Double-coated ternary material, preparation method thereof, positive electrode sheet, lithium ion battery and electric device

Abstract

The present application relates to the field of lithium ion battery materials, and discloses a double-layer coated ternary material, a preparation method thereof, a positive electrode sheet, a lithium ion battery and an electric device. The double-layer coated ternary material provided by the present application comprises a single-crystal high-nickel ternary material, a polycrystal nano ternary material layer coated on the single-crystal high-nickel ternary material, and a modified compound layer coated on the polycrystal nano ternary material layer; wherein the modified compound layer comprises a B-containing compound and an Al-containing compound. The polycrystal nano ternary material is used to coat the single-crystal high-nickel ternary material, so that the rate performance and the discharge specific capacity of the material can be improved, and the impedance can be reduced. The modified compound of the second layer coating has the advantages of the B-containing compound and the Al-containing compound, so that the first cycle charge-discharge specific capacity, the first efficiency, the normal temperature cycle performance and the high temperature cycle performance of the double-layer coated ternary material can be effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of lithium ion battery materials, in particular to a double-layer coated ternary material, a preparation method thereof, a positive electrode sheet, a lithium ion battery and an electric device. BACKGROUND

[0002] The layered nickel-cobalt-manganese ternary positive electrode material has the advantages of high discharge specific capacity, good cycle performance, and relatively stable structure. The mainstream morphology of the ternary material is divided into micron-sized single-crystal materials and nanometer primary particles composed of spherical polycrystalline materials. The spherical polycrystalline ternary material has relatively high discharge specific capacity and rate performance, but the high-temperature cycle performance is relatively poor. The micron-sized single-crystal ternary material has good high-temperature cycle performance, but the discharge specific capacity, rate and low-temperature performance are relatively poor.

[0003] CN113488634A discloses that LiNi x Mn y W z O2(0.9≤x<1, 0<y≤0.06, 0<z≤0.04, x+y+z=1) as the base material, mixing the TM source with it and calcining to obtain a single-layer coated ternary positive electrode material, mixing the single-layer coated ternary positive electrode material with a carbon source and calcining to obtain a double-layer coated modified high-nickel cobalt-free ternary positive electrode material, which improves the cycle performance and rate performance of the high-nickel cobalt-free single-crystal ternary material, but the discharge specific capacity of the final material in the examples is only about 210 mAh / g, and the 1C / 0.1C capacity retention rate is about 91%, which still has a relatively large room for improvement. The coated material is only tested for room temperature cycle performance, and the high-temperature cycle performance, which is also of great concern, is not tested.

[0004] CN112820865A adopts a lithium source, an aluminum source, a phosphorus source, a titanium source or a germanium source with mutual reactivity to fully mix with a high-nickel ternary single-crystal positive electrode material in a solvent-free condition in steps, to obtain a high-nickel ternary single-crystal material coated with a LISICON-type solid-state electrolyte with stability and ionic conductivity after low-temperature sintering, and to form a hydrophobic layer on the surface of the material after silane coupling agent treatment, which effectively improves the cycle and rate performance of the high-nickel ternary single-crystal positive electrode material, but the second silane coupling agent modification results in a low first efficiency of the finished product.

[0005] Therefore, there is an urgent need for a ternary positive electrode material that can simultaneously have the high-temperature cycle performance advantage of single-crystal ternary materials and the high discharge specific capacity and rate performance advantage of polycrystalline ternary materials, and does not affect the electrode compaction density, so that the prepared battery has high charge and discharge specific capacity and first efficiency, good low-temperature and rate performance, and good high-temperature cycle performance. SUMMARY

[0006] The application aims to overcome the problems of the prior art, such as the influence of ternary positive electrode materials on electrode compaction density, the inability to guarantee that the prepared battery has high charge-discharge specific capacity, excellent low-temperature and rate performance, high-temperature cycle and thermal stability, and a large amount of organic solvent, and provides a double-layer coated ternary material, a preparation method thereof, a positive electrode sheet, a lithium ion battery and an electric device.

[0007] To achieve the above-mentioned object, the application provides a double-layer coated ternary material, which comprises a single-crystal high-nickel ternary material, a polycrystalline nano ternary material layer coated on the single-crystal high-nickel ternary material, and a modified compound layer coated on the polycrystalline nano ternary material layer; wherein the modified compound layer comprises a B-containing compound and an Al-containing compound.

[0008] The application provides a preparation method of a double-layer coated ternary material, which comprises the following steps:

[0009] (1) mixing a single-crystal high-nickel ternary material and a polycrystalline nano ternary material, and then performing first sintering to obtain a single-layer coated material;

[0010] (2) mixing the single-layer coated material with a modified compound, and then performing second sintering to obtain the double-layer coated ternary material; wherein the modified compound comprises a B-containing compound and an Al-containing compound.

[0011] The application provides a double-layer coated ternary material prepared by the preparation method.

[0012] The application provides a positive electrode sheet comprising the double-layer coated ternary material.

[0013] The application provides a lithium ion battery comprising the positive electrode sheet.

[0014] The application provides an electric device comprising the lithium ion battery.

[0015] Through the above technical solution, the application has the following advantages:

[0016] The polycrystalline nano ternary material is used for coating the single-crystal high-nickel ternary material, a limited number of polycrystalline nano material coating layers are formed on the surface of the single-crystal high-nickel ternary material substrate, the lithium ion diffusion coefficient of the single-crystal material at the interface can be improved, and the rate performance and the discharge specific capacity of the material can be improved. The second layer of the modified compound has the advantages of the B-containing compound and the Al-containing compound, and can effectively improve the first efficiency of the battery, the normal temperature cycle and the high temperature cycle performance. In addition, compared with the single-crystal high-nickel ternary material, the double-layer coated ternary material prepared by the application does not affect the compaction density of the positive plate, the entire process does not introduce organic solvents, has no environmental safety risk, has low cost, and is easy to mass produce in industry. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a SEM image of the polycrystalline nano ternary material magnified 30,000 times in one specific embodiment of the application;

[0018] Figure 2 is a SEM image of the polycrystalline nano ternary material magnified 1,000 times in one specific embodiment of the application;

[0019] Figure 3 is a SEM image of the double-layer coated ternary material magnified 50,000 times in one specific embodiment of the application;

[0020] Figure 4 is a SEM image of the double-layer coated ternary material magnified 1,000 times in one specific embodiment of the application;

[0021] Figure 5 is a SEM image of the single-layer coated material magnified 50,000 times in Example 2 of the application, in which a modified compound is coated outside the single-crystal high-nickel ternary material, but no polycrystalline nano ternary material is coated;

[0022] Figure 6 is a SEM image of the single-layer coated material magnified 1,000 times in Example 2 of the application, in which a modified compound is coated outside the single-crystal high-nickel ternary material, but no polycrystalline nano ternary material is coated;

[0023] Figure 7 is an XRD image of the reaction product of boric acid and the single-layer coated material LiNi a Co b Mn c M d O2@nanoLiNi a Co b Mn c M d O2 surface after LiOH reaction;

[0024] Figure 8is a specific embodiment of the present application. Boric acid and single-layer coating material LiNi a Co b Mn c M d O2@nanoLiNi a Co b Mn c M d XRD pattern of the reaction product of Li2CO3 on the surface of O2. DETAILED DESCRIPTION

[0025] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the present application. Any numerical range recited herein is intended to include all sub-ranges of the same numbers (i.e., every subset of numbers within the indicated range). For ranges containing endpoints, any numerical or alphabetical sub-range falling within the indicated range is also a range included in the application. The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not critical to the present application. Any numerical range recited herein is intended to include all sub-ranges of the same numbers (i.e., every subset of numbers within the indicated range). For ranges containing endpoints, any numerical or alphabetical sub-range falling within the indicated range is also a range included in the application.

[0026] The first aspect of the present application provides a double-layer coated ternary material, which comprises a single-crystal high-nickel ternary material and a polycrystalline nano-ternary material layer coated on the surface of the single-crystal high-nickel ternary material, and a modified compound layer coated on the surface of the polycrystalline nano-ternary material layer; wherein the modified compound layer comprises a B-containing compound and an Al-containing compound.

[0027] The polycrystalline material has higher specific capacity and rate characteristics, and after nanocrystallization, the lithium ion migration rate is further improved. The present application uses a polycrystalline nano-ternary material to coat a single-crystal high-nickel ternary material, forming a limited number of polycrystalline nano-material coating layers on the surface of the single-crystal high-nickel ternary material substrate. The single-crystal high-nickel material and the polycrystalline nano-ternary material both belong to ternary materials, and the combination of the two is more likely to generate a stable interface that is easy for lithium ions to migrate from the polycrystalline to the single-crystal, thereby improving the lithium ion diffusion coefficient of the single-crystal material at the interface and improving the rate performance and discharge specific capacity of the material. The second layer of modified compounds, the B-containing compound and the Al-containing compound have a good synergistic effect, which can effectively improve the first efficiency, room temperature cycle and high temperature cycle performance of the double-layer coated ternary material.

[0028] In addition, the present application coats the modified compound on the surface of the polycrystalline nano-ternary material. If the polycrystalline nano-ternary material is coated on the surface of the modified compound, its contact area with the electrolyte will be larger than that of the single-crystal high-nickel ternary material. It is necessary to coat and modify the surface of the polycrystalline nano-ternary material to protect its surface and reduce the side reaction with the electrolyte. Therefore, the modified compound also has the effect of protecting the polycrystalline nano-ternary material. In addition, the outermost layer of the modified compound can form Li x B y Oz (1≤x≤5, 1≤y≤4, 2≤z≤10,) and Li m Al n O p (1≤m≤5, 1≤n≤4, 2≤p≤10) and the like lithium fast ion conductors, Li x B y O z and Li m Al n O p have good synergies, can improve the performance of the polycrystalline nanometer ternary material, and further improve the performance of the double-layer coated ternary material.

[0029] In addition, the entire process does not introduce organic solvents, has no environmental safety risks, is low in cost, and is easy to mass produce industrially.

[0030] According to the present application, preferably, the single-crystal high-nickel ternary material is a compound represented by the chemical formula LiNi a Co b Mn c M d O2; wherein 0.8≤a≤0.98, 0≤b≤0.1, 0.02≤c≤0.2, 0≤d≤0.005, a+b+c+d=1, and M is selected from at least one of B, Mg, Al, Ca, Ti, V, Sr, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Ba, La, Ce, Ta, and W.

[0031] According to the present application, preferably, the polycrystalline nanometer ternary material layer comprises a polycrystalline nanometer ternary material, and the polycrystalline nanometer ternary material is a compound represented by the chemical formula LiNi t Co q Mn s E f O2; wherein 0.5≤t≤0.98, 0≤q≤0.2, 0.02≤s≤0.3, 0≤f≤0.01, t+q+s+f=1, and E is selected from at least one of B, Mg, Al, Ca, Ti, V, Sr, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Ba, La, Ce, Ta, and W.

[0032] The doping of metal elements for structural modification of the single-crystal high-nickel ternary material or the polycrystalline nanometer ternary material can improve the structural stability of the double-layer coated ternary material, thereby improving the cycle performance, low-temperature performance, and rate performance of the battery, and can reduce the sintering temperature, free lithium content, and impedance of the single-crystal high-nickel ternary material or the polycrystalline nanometer ternary material.

[0033] Further, the polycrystal nano ternary material is a polycrystal nano high-nickel ternary material, and the polycrystal nano high-nickel ternary material is a compound represented by a chemical formula LiNi t Co q Mn s E f O2; wherein 0.8≤t≤0.98, 0≤q≤0.1, 0.02≤s≤0.2, and 0≤f≤0.005.

[0034] According to the present application, the chemical composition of the single-crystal high-nickel ternary material (single-crystal LiNi a Co b Mn c M d O2) and the polycrystal nano ternary material (nano LiNi t Co q Mn s E f O2) can be the same or different, and is preferably the same.

[0035] According to the present application, preferably, the average particle size of the double-layer coated ternary material is 0.5-11 μm. According to the present application, preferably, the average particle size of the single-crystal high-nickel ternary material is 0.5-10 μm. The average particle size of the single-crystal high-nickel ternary material refers to the average primary particle size of the single-crystal high-nickel ternary material.

[0036] In the present application, the primary particle size refers to the particle size of a single-crystal primary particle, and the secondary particle size refers to the particle size of a particle after agglomeration of a single-crystal primary particle. The single-crystal high-nickel ternary material is a single-crystal primary particle, and the average particle size of the single-crystal high-nickel ternary material is the average primary particle size of the single-crystal high-nickel ternary material. The average particle size of the single-crystal high-nickel ternary material as a substrate can be designed to be slightly smaller. When the average particle size satisfies the aforementioned range, the corresponding lithium ion diffusion path is shortened, and the discharge specific capacity, rate performance, and impedance are more advantageous.

[0037] Further, the average particle size of the single-crystal high-nickel ternary material is 2-6 μm.

[0038] According to the present application, preferably, the thickness of the polycrystal nano ternary material layer coated outside the single-crystal high-nickel ternary material is 2-200 nm. The polycrystal ternary material is composed of a large number of single-crystal particles. When the thickness of the introduced polycrystal nano ternary material is small, the total number of single-crystal particles in the polycrystal ternary material layer is small, and the grain boundary is also small, which can effectively avoid cracking of the polycrystal material in the later cycle.

[0039] Further, the thickness of the polycrystalline nanometer ternary material layer coated by the single-crystal high-nickel ternary material is 5-100 nm.

[0040] According to the present application, preferably, the content of B element contained in the modified compound layer is 100-2000 ppm, preferably 300-1500 ppm, and the content of Al element is 100-3000 ppm, preferably 500-2000 ppm, based on the total weight of the double-layer coated ternary material. Herein, ppm is by mass, specifically, the number of milligrams of B element or Al element contained is based on the total weight of the double-layer coated ternary material being 1 kg.

[0041] In the present application, the coating of the modified compound is a combination of point-like and island-like coating, and the outer surface of the polycrystalline nanometer ternary material is not completely covered, and the coating is a combination of dispersed point-like coating and island-like coating. The thickness of the polycrystalline nanometer ternary material layer and the amount of the modified compound introduced in the present application are relatively small, which will not affect the compaction density of the prepared pole piece; at the same time, when the content of B element and Al element meets the aforementioned range, the Li x B y O z and Li m Al n O p can each play its advantages and achieve better synergistic effect.

[0042] The second aspect of the present application provides a preparation method of a double-layer coated ternary material, which comprises the following steps:

[0043] (1) mixing single-crystal high-nickel ternary material and polycrystalline nanometer ternary material and then performing first sintering to obtain a single-layer coated material;

[0044] (2) mixing the single-layer coated material with a modified compound and then performing second sintering to obtain the double-layer coated ternary material; wherein the modified compound is a mixture comprising a B-containing compound and an Al-containing compound.

[0045] In the preparation method of the double-layer coated ternary material in the second aspect of the present application, the types and sizes of the single-crystal high-nickel ternary material and the polycrystalline nanometer ternary material are completely the same as those of the single-crystal high-nickel ternary material and the polycrystalline nanometer ternary material in the double-layer coated ternary material in the first aspect of the present application, and in order to avoid repetition, the present application will not be described again in this second aspect, and the person skilled in the art should not understand it as a limitation of the present application.

[0046] According to the present application, preferably, the average particle size of the single-crystal high-nickel ternary material is 0.5-10 μm, preferably 2-6 μm.

[0047] According to the present application, preferably, the average particle size of the polycrystalline nanometer ternary material is 10-50 nm.

[0048] According to the present application, preferably, in step (1), the single-crystal high-nickel ternary material and the polycrystalline nanometer ternary material are mixed in a weight ratio of (20-500):1.

[0049] According to the present application, preferably, in step (2), the weight ratio of the B-containing compound to the Al-containing compound in the modifying compound is 1:(0.1-5), wherein the B-containing compound is calculated based on the element B and the Al-containing compound is calculated based on the element Al.

[0050] According to the present application, preferably, the B-containing compound is selected from at least one of B2O3, H3BO3, LiBO2 and Li2B4O7.

[0051] According to the present application, preferably, the Al-containing compound is selected from at least one of Al2O3, boehmite, pseudoboehmite, LiAlO2, aluminum hydroxide and Li2Al4O7. When the Al-containing compound is Al2O3, the crystal form of Al2O3 can be a single one of α, β, γ, δ and θ, or a mixture of two or more crystal forms.

[0052] According to the present application, preferably, in step (2), the single-layer coating material and the modifying compound are mixed in a weight ratio of (100-1000):1.

[0053] According to the present application, preferably, the first sintering is performed at a temperature of 600-780℃ for 2-12h.

[0054] According to the present application, preferably, the second sintering is performed at a temperature of 200-500℃ for 2-8h.

[0055] According to the present application, preferably, in step (2), the single-layer coating material is first mixed with the B-containing compound, then mixed with the Al-containing compound, and then subjected to the second sintering.

[0056] According to the application, the B-containing compound is coated outside the single-layer coating material, which can react with the free lithium on the surface of the single-layer coating material at room temperature to generate a fast ion conductor containing B and Li elements, mainly improving the discharge specific capacity and the first efficiency of the material, while the Al-containing compound has a lower reactivity than the B-containing compound. If the Al-containing compound is coated first, part of the surface will be covered by the Al-containing compound, and the B-containing compound coated later will have a certain probability of adhering to the surface of the Al-containing compound. This part of the B-containing compound cannot react with the free lithium and cannot achieve the best effect. Even if the Al-containing compound is coated on the surface of the B-containing compound, it does not react with the free lithium and has a promoting effect on the high-temperature cycle of the material. Therefore, the order of coating the B-containing compound first and then the Al-containing compound can achieve the best coating effect.

[0057] According to the specific embodiment of the application, the preparation method of the double-layer coated ternary material comprises the following steps:

[0058] (1) The polycrystalline nano ternary material and the single-crystal high-nickel ternary material are weighed according to the proportion, mixed in a mechanical fusion machine, and then the mixed material is added to a box furnace for first sintering in an air or oxygen atmosphere. The first sintering temperature is 600-780℃, and the time is 2-12h. After cooling, sieving is performed to obtain a single-layer coated material, which is denoted as LiNi a Co b Mn c M d O2@nano LiNi t Co q Mn s E f O2.

[0059] (2) The single-layer coated material and the B-containing compound are added to a high-speed mixer at a weight ratio of (100-1000):1 (preferably (200-500):1), stirred at a speed of 500-1000rpm for 3-5min, and then stirred at a high speed of 1500-2000rpm for 20-30min. Then the Al-containing compound is added to the high-speed mixer, so that the weight ratio of the Al-containing compound to the single-layer coated material is 1:(100-1000) (preferably 1:(200-800)), stirred at a speed of 500-1000rpm for 3-5min, and then stirred at a high speed of 1500-2000rpm for 20-30min. The mixed material is placed in a box furnace and sintered at 200-500℃ for 2-8h in an air or oxygen atmosphere. After cooling, sieving is performed to obtain a double-layer coated single-crystal high-nickel ternary material, which is denoted as LiNi a Co b Mn c M dO2@nano LiNi t Co q Mn s E f O2@Li x B y O z &Li m Al n O p .

[0060] According to the application, preferably, the preparation method of the single-crystal high-nickel ternary material comprises the following steps: mixing a single-crystal high-nickel ternary material precursor, a lithium source 1 and a dopant 1, then performing third sintering and first crushing to obtain the single-crystal high-nickel ternary material; wherein the dopant 1 is an oxide of metal M and / or a hydroxide of metal M; M is selected from at least one of B, Mg, Al, Ca, Ti, V, Sr, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Ba, La, Ce, Ta and W.

[0061] The single-crystal high-nickel ternary material precursor used in the application is commercially available.

[0062] According to the application, preferably, the preparation method of the polycrystalline nano ternary material comprises: mixing a polycrystalline nano ternary material precursor, a lithium source 2 and a dopant 2, then performing fourth sintering and second crushing to obtain the polycrystalline nano ternary material; wherein the dopant 2 is an oxide of metal E and / or a hydroxide of metal E; E is selected from at least one of B, Mg, Al, Ca, Ti, V, Sr, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Ba, La, Ce, Ta and W.

[0063] The nano polycrystalline ternary material precursor used in the application is obtained by self-preparation, according to a specific embodiment of the application, the preparation method of the polycrystalline nano ternary material precursor comprises: mixing a nickel source, a cobalt source, a manganese source and water to prepare a mixed salt solution, then mixing with a precipitator to perform a co-precipitation reaction, and then performing aging, concentration, grinding, drying and depolymerization on the product after the co-precipitation reaction to obtain the polycrystalline nano ternary material precursor; preferably, the precipitator is a mixture of sodium hydroxide solution and ammonia water.

[0064] According to the application, preferably, the nickel source is selected from at least one of nickel sulfate, nickel chloride and nickel oxalate, and is preferably nickel sulfate.

[0065] According to the application, preferably, the cobalt source is selected from at least one of cobalt sulfate, cobalt chloride and cobalt oxalate, and is preferably cobalt sulfate.

[0066] According to the application, preferably, the manganese source is selected from at least one of manganese sulfate, manganese chloride and manganese oxalate, and is preferably manganese sulfate.

[0067] According to the present application, preferably, the lithium source 1 and the lithium source 2 are each independently selected from at least one of lithium hydroxide, lithium carbonate, lithium sulfate, lithium chloride, lithium acetate, lithium oxalate and lithium nitrate, preferably lithium hydroxide.

[0068] According to a specific embodiment of the present application, the preparation method of the single-crystal high-nickel ternary material comprises the following steps:

[0069] The single-crystal high-nickel ternary material precursor (Ni a’ Co b’ Mn c’ (OH)2, wherein a'+b'+c'=1, a':b':c'=a:b:c), a lithium source and a dopant are added into a high-speed mixer at a molar ratio of Li element: precursor: M element = (1-1.1):1:(0-0.005), stirred at a speed of 500-1000 rpm for 3-5 min, then high-speed stirred at a speed of 1500-2000 rpm for 20-30 min, and then the mixed material is placed in a box furnace, sintered at 450-780℃ for 1-3 h under air or oxygen atmosphere, then heated to 600-900℃ for sintering for 8-20 h, after sintering, rolled, and then air-pulverized in an air flow pulverizer to obtain a single-crystal high-nickel ternary material represented by the chemical formula LiNi a Co b Mn c M d O2, with an average particle size of 0.5-10 μm;

[0070] wherein 0.8≤a≤0.98, 0≤b≤0.1, 0.02≤c≤0.2, 0≤d≤0.005, a+b+c+d=1, and M is selected from at least one of B, Mg, Al, Ca, Ti, V, Sr, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Ba, La, Ce, Ta and W; the dopant is an oxide of the metal M and / or a hydroxide of the metal M.

[0071] According to a specific embodiment of the present application, the preparation method of the single-crystal high-nickel ternary material comprises the following steps:

[0072] (1) A nickel source, a cobalt source, and a manganese source are mixed with water to prepare a mixed salt solution having a total metal content of 0.5-5 mol / L, in which the molar ratio of Ni element:Co element:Mn element is t':q':s'. The mixed salt solution, a sodium hydroxide solution having a concentration of 1-10 mol / L, and ammonia water having a concentration of 0.5-5 mol / L are pumped into a reactor at a certain flow rate by a metering pump to perform a co-precipitation reaction, and the pH of the reaction solution (product after the co-precipitation reaction) is controlled to be greater than or equal to 11. During the reaction, the particle size distribution of the slurry is tested by sampling. When the average particle size of the particles in the slurry increases to 2-3 μm, the reaction solution is transported to an aging tank for aging for 2-15 h. The aged slurry is then pumped into the cavity of a sand mill after being concentrated by a concentration machine. The solid content of the concentrated slurry is 30%-60 wt%. The particle size of the zirconium beads of the sand mill is 0.1-1 mm. The sand milling time is 0.5-5 h. The average particle size of the particles in the slurry after sand milling is 50-300 nm. The slurry is then subjected to freeze-drying treatment. Finally, the slurry is further depolymerized by an air jet pulverizer. The frequency of the classification wheel, the feeding frequency, and the frequency of the air blower of the air jet pulverizer are 120-180 Hz, 1-5 Hz, and 5-15 Hz, respectively. The air crushing pressure is 0.2-1 MPa. A polycrystalline nano ternary material precursor represented by the chemical formula Ni t’ Co q’ Mn s’ (OH)2 is obtained.

[0073] (2) The polycrystalline nano ternary material precursor, a lithium source, and a dopant are added to a high-speed mixer at a molar ratio of Li element:precursor:E element=(1-1.1):1:(0-0.005). The mixture is stirred at a speed of 500-1000 rpm for 3-5 min, and then stirred at a high speed of 1500-2000 rpm for 20-30 min. The mixed material is placed in a box furnace and sintered at 450-700 ℃ for 1-3 h, and then heated to 600-820 ℃ for sintering for 8-20 h. After sintering, the material is ground by a rotary wheel mill, and then air-jet pulverized in an air jet pulverizer. A nano high-nickel ternary material having an average primary particle size of 10-100 nm and represented by the chemical formula LiNi t Co q Mn s E f O2 is obtained.

[0074] wherein 0.5≤t≤0.98, 0≤q≤0.2, 0.02≤s≤0.3, 0≤f≤0.01, t+q+s+f=1, and E is selected from at least one of B, Mg, Al, Ca, Ti, V, Sr, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Ba, La, Ce, Ta, and W.

[0075] According to the present application, the chemical composition of the polycrystal nanometer ternary material and the single crystal high-nickel ternary material can be the same or different, and is preferably the same. When the chemical composition of the polycrystal nanometer ternary material and the single crystal high-nickel ternary material is the same, the chemical composition of the polycrystal nanometer ternary material precursor and the single crystal high-nickel ternary material precursor is the same (the polycrystal nanometer ternary material precursor and the single crystal high-nickel ternary material precursor have different morphologies, and the polycrystal nanometer ternary material precursor can be divided into smaller primary particles), the lithium source used can be the same or different, and the dopant used is an oxide and / or hydroxide containing the same doping metal.

[0076] The third aspect of the present application provides a double-layer coated ternary material prepared by the preparation method provided by the present application.

[0077] The fourth aspect of the present application provides a positive electrode sheet comprising the double-layer coated ternary material provided by the present application.

[0078] Preferably, the compaction density of the positive electrode sheet is 3.5-3.9 g / cm 3 .

[0079] The fifth aspect of the present application provides a lithium ion battery comprising the positive electrode sheet provided by the present application.

[0080] Preferably, the 0.1C charge specific capacity of the lithium ion battery is 235 mAh / g or more, the 0.1C discharge specific capacity is 210 mAh / g or more, the 1C / 0.1C capacity retention rate is 90% or more, the capacity retention rate after 100 cycles at room temperature is 90% or more, and the capacity retention rate after 100 cycles at 45°C is 85% or more.

[0081] Preferably, the 0.1C charge specific capacity of the lithium ion battery is 240 mAh / g or more, the 0.1C discharge specific capacity is 220 mAh / g or more, the 1C / 0.1C capacity retention rate is 90% or more, the capacity retention rate after 100 cycles at room temperature is 95% or more, and the capacity retention rate after 100 cycles at 45°C is 90% or more.

[0082] The sixth aspect of the present application provides an electric device comprising the lithium ion battery provided by the present application.

[0083] The application will be described in detail below by examples. The reagents used in the following examples are conventional biochemical reagents unless otherwise specified; the raw materials, instruments and equipment used are commercially available or can be obtained by existing methods; the reagent amount is the amount used in conventional experimental operation unless otherwise specified; the experimental method is a conventional method unless otherwise specified. The determination methods involved in the following examples and comparative examples are as follows:

[0084] Method for SEM test: Zeiss Germany field emission scanning electron microscope Sigma 300 is used for morphology analysis of the relevant products, the scanning voltage is 3kV, and the magnification is selected as 3Kx, 5Kx, 10Kx, 30Kx and 50Kx. The powder sample is stuck on the conductive tape, and the sample is dried and stored in a vacuum drying box before test;

[0085] Method for determining the thickness of the first coating layer: ion milling equipment of Leica Company is used for cross-section processing of the material, and then the cross-section morphology of the material is tested on the GEMINI 300 field emission scanning electron microscope of Carl Zeiss Optical Co., Ltd., and the thickness of the first coating layer is determined by testing the thickness of the polycrystalline nanometer ternary material on the surface of the single-crystal high-nickel ternary material;

[0086] Method for determining the content of B and Al: an inductively coupled plasma emission spectrometer is used to test the content of B and Al of the material;

[0087] Method for determining the average particle size of the single-crystal high-nickel ternary material, the polycrystalline nanometer ternary material and the double-layer coated ternary material: 0.2g of the single-crystal high-nickel ternary material, the polycrystalline nanometer ternary material or the double-layer coated ternary material is weighed in a 50mL beaker, then 10mL of ethanol is added, 1mL of sodium hexametaphosphate dispersion solution is added, and ultrasonic dispersion is performed for 10min, and the particle size distribution of the material is tested on a Malvern 3000 device;

[0088] Specific capacity test: 0.1C (1C = 210mA / g) constant current and constant voltage charging to 4.3V, cutoff current 0.01C, then 0.1C constant current discharging to 2.5V, and the charging specific capacity, discharging specific capacity and initial efficiency are calculated;

[0089] Rate performance test: 0.1C constant current and constant voltage charging to 4.3V, the battery is cut off at 0.01C, then discharged at 0.1C, 0.2C, 0.5C and 1C respectively to 2.5V, and the 1C / 0.1C capacity retention rate is calculated;

[0090] Normal temperature cycle test: 0.5C constant current and constant voltage charging to 4.3V (cutoff voltage 0.02C) and then 1C constant current discharging to 2.5V, and the capacity retention rate is calculated after 100 cycles;

[0091] High temperature cycle test: same as normal temperature cycle test, the difference is that the battery is tested in a 45°C constant temperature oven.

[0092] The following examples are used to illustrate the preparation of double-coated single-crystal high-nickel ternary material.

[0093] Example 1

[0094] Step (1): Preparation of polycrystalline nano ternary material precursor

[0095] 1.183 kg of nickel sulfate hexahydrate, 0.07 kg of cobalt sulfate heptahydrate and 0.042 kg of manganese sulfate monohydrate were weighed separately to make the molar ratio of Ni:Co:Mn 0.9:0.05:0.05; deionized water was added to dissolve to obtain a mixed salt solution with a total metal ion concentration of 2 mol / L, a commercially available sodium hydroxide solution with a concentration of 32 wt% was diluted to 2 mol / L, and then the mixed salt solution, the sodium hydroxide solution with a concentration of 2 mol / L and the ammonia solution with a concentration of 4 mol / L were transported to a 10 L reaction kettle by a diaphragm pump for co-precipitation reaction, the pH value of the reaction solution was adjusted to 11.8, and when the average particle size of the particles in the slurry was tested to rise to 2.8 μm, the reaction product was transported to the aging kettle for aging for 2 h, then the aged slurry was concentrated to a solid content of 40 wt% by a concentration machine, and then transported to the internal sand mill cavity through the external circulation system of the sand mill, using 0.1 mm zirconium beads for sand milling for 3 h, the average particle size of the particles in the sand-milled slurry was measured to be 100 nm, and the sand-milled slurry was freeze-dried, then dispersed and depolymerized by using an air flow crusher, the classification wheel frequency, the feeding frequency and the induced draft fan frequency of the air flow crusher were 150 Hz, 3 Hz and 10 Hz respectively, the air crushing pressure was 0.5 MPa, and a polycrystalline nano ternary material precursor with the chemical formula of Ni 0.9 Co 0.05 Mn 0.05 (OH)2was obtained.

[0096] Step (2): Preparation of single-crystal high-nickel ternary material

[0097] Battery-grade lithium hydroxide, commercially available single-crystal Ni 0.9 Co 0.05 Mn 0.05 (OH)2precursor, nano-zirconium oxide and nano-tantalum oxide were mixed in a ratio of 1.04:0.995:

[0098] 0.003:0.001 molar ratio was added into a high-speed mixer for mixing, stirred at 800 rpm for 4 min, then high-speed stirred at 1800 rpm for 25 min, then the mixed material was placed in a box furnace, sintered at 700℃ for 2h under oxygen atmosphere, then the temperature was raised to 830℃ for sintering for 14h, then crushed by a roller mill and an air jet pulverizer, to obtain a single-crystal high-nickel ternary material represented by the chemical formula Li(Ni 0.9 Co 0.05 Mn 0.05 ) 0.995 Zr 0.003 Ta 0.002 O2.

[0099] Step (3): Preparation of polycrystalline nano ternary material

[0100] The battery-grade lithium hydroxide, the precursor prepared in step (1), nano-zirconium oxide and nano-tantalum oxide were added into a high-speed mixer for mixing in a molar ratio of 1.04:0.995:0.003:0.001, stirred at 800 rpm for 4 min, then high-speed stirred at 1800 rpm for 25 min, then the mixed material was placed in a box furnace, sintered at 600℃ for 2h under oxygen atmosphere, then the temperature was raised to 760℃ for sintering for 12h, then crushed by a rotary wheel mill and an air jet pulverizer, to obtain a polycrystalline nano ternary material represented by the chemical formula Li(Ni 0.9 Co 0.05 Mn 0.05 ) 0.995 Zr 0.003 Ta 0.002 O2.

[0101] It can be seen from Figure 1 and Figure 2 that the primary particle size of the polycrystalline nano ternary material is in the range of 10-50 nm, and is relatively uniform.

[0102] Step (4): Preparation of single-layer coated material

[0103] The single-crystal high-nickel ternary material prepared in step (2) and the polycrystalline nano ternary material prepared in step (3) were mixed in a mechanical fusion machine in a weight ratio of 100:1, then sintered at 700℃ for 10h under oxygen atmosphere in a box furnace, sieved after cooling, to obtain a single-layer coated material.

[0104] Step (5): Preparation of double-layer coated ternary material

[0105] The single-layer coating material obtained in step (4) and boric acid were added to a high-speed mixer at a weight ratio of 1:0.003. The mixture was stirred at 800 rpm for 5 min and then at 1800 rpm for 25 min. Then, boehmite was added to the high-speed mixer so that the weight ratio of boehmite to single-layer coating material was 0.0015:1, the weight ratio of single-layer coating material to modified compound (boric acid and boehmite) was 222:1, and the weight ratio of B element to Al element was 1:1.3. The mixture was stirred at 800 rpm for 5 min and then at 1800 rpm for 25 min. The mixed material was placed in a box furnace and sintered at 350℃ for 5 h in an oxygen atmosphere. After cooling, the mixture was sieved to obtain a double-layer coated ternary material, denoted as NCM1.

[0106] Depend on Figure 3 It can be seen that the surface of the single-crystal high-nickel ternary material is coated with a layer of polycrystalline nano-ternary material, and some white spots coated with alumina can also be seen on the polycrystalline nano-ternary material. Figure 4 It can be seen that the synthesized double-layer coated ternary material has obvious single-crystal particle characteristics.

[0107] Example 2

[0108] Step (1) is the same as in Example 1.

[0109] Step (2): Preparation of single-crystal high-nickel ternary materials

[0110] Battery-grade lithium hydroxide and commercially available batch-process synthesized single-crystal Ni with an average particle size of 3-5 μm were used. 0.9 Co 0.05 Mn 0.05 (OH)₂ precursor, nano-yttrium oxide, and nano-tungsten oxide were added to a high-speed mixer in a molar ratio of 1.03:0.996:0.0015:0.00033 and stirred at 800 rpm for 4 min, followed by high-speed stirring at 1800 rpm for 25 min. The mixture was then placed in a box furnace and sintered at 650°C for 3 h in an oxygen atmosphere, followed by sintering at 850°C for 16 h. After pulverization using a roller mill and an air jet mill, Li(Ni)₂ was obtained. 0.9 Co 0.05 Mn 0.05 ) 0.996 Y 0.003 W 0.001 The O2-shaped single-crystal high-nickel ternary material is shown.

[0111] Step (3): Preparation of polycrystalline ternary nanomaterials

[0112] Battery grade lithium hydroxide, precursor prepared in step (1) of Example 1, nano yttrium oxide and nano tungsten oxide were added into a high-speed mixer in a molar ratio of 1.03:0.996:0.0015:0.00033, stirred at a speed of 800 rpm for 4 min, then high-speed stirred at a speed of 1800 rpm for 25 min, then the mixed material was placed in a box furnace, sintered at 550°C for 3h under oxygen atmosphere, then the temperature was raised to 730°C for sintering for 12h, then the material was ground by a rotary wheel mill and pulverized by an air flow pulverizer, to obtain a polycrystalline nano ternary material represented by the chemical formula Li(Ni 0.9 Co 0.05 Mn 0.05 ) 0.996 Y 0.003 W 0.001 O2.

[0113] Step (4): preparation of single-layer coated material

[0114] The single-crystal high-nickel ternary material prepared in step (2) and the polycrystalline nano ternary material prepared in step (3) were mixed in a mechanical blender in a weight ratio of 200:1, then sintered at 720°C for 10h under oxygen atmosphere in a box furnace, and sieved after cooling to obtain a single-layer coated material.

[0115] Step (5): preparation of double-layer coated ternary material

[0116] The single-layer coated material prepared in step (4) and boron oxide were added into a high-speed mixer in a weight ratio of 1:0.004, stirred at a speed of 800 rpm for 5 min, then stirred at a speed of 1800 rpm for 25 min, then aluminum oxide was added into the high-speed mixer so that the weight ratio of aluminum oxide to single-layer coated material was 0.002:1, the weight ratio of single-layer coated material to modified compound (boron oxide and aluminum oxide) was 167:1, and the weight ratio of element B to element Al was 1:0.88; stirred at a speed of 800 rpm for 5 min, then stirred at a speed of 1800 rpm for 25 min, and the mixed material was placed in a box furnace and sintered at 380°C for 6h under oxygen atmosphere, and sieved after cooling to obtain a double-layer coated single-crystal high-nickel ternary material, denoted as NCM2.

[0117] Example 3

[0118] Step (1) is the same as Example 1.

[0119] Step (2): preparation of single-crystal high-nickel ternary material

[0120] Battery grade lithium hydroxide, single-crystal Ni 0.9 Co 0.05 Mn0.05 (OH)2 precursor, nano-strontium carbonate and nano-aluminum hydroxide were added into a high-speed mixer in a molar ratio of 1.05:0.993:0.003:0.004, stirred at a speed of 800 rpm for 4 min, then high-speed stirred at a speed of 1800 rpm for 25 min, and then the mixed material was placed in a box furnace, sintered at 600°C for 2h under oxygen atmosphere, then heated to 800°C for 12h, then crushed by a roller mill and an air flow crusher, to obtain a single-crystal high-nickel ternary material represented by the chemical formula Li(Ni 0.9 Co 0.05 Mn 0.05 ) 0.993 Sr 0.003 Al 0.004 O2.

[0121] Step (3): Preparation of polycrystalline nano ternary material

[0122] Battery-grade lithium hydroxide, the precursor prepared in step (1) of Example 1, nano-strontium carbonate and nano-aluminum hydroxide were added into a high-speed mixer in a molar ratio of 1.03:0.993:0.003:0.004, stirred at a speed of 800 rpm for 4 min, then high-speed stirred at a speed of 1800 rpm for 25 min, and then the mixed material was placed in a box furnace, sintered at 520°C for 2h under oxygen atmosphere, then heated to 710°C for 10h, then crushed by a rotary wheel mill and an air flow crusher, to obtain a polycrystalline nano ternary material represented by the chemical formula Li(Ni 0.9 Co 0.05 Mn 0.05 ) 0.993 Sr 0.003 Al 0.004 O2.

[0123] Step (4): Preparation of single-layer coated material

[0124] The single-crystal high-nickel ternary material prepared in step (2) and the polycrystalline nano ternary material prepared in step (3) were mixed in a mechanical blender in a weight ratio of 300:1, then sintered at 650°C for 10h under oxygen atmosphere in a box furnace, and then sieved after cooling, to obtain a single-layer coated material.

[0125] Step (5): Preparation of double-layer coated single-crystal high-nickel ternary material

[0126] The single-layer coated material prepared in step (4) and LiBO2 were added into a high-speed mixer at a weight ratio of 1:0.003, stirred at a speed of 800 rpm for 5 min, and then stirred at a speed of 1800 rpm for 25 min. Then, LiAlO2 was added into the high-speed mixer, so that the weight ratio of LiAlO2 to the single-layer coated material was 0.003:1, the weight ratio of the single-layer coated material to the modified compound (LiBO2 and LiAlO2) was 167:1, and the weight ratio of B element to Al element was 1:1.92. The mixture was stirred at a speed of 800 rpm for 5 min, and then stirred at a speed of 1800 rpm for 25 min. The mixed material was placed in a box furnace and sintered at 450°C for 6 h in an oxygen atmosphere. After cooling, the sintered material was sieved to obtain a double-layer coated single-crystal high-nickel ternary material, denoted as NCM3.

[0127] Example 4

[0128] Steps (1)-(4) were the same as the corresponding steps in Example 3.

[0129] Step (5): Preparation of a double-layer coated ternary material

[0130] The single-layer coated material prepared in step (4) of Example 3 and Li2B4O7 were added into a high-speed mixer at a weight ratio of 1:0.002, stirred at a speed of 800 rpm for 5 min, and then stirred at a speed of 1800 rpm for 25 min. Then, Li2Al4O7 was added into the high-speed mixer, so that the weight ratio of Li2Al4O7 to the single-layer coated material was 0.004:1, the weight ratio of the single-layer coated material to the modified compound (Li2B4O7 and Li2Al4O7) was 167:1, and the weight ratio of B element to Al element was 1:3.63. The mixture was stirred at a speed of 800 rpm for 5 min, and then stirred at a speed of 1800 rpm for 25 min. The mixed material was placed in a box furnace and sintered at 400°C for 5 h in an oxygen atmosphere. After cooling, the sintered material was sieved to obtain a double-layer coated ternary material, denoted as NCM4.

[0131] Example 5

[0132] A double-layer coated ternary material was prepared according to the method of Example 1, except that boric acid and pseudo-boehmite were simultaneously coated on the surface of the single-layer coated material.

[0133] Specifically, step (5) is: the single-layer coated material prepared in step (4) of Example 1, boric acid and pseudo-boehmite are added into a high-speed mixer at a weight ratio of 1:0.003:0.0015, stirred at a speed of 800 rpm for 5 min, and then stirred at a speed of 1800 rpm for 25 min, and the mixed material is placed in a box furnace and sintered at 350°C for 5h under an oxygen atmosphere, and after cooling, sieving is performed to obtain a double-layer coated ternary material, denoted as NCM5.

[0134] Example 6

[0135] The double-layer coated ternary material is prepared according to the method of Example 1, except that in step (4), “the single-crystal high-nickel ternary material prepared in step (2) and the polycrystal nano ternary material prepared in step (3) are replaced with a weight ratio of 10:1” is used instead of “the single-crystal high-nickel ternary material prepared in step (2) and the polycrystal nano ternary material prepared in step (3) are replaced with a weight ratio of 100:1”.

[0136] Finally, a double-layer coated ternary material is obtained, denoted as NCM6.

[0137] Example 7

[0138] The double-layer coated ternary material is prepared according to the method of Example 1, except that in step (5), “the single-layer coated material prepared in step (4) and boric acid are replaced with a weight ratio of 1:0.011” is used instead of “the single-layer coated material prepared in step (4) and boric acid are replaced with a weight ratio of 1:0.003”, and “the weight ratio of the single-layer coated material and the modified compound (boric acid and pseudo-boehmite) is 80:1, and the weight ratio of B element and Al element is 1:0.35” is used instead of “the weight ratio of the single-layer coated material and the modified compound (boric acid and pseudo-boehmite) is 222:1, and the weight ratio of B element and Al element is 1:1.3”.

[0139] Finally, a double-layer coated ternary material is obtained, denoted as NCM7.

[0140] Example 8

[0141] The double-layer coated ternary material is prepared according to the method of Example 1, except that in step (5), “the weight ratio of pseudo-boehmite to single-layer coated material is 0.0065:1, the weight ratio of single-layer coated material and modified compound (boric acid and pseudo-boehmite) is 105:1, and the weight ratio of B element and Al element is 1:5.5” is used instead of “the weight ratio of pseudo-boehmite to single-layer coated material is 0.0015:1, the weight ratio of single-layer coated material and modified compound (boric acid and pseudo-boehmite) is 222:1, and the weight ratio of B element and Al element is 1:1.3”.

[0142] Finally, a double-layer coated ternary material is obtained, denoted as NCM8.

[0143] Comparative Example 1

[0144] A single-crystal high-nickel ternary material is prepared according to the method of Example 1 (i.e., only step (2) of Example 1, without coating the polycrystalline nano ternary material and the modifying compound comprising a B-containing compound and an Al-containing compound).

[0145] A single-crystal high-nickel ternary material represented by the chemical formula Li(Ni 0.9 Co 0.05 Mn 0.05 ) 0.995 Zr 0.003 Ta 0.002 O2 is obtained, denoted as NCM-D1.

[0146] Comparative Example 2

[0147] A single-crystal high-nickel ternary material is prepared according to the method of Example 1 (i.e., only step (2) of Example 1), and a modifying compound is coated outside the single-crystal high-nickel ternary material, but a polycrystalline nano ternary material is not coated. Specifically, the single-crystal high-nickel ternary material prepared in step (2) is added to a high-speed mixer with boric acid at a weight ratio of 1:0.003, stirred at a speed of 800 rpm for 5 min, then stirred at a speed of 1800 rpm for 25 min, then pseudo-boehmite is added to the high-speed mixer so that the weight ratio of pseudo-boehmite to single-crystal high-nickel ternary material is 0.0015:1, stirred at a speed of 800 rpm for 5 min, then stirred at a speed of 1800 rpm for 25 min, and the mixed material is placed in a box furnace and sintered at 350°C for 5 h in an oxygen atmosphere, cooled and sieved to obtain a single-layer coated material, denoted as NCM-D2. Figure 5 and Figure 6 It can be seen that the obtained single-layer coated material is in the form of single-crystal particles as a whole, and the surface has obvious island-shaped coating.

[0148] Comparative Example 3

[0149] A single-layer coated material is prepared according to the method of steps (1)-(4) in Example 1, denoted as NCM-D3.

[0150] That is, a single-crystal high-nickel ternary material is prepared, and a polycrystalline nano ternary material is coated outside the single-crystal high-nickel ternary material, but a modifying compound is not coated.

[0151] The product parameters of NCM1-NCM8 prepared in the above examples and NCM-D1, NCM-D2 and NCM-D3 prepared in the comparative examples are shown in Table 1.

[0152] Table 1

[0153]

[0154]

[0155] Note: In Table 1, the first coating layer is a polycrystalline nano ternary material, and the second coating layer is a modified compound; the B content and the Al content are based on the total weight of the double-coated ternary material; the particle size of the single-crystal high-nickel ternary material and the polycrystalline nano ternary material both refer to the average primary particle size.

[0156] Test Example 1: Test of the compaction density of the electrode sheet

[0157] The NCM1-NCM8 prepared in the above examples and the NCM-D1, NCM-D2 and NCM-D3 prepared in the comparative examples were used as the positive electrode material to prepare samples, and the three materials were mixed in a mass ratio of positive electrode material: conductive agent: PVDF = 100:2.5:2.5, wherein PVDF was a PVDF / NMP solution with a concentration of 5wt%, and the conductive agent was Super-P and carbon nanotubes. After mixing, the slurry was sieved through a 200-mesh screen, and then coated on a smooth aluminum foil on a coating machine. The coated sample was dried in a 120°C oven, and then 10 pieces of positive electrode small discs with a diameter of d = 15mm and corresponding aluminum foil small discs were cut out using a sampler. The average weight of the electrode sheet m1 and the average weight of the aluminum foil m2 were measured and calculated. The electrode sheet was cut into a long strip with a width of 10cm, and then roll-pressed into a shape using a pressure of 2MPa on a roll press. The thickness of the electrode sheet after compaction a1 and the thickness of the aluminum foil a2 were measured using a vernier caliper, and the compaction density was calculated as (m1-m2) ÷ [π(d / 2) 2 (a1-a2)]. The results are shown in Table 2.

[0158] Test Example 2: Test of the battery performance

[0159] The NCM1-NCM8 prepared in the above examples and the NCM-D1, NCM-D2 and NCM-D3 prepared in the comparative examples were used as the positive electrode material to prepare samples, and the three materials were mixed in a mass ratio of positive electrode material: conductive agent: PVDF = 100:2.5:2.5, wherein PVDF was a PVDF / NMP solution with a concentration of 5wt%, and the conductive agent was Super-P and carbon nanotubes. After mixing, the slurry was sieved through a 200-mesh screen, and then coated on a smooth aluminum foil on a coating machine. The coated sample was dried in a 120°C oven, and then 10 pieces of positive electrode small discs with a diameter of d = 15mm and corresponding aluminum foil small discs were cut out using a sampler. The average weight of the electrode sheet m1 and the average weight of the aluminum foil m2 were measured and calculated. The electrode sheet was cut into a long strip with a width of 10cm, and then roll-pressed into a shape using a pressure of 2MPa on a roll press. The thickness of the electrode sheet after compaction a1 and the thickness of the aluminum foil a2 were measured using a vernier caliper, and the compaction density was calculated as (m1-m2) ÷ [π(d / 2) 2 (a1-a2)]. The results are shown in Table 2.

[0160] Table 2

[0161]

[0162] From the results of Table 2, it can be seen that the compacted density of the pole piece prepared from the double-layer coated ternary material of Examples 1-8 has no obvious change compared with the compacted density of the pole piece prepared from the single crystal high-nickel ternary material of Comparative Example 1, but the first cycle charge-discharge specific capacity, initial efficiency, 1C / 0.1C capacity retention rate, room temperature cycle performance and 45°C high temperature cycle performance of the battery prepared from the double-layer coated ternary material of Examples 1-8 have a great improvement compared with the original single crystal; the comparison data of Example 1 and Comparative Example 2 show that the single-layer coated material NCM-D2 of Comparative Example 2 has not been coated by the first layer of nano ternary material, and the first cycle charge-discharge specific capacity and initial efficiency of the battery prepared therefrom are relatively low, but the cycle performance is slightly better; the comparison data of Example 1 and Comparative Example 3 show that the single-layer coated material NCM-D3 of Comparative Example 3 has not been coated by the second layer of B-containing compound and Al-containing compound, and the first cycle charge-discharge specific capacity and initial efficiency of the battery prepared therefrom are also lower, and the cycle performance is much worse. In addition, the comparison data of Example 1 and Example 5 show that the first cycle charge-discharge specific capacity of the former is higher when the B-containing compound and the Al-containing compound are mixed first and then mixed with the first coating product, compared with the case where the two are mixed together with the first coating product, because the main role in improving the capacity is the compound Li x B y O z If the two are mixed at the same time, the surface of the single-layer coated material LiNi a Co b Mn c M d O2@nano LiNi a Co b Mn c M d O2 will be competed by the two, which will cause a part of the B-containing compound to be attached to the surface of the Al-containing compound, and thus cannot play a role in improving the capacity, resulting in a lower capacity, while when the B-containing compound is mixed first, due to the hydrogen bond and intermolecular force, the B-containing compound can react with LiOH and Li2CO3 on the surface at room temperature and be attached to the surface of the single-layer coated material, and then coated by the Al-containing compound to improve the cycle performance of the material. From Figure 7 and Figure 8 It can be seen that H3BO3 can react with LiOH or Li2CO3 to generate lithium-containing compounds such as lithium tetraborate or lithium pentaborate at room temperature.

[0163] The data comparison of Example 1 and Example 6 shows that when the thickness of the nano ternary material layer is too thick, although the rate performance and capacity of the prepared battery are better, the proportion of polycrystalline material increases, the anisotropy brings higher internal stress, the side reaction increases in the cycle process, and the normal temperature cycle and high temperature cycle decrease obviously. The data comparison of Example 1 and Example 7 and 8 shows that when the content of B coating on the surface of the double-layer coated material increases, the discharge specific capacity and the initial efficiency of the prepared battery are better, but when the content of B increases, it will be precipitated in the negative electrode during the cycle, and the normal temperature and high temperature cycle performance decreases; when the content of Al coating on the surface of the double-layer coated material increases, the capacity and the initial efficiency of the prepared battery are sacrificed, but the normal temperature cycle and high temperature cycle are greatly improved.

[0164] The above describes the preferred embodiments of the present application in detail, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as disclosed by the present application and belong to the protection scope of the present application.

Claims

1. A double-layer coated ternary material, characterized in that, The double-layer coated ternary material includes a single-crystal high-nickel ternary material and a polycrystalline nano-ternary material layer coated on the single-crystal high-nickel ternary material, as well as a modified compound layer coated on the polycrystalline nano-ternary material layer; wherein the modified compound layer includes a B-containing compound and an Al-containing compound.

2. The double-layer coated ternary material according to claim 1, characterized in that, The single-crystal high-nickel ternary material is chemically formulated as LiNi. a Co b Mn c M d The compound represented by O2; wherein 0.8≤a≤0.98, 0≤b≤0.1, 0.02≤c≤0.2, 0≤d≤0.005, a+b+c+d=1, and M is selected from at least one of B, Mg, Al, Ca, Ti, V, Sr, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Ba, La, Ce, Ta and W.

3. The double-layer coated ternary material according to claim 1, characterized in that, The polycrystalline nano-ternary material layer includes a polycrystalline nano-ternary material, which is chemically formulated as LiNi. t Co q Mn s E f The compound represented by O2; wherein 0.5≤t≤0.98; 0≤q≤0.2; 0.02≤s≤0.3; 0≤f≤0.01; t+q+s+f=1, and E is selected from at least one of B, Mg, Al, Ca, Ti, V, Sr, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Ba, La, Ce, Ta and W.

4. The double-layer coated ternary material according to claim 3, characterized in that, The polycrystalline nano-ternary material is chemically formulated as LiNi. t Co q Mn s E f The compound shown in O2; wherein, 0.8≤t≤0.98; 0≤q≤0.1; 0.02≤s≤0.2; 0≤f≤0.

005.

5. The double-layer coated ternary material according to any one of claims 1-4, characterized in that, The average particle size of the double-layer coated ternary material is 0.5-11 μm.

6. The double-layer coated ternary material according to any one of claims 1-4, characterized in that, The average particle size of the single-crystal high-nickel ternary material is 0.5-10 μm.

7. The double-layer coated ternary material according to claim 6, characterized in that, The average particle size of the single-crystal high-nickel ternary material is 2-6 μm.

8. The double-layer coated ternary material according to any one of claims 1-4, characterized in that, The thickness of the polycrystalline ternary nanomaterial layer is 2-200 nm.

9. The double-layer coated ternary material according to claim 8, characterized in that, The thickness of the polycrystalline nano-ternary material layer is 5-100 nm.

10. The double-layer coated ternary material according to any one of claims 1-4, characterized in that, Based on the total weight of the double-layer coated ternary material, the modified compound layer contains 100-2000 ppm of B element and 100-3000 ppm of Al element.

11. The double-layer coated ternary material according to claim 10, characterized in that, Based on the total weight of the double-layer coated ternary material, the modified compound layer contains 300-1500 ppm of B element and 500-2000 ppm of Al element.

12. A method for preparing a double-layer coated ternary material, characterized in that, The preparation method includes the following steps: (1) After mixing single-crystal high-nickel ternary material and polycrystalline nano ternary material, a first sintering is performed to obtain a single-layer coating material; (2) The single-layer coating material is mixed with the modified compound and then subjected to a second sintering to obtain the double-layer coated ternary material; wherein the modified compound includes a B-containing compound and an Al-containing compound.

13. The preparation method according to claim 12, characterized in that, The average particle size of the single-crystal high-nickel ternary material is 0.5-10 μm.

14. The preparation method according to claim 13, characterized in that, The average particle size of the single-crystal high-nickel ternary material is 2-6 μm.

15. The preparation method according to claim 12, characterized in that, The average particle size of the polycrystalline ternary nanomaterial is 10-50 nm.

16. The preparation method according to claim 12, characterized in that, In step (1), the single-crystal high-nickel ternary material and the polycrystalline nano ternary material are mixed at a weight ratio of (20-500):

1.

17. The preparation method according to claim 12, characterized in that, In step (2), the B-containing compound is calculated as B element, the Al-containing compound is calculated as Al element, and the weight ratio of the B-containing compound to the Al-containing compound in the modified compound is 1:(0.1-5).

18. The preparation method according to claim 12, characterized in that, The B-containing compound is selected from at least one of B2O3, H3BO3, LiBO2, and Li2B4O7.

19. The preparation method according to claim 12, characterized in that, The Al-containing compound is selected from at least one of Al2O3, boehmite, boehmite, LiAlO2, aluminum hydroxide, and Li2Al4O7.

20. The preparation method according to claim 12, characterized in that, In step (2), the monolayer coating material and the modified compound are mixed at a weight ratio of (100-1000):

1.

21. The preparation method according to any one of claims 12-20, characterized in that, The first sintering temperature is 600-780℃, and the time is 2-12h.

22. The preparation method according to claim 21, characterized in that, The second sintering temperature is 200-500℃, and the time is 2-8h.

23. The preparation method according to any one of claims 12-20, characterized in that, In step (2), the single-layer coating material is first mixed with the B-containing compound, then mixed with the Al-containing compound, and then the second sintering is performed.

24. The preparation method according to any one of claims 12-20, characterized in that, The preparation method of the single-crystal high-nickel ternary material includes the following steps: mixing the single-crystal high-nickel ternary material precursor, lithium source 1 and dopant 1, and then performing a third sintering and a first pulverization to obtain the single-crystal high-nickel ternary material; wherein, the dopant 1 is an oxide of metal M and / or a hydroxide of metal M; M is selected from at least one of B, Mg, Al, Ca, Ti, V, Sr, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Ba, La, Ce, Ta and W.

25. The preparation method according to any one of claims 12-20, characterized in that, The preparation method of the polycrystalline ternary nanomaterial includes: mixing the polycrystalline ternary nanomaterial precursor, lithium source 2 and dopant 2, and then performing a fourth sintering and a second pulverization to obtain the polycrystalline ternary nanomaterial; wherein, the dopant 2 is an oxide of metal E and / or a hydroxide of metal E; E is selected from at least one of B, Mg, Al, Ca, Ti, V, Sr, Y, Zr, Nb, Mo, Ag, In, Sn, Sb, Ba, La, Ce, Ta and W.

26. A double-layer coated ternary material prepared by the preparation method according to any one of claims 12-25.

27. A positive electrode sheet, characterized in that, The positive electrode sheet comprises the double-layer coated ternary material as described in any one of claims 1-11 and 26.

28. A lithium-ion battery, characterized in that, The lithium-ion battery comprises the positive electrode sheet as described in claim 27.

29. The lithium-ion battery according to claim 28, characterized in that, The lithium-ion battery has a 0.1C charging specific capacity of 235 mAh / g or higher, a 0.1C discharging specific capacity of 210 mAh / g or higher, a 1C / 0.1C capacity retention rate of 90% or higher, a capacity retention rate of 90% or higher after 100 cycles at room temperature, and a capacity retention rate of 85% or higher after 100 cycles at 45℃.

30. The lithium-ion battery according to claim 29, characterized in that, The lithium-ion battery has a 0.1C charging specific capacity of 240mAh / g or higher, a 0.1C discharging specific capacity of 220mAh / g or higher, a 1C / 0.1C capacity retention rate of 90% or higher, a capacity retention rate of 95% or higher after 100 cycles at room temperature, and a capacity retention rate of 90% or higher after 100 cycles at 45℃.

31. An electrical appliance, characterized in that, The electrical device comprises a lithium-ion battery as described in any one of claims 28-30.

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