CN116314833B

CN116314833B - Silicon-metal oxide composite material, method for producing same, secondary battery, and electricity-using device

Info

Publication number: CN116314833B
Application number: CN202310593937.3A
Authority: CN
Inventors: 梁静爽; 滕国鹏
Original assignee: Jiangsu Contemporary Amperex Technology Ltd
Current assignee: Jiangsu Contemporary Amperex Technology Ltd
Priority date: 2023-05-25
Filing date: 2023-05-25
Publication date: 2023-10-20
Anticipated expiration: 2043-05-25
Also published as: CN116314833A

Abstract

The application provides a silicon-metal oxide composite material, a method for producing the same, a secondary battery and an electric device. Wherein the silicon-metal oxide composite material has a core-shell structure, and the preparation method thereof comprises the following steps: uniformly mixing silicon particles and metal oxide particles and pressing the mixture into a block; and taking the block as an anode target material, and carrying out direct current arc discharge plasma treatment under the atmosphere of hydrogen and inert gas to obtain the silicon-metal oxide composite material, wherein the melting point of the metal oxide is lower than that of silicon. The method has simple steps, stable process and easily controlled product morphology, so that the composite material with uniform particle diameter and uniform particle diameter, wherein the surface of the silicon nanoparticle is uniformly and completely coated with the metal oxide layer, can be obtained.

Description

Silicon-metal oxide composite material, method for producing same, secondary battery, and electricity-using device

Technical Field

The application relates to the technical field of lithium batteries, in particular to a silicon-based negative electrode material and a preparation method thereof, a secondary battery, a battery module, a battery pack and an electric device.

Background

In recent years, along with the wider application range of lithium ion batteries, the lithium ion batteries are widely applied to energy storage power supply systems such as hydraulic power, firepower, wind power, solar power stations and the like, and a plurality of fields such as electric tools, electric bicycles, electric motorcycles, electric automobiles, military equipment, aerospace and the like. As lithium ion batteries have been greatly developed, higher demands are also being made on energy density, cycle performance, safety performance, and the like. Graphite is used as a traditional negative electrode material of a lithium ion battery, the theoretical specific capacity is only 372 mAh/g, the market demand is difficult to meet, and the development of the lithium ion battery with high energy density is severely limited. In recent years, silicon has a moderate lithium intercalation potential (0.4V vs. Li/Li ⁺ ) And a higher theoretical specific capacity (3579 mAh/g), glume-off in novel negative electrode material candidatesAnd (5) outputting.

However, the volume expansion of the silicon-based material as the negative electrode active material is up to 300% in the process of battery charge-discharge cycle, and a stable SEI film is difficult to form on the surface of the active material, which is two technical barriers of the silicon-based material in the industrialization process. In this regard, extensive studies and attempts have been made to overcome the above drawbacks by generally compounding silicon with a carbon material, a metal, an oxide, or the like. However, the silicon-based anode active material performance has yet to be further improved.

Disclosure of Invention

The present application has been made in view of the above problems, and an object of the present application is to provide a method for producing a silicon-metal oxide composite material having a core-shell structure as a negative electrode active material for a lithium ion battery. The method has simple steps, is easy to control the morphology of the silicon-metal oxide composite material, and can form a uniform and complete coating layer on the surface of the silicon particles, so that the silicon-metal oxide composite material with ideal core-shell structure morphology is prepared, the defect of the electrical property of the silicon particles is overcome, and the cycle characteristic of the cathode material is improved. The application also provides the silicon-metal oxide composite material, a negative electrode plate taking the material as a negative electrode active material, a secondary battery comprising the negative electrode plate and an electric device.

In order to achieve the above object, the present application provides a method of preparing a silicon-metal oxide composite material, a silicon-metal oxide composite material prepared by the method, a negative electrode tab including the silicon-metal oxide composite material as a negative electrode active material, a secondary battery including the negative electrode tab, and an electric device.

A first aspect of the present application provides a method of producing a silicon-metal oxide composite material, wherein the silicon-metal oxide composite material has a core-shell structure, the method comprising the steps of: uniformly mixing silicon particles and metal oxide particles and pressing the mixture into a block; and taking the block as an anode target material, and carrying out direct current arc discharge plasma treatment on the block in the atmosphere of hydrogen and inert gas to obtain the silicon-metal oxide composite material, wherein the melting point of the metal oxide is lower than that of silicon.

The application can conveniently prepare the silicon-metal oxide composite material which takes the silicon nano particles as the core outer layer to uniformly coat the metal oxide layer and has a core-shell structure through direct current arc discharge plasma treatment. The arc flame between the cathode and anode in a dc arc discharge plasma process can generate high temperatures up to thousands of degrees celsius with a gradual decrease in temperature from the flame core outward. At such high temperatures, the silicon particles and metal oxide particles evaporate into gaseous silicon atoms and metal oxide molecules and begin to spontaneously nucleate when the temperature is low to the melting point. The melting point of silicon is higher than that of metal oxide, so that gaseous silicon is first nucleated and grows into nano particles, and when the temperature is low to the melting point of metal oxide, gaseous metal oxide starts to heterogeneously nucleate on the surface of silicon nano particles, and finally a uniform and complete coating layer is formed on the surface of silicon nano particles. The metal oxide can contribute to capacity, and the interface stability of tin-lithium alloy formed in circulation is good, so that stable SEI film can be formed, and the thickness of the SEI film is reduced. In addition, lithium oxide formed by the reaction of lithium and metal oxide during the first cycle can serve as a buffer matrix to buffer the volume change of silicon. By the method, a uniform and complete metal oxide layer can be formed on the surface of the silicon, so that the performance defect of the silicon-based material can be overcome better, and the specific capacity, the cycle performance and the multiplying power performance of the battery are improved. The method has simple steps, stable process and easily controlled product morphology, thus being capable of obtaining products with uniform particle size.

In any embodiment, the mass ratio of the silicon particles to the metal oxide particles is 5:5 to 8:2, preferably 6:4 to 7:3. In the method, the thickness of the metal oxide layer can be easily controlled by controlling the raw material ratio of the silicon particles and the metal oxide particles, thereby conveniently obtaining the composite material with the required coating thickness.

In any embodiment, the partial pressure of hydrogen is 1X 10 ⁴ Pa-1.5×10 ⁴ Pa, and the partial pressure of the inert gas is 2×10 ⁴ Pa-2.5×10 ⁴ Pa. In the DC arc discharge plasma treatment, hydrogen gas is ionized into hydrogen plasma in which hydrogen is containedAtoms or hydrogen ions easily enter the melted target material, promoting the evaporation of the target material. The plasma formed after the inert gas is ionized has high conductivity, collides with the substance in the process of nucleation and growth of the substance, reduces the surface energy and promotes nucleation. When the gas pressures of the hydrogen gas and the inert gas are within the above ranges, the target can be promoted to evaporate, and particles having a suitable particle diameter can be formed.

According to a preferred embodiment, the ratio of the hydrogen to the inert gas is between 10:7.5 and 10:4. Within this ratio range, particles having a particle size in the range of 50-90nm, in particular 65-75nm, can be obtained.

In any embodiment, the inert gas is at least one selected from argon and helium.

In any embodiment, in the direct current arc discharge plasma treatment, the distance between the anode and the cathode is 10-25mm, the current is 10-200A, and the voltage is 5-30V. Preferably, the distance between the anode and the cathode is 10-20mm, the current is 50-150A, and the voltage is 15-25V.

In any embodiment, the method further comprises: after the dc arc discharge plasma treatment, a passivation treatment is performed to obtain the silicon-metal oxide composite material.

According to one embodiment, the passivation treatment is carried out in air for 6-10 hours.

In any embodiment, in the dc arc discharge plasma treatment, the cathode is a tungsten rod or a carbon rod.

In any embodiment, the metal oxide is tin dioxide or molybdenum oxide.

The second aspect of the present application also provides a silicon-metal oxide composite material, wherein the silicon-metal oxide composite material is a particle having a core-shell structure, the core-shell structure is that a metal oxide layer is uniformly and completely coated on the surface of silicon nanoparticles, and at least 50% of the particles have a particle diameter of 50-90nm, wherein the melting point of the metal oxide is lower than that of silicon.

The metal oxide layer in the silicon-metal oxide composite material with the structure can stably exist in the charge and discharge cycle of the secondary battery due to uniform and complete coating, so that the expansion of the silicon nano particles is effectively inhibited. In the first charge-discharge cycle, lithium oxide generated by the reaction of lithium and metal oxide has stable property, and can further buffer the expansion of silicon. In addition, the metal-lithium alloy formed in the electrode reaction has good stability, and is favorable for forming a stable and thinner SEI film. In addition, the metal oxide can also contribute to capacity due to its reactivity to intercalate and deintercalate lithium. Therefore, the silicon-metal oxide composite material can enable the battery to have excellent cycle characteristics, specific capacity and rate capability.

In any embodiment, the metal oxide layer has a thickness of 3-6nm, preferably 4-5nm. The metal oxide layer with the thickness in the range has better stability on one hand, is beneficial to improving the cycle performance of the composite material, and has the thickness as thin as possible so as to reduce the amount of metal oxide in the composite material as much as possible, fully exert the high specific capacity characteristic of silicon and improve the specific capacity of the cathode material.

In a preferred embodiment, the thickness of the metal oxide layer at different locations on the surface of each of the silicon nanoparticles differs by no more than 1nm. The thickness of the metal oxide layer is uniform, so that the metal oxide layer is more stable and is beneficial to improving the cycle performance of the composite material.

In any embodiment, the metal oxide is tin dioxide or molybdenum oxide. These metal oxides are each capable of reacting with lithium to donate capacity from intercalation-deintercalation of lithium ions. The metal oxides form a coating layer, so that stable alloy can be formed with lithium in electrode reaction, and stable and thinner SEI film can be formed.

In any embodiment, the silicon-metal oxide composite material is prepared by the method of the first aspect of the application.

A third aspect of the present application provides an anode material having an anode current collector and an anode film layer on at least one surface of the anode current collector, wherein the anode film layer comprises the silicon-metal oxide composite material according to the second aspect of the present application as an anode active material.

A fourth aspect of the application provides a secondary battery comprising the anode material according to the third aspect of the application.

A fifth aspect of the application provides an electric device comprising the secondary battery of the fourth aspect of the application.

According to the application, the silicon-metal oxide composite material with the core-shell structure is prepared by a direct current arc discharge plasma process, so that metal oxide is uniformly and completely coated on the surface of silicon nano particles, the obtained silicon-metal oxide composite material with a more stable coating layer can effectively inhibit the expansion of the silicon nano particles in the charge-discharge cycle of a secondary battery, and the favorable electrochemical properties of silicon and metal oxide are exerted to avoid the defect that silicon is used as a negative electrode active material, thereby improving the cycle characteristic, specific capacity and multiplying power performance of the battery, and further improving the performance of the lithium ion battery.

Drawings

Fig. 1 is a transmission electron microscope image of the silicon-tin dioxide composite material prepared in example 1.

Fig. 2 is a comparative diagram of transmission electron microscopy images of the silicon-tin dioxide composites prepared in examples 1, 10, 11 and 12.

Fig. 3 is a graph showing a change in specific capacity of an electrode using the silicon-tin dioxide composite material prepared in example 1 as a negative electrode material, which was cycled 100 times at 100 mA/g.

Fig. 4 is a graph showing change in coulombic efficiency of an electrode using the silicon-tin dioxide composite material prepared in example 1 as a negative electrode material, which was cycled 100 times at 100 mA/g.

Fig. 5 is a cycle performance chart of an electrode using the silicon-tin dioxide composite material prepared in example 12 as a negative electrode material, which was cycled 100 times at 100 mA/g.

Fig. 6 is a schematic view of a secondary battery according to an embodiment of the present application.

Fig. 7 is an exploded view of the secondary battery according to an embodiment of the present application shown in fig. 6.

Fig. 8 is a schematic view of a battery module according to an embodiment of the present application.

Fig. 9 is a schematic view of a battery pack according to an embodiment of the present application.

Fig. 10 is an exploded view of the battery pack of the embodiment of the present application shown in fig. 9.

Fig. 11 is a schematic view of an electric device in which a secondary battery according to an embodiment of the present application is used as a power source.

Reference numerals illustrate:

1, a battery pack; 2, upper box body; 3, lower box body; 4, a battery module; 5 a secondary battery; 51 a housing; 52 electrode assembly; 53 top cap assembly.

Detailed Description

Hereinafter, embodiments of a method for producing a silicon-metal oxide composite material, a secondary battery, and an electric device according to the present application are specifically disclosed with reference to the accompanying drawings as appropriate. However, unnecessary detailed description may be omitted. For example, detailed descriptions of well-known matters and repeated descriptions of the actual same structure may be omitted. This is to avoid that the following description becomes unnecessarily lengthy, facilitating the understanding of those skilled in the art. Furthermore, the drawings and the following description are provided for a full understanding of the present application by those skilled in the art, and are not intended to limit the subject matter recited in the claims.

The "range" disclosed herein is defined in terms of lower and upper limits, with the given range being defined by the selection of a lower and an upper limit, the selected lower and upper limits defining the boundaries of the particular range. Ranges that are defined in this way can be inclusive or exclusive of the endpoints, and any combination can be made, i.e., any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a particular parameter, it is understood that ranges of 60-110 and 80-120 are also contemplated. Furthermore, if the minimum range values 1 and 2 are listed, and if the maximum range values 3,4 and 5 are listed, the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise indicated, the numerical range "a-b" represents a shorthand representation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been listed throughout, and "0-5" is simply a shorthand representation of a combination of these values. When a certain parameter is expressed as an integer of 2 or more, it is disclosed that the parameter is, for example, an integer of 2, 3,4, 5, 6, 7, 8, 9, 10, 11, 12 or the like.

All embodiments of the application and alternative embodiments may be combined with each other to form new solutions, unless otherwise specified.

All technical features and optional technical features of the application may be combined with each other to form new technical solutions, unless specified otherwise.

All the steps of the present application may be performed sequentially or randomly, preferably sequentially, unless otherwise specified. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, or may comprise steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order, for example, the method may include steps (a), (b) and (c), may include steps (a), (c) and (b), may include steps (c), (a) and (b), and the like.

The terms "comprising" and "including" as used herein mean open ended or closed ended, unless otherwise noted. For example, the terms "comprising" and "comprises" may mean that other components not listed may be included or included, or that only listed components may be included or included.

The term "or" is inclusive in this application, unless otherwise specified. For example, the phrase "a or B" means "a, B, or both a and B. More specifically, either of the following conditions satisfies the condition "a or B": a is true (or present) and B is false (or absent); a is false (or absent) and B is true (or present); or both A and B are true (or present).

In the present application, the term "secondary battery" is any one form of a battery cell, a battery module, or a battery pack, unless otherwise specified.

As previously describedSilicon-based materials are suitable for their moderate lithium intercalation potential (0.4V vs. Li/Li ⁺ ) And a theoretical specific capacity (3579 mAh/g) of approximately 10 times that of the graphite material, as a potential candidate material for replacing the graphite-based anode active material. However, the volume expansion of the silicon-based material in charge and discharge cycles is as high as 300%, and a stable SEI film is difficult to form on the surface of an active substance, so that the application of the silicon-based material as a negative electrode material in a lithium ion battery is seriously hindered.

In order to solve the above-mentioned drawbacks of the silicon-based materials, it has been proposed to coat the surface of silicon particles with metal/metal oxide to suppress the volume expansion of silicon and promote the formation of a stable SEI film. Many metal oxides can intercalate and deintercalate lithium ions to contribute to capacity. And the metal oxide is not easy to form lithium dendrite in the electrode reaction, and the formed interface between the metal oxide and the metal-lithium alloy forming lithium has better stability, thereby being beneficial to forming a stable SEI film and reducing the thickness of the SEI film. In addition, the metal oxide reacts with lithium during the first cycle to form lithium oxide. Although the formation of lithium oxide will produce a partially irreversible capacity, it is stable in nature and can act as a buffer matrix, buffering the volume change of silicon. Therefore, a composite material of a silicon-metal oxide core-shell structure has also been proposed, which is expected to overcome the above-mentioned drawbacks of silicon-based materials, and is one of ideal candidate anode active materials in order to further improve the performance of the anode active materials.

However, heretofore, the silicon-metal oxide composite preparation method has complicated operation, difficult process control, and failure to form an ideal core-shell structure. For example, in chinese patent application CN114843479a, a silicon-tin dioxide composite material having a particle size of 1-2 μm is prepared by a high temperature calcination method. In the method, nano silicon particles and anhydrous stannous chloride serving as a stannic oxide source are mixed and then are melted at a high temperature in an inert atmosphere, and then the melted materials are calcined. From the electron micrograph provided in this document, it can be seen that, despite the use of nano-silicon particles as a starting material, the final calcined product is a multiparticulate aggregated secondary particle. And the coating thickness of the tin dioxide on the surface of the silicon particles is not uniform, even tin dioxide particles which can not form a core-shell structure are not few, so that the tin dioxide occupies more volume and the specific capacity is reduced. The method has difficulty in controlling the formation of a uniform coating layer of tin dioxide on the surface of silicon particles.

Furthermore, a material of silicon-tin dioxide chain and dendritic core-shell structure is provided in chinese patent application CN112599755 a. The material is prepared by reacting in ethanol water solution of tin tetrachloride dispersed with nano silicon powder at a certain temperature to adhere tin dioxide on the silicon surface. On one hand, the method has long reaction time and complex post-treatment; on the other hand, as can be seen from the electron micrograph, the surface of the silicon particles does not form a complete tin dioxide coating layer, but tin dioxide crystal fine particles are randomly attached. The tin dioxide particles thus adhered are difficult to stably exist in repeated charge and discharge cycles. In addition, the method is prepared by reaction in a solution, so that a material dispersed by primary particles cannot be obtained, but the particles are combined into a chain-shaped or dendritic structure through tin dioxide, and the method is unfavorable for obtaining the anode active material with high bulk density.

In view of this, the present inventors have proposed a method of preparing a silicon-metal oxide composite material, wherein the silicon-metal oxide composite material has a core-shell structure, the method comprising the steps of: uniformly mixing silicon particles and metal oxide particles and pressing the mixture into a block; and the block is used as an anode target material to be treated by direct current arc discharge plasma in the atmosphere of hydrogen and inert gas to obtain the silicon-metal oxide composite material, wherein the melting point of the metal oxide is lower than that of silicon.

The dc arc discharge plasma treatment generates an arc flame reaching a high temperature of thousands of degrees celsius through a dc arc discharge reaction between a cathode and an anode, and serves as a heat source for supplying a high-energy-state growth substance. The arc flame is taken as the center of the heat source, and the heat source has a certain temperature gradient from inside to outside and gradually decreases. In the above-described treatment method, silicon particles and metal oxide particles are uniformly mixed and pressed into a block as an anode target. First, the hydrogen and inert gas are ionized into a plasma in the arc region after the arcing. Hydrogen atoms or hydrogen ions in the hydrogen plasma easily enter the melted target to promote the evaporation of the target. The silicon particles in the target are evaporated to gaseous silicon atoms and the metal oxide particles are evaporated to gaseous metal oxide molecules. When the temperature of the gaseous silicon is lower than the melting point of silicon in a heat source region, the gaseous silicon starts to nucleate and spontaneously grows into silicon nano particles by utilizing the nucleation temperature difference of the silicon and the metal oxide; in the region of the heat source temperature which is lower than the melting point of the metal oxide, the gaseous metal oxide starts to perform heterogeneous nucleation on the surface of the silicon nano particle, so that a metal oxide coating layer is grown. In the nucleation process, the inert gas is ionized and has high conductivity, and the inert gas is mainly collided with the substance in the process of nucleation and growth of the substance, so that the surface energy is reduced. Since the heterogeneous nucleation has lower energy than the self-alone nucleation, the metal oxide preferentially heterogeneous nucleation. Thus, the metal oxide alone does not form particles in the process, but rather coats the surface of the silicon nanoparticles.

The application relates to a direct current arc discharge plasma treatment method, which belongs to a thermal plasma method. In addition to forming thermal plasma by arc discharge, both rf inductive coupling and spark discharge methods can produce thermal plasma. However, the rf inductive coupling method requires an additional rf or uhf coupling device to generate a locally thermally balanced plasma, which promotes instantaneous evaporation of the material and solidification during cooling. The process has poor stability, and a product with good uniformity cannot be obtained. While the spark discharge method is similar to the sintering process in the calcination method mentioned above, it is difficult to ensure the formation of a desired core-shell structure.

The arc flame generated by the direct current arc discharge is stable, the temperature is reduced from the center to the outside in a gradient manner, and the composite material with a core-shell structure and good particle size uniformity can be stably formed by utilizing the melting point temperature difference of silicon and metal oxide. In addition, since the metal oxide is nucleated on the surface of the silicon particles as gaseous molecules, a uniform and complete coating layer can be formed.

The present disclosure is not particularly limited as to the difference in melting point of the metal oxide that can form the clad layer below the melting point of silicon. The melting point of silicon is 1414 ℃, and the melting point of the metal oxide may be 1400 ℃ or lower, 1300 ℃ or lower, 1200 ℃ or lower, 1100 ℃ or lower, but is not limited thereto. On the other hand, the melting point of the metal oxide may be 600 ℃ or higher, 700 ℃ or higher, 800 ℃ or higher, or the like, but is not limited thereto.

In the method, the mass ratio of the silicon particles to the metal oxide particles is 5:5 to 8:2. In this method, the thickness of the metal oxide coating layer can be conveniently controlled by controlling the mass ratio of the silicon particles and the metal oxide particles. When the silicon particles are more, the metal oxide particles are less, the metal oxide layer is thinner, otherwise, the metal oxide layer is thicker. When the mass ratio of the two is in the above range, the thickness of the metal oxide layer can be controlled in the range of about 3nm to about 6 nm.

In this method, silicon is first nucleated into silicon nanoparticles. Thus, controlling the thickness of the metal oxide layer is critical to obtaining a negative electrode active material having desirable properties. The inventors found that the silicon-metal oxide core-shell structure prepared by using the direct current arc discharge plasma has a wide process window, and the thickness of the metal oxide layer can be easily controlled by adjusting the mass ratio of the silicon particles to the metal oxide particles.

According to a preferred embodiment, the mass ratio of silicon particles to metal oxide particles is 6:4 to 7:3, more preferably the mass ratio of silicon particles to metal oxide particles is 7:3.

Further experiments have found that with substantially the same particle size of the silicon nanoparticles, a good cycle volume retention and coulombic efficiency can be obtained with a metal oxide layer thickness in the range of about 3nm to about 6 nm. When the thickness of the metal oxide layer is less than 3nm, it is difficult to stably coat the silicon nanoparticles in circulation, resulting in a significant reduction in circulation capacity retention. And when the thickness of the metal oxide layer is thicker and reaches more than 6nm, the metal oxide ratio is too high, so that the overall capacity of the composite material is reduced.

According to a preferred embodiment, the silicon-metal oxide composite material achieves optimal performance at a thickness of the metal oxide layer of about 4nm to about 5nm, in particular about 4 nm.

In addition, as described above, since the metal oxide is a gaseous molecule when it is nucleated, it is possible to uniformly coat the surface of the silicon nanoparticle. In this way, the expansion of the silicon particles can be more uniformly suppressed during the charge-discharge cycle of the battery, thereby making the stability of the metal oxide layer better, contributing to the improvement of the cycle characteristics of the composite material. According to a preferred embodiment, the thickness of the metal oxide layer at different locations on the surface of each silicon nanoparticle differs by no more than 1nm.

In addition, the process is carried out in a plasma atmosphere generated from hydrogen and an inert gas. Specifically, the arc reaction chamber is first evacuated and then filled with hydrogen and inert gas.

According to one embodiment, the partial pressure of hydrogen is 1X 10 ⁴ Pa-1.5×10 ⁴ Pa, and a partial pressure of an inert gas of 2X 10 ⁴ Pa-2.5×10 ⁴ Pa. According to a preferred embodiment, the partial pressure of hydrogen is 1X 10 ⁴ Pa, and a partial pressure of an inert gas of 2X 10 ⁴ Pa。

As previously described, hydrogen plasma can promote evaporation of the target, while plasma of inert gas can collide with the substance to reduce surface energy, promoting nucleation of the substance, thereby forming uniform and suitable particle size nanoparticles. Within the above range, the particle size of at least 50% of the particles of the composite material may be controlled to be in the range of 50-90 nm.

According to one embodiment, the hydrogen and inert gas are at a pressure ratio of 10:7.5 to 10:4. The particle size of the composite particles can be controlled by controlling the ratio of hydrogen to inert gas. Within the above ratio ranges, the particle size of the composite particles may be controlled within a range of about 65 to about 75 nm. In the particle size range, better cycle characteristics, high-current charge-discharge characteristics and other electrical properties can be obtained. Illustratively, the pressure ratio of hydrogen to inert gas may be 10:7.5, 10:7, 10:6.5, 10:6, 10:5.5, 10:5, 10:4.5, 10:4, etc. Taking the ratio of hydrogen to inert gas of 2:1 as an example, the particle diameter D90 of the composite particles can be controlled to be about 70nm in a preferred embodiment, and the uniformity of the particle diameter is good.

The inert gas may be selected from argon, helium, etc., with argon being more preferred.

The composite material prepared by the above method may be dispersed in the form of primary particles (see transmission electron micrograph shown in fig. 1). When the particle diameter of the composite material is in the above range, the effect of more lithium intercalation sites and faster diffusion of lithium ions inside the composite material can be obtained.

In the direct current arc discharge process, a block pressed by silicon particles and metal oxide particles is placed on a copper frame as an anode target. The cathode may use a tungsten rod or a carbon rod.

Since the silicon particles and the metal oxide particles used as raw materials will be evaporated to a gaseous state and then re-nucleated in the arc flame, there is no particular limitation on the particle diameters of both in the method as long as both are easily uniformly mixed and can be pressed to form a block. The particle size of both may be in the order of micrometers, for example 1-500 μm, for example. Preferably 100-200 μm.

According to one embodiment, in the method, the anode and cathode are spaced apart by 10-25mm, the current is 10-200A, and the voltage is 5-30V. The inventors have found that the process window for preparing silicon-metal oxide composites by dc arc discharge is relatively wide. Within the above range, the variation of the process conditions has no obvious effect on the morphology and uniformity of the final product, and only has an effect on the unit yield. When the distance between the cathode and the anode is too large, arc breakage is easy; when the interval between the cathode and the anode is too small, the cathode and the anode are easily adhered. When the current or voltage is too large, the arc energy is high, more heat is generated, and potential safety hazards are easily caused; when the current or voltage is too small, the production efficiency is low.

According to a preferred embodiment, the anode-to-cathode spacing is 10-20mm, the current is 50-150A, and the voltage is 15-25V. According to one embodiment, the anode to cathode spacing is 15mm, the current is 90A, and the voltage is 20V.

The preparation method is not particularly limited in terms of the arcing time, and may be adjusted according to the specific equipment used and specific needs. For example, the larger the plant production capacity, the longer the arcing time; the larger the amount of target, the longer the arcing time. Illustratively, the arcing time may be selected in the range of 20 minutes to 3 hours, but is not limited thereto.

Further, the method for preparing the silicon-metal oxide composite material further comprises the step of performing passivation treatment after performing the direct current arc discharge plasma treatment, thereby obtaining the silicon-metal oxide composite material. The passivation treatment is to discharge the hydrogen and the inert gas out of the reaction cavity, and then to introduce a small amount of air for a certain time. The passivation treatment can reduce the surface energy of the nano composite material, so that the material is not easy to agglomerate and is more stable.

According to one embodiment, the passivation treatment is performed in air for between 6 and 10 hours. The passivation process is generally performed at room temperature, but is not limited thereto.

The method may use any suitable direct current arc device, as the application is not particularly limited.

According to the method, the melting point of the metal oxide used to form the silicon-metal oxide composite is lower than the melting point of silicon (1414 ℃). Preferably, the metal oxide is tin dioxide (melting point about 1100 ℃) or molybdenum oxide (melting point about 800 ℃). The tin dioxide theory has higher specific capacity which can reach 782mAh/g and is more than twice that of graphite, and the tin dioxide theory is conductive, thereby being more favorable for improving the electrical property of the material and being more preferable.

The application also provides a silicon-metal oxide composite material, wherein the silicon-metal oxide composite material is particles with a core-shell structure, the core-shell structure is that a metal oxide layer is uniformly and completely coated on the surface of silicon nano particles, at least 50% of the particles have a particle size of 50-90nm, and the melting point of the metal oxide is lower than that of silicon.

According to the above description of the method for preparing the silicon-metal oxide composite material, in the silicon-metal oxide composite material, silicon nano particles are taken as cores, and metal oxides are uniformly and completely coated on the surfaces of the silicon nano particles to be taken as shells, so that a stable and uniform core-shell structure is formed. Because the metal oxide can reversibly intercalate-deintercalate lithium, especially tin dioxide has higher theoretical specific capacity, the tin-lithium alloy interface formed in charge-discharge cycle has better stability, is favorable for forming a stable SEI film, and reduces the thickness of the SEI film. And in the first cycle process, lithium oxide formed by the metal oxide layer and lithium can be used as a buffer matrix to buffer the volume change of silicon. Therefore, when the metal oxide in the silicon-metal oxide composite material uniformly and completely coats silicon, a coating layer can exist stably during charge and discharge cycles of the secondary battery, thereby effectively inhibiting the expansion of the silicon nanoparticles; on the other hand, the metal oxide coating layer forms a stable SEI film, and the SEI film thickness is reduced, so that the performance defect of the silicon-based material can be overcome, and the cycle characteristic of the anode active material is improved.

The composite material has a relatively uniform particle size, and at least 50%, at least 60%, at least 70%, at least 80%, and even at least 90% of the particles in the composite material particles have a particle size of 50-90nm, preferably 60-80nm, more preferably 65-75 nm. Illustratively, the D50 particle size of the composite material may be 50nm, 60nm, 65nm, 70nm, 75nm, 80nm, or 90nm. As described above, when the particle diameter of the composite material is within the above range, lithium intercalation sites are more, and lithium ions are more rapidly diffused inside the composite material, thereby obtaining better electrical characteristics.

Furthermore, the thickness of the metal oxide layer in the silicon-metal oxide composite is only about 3-6nm, preferably about 4nm to about 5nm, and most preferably about 4nm. When the metal oxide layer is within this thickness range, the above properties of the composite material are ensured, and at the same time, the metal oxide ratio in the composite material can be reduced as much as possible, and the excellent properties of silicon having a higher specific capacity can be fully exerted, so that the properties of the negative electrode active material can be further improved.

The silicon-metal oxide composite material may be prepared by the method of any of the above embodiments.

The negative electrode tab, the secondary battery, the battery module, the battery pack, and the electric device according to the present application are described below with reference to the drawings.

In one embodiment of the present application, a secondary battery is provided.

In general, a secondary battery includes a positive electrode tab, a negative electrode tab, an electrolyte, and a separator. During the charge and discharge of the battery, active ions are inserted and extracted back and forth between the positive electrode plate and the negative electrode plate. The electrolyte plays a role in ion conduction between the positive electrode plate and the negative electrode plate. The isolating film is arranged between the positive pole piece and the negative pole piece, and mainly plays a role in preventing the positive pole piece and the negative pole piece from being short-circuited, and meanwhile ions can pass through the isolating film.

[ negative electrode sheet ]

The negative electrode tab comprises a negative electrode current collector and a negative electrode film layer arranged on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises the silicon-metal oxide composite material serving as the negative electrode active material provided in the second aspect of the application.

As an example, the anode current collector has two surfaces opposing in its own thickness direction, and the anode film layer is provided on either one or both of the two surfaces opposing the anode current collector.

In some embodiments, the negative electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, copper foil may be used. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, the anode active material may partially employ an anode active material for a battery, which is well known in the art. As an example, the anode active material may include the silicon-metal oxide composite material proposed as the anode active material in the second aspect of the present application, and at least one of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, tin-based materials, lithium titanate, and the like. The tin-based material may be at least one selected from elemental tin, tin oxide, and tin alloys.

In some embodiments, the negative electrode film layer further optionally includes a binder. The binder may be at least one selected from Styrene Butadiene Rubber (SBR), polyacrylic acid (PAA), sodium Polyacrylate (PAAs), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium Alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

In some embodiments, the negative electrode film layer further optionally includes a conductive agent. The conductive agent is at least one selected from superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene and carbon nanofibers.

In some embodiments, the negative electrode film layer may optionally further include other adjuvants, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)), and the like.

In some embodiments, the negative electrode sheet may be prepared by: dispersing the above components for preparing the negative electrode sheet, such as a negative electrode active material, a conductive agent, a binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; and coating the negative electrode slurry on a negative electrode current collector, and obtaining a negative electrode plate after the procedures of drying, cold pressing and the like.

[ Positive electrode sheet ]

The positive pole piece comprises a positive current collector and a positive film layer arranged on at least one surface of the positive current collector, wherein the positive film layer is made of a positive active material.

As an example, the positive electrode current collector has two surfaces opposing in its own thickness direction, and the positive electrode film layer is provided on either one or both of the two surfaces opposing the positive electrode current collector.

In some embodiments, the positive current collector may employ a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymeric material base layer and a metal layer formed on at least one surface of the polymeric material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

In some embodiments, when the secondary battery is a lithium ion battery, the positive electrode active material may be a positive electrode active material for a lithium ion battery, which is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: lithium-containing phosphates of olivine structure, lithium transition metal oxides, sodium transition metal oxides, polyanionic compounds, prussian blue-based compounds and their respective modified compounds. However, the present application is not limited to these materials, and other conventional materials that can be used as a battery positive electrode active material may be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxide (e.g., liCoO) ₂ ) Lithium nickel oxide (e.g. LiNiO) ₂ ) Lithium manganese oxide (e.g. LiMnO ₂ 、LiMn ₂ O ₄ ) Lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., liNi) _1/3 Co _1/3 Mn _1/3 O ₂ (also referred to as NCM) ₃₃₃ ）、LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (also referred to as NCM) ₅₂₃ ）、LiNi _0.5 Co _0.25 Mn _0.25 O ₂ (also referred to as NCM) ₂₁₁ ）、LiNi _0.6 Co _0.2 Mn _0.2 O ₂ (also referred to as NCM) ₆₂₂ ）、LiNi _0.8 Co _0.1 Mn _0.1 O ₂ (also referred to as NCM) ₈₁₁ ) Lithium nickel cobalt aluminum oxide (e.g. LiNi _0.85 Co _0.15 Al _0.05 O ₂ ) And at least one of its modified compounds and the like. Examples of olivine structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (e.g., liFePO ₄ (also abbreviated as LFP)), composite material of lithium iron phosphate and carbon, and manganese lithium phosphate (such as LiMnPO) ₄ ) At least one of a composite material of lithium manganese phosphate and carbon, and a composite material of lithium manganese phosphate and carbon.

In some embodiments, the positive electrode film layer further optionally includes a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluoroacrylate resin.

In some embodiments, the positive electrode film layer further optionally includes a conductive agent. As an example, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

In some embodiments, the positive electrode sheet may be prepared by: dispersing the above components for preparing the positive electrode sheet, such as the positive electrode active material, the conductive agent, the binder and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; and (3) coating the positive electrode slurry on a positive electrode current collector, and obtaining a positive electrode plate after the procedures of drying, cold pressing and the like.

[ electrolyte ]

The electrolyte plays a role in ion conduction between the positive electrode plate and the negative electrode plate. The electrolyte is in a liquid state in the present application.

In some embodiments, the electrolyte is an electrolyte. The electrolyte includes an electrolyte salt and a solvent.

In some embodiments, the electrolyte salt may be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis-fluorosulfonyl imide, lithium bis-trifluoromethanesulfonyl imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalato borate, lithium difluorodioxaato phosphate, and lithium tetrafluorooxalato phosphate.

In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methylethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1, 4-butyrolactone, sulfolane, dimethyl sulfone, methyl sulfone, and diethyl sulfone.

In some embodiments, the electrolyte further optionally includes an additive. For example, the additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives capable of improving certain properties of the battery, such as additives that improve the overcharge performance of the battery, additives that improve the high or low temperature performance of the battery, and the like.

[ isolation Membrane ]

In some embodiments, a separator is further included in the secondary battery. The type of the separator is not particularly limited, and any known porous separator having good chemical stability and mechanical stability can be used.

In some embodiments, the material of the isolating film may be at least one selected from glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride. The separator may be a single-layer film or a multilayer composite film, and is not particularly limited. When the separator is a multilayer composite film, the materials of the respective layers may be the same or different, and are not particularly limited.

In some embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.

In some embodiments, the secondary battery may include an outer package. The outer package may be used to encapsulate the electrode assembly and electrolyte described above.

In some embodiments, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like. The exterior package of the secondary battery may also be a pouch type pouch, for example. The material of the flexible bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, and polybutylene succinate.

The shape of the secondary battery is not particularly limited in the present application, and may be cylindrical, square, or any other shape. For example, fig. 6 is a secondary battery 5 of a square structure as one example.

In some embodiments, referring to fig. 7, the exterior package of the secondary battery 5 shown therein may include a case 51 and a cap plate 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, where the bottom plate and the side plate enclose a receiving chamber. The housing 51 has an opening communicating with the accommodation chamber, and the cover plate 53 can be provided to cover the opening to close the accommodation chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. The electrode assembly 52 is enclosed in the accommodating chamber. The electrolyte is impregnated in the electrode assembly 52. The number of electrode assemblies 52 included in the secondary battery 5 may be one or more, and those skilled in the art may select according to specific practical requirements.

In some embodiments, the secondary batteries may be assembled into a battery module, and the number of secondary batteries included in the battery module may be one or more, and the specific number may be selected by one skilled in the art according to the application and capacity of the battery module.

Fig. 8 is a battery module 4 as an example. Referring to fig. 8, in the battery module 4, a plurality of secondary batteries 5 may be sequentially arranged in the longitudinal direction of the battery module 4. Of course, the arrangement may be performed in any other way. The plurality of secondary batteries 5 may be further fixed by fasteners.

Alternatively, the battery module 4 may further include a case having an accommodating space in which the plurality of secondary batteries 5 are accommodated.

In some embodiments, the above battery modules may be further assembled into a battery pack, and the number of battery modules included in the battery pack may be one or more, and a specific number may be selected by those skilled in the art according to the application and capacity of the battery pack.

Fig. 9 and 10 are battery packs 1 as an example. Referring to fig. 9 and 10, a battery case and a plurality of battery modules 4 disposed in the battery case may be included in the battery pack 9. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

In addition, the application also provides an electric device which comprises at least one of the secondary battery, the battery module or the battery pack. The secondary battery, the battery module, or the battery pack may be used as a power source of the power consumption device, and may also be used as an energy storage unit of the power consumption device. The power utilization device may include mobile devices (e.g., cell phones, notebook computers, etc.), electric vehicles (e.g., electric-only vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto.

As the electricity consumption device, a secondary battery, a battery module, or a battery pack may be selected according to the use requirements thereof.

Fig. 11 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle or the like. In order to meet the high power and high energy density requirements of the secondary battery by the power consumption device, a battery pack or a battery module may be employed.

As another example, the device may be a cell phone, tablet computer, notebook computer, or the like. The device is generally required to be light and thin, and a secondary battery can be used as a power source.

Examples

Hereinafter, embodiments of the present application are described. The following examples are illustrative only and are not to be construed as limiting the application. The examples are not to be construed as limiting the specific techniques or conditions described in the literature in this field or as per the specifications of the product. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.

Preparation of silicon-tin dioxide composite material

Example 1 preparation of silicon-tin dioxide composite materials

The silicon-tin dioxide composite material was prepared by direct current arc discharge using an NP450 type apparatus from shenyang north vacuum apparatus limited. The specific steps are as follows.

And uniformly mixing silicon powder (200 micrometers) and tin dioxide powder (200 micrometers) according to a mass ratio of 7:3, and pressing into a cylindrical block target material with a diameter of 3cm and a thickness of 1 cm. The tungsten rod is placed on a copper seat to serve as an anode of arc discharge, the tungsten rod is used as a cathode, and the distance between the two electrodes is adjusted to be 15mm. Evacuating the reaction chamber to about 10 ^-2 Pa, filling argon and hydrogen according to the ratio of 2:1 to ensure that the partial pressure of the argon is 2 multiplied by 10 ⁴ Pa, hydrogen partial pressure of 1X 10 ⁴ Pa. And (3) starting a cooling water system, switching on a power supply, starting an arc, adjusting the current to 90A, adjusting the voltage to 20V, stabilizing the arc, and evaporating the block target. The arcing time lasts for 0.5 hour, and after the reaction is finished, the power supply is turned off. And closing the cooling water system after the temperature is reduced to room temperature. After passivation in air for 8 hours, the powder was collected from the inner wall of the reaction chamber. The product was measured by a laser particle size analyzer (LS-909) to obtain a silicon-tin dioxide composite material with a D90 particle size of about 70 nm. The morphology was observed by a transmission electron microscope (Tecnai G2F 30S-TWIN), and the photographs were shown in FIG. 1 and FIG. 2 (b). As can be seen from the figure, the composite material has uniform particle size, obvious core-shell structure, uniform shell and thickness of about 4nm.

Examples 2-17 preparation of silicon-tin dioxide composite materials

The same equipment as in example 1 is adopted, the same raw materials are pressed into a block target material, and the silicon-tin dioxide composite material of each example is prepared under different process conditions or with different raw material mass ratios. The conditions of the changes are shown in Table 1 below. The contents not shown are the same as those of embodiment 1.

The particle size of the silicon-tin dioxide composite of each example was measured in the same manner as in example 1 and is shown in table 2 below.

The morphology transmission electron microscopes of the silicon-tin dioxide composite materials prepared in examples 10, 11 and 12 are shown in (c), (d) and (a) in fig. 2.

TABLE 1 Process conditions for examples 1-17

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Test case

Preparation of secondary battery

The button cell for electrical property test was prepared as follows.

(1) Preparation of negative electrode plate

The silicon-tin dioxide composite materials prepared in the above examples are respectively used as negative electrode active materials, mixed with super carbon black used as a conductive agent and sodium carboxymethyl cellulose used as a binder according to the mass ratio of 80:10:10 to form slurry, and coated on a current collector to prepare the negative electrode membrane. Vacuum drying at 80℃for 12 hours. Cutting the dried membrane into a wafer with the diameter of 14mm, and taking the wafer as a negative electrode plate.

(2) Assembly of secondary battery

LiPF to be used as electrolyte ₆ Dissolving in a mixed solvent with the volume ratio of EC/DMC of 1:1 to form electrolyte. And assembling the prepared negative electrode plate, a metal lithium plate serving as a positive electrode plate and electrolyte into the button type lithium ion battery.

Electrical property test of secondary battery

The cycle performance and the rate performance of each secondary electron were tested by using an electrochemical performance tester for the martial arts (Land 2001A).

The testing method comprises the following steps:

(1) Specific capacity and coulombic efficiency: and placing the assembled secondary battery for 12 hours, so that the electrolyte fully infiltrates the negative electrode plate. The secondary battery was then clamped to the crocodile clip of the tester. The test current and the quality of the active substances, the cycle number and the test voltage range are input, and the tester itself displays the specific charge capacity and specific discharge capacity of the battery. Wherein the number of cycles is 100, the test voltage is in the range of 0.01-2V, the current density is 100mA/g, the test current = current density =mass of active material, mass of active material = paste mass =80%, mass of paste = mass of wafer-mass of blank current collector. The 100 th specific charge capacity and the specific discharge capacity value, which is the specific discharge capacity value in the embodiment of the application, are recorded. The coulomb efficiency value in the embodiment of the application is obtained by dividing the charge capacity by the discharge capacity and multiplying the divided charge capacity by 100%.

(3) And (3) multiplying power performance test: and placing the assembled secondary battery for 12 hours, so that the electrolyte fully infiltrates the negative electrode plate. The secondary battery was then clamped to the crocodile clip of the tester. The test current and the quality of the active substances, the cycle number and the test voltage range are input, and the tester itself displays the specific charge capacity and specific discharge capacity of the battery. Wherein the number of cycles is 100, the test voltage is in the range of 0.01-2V, the current density is 2A/g, the test current = current density =mass of active material, mass of active material = paste mass =80%, mass of paste = mass of wafer-mass of blank current collector. The 100 th charge specific capacity and discharge specific capacity value are recorded, wherein the discharge specific capacity value is the rate performance in the embodiment of the application.

The particle size, coating thickness, and the results of the above tests of the composite materials prepared in each example are shown in table 2. Further, the change curves of specific capacity and coulombic efficiency of the button cell, which was fabricated with the composite material prepared in example 1 as a negative electrode material and cycled 100 times at 100mA/g, are shown in fig. 4 and 3, respectively. The change curve of the specific capacity of the button cell, which was prepared by using the composite material prepared in example 12 as a negative electrode material and was cycled 100 times at 100mA/g, is shown in fig. 5.

Table 2: results of the electrical property test of the composite materials of examples 1 to 17

From fig. 1, it can be seen that the silicon-tin dioxide composite material prepared by using the direct current arc discharge plasma process in each embodiment has a uniform and complete coating of the tin dioxide layer, and can form an ideal core-shell structure.

However, the use of other methods for preparing silicon-tin dioxide composite materials, such as chinese patent application CN114843479a using calcination, or chinese patent application CN112599755A prepared by chemical reaction in solution, does not allow to obtain a uniform tin dioxide coating.

In addition, by adjusting the ratio of the silicon and tin dioxide used as raw materials, the thickness of the tin dioxide layer can be easily adjusted, so that the obtained composite material achieves the desired electrical properties. According to various embodiments, the ratio of silicon to tin dioxide is preferably between 5:5 and 8:2, more preferably between 6:4 and 7:3, with the thickness of the corresponding tin dioxide layer varying between 3 and 6nm, with the optimal thickness of the tin dioxide layer being between 4 and 5 nanometers. At this time, the cycle characteristics and the rate characteristics of the silicon-tin dioxide composite material are both good. And when the tin dioxide layer thickness is reduced to 2nm (see example 12), the cycle characteristics start to deteriorate, particularly the rate characteristics. On the other hand, when the thickness of the tin dioxide layer is as high as 10nm (see example 13), since the tin dioxide ratio is too high, the specific capacity of the material as a whole is lowered, and thus the cycle characteristics and the rate characteristics are also lowered as compared with the preferred embodiment.

Further, the particle size of the composite material can be adjusted by adjusting the partial pressure ratio of hydrogen and argon. As can be seen from examples 1, 6-8 and 16-17, too large or too small particle size results in a decrease in the electrical properties of the material. The particle size can be in the range of 40-95nm, and preferably, in the range of 50-90nm, good cycle characteristics and rate characteristics can be obtained. More preferably the particle size is 65-75nm, such as 70nm.

In addition, as can be seen from the above results, the adjustment of the voltage/current conditions in the dc arc discharge plasma process has substantially no effect on the structure of the obtained core-shell structure composite material, and thus has substantially no effect on the material properties. Those skilled in the art can select appropriate process conditions depending on the particular equipment.

The present application is not limited to the above embodiment. The above embodiments are merely examples, and embodiments having substantially the same configuration and the same effects as those of the technical idea within the scope of the present application are included in the technical scope of the present application. Further, various modifications that can be made to the embodiments and other modes of combining some of the constituent elements in the embodiments, which are conceivable to those skilled in the art, are also included in the scope of the present application within the scope not departing from the gist of the present application.

Claims

1. A method of preparing a silicon-metal oxide composite anode material, wherein the silicon-metal oxide composite anode material has a core-shell structure, the method comprising:

uniformly mixing silicon particles and metal oxide particles and pressing the mixture into a block; and

the block is used as an anode target material to obtain the silicon-metal oxide composite anode material through direct current arc discharge plasma treatment in the atmosphere of hydrogen and inert gas,

wherein the melting point of the metal oxide is lower than the melting point of silicon; the metal oxide is tin dioxide or molybdenum oxide;

the mass ratio of the silicon particles to the metal oxide particles is 5:5-8:2;

in the direct current arc discharge plasma treatment, the current is 10-200A, and the voltage is 5-30V.

2. The method of claim 1, wherein the mass ratio of the silicon particles to the metal oxide particles is 6:4-7:3.

3. The method of claim 1, wherein the partial pressure of hydrogen is 1 x 10 ⁴ Pa-1.5×10 ⁴ Pa, and the partial pressure of the inert gas is 2×10 ⁴ Pa-2.5×10 ⁴ Pa。

4. The method of claim 3, wherein the hydrogen and the inert gas are at a pressure ratio of 10:7.5-10:4.

5. The method according to claim 1, wherein the inert gas is at least one selected from argon and helium.

6. The method of claim 1, wherein the distance between the anode and the cathode in the dc arc discharge plasma treatment is 10-25mm.

7. The method of claim 6, wherein the anode is spaced from the cathode by 10-20mm, the current is 50-150A, and the voltage is 15-25V.

8. The method of claim 1, wherein the method further comprises:

and after the direct current arc discharge plasma treatment, performing passivation treatment to obtain the silicon-metal oxide composite anode material.

9. The method of claim 8, wherein the passivating treatment is performed in air for 6-10 hours.

10. The method of claim 1, wherein the cathode is a tungsten rod or a carbon rod in the dc arc discharge plasma treatment.

11. A silicon-metal oxide composite anode material, wherein the silicon-metal oxide composite anode material is a particle having a core-shell structure, the particle of the core-shell structure is a silicon nanoparticle uniformly and completely coated with a metal oxide layer, and at least 50% of the particles have a particle diameter of 50-90nm, wherein the melting point of the metal oxide is lower than that of silicon; the silicon-metal oxide composite anode material is prepared by the method of any one of claims 1 to 10.

12. The silicon-metal oxide composite anode material according to claim 11, wherein the thickness of the metal oxide layer is 3-6nm.

13. The silicon-metal oxide composite anode material according to claim 12, wherein the thickness of the metal oxide layer is 4-5nm.

14. The silicon-metal oxide composite anode material of claim 12, wherein the metal oxide layer thickness difference at different locations on the surface of each of the silicon nanoparticles is no more than 1nm.

15. A negative electrode tab having a negative electrode current collector and a negative electrode film layer on at least one surface of the negative electrode current collector, wherein the negative electrode film layer comprises the silicon-metal oxide composite negative electrode material according to any one of claims 11 to 14 as a negative electrode active material.

16. A secondary battery comprising the negative electrode tab according to claim 15.

17. An electric device comprising the secondary battery according to claim 16.