Asphalt-based hard carbon material for negative electrode of sodium-ion battery as well as preparation method and application of asphalt-based hard carbon material

Abstract

The invention belongs to the technical field of sodium-ion battery negative electrode materials, and particularly relates to an asphalt-based hard carbon material for a sodium-ion battery negative electrode and a preparation method and application of the asphalt-based hard carbon material. The content of C-O / C = O functional groups in the asphalt-based hard carbon material is greater than or equal to 18%; the interlayer spacing (d002) of the asphalt-based hard carbon material ranges from 0.38 nm to 0.42 nm; the specific surface area is 8-12m < 2 > / g. Through the synergistic effect of pre-oxidation and step-by-step activation, accurate regulation and control of interlayer spacing, porosity and surface chemistry are realized; the reversible specific capacity is greater than or equal to 350mAh / g, and the cycle The hard carbon material is superior to a commercial hard carbon material; the raw material cost is reduced by 40%, and the process energy consumption is reduced by 25% (compared with a molten salt method); waste liquid after acid and alkali removal can be automatically neutralized, and the recovery rate of the activator is gt; the wastewater treatment rate is 90%, and the wastewater treatment meets the GB 8978-1996 standard.

Description

Technical Field

[0001] The present invention belongs to the technical field of anode materials for sodium-ion batteries, and particularly relates to a pitch-based hard carbon material for an anode of a sodium-ion battery, a preparation method thereof, and an application thereof. Technical Background

[0002] Today's portable rechargeable electronic devices and new energy electric vehicles are being updated at an incredible speed, and it is urgent to develop efficient large-scale energy storage technologies that can meet the vast market demand. Among current electrochemical energy storage devices, alkali metal (Li, Na, K, etc.) ion batteries have the most significant potential. Among them, lithium-ion batteries (LIBs) stand out among various energy storage devices due to their high energy density, low self-discharge, good cycle stability, etc. However, lithium metal has problems such as low resource abundance, high cost, and uneven distribution, which hinder the sustainable development of LIBs. At the same time, with the diversification of market demands and the continuous upgrading of energy storage requirements, it has inspired researchers' enthusiasm to develop the next-generation energy storage technologies that coordinate high performance, low cost, and high safety.

[0003] The development of sodium-ion batteries (SIBs) is highly promoted by the "unlimited" resources of sodium in seawater and good electrochemical performance, and is considered the most promising alternative to lithium-ion batteries (LIBs). For sodium-ion batteries, their application prospects still largely depend on the innovation of low-cost and high-performance electrode active materials. To develop practical SIBs, it is necessary to develop electrode materials with large capacity to achieve performance comparable to LIBs. Therefore, to promote the commercialization of SIBs, it is crucial to develop electrode materials with high energy density, fast charge-discharge ability, and long cycle stability.

[0004] Hard carbon (HC) has a high capacity and rate capability due to its disordered and stacked microporous structure, presenting abundant sodium storage sites and efficient ion transport channels. HC is a carbonaceous material with a low degree of graphitization, consisting of two types of characteristic nano-domains. One is randomly oriented pseudo-graphite domains, which are composed of multiple stacked graphene sheets as vortex structures with various defects, and the other is an internal microporous structure formed by enclosing these pseudo-graphite domains. Currently, the detailed mechanism of Na storage in HC + is still controversial. Recent studies, including various in-situ characterizations and Na +In the theoretical calculations of embedded HC, it is generally believed that sodium ions fill the nanopores on a lower potential plateau to form quasi-metallic clusters, which also contribute more sodium storage capacity during this process. However, the high specific surface area caused by excessive porosity will increase the contact reaction area between the negative electrode and the electrolyte, leading to the large-scale formation of the solid electrolyte interphase (SEI). At the same time, the overly loose carbon skeleton will also reduce the cycle stability of the negative electrode material. Therefore, reasonably establishing the pore engineering of hard carbon is very important for improving the capacity of sodium-ion batteries.

[0005] As a by-product of petroleum or coal tar, asphalt is inexpensive and has a high carbon content. However, the direct carbonization products usually have poor sodium storage performance due to high graphitization degree (interlayer spacing < 0.38nm) and low porosity, and the reversible specific capacity is generally lower than 150 mAh / g. In the prior art, chemical activation (such as acid or base activation) is a common method to improve the performance of asphalt-based hard carbon materials, but there are still the following problems:

[0006] 1. Low single activation efficiency: Although acid activation (such as phosphoric acid) can introduce micropores (< 2nm), it is easy to cause uneven pore distribution; although base activation (such as potassium hydroxide) can expand the specific surface area, excessive use will damage the integrity of the carbon skeleton.

[0007] 2. Unclear pre-oxidation conditions: Air pre-oxidation can inhibit graphitization, but improper control of temperature and time will lead to over-oxidation or insufficient cross-linking.

[0008] 3. Poor process synergy: Such as the one-step oxidation molten salt method, which relies on coal-based raw materials and has a complex process. It is difficult to coordinate the oxidation and molten salt steps and cannot balance high capacity and low cost.

[0009] Therefore, developing a preparation method of hard carbon materials based on asphalt precursors, with a simple process and capable of precisely regulating the microstructure, has important application value. Summary of the Invention

[0010] Aiming at the deficiencies of the prior art, the present invention proposes an acid-base dual activation preparation method for asphalt-based hard carbon materials. Through the synergistic process of pre-oxidation - acid activation - base activation - high-temperature carbonization, the graphitization of the carbon layer is inhibited, and the cross-linking of asphalt molecules is promoted through air pre-oxidation to form a stable carbon skeleton; at the same time, a multi-stage pore structure is constructed, and the micropore and mesopore distributions are respectively regulated by stepwise acid / base activation; on the other hand, the sodium storage active sites are optimized by introducing oxygen-containing functional groups (C-O, C=O) and phosphorus doping to improve the surface chemistry; most importantly, the material structure is stabilized and the conductivity is optimized through high-temperature carbonization to balance the crystallinity and porosity.

[0011] The technical solution of the present invention is as follows:

[0012] In a first aspect, the present invention provides an asphalt-based hard carbon material for the negative electrode of a sodium-ion battery, wherein the content of C-O / C=O functional groups in the asphalt-based hard carbon material is ≥18%; the interlayer spacing (d 002 ) of the asphalt-based hard carbon material is 0.38 to 0.42 nm; the specific surface area is 8 to 12 m 2 / g.

[0013] SEM shows a honeycomb-like porous structure (uniform pore size distribution), and TEM observes the coexistence of disordered carbon layers and nanopores; the interlayer spacing (d 002 ) is 0.38 to 0.42 nm (XRD analysis), which satisfies the rapid insertion / extraction of sodium ions (diameter 0.204 nm); the specific surface area is 8 to 12 m 2 / g (BET test), the proportion of micropores is >65%, and the proportion of mesopores is 20 to 30%.

[0014] As a specific embodiment of the present invention, the phosphorus doping amount measured at the peak of the P1s peak in the asphalt-based hard carbon material is 0.5% to 1.2% and / or the sulfur doping amount measured at the peak of the S1s peak is 0.5% to 1.2%; the O1s content: 3-5%; the rest is C1s.

[0015] XPS analysis shows that the content of C-O / C=O functional groups is ≥18%, and the phosphorus doping amount is 0.5% to 1.2% (N 1s peak); sulfur doping (when using sulfuric acid activation) can further improve the surface reaction activity.

[0016] In a second aspect, the present invention provides a preparation method of an asphalt-based hard carbon material for the negative electrode of a sodium-ion battery, including the following steps: sequentially subjecting the raw material including asphalt to pre-oxidation treatment, acid activation treatment, alkali activation treatment, and carbonization.

[0017] As a specific embodiment of the present invention, the asphalt includes coal tar pitch and / or petroleum asphalt.

[0018] As a specific embodiment of the present invention, the pre-oxidation treatment conditions are: the air flow rate is controlled at 1 to 3 L / min, heated to 280 to 320 °C at a rate of 2 to 5 °C / min, and held for 2 to 4 hours.

[0019] During the pre-oxidation process, cross-linking reactions occur in the asphalt molecular chains (an exothermic peak is detected by DSC), and the interlayer spacing is increased from 0.36 nm to 0.40 nm (XRD test), inhibiting the subsequent graphitization trend.

[0020] As a specific embodiment of the present invention, the acid in the acid activation treatment includes at least one of phosphoric acid, sulfuric acid, and nitric acid;

[0021] As a specific embodiment of the present invention, the acid activation treatment process includes mixing and impregnating the pre-oxidized asphalt with an acid for 8 to 12 hours, then drying, and heating to 500 - 700 °C at a rate of 1 - 8 °C / min in an inert atmosphere, and holding for 1 to 3 hours to obtain the acid-activated powder.

[0022] As a specific embodiment of the present invention, the alkali in the alkali activation treatment includes at least one of potassium hydroxide, sodium hydroxide, and potassium carbonate;

[0023] Acid corrodes the carbon skeleton to form micropores (pore size 0.5 - 1.5 nm, BET analysis), and introduces phosphate groups (P - O - C bonds detected by FTIR).

[0024] As a specific embodiment of the present invention, the process of the alkali activation treatment includes: mixing and grinding the acid-activated powder with alkali powder; heating to 500 - 700 °C at a rate of 1 - 8 °C / min in an inert atmosphere, and holding for 1 to 3 hours.

[0025] The alkali reacts with carbon to generate K2CO3 and H2 (reaction formula: 6KOH + 2C → 2K2CO3 + 3H2↑), etching to generate mesopores (pore size 2 - 20 nm, BJH analysis), and the specific surface area increases from 500 m 2 / g to 1000 m 2 / g.

[0026] As a specific embodiment of the present invention, before carbonization, it also includes drying after water washing, specifically including washing with water until pH = 6 - 7, and vacuum drying.

[0027] As a specific embodiment of the present invention, the carbonization process includes: heating to 1300 - 1500 °C at a rate of 5 - 15 °C / min in an inert atmosphere, and holding for 3 to 5 hours.

[0028] In a second aspect, the present invention provides the application of the above asphalt-based hard carbon material for the negative electrode of a sodium-ion battery or the asphalt-based hard carbon material for the negative electrode of a sodium-ion battery prepared by the above preparation method in a sodium-ion battery.

[0029] The obtained sodium-ion battery has a reversible specific capacity ≥ 350 mAh / g (0.1C), an initial Coulombic efficiency > 90%; the capacity retention rate at 1C rate > 85%, and the capacity retention rate after 1000 cycles > 92%; the impedance spectrum (EIS) shows that the charge transfer resistance (Rct) < 50 Ω, indicating excellent conductivity.

[0030] Beneficial effects

[0031] 1. Technical breakthrough: Through the synergistic effect of pre-oxidation and stepwise activation, precise regulation of the interlayer spacing, porosity, and surface chemistry is achieved;

[0032] 2. Performance advantages: Reversible specific capacity ≥ 350 mAh / g, cycle life > 1000 times, superior to commercial hard carbon materials;

[0033] 3. Cost - effectiveness: Raw material cost reduced by 40%, process energy consumption reduced by 25% (compared with the molten salt method);

[0034] 4. Environmental friendliness: The waste liquid after acid - base removal can be neutralized by itself, the recovery rate of the activator > 90%, and the wastewater treatment meets the GB 8978 - 1996 standard. Brief Description of the Drawings

[0035] Figure 1 : SEM image of the material prepared in Example 1, showing a honeycomb - like porous structure;

[0036] Figure 2 : TEM image of the material prepared in Example 1;

[0037] Figure 3 : Nitrogen adsorption - desorption isotherm curve. Example 1 shows a composite isotherm of type I (micropores) and type IV (mesopores);

[0038] Figure 4 : Cycle performance comparison chart. The capacity attenuation rate of Example 1 is significantly lower than that of Comparative Example 1;

[0039] Figure 5 : First - cycle charge - discharge curve of the simulated battery assembled with the material of Example 1. Detailed Description of the Invention

[0040] Example 1

[0041] A preparation method of an asphalt - based double - activated hard carbon material for the negative electrode of a battery, the steps are as follows:

[0042] (1) Raw material pretreatment: Take 100 g of coal tar pitch, crush it to 150 mesh, sieve it, and then ball - mill the sieved material to 200 mesh;

[0043] (2) Pre - oxidation treatment: Heat it to 300 °C at a rate of 3 °C / min in an air atmosphere (flow rate 2 L / min) and keep it for 3 hours;

[0044] (3) Acid activation: Immerse the pre - oxidized asphalt powder in 60 g of phosphoric acid solution (concentration 85%) for 10 hours, vacuum - dry it, and then activate it in N2 at 600 °C for 2 hours;

[0045] (4) Alkali activation: Ball - mill the sample after acid activation with 30 g of KOH (mass ratio 60%) powder for 2 hours (rotation speed 300 rpm), and activate it in N2 at 600 °C for 2 hours;

[0046] (5) Wash and dry: Wash it with deionized water until neutral, filter it by suction, and vacuum - dry it at 80 °C for 5 hours;

[0047] (6) Final carbonization: Keep at 1400 °C for 4 hours in an Ar atmosphere.

[0048] Figure 1 SEM images of the above materials are given, and it can be seen that they are honeycomb-like porous structures; Figure 2 TEM images of the above materials are given; Figure 3 Nitrogen adsorption-desorption curves of the above materials are given, showing a composite isotherm of type I (micropores) and type IV (mesopores); Figure 4 A comparison chart of cycling performance is given, and the capacity decay rate of Example 1 is significantly lower than that of Comparative Example 1; Figure 5 The first charge-discharge curve of the simulated battery assembled with the material of Example 1 is given.

[0049] Example 2

[0050] A preparation method of an asphalt-based dual-activated hard carbon material for a battery negative electrode, the steps are as follows:

[0051] (1) Raw material pretreatment: Take 100 g of coal tar pitch, crush it to 150 mesh, sieve it, and then ball-mill the sieved material to 200 mesh;

[0052] (2) Pre-oxidation treatment: Heat up to 320 °C at a rate of 3 °C / min in an air atmosphere (flow rate 2 L / min) and keep it for 3 hours;

[0053] (3) Acid activation: Immerse the pre-oxidized asphalt powder in 60 g of phosphoric acid solution (concentration 85%) for 10 hours, vacuum dry it, and then activate it at 600 °C in N2 for 2 hours;

[0054] (4) Alkali activation: Ball-mill the sample after acid activation with 30 g of KOH (mass ratio 60%) powder for 2 hours (rotation speed 300 rpm), and activate it at 600 °C in N2 for 2 hours;

[0055] (5) Wash and dry: Wash with a large amount of deionized water until neutral, filter by suction, and vacuum dry at 80 °C for 5 hours;

[0056] (6) Final carbonization: Keep at 1400 °C for 4 hours in an Ar atmosphere.

[0057] XRD shows that the layer spacing is 0.45 nm, slightly higher than that of Example 1, but the cycling stability decreases slightly (due to excessive partial oxidation).

[0058] Example 3

[0059] A preparation method of an asphalt-based dual-activated hard carbon material for a battery negative electrode, the steps are as follows:

[0060] (1) Raw material pretreatment: Take 100 g of coal tar pitch, crush it to 150 mesh, sieve it, and then ball-mill the sieved material to 200 mesh;

[0061] (2) Pre-oxidation treatment: Heat to 300 °C at a rate of 3 °C / min in an air atmosphere (flow rate 2 L / min) and hold for 3 hours.

[0062] (3) Acid activation: Immerse the pre-oxidized asphalt powder in 50 g of phosphoric acid solution (concentration 50%) for 10 hours, vacuum dry, and then activate in N2 at 600 °C for 2 hours.

[0063] (4) Alkali activation: Ball-mill the acid-activated sample with 60 g of KOH (mass ratio 60%) powder for 2 hours (rotation speed 300 rpm), and activate in N2 at 600 °C for 2 hours.

[0064] (5) Wash and dry: Wash with a large amount of deionized water until neutral, filter by suction, and vacuum dry at 80 °C for 5 hours.

[0065] (6) Final carbonization: Hold at 1400 °C in an Ar atmosphere for 4 hours.

[0066] BET analysis shows that the micropore ratio is 60%, 5% less than that of Example 1, and the capacity is reduced to 332 mAh / g.

[0067] Example 4

[0068] A preparation method of a battery negative electrode asphalt-based dual-activated hard carbon material is as follows:

[0069] (1) Raw material pretreatment: Take 100 g of coal tar pitch, crush it to 150 mesh, sieve it, and then ball-mill the screened material to 200 mesh.

[0070] (2) Pre-oxidation treatment: Heat to 300 °C at a rate of 3 °C / min in an air atmosphere (flow rate 2 L / min) and hold for 3 hours.

[0071] (3) Acid activation: Immerse the pre-oxidized asphalt powder in 60 g of phosphoric acid solution (concentration 85%) for 10 hours, vacuum dry, and then activate in N2 at 600 °C for 2 hours.

[0072] (4) Alkali activation: Ball-mill the acid-activated sample with 70 g of KOH (mass ratio 70%) powder for 3 hours (rotation speed 300 rpm), and activate in N2 at 600 °C for 2 hours.

[0073] (5) Wash and dry: Wash with a large amount of deionized water until neutral, filter by suction, and vacuum dry at 80 °C for 5 hours.

[0074] (6) Final carbonization: Hold at 1400 °C in an Ar atmosphere for 4 hours.

[0075] Example 5

[0076] (1) Raw material pretreatment: Take 100 g of coal tar pitch, crush it to 150 mesh, sieve it, and then ball mill the sifted material to 200 mesh;

[0077] (2) Pre-oxidation treatment: Heat it to 300 °C at a rate of 3 °C / min in an air atmosphere (flow rate 2 L / min) and hold for 3 hours;

[0078] (3) Acid activation: Immerse the pre-oxidized asphalt powder in 60 g of sulfuric acid solution (concentration 85%) for 10 hours, vacuum dry it, and then activate it in N2 at 600 °C for 2 hours;

[0079] (4) Alkali activation: Ball mill the sample after acid activation with 60 g of KOH (mass ratio 60%) powder for 3 hours (rotation speed 300 rpm), and activate it in N2 at 600 °C for 2 hours;

[0080] (5) Washing and drying: Wash it with a large amount of deionized water until neutral, filter it by suction, and vacuum dry it at 80 °C for 5 hours;

[0081] (6) Final carbonization: Hold it at 1400 °C in an Ar atmosphere for 4 hours.

[0082] FTIR detected sulfate groups (S-O-C), but the micropore ratio decreased to 50%, and the capacity was 315 mAh / g.

[0083] Comparative Example 1

[0084] (1) Raw material pretreatment: Take 100 g of coal tar pitch, crush it to 150 mesh, sieve it, and then ball mill the sifted material to 200 mesh;

[0085] (2) Acid activation: Immerse the asphalt powder in 60 g of phosphoric acid solution (concentration 85%) for 10 hours, vacuum dry it, and then activate it in N2 at 600 °C for 2 hours;

[0086] (3) Alkali activation: Ball mill the sample after acid activation with 70 g of KOH (mass ratio 70%) powder for 3 hours (rotation speed 300 rpm), and activate it in N2 at 600 °C for 2 hours;

[0087] (4) Washing and drying: Wash it with a large amount of deionized water until neutral, filter it by suction, and vacuum dry it at 80 °C for 5 hours;

[0088] (5) Final carbonization: Hold it at 1400 °C in an Ar atmosphere for 4 hours.

[0089] Comparative Example 2

[0090] (1) Raw material pretreatment: Take 100 g of coal tar pitch, crush it to 150 mesh, sieve it, and then ball mill the sifted material to 200 mesh;

[0091] (2) Pre-oxidation treatment: Heat up to 300 °C at a rate of 3 °C / min in an air atmosphere (flow rate 2 L / min) and hold for 3 hours;

[0092] (3) Acid activation: Immerse the pre-oxidized asphalt powder in 60 g of phosphoric acid solution (concentration 85%) for 10 hours, vacuum dry and then activate at 600 °C in N2 for 2 hours;

[0093] (4) Alkali activation: Ball mill the sample after acid activation with 30 g of NaOH (mass ratio 60%) for 3 hours (rotation speed 300 rpm), and activate at 600 °C in N2 for 2 hours;

[0094] (5) Wash with water and dry: Wash with a large amount of deionized water until neutral, filter by suction, and vacuum dry at 80 °C for 5 hours;

[0095] (6) Final carbonization: Hold at 1400 °C in an Ar atmosphere for 4 hours.

[0096] The mesopore distribution is uneven (pore diameter > 50 nm), and the cycle retention rate is 84.7%.

[0097] Comparative Example 3

[0098] (1) Raw material pretreatment: Take 100 g of coal tar pitch, crush it to 150 mesh, sieve it, and then ball mill the sieved material to 200 mesh;

[0099] (2) Pre-oxidation treatment: Heat up to 300 °C at a rate of 3 °C / min in an air atmosphere (flow rate 2 L / min) and hold for 3 hours;

[0100] (3) Alkali activation: Ball mill the pre-oxidized sample with 70 g of KOH (mass ratio 70%) for 3 hours (rotation speed 300 rpm), and activate at 600 °C in N2 for 2 hours;

[0101] (4) Acid activation: Immerse the asphalt powder after alkali activation in 60 g of phosphoric acid solution (concentration 85%) for 10 hours, vacuum dry and then activate at 600 °C in N2 for 2 hours;

[0102] (5) Wash with water and dry: Wash with a large amount of deionized water until neutral, filter by suction, and vacuum dry at 80 °C for 5 hours;

[0103] (6) Final carbonization: Hold at 1400 °C in an Ar atmosphere for 4 hours.

[0104] BET shows that the specific surface area is only 600 m 2 / g, and the capacity is 293 mAh / g.

[0105] Comparative Example 4

[0106] (1) Raw material pretreatment: Take 100 g of coal tar pitch, crush it to 150 mesh, sieve it, and then ball mill the sifted material to 200 mesh;

[0107] (2) Pre-oxidation treatment: Heat it to 300 °C at a rate of 3 °C / min in an air atmosphere (flow rate 2 L / min) and hold for 3 hours;

[0108] (3) Acid activation: Immerse the pre-oxidized asphalt powder in 60 g of phosphoric acid solution (concentration 85%) for 10 hours, vacuum dry it, and then activate it at 600 °C in N2 for 2 hours;

[0109] (4) Water washing and drying: Wash it with a large amount of deionized water until neutral, filter it by suction, and vacuum dry it at 80 °C for 5 hours;

[0110] (5) Final carbonization: Hold it at 1400 °C in an Ar atmosphere for 4 hours.

[0111] Specific surface area 500 m 2 / g, capacity 280 mAh / g.

[0112] Comparative Example 5

[0113] (1) Raw material pretreatment: Take 100 g of coal tar pitch, crush it to 150 mesh, sieve it, and then ball mill the sifted material to 200 mesh;

[0114] (2) Pre-oxidation treatment: Heat it to 300 °C at a rate of 3 °C / min in an air atmosphere (flow rate 2 L / min) and hold for 3 hours;

[0115] (4) Alkali activation: Ball mill the pre-oxidized sample with 60 g of KOH (mass ratio 60%) powder for 3 hours (rotation speed 300 rpm), and activate it at 600 °C in N2 for 2 hours;

[0116] (5) Water washing and drying: Wash it with a large amount of deionized water until neutral, filter it by suction, and vacuum dry it at 80 °C for 5 hours;

[0117] (6) Final carbonization: Hold it at 1400 °C in an Ar atmosphere for 4 hours.

[0118] Micropore proportion < 40%, capacity 265 mAh / g.

[0119] Table 1 Properties of the materials prepared in Examples 1-5 and Comparative Examples 1-5

[0120]

[0121]

[0122] Assembly and testing of simulated batteries

[0123] The carbon material for the negative electrode of the sodium-ion battery prepared above was respectively ground and mixed evenly with a conductive agent and a sodium alginate binder according to a mass ratio of 90:5:5, and an appropriate amount of pure water was added and ground again to form a uniformly dispersed slurry. Then, the slurry was coated on a current collector aluminum foil (the areal density was controlled at 6 mg / cm 2 ), after drying at 70 °C, the electrode sheet was punched into an electrode sheet with a diameter of 12 mm, and the electrode sheet was dried at 120 °C for 5 hours under vacuum conditions, and then transferred to an inert glove box for standby. The assembly of the simulated battery was carried out in a glove box with an Ar atmosphere. Metallic sodium was used as the counter electrode, a solution of 1 mol / L NaPF6 was used as the electrolyte, the solvent of the NaPF6 solution was ethylene carbonate and diethyl carbonate with a volume ratio of 1:1, and glass fiber filter paper was used as the separator. The electrode sheets of the examples and comparative examples were assembled into CR2032 coin cells. Using a blue electrochemical charge-discharge tester, a constant current charge-discharge test was carried out at a current density of C / 10. The discharge cut-off voltage was 0 V, and the charge cut-off voltage was 2 V. The assembled simulated battery was subjected to a charge-discharge test, and the test results are shown in Table 2.

[0124] Table 2 Charge-discharge test of the assembled simulated battery

[0125]

[0126]

[0127] As can be seen from the above table, the necessity of pre-oxidation of the solution of the present application: in Comparative Example 1, due to no pre-oxidation, the layer spacing was only 0.36 nm, and the capacity decreased by 24%; regarding the advantages of acid treatment: in Comparative Example 3, sulfuric acid was used for activation, and the proportion of micropores decreased to 50%, and the capacity decreased by 12%; regarding the specificity of alkali treatment of the present application: in Comparative Example 2, NaOH was used, and the mesoporous distribution was uneven, and the cycle stability was significantly reduced; activation sequence: in Comparative Example 3, due to the reversed sequence, the specific surface area decreased by 30%, and the capacity decreased by 18%; double activation synergy: compared with single activation (Comparative Examples 4 and 5), the capacity of double activation increased by 25% - 35%.

Claims

1. An asphalt-based hard carbon material for the negative electrode of a sodium-ion battery, characterized in that, The content of C-O / C=O functional groups in the asphalt-based hard carbon material is ≥18%; the interlayer spacing (d 002 ) of the asphalt-based hard carbon material is 0.38 to 0.42 nm; the specific surface area is 8 to 12 m 2 / g.

2. The pitch-based hard carbon material for the negative electrode of a sodium-ion battery according to claim 1, wherein The phosphorus doping amount measured by the P1s peak top in the asphalt-based hard carbon material is 0.5% to 1.2% and / or the sulfur doping amount measured by the S1s peak top is 0.5% to 1.2%; the O1s content is 3-5%; the rest is C1s.

3. A preparation method of the pitch-based hard carbon material for the negative electrode of a sodium-ion battery according to claim 1 or 2, characterized in that, It includes the following steps: successively pre-oxidizing, acid-activating, alkali-activating, and carbonizing the raw material including asphalt.

4. The preparation method according to claim 3, characterized in that, The asphalt includes coal tar pitch and / or petroleum asphalt.

5. The preparation method according to claim 3, characterized in that, The pre-oxidation treatment conditions: the air flow rate is controlled at 1-3 L / min, heated to 280-320 °C at a rate of 2-5 °C / min, and kept warm for 2-4 hours.

6. The preparation method according to claim 3, characterized in that, The acid in the acid activation treatment includes at least one of phosphoric acid, sulfuric acid, and nitric acid; preferably phosphoric acid; And / or, the acid activation treatment process includes mixing the pre-oxidized asphalt with the acid, impregnating for 8-12 hours, then drying, heating to 500-700 °C at a rate of 1-8 °C / min in an inert atmosphere, and keeping warm for 1-3 hours to obtain the acid-activated powder.

7. The preparation method according to claim 3, characterized in that, The alkali in the alkali activation treatment includes at least one of potassium hydroxide, sodium hydroxide, and potassium carbonate; preferably potassium hydroxide; And / or, the alkali activation treatment process includes: mixing and grinding the acid-activated powder with the alkali powder; heating to 500-700 °C at a rate of 1-8 °C / min in an inert atmosphere, and keeping warm for 1-3 hours.

8. The preparation method according to claim 3, characterized in that, Before carbonization, it also includes drying after washing with water, specifically including washing with water until the pH = 6-7 and vacuum drying.

9. The preparation method according to any one of claims 3-8, characterized in that The carbonization process includes: heating to 1300-1500 °C at a rate of 5-15 °C / min in an inert atmosphere and keeping warm for 3-5 hours.

10. Application of the asphalt-based hard carbon material for the negative electrode of a sodium-ion battery described in claim 1 or 2 or the asphalt-based hard carbon material for the negative electrode of a sodium-ion battery prepared by the preparation method described in any one of claims 3-9 in a sodium-ion battery.

Images