WO2021226842A1

WO2021226842A1 - Negative electrode material, negative electrode plate, electrochemical device, and electronic device

Info

Publication number: WO2021226842A1
Application number: PCT/CN2020/089842
Authority: WO
Inventors: 张成波; 谢远森
Original assignee: 宁德新能源科技有限公司
Priority date: 2020-05-12
Filing date: 2020-05-12
Publication date: 2021-11-18

Abstract

A negative electrode material, a negative electrode plate, an electrochemical device, and an electronic device. The negative electrode material comprises a silicon-based material and a flake carbon-based material. The diameter-to-thickness ratio of the flake carbon-based material is greater than 2. The carbon-based material having a diameter-to-thickness ratio greater than 2 is added to the negative electrode material containing the silicon-based material, so that the compact density of the negative electrode material is improved, and the electric contact between silicon-based materials is increased. At the same time, the flake carbon-based material also improves the conductivity of the negative electrode material, and thus improving the cycle performance of the electrochemical device.

Description

Negative electrode material, negative pole piece, electrochemical device and electronic device

Technical field

The present disclosure relates to the field of electronic technology, and in particular to a negative electrode material, a negative pole piece, an electrochemical device and an electronic device.

Background technique

The theoretical specific capacity of silicon-based materials reaches 4200mAh/g, which is much higher than the theoretical specific capacity of carbon materials (372mAh/g). It is a promising negative electrode material for next-generation electrochemical devices (for example, lithium ion batteries).

However, the compacted density of the negative pole piece directly made of silicon-based negative electrode material is only 1.2g/cm ³ , which is far lower than the compacted density of graphite-based negative pole piece of 1.8g/cm ³ , and also far lower than that of silicon-based materials The theoretical true density is 2.3g/cm ³ , and the compact density is too low will cause more gaps between the negative electrode materials, affect the conductivity of the negative electrode material, and cause the reduction of the volume energy density of the electrochemical device and the deterioration of the cycle performance.

Summary of the invention

In view of the above-mentioned shortcomings of the prior art, the anode materials containing silicon-based materials in the present disclosure include sheet-like carbon-based materials with a diameter-to-thickness ratio greater than 2, thereby greatly increasing the compaction density of the anode materials, thereby improving the electrical conductivity. The volumetric energy density and cycle performance of chemical devices.

The present disclosure provides a negative electrode material, including: a silicon-based material and a sheet-shaped carbon-based material; wherein the diameter-to-thickness ratio of the sheet-shaped carbon-based material is greater than 2.

In the above-mentioned negative electrode material, wherein the sheet-shaped carbon-based material has Dv50=A, the silicon-based material has Dv50=B, and A/B<1.

In the above-mentioned negative electrode material, wherein the mass of the sheet-shaped carbon-based material accounts for 0.5%-40% of the total mass of the silicon-based material and the sheet-shaped carbon-based material.

In the above-mentioned negative electrode material, wherein the sheet-shaped carbon-based material includes graphite, and the graphitization degree of the graphite is above 90%.

In the above-mentioned negative electrode material, wherein the silicon-based material includes at least one of silicon oxide, silicon, silicon-carbon composite material, or silicon alloy.

In the above-mentioned negative electrode material, the silicon-based material satisfies at least one of the following: the surface of the silicon oxide has the flaky carbon-based material; the particle size range of the silicon oxide satisfies 1μm<Dv50<10μm The specific surface area of the silicon oxide is less than 10m ² /g; the general formula of the silicon oxide is SiO _x , where 0<x<2; the silicon includes silicon microparticles, silicon nanoparticles, and silicon nanowires Or at least one of silicon nano-film; the silicon alloy includes at least one of silicon-iron alloy, silicon-aluminum alloy, silicon-nickel alloy, or silicon-iron-aluminum alloy.

In the above-mentioned negative electrode material, wherein the sheet-like carbon-based material includes at least one of graphite, graphene, soft carbon or hard carbon, and the particle size range of the sheet-like carbon-based material satisfies Dv50<10 μm.

The present disclosure also provides a negative electrode piece, which includes: a current collector; an active material layer located on the current collector; wherein the active material layer includes any of the above-mentioned negative electrode materials.

The present disclosure also provides an electrochemical device, including: a positive pole piece; a negative pole piece; a separator, arranged between the positive pole piece and the negative pole piece; wherein the negative pole piece is the above-mentioned negative Pole piece.

The present disclosure also provides an electronic device, including the electrochemical device described above.

The present disclosure significantly increases the compaction density of the negative electrode material and improves the volume energy density and cycle performance of the electrochemical device by adding a sheet-like carbon-based material with a diameter-to-thickness ratio greater than 2 to the negative electrode material containing the silicon-based material.

Description of the drawings

Fig. 1 is a scanning electron image of flake graphite in a negative electrode material according to an embodiment of the present disclosure.

Fig. 2 is a cross-sectional scanning electron microscope view of flake graphite in a negative electrode material in an embodiment of the present disclosure.

Fig. 3 is an exemplary image of a negative pole piece of the present disclosure.

Fig. 4 is a schematic diagram of an electrode assembly of an electrochemical device of the present disclosure.

5 is a schematic diagram of the compaction density of the negative electrode materials in Example 3 and Comparative Example 1 of the present disclosure under different pressures.

6 is a schematic diagram of the volume energy density under different flake graphite contents in Examples 1 to 5 and Comparative Example 1 of the present disclosure.

7 is a schematic diagram of the discharge capacity retention rate under different cycle cycles in Examples 2 and 3 and Comparative Example 1 of the present disclosure.

Detailed ways

The following examples may enable those skilled in the art to understand the application more comprehensively, but do not limit the application in any way.

Silicon-based materials, as the next-generation high-capacity anode materials, can significantly increase the energy density of the electrode assembly. However, the compaction density of the anode pole piece prepared with silicon-based materials as the anode material is much lower than that of the anode prepared with graphite as the anode material. The compaction density of the pole piece. When the compaction density of the silicon-based material is low, poor contact between the silicon-based materials will cause the conductivity to deteriorate and affect the cycle performance.

In the present disclosure, a carbon-based material with a diameter-to-thickness ratio greater than 2 is added to the negative electrode material containing silicon-based material, thereby increasing the compaction density of the negative electrode plate prepared by the negative electrode material, increasing the electrical contact between the silicon-based materials, and at the same time The sheet-shaped carbon-based material also enhances the conductivity of the negative electrode material, thereby improving the cycle performance of the electrochemical device, and can also increase the volume energy density of the electrochemical device.

Some embodiments of the present disclosure propose a negative electrode material. The negative electrode material includes a silicon-based material and a sheet-shaped carbon-based material; wherein the diameter-to-thickness ratio of the sheet-shaped carbon-based material is greater than 2. The flake carbon-based material in some embodiments of the present disclosure may be flake graphite as shown in FIGS. 1 and 2. In some embodiments of the present disclosure, the diameter-to-thickness ratio of the sheet-shaped carbon-based material refers to the ratio L/H of the diameter L of the circumscribed circle projected by the sheet-shaped carbon-based material and the thickness H of the sheet-shaped carbon-based material. The cross-sectional view of the flaky carbon-based material was photographed by electron microscopy to measure and calculate the diameter-to-thickness ratio of the flaky carbon-based material. In some embodiments of the present disclosure, by adding a sheet-shaped carbon-based material with a diameter-to-thickness ratio greater than 2 to a negative electrode material containing a silicon-based material, it can improve The compaction density of the negative electrode material reduces the gap between the silicon-based materials in the negative electrode material and enhances the electrical contact between the silicon-based materials. At the same time, the sheet-shaped carbon-based material can increase the conductivity of the negative electrode material, thereby improving the negative electrode material Cycle performance. It should be noted that in this embodiment, the diameter-to-thickness ratio of the sheet-like carbon-based material is set to be greater than 2. This is because when the diameter-to-thickness ratio is greater than 2, the sheet-like carbon-based material easily slips along the direction of the sheet. Carbon-based materials are more likely to have a lubricating effect, so as to fully fill the gaps between silicon-based materials, improve compaction density and cycle performance, and help increase the volume energy density of electrochemical devices. When the thickness ratio is not greater than 2, the sheet-shaped carbon-based material is difficult to play a lubricating effect, and the gap between the silicon-based materials cannot be fully filled, so the compaction density of the negative electrode plate prepared by the negative electrode material cannot be significantly improved, and the It is beneficial to improve the volumetric energy density and cycle performance of the electrochemical device. In some embodiments, the powder compaction density of the negative electrode material at a pressure of 150 MPa is above ^{1.4 g/cm 3.}

In some embodiments of the present disclosure, the sheet-shaped carbon-based material has Dv50=A, the silicon-based material has Dv50=B, and A/B<1. In some embodiments, when the ratio of the Dv50 of the sheet-shaped carbon-based material to the Dv50 of the silicon-based material is greater than 1, the size of the sheet-shaped carbon-based material is too large compared to the size of the silicon-based material. The size of the gap is significantly smaller than the size of the sheet-shaped carbon-based material. Therefore, the sheet-shaped carbon-based material cannot effectively fill the gap between the silicon-based materials. The conductivity between the silicon-based materials is reduced, which is not conducive to the improvement of cycle performance. Therefore, in some embodiments of the present disclosure, the ratio of the Dv50 of the sheet-shaped carbon-based material to the Dv50 of the silicon-based material is controlled to be less than 1.

In some embodiments of the present disclosure, the mass of the flaky carbon-based material accounts for 0.5%-40% of the total mass of the silicon-based material and the flaky carbon-based material. In some embodiments, when the ratio of the flaky carbon-based material to the total mass of the silicon-based material and the flaky carbon-based material is less than 0.5%, since the content of the flaky carbon-based material is too low, the compaction of the negative electrode material cannot be significantly improved. Density, conductivity and cycle performance, and when the mass of the flaky carbon-based material accounts for more than 40% of the total mass of the silicon-based material and the flaky carbon-based material, the specific capacity of the flaky carbon-based material is much smaller than that of the silicon-based material. The specific capacity of the material, too high content of the flake carbon-based material will cause the specific capacity and volume energy density of the negative electrode material to decrease.

In some embodiments of the present disclosure, the sheet-shaped carbon-based material includes graphite, and the graphitization degree of the graphite is above 90%. In some embodiments, graphite is prone to slip along the direction of the sheet to play a lubricating effect to fill the gaps between silicon-based materials. However, when the graphitization degree of graphite is less than 90%, the defects in the graphite are relatively large. Many defects will prevent graphite from sliding along the direction of the sheet. Graphite is difficult to lubricate and can not effectively fill the gaps between silicon-based materials, which is not conducive to improving the compaction density, conductivity and cycle performance of the negative electrode material.

In some embodiments of the present disclosure, the silicon-based material includes at least one of silicon oxide, silicon, silicon-carbon composite material, or silicon alloy.

In some embodiments of the present disclosure, the silicon-based material at least satisfies one of the following (a) to (f): (a) the surface of the silicon oxide has a sheet-like carbon-based material. In some embodiments, the conductivity of silicon oxide is poor, so when (a) is satisfied, the conductivity of silicon oxide can be increased to improve cycle performance.

(b) The particle size range of silicon oxide satisfies 1 μm<Dv50<10 μm. If the particle size of silicon oxide is too small, it will increase the consumption of electrolyte and is not conducive to cycle performance. When the particle size of silicon oxide is too large, it will cause degradation of rate performance. Therefore, in some embodiments, it is necessary to meet (b) control The particle size range of the silicon oxide compound.

(c) The specific surface area of silicon oxide is less than 10 m ² /g. In some embodiments, when the specific surface area of silicon oxide is not less than 10m ² /g, more electrolyte will be consumed to form an SEI (solid electrolyte interface) film, resulting in excessive loss of first charge capacity and increased adhesion. Therefore, the specific surface area of silicon oxide is set to be less than 10 m ² /g.

(d) The general formula of silicon oxide is SiO _x , where 0<x<2. In some embodiments, since 0<x<2 in silicon oxide, certain point defects, such as holes, are introduced into silicon oxide. By introducing point defects, the conductivity of silicon oxide can be improved, thereby improving cycle performance. .

(e) Silicon includes at least one of silicon microparticles, silicon nanoparticles, silicon nanowires, or silicon nanofilms.

(f) The silicon alloy includes at least one of silicon-iron alloy, silicon-aluminum alloy, silicon-nickel alloy, or silicon-iron-aluminum alloy.

In some embodiments of the present disclosure, the flaky carbon-based material includes at least one of graphite, graphene, soft carbon, or hard carbon, and the particle size range of the flaky carbon-based material satisfies Dv50<10 μm. In some embodiments, the graphite includes artificial graphite, natural graphite, or a combination thereof, wherein the artificial graphite or natural graphite includes at least one of mesophase carbon microspheres, soft carbon, or hard carbon. In some embodiments of the present disclosure, the silicon-based material and the sheet-shaped carbon-based material in the negative electrode material are composited through at least one of physical mixing and mechanical nodular ink. In some embodiments, when preparing the negative electrode material, the flaky carbon-based material can be mixed with the silicon-based material according to a certain mass percentage. At least one of the airflow mixer or the horizontal mixer is mixed, and then the mixed silicon-based material and the flake carbon-based material can be further subjected to a ball milling mechanical reaction, so that at least a part of the outer surface of the silicon-based material is covered by the flake carbon-based material. The material adheres to the coating, that is, makes the surface of the silicon-based material have a sheet-like carbon-based material. The silicon-based material may be at least one of silicon oxide, pure silicon, silicon carbon, or silicon alloy. In some embodiments, pure silicon may be microparticles, nanoparticles, nanowires, nanofilms, or nanospheres. At least one.

As shown in FIG. 3, some embodiments of the present disclosure provide a negative pole piece. The negative pole piece includes a current collector 1 and an active material layer 2. The active material layer 2 is located on the current collector 1. It should be understood that although the active material layer 2 is shown as being located on one side of the current collector 1 in FIG. 2, this is only exemplary, and the active material layer 2 may be located on both sides of the current collector 1. In some embodiments, the current collector of the negative pole piece may include at least one of copper foil, aluminum foil, nickel foil, or carbon-based current collector. In some embodiments, the active material layer 2 includes any one of the above-mentioned negative electrode materials.

In some embodiments, the active material layer further includes a silicon-based material conductive agent and/or a binder. In some embodiments, the binder may include carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, polystyrene-butadiene At least one of rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. In some embodiments, the mass percentage of the binder in the active material layer is 0.5%-10%. In some embodiments, the thickness of the active material layer is 50 μm to 200 μm, and the compacted density of the negative electrode material in the active material layer under a pressure of 5 t is 0.8 g/cm ³ to 5 g/cm ³ . In some embodiments, the mass content of the carbon element in the active material layer is 0-80%. In some embodiments, the specific surface area of the negative electrode material in the active material layer ranges from 1 m ² /g to 50 m ² /g. In some embodiments, the conductive agent may include at least one of conductive carbon black, Ketjen black, acetylene black, carbon nanotubes, VGCF (Vapor Grown Carbon Fiber), or graphene.

As shown in FIG. 4, some embodiments of the present disclosure provide an electrochemical device. The electrochemical device includes a positive pole piece 10, a negative pole piece 12, and a separator disposed between the positive pole piece 10 and the negative pole piece 12. 11. The positive pole piece 10 may include a positive current collector and a positive active material layer coated on the positive current collector. In some embodiments, the positive active material layer may only be coated on a partial area of the positive current collector. The positive active material layer may include a positive active material, a conductive agent, and a binder. Al foil can be used as the positive electrode current collector, and similarly, other positive electrode current collectors commonly used in this field can also be used. The conductive agent of the positive pole piece may include at least one of conductive carbon black, sheet graphite, graphene, or carbon nanotubes. The binder in the positive pole piece may include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, styrene-acrylate copolymer, styrene-butadiene copolymer, polyamide, polyacrylonitrile, Polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene At least one of them. The positive electrode active material includes at least one of lithium cobaltate, lithium nickelate, lithium manganate, lithium nickel manganate, lithium nickel cobaltate, lithium iron phosphate, lithium nickel cobalt aluminate or lithium nickel cobalt manganate. The substance can be doped or coated.

In some embodiments, the isolation film 11 includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. Especially polyethylene and polypropylene, they have a good effect on preventing short circuits, and can improve the stability of the battery through the shutdown effect. In some embodiments, the thickness of the isolation film is in the range of about 5 μm to 500 μm.

In some embodiments, the surface of the isolation membrane may further include a porous layer, the porous layer is disposed on at least one surface of the isolation membrane, the porous layer includes inorganic particles and a binder, and the inorganic particles are selected from alumina (Al ₂ O ₃ ), Silicon oxide (SiO ₂ ), magnesium oxide (MgO), titanium oxide (TiO ₂ ), hafnium dioxide (HfO ₂ ), tin oxide (SnO ₂ ), ceria (CeO ₂ ), nickel oxide (NiO), oxide Zinc (ZnO), calcium oxide (CaO), zirconium oxide (ZrO ₂ ), yttrium oxide (Y ₂ O ₃ ), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or sulfuric acid At least one of barium. In some embodiments, the pores of the isolation membrane have a diameter in the range of about 0.01 μm to 1 μm. The binder is selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyethylene pyrrole At least one of alkanone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene. The porous layer on the surface of the isolation membrane can improve the heat resistance, oxidation resistance and electrolyte infiltration performance of the isolation membrane, and enhance the adhesion between the isolation membrane and the pole piece.

In some embodiments, the negative pole piece 12 may be the negative pole piece as described above.

In some embodiments of the present disclosure, the electrode assembly of the electrochemical device is a wound electrode assembly or a stacked electrode assembly.

In some embodiments, the electrochemical device includes a lithium ion battery, but the present disclosure is not limited thereto. In some embodiments, the electrochemical device may also include an electrolyte. In some embodiments, the electrolyte includes, but is not limited to, dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), ethylene carbonate (EC), propylene carbonate (PC), At least two of propyl propionate (PP). In addition, the electrolyte may additionally include at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC), or dinitrile compound as an additive to the electrolyte. In some embodiments, the electrolyte further includes a lithium salt.

In some embodiments of the present disclosure, taking a lithium ion battery as an example, the positive pole piece, the separator film, and the negative pole piece are wound or stacked in order to form electrode parts, and then packed into, for example, aluminum-plastic film for packaging, and electrolysis is carried out. Lithium-ion battery is made by liquid, formed and packaged. Then, perform performance test and cycle test on the prepared lithium-ion battery.

Those skilled in the art will understand that the method for preparing an electrochemical device (for example, a lithium ion battery) described above is only an example. Without departing from the content disclosed in this application, other methods commonly used in the art can be used.

The embodiments of the present disclosure also provide an electronic device including the above-mentioned electrochemical device. The electronic device of the present application is not particularly limited, and it can be used in any electronic device known in the prior art. In some embodiments, electronic devices may include, but are not limited to, notebook computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, headsets, Video recorders, LCD TVs, portable cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, assisted bicycles, bicycles, Lighting equipment, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries and lithium-ion capacitors, etc.

Some specific embodiments and comparative examples are listed below to better illustrate the present disclosure, in which a lithium ion battery is used as an example.

Example 1

Anode material preparation: SiO _x (0<x<2, Dv50: 6μm, specific surface area: 2m ² /g) and flake graphite (diameter-thickness ratio: 5, graphitization degree: 97%, Dv50: 4.2μm) After mixing with a mass ratio of 95:5, it is placed in a planetary ball mill for further surface adhesion treatment. _{The particle size ratio of flake graphite to SiO x} is 0.7 (that is, the ratio of Dv50 of flake graphite to Dv50 of SiO _x is 0.7). The sample after the ball milling treatment was used as the negative electrode material.

Preparation of the negative electrode piece: the negative electrode material, conductive agent conductive acetylene black, binder polyacrylic resin (PAA), according to the weight ratio of 80:10:10 in deionized water, fully stirred and mixed uniformly to make a negative electrode slurry, and then The negative electrode slurry is evenly coated on the front and back sides of the negative electrode current collector copper foil, and then dried at 85°C to form the negative electrode active material layer, and then cold press, slitting, cutting, and welding the negative electrode tabs to obtain Negative pole piece.

Preparation of positive pole piece: The positive electrode material lithium cobalt oxide (molecular formula is LiCoO ₂ ), conductive agent (acetylene black), binder (polyvinylidene fluoride, PVDF) in N-form at a mass ratio of 96:2:2 Stir and mix the base pyrrolidone thoroughly to make a positive electrode slurry. Then, the obtained positive electrode slurry is evenly coated on the positive and negative sides of the positive electrode collector aluminum foil, and then dried at 85°C and then cold pressed, slitted, and cut. Sheet and weld the positive electrode tab to obtain the positive electrode tab.

Battery preparation: LiPF ₆ lithium salt and non-aqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): propyl propionate (PP): vinylene carbonate ( VC) mass ratio=20:30:20:28:2) The solution prepared by mass ratio 8:92 is used as the electrolyte of the lithium ion battery. The isolation membrane adopts a ceramic-coated polyethylene (PE) material isolation membrane. The positive pole piece, the isolation film, and the negative pole piece are stacked in order to obtain an electrode assembly, and the isolation film is placed between the positive and negative electrodes to play a role of isolation. The electrode assembly is placed in a packaging case, electrolyte is injected and packaged, and the final lithium-ion battery is formed after chemical formation.

In Examples 2 to 10 and Comparative Examples 1 to 2, the methods for preparing the negative pole piece, the positive pole piece and the battery are the same as that of Embodiment 1, and the difference from Embodiment 1 is only in the preparation of the negative electrode material.

The difference between Example 2 and Example 1 is that the mass of flake graphite in Example 2 accounts for 10% of the total mass of _{SiO x and flake graphite.}

The difference between Example 3 and Example 1 is that the mass of flake graphite in Example 3 accounts for 20% of the total mass of _{SiO x and flake graphite.}

The difference between Example 4 and Example 1 is that the mass of flake graphite in Example 4 accounts for 30% of the total mass of _{SiO x and flake graphite.}

The difference between Example 5 and Example 1 is that the mass of flake graphite in Example 5 accounts for 40% of the total mass of _{SiO x and flake graphite.}

The difference between Example 6 and Example 1 is that the mass of flake graphite in Example 6 accounts _{for 20% of the total mass of SiO x} and flake graphite, and the diameter-to-thickness ratio of flake graphite in Example 6 is 2.

The difference between Example 7 and Example 1 is that the mass of flake graphite in Example 7 accounts for 20% of the total mass of _{SiO x} and flake graphite, and the ratio of Dv50 of _{flake graphite to Dv50 of SiO x in Example 7} Is 1.

The difference between Example 8 and Example 1 is that the mass of flake graphite in Example 8 accounts for 20% of the total mass of _{SiO x} and flake graphite, and the ratio of Dv50 of _{flake graphite to Dv50 of SiO x in Example 8} Is 2.

The difference between Example 9 and Example 1 is that the mass of flake graphite in Example 9 accounts _{for 20% of the total mass of SiO x} and flake graphite, and the graphitization degree of flake graphite in Example 9 is 94%.

The difference between Example 10 and Example 1 is that the mass of flake graphite in Example 10 accounts _{for 20% of the total mass of SiO x} and flake graphite, and the graphitization degree of flake graphite in Example 10 is 92%.

The difference between Comparative Example 1 and Example 1 is that in Comparative Example 1, SiO _x (0<x<2, Dv50: 6 μm, specific surface area: 2 m ² /g) is directly used as a negative electrode material without any treatment.

The difference between Comparative Example 2 and Example 1 is that: in Comparative Example 2, non-flaky graphite with a diameter-to-thickness ratio of 1 is used, and the mass of non-flaky graphite in Comparative Example 2 accounts for _{the total mass of SiO x} and non-flaky graphite. 20%.

The methods for measuring various performance parameters of the Examples and Comparative Examples are as follows.

Cycle performance test method:

Charge at a rate of 0.5C to 4.45V, change to 4.45V constant voltage charge until the current drops to 0.025C, after standing for 5 minutes, discharge to 3.0V at a rate of 0.5C to complete a cycle, record the discharge capacity as lithium ion The initial capacity of the battery. Repeat the 200-week cycle, and record the discharge capacity as the remaining capacity of the lithium-ion battery. Capacity retention rate=remaining capacity/initial capacity*100%.

Powder compaction density test:

The powder compaction density meter is used to put a specific weight of powder in the standard module, and the compression height of the powder in the standard module is measured under different pressures of MPa, so that the compression height and the cross-sectional area of the standard module can be calculated The volume of the powder under different pressures is then combined with the weight of the powder to calculate the compacted density of the powder.

Granularity test:

Add 0.02g powder sample to a 50ml clean beaker, add 20ml deionized water, and add a few drops of 1% surfactant to completely disperse the powder in the water. Ultrasound for 5 minutes in a 120W ultrasonic cleaning machine, and use MasterSizer 2000 to test the particle size distribution .

Specific capacity test method:

Discharge to 5mV at a constant current rate of 0.05C. After standing for 5 minutes, change to a current of 50uA and continue to discharge to 5mV. After standing still for 5 minutes, switch to a current of 10uA and continue to discharge to 5mV; then use a constant current of 0.05C. Charge to 2V and complete the charge-discharge specific capacity test after 30 minutes of inactivity.

Data statistics are performed on the test results of Examples 1-10 and Comparative Examples 1-2, and the statistical results are shown in Table 1.

Table 1

The flake graphite content in Table 1 is the ratio of the mass of flake graphite in the negative electrode material to the total mass of flake graphite and SiO _x , the diameter-to-thickness ratio is the diameter-to-thickness ratio of the flake graphite in the negative electrode material, and the Dv50 ratio is the flake graphite Dv50 and Dv50 ratio of SiO _x, the tap density × specific capacity negative electrode material = volume energy density of negative electrode material.

The compacted densities of the negative electrode materials of Example 3 and Comparative Example 1 were measured under different pressures. The measurement results are shown in Figure 5. It can be seen that the relationship between the compacted densities of Comparative Example 1 and Example 3 does not vary. The pressure varies. Under any pressure, the compaction density of the negative electrode material with flake graphite in Example 3 is greater than that of Comparative Example 1 without flake graphite.

Comparing the test results of Comparative Example 1 with Examples 1-10 and Comparative Example 2, it can be seen that in Comparative Example 1, when only silicon-based materials are used as the negative electrode material without adding flake graphite, the compaction density of the negative electrode material is It is only 1.35 g/cc and the 200-week cycle capacity retention rate is only 88.6%. In Examples 1-10 and Comparative Example 2 where flake graphite is added, the compaction density and the 200-week cycle capacity retention rate are higher than those of Comparative Example 1. This is because when the flake graphite is not added, the gap between the silicon-based materials in the negative electrode material is large, resulting in a lower compaction density, and the lower compaction density causes the silicon-based materials to be ineffective in electrical contact with each other, and The silicon-based material itself has poor conductivity, so the cycle performance of the battery is poor. After adding flake graphite to the negative electrode material containing silicon-based materials, the added flake graphite can fill the gaps of the silicon-based materials to increase the compaction density and achieve effective electrical contact between the silicon-based materials, thereby improving the negative electrode The overall conductivity of the material further improves the cycle performance. Therefore, in some embodiments of the present disclosure, a sheet-shaped carbon-based material is added to the negative electrode material containing a silicon-based material to improve the compaction density and cycle performance.

Comparing the test results of Examples 3, 6 and Comparative Example 2, it can be seen that the compaction density, volume energy density, and 200-cycle cycle capacity retention rate of the negative electrode material increase with the increase in the diameter-to-thickness ratio of the flake graphite, and decrease the flake graphite The diameter-to-thickness ratio will cause a decrease in the compaction density of the negative electrode material, which will result in a decrease in the volumetric energy density. This is because when the diameter and thickness of the flake graphite are relatively high, the weak van der Waals force between the flake graphite flakes makes it easier for the graphite to slide along the direction of the flakes, that is, the macroscopic layer structure of the flake graphite is easier. Play a role of lubrication, so as to fully fill the gap between the silicon-based materials, improve the compaction density of the negative electrode material, increase the electrical contact between the silicon-based materials, thereby improving the volumetric energy density and cycle performance. When the diameter and thickness of the flake graphite is relatively low, it is difficult for the flake graphite to fully fill the gap between the silicon-based materials, resulting in a decrease in the compaction density, and it is difficult to achieve electrical contact between the silicon-based materials, resulting in a deterioration of the conductive network of the negative electrode material. , Which in turn leads to a decrease in volumetric energy density and deterioration in cycle performance. Based on this, in some embodiments of the present disclosure, the diameter-to-thickness ratio of the sheet-shaped carbon-based material is greater than 2 to ensure the volumetric energy density and cycle performance.

Comparing the specific capacity test results of the negative electrode materials of Comparative Examples 1 to 5, it can be seen that the specific capacity of the negative electrode material decreases with the increase of the flake graphite content. This is because the specific capacity of the flake graphite is smaller than that of the silicon-based material. As the content of flake graphite in the negative electrode material increases, the specific capacity of the overall negative electrode material will decrease. Comparing the compaction density and volume energy density test results of Comparative Examples 1 to 5, it can be seen that the compaction density increases with the increase of the flake graphite content, and the volume energy density depends on the specific capacity and the compaction density. As the content of flake graphite increases, it decreases, so the volume energy density first increases and then decreases with the increase of the content of flake graphite (refer to Figure 6). The volume energy density reaches its maximum value near 10% of the flake graphite content.

Comparing the 200-week cycle capacity retention test results of Comparative Examples 1 to 5, it can be seen that the cycle performance is significantly improved after adding flake graphite (refer to Figure 7), and the cycle performance first increases with the increase of the flake graphite content Then it decreases and reaches the optimal value when the content of flake graphite is 20%. This is due to the poor conductivity of silicon-based materials. When the compaction density is low, poor contact between the silicon-based materials leads to further deterioration of the conductivity. The addition of flake graphite increases the compaction density of the negative electrode material, thereby increasing the electrical contact between the silicon particles, and the flake graphite itself as a carbon-based material can also increase the conductivity of the negative electrode material. In general, the introduction of flake graphite has improved the conductive network of the negative electrode material containing silicon-based materials, thereby improving the cycle performance. On the other hand, due to the higher orientation of the flake structure of flake graphite, it has High anisotropy will lead to poor ionic conductivity, so when the content of flake graphite is too high, it will cause poor lithium ion conductivity of the composite silicon substrate, which will worsen the cycle performance.

Based on the above reasons, in some embodiments of the present disclosure, the mass of the flake carbon-based material accounts for 0.5% to 40% of the total mass of the flake carbon-based material and the silicon-based material, thereby improving the cycle performance of the negative electrode material. Ensure the volumetric energy density of the negative electrode material.

Comparing the test results of Examples 3, 7 and 8, it can be seen that increasing the Dv50 particle size ratio of the flake graphite to the silicon-based material will result in a decrease in the compaction density, thereby resulting in a decrease in the volume energy density. This is because when the particle size of the flake graphite is larger than that of the silicon-based material, the flake graphite can only play the role of sliding, and the smaller gaps between the silicon-based materials cannot be effectively filled, thereby reducing the pressure of the negative electrode material. Real density, at the expense of volumetric energy density, the conductive network of the negative electrode material will also be affected, which is not conducive to cycle performance. Therefore, in some embodiments of the present disclosure, the ratio of the Dv50 of the sheet-shaped carbon-based material to the Dv50 of the silicon-based material less than 1.

Comparing the test results of Examples 3, 9 and 10, it can be seen that when the graphitization degree of flake graphite is reduced, the compaction density will be reduced, and the volume energy density will be reduced. This is because when the graphitization degree of the flake graphite is low, the flake graphite will contain more defects, and the slip between the flake graphite layers will become difficult due to the influence of the defects, resulting in the lubrication of the flake graphite It is difficult to fill the gaps between silicon-based materials, thereby reducing the compaction density and affecting the conductive network of the negative electrode material, which is not conducive to the improvement of cycle performance. Therefore, in some embodiments of the present disclosure, graphite in the sheet-shaped carbon-based material The degree of graphitization is above 90%.

The above description is only a preferred embodiment of the present disclosure and an explanation of the applied technical principles. Those skilled in the art should understand that the scope of disclosure involved in this disclosure is not limited to the technical solutions formed by the specific combination of the above technical features, and should also cover the above technical features or technical solutions without departing from the above disclosed concept. Other technical solutions formed by arbitrarily combining the equivalent features. For example, the above-mentioned features and the technical features with similar functions disclosed in the present disclosure are replaced with each other to form a technical solution.

Claims

A negative electrode material, including:

Silicon-based materials and sheet carbon-based materials;

Wherein, the diameter-to-thickness ratio of the sheet-shaped carbon-based material is greater than 2.
The negative electrode material according to claim 1, wherein the sheet-shaped carbon-based material has Dv50=A, and the silicon-based material has Dv50=B, and A/B<1.
The negative electrode material according to claim 1, wherein the mass of the sheet-shaped carbon-based material accounts for 0.5%-40% of the total mass of the silicon-based material and the sheet-shaped carbon-based material.
The negative electrode material according to claim 1, wherein the sheet-shaped carbon-based material comprises graphite, and the graphitization degree of the graphite is above 90%.
The anode material according to claim 1, wherein the silicon-based material includes at least one of silicon oxide, silicon, silicon-carbon composite material, or silicon alloy.
The negative electrode material according to claim 5, wherein the silicon-based material satisfies at least one of the following:

The surface of the silicon oxide has the sheet-shaped carbon-based material;

The particle size range of the silicon oxide satisfies 1μm<Dv50<10μm;

The specific surface area of the silicon oxide is less than 10 m 2 /g;

The general formula of the silicon oxide is SiO x , where 0<x<2;

The silicon includes at least one of silicon micro-particles, silicon nanoparticles, silicon nanowires, or silicon nano-films;

The silicon alloy includes at least one of silicon-iron alloy, silicon-aluminum alloy, silicon-nickel alloy, or silicon-iron-aluminum alloy.
The anode material according to claim 1, wherein the flake-shaped carbon-based material comprises at least one of graphite, graphene, soft carbon or hard carbon, and the particle size range of the flake-shaped carbon-based material satisfies Dv50< 10μm.
A negative pole piece, including:

Current collector

The active material layer is located on the current collector;

Wherein, the active material layer includes the anode material according to any one of claims 1 to 7.
An electrochemical device, including:

Positive pole piece

Negative pole piece

Separating membrane, arranged between the positive pole piece and the negative pole piece;

Wherein, the negative pole piece is the negative pole piece according to claim 8.
An electronic device comprising the electrochemical device according to claim 9.