A lithium nickel manganese oxide cathode material and a preparation method thereof

Abstract

The application relates to the technical field of lithium battery positive electrode materials, in particular to a lithium nickel-manganese oxide positive electrode material and a preparation method thereof. x Mn y T z O4, wherein 0.39<=x<=0.51, 1.4<=y<=1.6, 0.01<=z<=0.1, x+y+z<=2, the T element is selected from one or more of Al, Ti, Mg, V, La, Zr, Sr and Y, the intermediate layer is in-situ generated and doped with C, and the carbon network layer is sintered after hydrolysis and condensation of organosilane; the three-layer structure produces a positive synergistic effect, mutual influence and common action, and finally the cycle performance and rate performance of the positive electrode material are improved; the preparation method has good repeatability and energy production, and is helpful to realize industrialized production and commercial application of the lithium nickel-manganese oxide positive electrode material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery cathode material, and particularly relates to a lithium nickel manganese oxide cathode material and a preparation method thereof. BACKGROUND

[0002] The spinel lithium nickel manganese oxide cathode material, referred to as LNMO, has a high discharge voltage platform, a theoretical capacity of 147 mAh / g, can provide a high battery energy density, and has good cycle stability and thermal stability, and is one of the potential lithium ion battery cathode materials. However, at a high voltage, LNMO is prone to react with electrolyte, so that the strain and stress of the cathode material lattice structure increase, the grain boundary increases, the transition metal ions transition reduces, and the like, thereby reducing the structural stability of the cathode material, and long-time charge-discharge cycles can deteriorate the cycle performance of the battery, especially at high temperature, the cycle performance of the battery deteriorates, thus hindering the commercialization process of LNMO.

[0003] Therefore, it is urgent to improve it. SUMMARY

[0004] In view of the above-mentioned shortcomings of the prior art, the present application provides a lithium nickel manganese oxide cathode material and a preparation method thereof.

[0005] In order to achieve the above-mentioned purpose, the main technical scheme adopted by the present application includes:

[0006] On the one hand, the present application provides a lithium nickel manganese oxide cathode material, which comprises a core, an intermediate layer coated on the outer surface of the core, and a carbon network layer located on the outer surface of the intermediate layer.

[0007] The chemical formula of the core is LiNi x Mn y T z O4, wherein: 0.39≤x≤0.51, 1.4≤y≤1.6, 0.01≤z≤0.1, 1.87≤x+y+z≤2, and the T element is selected from one or more of Al, Ti, Mg, V, La, Zr, Sr and Y;

[0008] The intermediate layer is in-situ generated and doped with C Li3PS4;

[0009] The carbon network layer is sintered after hydrolysis and condensation of organosilane.

[0010] In the embodiment, x can be specifically 0.39, 0.4, 0.41, 0.42, 0.43, 0.44, 0.45, 0.46, 0.47, 0.48, 0.49, 0.5, 0.51, etc., y can be specifically 1.4, 1.41, 1.42, 1.43, 1.44, 1.45, 1.46, 1.47, 1.48, 1.49, 1.5, 1.51, 1.52, 1.53, 1.54, 1.55, 1.56, 1.57, 1.58, 1.59, 1.6, etc., z can be specifically 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, etc., and x+y+z can be specifically 1.87, 1.88, 1.89, 1.9, 1.91, 1.92, 1.93, 1.94, 1.95, 1.96, 1.97, 1.98, 1.99, 2, etc.

[0011] The present application takes lithium nickel manganese acid doped with one or more of Al, Ti, Mg, V, La, Zr, Sr, Y as the core, generates Li3PS4 doped with C in situ on the outer surface of the core, and then coats a carbon network layer on the outer surface of the Li3PS4, forming a three-layer structure of core-intermediate layer-outermost layer; the in-situ formed intermediate layer Li3PS4 doped with conductive C can significantly improve the ionic conductivity, provide abundant lithium ion transmission channels, and has strong electronic transmission capacity, thus significantly improving the cycle performance and rate performance; the outermost carbon network layer further promotes the transmission of electrons between the lithium nickel manganese acid positive electrode material and the electrolyte, reduces the internal resistance, improves the battery charge and discharge efficiency, and also plays a physical barrier role, effectively isolating the intermediate layer from moisture in the air, protecting the surface of the intermediate layer from corrosion, and more importantly, it can effectively prevent the intermediate layer from falling off during the battery cycle process, and enhance the structural integrity and stability of the positive electrode material; the three-layer structure produces a positive synergistic effect, mutual influence and joint action, and finally improves the cycle performance and rate performance of the positive electrode material.

[0012] Preferably, the thickness of the intermediate layer is not more than 25 nm, the thickness of the carbon network layer is 2-20 nm, such as specifically 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, 18 nm, 19 nm, 20 nm, and the like, more preferably 5-12 nm; the content of the carbon network layer is 0.5wt%-5wt%, such as specifically 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, 1.8wt%, 1.9wt%, 2wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, 3wt%, 3.1wt%, 3.2wt%, 3.3wt%, 3.4wt%, 3.5wt%, 3.6wt%, 3.7wt%, 3.8wt%, 3.9wt%, 4wt%, 4.1wt%, 4.2wt%, 4.3wt%, 4.4wt%, 4.5wt%, 4.6wt%, 4.7wt%, 4.8wt%, 4.9wt%, 5wt%, and the like, more preferably 2%-3%.

[0013] If the carbon network layer is too thick or contains too much carbon, on the one hand, it will increase the cost and complexity, and more carbon source, longer coating time and more difficult control process are required; on the other hand, it will hinder the diffusion path of lithium ions, affect the extraction and embedding of lithium ions, make the transmission of lithium ions difficult, and then affect the charge-discharge reaction of the battery, and reduce the cycle stability and rate performance of the battery. Through the creative labor, it is found that when the thickness and content of the carbon network layer are within the above range, the carbon network layer can play its role without obvious adverse effects on the diffusion performance of lithium ions, and the carbon network layer is difficult to obtain, low in cost, and relatively simple in control process.

[0014] Preferably, the contact angle of the carbon network layer is ≥150°, and the rolling angle of the carbon network layer is <5°.

[0015] The outermost carbon network layer not only plays a role in conducting electricity and a physical barrier, but also has hydrophobic properties. The present application finds that the carbon network layer of the product obtained in the previous embodiment: the contact angle is ≥ 150°, that is, it exhibits superhydrophobic properties, and the superhydrophobic surface can effectively resist the penetration of moisture and corrosive substances, thereby improving the corrosion resistance of the lithium nickel manganese oxide positive electrode material; the rolling angle is < 5°, and water droplets on the surface of the carbon network layer are very easy to move, the carbon network layer has good non-wetting and self-cleaning properties on the surface, and the carbon network layer is very stable when it is impacted by water droplets and is not easy to cause stress concentration or corrosion points due to the accumulation of water droplets. Therefore, the carbon network layer can more effectively resist the penetration of moisture and corrosive substances, thereby improving the corrosion resistance of the positive electrode material; at the same time, the good self-cleaning property also helps to reduce the contact time of moisture with the positive electrode material, further reducing the risk of water corrosion, and helping to significantly improve the cycle stability and safety of the battery.

[0016] Preferably, the D50, specific surface area a, and tap density b of the lithium nickel manganese oxide positive electrode material satisfy the following relationships: 4 μm < D50 < 6.5 μm, 0.6 m 2 / g < a < 1.5 m 2 / g, 1.2 g / cm 3 <b < 2.0 g / cm 3 .

[0017] Generally speaking, a smaller D50 is beneficial to lithium ion diffusion, but may cause the specific surface area of the lithium nickel manganese oxide positive electrode material to be too large, increasing the side reaction with the electrolyte.

[0018] The specific surface area has a significant impact on the electrochemical performance, and a larger specific surface area helps to improve the utilization rate of active substances and shorten the diffusion path of lithium ions in the positive electrode material, thereby improving the charge and discharge rate of the battery; however, a too large specific surface area may also cause an increase in structural defects on the surface of the positive electrode material, affecting the cycle stability and safety of the material.

[0019] For the positive electrode material, the size of the tap density is closely related to its specific capacity and the cycle performance of the battery, and as the tap density of the lithium nickel manganese oxide increases, the specific capacity of the positive electrode material will also increase, however, the increase in tap density will also have a certain negative impact on the cycle performance of the positive electrode material, especially under high-rate charge and discharge conditions, the lithium nickel manganese oxide positive electrode material with a larger tap density is prone to polarization, leading to a decrease in battery performance. In addition, when the tap density is too large, the lithium nickel manganese oxide positive electrode material will generate a large amount of heat during charging and discharging, which may cause the battery to overheat, catch fire, or even explode, and other safety accidents.

[0020] Therefore, the D50, specific surface area a, and tap density b of lithium nickel manganese oxide cathode materials need to be controlled within a reasonable range. Through experiments, this invention has found that when the product's D50, a, and b simultaneously satisfy: 4μm < D50 < 6.5μm, 0.6μm... 2 / g <a<1.5m 2 / g, 1.2g / cm 3 <b<2.0g / cm 3 When the desired electrochemical performance is achieved, the resulting lithium nickel manganese oxide cathode material exhibits good electrochemical properties.

[0021] On the other hand, the present invention proposes a method for preparing lithium nickel manganese oxide cathode material, comprising the following steps:

[0022] S1. Preparation of core materials

[0023] The lithium source, nickel manganese hydroxide and T element dopant source are mixed evenly according to the stoichiometric ratio shown in the chemical formula of the core, and then calcined at 700-1000℃ for 4-15h, preferably 8-14h. After cooling, they are crushed and sieved to obtain the final product.

[0024] S2, Preparation of intermediate layer material

[0025] First, a carbon source and a lithium-sulfur source are mixed evenly to form a carbon-lithium-sulfur precursor. Then, the carbon-lithium-sulfur precursor is sintered at 600-1000℃ in an inert atmosphere for 4-8 hours.

[0026] S3. Form an intermediate layer on the surface of the core material.

[0027] First, the core material obtained in step S1 and the intermediate layer material obtained in step S2 are mixed evenly with the phosphorus source, and then the resulting mixture is heat-treated at 200-400℃ for 0.5-2h.

[0028] S4, Coated Carbon Network Layer

[0029] First, the product obtained in step S3 and organosilane are added to deionized water and stirred evenly. Then, a mixture of concentrated sulfuric acid and concentrated nitric acid is added and stirred evenly to obtain a solid-liquid mixture. The solid-liquid mixture is then filtered, washed, and dried, and finally sintered at 150-200℃ for 1-3 hours.

[0030] It needs to be explained that:

[0031] In step S1, the core material is crushed and sieved, and the particle size after sieving is 2μm-10μm, more preferably 4μm-6.5μm.

[0032] In step S2, the method for forming the carbon-lithium-sulfur precursor is a prior art, which can adopt a dry method such as ball milling to mix uniformly, or a wet method such as adding the sulfur source into deionized water to stir uniformly, then adding the carbon source and a small amount of organic solvent (one or more of methanol, ethanol, cyclohexane, dimethylformamide, etc.), stirring uniformly again, and drying at 100-200 DEG C to obtain the carbon-lithium-sulfur precursor; the inert atmosphere can be provided by nitrogen, argon, helium or other inert gases; the inert gas flow rate during sintering is preferably 0.1-2 L / min.

[0033] In step S3, the inner core material, the intermediate layer material and the phosphorus source are preferably mixed by a dry method, that is, the three substances are mixed in proportion and placed in a ball mill for high-speed ball milling.

[0034] In step S4, the obtained material after suction filtration is cleaned with a mixture of anhydrous ethanol and deionized water, preferably in a mass ratio of 1:1:4; after cleaning, the material is dried at 80 DEG C for 5-10 h, and then sintered.

[0035] The preparation method provided by the present application first prepares the inner core material and the intermediate layer material, then mixes the inner core material, the intermediate layer material and the phosphorus source uniformly and sintering, to form an intermediate layer on the outer surface of the inner core material, and then coat a carbon network layer on the outer surface of the intermediate layer, to finally obtain the lithium nickel-manganese oxide positive electrode material provided by the present application. This preparation method has good repeatability, is easy to operate, and has energy production, which is helpful to realize the industrialized production and commercial application of the lithium nickel-manganese oxide positive electrode material.

[0036] Preferably, in step S1, the lithium source is selected from one or more of lithium acetate, lithium carbonate, lithium hydroxide and lithium nitrate; the T element doping source is selected from one or more of compounds containing Al, Ti, Mg, V, La, Zr, Sr and Y, such as acetate, carbonate and hydroxide; preferably, only a compound containing the T element is used without introducing other impurity elements.

[0037] Preferably, in step S2, the carbon source is selected from one or more of glucose, sucrose, polyethylene glycol, acetylene black, carbon nanotube, phenol formaldehyde resin and resorcinol-formaldehyde resin; the lithium-sulfur source is selected from one or more of lithium-germanium-phosphorus-sulfur, lithium-phosphorus-sulfur and lithium sulfate; preferably, the lithium-sulfur source contains phosphorus; the mass ratio of the carbon source to the lithium-sulfur source is 1:(0.3-0.75); in step S3, the phosphorus source is selected from one or more of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, lithium phosphate, lithium dihydrogen phosphate and phosphorus sulfide; the mass ratio of the inner core material, the intermediate layer material and the phosphorus source is 1:(0.01-0.05):(0.01-0.03).

[0038] In the embodiment, the raw materials are mixed in the defined mass ratio to form the intermediate layer Li3PS4 with appropriate amount of conductive C in situ on the surface of the core, and the thickness of the intermediate layer is not more than 25 nm.

[0039] Preferably, in step S4, the concentrated sulfuric acid is 90wt% sulfuric acid, the concentrated nitric acid is 75wt% nitric acid, and the deionized water, 90wt% sulfuric acid and 75wt% nitric acid are mixed in a mass ratio of 1:(0.25-0.3):(0.1-0.2); the product obtained in step S3 and the organosilane are first added to the deionized water and stirred for 1h, then 90wt% sulfuric acid and 75wt% nitric acid are added, and stirred at room temperature for 5-12h, and preferably for 8-10h, to obtain the solid-liquid mixture.

[0040] In the embodiment, the mixed acid solution is prepared by mixing deionized water, 90wt% sulfuric acid and 75wt% nitric acid in a mass ratio of 1:(0.25-0.3):(0.1-0.2). The mixed acid solution can etch the surface of the product obtained in step S3, and at the same time, break the C-Si bond in the organosilane adhered to the surface, then hydrolyze and condense to form siloxane bonds, and then build a complex organosilicon polymer structure and adhere to the outer surface of the intermediate layer, and after sintering, form the outermost carbon network layer. In addition to the conductive and physical shielding effects, the carbon network layer is more important in preventing the intermediate layer from falling off during the battery cycle process, and enhancing the structural integrity and stability of the positive electrode material. It is speculated that the chemical bonds such as Si-C, C-P, C-S and carboxyl groups exist between the carbon network layer and the intermediate layer obtained by the above preparation method, which helps to increase the inter-particle force and the interlayer adhesion strength, improve the long cycle stability of the positive electrode material, and prolong the service life of the positive electrode material.

[0041] In the embodiment, the composition of the mixed acid is of great significance for the firm, uniform and stable coating of the carbon network layer on the surface of the intermediate layer. For example, if the addition amount of concentrated sulfuric acid and concentrated nitric acid exceeds the above range, the surface of the particles will be etched excessively, affecting the structural strength of the product. If the addition amount of concentrated sulfuric acid and concentrated nitric acid is too small, the surface of the particles will not be etched completely, the carboxylation treatment will not be complete, and the uniformity and stability of the carbon network layer will be affected.

[0042] Preferably, in step S4, the content of the product obtained in step S3 in the solid-liquid mixture is 8wt%, and the content of the organosilane is 0.4wt%-0.8wt%.

[0043] In the embodiment, the raw materials are mixed in the defined mass ratio to form the intermediate layer Li3PS4 with appropriate amount of conductive C in situ on the surface of the core, and the thickness of the intermediate layer is not more than 25 nm.

[0044] Preferably, the organosilane is selected from one or more of methylsilane, vinylsilane, aminosilane, and hydrosilane, and the methylsilane is one or more of methylbutyltrichlorosilane, isopropoxytrimethylsilane, glycidoxypropyltrimethylsilane, and perfluoroalkyltrimethylsilane.

[0045] In the present embodiment, the organosilane is preferably methylsilane. Concentrated nitric acid is a strong oxidant, which can oxidize the methyl-containing silane to make it more hydrolyzable, and then generate corresponding silanol and alcohol compounds. These silanol compounds can further undergo condensation reactions to generate siloxane bonds, and then build complex organic silicon polymer structures and stably adhere to the outer surface of the intermediate layer, and generate a carbon network layer after sintering. BRIEF DESCRIPTION OF DRAWINGS

[0046] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0047] Figure 1 SEM image of the product obtained in Example 1.

[0048] Figure 2 SEM image of the product obtained in Example 2. DETAILED DESCRIPTION

[0049] The technical solutions in the embodiments of the present application will be described clearly and completely in the following with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0050] It should be noted that the technical means not described in detail below all use conventional technical means in the art. The test means not described in detail below all use conventional test means in the art. Those skilled in the art can combine them without creative labor.

[0051] Example 1

[0052] A nickel-lithium manganate positive electrode material, comprising a core, an intermediate layer coated on the outer surface of the core, and a carbon network layer located on the outer surface of the intermediate layer; the chemical formula of the core is LiNi 0.48 Mn 1.5 T 0.02O4, wherein: the T element is a combination of Al, Mg and Zr; the intermediate layer is Li3PS4 generated in situ and doped with C; and the carbon network layer is formed by hydrolysis, condensation and sintering of methylbutylated trichlorosilane.

[0053] The specific preparation method is as follows:

[0054] S1. Preparation of core materials

[0055] Lithium carbonate, nickel manganese hydroxide, aluminum oxide, magnesium oxide, and zirconium oxide are mixed evenly according to the stoichiometric ratio shown in the chemical formula of the core, then calcined at 850°C for 10 hours, cooled, pulverized, and sieved to obtain a product with a particle size of 4μm-6.5μm.

[0056] S2, Preparation of intermediate layer material

[0057] First, lithium phosphorus sulfur was added to deionized water and stirred evenly. Then, glucose and a small amount of methanol were added. The mass ratio of glucose to lithium phosphorus sulfur was 1:0.52. After stirring evenly again, the mixture was dried at 180°C to obtain a carbon lithium sulfur precursor. Finally, the carbon lithium sulfur precursor was sintered at 800°C under a nitrogen atmosphere for 6 hours. The inert gas flow rate during sintering was 1.5 L / min.

[0058] S3. Form an intermediate layer on the surface of the core material.

[0059] First, the core material obtained in step S1, the intermediate layer material obtained in step S2, and lithium phosphate are placed in a high-speed ball mill and mixed evenly at a mass ratio of 1:0.03:0.02. Then, the resulting mixture is heat-treated at 300°C for 1.5 hours.

[0060] S4, Coated Carbon Network Layer

[0061] First, the product obtained in step S3 and methylbutylated trichlorosilane were added to deionized water and stirred evenly. Then, 90 wt% concentrated sulfuric acid and 75 wt% concentrated nitric acid were added. The deionized water, 90 wt% sulfuric acid, and 75 wt% nitric acid were mixed at a mass ratio of 1:0.28:0.15. After stirring at room temperature for 9 hours, a solid-liquid mixture was obtained. The content of the product obtained in step S3 in the solid-liquid mixture was 8 wt%, and the content of organosilane was 0.6 wt%. Then, the solid-liquid mixture was filtered. The material obtained after filtration was washed with a mixture of anhydrous ethanol and deionized water. The mass ratio of material, anhydrous ethanol, and deionized water during washing was 1:1:4. After washing, the material was dried at 80°C for 8 hours and then sintered at 180°C for 2 hours.

[0062] Depend on Figure 1 It can be seen that the obtained product has a relatively uniform particle size distribution and a relatively smooth surface. Testing showed that the obtained product has a D50 of 5.5 μm and a specific surface area of ​​1.0 m².2 / g, tap density 1.8 g / cm 3 ; the thickness of the intermediate layer is 18 nm, the thickness of the carbon network layer is 10 nm and the content of the carbon network layer is 2.5 wt%, the contact angle of the carbon network layer is 155°, and the roll-off angle of the carbon network layer is 4°.

[0063] Example 2

[0064] Compared with Example 1, the methyl butylated trichlorosilane is adjusted to be equal amount of vinyl trimethoxysilane. The rest is consistent with Example 1.

[0065] From the above data, it can be seen that the particle size distribution of the obtained product is relatively uniform, and the surface is also relatively smooth. The product of Example 1 has little difference in appearance. Figure 2

[0066] Example 3

[0067] Compared with Example 1, the methyl butylated trichlorosilane is adjusted to be equal amount of γ-aminopropyl triethoxysilane. The rest is consistent with Example 1.

[0068] Example 4

[0069] Compared with Example 1, the methyl butylated trichlorosilane is adjusted to be equal amount of isopropoxy trimethylsilane. The rest is consistent with Example 1.

[0070] Example 5

[0071] Compared with Example 1, the methyl butylated trichlorosilane is adjusted to be equal amount of epoxy propyl trimethylsilane. The rest is consistent with Example 1.

[0072] Example 6

[0073] Compared with Example 1, the methyl butylated trichlorosilane is adjusted to be equal amount of perfluoroalkyl trimethylsilane. The rest is consistent with Example 1.

[0074] Example 7

[0075] Compared with Example 1, the chemical formula of the core is LiNi 0.46 Mn 1.4 T 0.1 O4, and the rest is consistent with Example 1.

[0076] Example 8

[0077] Compared with Example 1, the chemical formula of the core is LiNi 0.39 Mn 1.6 T 0.01 O4, and the rest is consistent with Example 1. ​

[0078] Example 9

[0079] The chemical formula of the core is LiNi 0.4 Mn 1.42 T 0.05 O4, and the rest is consistent with Example 1.

[0080] Example 10

[0081] The chemical formula of the core is LiNi 0.51 Mn 1.4 T 0.08 O4, and the rest is consistent with Example 1.

[0082] Example 11

[0083] The lithium nickel manganese acid positive electrode material is the same as Example 1, but during preparation, the deionized water, 90wt% sulfuric acid, and 75wt% nitric acid in step S4 are mixed in a mass ratio of 1:0.25:0.2. The rest is consistent with Example 1.

[0084] Example 12

[0085] The lithium nickel manganese acid positive electrode material is the same as Example 1, but during preparation, the deionized water, 90wt% sulfuric acid, and 75wt% nitric acid in step S4 are mixed in a mass ratio of 1:0.3:0.1. The rest is consistent with Example 1.

[0086] Example 13

[0087] The lithium nickel manganese acid positive electrode material is the same as Example 1, but during preparation, the mass ratio of glucose to lithium phosphorus sulfur in step S2 is 1:0.3. The rest is consistent with Example 1.

[0088] Example 14

[0089] The lithium nickel manganese acid positive electrode material is the same as Example 1, but during preparation, the mass ratio of glucose to lithium phosphorus sulfur in step S2 is 1:0.75. The rest is consistent with Example 1.

[0090] Example 15

[0091] The lithium nickel manganese acid positive electrode material is the same as Example 1, but during preparation, the mass ratio of each raw material in step S3 is adjusted from 1:0.03:0.02 to 1:0.01:0.03. The rest is consistent with Example 1.

[0092] Tested: The D50 of the obtained product is 5.1μm, the specific surface area is 0.8m 2 / g, and the tap density is 1.8g / cm 3; the intermediate layer has a thickness of 21 nm, the carbon network layer has a thickness of 10 nm and the carbon network layer has a content of 2 wt%, the carbon network layer has a contact angle of 155°, the carbon network layer has a roll-off angle of 4°.

[0093] Example 16

[0094] Compared with Example 1, the composition of the lithium nickel manganese oxide positive electrode material is the same, but the mass ratio of each raw material in step S3 is adjusted from 1:0.03:0.02 to 1:0.05:0.01 during preparation. The rest is consistent with Example 1.

[0095] Tested: the D50 of the obtained product is 5.3 μm, the specific surface area is 1.1 m 2 / g, the tap density is 1.8 g / cm 3 ; the intermediate layer has a thickness of 21 nm, the carbon network layer has a thickness of 10 nm and the carbon network layer has a content of 2 wt%, the carbon network layer has a contact angle of 155°, the carbon network layer has a roll-off angle of 4°.

[0096] Example 17

[0097] Compared with Example 1, the composition of the lithium nickel manganese oxide positive electrode material is the same, but the content of the product obtained in step S3 is 8 wt% and the content of the organic silane is 0.4 wt% in the solid-liquid mixture in step S4 during preparation. The rest is consistent with Example 1.

[0098] Tested: the D50 of the obtained product is 5.6 μm, the specific surface area is 1.3 m 2 / g, the tap density is 1.8 g / cm 3 ; the intermediate layer has a thickness of 21 nm, the carbon network layer has a thickness of 10 nm and the carbon network layer has a content of 2 wt%, the carbon network layer has a contact angle of 155°, the carbon network layer has a roll-off angle of 4°.

[0099] Example 18

[0100] Compared with Example 1, the composition of the lithium nickel manganese oxide positive electrode material is the same, but the content of the product obtained in step S3 is 8 wt% and the content of the organic silane is 0.8 wt% in the solid-liquid mixture in step S4 during preparation. The rest is consistent with Example 1.

[0101] Tested: the D50 of the obtained product is 5.5 μm, the specific surface area is 1.3 m 2 / g, the tap density is 1.8 g / cm 3; the intermediate layer has a thickness of 18 nm, the carbon network layer has a thickness of 12 nm and a content of 5 wt%, the carbon network layer has a contact angle of 157°, and the carbon network layer has a roll-off angle of 3°.

[0102] Comparative Example 1

[0103] The lithium nickel manganese oxide positive electrode material contains only the inner core, without the intermediate layer and the outermost layer, compared with Example 1; the remaining technical details are consistent with Example 1. The preparation method is only adaptively adjusted compared with Example 1.

[0104] Comparative Example 2

[0105] The lithium nickel manganese oxide positive electrode material contains the inner core and the intermediate layer, but does not set the carbon network layer, compared with Example 1; the remaining technical details are consistent with Example 1. The preparation method is only adaptively adjusted compared with Example 1.

[0106] Comparative Example 3

[0107] The lithium nickel manganese oxide positive electrode material does not set the intermediate layer, i.e. the carbon network layer is set on the surface of the inner core, compared with Example 1; the remaining technical details are consistent with Example 1. The preparation method is only adaptively adjusted compared with Example 1.

[0108] Comparative Example 4

[0109] The lithium nickel manganese oxide positive electrode material is compared with Example 1, the intermediate layer is doped with C, not doped with P, i.e. no phosphorus source is added in step S3 during preparation, and the remaining technical details are consistent with Example 1.

[0110] Comparative Example 5

[0111] The lithium nickel manganese oxide positive electrode material is compared with Example 1, the intermediate layer is not doped with P, not doped with C, i.e. no carbon source is added in step S2 and no phosphorus source is added in step S3 during preparation, and the remaining technical details are consistent with Example 1.

[0112] Comparative Example 6

[0113] The lithium nickel manganese oxide positive electrode material is the same as Example 1, but during preparation, deionized water, 90 wt% sulfuric acid, and 75 wt% nitric acid are mixed in a mass ratio of 1:0.2:0.05 in step S4. The rest is consistent with Example 1.

[0114] Comparative Example 7

[0115] The lithium nickel manganese oxide positive electrode material is the same as Example 1, but during preparation, deionized water, 90 wt% sulfuric acid, and 75 wt% nitric acid are mixed in a mass ratio of 1:0.4:0.3 in step S4. The rest is consistent with Example 1.

[0116] The products obtained from Example 1 to Example 18 and Comparative Example 1 to Comparative Example 7 were used as positive electrode materials, and a button cell was assembled and tested for the first cycle charging specific capacity, the first cycle discharging specific capacity, the capacity retention rate after 100 cycles at 1C / 1C at 45°C in the voltage range of 2.8-4.95V, and the test results are shown in Table 1.

[0117] Table 1

[0118]

[0119]

[0120] As shown in Table 1:

[0121] (1) The test results of Comparative Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3 show that: setting C-doped Li3PS4 on the surface of the core or setting a carbon network layer can improve the initial efficiency and high-temperature cycle performance of the lithium battery to a certain extent, but the improvement effect is limited; however, setting C-doped Li3PS4 on the surface of the core first, and then setting a carbon network layer, the initial efficiency and high-temperature cycle performance of the lithium battery are significantly improved. The test results of Comparative Example 1, Comparative Example 4, Comparative Example 5 show that: compared with selective doping or no doping, the intermediate layer simultaneously doped with C and P can more effectively improve the initial efficiency and high-temperature cycle performance of the lithium battery.

[0122] Obviously, the three-layer structure exists at the same time and the intermediate layer doped with C and P has a positive synergistic effect on the cycle performance and rate performance of the positive electrode material. Moreover, the test results of Example 1 to Example 17 show that: the lithium nickel-manganese phosphate positive electrode material obtained under the preparation conditions defined in the present application has good high-temperature cycle performance.

[0123] (2) The test results of Comparative Example 1, Example 2, Example 3, Example 4, Example 5, and Example 6 show that: under the premise of the same other conditions, when the organosilane used to prepare the outermost carbon network layer is selected from methylbutyltrichlorosilane, isopropoxytrimethylsilane, epoxypropyltrimethylsilane, and perfluoroheptyltrimethylsilane, the initial efficiency of the lithium battery composed of the obtained product is 93.71%-94.06%, and the capacity retention rate after 100 cycles at 45°C is 94%; while when the organosilane is selected from vinyltrimethoxysilane and γ-aminopropyltriethoxysilane, the initial efficiency of the lithium battery composed of the obtained product is about 91%, and the capacity retention rate after 100 cycles at 45°C is 92%-93%. Obviously, the carbon network layer obtained by using the organosilane containing methyl has a better effect on improving the electrochemical performance of the positive electrode material.

[0124] (3) The test results of Comparative Example 1, Comparative Example 6 and Comparative Example 7 show that: for the lithium nickel manganese oxide positive electrode material with the same composition, if the concentration of sulfuric acid and nitric acid in the mixed acid used in preparation is less than or greater than the amount defined in the application, the first efficiency of the lithium battery is not greatly affected, but the high-temperature cycle performance of the lithium battery is significantly deteriorated. The reason is that if the addition amount of concentrated sulfuric acid and concentrated nitric acid exceeds the above range, the etching of the particle surface will be excessive, which will affect the structural strength of the product, and then deteriorate the cycle performance. If the addition amount of concentrated sulfuric acid and concentrated nitric acid is too small, the etching of the particle surface will not be complete, and the carboxylation treatment will not be complete, which will affect the uniformity and stability of the carbon network layer, and also lead to the deterioration of the cycle performance.

[0125] In summary: the lithium nickel manganese oxide doped with one or more of Al, Ti, Mg, V, La, Zr, Sr and Y is used as the inner core, C-doped Li3PS4 is generated in situ on the outer surface of the inner core, and a carbon network layer is coated on the outer surface of the Li3PS4, forming a three-layer structure of inner core-intermediate layer-outermost layer, which can produce a positive synergistic effect, and finally improve the cycle performance and rate performance of the positive electrode material.

[0126] Although the embodiments of the application have been shown and described above, it should be understood that the above embodiments are exemplary and should not be construed as limiting the application, and those skilled in the art can modify, modify, replace and deform the above embodiments within the scope of the application. In addition, those skilled in the art can combine and combine the different embodiments or examples described in the specification and the features of the different embodiments or examples without contradiction.

Claims

1. A lithium nickel manganese oxide cathode material, characterized in that, The core, the intermediate layer coated on the surface of the core, and the carbon network layer on the surface of the intermediate layer; The chemical formula of the core is LiNi x Mn y T z O4, wherein: 0.39≤x≤0.51, 1.4≤y≤1.6, 0.01≤z≤0.1, 1.87≤x+y+z≤2, the T element is selected from one or more of Al, Ti, Mg, V, La, Zr, Sr, Y; The intermediate layer is Li3PS4 in-situ generated and doped with C; The carbon network layer is sintered after hydrolysis and condensation of organosilane. 2.The lithium nickel manganese oxide cathode material of claim 1, characterized in that, The thickness of the intermediate layer is not more than 25 nm, the thickness of the carbon network layer is 2-20 nm, and the content of the carbon network layer is 0.5wt%-5wt%. 3.The lithium nickel manganese oxide cathode material of claim 2, characterized in that, The contact angle of the carbon network layer is ≥150°, and the rolling angle of the carbon network layer is <5°. 4.The lithium nickel manganese oxide cathode material of claim 1, wherein, The D50, specific surface area a, and tap density b of the nickel-manganese lithium acid cathode material satisfy the following relationships: 4 μm < D50 < 6.5 μm, 0.6 m 2 / g < a < 1.5 m 2 / g, 1.2 g / cm 3 <b < 2.0 g / cm 3 .

5. A method for preparing the lithium nickel manganese oxide cathode material according to any one of claims 1-4, characterized in that, The method comprises the following steps: S1, preparing core material Mixing a lithium source, a nickel-manganese hydroxide, and a T element doping source according to the stoichiometric ratio shown in the chemical formula of the core, and then calcining at 700-1000°C for 4-15h, crushing and sieving after cooling to obtain the core material; S2, preparing intermediate layer material Mixing a carbon source and a lithium-sulfur source uniformly to form a carbon-lithium-sulfur precursor, and then sintering the carbon-lithium-sulfur precursor at 600-1000°C in an inert atmosphere for 4-8h; S3, forming an intermediate layer on the surface of the core material Mixing the core material obtained in step S1, the intermediate layer material obtained in step S2, and a phosphorus source uniformly, and then heat treating the mixture at 200-400°C for 0.5-2h; S4, coating a carbon network layer Mixing the product obtained in step S3 and organosilane in deionized water and stirring uniformly, then adding a mixed acid solution of concentrated sulfuric acid and concentrated nitric acid, and stirring uniformly to obtain a solid-liquid mixture, then performing suction filtration, washing, and drying on the solid-liquid mixture, and finally sintering at 150-200°C for 1-3h.

6. The preparation method according to claim 5, wherein In step S1, the lithium source is selected from one or more of lithium acetate, lithium carbonate, lithium hydroxide, and lithium nitrate, and the T element doping source is selected from one or more of compounds containing Al, Ti, Mg, V, La, Zr, Sr, and Y; In step S2, the carbon source is selected from one or more of glucose, sucrose, polyethylene glycol, acetylene black, carbon nanotubes, phenol formaldehyde resin, and resorcinol-formaldehyde resin, and the lithium-sulfur source is selected from one or more of lithium-germanium-phosphorus-sulfur, lithium-phosphorus-sulfur, and lithium sulfate, and the mass ratio of the carbon source to the lithium-sulfur source is 1:(0.3-0.75).

7. The production method according to claim 6, wherein In step S3, the phosphorus source is selected from one or more of diammonium hydrogen phosphate, ammonium dihydrogen phosphate, lithium phosphate, lithium dihydrogen phosphate, and phosphorus sulfide, and the mass ratio of the core material, the intermediate layer material, and the phosphorus source is 1:(0.01-0.05):(0.01-0.03).

8. The preparation method according to claim 5, characterized in that, In step S4, the concentrated sulfuric acid is 90wt% sulfuric acid, and the concentrated nitric acid is 75wt% nitric acid, and the mass ratio of deionized water, 90wt% sulfuric acid, and 75wt% nitric acid is 1:(0.25-0.3):(0.1-0.2); Mixing the product obtained in step S3 and organosilane in deionized water and stirring for 1h, then adding 90wt% sulfuric acid and 75wt% nitric acid, and stirring at room temperature for 5-12h to obtain the solid-liquid mixture.

9. The preparation method according to claim 5, characterized in that, The content of the product obtained in step S3 is 8 wt% and the content of the organosilane is 0.4 wt%-0.8 wt% in the solid-liquid mixture in step S4.

10. The method of claim 5, wherein, The organosilane in step S4 is selected from one or more of methylsilane, vinylsilane, aminosilane, and hydrosilane, and the methylsilane is one or more of methylbutyltrichlorosilane, isopropoxytrimethylsilane, epoxypropyltrimethylsilane, and perfluoroheptyltrimethylsilane.

Images