WO2024159930A1 - Carbon negative electrode active material and preparation method therefor, secondary battery, and electric device - Google Patents

Abstract

Disclosed in the present disclosure are a carbon negative electrode active material and a preparation method therefor, a secondary battery, and an electric device. The carbon negative electrode active material has a pore structure, the active specific surface area of the carbon negative electrode active material ranges from 0.03 m2/g to 0.12 m2/g, and the pore volume of the carbon negative electrode active material is greater than or equal to 0.005 cm3/g.

Description

Carbon negative electrode active material and preparation method, secondary battery and electric device

CROSS-REFERENCE TO RELATED APPLICATIONS

This disclosure claims the priority benefit of Chinese patent application No. 202310092124.6 filed on February 3, 2023, and incorporates the entirety of the patent application into this document.

Technical Field

The present disclosure relates to the field of battery negative electrode materials, and in particular, to carbon negative electrode active materials and preparation methods, secondary batteries and electrical devices.

Background Art

Secondary batteries have the advantages of high energy density, long cycle life, and good rate performance, and are widely used in portable electronic devices, electric vehicles, and energy storage systems. During the recycling of secondary batteries, the negative electrode active materials (such as carbon materials such as graphite) will continue to expose new internal pore interfaces due to expansion, and the new internal pore interfaces will continue to react with the electrolyte, resulting in the growth of SEI film (solid electrolyte interface film) and the aggravation of battery capacity decay.

Therefore, the current carbon negative electrode active materials and preparation methods, secondary batteries and electrical devices still need to be improved.

Summary of the invention

The present disclosure is based on the inventor's discovery and understanding of the following facts and problems:

During the battery cycle, as carbon negative electrode active materials such as graphite expand, the negative electrode active materials will continuously expose new internal pore interfaces (active sites that easily react with the electrolyte). These new pore interfaces will continue to react with the electrolyte, causing the SEI film to continue to grow and consume more active lithium, resulting in a rapid decline in battery capacity and a significant decrease in battery cycle performance.

In view of this, the present disclosure aims to alleviate or solve at least one of the above-mentioned problems to at least some extent.

In one aspect of the present disclosure, the present disclosure proposes a carbon negative electrode active material. According to an embodiment of the present disclosure, the carbon negative electrode active material has a pore structure, the active specific surface area of the carbon negative electrode active material is ^0.03m2/ g- ^0.12m2 /g, and the pore volume of the carbon negative electrode active material is greater than or equal to ^0.005cm3 /g. As a result, the carbon negative electrode active material has a suitable active specific surface area and a high pore volume. When used as a negative electrode active material for a battery, an effective SEI film can be formed during the first cycle of charging, and during the battery cycle charge and discharge process, the carbon negative electrode active material consumes less active lithium, which can effectively improve the long-term electrical performance of the battery.

According to an embodiment of the present disclosure, the active specific surface area of the carbon negative electrode active material is 0.03 m ² /g-0.08 m ² /g, which is beneficial to further improve the long-term electrical performance of the battery (eg, cycle performance and storage performance, etc.).

According to an embodiment of the present disclosure, the pore volume of the carbon negative electrode active material is 0.005 cm ³ /g-0.1 cm ³ /g.

According to the embodiments of the present disclosure, the carbon negative electrode active material contains one or more of micropores, mesopores or macropores, so that the carbon negative electrode active material can have a more suitable pore volume, which is beneficial to improve the long-term electrical performance of the battery.

According to an embodiment of the present disclosure, based on the total volume of the pores in the carbon negative electrode active material, the volume content of the micropores is less than or equal to 10%, and can be optionally less than or equal to 5%; and/or, based on the total volume of the pores in the carbon negative electrode active material, the volume content of the mesopores is 60%-95%, and can be optionally 70%-90%; and/or, based on the total volume of the pores in the carbon negative electrode active material, the volume content of the macropores is less than or equal to 25%, and can be optionally 5%-20%.

According to an embodiment of the present disclosure, the carbon negative electrode active material satisfies at least one of the following conditions (1)-(3): (1) the specific surface area of the carbon negative electrode active material is ^1.0m2 /g- ^8.0m2 /g, and can be ^2m2 /g- ^5m2 /g; (2) the volume distribution particle size Dv50 of the carbon negative electrode active material is 5μm-50μm, and can be 10μm-30μm; (3) the porosity of the carbon negative electrode active material is 20%-40%, and can be 25%-35%. This is conducive to further improving the electrochemical performance of the carbon negative electrode active material.

According to an embodiment of the present disclosure, the carbon negative electrode active material contains oxygen-containing functional groups, and the oxygen-containing functional groups include one or more of lactone, ether, phenol, carboxyl, anhydride and carbonyl. The presence of the above oxygen-containing functional groups is conducive to the carbon negative electrode active material reacting with the electrolyte to form an effective SEI film during the first cycle of charging.

In another aspect of the present disclosure, the present disclosure proposes a method for preparing the aforementioned carbon negative electrode active material. According to an embodiment of the present disclosure, the method for preparing the aforementioned carbon negative electrode active material includes: providing a carbon material; performing an oxidation treatment on the carbon material using an oxidizing gas probe to obtain an intermediate carbon material; performing a reduction treatment on the intermediate carbon material using a reducing gas to obtain a carbon negative electrode active material, wherein the carbon negative electrode active material has a pore structure, and the active specific surface area of the carbon negative electrode active material is ^0.03m2/ g- ^0.12m2 /g, and the pore volume of the carbon negative electrode active material is greater than or equal to ^0.005cm3 /g. Thus, the carbon negative electrode active material prepared by this method has a suitable active specific surface area and pore volume, and the carbon negative electrode active material can not only form an effective SEI film during the first cycle charging process, but also consume less active lithium during the cyclic charge and discharge process, thereby effectively improving the long-term electrical performance of the battery.

According to an embodiment of the present disclosure, the oxidizing gas probe includes one or more of oxygen, air, chlorine, nitrogen oxide, sulfur trioxide and argon plasma. Therefore, the above gas probes all have a certain oxidizing property, and can search for active sites (including unexposed sites) on the surface of carbon materials such as graphite, and oxidize the active sites in the carbon materials, so as to facilitate the subsequent reduction of oxygen-containing functional groups to passivate some sites.

According to an embodiment of the present disclosure, the reducing gas includes one or more of hydrogen, carbon monoxide, hydrogen sulfide, sulfur dioxide, ammonia, olefins and alkynes. The above gases all have good reducing properties and can reduce oxygen-containing functional groups, thereby reducing active sites in the carbon material.

According to an embodiment of the present disclosure, the oxidizing gas probe includes oxygen, and the reducing gas includes hydrogen; or, the oxidizing gas probe includes air, and the reducing gas includes carbon monoxide; or, The reducing gas probe includes argon plasma, and the reducing gas includes ammonia. Therefore, the reducing gas and the oxidizing gas probe are well adapted, and the reducing gas can react with the oxygen-containing functional groups more specifically to reduce and passivate the active sites on the surface of the carbon material.

According to an embodiment of the present disclosure, the temperature of the oxidation treatment is 300° C.-500° C., and/or the time of the oxidation treatment is 8 h-16 h. Thus, most or even almost all edge sites of the carbon material can be oxidized by the oxidation treatment.

According to an embodiment of the present disclosure, the temperature of the reduction treatment is 800°C-1000°C, and/or the time of the reduction treatment is 6h-15h. Thus, some oxygen-containing functional groups can be reduced and passivated by the reduction treatment, and some sites can be retained to react with the electrolyte to form an effective SEI film during the first cycle of charging.

According to an embodiment of the present disclosure, the carbon material includes one or more of natural graphite, artificial graphite, hard carbon, soft carbon, carbon fiber and mesophase carbon microspheres. The above carbon materials can be treated by the method proposed in the present disclosure, and the electrochemical performance of the treated carbon materials can be significantly improved.

In another aspect of the present disclosure, the present disclosure proposes a secondary battery, the secondary battery comprising a negative electrode plate, the negative electrode plate comprising the carbon negative electrode active material described above. Thus, the secondary battery has all the characteristics and advantages of the carbon negative electrode active material described above, which will not be repeated here. In general, the carbon negative electrode active material can react with the electrolyte to form an effective SEI film during the first cycle of charging of the secondary battery, and during the cycle and storage process, the carbon negative electrode active material in the negative electrode plate consumes less active lithium, which is beneficial to improve the long-term cycle performance and storage performance of the battery.

In another aspect of the present disclosure, the present disclosure provides an electric device. According to an embodiment of the present disclosure, the electric device includes the secondary battery described above. Therefore, the electric device has all the features and advantages of the secondary battery, which will not be described in detail here.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and/or additional aspects and advantages of the present disclosure will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

FIG. 1 shows a flow chart of a method for preparing a carbon negative electrode active material according to an embodiment of the present disclosure.

DETAILED DESCRIPTION

Embodiments of the present disclosure are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present disclosure, and cannot be understood as limiting the present disclosure.

In one aspect of the present disclosure, the present disclosure provides a carbon negative electrode active material. According to an embodiment of the present disclosure, the carbon negative electrode active material has a pore structure, and the active specific surface area of the carbon negative electrode active material can be 0.03m ² /g-0.12m ² /g. For example, the active specific surface area of the carbon negative electrode active material can be 0.03m ² /g, 0.05m ^{2 /} g, 0.07m ² /g, 0.09m ² /g, 0.10m ² /g, 0.12m ² /g, etc., and the pore volume of the carbon negative electrode active material is greater than or equal to 0.005cm ³ /g, for example, the pore volume of the carbon negative electrode active material can be 0.005cm ³ /g, 0.0053cm ³ /g, 0.0055cm ³ /g, 0.0058cm ³ /g, 0.006cm ³ /g, etc. Therefore, the carbon negative electrode active material has a suitable active specific surface area and pore volume, and the carbon negative electrode active material is used as the negative electrode active material of the battery. The carbon negative electrode active material can fully react with the electrolyte during the first cycle of charging to form an effective SEI film, and in the subsequent charging and discharging process, the carbon negative electrode active material will not expose too many active sites, thereby reducing the consumption of active lithium in the subsequent charging and discharging process, thereby effectively improving the long-term electrical performance of the battery, and making the battery have excellent cycle stability and a longer service life.

Preferably, the active specific surface area of the carbon negative electrode active material can be ^0.03m2/ g-0.08m2 ^/ g. For example, the active specific surface area of the carbon negative electrode active material can be 0.03m2 ^/ g, ^0.04m2 /g, ^0.05m2 /g, ^0.06m2/ g, ^0.07m2/ g, ^0.08m2 /g, etc., which is conducive to further improving the performance of the carbon negative electrode active material. Using the carbon negative electrode active material as the negative electrode active material of the battery can further improve the cycle stability of the battery and extend the service life of the battery.

Preferably, the pore volume of the carbon negative electrode active material can be 0.005 cm ³ /g-0.1 cm ³ /g. For example, the pore volume of the carbon negative electrode active material can be 0.005 cm ³ /g, 0.007 cm ³ /g, 0.01 cm ³ /g, 0.03 cm 3 /g, 0.05 cm ³ /g, 0.08 ^{cm 3 /} g, 0.1 cm ³ /g, etc. Therefore, the carbon negative electrode active material has a larger pore volume, which is conducive to further improving the performance of the carbon negative electrode active material.

According to some embodiments of the present disclosure, the specific surface area of the carbon negative electrode active material can be 1.0m ² /g-8.0m ² /g, for example, the specific surface area of the carbon negative electrode active material can be 1.0m ² /g, 2.0m ^{2 /} g, 4.0m ² /g, 6.0m ² /g, 8.0m ² /g, etc., thus, the carbon negative electrode active material has a suitable specific surface area, can be fully in contact with the electrolyte during the charge and discharge process, and is beneficial to improving the charge and discharge performance of the battery. Preferably, the specific surface area of the carbon negative electrode active material can be 2m ² /g-5m ² /g, for example, the specific surface area of the carbon negative electrode active material can be 2m ² /g, 3m ² /g, 4m ² /g, 5m ² /g, etc., thus, it is beneficial to further improve the performance of the carbon negative electrode active material.

According to some embodiments of the present disclosure, the volume distribution particle size Dv50 of the carbon negative electrode active material is 5μm-50μm, for example, the volume distribution particle size Dv50 of the carbon negative electrode active material can be 5μm, 8μm, 10μm, 20μm, 30μm, 40μm, 50μm, etc., thus, the carbon negative electrode active material has a suitable volume distribution particle size, and the carbon negative electrode active material can be in relatively sufficient contact with the electrolyte during the charge and discharge process, thereby facilitating the improvement of the battery electrical performance. Preferably, the volume distribution particle size Dv50 of the carbon negative electrode active material can be 10μm-30μm, for example, the volume distribution particle size Dv50 of the carbon negative electrode active material can be 10μm, 12μm, 15μm, 18μm, 22μm, 25μm, 27μm, 30μm, etc., thus, the carbon negative electrode active material has a more excellent volume distribution particle size, which is conducive to further improving the performance of the carbon negative electrode active material.

According to some embodiments of the present disclosure, the carbon negative electrode active material contains one or more of micropores (usually with a pore size less than 2 nm), mesopores (usually with a pore size of 2 nm-50 nm) and/or macropores (usually with a pore size greater than 50 nm), so that the carbon negative electrode active material has a more suitable pore volume, which is more conducive to improving the long-term electrical performance of the battery.

According to some embodiments of the present disclosure, based on the total volume of pores in the carbon negative electrode active material, the volume content of micropores is less than or equal to 10%, and can be optionally less than or equal to 5%.

According to some embodiments of the present disclosure, based on the total volume of the pores in the carbon negative electrode active material, the volume content of the mesopores is 60%-95%, and optionally 70%-90%.

According to some embodiments of the present disclosure, based on the total volume of the pores in the carbon negative electrode active material, the volume content of the macropores is less than or equal to 25%, and may be 5%-20%.

When the carbon negative electrode active material has an appropriate amount of micropores, mesopores and/or macropores, it is beneficial to further increase the contact area between the carbon negative electrode active material and the electrolyte, thereby further improving the overall performance of the battery.

According to some embodiments of the present disclosure, the porosity of the carbon negative electrode active material can be 20%-40%, for example, the porosity of the carbon negative electrode active material can be 20%, 22%, 26%, 30%, 32%, 36%, 38%, 40%, etc., thus, the carbon negative electrode active material has a higher porosity, which is beneficial to increase the contact area between the carbon negative electrode active material and the electrolyte, thereby facilitating the improvement of the battery performance. Preferably, the porosity of the carbon negative electrode active material can be 25%-35%, for example, the porosity of the carbon negative electrode active material can be 25%, 28%, 31%, 33%, 35%, etc., thus, the carbon negative electrode active material has a suitable porosity, and the contact area between the active material and the electrolyte is large, which is beneficial to further improve the battery performance.

According to an embodiment of the present disclosure, the carbon negative electrode active material contains oxygen-containing functional groups, wherein the oxygen-containing functional groups include one or more of lactone, ether, phenol, carboxyl, anhydride and carbonyl, etc. Thus, the above oxygen-containing functional groups can fully react with the electrolyte during the first cycle of battery charging to form an effective SEI film.

In another aspect of the present disclosure, the present disclosure provides a method for preparing a carbon negative electrode active material. According to an embodiment of the present disclosure, referring to FIG1 , the method for preparing a carbon negative electrode active material may include the following steps:

S100: Provides carbon materials.

According to an embodiment of the present disclosure, the carbon material may include one or more of natural graphite, artificial graphite, hard carbon, soft carbon, carbon fiber, and mesophase carbon microspheres. According to some embodiments of the present disclosure, the carbon material may be natural graphite, artificial graphite, hard carbon, soft carbon, carbon fiber, or mesophase carbon microspheres. According to other embodiments of the present disclosure, the carbon material may include two or more of natural graphite, artificial graphite, hard carbon, soft carbon, carbon fiber, and mesophase carbon microspheres.

Carbon materials usually contain some oxygen-containing functional groups. During the battery charging and discharging process, the oxygen-containing functional groups are easy to react with the electrolyte. In addition, carbon materials are also easy to expand during the battery cycle, constantly exposing new internal pore interfaces, which are easy to react with the electrolyte, causing SEI growth and consuming more active lithium. Taking graphite negative electrode materials as an example, during the battery cycle, graphite will expand, exposing some new internal pore interfaces, which are easy to react with the electrolyte, causing SEI to continue to grow, and also consume active lithium, resulting in a decrease in battery cycle performance and storage performance.

S200: using an oxidizing gas probe to oxidize the carbon material to obtain an intermediate carbon material.

According to the embodiments of the present disclosure, the carbon material is oxidized by using an oxidizing gas probe. The oxidizing gas probe can search the end face of the carbon material, search for active sites on the surface of the carbon material, and find the interface that is easily exposed due to expansion (active sites that are easily exposed but not exposed at the beginning), and oxidize the active sites into oxygen-containing functional groups to obtain the intermediate. The inter-carbon material can be subsequently treated with reduction to reduce and passivate some of the oxygen-containing functional groups. After the above-mentioned interfacial active sites are passivated, they are not easy to react with the electrolyte during the battery's charge and discharge cycle, thereby improving the battery's long-term cycle performance and storage performance. It should be noted that the more active sites there are on the surface of the carbon material, the larger the active specific surface area. In the present disclosure, an oxidizing gas probe is used to find the active sites and oxidize the active sites to oxygen-containing functional groups. Subsequently, a reduction treatment is performed to reduce and passivate some of the oxygen-containing functional groups. The content of the active sites can be regulated, and the active specific surface area of the material can be controlled within a suitable range, thereby improving the long-term electrical performance of the battery.

According to an embodiment of the present disclosure, the oxidizing gas probe may include one or more of oxygen, air, chlorine, nitrogen oxide, sulfur trioxide and argon plasma. The above-mentioned oxidizing gas can effectively search for active sites of carbon materials such as graphite, and can find most or even almost all active sites that are easily exposed, and oxidize the active sites to oxygen-containing functional groups so that the active sites can be passivated by subsequent reduction. According to some embodiments of the present disclosure, the oxidizing gas probe may be oxygen, air, chlorine, nitrogen oxide, sulfur trioxide or argon plasma. According to other embodiments of the present disclosure, the oxidizing gas probe may include two or more of oxygen, air, chlorine, nitrogen oxide, sulfur trioxide and argon plasma.

According to an embodiment of the present disclosure, the oxygen-containing functional group may include one or more of lactone, ether, phenol, carboxyl, anhydride and carbonyl, so that a certain amount of the above oxygen-containing functional groups can react with the electrolyte to form an effective SEI film during the first cycle of battery charging. According to some embodiments of the present disclosure, the oxygen-containing functional group in the intermediate carbon material may be lactone, ether, phenol, carboxyl, anhydride or carbonyl. According to other embodiments of the present disclosure, the oxygen-containing functional group in the intermediate carbon material may include two or more of lactone, ether, phenol, carboxyl, anhydride and carbonyl. It should be noted that the carbon material itself may also contain a certain amount of oxygen-containing functional groups, and the oxygen-containing functional groups possessed by the carbon material itself may also include one or more of lactone, ether, phenol, carboxyl, anhydride and carbonyl.

According to an embodiment of the present disclosure, the temperature for oxidizing the carbon material can be 300°C-500°C. For example, the temperature for oxidizing the carbon material can be 300°C, 320°C, 350°C, 370°C, 400°C, 430°C, 450°C, 480°C, 500°C, etc. When the temperature is set within the above range, the oxidizing gas probe can oxidize most or even almost all of the active sites on the end face of the carbon material, thereby facilitating the partial reduction of the active sites on the surface of the carbon material (including the active sites that may be exposed when the carbon material expands during the cycle) through subsequent reduction. The reduced active sites are not easy to react with the electrolyte, thereby improving the cycle performance and storage performance of the battery. The inventors found that if the temperature for oxidizing the carbon material is too high, for example, higher than 800°C, the carbon material may burn; if the temperature for oxidizing the carbon material is too low, for example, lower than 100°C, it is difficult to achieve oxidation of the active sites of the carbon material.

According to the embodiments of the present disclosure, the oxidation treatment time of the carbon material can be 8h-16h. For example, the oxidation treatment time of the carbon material can be 8h, 10h, 12h, 15h, 16h, etc. The oxidation treatment time is set within the above range, and the oxidizing gas probe can fully react with the carbon material so that most or even almost all active sites are oxidized. The inventors have found that if the oxidation treatment time of the carbon material is too short, for example, less than 1h, it is difficult to ensure that the oxidizing gas probe Fully react with the carbon material; if the oxidation treatment time of the carbon material is too long, for example, more than 24 hours, it may cause the carbon material such as graphite to be peeled off, causing the carbon material to lose its lithium insertion activity.

S300: reducing the intermediate carbon material using a reducing gas to obtain a carbon negative electrode active material.

According to the embodiment of the present disclosure, after the carbon material is oxidized to obtain the intermediate carbon material, the intermediate carbon material is reduced by using a reducing gas, so that the oxygen-containing functional groups in the intermediate carbon material are partially reduced to obtain a carbon negative electrode active material, the carbon negative electrode active material has a pore structure, the active specific surface area of the carbon negative electrode active material is 0.03m2 ^/ g- ^0.12m2 /g, and the pore volume of the carbon negative electrode active material is greater than or equal to ^0.005cm3 /g. During the oxidation treatment, the active sites on the surface of the carbon material and the active sites that are easily exposed during the expansion process can be oxidized by the oxidizing gas probe to generate oxygen-containing functional groups. By reducing the intermediate carbon material with a reducing gas, some oxygen-containing functional groups can be reduced and passivated. After the oxidation-reduction process, the active sites are not easy to react with the electrolyte during the battery cycle, thereby reducing the consumption of active lithium during the cycle, and further significantly improving the long-term cycle performance and storage performance of the battery; in addition, the retained oxygen-containing functional groups can still react with the electrolyte during the first cycle charging process to form an effective SEI film. After the carbon material is oxidized and reduced, the active specific surface area of the obtained carbon negative electrode active material is 0.03m2 ^/ g- ^0.12m2 /g, and the pore volume of the carbon negative electrode active material is greater than or equal to ^0.005cm3 /g. The carbon negative electrode active material has good long-term electrical properties.

According to an embodiment of the present disclosure, the reducing gas may include one or more of hydrogen, carbon monoxide, hydrogen sulfide, sulfur dioxide, ammonia, olefins and alkynes, etc., and the above reducing gas may react with oxygen-containing functional groups to reduce and passivate oxygen-containing functional groups such as lactones, ethers, phenols, carboxyls, anhydrides and carbonyls. According to some embodiments of the present disclosure, the reducing gas may be hydrogen, carbon monoxide, hydrogen sulfide, sulfur dioxide, ammonia, olefins or alkynes. According to other embodiments of the present disclosure, the reducing gas may include two or more of hydrogen, carbon monoxide, hydrogen sulfide, sulfur dioxide, ammonia, olefins and alkynes, etc.

According to a specific embodiment of the present disclosure, the oxidizing gas probe includes oxygen, and the reducing gas includes hydrogen. According to another specific embodiment of the present disclosure, the oxidizing gas probe includes air, and the reducing gas includes carbon monoxide. According to yet another specific embodiment of the present disclosure, the oxidizing gas probe includes argon plasma, and the reducing gas includes ammonia. The oxidizing gas probe and the reducing gas in the above specific embodiments have good matching, and can better achieve reduction passivation of oxygen-containing functional groups, which is more conducive to improving the long-term cycle performance and storage performance of the battery.

According to the embodiments of the present disclosure, the temperature of the reduction treatment can be 800°C-1000°C. For example, the temperature of the reduction treatment can be 800°C, 830°C, 850°C, 880°C, 900°C, 920°C, 950°C, 970°C, 1000°C, etc. The temperature of the reduction treatment is set within the above range. The reducing gas can reduce the oxygen-containing functional groups, so that part of the oxygen-containing functional groups are reduced, and the oxidized active sites are reduced and passivated. The passivated sites are not easy to react with the electrolyte during the battery cycle, thereby effectively improving the long-term cycle performance and storage performance of the battery. The inventors have found that if the temperature of the reduction treatment If the temperature is too low, for example, below 800°C, it will be difficult to achieve reduction passivation; if the temperature of the reduction treatment is too high, the carbon material may undergo methanation or carbon deposition reaction, which is not conducive to improving the battery performance.

According to the embodiments of the present disclosure, the time of the reduction treatment can be 6h-15h, for example, the time of the reduction treatment can be 6h, 8h, 10h, 13h, 15h, etc. The time of the reduction treatment is set within the above range, and the reducing gas can reduce and passivate the oxidized active sites, while retaining some sites to react with the electrolyte to generate an effective SEI film during the first cycle of charging. The inventors found that if the time of the reduction treatment is too short, for example, the time of the reduction treatment is less than 6h, it is easy for too many oxidation sites to remain, and too many oxidation sites will consume more active lithium, which is not conducive to improving the battery performance; if the time of the reduction treatment is too long, for example, the time of the reduction treatment is greater than 15h, it may result in insufficient sites, making it difficult to ensure the generation of an effective SEI film during the first cycle of charging.

In another aspect of the present disclosure, the present disclosure provides a secondary battery, the secondary battery includes a negative electrode plate, and the negative electrode plate includes the carbon negative electrode active material described above. Therefore, the secondary battery has all the characteristics and advantages of the carbon negative electrode active material described above, which will not be repeated here. In general, the secondary battery has excellent long-term cycle performance and storage performance.

According to an embodiment of the present disclosure, in a secondary battery, the negative electrode plate may further include a first conductive agent, a first binder, a thickener, etc. According to some embodiments of the present disclosure, the first conductive agent may include one or more of carbon nanotubes, carbon black, carbon fiber, graphene, etc., the first binder may include one or more of polyvinyl alcohol, polyurethane, polyacrylate, polyvinylidene fluoride, nitrile rubber, epoxy resin, vinyl acetate resin, chlorinated rubber, etc., and the thickener may include sodium hydroxymethyl cellulose, etc.

According to some embodiments of the present disclosure, in a secondary battery, the negative electrode plate may further include a negative electrode current collector, and the negative electrode current collector may be copper foil, aluminum foil, or the like.

According to an embodiment of the present disclosure, the battery may further include a positive electrode sheet, a separator, an electrolyte, etc. According to some embodiments of the present disclosure, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer, the positive electrode current collector may be copper foil, aluminum foil, etc., the positive electrode active material layer may include a positive electrode active material, a second conductive agent, and a second binder, etc., the positive electrode active material may include one or more of lithium iron phosphate, nickel-cobalt-manganese ternary material, lithium cobaltate, lithium manganate, lithium nickelate, lithium vanadate, lithium ferrate, etc., the second conductive agent may include one or more of carbon nanotubes, carbon black, carbon fiber, graphene, etc., the second binder may include one or more of polyvinyl alcohol, polyurethane, polyacrylate, polyvinylidene fluoride, nitrile rubber, epoxy resin, vinyl acetate resin, chlorinated rubber, etc.

The present disclosure does not specifically limit the specific material of the isolation membrane, and those skilled in the art can select it according to actual needs. The present disclosure does not specifically limit the specific components of the electrolyte, and those skilled in the art can select and adjust it according to actual needs.

In another aspect of the present disclosure, the present disclosure provides an electric device. According to an embodiment of the present disclosure, the electric device includes the secondary battery described above. Thus, the electric device has all the characteristics of the secondary battery described above. In general, the electrical device has good overall performance and good stability.

According to some embodiments of the present disclosure, the electric device may be a vehicle. According to some embodiments of the present disclosure, the vehicle may further include a vehicle chassis and a vehicle body disposed on the upper portion of the vehicle chassis, and the electric device satisfies at least one of the following conditions: the electric device is located on a side of the vehicle chassis close to the vehicle body; the electric device is located on a side of the vehicle chassis away from the vehicle body; the electric device is provided inside the vehicle chassis.

The present disclosure is described below by specific examples, and it will be appreciated by those skilled in the art that the following specific examples are only for illustrative purposes and do not limit the scope of the present disclosure in any way. In addition, in the following examples, unless otherwise specified, the materials and equipment used are all commercially available. If in the following examples, specific processing conditions and processing methods are not clearly described, then conditions and methods known in the art can be used for processing.

Example 1

【Preparation of carbon negative electrode active materials】

1000 g of NG-II-18-365 graphite (Dv50 of 18.0 μm±2.0 μm, interlayer spacing d002 of 0.3358 nm±0.0003 nm, tap density of 1.05 g/cm ³ , compaction density under 40000 N of 1.60 g/cm ³ , true density of 2.22 g/cm ³ ±0.02 g/cm ³ , specific surface area of 2.0 m ² /g±0.5 m ² /g, and first discharge specific capacity of 365.0 mA·h/g) was weighed and placed in a tubular furnace. Oxygen was continuously introduced at a flow rate of 50 mL/min at room temperature, and then the temperature was raised to 300°C at a heating rate of 10°C/min, and the temperature was maintained for 12 h (oxidation treatment) and then cooled to room temperature. After hydrogen was continuously introduced at a flow rate of 50 mL/min for 1 h, the temperature was increased to 800° C. at a heating rate of 10° C./min, and the temperature was maintained for 6 h (reduction treatment) and then cooled to room temperature to obtain a carbon negative electrode active material.

【Preparation of positive electrode】

The lithium nickel cobalt manganese (NCM811) ternary material, the conductive agent carbon black, the binder polyvinylidene fluoride (PVDF), and N-methylpyrrolidone (NMP) are stirred and mixed in a weight ratio of 97.36:28.86:2.7:1.1 to obtain a positive electrode slurry; then the positive electrode slurry is evenly coated on the positive electrode collector, and then dried, cold pressed, and cut to obtain a positive electrode sheet.

【Preparation of negative electrode sheet】

The carbon negative electrode active material, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium hydroxymethyl cellulose (CMC) prepared above are dissolved in deionized water solvent at a weight ratio of 96.2:0.8:0.8:1.2, mixed evenly to prepare negative electrode slurry; the negative electrode slurry is evenly coated on the negative electrode current collector copper foil, and the negative electrode sheet is obtained after drying, cold pressing, and slitting.

【Preparation of electrolyte】

In an argon atmosphere glove box (H ₂ O<0.1ppm, O ₂ <0.1ppm), organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 3:7. The total mass of the mixed organic solvents was taken as 100. parts by mass, and 12.5 parts by mass of _LiPF6 lithium salt are added to dissolve _LiPF6 in the organic solvent and stirred evenly to obtain an electrolyte.

【Preparation of lithium-ion batteries】

The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wound to obtain a bare cell, the bare cell is welded with a pole ear, and the bare cell is placed in an aluminum shell, and baked at 80°C to remove water, and then the electrolyte is injected and sealed to obtain an uncharged battery. The uncharged battery is then subjected to the processes of static, hot and cold pressing, formation, shaping, and capacity testing in sequence to obtain the lithium-ion battery product of Example 1.

Example 2

During the preparation process of the carbon negative electrode active material of Example 2, the oxidizing atmosphere used is air, the oxidation treatment temperature is 500°C, and the oxidation treatment time (the insulation time of the oxidation treatment process) is 16 hours; the reducing atmosphere used is carbon monoxide, the reduction treatment temperature is 1000°C, and the reduction treatment time (the insulation time of the reduction treatment process) is 10 hours. The other steps of Example 2 are the same as those of Example 1.

Example 3

During the preparation process of the carbon negative electrode active material of Example 3, the oxidizing atmosphere used is argon plasma, the oxidation treatment temperature is 300°C, and the oxidation treatment time is 8 hours; the reducing atmosphere used is ammonia, the reduction treatment temperature is 900°C, and the reduction treatment time is 15 hours. The other steps of Example 3 are the same as those of Example 1.

Example 4

In the preparation process of the carbon negative electrode active material of Example 4, the oxidation treatment temperature is 400° C., and the other steps are the same as those of Example 1.

Blank Example 1

NG-II-18-365 graphite was used as the carbon negative electrode active material, and the other steps were the same as those in Example 1.

Blank Example 2

NG-I-18-363 graphite (Dv50 of 18.0 μm±2.0 μm, interlayer spacing d002 of 0.3358 nm±0.0003 nm, tap density of 1.05 g/cm ³ , compaction density of 1.65 g/cm ³ under 40000 N, true density of 2.23 g/cm ³ ±0.03 g/cm ³ , specific surface area of 2.0 m ² /g±0.5 m ² /g, first discharge specific capacity ≥363.0 mA·h/g) was used as the carbon negative electrode active material, and the other steps were the same as those in Example 1.

Comparative Example 1

The reduction treatment temperature of Comparative Example 1 is 500° C., and the other steps of Comparative Example 1 are the same as those of Example 1.

Comparative Example 2

The oxidation treatment temperature of Comparative Example 2 is 600° C., and the other steps of Comparative Example 2 are the same as those of Example 2.

Comparative Example 3

The oxidation treatment temperature of Comparative Example 3 is 100° C., and the other steps of Comparative Example 3 are the same as those of Example 3.

Comparative Example 4

NG-I-18-363 graphite was used as the carbon material, and the preparation process and other steps were the same as those in Example 1.

In order to more clearly compare the processing conditions of graphite in each embodiment, comparative example and blank example, the corresponding data are recorded in the following Table 1.

Table 1 Treatment conditions of graphite in each embodiment, comparative example and blank example

【Battery performance test】

1. Battery capacity retention rate test

Taking Example 1 as an example, the battery capacity retention rate test process is as follows: at 25°C, the lithium ion battery of Example 1 is charged to 4.3V at a constant current of 1/3C, then charged to a current of 0.05C at a constant voltage of 4.3V, left for 5 minutes, and then discharged to 2.8V at 1/3C. The obtained capacity is recorded as the initial capacity C0. Repeat the above steps for the same battery, and simultaneously record the discharge capacity Cn of the battery after the nth cycle. Then, the battery capacity retention rate after each cycle is Pn=Cn/C0*100%. With the 100 point values of P1, P2...P100 as the ordinate and the corresponding number of cycles as the abscissa, a curve chart of the capacity retention rate and the number of cycles of the lithium ion battery of Example 1 can be obtained.

During the test, the first cycle corresponds to n=1, the second cycle corresponds to n=2, ... the 100th cycle corresponds to n=100. P100 is the capacity retention rate of the battery after 100 cycles under the above test conditions.

The battery capacity retention rate test method for other embodiments, comparative examples and blank examples is the same as above. The capacity retention rate of the battery after 100 cycles in Blank Example 1 is taken as 100%, and the capacity retention rate of the battery after 100 cycles in each embodiment and comparative example is divided by the capacity retention rate of the battery after 100 cycles in Blank Example 1 to obtain the capacity retention improvement. The rates are recorded in Table 2.

2. Battery DC impedance test

Taking Example 1 as an example, the battery DC impedance test process is as follows: At 25°C, the lithium ion battery of Example 1 is charged to 4.3V at a constant current of 1/3C, and then charged to a current of 0.05C at a constant voltage of 4.3V. After standing for 5 minutes, the voltage V1 is recorded. Then, it is discharged at 1/3C for 30 seconds, and the voltage V2 is recorded. Then (V2-V1)/(1/3C) is obtained to obtain the internal resistance DCR1 of the battery after the first cycle. Repeat the above steps for the same battery, and simultaneously record the internal resistance DCRn (n=1, 2, 3...100) of the battery after the nth cycle. The 100 point values of DCR1, DCR2, DCR3...DCR100 are used as the ordinate, and the corresponding number of cycles is used as the abscissa, and a curve diagram of the discharge DCR and the number of cycles of the lithium ion battery of Example 1 can be obtained.

During the test, the first cycle corresponds to n=1, the second cycle corresponds to n=2, ... the 100th cycle corresponds to n=100. Battery internal resistance increase ratio=(DCRn-DCR1)/DCR1*100%.

The battery DC impedance test process of other embodiments, comparative examples and blank examples is the same as above. The internal resistance increase ratio of the battery of Blank Example 1 after 100 cycles is taken as the benchmark 100%. The result obtained by dividing the internal resistance increase ratio of the battery after the 100th cycle of each embodiment and comparative example by the internal resistance increase ratio of the battery of Blank Example 1 after 100 cycles is taken as the internal resistance increase rate and recorded in Table 2.

3. Battery initial performance test

At 25°C, the secondary batteries prepared in each blank example, embodiment and comparative example are charged at a constant current of 1C to a charging cut-off voltage V3 (e.g., 5mV), then charged at a constant voltage to a current ≤ 0.05C, and left to stand for 5 minutes; then the secondary batteries prepared in each blank example, embodiment and comparative example are discharged at a constant current of 1C to a cut-off voltage V4 (e.g., 2.0V), and left to stand for 5 minutes. This is the first charge and discharge cycle. The first charge capacity and the first discharge capacity of each secondary battery are recorded respectively. The first efficiency (first coulomb efficiency) is the ratio of the first discharge capacity to the first charge capacity. The first efficiency test results are recorded in Table 2.

【Physical and chemical properties test】

1. BET specific surface area and pore volume test

The specific surface area of the negative electrode active material is a well-known meaning in the art, and the samples of each blank example, embodiment and comparative example can be tested by methods known in the art. For example, it can be tested by nitrogen adsorption specific surface area analysis test method with reference to GB/T 19587-2017, and calculated by BET (Brunauer Emmett Teller) method, wherein the nitrogen adsorption specific surface area analysis test can be performed by Tri-Star 3020 specific surface area pore size analysis tester of Micromeritics, USA, and the test results are recorded in Table 2.

Referring to GB/T 21650.2-2008, the samples of each blank example, embodiment and comparative example were tested by nitrogen adsorption-desorption pore volume analysis test method, and calculated by BJH (Barrett-Joiner-Halenda) method, wherein the nitrogen adsorption-desorption volume analysis test can be performed by ASAP 2460 full-pore pore size analysis tester of Micromeritics Company of the United States, and the test results are recorded in Table 2.

2. Active specific surface area test

Taking Example 1 as an example, the test was carried out using the AUTOCHEM II 2920 fully automatic chemisorption analyzer of Micromeritics, USA. 0.1g of the negative electrode active material sample was placed in a sample tube, and treated at 950°C for 2h at a vacuum degree of ^10-4 Pa. Oxygen was adsorbed at 300°C for 10h, and the mass spectrometry signals of CO and _CO2 desorbed at 300°C-950°C were collected. The area S was obtained by integration. The active specific surface area (ASA) was calculated based on the oxygen atom adsorption area of ^0.083nm2 . The calculation formula is as follows:

ASA(m ² /g)=0.083×S×10 ¹² m ² /g.

The testing process of the active specific surface area of the negative electrode active material in other embodiments, comparative examples and blank examples is the same as above, and the test results are recorded in Table 2.

Table 2 Performance test results of each embodiment, comparative example and blank example

It can be seen from Table 2 that the use of the method proposed in the present disclosure to prepare carbon negative electrode active materials has no significant effect on the BET specific surface area of the carbon material, and the active specific surface area of the material after treatment will change significantly. The carbon negative electrode active materials prepared in Examples 1-4 have a suitable active specific surface area, the initial efficiency of the battery is high, and the capacity retention rate of the battery is still high after 100 cycles. The following assumes that the capacity retention rate of the battery in Blank Example 1 after 100 cycles can reach 95% for illustration. Taking this benchmark as 100%, the capacity retention improvement rate in Example 3 can reach 105.1% of the benchmark. The capacity retention rate of the battery in Example 3 after 100 cycles can reach 99.85%, and the capacity retention rate improvement effect is significant. The capacity retention rates of the batteries in Comparative Examples 1 to 4 after 100 cycles were all lower than 95%. The materials in Blank Example 1, Blank Example 2, and Comparative Examples 1 to 4 could not simultaneously have suitable active specific surface areas and pore volumes, and the cycle performance of the prepared batteries was poor.

In general, the active specific surface area of the carbon negative electrode active material proposed in the present disclosure can be 0.03m2 ^/ g- ^0.12m2 /g, and the pore volume of the carbon negative electrode active material is greater than or equal to ^0.005cm3 /g. The active site content in the negative electrode active material is appropriate, and it can react with the electrolyte to form an effective SEI film during the first cycle charging of the battery. Moreover, during the battery cycle, it is not easy to generate more active sites to react with the electrolyte to cause SEI growth and aggravated battery capacity decay. Applying the carbon negative electrode active material to the battery can effectively improve the long-term cycle performance and storage performance of the battery.

In the description of this specification, the descriptions with reference to the terms "one embodiment", "a specific embodiment", "another specific embodiment", "yet another specific embodiment", "some embodiments", "other embodiments", etc., mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment are included in at least one embodiment of the present disclosure. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples, unless they are contradictory. In addition, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated.

Although the embodiments of the present disclosure have been shown and described above, it is to be understood that the above embodiments are illustrative and are not to be construed as limitations of the present disclosure. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present disclosure.

Claims (16)

1. A carbon negative electrode active material, wherein the carbon negative electrode active material has a pore structure, an active specific surface area of the carbon negative electrode active material is 0.03 m ² /g-0.12 m ² /g, and a pore volume of the carbon negative electrode active material is greater than or equal to 0.005 cm ³ /g.
2. The carbon negative electrode active material according to claim 1, wherein the active specific surface area of the carbon negative electrode active material is 0.03 m ² /g-0.08 m ² /g.
3. The carbon negative electrode active material according to claim 1 or 2, wherein the pore volume of the carbon negative electrode active material is 0.005 cm ³ /g-0.1 cm ³ /g.
4. The carbon negative electrode active material according to any one of claims 1 to 3, wherein the carbon negative electrode active material contains one or more of micropores, mesopores or macropores.
5. The carbon negative electrode active material according to claim 4, wherein the volume content of the micropores is less than or equal to 10%, optionally less than or equal to 5%, based on the total volume of the pores in the carbon negative electrode active material; and/or

   Based on the total volume of the pores in the carbon negative electrode active material, the volume content of the mesopores is 60%-95%, and optionally 70%-90%; and/or,

   Based on the total volume of the pores in the carbon negative electrode active material, the volume content of the macropores is less than or equal to 25%, and can be optionally 5%-20%.
6. The carbon negative electrode active material according to any one of claims 1 to 5, wherein the carbon negative electrode active material satisfies at least one of the following conditions (1) to (3):

   (1) The specific surface area of the carbon negative electrode active material is 1.0 m ² /g-8.0 m ² /g, and can be 2 m ² /g-5 m ² /g;

   (2) The volume distribution particle size Dv50 of the carbon negative electrode active material is 5 μm-50 μm, and can be optionally 10 μm-30 μm;

   (3) The porosity of the carbon negative electrode active material is 20%-40%, and can be optionally 25%-35%.
7. The carbon negative electrode active material according to any one of claims 1 to 6, wherein the carbon negative electrode active material contains oxygen-containing functional groups, and the oxygen-containing functional groups include one or more of lactone, ether, phenol, carboxyl, anhydride and carbonyl.
8. A method for preparing the carbon negative electrode active material according to any one of claims 1 to 7, comprising:

   Providing carbon materials;

   oxidizing the carbon material using an oxidizing gas probe to obtain an intermediate carbon material;

   The intermediate carbon material is reduced by reducing gas to obtain a carbon negative electrode active material having a pore structure, an active specific surface area of the carbon negative electrode active material of 0.03m2 ^/ g- ^0.12m2 /g, and a pore volume of greater than or equal to ^0.005cm3 /g.
9. The method of claim 8, wherein the oxidizing gas probe comprises one or more of oxygen, air, chlorine, nitrogen oxide, sulfur trioxide and argon plasma.
10. The method according to claim 8 or 9, wherein the reducing gas comprises one or more of hydrogen, carbon monoxide, hydrogen sulfide, sulfur dioxide, ammonia, olefins and alkynes.
11. The method of claim 8, wherein the oxidizing gas probe comprises oxygen and the reducing gas comprises hydrogen;

    Alternatively, the oxidizing gas probe comprises air, and the reducing gas comprises carbon monoxide;

    Alternatively, the oxidizing gas probe comprises argon plasma and the reducing gas comprises ammonia.
12. The method according to any one of claims 8 to 11, wherein the temperature of the oxidation treatment is 300° C.-500° C., and/or the time of the oxidation treatment is 8 h-16 h.
13. The method according to any one of claims 8 to 12, wherein the temperature of the reduction treatment is 800° C.-1000° C., and/or the time of the reduction treatment is 6 h-15 h.
14. The method according to any one of claims 8 to 13, wherein the carbon material comprises one or more of natural graphite, artificial graphite, hard carbon, soft carbon, carbon fiber and mesophase carbon microbeads.
15. A secondary battery comprises a negative electrode plate, wherein the negative electrode plate comprises the carbon negative electrode active material according to any one of claims 1 to 7.
16. An electrical device, comprising the secondary battery according to claim 15.