Vacancy Defects Research Articles

Enhanced Thermal and Photostability of Perovskite Solar Cells by a Multifunctional Eu (III) Trifluoromethanesulfonate Additive

AbstractPerovskite solar cells (PSCs) have witnessed a meteoric rise in device performance. However, maintaining photostability, particularly under thermal stress, remains a challenge due to defect formation in the perovskite layer. This study introduces europium (III) trifluoromethanesulfonate [Eu(OTF)3] as a multifunctional additive in two‐step processed perovskite films, significantly improving the performance and high‐temperature photostability of n‐i‐p PSCs. Density function theory (DFT) calculations reveal that the OTF− anion strongly coordinates with Pb2+, effectively inhibiting iodine vacancy defect formation. The addition of Eu(OTF)3 promotes perovskite grain growth to ≈2 µm and enhances film crystallinity. PSCs with a structure of ITO/SnO2/perovskite/PDCBT/NiOx/Au achieve a champion power conversion efficiency (PCE) of 23.8%. Under 85 ± 5 °C and 1 sun illumination at an open circuit in ambient air, the PSCs with Eu(OTF)3 retain 82% of their initial PCE after aging for 1500 h.

The Effect of Oxygen Vacancy Defects on the Structure and Electrochemical Behaviors of LiMn0.65Fe0.35PO4 Cathode

The presence of oxygen vacancy defects significantly impacts the crystal structure and electrochemical attributes of phosphate cathodes. In this investigation, LiMn0.65Fe0.35PO4 materials with varying levels of oxygen vacancy defects were synthesized via hydrogen plasma-induced reduction. It was observed that the content of oxygen vacancy defects on the crystal surface increased proportionately with the rise in hydrogen (H2) flow rate. Notably, the LMFP-3 sample, prepared with an H2 flow rate of 10 ml min−1, demonstrated superior electrochemical performance, characterized by a 159.7 mAh g−1 discharge capacity at 0.1 C and a remarkable 99.8% capacity retention at 5 C after 200 cycles. This enhancement in electrochemical performance is attributed to the improved intrinsic conductivity of the LiMn0.65Fe0.35PO4 material due to the presence of oxygen vacancy defects. However, it is important to note that an excessively high H2 flow rate can lead to the formation of Fe2P impurities, which hinder lithium ion (Li+) diffusion. Furthermore, theoretical calculations conducted using density functional theory provide a rational explanation for the observed improvement in electronic conductivity. The introduction of oxygen vacancy defects results in a significant reduction in the Band gap, which is highly beneficial for enhancing the intrinsic conductivity of the LiMn0.65Fe0.35PO4 materials.

Defect Passivation and Crystallization Regulation for Efficient and Stable Formamidinium Lead Iodide Solar Cells with Multifunctional Amidino Additive.

Amidino-based additives show great potential in high-performance perovskite solar cells (PSCs). However, the role of different functional groups in amidino-based additives have not been well elucidated. Herein, two multifunctional amidino additives 4-amidinobenzoic acid hydrochloride (ABAc) and 4-amidinobenzamide hydrochloride (ABAm) are employed to improve the film quality of formamidinium lead iodide (FAPbI3) perovskites. Compared with ABAc, the amide group imparts ABAm with larger dipole moment and thus stronger interactions with the perovskite components, i.e., the hydrogen bonds between N…H and I- anion and coordination bonds between C = O and Pb2+ cation. It strengthens the passivation effect of iodine vacancy defect and slows down the crystallization process of α-FAPbI3, resulting in the significantly reduced non-radiative recombination, long carrier lifetime of 1.7 µs, uniformly large crystalline grains, and enhances hydrophobicity. Profiting from the improved film quality, the ABAm-treated PSC achieves a high efficiency of 24.60%, and maintains 93% of the initial efficiency after storage in ambient environment for 1200 hours. This work provides new insights for rational design of multifunctional additives regarding of defect passivation and crystallization control toward highly efficient and stable PSCs.

Adjustment in phonon scattering through doping to boosting the Near-IR photoresponse performance of p-type SnSe nanosheets

As a p-type semiconductor, layered SnSe has attracted more and more attention because of its great potential application in the field of optoelectronics. However, the strong phonon scattering caused by abundant intrinsic vacancy defects dramatically reduces the performance of carrier transport. It is significant to effectively compensate for the intrinsic defects and reduce the phonon scattering for photodetection materials. In this letter, a novel and simple method is used to reduce the scattering and thus improve the detector performance. The inhibition effect of doping on phonon scattering is systematically studied by experiments and theoretical calculations. The Bi-doped SnSe photodetector exhibits great responsivities of 2.13 A W−1 (447 nm), 1.35 A W−1 (655 nm) and 1.91 A W−1 (980 nm) at 5 V, which are about 2∼3 folds better than those of the undoped device. Furthermore, for the Bi-doped SnSe photodetector, the Ion/Ioff are about 46.7, 20.3 and 30.3 for 447 nm, 655 nm and 980 nm, respectively, which are much higher than those of the SnSe photodetector. The photoluminescence and absorption are performed to confirm the bandgap and defects energy level. Meanwhile, the temperature-dependent current-voltage curves measurement is utilized to prove that the enhancement in response performance is because of the decrease in intensity of phonon scattering, which is attributed to the reduction of scattering centers and the weakening of the effect of vacancy defects on the structural translational asymmetry. All these results evidently illustrate that adjustment in phonon scattering is an effective way to achieve high-performance SnSe photodetectors.

UV and X-ray induced photochromic material based on defect state exchanges

Inorganic photochromic (PC) materials are gaining increasing recognition as promising candidates for applications in optical storage and information display. However, conventional photochromic materials exhibit sluggish coding rates and a deficiency in intelligent response for writing and erasing under multiple excitation sources. This deficiency contributes to suboptimal readout/decoding efficiency and storage security. Here, we show a Ba2NaNb5O15:Er3+ photochromic material with photoluminescence reversible modulation that can fast respond to both ultraviolet light and 532 nm laser within about 1 s, which accompanied by thermal bleaching. The PC mechanism which is based on defect state exchanges between oxygen vacancy defects and color centers is attributed to the structural flexibility of Nb-O systems and oxygen vacancy increased under irradiation. More importantly, it shows differential PC decay behavior in response to X-ray and UV light due to the difference in the number of trapped carriers. Therefore, a simple strategy based on different self-recovery levels induced by double excitation is constructed to develop an encrypted optical memory model. This fast and differential excitation source response behavior hopefully stimulates the development of new encrypted optical memory.

Quenching-induced oxygen vacancy engineering boosts photocatalytic activities of CaTiO3

Oxygen vacancies (VOs) play a pivotal role in promoting the photocatalytic activities of perovskite oxides. Herein, we proposed a simple and effective strategy of introducing both surface oxygen vacancies and bulk single electron trapped oxygen vacancies (SETOVs) into CaTiO3 by ethanol quenching. The purchased CaTiO3 was preheated at 800 °C and then the hot CaTiO3 was quenched in ethanol instantly. The ethanol-quenched QE-CaTiO3 delivers much improved photocatalytic activities towards both RhB degradation and hydrogen evolution under visible light irradiation by 6.5 and 65.2 times, respectively, in comparison with the pristine CaTiO3. Both the bulk SETOVs and surface VOs enhance light absorption, and the surface VOs serve as photocatalytic active sites. DFT calculations further reveal the narrowed band gap and accumulated charge density near the Fermi level in QE-CaTiO3, which help the visible light absorption, facilitate charge carriers generation and migration, and promote photocatalytic activities. Our findings provide an efficient and easily scalable approach to engineering oxygen vacancy defects in photocatalysts and other catalysts.

Enhancing Emission and Stability in Na-Doped Cs3Cu2I5 Nanocrystals.

Lead-free Cs3Cu2I5 metal halides have garnered significant attention recently due to their non-toxic properties and deep-blue emission. However, their relatively low photoluminescence quantum efficiency and poor stability have limited their applications. In this work, sodium iodide (NaI) is used to facilitate the synthesis of Cs3Cu2I5 nanocrystals (NCs), demonstrating improved photoluminescence intensity, photoluminescence quantum yield, and stability. Systematic optoelectronic characterizations confirm that Na+ is successfully incorporated into the Cs3Cu2I5 lattice without altering its crystal structure. The improved Photoluminescence Quantum Yield (PLQY) and stability are attributed to the strengthened chemical bonding, which effectively suppresses vacancy defects in the lattice. Additionally, light-emitting diodes (LEDs) based on 10% NaI-doped Cs3Cu2I5 NCs were assembled, emitting vibrant blue light with a maximum radiant intensity of 82 lux and Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of (0.15, 0.1). This work opens new possibilities for commercial lighting display applications.

Cation vacancy modulated Cu3P-CoP heterostructure electrocatalyst for boosting hydrogen evolution at high current densities and coupling Zn-H2O battery

Exploiting highly efficient, cost-effective and stable electrocatalysts is key to decreasing hydrogen evolution reaction (HER) kinetics energy barrier. Herein, the alkaline HER kinetics energy barrier can greatly reduce by the joint strategies of the cation vacancy and heterostructure engineering, which is seldom explored and remains ambiguous. In this study, an efficient and stable copper foam-supported Cu3P-CoP heterostructure electrocatalyst with cation vacancy defects (defined as Cu3P-CoP-VAl/CF) was designed for HER via the successive coprecipitation, electrodeposition, alkali etching and phosphorization treatments. As anticipated, the as-obtained Cu3P-CoP-VAl/CF electrocatalyst reveals a remarkable catalytic activity for HER with a low overpotential of 205 mV at a current density of 100 mA·cm−2, a high turnover frequency value of 1.05 s−1 at an overpotential of 200 mV and a small apparent activation energy (Ea) of 9 kJ·mol−1, while shows superior long-term stability at large current densities of 100 and 240 mA·cm−2. Systematic experiment and characterization data demonstrate that the formed cation vacancy could optimize the Ea, leading to the decrease of the kinetic barriers of Cu3P-CoP/CF heterostructure, as well as the established heterogeneous interface induced a synergistic effect between biphasic components on boosting the kinetics toward HER. The results of density functional theory disclose that the synergistic effect of Cu3P-CoP heterostructure could decrease the energy barrier and optimize Gibbs free energy of hydrogen adsorption, resulting in the enhancement of intrinsic catalytic activity of Cu3P-CoP-VAl/CF. More significantly, the alkali-cell assembled by Cu3P-CoP-VAl/CF (cathode) and RuO2/CF (anode) behaves outstanding water splitting performance, delivering a current density of 10 mA·cm−2 at a relatively small applied voltage of 1.58 V, along with encouraging long-term durability. In addition, the alkaline Zn-H2O battery with Cu3P-CoP-VAl/CF as the cathode has been fabricated for the simultaneous generation of electricity and hydrogen, which displays a large power density of up to 4.1 mW·cm−2. The work demonstrates that rational strategy for the design of competent electrocatalysts can effectively accelerate the kinetics of HER, which supplies valuable insights for practical applications in overall water splitting.

Stereochemically Active Lone Pairs Stabilizing Intrinsic Vacancy Defects in Thermoelectric InTe.

Harvesting waste heat efficiently with thermoelectric energy conversion requires materials with low thermal conductivity. Recently, it was demonstrated how dynamic lone pair expression in thermoelectric InTe is responsible for giant anharmonicity leading to a very low lattice thermal conductivity. InTe also contains correlated disorder of intrinsic defects due to vacancies, and this contributes to additional lowering of the thermal conductivity. Here we use the three-dimensional difference pair distribution function (3D-ΔPDF) to analyze 25 K single crystal diffuse X-ray scattering from InTe to unravel the local defect structure, and propose a microscopic structural model. Extended off-centering of In+ ions induced by vacancies allows for the local expression of stereochemically active lone pairs. The associated electronic stabilization is proposed to be a driving force for the formation of In+ vacancy defects in InTe.

Controlling the Orientation‐Dependent Second Harmonic Generation in Hybrid Germanium Perovskites

AbstractManipulating the crystal orientation plays a crucial role in the conversion efficiency during second harmonic generation (SHG). Here, we provide a new strategy in controlling the surface‐dependent anisotropic SHG with the precise design of (101) and (2 0) MAGeI3 facets. Based on the SHG measurement, the (101) MAGeI3 single crystal exhibits larger SHG (1.3×(2 0) MAGeI3). Kelvin probe force microscopy imaging shows a smaller work function for the (101) MAGeI3 compared with the (2 0), which indirectly demonstrates the stronger intrinsic polarization on the (101) surface. X‐ray photoelectron spectroscopy confirms the band bending within the (101) facet. Temperature‐dependent steady‐state and time‐resolved photoluminescence spectroscopy show shorter lifetime and wider emission band in the (101) MAGeI3 single crystal, revealing the higher defect states. Additionally, powder X‐ray diffraction patterns show the (101) MAGeI3 possesses larger in‐plane polar units [GeI3]− density, which could directly enhance the spontaneous polarization in the (101) facet. Density functional theory (DFT) calculation further demonstrates the higher intrinsic polarization in the (101) facet compared with the (2 0) facet, and the larger built‐in electric field in the (101) facet facilitates surface vacancy defect accumulation. Our work provides a new angle in tuning and optimizing hybrid perovskite‐based nonlinear optical materials.

Controlling the Orientation-Dependent Second Harmonic Generation in Hybrid Germanium Perovskites.

Manipulating the crystal orientation plays a crucial role in the conversion efficiency during second harmonic generation (SHG). Here, we provide a new strategy in controlling the surface-dependent anisotropic SHG with the precise design of (101) and (2 0) MAGeI3 facets. Based on the SHG measurement, the (101) MAGeI3 single crystal exhibits larger SHG (1.3×(2 0) MAGeI3). Kelvin probe force microscopy imaging shows a smaller work function for the (101) MAGeI3 compared with the (2 0), which indirectly demonstrates the stronger intrinsic polarization on the (101) surface. X-ray photoelectron spectroscopy confirms the band bending within the (101) facet. Temperature-dependent steady-state and time-resolved photoluminescence spectroscopy show shorter lifetime and wider emission band in the (101) MAGeI3 single crystal, revealing the higher defect states. Additionally, powder X-ray diffraction patterns show the (101) MAGeI3 possesses larger in-plane polar units [GeI3]- density, which could directly enhance the spontaneous polarization in the (101) facet. Density functional theory (DFT) calculation further demonstrates the higher intrinsic polarization in the (101) facet compared with the (2 0) facet, and the larger built-in electric field in the (101) facet facilitates surface vacancy defect accumulation. Our work provides a new angle in tuning and optimizing hybrid perovskite-based nonlinear optical materials.

Unveiling the impact of atomic-scale defects and surface roughness on interfacial properties in hexagonal boron nitride

Atomic-scale defects are ubiquitous in two-dimensional (2D) materials, yet their impact on interfacial properties remains insufficiently understood. Hexagonal boron nitride (hBN) is a 2D inorganic material with potential applications in nanofluidic devices and desalination. Here, we show that specific vacancy defects, in conjunction with monolayer roughness, can be used to manipulate the wetting and frictional behavior of hBN. Using combined first principles and classical modeling, we compute water contact angles and slip lengths on realistic hBN surfaces. Our findings demonstrate a significant alignment with experimental results. The combined effect of vacancy defects and surface roughness, known as exposed edges, provides a compelling explanation for the water contact angle (WCA) of 66° on pristine, uncontaminated hBN. Furthermore, this suggests that specific vacancy defects contribute to an enhanced hydrophilicity of hBN surfaces. The combined approach not only achieves high predictive accuracy but also predicts water slip length on hBN of roughly 1 nm, in agreement with the experiments. The findings emphasize the significance of incorporating vacancy defects and surface roughness in molecular simulations when modeling nanomaterial–water interfaces. This work will open up new avenues to understanding water flow through nanochannels and membranes, paving the way for revolutionary advancements in water purification and desalination.

Synergistic Effect of Zn2+ Cation Doping and Te2− Anion Passivation on CsPbBrxI3‐x Nanocrystals for Efficient Perovskite Light‐Emitting Diodes

AbstractThe challenges of instability and surface defects in CsPbBrxI3‐x nanocrystals (NCs) pose significant limitations on their potential application in high‐performance pure‐red perovskite light‐emitting diodes (PeLEDs). Herein, a synergistic strategy of divalent cation (Zn2+) doping and anion (Te2−) passivation is proposed to solve these issues. Density functional theory analysis reveals that the synergistic effect can not only reduce the formation energy of CsPbBrxI3‐x NCs but also increase theiodide vacancy defect formation energy of CsPbBrxI3‐x NCs. Consequently, the optimized Zn2+/Te2− co‐modified CsPbBrxI3‐x NCs exhibit significantly enhanced stability with a near‐unity photoluminescence efficiency. Pure‐red PeLEDs based on these CsPbBrxI3‐x NCs possess outstanding spectral stability with a maximum external quantum efficiency and luminance of 16.1% and 1397.2 cd m−2, respectively. This synergistic strategy provides a new approach for enhancing the performance of mixed halide perovskite NCs and the corresponding optoelectronic devices.

Critical role of vacancy defects in graphene nanosheets for enhancing asphalt binder

Clarifying the interaction between the intrinsic structure of graphene and asphalt binder is critical to achieve the practical application of graphene modified asphalt. Herein, the thermal-mechanical properties and thermal-oxidative aging resistance of asphalts modified by two types of exfoliated graphene (EG) with less vacancy and vacancy-defected graphene (VDG) were investigated via multi-scale methods, aiming at elucidating the role of vacancy defects in graphene. Rheological measurements demonstrate that VDG have stronger capability of improving the deformation resistance and aging resistance of asphalt than EG. Atomic force microscopy analysis further verifies that VDG has a strong interaction with the non-polar components of asphalt, forming dense micellar structures. In addition, molecular dynamics simulations evidence that the vacancy defects in graphene can form the electrostatic adsorption between asphalt hydrocarbon molecules (light components), increasing the concentration and densification of asphaltenes, promoting the transformation of asphalt from sol structure to gel structure, thereby significantly improving the thermal-mechanical and anti-aging properties of asphalt binder. And the interaction is also verified by infrared spectral analysis and gaussian calculation through peak displacement. The discovery of the effect of vacancy defects in graphene for reinforced asphalt deepens the understanding for developing high performance graphene modified asphalts.

Robust Nuclear Spin Polarization via Ground-State Level Anticrossing of Boron Vacancy Defects in Hexagonal Boron Nitride.

Nuclear spin polarization plays a crucial role in quantum information processing and quantum sensing. In this work, we demonstrate a robust and efficient method for nuclear spin polarization with boron vacancy (V_{B}^{-}) defects in hexagonal boron nitride (h-BN) using ground-state level anticrossing (GSLAC). We show that GSLAC-assisted nuclear polarization can be achieved with significantly lower laser power than excited-state level anticrossing, making the process experimentally more viable. Furthermore, we have demonstrated direct optical readout of nuclear spins for V_{B}^{-} in h-BN. Our findings suggest that GSLAC is a promising technique for the precise control and manipulation of nuclear spins in V_{B}^{-} defects in h-BN.

Unveiling the NIR modulation performance enhancement of VO2 endowed by oxygen vacancy elimination

Vanadium dioxide has emerged as a promising material for smart windows owing to the temperature-responsive variable near-infrared (NIR) transmittance. Yet, the poor NIR modulation ability challenges its efficiency in thermal management. In this study, by meticulously controlling the oxygen vacancy content at a low level, VO2 nanoparticles with excellent NIR modulation performance are achieved. Oxygen vacancy (VO) defects elimination leads to a remarkable decrease of reflectance in the monoclinic (M) phase, dramatically enhancing the near-infrared contrast of VO2 by 154 %. Density functional theory (DFT) calculations reveal that VO elimination favors low refractive index in the NIR region. The optimized experiment is carried out to prepare VO2 nanoparticles with low defects and high crystallinity. It shows the best NIR transmittance contrast at 1500 nm (ΔT1500 nm) of 24.4 %, simultaneously keeping a high luminous transmittance (Tlum) of 79.7 %. This study is believed to provide valuable guidance for the current defect and thermochromic performance study of VO2.

Novel bilayer 2D V2O5 as a potential catalyst for fast photodegradation of organic dyes

Two-dimensional (2D) materials have recently drawn interest in various applications due to their superior electronic properties, high specific surface area, and surface activity. However, studies on the catalytic properties of the 2D counterpart of V2O5 are scarce. In the present study, the catalytic properties of 2D V2O5 vis-à-vis bulk V2O5 for the degradation of methylene blue dye are discussed for the first time. The 2D V2O5 catalyst was synthesized using a modified chemical exfoliation technique. A massive increase in the electrochemically active surface area of 2D V2O5 by one order of magnitude greater than that of bulk V2O5 was observed in this study. Simultaneously, ~ 7 times increase in the optical absorption coefficient of 2D V2O5 significantly increases the number of photogenerated electrons involved in the catalytic performance. In addition, the surface activity of the 2D V2O5 catalyst is enhanced by generating surface oxygen vacancy defects. In the current study, we have achieved ~ 99% degradation of 16 ppm dye using the 2D V2O5 nanosheet catalysts under UV light exposure with a remarkable degradation rate constant of 2.31 min−1, which is an increase of the order of 102 from previous studies using V2O5 nanostructures and nanocomposites as catalysts. Since the enhanced photocatalytic activity emerged from the surface and optical properties of the catalyst, the current study shows great promise for the future application of 2D V2O5 in photo- and electrocatalysis.

Bivalent metal ion co-doped methylammonium lead tribromide perovskite nanocrystal scintillator for X-ray imaging

Perovskite scintillators with low cost, easy preparation, environmental stability, and high-resolution have become candidates for X-ray imaging applications. Here, based on the calculation results of surface formation energy (Ef) and vacancy defect energy (Evac), a series of co-doped perovskite nanocrystals (NCs) with photoluminescence high quantum yield (PLQY) and fast luminescence decay time had been prepared by doping several bivalent metal ions into the B-site of methylammonium lead tribromide (MAPbBr3). In addition, the scintillator with flexibility was prepared using poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) as the carrier, showing excellent stability and scintillation performance, with a light yield of 21,200 photons/MeV, imaging resolution reached 11.7 lp/mm, and low detection limits of 462 nGyair s−1. Finally, we demonstrated the scintillator characteristic with high-quality imaging results and excellent tolerance under high dose rate X-ray (25 mGy s−1). Therefore, the combination of co-doped nanocrystals with excellent optical properties and PVDF-HFP further paves the way for the development of a scintillator.

Size-Dependent Oxygen Vacancy of Iron Oxide Nanoparticles.

Prior research has highlighted the reduction of iron oxide nanoparticle (IONPs) sizes to the "ultra-small" dimension as a pivotal approach in developing T1-MRI contrast agents, and the enhancement in T1 contrast performance with the reducing size is usually attributed to the increased specific surface area and weakened magnetization. Nonetheless, as the size decreases, the variation in surface defects, particularly oxygen vacancy (VO) defects, significantly impacts the T1 imaging efficacy. In this study, the VO on IONPs is meticulously investigated through XPS, Raman, and EPR spectroscopy. As the nanoparticle size decreased, the VO concentration rose initially but subsequently declined, with the peak concentration observed in the size of 8.27nm. Further insights gained from synchrotron XAS analysis and DFT calculations indicate that both surface tension and phase transition in IONPs contribute to alterations in the Fe─O bond length, thereby influencing the VO formation energy across varying nanoparticle sizes. The MRI tests reveal that the VO in IONPs serve as pivotal sites for the attachment of water molecules to iron ions, and IONPs with fewer VO exhibited a deterioration in T1-MRI contrast effects. This research may provide a deeper understanding of the relationship between T1 contrast performance and the size of IONPs.

A N–CoSe/CoSe2–C@Cu hierarchical architecture as a current collector-integrated anode for potassium-ion batteries

The highly reversible insertion/extraction of large-radius K+ into electrode materials remains a tough goal, especially for conversion-type materials. Herein, we design a current collector-integrated electrode (N–CoSe/CoSe2–C@Cu) as an advanced anode for potassium-ion battery (PIBs). The conductive CoSe/CoSe2 heterojunction with rich Se vacancy defects, conductive sp2 N-doped carbon layer, and the elastic copper foil matrix can greatly accelerate the electron transfer and enhance the structural stability. Consequently, the well-designed N–CoSe/CoSe2–C@Cu current collector-integrated electrode displays enhanced potassium storage performance with regard to a high capacity (325.1 mAh·g−1 at 0.1 A·g−1 after 200 cycles), an exceptional rate capability (223.5 mAh·g−1 at 2000 mA·g−1), and an extraordinary long-term cycle stability (a capacity fading of only 0.019% per cycle over 1200 cycles at 2000 mA·g−1). Impressively, ex situ scanning electron microscopy (SEM) characterizations prove that the elastic structure of copper foil is merged into the cleverly designed N–CoSe/CoSe2–C@Cu heterostructure, which buffers the deformation of structure and volume and greatly promotes the cycle life during the potassium/depotassium process.Graphical abstract