Hard carbon material and preparation method thereof, negative pole piece and battery

Abstract

The invention relates to the field of new energy batteries, in particular to a hard carbon material, a preparation method of the hard carbon material, a negative pole piece and a battery. Wherein the sulfur element exists in the hard carbon material in the form of at least one of a sulfur-carbon single bond, a sulfur-carbon double bond and a sulfur-oxygen compound group; on the basis of the total weight of the hard carbon material, in terms of elements, the content of the sulfur element is 0.1-5 wt%. The hard carbon material disclosed by the invention is applied to the negative electrode of the sodium-ion battery, and the reversible specific capacity and the rate capability of the negative electrode of the sodium-ion battery can be remarkably improved when the negative electrode is charged and discharged at 0-2.5 V.

Description

Technical Field

[0001] The present invention relates to the field of new energy batteries, and in particular to a hard carbon material and a preparation method thereof, a negative electrode sheet and a battery. Background Art

[0002] As environmental pollution caused by the burning of fossil fuels becomes increasingly serious, replacing fossil fuels with renewable resources is a top priority for achieving sustainable development. However, electricity generated by renewable resources is limited by the natural environment and suffers from randomness, volatility, and intermittency, making it impossible to maintain stable power output. This situation can only be resolved by developing efficient and convenient large-scale energy storage technologies. Lithium-ion batteries, a type of electrochemical energy storage technology, are considered one of the most promising technologies due to their high energy consumption, long lifespan, and environmental friendliness. However, the limited reserves and uneven distribution of lithium resources have limited the development of lithium-ion batteries for large-scale energy storage. Sodium-ion batteries, developed at the same time as lithium-ion batteries, have become a focus of attention.

[0003] Sodium-ion batteries (SIBs) are secondary batteries that use sodium ions as metal ion carriers and operate on a similar principle to lithium-ion batteries. They offer advantages such as abundant reserves, low cost, high safety, excellent high- and low-temperature performance, and compatibility with existing lithium-ion equipment.

[0004] Since graphite has low sodium storage performance, this field is committed to the research of amorphous carbon materials with a low degree of graphitization. Hard carbon materials have the advantages of large carbon layer spacing, good conductivity, and high sodium storage capacity, but their precursors are expensive and not suitable for large-scale production. Asphalt has high output, low cost, and high carbon yield, and is a high-quality precursor for preparing carbon materials for sodium ion battery negative electrodes, but its carbon material exhibits soft carbon properties and has the disadvantage of low sodium storage capacity. Therefore, how to modify asphalt so that its carbon material exhibits a hard carbon structure and further improves its sodium storage capacity is an important issue worthy of study.

[0005] Currently, researchers primarily use furfural as a cross-linking agent and concentrated sulfuric acid as a catalyst to prepare pitch-based hard carbon materials. However, the preparation process is cumbersome, time-consuming, and unsafe, with numerous uncontrollable factors, making it difficult to maintain a stable material output. Therefore, this invention further enhances existing research results on pitch-based hard carbon materials, optimizing the production process and increasing the sodium storage capacity of pitch-based hard carbon materials. This has important guiding significance for achieving high-value utilization of asphalt and large-scale preparation of pitch-based hard carbon materials. Summary of the Invention

[0006] In view of this, the present invention is committed to providing a hard carbon material and a preparation method thereof, a negative electrode plate and a battery to solve the problem of insufficient sodium storage capacity of asphalt-based hard carbon materials in the prior art.

[0007] In order to solve the above-mentioned technical problems, the present invention is achieved as follows:

[0008] A first aspect of the present invention provides a hard carbon material, wherein the hard carbon material contains sulfur; wherein the sulfur is present in the hard carbon material in the form of at least one of a sulfur-carbon single bond, a sulfur-carbon double bond, and a sulfur oxide group;

[0009] Based on the total weight of the hard carbon material, the content of the sulfur element is 0.1 to 5 weight % in terms of element.

[0010] Optionally, based on the total weight of the hard carbon material, the content of the sulfur element is 1 to 3.5 weight %; optionally, the hard carbon material also contains carbon, oxygen, hydrogen and nitrogen elements; based on the total weight of the hard carbon material, the content of the carbon element is 80 to 95 weight %, the content of the oxygen element is 5 to 10 weight %, and the content of the nitrogen element is 1 to 2 weight %; preferably, based on the total weight of the hard carbon material, the content of the carbon element is 82 to 93 weight %, the content of the oxygen element is 6 to 8 weight %, and the content of the nitrogen element is 1.2 to 1.8 weight %.

[0011] Optionally, the specific surface area of the hard carbon material is 3 to 20 m 2 / g, preferably 8 to 15m 2 / g.

[0012] Optionally, the pore volume of the hard carbon material is 3 to 10 cm 3 / g, preferably 5 to 8 cm 3 / g.

[0013] A second aspect of the present invention provides a method for preparing a hard carbon material, the method comprising the following steps:

[0014] S1. Mixing an asphalt precursor, a sulfur source, and a crosslinking agent to obtain a mixture; and crosslinking and vulcanizing the mixture to obtain a primary material;

[0015] S2. Carbonizing the primary material in an inert atmosphere.

[0016] Optionally, the mass ratio of the asphalt precursor, the sulfur source and the cross-linking agent is 1:(1-9):(1-9).

[0017] Optionally, the asphalt precursor includes at least one of coal tar pitch, petroleum asphalt, coal liquefaction pitch, ethylene tar pitch and natural asphalt; and / or, the sulfur source includes elemental sulfur and / or thiourea; and / or, the cross-linking agent includes at least one of terephthalic acid methanol, terephthalaldehyde and polyformaldehyde.

[0018] Optionally, the cross-linking vulcanization treatment is carried out in a stainless steel sealed autoclave, or the cross-linking vulcanization treatment is carried out in a second inert atmosphere, which is selected from at least one of nitrogen, argon and helium; the conditions for the cross-linking vulcanization treatment include: a heating rate of 0.1 to 10°C / min, a temperature of 100 to 500°C, and a holding time of 0.5 to 48h; and / or, in step S2, the inert atmosphere is selected from at least one of nitrogen, argon and helium; the conditions for the carbonization treatment include: a heating rate of 0.1 to 10°C / min, a temperature of 1200 to 1600°C, and a holding time of 0.5 to 48h.

[0019] A third aspect of the present invention provides a negative electrode plate, comprising a current collector and a negative electrode active material disposed on the surface of the current collector, wherein the negative electrode active material comprises the hard carbon material described above and / or the hard carbon material prepared by the above preparation method.

[0020] A fourth aspect of the present invention provides a battery, comprising a negative electrode, wherein the negative electrode is the negative electrode sheet described above.

[0021] Through the above technical solution, the beneficial technical effects of the present invention are:

[0022] (1) The hard carbon material of the present invention contains 0.1 to 5 weight percent sulfur, wherein the sulfur is present in the hard carbon material in the form of at least one of a sulfur-carbon single bond, a sulfur-carbon double bond, and a sulfur oxide group. The hard carbon material of the present invention is applied to a negative electrode of a sodium ion battery, and the reversible specific capacity and rate performance of the negative electrode of the sodium ion battery can be significantly improved when charged and discharged between 0 and 2.5 V.

[0023] (2) In the method of the present invention, an asphalt precursor, a sulfur source, and a crosslinking agent are mixed during the preparation process. The introduction of the crosslinking agent can trigger a crosslinking reaction in the asphalt precursor, forming a stable three-dimensional network structure, preventing the orderly rearrangement of the asphalt precursor, and thus helping to obtain a hard carbon material. In the preparation method of the present invention, crosslinking and sulfurization are carried out simultaneously, which helps to optimize the production process and reduce production costs. The method of the present invention has a simple process flow, low cost, high process adaptability, and is conducive to industrial production.

[0024] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not constitute a limitation of the present invention.

[0026] Figure 1Shown are the rate performance test results of the battery prepared using the hard carbon material of Example 1.

[0027] Figure 2 Shown are the rate performance test results of the battery prepared using the hard carbon material of Example 2.

[0028] Figure 3 Shown are the rate performance test results of the battery prepared using the hard carbon material of Example 3.

[0029] Figure 4 Shown are the rate performance test results of the battery prepared using the hard carbon material of Example 4.

[0030] Figure 5 Shown are the rate performance test results of the battery prepared using the hard carbon material of Example 5.

[0031] Figure 6 Shown are the rate performance test results of the battery prepared using the hard carbon material of Example 6.

[0032] Figure 7 Shown are the rate performance test results of batteries prepared from the carbon materials of Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0033] The present invention discloses a hard carbon material, a preparation method thereof, a negative electrode plate, and a battery. Those skilled in the art can refer to the contents of this document and appropriately improve the process parameters to achieve the desired results. It is particularly important to note that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in the present invention. The methods and applications of the present invention have been described through preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of the present invention to implement and apply the technology of the present invention.

[0034] In the description of the present invention, a list of items connected by the term "at least one of" or other similar terms can mean any combination of the listed items. For example, if items A and B are listed, the phrase "at least one of A and B" means only A; only B; 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 only A; or only B; only C; 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 element or multiple elements. Item B can include a single element or multiple elements. Item C can include a single element or multiple elements.

[0035] The endpoints of the ranges and any values disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range or the individual point values, and the individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0036] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0037] Unless otherwise specified, all technical features and optional technical features of the present invention can be combined with each other to form a new technical solution.

[0038] Unless otherwise specified, the terms "include" and "comprising" used in the present invention 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.

[0039] In order to optimize the production process of hard carbon materials prepared from pitch and improve the sodium storage capacity of pitch-based hard carbon materials, the present invention adopts the following technical solutions:

[0040] A first aspect of the present invention provides a hard carbon material, wherein the hard carbon material contains sulfur; wherein the sulfur is present in the hard carbon material in the form of at least one of a sulfur-carbon single bond, a sulfur-carbon double bond, and a sulfur oxide group;

[0041] Based on the total weight of the hard carbon material, the content of the sulfur element is 0.1 to 5 weight % in terms of element.

[0042] The hard carbon material of the present invention contains 0.1 to 5% by weight of elemental sulfur, present in the form of at least one of a sulfur-carbon single bond, a sulfur-carbon double bond, and a sulfur oxide group. When applied to a sodium-ion battery anode, the hard carbon material significantly improves the reversible specific capacity and rate performance of the anode under charge and discharge conditions between 0 and 2.5V.

[0043] In the present invention, doping with sulfur can increase the sodium storage capacity of the hard carbon material and improve its rate performance. Preferably, the sulfur content, calculated as elemental sulfur, based on the total weight of the hard carbon material can be 1 to 3.5% by weight. At this ratio, the sodium storage performance and rate performance of the hard carbon material are further enhanced.

[0044] According to the present invention, the hard carbon material may further contain carbon, oxygen, hydrogen, and nitrogen. In an exemplary embodiment of the present invention, based on the total weight of the hard carbon material, the carbon content may be 80-95% by weight, the oxygen content may be 5-10% by weight, and the nitrogen content may be 1-2% by weight. Preferably, based on the total weight of the hard carbon material, the carbon content may be 82-93% by weight, the oxygen content may be 6-8% by weight, and the nitrogen content may be 1.2-1.8% by weight.

[0045] In the present invention, if the specific surface area of the hard carbon material is too large, it may cause the material's first coulombic efficiency in the electrochemical test to be too low, consume too many sodium ions, and reduce the cycle performance of the sodium ion battery; if the specific surface area of the hard carbon material is too small, it may cause the material's sodium storage capacity and rate performance to be poor. In an embodiment of the present invention, the specific surface area of the hard carbon material can be 3 to 20 m 2 / g, for example, the specific surface area of the hard carbon material can be 3m 2 / g、5m 2 / g、10m 2 / g、13m 2 / g、15m 2 / g、18m 2 / g and 20m 2 In a preferred embodiment of the present invention, the specific surface area of the hard carbon material can be 8 to 15 m 2 / g.

[0046] In the present invention, if the pore volume of the hard carbon material is too large, it may cause the material to have too low initial coulombic efficiency in electrochemical testing, consume too much sodium ions, and reduce the cycle performance of the sodium ion battery; if the pore volume of the hard carbon material is too small, it may cause the material to have poor sodium storage capacity and rate performance. In an embodiment of the present invention, the pore volume of the hard carbon material can be 3 to 10 cm 3 / g, for example, the pore volume of the hard carbon material can be 3cm 3 / g, 5cm 3 / g、7cm 3 / g、9cm 3 / g and 10cm 3 / g or any value within the range of any two of the above values. Preferably, the pore volume of the hard carbon material can be 5 to 8 cm 3 / g.

[0047] A second aspect of the present invention provides a method for preparing a hard carbon material, the method comprising the following steps:

[0048] S1. Mixing an asphalt precursor, a sulfur source, and a crosslinking agent to obtain a mixture; and crosslinking and vulcanizing the mixture to obtain a primary material;

[0049] S2. Carbonizing the primary material in an inert atmosphere.

[0050] In the method of the present invention, the asphalt precursor, sulfur source and crosslinking agent are mixed during the preparation process. The introduction of the crosslinking agent can trigger a crosslinking reaction in the asphalt precursor, forming a stable three-dimensional network structure, preventing the orderly rearrangement of the asphalt precursor, and thus helping to obtain a hard carbon material.

[0051] In the preparation method of the present invention, crosslinking and vulcanization are carried out simultaneously, which helps to optimize the production process and reduce production costs. The method of the present invention has a simple process flow, low cost, high process adaptability, and is conducive to industrial production.

[0052] In one embodiment of the present invention, the mass ratio of the asphalt precursor, the sulfur source and the cross-linking agent can be 1: (1 to 9): (1 to 9). In the present invention, the appropriate mass ratio of the asphalt precursor, the sulfur source and the cross-linking agent can achieve the technical effect of reducing production costs, and the produced hard carbon material has excellent sodium storage performance and rate performance. Exemplarily, the mass ratio of the asphalt precursor, the sulfur source and the cross-linking agent can be any value among 1:1:1, 1:1:3, 1:1:6, 1:1:9, 1:3:1, 1:3:1, 1:6:1, 1:9:1, 1:9:6, 1:9:3 and 1:9:1 or any value within the range of any two of the above values.

[0053] Illustratively, the pitch precursor may include at least one of coal tar pitch, petroleum pitch, coal liquefaction pitch, ethylene tar pitch, and natural pitch.

[0054] For example, the sulfur source may include elemental sulfur and / or thiourea. The reaction product of elemental sulfur, thiourea and the asphalt precursor used in the present invention is a gas. While introducing sulfur, the reaction product will not remain in the material, thereby avoiding the need for impurity removal of other elements.

[0055] Illustratively, the cross-linking agent may include at least one of terephthalic alcohol, terephthalaldehyde, and paraformaldehyde.

[0056] In one embodiment of the present invention, in step S1, the mixed material is placed in a stainless steel sealed kettle for crosslinking and vulcanization treatment. The sealed kettle can provide a closed environment to facilitate better reaction between the asphalt precursor, the sulfur source, and the crosslinking agent.

[0057] In another embodiment of the present invention, in step S1, the crosslinking and vulcanization treatment is carried out in a second inert atmosphere. For example, the second inert atmosphere can be selected from at least one of nitrogen, argon and helium. The crosslinking and vulcanization treatment is carried out in the second inert atmosphere, which can close the gas flow and thus create a sealed environment.

[0058] In some embodiments, the conditions of the cross-linking vulcanization treatment may include: a heating rate of 0.1 to 10°C / min, a temperature of 100 to 500°C, and a holding time of 0.5 to 48 hours. As an example, the temperature of the cross-linking vulcanization treatment may be 100°C, 200°C, 300°C, 400°C, 500°C, etc., and the time of the cross-linking vulcanization treatment may be 0.5h, 1h, 6h, 12h, 24h, 36h, 48h, etc.

[0059] In one embodiment of the present invention, in step S2, the inert atmosphere may be selected from at least one of nitrogen, argon and helium. The conditions of the carbonization treatment may include: a heating rate of 0.1 to 10°C / min, a temperature of 1200 to 1600°C, and a holding time of 0.5 to 48 hours. As an example, the temperature of the carbonization treatment may be 1200°C, 1300°C, 1400°C, 1500°C, 1600°C, etc., and the time of the carbonization treatment may be 0.5h, 1h, 6h, 12h, 24h, 36h, 48h, etc.

[0060] A third aspect of the present invention provides a negative electrode plate, comprising a current collector and a negative electrode active material disposed on the surface of the current collector, wherein the negative electrode active material comprises the hard carbon material described above and / or the hard carbon material prepared by the above preparation method.

[0061] A fourth aspect of the present invention provides a battery, comprising a negative electrode, wherein the negative electrode is the negative electrode sheet described above.

[0062] In the embodiment of the present invention, the battery structure includes but is not limited to button batteries, soft-pack batteries, cylindrical batteries, etc.

[0063] The present invention has no particular limitation on the positive electrode sheet, separator, and electrolyte in the battery, and those skilled in the art can select them according to actual needs, as long as the purpose of the present invention can be achieved.

[0064] The present invention is further described in detail below by way of examples. The raw materials used in the examples can all be obtained through commercial sources.

[0065] Example 1

[0066] (1) Preparation of sulfur-doped pitch-based hard carbon materials

[0067] 5g of a mixed powder of coal tar pitch and coal liquefaction pitch (coal tar pitch and coal liquefaction pitch mixed in a mass ratio of 1:1), 10g of elemental sulfur powder, and 15g of terephthalaldehyde powder were weighed, ground, and mixed to obtain a mixed material. Under an inert atmosphere (argon), the mixed material was placed in a stainless steel sealed autoclave and heated at 3°C / min to 280°C for 3 hours to obtain a primary product. The primary product was then ground and heated at 3°C / min to 1300°C under argon for 3 hours to obtain a sulfur-doped pitch-based hard carbon material.

[0068] (2) Preparation of negative electrode sheet

[0069] The sulfur-doped pitch-based hard carbon material used in this example was used as the negative electrode material. The negative electrode material, conductive carbon black, and PVDF were weighed in a mass ratio of 8:1:1. An appropriate amount of NMP dispersant was added and ground into a uniform slurry in a mortar. The slurry was coated onto carbon-coated aluminum foil and dried in a vacuum oven at 80°C for 12 hours. After drying, the slurry was cut into electrode sheets with a diameter of 14.5 mm.

[0070] (3) Assembly of sodium ion batteries

[0071] The assembly was carried out in an argon-filled glove box. The battery shell model was CR2032, 1 mol / L NaClO4, EC:DMC=1:1 (volume ratio), 5% FEC mixed solution was added as the electrolyte, Whatman GF / D glass fiber membrane was used as the diaphragm, and a sodium sheet with a diameter of 15.6 mm was used as the counter electrode to finally obtain a button battery.

[0072] Example 2

[0073] (1) Preparation of sulfur-doped pitch-based hard carbon materials

[0074] 5g of a mixed powder of coal tar pitch and petroleum pitch (coal tar pitch and coal tar pitch mixed in a mass ratio of 2:3), 20g of thiourea powder, and 35g of paraformaldehyde powder were weighed, ground, and mixed to obtain a mixed material. Under an inert atmosphere (nitrogen), the mixed material was placed in a stainless steel sealed kettle and heated at 5°C / min to 350°C for 2 hours to obtain a primary product. The primary product was then ground and heated at 4°C / min to 1200°C under an argon atmosphere for 3 hours to obtain a sulfur-doped pitch-based hard carbon material.

[0075] (2) Preparation of negative electrode sheet

[0076] The preparation method of the negative electrode sheet in this embodiment is the same as that in Example 1.

[0077] (3) Assembly of sodium ion batteries

[0078] The preparation method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0079] Example 3

[0080] (1) Preparation of sulfur-doped pitch-based hard carbon materials

[0081] 5g of natural asphalt powder, 5g of thiourea powder, 20g of terephthalaldehyde, and 20g of paraformaldehyde powder were weighed, ground, and mixed to obtain a mixture. Under an inert atmosphere (helium), the mixture was placed in a stainless steel sealed autoclave and heated at 4°C / min to 400°C for 4 hours to obtain a primary product. The primary product was then ground and heated at 3°C / min to 1600°C under an argon atmosphere for 2 hours to obtain a sulfur-doped pitch-based hard carbon material.

[0082] (2) Preparation of negative electrode sheet

[0083] The preparation method of the negative electrode sheet in this embodiment is the same as that in Example 1.

[0084] (3) Assembly of sodium ion batteries

[0085] The preparation method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0086] Example 4

[0087] (1) Preparation of sulfur-doped pitch-based hard carbon materials

[0088] 5g of a mixed powder of natural asphalt and petroleum asphalt (4:1 by mass), 20g of elemental sulfur powder, and 40g of p-phenylenediol powder were weighed, ground, and mixed to obtain a mixed material. Under an inert atmosphere (argon), the mixed material was placed in a stainless steel sealed kettle and heated at 7°C / min to 200°C for 2 hours to obtain a primary product. The primary product was then ground and heated at 2°C / min to 1400°C under argon for 4 hours to obtain a sulfur-doped pitch-based hard carbon material.

[0089] (2) Preparation of negative electrode sheet

[0090] The preparation method of the negative electrode sheet in this embodiment is the same as that in Example 1.

[0091] (3) Assembly of sodium ion batteries

[0092] The preparation method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0093] Example 5

[0094] (1) Preparation of sulfur-doped pitch-based hard carbon materials

[0095] 5g of a mixed powder of petroleum asphalt and ethylene tar pitch (the mass ratio of petroleum asphalt to ethylene tar pitch is 3:2), 5g of elemental sulfur powder, and 15g of paraformaldehyde powder were weighed, ground, and mixed to obtain a mixed material. Under an inert atmosphere (nitrogen), the mixed material was placed in a stainless steel sealed autoclave and heated at 2°C / min to 300°C for 12 hours to obtain a primary product. The primary product was then ground and heated at 3°C / min to 1200°C under an argon atmosphere for 6 hours to obtain a sulfur-doped pitch-based hard carbon material.

[0096] (2) Preparation of negative electrode sheet

[0097] The preparation method of the negative electrode sheet in this embodiment is the same as that in Example 1.

[0098] (3) Assembly of sodium ion batteries

[0099] The preparation method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0100] Example 6

[0101] (1) Preparation of sulfur-doped pitch-based hard carbon materials

[0102] 5g of a mixed powder of petroleum pitch and coal tar pitch (the mass ratio of petroleum pitch to coal tar pitch is 1:1), 30g of elemental sulfur and thiourea powder (the mass ratio of elemental sulfur to thiourea is 1:1), and 40g of paraformaldehyde powder were weighed, ground, and mixed to obtain a mixed material. Under an inert atmosphere (helium), the mixed material was placed in a stainless steel sealed kettle and heated at 5°C / min to 400°C for 16 hours to obtain a primary product. The primary product was then ground and heated at 5°C / min to 1500°C under an argon atmosphere for 12 hours to obtain a sulfur-doped pitch-based hard carbon material.

[0103] (2) Preparation of negative electrode sheet

[0104] The preparation method of the negative electrode sheet in this embodiment is the same as that in Example 1.

[0105] (3) Assembly of sodium ion batteries

[0106] The preparation method of the sodium ion battery in this embodiment is the same as that in Example 1.

[0107] Comparative Example 1

[0108] (1) Preparation of pitch-based hard carbon materials

[0109] 5g of a mixed powder of petroleum pitch and coal tar pitch (the mass ratio of petroleum pitch to coal tar pitch was 1:1) and 40g of paraformaldehyde powder were weighed, ground, and mixed to obtain a mixture. Under an inert atmosphere (helium), the mixture was placed in a stainless steel sealed kettle and heated at 5°C / min to 400°C for 16 hours to obtain a primary product. The primary product was then ground and heated at 5°C / min to 1500°C under an argon atmosphere for 12 hours to obtain a pitch-based hard carbon material.

[0110] (2) Preparation of negative electrode sheet

[0111] The preparation method of the negative electrode sheet in this comparative example is the same as that in Example 1.

[0112] (3) Assembly of sodium ion batteries

[0113] The preparation method of the sodium ion battery in this comparative example is the same as that in Example 1.

[0114] Comparative Example 2

[0115] (1) Preparation of sulfur-doped pitch-based carbon materials

[0116] 5g of a mixed powder of petroleum pitch and coal tar pitch (the mass ratio of petroleum pitch to coal tar pitch is 1:1) and 30g of elemental sulfur and thiourea powder were weighed, ground, and mixed to obtain a mixed material. Under an inert atmosphere (helium atmosphere), the mixed material was placed in a stainless steel sealed kettle and heated at 5°C / min to 400°C and maintained at this temperature for 16 hours to obtain a primary product. The primary product was ground and heated at 5°C / min to 1500°C under an argon atmosphere and maintained at this temperature for 12 hours to obtain a sulfur-doped pitch-based carbon material.

[0117] (2) Preparation of negative electrode sheet

[0118] The preparation method of the negative electrode sheet in this comparative example is the same as that in Example 1.

[0119] (3) Assembly of sodium ion batteries

[0120] The preparation method of the sodium ion battery in this comparative example is the same as that in Example 1.

[0121] Test Example 1

[0122] The button batteries prepared in Examples 1 to 6 and Comparative Examples 1 to 2 were subjected to rate performance tests.

[0123] The test method of rate performance test is as follows: 1) first stand for 5 minutes; 2) discharge at a current density of 25mA / g first, discharge to 0V; 3) jump to start charging, charge at a current density of 25mA / g to 2.5V, this is one cycle, and the cycle is 10 weeks; 4) stand for 5 minutes; 5) the same process is changed to different current densities of 50mA / g, 125mA / g, 0.25A / g, 0.5A / g, 1.25A / g, 2.5A / g, 25mA / g (the specific operation includes: charge and discharge at a current density of 25mA / g for 10 cycles; change the current density to 50mA / g; charge and discharge at a current density of 50mA / g for 10 cycles; change the current density The current density is 125mA / g, and then charge and discharge at a current density of 125mA / g for 10 cycles; the current density is changed to 0.25A / g, and then charge and discharge at a current density of 0.25A / g for 10 cycles; the current density is changed to 0.5A / g, and then charge and discharge at a current density of 0.5A / g for 10 cycles; the current density is changed to 1.25A / g, and then charge and discharge at a current density of 1.25A / g for 10 cycles; the current density is changed to 2.5A / g, and then charge and discharge at a current density of 2.5A / g for 10 cycles; the current density is changed to 25mA / g, and then charge and discharge at a current density of 25mA / g for 10 cycles); 6) After the test is completed with a current density of 25mA / g, the test process ends. Among them, 25mAg -1 The reversible specific capacity (charge capacity of the first cycle at a current density of 25 mA / g) and 2.5Ag -1 The reversible specific capacity (charging capacity when cycled at a current density of 2.5 A / g) is shown in Table 1.

[0124] The rate performance test results of Example 1 are shown in Figure 1 The rate performance test results of Example 2 are shown in Figure 2 The rate performance test results of Example 3 are shown in Figure 3 The rate performance test results of Example 4 are shown in Figure 4 The rate performance test results of Example 5 are shown in Figure 5 The rate performance test results of Example 6 are shown in Figure 6 The rate performance test results of the comparative example are shown in Figure 7 .

[0125] Table 1

[0126]

[0127]

[0128] pass Figures 1 to 7As can be seen from the data in Table 1, different pitch-based hard carbon materials were prepared in Examples 1 to 6 by adjusting the selection and dosage of the pitch precursor, sulfur source and cross-linking agent, and adjusting the reaction temperature of the cross-linking vulcanization. Under the combined action of the sulfur source and the cross-linking agent, the sodium storage capacity of the prepared pitch-based hard carbon materials was significantly improved. -1 The current density can reach 351mAh g -1 The above gram capacity is exerted at a large rate, that is, 2.5Ag -1 At a current density of 205 mAh g -1 In comparative example 1, no sulfur source was added, that is, the prepared material was a pitch-based hard carbon material. Since there was no sulfur atom in the pitch-based hard carbon material as an active site for sodium ions, there was no sulfur-containing functional group that reacted with sodium ions for redox reaction, resulting in a lower sodium storage capacity. The prepared material had a low sodium storage capacity at 25 mAg -1 The current density is only 281 mAh g -1 The gram capacity is played, which is 2.5Ag at a large rate -1 At a current density of only 147 mAh g -1 In comparative example 2, no cross-linking agent was added, and the prepared material was a sulfur-doped pitch-based carbon material, which is actually a soft carbon material. Due to the lack of some platform area capacity, its sodium storage capacity is low. The prepared material has a low sodium storage capacity at 25mAg -1 The current density is only 274 mAh g -1 The gram capacity is played, which is 2.5Ag at a large rate -1 At a current density of only 146 mAh g -1 This shows that under the combined effect of the sulfur source and the cross-linking agent, the sodium storage performance and rate performance of the pitch-based hard carbon material in the embodiment of the present invention are significantly improved.

[0129] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A hard carbon material, characterized in that The hard carbon material contains sulfur; wherein the sulfur element exists in the hard carbon material in the form of at least one of a sulfur-carbon single bond, a sulfur-carbon double bond, and a sulfur oxide group; Based on the total weight of the hard carbon material, the content of the sulfur element is 0.1 to 5 weight % in terms of element.

2. The hard carbon material according to claim 1, wherein Based on the total weight of the hard carbon material, the content of the sulfur element is 1 to 3.5 weight % in terms of element; Optionally, the hard carbon material further contains carbon, oxygen, hydrogen and nitrogen; based on the total weight of the hard carbon material, the carbon content is 80-95% by weight, the oxygen content is 5-10% by weight, and the nitrogen content is 1-2% by weight. Preferably, based on the total weight of the hard carbon material, the carbon content is 82-93 wt%, the oxygen content is 6-8 wt%, and the nitrogen content is 1.2-1.8 wt%.

3. The hard carbon material according to claim 1, wherein The specific surface area of the hard carbon material is 3 to 20 m 2 / g, preferably 8 to 15m 2 / g.

4. The hard carbon material according to claim 1, wherein The pore volume of the hard carbon material is 3 to 10 cm 3 / g, preferably 5 to 8 cm 3 / g.

5. A method for preparing a hard carbon material, characterized in that: The preparation method comprises the following steps: S1. Mixing an asphalt precursor, a sulfur source, and a crosslinking agent to obtain a mixture; and crosslinking and vulcanizing the mixture to obtain a primary material; S2. Carbonizing the primary material in a first inert atmosphere.

6. The preparation method according to claim 5, characterized in that The mass ratio of the asphalt precursor, the sulfur source and the cross-linking agent is 1:(1-9):(1-9).

7. The preparation method according to claim 5, characterized in that The asphalt precursor includes at least one of coal tar pitch, petroleum pitch, coal liquefaction pitch, ethylene tar pitch and natural asphalt; and / or, The sulfur source includes elemental sulfur and / or thiourea; and / or, The cross-linking agent includes at least one of terephthalic alcohol, terephthalaldehyde and paraformaldehyde.

8. The preparation method according to claim 5, characterized in that In step S1, the crosslinking and vulcanization treatment is carried out in a stainless steel sealed kettle, or the crosslinking and vulcanization treatment is carried out in a second inert atmosphere; optionally, the second inert atmosphere is selected from at least one of nitrogen, argon and helium; The crosslinking vulcanization treatment conditions include: a heating rate of 0.1 to 10°C / min, a temperature of 100 to 500°C, and a holding time of 0.5 to 48 hours; and / or, In step S2, the first inert atmosphere is selected from at least one of nitrogen, argon and helium; the conditions of the carbonization treatment include: a heating rate of 0.1 to 10°C / min, a temperature of 1200 to 1600°C, and a holding time of 0.5 to 48h.

9. A negative electrode plate, characterized in that: The negative electrode plate includes a current collector and a negative electrode active material arranged on the surface of the current collector, and the negative electrode active material includes the hard carbon material according to any one of claims 1 to 4 and / or the hard carbon material prepared by the preparation method according to any one of claims 5 to 8.

10. A battery, characterized in that: The battery includes a negative electrode, and the negative electrode is the negative electrode sheet according to claim 9.

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