Silicon oxide SiOx particle for negative electrode of lithium ion battery

Abstract

The invention discloses a silicon oxide SiOx particle for a negative electrode of a lithium ion battery, the outer layer of the silicon oxide SiOx particle is provided with a carbon coating layer, the silicon oxide SiOx particle is a porous silicon oxide with a spherical structure, and the average particle size of the porous silicon oxide particle is 3-30 [mu] m. The large-particle-size porous silicon oxide SiOx disclosed by the invention is applied to a lithium battery negative electrode material, the specific surface area is smaller, the stress distribution is more uniform, and the volume expansion is buffered by virtue of a porous structure, so that the cycling stability is remarkably improved. And the cycle performance and the first coulombic efficiency of the lithium battery using the material as the negative electrode are further improved. The capacity and the service life of the lithium battery can be further improved.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery material technology, specifically relating to silicon oxide (SiOx) particles for use as the negative electrode of lithium-ion batteries. Background Technology

[0002] Since their inception, lithium-ion batteries have become the mainstream in the market due to their superior performance (such as high operating voltage, high specific energy, good cycle performance, long service life, wide operating temperature range, no memory effect, low self-discharge, and no pollution). However, with the increasing demand for lithium-ion batteries in industries such as aviation and automobiles, the capacity and energy density of batteries urgently need to be significantly improved. Currently, there are several main types of anode materials for commercial lithium-ion batteries, including carbon-based materials and silicon-based materials. Carbon-based materials are the preferred anode material for lithium-ion batteries (especially consumer electronics and power batteries) due to their good conductivity, layered structure which facilitates lithium-ion intercalation, small volume change (<10%), and low cost. Silicon-based materials are the main alternative to carbon-based materials, and silicon-based materials are generally composed of SiO2. x (x < 2) Silicon-carbon composite anodes, which are combined with carbon materials, address the volume expansion issue through modification and have already achieved partial commercial applications. In the short term, silicon-carbon composite anodes, characterized by "high capacity + long cycle life + low cost," will gradually replace some carbon-based materials in power batteries and consumer electronics, and will become the mainstream in the medium to long term.

[0003] Currently, SiOx particles used in lithium-ion battery anodes are solid particles, ranging in size from nanometers to micrometers. Both sizes have distinct advantages and disadvantages. Micrometer-sized (large) SiOx particles offer the following advantages: 1. Excellent processing performance and engineering adaptability; compatible with existing electrode fabrication processes, with good processing performance; high tap density, beneficial for improving battery volumetric energy density; low cost for large-scale production, suitable for industrial manufacturing. 2. Improved interface stability and cycle durability; exhibits excellent cycle stability in full cells; forms a thinner and more stable SEI film, reducing electrolyte consumption; more stable interparticle contact, resulting in better overall electrode structure. However, they also present the following problems: 1. Limited electrochemical kinetic performance; long lithium-ion diffusion paths (up to several micrometers) lead to poor rate performance; severe polarization at high current densities significantly reduces specific capacity; reduced utilization of active materials, especially in the internal region of the particle. 2. More significant volume expansion effect; larger particles have greater absolute volume changes, leading to particle pulverization and electrode structure damage. 3. Reduced utilization of active materials and difficulty for lithium ions to fully penetrate the particle interior lead to capacity loss; furthermore, uneven electrode reactions result in significant differences in activity between the particle surface and interior. Currently, the most common SiOx particles used in lithium-ion battery anodes are solid particles, mainly 5 micrometers and 7 micrometers in size. Their addition to the battery anode cannot exceed 10%, as exceeding this amount causes severe expansion and a precipitous drop in electrochemical performance. Nanoscale (small-size) SiOx particles offer the following advantages: 1. Significantly alleviates volume expansion and stress concentration. 2. Significantly improves electrochemical kinetic performance. 3. Enhances cycle stability; the nanostructure makes volume changes more uniform, reducing the risk of electrode cracking. However, they also have the following disadvantages: 1. Significantly reduced initial coulombic efficiency. 2. Processing and engineering challenges. 3. Interface stability issues; high surface energy causes particles to easily detach during cycling, reducing electrode structural stability. Summary of the Invention

[0004] The purpose of this invention is to provide silicon oxide (SiOx) particles for lithium-ion battery anodes that exhibit low volume expansion and stress, strong electrochemical kinetic performance, high cycle stability, high initial coulombic efficiency, and excellent processing performance and engineering adaptability, thereby enabling lithium battery anodes to achieve high initial efficiency and high cycle life.

[0005] The technical solution of the present invention is: a silicon oxide (SiOx) particle for a negative electrode of a lithium-ion battery, wherein the outer layer of the silicon oxide (SiOx) particle has a carbon coating layer, characterized in that the silicon oxide (SiOx) particle is a porous silicon oxide with a spherical structure, and the average particle size of the porous silicon oxide particle is 3–30 μm.

[0006] Preferably, the characteristic parameters of the particle size distribution of the silicon oxide (SiOx) particles are: D10 is 3-10 μm, D50 is 10-20 μm, D90 is 20-30 μm, and the particle size distribution span is <2.5.

[0007] Preferably, the porosity of the porous silicon oxide (SiOx) particles is 40–60%.

[0008] Preferably, the specific surface area of ​​the porous silicon oxide (SiOx) particles is 20-70 m² / g.

[0009] Preferably, the mass percentage of the outer carbon coating of the porous silicon oxide (SiOx) particles is 2-6%.

[0010] A lithium-ion battery negative electrode includes graphite, silicon oxide (SiOx) particles, and a binder, wherein the silicon oxide (SiOx) particles are any of the silicon oxide (SiOx) particles described in the above technical solutions.

[0011] A lithium-ion battery includes a casing, a positive electrode, and a negative electrode, wherein the negative electrode of the lithium-ion battery adopts the above-mentioned technical solution.

[0012] The advantages of this invention are: The large-particle-size porous silicon oxide (SiO) of the present invention x When applied to lithium-ion battery anode materials, its smaller specific surface area, more uniform stress distribution, and porous structure that buffers volume expansion significantly improve cycle stability. This further enhances the cycle performance and initial coulombic efficiency of lithium-ion batteries using this material as the anode, ultimately increasing battery capacity and lifespan. Attached Figure Description

[0013] The present invention will be further described below with reference to the accompanying drawings and embodiments: Figure 1 This is a structural diagram of silicon oxide (SiOx) particles for lithium-ion battery anodes, magnified 2200 times under a scanning electron microscope.

[0014] Figure 2 This is a particle size test report (D50=3μm) of the silicon oxide (SiOx) particles of the present invention.

[0015] Figure 3 This is a particle size test report (D50=15μm) of the silicon oxide SiOx particles of the present invention.

[0016] Figure 4 This is a particle size test report (D50=30μm) of the silicon oxide (SiOx) particles of the present invention.

[0017] Figure 5The results show the electrical performance of the silicon oxide (SiOx) particles of this invention applied to the negative electrode of a lithium battery. Figure 6 This is a flowchart of the assembly process for a half-cell. Detailed Implementation Example

[0018] The preparation of silicon oxide (SiOx) particles involves using an organosilicon source (such as tetraethyl orthosilicate (TEOS) or methyltriethoxysilane) as a precursor, which is hydrolyzed and polymerized to form a sol. A soft template agent (surfactant such as CTAB, PEG, or PVP) is added, and the template agent molecules self-assemble in the sol to form a micelle structure. After drying and calcination to remove the template agent, the spaces occupied by the micelles form a porous structure. Finally, reduction treatment (such as lithium powder or magnesium powder reduction) is used to regulate the SiO content. x The x-value was determined. In this embodiment, tetraethyl orthosilicate (TEOS) was used as the silicon source, hexadecyltrimethylammonium bromide (CTAB) as the soft template agent, ethanol as the solvent, ammonia as the catalyst, and lithium metal powder as the reducing agent (to control the x-value). The mixture was then prepared by mixing TEOS, ethanol, deionized water, and ammonia in a molar ratio of 1:4:6:0.5, adding 5% (by mass) of CTAB, and stirring at 30°C and 300 rpm for 4 hours to form a homogeneous sol. The gel and template were then removed: the sol was aged at room temperature for 24 hours to form a gel, and the solvent was removed using supercritical drying (40°C, 10 MPa) to obtain a dry gel. The dry gel was calcined at 500°C in air for 2 hours to remove the CTAB template, yielding a porous SiOx precursor. Reduced x-value regulation: Porous SiOx precursor and lithium metal powder were mixed at a mass ratio of 100:3 and calcined at 800℃ for 3 h under an inert atmosphere (Ar). After cooling, spherical porous SiOx particles were obtained, where x = 1.3. In this embodiment, porous silicon oxide SiOx particles with sizes of 5–15 μm, 15–25 μm, and 25–40 μm can be obtained by selecting different template agents.

[0019] The obtained porous silicon oxide (SiOx) particles were subjected to carbon coating treatment. In this embodiment, phenolic resin was used as the carbon source and ethanol as the solvent. The particles were mixed at a mass ratio of SiOx to phenolic resin of 100:4 and ultrasonically dispersed for 30 min to form a uniform slurry. Then, the slurry was vacuum dried at 80°C for 6 h to remove the solvent, yielding carbon-coated SiOx particles. These particles were then calcined at 900°C for 2 h under an inert atmosphere (N2) to carbonize the phenolic resin and form a carbon coating layer, ultimately obtaining carbon-coated spherical porous SiOx particles. The structure of the carbon-coated spherical porous SiOx particles is as follows: Figure 1 As shown.

[0020] Electrochemical performance testing, test method: 1. Prepare the slurry (1) The mixing machine and model used: THINKY ARE-310; (2) The mixing sequence and proportion of each part of the slurry.

[0021] Add an appropriate amount of grinding beads to the container. ① Mix CMC and SBR solution (40%), add an appropriate amount of distilled water and stir. Stirring speed and time: 750 rpm for 1 min for pre-stirring; 1900 rpm for 4 min for stirring; 2200 rpm for 30 s for degassing; 2000 rpm for 3 min for stirring; 2200 rpm for 1 min for degassing.

[0022] ② Mix the negative electrode active material and conductive agent, add an appropriate amount of distilled water and stir again. Stirring speed and time: 750 rpm for 1 min for pre-stirring; 1900 rpm for 4 min for stirring; 2200 rpm for 30 s for degassing; 2000 rpm for 3 min for stirring; 2200 rpm for 1 min for degassing.

[0023] Table 1 Composition of Electrode Slurry Element Proportion Graphite + SiOx 90.5% Super P conductive agent 5% CMC 2.0% SBR 2.5% solvent distilled water

[0024] 2. Electrode coating (1) Machine and model used: Nanbeichao TBJ-X3-XB, scraper travel speed 1cm / s; scraper height 250um; (2) Electrode composition. The current collector used is copper foil (copper foil thickness 7um); load 2.5mg~3mg / cm 2 After coating, pre-dry under the following conditions: 60℃ for 10 minutes. 3. Roller pressing (1) Machine and model used: MRX-JS200; (2) Electrode density: 0.5~0.6 g / cm³ 3 .

[0025] 4. Electrode vacuum drying (1) Machine and model used: Shanghai Yiheng Scientific Instruments BV-50; (2) Drying conditions: vacuum degree: -0.1M Pa, drying temperature and time: 80℃*12h.

[0026] 5. Assembly of half-cells (1) Assemble button cells using 2025 model battery casings in an argon glove box. The argon glove box model is Braun Inert Gas Systems Ltd., model PRS269, with water and oxygen content <0.1ppm. The flow chart is as follows. Figure 6 As shown.

[0027] Five carbon-coated spherical porous SiOx particles with different particle size distributions were selected for testing. In the comparison test group, two existing SiOx particles with different particle size distributions were selected for testing.

[0028] Test 1: Select a particle size distribution D50 = 3 μm (rounded to the nearest integer), such as Figure 2 As shown; Pore structure: tested by BET method, porosity = 52%, specific surface area = 65 m² / g; Carbon coating content: tested by elemental analysis, mass percentage = 4.1%, total mass percentage of spherical porous SiOx particles in the negative electrode = 20%; Test 2: Particle size distribution D50 = 5 μm (rounded to the nearest integer); Pore structure: Porosity = 59%, Specific surface area = 58 m² / g; Carbon coating amount: Mass percentage = 3.5%, Total mass percentage of spherical porous SiOx particles in the negative electrode = 20%.

[0029] Test 3: Particle size distribution D50 = 15 μm (rounded to the nearest integer), such as Figure 3 As shown; Pore structure: porosity = 53%, specific surface area = 42 m² / g; carbon coating amount: mass percentage = 4.2%, total mass percentage of spherical porous SiOx particles in the negative electrode = 20%.

[0030] Test 4: Particle size distribution D50 = 20 μm (rounded to the nearest integer); Pore structure: Porosity = 51%, Specific surface area = 37 m² / g; Carbon coating amount: Mass percentage = 5.8%, Total mass percentage of spherical porous SiOx particles in the negative electrode = 20%.

[0031] Test 5: Particle size distribution D50 = 30 μm (rounded to the nearest integer), such as Figure 4 As shown; Pore structure: porosity = 48%, specific surface area = 25 m² / g; carbon coating amount: mass percentage = 2.2%, total mass percentage of spherical porous SiOx particles in the negative electrode = 20%.

[0032] Comparative Test 1: Particle size distribution D50 = 7μm (rounded to the nearest integer); no porous structure; carbon coating amount: tested by elemental analysis, mass percentage = 5.1%, total mass percentage of SiOx particles in the negative electrode = 20%.

[0033] Comparative Test 2: Particle size distribution D50 = 5μm (rounded to the nearest integer); no porous structure; carbon coating: tested by elemental analysis, mass percentage = 5.3%, total mass percentage of SiOx particles in the negative electrode = 20%.

[0034] like Figure 5 As shown, porous SiO₂ with different particle sizes x Particles (3μm, 5μm, 15μm, 20μm, 30μm) and non-porous SiO xParticles (5μm and 7μm) were composited with graphite at a ratio of 20 wt% and tested in batteries. The vertical axis represents the battery's capacity retention (reflecting cycle stability), and the initial coulombic efficiency (ICE) is also indicated. The figure shows that non-porous SiO₂... x ICE particles and porous SiO x The performance of the particles was similar, both around 80%. However, after 40 cycles, the capacity retention was only about 70%, far lower than that of porous SiO. x Data for over 90% of the particles. Porous SiO₂ x Even the lowest capacity retention rate of the particles can reach 91.2%. This is because of the large-particle-size porous SiO₂. x With a smaller specific surface area and a porous structure that provides ample buffer space for volume expansion, the stress distribution of large-diameter particles is more uniform, reducing the risk of particle breakage and electrode pulverization, thus resulting in better cycle stability.

[0035] Of course, the above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be used to limit the scope of protection of the present invention. All modifications made according to the spirit and essence of the main technical solution of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A silicon oxide (SiOx) particle for use as a negative electrode in a lithium-ion battery, wherein the silicon oxide (SiOx) particle has a carbon coating layer on its outer layer, characterized in that, The silicon oxide SiOx particles are porous silicon oxides with a spherical structure, and the average particle size of the porous silicon oxide particles is 3–30 μm.

2. The silicon oxide (SiOx) particles for lithium-ion battery anodes according to claim 1, characterized in that, The characteristic parameters of the particle size distribution of the silicon oxide (SiOx) particles are: D10 is 3-10 μm, D50 is 10-20 μm, D90 is 20-35 μm, and the particle size distribution span is <2.

5.

3. The silicon oxide (SiOx) particles for lithium-ion battery anodes according to claim 2, characterized in that, The porosity of the porous silicon oxide (SiOx) particles is 40–60%.

4. The silicon oxide (SiOx) particles for lithium-ion battery anodes according to claim 3, characterized in that, The specific surface area of ​​the porous silicon oxide (SiOx) particles is 20-70 m² / g.

5. The silicon oxide (SiOx) particles for lithium-ion battery anodes according to claim 3, characterized in that, The mass percentage of the outer carbon coating of the porous silicon oxide (SiOx) particles is 2-6%.

6. A lithium-ion battery negative electrode, comprising graphite, silicon oxide (SiOx) particles, and a binder, characterized in that, The silicon oxide SiOx particles are the silicon oxide SiOx particles as described in any one of claims 1-5.

7. A lithium-ion battery, comprising a casing, a positive electrode, and a negative electrode, characterized in that, The negative electrode of the lithium-ion battery is the negative electrode of the lithium-ion battery according to claim 6.

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