Negative electrode active material, negative electrode sheet, electrochemical device, and electronic apparatus

Abstract

The invention discloses a negative active material, a negative plate, an electrochemical device and electronic equipment. The negative electrode active material comprises amorphous carbon, and the amorphous carbon satisfies the following conditions: 1.00 < = A < = 1.70; wherein A = B / C; wherein B is equal to W1 * cos (theta1), and C is equal to W2 * cos (theta2); w1 and W2 are respectively half-peak widths of a 002 crystal face and a 100 crystal face in an XRD (X-Ray Diffraction) spectrum of amorphous carbon; theta1 and theta2 are respectively half of 2 theta values of a 002 crystal face and a 100 crystal face in an XRD (X-Ray Diffraction) spectrum of amorphous carbon; the amorphous carbon includes hard carbon. The electrochemical device prepared from the negative electrode active material has excellent dynamic performance, energy density and cycle performance at the same time.

Description

Technical Field

[0001] The invention relates to a negative electrode active material, a negative electrode sheet, an electrochemical device and an electronic device. Background Art

[0002] Lithium-ion batteries are currently widely used due to their high energy density, long cycle life, and good fast charging performance. However, the price of lithium salts remains high, and the cost of lithium-ion batteries is also relatively high. Sodium-ion batteries have a high abundance of sodium and their theoretical cost is much lower than that of lithium-ion batteries, making them one of the key development directions for low-cost secondary batteries.

[0003] Although sodium-ion batteries have a lower cost, their energy density and cycle performance are still inferior to those of lithium-ion batteries. At present, the positive electrode materials of sodium-ion batteries are mainly polyanion-type and layered oxide sodium-containing compounds. The polyanion type has a high cycle life, but a low energy density; the layered oxide has a higher energy density than the polyanion type, but a poor cycle life. The negative electrode material is mainly hard carbon, but the existing hard carbon materials still face problems such as low gram capacity and compaction density, many cycle side reactions, and easy sodium precipitation. How to simultaneously improve the energy density and cycle life of sodium-ion batteries has become the focus of current research in the industry. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the defect that sodium ion batteries in the prior art cannot simultaneously meet high energy density and high cycle life, and to provide a negative electrode active material, a negative electrode sheet, an electrochemical device and an electronic device. The electrochemical device (especially the sodium ion battery) prepared by using the negative electrode active material can simultaneously have high kinetic performance, high energy density and high cycle performance.

[0005] In a first aspect, the present invention provides a negative electrode active material, the negative electrode active material includes amorphous carbon, and the amorphous carbon satisfies: 1.00≤A≤1.70; wherein A=B / C;

[0006] Wherein, B=W1*cos(θ1), C=W2*cos(θ2); W1 and W2 are the half-peak widths of the 002 crystal plane and the 100 crystal plane in the XRD spectrum of the amorphous carbon, respectively; θ1 and θ2 are half of the 2θ values ​​of the 002 crystal plane and the 100 crystal plane in the XRD spectrum of the amorphous carbon, respectively;

[0007] The amorphous carbon includes hard carbon.

[0008] In a second aspect, the present invention provides a negative electrode sheet, which includes a current collector and a negative electrode material layer, and the negative electrode material layer includes the negative electrode active material as described above.

[0009] In a third aspect, the present invention provides an electrochemical device, which comprises the negative electrode sheet as described above.

[0010] In a fourth aspect, the present invention provides an electronic device comprising the electrochemical device as described above.

[0011] The positive and progressive effects of the present invention are:

[0012] The present invention provides an amorphous carbon with a specific grain structure, and the flatness of the grains is adjusted by adjusting the in-plane scale and out-of-plane scale of a single grain in the amorphous carbon. The amorphous carbon with the specific grain structure is used as a negative electrode active material of a negative electrode sheet of a sodium ion battery, and can produce a synergistic effect with ions in a battery electrolyte to improve the kinetic performance, energy density and cycle performance of the battery. DETAILED DESCRIPTION

[0013] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0014] Negative active material

[0015] In the negative electrode active material described in the first aspect of the present invention, the negative electrode active material includes amorphous carbon, and the amorphous carbon satisfies: 1.00≤A≤1.70; wherein A=B / C;

[0016] Wherein, B=W1*cos(θ1), C=W2*cos(θ2); W1 and W2 are the half-peak widths of the 002 crystal plane and the 100 crystal plane in the XRD spectrum of the amorphous carbon, respectively; θ1 and θ2 are half of the 2θ values ​​of the 002 crystal plane and the 100 crystal plane in the XRD spectrum of the amorphous carbon, respectively;

[0017] The amorphous carbon includes hard carbon.

[0018] Those skilled in the art generally understand that amorphous carbon can be hard carbon and / or soft carbon. The amorphous carbon in the present invention at least includes hard carbon, and the weight percentage of hard carbon in amorphous carbon is more than 90%.

[0019] Those skilled in the art generally understand that hard carbon is a type of amorphous carbon with low crystallinity, which is composed of grains with a graphite-like layer structure, dislocations between the grains, and a single grain is composed of multiple layers of graphite. The above parameter B is defined as the in-plane dimension, which is equivalent to the dimension along the stacking direction of the graphite layers of a single grain in the hard carbon; the above parameter C is defined as the out-of-plane dimension, which is equivalent to the dimension along the extension direction of the graphite layers of a single grain in the hard carbon; the above parameter A is defined as the flatness of the grain.

[0020] The inventors have found that when charging, sodium ions enter from the end face of the graphite sheet structure, diffuse along the direction of extension of the graphite sheet of a single grain in the hard carbon to the sodium insertion position to complete the sodium insertion process. Therefore, the out-of-plane scale C affects the diffusion distance, diffusion resistance and grain boundary structure, and the out-of-plane scale C needs to meet a certain range. If the out-of-plane scale C is too large, the diffusion distance will be too long and the diffusion resistance will be too large, which is not conducive to the dynamic performance and cycle performance; when the out-of-plane scale C is reduced, it is conducive to the improvement of the dynamic performance and cycle performance, but when the out-of-plane scale C is too small, it will cause the increase of the grain boundary structure, which is not conducive to the compaction density and gram capacity, and thus is not conducive to the energy density.

[0021] For the in-plane scale B, when B increases, the number of interlayer sodium embedding sites of the graphite flakes increases, which is beneficial to the improvement of energy density; but when B is too high, the end faces of a single grain will be too many, resulting in more side reactions, further affecting the energy density and cycle performance; when B is too low, the number of interlayer sodium embedding sites of the graphite flakes is too small, and the number of graphite flakes is also too small, which is easy to be peeled off, resulting in the destruction of the structure of a single grain, thereby causing a decrease in energy density and cycle performance.

[0022] For the grain flatness A, if A is too large or too small, the sodium ion transmission or compaction density is limited. When A is too low, it indicates that the grains in the hard carbon are flattened, such as too few graphite sheets in the grains, or the scale of the structural extension of the graphite sheets is too large, resulting in a reduction in sodium insertion sites and / or an increase in the transmission path of sodium ions, which is not conducive to energy density and cycle performance; when A is too high, it indicates that the grains in the hard carbon are elongated, such as too many graphite sheets in the grains, or the scale of the structural extension of the graphite sheets is too small, resulting in a reduction in the transmission path of sodium ions, but more end defects, resulting in a decrease in compaction density, an increase in side reactions, and a decrease in sodium insertion sites, which is not conducive to energy density and cycle performance.

[0023] The present application controls the grain flatness A in the hard carbon within a suitable range, so that the electronic device prepared from the hard carbon can have excellent dynamic performance, energy density and cycle performance.

[0024] In some optional embodiments, B satisfies: 5.00≤B≤6.00.

[0025] In some optional embodiments, C satisfies: 3.50≤C≤5.50.

[0026] In a specific embodiment, the amorphous carbon satisfies: A=1.63, B=5.90, C=3.62.

[0027] In a specific embodiment, the amorphous carbon satisfies: A=1.63, B=6.77, C=4.15.

[0028] In a specific embodiment, the amorphous carbon satisfies: A=1.00, B=5.90, C=5.90.

[0029] In a specific embodiment, the amorphous carbon satisfies: A=1.70, B=5.90, C=3.47.

[0030] In a specific embodiment, the amorphous carbon satisfies: A=1.00, B=3.62, C=3.62.

[0031] In a specific embodiment, the amorphous carbon satisfies: A=1.70, B=6.15, C=3.62.

[0032] In a specific embodiment, the amorphous carbon satisfies: A=1.23, B=5.21, C=4.25.

[0033] In a specific embodiment, the amorphous carbon satisfies: A=1.46, B=5.05, C=3.46.

[0034] In a specific embodiment, the amorphous carbon satisfies: A=1.54, B=5.00, C=3.26.

[0035] In a specific embodiment, the amorphous carbon satisfies: A=1.39, B=6.00, C=4.31.

[0036] In a specific embodiment, the amorphous carbon satisfies: A=1.47, B=4.32, C=2.93.

[0037] In a specific embodiment, the amorphous carbon satisfies: A=1.00, B=5.61, C=5.61.

[0038] In a specific embodiment, the amorphous carbon satisfies: A=1.70, B=5.83, C=3.42.

[0039] In some optional embodiments, the interlayer spacing between adjacent carbon layers in the amorphous carbon is 0.37-0.40 nm.

[0040] Wherein, the interlayer spacing refers to the interplanar spacing at the highest point of the characteristic peak height of the 002 plane in the XRD spectrum of the amorphous carbon. In this specification, the XRD spectrum is a fitting spectrum of the XRD test results, and the "highest point" refers to the result displayed by the fitting data in the XRD spectrum. Individual noise will not affect the overall trend of the spectrum. The fitting and interpretation of the XRD spectrum are conventional methods in the field.

[0041] In the present invention, the test of interlayer spacing can refer to the national standard "GB / T 24533-2019", specifically: weigh 0.15g silicon powder and 0.35g amorphous carbon in an agate mortar and grind them thoroughly for 10 minutes, put them into a sample holder and flatten them. The sample was scanned using an X-ray diffractometer (XRD) under the conditions of 20°-30° and a step size of 0.02°. The characteristic peak of the 002 face of amorphous carbon was corrected using the silicon 111 peak to obtain the characteristic peak of the 002 face after fitting, and the 2θ value corresponding to the highest peak height was read. The interplanar spacing of the 002 face was calculated by the Bragg equation, which is the interlayer spacing of adjacent carbon layers in the amorphous carbon described in this application. Among them, silicon powder is calibrated as an internal standard to make the test results more accurate.

[0042] In the present invention, the test of A, B and C can be carried out by the following method: an amorphous carbon sample is scanned by an X-ray diffractometer (XRD), the scanning width is 5°-80°, and the scanning speed is 5° / min, to obtain an amorphous carbon XRD spectrum. After deducting the baseline, two broad peaks of 14°-34° and 36°-56° can be observed, the 14°-34° broad peak is the 002 crystal plane diffraction peak, and the 36°-56° broad peak is the 100 crystal plane diffraction peak. The half-peak widths of the 002 crystal plane and the 100 crystal plane are defined as W1 and W2; half of the 2θ values ​​of the 002 crystal plane and the 100 crystal plane are defined as θ1 and θ2; B=W1*cos(θ1), C=W2*cos(θ2), and A=B / C are calculated.

[0043] In some optional embodiments, the average particle size D of the amorphous carbon is 4-8 μm.

[0044] In the present invention, the average particle size D of amorphous carbon can be tested by the following method: 50 mg of amorphous carbon to be tested is added to 5 drops of 1% ethylphenyl polyethylene glycol aqueous solution by mass fraction, and then 20 mL of deionized water is added to fully disperse it, and the particle size volume distribution is tested by a laser particle size analyzer, the particle refractive index is 2.68, the solvent refractive index is 1.33, and the light shielding degree is 5%-10%. The particle size that accounts for 50% of the particle size volume distribution from small to large is defined as the average particle size D.

[0045] Negative plate

[0046] In the negative electrode sheet described in the second aspect of the present invention, the negative electrode sheet comprises a current collector and a negative electrode material layer, and the negative electrode material layer comprises the negative electrode active material as described above.

[0047] In some optional embodiments, the mass content of the negative electrode active material in the negative electrode material layer is 90.0%-99.9%.

[0048] In the present invention, the negative electrode material layer may further include one or more of a conductive agent, a binder and a thickener.

[0049] In the embodiment of the present invention, the conductive agent can be a conductive agent conventionally used in the art for preparing negative electrodes, for example, specifically, graphite, such as natural graphite or artificial graphite; carbon-based materials, such as conductive carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black and carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives, etc. Preferably, the conductive agent is one or more of conductive carbon black, carbon nanotubes and graphene, more preferably conductive carbon black.

[0050] In an embodiment of the present invention, the binder may be a binder conventionally used in the art for preparing a negative electrode. For example, the following materials may be used as a binder: polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or various copolymers thereof, and any one thereof or a mixture of two or more thereof may be used.

[0051] In the embodiment of the present invention, the thickener is not particularly limited. The addition of the thickener can increase the system viscosity of each component in the negative electrode active material layer. Generally, a sodium carboxymethyl cellulose (CMC) solution can be selected.

[0052] In a specific embodiment of the present invention, the negative electrode material layer includes: amorphous carbon, conductive carbon black, sodium carboxymethyl cellulose and styrene-butadiene rubber (SBR).

[0053] In certain specific embodiments of the present invention, the mass ratio of amorphous carbon, conductive agent, thickener and binder in the negative electrode material layer is (90-100):1:1:2.

[0054] In the present invention, the current collector may be a current collector conventionally used for the negative electrode in the art, and may be a common current collector or a composite current collector. The current collector may use a material that does not cause chemical changes and has conductivity without restriction according to the actual needs of the electrochemical device. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon or aluminum-cadmium alloy, or copper, stainless steel material or aluminum-cadmium alloy surface-treated with carbon, nickel, titanium or silver may be used. In addition, in order to enhance the adhesion of the negative electrode active material, micro-embossing may be formed on the surface of the negative electrode current collector. The negative electrode current collector may be used in various forms, such as a film, a sheet, a foil, a mesh or a porous body.

[0055] The thickness of the current collector is, for example, 16 μm.

[0056] In the present invention, the negative electrode sheet can be prepared by conventional methods in the art. For example, the following method can be used: amorphous carbon, conductive agent, thickener and binder are mixed in a certain weight ratio, and a solvent is added to mix evenly to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on the current collector; and then the negative electrode sheet is prepared through drying, rolling, cutting and other processes.

[0057] Electrochemical Devices

[0058] In the electrochemical device described in the third aspect of the present invention, the electrochemical device comprises the negative electrode sheet as described above.

[0059] In the present invention, the electrochemical device may generally be a conventional device in the art containing the negative electrode sheet as described above, such as a secondary battery, a capacitor, and the like.

[0060] Optionally, the electrochemical device is a sodium ion battery.

[0061] In a specific embodiment of the present invention, the sodium ion battery includes the negative electrode sheet, the positive electrode sheet, the isolation membrane and the electrolyte.

[0062] In some embodiments, the positive electrode sheet is prepared by coating a positive electrode active material including a positive electrode active material on a positive electrode current collector, and a binder, a conductive agent, and a thickener may be further added as needed.

[0063] Taking a sodium ion battery as an example, the sodium positive electrode active material may be a sodium ion material such as a layered oxide, a Prussian blue compound or a polyanion compound, which is not limited here.

[0064] The conductive agent in the positive electrode active material can be a conductive agent conventionally used for the positive electrode in the art. For example, the following can be used: graphite, such as natural graphite or artificial graphite; amorphous carbon materials, such as conductive carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black and carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives, etc. Preferably, the conductive agent is one or more of conductive carbon black, carbon nanotubes and graphene, more preferably conductive carbon black.

[0065] For the binder in the positive electrode active material, it can be a binder conventionally used for the positive electrode in the art. For example, it can include polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or its various copolymers, and any one or a mixture of two or more thereof can be used.

[0066] In the embodiment of the present invention, there is no particular limitation on the thickener used for the positive electrode. The addition of the thickener can increase the system viscosity of each component in the positive electrode active material layer. Generally, a sodium carboxymethyl cellulose (CMC) solution can be selected.

[0067] For the positive electrode current collector, it can be a current collector conventionally used for the positive electrode in the art, and can be a common current collector or a composite current collector. The positive electrode current collector can use materials that do not cause chemical changes and have high conductivity without restriction according to the actual needs of the electrochemical device. For example, stainless steel, aluminum, nickel, titanium or calcined carbon can be generally used, or aluminum or stainless steel materials surface-treated with carbon, nickel, titanium, silver, etc. In order to enhance the adhesion of the positive electrode active material, micro-embossing can be formed on the surface of the positive electrode current collector. The positive electrode current collector can be used in various forms, such as a film, a sheet, a foil, a mesh or a porous body.

[0068] In some embodiments, the isolation membrane can be a polypropylene isolation membrane or a polyethylene isolation membrane.

[0069] In a specific embodiment of the present invention, the isolation membrane is a polyethylene membrane coated with a ceramic coating on both sides.

[0070] Wherein, the thickness of the ceramic coating may be 2 μm.

[0071] Wherein, the thickness of the isolation film may be 9 μm.

[0072] In some embodiments, the electrolyte may be an electrolyte conventionally used for batteries in the art, generally including a non-aqueous solvent, a sodium salt, and an additive.

[0073] Wherein, the non-aqueous solvent can be a conventional non-aqueous solvent in the art, preferably an ester solvent, and more preferably a carbonate solvent. The carbonate solvent can be selected from one or more of ethylene 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).

[0074] Among them, the additive can be selected from one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), dithiothreitol (DTD), vinylene sulfate, 1,3-propane sultone (PS), allyl sultone and 1,4-butane sultone.

[0075] The sodium salt may be a conventional sodium salt in the art, such as NaPF 6 .

[0076] In certain specific embodiments of the present invention, the electrolyte includes ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and propylene carbonate (PC), and the volume ratio of the ethylene carbonate, the ethyl methyl carbonate, the diethyl carbonate and the propylene carbonate is, for example, 1:1:1:1.

[0077] In a specific embodiment of the present invention, the concentration of the electrolyte is 1 mol / L.

[0078] In the present invention, the preparation method of the sodium ion battery can be a conventional preparation method in the art, which can be a battery cell obtained by winding the positive electrode sheet, the negative electrode sheet and the isolation film, and then packaging them in a packaging shell and injecting the electrolyte; or it can be a battery cell obtained by stacking the negative electrode sheet, the isolation film, the positive electrode sheet and the isolation film in this order, and then packaging them in a packaging shell and injecting the electrolyte.

[0079] On the basis of being in accordance with the common sense in the art, the above-mentioned optional conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0080] Electronic devices

[0081] In the electronic device described in the fourth aspect of the present invention, the electronic device includes the electrochemical device described above.

[0082] In the present invention, the electronic device described in 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 and satellites, energy storage systems and backup power supplies, etc.

[0083] Examples 1-13 and Comparative Examples 1-6

[0084] Preparation of amorphous carbon

[0085] The amorphous carbon in Examples 1-13 and Comparative Examples 1-6 is hard carbon, and the preparation method thereof adopts the following steps:

[0086] Wash coconut shells with deionized water for more than 3 times, then filter, dry and grind to obtain a coconut shell precursor; heat the coconut shell precursor to 200-600°C at a heating rate of 1-10°C / min in a nitrogen atmosphere, and keep it warm for 2-10 hours to obtain a carbon precursor; wash the carbon precursor with nitric acid / hydrochloric acid / hydrofluoric acid (volume ratio of 1:1:1) for 3 times, then wash with deionized water for more than 5 times, and dry to obtain an amorphous carbon precursor; heat the amorphous carbon precursor to 1000-1500°C at 1-10°C / min in a nitrogen atmosphere, and keep it warm for 2-10 hours; then grind it to the required particle size to obtain amorphous carbon, which is hard carbon.

[0087] The relevant parameters of the amorphous carbon in Examples 1-13 and Comparative Examples 1-6 are listed in Table 1 below.

[0088] Amorphous carbons with different grain structures in Examples 1-13 and Comparative Examples 1-6 were prepared by adjusting the specific parameters of the above process. The relevant parameters of the amorphous carbons in Examples 1-13 and Comparative Examples 1-6 are listed in Table 1 below.

[0089] Among them, the parameters A, B and C of the amorphous carbon of each embodiment and comparative example can be tested by the following method: the amorphous carbon sample is scanned by an X-ray diffractometer (XRD), the scanning width is 5°-80°, and the scanning speed is 5° / min to obtain the amorphous carbon XRD spectrum. After deducting the baseline, two broad peaks of 14°-34° and 36°-56° can be observed, the 14°-34° broad peak is the 002 crystal plane diffraction peak, and the 36°-56° broad peak is the 100 crystal plane diffraction peak. The half-peak widths of the 002 crystal plane and the 100 crystal plane are defined as W1 and W2; half of the 2θ values ​​of the 002 crystal plane and the 100 crystal plane are defined as θ1 and θ2; B=W1*cos(θ1), C=W2*cos(θ2), and A=B / C are calculated.

[0090] Among them, the test of the average particle size D of the amorphous carbon in each embodiment and comparative example can be carried out by the following method: take 50 mg of the amorphous carbon to be tested, add 5 drops of 1% mass fraction of ethylphenyl polyethylene glycol aqueous solution, and then add 20 mL of deionized water to fully disperse, and use a laser particle size analyzer to test its particle size volume distribution, the particle refractive index is 2.68, the solvent refractive index is 1.33, and the light shielding degree is 5%-10%. The particle size that accounts for 50% of the particle size volume distribution from small to large is defined as the average particle size D.

[0091] Among them, the test method for the interlayer spacing of adjacent carbon layers in amorphous carbon refers to the national standard "GB / T24533-2019", specifically: weigh 0.15g of silicon powder and 0.35g of amorphous carbon in an agate mortar and grind them thoroughly for 10 minutes, and put them into the sample holder and flatten them. The sample was scanned using an X-ray diffractometer (XRD) under the conditions of 20°-30° and a step size of 0.02°. The characteristic peak of the 002 face of amorphous carbon was corrected using the silicon 111 peak to obtain the characteristic peak of the 002 face after fitting, and the 2θ value corresponding to the highest peak height was read. The interplanar spacing of the 002 face was calculated by the Bragg equation, which is the interlayer spacing of adjacent carbon layers in amorphous carbon described in this application.

[0092] Preparation of negative electrode

[0093] The above-mentioned amorphous carbon is used as the negative electrode active material to prepare the negative electrode sheet. Specifically: the above-mentioned amorphous carbon, conductive carbon black (Super P), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 100:1:1:2, deionized water is added, and the mixture is mixed evenly to obtain a negative electrode slurry; the negative electrode slurry is evenly coated on a 16μm aluminum foil. After drying, rolling, cutting and other processes, a negative electrode sheet is prepared.

[0094] Table 1

[0095]

[0096] Effect Example 1

[0097] Preparation of sodium ion batteries:

[0098] Preparation of positive electrode sheet: O3 type layered positive electrode material NaNi 0.34 Fe 0.33 Mn 0.33 O 2, conductive carbon black (Super P), carbon nanotubes (CNT), and binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of (90-100): 2:1:2, and a solvent N-methylpyrrolidone (NMP) is added and stirred to make the mixture uniform to obtain a positive electrode slurry; the positive electrode slurry is uniformly coated on a 16μm aluminum foil current collector. After drying, rolling, cutting and other processes, a positive electrode sheet is prepared.

[0099] Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and propylene carbonate (PC) were uniformly mixed in a volume ratio of 1:1:1:1, and then dried high-purity sodium salt NaPF 6 Dissolve in the above-mentioned mixed solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0100] Preparation of the diaphragm: The diaphragm is a 9 μm polyethylene diaphragm coated on both sides with a ceramic coating with a thickness of 2 μm.

[0101] Preparation of sodium ion battery: The prepared positive electrode sheet, separator, negative electrode sheet of Examples 1-13 and Comparative Examples 1-6 and electrolyte are assembled in sequence, so that the positive electrode sheet, separator, negative electrode sheet of Examples 1-13 and Comparative Examples 1-6 and separator are combined alternately, and a soft-pack battery with a capacity of 1Ah is obtained through formation.

[0102] The performance of the sodium ion battery prepared according to the above method was tested as follows:

[0103] (1) Test method for rate retention of sodium ion battery: At a constant temperature of 25°C, charge to 4.0V at 1 / 3C rate with constant current and constant voltage (constant voltage cutoff current is 0.05C), then discharge to 1.5V at 1 / 3C rate with constant current, cycle 3 times, and the capacity of the last cycle is 1 / 3C capacity. Charge to 4.0V at 1 / 3C rate with constant current and constant voltage (constant voltage cutoff current is 0.05C), then discharge to 1.5V at 2C rate with constant current, cycle 3 times, and the capacity of the last cycle is 2C capacity. The ratio of 2C capacity to 1 / 3C capacity is recorded as the rate retention rate.

[0104] (2) Test method for energy density of sodium ion battery: At a constant temperature of 25°C, charge to 4.0V at a constant current and voltage of 1 / 3C (the constant voltage cut-off current is 0.05C), and then discharge to 1.5V at a constant current of 1 / 3C to obtain 1 / 3C energy. Repeat the charge and discharge process 3 times, and the last cycle of 0.33C energy is recorded as the cell energy; weigh the cell weight with a balance, and the ratio of 0.33C energy to the cell weight is the energy density.

[0105] (3) Test method for sodium ion battery cycle retention rate: Under a constant temperature environment of 25°C, charge to 4.0V at a constant current and voltage of 0.5C (constant voltage cut-off current is 0.05C), and then discharge to 1.5V at a constant current of 1C. This is one cycle. Perform 1000 cycles in this process. The ratio of the discharge capacity at the 1000th cycle to the discharge capacity at the first cycle is recorded as the cycle retention rate.

[0106] The above test results are listed in Table 2.

[0107] Table 2

[0108] Energy density (Wh / kg) Ratio retention rate Cycle retention rate Example 1 135.20 90.50％ 92.30％ Example 2 119.20 83.20％ 82.10％ Example 3 120.10 82.30％ 83.30％ Example 4 119.80 82.10％ 82.50％ Example 5 120.50 82.20％ 85.40％ Example 6 134.90 90.10％ 91.80％ Example 7 134.50 90.30％ 92.00％ Example 8 128.30 87.90％ 89.10％ Example 9 126.00 88.20％ 89.70％ Example 10 126.30 86.40％ 88.90％ Embodiment 11 124.20 84.10％ 90.00％ Example 12 127.30 89.40％ 87.60％ Example 13 129.10 86.50％ 88.30％ Comparative Example 1 116.40 80.10％ 83.40％ Comparative Example 2 117.50 79.40％ 84.10％ Comparative Example 3 110.20 78.90％ 82.00％ Comparative Example 4 112.60 79.10％ 78.60％ Comparative Example 5 104.50 72.80％ 75.60％ Comparative Example 6 106.30 69.10％ 67.90％

[0109] It can be seen from the data in Table 1 and Table 2 that the sodium ion battery prepared from the negative electrode sheets of Examples 1-13 has a rate retention rate of not less than 82%, an energy density of not less than 119Wh / kg, and a cycle retention rate of not less than 80%, indicating that it has excellent kinetic performance, energy density and cycle performance.

[0110] According to the data results of Comparative Example 1, Comparative Example 2 and Example 1, C of Comparative Example 1, Comparative Example 2 and Example 1 is the same, and A being too large or too small will significantly reduce the kinetic performance, energy density and cycle performance of the battery. The difference between Comparative Examples 3-6 and the Example is that A of Comparative Examples 3-6 is not in the range of 1-1.7, and its kinetic performance, energy density and cycle performance are poor, especially in Comparative Example 6, A is only 0.85, so that its rate retention rate is only 69.10% and the cycle retention rate is only 67.90%.

[0111] According to the data results of Example 1, Example 2 and Example 3, if the range of C is between 3.5-5.5, it is more beneficial to the kinetic performance, energy density and cycle performance of the battery.

[0112] According to the data results of Example 1 and Example 4, if the range of B is between 5 and 6, it is more beneficial to the battery kinetics performance, energy density and cycle performance.

[0113] According to the data results of Example 1 and Example 5, if the interlayer spacing is in the range of 0.37-0.40 nm, it is more beneficial to the kinetic performance, energy density and cycle performance of the battery.

[0114] According to the data results of Example 1, Example 12 and Example 13, if the range of D is between 4-8 μm, it is more beneficial to the electrical performance of the battery. In Example 1, Example 12 and Example 13, D is between 4-8 μm, and the rate retention rate is not less than 86.5%, the energy density is not less than 127.3 Wh / kg, and the cycle retention rate is not less than 87.6%.

[0115] Although the specific embodiments of the present invention are described above, it should be understood by those skilled in the art that this is only for illustration and the protection scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but these changes and modifications all fall within the protection scope of the present invention.

Claims

1. A negative electrode active material, It is characterized in that The negative electrode active material includes amorphous carbon, and the amorphous carbon satisfies: 1.00≤A≤1.70; wherein A=B / C; Wherein, B=W1*cos(θ1), C=W2*cos(θ2); W1 and W2 are the half-peak widths of the 002 crystal plane and the 100 crystal plane in the XRD spectrum of the amorphous carbon, respectively; θ1 and θ2 are half of the 2θ values ​​of the 002 crystal plane and the 100 crystal plane in the XRD spectrum of the amorphous carbon, respectively; The amorphous carbon includes hard carbon.

2. The negative electrode active material according to claim 1, It is characterized in that The B satisfies: 5.00≤B≤6.

00.

3. The negative electrode active material according to claim 1, It is characterized in that The C satisfies: 3.50≤C≤5.

50.

4. The negative electrode active material according to any one of claims 1 to 3, It is characterized in that The interlayer spacing between adjacent carbon layers in the amorphous carbon is 0.37-0.40 nm.

5. The negative electrode active material according to claim 1, It is characterized in that The average particle size D of the amorphous carbon is 4-8 μm.

6. A negative electrode sheet comprising a current collector and a negative electrode material layer, It is characterized in that The negative electrode material layer includes the negative electrode active material according to any one of claims 1 to 5.

7. The negative electrode sheet according to claim 6, It is characterized in that The mass content of the negative electrode active material in the negative electrode material layer is 90.0%-99.9%.

8. An electrochemical device, It is characterized in that It comprises the negative electrode sheet as claimed in claim 6 or 7.

9. The electrochemical device according to claim 8, It is characterized in that The electrochemical device is a sodium ion battery.

10. An electronic device, It is characterized in that It comprises the electrochemical device as claimed in claim 8 or 9.

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