Hard carbon materials, electrode sheets, and electrochemical devices

Abstract

The application relates to the technical field of electrochemical energy storage, in particular to a hard carbon material, a pole piece and an electrochemical device. The hard carbon material comprises a microporous structure, and the volume percentage of micropores in the total pores is greater than or equal to 65%. By increasing the content of micropores in the structure of the hard carbon material, especially the content of micropores with a pore diameter of 0.5-1.8 nm, the specific capacity of the hard carbon negative electrode is improved, and the energy density of the electrochemical device is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemical energy storage, in particular to a hard carbon material, a pole piece and an electrochemical device. BACKGROUND

[0002] The rapid development of society not only intensifies the consumption of fossil fuels, but also causes serious environmental pollution. Therefore, it is particularly important to develop high-performance electrochemical energy storage devices and effectively utilize intermittent renewable energy (wind energy, tidal energy, solar energy, etc.). Although lithium-ion batteries have been widely used in many fields due to their high energy density, wide voltage range, no memory effect, green environmental protection and wide working temperature range, the high cost and limited lithium resources are not conducive to their large-scale application in electric vehicles and static energy storage. In contrast, sodium resources are abundant in the earth's crust, and sodium-ion batteries have a similar working mechanism to lithium-ion batteries, so they are expected to become low-cost secondary batteries for large-scale applications in the future. However, unlike lithium ions, the larger radius of sodium ions means that the negative electrode material graphite of commercialized lithium-ion batteries cannot be directly used as the negative electrode of sodium-ion batteries. Therefore, developing high-performance negative electrode materials is conducive to promoting the commercialization of sodium-ion batteries.

[0003] Among the many negative electrode materials, hard carbon has attracted widespread attention due to its good overall performance. Although its sodium storage performance has been effectively improved through years of efforts, the energy density still needs to be further improved. Generally, there are three types of pores in the structure of hard carbon: macropores (> 50 nm), mesopores (2-50 nm) and micropores (< 2 nm). Since micropores can be used as active sites to store sodium or lithium ions, increasing their content can significantly improve the specific capacity of the hard carbon negative electrode, thereby improving the energy density of the electrochemical device. SUMMARY

[0004] Therefore, the present application provides a hard carbon material, a pole piece and an electrochemical device. By increasing the content of micropores in the structure of the hard carbon material, the present application improves the specific capacity of the hard carbon negative electrode, thereby improving the energy density of the electrochemical device.

[0005] In order to achieve the above-mentioned application purposes, the present application provides the following technical solutions:

[0006] The present application provides a hard carbon material, which comprises a microporous structure, and the volume percentage of micropores in the total pores is ≥ 65%.

[0007] Since micropores can be used as active sites to store sodium or lithium ions, the abundant micropores of the hard carbon material of the present application can improve the specific capacity of the hard carbon, thereby improving the energy density of the electrochemical device.

[0008] Preferably, the volume percentage of micropores in the total pores is 65% to 90%.

[0009] Preferably, the volume percentage of the micropores in the total pores is 66% to 72%.

[0010] Preferably, the volume of the micropores is 0.0015 to 0.018 cm 3 / g.

[0011] Preferably, the volume of the micropores is 0.0015 to 0.018 cm 3 / g.

[0012] More preferably, the volume of the micropores is 0.006 to 0.01 cm 3 / g.

[0013] Preferably, the pore size of the micropores in the nitrogen isothermal adsorption-desorption test is 0.5 to 1.8 nm. In this range, the micropores can store sodium ions or lithium ions as active sites, which helps to improve the energy density of the electrochemical device.

[0014] Preferably, the pore size of the micropores in the nitrogen isothermal adsorption-desorption test is 0.5 to 1.0 nm.

[0015] More preferably, the pore size of the micropores in the nitrogen isothermal adsorption-desorption test is 0.5 to 0.7 nm.

[0016] Preferably, the volume of the total pores is 0.003 to 0.02 cm 3 / g.

[0017] Preferably, the volume of the total pores is 0.003 to 0.02 cm 3 / g.

[0018] Preferably, the volume of the total pores is 0.009 to 0.014 cm 3 / g.

[0019] Preferably, the Raman spectrum of the hard carbon material has a D band and a G band, and the ratio of the peak intensity I D of the D band to the peak intensity I G of the G band is I D / I G ≤1.1. In this range, the hard carbon has high conductivity and moderate defects, which is beneficial to improve its initial coulombic efficiency and rate performance.

[0020] Preferably, the diffraction peak of the hard carbon material on the (002) crystal plane is located at 2θ = 21.3° to 25.6°, and the interlayer spacing is 0.35 to 0.42 nm. In this range, the hard carbon can store more sodium / lithium ions and is beneficial to the rapid insertion and extraction of sodium / lithium ions, thereby improving its capacity and rate performance.

[0021] Preferably, the half-height peak width of the (002) crystal plane diffraction peak is 2.3-15°. Within this range, the hard carbon material has moderate particle size and high conductivity, which is beneficial to improve its rate performance and sodium and / or lithium storage capacity.

[0022] Under the above XRD characteristics, the hard carbon has an amorphous structure, which can make the hard carbon not only have a large interlayer spacing, but also have good conductivity, which is beneficial to improve its specific capacity for sodium / lithium storage and rate performance.

[0023] In the specific embodiments of the present application, the hard carbon material further comprises a mesoporous structure.

[0024] Preferably, the volume of the mesopore is ≤0.0045cm 3 / g, and the volume percentage of the mesopore in the total pore is ≤35%.

[0025] Preferably, the volume of the mesopore is 0.001-0.0043cm 3 / g, and the volume percentage of the mesopore in the total pore is 20%-35%.

[0026] More preferably, the volume of the mesopore is 0.0028-0.004cm 3 / g, and the volume percentage of the mesopore in the total pore is 28%-34%.

[0027] Preferably, the pore size of the mesopore under nitrogen isothermal adsorption-desorption test is 2.0-3.0nm.

[0028] Preferably, the pore size of the mesopore under nitrogen isothermal adsorption-desorption test is 2.2-2.8nm.

[0029] More preferably, the pore size of the mesopore under nitrogen isothermal adsorption-desorption test is 2.4-2.6nm.

[0030] Preferably, the specific surface area of the hard carbon material is 1-41m 2 / g. Within this range, the structure of the hard carbon material can contain abundant micropores, thereby improving its sodium / lithium active sites and specific capacity. At the same time, the large specific surface area can improve the wettability of the electrolyte, thereby improving the kinetic performance of the electrochemical device.

[0031] Preferably, the specific surface area of the hard carbon material is 5-30m 2 / g.

[0032] Preferably, the total pore volume of the hard carbon material is denoted as V (cm 3 / g), and the specific surface area of the hard carbon material is denoted as B (m 2 / g), the percentage content of micropore volume is denoted as A%, and the radius of micropore is denoted as r (nm), A, B, V, and r satisfy any one of the following relationships:

[0033]

[0034] or,

[0035]

[0036] When the above formulae are satisfied, the hard carbon material containing micropores can improve its sodium or lithium storage capacity and the energy density of the battery.

[0037] Preferably, the particle size D50 of the hard carbon material is 1-11 μm. Within this range, the hard carbon has good sodium / lithium storage kinetics and processing performance.

[0038] Preferably, the particle size D50 of the hard carbon material is 4-6 μm.

[0039] More preferably, the particle size D50 of the hard carbon material is 4.5-5.6 μm.

[0040] Preferably, the particle size D90 of the hard carbon material is 1.8-15 μm, and the particle size D100 is 3-27 μm. Within this range, the hard carbon has good sodium / lithium storage kinetics and processing performance.

[0041] Preferably, the particle size D90 of the hard carbon material is 4.2-11.8 μm, and the particle size D100 is 4.8-18.5 μm.

[0042] The present application also provides a preparation method of the above hard carbon material, comprising the following steps:

[0043] Step (1): calcining a carbon source to obtain a hard carbon precursor;

[0044] Step (2): mixing the hard carbon precursor with an activating agent, and performing low-temperature carbonization treatment on the obtained mixture in an inert atmosphere to obtain a first carbonization product;

[0045] Step (3): removing impurities in the first carbonization product, and performing medium-temperature carbonization treatment in an organic atmosphere and an inert atmosphere to obtain a second carbonization product;

[0046] Step (4): performing high-temperature carbonization treatment on the second carbonization product in an inert atmosphere to obtain the hard carbon material.

[0047] Preferably, the temperature for the low-temperature carbonization is 300-800 ℃, the heating rate is 0.5-5 ℃ / min, and the holding time is 1-3 h.

[0048] Preferably, the temperature of the low-temperature carbonization is 700-800°C, the heating rate is 2-4°C / min, and the holding time is 1.5-2.5h.

[0049] Preferably, the cooling rate of the low-temperature carbonization is 0.5-5°C / min, preferably 2-4°C / min.

[0050] Preferably, the activating agent comprises, but is not limited to, one or more of potassium carbonate, potassium bicarbonate, sodium carbonate, sodium bicarbonate, potassium hydroxide, water vapor, carbon dioxide, phosphoric acid, and zinc hydroxide.

[0051] Preferably, the mass ratio of the hard carbon precursor to the activating agent is (2.5-12.5):1.

[0052] Preferably, the temperature of the medium-temperature carbonization is 500-1200°C, the heating rate is 3-10°C / min, and the holding time is 0.2-1.5h.

[0053] Preferably, the temperature of the medium-temperature carbonization is 1000-1200°C, the heating rate is 6-8°C / min, and the holding time is 0.5-1.5h.

[0054] In an embodiment of the present application, the temperature of the medium-temperature carbonization is higher than the temperature of the low-temperature carbonization.

[0055] Preferably, the temperature of the high-temperature carbonization is 1300-1500°C, the heating rate is 0.5-1.2°C / min, and the holding time is 2-4h.

[0056] Preferably, the temperature of the high-temperature carbonization is 1300-1500°C, the heating rate is 0.5-1.2°C / min, and the holding time is 2-4h.

[0057] Preferably, the inert atmosphere comprises at least one of nitrogen, helium, argon, xenon, and radon.

[0058] In an embodiment of the present application, in step (3), the substance that generates the organic atmosphere is a volatile solvent or a mixture of a volatile solvent and a non-volatile solvent.

[0059] In an embodiment of the present application, the volatile solvent comprises, but is not limited to, at least one of ethanol, methanol, and acetone.

[0060] In an embodiment of the present application, the non-volatile solvent comprises, but is not limited to, at least one of ethylene glycol, benzyl alcohol, dodecane, dimethyl carbonate, glycerol, ethyl benzoate, and N-methyl pyrrolidone.

[0061] Preferably, in step (1), the calcination temperature is 300-500°C, and the calcination time is 0.5-5h.

[0062] Preferably, the temperature of the calcination is 350-450℃, and the time of the calcination is 0.5-1.5h.

[0063] In the embodiments of the present application, in step (1), the carbon source includes, but is not limited to, one or more of glucose, epoxy resin, sucrose, starch, phenol-formaldehyde resin, polyvinylpyrrolidone, walnut shell, coconut shell, mangosteen shell, almond shell, acai berry shell, corn stalk, polyfurfuryl alcohol resin, polyacrylonitrile, coal, polyvinyl alcohol, polyvinyl chloride, peanut shell, cotton, bitter buckwheat, lotus, asphalt, etc.

[0064] In the embodiments of the present application, in step (3), the method for removing impurities in the first carbonization product includes: washing the first carbonization product with an acidic solution, and then washing to neutral with water and freeze-drying.

[0065] In the embodiments of the present application, the solute of the acidic solution includes, but is not limited to, at least one of hydrochloric acid, sulfuric acid, nitric acid or acetic acid.

[0066] The present application also provides an electrode sheet, which comprises the hard carbon material described above. The hard carbon material is used as a negative electrode active material.

[0067] In the embodiments of the present application, the electrode sheet is a negative electrode sheet.

[0068] In the embodiments provided by the present application, the negative electrode sheet comprises a negative electrode current collector and a negative electrode active material layer coated on at least one side surface of the negative electrode current collector, and the negative electrode active material layer comprises a negative electrode active material, a conductive agent and a binder. The negative electrode active material is the hard carbon material provided by the present application, or a mixture of the hard carbon material provided by the present application and other negative electrode active materials.

[0069] Preferably, the mass ratio of the negative electrode active material, the conductive agent and the binder in the negative electrode active material layer is (70-100):(0.5-15):(0.5-15).

[0070] In the embodiments of the present application, the mass ratio of the negative electrode active material, the conductive agent and the binder is (70-90):(5-15):(5-15).

[0071] Preferably, the conductive agent is selected from one or more of conductive carbon black, carbon fiber, ketjen black, acetylene black, carbon nanotube and graphene.

[0072] Preferably, the binder is selected from one or more of styrene-butadiene rubber, polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene and polyethylene oxide.

[0073] The present application also provides an electrochemical device, which comprises the hard carbon material and / or the electrode sheet described above.

[0074] Preferably, the electrochemical device is a sodium-ion battery or a lithium-ion battery.

[0075] In a specific embodiment provided by the present application, the electrochemical device is a sodium-ion battery.

[0076] In an embodiment of the present application, the electrochemical device comprises a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte.

[0077] In another embodiment of the present application, the electrochemical device comprises a counter electrode, a negative electrode sheet, a separator, and an electrolyte.

[0078] In a specific embodiment provided by the present application, the electrochemical device is a sodium-ion battery, and the counter electrode is a metal sodium sheet.

[0079] In an embodiment provided by the present application, the positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer coated on at least one side surface of the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material, a conductive agent, and a binder.

[0080] Preferably, the mass ratio of the positive electrode active material, the conductive agent, and the binder in the positive electrode active material layer is (70-100):(0.5-15):(0.5-15).

[0081] In a specific embodiment of the present application, the mass ratio of the positive electrode active material, the conductive agent, and the binder is (70-90):(5-15):(5-15).

[0082] Preferably, the positive electrode active material comprises at least one of a sodium transition metal oxide, a polyanion compound, and a Prussian blue compound.

[0083] In an embodiment provided by the present application, in the sodium transition metal oxide, the transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce. The sodium transition metal oxide is, for example, Na x MO2, wherein M is one or more of Ti, V, Mn, Co, Ni, Fe, Cr, and Cu.

[0084] In an embodiment provided by the present application, the polyanion compound can be a compound having a sodium ion, a transition metal ion, a tetrahedral (YO4) n- anion unit. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, and Ce; Y can be at least one of P, S, and Si; and n represents the valence state of (YO4) n- .

[0085] In an embodiment provided by the present application, the polyanion compound can also be a compound having a sodium ion, a transition metal ion, a tetrahedral (YO4)n- A compound of an anion unit, a halogen anion. The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, Ce; Y can be at least one of P, S, Si, n represents the valence of (YO4) n- ; the halogen can be at least one of F, Cl, Br.

[0086] In the embodiments provided by the present application, the polyanionic compound can also be a compound having a sodium ion, a tetrahedral (YO4) n- anion unit, a polyhedral (ZO y ) m+ anion unit, and optionally a halogen anion. Y can be at least one of P, S, Si, n represents the valence of (YO4) n- ; Z represents a transition metal, which can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, Ce, m represents the valence of (ZO y ) m+ ; the halogen can be at least one of F, Cl, Br.

[0087] In the embodiments provided by the present application, the polyanionic compound is at least one of NaFePO4, Na3V2(PO4)3, NaM’PO4F (M’ is one or more of V, Fe, Mn and Ni), and Na3(VO y )2(PO4)2F 3-2y (0≤y≤1).

[0088] In the embodiments provided by the present application, the Prussian blue compound can be a compound having a sodium ion, a transition metal ion and a cyanide ion (CN - ). The transition metal can be at least one of Mn, Fe, Ni, Co, Cr, Cu, Ti, Zn, V, Zr, Ce. The Prussian blue compound is, for example, Na a Me b Me’ c (CN)6, wherein Me and Me’ are each independently at least one of Ni, Cu, Fe, Mn, Co and Zn, 0

[0089] Compared with the prior art, the present application has the beneficial effects that:

[0090] The hard carbon material has abundant micropores, especially micropores with a pore size of 0.5-1.8 nm, and the volume of the micropores is ≥0.005 cm 3Pore Width represents pore width, Pore Volume represents pore volume; Figure 2 shows the pore size distribution of the hard carbon of Example 1; Pore Width represents pore width, Pore Volume represents pore volume; Figure 3 shows the XRD pattern of the hard carbon of Example 1; Intensity represents peak intensity, 2 Theta represents 2 theta; Figure 4 shows the SEM image of the hard carbon of Example 1; Figure 5 shows the particle size distribution of the hard carbon of Example 1; Figure 6 shows the cyclic performance of the hard carbon anode of Example 1. BRIEF DESCRIPTION OF DRAWINGS

[0091] Figure 1 Pore Width represents pore width, Pore Volume represents pore volume; Figure 2 shows the pore size distribution of the hard carbon of Example 1; Pore Width represents pore width, Pore Volume represents pore volume; Figure 3 shows the XRD pattern of the hard carbon of Example 1; Intensity represents peak intensity, 2 Theta represents 2 theta; Figure 4 shows the SEM image of the hard carbon of Example 1; Figure 5 shows the particle size distribution of the hard carbon of Example 1; Figure 6 shows the cyclic performance of the hard carbon anode of Example 1.

[0092] Figure 2 Pore Width represents pore width, Pore Volume represents pore volume; Figure 2 shows the pore size distribution of the hard carbon of Example 1; Pore Width represents pore width, Pore Volume represents pore volume; Figure 3 shows the XRD pattern of the hard carbon of Example 1; Intensity represents peak intensity, 2 Theta represents 2 theta; Figure 4 shows the SEM image of the hard carbon of Example 1; Figure 5 shows the particle size distribution of the hard carbon of Example 1; Figure 6 shows the cyclic performance of the hard carbon anode of Example 1.

[0093] Figure 3 Pore Width represents pore width, Pore Volume represents pore volume; Figure 2 shows the pore size distribution of the hard carbon of Example 1; Pore Width represents pore width, Pore Volume represents pore volume; Figure 3 shows the XRD pattern of the hard carbon of Example 1; Intensity represents peak intensity, 2 Theta represents 2 theta; Figure 4 shows the SEM image of the hard carbon of Example 1; Figure 5 shows the particle size distribution of the hard carbon of Example 1; Figure 6 shows the cyclic performance of the hard carbon anode of Example 1.

[0094] Figure 4 Pore Width represents pore width, Pore Volume represents pore volume; Figure 2 shows the pore size distribution of the hard carbon of Example 1; Pore Width represents pore width, Pore Volume represents pore volume; Figure 3 shows the XRD pattern of the hard carbon of Example 1; Intensity represents peak intensity, 2 Theta represents 2 theta; Figure 4 shows the SEM image of the hard carbon of Example 1; Figure 5 shows the particle size distribution of the hard carbon of Example 1; Figure 6 shows the cyclic performance of the hard carbon anode of Example 1.

[0095] Figure 5 Pore Width represents pore width, Pore Volume represents pore volume; Figure 2 shows the pore size distribution of the hard carbon of Example 1; Pore Width represents pore width, Pore Volume represents pore volume; Figure 3 shows the XRD pattern of the hard carbon of Example 1; Intensity represents peak intensity, 2 Theta represents 2 theta; Figure 4 shows the SEM image of the hard carbon of Example 1; Figure 5 shows the particle size distribution of the hard carbon of Example 1; Figure 6 shows the cyclic performance of the hard carbon anode of Example 1. DETAILED DESCRIPTION

[0096] The present application discloses hard carbon material, electrode sheet and electrochemical device, those skilled in the art can refer to the content herein, and appropriately improve process parameters to realize. It is particularly pointed out that all similar replacements and changes are obvious to those skilled in the art, and they are regarded as included in the present application. The method and application of the present application have been described by preferred embodiments, and relevant personnel can obviously modify or appropriately change and combine the method and application described herein without departing from the content, spirit and scope of the present application, to realize and apply the present application technology.

[0097] TERMS EXPLANATION:

[0098] Micropore refers to the pore with pore diameter < 2 nm. The radius of micropore in this paper refers to half of the pore diameter of micropore.

[0099] Mesopore refers to the pore with pore diameter between 2-50 nm.

[0100] Macropore refers to the pore with pore diameter > 50 nm.

[0101] Total pore refers to the collection of micropore, mesopore and macropore.

[0102] DETECTION METHOD:

[0103] Particle size test is measured by Mastersize 3000 (Malvern 3000) by laser method;

[0104] The instrument for the pore size test and the specific surface area test is a NOVA Touch BET tester, and the test is performed by the ASAP 2460 nitrogen adsorption method;

[0105] The Raman spectrum test is performed by using a Thermo Fisher Raman spectrometer;

[0106] The XRD test is performed by using a Shimadzu XRD-6100 type X-ray diffractometer, and the sample amount for the test is 0.5g / cm 2 Cu Kα line is used as incident X-ray, the working voltage of the X-ray source is 40kV, the test power is 2kW, 2θ is used as the abscissa and the unit is °, the signal intensity is used as the ordinate, the test interval is 10-80°, the scanning rate is 4° / min, and the data point interval is 0.02°.

[0107] The reagents, instruments or materials used in the present application can be obtained through commercial channels.

[0108] The present application is further described below in combination with examples:

[0109] Example 1

[0110] (1) A proper amount of crushed mangosteen shell is placed in a muffle furnace and calcined at 410℃ for 1h, then 1g of the obtained black powder is added to 28.6mL of a 3.5mg / mL potassium bicarbonate aqueous solution, and after being uniformly mixed, it is rapidly frozen with liquid nitrogen and freeze-dried to remove the solvent water;

[0111] (2) The mixture obtained in step (1) is transferred to a tube furnace and carbonized at 750℃ for 2h under nitrogen protection, and after completion, it is cooled to room temperature, and the heating and cooling rates are both 3℃ / min;

[0112] (3) The product obtained in step (2) is first washed several times with hydrochloric acid (5mol / L), then washed to neutral with deionized water, and then freeze-dried;

[0113] (4) The dried product in step (3) is placed in a tube furnace, and a porcelain boat containing a mixture of ethanol and ethylene glycol is placed near the gas inlet, then argon is introduced and heated to 1100℃ at a rate of 7℃ / min for 1h. After completion, it is further heated to 1400℃ at a rate of 0.5℃ / min and kept for 3h, and after cooling to room temperature, the target sample is obtained.

[0114] By Figure 1It can be seen that the hard carbon material mainly contains micropores and mesopores, the micropore size is concentrated between 0.5-0.7 nm, the mesopore size is mainly concentrated between 2.4-2.6 nm, and the content of micropores is higher than that of mesopores. It can be seen that the hard carbon obtained in Example 1 contains abundant micropores, and the pore volume and volume percentage are as high as 0.01 cm 3 / g and 73%, and the pore size is about 0.7 nm.

[0115] Figure 2 The XRD pattern of the hard carbon shows that the diffraction peak of the (002) crystal plane is located at 2θ = 23°, indicating that the interlayer spacing is 0.386 nm, and the half-height peak width of the (002) crystal plane diffraction peak is 6.5°. In addition, the wider (002) crystal plane diffraction peak indicates the amorphous structure. It can be seen that the hard carbon obtained in Example 1 is amorphous structure, and has a larger interlayer spacing (0.386 nm), indicating that it can store more sodium ions or lithium ions and has excellent rate performance.

[0116] Figure 3 The SEM image of the hard carbon shows that the morphology of the hard carbon is block structure.

[0117] Figure 4 The particle size of the hard carbon is D50 = 4.8 μm. The smaller particle size is beneficial to improve the rate performance and the processing performance in the tabletting process.

[0118] The specific characteristic parameters of the hard carbon of this example are shown in Table 1.

[0119] Example 2

[0120] The difference between Example 1 and Example 2 is the heating rate of high-temperature carbonization. The specific preparation method is as follows:

[0121] (1) A certain amount of crushed mangosteen shell was placed in a muffle furnace and calcined at 410°C for 1 h. Then 1 g of the obtained black powder was added to 28.6 mL of a 3.5 mg / mL aqueous solution of potassium bicarbonate, and after mixing evenly, it was quickly frozen with liquid nitrogen and freeze-dried to remove the solvent water;

[0122] (2) The mixture obtained in step (1) was transferred to a tube furnace and carbonized at 750°C for 2 h under nitrogen protection, and then cooled to room temperature. The heating and cooling rates were both 3°C / min;

[0123] (3) The product obtained in step (2) was washed with hydrochloric acid (5 mol / L) several times, then washed with deionized water until neutral, and then freeze-dried;

[0124] (4) Put the dried product of step (3) into a tube furnace, and put a porcelain boat containing a mixture of ethanol and ethylene glycol near the air inlet, then pass in argon and heat to 1100°C at a rate of 7°C / min for 1 h. After completion, continue to heat to 1400°C at a rate of 1°C / min for 3 h, and after cooling to room temperature, the target sample is obtained.

[0125] The specific characteristic parameters of the hard carbon of this example are shown in Table 1.

[0126] Example 3

[0127] The difference between this example and Example 1 is the heating rate of high-temperature carbonization, and the specific preparation method is as follows:

[0128] (1) Take an appropriate amount of crushed mangosteen shell and place it in a muffle furnace, and calcine it at 410°C for 1 h. Then add 1 g of the obtained black powder to 28.6 mL of a 3.5 mg / mL aqueous solution of potassium bicarbonate, mix well, and then quickly freeze with liquid nitrogen and freeze-dry to remove the solvent water;

[0129] (2) Transfer the mixture obtained in step (1) to a tube furnace and carbonize it at 750°C for 2 h under nitrogen protection. After completion, cool to room temperature. The heating and cooling rates are both 3°C / min;

[0130] (3) Wash the product obtained in step (2) with hydrochloric acid (5 mol / L) several times, then wash it to neutral with deionized water, and then freeze-dry;

[0131] (4) Put the dried product of step (3) into a tube furnace, and put a porcelain boat containing a mixture of ethanol and ethylene glycol near the air inlet, then pass in argon and heat to 1100°C at a rate of 7°C / min for 1 h. After completion, continue to heat to 1400°C at a rate of 1.2°C / min for 3 h, and after cooling to room temperature, the target sample is obtained.

[0132] The specific characteristic parameters of the hard carbon of this example are shown in Table 1.

[0133] Example 4

[0134] The difference between this example and Example 3 is the type of hard carbon precursor, and the specific preparation method is as follows:

[0135] (1) Take an appropriate amount of phenolic resin and place it in a muffle furnace, and calcine it at 410°C for 1 h. Then add 1 g of the obtained black powder to 28.6 mL of a 3.5 mg / mL aqueous solution of potassium bicarbonate, mix well, and then quickly freeze with liquid nitrogen and freeze-dry to remove the solvent water;

[0136] (2) The mixture obtained in step (1) was transferred into a tube furnace and carbonized at 750°C for 2h under nitrogen protection, and after the process was completed, it was cooled to room temperature, and the heating and cooling rates were both 3°C / min;

[0137] (3) The product obtained in step (2) was first washed several times with hydrochloric acid (5 mol / L), and then washed to neutral with deionized water, and then freeze-dried;

[0138] (4) The dried product of step (3) was placed in a tube furnace, and a porcelain boat containing a mixture of ethanol and ethylene glycol was placed near the gas inlet, then argon was introduced, and the temperature was raised to 1100°C at a rate of 7°C / min for 1h. After the process was completed, it was continued to be heated to 1400°C at a rate of 1.2°C / min for 3h, and after cooling to room temperature, the target sample was obtained.

[0139] The specific characteristic parameters of the hard carbon of this example are shown in Table 1.

[0140] Example 5

[0141] The specific preparation method is as follows, which is different from example 3 in the type of hard carbon precursor and high-temperature carbonization temperature.

[0142] (1) A certain amount of sucrose was weighed and placed in a muffle furnace, calcined at 410°C for 1h, then 1g of the obtained black powder was added to 28.6mL of 3.5mg / mL potassium bicarbonate aqueous solution, and after mixing evenly, it was quickly frozen with liquid nitrogen and freeze-dried to remove water;

[0143] (2) The mixture obtained in step (1) was transferred into a tube furnace and carbonized at 750°C for 2h under nitrogen protection, and after the process was completed, it was cooled to room temperature, and the heating and cooling rates were both 3°C / min;

[0144] (3) The product obtained in step (2) was first washed several times with hydrochloric acid (5 mol / L), and then washed to neutral with deionized water, and then freeze-dried;

[0145] (4) The dried product of step (3) was placed in a tube furnace, and a porcelain boat containing a mixture of ethanol and ethylene glycol was placed near the gas inlet, then argon was introduced, and the temperature was raised to 1100°C at a rate of 7°C / min for 1h. After the process was completed, it was continued to be heated to 1300°C at a rate of 1.2°C / min for 3h, and after cooling to room temperature, the target sample was obtained.

[0146] The specific characteristic parameters of the hard carbon of this example are shown in Table 1.

[0147] Example 6

[0148] The specific preparation method is as follows, which is different from example 5 in the temperature and heating rate of medium-temperature carbonization and high-temperature carbonization.

[0149] (1) A certain amount of sucrose was weighed and placed in a muffle furnace, calcined at 410°C for 1 h, then 1 g of the obtained black powder was added to 28.6 mL of a 3.5 mg / mL aqueous solution of potassium bicarbonate, mixed uniformly, quickly frozen with liquid nitrogen, and freeze-dried to remove solvent water;

[0150] (2) The mixture obtained in step (1) was transferred to a tube furnace and carbonized at 750°C for 2 h under nitrogen protection, and then cooled to room temperature, and the heating and cooling rates were both 3°C / min;

[0151] (3) The product obtained in step (2) was first washed several times with hydrochloric acid (5 mol / L), then washed to neutral with deionized water, and then freeze-dried;

[0152] (4) The dried product of step (3) was placed in a tube furnace, and a porcelain boat containing a mixture of ethanol and ethylene glycol was placed near the gas inlet, then argon was introduced and heated to 1000°C at a rate of 5°C / min for 1 h. After completion, it was further heated to 1500°C at a rate of 1°C / min and kept for 3 h, and then cooled to room temperature to obtain the target sample.

[0153] The specific characteristic parameters of the hard carbon of this example are shown in Table 1.

[0154] Comparative Example 1

[0155] The specific preparation method is as follows, which is different from example 1 in the heating rate of high-temperature carbonization, and step (4) does not include an organic atmosphere for medium-temperature carbonization.

[0156] (1) A certain amount of crushed mangosteen shell was weighed and placed in a muffle furnace, calcined at 410°C for 1 h, then 1 g of the obtained black powder was added to 28.6 mL of a 3.5 mg / mL aqueous solution of potassium bicarbonate, mixed uniformly, quickly frozen with liquid nitrogen, and freeze-dried to remove solvent water;

[0157] (2) The mixture obtained in step (1) was transferred to a tube furnace and carbonized at 750°C for 2 h under nitrogen protection, and then cooled to room temperature, and the heating and cooling rates were both 3°C / min;

[0158] (3) The product obtained in step (2) was first washed several times with hydrochloric acid (5 mol / L), then washed to neutral with deionized water, and then freeze-dried;

[0159] (4) The product after drying in step (3) was placed in a tube furnace, argon was introduced and heated to 1100°C at a rate of 7°C / min for 1 h. After completion, it was continued to be heated to 1400°C at a rate of 3°C / min for 3 h, and after cooling to room temperature, the target sample was obtained.

[0160] The specific characteristic parameters of the hard carbon of the present comparative example are shown in Table 1.

[0161] Comparative Example 2

[0162] Different from Example 1 is that no activating agent is added in step (1), and the specific preparation method is as follows:

[0163] (1) An appropriate amount of crushed mangosteen shell was placed in a muffle furnace and calcined at 410°C for 1 h;

[0164] (2) The 1 g of black powder obtained in step (1) was transferred to a tube furnace and carbonized at 750°C for 2 h under nitrogen protection, and after completion, it was cooled to room temperature. The heating and cooling rates in this process were both 3°C / min;

[0165] (3) The product obtained in step (2) was washed with hydrochloric acid (5 mol / L) several times, then washed to neutral with deionized water, and then freeze-dried;

[0166] (4) The product after drying in step (3) was placed in a tube furnace, and a porcelain boat containing a mixture of ethanol and ethylene glycol was placed near the gas inlet, then argon was introduced and heated to 1100°C at a rate of 7°C / min for 1 h. After completion, it was continued to be heated to 1400°C at a rate of 0.5°C / min for 3 h, and after cooling to room temperature, the target sample was obtained.

[0167] The specific characteristic parameters of the hard carbon of the present comparative example are shown in Table 1.

[0168] Comparative Example 3

[0169] Different from Example 1 is that the medium-temperature carbonization step is not included, and the heating rate of high-temperature carbonization is different, and the specific preparation method is as follows:

[0170] (1) An appropriate amount of crushed mangosteen shell was placed in a muffle furnace and calcined at 410°C for 1 h, then 1 g of the black powder obtained was added to 28.6 mL of a 3.5 mg / mL aqueous solution of potassium bicarbonate, mixed uniformly, quickly frozen with liquid nitrogen, and freeze-dried to remove the solvent water;

[0171] (2) The mixture obtained in step (1) was transferred to a tube furnace and carbonized at 750°C for 2 h under nitrogen protection, and after completion, it was cooled to room temperature. The heating and cooling rates in this process were both 3°C / min;

[0172] (3) The product obtained in step (2) is washed with hydrochloric acid (5 mol / L) several times, then washed with deionized water until neutral, and then freeze-dried;

[0173] (4) The dried product of step (3) is placed in a tube furnace, a porcelain boat containing a mixture of ethanol and ethylene glycol is placed near the gas inlet, then argon is introduced and heated to 1400℃ at a rate of 7℃ / min and kept for 3h, and the target sample is obtained after cooling to room temperature.

[0174] The specific characteristic parameters of the hard carbon of the present comparative example are shown in Table 1.

[0175] Comparative Example 4

[0176] Different from Example 1 is that the medium temperature carbonization step is not included, and the specific preparation method is as follows:

[0177] (1) A certain amount of crushed mangosteen shell is placed in a muffle furnace and calcined at 410℃ for 1h, then 1g of the obtained black powder is added to 28.6mL of 3.5mg / mL potassium bicarbonate aqueous solution, mixed uniformly, quickly frozen with liquid nitrogen and freeze-dried to remove water;

[0178] (2) The mixture obtained in step (1) is transferred to a tube furnace and carbonized at 750℃ for 2h under nitrogen protection, and then cooled to room temperature, and the heating and cooling rates are both 3℃ / min;

[0179] (3) The product obtained in step (2) is washed with hydrochloric acid (5 mol / L) several times, then washed with deionized water until neutral, and then freeze-dried;

[0180] (4) The dried product of step (3) is placed in a tube furnace, a porcelain boat containing a mixture of ethanol and ethylene glycol is placed near the gas inlet, then argon is introduced and heated to 1400℃ at a rate of 0.5℃ / min and kept for 3h, and the target sample is obtained after cooling to room temperature.

[0181] The specific characteristic parameters of the hard carbon of the present comparative example are shown in Table 1.

[0182] Comparative Example 5

[0183] Different from Example 1 is that no activator is added in step (1), and the medium temperature carbonization of step (4) does not include an organic atmosphere, and the specific preparation method is as follows:

[0184] (1) A certain amount of crushed mangosteen shell is placed in a muffle furnace and calcined at 410℃ for 1h;

[0185] (2) The black powder obtained in step (1) 1 g was transferred into a tube furnace and carbonized at 750°C for 2 h under nitrogen protection, and after the process was completed, it was cooled to room temperature, and the heating and cooling rates were both 3°C / min;

[0186] (3) The product obtained in step (2) was first washed several times with hydrochloric acid (5 mol / L), and then washed to neutral with deionized water, and then freeze-dried;

[0187] (4) The dried product of step (3) was placed in a tube furnace, argon was introduced, and the temperature was increased to 1100°C at a rate of 7°C / min and kept for 1 h. After the process was completed, the temperature was continued to increase to 1400°C at a rate of 0.5°C / min and kept for 3 h, and after cooling to room temperature, the target sample was obtained.

[0188] The specific characteristic parameters of the hard carbon of the present comparative example are shown in Table 1.

[0189] Assembly of sodium ion batteries

[0190] The hard carbon material obtained in step (4) of the above examples and comparative examples was pre-mixed with conductive carbon black and polyvinylidene fluoride at a mass ratio of 8:1:1, and then an appropriate amount of N-methyl pyrrolidone was added and mixed uniformly, and then coated on an aluminum foil and transferred to a vacuum drying oven for baking for 12 h (120°C). After the process was completed, the punched electrode, metal sodium sheet and glass fiber separator were assembled into a button cell, and the solvent of the electrolyte used was a mixture of ethylene carbonate and diethyl carbonate (volume ratio 1:1), the solute was 1M NaClO4, and the additive was 5% fluoroethylene carbonate.

[0191] Test of sodium storage performance

[0192] The sodium ion batteries assembled from Examples 1 to 6 and Comparative Examples 1 to 5 were placed on a Land battery tester for electrochemical performance test, and the voltage range was 0-2V. Among them, the current density of constant current charge and discharge was 25 mA / g, and the current density of rate performance test was 50 mA / g, 100 mA / g, 200 mA / g and 400 mA / g.

[0193] Table 1 Percentage of micropore content and particle size of hard carbon

[0194]

[0195] Table 2 Sodium storage performance of hard carbon

[0196]

[0197]

[0198] As Figure 1As shown, the structure of the hard carbon obtained in Example 1 contains abundant micropores, and the pore volume and volume percentage are as high as 0.01 cm 3 / g and 73%, and the pore size is about 0.7 nm. Since the smaller micropores can store sodium ions and / or lithium ions as active sites, the hard carbon negative electrode exhibits a high specific capacity: 478.3 mAh / g at a current density of 25 mA / g after 60 cycles Figure 5 ), indicating that the hard carbon negative electrode still has a charge specific capacity of 478.3 mAh / g at a current density of 25 mA / g after 60 cycles, and the capacity has not substantially decayed.

[0199] and the specific capacities at current densities of 50 mA / g, 100 mA / g, 200 mA / g and 400 mA / g are 463 mAh / g, 442.2 mAh / g, 412.1 mAh / g and 367.2 mAh / g, respectively (Table 2).

[0200] Meanwhile, it can also be found from Table 1 that the construction of the micropore-rich hard carbon needs to undergo three processes of low-temperature carbonization (an activating agent is needed), medium-temperature carbonization and high-temperature carbonization, and a higher heating rate of medium-temperature carbonization and a lower heating rate and carbonization temperature of high-temperature carbonization are beneficial to increasing the content of micropores in the structure of the hard carbon material.

[0201] The above only describes the preferred embodiments of the present application, and it should be noted that those of ordinary skill in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as the protection scope of the present application.

Claims

1. A hard carbon material, characterized in that, The hard carbon material comprises a microporous structure, and the micropores account for ≥65% of the total pore volume percentage; The total pore volume of the hard carbon material is denoted as V (cm 3 / g), the specific surface area of the hard carbon material is denoted as B (m 2 / g), the percentage content of micropore volume is denoted as A%, and the radius of the micropore is denoted as r (nm). A, B, V, and r satisfy the following relationship: 。 2. The hard carbon material of claim 1, wherein, The micropores account for 65%-90% of the total pore volume percentage.

3. The hard carbon material of claim 2, wherein, The micropores account for 66%-72% of the total pore volume percentage.

4. The hard carbon material of claim 1, wherein, The volume of the micropores is ≥ 0.0015 cm 3 / g; and / or, the micropores have a pore size of 0.5 to 1.8 nm under nitrogen isothermal adsorption-desorption test; and / or, the volume of the total pores is ≥ 0.0017 cm 3 / g.

5. The hard carbon material of claim 4, wherein, The volume of the micropores is 0.0015 to 0.018 cm3 / g 3 / g; And / or, the micropores have a pore size of 0.5-1.0 nm under nitrogen isothermal adsorption-desorption test; and / or the total volume of the pores is 0.003 to 0.02 cm3 / g. 3 / g.

6. The hard carbon material of claim 5, wherein, The volume of the micropores is 0.006 to 0.01 cm3 / g 3 / g; And / or, the micropores have a pore size of 0.5-0.7 nm under nitrogen isothermal adsorption-desorption test; and / or the total volume of the pores is 0.009 to 0.014 cm3 / g. 3 / g.

7. The hard carbon material of claim 1, wherein, The Raman spectrum of the hard carbon material has a D band and a G band, and the ratio ID / IG between the peak intensity ID of the D band and the peak intensity IG of the G band is ≤1.1; And / or, the diffraction peak of the (002) crystal face of the hard carbon material is located at 2θ=21.3°-25.6°; And / or, the interlayer spacing of the (002) crystal face is 0.35-0.42 nm; And / or, the half-peak width of the diffraction peak of the (002) crystal face is 2.3-15°.

8. The hard carbon material of claim 1, wherein, The hard carbon material further comprises a mesoporous structure.

9. The hard carbon material of claim 1, wherein, Mesoporous volume < 0.0045 cm 3 / g, mesopore volume < 35% of the total pore volume. And / or, the mesopores have a pore size of 2.0-3.0 nm under nitrogen isothermal adsorption-desorption test.

10. The hard carbon material of claim 9, wherein, The volume of the mesopores is 0.001 to 0.0043 cm 3 / g, and the volume percentage of the mesopores in the total pores is 20% to 35%. And / or, the mesopores have a pore size of 2.2-2.8 nm under nitrogen isothermal adsorption-desorption test.

11. The hard carbon material of claim 10, wherein, The volume of the mesopores is 0.0028-0.004 cm 3 / g, and the volume percentage of the mesopores in the total pores is 28-34%. And / or, the mesopores have a pore size of 2.4-2.6 nm under nitrogen isothermal adsorption-desorption test.

12. The hard carbon material of claim 1, wherein, The specific surface area of the hard carbon material is 1-41 m 2 / g.

13. The hard carbon material of claim 12, wherein, The specific surface area of the hard carbon material is 5-30 m 2 / g.

14. The hard carbon material of claim 1, wherein, A, B, V, r or satisfy the following relationship: 。 15. The hard carbon material of any one of claims 1-14, wherein, The particle size D50 of the hard carbon material is 1-11 μm; and / or, the particle size D90 of the hard carbon material is 1.8-15 μm; and / or, the particle size D100 of the hard carbon material is 3-27 μm.

16. The hard carbon material of claim 15, wherein, The particle size D50 of the hard carbon material is 4-6 μm.

17. The hard carbon material of claim 16, wherein, The particle size D50 of the hard carbon material is 4.5-5.6 μm.

18. A pole piece characterized by, The pole piece comprises the hard carbon material according to any one of claims 1-17.

19. An electrochemical device, characterized by, The electrochemical device comprises the hard carbon material according to any one of claims 1-17 and / or the pole piece according to claim 18.

20. An electrochemical device according to claim 19, wherein, The electrochemical device is a sodium ion battery or a lithium ion battery.

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