Manganese (Mn) -based phosphate is poised for commercial applications driven by its cost-effectiveness, robust NASICON framework, and multi-dimensional Na+ pathways. However, it encounters insufficient redox reactions and rapid structural collapse with severe lattice distortion as the culprit. Herein, one meticulously engineered substitutional solid solution cathode (integrating Na4MnCr(PO4)3 and Na3MnTi(PO4)3, denoted NMCTP) is proposed to regulate the local crystal structure of Mn & horbar;O bond to stabilize and promote the Mn redox reaction for optimizing the electrochemical performance. It is uncovered that the bulk framework with structural stability is constructed by strongly symmetric Mn & horbar;O bond lengths of MnO6 octahedrons and strengthened Mn & horbar;O covalency. In addition, the sufficient utilization of Mn redox is tightly correlated with redistributed Na2 occupancy and enhanced diffusion kinetics with accelerated electron transportation. By virtue of the above merits, The NMCTP performs ultra-high capacity (150.3 mAh g-1 at 0.1 C) and appealing cycling stability (84.7% retention over 1000 cycles). Sodium storage mechanisms and potential factors at high potentials are unveiled in NMCTP materials. This work sheds light on fire-new solid solution strengthening in view of the Mn & horbar;O bond structure for high-performance Mn-based phosphate cathodes. One substitutional solid solution cathode is proposed to regulate the local crystal structure of Mn & horbar;O bond to stabilize and promote the Mn redox reaction for optimizing the electrochemical performance. It is uncovered that the bulk framework with structural stability is constructed by strongly symmetric Mn & horbar;O bond lengths of MnO6 octahedrons and strengthened Mn & horbar;O covalency. image

Potassium metal batteries (PMBs) have become a paramount alternative energy storage technology to lithium-ion batteries, due to their low cost and potential energy density. However, uncontrolled dendrite growth interferes with the stability of the interfacial anode, leading to significant capacity degradation and safety hazards. Herein, a facile reactive prewetting strategy is proposed to discourage dendrite growth by constructing a functional KF/Znrich hybrid interface layer on K metal. The KF/Zn@K anode design functions like an interconnected paddy field, stabilizing the anode interface through the preferential redistribution of K+ flux/electrons, continuous transport paths, and enhanced transport dynamics. As anticipated, symmetrical batteries exhibit an extended cycling lifetime of over 2000 h, with reduced voltage hysteresis at 0.5 mA cm-2 and 0.5 mAh cm-2. Furthermore, when the KF/Zn@K anode is applied to full batteries coupled with PTCDA, a boosted reversible capacity of 61.6 mAh g-1 at 5 C is present over 3000 cycles. This interfacial control creates rational possibilities for constructing highefficiency, stable K metal anodes.

Layered iron (Fe) -based fluorophosphates, Na2FePO4F (NFPF) stands for a cost-effective and voltage-advantageous cathode material for sodium-ion batteries. Nevertheless, the lack of stability imposes constraints on its development and the decay mechanism remains shrouded in ambiguity. Herein, this work proposes the breakup of Fe & horbar;F bond in octahedral dimer accountable for the dissolution of redox centers and the formation of electrochemically inert phase, ultimately leading to the deterioration of electrochemical stability. To verify and address this, Boron (B) atoms situated in interstitial positions of PO4 tetrahedra appearing trigonal BO3 can be specifically targeted to enhance bond covalency and tailor electronic rearrangements at Fe & horbar;F bonds, thus stabilizing the octahedral dimer structure. This also facilitates rapid Na+ diffusion dynamics and accelerated electronic conductivity. As expected, NFPF-B exhibits an ultra-high discharge specific capacity (118.34 mAh g-1 at 0.1C) and excellent long-term durability (capacity retention of 91.9% after 1000 cycles). The stability of the octahedra dimer is underscored by minimal volume change (2.9%) within the two-stage biphase reaction of sodium storage mechanism. This work elucidates the enduring degradation mechanism of NFPF from octahedral dimers and offer theoretical guidance for Fe-based cathode materials with prolonged stability.

Sodium-ion batteries (SIBs) are a promising alternative to lithium-ion batteries for grid-scale energy-storage systems due to their low cost and abundant resource. Herein, Na4Fe3(PO4)(2)P2O7 with a porous structure was fabricated by a mechanochemical method. The porous structure and the uniform carbon coating layer of the material are beneficial to the electrolyte infiltration for better electron/ion transfer. The in situ and ex situ XRD analyses reveal that the cathode material undergoes an imperfect solid-resolution reaction during the charge/discharge process. The robust structural stability and high reversibility of the cathode material are attributed for the excellent rate performance and the long-term cycling life. The cathode material gives a high reversible capacity (124.5 mAh g(-1) at 0.1 C), a superior rate performance (97.6 mAh g(-1) at 50 C), and an excellent ultralong cycling life (capacity retention of 94.64% at 1 C after 1000 cycles and 93.98% at 10 C after 5000 cycles). Thus, the Na4Fe3(PO4)(2)P2O7 material with excellent electrochemical properties, low cost, and a simple synthesis method is a promising cathode electrode for SIBs.

Iron-based fluorophosphate (NFPF) is the most promising cathode materials integrating cost efficiency and voltage advantages. However, undesirable electrochemical performance is limited by poor electron conductivity and diffusion kinetics as well as ambiguous mechanism of plateau behavior. The article investigates the optimization of the voltage plateau mediated by local structure through Zr modification. In-depth experiment and theoretical calculations reveal that the heteroatom excites electrochemical Na activity and induces broadened Na+ pathway with the embellishment of intrinsic conductivity and highly stable framework. On the grounds of co-facilitation on electrons and ions, the first plateau is significantly extended and its proportion is increased, which liberates the confinement on electrochemical performance. The NFPF-0.07Zr sample maintains capacity of 73.78 mAh g -1 at 5 C with capacity retention of 68.67% and only 0.02% degradation per cycle over 2000 cycles. The sodium storage mechanism of the dual-biphase reaction is revealed by in situ XRD with slight volume change (3.48%). The assembled full cell outputs initial energy density of 222.3 Wh kg-1 based on the total electrode mass, enabling 150 stable cycles at 1 C. Such a fundamental understanding of the intrinsic mechanism of voltage plateaus offers a rational perspective for designing Fe-based fluorophosphate cathode.

Fe-based mixed phosphate cathodes for Na-ion batteries usually possess weak rate capacity and cycle stability challenges resulting from sluggish diffusion kinetics and poor conductivity under the relatively low preparation temperature. Here, the excellent sodium storage capability of this system is obtained by introducing the high-entropy doping to enhance the electronic and ionic conductivity. As designed high-entropy doping Na4 Fe2.85 (Ni,Co,Mn,Cu,Mg)0.03 (PO4 )2 P2 O7 (NFPP-HE) cathode can release 122 mAh g-1 at 0.1 C, even 85 mAh g-1 at ultrahigh rate of 50 C, and keep a high retention of 82.3% after 1500 cycles at 10 C. Besides, the cathode also exhibits outstanding fast charge capacity in terms of the cyclability and capacity with 105 mAh g-1 at 5 C/1 C, corresponding 94.3% retention after 500 cycles. The combination of in situ X-ray diffraction, density functional theory, conductive-atomic force microscopy, and galvanostatic intermittent titration technique tests reveal that the reversible structure evolution with optimized Na+ migration path and energy barrier boost the Na+ kinetics and improve the interfacial electronic transfer, thus improving performance.

Superior sodium-ion batteries (SIBs) greatly need cathode materials with higher capacity and better durability. Herein, the anion group substitution strategy is proposed to design a cathode material with extraordinary Na+ storage performance, NASICON-Na4Fe3(PO4)(1.9)(SiO4)(0.1)P2O7 (NFPP-Si0.1). The experimental and theoretical research revealed that modification in the local structure by anion substitution significantly boosts the ionic/electronic transfer kinetics via optimizing the electronic conductivity and reducing the Na+ diffusion energy barrier. Furthermore, the SiO4 (4-) substitution generates a slight expansion of the crystal lattice to broaden the Na+ diffusion channel. Specifically, the custom-designed NFPP-Si0.1 could deliver a high rate capability of 77.6 mAh g(-1) at constant 50 C charge-discharge and excellent recyclability of 79.4% retention rate after 7000 cycles at 10 C. Besides, it also possesses outstanding low temperature reversible capacity of 95.5 mAh g(-1) at 0.1 C and long-term cyclability of 93.6% capacity retention after 1000 cycles at 5 C in -10 C-degrees. This strategy of heterogeneous and isostructural anion group substitution provides a method for unlocking high-rate and long-life-span mixed polyanionic cathodes.

The iron-based polyanionic material Na 3 Fe 2 (PO 4 )P 2 O 7 is regarded as an excellent cathode due to its outstanding thermal stability and the three-dimensional (3D) open framework structure with facile sodium-ion transport.

The progress on electrode materials over the last few years has greatly facilitated sodium‐ion batteries (SIBs) toward practical applications. Cost‐effectiveness is the key character to realize practical applications of SIBs. The iron‐based phosphate materials (IPBMs) are composed of the resource abundant and low‐cost Na–Fe–P–O system and have demonstrated intriguing sodium‐storage properties to reach this goal. Starting from NaFePO 4 , through compositional and structural engineering, many IPBMs have been developed in recent years. This review offers a comprehensive overview about the development of IPBMs. Crystal structure, electrochemical performance, and reaction mechanism of three main categories (phosphates, pyrophosphates, mixed polyanions) of IPBMs and their represented materials are systematically introduced. Besides, the key challenges encountered by IPBMs, including the impurity phase issue, low‐quality carbon coating, limited energy density, and random morphology are proposed. Finally, perspectives on the future development of IPBMs from intrinsic properties regulation to full battery manufacturing are highlighted in aspects of electrochemical performance enhancements, mechanism investigation, surface and electrolytes, and commercialization. It is believed that this review is timely and is of great importance to promote applications of cost‐effective sodium‐ion batteries.

Na superionic conductor (NASICON) structured materials are promising cathode materials due to their high sodium diffusivity and thermostability. However, the limited specific capacity and poor reaction kinetics are key issues. In this work, a uniform reactive site network is successfully applied in Na4FeV(PO4)(3) by carbon modification. We demonstrate that the NASICON structure of Na4FeV(PO4)(3) is capable of delivering a high capacity of 156 mA h g(-1 )in the voltage range of 2.0-4.4 V. Phase transition determined by ex situ X-ray diffraction (XRD) indicates that the reaction is highly reversible during Na+ insertion/extraction. Notably, a high-mass-loading electrode (6.2 mg cm(-2)) is also fabricated, which displays decent performance due to the rational design of carbon networks. This work is of great significance for developing high-volumetric energy density sodium-ion batteries (SIBs).

The multiple issues of unstable electrode/electrolyte interphases, sluggish reaction kinetics, and transition-metal (TM) dissolution have long greatly affected the rate and cycling performance of cathode materials for Na-ion batteries. Herein, a multifunctional protein-based binder, sericin protein/poly(acrylic acid) (SP/PAA), is developed, which shows intriguing physiochemical properties to address these issues. The highly hydrophilic nature and strong H-bond interaction between crosslinking SP and PAA leads to a uniform coating of the binder layer, which serves as an artificial interphase on the high-voltage Na4 Mn2 Fe(PO4 )2 P2 O7 cathode material (NMFPP). Through systematic experiments and theoretical calculations, it is shown that the SP/PAA binder is electrochemically stable at high voltages and possesses increased ionic conductivity due to the interaction between sericin and electrolyte anion ClO4- , which can provide additional sodium-migration paths with greatly reduced energy barriers. Besides, the strong interaction force between the binder and the NMFPP can effectively protect the cathode from electrolyte corrosion, suppress Mn-dissolution, stabilize crystal structure, and ensure electrode integrity during cycling. Benefiting from these merits, the SP/PAA-based NMFPP electrode displays enhanced rate and cycling performance. Of note, the universality of the SP/PAA binder is further confirmed on Na3 V2 (PO4 )2 F3 . It is believed that the versatile protein-based binder is enlightening for the development of high-performance batteries.

Suspended arrays of small volume, high quality factor silicon nitride nanobeam cavities with lateral fin structure were designed and fabricated. The resonance wavelength and Q-factor can be tuned by changing the alignment of fin to airhole. The resulting nanobeam cavities with lateral fins are ideal candidates for high performance optical cavities.

Abstract Integration of quantum emitters in photonic structures is an important step in the broader quest to generate and manipulate on-demand single photons via compact solid-state devices. Unfortunately, implementations relying on material platforms that also serve as the emitter host often suffer from a tradeoff between the desired emitter properties and the photonic system practicality and performance. Here, we demonstrate “pick and place” integration of a Si3N4 microdisk optical resonator with a bright emitter host in the form of ∼20-nm-thick hexagonal boron nitride (hBN). The film folds around the microdisk maximizing contact to ultimately form a hybrid hBN/Si3N4 structure. The local strain that develops in the hBN film at the resonator circumference deterministically activates a low density of defect emitters within the whispering gallery mode volume of the microdisk. These conditions allow us to demonstrate cavity-mediated out-coupling of emission from defect states in hBN through the microdisk cavity modes. Our results pave the route toward the development of chip-scale quantum photonic circuits with independent emitter/resonator optimization for active and passive functionalities.

Photonic crystal lasers can be realized either based on photonic bandgap defect mode or defect-free bandedge mode, while the bandgap is not essential for the latter. We review here defect-free bandedge mode based photonic crystal surface-emitting lasers (PCSELs) for on-chip integration. We first discuss ultra-thin membrane reflector vertical-cavity surface-emitting lasers (MR-VCSELs), where single layer photonic crystal slabs can be designed as a broadband membrane reflector. Later, we discuss another type of defect-free PCSELs where the lasing cavity is formed based on evanescent coupling of gain medium with the photonic crystal bandedge mode near bandedge. Cavity designs were carried out for the optimal modal overlap and high confinement factors. Lateral cavity size scaling was also investigated both theoretically and experimentally in PCSELs. Buried tunnel junction based InGaAsP quantum well heterostructures were also designed and incorporated into electrically injected PCSELs. Finally, discussions are given toward energy efficient lasers.

To solve the problem of poor conductivity, monoclinic NaVPO4F with a uniform carbon coating layer is synthesized via a facile solution approach with assistance of polyvinyl pyrrolidone (PVP). On one hand, PVP acts as a surfactant, encapsulating the precursor and restraining the particle growth. On the other hand, PVP is used as carbon source, in-situ generating a uniform carbon coating layer on the surface of NaVPO4F particles. The obtained NaVPO4F/C composite shows much enhanced electronic conductivity of 4.2 x 10(-2) S cm(-1). As a result, the synthesized NaVPO4F/C cathode for sodium ion batteries demonstrates superior cyclic stability and rate capability, delivering a reversible capacity of 111 mAh g(-1) at 0.1 C, maintaining 81.8% capacity retention after 1000 cycles at 10 C and retaining a high capacity of 68 mAh g(-1) at 20 C.

With an ultimately thin active region, monolayer transition metal dichalcogenide lasers have the potential of realizing ultralow lasing threshold and power consumption. The flexibility also enables integration possibilities on unconventional substrates. Here, we report a photonic crystal surface emitting laser using monolayer tungsten disulfide as the gain medium. The cavity design utilizes a heterostructure in the photonic crystal lattice to provide lateral confinement for a high quality factor with a compact active region. Room-temperature continuous wave lasing is realized after integrating monolayer tungsten disulfide flakes onto the silicon nitride photonic crystal on a quartz substrate. Highly directional, near surface-normal emission has also been experimentally demonstrated. The work reported here demonstrates that a large-area single-mode directional laser can be realized from a monolayer gain medium, which is critical for laser scaling for on-chip integration in data and sensing applications.

We demonstrate coupling of hBN defect emission to Si3N4 microdisk cavities and high-Q plasmonic surface lattice resonances by exploiting the topography of the photonic elements to engineer strain-activated color centers within the element’s field-mode.

We demonstrate a hybrid microphotonic device by integrating a thin film of hexagonal Boron Nitride containing quantum emitters with Si3N4 microdisk resonators. We deterministicallyactive these emitters via strain within a microdisk's evanescent field. © 2019 The Author(s)

We report progresses made in continued scaling in laser cavity and gain medium towards potential few photon sources. Performance of an optically pumped continuous wave room temperature operation monolayer WS2 laser will be discussed, based on a heterostructure photonic crystal cavity for efficient light extraction and surface-emission.