A lithium battery negative electrode material and preparation method thereof

Abstract

The present invention relates to the technical field of lithium batteries, and discloses a lithium battery negative electrode material and a preparation method thereof. The lithium battery negative electrode material has a hierarchical multilayer structure, and comprises, from the inside to the outside, a nano metal oxide core material layer, a nitrogen-doped porous carbon layer and graphene. The nano cerium oxide core material layer has a high theoretical specific capacity, and can enable the lithium battery negative electrode material to have a higher specific capacity performance. The nitrogen-doped porous carbon layer is used as an intermediate layer to coat the nano cerium oxide core material layer, and can enable the lithium battery negative electrode material to have a higher specific capacity and rate performance. The graphene is used as the outermost layer, and a three-dimensional bridging structure is formed by using the graphene, so that the lithium battery negative electrode material exhibits higher conductivity, rate performance and cycle stability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium batteries, and in particular to a lithium battery negative electrode material and a preparation method thereof. Background Art

[0002] The rapid depletion of fossil energy has not only caused an energy crisis but also severe environmental damage. Therefore, the research and use of clean energy is of great significance. However, most clean energy sources, such as tidal energy, wind energy, and solar energy, suffer from intermittent and unstable characteristics. Therefore, energy storage and conversion devices are needed to convert these chemical energies into electrical energy for human use. Among the numerous energy storage and conversion devices, lithium-ion batteries, with their high energy conversion efficiency, excellent safety, and environmental friendliness, have become the preferred choice for various energy storage devices. In recent years, they have gradually occupied the vast majority of the battery market. However, the electrode materials used in most lithium-ion batteries are graphite, which not only has a low theoretical capacity but also is difficult to control in terms of cost. This has seriously hindered the application of lithium-ion batteries in large-scale energy storage systems such as electric vehicles. Therefore, the development of electrode materials with high specific capacity will contribute to the further development and application of lithium-ion batteries.

[0003] The invention patent with application number CN202110541664.9 discloses a method for preparing zinc nickelate bimetallic oxide, a negative electrode material for lithium-ion batteries. By preparing ZnNi2O4 secondary submicrospheres composed of primary nanoparticles as the negative electrode material of the lithium-ion battery, its special morphology and large specific surface area are utilized to enable the lithium-ion battery to exhibit a higher discharge specific capacity. However, the metal oxide is very prone to volume expansion during the continuous delithiation / intercalation process, resulting in an increase in the thickness of the SEI film, which affects the diffusion of lithium ions. At the same time, it also causes contact with the current collector, resulting in low battery efficiency or sudden failure. Therefore, the cycle stability is poor, which seriously affects the battery life. Moreover, the metal oxide has poor conductivity, resulting in the lithium-ion battery's rate performance being relatively general. Therefore, the use of metal oxide alone as the negative electrode material of lithium-ion batteries still has certain defects in practical applications.

[0004] Based on this, the present invention provides a composite negative electrode material that can be directly used in lithium-ion batteries and exhibits good electrochemical properties such as specific capacity and cycle stability. Summary of the Invention

[0005] The purpose of the present invention is to provide a lithium battery negative electrode material and a preparation method thereof, which solves the problem that metal oxides have poor conductivity and are prone to volume expansion when used alone as negative electrode materials for lithium ion batteries, resulting in poor electrochemical performance such as specific capacity and cycle stability of lithium ion batteries.

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A lithium battery negative electrode material has a hierarchical multilayer structure, which includes, from the inside to the outside, a nano metal oxide core material layer, a nitrogen-doped porous carbon layer and a graphene layer.

[0008] A method for preparing a negative electrode material for a lithium battery comprises the following steps:

[0009] Step 1: Surface modification of nano-metal oxide to obtain modified metal oxide;

[0010] Step 2: preparing cationic starch;

[0011] Step 3: preparing a metal oxide-cationic starch-graphene oxide composite;

[0012] Step 4: calcining the metal oxide-cationic starch-graphene oxide composite to obtain a lithium battery negative electrode material.

[0013] Furthermore, in step one, the preparation method of the modified metal oxide is specifically as follows: ultrasonically dispersing nano-cerium oxide in a mixed solution of deionized water and ethanol with a volume ratio of 9:1, adding 1,4-butanedisulfonic acid disodium salt and mixing, stirring at a temperature of 60-70°C for 4-6 hours, centrifuging, washing the solid material with hydrochloric acid and deionized water in sequence, and vacuum drying to obtain the modified metal oxide.

[0014] Through the above technical solution, hydroxyl groups are adsorbed on the surface of nano-cerium oxide, and 1,4-butanedisulfonic acid disodium salt is used as a surfactant to modify the nano-cerium oxide so that its surface contains strongly polar sulfonic acid groups to obtain a modified metal oxide.

[0015] Furthermore, the average particle size of the nano-cerium oxide is 500 nm.

[0016] Furthermore, in step 2, the preparation method of the cationic starch specifically comprises the following steps:

[0017] The first step is to mix starch with 95% ethanol and stir to mix evenly, add bromoacetyl chloride and a catalyst and stir to mix, place the system at a temperature of 45-55°C, keep warm for 6-8 hours, filter out the solid material, wash it with hydrochloric acid and deionized water in sequence, and dry it to obtain halogenated starch;

[0018] Step 2: Mix the halogenated starch, ditertiary amine monomer and tetrahydrofuran, stir evenly, pass nitrogen protection, increase the system temperature to 60-65°C, stir at constant temperature for 12-18 hours, filter and separate the solid material, wash, and dry to obtain cationic starch.

[0019] Furthermore, in the first step, the catalyst is any one of sodium hydroxide, triethylamine or pyridine.

[0020] Furthermore, in the second step, the di-tertiary amine monomer is any one of N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethyl-1,4-butanediamine or N,N,N',N'-tetramethyl-1,6-hexanediamine.

[0021] Through the above technical solution, the starch structure contains active hydroxyl groups, which can undergo an esterification condensation reaction with the acyl chloride groups in the bromoacetyl chloride structure under the action of a catalyst, thereby introducing halogen bromine atoms into the starch structure. The halogen bromine atoms can then undergo a quaternization reaction with the tertiary amine groups in the ditertiary amine monomer structure to produce cationic starch. Since the ditertiary amine monomer structure contains two equivalents of tertiary amine groups, the prepared cationic starch structure can contain rich quaternary ammonium nitrogen cations and exhibit a cross-linked structure.

[0022] Furthermore, in step three, the preparation method of the metal oxide-cationic starch-graphene oxide composite is specifically as follows: ultrasonically dispersing the modified metal oxide in deionized water, adding cationic starch and mixing, stirring at room temperature for 1-3 hours at a stirring rate of 200-400 r / min, adding graphene oxide, ultrasonically dispersing for 20-40 minutes, continuing to stir at a stirring rate of 200-400 r / min for 2-4 hours, filtering and separating the solid material, and vacuum drying.

[0023] Through the above technical solution, since the surface of the modified metal oxide contains sulfonic acid groups and is negatively charged in aqueous solution, and the rich nitrogen cations contained in the cationic starch structure are strongly positively charged in aqueous solution, they will attract each other under the action of electrostatics, first forming a metal oxide-cationic starch complex with a coated structure, and the oxygen-containing functional groups such as hydroxyl and carboxyl contained on the surface of graphene oxide also show negative charge in aqueous solution. Therefore, under the condition of continuous stirring, they can be adsorbed on the outside of the metal oxide-cationic starch complex again through electrostatic action to form a metal oxide-cationic starch-graphene oxide complex.

[0024] Furthermore, in step 4, the specific process of the calcination treatment is: placing the metal oxide-cationic starch-graphene oxide composite in a tubular furnace, passing nitrogen protection, and calcining the composite. After the calcination is completed, the material is allowed to cool naturally and then discharged.

[0025] Furthermore, the heating rate during the calcination treatment is 1-5°C / min, the temperature is raised to 550-600°C, and the heat preservation treatment is carried out for 2-4 hours.

[0026] Through the above technical solution, during the high-temperature calcination process of the metal oxide-cationic starch-graphene oxide composite, the cross-linked cationic starch has a high carbonization rate, and a carbon material with a porous morphology can be formed during the calcination process. The nitrogen cations in its structure will be doped into the porous carbon material after calcination to form a nitrogen-doped porous carbon layer, and the outermost layer of graphene oxide will be reduced to graphene after high-temperature calcination to form a graphene layer. Therefore, the prepared lithium battery negative electrode material has a hierarchical multilayer structure, which includes, from the inside to the outside, a nano metal oxide core layer, a nitrogen-doped porous carbon layer and a graphene layer.

[0027] Beneficial effects of the present invention:

[0028] (1) The lithium battery negative electrode material prepared by the present invention has a multilayer structure, wherein the core material layer is nano-cerium oxide, which has a high theoretical specific capacity, and can make the prepared lithium battery negative electrode material have a higher specific capacity performance. A nitrogen-doped porous carbon layer is used as an intermediate layer to coat the nano-cerium oxide core material layer. On the one hand, the porous carbon material coated on the outside of the core material layer can limit the volume expansion effect of nano-cerium oxide during the charge and discharge process to a certain extent, thereby improving the stability of the lithium battery negative electrode material. In addition, the porous carbon material has a large specific surface area, and its special pore structure is also conducive to the embedding and storage of lithium ions, and provides a fast channel for the transfer and diffusion of ions and electrons, thereby further improving the specific capacity of the lithium battery negative electrode material. In addition, the nitrogen-doped porous carbon contains defect structures such as pyridinic nitrogen and graphitic nitrogen, which can make the porous carbon material have more excellent conductivity, so that the prepared lithium battery negative electrode material can show good rate performance.

[0029] (2) In the process of high-temperature calcination of the metal oxide-cationic starch-graphene oxide composite of the present invention, the outermost graphene oxide is reduced to graphene. Driven by the stacking effect of π-π bonds, the graphene will further shrink, cross-link and curl, so that the formed graphene layer has a tighter three-dimensional bridge structure, further expanding the specific surface area of ​​the lithium battery negative electrode material. Combined with the lithium storage capacity of graphene, it has a more excellent specific capacity performance. In addition, graphene has strong conductivity and high strength, which not only enables the prepared lithium battery negative electrode material to exhibit higher conductivity, but also provides a buffer space for the volume expansion of nanocerium oxide. At the same time, the presence of the graphene layer can reduce the direct contact between nanocerium oxide and the electrolyte, avoid the formation of SEI film, and thus help the lithium battery negative electrode material to exhibit better rate performance and cycle stability.

[0030] Of course, any product implementing the present invention does not necessarily need to achieve all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 Electron micrographs of the negative electrode material for a lithium battery prepared in Example 3 of the present invention, wherein (A) is a scanning electron micrograph and (B) is a transmission electron micrograph;

[0033] Figure 2 This is a test chart of the cycle life of the lithium battery negative electrode materials prepared in Example 3 of the present invention and Comparative Example 1;

[0034] Figure 3 This is a rate performance test diagram of the lithium battery negative electrode materials prepared in Example 3 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0035] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0036] Example 1

[0037] Preparation of modified metal oxides

[0038] 2 g of nano-cerium oxide was ultrasonically dispersed in a mixed solution of deionized water and ethanol with a volume ratio of 9:1, 0.8 g of 1,4-butanedisulfonic acid disodium salt was added and mixed, and the mixture was stirred at 70°C for 6 hours, followed by centrifugation. The solid material was washed with hydrochloric acid and deionized water in sequence, and vacuum dried to obtain a modified metal oxide, wherein the average particle size of the nano-cerium oxide was 500 nm.

[0039] Example 2

[0040] Preparation of cationic starch

[0041] Step 1: Mix 3g of starch with 95% ethanol and stir to mix evenly, add 2.5g of bromoacetyl chloride and 4g of triethylamine and stir to mix, place the system at a temperature of 50°C, keep warm for 6 hours, filter out the solid material, wash with hydrochloric acid and deionized water in sequence, and dry to obtain halogenated starch;

[0042] Step 2: 2 g of halogenated starch, 4.5 g of N,N,N',N'-tetramethyl-1,6-hexanediamine and tetrahydrofuran were mixed and stirred evenly. After nitrogen protection, the system temperature was raised to 60°C. After constant temperature stirring for 16 hours, the solid material was filtered and separated, washed, and dried to obtain cationic starch.

[0043] The contents of C, H, and N elements in the cationic starch were determined using an Elemental Vavion EL elemental analyzer. The test showed that the C content in the cationic starch was 41.18%, the nitrogen content was 6.15%, and the H content was 5.03%.

[0044] Example 3

[0045] Preparation of lithium battery negative electrode materials

[0046] Step ①: ultrasonically disperse 0.5 g of the modified metal oxide prepared in Example 1 of the present invention in deionized water, add 12 g of the cationic starch prepared in Example 2 of the present invention, and stir at room temperature for 2 h at a stirring rate of 300 r / min. Then, add 0.1 g of graphene oxide, ultrasonically disperse for 30 min, continue stirring at a stirring rate of 100 r / min for 3 h, filter and separate the solid material, and vacuum dry to obtain a metal oxide-cationic starch-graphene oxide composite.

[0047] Step ②: Place 2 g of the metal oxide-cationic starch-graphene oxide composite in a tubular furnace, protect with nitrogen, control the heating rate to 2°C / min, raise the temperature in the tubular furnace to 600°C, and keep it warm for 3 hours for calcination. After the calcination is completed, wait for the material to cool naturally and discharge it to obtain a lithium battery negative electrode material.

[0048] The lithium battery negative electrode material was characterized using a FEIQuanta 400ESEM-FEG thermal field emission environmental scanning electron microscope and a JEOL JEM-3010 transmission electron microscope. Figure 1 , where (A) is a scanning electron microscope image and (B) is a transmission electron microscope image. It can be seen from (A) that the lithium battery negative electrode material has a three-dimensional bridged structure, and from (B) it can be observed that the outer side of the nano-cerium oxide core layer is sequentially coated with a nitrogen-doped porous carbon layer and a graphene layer, having a hierarchical multi-layer coating structure, and each other is bridged by a graphene layer, having a three-dimensional bridged structure.

[0049] Comparative Example 1

[0050] Preparation of lithium battery negative electrode materials

[0051] Step ①: Ultrasonic disperse 0.5 g of the modified metal oxide prepared in Example 1 of the present invention in deionized water, add 12 g of the cationic starch prepared in Example 2 of the present invention, and mix. After stirring at room temperature for 2 h at a stirring rate of 300 r / min, filter and separate the solid material, and vacuum dry to obtain a metal oxide-cationic starch complex.

[0052] Step ②: Place 2g of metal oxide-cationic starch complex in a tubular furnace, protect with nitrogen, control the heating rate to 2°C / min, raise the temperature in the tubular furnace to 600°C, and keep it warm for 2-4 hours for calcination. After calcination, wait for the material to cool naturally and discharge it to obtain a lithium battery negative electrode material.

[0053] Performance testing

[0054] The conductivity of the lithium battery negative electrode materials prepared in Example 3 of the present invention and Comparative Example 1 was tested using a DDS-307A conductivity tester; the specific surface area of ​​the lithium battery negative electrode materials prepared in Example 3 of the present invention and Comparative Example 1 was tested using a JB-2020 specific surface area analyzer. The test results are shown in the following table:

[0055]

[0056]

[0057] It can be seen from the above table that the lithium battery negative electrode material prepared in Example 3 of the present invention has strong conductivity and a large specific surface area, while the lithium battery negative electrode material prepared in Comparative Example 1 does not use graphene as a coating layer, and therefore cannot utilize the high conductivity and three-dimensional bridging structure of graphene. Therefore, the conductivity and specific surface area are relatively poor.

[0058] According to a mass ratio of 8:1:1, the lithium battery negative electrode material, acetylene black conductive agent and sodium carboxymethyl cellulose binder prepared in Example 3 of the present invention and Comparative Example 1 were ground and mixed, N-methyl pyrrolidone was added and stirred until a uniform paste was formed, and the paste was evenly coated on the surface of the aluminum foil. After drying, the aluminum foil was cut into a circular electrode sheet with a diameter of 18 mm. The circular electrode sheet was used as the working electrode, and a carbonate and vinyl acetate with a volume ratio of 1:1 were used as solvents and LiPF6 was used as a solute to prepare a LiPF6 electrolyte with a concentration of 1 mol / L. In a glove box, a CR2430 button battery shell, a lithium sheet, a Celgard 2320 diaphragm, an electrolyte and a working electrode were assembled into a button battery and sealed. The battery specific capacity, cycle life and rate performance were tested using a CT2001A battery testing system with a test voltage set to 0.01-3.0 V. The cycle life of the battery was evaluated by the specific capacity retention rate after 50 cycles. The test results are shown in FIG. Figure 2 and Figure 3 .

[0059] Depend on Figure 2 It can be seen that the lithium battery negative electrode material prepared in Example 3 of the present invention has an initial discharge specific capacity of 1163.2 mAh / g at a current density of 0.1 A / g, showing good capacity performance. After 50 cycles, it still has a discharge specific capacity of 1104.6 mAh / g, with a capacity retention rate of 94.96%, showing good cycle stability. Figure 3 It can be seen that the lithium battery negative electrode material prepared in Example 3 of the present invention still maintains a relatively high discharge specific capacity after recovering from a high-rate current density of 1 A / g to a low-rate current density of 0.1 A / g, and therefore has good rate performance.

[0060] The lithium battery negative electrode material prepared in Comparative Example 1 has an initial discharge specific capacity of 919.4 mAh / g at a current density of 0.1 A / g. After 50 cycles, the specific capacity value is 807.9 mAh / g, and the capacity retention rate is 87.87%. Moreover, after recovering from a high-rate current density to a low-rate current density, the discharge specific capacity loss is large, so the rate performance is general. This is because the lithium battery negative electrode material prepared in Comparative Example 1 is not coated with graphene oxide, and the strength of the carbon layer is not sufficient to support the volume expansion of nano-cerium oxide, resulting in its cycle stability being poorer than that of the lithium battery negative electrode material prepared in Example 3. In addition, due to its poor conductivity, its rate performance is also worse than that of the lithium battery negative electrode material prepared in Example 3.

[0061] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0062] The above content is merely an example and explanation of the concept of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a negative electrode material for a lithium battery, characterized in that: The lithium battery negative electrode material has a hierarchical multilayer structure, which includes, from the inside to the outside, a nano-metal oxide core layer, a nitrogen-doped porous carbon layer, and a graphene layer; The preparation method comprises the following steps: Step 1: Surface modification of nano-metal oxide to obtain modified metal oxide; The preparation method of the modified metal oxide is specifically as follows: ultrasonically dispersing nano-cerium oxide in a mixed solution of deionized water and ethanol with a volume ratio of 9:1, adding disodium 1,4-butanedisulfonic acid and mixing, stirring at a temperature of 60-70°C for 4-6 hours, centrifuging, washing the solid material with hydrochloric acid and deionized water in sequence, and vacuum drying to obtain the modified metal oxide; Step 2: preparing cationic starch; The preparation method of the cationic starch specifically comprises the following steps: Step 1: Mix starch with 95% ethanol, stir and mix evenly, add bromoacetyl chloride and a catalyst, stir and mix, place the system at a temperature of 45-55°C, keep warm for 6-8 hours, filter out the solid material, wash it with hydrochloric acid and deionized water in sequence, and dry it to obtain halogenated starch; Step 2: Mix the halogenated starch, ditertiary amine monomer and tetrahydrofuran, stir well, pass nitrogen protection, raise the system temperature to 60-65°C, stir at constant temperature for 12-18 hours, filter and separate the solid material, wash and dry to obtain cationic starch; Step 3: preparing a metal oxide-cationic starch-graphene oxide composite; The preparation method of the metal oxide-cationic starch-graphene oxide composite is specifically as follows: ultrasonically dispersing the modified metal oxide in deionized water, adding cationic starch and mixing, stirring at room temperature for 1-3 hours at a stirring rate of 200-400 r / min, adding graphene oxide, ultrasonically dispersing for 20-40 minutes, continuing to stir at a stirring rate of 200-400 r / min for 2-4 hours, filtering and separating the solid material, and vacuum drying; Step 4: calcining the metal oxide-cationic starch-graphene oxide composite to obtain a lithium battery negative electrode material.

2. The method for preparing a negative electrode material for a lithium battery according to claim 1, wherein: The average particle size of the nano-cerium oxide is 500 nm.

3. The method for preparing a negative electrode material for a lithium battery according to claim 1, wherein: In the first step, the catalyst is any one of sodium hydroxide, triethylamine or pyridine.

4. The method for preparing a negative electrode material for a lithium battery according to claim 1, wherein: In the second step, the ditertiary amine monomer is any one of N,N,N',N'-tetramethylethylenediamine, N,N,N',N'-tetramethyl-1,4-butanediamine or N,N,N',N'-tetramethyl-1,6-hexanediamine.

5. The method for preparing a negative electrode material for a lithium battery according to claim 1, wherein: In step 4, the specific process of the calcination treatment is: placing the metal oxide-cationic starch-graphene oxide composite in a tubular furnace, passing nitrogen protection, and calcining the composite. After the calcination is completed, the material is allowed to cool naturally and then discharged.

6. The method for preparing a negative electrode material for a lithium battery according to claim 5, characterized in that: The heating rate during the calcination treatment is 1-5°C / min, the temperature is raised to 550-600°C, and the heat preservation treatment is carried out for 2-4 hours.

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