Composite positive electrode material and preparation method and application thereof

Abstract

The invention relates to the technical field of lithium battery positive electrode materials, and particularly discloses a composite positive electrode material as well as a preparation method and application thereof. The preparation method comprises the following steps: firstly, mixing a nickel-cobalt-manganese hydroxide precursor with organic boron-containing gas or / and organic silicon-containing gas, and forming boron oxide or / and silicon oxide coated nickel-cobalt-manganese oxide through a CVD (Chemical Vapor Deposition) process; weighing the product in the previous step and a lithium source in proportion, matching the addition amount of the lithium source with the amount of the nickel-cobalt-manganese oxide and the content of boron oxide or / and silicon oxide on the surface of the nickel-cobalt-manganese oxide, uniformly mixing and sintering; and finally, crushing and screening the product obtained in the last step, uniformly mixing with a conductive carbon source in proportion, and sintering in air to form a three-dimensional conductive network layer. According to the invention, the defects of high residual alkali content on the surface of the existing positive electrode material, poor conductivity in the circulation process and easy side reaction between the surface and electrolyte under high voltage are overcome, and the obtained composite positive electrode material has the advantages of uniform and stable coating layer, good ion conductivity and conductivity, and excellent cycle performance and rate capability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium battery positive electrode materials, in particular to a composite positive electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-rich materials, high-nickel ternary materials, lithium nickel manganese oxide, etc. are the positive electrode materials that have attracted much attention in the current research of high-energy-density lithium-ion batteries. They have high energy density and power density and are regarded as ideal choices for the next generation of power battery positive electrode materials. However, these positive electrode materials currently have problems to varying degrees in their applications. Ultimately, this is because the materials themselves have the following defects: 1. The residual alkali on the surface of the material is high; 2. The conductivity is poor during the cycle; 3. The surface is prone to side reactions with the electrolyte during the cycle, and the interfacial reaction seriously affects its cycle performance and rate performance. To this end, the existing technology uses surface coating and shallow doping to overcome the above defects.

[0003] For example, Chinese invention patent CN110690435A discloses a fast ion conductor coated high nickel ternary positive electrode material and its preparation method, which first adds a high nickel ternary precursor to a mixed solution, then stirs, dries and grinds to obtain a high nickel ternary precursor powder coated with a fast ion conductor; the precursor powder is evenly mixed with a lithium salt, and sintered to obtain a high nickel ternary positive electrode material coated with a fast ion conductor. The fast ion conductor material as a coating material for the ternary positive electrode material can provide a fast transmission channel for lithium ion transmission, thereby achieving the purpose of reducing the internal resistance of the battery. After coating, the battery cycle stability is improved without reducing the battery discharge capacity. However, in actual preparation, since the fast ion conductor precursor cannot be dissolved in the solution, its coating uniformity is not ideal, and the uncoated part still has a large side reaction. In addition, this prior art also has the following defects: (1) The high-intensity ball milling during the preparation process will cause the precursor to dissociate, destroy the morphology and structure of the precursor, and even cause the precursor to crack, affecting the performance of the positive electrode material. (2) Fast ion conductors can significantly improve ionic conductivity, but although they can improve electronic conductivity, the improvement effect is limited. (3) After coating the fast ion conductor, the coating layer can react with some alkaline substances on the surface of the positive electrode material, thereby reducing the amount of residual alkali on the surface. However, due to the fact that the coating uniformity of the fast ion conductor is not ideal, this method is also limited in reducing the amount of residual alkali on the surface.

[0004] Obviously, the material and coating method of the positive electrode material surface have an important influence on improving the coating effect and overcoming the above-mentioned defects of the material itself. For this reason, this application is proposed. Summary of the invention

[0005] In view of the above-mentioned shortcomings of the prior art, the present invention provides a composite positive electrode material and a preparation method and application thereof.

[0006] In order to achieve the above object, the main technical solutions adopted by the present invention include:

[0007] First, the present invention provides a method for preparing a composite positive electrode material, comprising the following steps:

[0008] S1. Mixing a nickel-cobalt-manganese hydroxide precursor with an organic boron-containing gas or / and an organic silicon-containing gas, and using a vapor deposition process (referred to as a CVD process) to decompose the organic boron-containing gas or / and the organic silicon-containing gas under an inert atmosphere and uniformly deposit them on the surface of the material to form a nickel-cobalt-manganese oxide coated with boron oxide or / and silicon oxide. The chemical formula of the nickel-cobalt-manganese hydroxide precursor is Ni x Co y Mn 1-x-y (OH)2, wherein: 0<x<1, 0≤y<1, and the obtained product is represented by material A;

[0009] S2. Material A and a lithium source are weighed in proportion, the amount of the lithium source added being matched with the amount of nickel-cobalt-manganese oxide and the content of boron oxide and / or silicon oxide on its surface, mixed evenly and sintered through air to form a positive electrode material with a surface coated with lithium borate and / or boron silicate. The obtained product is represented by material B;

[0010] S3. Crush and screen the material B, mix it evenly with the conductive carbon source in proportion, and sinter it in air to form a three-dimensional conductive network layer on the surface of the material B to obtain the final product.

[0011] It should be noted that:

[0012] (1) In step S1, before the CVD process is performed, an inert gas is first used for purge to ensure that there is no air and moisture in the CVD furnace chamber; the inert atmosphere is specifically selected from at least one of nitrogen, argon, helium, neon, krypton, etc., and nitrogen or argon is preferred for cost considerations.

[0013] (2) In step S1, after the CVD process deposition is completed, the inert gas is used again for purge, and the CVD furnace is preferably cooled to about 300° C. by programmed cooling, and then cooled naturally.

[0014] (3) All operations not described in detail are routine operations in this field.

[0015] The preparation method proposed in the present invention firstly cracks the organic boron-containing gas and / or the organic silicon-containing gas through the CVD process and uniformly deposits them on the surface of the material to form nickel-cobalt-manganese oxide coated with boron oxide and / or silicon oxide, then adds a lithium source, generates lithium borate and / or lithium silicate in situ on the surface of material A through sintering, and finally adds a conductive carbon source, and forms a three-dimensional conductive network layer through sintering.

[0016] Compared with the prior art, the preparation method proposed by the present invention has the following beneficial effects:

[0017] (1) Organic boron-containing gas or / and organic silicon-containing gas are decomposed in an inert atmosphere to first obtain nano-scale boron or / and silicon, which will form nano-scale deposition and shallow doping on the surface of the material. The shallowly doped nano-scale boron or / and silicon exists stably, while the nano-scale boron or / and silicon on the surface of the material is rapidly oxidized by oxygen to form a boron oxide or / and silicon oxide coating layer; due to the inherent advantages of the CVD process, the boron oxide or / and silicon oxide coating layer is dense and uniform, has good bonding strength with the surface of the positive electrode material, and has good stability and durability;

[0018] (2) On the basis of uniformly coating the boron oxide or / and silicon oxide coating layer, by detecting the content of the boron oxide or / and silicon oxide on the surface of the material and calculating the amount of nickel cobalt manganese oxide, a corresponding amount of lithium source is added in a matching manner, and sintering is performed so that the surface boron oxide or / and silicon oxide coating layer is in situ converted into lithium borate or / and lithium silicate with improved ionic conductivity, and the nickel cobalt manganese oxide is converted into lithium nickel cobalt manganate. At the same time, the residual alkali on the surface of the material is neutralized, and the shallowly doped nano-sized boron or / and silicon cooperates with the in-situ generated lithium borate or / and lithium silicate, which not only helps to stabilize the structure of the material and effectively improve the ionic conductivity of the material, but also can block the direct contact between the material and the electrolyte, avoid interface reaction, and improve the rate performance and cycle performance of the material;

[0019] (3) Finally, a three-dimensional conductive network layer is formed on the surface of material B by sintering, which significantly improves the conductivity of the material and helps to further improve the rate performance and cycle performance of the material.

[0020] Furthermore, in step S1, the furnace heating rate is 1-20°C / min, specifically 1°C / min, 2°C / min, 3°C / min, 4°C / min, 5°C / min, 6°C / min, 7°C / min, n, 8℃ / min, 9℃ / min, 10℃ / min, 11℃ / min, 12℃ / min, 13℃ / min, 14℃ / min, 15℃ / min, 16℃ / min, 17℃ / min, 18℃ / min, 19℃ / min, 20℃ / min, etc., particularly preferably 5-10℃ / min; the deposition temperature is 500-1500℃, specifically 500℃, 550℃, 600℃, 650℃, 700℃, 750℃, 800℃, 850℃, 900℃, 950℃, 1000℃, 1050℃, 1100℃, 1150℃, 1200℃, 1250℃, 1300℃ ℃, 1350℃, 1400℃, 1450℃, 1500℃, etc., particularly preferably 650-1000℃; the deposition time is 5-600min, specifically 5min, 10min, 30min, 50min, 60min, 120min, 150min, 180min, 200min, 240min, 300min, 360min, 400min, 500min, 600min, etc., preferably 2-6h, for example, specifically 2h, 2.5h, 3h, 3.5h, 4h, 4.5h, 5h, 5.5h, 6h, etc.; the organic boron-containing gas and / or the organic silicon-containing gas and the inert The organic boron-containing gas and / or the organic silicon-containing gas are mixed to form a mixed gas flow, wherein the volume percentage of the organic boron-containing gas and / or the organic silicon-containing gas in the mixed gas flow is 0.1-1V%, and can be specifically 0.1V%, 0.15V%, 0.2V%, 0.25V%, 0.3V%, 0.35V%, 0.4V%, 0.45V%, 0.5V%, 0.55V%, 0.6V%, 0.65V%, 0.7V%, 0.75V%, 0.8V%, 0.85V%, 0.9V%, 0.95V%, 1V%, etc., preferably 0.2-0.5V%, particularly preferably 0.2-0.3V%; the flow rate of the mixed gas flow is 0.1-10L / min, and can be specifically The speed of the furnace is 0.1L / min, 0.5L / min, 1L / min, 1.5L / min, 2L / min, 2.5L / min, 3L / min, 3.5L / min, 4L / min, 4.5L / min, 5L / min, 5.5L / min, 6L / min, 6.5L / min, 7L / min, 7.5L / min, 8L / min, 8.5L / min, 9L / min, 9.5L / min, 10L / min, etc. After adding the material, the speed of the furnace is 0.1-10rpm, specifically 0.1rpm, 0.2rpm, 0.3rpm, 0.4rpm, 0.5rpm, 0.8rpm, 1rpm, 1.2rpm, 1.5rpm, 2rpm, 2.3rpm, 2.5rpm, 2.8rpm, 3rpm, 4rpm, 5rpm, 6rpm, 7rpm, 8rpm, 9rpm, 10rpm, etc., particularly preferably 0.5-3rpm.

[0021] When boron oxide and / or silicon oxide-coated nickel-cobalt-manganese oxide is formed on the surface of the material by vapor deposition, parameters such as the heating rate of the vapor deposition furnace, deposition temperature, deposition time, flow rate of organic boron-containing gas and / or organic silicon-containing gas, and furnace speed will have a significant impact on the coating.

[0022] The heating rate determines the time required for the temperature in the vapor deposition furnace to reach the set value. If the heating rate is too fast, it may lead to a large temperature gradient, making the thermal stress on the surface and inside of the material uneven, thereby affecting the uniformity and adhesion of the coating layer; if the heating rate is too slow, it may lead to low preparation efficiency.

[0023] Deposition temperature is one of the key factors affecting the quality and performance of the boron oxide or / and silicon oxide coating layer. Appropriate deposition temperature can promote the cracking reaction of organic boron-containing gas or / and organic silicon-containing gas at an appropriate rate, thereby forming a relatively dense coating layer. If the temperature is too high, the cracking reaction may be too fast, thus affecting the quality of the coating layer; if the temperature is too low, the cracking of organic boron-containing gas or / and organic silicon-containing gas may be insufficient and the product may be difficult to fully adsorb and deposit on the surface of the substrate material, which also affects the quality of the coating layer.

[0024] The flow rate and deposition time of organic boron-containing gas and / or organic silicon-containing gas determine the thickness and integrity of the coating layer. A lower flow rate and a shorter deposition time may result in insufficient coating thickness, affecting the coating performance; while an excessive flow rate and a too long deposition time may result in an overly thick coating layer with excessive boron and / or silicon content, which will form unnecessary impurity phases, affecting the coating performance and increasing production costs.

[0025] The furnace speed mainly affects the distribution and mixing of organic boron-containing gases and / or organic silicon-containing gases in the reaction chamber. An appropriate speed can promote their uniform distribution and mixing, improve the uniformity and quality of the coating layer, while a speed that is too high or too low may lead to uneven gas distribution, thereby affecting the coating effect.

[0026] In summary, when forming nickel-cobalt-manganese oxide coated with boron oxide and / or silicon oxide by CVD process, the above process parameters are the preferred choice obtained by the present invention through several creative experiments, which is helpful to obtain high-quality and high-performance coating layer under the above process parameters.

[0027] Preferably, in step S2, the sintering temperature is 800-1000°C, for example, the sintering temperature can be specifically selected from 800°C, 805°C, 810°C, 815°C, 820°C, 825°C, 830°C, 835°C, 840°C, 845°C, 850°C, 855°C, 860°C, 865°C, 870°C, 875°C, 880°C, 885°C, 890°C, 895°C, 900°C, 905°C, 910°C, 915°C, 920°C, 925°C, 930°C, 935°C, 940°C, 945°C, 950°C, 955°C, 960°C, 965℃, 970℃, 975℃, 980℃, 985℃, 990℃, 995℃, 1000℃, etc.; sintering time is 6-20h, for example, the sintering time can be selected as 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h, 12h, 12.5h, 13h, 13.5h, 14h, 14.5h, 15h, 15.5h, 16h, 16.5h, 17h, 17.5h, 18h, 18.5h, 19h, 19.5h, 20h, etc.

[0028] Further, in step S3, the mass percentage of the conductive carbon source and the material B is 0.1%-3%, for example, it can be 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3%, etc., and 0.5%-1.5% is particularly preferred; the sintering temperature is 250-600°C, and the ratio For example, the specific temperature may be 250°C, 260°C, 270°C, 280°C, 290°C, 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C, 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 500°C, 550°C, 600°C, etc., with 300-450°C being particularly preferred; the sintering time is 4-10h, for example, specifically 4h, 4.5h, 5h, 5.5h, 6h, 6.5h, 7h, 7.5h, 8h, 8.5h, 9h, 9.5h, 10h, etc., with 4-6h being particularly preferred.

[0029] Compared with the traditional carbon coating layer, the three-dimensional conductive network layer is more helpful in forming interconnected conductive channels inside the positive electrode material, thereby significantly improving the conductivity of the positive electrode material and making the transmission of electrons inside the positive electrode material more efficient; moreover, the three-dimensional conductive network layer can also provide additional ion transmission channels, further improving the rate performance.

[0030] In this embodiment, the specific parameters of the conductive carbon source, sintering temperature, and sintering time are all based on the consideration of forming a three-dimensional conductive network layer with stable adhesion and strong conductivity. If the amount of the conductive carbon source added is too much, a coating layer will be formed on the surface of material B instead of a three-dimensional conductive network. If the amount of the conductive carbon source added is too little, the coverage rate of the conductive carbon on the surface of material B is low, and an effective three-dimensional conductive network cannot be constructed. If the sintering temperature is too high and the sintering time is too long, on the one hand, the conductive carbon source will be over-sintered to form carbon dioxide, which will sharply reduce the content of conductive carbon and deteriorate the stability and firmness of the remaining conductive carbon attached to the surface of material B. On the other hand, it will affect the crystal structure and order of material B; if the sintering temperature is too low and the sintering time is too short, the sintering is insufficient, and the stability of the obtained three-dimensional conductive network layer is poor.

[0031] Through creative work, the present invention found that when the mass percentage of the conductive carbon source to the material B is 0.1%-3%, sintering at 250-600°C for 4-10h helps to obtain a three-dimensional conductive network layer with good performance, especially when the mass percentage of the conductive carbon source to the material B is 0.5%-1.5%, sintering at 300-450°C for 4-6h, the effect is particularly good.

[0032] Further, in step S1, the organic boron-containing gas includes at least one of borane, borane derivatives, boron fluoride, boron fluoride derivatives, boron chloride, and boron chloride derivatives, with borane being particularly preferred; the organic silicon-containing gas includes at least one of silane, silane derivatives, silicon fluoride, silicon fluoride derivatives, silicon chloride, and silicon chloride derivatives, with silane being particularly preferred; in step S2, the lithium source is selected from at least one of lithium carbonate, lithium acetate, and lithium hydroxide, with lithium carbonate and lithium acetate being preferred; in step S3, the conductive carbon source is selected from at least one of carbon nanotubes, graphene oxide, and carbon fibers, with single-walled carbon nanotubes being particularly preferred. Single-walled carbon nanotubes have excellent conductive properties, good mechanical properties, a large specific surface area, and customizable surface properties, and therefore have an advantage in constructing a stably attached three-dimensional conductive network.

[0033] Secondly, the present invention provides a composite positive electrode material prepared according to the above preparation method.

[0034] Compared with the prior art, the present invention overcomes the defects of the existing positive electrode materials, such as high residual alkali on the surface, poor conductivity during the cycle, and easy side reactions with the electrolyte on the surface. The obtained composite positive electrode material coating layer is uniform, stable, and has good ion conductivity and conductivity, and has excellent cycle performance and rate performance.

[0035] Thirdly, the present invention proposes a positive electrode sheet, which comprises the above-mentioned composite positive electrode material. The composite positive electrode material as an active positive electrode material is evenly mixed with other components such as a solvent, an adhesive, a conductive agent, etc. to form a positive electrode slurry and is coated on a positive electrode collector to form the positive electrode sheet. The solvent, the adhesive, the conductive agent, the positive electrode collector, etc. are all conventional choices in the field.

[0036] Fourthly, the present invention proposes a lithium battery, which includes the above-mentioned positive electrode sheet and the necessary structural components of a conventional lithium battery such as a negative electrode sheet, an electrolyte, and a separator. Except for the positive electrode sheet, the rest adopts the existing technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0038] Figure 1 is the SEM image of the product obtained in Example 15;

[0039] Figure 2 This is the SEM image of the product obtained in Comparative Example 2. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0041] It should be noted that the technical solutions not described in detail below all adopt conventional technical means in the art. Various raw materials involved in the following examples and comparative examples are commercially available.

[0042] Example 1

[0043] 100gNi 0.25 Mn 0.75(OH)2 was placed in a CVD reactor, purged with nitrogen three times, and then nitrogen was continuously introduced at a flow rate of 0.5L / min. At the same time, the CVD reactor was heated to 850°C at a heating rate of 8°C / min and then kept warm. A mixed gas of silane and argon (the content of silane in the mixed gas was 0.25V%) was introduced at a flow rate of 3L / min, 850°C, and kept warm for 30min. After the insulation was completed, nitrogen was introduced to cool to room temperature to obtain material A; 21.2132g of lithium carbonate was added to material A , after mixing evenly, heat it at 950℃ for 10h and sinter it with 200L / min air, and then cool it naturally to room temperature to obtain material B; 100g material B and 125g single-walled carbon nanotube slurry (the slurry is made by ultrasonically dispersing single-walled carbon nanotubes in ethanol solvent, and the content of single-walled carbon nanotubes is 0.4wt%), use a high-speed disperser to mix evenly and evaporate to dryness, heat it at 300℃ for 6h in an air atmosphere in a muffle furnace, cool it naturally after the heat preservation, crush and sieve, and finally obtain the double-coated final product: LiNi 0.5 Mn 1.5 O4&Li2SiO3&CNTs.

[0044] Example 2

[0045] 100gNi 0.25 Mn 0.75 (OH)2 was placed in a CVD reactor, purged with nitrogen for 3 times, and then nitrogen was continuously introduced at a flow rate of 0.5 L / min. At the same time, the CVD reactor was heated to 850°C at a heating rate of 10°C / min and then kept warm. A mixed gas of silane and argon (the content of silane in the mixed gas was 0.25 V%) was introduced at a flow rate of 4 L / min, 800°C, and kept warm for 20 min. After the insulation was completed, nitrogen was introduced and cooled to room temperature to obtain material A; 21.2132 g of lithium carbonate was added to material A, mixed evenly, and heated at 950 ℃ for 10h and sintered with 200L / min air, then naturally cooled to room temperature to obtain material B; 100g of material B and 125g of single-walled carbon nanotube slurry (the slurry is prepared by ultrasonically dispersing single-walled carbon nanotubes in ethanol solvent, the content of single-walled carbon nanotubes is 0.4wt%; the coating amount of the formed three-dimensional conductive network layer is 0.5wt%), mixed evenly using a high-speed disperser and evaporated to dryness, sintered in an air atmosphere in a muffle furnace at 350℃ for 4h, cooled naturally after the insulation, crushed and sieved, and finally the double-coated final product: LiNi 0.5 Mn 1.5 O4&Li2SiO3&CNTs.

[0046] Example 3

[0047] 100gNi 0.5 Co 0.3 Mn0.2 (OH)2 was placed in a CVD reactor, and after nitrogen was used for 3 times of washing, nitrogen was continuously introduced at a flow rate of 0.5L / min. At the same time, the CVD reactor was heated to 900°C at a heating rate of 8°C / min and then kept warm. A mixed gas of borane and argon was introduced (the content of borane in the mixed gas was 0.3V%), the flow rate of the mixed gas was 5L / min, 900°C, and kept warm for 30min. After the insulation was completed, nitrogen was introduced and cooled to room temperature to obtain material A; 41.7523g of lithium carbonate was added to material A, and after mixing evenly, it was kept warm at 800°C for 20h and sintered with 200L / min of air, and then naturally cooled to room temperature to obtain material B; 100g of material B was mixed evenly with 0.5g of graphene oxide, and the mixture was kept warm at 300°C for 4h and sintered in an air atmosphere in a muffle furnace. After the insulation was completed, it was naturally cooled, crushed and sieved, and finally the double-coated final product was obtained: LiNi 0.5 Co 0.3 Mn 0.2 O2&Li2B4O7&C.

[0048] Example 4

[0049] 100gNi 0.5 Co 0.3 Mn 0.2 (OH)2 was placed in a CVD reactor and purged with nitrogen three times. Then, nitrogen was continuously introduced at a flow rate of 0.5 L / min. At the same time, the CVD reactor was heated to 950°C at a heating rate of 8°C / min and then kept warm. A mixed gas of silane and argon and a mixed gas of borane and argon (the contents of silane and borane in the two mixed gases were 0.3 V %) were introduced. The flow rate of the mixed gas of silane and argon was 5 L / min, and the flow rate of the mixed gas of borane and argon was 1.5 L / min. The temperature was set at 950°C. , keep warm for 20 minutes, after the end of the heat preservation, pass nitrogen to cool to room temperature to obtain material A; add 41.7523g lithium carbonate to material A, mix evenly, keep warm at 1000℃ for 6h and pass 200L / min air for sintering, and then naturally cool to room temperature to obtain material B; 100g material B and 0.6g single-walled carbon nanotube powder are mixed evenly, kept warm at 300℃ for 4h in an air atmosphere in a muffle furnace, and naturally cooled after the heat preservation, crushed and sieved, and finally the double-coated final product can be obtained: LiNi 0.5 Co 0.3 Mn 0.2 O2&Li2SiO3+Li2B4O7&CNTs.

[0050] Example 5-Example 7

[0051] Compared with Example 3, the content of borane in the mixed gas of borane and argon is adjusted to 0.1V%, 0.5V%, and 1V% respectively, and the rest remains the same as Example 3.

[0052] Example 8-Example 11

[0053] Compared with Example 1, the flow rate of the mixed gas in Examples 8, 9, 10 and 11 is adjusted from 3 L / min to 0.1 L / min, 5 L / min, 8 L / min and 10 L / min, respectively, and the rest are the same as in Example 1.

[0054] Example 12-Example 14

[0055] Compared with Example 3, in Example 12, Example 13, and Example 14, the conductive carbon source graphene oxide is adjusted to an equal coating amount of single-walled carbon nanotube slurry (i.e., 125g of single-walled carbon nanotube slurry is added, and the slurry is made by ultrasonically dispersing single-walled carbon nanotubes in ethanol solvent, and the content of single-walled carbon nanotubes is 0.4wt%), single-walled carbon nanotube powder, and carbon fiber, and the rest are consistent with Example 3.

[0056] Embodiment 15

[0057] 100gNi 0.8 Co 0.1 Mn 0.1 (OH)2 was placed in a CVD reactor, purged with nitrogen three times, and then nitrogen was continuously introduced at a flow rate of 0.5L / min. At the same time, the CVD reactor was heated to 800°C at a heating rate of 8°C / min and then kept warm. A mixed gas of silane and argon (the content of silane in the mixed gas was 0.2V%) was introduced at a flow rate of 8L / min, 800°C, and kept warm for 70min. After the insulation was completed, nitrogen was introduced and cooled to room temperature to obtain material A. 41.6045g of lithium carbonate was added to material A, and the mixture was mixed. After being evenly mixed, the mixture was kept at 950°C for 10 hours and sintered with 200L / min air, and then naturally cooled to room temperature to obtain material B; 100g of material B and 125g of single-walled carbon nanotube slurry (the slurry is prepared by ultrasonically dispersing single-walled carbon nanotubes in ethanol solvent, and the content of single-walled carbon nanotubes is 0.4wt%) were mixed evenly using a high-speed disperser and then evaporated to dryness, kept at 350°C for 4 hours and sintered in an air atmosphere in a muffle furnace, cooled naturally after the end of the heat preservation, crushed and sieved, and finally a double-coated final product was obtained, and its microscopic morphology is as follows Figure 1 Shown: LiNi 0.8 Co 0.1 Mn 0.1 O2&Li2SiO3&CNTs. Compared with the ones without CVD process and without building a three-dimensional conductive network layer Figure 2In contrast, the surface of the final product of this embodiment is indeed covered with a three-dimensional conductive network layer.

[0058] Example 16

[0059] 100gNi 0.25 Co 0.09 Mn 0.66 (OH)2 is placed in a CVD reactor. After nitrogen is used for purging 3 times, nitrogen is continuously introduced at a flow rate of 0.5L / min. At the same time, the CVD reactor is heated to 800°C at a heating rate of 8°C / min and then kept warm. A mixed gas of silane and argon (the content of silane in the mixed gas is 0.3V%) and a mixed gas of borane and argon (the content of borane in the mixed gas is 0.2V%) are introduced. The flow rate of the mixed gas of silane and argon is 10L / min, and the flow rate of the mixed gas of borane and argon is 5L / min. The reactor is kept warm at 800°C for 70min. After the insulation is completed, nitrogen is introduced for cooling. The mixture was cooled to room temperature to obtain material A; 42.9385 g of lithium carbonate was added to material A, mixed evenly, and then kept at 950° C. for 10 h and sintered with 200 L / min of air, and then naturally cooled to room temperature to obtain material B; 100 g of material B and 125 g of single-walled carbon nanotube slurry (the slurry is prepared by ultrasonically dispersing single-walled carbon nanotubes in ethanol solvent, and the content of single-walled carbon nanotubes is 0.4 wt%) were mixed evenly using a high-speed disperser and then evaporated to dryness, kept at 350° C. for 4 h, and sintered in an air atmosphere in a muffle furnace. After the insulation was completed, it was naturally cooled, crushed and sieved, and finally the double-coated final product was obtained: Li 1.166 Ni 0.2134 Co 0.0752 Mn 0.5454 O2Li2SiO3+Li2B4O7&CNTs.

[0060] Example 17-Example 21

[0061] Compared with Example 16, the addition amount of single-walled carbon nanotube slurry is adjusted so that the coating amount of the three-dimensional conductive network layer is 0.1wt%, 0.4wt%, 1.5wt%, 2wt% and 3wt% respectively, and the rest remains the same as Example 16.

[0062] Comparative Example 1

[0063] Compared with Example 16, neither the CVD process is implemented nor the three-dimensional conductive network layer is constructed. The rest is the same as Example 16, that is, simply adding an equal amount of lithium carbonate and sintering under the same conditions.

[0064] Comparative Example 2

[0065] Compared with Example 15, neither the CVD process nor the three-dimensional conductive network layer was constructed, and the rest was the same as Example 15, that is, simply adding an equal amount of lithium carbonate and sintering under the same conditions. The final product obtained is as follows Figure 2 shown.

[0066] Comparative Example 3

[0067] Compared with Example 1, neither the CVD process is implemented nor the three-dimensional conductive network layer is constructed. The rest is the same as Example 1, that is, simply adding an equal amount of lithium carbonate and sintering under the same conditions.

[0068] Comparative Example 4

[0069] Compared with Example 15, the three-dimensional conductive network layer is constructed without implementing the CVD process, and the rest is the same as Example 15.

[0070] Comparative Example 5

[0071] Compared with Example 15, a CVD process is implemented, but a three-dimensional conductive network layer is not constructed. The rest is the same as Example 15.

[0072] The products obtained in each embodiment and each comparative example are used as positive electrode active materials to prepare positive electrode sheets for lithium-ion half-cells. The specific operation is as follows: the products obtained in each embodiment and comparative example, the conductive agent acetylene black Super P, and polyvinylidene fluoride PVDF are mixed in a mass ratio of 90:5:5 to form a mixture, and the mixture is adjusted into a slurry with N-methyl-pyrrolidone NMP, and then evenly applied on aluminum foil, vacuum dried, taken out and pressed, and cut into positive electrode sheets of the required size. The positive electrode sheet and the lithium negative electrode sheet are then assembled into a button battery, which is tested in the voltage range of 2.8V-4.3V. The test results are shown in Table 1.

[0073] Table 1 Electrochemical performance test results of various embodiments and comparative examples

[0074]

[0075]

[0076] As shown in Table 1:

[0077] (1) From the comparison of the test results of Comparative Example 2, Comparative Example 4, Comparative Example 5 and Example 15, it can be seen that: 0.8 Co 0.1 Mn 0.1 After the surface of O2 is coated with lithium silicate by CVD, it helps to significantly reduce the residual alkali content on its surface; 0.8 Co 0.1 Mn 0.1The construction of a three-dimensional conductive network layer on the surface of O2 helps to significantly improve its capacity retention rate during cycling; 0.8 Co 0.1 Mn 0.1 The surface of O2 first forms a lithium silicate coating layer, and then constructs a three-dimensional conductive network layer, which not only helps to reduce the residual alkali content, but also significantly improves the cycle performance, and the improvement effect of the cycle performance is significantly better than the improvement effect when the three-dimensional conductive network layer is set alone. Obviously, the lithium silicate coating layer and the three-dimensional conductive network layer have a positive synergistic effect on improving the cycle performance of the composite positive electrode material.

[0078] The positive synergistic effect of the lithium silicate coating layer and the three-dimensional conductive network layer on the cycle performance can also be seen from the comparison of the test results of Example 16 and Comparative Example 1: before the positive electrode material is coated with a lithium silicate layer and a three-dimensional conductive network layer is constructed, the 1C / 1C100 cycle capacity retention rate is only 84.6%. After the lithium silicate is coated and a three-dimensional conductive network is constructed to form a composite positive electrode material, the 1C / 1C100 cycle capacity retention rate of the composite positive electrode material rapidly increases to 95%, and the residual alkali content on the surface of the material is greatly reduced.

[0079] (2) From the comparison of the test results of Example 1, Example 8-Example 11, and Comparative Example 3, it can be seen that: within 0.1L / min-10L / min, the final product obtained has improved charge specific capacity, discharge specific capacity and first efficiency compared with the case where no CVD process is performed and no three-dimensional conductive carbon network layer is coated, the cycle performance is significantly improved and the residual alkali content is significantly reduced, and 5L / min is the most preferred flow rate; when the flow rate of the mixed gas is between 0.1-5L / min, the first efficiency and 100-cycle cycle retention rate both increase with the increase of the flow rate, while the residual alkali content decreases with the increase of the flow rate; and when the flow rate exceeds 5L / min, such as 8L / min (Example 10) and 10L / min (Example 11), both the electrochemical performance and the residual alkali content are deteriorated compared with 5L / min.

[0080] (3) From the comparison of the test results of Example 3, Example 12, Example 13, and Example 14, it can be seen that: under the premise that other conditions are exactly the same, when forming a three-dimensional conductive network layer, using carbon nanotubes as raw materials, especially single-walled carbon nanotubes, has a better effect on improving the cycle performance than using graphene and carbon fibers as raw materials. The reason is that carbon nanotubes have excellent electrical conductivity, good mechanical properties, large specific surface area and customizable surface properties, so they are more advantageous in constructing a stably attached three-dimensional conductive network; when single-walled carbon nanotubes are used as raw materials, it is preferred to first ultrasonically disperse them in an organic solvent to form a slurry and then add them. In this way, the dispersion effect of the single-walled carbon nanotubes is better and the performance of the formed three-dimensional conductive network layer is better.

[0081] Furthermore, the coating amount of the three-dimensional conductive network layer is related to the effect of improving the cycle performance. As shown in Examples 16 to 21: when the coating amount of the three-dimensional conductive network layer is between 0.1 and 3 wt%, the cycle performance of the obtained product is good, especially when the coating amount is between 0.5 and 1.5 wt%, the cycle performance is particularly good.

[0082] In summary, the present invention firstly decomposes organic boron-containing gas or / and organic silicon-containing gas through CVD process and uniformly deposits them on the surface of the material to form nickel-cobalt-manganese oxide coated with boron oxide or / and silicon oxide, then adds a lithium source, and generates lithium borate or / and lithium silicate that can stably conduct ions in situ on the surface of material A through sintering, and finally adds a conductive carbon source, and forms a three-dimensional conductive network layer through sintering, thereby improving the conductivity of the positive electrode material; the lithium borate or / and lithium silicate coating layer and the three-dimensional conductive network layer work synergistically, which not only improves the cycle performance of the positive electrode material, but also reduces the residual alkali amount on the surface of the positive electrode material, thereby significantly improving the electrochemical performance of the positive electrode material.

[0083] Although the embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and cannot be understood as limiting the present invention. Those skilled in the art may change, modify, replace and deform the above embodiments within the scope of the present invention. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples without contradiction.

Claims

1. A method for preparing a composite positive electrode material, characterized in that: The steps are as follows: S1. Mixing a nickel-cobalt-manganese hydroxide precursor with an organic boron-containing gas or / and an organic silicon-containing gas, and using a vapor deposition process to decompose the organic boron-containing gas or / and the organic silicon-containing gas in an inert atmosphere and uniformly deposit them on the surface of the material to form a nickel-cobalt-manganese oxide coated with boron oxide or / and silicon oxide. The chemical formula of the nickel-cobalt-manganese hydroxide precursor is Ni x Co y Mn 1-x-y (OH)2, wherein: 0<x<1, 0≤y<1, and the obtained product is represented by material A; S2. Material A and a lithium source are weighed in proportion, the amount of the lithium source added being matched with the amount of nickel-cobalt-manganese oxide and the content of boron oxide and / or silicon oxide on its surface, mixed evenly and sintered through air to form a positive electrode material with a surface coated with lithium borate and / or boron silicate. The obtained product is represented by material B; S3. Crush and screen the material B, mix it evenly with the conductive carbon source in proportion, and sinter it in air to form a three-dimensional conductive network layer on the surface of the material B to obtain the final product.

2. The method for preparing a composite positive electrode material according to claim 1, characterized in that: In step S1, the furnace heating rate is 1-20°C / min, the deposition temperature is 500-1500°C, the deposition time is 5-600min, the organic boron-containing gas and / or the organic silicon-containing gas are mixed with the inert gas to form a mixed gas flow, the volume percentage of the organic boron-containing gas and / or the organic silicon-containing gas in the mixed gas flow is 0.1-1V%, the flow rate of the mixed gas flow is 0.1-10L / min, and the furnace speed is 0.1-10rpm after the material is added.

3. The method for preparing a composite positive electrode material according to claim 2, characterized in that: In step S1, the furnace heating rate is 5-10°C / min, the deposition temperature is 650-1000°C, the deposition time is 2-6h, the volume percentage of organic boron-containing gas and / or organic silicon-containing gas in the mixed gas flow is 0.2-0.5V%, and after adding the material, the furnace speed is 0.5-3rpm.

4. The method for preparing a composite positive electrode material according to claim 1, characterized in that: In step S2, the sintering temperature is 800-1000°C, and the sintering time is 6-20 hours.

5. The method for preparing a composite positive electrode material according to claim 1, characterized in that: In step S3, the mass percentage of the conductive carbon source and the material B is 0.1%-3%, the sintering temperature is 250-600° C., and the sintering time is 4-10 hours.

6. The method for preparing a composite positive electrode material according to claim 5, characterized in that: In step S3, the mass percentage of the conductive carbon source and the material B is 0.5%-1.5%, the sintering temperature is 300-450° C., and the sintering time is 4-6 hours.

7. The method for preparing a composite positive electrode material according to any one of claims 1 to 6, characterized in that: In step S1, the organic boron-containing gas includes at least one of borane, borane derivatives, boron fluoride, boron fluoride derivatives, boron chloride, and boron chloride derivatives; the organic silicon-containing gas includes at least one of silane, silane derivatives, silicon fluoride, silicon fluoride derivatives, silicon chloride, and silicon chloride derivatives; In step S2, the lithium source is selected from at least one of lithium carbonate, lithium acetate, and lithium hydroxide; In step S3, the conductive carbon source is selected from at least one of carbon nanotubes, graphene oxide, and carbon fibers.

8. A composite positive electrode material prepared according to the preparation method according to any one of claims 1 to 7.

9. A positive electrode sheet, characterized in that: The positive electrode sheet comprises the composite positive electrode material as claimed in claim 8.

10. A lithium battery, characterized in that: The lithium battery comprises the positive electrode sheet as claimed in claim 9.

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