A negative electrode material, a preparation method and a sodium ion battery

Abstract

The application provides a negative electrode material, a preparation method thereof and a sodium ion battery. The negative electrode material provided by the application comprises hard carbon, a carbon coating layer covering the hard carbon, and closed pores formed by the carbon coating layer covering the pore opening on the outer surface of the hard carbon, the closed pores have a pore size ranging from 0.1 nm to 3 nm, the specific surface area A of the negative electrode material and the true density B satisfy AxB<8, the specific surface area A of the negative electrode material is 0.5 m 2 / g-6 m 2 / g, the true density B of the negative electrode material is 0.5 g / cm 3 -1.45 g / cm 3 The large number of closed pores of the negative electrode material can serve as a sodium storage site, that is, the negative electrode material has high closed pore volume, low true density and high closed pore volume, so that the negative electrode material has high gram capacity, and the energy density of the sodium ion battery is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a negative electrode material, a preparation method thereof and a sodium ion battery. BACKGROUND

[0002] Sodium ion batteries have the advantages of low price, moderate energy density, low temperature and good rate performance, and are widely used in low-speed electric vehicles, start-stop power sources, energy storage and the like. However, since the energy density of the current sodium ion battery is greatly reduced compared with the lithium ion battery, the application of the sodium ion battery is significantly limited.

[0003] Research has found that improving the specific capacity and charge-discharge voltage platform of the negative electrode material of the sodium ion battery can significantly improve the energy density of the sodium ion battery and improve the output voltage and power of the sodium ion battery, thereby greatly improving the user experience. Therefore, it is very important to improve the specific capacity and charge-discharge voltage platform of the negative electrode material of the sodium ion battery. However, the specific capacity and charge-discharge voltage platform of the negative electrode material of the sodium ion battery reported and applied in the prior art are generally low, which limits the application of the energy density of the sodium ion battery. SUMMARY

[0004] In view of the above problems in the prior art, the first aspect of the application provides a negative electrode material, wherein the specific surface area A and the true density B of the negative electrode material satisfy AxB<8; preferably AxB<6; more preferably AxB<4. When the AxB of the negative electrode material is within the above range, the true density and the specific surface area are both controlled within a certain range, so as to ensure the pore volume, the compaction density and the specific capacity of the negative electrode material.

[0005] In some embodiments of the application, the specific surface area A of the negative electrode material is 0.5m 2 / g-6m 2 / g; preferably 0.9m 2 / g-5m 2 / g; more preferably 1m 2 / g-4m 2 / g. The negative electrode material has the specific surface area within the above range, which can ensure that the closed porosity of the negative electrode material is high.

[0006] In some embodiments of the application, the true density B of the negative electrode material is 0.5g / cm 3 -1.45g / cm 3 ; preferably 0.8g / cm 3 -1.4g / cm 3 ; more preferably 0.95g / cm 3 -1.3g / cm 3The true density can also be referred to as a skeleton density. The true density is tested by using nitrogen as a medium. Due to the large number of closed pores in the interior of the negative electrode material particles, nitrogen cannot enter these closed pores during testing. The negative electrode material has a true density in the above range, indicating that the negative electrode material has a high closed pore rate, resulting in a high closed pore volume.

[0007] The negative electrode material provided in the present application comprises hard carbon, a carbon coating layer covering the hard carbon, and closed pores formed by the carbon coating layer covering the open pores on the outer surface of the hard carbon, wherein the proportion of the closed pore volume in the sum of all open pore volumes and closed pore volumes is more than 90%; preferably, the proportion of the closed pore volume in the sum of all open pore volumes and closed pore volumes is more than 95%; more preferably, the proportion of the closed pore volume in the sum of all open pore volumes and closed pore volumes is more than 99%.

[0008] In some embodiments of the present application, the closed pore diameter of the negative electrode material is 3 nm or less; preferably, 0.1 nm to 3 nm; preferably, 0.5 nm to 3 nm; more preferably, 1 nm to 3 nm.

[0009] In some embodiments of the present application, the negative electrode material I d / I g is in the range of 1.0 to 2.0; preferably, the negative electrode material I d / I g is in the range of 1.3 to 1.6. Wherein I d represents the intensity of the characteristic peak D peak of the negative electrode material existing near 1350±50 cm -1 in the Raman spectrum, and I g represents the intensity of the characteristic peak G peak of the negative electrode material existing near 1580±50 cm -1 in the Raman spectrum; the value of I d / I g represents the degree of disorder of the material, and the larger the value, the higher the degree of disorder. The closed pore volume of the negative electrode material increases the degree of disorder of the negative electrode material, and the value of I d / I g in the above range ensures that the degree of disorder of the negative electrode material is improved.

[0010] In some embodiments of the present application, the negative electrode material has a diffraction peak position in the X-ray diffraction spectrum in the range of 20° to 30°, and the half-peak width of the diffraction peak is 3° to 10°; preferably, the negative electrode material has a diffraction peak position in the range of 24° to 25°, and the half-peak width is 3° to 4°. The high degree of disorder of the negative electrode material can be tested by X-ray diffraction method. The negative electrode material has only one diffraction peak in the above numerical range, which is due to the high degree of disorder of the negative electrode material, the random arrangement of the internal microcrystals, and the disordered distribution of the interlayer spacing.

[0011] According to a second aspect of this application, this application provides a method for preparing the negative electrode material, the method including but not limited to the following steps: adjusting the closed-pore ratio and disorder of the negative electrode material by changing the hard carbon precursor raw material and the pore-forming agent, changing the sintering temperature, adding a water activation step, and changing the number of carbon coating treatments, thereby adjusting the specific capacity.

[0012] In some embodiments of this application, the preparation method includes, but is not limited to, the following steps:

[0013] S1, Obtaining initial raw materials: Mix one or more precursor raw materials with the required pore-forming agent evenly;

[0014] S2, Obtaining the first precursor: Under a protective atmosphere, the initial raw materials are sintered and heat-preserved;

[0015] S3, Obtaining the second precursor: Purifying and screening the first precursor;

[0016] S4, Obtaining the negative electrode material: The second precursor is carbon-coated to obtain the negative electrode material.

[0017] In some embodiments of this application, step S2 is carried out entirely under a protective atmosphere. When a water activation step is added during the heat preservation process, the protective atmosphere is switched to water vapor for heat preservation and activation.

[0018] In some embodiments, the protective atmosphere is an inert gas; in some embodiments, the inert gas includes, but is not limited to, at least one of nitrogen, argon, helium, neon, krypton, and xenon; preferably, the inert gas is nitrogen.

[0019] In some embodiments of this application, the precursor raw materials for step S1 include, but are not limited to, one or any mixture of resin-based precursors, petroleum-based precursors, and biomass-based precursors; in some embodiments, the precursor raw materials include, but are not limited to, one or any mixture of epoxy resin, phenolic resin, polyfurfuryl alcohol, polyvinyl alcohol, polythiophene, petroleum coke, asphalt, coal, nutshell, lignin, sodium lignin sulfonate, glucose, starch, and tannic acid; the pore-forming agent includes, but is not limited to, one or any mixture of cetyltrimethylammonium bromide, melamine, styrene, biphenyl, naphthalene, potassium hydroxide, sodium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium aminophosphate, sodium dihydrogen phosphate, and ammonium hydrogen phosphate.

[0020] In some embodiments of the present application, the precursor raw material and the pore-forming agent of step S1 are mixed in a certain ratio, and the mixing ratio of the precursor and the pore-forming agent is (50-150):(50-150) by mass ratio; preferably, the mixing ratio of the precursor and the pore-forming agent is (80-120):(80-120) by mass ratio; more preferably, the mixing ratio of the precursor and the pore-forming agent is (95-100):(95-100) by mass ratio.

[0021] In some embodiments of the present application, the sintering treatment temperature of step S2 can be 700-1000°C; preferably, the sintering treatment temperature of step S2 can be 750-800°C; more preferably, the sintering treatment temperature of step S2 is 800°C. In some embodiments of the present application, the heating rate of the sintering treatment temperature of step S2 can be 3-10°C / min; preferably, the heating rate of the sintering treatment temperature of step S2 can be 5-7 / min.

[0022] In some embodiments of the present application, the carbon coating process includes at least one carbon coating; preferably, the carbon coating process is a double carbon coating process. In some embodiments of the present application, the carbon coating process includes a gas phase carbon coating process; specifically, a carbon coating required gas atmosphere is introduced at a certain temperature, and carbon is deposited on the surface of the hard carbon negative electrode material. The pores are coated to form closed pores, and the formation of closed pores enhances the sodium storage capacity.

[0023] In some embodiments of the present application, the carbon coating gas atmosphere includes a gas phase hydrocarbon carbon source, which is at least one of but not limited to methane, acetylene, ethylene, ethane, propane, propylene, propyne, acetone and benzene.

[0024] In some embodiments of the present application, the carbon coating process can include introducing a gas phase hydrocarbon carbon source at a certain temperature for a certain period of time for the first carbon coating; preferably, the carbon coating process can include introducing a gas phase hydrocarbon carbon source at a certain temperature for a certain period of time for the first carbon coating, and then switching to another gas phase hydrocarbon carbon source atmosphere for a certain period of time for the second carbon coating.

[0025] According to the third aspect of the present application, the present application provides a negative electrode sheet, which comprises a binder, a thickening agent, and the negative electrode material and a negative electrode current collector, or the negative electrode sheet comprises a binder, a thickening agent, and the negative electrode material prepared by the preparation method and a negative electrode current collector.

[0026] In some embodiments of the present application, the cutting 1540.25mm 2The average coating weight (CW) of the negative electrode material coated on the surface of the negative electrode sheet is 30 mg-200 mg, the thickness (h) is 0.039 mm-0.433 mm, and CW / h is between 900-1600.

[0027] According to a fourth aspect of the present application, the present application provides an electrochemical device comprising the negative electrode sheet of the third aspect; the electrochemical device is a sodium ion battery.

[0028] According to a fifth aspect of the present application, the present application provides an electronic device, characterized in that the electronic device comprises the electrochemical device of the fourth aspect.

[0029] The negative electrode material provided by the present application is prepared by using a specific precursor and a specific double-coating method, so that the closed porosity of the negative electrode material obtained in the present application reaches more than 90%. The higher closed porosity results in larger closed pore volume and greater disorder degree, which improves the sodium storage capacity. The prepared sodium ion battery has higher capacity and energy density, in addition, it also has higher average discharge voltage, and the sodium ion battery has higher output power. The present application overcomes the problem of low capacity and energy density of the sodium ion battery in the prior art. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 The SEM diagram of the negative electrode material provided by the present application is shown in the following figure. DETAILED DESCRIPTION

[0031] The technical solutions of the present application are further illustrated by specific examples below, and the specific examples do not represent a limitation on the protection scope of the present application. Some non-essential modifications and adjustments made by others according to the concept of the present application still belong to the protection scope of the present application.

[0032] For the sake of simplicity, only some numerical ranges are specifically disclosed for a certain parameter in this document. However, any lower limit can be combined with any upper limit to form a range not explicitly recited, any lower limit can be combined with other lower limits to form a range not explicitly recited, and similarly any upper limit can be combined with any other upper limit to form a range not explicitly recited. In addition, each individually disclosed point or single numerical value can itself serve as a lower limit or upper limit to be combined with any other point or single numerical value or with other lower limits or upper limits to form a range not explicitly recited.

[0033] In the description herein, unless otherwise specified, "above", "below" include the number.

[0034] The terms used in this application, unless otherwise indicated, have their ordinary meanings in the art. Unless otherwise specified, the values of the parameters recited in this application can be measured using any method known in the art (e.g., can be tested according to the methods given in the examples of this application).

[0035] The conjunctive use of the terms “at least one,” “at least one of,” “at least one of the,” or other similar phrases, with a list of items means that any combination of the listed items is possible. For example, if items A and B are listed, the phrase “at least one of A and B” means A alone, B alone, or A and B. In another example, if items A, B, and C are listed, the phrase “at least one of A, B, and C” means A alone, B alone, C alone, A and B (excluding C), A and C (excluding B), B and C (excluding A), or all of A, B, and C. Item A can include a single component or multiple components. Item B can include a single component or multiple components. Item C can include a single component or multiple components.

[0036] The terms “first,” “second,” and the like, in the description and in the claims of this application, are used for distinguishing between similar objects and are not necessarily used to describe a particular sequential or chronological order. Moreover, the terms “comprises,” “comprising,” “includes,” “including,” and the like, are used in the sense of “including but not limited to.” For example, a process, method, system, product, or apparatus that comprises a list of steps or elements is not necessarily limited to the listed steps or elements, but can optionally include additional steps or elements not expressly listed or inherent to such process, method, system, product, or apparatus. The terms “plurality” and “a plurality” mean two or more.

[0037] The terms used in this application have their ordinary meanings in the art, such as:

[0038] Open pores refer to the pore structure on the surface of a porous material that is accessible to fluids and is in communication with the outside.

[0039] Closed pores refer to the pore structure on the surface of a porous material that is not accessible to fluids and is not in communication with the outside, for example, by being coated with a carbon material.

[0040] Closed pore ratio refers to the percentage of closed pores in the total amount of open and closed pores.

[0041] Pore-forming agent refers to an additive that creates a pore structure in a material, for example, that can be mixed with a hard carbon precursor material to form a pore structure in a hard carbon material.

[0042] According to a first aspect of the present application, the present application provides a negative electrode material, a specific surface area A of the negative electrode material and a true density B of the negative electrode material satisfy AxB<8; preferably AxB<6; more preferably AxB<4. When the AxBof the negative electrode material is within the above range, the true density and the specific surface area are both controlled within a certain range, thereby ensuring the pore volume, the compaction density and the gravimetric capacity of the negative electrode material.

[0043] In some embodiments of the present application, the specific surface area A of the negative electrode material is 0.5m 2 / g-6m 2 / g; preferably 0.9m 2 / g-5m 2 / g; more preferably 1m 2 / g-4m 2 / g. For example, the specific surface area of the negative electrode material can be 0.5m 2 / g, 1m 2 / g, 1.5m 2 / g, 2m 2 / g, 2.5m 2 / g, 3m 2 / g, 3.5m 2 / g, 4m 2 / g, 4.5m 2 / g, 5m 2 / g, 5.5m 2 / g, 6m 2 / g or a range composed of any two of the above values. The negative electrode material has a specific surface area within the above range, which can ensure a higher closed porosity of the negative electrode material.

[0044] In some embodiments of the present application, the true density B of the negative electrode material is 0.5g / cm 3 -1.45g / cm 3 ; preferably 0.8g / cm 3 -1.4g / cm 3 ; more preferably 0.95g / cm 3 -1.3g / cm 3 . For example, the true density of the negative electrode material can be 0.5g / cm 3 , 0.6g / cm 3 , 0.7g / cm 3 , 0.8g / cm 3 , 0.9g / cm 3 , 1.0g / cm 3 , 1.1g / cm 3 , 1.2g / cm 3 , 1.3g / cm 3 , 1.4g / cm 31.45 g / cm3 3 or a range consisting of any two of the above values. The true density is also referred to as the skeleton density. The true density is tested by using nitrogen as the medium. Since the interior of the negative electrode material particle has a large number of closed pores, nitrogen cannot enter these closed pores during the test. The negative electrode material has a true density in the above range, indicating that the negative electrode material has a high closed pore rate, resulting in a high closed pore volume.

[0045] The negative electrode material includes hard carbon and a carbon coating layer coating the hard carbon, and closed pores formed by the open pores of the carbon coating layer coating the outer surface of the hard carbon. The proportion of the closed pore volume in the sum of all open pore volumes and closed pore volumes is more than 90%. Preferably, the proportion of the closed pore volume in the sum of all open pore volumes and closed pore volumes is more than 95%; more preferably, the proportion of the closed pore volume in the sum of all open pore volumes and closed pore volumes is more than 99%. When the proportion of closed pores is high, the skeleton density of the negative electrode material is low, and the sodium storage capacity is strong.

[0046] In some embodiments of the present application, the closed pore diameter of the negative electrode material is 3 nm or less; preferably 0.1 nm to 3 nm; preferably 0.5 nm to 3 nm; more preferably 1 nm to 3 nm. Specifically, the closed pore diameter of the negative electrode material can be 0.1 nm, 0.5 nm, 1.0 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, 2.0 nm, 2.1 nm, 2.2 nm, 2.3 nm, 2.4 nm, 2.5 nm, 2.6 nm, 2.7 nm, 2.8 nm, 2.9 nm, 3.0 nm, or a range consisting of any two of the above values. By adjusting the size of the closed pore diameter of the negative electrode material, the negative electrode material can have a suitable closed pore volume.

[0047] In some embodiments of the present application, the negative electrode material I d / I g is in the range of 1.0 to 2.0; preferably, the negative electrode material I d / I g is in the range of 1.3 to 1.6; specifically, the value of I d / I g may be 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, or a range consisting of any two of the above values. The value of I d represents the intensity of the characteristic peak D peak in the Raman spectrum of the negative electrode material near 1350±50 cm -1 , which is caused by the symmetric stretching vibration radial breathing mode of sp2 carbon atoms in the aromatic ring; I gThe value represents the intensity of the characteristic peak G peak in the Raman spectrum of the negative electrode material, which is caused by the stretching vibration between sp2 carbon atoms. -1 The value of I d / I g The value represents the degree of disorder of the material, and the larger the ratio, the higher the degree of disorder. The increase in the closed pore volume of the negative electrode material increases the degree of disorder of the negative electrode material, and the value of I d / I g The value ensures that the degree of disorder of the negative electrode material is improved.

[0048] In some embodiments of the present application, the negative electrode material has a diffraction peak position in the range of 20° to 30° in the X-ray diffraction spectrum, and the half-peak width of the diffraction peak is 3° to 10°; preferably, the diffraction peak position of the negative electrode material is in the range of 24° to 25°, and the half-peak width is 3° to 4°. The high degree of disorder of the negative electrode material can be tested by X-ray diffraction method, and the negative electrode material has only one diffraction peak in the above numerical range, which is due to the high degree of disorder of the negative electrode material, the random arrangement of the internal microcrystals, and the disordered distribution of the interlayer spacing.

[0049] According to a second aspect of the present application, the present application provides a preparation method of the negative electrode material, which includes but is not limited to the following steps: adjusting the closed pore rate and the degree of disorder of the negative electrode material by changing at least one of the hard carbon precursor raw material and the pore-forming agent material, changing the sintering treatment temperature, increasing the water activation step, and changing the number of carbon coating treatments, and then adjusting the specific capacity.

[0050] In some embodiments of the present application, the preparation method includes but is not limited to the following steps:

[0051] S1, obtaining of initial raw materials: uniformly mixing one or more precursor raw materials with a required pore-forming agent;

[0052] S2, obtaining of a first precursor: performing sintering treatment and heat preservation treatment on the initial raw materials under a protective atmosphere;

[0053] S3, obtaining of a second precursor: performing purification and screening treatment on the first precursor;

[0054] S4, obtaining of a negative electrode material: performing carbon coating on the second precursor to obtain the negative electrode material.

[0055] In some embodiments of the present application, in step S2, the whole process is performed under a protective atmosphere, and when a water activation step is added during the heat preservation process, the protective atmosphere is switched to water vapor for heat preservation and activation.

[0056] In some embodiments, the protective atmosphere is an inert gas; in some embodiments, the inert gas includes, but is not limited to, at least one of nitrogen, argon, helium, neon, krypton, and xenon; preferably, the inert gas is nitrogen.

[0057] In the above preparation method, the closed porosity and disorder degree of the negative electrode material are regulated by at least one of changing the hard carbon precursor raw material and the pore-forming agent substance, changing the sintering treatment temperature, adding a water activation step, and changing the number of carbon coating treatments. For example, changing the hard carbon precursor raw material and the pore-forming agent substance can change the specific surface area and the disorder degree, and change the specific capacity size; selecting a suitable sintering temperature can change the ratio of the specific surface area to the skeleton density of the negative electrode material and the closed pore diameter, and too high or too low a temperature can result in a decrease in the final specific capacity and energy density; adding a water activation step during the holding process after the sintering treatment can effectively increase the closed pore diameter and the disorder degree of the negative electrode material, so that the final specific capacity and energy density are effectively enhanced; increasing the number of carbon coating from one time to two times can obviously reduce the specific surface area and the skeleton density of the negative electrode material, and ensure that the ratio of the two is within a certain range, the disorder degree is increased, the closed porosity and pore volume of the negative electrode material are increased, and the final specific capacity and energy density are effectively increased.

[0058] In some embodiments of the present application, the precursor raw material of step S1 includes, but is not limited to, a mixture of one or any combination of resin-based precursors, petroleum-based precursors, and biomass-based precursors; in some embodiments, the precursor raw material includes, but is not limited to, a mixture of one or any combination of epoxy resin, phenolic resin, polyfurfuryl alcohol, polyvinyl alcohol, polythiophene, petroleum coke, pitch, coal, fruit shell, lignin, sodium lignosulfonate, glucose, starch, tannic acid; the pore-forming agent includes, but is not limited to, a mixture of one or any combination of cetyltrimethylammonium bromide, melamine, styrene, biphenyl, naphthalene, potassium hydroxide, sodium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, sodium amide, sodium dihydrogen phosphate, ammonium hydrogen phosphate.

[0059] In some embodiments of the present application, the precursor raw material and the pore-forming agent of step S1 are mixed in a certain ratio, and the mixing ratio of the precursor to the pore-forming agent is mass ratio (50-150):(50-150); preferably, the mixing ratio of the precursor to the pore-forming agent is mass ratio (80-120):(80-120); more preferably, the mixing ratio of the precursor to the pore-forming agent is mass ratio (95-100):(95-100).

[0060] In some embodiments of the present application, the sintering temperature of step S2 can be 700-1000°C; preferably, the sintering temperature of step S2 can be 750-800°C; more preferably, the sintering temperature of step S2 is 800°C. Specifically, the sintering temperature can be 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, or a range between any two of the aforementioned values.

[0061] In some embodiments of the present application, the heating rate of the sintering temperature of step S2 can be 3-10°C / min; preferably, the heating rate of the sintering temperature of step S2 can be 5-7 / min. Specifically, the heating rate of the sintering temperature of step S2 can be 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min, 10°C / min, or a range between any two of the aforementioned values.

[0062] In some embodiments of the present application, the holding time of step S2 is 1-10h; preferably, the holding time of step S2 is 1-4h. Specifically, the holding time of step S2 is 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, or a range between any two of the aforementioned values.

[0063] In some embodiments of the present application, the carbon coating process includes at least one carbon coating; preferably, the carbon coating process is a double carbon coating process. In some embodiments of the present application, the carbon coating process includes a gas phase carbon coating process; specifically, a carbon coating required gas atmosphere is introduced at a certain temperature, and carbon is deposited on the surface of the hard carbon negative electrode material. The pores are coated to form closed pores, and the formation of closed pores enhances the sodium storage capacity.

[0064] In some embodiments of the present application, the carbon coating gas atmosphere includes a gas phase hydrocarbon carbon source, which is at least one of methane, acetylene, ethylene, ethane, propane, propylene, propyne, acetone, and benzene.

[0065] In some embodiments of the present application, the carbon coating process can include introducing a gas phase hydrocarbon carbon source at a certain temperature for a certain duration of time for the first carbon coating; preferably, the carbon coating process can include introducing a gas phase hydrocarbon carbon source at a certain temperature for a certain duration of time for the first carbon coating, and then switching to another gas phase hydrocarbon carbon source atmosphere for a certain duration of time for the second carbon coating.

[0066] In some embodiments of the present application, the temperature of the carbon coating can be 800℃-1500℃; preferably, the temperature of the carbon coating can be 800℃-1200℃; specifically, the temperature of the carbon coating can be 800℃, 900℃, 1000℃, 1100℃, 1200℃, 1300℃, 1400℃, 1500℃ or a range between any two of the aforementioned values.

[0067] In some embodiments of the present application, the duration of the carbon coating can be 1-10h; preferably, the duration of the carbon coating can be 2-5h; specifically, the duration of the carbon coating can be 1h, 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h or a range between any two of the aforementioned values.

[0068] According to a third aspect of the present application, the present application provides a negative electrode tab, which comprises a binder, a thickening agent and the negative electrode material and a negative electrode current collector, or the negative electrode tab comprises a binder, a thickening agent and the negative electrode material prepared by the preparation method and a negative electrode current collector.

[0069] In some embodiments of the present application, the negative electrode tab is cut to 1540.25mm 2 In some embodiments of the present application, the average coating weight (CW) of the negative electrode material coated on the surface of the negative electrode tab is 30mg-200mg, the thickness (h) is 0.039mm-0.433mm, and CW / h is between 900-1600.

[0070] In some embodiments of the present application, the binder comprises but is not limited to any one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymer, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin or nylon.

[0071] In some embodiments of the present application, the thickening agent comprises but is not limited to at least one of carboxymethyl cellulose (sodium), hydroxymethyl cellulose, methyl cellulose, ethyl cellulose, polyvinyl alcohol, polyacrylic acid, oxidized starch, phosphorus oxidized starch, casein, etc.

[0072] In some embodiments of the present application, the negative electrode current collector comprises but is not limited to any one of copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, polymer substrate coated with conductive metal or any combination thereof.

[0073] In some embodiments of the present application, the negative active material layer further comprises a conductive agent, which includes but is not limited to carbon-based materials, metal-based materials, conductive polymers and mixtures thereof; in some embodiments, the carbon-based materials are selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers or any combination thereof; in some embodiments, the metal-based materials are selected from metal powder, metal fiber, copper, nickel, aluminum or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0074] According to a fourth aspect of the present application, the present application provides an electrochemical device comprising the negative electrode tab as in any of the preceding embodiments.

[0075] In some embodiments, the electrochemical device includes but is not limited to a sodium ion battery.

[0076] In some embodiments of the present application, the sodium ion battery provided by the present application comprises the negative electrode tab, the positive electrode tab, the electrolyte and the separator between the positive and negative electrode tabs as in any of the preceding embodiments. Therefore, the sodium ion battery provided by the present application has higher gravimetric capacity and energy density.

[0077] In some embodiments, the positive electrode tab comprises a positive electrode current collector and a positive active material, a binder and a conductive carbon additive on the surface of the positive electrode current collector.

[0078] The present application does not have special restrictions on the positive electrode current collector, the positive active material, the conductive agent and the binder, as long as they can achieve the purpose of the present application.

[0079] In some embodiments, the positive electrode current collector can include aluminum foil, aluminum alloy foil and the like; in some embodiments, the positive active material can include at least one of layered oxides (such as NaCu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 O2], Prussian blue series (such as NaFe[Fe(CN)6] or Na2Fe[Fe(CN)6]), or polyanionic compounds (such as sodium vanadium phosphate) and the like; in some embodiments, the thickness of the positive electrode current collector is 5 μm to 20 μm, preferably 6 μm to 18 μm, and the thickness of the positive active material layer is 30 μm to 120 μm; in some embodiments, the mass ratio of the positive active material, the positive conductive agent and the positive binder in the positive active material layer is (94-98):(0.5-2.5):(1.5-3.5).

[0080] The electrolyte is not particularly limited in the present application, and any electrolyte that can achieve the purpose of the present application can be used. In some embodiments, the electrolyte can include a sodium salt and a non-aqueous solvent. In some embodiments of the present application, the sodium salt can include at least one of sodium perchlorate or sodium hexafluorophosphate (NaPF6). In some embodiments, the non-aqueous solvent can be a carbonate compound, a carboxylate compound, an ether compound, other organic solvents, or a combination thereof. In some embodiments, the carbonate compound can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluorinated carbonate compound. In some embodiments, the chain carbonate compound can include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). In some embodiments, the cyclic carbonate compound can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). In some embodiments, the fluorinated carbonate compound can include, but is not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methyl ethylene carbonate, 1-fluoro-1-methyl ethylene carbonate, 1,2-difluoro-1-methyl ethylene carbonate, 1,1,2-trifluoro-2-methyl ethylene carbonate, or trifluoromethyl ethylene carbonate. In some embodiments, the carboxylate compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decalactone, valerolactone, methylvaleronolactone, or caprolactone. In some embodiments, the ether compound can include, but is not limited to, at least one of dibutyl ether, tetraglyme, diglyme, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. In some embodiments, the other organic solvents can include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphates.

[0081] The isolation film is not particularly limited in the present application, and any material that can achieve the purpose of the present application can be used. In some embodiments, the material of the isolation film includes, but is not limited to, at least one of polyethylene (PE), polyolefin (PO) mainly including polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of the isolation film can include at least one of a woven film, a non-woven film, a microporous film, a composite film, a calendered film, or a spunlaced film.

[0082] In some embodiments, the sodium-ion battery of the present application further includes a packaging bag, and the electrolyte, the positive electrode sheet, the isolation film, and the negative electrode sheet are contained in the packaging bag. The packaging bag is not particularly limited in the present application, and can be any packaging bag known in the art as long as it can achieve the purpose of the present application. In some embodiments, the packaging bag can be an aluminum plastic film or a steel shell.

[0083] According to a fifth aspect of the present application, an electronic device is provided, characterized in that the electronic device includes the electrochemical device.

[0084] The electronic device is not particularly limited in the present application, and can be any electronic device known in the art. In some embodiments, the electronic device can include, but is not limited to, a drone, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile machine, a portable copying machine, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio player, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a clock, a power tool, a flashlight, a camera, a household large storage battery, and the like.

[0085] The present application is described in more detail below through examples.

[0086] Example 1

[0087] Example 1 provides a negative electrode material, which includes hard carbon and a carbon coating layer coating the hard carbon, and closed pores formed by pore openings of the carbon coating layer coating the outer surface of the hard carbon.

[0088] The preparation method of the negative electrode material includes the following steps:

[0089] (1) Obtain initial raw materials: weigh 100 g of petroleum coke raw materials and 100 g of potassium hydroxide, mix them uniformly in a shear mixer to obtain initial raw materials;

[0090] (2) Preparation of the first precursor: under a nitrogen atmosphere, the initial raw material is heated to a first temperature of 800°C at a heating rate of 5°C / min, and the nitrogen atmosphere is maintained at the first temperature of 800°C for 2h for sintering treatment, and then natural cooling is performed to obtain the first precursor;

[0091] (3) Preparation of the second precursor: the first precursor is cleaned several times with 1M hydrochloric acid, dried, and then subjected to airflow breaking and grading and particle size screening to obtain the second precursor;

[0092] (4) Carbon-coated final negative electrode material: under a nitrogen atmosphere, the second precursor is heated to a second temperature of 900°C at a heating rate of 5°C / min, the atmosphere is switched to CH4, and after 4h of heat preservation, the atmosphere is switched to C2H2 again, and after 2h of heat preservation, automatic cooling is started to obtain the final negative electrode material.

[0093] Example 2

[0094] The negative electrode material provided in Example 2 is different from the negative electrode material in Example 1 in that in Example 2, the initial raw material component is changed from petroleum coke to medium-temperature pitch, and the other steps are completely the same as in Example 1.

[0095] Example 3

[0096] The negative electrode material provided in Example 3 is different from the negative electrode material in Example 1 in that in the preparation method of Example 3, the atmosphere under the 800°C constant temperature condition for 2h in the preparation process of the first precursor is changed from nitrogen to water vapor, and the other steps are completely the same as in Example 1.

[0097] Example 4

[0098] The negative electrode material provided in Example 4 is different from the negative electrode material in Example 2 in that in the preparation method of Example 4, the atmosphere under the 800°C constant temperature condition for 2h in the preparation process of the first precursor is changed from nitrogen to water vapor, and the other steps are completely the same as in Example 2.

[0099] Example 5

[0100] The negative electrode material provided in Example 5 is different from the negative electrode material in Example 1 in that in Example 5, the initial raw material component is changed from petroleum coke to a mixture of petroleum coke and glucose (the mass ratio of petroleum coke to glucose is 1:2), and the other steps are completely the same as in Example 1.

[0101] Example 6

[0102] The negative electrode material provided in Example 6 is different from the negative electrode material in Example 3 in that, in Example 6, the initial raw material component changes the raw material petroleum coke to a mixture of petroleum coke and glucose (mass ratio of petroleum coke to glucose is 1:2), and other steps are completely the same as in Example 3.

[0103] Example 7

[0104] The negative electrode material provided in Example 7 is different from the negative electrode material in Example 3 in that, in Example 7, the potassium hydroxide in the initial raw material component is replaced by sodium hydroxide, and other steps are completely the same as in Example 3.

[0105] Example 8

[0106] The negative electrode material provided in Example 8 is different from the negative electrode material in Example 4 in that, in Example 8, the potassium hydroxide in the initial raw material component is replaced by sodium hydroxide, and other steps are completely the same as in Example 4.

[0107] Example 9

[0108] The negative electrode material provided in Example 9 is different from the negative electrode material in Example 3 in that, in Example 9, the potassium hydroxide in the initial raw material component is replaced by potassium carbonate, and other steps are completely the same as in Example 3.

[0109] Example 10

[0110] The negative electrode material provided in Example 10 is different from the negative electrode material in Example 1 in that, in Example 10, the potassium hydroxide in the initial raw material component is replaced by potassium carbonate, and other steps are completely the same as in Example 1.

[0111] Example 11

[0112] The negative electrode material provided in Example 11 is different from the negative electrode material in Example 3 in that, in the preparation method of Example 11, the first temperature in the preparation process of the first precursor is changed from 800°C to 750°C, and other steps are completely the same as in Example 3.

[0113] Example 12

[0114] The negative electrode material provided in Example 12 is different from the negative electrode material in Example 3 in that, in the preparation method of Example 12, the first temperature in the preparation process of the first precursor is changed from 800°C to 900°C, and other steps are completely the same as in Example 3.

[0115] Comparative Example 1

[0116] The negative electrode material provided by Comparative Example 1 is different from the negative electrode material in Example 1 in that, in the carbon coating stage of Comparative Example 1, the two carbon coatings are changed to only one CH4coating, and the other steps are completely the same as those in Example 1.

[0117] Comparative Example 2

[0118] The negative electrode material provided by Comparative Example 2 is different from the negative electrode material in Example 2 in that, in the carbon coating stage of Comparative Example 2, the two carbon coatings are changed to only one CH4coating, and the other steps are completely the same as those in Example 2.

[0119] Assembly of negative electrode sheet and sodium ion battery

[0120] The negative electrode materials provided by Examples 1 to 12 and the negative electrode materials provided by Comparative Examples 1 to 2 are respectively assembled into negative electrode sheets and sodium ion batteries according to the following methods:

[0121] Negative electrode sheet: the negative electrode active material (i.e. the negative electrode materials provided by Examples 1 to 12 and the negative electrode materials provided by Comparative Examples 1 to 2), the binder styrene-butadiene rubber (SBR), and the thickening agent sodium carboxymethyl cellulose (CMC) are mixed in a mass ratio of 97:2:1 in an appropriate amount of solvent deionized water, and are fully stirred to form a negative electrode slurry with a solid content of 40wt%; the negative electrode slurry is coated on a negative electrode current collector aluminum foil with a thickness of 10μm, and is dried at 85°C; after cold pressing, cutting, slitting, and vacuum drying at 120°C for 12 hours, a negative electrode sheet is obtained.

[0122] Positive electrode sheet: the positive electrode active material NaCu 1 / 9 Ni 2 / 9 Fe 1 / 3 Mn 1 / 3 O2, the positive electrode conductive agent conductive carbon black (Super P), and the positive electrode binder polyvinylidene fluoride (abbreviated as PVDF) are mixed in a mass ratio of 97:1.4:1.6, N-methyl pyrrolidone (NMP) is added as a solvent, and the mixture is fully stirred to obtain a positive electrode slurry with a solid content of 72wt% and a uniform system. The positive electrode slurry is uniformly coated on the surface of a positive electrode current collector aluminum foil with a thickness of 10μm, and is dried at 85°C to obtain a positive electrode sheet.

[0123] Electrolyte: In a dry (H2O < 1 ppm) argon glove box, ethylene carbonate (EC), diethyl carbonate (DEC) were mixed in a mass ratio of 50:50, then 1,3-propane sultone and fluoroethylene carbonate were added, dissolved and stirred well, then sodium hexafluorophosphate was added, and the electrolyte was obtained after mixing evenly. Among them, based on the mass of the electrolyte, the mass percentage of 1,3-propane sultone in the electrolyte is 1.5%, the mass percentage of fluoroethylene carbonate in the electrolyte is 2%, the mass percentage of sodium hexafluorophosphate in the electrolyte is 11%, and the rest is EC and DEC.

[0124] Separator: The separator includes a 7 μm thick polyethylene (PE) substrate, and an aluminum oxide ceramic layer with a thickness of 1 μm arranged on both surfaces of the substrate along the thickness direction of the substrate, and the total thickness of the separator is 9 μm.

[0125] Sodium ion battery assembly: The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, with the separator between the positive electrode and the negative electrode to play a separating role, then after winding and welding the tab, the soft package sodium ion battery is obtained by placing in an outer packaging aluminum plastic film, injecting electrolyte, and going through processes such as vacuum packaging, standing, formation, shaping, and capacity testing.

[0126] Performance test

[0127] The negative electrode material, the assembled negative electrode sheet, and the electrochemical performance of each sodium ion battery in the above examples were tested by the following test conditions, and the test results are shown in Tables 1-3.

[0128] (1) BET test method: The specific surface area test method refers to GB / T 19587-2017, and the specific process is as follows: 1 g to 8 g of the negative electrode material sample (the sample is weighed to be at least 1 / 3 of the volume of the sphere) is placed in a 1 / 2 inch long tube with a ball bubble (the diameter of the spherical part of the tube is 12 mm), and after pretreatment at 200°C for 2 h, it is placed in the test equipment TriStar3030 (USA Micromeritics) for testing. The adsorption gas used is N2 (purity: 99.999%), the test condition is carried out at 77 K, and the specific surface area is tested by the BET calculation method.

[0129] (2) Gas volume method to test the skeleton density (true density) of the negative electrode material: The accurately weighed test negative electrode material is placed in a sample chamber of a known volume of true density tester (USA Micromeritics AccuPyc II 1345), and nitrogen gas is used as the medium to fill the sample chamber, and gradually pressurized to a specified value (19.50 psi) in the measurement chamber, then the nitrogen gas diffuses into the expansion chamber, and the equilibrium pressure of the two processes is automatically recorded by the instrument. According to the pressure before and after gas diffusion, according to the Boyle-Mariotte law, the volume of the sample can be calculated, and thus the true density can be calculated.

[0130] (3) Pore size test: The pore size of the hard carbon before coating is tested as the closed pore size of the hard carbon using the instrument Micromeritics TriStar II Plus 3030 three-station specific surface and porosity analyzer (the closed pore size cannot be obtained by the gas adsorption method after coating to form a closed pore); the specific process is as follows: 1 g to 8 g of the hard carbon sample before coating (the sample is weighed to be at least 1 / 3 of the volume of the sphere) is placed in a 1 / 2 inch long tube with a ball bubble (the diameter of the spherical part of the tube is 12 mm), and after 200°C pretreatment for 2 h, it is placed in the test equipment for testing, the adsorption and desorption gas used is N2 (purity: 99.999%), the test condition is carried out at 77 K, the adsorption and desorption curve is obtained, the data obtained is simulated by using the advanced non-local density functional theory (NLDFT) model, so as to obtain the pore size distribution of the material; the pore volume corresponding to each pore size can be calculated by the cumulative pore volume; the open pore volume of the hard carbon after coating is tested by using the above test process.

[0131] (4) Raman surface defect degree test: A 100 μm x 100 μm area is selected on the negative electrode active material layer, and the particles in the area are scanned by using a laser microscopic confocal Raman spectrometer (Raman, HR Evolution, HORIBA Scientific Instrument Division) to obtain the D peak and G peak of all particles in the area range, and the data is processed by using LabSpec software to obtain the peak intensity of the D peak and G peak of each particle after deducting the substrate, which are Id and Ig respectively, and the ratio thereof is obtained by dividing, which is Id / Ig. The laser wavelength of the Raman spectrometer can be in the range of 532 nm to 785 nm. The value of Id / Ig in the text is the average value of the Id and Ig ratio of all particles measured in the range. D peak: generally in 1350±50 cm -1 nearby, caused by the radial breathing mode of the symmetric stretching vibration of sp2 carbon atoms in the aromatic ring (structural defect); G peak: appears in 1580±50 cm -1 nearby, caused by the stretching vibration between sp2 carbon atoms, which corresponds to the vibration of E2g optical phonon in the center of the Brillouin zone (in-plane vibration of carbon atoms).

[0132] (5) X-ray diffraction (XRD) test: the negative electrode material is tested by an X-ray powder diffractometer (XRD, instrument model: Bruker D8 ADVANCE), the target is Cu Ka, the voltage and current are 40 KV / 40 mA, the scanning angle range is 10° to 80°, the scanning step is 0.00836°, and the time for each step is 0.3 s. After obtaining the original data, the base is deducted, and the angle corresponding to the peak value of the wide peak in the range of 10° to 30° is taken as the position of the 002 peak; the half of the difference between the intensity on the right side and the intensity on the left side at the 1 / 2 intensity of the peak is taken as the value of the half peak width.

[0133] (6) Test of the compaction density: the test standard of powder compaction refers to GB / T 24533-2009 "Graphite-based negative electrode material for lithium ion batteries". The specific test method is as follows: 1.0000±0.0500 g of the sample is weighed and placed in a test mold (CARVER #3619 (13 mm)), and then the sample is placed in a test device, which is a Sansi Zongheng UTM7305 with a test tonnage of 5.0 tons. The calculation formula of the compaction density is as follows: compaction density = negative electrode material mass / negative electrode material force area / negative electrode material sample thickness.

[0134] (7) Test of CW / h: 10 small circular pieces with an area of 1540.25 mm 2 + +

[0135] (8) Sodium ion battery discharge test (C and D): the negative electrode sheet is prepared by the negative electrode sheet preparation method to obtain the negative electrode sheet with the negative electrode material of each embodiment, and then punched into a raw sheet with a diameter of 14 mm. After weighing (weighing the corresponding empty copper foil area to obtain the weight of the base material) and calculating the weight of the negative electrode material (negative electrode active material), the discharge test is started. The assembly of the discharge battery takes the obtained negative electrode sheet as the working electrode, takes the metal sodium sheet as the counter electrode, aligns the two up and down, uses a separator to separate them, and then adds the electrolyte (the electrolyte used in the preparation of the sodium ion battery described above) to assemble the discharge battery. After the discharge battery is assembled and stands for 8 h, the test is started. First, discharge at a current density of 25 mA / g to 0 V vs Na + / Na, then discharge at a current density of 2.5 mA / g at 0 V, and record the gram capacity of this step; then charge at a current density of 25 mA / g to 1.5 V vs Na + / Na, the gram capacity of 0-0.15V is C, and the gram capacity of 0-1V is D.

[0136] (9) Sodium ion battery cycle performance test: the sodium ion battery in each example and the comparative example is tested at 25℃ test temperature, static for 5min, then charged to voltage 3.95V at 1C constant current, then charged to 0.05C at constant voltage; discharged to voltage 1.5V at 1C constant current, which is recorded as one cycle, and the capacity at this time is recorded as D0. Such cycle is repeated for 800 cycles, and the discharge capacity of the last cycle is recorded as D1; the capacity decay rate after 25℃ cycle is D1 / D0, and the unit is %. Five samples are tested for each example or comparative example, and the average value is taken.

[0137] (10) Sodium ion battery weight energy density and average discharge voltage test: in the environment of 25℃, the sodium ion battery is charged to voltage 3.95V at 0.2C constant current, then charged to 0.02C at constant voltage; discharged to voltage 1.5V at 0.2C constant current, which is recorded as one cycle, and the discharge capacity and discharge energy of the first cycle are recorded; the average discharge voltage can be obtained by dividing the discharge energy by the discharge capacity; and the weight of the sodium ion battery at 50% SOC is tested to obtain the weight of the sodium ion battery. Energy density = discharge capacity x average discharge voltage / sodium ion battery weight.

[0138] Table 1 Performance test of negative electrode material prepared in each example and comparative example

[0139]

[0140] Table 2 Performance test of negative electrode material prepared in each example and comparative example

[0141]

[0142] Table 3 Performance test results of sodium ion battery prepared in each example and comparative example

[0143]

[0144] As can be seen from examples 1 to 12 and comparative examples 1 to 2, the specific surface area A and the skeleton density B of the negative electrode material subjected to twice carbon coating are significantly reduced, when the specific surface area A and the skeleton density B are controlled in the range of AxB<10, the negative electrode material of the application has lower skeleton density and compaction density, higher gram capacity, so that the sodium ion battery prepared therefrom obtains higher energy density and average discharge voltage.

[0145] As can be seen from Examples 3 and 11 to 12, a lower activation temperature has a larger skeleton density and a smaller closed pore aperture, resulting in a decrease in the closed pore sodium storage capacity and the gram capacity; and a high activation temperature has a too large closed pore aperture of the negative electrode material, forming invalid pores, affecting the gram capacity and energy density of the battery; therefore, the closed pore aperture of the negative electrode material also needs to be kept within a suitable range.

[0146] As can be seen from Examples 1, 2, 5, Examples 3, 6, 7 and Examples 7, 8, the gram capacity of the battery can be adjusted by adjusting the hard carbon raw material; the negative electrode material after water vapor activation has a smaller skeleton density and a larger pore volume, and the gram capacity, battery density and average discharge voltage of the prepared battery are all significantly improved.

[0147] The negative electrode material, the preparation method and the application thereof provided by the embodiments of the present application are described in detail above, and the principles and embodiments of the present application are described by applying specific examples; the above description of the embodiments is only used to help understand the method and the core idea thereof; meanwhile, for those skilled in the art, according to the idea of the present application, the specific embodiments and the application range can be changed; in conclusion, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A negative electrode material, a specific surface area A and a true density B of the negative electrode material satisfying 1 < A × B < 6. The specific surface area A of the negative electrode material is 0.95 m 2 / g-5m 2 / g; The true density B of the negative electrode material is 1.05 g / cm 3 -1.3 g / cm 3 ; The compaction density of the negative electrode material is 0.7 g / cm 3 -0.89 g / cm 3 .

2. The negative electrode material of claim 1, wherein, A specific surface area A and a true density B of the negative electrode material satisfying 1 < A × B < 4.

3. The negative electrode material of claim 1, wherein The specific surface area A of the negative electrode material is 1 m 2 / g-4 m 2 / g.

4. The negative electrode material of any one of claims 1 to 3, wherein The negative electrode material comprises hard carbon, a carbon coating layer coating the hard carbon, and closed pores formed by the carbon coating layer coating the open pores on the outer surface of the hard carbon. 5.The negative electrode material of claim 4, a proportion of the closed pore volume in a sum of all open pore volume and closed pore volume being more than 90%. 6.The negative electrode material of claim 5, a proportion of the closed pore volume in a sum of all open pore volume and closed pore volume being more than 95%. 7.The negative electrode material of claim 6, a proportion of the closed pore volume in a sum of all open pore volume and closed pore volume being more than 99%. 8.The negative electrode material of claim 4, a closed pore diameter of the negative electrode material being in a range of 3 nm or less. 9.The negative electrode material of claim 8, a closed pore diameter of the negative electrode material being in a range of 0.1 nm to 3 nm. 10.The negative electrode material of claim 9, a closed pore diameter of the negative electrode material being in a range of 0.5 nm to 3 nm. 11.The negative electrode material of claim 10, a closed pore diameter of the negative electrode material being in a range of 1 nm to 3 nm. 12.The negative electrode material of any one of claims 1 to 3, the negative electrode material satisfying at least one of the following conditions: (1) the negative electrode material I d / I g is in the range of 1.0-2.0; (2) a diffraction peak position in an X-ray diffraction spectrum of the negative electrode material being in a range of 20° to 30° in 2θ, and a half-peak width of the diffraction peak being 3° to 10°.

13. The negative electrode material of claim 12, wherein, The negative electrode material I d / I g is in the range of 1.3-1.

6.

14. The negative electrode material of claim 12, wherein, a diffraction peak position of the negative electrode material being in a range of 24° to 25° in 2θ, and a half-peak width of the diffraction peak being 3° to 4°.

15. A sodium-ion battery, characterized in that, The sodium ion battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte; the negative electrode sheet comprises the negative electrode material of any one of claims 1 to 12.

16. An electronic device, comprising: The sodium ion battery of claim 15 is included.

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