HARD CARBON, MANUFACTURING METHODS, SECONDARY BATTERIES, AND ELECTRICAL EQUIPMENT

Abstract

The invention relates to hard carbon, a method of its creation, a secondary battery, and an electrical device. Based on the total mass of hard carbon, the total mass percentage of water-soluble cations in the hard carbon does not exceed 500 ppm. Hard carbon can improve the viscosity of cathode paste and can improve the cycle performance of the battery.

Description

Hard carbon, preparation method, secondary battery and electrical device

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202311479725.9, filed on November 8, 2023, entitled “Hard Carbon, Preparation Method, Secondary Battery and Electrical Device,” which is incorporated herein by reference in its entirety. Technical Field

[0003] The present application relates to the technical field of secondary batteries, and in particular to hard carbon, a preparation method, a secondary battery and an electrical device. Background Art

[0004] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields.

[0005] Hard carbon is a commonly used negative electrode material in sodium secondary batteries. However, hard carbon has a high impurity content, poor stability during battery preparation, and high processing difficulty. Therefore, existing hard carbon still needs to be improved.

[0006] Summary of the Invention

[0007] The present application has been made in view of the above-mentioned problems, and an object of the present application is to provide a hard carbon that improves the viscosity of a slurry containing the hard carbon and improves the processing performance of the hard carbon.

[0008] In a first aspect, the present application provides a hard carbon, wherein the total mass proportion of water-soluble cations in the hard carbon does not exceed 500 ppm based on the total mass of the hard carbon.

[0009] Studies have shown that the processing properties of hard carbon are closely related to the content of water-soluble cations present therein. Since the precursors for preparing hard carbon inevitably contain metal impurities, they will remain in the final product hard carbon during the sintering process. When preparing the negative electrode slurry, the water-soluble cations in the hard carbon will inhibit the ionization of the thickener (such as sodium carboxymethyl cellulose) in the slurry, causing its ionization equilibrium to move towards the non-ionized equilibrium, resulting in a decrease in the charge density on the thickener, weakening the electrostatic repulsion between charges, and making it difficult for the thickener to fully stretch under the action of the electrostatic repulsion force, reducing the contact area between the thickener (such as sodium carboxymethyl cellulose) and the solvent (such as water), making it difficult for the two to fully associate, and the thickener is difficult to fully exert its thickening effect. In addition, the divalent cations and trivalent cations in the water-soluble ions are very easy to coordinate with the carboxyl groups in the thickener (such as sodium carboxymethyl cellulose), reducing the association sites of the thickener with water molecules, resulting in further deterioration of the thickening effect of the thickener and a significant reduction in the viscosity of the negative electrode slurry. When the total mass proportion of water-soluble cations in hard carbon is controlled to not exceed 500 ppm, the thickener in the slurry can fully exert its thickening effect, so that the slurry has a suitable and stable viscosity, which is beneficial to improving the battery processing performance.

[0010] It can be understood that since some metal impurities in hard carbon exist in the bulk structure or are difficult to dissolve in water solvents, the mass proportion of water-soluble cations in hard carbon is not equivalent to the mass proportion of metal elements in hard carbon. Compared with the mass proportion of metal elements in hard carbon, the mass proportion of water-soluble cations in hard carbon is more instructive for improving processing performance. By monitoring the total mass proportion of water-soluble cations in hard carbon in the early stage, the problem of poor coating quality of negative electrode slurry in the later coating process can be effectively reduced. Moreover, using the total mass proportion of water-soluble cations in hard carbon as a monitoring indicator can reduce the problem of different standards caused by different impurity element contents in hard carbon of different precursors, and it is universal for hard carbon of different precursors.

[0011] In any embodiment, the total mass ratio of the water-soluble cations in the hard carbon is 5 ppm to 450 ppm based on the total mass of the hard carbon.

[0012] When the total mass proportion of water-soluble cations is in the range of 5ppm to 450ppm, the hard carbon can not only make the negative electrode slurry have a suitable viscosity, but also will not introduce too many defects in the hard carbon in the process of reducing the total mass of water-soluble cations, so that the hard carbon has both good processing performance and electrochemical performance, and the secondary battery has high first efficiency and cycle stability.

[0013] In any embodiment, the water-soluble cations include sodium ions (Na + ), potassium ion (K + ), magnesium ions (Mg 2+ ), calcium ions (Ca 2+), aluminum ions (Al 3+ ) at least one of.

[0014] In any embodiment, based on the total mass of the hard carbon, the mass proportion of silicon in the hard carbon does not exceed 570 ppm, and may be 300 ppm to 550 ppm.

[0015] Silicon in biomass-based hard carbon acts as a pore-forming agent during the sintering process, remaining in the bulk and surface of the biomass-based hard carbon after sintering. Hard carbon with a silicon content of no more than 570 ppm by weight ensures a suitable and stable viscosity in the slurry, which is beneficial for improving battery processing performance.

[0016] Hard carbon with a silicon mass fraction in the range of 300ppm to 550ppm can not only make the negative electrode slurry have suitable viscosity and low impurity content, but also will not introduce too many defects in the hard carbon in the process of reducing the total silicon mass fraction, or affect the pore-forming function of the hard carbon, so that the hard carbon has both good processing performance and electrochemical performance, and the secondary battery has high gram capacity, first efficiency and cycle stability.

[0017] In any embodiment, the mass ratio of any one of water-soluble sodium ions, water-soluble potassium ions, water-soluble magnesium ions, water-soluble calcium ions, and water-soluble aluminum ions in the hard carbon is 1 ppm to 260 ppm based on the total mass of the hard carbon.

[0018] In any embodiment, the true density of hard carbon at room temperature is 1.45 g / cm 3 ~1.65g / cm 3 , optional 1.45g / cm 3 ~1.6g / cm 3 .

[0019] True density is 1.45g / cm 3 ~1.65g / cm 3 Hard carbon within this range has a certain amount of porosity. The filling of active metal ions, such as sodium ions, in the micropores of hard carbon is an important mechanism for its capacity development. Therefore, hard carbon with a true density within the above range has a high specific capacity.

[0020] A second aspect of the present application provides a method for preparing hard carbon, which includes a water washing step so that the total mass proportion of water-soluble cations in the hard carbon does not exceed 500 ppm based on the mass of the hard carbon, and can be optionally 5 ppm to 450 ppm.

[0021] Water washing has the advantage of being mild, which can effectively reduce the water-soluble ion content in hard carbon without leaving too many defects on the hard carbon surface, thereby making the battery have good processing performance, first efficiency and cycle performance.

[0022] In any embodiment, the preparation method specifically includes the following steps: providing a biomass-based carbon source; pre-sintering the carbon source to prepare a precursor; sintering the precursor at high temperature to prepare a product; and washing the product with water to prepare hard carbon.

[0023] When the water washing step is carried out after high-temperature sintering, it can not only retain sufficient inorganic elements for pore formation during the sintering process, so that the biomass-based hard carbon has good porosity and gram capacity, but also make the water-soluble cations in the biomass-based hard carbon within an appropriate range, the viscosity of the slurry is high, and the coating performance is good.

[0024] In any embodiment, the precursor and product are not acid treated.

[0025] Acid treatment of the precursor will cause the micropores formed in the pre-sintering process in the precursor to become closed or shrunken, resulting in a decrease in the true density of the hard carbon and a decay in the specific capacity; after acid treatment, the product is prone to defects on the surface / micropores of the hard carbon, resulting in a decrease in the specific capacity of the hard carbon and a deterioration in the first efficiency and cycle stability of the secondary battery.

[0026] A third aspect of the present application provides a secondary battery comprising the hard carbon in any embodiment or the hard carbon prepared by the preparation method in any embodiment.

[0027] A fourth aspect of the present application provides an electrical device comprising the secondary battery of the third aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] FIG1 is a schematic diagram of a secondary battery according to an embodiment of the present application;

[0029] FIG2 is an exploded view of the secondary battery according to one embodiment of the present application shown in FIG1 ;

[0030] FIG3 is a schematic diagram of a battery module according to an embodiment of the present application;

[0031] FIG4 is a schematic diagram of a battery pack according to an embodiment of the present application;

[0032] FIG5 is an exploded view of the battery pack according to an embodiment of the present application shown in FIG4 ;

[0033] FIG6 is a schematic diagram of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0034] Description of reference numerals:

[0035] 1 battery pack; 2 upper box; 3 lower box; 4 battery module; 5 secondary battery; 51 shell; 52 electrode assembly; 53 cover plate. DETAILED DESCRIPTION

[0036] Below, the embodiments of the hard carbon, preparation method, secondary battery, and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description are provided to enable those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0037] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range " ab " represents the abbreviation of any real number combination between a and b, wherein a and b are all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0038] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0039] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0040] Unless otherwise specified, all steps of the present 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 may include steps (b) and (a) performed sequentially. For example, the method may further 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 may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0041] Unless otherwise specified, the terms "include" and "comprising" used in this application may be open-ended or closed-ended. For example, "include" and "comprising" may mean that other components not listed may also be included or that only the listed components are included.

[0042] Unless otherwise specified, the term "or" is used in this application to be inclusive. For example, the phrase "A or B" means "A, B, or both A and B." More specifically, the condition "A or B" is satisfied if any of the following conditions are met: 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).

[0043] According to the classification of hard carbon sources, hard carbon mainly includes biomass-based hard carbon, carbohydrate hard carbon and resin-based hard carbon. Among them, biomass-based hard carbon uses biomass materials as raw materials, and has the advantages of moderate performance, wide material sources and low cost. It is a very promising negative electrode active material in sodium secondary batteries. However, biomass-based hard carbon exhibits disadvantages such as large slurry viscosity differences, poor stability and poor reproducibility in the process of preparing negative electrode slurry. The slurry viscosity is often too low to be extruded and coated, or the slurry after coating is easy to gather around the periphery due to the low viscosity to form a bulging edge, and then collapse occurs during the cold pressing process, resulting in a low qualified rate of the prepared negative electrode sheets, poor uniformity, and large differences between batches, which is not conducive to the effective improvement of secondary battery performance.

[0044] [Hard Carbon]

[0045] Based on this, the present application proposes a hard carbon, in which the total mass proportion of water-soluble cations in the hard carbon does not exceed 500 ppm based on the mass of the hard carbon.

[0046] As used herein, the term "ppm" means parts per million.

[0047] As used herein, "water-soluble cation" refers to a metal cation that is soluble in water.

[0048] In some embodiments, the water-soluble cations include sodium ions (Na + ), potassium ion (K + ), magnesium ions (Mg 2+ ), calcium ions (Ca 2+ ), aluminum ions (Al 3+ ) at least one of.

[0049] In the present application, based on the mass of the hard carbon, the total mass proportion of water-soluble cations can be tested by the following method. As an example, 100g of hard carbon is dispersed in 400g of aqueous solution to form a slurry with a solid content of 20%. After stirring and dispersing at a speed of 1200r / min for 120min, the obtained hard carbon slurry is filtered, the filtrate is collected, 8mL of the filtrate is measured, and added to 2ml of reverse aqua regia (the volume ratio of HNO3:HCl is 3:1), and microwave digestion is performed. The microwave digester can be Anton Paar Multiwave 7000, the microwave frequency can be 2450MHz, and the digestion time can be 5min. The solution to be tested is then transferred to a plasma spectrometer to test the ion species and mass in the filtrate. The plasma spectrometer can be a Thermo Scientific single quadrupole inductively coupled plasma mass spectrometer (SQ-ICP-MS) model. The test results obtain the mass concentration of water-soluble cations in the solution to be tested in ppm, in g / mL. The total mass of water-soluble cations in the test solution (10a ppm, in g) is obtained by multiplying the mass concentration of water-soluble cations in the test solution (a ppm g / mL) by the volume of the test solution (10 mL). The total mass of water-soluble cations in the test solution is converted to the total mass of water-soluble cations in the slurry (500a ppm, in g); the total mass of water-soluble cations in the slurry is divided by the mass of the hard carbon in the slurry to obtain the total mass of water-soluble cations per unit mass of hard carbon (5appm g / g), that is, the total mass proportion of water-soluble cations based on the mass of the hard carbon.

[0050] In some embodiments, based on the mass of the hard carbon, the total mass proportion of the water-soluble cations in the hard carbon is 5 ppm, 50 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm or any range therebetween.

[0051] In some embodiments, the hard carbon comprises biomass-based hard carbon.

[0052] Studies have shown that the processing properties of hard carbon are closely related to the content of water-soluble cations present therein. Since biomass inevitably contains metal impurities, they will remain in the biomass-based hard carbon during the sintering process. When preparing the negative electrode slurry, the water-soluble cations in the hard carbon will inhibit the ionization of the thickener (such as sodium carboxymethyl cellulose) in the slurry, causing its ionization equilibrium to move towards the non-ionization equilibrium, resulting in a decrease in the charge density on the thickener, weakening the electrostatic repulsion between charges, and making it difficult for the thickener to fully stretch under the action of the electrostatic repulsion force, reducing the contact area between the thickener (such as sodium carboxymethyl cellulose) and the solvent (such as water), making it difficult for the two to fully associate, and the thickener is difficult to fully exert its thickening effect. In addition, the divalent cations and trivalent cations in the water-soluble ions are very easy to coordinate with the carboxyl groups in the thickener (such as sodium carboxymethyl cellulose), reducing the association sites of the thickener with water molecules, resulting in further deterioration of the thickening effect of the thickener and a significant decrease in the viscosity of the negative electrode slurry. When the water-soluble cations in the hard carbon are controlled within the above range, the thickener in the slurry can fully exert its thickening effect, so that the slurry has a suitable and stable viscosity, which is beneficial to improving the battery processing performance.

[0053] It can be understood that since some metal impurities in hard carbon exist in the bulk structure or are difficult to dissolve in water solvents, the mass proportion of water-soluble cations in hard carbon is not equivalent to the mass proportion of metal elements in hard carbon. Compared with the mass proportion of metal elements in hard carbon, the mass proportion of water-soluble cations in hard carbon is more instructive for improving processing performance. By monitoring the total mass proportion of water-soluble cations in hard carbon in the early stage, the problem of poor coating quality of negative electrode slurry in the later coating process can be effectively reduced. Moreover, using the total mass proportion of water-soluble cations in hard carbon as a monitoring indicator can reduce the problem of different standards caused by different impurity element contents in different types of biomass-based hard carbons, and is universally applicable to different biomass-based hard carbons.

[0054] In some embodiments, based on the mass of the hard carbon, the total mass proportion of the water-soluble cations in the hard carbon is 5 ppm to 450 ppm.

[0055] Hard carbon with water-soluble cations within the above-mentioned mass proportion range can not only make the negative electrode slurry have a suitable viscosity, but also will not introduce too many defects in the hard carbon in the process of reducing the total mass of water-soluble cations, so that the hard carbon has both good processing performance and electrochemical performance, and the secondary battery has high first efficiency and cycle stability.

[0056] In some embodiments, the mass proportion of silicon in the hard carbon is no more than 570 ppm based on the total mass of the hard carbon.

[0057] In this application, the mass proportion of silicon element can be tested by any method known in the art. As an example, a plasma spectrometer is used for testing. Weigh 0.2g of hard carbon and add it to 10ml of reverse aqua regia (a mixed solution of HNO3 and HCl in a volume ratio of 3:1). The sample is subjected to microwave digestion in a microwave digester. The microwave digester is Anton Paar Multiwave 7000, the microwave frequency is 2450MHz, and the digestion time is 5min. The sample is then transferred to the plasma spectrometer for testing to obtain the mass of silicon element per unit mass of hard carbon.

[0058] In some embodiments, based on the total mass of the hard carbon, the mass content of silicon in the hard carbon may be 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm, 550 ppm or any range therebetween.

[0059] Silicon in biomass-based hard carbon acts as a pore-forming agent during the sintering process, remaining in the bulk and surface of the biomass-based hard carbon after sintering. Hard carbon with a silicon content of no more than 570 ppm by weight ensures a suitable and stable viscosity in the slurry, which is beneficial for improving battery processing performance.

[0060] In some embodiments, based on the total mass of the hard carbon, the mass proportion of silicon in the hard carbon is 300 ppm to 550 ppm.

[0061] Hard carbon with silicon element in the above-mentioned mass proportion range can not only make the negative electrode slurry have suitable viscosity and low impurity content, but also will not introduce too many defects in the hard carbon in the process of reducing the total mass proportion of silicon element, or affect the pore-forming function of the hard carbon, so that the hard carbon has both good processing performance and electrochemical performance, and the secondary battery has high gram capacity, first efficiency and cycle stability.

[0062] In some embodiments, based on the total mass of the hard carbon, the mass proportion of any one of the water-soluble sodium ions, water-soluble potassium ions, water-soluble magnesium ions, water-soluble calcium ions, and water-soluble aluminum ions in the hard carbon is 1 ppm to 260 ppm.

[0063] In some embodiments, based on the total mass of the hard carbon, the mass proportion of any one of the water-soluble sodium ions, water-soluble potassium ions, water-soluble magnesium ions, water-soluble calcium ions, and water-soluble aluminum ions in the hard carbon is 1 ppm, 5 ppm, 25 ppm, 50 ppm, 75 ppm, 100 ppm, 125 ppm, 150 ppm, 175 ppm, 200 ppm, 230 ppm, 260 ppm or any numerical range therebetween.

[0064] In some embodiments, the true density of the hard carbon at room temperature is 1.45 g / cm 3 ~1.65g / cm 3 In some embodiments, the true density of the hard carbon at room temperature may be 1.45 g / cm 3 ~1.6g / cm 3 .

[0065] True density refers to the mass of a material per unit actual volume (excluding internal voids, i.e., open and closed pores and voids between particles) in an absolutely dense state.

[0066] In this application, the true density of hard carbon has a well-known meaning in the art and can be tested by methods known in the art. As an example, weigh hard carbon with a mass of M, place the hard carbon in a true density tester (Accu Pyc II 1340 analyzer) at room temperature (15°C-25°C), seal the test system, and introduce helium according to the procedure. By detecting the gas pressure in the sample chamber and the expansion chamber, and then calculating the gas volume of the sample chamber and the expansion chamber respectively according to the ideal gas state equation, the difference between the two is used to obtain the volume of gas displaced by the hard carbon under certain temperature and pressure conditions, which is the true volume V of the hard carbon. The true density of hard carbon is the mass of hard carbon M / the true volume V of hard carbon, and the unit of true density is g / cm 3 .

[0067] In some embodiments, the true density of the hard carbon at room temperature is 1.45 g / cm 3 , 1.5g / cm 3 , 1.55g / cm 3 , 1.6g / cm 3 , 1.65g / cm 3 or any range of values ​​between them.

[0068] Hard carbon with a true density within the above range has a certain amount of porosity. The filling of active metal ions, such as sodium ions, within the micropores of hard carbon is an important mechanism for its capacity development. Therefore, hard carbon with a true density within the above range has a high specific capacity.

[0069] In one embodiment of the present application, a method for preparing hard carbon is provided. The method includes a water washing step, wherein the total mass fraction of water-soluble cations in the hard carbon does not exceed 500 ppm, based on the total mass of the hard carbon. In some embodiments, the total mass fraction of water-soluble cations in the hard carbon can be 5 ppm to 450 ppm.

[0070] In this article, "water washing" refers to the process of washing the product with an aqueous solvent. The aqueous solvent includes but is not limited to deionized water, and a mixed solution of deionized water and other solvents.

[0071] In some embodiments, the water washing temperature is 1°C-85°C. In some embodiments, the water washing temperature can be selected from 5°C-40°C.

[0072] In some embodiments, the water washing temperature is 1°C, 10°C, 30°C, 50°C, 65°C, 75°C, 85°C, or any range therebetween.

[0073] In some embodiments, the water washing time is 0.5 h-1 h.

[0074] In some embodiments, the water washing time is 0.5 h, 0.6 h, 0.7 h, 0.8 h, 0.9 h, 1 h, or any range therebetween.

[0075] In some embodiments, the washing process is accompanied by stirring at a stirring speed of 400 rpm to 1200 rpm.

[0076] In some embodiments, the stirring speed of water washing is 400 r / min, 500 r / min, 600 r / min, 700 r / min, 800 r / min, 900 r / min, 1000 r / min, 1100 r / min, 1200 r / min or any range therebetween.

[0077] Water washing has the advantage of being mild, which can effectively reduce the water-soluble ion content in hard carbon without leaving too many defects on the hard carbon surface, thereby making the battery have good processing performance, first efficiency and cycle performance.

[0078] In some embodiments, the preparation method specifically includes the following steps: providing a biomass-based carbon source; pre-sintering the carbon source to prepare a precursor; sintering the precursor at a high temperature to prepare a product; and washing the product with water to prepare the hard carbon.

[0079] In some embodiments, the preparation method specifically includes the following steps: providing a biomass-based carbon source; pre-sintering the carbon source to prepare a precursor; washing the precursor with water and performing high-temperature sintering to prepare hard carbon.

[0080] In some embodiments, the preparation method specifically includes the following steps: providing a biomass-based carbon source; pre-sintering the carbon source to prepare a precursor; washing the precursor with water and sintering it at high temperature to prepare a product; and washing the product with water to prepare the hard carbon.

[0081] When the water washing step is carried out after high-temperature sintering rather than before high-temperature sintering, it can not only retain sufficient inorganic elements for pore formation during the sintering process, so that the hard carbon has good porosity and gram capacity, but also make the water-soluble cations in the hard carbon within an appropriate range, the viscosity of the slurry is high, and the coating performance is good.

[0082] In some embodiments, the biomass-based carbon source includes at least one of sorghum stalks, sawdust, walnut shells, sugarcane bagasse, rice bran, wheat husks, coconut shells, apricot shells, peanut shells, wood, lignin, grapefruit peels, and animal or plant tissues.

[0083] In some embodiments, the biomass-based carbon source is sorghum stalks. In some embodiments, the biomass-based carbon source is coconut shell. In some embodiments, the biomass-based carbon source is wood.

[0084] Compared with other carbon source precursors, biomass-based carbon sources have the advantages of abundant resources and cost savings.

[0085] In some embodiments, the pre-sintering temperature ranges from 300° C. to 900° C.; the pre-sintering environment is nitrogen or air; and the pre-sintering time is from 1 hour to 4 hours.

[0086] In some embodiments, the pre-sintering temperature can be selected as 300°C, 400°C, 500°C, 600°C, 700°C, 800°C, 900°C or any range therebetween; the pre-sintering environment is nitrogen or air; and the pre-sintering time can be selected as 1h, 2h, 3h, 4h or any range therebetween.

[0087] In some embodiments, the temperature range of high-temperature sintering is 1000° C.-1400° C.; the sintering environment of high-temperature sintering is an inert atmosphere, which can be at least one of nitrogen, argon, and helium; and the time of high-temperature sintering is 1 hour-5 hours.

[0088] In some embodiments, the high temperature sintering temperature can be selected as 1000°C, 1100°C, 1200°C, 1300°C, 1400°C or any range therebetween; the high temperature sintering time can be selected as 1h, 2h, 3h, 4h, 5h or any range therebetween.

[0089] In some embodiments, the precursor and the product are not acid treated.

[0090] In this article, "acid treatment" refers to the process of treating a material with an acidic substance. In some embodiments, the acidic substance includes but is not limited to hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, hydrofluoric acid and mixtures thereof.

[0091] Acid treatment of the precursor will cause the micropores formed in the pre-sintering process in the precursor to become closed or shrunken, resulting in a decrease in the true density of the hard carbon and a decay in the specific capacity; after acid treatment, the product is prone to defects on the surface / micropores of the hard carbon, resulting in a decrease in the specific capacity of the hard carbon and a deterioration in the first efficiency and cycle stability of the secondary battery.

[0092] In one embodiment of the present application, a method for treating hard carbon is provided. The method comprises: dispersing the hard carbon in an aqueous solvent to obtain a slurry, filtering the slurry to obtain a filtrate, and performing inductively coupled plasma spectroscopy on a supernatant of the filtrate to obtain a total mass of water-soluble cations in the filtrate.

[0093] The above-mentioned treatment method can accurately detect the quality of water-soluble cations in hard carbon, effectively reduce the influence of different types of biomass raw materials on the types and contents of impurity elements in hard carbon, and provide a universal measurement method for the evaluation of hard carbon processing performance.

[0094] In some embodiments, the solid content of the slurry is 45%-53%.

[0095] In some embodiments, the solids content of the slurry is 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, or any range therebetween.

[0096] In some embodiments, the hard carbon is water-washed in response to the mass proportion of the water-soluble cations based on the total mass of the hard carbon being greater than 500 ppm.

[0097] Through a simple water washing process and evaluation standards, the process stability of the hard carbon processing and preparation process can be greatly improved, and the low-cost and high-impurity biomass-based hard carbon materials that cannot be used to prepare electrodes can be successfully used in the processing and preparation of electrodes, thereby reducing the production cost of batteries.

[0098] [Anode slurry]

[0099] The negative electrode slurry includes the hard carbon in some embodiments, or the hard carbon prepared by the preparation method in some embodiments, or the hard carbon treated by the treatment method in some embodiments.

[0100] In some embodiments, the negative electrode slurry has a solid content of 45% to 53% and a viscosity of 4000 mPa·s to 20000 mPa·s.

[0101] In the present application, the viscosity of the negative electrode slurry can be tested by methods known in the art, such as selecting a suitable rotor, fixing the viscometer, placing the negative electrode slurry under the viscometer, and the slurry just submerging the scale line of the rotor. Instrument model: Shanghai Fangrui NDJ-5S, rotor: 63# (2000-10000mPa.s), 64# (10000-50000mPa.s), speed: 12r / min, test temperature: 25°C, test time is 5min, and read the data after the display is stable.

[0102] In some embodiments, the solids content of the slurry is 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, or any range therebetween.

[0103] In some embodiments, the viscosity of the negative electrode slurry may be 4000 mPa·s, 5000 mPa·s, 6000 mPa·s, 7000 mPa·s, 8000 mPa·s, 9000 mPa·s, 10000 mPa·s, 12000 mPa·s, 14000 mPa·s, 16000 mPa·s, 18000 mPa·s, 20000 mPa·s, or any range therebetween.

[0104] The negative electrode slurry with a solid content and a viscosity within the above ranges has a suitable viscosity, can be evenly coated, and thus improves the cycle performance of the battery.

[0105] In some embodiments, the negative electrode slurry includes a thickener, and the thickener can be any one of sodium carboxymethyl cellulose and modified sodium polyacrylate.

[0106] In some embodiments, the negative electrode slurry includes a solvent, and the solvent includes an aqueous solvent, such as deionized water.

[0107] [Negative electrode]

[0108] The negative electrode sheet includes a negative electrode film layer prepared from a negative electrode slurry in some embodiments.

[0109] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, the negative electrode film layer includes a negative electrode active material, and the negative electrode active material includes hard carbon in some embodiments or hard carbon prepared by the preparation method in some embodiments or hard carbon treated by the treatment method in some embodiments.

[0110] As an example, the negative electrode current collector has two surfaces opposite to 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 electrode current collector.

[0111] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil or aluminum foil may be used as the metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer base material (such as a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0112] In some embodiments, the negative electrode film layer may further include a binder. The binder may be selected from at least one of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0113] In some embodiments, the negative electrode film layer may further include a conductive agent, which may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0114] In some embodiments, the negative electrode sheet can be prepared by the following method: the components for preparing the negative electrode sheet, such as the negative electrode active material, the conductive agent, the binder and any other components, are dispersed in a solvent (such as deionized water) to form a negative electrode slurry; the negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode sheet can be obtained.

[0115] [Positive electrode]

[0116] The positive electrode sheet generally includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material.

[0117] As an example, the positive electrode current collector has two surfaces opposite to 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 electrode current collector.

[0118] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material base and a metal layer formed on at least one surface of the polymer material base. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0119] In some embodiments, the positive electrode film layer may further optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0120] In some embodiments, the positive electrode film layer may also optionally include a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0121] In some embodiments, the positive electrode active material may be a positive electrode active material for a battery known in the art. As an example, the positive electrode active material may include at least one of the following materials: Prussian blue analogs, sodium-containing phosphates, sodium-containing transition metal oxides, and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as the positive electrode active material of the battery may also be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, the Prussian blue analog is NaxP[R(CN)6] δ ·zH2O, where P and R are each independently selected from at least one of transition metal elements, 0 < x ≤ 2, 0 < δ ≤ 1, and 0 ≤ z ≤ 10; the sodium-containing phosphate is Na b Me c (PO4) d O2X, where Me is one or more of Ti, Cr, Mn, Fe, Co, Ni, V, Cu, and Zn, X is one or more of F, Cl, and Br, 0 < b ≤ 4, 0 < c ≤ 2, 1 ≤ d ≤ 3; the sodium-containing transition metal oxide is Na a M b N c Fe d Mn e O2, M and N include at least one of Sc, Ti, V, Cr, Co, Ni, Cu, Zn, Zr, Nb, Mo, Sn, Hf, Ta, W, and Pb, 0.05 ≤ b ≤ 0.2, 0.2 ≤ c ≤ 0.3, 0.2 ≤ d ≤ 0.3, 0.3 ≤ e ≤ 0.4, 0.75 ≤ a / (b + c + d + e) ≤ 1.

[0122] In some embodiments, the positive electrode sheet can be prepared by the following method: dispersing the above components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry on the positive electrode current collector, and after processes such as drying and cold pressing, the positive electrode sheet can be obtained.

[0123] [Electrolyte]

[0124] The electrolyte plays a role in conducting ions between the positive electrode sheet and the negative electrode sheet. The present application does not specifically limit the type of the electrolyte, and it can be selected according to requirements. For example, the electrolyte can be liquid, gel-like, or all-solid-state.

[0125] In some embodiments, the electrolyte is an electrolyte solution comprising an electrolyte salt and a solvent.

[0126] In some embodiments, the electrolyte includes an electrolyte salt selected from at least one of NaPF6, NaBF4, NaN(SO2F)2(NaFSI), NaClO4, NaAsF6, NaB(C2O4)2(NaBOB), NaBF2(C2O4)(NaDFOB), NaN(SO2RF)2, and NaN(SO2F)(SO2RF), wherein RF is represented by C b F 2b+1 , b is an integer between 1 and 10. In some embodiments, b can be an integer between 1 and 3.

[0127] In some embodiments, the electrolyte salt is selected from one or more of NaPF6, NaN(SO2F)2, NaN(CF3SO2)2, NaB(C2O4)2, and NaBF2(C2O4). In some embodiments, the electrolyte salt is selected from one or more of NaPF6, NaN(SO2RF)2, and NaBF2(C2O4). In some embodiments, RF is -CF3, -C2F5, or -CF2CF2CF3.

[0128] In some embodiments, the electrolyte includes a solvent, and the solvent includes at least one of a chain carbonate, a chain carboxylate, a cyclic carbonic acid, an ether solvent, a sulfone solvent, and a nitrile solvent. In some embodiments, the chain carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), methyl isopropyl carbonate (MIPC), methyl butyl carbonate, ethyl propyl carbonate, dipropyl carbonate, and dibutyl carbonate. In some embodiments, the chain carbonate includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and methyl propyl carbonate (MPC). In some embodiments, the chain carboxylate includes at least one of methyl formate (MF), ethyl formate (EF), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), ethyl butyrate (EB), methyl acetate (MA), ethyl acetate (EA), and propyl acetate (PA). In some embodiments, the linear carboxylic acid ester includes at least one of methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl acetate (MA), ethyl acetate (EA), and propyl acetate (PA). In some embodiments, the ether solvent includes at least one of dioxolane (DOL), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2Me-THF), tetrahydropyran (THP), 1,2-dimethoxyethane (DME), diethylene glycol dimethyl ether (DG), 1,2-diethoxyethane, and 1,2-dibutoxyethane.

[0129] In some embodiments, the electrolyte may further 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 properties, such as additives that improve battery overcharge performance, and additives that improve battery high or low temperature performance.

[0130] [Isolation film]

[0131] In some embodiments, the secondary battery further includes a separator. The present application has no particular limitation on the type of separator, and any known porous separator with good chemical and mechanical stability can be selected.

[0132] In some embodiments, the material of the separator can be selected from at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0133] [Secondary battery]

[0134] In one embodiment of the present application, a secondary battery is provided, including an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a separator, and a negative electrode sheet according to any embodiment.

[0135] In some embodiments, the positive electrode sheet, the negative electrode sheet, and the separator can be formed into an electrode assembly through a winding process or a lamination process.

[0136] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0137] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. Alternatively, the outer packaging of the secondary battery can be a soft shell, such as a pouch-type soft shell. The soft shell can be made of plastic, such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0138] The present application has no particular limitation on the shape of the secondary battery, which may be cylindrical, square, or any other shape. For example, FIG1 shows a secondary battery 5 having a square structure as an example. Optionally, the secondary battery is a lithium-ion battery or a sodium-ion battery.

[0139] In some embodiments, referring to Figure 2, the outer packaging may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 can be covered on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet and the isolation membrane can be formed into an electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the secondary battery 5 can be one or more, and those skilled in the art can select according to specific actual needs.

[0140] In some embodiments, secondary batteries can be assembled into a battery module. The number of secondary batteries contained in the battery module can be one or more. The specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0141] FIG3 illustrates an exemplary battery module 4. Referring to FIG3 , within the battery module 4, multiple secondary batteries 5 may be arranged sequentially along the length of the battery module 4. Alternatively, the arrangement may be arranged in any other manner. Furthermore, the multiple secondary batteries 5 may be secured together using fasteners.

[0142] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of secondary batteries 5 are received in the receiving space.

[0143] In some embodiments, the battery modules described above may also be assembled into a battery pack. The battery pack may contain one or more battery modules, and the specific number may be selected by those skilled in the art based on the application and capacity of the battery pack.

[0144] Figures 4 and 5 illustrate an example battery pack 1. Referring to Figures 4 and 5 , the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 can be placed over the lower case 3 to form an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0145] In one embodiment of the present application, an electric device is provided, comprising at least one of a secondary battery according to any embodiment, a battery module according to any embodiment, or a battery pack according to any embodiment.

[0146] The electrical device includes at least one of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as a power source for the electrical device, and can also be used as an energy storage unit for the electrical device. The electrical device may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

[0147] As the electrical device, a secondary battery, a battery module or a battery pack can be selected according to its usage requirements.

[0148] Figure 6 shows an example of an electric device. This device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the secondary battery, a battery pack or battery module can be used.

[0149] Another example device may be a mobile phone, a tablet computer, a notebook computer, etc. Such a device is generally required to be lightweight and thin, and may use a secondary battery as a power source.

[0150] Example

[0151] Below, the embodiment of the present application is described. The embodiment described below is exemplary and is only used to explain the present application, and is not to be construed as limiting the present application. Where specific techniques or conditions are not specified in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. Reagents or instruments used that do not specify the manufacturer are conventional products that can be obtained commercially.

[0152] 1. Preparation method

[0153] Example 1

[0154] 1) Preparation of hard carbon

[0155] The selected biomass carbon source sorghum stalks are washed and dried, and then crushed by a machine; pre-sintered at 800°C in a nitrogen atmosphere for 2 hours; the pre-sintered sample is crushed and screened using a crusher to form a hard carbon precursor; sintered at 1200°C in a nitrogen atmosphere for 2 hours and then screened a second time; the high-temperature sintered product is impregnated with deionized water at room temperature to form a hard carbon slurry with a solid content of 20%, and stirred at a speed of 1200r / min for 1 hour; then transferred to a centrifuge to remove moisture, and dried to obtain hard carbon.

[0156] 2) Preparation of negative electrode sheet

[0157] The prepared hard carbon, conductive agent acetylene black, binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC-Na) were fully stirred and mixed in a deionized water solvent system according to a weight ratio of 90:4:4:2 to obtain a negative electrode slurry with a solid content of 50%. The negative electrode slurry was prepared by mixing 0.14 g (dry weight) / 1540.25 mm 2 The amount of the coating was evenly coated on the negative electrode current collector copper foil with a thickness of 13 μm, the coating speed was 25 m / min, and the temperature of the coating oven was 110°C; then the negative electrode sheet was obtained by cold pressing and slitting.

[0158] 3) Preparation of positive electrode sheet

[0159] The positive electrode active material Na3V2(PO4)2O2F, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) were fully stirred and mixed in an appropriate amount of N-methylpyrrolidone (NMP) at a weight ratio of 80:10:10 to form a uniform positive electrode slurry; the positive electrode slurry was mixed at a ratio of 0.28g (dry weight) / 1540.25mm 2 The density is evenly coated on the positive electrode current collector aluminum foil with a thickness of 13μm, and the coating speed is 30m / min; the temperature of the coating oven is 110℃, and then the positive electrode sheets are obtained through cold pressing and slitting.

[0160] 4) Preparation of electrolyte

[0161] In an argon atmosphere glove box (H2O content <10ppm, O2 content <1ppm), sodium hexafluorophosphate NaPF6 was dissolved in a mixed system of organic solvents ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC volume ratio of 3:7) and stirred evenly to obtain an electrolyte with a sodium salt concentration of 1 mol / L.

[0162] 5) Isolation film

[0163] A 9 μm polyethylene (PE) porous polymer film was used as the separator.

[0164] 6) Preparation of batteries

[0165] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is placed between the positive and negative electrode sheets to isolate the positive and negative electrode sheets. The bare battery cell is wound, the tabs are welded, and the bare battery cell is placed in an outer package. The above-prepared electrolyte is injected into the dried battery cell, and then the sodium secondary battery product of Example 1 is obtained after packaging, standing, formation, shaping, and capacity testing.

[0166] The preparation methods of the batteries of Examples 2 to 4 are similar to those of the battery of Example 1, but the rotation speed and / or washing time of the water washing are adjusted respectively. The specific parameters are shown in Table 1.

[0167] The preparation method of the battery of Example 5 is similar to that of the battery of Example 1, but the water washing step is adjusted to be performed before high-temperature sintering.

[0168] The preparation methods of the batteries of Examples 6 to 7 are similar to those of the battery of Example 1, but the type of biomass carbon source is adjusted. The specific parameters are shown in Table 1.

[0169] The preparation method of the battery in Example 8 is similar to that of Example 1, except that, during the preparation of the hard carbon, an acid washing step is added after high-temperature sintering and before water washing. The process conditions of the acid washing step are:

[0170] The hard carbon particles prepared above were impregnated with 5% dilute hydrochloric acid to form a hard carbon slurry with a solid content of 20%, and stirred at 1200 r / min in a polytetrafluoroethylene container for 2 hours; then transferred to a centrifuge to remove water, and then washed twice with water using the method in Example 1 to reduce residual acid and impurities in the hard carbon.

[0171] The preparation method of the battery in Example 9 is basically the same as that in Example 1, except that in the preparation process of the hard carbon, the pickling process is performed after pre-sintering and before high-temperature sintering. The process conditions of the pickling step are:

[0172] The pre-sintered product was impregnated with 5% dilute hydrochloric acid to form a hard carbon slurry with a solid content of 20%, and stirred at 1200 r / min in a polytetrafluoroethylene container for 2 hours; then transferred to a centrifuge to remove water, and then washed twice with water using the method in Example 1 to reduce residual acid and impurities.

[0173] The preparation method of the battery in Comparative Example 1 is basically the same as that in Example 1, except that there is no water washing step in Comparative Example 1.

[0174] The preparation method of the battery in Comparative Example 2 is basically the same as that in Example 1, except that the washing speed and washing time in the washing step are adjusted, as shown in Table 1.

[0175] The preparation method of the battery in Comparative Example 3 is basically the same as that in Example 6, except that there is no water washing step in Comparative Example 3.

[0176] The preparation method of the battery in Comparative Example 4 is basically the same as that in Example 7, except that there is no water washing step in Comparative Example 4.

[0177] 2. Test Method

[0178] 1. Performance test of hard carbon

[0179] 1) Test method for mass ratio of water-soluble cations

[0180] 100g of hard carbon was dispersed in 400g of deionized water to form a hard carbon slurry with a solid content of 20%. The mixture was stirred and dispersed at 1200r / min for 120min. The resulting hard carbon slurry was filtered, and the filtrate was collected. 8mL of the filtrate was added to 2ml of reverse aqua regia (HNO3:HCl volume ratio of 3:1). Microwave digestion was performed, and the filtrate was then transferred to an inductively coupled plasma spectrometer (ICP) to measure the types and masses of different ions in the filtrate. The total mass of water-soluble cations in the hard carbon per unit mass was obtained by summing and conversion. The plasma spectrometer was a Thermo Scientific single quadrupole inductively coupled plasma mass spectrometer (SQ-ICP-MS).

[0181] 2) Test of the mass ratio of elements in hard carbon

[0182] The mass fractions of elements in hard carbon were determined using an inductively coupled plasma spectrometer (ICP), a Thermo Scientific single quadrupole inductively coupled plasma mass spectrometer (SQ-ICP-MS). The test was performed as follows: 0.2 g of hard carbon was weighed and added to 10 ml of reverse aqua regia (a mixture of HNO₃ and HCl in a volume ratio of 3:1). The sample was then microwave-digested in an Anton Paar Multiwave 7000 at a frequency of 2450 MHz for 5 minutes. The sample was then transferred to the ICP spectrometer for analysis to determine the mass fractions of the different elements per unit mass of the hard carbon.

[0183] 3) Hard carbon true density test

[0184] Based on the Archimedean principle, skeletal density (also known as true density) analysis using helium (He) as a probe provides accurate values ​​for skeletal density because helium can enter almost all open pores except closed pores. The van der Waals (vd W) radius, or aerodynamic diameter, of the measuring medium (He) must be small enough to ensure effective probing depth.

[0185] The true density of hard carbon is measured as follows: Weigh a mass of hard carbon, M, and place it in a true density tester (Accu Pyc II 1340 analyzer) at 25°C. The test system is sealed and helium is introduced according to the program. The gas pressures in the sample chamber and expansion chamber are measured, and the gas volumes in the sample chamber and expansion chamber are calculated based on the ideal gas state equation (v = nRT / P). The volume of gas displaced by the hard carbon under certain temperature and pressure conditions is then calculated, which is the true volume V of the hard carbon. The true density of the hard carbon is then M / V, and the unit of true density is g / cm 3 .

[0186] 4) Hard carbon gram capacity test

[0187] The gram capacity test was conducted in a button cell. The negative electrode slurry prepared in the example was manually applied to the positive electrode sheet of the button cell, and a sodium metal sheet was used as the negative electrode sheet. The prepared button cell was placed in a Xinwei 5V 10mA test cabinet for testing. The test process was to discharge at a constant current of 0.05C for 2 hours, then discharge at a constant current of 0.1C to a lower voltage of 0.05V. After 5 minutes of stagnation, the cell was charged at a current of 0.1C to an upper voltage of 2.0V, then switched to constant voltage charging at 0.03C, and then discharged at a constant current of 0.1C to a lower voltage of 0.05V. The actual discharge capacity of the button cell was recorded. Hard carbon gram capacity = actual discharge capacity of the button cell / [hard carbon mass percentage × (electrode sheet mass - aluminum foil mass)] × 100%.

[0188] 2. Property test of negative electrode slurry

[0189] 1) Slurry viscosity test

[0190] Select a suitable rotor, fix the viscometer, place the negative electrode slurry under the viscometer so that the slurry just submerges the scale line of the rotor. Instrument model: Shanghai Fangrui NDJ-5S, rotor: 63# (2000-10000mPa.s), 64# (10000-50000mPa.s), speed: 12r / min, test temperature: 25℃, test time is 5min, read the data after the display is stable.

[0191] 3. Battery performance test

[0192] 1) Battery cycle test

[0193] At 25°C, charge the battery at a constant current of 1 / 3C to 3.95V. Then charge it at a constant voltage of 3.95V to a current of 0.05C. Let it rest for 5 minutes, and then discharge it at a constant current of 1 / 3C to 1.5V. The resulting capacity is recorded as the initial capacity C0. The cutoff condition is Pn ≤ 80%. Repeat the above steps for the same battery and record the discharge capacity Cn of the battery after the nth cycle. The battery capacity retention rate after each cycle is Pn = Cn / C0 × 100%. When Pn ≤ 80%, stop the test and record the number of cycles.

[0194] 2) Battery initial performance test

[0195] At 25°C, charge the battery at a constant current of 1 / 3C to 4.2V, then charge it at a constant voltage of 4.2V to a current of 0.05C, and record the charge capacity C1. After 5 minutes of storage, discharge it at a constant current of 1 / 3C to 1.5V. The resulting capacity is recorded as the initial discharge capacity C0. C0 / C1 is recorded as the first efficiency.

[0196] 3. Analysis of test results of various embodiments and comparative examples

[0197] Batteries of various examples and comparative examples were prepared according to the above methods, and various performance parameters were measured. The results are shown in the table below.

[0198] Table 1

[0199] Table 2

[0200] The hard carbon in the comparative example contains high-quality water-soluble ions, which causes the viscosity of the slurry containing the hard carbon to be too low, making the slurry difficult to coat and form, or there are serious thick edges after the slurry is coated, which is easy to burst during the cold pressing process and difficult to prepare and form.

[0201] From the comparison between the examples and the comparative examples, it can be seen that when the total mass proportion of water-soluble cations in the hard carbon does not exceed 500 ppm based on the total mass of the hard carbon, the viscosity of the negative electrode slurry is suitable for coating and has good processing performance.

[0202] From the comparison between the embodiments, it can be seen that when the total mass proportion of the water-soluble cations in the hard carbon is 5 ppm to 450 ppm based on the total mass of the hard carbon, the secondary battery has good processing performance, first efficiency and cycle stability.

[0203] From the comparison of the embodiment and the comparative example, it can be seen that when the mass proportion of silicon element in the hard carbon does not exceed 570 ppm based on the total mass of the hard carbon, the viscosity of the negative electrode slurry is suitable for coating, has good processing performance, and the battery has good cycle stability.

[0204] From the comparison between the embodiments, it can be seen that when the mass proportion of silicon element in the hard carbon is 300ppm to 550ppm based on the total mass of the hard carbon, the secondary battery has good processing performance, gram capacity, first efficiency and cycle performance.

[0205] From the comparison between Examples 1-8 and Example 9, it can be seen that the true density of hard carbon is 1.45 g / cm 3 ~1.65g / cm 3 When the hard carbon has good pore-forming ability, the secondary battery has a higher gram capacity.

[0206] From the comparison between Example 1 and Example 5, it can be seen that the water washing process after high-temperature sintering helps to maintain the pore-forming effect of impurities in the high-temperature sintering step and improve the specific capacity of hard carbon.

[0207] From the comparison between Example 1 and Examples 8 and 9, it can be seen that although acid washing can further reduce the content of water-soluble cations, it will also lead to a decrease in the specific capacity of the hard carbon and / or the first efficiency of the secondary battery.

[0208] As can be seen from the examples, the hard carbon processing method provided in the present application is applicable to different types of hard carbon. Based on this, the processing performance of different hard carbons can be effectively predicted, thereby improving production efficiency and reducing production costs.

[0209] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are merely examples, and any embodiments having substantially the same structure and effect as the technical concept within the scope of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the present application, any other embodiments that can be conceived by those skilled in the art and that combine some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A hard carbon, characterized in that The total mass proportion of water-soluble cations in the hard carbon does not exceed 500 ppm based on the mass of the hard carbon.

2. The hard carbon according to claim 1, characterized in that The total mass proportion of the water-soluble cations in the hard carbon is 5 ppm to 450 ppm based on the mass of the hard carbon.

3. The hard carbon according to claim 1 or 2, characterized in that The water-soluble cations include sodium ions (Na + ), potassium ion (K + ), magnesium ion (Mg 2+ ), calcium ions (Ca 2+ ), aluminum ions (Al 3+ ) at least one of.

4. The hard carbon according to any one of claims 1 to 3, characterized in that Based on the total mass of the hard carbon, the mass proportion of silicon element in the hard carbon does not exceed 570 ppm.

5. The hard carbon according to any one of claims 1 to 4, characterized in that Based on the total mass of the hard carbon, the mass proportion of silicon element in the hard carbon is 300 ppm to 550 ppm.

6. The hard carbon according to any one of claims 1 to 5, characterized in that Based on the total mass of the hard carbon, the mass proportion of any one of the water-soluble sodium ions, water-soluble potassium ions, water-soluble magnesium ions, water-soluble calcium ions, and water-soluble aluminum ions in the hard carbon is 1 ppm to 260 ppm.

7. The hard carbon according to any one of claims 1 to 6, characterized in that The true density of the hard carbon at room temperature is 1.45 g / cm 3 ~1.65g / cm 3 .

8. The hard carbon according to any one of claims 1 to 7, characterized in that The true density of the hard carbon at room temperature is 1.45 g / cm 3 ~1.6g / cm 3 .

9. A method for preparing hard carbon, characterized in that: The preparation method includes a water washing step, so that the total mass proportion of water-soluble cations in the hard carbon does not exceed 500 ppm based on the mass of the hard carbon.

10. The preparation method according to claim 9, characterized in that: The preparation method is such that the total mass proportion of water-soluble cations in the hard carbon is 5 ppm to 450 ppm based on the mass of the hard carbon.

11. The preparation method according to claim 9 or 10, characterized in that: The preparation method specifically comprises the following steps: Providing a biomass-based carbon source; Pre-sintering the carbon source to prepare a precursor; Sintering the precursor at high temperature to prepare a product; The product is washed with water to prepare the hard carbon.

12. The preparation method according to any one of claims 9 to 11, characterized in that: The precursor and the product have not been acid treated.

13. A secondary battery, characterized in that: The invention comprises the hard carbon according to any one of claims 1 to 8 or the hard carbon prepared by the preparation method according to any one of claims 9 to 12.

14. An electrical device, characterized in that: Includes the secondary battery as claimed in claim 13.

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