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

Abstract

The present application provides a negative electrode material, a preparation method thereof, and an electrochemical device. The negative electrode material includes: a first silicon-based material, a second silicon-based material, passivated lithium powder, and an organic polymer; the particle size Dv50 of the first silicon-based material is A, 2 μm ≤ A ≤ 5 μm, the particle size Dv50 of the second silicon-based material is B, where 4B < A < 20B; the particle size Dv50 of the passivated lithium powder is C, 0.01 μm ≤ C ≤ 0.1 μm. The negative electrode material provided by the present application can combine the advantages of the long cycle performance of the first silicon-based material and the high rate performance of the second silicon-based material, can effectively alleviate the fragmentation and pulverization of the silicon-carbon negative electrode material during the cycle process and inhibit the growth of the SEI film, reduce the volume expansion rate after cycling of the electrochemical device, and improve the cycle performance and rate performance of the electrochemical device.

Description

Technical Field

[0001] This application relates to the field of electrochemical energy storage, and particularly to a negative electrode material, a preparation method thereof, and an electrochemical device. Background Art

[0002] Graphite is the most widely used negative electrode material, which has advantages such as high efficiency and stable charge-discharge platforms. However, its low specific capacity per gram hinders its further application. Compared with graphite, elemental silicon is considered an ideal negative electrode material that can replace graphite due to its high theoretical specific capacity and suitable working voltage.

[0003] However, the volume of silicon expands by up to 400% after lithium intercalation. The repeated expansion and contraction of silicon-based materials during cycling can lead to the destruction and growth of the solid electrolyte interface membrane (SEI) and the fragmentation of silicon-based negative electrode particles, resulting in huge electrode expansion and rapid capacity decay, affecting the cycling performance and rate performance of electrochemical devices and restricting the large-scale application of silicon negative electrode materials in electrochemical devices. Summary of the Invention

[0004] The purpose of the present invention is to provide a negative electrode material to improve the cycling performance and rate performance of electrochemical devices.

[0005] The first aspect of this application provides a negative electrode material, which includes: a first silicon-based material, a second silicon-based material, passivated lithium powder, and an organic polymer; the particle size Dv50 of the first silicon-based material is A, 2 μm ≤ A ≤ 5 μm, the particle size Dv50 of the second silicon-based material is B, where 4B < A < 20B; the particle size Dv50 of the passivated lithium powder is C, 0.01 μm ≤ C ≤ 0.1 μm.

[0006] In an embodiment of this application, the first silicon-based negative electrode material and the second silicon-based material respectively include a core, a carbon layer outside the core, and a lithium salt layer outside the carbon layer.

[0007] In an embodiment of this application, the negative electrode material satisfies at least one of the following: (1) the core includes at least one of silicon-carbon particles or silicon-oxygen particles; (2) the lithium salt includes at least one of LiF or Li2CO3; (3) based on the mass of the first silicon-based material, the mass percentage of the carbon layer of the first silicon-based particles is 1% to 5.2%, and the mass percentage of the lithium salt layer is 0.53% to 2.1%; (4) based on the mass of the second silicon-based material, the mass percentage of the carbon layer of the second silicon-based particles is 1% to 5.2%, and the mass percentage of the lithium salt layer is 0.53% to 2.1%.

[0008] In one embodiment of this application, the average size of silicon grains in the core of the first silicon-based material is a, and the average size of silicon grains in the core of the second silicon-based material is b; 1nm≤a≤1.5nm, 1.5nm≤b≤2nm, and a<b.

[0009] In one embodiment of this application, 0.1μm≤B≤0.5μm.

[0010] In one embodiment of this application, the mass of the first silicon-based material is m1 g, the mass of the second silicon-based material is m2 g, and the mass of the passivated lithium powder is m3 g, with a mass ratio satisfying: m1:m2:m3 = 100:10 to 40:0.5 to 5; based on the mass of the negative electrode material, the mass percentage content of the organic polymer is 3% to 7%.

[0011] 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) the organic polymer includes polyurethane; and (4) the mass percentage of silicon element is 40% to 50% based on the mass of the negative electrode material.

[0012] The second aspect of this application provides a method for preparing the negative electrode material described in the first aspect of this application, comprising:

[0013] A first silicon-based material core is provided, and the core is coated with carbon to obtain a first intermediate. The first intermediate is dispersed in water to obtain a first dispersion. An aqueous solution of a lithium source material is added to the first dispersion to obtain a second dispersion. The dispersion is fully dispersed and stirred, and then dried in an oven to obtain the first silicon-based material.

[0014] A second silicon-based material core is provided, and the core is coated with carbon to obtain a first intermediate. The first intermediate is dispersed in water to obtain a first dispersion. An aqueous solution of a lithium source material is added to the first dispersion to obtain a second dispersion. The dispersion is fully dispersed and stirred, and then dried in an oven to obtain the second silicon-based material.

[0015] The first silicon-based material, the second silicon-based material, and the passivated lithium powder are dispersed and then added to deionized water to obtain a third dispersion; the polymer is dispersed in water to obtain a fourth dispersion; the fourth dispersion is added to the third dispersion, mixed and stirred thoroughly, and then spray-dried to obtain the negative electrode material.

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

[0017] In one embodiment of the present application, the electrolyte contains at least one of lithium bis(trifluoromethylsulfonyl)imide or lithium bis(fluorosulfonyl)imide;

[0018] Based on the mass of the electrolyte, the mass percentage content of lithium bis(trifluoromethylsulfonyl)imide and / or lithium bis(fluorosulfonyl)imide is 0.1% to 5%.

[0019] The fourth aspect of the present application provides an electronic device, which includes the electrochemical device provided by the third aspect of the present application.

[0020] Beneficial effects of the embodiments of the present invention:

[0021] The present application provides a negative electrode material, which includes: a first silicon-based material, a second silicon-based material, passivated lithium powder and an organic polymer; the particle size Dv50 of the first silicon-based material is A, 2μm ≤ A ≤ 5μm, and the particle size Dv50 of the second silicon-based material is B, where 4B < A < 20B; the particle size Dv50 of the passivated lithium powder is C, 0.01μm ≤ C ≤ 0.1μm. The negative electrode material includes a first silicon-based material, a second silicon-based material, passivated lithium powder and an organic polymer, which can combine the advantages of the long cycle performance of the first silicon-based material and the high rate performance of the second silicon-based material, can effectively alleviate the fragmentation and pulverization of the silicon-carbon negative electrode material during the cycle and inhibit the growth of SEI, reduce the volume expansion rate after cycling of the electrochemical device, and improve the cycle performance and rate performance of the electrochemical device.

[0022] Of course, it is not necessary for any product or method implementing the present invention to achieve all the above-mentioned advantages simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention, and those of ordinary skill in the art can also obtain other embodiments based on these drawings.

[0024] Figure 1 Schematic structural diagram of the negative electrode material prepared for Example 1-1;

[0025] Figure 2 Comparison chart of the cycle performance of the lithium-ion batteries of Example 2-1 and Comparative Examples 4 to 6 at 25°C;

[0026] Figure 3 Comparison chart of the cycle performance of the lithium-ion batteries of Example 2-1 and Comparative Examples 4 to 6 at 45°C;

[0027] Figure 4This is a comparison graph showing the expansion rate of lithium-ion batteries from Examples 2-1 and Comparative Examples 4 to 6 at 25°C.

[0028] Figure 5 This is a comparison graph showing the expansion rate of lithium-ion batteries from Examples 2-1 and Comparative Examples 4 to 6 at 45°C.

[0029] Figure 6 This is a comparison chart of the capacity retention of lithium-ion batteries from Examples 2-1 and Comparative Examples 4 to 6 at different rates at 25°C. Detailed Implementation

[0030] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only 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.

[0031] 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.

[0032] The first aspect of the present application provides a negative electrode material, which includes: a first silicon-based material, a second silicon-based material, passivated lithium powder, and an organic polymer; the particle size Dv50 of the first silicon-based material is A, 2μm ≤ A ≤ 5μm, and the particle size Dv50 of the second silicon-based material is B, where 4B < A < 20B; the particle size Dv50 of the passivated lithium powder is C, 0.01μm ≤ C ≤ 0.1μm. For example, the particle size Dv50 of the first silicon-based material is A, and A can be 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, or a range composed of any two of these values; the particle size Dv50 of the second silicon-based material is B, and B can be 0.05A, 0.1A, 0.15A, 0.2A, 0.25A, or a range composed of any two of these values; the particle size Dv50 of the passivated lithium powder is C, and C can be 0.01μm, 0.02μm, 0.04μm, 0.06μm, 0.08μm, 0.1μm, or a range composed of any two of these values. By adjusting the particle size Dv50 of the first silicon-based material within the range of 2μm to 5μm, the first silicon-based material has relatively excellent cycling performance, but slightly poor rate performance and a relatively large specific surface area; by adjusting the particle size Dv50 of the second silicon-based material within the above range, the second silicon-based material has excellent rate performance, but slightly poor cycling performance and a relatively large specific surface area. By adjusting the particle size Dv50 of the first silicon-based material, the second silicon-based material, and the passivated lithium powder, and performing secondary granulation on the first silicon-based material, the second silicon-based material, and the passivated lithium powder after grading with the help of a polymer binder, the advantages of the long cycling performance of the first silicon-based material and the high rate performance of the second silicon-based material can be combined, while further reducing the specific surface area of the silicon-carbon particles, effectively alleviating the fragmentation and pulverization of the silicon-carbon negative electrode material during the cycling process and inhibiting the growth of the SEI film, reducing the volume expansion after cycling of the electrochemical device, and improving the cycling performance and rate performance of the electrochemical device.

[0033] In an embodiment of the present application, the first silicon-based material and the second silicon-based material respectively include a core, a carbon layer outside the core, and a lithium salt layer outside the carbon layer. Specifically, the schematic structural diagram of the negative electrode material is as Figure 1 shown, from the inside out are the core 11, the carbon layer 12, the lithium salt layer 13, the organic polymer 14, and the passivated lithium powder 15.

[0034] In one embodiment of this application, the negative electrode material satisfies at least one of the following: (1) the core comprises at least one of silicon-carbon particles or silicon-oxygen particles; (2) the lithium salt comprises at least one of LiF or Li2CO3; (3) based on the mass of the first silicon-based material, the carbon layer of the first silicon-based particles has a mass percentage content of 1% to 5.2%, and the lithium salt layer has a mass percentage content of 0.53% to 2.1%; (4) based on the mass of the second silicon-based material, the carbon layer of the second silicon-based particles has a mass percentage content of 1% to 5.2%, and the lithium salt layer has a mass percentage content of 0.53% to 2.1%. For example, based on the mass of the first or second silicon-based material, the mass percentage of their respective carbon layers can be 1%, 2%, 3%, 4%, 5%, 5.2%, or a range of any two of these values, and the mass percentage of their respective lithium salt layers can be 0.53%, 0.6%, 0.8%, 1%, 1.2%, 1.4%, 1.6%, 1.8%, 2%, 2.1%, or a range of any two of these values. The introduction of the carbon layers protects the active silicon on the first and second silicon-based materials, reducing gas generation problems caused by direct contact between water and active silicon during stirring. The introduction of lithium salts and organic polymers inhibits direct contact between the electrolyte and active silicon, and also changes the composition of the SEI, thereby improving the cycle performance of the electrochemical device.

[0035] In one embodiment of this application, the average size of silicon grains in the core of the first silicon-based material is 'a', and the average size of silicon grains in the core of the second silicon-based material is 'b'; 1 nm ≤ a ≤ 1.5 nm, 1.5 nm ≤ b ≤ 2 nm, and a < b. For example, the average size 'a' of silicon grains in the core of the first silicon-based material can be 1 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, or a range consisting of any two of these values; the average size 'b' of silicon grains in the core of the second silicon-based material can be 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, 2 nm, or a range consisting of any two of these values. By controlling the average size of silicon grains in the core of the first silicon-based material to be between 1 nm and 1.5 nm, the first silicon-based material exhibits superior cycle performance but slightly inferior rate performance and a larger specific surface area. Similarly, by controlling the average size of silicon grains in the core of the second silicon-based material to be between 1.5 nm and 2 nm, the second silicon-based material exhibits excellent rate performance but slightly inferior cycle performance and a larger specific surface area. Secondary granulation of the first silicon-based material, the second silicon-based material, and passivated lithium powder with the aid of a polymer binder combines the long cycle performance of the first silicon-based material with the high rate performance of the second silicon-based material. Simultaneously, it further reduces the specific surface area of ​​the silicon-carbon material particles, effectively mitigating the fragmentation and pulverization of the silicon-carbon material during cycling, inhibiting SEI film growth, reducing volume expansion after cycling of the electrochemical device, and improving the cycle performance and rate performance of the electrochemical device.

[0036] In one embodiment of this application, 0.1 μm ≤ B ≤ 0.5 μm. For example, B can be 0.1 μm, 0.15 μm, 0.2 μm, 0.25 μm, 0.3 μm, 0.35 μm, 0.4 μm, 0.45 μm, 0.5 μm, or a range of any two of these values. By controlling the particle size Dv50 of the second silicon-based material within the above range, the first silicon-based material, the second silicon-based material, and the passivated lithium powder are graded and then granulated again with the help of a polymer binder. This combines the advantages of the long cycle performance of the first silicon-based material and the high rate performance of the second silicon-based material, while further reducing the specific surface area of ​​the silicon-carbon particles. This effectively alleviates the fragmentation and pulverization of the silicon-carbon anode material during cycling and inhibits the growth of the SEI film, reduces the volume expansion of the electrochemical device after cycling, and improves the cycle performance and rate performance of the electrochemical device.

[0037] In one embodiment of this application, the mass of the first silicon-based material is m1 g, the mass of the second silicon-based material is m2 g, and the mass of the passivated lithium powder is m3 g, and the mass ratio satisfies: m1:m2:m3=100:10 to 40:0.5 to 5. For example, m1:m2:m3 can be 100:10:0.5, 100:15:0.5, 100:20:0.5, 100:25:0.5, 100:30:0.5, 100:35:0.5, 100:40:0.5, 100:10:1, 100:10:2, 100:10:3, 100:10:4, 100:10:5, 100:25:1, 100:25:2, 100:25:3, 100:25:4, 100:25:5, or a range consisting of any two of these values. By adjusting the mass ratio of the first silicon-based material, the second silicon-based material, and passivated lithium powder, and with the help of a polymer binder, secondary granulation can be performed. This combines the advantages of the long cycle performance of the first silicon-based material and the high rate performance of the second silicon-based material. At the same time, it further reduces the specific surface area of ​​silicon-carbon particles, which can effectively alleviate the fragmentation and pulverization of silicon-carbon materials during cycling and inhibit the growth of SEI. This reduces the volume expansion of the electrochemical device after cycling and improves the cycle performance and rate performance of the electrochemical device.

[0038] In one embodiment of this application, the mass percentage of the organic polymer is 3% to 7% based on the mass of the negative electrode material. For example, the mass percentage of the organic polymer can be 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, or a range consisting of any two of these values. By controlling the mass percentage of the organic polymer within the above range, the polymer can perform secondary granulation while inhibiting direct contact between the electrolyte and active silicon, changing the composition of the SEI, thereby improving the cycle performance and rate performance of the electrochemical device.

[0039] 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) the organic polymer includes polyurethane; and (4) the mass percentage of silicon element is 40% to 50% based on the mass of the negative electrode material.

[0040] In one embodiment of this application, the Dv50 of the negative electrode material is from 6 μm to 10 μm. For example, the 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. By controlling the Dv50 of the negative electrode material within the above range, the particle size of the negative electrode material can be reduced, which helps to shorten the Li-P-E ratio. +The diffusion path improves the rate performance of the electrochemical device, but the specific surface area increases as the particle size of the negative electrode material decreases, thus increasing the contact area between the negative electrode material and the electrolyte, leading to more side reactions and consequently worsening cycle performance. The inventors of this application have discovered that when the particle size Dv50 of the negative electrode material is 6 μm to 10 μm, the diffusion path of the Li... + A good balance is achieved between improving the diffusion path and reducing the specific surface area, thereby improving the ionic conductivity of the anode material while maintaining good cycle performance and rate performance.

[0041] In one embodiment of this application, the Dv90 of the negative electrode material is less than or equal to 30 μm. The Dv90 of the negative electrode material can be 11 μm, 12 μm, 13 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. When the particle size Dv90 of the negative electrode material is too large (exceeding 30 μm), it is not conducive to the processing of the negative electrode sheet, and particle defects will occur on the electrode sheet during coating. When the particle size Dv90 of the negative electrode material is less than or equal to 30 μm, it can improve the dispersion uniformity of the slurry during the preparation of the negative electrode material layer, and improve the Li... + This improves the transport of energy, thereby enhancing the cycle performance and expansion performance of lithium-ion batteries.

[0042] In one embodiment of this application, the organic polymer includes polyurethane. By selecting the above-mentioned organic polymer, a secondary granulation function can be achieved, while inhibiting direct contact between the electrolyte and the active silicon, changing the composition of the SEI, thereby improving the cycle performance and rate performance of the electrochemical device.

[0043] In one embodiment of this application, the mass percentage of silicon is 40% to 50% based on the mass of the anode material. For example, the mass percentage of silicon can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, or a range of any two of these values. By controlling the mass percentage of silicon within the above range, the anode material exhibits high reversible capacity and first-cycle efficiency, while also improving the energy density, cycle performance, and rate performance of the electrochemical device.

[0044] The second aspect of this application provides a method for preparing the negative electrode material described in the first aspect of this application, comprising:

[0045] A first silicon-based material core is provided, and the core is coated with carbon to obtain a first intermediate. The first intermediate is dispersed in water to obtain a first dispersion. An aqueous solution of a lithium source material is added to the first dispersion to obtain a second dispersion. The dispersion is fully dispersed and stirred, and then dried in an oven to obtain the first silicon-based material.

[0046] A second silicon-based material core is provided, and the core is coated with carbon to obtain a first intermediate. The first intermediate is dispersed in water to obtain a first dispersion. An aqueous solution of a lithium source material is added to the first dispersion to obtain a second dispersion. The dispersion is fully dispersed and stirred, and then dried in an oven to obtain the second silicon-based material.

[0047] The first silicon-based material, the second silicon-based material, and the passivated lithium powder are dispersed and then added to deionized water to obtain a third dispersion; the polymer is dispersed in water to obtain a fourth dispersion; the fourth dispersion is added to the third dispersion, mixed and stirred thoroughly, and then spray-dried to obtain the negative electrode material.

[0048] In one embodiment of this application, the core particle size Dv50 of the first silicon-based material is from 1.985 μm to 4.985 μm, and the core particle size Dv50 of the second silicon-based material is from 0.095 μm to 0.495 μm. For example, the core particle size Dv50 of the first silicon-based material can be 1.985μm, 2μm, 2.2μm, 2.4μm, 2.6μm, 2.8μm, 2.985μm, 3μm, 3.2μm, 3.4μm, 3.6μm, 3.8μm, 3.985μm, 4μm, 4.2μm, 4.4μm, 4.6μm, 4.985μm, or a range of any two of these values; the core particle size Dv50 of the second silicon-based material can be 0.095μm, 0.1μm, 0.15μm, 0.2μm, 0.25μm, 0.3μm, 0.35μm, 0.4μm, 0.495μm, or a range of any two of these values.

[0049] In one embodiment of this application, the average size of silicon grains in the core of the first silicon-based material is 'a', and the average size of silicon grains in the core of the second silicon-based material is 'b'; 1 nm ≤ a ≤ 1.5 nm, 1.5 nm ≤ b ≤ 2 nm, and a < b. For example, the average size 'a' of silicon grains in the core of the first silicon-based material can be 1 nm, 1.1 nm, 1.2 nm, 1.3 nm, 1.4 nm, 1.5 nm, or a range consisting of any two of these values; the average size 'b' of silicon grains in the core of the second silicon-based material can be 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, 2 nm, or a range consisting of any two of these values.

[0050] In one embodiment of this application, the first intermediate used in preparing the first silicon-based material and the second silicon-based material is obtained by silane deposition of two porous carbon particles of different sizes obtained through air jet milling and classification at different temperatures. This application does not impose any particular limitation on particle classification technology; any method known in the art that can achieve the purpose of this application is acceptable.

[0051] In one embodiment of this application, the carbon coating process of the first silicon-based material involves placing the core particles of the first silicon-based material in a fluidized bed at a temperature of 590°C to 610°C, and the carbon coating process of the second silicon-based material involves placing the core particles of the second silicon-based material in a fluidized bed at a temperature of 540°C to 560°C. Under these conditions, a carbon source gas is introduced, and the reaction is carried out for 2 to 3 hours. The carbon source gas includes at least one of acetylene, methane, and propylene. For example, the coating temperature of the first silicon-based material can be 590°C, 595°C, 600°C, 605°C, 610°C, or a range consisting of any two of these values; the coating temperature of the second silicon-based material can be 540°C, 545°C, 550°C, 555°C, 560°C, or a range consisting of any two of these values. For example, the coating time can be 2 hours, 2.2 hours, 2.4 hours, 2.6 hours, 2.8 hours, 3 hours, or a range consisting of any two of these values. By controlling the carbon coating time and temperature within the aforementioned range, the carbon material content during the carbon coating process can be controlled. After the carbon source gas is decomposed at high temperature, it is deposited on the outside of the core particles. Within a suitable temperature range, the higher the deposition temperature, the faster the carbon source gas decomposition rate, the higher the utilization rate, and the faster the carbon layer growth rate. At the same deposition temperature, the deposition time determines the thickness and integrity of the carbon layer.

[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. The use of an inert gas helps to improve the uniformity of carbon element distribution in the carbon layer.

[0053] In one embodiment of this application, the solid content of the first dispersion is 15% to 20%. For example, the solid content of the first dispersion can be 15%, 16%, 17%, 18%, 19%, 20%, or a range consisting of any two of these values. By controlling the solid content of the first intermediate in deionized water within the above range, the particle size distribution of the first and second silicon-based material particles after spray drying can be controlled while taking into account the drying capacity and production capacity of the equipment, effectively reducing the risk of particle size increase caused by particle adhesion.

[0054] Without being limited to any particular theory, the lithium source material can be LiF. The inventors believe that by adding the aqueous solutions of ammonium fluoride and the lithium source compound to the first dispersion in sequence and stirring thoroughly to generate lithium fluoride, the lithium source compound can be more uniformly coated on the outside of the first intermediate. The lithium source compound includes at least one of lithium acetate, lithium nitrate, and lithium sulfate.

[0055] Without being limited to any particular theory, the lithium source material can be Li2CO3. The inventors believe that dissolving the lithium source compound in an aqueous solution and adding it to the first dispersion, followed by introducing carbon dioxide and stirring thoroughly to react and generate lithium carbonate, can more uniformly coat the outside of the first intermediate. The lithium source compound includes lithium hydroxide.

[0056] In one embodiment of this application, the concentration of the aqueous solution of the lithium source compound is from 1% to 10%. For example, the concentration of the aqueous solution of the lithium source compound can be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or a range consisting of any two of these values.

[0057] In one embodiment of this application, the lithium source material may include LiF and Li2CO3, with a mass ratio of LiF to Li2CO3 ranging from 1:1 to 10:1, and the concentration of the corresponding aqueous solution of the lithium source compound ranging from 1% to 10%. For example, the mass ratio of LiF to Li2CO3 may be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, or any range of two such values; similarly, the concentration of the aqueous solution of the lithium source compound may be 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any range of two such values. The introduction of LiF and Li2CO3 can improve the composition of the SEI, enhance its mechanical strength and ionic and electronic conductivity, thereby improving the cycle performance of the lithium-ion battery.

[0058] In one embodiment of this application, the mass ratio of the first intermediate to the lithium salt is from 100:0.5 to 100:3. For example, the mass ratio can be 100:0.5, 100:0.6, 100:0.7, 100:0.8, 100:0.9, 100:1, 100:1.5, 100:2, 100:2.5, 100:3, or a range of any two of the above values. By controlling the mass ratio of the first intermediate to the lithium salt within the above range, the composition of the SEI film can be changed and the thickness of the SEI can be reduced, thereby increasing the lithium-ion mobility of the SEI and improving the cycle performance of the electrochemical device. Simultaneously, the silicon content in the final anode material is not significantly reduced, thus ensuring that the anode material has sufficient reversible capacity.

[0059] In one embodiment of this application, the solid content of the second dispersion is 8% to 20%. For example, the solid content of the second dispersion can be 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, or a range consisting of any two of these values. By controlling the solid content within the above range, the particle size distribution of secondary particles after spray drying can be controlled while taking into account both the drying capacity and production capacity of the equipment.

[0060] In one embodiment of this application, the stirring and dispersion time of the second dispersion is 3 to 6 hours. For example, the stirring and dispersion time can be 3 hours, 4 hours, 5 hours, 6 hours, or a range consisting of any two of the above values. By controlling the stirring and dispersion time within the above range, sufficient stirring can ensure that the first intermediate and the lithium source material in the aqueous solution are in full and uniform contact, thereby improving the uniformity of the lithium salt layer.

[0061] In one embodiment of this application, the drying temperature in the oven is 100°C to 150°C, and the drying time is 12 hours to 24 hours. For example, the drying temperature can be 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, or any combination of two of these values; the drying time can be 12 hours, 13 hours, 14 hours, 15 hours, 16 hours, 17 hours, 18 hours, 19 hours, 20 hours, 21 hours, 22 hours, 23 hours, 24 hours, or any combination of two of these values. By adjusting the drying parameters of the oven within the above range, the particle size distribution of the dried particles can be controlled, effectively reducing the risk of particle size increase caused by particle adhesion.

[0062] In one embodiment of this application, the solid content of the third dispersion is 15% to 30%. For example, the solid content can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, or a range of any two of the above values. By controlling the solid content of the second intermediate in deionized water within the above range, the particle size distribution of the secondary particles after spray drying can be controlled while taking into account both the drying capacity and production capacity of the equipment.

[0063] In one embodiment of this application, the mass ratio of the mixture of the first silicon-based material, the second silicon-based material, and the passivated lithium powder is m1:m2:m3 = 100:10 to 40:0.5 to 5. For example, the mass ratio of the mixture of the first silicon-based material, the second silicon-based material, and passivated lithium powder can be 100:10:0.5, 100:15:0.5, 100:20:0.5, 100:25:0.5, 100:30:0.5, 100:35:0.5, 100:40:0.5, 100:10:1, 100:10:2, 100:10:3, 100:10:4, 100:10:5, 100:25:1, 100:25:2, 100:25:3, 100:25:4, 100:25:5, or a range of any two of these values.

[0064] In one embodiment of this application, the solid content of the fourth dispersion is 18% to 22%, for example, the solid content can be 18%, 19%, 20%, 21%, 22% or a range of any two of the above values.

[0065] In one embodiment of this application, the solid content of the mixture of the third dispersion and the fourth dispersion is 15% to 25%. For example, the solid content can be 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, or a range of any two of the above values.

[0066] In one embodiment of this application, the stirring and dispersion time of the negative electrode material is 3 to 6 hours. For example, the stirring and dispersion time can be 3 hours, 4 hours, 5 hours, 6 hours, or a range consisting of any two of the above values. Sufficient stirring allows the mixture of the first silicon-based material, the second silicon-based material, the passivated lithium powder, and the polyurethane in the aqueous solution to come into full and uniform contact, improving the uniformity of the organic polymer on the outside of the negative electrode material.

[0067] In one embodiment of this application, the inlet air temperature for spray drying of the negative electrode material is 200–230°C, and the outlet air temperature is 100–110°C. For example, the inlet air temperature for spray drying of the negative electrode material can be a range of 200°C, 205°C, 210°C, 215°C, 220°C, 225°C, 230°C, or any two of these values; the outlet air temperature can be a range of 100°C, 102°C, 104°C, 106°C, 108°C, 110°C, or any two of these values. The spray drying parameters are within the above ranges, controlling the particle size distribution of the secondary particles after spray drying while considering both the drying capacity and production output of the equipment.

[0068] A third aspect of this application provides an electrochemical device comprising a positive electrode, a negative electrode, and an electrolyte, wherein the negative electrode comprises a negative electrode active material layer comprising the negative electrode material described in the first aspect of this application.

[0069] In one embodiment of this application, the electrolyte comprises at least one of lithium bis(trifluoromethanesulfonyl)imide or lithium bis(fluorosulfonyl)imide; based on the mass of the electrolyte, the mass percentage of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and / or lithium bis(fluorosulfonyl)imide (LiFSI) is from 0.1% to 5%. For example, the mass percentage of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and / or lithium bis(fluorosulfonyl)imide (LiFSI) can be 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two of these values. By adjusting within the above range, LiTFSI and / or LiFSI can improve the contact interface and enhance the cycle performance and rate performance of the electrochemical device during cycling by interacting with the negative electrode material.

[0070] In the electrochemical device of this application, the electrolyte also includes electrolyte lithium salt and non-aqueous solvent.

[0071] In some embodiments of this application, the electrolyte lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylboronate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium trifluoromethanesulfonate (LiCF3SO3), LiC(SO2CF3)3, lithium hexafluorosilicate (LiSiF6), lithium bis(oxalato)borate (LiBOB), and lithium difluoroborate (LiF2OB). For example, LiPF6 can be selected as the electrolyte lithium salt because it has high ionic conductivity and improves cycle characteristics. Based on the mass of the electrolyte, the mass percentage of the electrolyte lithium salt can be from 8% to 20%, for example, the mass percentage of the electrolyte lithium salt can be 8%, 10%, 12%, 14%, 16%, 18%, 20%, or a range of any two of these values.

[0072] The non-aqueous solvent may be a carbonate compound, a carboxylic acid ester compound, an ether compound, other organic solvents, or a combination thereof.

[0073] The aforementioned carbonate compounds may be chain carbonate compounds, cyclic carbonate compounds, fluorocarbonate compounds, or combinations thereof. Examples of the aforementioned chain carbonate compounds are dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (EMC), and combinations thereof. Examples of cyclic carbonate compounds are ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof. Examples of fluorocarbonate compounds are fluoroethylene carbonate (FEC), 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, trifluoromethylethylene carbonate, and combinations thereof.

[0074] Examples of the above-mentioned carboxylic acid ester compounds are methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanoic acid lactone, valerate lactone, mevalonic acid lactone, caprolactone, and combinations thereof.

[0075] Examples of the above-mentioned ether compounds are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0076] Examples of other organic solvents mentioned above include dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters and combinations thereof.

[0077] In this application, the electrochemical device further includes a negative electrode sheet, 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.

[0078] 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.

[0079] The negative electrode active material layer also contains carbon material, which may include at least one of natural graphite, artificial graphite, hard carbon material, soft carbon material, or mesophase microcarbon spheres. Based on the mass of the negative electrode active material layer, the carbon material content ranges from 30% to 95%. For example, it can be 30%, 35%, 40%, 45%, 50%, 55%, 60%, 70%, 80%, 90%, 95%, or a range of any two of these values.

[0080] 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 restrictions on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, binders may include, but are not limited to, polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, or nylon, etc. Conductive agents may include, but are not limited to, carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. Carbon-based materials are selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof; metal-based materials are selected from metal powder, metal fiber, copper, nickel, aluminum, or silver; and conductive polymers are polyphenylene derivatives. This application does not impose any particular restrictions on the mass ratio of the negative electrode material, conductive agent, and binder in the negative electrode active material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0081] 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.

[0082] 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.

[0083] In this application, the electrochemical device further includes a positive electrode sheet, which comprises a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector. The aforementioned "positive active material layer disposed on at least one surface of the positive current collector" means that the positive active material layer can be disposed on one surface of the positive current collector along its own thickness direction, or it can be disposed on two surfaces of the positive current collector along its own thickness direction. It should be noted that the "surface" here can be the entire surface area of ​​the positive current collector, or it can be a partial surface area of ​​the positive current collector; this application has no particular limitation, as long as the purpose of this application is achieved.

[0084] 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).

[0085] This application does not impose any particular restrictions on the cathode material, as long as it can achieve the purpose of this application. For example, the cathode 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.

[0086] The positive electrode active 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 achieve the purpose of this application. This application does not impose any particular restrictions on the mass ratio of the positive electrode material, conductive agent, and binder in the positive electrode active material layer; those skilled in the art can select them according to actual needs, as long as the purpose of this application is achieved.

[0087] 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 styrene-butadiene rubber, or polyurethane, wherein polyolefin adhesives include at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0088] 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.

[0089] This application does not impose any particular limitations on the thickness of the positive electrode current collector and the positive electrode active material layer, as long as the purpose of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the single-sided positive electrode active material layer is 30 μm to 120 μm.

[0090] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive active 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.

[0091] 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.

[0092] 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.

[0093] Optionally, a surface treatment layer is provided 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 substances.

[0094] 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).

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] A fourth aspect of this application provides an electronic device that includes the electrochemical device provided in the third aspect of this application.

[0100] The electronic device described in this application is not particularly limited and can be any electrical device known in the prior art. In some embodiments, the electrical device 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.

[0101] Example

[0102] 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.

[0103] Test methods and equipment

[0104] Si element mass percentage test

[0105] Preparation of digested sample: Take 0.1000g of silicon-based anode particles or anode material, place them in a nickel crucible, add 1.5g of KOH, and cover the crucible. Heat the muffle furnace to 400℃. The heating program is as follows: increase the temperature from room temperature to 300℃ within 2 hours, and then increase 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 an F4 beaker.

[0106] Titration with sodium hydroxide standard solution of digested sample: Add 30 mL of boiling water to an F4 beaker and soak for 1 hour. Then, use tweezers to clean the crucible, 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 while continuously stirring, with an excess of 2 g. Then add 10 mL of 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.

[0107] 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.

[0108] 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 the titration, in L; V0 is the volume of sodium hydroxide standard solution consumed by the blank sample, in L; 7.02 is the molar mass of 1 / 4 Si, in g / mol; m is the mass of the sample, in g.

[0109] Carbon element mass percentage test

[0110] The negative electrode material is heated and burned at high temperature in a high-frequency furnace under oxygen-enriched conditions to oxidize carbon into carbon dioxide. This gas is then treated and enters a corresponding absorption cell, where it absorbs the corresponding infrared radiation, which is then converted into a corresponding signal by a detector. This signal is sampled by a computer, linearly corrected, and converted into a value proportional to the carbon dioxide concentration. The values ​​from the entire analysis process are then accumulated. After the analysis, this accumulated value is divided by the weight value in the computer, multiplied by a correction factor, and the blank is subtracted to obtain the carbon mass percentage. The test is performed using a high-frequency infrared carbon-sulfur analyzer (Shanghai Dekai HCS-140).

[0111] Powder conductivity test

[0112] The conductivity of each synthesized negative electrode material was tested using a powder resistivity meter in a drying chamber. The reciprocal of the conductivity is the resistance of the negative electrode material.

[0113] Particle size testing

[0114] The Dv50 and Dv90 of the first silicon-based material, the second silicon-based material particles, and the anode material were measured using a Mastersizer 3000 particle size analyzer manufactured by Malvern Corporation.

[0115] XRD testing and silicon grain size calculation

[0116] First and second silicon-based material powders were placed in the sample stage of an XRD instrument (Bruker D8 ADVANCE). Using a scan rate of 2° / min and a scan angle range of 10° to 90°, Cu Kα rays were used to obtain XRD diffraction patterns. The silicon grain size was calculated in the testing software using the XRD diffraction data and fitted according to the Scherrer formula.

[0117] The fabrication process of a coin cell includes:

[0118] (1) Preparation process of the positive electrode sheet: The negative electrode material prepared in the examples or comparative examples is used as the active material, acetylene black as the conductive agent, and sodium alginate as the binder. The mass ratio of active material, acetylene black, and sodium alginate is 90:5:5. The active material and acetylene black are thoroughly mixed in the ratio and ground evenly. Sodium alginate aqueous solution is added in the ratio and stirred for 4 hours. Finally, the mixture slurry is evenly coated on copper foil and vacuum dried at 70°C to form a circular electrode sheet with a diameter of 10 mm.

[0119] Electrolyte and separator: In an argon-atmospheric glove box with a water content of <10ppm, propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) were mixed in a 1:1:1 ratio to obtain the base solvent. Lithium salt LiPF6 was then added, dissolved, and mixed thoroughly to obtain the electrolyte. The lithium salt LiPF6 comprised 12.5% ​​of the total electrolyte mass, with the remainder being the base solvent. An 8μm thick PE / PP composite film was used as the separator.

[0120] (2) Assembly of button half-cell: In an argon atmosphere glove box with a water content of <10ppm, lithium metal sheet is used as negative electrode. The negative electrode, the separator prepared above and the positive electrode are stacked in sequence, so that the separator is placed between the positive electrode and the negative electrode to play a role in isolation. After assembly, the electrolyte prepared above is injected to obtain button half-cell.

[0121] The test methods for the first charge-discharge specific capacity include:

[0122] At 25℃ and normal pressure, the prepared coin cell was discharged at a constant current rate of 0.1C to 0.01V, and then left to stand for 5 minutes. The discharge specific capacity at this time was recorded, which is the first discharge specific capacity.

[0123] Then charge at a constant current rate of 0.1C to 1.5V, then charge at a constant voltage rate to 0.05C, and then let it stand for 5 minutes. This is one cycle of charge and discharge. Record the charging capacity at this time, which is the specific capacity of the first charge cycle.

[0124] First-cycle charge / discharge efficiency = First-cycle charge specific capacity / First-cycle discharge specific capacity × 100%.

[0125] Lithium-ion battery cycle performance test

[0126] For the lithium-ion batteries in the examples or comparative cases, the test temperatures were 25°C / 45°C. They were charged at a constant current of 3.4C to 4.4V, then charged at a constant voltage of 0.025C, and after a 5-minute rest period, discharged at 0.5C to 3.0V. The capacity obtained in this process was used as the initial capacity. Cyclic tests were then performed using 3.4C charge / 0.5C discharge for 500 cycles. The ratio of the capacity at each step to the initial capacity was used to obtain a cycle performance comparison chart. Figure 2 and Figure 3 .

[0127] The room temperature cycling performance of a battery is defined as the number of cycles from 25°C until 90% capacity retention is achieved.

[0128] The high-temperature cycle performance of a battery is defined as the number of cycles at 45°C until the capacity retention rate reaches 80%. The cycle performance of lithium-ion batteries is compared by comparing the number of cycles under the two conditions mentioned above.

[0129] Lithium-ion battery rate cycle capacity retention test

[0130] The lithium-ion battery was placed in a constant temperature chamber at 25°C for 1 hour to allow it to reach a constant temperature; it was then charged at a constant current of 0.2C to 4.4V, charged at a constant voltage of 0.025C, and left to stand for 30 minutes; it was then discharged at 0.2C to 3.0V and left to stand for 30 minutes. The capacity (D0) obtained in this step was used as a baseline.

[0131] At 25℃, charge to 4.4V with a constant current of 0.7C, then charge to 0.025C with a constant voltage, and let stand for 30 minutes; discharge to 3.0V with a constant current at different rates of 0.2C / 0.5C / 0.7C / 1C / 1.5C / 2C, and record the capacity as D at each rate. x (x is 0.2, 0.5, 0.7, 1, 1.5, or 2). Discharge capacity ratio at different rates = D x / D0×100%, generate a capacity retention curve, i.e. Figure 6 The 2C rate discharge capacity ratio is the 2C capacity retention rate.

[0132] Lithium-ion battery cycle expansion rate test

[0133] For lithium-ion batteries, the relative difference between the battery thickness after 400 discharge cycles at 25°C to 3.0V and the original battery thickness, divided by the original battery thickness, is recorded as the room temperature cycle expansion rate of the battery.

[0134] The relative difference between the battery thickness after 400 discharge cycles at 45℃ to 3.0V and the original battery thickness, divided by the original battery thickness, is recorded as the high-temperature cycle expansion rate of the battery.

[0135] The thickness was adjusted by cycling at 25℃ for 400 cycles to discharge to 3.0V, and the thickness at each step was compared with the original thickness. Similarly, the thickness was adjusted by cycling at 45℃ for 400 cycles to discharge to 3.0V, and the thicknesses at 0, 50, 100, 150, 200, 300, and 400 cycles were compared with the original thickness to obtain an expansion rate comparison chart. Figure 4 and Figure 5 .

[0136] Example 1

[0137] <Preparation of Anode Materials>

[0138] (1) Take 200 kg of silicon-carbon particles and classify them using jet classification (or cyclone classification) to obtain the core particles of the first silicon-based material.

[0139] (2) Take 1 kg of silicon-carbon core particles of the first silicon-based material with a Dv50 of 2.985 μm and a silicon grain size of 1.31 nm. Transfer 1 kg of silicon-carbon particles into a fluidized bed through high-pressure transmission. After standing for about 30 min, close the fluidized bed inlet valve and outlet valve and evacuate. When the chamber pressure reaches -101 kPa, close the vacuum and introduce nitrogen at a rate of 10 L / min to bring it to positive pressure. Repeat the vacuuming and nitrogen introduction at least 5 times, and then check the oxygen content inside the chamber. When the oxygen content drops below 10 ppm, open the outlet valve, start the fluidized bed agitator at a speed of 150 rpm, introduce nitrogen at a rate of 20 L / min, and heat to 600℃ at a heating rate of 5℃ / min. Hold at this temperature for 1 h. After the heat preservation period, the valve of the fluidized bed inlet pipeline was switched to introduce an acetylene / nitrogen mixture into the fluidized bed. The acetylene volume percentage was 25%, the gas flow rate was 20 L / min, and the reaction time was 150 min. After the reaction, nitrogen was introduced at a flow rate of 15 L / min, and the agitator speed was adjusted to 100 rpm for cooling. The material was discharged at room temperature to obtain the first intermediate of the first silicon-based material.

[0140] (3) Prepare 508.8g of lithium acetate aqueous solution with a lithium acetate concentration of 10%, prepare 285.5g of ammonium fluoride aqueous solution with an ammonium fluoride concentration of 10%, and prepare 64.8g of lithium hydroxide aqueous solution with a lithium hydroxide concentration of 10%.

[0141] (4) Prepare 5 kg of deionized water, add 1 kg of the first intermediate, and stir thoroughly to obtain the first dispersion. While stirring, pour 508.8 g of 10% lithium acetate aqueous solution into the first dispersion and stir thoroughly for 1 h. While stirring, slowly pour 285.5 g of 10% ammonium fluoride aqueous solution and react thoroughly for 2 h. While stirring, slowly pour 64.8 g of 10% lithium hydroxide aqueous solution and stir thoroughly for 1 h. While stirring, pass CO2 gas through the mixture at a rate of 5 L / min for 2 h and stir thoroughly for 3 h to obtain the second dispersion. Filter the second dispersion, wash it 3 times, and then dry it in a 100℃ oven (a constant vacuum drying oven, DZF-6020) for 24 h to obtain the first silicon-based material.

[0142] (5) The core particles of the second silicon-based material are obtained by jet classification (or cyclone classification). Take 1 kg of the core particles of the second silicon-based material with a Dv50 of 0.295 μm and a silicon grain size of 1.8 nm, and repeat steps (2) to (4). The coating temperature of carbon coating is reduced to 550 °C to obtain the second silicon-based material.

[0143] (6) Take 1000g of the first silicon-based material, 300g of the second silicon-based material, and 30g of passivated lithium powder, add them to 7kg of deionized water, and stir thoroughly for 2 hours to obtain the third dispersion. While stirring, add 333g of the fourth dispersion (solute is polyurethane, solvent is deionized water) with a solid content of 20% to the third dispersion, and stir thoroughly for 3 hours. Start the spray dryer, set the inlet air temperature to 220℃ and the outlet air temperature to 105℃. After the inlet and outlet air temperatures reach the set range, first supply deionized water at a supply rate of 300mL / min, and after running stably for about 30 minutes, switch to supplying slurry. The dried negative electrode material after secondary granulation is obtained from the discharge port.

[0144] In the first silicon-based material, the carbon layer has a mass percentage of 3%, and the total mass percentage of LiF and Li2CO3 is 2% (LiF has a mass percentage of 1.4%, and Li2CO3 has a mass percentage of 0.6%). The particle size Dv50 of the first silicon-based material is 3 μm. In the second silicon-based material, the carbon layer has a mass percentage of 3%, and the total mass percentage of LiF and Li2CO3 is 2% (LiF has a mass percentage of 1.4%, and Li2CO3 has a mass percentage of 0.6%). The particle size Dv50 of the second silicon-based material is 0.3 μm. The Dv50 of the passivated lithium powder is 0.07 μm.

[0145] The mass ratio of the first silicon-based material, the second silicon-based material, and the passivated lithium powder satisfies the following condition: m1:m2:m3 = 100:30:3. Based on the mass of the negative electrode material, the mass percentage of polyurethane is 4.6%.

[0146] The negative electrode material prepared in Example 1-1 has a Dv50 of 7.6 μm and a Dv90 of 26.7 μm. The structural schematic diagram is shown in Figure 1.

[0147] Examples 1-2 to Examples 1-4

[0148] Except for adjusting the particle size Dv50 of the first silicon-based material according to Table 1, which causes the average size of the core silicon grains to change accordingly, the rest is the same as in Examples 1-1.

[0149] Examples 1-5

[0150] Except for the simultaneous adjustment of the carbon layer mass percentage of the first silicon-based material and the second silicon-based material to 1%, and the unchanged mass percentage of lithium salt, the rest is the same as in Example 1-1.

[0151] Examples 1-6

[0152] Except for the simultaneous adjustment of the carbon layer mass percentage of the first silicon-based material and the second silicon-based material to 5.2%, and the unchanged mass percentage of lithium salt, the rest is the same as in Example 1-1.

[0153] Examples 1-7

[0154] Except for the simultaneous adjustment of the mass percentage of lithium salts in the first silicon-based material and the second silicon-based material to 1.2% (the mass percentage of LiF is 0.6% and the mass percentage of Li2CO3 is 0.6%), and the unchanged mass percentage of carbon layer, the rest is the same as in Example 1-1.

[0155] Examples 1-8

[0156] Except for the simultaneous adjustment of the mass percentage of lithium salts in the first silicon-based material and the second silicon-based material to 0.6% (the mass percentage of LiF is 0.3% and the mass percentage of Li2CO3 is 0.3%), and the unchanged mass percentage of carbon layer, the rest is the same as in Examples 1-1.

[0157] Examples 1-9

[0158] Except for the synchronous adjustment of the lithium salt type of the first silicon-based material and the second silicon-based material to LiF, with a mass percentage of 2%, and the carbon layer mass percentage remaining unchanged, the rest is the same as in Example 1-1.

[0159] Examples 1-10 to Examples 1-23

[0160] Except for adjusting the relevant parameters according to Table 1, everything else is the same as in Example 1-1.

[0161] Comparative Example 1

[0162] Except for not adding the first silicon-based material as per Table 1, the rest is the same as in Example 1-1.

[0163] Comparative Example 2

[0164] Except for not adding a second silicon-based material as per Table 1, the rest is the same as in Examples 1-1.

[0165] Comparative Example 3

[0166] Except for adjusting the relevant parameters according to Table 1, everything else is the same as in Example 1-1.

[0167] Example 2-1

[0168] <Preparation of Negative Electrode Sheets>

[0169] Graphite, the negative electrode material prepared according to Examples 1-1, and the conductive agent (conductive carbon black, Super) were used. The negative electrode slurry, containing 70 wt% solids, was prepared by dissolving polyacrylic acid (PAA) and binder in a ratio of 80:10:5:5 in deionized water. Deionized water was then 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 current collector and dried at 120°C to obtain a single-sided coated negative electrode sheet. 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 later use. The thickness of the single-sided negative electrode active material layer is 54.5μm.

[0170] <Preparation of the positive electrode>

[0171] 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.

[0172] <Preparation of Electrolyte>

[0173] In a dry argon atmosphere, propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) are mixed in a 1:1:1 ratio 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.

[0174] <Isolation membrane>

[0175] An 8μm PE / PP composite film was used as the separator.

[0176] <Preparation of Lithium-ion Batteries>

[0177] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. This is then wound to obtain a bare battery cell. The bare cell is placed in outer packaging, electrolyte is injected, and it is sealed. After processes such as formation, degassing, and edge trimming, a lithium-ion battery is obtained.

[0178] Examples 2-2 to 2-23

[0179] Except for the negative electrode materials in <Preparation of Negative Electrode Sheet>, which are selected from the negative electrode materials prepared in the corresponding Examples 1-2 to 1-23 according to Table 2, the rest are the same as in Example 2-1.

[0180] Comparative Examples 4 to 6

[0181] Except for the negative electrode materials used in <Preparation of Negative Electrode Sheet>, which were selected from Comparative Examples 1 to 3 according to Table 2, the rest are the same as in Example 2-1.

[0182] Examples 3-1 to 3-9

[0183] Except for the addition of LiTFSI and LiFSI to the electrolyte according to Table 3 in the <Preparation of Electrolyte>, and the adjustment of the mass percentage of LiTFSI and LiFSI, the mass percentage of the base solvent and the mass percentage of lithium salt LiPF6 are changed accordingly, the rest is the same as in Examples 2-21.

[0184] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 3.

[0185]

[0186]

[0187]

[0188]

[0189] Table 3

[0190]

[0191] Note: " / " in Table 3 indicates that there is no corresponding preparation parameter, substance or performance parameter.

[0192] The mass percentage and type of additives in the electrolyte affect the cycle performance and rate performance of lithium-ion batteries. As can be seen from Examples 2-21 and 3-1 to 3-9, when the mass percentage of lithium bis(trifluoromethanesulfonyl)imide and / or lithium bis(fluorosulfonyl)imide in the electrolyte is between 0.1% and 5%, the lithium-ion battery made using the negative electrode material provided in this application exhibits lower room temperature cycle expansion rate, higher high temperature cycle expansion rate, and higher room temperature cycle performance, higher high temperature cycle performance, and 2C capacity retention.

[0193] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0194] 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.

Claims

1. A negative electrode material, comprising: a first silicon-based material, a second silicon-based material, a passivated lithium powder, and an organic polymer; The first silicon-based material and the second silicon-based material each include an inner core, a carbon layer outside the inner core, and a lithium salt layer outside the carbon layer, a particle size Dv50 of the first silicon-based material is A, 2 pm ≤ A ≤ 5 pm, a particle size Dv50 of the second silicon-based material is B, and 2 pm ≤ B ≤ 5 pm. 4B < A < 20B; a particle size Dv50 of the passivated lithium powder is C, 0.01 μm ≤ C ≤ 0.1 μm.

2. The negative electrode material of claim 1, wherein, The negative electrode material satisfies at least one of the following: (1) the inner core comprises at least one of silicon-carbon particles or silicon-oxygen particles; (2) the lithium salt comprises at least one of LiF or Li2CO3; (3) a mass percentage content of the carbon layer of the first silicon-based material is 1% to 5.2%, and a mass percentage content of the lithium salt layer is 0.53% to 2.1%, based on a mass of the first silicon-based material; (4) a mass percentage content of the carbon layer of the second silicon-based material is 1% to 5.2%, and a mass percentage content of the lithium salt layer is 0.53% to 2.1%, based on a mass of the second silicon-based material.

3. The negative electrode material of claim 1, wherein, a silicon grain average size in the inner core of the first silicon-based material is a, and a silicon grain average size in the inner core of the second silicon-based material is b; 1 nm ≤ a ≤ 1.5 nm, 1.5 nm ≤ b ≤ 2 nm, and a < b.

4. The negative electrode material of claim 1, wherein, 0.1 μm ≤ B ≤ 0.5 μm.

5. The negative electrode material of claim 1, wherein, a mass of the first silicon-based material is m1 g, a mass of the second silicon-based material is m2 g, and a mass of the passivated lithium powder is m3 g; a mass ratio satisfies: m1:m2:m3 = 100:10 to 40:0.5 to 5; a mass percentage content of the organic polymer is 3% to 7%, based on a mass of the negative electrode material.

6. The negative electrode material according to any one of claims 1 to 5, wherein The negative electrode material satisfies at least one of the following: (1) a Dv50 of the negative electrode material is 6 μm to 10 μm; (2) a Dv90 of the negative electrode material is less than or equal to 30 μm; (3) the organic polymer comprises polyurethane; (4) a mass percentage content of silicon elements is 40% to 50%, based on a mass of the negative electrode material. 7.An electrochemical device, comprising a positive electrode sheet, a negative electrode sheet, and an electrolyte, the negative electrode sheet comprising a negative electrode active material layer, the negative electrode active material layer comprising the negative electrode material according to any one of claims 1 to 6.

8. The electrochemical device of claim 7, wherein, The electrolyte comprises at least one of lithium bis(trifluoromethylsulfonyl)imide or lithium bis(fluorosulfonyl)imide; a mass percentage content of the lithium bis(trifluoromethylsulfonyl)imide and / or the lithium bis(fluorosulfonyl)imide is 0.1% to 5%, based on a mass of the electrolyte. 9.A preparation method of the negative electrode material according to any one of claims 1 to 6, comprising: providing an inner core of a first silicon-based material, carbon-coating the inner core to obtain a first intermediate, dispersing the first intermediate in water to obtain a first dispersion, adding an aqueous solution of a lithium source substance to the first dispersion to obtain a second dispersion, sufficiently dispersing and stirring, and drying through an oven to obtain a first silicon-based material; An inner core of a second silicon-based material is provided, carbon-coated to obtain a first intermediate, which is dispersed in water to obtain a first dispersion, an aqueous solution of a lithium source is added to the first dispersion to obtain a second dispersion, which is sufficiently dispersed and stirred, and dried through an oven to obtain a second silicon-based material; The first silicon-based material, the second silicon-based material and the passivated lithium powder are dispersed and then added to deionized water to obtain a third dispersion; a polymer is dispersed in water to obtain a fourth dispersion, the fourth dispersion is added to the third dispersion, mixed and sufficiently stirred, and spray-dried to obtain a negative electrode material.

Images