A negative electrode material, a preparation method thereof, and application thereof

Abstract

The application provides a negative electrode material, which comprises hard carbon, wherein the hard carbon has a multi-stage pore structure, micropores and / or mesopores are distributed in the core of the hard carbon, and macropores are distributed in the surface layer of the hard carbon. The application also provides a preparation method of the negative electrode material. Furthermore, the application also provides a secondary battery. The hard carbon material in the negative electrode material provided by the application is beneficial to reducing the specific surface area of the negative electrode material, improving the initial efficiency of the negative electrode material as a negative electrode material, and improving the lithium (sodium) storage capacity of the negative electrode material. In addition, the preparation process of the hard carbon material provided by the application is simple, easy to operate, and low in energy consumption, which is beneficial to large-scale production, has excellent performance, and is high in practicability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of secondary batteries, in particular to a negative electrode material, a preparation method thereof and application thereof. BACKGROUND

[0002] Hard carbon is a lithium ion energy storage negative electrode material which is difficult to graphitize, and is applied in high-power sodium, lithium ion batteries and other fields due to its large interlayer spacing, wide material sources, excellent high-rate charging and low-temperature performance and the like.

[0003] At present, the raw materials for preparing hard carbon mainly include biomass materials and high molecular compounds. These raw materials are prone to generate pores in the process of sintering and crushing, resulting in a high specific surface area of the hard carbon, easy absorption of water and oxygen, more side reactions, low first coulomb efficiency and short service life. The prior art directly reduces the specific surface area of the hard carbon by increasing closed pores, which is beneficial to improving the first coulomb efficiency of the negative electrode material, but reduces the lithium (sodium) storage capacity of the negative electrode material. SUMMARY

[0004] The technical problem solved by the present application is to provide a negative electrode material, which aims to reduce the specific surface area of the negative electrode material, improve the first coulomb efficiency, and at the same time has a high lithium (sodium) storage capacity.

[0005] Therefore, the present application provides a negative electrode material, which comprises hard carbon, the hard carbon has a hierarchical pore structure, micropores and / or mesopores are distributed in the core of the hard carbon, and macropores are distributed in the surface layer of the hard carbon.

[0006] Preferably, the hierarchical pore structure comprises micropores, mesopores and macropores in sequence from the core to the surface pores.

[0007] Preferably, the pore size of the micropores is < 2 nm, the pore size of the mesopores is 2-50 nm, and the pore size of the macropores is > 50 nm; and / or, the average particle size D50 of the hard carbon is 1-35 μm, the specific surface area is 1-500 m 2 / g, and the true density is 0.9-1.4 g / cm 2 . 3 3 .

[0008] Preferably, the open porosity of the hard carbon is 30-60%, and the proportion of the micropores, the mesopores and the macropores in the total number of all open pores of the hard carbon is 20-50: 0-30: 50.

[0009] Preferably, the negative electrode material further comprises a porous molecular sieve, and the porous molecular sieve is filled in the hard carbon.

[0010] ​Preferably, the porous molecular sieve comprises one or more of a full-silica molecular sieve, a silicoaluminophoric molecular sieve, a phosphoaluminophoric molecular sieve, and a framework heteroatom molecular sieve.

[0011] Preferably, the surface of the hard carbon is distributed with hydrophobic molecular sieves; and / or, the hard carbon is doped with silicon dioxide.

[0012] The application also provides a preparation method of the negative electrode material, comprising the following steps:

[0013] A1) low-temperature sintering of the broken hard carbon raw material comprising biomass material to obtain a first-stage post material;

[0014] B1) mixing the first-stage post material with a molecular sieve having micropores first and then with a molecular sieve having mesopores, and then high-temperature sintering to obtain a second-stage post material;

[0015] C1) etching of the second-stage post material with an etchant, and sintering to obtain a hard carbon;

[0016] or A2) low-temperature sintering of the broken biomass hard carbon raw material and the broken high-molecular compound hard carbon raw material respectively to obtain a first-stage post material-1 and a first-stage post material-2 respectively;

[0017] B2) mixing the first-stage post material-1 with a molecular sieve having micropores first and then with a molecular sieve having mesopores to obtain a first mixed material;

[0018] mixing the first-stage post material-2 with a molecular sieve having macropores to obtain a second mixed material;

[0019] mixing the first mixed material and the second mixed material and then high-temperature sintering to obtain a second-stage post material;

[0020] C2) etching of the second-stage post material with an etchant, and sintering to obtain a hard carbon.

[0021] The application also provides a secondary battery comprising a positive electrode and a negative electrode, wherein the negative electrode comprises the negative electrode material or the negative electrode material prepared by the preparation method.

[0022] Preferably, the secondary battery is a sodium ion battery, and the sodium ion battery has a first charge-discharge capacity ≥ 200 mAh / g and a first efficiency ≥ 60%.

[0023] The application provides a negative electrode material, which comprises hard carbon, wherein the hard carbon has a multi-stage pore structure, micropores and / or mesopores are distributed in the core of the hard carbon, and macropores are distributed in the surface layer of the hard carbon. The negative electrode material provided by the application has a multi-stage pore structure due to the hard carbon, so that the specific surface area of the negative electrode material is reduced, thereby improving the initial efficiency of the negative electrode material; meanwhile, the lithium (sodium) ion transmission distance is shortened, which is beneficial to the diffusion of lithium (sodium) ions into the core of the hard carbon, and can provide part of the lithium (sodium) storage capacity, thereby greatly improving the lithium (sodium) storage capacity of the negative electrode material.

[0024] The application also provides a preparation method of the negative electrode material, wherein the hard carbon material is prepared by introducing a molecular sieve with a porous structure and using an alkali etching agent to control the pore structure of the hard carbon, so that the hard carbon material has a pore structure with micropores and / or mesopores distributed in the core and macropores distributed in the surface layer, thereby reducing the specific surface area of the hard carbon material, improving the initial efficiency of the hard carbon material, and improving the lithium (sodium) storage capacity of the negative electrode material. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 A BJH pore size distribution curve of the hard carbon material prepared in Example 2 of the application;

[0026] Figure 2 An XRD spectrum of the hard carbon material prepared in Example 2 of the application;

[0027] Figure 3 A first circle charge-discharge curve spectrum of the hard carbon material prepared in Example 2 of the application. DETAILED DESCRIPTION

[0028] In order to further understand the application, the preferred embodiments of the application are described below in combination with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the application, and are not limitations on the claims of the application.

[0029] In the application, the term "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B can mean that A exists alone, A and B exist together, and B exists alone. Wherein A and B can be singular or plural.

[0030] In the application, "at least one" means one or more, and "a plurality of" means two or more. "At least one of the following" or the like means any combination of these items, including any combination of single item (s) or multiple items (s).

[0031] It should be understood that the size of the sequence number of the above processes does not mean the order of execution in various embodiments of the present application, and part or all of the steps can be executed in parallel or in sequence, and the execution order of the processes should be determined according to its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0032] In order to solve the problems of high specific surface area of hard carbon and low first coulombic efficiency, the present application provides a negative electrode material, which comprises hard carbon, the hard carbon has a multi-level pore structure with micropores and / or mesopores and macropores distributed, thereby reducing the specific surface area of the hard carbon material. Specifically, the present application first provides a negative electrode material, which comprises hard carbon, the hard carbon has a multi-level pore structure, the core of the hard carbon is distributed with micropores and / or mesopores, and the surface layer of the hard carbon is distributed with macropores.

[0033] According to the present application, the hard carbon has a multi-level pore structure, the core of which is distributed with micropores and the surface of which is distributed with macropores; or, the hard carbon has a multi-level pore structure, the core of which is distributed with mesopores and the surface layer of which is distributed with macropores; or, the hard carbon has a multi-level pore structure, which sequentially includes micropores, mesopores and macropores from the core to the surface.

[0034] In the present application, the hard carbon is more preferably a structure that sequentially includes micropores, mesopores and macropores from the core to the surface, which further reduces the specific surface area of the negative electrode material, is beneficial to improve the first efficiency of the negative electrode material, and shortens the lithium (sodium) ion transmission distance, which is beneficial to the diffusion of lithium (sodium) ions into the core of the hard carbon, and can provide part of the lithium (sodium) storage capacity, greatly improving the lithium (sodium) storage capacity of the negative electrode material.

[0035] On the basis of the above, the pore size of the micropores is < 2 nm, the pore size of the mesopores is 2-50 nm, and the pore size of the macropores is > 50 nm. The average particle size D50 of the hard carbon material is 1 μm-35 μm. The specific surface area of the hard carbon material is 1 m 2 / g-500 m 2 / g, specifically, the specific surface area of the hard carbon material is 100 m 2 / g-485 m 2 / g, more specifically, the specific surface area of the hard carbon material is 150-250 m 2 / g; it can be understood that if the specific surface area of the hard carbon material is too high, the first efficiency will be reduced, which will affect the performance of the battery, and if the specific surface area of the hard carbon material is too low, the capacity will be reduced, which will also affect the performance of the battery. Therefore, the present embodiment can control the specific surface of the hard carbon material within a reasonable range to improve the first efficiency of the negative electrode material while taking into account the higher capacity. In addition, the true density of the hard carbon material is 0.9 g / cm 3 -1.4 g / cm 3 .

[0036] In the present application, the open porosity of the hard carbon material is 30-60%. In the total number of the pores of the hard carbon material, the ratio of the micropores, the mesopores and the macropores is 20-50:0-30:50; specifically, the ratio of the micropores, the mesopores and the macropores is 22-40:10-28:50. The high proportion of the macropores in the pore structure of the hard carbon material is more conducive to the transmission of lithium (sodium) ions, thereby providing the electrochemical performance of the negative electrode material.

[0037] The negative electrode material provided by the present application further comprises a porous molecular sieve filled in the hard carbon. The filling of the porous molecular sieve in the hard carbon helps to form a hierarchical pore structure, further improves the capacity, and also can reduce the specific surface area and improve the initial efficiency. The appropriate filling of the porous molecular sieve can improve the initial efficiency of the negative electrode material, and too much filling will reduce the capacity of the negative electrode material. In the present application, the porous molecular sieve is selected from one or more of a full-silicon molecular sieve, a silicon-aluminum molecular sieve, a phosphorus-aluminum molecular sieve and a framework heteroatom molecular sieve; specifically, the phosphorus-aluminum molecular sieve is selected from an aluminum phosphate molecular sieve or a silicon-aluminum phosphate molecular sieve; more specifically, the aluminum phosphate molecular sieve is selected from one or more of SAPO-5, SAPO-34 and SAPO-11, and the silicon-aluminum phosphate molecular sieve is selected from one or more of AlPO-5, AlPO-15 and AlPO-21.

[0038] According to the present application, the surface of the hard carbon can be distributed with hydrophobic molecular sieves, which are conducive to improving the hydrophobicity of the hard carbon, preventing moisture in the external environment from entering the inside of the hard carbon, and thereby prolonging the service life of the hard carbon. The hard carbon can also be doped with silicon dioxide, and the content of silicon dioxide is 0-1.0wt%, more specifically 0.2-0.8wt%. If the content of silicon dioxide in the hard carbon is too low, the capacity of the hard carbon is limited, and if the content of silicon dioxide is too high, the hard carbon will expand, causing the electrode sheet to fall off and affecting the performance of the battery.

[0039] Some of the above-mentioned molecular sieves have high thermal stability, and their structure does not change after sintering, and can be coated on the surface of the hard carbon or form a multi-level pore hard carbon or be filled in the multi-level pores of the hard carbon. Some molecular sieves with poor thermal stability, such as molecular sieves that decompose at about 1300°C, will collapse after sintering, but will become amorphous oxides, which exist in the hard carbon material, and can also be coated on the surface of the hard carbon or form a multi-level pore hard carbon or be filled in the multi-level pores of the hard carbon.

[0040] Further, the present application also provides a preparation method of the negative electrode material, comprising the following steps:

[0041] A1) sintering the broken hard carbon raw material including biomass material at a low temperature to obtain a first-stage post-material;

[0042] B1) mixing the first post-material with a molecular sieve having micropores first and then with a molecular sieve having mesopores, and then high-temperature sintering to obtain a second post-material;

[0043] C1) etching the second post-material with an etchant, and obtaining hard carbon after sintering;

[0044] or, A2) separately performing low-temperature sintering on the broken biomass-based hard carbon raw material and the broken high-molecular compound hard carbon raw material to obtain a first post-material-1 and a first post-material-2, respectively;

[0045] B2) mixing the first post-material-1 with a molecular sieve having micropores first and then with a molecular sieve having mesopores to obtain a first mixed material;

[0046] mixing the first post-material-2 with a molecular sieve having macropores to obtain a second mixed material;

[0047] mixing the first mixed material and the second mixed material and then high-temperature sintering to obtain a second post-material;

[0048] C2) etching the second post-material with an etchant, and obtaining hard carbon after sintering.

[0049] In the process of preparing the negative electrode material, the molecular sieve having micropores is specifically a full-silicon molecular sieve with a microporous core, and is specifically selected from one or more of SSZ-24, SSZ-55, SSZ-44 and SSZ-73; and the molecular sieve having mesopores is a full-silicon molecular sieve with a mesoporous core, and is specifically selected from one or more of CDS-1, ITQ-1, RUB-41 and CIT-7.

[0050] Further, the molecular sieve having micropores and the molecular sieve having mesopores can also be selected from one or more of a full-silicon molecular sieve, a silicon-aluminum molecular sieve, a phosphorus-aluminum molecular sieve and a framework heteroatom molecular sieve. Some of the above molecular sieves have high thermal stability, and their structures do not change after sintering, and can be coated on the surface of hard carbon or filled in the multi-level pores of hard carbon; and some of the molecular sieves with poor thermal stability, such as a molecular sieve that decomposes at about 1300℃, will collapse after sintering, but will become amorphous oxide and exist in the hard carbon material, and can also be coated on the surface of hard carbon or filled in the multi-level pores of hard carbon.

[0051] For example, the molecular sieve having micropores is selected from SAPO-5, and correspondingly, the molecular sieve having mesopores is selected from SAPO-11; or, the molecular sieve having micropores is selected from AIPO-5, and correspondingly, the molecular sieve having mesopores is selected from AIPO-15.

[0052] The molecular sieve described in the present application is selected from the above-mentioned molecular sieve, which not only has a porous structure, but also can be used as a doping material according to the composition of the molecular sieve in the silica dioxide, thereby improving the hard carbon capacity. The above-mentioned molecular sieve can also form a hydrophobic material on the surface of the hard carbon, which can impart a certain hydrophobic structure to the hard carbon, prevent moisture in the external environment from entering the interior of the hard carbon, thereby prolonging the service life of the hard carbon, and the molecular sieve can also be used as a filler to reduce the surface area of the hard carbon negative material, thereby improving the initial coulombic efficiency.

[0053] According to the timing of the introduction of the molecular sieve, the preparation method of the hard carbon material of the present application includes two schemes, which are described below.

[0054] For the first preparation scheme:

[0055] The present application first crushes the hard carbon raw material including biomass material to obtain coarse crushed material, and the crushing method is well known to those skilled in the art, which is not particularly limited herein. Then the obtained coarse crushed material is sintered at low temperature under inert atmosphere to remove water, ash and easily volatile organic matter in the hard carbon raw material to obtain the first stage post material. The inert atmosphere is selected from one or both of argon and nitrogen; the temperature of the low-temperature sintering is 200-600°C, and the time is 2-5h, specifically, the temperature of the low-temperature sintering is 300-500°C, and the time is 3-4h. The hard carbon raw material can also include a polymer macromolecule.

[0056] The present application then mixes the first stage post material with the molecular sieve having micropores, mixes uniformly, and then mixes with the molecular sieve having mesopores, mixes again, and then high-temperature sintering of the obtained mixture to obtain the second stage post material; the mass ratio of the first stage post material to the molecular sieve is 100:1-5, and the proportion of the molecular sieve is too low, which is not conducive to the formation of multi-level pores, and the proportion of the molecular sieve is too high, which affects the proportion of the hard carbon material in the negative electrode, and further affects the capacity of the hard carbon. In this process, the high-temperature sintering is actually a high-temperature carbonization process, which is beneficial to obtain a hard carbon material with reduced specific surface area, reduced interlayer spacing, long-range disorder and short-range order. The temperature of the high-temperature sintering is 900-1500°C, and the time is 3-10h, specifically, the temperature of the high-temperature sintering is 1000-1300°C, and the time is 5-8h.

[0057] The second section of the material is etched by an etchant, and a hard carbon material is obtained after sintering. In the above process, the etchant volatilizes gradually from the inside to the outside during sintering, and a large pore structure is formed on the outer surface, and the core has a microporous and / or mesoporous pore structure. The etchant can be selected from one or more of potassium carbonate, potassium hydroxide, potassium bicarbonate, sodium carbonate, sodium hydroxide and sodium bicarbonate. In a specific application, the etchant acts in the form of an etchant solution, the concentration of the etchant solution is 0.1-10 mol / L, and specifically, the concentration of the etchant solution is 1-5 mol / L. In the process of etching the second section of the material by the etchant, according to the concentration of the etchant solution, a hard carbon with a core of micropores and a shell of large pores can be formed, a hard carbon with a core of mesopores and a shell of large pores can be formed, and a hard carbon with a core of micropores and mesopores and a shell of large pores can be formed. If the concentration of the etchant solution is too low, it is difficult to achieve the hard carbon with the above-mentioned core and shell pore structure distribution, and if the concentration of the etchant solution is too high, only a hard carbon with large pores can be formed. The sintering temperature is 400-600°C, and the time is 1-6h, and specifically, the sintering temperature is 450-550°C, and the time is 2-4h.

[0058] In the above method for preparing a hard carbon material, the hard carbon raw material of the biomass material is specifically selected from one or more of rice husk, peanut shell, pistachio shell, walnut shell, chestnut shell, almond shell, sunflower seed shell, pinecone, rice, coconut shell, bamboo, corn cob, rape straw and sugarcane residue. The high molecular compound is selected from one or more of polyvinyl chloride resin, acrylic resin, phenolic resin, epoxy resin, polyester resin, polyamide resin and bismaleimide.

[0059] For the second preparation scheme:

[0060] The biomass hard carbon raw material is first crushed to obtain coarse crushed material 1, and the high molecular compound hard carbon raw material is also crushed to obtain coarse crushed material 2. The crushing method is well known to those skilled in the art, and the present application does not have special restrictions. Then the obtained coarse crushed material 1 and coarse crushed material 2 are respectively subjected to low-temperature sintering in an inert atmosphere. The coarse crushed material 1 is subjected to low-temperature sintering to remove water, ash and easily volatile organic matter in the hard carbon raw material to obtain first section of the material-1, and the coarse crushed material 2 is subjected to low-temperature sintering pre-carbonization to obtain first section of the material-2. The inert atmosphere is selected from one or both of argon and nitrogen, and the low-temperature sintering temperature is independently 200-600°C, and the time is independently 2-5h, and specifically, the low-temperature sintering temperature is independently 300-500°C, and the time is independently 3-4h.

[0061] The first post-raw material-1 is then mixed with a microporous molecular sieve, and after uniform mixing, is mixed with a mesoporous molecular sieve to obtain a first mixed material; the first post-raw material-2 is mixed with a macroporous molecular sieve to obtain a second mixed material; and the first mixed material and the second mixed material are mixed and high-temperature sintered to obtain a second post-raw material. In this process, the high-temperature sintering is actually a high-temperature carbonization process, which is beneficial to obtain a hard carbon material with reduced specific surface area, reduced interlayer spacing, long-range disorder and short-range order. At the same time, a large number of pore structures are formed on the surface of the high molecular compound, which can better adhere to the outer surface of the first mixed material, and is more conducive to the formation of a multi-level pore structure.

[0062] In the present application, the macroporous molecular sieve is selected from a full-silicon molecular sieve with macropores, and is specifically selected from one or more of ITQ-50, ITQ-31, ITQ-7 and ITQ-13. The total of the microporous molecular sieve and the mesoporous molecular sieve (mass ratio of 30-100%:0-70%) is in a mass ratio of (1-5):100 to the first post-raw material-1; and the first post-raw material-2 and the macroporous molecular sieve are in a mass ratio of 100:(1-5). The high-temperature sintering is performed at a temperature of 900-1500°C for 3-10h, and specifically, the high-temperature sintering is performed at a temperature of 1000-1300°C for 5-8h. After the biomass-based hard carbon raw material and the high molecular compound are respectively pre-carbonized, the first post-raw material-1 and the first post-raw material-2 obtained are respectively mixed with microporous, mesoporous molecular sieves and macroporous molecular sieves in sequence, and the macroporous molecular sieve mixed high molecular compound pre-carbonization product can adhere to the surface of the biomass pre-carbonization product mixed with microporous and mesoporous materials after high-temperature sintering, which is more conducive to the formation of a gradient distribution of pore structures.

[0063] The second section of the material is etched by an etchant, and a hard carbon material is obtained after sintering. In the above process, the etchant volatilizes gradually from inside to outside during the sintering process, and a large pore structure is formed on the outer surface, and the core has a micropore-mesopore pore structure. The etchant can be selected from one or more of potassium carbonate, potassium hydroxide, potassium bicarbonate, sodium carbonate, sodium hydroxide and sodium bicarbonate. In a specific application, the etchant acts in the form of an etchant solution, the concentration of the etchant solution is 0.1-10 mol / L, and specifically, the concentration of the etchant solution is 1-5 mol / L. During the etching of the second section of the material by the etchant, according to the concentration of the etchant solution, a hard carbon with a core of micropores and a shell of large pores can be formed, a hard carbon with a core of mesopores and a shell of large pores can be formed, and a hard carbon with a core of micropores and mesopores and a shell of large pores can be formed. If the concentration of the etchant solution is too low, it is difficult to achieve the hard carbon with the above core and shell pore structure distribution, and if the concentration of the etchant solution is too high, only a hard carbon with large pores can be formed. The sintering temperature is 400-600°C, and the time is 1-6 h. Specifically, the sintering temperature is 450-550°C, and the time is 2-4 h.

[0064] In the above method for preparing a hard carbon material, the biomass-based hard carbon raw material is specifically selected from one or more of rice husk, peanut shell, pistachio shell, walnut shell, chestnut shell, almond shell, sunflower seed shell, pinecone, rice, coconut shell, bamboo, corn cob, rape straw and sugarcane residue. The high molecular compound is selected from one or more of polyvinyl chloride resin, acrylic resin, phenolic resin, epoxy resin, polyester resin, polyamide resin and bismaleimide.

[0065] Further, the application also provides a secondary battery including a positive electrode and a negative electrode, and the material of the negative electrode is the negative electrode material described in the above scheme. In the application, the secondary battery can be a lithium ion secondary battery or a sodium ion secondary battery. In the sodium ion secondary battery, the first charge-discharge capacity of the sodium ion secondary battery is ≥200 mAh / g, and the first efficiency is ≥60%.

[0066] In order to further understand the application, the preparation method of the negative electrode material and the application of the hard carbon provided by the application are described in detail below in combination with examples, and the protection scope of the application is not limited by the following examples.

[0067] Example 1

[0068] The example provides a negative electrode material including a hard carbon, the hard carbon has a hierarchical pore structure, the core of the hard carbon is distributed with micropores, and the surface layer of the hard carbon is distributed with large pores, wherein the micropores:large pores = 50%:50%, the pore size of the micropores is 2 nm, the pore size of the large pores is 55 nm, and the specific surface area of the hard carbon is 140 m 2 / g.

[0069] The preparation method of the negative electrode material comprises the following steps:

[0070] (1) The peanut shell is crushed, then is placed in a tube furnace, argon gas is introduced as a protective gas, the temperature is raised to 450 DEG C, and carbonization is performed for 3h. After the material is naturally cooled, it is crushed and sieved to obtain a first-stage post-material;

[0071] (2) The first-stage post-material: the mass percentage of the molecular sieve = 100wt%:1wt%, wherein the molecular sieve with micropores: the molecular sieve with mesopores = 70wt%:30wt%. 5g of the first-stage post-material is weighed, and is mixed with 0.035g of SSZ-24 microporous molecular sieve and 0.015g of CDS-1 mesoporous molecular sieve in sequence. After mixing, argon gas is introduced, high-temperature sintering is performed at 1000 DEG C for 5h, and a second-stage post-material is obtained;

[0072] (3) 4g of the second-stage post-material is weighed, 50mL of a sodium hydroxide etching agent with a concentration of 1mol / L is added, 120 DEG C water bath heating and stirring are performed for 1h, deionized water washing and filtration are performed, and 600 DEG C calcination is performed for 5h. After cooling, the material is broken, and a hard carbon negative electrode material with a hierarchical pore structure is obtained.

[0073] Example 2

[0074] The negative electrode material provided in this embodiment comprises hard carbon, and the hard carbon has a hierarchical pore structure. The hard carbon comprises micropores, mesopores and macropores in sequence from the core to the surface pores, and the micropores:mesopores:macropores = 20%:30%:50%. The pore diameter of the micropores is 1.4nm, the pore diameter of the mesopores is 35.5nm, and the pore diameter of the macropores is 57nm. The specific surface area of the hard carbon is 185m 2 / g.

[0075] The preparation method of the negative electrode material comprises the following steps:

[0076] (1) The preparation method is the same as (1) in Example 1, except that the peanut shell is replaced by chestnut shell;

[0077] (2) The preparation method is the same as (2) in Example 1, except that the mass percentage of the molecular sieve in the first-stage post-material is 100wt%:2wt%, the microporous molecular sieve is SSZ-55, and the mesoporous molecular sieve is RUB-41;

[0078] (3) The preparation method is the same as (2) in Example 1, except that the concentration of the sodium hydroxide etching agent is 1.5mol / L.

[0079] Example 3

[0080] The embodiment provides a negative electrode material, which comprises hard carbon, the hard carbon has a multi-stage pore structure, and the hard carbon comprises micropores, mesopores and macropores in sequence from the core to the surface pores, wherein the micropores:mesopores:macropores = 22%:28%:50%, the pore size of the micropores is 1.5 nm, the pore size of the mesopores is 46.9 nm, and the pore size of the macropores is 89 nm; and the specific surface area of the hard carbon is 210 m 2 / g.

[0081] The preparation method of the negative electrode material comprises the following steps:

[0082] (1) peanut shells and phenolic resin are respectively crushed, then argon gas is introduced into a tube furnace as a protective gas, the temperature is raised to 450 DEG C, carbonization is carried out for 4 h, the material is naturally cooled, and then crushing and screening are carried out, to obtain first-stage post material-1 and first-stage post material-2 respectively;

[0083] (2) the mass percentage of the first-stage post material-1 and molecular sieves is 100wt%:2wt%, wherein the mass percentage of the microporous SSZ-55 and the mesoporous RUB-41 in the molecular sieves is 70wt%:30wt%; 5 g of the first-stage post material-1 is weighed, and then 0.035 g of the microporous SSZ-55 molecular sieve and 0.015 g of the mesoporous RUB-41 molecular sieve are added thereto in sequence, and the mixture is uniformly mixed to obtain a first mixture;

[0084] The mass percentage of the first-stage post material-2 and the macroporous ITQ-50 molecular sieve is 100wt%:2wt%, and the mixture is uniformly mixed to obtain a second mixture;

[0085] The first mixture and the second mixture are uniformly mixed, argon gas is introduced, high-temperature sintering is carried out at 1200 DEG C for 5 h, and the second-stage post material is obtained;

[0086] (3) 4 g of the second-stage post material is weighed, 70 mL of 2mol / L sodium hydroxide etching agent is added, 100 DEG C water bath heating and stirring are carried out for 2 h, deionized water washing and filtration are carried out, and 550 DEG C calcination is carried out for 5 h, so that the multi-stage pore structure hard carbon negative electrode material is obtained after cooling and crushing.

[0087] Embodiment 4

[0088] The embodiment provides a negative electrode material, which comprises hard carbon, the hard carbon has a multi-stage pore structure, and the hard carbon comprises micropores, mesopores and macropores in sequence from the core to the surface pores, wherein the micropores:mesopores:macropores = 22%:28%:50%, the pore size of the micropores is 1.7 nm, the pore size of the mesopores is 48.9 nm, and the pore size of the macropores is 95 nm. The specific surface area of the hard carbon is 320 m 2 / g.

[0089] The preparation method of the negative electrode material comprises the following steps:

[0090] (1) The preparation method is the same as (1) in Example 3, except that the peanut shell is pinecone.

[0091] (2) The preparation method is the same as (2) in Example 3, except that: the mass percentage of the molecular sieve in the first-stage post-material-1 is = 100wt%:4wt%, the type of the molecular sieve is aluminum phosphate molecular sieve, and the molecular sieve with micropores is SAPO-5, and the molecular sieve with mesopores is SAPO-11; the mass percentage of the molecular sieve in the first-stage post-material-2 is = 100wt%:4wt%;

[0092] (3) The preparation method is the same as (3) in Example 3, except that the concentration of the sodium hydroxide etchant is 8mol / L.

[0093] Example 5

[0094] The negative electrode material provided in this example includes hard carbon, and the hard carbon has a hierarchical pore structure, and the hard carbon includes micropores, mesopores and macropores in order from the core to the surface pores, wherein the micropores:mesopores:macropores = 21%:29%:50%, the pore size of the micropores is 1.9nm, the pore size of the mesopores is 49.3nm, and the pore size of the macropores is 100nm; the specific surface area of the hard carbon is 483m 2 / g.

[0095] The preparation method of the negative electrode material includes the following steps:

[0096] (1) The preparation method is the same as (1) in Example 3;

[0097] (2) The preparation method is the same as (2) in Example 3, except that: the mass percentage of the molecular sieve in the first-stage post-material-1 is = 100wt%:4.9wt%, the type of the molecular sieve is silicon aluminum phosphate molecular sieve, and the molecular sieve with micropores is AlPO-5, and the molecular sieve with mesopores is AlPO-15;

[0098] The mass percentage of the molecular sieve in the first-stage post-material-2 is = 100wt%:4.9wt%;

[0099] (3) The preparation method is the same as (3) in Example 3, except that the concentration of the sodium hydroxide etchant is 9mol / L.

[0100] Comparative Example 1

[0101] The negative electrode material provided in this comparative example includes hard carbon, and the pores in the hard carbon are disordered, and the specific surface area of the hard carbon is 792m 2 / g.

[0102] The preparation method of the negative electrode material includes the following steps:

[0103] (1) The peanut shell is crushed, then placed in a tube furnace, argon gas is introduced as a protective gas, heated to 450 DEG C, carbonized for 3h, after the material is naturally cooled, crushing and screening are carried out, and the first section of the material is obtained;

[0104] (2) The first section of the material obtained in step (1) is placed in a tube furnace, argon gas is introduced as a protective gas, heated to 1000 DEG C, carbonized for 5h, and a hard carbon material is prepared.

[0105] The performance of the negative electrode material prepared in the above examples and comparative examples is detected:

[0106] (1) Physical property characterization

[0107] Figure 1 The BJH pore size distribution test result curve of the hard carbon material prepared in example 2 is shown in the figure, Figure 1 It can be seen that the hard carbon material prepared in example 2 has three different sizes of pore size, which are mainly concentrated in 1.4nm, 35.5nm and 57.0nm respectively, which shows that the pore structure of the hard carbon material prepared in example 2 is distributed in a gradient from the shell to the core, forming a ladder distribution of the pore structure.

[0108] Figure 2 The XRD spectrum of the hard carbon material prepared in example 2 is shown in the figure, it can be seen from the figure that the figure contains two characteristic peaks of amorphous carbon material, and the interlayer spacing d002 = 0.384nm, which shows that the carbon material prepared in example 2 is a hard carbon material.

[0109] (2) Preparation of battery sheet and assembly of battery

[0110] The hard carbon materials provided by the above examples 1-5 and the hard carbon material provided by the comparative example are respectively assembled into negative electrodes and sodium ion batteries according to the following method:

[0111] Negative electrode: the hard carbon negative electrode materials provided by examples 1-5 and comparative example 1 are respectively mixed with polyvinylidene fluoride and SP-Li according to the mass ratio of 90:5:5, and ball milling is carried out to obtain negative electrode slurry, the negative electrode slurry is coated on the surface of copper foil, and roll pressing is carried out, and vacuum drying is carried out at a temperature of 110 DEG C overnight to obtain a negative electrode sheet;

[0112] Counter electrode: sodium metal sheet;

[0113] Electrolyte: 1.0M NaPF6 / EC:DEC = 1:1 Vol%;

[0114] Separator: 20μm PP / PE / PP separator (glass fiber separator) is used;

[0115] Sodium-ion battery assembly: Sodium-ion batteries are assembled in an inert atmosphere glove box according to the assembly sequence of sodium metal sheet-separator-electrolyte-negative electrode.

[0116] (3) Electrochemical performance testing

[0117] The electrochemical performance of each sodium-ion battery assembled in the above sodium-ion battery examples was tested under the following conditions: charge / discharge voltage range of 0.1V to 1.5V; initial discharge capacity and corresponding initial coulombic efficiency at 0.1C; and electrochemical performance at 25°C for 1000 cycles at 1C and 3C. The electrochemical performance is shown in Table 1 below.

[0118] Table 1. Electrochemical performance data of sodium-ion batteries prepared in the examples.

[0119]

[0120]

[0121] As can be seen from the data results of the examples and comparative examples in Table 1, the electrochemical performance of the hard carbon anode material prepared in this application is better than that of the comparative example. Furthermore, it can be observed from the data of Examples 2 and 3 that the electrochemical performance of the two multi-level porous hard carbon materials differs due to the use of two different technical routes for preparation. The hard carbon material prepared using the second experimental technical route (Example 3) has a slightly larger macroporous structure on its surface, and its initial discharge capacity is 18.2 mAh / g greater than that of the hard carbon material prepared using the first experimental technical route (Example 2). Furthermore, its initial coulombic efficiency was only 1.2% lower than that of Example 2, so the cycling stability of Example 3 at room temperature (1C and 3C) was also better than that of Example 2. In Examples 4 and 5, due to the presence of more filler, the capacity decreased, the concentration of alkaline etchant used was higher, and the specific surface area was larger than that of other examples. These factors reduced the electrochemical performance of Examples 4 and 5. In Comparative Example 1, since the hard carbon experimental route prepared in this application was not used, its initial discharge capacity, initial efficiency, and cycling performance at room temperature (1C and 3C) were even lower.

[0122] Figure 3 The first charge-discharge curve of the hard carbon material prepared in Example 2 is shown below. Figure 3 It can be seen that the sodium-ion battery assembled using the negative electrode material provided in Example 2 achieved a high initial coulombic efficiency (89.4%) and a high initial discharge capacity (321.9 mAh / g).

[0123] In summary, the hard carbon anode material prepared by this invention has a multi-level pore structure, which accelerates the diffusion rate of sodium ions into the hard carbon core. Furthermore, its inherent pore structure increases its sodium storage capacity, thereby improving its reversible capacity. The molecular sieve filler used can also fill / coat part of the pores on the open surface, reducing the specific surface area of ​​the material and improving the first-efficiency of the hard carbon material. Moreover, the process of this invention is simple and conducive to large-scale production.

[0124] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0125] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A negative electrode material comprising hard carbon, said hard carbon having a hierarchical porous structure, The multi-level pore structure includes micropores, mesopores, and macropores sequentially from the core to the surface pores. The method for preparing the negative electrode material includes the following steps: A1) The crushed hard carbon raw material, including biomass materials, is sintered at low temperature to obtain the first stage of feedstock; B1) The first stage of the feed material is first mixed with a molecular sieve with micropores and then mixed with a molecular sieve with mesopores, and then sintered at high temperature to obtain the second stage of the feed material; C1) The second section of the material is etched with an etchant and then sintered to obtain hard carbon; Or; A2) The crushed biomass hard carbon raw material and the crushed polymer hard carbon raw material are sintered at low temperature to obtain the first stage post-material-1 and the first stage post-material-2 respectively; B2) The first section of material-1 is first mixed with a molecular sieve with micropores and then mixed with a molecular sieve with mesopores to obtain the first mixture; The first section of material-2 is mixed with a molecular sieve with large pores to obtain a second mixture; The first mixture and the second mixture are mixed and sintered at high temperature to obtain the second stage of material; C2) The second section of material is etched with an etchant and then sintered to obtain hard carbon.

2. The negative electrode material according to claim 1, characterized in that, The micropores have a diameter < 2 nm, the mesopores have a diameter of 2~50 nm, and the macropores have a diameter > 50 nm; and / or, the hard carbon has an average particle size D50 of 1 μm~35 μm and a specific surface area of ​​1 m². 2 / g~500m 2 / g, true density is 0.9g / cm³ 3 ~1.4g / cm 3 .

3. The negative electrode material according to claim 1, characterized in that, The porosity of the hard carbon is 30-60%; the ratio of micropores, mesopores and macropores in the total number of openings in the hard carbon is 20-50:0-30:

50.

4. The negative electrode material according to claim 1, characterized in that, The negative electrode material also includes a porous molecular sieve, which is filled in the hard carbon.

5. The negative electrode material according to claim 4, characterized in that, The porous molecular sieve includes one or more of the following: all-silica molecular sieve, silica-alumina molecular sieve, phosphorus-alumina molecular sieve, and framework heteroatom molecular sieve.

6. The negative electrode material according to claim 1 or 5, characterized in that, The surface of the hard carbon is distributed with hydrophobic molecular sieves; and / or, the hard carbon is doped with silicon dioxide.

7. A secondary battery, comprising a positive electrode and a negative electrode, characterized in that, The negative electrode comprises the negative electrode material as described in any one of claims 1 to 6.

8. The secondary battery according to claim 7, characterized in that, The secondary battery is a sodium-ion battery, and the initial charge / discharge capacity of the sodium-ion battery is ≥200mAh / g, with an initial efficiency of ≥60%.

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