Negative electrode material and preparation method therefor, and electrochemical device

Abstract

The present application provides a negative electrode material and a preparation method therefor, and an electrochemical device using the negative electrode material. The negative electrode material comprises: a core, the core comprising silicon-based particles; a first layer comprising carbon, the first layer being present outside the core; a second layer comprising a first conductive material and a metal oxide, the second layer being present outside the first layer; and a third layer comprising a second conductive material and a polymer, the third layer being present outside the second layer. The negative electrode material provided in the present application can reduce the volume expansion of the electrochemical device after cycling, and improve the cycling performance of the electrochemical device.

Description

A negative electrode material and its preparation method, and an electrochemical device thereof.

[0001] This application claims priority to Chinese Patent Application No. 202410851029.4, filed on June 27, 2024, entitled "An Anode Material and Its Preparation Method and Electrochemical Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical energy storage, and in particular to a negative electrode material and its preparation method, and an electrochemical device using the negative electrode material. Background Technology

[0003] Silicon is widely used in anode materials due to its high specific capacity. Furthermore, silicon anodes possess high energy density and suitable operating voltage, showing great promise for future applications. However, silicon expands by up to 400% in volume after lithium intercalation. The repeated expansion and contraction of silicon-based anode materials during cycling leads to the destruction and growth of the solid electrolyte interphase (SEI) film and the fragmentation of silicon particles, resulting in significant electrode expansion and rapid capacity decay. This affects the thickness and cycle performance of electrochemical devices, limiting the large-scale application of silicon anode materials in lithium-ion batteries. Summary of the Invention

[0004] The purpose of this application is to provide a negative electrode material and its preparation method, as well as an electrochemical device using the negative electrode material, to improve the cycle performance of the electrochemical device. The specific technical solution is as follows:

[0005] The first aspect of this application provides a negative electrode material comprising: a core containing silicon-based particles; a first layer existing outside the core; a second layer existing outside the first layer; and a third layer existing outside the second layer. The first layer contains carbon; the second layer contains a first conductive material and a metal oxide; and the third layer contains a second conductive material and a polymer. The introduction of the carbon-containing first layer can improve the gas generation problem caused by direct contact between the silicon-based particles and water during the stirring process of preparing the slurry. The introduction of the second layer can reduce side reactions between the negative electrode material and the electrolyte, improving the cycle performance of the lithium-ion battery. The introduction of the third layer can reduce the thickness expansion rate of the lithium-ion battery and reduce the specific surface area of ​​the silicon-based particles, improving the initial efficiency of the lithium-ion battery. The introduction of the first and second conductive materials enables the negative electrode material to have good conductivity. The synergistic effect of the three layers reduces the expansion rate of the lithium-ion battery and improves its cycle performance.

[0006] In one embodiment of this application, the silicon-based particles comprise at least one of silicon-carbon particles or silicon-oxygen particles.

[0007] In one embodiment of this application, the metal oxide includes at least one of aluminum oxide or titanium oxide.

[0008] In one embodiment of this application, the polymer comprises polyurethane.

[0009] In one embodiment of this application, the first conductive material and the second conductive material are each independently selected from at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, and conductive carbon black.

[0010] By selecting silicon-based particles within the aforementioned range, the negative electrode can achieve a higher capacity. Therefore, applying the negative electrode to lithium-ion batteries results in higher energy density and better cycle performance. Selecting metal oxides within the aforementioned range reduces the erosion of the negative electrode by electrolyte decomposition products, improving the cycle performance of the lithium-ion battery. Choosing polyurethane polymers reduces the volume expansion of the negative electrode, decreasing the thickness expansion rate of the lithium-ion battery. Simultaneously, it lowers the specific surface area of ​​the negative electrode material, improving its initial charge-discharge efficiency. Selecting the first and second conductive materials within the aforementioned range mitigates the decrease in conductivity of the negative electrode material caused by metal oxide and polymer coatings.

[0011] In one embodiment of this application, the silicon content by mass is 40% to 50% based on the mass of the negative electrode material. When the silicon content by mass is within the above range, the lithium-ion battery using the negative electrode material of this application has both high reversible capacity and good cycle performance, thereby improving the energy density and cycle performance of the lithium-ion battery.

[0012] In one embodiment of this application, the negative electrode material satisfies at least one of the following: (1) the Dv50 of the negative electrode material is 6 μm to 10 μm; (2) the Dv90 of the negative electrode material is less than or equal to 30 μm; (3) based on the mass of the negative electrode material, the mass percentage of carbon in the first layer is 1% to 5%; (4) based on the mass of the negative electrode material, the mass percentage of metal oxide is 0.2% to 1%; (5) based on the mass of the negative electrode material, the mass percentage of polymer is 0.9% to 9%; (6) based on the mass of the negative electrode material, the mass percentage of the first conductive material is 0.1% to 0.4%; (7) based on the mass of the negative electrode material, the mass percentage of the second conductive material is 0.1% to 1%. When the negative electrode material satisfies at least one of the above characteristics, the initial charge-discharge efficiency of the negative electrode material is improved, and the cycle performance of the lithium-ion battery is enhanced, while the thickness expansion rate of the lithium-ion battery is reduced.

[0013] In one embodiment of this application, the mass ratio of the polymer to the second conductive material is 9:1 to 9:2, based on the mass of the negative electrode material. When the mass ratio of the polymer to the second conductive material is within the above range, the negative electrode material exhibits both good performance and good conductivity.

[0014] The second aspect of this application provides a method for preparing the negative electrode material provided in the first aspect of this application, comprising: providing silicon-based particles; carbon coating the silicon-based particles to obtain a first intermediate; dispersing the first intermediate, an organometallic salt, polyvinylpyrrolidone, and a first conductive material in ethanol to obtain a first dispersion; fully dispersing and stirring the first dispersion; spray drying and heat-treating at a temperature of 500°C to 600°C to obtain a second intermediate, wherein the organometallic salt includes at least one of aluminum isopropoxide or titanium isopropoxide; dispersing the second intermediate in water to obtain a second dispersion; dispersing the polymer and the second conductive material in water to obtain a third dispersion; mixing the second dispersion and the third dispersion and stirring evenly; and spray drying to obtain the negative electrode material. The above preparation method is simple, easy to operate, and suitable for industrial production. The coating can be partial or complete.

[0015] In one embodiment of this application, carbon coating involves placing silicon-based particles in a fluidized bed, introducing a carbon source gas at a temperature of 500°C to 600°C, and reacting for 2 to 3 hours to obtain a first intermediate. The carbon source gas contains at least one of acetylene, methane, and propylene. When the reaction temperature and time for carbon coating are within the above range, the carbon source gas can be cracked and deposited on the outside of the silicon-based particles at a relatively fast cracking rate and with high utilization.

[0016] A third aspect of this application provides an electrochemical device comprising a positive electrode, a separator, an electrolyte, and a negative electrode, wherein the negative electrode comprises a negative electrode active material layer, and the negative electrode active material layer comprises the negative electrode material provided in the first aspect of this application.

[0017] In one embodiment of this application, the electrolyte includes an additive comprising at least one selected from 1,3,6-hexanetrionitrile, 1,2,3-propanetricarbonyl, or 1,2,3-tris(2-cyanoxy)propane, wherein the mass percentage of the additive is 0.1% to 5% based on the total mass of the electrolyte. When the mass percentage of the additive is within the above range, it can improve the erosion of the negative electrode active material by electrolyte decomposition products, thereby enhancing the high-temperature storage performance of the lithium-ion battery.

[0018] A fourth aspect of this application provides an electrical device that includes the electrochemical device provided in the third aspect of this application.

[0019] The beneficial effects of this application are:

[0020] The negative electrode material provided in this application incorporates a first carbon layer, which mitigates the gas generation problem caused by direct contact between silicon-based particles and water during contact with aqueous solvents. The second layer reduces direct contact between the electrolyte and silicon-based particles, minimizing side reactions between the negative electrode material and the electrolyte, thereby improving the cycle performance of the lithium-ion battery. Furthermore, the second layer improves the composition of the SEI film, further enhancing the cycle performance. The third layer, through its excellent adhesion, forms a stable coating layer and synergizes with the first and second layers to form the negative electrode material, reducing volume expansion and thickness expansion rate of the lithium-ion battery. It also reduces the specific surface area of ​​the silicon-based particles, improving the initial charge-discharge efficiency of the negative electrode material. Additionally, the introduction of the first and second conductive materials endows the negative electrode material with good conductivity. Therefore, the negative electrode material provided in this application, through the synergistic effect of the three coating layers, reduces the expansion rate of the lithium-ion battery and improves its cycle performance. Attached Figure Description

[0021] The accompanying drawings, which are provided to further understand this application and constitute a part of this application, illustrate exemplary embodiments of this application and are used to explain this application, but do not constitute an undue limitation of this application.

[0022] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these drawings.

[0023] Figure 1 is a schematic diagram of the structure of the negative electrode material prepared in Example 1 of this application;

[0024] Figure 2 is a comparison of the cycle performance of lithium-ion batteries assembled with the negative electrode materials in Examples 1-1 and Comparative Examples 1 to 3 at 25°C.

[0025] Figure 3 is a comparison of the cycle performance of lithium-ion batteries assembled with the negative electrode materials in Examples 1-1 and Comparative Examples 1 to 3 at 45°C.

[0026] Figure 4 is a comparison of the expansion rates of lithium-ion batteries assembled with the negative electrode materials in Examples 1-1 and Comparative Examples 1 to 3 at 25°C.

[0027] Figure 5 is a comparison of the expansion rates of lithium-ion batteries assembled with the negative electrode materials in Examples 1-1 and Comparative Examples 1 to 3 at 45°C. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are merely some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0029] It should be noted that, in the specific embodiments of this application, lithium-ion batteries are used as an example of electrochemical devices to explain this application, but the electrochemical devices of this application are not limited to lithium-ion batteries.

[0030] The first aspect of this application provides a negative electrode material comprising: a core containing silicon-based particles; a first layer existing outside the core; a second layer existing outside the first layer; and a third layer existing outside the second layer; wherein the first layer contains carbon; the second layer contains a first conductive material and a metal oxide; and the third layer contains a second conductive material and a polymer. In this application, the first layer exists entirely or partially outside the core, the second layer exists entirely or partially outside the first layer, and the third layer exists entirely or partially outside the second layer. Specifically, a schematic diagram of the negative electrode material is shown in Figure 1, with the layers arranged from the inside out as a core 11, a first layer 12, a second layer 13, and a third layer 14. In one embodiment of this application, a mutually soluble layer may be formed between the core and the first layer. In another embodiment of this application, a mutually soluble layer may be formed between the first layer and the second layer. In yet another embodiment of this application, a mutually soluble layer may be formed between the second layer and the third layer. The mutually soluble layers described above are not the first, second, or third layers described in this application.

[0031] Not limited to any particular theory, the inventors of this application have discovered that the introduction of a carbon-containing first layer can improve the gas generation problem caused by direct contact between silicon-based particles and water during contact with aqueous solvents. The introduction of a second layer can reduce direct contact between the electrolyte and silicon-based particles, reducing side reactions between the negative electrode material and the electrolyte, thereby improving the cycle performance of the lithium-ion battery. Furthermore, the introduction of the second layer can improve the composition of the SEI film, further enhancing the cycle performance of the lithium-ion battery. The introduction of a third layer, through its excellent adhesion, forms a stable coating layer, which, together with the first and second layers, forms the negative electrode material, reducing the volume expansion of the negative electrode, decreasing the thickness expansion rate of the lithium-ion battery, and reducing the specific surface area of ​​the silicon-based particles, thus improving the initial charge-discharge efficiency of the negative electrode material. Additionally, the introduction of the first and second conductive materials enables the negative electrode material to possess good conductivity. Therefore, the negative electrode material provided by this application, through the synergistic effect of the three coating layers, reduces the expansion rate of the lithium-ion battery and improves its cycle performance.

[0032] In one embodiment of this application, the silicon-based particles comprise at least one of silicon-carbon particles or silicon-oxygen particles.

[0033] In one embodiment of this application, the metal oxide includes at least one of aluminum oxide or titanium oxide.

[0034] In one embodiment of this application, the polymer comprises polyurethane.

[0035] In one embodiment of this application, the first conductive material and the second conductive material are each independently selected from at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, or conductive carbon black.

[0036] Without being limited to any particular theory, the inventors of this application have discovered that selecting silicon-based particles within the aforementioned range can result in a negative electrode with higher capacity, thereby enabling the application of the negative electrode in lithium-ion batteries to achieve higher energy density. Selecting metal oxides within the aforementioned range can reduce the erosion of the negative electrode by electrolyte decomposition products, improving the cycle performance of the lithium-ion battery. Selecting polyurethane polymers, which have good adhesion, can form a stable coating layer and bond the second intermediate together to form the negative electrode material, reducing the volume expansion of the negative electrode and thus lowering the thickness expansion rate of the lithium-ion battery. Simultaneously, the specific surface area of ​​the negative electrode material is also reduced, improving the initial charge-discharge efficiency of the negative electrode material. Selecting the first and second conductive materials within the aforementioned range enables the negative electrode material to possess good conductivity.

[0037] In one embodiment of this application, the silicon-based particles satisfy at least one of the following: (1) the specific surface area of ​​the silicon-based particles is 0.5 m². 2 / g to 10m 2 / g; (2) The particle size Dv50 of the silicon-based particles is 1.5μm to 2.5μm; (3) The particle size Dv90 of the silicon-based particles is less than or equal to 10μm. This application does not impose any particular limitation on particle classification technology, as long as it can achieve the purpose of this application. The particle classification technology can be any classification method known in the art, such as jet classification and cyclone classification. In this application, Dv50 refers to the particle size that reaches 50% of the volume accumulation in the particle size distribution based on the volume of the material; Dv90 refers to the particle size that reaches 90% of the volume accumulation in the particle size distribution based on the volume of the material.

[0038] In one embodiment of this application, the specific surface area of ​​the silicon-based particles can be 0.5 m². 2 / g、1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g or a range consisting of any two of these values; the shape of the silicon-based particles can be at least one of spherical, near-spherical, sheet-like, or blocky; not limited to any theory, the inventors of this application have discovered that the specific surface area of ​​the silicon-based particles is 0.5m². 2 / g to 10m 2 At / g, it can improve the gas generation problem caused by direct contact between silicon-based particles and water during stirring with aqueous solvents, and at the same time, it can achieve a high coating degree in subsequent coating layers.

[0039] In one embodiment of this application, the particle size Dv50 of the silicon-based particles can be 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, or a range of any two values ​​therein, without being limited to any theory. The inventors of this application have discovered that when the particle size Dv50 of the silicon-based particles is between 1.5μm and 2.5μm, Li + The diffusion path is relatively short, which can improve the ionic conductivity of the negative electrode material and reduce the volume expansion of silicon-based particles.

[0040] In one embodiment of this application, the particle size Dv90 of the silicon-based particles can be 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, or a range of any two values ​​therein, without being limited to any theoretical value. The inventors of this application have discovered that when the particle size Dv90 of the silicon-based particles is less than or equal to 10μm, it is beneficial for the silicon-based particles to be uniformly dispersed during the coating process, thereby controlling the particle size of the negative electrode material and enabling it to improve the performance of Li when used in the negative electrode. + This improves the transport of energy, thereby enhancing the cycle performance and expansion performance of lithium-ion batteries.

[0041] In one embodiment of this application, the silicon content by mass percentage is 40% to 50% based on the mass of the negative electrode material. For example, the silicon content by mass percentage can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or a range of any two of these values. Without being limited to any theory, the inventors of this application have found that when the silicon content by mass percentage is 40% to 50%, the negative electrode material exhibits high reversible capacity and initial charge-discharge efficiency, while also contributing to improved energy density and cycle performance of the lithium-ion battery.

[0042] In one embodiment of this application, the particle size Dv50 of the negative electrode material is from 6 μm to 10 μm. For example, the particle size Dv50 of the negative electrode material can be 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, or a range of any two of these values. Without being limited to any theory, the inventors of this application have discovered that by controlling the particle size Dv50 of the negative electrode material to be from 6 μm to 10 μm, Li + The diffusion path is shorter, thus improving the efficiency of Li. + The high ionic conductivity can improve the initial charge and discharge efficiency of the negative electrode material; at the same time, it can also reduce electrolyte consumption, increase the compaction density of the material, and give the negative electrode material high ionic conductivity and high rate performance, thereby improving the energy density and cycle performance of lithium-ion batteries.

[0043] In one embodiment of this application, the particle size Dv90 of the negative electrode material is less than or equal to 30 μm. For example, the particle size Dv90 of the negative electrode material can be 12 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, or a range of any two of these values. Without being limited to any theory, the inventors of this application have discovered that a particle size Dv90 of the negative electrode material less than or equal to 30 μm can improve the dispersion uniformity of the negative electrode material in the preparation of the negative electrode slurry, improve the consistency of the coating weight and thickness of the negative electrode sheet, make the expansion and contraction of each layer of the negative electrode sheet more consistent during charge and discharge cycles, and make the stress distribution caused by expansion and contraction more consistent, reducing the possibility of stress concentration causing the negative electrode material layer to peel off from the current collector, thereby improving the cycle performance and expansion performance of the lithium-ion battery.

[0044] In one embodiment of this application, the carbon content in the first layer is 1% to 5% by mass, based on the mass of the negative electrode material. For example, the carbon content in the first layer can be 1%, 1.5%, 2%, 2.5%, 3%, 4%, 4.5%, 5%, or a range of any two of these values. When the carbon content in the first layer is within the above range, the contact between the active silicon in the silicon-based particles and air or solution can be effectively reduced, protecting the active silicon and enabling the negative electrode material to have higher specific capacity and stability, thereby improving the cycle stability and capacity of the lithium-ion battery.

[0045] In one embodiment of this application, the mass percentage of the metal element in the metal oxide is 0.2% to 1%, based on the mass of the negative electrode material. For example, the mass percentage of the metal oxide can be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range consisting of any two of these values. When the mass percentage of the metal oxide is within the above range, the composition of the SEI film can be improved, the erosion of the negative electrode by electrolyte decomposition products can be reduced, and the cycle performance of the lithium-ion battery can be improved.

[0046] In one embodiment of this application, the polymer mass percentage is 0.9% to 9% based on the mass of the negative electrode material. For example, the polymer mass percentage can be 0.9%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or a range of any two of these values. When the polymer mass percentage is within the above range, its good adhesion allows for the formation of a stable coating layer, which binds the second intermediate together to form the negative electrode material, reducing the volume expansion of the negative electrode, decreasing the thickness expansion rate of the lithium-ion battery, and simultaneously reducing the specific surface area of ​​the negative electrode material.

[0047] In one embodiment of this application, the mass percentage of the first conductive material is 0.1% to 0.4% based on the mass of the negative electrode material. For example, the mass percentage of the first conductive material can be 0.1%, 0.2%, 0.3%, 0.4%, or a range consisting of any two of these values. When the mass percentage of the first conductive material is within the above range, the negative electrode material can still have good conductivity while introducing the second layer of metal oxide.

[0048] In one embodiment of this application, the mass percentage of the second conductive material is 0.1% to 1%, based on the mass of the negative electrode material. For example, the mass percentage of the second conductive material can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or a range consisting of any two of these values. When the mass percentage of the second conductive material is within the above range, the negative electrode material can still exhibit good conductivity while introducing a polymer-containing third layer.

[0049] In one embodiment of this application, the mass ratio of the polymer to the second conductive material is 9:1 to 9:2, based on the mass of the negative electrode material. For example, the mass ratio of the second conductive material to the polymer can be 9:1, 9:1.1, 9:1.2, 9:1.3, 9:1.4, 9:1.5, 9:1.6, 9:1.7, 9:1.8, 9:1.9, 9:2, or a range of any two of these values. When the mass ratio of the polymer to the second conductive material is within the above range, the polymer, through its good adhesion, forms a stable coating layer and bonds the second intermediate together to form the negative electrode material. This reduces the volume expansion of the negative electrode while the negative electrode material has good conductivity, thus reducing the thickness expansion rate of the lithium-ion battery.

[0050] The second aspect of this application provides a method for preparing the negative electrode material provided in the first aspect of this application, comprising: providing silicon-based particles; carbon-coating the silicon-based particles to obtain a first intermediate; dispersing the first intermediate, an organometallic salt, polyvinylpyrrolidone, and a first conductive material in ethanol to obtain a first dispersion; thoroughly dispersing and stirring the first dispersion; spray drying and heat-treating at a temperature of 500°C to 600°C to obtain a second intermediate, wherein the organometallic salt includes at least one of aluminum isopropoxide or titanium isopropoxide; dispersing the second intermediate in water to obtain a second dispersion; dispersing the polymer and the second conductive material in water to obtain a third dispersion; mixing the second dispersion and the third dispersion and stirring evenly; and spray drying to obtain the negative electrode material. The above preparation method is simple in steps, easy to operate, and suitable for industrial production.

[0051] In one embodiment of this application, carbon coating involves placing silicon-based particles in a fluidized bed, introducing a carbon source gas at a temperature of 500°C to 650°C, and reacting for 2 to 3 hours to obtain a first intermediate. The carbon source gas contains at least one of acetylene, methane, and propylene. For example, the coating temperature can be 500°C, 510°C, 520°C, 530°C, 540°C, 650°C, 560°C, 570°C, 580°C, 590°C, 600°C, 610°C, 620°C, 630°C, 640°C, 650°C, or a range of any two of these values; the coating time can be 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, or a range of any two of these values. Without being limited to any particular theory, the inventors of this application have discovered that after the carbon source gas is cracked at high temperatures, it is deposited on the outside of the target particles. Within a suitable temperature range, the higher the deposition temperature, the faster the cracking rate of the carbon source gas and the higher its utilization rate, resulting in a faster coating layer growth rate. At the same deposition temperature, the deposition time determines the thickness and integrity of the coating layer. By controlling the carbon coating time and temperature, the carbon material content during the carbon coating process can be controlled.

[0052] In one embodiment of this application, a carbon source gas and an inert gas are mixed and then introduced into a fluidized bed. The inert gas includes at least one of nitrogen or argon. Based on the volume of the mixed gas, the volume percentage of the carbon source gas is 10% to 50%. For example, the volume percentage of the carbon source gas can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, or a range of any two of these values. Without being limited to any theory, the inventors of this application have found that the use of an inert gas is beneficial for improving the uniformity of carbon element distribution in the shell.

[0053] In one embodiment of this application, the Dv50 of the first intermediate is from 1.5 μm to 2.5 μm. For example, the particle size Dv50 can be 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, or a range of any two of these values.

[0054] In one embodiment of this application, the mass ratio of the first intermediate, the organometallic salt, polyvinylpyrrolidone, and the first conductive material is 100:(0.4 to 4):(0.4 to 4):(0.11 to 0.44). Without being limited to any theory, the inventors of this application have discovered that when the mass ratio of the first intermediate, the organometallic salt, polyvinylpyrrolidone, and the first conductive material is within the above range, the organometallic salt and the first conductive material can be better coated on the outside of the first intermediate under the binding effect of polyvinylpyrrolidone.

[0055] In one embodiment of this application, the solid content of the first dispersion is 18% to 22%. For example, the solid content of the first dispersion can be 18%, 19%, 20%, 21%, 22%, or a range consisting of any two of these values.

[0056] In one embodiment of this application, the mass ratio of the first intermediate to the mixture of the metal oxide and the first conductive material is 100:1 to 100:4. For example, the mass ratio of the first intermediate to the mixture of the metal oxide and the first conductive material can be 100:1, 100:1.5, 100:2, 100:2.5, 100:3, 100:3.5, 100:4, or a range of any two of these values. Without being limited to any theory, the inventors of this application have discovered that when the mass ratio of the first intermediate to the mixture of the metal oxide and the first conductive material is 100:1 to 100:4, the erosion of the negative electrode material by electrolyte decomposition products can be reduced, improving the cycle performance of the lithium-ion battery. Simultaneously, the mass percentage of silicon in the negative electrode material can be kept within the range specified in this application, thereby enabling the negative electrode material to possess a higher reversible capacity.

[0057] In one embodiment of this application, the inlet air temperature for spray drying of the second intermediate is 170°C to 190°C, and the outlet air temperature is 90°C to 100°C. Without being limited to any theory, the inventors of this application have discovered that when the spray drying parameters are within the above range, it is possible to control the particle size distribution of the second intermediate after spray drying while taking into account both the drying capacity and production capacity of the machine, and at the same time, to reduce particle size increase caused by particle adhesion.

[0058] In one embodiment of this application, the heat treatment process of the second intermediate at 500°C to 600°C involves placing the dried first intermediate coated with aluminum isopropoxide and polyvinylpyrrolidone into a graphite crucible, placing it in a box furnace, closing the furnace door, and then passing nitrogen gas at a flow rate of 1.5L / min to 2.5L / min for 20 to 40 minutes. After that, heating is turned on, and the temperature is increased to 500°C to 600°C at a heating rate of 5°C / min to 10°C / min. The temperature is then maintained for 0.5 to 3 hours. After that, the heating is turned off, nitrogen gas is passed through again, and the mixture is cooled to room temperature. The crucible is then removed to obtain the second intermediate.

[0059] In one embodiment of this application, the Dv50 of the second intermediate is from 1.6 μm to 2.7 μm. For example, the particle size Dv50 can be 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, 2 μm, 2.1 μm, 2.2 μm, 2.3 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.7 μm, or a range consisting of any two of these values.

[0060] In one embodiment of this application, the solid content of the second dispersion is 20% to 35%. For example, the solid content of the second dispersion can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, or a range of any two of these values.

[0061] In one embodiment of this application, the mass ratio of the polymer to the second conductive material is 9:1 to 9:2, based on the mass of the negative electrode material. For example, the mass ratio of the polymer to the second conductive material can be 9:1, 9:1.1, 9:1.2, 9:1.3, 9:1.4, 9:1.5, 9:1.6, 9:1.7, 9:1.8, 9:1.9, 9:2, or a range of any two of these values. Without being limited to any particular theory, the inventors of this application have found that the introduction of a conductive material can alleviate the problem of reduced conductivity of the negative electrode material caused by polymer coating.

[0062] In one embodiment of this application, the solid content of the third dispersion is 18% to 22%. For example, the solid content of the third dispersion may be 18%, 18.5%, 19%, 19.5%, 20%, 20.5%, 21%, 21.5%, 22%, or a range of any two of these values.

[0063] In one embodiment of this application, the mass ratio of the mixture of the second intermediate and the binder and the second conductive material is 100:1 to 100:10. For example, the mass ratio of the mixture of the second intermediate and the binder and the second conductive material can be 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, or a range of any two of these values. Not limited to any particular theory, the inventors of this application have discovered that when the mass ratio of the mixture of the second intermediate and the polymer and the second conductive material is 100:1 to 100:10, due to the better adhesion of the polymer, the volume expansion of the negative electrode material is reduced, the thickness expansion rate of the lithium-ion battery is decreased, and the specific surface area of ​​the negative electrode material is reduced, thus improving the initial charge-discharge efficiency. The addition of the conductive material can alleviate the problem of reduced conductivity of the negative electrode material caused by polyurethane coating.

[0064] In one embodiment of this application, the solid content of the mixed slurry after mixing the second dispersion and the third dispersion is 20% to 25%. For example, the solid content of the mixed slurry after mixing the second dispersion and the third dispersion can be 20%, 21%, 22%, 23%, 24%, 25%, or a range of any two of these values.

[0065] In one embodiment of this application, the inlet air temperature for spray drying of the negative electrode material is 200°C to 230°C, and the outlet air temperature is 100°C to 110°C. Without being limited to any theory, the inventors of this application have discovered that when the spray drying parameters are within the above range, the particle size distribution of the negative electrode material after spray drying can be controlled while taking into account both the drying capacity and production capacity of the equipment.

[0066] In one embodiment of this application, the covering involved in this application may be partial covering or complete covering.

[0067] A third aspect of this application provides an electrochemical device comprising a positive electrode, a separator, an electrolyte, and a negative electrode, wherein the negative electrode comprises a negative electrode active material layer, and the negative electrode active material layer comprises the negative electrode material of the first aspect of this application.

[0068] In one embodiment of this application, the electrolyte includes an additive comprising at least one selected from 1,3,6-hexanetrionitrile, 1,2,3-propanetricarbonyl, or 1,2,3-tris(2-cyanoxy)propane, wherein the mass percentage of the additive is 0.1% to 5% based on the total mass of the electrolyte. For example, the mass percentage of the additive can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4.5%, 5%, or a range of any two of these values. Without being limited to any theory, the inventors of this application have discovered that the above-mentioned additive can reduce the reactivity of the positive electrode transition metal, thereby reducing the degradation of the electrolyte during cycling, significantly improving the erosion of the negative electrode active material by electrolyte decomposition products, and thus improving the high-temperature storage performance of lithium-ion batteries.

[0069] In this application, the electrolyte also contains a lithium salt. There are no particular limitations on the lithium salt used; any lithium salt known in the art can be used, as long as it achieves the purpose of this application. For example, the lithium salt can be selected from at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, and LiPO2F2. Based on the mass of the electrolyte, the mass percentage of the lithium salt can be from 8% to 15%, for example, the mass percentage of the lithium salt can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, or a range consisting of any two of these values.

[0070] In this application, the electrolyte also includes a base solvent. This application does not have any particular restrictions on the base solvent, as long as it can achieve the purpose of this application. For example, the base solvent may include, but is not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds or other organic solvents.

[0071] The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The aforementioned chain carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are not limited to, at least one of 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. Other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of the base solvent in the electrolyte, as long as the purpose of this application is achieved.

[0072] In this application, the electrochemical device further includes a positive electrode, which comprises a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The aforementioned "positive electrode active material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode active material layer can be disposed on one surface of the positive electrode current collector along its own thickness direction, or it can be disposed on two surfaces of the positive electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the positive electrode current collector, or it can be a partial surface area of ​​the positive electrode current collector; this application has no particular limitation, as long as the purpose of this application is achieved.

[0073] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0074] This application does not impose any particular restrictions on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include, but is not limited to, lithium cobalt oxide, lithium nickel manganese cobalt oxide, lithium nickel manganese aluminum oxide, lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, lithium manganese silicate, spinel type lithium manganese oxide, spinel type lithium nickel manganese oxide, and lithium titanate.

[0075] The positive electrode material layer may also include a conductive agent and a binder. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they can achieve the purpose of this application. This application does not impose any particular restrictions on the mass ratio of positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0076] This application does not impose any particular limitation on the adhesive, as long as it can achieve the purpose of this application. For example, the adhesive may include, but is not limited to, adhesive polymers, such as at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane, wherein polyolefin adhesives include at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0077] This application does not impose any particular limitation on conductive agents, as long as they can achieve the purpose of this application. For example, conductive agents may include, but are not limited to, carbon-based materials, metal-based materials, conductive polymers, or mixtures thereof; wherein carbon-based materials include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, or carbon fiber; metal-based materials include, for example, metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; and conductive polymers include polyphenylene derivatives.

[0078] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector can be 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer can be 30 μm to 120 μm.

[0079] Optionally, the positive electrode may further include a conductive layer located between the positive electrode current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0080] In this application, the electrochemical device also includes a separator membrane. This application does not impose any particular limitation on the separator membrane, as long as it achieves the purpose of this application. For example, the material of the separator membrane may include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) primarily composed of polypropylene (PP), polyester (e.g., polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex, or aramid. The type of separator membrane may include at least one of woven membrane, nonwoven membrane, microporous membrane, composite membrane, rolled membrane, or spun membrane.

[0081] In some embodiments of this application, the separator may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic materials.

[0082] In some embodiments of this application, the inorganic layer comprises inorganic particles and a binder. This application does not particularly limit the inorganic particles; for example, the inorganic particles may include at least one selected from alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. This application does not particularly limit the binder; for example, the binder may be at least one of the binders described above. In some embodiments of this application, the polymer layer comprises a polymer, the polymer material of which includes at least one selected from polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, or polyvinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

[0083] In some embodiments of this application, the inorganic layer may also include a thickener and a wetting agent. This application does not have any particular restrictions on the types of thickeners and wetting agents, as long as they can achieve the purpose of this application. For example, the thickener may include, but is not limited to, at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose; the wetting agent may include, but is not limited to, at least one of dimethylsiloxane, sodium dodecyl sulfate, trialkyl phosphate, methyl decanoate, and dodecyl acetate.

[0084] In this application, there is no particular limitation on the thickness of the separator, as long as it can achieve the purpose of this application. For example, the thickness of the separator can be from 4 μm to 30 μm.

[0085] In this application, the electrochemical device further includes a negative electrode, which comprises a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The phrase "the negative electrode active material layer is disposed on at least one surface of the negative electrode current collector" means that the negative electrode active material layer can be disposed on one surface of the negative electrode current collector along its thickness direction, or on two surfaces of the negative electrode current collector along its thickness direction. It should be noted that the term "surface" here can refer to the entire surface area of ​​the negative electrode current collector, or only a portion thereof; this application does not impose any particular limitation, as long as the purpose of this application is achieved.

[0086] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0087] In some embodiments of this application, the negative electrode active material layer may further include a conductive agent and a binder. This application does not impose any particular limitation on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the binder may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon. The conductive agent may include, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. Carbon-based materials include at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, and carbon fiber; metal-based materials include at least one of metal powder, metal fiber, copper, nickel, aluminum, or silver; and conductive polymers include polyphenylene derivatives. This application does not impose any particular restrictions on the mass ratio of negative electrode material, conductive agent, and binder in the negative electrode active material layer. Those skilled in the art can choose according to actual needs, as long as the purpose of this application can be achieved.

[0088] This application does not impose any particular limitation on the thickness of the negative electrode active material layer, as long as it can achieve the purpose of this application. For example, the thickness of the single-sided negative electrode active material layer is 30 μm to 120 μm.

[0089] This application does not impose any particular limitation on the thickness of the negative electrode current collector, as long as it can achieve the purpose of this application. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm.

[0090] The electrochemical device also includes a housing for accommodating the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the field of electrochemical devices. This application does not limit the scope of these other components. This application does not impose any particular limitation on the housing; it can be a housing known in the art, as long as it achieves the purpose of this application. For example, the housing can be a rigid housing or a flexible housing. The material of the rigid housing can be metal; this application does not limit the type of metal and can use known metal rigid housings, as long as they achieve the purpose of this application. The flexible housing can be a metal-plastic film, such as aluminum-plastic film, steel-plastic film, etc.

[0091] The preparation process of the electrochemical device described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, the preparation process of the electrochemical device may include, but is not limited to, the following steps: stacking the positive electrode, the separator, and the negative electrode in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the electrochemical device. Alternatively, stacking the positive electrode, the separator, and the negative electrode in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into a housing; injecting electrolyte into the housing and sealing it to obtain the electrochemical device. In addition, overcurrent protection elements, conductive plates, etc., may be placed in the housing as needed to prevent pressure rise and overcharging / discharging inside the electrochemical device.

[0092] A fourth aspect of this application provides an electrical device that includes the electrochemical device provided in the third aspect of this application.

[0093] The electrical equipment used in this application is not particularly limited and can be any electrical equipment known in the prior art. In some embodiments, the electrical equipment may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0094] Example

[0095] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0096] Test methods and equipment

[0097] Si element content test

[0098] Preparation of digestion sample: Take 0.1000g of silicon-based particles or negative electrode material, place it in a nickel crucible, add 1.5g of KOH, and cover the crucible. Heat the muffle furnace to 400℃. The heating program is to raise the temperature from room temperature to 300℃ within 2 hours, and then raise the temperature from 300℃ to 400℃ within 2 hours. After that, start cooling and allow it to cool naturally to 80℃. The digestion program is then complete. Remove the crucible, cool it to room temperature, and then remove the digested sample and place it in a polytetrafluoroethylene beaker.

[0099] Titration with sodium hydroxide standard solution for digested samples: Add 30 mL of boiling water to a polytetrafluoroethylene beaker and soak for 1 hour. Then, clean the crucible with tweezers, maintaining a volume of 50 mL. Filter the solution and transfer it to a 400 mL beaker. After filtration, add 20 mL of concentrated nitric acid to the beaker to neutralize the solution, making it acidic. After the solution cools to room temperature, add solid KCl to saturation with continuous stirring, adding an excess of 2 g. Then, add 10 mL of 200 g / L potassium fluoride solution, resulting in a white precipitate. Let it age for 15 minutes, then filter with medium-speed quantitative filter paper. Wash the beaker and precipitate three times, each time with 8 mL of potassium chloride solution. Remove the filter paper and return it to the original beaker. Add 20 mL of potassium chloride ethanol solution and 10 drops of phenolphthalein. Then, neutralize the residual acid with sodium hydroxide standard solution, stirring the filter paper and wiping the beaker walls until the solution turns light red. During this process, break up the pulp with a glass rod. React for 1 hour. Add 200 mL of neutralized boiling water to the cup (after boiling, add 10 drops of phenolphthalein and neutralize with sodium hydroxide standard solution until slightly red). Titrate with sodium hydroxide standard solution until the endpoint is light red, and record the volume V of sodium hydroxide standard solution consumed in the titration.

[0100] Titration of blank sample with sodium hydroxide standard solution: Except for the sample without digestion, the other steps are the same as those for titrating the digested sample with sodium hydroxide standard solution. A blank sample is prepared, and the volume of sodium hydroxide standard solution consumed in the titration of the blank sample is recorded as V0.

[0101] The mass percentage of silicon is calculated using the following formula: ω Si = (V-V0)×c×7.02 / m×100%, where: c is the concentration of sodium hydroxide standard solution, in mol / L; V is the volume of sodium hydroxide standard solution consumed in titration, in L; V0 is the volume of sodium hydroxide standard solution consumed in blank titration, in L; 7.02 is the molar mass of 1 / 4 Si, in g / mol; m is the sample mass, in g.

[0102] Specific surface area test

[0103] The specific surface area of ​​the silicon-based particles in each embodiment and comparative example was measured using a TriStar II 3020M surface area analyzer (provided by Micron Technology, USA) via nitrogen adsorption. The specific tests were conducted according to the national standard GB / T 19587-2017, "Determination of Specific Surface Area of ​​Solid Substances by Gas Adsorption BET Method".

[0104] Particle size testing

[0105] The Dv50 and Dv90 of silicon-based particles and anode materials were measured using a Mastersizer 3000 particle size analyzer manufactured by Malvern Corporation.

[0106] Calculation of the mass percentage of carbon, polymer, primary conductive material, and secondary conductive material.

[0107] Let W0 be the mass of the silicon-based particles, W1 be the mass of the first intermediate coated with the silicon-based particles, W2 be the mass of the anode material coated with the second and third layers of the first intermediate, and W be the mass percentage of carbon in the first layer of the anode material. C = (W1-W0) / W2×100%.

[0108] polymer mass percentage W J = Mass of polymer added during preparation / W2.

[0109] The mass percentage of the first conductive material W D1 = Mass of the first conductive material added during the preparation process / W2.

[0110] The mass percentage of the second conductive material W D2 = Mass of the second conductive material added during the preparation process / W2.

[0111] Metal oxide mass percentage test

[0112] The content of aluminum or titanium in the negative electrode material was obtained by ICP elemental analysis and then converted into the corresponding mass percentage W of alumina or titanium oxide. M .

[0113] Resistivity testing of negative electrode materials

[0114] The resistivity of the negative electrode materials in each embodiment and comparative example was tested using a powder resistivity meter in a drying chamber.

[0115] Preparation of coin cell half-cell

[0116] (1) The negative electrode material prepared in each embodiment or comparative example, acetylene black and sodium alginate were added to deionized water at a mass ratio of 80:10:10 and stirred thoroughly to form a slurry with a solid content of 40%. The slurry was coated onto an 8μm thick copper foil with a doctor blade to form a 100μm thick coating. After drying in a vacuum drying oven at 85°C for 12 hours, the coating was cut into 1cm diameter discs using a stamping machine in a dry environment to obtain the positive electrode.

[0117] Electrolyte and separator: Ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed uniformly at a volume ratio of 1:1 under a dry argon atmosphere to obtain a mixed solution. 1 mol / L LiPF6 and 5 vol% fluoroethylene carbonate (FEC) were added to the mixed solution and stirred until homogeneous to obtain the electrolyte. A 12 μm thick polyethylene film was used as the separator.

[0118] (2) Assembly of button cell:

[0119] The positive electrode is made of lithium metal sheet as counter electrode, and the above-mentioned electrolyte is added in the order of positive electrode, separator and lithium metal sheet to assemble a button half cell in a glove box.

[0120] First full-lithium insertion expansion rate test

[0121] Before assembling the coin cell, the thickness H0 of the positive electrode was measured using a micrometer. At 25°C and normal pressure, the prepared coin cell was discharged at a constant current rate of 0.1C to 0.01V. After standing for 30 minutes, the coin cell was disassembled in a glove box, and the thickness H1 of the positive electrode after full lithium insertion was measured using a micrometer. The initial full lithium insertion expansion rate of the coin cell positive electrode = (H1 - H0) / H0 × 100%.

[0122] First charge / discharge specific capacity test

[0123] Under normal temperature and pressure conditions, the coin cell half-cell prepared above was discharged at a constant current rate of 0.1C to 0.01V, and then allowed to stand for 5 minutes. The discharge specific capacity at this time was recorded, which is the first discharge specific capacity. Then, it was charged at a constant current rate of 0.1C to 1.5V, and then charged at a constant voltage of 1.5V to a current of 0.05C. After that, it was allowed to stand for 5 minutes. This is one cycle of charge and discharge. The charging capacity at this time is recorded, which is the first charging specific capacity. The first charge and discharge efficiency = (first charging specific capacity / first discharge specific capacity) × 100%.

[0124] Cyclic performance test and expansion rate test

[0125] Before testing, the thickness of the original lithium-ion battery was measured using a micrometer. At test temperatures of 25°C and 45°C, the lithium-ion battery was charged at a constant current of 3.4C to 4.4V, then charged at a constant voltage of 4.4V to 0.025C, allowed to stand for 5 minutes, and then discharged at a constant current of 0.5C to 3.0V. The capacity obtained from this process was taken as the initial capacity of the lithium-ion battery. Cycling tests were performed using a 3.4C charge / 0.5C discharge cycle, and the capacity decay curve was obtained by comparing the capacity at each step with the initial capacity. The number of cycles at 25°C until 90% capacity retention was achieved characterizes the room temperature cycling performance of the lithium-ion battery, and the number of cycles at 45°C until 80% capacity retention was achieved characterizes the high-temperature cycling performance. The above cycles were performed at 25°C and 45°C for 600 cycles, resulting in Figures 2 and 3, which compare the cycling performance of the lithium-ion battery at 25°C and 45°C, respectively.

[0126] The thickness of lithium-ion batteries was measured after 400 cycles at 25°C and 45°C, respectively, to a discharge voltage of 3.0V. The room temperature cycling expansion rate of the lithium-ion battery was characterized by the ratio of the relative difference between the thickness of the lithium-ion battery after 400 cycles at 25°C and the original thickness to the original thickness. Similarly, the high temperature cycling expansion rate was characterized by the ratio of the relative difference between the thickness of the lithium-ion battery after 400 cycles at 45°C and the original thickness to the original thickness. Figures 4 and 5, showing the comparison of the expansion rate of lithium-ion batteries at 25°C and 45°C respectively, were obtained after 500 cycles at both 25°C and 45°C.

[0127] At 25°C, when cycling to the 2nd, 4th, 50th, 100th, 150th, 200th, 300th, 400th, and 500th cycles, the lithium-ion battery was subjected to low-rate charge and discharge as follows: the lithium-ion battery was charged to 4.53V at a constant current of 0.7C, then charged to 0.05C at a constant voltage of 4.53V, left to stand for 5 minutes, and then discharged to 3.0V at a constant current of 0.2C. After leaving to stand for 5 minutes, the cycle continued.

[0128] High-temperature storage performance test

[0129] The lithium-ion battery was discharged to 3.0V at 0.5C at 25℃, then charged to 4.4V at 0.5C, and then charged at a constant voltage of 0.05C at 4.4V. The thickness of the lithium-ion battery at this point was measured using a PPG lithium-ion battery thickness gauge and recorded as 'a'. The lithium-ion battery was then placed in a 45℃ oven and stored at a constant voltage of 4.4V for 400 hours at 45℃. The thickness after 400 hours was recorded as 'b'. The high-temperature storage performance of the lithium-ion battery was characterized by the storage thickness expansion rate. The formula for calculating the storage thickness expansion rate is: (ba) / a × 100%.

[0130] Example 1-1

[0131] <Preparation of Anode Materials>

[0132] (1) Take 200 kg of silicon-carbon particles and classify them using jet fractionation to obtain silicon-based particles with a silicon content of 50.1% by mass and a specific surface area of ​​7.2 m². 2 / g, particle size Dv50 is 1.97μm, and Dv90 is 7.4μm.

[0133] (2) 20 kg of graded silicon-based particles were transferred into a fluidized bed via high-pressure transmission. After standing for 30 min, the fluidized bed inlet and outlet valves were closed, and a vacuum was applied. When the chamber pressure reached -101 kPa, the vacuum was closed, and nitrogen was introduced at a rate of 100 L / min to bring the pressure to positive. The vacuuming and nitrogen introduction were repeated more than 5 times, and then the oxygen content inside the chamber was measured. When the oxygen content dropped below 10 ppm, the outlet valve was opened, the fluidized bed agitator was started at a speed of 150 rpm, and nitrogen was introduced at a rate of 200 L / min. The temperature was increased to 550°C at a heating rate of 5°C / min and held for 1 h. After the holding period, the fluidized bed inlet valve was switched, and an acetylene / nitrogen mixture was introduced into the fluidized bed. The acetylene volume percentage was 25%, the gas flow rate was 200 L / min, and the reaction time was 150 min. After the reaction was completed, nitrogen gas was introduced at a flow rate of 150 L / min, and the stirring speed was adjusted to 100 rpm for cooling. The mixture was discharged at room temperature to obtain the first intermediate.

[0134] (3) Take 10L of anhydrous ethanol and add 2kg of the first intermediate powder, 40g of aluminum isopropoxide, 40g of polyvinylpyrrolidone, and 1kg of ethanol slurry with a solid content of 1.2% (0.4wt% of single-walled carbon nanotubes and 0.8wt% of dispersant) to the anhydrous ethanol while stirring. After stirring thoroughly for 4 hours, the first dispersion is obtained. Based on the mass of the first intermediate, the amount of aluminum isopropoxide added is 2%, and the amount of single-walled carbon nanotubes added is 0.2%. Start the spray dryer, set the inlet air temperature to 180℃ and the outlet air temperature to 95℃. After the inlet and outlet air temperatures reach the set range, supply anhydrous ethanol at a supply rate of 70mL / min. After running stably for 30min, switch to supplying the first dispersion. The dried powder obtained from the outlet was loaded into a graphite crucible and placed in a box furnace. After closing the chamber door, nitrogen gas was passed through at a flow rate of 2 L / min for 30 min. Then, heating was started and heated to 550°C at a heating rate of 5°C / min. The temperature was then held for 1 h. After turning off the heating, nitrogen gas was passed through again and the mixture was cooled to room temperature. The crucible was then removed to obtain the heat-treated second intermediate powder.

[0135] (4) Take 6 kg of deionized water and add 2 kg of the second intermediate powder while stirring to obtain the second dispersion. Add 180 g of polyurethane and 20 g of single-walled carbon nanotubes to 800 g of deionized water to obtain the third dispersion with a solid content of 20%. After stirring the second dispersion thoroughly for 2 hours, add 0.5 kg of the third dispersion while stirring and stir thoroughly for 3 hours. Obtain a mixed slurry of the second and third dispersions. Based on the mass of the second intermediate, the amount of polyurethane added is 4.5% and the amount of single-walled carbon nanotubes added is 0.5%. Start the spray dryer, set the inlet air temperature to 220℃, the outlet air temperature to 105℃, and the atomizing disc speed to 16500 rpm. After the inlet and outlet air temperatures reach the set range, first supply deionized water at a supply rate of 300 mL / min, and after stable operation for 30 minutes, switch to supplying the mixed slurry. Dry negative electrode material is obtained from the outlet. Based on the mass of the anode material, the carbon content in the first layer is 3%, the aluminum oxide content is 0.44%, the first conductive material content is 0.18%, the polyurethane content is 4.32%, and the second conductive material content is 0.48%. The anode material has a Dv50 of 7.8 μm and a Dv90 of 27 μm.

[0136] Figure 1 shows a schematic diagram of the structure of the negative electrode material prepared in Example 1-1.

[0137] Examples 1-2 to Examples 1-11

[0138] Except for adjusting the mass percentage of carbon in the first layer, the mass percentage of metal oxide in the second layer, the mass percentage of the first conductive material, the mass percentage of polyurethane, the mass percentage of the second conductive material, and the mass ratio of polyurethane to the second conductive material according to Table 1 in the <Preparation of Anode Material>, the rest is the same as in Example 1-1.

[0139] Examples 1-12

[0140] Except for replacing silicon-carbon particles with silicon-oxygen particles in the <Preparation of Anode Materials>, its silicon element mass percentage is 49.4% and its specific surface area is 3.8 m². 2 Except for the g, Dv50 being 2.1 μm and Dv90 being 7.5 μm, the rest are the same as in Example 1-1.

[0141] Examples 1-13

[0142] Except for replacing aluminum isopropoxide with titanium isopropoxide in the <Preparation of Anode Material> section, the rest is the same as in Example 1-1.

[0143] Examples 1-14

[0144] Except for replacing the single-walled carbon nanotubes of the first conductive material with multi-walled carbon nanotubes in the <Preparation of Anode Material>, the rest is the same as in Example 1-1.

[0145] Examples 1-15

[0146] Except for replacing the single-walled carbon nanotubes of the first conductive material with conductive carbon black in the <Preparation of Anode Material>, the rest is the same as in Example 1-1.

[0147] Examples 1-16

[0148] Except for replacing the single-walled carbon nanotubes of the second conductive material with multi-walled carbon nanotubes in the <Preparation of Anode Material>, the rest is the same as in Example 1-1.

[0149] Examples 1-17

[0150] Except for replacing the single-walled carbon nanotubes of the second conductive material with conductive carbon black in the <Preparation of Anode Material>, the rest is the same as in Example 1-1.

[0151] Example 2-1

[0152] <Preparation of the negative electrode>

[0153] Graphite, the negative electrode material prepared in Examples 1-1, conductive agent (conductive carbon black, Super P), and binder polyacrylic acid (PAA) were dissolved in deionized water at a ratio of 80:10:5:5 and mixed evenly to prepare a negative electrode slurry with a solid content of 70 wt%. Deionized water was added to adjust the viscosity of the slurry to 5000 Pa·s. The negative electrode slurry was then uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector and dried at 120 °C to obtain a negative electrode sheet with a single-sided coating of negative electrode material layer. The coating weight of the negative electrode material layer was 142 mg / 1540 mm². 2 Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After drying at 120℃, it is cold-pressed, then cut and welded with tabs to obtain a negative electrode sheet with a size of 78mm×875mm for use. The thickness of the single-sided negative electrode material layer is 54.5μm.

[0154] <Preparation of the positive electrode>

[0155] LiCoO2 (positive electrode active material), conductive carbon black, and polyvinylidene fluoride (PVDF) were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 95:2.5:2.5 to prepare a positive electrode slurry. The positive electrode slurry was then uniformly coated onto one surface of a 10 μm thick aluminum foil used as a positive electrode current collector and dried at 120°C to obtain a single-sided coated positive electrode sheet. The coating weight of the positive electrode material layer was 267.8 mg / 1540 mm². 2 The above steps are then repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After drying at 120℃, it is cold-pressed, then cut and welded with tabs to obtain a positive electrode sheet with a size of 74mm×867mm for later use. The thickness of the single-sided positive electrode material layer is 42μm.

[0156] <Preparation of Electrolyte>

[0157] In a dry argon atmosphere, propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) are mixed in a mass ratio of 1:1:1 to obtain a base solvent. Lithium salt LiPF6 is then added and mixed thoroughly to obtain an electrolyte. The electrolyte contains 12.5% ​​lithium salt LiPF6 based on the total mass of the electrolyte, with the remainder being the base solvent.

[0158] <Isolation membrane>

[0159] A polyethylene / polypropylene composite film with a thickness of 8μm was used as the separator.

[0160] <Preparation of Lithium-ion Batteries>

[0161] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The cells are then wound to obtain a bare cell. After welding the tabs, the bare cell is placed in an outer packaging foil aluminum-plastic film. The prepared electrolyte is injected into the dried bare cell. The lithium-ion battery is obtained through processes such as vacuum sealing, settling, formation, shaping, degassing, and capacity testing.

[0162] Examples 2-2 to 2-17

[0163] Except for the negative electrode materials prepared in Examples 1-2 to 1-17 used in <Preparation of Negative Electrode>, the rest are the same as in Example 2-1.

[0164] Examples 3-1 to 3-11

[0165] Except for the addition of additives to the electrolyte according to Table 3 in the <Preparation of Electrolyte>, and the adjustment of the mass percentage of the additives, the mass percentage of the base solvent is changed accordingly, the mass ratio of each component of the base solvent remains unchanged, and the mass percentage of lithium salt LiPF6 remains unchanged, the rest is the same as in Example 2-1.

[0166] Comparative Example 1

[0167] Except for the fact that the silicon-based particles were not coated in the <Preparation of Anode Material>, the rest is the same as in Example 1-1. Specific data are shown in Table 1.

[0168] Comparative Example 2

[0169] Except for the absence of a second layer in the silicon-based particles in the <Preparation of Anode Material>, the rest is the same as in Example 1-1. Specific data are shown in Table 1.

[0170] Comparative Example 3

[0171] Except for the absence of a third layer in the silicon-based particles in the <Preparation of Anode Material>, the rest is the same as in Example 1-1. Specific data are shown in Table 1.

[0172] Comparative Examples 4 to 6

[0173] Except for the negative electrode materials prepared in Comparative Examples 1, 2, and 3 in the <Preparation of Negative Electrode> section, the rest are the same as in Example 2-1.

[0174] The preparation parameters and performance tests of each embodiment and comparative example are shown in Tables 1 to 3.

[0175] As can be seen from Examples 1-1 to 1-17, Examples 2-1 to 2-17, and Comparative Examples 1 to 6, when the negative electrode material has the three-layer coating structure of this application, the resistivity of the negative electrode material is low, the mass percentage of silicon element is high, and it has higher initial charge-discharge efficiency and lower initial full lithium insertion expansion rate; the resulting lithium-ion battery has higher cycle count and lower lithium-ion battery expansion rate at room temperature and high temperature, thus indicating that the cycle performance of the lithium-ion battery is improved and the expansion rate is reduced.

[0176] As can be seen from Figures 2 and 3 in the specification, when the negative electrode material of Example 1-1 is applied to a lithium-ion battery, the lithium-ion battery exhibits a higher cycle capacity retention rate after 200 cycles at both room temperature and high temperature compared to Comparative Examples 4 to 6. As can be seen from Figures 4 and 5, the thickness expansion rate is lower after 200 cycles. Therefore, the lithium-ion battery of Example 2-1 demonstrates superior cycle performance and expansion performance compared to Comparative Examples 4 to 6.

[0177] As can be seen from Examples 1-1 to 1-17 and Examples 2-1 to 2-17, when the mass percentage content of silicon in the negative electrode material is 40% to 50%, Dv50 is 6 μm to 10 μm, Dv90 is less than or equal to 30 μm, and the mass percentage content of carbon in the first layer is W C The mass percentage of metal oxides is 1% to 5% W. M The mass percentage W of the first conductive material is 0.2% to 1%. D1 The mass percentage of polyurethane is 0.1% to 0.4% W. J The content of W is 0.9% to 9% by mass and / or the type of the second conductive material. D2 When the content is between 0.1% and 1%, the resistivity of the negative electrode material is low, the mass percentage of silicon is high, and it has higher initial charge-discharge efficiency and lower initial full lithium insertion expansion rate. The resulting lithium-ion battery has higher cycle count and lower lithium-ion battery expansion rate at room temperature and high temperature, which indicates that the cycle performance of the lithium-ion battery is improved and the expansion rate is reduced.

[0178] Table 3

[0179] Note: " / " in Table 3 indicates that the corresponding preparation parameters or substances do not exist.

[0180] The type and content of additives in the electrolyte typically affect the cycle performance and high-temperature storage performance of lithium-ion batteries.

[0181] Examples 1-1, 3-1 to 3-11 show that, compared to Example 1-1 without the additive, introducing the additive of this application into the electrolyte results in a higher number of cycle times at both room temperature and high temperature, and a lower storage thickness expansion rate, indicating that the cycle performance of the lithium-ion battery is improved. When the amount of additive added is between 1% and 3%, the cycle performance of the lithium-ion battery is further improved.

[0182] The terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed or inherent to such process, method, or article.

[0183] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0184] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the principles of this application should be included within the scope of protection of this application.

Claims

1. A negative electrode material comprising: The core comprises silicon-based particles; The first layer exists outside the kernel; The second layer exists outside the first layer; The third layer exists outside the second layer; in, The first layer contains carbon; the second layer contains a first conductive material and a metal oxide; and the third layer contains a second conductive material and a polymer.

2. The negative electrode material according to claim 1, wherein, The silicon-based particles include at least one of silicon-carbon particles or silicon-oxygen particles; or the metal oxide includes at least one of aluminum oxide or titanium oxide; or the polymer includes polyurethane; or the first conductive material and the second conductive material are each independently selected from at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, or conductive carbon black.

3. The negative electrode material according to claim 1 or 2, wherein, Based on the mass of the negative electrode material, the silicon content is 40% to 50% by mass.

4. The negative electrode material according to any one of claims 1 to 3, wherein, The negative electrode material satisfies at least one of the following: (1) The Dv50 of the negative electrode material is 6 μm to 10 μm; (2) The Dv90 of the negative electrode material is less than or equal to 30 μm; (3) Based on the mass of the negative electrode material, the mass percentage of carbon in the first layer is 1% to 5%; (4) Based on the mass of the negative electrode material, the mass percentage of the metal oxide is 0.2% to 1%; (5) Based on the mass of the negative electrode material, the polymer has a mass percentage content of 0.9% to 9%; (6) Based on the mass of the negative electrode material, the mass percentage of the first conductive material is 0.1% to 0.4%; (7) Based on the mass of the negative electrode material, the mass percentage of the second conductive material is 0.1% to 1%.

5. The negative electrode material according to claim 4, wherein, Based on the mass of the negative electrode material, the mass ratio of the polymer to the second conductive material is 9:1 to 9:

2.

6. A method for preparing a negative electrode material according to any one of claims 1 to 5, comprising: Provides silicon-based particles; The silicon-based particles are carbon-coated to obtain a first intermediate. The first intermediate, organometallic salt, polyvinylpyrrolidone, and first conductive material are dispersed in ethanol to obtain a first dispersion. The first dispersion is fully dispersed and stirred, and then spray-dried and heat-treated at a temperature of 500°C to 600°C to obtain a second intermediate. The organometallic salt includes at least one of aluminum isopropoxide or titanium isopropoxide. The second intermediate is dispersed in water to obtain a second dispersion. The polymer and the second conductive material are dispersed in water to obtain a third dispersion. The second dispersion and the third dispersion are mixed and stirred evenly, and the negative electrode material is obtained by spray drying.

7. The preparation method according to claim 6, wherein, The carbon coating process involves placing the silicon-based particulate material in a fluidized bed, introducing a carbon source gas at a temperature of 500°C to 600°C, and reacting for 2 to 3 hours to obtain the first intermediate. The carbon source gas includes at least one of acetylene, methane, and propylene.

8. An electrochemical device comprising a positive electrode, a separator, an electrolyte, and a negative electrode, wherein the negative electrode comprises a negative electrode active material layer comprising the negative electrode material according to any one of claims 1 to 5.

9. The electrochemical device according to claim 8, wherein, The electrolyte includes an additive comprising at least one of 1,3,6-hexanetrionitrile, 1,2,3-propanetrimethylonitrile, or 1,2,3-tris(2-cyanoxy)propane, wherein the additive comprises 0.1% to 5% by mass based on the total mass of the electrolyte.

10. An electrical device comprising the electrochemical device according to any one of claims 8 to 9.

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