A ternary cathode material, a preparation method thereof, a cathode sheet and a battery

Abstract

The present invention discloses a ternary cathode material, a preparation method thereof, a cathode sheet and a battery, relating to the technical field of batteries; the ternary cathode material includes a lithium nickel cobalt manganese oxide substrate, an iron phosphate coating layer and a boron coating layer; the iron phosphate coating layer is coated on the outer peripheral side of the lithium nickel cobalt manganese oxide substrate; the boron coating layer is coated on the outer peripheral side of the iron phosphate coating layer, and the boron coating layer penetrates into the pores of the iron phosphate coating layer to bind to the outer surface of the lithium nickel cobalt manganese oxide substrate. On the one hand, the iron phosphate coating layer can reduce the direct contact between the substrate and the electrolyte and improve the cycling performance of the substrate; the boron coating layer can fill the pores of the iron phosphate coating layer, further prevent the electrolyte from contacting the substrate and improve the cycling performance of the substrate; on the other hand, the combination of the boron coating layer and the substrate can improve the bonding strength between the iron phosphate coating layer and the substrate, and boron has excellent conductivity, which can form a conductive network after filling the pores and fully improve the stability of the iron phosphate coating layer.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and more particularly, to a ternary cathode material, a preparation method thereof, a cathode sheet, and a battery. Background Art

[0002] For ternary cathode materials, especially high-nickel cathode materials, their cycling performance is poor. Generally, surface coating is used to protect their surfaces to avoid direct contact between the electrolyte and the cathode material, so as to improve the cycling performance. However, some existing coating layers, such as those prepared by the coprecipitation method, have poor binding performance and are prone to peeling off during cycling. Therefore, there is currently a lack of a ternary cathode material that can both ensure cycling performance and the binding strength of the coating layer.

[0003] In view of this, the present invention is specifically proposed. Summary of the Invention

[0004] The purpose of the present invention is to provide a ternary cathode material that can both ensure cycling performance and the binding strength of the coating layer, as well as a preparation method thereof.

[0005] The present invention also aims to provide a cathode sheet and a battery, which include the above-mentioned ternary cathode material. Therefore, they have the advantage of excellent cycling performance.

[0006] The embodiments of the present invention are implemented as follows:

[0007] In a first aspect, the present invention provides a ternary cathode material, including:

[0008] Lithium nickel cobalt manganese oxide substrate;

[0009] An iron phosphate coating layer, coated on the outer peripheral side of the lithium nickel cobalt manganese oxide substrate;

[0010] A boron coating layer, coated on the outer peripheral side of the iron phosphate coating layer, and a part of the boron coating layer penetrates through the pores of the iron phosphate coating layer to bind to the outer surface of the lithium nickel cobalt manganese oxide substrate.

[0011] In an alternative embodiment, the mass of the iron phosphate coating layer accounts for 0.5 - 5% of the total mass of the ternary cathode material.

[0012] In an alternative embodiment, the mass of the boron coating layer accounts for 0.5 - 5% of the total mass of the ternary cathode material.

[0013] In a second aspect, the present invention provides a preparation method of the ternary cathode material according to any one of the foregoing embodiments, including:

[0014] Mixing a suspension containing the lithium nickel cobalt manganese oxide substrate with an iron phosphate solution, and performing a first sintering after drying to form an iron phosphate coating layer on the outer peripheral side of the lithium nickel cobalt manganese oxide substrate;

[0015] Mix a boron source with a lithium nickel cobalt manganese phosphate substrate coated with an iron phosphate coating layer, and perform secondary sintering to form a boron coating layer on the outer peripheral side of the iron phosphate coating layer, and allow a part of the boron coating layer to penetrate through the pores of the iron phosphate coating layer to combine with the outer surface of the lithium nickel cobalt manganese phosphate substrate.

[0016] In an alternative embodiment, the suspension is obtained by dispersing the lithium nickel cobalt manganese phosphate substrate in a first solvent. The first solvent includes an organic solvent or water.

[0017] The iron phosphate solution is obtained by dispersing an iron source and a phosphorus source together in a second solvent. The second solvent includes water.

[0018] In an alternative embodiment, the iron source includes an iron salt soluble in water; and / or, the phosphorus source includes at least one of phosphoric acid and a phosphorus salt soluble in water; and / or, the boron source includes at least one of boron oxide, boric acid, and borate.

[0019] In an alternative embodiment, in the iron phosphate solution, the iron ion concentration is 0.05 - 2.5 mol / L, and the phosphate radical is 0.05 - 2.5 mol / L.

[0020] In an alternative embodiment, the drying temperature is 100 - 250 °C, and the drying time is 4 - 6 h; and / or, the sintering temperature of the first sintering is 400 - 800 °C, the sintering time is 6 - 12 h, and the sintering environment is a pure oxygen environment; and / or, the sintering temperature of the second sintering is 700 - 800 °C, the sintering time is 4 - 8 h, and the sintering environment is a pure oxygen environment.

[0021] In a third aspect, the present invention provides a positive electrode sheet, including:

[0022] A positive electrode current collector;

[0023] A positive electrode active material layer, which is obtained by coating a positive electrode active material slurry on at least one side of the positive electrode current collector; the positive electrode active material slurry includes the ternary positive electrode material according to any one of the foregoing embodiments.

[0024] In a fourth aspect, the present invention provides a battery, including the positive electrode sheet according to the foregoing embodiment.

[0025] The embodiments of the present invention have at least the following advantages or beneficial effects:

[0026] The embodiments of the present invention provide a ternary positive electrode material, which includes a lithium nickel cobalt manganese phosphate substrate, an iron phosphate coating layer, and a boron coating layer; the iron phosphate coating layer is coated on the outer peripheral side of the lithium nickel cobalt manganese phosphate substrate; the boron coating layer is coated on the outer peripheral side of the iron phosphate coating layer, and a part of the boron coating layer penetrates through the pores of the iron phosphate coating layer to combine with the outer surface of the lithium nickel cobalt manganese phosphate substrate.

[0027] On the one hand, through the setting of the iron phosphate coating layer, the direct contact between the substrate and the electrolyte can be reduced, and the cycle performance of the substrate can be improved; at the same time, through the setting of the boron coating layer, the pores of the iron phosphate coating layer can be filled to further prevent the electrolyte from contacting the substrate and further improve the cycle performance of the substrate; on the other hand, after the boron coating layer penetrates through the pores of the iron phosphate coating layer and combines with the outer surface of the substrate, the bonding strength between the iron phosphate coating layer and the substrate can be improved, and the excellent conductivity of boron can be utilized to form a conductive network after filling the pores of the iron phosphate coating layer, fully improving the stability of the iron phosphate coating layer and fully ensuring the cycle performance of the substrate.

[0028] An embodiment of the present invention provides a method for preparing a ternary cathode material. First, through the precipitation method, an iron phosphate coating layer can be formed on the surface of the substrate, which can reduce the direct contact between the substrate and the electrolyte and improve the cycle performance of the substrate; the method can also coat a boron coating layer on the outer peripheral side of the iron phosphate coating layer through the solid-phase method, and part of the boron coating layer can fill the pores and penetrate through the pores to combine with the outer surface of the substrate. Therefore, it can further prevent the electrolyte from contacting the substrate, improve the cycle performance of the substrate, and also improve the bonding strength between the iron phosphate coating layer and the substrate. In addition, the excellent conductivity of boron can be utilized to form a conductive network after filling the pores of the iron phosphate coating layer, fully improving the stability of the iron phosphate coating layer and fully ensuring the cycle performance of the substrate.

[0029] An embodiment of the present invention also provides a positive electrode sheet and a battery, which include the above-mentioned ternary cathode material. Therefore, it has the advantage of excellent cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can be obtained based on these drawings without creative efforts.

[0031] Figure 1 It is a SEM diagram of the ternary cathode material provided in Embodiment 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Those not specified in the embodiments are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer are all conventional products that can be obtained through commercial purchase.

[0033] The features and performance of the present invention will be further described in detail below in conjunction with the embodiments.

[0034] An embodiment of the present invention provides a ternary cathode material, which includes a lithium nickel cobalt manganese oxide substrate, an iron phosphate coating layer, and a boron coating layer. Specifically, the iron phosphate coating layer coats the outer peripheral side of the lithium nickel cobalt manganese oxide substrate. The boron coating layer coats the outer peripheral side of the iron phosphate coating layer, and a part of the boron coating layer penetrates through the pores of the iron phosphate coating layer to combine with the outer surface of the lithium nickel cobalt manganese oxide substrate.

[0035] On the one hand, through the setting of the iron phosphate coating layer, the direct contact between the substrate and the electrolyte can be reduced, and the cycle performance of the substrate can be improved; at the same time, through the setting of the boron coating layer, the pores of the iron phosphate coating layer can be filled to further prevent the electrolyte from contacting the substrate and further improve the cycle performance of the substrate; on the other hand, after the boron coating layer penetrates through the pores of the iron phosphate coating layer and combines with the outer surface of the substrate, the bonding strength between the iron phosphate coating layer and the substrate can be improved, and the excellent conductivity of boron can be utilized to form a conductive network after filling the pores of the iron phosphate coating layer, fully improving the stability of the iron phosphate coating layer and fully ensuring the cycle performance of the substrate.

[0036] It should be noted that in the embodiment of the present invention, the mass of the iron phosphate coating layer accounts for 0.5-5% of the total mass of the ternary cathode material. That is, the coating amount of the iron phosphate coating layer is 0.5-5%. By limiting the coating amount of the iron phosphate coating layer, on the one hand, the contact between the electrolyte and the substrate can be blocked to a certain extent, improving the cycle performance of the substrate; on the other hand, it is also convenient for a part of the boron coating layer to fill the pores and penetrate through the pores to combine with the substrate, so as to improve the bonding strength between the iron phosphate coating layer and the substrate and fully improve the cycle performance of the substrate.

[0037] It should also be noted that in this embodiment, the mass of the boron coating layer accounts for 0.5-5% of the total mass of the ternary cathode material. By limiting the coating amount of the iron phosphate coating layer and the coating amount of the boron coating layer, both the cycle performance of the substrate and the bonding strength and stability between the iron phosphate coating layer and the substrate can be ensured, fully improving the use performance of the substrate and improving the use performance of the battery.

[0038] The embodiment of the present invention also provides a preparation method of the ternary cathode material with the above structure, which includes:

[0039] S1: Mix a suspension containing a lithium nickel cobalt manganese oxide substrate with an iron phosphate solution, and perform a first sintering after drying to form an iron phosphate coating layer on the outer peripheral side of the lithium nickel cobalt manganese oxide substrate;

[0040] S2: Mix a boron source with the lithium nickel cobalt manganese oxide substrate coated with the iron phosphate coating layer, and perform a second sintering to form a boron coating layer on the outer peripheral side of the iron phosphate coating layer, and make a part of the boron coating layer fill the pores and penetrate through the pores to combine with the outer surface of the lithium nickel cobalt manganese oxide substrate.

[0041] Specifically, in step S1, the suspension is obtained by dispersing lithium nickel cobalt manganese oxide substrate in a first solvent. The dispersion process can be carried out in a stirrer, and the first solvent includes an organic solvent or water. The iron phosphate solution is obtained by dispersing an iron source and a phosphorus source in a second solvent. The dispersion process can also be carried out in a stirrer, and the second solvent includes water. At the same time, the iron source can be selected as an iron salt soluble in water. Exemplarily, iron nitrate, iron chloride, etc. can be selected. The phosphorus source includes at least one of phosphoric acid and a phosphorus salt soluble in water. Exemplarily, either phosphoric acid or a phosphorus salt soluble in water such as sodium phosphate or diammonium hydrogen phosphate can be selected. After mixing the suspension and the iron phosphate solution, the first sintering is carried out. A ferric phosphate coating layer can be formed on the surface of the substrate by the precipitation method, which can reduce the direct contact between the substrate and the electrolyte and improve the cycling performance of the substrate. At the same time, by the coprecipitation method, the ferric phosphate coating layer is formed in a porous state.

[0042] As an alternative solution, in the embodiment of the present invention, in the iron phosphate solution, the iron ion concentration is 0.05 - 2.5 mol / L, and the phosphate radical is 0.05 - 2.5 mol / L. By controlling the concentrations of iron ions and phosphate ions, it can be ensured that the ferric phosphate coating layer formed after the sintering operation can form multiple pores in structure, so as to facilitate the infiltration of the boron coating layer through the pores, ensure the bonding strength between the ferric phosphate coating layer and the substrate, and ensure the cycling performance of the substrate.

[0043] Furthermore, the drying temperature is 100 - 250 °C, and the drying time is 4 - 6 h. As the drying temperature increases, the drying time decreases accordingly and can be adjusted according to requirements. At the same time, the sintering temperature of the first sintering is 400 - 800 °C, the sintering time is 6 - 12 h, and the sintering environment is a pure oxygen environment. As the sintering temperature increases, the sintering time also correspondingly decreases. By selecting the drying and sintering temperatures, times, and environments, on the one hand, the operation efficiency can be ensured, and the formation efficiency and quality of the ferric phosphate coating layer can be guaranteed; on the other hand, the formation of pores in the ferric phosphate coating layer can be ensured, so as to facilitate the infiltration of the boron source during the boron source coating process, further improve the bonding strength between the ferric phosphate coating layer and the substrate, and at the same time improve the stability of the ferric phosphate coating layer to improve the cycling performance of the substrate.

[0044] In step S2, the boron source can be selected from boron oxide, boric acid or borate. The method of mixing the boron source with the lithium nickel cobalt manganese oxide substrate coated with a iron phosphate coating is to mix them using a ball mill, which can improve the particle uniformity. After mixing, secondary sintering can form a boron coating on the outer peripheral side of the iron phosphate coating by the solid-phase method, and part of the boron coating can fill the pores and penetrate through the pores to bond with the outer surface of the lithium nickel cobalt manganese oxide substrate. By coating the boron coating on the outer peripheral side of the iron phosphate coating by the solid-phase method, and making part of the boron coating fill the pores and penetrate through the pores to bond with the substrate outer surface, it can not only further prevent the electrolyte from contacting the substrate, improve the cycling performance of the substrate, but also improve the bonding strength between the iron phosphate coating and the substrate. Moreover, the excellent conductivity of boron can be utilized to form a conductive network after filling the pores of the iron phosphate coating, fully improving the stability of the iron phosphate coating and fully ensuring the cycling performance of the substrate.

[0045] As an alternative solution, in the embodiment of the present invention, the sintering temperature of the second sintering is 700 - 800 °C, the sintering time is 4 - 8 h, and the sintering environment is a pure oxygen environment. The purpose of the second sintering is to coat the boron source by the solid-phase method to obtain a ternary material coated with both boron and iron phosphate. At the same time, by limiting the temperature, time and environment of the second sintering, on the one hand, it can ensure the coating quality of the boron coating, ensure that part of the boron coating can penetrate through the pores to bond with the substrate, so as to fully improve the bonding strength between the iron phosphate coating and the substrate and improve the cycling performance of the entire ternary cathode material; on the other hand, it can also ensure the uniformity when the boron coating penetrates into multiple pores, so as to ensure that a conductive network can be formed within the iron phosphate coating, fully improving the stability of the iron phosphate coating and further improving the cycling performance of the ternary cathode material.

[0046] The embodiment of the present invention also provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode active material layer. Among them, the positive electrode current collector can be selected as aluminum foil or a composite current collector. In the embodiment of the present invention, the description is made taking aluminum foil as an example. The positive electrode active material layer is obtained by drying after coating the positive electrode current collector on at least one side with a positive electrode active slurry. The positive electrode active slurry includes the above-mentioned ternary cathode material, and also includes a conductive agent, a binder and a solvent. Exemplarily, the conductive agent can be selected from acetylene black, carbon black, etc., the binder can be selected from polyvinylidene fluoride (PVDF), and the solvent can be selected from N-methylpyrrolidone. The mass ratio of the ternary cathode material, the conductive agent and the binder can be selected as (5 - 10):(0.1 - 1):(0.1 - 1). Exemplarily, it can be selected as 9.2:0.5:0.3. The drying temperature can be selected as 80 - 120 °C, and the drying time is 10 - 24 h.

[0047] This positive electrode sheet is prepared from the above-mentioned ternary cathode material. Therefore, this positive electrode sheet also has the characteristic of excellent cycling performance.

[0048] Embodiments of the present invention also provide a battery, which includes the above-mentioned positive electrode sheet, and further includes a housing, a negative electrode sheet, a separator, and an electrolyte. The positive electrode sheet, the separator, and the negative electrode sheet are stacked in sequence, and are laminated or wound to form an electrode core. After the electrode core is placed in the housing and the electrolyte is injected, the battery can be obtained. The battery can be a square lithium-ion battery, a cylindrical battery, or a button battery. Embodiments of the present invention will be described by taking the button battery as an example.

[0049] As an alternative solution, the negative electrode sheet can be selected as a metallic lithium sheet, or can be selected as a composite structure formed by a current collector and a negative electrode active layer. The active particles in the negative electrode active layer can be selected as graphite, etc. Embodiments of the present invention will be described by taking the metallic lithium sheet as an example. The separator can be selected as a PP material, or can be selected as a PE (polyethylene) material, or can be selected as a composite structure obtained by compounding a PP (polypropylene) material and a PE material. Embodiments of the present invention will be described by taking PP as an example. The electrolyte can be selected as a lithium hexafluorophosphate mixed solution, and is specifically selected as LiPF 6 -EC / DMC system, where EC is ethylene carbonate and DMC is dimethyl carbonate.

[0050] The battery includes the above-mentioned positive electrode sheet. Therefore, the battery also has the advantage of relatively high cycle performance.

[0051] The following will introduce the preparation process and cycle performance of the battery in detail with reference to examples and comparative examples:

[0052] Example 1

[0053] This example provides a battery, which is prepared by the following method:

[0054] S1: Prepare a ternary positive electrode material, and step S1 specifically includes:

[0055] S11: Take 5 g of lithium nickel cobalt manganese oxide substrate (LiNi 0.8 Co 0.10 Mn 0.10 O 2 ) and 20 mL of water and stir evenly in a stirrer to obtain a suspension containing the lithium nickel cobalt manganese oxide substrate;

[0056] S12: Weigh 0.18 g of ferric chloride hexahydrate and 0.076 g of diammonium hydrogen phosphate, dissolve them in 5 ml of water to obtain an iron-phosphorus solution, where the iron ion concentration is 0.88 mol / L and the phosphate ion concentration is 0.88 mol / L;

[0057] S13: Slowly mix the ferrophosphorus solution with the suspension. After mixing evenly, place it in an oven and dry at 160 °C for 4 h, and then place it in a roller hearth kiln and calcine at 700 °C in a pure oxygen atmosphere for 8 h to form a ferric phosphate coating layer on the outer peripheral side of the lithium nickel cobalt manganese oxide substrate;

[0058] S14: Mix 0.15 g of boron oxide with the lithium nickel cobalt manganese oxide substrate coated with the ferric phosphate coating layer, place it in a roller hearth kiln and calcine at 700 °C in a pure oxygen atmosphere for 6 h to form a boron coating layer on the outer peripheral side of the ferric phosphate coating layer, and make part of the boron coating layer fill the pores and penetrate through the pores to combine with the outer surface of the lithium nickel cobalt manganese oxide substrate. Its morphology is as Figure 1 shown. It can be seen that the surface of the secondary spherical ternary cathode material is wrapped with a uniform coating structure.

[0059] S2: Prepare the positive electrode sheet;

[0060] Step S2 specifically includes: Select aluminum foil as the positive electrode current collector, coat the positive electrode active paste on both sides of the aluminum foil, and after drying in a blast dryer at 80 °C for 8 h, vacuum dry at 120 °C for 12 h; among them, the positive electrode active paste includes the ternary cathode material prepared in step S1, and also includes a conductive agent, a binder and a solvent. The conductive agent is acetylene black, the binder is PVDF, the solvent is N-methylpyrrolidone, and the mass ratio of the ternary cathode material, the conductive agent and the binder is 9.2:0.5:0.3.

[0061] S3: Prepare the battery

[0062] Use a lithium metal sheet as the negative electrode sheet, use the structure prepared in S2 as the positive electrode sheet, use PP as the separator, and use 1M LiPF6-EC / DMC (1:1, v / v) as the electrolyte to assemble a 2032-type button battery in a glove box under argon protection.

[0063] Example 2

[0064] This example provides a battery, and the difference between its preparation method and the battery provided in Example 1 is that in Example 2, step S1 specifically includes:

[0065] S11: Take 5 g of lithium nickel cobalt manganese oxide substrate (LiNi 0.8 Co 0.10 Mn 0.10 O 2 ) and 20 mL of water and stir evenly in a stirrer to obtain a suspension containing the lithium nickel cobalt manganese oxide substrate;

[0066] S12: Weigh 0.36 g of ferric chloride hexahydrate and 0.152 g of diammonium hydrogen phosphate and dissolve them in 5 ml of water to obtain an iron phosphorus solution, in which the iron ion concentration is 0.22 mol / L and the phosphate ion concentration is 0.22 mol / L;

[0067] S13: Slowly mix the ferrophosphorus solution with the suspension. After mixing evenly, place it in an oven and dry at 160 °C for 4 h, and then place it in a roller hearth kiln and calcine at 700 °C in a pure oxygen atmosphere for 8 h to form a ferric phosphate coating layer on the outer peripheral side of the lithium nickel cobalt manganese oxide substrate;

[0068] S14: Mix the lithium nickel cobalt manganese oxide substrate coated with the ferric phosphate coating layer and 0.075 g of boron oxide evenly, place it in a roller hearth kiln and calcine at 700 °C in a pure oxygen atmosphere for 6 h to form a boron coating layer on the outer peripheral side of the ferric phosphate coating layer, and make part of the boron coating layer fill the pores and penetrate through the pores to combine with the outer surface of the lithium nickel cobalt manganese oxide substrate.

[0069] Example 3

[0070] This example provides a battery, the difference in the preparation method of the battery provided in this example from that in Example 1 is that in Example 3, step S1 specifically includes:

[0071] S11: Take 5 g of lithium nickel cobalt manganese oxide substrate (LiNi 0.8 Co 0.10 Mn 0.10 O 2 ) and 20 mL of water and stir evenly in a stirrer to obtain a suspension containing the lithium nickel cobalt manganese oxide substrate;

[0072] S12: Weigh 0.09 g of ferric chloride hexahydrate and 0.038 g of diammonium hydrogen phosphate and dissolve them in 5 ml of water to obtain an iron-phosphorus solution, where the iron ion concentration is 0.44 mol / L and the phosphate ion concentration is 0.44 mol / L;

[0073] S13: Slowly mix the ferrophosphorus solution with the suspension. After mixing evenly, place it in an oven and dry at 160 °C for 4 h, and then place it in a roller hearth kiln and calcine at 700 °C in a pure oxygen atmosphere for 8 h to form a ferric phosphate coating layer on the outer peripheral side of the lithium nickel cobalt manganese oxide substrate;

[0074] S14: Mix the lithium nickel cobalt manganese oxide substrate coated with the ferric phosphate coating layer and 0.3 g of boron oxide evenly, place it in a roller hearth kiln and calcine at 700 °C in a pure oxygen atmosphere for 6 h to form a boron coating layer on the outer peripheral side of the ferric phosphate coating layer, and make part of the boron coating layer fill the pores and penetrate through the pores to combine with the outer surface of the lithium nickel cobalt manganese oxide substrate.

[0075] Comparative Example 1

[0076] Comparative Example 1 provides a battery, the difference in the preparation method of the battery provided in Comparative Example 1 from that in Example 1 is that in Comparative Example 1, step S1 specifically includes:

[0077] S11: Take 5 g of lithium nickel cobalt manganese oxide substrate (LiNi 0.8 Co 0.10 Mn 0.10 O 2 ) and 20 mL of water, and stir them evenly in a stirrer to obtain a suspension containing the lithium nickel cobalt manganese oxide substrate;

[0078] S12: Weigh 0.18 g of ferric chloride hexahydrate and 0.076 g of diammonium hydrogen phosphate, dissolve them in 5 ml of water to obtain an iron-phosphorus solution, where the iron ion concentration is 0.88 mol / L and the phosphate ion concentration is 0.88 mol / L;

[0079] S13: Slowly mix the iron-phosphorus solution with the suspension. After mixing evenly, place it in an oven and dry it at 160 °C for 4 h, and then place it in a roller hearth kiln and calcine it at 700 °C in a pure oxygen atmosphere for 8 h to form an iron phosphate coating layer on the outer peripheral side of the lithium nickel cobalt manganese oxide substrate.

[0080] Comparative Example 2

[0081] Comparative Example 2 provides a battery, and the difference between its preparation method and the battery provided in Example 1 is that in Comparative Example 2, step S1 specifically includes:

[0082] S11: Take 5 g of lithium nickel cobalt manganese oxide substrate (LiNi 0.8 Co 0.10 Mn 0.10 O 2 ) and 0.15 g of boron oxide, mix them evenly, place them in a roller hearth kiln and calcine them at 700 °C in a pure oxygen atmosphere for 6 h to obtain a boron-coated lithium nickel cobalt manganese oxide cathode material.

[0083] Experimental Example

[0084] Perform electrochemical performance tests on the batteries prepared in Examples 1-3 and Comparative Examples 1-2 at 25 °C under the conditions of 3.0 - 4.5 V. The results are shown in Table 1.

[0085] Table 1. Test Results of Battery Electrochemical Performance

[0086]

[0087] According to the data shown in Table 1, compared with the batteries prepared from the cathode materials coated only with iron phosphate or only with boron, the batteries prepared from the cathode materials coated with both iron phosphate and boron provided in Examples 1-3 of the present invention have better cycling performance and more excellent cycling stability. At the same time, by comparing the performance test results of Example 1 and Example 2, it can be seen that when the coating amount of iron phosphate is increased and the coating amount of boron is decreased, the coating effect of iron phosphate deteriorates, resulting in a relatively lower cycling stability of the battery. By comparing the performance test results of Example 1 and Example 3, it can be seen that when the coating amount of iron phosphate is decreased and the coating amount of boron is increased, due to the uneven coating of boron, the cycling stability of the battery is relatively low.

[0088] In summary, the embodiments of the present invention provide a ternary cathode material and a preparation method thereof that can ensure both cycling performance and the bonding strength of the coating layer. The embodiments of the present invention also provide a cathode sheet and a battery, which include the above ternary cathode material. Therefore, it has the advantage of excellent cycling performance.

[0089] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A ternary cathode material, characterized in that, it comprises: a lithium nickel cobalt manganese oxide substrate; an iron phosphate coating layer coated on the outer peripheral side of the lithium nickel cobalt manganese oxide substrate; a boron oxide coating layer coated on the outer peripheral side of the iron phosphate coating layer, and a part of the boron oxide coating layer penetrates into the outer surface of the lithium nickel cobalt manganese oxide substrate through the pores of the iron phosphate coating layer and combines with the outer surface of the lithium nickel cobalt manganese oxide substrate.

2. The ternary cathode material according to claim 1, characterized in that: the mass of the iron phosphate coating layer accounts for 0.5-5% of the total mass of the ternary cathode material.

3. The ternary cathode material according to claim 1, characterized in that: the mass of the boron oxide coating layer accounts for 0.5-5% of the total mass of the ternary cathode material.

4. A preparation method of the ternary cathode material according to any one of claims 1 to 3, characterized in that, it comprises: mixing a suspension containing the lithium nickel cobalt manganese oxide substrate with an iron phosphate solution, and performing a first sintering after drying to form the iron phosphate coating layer on the outer peripheral side of the lithium nickel cobalt manganese oxide substrate; the iron phosphate solution is obtained by dispersing an iron source and a phosphorus source in a second solvent together, and the second solvent includes water; mixing a boron source with the lithium nickel cobalt manganese oxide substrate coated with the iron phosphate coating layer, and performing a second sintering to form the boron oxide coating layer on the outer peripheral side of the iron phosphate coating layer, and enabling a part of the boron oxide coating layer to penetrate into the outer surface of the lithium nickel cobalt manganese oxide substrate through the pores of the iron phosphate coating layer and combine with the outer surface of the lithium nickel cobalt manganese oxide substrate.

5. The preparation method of the ternary cathode material according to claim 4, characterized in that: the suspension is obtained by dispersing the lithium nickel cobalt manganese oxide substrate in a first solvent, and the first solvent includes an organic solvent or water.

6. The preparation method of the ternary cathode material according to claim 5, characterized in that: the iron source includes an iron salt soluble in water; and / or, the phosphorus source includes at least one of phosphoric acid and a phosphorus salt soluble in water; and / or, the boron source includes at least one of boron oxide, boric acid and borate.

7. The preparation method of the ternary cathode material according to claim 4, characterized in that: in the iron phosphate solution, the iron ion concentration is 0.05-2.5 mol / L, and the phosphate radical is 0.05-2.5 mol / L.

8. The preparation method of the ternary cathode material according to claim 4, characterized in that: the drying temperature is 100-250 °C, and the drying time is 4-6 h; and / or; the sintering temperature of the first sintering is 400-800 °C, the sintering time is 6-12 h, and the sintering environment is a pure oxygen environment; and / or, the sintering temperature of the second sintering is 700-800 °C, the sintering time is 4-8 h, and the sintering environment is a pure oxygen environment.

9. A positive electrode sheet, characterized in that, it comprises: a positive electrode current collector; a positive electrode active material layer obtained by coating the positive electrode active material paste on at least one side of the positive electrode current collector; the positive electrode active material paste includes the ternary cathode material according to any one of claims 1 to 3.

10. A battery, characterized in that, it includes the positive electrode sheet described in claim 9.

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