Silicon-based negative electrode material for high-capacity lithium battery as well as preparation method and application of silicon-based negative electrode material

Abstract

The invention discloses a silicon-based negative electrode material for a high-capacity lithium battery as well as a preparation method and application of the silicon-based negative electrode material, the silicon-based negative electrode material is a micro-nano silicon-based negative electrode material prepared by taking micron silicon, a hydroxyl-containing organic matter and a cyano-containing organic matter as raw materials through a simple one-step mixing ball milling and one-time heat treatment method. The conductivity of the silicon-based negative electrode material is improved through simple mixed ball milling and primary heat treatment, and meanwhile, a transition layer formed by a mixed phase composed of Si, C, N and O and a coating layer formed by a mixed phase composed of C, N and O are generated on the surface of a silicon-based main body material with micro-nano silicon. The preparation method disclosed by the invention is simple, efficient and safe, and the prepared silicon-based negative electrode material has excellent capacity, efficiency and cycling stability and has a prospect of industrial large-scale production and application.

Description

Technical Field

[0001] The present invention belongs to the field of negative electrode materials for lithium-ion batteries, and relates to a silicon-based negative electrode material and a preparation method thereof, and a lithium-ion battery comprising the silicon-based negative electrode material, and in particular to a method for preparing a silicon-based negative electrode material by one-step mixed ball milling, and a high-capacity lithium-ion battery comprising the silicon-based negative electrode material. Background Art

[0002] Lithium-ion battery is an energy storage device that uses lithium ions to move back and forth between positive and negative electrodes to achieve charging and discharging. Lithium-ion battery has the advantages of high energy density, high power density, low self-discharge, no memory effect and environmental friendliness. It is one of the most advanced rechargeable batteries. Among many metals, lithium has the smallest specific gravity. Its relative atomic mass is 6.94 and its density is 0.53g / cm 3 , and has the lowest standard electrode potential (-3.04Vvs. standard hydrogen electrode), and its theoretical specific capacity is 3862mAh / g. Therefore, in theory, the lithium-ion battery system has a very high energy density, which can effectively meet the energy storage system's requirements for high energy density and high power density. In addition, lithium-ion batteries can effectively reduce the volume and weight of the battery, making it more convenient to carry and use, thereby helping to improve the efficiency of the energy storage system.

[0003] At present, the negative electrode material of commercial lithium-ion batteries is mainly graphite, whose theoretical specific capacity is 372mAh / g, which is close to its theoretical limit. Therefore, finding new high-capacity negative electrode materials is one of the important ways to improve the performance of lithium-ion batteries. Ideal negative electrode materials for lithium-ion batteries should generally meet the following requirements: (1) relatively low standard electrode potential; (2) high specific capacity and energy density; (3) high conductivity; (4) excellent cycle performance and rate performance; (5) structural stability during lithium ion insertion / extraction; (6) simple preparation process and easy commercialization; (7) low cost and no environmental pollution. Compared with carbon negative electrode, the advantages of silicon negative electrode are: (1) extremely high theoretical specific capacity. For currently commercialized lithium-ion batteries, the theoretical specific capacity of graphite is about 300mAh / g, while the theoretical specific capacity of silicon negative electrode is 4200mAh / g, which is close to more than 10 times the theoretical specific capacity of traditional graphite; (2) suitable working potential. Among all positive electrode materials, silicon has the electrochemical properties closest to those of graphite, making it suitable as a negative electrode material; (3) Silicon materials are naturally abundant, environmentally friendly, and non-toxic. Silicon negative electrodes have been widely used in fields such as semiconductors and solar energy, and are compatible with relevant mature technologies and are easy to achieve large-scale industrial production. Therefore, silicon is considered to be one of the most promising negative electrode materials for the next generation of lithium-ion batteries.

[0004] Silicon is a typical alloyed negative electrode material for lithium-ion batteries, which achieves lithium insertion / de-lithiation through alloying / de-alloying with lithium ions. Under high temperature (above 450°C), the alloying process of silicon and lithium undergoes Li 12 Si7、Li7Si3、Li 13 Si4 and Li 22 The transformation of Si5 and other alloy phases. Silicon-based materials have ultra-high specific capacity, but due to the huge volume change (about 300%) of silicon when inserting and removing lithium, the material will break, peel, pulverize and destroy the solid electrolyte interface film (SEI), resulting in capacity decay and cycle instability. Therefore, lithium-ion batteries based on silicon-based materials face the disadvantages of poor cycle stability and poor conductivity. Summary of the invention

[0005] To improve the above technical problems, the present invention provides a silicon-based negative electrode material having excellent capacity, efficiency and cycle stability. The present invention also provides a method for preparing the silicon-based negative electrode material, which uses micron silicon and organic matter as raw materials, and prepares the material through a simple one-step mixing ball milling and one-time heat treatment process. The preparation method is simple, efficient and safe.

[0006] The technical solution of the present invention is as follows:

[0007] A silicon-based negative electrode material, which uses micro-nano silicon as the silicon-based main material, i.e., a micro-nano silicon-based main material. A transition layer and a coating layer exist on the surface of the silicon-based main material. The transition layer contains a mixed phase interacting with Si, N, O, and C, and the coating layer contains a mixed phase interacting with N, O, and C.

[0008] According to an embodiment of the present invention, the transition layer and the coating layer are formed in situ and uniformly coated on the surface of the silicon-based main material. Further, the transition layer is located between the main material and the coating layer.

[0009] According to an embodiment of the present invention, the transition layer is composed of a mixed phase in which Si, N, O and C interact with each other.

[0010] According to an embodiment of the present invention, the thickness of the transition layer is about 1 to 10 nm, preferably 2 to 4 nm, for example, 1.0 nm, 2.0 nm, 3.0 nm, 4.0 nm, 5.0 nm, 8.0 nm or 10.0 nm.

[0011] According to an embodiment of the present invention, the coating layer is composed of a mixed phase in which N, O, and C interact with each other.

[0012] According to an embodiment of the present invention, the coating layer has a thickness of 0.3 to 3 nm, preferably 0.5 to 1.0 nm, for example, 0.5 nm, 0.6 nm, 0.7 nm, 0.8 nm, 0.9 nm, 1.0 nm, 2.0 nm or 3.0 nm.

[0013] According to an embodiment of the present invention, the particle size of the silicon-based negative electrode material is 10 nm to 1 μm.

[0014] According to an embodiment of the present invention, in the silicon-based negative electrode material, the mass percentage content of Si is 20-90%, the mass percentage content of O is 1-15%, the mass percentage content of C is 3-55%, and the mass percentage content of N is 1-20%.

[0015] The present invention also provides a method for preparing a silicon-based negative electrode material, comprising the following steps:

[0016] S1: ball-milling micron silicon, hydroxyl-containing organic matter and cyanide-containing organic matter in an inert gas to obtain a ball-milling product;

[0017] S2: heat-treating the ball-milled product prepared in step S1 under an inert atmosphere or a vacuum atmosphere to obtain the silicon-based negative electrode material.

[0018] In the preparation method of the present invention, during the ball milling of micron silicon and organic matter, chemical reactions occur between silicon and C, N, and O in the organic matter. Carbon materials have the advantages of good cycle stability and high conductivity. Since silicon and carbon belong to the same family and have similar discharge platforms, silicon-carbon composites can achieve complementary advantages between the two. The product after ball milling is micronized and heat-treated in an inert atmosphere or a vacuum atmosphere. The structure of the mixed ball milling product of silicon and organic matter changes, and the conductivity is improved. At the same time, a coating layer is formed, which is tightly combined with the ball milling product and has good structural stability. The preparation method of the present invention has simple process, abundant raw materials, low cost, and is environmentally friendly. The obtained silicon-based negative electrode material has the advantages of high capacity, high efficiency, and excellent stability.

[0019] According to an embodiment of the present invention, in step S1, the micron silicon is selected from commercial silicon, and preferably the particle size of the micron silicon is 3-4 μm.

[0020] According to an embodiment of the present invention, the hydroxyl-containing organic matter and the cyanide-containing organic matter are both low-molecular organic matter and / or high-molecular organic matter, and two / more low-molecular organic matter and / or high-molecular organic matter can be selected for co-milling.

[0021] According to an embodiment of the present invention, in step S1, the mass percentage of the micron silicon to the hydroxyl-containing organic matter and the cyano-containing organic matter is 20-90%: 1-79%: 1-79%. Preferably, the mass percentage of the micron silicon to the hydroxyl-containing organic matter and the cyano-containing organic matter is 40-80%: 5-40%: 5-40%, and illustratively, the mass percentage of the micron silicon to the hydroxyl-containing organic matter and the cyano-containing organic matter is 60%: 20%: 20%.

[0022] According to an embodiment of the present invention, the hydroxyl-containing organic substance is selected from at least one of 4-(2-pyridyl azo) resorcinol, polyacrylic acid, polyvinyl alcohol, dimethyl butyric acid and similar substances with similar structures to the above substances.

[0023] According to an embodiment of the present invention, the cyano group-containing organic compound is selected from at least one of polyacrylonitrile, methacrylonitrile, cis-butenenitrile and 3-chloroacrylonitrile.

[0024] According to an embodiment of the present invention, in step S1, the inert gas is at least one of Ar and N2.

[0025] According to an embodiment of the present invention, in step S1, the rotation speed of the ball mill is 300 to 600 rpm, exemplarily 300 rpm, 500 rpm or 600 rpm; the time of the ball mill is 4 to 18 hours, exemplarily 4 hours, 8 hours, 12 hours or 18 hours.

[0026] According to an embodiment of the present invention, in step S2, the inert gas is at least one of Ar and N2.

[0027] According to an embodiment of the present invention, in step S2, the temperature of the heat treatment is 300-600°C, preferably 300-500°C, further preferably 350-450°C, exemplarily 300°C, 350°C, 400°C, 500°C or 600°C; the holding time of the heat treatment is 4-20 hours, exemplarily 4 hours, 8 hours, 12 hours, 18 hours or 20 hours.

[0028] The silicon-based negative electrode material of the present invention is prepared by the above method.

[0029] The present invention also provides application of the silicon-based negative electrode material in lithium-ion batteries.

[0030] The present invention also provides a negative electrode, which comprises the above silicon-based negative electrode material.

[0031] According to an embodiment of the present invention, the negative electrode further comprises a binder and a conductive agent. For example, the mass ratio of the silicon-based negative electrode material to the binder and the conductive agent is (60-80): (10-20): (10-20).

[0032] According to an exemplary embodiment of the present invention, the binder is selected from at least one of polyacrylic acid, polyacrylonitrile, lithium polyacrylate, carboxymethyl cellulose, lithium carboxymethyl cellulose, polyvinylidene fluoride and polyvinyl alcohol.

[0033] According to an exemplary embodiment of the present invention, the conductive agent is selected from at least one of acetylene black, carbon black and graphene.

[0034] The present invention also provides a method for preparing the above-mentioned negative electrode, comprising mixing the above-mentioned silicon-based negative electrode material with a solvent (such as N-methyl-pyrrolidone, water, N,N-dimethylformamide), a binder and a conductive agent, coating it on a current collector (such as copper foil, foam copper, stainless steel, carbon, etc.), and drying after heat treatment to obtain the negative electrode.

[0035] According to an embodiment of the present invention, the coating amount coated on the current collector is about 0.5 to 2.5 mg / cm 2 , exemplified by 1.5 mg / cm 2 .

[0036] The present invention also provides a lithium ion battery, which comprises the negative electrode.

[0037] Beneficial effects of the present invention:

[0038] The present invention discloses a silicon-based negative electrode material. The silicon-based negative electrode material of the present invention has a high elastic modulus, which can effectively slow down the volume change of the silicon-based active material during the charge and discharge cycle, thereby improving the cycle performance of the material. The C in the transition layer and the coating layer of the silicon-based negative electrode material of the present invention can effectively improve the electronic conductivity of the electrode material. The silicon-based negative electrode material of the present invention also has high lithium ion transmission performance, which is beneficial to improve the cycle performance of the silicon-based negative electrode material. In the button battery test, the silicon-based negative electrode material of the present invention has a capacity of up to 3000mAh / g after 50 cycles at a current density of 500mAh / g, a cycle efficiency of more than 0.99, a good capacity retention rate, and has good prospects for industrial application.

[0039] The present invention also discloses a method for preparing a silicon-based negative electrode material, which uses micron silicon and organic matter as raw materials, is easy to obtain, and has a safe production process; after simple mixed ball milling and one heat treatment, a transition layer and a coating layer formed by a mixed phase composed of Si, C, N, and O are generated on the surface of the silicon main material; the silicon-based negative electrode material thus prepared has a high elastic modulus, which can effectively slow down the volume change of the silicon-based active material during the charge and discharge cycle, thereby improving the cycle performance of the material; the composite silicon-based negative electrode material obtained by heat treatment after ball milling effectively improves the electronic conductivity of the electrode material, and the silicon-based negative electrode material of the present invention also has high lithium ion transmission performance, which is conducive to the improvement of the material rate performance. The present invention adopts a one-step mixed ball milling method to prepare a silicon-based negative electrode material. In a button battery test, the material has a reversible specific capacity of up to 1500mAh / g after 300 cycles at a large current density of 2A / g, and the cycle efficiency exceeds 0.99, and the capacity retention rate is good, which has good prospects for industrial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 This is the X-ray diffraction spectrum of the silicon-based negative electrode material prepared in Example 1 of the present invention.

[0041] Figure 2 The cycle performance curve of a lithium-ion battery assembled with the silicon-based negative electrode material prepared in Example 1 of the present invention with a cut-off voltage in the range of 0.01-2V and a current density of 500mA / g for 50 cycles.

[0042] Figure 3 This is the Nyquist curve of the open circuit voltage of the silicon-based negative electrode material prepared in Example 1.

[0043] Figure 4 This is a scanning electron microscope image of the silicon-based negative electrode material prepared in Example 1 of the present invention.

[0044] Figure 5 The cycle performance curve of a lithium-ion battery assembled with the silicon-based negative electrode material prepared in Example 1 of the present invention with a cut-off voltage in the range of 0.01-2V and a current density of 2A / g for 300 cycles.

[0045] Figure 6 This is a transmission electron microscope image of the silicon-based negative electrode material prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0046] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0047] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0048] Example 1

[0049] A high-capacity lithium battery silicon-based negative electrode material is prepared by one-step mixing and ball milling, specifically:

[0050] Micron silicon (particle size of 3-4 μm, purchased from Myrel), hydroxyl-containing organic PAR (i.e. 4-(2-pyridyl azo) resorcinol, purchased from McLean) and cyano-containing organic polyacrylonitrile were ball-milled in a ball mill filled with Ar atmosphere at a mass ratio of 6:2:2. The ball milling parameters were: 500 rpm, ball milling for 12 hours, the ball milling beads were tungsten balls, and the ball-to-material mass ratio was 15:1. After the ball milling, the product was placed in a tubular furnace in an Ar atmosphere for heat treatment. The heat treatment parameters were: 350°C, the holding time was 12 hours, and it was naturally cooled to room temperature to obtain a silicon-based negative electrode material.

[0051] Figure 1 This is the X-ray diffraction spectrum of the silicon-based negative electrode material prepared in this embodiment. It can be seen from the figure that after ball milling and heat treatment of micron-sized silicon and organic matter, an obvious Si diffraction peak appears in the obtained silicon-based negative electrode material, which has obvious crystal state and good conductivity.

[0052] Electrochemical performance test: The cycle performance of the silicon-based negative electrode material prepared in this embodiment was tested using a button half-cell. The battery assembly was completed in a glove box with an argon atmosphere. A 2032-type button cell was used, and the silicon-based negative electrode material prepared in this embodiment was used as one electrode of the battery (the silicon-based negative electrode material prepared in this embodiment was coated on the current collector copper foil, with a coating amount of about 1.5 mg / cm 2 , and dried under vacuum atmosphere), with metal lithium sheet as the counter electrode, stainless steel sheet as the gasket, polypropylene (PP) as the diaphragm, and 1 mol / L LiPF6 (obtained by dissolving LiPF6 in a mixed solvent of ethylene carbonate (EC): diethyl carbonate (DEC): dimethyl carbonate (DMC) = 1:1:1 (mass ratio)) as the electrolyte.

[0053] The assembled battery was subjected to constant current charge and discharge tests, the current density of the electrochemical cycle test was 500 mA / g, the voltage range was 0.01 to 2 V, and the test temperature was 25°C. Figure 2The cycle performance curve of the lithium-ion battery assembled with the silicon-based negative electrode material prepared in this embodiment with a cut-off voltage in the range of 0.01-2V and a current density of 500mA / g for 50 cycles. As can be seen from the figure, the lithium-ion battery assembled with the silicon-based negative electrode material prepared in this embodiment has an initial discharge specific capacity of 3941.1mAh / g at 500mA / g, and the reversible capacity remains at 3139.1mAh / g after 50 cycles, and the cycle efficiency reaches 99.0%, showing excellent cycle stability.

[0054] Figure 3 This is the Nyquist curve of the silicon-based negative electrode material prepared in this embodiment. As can be seen from the figure, the impedance EIS of the silicon-based negative electrode material prepared in this embodiment at open circuit voltage presents a curve of two semicircular arcs, and its electrochemistry conforms to the double electric layer structure, and the impedance is 5.52Ω.

[0055] Figure 4 The SEM picture of the silicon-based negative electrode material prepared in this embodiment shows that the composite materials after ball milling are irregularly spherical, with a particle size of micro-nanoscale and good dispersibility. A transition layer and a coating layer of a mixed phase of Si, N, O, and C interacting with each other are formed on the surface of the silicon-based negative electrode nanocomposite material of the present invention, which provides a beneficial effect on maintaining electrochemical performance.

[0056] Figure 5 The cycle performance curve of the lithium-ion battery assembled with the silicon-based negative electrode material prepared in this embodiment with a cut-off voltage in the range of 0.01-2V and a current density of 2A / g for 300 cycles. As can be seen from the figure, the lithium-ion battery assembled with the silicon-based negative electrode material prepared in this embodiment has an initial discharge capacity of 2050mAh / g at 2A / g, and the reversible capacity after 300 cycles is still 1500mAh / g, with a capacity retention rate of up to 73.2%, and a cycle efficiency of more than 99.0%, showing excellent cycle stability, and thus has a certain boost to industrial production.

[0057] Figure 6 This is a transmission electron microscope image of the silicon-based negative electrode material prepared in Example 1 of the present invention. It can be seen from the figure that a transition layer of a mixed phase interacting with Si, N, O, and C with a thickness of about 3.0 nm and a coating layer of a mixed phase interacting with N, O, and C with a thickness of about 0.8 nm are formed on the surface of the silicon-based negative electrode nanocomposite material of the present invention, which provides a beneficial effect on maintaining the electrochemical performance.

[0058] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A silicon-based negative electrode material, characterized in that: The silicon-based main material is micro-nano silicon, the surface of which is coated with a transition layer and a coating layer. The transition layer contains a mixed phase interacting with Si, N, O and C, and the coating layer contains a mixed phase interacting with N, O and C.

2. The silicon-based negative electrode material according to claim 1, characterized in that: The transition layer and the coating layer are formed in situ and uniformly coated on the surface of the silicon-based main material; Preferably, the particle size of the silicon-based negative electrode material is 10 nm to 1 μm. Preferably, in the silicon-based negative electrode material, the mass percentage content of Si is 20-90%, the mass percentage content of O is 1-15%, the mass percentage content of C is 3-55%, and the mass percentage content of N is 1-20%. Preferably, the thickness of the transition layer is 1-10 nm. Preferably, the coating layer has a thickness of 0.3-3 nm.

3. The method for preparing the silicon-based negative electrode material according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: S1: ball-milling micron silicon, hydroxyl-containing organic matter and cyanide-containing organic matter in an inert gas to obtain a ball-milling product; S2: heat-treating the ball-milled product prepared in step S1 under an inert atmosphere or a vacuum atmosphere to obtain the silicon-based negative electrode material.

4. The preparation method according to claim 3, characterized in that: In step S1, the mass percentage of the micron silicon to the hydroxyl-containing organic matter and the cyanide-containing organic matter is 20-90%: 1-79%: 1-79%. Preferably, the mass percentage of the micron silicon to the hydroxyl-containing organic matter and the cyanide-containing organic matter is 40-80%: 5-40%: 5-40%.

5. The preparation method according to claim 3 or 4, characterized in that: The hydroxyl-containing organic substance is selected from at least one of 4-(2-pyridyl azo) resorcinol, polyacrylic acid, polyvinyl alcohol, dimethyl butyric acid and similar substances with similar structures to the above substances. Preferably, the cyano-containing organic compound is selected from at least one of polyacrylonitrile, methacrylonitrile, cis-butenenitrile and 3-chloroacrylonitrile. Preferably, in step S1, the rotation speed of the ball mill is 300 to 600 rpm; and the time of the ball mill is 4 to 18 hours. Preferably, the temperature of the heat treatment is 300-600° C.; and the insulation time of the heat treatment is 4-20 hours.

6. Use of the silicon-based negative electrode material according to any one of claims 1 to 2 and / or the silicon-based negative electrode material prepared by the preparation method according to any one of claims 3 to 5 in lithium-ion batteries.

7. A negative electrode, characterized in that It includes the silicon-based negative electrode material according to any one of claims 1 to 2 and / or the silicon-based negative electrode material prepared by the preparation method according to any one of claims 3 to 5.

8. The negative electrode according to claim 7, characterized in that The negative electrode further includes a binder and a conductive agent.

9. The method for preparing the negative electrode according to claim 8, characterized in that: The preparation method comprises mixing the silicon-based negative electrode material with a solvent, a binder and a conductive agent, coating the mixture on a current collector, and drying the mixture after heat treatment to obtain the negative electrode.

10. A lithium ion battery, characterized in that: It comprises the negative electrode according to claim 7 or 8.

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