Carbon material, preparation method and application thereof, negative plate, secondary battery and electric device

Abstract

The invention provides a carbon material, a preparation method and application thereof, a negative plate, a secondary battery and an electric device. The carbon material comprises a porous carbon base material and an amorphous carbon layer arranged on at least part of the surface of the porous carbon base material. When the carbon material is used as a negative electrode active material, abundant porous structures in the porous carbon base material can be fully utilized to separate out lithium / sodium or intercalate lithium / sodium, and abundant active sites on the surface of the porous carbon base material are prevented from being in contact with electrolyte to generate side reaction, so that the first coulombic efficiency and the actual capacity of a secondary battery can be improved.

Description

[0001] Related applications

[0002] This application is a divisional application of the Chinese patent application filed by the applicant on August 25, 2022, with application number 202280087936.5, entitled "Carbon materials and their preparation methods and applications, negative electrode sheets, secondary batteries and electrical devices". Technical Field

[0003] This application relates to the field of batteries, specifically to carbon materials and their preparation methods and applications, negative electrode sheets, secondary batteries and electrical devices. Background Technology

[0004] Secondary batteries are increasingly widely used due to their clean and renewable characteristics, and have advantages such as high energy density, low self-discharge, and excellent cycle performance.

[0005] Secondary batteries primarily generate electrical energy by the movement of active ions between the positive and negative electrodes. During charging, active ions are deintercalated from the positive electrode and intercalated into the negative electrode via the electrolyte; the reverse occurs during discharging. However, during the first charge and discharge cycle, some of the active ions deintercalated from the positive electrode material are consumed, forming an SEI film on the negative electrode surface. These active ions cannot return to the positive electrode material during subsequent discharges, thus reducing the initial charge and discharge efficiency of the secondary battery and consequently decreasing its actual capacity.

[0006] As demand increases, the charge / discharge efficiency of traditional secondary batteries is increasingly unable to meet people's needs and needs further improvement. Summary of the Invention

[0007] In view of the above problems, this application provides a carbon material, its preparation method and application, a negative electrode, a secondary battery and an electrical device, aiming to improve the first coulombic efficiency of the secondary battery.

[0008] To achieve the above objectives, a first aspect of this application provides a carbon material comprising a porous carbon substrate and an amorphous carbon layer disposed on at least a portion of the surface of the porous carbon substrate.

[0009] In the aforementioned carbon materials, at least a portion of the surface of the porous carbon substrate is provided with an amorphous carbon layer. When used as a negative electrode active material in the preparation of a secondary battery, during the charge and discharge process of the secondary battery, on the one hand, the amorphous carbon layer can prevent the electrolyte from penetrating into the interior of the porous carbon substrate, avoiding a large number of SEI side reactions between the abundant active sites on the surface of the porous carbon substrate and the electrolyte; on the other hand, it can prevent alkali metals such as lithium or sodium adsorbed in the porous structure of the porous carbon substrate from directly contacting the electrolyte, thereby preventing the consumption of active ions in the electrolyte. Thus, it is possible to fully utilize the abundant porous structure in the porous carbon substrate for lithium / sodium plating or lithium / sodium intercalation while avoiding side reactions caused by contact between the abundant active sites on the surface of the porous carbon substrate and the electrolyte, thereby improving the reversible capacity of the secondary battery and its initial coulombic efficiency.

[0010] In any embodiment of this application, the thickness of the amorphous carbon layer is 15 nm to 250 nm;

[0011] Optionally, the thickness of the amorphous carbon layer is 20 nm to 220 nm;

[0012] Optionally, the thickness of the amorphous carbon layer is 20 nm to 200 nm;

[0013] Optionally, the thickness of the amorphous carbon layer is 50 nm to 130 nm.

[0014] By adjusting the thickness of the amorphous carbon layer, while ensuring that the excellent lithium / sodium or lithium / sodium intercalation capabilities of the porous carbon substrate are maximized, the coating effect of the amorphous carbon layer is further improved, thereby further improving the first coulombic efficiency of the secondary battery.

[0015] In any embodiment of this application, the amorphous carbon layer is formed by vapor deposition of an aryl compound having 6 to 40 carbon atoms.

[0016] Using aryl compounds with 6 to 40 carbon atoms as a carbon source, a dense amorphous carbon layer can be formed by vapor deposition.

[0017] In any embodiment of this application, the porous structure of the porous carbon substrate includes microporous structure, mesoporous structure and macroporous structure.

[0018] The porous carbon substrate has a hierarchical porous structure, in which mesopores / macropores are used for lithium / sodium plating, and micropores are used for lithium / sodium intercalation, which is beneficial to fully releasing the capacity of the secondary battery.

[0019] In any embodiment of this application, the specific surface area of ​​the porous carbon substrate is ≥500 m². 2 / g.

[0020] In any embodiment of this application, the porous carbon substrate is activated carbon.

[0021] A second aspect of this application provides a method for preparing the carbon material of the first aspect, comprising the following steps:

[0022] The carbon material is obtained by performing vapor phase deposition on the surface of the porous carbon substrate using carbon source to form an amorphous carbon layer.

[0023] In a third aspect of this application, the application of the carbon material of the first aspect as a negative electrode active material is provided.

[0024] A fourth aspect of this application provides a negative electrode sheet, the negative electrode sheet comprising a current collector and a negative electrode active layer disposed on the surface of the current collector, the composition of the negative electrode active layer comprising the carbon material of the first aspect.

[0025] In any embodiment of this application, the carbon material accounts for 90% to 95% of the mass of the negative electrode active layer.

[0026] A fifth aspect of this application provides a secondary battery comprising the negative electrode sheet of the fourth aspect of this application.

[0027] A sixth aspect of this application provides an electrical device comprising a secondary battery as described in the fifth aspect of this application.

[0028] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0029] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0030] Figure 1 This is a schematic diagram of one embodiment of a secondary battery.

[0031] Figure 2 yes Figure 1 The exploded diagram.

[0032] Figure 3 This is a schematic diagram of one embodiment of the battery pack.

[0033] Figure 4 yes Figure 3 The exploded diagram.

[0034] Figure 5This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source;

[0035] Figure 6 These are electron microscope comparison images of uncoated activated carbon and the carbon material prepared in Example 1;

[0036] Figure 7 This is an electron microscope image of the carbon material prepared in Example 1.

[0037] Explanation of reference numerals in the attached figures:

[0038] 1. Battery pack; 2. Upper casing; 3. Lower casing; 4. Secondary battery; 41. Housing; 42. Electrode assembly; 43. Cover plate; 5. Electrical device. Detailed Implementation

[0039] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0041] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0042] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0043] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0044] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0045] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0046] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0047] In summary, as described in the background section, during the charging and discharging process of traditional secondary batteries, some active ions that have been extracted from the positive electrode material are inevitably consumed, thereby reducing the initial charge and discharge efficiency of the secondary battery and consequently reducing its actual capacity.

[0048] Through long-term production and research, the technicians of this application discovered that the direct factor affecting the initial charge-discharge efficiency of a secondary battery is the specific surface area of ​​the graphite anode. The larger the specific surface area of ​​the graphitized anode, the larger the area for forming the SEI film, which consumes more active ions and thus reduces the initial efficiency of the secondary battery. Therefore, graphite with a layered structure is commonly used as the anode active material, as its small specific surface area results in a smaller area for forming the SEI film, thus avoiding excessive consumption of active ions.

[0049] However, while using graphite as the negative electrode active material can avoid the consumption of active ions to some extent, the small specific surface area and layered structure of graphite result in insufficient active sites, limiting the intercalation and deintercalation of active ions and thus restricting the capacity release of the secondary battery. Therefore, traditional technologies focus on modifying graphite. For example, one approach involves sintering graphite with amorphous carbon to form composite carbon particles with specific interface peaks, thereby improving the ease of intercalation and deintercalation of active ions.

[0050] The inventors of this application have broken through the constraints of traditional technology and taken a different approach, creatively proposing to directly use a porous carbon substrate with a porous structure and a large specific surface area to form a "barrier layer" on its surface. This avoids the abundant active sites on the surface of the porous carbon substrate from coming into contact with the electrolyte and causing side reactions. At the same time, it ensures that the abundant porous structure in the porous carbon substrate is fully utilized for lithium / sodium plating or lithium / sodium intercalation, thereby improving the reversible capacity of the secondary battery and its first coulombic efficiency.

[0051] One embodiment of this application provides a carbon material comprising a porous carbon substrate and an amorphous carbon layer disposed on at least a portion of the surface of the porous carbon substrate.

[0052] In the aforementioned carbon materials, at least a portion of the surface of the porous carbon substrate is coated with an amorphous carbon layer. When used as a negative electrode active material in the preparation of secondary batteries, during the charging and discharging process, the amorphous carbon layer can, on the one hand, prevent the electrolyte from penetrating into the interior of the porous carbon substrate, avoiding a large number of SEI side reactions between the abundant active sites on the surface of the porous carbon substrate and the electrolyte. Simultaneously, it prevents alkali metals such as lithium or sodium adsorbed in the porous structure of the porous carbon substrate from directly contacting the electrolyte, thereby avoiding the consumption of active ions in the electrolyte. Thus, it is possible to fully utilize the abundant porous structure in the porous carbon substrate for lithium / sodium plating or lithium / sodium intercalation while preventing the abundant active sites on the surface of the porous carbon substrate from contacting the electrolyte and generating side reactions, thereby improving the reversible capacity of the secondary battery and its initial coulombic efficiency.

[0053] In any embodiment of this application, based on the total surface area of ​​the porous carbon substrate, the area ratio of the surface with the amorphous carbon layer is ≥50%; further, the area ratio of the surface with the amorphous carbon layer is ≥60%; further, the area ratio of the surface with the amorphous carbon layer is ≥70%; further, the area ratio of the surface with the amorphous carbon layer is ≥80%; further, the area ratio of the surface with the amorphous carbon layer is ≥90%; further, the area ratio of the surface with the amorphous carbon layer is 90%~100%.

[0054] In any embodiment of this application, an amorphous carbon layer coats a porous carbon substrate.

[0055] In any embodiment of this application, the thickness of the amorphous carbon layer is 15 nm to 250 nm.

[0056] In any embodiment of this application, the thickness of the amorphous carbon layer is 20 nm to 220 nm.

[0057] In any embodiment of this application, the thickness of the amorphous carbon layer is 20 nm to 200 nm.

[0058] In any embodiment of this application, the thickness of the amorphous carbon layer is 50 nm to 130 nm.

[0059] By adjusting the thickness of the amorphous carbon layer, while ensuring that the excellent lithium / sodium or lithium / sodium intercalation capabilities of the porous carbon substrate are maximized, the coating effect of the amorphous carbon layer is further improved, thereby further improving the first coulombic efficiency of the secondary battery.

[0060] The values ​​in the above "15nm~250nm" range include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and: 15nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, 110nm, 120nm, 130nm, 140nm, 150nm, 160nm, 170nm, 180nm, 190nm, 200nm, 210nm, 220nm, 230nm, 240nm, 250nm.

[0061] It should be noted that the thickness of the amorphous carbon layer mentioned above is measured with the contact interface between the amorphous carbon layer and the outer surface of the porous carbon substrate as the measurement baseline; furthermore, it can be measured by electron microscopy analysis.

[0062] In any embodiment of this application, the amorphous carbon layer is formed by deposition of an aryl compound having 6 to 40 carbon atoms.

[0063] Using aryl compounds with 6 to 40 carbon atoms as a carbon source can form a dense amorphous carbon layer.

[0064] Examples of aryl compounds with 6 to 40 carbon atoms include, but are not limited to: benzene, toluene, and xylene.

[0065] In any embodiment of this application, the porous structure of the porous carbon substrate includes microporous structure, mesoporous structure and macroporous structure.

[0066] The porous carbon substrate has a hierarchical porous structure, in which mesopores / macropores are used for lithium / sodium plating, and micropores are used for lithium / sodium intercalation, which is beneficial to fully releasing the capacity of the secondary battery.

[0067] Pore ​​sizes < 2 nm are called microporous structures, pore sizes between 2 nm and 50 nm are called mesoporous structures, and pore sizes > 50 nm are called macroporous structures.

[0068] It should be noted that, during the preparation process, because the porous carbon substrate has a porous structure, an amorphous carbon layer may also be formed on the surface of the internal pores of the porous structure. It may or may not exist. When it does exist, this application does not have any special requirements on the thickness of the amorphous carbon layer on the surface of the internal pores of the porous structure.

[0069] In any embodiment of this application, the specific surface area of ​​the porous carbon substrate is ≥500 m². 2 / g.

[0070] In any embodiment of this application, the porous carbon substrate is activated carbon.

[0071] In any embodiment of this application, the volumetric particle size D(v)50 of the porous carbon substrate is ≤5μm; further, 0.1μm≤D(v)50≤5μm.

[0072] In any embodiment of this application, the volumetric particle size D(v)90 of the porous carbon substrate is ≤20μm; further, 7μm≤D(v)90≤20μm.

[0073] In any embodiment of this application, the volumetric particle size D(v)50 of the porous carbon substrate is μm and D(v)90 is 10 μm.

[0074] D(v)50 or D(v)90 refers to the particle size corresponding to 50% of the volume distribution in the particle size cumulative distribution curve. It can be obtained based on the volume cumulative distribution curve and can be measured using a Malvern laser particle size analyzer.

[0075] One embodiment of this application provides a method for preparing the above-mentioned carbon material, including the following step S10.

[0076] Step S10: Use carbon source to perform vapor phase deposition on the surface of porous carbon substrate to form an amorphous carbon layer, thereby obtaining the carbon material.

[0077] In any embodiment of this application, the carbon source is an aryl compound having 6 to 40 carbon atoms.

[0078] Using aryl compounds with 6 to 40 carbon atoms as a carbon source can form a dense amorphous carbon layer.

[0079] In any embodiment of this application, the carbon source includes at least one of benzene, toluene, and xylene.

[0080] In any embodiment of this application, the temperature of the above-mentioned vapor deposition process is controlled at 750°C to 1000°C.

[0081] The values ​​in the above "750℃~1000℃" include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and: 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃.

[0082] By controlling the temperature, a dense amorphous carbon layer can be formed without damaging the structure and properties of the activated carbon itself.

[0083] In any embodiment of this application, the above-described vapor deposition process employs chemical vapor deposition.

[0084] In any embodiment of this application, the flow rate of the carbon source is 0.9 mL / h to 4 mL / h.

[0085] In any embodiment of this application, the flow rate of the carbon source is 0.95 mL / h to 3.8 mL / h.

[0086] The values ​​in the range “0.9 mL / h ~ 4 mL / h” include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and: 0.9 mL / h, 0.95 mL / h, 1 mL / h, 1.5 mL / h, 1.9 mL / h, 2 mL / h, 2.5 mL / h, 3 mL / h, 3.5 mL / h, 3.8 mL / h, 4 mL / h.

[0087] In any embodiment of this application, the deposition time is 0.3h to 4h.

[0088] The values ​​in "0.3h~8h" above include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and: 0.3h, 0.5h, 1h, 1.5h, 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h.

[0089] The thickness of the amorphous carbon layer formed can be controlled by adjusting the temperature and time of vapor deposition.

[0090] In any embodiment of this application, the above-described vapor deposition is performed in a protective gas atmosphere.

[0091] Protective gases include at least one of nitrogen and inert gases.

[0092] The inert gas can be selected from at least one of helium (He), neon (Ne), argon (Ar), and krypton (Kr).

[0093] One embodiment of this application provides the application of the above-described carbon material as a negative electrode active material.

[0094] When the aforementioned carbon materials are used as negative electrode active materials, they can improve the reversible capacity of secondary batteries and increase their initial coulombic efficiency.

[0095] One embodiment of this application also provides a negative electrode sheet, which includes a current collector and a negative electrode active layer disposed on the surface of the current collector, wherein the composition of the negative electrode active layer includes the aforementioned carbon material.

[0096] In any embodiment of this application, the mass percentage of carbon material in the negative electrode active layer is 90% to 95%.

[0097] In any embodiment of this application, the components of the above-mentioned negative electrode active layer further include a negative electrode conductive agent and a negative electrode binder.

[0098] In any embodiment of this application, the aforementioned negative electrode conductive agent can be a commonly used conductive material in the art, including but not limited to at least one of graphite, carbon nanotubes, nanofibers, carbon black, and graphene. Specifically, it can be selected from at least one of SP, KS-6, acetylene black, branched Ketjen black ECP, SFG-6, vapor-grown carbon fiber VGCF, carbon nanotubes CNTs, and graphene and their composite conductive agents.

[0099] Based on the total weight of the negative electrode active layer, the weight ratio of the negative electrode conductive agent in the negative electrode active layer is 0~20wt%.

[0100] The aforementioned negative electrode binder can be a commonly used binder in the art, and can be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA) and carboxymethyl chitosan (CMCS).

[0101] Based on the total weight of the negative electrode active layer, the weight ratio of the negative electrode binder in the negative electrode active layer is 0~30wt%.

[0102] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners, like sodium carboxymethyl cellulose (CMC-Na). The weight percentage of these other additives in the negative electrode active layer is 0–15 wt%, based on the total weight of the negative electrode active layer.

[0103] In some embodiments, the current collector in the negative electrode may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0104] The aforementioned negative electrode sheet can be used as the negative electrode sheet for various types of secondary batteries, including but not limited to: sodium-ion batteries and lithium-ion batteries.

[0105] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as carbon materials, conductive agents, binders, and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then subjecting it to drying, cold pressing, and other processes to obtain the negative electrode sheet. The negative electrode slurry has a solid content of 30 wt% to 70 wt% and a viscosity at room temperature adjusted to 2000 mPa·s to 10000 mPa·s; the obtained negative electrode slurry is coated onto a negative electrode current collector, and after drying and cold pressing (e.g., with rollers), the negative electrode sheet is obtained. The compacted density of the negative electrode sheet is 0.8 g / cm³. 3 ~1.5 g / cm 3 .

[0106] One embodiment of this application provides a secondary battery comprising the aforementioned negative electrode sheet.

[0107] This secondary battery has a high initial coulombic efficiency and releases a higher actual capacity.

[0108] In any embodiment of this application, the secondary battery further includes a positive electrode, an electrolyte, and a separator.

[0109] The following examples illustrate positive electrode plates and electrolyte separators, but are not limited to the following scope.

[0110] [Positive electrode tablets]

[0111] The positive electrode includes a current collector and a positive electrode active layer disposed on the surface of the current collector. The components of the positive electrode active layer include positive electrode active materials.

[0112] As an example, the current collector in the positive electrode has two surfaces opposite each other in its own thickness direction, and the positive electrode active material layer is disposed on either or both of the two opposite surfaces of the positive electrode current collector.

[0113] In some embodiments, the current collector in the positive electrode may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0114] The aforementioned positive electrode active material can be a commonly used positive electrode active material in this application, such as lithium-ion positive electrode active material or sodium-ion positive electrode active material.

[0115] Further, as an example, lithium-ion active materials may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, at least one of lithium iron phosphate (such as LiFePO4 (also known as LFP)), lithium manganese phosphate (such as LiMnPO4), and lithium manganese iron phosphate.

[0116] In any embodiment of this application, the molecular formula of the lithium-ion active material is: LiFe x Mn (1-x) PO4, where x takes any number from 0 to 1.

[0117] It is understandable that when x is 0, LiFe x Mn (1-x) PO4 is LiMnPO4, which is lithium manganese phosphate. When x is 1, LiFePO4 is LiFePO4, which is lithium iron phosphate.

[0118] As an example, sodium ion-active materials may include at least one of the following materials: sodium transition metal oxides, polyanionic compounds, and Prussian blue compounds.

[0119] As an optional technical solution in this application, the transition metal in the sodium transition metal oxide includes at least one selected from Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. For example, the sodium transition metal oxide is Na. x MO2, wherein M includes at least one or more of Ti, V, Mn, Co, Ni, Fe, Cr and Cu, and 0 < x ≤ 1.

[0120] As an optional technical solution in this application, the polyanionic compound can be a compound containing sodium ions, transition metal ions, or a tetrahedral (YO4) structure. n- A class of compounds with anionic units. Transition metals include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y includes at least one of P, S, and Si; n represents (YO4). n- The price state.

[0121] Polyanionic compounds can also contain sodium ions, transition metal ions, or tetrahedral (YO4) ions. n- A class of compounds comprising anionic units and halide anions. Transition metals include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y includes at least one of P, S, and Si, where n represents (YO4). n- The valence state; the halogen can be at least one of F, Cl and Br.

[0122] Polyanionic compounds can also be sodium-containing tetrahedral (YO4) compounds. n-Anionic unit, polyhedral unit (ZO) y ) m+ And a class of compounds with optional halide anions. Y includes at least one of P, S, and Si, and n represents (YO4). n- The valence state; Z represents a transition metal, including at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce, and m represents (ZO). y ) m+ The valence state; the halogen can be at least one of F, Cl and Br.

[0123] Polyanionic compounds include, for example, NaFePO4, Na3V2(PO4)3 (sodium vanadium phosphate, abbreviated as NVP), Na4Fe3(PO4)2(P2O7), NaM'PO4F (M' is one or more of V, Fe, Mn and Ni), and Na3(VO y )2(PO4)2F 3-2y At least one of (0≤y≤1).

[0124] Prussian blue compounds can be compounds containing sodium ions, transition metal ions, and cyanide ions (CN). - A class of compounds. Transition metals include at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. Prussian blue compounds are, for example, Na. a Me b Me' c (CN)6, wherein Me and Me' each independently include at least one of Ni, Cu, Fe, Mn, Co and Zn, 0 < a ≤ 2, 0 < b < 1, 0 < c < 1.

[0125] Based on the total weight of the positive electrode active layer, the weight ratio of the positive electrode active material in the positive electrode active layer is 80wt%~100wt%.

[0126] In any embodiment of this application, the positive electrode active layer further comprises a positive electrode conductive agent and a positive electrode binder.

[0127] The aforementioned positive electrode conductive agent can be a commonly used conductive agent in the art, including but not limited to at least one of graphite, carbon nanotubes, nanofibers, carbon black, and graphene. Specifically, it can be selected from at least one of SP, KS-6, acetylene black, branched Ketjen black ECP, SFG-6, vapor-grown carbon fiber VGCF, carbon nanotubes CNTs, and graphene and their composite conductive agents.

[0128] Based on the total weight of the positive electrode active layer, the weight ratio of the positive electrode conductive agent in the positive electrode active layer is 0~20wt%.

[0129] In any embodiment of this application, the binder of the above-mentioned positive electrode binder may be at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-tetrafluoroethylene-propylene terpolymer, ethylene-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, hydrogenated nitrile rubber, styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), carboxymethyl chitosan (CMCS), and fluorinated acrylate resin.

[0130] Based on the total weight of the positive electrode active layer, the weight ratio of the positive electrode binder in the positive electrode active layer is 0~30wt%.

[0131] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto a current collector, and then drying and cold pressing to obtain the positive electrode sheet. The solid content of the positive electrode slurry is 40 wt%~80 wt%, and the viscosity at room temperature is adjusted to 5000 mPa·s~25000 mPa·s. The positive electrode slurry is coated on the surface of the positive electrode current collector, dried, and then cold-pressed using a cold rolling mill to form the positive electrode sheet; the areal density of the positive electrode powder coating is 150~350 mg / m³. 2 The compaction density of the positive electrode sheet is 3.0~3.6 g / cm³. 3 The concentration can be selected as 3.3~3.5 g / cm³. 3 The formula for calculating compacted density is:

[0132] Compacted density = Coated surface density / (Extreme electrode thickness after extrusion - Current collector thickness).

[0133] Electrolyte

[0134] Electrolytes include electrolyte salts and solvents.

[0135] In some embodiments, the electrolyte salt may be selected from electrolyte salts commonly used in the art, including lithium-ion electrolyte salts and sodium-ion electrolyte salts.

[0136] The lithium-ion electrolyte salt is selected from one or more of the following: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0137] The sodium ion electrolyte salt is selected from one or more of the following: sodium difluorooxalate borate, sodium hexafluorophosphate, sodium tetrafluoroborate, and sodium perchlorate.

[0138] In some embodiments, the solvent may be selected from one or more of fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0139] In some implementations, the concentration of the electrolyte salt is typically 0.5 mol / L to 15 mol / L.

[0140] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0141] [Isolation membrane]

[0142] The separator is placed between the positive electrode and the negative electrode.

[0143] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0144] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0145] The aforementioned secondary battery also includes a casing for packaging the positive electrode, negative electrode, separator, and electrolyte.

[0146] In some embodiments, the outer shell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. It can also be a soft package, such as a pouch. The material of the soft package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0147] The secondary battery in this application is a lithium-ion battery or a sodium-ion battery.

[0148] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured secondary battery 4.

[0149] In any embodiment of this application, reference is made to Figure 2 The outer casing may include a housing 41 and a cover plate 43. The housing 41 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 41 has an opening communicating with the receiving cavity, and the cover plate 43 can be placed over the opening to close the receiving cavity.

[0150] The positive electrode, negative electrode, and separator can be formed into electrode assembly 42 by a winding or stacking process. Electrode assembly 42 is encapsulated within a receiving cavity. Electrolyte is immersed in electrode assembly 42. The battery 4 can contain one or more electrode assemblies 42, which can be adjusted according to requirements.

[0151] This application also provides an electrical device that includes the aforementioned secondary battery.

[0152] Furthermore, in the aforementioned electrical device, the secondary battery can exist in the form of a single battery cell, or it can be further assembled into a battery pack.

[0153] Figure 3 and Figure 4 Here is an example of a battery pack 1. The battery pack 1 includes a battery box and one or more secondary batteries 4 disposed in the battery box. The battery box includes an upper box 2 and a lower box 3, the upper box 2 being able to cover the lower box 3 and form a closed space for the secondary batteries 4.

[0154] Multiple secondary batteries 4 can be arranged in the battery box in any way.

[0155] Electrical appliances can be equipped with either rechargeable batteries or battery packs based on their usage requirements.

[0156] The aforementioned secondary batteries or battery packs assembled from them can be used as power sources for electrical devices or as energy storage units for electrical devices.

[0157] The aforementioned electrical devices may include, but are not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0158] Figure 5 This is an example of an electrical device 5. This electrical device 5 can be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device 5, a battery pack can be used.

[0159] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use batteries as their power source.

[0160] The present invention will now be described with reference to specific embodiments. However, the present invention is not limited to the embodiments described below. It should be understood that the appended claims summarize the scope of the present invention. Under the guidance of the inventive concept, those skilled in the art should realize that any changes made to the various embodiments of the present invention will be covered by the spirit and scope of the claims of the present invention.

[0161] The following are specific examples.

[0162] Example 1

[0163] (1) Preparation of the positive electrode:

[0164] 1. Preparation of lithium-ion positive electrode sheet: Lithium iron phosphate material, conductive agent carbon black, binder PVDF are dissolved in deionized water at a weight ratio of 97.4:1.74:0.86 and mixed evenly to prepare a positive electrode slurry; the positive electrode slurry is uniformly coated on the negative electrode current collector copper foil in one step, and after drying, cold pressing and slitting, lithium-ion positive electrode sheet is obtained.

[0165] 2. Preparation of sodium ion positive electrode sheet: Prussian white material, conductive agent carbon black, and polyvinylidene fluoride (PVDF) are dissolved in deionized water at a weight ratio of 95:5:5 and mixed evenly to prepare a positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector copper foil in one step, and then dried, cold pressed, and slit to obtain sodium ion positive electrode sheet.

[0166] (2) Preparation of the negative electrode:

[0167] 1. Preparation of carbon materials: Take 10g of activated carbon particles (volume particle size D(v)50 is 5μm, D(v)90 is 10μm), spread them evenly at the bottom of the crucible to form an activated carbon base layer with a thickness of 2mm, then place the crucible in a tube furnace, heat it to 800℃ at 5℃ / min, keep it at the temperature for 4h, then charge N2 at a flow rate of 200mL / min as a protective atmosphere, when the temperature is maintained at 800℃, xylene gas is introduced at a flow rate of 1.9mL / h as a carbon source for chemical vapor deposition to form an amorphous carbon layer, thus obtaining carbon materials.

[0168] Uncoated activated carbon and the prepared carbon material were placed under a ZEISS Sigma 300 scanning electron microscope and tested according to standard JY / T010-1996 to observe the morphology of the samples. The electron microscope images of uncoated activated carbon and the prepared carbon material are shown below. Figure 6 As shown in (a) and (b), the electron microscope images of the prepared carbon material are as follows: Figure 7 As shown, it can be clearly observed that the surface of the prepared carbon material is coated with an amorphous carbon layer.

[0169] The thickness of the amorphous carbon layer formed was controlled by adjusting the duration of xylene gas introduction. The thickness of the amorphous carbon layer was measured as follows:

[0170] The morphology of the prepared carbon material was tested using a ZEISS Sigma 300 nanofilm scanning probe microscope according to standard JY / T010-1996. Ten different locations were randomly selected from the sample to be tested for the thickness calibration of the amorphous carbon layer (using the interface between the shaped carbon layer and the outer surface of the porous carbon substrate as the measurement baseline). The average value was taken as the thickness of the amorphous carbon layer. The results are shown in Table 1.

[0171] The volume average particle size D(v)50 or D90(v) tests are as follows:

[0172] Equipment Model: MasterSizer 2000 laser particle size analyzer; Reference Standard Procedure: GB / T19077-2016 / ISO 13320:2009; Specific Test Procedure: Take an appropriate amount of the sample to be tested (the sample concentration should be 8%~12% light-blocking), add 20ml of deionized water, and simultaneously sonicate for 5 minutes (53KHz / 120W) to ensure complete dispersion of the sample. Then, measure the sample according to the GB / T19077-2016 / ISO 13320:2009 standard.

[0173] 2. The prepared carbon material, conductive carbon black, binder SD-3, and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water at a weight ratio of 95:1.74:2.3:0.96 and mixed evenly to prepare a negative electrode slurry. The negative electrode slurry is then uniformly coated onto the negative electrode current collector copper foil in one step, and after drying, cold pressing, and slitting, a negative electrode sheet is obtained.

[0174] (3) Preparation of the isolation membrane: Polypropylene membrane is used as the isolation membrane.

[0175] (4) Preparation of electrolyte:

[0176] 1. In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed evenly at a volume ratio of 3:7. LiPF6 lithium salt was added and dissolved in the organic solvent and stirred evenly to obtain a lithium-ion battery electrolyte with a LiPF6 lithium salt concentration of 12.5wt%.

[0177] 2. In an argon atmosphere glove box (H2O<0.1ppm, O2<0.1ppm), ethylene carbonate (EC) / dimethyl carbonate (DMC) organic solvents are mixed evenly at a volume ratio of 1:1. Sodium NaClO4 salt is added and dissolved in the organic solvent and stirred evenly to obtain a sodium-ion battery electrolyte with a sodium NaClO4 salt concentration of 10.4wt%.

[0178] (5) The lithium-ion positive electrode sheet and negative electrode sheet are sequentially cut, shaped, assembled, shelled, injected with lithium-ion battery electrolyte, formed and aged to prepare a lithium-ion battery.

[0179] Sodium-ion batteries are prepared by sequentially cutting, shaping, assembling, casing, injecting sodium-ion battery electrolyte, forming, and aging sodium-ion positive and negative electrode sheets.

[0180] (6) Capacity testing of lithium-ion and sodium-ion batteries:

[0181] 1. Battery capacity utilization test

[0182] The battery capacity testing process is as follows: At 25°C, the half-coin cell corresponding to Example 1 was discharged to 5mV at a constant current of 0.05C, then discharged to 5mV at a constant voltage of 50μA, left to stand for 1 hour, and then discharged to 5mV at 10μA. The resulting capacity is recorded as the discharge capacity C0. After standing for another hour, it was charged to 2V at a constant current of 0.05C. The resulting capacity is the charging capacity C1. The initial coulombic efficiency P0 = C1 / C0 * 100%. The plateau capacity is the capacity at 0.2V during the charging process.

[0183] Please see Table 1 for specific test results.

[0184] Examples 2-15

[0185] Examples 2-15 are basically the same as Example 1, except that in step (2) the preparation of carbon materials, the deposition temperature or deposition time or the flow rate of xylene gas or the thickness of activated carbon base layer are adjusted to change the thickness of the amorphous carbon layer in the carbon material. For specific parameters, please refer to Table 1.

[0186] The remaining steps are the same as in Example 1. Please see Table 1 for specific parameters and test results.

[0187] Comparative Example 1

[0188] Comparative Example 1 is basically the same as Example 1, except that: in Comparative Example 1, the activated carbon is used directly as the negative electrode active material to prepare the negative electrode sheet without coating treatment.

[0189] The remaining steps are the same as in Example 1. Please see Table 1 for specific parameters and test results.

[0190] Please refer to Table 1 for the relevant parameters and test results in each embodiment and comparative example.

[0191] Table 1

[0192]

[0193] In this context, " / " indicates that the structure does not exist.

[0194] Analysis of the data in Table 1 shows that when the carbon material of this application is used as a negative electrode active material in a secondary battery, it can improve the reversible capacity of the secondary battery and increase its initial coulombic efficiency.

[0195] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A carbon material, characterized in that, The carbon material includes a porous carbon substrate and an amorphous carbon layer disposed on at least a portion of the surface of the porous carbon substrate. The porous structure of the porous carbon substrate includes microporous structure, mesoporous structure and macroporous structure.

2. The carbon material as described in claim 1, characterized in that, The thickness of the amorphous carbon layer is 15nm~250nm; Optionally, the thickness of the amorphous carbon layer is 20 nm to 220 nm; Optionally, the thickness of the amorphous carbon layer is 20 nm to 200 nm; Optionally, the thickness of the amorphous carbon layer is 50 nm to 130 nm.

3. The carbon material according to any one of claims 1 to 2, characterized in that, The amorphous carbon layer is formed by vapor deposition of aryl compounds with 6 to 40 carbon atoms; Optionally, the aryl compound includes one or more of benzene, toluene, and xylene.

4. The carbon material according to any one of claims 1 to 3, characterized in that, The carbon material possesses one or more of the following characteristics: (1) The volumetric particle size D(v)50 of the porous carbon substrate is ≤5μm; optionally, 0.1μm≤D(v)50≤5μm; (2) The volumetric particle size D(v) of the porous carbon substrate is 90 ≤ 20 μm; optionally, 7 μm ≤ D(v) 90 ≤ 20 μm.

5. The carbon material according to any one of claims 1 to 4, characterized in that, Based on the total surface area of ​​the porous carbon substrate, the area of ​​the surface of the porous carbon substrate with the amorphous carbon layer accounts for ≥50%; Optionally, the area of ​​the porous carbon substrate with the amorphous carbon layer accounts for ≥60%; Optionally, the surface area of ​​the porous carbon substrate with the amorphous carbon layer accounts for ≥70%; Optionally, the surface area of ​​the porous carbon substrate with the amorphous carbon layer accounts for ≥80%; Optionally, the surface area of ​​the porous carbon substrate with the amorphous carbon layer accounts for ≥90%; Optionally, the area of ​​the porous carbon substrate on which the amorphous carbon layer is disposed is 90% to 100%.

6. The carbon material according to any one of claims 1 to 5, characterized in that, The specific surface area of ​​the porous carbon substrate is ≥500m². 2 / g.

7. The carbon material according to any one of claims 1 to 6, characterized in that, The porous carbon substrate is activated carbon.

8. The method for preparing the carbon material according to any one of claims 1 to 7, characterized in that, Includes the following steps: The carbon material is obtained by performing vapor phase deposition on the surface of the porous carbon substrate using carbon source to form an amorphous carbon layer.

9. The use of at least one of the carbon materials according to any one of claims 1 to 7 and the carbon materials prepared by the preparation method according to claim 8 as a negative electrode active material.

10. A negative electrode sheet, characterized in that, The negative electrode sheet includes a current collector and a negative electrode active layer disposed on the surface of the current collector, wherein the components of the negative electrode active layer include at least one of the carbon materials according to any one of claims 1 to 7 and the carbon materials prepared by the preparation method according to claim 8.

11. The negative electrode sheet as described in claim 10, characterized in that, The carbon material accounts for 90% to 95% of the mass of the negative electrode active layer.

12. A secondary battery, characterized in that, The secondary battery comprises the negative electrode sheet as described in any one of claims 10 to 11.

13. An electrical appliance, characterized in that, The electrical device includes the secondary battery as described in claim 12.

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