High-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material as well as preparation method and application thereof

Abstract

The invention discloses a high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material and a preparation method and application thereof, the negative electrode material comprises a nitrogen-doped carbon material and a biomass porous silicon-oxygen material, the nitrogen-doped carbon material coats the biomass porous silicon-oxygen material, and the content of nitrogen in the negative electrode material is greater than or equal to 13at%. According to the preparation method disclosed by the invention, an amino acid material is crosslinked with Si-OH groups on the surface of a biomass porous silica material, and polymerization-cyclization-condensation of the amino acid material is promoted through carbonization to form a high-content nitrogen-doped carbon material which uniformly coats the biomass porous silica material; by optimizing the surface structure of a biomass porous silica material, the polymerization effect of an amino acid material or a pyrolysis product and the biomass porous silica material is promoted, and the nitrogen-doped silica carbon material rich in pore structures is prepared; by optimizing the lithium affinity of the biomass porous silica material, the prepared nitrogen-doped biomass porous silica carbon material has excellent electrochemical performance and cycle stability.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and particularly relates to a high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material and a preparation method and application thereof. BACKGROUND

[0002] With the rapid growth of energy demand for applications such as electric vehicles, hybrid electric vehicles and portable electronic devices, the development of lithium ion batteries (LIBs) with high specific capacity and long life has become a research hotspot in recent years. Graphite has become the most commonly used negative electrode material for lithium ion batteries due to its low working potential and high coulombic efficiency, but the theoretical capacity (372 mAh g -1 ) of the graphite negative electrode is far from meeting the rapidly growing energy density demand, especially in large-scale applications such as electric vehicles and energy storage power stations. Therefore, it is necessary to explore new electrode materials with high reversible capacity and cycle stability. Compared with graphite negative electrodes, silicon-based materials with abundant reserves and no pollution have higher theoretical specific capacity (4200-1965 mAh g -1 ) and lower working potential (<1.0 V vs. Li / Li + ), and have greater application prospects. Among them, the alloying process of pure silicon material with lithium will produce a volume expansion of nearly 400%, while the silicon-oxygen material with stable properties has a smaller volume expansion (<200%), and exhibits longer cycle stability, and is the most potential high-energy-density lithium ion battery negative electrode material.

[0003] Due to the high content of oxygen elements and the intrinsic semiconductor properties of the silicon-oxygen material, the thermodynamics and kinetics in the charging and discharging process are affected, and the first coulombic efficiency (20-35%) and rate performance are poor. Therefore, it is urgent to find a method to improve the exposure of active silicon and the conductivity of the silicon-oxygen material, while as much as possible improving the electrochemical performance of the silicon-oxygen material. SUMMARY

[0004] The present application aims to at least solve one of the above-mentioned defects of the prior art silicon-oxygen material, thereby alleviating the technical problems of poor first coulombic efficiency and rate performance of lithium ion batteries. To this end, the present application proposes a high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material and a preparation method and application thereof. The negative electrode material can effectively alleviate the volume expansion of the silicon-oxygen material in the charging and discharging process, and ensure the cycle stability and electrochemical performance of the battery.

[0005] To solve the above technical problems, the first aspect of the present application provides a negative electrode material, which comprises a nitrogen-doped carbon material and a biomass porous silicon-oxygen material, and the nitrogen-doped carbon material coats the biomass porous silicon-oxygen material; in the negative electrode material, the content of nitrogen element is ≥13 at%.

[0006] Specifically, the negative electrode material of the present application can reduce the internal resistance of the porous silicon-oxygen negative electrode, enhance the interface bonding force between the carbon material and the porous silicon-oxygen material, and build a flexible coating layer on the basis of the porous structure of the biomass silicon-oxygen material to buffer the mechanical stress of the alloying process phase change, thereby enhancing the cycle stability of the electrode material. At the same time, the nitrogen-doped carbon surface containing nitrogen polar groups is beneficial to increase the adsorption capacity of lithium ions and promote the diffusion rate of lithium ions, thereby improving the reversible specific capacity of the porous silicon-oxygen material. In addition, the silicon-oxygen material will have more side reactions with the electrolyte during the first discharge process, thereby consuming the lithium source in the electrolyte and reducing the charge-discharge coulombic efficiency of the battery. The use of a nitrogen-doped carbon layer coating can act as a physical barrier to reduce the direct contact between the electrolyte and the silicon-oxygen material, form a stable solid electrolyte film, thereby inhibiting the occurrence of side reactions and improving the coulombic efficiency and cycle stability of the lithium ion battery. Therefore, the high-nitrogen-content negative electrode material of the present application not only helps to enhance the stability of the electrode material, but also can improve the reversible specific capacity of the material, thereby improving the coulombic efficiency and cycle stability of the lithium ion battery.

[0007] In some embodiments of the present application, the content of nitrogen element in the negative electrode material is 13.12-20.27 at%.

[0008] In some embodiments of the present application, the negative electrode material has a hierarchical pore structure including micropores, mesopores and macropores, and the proportion of micropores is greater than 80%.

[0009] In some embodiments of the present application, the proportions of micropores, mesopores and macropores are 80-85%, 12-18% and 1-5%, respectively.

[0010] In some embodiments of the present application, the pore size of the micropores is 0.35-2 nm, the pore size of the mesopores is 2-50 nm, and the pore size of the macropores is 50-200 nm.

[0011] In some embodiments of the present application, the specific surface area of the negative electrode material is 160-360 m 2 / g.

[0012] Specifically, the high specific surface area and hierarchical pore distribution of the negative electrode material of the present application can greatly shorten the diffusion path of lithium ions, accelerate the migration rate of lithium ions, promote the uniform deposition of the solid electrolyte film, and reduce the material rupture caused by local polarization. At the same time, the existence of a large number of micropore structures can not only expose more active sites, but also limit the excessive penetration of the electrolyte, reduce the decomposition of the electrolyte, and effectively improve the reversible capacity of the silicon-oxygen material.

[0013] In some embodiments of the present application, the raw materials for preparing the negative electrode material include a biomass porous silicon-oxygen material and an amino acid material.

[0014] Specifically, the negative electrode material of the present application takes biomass porous silicon-oxygen material and amino acid material as raw materials. Due to the developed three-dimensional porous structure of the biomass porous silicon-oxygen material, by controlling the carbonization temperature and carbonization time, the nitrogen-doped carbon material coated biomass silicon-oxygen material prepared can have the characteristics of high disorder. At the same time, the rich Si-OH surface of the biomass porous silicon-oxygen material can effectively crosslink the amino acid material, reduce the loss of the amino acid material in the high-temperature pyrolysis process, form a nitrogen-doped carbon-wrapped biomass porous silicon-oxygen material with stable structure, and increase the nitrogen content in the negative electrode material. In addition, the decomposition of the amino acid material under high temperature conditions can generate NH3, HCNO and HCN gases, which can help to optimize the pore structure and surface structure of the biomass porous silicon-oxygen material, and further improve the affinity of the negative electrode material for lithium ions.

[0015] In some embodiments of the present application, the mass ratio of the biomass porous silicon-oxygen material and the amino acid material is 1:(0.5-5); such as 1:0.5, 1:1, 1:2, 1:3, 1:4 or 1:5, etc., including but not limited to the listed values, and other values not listed in the value range are also applicable.

[0016] In some embodiments of the present application, the mass ratio of the biomass porous silicon-oxygen material and the amino acid material is 1:(2-4).

[0017] It is found that when the content of amino acid is too low, the biomass porous silicon-oxygen material is not fully coated with nitrogen-doped carbon material, forming a poor stability conductive network. When the content of amino acid is too high, too many nitrogen defects are easily formed on the surface of the biomass porous silicon-oxygen material, causing the generation of irreversible capacity. Therefore, by controlling the mass ratio of the biomass porous silicon-oxygen material and the amino acid material, the present application promotes the good combination between the biomass porous silicon-oxygen material and the amino acid material matrix, forms a uniform and dense network structure, so that the carbon-coated biomass porous silicon-oxygen material can be suitable for reaction with lithium ions on one hand, and ensure the structural stability during the cycle process on the other hand.

[0018] In some embodiments of the present application, the biomass porous silicon-oxygen material includes diatom, and the diatom is selected from at least one of round diatom and boat-shaped diatom.

[0019] In some embodiments of the present application, the amino acid material is selected from at least one of glutamic acid, proline, cysteine, glycine and alanine.

[0020] The second aspect of the present application provides a preparation method of the above-mentioned negative electrode material, comprising the following steps:

[0021] (1) mixing biomass porous silicon-oxygen material with amino acid material to obtain a mixed material;

[0022] (2) annealing the mixed material in an inert atmosphere to obtain the negative electrode material.

[0023] In some embodiments of the present application, the temperature regime of the annealing treatment is as follows: heating at a rate of 3-10℃ / min to 400-800℃, and then maintaining the temperature for 2-4 hours.

[0024] Specifically, the present application controls the temperature regime of the annealing treatment, i.e. carbonization temperature and carbonization time, so that the amino acid is stably combined with the surface of the biomass porous silicon-oxygen material, and the optimal nitrogen content and the area of the porous silicon-oxygen material covered by the nitrogen-doped carbon material are controlled, thereby obtaining a nitrogen-doped biomass porous silicon-oxygen carbon material with high disorder and high nitrogen content. When used as a negative electrode material of a lithium ion battery, it can adsorb more lithium ions, thereby greatly improving the energy density of the battery.

[0025] In some embodiments of the present application, the inert atmosphere is an atmosphere of at least one of nitrogen, argon, nitrogen and argon.

[0026] In some embodiments of the present application, the biomass porous silicon-oxygen material further comprises a grinding step before being mixed with the amino acid material. The grinding process conditions are as follows: using grinding balls with a particle size of 1-10mm (such as zirconia balls, alumina balls, agate balls, etc.), and ball milling at a speed of 200-600rpm for 3-48 hours. For example, the ball milling can be performed at the above particle size and speed for 3 hours, 6 hours, 12 hours, 28 hours, 24 hours, 30 hours, 36 hours, 42 hours or 48 hours, etc., including but not limited to the listed values, and other values not listed within the range are also applicable.

[0027] In some embodiments of the present application, the grinding process conditions are as follows: using grinding balls with a particle size of 1-10mm, and ball milling at a speed of 200-600rpm for 3-12 hours.

[0028] The research finds that the ball milling time of the biomass porous silicon-oxygen material affects the particle size, and further affects the electrochemical performance of the porous silicon-oxygen material. If the ball milling time is too short, the biomass porous silicon-oxygen material is micron level, and a unstable solid electrolyte film (SEI) is formed, which is not conducive to subsequent carbonization; if the ball milling time is too long, the pore structure of the biomass porous silicon-oxygen material is easily damaged, which will hinder the transmission and diffusion of lithium ions, and cause the generation of irreversible capacity. Therefore, by controlling the ball milling time of the biomass porous silicon-oxygen material, the present application promotes the good combination between the amino acid material and the biomass porous silicon-oxygen material matrix, forms a uniform and dense carbon layer network structure, so that the mixed material can adapt to the lithium ion reaction and diffusion after carbonization, and ensure the structural stability during the cycle process.

[0029] The third aspect of the present application provides a negative electrode sheet, which comprises the above-mentioned negative electrode material or the negative electrode material prepared by the above-mentioned preparation method.

[0030] In some embodiments of the present application, the preparation method of the negative electrode sheet comprises the following steps:

[0031] 1) mixing the negative electrode material, the conductive agent and the binder in proportion to obtain a negative electrode slurry;

[0032] 2) coating the negative electrode slurry on a current collector and drying to obtain the negative electrode sheet.

[0033] In some embodiments of the present application, the conductive agent can be selected from conventional negative electrode conductive agents, and preferably is conductive carbon black.

[0034] In some embodiments of the present application, the binder can be selected from conventional negative electrode binders, such as polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), sodium alginate, etc., and preferably is PAA. The binder uses water as a solvent.

[0035] In some embodiments of the present application, the mass ratio of the negative electrode material, the conductive agent and the binder is (7-8) : (2-1) : 1, for example, can be 7:2:1 or 8:1:1, etc.

[0036] In some embodiments of the present application, the current collector is a copper foil or an aluminum foil; preferably is a copper foil.

[0037] In some embodiments of the present application, the drying temperature is 60-120 DEG C, and the drying time is 12-24 hours.

[0038] The fourth aspect of the present application provides a lithium ion battery, which comprises the above-mentioned negative electrode sheet.

[0039] In some embodiments of the present application, the lithium ion battery further comprises a positive electrode sheet, a separator and an electrolyte.

[0040] In some embodiments of the present application, the electrolyte is a lithium salt and a non-aqueous solvent.

[0041] In some embodiments of the present application, the lithium salt is selected from any one of LiClO4, LiPF6.

[0042] In some embodiments of the present application, the non-aqueous solvent is selected from at least one of ethylene carbonate (EC), diethyl carbonate (DEC), methyl ethyl carbonate (DME), dimethyl carbonate (DMC). When the lithium salt is LiClO4, the non-aqueous solvent is selected from a mixture of EC and DEC in a volume ratio of 1:1; when the lithium salt is LiPF6, the non-aqueous solvent is selected from a mixture of EC, DMC and DEC in a volume ratio of 1:1:1, or a mixture of EC and DME in a volume ratio of 1:1.

[0043] In some embodiments of the present application, the concentration of the lithium salt in the electrolyte is 0.8-1.5 mol / L.

[0044] The above technical solution of the present application has at least the following technical effects or advantages compared with the prior art:

[0045] (1) The negative electrode material of the present application is a biomass porous silicon-oxygen material coated with a carbon material doped with a high nitrogen content (≥13 at%). This negative electrode material not only helps to enhance the stability of the electrode material, but also improves the reversible specific capacity of the material, thereby improving the coulombic efficiency and cycle stability of the lithium ion battery.

[0046] (2) The negative electrode material of the present application uses amino acid materials and biomass porous silicon-oxygen materials as raw materials, which are abundant in resources, widely available and green and environmentally friendly. The cost is low and the energy consumption is low. In addition, the three-dimensional pore structure of the biomass porous silicon-oxygen material is developed, and by controlling the mass ratio of the two, the carbonization temperature and the carbonization time, the nitrogen-doped carbon material coated biomass silicon-oxygen material prepared has the characteristics of high disorder and rich nitrogen elements. At the same time, the abundant Si-OH surface of the biomass porous silicon-oxygen material can effectively crosslink the amino acid materials, reduce the loss of the amino acid materials during high-temperature pyrolysis, form a nitrogen-doped carbon-coated biomass porous silicon-oxygen material with stable structure, and increase the nitrogen content in the negative electrode material. In addition, the decomposition of amino acid materials under high temperature conditions helps to optimize the pore structure and surface structure of the biomass porous silicon-oxygen material, further improving the affinity of the negative electrode material for lithium ions.

[0047] (3) The preparation method of the negative electrode material of the application is simple in operation and short in process flow, and is suitable for large-scale industrial production; the prepared nitrogen-doped biomass porous silicon-oxygen-carbon material has a unique hierarchical pore structure, and the combination of nitrogen-doped carbon material coating promotes the interaction between the silicon-oxygen material and lithium ions, and at the same time, the volume expansion of the silicon-oxygen material in the charging and discharging process is relieved, the cycle stability of the battery is ensured, the application of the material in a lithium ion battery can ensure the integrity of the electrode, and good cycle stability and electrochemical performance of the battery are achieved. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The XRD pattern of the negative electrode material prepared in Example 2 of the application;

[0049] Figure 2 The SEM pattern of the negative electrode material prepared in Example 2 of the application;

[0050] Figure 3 The pore size distribution pattern of the negative electrode material prepared in Example 2 of the application;

[0051] Figure 4 The charge-discharge pattern of the lithium ion battery assembled by the negative electrode material prepared in Example 2 of the application and Comparative Example 1;

[0052] Figure 5 The cycle performance pattern of the lithium ion battery assembled by the negative electrode material prepared in Example 2 of the application and Comparative Example 1. DETAILED DESCRIPTION

[0053] The application will be described in detail below with reference to examples, so as to facilitate the understanding of the application by those skilled in the art. It is necessary to point out here that the examples are only used to further illustrate the application and cannot be understood as limiting the protection scope of the application. Non-essential improvements and adjustments of the application made by those skilled in the art according to the above application content shall still fall within the protection scope of the application. Meanwhile, the raw materials mentioned below which are not described in detail are all commercially available products; the process steps or preparation methods which are not mentioned in detail are all process steps or preparation methods known to those skilled in the art.

[0054] Example 1

[0055] A preparation method of a high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material, comprising the following steps:

[0056] (1) Biomass porous silicon material (round diatom) 5 g is placed in a ball mill jar, grinding aid (ethanol) 10 mL is added, ball milling medium (zirconia ball with a particle size of 1-10 mm) 50 g is added, and the ball mill is put into a ball mill at a speed of 400 revolutions per minute for 12 hours. After the ball milling suspension is filtered, it is placed in a forced air oven and dried at 80°C for 24 hours to obtain small-particle-size biomass porous silicon-oxygen material;

[0057] (2) Weigh 1 g of the biomass porous silicon-oxygen material prepared in step (1), add 2 g of an amino acid material (glutamic acid), and mix and grind at a rotation speed of 400 rpm for 1 hour to obtain a uniform mixed material;

[0058] (3) Transfer the mixed material prepared in step (2) to a tube furnace, heat to 600°C at a heating rate of 5°C / min under an argon protective atmosphere, and heat for calcination for 3 hours to prepare the high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material of the present example.

[0059] Example 2

[0060] A method for preparing a high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material, comprising the following steps:

[0061] (1) Place 5 g of a biomass porous silicon material (round diatom) in a ball mill jar, add 10 mL of a grinding aid (ethanol), and 50 g of a ball milling medium (zirconia balls with a particle size of 1-10 mm), and place in a ball mill to ball mill at a rotation speed of 400 rpm for 6 hours. After ball milling, filter the solution and place in a forced air oven at 80°C for drying for 24 hours to obtain a small-particle-size biomass porous silicon-oxygen material;

[0062] (2) Weigh 1 g of the biomass porous silicon-oxygen material prepared in step (1), add 2 g of an amino acid material (glutamic acid), and mix and grind at a rotation speed of 400 rpm for 1 hour to obtain a uniform mixed material;

[0063] (3) Transfer the mixed material prepared in step (2) to a tube furnace, heat to 600°C at a heating rate of 5°C / min under an argon protective atmosphere, and heat for calcination for 3 hours to prepare the high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material of the present example.

[0064] Example 3

[0065] A method for preparing a high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material, comprising the following steps:

[0066] (1) Place 5 g of a biomass porous silicon material (round diatom) in a ball mill jar, add 10 mL of a grinding aid (ethanol), and 50 g of a ball milling medium (zirconia balls with a particle size of 1-10 mm), and place in a ball mill to ball mill at a rotation speed of 400 rpm for 3 hours. After ball milling, filter the suspension and place in a forced air oven at 80°C for drying for 24 hours to obtain a small-particle-size biomass porous silicon-oxygen material;

[0067] (2) Weigh 1 g of the biomass porous silicon-oxygen material prepared in step (1), add 2 g of an amino acid material (glutamic acid), and mix and grind at a rotation speed of 400 rpm for 1 hour to obtain a uniform mixed material;

[0068] (3) The mixed material prepared in step (2) is transferred to a tube furnace, and calcined at 600°C for 3 hours under an argon protective atmosphere at a temperature rising rate of 5°C / min to obtain the high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material of the present embodiment.

[0069] Example 4

[0070] A method for preparing a high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material, comprising the following steps:

[0071] (1) Biomass porous silicon material (circular diatom) 5g is placed in a ball mill jar, 10mL of grinding aid (ethanol) is added, 50g of ball milling medium (zirconia balls with a particle size of 1-10mm) is added, and the mixture is ball milled in a ball mill at a speed of 400rpm for 6 hours. After the suspension is filtered, it is dried in a forced air oven at 80°C for 24 hours to obtain small-particle-size biomass porous silicon-oxygen material;

[0072] (2) 1g of the biomass porous silicon-oxygen material prepared in step (1) is weighed, 1g of amino acid material (glutamic acid) is added, and the mixture is mixed and ground at a speed of 400rpm for 1 hour to obtain a uniform mixed material;

[0073] (3) The mixed material prepared in step (2) is transferred to a tube furnace, and calcined at 600°C for 3 hours under an argon protective atmosphere at a temperature rising rate of 5°C / min to obtain the high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material of the present embodiment.

[0074] Example 5

[0075] A method for preparing a high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material, comprising the following steps:

[0076] (1) Biomass porous silicon material (circular diatom) 5g is placed in a ball mill jar, 10mL of grinding aid (ethanol) is added, 50g of ball milling medium (zirconia balls with a particle size of 1-10mm) is added, and the mixture is ball milled in a ball mill at a speed of 400rpm for 6 hours. After the suspension is filtered, it is dried in a forced air oven at 80°C for 24 hours to obtain small-particle-size biomass porous silicon-oxygen material;

[0077] (2) 1g of the biomass porous silicon-oxygen material prepared in step (1) is weighed, 1g of amino acid material (glutamic acid) is added, and the mixture is mixed and ground at a speed of 400rpm for 1 hour to obtain a uniform mixed material;

[0078] (3) The mixed material prepared in step (2) is transferred to a tube furnace, and heated to 600°C at a heating rate of 5°C / min under an argon protective atmosphere, and kept at 600°C for 3 hours to obtain the high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material of the example.

[0079] Example 6

[0080] A method for preparing a high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material, comprising the following steps:

[0081] (1) Biomass porous silicon material (circular diatom) 5 g is placed in a ball mill jar, grinding aid (ethanol) 10 mL is added, and ball mill medium (zirconia balls with a particle size of 1-10 mm) 50 g is added, and the mixture is ball milled in a ball mill at a speed of 400 revolutions / min for 6 hours. After the suspension is filtered, it is placed in a forced air oven and dried at 80°C for 24 hours to obtain small-particle-size biomass porous silicon-oxygen material;

[0082] (2) Biomass porous silicon-oxygen material 1 g prepared in step (1) is weighed, 2 g of amino acid material (glutamic acid) is added, and the mixture is mixed and ground at a speed of 400 revolutions / min for 1 hour to obtain a uniform mixed material;

[0083] (3) The mixed material prepared in step (2) is transferred to a tube furnace, and heated to 500°C at a heating rate of 5°C / min under an argon protective atmosphere, and kept at 500°C for 3 hours to obtain the high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material of the example.

[0084] Example 7

[0085] A method for preparing a high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material, comprising the following steps:

[0086] (1) Biomass porous silicon material (circular diatom) 5 g is placed in a ball mill jar, grinding aid (ethanol) 10 mL is added, and ball mill medium (zirconia balls with a particle size of 1-10 mm) 50 g is added, and the mixture is ball milled in a ball mill at a speed of 400 revolutions / min for 6 hours. After the suspension is filtered, it is placed in a forced air oven and dried at 80°C for 24 hours to obtain small-particle-size biomass porous silicon-oxygen material;

[0087] (2) Biomass porous silicon-oxygen material 1 g prepared in step (1) is weighed, 2 g of amino acid material (glutamic acid) is added, and the mixture is mixed and ground at a speed of 400 revolutions / min for 1 hour to obtain a uniform mixed material;

[0088] (3) The mixed material prepared in step (2) is transferred to a tube furnace, and heated to 700°C at a heating rate of 5°C / min under an argon protective atmosphere, and kept at 700°C for 3 hours to obtain the high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material of the example.

[0089] Comparative Example 1

[0090] The difference between Comparative Example 1 and Example 2 is only that no amino acid material is added in the preparation process of the negative electrode material.

[0091] Comparative Example 2

[0092] The difference between Comparative Example 2 and Example 2 is only that the amino acid material in Example 2 is replaced by an equal amount of melamine material in the preparation process of the negative electrode material.

[0093] Comparative Example 3

[0094] The difference between Comparative Example 3 and Example 2 is that the amino acid material in Example 2 is replaced by an equal amount of dicyandiamide material in the preparation process of the negative electrode material.

[0095] Application Example

[0096] The negative electrode materials prepared in Examples 1-7 and Comparative Examples 1-3 above are respectively used as the active material of the negative electrode sheet to make 2032 button-type lithium ion batteries, and the specific steps are as follows:

[0097] 1) Preparation of the negative electrode sheet: the negative electrode material, PAA and conductive carbon black are mixed uniformly in a mass ratio of 7:2:1, water is added, and a negative electrode slurry is prepared; then the negative electrode slurry is uniformly coated on both sides of the negative electrode current collector copper foil, dried in a vacuum drying oven at 80°C for 24 hours, and then rolled and punched to obtain the negative electrode sheet.

[0098] 2) Preparation of the electrolyte: EC, DMC and DEC are mixed in a volume ratio of 1:1:1 to obtain an organic solvent, and then fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a concentration of 1 mol / L, and the electrolyte is obtained after fully dissolving.

[0099] 3) Preparation of the lithium ion battery: the above negative electrode sheet, separator film (polyolefin film), positive electrode sheet (lithium sheet), and electrolyte are assembled into a 2032 button-type lithium ion battery in a glove box with water and oxygen content less than 0.1 ppm in an argon protective atmosphere.

[0100] Performance Test

[0101] 1. Material characterization

[0102] Figure 1 The XRD of the negative electrode material prepared in Example 2 is shown in the figure, where the horizontal coordinate 2θ represents the diffraction angle, and the vertical coordinate Intensity represents the intensity of the diffraction peak. From Figure 1 It can be seen that the negative electrode material only has a hump near an angle of 21.7°, and no obvious crystalline diffraction peak appears, indicating that the structure of the negative electrode material is highly disordered.

[0103] The negative electrode material prepared in Example 2 was further subjected to elemental analysis, and the test results are shown in Table 1.

[0104] Table 1:

[0105] Element Content (at%) C 44.67 N 13.12 O 31.37 Si 10.84

[0106] As can be seen from Table 1, the negative electrode material prepared in Example 2 has a higher content of nitrogen. This is mainly due to the strong interaction between the amino acid material and the Si-OH on the surface of the biomass porous silicon material, thereby retaining more nitrogen.

[0107] Figure 2 This is the SEM image of the negative electrode material prepared in Example 2. Figure 2 It can be seen that the negative electrode material has a rich multi-level pore structure, and its pore structure distribution is as follows Figure 3 As shown in the figure, it includes micropores (0.35-2nm), mesopores (2-50nm) and macropores (50-200nm), and the proportions of micropores, mesopores and macropores are 83%, 15% and 2% respectively. The presence of a large number of microporous structures can not only expose more active sites, but also limit the excessive penetration of the electrolyte, reduce the decomposition of the electrolyte, and effectively improve the reversible capacity of the silicon oxide material. The negative electrode material was subjected to nitrogen adsorption and desorption tests, and its specific surface area was measured to be distributed in the range of 160-360m 2 / g, the high specific surface area and porous nano-scale pores greatly shorten the diffusion path of lithium ions, accelerate the migration rate of lithium ions, promote the uniform deposition of solid electrolyte membrane, and reduce material rupture caused by local polarization.

[0108] 2. Electrochemical performance

[0109] The first cycle charge capacity and first coulombic efficiency of the lithium ion battery prepared in the above application example were tested under the conditions of 30°C and 50 mA / g current density; and the cycle performance of the lithium ion battery prepared by the negative electrode materials prepared in Example 2 and Comparative Example 1 was tested under the conditions of 100 mA / g current density for 100 cycles; the results are shown in Table 2 and Figures 4-5 As shown. Among them: Figure 4 The horizontal axis Specific capacity represents the first cycle charging capacity, and the vertical axis Voltage represents the voltage; Figure 5 The horizontal axis Cycle number in the middle represents the number of cycles, the vertical axis Specific capacity on the left represents the reversible specific capacity, and the vertical axis Coulombic efficiency on the right represents the Coulombic efficiency.

[0110] Table 2:

[0111]

[0112]

[0113] From Table 2 and Figures 4-5 It can be seen that the high-capacity nitrogen-doped porous silicon-oxygen-carbon negative electrode material prepared in Example 2 has the best electrochemical performance. The specific charge capacity of the first cycle is 1112.26 mAh / g at 30°C and a current density of 50 mA / g, and the first coulombic efficiency is 65.47%. The reversible specific capacity after 100 cycles of the battery is 586.01 mAh / g at a current density of 100 mA / g, and the capacity retention rate is 92%. The biomass porous silicon-oxygen material coated with a non-nitrogen-doped carbon material (Comparative Example 1) has a specific charge capacity of only 469.05 mAh / g in the first cycle under the same test conditions, and the first coulombic efficiency is only 39.88%. The reversible specific capacity after 100 cycles of the battery is 101.36 mAh / g, and the capacity retention rate is 69.65%. Therefore, the addition of the amino acid material can greatly improve the battery performance of the biomass porous silicon-oxygen negative electrode.

[0114] Comparing Example 2 with Examples 1 and 3, it can be seen that the ball milling time of the biomass porous silicon-oxygen material affects the change in the particle size of the material, and thus affects the electrochemical performance of the porous silicon-oxygen material. This is because when the ball milling time of the biomass porous silicon-oxygen material is short, the biomass porous silicon-oxygen material is micron-sized, forming an unstable solid electrolyte film (SEI), which is not conducive to subsequent carbonization. When the ball milling time of the biomass porous silicon-oxygen material is long, the pore structure of the biomass porous silicon-oxygen material is easily damaged, hindering the transport and diffusion of lithium ions, resulting in the generation of irreversible capacity. Therefore, by controlling the ball milling time of the biomass porous silicon-oxygen material, the present application promotes the good combination between the amino acid material and the biomass porous silicon-oxygen material matrix, forms a uniform and dense carbon layer network structure, so that the mixed material can adapt to the lithium ion reaction and diffusion after carbonization, and ensure the structural stability during the cycle process.

[0115] Comparing example 2 with example 4, 5, it can be seen that the addition amount of the amino acid material will affect the generation of the nitrogen-doped carbon layer structure of the biomass porous silicon-oxygen material and the content of the in-situ doped nitrogen. By controlling the addition amount of the amino acid material, the regulation of the carbon layer structure and the nitrogen content can be completed in one step, and the process is simpler and more conducive to industrial production. During carbonization, if the addition amount of the amino acid material is too small, the nitrogen-doped carbon layer structure cannot completely cover the porous silicon-oxygen material, and an unstable SEI film is easily formed, which leads to the pulverization of the material during the electrochemical reaction. When the addition amount of the amino acid material is too large, the carbon layer is too thick, and the nitrogen content is too high, which increases the diffusion rate of lithium ions during the reaction and reduces the electrochemical performance of the material. Therefore, by controlling the amount of the amino acid material, the present application promotes the good combination of the amino and carbon-based groups with the biomass porous silicon-oxygen material, so that the biomass porous silicon-oxygen material is suitable for reacting with lithium ions on one hand, and ensures the structural stability during the cycle process on the other hand.

[0116] Comparing example 2 with example 6, 7, it can be seen that the carbonization calcination temperature will affect the types of pyrolysis products of the amino acid material and the content of the carbonization product, and the combination structure of the pyrolysis products and the carbonization products with the biomass porous silicon-oxygen material matrix. Therefore, by controlling the pyrolysis temperature of the amino acid material, the nitrogen-doped biomass porous silicon-oxygen carbon material can exhibit the best electrochemical performance.

[0117] Comparing comparative example 2 and comparative example 3 with example 2, since melamine and dicyandiamide and other similar amino acid materials are used to replace the amino acid material of example 2, the first circle discharge specific capacity and the first coulomb efficiency of the lithium ion battery are both significantly lower than those of example 2, which proves that the biomass porous silicon-oxygen material modified by the amino acid material has more excellent electrochemical performance.

[0118] For those skilled in the art to which the present application belongs, without departing from the concept of the present application, a number of simple deductions or substitutions can be made without having to have creative labor. Therefore, the simple improvements made by those skilled in the art to the present application according to the disclosure of the present application should be within the protection scope of the present application. The above examples are preferred embodiments of the present application, and any similar processes and equivalent changes made should be within the protection scope of the present application.

Claims

1. A negative electrode material, characterized in that The negative electrode material comprises a nitrogen-doped carbon material and a biomass porous silicon material, wherein the nitrogen-doped carbon material covers the biomass porous silicon material; and in the negative electrode material, the content of nitrogen element is ≥13 at %.

2. The negative electrode material according to claim 1, characterized in that The negative electrode material has a multi-level pore structure including micropores, mesopores and macropores, and the proportion of the micropores is greater than 80%.

3. The negative electrode material according to claim 1 or 2, characterized in that The raw materials for preparing the negative electrode material include biomass porous silicon oxide material and amino acid material.

4. The negative electrode material according to claim 3, characterized in that The mass ratio of the biomass porous silicon material to the amino acid material is 1:(0.5-5).

5. The negative electrode material according to claim 3, characterized in that The biomass porous silica material includes diatoms, and the diatoms are selected from at least one of round diatoms and boat-shaped diatoms; and / or the amino acid material is selected from at least one of glutamic acid, proline, cysteine, glycine, and alanine.

6. A method for preparing the negative electrode material according to any one of claims 1 to 5, characterized in that: The following steps are involved: (1) mixing a biomass porous silicon material with an amino acid material to obtain a mixed material; (2) Annealing the mixed material in an inert atmosphere to obtain the negative electrode material.

7. The method for preparing the negative electrode material according to claim 6, wherein: The temperature regime of the annealing treatment is: heating to 400-800° C. at a rate of 3-10° C. / min, and then keeping the temperature for 2-4 hours.

8. The method for preparing the negative electrode material according to claim 6, wherein: The biomass porous silicon material further comprises a grinding step before being mixed with the amino acid material. The grinding process conditions are: using grinding balls with a particle size of 1-10 mm and ball milling at a speed of 200-600 rpm for 3-48 hours.

9. A negative electrode plate, characterized in that: The negative electrode plate comprises the negative electrode material according to any one of claims 1 to 5, or comprises the negative electrode material prepared by the preparation method according to any one of claims 6 to 8.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the negative electrode sheet according to claim 9.

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