Negative electrode material for sodium ion battery and preparation method of negative electrode material

Abstract

The invention discloses a negative electrode material for a sodium ion battery and a preparation method of the negative electrode material. The material comprises 60-80 parts of a hard carbon-based material, 10-20 parts of modified tin dioxide, 5-15 parts of nitrogen-doped graphene and 2-5 parts of a composite binder, the specific surface area of the hard carbon-based material is 50-150m < 2 > / g, the porosity is 20-40%, and the proportion of 2-5nm mesopores is greater than or equal to 60%; the modified tin dioxide is core-shell structure nanoparticles, the core tin dioxide is coated with a titanium dioxide shell layer of 5-20 nm, and the overall particle size is 50-200 nm; the nitrogen content of the nitrogen-doped graphene is 3-8 at%; the composite binder is prepared by compounding polydopamine, sodium alginate and nano cellulose according to the ratio of (2-3): (0.5-1): 1. Through the synergistic effect of multiple components, the first coulombic efficiency is larger than or equal to 88%, the 100-time cycle capacity retention ratio is larger than or equal to 90%, and the lithium ion battery has high capacity and long cycle stability and is suitable for the field of high-performance sodium ion batteries.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and in particular to a negative electrode material for sodium-ion batteries and its preparation method. Background Technology

[0002] Sodium-ion batteries are rechargeable batteries that primarily function by the movement of sodium ions between the positive and negative electrodes, similar in principle to lithium-ion batteries. With the accelerating global energy transition, sodium-ion batteries, due to the abundance, widespread distribution, and cost advantages of sodium resources, have become a key complementary technology to lithium-ion batteries in large-scale energy storage and commercial vehicles. However, their commercialization still faces many challenges, with the performance of the negative electrode material being one of the key bottlenecks restricting its development.

[0003] Currently, traditional sodium-ion battery anodes are mostly based on single hard carbon, metal oxides, or carbon materials, which suffer from problems such as low capacity, poor cycle stability, or insufficient conductivity. The main issues are: the low capacity of single hard carbon-based anodes, with existing commercially available hard carbon materials typically exhibiting an initial discharge specific capacity of only 250-300 mAh / g; and due to insufficient pore structure control, sodium ion insertion / extraction channels are limited, leading to significant capacity decay at low temperatures, making it difficult to meet the demands of high-energy-density batteries. Secondly, metal oxide anodes suffer from poor cycle stability. In particular, while metal oxides such as tin dioxide (SnO2) have theoretically high capacities, their high volume expansion rate during charge and discharge easily leads to particle breakage and electrode structure collapse, resulting in low capacity retention after 100 cycles, failing to balance high capacity and long lifespan. In addition, the conductive network and interface stability are insufficient. Traditional anodes mostly use pure carbon materials, such as graphite and ordinary graphene, to construct the conductive network, which makes it difficult to balance conductivity and active sites. Moreover, the binders are mainly sodium carboxymethyl cellulose (CMC) or styrene-butadiene rubber (SBR), which have poor flexibility and interfacial bonding force, and cannot adapt to changes in electrode volume. This easily causes repeated rupture and reconstruction of the SEI film, resulting in low initial coulombic efficiency and serious irreversible capacity loss. Summary of the Invention

[0004] Therefore, this invention proposes a negative electrode material for sodium-ion batteries and its preparation method to solve the above problems.

[0005] The technical solution of the present invention is implemented as follows: A negative electrode material for sodium-ion batteries, comprising the following raw materials in parts by weight: 60-80 parts of hard carbon-based material, 10-20 parts of modified tin dioxide, 5-15 parts of nitrogen-doped graphene, and 2-5 parts of composite binder.

[0006] Preferably, the specific surface area of ​​the hard carbon matrix is ​​50-150 m². 2 / g, with a porosity of 20-40%, and mesopores with a pore size distribution of 2-5nm accounting for no less than 60% of the total pore volume.

[0007] More preferably, the hard carbon-based material is prepared by soaking coconut shells in a 5-10% w / v phosphoric acid solution and holding them at 80-100°C for 2-4 hours; the carbonization temperature is 800-1000°C and the holding time is 2-3 hours; the graphitization temperature is 1200-1500°C, and during the graphitization process, an argon atmosphere containing 0.5-2 vol% hydrogen is introduced and the holding time is 1-3 hours.

[0008] Preferably, the modified tin dioxide is a nanoparticle with a core-shell structure, the core being tin dioxide and the outer shell being titanium dioxide, the thickness of the titanium dioxide shell being 5-20 nm, and the overall particle size of the nanoparticle being 50-200 nm.

[0009] More preferably, the modified tin dioxide is a core-shell structured composite material, and the specific modification methods include:

[0010] (1) Pretreatment: Place the nano tin dioxide particles in a 1-3% w / v hydrofluoric acid solution and ultrasonically clean them for 5-10 min at 25-35℃ and 200-300W to remove surface hydroxyl impurities. Then wash them with deionized water until neutral and vacuum dry them at 80-100℃ for 4-6 h.

[0011] (2) Atomic layer deposition: The pretreated nano-tin dioxide particles are loaded into the reaction chamber of the atomic layer deposition equipment. Titanium tetrachloride is used as the titanium source, deionized water is used as the oxygen source, and high-purity nitrogen (purity ≥99.999%) is used as the carrier gas. The carrier gas flow rate is 50-100 sccm. The reaction temperature is controlled at 160-220℃ and the reaction pressure is maintained at 1-3 Torr. Atomic layer deposition cycle is carried out to form a titanium dioxide shell.

[0012] The atomic layer deposition cycle includes: titanium tetrachloride pulse introduction for 1-3 seconds, nitrogen purification for 10-15 seconds, deionized water pulse introduction for 2-5 seconds, nitrogen purification for 15-20 seconds, for a total of 60-120 cycles.

[0013] (3) Post-treatment: The particles after the deposited shell are heated to 300-400℃ at a heating rate of 2-5℃ / min under the protection of inert gas and held for 1-3h to achieve shell crystallization. After cooling to room temperature, core-shell structure modified tin dioxide is obtained.

[0014] Preferably, the nitrogen doping amount of the nitrogen-doped graphene is 3-8 at%, and the composite binder is a mixture of polydopamine (PDA), sodium alginate (SA), and nanocellulose (CNF) in a mass ratio of (2-3):(0.5-1):1.

[0015] More preferably, nitrogen-doped graphene is prepared by chemical vapor deposition, using ammonia as the nitrogen source and methane as the carbon source. The copper foil substrate is pretreated by ultrasonic cleaning in 0.1-0.5 mol / L hydrochloric acid solution for 10-15 min. During deposition, the volume ratio of methane to ammonia is 1:0.3-0.8, the deposition temperature is 900-1000℃, and the deposition time is 30-60 min.

[0016] This invention also provides a method for preparing the above-mentioned negative electrode material for sodium-ion batteries, comprising the following steps:

[0017] S1. Place the modified tin dioxide and nitrogen-doped graphene in a high-speed mixer in a certain proportion, and dry mix them at a speed of 1000-1500 rpm for 20-40 minutes under the protection of inert gas, so that the graphene sheets are initially coated on the surface of the modified tin dioxide particles to obtain a premix.

[0018] S2. Add the hard carbon-based material and premix to 2-5 times the total mass of deionized water, and disperse using ultrasonic-mechanical stirring for 30-60 minutes. The ultrasonic power is 300-500W, and the mechanical stirring speed is 800-1200rpm to obtain a uniform primary slurry.

[0019] S3. Add composite binder to primary slurry, stir at 1500-2000 rpm for 15-30 min, then keep warm at 50-60℃ and stir for 10-15 min, adjust the solid content of slurry to 40-60%, and obtain negative electrode slurry.

[0020] S4. The negative electrode slurry is coated on the copper foil current collector, with a wet film thickness of 100-200μm. After drying, cooling, rolling, and slitting, the dry film thickness is 30-50μm, thus obtaining the negative electrode material for sodium-ion batteries.

[0021] Preferably, in the ultrasonic-assisted dispersion process of step S2, pulsed ultrasound is used with a pulse frequency of 10-20kHz and a duty cycle of 50-70%.

[0022] Preferably, the drying process in step S4 is as follows: first stage: drying at 65-75℃ for 30-60 min; second stage: drying at 95-105℃ for 60-120 min; third stage: vacuum drying at 115-125℃ for 1-2 h; after cooling, rolling is performed with a rolling pressure of 5-10 MPa and 2-3 rolling cycles.

[0023] The negative electrode of a sodium-ion battery is prepared using the aforementioned negative electrode material.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] This invention achieves an initial coulombic efficiency of ≥88% and a capacity retention of ≥90% after 100 cycles by utilizing the high sodium storage capacity of hard carbon-based materials, the suppression of volume expansion in the modified tin dioxide core-shell structure, the construction of a three-dimensional conductive network of nitrogen-doped graphene, and the interfacial stabilization effect of composite binders. This solves the technical contradiction of the difficulty in balancing capacity and cycle stability in traditional sodium-ion battery anode materials.

[0026] The modified tin dioxide TiO2 shell effectively suppresses SnO2 volume expansion and reduces side reactions. Combined with the fast electron transport channels of nitrogen-doped graphene, it improves electrode rate performance. The polydopamine / sodium alginate / nanocellulose composite binder, through multiple hydrogen bonds, combines high bonding strength with flexibility, adapting to electrode volume changes and preventing electrode detachment. It maintains electrode integrity even after 100 cycles. This invention's anode material solves the problems of low capacity and poor cycle life of traditional anodes, can be used in sodium-ion batteries, and its process is suitable for industrialization, reducing costs. Detailed Implementation

[0027] To better understand the technical content of this invention, specific embodiments are provided below to further illustrate the invention.

[0028] Unless otherwise specified, the experimental methods used in the embodiments of this invention are all conventional methods.

[0029] Unless otherwise specified, all materials and reagents used in the embodiments of this invention are commercially available.

[0030] Example 1

[0031] The raw material ratio for the negative electrode material of the sodium-ion battery in this embodiment is as follows:

[0032] The mixture consists of 60 parts of hard carbon-based material, 10 parts of modified tin dioxide, 5 parts of nitrogen-doped graphene, and 2 parts of composite binder. The composite binder is composed of polydopamine, sodium alginate, and nanocellulose in a mass ratio of 2:0.5:1.

[0033] Preparation of hard carbon-based materials:

[0034] Coconut shells were soaked in an 8% w / v phosphoric acid solution and kept at 100℃ for 3 hours; carbonization was carried out at 900℃ for 2 hours; graphitization was carried out at 1400℃, and an argon atmosphere containing 1 vol% hydrogen was introduced during the graphitization process for 2 hours.

[0035] Modification methods for modified tin dioxide:

[0036] (1) Pretreatment: The nano tin dioxide particles were placed in a 2% w / v hydrofluoric acid solution and ultrasonically cleaned for 10 min at 30℃ and 300W power. Then they were washed with deionized water until neutral and vacuum dried at 100℃ for 5 h.

[0037] (2) Atomic layer deposition: The pretreated nano-tin dioxide particles are loaded into the reaction chamber of the atomic layer deposition equipment. Titanium tetrachloride is used as the titanium source, deionized water is used as the oxygen source, high-purity nitrogen is used as the carrier gas, and the carrier gas flow rate is 80 sccm. The reaction temperature is controlled at 200℃ and the reaction pressure is maintained at 2 Torr. Atomic layer deposition cycle is carried out to form a titanium dioxide shell.

[0038] The atomic layer deposition cycle includes: titanium tetrachloride pulse introduction for 2 seconds, nitrogen purification for 12 seconds, deionized water pulse introduction for 4 seconds, nitrogen purification for 20 seconds, and a total of 100 cycles.

[0039] (3) Post-treatment: The particles after the deposited shell are heated to 350°C at a heating rate of 3°C / min under inert gas protection and held for 2 hours to achieve shell crystallization. After cooling to room temperature, core-shell structure modified tin dioxide is obtained.

[0040] Preparation of nitrogen-doped graphene:

[0041] Ammonia was used as the nitrogen source and methane as the carbon source. The copper foil substrate was pretreated by ultrasonic cleaning in 0.3 mol / L hydrochloric acid solution for 12 min. During the deposition process, the volume ratio of methane to ammonia was 1:0.5, the deposition temperature was 1000℃, and the deposition time was 30 min.

[0042] Example 2

[0043] The raw material ratio for the negative electrode material of the sodium-ion battery in this embodiment is as follows:

[0044] The mixture consists of 80 parts of hard carbon-based material, 20 parts of modified tin dioxide, 15 parts of nitrogen-doped graphene, and 5 parts of composite binder. The composite binder is composed of polydopamine, sodium alginate, and nanocellulose in a mass ratio of 3:1:1.

[0045] Hard carbon-based materials, modified tin dioxide, and nitrogen-doped graphene were prepared according to the method in Example 1.

[0046] Example 3

[0047] The raw material ratio for the negative electrode material of the sodium-ion battery in this embodiment is as follows:

[0048] The mixture consists of 70 parts of hard carbon-based material, 15 parts of modified tin dioxide, 10 parts of nitrogen-doped graphene, and 3 parts of composite binder. The composite binder is composed of polydopamine, sodium alginate, and nanocellulose in a mass ratio of 2.5:0.8:1.

[0049] Hard carbon-based materials, modified tin dioxide, and nitrogen-doped graphene were prepared according to the method in Example 1.

[0050] The negative electrode materials in Examples 1-3 above were prepared using the following methods:

[0051] S1. Modified tin dioxide and nitrogen-doped graphene are placed in a high-speed mixer in a certain proportion and dry-mixed at 1200 rpm for 30 minutes under inert gas protection, so that the graphene sheets are initially coated on the surface of the modified tin dioxide particles to obtain a premix.

[0052] S2. Add the hard carbon-based material and premix to 3 times the total mass of deionized water, and disperse it for 50 minutes by ultrasonic-mechanical stirring. Use pulsed ultrasound with a pulse frequency of 15kHz, a duty cycle of 60%, an ultrasonic power of 400W, and a mechanical stirring speed of 1000rpm to obtain a uniform primary slurry.

[0053] S3. Add composite binder to primary slurry, stir at 1800 rpm for 25 min, then keep stirring at 55℃ for 12 min, adjust the solid content of slurry to 50%, and obtain negative electrode slurry.

[0054] S4. The negative electrode slurry is coated on the copper foil current collector, with a wet film thickness of 150μm. After drying, cooling, rolling, and slitting, the dry film thickness is 40μm, thus obtaining the negative electrode material for sodium-ion batteries.

[0055] The drying procedure described above is as follows:

[0056] First stage: Dry at 70℃ for 50 min; Second stage: Dry at 100℃ for 80 min; Third stage: Vacuum dry at 120℃ for 2 h; After cooling, roll press at a pressure of 8 MPa for 3 times.

[0057] Comparative Example 1

[0058] The difference between this comparative example and Example 3 is that uncoated TiO2 nanoparticles of tin dioxide are used instead of modified tin dioxide.

[0059] Comparative Example 2

[0060] The difference between this comparative example and Example 3 is that nitrogen-doped graphene is not used; its proportion is made up with an equal amount of hard carbon matrix.

[0061] Comparative Example 3

[0062] The difference between this comparative example and Example 3 is that the polydopamine, sodium alginate, and nanocellulose composite binder are replaced with traditional sodium carboxymethyl cellulose / styrene-butadiene rubber (CMC / SBR) at a mass ratio of 1:2.

[0063] Performance testing:

[0064] The negative electrode materials prepared in Examples 1-3 and Comparative Examples 1-3 were assembled with sodium metal sheets to form CR2032 coin cells. The electrolyte was a 1 mol / L NaClO4 solution of ethylene carbonate / propylene carbonate (1:1, v / v), with 5% (w / w) of fluoroethylene carbonate added. Charge-discharge tests were conducted at 0.1C, and the results are shown in the table below:

[0065]

[0066]

[0067] Results analysis:

[0068] The embodiments of the present invention all exhibit high initial coulombic efficiency and excellent cycle stability, achieving a good balance between high capacity and long lifetime.

[0069] Compared with Comparative Example 1, although Comparative Example 1 had a higher initial discharge capacity, its initial coulombic efficiency was significantly lower and its cycle stability was extremely poor, with a capacity retention rate of 65.4%. This fully demonstrates that the TiO2 shell is crucial for suppressing side reactions, improving initial efficiency, buffering volume expansion, and stabilizing the electrode structure.

[0070] A comparison of the Example Group with Comparative Example 2 shows that the capacity and cycling performance of Comparative Example 2 are significantly reduced. This demonstrates that the three-dimensional conductive network constructed from nitrogen-doped graphene is indispensable for improving the overall conductivity and structural integrity of the electrode.

[0071] A comparison of the Example Group and Comparative Example 3 shows that, with the same active material system, Comparative Example 3, which uses a conventional binder, has inferior initial efficiency, capacity, and cycle stability.

[0072] The initial efficiency reduction indicates that the composite binder system of this invention is more effective in suppressing side reactions in the early stages of cycling, forming a more stable SEI film. The significant decrease in capacity retention directly proves that traditional CMC / SBR binders are ill-suited to the composite electrode material of this invention, especially those containing modified tin dioxide. Volume changes during long-term cycling lead to gradual damage to the electrode structure and continuous capacity decay. In contrast, the PDA / SA / CNF composite binder of this invention, with its excellent bonding strength, toughness, and adaptability, better maintains electrode integrity, thereby achieving ultra-high cycling stability.

[0073] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A negative electrode material for sodium-ion batteries, characterized in that, The raw materials include the following parts by weight: 60-80 parts of hard carbon-based material, 10-20 parts of modified tin dioxide, 5-15 parts of nitrogen-doped graphene, and 2-5 parts of composite binder.

2. The negative electrode material for sodium-ion batteries as described in claim 1, characterized in that, The specific surface area of ​​the hard carbon-based material is 50-150 m². 2 / g, with a porosity of 20-40%, and the proportion of mesopores of 2-5nm in the pore size distribution is ≥60%.

3. The negative electrode material for sodium-ion batteries as described in claim 1, characterized in that, The modified tin dioxide is a core-shell structured nanoparticle with tin dioxide as the core and titanium dioxide as the outer shell. The thickness of the titanium dioxide shell is 5-20 nm, and the overall particle size of the nanoparticle is 50-200 nm.

4. The negative electrode material for sodium-ion batteries as described in claim 1, characterized in that, The nitrogen doping amount of the nitrogen-doped graphene is 3-8 at%; the composite binder is a mixture of polydopamine, sodium alginate and nanocellulose in a mass ratio of (2-3):(0.5-1):

1.

5. The negative electrode material for sodium-ion batteries as described in claim 2, characterized in that, The hard carbon-based material is made by soaking coconut shells in a 5-10% w / v phosphoric acid solution and holding them at 80-100℃ for 2-4 hours; the carbonization temperature is 800-1000℃ and the holding time is 2-3 hours; the graphitization temperature is 1200-1500℃, and during the graphitization process, an argon atmosphere containing 0.5-2 vol% hydrogen is introduced and the holding time is 1-3 hours.

6. The negative electrode material for sodium-ion batteries as described in claim 3, characterized in that, The modified tin dioxide is a core-shell structured composite material, and the specific modification methods include: (1) Pretreatment: Place the nano tin dioxide particles in a 1-3% w / v hydrofluoric acid solution and ultrasonically clean them for 5-10 min at 25-35℃ and 200-300W. Then wash them with deionized water until neutral and vacuum dry them at 80-100℃ for 4-6 h. (2) Atomic layer deposition: The pretreated nano-tin dioxide particles are loaded into the reaction chamber of the atomic layer deposition equipment. Titanium tetrachloride is used as the titanium source, deionized water is used as the oxygen source, and high-purity nitrogen is used as the carrier gas with a flow rate of 50-100 sccm. The reaction temperature is controlled at 160-220℃ and the reaction pressure is maintained at 1-3 Torr. Atomic layer deposition cycle is performed to form a titanium dioxide shell. The atomic layer deposition cycle includes: titanium tetrachloride pulse introduction for 1-3 seconds, nitrogen purification for 10-15 seconds, deionized water pulse introduction for 2-5 seconds, nitrogen purification for 15-20 seconds, for a total of 60-120 cycles. (3) Post-treatment: The particles after the deposited shell are heated to 300-400℃ at a heating rate of 2-5℃ / min under the protection of inert gas and held for 1-3h to achieve shell crystallization. After cooling to room temperature, core-shell structure modified tin dioxide is obtained.

7. The negative electrode material for sodium-ion batteries as described in claim 4, characterized in that, The nitrogen-doped graphene was prepared by chemical vapor deposition, using ammonia as the nitrogen source and methane as the carbon source. The copper foil substrate was pretreated by ultrasonic cleaning in 0.1-0.5 mol / L hydrochloric acid solution for 10-15 min. During deposition, the volume ratio of methane to ammonia was 1:0.3-0.8, the deposition temperature was 900-1000℃, and the deposition time was 30-60 min.

8. A method for preparing a negative electrode material for a sodium-ion battery as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Place the modified tin dioxide and nitrogen-doped graphene in a high-speed mixer in a certain proportion, and dry mix them at a speed of 1000-1500 rpm for 20-40 minutes under the protection of inert gas, so that the graphene sheets are initially coated on the surface of the modified tin dioxide particles to obtain a premix. S2. Add the hard carbon-based material and premix to 2-5 times the total mass of deionized water, and disperse using ultrasonic-mechanical stirring for 30-60 minutes. The ultrasonic power is 300-500W, and the mechanical stirring speed is 800-1200rpm to obtain a uniform primary slurry. S3. Add composite binder to primary slurry, stir at 1500-2000 rpm for 15-30 min, then keep warm at 50-60℃ and stir for 10-15 min, adjust the solid content of slurry to 40-60%, and obtain negative electrode slurry. S4. The negative electrode slurry is coated on the copper foil current collector, with a wet film thickness of 100-200μm. After drying, cooling, rolling, and slitting, the dry film thickness is 30-50μm, thus obtaining the negative electrode material for sodium-ion batteries.

9. The negative electrode material for sodium-ion batteries as described in claim 1, characterized in that, In the ultrasonic-assisted dispersion process of step S2, pulsed ultrasound is used with a pulse frequency of 10-20kHz and a duty cycle of 50-70%. The drying process in step S4 is as follows: First stage: drying at 65-75℃ for 30-60 min; Second stage: drying at 95-105℃ for 60-120 min; Third stage: vacuum drying at 115-125℃ for 1-2 h; After cooling, roll pressing is performed with a rolling pressure of 5-10 MPa and 2-3 times.

10. A sodium-ion battery, characterized in that, Its negative electrode is made of the negative electrode material as described in any one of claims 1-7.

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