Negative electrode material, electrochemical device, and electronic device

Abstract

The application discloses a negative electrode material, an electrochemical device and an electronic equipment. The negative electrode material comprises amorphous carbon and a carbon-based additive; wherein the amorphous carbon comprises hard carbon, and a dimensional matching degree of the amorphous carbon and the carbon-based additive is W, and the W satisfies 3.5<=W<=4.5; the W is calculated according to the following formula: W=2(d90-d10) / d50+D; wherein d10, d50 and d90 represent particle sizes of the amorphous carbon; and D represents a dimension of the carbon-based additive, and D is 0, 1, 2 or 3. The electrochemical device containing the negative electrode material has high energy density and excellent rate performance.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of negative materials, electrochemical device and electronic equipment. BACKGROUND

[0002] Sodium-ion battery has potential application value in two-wheeled vehicle, low-speed vehicle, energy storage and other fields due to its relatively low cost compared with lithium-ion battery and relatively high energy density compared with lead-acid battery. However, the sodium-ion battery is relatively low in maturity at present, and there is still a large room for improvement in energy density, rate performance and other aspects.

[0003] The main negative electrode material of the currently commercialized sodium-ion battery is hard carbon material, which has the advantages of high specific capacity, low cost and good low-temperature performance. However, the hard carbon material has a large number of pore structures and a large interlayer spacing, resulting in a low compaction density. In addition, the hard carbon mainly relies on pore filling to complete sodium storage at low voltage, which has a large risk of sodium precipitation, thereby resulting in a low energy density and poor rate performance of the hard carbon when used as a negative electrode material of sodium-ion battery. Therefore, how to improve the compaction density and kinetic performance of the hard carbon material to improve its energy density and rate performance has become one of the key work in the development of hard carbon negative electrode. SUMMARY

[0004] In order to solve the defects of low energy density and poor rate performance of the negative electrode material for sodium-ion battery in the prior art, the present application provides a negative electrode material, an electrochemical device and an electronic equipment. The electrochemical device containing the negative electrode material of the present application has high energy density and excellent rate performance.

[0005] In a first aspect, the present application provides a negative electrode material, which comprises amorphous carbon and carbon-based additive; wherein the amorphous carbon comprises hard carbon, and the dimensional matching degree W of the amorphous carbon and the carbon-based additive satisfies: 3.5≤W≤4.5; wherein the W is calculated according to the following formula: W=2(d90-d10) / d50+D.

[0006] Wherein, d10, d50 and d90 represent the particle size of the amorphous carbon.

[0007] D represents the dimension of the carbon-based additive, and D is 0, 1, 2 or 3.

[0008] In a second aspect, the present application provides an electrochemical device, which comprises a negative electrode sheet, the negative electrode sheet comprises a current collector layer and a negative electrode material layer on the current collector layer, and the negative electrode material layer comprises the negative electrode material as described above.

[0009] In a third aspect, the present application provides an electronic equipment, which comprises the electrochemical device as described above.

[0010] The positive progress effect of the present application is that:

[0011] The present application provides a negative electrode material with a specific dimensional matching degree W, by controlling the particle size distribution of amorphous carbon and the dimension of carbon-based additives in the negative electrode material, the carbon-based additives form a uniform and stable three-dimensional electron and ion conduction network on the surface of amorphous carbon and between particles; further, by adjusting the ratio of the average particle size d50' of the carbon-based additives and the d50 of the amorphous carbon, the energy density and rate performance of the electrochemical device are significantly improved. DETAILED DESCRIPTION

[0012] The present application is further illustrated by the following examples, but the present application is not limited to the scope of the examples. The experimental methods in the following examples without specific conditions are selected according to conventional methods and conditions, or according to the instructions of the goods.

[0013] Negative electrode material

[0014] In the negative electrode material of the first aspect of the present application: the negative electrode material comprises amorphous carbon and carbon-based additives; wherein the amorphous carbon contains hard carbon, the dimensional matching degree of the amorphous carbon and the carbon-based additives is W, and the W satisfies: 3.5≤W≤4.5; wherein the W is calculated as follows: W=2(d90-d10) / d50+D;

[0015] Wherein d10, d50 and d90 represent the particle size of the amorphous carbon;

[0016] D represents the dimension of the carbon-based additives, D is 0, 1, 2 or 3.

[0017] In the present application, the maximum particle size of the amorphous carbon particles with a volume fraction of 10% from small to large is denoted as d10, the maximum particle size of the amorphous carbon particles with a volume fraction of 50% from small to large is denoted as d50, and the maximum particle size of the amorphous carbon particles with a volume fraction of 90% from small to large is denoted as d90. The d10, d50 and d90 of the amorphous carbon refer to the d10, d50 and d90 of the amorphous whole. The d10, d50 and d90 of the amorphous carbon are measured by the following method: 50mg of sample is added into 5 drops of 1% ethyl phenyl polyethylene glycol aqueous solution, and then 20mL of deionized water is added for ultrasonic dispersion, and then a laser particle size analyzer is used to test the particle size volume distribution, the particle refractive index is 2.68, the solvent refractive index is 1.33, and the obscuration is 5%-10%.

[0018] In the present application, the d50' of the carbon-based additive is measured by the following method: the carbon-based additive particles are placed under a transmission electron microscope for observation, more than 100 particles in an arbitrary selected area are counted, the size of the longest direction of each particle is counted, and the average value is calculated to obtain the average diameter, i.e. d50'.

[0019] The difference (d90-d10) between d90 and d10 can be used to evaluate the difference in particle size distribution of most amorphous carbon (mainly hard carbon) particles, and (d90-d10) / d50 can be used to evaluate the width of the particle size distribution of most amorphous carbon particles. When the width of the particle size distribution is different, the packing mode of the amorphous carbon particles in the pole piece, the porosity and the pore size will also be different.

[0020] As is generally known by those skilled in the art, amorphous carbon includes hard carbon and / or soft carbon, and the amorphous carbon in the present application at least contains hard carbon, and optionally, the weight percentage of hard carbon in the amorphous carbon is more than 90%, which refers to the weight percentage of hard carbon in the whole amorphous carbon.

[0021] In the present application, the amount of the carbon-based additive can be 0.1%-12%.

[0022] In an optional embodiment of the present application, the amount of the carbon-based additive is 0.1%-12%, more preferably 0.1%-10%, for example 0.5%, 1.0% or 2.0%, and the percentage refers to the weight percentage of the carbon-based additive in the amorphous carbon.

[0023] In some optional embodiments, the negative electrode material also satisfies 0.001≤d50' / d50≤0.12, preferably 0.001≤d50' / d50≤0.1, wherein d50' represents the average particle size of the carbon-based additive.

[0024] The carbon-based additive of the present application has two main effects: firstly, it fills the pores between amorphous carbon particles to increase the compaction density of the electrode sheet, thereby improving the energy density of the battery (sodium ion battery); secondly, it serves to connect amorphous carbon particles, improving the electrical conductivity of the electrode sheet, thereby improving the rate performance of the electrochemical device, such as a sodium ion battery. Selecting a carbon-based additive that matches the amorphous carbon particles helps to simultaneously improve the energy density and rate performance of the electrochemical device. The inventors have found that when (d90-d10) / d50 is small, the particle size distribution of the amorphous carbon particles is narrow, there are a large number of large-sized pores in the amorphous carbon particles during the stacking process, and most of the amorphous carbon particles are in point contact with each other, resulting in poor compaction density and electrical conductivity. By filling the pores with high-dimensional carbon-based additives, and further selecting carbon-based additives with large particle sizes, the energy density and rate performance can be improved. When (d90-d10) / d50 is large, the particle size distribution of the amorphous carbon particles is wide, and small particles will fill the pores between large particles during the stacking process. At this time, there are a large number of small-sized pores. By using low-dimensional carbon-based additives, the pores can be more efficiently filled, and further by selecting carbon-based additives with small particle sizes, the energy density and rate performance can be improved. When (d90-d10) / d50 is moderate, the particle size distribution of the amorphous carbon particles is moderate, and the pores of the amorphous carbon particles are moderate during the stacking process. At this time, if high-dimensional and large-sized carbon-based additives are used, they cannot fill the pores. If low-dimensional and small-sized carbon-based additives are used, the electron transport distance will increase, so carbon-based additives with appropriate dimensions and particle sizes need to be matched.

[0025] When the negative electrode material satisfies 3.5≤2(d90-d10) / d50+D≤4.5 and 0.001≤d50’ / d50≤0.1, the dimensions and particle sizes of the carbon-based additives match the amorphous carbon particles, which can obtain the best packing density and conductive network, and help to obtain the optimal energy density and rate performance of the electrochemical device.

[0026] As known to those skilled in the art, carbon-based additives can be classified as 0-dimensional, 1-dimensional, 2-dimensional and 3-dimensional according to the degree of constraint in the nanoscale.

[0027] When the dimension D of the carbon-based additive is 0, the carbon-based additive can be selected from one or more of conductive carbon black, carbon quantum dots and fullerenes.

[0028] When the dimension D of the carbon-based additive is 1, the carbon-based additive can be selected from one or more of carbon nanotubes, carbon fibers and carbon nanowires.

[0029] When the dimension D of the carbon-based additive is 2, the carbon-based additive can include thin-layer graphene, wherein the thin-layer graphene is graphene with a layer number of 5 or less.

[0030] When the dimension D of the carbon-based additive is 3, the carbon-based additive can be selected from one or more of artificial graphite, natural graphite, multi-layer graphene, and mesocarbon microbeads, wherein the multi-layer graphene is graphene with a layer number of 5 or more.

[0031] It should be noted that in the present application, two or more dimensions of carbon-based additives can be used together with amorphous carbon according to actual needs. When the carbon-based additive is a mixture of two or more dimensions of carbon-based additives, the dimension D is the dimension of the carbon-based additive with the highest weight percentage. For example, the carbon-based additive is a mixture of two dimensions of carbon-based additives, and the dimension D is the dimension of the carbon-based additive with a weight percentage of more than 50%. That is, in the first aspect of the present application, when D = 0, it does not necessarily mean that all carbon-based additives in the negative electrode material are 0-dimensional carbon-based additives, but also means that 0-dimensional carbon-based additives are the dominant component in terms of weight percentage. When D = 1, D = 2, or D = 3, the situation is similar.

[0032] In some optional embodiments, the negative electrode material comprises: amorphous carbon and conductive carbon black; and the negative electrode material satisfies: 0.001≤d50’ / d50≤0.05.

[0033] In a specific embodiment, the negative electrode material comprises: amorphous carbon and conductive carbon black; the dimension matching degree W of the amorphous carbon and the conductive carbon black is 3.76, and the d50’ / d50 is 0.003.

[0034] In a specific embodiment, the negative electrode material comprises: amorphous carbon and conductive carbon black; the dimension matching degree W of the amorphous carbon and the conductive carbon black is 3.50, and the d50’ / d50 is 0.003.

[0035] In a specific embodiment, the negative electrode material comprises: amorphous carbon and conductive carbon black; the dimension matching degree W of the amorphous carbon and the conductive carbon black is 4.50, and the d50’ / d50 is 0.003.

[0036] In some optional embodiments, the negative electrode material comprises: amorphous carbon and carbon nanotubes; and the negative electrode material satisfies: 0.001≤d50’ / d50≤0.12, preferably 0.001≤d50’ / d50≤0.1.

[0037] In one embodiment, the negative electrode material comprises: amorphous carbon and carbon nanotubes; the dimensional matching degree W of the amorphous carbon and the carbon nanotubes is 3.5, and the d50' / d50 is 0.003.

[0038] In one embodiment, the negative electrode material comprises: amorphous carbon and carbon nanotubes; the dimensional matching degree W of the amorphous carbon and the carbon nanotubes is 4.16, and the d50' / d50 is 0.001.

[0039] In one embodiment, the negative electrode material comprises: amorphous carbon and carbon nanotubes; the dimensional matching degree W of the amorphous carbon and the carbon nanotubes is 4.16, and the d50' / d50 is 0.100.

[0040] In one embodiment, the negative electrode material comprises: amorphous carbon and carbon nanotubes; the dimensional matching degree W of the amorphous carbon and the carbon nanotubes is 4.16, and the d50' / d50 is 0.0007.

[0041] In one embodiment, the negative electrode material comprises: amorphous carbon and carbon nanotubes; the dimensional matching degree W of the amorphous carbon and the carbon nanotubes is 4.16, and the d50' / d50 is 0.120.

[0042] In one embodiment, the negative electrode material comprises: amorphous carbon and carbon nanotubes; the dimensional matching degree W of the amorphous carbon and the carbon nanotubes is 4.50, and the d50' / d50 is 0.003.

[0043] In some alternative embodiments, the negative electrode material comprises: amorphous carbon and thin-layer graphene, wherein the number of layers of the thin-layer graphene is 3; the negative electrode material satisfies: 0.001≤d50' / d50≤0.02.

[0044] In one embodiment, the negative electrode material comprises: amorphous carbon and thin-layer graphene, wherein the number of layers of the thin-layer graphene is 3; the dimensional matching degree W of the amorphous carbon and the thin-layer graphene is 3.50, and the d50' / d50 is 0.003.

[0045] In one embodiment, the negative electrode material comprises: amorphous carbon and thin-layer graphene, wherein the number of layers of the thin-layer graphene is 3; the dimensional matching degree W of the amorphous carbon and the thin-layer graphene is 3.66, and the d50' / d50 is 0.014.

[0046] In a specific embodiment, the negative electrode material comprises: amorphous carbon and thin-layer graphene, wherein the number of layers of the thin-layer graphene is 3; the dimensional matching degree W of the amorphous carbon and the thin-layer graphene is 4.50, and the d50’ / d50 is 0.003.

[0047] In some alternative embodiments, the negative electrode material comprises: amorphous carbon and artificial graphene; the negative electrode material satisfies: 0.001≤d50’ / d50≤0.07.

[0048] In a specific embodiment, the negative electrode material comprises: amorphous carbon and artificial graphene; the dimensional matching degree W of the amorphous carbon and the artificial graphene is 3.50, and the d50’ / d50 is 0.003.

[0049] In a specific embodiment, the negative electrode material comprises: amorphous carbon and artificial graphene; the dimensional matching degree W of the amorphous carbon and the artificial graphene is 4.26, and the d50’ / d50 is 0.061.

[0050] In a specific embodiment, the negative electrode material comprises: amorphous carbon and artificial graphene; the dimensional matching degree W of the amorphous carbon and the artificial graphene is 4.50, and the d50’ / d50 is 0.003.

[0051] Electrochemical device

[0052] In the electrochemical device according to the third aspect of the present application, the negative electrode sheet comprises a current collector layer and a negative electrode material layer on the current collector layer, and the negative electrode material layer comprises the negative electrode material as described above.

[0053] In the present application, the electrochemical device can generally be a device of the prior art containing a negative electrode sheet as described above, such as a secondary battery, a capacitor, etc.

[0054] In the present application, the content of the negative electrode material in the negative electrode material layer can be 80.0wt%-99.9wt%, and the percentage is the weight percentage of the negative electrode material in the negative electrode material layer.

[0055] Optionally, the negative electrode material layer further comprises a binder and a thickening agent.

[0056] The thickening agent is not particularly limited, and the addition of the thickening agent can improve the system viscosity of each component in the negative electrode active material layer, and a sodium carboxymethyl cellulose (CMC) solution can be generally selected.

[0057] The binder can be a binder conventionally used in the art for preparing a negative electrode, for example, one or more of SBR, PAA, CMC, and PVDF can be used as the binder.

[0058] In an embodiment of the present application, the negative electrode material layer includes: amorphous carbon, a carbon-based additive, a thickening agent, and a binder.

[0059] In an embodiment of the present application, the negative electrode material layer includes: amorphous carbon, a carbon-based additive, sodium carboxymethyl cellulose, and styrene butadiene rubber.

[0060] In an embodiment of the present application, the current collector used in the current collector layer can be a general current collector or a composite current collector according to the actual needs of the electrochemical device. The negative electrode current collector can use, without limitation, a material that does not cause a chemical change and has electrical conductivity. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or an aluminum-cadmium alloy, or copper, stainless steel material, or an aluminum-cadmium alloy surface-treated with carbon, nickel, titanium, or silver can be used. 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 a film, a sheet, a foil, a mesh, or a porous body.

[0061] The thickness of the current collector is, for example, 16 μm.

[0062] In the present application, the negative electrode sheet can be prepared using a method conventionally used in the art. For example, the following method can be used: amorphous carbon, a carbon-based additive, a thickening agent, and a binder are mixed in a certain mass ratio, a solvent is added, and then mixed uniformly to obtain a negative electrode slurry; the negative electrode slurry is uniformly coated on a current collector; and then, drying, rolling, sheet cutting, and the like are performed to prepare a negative electrode sheet.

[0063] Alternatively, in an embodiment of the present application, the electrochemical device is a sodium ion battery, and the sodium ion battery includes the negative electrode sheet, a positive electrode sheet, a separator, and an electrolyte.

[0064] In some embodiments of the present application, a 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 thickening agent can be further added as needed.

[0065] For the positive electrode current collector, a material that does not cause a chemical change and has high electrical conductivity can be used without limitation according to the actual needs of the electrochemical device. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon, or aluminum or stainless steel material surface-treated with carbon, nickel, titanium, silver, or the like can be generally used. 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.

[0066] In some embodiments of the present application, the positive active material can be a sodium ion material such as a layered oxide, a Prussian blue compound or a polyanion compound, and further, the general formula of the layered oxide can be Na x [MFeMn]O2, M is selected from at least one of Cu, Ni, Li, Mg, Al, Zn, Ti, Zr and Sn, and optionally x≤0.7.

[0067] In a specific embodiment of the present application, the positive active material has a molecular formula of NaNi 0.34 Fe 0.33 Mn 0.33 O2.

[0068] In some embodiments, the separator film can be a polypropylene separator film or a polyethylene separator film.

[0069] In some embodiments, the thickness of the separator film can be 9 μm.

[0070] In a preferred embodiment, the separator film is a 9 μm polyethylene separator film coated with a ceramic coating on both sides, and the thickness of the ceramic coating is 2 μm.

[0071] In some embodiments, the electrolyte can be a conventional electrolyte used in the art for batteries, and generally includes a non-aqueous solvent, a sodium salt and an additive.

[0072] In some embodiments, the non-aqueous solvent can be a conventional non-aqueous solvent in the art, and preferably an ester solvent, and more preferably a carbonate ester solvent. The carbonate ester solvent can be 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).

[0073] In some embodiments, the additive can be one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), vinylene sulfide, 1,3-propane sultone (PS), propylene sulfonic acid lactone and 1,4-butane sulfonic acid lactone.

[0074] In some embodiments, the sodium salt can be a conventional sodium salt in the art, such as NaPF6.

[0075] In the present application, the preparation method of the sodium ion battery can be a conventional preparation method in the art, which can be that the positive electrode sheet, the negative electrode sheet and the separator film are wound to obtain an electric core, and then the electric core is packaged by a packaging shell and injected with the electrolyte; or the negative electrode sheet, the separator film, the positive electrode sheet and the separator film are sequentially stacked in the order to obtain an electric core, and then the electric core is packaged by a packaging shell and injected with the electrolyte.

[0076] Electronic device

[0077] In the electronic device of the fourth aspect of the present application, the above-mentioned electrochemical device is included.

[0078] In the present application, the electronic device of the present application can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a notebook computer, a video recorder, a portable printer / copier, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system and a backup power supply, etc.

[0079] On the basis of common sense in the art, the above-mentioned optional conditions can be arbitrarily combined, i.e. to obtain each preferred example of the present application.

[0080] The reagents and raw materials used in the present application are conventional reagents and raw materials, which are commercially available.

[0081] Examples 1-16 and Comparative Examples 1-4

[0082] Preparation of amorphous carbon

[0083] The amorphous carbon in Examples 1-16 and Comparative Examples 1-4 is hard carbon, and the preparation method thereof adopts the following steps:

[0084] The coconut shell is washed 3 times with a mixed solution of water and ethanol (volume ratio 1:1), and then filtered, dried and ground into powder to obtain a coconut shell precursor; the coconut shell precursor is placed in a crucible and heated to 200-600℃ at a rate of 1-10℃ / min under a nitrogen atmosphere, and kept for 2-10h to obtain a carbon precursor; the carbon precursor is washed 3 times with nitric acid / hydrochloric acid / hydrofluoric acid (volume ratio 1:1:1), and then washed with deionized water for more than 5 times, and dried to obtain an amorphous carbon precursor; the amorphous carbon precursor is heated to 1000-1500℃ at a rate of 1-10℃ / min under a nitrogen atmosphere, and kept for 2-10h; and then ball-milled to the desired particle size to obtain amorphous carbon, and the prepared amorphous carbon is hard carbon.

[0085] By adjusting the above-mentioned process parameters, amorphous carbon with different particle size distributions in Examples 1-16 and Comparative Examples 1-4 is prepared.

[0086] The carbon-based additives in Examples 1-16 and Comparative Examples 1-4 are all commercially available, such as those available from Cabot, Timcal, or Tianmi, and have little difference in performance, which does not affect the realization of the purposes of the present application.

[0087] Test of particle size distribution of amorphous carbon and carbon-based additives

[0088] Test method of d10, d50 and d90 of amorphous carbon: 50 mg of sample was added to 5 drops of 1% ethylphenyl polyethylene glycol aqueous solution, and then 20 mL of deionized water was added and ultrasonicated to fully disperse. The particle size volume distribution was tested by a laser particle size analyzer, the particle refractive index was 2.68, the solvent refractive index was 1.33, and the obscuration was 5%-10%. The maximum particle size at 10% volume fraction from small to large was recorded as d10, the maximum particle size at 50% volume fraction from small to large was recorded as d50, and the maximum particle size at 90% volume fraction from small to large was recorded as d90.

[0089] Test method of particle size d50' of carbon-based additives: The carbon-based additive particles were observed under a transmission electron microscope, more than 100 particles in an arbitrary selected area were counted, the size of the longest direction of each particle was counted, and the average value was calculated to obtain the average diameter, which was d50' (the counted particles were single particles, and the agglomerated particles were counted as single bodies).

[0090] In the negative electrode sheets of Examples 1-16 and Comparative Examples 1-4, the types, particle size distribution, dimension of amorphous carbon and carbon-based additives in the negative electrode material layer, and the amount ratio therebetween are shown in Table 1.

[0091] Preparation of negative electrode sheet

[0092] The preparation method of the negative electrode sheet adopts the following steps:

[0093] In the negative electrode sheets of Examples 1-16 and Comparative Examples 1-4, amorphous carbon, carbon-based additives, thickening agent carboxymethyl cellulose sodium (CMC), and binder styrene-butadiene rubber (SBR) were mixed in a mass ratio of 100:(0.1-12):1:2 according to the amount in Table 1, and then deionized water was added and stirred to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated on a 16 μm aluminum foil current collector. After drying, rolling, and sheet cutting processes, the negative electrode sheets of Examples 1-16 and Comparative Examples 1-4 were prepared.

[0094] Table 1 Composition of negative electrode material of Examples 1-16 and Comparative Examples 1-4

[0095]

[0096]

[0097] Effect Example 1

[0098] (1) Preparation of sodium-ion battery:

[0099] Preparation of positive electrode sheet: Layered oxide, positive electrode active material with a molecular formula of NaNi 0.34 Fe 0.33 Mn 0.33 O2, conductive carbon black (Super P), carbon nanotubes (CNT), and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 100:2:1:3, and then N-methyl pyrrolidone (NMP) was added and stirred to obtain a sodium-ion battery positive electrode slurry. The positive electrode slurry was uniformly coated on a 16 μm thick aluminum foil. After drying, rolling, and cutting, a positive electrode sheet was obtained.

[0100] Preparation of electrolyte: Ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC) were uniformly mixed in a volume ratio of 1:1:1:1, and then appropriate NaPF6 was dissolved in the above mixed solution to prepare an electrolyte with a concentration of 1 mol / L.

[0101] Preparation of separator: The separator was a 9 μm polyethylene separator coated with a 2 μm thick ceramic coating on both sides.

[0102] Preparation of sodium-ion battery: The prepared positive electrode sheet, separator, negative electrode sheet of Examples 1-16 and Comparative Examples 1-4, and electrolyte were sequentially assembled, and the positive electrode sheet, separator, negative electrode sheet of Examples 1-16 and Comparative Examples 1-4, and separator were alternately combined to obtain a soft pack battery with a capacity of 1 Ah after formation.

[0103] (2) The sodium-ion batteries prepared from the negative electrode materials of Examples 1-16 and Comparative Examples 1-4 were tested as follows:

[0104] Test method for 2C rate retention rate of sodium-ion battery: At 25°C, charge at a rate of 0.33C to 4.0V (constant voltage cutoff current is 0.05C), then discharge at a rate of 0.33C to 1.5V to obtain a 0.33C capacity. Charge at a rate of 0.33C to 4.0V (constant voltage cutoff current is 0.05C), then discharge at a rate of 2C to 1.5V to obtain a 2C capacity. The ratio of 2C capacity to 0.33C capacity is the 2C rate retention rate.

[0105] The test method for the energy density of the sodium-ion battery: under the constant temperature environment of 25℃, charge to 4.0V at 0.33C rate constant current and constant voltage (the constant voltage cut-off current is 0.05C), then discharge to 1.5V at 0.33C rate constant current, the 0.33C energy is obtained. Repeat the charge and discharge process for 3 times, the 0.33C energy of the last cycle is recorded as the cell energy; the mass of the cell is weighed by the balance, and the ratio of the cell energy to the mass of the cell is the energy density.

[0106] The results of the above tests are listed in Table 2.

[0107] Table 2: Electrochemical performance data of sodium-ion batteries prepared from the negative electrode materials of Examples 1-16 and Comparative Examples 1-4

[0108]

[0109]

[0110] According to the data in Table 2, the sodium-ion batteries prepared from the amorphous carbon and the negative electrode sheet of Examples 1-16 have a 2C rate retention rate of not less than 79.1% and an energy density of not less than 129.5Wh / kg, indicating that they have excellent rate performance and energy density.

[0111] When the carbon-based additive is 0-dimensional conductive carbon black, the d10, d50, d90, (d90-d10) / d50 and W of Example 10 are slightly higher than those of Example 1, the d10, d50 and d90 of Example 11 are slightly higher than those of Example 1, but the (d90-d10) / d50 and W are slightly lower than those of Example 1, and compared with the three, Example 1 has the optimal 2C rate retention rate and energy density.

[0112] When the carbon-based additive is 1-dimensional carbon nanotube, the d10, d90, (d90-d10) / d50 and W of Example 12 are slightly higher than those of Example 5, and the d50 is slightly lower than that of Example 5; the W of Examples 6-9 is all 4.16, the d10, d50, d90 and d50’ / d50 of Example 7 are slightly higher than those of Example 6, the d10 and d90 of Example 8 are slightly higher than those of Example 6, and the d50 and d50’ / d50 are slightly lower than those of Example 6; the d50, d90 and d50’ / d50 of Example 9 are all slightly higher than those of Example 6, and the d10 is slightly lower than that of Example 6; among Examples 5-9 and 12, Example 7 has the optimal 2C rate retention rate and energy density.

[0113] When the carbon-based additive is 2-dimensional 3-layer graphene, the carbon-based additive content, d10, d50, d90 and d50’ / d50 of Example 4 are slightly lower than those of Example 2, (d90-d10) / d50 and W are higher than those of Example 2, the carbon-based additive content, d10, d50, d90, (d90-d10) / d50, d50’ / d50 and W of Example 13 are all slightly lower than those of Example 2, and among Examples 2, 4 and 13, Example 2 has the most excellent 2C rate retention and energy density.

[0114] When the carbon-based additive is 3-dimensional artificial graphite, the d50, d90, (d90-d10) / d50 and W of Example 14 are slightly higher than those of Example 3, and the carbon-based additive content, d10, d50’ / d50 are slightly lower than those of Example 3; the d10, d50 and d90 of Example 15 are slightly higher than those of Example 3, and the carbon-based additive content, (d90-d10) / d50, W and d50’ / d50 are slightly lower than those of Example 3; among Examples 3, 14 and 15, Example 3 has the most excellent 2C rate retention and energy density.

[0115] The carbon-based additive content of Example 16 is higher than that of Example 1, and compared with each other, Example 1 has more excellent 2C rate retention and energy density.

[0116] Comparative Example 1 does not contain a carbon-based additive, and the 2C rate retention and energy density of the battery prepared therefrom are both poor.

[0117] Comparative Example 2 has excessively high W, and Comparative Example 3 has excessively low W, and the 2C rate retention and energy density of the batteries prepared from Comparative Examples 2 and 3 are both lower than those of the Examples.

[0118] Comparative Example 4 has excessively high W, and further, d50’ / d50 is 0.1520, and compared with the Examples, the 2C rate retention and energy density of the battery prepared from Comparative Example 4 are also both poor.

[0119] Although the specific embodiments of the present application are described above, those skilled in the art should understand that this is only an illustration, and the protection scope of the present application is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present application, and these changes and modifications all fall within the protection scope of the present application.

Claims

1. A negative electrode material, characterized by, It comprises amorphous carbon and carbon-based additives; wherein the amorphous carbon contains hard carbon, and a dimensional matching degree W of the amorphous carbon and the carbon-based additives satisfies 3.5≤W≤4.5; wherein the W is calculated according to the following formula: W=2(d90-d10) / d50+D; wherein d10, d50 and d90 represent particle sizes of the amorphous carbon; D represents a dimension of the carbon-based additives, and D is 0, 1, 2 or 3; 0.001≤d50’ / d50≤0.12, wherein d50’ represents an average particle size of the carbon-based additives; The amount of the carbon-based additives is 0.1wt%-12wt%, and the percentage is the weight percentage of the carbon-based additives in the amorphous carbon.

2. The negative electrode material of claim 1, wherein, The negative electrode material satisfies 0.001≤d50’ / d50≤0.

1.

3. The negative electrode material of claim 1, wherein, The amount of the carbon-based additives is 0.1wt%-10wt%.

4. The negative electrode material of claim 1, wherein, The carbon-based additives satisfy any one of the following conditions: a. The D=0, and the carbon-based additives are selected from one or more of conductive carbon black, carbon quantum dots and fullerenes; b. The D=1, and the carbon-based additives are selected from one or more of carbon nanotubes, carbon fibers and carbon nanowires; c. The D=2, and the carbon-based additives comprise thin-layer graphene, wherein the thin-layer graphene is graphene with a layer number of 5 or less; d. The D=3, and the carbon-based additives are selected from one or more of artificial graphite, natural graphite, multi-layer graphene and mesocarbon microbeads, wherein the multi-layer graphene is graphene with a layer number of 5 or more.

5. The negative electrode material of claim 1, wherein, The negative electrode material comprises amorphous carbon and conductive carbon black, and satisfies 0.001≤d50’ / d50≤0.05; Alternatively, the negative electrode material comprises amorphous carbon and carbon nanotubes, and satisfies 0.001≤d50’ / d50≤0.

1.

6. The negative electrode material of claim 1, wherein, The negative electrode material comprises amorphous carbon and thin-layer graphene, wherein the thin-layer graphene has a layer number of 3, and the negative electrode material satisfies 0.001≤d50’ / d50≤0.02; Alternatively, the negative electrode material comprises amorphous carbon and artificial graphite, and satisfies 0.001≤d50’ / d50≤0.

07.

7. An electrochemical device comprising a negative electrode sheet, characterized by The negative electrode sheet comprises a current collector layer and a negative electrode material layer on the current collector layer, and the negative electrode material layer comprises the negative electrode material according to any one of claims 1-6.

8. The electrochemical device of claim 7, wherein, In the negative electrode material layer, the content of the negative electrode material is 80.0wt%-99.9wt%, and the percentage is the weight percentage of the negative electrode material in the negative electrode material layer.

9. The electrochemical device of claim 7, wherein The electrochemical device is a sodium ion battery.

10. An electronic device, comprising: It comprises the electrochemical device according to any one of claims 7-9. The electrochemical device is a sodium ion battery.

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