CN105375012B

CN105375012B - Silicon-tin composite material for lithium ion battery cathode and preparation method thereof

Info

Publication number: CN105375012B
Application number: CN201510850077.2A
Authority: CN
Inventors: 朱正旺; 吴金波; 张海峰; 王爱民; 付华萌; ***; 李宏
Original assignee: Institute of Metal Research of CAS
Current assignee: Institute of Metal Research of CAS
Priority date: 2015-11-30
Filing date: 2015-11-30
Publication date: 2020-05-12
Anticipated expiration: 2035-11-30
Also published as: CN105375012A

Abstract

The invention discloses a silicon-tin composite material for a lithium ion battery cathode and a preparation method thereof, wherein the cathode composite material is of a tin fiber wound silicon particle composite structure and consists of silicon and tin, wherein the silicon content is 20-70 at.%, and the balance is tin. The preparation method of the cathode composite material comprises the steps of mixing silicon and tin powder, and carrying out ball milling on the mixed powder under the protection of argon atmosphere by adopting a high-energy ball milling method; under high-energy impact, the metal tin particles are violently deformed, cold welded and torn to form tin fibers; in the process of continuing ball milling, tough phase metallic tin which forms a fibrous structure after high-energy ball milling is compounded with silicon particles which are crushed and refined under high-energy impact in the process of ball milling to form a tin fiber winding silicon particle composite structure. The novel fiber winding wrapping type silicon-containing composite material is simple in preparation process and low in cost, and meanwhile, the composite material is novel and unique in structure, excellent in electrochemical performance and has a very good application prospect.

Description

Silicon-tin composite material for lithium ion battery cathode and preparation method thereof

Technical Field

The invention relates to the technical field of electrochemical power supplies, in particular to a silicon-containing composite material for a lithium ion battery, and particularly provides a silicon-containing fiber winding and wrapping type lithium ion battery composite material and a preparation method thereof.

Background

The lithium ion battery is an ideal green energy source in the 21 st century because of the characteristics of small volume, light weight, high specific energy, long service life, high output voltage, low self-discharge, environmental friendliness and the like, and is widely used as an energy storage system in the fields of aerospace, military, automobile industry, electronic equipment and biomedicine. However, at present, the commercial lithium ion battery mainly adopts a carbon material (such as carbon, graphite, etc.) as a negative electrode, and the theoretical lithium intercalation capacity is 372mAh/g, which is difficult to meet the requirements of large-scale electric energy transmission units, electric automobiles and hybrid electric automobiles on high capacity and high energy density of the lithium ion battery. Therefore, extensive researchers are continuously making efforts to find a novel anode material system capable of replacing carbon materials.

In recent years, many new materials with development prospects have been reported, and among them, silicon materials are receiving attention because of having a huge lithium storage capacity. Silicon has a small atomic weight and a high specific capacity (theoretically forming Li)₂₂Si₅The specific capacity of the lithium battery reaches 4200mAh/g), the lithium intercalation potential is low, and the like, thereby bringing wide attention to scientific researchers. However, the commercialization process of the lithium ion battery using a silicon material as a negative electrode is hindered so far, and the lithium ion battery has not yet fully entered the market of the product, and one of the main reasons is that during the charging and discharging process, along with the insertion and extraction of lithium ions, the silicon negative electrode material undergoes a huge volume change (more than 300%), which causes mechanical disintegration (fragmentation and pulverization) of the negative electrode material, and further causes the collapse of the electrode structure, and the peeling of the electrode material causes the electrode material to lose electrical contact with the current collector, thereby causing the rapid attenuation of capacity, the rapid decrease of cycle performance, and finally the failure of the electrode.

Aiming at the problem of volume expansion of silicon materials in the charging and discharging processes, the current solutions proposed by researchers mainly comprise: 1) the structure of the material is changed to prepare the material with different shapes. For example, a linear shape, a film shape, a porous shape, a core-shell shape, and the like. Researches show that the silicon cathode silicon materials with different structural appearances can effectively reduce the volume expansion effect in the charging and discharging processes, and the capacity and the cycle performance are greatly improved; 2) synthesizing silicon and an active/inactive composite system. The expansion of silicon material is compensated by using a buffer skeleton in a composite system, so that the silicon material can keep good electric contact. However, in the preparation of composite materials, electrochemical deposition, magnetron sputtering and other preparation methods are often used, and these preparation methods have complex processes, low production efficiency and high preparation cost, and are difficult to realize large-scale industrial production.

Disclosure of Invention

The invention aims to provide a novel silicon-tin composite material for a lithium ion battery cathode and a preparation method thereof. The composite material with novel and unique structure and excellent electrochemical performance is prepared by a high-energy ball milling method with simple process operation and low production cost. The basic principle is that ductile metallic tin is subjected to cold welding and tearing under the high-energy impact condition to form a fiber shape, and is compounded with silicon particles which are crushed and refined after high-energy impact in the ball milling process, part of the silicon particles are attached to the fiber-shaped tin, and part of the silicon particles are wound and wrapped by the fiber-shaped tin, so that the fiber winding and wrapping type composite material is obtained. The preparation method of the high-energy ball milling has simple process operation and low cost.

The technical scheme of the invention is as follows:

a new silicon-tin composite material for the cathode of a lithium ion battery is composed of simple substance state silicon and simple substance state tin; wherein: the silicon content is 20-70 at.%, and the rest is tin. The silicon content of the silicon-tin composite material is preferably 50 at.%.

In the composite material, the tin is fibrous, the fiber forms an open three-dimensional winding structure, part of silicon particles are attached to the fiber, part of the silicon particles are wound and wrapped by the fibrous tin, and the size of the silicon particles is 10-20 microns.

A preparation method of a novel silicon-tin composite material for a lithium ion battery cathode comprises the steps of mixing silicon powder and tin powder according to a required proportion (atom percentage content: 20-70 at.%, preferably 50 at.%, and the balance being tin powder), then carrying out high-energy ball milling under the protection of argon atmosphere, wherein the ball milling time is 1-30 hours, and then obtaining the composite material. Wherein the silicon particles have a particle size distribution in the range of 10-20 μm.

In the high-energy ball milling process, the mass ratio of the milling balls to the mixed powder (silicon powder and tin powder) is 5-20:1 (preferably 16: 1).

In the present invention, the specifications of the raw materials used are as follows:

the purity of the silicon powder is more than or equal to 99.99 percent, and the particle size is 20-30 mu m; the purity of the tin powder is more than or equal to 99.5 percent, and the granularity is 20-30 mu m.

And preparing the composite material into a negative pole piece, assembling the half-cell in a glove box, and then testing the electrochemical performance of the half-cell.

Compared with the prior silicon-containing battery cathode material and the preparation method thereof, the invention has the following characteristics:

1. in the silicon fiber-containing winding and wrapping type lithium ion battery composite material, the ductile phase metal tin after ball milling is fibrous and is compounded with crushed and refined silicon particles after ball milling, part of the silicon particles are attached to tin fibers, and part of the silicon particles are wrapped by the tin fibers to form an open three-dimensional winding and wrapping type structure.

2. The metal tin belongs to lithiation active metal, the theoretical lithium embedding capacity of the metal tin is 992mAh/g, the metal tin is higher than that of a carbon material, the integral specific capacity of the composite material cannot be greatly reduced by compounding the metal tin with silicon, and the prepared silicon-tin composite material can still keep high specific capacity.

3. In the silicon-tin composite material, in a tin fiber wound silicon particle composite structure, part of silicon particles are attached to tin fibers, and part of silicon particles are wrapped by the tin fibers. The composite structure effectively improves the toughness of the material, and in the charging and discharging process, the silicon particles are subjected to volume expansion after being embedded with lithium, but can be effectively prevented from cracking and damaging due to being wrapped by tin fibers, so that the stable electrical contact with a current collector is maintained, the cycle performance is improved, and the cycle life of a battery is prolonged.

4. The intrinsic conductivity of the metallic tin is higher than that of semiconductor silicon and common carbon materials, which is beneficial to the transmission of lithium ions in the electrode material in the charging and discharging process.

5. In the silicon-tin composite material, the lithium counter potentials of silicon and tin are different, and lithium can be deintercalated under different potentials. The buffer layers are used for releasing stress, so that stress concentration in the charging and discharging process is relieved, mechanical stress caused by volume effect is reduced, collapse of the active material due to excessive stress concentration is prevented, and the cycle life of the cathode material is further prolonged.

6. The preparation method provided by the invention is simple to operate, low in production cost, mature in technology, easy to industrialize and capable of being put into production without large amount of capital and technical investment. The preparation method of the silicon-containing composite material has a huge application prospect in the industrial production process of the lithium ion battery cathode material.

Drawings

FIG. 1 shows the silicon-containing (component: Si) obtained by the preparation₅₀Sn₅₀) Microscopic morphology SEM image of fiber winding wrapping type composite material

FIG. 2 (a) shows Si-containing (component: Si)₅₀Sn₅₀) SEM image of microstructure of fiber winding wrapping type composite material; (b) EDS analysis spectrum of the corresponding fiber.

FIG. 3 shows a silicon-containing (component: Si)₅₀Sn₅₀) The fiber winding wrapping type composite material is used as an active substance to prepare an electrode, and the lithium metal is used as a counter electrode to assemble a battery charging and discharging specific capacity-voltage diagram.

FIG. 4 shows Si prepared under different ball milling time conditions₅₀Sn₅₀XRD contrast pattern of the composite material. The samples selected were 1 hour, 10 hours, 15 hours, 19 hours, 20 hours, 26 hours, 30 hours.

FIG. 5 shows Si prepared under different ball milling time conditions₅₀Sn₅₀SEM comparison of the microstructure of the composite material. The samples selected were (a), 1 hour, (b), 10 hours, (c), 15 hours, (e), 20 hours, (f), 25 hours.

FIG. 6 shows Si prepared under different ball milling time conditions₅₀Sn₅₀Comparative plot of cycle performance of the composite. The samples selected were 1 hour, 10 hours, 15 hours, 20 hours, 25 hours.

FIG. 7 shows Si prepared under different ball milling time conditions₅₀Sn₅₀Graph comparing the rate performance of the composite material. The samples selected were 15 hours, 20 hours, 25 hours.

FIG. 8 shows XRD patterns of silicon-containing composites prepared under ball milling conditions for 20 hours with different compositions.

FIG. 9 is a graph of the charge and discharge cycle performance of the silicon-containing composite material prepared under the condition of ball milling for 20 hours with different components.

Detailed Description

The invention is described in detail below with reference to the accompanying drawings and examples. The essential features and advantages of the present invention are further illustrated by the description of examples and comparative examples. For convenience of description, the preparation method and test procedure of the material are first illustrated by example 1, and the structural and performance characteristics of the material of the present invention are illustrated by microstructure observation and performance test, and then described by comparative example 1, illustrating the unique and structural novelty of the preparation method. Then, the embodiments 2 to 6 will be described again to show the corresponding effects.

Example 1

Si is prepared by a high-energy ball milling method₅₀Sn₅₀And winding the fiber on the wrapping composite material, and performing electrochemical performance test by using the fiber as a lithium ion battery cathode material.

1. For nominal composition Si₅₀Sn₅₀Wherein the atomic percent of silicon is 50 at.%, and the atomic percent of tin is 50 at.%, satisfies the compositional interval required in the specification.

2. Mixing the selected raw materials of silicon powder and tin powder according to a proportion (silicon: 50 at.%, tin: 50 at.%) and then filling the mixture into a ball-milling tank matched with ball-milling equipment. In the embodiment, bearing steel balls with the diameters of 10mm, 8mm and 5mm are selected for high-energy ball milling, and the mass ratio of the balls to the mixed powder is 16: 1. Ball milling is carried out under the protection atmosphere of argon, and the rotating speed of the ball milling is 250 rpm. Si is obtained after 20 hours of high-energy ball milling₅₀Sn₅₀A filament wound and wrapped composite material comprising a plurality of fibers and particles, the composite material having a width of about 10 microns, a thickness of about 2 microns and a particle size of about 10 to 20 microns. FIG. 1 is Si₅₀Sn₅₀SEM image of microstructure of the fiber winding wrapping type composite material; fig. 2 is an EDS image of the microstructure and corresponding fiber spectral analysis. Due to the cold welding and tearing action under high energy impact, a large amount of fibrous materials are generated, and simultaneously, the particles are crushed and refined, as can be seen in an EDS (electronic discharge spectroscopy) chart,the fibrous material formed is a tough phase metallic tin.

3. Assembling and testing the battery: to obtain Si₅₀Sn₅₀After the wrapping type composite material was wound with fibers, it was used as an active material, made into a slurry with conductive carbon black (Super-P) and polyvinylidene fluoride (PVDF) in a mass ratio of 40:40:20 in an N-methylpyrrolidone (NMP) medium, coated on a copper foil and dried at 120 ℃ under vacuum for 12 hours, thereby making a negative electrode film. Then, using metal lithium as a counter electrode, 25 μm American celgard as a diaphragm, 1mol of LiPF₆(PC + DMC) (1:1) was used as an electrolyte, and the cell was assembled in a glove box with the water content controlled to 0.1ppm or less. The assembled battery was subjected to charge and discharge performance tests under various conditions. FIG. 3 is Si₅₀Sn₅₀The charge-discharge curve of the fiber winding and wrapping type composite material shows that the material has excellent electrochemical performance, the first discharge capacity reaches 1380mAh/g, and the discharge capacity is still kept at 1000mAh/g after 50 cycles.

Comparative example 1

Respectively preparing Si under different ball milling time by a high-energy ball milling method₅₀Sn₅₀Composite materials were compared and Si prepared in the manner of example 1₅₀Sn₅₀And (3) respectively manufacturing negative pole pieces by using the composite material as an active substance, and assembling the negative pole pieces into the battery. And carrying out charge and discharge tests under the condition of 0.1C, wherein the test voltage range is 0.03-1.5V.

FIG. 4 shows Si prepared under different ball milling time conditions₅₀Sn₅₀XRD contrast patterns of the composite material selected samples were 1 hour, 10 hours, 15 hours, 19 hours, 20 hours, 26 hours, 30 hours. As can be seen from FIG. 4, the intensity of the diffraction peak changes with the increase of the ball milling time, and the change rule from strong to weak to strong appears, and Si prepared under the condition of ball milling for 20 hours₅₀Sn₅₀The XRD diffraction peak intensity of the composite material is lowest. From this, it is presumed that the structural change of the material is the greatest when the ball milling is carried out for 20 hours. Meanwhile, no diffraction peak of inactive phases such as silicon oxide appears on an XRD (X-ray diffraction) spectrum, which indicates that the inert gas is reasonably protected in the ball milling process and cannot be introducedInclusion is beneficial to ensuring high lithium intercalation specific capacity.

FIG. 5 shows Si prepared under different ball milling time conditions₅₀Sn₅₀SEM comparison of the microstructure of the composite material, and the selected samples were 1 hour, 10 hours, 15 hours, 20 hours, and 25 hours. As can be seen from FIG. 5, during the ball milling process, as the cold welding and tearing are continuously performed, the tin fiber is increased, and the Si is ball-milled for 20 hours₅₀Sn₅₀The tin fiber content in the composite material is the largest, and the most ideal fiber winding and wrapping type structure is obtained. Agglomeration occurs when the ball milling is carried out for more than 20 hours, and a large number of clusters are formed.

FIG. 6 shows Si prepared under different ball milling time conditions₅₀Sn₅₀The cycle performance of the composite material is compared with a graph, and samples of 1 hour, 10 hours, 15 hours, 20 hours and 25 hours are selected in the experiment to carry out cycle performance tests. As can be seen from the figure, Si having the most desirable filament winding type structure was ball-milled for 20 hours₅₀Sn₅₀The composite material is compared with Si under other different ball milling time conditions₅₀Sn₅₀The composite material has good cycle performance and higher capacity retention rate under the same cycle number.

FIG. 7 shows Si prepared under different ball milling time conditions₅₀Sn₅₀The multiplying power performance comparison graph of the composite material selects samples of 15 hours, 20 hours and 25 hours in the experiment to carry out multiplying power performance comparison test. The test conditions were: the charge-discharge voltage range is 0.03-1.5V, and the charge-discharge is firstly carried out for 10 cycles at the multiplying factor of 0.1C, then the charge-discharge is carried out for 10 cycles at the multiplying factor of 0.5C, then the charge-discharge is carried out for 10 cycles at the multiplying factor of 1C, and then the charge-discharge is carried out for 10 cycles at the multiplying factor of 0.1C. As can be seen from fig. 7, the electrode was charged and discharged at a rate of 0.1C, and the specific capacity was maintained at 1000mAh/g after 10 cycles, and was maintained at 750mAh/g after 10 cycles when the charging and discharging rate was increased to 0.5C, and was maintained at 700mAh/g after 10 cycles when the charging and discharging rate was increased to 1C, and was maintained at 980mAh/g after 10 cycles when the charging and discharging rate was returned to 0.1C. Shows that the ideal winding package is obtained after ball milling for 20 hoursSi of wrapped structure₅₀Sn₅₀The composite material has better rate capability, and can keep higher specific capacity under the conditions of heavy current charge and discharge.

Combining the preparation and performance test of the composite material in the comparative example 1, the method can be obtained that the tough metal phase tin is added to be compounded with the silicon, and the Si with the winding and wrapping type structure is obtained after ball milling₅₀Sn₅₀The composite material has novel structure and also has advantages in electrochemical performance.

Example 2

Preparing the fiber winding wrapping type Si by a high-energy ball milling method under the condition of ball milling for 20 hours₂₀Sn₈₀The composite material is used as a lithium ion battery cathode material for electrochemical performance test. The difference from the embodiment 1 is that: different proportions are adopted in the component proportion. The preparation method and the testing process are the same as those of example 1.

The silicon-containing fiber wrapped Si prepared in this example₂₀Sn₈₀The composite material contains 20 at% of silicon element and 80 at% of tin element, and an XRD (X-ray diffraction) pattern of the composite material is shown in figure 8, and silicon and tin exist in a simple substance state. The silicon-containing composite material has a low content of fibrous structures and a particle size of about 20 to 30 μm. The result of the charge-discharge cycle performance test is shown in FIG. 9, in which the first discharge capacity is 1050mAh/g and the capacity is maintained at 350mAh/g after 20 cycles.

Example 3

Preparing the fiber winding wrapping type Si by a high-energy ball milling method under the condition of ball milling for 20 hours₃₀Sn₇₀The composite material is used as a lithium ion battery cathode material for electrochemical performance test. The difference from the embodiment 1 is that: different proportions are adopted in the component proportion. The preparation method and the testing process are the same as those of example 1.

The silicon-containing fiber wrapped Si prepared in this example₃₀Sn₇₀The composite material contains 30 at% of silicon element and 70 at% of tin element, and an XRD (X-ray diffraction) pattern of the composite material is shown in figure 8, and silicon and tin exist in a simple substance state. The silicon-containing composite material has a reduced content of fibrous structures and a particle size of about20-30 μm. The result of the charge-discharge cycle performance test is shown in FIG. 9, where the first discharge capacity was 1300mAh/g and the capacity remained at 600mAh/g after 20 cycles.

Example 4

Preparing the fiber winding wrapping type Si by a high-energy ball milling method under the condition of ball milling for 20 hours₄₀Sn₆₀The composite material is used as a lithium ion battery cathode material for electrochemical performance test. The difference from the embodiment 1 is that: different proportions are adopted in the component proportion. The preparation method and the testing process are the same as those of example 1.

The silicon-containing fiber wrapped Si prepared in this example₄₀Sn₆₀The composite material contains 40 at% of silicon element and 60 at% of tin element, and an XRD (X-ray diffraction) pattern of the composite material is shown in figure 8, and silicon and tin exist in a simple substance state. The silicon-containing composite material has a low content of fibrous structures and a particle size of about 20 to 30 μm. The result of the charge-discharge cycle performance test is shown in FIG. 9, where the first discharge capacity is 1400mAh/g and the capacity is maintained at 500mAh/g after 20 cycles.

Example 5

Preparing the fiber winding wrapping type Si by a high-energy ball milling method under the condition of ball milling for 20 hours₆₀Sn₄₀The composite material is used as a lithium ion battery cathode material for electrochemical performance test. The difference from the embodiment 1 is that: different proportions are adopted in the component proportion. The preparation method and the testing process are the same as those of example 1.

The silicon-containing fiber wrapped Si prepared in this example₆₀Sn₄₀The composite material contains 60 at% of silicon element and 40 at% of tin element, and an XRD (X-ray diffraction) pattern of the composite material is shown in figure 8, and silicon and tin exist in a simple substance state. The silicon-containing composite material has a low content of fibrous structures and a particle size of about 20 to 30 μm. The result of the charge-discharge cycle performance test is shown in FIG. 9, where the first discharge capacity is 1400mAh/g and the capacity is maintained at 700mAh/g after 20 cycles.

Example 6

Preparing the fiber winding wrapping type by using a high-energy ball milling method under the condition of ball milling for 20 hoursSi₇₀Sn₃₀The composite material is used as a lithium ion battery cathode material for electrochemical performance test. The difference from the embodiment 1 is that: different proportions are adopted in the component proportion. The preparation method and the testing process are the same as those of example 1.

The silicon-containing fiber wrapped Si prepared in this example₇₀Sn₃₀The composite material contains 70 at% of silicon element and 30 at% of tin element, and an XRD (X-ray diffraction) pattern of the composite material is shown in figure 8, and silicon and tin exist in a simple substance state. The silicon-containing composite material has a low content of fibrous structures and a particle size of about 20 to 30 μm. The result of the charge-discharge cycle performance test is shown in fig. 9, and shows that the first discharge capacity is 1600mAh/g, and the capacity is kept at 350mAh/g after 20 cycles.

The above embodiments are merely illustrative of the technical ideas and features of the present invention, and the purpose thereof is to enable those skilled in the art to understand the contents of the present invention and implement the present invention, and not to limit the protection scope of the present invention. All equivalent changes and modifications made according to the spirit of the present invention should be covered within the protection scope of the present invention.

Claims

1. A silicon-tin composite material for a negative electrode of a lithium ion battery, characterized in that: the cathode composite material is of a tin fiber wound silicon particle composite structure and consists of two elements, namely silicon and tin, wherein the content of silicon is 20-70 at.%, and the balance is tin; in the composite material, the metal tin is fibrous and forms an open three-dimensional winding structure, and in the composite material, silicon particles are partially attached to the fibrous tin and partially wound and wrapped by the fibrous tin.

2. The silicon-tin composite of claim 1, wherein: the silicon particles have a particle size of 10 to 20 μm.

3. A method for preparing the silicon-tin composite material according to claim 1, characterized in that: the method comprises the steps of mixing silicon powder and tin powder according to a required proportion, and then preparing the composite material by a high-energy ball milling method.

4. A method for preparing a silicon-tin composite material according to claim 3, characterized in that: in the high-energy ball milling method, the mass ratio of the milling balls to the mixed powder is 5-20: 1.

5. A method for preparing a silicon-tin composite material according to claim 3, characterized in that: the high-energy ball milling is carried out under the protection of argon atmosphere.

6. A method for preparing a silicon-tin composite material according to claim 3, characterized in that: the time of the high-energy ball milling is 1 to 30 hours.

7. A method for preparing a silicon-tin composite material according to claim 3, characterized in that: the purity of the silicon powder in the raw materials is more than or equal to 99.99 percent, and the particle size is 20-30 mu m; the purity of the tin powder is more than or equal to 99.5 percent, and the granularity is 20-30 mu m.