阅读说明：本技术 一种负极复合材料的制备方法及负极复合材料 (Preparation method of negative electrode composite material and negative electrode composite material ) 是由 易婷 陈志焕 崔航 谢远森 于 2020-04-27 设计创作，主要内容包括：本申请实施例提供了一种负极复合材料的制备方法,包括将碳源溶解于有机溶剂中,加入有机硅充分混合,随后加热搅拌去除有机溶剂,干燥；在惰性气体的保护下,在900℃至1500℃高温裂解得到Si-M-C复合材料；将Si-M-C复合材料与石墨烯浆料混合搅拌得到混合浆料；喷雾干燥造粒。采用本申请实施例提供的负极复合材料的制备方法,所获得的负极复合材料具有更低的膨胀性；此外,本申请的Si-M-C复合材料表面存在的石墨烯能够提高负极复合材料的导电性,使应用所述负极复合材料的负极极片、电化学装置具有良好的循环性能。(The embodiment of the application provides a preparation method of a negative electrode composite material, which comprises the steps of dissolving a carbon source in an organic solvent, adding organic silicon for fully mixing, heating and stirring to remove the organic solvent, and drying; under the protection of inert gas, carrying out pyrolysis at 900-1500 ℃ to obtain a Si-M-C composite material; mixing and stirring the Si-M-C composite material and the graphene slurry to obtain mixed slurry; spray drying and granulating. By adopting the preparation method of the cathode composite material provided by the embodiment of the application, the obtained cathode composite material has lower expansibility; in addition, the graphene on the surface of the Si-M-C composite material can improve the conductivity of the negative electrode composite material, so that a negative electrode plate and an electrochemical device using the negative electrode composite material have good cycle performance.)

1. The preparation method of the negative electrode composite material is characterized by comprising the following steps of:

1) dissolving a carbon source in an organic solvent, adding organic silicon after the carbon source is completely dissolved, stirring for 3 to 5 hours to fully mix the carbon source solution with the organic silicon, then heating and stirring to remove the organic solvent, and drying;

wherein the mass ratio of the carbon source to the organic silicon is 1:2 to 2: 1;

2) cracking the product obtained in the step 1) at the high temperature of 900-1500 ℃ under the protection of inert gas to obtain a Si-M-C composite material; wherein M comprises at least one of boron, nitrogen or oxygen;

3) mixing and stirring the Si-M-C composite material and the graphene slurry to obtain mixed slurry;

wherein the mass ratio of the Si-M-C composite material to the graphene is 4:1 to 99: 1;

4) and (4) spray drying and granulating the mixed slurry.

2. The method of claim 1, wherein the carbon source comprises at least one of glucose or sucrose.

3. The method of claim 1, wherein the organic solvent comprises at least one of xylene, acetone, cyclohexane, or triethylamine.

4. The method of claim 1, wherein the silicone comprises at least one of polysiloxane, polysilazane, polycarboborosilazane, or polysilaborazane.

5. The method according to any one of claims 1 to 4, wherein the mass-to-volume ratio of the carbon source to the organic solvent is 0.01g/ml to 0.1 g/ml.

6. The process according to any one of claims 1 to 4, wherein in step 2), pyrolysis is carried out at 900 ℃ to 1500 ℃ under the following reaction conditions: heating to 500 deg.C at 1 deg.C/min, holding for 30min, heating to 900-1500 deg.C at 3 deg.C/min, and holding for 3 hr.

7. The preparation method according to any one of claims 1 to 4, wherein in the step 4), deionized water is added to the mixed slurry before spray drying granulation, and the solid content of the mixed slurry is adjusted to 30% to 60%.

8. The method according to any one of claims 1 to 4, wherein the spray-dried granulation is centrifugal spray-dried granulation, and the centrifugal rotation speed is 500rpm to 5000 rpm.

9. The method according to any one of claims 1 to 4, wherein in step 2), the inert gas comprises nitrogen or argon.

10. The negative electrode composite material produced by the production method according to any one of claims 1 to 9.

Technical Field

The application relates to the technical field of negative electrode composite materials, in particular to a preparation method of a negative electrode composite material and the negative electrode composite material prepared by the method.

Background

The lithium ion battery has the characteristics of large specific energy, high working voltage, low self-discharge rate, small volume, light weight and the like, and has wide application in the field of consumer electronics. With the rapid development of electric vehicles and mobile electronic devices, people have increasingly high requirements on energy density, safety, cycle performance and the like of lithium ion batteries. Wherein, the silicon material has high theoretical specific capacity (4200mAh/g), and has wide application prospect in lithium ion batteries. The silicon-based material can generate 120 to 300 percent volume change along with the intercalation and deintercalation of lithium ions, so that the silicon-based material is pulverized and separated from a current collector, and the problems can reduce the cycle performance of the lithium ion battery and prevent the further application of the silicon-based negative electrode material.

At present, the research on silicon-based negative electrode materials is mostly focused on preparing composite silicon-based materials, so as to try to limit the expansion of the silicon-based materials through the compounding of the silicon-based materials and other elements.

Disclosure of Invention

The present inventors found in their research that the performance of a silicon-based composite material is greatly affected by the preparation method, the raw materials are different, the reaction conditions are different, and the product composition is the same, and the performance, such as the swelling performance, may have a great difference. The specific technical scheme is as follows:

the application provides a preparation method of a negative electrode composite material, which comprises the following steps:

1) dissolving a carbon source in an organic solvent, adding organic silicon after the carbon source is completely dissolved, stirring for 3 to 5 hours to fully mix the carbon source solution with the organic silicon, then heating and stirring to remove the organic solvent, and drying;

wherein the mass ratio of the carbon source to the organic silicon is 1:2 to 2: 1;

2) cracking the product obtained in the step 1) at the high temperature of 900-1500 ℃ under the protection of inert gas to obtain a Si-M-C composite material; wherein M comprises at least one of boron, nitrogen or oxygen;

3) mixing and stirring the Si-M-C composite material and the graphene slurry to obtain mixed slurry;

wherein the mass ratio of the Si-M-C composite material to the graphene is 4:1 to 99: 1;

4) and (4) spray drying and granulating the mixed slurry.

In some embodiments of the first aspect of the present application, the carbon source comprises at least one of glucose or sucrose.

In some embodiments of the first aspect of the present application, the organic solvent comprises at least one of xylene, acetone, cyclohexane or triethylamine.

In some embodiments of the first aspect of the present application, the silicone comprises at least one of a polysiloxane, a polysilazane, a polycarboboranomethylsiloxane, or a polysilazane.

In some embodiments of the first aspect of the present application, the mass to volume ratio of the carbon source to the organic solvent is from 0.01g/ml to 0.1 g/ml.

In some embodiments of the first aspect of the present application, in step 2), the pyrolysis is carried out at 900 ℃ to 1500 ℃ under the following reaction conditions: heating to 500 deg.C at 1 deg.C/min, holding for 30min, heating to 900-1500 deg.C at 3 deg.C/min, and holding for 3 hr.

In some embodiments of the first aspect of the present application, in step 4), deionized water is added to the mixed slurry before spray drying granulation, and the solid content of the mixed slurry is adjusted to 30% to 60%.

In some embodiments of the first aspect of the present application, the spray-dried granulation is centrifugal spray-dried granulation, and the centrifugal rotation speed is 500rpm to 5000 rpm.

In certain embodiments of the first aspect of the present application, in step 2), the inert gas comprises nitrogen or argon.

In a second aspect, the present application provides an anode composite prepared according to the preparation method of the first aspect of the present application.

By adopting the preparation method of the cathode composite material provided by the embodiment of the application, the obtained cathode composite material has lower expansibility; in addition, the graphene on the surface of the Si-M-C composite material can improve the conductivity of the negative electrode composite material, so that a negative electrode plate and an electrochemical device using the negative electrode composite material have good cycle performance.

Herein, the particle diameters of the negative electrode composite material and the Si-M-C composite material are represented by Dv50, "Dv 50" represents a particle diameter at which the cumulative distribution of particles is 50%; i.e. the volume content of particles smaller than this size is 50% of the total particles. The particle size is measured with a laser particle sizer.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1 is a solid NMR spectrum of a Si-M-C composite material of example 7.

Fig. 2 is a capacity fade curve for example 7 and comparative example 1.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

The application provides a preparation method of a negative electrode composite material, which comprises the following steps:

1) dissolving a carbon source in an organic solvent, adding organic silicon after the carbon source is completely dissolved, stirring for 3 to 5 hours to fully mix the carbon source solution with the organic silicon, then heating and stirring to remove the organic solvent, and drying;

wherein the mass ratio of the carbon source to the organic silicon is 1:2 to 2: 1;

2) cracking the product obtained in the step 1) at the high temperature of 900-1500 ℃ under the protection of inert gas to obtain a Si-M-C composite material; wherein M comprises at least one of boron, nitrogen or oxygen;

3) mixing and stirring the Si-M-C composite material and the graphene slurry to obtain mixed slurry;

wherein the mass ratio of the Si-M-C composite material to the graphene is 4:1 to 99: 1;

4) and (4) spray drying and granulating the mixed slurry.

The inventors have found in their research that Si-M-C composites containing different elemental compositions can be prepared when different silicones are used, which in some embodiments of the first aspect of the present application include at least one of polysiloxane, polysilazane, polycarboboranomethylsiloxane, or polysilaborazane; depending on the elements contained in the organosilicon, M in the Si-M-C composite material prepared herein may be at least one of boron, nitrogen, or oxygen.

The inventor also finds in research that the pyrolysis reaction temperature affects the performance of the Si-M-C composite material, on one hand, the pyrolysis temperature affects the particle size of the Si-M-C composite material, and the higher the pyrolysis temperature is, the larger the particle size of the Si-M-C composite material is; in addition, the inventors have also surprisingly found that too high or too low a pyrolysis temperature results in an increase in the expansion rate of the anode composite, and that the prepared anode composite has a lower expansion rate when the reaction temperature is between 900 ℃ and 1500 ℃.

In some embodiments of the first aspect of the present application, the carbon source comprises at least one of glucose or sucrose.

In some embodiments of the first aspect of the present application, the organic solvent comprises at least one of xylene, acetone, cyclohexane or triethylamine.

The heating and stirring in step 1) are common technical means in the art, and the purpose of the heating and stirring is to remove the organic solvent, for example, the heating and stirring can be performed at 60 ℃ to 100 ℃, and the application is not limited herein.

The drying in step 1) is a common technique in the art, and may be performed, for example, in a drying oven at 60 ℃ to 100 ℃ for 20 to 30 hours, which is not limited herein.

In some embodiments of the first aspect of the present application, the mass to volume ratio of the carbon source to the organic solvent is from 0.01g/ml to 0.1g/ml, preferably from 0.04g/ml to 0.06g/ml, more preferably 0.05 g/ml.

In some embodiments of the first aspect of the present application, in step 2), the pyrolysis is carried out at 900 ℃ to 1500 ℃ under the following reaction conditions: heating to 500 deg.C at 1 deg.C/min, holding for 30min, heating to 900-1500 deg.C at 3 deg.C/min, and holding for 3 hr.

The "graphene paste" referred to herein means a paste in which graphene is dispersed in water, and the solid content of the graphene paste is not particularly limited as long as the object of the present invention can be achieved, and may be, for example, 1% to 10%.

In some embodiments of the first aspect of the present application, in step 4), deionized water is added to the mixed slurry before spray drying granulation, and the solid content of the mixed slurry is adjusted to 30% to 60%.

The inventor also finds in research that the existence of graphene can increase the conductivity of the negative electrode composite material, however, as the content of graphene increases, the cycle expansion of the battery increases, which is not limited to any theory, and may be caused by the fact that the conductivity increases to increase the lithium intercalation depth, and in addition, the large specific surface area of graphene causes a larger contact area with the electrolyte, and by-products increase, and the cycle expansion increases; therefore, in the application, the mass ratio of the Si-M-C composite material to the graphene is controlled to be 4:1 to 99: 1.

in some embodiments of the first aspect of the present application, the spray-dried granulation may be centrifugal spray-dried granulation, with a centrifugal speed of 500rpm to 5000 rpm.

The centrifugal rate influences the particle size of the negative electrode composite material, and the inventor finds in research that when the centrifugal rate is 500rpm to 5000rpm, the Dv50 of the negative electrode composite material is 6.0 μm to 15.0 μm, of course, other spray drying granulation methods can be adopted by those skilled in the art, and the parameters of the spray drying granulation can be controlled by those skilled in the art according to actual conditions, so that the particle size of the obtained negative electrode composite material is 6.0 μm to 15.0 μm; the equipment for spray drying granulation is not limited in the present application as long as the object of the present application can be achieved, and for example, a small spray drying equipment QM-1500-a of shanghaimeng or a tin-free super-large spray drying equipment can be used.

The inlet and outlet temperatures of the spray drying granulator are not limited in the present application as long as the purpose of the present application can be achieved, for example, the inlet temperature may be 240-; the outlet temperature may be 100-110 deg.C, preferably 105 deg.C.

In certain embodiments of the first aspect of the present application, in step 2), the inert gas comprises nitrogen or argon.

In a second aspect, the present application provides an anode composite prepared according to the preparation method of the first aspect of the present application.

The inventor finds in research that the chemical shift of the silicon element in the Si-M-C composite material prepared by the method of the application comprises-5 ppm +/-5 ppm, -35ppm +/-5 ppm, -75ppm +/-5 ppm, -110ppm +/-5 ppm, and the half-peak width K at-5 ppm +/-5 ppm meets the following conditions: k is more than 7ppm and less than 28 ppm. The inventors have also found that the temperature of pyrolysis affects the half-width at-5 ppm ± 5ppm, the half-width K at-5 ppm ± 5ppm at pyrolysis temperatures of 900 ℃ to 1500 ℃ satisfies: 7ppm < K < 28ppm, the negative electrode composite material has lower expansibility.

The inventor also finds that the Raman test peak is at the high temperature cracking temperature of less than 900 DEG CIntensity ratio I₁₃₅₀/I₁₅₈₀More than 1, the Si-M-C composite material has more surface defects, so that the first coulombic efficiency and the first cyclicity of the full battery are deteriorated, and the cyclic expansion is increased.

The negative electrode composite material prepared by the method of the present application may be prepared into a negative electrode sheet by a conventional method in the art, for example, a mixture of the negative electrode composite material of the present application and graphite is used as a negative electrode active material, and the negative electrode composite material may be mixed with a binder and a conductive agent to form a mixture layer, and coated on one or both surfaces of a current collector, and those skilled in the art may specifically select the mixture layer according to actual needs, and the present application is not limited herein.

The graphite may be selected from one or more of natural graphite, artificial graphite, mesocarbon microbeads, and the like.

The binder is not particularly limited, and may be any binder or combination thereof known to those skilled in the art, and for example, at least one of polyacrylate, polyimide, polyamide, polyamideimide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium hydroxymethyl cellulose, potassium hydroxymethyl cellulose, and the like may be used. These binders may be used alone, or two or more thereof may be used in combination at an arbitrary ratio.

The conductive agent is not particularly limited, and may be any conductive agent or a combination thereof known to those skilled in the art, and for example, at least one of a zero-dimensional conductive agent, a one-dimensional conductive agent, and a two-dimensional conductive agent may be used. Preferably, the conductive agent may include at least one of carbon black, conductive graphite, carbon fiber, carbon nanotube, VGCF (vapor grown carbon fiber), or graphene. The amount of the conductive agent is not particularly limited and may be selected according to the common general knowledge in the art. The conductive agent may be used alone, or two or more of them may be used in combination at an arbitrary ratio.

The current collector is not particularly limited, and any current collector known to those skilled in the art may be used. Specifically, for example, a current collector formed of at least one of iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, and the like may be used. Among them, copper foil or copper alloy foil is particularly preferable as the negative electrode current collector. One of the above materials may be used alone, or two or more of them may be used in combination in any ratio.

The negative pole piece prepared by the negative pole composite material can be applied to various electrochemical devices: such as all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. A typical electrochemical device is a lithium ion battery, which is a type of secondary battery. Electrochemical devices, such as lithium ion batteries, generally include a negative electrode sheet, a positive electrode sheet, a separator, and an electrolyte.

Taking a lithium ion battery as an example, the battery can be assembled in a conventional manner, which is not limited herein, for example, the negative electrode plate provided by the present application is used as the negative electrode plate; the other components including the positive electrode sheet, the separator, the electrolyte, and the like are not particularly limited. Illustratively, the positive electrode material included in the positive electrode sheet may include, but is not limited to, lithium cobaltate, lithium manganate, lithium iron phosphate, and the like. The material of the diaphragm may include, but is not limited to, fiberglass, polyester, polyethylene, polypropylene, polytetrafluoroethylene, or a combination thereof. The electrolyte generally includes an organic solvent, a lithium salt, and an additive. The organic solvent may include, but is not limited to, at least one of Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, and ethyl propionate. The lithium salt may include at least one of an organic lithium salt or an inorganic lithium salt; for example, the lithium salt may include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF)₄) Lithium difluorophosphate (LiPO)₂F₂) Lithium bis (trifluoromethanesulfonylimide) LiN (CF)₃SO₂)₂(LiTFSI), lithium bis (fluorosulfonyl) imide Li (N (SO)₂F)₂) (LiFSI), lithium bis (oxalato) borate LiB (C)₂O₄)₂(LiBOB), lithium difluoro (oxalato) borate LiBF₂(C₂O₄) (LiDFOB).

The preparation process of the battery is well known to those skilled in the art, and the present application is not particularly limited. For example, the secondary battery may be manufactured by the following process: the positive electrode and the negative electrode are overlapped through a spacer, and are placed into a battery container after operations such as winding, folding and the like are performed according to needs, an electrolyte is injected into the battery container and the battery container is sealed, wherein the negative electrode used is the negative electrode plate provided by the application. In addition, an overcurrent prevention element, a guide plate, or the like may be placed in the battery container as necessary to prevent a pressure rise, overcharge, and discharge inside the battery.

The present application will be specifically described below with reference to examples, but the present application is not limited to these examples.

Solid nuclear magnetic:

²⁹the Si solid NMR spectrum test is carried out on an AVANCE III 400WB wide-cavity solid NMR spectrometer with the rotation rate of 8kHz corresponding to²⁹And (3) Si. The solid NMR spectrum of the Si-M-C composite material of example 7 is shown in FIG. 1.

Raman testing:

adopting Jobin Yvon LabRAM HR spectrometer with excitation light source of 532nm and scanning wave number range of 0cm^-1～4000cm^-1The area of the test sample is 100 μm × 100 μm, and 100I samples are counted₁₃₅₀/I₁₅₈₀Value to obtain final I₁₃₅₀/I₁₅₈₀The value is obtained.

And (3) testing the granularity:

about 0.02g of each sample powder was added to a 50ml clean beaker, about 20ml of deionized water was added, several drops of 1% surfactant were added dropwise to completely disperse the powder in water, and the resulting mixture was ultrasonically cleaned in a 120W ultrasonic cleaner for 5 minutes, and the particle size distribution was measured using a MasterSizer 2000.

Testing the specific surface area of the composite material:

after the adsorption amount of the gas on the solid surface at different relative pressures is measured at constant temperature and low temperature, the adsorption amount of the monolayer of the sample is obtained based on the Bronuore-Eltt-Taylor adsorption theory and the formula (BET formula) thereof, and the specific surface area of the solid is calculated.

Composite powder conductivity test:

taking 5g of negative electrode composite material powder sample, and using electronsThe pressure machine is kept at constant pressure of 5000kg plus or minus 2kg for 15-25s, a sample is placed between electrodes of a resistivity tester (Suzhou lattice electron ST-2255A), the height h (cm) of the sample, the voltage U at two ends, the current I and the resistance R (K omega) are measured; the area S after powder compression was 3.14cm²The electronic conductivity of the powder was calculated according to the formula δ ═ h/(S × R)/1000, with the unit of S/cm.

Testing the resistance of the negative membrane:

the resistance of the cathode mixture layer is tested by adopting a four-probe method, an instrument used for testing by adopting the four-probe method is a precision direct-current voltage current source (SB118 type), four copper plates with the length of 1.5cm, the width of 1cm, the thickness of 2mm are equidistantly fixed on a line, the distance between the two copper plates in the middle is L (1-2cm), and the base material for fixing the copper plates is an insulating material. During testing, the lower end faces of four copper plates are pressed on the mixture layer of the tested negative electrode (the pressure is 3000Kg), the time is maintained for 60s, the copper plates at two ends are connected with a direct current I, the voltage V is measured at the two copper plates in the middle, the values of I and V are read for three times, the average values Ia and Va of I and V are respectively taken, and the value of Va/Ia is the mixture layer resistance at the testing position. 12 points of each pole piece are tested, and the average value is taken.

Detecting the specific capacity of the negative electrode composite material:

mixing the negative electrode composite material obtained in each example or comparative example with conductive carbon black and a binder PAA according to a mass ratio of 80: 10: 10 adding deionized water, stirring to form slurry with the solid content of 30%, coating the slurry with the mass M on a copper foil, drying the slurry in a vacuum drying oven at 85 ℃ for 12 hours, cutting the slurry into round pieces with the diameter of 1.4cm by using a punching machine in a drying environment, taking a metal lithium piece as a counter electrode in a glove box, selecting a ceglard composite film as an isolating film, and adding electrolyte to assemble the button cell. And (3) carrying out charge and discharge tests on the battery by using a blue electricity (LAND) series battery test system, and testing the charge and discharge performance of the battery, wherein the obtained capacity is C (mAh), and the specific capacity of the negative electrode composite material is C/(M multiplied by 30% multiplied by 80%).

And (3) testing the performance of the full battery:

and (3) testing the first efficiency of the full battery: in the first charge and discharge process of the full cell, the full cell is charged to 4.45V at a constant current of 0.5C, then charged to 0.025C at a constant voltage of 4.45V, (the obtained capacity is C0), and after standing for 5min, the full cell is discharged to 3.0V at 0.5C (the obtained discharge capacity is D0). Full cell first efficiency D0/C0.

And (3) cycle testing:

the test temperature was 45 ℃, and the voltage was charged to 4.45V at a constant current of 0.5C and 0.025C at a constant voltage, and discharged to 3.0V at 0.5C after standing for 5 minutes. Taking the capacity obtained in the step as initial capacity, carrying out 0.5C charging/0.5C discharging for cycle test, and taking the ratio of the capacity of each step to the initial capacity to obtain a capacity fading curve; wherein, the capacity fade curves of example 7 and comparative example 1 are shown in fig. 2; the capacity retention after 400 cycles of each example and comparative example is shown in table 1.

And (3) testing the full charge expansion rate of the lithium ion battery:

and testing the thickness of the lithium ion battery during initial half-charging by using a spiral micrometer. And (3) at the temperature of 45 ℃, when the charging and discharging are cycled to 400 times, the lithium ion battery is in a full charge state, the thickness of the lithium ion battery at the moment is tested by using a spiral micrometer, and the thickness is compared with the thickness of the lithium ion battery at the initial half charge, so that the expansion rate of the full charge lithium ion battery at the moment can be obtained.

Preparing a full battery:

preparing a negative pole piece:

mixing the negative electrode composite materials prepared in the embodiments and the comparative examples with graphite according to a certain proportion to obtain negative electrode active material powder with the designed specific capacity of 500mAh/g, and mixing the negative electrode active material powder, conductive agent acetylene black and PAA according to the weight ratio of 95: 1.2: 3.8, fully stirring and uniformly mixing in a deionized water solvent system, and then coating the mixture on two surfaces of a copper foil current collector with the thickness of 10 microns, wherein the coating thickness is 100 microns; drying the pole piece and then cold-pressing the pole piece, wherein the double-sided compaction density is 1.8g/cm³And obtaining the negative pole piece.

Preparing a positive pole piece:

active material LiCoO₂The conductive carbon black and the adhesive polyvinylidene fluoride (PVDF) are mixed according to the weight ratio of 96.7: 1.7: 1.6 in N-methyl pyrrolidone solvent system, preparing into slurry with solid content of 0.75, and stirring uniformly. And uniformly coating the slurry on one surface of an aluminum foil of the positive current collector with the thickness of 12 microns, drying at 90 ℃, and cold pressing to obtain the positive pole piece, wherein the coating thickness is 115 microns.

Assembling the whole battery:

a PE porous polymer film having a thickness of 15 μm was used as a separator. And stacking the positive pole piece, the isolating film and the negative pole piece in sequence to enable the isolating film to be positioned between the cathode and the anode to play an isolating role, and winding to obtain the electrode assembly. The electrode assembly was placed in an external pack and the prepared electrolyte (EC: DMC: DEC: 1:1 vol%, 10 wt% FEC, 1mol/L LiPF) was injected₆) And packaging, and carrying out technological processes of formation, degassing, edge cutting and the like to obtain the full cell.

Preparation of negative electrode composite material

Example 1

10g of glucose was completely dissolved in 200mL of xylene solvent, and 20g of polydimethylsiloxane (monomer C)₂H₆Adding OSi), stirring for 4 hr to mix glucose solution with polydimethylsiloxane, stirring at 80 deg.C, heating to remove solvent, oven drying at 80 deg.C for 24 hr to obtain product, and pyrolyzing in tubular furnace with N₂Cracking at 900 ℃ in a protective atmosphere, and performing a temperature rise procedure: heating to 500 ℃ at a speed of 1 ℃/min, preserving heat for 30min, further heating to 900 ℃ at a speed of 3 ℃/min, and keeping for 3h to obtain the Si-O-C composite material;

adding 10g of Si-O-C composite material and 1.01g of graphene slurry with the solid content of 10% into an MSK-SFM-10 vacuum stirrer for stirring, wherein the mass ratio of the Si-M-C composite material to the graphene is 99:1, the revolution speed is 10-40 rpm, stirring for 180 minutes, adding 100mL of deionized water, the revolution speed is 10-40 rpm, the rotation speed is 1000-1500 rpm, and continuously stirring for 120 minutes to obtain mixed slurry;

and transferring the mixed slurry to a centrifugal turntable spray head of a spray drying granulator, wherein the centrifugal rotating speed is 2000rpm, and forming tiny fog drops. And cooling and collecting powder at the inlet temperature of 260 ℃ and the outlet temperature of 105 ℃ of a spray drying granulator to obtain the negative electrode composite material with the graphene on the surface, wherein the content of the graphene is 1%.

Example 2

Except that the polydimethylsiloxane was replaced by polyhexamethylcyclotrisilazane (monomer C)₆H₂₁N₃Si₃) Which isHe prepared an anode composite comprising a Si-N-C composite in the same manner as in example 1.

Example 3

Except that the polydimethylsiloxane was replaced by polycarboborane methylsiloxane (monomer C)₁₀H₃₄B₁₀Si₄) Otherwise, the same as in example 1 was carried out to prepare a negative electrode composite material containing a Si-B-C composite material.

Example 4

The same procedure as in example 1 was repeated, except that the pyrolysis temperature was 1100 ℃.

Example 5

The same procedure as in example 1 was repeated, except that the pyrolysis temperature was 1300 ℃.

Example 6

The same procedure as in example 1 was repeated, except that the pyrolysis temperature was 1500 ℃.

Example 7

The procedure of example 4 was repeated, except that the mass of the graphene paste was 5.26g, and the mass ratio of the Si-M-C composite material to the graphene was 19: 1.

Example 8

The same as example 4 was repeated, except that the mass of the graphene paste was 11.11g and the mass ratio of the Si-M-C composite material to the graphene was 9: 1.

Example 9

The procedure of example 4 was repeated, except that the mass of the graphene paste was 17.65g and the mass ratio of the Si-M-C composite material to the graphene was 17: 3.

Example 10

The same as example 4 was repeated, except that the mass of the graphene paste was 25g and the mass ratio of the Si-M-C composite material to the graphene was 4: 1.

Example 11

The procedure of example 7 was repeated, except that the centrifugal rotation speed of the spray-dried granules was 6000 rpm.

Example 12

The procedure of example 7 was repeated, except that the centrifugal speed of the spray-dried granules was 5000 rpm.

Example 13

The procedure of example 7 was repeated, except that the centrifugal speed of the spray-dried granules was 3000 rpm.

Example 14

The procedure of example 7 was repeated, except that the centrifugal rotation speed of the spray-dried granules was 500 rpm.

Example 15

The procedure of example 7 was repeated, except that the centrifugal rotation speed of the spray-dried granules was 200 rpm.

Example 16

The amount of glucose was adjusted to 20g, and the rest was the same as in example 7.

Example 17

The amount of polydimethylsiloxane was adjusted to 10g, and the procedure was repeated as in example 16.

Example 18

The same procedures used in example 7 were repeated except that 10g of polydimethylsiloxane and 10g of polycarboborane methylsiloxane were added to the xylene solution of glucose, thereby obtaining a negative electrode composite material comprising a Si-B-O-C composite material.

Comparative example 1

The Si-O-C composite material prepared in example 7 was directly used as a negative electrode composite material for preparation of a negative electrode sheet without being compounded with graphene for granulation, and the rest was the same as in example 7.

Comparative example 2

The same procedure as in example 1 was repeated, except that the pyrolysis temperature was 600 ℃.

Comparative example 3

The same procedure as in example 1 was repeated, except that the pyrolysis temperature was 1800 ℃.

Comparative example 4

The same as example 4 was repeated, except that the mass of the graphene paste was 42.86g and the mass ratio of the Si-M-C composite material to the graphene was 4: 1.

Comparative example 5

Adding 10g of the Si-O-C composite material prepared in the embodiment 4 into 100mL of deionized water, and continuously stirring for 120min to obtain mixed slurry with the revolution rotating speed of 10-40 rpm and the rotation rotating speed of 1000-1500 rpm;

and transferring the mixed slurry to a centrifugal turntable spray head of a spray drying granulator, wherein the centrifugal rotating speed is 2000rpm, and forming tiny fog drops. And cooling and collecting powder to obtain the cathode composite material without graphene on the surface, wherein the inlet temperature of the spray drying granulator is 260 ℃, the outlet temperature of the spray drying granulator is 105 ℃.

Mixing the negative electrode composite material with graphite according to a certain proportion to obtain negative electrode active material powder with the designed specific capacity of 500mAh/g, and mixing the negative electrode active material powder, conductive agent acetylene black and PAA according to the weight ratio of 95: 1.2: 3.8 stirring in a deionized water solvent system for 30 minutes, and adding graphene slurry to ensure that the mass of the graphene accounts for 5% of the total mass of the negative active material powder, the conductive agent acetylene black and the PAA; adding deionized water, stirring to a kneading state, and coating on two surfaces of a copper foil current collector with the thickness of 10 micrometers, wherein the coating thickness is 100 micrometers; drying the pole piece and then cold-pressing the pole piece, wherein the double-sided compaction density is 1.8g/cm³And obtaining the negative pole piece.

The parameters and test results of the examples and comparative examples are shown in Table 1.

As can be seen from examples 1, 2 and 3, with the preparation method of the present application, Si-M-C composite materials with different compositions can be obtained by using different organosilanes; when the high-temperature cracking temperature is the same, the Si-M-C composite materials with different compositions are obtained, the half-peak widths of displacement peaks at-5 ppm +/-5 ppm of the silicon element in a solid nuclear magnetic test are the same, and the silicon element have lower expansion rate and higher capacity retention rate. The inventor also finds that the larger the molecular weight of the organosilicon monomer is, the larger the particle size of the prepared Si-M-C composite material is, and the higher the first coulombic efficiency of the full battery is.

Compared with the comparative example 1, the examples show that the surface of the negative electrode composite material with graphene is obviously improved in conductivity, the resistance of the electrode plate mixture layer is reduced, and the cycle performance of the full battery is obviously improved.

As can be seen from the comparison of examples 1, 4, 5 and 6 with comparative examples 2 and 3, the expansion rate of the battery increases with the increase of the pyrolysis temperature at the pyrolysis temperature of 1100 ℃ or more, and the expansion rate of the battery increases with the decrease of the pyrolysis temperature at the temperature of 1100 ℃ or less; thus, in the present application, the battery has a low expansion rate at a pyrolysis temperature of 900 to 1500 ℃. In addition, the battery has higher cycle capacity retention rate and coulombic efficiency when the cracking temperature is 900-1500 ℃.

In addition, under the same graphene content, the higher the pyrolysis temperature of the Si-M-C composite material is, the higher the Raman test temperature I of the obtained cathode composite material₁₃₅₀/I₁₅₈₀The smaller the value, I₁₃₅₀Indicating defects in carbon in the material, i.e. at temperatures < 900 deg.C₁₃₅₀/I₁₅₈₀More than 1, more surface defects of the Si-M-C composite material, no limitation to any theory, more surface defects of the material, increased barrier factors for free electron flow, high resistance, poor conductivity of the material, poor first coulombic efficiency and cycle performance of the full cell, increased reaction byproducts and increased cycle expansion.

As can be seen from examples 7 to 10 compared with comparative example 4, as the content of graphene increases, the cycle expansion of the battery increases, not being limited to any theory, which may be caused by the increase in lithium intercalation depth due to the increase in conductivity, and in addition, the large specific surface area of graphene may result in a larger contact area with the electrolyte, increased by-products, and increased cycle expansion; therefore, the amount of the graphene should be controlled to be 1-20% of the mass of the negative electrode composite material, that is, the mass ratio of the Si-M-C composite material to the graphene is 4:1 to 99: 1.

it can be seen from examples 11 to 15 that the larger the particle size of the negative electrode composite material is, the higher the first coulombic efficiency of the full cell is, without being limited to any theory, which may be caused by the fact that the smaller particle size causes the specific surface area of the material to increase, the contact area with the electrolyte to be large, and the consumption of lithium source to be more; meanwhile, it can be seen that, in a certain range, the larger the particle size of the negative electrode composite material is, the higher the capacity retention rate is, and the lower the expansion rate is; however, when the particle size is larger than 15 μm, the capacity retention rate of the full battery is reduced, and the expansion is increased, which is not limited to any theory, and may be caused by that the local expansion of the negative electrode is too large in the circulation process due to too large particle size, and finally the circulation stability is affected; thus in some preferred embodiments of the present application, the particle size of the negative electrode composite is in the range of 6 μm to 15 μm.

Example 7 compares with comparative example 5 and demonstrates that compared with the method of directly adding graphene to slurry of negative active material, the negative composite material obtained by compounding and granulating graphene and Si-M-C composite material by the preparation method of the present application has smaller sheet resistance of negative electrode sheet, better cycle performance and expansion performance, and is not limited to any theory, which may be because the uniformity of dispersion cannot be guaranteed by directly adding graphene to slurry, and the graphene cannot be in better contact with Si-M-C composite material, and it is difficult to improve the conductivity thereof, resulting in accelerated cycle decay and increased expansion.

All the embodiments in the present specification are described in a related manner, and the same and similar parts among the embodiments may be referred to each other, and each embodiment focuses on the differences from the other embodiments. In particular, for the system embodiment, since it is substantially similar to the method embodiment, the description is simple, and for the relevant points, reference may be made to the partial description of the method embodiment.

The above description is only for the preferred embodiment of the present application and is not intended to limit the scope of the present application. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application are included in the protection scope of the present application.