CN113903892A - Silicon monoxide composite negative electrode material and preparation method thereof - Google Patents
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Abstract
The application provides a silicon monoxide composite negative electrode material and a preparation method thereof. The silicon oxide composite negative electrode material comprises silicon oxide, Si-B alloy, a conductive carbon layer and a carbon coating layer. The first coulombic efficiency of the silicon monoxide composite negative electrode material is high, the specific capacity is large, and the electrical performance of the negative electrode material can be improved.
Description
Technical Field
The invention relates to the technical field of new materials, in particular to a silicon monoxide composite negative electrode material and a preparation method thereof.
Background
Lithium ion batteries are widely used in the fields of new energy vehicles, energy storage, portable electronic devices, and the like due to the advantages of high energy density, long cycle life, and the like. The graphite cathode material mainly adopted at present cannot meet the requirement of higher specific energy of the lithium ion power battery due to low theoretical capacity. Because of its suitable working potential and higher theoretical capacity, silica is considered to be one of the most promising negative electrode materials in the next generation of lithium ion batteries.
However, the silicon monoxide negative electrode material is easy to generate irreversible side reaction in the process of lithium intercalation for the first time, so that the first coulombic efficiency is low; in addition, the intrinsic conductivity of the silicon monoxide is low, and certain volume expansion exists in the charging and discharging process, so that the capacity of the material is attenuated quickly, and the charging and discharging cycle performance of the negative electrode material is poor.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides the silicon oxide composite negative electrode material which has higher coulombic efficiency and larger specific capacity for the first time and can improve the electrical property of the negative electrode material and the preparation method thereof.
The purpose of the invention is realized by the following technical scheme:
a silicon oxide composite negative electrode material comprises silicon oxide, Si-B alloy, a conductive carbon layer and a carbon coating layer.
In one embodiment, the Si-B alloy is present in an amount of 0 wt% to 10 wt%.
In one embodiment, the content of B in the Si-B alloy is 0.1 wt% to 0.5 wt%.
In one embodiment, the conductive carbon layer is made of at least one of graphene and carbon nanotubes.
In one embodiment, the carbon source of the carbon coating layer is at least one of PVA and SBR.
In one embodiment, the particle size of the silica is 1 micron to 10 microns.
In one embodiment, the Si-B alloy has a grain size of 1 to 5 microns.
A method of making a silica composite anode material as in any one of the previous embodiments, comprising the steps of:
carrying out primary stirring and mixing operation on the silicon monoxide and the Si-B alloy powder to obtain a silicon mixture;
performing ball milling mixing operation on the silicon mixture and a solvent to obtain a silicon monoxide compound slurry;
adding a conductive carbon material and a coated carbon source into the silicon monoxide composite slurry, and carrying out secondary stirring and mixing operation to obtain composite cathode slurry;
carrying out spray drying operation on the composite negative electrode slurry to obtain a composite negative electrode material precursor;
and carrying out pyrolysis operation on the composite anode material precursor to obtain the silicon monoxide composite anode material.
In one embodiment, the solvent is at least one of water, ethanol, and isopropanol.
In one embodiment, the spray drying operation has an inlet temperature of 140 ℃ to 250 ℃ and an outlet temperature of 80 ℃ to 120 ℃.
Compared with the prior art, the invention has at least the following advantages:
1. the silicon oxide composite negative electrode material contains Si-B alloy, and not only can effectively buffer stress generated during lithium intercalation through B, but also can improve the conductivity of Si, so that the specific capacity of the silicon oxide negative electrode material is improved, and the first discharge efficiency of the silicon oxide negative electrode material is improved. In addition, B can improve the dispersibility of Si and prevent the Si from agglomerating.
2. The silicon oxide composite negative electrode material is composed of silicon oxide and Si-B alloy, and is also added with a conductive carbon layer, and the silicon oxide, the Si-B alloy and the conductive carbon layer form a conductive network in the silicon oxide composite negative electrode material, so that the problem of low intrinsic conductivity of the silicon oxide is solved, and the electrochemical performance of the silicon oxide composite negative electrode material is improved.
3. The silicon oxide composite negative electrode material also comprises a carbon coating layer, and the carbon coating layer is uniformly coated on the surface of the silicon oxide composite negative electrode material, so that the conductivity of the silicon oxide composite negative electrode material can be improved, and the cycle performance of the silicon oxide composite negative electrode material is improved; further, the carbon coating layer can prevent the sub-outer layer of the silicon oxide/Si-B alloy composite layer from being affected by external environment, such as moisture and oxygen; furthermore, the carbon coating layer can also prevent a silicon monoxide core in the battery from directly contacting with the electrolyte, so that the consumption of the electrolyte and effective Li in the battery is effectively reduced, the electrolyte injection amount required by the production of the lithium ion battery and the generation of gas during the working of a lithium battery product can be reduced, and the stability of the SEI film is improved.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is a flow chart of a method for preparing a silicon oxide composite negative electrode material according to an embodiment of the present invention;
FIG. 2 is an overall SEM image of a composite negative electrode material prepared by the preparation method of the silicon monoxide composite negative electrode material shown in FIG. 1;
FIG. 3 is a partially enlarged SEM image of a composite negative electrode material prepared by the preparation method of the silicon monoxide composite negative electrode material shown in FIG. 1;
FIG. 4 is an X-ray diffraction (XRD) pattern of a composite anode material prepared by the method for preparing a silicon monoxide composite anode material shown in FIG. 1;
fig. 5 is a raman spectrum of the composite negative electrode material prepared by the preparation method of the silicon monoxide composite negative electrode material shown in fig. 1.
Detailed Description
To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
It will be understood that when an element is referred to as being "secured to" another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and the like as used herein are for illustrative purposes only and do not represent the only embodiments.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
The application provides a silicon monoxide composite negative electrode material. The silicon oxide composite negative electrode material comprises silicon oxide, Si-B alloy, a conductive carbon layer and a carbon coating layer.
The silicon oxide composite negative electrode material contains the Si-B alloy, and the conductivity of Si can be improved through B, so that the specific capacity of the silicon oxide negative electrode material is improved, and the first discharge efficiency of the silicon oxide negative electrode material is improved. It is understood that the charge and discharge mechanism of the negative electrode of silica, i.e., SiO, is as follows:
SiO+Li→Li2O+Si(1)；
SiO+Li→Li4SiO4+Si(2)；
Si+Li→Li4.4Si(3)；
when SiO is used as a negative electrode material, the first coulombic efficiency is low, mainly because the first step reaction (formula 1) and the first step reaction (formula 2) are irreversible reactions, and the generated productsLi2O、Li4SiO4And the reaction of the silicon oxide with the organic electrolyte, such as decomposition and condensation, consumes a large amount of lithium ions. In order to improve the specific capacity and the first discharge efficiency of the negative electrode material, in the application, the Si-B alloy is added into the silicon monoxide composite negative electrode material, and the stress generated during lithium intercalation can be effectively buffered through B, and the conductivity of Si can be improved, so that the specific capacity of the silicon monoxide negative electrode material is improved, and the first discharge efficiency of the silicon monoxide negative electrode material is improved. In addition, B can improve the dispersibility of Si and prevent the Si from agglomerating. Furthermore, a conductive carbon layer is added into the silicon oxide composite negative electrode material, and the silicon oxide, the Si-B alloy and the conductive carbon layer form a conductive network in the silicon oxide composite negative electrode material, so that the problem of low intrinsic conductivity of the silicon oxide is solved, and the electrochemical performance of the silicon oxide composite negative electrode material is improved. The carbon coating layer is uniformly coated on the surface of the silicon oxide composite negative electrode material, so that the conductivity of the silicon oxide composite negative electrode material can be improved, and the cycle performance of the silicon oxide composite negative electrode material is improved; further, the carbon coating layer can prevent the sub-outer layer of the silicon oxide/Si-B alloy composite layer from being affected by external environment, such as moisture and oxygen; furthermore, the carbon coating layer can also prevent a silicon monoxide core in the battery from directly contacting with the electrolyte, so that the consumption of the electrolyte and effective Li in the battery is effectively reduced, the electrolyte injection amount required by the production of the lithium ion battery and the generation of gas during the working of a lithium battery product can be reduced, and the stability of the SEI film is improved.
In one embodiment, the Si-B alloy is present in an amount of 0 wt% to 10 wt%. It can be understood that the Si-B alloy is added into the silicon monoxide composite negative electrode material, and the conductivity of Si can be improved through B, so that the specific capacity of the silicon monoxide negative electrode material is improved, and the first discharge efficiency of the silicon monoxide negative electrode material is improved at the same time. However, if the content of the Si-B alloy is too high, particles in a fine dispersed metal silicon aggregation area are easy to aggregate in the later charge-discharge cycle process, so that the cycle stability of the negative electrode material is damaged; if the content of the Si-B alloy is too low, the specific capacity of the silicon oxide composite material cannot be increased, and if the content of the B is too low, the conductivity of Si cannot be increased, so that the first discharge efficiency of the silicon oxide negative electrode material cannot be increased. In order to improve the specific capacity and the first discharge efficiency of the silicon monoxide composite negative electrode material, in this embodiment, the content of the Si-B alloy is 0 wt% to 10 wt%, so that the specific capacity of the silicon monoxide negative electrode material can be effectively improved by the Si-B alloy, and the conductivity of Si can be effectively improved by B, thereby effectively improving the first discharge efficiency of the silicon monoxide negative electrode material.
Further, the content of B in the Si-B alloy is 0.1 wt% -0.5 wt%. It can be understood that the Si-B alloy can effectively improve the conductivity of Si by doping B, thereby improving the specific capacity of the silicon oxide negative electrode material and simultaneously improving the first discharge efficiency of the silicon oxide negative electrode material. However, if the content of B in the Si-B alloy is too low, effective electrical bonding cannot be easily formed, so that the conductivity of Si cannot be improved by B, and the Si in the Si-B alloy is too high, so that the Si-B alloy is easily agglomerated, and the electrical property of the cathode material is reduced; if the content of B in the Si-B alloy is too high, the capacity and conductivity of the Si-B alloy are adversely affected. In the embodiment, the content of B in the Si-B alloy is 0.1 wt% to 0.5 wt%, and when the content of B in the Si-B alloy reaches 0.1 wt% to 0.5 wt%, B can form effective electrical bonding in Si, so that the bonding stability of B and Si is good, and the Si-B alloy has a high carrier concentration, thereby effectively enhancing the conductivity of the Si-B alloy, further improving the first discharge efficiency of the silicon oxide negative electrode material, and further improving the specific capacity of the silicon oxide negative electrode material.
In one embodiment, the conductive carbon layer is made of at least one of graphene and carbon nanotubes. It can be understood that the conductive carbon layer, the silicon oxide and the Si-B alloy form a conductive network in the silicon oxide composite negative electrode material, so that the problem of low intrinsic conductivity of the silicon oxide is solved, and the electrochemical performance of the silicon oxide composite negative electrode material is improved. In order to further improve the conductivity of the conductive carbon layer, in this embodiment, the conductive carbon layer is made of at least one of graphene and carbon nanotubes, the graphene is a carbon material with a two-dimensional layered structure, pz orbitals perpendicular to a layer plane of each carbon atom of the graphene can form a large pi bond penetrating through all layers of multiple atoms, and the graphene has a high aspect ratio, excellent hydrophobicity, thermal conductivity and chemical stability, a conjugated system enables the electron conductivity of the graphene to be very strong, and the graphene has excellent conductivity, and a conductive network is formed by the graphene, silicon oxide and a Si-B alloy in the silicon oxide composite negative electrode material, so that the conductivity of the conductive network can be effectively improved. The P electrons of the carbon atoms on the carbon nano tube form a large-range delocalized pi bond, the carbon nano tube has better conductivity due to the obvious conjugation effect, and the carbon nano tube, the silicon monoxide and the Si-B alloy form a conductive network in the silicon monoxide composite cathode material, so that the conductivity of the conductive network can be effectively improved.
In one embodiment, the carbon source of the carbon coating layer is at least one of PVA and SBR. It can be understood that the carbon coating layer is uniformly coated on the surface of the silicon oxide composite negative electrode material, so that the conductivity of the silicon oxide composite negative electrode material can be improved, and the cycle performance of the silicon oxide composite negative electrode material is improved; further, the carbon coating layer can prevent the sub-outer layer of the silicon oxide/Si-B alloy composite layer from being affected by external environment, such as moisture and oxygen; furthermore, the carbon coating layer can also prevent a silicon monoxide core in the battery from directly contacting with the electrolyte, so that the consumption of the electrolyte and effective Li in the battery is effectively reduced, the electrolyte injection amount required by the production of the lithium ion battery and the generation of gas during the working of a lithium battery product can be reduced, and the stability of the SEI film is improved. In order to further improve the uniformity and conductivity of the carbon coating layer, in this embodiment, the carbon source of the carbon coating layer is at least one of PVA and SBR, the PVA is polyvinyl alcohol, the PVA has good receptivity and can contain more other conductive substances, and the PVA has good film-forming property and adhesion property after being dried. The SBR is styrene butadiene rubber, has the advantages of wear resistance, cold resistance, low heat generation, low shrinkage, good color, low ash content, high purity and high vulcanization speed, and is used as a carrier of the conductive carbon material, so that the conductive carbon material is uniformly distributed in the carbon coating layer, the conductivity of the silicon oxide composite negative electrode material is effectively improved, and the cycle performance of the silicon oxide composite negative electrode material is improved. Furthermore, the styrene butadiene rubber has a flexible chain segment, and is connected with the silicon particles in multiple dimensions through chemical bonds, so that the binding force between the binder and the silicon electrode is enhanced, and the electrochemical performance of the composite anode material is improved.
In one embodiment, the particle size of the silica is 1 micron to 10 microns. It can be understood that the silicon oxide, the Si-B alloy and the conductive carbon layer can form a conductive network in the silicon oxide composite negative electrode material, so that the problem of low intrinsic conductivity of the silicon oxide is solved, and the electrochemical performance of the silicon oxide composite negative electrode material is improved. However, in the process of mixing the silicon monoxide with the Si-B alloy and the conductive carbon layer, agglomeration phenomenon is easy to occur, thereby influencing the uniformity of the silicon monoxide composite negative electrode material. In order to improve the mixing uniformity of the silicon monoxide, the Si-B alloy and the conductive carbon layer, in this embodiment, the particle size of the silicon monoxide is 1 to 10 microns, so that the dispersibility and uniformity of the silicon monoxide in the composite anode material system are better, that is, the mixing uniformity of the silicon monoxide, the Si-B alloy and the conductive carbon layer is improved, thereby being beneficial to improving the electrochemical performance of the silicon monoxide composite anode material.
In one embodiment, the Si-B alloy has a grain size of 1 micron to 5 microns. It can be understood that, since the conductivity of Si can be improved by B in the Si-B alloy, the specific capacity of the silicon oxide negative electrode material is improved, and the first discharge efficiency of the silicon oxide negative electrode material is improved at the same time. However, if the particle size of the Si — B alloy is too large, the Si — B alloy and the silicon monoxide tend to be weakly bonded to each other, and the Si — B alloy may easily fall off after mixing; if the particle size of the Si-B alloy is too small, dispersion unevenness is liable to occur, and the Si-B alloy is inferior in conductivity. In order to improve the conductivity of the Si-B alloy and the uniformity of the Si-B alloy in the composite negative electrode material, in this embodiment, the particle size of the Si-B alloy is 1 to 5 micrometers, which can effectively increase the specific surface area of the Si-B alloy, so that the combination effect of the Si-B alloy and the silicon monoxide is better, thereby improving the conductivity of the Si-B alloy to the silicon monoxide composite negative electrode material. Furthermore, the Si-B alloy with the particle size of 1-5 microns is combined with the silicon monoxide, so that the granularity of primary particles is easier to form, the phenomenon of agglomeration after the Si-B alloy is combined with the silicon monoxide is effectively prevented, the uniformity of the Si-B alloy in the composite negative electrode material is effectively improved, the specific capacity of the silicon monoxide negative electrode material is further improved, and the first discharge efficiency of the silicon monoxide negative electrode material is also improved.
The present application further provides a method for preparing a silica composite anode material according to any one of the above embodiments, including the following steps: carrying out primary stirring and mixing operation on the silicon monoxide and the Si-B alloy powder to obtain a silicon mixture; performing ball milling mixing operation on the silicon mixture and a solvent to obtain a silicon monoxide compound slurry; adding a conductive carbon material and a coated carbon source into the silicon monoxide composite slurry, and carrying out secondary stirring and mixing operation to obtain composite cathode slurry; carrying out spray drying operation on the composite negative electrode slurry to obtain a composite negative electrode material precursor; and carrying out pyrolysis operation on the composite anode material precursor to obtain the silicon monoxide composite anode material.
In the preparation method of the silicon oxide composite negative electrode material, the Si-B alloy powder is added into the silicon oxide and mixed, the conductivity of Si can be improved through B in the Si-B alloy, so that the conductivity of the Si-B alloy is improved, the specific capacity of the silicon oxide negative electrode material can be improved through adding the Si-B alloy, and the first discharge efficiency of the silicon oxide negative electrode material is improved. After the Si-B alloy powder and the silicon monoxide are uniformly mixed, a solvent is added for mixing and dissolving, and ball milling mixing operation is carried out, so that on one hand, the mixing of the Si-B alloy and the silicon monoxide can be accelerated, and the preparation efficiency of the silicon monoxide composite negative electrode material is improved; on the other hand, the particle size of the mixed slurry of the silicon monoxide and the Si-B alloy can be effectively reduced through ball milling operation, so that the bonding property and uniformity of the Si-B alloy and the silicon monoxide are realized. Further, the precursor of the composite negative electrode material is subjected to pyrolysis operation, so that the carbon source material is pyrolyzed and then uniformly coated on the surface of the composite negative electrode material to form a carbon coating layer, thereby improving the conductivity of the silicon oxide composite negative electrode material and improving the cycle performance of the silicon oxide composite negative electrode material; further, the carbon coating layer can prevent the sub-outer layer of the silicon oxide/Si-B alloy composite layer from being affected by external environment, such as moisture and oxygen; furthermore, the carbon coating layer can also prevent a silicon monoxide core in the battery from directly contacting with the electrolyte, so that the consumption of the electrolyte and effective Li in the battery is effectively reduced, the electrolyte injection amount required by the production of the lithium ion battery and the generation of gas during the working of a lithium battery product can be reduced, and the stability of the SEI film is improved.
Referring to fig. 1, in order to better understand the preparation method of the negative electrode material of the present application, the following further explains the preparation method of the negative electrode material of the present application, and the preparation method of the negative electrode material of the present application includes the following steps:
s100, stirring and mixing the silicon monoxide and the Si-B alloy powder for the first time to obtain a silicon mixture.
It is understood that the charge and discharge mechanism of the negative electrode of silica, i.e., SiO, is as follows:
SiO+Li→Li2O+Si(1)；
SiO+Li→Li4SiO4+Si(2)
Si+Li→Li4.4Si(3)
when SiO is used as a negative electrode material, the first coulombic efficiency is low, mainly because the first step reactions (formula 1) and (formula 2) are irreversible reactions, and the generated Li2O、Li4SiO4And the reaction of the silicon oxide with the organic electrolyte, such as decomposition and condensation, consumes a large amount of lithium ions. In this embodiment, the Si-B alloy powder is added to the silicon monoxide to perform a mixing reaction, B forms an effective electrical bond in Si, and improves the conductivity of the Si-B alloy powder, and the Si-B alloy powder and the silicon monoxide perform a mixing reaction, thereby improving the specific capacity of the silicon monoxide negative electrode material and simultaneously improving the first discharge efficiency of the silicon monoxide negative electrode material.
And S200, performing ball milling mixing operation on the silicon mixture and a solvent to obtain the silicon monoxide composite slurry.
In the embodiment, after the Si-B alloy powder and the silicon monoxide are uniformly mixed, a solvent is added for mixing and dissolving, then the mixed solution is added into a ball mill, and is ball-milled by a sand mill to obtain silicon monoxide mixed slurry, and through carrying out ball-milling mixing operation, on one hand, the mixing of the Si-B alloy and the silicon monoxide can be accelerated, and the preparation efficiency of the silicon monoxide composite negative electrode material is improved; on the other hand, the particle size of the mixed slurry of the silicon monoxide and the Si-B alloy can be effectively reduced through ball milling operation, so that the bonding property and uniformity of the Si-B alloy and the silicon monoxide are realized.
And S300, adding a conductive carbon material and a coated carbon source into the silicon monoxide composite slurry, and carrying out secondary stirring and mixing operation to obtain the composite cathode slurry.
In this embodiment, the conductive carbon material and the coated carbon source are added to the milled silica composite slurry, and a second stirring and mixing operation is performed to sufficiently mix the conductive carbon material and the coated carbon source in the silica composite slurry. The conductive carbon material is combined with the silicon oxide and the Si-B alloy to react, and a conductive network is formed in the silicon oxide composite negative electrode material, so that the problem of low intrinsic conductivity of the silicon oxide is solved, and the electrochemical performance of the silicon oxide composite negative electrode material is improved. Further, a carbon coating layer can be formed by coating the carbon source, so that the conductivity of the silicon oxide composite negative electrode material is improved, and the cycle performance of the silicon oxide composite negative electrode material is improved.
S400, carrying out spray drying operation on the composite negative electrode slurry to obtain a composite negative electrode material precursor.
In this example, the spray drying operation dispersed the composite anode slurry into fine mist-like particles by mechanical action, and the particles were contacted with hot air to instantaneously remove most of the water, so that the solid matter in the composite anode slurry was dried into powder. In addition, the spray drying operation can also increase the water evaporation area and accelerate the drying process, thereby improving the preparation efficiency of the silicon monoxide composite negative electrode material.
And S500, carrying out pyrolysis operation on the composite cathode material precursor to obtain the silicon monoxide composite cathode material.
In this embodiment, the composite anode material precursor is placed in a pyrolysis furnace under an argon protective atmosphere to perform pyrolysis operation, and is cooled to room temperature after the pyrolysis operation is completed. The carbon source material can be uniformly coated on the surface of the composite negative electrode material after pyrolysis through pyrolysis operation to form a carbon coating layer, so that the conductivity of the silicon oxide composite negative electrode material can be improved, and the cycle performance of the silicon oxide composite negative electrode material can be improved; further, the carbon coating layer can prevent the sub-outer layer of the silicon oxide/Si-B alloy composite layer from being affected by external environment, such as moisture and oxygen; furthermore, the carbon coating layer can also prevent a silicon monoxide core in the battery from directly contacting with the electrolyte, so that the consumption of the electrolyte and effective Li in the battery is effectively reduced, the electrolyte injection amount required by the production of the lithium ion battery and the generation of gas during the working of a lithium battery product can be reduced, and the stability of the SEI film is improved.
In one embodiment, the solvent is at least one of water, ethanol, and isopropanol. In this embodiment, the silicon mixture is added into the solvent for mixing and dissolving, so that on one hand, the mixing reaction of the silicon mixture and other auxiliaries can be accelerated, and the preparation efficiency of the composite negative electrode material is improved; on the other hand, the uniformity of the composite anode material can be further improved through the solvent. Furthermore, the solvent is at least one of water, ethanol and isopropanol, the ethanol has good solubility to silicon mixture and carbon mixture, and the ethanol has good environmental protection property, no toxicity and good compatibility with other organic solvents. The isopropanol has good solubility to organic matters, can be freely mixed with water, and has stronger solubility to lipophilic substances than ethanol. In addition, the isopropanol can also play a certain role in dispersion, so that the uniformity of the composite slurry is improved.
Further, the mass ratio of the solvent to the silicon mixture is 3/1-8/1. It can be understood that the silicon mixture is added into the solvent for mixing and dissolving, so that on one hand, the mixing reaction of the silicon mixture and other auxiliaries can be accelerated, and the preparation efficiency of the composite negative electrode material is improved; on the other hand, the uniformity of the composite anode material can be further improved through the solvent. In order to further control the concentration of the mixture slurry and improve the uniformity of the mixture slurry, in the embodiment, the mass ratio of the solvent to the silicon mixture is 3/1-8/1, so that the silicon mixture is fully dissolved in the solvent, and the dissolved mixture slurry reaches a viscous concentration which is easy to stir, thereby improving the uniformity of the mixture slurry.
In one embodiment, the particle size of the silica composite slurry is 0.1 to 1.5 microns. It can be understood that after the silica composite slurry is uniformly mixed, the silica composite slurry also needs to be mixed with the conductive carbon material and the coating carbon source, and the particle size of the silica composite slurry easily affects the uniformity of the composite negative electrode slurry. In addition, the particle size of the silica composite slurry may directly affect the electrochemical performance of the silica composite negative electrode material. In order to improve the uniformity of the composite cathode slurry and improve the first discharge efficiency of the silicon oxide composite cathode material, in this embodiment, the particle size of the silicon oxide composite slurry is 0.1 to 1.5 micrometers, so as to increase the specific surface area of the silicon oxide composite slurry particles, make the contact between the silicon oxide composite slurry and the conductive carbon material and the coating carbon source more sufficient, and further improve the uniformity of the composite cathode slurry. Furthermore, the 0.1-1.5 micron particle size of the silicon oxide composite slurry is easier to form a conductive network with a conductive carbon material in the silicon oxide composite anode material, so that the problem of low intrinsic conductivity of the silicon oxide is further improved, and the electrochemical performance of the silicon oxide composite anode material is further improved.
In one embodiment, the spray drying operation has an inlet temperature of 140 ℃ to 250 ℃ and an outlet temperature of 80 ℃ to 120 ℃. It is understood that the spray drying operation disperses the composite anode slurry into fine mist-like particles by mechanical action, and the particles contact with hot air to instantaneously remove most of the moisture, so that the solid matter in the composite anode slurry is dried into powder. In addition, the spray drying operation can also increase the water evaporation area and accelerate the drying process, thereby improving the preparation efficiency of the silicon monoxide composite negative electrode material. However, the composite anode material is easy to have the problem of uneven drying in the spray drying process. In order to improve the drying uniformity of the composite cathode material in the spray drying operation, in the embodiment, the inlet temperature in the spray drying operation is 140-250 ℃, the outlet temperature is 80-120 ℃, when the composite cathode slurry enters the spray dryer, the solvent content of the composite cathode slurry is high, and the composite cathode slurry is dried at 140-250 ℃ at the inlet, so that most of moisture in the composite cathode slurry can be effectively removed, and meanwhile, the drying efficiency of the composite cathode slurry is improved. Furthermore, when the composite cathode slurry is dried and then is output from an outlet, the outlet temperature is controlled to be 80-120 ℃, on one hand, the composite cathode slurry can be further dried, and the drying uniformity of the composite cathode material is effectively improved; on the other hand can also play the transition cooling effect to the compound cathode material after the drying, prevent that compound cathode material quench after the drying and absorb the moisture in the air, influence compound cathode material's aridity, also can play the heat preservation effect to the compound cathode material after the drying simultaneously, thereby can make the compound cathode material after the drying directly carry out the pyrolysis process on next step, improve compound cathode material's pyrolysis efficiency, simultaneously to the pyrolysis process, 80 ℃ -120 ℃ drying process in exit can also play preheating effect, thereby promote compound cathode material's pyrolysis effect.
In one embodiment, the conductive carbon material is added in an amount of 1 wt% to 2 wt%. It can be understood that after pyrolysis, the conductive carbon material can form a conductive carbon layer, the silicon oxide, the Si-B alloy and the conductive carbon layer to form a conductive network in the silicon oxide composite anode material, so that the problem of low intrinsic conductivity of the silicon oxide is solved, and the electrochemical performance of the silicon oxide composite anode material is improved. However, if the amount of the conductive carbon material added is too large, the performance of the negative electrode material is easily affected; if the amount of the conductive carbon material added is too small, a good conductive effect cannot be obtained. In order to further improve the electrochemical performance of the silicon oxide composite negative electrode material, in this embodiment, the addition amount of the conductive carbon material is 1 wt% to 2 wt% to form a conductive carbon layer with good conductivity, so as to further improve the problem of low intrinsic conductivity of silicon oxide, and further improve the electrochemical performance of the silicon oxide composite negative electrode material.
In one embodiment, the amount of the coated carbon source is 5 wt% to 20 wt%. In this embodiment, the PVA can be used as a carrier of the conductive carbon material, so that the conductive carbon material is uniformly distributed in the carbon coating layer, thereby effectively improving the conductivity of the silicon oxide composite negative electrode material and simultaneously improving the cycle performance of the silicon oxide composite negative electrode material. The SBR is styrene butadiene rubber, has the advantages of wear resistance, cold resistance, low heat generation, low shrinkage, good color, low ash content, high purity and high vulcanization speed, and is used as a carrier of the conductive carbon material, so that the conductive carbon material is uniformly distributed in the carbon coating layer, the conductivity of the silicon oxide composite negative electrode material is effectively improved, and the cycle performance of the silicon oxide composite negative electrode material is improved. Furthermore, the addition amount of the coated carbon source is 5 wt% -20 wt%, so that the conductivity of the silicon oxide composite negative electrode material is further improved, and the cycle performance of the silicon oxide composite negative electrode material is further improved. In addition, the negative influence on the silicon oxide composite negative electrode material caused by too low or too high addition amount of the coated carbon source can be avoided.
In one embodiment, the pyrolysis temperature in the pyrolysis operation is 600 ℃ to 950 ℃ and the pyrolysis time is 2 hours to 4 hours. It can be understood that the composite anode material precursor is placed in a pyrolysis furnace under the protection of argon gas for pyrolysis operation, and is cooled to room temperature after the pyrolysis operation is completed. The carbon source material can be uniformly coated on the surface of the composite negative electrode material after pyrolysis through pyrolysis operation to form a carbon coating layer, so that the conductivity of the silicon oxide composite negative electrode material can be improved, and the cycle performance of the silicon oxide composite negative electrode material can be improved; further, the carbon coating layer can prevent the sub-outer layer of the silicon oxide/Si-B alloy composite layer from being affected by external environment, such as moisture and oxygen; furthermore, the carbon coating layer can also prevent a silicon monoxide core in the battery from directly contacting with the electrolyte, so that the consumption of the electrolyte and effective Li in the battery is effectively reduced, the electrolyte injection amount required by the production of the lithium ion battery and the generation of gas during the working of a lithium battery product can be reduced, and the stability of the SEI film is improved. However, if the pyrolysis temperature is too high or the pyrolysis time is too long, the components in the silicon oxide composite material are easily damaged, so that the electrical property and the cycle performance of the silicon oxide composite negative electrode material are influenced; if the pyrolysis temperature is too high or the pyrolysis time is too long, the conductive carbon material and the coated carbon source cannot be effectively pyrolyzed, namely, the problems of insufficient pyrolysis and excessive pyrolysis exist. In order to improve the pyrolysis effect on the anode material precursor, in this embodiment, the pyrolysis temperature in the pyrolysis operation is 600 ℃ to 950 ℃, and the pyrolysis time is 2 hours to 4 hours. The carbon source material is fully pyrolyzed and is coated on the surface of the composite negative electrode material after pyrolysis to form a carbon coating layer, so that the conductivity of the silicon oxide composite negative electrode material can be improved, and the cycle performance of the silicon oxide composite negative electrode material is improved.
In one embodiment, the particle size of the silicon oxide composite negative electrode material is 5-15 microns. It can be understood that if the particle size of the silicon oxide composite negative electrode material is too small, agglomeration is easy to occur between the silicon oxide composite negative electrode material particles, primary particles cannot be formed, and a silicon oxide composite negative electrode material particle accumulation body, namely the porosity of the silicon oxide composite negative electrode material, is adversely affected; if the particle size of the silicon oxide composite negative electrode material is too large, the further forming of the silicon oxide composite negative electrode material is not facilitated, and the coating operation of the silicon oxide composite negative electrode material is not facilitated, so that the flatness of the silicon oxide composite negative electrode material is influenced. In order to improve the uniformity and the evenness of the silicon oxide composite negative electrode material, in the embodiment, the particle size of the silicon oxide composite negative electrode material is 5-15 micrometers, so that the dispersibility and the uniformity of the silicon oxide composite negative electrode material can be effectively improved, and the silicon oxide coating rate of the Si-B alloy is improved, so that the specific capacity and the first discharge efficiency of the silicon oxide composite negative electrode material are effectively improved. Further, the smoothness of the silicon monoxide composite negative electrode material can be improved, so that the silicon monoxide composite negative electrode material is further processed, and the performance of the lithium ion battery is improved.
Some specific examples are listed below, and if mentioned%, all are expressed in weight percent. It should be noted that the following examples are not intended to be exhaustive of all possible cases, and that the materials used in the following examples are commercially available without specific recitation.
Example 1
Adding 5% of Si-B alloy powder into the silicon monoxide, wherein the content of B in the Si-B alloy is 0.3%, and uniformly mixing; adding the mixture into an ethanol solvent, wherein the weight ratio of the mixture to the ethanol is 1:5, adding the mixture into a sand mill, and performing ball milling on the mixture by the sand mill to obtain a silicon monoxide mixed slurry; adding 1.5% of carbon nano tube and 10% of PVA into the mixed slurry, and uniformly stirring; spray drying the mixed slurry to obtain a composite anode material precursor, wherein the inlet temperature of the spray drying is 180 ℃, and the outlet temperature of the spray drying is 80 ℃; and (3) putting the precursor into a pyrolysis furnace with the temperature of 800 ℃ for pyrolysis for 2h under the protection of argon, and cooling to room temperature to obtain the silicon monoxide composite negative electrode material.
Example 2
Adding 10% of Si-B alloy powder into the silicon monoxide, wherein the content of B in the Si-B alloy is 0.5%, and uniformly mixing; adding the mixture into an ethanol solvent, wherein the weight ratio of the mixture to the ethanol is 1:4, adding the mixture into a sand mill, and performing ball milling on the mixture by the sand mill to obtain a silicon monoxide mixed slurry; adding 2% of carbon nano tube and 10% of SBR into the mixed slurry, and uniformly stirring; spray drying the mixed slurry to obtain a composite anode material precursor, wherein the inlet temperature of the spray drying is 200 ℃, and the outlet temperature of the spray drying is 90 ℃; and (3) putting the precursor into a pyrolysis furnace with the temperature of 850 ℃ for pyrolysis for 2h under the protection of argon, and cooling to room temperature to obtain the silicon monoxide composite negative electrode material.
Example 3
Adding 3% of Si-B alloy powder into the silicon monoxide, wherein the content of B in the Si-B alloy is 0.3%, and uniformly mixing; adding the mixture into deionized water, wherein the weight ratio of the mixture to the deionized water is 1:3, adding the mixture into a sand mill, and performing ball milling on the mixture by the sand mill to obtain a silicon monoxide mixed slurry; adding 1% of graphene and 15% of PVA into the mixed slurry, and uniformly stirring; spray drying the mixed slurry to obtain a composite anode material precursor, wherein the inlet temperature of the spray drying is 240 ℃, and the outlet temperature of the spray drying is 120 ℃; and (3) putting the precursor into a pyrolysis furnace with the temperature of 850 ℃ for pyrolysis for 4h under the protection of argon, and cooling to room temperature to obtain the silicon monoxide composite negative electrode material.
Example 4
Adding 5% of Si-B alloy powder into the silicon monoxide, wherein the content of B in the Si-B alloy is 0.5%, and uniformly mixing; adding the mixture into isopropanol solvent, wherein the weight ratio of the mixture to the isopropanol is 1:4, adding the mixture into a sand mill, and performing ball milling on the mixture by the sand mill to obtain silicon monoxide mixed slurry; adding 1.5% of carbon nano tube and 20% of SBR into the mixed slurry, and uniformly stirring; spray drying the mixed slurry to obtain a composite anode material precursor, wherein the inlet temperature of the spray drying is 200 ℃, and the outlet temperature of the spray drying is 90 ℃; and (3) putting the precursor into a pyrolysis furnace with the temperature of 850 ℃ for pyrolysis for 2h under the protection of argon, and cooling to room temperature to obtain the silicon monoxide composite negative electrode material.
Example 5
Adding 5% of Si-B alloy powder into the silicon monoxide, wherein the content of B in the Si-B alloy is 0.3%, and uniformly mixing; adding the mixture into isopropanol solvent, wherein the weight ratio of the mixture to the isopropanol is 1:5, adding the mixture into a sand mill, and performing ball milling on the mixture by the sand mill to obtain silicon monoxide mixed slurry; adding 1% of carbon nano tube, 0.5% of graphene and 15% of SBR into the mixed slurry, and uniformly stirring; spray drying the mixed slurry to obtain a composite anode material precursor, wherein the inlet temperature of the spray drying is 200 ℃, and the outlet temperature of the spray drying is 90 ℃; and (3) putting the precursor into a pyrolysis furnace with the temperature of 800 ℃ for pyrolysis for 2h under the protection of argon, and cooling to room temperature to obtain the silicon monoxide composite negative electrode material.
Example 6
Adding 10% of Si-B alloy powder into the silicon monoxide, wherein the content of B in the Si-B alloy is 0.5%, and uniformly mixing; adding the mixture into deionized water, wherein the weight ratio of the mixture to the deionized water is 1:6, adding the mixture into a sand mill, and performing ball milling on the mixture by the sand mill to obtain a silicon monoxide mixed slurry; adding 2% of carbon nano tube and 10% of PVA into the mixed slurry, and uniformly stirring; spray drying the mixed slurry to obtain a composite anode material precursor, wherein the inlet temperature of the spray drying is 240 ℃, and the outlet temperature of the spray drying is 120 ℃; and (3) putting the precursor into a pyrolysis furnace with the temperature of 900 ℃ for pyrolysis for 2h under the protection of argon, and cooling to room temperature to obtain the silicon monoxide composite negative electrode material.
Example 7
Adding 5% of Si-B alloy powder into the silicon monoxide, wherein the content of B in the Si-B alloy is 0.3%, and uniformly mixing; adding the mixture into isopropanol solvent, wherein the weight ratio of the mixture to the isopropanol is 1:4, adding the mixture into a sand mill, and performing ball milling on the mixture by the sand mill to obtain silicon monoxide mixed slurry; adding 1.0% of carbon nano tube, 0.5% of graphene and 15% of SBR into the mixed slurry, and uniformly stirring; spray drying the mixed slurry to obtain a composite anode material precursor, wherein the inlet temperature of the spray drying is 190 ℃, and the outlet temperature of the spray drying is 80 ℃; and (3) putting the precursor into a pyrolysis furnace with the temperature of 750 ℃ for pyrolysis for 3h under the protection of argon, and cooling to room temperature to obtain the silicon monoxide composite negative electrode material.
Example 8
Adding 10% of Si-B alloy powder into the silicon monoxide, wherein the content of B in the Si-B alloy is 0.5%, and uniformly mixing; adding the mixture into an ethanol solvent, wherein the weight ratio of the mixture to the ethanol is 1:5, adding the mixture into a sand mill, and performing ball milling on the mixture by the sand mill to obtain a silicon monoxide mixed slurry; adding 1.0% of graphene and 10% of SBR into the mixed slurry, and uniformly stirring; spray drying the mixed slurry to obtain a composite anode material precursor, wherein the inlet temperature of the spray drying is 200 ℃, and the outlet temperature of the spray drying is 100 ℃; and (3) putting the precursor into a pyrolysis furnace with the temperature of 800 ℃ for pyrolysis for 2h under the protection of argon, and cooling to room temperature to obtain the silicon monoxide composite negative electrode material.
Example 9
Adding 5% of Si-B alloy powder into the silicon monoxide, wherein the content of B in the Si-B alloy is 0.3%, and uniformly mixing; adding the mixture into deionized water, wherein the weight ratio of the mixture to the deionized water is 1:5, adding the mixture into a sand mill, and performing ball milling on the mixture by the sand mill to obtain a silicon monoxide mixed slurry; adding 2.0% of carbon nano tube and 10% of PVA into the mixed slurry, and uniformly stirring; spray drying the mixed slurry to obtain a composite anode material precursor, wherein the inlet temperature of the spray drying is 240 ℃, and the outlet temperature of the spray drying is 120 ℃; and (3) putting the precursor into a pyrolysis furnace with the temperature of 850 ℃ for pyrolysis for 2h under the protection of argon, and cooling to room temperature to obtain the silicon monoxide composite negative electrode material.
Comparative example 1
Adding silicon monoxide and 5% of Si powder into the silicon monoxide, and uniformly mixing; adding the mixture into isopropanol solvent, wherein the weight ratio of the mixture to the isopropanol is 1:4, adding the mixture into a sand mill, and performing ball milling on the mixture by the sand mill to obtain silicon monoxide mixed slurry; adding 1.5% of carbon nano tube and 20% of SBR into the mixed slurry, and uniformly stirring; spray drying the mixed slurry to obtain a composite anode material precursor, wherein the inlet temperature of the spray drying is 200 ℃, and the outlet temperature of the spray drying is 90 ℃; and (3) putting the precursor into a pyrolysis furnace with the temperature of 850 ℃ for pyrolysis for 2h under the protection of argon, and cooling to room temperature to obtain the silicon monoxide composite negative electrode material.
And (3) testing the electrochemical performance of the silicon oxide composite negative electrode material:
uniformly mixing the prepared silicon monoxide composite negative electrode material, acetylene black, CMC (carboxymethyl cellulose) and SBR according to the mass ratio of 8:1:0.5:0.5, adding a proper amount of deionized water, uniformly stirring to prepare slurry, coating the obtained viscous slurry on a circular copper foil with the diameter of 10mm to prepare a pole piece, and then drying the pole piece in a vacuum drying oven at 80 ℃ for 12 hours to remove water. In a glove box filled with argon, a metal lithium sheet is used as a counter electrode, a Celgard2500 polypropylene porous membrane is used as a diaphragm, and 1mol/L LiPF6/EC-EMC-DMC (volume ratio of 1:1:1) solution is used as electrolyte to assemble the CR2032 button half cell. The battery is subjected to constant current charge and discharge performance test on a battery test system (LAND CTR 2001A). The voltage range is 0.01-1.5V, the specific capacity of the negative electrode material is tested by 100mA/g charging and discharging, and the cycle performance of the negative electrode material is tested by 1000mA/g charging and discharging. Electrochemical performance of the tested anode materials is shown in table 1:
TABLE 1
As can be seen from table 1, examples 1 to 9 each added Si — B alloy powder in different amounts, whereas comparative example 1 added no Si — B alloy powder, and the other conditions were the same as in example 4. The specific capacity of the examples 1 to 9 is larger than that of the comparative example 1, the first charge-discharge efficiency of the examples 1 to 9 is higher than that of the comparative example 1, the 100-time cycle capacity retention rate of the examples 1 to 9 is larger than that of the comparative example 1, and the electrochemical comprehensive performance of the negative electrode material of the example 4 is the best. From the above, the first coulombic efficiency of the silicon monoxide composite negative electrode material is high, the specific capacity is large, and the electrical performance of the negative electrode material can be improved.
As shown in fig. 2 and 3, wherein fig. 2 is an overall SEM image of the composite anode material, and fig. 3 is a partially enlarged SEM image of the composite anode material, as can be seen from fig. 2 and 3, the composite anode material prepared in example 4 is spherical, and the conductive network formed by the carbon nanotube material uniformly distributed in the spherical particles is formed inside the spherical particles, which illustrates that the Si-B alloy, the silicon monoxide and the conductive carbon layer form the conductive network inside the silicon monoxide composite anode material, so that the problem of low intrinsic conductivity of the silicon monoxide is solved, and the electrochemical performance of the silicon monoxide composite anode material is further improved.
Fig. 4 is an X-ray diffraction (XRD) pattern of the negative composite material of the silicon oxide of example 4, wherein a sample of the negative composite material of the silicon oxide has a sharp peak with Si crystal face characteristic in the range of 20 ° to 30 ° 2 θ, and Si crystals are precipitated on the surface of the composite material after high temperature treatment. Fig. 5 is a raman spectrum of the silicon oxide composite negative electrode material, and as can be seen from fig. 4, diffraction peaks respectively representing disordered carbon and graphitized carbon appear at 1345cm-1 and 1584cm-1 of the silicon oxide composite negative electrode material, which indicates that the silicon oxide, the Si-B alloy and the conductive carbon layer form a conductive network in the silicon oxide composite negative electrode material, so that the problem of low intrinsic conductivity of the silicon oxide is solved, and the electrochemical performance of the silicon oxide composite negative electrode material is improved. In addition, the carbon coating layer is uniformly coated on the surface of the silicon oxide composite negative electrode material, so that the conductivity of the silicon oxide composite negative electrode material can be improved, and the cycle performance of the silicon oxide composite negative electrode material is improved.
Compared with the prior art, the invention has at least the following advantages:
1. the silicon oxide composite negative electrode material contains Si-B alloy, and not only can effectively buffer stress generated during lithium intercalation through B, but also can improve the conductivity of Si, so that the specific capacity of the silicon oxide negative electrode material is improved, and the first discharge efficiency of the silicon oxide negative electrode material is improved. In addition, B can improve the dispersibility of Si and prevent the Si from agglomerating.
2. The silicon oxide composite negative electrode material is composed of silicon oxide and Si-B alloy, and is also added with a conductive carbon layer, and the silicon oxide, the Si-B alloy and the conductive carbon layer form a conductive network in the silicon oxide composite negative electrode material, so that the problem of low intrinsic conductivity of the silicon oxide is solved, and the electrochemical performance of the silicon oxide composite negative electrode material is improved.
3. The silicon oxide composite negative electrode material also comprises a carbon coating layer, and the carbon coating layer is uniformly coated on the surface of the silicon oxide composite negative electrode material, so that the conductivity of the silicon oxide composite negative electrode material can be improved, and the cycle performance of the silicon oxide composite negative electrode material is improved; further, the carbon coating layer can prevent the sub-outer layer of the silicon oxide/Si-B alloy composite layer from being affected by external environment, such as moisture and oxygen; furthermore, the carbon coating layer can also prevent a silicon monoxide core in the battery from directly contacting with the electrolyte, so that the consumption of the electrolyte and effective Li in the battery is effectively reduced, the electrolyte injection amount required by the production of the lithium ion battery and the generation of gas during the working of a lithium battery product can be reduced, and the stability of the SEI film is improved.
The above examples only show some embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
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