CN118335945A

CN118335945A - Silicon-carbon composite material of lithium ion battery, negative electrode and lithium ion battery

Info

Publication number: CN118335945A
Application number: CN202410457226.8A
Authority: CN
Inventors: 何畅雷; 李辉; 于立娟; 胡大林
Original assignee: Shenzhen Highpower Technology Co Ltd
Current assignee: Shenzhen Highpower Technology Co Ltd
Priority date: 2024-04-16
Filing date: 2024-04-16
Publication date: 2024-07-12

Abstract

The application relates to a silicon-carbon composite material of a lithium ion battery, a negative electrode and the lithium ion battery. The silicon-carbon composite material of the lithium ion battery comprises secondary particles, wherein the secondary particles comprise a buffer layer, a conductive additive and a plurality of primary particles; the conductive additive and the primary particles are dispersed in the buffer layer; the primary particles comprise an inner core and a shell layer coating the inner core, wherein the inner core comprises a porous carbon material and a silicon material embedded in the porous carbon material. The scheme provided by the application can effectively inhibit and buffer the expansion of the silicon material and improve the cycle performance of the battery.

Description

Silicon-carbon composite material of lithium ion battery, negative electrode and lithium ion battery

Technical Field

The application relates to the technical field of batteries, in particular to a silicon-carbon composite material of a lithium ion battery, a negative electrode and the lithium ion battery.

Background

Due to the rapid development and wide application of various portable electronic devices and electric vehicles in recent years, the demand for lithium ion batteries having high energy density and long cycle life is increasing. At present, although the lithium ion battery using graphite as a negative electrode material has a large specific gravity in the market, the theoretical specific gravity value of the graphite is low, and the requirements of miniaturization of electronic equipment and high power and high capacity of the lithium ion battery for vehicles are not met. Therefore, development of a novel anode material to enhance battery performance is currently the focus of research in this field.

Silicon is considered to be typical of the next-generation commercial negative electrode because of high specific capacity and good compatibility with carbon, and thus a great deal of research is focused on the research of silicon-carbon composite negative electrode materials of different sizes, structures and types.

In the related art, the silicon-carbon composite material is secondary particles, the secondary particles are subjected to secondary granulation by primary particles of 0.01-5 mu m, and then crushed to obtain irregularly-shaped secondary particles, the conductive agent is uniformly dispersed in the secondary particles, and the surface of the secondary particles is coated with a layer of amorphous carbon. Because the silicon with the median particle diameter of 0.01-5 mu m is selected as the primary particle, the silicon particles which can be covered and connected by the conductive agent can be added, so that the synthesized irregular secondary particles are applied to the lithium ion battery, and the negative electrode has the advantages of high compaction density, difficult breakage of the secondary particles, more contact points among the pole piece particles and lower polarization.

However, as the primary particles are pure silicon particles, the expansion of the silicon particles cannot be effectively inhibited and buffered in the circulation process, and submicron or smaller nano particles are formed after the silicon particles are broken due to the expansion of the silicon particles, so that the pulverization of the particles is caused, and the circulation performance of the battery is further deteriorated.

Disclosure of Invention

In order to solve or partially solve the problems in the related art, the application provides a silicon-carbon composite material of a lithium ion battery, a negative electrode and the lithium ion battery, wherein primary particles are silicon-carbon materials, and the silicon materials are embedded in the carbon materials, so that the expansion of the silicon materials can be effectively inhibited and buffered, and the cycle performance of the battery is improved.

The first aspect of the application provides a silicon-carbon composite material of a lithium ion battery, comprising secondary particles, wherein the secondary particles comprise a buffer layer, a conductive additive and a plurality of primary particles, and the conductive additive and the primary particles are dispersed in the buffer layer; the primary particles comprise an inner core and a shell layer coating the outer surface of the inner core, wherein the inner core comprises a porous carbon material and a silicon material embedded in the porous carbon material.

As an alternative embodiment, the silicon-carbon composite material further comprises an outer layer and an inner layer, wherein the inner layer is the secondary particles, and the outer layer comprises an adhesive layer, and the adhesive layer is adhered to the outer surface of the secondary particles.

As an alternative embodiment, the adhesive layer is insoluble in water.

As an alternative embodiment, the mass ratio of the adhesive layer to the secondary particles is 0.03 to 2:100.

As an alternative embodiment, the mass ratio of the outer layer to the inner layer is 0.03-2: 100.

As an alternative embodiment, in the inner layer, the mass ratio of the buffer layer, the conductive additive, and the primary particles is 5 to 20:0.05 to 1:79 to 94.95.

As an alternative embodiment, the adhesive layer is made of a linear lithium polyacrylate material or a granular lithium polyacrylate material after being crosslinked.

As an alternative embodiment, the outer layer further comprises a conductive layer, and the conductive layer is compounded on the surface of the secondary particles through the bonding layer.

As an alternative embodiment, the conductive layer is one or both of single-walled carbon nanotubes and multi-walled carbon nanotubes.

As an alternative embodiment, in the outer layer, the mass ratio of the adhesive layer to the conductive layer is 1-9: 9 to 1.

As an alternative embodiment, the silicon material includes at least one of a granular shape formed of a single silicon particle and a linear shape formed of a plurality of silicon particles arranged.

As an alternative embodiment, the porous carbon material has an average pore size of no more than 7nm.

As an alternative embodiment, the porous carbon material has a pore volume of 0.55mL/g to 0.95mL/g.

As an alternative embodiment, the porous carbon material has a specific surface area of 1000m ²/g～3000m²/g.

As an alternative embodiment, the silicon material accounts for 35-65% of the mass of the primary particles.

As an alternative embodiment, the shell layer is amorphous carbon.

As an alternative embodiment, the average thickness of the shell layer is 2nm to 20nm.

As an alternative embodiment, the conductive additive is one or both of single-walled carbon nanotubes and multi-walled carbon nanotubes.

As an alternative embodiment, the primary particles have an average particle size of 0.1 μm to 1. Mu.m.

As an alternative embodiment, the primary particles have a specific surface area of not more than 20m ²/g.

As an alternative embodiment, the secondary particles have an average particle size of 4 μm to 15. Mu.m.

As an alternative embodiment, the secondary particles have a specific surface area of not more than 10m ²/g.

As an alternative embodiment, the buffer layer is amorphous carbon.

The second aspect of the present application provides a method for preparing the silicon-carbon composite material, which comprises the following steps:

Placing a porous carbon material into a sintering furnace, introducing silane gas into an inert atmosphere at 400-600 ℃, and depositing a silicon material in the porous carbon material;

After the deposition is completed, the silane gas is switched into acetylene gas, the temperature is increased to 500-600 ℃, and the surface of the porous carbon material is coated with amorphous carbon to obtain primary particles;

taking out the primary particles, and uniformly mixing the primary particles, the conductive additive, the dispersing agent and the carbon precursor to obtain mixed slurry;

spray drying the mixed slurry to obtain a micron-sized secondary particle precursor;

and (3) placing the secondary particle precursor into a sintering furnace, and sintering for a preset time in an inert atmosphere at 500-600 ℃ to obtain secondary particles.

The third aspect of the application provides a lithium ion battery anode, which comprises the silicon-carbon composite material or the silicon-carbon composite material prepared by the preparation method of the silicon-carbon composite material.

According to a fourth aspect of the application, a lithium ion battery is provided, comprising the lithium ion battery cathode.

The technical scheme provided by the application can comprise the following beneficial effects:

According to the silicon-carbon composite material, the secondary particles and the inner layer are formed by compounding the conductive additive and the primary particles through the coating of the buffer layer, on one hand, the conductive contact between the primary particles is enhanced by tightly covering and connecting the primary particles by the conductive additive, and in the battery circulation process, broken primary particles caused by expansion can still be connected through the conductive additive, so that the inactivation of silicon materials in the primary particles is reduced, and the coulomb efficiency and the circulation performance of the battery can be remarkably improved; on the other hand, the buffer layer fills gaps among the primary particles, and the contact between the silicon material in the primary particles and the electrolyte is blocked, so that the coulomb efficiency of the battery is further improved, and meanwhile, the buffer layer can effectively inhibit and buffer the expansion of the silicon material in the primary particles, so that the cycle performance of the battery can be further improved. Furthermore, the primary particles of the application are not pure silicon materials, but silicon-carbon materials with shell-core structures, the shell-core can enhance the tight connection of the silicon-carbon materials in the core, the silicon materials in the core are embedded into the holes of the porous carbon materials, and the expansion of the silicon materials can be further inhibited, thereby greatly increasing the cycle performance of the battery.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application as claimed.

Drawings

The foregoing and other objects, features and advantages of the application will be apparent from the following more particular descriptions of exemplary embodiments of the application as illustrated in the accompanying drawings wherein like reference numbers generally represent like parts throughout the exemplary embodiments of the application.

FIG. 1 is a schematic structural view of secondary particles in a silicon-carbon composite material according to an embodiment of the present application;

Fig. 2 is a schematic structural view of the primary particles shown in fig. 1;

FIG. 3 is a schematic structural view of a linear lithium polyacrylate material with a crosslinked bonding layer in the secondary particles according to an embodiment of the present application;

fig. 4 is a schematic structural view of a granular lithium polyacrylate material as an adhesive layer in secondary particles according to an embodiment of the present application;

FIG. 5 is a schematic view showing a structure in which the outer layer of the secondary particles includes an adhesive layer and a conductive layer according to an embodiment of the present application;

Fig. 6 is a schematic diagram showing battery cycle performance test results of each of examples and comparative examples shown in the examples of the present application;

Fig. 7 is a schematic diagram showing the battery cycle performance test results of example 3 and comparative example 1, which are examples of the present application.

Reference numerals:

1. Secondary particles; 11. a buffer layer; 12. a conductive additive; 13. primary particles; 14. a kernel; 141. a porous carbon material; 142. a silicon material; 1421. silicon particles; 15. a shell layer; 2. an outer layer; 20. an adhesive layer; 21. a conductive layer; 3. an inner layer.

Detailed Description

Embodiments of the present application will be described in more detail below with reference to the accompanying drawings. While embodiments of the present application are illustrated in the drawings, it should be understood that the present application may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the application to those skilled in the art.

It should be understood that although the terms "first," "second," "third," etc. may be used herein to describe various information, these information should not be limited by these terms. These terms are only used to distinguish one type of information from another. For example, first information may also be referred to as second information, and similarly, second information may also be referred to as first information, without departing from the scope of the application. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature. In the description of the present application, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.

In the description of the present application, it should be understood that the terms "length," "width," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," and the like indicate orientations or positional relationships based on the orientation or positional relationships shown in the drawings, merely to facilitate describing the present application and simplify the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the present application.

Unless specifically stated or limited otherwise, the terms "mounted," "connected," "secured" and the like are to be construed broadly and may be, for example, fixedly connected or detachably connected or integrally formed; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art according to the specific circumstances.

In view of the above problems, the embodiment of the application provides a silicon-carbon composite material of a lithium ion battery, which contains primary particles made of a silicon-carbon material, wherein the silicon material is embedded in the carbon material, so that the expansion of the silicon material can be effectively inhibited and buffered, and the cycle performance of the battery is improved.

The following describes the technical scheme of the embodiment of the present application in detail with reference to the accompanying drawings.

FIG. 1 is a schematic structural view of secondary particles in a silicon-carbon composite material according to an embodiment of the present application; fig. 2 is a schematic structural view of the primary particles shown in fig. 1.

Referring to fig. 1 and 2, an embodiment of the present application provides a silicon-carbon composite material of a lithium ion battery, including secondary particles 1, the secondary particles 1 including a buffer layer 11, a conductive additive 12, and primary particles 13, wherein the conductive additive 12 and the primary particles 13 are uniformly dispersed in the buffer layer 11; the primary particles 13 include an inner core 14, and a shell layer 15 coating the inner core 14, the inner core 14 including a porous carbon material 141, and a silicon material 142 embedded in the porous carbon material 141.

In the silicon-carbon composite material provided by the embodiment of the application, the secondary particles 1 can be spherical or irregular particles, and the inner layer 3 is formed by compounding the conductive additive 12 and the primary particles 13 through the buffer layer 11, on one hand, the conductive additive 12 tightly covers and connects the primary particles 13, so that the conductive contact between the primary particles 13 is enhanced, and in the battery circulation process, the broken primary particles 13 caused by expansion can still be connected through the conductive additive 12, so that the inactivation of the silicon material 142 in the primary particles 13 is reduced, and the coulomb efficiency and the circulation performance of the battery can be remarkably improved; on the other hand, the buffer layer 11 fills the gaps between the primary particles 13, and the contact of the silicon material 142 in the primary particles 13 with the electrolyte is blocked, so that the coulomb efficiency of the battery is further improved, and the buffer layer 11 can effectively suppress and buffer the expansion of the silicon material 142 in the primary particles 13, so that the cycle performance of the battery can be further improved. Furthermore, the primary particles 13 of the embodiment of the present application are not pure silicon materials, but silicon-carbon materials having a core-shell structure, the core-shell structure can enhance the tight connection of the silicon-carbon materials in the core 14, and the silicon material 142 in the core 14 is embedded in the pores of the porous carbon material 141, so that the expansion of the silicon material 142 can be further suppressed, thereby greatly increasing the cycle performance of the battery.

As an alternative embodiment, referring to fig. 2, the silicon material 142 includes at least one of a granular shape formed of a single silicon particle 1421 and a linear shape formed by arranging a plurality of silicon particles 1421.

The silicon material 142 in the embodiment of the present application may be granular (see the structure in the circular dotted line box in fig. 2) formed by a single silicon particle 1421, linear (see the structure in the square dotted line box in fig. 2) formed by a plurality of silicon particles 1421 arranged, or granular formed by a single silicon particle 1421 and linear formed by a plurality of silicon particles 1421 arranged. Preferably, the silicon particles 1421 are formed into a granular shape and the silicon particles 1421 are arranged in a linear shape. This is because the pores of the porous carbon material 141 are not exactly the same shape, small pores may form small particle silicon, large pores may form large particle silicon, and continuous smooth pores may form linear silicon (a plurality of silicon particles 1421 are deposited within continuous smooth pores to form a line).

As a preferred embodiment, the particle size of the granular silicon material 142 and/or the particle size of the largest silicon particle 1421 in the wire-like silicon material 142 does not exceed the pore size of the porous carbon material 141.

Since the porous carbon material 141 is prepared first and then the silicon material 142 is deposited in the porous carbon material 141 in the material preparation sequence, the particle size of the silicon material 142 cannot exceed the pore size of the porous carbon material 141 due to the pore size of the porous carbon material 141.

As an alternative embodiment, referring to fig. 3 and 4, the silicon carbon composite material further includes an outer layer 2 and an inner layer 3, the inner layer 3 being the secondary particles 1, the outer layer 2 including an adhesive layer 20, the adhesive layer 20 being adhered to the outer surface of the secondary particles 1.

In the related art, a battery anode material is mainly made of graphite material, doped with silicon material, and added with a conductive agent and an adhesive to prepare anode slurry. Because graphite itself expands less, less binder is needed, and silicon material expands more, more binder is needed, and more binder is needed for the formulation.

However, the adhesive added during the material proportioning is not preferentially combined with the silicon material, so that more adhesive added due to the introduction of the silicon material is not effectively utilized, the expansion of the silicon material cannot be effectively inhibited, the doping amount of the silicon material is influenced, and the service life of the battery is influenced.

According to the embodiment of the application, the bonding layer 20 is coated on the outer surface of the secondary particles 1, so that the secondary particles 1 can be tightly covered and connected, the expansion of the silicon material is further reduced, and the service life of the battery is prolonged; the use efficiency of the adhesive layer 20 is also increased, thereby increasing the doping amount of the silicon carbon composite material and improving the battery capacity.

As an alternative embodiment, the adhesive layer 20 is insoluble in water.

The silicon-carbon composite material in the embodiment of the application is mainly applied to a high-safety water-based lithium ion battery, and the bonding layer 20 is insoluble in water to ensure that the bonding layer 20 is compounded on the surface of the secondary particles 1, and the bonding layer 20 is not dissolved in water to fall off and lose efficacy when preparing the negative electrode slurry, so that the processing stability can be ensured.

As a preferred embodiment, and as shown in FIG. 3, the adhesive layer 20 is made of a cross-linked linear lithium polyacrylate material.

Compared with polyacrylic acid or sodium polyacrylate, the lithium polyacrylate has better dynamic performance, the linear lithium polyacrylate is crosslinked at 180 ℃ for 3H, the obtained crosslinked linear lithium polyacrylate is insoluble in water, and the crosslinked linear lithium polyacrylate is used as a material for preparing the bonding layer 20, so that the bonding layer 20 has stronger coating property on the surface of the secondary particles 1, and the recombination rate of the conductive agent in the slurry on the surface of the secondary particles 1 can be increased.

As a preferred embodiment, and as shown in FIG. 4, the adhesive layer 20 is formed from a granular lithium polyacrylate material.

The granular lithium polyacrylate can not be unfolded in water and is insoluble in water; compared with the conventional chain-shaped lithium polyacrylate, the granular lithium polyacrylate has weaker coating property on the surfaces of the secondary particles 1, and the secondary particles 1 can be more contacted with electrolyte, so that the dynamic performance of the secondary particles 1 is greatly improved.

As a preferred embodiment, the particulate lithium polyacrylate has an average particle size of 30nm to 300nm.

The average particle size of the granular lithium polyacrylate in the embodiment of the application can reach submicron level, can enhance the coverage of the surface of the secondary particles 1, increase the recombination rate of the conductive layer 21 on the surface of the secondary particles 1, and improve the electrical property of the silicon-carbon material. The average particle diameter of the granular lithium polyacrylate may be 30nm, 50nm, 100nm, 200nm, 300nm or any value within the above-defined range.

As an alternative embodiment, the mass ratio of the adhesive layer 20 to the secondary particles 1 is 0.03 to 2:100.

The mass ratio of the bonding layer 20 to the secondary particles 1 is limited to 0.03-2: the reason for 100 is that: when the content of the adhesive layer 20 is too low, the application efficiency of the conductive agent in the slurry cannot be improved, resulting in poor electrochemical performance; when the content of the adhesive layer 20 is too high, the ion diffusion path is too long, resulting in serious polarization problems during charge and discharge. Therefore, it is necessary to select a proper mass ratio of the secondary particles 1 to the adhesive layer 20, and by controlling the mass ratio of the adhesive layer 20 to the secondary particles 1 within the above-mentioned range, the doping amount of the silicon-carbon composite material can be increased while effectively relieving the volume expansion of the silicon material 142. In the embodiment of the present application, the mass ratio of the adhesive layer 20 to the secondary particles 1 may be 0.03: 100. 0.05: 100. 0.1: 100. 1: 100. 1.5: 100. 2:100 or any number within the above-defined range.

As an alternative embodiment, see fig. 5, the outer layer 2 further comprises a conductive layer 21, the conductive layer 21 being composited to the surface of the secondary particles 1 by means of an adhesive layer 20.

The embodiment of the application can improve the problem of volume expansion of the secondary particles 1 by modifying the surfaces of the secondary particles 1. By bonding the conductive layer 21 on the surface of the secondary particles 1, on one hand, the bonding layer 20 tightly covers and connects the secondary particles 1, so that the volume expansion of the secondary particles 1 is further reduced, and the cycle life of the battery is prolonged; on the other hand, during the long cycle of the battery, although the silicon material in the primary particles 13 generates an increasingly thick SEI film, conductive contact can be achieved through the conductive layer 21 covering the surface of the secondary particles 1, maintaining the conductivity of the silicon carbon composite material, thereby improving the long cycle life of the battery.

In addition, the pure graphite cathode has good conductivity of graphite, so that the addition amount of the conductive agent is small or even no conductive agent is needed during the batching, the expansion of the graphite is small, and the addition amount of the binder is small. And the silicon material has poor conductivity and large expansion, more conductive agent and binder are needed to be added during batching, and even the conductive agent needs to use expensive single-wall carbon nano tubes. However, the conductive agent and the adhesive added during the batching are not combined with the silicon material preferentially, so that more adhesive and conductive agent added due to the introduction of the silicon material are not effectively utilized, and therefore, the use efficiency of the adhesive and the conductive agent can be effectively improved by directly compounding the adhesive and the conductive agent on the surface of the silicon material, and the long cycle life of the battery is further improved.

Preferably, referring to fig. 5, the adhesive layer 20 is a granular lithium polyacrylate material.

As an alternative embodiment, in the outer layer 2, the mass ratio of the adhesive layer 20 to the conductive layer 21 is 1 to 9:9 to 1.

In the embodiment of the present application, the mass ratio of the adhesive layer 20 to the conductive layer 21 may be 1, with the mass percentage of the outer layer 2 being 100): 9. 2: 8. 3: 7. 4: 6. 5: 5. 6: 4. 7: 3. 8: 2. 9:1 or any number within the above-defined range.

As an alternative embodiment, the porous carbon material 141 has an average pore size of no greater than 7nm.

In the embodiment of the application, the average pore diameter of the porous carbon material 141 is controlled to be nano-scale, so that the particle diameter of the silicon particles 1421 embedded in the porous carbon material 141 is also nano-scale, and the volume expansion of the silicon particles 1421 can be slowed down. The average pore diameter of the porous carbon material 141 may be 7nm, 5nm, 3nm, 1nm or any value within the above-defined range.

As an alternative example, the pore volume of porous carbon material 141 is 0.55mL/g to 0.95mL/g.

The embodiment of the application can change the doping amount of the silicon material 142 by adjusting the pore volume of the porous carbon material 141, thereby adjusting the capacitance of the battery. The pore volume of the porous carbon material 141 may be 0.55mL/g, 0.6mL/g, 0.65mL/g, 0.7mL/g, 0.8mL/g, 0.85mL/g, 0.9mL/g, 0.95mL/g, or any value within the above-defined range.

As an alternative embodiment, the porous carbon material 141 has a specific surface area of 1000m ²/g～3000m²/g.

In the embodiment of the present application, the specific surface area of the porous carbon material 141 is associated with the pore volume of the porous carbon material 141, and Kong Rongyue is larger, which means that the more pores are in the porous carbon material 141, the more silicon materials 142 can be deposited, and the more silicon materials 142 are deposited, the higher the material volume is. And under the condition of the same pore diameter, the larger the Kong Rongyue large specific surface area is. The specific surface area of the porous carbon material 141 may be 1000m ²/g、1500m²/g、2000m²/g、2500m²/g、3000m²/g or any value within the above-defined range.

As an alternative embodiment, the silicon material 142 accounts for 35-65% of the mass of the primary particles 13.

In embodiments of the present application, the silicon material 142 may be 35%, 40%, 50%, 60%, 65% or any value within the above-defined range by mass of the primary particles 13.

As an alternative embodiment, the shell layer 15 is amorphous carbon.

According to the embodiment of the application, the inner core 14 of the primary particles 13 is coated by amorphous carbon, so that on one hand, oxidation of the silicon material 142 in a subsequent process can be relieved, and on the other hand, the intermediate interface between the silicon material 142 and the secondary particles 1 is used, so that the bonding degree of the primary particles 13, the buffer layer 11 and the conductive additive 12 is favorably improved, and the volume expansion buffer capacity of the negative electrode is improved. And amorphous carbon may further fill pores of the porous carbon material 141 or close the surface of the porous carbon material 141, reducing the specific surface area of the porous carbon material 141 while avoiding oxidation of the silicon material 142 inside the porous carbon material 141.

As an alternative embodiment, the average thickness of the shell layer 15 is 2nm to 20nm.

The shell 15 in the embodiments of the present application has a nano-scale thickness and little capacity because the coating is too thick, which results in too high an intangible carbon ratio in the silicon-carbon composite and a reduced capacity. The average thickness of the shell layer 15 may be 2nm, 5nm, 10nm, 15nm, 20nm or any value within the above-defined range.

As an alternative embodiment, in the inner layer 3, the mass ratio of the buffer layer 11, the conductive additive 12 and the primary particles 13 is 5 to 20:0.05 to 1:79 to 94.95.

In the embodiment of the present application, the mass ratio of the buffer layer 11, the conductive additive 12 and the primary particles 13 may be 5:0.05:94.95, 10:0.08:89.92, 20:1:79 or any value within the above-defined range, with the mass percentage of the inner layer 3 being 100%.

As an alternative embodiment, the conductive additive 12 is one or both of single-walled carbon nanotubes and multi-walled carbon nanotubes.

The conductive additive 12 of embodiments of the present application is preferably a single-walled carbon nanotube. This is because the single-walled carbon nanotubes have a smaller diameter and a high aspect ratio than the multi-walled carbon nanotubes, and can increase the coverage rate and the connection strength of the primary particles 13, enhance the conductive contact between the primary particles 13, reduce the deactivation of the silicon material 142 in the primary particles 13, and significantly improve the coulombic efficiency and the cycle performance of the battery. Meanwhile, the single-wall carbon nano tube has a single-layer structure, so that the conductivity is better, and the addition amount can be lower.

As an alternative example, the primary particles 13 have an average particle diameter of 0.1 μm to 1 μm.

The average particle diameter of the primary particles 13 can reach submicron level, which is beneficial to improving the dynamic performance of the material, reducing the specific surface area of the primary particles 13 and reducing side reactions; and then secondary granulation is carried out to obtain micron-sized secondary particles 1, so that the transmission path of lithium ions in the primary particles 13 is reduced, the primary particles 13 are ensured to always keep conductive contact in the cyclic expansion and contraction process, and the conductivity and the dynamic performance of the silicon-carbon composite material are improved. The average particle diameter of the primary particles 13 may be 0.1 μm, 0.3 μm, 0.5 μm, 0.7 μm, 0.8 μm, 1 μm or any value within the above-defined range.

As an alternative embodiment, the specific surface area of the primary particles 13 is not more than 20m ²/g.

Because the porous carbon material 141 is used as the skeleton of the primary particles 13, the specific surface area of the deposited silicon material 142 is greatly reduced from thousands to below 20, so that the specific surface area of the primary particles 13 in the embodiment of the application is smaller, the coulomb efficiency of the battery is higher, and the energy density of the battery is improved. The specific surface area of the primary particles 13 may be 20m ²/g、10m²/g、5m²/g、1m²/g or any value within the above-defined range.

As an alternative example, the secondary particles 1 have an average particle diameter of 4 μm to 15. Mu.m.

The average particle size of the secondary particles 1 is in the micron level, the contact interface in the negative electrode of the lithium ion battery is greatly reduced, and the rate capability of the battery is obviously improved. The average particle diameter of the secondary particles 1 may be 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm or any value within the above-defined range.

As an alternative embodiment, the specific surface area of the secondary particles 1 is not more than 10m ²/g.

The secondary particles 1 of the embodiment of the application have small specific surface area, high coulomb efficiency of the battery and improved energy density of the battery. The specific surface area of the secondary particles 1 may be 10m ²/g、5m²/g、1m²/g or any value within the above-defined range.

As an alternative embodiment, the buffer layer 11 is amorphous carbon.

The amorphous carbon serves as a buffer layer, the amorphous carbon network structure can block the electrolyte from contacting the surface of the silicon material 142, the coulomb efficiency of the battery is improved, and meanwhile, the amorphous carbon network structure can effectively inhibit and buffer the expansion of the silicon material 142 and prevent the silicon material 142 from being gradually fused into particles with larger sizes in the charge-discharge process, so that the larger expansion and the failure of part of the silicon material 142 are caused.

Corresponding to the embodiment of the application function realizing device, the application also provides a preparation method of the silicon-carbon composite material, a lithium ion battery cathode, a lithium ion battery and corresponding embodiments.

The embodiment of the application also provides a preparation method of the silicon-carbon composite material, which comprises the following steps:

S1: placing the porous carbon material 141 in a sintering furnace, introducing silane gas in an inert atmosphere at 400-600 ℃, and depositing a silicon material 142 in the porous carbon material 141;

S2: after the deposition is completed, the silane gas is switched into acetylene gas, the temperature is increased to 500-600 ℃, and amorphous carbon is coated on the surface of the porous carbon material 141 to obtain primary particles 13;

S3: taking out the primary particles 13, and uniformly mixing the primary particles 13, the conductive additive 12, the dispersing agent and the carbon precursor to obtain mixed slurry;

S4: spray drying the mixed slurry to obtain a micron-sized secondary particle precursor;

S5: placing the secondary particle precursor into a sintering furnace, and sintering for a preset time in an inert atmosphere at 500-600 ℃ to obtain secondary particles; wherein the third preset temperature is not less than the second preset temperature.

In the embodiment of the application, the preset time can be 2.5h, 3h, 3.5h and 4h, and the preset time can be adjusted according to different requirements, and the application is not limited.

In the embodiment of the application, the carbon precursor can be glucose, and the carbon precursor is called an amorphous carbon buffer layer after sintering. Since the silicon particles in the porous carbon material 141 are already at the nano-scale and easily react with carbon at high temperature to generate silicon carbide, the subsequent heat treatment temperature is generally controlled to be not higher than 600 ℃ after the silicon is deposited. Glucose is more readily carbonized at low temperatures than is common for pitch, resin, and like carbon precursors.

In addition, the temperature in step S1 is generally 400 to 600 ℃, and the temperatures in steps S2 and S5 are preferably set to be slightly higher than the temperature in step S1, but too high a temperature may cause the reaction of nano-silicon with porous carbon to produce silicon carbide, so that setting at 500 to 600 ℃ is more preferable.

The embodiment of the application also provides a lithium ion battery cathode, which comprises the silicon-carbon composite material or the silicon-carbon composite material prepared by the preparation method of the silicon-carbon composite material.

The negative electrode comprises a negative electrode current collector and a negative electrode active slurry layer positioned on the negative electrode current collector, wherein the negative electrode active slurry layer comprises a negative electrode active material, a conductive agent and an adhesive, and the negative electrode active material comprises graphite and the silicon-carbon composite material.

Because the primary particles 13 of the embodiment of the application are not pure silicon materials, but silicon-carbon materials with a shell-core structure, the shell-core can enhance the tight connection of the silicon-carbon materials in the core 14, and the silicon materials 142 in the core 14 are embedded into the holes of the porous carbon materials 141, so that the expansion of the silicon materials 142 can be further inhibited, thereby greatly increasing the cycle performance of the battery.

The embodiment of the application also provides a lithium ion battery, which comprises the lithium ion battery cathode.

The lithium ion battery provided by the embodiment of the application further comprises a positive electrode, a diaphragm and electrolyte. The positive electrode comprises a positive electrode current collector and a positive electrode active slurry layer positioned on the positive electrode current collector, wherein the positive electrode active slurry layer comprises a positive electrode active material; the negative electrode comprises a negative electrode current collector and a negative electrode active slurry layer positioned on the negative electrode current collector, wherein the negative electrode active slurry layer comprises a negative electrode active material, a conductive agent and an adhesive, and the negative electrode active material comprises graphite and the silicon-carbon composite material.

For a further understanding of the present application, the present application is illustrated below in conjunction with the following examples, which are provided to illustrate the application and not to limit the scope of the application.

Example 1

1. Preparation of a silicon-carbon composite material:

A porous carbon material 141 with an average grain diameter of 0.8 mu m, an average pore diameter of 2nm and a pore volume of 0.9mL/g is selected, placed in a sintering furnace, silane (SiH ₄) gas is introduced under an inert atmosphere at 550 ℃, and 50% of silicon material 142 is deposited in the porous carbon material 141. Then, the silane gas was switched to acetylene gas, the temperature was increased to 600 ℃, and amorphous carbon was coated on the surface of the porous carbon material 141 in an amount of 3%, to obtain primary particles 13.

Taking out the primary particles 13, mixing the primary particles 13, single-wall carbon nano tube, dispersant CMC and glucose according to 80:0.8:1.2:18, preparing slurry with the solid content of 10%, and then spray drying to obtain the secondary particle precursor with the particle size of 10 mu m.

Then placing the secondary particle precursor in a sintering furnace, and sintering for 3 hours in an inert atmosphere at 600 ℃ to obtain a buffer layer 11: conductive additive 12: primary particles 13 = 5.54:0.94:93.52 secondary particles 1.

2. Preparing a negative plate:

Mixing the secondary particles 1 with graphite to prepare a cathode active material of 450mAh/g, and mixing the active materials according to the following proportion: and (2) a binder: conductive agent=95: 3:2 preparing the cathode slurry, and coating the cathode slurry on a copper foil to prepare the cathode plate.

3. Preparation of a lithium ion battery:

And assembling the negative plate, the lithium cobaltate positive plate, the electrolyte, the diaphragm, the aluminum plastic film and the like into the coiled soft-package battery.

Example 2

Unlike example 1, the following is: the surface of the secondary particles 1 is coated with an adhesive layer 20, which is a granular lithium polyacrylate material.

The preparation method comprises the following steps: the secondary particles 1 obtained in example 1 were mixed with granular lithium polyacrylate at a ratio of 100:1 preparing slurry with the solid content of 35%, spray drying to obtain a silicon-carbon composite material with the surface attached with granular lithium polyacrylate, and sintering for 3 hours at 180 ℃ in an inert atmosphere to obtain the silicon-carbon composite material with the surface coated with granular lithium polyacrylate.

Example 3:

Unlike example 2, the following is: a conductive layer 21 is also provided, which is laminated to the surface of the secondary particles 1 via an adhesive layer 20.

The preparation method comprises the following steps:

the secondary particles 1 obtained in example 1 were mixed with single-walled carbon nanotubes, a dispersant, and granular lithium polyacrylate at a ratio of 100:1:1.5:1, preparing slurry with the solid content of 12%, spray drying, and sintering for 3 hours at 180 ℃ in inert atmosphere to obtain the silicon-carbon composite material with the surface coated with granular lithium polyacrylate and single-wall carbon nano tubes.

The preparation method comprises the following steps:

The secondary particles 1 obtained in example 2 were mixed with single-walled carbon nanotubes and lithium dispersant according to a ratio of 100:1:1.5, preparing into slurry with the solid content of 12%, spray drying, and sintering for 3 hours at 180 ℃ in inert atmosphere to obtain the silicon-carbon composite material with the surface coated with granular lithium polyacrylate and single-wall carbon nano tubes.

Comparative example 1:

A porous carbon material 141 with an average particle size of 10 mu m, an average pore size of 2nm and a pore volume of 0.9mL/g is selected to be placed in a sintering furnace, silane (SiH ₄) gas is introduced under an inert atmosphere at 550 ℃, and 50% of silicon material is deposited in the porous carbon material. And then, switching the silane gas into acetylene gas, increasing the temperature to 600 ℃, and coating amorphous carbon on the surface of the porous carbon material 141 with the coating amount of 3 percent to obtain the silicon carbon material.

4. Performance testing

The lithium ion batteries manufactured in the above examples and comparative examples were subjected to cycle life test in accordance with the following methods, and the test data in table 1 were calculated.

The testing method comprises the following steps: the batteries were subjected to a 1C/1C charge-discharge cycle test at 25℃in the range of 3V to 4.5V, and the capacity retention rate of each battery after 500 weeks of cycle was calculated, respectively.

The calculation formula is as follows: capacity retention (%) = discharge capacity corresponding to cycle number discharge capacity (mAh)/discharge capacity of the third cycle (mAh) x 100%.

Table 1 test results

The test results are shown in fig. 6 and 7, fig. 6 is a schematic view of the battery cycle performance test results of each of the examples and comparative examples (example 3 was prepared by the method one), and fig. 7 is a schematic view of the battery cycle performance test results of example 3 (prepared by the method one) and comparative example 1.

By combining the related data of table 1, fig. 6 and fig. 7, it was found by comparing examples 1 to 3 with comparative example 1 that the cycle life of the lithium ion battery prepared by using the silicon carbon composite material provided in the examples of the present application was greatly improved, and the battery capacity retention rate of coating the adhesive layer 20 and the conductive layer 21 on the outer surface of the secondary particle 1 was the highest, so that the cycle performance of the battery was improved by compounding the adhesive layer 20 and the conductive layer 21 on the outer surface of the secondary particle 1.

Comparing the test results of the two preparation methods in example 3, it is found that the battery cycle performance prepared by the first method and the battery cycle performance prepared by the second method have no obvious difference, and it is clear that the coating difference between the coating binder and the coating carbon nano tube is not obvious.

The aspects of the present application have been described in detail hereinabove with reference to the accompanying drawings. In the foregoing embodiments, the descriptions of the embodiments are focused on, and for those portions of one embodiment that are not described in detail, reference may be made to the related descriptions of other embodiments. Those skilled in the art will also appreciate that the acts and modules referred to in the specification are not necessarily required for the present application. In addition, it can be understood that the steps in the method of the embodiment of the present application may be sequentially adjusted, combined and pruned according to actual needs, and the modules in the device of the embodiment of the present application may be combined, divided and pruned according to actual needs.

The foregoing description of embodiments of the application has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the various embodiments described. The terminology used herein was chosen in order to best explain the principles of the embodiments, the practical application, or the improvement of technology in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims

1. A silicon-carbon composite material of a lithium ion battery, characterized by comprising secondary particles (1), the secondary particles (1) comprising a buffer layer (11), a conductive additive (12) and a plurality of primary particles (13), the conductive additive (12) and the primary particles (13) being dispersed within the buffer layer (11); the primary particles (13) comprise an inner core (14) and a shell layer (15) coating the outer side of the inner core (14), wherein the inner core (14) comprises a porous carbon material (141) and a silicon material (142) embedded in the porous carbon material (141).

2. The silicon-carbon composite material according to claim 1, further comprising an outer layer (2) and an inner layer (3), the inner layer (3) being the secondary particles (1), the outer layer (2) comprising an adhesive layer (20), the adhesive layer (20) being adhered to the outer surface of the secondary particles (1).

3. The silicon-carbon composite according to claim 2, wherein the bonding layer (20) is insoluble in water; and/or the mass ratio of the adhesive layer (20) to the secondary particles (1) is 0.03-2: 100; and/or the mass ratio of the outer layer (2) to the inner layer (3) is 0.03-2: 100; and/or, in the inner layer (3), the mass ratio of the buffer layer (11), the conductive additive (12) and the primary particles (13) is 5 to 20:0.05 to 1:79 to 94.95.

4. A silicon-carbon composite material according to claim 3, wherein the adhesive layer (20) is made of a cross-linked linear lithium polyacrylate material or a granular lithium polyacrylate material.

5. The silicon carbon composite according to claim 2, wherein the outer layer (2) further comprises a conductive layer (21), the conductive layer (21) being composited to the surface of the secondary particles (1) by the adhesive layer (20).

6. The silicon-carbon composite according to claim 5, wherein the conductive layer (21) is one or both of single-walled carbon nanotubes and multi-walled carbon nanotubes; and/or, in the outer layer (2), the mass ratio of the adhesive layer (20) to the conductive layer (21) is 1-9: 9 to 1.

7. The silicon-carbon composite material according to any one of claims 1 to 6, wherein the silicon material (142) comprises at least one of a granular form formed of a single silicon particle (1421) and a linear form formed by arranging a plurality of silicon particles (1421); and/or, the porous carbon material (141) has an average pore size of no more than 7nm; and/or the pore volume of the porous carbon material (141) is 0.55-0.95 mL/g; and/or the porous carbon material (141) has a specific surface area of 1000m ²/g～3000m²/g; and/or the silicon material (142) accounts for 35-65% of the mass of the primary particles (13); and/or the shell layer (15) is amorphous carbon; and/or the average thickness of the shell layer (15) is 2 nm-20 nm; and/or the conductive additive (12) is one or two of single-wall carbon nanotubes and multi-wall carbon nanotubes; and/or the primary particles (13) have an average particle diameter of 0.1-1 [ mu ] m; and/or the specific surface area of the primary particles (13) is not more than 20m ²/g; and/or the secondary particles (1) have an average particle diameter of 4-15 [ mu ] m; and/or the specific surface area of the secondary particles (1) is not more than 10m ²/g; and/or the buffer layer (11) is amorphous carbon.

8. A method of producing the silicon-carbon composite material as defined in any one of claims 1 to 7, comprising:

Placing the porous carbon material (141) in a sintering furnace, introducing silane gas in an inert atmosphere at 400-600 ℃, and depositing a silicon material (142) in the porous carbon material (141);

After the deposition is completed, the silane gas is switched into acetylene gas, the temperature is increased to 500-600 ℃, amorphous carbon is coated on the surface of the porous carbon material (141), and primary particles (13) are obtained;

taking out the primary particles (13), and uniformly mixing the primary particles (13), the conductive additive (12), the dispersing agent and the carbon precursor to obtain mixed slurry;

and (3) placing the secondary particle precursor into a sintering furnace, and sintering for a preset time in an inert atmosphere at 500-600 ℃ to obtain the secondary particles (1).

9. A lithium ion battery anode, which is characterized by comprising the silicon-carbon composite material according to any one of claims 1 to 7 or the silicon-carbon composite material prepared by the preparation method of the silicon-carbon composite material according to claim 8.

10. A lithium ion battery comprising the lithium ion battery anode of claim 9.