-metal batteries is significantly impeded by the presence of unstable solid electrolyte interphase and Li dendrites upon cycling. Herein, we present an innovative approach to address these issues through the synergetic regulation of solid electrolyte interphase mechanics and Li crystallography using yttrium fluoride/polymethyl methacrylate composite layer. Specifically, we demonstrate the in-situ generation of Y-doped lithium metal through the reaction of composite layer with Li metal, which reduces the surface energy of the (200) plane, and tunes the preferential crystallographic orientation to (200) plane from conventional (110) plane during Li plating. These changes effectively passivate Li metal, thereby significantly reducing undesired side reactions between Li and electrolytes by 4 times. Meanwhile, the composite layer with suitable modulus (~1.02 GPa) can enhance mechanical stability and maintain structural stability of SEI. Consequently, a 4.2 Ah pouch cell with high energy density of 468 Wh kg-1 and remarkable capacity stability of 0.08% decay/cycle is demonstrated under harsh condition, such as high-areal-capacity cathode (6 mAh cm-2), lean electrolyte (1.98 g Ah-1), and high current density (3 mA cm-2). Our findings highlight the potential of reactive composite layer as a promising strategy for the development of stable Li-metal batteries.

Out-of-plane pressure and electron doping inducing phase and magnetic transitions in GeC/CrS2/GeC van der Waals heterostructure.

Out-of-plane pressure and electron doping can affect interlayer interactions in van der Waals materials, modifying their crystal structure and physical and chemical properties. In this study, we used magnetic monolayer 1T/1T'-CrS2 and high symmetry 2D-honeycomb material GeC to construct a GeC/CrS2/GeC triple layered van der Waals heterostructure (vdWH). Based on density functional theory calculations, we found that applying out-of-plane strain and doping with electrons could induce a 1T'-to-1T phase transition and consequently the ferromagnetic (FM)-to-antiferromagnetic (AFM) transition in the CrS2 layer. Such a phase and magnetic transition arises from the pressure and electron-induced interlayer interaction enhancement. The electron doping can effectively decrease the critical compressive stress from ∼4.3 GPa (charge neutrality) to ∼664 MPa (Q = 9 × 10-3 e- per atom) for the FM-to-AFM transition. These properties could be used to fabricate and program the 2D lateral FM/AFM heterostructures for artificial controlled spin texture and miniaturized spintronic devices.

Writing-Speed Dependent Thresholds of Ferroelectric Domain Switching in Monolayer α-In2 Se3.

An electrical-biased or mechanical-loaded scanning probe written on the ferroelectric surface can generate programmable domain nanopatterns for ultra-scaled and reconfigurable nanoscale electronics. Fabricating ferroelectric domain patterns by direct-writing as quickly as possible is highly desirable for high response rate devices. Using monolayer α-In2 Se3 ferroelectric with ≈1.2 nm thickness and intrinsic out-of-plane polarization as an example, a writing-speed dependent effect on ferroelectric domain switching is discovered. The results indicate that the threshold voltages and threshold forces for domain switching can be increased from -4.2 to -5 V and from 365 to 1216 nN, respectively, as the writing-speed increases from 2.2 to 10.6 µm s-1 . The writing-speed dependent threshold voltages can be attributed to the nucleations of reoriented ferroelectric domains, in which sufficient time is needed for subsequent domain growth. The writing-speed dependent threshold forces can be attributed to the flexoelectric effect. Furthermore, the electrical-mechanical coupling can be employed to decrease the threshold force, achieving as low as ≈189±41 nN, a value smaller than those of perovskite ferroelectric films. Such findings reveal a critical issue of ferroelectric domain pattern engineering that should be carefully addressed for programmable direct-writing electronics applications.

Size Limiting Elemental Ferroelectricity in Bi Nanoribbons: Observation, Mechanism, and Opportunity.

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.

Enabling 420 Wh kg-1 Stable Lithium-Metal Pouch Cells by Lanthanum Doping.

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||LaF3 -Cu cells. A 3.1 Ah LaF3 -Li||LiNi0.8 Co0.1 Mn0.1 O2 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.

Reducing Threshold of Ferroelectric Domain Switching in Ultrathin Two-Dimensional CuInP2S6 Ferroelectrics via Electrical-Mechanical Coupling.

Room-temperature out-of-plane two-dimensional ferroelectrics have promising applications in miniaturized non-volatile memory appliances. The feasible manipulation of polarization switching significantly influences the memory performance of ferroelectrics. However, conventional high-voltage-induced polarization switching inevitably generates charge injection or electric breakdown, and large-mechanical-loading-induced polarization switching may damage the structure of ferroelectrics. Hence, decreasing critical voltage/loading for ferroelectric polarization reversal is highly required. Herein, using atomic force microscopy experiments, the ferroelectric domain switching via both electric field and mechanical loading was demonstrated for an ultrathin (∼4.1 nm) CuInP2S6 nanoflake. The relevant threshold voltage/loading for polarization switching was ∼ -5 V/1095 nN, resulting from the electric field and flexoelectric effect, respectively. Finally, the electrical-mechanical coupling was adopted to reduce the threshold voltage/loading of CuInP2S6 significantly. It can be explained by the Landau-Ginzburg-Devonshire double-well model. This effective way for easily tuning the polarization states of CuInP2S6 opens up new prospects for mechanically written and electrically erased memory devices.

3D Co-Doping α-Ni(OH)2 Nanosheets for Ultrastable, High-Rate Ni-Zn Battery.

The α-Ni(OH)2 is regarded as one promising cathode for aqueous nickel-zinc batteries due to its high theoretical capacity of ≈480 mAh g-1 , its practical deployment however suffers from the poor stability in strong alkaline solution, intrinsic low electrical conductivity as well as the retarded ionic diffusion. Herein, a 3D (three dimensional) macroporous α-Ni(OH)2 nanosheets with Co doping is designed through a facile and easily scalable electroless plating combined with electrodeposition strategy. The unique micrometer-sized 3D pores come from Ni substrate and rich voids between Co-doping α-Ni(OH)2 nanosheets can synergistically afford facile, interconnected ionic diffusion channels, sufficient free space for accommodating its volume changes during cycling; meanwhile, the Co-doping can stabilize the structural robustness of the α-Ni(OH)2 in the alkaline electrolyte during cycling. Thus, the 3D α-Ni(OH)2 shows a high capacity of 284 mAh g-1 at 0.5 mA cm-2 with an excellent retention of 78% even at 15 mA cm-2 , and more than 2000 stable cycles at 6 mA cm-2 , as well as the robust cycling upon various flexible batteries. This work provides a simple and efficient pathway to enhance the electrochemical performance of Ni-Zn batteries through improving ionic transport kinetics and stabilizing crystal structure of cathodes.

Gradient H-Bonding Binder Enables Stable High-Areal-Capacity Si-Based Anodes in Pouch Cells.

Alleviating large stress is critical for high-energy batteries with large volume change upon cycling, yet this still presents a challenge. Here, a gradient hydrogen-bonding binder is reported for high-capacity silicon-based anodes that are highly desirable for the next-generation lithium-ion batteries. The well-defined gradient hydrogen bonds, with a successive bond energy of -2.88- -10.04 kcal mol-1 , can effectively release the large stress of silicon via the sequential bonding cleavage. This can avoid recurrently abrupt structure fracture of traditional binder due to lack of gradient energy dissipation. Certainly, this regulated binder endows stable high-areal-capacity silicon-based electrodes >4 mAh cm-2 . Beyond proof of concept, this work demonstrates a 2 Ah silicon-based pouch cell with an impressive capacity retention of 80.2% after 700 cycles (0.028% decay/cycle) based on this gradient hydrogen-bonding binder, making it more promising for practical application.

Improved magnetostriction in Galfenol alloys by aligning crystal growth direction along easy magnetization axis.

Galfenol (Iron-gallium) alloys have attracted significant attention as the promising magnetostrictive materials. However, the as-cast Galfenols exhibit the magnetostriction within the range of 20-60 ppm, far below the requirements of high-resolution functional devices. Here, based on the geometric crystallographic relationship, we propose to utilize the 90°-domain switching to improve the magnetostriction of Galfenols by tuning the crystal growth direction (CGD) along the easy magnetization axis (EMA). Our first-principles calculations demonstrate that Pt doping can tune the CGD of Galfenol from [110] to [100], conforming to the EMA. Then, it is experimentally verified in the (Fe0.83Ga0.17)100-xPtx (x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) alloys and the magnetostriction is greatly improved from 39 ppm (x = 0, as-cast) to 103 ppm (x = 0.8, as-cast) and 188 ppm (x = 0.8, directionally solidified), accompanying with the increasing CGD alignment along [100]. The present study provides a novel approach to design and develop high-performance magnetostrictive materials.

Charge doping induced reversible multistep structural phase transitions and electromechanical actuation in two-dimensional 1T'-MoS2.

The 1T' phase of transition metal dichalcogenides (TMDs) is a low symmetry charge density wave (CDW) phase, which can be viewed as a periodically distorted structure (Peierls distortion) of the high symmetry 1T phase. In this paper, using density functional theory (DFT) calculations, we report that the positive charge (hole) injection is an effective method to modulate the Peierls distortion of MoS2 1T' for a new CDW phase and superior electromechanical properties. A new stable CDW phase is discovered at a hole doping level of 0.10 h+ per atom, named 1T't. Hole charging and discharging can induce a reversible phase transition of MoS2 among the three phases, 1T, 1T' and 1T't. Such a reversible phase transition leads to superior electromechanical properties including a strain output as high as -5.8% with a small hysteresis loop, multi-step super-elasticity, and multi-shape memory effect, which are valuable in active electromechanical device designs at the nanoscale. In-depth analysis of the change of the electronic structure under hole doping was performed to understand the new CDW phase and the observed phase transition. Using charge doping to modulate the Peierls distortion in two-dimensional materials can serve as a general concept for nano-active material designs.

Ferromagnetism of 1T'-MoS2 Nanoribbons Stabilized by Edge Reconstruction and Its Periodic Variation on Nanoribbons Width.

Nanoribbons (NRs) of two-dimensional (2D) materials have attracted intensive research interests because of exotic physical properties at edges as well as tunable properties via width control. In this paper, using density functional theory (DFT) calculations, we discover sensitive dependence of magnetic properties of 1T'-MoS2 NRs, that is, periodic variation of magnetic moments between 0.1 and 1.2 µ B, on NR width (even or odd number of MoS2 units). Our results reveal that a special edge reconstruction, which is not recognized before, stabilizes the ferromagnetic (FM) ground state. Our results also suggest that the FM state could be stable under ambient condition. This study indicates a promising means to integrate multiple magnetic units for small-scale functional devices, such as information storage and spintronics, on a single piece of MoS2 NR by designing segments with different width.

Density functional theory computational study of ferroelectricity and piezoelectricity in BaTiO3/PbTiO3 (0 1 1) superlattices.

The structure, ferroelectricity (FE), and piezoelectricity of epitaxial BaTiO3/PbTiO3 (BTO/PTO) (0 1 1) superlattices are studied using density functional theory calculations. Our results show that compressive strain arising from the SrTiO3 (0 1 1) substrate stabilizes the (BTO) m /(PTO) n (0 1 1) superlattices in orthorhombic phase with the FE polarization along [0 1 1] direction. Tuning the BTO contents significantly changes the structural, ferroelectric and piezoelectric properties. The FE polarization of superlattices significantly drops with increasing BTO contents, which can be attributed to depolarization of the PTO layers. The averaged c/a ratio of the whole superlattices exhibits anomalous non-monotonic relation with respect to BTO contents. Interestingly, our results predict the (0 1 1) superlattices can enhance the piezoelectric coefficient e 33 with a maximum value at ~67% BTO concentration. This result suggests a potential avenue to design high performance piezoelectric materials with less Pb contents. In-depth analysis reveals the B-site Ti cation as the origin for the enhanced e 33 value, which implies the potential of B-site cation engineering in perovskite heterostructure designs.

Fabrication of phosphorus nanostructures/TiO2 composite photocatalyst with enhancing photodegradation and hydrogen production from water under visible light.

As the world faces serious environmental pollution and energy shortage, developing Vis-light-driven photocatalysts for water splitting is highly attractive in clean energy utilization. Fabricating heterostructures has been proposed to be an efficient system to enhance the photocatalytic activity. However, synthesizing heterostructures with good contact and understanding charge transfer dynamics are still unresolved issues. In this work, a facile calcination approach was used to synthesize red phosphorus (RP) nanostructures/TiO2 heterostructured composites. The RP nanostructures were directly grown on the TiO2 nanoparticles with an intimate surface contact. By adjusting the molar ratio of amorphous RP to TiO2 and the synthesizing temperature, thin nanorod-like RP nanostructures with a large exposed surface and a good surface contacting with TiO2 were obtained. The synergetic effect of heterostructured RP/TiO2 composites leads to an enhanced charge separation and transfer, and a better utilization of visible-light. As expected, the RP/TiO2-700 °C composites exhibit good photocatalytic activity of degrading RhB and the optimal H2 evolution rate. This work not only provides a method to prepare earth abundant elemental phosphorus well-contacted heterostructures, expand the well-known UV-active TiO2 photocatalyst to visible active, but also deepens understanding of charge transfer dynamics in heterostructured photocatalyst.

The Edge Stresses and Phase Transitions for Magnetic BN Zigzag Nanoribbons.

The edge states are of particular importance to understand fundamental properties of finite two-dimensional (2D) crystals. Based on first-principles calculations, we investigated on the bare zigzag boron nitride nanoribbons (zzBNNRs) with different spin-polarized states well localized at and extended along their edges. Our calculations examined the edge stress, which is sensitively dependent on the magnetic edge states, for either B-terminated edge or N-terminated edge. Moreover, we revealed that different magnetic configurations lead to a rich spectrum of electronic behaviors at edges. Using an uniaxial tensile strain, we proposed the magnetic phase transitions and thereby obtained the metallic to half-metallic (or reverse) phase transitions at edges. It suggests zzBNNR as a promising candidate for potential applications of non-metal spintronic devices.

One step in situ synthesis of core-shell structured Cr2O3:P@fibrous-phosphorus hybrid composites with highly efficient full-spectrum-response photocatalytic activities.

Making full use of solar energy and achieving high charge separation efficiency are critical factors for the photocatalysis technique. In this work, we report core-shell structured fibrous phosphorus (f-P) coated P-doped Cr2O3 (Cr2O3:P@f-P) hybrid composites with a strong optical absorption in the full region of 200-2600 nm. The Cr2O3:P@f-P hybrid composites exhibit a record photocatalytic efficiency under UV, visible and near-infrared light irradiation, demonstrating as promising photocatalysts for the full utilization of solar energy. Systematical investigations combining experimental and theoretical work show that P doping modifies the electronic band structures and creates defective levels in the forbidden gap of Cr2O3 which extends the optical absorption to the visible and near-infrared regions. Highly crystalline fibrous phosphorus in situ grown on the Cr2O3 particles constructs a core-shell hybrid structure which guarantees intimate interfacial contact between f-P and Cr2O3:P and facilitates the separation of photogenerated electron-hole pairs. This study develops a promising system based on earth abundant element P to utilize the overall spectrum of sunlight for photochemical applications.

Two-dimensional shape memory graphene oxide.

Driven by the increasing demand for micro-/nano-technologies, stimuli-responsive shape memory materials at nanoscale have recently attracted great research interests. However, by reducing the size of conventional shape memory materials down to approximately nanometre range, the shape memory effect diminishes. Here, using density functional theory calculations, we report the discovery of a shape memory effect in a two-dimensional atomically thin graphene oxide crystal with ordered epoxy groups, namely C8O. A maximum recoverable strain of 14.5% is achieved as a result of reversible phase transition between two intrinsically stable phases. Our calculations conclude co-existence of the two stable phases in a coherent crystal lattice, giving rise to the possibility of constructing multiple temporary shapes in a single material, thus, enabling highly desirable programmability. With an atomic thickness, excellent shape memory mechanical properties and electric field stimulus, the discovery of a two-dimensional shape memory graphene oxide opens a path for the development of exceptional micro-/nano-electromechanical devices.

Electric Field Induced Reversible Phase Transition in Li Doped Phosphorene: Shape Memory Effect and Superelasticity.

Phosphorene, the single-layer form of black phosphorus, as a new member of atomically thin material family, has unique puckered atomistic structure and remarkable physical and chemical properties. In this paper, we report a discovery of an unexpected electromechanical energy conversion phenomenon-shape memory effect-in Li doped phosphorene P4Li2, using ab initio density functional theory simulations. Two stable phases are found for the two-dimensional (2D) P4Li2 crystal. Applying an external electric field can turn on or off the unique adatom switches in P4Li2 crystals, leading to a reversible structural phase transition and thereby the shape memory effect with an tunable strain output as high as 2.06%. Our results demonstrate that multiple temporary shapes are attainable in one piece of P4Li2 material, offering programmability that is particularly useful for device designs. Additionally, the P4Li2 displays superelasticity that can generate a pseudoelastic tensile strain up to 6.2%. The atomic thickness, superior flexibility, excellent electromechanical strain output, the special shape memory phenomenon, and the programmability feature endow P4Li2 with great application potential in high-efficient energy conversion at nanoscale and flexible nanoelectromechanical systems.

Enhanced charge carrier mobility in two-dimensional high dielectric molybdenum oxide.

We demonstrate that the energy bandgap of layered, high-dielectric α-MoO(3) can be reduced to values viable for the fabrication of 2D electronic devices. This is achieved through embedding Coulomb charges within the high dielectric media, advantageously limiting charge scattering. As a result, devices with α-MoO(3) of ∼11 nm thickness and carrier mobilities larger than 1100 cm(2) V(-1) s(-1) are obtained.