Coated ternary positive electrode material, preparation method thereof and lithium ion battery

Abstract

The application belongs to the technical field of lithium ion battery materials, and particularly relates to a coated ternary positive electrode material, a preparation method thereof and a lithium ion battery. The coated ternary positive electrode material comprises a substrate and a coating layer on the surface of the substrate; the substrate is a ternary positive electrode material LiNi x Co y Mn 1‑x‑y O2, wherein x>0, y>0, and 1-x-y>0; the coating layer is a composite of graphene and WNb 12 O 33 O. The preparation method of the coated ternary positive electrode material comprises the following steps: adding the ternary positive electrode material into a dispersion liquid containing graphene and WNb 12 O 33 O, and stirring and heating until the solvent is evaporated to dryness to obtain a precursor; and performing first sintering on the precursor to obtain the coated ternary positive electrode material. The composite coating layer of graphene and WNb 12 O 33 O on the surface of the ternary positive electrode material is stable and uniform in property, and the lithium battery prepared from the positive electrode material has relatively excellent electrochemical performance.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery materials, and particularly relates to a coated ternary positive electrode material and a preparation method thereof and a lithium ion battery. BACKGROUND

[0002] At present, lithium ion batteries have been widely applied due to the advantages of high energy density, long cycle life, environmental friendliness and fast charging and discharging. As the positive electrode material of lithium ion batteries, nickel-based layered oxides are considered to be one of the most promising materials, which have high energy density, but when they work at high voltage, the surface of the particles will be reconstructed, that is, irreversible phase transition and increase of side reactions with electrolyte will occur, which will lead to the decrease of the cycle performance of the positive electrode material. Therefore, the surface coating technology is usually used to reduce the structural evolution of the surface of the nickel-based ternary positive electrode material particles and the direct contact with the electrolyte, so as to reduce the occurrence of side reactions on the surface of the particles and improve the service life of the positive electrode material.

[0003] Generally, the ideal modification coating on the surface of the ternary positive electrode material should not only have high electronic conductivity and ionic conductivity, but also have high chemical resistance to the electrolyte and strong mechanical strength to inhibit the cracking of the positive electrode material particles. At present, the traditional modification coating is mostly metal oxides / flourides, lithium conductors and conductive polymers, which are coated on the surface of the positive electrode material by dry / wet method or physical / chemical vapor deposition method. However, the coating coated by these methods has the problems of poor combination with the positive electrode material matrix and uneven coating, and the physicochemical property stability of the traditional coating is also poor, which will reduce the specific capacity of the positive electrode material and imbalance the electrochemical stability.

[0004] In view of this, the application is proposed. SUMMARY

[0005] The application aims to provide a coated ternary positive electrode material and a preparation method thereof and a lithium ion battery, which aims to coat the surface of the ternary positive electrode material with a stable modification layer with excellent physicochemical properties, and further improve the electrochemical performance of the lithium ion battery.

[0006] In order to achieve the purpose of the application, the following technical solutions are adopted in the application:

[0007] In a first aspect, the application provides a coated ternary positive electrode material, which comprises a matrix and a coating layer on the surface of the matrix; the matrix is a ternary positive electrode material LiNi x Co y Mn 1-x-y O2, wherein x>0, y>0, 1-x-y>0; the coating layer is a composite of graphene and WNb 12 O 33 .

[0008] In an optional embodiment, the substrate of the coated ternary positive electrode material is LiNi x Co y Mn 1-x-y O2, wherein 1>x≥0.6, y>0, 1-x-y>0.

[0009] In an optional embodiment, the mass percentage of carbon element in the coated ternary positive electrode material is 0.1% to 0.4%, the mass percentage of tungsten element is 0.01% to 0.05%, and the mass percentage of niobium element is 0.06% to 0.3%.

[0010] In a second aspect, the application provides a preparation method of a coated ternary positive electrode material, which comprises the following steps:

[0011] adding the ternary positive electrode material into a dispersion liquid containing graphene and WNb 12 O 33 , heating and stirring until the solvent is evaporated to dryness to obtain a precursor; and performing first sintering on the precursor to obtain the coated ternary positive electrode material.

[0012] In an optional embodiment, the solvent in the dispersion liquid is an ethanol aqueous solution, and the mass ratio of the ternary positive electrode material to the solvent is 1: (1 to 1.1).

[0013] In an optional embodiment, the heating temperature is 60 to 80°C.

[0014] In an optional embodiment, the first sintering temperature is 300 to 580°C, and the first sintering time is 7 to 9h.

[0015] In an optional embodiment, the ternary positive electrode material is prepared by mixing a ternary precursor with a lithium source and performing second sintering.

[0016] In an optional embodiment, the ternary precursor is a nickel-cobalt-manganese hydroxide Ni x Co y Mn 1-x-y (OH)2, wherein x>0, y>0, 1-x-y>0.

[0017] In an optional embodiment, the ternary precursor is a nickel-cobalt-manganese hydroxide Ni x Co y Mn 1-x-y (OH)2, wherein 1>x≥0.6, y>0, 1-x-y>0, and the ratio of the total moles of nickel, cobalt and manganese elements in the nickel-cobalt-manganese hydroxide to the moles of lithium element in the lithium source is 1: (1.02 to 1.05).

[0018] In an optional embodiment, the lithium source comprises at least one of lithium nitrate, lithium chloride, lithium hydroxide or lithium carbonate.

[0019] In an optional embodiment, the second sintering temperature is 700-1050℃, and the second sintering time is 10-24h.

[0020] In an optional embodiment, the preparation method of the dispersion liquid comprises: ball-milling WO3 and Nb2O5 at a molar ratio of 1:6, third sintering to obtain WNb 12 O 33 nanooxide; dispersing graphene in an ethanol aqueous solution to obtain a graphene dispersion liquid; dispersing the WNb 12 O 33 nanooxide into the graphene dispersion liquid to obtain the dispersion liquid.

[0021] In an optional embodiment, the ball-milling speed is 400-600 r / min, and the ball-milling time is 1-3h.

[0022] In an optional embodiment, the third sintering temperature is 1050-1200℃, and the third sintering time is 6-12h.

[0023] In an optional embodiment, the volume ratio of ethanol to water in the ethanol aqueous solution is (3-4):1.

[0024] In an optional embodiment, the mass ratio of the graphene to the ethanol aqueous solution is (0.001-0.004):1.

[0025] In an optional embodiment, the WNb 12 O 33 nanooxide has a mass ratio of (0.001-0.005):1 to the ethanol aqueous solution.

[0026] In a third aspect, the application provides a positive electrode sheet, which comprises the coated ternary positive electrode material according to the first aspect.

[0027] In a fourth aspect, the application provides a lithium ion battery, which comprises the positive electrode sheet according to the third aspect.

[0028] The application has the following beneficial effects:

[0029] (1) The ternary positive electrode material according to the application is coated with a graphene and WNb 12 O 33 nanooxide composite on the surface, wherein the sheet-shaped graphene can not only improve the conductivity of the WNb 12 O 33Small particles are connected and stably attached to the surface of the positive electrode material, which can also improve the conductivity of the positive electrode material; WNb 12 O 33 The internal NbO6 octahedron and WO3 tetrahedron, the NbO6 octahedron between the sharing angle can form a 3x4x∞ ReO3 structure unit, and these structure units can be connected with the shared angle of the WO3 tetrahedron through sharing edges. Such a special structure can provide more isotropic Li + diffusion tunnels, thereby forming a clear conductive interface on the surface of the positive electrode material particles, further improving the migration rate of lithium ions in the positive electrode material and the rapid charge and discharge capability of the lithium battery.

[0030] (2) The graphene and WNb 12 O 33 compound layer coated on the surface of the ternary positive electrode material in the present application has stable physical and chemical properties, which not only effectively hinders the phase transition on the surface of the positive electrode material particles and increases the crack resistance of the particles; also has high corrosion resistance, which can effectively reduce the side reaction between the positive electrode material particles and the electrolyte, and further improve the cycle stability of the ternary positive electrode material.

[0031] (3) The present application uses a liquid phase coating method to uniformly coat the graphene and WNb 12 O 33 compound on the surface of the ternary positive electrode material. This preparation method has the advantages of simple process, low cost, environmental friendliness and easy scale production.

[0032] Other aspects can be understood after reading and understanding the drawings and detailed description. BRIEF DESCRIPTION OF DRAWINGS

[0033] The drawings are used to provide a further understanding of the technical solutions herein and constitute a part of the specification, together with the embodiments of the present application, to explain the technical solutions herein, and do not constitute a limitation on the technical solutions herein.

[0034] Figure 1 SEM image of the coated ternary positive electrode material prepared in Example 4;

[0035] Figure 2 SEM image of the ternary positive electrode material prepared in Comparative Example 1;

[0036] Figure 3 XRD image of the coated ternary positive electrode material prepared in Example 1. DETAILED DESCRIPTION

[0037] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present disclosure, and should not be regarded as a specific limitation on the present application.

[0038] It should be noted that, in the examples, the specific conditions are not specified, and the conventional conditions or the conditions recommended by the manufacturer are used. The reagents or instruments used are not specified by the manufacturer, and are conventional products that can be purchased on the market.

[0039] The technical terms "first", "second" and the like in the present application are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features.

[0040] In the present application, the phrase "embodiment" means that the specific features, structures or properties described in conjunction with the embodiment can be included in at least one embodiment of the present application. The appearance of this phrase at various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is not mutually exclusive with other embodiments.

[0041] The technical term "and / or" in the present application is only a description of the association relationship of the associated objects, which means that there can be three relationships, for example, A and / or B, which can represent the three cases of A alone, A and B together, and B alone.

[0042] In addition, the character " / " in the present application generally represents an "or" relationship between the front and rear associated objects.

[0043] In the present application, the meaning of "multiple" is two or more (including two), and the meaning of "at least one" is one or more than one.

[0044] In a first aspect, the present application provides a coated ternary positive electrode material, which comprises a substrate and a coating layer on the surface of the substrate; the substrate is a ternary positive electrode material LiNi x Co y Mn 1-x-y O2, wherein x>0, y>0, 1-x-y>0; the coating layer is a composite of graphene and WNb 12 O 33 .

[0045] In the present application, a layer of composite protective layer of graphene and WNb 12 O 33 with stable physicochemical properties is coated on the surface of the nickel-cobalt-manganese ternary positive electrode material, wherein the graphene can improve the conductivity of the material, and the WNb 12 O 33 has a special structure that can provide more Li + channels, and the coating of the composite layer on the surface of the positive electrode material not only reduces the direct contact of the material with the electrolyte and inhibits the occurrence of side reactions on the surface of the material, but also reduces the volume change of the material during charging and discharging, improves the structural stability and cycle life of the material.

[0046] In some embodiments, the coated ternary cathode material satisfies one or more of the following characteristics:

[0047] Characteristic one: the substrate of the coated ternary cathode material is LiNi x Co y Mn 1-x-y O2, wherein 1>x>0.6, y>0, 1-x-y>0;

[0048] Characteristic two: the mass percentage of carbon element in the coated ternary cathode material is 0.1% to 0.4%, the mass percentage of tungsten element is 0.01% to 0.05%, and the mass percentage of niobium element is 0.06% to 0.3%.

[0049] The ternary cathode material with high nickel content can make the battery prepared therefrom have high specific capacity and energy density. The surface coating modification of the high-nickel ternary cathode material can further improve the cycle stability of the battery prepared therefrom. Controlling the amount of the coating (graphene and WNb 12 O 33 ) within an appropriate range can make the ternary cathode material have excellent electrochemical performance.

[0050] In a second aspect, the application provides a preparation method of a coated ternary cathode material, which comprises:

[0051] adding the ternary cathode material into a dispersion liquid containing graphene and WNb 12 O 33 , heating and stirring until the solvent is evaporated to dryness to obtain a precursor; and performing first sintering on the precursor to obtain the coated ternary cathode material.

[0052] In the application, the ternary cathode material is added into a dispersion liquid containing graphene and WNb 12 O 33 , and is subjected to heating and first sintering in sequence. Since WNb 12 O 33 has a Wadsley-Roth crystal shear structure, it has the same parallel structure as the R-3m layer of the ternary cathode material in the

[100] direction. The similar crystal structure makes the WNb 12 O 33 permeated by the graphene nanosheet in the grain boundary to grow in a specific direction on the surface of the ternary cathode material during the heat treatment, thereby forming a composite layer of the graphene and WNb 12 O 33 with uniform coating.

[0053] In some embodiments, the heating temperature is 60-80℃, for example, it can be 60℃, 70℃ or 80℃, but not limited to the listed values, other values not listed in the above value range are also applicable.

[0054] In some embodiments, the first sintering temperature is 300-580℃, for example, it can be 300℃, 380℃ or 580℃, and the first sintering time is 7-9h, for example, it can be 7h, 8h or 9h, but not limited to the listed values, other values not listed in the above value range are also applicable.

[0055] The first sintering temperature in the present application will affect the electrochemical performance of the ternary positive electrode material. If the sintering temperature is too low, it will lead to low bonding strength of the composite layer and the positive electrode material, thereby hindering the migration and diffusion of lithium ions. If the sintering temperature is too high, it will easily lead to damage of the composite coating layer, thereby reducing the cycle performance of the positive electrode material.

[0056] In some embodiments, the ternary positive electrode material is prepared by mixing a ternary precursor and a lithium source and performing second sintering.

[0057] In some embodiments, the ternary precursor is a nickel-cobalt-manganese hydroxide Ni x Co y Mn 1-x-y (OH)2, wherein x>0, y>0, 1-x-y>0.

[0058] In some embodiments, the ternary precursor is a nickel-cobalt-manganese hydroxide Ni x Co y Mn 1-x-y (OH)2, wherein 1>x≥0.6, y>0, 1-x-y>0, and the ratio of the total number of moles of nickel, cobalt and manganese elements in the nickel-cobalt-manganese hydroxide to the number of moles of lithium element in the lithium source is 1:(1.02-1.05), for example, it can be 1:1.02, 1:1.04 or 1:1.05, but not limited to the listed values, other values not listed in the above value range are also applicable.

[0059] In some embodiments, the second sintering temperature is 700-1050℃, for example, it can be 700℃, 800℃ or 1050℃, and the second sintering time is 10-24h, for example, it can be 10h, 15h or 24h, but not limited to the listed values, other values not listed in the above value range are also applicable.

[0060] In some embodiments, the preparation method of the dispersion liquid comprises: ball milling WO3 and Nb2O5 at a molar ratio of 1:6, and third sintering to obtain WNb 12 O 33nanometer oxide; dispersing graphene in an ethanol aqueous solution to obtain a graphene dispersion liquid; dispersing WNb 12 O 33 nanometer oxide into the graphene dispersion liquid to obtain the dispersion liquid.

[0061] The prepared WNb 12 O 33 nanometer oxide is dispersed in the graphene dispersion liquid, and under the action of stirring, the nanometer WNb 12 O 33 can provide more active sites, so that the graphene nanosheet is attached to its surface and fully penetrates into the grain boundary of the WNb 12 O 33 , and then the ternary positive electrode material is mixed with the dispersion liquid containing graphene and WNb 12 O 33 .

[0062] In some embodiments, the rotation speed of the ball milling is 400-600 r / min, for example, it can be 400 r / min, 500 r / min or 600 r / min, and the ball milling time is 1-3 h, for example, it can be 1 h, 2 h or 3 h, but not only limited to the listed values, other values not listed in the above value range are also applicable.

[0063] In some embodiments, the temperature of the third sintering is 1050-1200℃, for example, it can be 1050℃, 1100℃ or 1200℃, and the time of the third sintering is 6-12 h, for example, it can be 6 h, 8 h or 12 h, but not only limited to the listed values, other values not listed in the above value range are also applicable. In some embodiments, the dispersing of the graphene in the ethanol aqueous solution is carried out under stirring, and the stirring time is 25-50 min, for example, it can be 25 min, 30 min or 50 min, but not only limited to the listed values, other values not listed in the above value range are also applicable.

[0064] In some embodiments, the mass ratio of the graphene to the ethanol aqueous solution is (0.001-0.004):1, for example, it can be 0.001:1, 0.002:1 or 0.004:1, but not only limited to the listed values, other values not listed in the above value range are also applicable.

[0065] In some embodiments, the WNb 12 O 33The mass ratio of the nano-oxide to the ethanol aqueous solution is (0.001-0.005):1, for example, can be 0.001:1, 0.002:1 or 0.005:1, but is not limited to the listed values, and other values not listed in the above value range are also applicable.

[0066] In the present application, the composite of graphene and WNb 12 O 33 The coating amount of the composite of graphene and WNb on the surface of the ternary positive electrode material will affect the performance of the material. If the coating amount is too much, the composite layer on the surface of the material will be too thick, which is not conducive to the migration and transmission of lithium ions. If the coating amount is too little, the composite layer on the surface of the material will not be uniformly coated, and thus the contact between the positive electrode material and the electrolyte cannot be effectively isolated.

[0067] In a third aspect, the present application provides a positive electrode sheet, which comprises the coated ternary positive electrode material obtained by any of the above embodiments. The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer comprises the coated ternary positive electrode material provided in the first aspect of the present application. A person skilled in the art can select a suitable method to prepare the positive electrode sheet, for example, which can comprise the following steps: mixing the positive electrode active material, the binder and the conductive agent to form a slurry, and then coating the slurry on the positive electrode current collector.

[0068] In a fourth aspect, the present application provides a lithium ion battery comprising the coated ternary positive electrode material provided in the first aspect of the present application or the positive electrode sheet provided in the third aspect of the present application. The lithium ion battery provided in the present application can generally comprise a positive electrode sheet, a negative electrode sheet, a separator film interposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte. The method for preparing the lithium ion battery should be known to a person skilled in the art, for example, the positive electrode sheet, the separator film and the negative electrode sheet can each be a sheet layer, which can be cut to a target size and then stacked in sequence, or can be wound to a target size for forming an electric core, and can be further combined with the electrolyte to form a lithium ion battery.

[0069] Specifically, the features and properties of the present application are further described in detail below in combination with the drawings, examples and comparative examples.

[0070] Example 1

[0071] The present embodiment provides a preparation method of a coated ternary positive electrode material, which comprises:

[0072] S1, nickel sulfate, cobalt sulfate and manganese sulfate were dissolved in deionized water according to the molar ratio of Ni:Co:Mn=90:5:5 to obtain a 6L, 2mol / L transition metal sulfate solution; at the same time, 7.2L, 2mol / L NH3·H2O and 5L, 5mol / L NaOH solution were prepared; the flow rate of the transition metal sulfate solution, ammonia water and sodium hydroxide solution was 0.3L / h, which were continuously injected into the batch reactor by peristaltic pump for co-precipitation reaction, the reaction temperature was controlled at 60℃, the pH value of the reaction was maintained at 11.15 by controlling the flow rate of ammonia water and sodium hydroxide solution, nitrogen gas was continuously introduced as a protective gas during the reaction, after the sulfate solution was completely injected into the reactor, all the liquid was stopped, and then the precipitate was aged until the particle size Dv50 of the product was maintained in the range of 8.0-10.0μm, then the product was filtered and washed with deionized water and anhydrous ethanol, finally the product was placed in a vacuum oven at 120℃ and dried for 18h to obtain the ternary positive electrode material precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2; the ternary positive electrode material precursor Ni 0.90 Co 0.05 Mn 0.05 (OH)2 and LiOH·H2O were poured into a ball mill jar for mixing, the ball milling speed was controlled at 150r / min, and the ball milling time was 6h, the mixed powder after ball milling was placed in a muffle furnace and sintered at 800℃ in an oxygen atmosphere for 15h, after sintering, it was cooled to room temperature and sieved through a 400 mesh sieve to obtain the ternary positive electrode material LiNi 0.9 Co 0.05 Mn 0.05 O2, denoted as NCM;

[0073] S2, 4.636g of tungsten trioxide and 31.896g of niobium pentoxide (the molar ratio of WO3 and Nb2O5 is 1:6) were weighed and mixed in a ball mill jar, the ball milling speed was controlled at 500r / min, and the ball milling time was 2h, the mixed powder after ball milling was placed in a muffle furnace and sintered at 1100℃ in air for 8h to obtain WNb 12 O 33 nanooxide;

[0074] S3, 0.1g of graphene was dispersed in 100g of ethanol aqueous solution (V (ethanol):V (water)=3:1) and stirred for 30min to obtain a graphene dispersion; then 0.1g of WNb 12 O 33 nanooxide was added to the graphene dispersion and stirred to obtain a graphene and WNb 12 O 33A mixed dispersion liquid of nano-oxides; 100 g of a ternary cathode material (NCM) is added to the above mixed dispersion liquid, heated and stirred at 70℃ until the solvent is evaporated, to obtain a precursor, and the precursor is sintered in a muffle furnace at 380℃ for 8h in an oxygen atmosphere to obtain a ternary cathode material coated with a composite of graphene and WNb 12 O 33 12 33 The mass ratio of graphene to an ethanol aqueous solution is 0.001:1, and the mass ratio of WNb 12 O 33 to an ethanol aqueous solution is 0.001:1.

[0075] Example 2

[0076] The difference between this embodiment and Example 1 is that:

[0077] S1, the same as S1 of Example 1;

[0078] In S2, the ball milling speed is 400 r / min, and the ball milling time is 3h; the mixed powder after ball milling is placed in a muffle furnace and sintered at 1200℃ for 6h in air;

[0079] In S3, the mass ratio of graphene to an ethanol aqueous solution is 0.002:1, and the stirring time is 25min; the mass ratio of WNb 12 O 33 to an ethanol aqueous solution is 0.003:1; the temperature for heating and stirring until the solvent is evaporated is 60℃; and the precursor is placed in a muffle furnace and sintered at 580℃ for 7h in an oxygen atmosphere.

[0080] Example 3

[0081] The difference between this embodiment and Example 1 is that:

[0082] S1, the same as S1 of Example 1;

[0083] In S2, the ball milling speed is 600 r / min, and the ball milling time is 1h; the mixed powder after ball milling is placed in a muffle furnace and sintered at 1050℃ for 12h in air;

[0084] In S3, the mass ratio of graphene to an ethanol aqueous solution is 0.004:1, and the stirring time is 50min; the mass ratio of WNb 12 O 33 to an ethanol aqueous solution is 0.005:1; the temperature for heating and stirring until the solvent is evaporated is 60℃; and the precursor is placed in a muffle furnace and sintered at 300℃ for 9h in an oxygen atmosphere.

[0085] Example 4

[0086] The difference between this embodiment and Example 1 is that:

[0087] S1-S2, same as step S1-S2 of Example 1;

[0088] In S3, the mass ratio of graphene to the ethanol aqueous solution was 0.002:1, WNb 12 O 33 The mass ratio to the ethanol aqueous solution was 0.002:1.

[0089] Example 5

[0090] The difference between this example and Example 1 is that:

[0091] S1-S2, same as step S1-S2 of Example 1;

[0092] In S3, the mass ratio of graphene to the ethanol aqueous solution was 0.003:1, WNb 12 O 33 The mass ratio to the ethanol aqueous solution was 0.003:1.

[0093] Example 6

[0094] The difference between this example and Example 1 is that:

[0095] S1-S2, same as step S1-S2 of Example 1;

[0096] In S3, the precursor was sintered in a muffle furnace in an oxygen atmosphere at 330°C for 8h.

[0097] Example 7

[0098] The difference between this example and Example 1 is that:

[0099] S1-S2, same as step S1-S2 of Example 1;

[0100] In S3, the precursor was sintered in a muffle furnace in an oxygen atmosphere at 500°C for 8h.

[0101] Comparative Example 1

[0102] Compared with Example 1, the ternary positive electrode material prepared in this comparative example has no coating on the surface.

[0103] The difference between this comparative example and Example 1 is that:

[0104] This comparative example only has step S1 of Example 1, and does not have steps S2-S3.

[0105] Comparative Example 2

[0106] Compared with Example 1, the ternary positive electrode material prepared in this comparative example has a mixture of WO3 and Nb2O5 coated on the surface.

[0107] The difference between the present comparative example and Example 1 is that:

[0108] S1, same as step S1 of Example 1;

[0109] S2, 100 g of ternary positive electrode material (NCM), 0.025 g of WO3 and 0.175 g of Nb2O5 were respectively weighed and uniformly dispersed in 100 g of ethanol aqueous solution, heated and stirred at 70°C until the solvent was evaporated to dryness, to obtain a precursor, and the precursor was placed in a muffle furnace and sintered at 380°C for 8 h in an oxygen atmosphere, to obtain a ternary positive electrode material coated with WO3 and Nb2O5 on the surface.

[0110] Comparative Example 3

[0111] Compared with Example 1, the present comparative example prepared a ternary positive electrode material coated with only graphene on the surface.

[0112] The difference between the present comparative example and Example 1 is that:

[0113] S1, same as step S1 of Example 1;

[0114] S2, 100 g of ternary positive electrode material (NCM) and 0.1 g of graphene were respectively weighed and uniformly dispersed in 100 g of ethanol aqueous solution, heated and stirred at 70°C until the solvent was evaporated to dryness, to obtain a precursor, and the precursor was placed in a muffle furnace and sintered at 380°C for 8 h in an oxygen atmosphere, to obtain a ternary positive electrode material coated with graphene on the surface.

[0115] Comparative Example 4

[0116] Compared with Example 1, the present comparative example prepared a ternary positive electrode material coated with only WNbO4 on the surface. 12 O 33

[0117] The difference between the present comparative example and Example 1 is that:

[0118] S1-S2, same as steps S1-S2 of Example 1;

[0119] S3, 100 g of ternary positive electrode material (NCM) and 0.1 g of WNbO4 were respectively weighed and uniformly dispersed in 100 g of ethanol aqueous solution, heated and stirred at 70°C until the solvent was evaporated to dryness, to obtain a precursor, and the precursor was placed in a muffle furnace and sintered at 380°C for 8 h in an oxygen atmosphere, to obtain a ternary positive electrode material coated with WNbO4 on the surface. 12 O 33 12 O 33

[0120] Performance detection:

[0121] 1. Particle size test​​​

[0122] The particle size of the coated ternary positive electrode material was tested using a GSL-101B1 type laser particle size analyzer.

[0123] 2. Electrochemical performance test

[0124] 1) Preparation of button cell

[0125] The coated ternary positive electrode material was uniformly mixed according to the mass ratio of positive electrode: conductive agent: binder = 80:10:10, and the slurry was uniformly coated on the electrode sheet. The electrode sheet was placed in an oven and dried at 80°C for 8h. After drying, the electrode sheet was punched into a circular positive electrode sheet and assembled into a button cell for electrochemical performance test.

[0126] 2) Electrochemical performance test

[0127] The prepared button cell was subjected to electrochemical performance test at a charge-discharge voltage range of 2.8-4.3V. The test results are shown in Table 1.

[0128] Table 1

[0129]

[0130] In the drawings:

[0131] Figure 1 (a-b) and Figure 2 are scanning electron microscope images of the ternary positive electrode material prepared in Example 4 and Comparative Example 1, respectively. As can be seen from the figures, the ternary positive electrode material coated with the compound layer of graphene and WNb 12 O 33 has a surface that is rougher than the ternary positive electrode material without the coating layer modification ( Figure 1 a) and the surface of the ternary positive electrode material coated with the compound layer of graphene and WNb Figure 2 b) can be seen under a high-power lens. Figure 1 b).

[0132] Figure 3 is an XRD pattern of the coated ternary positive electrode material prepared in Example 1. As can be seen from the figure, the coated ternary positive electrode material of Example 1 has the same characteristic peaks as the standard card of lithium nickel cobalt manganese oxide, without other impurity diffraction peaks, indicating that the coating of the compound layer of graphene and WNb 12 O 33 does not affect its phase structure.

[0133] As can be seen from Table 1:

[0134] From Examples 1-7, it can be seen that the ternary positive electrode material prepared by the method described in the present application is coated with graphene and WNb 12 O 33The lithium ion battery prepared from the positive electrode material has excellent cycle performance and fast charge and discharge capacity.

[0135] From the comparison of Example 4 and Example 1 and Example 5, it can be seen that, in the preparation process of the coated ternary positive electrode material, the amount of graphene and WNb 12 O 33 will affect the coating amount of the composite layer on the surface of the ternary positive electrode material, and in turn affect the electrochemical performance of the positive electrode material. If the mass ratio of graphene and the ethanol aqueous solution and WNb 12 O 33 and the ethanol aqueous solution is too low, the coating amount of the composite layer on the surface of the ternary positive electrode material is too small, and the coating uniformity is poor, which will increase the generation of side reactions between the electrolyte and the positive electrode material, and in turn reduce the cycle performance of the positive electrode material. If the mass ratio of graphene and the ethanol aqueous solution and WNb 12 O 33 and the ethanol aqueous solution is too high, the coating amount of the composite layer on the surface of the ternary positive electrode material is too much, and the composite coating is too thick, which will hinder the migration and diffusion of lithium ions, and in turn reduce the fast charge and discharge capacity of the positive electrode material.

[0136] From the comparison of Example 1 and Example 6-7, it can be seen that, in the preparation process of the coated ternary positive electrode material, the sintering temperature of the precursor product in step S3 will significantly affect the electrochemical performance of the material. If the sintering temperature is too low, the bonding strength of the composite and the positive electrode material is low, which will hinder the migration of lithium ions. If the sintering temperature is too high, the coating layer is easily damaged, and in turn the cycle performance of the material is reduced.

[0137] From the comparison of Example 1 and Comparative Example 1, it can be seen that the surface of the ternary positive electrode material prepared in Comparative Example 1 has no coating layer, and compared with Comparative Example 1, the lithium ion battery prepared from the positive electrode material of Example 1 has better electrochemical performance,

[0138] This is because the surface of the positive electrode material of Example 1 is coated with a composite of graphene and WNb 12 O 33 , the composite layer has high bonding degree with the positive electrode material matrix and stable physicochemical properties, the existence of the composite layer effectively avoids the dissolution of the active material, the side reactions between the electrolyte and the positive electrode material are reduced, and therefore the cycle stability and charge and discharge performance are good.

[0139] From the comparison of Example 1 and Comparative Examples 2-4, it can be seen that the surface of the ternary positive electrode material prepared in Comparative Example 2 is coated with a mixture of WO3 and Nb2O5, the surface of the ternary positive electrode material prepared in Comparative Example 3 is only coated with graphene, and the surface of the ternary positive electrode material prepared in Comparative Example 4 is only coated with nano-oxide WNb 12 O 33and the ternary positive electrode material prepared in Example 1 is coated with graphene and WNb on the surface 12 O 33 The coating on the surface of the positive electrode material in Example 1 is a composite of graphene and WNb 12 O 33 In addition to the high-conductivity graphene nanosheet capable of connecting WNb 12 O 33 The nanosheet has NbO6 octahedron and WO3 tetrahedron inside, the NbO6 octahedron can form 3×4×∞ ReO3 structural units by sharing corners, and these structural units can be connected with each other by sharing corners of WO3 tetrahedron, such special structure can provide more isotropic Li + diffusion tunnels, which is beneficial to improve the migration rate of lithium ions in the positive electrode material and the fast charge and discharge capability of the lithium battery; the coating on the surface of the positive electrode material in Comparative Examples 2-4 does not have such structure, so the lithium battery prepared therefrom has poor electrochemical performance compared with the lithium battery prepared from the positive electrode material in Example 1.

[0140] The applicant declares that the above description is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and it should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed in the present application can be easily thought of by those skilled in the art, and all such changes or replacements fall within the protection scope and disclosure scope of the present application.

Claims

1. A coated ternary cathode material, characterized in that, The coated ternary positive electrode material comprises a substrate and a coating layer on the surface of the substrate; the substrate is a ternary positive electrode material LiNi x Co y Mn 1-x-y O2, wherein x>0, y>0, 1-x-y>0; the coating layer is a composite of graphene and WNb 12 O 33 ​ The graphene is flaky graphene. The preparation method of the coated ternary positive electrode material comprises the following steps: The ternary cathode material is added into a dispersion liquid containing graphene and WNb 12 O 33 , heated and stirred until the solvent is evaporated to dryness to obtain a precursor; the precursor is subjected to first sintering to obtain a coated ternary cathode material, and the graphene and WNb 12 O 33 composite uniformly coats the surface of the ternary cathode material.

2. The coated ternary cathode material of claim 1, wherein, The coated ternary positive electrode material meets one or more of the following characteristics: Feature one: the base body of the coated ternary positive electrode material is LiNi x Co y Mn 1-x-y O2, wherein 1>x≥0.6, y>0, 1-x-y>0; Characteristic two: the mass percentage content of carbon element in the coated ternary positive electrode material is 0.1% to 0.4%, the mass percentage content of tungsten element is 0.01% to 0.05%, and the mass percentage content of niobium element is 0.06% to 0.3%.

3. A method for preparing the coated ternary cathode material according to any one of claims 1-2, characterized in that, The preparation method comprises the following steps: The ternary cathode material is added into a dispersion liquid containing graphene and WNb 12 O 33 , heated and stirred until the solvent is evaporated to dryness to obtain a precursor; the precursor is subjected to first sintering to obtain a coated ternary cathode material.

4. The method of claim 3, wherein the coated ternary cathode material is prepared by the steps of: The solvent in the dispersion liquid is an ethanol aqueous solution, and the mass ratio of the ternary positive electrode material to the solvent is 1: (1-1.1); ​ And / or, the heating temperature is 60-80℃; And / or, the first sintering temperature is 300-580℃, and the first sintering time is 7-9h.

5. The method for preparing the coated ternary cathode material according to claim 3, characterized in that, The ternary positive electrode material is prepared by mixing a ternary precursor with a lithium source and performing second sintering.

6. The method of claim 5, wherein the coated ternary cathode material is prepared by the steps of: The ternary precursor is a nickel cobalt manganese hydroxide Ni x Co y Mn 1-x-y (OH)2, wherein 1 > x > 0.6, y > 0, 1 - x - y > 0; ​ The ratio of the total number of moles of nickel, cobalt and manganese elements in the nickel-cobalt-manganese hydroxide to the number of moles of lithium element in the lithium source is 1: (1.02-1.05); And / or, the lithium source comprises at least one of lithium nitrate, lithium chloride, lithium hydroxide or lithium carbonate; And / or, the second sintering temperature is 700-1050℃, and the second sintering time is 10-24h.

7. The method for preparing the coated ternary cathode material according to claim 3, characterized in that, The preparation method of the dispersion liquid comprises: ball-milling mixing WO3 and Nb2O5 at a molar ratio of 1:6, and obtaining WNb by third sintering 12 O 33 nanooxide; dispersing the graphene in an ethanol aqueous solution to obtain a graphene dispersion liquid; dispersing the WNb 12 O 33 nanooxide into the graphene dispersion liquid to obtain the dispersion liquid.

8. The method of claim 7, wherein the coated ternary cathode material is prepared by the steps of: The ball milling speed is 400-600 r / min, the ball milling time is 1-3h; and / or, the third sintering temperature is 1050-1200℃, and the third sintering time is 6-12h; ​ And / or, the volume ratio of ethanol to water in the ethanol aqueous solution is (3-4):1; And / or, the mass ratio of graphene to the ethanol aqueous solution is (0.001-0.004):1; and / or, the WNb 12 O 33 The mass ratio of the nano-oxide to the aqueous ethanol solution is (0.001-0.005):

1.

9. A positive electrode sheet characterized by comprising: The positive electrode sheet comprises the coated ternary positive electrode material according to any one of claims 1-2.

10. A lithium-ion battery, characterized by, The lithium ion battery comprises the positive electrode sheet according to claim 9.

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