Binder-Free Cathode for Stable Zinc Ion Storage, Dendrite-Suppressing Anode Thereof, and Zinc Ion Capacitor Comprising the Same

Abstract

One embodiment of the present invention provides a positive electrode active material with improved energy density, a positive electrode composite including the same, and a zinc ion capacitor. The positive electrode active material according to one embodiment of the present invention is a composite structure in which niobium pyrophosphate is infiltrated between each layer of two-dimensional MXene, and can significantly improve the performance of the capacitor by increasing electrical conductivity and increasing storage capacity.

Description

Technology Field

[0001] The present invention aims to improve the energy density of a zinc ion capacitor and relates to a positive electrode active material having a composite structure in which niobium pyrophosphate is infiltrated between each layer of a three-dimensional MXene, a dendrite formation-inhibiting negative electrode including the same, and a zinc ion capacitor. Background Technology

[0002] Conventional electrochemical capacitors (EC) and lithium-ion batteries (LIB) provide high energy and power density, but they have the disadvantage of low power density and cycle performance.

[0003] While hybrid metal ion capacitors (MICs) utilizing Na+, Li+, and K+ ions must focus significantly on addressing safety issues arising from the explosive nature of metal ions, Ca 2+ , Mn 2+ , Zn 2+ and Al 3+ Hybrid metal-ion capacitors (MICs) based on multivalent metal ions such as [the above] can provide enhanced safety and rapidly transfer charge dynamics along with higher energy and power density.

[0004] At this time, Zn metal has a high theoretical capacity of 820 mAh / g and exhibits a significantly high overvoltage for hydrogen generation. Due to its high level of safety, simple manufacturing process, use of inexpensive, earth-abundant metal-based electrodes, and output similar to that of lithium-ion batteries (LIBs), zinc-ion capacitors (ZICs) are the most suitable candidates for next-generation ESS.

[0005] A zinc ion capacitor (ZIC) can generally be composed of a Zn metal anode similar to a conventional battery anode and a capacitive or pseudo-capacitive cathode of an aqueous electrolyte.

[0006] The above ZIC exhibits remarkable long-term Coulombic efficiency, but divalent Zn 2+Faced with various problems such as insufficient cation diffusion and dendritic growth accompanied by side reactions, it prevents strong electrostatic interactions and causes unsustainable cathode and anode structures in aqueous electrolytes.

[0007] Furthermore, to enhance the energy storage capacity of ZIC and manage the dendritic growth of the Zn anode caused by side reactions, it is necessary to develop an optimal cell system by selecting a suitable electrolyte system; however, the bare Zn foil anode has problems such as short circuits occurring after a few cycles at higher current densities due to uncontrolled dendrite formation, and performance degradation caused by the hydrogen evolution reaction (HER) during long-term electrochemical cycling.

[0008] Therefore, many challenges still remain for the development of zinc ion capacitors with enhanced hydrogen generation reactions during long-term electrochemical cycles. Prior art literature

[0009] Republic of Korea Published Patent Application No. 2024-0108344 The problem to be solved

[0010] The technical problem to be solved by the present invention is to improve energy density, and relates to a positive electrode active material having a composite structure in which niobium pyrophosphate is infiltrated between each layer of a three-dimensional MXene, a positive electrode composite including the same, and a zinc ion capacitor.

[0011] The technical problems that the present invention aims to solve are not limited to those mentioned above, and other unmentioned technical problems will be clearly understood by those skilled in the art to which the present invention belongs from the description below. means of solving the problem

[0012] To achieve the above technical problem, one embodiment of the present invention provides a positive electrode active material.

[0013] The positive active material according to one embodiment of the present invention is,

[0014] Two-dimensional MXene nanosheets having a layered structure; and

[0015] It may include niobium pyrophosphate (NbP2O7) particles dispersed between each layer of the above-mentioned MXene compounds.

[0016] In addition, according to one embodiment of the present invention, the two-dimensional material is Ti3C2T X (MXene) , It may include one or more selected from the group consisting of graphene and MWCNT (Multi-Wall Carbon Nano Tube).

[0017] In addition, according to one embodiment of the present invention, the content of the niobium pyrophosphate (NbP2O7) particles may be 1.4 wt% to 5.6 wt% relative to the total positive electrode active material.

[0019] To achieve the above technical problem, another embodiment of the present invention provides an anode composite.

[0020] The anode composite according to one embodiment of the present invention may include an anode comprising carbon fibers; and an anode active material layer coated on the surface of the anode and comprising niobium pyrophosphate (NbP2O7) particles dispersed between each layer of the two-dimensional MXene nanosheets.

[0021] In addition, according to one embodiment of the present invention, the carbon fiber and the anode active material layer are carbon and Ti3C2T x It can be covalently bonded.

[0022] In addition, according to one embodiment of the present invention, the carbon of the carbon fiber and the functional groups (F, OH, Cl) of the MXene compound can be covalently bonded by π-π interaction and interfacial interaction arrangement combination.

[0023] In addition, according to one embodiment of the present invention, the positive active material layer can be coated by performing a drop casting method without a binder.

[0024] In addition, the thickness of the positive active material layer may be 500 (nm) to 5 (μm).

[0025] A zinc ion capacitor comprises a positive electrode including a positive electrode complex;

[0026] A cathode spaced apart from the anode composite and comprising a MXene nanosheet layer coated on the surface of a zinc substrate;

[0027] A separator disposed between the anode and the cathode; and

[0028] The above-mentioned anode, the above-mentioned separator, and the above-mentioned cathode may include an electrolyte impregnated with the above-mentioned anode.

[0029] The MXene nanosheet layer coated on the surface of the zinc substrate at the above cathode may be 1 (μm) to 10 (μm).

[0030] The above electrolyte may include an NaClO4 electrolyte additive. Effects of the invention

[0031] A positive electrode active material according to one embodiment of the present invention is a composite structure in which niobium pyrophosphate is infiltrated between each layer of a two-dimensional MXene, and can significantly improve the performance of a capacitor by increasing electrical conductivity and increasing storage capacity.

[0032] In addition, the cathode composite containing the cathode active material has the effect of simultaneously improving mechanical and electrical properties because the interfacial adhesion is strengthened by the high-density bonding between the cathode active material composed of the NbP2O7 / Ti3C2TX compound and the carbon fiber.

[0033] In addition, the zinc ion capacitor containing the above-mentioned positive electrode active material has high capacitance because dendrite formation is suppressed by the MXene compound coated on the negative electrode and the sodium ions added to the electrolyte, and has high energy density due to the positive electrode active material composed of NbP2O7 / Ti3C2TX compound, and can exhibit an excellent capacitance retention rate while undergoing multiple charge and discharge cycles.

[0034] The effects of the present invention are not limited to the effects described above, and should be understood to include all effects that can be inferred from the configuration of the invention described in the detailed description of the invention or the claims. Brief explanation of the drawing

[0035] FIG. 1 is a schematic diagram illustrating a positive electrode active material according to one embodiment of the present invention. FIG. 2 is a schematic diagram showing an anode composite according to one embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a method for manufacturing an anode composite according to one embodiment of the present invention. Fig. 4 shows the cathode active material niobium pyrophosphate (NbP2O7) / Ti3C2T X This is an image showing the FESEM, TEM, HRTEM, and SEM-EDS spectra of a heterostructure (MXene). Figure 5 shows the cathode active material niobium pyrophosphate (NbP2O7) / Ti3C2T X This is a graph showing the XRD, XPS, XANES, and EXAFS spectra of a heterostructure (MXene). Fig. 6 shows niobium pyrophosphate (NbP2O7) / Ti3C2T X (MAXINE) This is a schematic diagram representing the geometric structure of a heterogeneous structure. Figure 7 is a graph showing the performance of a zinc ion capacitor. Specific details for implementing the invention

[0036] The present invention will be described below with reference to the attached drawings. However, the present invention may be implemented in various different forms and is therefore not limited to the embodiments described herein. Furthermore, in order to clearly explain the present invention in the drawings, parts unrelated to the explanation have been omitted, and similar parts throughout the specification have been given similar reference numerals.

[0037] Throughout the specification, when it is stated that a part is "connected (connected, in contact, combined)" with another part, this includes not only cases where they are "directly connected," but also cases where they are "indirectly connected" with other members interposed between them. Furthermore, when it is stated that a part "includes" a certain component, this means that, unless specifically stated otherwise, it does not exclude other components but rather allows for the inclusion of additional components.

[0038] The terms used herein are merely for describing specific embodiments and are not intended to limit the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, terms such as “comprising” or “having” are intended to indicate the presence of the features, numbers, steps, actions, components, parts, or combinations thereof described in the specification, and should be understood as not precluding the existence or addition of one or more other features, numbers, steps, actions, components, parts, or combinations thereof.

[0040] Hereinafter, the present invention will be described with reference to the drawings presented in this specification. For reference, the drawings may be partially exaggerated to illustrate the features of the present invention. In such cases, it is preferable to interpret them in light of the entire intent of this specification.

[0042] A positive electrode active material according to one embodiment of the present invention is described.

[0043] FIG. 1 is a schematic diagram illustrating a positive electrode active material according to one embodiment of the present invention.

[0044] A positive active material (10) according to one embodiment of the present invention may include a two-dimensional MXene nanosheet (100) having a layered structure; and niobium pyrophosphate (NbP2O7) particles (200) dispersed between each layer of the MXene compound.

[0045] First, the positive active material of the present invention may include a two-dimensional MXene nanosheet (100).

[0046] At this time, the above two-dimensional MXene nanosheet is characterized by having a layered structure.

[0047] At this time, since MXene, as a component of the cathode active material, has a layered structure, it can provide sufficient space for ions to be inserted and stored between the layers. This means that MXene can store more zinc ions. In addition, the two-dimensional layered structure of MXene provides a path for ions to move freely between the layers, causing rapid ion diffusion, which can improve the charging and discharging speed of the battery.

[0048] Furthermore, because MXenes have higher electronic conductivity compared to other cathode materials, electrons can flow easily. This can contribute to reducing internal resistance and increasing the electrical efficiency of the battery. Additionally, the layered structure of MXenes allows for the control of interlayer spacing by introducing various functional groups to the surface. Moreover, since the layered structure of MXenes can effectively absorb structural changes that occur when ions are inserted or emitted, preventing structural collapse, it can play a crucial role in extending battery life.

[0049] At this time, the above two-dimensional material is Ti3C2T X It may include one or more selected from the group consisting of graphene and MWCNT (Multi-Wall Carbon Nano Tube).

[0050] At this time, as the above two-dimensional material, Ti3C2T X The reason for using graphene and MWCNT is that they provide excellent electrical conductivity and a large surface area to facilitate electron transfer and maximize activation during ion insertion and deinsertion processes. In addition, they are structurally stable and have high mechanical strength, which can contribute to extending battery life and maintaining long-term cycle stability.

[0052] At this time, the positive active material of the present invention may include niobium pyrophosphate (NbP2O7) particles (200).

[0053] At this time, the niobium pyrophosphate particles can be dispersed between each layer of the MXene compound, and the niobium pyrophosphate (NbP2O7) particles can be dispersed between the two-dimensional MXene nanosheets to act as spacers that prevent the two-dimensional MXene nanosheets from stacking up again.

[0054] At this time, the content of the niobium pyrophosphate (NbP2O7) particles is characterized as being 1.4 wt% to 5.6 wt% relative to the total positive active material.

[0055] At this time, if the content of the niobium pyrophosphate (NbP2O7) particles is less than 1.4 wt% relative to the total positive electrode active material, the film thickness becomes thin due to the excessively strong interaction between the carbon fiber and the MXene nanosheet, and consequently, there is a problem with the ion conductivity of the electrolyte, and if it exceeds 5.6 wt%, the thickness of the deposited active material becomes thick, which may cause a problem with ions reaching deep into the electrode active material.

[0056] At this time, the structure may have a two-dimensional MXene nanosheet surrounding the niobium pyrophosphate (NbP2O7) particles, and the thickness of the structure in which the niobium pyrophosphate (NbP2O7) particles are dispersed in the two-dimensional MXene nanosheet may be 150 nm to 500 nm.

[0058] A positive electrode composite according to another embodiment of the present invention is described.

[0059] FIG. 2 is a schematic diagram showing an anode composite according to one embodiment of the present invention.

[0060] Referring to FIG. 2, an anode composite according to one embodiment of the present invention comprises: an anode comprising carbon fibers; and an anode active material layer coated on the surface of the anode and comprising niobium pyrophosphate (NbP2O7) particles dispersed between a two-dimensional MXene nanosheet and each layer of the MXene nanosheets, wherein the carbon fibers and the anode active material layer comprise carbon and Ti3C2T x The carbon and the functional groups (F, OH, Cl) of the MXene compound can be covalently bonded through π-π interactions and can be covalently bonded by the combination of interfacial interaction arrangements.

[0061] The anode composite of the present invention may include carbon fibers as an electrode material, and may include one or more materials selected from the group consisting of copper and nickel in addition to carbon fibers as the electrode material.

[0062] In addition, the anode composite of the present invention may further include an anode active material layer on the substrate, and the anode composite of the present invention may be coated with an anode active material comprising niobium pyrophosphate (NbP2O7) particles dispersed between the above-described two-dimensional MXene nanosheets and each layer of the MXene nanosheets.

[0063] At this time, the carbon fiber and the cathode active material layer are carbon and Ti3C2T x They can be covalently bonded, and the carbon of the carbon fiber and the functional groups (F, OH, Cl) of the MXene compound can be covalently bonded through π-π interactions and interfacial interaction arrangement combinations.

[0064] At this time, when two-dimensional MXene nanosheets are attached to a carbon substrate by the above-mentioned covalent bonds and π-π interactions, excellent adhesion and various types of interactions occur at the interface, thereby simultaneously enhancing high conductivity, structural stability, active surface area, ion diffusion efficiency, and durability, which can have the effect of maximizing the electrochemical performance and lifespan of the electrode.

[0065] At this time, referring to FIG. 2, the positive active material layer can be coated by performing a drop casting method without a binder.

[0066] In this case, when the positive active material layer is drop-cast onto the positive surface without a binder, the electrical resistance between the positive active material and the substrate is reduced, which can significantly improve electrical conductivity. As a result, electrons can move more easily, which can improve the overall performance of the battery or capacitor.

[0067] Furthermore, in the absence of a binder, the active material adheres more evenly to the substrate, maximizing the active surface area of ​​the electrode. This increases the contact area between the electrolyte and the electrode, thereby raising the reaction rate and improving charge-discharge performance.

[0068] Furthermore, binders play a role in reducing the proportion of active material in the cathode. Drop casting without a binder can maximize the amount of active material in the electrode, thereby increasing the theoretical capacity of the battery. However, while binders can break down or cause structural instability in the electrode over time, applying the cathode active material without a binder can avoid these long-term stability issues.

[0069] At this time, the thickness of the positive active material layer of the positive composite of the present invention may be 500 (nm) to 5 (μm).

[0070] At this time, if the thickness of the positive active material layer is less than 500 nm, a thin active material layer may cause a decrease in capacity and mechanical stability, and may result in limited electrolyte penetration. If it exceeds 5 μm, a thick active material layer may cause ion diffusion and electron transfer to become difficult, and may result in structural damage due to volume expansion.

[0072] A zinc ion capacitor according to another embodiment of the present invention is described.

[0073] An anode composite according to one embodiment of the present invention is,

[0074] The apparatus may include an anode comprising the anode composite described above; a cathode spaced apart from the anode composite and comprising a MXene nanosheet layer coated on the surface of a zinc substrate; a separator disposed between the anode and the cathode; and an electrolyte impregnated with the anode, the separator, and the cathode.

[0075] First, the anode of the present invention is characterized by comprising the anode composite described above.

[0076] The description regarding the anode is replaced by the description regarding the anode complex above.

[0078] Next, the zinc ion capacitor of the present invention may include a negative electrode.

[0079] At this time, the cathode is spaced apart from the anode composite and may include a MXene nanosheet layer coated on the surface of a zinc substrate.

[0080] At this time, the cathode used in the present invention may be zinc foil, and any zinc foil commonly used by a person skilled in the art in zinc ion capacitors may be used without limitation.

[0081] At this time, the cathode is characterized by having a MXene nanosheet layer coated on the surface of a zinc substrate.

[0082] At this time, dendritic formation can be suppressed by the MXene nanosheet layer coated on the cathode, and the side reaction can be suppressed by physically separating the zinc electrode and the electrolyte with the MXene nanosheet.

[0083] At this time, the MXene nanosheet layer coated on the surface of the zinc substrate at the cathode may be 1 μm to 10 μm. If the MXene nanosheet layer is less than 1 μm, there may be a problem with reduced durability due to incomplete surface protection, and if it exceeds 10 μm, there may be a problem with slowed electrochemical reactions and reduced performance by restricting the diffusion path of zinc ions.

[0085] At this time, the above cathode may have the above MXene nanosheet layer applied as a protective layer, and as a method for manufacturing the above cathode, a zinc foil may be polished, and a MXene-zinc foil cathode may be produced by coating MXene ink thereon through drop casting and then vacuum drying.

[0086] In this way, an MXene layer is formed on the zinc foil and acts as a protective layer against dendrite formation.

[0088] In addition, the zinc ion capacitor of the present invention may include an electrolyte.

[0089] In this case, when the above ZnSO4 electrolyte is used, dendrites are formed on the zinc foil, but after covering the zinc foil with an MXene layer, Na + When using an electrolyte containing additives, the formation of dendrites can be suppressed.

[0090] At this time, the electrolyte used in the present invention may include an NaClO4 electrolyte additive.

[0092] The present invention will be explained in more detail below through manufacturing examples and experimental examples. These manufacturing examples and experimental examples are solely for the purpose of illustrating the present invention, and the scope of the present invention is not limited by these manufacturing examples and experimental examples.

[0094] Preparation Example: Preparation of anode composite

[0095] Referring to FIG. 3, a method for manufacturing an anode composite according to one embodiment of the present invention will be described.

[0096] 1) Niobium pyrophosphate (NbP 2 O 7 )Particle manufacturing

[0097] First, using a solution-free materials synthesis approach, Nb was synthesized through vacuum annealing of a stoichiometric mixture of niobium chloride (NbCl5) and phosphoric acid (H3PO4). 4+ A reduced phase of NbP2O7 layered nanosheets containing was produced.

[0098] Next, shaded pyrophosphate ions (P2O7 4- A group of Pa3 spaces with a cubic structure was generated in pairs of ) and octahedral NbO6 units.

[0099] Next, the oxidation state of Nb was maintained at +5 for NbP2O7 throughout the air annealing step of the material development process.

[0101] 2) Fabrication of 2D MXene Nanosheets

[0102] Exfoliation and exfoliated Ti3C2T x -MXene nanosheets were fabricated using a mild exfoliation (MILD) approach, and Ti3C2Tx was prepared by etching the Al layer from adjacent Ti and C layers through in-situ hydrofluoric acid (HF) etching using lithium fluoride (LiF) and hydrochloric acid (HCl).

[0104] 3) MXene nanosheet-niobium pyrophosphate (NbP 2 O 7 ) Manufacturing of composite structured cathode active material

[0105] In the third step, a binder-free NbP2O7 / Ti3C2Tx electrode was developed using a Ti3C2Tx-MXene ink solution and ultrasonically treated NbP2O7.

[0106] This electrode is fabricated on the CF surface via a simple drop casting approach.

[0107] At this time, an NbP2O7 / Ti3C2Tx heteromaterial is formed on the surface of the carbon fiber, and a combination of covalent bonding, π-π bridging, and various interfacial interactions is formed on the CF surface Ti3C2T X This led to the strong and adhesive attachment of the nanosheets.

[0108] In addition, simultaneous improvement of the mechanical and electrical properties of NbP2O7 / Ti3C2Tx is possible through Ti-OC or Nb-P bonds at the interface between the two materials and attachment to the CF surface.

[0109] Furthermore, the 2D planar surfaces of the two materials were bonded to CF to form a nanosheet-wrapped electrode. The nanosheet structures of the two materials led to dense bonding, resulting in greater adhesion at the interface. Most importantly, the binder-free framework of the electrode affected the electrical conductivity of the electrode by preventing the use of binders and unnecessary solvents. Additionally, NbP2O7 can act as a spacer to prevent the MXene nanosheets from re-stacking.

[0111] Experimental Example

[0112] Fig. 4 shows the cathode active material niobium pyrophosphate (NbP2O7) / Ti3C2T X This is an image showing the FESEM, TEM, HRTEM, and SEM-EDS spectra of a heterostructure (MXene).

[0113] Figures 4a-4d show field emission scanning electron microscope (FESEM), transmission electron microscope (TEM), and scanning TEM (STEM) mapping images using energy dispersive spectroscopy (EDS) of NbP2O7 powder samples.

[0114] STEM mapping showed the presence of niobium, phosphorus, and oxygen in a 2D laminated sheet (thickness: 150 nm).

[0115] However, the defect-prone nature of the ZrP2O7 cubic structure is likely due to excessive Nb, P, and O deficiencies caused by air contact and the vacuum annealing process.

[0116] Figures 2e and 2f show NbP2O7 / Ti3C2T wrapped on the CF surface X Showing SEM images of Ti3C2T on the CF surface through π-π and covalent bonding X - It shows that MXene sheets are attached, resulting in an excellent 2D-on-2D adhesive structure and various types of interactions occurring at the interface.

[0117] Ti3C2T X To evaluate the charge storage contribution of Ti3C2T using the drop casting method X A CF electrode wrapped in [material] was fabricated.

[0118] FESEM and elemental mapping results show uniform wrapping of Ti CT and excellent stoichiometry.

[0119] TEM analysis of Ti3C2T wrapping the NbP2O7 framework X -Verification of uniform dispersion of the MXene layer for larger dimensional Ti3C2T X The NbP2O7 nanosheet located within the sheet was exposed.

[0120] Figure 4h shows Ti3C2T, which is tightly wrapped by NbP2O7 sheets and forms multiple layers only a few nanometers thick. X It clearly shows the 2D layer structure of.

[0121] Grid margins of various interplanar distances were explored using high-resolution TEM (HRTEM) images.

[0122] The interplanar distances were calculated using line profile fitting obtained from the Digital Micrograph, and the interplanar distances were expressed as 0.361 and 0.285 nm to verify the (210) and (220) hkl planes of NbP2O7, respectively (Figures 4i and 4j).

[0123] The aforementioned SEM, TEM, elemental mapping using Nb, P, O, Ti, and C, and EDS spectral results reflect the development of a uniform Ti CT sheet wrapped in NbP2O7 material on a CF with good stoichiometry (Figure 4k-4q).

[0125] Figure 5 shows the cathode active material niobium pyrophosphate (NbP2O7) / Ti3C2T X This is a graph showing the XRD, XPS, XANES, and EXAFS spectra of a heterostructure (MXene).

[0126] XRD and XPS analysis of Ti3C2T X / CF, NbP2O7 powder and NbP2O7 / Ti3C2T X / CF was performed to investigate the crystal structure, chemical composition, and oxidation state of the elements present in the compound.

[0127] Ti3C2T shown in Figure 3a X / CF, NbP2O7 powder and NbP2O7 / Ti3C2T X The XRD pattern of / CF shows the crystal planes of the (002), (004), (006), (008), (0010), and (0012) planes of the 2D Ti C TX nanosheet wrapped on the surface of CF.

[0128] Likewise, the XRD pattern of NbP2O7 shows (111), (200), (210), (211), (220), (311), (222), (024), 27 (422), (511) crystal planes, confirming the cubic structure of the Pa3 space group and is in good agreement with Joint Committee on Powder Diffraction Standards (JCPDS) number 85-2234.

[0129] NbP2O7 / Ti3C2T X The XRD pattern of the electrode is Ti3C2T X The two materials exhibited well-preserved diffraction peaks, such as the (002), (004), (006) planes of and the (111), (200), (210), (211), (220) planes of NbP O.

[0130] We confirmed that the average oxidation state of Nb in both brown and gray NbP2O7 is +4.88.

[0131] This composition is 12% Nb 4+ and 88% Nb 5+ It consists of a non-stoichiometric phase within the ZrP2O7 structure and shows that various oxidation states of Nb exist.

[0132] Nevertheless, the low oxidation state of niobium (approaching +4) and its upper limit (exceeding +4.88 but falling short of +5) were influenced by the pseudocubic symmetry of white NbP2O7.

[0133] Furthermore, Nb 4+ from Nb 5+ The increase in the oxidation state of the furnace was probably related to phosphorus atomic defects.

[0134] The general oxidation states of niobium for the different phases of NbP2O7 were +3.9 and +4.4 (brown) and +4.95 (gray).

[0135] CF showed weak and broad peaks at 2θ = 26.2° and 43.4°, which were highlighted with an asterisk (*).

[0136] Ti3C2T terminated on CF X It exhibited a prominent (002) peak 32 at a diffraction angle 2θ of 6.9°, which corresponds to a d-spacing of 1.3 nm, and NbP2O7 / Ti3C2T on the CF surface X It reflects that the composition of has been formed.

[0137] XPS irradiation spectrum is Ti3C2T X In the case of / CF, characteristic peaks of Ti, C, O, and F were displayed, while in the case of NbP2O7, peaks of Nb, P, and O were displayed.

[0138] NbP2O7 / Ti3C2T X In the case of / CF, peaks corresponding to Nb, P, O, Ti, C, and F were observed.

[0139] In the exposed NbP2O7 samples, Nb 3d peaks with binding energies of 210.19 and 207.48 eV and 27 were observed, indicating the coexistence of 3d3 / 2 and 3d5 / 2 components, respectively.

[0140] The energy difference between the two peaks (2.71 eV) corresponds to the core level of the Nb5+ state.

[0141] NbP2O7 / Ti3C2T X The higher binding energy shift of the peak (~0.8 eV) indicates that the 2D-on-2D composite material structure was successfully developed.

[0142] The chemical composition of these materials led to interactions of unique bonding types, such as Nb-OC bonds.

[0143] The Nb 3d peak shows a positive shift compared to the metal Nb binding energy of 207 eV, indicating that electron density has been transferred from Nb to P, as Nb has a positive charge (δ) while P has a negative charge (δ-).

[0144] Figure 5c shows NbP2O7 and NbP2O7 / Ti3C2T X Shows the deconvolved Nb 3d XPS narrowband scan spectrum of the sample.

[0145] The NbP2O7 spectrum shows two peaks at binding energies of 210.19 27 and 207.48 eV, indicating the coexistence of Nb 3d3 / 2 and Nb 3d5 / 2 spin orbits, respectively.

[0146] However, Ti3C2T X When combined with, the peaks shifted to higher binding energies of 210.99 32X and 208.28 eV, respectively, and the shift energy of 0.8 eV reflected the formation of a 2D-on-2D layered electrode.

[0147] Nb 5+ Compared to the core level of the state, a spin-orbit splitting energy of 2.71 eV is appropriate.

[0148] The P 2p narrow scan XPS spectra of the two samples displayed a broad peak, which could be separated and aligned with three distinct peaks of NbP O at binding energies of 135.04, 133.90, 27, and 133.21 eV, with the peaks shifted to positive energies of 135.29, 134.15, and 133.46 eV, respectively (Figure 5d).

[0149] Changes in the amounts of these three peaks confirm the formation of 2D-on-2D layered materials.

[0150] The core-level O 1s spectra of the two samples showed a single broad peak, which was separated into three peaks O 2- , Nb-O and surface oxygen bonds were confirmed (Figure 5e).

[0151] Figure 5f shows the XPS Ti 2p narrowband scan spectra of the two samples.

[0152] NbP2O7 / Ti3C2T X The sample exhibited two broad peaks of Ti 2p3 / 2 and Ti 2p1 / 2 at binding energies of 455.24 and 461.16 eV, respectively, which were further separated into three peaks.

[0153] The separated peaks consist of Ti-C, Ti(II), and Ti(III) peaks, mixed oxide (TiO2). x F y ) and xy carboxyside (TiC x O y This indicates that ) was formed, which is Ti3C2T X - This suggests the existence of multiple ends of the MXene. The less prominent x peak in the center of xy [2d, 35] has a formula valence of +4 and represents TiO2 and TiO2-xF, which likely originated from spontaneous surface oxidation.

[0154] In the high-resolution XPS spectrum of the C1s region, three distinct peaks were detected at binding energies of 281.66, 284.67, and 286.91 eV, indicating NbP2O7 / Ti3C2T X It was confirmed that C-Ti-T, CC, and CO bonds were present in the samples, respectively (Figure 5g).

[0155] The CC peak attributed to graphite carbon was generated due to CO resulting from the selective dissolution of Ti and subsequent surface contamination after the chemical etching process.

[0156] The C1s spectrum of the NbP2O7 sample was observed because carbon tape 27 was used during the XPS test.

[0157] The high-resolution spectrum of F1s was resolved into four distinct binding energies of 683.97, 684.85, 685.98, and 687 eV, attributed to C-Ti-F, Ti-O2-XF, AlF, Al(OF), and x3 x, respectively, which may have been formed because LiF was used during the etching process.

[0158] Ultimately, XRD and XPS results show NbP2O7 / Ti3C2T on the CFs surface X It supported material development.

[0159] Nb and Ti K-edge X-ray absorption spectroscopy (XAS) experiments were performed at the 8C beamline of Pohang Light Source (PLS), and data were recorded in fluorescence mode at room temperature (~25º).

[0160] XAS was used to identify the oxidation state and local structure of NbP O / Ti CT.

[0161] The Nb K-edge X-ray absorption near-edge structure (XANES) spectra including Nb standard references (Nb foil and Nb O) are shown in Figure 3h and S7b.

[0162] NbP2O7 / Ti3C2T XThe 25 spectrum was measured between references and was detected close to the Nb O spectrum of oxidation state +5.

[0163] Therefore, NbP2O7 / Ti3C2T X The oxidation state of NbP2O7(+4) was measured in the energy region below Nb-O.

[0164] In addition, the extended X-ray 25 absorption fine structure (EXAFS) spectrum suggested that there is an atomic distribution around Nb atoms, as shown in Figure 5i.

[0165] The Nb-Nb bond length was ~2.5 Å, mainly detected in the Nb foil, and the Nb-O interaction was 1.5-2.0 Å in the Nb O.

[0166] Therefore, NbP2O7 / Ti3C2T X It was found that NbP2O7 has Nb-O bonds, unlike the peak of the standard reference.

[0167] Figure 5j shows the Ti standard reference (Ti foil and TiO) and NbP2O7 / Ti3C2T X Shows the Ti K-edge XANES and EXAFS spectra.

[0168] NbP2O7 / Ti3C2T X The XANES spectrum of is detected in an energy region higher than that of Ti foil (0) and lower than that of TiO2 (+4), indicating that the oxidation is less than +4.

[0169] Also, using the EXAFS spectrum, NbP2O7 / Ti3C2T X The local structure of the Ti atomic state was investigated.

[0170] Ti-Ti bonds (length: 2.5 Å) were mainly observed in Ti foils, and peaks associated with Ti-C / N / O interactions (1.0-2.0 Å) were found in the Ti-O bonds of TiO2.

[0171] Based on these results, NbP2O7 / Ti3C2T XTi3C2T X It shows a major peak at 1.0-2.0 Å, which can be attributed to the Ti-C bond, and a peak at 2.5 Å due to Nb-Nb interactions.

[0173] Fig. 6 shows niobium pyrophosphate (NbP2O7) / Ti3C2T X (MAXINE) This is a schematic diagram representing the geometric structure of a heterogeneous structure.

[0174] The enhanced electrical conductivity and storage capacity of the NbP2O7 / Ti3C2O227 heterostructure anode material were compared with bare 2D Ti CO MXene through DFT 322 calculations.

[0175] Several studies have concluded that the electrochemical performance of hybrid ZIC is related to the strength of Zn atomic adsorption on the electrode.

[0176] For example, the higher negative adsorption energy of Zn atoms, which exhibits stronger adsorption, facilitates the chemical adsorption of Zn ions on the electrode surface, thereby promoting adsorption kinetics and Zn ion storage capacity.

[0177] Therefore, the adsorption energies of Zn atoms for the NbP2O7 / Ti3C2O2 heterostructure cathode material and bare Ti3C2O2MXene were calculated to investigate the effect of NbP2O7 nanosheets surrounding Ti3C2O2MXene on the adsorption and kinetics of Zn ions in the NbP2O7 / Ti3C2O2 heterostructure cathode material.

[0178] According to the calculation results, the adsorption of Zn atoms is more favorable in the NbP2O7 / Ti3C2O2 heterostructure than in bare Ti3C2O2MXene.

[0179] These heterostructures, featuring an NbP2O7 / Ti3C2O2 interface and a stronger Zn adsorption function, can serve as active sites to improve Zn ion storage capacity.

[0180] Energy is expressed relative to the Fermi level (EF).

[0181] The illustration on the right shows the Zn-O bond used in the COHP calculation.

[0182] (e) Migration paths of Zn atoms in the initial (I) and final (F) states in Ti3C2O2MXene and (f) NbP2O7 / Ti3C2O2 heterostructures. Green, light purple, red, blue, brown, and black spheres represent Nb, P, O, Ti, C, and Zn atoms, respectively.

[0183] Energy is expressed relative to the Fermi level (EF).

[0184] The illustration on the right shows the Zn-O bond used in the COHP calculation.

[0185] (e) The movement path of a Zn atom having an initial (I) and final (F) state in a Ti CO MXene and (f) NbP O / Ti CO heterostructure.

[0186] The green, light purple, red, blue, brown, and black spheres represent Nb, P, O, Ti, C, and Zn atoms, respectively.

[0187] We further analyzed the interaction between oxygen and Zn atoms using COHP calculations to identify the reason why the adsorption capacity of Zn is stronger in the NbP2O7 / Ti3C2O2 heterostructure than in pure Ti3C2O2MXene (Figure 6d).

[0188] The positive and negative values ​​in the COHP diagram represent the bonding and antibonding states of the Zn-O bond, respectively.

[0189] After applying NbP2O7 to pure Ti3C2O2MXene, the antibonding state between oxygen and Zn atoms disappeared near the Fermi level.

[0190] Furthermore, the integral value of COHP (ICOHP) below the Fermi level, which allows for the quantitative determination of the bond strength between paired atoms, clearly showed that the average -ICOHP value of the Zn-O bond in pure Ti3C2O2MXene (0.44 eV) is lower than in the NbP2O7 / Ti3C2O2 heterostructure (0.66 eV).

[0191] Since a larger amount of ICOHP value indicates stronger binding interactions, introducing NbP2O7 into Ti3C2O2MXene facilitates Zn adsorption and improves Zn ion capacity.

[0192] To better understand interlayer interface interactions, charge transfer between NbP2O7 and Ti3C2O2MXene was investigated.

[0193] Bader charge analysis results showed that a charge transfer of 1.10 e- occurred from Ti3C2O2MXene to NbP2O7.

[0194] Charge transfer between Ti3C2O2MXene and NbP2O7 induces interfacial charge redistribution, facilitating electron transfer and improving electrochemical performance.

[0195] In addition, the diffusion characteristics of Zn atoms in the Ti3C2O2MXene and NbP2O7 / Ti3C2O2 heterostructures were investigated.

[0196] Calculated results of Zn atomic diffusion in the NbP2O7 / Ti3C2O2 heterostructure showed a slightly higher migration barrier (0.71 eV) than that of bare Ti CO MXene (0.45 eV).

[0197] The higher Zn atom migration barrier in the NbP2O7 / Ti3C2O2 heterostructure (0.71 eV) compared to bare Ti3C2O2MXene (0.45 eV) can be attributed to the stronger adsorption of Zn atoms in the NbP2O7 / Ti3C2O2 heterostructure (3.43 eV) compared to bare Ti3C2O2MXene (0.73 eV).

[0198] Therefore, the complex heterostructure NbP2O7 / Ti3C2O2 significantly promotes the adsorption kinetics and electron transfer of Zn atoms.

[0199] The presence of NbP2O7, which acts as a robust anchor for Zn adsorption, restricts the diffusion of Zn atoms in Ti3C2O2MXene. However, considering that the adsorption strength of Zn atoms was enhanced by introducing NbP2O7 into Ti3C2O2MXene, the diffusion barrier of Zn atoms remained at a similar level. Therefore, the composite anode of the heterostructured NbP2O7 / Ti3C2O2 improved Zn ion storage capacity and electrical conductivity, and enhanced electrochemical performance through moderate diffusion of Zn atoms.

[0201] Figure 7 is a graph showing the performance of a zinc ion capacitor.

[0202] MIC is designed to power electronic devices with excellent functionality and is used in the field of flexible electronic devices.

[0203] 2D-on-2D NbP2O7 / Ti3C2T paired with Na+-doped electrolyte X To evaluate the adaptability and efficacy of the anode, the performance of a high-performance flexible solid-state cell design (experimental section) was evaluated.

[0204] Fine-tuned NbP2O7 / Ti3C2T X Anode, Zn / Ti3C2T X Solid-state ZIC was produced by combining an anode with a PVA-0.2 M ZnSO4-6 M NaClO4 addition electrolyte, which is abbreviated as FSS-Nb-MX / MZ-ZIC.

[0205] The cell design of FSS-Nb-MX / MZ-ZIC is schematically shown in Figure 7a.

[0206] The operating potential of the solid electrolyte cell was confirmed by evaluating the CV curve of FSS-Nb-MX / MZ-ZIC in the potential range of 0.2 to 1.0 to 2.1 V.

[0207] The potential window of the FSS-Nb-MX / MZ-ZIC cell can be extended up to 2.0V, as can be seen from the CV curve (Figure 7b).

[0208] Consequently, within a potential range of 0.2–2.0 V, CV curves were verified at various scan rates of 5–100 mV s⁻¹ (Figure 7c).

[0209] NbP2O7 / Ti3C2T X The redox process of the electrode material improved charge storage, as indicated by the appearance of discontinuous redox peaks in the charge / discharge profile of the CV curve.

[0210] Distinct redox peaks in the charge and discharge profiles (both exhibiting excellent symmetry) indicate the outstanding reversibility of FSS-Nb-MX / MZ-ZIC.

[0211] GCD measurements of the FSS-Nb-MX / MZ-ZIC cell were performed at current densities of 0.2–5 A g-1 within a potential range of 0.2–1.9 V (Figure 7d).

[0212] Charge storage through reversible redox processes was confirmed through nonlinear and symmetric charge-discharge profiles and corresponding CV analysis.

[0213] The shapes of the GCD and CV curves show that surface capacitance contributes less to the total charge stored in the cell than charge diffusion reactions. Charge diffusion reactions account for the majority of the charge stored in the cell.

[0214] As can be seen in Figure 7e, the FSS-Nb-MX / MZ-ZIC cell demonstrates excellent rate performance with a specific capacitance of 62.3 F g-1 (31.14 mF cm-2) at 0.2 A g-1 and a retention rate of 20.76 F g-1 (34.8%) at a current density of 2 A g-1, which is 10 times higher.

[0215] The FSS-Nb-MX / MZ-ZIC cell shows an amazing specific energy density of 25 Wh kg-1 and a maximum power density of 3.75 kW kg-1 (6.25 Wh kg-1) at a power density of 164.8 W kg-1 (Figure 7f).

[0216] In addition, this device is 2.29 mW cm⁻¹ each -3 and 0.085 mW cm -2 0.347 mWh cm² at volumetric and area power density -3 and 12.89 μWh cm⁻¹ -2 It showed the volumetric and area energy densities.

[0217] Figure 7g shows the flexibility characteristics of the FSS-Nb-MX / MZ-ZIC device for various bending angles and shapes.

[0218] The thickness of the FSS-Nb-MX / MZ-ZIC device is approximately 0.2mm, and it can be bent into various shapes including C, U, and S. The device's excellent flexibility was demonstrated by wrapping it around a circular object.

[0219] In addition, CV measurements were performed at a scan rate of 100 mV s⁻¹ at original, 90°, and 180° bending angles to verify the function of the device during bending (Figure 7h).

[0220] The CV curves showed similar profiles and shapes, and the integration region under the initial, 90°, and 180° CV curves did not change significantly.

[0221] The cycle stability and durability of the FSS-Nb-MX / MZ-ZIC device were evaluated by completing 38,000 charge-discharge cycles at 2 A g-1 (Figure 7i).

[0222] Capacitance retention exceeding 100% was observed after 38,000 cycles, indicating the durability of the FSS-Nb-MX / MZ-ZIC device.

[0223] In addition, the Coulomb efficiency was maintained at ~98% throughout all cycles, indicating that the device's performance was improved.

[0224] In addition, energy efficiency was maintained at ~35% throughout all cycles.

[0225] The Nyquist plots of the FSS-Nb-MX / MZ-ZIC device before and after the cycle were obtained and applied to the equivalent circuit to determine R and R s ct (Fig. 7j).

[0226] FSS-Nb-MX / MZ-ZIC exhibited Rs and Rct values ​​of 3.06 and 0.63 Ω cm, respectively, indicating a good electrode / electrolyte interface prior to the stability test.

[0227] The Nyquist plot showed changes in the mid-to-high frequency region with an increase in semicircle width and Rct values ​​after 10,000 charge / discharge cycles (R: 3.66 Ω cm s 2 and R: 0.71 Ω cm).

[0228] After cycle stability, the R and R ct 2 s ct values ​​of the FSS-Nb-MX / MZ-ZIC device increased slightly by 0.06 and 0.07 Ω cm, respectively, suggesting that the device continued to operate well even after 2 cycles.

[0229] This device was tested using a light-emitting diode (LED) to verify that it operates properly and has an extended operating potential window (Figure 7k).

[0230] Initially, two series-connected FSS-Nb-MX / MZ-ZIC devices (expected potential: 3.8V) were charged for 30 seconds using a constant voltage source at the specified potential.

[0231] These serial connection devices were immediately connected to the LED during discharge.

[0232] After charging for 30 seconds, the FSS-Nb-MX / MZ-ZIC device was able to power an LED for several minutes or more, demonstrating the capacity of the ZIC device in actual applications.

[0234] The foregoing description of the present invention is for illustrative purposes only, and those skilled in the art will understand that other specific forms can be easily modified without altering the technical spirit or essential features of the present invention. Therefore, the embodiments described above should be understood as illustrative in all respects and not restrictive. For example, each component described as a single unit may be implemented in a distributed manner, and components described as distributed may likewise be implemented in a combined form.

[0235] The scope of the present invention is defined by the claims set forth below, and all modifications or variations derived from the meaning and scope of the claims and equivalent concepts thereof should be interpreted as being included within the scope of the present invention. Explanation of the symbols

[0237] 10: Cathode active material 20: Carbon fiber 100: MXene nanosheet 200: Niobium pyrophosphate

Claims

Claim 1 A positive electrode active material comprising: a two-dimensional MXene nanosheet having a layered structure; and niobium pyrophosphate (NbP2O7) particles dispersed between each layer of the two-dimensional MXene nanosheet, wherein the content of the niobium pyrophosphate (NbP2O7) particles is 1.4 wt% to 5.6 wt% relative to the total positive electrode active material. Claim 2 In claim 1, the two-dimensional MXene nanosheet is Ti3C2T X A positive electrode active material characterized by comprising one or more selected from the group consisting of (MXene), graphene, and MWCNT (Multi-Wall Carbon Nano Tube). Claim 3 delete Claim 4 An anode composite characterized by comprising: an anode comprising carbon fibers; and an anode active material layer coated on the surface of the anode and comprising niobium pyrophosphate (NbP2O7) particles dispersed between each layer of two-dimensional MXene nanosheets. Claim 5 In paragraph 4, the carbon fiber and the anode active material layer are carbon and Ti3C2T x A positive electrode composite characterized by covalent bonding. Claim 6 An anode composite according to claim 4, characterized in that the carbon of the carbon fiber and the functional groups (F, OH, Cl) of the MXene compound interact π-π and are covalently bonded by an interfacial interaction arrangement combination. Claim 7 In claim 4, the anode composite is characterized in that the anode active material layer is coated by performing a drop casting method without a binder. Claim 8 A positive electrode composite according to claim 4, characterized in that the thickness of the positive electrode active material layer is 500 (nm) to 5 (μm). Claim 9 A zinc ion capacitor characterized by comprising: an anode including an anode complex of claim 4; a cathode spaced apart from the anode complex and comprising a MXene nanosheet layer coated on the surface of a zinc substrate; a separator disposed between the anode and the cathode; and an electrolyte impregnated with the anode, the separator, and the cathode. Claim 10 A zinc ion capacitor according to claim 9, characterized in that the MXene nanosheet layer coated on the surface of the zinc substrate at the cathode is 1 (μm) to 10 (μm). Claim 11 A zinc ion capacitor according to claim 9, characterized in that the electrolyte comprises an NaClO4 electrolyte additive.

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