Negative electrode material layer, and electrochemical device and electronic equipment comprising same

Abstract

The application discloses a negative electrode material layer, an electrochemical device containing the same and an electronic device. The negative electrode material layer comprises a first active material layer and a second active material layer arranged on the surface of the first active material layer; the first active material layer contains a first active material; the first active material contains amorphous carbon; the second active material layer contains a second active material; the second active material contains amorphous carbon; the amorphous carbon contains hard carbon; the first active material and the second active material satisfy 1.05<=A / B<=2.00 and 0.90<=C / D<=0.98; wherein A represents the micropore volume of the first active material; B represents the micropore volume of the second active material; C represents the interplanar spacing of the 002 plane of the first active material; and D represents the interplanar spacing of the 002 plane of the second active material. When the negative electrode material layer provided in the application is applied to an electrochemical device, the energy density and the cycle life are simultaneously improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a negative electrode material layer, and an electrochemical device and an electronic device comprising the same. BACKGROUND

[0002] Sodium-ion batteries have the advantages of high energy density, good cycle life, excellent low-temperature performance, and low cost, and gradually become one of the alternatives to lithium-ion batteries and lead-acid batteries in the fields of energy storage, low-end power, and two-wheeled vehicles. The current mainstream positive electrode materials for sodium-ion batteries are layered oxides and polyanions, and the mainstream negative electrode materials are amorphous carbons such as soft carbon and hard carbon. To have greater competitiveness, sodium-ion batteries still need breakthroughs in energy density and cycle life.

[0003] The most commonly used negative electrode material for sodium-ion batteries is hard carbon. The specific capacity of hard carbon material is generally 280-320 mA / g, the compaction density is 0.9-1.05 g / cc, the energy density of the system with layered oxides is generally 115-140 Wh / kg, and the cycle life is 2000-4000 cycles. However, compared with lithium iron phosphate batteries, there is still a certain gap in energy density and cycle life. How to simultaneously improve the energy density and cycle life of sodium-ion batteries has become the focus of research in the industry. SUMMARY

[0004] The present application relates to a negative electrode material layer, and an electrochemical device and an electronic device comprising the same. The negative electrode material layer provided in the present application can be applied to an electrochemical device to simultaneously improve the energy density and cycle life.

[0005] In a first aspect, the present application provides a negative electrode material layer, comprising a first active material layer and a second active material layer arranged on the surface of the first active material layer.

[0006] The first active material layer comprises a first active material; the first active material comprises amorphous carbon.

[0007] The second active material layer comprises a second active material; the second active material comprises amorphous carbon.

[0008] The amorphous carbon comprises hard carbon.

[0009] The first active material and the second active material satisfy 1.05≤A / B≤2.00 and 0.90≤C / D≤0.98.

[0010] A represents the micropore volume of the first active material;

[0011] B represents the micropore volume of the second active material.

[0012] C represents the interplanar spacing of the 002 plane of the first active material;

[0013] D represents the interplanar spacing of the 002 plane of the second active material.

[0014] In a second aspect, the present application provides an electrochemical device comprising a negative electrode sheet, the negative electrode sheet comprising a negative electrode material layer and a negative electrode current collector as previously described.

[0015] In a third aspect, the present application provides an electronic device comprising an electrochemical device as previously described.

[0016] On the basis of common general knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, thereby obtaining preferred examples of the present application.

[0017] The reagents and raw materials used in the present application are commercially available.

[0018] The positive progress effect of the present application is that:

[0019] The present application realizes the synchronous improvement of the energy density and the cycle life of the sodium ion battery by regulating the micropore volume and the interplanar spacing of the 002 plane of the two layers of negative electrode active materials. DETAILED DESCRIPTION

[0020] The present application will be further described by way of examples, but the present application is not limited to the examples. The experimental methods in the following examples are not specified, and the methods are selected according to the conventional methods and conditions or the instructions of the commercial products.

[0021] Negative electrode material layer

[0022] In the negative electrode material layer provided in the first aspect of the present application, it comprises a first active material layer and a second active material layer arranged on the surface of the first active material layer; the first active material layer comprises a first active material; the first active material comprises amorphous carbon; the second active material layer comprises a second active material; the second active material comprises amorphous carbon; and the amorphous carbon comprises hard carbon.

[0023] The first active material and the second active material satisfy 1.05≤A / B≤2.00 and 0.90≤C / D≤0.98; wherein A represents the micropore volume of the first active material; B represents the micropore volume of the second active material; C represents the interplanar spacing of the 002 plane of the first active material; and D represents the interplanar spacing of the 002 plane of the second active material.

[0024] In the present application, the micropore volume is the average micropore volume of the first active material or the second active material as a whole. The testing method of the micropore volume is to take an appropriate amount of active material, place it in a 9mm ball sample tube, degas at 300°C for 2h, measure the adsorption amount of the sample with nitrogen as the adsorbate (P / P0 range is 0-1, 0-0.05 range is every 0.002 selected point, 0.05-1 range is every 0.05 selected point), and the pore volume below 2nm obtained by non-local density functional theory (NLDFT) method is the micropore volume.

[0025] In the present application, the interplanar spacing of the 002 plane refers to the interplanar spacing of the highest peak of the characteristic peak of the 002 plane in the XRD spectrum of the first active material or the second active material. In the present application, the XRD spectrum is the fitting spectrum of the XRD test result, and the "highest point" refers to the result shown 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 art.

[0026] The testing method of the interplanar spacing of the 002 plane is to refer to the description in the national standard GB / T 24533-2019, take 0.15g of silicon powder and 0.35g of active material in a marquis mortar and grind thoroughly for 10min, and then flatten in a sample holder. The sample is scanned by an X-ray diffractometer under the condition of 25°-30° with a step size of 0.02°. The 002 peak of the active material is corrected by using the silicon 111 peak, and the 2theta value of the 002 peak is obtained. The interplanar spacing of the 002 plane is calculated by the Bragg equation.

[0027] In the present application, the weight percentage of the hard carbon in the amorphous carbon is 90wt% or more, which refers to the weight percentage of the hard carbon in the whole amorphous carbon. Preferably, the amorphous carbon is hard carbon.

[0028] In some optional embodiments, the first active material is amorphous carbon, and the second active material is amorphous carbon.

[0029] In some optional embodiments, the first active material and the second active material can satisfy 1.20≤A / B≤1.95.

[0030] In some specific embodiments, the A / B can be selected from 1.05, 1.09, 1.32, 1.62, 1.78, 1.91 or 2.00.

[0031] In some optional embodiments, the first active material and the second active material can satisfy 0.91≤C / D≤0.96.

[0032] In some embodiments, the C / D can be selected from 0.90, 0.91, 0.92, 0.93, 0.95, or 0.98.

[0033] In some embodiments, the A / B = 1.62, and the C / D = 0.93.

[0034] In some embodiments, the A / B = 1.78, and the C / D = 0.91.

[0035] In some embodiments, the A / B = 1.91, and the C / D = 0.95.

[0036] In some embodiments, the A / B = 1.05, and the C / D = 0.95.

[0037] In some embodiments, the A / B = 2.00, and the C / D = 0.92.

[0038] In some embodiments, the A / B = 1.09, and the C / D = 0.90.

[0039] In some embodiments, the A / B = 1.32, and the C / D = 0.98.

[0040] In the present application, the thickness ratio of the first active material layer to the second active material layer can be (1:3)-(3:1).

[0041] In some embodiments, the thickness ratio of the first active material layer to the second active material layer is 1:1, 1:3, or 3:1.

[0042] In the present application, the thickness of the first active material layer can be 32 μm-96 μm, for example, 32 μm, 62 μm, or 96 μm.

[0043] In the present application, the thickness of the second active material layer can be 32 μm-96 μm, for example, 32 μm, 62 μm, or 96 μm.

[0044] In the present application, the weight ratio of the first active material to the second active material can be (1:3)-(3:1).

[0045] In some embodiments, the weight ratio of the first active material to the second active material is 1:1, 1:3, or 3:1.

[0046] In the present application, in the first active material layer, the content of the first active material can be 90.0 wt%-99.9 wt%, and the percentage is the weight percentage of the first active material in the first active material layer.

[0047] In some embodiments, the content of the first active material in the first active material layer can be 90.0 wt%, 98 wt%, or 99.9 wt%, the percentage being the weight percentage of the first active material in the first active material layer.

[0048] In the present application, the content of the second active material in the second active material layer is 90.0 wt%-99.9 wt%, the percentage being the weight percentage of the first active material in the first active material layer.

[0049] In some embodiments, the content of the second active material in the second active material layer is 90.0 wt%, 98 wt%, or 99.9 wt%, the percentage being the weight percentage of the first active material in the first active material layer.

[0050] In the present application, the first active material layer and the second active material layer each independently can further comprise one or more of a conductive agent, a thickening agent, and a binder.

[0051] The conductive agent is a conductive agent conventionally used in the art for preparing a negative electrode, preferably the conductive agent is one or more of conductive carbon black, carbon nanotubes, and graphene, more preferably conductive carbon black.

[0052] The thickening agent is not particularly limited, and the addition of the thickening agent can increase the system viscosity of the components in the negative active material layer, and a sodium carboxymethyl cellulose (CMC) solution can be generally selected.

[0053] The binder can be a binder conventionally used in the art for preparing a negative electrode, for example, one or more of the following materials can be used as the binder: styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), and polyvinylidene fluoride (PVDF).

[0054] In some embodiments, the first active material layer comprises amorphous carbon, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0055] In some embodiments, the second active material layer comprises amorphous carbon, conductive carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber.

[0056] Electrochemical device

[0057] The electrochemical device according to the second aspect of the present application comprises a negative electrode sheet; the negative electrode sheet comprises a negative electrode material layer and a negative electrode current collector as described above.

[0058] In some alternative embodiments, the negative electrode sheet can be prepared by a method conventional in the art. For example, the following method can be used: a first active material (or a second active material), a conductive agent, a thickening agent, and a binder are mixed in a certain weight ratio, a solvent is then added and mixed uniformly to obtain a first active material slurry or a second active material slurry; the first active material slurry is then uniformly coated on the negative electrode current collector; the second active material slurry is then coated on the first active material layer; and the negative electrode sheet is prepared by subsequent processes such as drying, rolling, and sheet cutting.

[0059] In some alternative embodiments, in the negative electrode sheet, the negative electrode current collector is in direct contact with the first active material layer.

[0060] In the present application, the negative electrode current collector can be a current collector conventional in the art for use in a negative electrode, and can be a general current collector or a composite current collector. The negative electrode current collector can use, without limitation, a material that does not cause chemical changes 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, a 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] In some alternative embodiments, the thickness of the negative electrode current collector can be about 16 μm.

[0062] In the present application, the electrochemical device can be a sodium ion battery. The sodium ion battery includes the negative electrode sheet, a positive electrode sheet, a separator, and an electrolyte.

[0063] Positive electrode sheet

[0064] 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 thickening agent can be further added as needed.

[0065] In some specific embodiments, the weight ratio of the positive electrode active material, conductive carbon black (Super P), carbon nanotube (CNT), and binder polyvinylidene fluoride (PVDF) is 100:2:1:3.

[0066] For the positive electrode active material, it can be a positive electrode active material conventional in the art for use in a positive electrode of a sodium ion battery, and can be selected from a layered oxide, a Prussian blue compound, or a polyanion compound. Further alternatively, the general formula of the layered oxide is Na x[MFeMn]02, M is at least one selected from Cu, Ni, Li, Mg, Al, Zn, Ti, Zr and Sn, and x ranges from 0 < x < 0.7. In a specific embodiment, the positive electrode active material has a formula of NaNi 0.34 Fe 0.33 Mn 0.33 02.

[0067] For the positive electrode current collector, a material that does not cause chemical change and has high conductivity can be used without limitation. 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, etc. Among them, the thickness of the positive electrode current collector can be about 16 μm.

[0068] In some embodiments, the positive electrode current collector is an aluminum foil having a thickness of 16 μm.

[0069] Separator

[0070] In some embodiments, the separator can be selected from a polypropylene separator or a polyethylene separator.

[0071] Among them, the thickness of the separator can be about 9 μm.

[0072] In an embodiment, the separator is a 9 μm polyethylene separator coated with a ceramic coating having a thickness of 2 μm on both sides.

[0073] Electrolyte

[0074] In some embodiments, the electrolyte can be an electrolyte conventionally used in the art for a battery, generally including a non-aqueous solvent, a sodium salt and an additive.

[0075] Among them, the non-aqueous solvent can be a non-aqueous solvent conventionally used in the art, preferably an ester solvent, more preferably a carbonate solvent. The carbonate solvent is preferably one or more of ethylene carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate (MEC), ethyl methyl carbonate (EMC), ethylene carbonate (EC), propylene carbonate (PC) and butylene carbonate (BC).

[0076] In some preferred embodiments, the non-aqueous solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC) and propylene carbonate (PC) in a volume ratio of 1:1:1:1.

[0077] The additive is preferably one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), vinyl ethylene carbonate (VEC), vinyl sulfate (DTD), vinylene sulfide, 1,3-propane sultone (PS), propenyl sulfonic acid lactone, and 1,4-butane sulfonic acid lactone.

[0078] The sodium salt can be a conventional sodium salt in the art, for example NaPF6.

[0079] In the present application, the preparation method of the sodium-ion battery can be a conventional preparation method in the art, which can be winding the positive electrode sheet, the negative electrode sheet and the separator film to obtain an electric core, then packaging with a packaging shell and injecting the electrolyte; or can be sequentially stacking the negative electrode sheet, the separator film, the positive electrode sheet and the separator film in order to obtain an electric core, then packaging with a packaging shell and injecting the electrolyte.

[0080] Electronic device

[0081] In the electronic device provided in the third aspect of the present application, the electrochemical device is as described above.

[0082] Exemplarily, 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.

[0083] On the basis of common knowledge in the art, the above-mentioned preferred conditions can be combined arbitrarily, i.e. to obtain each preferred example of the present application.

[0084] Examples 1-13 and Comparative Examples 1-5

[0085] Preparation of amorphous carbon

[0086] The amorphous carbon in Examples 1-13 and Comparative Examples 1-5 is hard carbon, and its preparation method adopts the following steps:

[0087] The coconut shell is washed 3 times with a mixed solution of water and ethanol (volume ratio 1:1), 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°C at a rate of 1-10°C / min under a nitrogen atmosphere, and held 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), then washed with deionized water for more than 5 times, and dried to obtain a hard carbon precursor; the hard carbon precursor is heated to 1000-1500°C at a rate of 1-10°C / min under a nitrogen atmosphere, and held for 2-10h; then ball-milled to the desired particle size to obtain amorphous carbon, which is hard carbon.

[0088] The micropore volume test method is as follows: an appropriate amount of amorphous carbon sample is placed in a 9mm ball sample tube, degassed at 300°C for 2h, and the sample adsorption amount is determined with nitrogen as the adsorbate (P / P0 range is 0-1, wherein 0-0.05 is selected as one point every 0.002, and 0.05-1 is selected as one point every 0.05), and the pore volume below 2nm obtained by the non-local density functional theory (NLDFT) method is the micropore volume.

[0089] The test method for the interplanar spacing of the 002 plane is as follows: 0.15g of silicon powder and 0.35g of amorphous carbon are weighed into an agate mortar and ground thoroughly for 10min, and then placed in a sample holder and flattened. The sample is scanned by an X-ray diffractometer under the conditions of 25°-30° and a step size of 0.02°. The 002 peak of the amorphous carbon is corrected using the silicon 111 peak, and the 002 peak 2θ value is obtained, and the interplanar spacing of the 002 plane is calculated by the Bragg equation.

[0090] Preparation of the negative electrode sheet

[0091] The preparation method of the negative electrode sheet in Examples 1-13 and Comparative Examples 1-5 adopts the following steps, and the specific parameter settings are shown in Table 1:

[0092] Preparation of the first active material layer: the first active material, conductive carbon black (Super P), thickening agent carboxymethyl cellulose sodium (CMC), and binder styrene-butadiene rubber (SBR) are mixed uniformly at a weight ratio of 100:1:1:2, and appropriate deionized water is added, stirred and dispersed uniformly to obtain a first active material slurry; the first active material slurry is uniformly coated on a 16μm thick aluminum foil, dried to obtain a first active material layer;

[0093] Preparation of the second active material layer: the second active material, conductive carbon black (Super P), thickening agent sodium carboxymethyl cellulose (CMC), binder styrene-butadiene rubber (SBR) were mixed uniformly according to the weight ratio of 100:1:1:2, and then deionized water was added and stirred to disperse uniformly to obtain a second active material slurry; the second active material slurry was uniformly coated on the surface of the first active material layer, and then dried to obtain the second active material layer.

[0094] wherein the first active material and the second active material are both amorphous carbon, and satisfy the conditions described in Table 1; the thickness of the first active material layer and the second active material layer, the weight ratio of the first active material to the second active material, and the percentage of the active material in the active material layer are as described in Table 1.

[0095] After the pole piece coated with the first active material layer and the second active material layer was rolled and cut, a negative pole piece was obtained.

[0096] Table 1

[0097]

[0098]

[0099] Effect implementation example

[0100] Preparation of a sodium ion battery:

[0101] (1) Preparation of a positive pole piece

[0102] The positive active material is a layered oxide with a molecular formula of NaNi 0.34 Fe 0.33 Mn 0.33 O2, the active material, conductive carbon black (Super P), carbon nanotubes (CNT), and binder polyvinylidene fluoride (PVDF) were mixed uniformly according to the weight ratio of 100:2:1:3, and then N-methyl pyrrolidone (NMP) was added and stirred to disperse uniformly to obtain a sodium ion battery positive electrode slurry; the positive electrode slurry was uniformly coated on a 16 μm thick aluminum foil, and then dried, rolled, and cut to obtain a positive pole piece.

[0103] (2) Preparation of an electrolyte

[0104] Ethylene carbonate (EC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), and propylene carbonate (PC) were uniformly mixed according to the 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.

[0105] (3) Preparation of a separator

[0106] The separator is a 9 μm polyethylene separator coated with a 2 μm ceramic coating on both sides.

[0107] (4) Preparation of sodium-ion secondary battery

[0108] The positive electrode sheet, the separator, and the electrolyte prepared in the above steps, and the negative electrode sheet prepared in Examples 1-13 and Comparative Examples 1-5 were assembled into a sodium-ion battery, and the positive electrode sheet, the separator, the negative electrode sheet, and the separator were alternately combined, and a soft pack battery with a capacity of 1 Ah was obtained by formation, and the effect was tested.

[0109] 1. Energy density (Wh / kg)

[0110] At 25°C in a constant temperature environment, the 0.33C rate constant current constant voltage charging was carried out to 4.0V (the constant voltage cutoff current was 0.05C), and then the 0.33C rate constant current discharging was carried out to 1.5V, after 3 cycles, the data after the last discharging was taken as the 0.33C energy, and the weight of the battery was taken by a balance, and the ratio of the 0.33C energy to the weight of the battery was the energy density. The test results are recorded in Table 2.

[0111] 2. Cycle life (%)

[0112] At 25°C in a constant temperature environment, the 1C rate constant current constant voltage charging was carried out to 4.0V (the constant voltage cutoff current was 0.05C), and then the 0.33C rate constant current discharging was carried out to 1.5V, which was one cycle. The cycle was repeated for 1000 times, and the ratio of the discharging capacity of the 1000th cycle to the 1st cycle was calculated as the cycle life. The test results are recorded in Table 2.

[0113] Table 2

[0114]

[0115]

[0116] The negative electrode material layer provided by the application is applied in a sodium-ion battery, which improves the energy density of the sodium-ion battery and improves the cycle life of the sodium-ion battery, and a sodium-ion battery with high capacity and long cycle is obtained. The negative electrode material layer prepared in Examples 1-13 is applied in a sodium-ion battery, and the energy density can reach 128.9 Wh / kg or more, and the capacity retention rate after 1000 cycles can be 85.8% or more.

[0117] Comparative Examples 1 and 2 differ from the examples in that the values of the micropore volume A / B of the negative active material are not within the range of the present application, being too large or too small, and as can be seen from the data in Table 2, both the energy density and the cycle life are poor, which can be because the micropore filling sodium storage mechanism of the amorphous carbon is mainly in the low voltage range close to 0 V, and a large micropore volume of the active material is conducive to micropore sodium storage, and the gravimetric capacity is high; therefore, to some extent, increasing the micropore volume of the amorphous carbon helps to increase the sodium storage capacity of the amorphous carbon. However, excessively increasing the micropore volume will reduce the tap density of the amorphous carbon, and will also cause more side reactions, reducing the energy density and cycle life. Therefore, A / B must be within a reasonable range in order to simultaneously consider the energy density and cycle life.

[0118] Comparative Examples 3 and 4 differ from the examples in that the interplanar spacing C / D of the 002 plane of the negative active material is not within the range of the present application, being too large or too small, and both the energy density and the cycle life are poor; this can be because the interplanar spacing of the 002 plane of the amorphous carbon is related to the sodium ion diffusion resistance, and a large interplanar spacing means small sodium ion transmission resistance, which is conducive to sodium ion transmission, and the energy density and cycle life will be improved; but excessively increasing the interlayer spacing will reduce the tap density of the amorphous carbon and decrease the structural stability, resulting in a decrease in the energy density and cycle life. Therefore, C / D must be within a reasonable range in order to simultaneously consider the energy density and cycle life.

[0119] In Comparative Example 5, both A / B and C / D are not within the range of the present application, and the cycle life and energy density are the worst. This is because the micropore volume of the first active material is smaller than that of the second active material, which is not conducive to micropore sodium storage; and the interplanar spacing of the first active material is larger than that of the second active material, which is not conducive to sodium ion transmission, and therefore the cycle life and energy density are the worst.

[0120] As can be seen from Examples 1-7, when the first active material and the second active material satisfy 1.05≤A / B≤2.00 and 0.90≤C / D≤0.98, the sodium ion battery prepared has good energy density and cycle life; especially when 1.20≤A / B≤1.95 or 0.91≤C / D≤0.96 is satisfied, the energy density and cycle life are even higher, and it is precisely by adjusting and optimizing the ratio of the micropore volume and the interplanar spacing of the 002 plane of the two active material layers that the present application obtains a sodium ion battery that simultaneously has high capacity and long cycle life.

[0121] It can be seen from embodiments 1, 8 and 9 that the thickness ratio and weight ratio of the first active material layer and the second active material layer also have certain influences on the energy density and cycle life of the prepared sodium ion battery; this may be because the two layers of active materials have different interlayer spacings, and different interlayer spacings affect the sodium ion transmission, and the thickness ratio or weight ratio of the two layers affects the sodium ion transmission path, so within a certain thickness ratio range, there is a better transmission effect, thereby having a better energy density and cycle life.

[0122] It can be seen from embodiments 1 and 10-13 that when A / B and C / D are the same and within the scope of the present application, the weight proportion of the active material in each active material layer also affects the effect of the sodium ion battery, and a better effect is obtained within a suitable weight proportion range. This may be because if the proportion of amorphous carbon is too large, the electrode sheet adhesion and conductivity are poor, affecting the sodium intercalation capacity and electrode sheet stability, thereby affecting the cycle life and energy density; if the proportion is too small, there is not enough micropore for sodium storage, which also affects the energy density and cycle life.

[0123] Although the specific embodiments of the present application are described above, those skilled in the art should understand that this is only an example, 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 layer, characterized by, It comprises a first active material layer and a second active material layer disposed on the surface of the first active material layer; The first active material layer comprises a first active material; the first active material comprises amorphous carbon; The second active material layer comprises a second active material; the second active material comprises amorphous carbon; The amorphous carbon comprises hard carbon; The first active material and the second active material satisfy: 1.05≤A / B≤2.00, and 0.90≤C / D≤0.98; Wherein A represents the micropore volume of the first active material; B represents the micropore volume of the second active material; C represents the interplanar spacing of the 002 plane of the first active material; D represents the interplanar spacing of the 002 plane of the second active material; The thickness ratio of the first active material layer to the second active material layer is (1:3)-(3:1); The weight ratio of the first active material to the second active material is (1:3)-(3:1).

2. The negative electrode material layer according to claim 1, wherein The first active material and the second active material satisfy: 1.20≤A / B≤1.

95.

3. The negative electrode material layer according to claim 1, wherein The first active material and the second active material satisfy: 0.91≤C / D≤0.

96.

4. The negative electrode material layer according to claim 1, wherein In the first active material layer, the content of the first active material is 90.0 wt%-99.9 wt %, and the percentage is the weight percentage of the first active material in the first active material layer.

5. The negative electrode material layer according to claim 1, wherein In the second active material layer, the content of the second active material is 90.0 wt%-99.9 wt %, and the percentage is the weight percentage of the second active material in the second active material layer.

6. An electrochemical device, characterized by, It comprises a negative electrode sheet; the negative electrode sheet comprises a negative electrode material layer and a negative electrode current collector.

7. The electrochemical device of claim 6, wherein The electrochemical device is a sodium ion battery.

8. An electronic device, comprising: It comprises the electrochemical device according to claim 7. The electrochemical device is a sodium ion battery.

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