A method for preparing a high-capacity lithium-ion battery negative electrode material

Abstract

The present application belongs to the technical field of lithium ion battery, and particularly relates to a preparation method of high-capacity lithium ion battery negative electrode material, comprising the following steps: (1) using an activating agent to activate a primary particle needle-shaped coke and a secondary particle needle-shaped coke mixture, the activation temperature is 350-670 DEG C, and cooling to room temperature; (2) adding distilled water dropwise to the product of step (1) to a viscous state, stirring, then drying the solid, and adding into a tube furnace, heat treatment under air condition, and cooling to room temperature; (3) mixing the product of step (2) and titanium silicate and ball milling, and then mechanical fusion; (4) calcining the natural graphite and the product of step (3) under a protective atmosphere at a temperature of 1850-2450 DEG C for 4-10 h, mixing, screening and magnetic separation after cooling, to obtain the negative electrode material. The negative electrode material can improve the energy density, discharge capacity and cycle stability of the lithium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for preparing a high-capacity lithium-ion battery anode material. Background Technology

[0002] Carbon materials possess advantages such as low chemical potential, good cycle performance, low cost, and environmental friendliness, making them the most ideal and commonly used anode materials for lithium-ion batteries. Among carbon materials, graphite materials have significant advantages over soft and hard carbon in terms of specific capacity, discharge plateau, and cost. Natural graphite has advantages such as high specific capacity and low cost, but it has a large initial irreversible capacity and poor cycle performance and rate performance. To overcome the shortcomings of natural graphite, improve the electrochemical performance of carbon anode materials, and reduce manufacturing costs, carbon / graphite materials have been widely used as anode materials for lithium-ion batteries due to their high theoretical specific energy, low cost, easy availability, and mature preparation process. However, carbon / graphite anodes have the following problems: the formation of a solid electrolyte interphase (SEI) film on the surface of carbon particles during the first charge causes battery capacity loss, and the amount of SEI film formation increases with the number of charge-discharge cycles. At the same time, the internal impedance of the battery increases, and the energy density, discharge capacity, and cycle life decrease.

[0003] Silicon-based materials, as anodes for lithium-ion batteries, offer advantages such as high capacity, wide availability, and environmental friendliness, and are expected to replace the currently widely used graphite anodes as the primary anode material for next-generation lithium-ion batteries. However, silicon exhibits severe volume expansion during charge and discharge, and the significant volume effect and low conductivity limit the commercial application of silicon anode technology. To overcome these shortcomings, researchers have conducted numerous attempts, employing composite techniques and utilizing a "buffer framework" to compensate for material expansion. Carbon-based anode materials exhibit smaller volume changes during charge and discharge, demonstrating better cycle stability, and are themselves mixed conductors of ions and electrons. Furthermore, silicon and carbon have similar chemical properties and can bond tightly together, making carbon a commonly preferred matrix for silicon composites. In the Si / C composite system, Si particles act as the active material, providing lithium storage capacity; C buffers the volume changes of the silicon anode during charge and discharge, improves the conductivity of Si materials, and prevents Si particles from agglomerating during charge and discharge cycles. Therefore, Si / C composite materials combine the advantages of both, exhibiting high specific capacity and long cycle life, and are expected to replace graphite as the next generation of lithium-ion battery anode materials. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing high-capacity lithium-ion battery anode materials.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for preparing a high-capacity lithium-ion battery anode material includes the following steps:

[0007] (1) Activate the primary granular needle coke and the secondary granular needle coke mixture with an activator for 5 to 45 hours at an activation temperature of 350 to 670°C, and then cool to room temperature.

[0008] (2) Add distilled water dropwise to the product in step (1) until it becomes viscous, stir for 2 to 4 hours, then dry the solid and put it into a tube furnace, heat treat it under air conditions for 6 to 12 hours, and cool it to room temperature.

[0009] (3) Mix the product from step (2) with titanium silicate and ball mill, then mechanically fuse them;

[0010] (4) Calcine natural graphite and the product of step (3) at a weight ratio of 10-50:1-25 in a protective atmosphere at a temperature of 1850-2450°C for 4-10 hours. After cooling, mix, sieve and magnetically separate to obtain the negative electrode material.

[0011] In a preferred embodiment of the present invention, in step (1), the activator is sodium peroxide or potassium peroxide.

[0012] In a preferred embodiment of the present invention, the weight ratio of the primary granular needle coke and the secondary granular needle coke mixture to the activator in step (1) is 1-2:0.05-0.1.

[0013] In a preferred embodiment of the present invention, step (1) involves the mixture of primary and secondary granular needle coke, with particle D... 50 ≤10μm.

[0014] In a preferred embodiment of the present invention, step (2) involves the following heat treatment: first heating to 200-350°C and holding at that temperature, then heating to 650-800°C and holding at that temperature.

[0015] In a preferred embodiment of the present invention, the heating rate is 0.5–25 °C / min, the holding time at 200–350 °C is 2–3 h, and the holding time at 650–800 °C is 4–10 h.

[0016] In a preferred embodiment of the present invention, in step (3), the ball milling is a dry ball milling or a wet ball milling, the ball milling speed is 200-800 r / min, and the ball milling time is 1-12 h.

[0017] In a preferred embodiment of the present invention, in step (3), the rotational speed of the mechanical fusion is 300 to 2500 r / min, the mechanical fusion time is 0.5 to 10 h, and the equipment used for the mechanical fusion is a horizontal fusion machine or a vertical fusion machine.

[0018] In a preferred embodiment of the present invention, in step (4), the protective atmosphere is selected from helium, nitrogen, argon or xenon.

[0019] This invention employs a mixture of primary and secondary granular needle coke as the negative electrode active material to improve the dispersion effect of the negative electrode slurry. On the one hand, this reduces the current density of the electrode, thereby decreasing electrode polarization; on the other hand, it provides more lithium-ion migration channels, shortens the migration path, and reduces diffusion resistance, thus improving the high-rate performance of the electrode.

[0020] The preparation method of this invention starts from the interparticle structure of the material. By mixing needle-like coke particles of different sizes, the compaction density is improved. At the same time, while maintaining the original properties of needle-like coke such as high capacity, small specific surface area, and long life, the contact and conductivity are significantly improved, the interfacial resistance is low, the volume expansion is small, side reactions are reduced, and the cell volume expansion is kept within a reasonable range, ensuring cell safety and improving the energy density of lithium-ion batteries. The mixing of needle-like coke particles of different sizes is activator sodium peroxide or potassium peroxide, followed by oxidation treatment in the presence of water. Heat treatment then increases the interlayer spacing, and the generated hydroxide enters the interlayer. After ball milling and mechanical fusion, a Si / C composite system is formed. Si particles act as the active material to provide lithium storage capacity; C buffers the volume change of the silicon anode during charge and discharge, improves the conductivity of the Si material, and prevents Si particles from agglomerating during charge and discharge cycles. The Si / C composite system is calcined with natural graphite under a protective atmosphere to introduce nanoscale micropores into the carbon layers and between the carbon layers of the carbon anode material, increasing the lithium intercalation channels and greatly improving the cycle performance. The resulting anode material is then tested with lithium iron phosphate as the cathode material to obtain a battery that exhibits excellent discharge capacity and cycle stability. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is further described in conjunction with specific embodiments. However, this invention is not limited to these embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments. In this invention, unless otherwise specified, all parts and percentages are units of mass, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0022] The terms “comprising,” “including,” “containing,” or any other variations thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0023] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1 to 5” is disclosed, the described range should be interpreted as including the ranges “1 to 4”, “1 to 3”, “1 to 2”, “1 to 2 and 4 to 5”, “1 to 3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0024] Example 1

[0025] A method for preparing a high-capacity lithium-ion battery anode material includes the following steps:

[0026] (1) The primary granular needle coke and the secondary granular needle coke mixture were activated with sodium peroxide for 15 h at an activation temperature of 650 °C and then cooled to room temperature.

[0027] Among them, the primary granular needle coke and the secondary granular needle coke mixture (particle D) 50 The weight ratio of ≤10μm) to activator is 1:0.06;

[0028] (2) Add distilled water dropwise to the product in step (1) until it becomes viscous, stir for 3 hours, then dry the solid and put it into a tube furnace, heat treat it for 9 hours under air conditions, and cool it to room temperature.

[0029] The heat treatment is as follows: first, the temperature is raised to 320℃ and held, then the temperature is raised to 720℃ and held, wherein the heating rate is 15℃ / min, the holding time at 320℃ is 2h, and the holding time at 720℃ is 7h.

[0030] (3) Mix the product from step (2) with titanium silicate and ball mill, then mechanically fuse them;

[0031] The ball milling is a dry ball milling process with a rotation speed of 600 r / min and a milling time of 6 h; the mechanical fusion process has a rotation speed of 1200 r / min and a mechanical fusion time of 4.5 h, and the mechanical fusion process uses a horizontal fusion machine.

[0032] (4) Calcine natural graphite and the product of step (3) in nitrogen at a weight ratio of 35:9 for 6.5 hours. After cooling, mix, sieve and magnetically separate to obtain the negative electrode material.

[0033] Example 2

[0034] A method for preparing a high-capacity lithium-ion battery anode material includes the following steps:

[0035] (1) Potassium peroxide was used to activate the primary granular needle coke and the secondary granular needle coke mixture for 45 h at an activation temperature of 380 °C, and then cooled to room temperature.

[0036] Among them, the primary granular needle coke and the secondary granular needle coke mixture (particle D) 50 The weight ratio of ≤10μm) to activator is 2:0.07;

[0037] (2) Add distilled water dropwise to the product in step (1) until it becomes viscous, stir for 3.5 hours, then dry the solid and put it into a tube furnace, heat treat it for 12 hours under air conditions, and then cool it to room temperature.

[0038] The heat treatment is as follows: first, the temperature is raised to 350°C and held, then the temperature is raised to 650°C and held, wherein the heating rate is 25°C / min, the holding time at 350°C is 2.5h, and the holding time at 650°C is 9.5h.

[0039] (3) Mix the product from step (2) with titanium silicate and ball mill, then mechanically fuse them;

[0040] The ball milling is a wet ball milling process with a rotation speed of 800 r / min and a milling time of 1 hour; the mechanical fusion process has a rotation speed of 2500 r / min and a mechanical fusion time of 0.5 hours, and the mechanical fusion process uses a horizontal-vertical fusion machine.

[0041] (4) Calcine natural graphite and the product of step (3) in helium at a weight ratio of 50:1 for 4 hours. After cooling, mix, sieve and magnetically separate to obtain the negative electrode material.

[0042] Example 3

[0043] A method for preparing a high-capacity lithium-ion battery anode material includes the following steps:

[0044] (1) The primary granular needle coke and the secondary granular needle coke mixture were activated with sodium peroxide for 25 h at an activation temperature of 580 °C and then cooled to room temperature.

[0045] Among them, the primary granular needle coke and the secondary granular needle coke mixture (particle D) 50 The weight ratio of the ≤10μm sample to the activator is 1.5:0.08;

[0046] (2) Add distilled water dropwise to the product in step (1) until it becomes viscous, stir for 2.1 h, then dry the solid and put it into a tube furnace, heat treat it for 6 h under air conditions, and cool it to room temperature.

[0047] The heat treatment is as follows: first, the temperature is raised to 200℃ and held, then the temperature is raised to 800℃ and held, wherein the heating rate is 10.5℃ / min, the holding time at 200℃ is 2h, and the holding time at 800℃ is 4h.

[0048] (3) Mix the product from step (2) with titanium silicate and ball mill, then mechanically fuse them;

[0049] The ball milling is a dry ball milling process with a rotation speed of 200 r / min and a milling time of 12 h; the mechanical fusion process has a rotation speed of 300 r / min and a mechanical fusion time of 10 h, and the mechanical fusion process uses a vertical fusion machine.

[0050] (4) Calcine natural graphite and the product of step (3) in argon or xenon at a weight ratio of 8:15 for 10 hours. After cooling, mix, sieve and magnetically separate to obtain the negative electrode material.

[0051] Test case

[0052] The negative electrode materials prepared in Examples 1-3 were used as negative electrode active materials to prepare negative electrodes and assemble them into batteries. The specific process is as follows:

[0053] (1) Positive electrode plate

[0054] Lithium iron phosphate, Ketjen Black ECP, single-walled carbon nanotubes and positive electrode binder PVDF were mixed with NMP in a ratio of 98:0.6:0.4:1 to prepare a positive electrode slurry. The positive electrode slurry was then uniformly coated on both sides of a 12μm aluminum foil, rolled, and compacted to a density of 2.6g / cc. Finally, it was die-cut to obtain a positive electrode sheet.

[0055] (2) Preparation of negative electrode

[0056] The negative electrode active material, SP (conductive carbon black), CMC and SBR are mixed with deionized water to prepare a negative electrode slurry. The negative electrode slurry is evenly coated on both sides of a 4.5μm copper foil, then rolled and pressed to a compaction density of 1.7g / cc, and then die-cut to obtain a negative electrode sheet.

[0057] (3) Preparation of the core

[0058] The positive and negative electrode sheets prepared by (1) and (2) are wound together with the ceramic-coated separator (7+3) to form a core.

[0059] (4) Preparation of electrolyte

[0060] LiPF6 (1 mol / L concentration) and additive VC (1%) were dissolved in a mixed solvent of PC (propylene carbonate) / EC (ethylene carbonate) / DMC (dimethyl carbonate) = 1:1:1 (volume ratio) to form an electrolyte.

[0061] (5) Battery assembly

[0062] The core obtained in step (3) is placed inside the casing, and then the electrolyte prepared in step (4) is injected to make a lithium iron phosphate battery.

[0063] The manufactured batteries underwent performance testing according to GB / T 31484-2015 and GB / T 31486-2015 standards. The formula for calculating the energy density of the batteries is as follows:

[0064] Energy density = Discharge capacity × Plateau voltage / Battery weight

[0065] Platform voltage = 3.2V

[0066] The discharge performance and cycle life of lithium-ion batteries made from the negative electrode materials of Examples 1-3 were tested, and their energy density was calculated. The results are shown in Table 1 below.

[0067] Table 1. Performance test results of lithium iron phosphate batteries prepared in Examples 1-3

[0068]

[0069] The negative electrode material prepared by this invention can improve the energy density of lithium-ion batteries and give them excellent discharge capacity and cycle stability.

[0070] The above embodiments are merely preferred embodiments of the present invention. Any simple modifications, alterations, and substitutions made to the above embodiments based on the technical essence of the present invention shall fall within the scope of the technical solution of the present invention.

Claims

1. A method for preparing a high capacity anode material for lithium ion batteries, characterized in that, The method comprises the following steps: (1) activating the mixture of primary particle needle coke and secondary particle needle coke with an activator for 5-45 hours at a temperature of 350-670 DEG C, and cooling to room temperature; the activator is sodium peroxide or potassium peroxide; (2) adding distilled water dropwise to the product of step (1) until it becomes viscous, stirring for 2-4 hours, then drying, and adding into a tube furnace, first heating to 200-350 DEG C under air for 2-3 hours, then heating to 650-800 DEG C for 4-10 hours, and cooling to room temperature; (3) mixing the product of step (2) with titanium silicate and ball milling, and then mechanically fusing; the mechanical fusing device is a horizontal fusing machine or a vertical fusing machine; (4) calcining natural graphite and the product of step (3) in a protective atmosphere at a temperature of 1850-2450 DEG C for 4-10 hours, after cooling, mixing, screening and magnetic separation of the calcined product, a negative electrode material is obtained.

2. The method for preparing a high-capacity lithium-ion battery anode material according to claim 1, characterized in that, In step (1), the weight ratio of the mixture of primary particle needle coke and secondary particle needle coke to the activator is 1-2:0.05-0.

1.

3. The method for preparing a high-capacity lithium-ion battery anode material according to claim 1, characterized in that, In step (2), the heating rate is 0.5-25 DEG C / min.

4. The method for preparing a high-capacity lithium-ion battery anode material according to claim 1, characterized in that, In step (3), the ball milling is dry ball milling or wet ball milling, the rotation speed of the ball milling is 200-800 r / min, and the ball milling time is 1-12 hours.

5. The method for preparing a high-capacity lithium-ion battery anode material according to claim 1, characterized in that, In step (3), the rotation speed of the mechanical fusing is 300-2500 r / min, and the mechanical fusing time is 0.5-10 hours.

6. The method for preparing a high-capacity lithium-ion battery anode material according to claim 1, characterized in that, In step (4), the protective atmosphere is selected from one of helium, nitrogen, argon or xenon.

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