A heteroatom-doped defect graphene material, an electrochemical energy storage device and a material preparation method

Abstract

The application provides a kind of heteroatom doped defect graphene material, electrochemical energy storage device and material preparation method, including graphene matrix, lattice defect is distributed in graphene matrix, and lattice defect is combined with heteroatom;Heteroatom occupies lattice defect site to form doped graphene material, doped graphene material changes the electronic state density near Fermi level of graphene matrix and the position of Fermi level by regulating local electron cloud distribution;Heteroatom is selected from one or more of nitrogen, boron, phosphorus, sulfur or fluorine.The application has the beneficial effects: the application provides a kind of nitrogen or boron doped defect graphene material, which can be applied to supercapacitor, electrode material design in electrochemical battery (such as lithium ion battery, sodium ion battery, lithium-sulfur battery, etc.) by optimizing the microstructure of graphene to improve the performance of electrochemical capacitor and battery electrode.

Description

Technical Field

[0001] This invention belongs to the field of new energy materials and electrochemical energy storage technology, and in particular relates to a heteroatom-doped defect graphene material, an electrochemical energy storage device, and a material preparation method. Background Technology

[0002] Graphene is a single-atom-thick two-dimensional crystal composed of sp^2 hybrid carbon atoms, possessing an ultra-high specific surface area and excellent electrical and mechanical properties. In the field of energy storage, graphene is considered one of the ideal electrode materials. However, perfect graphene crystals have some limitations in electrochemical applications due to their zero band gap and surface chemical inertness: their density of states near the Fermi level is low, lacking intrinsic pseudocapacitance, making it difficult to store large amounts of charge at electrode potentials; the graphene plane lacks active functional groups, resulting in weak interactions with ions or electrolytes; furthermore, the isotropic electrochemical behavior of graphene cannot meet the specific requirements of different potential regions of the positive and negative electrodes in batteries.

[0003] To overcome the aforementioned shortcomings, researchers have attempted to chemically modify graphene, with heteroatom doping being an effective method. Doping fundamentally alters the electronic structure and surface chemistry of graphene by replacing some carbon atoms with other elements, introducing additional electrons or holes. For example, nitrogen (N) atoms have a similar radius to carbon and readily enter the carbon framework through substitution. Their lone pairs of electrons form conjugations with the graphene π-system, increasing local electron density and enhancing the conductivity and electrochemical activity of graphene. Boron (B) atoms have lower electronegativity than carbon, and as dopants, they enrich the electron cloud of surrounding carbon atoms, thereby introducing electron acceptor sites into carbon materials. Based on this, different doping elements often endow graphene with different performance tendencies: nitrogen doping is generally considered to enhance the adsorption of positive ions and redox catalysis, while boron doping can enhance the bonding with anions or metallic lithium.

[0004] Several existing technologies have explored the application of nitrogen- or boron-doped graphene in electrochemical energy devices. For example, a method for preparing nitrogen-doped graphene materials has been disclosed, which introduces nitrogen element by calcining graphene oxide with ammonium carbonate to obtain nitrogen-doped graphene. This method is low-cost, easy to scale up, and the resulting nitrogen-doped graphene has been used as an electrode material for supercapacitors, demonstrating that nitrogen doping can improve the voltage withstand capability and capacity of graphene electrodes to some extent. However, this technology mainly focuses on the preparation process itself and lacks targeted design for optimizing the performance of graphene in different potential regions.

[0005] Laser-induced graphene (LIG) technology has also been used to dope and modify graphene electrodes. Existing techniques have reported the introduction of boron doping during the LIG process, resulting in micro-supercapacitors with an areal capacitance as high as 16.5 mF / cm². 2The capacitance was three times that of the undoped control, and the energy density was increased by 5 to 10 times at multiple power densities. This indicates that heteroatom doping can significantly improve the electrochemical energy storage performance of graphene electrodes. However, the above techniques mainly focus on the improvement of capacitance performance by a single dopant, without distinguishing the different needs of the positive and negative electrodes.

[0006] In the field of metal-ion batteries, the role of heteroatom doping is receiving increasing attention. For example, existing technologies indicate that the interaction between intrinsic graphene and sodium ions is too weak to make it suitable as a high-capacity anode in sodium-ion batteries. In contrast, boron-doped graphene can significantly improve the adsorption capacity for sodium and battery performance, exhibiting a capacity as high as 762 mAh / g and good cycle stability. This demonstrates that altering the electronic structure of graphene surfaces through doping can endow it with the activity of storing metal ions, showing great potential in systems such as sodium-ion batteries. Similarly, in lithium metal batteries, boron-doped graphene has been shown to enhance the affinity for lithium, promoting the uniform nucleation and deposition of lithium ions on the graphene surface. Existing technologies have prepared boron-doped graphene using a calcination method with boric acid and graphene oxide precursors, using it as a protective material for lithium metal anodes. Results show that boron doping makes the carbon atoms in graphene electron cloud enrichment centers, significantly improving the adsorption capacity for lithium atoms, effectively guiding the uniform nucleation of lithium on the surface, reducing the risk of dendrite formation, and thus significantly improving the cycle life of the battery. In contrast, nitrogen-doped graphene is often used as a conductive additive or functional coating for the cathode of lithium-ion batteries to improve the cathode interface reaction. For example, in all-vanadium redox flow batteries, nitrogen-doped graphene improves the reversibility of the electrode to redox reactions and reduces charge transfer impedance.

[0007] Although existing technologies have shown that heteroatom doping can improve the electrochemical performance of graphene to varying degrees, there are still some shortcomings and room for improvement: The role of defects has not been fully utilized: Traditional methods typically involve doping in near-perfect graphene lattices or attempting to avoid introducing excessive structural defects. For example, existing techniques propose doping nitrogen within graphite through pre-nitridation followed by exfoliation to obtain low-defect nitrogen-doped graphene. This is because pyridine and pyrrole nitrogen atoms are often located at the edges of carbon layers or in pore defects; their introduction would create numerous pores in graphene, disrupting the crystal structure and severely impacting the material's electrical and mechanical properties. Therefore, existing techniques often treat defects as negative factors and suppress them. However, from another perspective, defects such as vacancies, five- or seven-membered rings, and edge unsaturated bonds can themselves provide active sites for electrochemical reactions and regulate the electronic density of states in graphene. If doping and defect engineering can be organically combined, their synergistic effect could be leveraged to further improve the performance of graphene materials—a direction that has not been fully explored in previous research.

[0008] The lack of differentiated design for the positive and negative electrodes: Most current graphene doping technologies focus on only one doping element, resulting in a global improvement in material performance without considering the differences in operating potential and reaction mechanisms between the positive and negative electrodes. For example, in the aforementioned existing technologies, either nitrogen doping is used alone to improve the conductivity and surface activity of graphene, or boron doping is used alone to increase the affinity for metal ions. However, in practical electrochemical energy storage devices, the positive electrode needs to store and transfer charge at a higher potential, while the negative electrode operates at a lower or even negative potential. The requirements for the electronic states and interface reactions of the materials are not the same. Taking lithium-ion batteries as an example, positive electrode materials often experience problems such as transition metal dissolution and side reactions at high potentials, requiring the electrode surface to have stronger redox catalysis and the ability to suppress side reactions; while negative electrodes, such as lithium metal or silicon negative electrodes, are prone to dendrite formation or electrolyte consumption at low potentials, requiring the surface to uniformly nucleate and deposit lithium ions and stabilize the SEI film. Obviously, single-doped graphene materials cannot simultaneously meet the different requirements of the positive and negative electrodes. Currently, there is no publicly available literature or existing technology that proposes a material design scheme that can optimize the positive and negative electrodes of a battery separately, so as to give full play to the role of graphene in the electrodes.

[0009] Limited Performance Improvement: While heteroatom doping improves graphene performance, this improvement is often limited when defect content is low or with simple doping. At the same doping concentration, the additional carrier concentration and active sites introduced by the doping itself may not be sufficient to fundamentally alter the density of states distribution of graphene in a specific potential region. Furthermore, the introduction of defects, if not combined with appropriate doping, can lead to decreased conductivity or increased instability. Therefore, a synergistic strategy is needed to significantly improve the quantum capacitance and interfacial reactivity of the graphene substrate without compromising its excellent conductive network.

[0010] In summary, there is an urgent need for a novel graphene material design that combines heteroatom doping with defect engineering to perform targeted optimization for the specific needs of the positive and negative electrodes of electrochemical devices, thereby significantly improving the electrochemical performance of graphene electrodes over a wider potential range. This is precisely the technical problem that this invention aims to solve. Summary of the Invention

[0011] In view of this, the present invention aims to provide a heteroatom-doped defect graphene material, an electrochemical energy storage device, and a material preparation method to solve at least one problem existing in the prior art.

[0012] To achieve the above objectives, the technical solution of the present invention is implemented as follows: In a first aspect, the present invention provides a heteroatom-doped defect graphene material, comprising a graphene matrix, wherein lattice defects are distributed in the graphene matrix and heteroatoms are bonded at the lattice defects; the heteroatoms occupy the lattice defect sites to form the doped graphene material, and the doped graphene material changes the electronic state density near the Fermi level of the graphene matrix and the Fermi level position by regulating the local electron cloud distribution; the heteroatoms are selected from one or more of nitrogen, boron, phosphorus, sulfur or fluorine.

[0013] Furthermore, the heteroatom is a nitrogen atom; the nitrogen atom acts as an electron donor, occupying lattice defect sites, causing the Fermi level of the graphene matrix to shift upward, and the material is configured as a positive electrode active material for high-potential operation.

[0014] Furthermore, the heteroatoms are boron atoms; boron atoms occupy lattice defect sites as electron acceptors, causing the Fermi level of the graphene matrix to shift downward, and the material is configured as a negative electrode active material or a metal ion deposition host material for low-potential operation.

[0015] Furthermore, the material is a graphene film with a planar heterostructure; the film is divided into a first region and a second region along the planar direction, the first region is enriched with nitrogen atom doped defect structures, the second region is enriched with boron atom doped defect structures, and the first region and the second region are connected or physically separated by a transition region.

[0016] Secondly, based on the same concept, the present invention also provides a method for preparing heteroatom-doped defective graphene materials, comprising the following steps: S1. Defect construction: Introducing lattice defects into the graphene lattice, including carbon vacancies, grain boundaries, or edge dangling bonds; S2, Defect Anchoring Doping: Provides a source of heteroatoms, which, under thermodynamic or kinetic drive, preferentially diffuse and occupy lattice defect sites to form doped graphene materials.

[0017] Furthermore, steps S1 and S2 are carried out in situ in synergy using chemical vapor deposition: carbon source gas is introduced into the substrate to grow graphene, and lattice defects are introduced by adjusting the partial pressure of the carbon source or the growth parameters; during or after the growth of graphene, nitrogen-containing gas or boron-containing gas is introduced, and high temperature is used to make heteroatoms occupy the lattice defects in situ.

[0018] Furthermore, step S1 includes preparing graphene powder with abundant oxygen-containing functional groups and defects using a redox method; step S2 includes uniformly mixing the graphene powder with a solid heteroatom-containing compound and performing high-temperature heat treatment under an inert or reducing atmosphere, so that the active species generated by the decomposition of the heteroatom-containing compound are embedded in the lattice defects.

[0019] Furthermore, step S2 includes region-selective doping: using a mask to cover a first region of the graphene film, the exposed second region is subjected to a first type of heteroatom doping treatment; subsequently, the mask is removed or moved to expose the first region, and the first region is subjected to a second type of heteroatom doping treatment, wherein the first and second heteroatoms are nitrogen atoms and boron atoms, respectively.

[0020] Thirdly, based on the same concept, the present invention also provides an electrochemical energy storage device, including a positive electrode, a negative electrode, and an electrolyte or a separator, wherein the positive electrode and / or the negative electrode comprises an electrode; the electrode comprises a current collector and an active material layer loaded on the surface of the current collector, the active material layer comprising heteroatom-doped defective graphene material; when the device is a supercapacitor, the active material layer of the positive electrode is made of nitrogen atom-doped defective graphene material, and the active material layer of the negative electrode is made of boron atom-doped defective graphene material.

[0021] Compared with existing technologies, the heteroatom-doped defect graphene material, electrochemical energy storage device, and material preparation method described in this invention have the following advantages: This invention discloses a heteroatom-doped defect graphene material, an electrochemical energy storage device, and a material preparation method. Through a unique material design approach and implementation scheme, this invention achieves a significant performance improvement in graphene within the field of electrochemical energy storage, demonstrating remarkable innovation and superiority. It should be emphasized that the heteroatom types and substrate materials of this invention are not limited to nitrogen, boron, and graphene in the examples given. The doping-defect synergistic strategy of this invention is also applicable to the doping of carbon-based materials with other heteroatoms (such as phosphorus, sulfur, and fluorine), and similar modifications to other two-dimensional carbon materials (such as graphyne and carbon nitride nanosheets), to achieve the purpose of regulating electronic structure and improving performance. These variations all fall within the scope of this invention. Any solutions formed by improvements or equivalent substitutions using the ideas of this invention should be covered within the protection scope of this invention. Attached Figure Description

[0022] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a schematic diagram illustrating the materials, apparatus, and preparation principles described in the embodiments of the present invention; Figure 2 This is a schematic diagram illustrating the electronic state density and quantum capacitance modulation of nitrogen / boron-doped defect graphene according to an embodiment of the present invention; Figure 3 The electrochemical impedance spectroscopy is shown in the embodiments of the present invention; Figure 4The above is a characterization diagram of the boron content and chemical bonding form in the product using inductively coupled plasma optical emission spectroscopy (ICP-OES) and XPS as described in the embodiments of the present invention. Detailed Implementation

[0023] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0024] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0025] like Figures 1 to 3 As shown, a heteroatom-doped defect graphene material includes a graphene matrix in which lattice defects are distributed, and heteroatoms are bonded to the lattice defects. The heteroatoms occupy the lattice defect sites to form the doped graphene material. The doped graphene material changes the electronic state density near the Fermi level of the graphene matrix and the Fermi level position by controlling the local electron cloud distribution. The heteroatoms are selected from one or more of nitrogen, boron, phosphorus, sulfur or fluorine.

[0026] In a preferred embodiment of the present invention, the heteroatom is a nitrogen atom; the nitrogen atom occupies the lattice defect site as an electron donor, causing the Fermi level of the graphene matrix to shift upward, and the material is configured as a positive electrode active material for high-potential operation.

[0027] In a preferred embodiment of the present invention, the heteroatom is a boron atom; the boron atom occupies the lattice defect site as an electron acceptor, causing the Fermi level of the graphene matrix to shift downward, and the material is configured as a negative electrode active material or a metal ion deposition host material for low-potential operation.

[0028] In this embodiment, the heteroatom doping concentration is 0.5–10 at%, preferably 1–5 at%; the structural defects include vacancy defects, five-membered / seven-membered ring topological defects, and edge unsaturated bonds, and the defect density is expressed as the Raman D-peak to G-peak intensity ratio I_D / I_G is 0.1–1.2, preferably 0.2–0.6; the heteroatoms are bonded to the graphene carbon framework in the form of substitutional doping and are enriched and distributed at defects or boundaries.

[0029] In a preferred embodiment of the present invention, the material is a graphene film with a planar heterostructure; the film is divided into a first region and a second region along the planar direction, the first region is enriched with nitrogen atom doped defect structures, the second region is enriched with boron atom doped defect structures, and the first region and the second region are connected or physically separated by a transition region.

[0030] This invention also proposes a method for preparing defective graphene materials, such as heteroatom-doped graphene, comprising the following steps: S1. Defect construction: Introducing lattice defects into the graphene lattice, including carbon vacancies, grain boundaries, or edge dangling bonds; S2, Defect-anchored doping: Provide a source containing heteroatoms, and under thermodynamic or kinetic drive, allow heteroatoms to preferentially diffuse and occupy the lattice defect sites to form doped graphene material.

[0031] Specifically, in this embodiment, the preparation method includes: Providing graphene precursor materials and introducing defects: using methods such as chemical vapor deposition, post-growth plasma treatment, or chemical oxidation-reduction to generate lattice defects of a predetermined concentration in graphene; Introducing heteroatom doping: Introducing heteroatoms into a defective graphene precursor, allowing the heteroatoms to replace carbon atoms and preferentially bind to defect sites, resulting in heteroatom-doped defective graphene. Subsequent processing and characterization: The obtained material was subjected to necessary heat treatment, cleaning and purification, and the heteroatom doping state and defect structure were verified by material analysis.

[0032] The graphene precursor is prepared using one of the following methods: a) CVD-grown defective graphene: When CVD-deposit graphene on a transition metal substrate, graphene films containing vacancies and polycrystalline domain boundaries can be obtained by reducing the carbon source concentration, adding trace amounts of oxidant, or increasing the growth temperature. b) Plasma-introduced defects: The graphene film is exposed to a plasma environment such as radio frequency argon plasma or nitrogen plasma for a certain period of time to generate defect sites in the graphene lattice. c) Chemical oxidation-reduction: Graphene materials such as graphene powder or film are chemically oxidized to form graphene oxide, and then thermally or chemically reduced to remove some oxygen functional groups, forming a graphene structure with random defects. d) Defects introduced by heteroatom predoping: After predoping heteroatoms into graphite or carbon source materials, graphene is generated or exfoliated. For example, graphene is pretreated by nitriding and then exfoliated by oxidation. Due to the heteroatoms entering the lattice, rearrangement defects are caused, thereby obtaining a heteroatom predoped defect graphene precursor.

[0033] The introduction of heteroatoms can be achieved through one of the following methods: a) In-situ doping CVD method: During the graphene CVD growth process, a gaseous precursor containing heteroatoms is simultaneously introduced. For example, ammonia (NH3) is introduced to achieve in-situ nitrogen doping, and trimethylborane (B(CH3)3) or borane gas is introduced to achieve in-situ boron doping, so that heteroatoms are embedded in the defects during graphene growth. b) High-temperature diffusion doping method: defective graphene is mixed with precursor compounds containing heteroatoms, such as boric acid and urea, and then heat-treated at high temperature in an inert or reducing atmosphere to decompose the precursor and release heteroatoms, which diffuse into the graphene lattice to complete the doping. c) Plasma doping method: Defective graphene is exposed to plasma containing heteroatoms, such as nitrogen plasma or plasma containing BF3 gas. The heteroatoms are embedded into the defect sites of graphene under plasma bombardment. d) Electrochemical / solution doping method: Defective graphene is immersed in a solution containing heteroatom precursors (such as nitrogen-containing organic amines or boron-containing organic compounds). The precursors are decomposed by electrochemical reduction or thermal treatment, and heteroatoms are deposited and embedded into the graphene defects. The process can be supplemented by ultrasound and stirring to improve uniformity.

[0034] Material characterization included X-ray photoelectron spectroscopy (XPS) to identify the chemical states and relative abundance of heteroatoms, Raman spectroscopy to determine defect concentration and lattice integrity, and transmission electron microscopy (TEM) and energy-dispersive spectroscopy (EDS) to observe the distribution of heteroatoms in the graphene lattice. These characterization results ensured that heteroatoms in the prepared material were primarily substituted at defects, with nitrogen doping occurring in the form of pyridine nitrogen and graphitic nitrogen, and boron doping predominantly in BC3 structures bonded to carbon.

[0035] In a preferred embodiment of the present invention, steps S1 and S2 are performed in situ in synergy using a chemical vapor deposition process: a carbon source gas is introduced into the substrate to grow graphene, and the lattice defects are introduced by adjusting the partial pressure of the carbon source or the growth parameters; during or after the graphene growth process, a nitrogen-containing gas or a boron-containing gas is introduced, and the heteroatoms are used to occupy the lattice defects in situ using high temperature.

[0036] In a preferred embodiment of the present invention, step S1 includes preparing graphene powder with abundant oxygen-containing functional groups and defects using a redox method; step S2 includes uniformly mixing the graphene powder with a solid heteroatom-containing compound and performing high-temperature heat treatment under an inert or reducing atmosphere, so that the active species generated by the decomposition of the heteroatom-containing compound are embedded in the lattice defects.

[0037] In a preferred embodiment of the present invention, step S2 includes region-selective doping: using a mask to cover a first region of the graphene film, performing a first heteroatom doping treatment on the exposed second region; subsequently removing or moving the mask to expose the first region, and performing a second heteroatom doping treatment on the first region, wherein the first and second heteroatoms are nitrogen atoms and boron atoms, respectively.

[0038] In this embodiment, when selectively doping different regions of the same graphene film, a masking or selective coating technique is used. Specifically, the area to be protected is covered, allowing only the area to be doped to be exposed to the heteroatom source environment for processing. Then, the mask positions are swapped to dope another part with different elements, thereby obtaining a graphene film with spatially different distributions of doped elements.

[0039] The present invention also proposes an electrode comprising a current collector and an active material layer loaded on the surface of the current collector, the active material layer comprising the heteroatom-doped defect graphene material.

[0040] In this embodiment, the electrode can be used as the positive or negative electrode of the electrochemical energy storage device: when used as the positive electrode, nitrogen-doped defective graphene material is used, and when used as the negative electrode, boron-doped defective graphene material is used, so as to meet the performance requirements of different potential regions of the positive and negative electrodes respectively.

[0041] The electrodes are either supercapacitor electrodes or battery electrodes. For supercapacitors, the nitrogen-doped defective graphene in the positive electrode and the boron-doped defective graphene in the negative electrode form a pair of symmetrical electrodes, enabling the device to operate at a voltage higher than 2.8V and increase its capacity. For battery electrodes, the doped defective graphene active layer is used as a conductive additive or functional coating for the positive electrode of a lithium-ion battery to improve the stability of the positive electrode under high voltage, or as a pre-lithiation framework or protective layer for the negative electrode of a lithium-ion battery to induce uniform lithium deposition and suppress dendrites.

[0042] The present invention also proposes an electrochemical energy storage device, comprising a positive electrode, a negative electrode, and an electrolyte or a separator, wherein the positive electrode and / or the negative electrode comprises an electrode; when the device is a supercapacitor, the active material layer of the positive electrode is made of nitrogen-doped defective graphene material, and the active material layer of the negative electrode is made of boron-doped defective graphene material.

[0043] In this embodiment, the positive electrode is composed of or composited with nitrogen-doped defective graphene material, and the negative electrode is composed of or composited with boron-doped defective graphene material, separated by an ion-permeable membrane. By combining different doped defective graphene materials for the positive and negative electrodes, the device maintains high capacitance performance at high and low potentials respectively during charging and discharging, giving the device a wider operating voltage range, higher energy density and power density, and excellent cycle stability.

[0044] The device is an electric double-layer electrochemical capacitor. When using an organic electrolyte, its single-cell operating voltage reaches 3.0–3.5V, which is significantly higher than the approximately 2.5V of traditional carbon-based capacitors. Furthermore, at a discharge current of 1A / g, the single-electrode specific capacitance is not less than 150F / g, which is more than 1.5 times that of an undoped graphene symmetric capacitor. When the device is a lithium-ion battery, it can safely operate at a higher positive electrode cutoff voltage and a lower negative electrode potential without significant side reactions. After more than 500 deep cycles, the battery capacity retention rate increases by at least 5–10 percentage points.

[0045] The application of materials in electrochemical energy storage involves using the materials as: a) Positive and negative electrode materials of supercapacitors: the positive electrode uses nitrogen-doped defective graphene to improve the capacitance in the high potential region, and the negative electrode uses boron-doped defective graphene to enhance the capacitance in the low potential region. The symmetrical or asymmetrical capacitors assembled in this way have higher operating voltage and energy density. b) Conductive additives or coatings for the positive electrode of lithium-ion batteries: The nitrogen-doped defective graphene is combined with the positive electrode active material to improve the stability and conductivity of the positive electrode under high voltage; and the pre-lithiation framework or protective layer for the negative electrode of lithium-ion batteries: The boron-doped defective graphene is used as an additive for negative electrodes such as graphite / silicon to improve the first coulombic efficiency, or coated on the surface of lithium metal negative electrode to induce uniform lithium deposition and reduce dendrites and interfacial side reactions. c) Catalyst support for metal-air battery or flow battery electrodes: Utilizing pyridine nitrogen and graphitic nitrogen sites on nitrogen-doped defective graphene to catalyze oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), while boron-doped defective graphene has an inhibitory effect on side reactions of the air electrode, thereby improving discharge efficiency and stability.

[0046] When using materials for electrodes, the electrode structure can be constructed in one of the following ways: Doped defect graphene material is directly coated onto the surface of the electrode current collector to form a functional coating with a thickness of 1–5 μm, thereby modifying the electrode interface; Doped defective graphene materials are mixed with other active materials to form a composite electrode, which forms a conductive network in the electrode and provides active sites. Doped defect graphene is prepared into free-supported films or aerogel electrodes and used directly as electrodes, with nitrogen-doped films used as positive electrodes and boron-doped films used as negative electrodes. Alternatively, a method of coating both sides of the separator with graphene-doped material can be used. The front side of the separator is coated with nitrogen-doped defective graphene facing the positive electrode, while the back side is coated with boron-doped defective graphene facing the negative electrode. This allows for simultaneous modification of the positive and negative electrode surfaces during battery assembly. This method can impart different surface / interface functions to the positive and negative electrodes without altering the electrode formulation.

[0047] In this embodiment, the core idea of ​​the present invention is to simultaneously perform heteroatom doping and defect engineering in graphene materials, and select different doping elements according to application requirements to achieve a synergistic effect. The specific solution is as follows: Synergistic Regulation of Heteroatom Doping and Defects: A certain concentration of defects, such as vacancies, distorted five- or seven-membered ring structures, or edge unsaturated bonds, are pre-introduced into the graphene lattice, and then heteroatom doping is performed using these defects as anchor points. For example, N or B heteroatoms tend to occupy defect sites and can be stably embedded into the graphene framework. This synergistic design allows the dopant element to effectively alter the local electronic structure: on the one hand, the local energy levels introduced by the defects themselves increase the density of states (DOS) of graphene near the Fermi level; on the other hand, the dopant element provides or attracts additional electrons, further regulating the Fermi level position and DOS distribution. For instance, in nitrogen-doped defective graphene, nitrogen acts as an electron donor, shifting the Fermi level upwards and increasing the DOS near the Fermi level, thus resulting in higher quantum capacitance at the positive electrode working potential; in boron-doped defective graphene, boron acts as an electron acceptor, lowering the Fermi level and increasing the ability to accept electrons, resulting in a stronger capacitive response in the negative electrode working region. This strategy of synergistic use of defects and doping achieves more significant performance improvements at the same doping concentration compared to traditional methods that use only doping or only defects. In fact, our simulation and experimental results both show that the improvement in electrochemical performance when doping and defects are present simultaneously in graphene is superlinear, meaning the performance improvement is greater than the sum of the two.

[0048] Regarding the selection of doping elements for the positive / negative electrodes: This invention is the first to propose selecting doping elements based on the polarity and potential requirements of the electrodes, breaking through the previous design mode of using a single material for both electrodes. Specifically, for the positive electrode of a battery or capacitor, nitrogen-doped defective graphene is preferred; for the negative electrode, boron-doped defective graphene is preferred. This differentiated selection is based on the following considerations: Nitrogen-doped defective graphene is used in cathodes: Nitrogen atoms have a pair of lone electrons, which is equivalent to introducing n-type doping into graphene, raising the Fermi level. When cathodes operate at high positive potentials, materials typically require high electron density to provide charge storage capacity. Nitrogen doping increases the electron state density of graphene near the Fermi level, significantly improving the double-layer capacitance and pseudocapacitance of the cathode at high potentials. The nitrogen-doped defective graphene of this invention exhibits approximately twice the sheet capacitance of undoped defective graphene near +2.5V, demonstrating a significantly enhanced charge storage capacity in the high-potential region. Furthermore, the surface functional groups such as pyridine nitrogen and graphitic nitrogen introduced by nitrogen doping can play a catalytic role at the cathode-electrolyte interface, for example, promoting rapid valence state transitions of transition metal ions and reducing electrolyte decomposition at high potentials, thereby reducing side reactions and impedance at the cathode interface.

[0049] Boron-doped defective graphene is used as an anode: Boron atoms are electron-deficient, which is equivalent to p-type doping of graphene, lowering the Fermi level. When the anode operates at low or even negative potentials, the material needs to readily accept electrons / lithium ions, i.e., possess high cathode lithium storage capacity and surface lithiophilicity. The electron acceptor sites introduced by boron doping increase the density of states of graphene at low potentials, resulting in stronger capture and retention capabilities for electrons / lithium ions entering the anode. Our tests at –0.5V relative to Ag / AgCl showed that the capacitance response of boron-doped defective graphene was several times that of the undoped control, demonstrating extremely strong low-potential charge acceptance. Furthermore, boron doping significantly improves the deposition behavior of lithium metal on the graphene surface: due to the difference in electronegativity, the carbon surrounding the boron becomes an electron-rich center, uniformly adsorbing Li. + This guides lithium nucleation at these sites. Almost all carbon atoms adjacent to boron exhibit high binding energies to lithium, demonstrating uniform lithiophilic properties, which effectively prevents disordered lithium deposition and dendrite growth on the anode surface. Therefore, using the boron-doped defect graphene of this invention as a lithium anode host or coating material can reduce local current density and the risk of lithium dendrite formation, thereby improving the cycle stability of the anode.

[0050] Regionally Selective Doping and Multi-functionality of a Single Membrane: This invention also proposes a strategy for partitioning different elements onto the same graphene film. Specifically, through masking or selective coating techniques, one region of the graphene film is exposed to a nitrogen-containing precursor environment for nitrogen doping, while another region is exposed to a boron-containing precursor environment for boron doping while protecting the former. This results in a graphene film with spatially heterogeneous doping distribution. This dual-doping design allows a single graphene film to simultaneously possess both positive (nitrogen-doped) and negative (boron-doped) portions, enabling it to function as the positive and negative electrodes in symmetrical electrochemical devices. For example, sandwiching this heterogeneously doped graphene film between two current collectors can form the positive and negative electrodes of a supercapacitor; or it can be used as a coating layer on a battery separator, with both sides facing the positive and negative electrodes respectively, achieving simultaneous improvement of the electrode interface during a single assembly. Experiments have shown that this multi-functional single-film design enables electrochemical devices to have higher single-cell operating voltages and better overall performance. This strategy fully demonstrates the flexibility and innovation of material design, opening up new avenues for the application of graphene in energy storage.

[0051] Quantum Capacitance and Enhanced Surface Activity: Through the synergy of doping and defects, this invention significantly improves the quantum capacitance of graphene at different potentials. Quantum Capacitance C Q The density of states (DOS) is directly related to the density of states near the Fermi level of the material; the higher the DOS, the higher the C. Q The larger the value, the higher the value. Nitrogen-doped defective graphene exhibits a high DOS peak near the Fermi level due to the upward shift of the Fermi level and the introduction of local states by defects, resulting in a higher C0 value. QSignificantly increased; boron-doped defective graphene, due to the downward shift of the Fermi level, also introduces new states and improves the DOS in the low-energy region. This method of increasing the density of states at both the positive and negative electrodes allows the entire electrochemical device to maintain high capacitance over a wider voltage range. Compared with undoped defective graphene, the material of this invention exhibits an improvement of more than 50% in quantum capacitance in experiments; the improvement is particularly significant on the positive electrode side, especially in the high potential range C. Q Increased by approximately 100%, the negative electrode side is in the low potential range C Q The improvement is several times greater. Besides quantum capacitance, the synergistic defects from doping also create more surface active sites: nitrogen doping produces pyridine (N) and pyrrole (N), which can serve as pseudocapacitive sources providing redox functional groups and catalyzing electrode reactions; boron doping produces electron-deficient sites that strengthen the bonding of anions and neutral molecules to the negative electrode surface, accelerating processes such as lithium-ion reduction and lithium plating. Therefore, in cyclic voltammetry tests, the nitrogen / boron-doped defective graphene electrode exhibits a larger pseudocapacitive current and faster electrochemical reaction kinetics. The charge transfer impedance in the electrochemical impedance spectroscopy (EIS) is significantly reduced by 20-30%, lower than the undoped control, indicating that the interfacial reaction is effectively catalyzed and accelerated.

[0052] Cycle life and structural stability: By selecting appropriate doping elements and introducing defects, this invention improves capacity while maintaining material stability. On the one hand, doped atoms stabilize the defect structure through chemical bonding, preventing excessive defect merging or sheet aggregation in graphene during cycling. On the other hand, doping participates in the initial formation of the SEI on the electrode surface, making the SEI more uniform and dense, reducing capacity loss due to continuous growth. For example, nitrogen-doped surface functional groups can react with electrolyte decomposition products to form a stable nitrogen-rich SEI component; boron doping can combine with anionic components to generate a stable boron-containing compound film. Due to these effects, the electrode made from the material of this invention exhibits significantly better capacity retention during long cycles than the undoped control. In a comparative experiment of 500 cycles in a full lithium-ion battery, the capacity retention of the electrode containing the material of this invention was approximately 5-10 percentage points higher than that of the undoped defective graphene electrode, indicating a significant reduction in cycle decay. Furthermore, the morphology and structure of the doped defective graphene electrode remained good during repeated charge-discharge cycles, without significant sheet peeling or conductive network damage. These results demonstrate that the present invention effectively improves the structural integrity and cycle life of graphene electrodes by stabilizing defects through heteroatoms.

[0053] This invention achieves a significant improvement in the electrochemical performance of graphene through novel material design, specifically in the following aspects: An innovative approach to synergistic regulation: Traditionally, doping research has focused on perfect graphene or carbon materials, while defect engineering typically does not involve exogenous dopants. This invention transcends the scope of single modification, pioneering the integration of doping and defect engineering, allowing both to complement each other's strengths and weaknesses. We cleverly utilize the material characteristic that heteroatoms tend to occupy defect sites, making doping more stable and effective. Furthermore, we amplify the doping effect by perturbing the electronic structure of defects, achieving performance enhancement. This design, using defects as doping hosts, has not been reported in other related existing technologies.

[0054] This invention addresses the differentiated optimization of the two electrodes: Previous graphene modification methods typically involved applying one material to one electrode of a battery, or using the same modified material for both electrodes. This invention proposes a concept of selecting different doping strategies based on the different needs of the positive and negative electrodes: nitrogen-doped defective graphene is selected for the positive electrode, and boron-doped defective graphene for the negative electrode, respectively solving the performance bottlenecks at high potentials for the positive electrode and low potentials for the negative electrode. This site-specific design significantly broadens the battery's operating voltage window. When the material of this invention is applied to a symmetric electrochemical double-layer capacitor, the single-cell voltage of the device is increased by approximately 0.3~0.5V compared to traditional carbon-based capacitors; when applied to lithium-ion batteries, the positive electrode can withstand a higher cutoff voltage while the negative electrode remains stable. This differentiated doping scheme for positive and negative electrodes is currently unreported in the literature, and most existing technologies have failed to break through the one-size-fits-all material design paradigm.

[0055] Significant performance advantages: At the same doping concentration, the performance improvement of the material of this invention far exceeds that of existing doped graphene materials. For example, existing technologies maintain performance stability by reducing defects, but this method achieves limited electrochemical performance improvement within the nitrogen doping range of 1-10%, primarily improving conductivity rather than capacitance. Existing technologies have improved the performance of lithium / sodium anodes through boron doping, but have not considered cathode optimization, thus limiting the overall battery energy density. In contrast, this invention, while ensuring a good conductive framework of graphene, achieves a significant increase in quantum capacitance through a two-pronged approach of doping and defect reduction, resulting in a qualitative leap in electrode specific capacity and rate performance. Particularly noteworthy is the excellent stability and electrochemical activity of the material of this invention even at extreme potentials. After more than 500 deep charge-discharge cycles, the capacity retention rate is improved by at least 5-10 percentage points. These performance breakthroughs lay the foundation for developing new high-energy-density and safe and stable batteries.

[0056] Process Compatibility and Practical Feasibility: The preparation processes proposed in this invention, including in-situ CVD doping, post-treatment doping, and region-selective doping, are all based on ingenious combinations and improvements of existing mature technologies, demonstrating feasibility. For example, introducing ammonia or trimethylborane into CVD growth can prepare doped defect graphene films in a single step; high-temperature ammonia annealing or plasma treatment of graphene films can also achieve doping. These processes are easily accepted by current graphene film preparation production lines, facilitating large-scale application. Furthermore, the materials of this invention can be directly incorporated into electrode coatings as conductive additives or applied as coatings to existing electrode surfaces, ensuring compatibility with existing battery manufacturing processes without requiring significant changes to the battery structure, thus promoting industrialization.

[0057] In summary, this invention, through its unique material design approach and implementation scheme, achieves a significant performance improvement of graphene in the field of electrochemical energy storage, demonstrating remarkable innovation and superiority. It should be emphasized that the heteroatom types and substrate materials of this invention are not limited to nitrogen, boron, and graphene in the examples given. The doping-defect synergistic strategy of this invention is also applicable to the doping of carbon-based materials with other heteroatoms such as phosphorus, sulfur, and fluorine, as well as similar modifications to other two-dimensional carbon materials such as graphodyne and carbon nitride nanosheets, to achieve the purpose of regulating electronic structure and improving performance. These variations all fall within the scope of this invention. Any solutions formed by improving or equivalently replacing the concepts of this invention should be covered within the protection scope of this invention.

[0058] This invention provides a defective graphene material doped with heteroatoms such as nitrogen or boron. By optimizing the microelectronic structure of graphene, it can improve the performance of electrochemical capacitors and battery electrodes. It can be applied to the design of electrode materials in supercapacitors, electrochemical batteries such as lithium-ion batteries, sodium-ion batteries, and lithium-sulfur batteries.

[0059] In this invention, structural defects are pre-introduced into the graphene material and doped with nitrogen or boron heteroatoms. These heteroatoms preferentially occupy defect sites or edge positions, significantly altering the local electronic structure and optimizing different potential ranges for the positive and negative electrodes. At the high potential of the positive electrode, nitrogen-doped defective graphene, acting as an electron donor, increases the density of states near the Fermi level, enhancing quantum capacitance and charge storage capacity at high potentials. At the low potential of the negative electrode, boron-doped defective graphene, acting as an electron acceptor, lowers the Fermi level, enhancing electron / lithium ion acceptance and capacitive response at low potentials. The synergistic effect of doping elements and defects also improves the surface chemical activity of graphene: nitrogen doping generates active sites such as pyridine nitrogen and graphitic nitrogen, enhancing catalytic performance for redox reactions and Lithium ion concentration. +The boron doping process generates electron defects, making surrounding carbon electron enrichment centers, promoting anionic bonding and controllable deposition of lithium metal. Compared with existing technologies, this invention achieves a greater performance improvement at a comparable doping concentration: quantum capacitance is increased by more than 50% at a specific potential; the capacitance at +2.5V on the positive electrode is increased by about 2 times, and the capacitance at -0.5V on the negative electrode is increased by several times. The graphene electrode maintains a high capacitance value over a wider potential range, significantly expanding the safe operating voltage window of the device; charge transfer impedance is reduced by 20-30%, and capacity decay is reduced by 5-10 percentage points after 500 cycles. To achieve the above performance, this invention provides a method for preparing nitrogen / boron-doped defective graphene materials, including in-situ doping by chemical vapor deposition (CVD), post-treatment thermal annealing or plasma doping, and differentiated doping of different regions of the same graphene film, and describes examples of using this material for applications such as positive electrode coating and negative electrode host of lithium-ion batteries, and electrochemical double-layer capacitor electrodes. Experimental results show that the material of this invention can improve energy density while taking into account power performance and cycle life, and has important application value.

[0060] This invention proposes a nitrogen / boron-doped defective graphene material and its optimization strategy for electrochemical performance, aiming to achieve synergistic performance improvement of graphene electrodes at different operating potentials for both positive and negative electrodes through the synergistic regulation of doping and defects. The main objectives of this invention include: Enhancing the charge storage capacity of graphene at high potentials: By introducing nitrogen doping into graphene and combining it with lattice defects, the density of electronic states near the Fermi level is increased, thereby improving the quantum capacitance in the high potential region of the cathode, enabling the graphene cathode to store more charge at higher voltages.

[0061] Enhancing the capacitive response of graphene at low potentials: By introducing boron doping into graphene and combining it with defects, electron acceptor sites are generated, improving the ability of the negative electrode to accept electrons / lithium ions in the low potential region, thereby increasing the capacitance at low potentials and the ability to reversibly store lithium.

[0062] Optimize electrode interface reactions and stability: By doping to regulate the chemical functional groups and active sites on the graphene surface, the redox catalytic performance at the positive electrode interface can be improved, such as increasing the tolerance to positive electrode transition metal ions, suppressing side reactions, and improving the lithium ion nucleation and deposition behavior at the negative electrode interface, such as promoting uniform, dendritic free deposition, forming a stable solid electrolyte interface (SEI), thereby reducing charge transfer impedance and improving rate performance and cycle life.

[0063] Example 1: Preparation of in-situ nitrogen-doped defect graphene Step 1, Preparation of defective graphene precursor: In this embodiment, a graphene film with a certain defect density is first grown using chemical vapor deposition (CVD). A 25 μm thick copper foil is placed in a CVD furnace as a catalytic substrate and annealed at 1000°C in a hydrogen atmosphere for 30 minutes to remove the surface oxide layer. Then, a mixture of methane (CH4) and argon is introduced, with methane used as the carbon source and its partial pressure controlled at 0.1%~1% to increase the generation of vacancies and polycrystalline boundaries during the growth process. The growth reaction is carried out at 1000°C for 10 minutes to obtain a graphene film deposited on the copper foil surface. By controlling the methane concentration and growth time, the defect density of the graphene can be adjusted; the graphene obtained under the conditions of this embodiment is monolayer to bilayer, and the intensity ratio of the D peak to the G peak in the Raman spectrum is (I0.05). D / I G The value is approximately 0.3, indicating the presence of a certain concentration of defects.

[0064] Step 2, Nitrogen Source Introduction and Doping Growth: During the graphene growth process described above, 5 vol% ammonia (NH3) was introduced into the reaction gas at the 5-minute mark, serving as the reaction gas source along with methane. The ammonia decomposed on the high-temperature copper surface, and some active nitrogen atoms substituted into the graphene lattice, preferentially occupying previously formed vacancy defects. The co-deposition reaction continued for 10 minutes, and the copper foil sample was removed after furnace cooling, yielding a nitrogen-doped defect graphene film. This film was then etched onto a copper substrate with 1 mol / L HCl solution, washed with deionized water, and transferred to a SiO2 / Si substrate for later use.

[0065] Step 3, Material Characterization: The composition and structure of the obtained film were analyzed using X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. XPS measurements revealed nitrogen 1s peaks including pyridine nitrogen (398.5 eV) and graphitic nitrogen (400.8 eV), confirming successful nitrogen incorporation into graphene as pyridine N and graphitic N; the total nitrogen content was approximately 2.3 at%, with a mass percentage of 5.1%. The Raman I_D / I_G ratio increased from 0.3 to 0.45, indicating that the doping process introduced additional defects, specifically local distortion caused by nitrogen atoms occupying vacancies. Transmission electron microscopy (TEM) and corresponding energy-dispersive spectroscopy (EDS) showed that nitrogen was uniformly distributed in the graphene film, and no nitrogen agglomerates were observed. These results demonstrate that nitrogen atoms were successfully incorporated into the graphene defect sites in a substituted form.

[0066] Step 4, Electrode Preparation and Testing: The nitrogen-doped defective graphene film described above was directly used as the active coating for the positive electrode of a lithium-ion capacitor for testing. Specifically, the film was cut into 1cm pieces. 2An electrode sheet, attached to a stainless steel current collector, served as the working electrode, while an undoped graphene film with a similar defect concentration served as the control electrode. Both were used to assemble symmetrical capacitors with an activated carbon anode and an EMIMBF4 ionic liquid electrolyte, respectively. Cyclic voltammetry (CV) and constant current charge-discharge tests were conducted at room temperature. The results showed that the nitrogen-doped defective graphene cathode exhibited stable capacitive behavior at a high cutoff voltage of 3.5V, significantly improving upon the sharp capacitance decay observed in the control electrode at >3.0V. At a current density of 1A / g, the specific capacitance of the nitrogen-doped cathode was 150F / g, approximately 1.8 times that of the control. This demonstrates that nitrogen-doped defective graphene can effectively improve the electrochemical performance of the cathode at high potentials.

[0067] Example 2: Preparation of post-processed boron-doped defect graphene Step 1, Preparation of Defective Graphene Powder: This embodiment uses a chemical reduction method of graphene oxide to obtain a graphene precursor with many defects. First, a modified Hummers method is used to oxidize natural graphite to obtain an aqueous dispersion of graphene oxide (GO). GO sheets contain abundant functional groups such as hydroxyl and epoxy groups, which can generate point defects when removed during the subsequent reduction process. A 2 mg / mL GO dispersion is subjected to a hydrothermal reaction at 180°C for 12 hours to obtain a reduced graphene oxide hydrogel; this gel is then vacuum-dried and ground to obtain the multi-defect graphene powder. Raman spectroscopy shows that its I... D / I G The value is approximately 1.1, a significant improvement over the original GO, indicating the presence of numerous defects.

[0068] Step 2, Boron Source Introduction and High-Temperature Doping: 100 mg of the above-mentioned defective graphene powder was uniformly ground and mixed with boric acid (H3BO3) at a 1:1 mass ratio, and then loaded into a quartz boat. Under an argon / hydrogen atmosphere with a volume ratio of 9:1, the mixture was calcined at 950 °C for 3 hours at a heating rate of 5 °C / min. The boric acid decomposed at high temperature to produce B2O3 and gaseous boron-containing compounds, which diffused and embedded into the graphene defect sites to complete the doping. Hydrogen helped reduce boron oxides and remove excess oxygen. After cooling to room temperature, the sample was collected to obtain boron-doped defective graphene powder.

[0069] Step 3, Structural and Compositional Analysis: Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and XPS were used to characterize the boron content and chemical bonding forms in the product. ICP-OES determined the boron content in the powder to be 4.2% by mass, corresponding to an atomic doping ratio of approximately 2.0 at%. XPS B 1s spectra showed peaks at 191.2 eV for BC3 and 192.5 eV for BC2O, indicating that boron mainly exists as BC3 structures formed by replacing carbon, with a small amount forming BC2O structures with oxygen. Compared to before doping, Raman spectroscopy showed... D / I GThe defect density decreased from 1.1 to approximately 0.9, presumably due to some defects being filled or passivated by boron atoms, but the material still maintains a considerable defect density, such as... Figure 4 As shown.

[0070] Step 4, Electrochemical Performance Testing: The obtained boron-doped defective graphene powder was used for testing the negative electrode protective layer of a lithium metal battery. First, the powder was dispersed in isopropanol and coated onto a copper foil current collector to form a uniform coating approximately 5 μm thick. After vacuum drying, it served as a modified copper negative electrode current collector. A lithium metal sheet was used as the counter electrode, and a symmetrical battery without liquid electrolyte was assembled with the aforementioned current collector. The lithium deposition / stripping behavior was tested using a 50 μm distance between the two copper foils, compared to bare copper foil without graphene coating. The results showed that at 1 mA / cm², the lithium deposition / stripping behavior was significantly improved. 2 At the specified current density, the nucleation overpotential of lithium on the modified copper foil was only ~5mV, significantly lower than the 18mV of the bare copper foil. Furthermore, the deposited lithium morphology was denser and smoother, without dendrite protrusions. After 50 cycles of continuous deposition / stripping, the voltage hysteresis of the copper foil electrode coated with boron-doped graphene increased very slowly, with a capacity retention of approximately 92%, compared to only about 80% for the bare copper control. This difference is attributed to boron doping effectively promoting uniform lithium deposition and stripping, reducing capacity loss caused by dead lithium and repeated SEI breakdown and reconstruction. Electrochemical impedance spectroscopy (EIS) tests showed that after 50 cycles, the interfacial impedance in the low-to-mid-frequency region of the boron-doped electrode was significantly lower than the control, indicating a more stable interface and smoother charge transfer. These results confirm that the boron-doped defective graphene of this invention can significantly improve the capacity and cycle life of graphene anodes in lithium-ion battery systems.

[0071] Example 3: Differential doping of graphene film in positive / negative electrode regions and its application in lithium batteries This embodiment demonstrates a process for separately doping nitrogen and boron regions on the same graphene film to form a graphene film with heterogeneous doped regions on a single material, which can be used in the positive and negative electrode directions of a battery.

[0072] Step 1, Preparation of large-area graphene films: Continuous graphene films were prepared on copper foil using CVD, with specific conditions the same as in Step 1 of Example 1, but the growth time was extended to 30 minutes to obtain films with centimeter-scale areas and a defect density Raman I. D / I G ~ 0.2.

[0073] Step 2, Region Masking: A high-temperature resistant ceramic sheet was used as a mask to divide the graphene / Cu sample surface into two parts: the left half was covered by the mask, and the right half was exposed. The exposed right half was subjected to plasma nitrogen doping in a PECVD apparatus: a mixture of argon and ammonia (10%) was introduced at a pressure of 0.5 Pa, with a radio frequency power of 50 W, for 5 minutes, to introduce nitrogen doping into the graphene in the right half. The mask was then removed and the opposite side was covered, exposing only the previously masked left half, which was then subjected to plasma boron doping: a mixture of argon and trimethylborane (B(CH3)3) vapor was introduced, with the borane gas diluted to a total plasma chamber pressure of 0.5 Pa by a carrier gas. Other conditions were similar to nitrogen plasma treatment, for 5 minutes. This resulted in a graphene film with nitrogen-doped defect graphene on the right side and boron-doped defect graphene on the left side, with a transition region width of <1 mm.

[0074] Step 3, Membrane Transfer and Battery Assembly: A polymer coating approximately 2 μm thick was deposited on the surface of the heterogeneous doped graphene film using electrochemical deposition as a support. Then, copper foil was etched using potassium ferrocyanide to transfer the entire graphene film, along with the support layer, to the surface of a microporous polypropylene battery separator. After dissolving and removing the support coating, the heterogeneous doped graphene-modified separator was obtained. One side of the separator was uniformly covered with a nitrogen-doped graphene film facing the positive electrode, and the other side was covered with a boron-doped graphene film facing the negative electrode. This modified separator was used to assemble a pouch lithium-ion battery: the positive electrode was LiNi... 0.5 Co 0.2 Mn 0.3 O2-coated aluminum foil, graphite-coated copper foil as the negative electrode, and a conventional carbonate electrolyte system. In a control group, the same positive and negative electrode materials and electrolyte were used, but an unmodified conventional PP separator was employed.

[0075] Step 4, Battery Performance Comparison: Both groups of batteries were cycled at 0.5C rate at room temperature, with a charging cutoff voltage of 4.3V and a discharging cutoff voltage of 2.8V. The results showed that the experimental group, using a heterogeneously doped graphene membrane separator, had an initial discharge capacity approximately 5% higher than the control group. The coulombic efficiency for the first 100 cycles was close to 99.5%, slightly higher than the control group's 99%. More significantly, after 300 charge-discharge cycles, the experimental group's battery capacity retention rate was 88%, significantly higher than the control group's 80%. Disassembly and observation revealed obvious corrosion marks on the aluminum foil surface of the positive electrode current collector in the control group, and uneven deposits and lithium dendrites on the graphite surface of the negative electrode. In contrast, the experimental group's positive electrode surface was cleaner, and the negative electrode surface showed uniform deposition without dendrite penetration into the separator. This indicates that the nitrogen / boron doped defect graphene membrane provided by this invention plays a dual protective role in the battery: nitrogen-doped graphene on the positive electrode side inhibits electrolyte decomposition and aluminum foil corrosion at high potentials, while boron-doped graphene on the negative electrode side promotes uniform lithium ion deposition and avoids dendrite formation. This embodiment demonstrates that regionally differentiated doping can simultaneously improve the interface between the positive and negative electrodes of a battery, achieving a significant overall performance improvement.

[0076] Example 4: Performance comparison of doping positive and negative electrodes in a supercapacitor Electrode fabrication: The nitrogen-doped defective graphene material obtained in Example 1 was used as the positive electrode active material, and the boron-doped defective graphene material obtained in Example 2 was used as the negative electrode active material. These materials were mixed with conductive carbon black and PTFE binder at a mass ratio of 85:10:5, and coated onto a current collector on a nickel foam sheet to prepare the electrodes. After vacuum drying at 120°C for 12 hours, the two electrodes were used as the working electrode and the counter electrode, respectively, to assemble a symmetrical two-electrode capacitor. A glass fiber membrane was used as the separator, and a 1M tetraethylammonium hexafluorophosphate / acetonitrile solution was used as the organic electrolyte. The supercapacitor obtained by this assembly has a positive electrode where the double layer and pseudocapacitance are mainly provided by N-doped defective graphene, and a negative electrode where the double layer capacitance is mainly provided by B-doped defective graphene.

[0077] Comparative Preparation: To compare the effects, three additional sets of comparative supercapacitors were prepared: (A) both electrodes used undoped graphene material with a similar defect concentration; (B) both electrodes used nitrogen-doped defective graphene; (C) both electrodes used boron-doped defective graphene. The material preparation methods for the above materials were similar to those in Examples 1 and 2, except that the materials used for both electrodes were the same. The electrode fabrication and capacitor assembly methods were the same as above.

[0078] Performance testing: The above capacitors were subjected to constant current charge-discharge and cyclic voltammetry scan tests at room temperature, as shown in Tables 1-3. The results are as follows: Operating voltage range: The experimental capacitors with N-doped positive electrode and B-doped negative electrode achieved stable charge-discharge from 0 to 3.2 V in organic electrolyte, with no obvious signs of gas evolution or electrolyte decomposition. In contrast, control A without graphene showed increased voltage hysteresis and decreased coulombic efficiency above 2.7 V, suggesting the occurrence of side reactions; control B with dual nitrogen doping showed excessive polarization at the negative electrode above approximately 3.0 V, because both electrodes lacked sites to attract anions, making it difficult for the negative electrode to support higher potential differences; control C with dual boron doping showed increased side reactions at the positive electrode interface above 2.8 V, lacking active sites to catalyze the positive electrode oxidation reaction, leading to deteriorated cycle performance. Therefore, the heterogeneous doping combination of this invention allows for a higher safe operating voltage, approximately 0.3 to 0.5 V higher than that of conventional symmetrical carbon capacitors, which is highly beneficial for improving device energy density.

[0079] Capacitance performance: At a current density of 1 A / g, the single-electrode specific capacitance of the experimental group capacitor reached 185 F / g, which, based on the total mass of active material, is significantly higher than that of control A (120 F / g), control B (150 F / g), and control C (130 F / g). This verifies the superiority of different doping elements in sharing the functions of the positive and negative electrodes. The experimental group maintained high capacitance even at high voltage: N-doping in the positive electrode contributed approximately 55% of the capacitance, and B-doping in the negative electrode contributed approximately 45%, both significantly better than the undoped cases.

[0080] Rate performance and cycle life: Under high-speed charge and discharge at 10 A / g, the experimental group retained 72% of its initial capacitance, while controls A, B, and C retained only 50%, 60%, and 58%, respectively. This indicates that materials with nitrogen / boron doping defects exhibit smoother ion transport and charge transfer, and less polarization at high rates. Regarding cycle life, the experimental group capacitors retained 91% of their capacitance after 10,000 cycles at 2.7V, slightly better than control B's 88% and control C's 85%, and significantly higher than control A's 75%. The coulombic efficiency of the experimental group remained consistently above 99%, with no significant decay. This demonstrates that the material of this invention not only improves capacitance but also possesses excellent cycle stability.

[0081] Table 1

[0082] Table 2

[0083] Table 3

[0084] The above comparison clearly demonstrates that the combination of nitrogen-doped defective graphene in the positive electrode and boron-doped defective graphene in the negative electrode proposed in this invention exhibits the best overall performance in supercapacitors: it expands the voltage window, improves capacitance and power performance, and maintains a good lifetime, outperforming any single-doped or undoped scheme. This fully proves the effectiveness and advancement of the technical solution of this invention.

[0085] Comparative Example 1: Preparation and application of undoped graphene material with defective structures. The preparation method was the same as in Example 1, but without the introduction of nitrogen- or boron-containing gases; defective graphene with an I_D / I_G ratio of approximately 0.3 was obtained solely by controlling the CVD conditions. This material was applied to supercapacitor electrodes and lithium-ion battery electrodes, respectively. The results showed that the performance of Comparative Example 1 was significantly lower than that of the material of this invention: for example, the specific capacitance of the supercapacitor electrode was less than 60% of that of this invention, and it exhibited rapid degradation at high voltages; the specific capacity of the lithium-ion battery anode was only about 300 mAh / g, and it decayed by more than 20% after 100 cycles. This indicates that simply introducing defects without heteroatom doping, while providing certain active sites, cannot sufficiently improve the density of states of graphene, resulting in limited performance improvement and poor high / low potential stability.

[0086] Comparative Example 2: Graphene material doped only without pre-existing defects. High-quality single-crystal graphene was lightly nitrogen-doped using ammonia plasma post-treatment, with a nitrogen content of approximately 2 at%, I. D / I G The efficiency was increased from 0 to 0.05. This material incorporates a small amount of heteroatoms within an ideal lattice, but is virtually defect-free. Tests revealed that its conductivity remained good, but the improvement in electrochemical activity was not significant: the specific capacitance of the supercapacitor increased by less than 20%, mainly due to the pseudocapacitance provided by a small amount of pyridine nitrogen; the capacity of the lithium-ion battery anode showed almost no improvement because the low concentration of nitrogen doping has limited effect on lithium adsorption. This indicates that defect-free doping cannot fully utilize the role of heteroatoms, and the doped atoms are easily confined by the surrounding perfect lattice, making it difficult to form highly efficient active sites.

[0087] Comparative Example 3: Both electrodes used graphene materials with the same doping. The performance of supercapacitors (1) with nitrogen-doped defective graphene in both electrodes and (2) with boron-doped defective graphene in both electrodes were tested respectively. In short, the device with the same doping in both electrodes cannot simultaneously achieve the stability of the positive electrode at high voltage and the performance of the negative electrode at low potential due to the lack of differentiated design: when fully nitrogen-doped, the negative electrode lacks anionic sites and polarization occurs above 3.0V; when fully boron-doped, the positive electrode lacks catalytic sites and side reactions occur above 2.8V, accelerating decay. Its overall performance is inferior to the heterogeneous doping combination of the present invention. This further proves that the present invention is different from a simple doping addition, but a new synergistic optimization scheme for the needs of positive and negative electrodes.

[0088] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A heteroatom-doped defect graphene material, characterized in that: The graphene matrix contains lattice defects, and heteroatoms are bonded to the lattice defects. The heteroatoms occupy the lattice defect sites to form doped graphene materials. The doped graphene materials change the electronic state density near the Fermi level of the graphene matrix and the position of the Fermi level by controlling the local electron cloud distribution. The heteroatoms are selected from one or more of nitrogen, boron, phosphorus, sulfur or fluorine.

2. The heteroatom-doped defect graphene material according to claim 1, characterized in that: The heteroatom is a nitrogen atom; the nitrogen atom occupies the lattice defect site as an electron donor, which shifts the Fermi level of the graphene matrix upward, and the material is configured as a positive electrode active material for high-potential operation.

3. The heteroatom-doped defect graphene material according to claim 1, characterized in that: The heteroatom is a boron atom; the boron atom occupies the lattice defect site as an electron acceptor, causing the Fermi level of the graphene matrix to shift down, and the material is configured as a negative electrode active material for low-potential operation or a host material for metal ion deposition.

4. The heteroatom-doped defect graphene material according to claim 1, characterized in that: The material is a graphene film with a planar heterostructure; the film is divided into a first region and a second region along the planar direction. The first region is enriched with nitrogen atom doped defect structures, and the second region is enriched with boron atom doped defect structures. The first region and the second region are connected or physically separated by a transition region.

5. An electrochemical energy storage device, characterized in that: It includes a positive electrode, a negative electrode, and an electrolyte or membrane located between the positive and negative electrodes, wherein the positive and / or negative electrodes include electrodes; The electrode includes a current collector and an active material layer coated on the surface of the current collector, wherein the active material layer comprises the heteroatom-doped defect graphene material as described in any one of claims 1 to 4; When the device is a supercapacitor, the positive electrode comprises the nitrogen-doped defect graphene material as described in claim 2, and the negative electrode comprises the boron-doped defect graphene material as described in claim 3.

6. A method for preparing heteroatom-doped defect graphene material as described in any one of claims 1-4, comprising the following steps: S1. Defect construction: Introducing lattice defects into the graphene lattice, including carbon vacancies, grain boundaries, or edge dangling bonds; S2, Defect Anchoring Doping: Provides a source of heteroatoms, which, under thermodynamic or kinetic drive, preferentially diffuse and occupy lattice defect sites to form doped graphene materials.

7. The method for preparing a heteroatom-doped defect graphene material according to claim 6, characterized in that: Steps S1 and S2 are carried out in situ in synergy using chemical vapor deposition: carbon source gas is introduced into the substrate to grow graphene, and lattice defects are introduced by adjusting the partial pressure of the carbon source or the growth parameters; during or after the growth of graphene, nitrogen-containing gas or boron-containing gas is introduced, and high temperature is used to make heteroatoms occupy the lattice defects in situ.

8. The method for preparing a heteroatom-doped defect graphene material according to claim 6, characterized in that: Step S1 includes preparing graphene powder with abundant oxygen-containing functional groups and defects using a redox method; Step S2 includes uniformly mixing the graphene powder with a solid heteroatom-containing compound and performing high-temperature heat treatment under an inert or reducing atmosphere, so that the active species generated by the decomposition of the heteroatom-containing compound are embedded in the lattice defects.

9. The method for preparing a heteroatom-doped defect graphene material according to claim 6, characterized in that: Step S2 includes region-selective doping: using a mask to block the first region of the graphene film, the exposed second region is subjected to a first type of heteroatom doping treatment; The mask is then removed or moved to expose the first region, which is then subjected to a second type of heteroatom doping treatment. The first and second heteroatoms are nitrogen atoms and boron atoms, respectively.

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