Amorphous carbon and preparation method thereof, electrochemical device and electronic equipment

Abstract

The invention discloses amorphous carbon and a preparation method thereof, an electrochemical device and electronic equipment. The amorphous carbon provided by the invention meets the following conditions: the contact angle between the amorphous carbon and dimethyl carbonate is 15-40 degrees; and the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 cm <-1 > and 1820 cm <-1 > is 0-20%. The electrochemical device containing the amorphous carbon disclosed by the invention also has relatively good storage and quick charge capacities on the premise of ensuring excellent first effect and cycling stability.

Description

Technical Field

[0001] The invention relates to amorphous carbon and a preparation method thereof, an electrochemical device and an electronic device. Background Art

[0002] Amorphous carbon is the preferred material for the negative electrode of sodium ion batteries. Amorphous carbon usually includes hard carbon and / or soft carbon, and has excellent fast charging and low temperature performance. However, its high specific surface area and the porous structure of the material itself cause the first efficiency of the material to be low. At present, the methods for improving the first efficiency of amorphous carbon negative electrodes mainly include pre-sodiumization, surface coating, electrolyte regulation and other means, but there are still major limitations. Surface coating generally blocks pores, deteriorates dynamics, and increases costs. For electrolyte regulation, ether electrolytes have been found to have a higher first efficiency, but poor cycle stability. Pre-sodiumization generally uses metallic sodium to achieve pre-sodiumization by first assembling a half-cell, or dissolving organic sodium molecules in an organic solvent and soaking in metallic sodium to form a pre-sodiumized solution, and then soaking the carbon material in the pre-sodiumized solution to achieve pre-sodiumization. However, the above methods are more dangerous, the process is more complicated and time-consuming, which is not conducive to the cycle stability and commercial production of sodium ion batteries. Summary of the invention

[0003] In order to solve the defect that the first effect and cycle stability of sodium ion batteries in the prior art cannot be taken into account at the same time, the present invention provides an amorphous carbon and a preparation method thereof, an electrochemical device and an electronic device. The electrochemical device containing the amorphous carbon of the present invention has good storage and fast charging capabilities while ensuring excellent first effect and cycle stability.

[0004] In a first aspect, the present invention provides an amorphous carbon, wherein the amorphous carbon satisfies: the contact angle of the amorphous carbon with dimethyl carbonate is 15°-40°; the amorphous carbon has a surface area of 1600-1820 cm -1 The absorption intensity of the infrared absorption peak is between 0-20%.

[0005] In a second aspect, the present invention provides a method for preparing amorphous carbon as described above, comprising the following steps:

[0006] S1, performing a first sintering on the amorphous carbon precursor, and cooling to room temperature to obtain a first precursor; wherein the temperature of the first sintering is 1200-1600° C.;

[0007] S2, performing a second sintering on the first precursor, and cooling to room temperature to obtain a second precursor; wherein the temperature of the second sintering is 600-1000° C.;

[0008] S3, spray drying the slurry containing the second precursor to obtain a third precursor;

[0009] S4. Subject the third precursor to a third sintering and cool it to room temperature to obtain the amorphous carbon; wherein, the temperature of the third sintering is 120 - 320°C.

[0010] In a third aspect, the present invention provides an electrochemical device, and the negative electrode sheet of the electrochemical device includes the amorphous carbon as described above.

[0011] In a fourth aspect, the present invention provides an electronic device, which includes the electrochemical device as described above.

[0012] On the basis of conforming to common general knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of the present invention.

[0013] The reagents and raw materials used in the present invention are all commercially available.

[0014] The positive and progressive effects of the present invention are as follows:

[0015] The present invention provides an amorphous carbon, which has a specific contact angle with dimethyl carbonate and a specific absorption intensity of the infrared absorption peak between 1600 - 1820 cm -1 By regulating the above characteristics, an electrochemical device (especially a sodium-ion battery) containing the amorphous carbon has good storage and fast charging capabilities while ensuring excellent initial efficiency and cycle stability. Specific Embodiments

[0016] The present invention will be further illustrated by the following examples, but the present invention is not limited to the scope of the described examples. The experimental methods without specific conditions noted in the following examples are carried out according to conventional methods and conditions, or are selected according to the product specifications.

[0017] Amorphous carbon

[0018] In the amorphous carbon provided in the first aspect of the present invention, the amorphous carbon satisfies: the contact angle between the amorphous carbon and dimethyl carbonate is 15° - 40°; the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is 0 - 20%.

[0019] In the present invention, the contact angle refers to the angle θ between the tangent of the gas-liquid interface made at the three-phase intersection point of gas, liquid, and solid and the solid-liquid junction line, which is a measure of the wetting degree.

[0020] The inventors believe through research that the contact angle reflects the wettability of the amorphous carbon surface to the electrolyte. When the contact angle is within an appropriate range, it is conducive to the wetting speed of the electrolyte on the material. An overly large contact angle indicates poor wettability and poor fast charging performance of the material; an overly small contact angle indicates good affinity between the material surface and the electrolyte surface, which means there are more surface functional groups and more side reactions are likely to occur.

[0021] In the present invention, the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is the characteristic peak of the carbonyl functional group.

[0022] The inventors believe through research that the carbonyl has an affinity for the sodium salt component in the sodium ion battery electrolyte. An appropriate abundance of carbonyl functional groups can induce film formation on the amorphous carbon surface and inhibit the decomposition of organic sodium salts in the electrolyte. However, an overly high carbonyl abundance is prone to additional side reactions with sodium ions.

[0023] In the present invention, the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is preferably 0 - 12%, for example, 1.3%, 2.1%, 5.1%, 6.4%, 8.3%, 9.2%, 10.2%, 10.7%, 19.2% or 19.29%.

[0024] In the present invention, the contact angle between the amorphous carbon and dimethyl carbonate is preferably 20° - 35°, for example, 16.2°, 21°, 21.2°, 23.5°, 25.2°, 26.2°, 29.7°, 31.3° or 38.2°.

[0025] In a specific embodiment, the amorphous carbon satisfies that the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is 8.3%, and the contact angle between the amorphous carbon and dimethyl carbonate is 25.2°.

[0026] In a specific embodiment, the amorphous carbon satisfies that the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is 5.1%, and the contact angle between the amorphous carbon and dimethyl carbonate is 29.7°.

[0027] In a specific embodiment, the amorphous carbon satisfies that the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is 10.2%, and the contact angle between the amorphous carbon and dimethyl carbonate is 21.2°.

[0028] In a specific embodiment, the amorphous carbon satisfies that the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm-1 The absorption intensity of the infrared absorption peak between them is 2.1%, and the contact angle between the amorphous carbon and dimethyl carbonate is 31.3°.

[0029] In a specific embodiment, the amorphous carbon satisfies that the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is 10.7%, and the contact angle between the amorphous carbon and dimethyl carbonate is 23.5°.

[0030] In a specific embodiment, the amorphous carbon satisfies that the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is 9.2%, and the contact angle between the amorphous carbon and dimethyl carbonate is 21°.

[0031] In a specific embodiment, the amorphous carbon satisfies that the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is 6.4%, and the contact angle between the amorphous carbon and dimethyl carbonate is 26.2°.

[0032] In a specific embodiment, the amorphous carbon satisfies that the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is 19.29%, and the contact angle between the amorphous carbon and dimethyl carbonate is 16.2°.

[0033] In a specific embodiment, the amorphous carbon satisfies that the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is 0%, and the contact angle between the amorphous carbon and dimethyl carbonate is 38.2°.

[0034] In a specific embodiment, the amorphous carbon satisfies that the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is 19.2%, and the contact angle between the amorphous carbon and dimethyl carbonate is 15°.

[0035] In a specific embodiment, the amorphous carbon satisfies that the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is 1.3%, and the contact angle between the amorphous carbon and dimethyl carbonate is 40°.

[0036] Preparation method of amorphous carbon

[0037] In the method for preparing amorphous carbon provided in the second aspect of the present invention, it includes the following steps:

[0038] S1. First sinter the amorphous carbon precursor and cool it to room temperature to obtain the first precursor. Among them, the temperature of the first sintering is 1200 - 1600 °C;

[0039] S2. Second sinter the first precursor and cool it to room temperature to obtain the second precursor. Among them, the temperature of the second sintering is 600 - 1000 °C;

[0040] S3. Spray-dry the slurry containing the second precursor to obtain the third precursor;

[0041] S4. Third sinter the third precursor and cool it to room temperature to obtain the amorphous carbon. Among them, the temperature of the third sintering is 120 - 320 °C.

[0042] In step S1, the median particle size of the amorphous carbon precursor can be selected as 3 - 12 μm, for example 6 μm.

[0043] In step S1, the preparation method of the amorphous carbon precursor may include the following steps: pre-carbonize the carbon source to obtain a pre-carbonized material, and then mix and impregnate the pre-carbonized material with a hydrochloric acid solution, wash, centrifuge, and dry to obtain the amorphous carbon precursor.

[0044] Among them, the carbon source can be a conventional carbon source in the art, and usually includes synthetic polymer carbon sources, optionally one or more of phenolic resin, epoxy resin, asphalt, and coal tar.

[0045] Among them, the temperature of the pre-carbonization is preferably 400 - 800 °C.

[0046] Among them, the time of the pre-carbonization is preferably 0.5 - 4 h.

[0047] Among them, the concentration of the hydrochloric acid solution is preferably 1 - 3 mol / L, where the concentration of HCl is the molar concentration of the hydrochloric acid solution in the total volume.

[0048] Among them, the mass ratio of the pre-carbonized material to the hydrochloric acid solution is preferably 1:(2 - 10), for example 1:5.

[0049] Among them, the time of the impregnation can be 12 - 30 h, for example 24 h.

[0050] Among them, the washing can be carried out with deionized water until the pH of the washed material is about 7.

[0051] In step S1, the first sintering can be carried out in a conventional device in the art, such as a rotary furnace.

[0052] In step S1, the temperature of the first sintering is, for example, 1400 °C.

[0053] In step S1, the time of the first sintering can be selected from 1 to 6 h, for example, 3 h.

[0054] In step S1, the pressure of the first sintering can be selected as 0.1 Mpa.

[0055] In step S1, the atmosphere of the first sintering can be an inert atmosphere commonly used in the art, such as nitrogen or inert gas.

[0056] In step S2, the second sintering can be carried out in a conventional device in the art, such as an intermediate frequency furnace.

[0057] In step S2, the temperature of the second sintering is, for example, 800 °C.

[0058] In step S2, the time of the second sintering can be selected from 2 to 6 h, for example, 2 h, 4 h, 5 h or 5.5 h.

[0059] In step S2, the pressure of the second sintering can be selected as 0.08 MPa.

[0060] In step S2, the atmosphere of the second sintering can be an inert atmosphere commonly used in the art, such as nitrogen or inert gas.

[0061] In step S3, the slurry containing the second precursor may further include a carbonyl compound, and the carbon chain length of the carbonyl compound is 12 or less.

[0062] Among them, the carbonyl compound is added in the form of an aqueous solution. In the aqueous solution of the carbonyl compound, the mass fraction of the carbonyl compound is preferably 0 - 4%, and not 0, for example, 0.1%, 0.5%, 2% or 3.8%.

[0063] Among them, the carbonyl compound is preferably chlorogenic acid.

[0064] Among them, the mass ratio of the second precursor to the carbonyl compound can be 1:(3 - 10), for example, 1:5.

[0065] In step S3, the spray drying can be carried out in a conventional spray dryer in the art.

[0066] In step S3, the temperature of the spray drying can be 70 - 120 °C, for example, 80 °C.

[0067] In step S4, the temperature of the third sintering is, for example, 180 °C, 150 °C or 210 °C.

[0068] In step S4, the time of the third sintering can be selected from 3 to 8 h, for example, 5 h.

[0069] In step S4, the pressure of the third sintering can be optionally 0.02 MPa.

[0070] In step S4, the atmosphere of the third sintering can be an inert atmosphere conventionally used in the art, such as nitrogen or inert gas.

[0071] In step S4, the third sintering can be carried out in a conventional device in the art, such as a rotary furnace.

[0072] Electrochemical device

[0073] In the electrochemical device described in the third aspect of the present invention, the negative electrode sheet of the electrochemical device includes the amorphous carbon as described above.

[0074] Those skilled in the art generally understand that amorphous carbon includes hard carbon and / or soft carbon. The amorphous carbon described in the present invention at least includes hard carbon. Optionally, the mass percentage of hard carbon in the amorphous carbon is 80% or more, and this mass percentage refers to the mass percentage of hard carbon in the whole amorphous carbon.

[0075] In some alternative embodiments, the negative electrode sheet can be prepared by a conventional method in the art. For example, the following method can be used: the amorphous carbon, binder, thickener and conductive agent are mixed in a certain mass ratio, and then a solvent is added and mixed evenly to obtain a negative electrode slurry; then the negative electrode slurry is evenly coated on the negative electrode current collector to obtain a negative electrode material layer; and then through processes such as drying, rolling, and cutting, the negative electrode sheet is prepared.

[0076] Wherein, in the negative electrode material layer, the content of the amorphous carbon can be 80.0%-99.9%, and the percentage is the mass percentage of the amorphous carbon in the negative electrode material layer.

[0077] In some specific embodiments, the mass ratio of the amorphous carbon, binder styrene-butadiene rubber, thickener sodium carboxymethyl cellulose and conductive agent carbon black (Super P) is 94.7:2.5:1.8:1.

[0078] In the present invention, the negative electrode current collector can be a current collector conventionally used for the negative electrode in the art, and can be a common current collector or a composite current collector. The negative electrode current collector can be used without limitation with materials that do not cause chemical changes and have conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon or aluminum cadmium alloy can be used, or copper, stainless steel material or aluminum cadmium alloy surface-treated with carbon, nickel, titanium or silver. In addition, in order to enhance the adhesion of the negative electrode active material, micro embossing can be formed on the surface of the negative electrode current collector. The negative electrode current collector can be used in various forms, such as film, sheet, foil, net or porous body, etc.

[0079] In some alternative embodiments, the thickness of the negative electrode current collector may be 5 - 10 μm.

[0080] In some specific embodiments, the negative electrode current collector is a copper foil with a thickness of 8 μm.

[0081] In the present invention, the electrochemical device may be a sodium-ion battery. The sodium-ion battery includes the negative electrode sheet, the positive electrode sheet, the separator, and the electrolyte as described above.

[0082] Positive electrode sheet

[0083] In some alternative embodiments, the positive electrode sheet may be prepared by a conventional method in the art. For example, the following method may be used: The positive electrode active material, the conductive agent, and the binder are mixed in a certain mass ratio, and then a solvent is added and mixed evenly to obtain a positive electrode slurry; then the positive electrode slurry is evenly coated on the positive electrode current collector; and then through processes such as drying, rolling, and cutting, the positive electrode sheet is prepared.

[0084] In a specific embodiment, the mass ratio of the positive electrode active material, conductive carbon black (Super P), carbon nanotubes (CNT), and binder polyvinylidene fluoride (PVDF) is 94:2:1:3.

[0085] For the positive electrode active material, it may be a positive electrode active material conventionally used in the positive electrode of a sodium-ion battery in the art. The positive electrode active material may be a sodium-ion material such as a layered oxide, a polyanion-type compound, a Prussian blue / white compound, etc.

[0086] Optionally, the general formula of the layered oxide is Na x [MFeMn]O2, where M is selected from at least one of Cu, Ni, Li, Mg, Al, Zn, Ti, Zr, and Sn, and optionally x ≤ 1.

[0087] Optionally, the general formula of the polyanion-type compound is NaxMy(XaOb)zZw, where M is selected from one or more of Ti, V, Cr, Mn, Fe, Co, Ni, Ca, Mg, Al, and Nb; X is selected from one or more of Si, S, P, As, B, Mo, W, and Ge, and Z is selected from F and / or OH.

[0088] Optionally, the general formula of the Prussian blue / white compound is Na x M1[M2(CN)6], where M is selected from one or more of Mn, Ni, Co, Zn, Cu, and Fe; optionally, 0 < x ≤ 2.

[0089] In a specific embodiment, the molecular formula of the positive electrode active material is NaFe2(MoO4)3.

[0090] For the positive current collector, materials that do not cause chemical changes and have high electrical conductivity can be used without limitation. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon can usually be used, or aluminum or stainless steel materials surface-treated with carbon, nickel, titanium, silver, etc. To enhance the adhesion of the positive active material, micro-embossing can be formed on the surface of the positive current collector. The positive current collector can be used in various forms, such as membranes, sheets, foils, meshes, or porous bodies, etc.

[0091] In some alternative embodiments, the thickness of the positive current collector can be 8 - 16 μm.

[0092] In some specific embodiments, the positive current collector is an aluminum foil with a thickness of 13 μm.

[0093] Separator

[0094] In some alternative embodiments, the separator can be a polypropylene film or a polyethylene film.

[0095] Among them, the air permeability of the separator can be 180 - 380 s / 100 mL.

[0096] Among them, the porosity of the separator can be 30% - 50%.

[0097] Among them, the thickness of the separator can be 12 μm.

[0098] In a specific embodiment, the separator is a polypropylene film; the thickness of the separator is 12 μm; the air permeability of the separator is 230 s / 100 mL; the porosity of the separator is 40%.

[0099] Electrolyte solution

[0100] In some embodiments, the electrolyte can be a conventional electrolyte used in batteries in the art, generally including a non-aqueous solvent, a sodium salt, and an additive.

[0101] Among them, the non-aqueous solvent can be a conventional non-aqueous solvent in the art, preferably an ester solvent, more preferably a carbonate solvent. The carbonate solvent can be selected from one or more of dimethyl carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).

[0102] Among them, the additive can be selected from one or more of vinylene carbonate (VC), fluorodimethyl carbonate (FEC), ethylene vinylene carbonate (VEC), divinyl sulfate (DTD), vinylene sulfite, 1,3 - propane sultone (PS), allyl sulfonic acid lactone, and 1,4 - butane sultone.

[0103] Among them, the sodium salt can be a conventional sodium salt in the art, for example, NaPF6.

[0104] Among them, the content of the sodium salt can be 4% - 24%, and the percentage is the mass percentage of the sodium salt in the total mass of the electrolyte.

[0105] In a specific embodiment, the electrolyte includes NaPF6, ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and propylene carbonate.

[0106] Among them, the mass ratio of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and propylene carbonate is preferably (2 - 4):(3 - 5):(2 - 4):(0 - 1). When the mass ratio is (2 - 4):(3 - 5):(2 - 4):0, it means that the non - aqueous solvent does not contain propylene carbonate.

[0107] In some embodiments, the electrolyte can be prepared by a conventional method in the art. Optionally, it is prepared by the following method: In an argon - atmosphere glove box with a water content < 10 ppm, battery - grade ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and propylene carbonate are mixed according to the ratio to form an organic solvent, and then a sodium salt is added and mixed evenly to obtain the electrolyte.

[0108] In the present invention, the preparation method of the sodium - ion battery can be a conventional preparation method in the art. It can be that the positive electrode sheet, the negative electrode sheet, and the separator are wound to obtain an electrode core, and then packaged with a packaging shell and injected with the electrolyte; or it can be that the negative electrode sheet, the separator, the positive electrode sheet, and the separator are stacked in sequence to obtain an electrode core, and then packaged with a packaging shell and injected with the electrolyte.

[0109] In some embodiments, the preparation method of the sodium - ion battery includes the following steps: The positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence, and the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolation role. Then it is wrapped with an aluminum - plastic film, transferred to a vacuum oven for drying at 120 °C, injected with 3.0 g / Ah of electrolyte and then sealed, and subjected to electrolytic liquefaction. Finally, a ternary system soft - package battery with a capacity of 1 Ah is prepared. The electrolyte injection coefficient in the sodium - ion battery is 3 g / Ah, the capacity of the electrode core is 1 Ah, and the mass of the electrolyte is 3 g.

[0110] Among them, the formation of the electrolyte includes the following steps: the sodium-ion battery after liquid injection is charged at 0.02C for 17 min at 45°C in a static state under a hot pressing environment of 0.1 MPa, left standing for 5 min and then charged to 0.3 Ah at 0.02C. After that, the air bag is cut off and vacuum packaged, and left standing at room temperature for 48 h, so that the electrolyte is formed.

[0111] Electronic device

[0112] In the electronic device provided in the fourth aspect of the present invention, it includes the electrochemical device as described above.

[0113] Exemplarily, the electronic device of the present invention can be but is not limited to mobile devices (such as mobile phones, tablet computers, laptop computers, video recorders, portable printers / copiers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships, satellites, energy storage systems, backup power supplies, etc.

[0114] On the basis of conforming to the common knowledge in the art, the above preferred conditions can be combined arbitrarily to obtain various preferred examples of the present invention.

[0115] Examples 1-11 and Comparative Examples 1-10

[0116] Preparation of amorphous carbon

[0117] S0: The phenolic resin (Jinan Shengquan Group Co., Ltd.) is pre-carbonized at 600°C for 4 h under the protection of a nitrogen atmosphere, and the pre-carbonized material is obtained by airflow pulverization. The pre-carbonized material and hydrochloric acid solution (1 mol / L) are mixed, and the mass ratio of the pre-carbonized material to the hydrochloric acid solution is 1:5. After impregnation for 24 h, the material is washed with deionized water until the pH is about 7, centrifuged and dried to obtain an amorphous carbon precursor; among them, the median particle size of the amorphous carbon precursor is 6 μm.

[0118] S1: The amorphous carbon precursor is placed in a rotary furnace and subjected to a first sintering under the protection of a nitrogen atmosphere, and cooled to room temperature to obtain a first precursor. Among them, the pressure of the first sintering is 0.1 Mpa.

[0119] S2: The first precursor is transferred to an intermediate frequency furnace for a second sintering, and cooled to room temperature to obtain a second precursor. Among them, the pressure of the second sintering is 0.08 Mpa.

[0120] S3: The second precursor is mixed with an aqueous chlorogenic acid solution and transferred to a spray dryer (ADL311-A / 311S-A), stirred evenly at 80°C for 2 h, and then spray-dried to obtain a third precursor. Among them, the mass ratio of the second precursor to chlorogenic acid is 1:5.

[0121] S4. Introduce nitrogen gas into the rotary kiln for the third precursor, conduct the third sintering, and cool it to room temperature to obtain amorphous carbon. Among them, the pressure of the third sintering is 0.02 Mpa.

[0122] The specific process parameters for the preparation of amorphous carbon in Examples 1-11 and Comparative Examples 1-10 are shown in Table 1.

[0123] The absorption intensity of the infrared absorption peak between 1600 - 1820 cm -1 for the amorphous carbon prepared in Examples 1-11 and Comparative Examples 1-10 is 0 - 20%, and the contact angle between the amorphous carbon and dimethyl carbonate is 15° - 40°, as shown in Table 1 specifically.

[0124] Among them, the test method for the contact angle between the amorphous carbon and dimethyl carbonate: Grind the prepared amorphous carbon into powder, use a tablet press to make tablets with a size of 2 cm × 2 cm, a pressure of 5 T, and a density of 1.0 g / cc. Drop 50 μL of dimethyl carbonate onto the tablet surface with a pipette gun, take pictures with an optical camera configured by Theta Flow and automatically calculate the contact angle, and take the average value of three tests as the contact angle between the amorphous carbon and dimethyl carbonate.

[0125] Among them, the test method for the infrared spectrum: Refer to the national standard GB / T 6040-2019 for the test of the infrared spectrum.

[0126] Preparation of the negative electrode sheet

[0127] The preparation methods of the negative electrode sheets in Examples 1-11 and Comparative Examples 1-10 are as follows:

[0128] Mix the above-prepared amorphous carbon, conductive agent carbon black (Super P), thickening agent sodium carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) in a mass ratio of 94.7:1:1.8:2.5 (a total of 100 mass parts), then add 82 mass parts of deionized water, and stir to mix evenly to obtain a negative electrode slurry (mass concentration of 52%); evenly coat the negative electrode slurry on both sides of an 8-μm copper foil current collector. After processes such as drying, rolling, and cutting, the negative electrode sheets of Examples 1-11 and Comparative Examples 1-10 are prepared. Among them, the rolling pressure is 5 T.

[0129] Table 1

[0130]

[0131] Effect Example 1

[0132] (1) Preparation of the sodium-ion battery:

[0133] Preparation of the positive electrode sheet: Mix the positive active material polyanion compound NaFe2(MoO4)3, conductive carbon black (SuperP), carbon nanotubes (CNT), and binder polyvinylidene fluoride (PVDF) in a mass ratio of 94:2:1:3, and stir in a vacuum mixer until the system becomes homogeneous to obtain the positive electrode slurry; uniformly coat the positive electrode slurry on an aluminum foil with a thickness of 13 μm, air-dry the aluminum foil at room temperature and then transfer it to an oven for drying, and then obtain the positive electrode sheet through cold pressing and slitting.

[0134] Preparation of the electrolyte: Uniformly mix ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and propylene carbonate (PC) in a mass ratio of (2 - 4):(3 - 5):(2 - 4):(0 - 1), and then dissolve dry high-purity sodium salt NaPF6 in the above mixed solvent to prepare an electrolyte with a concentration of 4% - 24%.

[0135] Preparation of the separator: The separator is a polypropylene film; the thickness of the separator is 12 μm; the air permeability of the separator is 230 s / 100 mL; the porosity of the separator is 40%.

[0136] Preparation of the sodium-ion battery: Assemble the prepared positive electrode sheet, separator, negative electrode sheets of Examples 1 - 11 and Comparative Examples 1 - 10, and electrolyte in sequence, so that the positive electrode sheet, separator, negative electrode sheets of Examples 1 - 11 and Comparative Examples 1 - 10, and separator are alternately combined, and a soft-pack battery with a capacity of 1 Ah is obtained through formation.

[0137] (2) Perform the following tests on the sodium-ion batteries prepared in Examples 1 - 11 and Comparative Examples 1 - 10 according to the above method:

[0138] 1. Test method for the cycle capacity of the sodium-ion battery

[0139] During the cycle, charge it with a 1C current to 4.1V, then charge it at a constant voltage until the cut-off current is 0.05C, rest for 30 min, discharge it with a 1C current to 2.5V, and then discharge it with a 1.0C current to 2.0V. The sum of the two discharge capacities is recorded as the cycle capacity.

[0140] 2. Test method for the initial efficiency of the sodium-ion battery

[0141] At 25°C, charge it with a 0.33C current to 4.1V, then charge it at a constant voltage until the cut-off current is 0.05C, denoted as C, rest for 30 min, discharge it with a 1C current to 2.0V, repeat three times and record the third discharge capacity as the battery capacity, denoted as C0, and then use C0 / (C + 0.3), where 0.3 is the formation charge capacity, which is a fixed value.

[0142] 3. Test method for the fast charging time of the sodium-ion battery

[0143] The battery cell is directly charged at a current of 0.33C to 8% SOC state, and then according to the measured three-electrode window of the battery cell, the charging windows at 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% are C1, C2, C3, C4, C5, C6, C7, and C8 respectively. It is charged step by step to 80%, that is, 8% - 10% uses C1, 10% to 20% uses C2, and so on. The charging time from 8% to 80% SOC state is recorded as the measurement standard for fast charging ability. The calculation formula is:

[0144] T = (0.02 / C1 + 0.1 / C2 + 0.1 / C3 + 0.1 / C4 + 0.1 / C5 + 0.1 / C6 + 0.1 / C7 + 0.1 / C8) × 60.

[0145] 4. Test method for the number of cycles of sodium-ion battery

[0146] Under the condition of 25°C, in the voltage range of 2.0 - 4.1V, it is cycled with a 1C / 1C charge-discharge regime, and the number of cycles until the measured capacity reaches 80% of the initial capacity is recorded to characterize the cycle ability of the battery.

[0147] 5. Test method for the storage time of sodium-ion battery

[0148] At 25°C, it is constant-capacitanced with a current of 0.33C and denoted as C0, then the battery cell is stored at a high temperature of 60°C. After that, the battery cell is taken out every 7 days to test the capacity at room temperature and denoted as C1, C2... Cn. When Cn is less than or equal to 80% of C0, the number of days of Cn test is used as the measurement standard for storage ability.

[0149] The above test results are listed in Table 2.

[0150] Table 2

[0151]

[0152] According to Table 1 and Table 2, it can be seen that the contact angle between the amorphous carbon and dimethyl carbonate prepared in Examples 1 - 11 is between 15° and 40°; the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is between 0 and 19.29%. The electrochemical device containing this amorphous carbon has good storage and fast charging ability on the premise of ensuring excellent initial efficiency and cycle stability. When the amorphous carbon prepared in Examples 1 - 11 is applied to sodium-ion batteries, the number of cycles can reach more than 1900, the storage time can reach more than 200 days, the fast charging time can reach less than 32 min, and the initial efficiency can reach more than 90%.

[0153] The differences between Comparative Examples 1, 4, 7, and 8 and Examples 1-11 are that the contact angles between the amorphous carbon and dimethyl carbonate are not within the scope of the present invention, being either too large or too small. From the data in Table 2, it can be seen that they cannot have good storage and fast charging capabilities while ensuring the initial efficiency and cycle stability. This may be because the contact angle reflects the wettability of the amorphous carbon surface to dimethyl carbonate. When the contact angle is within an appropriate range, an appropriate wetting rate of dimethyl carbonate on the amorphous carbon surface can be ensured. An overly large contact angle reflects poor wettability and poor fast charging performance of the electrochemical device; an overly small contact angle reflects good affinity between the material surface and the electrolyte surface, which means there are more surface functional groups and more side reactions are likely to occur.

[0154] The differences between Comparative Example 2 and Examples 1-11 are that both the temperature of the second sintering and the contact angle between the amorphous carbon and dimethyl carbonate are not within the scope of the present invention and are both on the high side. The sodium-ion battery has poor fast charging ability and poor cycle stability. This may be because too high a temperature is not conducive to the chemical and physical adsorption of carbonyl functional groups, and thus an effective SEI film cannot be formed on the amorphous carbon surface, which is not conducive to ion transport.

[0155] The differences between Comparative Examples 3 and 6 and Examples 1-11 are that the contact angles between the amorphous carbon and dimethyl carbonate are not within the scope of the present invention and are on the low side, and the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is also not within the scope of the present invention and is on the high side. The sodium-ion battery cannot have good storage and fast charging capabilities while ensuring the initial efficiency and cycle stability. This may be because an overly small contact angle reflects good affinity between the material surface and the electrolyte surface, which means there are more surface functional groups and more side reactions are likely to occur, and the carbonyl groups on the amorphous carbon surface are reduced, which is not conducive to inducing film formation on the amorphous carbon surface.

[0156] The differences between Comparative Example 5 and Examples 1-11 are that the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600 - 1820 cm -1 is not within the scope of the present invention and is on the high side. The sodium-ion battery cannot have good storage and fast charging capabilities while ensuring the initial efficiency and cycle stability. This may be because an overly small contact angle reflects good affinity between the material surface and the electrolyte surface, which means that an appropriate abundance of carbonyl functional groups can induce film formation on the amorphous carbon surface and inhibit the decomposition of organic sodium salts in the electrolyte.

[0157] The difference between Comparative Example 9 and Examples 1-11 is that the temperatures of the first sintering and the second sintering are both 1400 °C. The temperature of the second sintering is on the high side, and the contact angle is not within the scope of the present invention. On the high side, the sodium-ion battery has poor fast charging ability and poor cycle stability on the basis of ensuring the initial efficiency. It shows that a specific second sintering temperature lower than the first sintering temperature is beneficial to the chemical and physical adsorption of carbonyl functional groups, thereby enabling an appropriate affinity between the surface of the amorphous carbon and the surface of the electrolyte, which is conducive to forming a SEI film rich in NaF components on the surface of the amorphous carbon.

[0158] The difference between Comparative Example 10 and Examples 1-11 is that the temperature of the third sintering is not within the scope of the present invention. On the high side, the contact angle is not within the scope of the present invention. On the high side, both the initial efficiency and the fast charging ability of the sodium-ion battery are reduced, and the cycle stability is poor. It can be seen that when the temperature of the third sintering is on the high side, it is not conducive to the chemical and physical adsorption of carbonyl functional groups, and the affinity between the surface of the amorphous carbon and the surface of the electrolyte is poor, so that the amorphous carbon cannot be effectively induced to form a SEI film rich in NaF components.

[0159] Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that this is only an example. The protection scope of the present invention is defined by the appended claims. Without departing from the principle and essence of the present invention, those skilled in the art can make various changes or modifications to these embodiments, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. An amorphous carbon, characterized in that, The amorphous carbon satisfies the following: the contact angle between the amorphous carbon and dimethyl carbonate is 15°-40°; the absorption intensity of the infrared absorption peak of the amorphous carbon between 1600-1820 cm -1 is 0-20%.

2. The amorphous carbon according to claim 1, characterized in that, The absorption intensity of the infrared absorption peak of the amorphous carbon between 1600-1820 cm -1 is 0-12%.

3. The amorphous carbon according to claim 1, characterized in that, The contact angle between the amorphous carbon and dimethyl carbonate is 20°-35°.

4. A method for preparing amorphous carbon according to any one of claims 1-3, characterized in that, It includes the following steps: S1. First sinter the amorphous carbon precursor, and cool it to room temperature to obtain the first precursor; wherein, the temperature of the first sintering is 1200-1600 °C; S2. Second sinter the first precursor, and cool it to room temperature to obtain the second precursor; wherein, the temperature of the second sintering is 600-1000 °C; S3. Spray-dry the slurry containing the second precursor to obtain the third precursor; S4. Third sinter the third precursor, and cool it to room temperature to obtain the amorphous carbon; wherein, the temperature of the third sintering is 120-320 °C.

5. The method for preparing amorphous carbon according to claim 4, characterized in that, It satisfies one or more of the following conditions (a)-(l): (a) In step S1, the median particle size of the amorphous carbon precursor is 3-12 μm; (b) In step S3, the slurry containing the second precursor further includes a carbonyl compound, and the carbon chain length of the carbonyl compound is 12 or less; (c) In step S1, the time of the first sintering is 1-6 h; (d) In step S1, the pressure of the first sintering is 0.1 Mpa; (e) In step S1, the atmosphere of the first sintering is an inert atmosphere; (f) In step S2, the time of the second sintering is 2-6 h; (g) In step S2, the pressure of the second sintering is 0.08 MPa; (h) In step S2, the atmosphere of the second sintering is an inert atmosphere; (i) In step S3, the temperature of the spray drying is 70-120 °C; (j) In step S3, the time of the third sintering is 3-8 h; (k) In step S3, the pressure of the third sintering is 0.02 MPa; (l) In step S3, the atmosphere of the third sintering is an inert atmosphere.

6. The method for preparing amorphous carbon according to claim 5, wherein The carbonyl compound satisfies one or more of the following conditions (a)-(c): (a) The carbonyl compound is added in the form of an aqueous solution, wherein, in the aqueous solution of the carbonyl compound, the mass fraction of the carbonyl compound is 0-4%, and it is not 0; (b) The carbonyl compound is chlorogenic acid; (c) The mass ratio of the second precursor to the carbonyl compound is 1:(3-10).

7. The method for preparing amorphous carbon according to claim 4, characterized in that, The preparation method of the amorphous carbon precursor includes the following steps: pre-carbonize the carbon source to obtain a pre-carbonized material, and then mix, impregnate, wash, centrifuge, and dry the pre-carbonized material with a hydrochloric acid solution to obtain the amorphous carbon precursor.

8. The method for preparing amorphous carbon according to claim 7, characterized in that, The preparation method of the amorphous carbon precursor satisfies one or more of the following conditions (a)-(f): (a) The carbon source is one or more of phenolic resin, epoxy resin, asphalt, and coal tar; (b) The temperature of the pre-carbonization is 400-800 °C; (c) The time of the pre-carbonization is 0.5-4 h; (d) The concentration of the hydrochloric acid solution is 1-3 mol / L, wherein the concentration is the molar concentration of HCl in the total volume of the hydrochloric acid solution; (e) The mass ratio of the pre-carbonized material to the hydrochloric acid solution is 1:(2-10); (f) The time of the impregnation is 12-30 h.

9. An electrochemical device, characterized in that, The negative electrode sheet of the electrochemical device includes the amorphous carbon as described in any one of claims 1-3.

10. An electronic device, characterized in that, It includes the electrochemical device as described in claim 9.

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