CN111446431A

CN111446431A - Method for enhancing interface contact of silicon-oxygen-carbon cathode material of lithium ion battery through oxygen transfer reaction

Info

Publication number: CN111446431A
Application number: CN202010289293.5A
Authority: CN
Inventors: 赵悦; 张会刚
Original assignee: Nanjing Ningzhi High New Material Research Institute Co ltd
Current assignee: Nanjing Ningzhi High New Material Research Institute Co ltd
Priority date: 2020-04-14
Filing date: 2020-04-14
Publication date: 2020-07-24
Anticipated expiration: 2040-04-14
Also published as: CN111446431B

Abstract

The invention provides a method for enhancing interface contact of a silicon-oxygen-carbon cathode material of a lithium ion battery through oxygen transfer reaction, which comprises the steps of mixing crushed and refined crude silicon powder with graphene oxide GO with a large number of oxygen functional groups under a sealed condition to carry out high-energy reaction ball milling, so that oxygen in the graphene oxide is transferred to silicon through a solid-state reaction mode to form oxygen-containing silicon powder consisting of SiOx and deoxidized graphene rGO to form a silicon-oxygen-carbon composite material, wherein x is less than or equal to 1. The invention has the following technical effects: according to the method for improving silicon-carbon cathode interface contact through the oxygen transfer reaction, graphene oxide and Si particles are mixed and are subjected to ball milling in a high-energy reaction ball mill, the high-temperature and high-pressure environment generated by ball milling is utilized to realize the oxygen transfer process, the reduced graphene improves the conductivity of composite particles, oxygen is transferred into the silicon particles, and meanwhile, the circulation stability of the silicon particles is improved.

Description

Method for enhancing interface contact of silicon-oxygen-carbon cathode material of lithium ion battery through oxygen transfer reaction

Technical Field

The invention relates to a method for enhancing interface contact of a silicon-oxygen-carbon cathode material of a lithium ion battery by an oxygen transfer reaction, belonging to the technical field of lithium ion battery materials.

Background

Lithium ion batteries have been widely used in the fields of portable consumer electronics, electric tools, medical electronics, and the like because of their excellent properties. Meanwhile, the method has good application prospect in the fields of pure electric vehicles, hybrid electric vehicles, energy storage and the like. At present, the commercial lithium ion battery mainly uses graphite as a negative electrode material, but with the rapid increase of the demand for the energy density of the battery in various fields in recent years, the development of the lithium ion battery with higher energy density is urgently needed. Under the background, the silicon-based negative electrode material is considered to be the next generation high energy density lithium ion battery negative electrode material with great potential due to the advantages of high theoretical specific capacity (4200 mAh/g at high temperature, 3580mAh/g at room temperature), low lithium removal potential (< 0.5V), environment friendliness, abundant storage capacity, low cost and the like. However, there are two key problems to be solved in the scale use process of the silicon-based anode material:

(1) the silicon material repeatedly expands and contracts in the process of lithium intercalation and deintercalation, so that the negative electrode material is pulverized and falls off, and finally the negative electrode material loses electric contact to completely lose effectiveness of the battery; (2) the continuous growth of a Solid Electrolyte (SEI) film on the surface of a silicon material can irreversibly consume the limited electrolyte and lithium from the positive electrode in the battery, eventually leading to rapid degradation of the battery capacity.

The nano silicon-carbon cathode material is one of the directions for effectively solving the problems, and the silicon-carbon cathode material is mainly divided into the following components according to the structural types:

1) coated silicon-carbon cathode

Coated silicon-carbon negative electrode materials are usually carbon-coated with silicon materials with different nano structures, the materials use silicon as a main body to provide reversible capacity, a carbon layer is mainly used as a buffer layer to reduce the volume effect, meanwhile, the conductivity is enhanced, the carbon coating layer is usually amorphous carbon, Chinese patent CN110148743A provides a method for preparing a silicon-carbon composite negative electrode material, the nano silicon composite material coated by carbon nano tubes is used as a core body, a shell is used as a carbon coating layer, a cavity structure is arranged between the core body and the shell, the mesoporous structure can meet the problems of retaining electrolyte in practical application, the specific capacity is reduced and the like, and the dynamic change of the pore structure in the circulating process can also influence the practical performance of a battery.

2) Load type silicon carbon negative electrode

The load type negative electrode material is usually loaded or embedded in silicon films, silicon particles and the like on the surface or inside carbon materials (such as carbon fibers, carbon nanotubes, graphene and the like) with different structures, in the silicon-carbon composite material, the carbon materials often play a mechanical role of structural support, the good mechanical properties of the carbon materials are favorable for the volume stress release of silicon in circulation, and a formed conductive network improves the electronic conductivity of the whole electrode;

3) dispersion type silicon carbon negative electrode

The dispersed silicon-carbon cathode material is a wider composite material system, comprises physical mixing of silicon and different materials, and also covers a highly uniform dispersed composite system in which silicon and carbon elements form molecular contact. It has been proved that the silicon material is uniformly dispersed in the carbon buffer matrix, and the volume expansion of the silicon can be inhibited to some extent, and chinese patents CN110048097A and CN106025218B provide the idea of inhibiting the silicon expansion by using the carbon buffer matrix.

In the actual application process, the requirements of industrial production are often not easy to meet. For example, during charging and discharging, the volume of silicon expands 100% to 300%, and the continuous shrinkage and expansion can cause powdering of the silicon-carbon negative electrode material, which seriously affects the battery life. The expansion of silicon can generate huge stress in the battery, and the stress can extrude the pole piece, so that the pole piece is broken; and the internal porosity of the battery is reduced, so that the metal lithium is precipitated, and the safety of the battery is influenced.

Graphene is a flaky two-dimensional carbon material, has good conductivity, and can improve the cycle performance of the battery to a certain extent by compounding graphene and silicon particles. The conductivity and volume buffer effect of the graphene improve the cycle performance of silicon and reduce the attenuation rate. Many patents for compounding graphene and silicon, for example, chinese patent CN103022436B, provide a composite material of rGO/Si obtained by mixing Graphene Oxide (GO) with ground silicon particles in a solution and finally treating the mixture in a reducing gas. Chinese patent application CN106920954A provides a method of mixing porous Si and GO, followed by spray drying and pyrolysis at high temperature to form graphene-wrapped porous silicon composite material, where the porous structure in the material can buffer the volume expansion of Si during lithiation and delithiation. Chinese patent CN104253266B utilizes physical deposition to deposit a multilayer stacked structure of graphene and Si thin films alternately. US2008/0261116a1 Si anode material vapor deposited on carbon nanofibers. According to the Chinese patent application CN103441247A, the surface of silicon powder is modified, so that the combination between silicon particles and graphene oxide is improved, and the performance of the modified composite material is improved due to the fact that the chemical bond action between Si and graphene is enhanced. Similarly, combining Si with graphene or graphene oxide to form a composite material for use as a lithium ion battery cathode has generated a number of patents.

However, in practice it has been found that pure silicon particles decay relatively rapidly during cycling even when the particle size is reduced to the nanometer scale. In contrast, SiOx (x. ltoreq.1) with a certain oxygen content has very good cycling properties, but is first of all less coulombic efficient. For example, chinese patent application CN106410158A mixes SiO, which is a metastable substance, with pitch or graphene, and decomposes into Si and silica by disproportionation reaction at high temperature. Chinese patent application CN107611360A proposes that silicon oxide is coated with ferroferric oxide and compounded with graphene. Chinese patent CN103811729B provides a method for synthesizing a composite material of silicon monoxide and graphene inside a cavity of a microwave pyrolysis device under a condition of extremely low oxygen partial pressure.

Therefore, the problem to be solved in the development process of the silicon-carbon material is to design a silicon-carbon composite structure capable of stabilizing charge and discharge cycles. The silicon simple substance particles have poor cycle performance, the silicon simple substance particles are combined with graphene to be improved to a certain extent, but in order to realize a silicon-based composite material with high cycle times, a certain oxygen component needs to be introduced into the silicon particles, but the silicon monoxide is unstable, and disproportionation reaction is easy to occur in the process of compounding the graphene to generate simple substance silicon and inactive silicon dioxide.

Compared with the prior literature report, the uniqueness of the method is that SiOx and graphene are formed in situ in one step, the contact between the active SiOx and the conductive graphene is tight, the electron transport in the battery circulation process is improved, the micro-open circuit condition caused by volume expansion is inhibited, and the circulation performance is effectively improved.

Disclosure of Invention

The invention aims to overcome the defects of the prior art, improve the interface conductivity of graphene and silicon particles and provide a method for enhancing the interface contact of a silicon-oxygen-carbon negative electrode material of a lithium ion battery through an oxygen transfer reaction.

The introduction of a certain oxygen component into the Si particles can significantly improve the cycle performance of the Si particles, but can reduce the first coulombic efficiency of the Si particles and reduce the rate capability of the Si particle cathode. Aiming at the problems that pure Si materials are serious in volume expansion, Si-oxygen combination circulation is improved, but multiplying power is reduced, the invention provides a method for improving silicon-carbon cathode interface contact by an in-situ oxygen transfer technology. The raw materials of the process all belong to the necessary materials of battery powder, the reaction ball milling process realizes the oxygen transfer process to improve the conductivity, and the process is different from various strategies of adding reducing agents in the past documents and patent reports (for example, Chinese patents CN109659529A and CN109713259A) and does not introduce impurity materials (such as acid washing and the like) which need to be removed finally.

Adding a soluble binder to improve the structure of the silicon nano particles coated by the graphene oxide, and further forming a compact silicon structure coated by the graphene in the subsequent carbonization process; so as to improve the structural stability of the silicon-based material and fully show the high specific capacity of the silicon-based material.

The technical scheme of the invention is as follows:

a method for enhancing interface contact of silicon-oxygen-carbon cathode materials of lithium ion batteries through oxygen transfer reaction comprises the steps of mixing crushed and refined crude silicon powder with Graphene Oxide (GO) with a large number of oxygen functional groups under a sealing condition to carry out high-energy reaction ball milling, and transferring oxygen in the graphene oxide to silicon to form silicon-oxygen-containing silicon powder consisting of SiOx and deoxidized graphene (rGO) to form a silicon-oxygen-carbon composite material through a solid-state reaction mode, wherein x is less than or equal to 1; the preparation method comprises the following steps:

1) compounding silicon/graphene oxide: mixing the refined grain size Si powder with graphene oxide and a binder, and then carrying out high-energy reaction ball milling in a closed environment to realize an oxygen transfer process; during the reaction ball milling process, partial Si is oxidized into SiOx, and compared with Si, the volume expansion rate of the SiOx in the lithium extraction process is obviously reduced; meanwhile, the graphene oxide is reduced, so that the conductivity is improved;

2) drying the product obtained in the step 1), and then carrying out heat treatment in an inert atmosphere; carbonizing the binder, so as to further improve the interface contact between the silicon and the graphene, improve the conductivity, and simultaneously form secondary particles to inhibit the expansion of the silicon;

3) the product in the step 2) is used for preparing a silicon-carbon cathode.

Preferably, the first and second electrodes are formed of a metal,

in the step 1) described above, the step of,

the high-energy reaction ball milling is carried out by adopting a ball milling tank and grinding balls which are sealed by gas;

the ball milling tank and the grinding balls are made of any one of agate, zirconia and corundum;

the particle size of the grinding ball is 6-20 mm;

the reaction ball milling time is 3-100 h, and the ball milling speed is 800-1000 rpm;

the grain size of the refined grain size Si powder is 50 nm-10 mu m;

the graphene oxide is single-layer or multi-layer;

the binder is any one of sodium carboxymethylcellulose, polyvinylidene fluoride, polyacrylic acid and sodium salicylate;

the refined grain size Si powder is as follows: and (3) graphene oxide: the mass ratio of the binder is (10-85): (10-85): 5;

the mass ratio of the powder to the grinding balls is 1: 1-10; the powder mass is the mass sum of the refined grain size Si powder, the graphene oxide and the binder.

In the step 2) described above, the step of,

the heat treatment is carried out at Ar/H₂Or heating to 450-950 ℃ at the heating rate of 2-10 ℃/min under Ar atmosphere, and preserving heat for 1-5 h.

In the step 3), the step of the method is that,

the preparation of the silicon-carbon cathode is to mix the product of the step 2) with the graphite cathode, sodium carboxymethyl cellulose (CMC), Carbon Nano Tube (CNT) and acetylene black (ACET) according to a certain proportion and then perform low-speed ball milling to obtain the silicon-carbon cathode material to be improved, thereby ensuring that all the components are fully and uniformly mixed. Specifically, the product obtained in the step 2) can be mixed with graphite, CMC, CNT and ACET in a weight ratio of 10:25:4:2:2 and then mixed at a rotating speed of 250 rpm. Or mixing the product obtained in the step 2) with graphite, CMC and ACET in a weight ratio of 10:25:4:2, and then mixing at a rotating speed of 250 rpm.

More preferably still, the first and second liquid crystal compositions are,

in the step 1), the ball milling tank and the grinding balls are made of zirconia, the grain diameters of the grinding balls are 6mm, 10mm and 15mm, and the mass ratio of the three grinding balls is 15-35:25-65: 20-50.

In the step 1), the rotation speed of the ball milling tank is 800-.

In the step 1), thinning the grain size Si powder: and (3) graphene oxide: the mass ratio of the binder is 5: 4.5:0.5.

In the step 1), the mass ratio of the powder to the grinding balls is 1: 3-5; the powder mass is the mass sum of the refined grain size Si powder, the graphene oxide and the binder.

In the step 1), a grinding aid is added into the ball milling tank, wherein the grinding aid is any one of water, ethanol and N-methylpyrrolidone.

In the step 2), the heat treatment is to put the sample dried in the step 1) in Ar/H₂Sintering for 1-3h at the temperature of 900 ℃ under the protective atmosphere of 450-.

The high-energy ball milling reaction is carried out in a high-energy closed reactor, wherein collision among grinding balls and between the grinding balls and a ball milling tank generates a high-energy high-pressure reaction micro-area, oxygen components in the micro-area are limited, and the oxygen components are transferred from GO with high oxygen chemical potential to the surface of Si nano-particles with low oxygen chemical potential. The method is the core content of the invention, firstly, the oxygen component comes from a solid material GO, and the GO has higher chemical potential and is easy to be reduced; silicon particles react readily with oxygen, but excess oxygen readily produces silica, resulting in material deactivation. When the oxygen source that GO provided is not enough, grinding aids such as moisturizing and ethanol further provide oxygen component, notice water and silicon reaction and produce hydrogen, produce pressure in airtight environment, produce the spark explosion easily when opening the jar. In order to improve the reaction ball milling efficiency, N-Methyl pyrrolidone (NMP) can be properly added as a grinding aid, NMP is used, and after the reaction ball milling is finished, NMP needs to be volatilized to obtain SiOx/rGO powder.

The ball milling technology used in the invention belongs to high-energy reaction ball milling, and air is required to be isolated, so that the generation of silicon dioxide by oxygen and silicon dioxide particles in the air is avoided. The high-energy ball milling can be in a material vibration impact mode, and can also adopt a planetary ball milling process, and the revolution and rotation directions of a ball milling tank are opposite to each other to generate a violent collision effect when the planetary ball milling speed is generally above 500 rpm. The ball milling tank and the grinding balls are made of any one of agate, zirconia and corundum materials, and the particle size of the grinding balls is 6-20 mm or more.

The graphene oxide used in the invention contains abundant oxygen-containing functional groups on the surface, which is beneficial to the dispersion of the graphene oxide, and the graphene oxide can be a single layer or multiple layers. The reduced graphene is easy to agglomerate, so that dispersion is difficult, and the graphene is agglomerated into particles although the conductivity is improved, so that a good conductive network is not easy to form.

The Si powder used in the present invention has a particle size in the range of 50nm to 10 μm, and commercial silicon powder may be used as it is, or coarse-grained commercial silicon powder may be ground in a ball mill to produce fine silicon powder of smaller particles. Usually, high proportion of Si is not used when preparing practical silicon negative electrodes, and the volume change caused by high silicon content is too large and exceeds the tolerable limit of the electrodes, so that the pole pieces are easy to fall off, and the cycle attenuation is obvious. Therefore, a certain proportion of graphite cathode material is usually introduced in the process of preparing the silicon-carbon cathode pole piece, and the silicon content is controlled to be 1-40 wt% in the invention. The graphite is flake graphite or spherical graphite, and the particle size is 1.2-20 μm.

The binder used in the present invention is any one of Sodium carboxymethylcellulose (CMC), polyvinylidene fluoride (PVDF), Polyacrylic acid (PAA), and Sodium Salicylate (SA); the purpose of adding the binder for ball milling is to perform secondary granulation on particles formed by SiOx and rGO subjected to reaction ball milling to form particles with larger particle size, so that poor rheological property in the process of brushing slurry and coating is avoided. Thus, after the completion of the ball milling with the binder, a simple heat treatment is carried out, i.e. at Ar/H₂Or heating to 450-950 ℃ at the heating rate of 2-10 ℃/min under Ar atmosphere, and preserving the heat for 1-5 h. The weak conductivity between active particles can limit the performance of the material, so that carbon nano-tubes (CNT) with good conductivity can be introduced in the material mixing step in the process of preparing the silicon carbon estimation pole piece. Outside the inner diameter of the CNT used in the present inventionThe diameter is not important, the length is required to be at least 3-12 mu m, long CNT is easy to bridge between particles to form a conductive network, and too long carbon nano fiber influences the rheological property of powder materials, so that the brushing coating is not easy.

The innovation point of the method is that the fine structure of Graphene Oxide (GO) coated silicon (Si) nanoparticles is improved through an oxygen transfer reaction to form a compact Graphene coated silicon structure. Oxygen in the graphene oxide is transferred to Si, so that the high conductive activity of Si nanoparticles is ensured, the agglomeration of the Si nanoparticles is effectively prevented, the structural stability of the silicon-based material is improved, and the high specific capacity of the silicon-based material is fully exerted.

The invention has the following technical effects: according to the method for improving silicon-carbon cathode interface contact through the oxygen transfer reaction, graphene oxide and Si particles are mixed and are subjected to ball milling in a high-energy reaction ball mill, the high-temperature and high-pressure environment generated by ball milling is utilized to realize the oxygen transfer process, the reduced graphene improves the conductivity of composite particles, oxygen is transferred into the silicon particles, and meanwhile, the circulation stability of the silicon particles is improved. And finally, carrying out heat treatment in an inert/reducing atmosphere at high temperature, and realizing sintering and agglomeration from small particles to secondary large particles by utilizing a high-temperature environment. The formed secondary particles reserve space, and can buffer the expansion of the silicon material in the charging and discharging process and release stress.

Drawings

Fig. 1 is a schematic view of a silicon-carbon negative electrode obtained in example 1. Wherein rGO represents reduced graphene oxide and SiOx represents silicon particles doped with partial oxygen. (x.ltoreq.1)

Fig. 2 is an X-ray diffraction pattern of the silicon-carbon negative electrode obtained in example 1.

Fig. 3 shows the scanning electron microscope results of the silicon-carbon negative electrode obtained in example 1.

Fig. 4 is a capacity-voltage graph of a battery assembled by using the silicon-carbon composite material obtained in example 1 as a negative electrode and a lithium sheet as a counter electrode.

Fig. 5 is a cycle-efficiency & specific capacity curve diagram of a battery assembled by using the silicon-carbon composite material obtained in example 1 as a negative electrode and a lithium sheet as a counter electrode.

Fig. 6 is a cycle-efficiency & specific capacity curve diagram of a battery assembled by using the silicon-carbon composite material obtained in example 2 as a negative electrode and a lithium sheet as a counter electrode.

Fig. 7 is a cycle-efficiency & specific capacity curve diagram of a battery assembled by using the silicon-carbon composite material obtained in example 3 as a negative electrode and a lithium sheet as a counter electrode.

Fig. 8 is a cycle-efficiency & specific capacity curve diagram of a battery assembled by using the silicon-carbon composite material obtained in example 4 as a negative electrode and a lithium sheet as a counter electrode.

Fig. 9 is a cycle-efficiency & specific capacity graph of a battery assembled with the silicon-carbon composite obtained in comparative example 1 as a negative electrode and a lithium sheet as a counter electrode.

Detailed Description

The present invention is further illustrated by the following examples, but the scope of the present invention is not limited to the following examples.

Example 1

In this embodiment, the method for enhancing the interface contact of the silicon-oxygen-carbon negative electrode material of the lithium ion battery by the oxygen transfer reaction includes the following steps:

step 1, firstly, mechanically milling large-particle-size Si with the commercial average particle size of 50 microns for 12 hours at the rotating speed of 700rpm to achieve the purpose of thinning the particle size, and using a 100m L zirconia ball milling tank and zirconia milling balls, wherein the particle sizes of the milling balls are 6mm, 10mm and 15mm, and the mass ratio of Si powder to zirconia balls is 35:45:20, and is 1: 2.

And 2, mixing the obtained Si powder with the refined particle size, graphene oxide and a binding agent PAA in a weight ratio of (5: 4.5:0.5), placing the mixture in a 100m L ball milling tank, using a gas-sealed zirconia ball milling tank and zirconia grinding balls with the particle sizes of 6mm, 10mm and 15mm in a mass ratio of 15:65:30, adding a proper amount of ethanol for wet ball milling at a rotation speed of 900rpm for 64h, and using the powder (the Si powder with the refined particle size, the graphene oxide and the binding agent PAA) and the zirconia grinding balls with the mass ratio of 1: 5.

And step 3: putting the sample dried in the step 2 in Ar/H₂Sintering for 2h at 750 ℃ under the protective atmosphere.

And 4, step 4: and (3) mixing the powder obtained in the step (3) with graphite, CMC, CNT and ACET in a weight ratio of 10:25:4:2:2, and then mixing at a rotating speed of 250rpm to obtain the silicon-carbon anode material with improved interface contact of the required 15% Si content, wherein the average length value of the CNT is 5 micrometers, the diameter of the tube is not limited, and the conductivity is more than 1S/cm. The mixed material uses a zirconium oxide ball milling tank and zirconium oxide grinding balls, the grain diameters of the grinding balls are 6mm and 20mm, and the mass ratio of powder (mixed powder of graphene and SiOx) to the zirconium oxide balls is 1: 7.

Fig. 1 is a schematic view of the obtained silicon carbon negative electrode. Wherein rGO represents reduced graphene oxide and SiOx represents silicon particles doped with partial oxygen.

Fig. 2 is a silicon carbon negative electrode X-ray diffraction pattern showing that the powder particles obtained are mainly graphite and Si, because the surface transfer oxygen is present in amorphous form in SiOx, with no diffraction peak.

Fig. 3 is a scanning electron microscope result of silicon carbon cathode, and it can be seen that the silicon particles are tightly wrapped by graphene.

Fig. 4 is a graph of capacity versus voltage for a silicon carbon composite. As can be seen from FIG. 4, the initial discharge capacity of the Si-C negative electrode under 1C condition is 5.4mAh/cm²The charging capacity is 4.64mAh/cm²。

Fig. 5 is a graph of cycle-efficiency versus specific capacity. As can be seen from fig. 5, under the condition of 1C, the initial coulombic efficiency of the battery rapidly increases from 85% to nearly 100%, and the specific capacity can be relatively kept stable and does not decrease by more than 5% within 300 circles. Showing good cycling performance.

Example 2

step 1, firstly, mechanically milling large-particle-size Si with the commercial average particle size of 20 microns for 24 hours at the rotating speed of 500rpm to achieve the purpose of thinning the particle size, and using a 100m L zirconia ball milling tank and zirconia milling balls, wherein the particle sizes of the milling balls are 6mm and 20mm, and the mass ratio of Si powder to zirconia balls is 1: 3.

And 2, mixing the obtained Si powder with the refined particle size, graphene oxide and a binder CMC in a weight ratio of 5: 4.5:0.5, putting the mixture into a 100m L ball milling tank, adding a proper amount of water into the gas-sealed zirconia ball milling tank and zirconia grinding balls with the particle sizes of 6mm, 10mm and 15mm in a mass ratio of 35:45:20, and performing wet ball milling at the rotation speed of 900rpm for 64h, wherein the mass ratio of powder (the Si powder with the refined particle size, the graphene oxide and the binder CMC) to the zirconia grinding balls is 1: 5.

And step 3: putting the sample dried in the step 2 in Ar/H₂Sintering for 2h at 550 ℃ under the protective atmosphere.

And 4, step 4: and (3) mixing the powder obtained in the step (3) with graphite, CMC and ACET in a weight ratio of 10:25:4:2, and then mixing at a rotating speed of 250rpm to obtain the silicon-carbon negative electrode material with the required interface contact of 15% of Si content and improved quality. The mixed material uses a zirconium oxide ball milling tank and zirconium oxide grinding balls, the grain diameters of the grinding balls are 6mm and 20mm, and the mass ratio of powder (mixed powder of graphene and SiOx) to the zirconium oxide balls is 1: 7.

Fig. 6 is a cycle-efficiency & specific capacity curve diagram of a battery assembled by using the silicon-carbon composite material obtained in example 2 as a negative electrode and a lithium sheet as a counter electrode. As can be seen in fig. 6: under the condition of 1C, the initial charge capacity is 562mAh/g, the capacity can still be kept at 475mAh/g after the circulation is 300 circles, and in addition, the coulombic efficiency of the silicon-carbon negative electrode can be close to 100% after the circulation for several cycles around 85%.

Example 3

step 1, firstly, mechanically milling large-particle-size Si with the commercial average particle size of 30 microns at the rotating speed of 600rpm for 18h to achieve the purpose of thinning the particle size, using a 100m L zirconia ball milling tank and zirconia milling balls, using the milling balls with the particle sizes of 6mm, 10mm and 15mm and the mass ratio of 35:45:20, and using the powder and the zirconia balls with the mass ratio of 1: 5.

And 2, mixing the obtained refined grain size Si powder, graphene oxide and a binder SA according to the weight ratio of (5: 4.5:0.5), placing the mixture in a 100m L ball milling tank, using a gas-sealed zirconia ball milling tank and zirconia grinding balls, using the grinding balls with the grain sizes of 6mm, 10mm and 15mm and the mass ratio of 25:45:30, adding a proper amount of water for wet ball milling, rotating at 1000rpm, and milling for 56h, wherein the mass ratio of powder (the refined grain size Si powder, the graphene oxide and the binder SA) to the zirconia grinding balls is 1: 3.

And step 3: putting the sample dried in the step 2 in Ar/H₂Sintering for 3h at 450 ℃ under the protective atmosphere.

And 4, step 4: and (3) mixing the powder obtained in the step (3) with graphite, CMC, CNT and ACET in a weight ratio of 10:25:4:2:2, and then mixing the mixture at a rotating speed of 250rpm to obtain the silicon-carbon anode material with the required 15% Si content and improved interface contact, wherein the average length value of the CNT is 2 micrometers, the diameter of the tube is not limited, and the conductivity is more than 0.1S/cm. The mixed material uses a zirconium oxide ball milling tank and zirconium oxide grinding balls, the grain diameters of the grinding balls are 10mm and 20mm, and the mass ratio of powder (mixed powder of graphene and SiOx) to the zirconium oxide balls is 1: 10.

Fig. 7 is a cycle-efficiency & specific capacity curve diagram of a battery assembled by using the silicon-carbon composite material obtained in example 3 as a negative electrode and a lithium sheet as a counter electrode. As can be seen in fig. 7: under 1C, its initial coulombic efficiency rises to a high value after several cycles, and the fluctuation within 300 cycles is small, and the specific capacity also experiences slight vibration, but the whole change is not large.

Example 4

step 1, firstly, mechanically milling large-particle-size Si with the commercial average particle size of 40 microns at the rotating speed of 600rpm for 18h to achieve the purpose of thinning the particle size, using a 100m L zirconia ball milling tank and zirconia milling balls, using the milling balls with the particle sizes of 6mm, 10mm and 15mm and the mass ratio of 35:45:20, and using the powder and the zirconia balls with the mass ratio of 1: 6.

And 2, mixing the obtained refined grain size Si powder, graphene oxide and a binder PVDF in a weight ratio of (5: 4.5:0.5), placing the mixture in a 100m L ball milling tank, using a gas-sealed zirconia ball milling tank and zirconia grinding balls, using grinding balls with grain sizes of 6mm, 10mm and 15mm and a mass ratio of 25:25:50, adding a proper amount of NMP to perform wet ball milling, rotating at 800rpm, and milling for 72h, wherein the mass ratio of powder (the refined grain size Si powder, the graphene oxide and the binder PVDF) to the zirconia grinding balls is 1: 5.

And step 3: putting the sample dried in the step 2 in Ar/H₂Sintering for 1h at 900 ℃ under the protective atmosphere.

And 4, step 4: and (3) mixing the powder obtained in the step (3) with graphite, CMC, CNT and ACET in a weight ratio of 10:25:4:2:2, and then mixing the mixture at a rotating speed of 250rpm to obtain the silicon-carbon anode material with improved interface contact of the required 15% Si content, wherein the average length value of the CNT is 10 micrometers, the diameter of the tube is not limited, and the conductivity is more than 0.5S/cm. The mixed material uses a zirconium oxide ball milling tank and zirconium oxide grinding balls, the grain diameters of the grinding balls are 6mm and 15mm, and the mass ratio of powder (mixed powder of graphene and SiOx) to the zirconium oxide balls is 1: 8.

Fig. 8 is a cycle-efficiency & specific capacity curve diagram of a battery assembled by using the silicon-carbon composite material obtained in example 4 as a negative electrode and a lithium sheet as a counter electrode. As can be seen from fig. 8: under the condition of 1C, when the silicon-carbon negative electrode is cycled within 300 circles, the coulombic efficiency and the specific capacity change are similar to those in the examples 1,2 and 3.

Comparative example 1

In this comparative example, the same raw materials as those in example 2 were mixed with a conductive agent and graphite, and then a conventional slurry brushing and coating process was used to prepare a silicon-oxygen-carbon negative electrode, including the following steps:

step 1, firstly, a large-particle-size Si with the commercial average particle size of 30 μm is mechanically ball-milled for 20 hours at the rotation speed of 550rpm to achieve the purpose of thinning the particle size, a zirconia ball-milling tank with the size of 100m L and zirconia milling balls are used, the particle sizes of the milling balls are 6mm, 10mm and 15mm, the mass ratio is 35:45:20, and the mass ratio of powder to the zirconia balls is 1: 5.

Step 2: the resulting powder was simply mixed with graphene oxide in a weight ratio of (5: 5).

And step 3: and (3) sintering the sample in the step 2 for 1.5H at 800 ℃ under the protective atmosphere of Ar/H2.

And 4, step 4: and (3) mixing the powder obtained in the step (3) with graphite, CMC, CNT and ACET in a weight ratio of 10:25:4:2:2, and then mixing the mixture at a rotating speed of 250rpm to obtain the silicon-carbon anode material with improved interface contact of the required 15% Si content, wherein the average length value of the CNT is 10 micrometers, the diameter of the tube is not limited, and the conductivity is more than 1S/cm.

And 5, dispersing the powder and NMP, then brushing slurry on a copper foil, preparing a sample, and assembling a battery.

The performance results of the obtained battery are shown in fig. 9, and fig. 9 is a cycle-efficiency & specific capacity graph of a battery assembled by using the silicon-carbon composite material obtained in comparative example 1 as a negative electrode and a lithium sheet as a counter electrode.

As can be seen from fig. 9, the battery can exhibit a relatively high capacity at the beginning, but the capacity rapidly decays during the cycle because the graphene and Si particles are not in sufficient contact, and the capacity exertion is reduced.

Claims

1. A method for enhancing interface contact of a silicon-oxygen-carbon cathode material of a lithium ion battery through oxygen transfer reaction is characterized in that coarse silicon powder is mixed with graphene oxide GO with a large number of oxygen functional groups after being crushed and refined, high-energy reaction ball milling is carried out under a sealing condition, oxygen in the graphene oxide is transferred to silicon through a solid-state reaction mode to form oxygen-containing silicon powder consisting of SiOx and graphene rGO losing oxygen to form a silicon-oxygen-carbon composite material, and x is less than or equal to 1; the preparation method comprises the following steps:

1) compounding silicon/graphene oxide: mixing the refined grain size Si powder with graphene oxide and a binder, and then carrying out high-energy reaction ball milling in a closed environment to realize an oxygen transfer process;

2) drying the product obtained in the step 1), and then carrying out heat treatment in an inert atmosphere;

3) the product in the step 2) is used for preparing a silicon-carbon cathode.

2. The method according to claim 1, wherein, in the step 1),

the particle size of the grinding ball is 6-20 mm;

the grain size of the refined grain size Si powder is 50 nm-10 mu m;

the graphene oxide is single-layer or multi-layer;

3. The method according to claim 1, wherein in the step 2), the heat treatment is performed in Ar/H₂Or heating to 450-950 ℃ at the heating rate of 2-10 ℃/min under Ar atmosphere, and preserving heat for 1-5 h.

4. The method according to claim 1, wherein, in the step 3),

the preparation method of the silicon-carbon cathode comprises the steps of mixing the product obtained in the step 2) with a graphite cathode, sodium carboxymethyl cellulose (CMC), a Carbon Nano Tube (CNT) and acetylene black (ACET) according to a certain proportion, and then carrying out low-speed ball milling to obtain the silicon-carbon cathode material to be improved.

5. The method as claimed in claim 2, wherein in the step 1), the material of the ball milling pot and the milling balls is zirconia, the particle size of the milling balls is 6mm, 10mm and 15mm, and the mass ratio of the three milling balls is 15-35:25-65: 20-50.

6. The method as claimed in claim 2, wherein in the step 1), the rotation speed of the ball milling pot is 800-.

7. The method according to claim 2, wherein in the step 1), the grain size Si powder is refined: and (3) graphene oxide: the mass ratio of the binder is 5: 4.5:0.5.

8. The method of claim 2, wherein in the step 1), the mass ratio of the powder to the grinding balls is 1: 3-5; the powder mass is the mass sum of the refined grain size Si powder, the graphene oxide and the binder.

9. The method as claimed in claim 2, wherein in the step 1), a grinding aid is further added into the ball milling tank, and the grinding aid is any one of water, ethanol and N-methylpyrrolidone.

10. The method as claimed in claim 3, wherein in the step 2), the heat treatment is performed to make the sample dried in the step 1) in Ar/H₂Sintering for 1-3h at the temperature of 900 ℃ under the protective atmosphere of 450-.