Ternary positive electrode material, preparation method thereof and battery

Abstract

The invention belongs to the field of positive electrode materials, and provides a ternary positive electrode material, a preparation method thereof and a battery. The content of the tungsten element in the ternary positive electrode material provided by the invention is gradually reduced along the direction perpendicular to the surface of the ternary positive electrode material to the interior, and the tungsten element in the ternary positive electrode material is mainly distributed in a range with the depth of 100nm; the tungsten element substances on the outer surface of the ternary active material comprise tungsten oxide and lithium tungstate, the formed lithium tungstate consumes residual lithium on the surface of the ternary active material, and the residual lithium content on the surface of the ternary positive electrode material is reduced. According to the preparation method of the ternary positive electrode material provided by the invention, tungsten chloride with a low melting point is deposited on the surface of the ternary active material, and tungsten chloride is oxidized into tungsten oxide by utilizing oxidation reaction to obtain the ternary positive electrode material, so that the tungsten element is uniformly distributed on the surface of the ternary positive electrode material while the heat consumption is reduced; therefore, the ternary positive electrode material with relatively high compressive strength, low surface residual lithium content and good cycle performance is obtained.

Description

Technical Field

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

[0002] Under the background of global carbon neutrality, all countries are accelerating the development of green new energy. As a device for storing and releasing electric energy, lithium-ion batteries play a vital role in the development of new energy.

[0003] Lithium nickel cobalt manganese oxide, a ternary positive electrode material in lithium-ion batteries, is considered to be the most likely positive electrode material for power batteries to be widely used at present because of its advantages such as high discharge capacity, low production cost, stable layered structure and good thermal stability. However, there are still problems such as low capacity retention rate, large irreversible phase change, poor cycle performance and poor high-temperature thermal stability. The surface coating process is considered to be a simple and effective method to improve multiple performances of materials. Common coating elements are mainly Al, B, Mg, W, Zr, Ti, etc. Among them, the oxide of W, namely WO3, is an acidic oxide, which can neutralize the residual alkali on the surface of the positive electrode material, and the W compound formed on the surface can effectively protect the positive electrode material from electrolyte erosion, improve the compressive strength of the positive electrode material, and improve the cycle performance of the positive electrode material. Moreover, Li2WO4 generated by WO3 and residual alkali has a certain ionic conductivity, which can increase the ionic conductivity of the positive electrode material and improve the rate performance.

[0004] At present, WO3 coating generally adopts dry coating process. Although dry coating process is simple to operate, it is difficult to ensure the uniformity of coating. The coating layer has low uniformity, cannot effectively protect the positive electrode material from electrolyte erosion, cannot effectively improve the compressive strength of the positive electrode material, and cannot effectively neutralize the residual alkali on the surface of the positive electrode material, and ultimately cannot effectively improve the cycle performance.

[0005] In view of this, the present invention is proposed. Summary of the invention

[0006] The purpose of the present invention includes providing a ternary positive electrode material and a preparation method thereof, and a battery, increasing the compressive strength of the ternary positive electrode material, reducing the residual alkali content on the surface, and improving the cycle performance.

[0007] In order to achieve the above-mentioned object, the present invention provides a ternary positive electrode material in a first aspect, wherein the tungsten content of the ternary positive electrode material gradually decreases along a direction perpendicular to the surface of the ternary positive electrode material and pointing inward; The accumulated tungsten content of the ternary positive electrode material at a depth of 50 nm along the direction perpendicular to the surface of the ternary positive electrode material and pointing inward is 60%-90% of the total tungsten content of the ternary positive electrode material; The accumulated tungsten content of the ternary positive electrode material at a depth of 100 nm along the direction perpendicular to the surface of the ternary positive electrode material and pointing inward is 80%-95% of the total tungsten content of the ternary positive electrode material.

[0008] In some embodiments, the ternary cathode material satisfies: 30%≤(D v10 -D v10 ') / D v10 ×100%≤55%; And / or, the ternary cathode material satisfies: 15%≤(D v50 -D v50 ') / D v50 ×100%≤25%; And / or, the ternary positive electrode material satisfies: 8%≤(D v90 -D v90 ') / D v90 ×100%≤20%; Among them, D v10 , D v50 and D v90 are the particle sizes corresponding to the volume cumulative distribution of the ternary positive electrode material when it reaches 10%, 50%, and 90%, respectively, in μm; D v10 '、D v50 ' and D v90 ' are the particle sizes corresponding to 10%, 50% and 90% of the volume cumulative distribution of the ternary positive electrode material after being pressed at a pressure of 30 kN, in μm.

[0009] In a second aspect, the present invention provides a method for preparing a ternary positive electrode material, comprising the following steps: The ternary active material and tungsten chloride are subjected to a vapor deposition reaction to obtain a ternary positive electrode material precursor; The ternary cathode material precursor is oxidized to obtain a ternary cathode material.

[0010] In some embodiments, the vapor deposition reaction includes: spreading the ternary active material on one side of the tubular reactor close to the exhaust pipe, placing the tungsten chloride in a porcelain boat and placing it on one side of the tubular reactor close to the air inlet, introducing an inert gas into the tubular reactor, and then evacuating the tubular reactor; rotating the tubular reactor and performing a first reaction at a first reaction temperature to obtain a ternary positive electrode material precursor.

[0011] In some embodiments, the oxidation includes: sequentially introducing an inert gas and oxygen into the tubular reactor, and performing a second reaction at a second reaction temperature to obtain a ternary cathode material.

[0012] In some embodiments, the tungsten chloride is at least one of WCl6 and WCl5; and / or, the inert gas is at least one of N2, Ar and He.

[0013] In some embodiments, the mass ratio of the ternary active material to tungsten chloride is 100:1.5-2.5.

[0014] In some embodiments, the vacuuming refers to making the vacuum degree in the tubular reactor -0.09 MPa to -0.05 MPa; And / or, the rotation speed is 10~60rpm.

[0015] In some embodiments, the first reaction temperature includes the temperature T1 of the region where the tungsten chloride is located, the temperature T2 of the region where the ternary active material is located, and the temperature T3 of the remaining regions in the tubular reactor; the second reaction temperature includes a first-stage reaction temperature T4 and a second-stage reaction temperature T5; the second reaction includes a first-stage reaction at the first-stage reaction temperature T4 and a second-stage reaction at the second-stage reaction temperature T5; Wherein, the temperature T1 is 280°C to 400°C; And / or, the temperature T2 is 150° C. to 300° C.; And / or, the temperature T3 is 250°C to 400°C; And / or, the first reaction time is 1 to 5 hours; And / or, the temperature T4 is 150°C to 300°C; And / or, the temperature T5 is 300° C. to 700° C.; And / or, a reaction time in the second reaction is 0.5 to 2 hours; And / or, the second reaction time in the second reaction is 0.5 to 2.5 hours.

[0016] In a third aspect, the present invention provides a battery, comprising the ternary positive electrode material described in the first aspect, or the ternary positive electrode material obtained by the preparation method of the ternary positive electrode material described in the second aspect.

[0017] The beneficial effects of the present invention include: The tungsten element in the ternary positive electrode material provided by the present invention is mainly distributed within a range of 100 nm in a direction perpendicular to the surface of the ternary positive electrode material and pointing inward, which can effectively increase the compressive strength of the ternary positive electrode material; the tungsten element substances on the outer surface of the ternary active material include tungsten oxide and lithium tungstate, and the formed lithium tungstate consumes the residual lithium on the surface of the ternary active material, reduces the residual lithium content on the surface of the ternary positive electrode material, and thus improves the cycle performance of the positive electrode material.

[0018] In the preparation method of the ternary positive electrode material provided by the present invention, tungsten chloride with a low melting point is deposited on the surface of the ternary active material, and then the tungsten chloride is oxidized into tungsten oxide by an oxidation reaction to obtain the ternary positive electrode material, thereby reducing heat consumption and making the tungsten element evenly distributed on the surface of the ternary positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0020] Figure 1 A schematic diagram of a tubular reactor used in an embodiment of the present invention; Figure 2 (a) is a SEM image of the ternary positive electrode material obtained in Comparative Example 4 of the present invention; Figure 2 (b) is a SEM image of the ternary cathode material obtained in Example 1; Figure 2 (c) is a SEM image of the ternary cathode material obtained in Example 2; Figure 2 (d) is a SEM image of the ternary cathode material obtained in Comparative Example 1; Figure 2 (e) is a SEM image of the ternary positive electrode material obtained in Comparative Example 2; Figure 2 (f) is a SEM image of the ternary positive electrode material obtained in Comparative Example 3; Figure 3 (a)-(b) are 3D time-of-flight secondary ion mass spectra of tungsten in different micro-regions of the ternary cathode material obtained in Example 1; Figure 3 (c)-(d) are 3D time-of-flight secondary ion mass spectra of tungsten in different micro-regions of the ternary cathode material obtained in Comparative Example 1; Figure 3 (e)-(f) are 3D time-of-flight secondary ion mass spectra of tungsten in different micro-regions of the ternary cathode material obtained in Comparative Example 2; Figure 3 (g)-(h) are 3D time-of-flight secondary ion mass spectra of tungsten in different micro-areas of the ternary cathode material obtained in Comparative Example 3; Figure 4 The trend diagram of the cumulative amount of tungsten element in different micro-regions of the ternary positive electrode materials obtained in Example 1 and Comparative Examples 1-3 along the direction perpendicular to the surface of the ternary positive electrode material and pointing inward; Figure 5 It is a comparison chart of the cycle performance of Examples 1-2 and Comparative Examples 1-5. DETAILED DESCRIPTION

[0021] Below, a ternary positive electrode material, a preparation method thereof, and a battery of the present invention are specifically disclosed in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0022] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit, and a given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundaries of the particular range. In particular, "()", ")", "[" and "]" represent intervals, where "(" or ")" represents an open interval, that is, the endpoint values ​​of the interval are not included; "[" and "]" represent a closed interval, that is, the endpoints within the interval are included. The range defined in this way can be inclusive or exclusive of the end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a range.

[0023] Specifically, for example, if a range of 60-120 and 80-110 is listed for a particular parameter, it is understood that the range of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following ranges can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise specified, the numerical range "ab" represents an abbreviation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" have been fully listed in this article, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a certain parameter is expressed as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. If (10, 20) is listed, it is understood as any value between 10 and 20, excluding 10 and 20; (10, 20] is understood as any value between 10 and 20, excluding 10 but including 20.

[0024] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0025] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0026] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0027] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0028] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0029] A first aspect of the present invention provides a ternary positive electrode material, wherein the tungsten content of the ternary positive electrode material gradually decreases along a direction perpendicular to the surface of the ternary positive electrode material and pointing inward; The accumulated tungsten content of the ternary positive electrode material at a depth of 50 nm along the direction perpendicular to the surface of the ternary positive electrode material and pointing inward is 60%-90% of the total tungsten content of the ternary positive electrode material; The accumulated tungsten content of the ternary positive electrode material at a depth of 100 nm along the direction perpendicular to the surface of the ternary positive electrode material and pointing inward is 80%-95% of the total tungsten content of the ternary positive electrode material.

[0030] The depth is the length of the ternary positive electrode material from the surface to the inside along the direction perpendicular to the surface of the ternary positive electrode material, and the unit is nm.

[0031] The tungsten element in the ternary positive electrode material is mainly distributed within a depth of 100nm in the direction perpendicular to the surface of the ternary positive electrode material pointing inward, ensuring the effective content of the tungsten element on the outer surface of the ternary active material, effectively improving the compressive strength of the ternary positive electrode material, reducing surface residual lithium, and improving the cycle performance of the material.

[0032] In some embodiments, the ternary cathode material satisfies: 30%≤(D v10 -Dv10 ') / D v10 ×100%≤55%; And / or, the ternary cathode material satisfies: 15%≤(D v50 -D v50 ') / D v50 ×100%≤25%; And / or, the ternary cathode material satisfies: 8%≤(D v90 -D v90 ') / D v90 ×100%≤20%; Among them, D v10 , D v50 and D v90 are the particle sizes corresponding to the volume cumulative distribution of the ternary positive electrode material when it reaches 10%, 50%, and 90%, respectively, in μm; D v10 '、D v50 ' and D v90 ' are the particle sizes corresponding to 10%, 50% and 90% of the volume cumulative distribution of the ternary positive electrode material after being pressed at a pressure of 30 kN, in μm.

[0033] The ternary positive electrode material provided by the present invention has good mechanical strength and little change in particle size after pressing, so it has high compressive strength and good structural stability.

[0034] A second aspect of the present invention provides a method for preparing a ternary positive electrode material, characterized in that it comprises the following steps: The ternary active material and tungsten chloride are subjected to a vapor deposition reaction to obtain a ternary positive electrode material precursor; The ternary cathode material precursor is oxidized to obtain a ternary cathode material.

[0035] In some embodiments, the vapor deposition reaction includes: spreading the ternary active material on one side of the tubular reactor close to the exhaust pipe, placing the tungsten chloride in a porcelain boat and placing it on one side of the tubular reactor close to the air inlet, introducing an inert gas into the tubular reactor, and then evacuating the tubular reactor; rotating the tubular reactor and performing a first reaction at a first reaction temperature to obtain a ternary positive electrode material precursor.

[0036] In some embodiments, the oxidation includes: sequentially introducing an inert gas and oxygen into the tubular reactor, and performing a second reaction at a second reaction temperature to obtain a ternary cathode material.

[0037] In some embodiments, the tungsten chloride is first uniformly deposited on the surface of the ternary active material, and then oxygen is introduced under heating conditions to oxidize the tungsten chloride to tungsten oxide. The reaction mechanism includes: 2WCl6+3O2= 2WO3+6Cl2 2WCl5+3O2= 2WO3+5Cl2 The above process allows the oxide to be uniformly deposited on the surface of the ternary active material, while part of the tungsten oxide reacts with the residual lithium on the surface of the active material to form lithium tungstate, and finally the tungsten element on the surface of the ternary positive electrode material exists in the form of tungsten oxide or lithium tungstate. By low-temperature vapor deposition followed by oxidation, the uniformity of the tungsten element on the outer surface of the ternary active material and the effective content of the tungsten element on the outer surface of the ternary active material are ensured, which effectively improves the compressive strength of the ternary positive electrode material, reduces the residual lithium on the surface, and improves the cycle performance of the material.

[0038] In some embodiments, the first reaction temperature includes the temperature T1 of the region where the tungsten chloride is located, the temperature T2 of the region where the ternary active material is located, and the temperature T3 of the remaining regions in the tubular reactor; the second reaction temperature includes a first-stage reaction temperature T4 and a second-stage reaction temperature T5; the second reaction includes a first-stage reaction at the first-stage reaction temperature T4 and a second-stage reaction at the second-stage reaction temperature T5; Wherein, the temperature T1 is 280°C to 400°C; And / or, the temperature T2 is 150° C. to 300° C.; And / or, the temperature T3 is 250°C to 400°C; And / or, the first reaction time is 1 to 5 hours; And / or, the temperature T4 is 150°C to 300°C; And / or, the temperature T5 is 300° C. to 700° C.; And / or, a reaction time in the second reaction is 0.5 to 2 hours; And / or, the second reaction time in the second reaction is 0.5 to 2.5 hours.

[0039] The temperature of the above-mentioned vapor deposition reaction is low and the oxidation time is short, so the heat consumption of the entire ternary positive electrode material preparation process is low.

[0040] In some embodiments, the tubular reactor is rotatable, and has an air inlet pipe, an exhaust pipe and a vacuum pipe at both ends respectively; and a separately heatable zone is provided inside the tubular reactor along the length axis direction.

[0041] Hereinafter, the embodiments of the present application will be described. The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application. If no specific techniques or conditions are indicated in the embodiments, the techniques or conditions described in the literature in this area or the product specifications are used. If the manufacturer is not indicated in the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0042] Tubular Reactor Figure 1 The features and performance of the present invention are further described in detail below in conjunction with the examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0043] Example 1 (1) 100.0 g of ternary active material LiNi 0.8 Co 0.1 Mn 0.1 O2 was spread evenly on one side of the exhaust port of the tubular reactor, and then 2.2 g of WCl6 was loaded into a porcelain boat and placed on the side of the gas inlet.

[0044] (2) N2 was introduced into the tubular reactor until the chamber was filled with N2, the inlet valve and the exhaust valve were closed, the vacuum pump was turned on and the vacuum valve was opened. After the vacuum degree in the tubular reactor reached -0.09 MPa, the vacuum valve was closed. The above steps were repeated three times to maintain the vacuum degree in the tubular reactor at -0.09 MPa.

[0045] (3) The tubular reactor rotates at a speed of 15 rpm, and the temperature T1 of the area where the tungsten chloride is located is set to 380°C, the temperature T2 of the area where the ternary active material is located is set to 250°C, and the temperature T3 of the remaining areas is set to 380°C. After each area reaches the set temperature, keep it warm for 2 hours.

[0046] (4) After the insulation in step (3) is completed, the set temperature of each zone is maintained and N2 is continuously introduced into the tubular reactor, and the exhaust valve is opened to discharge the residual WCl6 gas in the tubular reactor.

[0047] (5) After the residual WCl6 gas in the tubular reactor is completely discharged, stop introducing N2, switch to O2, and set the temperature T4 of all areas in the tubular reactor to 250°C. After the temperature of each area is stable, keep it warm for 1 hour. Then set the temperature T5 of all areas in the tubular reactor to 600°C and continue to keep it warm for 2 hours.

[0048] (6) After the insulation is completed, the heating is stopped and O2 is continuously introduced. After the tubular reactor is cooled to room temperature, the introduction of O2 into the tubular reactor is stopped and the rotation of the tubular reactor is stopped to obtain the ternary positive electrode material.

[0049] Example 2 (1) 100.0 g of ternary active material LiNi 0.8 Co 0.1 Mn 0.1 O2 was spread evenly on one side of the exhaust port of the tubular reactor, and then 2.0 g of WCl5 was loaded into a porcelain boat and placed on the side of the gas inlet.

[0050] (2) Introduce N2 into the tubular reactor until the chamber is full of N2, close the inlet valve and the exhaust valve, start the vacuum pump and open the vacuum valve. After the vacuum degree in the tubular reactor reaches -0.09 MPa, close the vacuum valve. Repeat the above steps 3 times to maintain the vacuum degree in the tubular reactor at -0.09 MPa.

[0051] (3) After the vacuum degree in the tubular reactor is stabilized, the tubular reactor is rotated at a speed of 20 rpm, and the temperature T1 of the area where the tungsten chloride is located is set to 310°C, the temperature T2 of the area where the ternary active material is located is set to 230°C, and the temperature T3 of the remaining areas is set to 310°C. After each area reaches the set temperature, keep it warm for 3 hours.

[0052] (4) After the insulation in step (3) is completed, the set temperature of each zone is maintained and N2 is continuously introduced into the tubular reactor, and the exhaust valve is opened to discharge the residual WCl5 gas in the tubular reactor.

[0053] (5) After the residual WCl5 gas in the tubular reactor is completely discharged, stop introducing N2, switch to O2, and set the temperature T4 of all areas in the tubular reactor to 230°C. After the temperature of each area is stable, keep it warm for 1.5 hours. Then, set the temperature T5 of all areas in the tubular reactor to 650°C and continue to keep it warm for 2.5 hours.

[0054] (6) After the insulation is completed, the heating is stopped and O2 is continuously introduced. After the tubular reactor is cooled to room temperature, the introduction of O2 into the tubular reactor is stopped and the rotation of the tubular reactor is stopped to obtain the ternary positive electrode material.

[0055] Example 3 (1) 100.0 g of ternary active material LiNi 0.8 Co 0.1 Mn 0.1 O2 was spread evenly on one side of the exhaust port of the tubular reactor, and then 1.5 g of WCl6 was loaded into a porcelain boat and placed on the side of the gas inlet.

[0056] (2) N2 was introduced into the tubular reactor until the chamber was filled with N2, the inlet valve and the exhaust valve were closed, the vacuum pump was turned on and the vacuum valve was opened. After the vacuum degree in the tubular reactor reached -0.09 MPa, the vacuum valve was closed. The above steps were repeated three times to maintain the vacuum degree in the tubular reactor at -0.09 MPa.

[0057] (3) The tubular reactor rotates at a speed of 10 rpm, and the temperature T1 of the area where the tungsten chloride is located is set to 360°C, the temperature T2 of the area where the ternary active material is located is set to 150°C, and the temperature T3 of the remaining areas is set to 360°C. After each area reaches the set temperature, keep it warm for 2 hours.

[0058] (4) After the insulation in step (3) is completed, the set temperature of each zone is maintained and N2 is continuously introduced into the tubular reactor, and the exhaust valve is opened to discharge the residual WCl6 gas in the tubular reactor.

[0059] (5) After the residual WCl6 gas in the tubular reactor is completely discharged, stop introducing N2, switch to O2, and set the temperature T4 of all areas in the tubular reactor to 150°C. After the temperature of each area is stable, keep it warm for 1 hour. Then set the temperature T5 of all areas in the tubular reactor to 400°C and continue to keep it warm for 2 hours.

[0060] (6) After the insulation is completed, the heating is stopped and O2 is continuously introduced. After the tubular reactor is cooled to room temperature, the introduction of O2 into the tubular reactor is stopped and the rotation of the tubular reactor is stopped to obtain the ternary positive electrode material.

[0061] Comparative Example 1 WO3 is coated with 5000 ppm W and mixed with the ternary active material LiNi 0.8 Co 0.1 Mn 0.1 O2 is fully mixed, and then kept at 600 ℃ for 6 h in an oxygen atmosphere to obtain a WO3-coated positive electrode material.

[0062] Comparative Example 2 (1) 100.0 g of ternary active material LiNi 0.8 Co 0.1 Mn 0.1 O2 was spread evenly on one side of the exhaust port of the tubular reactor, and then 2.2 g of WCl6 was loaded into a porcelain boat and placed on the side of the gas inlet.

[0063] (2) The tubular reactor is rotated at a speed of 15 rpm, and air free of water and CO2 is introduced into the tubular reactor. The exhaust valve is opened and the air in the tubular reactor is replaced.

[0064] (4) Set the temperature T1 of the area where tungsten chloride is located to 380°C, the temperature T2 of the area where the ternary active material is located to 250°C, and the temperature T3 of the remaining areas to 380°C. After each area reaches the set temperature, keep it warm for 2 hours.

[0065] (3) After the insulation is completed, stop introducing air that has removed water and CO2, keep the exhaust valve open, switch on the O2 supply, and set all areas to 600°C. After each area reaches the set temperature, continue insulation for 2 hours.

[0066] (4) After the insulation is completed, the heating is stopped and O2 is continuously introduced. After the tubular reactor is cooled to room temperature, the introduction of O2 into the tubular reactor is stopped and the rotation of the tubular reactor is stopped to obtain the ternary positive electrode material.

[0067] Comparative Example 3 (1) 100.0 g of ternary active material LiNi 0.8 Co 0.1 Mn 0.1 O2 was spread evenly on one side of the exhaust port of the tubular reactor, and then 2.2 g of WCl6 was loaded into a porcelain boat and placed on the side of the gas inlet.

[0068] (2) The tubular reactor is rotated at a speed of 15 rpm, and air free of water and CO2 is introduced into the tubular reactor. The exhaust valve is closed, the vacuum pump is turned on, and the vacuum valve is opened. The vacuum valve is adjusted so that the vacuum degree in the tubular reactor reaches -0.085 MPa and remains stable, so that the tubular reactor is maintained in a state of continuous ventilation and vacuum.

[0069] (3) Set the temperature T1 of the tungsten chloride area to 300°C, the temperature T2 of the ternary active material area to 150°C, and the temperature T3 of the remaining areas to 300°C. After each area reaches the set temperature, keep it warm for 2 hours.

[0070] (4) After the insulation is completed, close the vacuum valve and vacuum pump, stop the air flow, switch to O2 flow, open the exhaust valve, and set the temperature T4 of all areas in the tubular reactor to 250°C. After the temperature of each area is stable, keep it warm for 1 hour, then set the temperature T5 of all areas in the tubular reactor to 600°C and continue to keep it warm for 2 hours.

[0071] (7) After the insulation is completed, the heating is stopped and O2 is continuously introduced. After the tubular reactor is cooled to room temperature, the introduction of O2 into the tubular reactor is stopped and the rotation of the tubular reactor is stopped to obtain the ternary positive electrode material.

[0072] Comparative Example 4 Ternary active material without treatment.

[0073] Comparative Example 5 (1) 100.0 g of ternary active material LiNi 0.8 Co 0.1 Mn 0.1 O2 was spread evenly on one side of the exhaust port of the tubular reactor, and then 2.2 g of WCl6 was loaded into a porcelain boat and placed on the side of the gas inlet.

[0074] (2) Introduce air without water and CO2 into the tubular reactor until the reactor is full, close the air inlet valve and exhaust valve, start the vacuum pump and open the vacuum valve. When the vacuum degree in the tubular reactor reaches -0.09 MPa, close the vacuum valve. (3) The tubular reactor rotates at a speed of 15 rpm, and the temperature T1 of the area where the tungsten chloride is located is set to 380°C, the temperature T2 of the area where the ternary active material is located is set to 250°C, and the temperature T3 of the remaining areas is set to 380°C. After each area reaches the set temperature, keep it warm for 2 hours.

[0075] (4) After the insulation in step (3) is completed, the set temperature of each zone is maintained and air free of water and CO2 is continuously introduced into the tubular reactor, and the exhaust valve is opened to exhaust the residual WCl6 gas in the tubular reactor.

[0076] (5) After the residual WCl6 gas in the tubular reactor is completely discharged, stop introducing air that removes water and CO2, switch to O2 introduction, and set the temperature T4 of all areas in the tubular reactor to 250°C. After the temperature of each area is stable, keep it warm for 1 hour, then set the temperature T5 of all areas in the tubular reactor to 600°C and continue to keep it warm for 2 hours.

[0077] (6) After the insulation is completed, the heating is stopped and O2 is continuously introduced. After the tubular reactor is cooled to room temperature, the introduction of O2 into the tubular reactor is stopped and the rotation of the tubular reactor is stopped to obtain the ternary positive electrode material.

[0078] Effect example 1: The morphologies of the positive electrode materials obtained in Examples 1-2 and Comparative Examples 1-4 were respectively detected using a scanning electron microscope.

[0079] from Figure 2 (a) It can be seen that the surface of the ternary active material without coating treatment is smooth.

[0080] from Figure 2 (b)-(c) and Figure 2 (e)-(f) show that the surface of the ternary positive electrode material obtained by vapor deposition is relatively smooth.

[0081] from Figure 2 (d) It can be seen that the ternary positive electrode material obtained by direct dry coating with tungsten oxide has a large number of point-like coatings on the surface and has not formed a uniform and effective coating layer.

[0082] Effect example 2: (1) Using a time-of-flight secondary ion mass spectrometer, the time-of-flight secondary ion mass spectrometer 3D graphs of tungsten in different micro-areas of the ternary cathode materials provided in Example 1 and Comparative Examples 1-3 were measured respectively.

[0083] from Figure 3 As can be seen from (a)-(b), the preparation scheme provided by the present invention obtains a ternary positive electrode material with a uniform coating layer in different micro-regions.

[0084] from Figure 3As can be seen from (c)-(d), the tungsten content in different micro-areas of the ternary positive electrode material obtained by dry coating with tungsten oxide varies greatly, and a uniformly coated ternary positive electrode material cannot be obtained.

[0085] from Figure 3 (e)-(f) and Figure 3 (g)-(h) It can be seen that failure to evacuate the tubular reactor and failure to use inert gas to protect the tungsten chloride gasification process will result in the inability to form a coating layer of uniform depth on the surface of the ternary positive electrode material.

[0086] (2) Calculation method of the cumulative amount of tungsten element at different depths: The distribution value of the tungsten element signal intensity of the ternary positive electrode material particles along the radial direction (in the direction perpendicular to the particle surface pointing inward) is obtained by time-of-flight secondary ion mass spectrometry, and the relationship curve of the cumulative amount of tungsten element changing with depth is further calculated. At least 3 micro-areas are selected for measurement for each sample, and the average of the cumulative amount of tungsten element at a certain depth is calculated as the cumulative amount of tungsten element at the depth. Using a time-of-flight secondary ion mass spectrometer, the proportion of the cumulative amount of tungsten element at different depths in the direction perpendicular to the surface of the ternary positive electrode material pointing inward of the ternary positive electrode material provided by Examples 1-3 and Comparative Examples 1-3 is measured respectively. The results are shown in Table 1.

[0087] Table 1 The proportion of the accumulated amount of tungsten in the total tungsten content at different depths along the direction perpendicular to the surface of the ternary positive electrode material pointing inward

[0088] It can be seen from Table 1 that the ternary positive electrode materials provided in Examples 1-3 have a cumulative tungsten content at a depth of 50 nm in the direction perpendicular to the surface of the ternary positive electrode material pointing inward that is 60%-90% of the total tungsten content of the ternary positive electrode material; the cumulative tungsten content of the ternary positive electrode material at a depth of 100 nm in the direction perpendicular to the surface of the ternary positive electrode material pointing inward that is 80%-95% of the total tungsten content of the ternary positive electrode material.

[0089] Figure 4 The following is a trend chart of the cumulative amount of tungsten elements in different micro-areas obtained in Example 1 and Comparative Examples 1-3 along the direction perpendicular to the surface of the ternary positive electrode material and pointing inward as the depth increases. It can be seen from the figure that the tungsten element in the ternary positive electrode material of Example 1 is mainly concentrated within a depth of 100nm; the tungsten element in the ternary positive electrode material of Comparative Examples 1-3 is evenly distributed throughout the test depth range. The surface of the ternary positive electrode material obtained in Example 1 has an effective tungsten coating layer, which effectively protects it, increases its compressive strength, and enhances its pressure resistance.

[0090] Effect example 3: The strength performance test results of the positive electrode materials obtained in Examples 1-3 and Comparative Examples 1-5 are shown in Table 2.

[0091] The test steps include: first, using a Malvern laser particle size analyzer to test the particle size distribution of the positive electrode material to obtain the original particle size distribution; pressing the above positive electrode material at a pressure of 30 kN to obtain a pressed positive electrode material; and then using a Malvern laser particle size analyzer to test the particle size distribution of the pressed positive electrode material to obtain the particle size distribution of the pressed positive electrode material.

[0092] Particle size crushing rate = (D vx -D vx ') / D vx ×100%, where D vx Refers to the particle size corresponding to the cumulative volume distribution of the original ternary cathode material reaching x%, D vx ' refers to the particle size corresponding to the cumulative volume distribution of the ternary positive electrode material after pressing reaching x%.

[0093] Table 2 Strength performance test of Examples 1-3 and Comparative Examples 1-5

[0094] It can be seen from Table 2 that the breakage rates when the volume cumulative distribution of the ternary cathode materials in Examples 1-3 reaches 10%, 50% and 90% are 48%-54.1%, 18.7%-23.8% and 15.1%-19.3%, respectively.

[0095] Compared with Example 1, the crushing rates of the ternary positive electrode materials in Comparative Examples 1-3 when the volume cumulative distribution reaches 10%, 50% and 90% are higher. This is because the accumulated tungsten content at a depth of 50nm or 100nm in different micro-regions of the ternary positive electrode materials obtained in Comparative Examples 1-3 along the direction perpendicular to the surface of the ternary positive electrode material pointing inward is relatively low, so its compressive strength is low and its pressure resistance is low.

[0096] Compared with Examples 1-3 and Comparative Examples 1-3, the crushing rate of the ternary positive electrode material in Comparative Example 4 when the volume cumulative distribution reaches 10%, 50% and 90% is higher. This is because the ternary positive electrode material has not undergone vapor deposition and oxidation treatment and is a pure ternary active material. Therefore, it has the lowest compressive strength and the lowest pressure resistance.

[0097] Compared with Example 1, the crushing rate of the ternary positive electrode material in Comparative Example 5 when the volume cumulative distribution reaches 10%, 50% and 90% is slightly higher. This is because the air without water and CO2 is used instead of N2 in the vacuum process, and the vacuum step is not repeated. Therefore, some oxygen remains in the tubular reactor after the vacuum treatment, so that when the ternary active material and tungsten chloride are subjected to vapor deposition reaction, part of the tungsten chloride is directly oxidized to tungsten oxide, reducing the uniformity of tungsten element dispersion on the surface of the ternary active material. Therefore, its compressive strength is slightly lower and its pressure resistance is slightly lower.

[0098] Effect Example 4: Surface residual lithium content test: The residual lithium content in Examples 1-3 and Comparative Examples 1-5 was tested by potentiometric titration. The results are shown in Table 3.

[0099] Table 3 Residual lithium test results of Examples 1-3 and Comparative Examples 1-5

[0100] It can be seen from Table 3 that the residual lithium content in Examples 1-3 is significantly lower than that in Comparative Examples 1-5.

[0101] Effect Example 5: Battery preparation method: The prepared positive electrode material, acetylene black and PVDF were weighed in a mass ratio of 90:5:5, and the above three substances were added into NMP solvent and stirred and mixed thoroughly. The slurry was made after ultrasonic dispersion, and the slurry was evenly coated on aluminum foil, and then transferred to a 120 ℃ vacuum oven for drying. After 12 h, the dried electrode was taken out and rolled, and then punched to obtain a circular positive electrode with a diameter of 14 mm; a metal lithium sheet was used as the negative electrode, and 1 mol·L -1 LiPF6 organic solution (EC:DEC:DMC=1:1:1, volume ratio) was used as the electrolyte, Celgrd2400 polypropylene microporous membrane was used as the separator, and button cells were assembled in a glove box protected by high-purity argon. After the battery was assembled, it was left to stand for 4 hours, and then the electrical performance was tested using the LAND battery test system. Electrochemical performance test: The positive electrode materials prepared in Examples 1-3 and Comparative Examples 1-5 were made into button batteries, and the 0.1C first discharge specific capacity, 0.1C first efficiency, and 5C discharge specific capacity were tested at 25°C; the performance change after 100 cycles was tested at 45°C. The cycle performance test conditions are: using a LAND charge and discharge instrument, 2.8~4.30V, 1C charge and discharge, and the discharge capacity retention rate after 100 cycles is shown in Table 4.

[0102] Comparison of the cycle performance of the batteries of Examples 1-2 and Comparative Examples 1-5 Figure 5As shown, it can be seen from the figure that the capacity retention rate of the lithium ion battery containing the positive electrode material of the present invention decreases slowly, and after 100 cycles, the capacity retention rate is high.

[0103] Table 4 Comparison of electrochemical performance of Examples 1-3 and Comparative Examples 1-5

[0104] It can be clearly seen from Table 4 that the rate performance of Example 1-3 is significantly higher than that of Comparative Example 1-5, the capacity retention rate of Example 1-3 after 100 cycles is significantly higher than that of Comparative Example 1-5, and the electrochemical performance of Example 1-3 is significantly better than that of Comparative Example 1-5.

[0105] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and exerting the same effect within the scope of the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

1. A ternary positive electrode material, characterized in that: The tungsten content of the ternary positive electrode material gradually decreases in a direction perpendicular to the surface of the ternary positive electrode material and pointing inward; The accumulated tungsten content of the ternary positive electrode material at a depth of 50 nm along the direction perpendicular to the surface of the ternary positive electrode material and pointing inward is 60%-90% of the total tungsten content of the ternary positive electrode material; The accumulated tungsten content of the ternary positive electrode material at a depth of 100 nm along the direction perpendicular to the surface of the ternary positive electrode material and pointing inward is 80%-95% of the total tungsten content of the ternary positive electrode material.

2. The ternary cathode material according to claim 1, characterized in that: The ternary positive electrode material meets the following requirements: 30%≤(D v10 -D v10 ') / D v10 ×100%≤55%; And / or, the ternary cathode material satisfies: 15%≤(D v50 -D v50 ') / D v50 ×100%≤25%; And / or, the ternary cathode material satisfies: 8%≤(D v90 -D v90 ') / D v90 ×100%≤20%; Among them, D v10 , D v50 and D v90 are the particle sizes corresponding to the volume cumulative distribution of the ternary positive electrode material when it reaches 10%, 50%, and 90%, respectively, in μm; D v10 '、D v50 ' and D v90 ' are the particle sizes corresponding to 10%, 50% and 90% of the volume cumulative distribution of the ternary positive electrode material after being pressed at a pressure of 30 kN, in μm.

3. A method for preparing a ternary positive electrode material according to claim 1 or 2, characterized in that: The following steps are involved: The ternary active material and tungsten chloride are subjected to a vapor deposition reaction to obtain a ternary positive electrode material precursor; The ternary cathode material precursor is oxidized to obtain a ternary cathode material.

4. The method for preparing the ternary cathode material according to claim 3, characterized in that: The vapor deposition reaction includes: spreading the ternary active material on one side of the tubular reactor close to the exhaust pipe, placing the tungsten chloride in a porcelain boat and placing it on one side of the tubular reactor close to the air inlet, introducing an inert gas into the tubular reactor, and then evacuating the tubular reactor; rotating the tubular reactor and performing a first reaction at a first reaction temperature to obtain a ternary positive electrode material precursor.

5. The method for preparing the ternary cathode material according to claim 4, characterized in that: The oxidation comprises: introducing an inert gas and oxygen into the tubular reactor in sequence, and performing a second reaction at a second reaction temperature to obtain a ternary positive electrode material.

6. The method for preparing the ternary cathode material according to any one of claims 3 to 5, characterized in that: The tungsten chloride is at least one of WCl6 and WCl5; And / or, the inert gas is at least one of N2, Ar and He.

7. The method for preparing the ternary positive electrode material according to claim 4 or 5, characterized in that: The mass ratio of the ternary active material to tungsten chloride is 100:1.5-2.

5.

8. The method for preparing a ternary cathode material according to claim 4, characterized in that: The vacuuming means making the vacuum degree in the tubular reactor be -0.09MPa~-0.05MPa; And / or, the rotation speed is 10~60rpm.

9. The method for preparing the ternary cathode material according to claim 5, characterized in that: The first reaction temperature includes the temperature T1 of the region where the tungsten chloride is located, the temperature T2 of the region where the ternary active material is located, and the temperature T3 of the remaining regions in the tubular reactor; the second reaction temperature includes a first-stage reaction temperature T4 and a second-stage reaction temperature T5; the second reaction includes a first-stage reaction at the first-stage reaction temperature T4 and a second-stage reaction at the second-stage reaction temperature T5; Wherein, the temperature T1 is 280°C to 400°C; And / or, the temperature T2 is 150° C. to 300° C.; And / or, the temperature T3 is 250°C to 400°C; And / or, the first reaction time is 1 to 5 hours; And / or, the temperature T4 is 150°C to 300°C; And / or, the temperature T5 is 300° C. to 700° C.; And / or, a reaction time in the second reaction is 0.5 to 2 hours; And / or, the second reaction time in the second reaction is 0.5 to 2.5 hours.

10. A battery, characterized in that: The battery comprises the ternary positive electrode material described in any one of claims 1-2, or the ternary positive electrode material obtained by the preparation method of the ternary positive electrode material described in any one of claims 3-9.

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