A battery negative electrode material and a preparation method thereof

Abstract

The present invention discloses a battery negative electrode material and a preparation method thereof, relating to the technical field of batteries. The battery negative electrode material includes a core, a titanium dioxide coating layer coated on the surface of the core, a lithium titanate coating layer coated on the surface of the titanium dioxide coating layer, a carbon coating layer coated on the surface of the lithium titanate coating layer, and a polymer coating layer coated on the surface of the carbon coating layer; the core includes a silicon-based negative electrode material; the polymer coating layer includes at least one of polyaniline, polythiophene, and polypyrrole. Under the action of the four coating layers, the integrity of the silicon-based negative electrode material can be maintained, the direct contact between the silicon-based negative electrode material and the electrolyte is avoided, the occurrence of side reactions is reduced, the capacity attenuation of the battery during the charge and discharge cycle process is reduced, and the rate performance and cycle stability of the battery are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a battery anode material and a preparation method thereof. Background Art

[0002] At present, the relatively low theoretical specific capacity (372 mAh·g -1 ) of graphite-based anode materials can no longer meet the requirements of high-energy-density battery systems. Silicon-based anode materials, due to their high specific capacity and low lithium deintercalation potential (for example, the theoretical specific capacity of Si is 3579 mAh·g -1 , and the lithium deintercalation potential is about 0.4 V vs. Li|Li + ), are attractive alternatives to commercial graphite anode materials in lithium-ion batteries. However, silicon-based anode materials will undergo a huge volume expansion during the lithiation and delithiation processes, resulting in irreversible changes in particle morphology and size, continuous destruction and growth of the solid electrolyte interface (SEI) film, continuous consumption of active lithium, pulverization of the electrode sheet, increase in resistance and polarization, and reduction in the capacity and cycle life of the battery.

[0003] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0004] Based on the above deficiencies of the existing technology, the purpose of the present invention is to provide a battery anode material and a preparation method thereof, aiming to solve the problem that the cycle life of batteries based on silicon-based anode materials is relatively low due to the volume expansion during the lithiation and delithiation processes of silicon-based anode materials.

[0005] The technical solution of the present invention is as follows:

[0006] In the first aspect of the present invention, a battery anode material is provided, wherein the battery anode material includes a core, and a titanium dioxide coating layer coated on the surface of the core, a lithium titanate coating layer coated on the surface of the titanium dioxide coating layer, a carbon coating layer coated on the surface of the lithium titanate coating layer, and a polymer coating layer coated on the surface of the carbon coating layer;

[0007] The core includes a silicon-based anode material; the polymer coating layer includes at least one of polyaniline, polythiophene, and polypyrrole.

[0008] Optionally, the silicon-based anode material includes at least one of a silicon anode material, a silicon oxide anode material, and a silicon carbon anode material.

[0009] Optionally, the particle size of the silicon-based anode material is 0.1~50 μm;

[0010] The thickness of the titanium dioxide coating layer is 2 to 18 nm; the thickness of the lithium titanate coating layer is 2 to 10 nm; the thickness of the carbon coating layer is 5 to 10 nm; the thickness of the polymer coating layer is 2 to 8 nm.

[0011] In a second aspect of the present invention, there is provided a method for preparing the battery anode material as described above in the present invention, which includes the following steps:

[0012] Provide a silicon-based anode material;

[0013] Form a titanium dioxide coating layer on the surface of the silicon-based anode material, and form a lithium titanate coating layer on the surface of the titanium dioxide coating layer to obtain a first composite;

[0014] Form a carbon coating layer on the surface of the first composite to obtain a second composite;

[0015] Form a polymer coating layer on the surface of the second composite to obtain the battery anode material.

[0016] Optionally, the step of forming a titanium dioxide coating layer on the surface of the silicon-based anode material and forming a lithium titanate coating layer on the surface of the titanium dioxide coating layer to obtain a first composite specifically includes:

[0017] Coat titanium dioxide on the surface of the silicon-based anode material by liquid-phase coating method;

[0018] Mix the silicon-based anode material with a surface coated with titanium dioxide with a lithium source, and keep it at 500 to 700 °C for 3 to 5 h in an inert atmosphere, then a titanium dioxide coating layer and a lithium titanate coating layer are sequentially formed on the surface of the silicon-based anode material to obtain a first composite.

[0019] Optionally, the step of coating titanium dioxide on the surface of the silicon-based anode material by liquid-phase coating method specifically includes:

[0020] Add the silicon-based anode material to a first solvent, then add a titanium source and water, and coat titanium dioxide on the surface of the silicon-based anode material through a hydrolysis reaction.

[0021] Optionally, the titanium source includes at least one of titanium tetrachloride, tetrabutyl titanate, titanium isopropoxide, titanium sulfate, titanium oxysulfate, and titanium trichloride;

[0022] The lithium source includes at least one of lithium nitrate, lithium acetate, lithium phosphate, lithium sulfate, lithium chloride, lithium bromide, and lithium iodide.

[0023] Optionally, the step of forming a carbon coating layer on the surface of the first composite to obtain a second composite specifically includes:

[0024] Mix the first composite with a carbon source and heat it at 500 - 700 °C for 2 - 3 h in an inert gas atmosphere to form a carbon coating layer on the surface of the first composite, obtaining a second composite.

[0025] Optionally, the carbon source includes at least one of tetrahydrofuran, pitch, acetone, citric acid, and phenolic resin.

[0026] Optionally, the steps of forming a polymer coating layer on the surface of the second composite to obtain the battery anode material specifically include:

[0027] Add the second composite, polymer monomer, coupling agent, and initiator to a second solvent. After the reaction, a polymer coating layer is formed on the surface of the second composite to obtain the battery anode material;

[0028] The polymer monomer includes at least one of aniline, thiophene, and pyrrole.

[0029] Beneficial effects: In the present invention, the titanium dioxide coating layer has a certain rigidity, which can buffer the volume expansion generated during the lithiation and delithiation processes of the silicon-based anode material, reduce the mechanical stress of the silicon-based anode material, and enhance the structural stability. The lithium titanate coating layer can serve as a lithium ion conductive layer to enhance the lithium ion transport, and it can also act as an artificial SEI film to avoid the natural formation of the SEI film during cycling. The carbon coating layer can enhance the conductivity of the silicon-based anode material on the one hand and also has a certain buffering effect on the volume expansion of the silicon-based anode material on the other hand. The polymer coating layer has good toughness and conductivity, can effectively relieve the volume expansion of the silicon-based anode material, prevent the silicon-based anode material from breaking, and in addition, it can not only act as an intermediate isolation layer between the active material (i.e., the silicon-based anode material) and the electrolyte to reduce side reactions and is more friendly to the electrolyte, but also promote interfacial ion diffusion, thus ensuring the smooth insertion and extraction of lithium ions. Under the action of these four coating layers, the integrity of the silicon-based anode material can be maintained, avoiding direct contact between the silicon-based anode material and the electrolyte, reducing the occurrence of side reactions, reducing the capacity decay of the battery during the charge-discharge cycle, and improving the rate performance and cycle stability of the battery. Description of the Drawings

[0030] Figure 1 It is a schematic structural diagram of the battery anode material.

[0031] Figure 2 It is the X-ray diffraction pattern of the battery anode material in Example 1.

[0032] Figure 3 It is the X-ray photoelectron spectroscopy diagram of the battery anode material in Example 2, where (a) are the characteristic peaks of SiO2 and Si, and (b) are the characteristic peaks of TiO2.

[0033] Figure 4 It is the energy spectrum diagram of the battery anode material in Example 3.

[0034] Figure 5 It is the cyclic test result diagram of the lithium-ion battery prepared with the battery anode materials in Example 1 and Comparative Example 1.

[0035] Figure 6 It is the cyclic test result diagram of the lithium-ion battery prepared with the battery anode materials in Example 2 and Comparative Example 2.

[0036] Figure 7 It is the cyclic test result diagram of the lithium-ion battery prepared with the battery anode materials in Example 3 and Comparative Example 3.

[0037] Figure 8 It is the cyclic test result diagram of the lithium-ion battery prepared with the battery anode materials in Example 1, Example 2, Example 3 and Comparative Example 4.

[0038] Figure 9 It is the rate test result diagram of the lithium-ion battery prepared with the battery anode materials in Example 1 and Comparative Examples 1, 2 and 3.

[0039] Figure 10 It is the impedance diagram of the lithium-ion battery prepared with the battery anode materials in Example 2 and Comparative Example 1 after 0.5 cycles and 50.5 cycles, where (a) is the impedance diagram after 0.5 cycles and (b) is the impedance diagram after 50.5 cycles. Detailed implementation manners

[0040] The present invention provides a battery anode material and a preparation method thereof. To make the objectives, technical solutions and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0041] Unless otherwise defined, all technical terms and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the description of the present invention are only for the purpose of describing specific implementation manners and are not intended to limit the present invention.

[0042] If there are descriptions involving "first", "second", etc. in the embodiments of the present invention, the descriptions of "first", "second", etc. are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features.

[0043] The embodiments of the present invention provide a battery anode material, wherein, as Figure 1As shown, the negative electrode material of the battery has a core-shell structure. Specifically, the negative electrode material of the battery includes a core 1, a titanium dioxide coating layer 2 coated on the surface of the core 1, a lithium titanate coating layer 3 coated on the surface of the titanium dioxide coating layer 2, a carbon coating layer 4 coated on the surface of the lithium titanate coating layer 3, and a polymer coating layer 5 coated on the surface of the carbon coating layer 4;

[0044] The core includes a silicon-based negative electrode material; the polymer coating layer includes at least one of polyaniline, polythiophene, and polypyrrole.

[0045] In the present invention, the titanium dioxide coating layer has a certain rigidity, which can buffer the volume expansion generated by the silicon-based negative electrode material during the lithiation process, reduce the mechanical stress of the silicon-based negative electrode material, and enhance the structural stability. The lithium titanate coating layer can serve as a lithium ion conductive layer to enhance the transport of lithium ions, and it can also act as an artificial SEI film to avoid the natural formation of the SEI film during the cycling process. The carbon coating layer can enhance the conductivity of the silicon-based negative electrode material on the one hand and also has a certain buffering effect on the volume expansion of the silicon-based negative electrode material on the other hand. The polymer coating layer has good toughness and conductivity, can effectively relieve the volume expansion of the silicon-based negative electrode material, prevent the silicon-based negative electrode material from breaking, and in addition, it can not only act as an intermediate isolation layer between the active material (i.e., the silicon-based negative electrode material) and the electrolyte to reduce side reactions and be more friendly to the electrolyte, but also promote interfacial ion diffusion, thereby ensuring the smooth insertion and extraction of lithium ions. Under the action of these four coating layers, the integrity of the silicon-based negative electrode material can be maintained, the direct contact between the silicon-based negative electrode material and the electrolyte is avoided, the occurrence of side reactions is reduced, the capacity attenuation of the battery during the charge-discharge cycle process is reduced, and the rate performance and cycle stability of the battery are improved.

[0046] In some embodiments, the silicon-based negative electrode material includes at least one of a silicon negative electrode material (such as nano-silicon particles, micro-silicon particles, nano-silicon wires, etc.), a silicon oxide negative electrode material, and a silicon carbon negative electrode material, but is not limited thereto. The silicon negative electrode material, the silicon oxide negative electrode material, and the silicon carbon negative electrode material can all be commercially available products obtained through commercial channels.

[0047] In some embodiments, the particle size of the silicon-based negative electrode material is 0.1~50 μm, for example, it can be 0.1 μm, 0.5 μm, 1 μm, 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm, etc.

[0048] In some embodiments, the thickness of the titanium dioxide coating layer is 2 to 18 nm, for example, it can be 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm or 18 nm, etc. Such a thickness can effectively buffer the volume expansion of the silicon-based anode material during charge and discharge. If it is too thick, it will lead to too large a resistance to lithium-ion insertion and affect the electrochemical performance.

[0049] In some embodiments, the thickness of the lithium titanate coating layer is 2 to 10 nm, for example, it can be 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm, etc. The lithium titanate coating layer with this thickness can better enhance the lithium-ion transport, act as an artificial SEI film, and avoid the natural formation of the SEI film during cycling.

[0050] In some embodiments, the thickness of the carbon coating layer is 5 to 10 nm, for example, it can be 5 nm, 6 nm, 7 nm, 8 nm, 9 nm or 10 nm, etc. If the carbon coating layer is too thin, it is very easy to be incompletely coated, resulting in poor conductivity. If it is too thick, the side reactions will intensify, resulting in a reduction in battery life.

[0051] In some embodiments, the thickness of the polymer coating layer is 2 to 8 nm, for example, it can be 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm or 8 nm, etc. The polymer coating layer with such a thickness has the following functions: it can provide an additional conduction path to improve the overall conductivity of the battery anode material; it can protect the internal silicon-based anode material and each coating layer; it has good adhesion and can better make the polymer coating layer contact with the carbon coating layer; it can reduce the contact resistance between the coating materials and reduce energy loss; it has good flexibility and mechanical properties to prevent the silicon-based anode material particles from breaking.

[0052] The embodiment of the present invention also provides a preparation method of the battery anode material as described above in the present invention, which includes the following steps:

[0053] S1. Provide a silicon-based anode material;

[0054] S2. Form a titanium dioxide coating layer on the surface of the silicon-based anode material, and form a lithium titanate coating layer on the surface of the titanium dioxide coating layer to obtain a first composite; the first composite includes a silicon-based anode material, a titanium dioxide coating layer coated on the surface of the silicon-based anode material, and a lithium titanate coating layer coated on the surface of the titanium dioxide coating layer;

[0055] S3. Form a carbon coating layer on the surface of the first composite to obtain a second composite; the second composite includes a silicon-based anode material, a titanium dioxide coating layer coated on the surface of the silicon-based anode material, a lithium titanate coating layer coated on the surface of the titanium dioxide coating layer, and a carbon coating layer coated on the surface of the lithium titanate coating layer;

[0056] S4. Form a polymer coating layer on the surface of the second composite to obtain the battery anode material.

[0057] The preparation method provided by the present invention is simple, has low equipment requirements, is pollution-free during the reaction process, has good product uniformity, and the prepared battery anode material has a high specific capacity, good cycle and rate performance, and safety.

[0058] In step S1, the selection of the silicon-based anode material can be referred to as described above and will not be elaborated here.

[0059] In step S2, in some embodiments, the steps of forming a titanium dioxide coating layer on the surface of the silicon-based anode material and forming a lithium titanate coating layer on the surface of the titanium dioxide coating layer to obtain the first composite specifically include:

[0060] S21. Coating titanium dioxide on the surface of the silicon-based anode material by using the liquid-phase coating method;

[0061] S22. Mix the silicon-based anode material coated with titanium dioxide on the surface with a lithium source, and keep it at 500-700 °C for 3-5 h under an inert atmosphere, then a titanium dioxide coating layer and a lithium titanate coating layer are successively formed on the surface of the silicon-based anode material to obtain the first composite.

[0062] In this embodiment, the liquid-phase coating method can be used to uniformly coat a layer of titanium dioxide on the surface of the silicon-based anode material, and then the surface layer of the titanium dioxide layer is lithiated to lithium titanate at a temperature of 500-700 °C by using the lithium source to form a lithium titanate coating layer, and the un-lithiated titanium dioxide layer constitutes the titanium dioxide coating layer.

[0063] In step S21, in some embodiments, the steps of coating titanium dioxide on the surface of the silicon-based anode material by using the liquid-phase coating method specifically include:

[0064] Add the silicon-based anode material to the first solvent, then add a titanium source and water, and coat titanium dioxide on the surface of the silicon-based anode material through a hydrolysis reaction.

[0065] Among them, the first solvent includes at least one of ethanol, ethylene glycol, and methanol, but is not limited thereto. The titanium source includes at least one of titanium tetrachloride, tetrabutyl titanate, titanium isopropoxide, titanium sulfate, titanium oxysulfate, and titanium trichloride, but is not limited thereto.

[0066] In step S21, in some embodiments, the mass ratio of the titanium source to the silicon-based anode material is (0.001~0.05):1. For example, it can be 0.001:1, 0.002:1, 0.005:1, 0.01:1, 0.02:1, 0.03:1, 0.04:1, or 0.05:1, etc.

[0067] In steps S21 and S22, in some embodiments, the mass ratio of the lithium source to the silicon-based anode material is (0.005~0.05):1. For example, it can be 0.005:1, 0.01:1, 0.02:1, 0.03:1, 0.04:1, or 0.05:1, etc.

[0068] In step S22, in some embodiments, the lithium source includes at least one of lithium nitrate, lithium acetate, lithium phosphate, lithium sulfate, lithium chloride, lithium bromide, and lithium iodide, but is not limited thereto.

[0069] In some embodiments, the silicon-based anode material coated with titanium dioxide is mixed with the lithium source, heated and stirred at 80°C in a water bath for 12~24 h. After drying, it is kept at 500~700°C for 3~5 h in an inert atmosphere to obtain the first composite.

[0070] In step S3, in some embodiments, the step of forming a carbon coating layer on the surface of the first composite to obtain the second composite specifically includes:

[0071] The first composite is mixed with a carbon source and heated at 500~700°C for 2~3 h in an inert gas atmosphere to form a carbon coating layer on the surface of the first composite, thereby obtaining the second composite.

[0072] In some embodiments, the mass ratio of the carbon source to the silicon-based anode material in the first composite is (20~80):1. For example, it can be 20:1, 30:1, 40:1, 50:1, 60:1, 70:1, or 80:1, etc.

[0073] In some embodiments, the carbon source includes at least one of tetrahydrofuran, asphalt, acetone, citric acid, and phenolic resin, but is not limited thereto.

[0074] In step S4, in some embodiments, the step of forming a polymer coating layer on the surface of the second composite to obtain the battery anode material specifically includes:

[0075] The second composite, a polymer monomer, a coupling agent, and an initiator are added to a second solvent. After the reaction, a polymer coating layer is formed on the surface of the second composite to obtain the battery anode material;

[0076] The polymer monomer includes at least one of aniline, thiophene, and pyrrole.

[0077] In some embodiments, the mass ratio of the second complex, the polymer monomer, the coupling agent, and the initiator is 1:(0.05 - 0.5):(0.01 - 0.3):(0.01 - 0.2), and for example, it can be 1:0.05:0.01:0.01, 1:0.1:0.01:0.01, 1:0.5:0.01:0.01, 1:0.05:0.3:0.01, 1:0.05:0.01:0.1, or 1:0.05:0.01:0.2, etc.

[0078] In some embodiments, the coupling agent includes a silane coupling agent (for example, the silane coupling agent includes at least one of 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, aminoethylaminopropyltrimethoxysilane, and 3-(2-aminoethylamino)propyltrimethoxysilane), the initiator includes at least one of ammonium persulfate, sodium persulfate, and potassium persulfate, and the second solvent includes at least one of ethanol, ethylene glycol, and methanol.

[0079] The present invention will be further described below through specific examples.

[0080] Unless otherwise specified, the materials used in the following examples and comparative examples are all commercially available products that can be obtained through commercial channels. Among them, the silicon-oxygen anode materials used in the following examples and comparative examples are all from Shenzhen Solide New Materials Technology Co., Ltd., and the product name is SH-1490 (particle size is 1 - 50 μm).

[0081] Example 1

[0082] This example provides a method for preparing a battery anode material, including the following steps:

[0083] (1) Disperse 10 g of the silicon-oxygen anode material in 400 mL of absolute ethanol, add 0.3 g of tetrabutyl titanate and 20 mL of deionized water. After stirring for 20 min, tetrabutyl titanate hydrolyzes to form titanium dioxide coated on the surface of the silicon-oxygen anode material; then add 10 mL of lithium nitrate solution (wherein, containing 0.1 g of lithium nitrate), mix evenly, and heat and stir at 80 °C in a water bath for 20 h. After drying, heat to 700 °C in a nitrogen atmosphere and keep warm for 3 h to convert the surface layer of titanium dioxide into lithium titanate, obtaining a first complex (which includes the silicon-oxygen anode material, a titanium dioxide coating layer coated on the surface of the silicon-oxygen anode material, and a lithium titanate coating layer coated on the surface of the titanium dioxide coating layer).

[0084] (2) Take 10 g of the first composite and add it to 200 g of tetrahydrofuran, stir, and dry at 100 °C. Then place it in a horizontal tube furnace, and under an argon gas flow, heat it at a heating rate of 5 °C / min to 600 °C and heat at 600 °C for 2 h to form a carbon coating layer on the surface of the first composite to obtain the second composite.

[0085] (3) Take 10 g of the second composite and add it to 200 mL of absolute ethanol for magnetic stirring for 10 minutes. At a temperature of 80 °C, add 0.5 g of 3-aminopropyltrimethoxysilane. After reacting for 1.5 h, add 2 mL of aniline and stir well to obtain a mixed solution A; dissolve 0.3 g of ammonium persulfate in 10 mL of deionized water to obtain an ammonium persulfate solution. Slowly add the obtained ammonium persulfate solution dropwise to the mixed solution A through a separatory funnel and react for 3 h. After the reaction is completed, wash repeatedly with deionized water and ethanol and filter by suction 2 times, and then place it in a vacuum environment at 100 °C until completely dry to obtain the battery anode material. The battery anode material includes a silicon-oxygen anode material core, and a titanium dioxide coating layer (with a thickness of 10 nm), a lithium titanate coating layer (with a thickness of 3 nm), a carbon coating layer (with a thickness of 5 nm), and a polyaniline coating layer (with a thickness of 4 nm) that are sequentially coated on the surface of the silicon-oxygen anode material core from the inside to the outside.

[0086] Example 2

[0087] This example provides a method for preparing a battery anode material, which is only different from Example 1 in that: in step (1), 0.05 g of tetrabutyl titanate is added.

[0088] The obtained battery anode material includes a silicon-oxygen anode material core, and a titanium dioxide coating layer (with a thickness of 2 nm), a lithium titanate coating layer (with a thickness of 3 nm), a carbon coating layer (with a thickness of 5 nm), and a polyaniline coating layer (with a thickness of 4 nm) that are sequentially coated on the surface of the silicon-oxygen anode material core from the inside to the outside.

[0089] Example 3

[0090] This example provides a method for preparing a battery anode material, which is only different from Example 1 in that: in step (1), 0.1 g of tetrabutyl titanate is added.

[0091] The obtained battery anode material includes a silicon-oxygen anode material core, and a titanium dioxide coating layer (with a thickness of 5 nm), a lithium titanate coating layer (with a thickness of 3 nm), a carbon coating layer (with a thickness of 5 nm), and a polyaniline coating layer (with a thickness of 4 nm) that are sequentially coated on the surface of the silicon-oxygen anode material core from the inside to the outside.

[0092] Comparative Example 1

[0093] This example provides a battery anode material, namely a silicon-oxygen anode material.

[0094] Comparative Example 2

[0095] This comparative example provides a method for preparing a battery anode material, which is only different from Example 1 in that: a carbon coating layer is first coated on the surface of the silicon-oxygen anode material, and then a titanium dioxide coating layer, a lithium titanate coating layer, and a polyaniline coating layer are coated. Specifically, the method includes the following steps:

[0096] (1) Add 10 g of the silicon-oxygen anode material to 200 g of tetrahydrofuran, stir, and dry at 100 °C. Then place it in a horizontal tube furnace, and under an argon gas flow, heat it at a heating rate of 5 °C / min to 600 °C, and heat at 600 °C for 2 h to form a carbon coating layer on the surface of the silicon-oxygen anode material, obtaining Complex A.

[0097] (2) Disperse the obtained Complex A in 400 mL of absolute ethanol, add 0.3 g of tetrabutyl titanate and 20 mL of deionized water, and stir for 20 min. Then, titanium dioxide is generated and coated on the surface of Complex A; then add 10 mL of lithium nitrate solution (containing 0.1 g of lithium nitrate), mix evenly, heat and stir at 80 °C in a water bath for 20 h, dry, and then heat to 700 °C in a nitrogen atmosphere and keep warm for 3 h to convert the surface layer of titanium dioxide into lithium titanate, obtaining Complex B.

[0098] (3) Take 10 g of Complex B and add it to 200 mL of absolute ethanol for magnetic stirring for 10 minutes. At a temperature of 80 °C, add 0.5 g of 3-aminopropyltriethoxysilane, react for 1.5 h, then add 2 mL of aniline, stir well, and obtain a mixed solution A; dissolve 0.3 g of ammonium persulfate in 10 mL of deionized water to obtain an ammonium persulfate solution, and slowly drop the obtained ammonium persulfate solution into the mixed solution A through a separatory funnel, react for 3 h. After the reaction, repeatedly wash with deionized water and ethanol and filter by suction 2 times, and then place it in a vacuum environment at 100 °C until completely dry to obtain the battery anode material. The battery anode material includes a silicon-oxygen anode material core, and a carbon coating layer, a titanium dioxide coating layer, a lithium titanate coating layer, and a polyaniline coating layer coated on the surface of the silicon-oxygen anode material core in sequence from the inside to the outside.

[0099] Comparative Example 3

[0100] This comparative example provides a method for preparing a battery anode material, which is only different from Example 1 in that:

[0101] In step (3), an ion conductor polymer (specifically a styrene sulfonic acid lithium-eugenol-caprolactone triblock copolymer conductive polymer) is coated on the surface of the second complex.

[0102] The obtained battery anode material includes a silicon oxyanode material core, and a titanium dioxide coating layer, a lithium titanate coating layer, a carbon coating layer, and a styrene sulfonic acid lithium-eugenol-caprolactone triblock copolymer conductive polymer coating layer that are sequentially coated on the surface of the silicon oxyanode material core from the inside to the outside.

[0103] Comparative Example 4

[0104] This comparative example provides a method for preparing a battery anode material, which is only different from Example 1 in that: the lithium titanate coating layer is not coated, that is, 10 mL of lithium nitrate solution (containing 0.1 g of lithium nitrate) is not added in step (1).

[0105] The obtained battery anode material includes a silicon oxyanode material core, and a titanium dioxide coating layer, a carbon coating layer, and a polyaniline coating layer that are sequentially coated on the surface of the silicon oxyanode material core from the inside to the outside.

[0106] Test:

[0107] (1) The X-ray diffraction pattern of the battery anode material in Example 1 is as Figure 2 shown. Since the titanium dioxide coating layer and the lithium titanate coating layer are very thin, there are no obvious diffraction peaks of titanium dioxide and lithium titanate.

[0108] (2) The X-ray photoelectron spectroscopy pattern of the battery anode material in Example 2 is as Figure 3 shown, and the results show the successful coating of titanium dioxide.

[0109] (3) The energy spectrum pattern of the battery anode material in Example 3 is as Figure 4 shown. It can be seen that Ti, O, and C elements are uniformly coated on the surface of the silicon oxyanode material.

[0110] (4) The battery anode materials in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4 were all prepared into lithium-ion batteries (the difference between each lithium-ion battery is only that: the anode materials respectively use the battery anode materials in Example 1, Example 2, Example 3, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4), and cycle tests and rate tests were carried out under the same conditions.

[0111] The cycle test results of the lithium-ion batteries prepared with the battery anode materials in Example 1 and Comparative Example 1 are as Figure 5 shown. It can be seen that the capacity retention rate of the lithium-ion battery prepared with the battery anode material in Example 1 after 100 cycles is 86.6%, while the capacity retention rate of the lithium-ion battery prepared with the battery anode material in Comparative Example 1 after 100 cycles is only 52.1%.

[0112] The cycle test results of the lithium-ion batteries prepared with the battery anode materials in Example 2 and Comparative Example 2 are asFigure 6 As shown, it can be seen that the capacity retention rate of the lithium-ion battery prepared with the negative electrode material in Example 2 after 100 cycles is 85.0%, while the capacity retention rate of the lithium-ion battery prepared with the negative electrode material in Comparative Example 2 after 100 cycles is only 58.3%.

[0113] The cycle test results of the lithium-ion batteries prepared with the negative electrode materials in Example 3 and Comparative Example 3 are as Figure 7 shown. It can be seen that the capacity retention rate of the lithium-ion battery prepared with the negative electrode material in Example 3 after 100 cycles is 80.6%, while the capacity retention rate of the lithium-ion battery prepared with the negative electrode material in Comparative Example 3 after 100 cycles is only 58.8%.

[0114] In addition, as Figure 8 shown, the capacity retention rate of the lithium-ion battery prepared with the negative electrode material in Comparative Example 4 after 100 cycles is 54.1%, which is significantly worse than the cycle performance of the lithium-ion batteries prepared with the negative electrode materials in Example 1, Example 2, and Example 3.

[0115] It can be thus illustrated that the inorganic-carbon layer-organic coating can significantly improve the cycle capacity retention rate and the first-cycle Coulombic efficiency of the battery. This improvement is mainly attributed to the functions of the four coating layers, which effectively reduce the formation of the SEI film and side reactions in the battery.

[0116] The rate test results of the lithium-ion batteries prepared with the negative electrode materials in Example 1 and Comparative Example 1, Comparative Example 2, and Comparative Example 3 are as Figure 9 shown (where 0.1C, 0.3C, 0.5C, etc. refer to the discharge rate. If the rated capacity of the battery is 500 mAh, when discharging at a 0.1C discharge rate, the current used is 50 mA). Compared with the negative electrode materials in Comparative Example 1, Comparative Example 2, and Comparative Example 3, the lithium-ion battery prepared with the negative electrode material in Example 1 has better rate performance.

[0117] (5) The impedance diagrams of the lithium-ion batteries prepared with the negative electrode materials in Example 2 and Comparative Example 1 after 0.5 cycles and 50.5 cycles are as Figure 10 shown (where Z′ represents the real part of the impedance value and Z″ represents the imaginary part of the impedance value). It can be seen that the coating layer helps to enhance the overall conductivity of the coated material, thereby improving the charge-discharge performance of the battery.

[0118] In summary, the present invention provides a battery anode material and a preparation method thereof. In the present invention, the titanium dioxide coating layer has a certain rigidity, which can buffer the volume expansion generated during the lithiation process of the silicon-based anode material, reduce the mechanical stress of the silicon-based anode material, and enhance the structural stability. The lithium titanate coating layer can serve as a lithium-ion conductive layer to enhance the transmission of lithium ions. It can also act as an artificial SEI film to avoid the natural formation of the SEI film during the cycling process. On the one hand, the carbon coating layer can enhance the conductivity of the silicon-based anode material, and on the other hand, it also has a certain buffering effect on the volume expansion of the silicon-based anode material. The polymer coating layer has good toughness and conductivity, which can effectively relieve the volume expansion of the silicon-based anode material and prevent the silicon-based anode material from breaking. In addition, it can not only act as an intermediate isolation layer between the active material (i.e., the silicon-based anode material) and the electrolyte to reduce side reactions and be more friendly to the electrolyte, but also promote interfacial ion diffusion, thereby ensuring the smooth insertion and extraction of lithium ions. Under the action of these four coating layers, the integrity of the silicon-based anode material can be maintained, avoiding direct contact between the silicon-based anode material and the electrolyte, reducing the occurrence of side reactions, reducing the capacity attenuation of the battery during the charge and discharge cycling process, and improving the rate performance and cycling stability of the battery.

[0119] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description. All such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A battery negative electrode material, characterized in that: The battery negative electrode material comprises a core, a titanium dioxide coating layer coated on the surface of the core, a lithium titanate coating layer coated on the surface of the titanium dioxide coating layer, a carbon coating layer coated on the surface of the lithium titanate coating layer, and a polymer coating layer coated on the surface of the carbon coating layer; The core includes a silicon-based negative electrode material; the polymer coating layer includes at least one of polyaniline, polythiophene and polypyrrole; The thickness of the titanium dioxide coating layer is 2-18 nm; the thickness of the lithium titanate coating layer is 2-10 nm; the thickness of the carbon coating layer is 5-10 nm; and the thickness of the polymer coating layer is 2-8 nm.

2. The battery negative electrode material according to claim 1, characterized in that: The silicon-based negative electrode material includes at least one of a silicon negative electrode material, a silicon-oxygen negative electrode material and a silicon-carbon negative electrode material.

3. The battery negative electrode material according to claim 2, characterized in that: The particle size of the silicon-based negative electrode material is 0.1-50 μm.

4. A method for preparing a negative electrode material for a battery according to claim 1, characterized in that: The steps include: Provide silicon-based negative electrode materials; forming a titanium dioxide coating layer on the surface of the silicon-based negative electrode material, and forming a lithium titanate coating layer on the surface of the titanium dioxide coating layer to obtain a first composite; forming a carbon coating layer on the surface of the first composite to obtain a second composite; A polymer coating layer is formed on the surface of the second composite to obtain a battery negative electrode material.

5. The preparation method according to claim 4, characterized in that: The steps of forming a titanium dioxide coating layer on the surface of the silicon-based negative electrode material and forming a lithium titanate coating layer on the surface of the titanium dioxide coating layer to obtain the first composite specifically include: The liquid phase coating method is used to coat titanium dioxide on the surface of the silicon-based negative electrode material; The silicon-based negative electrode material coated with titanium dioxide on the surface is mixed with a lithium source and kept at 500-700° C. for 3-5 hours in an inert atmosphere, so that a titanium dioxide coating layer and a lithium titanate coating layer are sequentially formed on the surface of the silicon-based negative electrode material to obtain a first composite.

6. The preparation method according to claim 5, characterized in that: The steps of coating titanium dioxide on the surface of silicon-based negative electrode material by liquid phase coating method specifically include: The silicon-based negative electrode material is added into a first solvent, and then a titanium source and water are added, so that titanium dioxide is coated on the surface of the silicon-based negative electrode material through a hydrolysis reaction.

7. The preparation method according to claim 6, characterized in that: The titanium source includes at least one of titanium tetrachloride, tetrabutyl titanate, titanium isopropoxide, titanium sulfate, titanyl sulfate and titanium trichloride; The lithium source includes at least one of lithium nitrate, lithium acetate, lithium phosphate, lithium sulfate, lithium chloride, lithium bromide and lithium iodide.

8. The preparation method according to claim 4, characterized in that: The step of forming a carbon coating layer on the surface of the first composite to obtain the second composite specifically comprises: The first composite is mixed with a carbon source, and heated at 500-700° C. for 2-3 hours under an inert gas atmosphere to form a carbon coating layer on the surface of the first composite, thereby obtaining a second composite.

9. The preparation method according to claim 8, characterized in that: The carbon source includes at least one of tetrahydrofuran, asphalt, acetone, citric acid and phenolic resin.

10. The preparation method according to claim 4, characterized in that: The step of forming a polymer coating layer on the surface of the second composite to obtain a negative electrode material for a battery specifically comprises: Adding the second complex, polymer monomers, coupling agent and initiator into the second solvent, and after reaction, forming a polymer coating layer on the surface of the second complex to obtain a battery negative electrode material; The polymer monomer includes at least one of aniline, thiophene and pyrrole.

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