Hard carbon material, electrochemical device, and electronic device

Abstract

The present application relates to a hard carbon material, an electrochemical device and an electronic device, the hard carbon material comprising a porous framework and at least a first element and a zinc element located within the porous framework, the first element comprising one or more of a nitrogen element, a sulfur element, a boron element, a phosphorus element and a selenium element. The hard carbon material of the present application can significantly improve the energy density of an electrochemical device when applied thereto.

Description

[0001] This application is a divisional application based on the invention with application number 202211248809.7, application date October 12, 2022, applicant being CATL (Contemporary Amperex Technology Co., Ltd.), entitled "Hard Carbon Material and its Preparation Method, Electrochemical Device and Electronic Device". Technical Field

[0002] This application relates to the field of energy storage technology, and more specifically, to hard carbon materials, electrochemical devices, and electronic devices. Background Technology

[0003] Electrochemical devices, characterized by high energy density, high operating voltage, and light weight, are widely used in electronic products such as mobile phones, laptops, and cameras. While improving the electrochemical performance of these devices, their safety performance is equally important. As the performance requirements for electronic products increase, the performance requirements for electrochemical devices are also gradually rising.

[0004] Research has found that the migration of active ions between the positive and negative electrode active materials in an electrochemical device is the core process of charging and discharging. As a result, the negative electrode active material has a significant impact on the performance of the electrochemical device, such as its energy density. However, the reversible capacity and low plateau capacity of existing negative electrode active materials are relatively low, resulting in a low energy density of the electrochemical device when the negative electrode active material is used. Summary of the Invention

[0005] This application provides a hard carbon material and its preparation method, an electrochemical device, and an electronic device. The hard carbon material has high reversible capacity and low plateau capacity. When the hard carbon material is applied to the electrochemical device, the performance of the electronic device can be significantly improved.

[0006] In a first aspect, this application proposes a hard carbon material, the hard carbon material comprising a porous framework and at least a first element and a zinc element located within the porous framework, the first element comprising one or more of nitrogen, sulfur, boron, phosphorus and selenium.

[0007] The hard carbon material also satisfies at least one of the following conditions:

[0008] (1) The hard carbon material uses lithium metal as the counter electrode, and operates at 0 to 2.5V vs Li + The charge-discharge curves obtained from the test within the / Li range

[0009] 0 (vs Li) + / Li) to 0.15V (vs Li) + The specific capacity of / Li) is denoted as C. 11 mAh / g;

[0010] 0.15V (vs Li) + / Li) to 0.8V (vs Li) + The specific capacity of / Li) is denoted as C. 12 mAh / g,

[0011] The hard carbon material satisfies: 1.6 ≤ C 11 / C 12 ≤2.1;

[0012] (2) The hard carbon material uses sodium metal as the counter electrode, and is subjected to a voltage of 0 to 2.5V vs Na. + The charge-discharge curves obtained from tests within the / Na range

[0013] 0(vs Na + / Na) to 0.15V (vs Na) + The specific capacity of (Na) is denoted as C. 21 mAh / g;

[0014] 0.15V (vs Na) + / Na) to 1.00V (vs Na) + The specific capacity of (Na) is denoted as C. 22 mAh / g,

[0015] The hard carbon material satisfies: 3.55 ≤ C 21 / C 22 ≤3.95.

[0016] In some embodiments, the content of the first element relative to the total mass of the hard carbon material is denoted as A1wt%.

[0017] The zinc content relative to the total mass of the hard carbon material is denoted as A2wt%.

[0018] The hard carbon material satisfies the following condition: 1.5≤A1 / A2≤5.

[0019] In some embodiments, the content of the first element relative to the total mass of the hard carbon material is denoted as A1 wt%; the content of zinc relative to the total mass of the hard carbon material is denoted as A2 wt%; the first element includes nitrogen, 2 ≤ A1 / A2 ≤ 4.5; and / or

[0020] The first element includes nitrogen, and the nitrogen content based on the total mass of the hard carbon material is denoted as W1wt%, 2≤W1≤5.

[0021] In some embodiments, the content of the first element relative to the total mass of the hard carbon material is denoted as A1 wt%; the content of zinc relative to the total mass of the hard carbon material is denoted as A2 wt%; the first element includes one or more of sulfur, boron, phosphorus, and selenium, and 2 ≤ A1 / A2 ≤ 4; and / or

[0022] The first element includes one or more of sulfur, boron, phosphorus and selenium, and the content of the first element based on the total mass of the hard carbon material is denoted as W2wt%, where 2.5≤W2≤9.

[0023] In some embodiments, the content of zinc relative to the total mass of the hard carbon material is denoted as A2wt%, 0.6≤A2≤1.2.

[0024] In some embodiments, the hard carbon material satisfies at least one of the following conditions:

[0025] (1) 250≤C 11 ≤350;

[0026] (2) 300≤C 21 ≤340.

[0027] In some embodiments, the X-ray diffraction pattern of the hard carbon material contains diffraction peaks with a 2x scattering angle in the range of 15° to 30°, wherein the 2x scattering angle of the diffraction peaks is <24°; and / or

[0028] In the Raman spectrum of the hard carbon material within a 200µm x 500µm scanning area, at 1320 cm⁻¹... -1 Up to 1370cm -1 A characteristic peak D exists within the range, at 1570 cm⁻¹. -1 Up to 1620cm -1 A characteristic peak G exists within the range, and the peak intensity of the characteristic peak D is I. D The peak intensity of the characteristic peak G is I. G 0.5 < I D / I G ≤1.5.

[0029] In some embodiments, the hard carbon material also satisfies the following conditions (1) and / or condition (2):

[0030] (1) The volume distribution particle size Dv50μm of the hard carbon material satisfies: 3≤Dv50≤15;

[0031] (2) The volume distribution particle size Dv99μm of the hard carbon material satisfies: 10≤Dv99≤45.

[0032] In some embodiments, the hard carbon material further includes a carbon layer covering the porous framework.

[0033] Secondly, this application proposes an electrochemical device comprising a negative electrode plate comprising a hard carbon material as described in any embodiment of the first aspect of this application.

[0034] Thirdly, this application proposes an electronic device including the electrochemical device as described in the second aspect of this application.

[0035] According to the embodiments of the present application, when the hard carbon material satisfies 1.5≤A1 / A2≤5, the first element can be uniformly distributed in the porous framework. Due to the combination of the first element and the zinc element, the zinc element can be uniformly distributed in the porous framework, thereby giving the porous framework sufficient pore structure and more uniform pore distribution, which is beneficial to improving the reversible capacity and low plateau capacity of the hard carbon material. Thus, when the hard carbon material is applied to an electrochemical device, it can significantly improve the energy density of the electrochemical device. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0037] Figure 1 These are charge / discharge curves of the lithium-ion batteries in Examples 1-5 of this application. Detailed Implementation

[0038] Embodiments of this application will be described in detail below. Throughout this specification, identical or similar components and components having identical or similar functions are indicated by similar reference numerals. The embodiments described herein with reference to the accompanying drawings are illustrative and diagrammatic in nature and are intended to provide a basic understanding of this application. The embodiments of this application should not be construed as limiting this application.

[0039] Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format in this document. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only the numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0040] In the detailed description and claims, a list of items connected by the terms "one or more of," "one or more of," "one or more of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0041] The electrochemical device includes a positive electrode, a negative electrode, and a separator. The negative electrode includes an active material, such as graphite or hard carbon. Graphite has a theoretical capacity of 372 mAh / g, and its theoretical capacity has been largely reached in recent years, leaving little room for further improvement. Hard carbon materials have been extensively studied due to their advantages such as small volume expansion, strong fast charge / discharge capability, and high specific capacity. The inventors discovered that hard carbon materials have lower reversible capacity and lower low-plateau capacity, which limits the energy density of the electrochemical device.

[0042] In view of this, the inventors, from the perspective of improving hard carbon materials, created pores in the hard carbon materials to make them porous, thereby increasing the reversible capacity and low plateau capacity of the hard carbon materials. The solution of this application will be further explained below.

[0043] Hard carbon materials

[0044] The first aspect of this application proposes a hard carbon material comprising a porous framework and at least one first element and zinc element located within the porous framework. The first element includes one or more of nitrogen, sulfur, boron, phosphorus, and selenium. The content of the first element relative to the total mass of the hard carbon material is denoted as A1 wt%, and the content of zinc element relative to the total mass of the hard carbon material is denoted as A2 wt%. The hard carbon material satisfies the condition: 1.5 ≤ A1 / A2 ≤ 5. Although the mechanism is not yet clear, the hard carbon material of this application, when satisfying the above relationship, exhibits relatively high reversible capacity and relatively high low-plateau capacity. When applied to electrochemical devices, it can improve the energy density and other performance characteristics of the electrochemical devices.

[0045] The inventors speculate that the mechanism of action of this application is as follows:

[0046] The microstructure of hard carbon materials consists of short-range ordered microregions formed by the disordered stacking of curved graphite-like sheets, along with defects such as micropores. During charging, active ions, such as lithium ions and sodium ions, migrate from the positive electrode active material to the negative electrode active material, such as hard carbon material, and embed themselves within it. In the charge-discharge curve of hard carbon materials storing active ions, the low-voltage plateau region (0 to 0.15V vs Li+ / Li) represents the capacity provided by lithium ions or sodium ions filling the pores of hard carbon, while the high-voltage slope region (0.15V to 0.8V) represents the capacity provided by lithium ions intercalating into the hard carbon microcrystal layers, or sodium ions adsorbing on the end faces of the hard carbon microcrystals. The relatively low voltage region in the charge-discharge curve is generally considered to contribute more to energy density; therefore, improving the capacity of the low-voltage plateau region can significantly improve the energy density of the electrochemical device.

[0047] Optionally, hard carbon materials can be obtained through hydrothermal or chemical processes of precursor materials. Precursor materials include one or more of resin-based, pitch-based, and biomass-based precursors. For example, resin-based precursors include one or more of phenolic resin, epoxy resin, and polyfurfuryl alcohol; pitch-based precursors include one or more of coal tar pitch, petroleum pitch, and natural pitch; and biomass-based precursors include one or more of cellulose, lignin, starch, chitosan, sucrose, and glucose. Hard carbon formed from relatively low molecular weight precursors has more defects compared to hard carbon formed from high molecular weight precursors, providing more active sites for reactive ions and improving the capacity of the hard carbon material. In this application, the precursor material can be a biomass-based precursor.

[0048] The porous framework contains zinc, which is mainly distributed within the framework and can also be distributed on its surface. In the preparation of hard carbon materials, porogens containing zinc are selected, such as one or more of zinc gluconate, zinc citrate, zinc sulfate, and zinc nitrate. These porogens volatilize during the carbonization of the precursor material, thereby etching the structure of the precursor material to form pores, resulting in a porous framework in the hard carbon material after carbonization. The formation of the porous framework increases the pore volume and the number of insertion sites for active ions, thus significantly improving the reversible capacity of the hard carbon material, especially the capacity in the low plateau region.

[0049] The porous framework contains a first element, which is mainly distributed within the porous framework but can also be distributed on its surface. In the preparation of hard carbon materials, a first material containing the first element is selected. For example, when the first element includes nitrogen, the corresponding first material can include melamine, urea, dicyandiamide, etc. Another example is when the first element includes sulfur, the corresponding first material can include sulfur powder. Yet another example is when the first element includes boron, the corresponding first material can include boric acid. Yet another example is when the first element includes phosphorus, the corresponding first material can include ammonium dihydrogen phosphate. Yet another example is when the first element includes selenium, the corresponding first material can include diphenylselenosesene. When the precursor material and the substance containing the first element are mixed, the first element can be more uniformly distributed in the precursor material, and the first element can provide binding sites for zinc, which is beneficial to the uniform distribution of zinc. This allows the pore-forming agent to uniformly create pores, resulting in a more uniform pore structure distribution in the hard carbon material, more efficient pore utilization, and improved initial coulombic efficiency of the electrochemical device. Furthermore, the first element has good lithium-affinity wettability, which is beneficial for lithium ions to be embedded in the porous framework, thus significantly improving the capacity at low plateau voltage.

[0050] Although the above analysis focuses on the porous framework, the first element, and zinc as individual components of the hard carbon material, they form an organic whole and are interconnected, collectively influencing the final performance of the hard carbon material. In the hard carbon material of this application, when 1.5 ≤ A1 / A2 ≤ 5, the first element can be uniformly distributed within the porous framework. Due to the combined effect of the first element and zinc, zinc can also be uniformly distributed within the porous framework, resulting in a sufficient and more uniform pore structure within the framework. This is beneficial for improving the reversible capacity and low plateau capacity of the hard carbon material; thus, when applied to electrochemical devices, the hard carbon material can significantly improve the energy density of the electrochemical device. For example, A1 / A2 can be 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5, or a range consisting of any two of the above values.

[0051] This application regulates the wetting performance of hard carbon materials for active ions, such as lithium ions, by controlling the amount of the first element added. As the amount of the first element increases, the wetting performance for lithium ions improves, which is more conducive to lithium ion embedding in the porous framework and thus beneficial for improving low-plateau voltage capacity. Furthermore, it can also adjust the number of binding sites provided for zinc. As the amount of the first element increases, more binding sites are provided for zinc, which is beneficial for a more uniform distribution of zinc, resulting in more uniform pore formation. This application further improves the reversible capacity, low-plateau capacity, and structural stability of hard carbon materials by controlling the amount of the first element added to meet one or more of the following conditions.

[0052] In some embodiments, the first element includes nitrogen, where 2 ≤ A1 / A2 ≤ 4.5.

[0053] In some embodiments, the first element includes nitrogen, and the content of the first element relative to the total mass of the hard carbon material is denoted as W1wt%, where 2≤W1≤5. Exemplarily, the content of the first element W1wt% can be 2wt%, 3wt%, 4wt%, or 5wt%, or a range of any two of the above values. The nitrogen content can be tested using equipment and methods known in the art, such as using an elemental analyzer. Specifically, the sample is placed in the elemental analyzer, heated to completely burn the sample into elemental substances, then the moisture in the sample is removed using a condenser, and unwanted compounds and oxygen are eliminated using a reduction reaction tube, converting nitrogen oxides into nitrogen gas. Moisture in the sample is then further removed, and the nitrogen content is detected.

[0054] In some embodiments, the first element includes one or more of sulfur, boron, phosphorus and selenium, where 2 ≤ A1 / A2 ≤ 4.

[0055] In some embodiments, the first element includes one or more of sulfur, boron, phosphorus, and selenium, and the content of the first element relative to the total mass of the hard carbon material is denoted as W2wt%, where 2.5 ≤ W2 ≤ 9. Exemplarily, the content of the first element, W2wt%, can be 2.5wt%, 3wt%, 4wt%, or 5wt%, or a range of any two of the above values. The content of sulfur, boron, phosphorus, and selenium can be tested using equipment and methods known in the art, such as elemental analyzers. Specifically, elements such as sulfur, boron, phosphorus, and selenium are quantitatively obtained by X-ray photoelectron spectroscopy (XPS).

[0056] This application regulates the pore structure of the porous framework of hard carbon materials by controlling the amount of zinc added. Too little zinc may result in fewer channels in the porous framework, and the pore volume of the hard carbon material will not change significantly, which is not conducive to improving the low voltage plateau capacity. As the amount of zinc added increases, the number of channels in the porous framework increases, and the low voltage plateau capacity is significantly improved. However, too much zinc may lead to an excessive number of channels, resulting in poor stability of the porous framework structure. Therefore, controlling the amount of zinc added to meet the following conditions can further improve the reversible capacity, low plateau capacity, and structural stability of hard carbon materials.

[0057] In some embodiments, the zinc content relative to the total mass of the hard carbon material is denoted as A2wt%, where 0.6 ≤ A2 ≤ 1.2. Exemplarily, the zinc content A2wt% can be 0.6wt%, 0.7wt%, 0.9wt%, 1.0wt%, or 1.2wt%, or a range of any two of these values. The zinc content can be tested using equipment and methods known in the art, such as inductively coupled plasma atomic emission spectrometry (ICP-AES). Specifically, a plasma excitation source can be used to vaporize and dissociate or decompose the sample into atomic states. The atoms may further ionize into ionic states, and the atoms and ions are excited to emit light in the light source. ICP-AES decomposes the light emitted by the light source into a spectrum arranged by wavelength. The spectrum is detected using photoelectric devices, and the sample is qualitatively analyzed according to the measured spectral wavelengths and quantitatively analyzed according to the emitted light intensity.

[0058] In some embodiments, the hard carbon material further includes hydrogen and carbon elements, wherein the content of hydrogen elements relative to the total mass of the hard carbon material is denoted as W4wt%, and the content of carbon elements relative to the total mass of the hard carbon material is denoted as W5wt%, and the hard carbon material satisfies: 0.02≤W4 / W5≤0.20.

[0059] Through in-depth research on hard carbon materials, the inventors have discovered that the hard carbon material of this application is suitable not only for lithium-ion batteries but also for sodium-ion batteries. Lithium-ion batteries possess advantages such as high volumetric and gravimetric energy density, environmental friendliness, high operating voltage, small size, light weight, and long cycle life. When applied to lithium-ion batteries, the hard carbon material of this application can improve the energy density and other performance characteristics of lithium-ion batteries. Compared to lithium, sodium has a higher standard electrode potential, resulting in a lower energy density for sodium-ion batteries compared to lithium-ion batteries. Furthermore, the large ionic radius of sodium ions makes intercalation and deintercalation reactions difficult. The hard carbon material of this application is also suitable for sodium-ion batteries, facilitating the intercalation of sodium ions into the hard carbon material and improving the energy density and other performance characteristics of sodium-ion batteries.

[0060] The inventors discovered that when hard carbon materials also meet one or more of the following conditions, the reversible capacity and low plateau voltage capacity of hard carbon materials can be further improved.

[0061] In some embodiments, the hard carbon material uses lithium metal as the counter electrode, at 0 to 2.5V vs Li + In the charge-discharge curves obtained from the / Li range, 0(vs Li) + / Li) to 0.15V (vs Li) + The specific capacity of / Li) is denoted as C. 11 mAh / g; 0.15V (vsLi + / Li) to 0.8V (vs Li) +The specific capacity of / Li) is denoted as C. 12 mAh / g, hard carbon materials satisfy: 1.6≤C 11 / C 12 ≤2.1. Optionally, 250≤C 11 ≤350.

[0062] Hard carbon material was used as the negative electrode, and lithium metal (a lithium sheet with a diameter of 18 mm and a thickness of 0.6 mm) was used as the counter electrode. The hard carbon electrode, separator, and lithium sheet were assembled and stacked in sequence, and an electrolyte (1 mol / L lithium salt LiPF6) was added. The battery was then encapsulated in a coin cell stainless steel casing to obtain a coin cell battery. The charge-discharge curves of the coin cell battery were tested to obtain the specific capacity distribution during the delithiation process.

[0063] The hard carbon material of this application embodiment can further significantly improve the capacity of the hard carbon material on the low voltage platform under the condition of satisfying the above-mentioned specific capacity relationship.

[0064] In some embodiments, the hard carbon material uses sodium metal as the counter electrode, at 0 to 2.5V vs Na + In the charge-discharge curves obtained from the test within the / Na range, 0(vs Na) + / Na to 0.15V (vs Na) + The specific capacity of (Na) is denoted as C. 21 mAh / g; 0.15V (vsNa) + / Na) to 1.00V (vs Na) + The specific capacity of (Na) is denoted as C. 22 mAh / g, hard carbon materials satisfy: 3.55≤C 21 / C 22 ≤3.95. Optionally, 300≤C 21 ≤340.

[0065] Hard carbon material was used as the negative electrode, and sodium metal (a sodium sheet with a diameter of 18 mm and a thickness of 0.6 mm) was used as the counter electrode. The hard carbon electrode, separator, and sodium sheet were assembled and stacked in sequence, and an electrolyte (1 mol / L sodium salt NaPF6) was added. The cells were then encapsulated in a coin cell stainless steel casing to obtain a coin cell battery. The charge-discharge curves of the coin cell battery were tested to obtain the specific capacity distribution during sodium removal.

[0066] The hard carbon material of this application embodiment can further significantly improve the capacity of the hard carbon material on the low voltage platform under the condition of satisfying the above-mentioned specific capacity relationship.

[0067] In some embodiments, the X-ray diffraction (XRD) patterns of hard carbon materials exhibit diffraction peaks in the range of 15° to 30° at twice the scattering angle, with the twice-scattering angle of the diffraction peaks being <24°. The relatively large interlayer spacing of hard carbon materials facilitates the interlayer transport of active ions such as lithium ions and sodium ions.

[0068] In some embodiments, the Raman spectrum of hard carbon material in a 200µm*500µm scanning area is at 1320cm⁻¹. -1 Up to 1370cm -1 A characteristic peak D exists within the range, at 1570 cm⁻¹. -1 Up to 1620cm -1 There exists a characteristic peak G within the range, and the peak intensity of characteristic peak D is I. D The peak intensity of characteristic peak G is I G 0.5 < I D / I G ≤1.5.

[0069] In some embodiments, the volumetric particle size distribution (Dv50 μm) of the hard carbon material satisfies: 3 ≤ Dv50 ≤ 15. The physical definition of Dv50 is the particle size corresponding to a cumulative volumetric distribution percentage of 50%; it can be tested using methods known in the art. For example, it can be determined using a laser particle size analyzer (such as a Malvern MasterSize3000) in accordance with standard GB / T 19077.1-2016.

[0070] In some embodiments, the volumetric particle size distribution (Dv99 μm) of the hard carbon material satisfies: 10 ≤ Dv99 ≤ 45. The physical definition of Dv99 is the particle size corresponding to a cumulative volumetric distribution percentage of 99%; it can be tested using methods known in the art. For example, it can be determined using a laser particle size analyzer (such as a Malvern MasterSize3000) with reference to standard GB / T 19077.1-2016.

[0071] When the particle size of the hard carbon material in this application meets the above-mentioned range, the diffusion distance of active ions in the hard carbon material is relatively short, which is conducive to the full utilization of the specific capacity of the hard carbon material; and the particle specific surface area of ​​the hard carbon material is relatively small, and the kinetic performance is relatively good, which is conducive to improving the first-cycle coulombic efficiency of the hard carbon material.

[0072] In some embodiments, the hard carbon material further includes a carbon layer covering the porous framework.

[0073] The porous framework, due to etching by porogens, may form open-pore structures on its surface. These open-pore structures can provide more active sites for storing active ions, improving the capacity of hard carbon materials at low voltage levels. However, excessive open-pore structures can lead to a relatively large specific surface area of ​​the hard carbon material, resulting in excessive formation of a solid electrolyte interface (SEI) film and deteriorating the first-cycle coulombic efficiency. This application incorporates a carbon layer outside the porous framework, enabling the hard carbon material to maintain a high capacity at low voltage levels while improving the first-cycle coulombic efficiency.

[0074] Methods for preparing hard carbon materials

[0075] The second aspect of this application also provides a method for preparing hard carbon materials.

[0076] The method includes:

[0077] Step S100: The carbon-containing precursor material, the zinc-containing pore-forming agent, and the first material containing the first element are uniformly mixed to form a mixed system.

[0078] Step S200: Heat-treat the mixed system to carbonize the precursor material. During the carbonization process, the pore-forming agent volatilizes and etches the precursor material to form a porous framework. The porous framework contains the first element and zinc.

[0079] The first element includes one or more of nitrogen, sulfur, boron, phosphorus and selenium.

[0080] The content of the first element relative to the total mass of the hard carbon material is denoted as A1 wt%.

[0081] The zinc content relative to the total mass of the hard carbon material is denoted as A2 wt%.

[0082] The hard carbon material satisfies the following condition: 1.5≤A1 / A2≤5.

[0083] The types of precursor materials, pore-forming agents, and first materials in this application have been described above and will not be repeated here. This application utilizes a mixture of these three types of substances to facilitate pore formation in the precursor material during the carbonization process. The mixing method can include ball milling.

[0084] In some embodiments, the heat treatment in step S200 may include a first heat treatment and a second heat treatment, wherein the temperature of the first heat treatment is lower than the temperature of the second heat treatment.

[0085] The first heat treatment can serve as a pre-carbonization process, such as calcining the mixture in the range of 400°C to 700°C. This step helps to fix the zinc element in the pore-forming agent onto the precursor material, and, based on the uniform distribution of the first element in the precursor material, enables the zinc element to be uniformly distributed on the precursor material. Optionally, the mixture can be crushed and classified after the first heat treatment to make the particle size more consistent with production requirements.

[0086] The second heat treatment can be a carbonization process, such as calcining the mixture in the range of 900℃ to 1300℃, which carbonizes the precursor material into a porous framework. In particular, performing the second heat treatment after crushing and classification is beneficial for obtaining hard carbon materials with particle sizes that meet production requirements.

[0087] In some embodiments, the method further includes step S300, coating a carbon layer onto the porous framework. The carbon layer can be formed by coating the carbon source onto the porous framework using methods such as vapor deposition (e.g., chemical vapor deposition, sol-gel method), or bitumen coating. Specific process parameters can be those already available in the art, and will not be elaborated further here.

[0088] Electrochemical device

[0089] A third aspect of this application also provides an electrochemical device, the electrochemical device including a negative electrode plate, wherein the negative electrode active material of the negative electrode plate may include the hard carbon material of any embodiment of the first aspect of this application or the hard carbon material prepared by the method described in any embodiment of the second aspect of this application.

[0090] In some embodiments, the voltage drop K value per unit time of the electrochemical device satisfies: 0.01mV / h ≤ K ≤ 2mV / h. The K value is an indicator of the self-discharge rate of the electrochemical device, and when the K value is within the above range, the self-discharge performance of the electrochemical device is relatively excellent.

[0091] [Negative electrode plate]

[0092] The negative electrode sheet is a type of negative electrode sheet known in the art and used in electrochemical devices. In some embodiments, the negative electrode sheet includes a negative current collector and a negative active material layer. The negative active material layer is disposed on the surface of the negative current collector. The negative active material layer contains a negative active material. The negative active material may include the hard carbon material of any embodiment of the first aspect of this application or the hard carbon material prepared by the method described in any embodiment of the second aspect of this application.

[0093] In some embodiments, the structure of the negative electrode is a structure known in the art that can be used as a negative electrode in an electrochemical device.

[0094] In some embodiments, the negative current collector is a metal, such as, but not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a polymer substrate coated with a conductive metal, or a combination thereof.

[0095] In addition to the hard carbon material prepared by the method described in any embodiment of the first aspect of this application or any embodiment of the second aspect of this application, the negative electrode active material may also be selected from various conventionally known materials known in the art that can be used as negative electrode active materials for electrochemical devices, which are capable of reversibly inserting and de-inserting active ions or reversibly doping and de-doping active ions.

[0096] In some embodiments, the negative electrode active material comprises at least one of lithium metal, lithium metal alloy, carbon material, materials capable of doping / dedoping lithium, or transition metal oxide. In some embodiments, the carbon material may be any carbon material known in the art that can be used as a carbon-based negative electrode active material in an electrochemical device. In some embodiments, the carbon material comprises at least one of crystalline carbon and amorphous carbon. In some embodiments, the crystalline carbon is natural graphite or artificial graphite. In some embodiments, the crystalline carbon is in the shape of amorphous, plate-like, flake-like, spherical, or fibrous. In some embodiments, the crystalline carbon is low-crystallinity carbon or high-crystallinity carbon. In some embodiments, low-crystallinity carbon comprises at least one of soft carbon and hard carbon. In some embodiments, high-crystallinity carbon comprises at least one of natural graphite, crystalline graphite, pyrolytic carbon, mesophase pitch-based carbon fiber, mesophase carbon microspheres, mesophase pitch, and high-temperature calcined carbon.

[0097] In some embodiments, the high-temperature calcined carbon is petroleum coke or coke derived from coal tar pitch. In some embodiments, the amorphous carbon includes at least one of soft carbon, hard carbon, mesophase pitch carbonization product, and calcined coke. In some embodiments, the negative electrode active material includes a transition metal oxide. In some embodiments, the transition metal oxide includes at least one of vanadium oxide and lithium vanadium oxide. In some embodiments, the negative electrode active material includes at least one of Si, SiOx (0 < x < 2), Si / C composite, Si-Q alloy, Sn, SnOz, Sn-C composite, Sn-R alloy, where Q is selected from at least one of alkali metals, alkaline earth metals, Group 13 to Group 16 elements, transition elements, and rare earth elements and Q is not Si, and R is selected from at least one of alkali metals, alkaline earth metals, Group 13 to Group 16 elements, transition elements, and rare earth elements and R is not Sn. In some embodiments, Q and R include at least one of Mg, Ca, Sr, Ba, Ra, Sc, Y, Ti, Zr, Hf, Rf, V, Nb, Ta, Db, Cr, Mo, W, Sg, Tc, Re, Bh, Fe, Pb, Ru, Os, Hs, Rh, Ir, Pd, Pt, Cu, Ag, Au, Zn, Cd, B, Al, Ga, Sn, In, Tl, Ge, P, As, Sb, Bi, S, Se, Te, Po.

[0098] In some embodiments, the negative electrode active material layer further includes a negative electrode binder and a negative electrode conductive agent. In some embodiments, the negative electrode binder includes at least one of vinylidene fluoride - hexafluoropropylene copolymer (PVDF-co-HFP), polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon. In some embodiments, the negative electrode conductive agent is used to provide conductivity to the electrode, and it can include any conductive material as long as it does not cause chemical changes. In some embodiments, the negative electrode conductive agent includes any one or a mixture of carbon-based materials, metal-based materials, and conductive polymers. In some embodiments, the carbon-based materials include at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber. In some embodiments, the metal-based materials include at least one of metal powders or metal fibers of copper, nickel, aluminum, silver, etc. In some embodiments, the conductive polymers include polyphenylene derivatives.

[0099] In some embodiments, the method for preparing the negative electrode sheet is a method known in the art for preparing a negative electrode that can be used in electrochemical devices. In some embodiments, in the preparation of the negative electrode slurry, a solvent is typically added, and the negative electrode active material is added to a binder, and conductive materials and thickeners are added as needed, and then dissolved or dispersed in the solvent to form the negative electrode slurry. The solvent is evaporated and removed during the drying process. The solvent is a solvent known in the art that can be used as a layer of negative electrode active material, such as, but not limited to, water. The thickener is a thickener known in the art that can be used as a layer of negative electrode active material, such as, but not limited to, sodium carboxymethyl cellulose.

[0100] This application does not impose any particular restrictions on the mixing ratio of the negative electrode active material, binder, and thickener in the negative electrode active material layer, and the mixing ratio can be controlled according to the desired performance of the electrochemical device.

[0101] [Positive electrode plate]

[0102] The electrochemical device in this application embodiment may further include a positive electrode. The positive electrode is a type of positive electrode known in the art and suitable for use in electrochemical devices. In some embodiments, the positive electrode includes a positive current collector and a positive active material layer. The positive active material layer is disposed on the surface of the positive current collector. The positive active material layer contains a positive active material.

[0103] In some embodiments, the structure of the positive electrode is a structure known in the art for use in electrochemical devices.

[0104] In some embodiments, the positive current collector is a metal, such as, but not limited to, aluminum foil.

[0105] The positive electrode active material can be any conventionally known material known in the art that can be used as a positive electrode active material in electrochemical devices and is capable of reversibly inserting and deintercalating active ions. For lithium-ion batteries, the positive electrode active material typically contains lithium ions; for sodium-ion batteries, the positive electrode active material typically contains sodium ions. The following explanation uses lithium ions as an example.

[0106] In some embodiments, the positive electrode active material comprises lithium and a composite oxide of at least one selected from cobalt, manganese, and nickel. Specifically, the following compounds may be used: LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(Ni a Co b Mn c )O2(0 <a<1,0<b<1,0<c<1,a+b+c=1)、LiMn2O4LiNi 1-y Co y O2, LiCo l-y Mn yO2, LiNi l- y Mn y O2(0 < y < 1), Li(Ni a Mn b Co c )04(0 < a < 2, 0 < b < 2, 0 < c < 2, a + b + c = 2), LiMn 2-z Ni z O4, LiMn 2- z Co z O4(0 < z < 2), Li(Ni a Co b Al c )O2(0 < a < 1, 0 < b < 1, 0 < c < 1, a + b + c = 1), at least one or a mixture of two or more of LiCoPO4 and LiFePO4. In some embodiments, the positive electrode active material further comprises at least one of sulfides, selenides, and halides.

[0107] In some embodiments, the positive electrode active material layer further comprises a positive electrode binder and a positive electrode conductive agent. The positive electrode binder is used to improve the adhesion performance between the positive electrode active material particles and between the positive electrode active material particles and the current collector. In some embodiments, the positive electrode binder includes at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon. The positive electrode conductive agent is used to provide conductivity to the electrode, and it can include any conductive material as long as it does not cause chemical changes. In some embodiments, the positive electrode conductive agent includes at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, metal powder, metal fiber, polyphenylene derivatives. In some embodiments, the metal in the metal powder and metal fiber includes at least one of copper, nickel, aluminum, and silver.

[0108] In some embodiments, the method for preparing the positive electrode plate is a method well-known in the art and can be used for preparing the positive electrode plate of an electrochemical device. In some embodiments, in the preparation of the positive electrode slurry, a solvent is usually added, and the positive electrode active material is added with a binder and, if necessary, a conductive material and a thickening agent and then dissolved or dispersed in the solvent to form the positive electrode slurry. The solvent is volatilized and removed during the drying process. The solvent is a solvent well-known in the art and can be used as the solvent for the positive electrode active material layer, and the solvent is, for example, but not limited to N-methylpyrrolidone (NMP).

[0109] [Separator membrane]

[0110] The separator is a separator known in the art that can be used in electrochemical devices, such as, but not limited to, polyolefin microporous membranes. In some embodiments, the separator comprises at least one selected from polyethylene (PE), ethylene-propylene copolymer, polypropylene (PP), ethylene-butene copolymer, ethylene-hexene copolymer, and ethylene-methyl methacrylate copolymer.

[0111] In some embodiments, the separator is a single-layer separator or a multi-layer separator.

[0112] In some embodiments, the separator is coated with a coating. In some embodiments, the coating comprises at least one of an organic coating and an inorganic coating, wherein the organic coating is selected from at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylonitrile, polyimide, acrylonitrile-butadiene copolymer, acrylonitrile-styrene-butadiene copolymer, polymethyl methacrylate, polymethyl acrylate, polyethyl acrylate, acrylic-styrene copolymer, polydimethylsiloxane, sodium polyacrylate, and sodium carboxymethyl cellulose, and the inorganic coating is selected from at least one of SiO2, Al2O3, CaO, TiO2, ZnO2, MgO, ZrO2, and SnO2.

[0113] This application does not impose any particular limitations on the morphology and thickness of the separator. The method for preparing the separator is a well-known method in the art and can be used in electrochemical devices.

[0114] Electrolyte

[0115] The electrochemical device in this application embodiment may further include an electrolyte. The electrolyte in this application contains an electrolyte salt. The electrolyte salt is a type of electrolyte salt known in the art suitable for electrochemical devices. Appropriate electrolyte salts can be selected for different electrochemical devices. For example, for lithium-ion batteries, lithium salts are typically used as the electrolyte salt. As another example, for sodium-ion batteries, sodium salts are typically used as the electrolyte salt. The following description uses a lithium-ion battery as an example.

[0116] In some embodiments, the lithium salt includes or is selected from at least one of organic lithium salts and inorganic lithium salts.

[0117] In some embodiments, the lithium salt includes or is selected from lithium hexafluorophosphate (LiPF6), lithium hexafluoroantimony oxide (LiSbF6), lithium hexafluoroarsenate (LiAsF6), lithium perfluorobutyl sulfonate (LiC4F9SO3), lithium perchlorate (LiClO4), lithium aluminate (LiAlO2), lithium tetrachloroaluminate (LiAlCl4), and lithium bis(fluorosulfonyl imide) (LiN(C x F 2x+1 SO2)(C y F 2y+1SO2), where x and y are natural numbers, lithium chloride (LiCl), or lithium fluoride (LiF). In some embodiments, the mass percentage of lithium salt in the electrolyte of this application is 10 wt% to 15 wt%, for example, it can be 10%, 11%, 12%, 13%, 14%, 15%, or any range therebetween.

[0118] The electrolyte of this application may also contain a non-aqueous organic solvent. In some embodiments, the non-aqueous organic solvent comprises at least one of carbonates, carboxylic esters, ether compounds, sulfone compounds, or other aprotic solvents. In some embodiments, the mass percentage of the non-aqueous organic solvent is 21% to 90%, for example, it can be 21%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or any range thereto.

[0119] In some embodiments, the carbonate solvent comprises at least one of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, dipropyl carbonate, ethylene carbonate, propylene carbonate, butene carbonate, and di(2,2,2-trifluoroethyl) carbonate.

[0120] In some embodiments, the carboxylic acid ester solvent comprises at least one of methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, methyl butyrate, ethyl butyrate, propyl butyrate, butyl butyrate, γ-butyrolactone, valproic acid lactone, and butyrolactone.

[0121] In some embodiments, the ether compound solvent comprises at least one selected from ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dibutyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, bis(2,2,2-trifluoroethyl) ether, 1,3-dioxane, and 1,4-dioxane.

[0122] In some embodiments, the sulfone compound comprises at least one of ethyl vinyl sulfone, methyl isopropyl sulfone, isopropyl sec-butyl sulfone, and sulfolane.

[0123] The non-aqueous organic solvent in the electrolyte can be a single non-aqueous organic solvent or a mixture of multiple non-aqueous organic solvents. When using a mixed solvent, the mixing ratio can be controlled according to the desired performance of the electrochemical device.

[0124] The electrolyte of this application may also contain functional additives, such as film-forming additives and positive electrode film-forming additives. Film-forming additives can form an interfacial film on the surface of the negative electrode and / or the positive electrode, thereby protecting the negative electrode and / or the positive electrode. In some embodiments, the film-forming additives may be polynitrile additives, sulfonate additives, etc.

[0125] Based on the same inventive concept, this application also provides an electronic device.

[0126] The electronic device covered by this application is any electronic device, such as, but not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors. It should be noted that the electrochemical device covered by this application is applicable not only to the electronic devices listed above, but also to energy storage power stations, maritime transport vehicles, and air transport vehicles. Air transport vehicles include both intra-atmosphere and extra-atmosphere air transport vehicles.

[0127] In some embodiments, the electronic device includes the electrochemical device described above in this application.

[0128] The technical solution of this application will be further described below using a lithium-ion battery as an example, in conjunction with comparative examples and embodiments, but it is not limited thereto. Those skilled in the art will understand that the preparation methods described in this application are merely exemplary embodiments, and any modifications or substitutions to the technical solution of this application that do not depart from the scope of the technical solution of this application should be covered within the protection scope of this application.

[0129] Unless otherwise specified, all reagents, materials and instruments used in the following examples and comparative examples are commercially available or synthesized.

[0130] Examples to Comparative Examples

[0131] Example 1-1 Preparation of Lithium-ion Batteries

[0132] Example 1-1

[0133] 1. Preparation of hard carbon materials

[0134] 400 parts by weight of zinc gluconate, 100 parts by weight of glucose, and 10 parts by weight of melamine were thoroughly mixed by mechanical ball milling and then transferred to a box furnace for calcination at 400°C for 2 hours under nitrogen protection. The mixture was then cooled, crushed, and graded to control the Dv99 at 45 μm. The graded powder was then transferred to a nitrogen atmosphere furnace for a second calcination at 1200°C for 2 hours. The furnace temperature was then lowered to 900°C, methane gas was introduced, and CVD deposition was performed for 1 hour. The methane gas was then turned off, and the mixture was cooled to room temperature to obtain the final product, hard carbon.

[0135] 2. Preparation of negative electrode sheet

[0136] The hard carbon prepared above, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 97:2:1 to form a uniform negative electrode slurry with a solid content of 40 wt%. This slurry was coated onto a negative electrode current collector (copper foil), dried at 85°C, and then cold-pressed, cut, and slit before being dried under vacuum at 120°C for 12 hours to obtain the negative electrode sheet.

[0137] 3. Preparation of the positive electrode sheet

[0138] Lithium cobalt oxide (LiCoO2) is used as the positive electrode active material in lithium-ion batteries.

[0139] The positive electrode active material (LiCoO2), conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were thoroughly mixed in an appropriate amount of N-methylpyrrolidone (NMP) solvent at a weight ratio of 97:1.4:1.6 to form a uniform positive electrode slurry with a solid content of 72 wt%. This slurry was coated onto a positive electrode current collector aluminum foil, dried at 85°C, and then cold-pressed, cut, and slit before being dried under vacuum at 85°C for 4 hours to obtain the positive electrode sheet.

[0140] 4. Preparation of electrolyte

[0141] In a dry argon atmosphere glove box, ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a mass ratio of EC:DEC = 50:50. Then, 2% (volume ratio) of vinylene carbonate is added, dissolved, and stirred thoroughly. Lithium salt LiPF6 or sodium salt NaPF6 is then added and mixed evenly to obtain an electrolyte, wherein the concentration of LiPF6 or NaPF6 is 1 mol / L.

[0142] 5. Preparation of the separating membrane

[0143] A 9μm thick porous polyethylene (PE) polymer film coated with Al2O3 was used as the separator.

[0144] 6. Preparation of lithium-ion / sodium-ion full cells

[0145] Full cell preparation: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. Then, the electrodes are wound, the tabs are welded, and the cells are placed in an outer packaging foil-aluminum-plastic film. Electrolyte is injected, and the cells undergo vacuum sealing, settling, formation, shaping, and capacity testing to obtain a soft-pack full cell.

[0146] Examples 1-2

[0147] Examples 1-2 prepared hard carbon using a method similar to that of Example 1-1. The difference from Example 1-1 is that the weight parts of the raw materials were adjusted to: 268 parts by weight of zinc gluconate, 133 parts by weight of glucose, and 10 parts by weight of melamine.

[0148] Examples 1-3

[0149] Examples 1-3 prepared hard carbon using a method similar to that of Example 1-1. The difference from Example 1-1 is that the weight parts of the raw materials in Examples 1-3 were adjusted to: 532 parts by weight of zinc gluconate, 67 parts by weight of glucose, and 10 parts by weight of melamine.

[0150] Examples 1-4

[0151] Examples 1-4 prepared hard carbon using a method similar to that of Example 1-1. The difference from Example 1-1 is that the weight parts of the raw materials in Examples 1-4 were adjusted to: 400 parts by weight of zinc gluconate, 100 parts by weight of glucose, and 5 parts by weight of melamine.

[0152] Examples 1-5

[0153] Examples 1-5 prepared hard carbon using a method similar to that of Example 1-1. The difference from Example 1-1 is that the weight parts of the raw materials in Examples 1-5 were adjusted to: 400 parts by weight of zinc gluconate, 100 parts by weight of glucose, and 15 parts by weight of melamine.

[0154] Examples 1-6

[0155] Examples 1-6 prepared hard carbon using a method similar to that of Example 1-1. The difference from Example 1-1 is that the weight parts of the raw materials in Examples 1-6 were adjusted to: 400 parts by weight of zinc gluconate, 100 parts by weight of glucose, and 20 parts by weight of melamine.

[0156] Examples 1-7

[0157] Examples 1-7 prepared hard carbon using a method similar to that of Examples 1-5. The difference between Examples 1-5 and Examples 1-7 is that the raw material melamine was changed to urea.

[0158] Examples 1-8

[0159] Examples 1-8 prepared hard carbon using a method similar to that of Examples 1-5. The difference between Examples 1-5 and Examples 1-8 is that the raw material glucose was changed to sucrose.

[0160] Comparative Example 1-1 Preparation of Lithium-ion Batteries

[0161] Comparative Example 1-1 prepared hard carbon using a method similar to that of Example 1-1. The difference from Example 1-1 is that the raw material in Comparative Example 1-1 was adjusted to 100 parts by weight of glucose, and zinc gluconate and melamine were not added.

[0162] Comparative Examples 1-2: Preparation of Lithium-ion Batteries

[0163] Comparative Examples 1-2 prepared hard carbon using a method similar to that of Example 1-1. The difference from Example 1-1 was that the raw materials in Comparative Examples 1-2 were adjusted to 400 parts by weight of zinc gluconate and 100 parts by weight of glucose, and melamine was not added.

[0164] Preparation of lithium-ion batteries (Comparative Examples 1-3)

[0165] Comparative Examples 1-3 prepared hard carbon using a method similar to that of Examples 1-1. The difference from Examples 1-1 was that the raw materials in Comparative Examples 1-3 were adjusted to 10 parts by weight of melamine and 100 parts by weight of glucose, and zinc gluconate was not added.

[0166] Example 2: Preparation of Lithium-ion Batteries

[0167] Example 2-1

[0168] Example 2-1 prepared hard carbon using a method similar to that of Examples 1-5. The difference from Examples 1-5 is that the raw material melamine was changed to diphenylselenium in Example 2-1.

[0169] Example 2-2

[0170] Example 2-2 prepared hard carbon using a method similar to that of Examples 1-5. The difference from Examples 1-5 is that the raw material melamine was changed to sulfur powder in Example 2-2.

[0171] Example 2-3

[0172] Examples 2-3 prepared hard carbon using a method similar to that of Examples 1-5. The difference from Examples 1-5 is that the raw material melamine was changed to ammonium dihydrogen phosphate in Examples 2-3.

[0173] Examples 2-4

[0174] Examples 2-4 prepared hard carbon using a method similar to that of Examples 1-5. The difference from Examples 1-5 is that the raw material melamine was replaced with boric acid in Examples 2-4.

[0175] Example 3-1

[0176] Example 3-1 prepared hard carbon using a method similar to that of Examples 1-5. The difference from Examples 1-5 is that in Example 3-1, the particle size Dv99 was controlled at 70 μm during crushing and grading.

[0177] Example 3-2

[0178] Example 3-2 prepared hard carbon using a method similar to that of Examples 1-5. The difference from Examples 1-5 is that in Example 3-2, the particle size Dv99 was controlled at 21 μm during crushing and grading.

[0179] Example 4: Preparation of Sodium-ion Batteries

[0180] 1. Preparation of hard carbon materials

[0181] Example 4-1 prepared hard carbon using a method similar to that of Example 1-1. The difference from Example 1-1 is that the secondary calcination temperature was adjusted to 1400℃ in Example 4-1.

[0182] 2. Preparation of negative electrode sheet

[0183] The hard carbon prepared above, styrene-butadiene rubber (SBR), and sodium carboxymethyl cellulose (CMC) were thoroughly mixed in an appropriate amount of deionized water at a weight ratio of 97:2:1 to form a uniform negative electrode slurry with a solid content of 40 wt%. This slurry was coated onto a negative electrode current collector (aluminum foil), dried at 85°C, and then cold-pressed, cut, and slit before being dried under vacuum at 120°C for 12 hours to obtain the negative electrode sheet.

[0184] 3. Preparation of the positive electrode sheet

[0185] Using copper-nickel-iron-manganese oxide (NaCu) 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 O2 is used as the positive electrode active material in sodium-ion batteries.

[0186] The positive electrode active material (NaCu) 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 O2), conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were mixed thoroughly in an appropriate amount of N-methylpyrrolidone (NMP) solvent at a weight ratio of 97:1.4:1.6 to form a uniform positive electrode slurry with a solid content of 72wt%. This slurry was coated onto a positive electrode current collector aluminum foil, dried at 85°C, and then cold-pressed, cut, and slit before being dried under vacuum at 85°C for 4 hours to obtain the positive electrode sheet.

[0187] 4. Preparation of electrolyte

[0188] In a dry argon atmosphere glove box, ethylene carbonate (EC) and diethyl carbonate (DEC) are mixed at a mass ratio of EC:DEC = 50:50. Then, 2% (volume ratio) of fluoroethylene carbonate is added, dissolved, and stirred thoroughly. Sodium salt NaPF6 is then added and mixed evenly to obtain an electrolyte with a NaPF6 concentration of 1 mol / L.

[0189] 5. Preparation of the separating membrane

[0190] A 9μm thick porous polyethylene (PE) polymer film coated with Al2O3 was used as the separator, with a porosity of 35%.

[0191] 6. Preparation of sodium-ion full cells

[0192] Full cell preparation: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. Then, the electrodes are wound, the tabs are welded, and the cells are placed in an outer packaging foil-aluminum-plastic film. Electrolyte is injected, and the cells undergo vacuum sealing, settling, formation, shaping, and capacity testing to obtain a soft-pack full cell.

[0193] Example 4-2

[0194] Example 4-2 prepared sodium-ion full cells using a method similar to that of Example 4-1. The difference between Example 4-2 and Example 4-1 is that Example 4-2 prepared hard carbon using a method similar to that of Examples 1-5, and the secondary calcination temperature was adjusted to 1400°C.

[0195] Example 4-3

[0196] Example 4-3 prepared sodium-ion full cells using a method similar to that of Example 4-1. The difference between Example 4-3 and Example 4-1 is that Example 4-3 prepared hard carbon using a method similar to that of Examples 1-6, and the secondary calcination temperature was adjusted to 1400°C.

[0197] Example 4-4

[0198] Example 4-4 prepared sodium-ion full cells using a method similar to that of Example 4-1. The difference between Example 4-4 and Example 4-5 is that hard carbon was prepared using a method similar to that of Examples 1-7, and the secondary calcination temperature was adjusted to 1400°C in Example 4-4.

[0199] Comparative Example 4-1

[0200] Comparative Example 4-1 prepared a sodium-ion full cell using a method similar to that of Example 4-1. The difference between Comparative Example 4-1 and Example 4-1 is that Comparative Example 4-1 prepared hard carbon using a method similar to that of Comparative Example 1-1, and the secondary calcination temperature of Comparative Example 4-1 was adjusted to 1400°C.

[0201] Test section:

[0202] 1. Test method for charge / discharge curves of button cells:

[0203] Coin cell manufacturing: Coin cells use metallic lithium or metallic sodium as the counter electrode. A lithium / sodium sheet with a diameter of 18 mm and a thickness of 0.6 mm is assembled and stacked with a separator and a hard carbon electrode in sequence. Electrolyte is added, and the cells are packaged in a coin cell stainless steel shell for positive and negative electrodes to obtain a coin cell.

[0204] In an environment of 25℃, the assembled button cells were left to stand for 5 hours before being subjected to charge and discharge tests. The test procedure was as follows: constant current discharge at a current density of 0.1mA / cm2 to 0V, and then constant voltage discharge at 0V until the current dropped to 12uA / cm2; the discharge (lithium insertion / sodium) process ended; after resting for 5 minutes, the charging (lithium removal / sodium) test was started. The test procedure was as follows: constant current charging at a current density of 0.1mA / cm2 to 2V.

[0205] Record the specific capacity for the first discharge and the first charge respectively. The initial coulombic efficiency = initial charge capacity / initial discharge capacity * 100%;

[0206] Record the specific capacity and voltage during the charge and discharge processes, and statistically analyze the specific capacity distribution within each voltage range of the lithium / sodium removal process. For example, in the first lithium removal curve, record the capacities from 0 to 0.15V and from 0.15V to 0.8V; in the first sodium removal curve, record the capacities from 0 to 0.15V and from 0.15V to 1V.

[0207] 2. Test method for energy density (ED)

[0208] In an environment of 25℃, lithium-ion or sodium-ion batteries are charged at a constant current of 0.2C to a voltage of 4.48V or 3.95V, and then charged at a constant voltage; they are then discharged at a constant current of 0.2C to a voltage of 2V. This is recorded as one cycle, and the discharge capacity and discharge energy of the first cycle are recorded. The average discharge voltage is obtained by dividing the discharge energy by the discharge capacity. The length, width, and height of the battery are measured at 50% SOC to obtain the battery volume. Therefore:

[0209] Energy density ED = Discharge capacity × Average discharge voltage / Cell volume.

[0210] 3. Raman test

[0211] An electrode containing hard carbon material was cut into a cross-section using ion polishing. This cross-section was then placed on a Raman spectroscopy stage and focused for measurement. A 200µm x 500µm area was selected for testing, with over 200 points evenly spaced within this range. Each point was measured over a 1000cm² area. -1 Up to 2000cm-1 Between; recorded at 1320cm -1 Up to 1370cm -1 The peak that appears between these two points is the D peak, located at 1570 cm⁻¹. -1 Up to 1620cm -1 The peaks that appear between them are called G peaks, and the I values ​​at each point are statistically analyzed. D / I G The intensity ratio is then calculated, and the average value of multiple points is taken as the final I. D / I G The strength ratio.

[0212] 4. XRD Testing

[0213] Hard carbon materials were subjected to powder XRD testing, with the test scanning range from 10 degrees to 60 degrees, which is twice the scattering angle. The obtained scanning curves were processed, and the peak (with a half-width of the peak greater than 3 degrees) appearing in the range of 15° to 30° at twice the scattering angle was recorded as peak A. The scattering angle twice the peak value of peak A was then obtained.

[0214] 5. Elemental Analysis

[0215] Zn was digested and tested using inductively coupled plasma atomic emission spectrometry; N, S, H, C and other elements were tested using an elemental analyzer, and the atmospheric content was tested after the hard carbon material was fully burned in oxygen to obtain the elemental ratio and content; P, B, Se and other elements were quantitatively obtained using XPS.

[0216] 6. Dv50 and Dv99 tests

[0217] This application uses a Malvern particle size analyzer to measure the particle size of hard carbon particles: the hard carbon particle material is dispersed in a dispersant (ethanol), sonicated for 30 minutes, and then the sample is added to the Malvern particle size analyzer to begin testing. The particle size that reaches 50% of the volumetric particle size distribution from the smallest particle size side is defined as the Dv50 of the hard carbon particle, i.e., the average particle size; simultaneously, the particle size that reaches 99% of the volumetric particle size distribution from the smallest particle size side is defined as the Dv99 of the hard carbon particle.

[0218] Test Results

[0219] The test results are shown in Tables 1 to 4:

[0220] Table 1

[0221]

[0222]

[0223] As can be seen from Table 1, compared with Comparative Example 1-1, the reversible capacity of Comparative Example 1-2 increased rapidly after the addition of zinc salt. The capacity increase was mainly in the 0V to 0.15V range, indicating that the addition of zinc salt is beneficial to the capacity improvement in the low voltage plateau range. This is attributed to the increase in pore volume, which improves the capacity in the low voltage plateau range.

[0224] Compared to Comparative Example 1-1, Comparative Example 1-3 added heteroatom N element. N element can increase the defect concentration of the sample, thus improving the capacity of the sloping segment from 0.15V to 0.8V. At the same time, N element can also increase the lithium-loving wettability of the sample, thereby improving the capacity of the low voltage plateau segment.

[0225] Compared to the comparative examples, Examples 1-1 to Examples 1-8 (e.g.) Figure 1 As shown, Figure 1 (The diagram shows the charge-discharge curves of the lithium-ion batteries in Examples 1-5.) The addition of zinc and nitrogen (N) elements significantly improves the capacity in the low-voltage plateau segment, while nitrogen enhances the capacity in the 0.15V to 0.8V range. Simultaneously, nitrogen increases the sample's lithiophilic wettability, further enhancing the capacity in the low-voltage plateau segment. Hard carbon exhibits a higher capacity in the low-voltage plateau stage, with increased total capacity and first-cycle coulombic efficiency, resulting in a substantial increase in its energy density (ED) compared to Comparative Examples 1 and 2. However, for coin cells, the high voltage plateau leads to a low voltage output in the overall cell, lowering their energy density. Therefore, improving the specific capacity in the low-voltage plateau segment (0V to 0.15V) of coin cells is crucial for improving the energy density (ED).

[0226] Table 2

[0227]

[0228] As can be seen from Table 2, replacing the N element with other inorganic heteroatoms in Examples 2-1 to 2-4 still increases the lithium-friendly wettability of the samples, resulting in a significant further improvement in the capacity of the low plateau segment.

[0229] Table 3

[0230]

[0231] As can be seen from Table 3, in the XRD diffraction patterns of the hard carbon materials prepared in Examples 1-5, 3-1 and 3-2, the 2x diffraction peak of the 002 peak is around 21°, indicating that the interfacial spacing of the hard carbon materials is relatively large, which is conducive to the transport of lithium ions between layers.

[0232] Examples 1-5, 3-1, and 3-2 also illustrate that particle size has a slight impact on the sample. Larger particles result in a longer diffusion distance, which is not conducive to the full utilization of the specific capacity. Smaller particles result in a larger specific surface area (BET) and a lower initial coulombic efficiency. Therefore, the particle size should be controlled within an appropriate range.

[0233] Table 4

[0234]

[0235] As shown in Table 4, in sodium-ion batteries, compared to Comparative Example 4-1, the addition of zinc salt and heteroatom N effectively improves the capacity in the low plateau region (0-0.15V), increasing the ratio of 0-0.15V capacity to 0.15V capacity to 1V capacity. This helps to reduce the average potential of the negative electrode, increase the average output potential of the entire cell, and thus improve the energy density. Furthermore, the significant increase in 0-0.15V capacity leads to a significant increase in the total reversible capacity, which will also improve the energy density.

[0236] Although illustrative embodiments have been demonstrated and described, those skilled in the art should understand that the above embodiments should not be construed as limiting the present application, and that changes, substitutions and modifications can be made to the embodiments without departing from the spirit, principles and scope of the present application.

Claims

1. A hard carbon material, characterized in that, The hard carbon material comprises a porous framework and a first element and a zinc element located at least within the porous framework, and the hard carbon material further satisfies at least one of the following conditions: (1) The hard carbon material uses lithium metal as the counter electrode, and is applied at 0 to 2.5V vs Li + The charge-discharge curves obtained from the test within the / Li range 0 (vs Li) + / Li) to 0.15V (vs Li) + The specific capacity of / Li) is denoted as C. 11 mAh / g; 0.15V (vs Li) + / Li) to 0.8V (vs Li) + The specific capacity of / Li) is denoted as C. 12 mAh / g, The hard carbon material satisfies: 1.6 ≤ C 11 / C 12 ≤2.1; (2) The hard carbon material uses sodium metal as the counter electrode, and is subjected to a voltage of 0 to 2.5V vs Na. + The charge-discharge curves obtained from tests within the / Na range 0(vs Na + / Na) to 0.15V (vs Na) + The specific volume of (Na) is denoted as C. 21 mAh / g; 0.15V (vs Na) + / Na) to 1.00V (vs Na) + The specific volume of (Na) is denoted as C. 22 mAh / g, The hard carbon material satisfies: 3.55 ≤ C 21 / C 22 ≤3.95, The first element includes nitrogen, and the nitrogen content based on the total mass of the hard carbon material is denoted as W1wt%, 2≤W1≤5.

2. The hard carbon material according to claim 1, characterized in that, The content of the first element relative to the total mass of the hard carbon material is denoted as A1wt%; The zinc content relative to the total mass of the hard carbon material is denoted as A2wt%. The hard carbon material satisfies the following condition: 1.5≤A1 / A2≤5.

3. The hard carbon material according to claim 1, characterized in that, The content of the first element relative to the total mass of the hard carbon material is denoted as A1 wt%; the content of zinc relative to the total mass of the hard carbon material is denoted as A2 wt%, and the first element includes nitrogen, 2≤A1 / A2≤4.

5.

4. The hard carbon material according to claim 1, characterized in that, The first element also includes one or more of sulfur, boron, phosphorus and selenium.

5. The hard carbon material according to claim 4, characterized in that, The content of zinc relative to the total mass of the hard carbon material is denoted as A2 wt%, and the ratio of the content of the first element relative to the total mass of the hard carbon material to A2 wt% is 2 to 4; and / or The content of the first element based on the total mass of the hard carbon material is denoted as W2wt%, where 2.5≤W2≤9.

6. The hard carbon material according to claim 1, characterized in that, The zinc content relative to the total mass of the hard carbon material is denoted as A2wt%, where 0.6≤A2≤1.

2.

7. The hard carbon material according to claim 1, characterized in that, The hard carbon material satisfies: 250 ≤ C 11 ≤350.

8. The hard carbon material according to claim 1, characterized in that, In the X-ray diffraction pattern of the hard carbon material, diffraction peaks exist in the range of 15° to 30° at twice the scattering angle, and the twice-scattering angle of the diffraction peaks is <24°; and / or In the Raman spectrum of the hard carbon material within a 200µm x 500µm scanning area, at 1320 cm⁻¹... -1 Up to 1370cm -1 A characteristic peak D exists within the range, at 1570 cm⁻¹. -1 Up to 1620cm -1 A characteristic peak G exists within the range, and the peak intensity of the characteristic peak D is I. D The peak intensity of the characteristic peak G is I. G 0.5 < I D / I G ≤1.

5.

9. The hard carbon material according to claim 1, characterized in that, The hard carbon material also satisfies the following conditions (1) and / or condition (2): (1) The volume distribution particle size Dv50 μm of the hard carbon material satisfies: 3≤Dv50≤15; (2) The volume distribution particle size Dv99 μm of the hard carbon material satisfies: 10≤Dv99≤45.

10. The hard carbon material according to claim 1, characterized in that, The hard carbon material also includes a carbon layer covering the porous framework.

11. An electrochemical device comprising a negative electrode, said negative electrode comprising a hard carbon material as claimed in any one of claims 1 to 10.

12. An electronic device comprising the electrochemical device as claimed in claim 11.

Images