Carbonaceous material, method for preparing same, and secondary battery and electric device comprising same

Abstract

The invention relates to a carbonaceous material and a preparation method thereof, and a secondary battery and an electric device containing the carbonaceous material, the adsorption rate v of the carbonaceous material is greater than or equal to 0.015 and less than or equal to 0.050 when the carbonaceous material is subjected to an adsorption test by using water vapor under the conditions of constant temperature and humidity of 25 DEG C and 40% RH, and the water vapor adsorption test is carried out under the following conditions: in a constant temperature and humidity chamber of 25 DEG C and 40% RH, the adsorption rate v is greater than or equal to 0.015 and less than or equal to 0.050; a carbonaceous material with the mass of m1 is placed in a container, the water vapor adsorption mass m2 and the water vapor adsorption time t when the carbonaceous material adsorbs water vapor to be balanced are recorded, the water vapor adsorption rate v is equal to m2 / (m1 * t), the measurement unit of m1 is g, the measurement unit of m2 is g, and the measurement unit of t is h. The carbonaceous material can give consideration to relatively high gram volume, relatively high first coulombic efficiency and relatively high structural stability.

Description

[0001] This application is a divisional application based on the invention with application number 202280095632.3, application date October 21, 2022, applicant CATL, and invention title "Carbon-based materials and their preparation methods, as well as secondary batteries and electrical devices containing the same". Technical Field

[0002] This application belongs to the field of battery technology, specifically relating to a carbonaceous material and its preparation method, as well as a secondary battery and electrical device containing the same. Background Technology

[0003] In recent years, rechargeable batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power, and solar power plants, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, and many other fields. With the application and promotion of rechargeable batteries, their energy density, lifespan, and rate performance have received increasing attention. Graphite is the most commonly used negative electrode active material in rechargeable batteries, but its theoretical specific capacity is only 372 mAh / g, limiting the potential for energy density improvement; at the same time, the small interlayer spacing of graphite also limits the improvement of rate performance. Hard carbon, as a novel negative electrode active material, can achieve rapid insertion and extraction of active ions during the charging and discharging process of rechargeable batteries, thus showing great development potential. However, hard carbon has low specific capacity and initial coulombic efficiency, limiting its contribution to improving the energy density, lifespan, and rate performance of rechargeable batteries. Summary of the Invention

[0004] The purpose of this application is to provide a carbonaceous material and its preparation method, as well as a secondary battery and an electrical device containing the same. The carbonaceous material can achieve a high specific capacity, a high initial coulombic efficiency, and a high structural stability, and enables the secondary battery to simultaneously have high energy density, long service life, and good rate performance.

[0005] The first aspect of this application provides a carbonaceous material, wherein the adsorption rate v of the carbonaceous material under constant temperature and humidity conditions of 25℃ and 40%RH satisfies 0.015 ≤ v ≤ 0.050 when subjected to water vapor adsorption test. The water vapor adsorption test is carried out under the following conditions: in a constant temperature and humidity chamber of 25℃ and 40%RH, the carbonaceous material of mass m1 is placed in a container, and the adsorption mass m2 of water vapor and the water vapor adsorption time t when the adsorption of water vapor by the carbonaceous material reaches equilibrium are recorded. Then the water vapor adsorption rate v = m2 / (m1×t), where the unit of measurement of m1 is g, the unit of measurement of m2 is g, and the unit of measurement of t is h.

[0006] Compared with currently commercially available carbonaceous materials, the carbonaceous material provided in this application can achieve a balance of high specific capacity, high initial coulombic efficiency, and high structural stability, and enables the secondary battery to simultaneously possess high energy density, long service life, and good rate performance. Although the mechanism is not yet clear, the inventors of this application speculate that one possible reason is that when the water vapor adsorption rate v is between 0.015 and 0.050, the carbonaceous material of this application has high structural stability and a unique pore structure, which facilitates the insertion, storage, and extraction of active ions. Therefore, the carbonaceous material of this application can achieve a balance of high specific capacity and initial coulombic efficiency, and enables the secondary battery to simultaneously possess high energy density, long service life, and good rate performance.

[0007] In any embodiment of this application, 0.020 ≤ v ≤ 0.050. This helps to further improve the specific capacity, initial coulombic efficiency, and structural stability of carbonaceous materials, and further improves the energy density, lifespan, and rate performance of secondary batteries.

[0008] In any embodiment of this application, the water vapor adsorption time t when the carbonaceous material reaches equilibrium is 1h-12h, and can be selected as 4.5h-7h. When the water vapor adsorption time when the carbonaceous material reaches equilibrium meets the above-mentioned specific range, it helps to further improve the specific capacity, initial coulombic efficiency and structural stability of the carbonaceous material, thereby further improving the energy density, service life and rate performance of the secondary battery.

[0009] In any embodiment of this application, the true density ρ of the carbonaceous material is 1.0 g / cm³. 3 -2.2g / cm 3 1.3g / cm³ is an optional value. 3 -1.7g / cm 3 When the true density of carbonaceous materials meets the specific range mentioned above, it helps to further improve the specific capacity and first coulombic efficiency of carbonaceous materials.

[0010] In any embodiment of this application, the carbonaceous material includes multiple nanoporous structures; optionally, the carbonaceous material includes multiple pore structures with pore sizes below 10 nm.

[0011] In any embodiment of this application, in the Raman spectrum of the carbonaceous material, I d / I g The value is 1.0-1.3, and can be selected as 1.05-1.15, I d This indicates that the Raman displacement is within 1350±50cm. -1 The d-peak intensity within the range, I g This indicates that the Raman displacement is within 1580±50cm. -1The g-peak intensity is within the specified range. At this point, carbonaceous materials exhibit higher specific capacity and higher initial coulombic efficiency, while also possessing good rate performance.

[0012] In any embodiment of this application, the interlayer spacing of the (002) crystal plane of the carbonaceous material is ≥0.37nm, and can be selected as 0.37nm-0.42nm.

[0013] In any embodiment of this application, in the X-ray diffraction spectrum of the carbonaceous material, the 2θ value corresponding to the (002) crystal plane peak is between 22° and 24°.

[0014] In any embodiment of this application, the volumetric particle size Dv50 of the carbonaceous material is 4μm-6μm.

[0015] In any embodiment of this application, the volumetric particle size Dv90 of the carbonaceous material is 8μm-16μm.

[0016] When the volumetric particle size Dv50 and / or Dv90 of carbonaceous materials are within a suitable range, it is beneficial to improve the active ion and electron transport performance, thereby further improving the rate performance of secondary batteries.

[0017] In any embodiment of this application, the specific surface area of ​​the carbonaceous material is 0.1 m². 2 / g-20m 2 / g, optional 1m 2 / g-20m 2 / g. When the specific surface area of ​​carbonaceous materials is within a suitable range, carbonaceous materials can simultaneously possess higher specific capacity and first coulombic efficiency, as well as better rate performance.

[0018] In any embodiment of this application, the compacted density of the carbonaceous material powder under a force of 50,000 N is 0.90 g / cm³. 3 -1.05g / cm 3 The option is 0.92g / cm³. 3 -1.02g / cm 3 When the compaction density of carbonaceous material powder is within a suitable range, the compaction density of the negative electrode sheet can be increased, thereby improving the energy density of the secondary battery.

[0019] In any embodiment of this application, the tap density of the carbonaceous material is 0.78 g / cm³. 3 -0.95g / cm 3 The option is 0.83g / cm³. 3 -0.93g / cm 3When the tap density of carbonaceous materials is within a suitable range, the tap density of the negative electrode sheet can be increased, thereby improving the energy density of the secondary battery.

[0020] The second aspect of this application provides a method for preparing a carbonaceous material, comprising the following steps: S10, providing a carbon source: the carbon source is a cellulose-based biomass material; S20, low-temperature pre-carbonization treatment: the carbon source is heated to a first temperature T1 at a first heating rate under a protective gas atmosphere and then held at that temperature for a first time t1 to obtain a first intermediate product; S30, high-temperature carbonization treatment: the obtained first intermediate product is heated to a second temperature T2 at a second heating rate under a protective gas atmosphere and then held at that temperature for a second time t2 to obtain a carbonaceous material, wherein the adsorption rate v of the carbonaceous material under constant temperature and humidity conditions of 25℃ and 40%RH, when subjected to an adsorption test using water vapor, satisfies 0.015 ≤ v ≤ 0.050, the water vapor adsorption test is carried out under the following conditions: in a constant temperature and humidity chamber at 25℃ and 40%RH, the carbonaceous material with a mass of m1 is placed in the container, and the water vapor adsorption mass m2 and the water vapor adsorption time t when the carbonaceous material reaches the water vapor adsorption equilibrium are recorded. Then the water vapor adsorption rate v = m2 / (m1×t), where the unit of measurement for m1 is g, the unit of measurement for m2 is g, and the unit of measurement for t is h.

[0021] The carbonaceous material obtained by the preparation method provided in this application can achieve a balance of high specific capacity, high initial coulombic efficiency, and high structural stability, thereby enabling secondary batteries to simultaneously possess high energy density, long service life, and good rate performance. Furthermore, compared with existing commercially available hard carbon, the carbonaceous material obtained by the preparation method of this application shows significant improvements in specific capacity, initial coulombic efficiency, and rate performance.

[0022] In any embodiment of this application, the cellulose content in the cellulosic biomass material is greater than 0 wt% and less than or equal to 100 wt%, and the ash content is 0 wt%-5 wt%.

[0023] In any embodiment of this application, the cellulose content in the cellulosic biomass material is greater than or equal to 20 wt% and less than 100 wt%, and the ash content is 0 wt%-5 wt%.

[0024] In any embodiment of this application, the cellulose content in the cellulosic biomass material is greater than 0 wt% and less than or equal to 100 wt%, and the ash content is 0 wt%-2 wt%.

[0025] In any embodiment of this application, the cellulose content in the cellulosic biomass material is greater than or equal to 20 wt% and less than 100 wt%, and the ash content is 0 wt%-2 wt%.

[0026] In any embodiment of this application, the hemicellulose content in the cellulosic biomass material is 0wt%-70wt%, and can be selected as 0wt%-30wt%.

[0027] In any embodiment of this application, the lignin content in the cellulosic biomass material is 0wt%-60wt%, and can be selected as 10wt%-60wt%.

[0028] By adjusting the content of one or more of cellulose, ash, hemicellulose and lignin in cellulosic biomass materials to meet the above range, it is helpful to obtain carbonaceous materials that have high specific capacity, high initial coulombic efficiency and high structural stability, thereby further improving the energy density, service life and rate performance of secondary batteries.

[0029] In any embodiment of this application, the cellulosic biomass material includes one or more woody biomass materials, which may be selected as one or more of hardwood, softwood and nut shells, and more preferably one or more of pine, bamboo and walnut shells.

[0030] In any embodiment of this application, the first heating rate is 1℃ / min-10℃ / min, and can be selected as 1℃ / min-3℃ / min.

[0031] In any embodiment of this application, the first temperature T1 is 150℃-1000℃, and can be selected as 300℃-700℃.

[0032] In any embodiment of this application, the first time t1 is 1h-20h, and can be selected as 5h-20h.

[0033] In S20, by adjusting one or more of the first heating rate, the first temperature, and the first time within the above range, it is beneficial to better control the carbon skeleton structure and surface, improve the effect of low-temperature pre-carbonization treatment, and obtain carbonaceous materials with a suitable water vapor adsorption rate.

[0034] In any embodiment of this application, the second heating rate is ≤10℃ / min, and can be selected as 0.5℃ / min-10℃ / min.

[0035] In any embodiment of this application, the second temperature T2 is 1000℃-1600℃, and can be selected as 1200℃-1500℃.

[0036] In any embodiment of this application, the second time t2 is 1h-12h, and can be 3h-10h.

[0037] In S30, by adjusting one or more of the second heating rate, the second temperature, and the second time to be within the above range, it is beneficial to improve the pore-closing effect of the pore structure, improve the high-temperature carbonization treatment effect, and obtain a carbonaceous material with a suitable water vapor adsorption rate.

[0038] In any embodiment of this application, t1+t2 is 10h-30h. This helps the obtained carbonaceous material to have a suitable water vapor adsorption rate, high capacity, high initial coulombic efficiency, and high structural stability.

[0039] In any embodiment of this application, the method after S20 and before S30 further includes the steps of: crushing the first intermediate product obtained in S20, or washing and removing impurities from the first intermediate product obtained in S20, or crushing the first intermediate product obtained in S20 followed by washing and removing impurities to obtain a first intermediate product with an ash content ≤0.01wt%. The washing and removing impurities process includes at least an acidic solution washing step and an alkaline solution washing step. This helps to further improve the specific capacity, initial coulombic efficiency, and structural stability of carbonaceous materials, while also helping to reduce the true density of carbonaceous materials.

[0040] In any embodiment of this application, the washing and impurity removal process sequentially includes the following steps: acidic solution washing, water washing, alkaline solution washing, water washing, and drying; or, the washing and impurity removal process sequentially includes the following steps: alkaline solution washing, water washing, acidic solution washing, water washing, and drying.

[0041] In any embodiment of this application, the H of the acidic solution + The concentration is 0.1 mol / L to 6 mol / L, and can be selected as 1 mol / L to 6 mol / L.

[0042] In any embodiment of this application, the washing temperature of the acidic solution is 10℃-95℃, and can be selected as 30℃-95℃.

[0043] In any embodiment of this application, the washing time of the acidic solution is 1h-24h, and can be selected as 10h-24h.

[0044] In any embodiment of this application, the solute of the acidic solution includes one or more of hydrochloric acid, nitric acid, sulfuric acid and perchloric acid, and the solvent includes water.

[0045] By adjusting the H+ of the acidic solution + When one or more of the following factors—concentration, washing temperature, washing time, and type of solute—are within the above range, it is beneficial to achieve thorough washing and better remove metal impurities.

[0046] In any embodiment of this application, the OH- of the alkaline solution - The concentration is 0.1 mol / L to 6 mol / L, and can be selected as 1 mol / L to 6 mol / L.

[0047] In any embodiment of this application, the washing temperature of the alkaline solution is 10℃-95℃, and can be selected as 30℃-95℃.

[0048] In any embodiment of this application, the washing time of the alkaline solution is 1h-24h, and can be selected as 10h-24h.

[0049] In any embodiment of this application, the solute of the alkaline solution includes NaOH, KOH, or a combination thereof, and the solvent includes water.

[0050] By adjusting the OH- of the alkaline solution - When one or more of the following factors—concentration, washing temperature, washing time, and type of solute—are within the above range, it is beneficial to achieve thorough washing.

[0051] A third aspect of this application provides a secondary battery comprising a negative electrode, wherein the negative electrode comprises the carbonaceous material of the first aspect of this application or the carbonaceous material prepared by the method of the second aspect of this application.

[0052] The fourth aspect of this application provides an electrical device that includes the secondary battery of the third aspect of this application.

[0053] This application provides carbonaceous materials that can achieve a balance of high specific capacity, high initial coulombic efficiency, and high structural stability, thereby enabling secondary batteries to simultaneously possess high energy density, long service life, and good rate performance. The electrical devices of this application include the secondary batteries provided herein and therefore possess at least the same advantages as those secondary batteries. Attached Figure Description

[0054] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments of this application will be briefly described below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0055] Figure 1 This is a schematic diagram of one embodiment of the battery cell of this application.

[0056] Figure 2 This is an exploded view of one embodiment of the battery cell of this application.

[0057] Figure 3 This is a schematic diagram of one embodiment of the battery module of this application.

[0058] Figure 4 This is a schematic diagram of one embodiment of the battery pack of this application.

[0059] Figure 5 yes Figure 4 An exploded view of an embodiment of the battery pack shown.

[0060] Figure 6 This is a schematic diagram of one embodiment of an electrical device that uses a secondary battery as a power source, as described in this application.

[0061] Figures 7 to 9 These are scanning electron microscope images of the carbonaceous material provided in this application at different magnifications.

[0062] The accompanying drawings are not necessarily drawn to scale. The reference numerals are explained as follows: 1 Battery pack, 2 Upper casing, 3 Lower casing, 4 Battery module, 5 Individual battery cell, 51 Housing, 52 Electrode assembly, 53 Cover plate. Detailed Implementation

[0063] The carbonaceous material and its preparation method, as well as embodiments of secondary batteries and power-consuming devices containing the same, are disclosed in detail below with appropriate reference to the accompanying drawings. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0064] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0065] Unless otherwise specified, all embodiments and optional embodiments of this application may be combined with each other to form new technical solutions, and such technical solutions should be considered to be included in the disclosure of this application.

[0066] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions, and such technical solutions shall be deemed to be included in the disclosure of this application.

[0067] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0068] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0069] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0070] Unless otherwise specified, the terms used in this application have the common meanings as commonly understood by those skilled in the art.

[0071] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be determined using various testing methods commonly used in the art, for example, according to the testing methods given in this application.

[0072] Unless otherwise specified, in this application, the term "active ion" refers to ions that can be inserted and extracted back and forth between the positive and negative electrodes of a secondary battery, including but not limited to lithium ions, sodium ions, etc.

[0073] In this application, the terms "multiple" or "various" refer to two or more kinds of things.

[0074] According to the International Union of Pure and Applied Chemistry (IUPAC), micropores are pores with a diameter < 2 nm, mesopores are pores with a diameter between 2 nm and 50 nm, and macropores are pores with a diameter > 50 nm.

[0075] In the context of this application, the term "micropore" refers to a pore with a diameter < 2 nm; the term "mesopore" refers to a pore with a diameter of 2 nm to 50 nm; and the term "macropore" refers to a pore with a diameter > 50 nm.

[0076] In the context of this application, the term "small mesopore" refers to a pore with a diameter of 2nm-10nm, and the term "large mesopore" refers to a pore with a diameter greater than 10nm and less than or equal to 50nm.

[0077] In the context of this application, the term "capillary" refers to micropores and / or small mesopores, i.e., pores with a diameter ≤ 10 nm.

[0078] In the context of this application, the terms "larger hole" and "smaller hole" are relative concepts.

[0079] With the application and promotion of rechargeable batteries, their energy density, lifespan, and rate performance have received increasing attention. The performance of the negative electrode active material largely determines the energy density, lifespan, and safety of the rechargeable battery. Graphite (including natural and artificial graphite) is the most commonly used negative electrode active material in rechargeable batteries, but its theoretical specific capacity is only 372 mAh / g, leaving very limited room for energy density improvement. At the same time, the small interlayer spacing of graphite also limits the improvement of rate performance, making it unable to meet the actual needs of high-rate rechargeable batteries.

[0080] Compared to graphite, hard carbon has a larger interlayer spacing, which facilitates the rapid insertion and extraction of active ions. This results in superior low-temperature performance, power performance, and safety performance in rechargeable batteries, giving hard carbon a unique advantage, especially in the field of power batteries. However, most commercially available hard carbon batteries are currently low-capacity types, with low capacity and initial coulombic efficiency. For example, the capacity is typically between 200 mAh / g and 280 mAh / g, and the initial coulombic efficiency is usually below 75%, which severely limits their practical applications.

[0081] Therefore, how to simultaneously improve the specific capacity and first coulombic efficiency of hard carbon remains a pressing technical challenge.

[0082] In view of this, the first aspect of the present application provides a carbonaceous material that combines high specific capacity, high initial coulombic efficiency and high structural stability, and enables secondary batteries to simultaneously have high energy density, long service life and good rate performance.

[0083] carbonaceous materials The adsorption rate v of the carbonaceous material provided in this application, when subjected to adsorption tests using water vapor under constant temperature and humidity conditions of 25℃ and 40%RH, satisfies 0.015 ≤ v ≤ 0.050.

[0084] The water vapor adsorption test was conducted under the following conditions: In a constant temperature and humidity chamber at 25℃ and 40%RH, a mass of the carbonaceous material (m1) was placed in a container. The adsorbed water vapor mass (m2) and adsorption time (t) when the carbonaceous material reached equilibrium were recorded. The water vapor adsorption rate v = m2 / (m1×t), where m1 and m2 are measured in grams (g), and t is measured in hours (h). The thickness of the carbonaceous material in the container was ≤5mm.

[0085] In the water vapor adsorption test, when the total mass of the carbonaceous material after adsorbing water vapor no longer increases, it is considered that the adsorption of water vapor by the carbonaceous material has reached equilibrium. The test time at this time is recorded as the water vapor adsorption time t. The water vapor adsorption mass m2 (i.e., the mass increase when the adsorption of water vapor by the carbonaceous material reaches equilibrium) is obtained by subtracting the initial mass m1 of the carbonaceous material from the total mass obtained at this time.

[0086] RH (Relative Humidity) refers to the percentage of the partial pressure of water vapor in the air to the saturated vapor pressure of water at the same temperature.

[0087] Compared with currently commercially available carbonaceous materials, the carbonaceous material provided in this application can achieve a balance of high specific capacity, high initial coulombic efficiency, and high structural stability, and enables the secondary battery to simultaneously possess high energy density, long service life, and good rate performance. Although the mechanism is not yet clear, the inventors of this application speculate that one possible reason is that when the water vapor adsorption rate v is between 0.015 and 0.050, the carbonaceous material of this application has high structural stability and a unique pore structure, which facilitates the insertion, storage, and extraction of active ions. Therefore, the carbonaceous material of this application can achieve a balance of high specific capacity and initial coulombic efficiency, and enables the secondary battery to simultaneously possess high energy density, long service life, and good rate performance.

[0088] During the research process, the inventors of this application discovered that under constant temperature and humidity conditions of 25°C and 40%RH, water vapor preferentially adsorbs into the capillary structure (i.e., microporous structure and / or small mesoporous structure) of carbonaceous materials, and usually does not enter the large mesoporous structure and / or macroporous structure of carbonaceous materials. Therefore, the water vapor adsorption rate v under constant temperature and humidity conditions of 25°C and 40%RH can intuitively reflect the content of sites suitable for active ion storage in carbonaceous materials.

[0089] When the water vapor adsorption rate v is less than 0.015, it is considered that the carbonaceous material contains very few capillary structures, and the pore structures are mostly mesoporous and / or macroporous. Therefore, the carbonaceous material has poor structural stability and contains very little space to accommodate active ions, making it unsuitable for the storage of active ions. Consequently, the specific capacity of the carbonaceous material is also low. In addition, since the pore structures are mostly mesoporous and / or macroporous, the proportion of the electrolyte wetting area inside the carbonaceous material increases, the consumption of active ions during the formation of the solid electrolyte interphase (SEI) film increases, the first irreversible capacity loss increases, and thus the specific capacity and first coulombic efficiency of the carbonaceous material are both low.

[0090] When the water vapor adsorption rate v is greater than 0.050, the specific surface area of ​​the carbonaceous material is considered to be relatively high. This leads to increased consumption of active ions during SEI film formation, increased initial irreversible capacity loss, and decreased initial coulombic efficiency. Furthermore, carbonaceous materials are highly hygroscopic. During the preparation and use of the secondary battery, some water molecules will be strongly bonded to the functional groups (e.g., oxygen-containing functional groups) on the surface of the carbonaceous material. These water molecules are difficult to remove, thus clogging the capillary structure of the carbonaceous material and hindering the insertion and extraction of active ions. Simultaneously, the water molecules adsorbed on the surface of the carbonaceous material may also react with the electrolyte, further reducing both the specific capacity and initial coulombic efficiency of the carbonaceous material.

[0091] In some embodiments, v can be 0.016, 0.018, 0.020, 0.022, 0.024, 0.026, 0.028, 0.030, 0.032, 0.034, 0.036, 0.038, 0.040, 0.042, 0.044, 0.046, 0.048, 0.050, or any range of values ​​within the above ranges. Optionally, 0.018 ≤ v ≤ 0.050, 0.020 ≤ v ≤ 0.050. This helps to further improve the specific capacity, initial coulombic efficiency, and structural stability of carbonaceous materials, and further improves the energy density, lifespan, and rate performance of secondary batteries.

[0092] In some embodiments, the water vapor adsorption time t when the carbonaceous material reaches equilibrium with adsorbed water vapor is 1h-12h. Optionally, the water vapor adsorption time t when the carbonaceous material reaches equilibrium with adsorbed water vapor is 3h-12h, 4h-12h, 4h-9h, or 4.5h-7h. Further research by the inventors has revealed that when the water vapor adsorption time when the carbonaceous material reaches equilibrium with adsorbed water vapor meets the above-mentioned specific ranges, it helps to further improve the specific capacity, initial coulombic efficiency, and structural stability of the carbonaceous material, thereby further improving the energy density, lifespan, and rate performance of the secondary battery.

[0093] When the water vapor adsorption time is long, it is believed that the carbonaceous material contains a large number of capillary structures. At this time, the framework structure of the carbonaceous material is relatively fragile and is prone to collapse to form larger pores. This leads to an increase in the proportion of the electrolyte wetting area inside the carbonaceous material, an increase in the initial irreversible capacity loss, and a decrease in the initial coulombic efficiency. When the water vapor adsorption time is short, it is believed that the carbonaceous material contains fewer capillary structures, which is not suitable for the insertion, storage, and extraction of active ions. This also leads to a decrease in the specific capacity and initial coulombic efficiency of the carbonaceous material.

[0094] In some embodiments, the carbonaceous material comprises multiple nanoporous structures. Optionally, the carbonaceous material comprises multiple pore structures with pore sizes less than 10 nm. In some embodiments, the carbonaceous material may further comprise one or more pore structures with pore sizes greater than 10 nm.

[0095] In some embodiments, the true density ρ of the carbonaceous material is 1.0 g / cm³. 3 -2.2g / cm 3 1.3g / cm³ is an optional value. 3 -2.0g / cm 3 1.3g / cm 3 -1.7g / cm 3 1.3g / cm 3 -1.65g / cm 3 1.3g / cm 3 -1.6g / cm 3 1.3g / cm 3 -1.55g / cm 3 Further research by the inventors revealed that when the true density of carbonaceous materials meets the aforementioned specific range, it helps to further improve the specific capacity and first coulombic efficiency of carbonaceous materials.

[0096] When the true density of carbonaceous materials is low, it is assumed that the carbonaceous material has abundant capillary structures and good pore-closing effect. In this case, the space into which the calibration liquid (e.g., n-butanol) enters is less than the actual pore space of the carbonaceous material. These unentered pore structures can store active ions. At the same time, the electrolyte does not easily penetrate into the interior of the carbonaceous material particles, thus reducing the consumption of active ions during SEI film formation. On the other hand, the true density of carbonaceous materials should not be too low, as the excellent pore-closing effect may prevent active ions from being easily embedded. When the true density of carbonaceous materials is high, the calibration liquid (e.g., n-butanol) easily wets the interior of the particles. In this case, the carbonaceous material has poor pore-closing effect and abundant mesoporous and / or macroporous structures. This leads to the capillary structures being easily exposed to the electrolyte, resulting in a reduction in the active ion storage space, and consequently, a decrease in the specific capacity and initial coulombic efficiency of the carbonaceous material.

[0097] In this application, the true density of carbonaceous materials has a meaning known in the art and can be determined using instruments and methods known in the art. For example, the Archimedes impregnation volume displacement method can be used for testing, and n-butanol can be used as the calibration liquid. A powder true density meter can be used as the testing instrument.

[0098] In some embodiments, the carbonaceous material may have a regular or irregular morphology; for example, the morphology of the carbonaceous material may be an irregular polygonal shape.

[0099] In some embodiments, the carbon content in the carbonaceous material may be 95wt%-98wt%.

[0100] In some embodiments, the oxygen content in the carbonaceous material may be 1wt%-5wt%.

[0101] In some embodiments, the H content in the carbonaceous material may be <0.4wt%.

[0102] In some embodiments, the nitrogen content in the carbonaceous material may be <2wt%.

[0103] In some embodiments, the total content of C, O, H and N elements in the carbonaceous material may be 99wt%-99.5wt%.

[0104] In some embodiments, the carbonaceous material contains a small amount of impurity elements, which mainly include S, K, Ca, and Fe. The content of S can be <0.0021wt%, the content of K can be <0.0019wt%, the content of Ca can be <0.0011wt%, and the content of Fe can be <0.0010wt%.

[0105] In some embodiments, in the Raman spectrum of the carbonaceous material, I d / I g The value is 1.0-1.3, I d This indicates that the Raman displacement is within 1350±50cm. -1 The d-peak intensity within the range, I g This indicates that the Raman displacement is within 1580±50cm. -1 The intensity of the g peak within the range. For example, I d / I g It can be a range consisting of any values ​​of 1.0, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, or higher. Optionally, I d / I g It can be 1.05-1.15.

[0106] The Raman spectra of carbonaceous materials can be measured using a Raman spectrometer. During the test, the d-peak and g-peak intensities at 100 points are acquired, and the Ig at these 100 points is calculated. d / I g Remove the largest and smallest 30 I's. d / I g 40 I's remaining d / I g The average value is used as the I of carbonaceous materials d / I gThe testing instrument can be a Horiba LabRAM HR800 Raman spectrometer. The testing conditions can be: excitation wavelength 532 nm, grating 600 lines, objective lens 50x, integration time 10 s, cumulative count 3, area scan.

[0107] The d-peak originates from lattice defects in carbon atoms, while the g-peak originates from in-plane vibrations of sp2 carbon atoms. In carbonaceous materials, the intensity of the d-peak is related to the number of defects in the structure, and the intensity of the g-peak is related to the number of graphite crystallites. Therefore, I d / I g It can characterize the degree of order in the structure of carbonaceous materials. d / I g The smaller the value, the higher the orderliness of the carbonaceous material structure, the higher the integrity of the carbon plane, and the higher the initial coulombic efficiency of the carbonaceous material, but the specific capacity decreases and the rate performance deteriorates. The carbonaceous material of this application satisfies I... d / I g The value is 1.0-1.3. At this value, the degree of order in the carbonaceous material structure is moderate, which results in higher specific capacity and higher initial coulombic efficiency, as well as good rate performance.

[0108] In some embodiments, the interlayer spacing of the (002) crystal plane of the carbonaceous material is ≥0.37nm, and can be selected as 0.37nm-0.42nm.

[0109] In some embodiments, in the X-ray diffraction spectrum of the carbonaceous material, the 2θ value corresponding to the (002) crystal plane peak is between 22° and 24°.

[0110] In this application, the interlayer spacing of the (002) crystal plane of the carbonaceous material can be measured using an X-ray diffractometer, referring to JIS K 0131-1996 and JB / T4220-2011. The measuring instrument can be a Bruker D8 Discover X-ray diffractometer.

[0111] In some embodiments, the volumetric particle size Dv50 of the carbonaceous material can be 4μm-6μm.

[0112] In some embodiments, the volumetric particle size Dv90 of the carbonaceous material can be 8 μm-16 μm.

[0113] In some embodiments, the carbonaceous material simultaneously satisfies a volumetric particle size Dv50 of 4 μm-6 μm and a volumetric particle size Dv90 of 8 μm-16 μm.

[0114] When the volumetric particle size Dv50 and / or Dv90 of carbonaceous materials are within a suitable range, it is beneficial to improve the active ion and electron transport performance, thereby further improving the rate performance of secondary batteries.

[0115] In this application, the volumetric particle sizes Dv50 and Dv90 of carbonaceous materials have meanings known in the art, representing the particle size corresponding to a cumulative volumetric distribution percentage of 50% and 90%, respectively, and can be determined using instruments and methods known in the art. For example, they can be conveniently determined using a laser particle size analyzer, referring to GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method. The testing instrument can be a Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK.

[0116] In some embodiments, the specific surface area of ​​the carbonaceous material is 0.1 m². 2 / g-20m 2 / g, optional 1m 2 / g-20m 2 / g. When the specific surface area of ​​carbonaceous materials is within a suitable range, they can simultaneously exhibit higher specific capacity and initial coulombic efficiency, as well as better rate performance. Furthermore, when the specific surface area of ​​carbonaceous materials is within a suitable range, the carbonaceous materials and binders also possess strong bonding forces, thereby improving the cohesion and adhesion of the negative electrode sheet, reducing the volume expansion of the negative electrode sheet during cycling, and resulting in better cycle performance of the secondary battery.

[0117] In this application, the specific surface area of ​​carbonaceous materials has a meaning known in the art and can be measured using instruments and methods known in the art. For example, it can be measured using the nitrogen adsorption specific surface area analysis method according to GB / T 19587-2017 and calculated using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis can be performed using the ASAP 3020 surface area and pore size analyzer from Micromeritics, Inc., USA.

[0118] In some embodiments, the compacted density of the carbonaceous material powder under a force of 50,000 N is 0.90 g / cm³. 3 -1.05g / cm 3 The option is 0.92g / cm³. 3 -1.02g / cm 3 When the compaction density of carbonaceous material powder is within a suitable range, the compaction density of the negative electrode sheet can be increased, thereby improving the energy density of the secondary battery.

[0119] In this application, the compacted density of carbonaceous material powder has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using an electronic pressure testing machine (e.g., a UTM7305 model) in accordance with standard GB / T24533-2009. An exemplary test method is as follows: Weigh 1g of carbonaceous material powder and add it to a container with a bottom area of ​​1.327cm². 2 In the mold, the pressure is increased to 5000 kg (equivalent to 50000 N), held for 30 seconds, then depressurized and held for 10 seconds. The compaction density of the carbonaceous material powder under a force of 50000 N is then recorded and calculated.

[0120] In some embodiments, the tap density of the carbonaceous material is 0.78 g / cm³. 3 -0.95g / cm 3 The option is 0.83g / cm³. 3 -0.93g / cm 3 When the tap density of carbonaceous materials is within a suitable range, the tap density of the negative electrode sheet can be increased, thereby improving the energy density of the secondary battery.

[0121] In this application, the tap density of carbonaceous materials has a meaning known in the art and can be determined using instruments and methods known in the art. For example, it can be determined using a powder tap density tester according to GB / T 5162-2006. The testing instrument can be the Dandong Baite BT-301.

[0122] Preparation methods of carbonaceous materials The second aspect of this application provides a method for preparing a carbonaceous material, comprising the following steps: S10, providing a carbon source: the carbon source is a cellulose-based biomass material; S20, low-temperature pre-carbonization treatment: the carbon source is heated to a first temperature T1 at a first heating rate under a protective gas atmosphere and then held at that temperature for a first time t1 to obtain a first intermediate product; S30, high-temperature carbonization treatment: the obtained first intermediate product is heated to a second temperature T2 at a second heating rate under a protective gas atmosphere and then held at that temperature for a second time t2 to obtain a carbonaceous material, wherein the adsorption rate v of the carbonaceous material under constant temperature and humidity conditions of 25°C and 40%RH, when subjected to adsorption testing with water vapor, satisfies 0.015 ≤ v ≤ 0.050.

[0123] The water vapor adsorption test was conducted under the following conditions: In a constant temperature and humidity chamber at 25℃ and 40%RH, a mass of the carbonaceous material with a mass of m1 was placed in the container, and the mass of water vapor adsorbed, m2, and the water vapor adsorption time, t, were recorded when the carbonaceous material reached equilibrium. Then, the water vapor adsorption rate v = m2 / (m1×t), where the unit of measurement for m1 is g, the unit of measurement for m2 is g, and the unit of measurement for t is h.

[0124] This application uses cellulosic biomass materials as a carbon source to prepare carbonaceous materials. Cellulose is a highly crystalline chain-like macromolecular organic compound among biomass materials. On the one hand, it has high thermal stability and a wide range of adjustable pyrolysis process parameters. On the other hand, the pore structure formed during the conversion of chain-like macromolecular organic compounds into carbonaceous materials is highly controllable, enabling it to have a suitable water vapor adsorption rate and also helping to improve the platform capacity. When cellulosic biomass materials are not used as the carbon source or the biomass materials used do not contain cellulose, the controllability of the pore structure of the carbonaceous materials prepared from them is poor, and the content of capillary structure is low, resulting in a low water vapor adsorption rate. In some embodiments, the cellulose content in the cellulosic biomass material can be greater than 0 wt% and less than or equal to 100 wt%, optionally 10 wt%-100 wt%, 20 wt%-100 wt%, 30 wt%-100 wt%, or 40 wt%-100 wt%. This is beneficial for increasing the controllability of the pore structure of the carbonaceous material and enabling it to have a suitable water vapor adsorption rate.

[0125] The preparation process of carbonaceous materials includes at least a low-temperature pre-carbonization treatment and a high-temperature carbonization treatment. Low-temperature pre-carbonization can regulate the structural and surface properties of the carbon skeleton and appropriately increase carbon yield; it also reduces the toughness of cellulosic biomass materials, facilitating subsequent crushing and washing processes. High-temperature carbonization can create a closed-pore effect on the biochar obtained from low-temperature pre-carbonization, thereby reducing the contact area between the carbonaceous material and the electrolyte, thus reducing the consumption of active ions during SEI film formation and improving the initial coulombic efficiency of the carbonaceous material. High-temperature carbonization can also cause aromatic cyclization of the biochar obtained from low-temperature pre-carbonization, thereby improving the order and conductivity of the carbonaceous material, while removing excess O and H elements from the carbon skeleton structure and contributing to the formation of an ordered pseudographite microcrystalline structure.

[0126] Therefore, the carbonaceous material obtained by the preparation method provided in this application can achieve a balance of high specific capacity, high initial coulombic efficiency, and high structural stability, thereby enabling secondary batteries to simultaneously possess high energy density, long service life, and good rate performance. Furthermore, compared to existing commercially available hard carbon, the carbonaceous material obtained by the preparation method of this application shows significant improvements in specific capacity, initial coulombic efficiency, and rate performance.

[0127] The inventors also discovered in their research that cellulosic biomass materials require a low ash content. Ash not only catalyzes reactions during low-temperature pre-carbonization, consuming carbon and reducing active ion storage sites, but also increases the complexity and production cost of the washing and impurity removal process. Furthermore, during subsequent high-temperature carbonization, metallic impurities in the ash are reduced to elemental metals and then agglomerate. This agglomeration of elemental metals leads to the collapse of the carbon skeleton structure, especially the capillary structure, resulting in a reduction in the active ion storage space and capacity of the obtained carbonaceous material, manifested as a low water vapor adsorption rate. Simultaneously, the metallic impurities also possess catalytic activity, intensifying the decomposition of the carbon skeleton structure during pyrolysis, causing the pore structure to tend towards larger mesoporous and / or macroporous structures. This results in poor carbon skeleton stability and an increased proportion of the electrolyte wetting area within the obtained carbonaceous material, leading to increased consumption of active ions during SEI film formation and increased initial irreversible capacity loss. Therefore, the initial coulombic efficiency of the carbonaceous material decreases. In some embodiments, the ash content in the cellulosic biomass material may be 0wt%-5wt%, optionally 0wt%-4wt%, 0wt%-3wt%, 0wt%-2wt%, or 0wt%-1wt%. This can reduce the adverse effects of impurities on carbonaceous materials, improve the specific capacity, initial coulombic efficiency, and structural stability of carbonaceous materials, and also help to reduce the true density of carbonaceous materials.

[0128] In some embodiments, optionally, the cellulose content in the cellulosic biomass material is greater than 0 wt% and less than or equal to 100 wt%, and the ash content is 0 wt%-5 wt%.

[0129] Cellulose biomass materials may also include hemicellulose. Hemicellulose is an amorphous polymer with a relatively small molecular weight in biomass materials. During low-temperature pre-carbonization, it easily decomposes into small-molecule sugars and volatilizes, which is beneficial for forming a porous structure. However, its content should not be too high. When it exceeds 70 wt%, it will result in poor stability of the carbon skeleton structure, poor pore-closing effect, increased content of macroporous and / or macroporous structures in the carbonaceous material, increased proportion of electrolyte wetting area inside the carbonaceous material, increased initial irreversible capacity loss, and decreased initial coulombic efficiency. In some embodiments, the hemicellulose content in the cellulose biomass material can be 0 wt%-70 wt%, optionally 0 wt%-60 wt%, 0 wt%-50 wt%, 0 wt%-40 wt%, 0 wt%-30 wt%, or 0 wt%-20 wt%.

[0130] Cellulose biomass materials may also contain lignin. Lignin is a large organic molecule containing benzene rings and with a high degree of cross-linking. During low-temperature pre-carbonization treatment, it helps to form a six-membered carbon ring, which helps to improve the stability of the carbon skeleton structure, thus benefiting the rate performance of secondary batteries. However, the controllability of the pore structure formed by lignin is poor. Therefore, when its content is too high, for example, greater than 60 wt%, the capacity improvement space of the obtained carbonaceous material platform will be limited. In some embodiments, the lignin content in the cellulose biomass material is 0 wt%-60 wt%, optionally 5 wt%-60 wt%, 10 wt%-60 wt%, 10 wt%-50 wt%, or 15 wt%-50 wt%.

[0131] In some embodiments, the cellulose biomass material contains cellulose with a content greater than 0 wt% and less than or equal to 100 wt%, hemicellulose with a content of 0 wt%-70 wt%, lignin with a content of 0 wt%-60 wt%, and ash with a content of 0 wt%-5 wt%. Optionally, the cellulose biomass material contains cellulose with a content greater than or equal to 20 wt% and less than 100 wt%, hemicellulose with a content of 0 wt%-30 wt%, lignin with a content of 10 wt%-60 wt%, and ash with a content of 0 wt%-2 wt%. This helps the obtained carbonaceous material to better balance higher specific capacity, higher initial coulombic efficiency, and higher structural stability, thereby further improving the energy density, lifespan, and rate performance of the secondary battery.

[0132] In some embodiments, the cellulose content in the cellulosic biomass material can be 100 wt%, meaning that the cellulosic biomass material can directly use cellulose as a carbon source. This helps to obtain carbonaceous materials with high capacity, but the stability of the carbon skeleton structure formed during the preparation process is slightly reduced, resulting in a slight decrease in the improvement effect on the rate performance of secondary batteries.

[0133] In this application, the cellulose content can be detected using an acid hydrolysis anthrone colorimetric method. Cellulose can be hydrolyzed to β-D-glucose under acidic conditions. β-D-glucose dehydrates in a strongly acidic environment to form β-furfural compounds, which then dehydrate and condense with anthrone to form a blue-green furfural derivative. The product has a characteristic absorption peak at 620 nm, and the cellulose content can be quantitatively detected by observing the change in absorbance. For example, the acid can be sulfuric acid.

[0134] In this application, the hemicellulose content can be detected using the DNS colorimetric method. Hemicellulose is converted into reducing sugars after acid treatment. These reducing sugars react with DNS to produce a reddish-brown substance. The product exhibits a characteristic absorption peak at 540 nm, and the hemicellulose content can be quantitatively detected by observing changes in absorbance.

[0135] In this application, the lignin content can be detected using the acetylation method. After the phenolic hydroxyl groups in lignin undergo acetylation, acetylated lignin is formed. The product has a characteristic absorption peak at 280 nm, and the lignin content can be quantitatively detected by observing changes in absorbance.

[0136] In this application, the ash content can be determined in accordance with GB / T 28731-2012.

[0137] In some embodiments, the cellulosic biomass material includes one or more woody biomass materials that meet the above requirements of this application, and may be selected as one or more of hardwood, softwood and nut shells, such as one or more of pine, bamboo and walnut shells.

[0138] In some embodiments, the preparation method further includes the step of pretreating the cellulosic biomass material. The pretreatment process may include crushing, washing, and drying steps. Crushing the cellulosic biomass material facilitates the filling process. Washing removes impurities that are clearly attached to the surface of the cellulosic biomass material, preventing them from affecting subsequent low-temperature pre-carbonization treatment processes. Drying removes moisture attached to the surface of the cellulosic biomass material and some bulk moisture, thereby reducing the impact of moisture on subsequent low-temperature pre-carbonization treatment processes.

[0139] In some embodiments, the first heating rate is ≤10℃ / min, and can be selected as 1℃ / min-10℃ / min, 1℃ / min-5℃ / min, or 1℃ / min-3℃ / min. When the first heating rate is within a suitable range, it helps the obtained carbonaceous material to have a suitable water vapor adsorption rate, exhibiting high capacity, high initial coulombic efficiency, and high structural stability. If the first heating rate is too high, the controllability of the pore structure of the prepared carbonaceous material is poor, and the content of capillary structures is low, resulting in a lower water vapor adsorption rate.

[0140] In some embodiments, the first temperature T1 is 150°C-1000°C. For example, the first temperature T1 can be a range of 200°C, 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C, 1000°C, or any value above. Optionally, the first temperature T1 is 200°C-900°C, 300°C-700°C, or 300°C-600°C. When the first temperature is within a suitable range, it helps the obtained carbonaceous material to have a suitable water vapor adsorption rate, high capacity, high initial coulombic efficiency, and high structural stability. As the initial temperature increases, the pore structure forms more fully, and the content of capillary structures increases. However, when the initial temperature is too high, the volatile matter volatilization rate accelerates, the size of the formed pore structure increases, the stability of the carbon skeleton structure deteriorates, and it also leads to poor pore-closing effect during the high-temperature carbonization process. The content of mesoporous and / or macroporous structures in carbonaceous materials increases, the proportion of electrolyte wetting area inside carbonaceous materials increases, the initial irreversible capacity loss increases, the initial coulombic efficiency decreases, and the content of capillary structures in carbonaceous materials decreases, resulting in a lower water vapor adsorption rate.

[0141] In some embodiments, the first time t1 is 1h-20h, and can be selected as 5h-20h. Those skilled in the art can select a suitable first time within the above range according to the first temperature and the first heating rate used. For example, when the first temperature is high and / or the first heating rate is low, the first time can be appropriately shortened.

[0142] In S20, by adjusting one or more of the first heating rate, the first temperature, and the first time within the above range, it is beneficial to better control the carbon skeleton structure and surface, improve the effect of low-temperature pre-carbonization treatment, and obtain carbonaceous materials with a suitable water vapor adsorption rate.

[0143] In some embodiments, the second heating rate is ≤10℃ / min, and can be selected as 0.5℃ / min-10℃ / min. However, this application is not limited to this, and the second heating rate can be adjusted according to actual conditions.

[0144] In some embodiments, the second temperature T2 is 1000℃-1600℃, for example, it can be a range of 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, 1300℃, 1350℃, 1400℃, 1450℃, 1500℃, 1550℃, 1600℃ or any value above. Optionally, the second temperature T2 is 1200℃-1500℃. When the second temperature is within a suitable range, it helps the obtained carbonaceous material to have a suitable water vapor adsorption rate, high capacity and high initial coulombic efficiency. At lower temperatures, the carbonaceous material surface has more oxygen-containing functional groups, which are more hydrophilic. This results in a faster water vapor adsorption rate and shorter adsorption time. However, the pore-closing effect is poor, and there are more mesoporous and / or macroporous structures in the carbonaceous material. This leads to an increase in the proportion of the electrolyte wetting area inside the carbonaceous material, an increase in the initial irreversible capacity loss, and a decrease in the initial coulombic efficiency. At higher temperatures, the pore-closing effect improves, thereby reducing the consumption of active ions during SEI film formation and increasing the number of active ion storage sites in the carbonaceous material, which can also increase its capacity and initial coulombic efficiency. However, at excessively high temperatures, the microstructure of the carbonaceous material undergoes a qualitative change, which is detrimental to active ion storage, resulting in a decreased water vapor adsorption rate.

[0145] In some embodiments, the second time t2 is 1h-12h, and can be selected as 3h-10h. Those skilled in the art can select a suitable first time within the above range according to the second temperature and the second heating rate used. For example, when the second temperature is high and / or the second heating rate is low, the second time can be appropriately shortened.

[0146] In S30, by adjusting one or more of the second heating rate, the second temperature, and the second time to be within the above range, it is beneficial to improve the pore-closing effect of the pore structure, improve the high-temperature carbonization treatment effect, and obtain a carbonaceous material with a suitable water vapor adsorption rate.

[0147] In some embodiments, t1+t2 is 10h-30h. This helps the obtained carbonaceous material to have a suitable water vapor adsorption rate, high capacity, high initial coulombic efficiency, and high structural stability.

[0148] In some embodiments, after S20 and before S30, the process further includes the following steps: crushing the first intermediate product obtained in S20, or washing and removing impurities from the first intermediate product obtained in S20, or crushing the first intermediate product obtained in S20 followed by washing and removing impurities to obtain a first intermediate product with an ash content ≤0.01wt%. The washing and removing impurities process includes at least an acidic solution washing step and an alkaline solution washing step. This helps to further improve the specific capacity, initial coulombic efficiency, and structural stability of carbonaceous materials, while also helping to reduce the true density of carbonaceous materials.

[0149] Crushing can reduce the particle size of the first intermediate product, thereby helping to obtain carbonaceous materials of the desired size. In some embodiments, the volumetric particle size Dv50 of the crushed particles is 4 μm-6 μm. In some embodiments, the volumetric particle size Dv90 of the crushed particles is 8 μm-16 μm. In some embodiments, the volumetric particle size Dv50 of the crushed particles is 4 μm-6 μm and the volumetric particle size Dv90 is 8 μm-16 μm. Of course, in some embodiments, the crushing step may be omitted.

[0150] Washing and impurity removal treatment can remove inorganic and water-soluble impurities from the first intermediate product, preventing metal impurities from being reduced to elemental metals and then agglomerating during subsequent high-temperature carbonization. This is because the agglomeration of elemental metals leads to the collapse of the carbon skeleton structure, especially the capillary structure, resulting in a reduction in the active ion storage space and capacity of the obtained carbonaceous material. Simultaneously, metal impurities also have catalytic activity, which will intensify the decomposition of the carbon skeleton structure during pyrolysis, causing the pore structure to tend towards larger mesoporous and / or macroporous structures. This leads to an increase in the proportion of the electrolyte wetting area inside the obtained carbonaceous material, increased consumption of active ions during SEI film formation, increased initial irreversible capacity loss, and decreased initial coulombic efficiency. The washing and impurity removal process includes at least an acidic solution washing step and an alkaline solution washing step. The acidic solution is mainly used to remove metal impurities from the first intermediate product, while the alkaline solution is mainly used to remove Si-containing impurities that cannot react with acid. This ensures sufficient removal of impurities, reduces their adverse effects on the carbonaceous material, and improves the specific capacity and initial coulombic efficiency of the carbonaceous material.

[0151] In this application, the crushing process needs to be carried out before the washing and impurity removal process. This is to ensure that as much surface area of ​​the first intermediate product as possible is exposed during the subsequent washing and impurity removal process, so as to facilitate sufficient contact between the particles and the washing liquid and improve the washing and impurity removal effect. If the crushing process is carried out after the washing and impurity removal process, some large pieces of raw material will basically retain their original shape after pyrolysis. The washing liquid may not be able to penetrate into the bulk phase of the large particles, and thus the impurities deeply encapsulated in the bulk phase of the large particles cannot be removed, resulting in an insignificant washing and impurity removal effect.

[0152] Crushing can be performed using processes known in the art suitable for crushing in the preparation of carbonaceous materials. In some embodiments, the crushing may include ball milling or air jet milling.

[0153] The order of acidic and alkaline solution washing is not particularly limited. In some embodiments, the washing and impurity removal process sequentially includes the following steps: acidic solution washing, water washing, alkaline solution washing, water washing, and drying; or, the washing and impurity removal process sequentially includes the following steps: alkaline solution washing, water washing, acidic solution washing, water washing, and drying. Deionized water can be used for water washing, and the number of washes can be one or more, until the pH of the filtrate is neutral (i.e., pH 7 ± 0.5), at which point the water washing step is considered complete. Drying can be done by forced-air drying or vacuum drying, until the mass change rate of the material after a 2-hour interval is ≤0.1 wt%, at which point the drying step is considered complete.

[0154] This application does not impose any particular restrictions on parameters such as the type and concentration of solute, washing temperature, and washing time of acidic and alkaline solutions, as long as the impurities are sufficiently removed.

[0155] In some embodiments, the H+ of the acidic solution + The concentration is 0.1 mol / L to 6 mol / L, and can be selected as 1 mol / L to 6 mol / L.

[0156] In some embodiments, the washing temperature of the acidic solution is 10℃-95℃, and optionally 30℃-95℃.

[0157] In some embodiments, the washing time of the acidic solution is 1h-24h, optionally 10h-24h.

[0158] In some embodiments, the solute of the acidic solution includes one or more of hydrochloric acid, nitric acid, sulfuric acid, and perchloric acid, and the solvent includes water.

[0159] By adjusting the H+ of the acidic solution + When one or more of the following factors—concentration, washing temperature, washing time, and type of solute—are within the above range, it is beneficial to achieve thorough washing and better remove metal impurities.

[0160] In some embodiments, the OH- of the alkaline solution - The concentration is 0.1 mol / L to 6 mol / L, and can be selected as 1 mol / L to 6 mol / L.

[0161] In some embodiments, the washing temperature of the alkaline solution is 10℃-95℃, and optionally 30℃-95℃.

[0162] In some embodiments, the washing time of the alkaline solution is 1h-24h, optionally 10h-24h.

[0163] In some embodiments, the solute of the alkaline solution includes NaOH, KOH, or a combination thereof, and the solvent includes water.

[0164] By adjusting the OH- of the alkaline solution - When one or more of the following factors—concentration, washing temperature, washing time, and type of solute—are within the above range, it is beneficial to achieve thorough washing.

[0165] In some embodiments, the washing and impurity removal step may be omitted.

[0166] In some embodiments, when the ash content of the obtained first intermediate product is ≥0.5wt%, a washing and impurity removal process is required to ensure that the ash content in the material before high-temperature carbonization is ≤0.01wt%.

[0167] This application does not impose any particular limitation on the type of protective gas atmosphere in S20 and S30. In some embodiments, the protective gas includes nitrogen, an inert gas, or a combination thereof. Optionally, the inert atmosphere includes argon, helium, or a combination thereof. Optionally, the volume concentration of the gas may be 99.9% or higher.

[0168] In some embodiments, the preparation method further includes: S40, crushing: crushing the carbonaceous material obtained in S30. At this time, the agglomerated carbonaceous material during the preparation process can be crushed to meet the required particle size, which is convenient for preparing the negative electrode slurry and negative electrode sheet. Of course, in some embodiments, this step can be omitted.

[0169] In some embodiments, the preparation method includes the following steps: providing a carbon source: the carbon source is a cellulose biomass material, wherein the cellulose content in the cellulose biomass material is greater than 0 wt% and less than or equal to 100 wt%, and the ash content is 0 wt%-5 wt%; low-temperature pre-carbonization treatment: the carbon source is heated to 150℃-1000℃ at a rate of ≤10℃ / min under a protective gas atmosphere, optionally at 300℃-700℃ followed by heat treatment for 1h-20h. The first intermediate product is obtained after 5-20 hours of heating. High-temperature carbonization treatment involves heating the obtained first intermediate product to 1000-1600℃ at a rate ≤10℃ / min under a protective gas atmosphere, optionally to 1200-1500℃, followed by holding at that temperature for 1-12 hours, optionally 3-10 hours, to obtain a carbonaceous material. The adsorption rate v of the carbonaceous material, under constant temperature and humidity conditions of 25℃ and 40%RH, using water vapor for adsorption testing, satisfies 0.015 ≤ v ≤ 0.050. The resulting carbonaceous material better balances higher specific capacity, higher initial coulombic efficiency, and higher structural stability, thereby further improving the energy density, lifespan, and rate performance of the secondary battery.

[0170] In some embodiments, the preparation method includes the following steps: providing a carbon source: the carbon source is a cellulose biomass material, wherein the cellulose content in the cellulose biomass material is greater than 0 wt% and less than or equal to 100 wt%, and the ash content is 0 wt%-5 wt%; low-temperature pre-carbonization treatment: the carbon source is heated to 150℃-1000℃ at a rate of ≤10℃ / min under a protective gas atmosphere, optionally 300℃-700℃ followed by heat treatment for 1h-20h, optionally 5h-20h, to obtain a first intermediate product; high-temperature carbonization. Chemical treatment: The obtained first intermediate product is crushed to a volumetric particle size Dv50 of 4μm-6μm and / or a volumetric particle size Dv90 of 8μm-16μm, and then heated to 1000℃-1600℃ (optionally 1200℃-1500℃) at a rate of ≤10℃ / min under a protective gas atmosphere, followed by heat treatment for 1h-12h (optionally 3h-10h) to obtain a carbonaceous material. The adsorption rate v of the carbonaceous material, under constant temperature and humidity conditions of 25℃ and 40%RH, when tested with water vapor, satisfies 0.015 ≤ v ≤ 0.050. The resulting carbonaceous material better balances higher specific capacity, higher initial coulombic efficiency, and higher structural stability, thereby further improving the energy density, lifespan, and rate performance of the secondary battery.

[0171] In some embodiments, the preparation method includes the following steps: providing a carbon source: the carbon source is a cellulose biomass material, wherein the cellulose content in the cellulose biomass material is greater than 0 wt% and less than or equal to 100 wt%, and the ash content is 0 wt%-5 wt%; low-temperature pre-carbonization treatment: the carbon source is heated to 150℃-1000℃ at a rate of ≤10℃ / min under a protective gas atmosphere, optionally 300℃-700℃ followed by heat treatment for 1h-20h, optionally 5h-20h, to obtain a first intermediate product; high-temperature carbonization treatment: the obtained first intermediate product is subjected to high-temperature carbonization treatment. After being crushed to a particle size Dv50 of 4μm-6μm and / or a particle size Dv90 of 8μm-16μm, the material undergoes sequential washing with acidic solution, water washing, alkaline solution, water washing, and drying. Then, under a protective gas atmosphere, it is heated to 1000℃-1600℃ (optionally 1200℃-1500℃) at a rate of ≤10℃ / min, followed by heat treatment for 1h-12h (optionally 3h-10h) to obtain a carbonaceous material. The adsorption rate v of this carbonaceous material, under constant temperature and humidity conditions of 25℃ and 40%RH using water vapor, satisfies 0.015 ≤ v ≤ 0.050. The resulting carbonaceous material better balances higher specific capacity, higher initial coulombic efficiency, and higher structural stability, thereby further improving the energy density, lifespan, and rate performance of the secondary battery.

[0172] The preparation method of the second aspect of this application can prepare carbonaceous materials according to any embodiment of the first aspect of this application. The preparation method of carbonaceous materials provided by this application is simple and suitable for commercial production. The preparation method of carbonaceous materials provided by this application does not require the addition of additional conductive agents or other additives, thereby the carbonaceous materials obtained by the preparation method provided by this application have a lower heteroatom content.

[0173] Secondary batteries The third aspect of this application provides a secondary battery.

[0174] The secondary battery mentioned in the embodiments or implementations of this application refers to a single physical module comprising one or more battery cells to provide higher voltage and capacity. For example, the secondary battery mentioned in this application may include battery cells, battery modules, or battery packs. A battery cell is the smallest unit constituting a secondary battery, capable of charging and discharging independently. This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. Figure 1 The example shown is a square-structured battery cell 5.

[0175] In some embodiments, a single battery cell includes an electrode assembly and an electrolyte, and the single battery cell may also include an outer packaging. The outer packaging can be used to encapsulate the electrode assembly and the electrolyte. The outer packaging can be a rigid shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging can also be a flexible package, such as a pouch. The material of the flexible package can be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0176] Electrode assemblies typically include positive and negative electrodes. During the charging and discharging process of a secondary battery, active ions move back and forth between the positive and negative electrodes, inserting and extracting. The electrolyte acts as a conductor for these active ions between the positive and negative electrodes. Electrode assemblies can be manufactured using winding and / or stacking processes.

[0177] In some embodiments, such as Figure 2 As shown, the outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates enclosing a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 is used to cover the opening to close the receiving cavity. Electrode assemblies 52 are encapsulated in the receiving cavity. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, and can be adjusted as needed.

[0178] In some embodiments of this application, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module. Figure 3 This is a schematic diagram of battery module 4 as an example. Figure 3 As shown, in battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0179] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0180] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be adjusted according to the application and capacity of the battery pack. Figure 4 and Figure 5 This is a schematic diagram of battery pack 1 as an example. Figure 4 and Figure 5As shown, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3. The upper body 2 covers the lower body 3, forming a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0181] [Negative electrode plate] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector. For example, the negative current collector has two surfaces opposite each other in its thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative current collector.

[0182] In some embodiments, the negative electrode film layer comprises a carbonaceous material according to the first aspect of this application or a carbonaceous material prepared by the method described in the second aspect of this application. This enables the secondary battery to simultaneously possess high energy density, long lifespan, and good rate performance.

[0183] In some embodiments, the negative electrode film layer may further include other negative electrode active materials besides the carbonaceous materials described above. In some embodiments, the other negative electrode active materials include, but are not limited to, one or more of natural graphite, artificial graphite, soft carbon, silicon-based materials, tin-based materials, and lithium titanate. The silicon-based materials may include one or more of elemental silicon, silicon oxide, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based materials may include one or more of elemental tin, tin oxide, and tin alloys.

[0184] In some embodiments, the negative electrode film layer may optionally include a negative electrode conductive agent. This application does not impose any particular limitation on the type of negative electrode conductive agent. As an example, the negative electrode conductive agent may include one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0185] In some embodiments, the negative electrode film layer may optionally include a negative electrode binder. This application does not impose any particular limitation on the type of negative electrode binder. As an example, the negative electrode binder may include one or more of the following: styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0186] In some embodiments, the negative electrode film may optionally include other additives. As an example, other additives may include thickeners, such as sodium carboxymethyl cellulose (CMC), PTC thermistor materials, etc.

[0187] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper foil may be used. The composite current collector may include a polymeric material substrate and a metal material layer formed on at least one surface of the polymeric material substrate. As an example, the metal material may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymeric material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0188] The negative electrode film layer is typically formed by coating a negative electrode slurry onto a negative electrode current collector, followed by drying and cold pressing. The negative electrode slurry is typically formed by dispersing the negative electrode active material, optional conductive agent, optional binder, and other optional additives in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water, but is not limited to these.

[0189] The negative electrode sheet does not exclude other additional functional layers besides the negative electrode film layer. For example, in some embodiments, the negative electrode sheet of this application further includes a conductive undercoat layer (e.g., composed of a conductive agent and an adhesive) sandwiched between the negative electrode current collector and the negative electrode film layer and disposed on the surface of the negative electrode current collector; in some embodiments, the negative electrode sheet of this application further includes a protective layer covering the surface of the negative electrode film layer.

[0190] [Positive electrode plate] In some embodiments, the positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. For example, the positive current collector has two surfaces opposite each other in its thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0191] The positive electrode current collector can be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil can be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0192] The positive electrode film typically comprises a positive electrode active material, an optional binder, and an optional conductive agent. The positive electrode film is typically formed by coating a positive electrode slurry onto the positive electrode current collector, followed by drying and cold pressing. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring until homogeneous. The solvent may be N-methylpyrrolidone (NMP), but is not limited to this. As an example, the binder used for the positive electrode film may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. As an example, the conductive agent used for the positive electrode film includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0193] The positive electrode active material may be a positive electrode active material known in the art for use in secondary batteries.

[0194] When the secondary battery of this application is a lithium-ion battery, the positive electrode active material may include, but is not limited to, one or more of lithium transition metal oxides, lithium phosphates, and their respective modified compounds. Examples of lithium transition metal oxides may include, but are not limited to, one or more of lithium cobalt oxides, lithium nickel oxides, lithium manganese oxides, lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, lithium nickel cobalt manganese oxides, lithium nickel cobalt aluminum oxides, and their respective modified compounds. Examples of lithium phosphates may include, but are not limited to, lithium iron phosphate, lithium iron phosphate and carbon composites, lithium manganese phosphate, lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, lithium manganese iron phosphate and carbon composites, and their respective modified compounds.

[0195] In some embodiments, to further improve the energy density of secondary batteries, the positive electrode active material for lithium-ion batteries may include materials with the general formula Li. a Ni b Coc M d O e A f One or more of lithium transition metal oxides and their modified compounds. 0.8≤a≤1.2, 0.5≤b<1, 0<c<1, 0<d<1, 1≤e≤2, 0≤f≤1, M includes one or more selected from Mn, Al, Zr, Zn, Cu, Cr, Mg, Fe, V, Ti and B, and A includes one or more selected from N, F, S and Cl.

[0196] As an example, positive electrode active materials for lithium-ion batteries may include LiCoO2, LiNiO2, LiMnO2, LiMn2O4, and LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2 (NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), LiNi 0.85 Co 0.15 Al 0.05 One or more of O2, LiFePO4 and LiMnPO4.

[0197] When the secondary battery of this application is a sodium-ion battery, the positive electrode active material may include, but is not limited to, one or more of sodium-containing transition metal oxides, polyanionic materials (such as phosphates, fluorophosphates, pyrophosphates, sulfates, etc.), and Prussian blue materials.

[0198] As an example, positive electrode active materials for sodium-ion batteries may include NaFeO2, NaCoO2, NaCrO2, NaMnO2, NaNiO2, and NaNi 1 / 2 Ti 1 / 2 O2, NaNi 1 / 2 Mn 1 / 2 O2, Na 2 / 3 Fe 1 / 3 Mn 2 / 3 O2, NaNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, NaFePO4, NaMnPO4, NaCoPO4, Prussian blue materials and materials with the general formula X p M' q (PO4)r O x Y 3-x One or more of the materials. In general formula X p M' q (PO4) r O x Y 3-x In the given condition, 0 < p ≤ 4, 0 < q ≤ 2, 1 ≤ r ≤ 3, 0 ≤ x ≤ 2, and X includes elements selected from H. + Li + Na + K + and NH4 + One or more of the following, M' is a transition metal cation, optionally including one or more selected from V, Ti, Mn, Fe, Co, Ni, Cu and Zn, and Y is a halide anion, optionally including one or more selected from F, Cl and Br.

[0199] In this application, the modified compounds of the above-mentioned positive electrode active materials may be those that have undergone doping modification and / or surface coating modification of the positive electrode active materials.

[0200] [Electrolytes] This application does not impose any particular limitation on the type of electrolyte, which can be selected according to actual needs. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0201] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0202] The type of electrolyte salt is not specifically limited and can be selected according to actual needs.

[0203] When the secondary battery of this application is a lithium-ion battery, as an example, the electrolyte salt may include one or more of 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).

[0204] When the secondary battery of this application is a sodium-ion battery, the electrolyte salt may include one or more of the following: sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium hexafluoroarsenate (NaAsF6), sodium bis(fluorosulfonyl)imide (NaFSI), sodium bis(trifluoromethanesulfonyl)imide (NaTFSI), sodium trifluoromethanesulfonate (NaTFS), sodium difluorooxalate borate (NaDFOB), sodium dioxalate borate (NaBOB), sodium difluorophosphate (NaPO2F2), sodium difluorodioxalate phosphate (NaDFOP), and sodium tetrafluorooxalate phosphate (NaTFOP).

[0205] The type of solvent is not specifically limited and can be selected according to actual needs. In some embodiments, as an example, the solvent may include one or more of the following: ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl ethylene carbonate (BC), fluoroethylene carbonate (FEC), 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).

[0206] In some embodiments, the electrolyte may optionally include additives. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature power performance.

[0207] [Isolation membrane] Secondary batteries using electrolytes, and some secondary batteries using solid electrolytes, also include a separator. The separator is disposed between the positive electrode and the negative electrode, serving as a barrier. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0208] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film. When the separator is a multi-layer composite film, the materials of each layer may be the same or different.

[0209] [Preparation Method] The method for preparing the secondary battery described in this application is well known. In some embodiments, a positive electrode, a separator, a negative electrode, and an electrolyte can be assembled to form a secondary battery. As an example, the positive electrode, separator, and negative electrode can be formed into an electrode assembly through a winding process and / or a stacking process. The electrode assembly is placed in an outer packaging, dried, and then injected with an electrolyte. After vacuum sealing, settling, formation, and shaping processes, a battery cell is obtained. Multiple battery cells can be further connected in series, parallel, or a combination thereof to form a battery module. Multiple battery modules can also be connected in series, parallel, or a combination thereof to form a battery pack. In some embodiments, multiple battery cells can also be directly assembled into a battery pack.

[0210] Electrical appliances A fourth aspect of this application provides an electrical device, which includes the secondary battery described in this application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit. The electrical device can be, but is not limited to, mobile devices (e.g., mobile phones, tablets, laptops, etc.), electric vehicles (e.g., 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.

[0211] The electrical device can select the specific type of secondary battery according to its usage requirements, such as a battery cell, battery module, or battery pack.

[0212] Figure 6 This is a schematic diagram illustrating an example of an electrical device. This device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density, a battery pack or battery module can be used as the power source.

[0213] 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 a single battery cell as their power source.

[0214] Example The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0215] Example 1 Using pine wood as the carbon source, the particle size is ≤1mm, the cellulose content is 40wt%, the hemicellulose content is 23%, the lignin content is 27%, and the ash content is 1wt%.

[0216] Pine wood was heated to 150°C (first temperature T1) at a rate of 1°C / min under a nitrogen atmosphere and then held at that temperature for 10 hours (first time t1). After the treatment, the wood was cooled to room temperature to obtain the first intermediate product.

[0217] The first intermediate product was crushed by air jet milling to a volumetric particle size Dv50 of 4μm-6μm. Then it was washed with 3mol / L perchloric acid aqueous solution at 50℃ for 10h, followed by washing with deionized water until neutral, then washing with 3mol / L NaOH aqueous solution at 80℃ for 20h, followed by washing with deionized water until neutral, and finally drying with forced air to remove moisture, to obtain the first intermediate product with an ash content of ≤0.01wt%.

[0218] The first intermediate product obtained above was heated to 1400℃ (as the second temperature T2) at a nitrogen atmosphere at a rate of 0.5℃ / min (as the second heating rate) and then held at that temperature for 6 hours (as the second time t2). After the treatment, carbonaceous material was obtained.

[0219] In a constant temperature and humidity chamber at 25℃ and 40%RH (i.e., the ratio of the partial pressure of water vapor in the air to the saturated vapor pressure of water is 40%), a carbonaceous material of mass m1 is uniformly placed in the container with a stacking thickness of ≤5mm. The adsorption mass m2 of water vapor and the adsorption time t when the adsorption of water vapor by the carbonaceous material reaches equilibrium are recorded. Then, the water vapor adsorption rate v = m2 / (m1×t), where the unit of measurement for m1 is g, the unit of measurement for m2 is g, and the unit of measurement for t is h.

[0220] The true density of carbonaceous materials was tested using the Archimedes impregnation volume displacement method with n-butanol as the medium.

[0221] Examples 2-19 and Comparative Examples 1-7 The preparation method of carbonaceous materials is similar to that in Example 1, except that the preparation process parameters of carbonaceous materials are adjusted, as detailed in Table 1.

[0222] Performance testing The carbonaceous materials prepared in the various embodiments and comparative examples were thoroughly mixed with styrene-butadiene rubber (SBR) as a binder, sodium carboxymethyl cellulose (CMC-Na) as a thickener, and carbon black as a conductive agent in a mass ratio of 96.2:1.8:1.2:0.8 in an appropriate amount of deionized water to form a uniform negative electrode slurry. The negative electrode slurry was uniformly coated onto the surface of the copper foil current collector and dried in an oven for later use. Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. NaPF6 was then dissolved in the organic solvent to prepare an electrolyte with a concentration of 1 mol / L. A CR2430 coin cell was then assembled in an argon-protected glove box using a sodium metal sheet as the counter electrode and a polyethylene (PE) film as the separator.

[0223] At 25°C, the coin cells prepared in each example and comparative example were first discharged to 0V at a constant current density of 10mA / g, and the first discharge capacity of the coin cells was recorded; then, they were charged to 2.0V at a constant current density of 10mA / g, and the first charge capacity of the coin cells was recorded.

[0224] The reversible specific capacity (mAh / g) of carbonaceous material = the first charge capacity of the coin cell / the mass of the carbonaceous material.

[0225] The initial coulombic efficiency (%) of carbonaceous materials = the first charge capacity of the coin cell / the first discharge capacity of the coin cell × 100%.

[0226] After fully charging and discharging the button cell at 0.33C and 1C respectively, the discharge capacity at 0.33C and 1C was obtained. The rate performance was characterized by the ratio of the discharge capacity at 1C to the discharge capacity at 0.33C. The higher the ratio, the better the rate performance.

[0227] Table 1 Table 2 Figures 7 to 9 These are scanning electron microscope images of the carbonaceous material provided in this application at different magnifications, such as... Figures 7 to 9 As shown, the carbonaceous material provided in this application has an irregular multi-faceted morphology. Based on the test results in Table 2, it can be seen that when the carbonaceous material meets the conditions of constant temperature and humidity at 25℃ and 40%RH, and the water vapor adsorption rate v is between 0.015 and 0.050, the carbonaceous material achieves a balance between high specific capacity, high initial coulombic efficiency, and good rate performance.

[0228] The carbonaceous materials prepared in Comparative Examples 1-7, under constant temperature and humidity conditions of 25℃ and 40%RH, had water vapor adsorption rates v that were either less than 0.015 or greater than 0.050. Consequently, the carbonaceous materials could not simultaneously achieve high specific capacity, high initial coulombic efficiency, and good rate performance.

[0229] Comparative Example 1 used rice husks as the carbon source, with an ash content higher than 5 wt%. Ash not only catalyzes during the low-temperature pre-carbonization process, consuming carbon and reducing active ion storage sites, but also causes metallic impurities in the ash to agglomerate into elemental metals during subsequent high-temperature carbonization. This agglomeration of elemental metals leads to the collapse of the carbon skeleton structure, especially the capillary structure, resulting in reduced active ion storage space and decreased capacity in the obtained carbonaceous material, manifested as a low water vapor adsorption rate. Simultaneously, the metallic impurities also possess catalytic activity, intensifying the decomposition of the carbon skeleton structure during pyrolysis, causing the pore structure to tend towards larger mesoporous and / or macroporous structures. This results in an increased proportion of the electrolyte wetting area within the obtained carbonaceous material, increased consumption of active ions during SEI film formation, increased initial irreversible capacity loss, and decreased initial coulombic efficiency.

[0230] In Comparative Example 2, no low-temperature pre-carbonization treatment was performed during the preparation of the carbonaceous material. As a result, the carbonaceous material had poor pore-closing effect, low capillary structure content and high content of mesoporous and / or macroporous structures. Consequently, the proportion of electrolyte wetting area inside the carbonaceous material was high, the initial irreversible capacity loss was high, and the initial coulombic efficiency was low.

[0231] The test results from Examples 1-19 also show that when the water vapor adsorption time t of the carbonaceous material is further satisfied to be between 4.5h and 7h, the carbonaceous material can have higher specific capacity, first coulombic efficiency and / or rate performance.

[0232] The test results from Examples 1-19 also show that when the true density ρ of the carbonaceous material further satisfies 1.3 g / cm³, 3 -1.7g / cm 3 In between, carbonaceous materials can have higher specific capacity, first coulombic efficiency, and / or rate performance.

[0233] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A method for preparing a carbonaceous material, comprising the following steps: S10, providing a carbon source: the carbon source is a cellulose-based biomass material, and the ash content of the cellulose-based biomass material is less than or equal to 5 wt%; S20, Low-temperature pre-carbonization treatment: The carbon source is heated to a first temperature T1 at a first heating rate under a protective gas atmosphere and then held at that temperature for a first time t1 to obtain a first intermediate product. S30, High-temperature carbonization treatment: The obtained first intermediate product is heated to a second temperature T2 at a second heating rate under a protective gas atmosphere, and then held at that temperature for a second time t2 to obtain a carbonaceous material. The adsorption rate v of the carbonaceous material under constant temperature and humidity conditions of 25℃ and 40%RH satisfies 0.015 ≤ v ≤ 0.050 when adsorbed with water vapor. The water vapor adsorption test is carried out under the following conditions: In a constant temperature and humidity chamber of 25℃ and 40%RH, the carbonaceous material with a mass of m1 is placed in a container, and the adsorption mass m2 of water vapor and the water vapor adsorption time t when the adsorption of water vapor by the carbonaceous material reaches equilibrium are recorded. Then the water vapor adsorption rate v = m2 / (m1×t), where the unit of measurement of m1 is g, the unit of measurement of m2 is g, and the unit of measurement of t is h.

2. The method according to claim 1, wherein, The cellulose content in the cellulosic biomass material is greater than 0 wt% and less than or equal to 100 wt%.

3. The method according to claim 1 or 2, wherein, The cellulose content in the cellulosic biomass material is greater than or equal to 20 wt% and less than 100 wt%; and / or, The ash content of the cellulosic biomass material is less than or equal to 2 wt%.

4. The method according to claim 2 or 3, wherein, The hemicellulose content in the cellulosic biomass material is less than or equal to 70 wt%, and may be less than or equal to 30 wt%; and / or, The lignin content in the cellulosic biomass material is less than or equal to 60 wt%, and can be selected as 10 wt%-60 wt%.

5. The method according to any one of claims 2-4, wherein, The cellulosic biomass material includes one or more woody biomass materials, which may be selected as one or more of hardwood, softwood and nut shells, and more preferably one or more of pine, bamboo and walnut shells.

6. The method according to any one of claims 1-5, wherein, The first heating rate is 1℃ / min-10℃ / min, and can be selected as 1℃ / min-3℃ / min; and / or, The first temperature T1 is 150℃-1000℃, and can be selected as 300℃-700℃; and / or, The first time interval t1 is 1h-20h, which can be selected as 5h-20h.

7. The method according to any one of claims 1-6, wherein, The second heating rate is ≤10℃ / min, and can be selected as 0.5℃ / min-10℃ / min; and / or, The second temperature T2 is 1000℃-1600℃, and can be selected as 1200℃-1500℃; and / or, The second time t2 is 1h-12h, and can be selected as 3h-10h.

8. The method according to any one of claims 1-7, wherein, t1+t2 is 10h-30h.

9. The method according to any one of claims 1-8, wherein, The process after S20 and before S30 includes the following steps: crushing the first intermediate product obtained in S20, or washing and removing impurities from the first intermediate product obtained in S20, or crushing the first intermediate product obtained in S20 and then washing and removing impurities to obtain a first intermediate product with an ash content ≤0.01wt%. The washing and removing impurities process includes at least an acidic solution washing step and an alkaline solution washing step.

10. The method according to claim 9, wherein, The washing and impurity removal process includes the following steps in sequence: washing with acidic solution, washing with water, washing with alkaline solution, washing with water, and drying; or, the washing and impurity removal process includes the following steps in sequence: washing with alkaline solution, washing with water, washing with acidic solution, washing with water, and drying.

11. The method according to claim 9 or 10, wherein, The acidic solution satisfies at least one of the following conditions (1) to (4): (1) The H+ of the acidic solution + The concentration is 0.1 mol / L-6 mol / L, and can be selected as 1 mol / L-6 mol / L; (2) The washing temperature of the acidic solution is 10℃-95℃, and can be selected as 30℃-95℃; (3) The washing time of the acidic solution is 1h-24h, and can be selected as 10h-24h; (4) The solute of the acidic solution includes one or more of hydrochloric acid, nitric acid, sulfuric acid and perchloric acid, and the solvent includes water.

12. The method according to any one of claims 9-11, wherein, The alkaline solution satisfies at least one of the following conditions (1) to (4): (1) The OH- of the alkaline solution - The concentration is 0.1 mol / L-6 mol / L, and can be selected as 1 mol / L-6 mol / L; (2) The washing temperature of the alkaline solution is 10℃-95℃, and can be selected as 30℃-95℃; (3) The washing time of the alkaline solution is 1h-24h, and can be selected as 10h-24h; (4) The solute of the alkaline solution includes NaOH, KOH or a combination thereof, and the solvent includes water.

13. A carbonaceous material, wherein, The carbonaceous material is prepared by the method described in any one of claims 1-12.

14. A negative electrode plate, wherein, The negative electrode sheet comprises the carbonaceous material as described in claim 13.

15. A secondary battery, comprising a negative electrode sheet, said negative electrode sheet comprising the carbonaceous material of claim 13.

16. An electrical device comprising the secondary battery of claim 15.

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