CN110098402B

CN110098402B - Silicon-carbon negative electrode material for lithium ion battery and preparation method thereof

Info

Publication number: CN110098402B
Application number: CN201910485648.5A
Authority: CN
Inventors: 张和宝; 李喆; 陆玉婷; 叶兰; 罗姝; 王岑
Original assignee: Amprius Nanjing Co ltd
Current assignee: Boselis Hefei Co ltd; Bosellis Nanjing Co ltd
Priority date: 2019-06-05
Filing date: 2019-06-05
Publication date: 2020-12-01
Anticipated expiration: 2039-06-05
Also published as: CN110098402A

Abstract

The invention relates to a silicon-carbon composite material for a lithium ion battery and a preparation method thereof, wherein the silicon-carbon composite material is a silicon-carbon composite material containing copper doping, and the silicon-carbon composite material is obtained by crushing secondary particles formed by compounding a silicon material, a copper compound and a carbon material; and the surface of the silicon-carbon composite material is coated with a layer of carbon or not coated with carbon. Compared with the traditional silicon-carbon cathode, the silicon-carbon composite material prepared by the invention has higher coulombic efficiency and capacity when being used for a lithium ion battery, has lower electrochemical polarization effect, obviously improves the energy density, rate capability and cycle performance of the lithium ion battery, has simple process and is easy to realize industrial production.

Description

Silicon-carbon negative electrode material for lithium ion battery and preparation method thereof

Technical Field

The invention relates to the field of lithium ion batteries, in particular to a silicon-carbon composite material for a lithium ion battery and a preparation method thereof.

Background

Due to rapid development and wide application of various portable electronic devices and electric vehicles in recent years, demand for lithium ion batteries having high energy density and long cycle life is increasingly urgent. The negative electrode material of the lithium ion battery which is commercialized at present is mainly graphite, but due to low theoretical capacity (372mAh/g), the further improvement of the energy density of the lithium ion battery is limited. Among many novel lithium ion battery cathode materials, silicon cathode materials have the advantage of high capacity (Li) that other cathode materials cannot match₂₂Si₅Theoretical lithium storage capacity of 4200mAh/g) which is more than 11 times of the theoretical capacity of the current commercial carbon negative electrode material. However, silicon is accompanied by a large volume expansion, which results in a loss of capacity during cycling. Meanwhile, silicon is used as a semiconductor, and the conductivity of the silicon is low, so that the polarization of a silicon cathode is large, the internal resistance of the battery is further large, and the rate performance is poor. And has serious volume effect in the process of lithium intercalation and deintercalation, the volume change rate is about 400 percent, andcausing pulverization of the electrode material and separation of the electrode material from the current collector. In addition, due to the volume effect during charge and discharge, the silicon negative electrode material exposed to the electrolyte continuously forms a fresh surface, and thus the electrolyte is continuously consumed to generate an SEI film, reducing the cycle performance of the electrode material. The above-mentioned drawbacks of silicon-based materials severely limit their commercial applications.

In order to solve the above problems of silicon negative electrodes, the current domestic and foreign research on silicon negative electrode materials mainly focuses on the following aspects: (1) the size of the silicon particles is simply reduced, for example, by using silicon nanoparticles, so as to reduce the volume effect of the silicon particles. However, the nano silicon particles have a large specific surface area, so that the coulombic efficiency of the battery is very low, and in the circulation process, SEI on the surfaces of the silicon particles are repeatedly generated, so that SEI films on the surfaces are thick, the conduction of electrons is blocked, the particles are inactivated, and the circulation performance of the battery is limited. (2) The silicon material with special nano structure, such as silicon nano tube, silicon nano wire, porous silicon, etc. is prepared, but the method has higher cost and lower yield, and is only suitable for laboratory research at present. (3) Compounding silicon with carbon materials such as conductive additives, amorphous carbon, graphite and the like to prepare the silicon-carbon composite material. The composite material has attracted the attention of many researchers due to the combination of the high capacity of silicon and the cycle performance of graphite materials. However, when the content of graphite and amorphous carbon is too high and the content of silicon is low, the practical use capacity of the material is low. (4) The surface of the silicon material or the silicon-carbon composite material is coated, so that the material keeps stable SEI in the circulation of the lithium ion battery, and the occurrence of side reactions is reduced to improve the coulombic efficiency.

Chinese patent CN108832077A discloses a preparation method of a copper-doped core-shell structure silicon-carbon composite material, which comprises the steps of coating phenolic resin and polyethyleneimine on the surface of nano-silicon, complexing the polyethyleneimine with copper ions to form a chelate, uniformly distributing the chelate on the surface of the nano-silicon, and carrying out high-temperature treatment to obtain the silicon-carbon composite material. The method synthesizes the copper-doped silicon-carbon composite material, but in the synthesis process, the amount of copper ions is difficult to control, the doping of silicon is difficult to quantify, and the copper-silicon alloy is difficult to form. According to the method, the nano silicon powder with the median particle size of less than 100nm is required, the specific surface area of the material is large, and more SEI is generated during lithium intercalation for the first time, so that the first effect is low. The chelate is generated by utilizing the complexation reaction, the reaction conditions are harsh, meanwhile, the nano silicon powder needs to be subjected to surface treatment by using hydrofluoric acid, and the specific operation process is complex. The silicon-carbon composite material synthesized by the method has lower first effect and capacity in a graphite blending system, and has poorer cycle.

Chinese patent CN102891297A discloses a silicon-carbon composite material and a preparation method thereof, the composite material is a graphite, asphalt and nano-silicon composite structure, and a nano-level silicon-carbon composite material precursor is obtained by adding graphite, asphalt and micron silicon into an aqueous solution of sodium carboxymethylcellulose for ball milling. And carrying out spray drying and carbonization on the precursor to obtain the silicon-carbon composite material. The method improves the conductivity among silicon particles and on the surface of the silicon particles by the graphite and the amorphous carbon, but does not solve the problem of high resistivity of the silicon material and still shows large polarization after the silicon material is manufactured into a battery. Meanwhile, the method has a complex synthesis process, utilizes the high molecular polymer as a stabilizer of the system, but easily breaks the high molecular polymer in the ball milling process, so that the slurry system is unstable, the nano silicon is easily agglomerated, and after the battery is manufactured, the local expansion is overlarge, the pulverization is carried out, and the cycle performance is poor.

Chinese patent CN107785095A discloses a copper-and graphene-doped porous silicon conductive paste and a preparation method thereof. According to the method, porous silicon, copper and graphene are mixed and ball-milled together to prepare nano powder, and a stabilizing agent, a dispersing agent and an organic carrier are added to prepare the lithium battery negative electrode slurry. The method mixes copper and silicon, aims to improve the stability and the conductivity of the slurry, and the introduction of the copper only provides the function of a conductive agent, so that the conductivity of the silicon is not effectively improved.

Chinese patent publication No. CN108807861A discloses irregularly shaped secondary particles for lithium ion batteries and a method for preparing the same. And the secondary particles are subjected to secondary granulation by using a silicon-carbon composite material with the particle size of 0.01-5 mu m, and then are crushed to obtain secondary particles with irregular shapes, the conductive agent is uniformly dispersed in the secondary particles, and a layer of amorphous carbon is coated on the surfaces of the secondary particles. The synthesized irregular secondary particles are applied to lithium ion batteries, and the negative electrode has the advantages of high compaction density, difficult breakage of the secondary particles, more contact points among pole piece particles and lower polarization. The secondary particles are synthesized by adopting unmodified silicon materials, the resistivity of the original silicon materials is higher, the conductivity of the synthesized secondary particles is poorer, the primary efficiency of the battery is further reduced, and the energy density and the rate capability of the battery are poorer.

Chinese patent publication No. CN105161695A discloses spherical active material particles for a negative electrode of a lithium ion battery, and a preparation method and application thereof. The spherical active substance particles are spherical composite particles prepared by spray drying active substance particles such as fibrous carbon, silicon with a micro-nano scale and the like. The spherical active material particles are not secondarily coated and have a porous structure having a larger specific surface area. Therefore, the first coulombic efficiency of the lithium ion battery made of the material is low, and the first round efficiency is only 60% as shown in the embodiment. In addition, the porous structure means that the material has a low density, which results in a low energy density of the lithium ion battery made of the material. Furthermore, the spherical active material particles contain up to 16.7% or more of fibrous carbon, which, in addition to a high specific surface area and a low density, also leads to a low content of active material in the material and thus to a low capacity of the composite material.

Therefore, the problems of large battery polarization, high resistance, low energy density and poor rate capability caused by low intrinsic conductivity of silicon are not effectively solved, and are technical problems in the field.

Disclosure of Invention

The invention aims to provide a silicon-carbon composite material for a lithium ion battery and a preparation method thereof, and solves the problems that silicon used as a semiconductor has high resistivity, and has large polarization, low energy density and poor cycle in the application of the lithium ion battery.

In order to achieve the purpose, the technical scheme provided by the invention is as follows:

the silicon-carbon composite material is a silicon-carbon composite material containing copper doping, and is formed by crushing secondary particles formed by compounding a silicon material, a copper compound and a carbon material.

Further, the surface of the silicon-carbon composite material is coated with a layer of carbon.

The median particle size of the silicon material is 0.1-10 mu m; the median particle diameter of the secondary particles is 2-50 mu m; the median particle size of the silicon-carbon composite material is 0.2-15 mu m.

Preferably, the median particle size of the silicon material silicon carbon composite material is 1-10 μm; preferably, the median particle size of the silicon-carbon composite material is 2-7 mu m; more preferably, the median particle size of the silicon-carbon composite material is 3-8.

Preferably, the median diameter of the secondary particles is 10-40 μm; more preferably, the median diameter of the secondary particles is between 15 and 30 μm.

Preferably, the median particle diameter of the silicon-carbon composite material is 1-10 μm; preferably, the median particle size of the silicon-carbon composite material is 2-7 mu m; more preferably, the median particle size of the silicon-carbon composite material is between 3 and 8 mu m.

In the silicon-carbon composite material, the silicon content is 74-98%, the copper element content is 0.1-20%, and the carbon content is 0.1-20%; the coating carbon layer on the surface of the silicon-carbon composite material is amorphous carbon or graphitized carbon.

The invention also discloses a preparation method of the silicon-carbon composite material for the lithium ion battery, which comprises the following steps: the method comprises the following steps:

1) dissolving a first carbon precursor and a copper precursor in a solvent, mixing the first carbon precursor and the copper precursor to prepare a mixed solution, adding a silicon material and a dispersing agent, and uniformly mixing to obtain a silicon/first carbon precursor/copper precursor mixed slurry;

2) drying and granulating the mixed slurry obtained in the step 1), and then carrying out high-temperature carbonization treatment in a non-oxidizing atmosphere;

3) crushing the product obtained in the step 2) to obtain a crushed material;

4) screening and demagnetizing the product obtained in the step 3) to prepare the silicon-carbon composite material of which the surface is not coated with carbon;

preparing the silicon-carbon composite material with the carbon-coated surface, and further processing the product obtained in the step 3) by the following steps:

5) coating the product obtained in the step 3) with carbon by using a second carbon precursor, and then performing high-temperature carbonization treatment in a non-oxidizing atmosphere,

6) screening and demagnetizing the product obtained in the step 5) to obtain the carbon-coated silicon-carbon composite material.

In the step 1), the first carbon precursor is one or a combination of more of glucose, sucrose, chitosan, starch, citric acid, gelatin, alginic acid, carboxymethyl cellulose, sodium carboxymethyl cellulose, coal pitch, petroleum pitch, phenolic resin, tar, naphthalene oil, anthracene oil, polyvinyl chloride, polystyrene, polyvinylidene fluoride, polyvinylpyrrolidone, polyethylene oxide, polyvinyl alcohol, epoxy resin, polyacrylonitrile and polymethyl methacrylate;

the copper precursor is one or a combination of more of copper acetate, copper sulfate, copper chloride, copper nitrate, copper carbonate and copper hydroxide;

the solvent is one or more of water, methanol, ethanol, isopropanol, N-butanol, ethylene glycol, diethyl ether, acetone, N-methyl pyrrolidone, methyl butanone, tetrahydrofuran, benzene, toluene, xylene, N-dimethylformamide, N-dimethylacetamide and chloroform;

the silicon material is crystalline silicon or amorphous silicon;

in step 2):

the drying granulation is carried out in a spray drying mode;

the high-temperature carbonization adopts any one of a rotary furnace, a roller kiln, a pushed slab kiln, an atmosphere box furnace or a tubular furnace;

the temperature of the high-temperature carbonization reaction is 500-;

the non-oxidizing atmosphere is provided by at least one of the following gases: nitrogen, argon, hydrogen, helium, neon, krypton.

In the step 3), the crushing mode is carried out by adopting an airflow crushing mode or a mechanical crushing mode.

Step 5):

the coating and carbonizing equipment of the second carbon precursor can be simultaneously completed by adopting a chemical vapor deposition reaction furnace;

the second carbon precursor coating equipment can also adopt any one of a mechanical fusion machine, a VC mixer, a high-speed dispersion machine and a reaction kettle;

the second carbon precursor is one or a combination of more of coal pitch, petroleum pitch, mesophase pitch, acetylene, ethylene, ethane, methane, polyvinyl alcohol, epoxy resin, polyacrylonitrile and polymethyl methacrylate;

the equipment used for high-temperature carbonization is any one of a rotary furnace, a roller kiln, a pushed slab kiln, an atmosphere box furnace or a tubular furnace;

the temperature of the high-temperature carbonization reaction is 600-;

The invention also protects the lithium ion battery cathode containing the silicon-carbon composite material.

Furthermore, in the lithium ion battery cathode, the mass ratio of the silicon-carbon cathode material is 80-96%; the negative electrode also contains an organic polymer binder, wherein the organic polymer binder is at least one or a combination of more of carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, sodium polyacrylate, lithium polyacrylate, a polystyrene acrylic copolymer, a polyacrylate copolymer, a carboxymethyl cellulose-acrylic acid copolymer, polyimide, polyamide imide, polyacrylonitrile, a polyacrylonitrile acrylic acid copolymer, alginic acid, sodium alginate, lithium alginate, an ethylene acrylic acid copolymer, hydrogel, xanthan gum, polyethylene oxide, polyvinyl alcohol and a polyacrylic acid-polyvinyl alcohol cross-linked copolymer.

Preferably, the organic polymer binder in the negative electrode contains at least one binder having high tensile strength and high elastic deformation. By combining the organic polymer binders with high tensile strength and high elastic deformation characteristics, the surface of the silicon material is wrapped by the binders, so that on one hand, the expansion of particles can be inhibited to a certain extent, the damage to an SEI (solid electrolyte interphase) film is reduced, on the other hand, the particles can still be tightly connected with the particles and a current collector after the repeated expansion-contraction of the silicon material, the electrical activity of the material is kept, and the cycle performance of the battery is improved.

The invention also protects the lithium ion battery prepared by the lithium ion battery cathode.

According to the invention, the copper precursor is uniformly mixed with the silicon material and the carbon material, the carbon reduces the copper precursor into elemental copper through high-temperature calcination, copper atoms diffuse into the silicon material at high temperature and are combined with the silicon atoms to form Cu-Si alloy, and the diffusion resistance of the copper atoms is relatively small, so that the Cu-Si alloy in the silicon material is generated relatively uniformly.

As a semiconductor, silicon has an extremely high resistivity of up to 2.3 x 10⁵Ω · m, resistivity of metallic copper only 1.75 × 10^-8Omega.m, the Cu atoms in the Cu-Si alloy play a role in excellent electron conduction, so that the resistivity of the silicon doped with copper is obviously reduced, and the self conductivity of the silicon is greatly improved.

Compared with the prior art, the invention has the beneficial effects that:

1. according to the copper-doped silicon-carbon composite material prepared by the invention, the copper atoms and the silicon atoms form a Cu-Si alloy, so that the resistivity of the material is greatly reduced, and the copper-doped silicon-carbon composite material is applied to a lithium ion battery, so that the internal resistance of the battery is remarkably reduced, the first coulomb efficiency of the battery is improved, and the rate capability and the energy density of the battery are further improved;

2. the silicon-carbon composite material prepared by the invention has an irregular shape, when the electrode is manufactured, irregular particles fill gaps among the particles, the compaction density of the electrode is greatly improved, the contact performance among the irregular particles is better, the contact internal resistance of the electrode is obviously reduced, and the rate capability of the battery is further improved.

3. The silicon-carbon composite material prepared by the invention is irregular in shape, and after the silicon-carbon composite material is prepared into an electrode and assembled into a battery, the contact surface of particles is larger, the conduction of lithium ions is easier to realize, and the rate capability of the battery is greatly improved.

Drawings

Fig. 1 is an X-ray diffraction (XRD) pattern of the silicon carbon composite prepared in example 1.

Fig. 2 is an XRD spectrum of the silicon carbon composite material prepared in comparative example 2.

Fig. 3 is a Scanning Electron Microscope (SEM) photograph of the silicon carbon composite prepared in example 1.

Fig. 4 is an SEM photograph of the silicon carbon composite prepared in example 1.

Fig. 5 is an SEM photograph of the silicon carbon composite prepared in comparative example 2.

Fig. 6 is a full cell cycle curve of the silicon carbon composite prepared in example 1.

Detailed Description

The present invention will be further described with reference to the following specific examples.

Example 1

500g of sucrose and 24.9g of copper sulfate were weighed and dissolved in 2000g of deionized water to form a homogeneous solution. 1000g of crystalline silicon powder with the median particle size of 1 mu m is taken and fully stirred with the slurry and uniformly mixed. And (3) carrying out spray drying granulation on the slurry to obtain secondary particles with the median particle size of 13 mu m. And heating the spray-dried dry powder at 600 ℃ for 10 hours in an inert atmosphere of argon to carbonize the sucrose, thereby obtaining carbonized secondary particles. And (3) carrying out airflow crushing on the secondary particles, adding 800g of crushed silicon-carbon composite material and 114g of coal pitch into a mechanical fusion machine, and carrying out high-speed fusion treatment at 1500rpm for 30 minutes to obtain coal pitch coated spherical silicon composite particles. And (2) preserving the heat of the materials at 300 ℃ for 2 hours in an argon inert atmosphere, then heating to 850 ℃ for carbonization for 3 hours, naturally cooling to room temperature, and sieving to obtain the silicon-carbon composite material with the median particle size of 1.3 mu m and coated with amorphous carbon.

The silicon-carbon composite material prepared above was characterized using the following equipment, which was used in the following examples.

The particle size distribution of the silicon-carbon composite material is tested by a Dandongbott BetterSize 2000 laser particle size analyzer.

The crystal structure of the silicon-carbon composite material is tested by a Rigaku miniFlex 600X-ray diffractometer.

And observing the surface morphology of the silicon-carbon composite material by using a Hitachi SU8010 scanning electron microscope.

Fig. 1 shows XRD patterns of the silicon-carbon composite material prepared in example 1, from which it can be seen that there are distinct Cu-Si alloy peaks at 44.5 ° and 45.1 ° 2 θ, indicating that there is Cu-Si alloy formation inside the prepared silicon-carbon composite material.

Fig. 2 shows XRD patterns of the silicon carbon composite material prepared in comparative example 2, from which it can be seen that there are no Cu-Si alloy peaks at 44.5 ° and 45.1 ° 2 θ, indicating that the silicon carbon composite material prepared under the comparative example condition does not produce Cu-Si alloy.

Fig. 3 is an SEM photograph of the silicon-carbon composite material prepared in example 1, which is magnified 500 times, and it can be seen that the silicon-carbon composite material prepared in example 1 has a random morphology, and bright spots uniformly distributed on the surface are Cu element-enriched areas.

Fig. 4 is an SEM photograph of the silicon carbon composite material prepared in example 1 at magnification of 20000 times, and it can be seen that the surface of the silicon carbon composite material prepared in example 1 has a significant Cu — Si alloy distribution.

Fig. 5 is an SEM photograph of the silicon-carbon composite material prepared in comparative example 2, magnified 20000 times, showing that the silicon-carbon composite material prepared in comparative example 2 has a carbon film uniformly coated on the surface and no Cu — Si alloy distribution on the surface.

And (3) homogenizing, coating, drying and rolling 80 parts of the silicon-carbon composite material, 10 parts of the conductive additive and 10 parts of the binder in a water-based system to obtain the silicon-containing negative pole piece.

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 25.4 omega cm.

Full cell evaluation: the prepared silicon-containing negative pole piece is cut, vacuum-baked, wound together with a matched positive pole piece and a diaphragm, filled into an aluminum plastic shell with a corresponding size, injected with a certain amount of electrolyte, sealed and formed to obtain a complete silicon-containing negative pole lithium ion full battery. The capacity and the average voltage of the full battery under the discharge current of 0.2C are tested by using a battery tester of New Wille electronics Limited of Shenzhen, and the capacity retention rate data is cycled for 200 times at the charge-discharge rate of 0.5C. The first constant current charging proportion of the full battery is 94.1%, the volume energy density is 815.4Wh/L, and the capacity retention rate after 200 charge-discharge cycles is 84.3%.

Example 2

25g of glucose and 156g of copper sulfate were weighed and dissolved in 2000g of ethanol to form a homogeneous solution. 1000g of crystalline silicon powder with the median particle size of 4.5 mu m is taken and fully stirred with the slurry and evenly mixed. And (3) carrying out spray drying granulation on the slurry to obtain secondary particles with the median particle size of 26 mu m. And heating the spray-dried dry powder at 700 ℃ for 6 hours in an inert atmosphere of argon to carbonize glucose, thereby obtaining carbonized secondary particles. And (2) carrying out jet milling on the carbonized secondary particles, taking 800g of the crushed particles, taking 50g of petroleum asphalt sieved by a 200-mesh sieve, mechanically mixing for 10 minutes by using a VC mixer, heating the equipment to 300 ℃ while stirring in the atmosphere of nitrogen protection, continuing stirring for 30 minutes, and then cooling to room temperature. And (2) preserving the heat of the materials at 300 ℃ for 2 hours in an argon inert atmosphere, then heating to 900 ℃ for carbonization for 2 hours, naturally cooling to room temperature, and sieving to obtain the silicon-carbon composite material with the median particle size of 5.3 mu m and coated with amorphous carbon.

Taking 87 parts of the silicon-carbon composite material, 3 parts of a conductive additive and 10 parts of a binder, and homogenizing, coating, drying and rolling the mixture in a water-based system to obtain the silicon-containing negative pole piece.

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 1.8 omega cm.

The volume energy density of the full battery is measured to reach 824.5Wh/L, the constant current charging proportion is 94.7%, and the capacity retention rate after 200 charge-discharge cycles is 81.9%.

Example 3

667g of sucrose and 156g of cupric acetate were weighed and dissolved in 2000g of deionized water to form a homogeneous solution. 1000g of amorphous silicon powder with the median particle size of 8 mu m, 25g of single-walled carbon nanotube slurry with the solid content of 0.4 percent and 50g of polyvinylpyrrolidone are taken, fully stirred and uniformly mixed with the slurry. And (3) carrying out spray drying granulation on the slurry to obtain secondary particles with the median particle size of 46 mu m. And heating the spray-dried dry powder for 2 hours at 800 ℃ in an inert atmosphere of argon to carbonize the sucrose, thereby obtaining the carbonized secondary particle material. And (3) carrying out airflow crushing treatment on the carbonized secondary particle material to obtain the silicon-carbon composite material with the median particle size of 10 microns.

And (3) homogenizing, coating, drying and rolling 90 parts of the silicon-carbon composite material, 4 parts of a conductive additive and 6 parts of a binder in a water-based system to obtain the silicon-containing negative pole piece.

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 6.4 omega cm.

The full-cell evaluation method is the same as that in example 1, and the volume energy density of the full cell is measured to reach 840.8Wh/L, the constant-current charging ratio is 94.0%, and the capacity retention rate after 200 charge-discharge cycles is 81.6%.

Example 4

74.8g of copper sulfate was weighed and dissolved in 1500g of deionized water to form a homogeneous solution, and 12.5g of sodium carboxymethylcellulose was weighed and added to the above solution to prepare a mixed solution. 1000g of amorphous silicon powder with the median particle size of 5 mu m is taken and fully stirred with the slurry and evenly mixed. And carrying out spray drying granulation on the slurry to obtain secondary particles with the median particle size of 30 mu m. And heating the spray-dried dry powder in an inert atmosphere of argon at 500 ℃ for 6 hours to carbonize the sodium carboxymethyl cellulose to obtain carbonized secondary particles. And (3) mechanically crushing the secondary particles, taking 800g of the crushed silicon-carbon composite material, 100g of petroleum asphalt sieved by a 200-mesh sieve, adding the crushed silicon-carbon composite material into a mechanical fusion machine, and performing high-speed fusion treatment at 1500rpm for 30 minutes to obtain the coal asphalt coated spherical silicon composite particles. And (2) preserving the heat of the materials at 300 ℃ for 2 hours in an argon inert atmosphere, then heating to 1000 ℃ for carbonization for 2 hours, naturally cooling to room temperature, and sieving to obtain the silicon-carbon composite material with the median particle size of 6 microns and coated with the amorphous carbon.

And (3) homogenizing, coating, drying and rolling 85 parts of the silicon-carbon composite material, 7 parts of a conductive additive and 8 parts of a binder in a water-based system to obtain the silicon-containing negative pole piece.

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 7.0 omega cm.

The full-cell evaluation method is the same as that in example 1, and the volume energy density of the full cell is measured to reach 830.6Wh/L, the constant-current charging ratio is 94.3%, and the capacity retention rate after 200 charge-discharge cycles is 82.3%.

Example 5

167g of sucrose and 63g of cupric chloride were weighed and dissolved in 2000g of methanol to form a homogeneous solution. 1000g of amorphous silicon powder with the median particle size of 5.2 mu m is taken and fully stirred with the slurry and uniformly mixed. And (3) carrying out spray drying granulation on the slurry to obtain secondary particles with the median particle size of 35 mu m. And heating the spray-dried dry powder for 2 hours at 600 ℃ in an inert atmosphere of argon to carbonize the sucrose, thereby obtaining carbonized secondary particles. Mechanically pulverizing the carbonized secondary particles to obtain crushed material, adding 1000g of the crushed material into a CVD furnace, and setting N₂The flow rate is 25L/h, the temperature is increased to 900 ℃ at the speed of 10 ℃/min, and C is introduced at the moment₂H₂Gas, N is₂And C₂H₂The flow rate is adjusted to be 20L/h, the temperature is kept at 900 ℃ for 2 hours, and the carbon-coated silicon-carbon composite material with the median particle size of 6.5 mu m is obtained after sieving and removing magnetism.

Taking 80 parts of the silicon-carbon composite material, 10 parts of conductive additive and 10 parts of binder, homogenizing, coating, drying and rolling in a water-based system to obtain the silicon-containing negative pole piece

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 2.4 omega cm.

The evaluation method of the full battery is the same as that in example 1, and the volume energy density of the full battery is measured to reach 838.9Wh/L, the constant current charging proportion is 94.5%, and the capacity retention rate after 200 charge-discharge cycles is 83.7%

Example 6

100g of petroleum asphalt is taken and added with 1000g of N, N-dimethylformamide to be stirred, and mixed slurry is prepared. Weighing 74.8g of copper sulfate, dissolving in 500g of methanol, adding the copper sulfate solution into the slurry, weighing 1000g of amorphous silicon powder with the median particle size of 7 mu m, adding into the mixed slurry, stirring and uniformly mixing. And (3) carrying out spray drying granulation on the slurry to obtain secondary particles with the median particle size of 42 mu m. And heating the spray-dried dry powder at 900 ℃ for 5 hours in an inert atmosphere of argon to carbonize the petroleum asphalt to obtain a secondary granular material. And (3) airflow crushing the secondary particle material, and screening and demagnetizing to obtain the silicon-carbon composite material with the median particle size of 8.8 microns.

And (3) homogenizing, coating, drying and rolling 96 parts of the silicon-carbon composite material, 1 part of a conductive additive and 3 parts of a binder in a water-based system to obtain the silicon-containing negative pole piece.

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 27.7 omega cm.

The full-cell evaluation method is the same as that in example 1, and the volume energy density of the full cell is measured to reach 845.6Wh/L, the constant-current charging ratio is 94.0%, and the capacity retention rate after 200 charge-discharge cycles is 80.7%.

Example 7

29g of coal tar pitch was weighed, 1500g of tetrahydrofuran was added, and stirring was carried out to form a slurry which was uniformly mixed. Weighing 2.5g of copper sulfate, dissolving in 500g of methanol, adding the copper sulfate solution into the slurry, weighing 1000g of crystalline silicon powder with the median particle size of 4 mu m, adding into the slurry, stirring, and uniformly mixing. And carrying out spray drying granulation on the slurry to obtain secondary particles with the median particle size of 25 mu m. And heating the spray-dried dry powder at 800 ℃ for 4 hours in an inert atmosphere of argon to carbonize the coal pitch to obtain carbonized secondary particles. And (3) carrying out air flow crushing on the secondary particles to obtain a crushed material. 800g of the crushed material, 46g of coal pitch, was mechanically mixed in a VC mixer for 10 minutes, and then the apparatus was heated to 300 ℃ under stirring in a nitrogen atmosphere, and further stirred for 30 minutes, followed by cooling to room temperature. And (2) preserving the heat of the materials at 300 ℃ for 2 hours in an argon inert atmosphere, then heating to 800 ℃ for carbonization for 4 hours, naturally cooling to room temperature, and sieving to obtain the silicon-carbon composite material with the median particle size of 5 microns and coated with the amorphous carbon.

And (2) homogenizing, coating, drying and rolling 82 parts of the silicon-carbon composite material, 8 parts of a conductive additive and 10 parts of a binder in a water-based system to obtain the silicon-containing negative pole piece.

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 37.1 omega cm.

The full-cell evaluation method is the same as that in example 1, and the volume energy density of the full cell is measured to reach 829.5Wh/L, the constant-current charging ratio is 93.3%, and the capacity retention rate after 200 charge-discharge cycles is 83.1%.

Example 8

5g of glucose and 467.9g of copper acetate were weighed and dissolved in 1700g of ethanol to form a mixed solution. Taking 1000g of amorphous silicon powder with the median particle size of 10 mu m, stirring and uniformly mixing. And carrying out spray drying granulation on the slurry to obtain secondary particles with the median particle size of 50 microns. And heating the spray-dried dry powder at 1000 ℃ for 3 hours in an inert atmosphere of argon to carbonize glucose, thereby obtaining carbonized secondary particles. And (3) performing jet milling on the secondary particles, screening and demagnetizing to obtain the silicon-carbon composite material with the median particle size of 15 microns.

And (3) homogenizing, coating, drying and rolling 91 parts of the silicon-carbon composite material, 0.5 part of conductive additive and 8.5 parts of binder in a water-based system to obtain the silicon-containing negative pole piece.

The full-cell evaluation method is the same as that in example 1, and the volume energy density of the full cell is measured to reach 853.5Wh/L, the constant-current charging ratio is 94.2%, and the capacity retention rate after 200 charge-discharge cycles is 79.4%.

Example 9

156g of copper acetate is weighed and dissolved in 1800g of deionized water, 1000g of crystalline silicon powder with the median particle size of 0.1 mu m is taken, 286g of sodium polyacrylate glue solution with the solid content of 10 percent is added, and the mixture is stirred and mixed evenly. And carrying out spray drying granulation on the slurry to obtain secondary particles with the median particle size of 2 mu m. And heating the spray-dried dry powder at 600 ℃ for 2 hours in an inert atmosphere of argon to carbonize the sodium polyacrylate, thereby obtaining the carbonized secondary particle material. And (3) carrying out airflow crushing on the secondary particle material to obtain a crushed material. Taking 800g of the crushed silicon-carbon composite material, adding the crushed silicon-carbon composite material into a CVD (chemical vapor deposition) kiln, and setting N₂The flow rate is 25L/h, the temperature is increased to 900 ℃ at the speed of 10 ℃/min, and C is introduced at the moment₂H₂Gas, N is₂And C₂H₂The flow rate was adjusted to 20L/h and the temperature was maintained at 900 ℃ for 2 hours. The silicon-carbon composite material with the carbon coating and the median particle size of 0.2 mu m is obtained.

And (3) homogenizing, coating, drying and rolling 86 parts of the silicon-carbon composite material, 7 parts of the conductive additive and 7 parts of the binder in a water-based system to obtain the silicon-containing negative pole piece.

The full-cell evaluation method is the same as that in example 1, and the volume energy density of the full cell is measured to reach 812.4Wh/L, the constant-current charging ratio is 95.0%, and the capacity retention rate after 200 charge-discharge cycles is 85.3%.

Example 10

623.9g of copper acetate was weighed and dissolved in 2000g of deionized water to form a homogeneous solution, and 12.5g of sodium carboxymethylcellulose was weighed and added to the above solution to prepare a mixed solution. 1000g of crystalline silicon powder with the median particle size of 1 mu m is taken and fully stirred with the slurry and uniformly mixed. And carrying out spray drying granulation on the slurry to obtain secondary particles with the median particle size of 10 mu m. And heating the spray-dried dry powder at 600 ℃ for 2 hours in an inert atmosphere of argon to carbonize the sodium carboxymethyl cellulose, thereby obtaining carbonized secondary particles. And carrying out air flow crushing on the secondary particles to obtain a crushed material. And taking 800g of the materials, adding 34.3g of petroleum asphalt which is sieved by a 200-mesh sieve into a mechanical fusion machine, and carrying out high-speed fusion treatment for 30 minutes at 1500rpm to obtain the coal asphalt coated material. And (2) preserving the heat of the materials at 300 ℃ for 2 hours in an argon inert atmosphere, then heating to 900 ℃ for carbonization for 2 hours, naturally cooling to room temperature, sieving and demagnetizing to obtain the silicon-carbon composite material with the median particle size of 1.3 mu m and coated by the amorphous carbon.

And (3) homogenizing, coating, drying and rolling 93 parts of the silicon-carbon composite material, 2 parts of a conductive additive and 5 parts of a binder in a water-based system to obtain the silicon-containing negative pole piece.

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 0.4 omega cm.

The full-cell evaluation method is the same as that in example 1, and the volume energy density of the full cell is measured to reach 816.2Wh/L, the constant-current charging ratio is 95.1%, and the capacity retention rate after 200 charge-discharge cycles is 83.5%.

Example 11

Taking 13g of petroleum asphalt, adding 1000g of N, N-dimethylformamide, and stirring to prepare mixed slurry. Weighing 74.8g of copper sulfate, dissolving in 500g of methanol, adding the copper sulfate solution into the slurry, weighing 1000g of crystalline silicon powder with the median particle size of 2 mu m, stirring and mixing uniformly. And (3) carrying out spray drying granulation on the slurry to obtain secondary particles with the median particle size of 13 mu m. And heating the spray-dried dry powder for 4 hours at 850 ℃ in an inert atmosphere of argon to carbonize the petroleum asphalt, thereby obtaining a carbonized secondary particle material. And mechanically crushing the secondary particles to obtain a crushed material. 800g of the crushed material is taken, 45.7g of petroleum asphalt which is sieved by a 200-mesh sieve is mechanically mixed for 10 minutes by a VC mixer, the temperature of the equipment is raised to 300 ℃ while stirring in the atmosphere of nitrogen protection, the stirring is continued for 30 minutes, and then the temperature is cooled to room temperature. And (2) preserving the heat of the materials at 300 ℃ for 2 hours in an argon inert atmosphere, then heating to 800 ℃ for carbonization for 4 hours, naturally cooling to room temperature, sieving and demagnetizing to obtain the silicon-carbon composite material with the median particle size of 2.5 mu m and coated by the amorphous carbon.

And (3) homogenizing, coating, drying and rolling 88 parts of the silicon-carbon composite material, 6 parts of the conductive additive and 6 parts of the binder in a water-based system to obtain the silicon-containing negative pole piece.

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 6.8 omega cm.

The full-cell evaluation method is the same as that in example 1, and the volume energy density of the full cell is measured to reach 816.7Wh/L, the constant-current charging ratio is 94.6%, and the capacity retention rate after 200 charge-discharge cycles is 84.2%.

Example 12

167g of sucrose and 312g of copper acetate are added into 2000g of deionized water and stirred to prepare a mixed solution. Weighing 1000g of crystalline silicon powder with the median particle size of 3 mu m, stirring and uniformly mixing. And carrying out spray drying granulation on the slurry to obtain secondary particles with the median particle size of 15 mu m. And heating the spray-dried dry powder for 4 hours at 600 ℃ in an inert atmosphere of argon to carbonize the sucrose, thereby obtaining the carbonized secondary particle material. And carrying out airflow crushing on the secondary particle material to obtain a crushed material. 800g of the above-mentioned material was taken, 34.3g of petroleum asphalt sieved with a 200 mesh sieve was taken, mechanically mixed for 10 minutes by a VC mixer, and then the temperature of the apparatus was raised to 300 ℃ under stirring in a nitrogen atmosphere, and further stirred for 30 minutes, followed by cooling to room temperature. And (2) preserving the heat of the materials at 300 ℃ for 2 hours in an argon inert atmosphere, then heating to 900 ℃ for carbonization for 2 hours, naturally cooling to room temperature, sieving and demagnetizing to obtain the silicon-carbon composite material with the median particle size of 3.8 mu m and coated by the amorphous carbon.

And (2) homogenizing, coating, drying and rolling 92 parts of the silicon-carbon composite material, 6 parts of a conductive additive and 2 parts of a binder in a water-based system to obtain the silicon-containing negative pole piece.

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 2.5 omega cm.

The full-cell evaluation method is the same as that in example 1, and the volume energy density of the full cell is measured to reach 824.7Wh/L, the constant-current charging ratio is 94.8%, and the capacity retention rate after 200 charge-discharge cycles is 81.6%.

Comparative example 1:

taking 1000g of amorphous silicon nano-powder with the median particle size of 0.1 mu m, 1500g of ethanol and 10g of hexadecyl trimethyl ammonium bromide, and sanding and dispersing the amorphous silicon nano-powder with the median particle size of 0.1 mu m in a sand mill by using zirconia beads with the diameter of 0.3mm until silicon nano-particle slurry with the median particle size of 0.1 mu m is obtained. To the slurry was added 20g of ketjen black powder, and sanding was continued for 30 minutes. 250g of sucrose was dissolved in 2250g of deionized water to prepare an aqueous sucrose solution. The sucrose aqueous solution was poured into a sand mill and thoroughly mixed with the silicon nanoparticle slurry for 30 minutes. The uniformly mixed anhydrous ethanol/water slurry of silicon particles/ketjen black/sucrose was further diluted with deionized water to a solid content of 10%, followed by spray drying treatment. The resulting spherical secondary particles had a median particle diameter of about 28 μm. And heating the spray-dried dry powder at 700 ℃ for 2 hours in an inert atmosphere of argon gas to carbonize the sucrose, thereby obtaining amorphous carbon bonded and coated silicon particles/ketjen black composite particles. And (3) carrying out jet milling treatment on all the spherical composite particles to obtain irregular composite particles with the median diameter of 11 mu m. And (3) mixing 530g of the composite particles and 424g of 2000-mesh petroleum asphalt at a high speed for 10 minutes by using a VC mixer, adding a mechanical fusion machine, and performing high-speed fusion treatment at 1500rpm for 30 minutes to obtain the petroleum asphalt-coated silicon particle/Ketjen black/amorphous carbon composite particles. And (2) preserving the heat of the materials at 300 ℃ for 2 hours in an argon inert atmosphere, then heating to 900 ℃ for carbonization for 2 hours, naturally cooling to room temperature, crushing and sieving to obtain the silicon particles/Ketjen black/amorphous carbon composite particles with the amorphous carbon coating.

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 231.2 omega cm.

The full-cell evaluation method is the same as that in example 1, and the volume energy density of the full cell is measured to reach 771.0Wh/L, the constant current charging ratio of the cell is 91.6%, and the capacity retention rate after 200 charge-discharge cycles is 82.5%.

Fig. 5 is an XRD spectrum of the silicon carbon composite material prepared in comparative example 1, from which it can be seen that no Cu — Si alloy peak appears in the synthesized silicon carbon material.

Comparative example 2:

a silicon carbon composite was prepared in substantially the same manner as in example 1, except that: no copper sulfate is added in the slurry mixing process. A battery was produced in the same manner as in example 1.

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 104.9 omega cm.

The full-cell evaluation method is the same as that in example 1, and the volume energy density of the full cell is measured to reach 789.3Wh/L, the constant current charging ratio of the cell is 90.3%, and the capacity retention rate after 200 charge-discharge cycles is 80.3%.

Comparative example 3:

a silicon carbon composite was prepared in substantially the same manner as in example 2, except that: copper acetate is not added in the slurry mixing process. A battery was produced in the same manner as in example 2.

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 209.7 omega cm.

The full-battery evaluation method is the same as that in example 1, and the volume energy density of the full battery is 798.1Wh/L, the constant current charging ratio of the battery is 90.9%, and the capacity retention rate after 200 charge-discharge cycles is 78.1%.

Comparative example 4:

a silicon carbon composite was prepared in substantially the same manner as in example 3, except that: copper acetate is not added in the slurry mixing process. A battery was produced in the same manner as in example 3.

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 280.9 omega cm.

The full-cell evaluation method is the same as that in example 1, and the volume energy density of the full cell is measured to reach 813.9Wh/L, the constant current charging ratio of the cell is 90.2%, and the capacity retention rate after 200 charge-discharge cycles is 77.8%.

Comparative example 5:

a silicon carbon composite was prepared in substantially the same manner as in example 5, except that: copper acetate is not added in the slurry mixing process. A battery was produced in the same manner as in example 5.

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 349.5 omega cm.

The full-cell evaluation method is the same as that in example 1, and the volume energy density of the full cell is measured to reach 812.1Wh/L, the constant current charging ratio of the cell is 90.7%, and the capacity retention rate after 200 charge-discharge cycles is 79.8%.

Comparative example 6:

a silicon carbon composite material was prepared in substantially the same manner as in example 7 except that: in the slurry mixing process, a sand grinding process is added, and the material is crushed until the median particle size is 0.08 mu m. A battery was produced in the same manner as in example 7.

And testing the resistivity of the pole piece by RTS-9 type four-probe equipment, wherein the resistivity of the pole piece is 33.9 omega cm.

The full-cell evaluation method is the same as that in example 1, and the volume energy density of the full cell is measured to reach 803.0Wh/L, the constant current charging ratio of the cell is 89.6%, and the capacity retention rate after 200 charge-discharge cycles is 79.2%.

The above description is only a preferred embodiment of the present invention, and should not be taken as limiting the invention in any way, and any person skilled in the art can make any simple modification, equivalent replacement, and improvement on the above embodiment without departing from the technical spirit of the present invention, and still fall within the protection scope of the technical solution of the present invention.

Claims

1. A carbon-coated silicon-carbon composite material for a lithium ion battery, characterized in that: the silicon-carbon composite material contains copper doping, and is formed by crushing secondary particles formed by compounding a silicon material, a copper compound and a carbon material; the surface of the silicon-carbon composite material is coated with a layer of carbon; the median particle size of the silicon material is 0.1-10 mu m; the median particle diameter of the secondary particles is 2-50 mu m; the median particle size of the silicon-carbon composite material is 0.2-15 mu m; in the silicon-carbon composite material, the silicon content is 74-98%, the copper content is 0.1-20%, and the carbon content is 0.1-20%; the carbon coating layer on the surface of the silicon-carbon composite material is amorphous carbon or graphitized carbon; the preparation method comprises the following steps:

1) dissolving a first carbon precursor and a copper precursor in a solvent, mixing the first carbon precursor and the copper precursor to prepare a mixed solution, adding a silicon material, and uniformly mixing to obtain a silicon/first carbon precursor/copper precursor mixed slurry;

2) drying and granulating the mixed slurry obtained in the step 1), and then carrying out high-temperature heat treatment in a non-oxidizing atmosphere;

3) crushing the product obtained in the step 2) to obtain a silicon-carbon composite material;

4) carrying out carbon coating on the product obtained in the step 3) by using a second carbon precursor, and then carrying out high-temperature carbonization treatment in a non-oxidizing atmosphere;

5) and 4) screening and demagnetizing the product obtained in the step 4) to obtain the carbon-coated silicon-carbon composite material.

2. The carbon-coated silicon-carbon composite material for a lithium ion battery according to claim 1,

in the step 2), the drying granulation is carried out in a spray drying mode;

the high-temperature heat treatment adopts any one of a rotary furnace, a roller kiln, a pushed slab kiln, an atmosphere box furnace or a tubular furnace;

the temperature of the high-temperature heat treatment is 500-1100 ℃, and the heat preservation time is 0.5-72 hours;

the non-oxidizing atmosphere is provided by at least one of the following gases: nitrogen, argon, hydrogen or helium;

in the step 3), the crushing adopts a mode of airflow crushing or mechanical crushing.

3. The carbon-coated silicon-carbon composite material for lithium ion batteries according to claim 2, wherein, in step 4),

the second carbon precursor coating and carbonizing equipment is simultaneously completed by adopting a chemical vapor deposition reaction furnace;

the reaction temperature of the high-temperature carbonization is 500-1100 ℃;

the heating time of high-temperature carbonization is 0.5-72 hours;

the non-oxidizing atmosphere is provided by at least one of the following gases: nitrogen, argon, hydrogen, helium, neon, or krypton.

4. A lithium ion battery negative electrode, characterized in that: the carbon-coated silicon-carbon composite material of any one of claims 1 to 3, wherein in the lithium ion battery cathode, the mass ratio of the silicon-carbon cathode material is 80-96%; the negative electrode further contains an organic polymer binder.

5. A lithium ion battery, characterized by: prepared using the lithium ion battery negative electrode of claim 4.