CN111446431B - Method for enhancing interface contact of silicon-oxygen-carbon cathode material of lithium ion battery through oxygen transfer reaction - Google Patents
Method for enhancing interface contact of silicon-oxygen-carbon cathode material of lithium ion battery through oxygen transfer reaction Download PDFInfo
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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 oxygen transfer process is realized by utilizing a high-temperature and high-pressure environment generated by ball milling, the conductivity of composite particles is improved through reduced graphene, oxygen is transferred into silicon particles, and meanwhile, the circulation stability of the silicon particles is improved.
Description
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 also shows good application prospects 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, rich storage capacity, low cost and the like. However, two key problems still exist in the scale use process of the silicon-based anode material, and need to be solved:
(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 efficacy; (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 structural types:
1) Coated silicon-carbon cathode
Coated silicon-carbon negative electrode materials are usually prepared by carbon coating 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 and enhance the conductivity, the carbon coating layer is usually amorphous carbon, chinese patent CN110148743A provides a method for 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 a carbon coating layer, a cavity structure is arranged between the core body and the shell, the mesoporous structure can retain electrolyte in practical application, the specific capacity is reduced, and the like, and the dynamic change of the pore structure in the circulation 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, a formed conductive network improves the electronic conductivity of the whole electrode, chinese patent CN109950511A describes in detail the silicon-carbon negative electrode material of a carbon fiber current collector, carbon fibers are interwoven into a sheet structure by cylindrical fiber yarns, the cylindrical fiber yarns are formed by a carbon fiber current collector at the inner layer, nano silicon at the middle layer and carbon at the outer layer, in the structure, the silicon particles and the conductive fibers are in physical contact, and short circuit is easily caused in the circulation process;
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. The fact proves that the silicon material is uniformly dispersed in the carbon buffer matrix, and the volume expansion of the silicon can be inhibited to a certain degree, and Chinese patents CN110048097A and CN106025218B provide a concept 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 relating to graphene and silicon composite are available, for example, chinese patent CN103022436B provides a composite material in which Graphene Oxide (GO) is mixed with ground silicon particles in a solution, and then treated in a reducing gas to obtain rGO/Si. Chinese patent application CN106920954A provides a method, in which porous Si and GO are mixed, then spray-dried, and pyrolyzed at high temperature to form a graphene-coated porous silicon composite material, and the porous structure in this material can buffer the volume expansion of Si during lithiation and delithiation. The chinese patent CN104253266B uses a physical deposition mode to alternately deposit a multilayer stack structure of graphene and Si thin films. US2008/0261116A1 Si negative electrode material vapor deposited on carbon nanofibers. In the chinese patent application CN103441247A, the surface of the silicon powder is modified to improve the bonding between the silicon particles and the graphene oxide, and the modified composite material has enhanced performance due to the enhanced chemical bond between Si and graphene. Similarly, the combination of Si and graphene or graphene oxide to form a composite material for use as a negative electrode of a lithium ion battery 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 silica SiO, which is a metastable substance and undergoes disproportionation reaction at high temperature to decompose into elemental Si and silica, with pitch or graphene. Chinese patent application CN107611360A proposes to use ferroferric oxide to wrap the silica, which is compounded with graphene. Chinese patent CN103811729B provides a method for synthesizing a composite material of silica and graphene inside a cavity of a microwave pyrolysis apparatus under an extremely low oxygen partial pressure condition.
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 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 patent CN109659529A and CN 109713259A), 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 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 Si powder with the refined particle size, 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 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) of the method, the step,
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: 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 to 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/H 2 Or heating to 450-950 ℃ at the heating rate of 2-10 ℃/min under Ar atmosphere, and preserving the heat for 1-5 h.
In the step 3), the step (c) is carried out,
the preparation of the silicon-carbon cathode is to mix the product of the step 2) with a graphite cathode, sodium carboxymethyl cellulose (CMC), carbon Nano Tubes (CNT) and acetylene black (ACET) according to a certain proportion and then ball mill the mixture at a low speed to obtain the silicon-carbon cathode material which needs to be improved, thereby ensuring that all components are fully and uniformly mixed. Specifically, the product obtained in step 2) can be mixed with graphite, CMC, CNT and ACET in the weight ratio of 10. Or mixing the product obtained in the step 2) with graphite, CMC and ACET in a weight ratio of 10.
More preferably still, the first and second liquid crystal compositions are,
in the step 1), the material of the ball milling tank and the grinding balls is 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.
In the step 1), the rotation speed of the ball milling tank is 800-1000rpm, and the ball milling time is 56-72h.
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 Si powder with the refined particle size, 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/H 2 Sintering for 1-3h at 450-900 ℃ under protective atmosphere.
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 core content of the invention is that firstly, the oxygen component comes from a solid material GO, and the GO has high 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, generate 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, the 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, 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 the SiOx and the rGO subjected to reaction ball milling to form particles with larger particle size, so that the poor rheological property in the brushing and coating process is avoided. Thus, after the completion of the ball milling with the binder, a simple heat treatment is carried out, i.e. at Ar/H 2 Or heating to 450-950 ℃ at the heating rate of 2-10 ℃/min under the 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. The inner diameter and the outer diameter of the CNT used by the invention are not important, the length is required to be at least 3-12 mu m, the long CNT is easy to bridge between particles to form a conductive network, and the overlong carbon nanofiber can influence the rheological property of a powder material, so that the slurry brushing and film coating are 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 oxygen transfer process is realized by utilizing a high-temperature and high-pressure environment generated by ball milling, the conductivity of composite particles is improved through reduced graphene, oxygen is transferred into 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 Si-C cathode 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 graph 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 graph 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 μm at the rotation speed of 700rpm for 12h to achieve the purpose of thinning the particle size, wherein a 100mL zirconia ball milling tank and zirconia milling balls are used, the particle sizes of the milling balls are 6mm, 10mm and 15mm, and the mass ratio is 35. The mass ratio of the Si powder to the zirconia balls is 1.
Step 2: mixing the obtained refined particle size Si powder, graphene oxide and a binder PAA in a weight ratio of (5. The mass ratio of the powder (refined grain size Si powder, graphene oxide and binder PAA) to the zirconia grinding ball is 1.
And step 3: putting the sample dried in the step 2 in Ar/H 2 Sintering for 2h at 750 ℃ under the protective atmosphere.
And 4, step 4: mixing the powder obtained in the step 3 with graphite, CMC, CNT and ACET in a weight ratio of 10. The mixed material uses a zirconia ball milling tank and zirconia grinding balls, the grain sizes of the grinding balls are 6mm and 20mm, and the mass ratio of powder (mixed powder of graphene and SiOx) to zirconia balls is 1.
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/cm 2 The charging capacity is 4.64mAh/cm 2 。
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
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, a large-particle-size Si with the commercial average particle size of 20 mu m is mechanically ball-milled for 24h at the rotating speed of 500rpm so as to achieve the purpose of thinning the particle size, a 100mL zirconia ball-milling tank and zirconia grinding balls are used, the particle size of the grinding balls is 6mm and 20mm, and the mass ratio of Si powder to zirconia balls is 1.
Step 2: mixing the obtained refined grain size Si powder, graphene oxide and a binder CMC in a proportion of 5:4.5, and then placing the mixture in a 100mL ball-milling tank, using a gas-sealed zirconia ball-milling tank and zirconia milling balls with particle sizes of 6mm, 10mm and 15mm, a mass ratio of 35 to 45, adding a proper amount of water to perform wet ball-milling, wherein the rotation speed is 900rpm, and the ball-milling time is 64h. The mass ratio of the powder (refined grain size Si powder, graphene oxide and binder CMC) to the zirconia grinding ball is 1.
And step 3: putting the sample dried in the step 2 in Ar/H 2 Sintering for 2h at 550 ℃ under the protective atmosphere.
And 4, step 4: mixing the powder obtained in step 3 with graphite, CMC and ACET in a weight ratio of 10. The mixed material uses a zirconia ball-milling tank and zirconia grinding balls, the grain sizes of the grinding balls are 6mm and 20mm, and the mass ratio of powder (mixed powder of graphene and SiOx) to the zirconia balls is 1.
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 300 cycles of circulation, and in addition, the coulombic efficiency of the silicon-carbon cathode can approach 100 percent after being circulated for a plurality of cycles around 85 percent.
Example 3
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, a large-particle-size Si with the commercial average particle size of 30 μm is subjected to mechanical ball milling for 18h at the rotating speed of 600rpm so as to achieve the purpose of thinning the particle size, a 100mL zirconia ball milling tank and zirconia grinding balls are used, the particle sizes of the grinding balls are 6mm, 10mm and 15mm, and the mass ratio is 35. And the mass ratio of the powder to the zirconia balls is 1.
And 2, step: mixing the obtained refined particle size Si powder, graphene oxide and a binder SA in a weight ratio of (5. The mass ratio of the powder (refined grain size Si powder, graphene oxide and binder SA) to the zirconia grinding ball is 1.
And 3, step 3: putting the sample dried in the step 2 in Ar/H 2 Sintering for 3h at 450 ℃ under the protective atmosphere.
And 4, step 4: mixing the powder obtained in step 3 with graphite, CMC, CNT and ACET in a weight ratio of 10. The mixed material uses a zirconia ball milling tank and zirconia grinding balls, the grain sizes of the grinding balls are 10mm and 20mm, and the mass ratio of powder (mixed powder of graphene and SiOx) to the zirconia balls is 1.
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
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, a large-particle-size Si with the commercial average particle size of 40 μm is subjected to mechanical ball milling for 18h at the rotating speed of 600rpm so as to achieve the purpose of thinning the particle size, a 100mL zirconia ball milling tank and zirconia grinding balls are used, the particle sizes of the grinding balls are 6mm, 10mm and 15mm, and the mass ratio is 35. And the mass ratio of the powder to the zirconia balls is 1.
And 2, step: mixing the obtained refined particle size Si powder, graphene oxide and binder PVDF in a weight ratio of (5.5. The mass ratio of the powder (refined grain size Si powder, graphene oxide and binder PVDF) to the zirconia grinding ball is 1.
And step 3: putting the sample dried in the step 2 in Ar/H 2 Sintering for 1h at 900 ℃ under the protective atmosphere.
And 4, step 4: mixing the powder obtained in the step 3 with graphite, CMC, CNT and ACET in a weight ratio of 10. The mixed material uses a zirconia ball milling tank and zirconia grinding balls, the grain sizes of the grinding balls are 6mm and 15mm, and the mass ratio of powder (mixed powder of graphene and SiOx) to the zirconia balls is 1.
Fig. 8 is a cycle-efficiency & specific capacity graph 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, the coulombic efficiency and the specific capacity of the silicon-carbon negative electrode are similar to those of the silicon-carbon negative electrode in the examples 1,2,3 when the silicon-carbon negative electrode is cycled within 300 circles.
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 subjected to mechanical ball milling for 20h at the rotation speed of 550rpm so as to achieve the purpose of thinning the particle size, a 100mL zirconia ball milling tank and zirconia grinding balls are used, the particle sizes of the grinding balls are 6mm, 10mm and 15mm, and the mass ratio is 35. And the mass ratio of the powder to the zirconia balls is 1.
Step 2: the obtained powder was simply mixed with graphene oxide in the weight ratio of (5.
And step 3: and (3) sintering the sample in the step 2 for 1.5H at 800 ℃ under the Ar/H2 protective atmosphere.
And 4, step 4: mixing the powder obtained in step 3 with graphite, CMC, CNT and ACET in a weight ratio of 10.
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 (10)
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 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) Using the product in the step 2) to prepare the silicon-carbon cathode.
2. The method according to claim 1, wherein in step 1),
the high-energy reaction ball milling is carried out by adopting a ball milling tank and grinding balls which are sealed by gas;
the material of the ball milling tank and the grinding balls is any one of agate, zirconia and corundum;
the particle size of the grinding ball is one or more of 6 mm-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 a single layer or a plurality of layers;
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 to 10; the powder mass is the mass sum of the refined grain size Si powder, the graphene oxide and the binder.
3. The method of claim 1, wherein in the step 2), the heat treatment is performed in Ar/H 2 Or heating to 450-950 ℃ at the heating rate of 2-10 ℃/min under Ar atmosphere, and preserving the 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.
6. The method as claimed in claim 2, wherein in the step 1), the rotation speed of the ball milling tank is 800-1000rpm, and the ball milling time is 56-72h.
7. The method according to claim 2, wherein in the step 1), the grain size of 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/H 2 Sintering for 1-3h at 450-900 ℃ under protective atmosphere.
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| CN113184858A (en) * | 2021-04-27 | 2021-07-30 | 郑州市博卓科技有限公司 | Silicon-oxygen negative electrode material composition and preparation method thereof |
| CN113471436B (en) * | 2021-06-07 | 2022-10-14 | 四川启睿克科技有限公司 | In-situ coated silicon-carbon negative electrode material, preparation method thereof and lithium ion battery |
| CN113644243A (en) * | 2021-07-30 | 2021-11-12 | 清华大学 | Nitrogen-doped hollow-structure graphite microsphere, composite negative electrode material and preparation method of composite negative electrode material |
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