Composite cathode active material, preparation method, cathode sheet and lithium ion secondary battery

Abstract

The present application provides a kind of composite positive electrode active material, it is characterized in that, including core layer, contains positive electrode active material;Hydrogen fluoride barrier layer, cover core layer, hydrogen fluoride barrier layer contains by Nb, Ba, Zr, Mn, Mg, Al and Ca in any one or any combination thereof and O, F, B and P in any one or any combination thereof constitute the substance;And physical barrier layer, cover hydrogen fluoride barrier layer.By the composite positive electrode active material of the present application, preparation method, positive plate and lithium ion secondary battery, effectively prevent the contact and reaction of hydrogen fluoride and positive electrode active material, inhibit the dissolution of metal in positive electrode active material, ensure the stability of crystal structure in positive electrode active material body phase, and realize the increase of cycle retention rate and the reduction of impedance growth rate.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion secondary batteries, and more specifically, to a composite positive electrode active material, its preparation method, a positive electrode sheet containing the same, and a lithium-ion secondary battery. Background Technology

[0002] In recent years, with the continuous development of electronic technology, the demand for battery devices to power electronic devices has been increasing. Currently, there is a need for batteries capable of storing more electricity and outputting higher power. Traditional lead-acid and nickel-metal hydride batteries can no longer meet the needs of new electronic products. Therefore, lithium batteries have attracted wider attention. In the development of lithium batteries, their capacity and performance have been effectively improved.

[0003] Lithium cobalt oxide (LCO), lithium nickel cobalt aluminum oxide (NCA), and lithium nickel cobalt manganese oxide (NCM) are commonly used as positive electrode active materials in existing technologies. During the use of lithium-ion secondary batteries, trace amounts of water molecules inevitably exist in the electrolyte. When these trace water molecules come into contact with fluorine-containing substances in the electrolyte, the electrolyte will hydrolyze, producing hydrofluoric acid (HF). After numerous electrical cycles, the accumulated hydrofluoric acid will react with the positive electrode active material in the following way:

[0004] 2HF + LiCoO2 → CoO + LiF + H2O;

[0005] 10HF+10LiNi 0.5 Co 0.3 Mn 0.2 O 1.8 →10LiF + 5H₂O + 5NiO + 2MnO₂ + Co₃O₄; and

[0006] 10HF+10LiNi 0.5 Co 0.3 Al 0.2 O 1.7 →10LiF+5H2O+5NiO+Al2O3+Co3O4

[0007] This corrosion leads to oxygen evolution in the positive electrode active material, thereby damaging its crystal structure. When the positive electrode active material is extensively corroded, reaction products accumulate on the surface, adversely affecting lithium-ion transport. Furthermore, the destruction of the crystal structure and the accumulation of byproducts also reduce the capacity of the positive electrode active material and increase its impedance. Ultimately, this results in increased impedance, decreased cycle retention, and reduced expansion performance in the lithium-ion secondary battery, severely impacting its overall performance.

[0008] To prevent hydrogen fluoride from corroding the positive electrode active material, existing technologies typically employ coating methods to prevent contact between the active material and hydrogen fluoride. Commonly used coating materials include aluminum, aluminum oxide, and aluminates. However, because the positive electrode active material needs to allow lithium ions in the electrolyte to intercalate and deintercalate, the coating layer cannot be a dense material. This allows some hydrogen fluoride to penetrate the coating layer and react with the active material, adversely affecting the electrical performance of the lithium-ion secondary battery. Furthermore, while existing technologies use only aluminum, aluminum oxide, or aluminates as barrier layers to coat the active material, which to some extent prevents contact between hydrogen fluoride and the active material, the higher impedance of the coating material leads to an unfavorable increase in the impedance of the resulting positive electrode composite. Summary of the Invention

[0009] The main objective of this invention is to provide a composite positive electrode active material, a preparation method, a positive electrode sheet, and a lithium-ion secondary battery, in order to solve the problem that the positive electrode active material used in the prior art to coat lithium-ion secondary batteries cannot effectively prevent the contact between hydrogen fluoride and the positive electrode active material.

[0010] To achieve the above objectives, according to one aspect of the present invention, a composite positive electrode active material is provided, characterized in that it comprises a core layer containing a positive electrode active material; a hydrogen fluoride barrier layer covering the core layer, the hydrogen fluoride barrier layer comprising a substance composed of any one or any combination of Nb, Ba, Zr, Mn, Mg, Al and Ca, and any one or any combination of O, F, B and P; and a physical barrier layer covering the hydrogen fluoride barrier layer.

[0011] Furthermore, in the aforementioned composite positive electrode active material, the hydrogen fluoride barrier layer comprises a substance composed of any one or any combination of Nb, Zr, Mg, Al and Mn, and any one or any combination of O, F, B and P.

[0012] Furthermore, in the above-mentioned composite positive electrode active material, based on 100 parts by weight of the core layer, the hydrogen fluoride barrier layer is in the range of 0.02 to 10 parts by weight, preferably in the range of 5 to 10 parts by weight.

[0013] Furthermore, in the above-mentioned composite positive electrode active material, the thickness of the hydrogen fluoride barrier layer is in the range of 1 to 500 nm, preferably in the range of 50 to 500 nm, and more preferably in the range of 250 to 500 nm.

[0014] Furthermore, in the aforementioned composite positive electrode active material, the physical barrier layer comprises a substance composed of any one or any combination of Ta, W, Hf, Zr, Nb, Sc, Zn and Al, and any one or any combination of O and P; preferably, the physical barrier layer comprises a substance composed of any one or any combination of Ta, W, Zr, Nb, Sc, Zn and Al, and any one or any combination of O and P.

[0015] Furthermore, in the above-mentioned composite positive electrode active material, based on 100 parts by weight of the core layer, the physical barrier layer is in the range of 0.02 to 5 parts by weight, preferably in the range of 0.02 to 2.5 parts by weight.

[0016] Furthermore, in the above-mentioned composite positive electrode active material, the thickness of the physical barrier layer is in the range of 1 to 250 nm, preferably in the range of 1 to 125 nm, and more preferably in the range of 25 to 125 nm.

[0017] Furthermore, in the above-mentioned composite positive electrode active material, the positive electrode active material contains materials with the general formula LiCo1. -α M α Lithium cobalt oxide with O2, general formula LiNi 1-x-y Co x Mn y Lithium nickel cobalt manganese oxide (O2) and LiNi 1-x-y Co x Al y O2 is any one or any combination of lithium nickel cobalt aluminum oxide, wherein 0 < α ≤ 0.2, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1 and 0 ≤ x + y ≤ 1, and M is selected from any one or any combination of alkaline earth metal elements and transition metal elements, such that the sum of the valence states of the above general formula compound is zero.

[0018] Furthermore, in the above-mentioned composite positive electrode active material, the composite positive electrode active material further includes a sacrificial layer, which is disposed between the core layer and the hydrogen fluoride barrier layer.

[0019] Furthermore, in the above-mentioned composite positive electrode active material, the sacrificial layer comprises a substance composed of any one or any combination of Ti, Al, Mg, Zr, Sr, Zn, W and Sc, and any one or any combination of O, F and B; preferably, the sacrificial layer comprises a substance composed of any one or any combination of elements Ti, Al, Zr, W and Mg, and any one or any combination of O, F and B.

[0020] Furthermore, in the above-mentioned composite positive electrode active material, based on 100 parts by weight of the core layer, the sacrificial layer is in the range of 0.02 to 5 parts by weight, preferably in the range of 2.5 to 5 parts by weight.

[0021] Furthermore, in the above-mentioned composite positive electrode active material, the thickness of the sacrificial layer is in the range of 1 to 250 nm, preferably in the range of 25 to 250 nm, and more preferably in the range of 125 to 250 nm.

[0022] According to another aspect of the present invention, a method for preparing a composite positive electrode active material is provided, comprising: step S1-1, mixing a hydrogen fluoride barrier layer precursor material with active material particles to obtain a first mixture, calcining the first mixture at a temperature range of 250°C to 350°C for 2 to 4 hours, crushing the calcined product and sieving it through a 200-mesh to 400-mesh sieve to obtain a hydrogen fluoride barrier layer coated product, wherein the hydrogen fluoride barrier layer precursor material comprises any one or any combination of elemental Nb, Ba, Zr, Mn, Ca, Mg, Al, and their oxides, fluorides, borates, sulfates, and phosphates; and step S2-1, mixing a physical barrier layer precursor material with the hydrogen fluoride barrier layer coated product to obtain a second mixture, calcining the second mixture at a temperature range of 500°C to 600°C for 2 to 4 hours, crushing the calcined product and sieving it through a 200-mesh to 400-mesh sieve to obtain the composite positive electrode active material.

[0023] According to another aspect of the present invention, a method for preparing a composite positive electrode active material is provided, comprising: step S1-2, mixing a sacrificial layer precursor material with active material particles to obtain a first mixture, calcining the first mixture at a temperature range of 250°C to 350°C for 2 to 4 hours, crushing the calcined product and sieving it through a 200-mesh to 400-mesh sieve to obtain a first coated product, wherein the sacrificial layer precursor material comprises any one or any combination of elemental Ti, Al, Mg, Zr, Sr, Zn, Sc, W and their oxides, fluorides, and borates; step S2-2, mixing a hydrogen fluoride barrier layer precursor material with the first coated product to obtain a second mixture, and calcining the second mixture... The compound is calcined at a temperature range of 250°C to 350°C for 2 to 4 hours. The calcined product is crushed and sieved through a 200-400 mesh sieve to obtain a second coated product. The hydrogen fluoride barrier layer precursor material includes any one or any combination of elemental Nb, Ba, Zr, Mn, Ca, Mg, and Al, as well as their oxides, fluorides, borates, sulfates, and phosphates. In step S3-2, the physical barrier layer precursor material is mixed with the second coated product to obtain a third mixture. The third mixture is calcined at a temperature range of 500°C to 600°C for 2 to 4 hours. The calcined product is crushed and sieved through a 200-400 mesh sieve to obtain a composite positive electrode active material.

[0024] Furthermore, in the above method, the sacrificial layer precursor material comprises a first sacrificial layer precursor substance, a second sacrificial layer precursor substance, and an optional third sacrificial layer precursor substance, wherein the first sacrificial layer precursor substance, the second sacrificial layer precursor substance, and the optional third sacrificial layer precursor substance are different from each other, and wherein the amount of the first sacrificial layer precursor substance and the amount of the second sacrificial layer precursor substance are respectively in the range of 20 parts by weight to 70 parts by weight, and the amount of the optional third sacrificial layer precursor substance is in the range of 0 parts by weight to 50 parts by weight, such that the first sacrificial layer precursor substance, the second sacrificial layer precursor substance, and the optional third sacrificial layer precursor substance constitute 100 parts by weight of the sacrificial layer precursor material.

[0025] Furthermore, in the above method, the hydrogen fluoride barrier layer precursor material comprises a first hydrogen fluoride barrier layer precursor substance and a second hydrogen fluoride barrier layer precursor substance, the first hydrogen fluoride barrier layer precursor substance and the second hydrogen fluoride barrier layer precursor substance being different from each other, and wherein the amounts of the first hydrogen fluoride barrier layer precursor substance and the second hydrogen fluoride barrier layer precursor substance are in the range of 30 parts by weight to 70 parts by weight, such that the first hydrogen fluoride barrier layer precursor substance and the second hydrogen fluoride barrier layer precursor substance constitute 100 parts by weight of the hydrogen fluoride barrier layer precursor material.

[0026] Further, in the above method, the physical barrier layer precursor material comprises any one or any combination of elemental Ta, W, Hf, Zr, Nb, Sc, Zn, Al, their oxides, and phosphates; preferably, the physical barrier layer precursor material comprises a first physical barrier layer precursor material, a second physical barrier layer precursor material, and an optional third physical barrier layer precursor material, wherein the first physical barrier layer precursor material, the second physical barrier layer precursor material, and the optional third physical barrier layer precursor material are different from each other, and wherein the amount of the first physical barrier layer precursor material and the amount of the second physical barrier layer precursor material are each in the range of 20 parts by weight to 70 parts by weight, and the amount of the optional third physical barrier layer precursor material is in the range of 0 parts by weight to 50 parts by weight, such that the first physical barrier layer precursor material, the second physical barrier layer precursor material, and the optional third physical barrier layer precursor material constitute 100 parts by weight of the physical barrier layer precursor material.

[0027] According to another aspect of the present invention, a positive electrode sheet for a lithium-ion secondary battery is provided, comprising a composite positive electrode active material comprising any one of the above.

[0028] According to another aspect of the present invention, a lithium-ion secondary battery is provided, comprising: a positive electrode, a negative electrode, and a separator, characterized in that the positive electrode comprises a composite positive electrode active material of any one of the above.

[0029] The composite positive electrode active material, preparation method, positive electrode sheet, and lithium-ion secondary battery of the present invention effectively prevent the contact and reaction between hydrogen fluoride and the positive electrode active material, inhibit the dissolution of metals in the positive electrode active material, and ensure the stability of the crystal structure in the bulk phase of the positive electrode active material. As a result, the lithium-ion secondary battery containing it can still maintain good power discharge capability after multiple cycles, and achieves an increase in cycle retention rate and a decrease in impedance growth rate. Detailed Implementation

[0030] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will be described in detail below with reference to the embodiments. The following embodiments are merely exemplary and do not constitute a limitation on the scope of protection of the present invention.

[0031] As explained in the background section, in the prior art, aluminum, aluminum oxide, or aluminates are typically used to coat the positive electrode active material of lithium-ion secondary batteries. However, since the above materials cannot effectively prevent hydrogen fluoride from contacting the positive electrode active material, further improvements are still needed. To address the problems in the prior art, according to a typical embodiment of this application, a composite positive electrode active material is provided, comprising: a core layer, a hydrogen fluoride barrier layer, and a physical barrier layer, wherein the core layer contains the positive electrode active material, the hydrogen fluoride barrier layer coats the core layer, and the physical barrier layer coats the hydrogen fluoride barrier layer. The hydrogen fluoride barrier layer comprises a substance composed of any one or any combination of Nb, Ba, Zr, Mn, Mg, Al, and Ca, and any one or any combination of O, F, B, and P.

[0032] Unlike existing technologies that use aluminum, aluminum oxide, or aluminates to coat the positive electrode active material of lithium-ion secondary batteries, the composite positive electrode active material of this application first has a core layer coated with a hydrogen fluoride barrier layer, followed by a physical barrier layer coating the hydrogen fluoride barrier layer. Because this application employs a two-layer structure of physical and hydrogen fluoride barrier layers, hydrogen fluoride present in the electrolyte is completely blocked outside both barrier layers. In some embodiments, hydrogen fluoride is completely blocked outside the physical barrier layer, thus not affecting the positive electrode active material inside the two barrier layers. In other embodiments, hydrogen fluoride can partially permeate between the physical and hydrogen fluoride barrier layers, but will not enter the hydrogen fluoride barrier layer and corrode the positive electrode active material. Therefore, when using the composite positive electrode active material of this application, the contact and reaction between hydrogen fluoride and the positive electrode active material are effectively prevented, the dissolution of metals in the positive electrode active material is suppressed, and the stability of the crystal structure in the bulk phase of the positive electrode active material is ensured. This allows the lithium-ion secondary battery containing it to maintain good power discharge capability after multiple cycles, and also suppresses the phenomenon of battery gas generation at high temperatures.

[0033] In this application, the hydrogen fluoride barrier layer comprises a substance composed of any one or any combination of Nb, Ba, Zr, Mn, Mg, Al, and Ca, and any one or any combination of O, F, B, and P. Preferably, the hydrogen fluoride barrier layer comprises a substance represented by the following formula:

[0034] M x A y O z

[0035] Where x is an integer from 1 to 5, y is an integer from 0 to 6, and z is an integer from 0 to 24, provided that at least two of y and z are not zero, and the sum of the valence states of the compounds of the above general formula is zero.

[0036] M is selected from any one of the group consisting of Nb, Ba, Zr, Mn, Mg, Al, and Ca, or any combination thereof; A is selected from any one of the group consisting of F, B, and P, or any combination thereof.

[0037] In some embodiments of this application, the hydrogen fluoride barrier layer comprises one or any combination of the following substances: NbBO4, BaSO4, ZrP2O7, Mn2PO4F, CaSn4(PO4)6, MgF2, Nb2O3, ZrO2, MnO2, Nb3(PO4)5, Nb(BO3)3, Zr(BO3)4, or Mn(BO3)4.

[0038] Because a hydrogen fluoride barrier layer is added between the core layer and the physical barrier layer, and this hydrogen fluoride barrier layer contains Nb, Ba, Zr, Mn, Mg, Al, or Ca elements that can effectively improve conductivity, the composite positive electrode active material of this application not only provides a physical barrier to effectively prevent hydrogen fluoride from contacting the positive electrode active material, but also effectively improves conductivity, thereby overcoming the problem of increased impedance in existing composite positive electrode active materials. The composite positive electrode active material of this invention not only maintains good power discharge capability of the battery, but also effectively suppresses the increase in battery impedance.

[0039] In some embodiments of this application, the hydrogen fluoride barrier layer comprises a substance composed of any one or any combination of Nb, Zr, Mg, Al, and Mn, and any one or any combination of O, F, B, and P. When using a hydrogen fluoride barrier layer containing the above elements, the hydrogen fluoride barrier layer of this application can more effectively suppress the increase in battery impedance.

[0040] Preferably, the hydrogen fluoride barrier layer comprises one or any combination of the following substances: NbBO4, BaSO4, ZrP2O7, Mn2PO4F, CaSn4(PO4)6, Zr(BO3)4, and MgF2. In a further preferred embodiment, the hydrogen fluoride barrier layer comprises one or any combination of the following substances: NbBO4, MgF2, and Mn2PO4F.

[0041] In a further embodiment of this application, based on 100 parts by weight of the core layer, the hydrogen fluoride barrier layer is in the range of 0.02 to 10 parts by weight, preferably in the range of 5 to 10 parts by weight. When the hydrogen fluoride barrier layer is less than 0.02 parts by weight, the resulting layer thickness is too small, and therefore cannot effectively block the penetration of hydrogen fluoride. When the hydrogen fluoride barrier layer is greater than 10 parts by weight, the resulting layer thickness is too thick, thereby reducing the insertion and extraction efficiency of free lithium ions in the electrolyte, and consequently adversely reducing the capacity of the lithium-ion secondary battery.

[0042] In some embodiments of the present invention, for different examples, the lower limit of the amount of hydrogen fluoride barrier layer, based on 100 parts by weight of the core layer, can be 0.02 parts by weight, 0.03 parts by weight, 0.04 parts by weight, 0.05 parts by weight, 0.06 parts by weight, 0.07 parts by weight, 0.08 parts by weight, 0.09 parts by weight, 0.1 parts by weight, 0.15 parts by weight, 0.2 parts by weight, 0.25 parts by weight, 0.3 parts by weight, 0.35 parts by weight, 0.4 parts by weight, 0.45 parts by weight, 0.5 parts by weight, 0.55 parts by weight, 0.6 parts by weight, 0. The amounts are 65 parts by weight, 0.7 parts by weight, 0.75 parts by weight, 0.8 parts by weight, 0.85 parts by weight, 0.9 parts by weight, 0.95 parts by weight, 1 part by weight, 1.5 parts by weight, 2 parts by weight, 2.5 parts by weight, 3 parts by weight, 3.5 parts by weight, 4 parts by weight, 4.5 parts by weight, or 5 parts by weight, and the upper limit of the amount of hydrogen fluoride barrier layer, based on 100 parts by weight of core layer, can be 10 parts by weight, 9.5 parts by weight, 9 parts by weight, 8.5 parts by weight, 8 parts by weight, 7.5 parts by weight, 7 parts by weight, 6.5 parts by weight, 6 parts by weight, or 5.5 parts by weight.

[0043] Specifically, based on 100 parts by weight of the core layer, the amount of the hydrogen fluoride barrier layer can be within the following ranges: 0.02 parts by weight - 10 parts by weight, 0.05 parts by weight - 10 parts by weight, 0.1 parts by weight - 10 parts by weight, 0.2 parts by weight - 10 parts by weight, 0.5 parts by weight - 10 parts by weight, 1 part by weight - 10 parts by weight, 2 parts by weight - 10 parts by weight, 3 parts by weight - 10 parts by weight, 4 parts by weight - 10 parts by weight, 5 parts by weight - 10 parts by weight, 0.5 parts by weight - 9.5 parts by weight, 0.5 parts by weight - 9 parts by weight, 0.5 parts by weight - 8.5 parts by weight, 0.5 parts by weight - 8 parts by weight, 1 part by weight - 9 parts by weight, 1 part ... Quantities: -8 parts by weight, 1 part by weight, 1 part by weight, 6 parts by weight, 2 parts by weight, 9.5 parts by weight, 2 parts by weight, 9 parts by weight, 8 parts by weight, 7 parts by weight, 6 parts by weight, 5.5 parts by weight, 9.5 parts by weight, 8 parts by weight, 7 parts by weight, 6 parts by weight, 5.5 parts by weight, 9 parts by weight, 8 parts by weight, 7 parts by weight, 6 parts by weight, or 5.5 parts by weight.

[0044] In a further embodiment of the present invention, the thickness of the hydrogen fluoride barrier layer is in the range of 1 to 500 nm, preferably in the range of 50 to 500 nm, and more preferably in the range of 250 to 500 nm. The thickness of the hydrogen fluoride barrier layer can be 1nm, 1.5nm, 2nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 7.5nm, 10nm, 12.5nm, 15nm, 17.5nm, 20nm, 22.5nm, 25nm, 27.5nm, 30nm, 32.5nm, 37.5nm, 40nm, 42.5nm, 45nm, 47.5nm, 50nm, 75nm, 100nm, 125nm, 150nm, 175nm, 200nm, 225nm, or 250nm for different embodiments, and its upper limit can be 500nm, 475nm, 450nm, 425nm, 400nm, 375nm, 350nm, 325nm, 300nm, or 275nm.

[0045] Specifically, the thickness of the hydrogen fluoride barrier layer can be within the following ranges: 1nm-500nm, 2.5nm-500nm, 5nm-500nm, 10nm-500nm, 25nm-500nm, 50nm-500nm, 100nm-500nm, 150nm-500nm, 200nm-500nm, 250nm-500nm, 25nm-475nm, 25nm-450nm, 25nm-425nm, 25nm-400nm, 50nm-450nm, 50nm-400nm, 50nm-350nm, 50nm-300nm. 0nm, 100nm-475nm, 100nm-450nm, 100nm-400nm, 100nm-350nm, 100nm-300nm, 100nm-275nm, 150nm-475nm, 150nm-450nm, 150nm-400nm, 150nm-350nm, 150nm-300nm, 150nm-275nm, 200nm-475nm, 200nm-450nm, 200nm-400nm, 200nm-350nm, 200nm-300nm, or 200nm-275nm.

[0046] In some embodiments of this application, the physical barrier layer comprises a substance composed of any one or any combination of Ta, W, Hf, Zr, Nb, Sc, Zn, and Al, and any one or any combination of O and P. Because the physical barrier layer of this invention contains the aforementioned elements, the resulting physical barrier layer has a denser structure. This structure allows lithium ions in the electrolyte to effectively pass through the physical barrier layer for insertion and extraction onto the positive electrode active material, while hydrogen fluoride in the electrolyte cannot pass through the dense physical barrier layer, thereby effectively preventing the corrosion of the positive electrode active material by hydrogen fluoride.

[0047] In some preferred embodiments of this application, the physical barrier layer comprises a substance represented by the following formula:

[0048] M' x P y O z

[0049] Where x is an integer from 1 to 3, y is an integer from 0 to 5, and z is an integer from 0 to 20, provided that y and z are not both zero, and the sum of the valence states of the compounds of the above general formula is zero.

[0050] M' is selected from any one of the groups consisting of Ta, W, Hf, Zr, Nb, Sc, Zn, and Al, or any combination thereof.

[0051] In some embodiments of this application, the hydrogen fluoride barrier layer comprises one or any combination of the following substances: Ta3(PO4)5, Nb3(PO4)5, W(PO4)2, Zr3(PO4)4, ZrO2, Al2O3, ZnO, AlPO4, NbO2, WO3 and Ta2O5.

[0052] In some preferred embodiments, the physical barrier layer comprises a substance consisting of any one or any combination of Ta, W, Zr, Nb, Sc, Zn, and Al, and any one or any combination of O and P.

[0053] In a preferred embodiment, M' is selected from any one or any combination of Ta, Nb, W, Zr and Al.

[0054] In some embodiments of this application, the physical barrier layer comprises one or any combination of the following substances: W(PO4)2, Zr3(PO4)4, ZrO2, Al2O3, ZnO, AlPO4, NbO2, WO3, and Ta2O5. In a more preferred embodiment, the physical barrier layer comprises one or any combination of the following substances: W(PO4)2, Zr3(PO4)4, Al2O3, ZrO2, and AlPO4.

[0055] In a further embodiment of this application, based on 100 parts by weight of the core layer, the physical barrier layer ranges from 0.02 parts by weight to 5 parts by weight, preferably from 0.02 parts by weight to 2.5 parts by weight. When the physical barrier layer is less than 0.02 parts by weight, the formed physical barrier layer cannot form a dense structure, allowing hydrogen fluoride in the electrolyte to permeate through the physical barrier layer, thus failing to effectively isolate the hydrogen fluoride from the positive electrode active material. When the physical barrier layer is greater than 5 parts by weight, the thickness of the formed physical barrier layer is too large, resulting in an unfavorable increase in impedance. Furthermore, because the formed physical barrier layer has an overly dense structure, lithium ions cannot effectively intercalate and deintercalate, adversely reducing the capacity of the lithium-ion secondary battery.

[0056] In some embodiments of the present invention, for different implementations, the lower limit of the physical barrier layer amount, based on 100 parts by weight of the core layer, can be 0.02 parts by weight, 0.03 parts by weight, 0.04 parts by weight, 0.05 parts by weight, 0.06 parts by weight, 0.07 parts by weight, 0.08 parts by weight, 0.09 parts by weight, 0.1 parts by weight, 0.15 parts by weight, 0.2 parts by weight, 0.25 parts by weight, 0.3 parts by weight, 0.35 parts by weight, 0.4 parts by weight, 0.45 parts by weight, or 0.5 parts by weight. The amounts are 0.55 parts by weight, 0.6 parts by weight, 0.65 parts by weight, 0.7 parts by weight, 0.75 parts by weight, 0.8 parts by weight, 0.85 parts by weight, 0.9 parts by weight, 0.95 parts by weight, 1 part by weight, 1.5 parts by weight, 2 parts by weight, or 2.5 parts by weight, and the upper limit of the amount of physical barrier layer, based on 100 parts by weight of core layer, can be 2.6 parts by weight, 2.7 parts by weight, 2.8 parts by weight, 2.9 parts by weight, 3 parts by weight, 3.5 parts by weight, 4 parts by weight, 4.5 parts by weight, or 5 parts by weight.

[0057] Specifically, based on 100 parts by weight of the core layer, the physical barrier layer can be in the following ranges: 0.02 parts by weight to 5 parts by weight, 0.02 parts by weight to 4.5 parts by weight, 0.02 parts by weight to 4 parts by weight, 0.02 parts by weight to 3.5 parts by weight, 0.02 parts by weight to 3 parts by weight, 0.02 parts by weight to 2.6 parts by weight, 0.1 parts by weight to 5 parts by weight, 0.1 parts by weight to 4.5 parts by weight, 0.1 parts by weight to 4 parts by weight, 0.1 parts by weight to 3.5 parts by weight, 0.1 parts by weight to 3 parts by weight, 0.1 parts by weight to 2.6 parts by weight, 0.5 parts by weight to 5 parts by weight, 0.5 parts by weight to 4.5 parts by weight, 0.5 parts by weight to 4 parts by weight, 0.5 parts by weight to 3.5 parts by weight. Parts by weight, 0.5 to 3 parts by weight, 0.5 to 2.6 parts by weight, 1 to 5 parts by weight, 1 to 4.5 parts by weight, 1 to 4 parts by weight, 1 to 3.5 parts by weight, 1 to 3 parts by weight, 1 to 2.6 parts by weight, 2 to 5 parts by weight, 2 to 4.5 parts by weight, 2 to 4 parts by weight, 2 to 3.5 parts by weight, 2 to 3 parts by weight, 2 to 2.6 parts by weight, 2.5 to 5 parts by weight, 2.5 to 4.5 parts by weight, 2.5 to 4 parts by weight, 2.5 to 3.5 parts by weight, 2.5 to 3 parts by weight, or 2.5 to 2.6 parts by weight.

[0058] In a further embodiment of the present invention, the thickness of the physical barrier layer is in the range of 1 to 250 nm, preferably in the range of 1 to 125 nm, and more preferably in the range of 25 to 125 nm. The thickness of the physical barrier layer can be limited to a lower limit of 1nm, 1.5nm, 2.5nm, 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 7.5nm, 10nm, 12.5nm, 15nm, 17.5nm, 20nm, 22.5nm, 25nm, 27.5nm, 30nm, 32.5nm, 35nm, 37.5nm, 40nm, 42.5nm, 45nm, 47.5nm, 50nm, 100nm, or 125nm for different embodiments, and its upper limit can be 250nm, 225nm, 200nm, 175nm, 150nm, 145nm, 140nm, 135nm, or 130nm for different embodiments.

[0059] Specifically, the thickness of the physical barrier layer can be within the following ranges: 1nm-250nm, 1nm-225nm, 1nm-200nm, 1nm-175nm, 1nm-150nm, 1nm-130nm, 5nm-250nm, 5nm-225nm, 5nm-200nm, 5nm-175nm, 5nm-150nm, 5nm-130nm, 25nm-250nm, 25nm-225nm, 25nm-200nm, 25nm-175nm, 25nm-150nm, 25nm-130nm, 5 0nm-250nm, 50nm-225nm, 50nm-200nm, 50nm-175nm, 50nm-150nm, 50nm-130nm, 100nm-250nm, 100nm-225nm, 100nm-200nm, 100nm-175nm, 100nm-150nm, 100nm-130nm, 125nm-250nm, 125nm-225nm, 125nm-200nm, 125nm-175nm, 125nm-150nm, or 125nm-130nm.

[0060] In some embodiments of the present invention, the positive electrode active material included in the core layer comprises a material with the general formula LiCo. 1-α M α O2-based lithium cobalt oxide, with the general formula LiNi 1-x-y Co x Mn y Lithium nickel cobalt manganese oxide (O2) and LiNi 1-x-y Co x Al y O2 is any one or any combination of lithium nickel cobalt aluminum oxide, wherein 0 < α ≤ 0.2, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1 and 0 ≤ x + y ≤ 1, M is selected from any one or any combination of alkaline earth metals and transition metals, and the sum of the valence states of the above general formula compound is zero. In some preferred embodiments, the general formula LiCo 1-α M α In O2, M is one or more of Mg, Sc, Ti, Fe, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ru, Rh, Pd, In, Sn, Hf, Ta, W, Re, Cr, Y, Sb, Lu, Au, Pb, Er, Na, Al, Si, Ge, Mn, Ca, Te, Hg, Bi, La, Ce, Pr, Nd, Sm, and V.

[0061] In some embodiments of the present invention, the composite positive electrode active material further includes a sacrificial layer disposed between the core layer and the hydrogen fluoride barrier layer. The sacrificial layer can react with hydrogen fluoride as follows:

[0062] HF + MO → MF + H₂O; and

[0063] HF+M→MF+H2

[0064] Thus, further protection is provided to the positive electrode active material even when hydrogen fluoride permeates through both the physical barrier layer and the hydrogen fluoride barrier layer. In this invention, the sacrificial layer may include any material with a Gibbs free energy G that reacts with hydrogen fluoride. s-HF Materials with a density of <0 are used to ensure that the reaction can occur when in contact with hydrogen fluoride, thereby consuming the hydrogen fluoride that has permeated through the physical barrier layer and the hydrogen fluoride barrier layer.

[0065] In some embodiments of the present invention, the sacrificial layer comprises a substance composed of any one or any combination thereof of Ti, Al, Mg, Zr, Sr, Zn, W, and Sc, and any one or any combination thereof of O, F, and B; preferably, the sacrificial layer comprises a substance represented by the following formula:

[0066] M” x A' y O z

[0067] Where x is an integer from 1 to 3, y is an integer from 0 to 4, and z is an integer from 0 to 12, provided that y and z are not both zero, and the sum of the valence states of the compounds of the above general formula is zero.

[0068] M” is selected from any one of the groups consisting of Ti, Al, Mg, Zr, Sr, Zn, W, and Sc, or any combination thereof, and A' is selected from any one of the groups consisting of F and B, or any combination thereof.

[0069] In some embodiments of this application, the sacrificial layer comprises one or any combination of the following substances: Ti(BO3)4, Al(BO3)3, Zr(BO3)4, SrB4O7, Zn(BO3)2, Sc(BO3)3, Mg(BO3)2, Sr2Mg(BO3)4, TaBO4, AlF3, ZnO, Sc2O3, TiO2, Al2O3, MgO, ZrO2, SrO2, and MgF2.

[0070] In a further preferred embodiment, the sacrificial layer comprises a substance consisting of any one or any combination of Ti, Al, W, Zr and Mg, and any one or any combination of O and B.

[0071] In a preferred embodiment, M” is selected from any one of the group consisting of Ti, Al, W and Mg or any combination thereof.

[0072] In a more preferred embodiment, the sacrificial layer comprises one or any combination of the following substances: Ti(BO3)4, Al(BO3)3, SrB4O7, TiO2, Al2O3, MgO, ZrO2 and MgF2.

[0073] In a further embodiment of this application, based on 100 parts by weight of the core layer, the sacrificial layer ranges from 0.02 parts by weight to 5 parts by weight, preferably from 2.5 parts by weight to 5 parts by weight. When the sacrificial layer is less than 0.02 parts by weight, the resulting layer thickness is too small, failing to effectively consume the permeated hydrogen fluoride, causing the hydrogen fluoride to come into contact with the positive electrode active material of the core layer, thereby adversely affecting the capacity and cycle retention rate of the lithium-ion secondary battery. When the sacrificial layer is greater than 10 parts by weight, the resulting layer thickness is too thick, leading to an unfavorable increase in impedance, which will adversely reduce the capacity of the lithium-ion secondary battery.

[0074] In some embodiments of the present invention, for different implementations, the lower limit of the sacrificial layer, based on 100 parts by weight of the core layer, can be 0.02 parts by weight, 0.03 parts by weight, 0.04 parts by weight, 0.05 parts by weight, 0.06 parts by weight, 0.07 parts by weight, 0.08 parts by weight, 0.09 parts by weight, 0.1 parts by weight, 0.15 parts by weight, 0.2 parts by weight, 0.25 parts by weight, 0.3 parts by weight, 0.35 parts by weight, 0.4 parts by weight, 0.45 parts by weight, or 0.5 parts by weight. The amounts are 0.55 parts by weight, 0.6 parts by weight, 0.65 parts by weight, 0.7 parts by weight, 0.75 parts by weight, 0.8 parts by weight, 0.85 parts by weight, 0.9 parts by weight, 0.95 parts by weight, 1 part by weight, 1.5 parts by weight, 2 parts by weight, or 2.5 parts by weight, and the upper limit of the sacrificial layer, based on 100 parts by weight of the core layer, can be 2.6 parts by weight, 2.7 parts by weight, 2.8 parts by weight, 2.9 parts by weight, 3 parts by weight, 3.5 parts by weight, 4 parts by weight, 4.5 parts by weight, or 5 parts by weight.

[0075] Specifically, based on 100 parts by weight of the core layer, the amount of the sacrificial layer can be within the following ranges: 0.02 parts by weight to 5 parts by weight, 0.02 parts by weight to 4.5 parts by weight, 0.02 parts by weight to 4 parts by weight, 0.02 parts by weight to 3.5 parts by weight, 0.02 parts by weight to 3 parts by weight, 0.02 parts by weight to 2.6 parts by weight, 0.1 parts by weight to 5 parts by weight, 0.1 parts by weight to 4.5 parts by weight, 0.1 parts by weight to 4 parts by weight, 0.1 parts by weight to 3.5 parts by weight, 0.1 parts by weight to 3 parts by weight, 0.1 parts by weight to 2.6 parts by weight, 0.5 parts by weight to 5 parts by weight, 0.5 parts by weight to 4.5 parts by weight, 0.5 parts by weight to 4 parts by weight, 0.5 parts by weight to 3.5 parts by weight. Parts by weight, 0.5 to 3 parts by weight, 0.5 to 2.6 parts by weight, 1 to 5 parts by weight, 1 to 4.5 parts by weight, 1 to 4 parts by weight, 1 to 3.5 parts by weight, 1 to 3 parts by weight, 1 to 2.6 parts by weight, 2 to 5 parts by weight, 2 to 4.5 parts by weight, 2 to 4 parts by weight, 2 to 3.5 parts by weight, 2 to 3 parts by weight, 2 to 2.6 parts by weight, 2.5 to 5 parts by weight, 2.5 to 4.5 parts by weight, 2.5 to 4 parts by weight, 2.5 to 3.5 parts by weight, 2.5 to 3 parts by weight, or 2.5 to 2.6 parts by weight.

[0076] In a further embodiment of the present invention, the thickness of the sacrificial layer is in the range of 1 to 250 nm, preferably in the range of 25 to 250 nm, and more preferably in the range of 125 to 250 nm. The thickness of the sacrificial layer, for different embodiments, can have a lower limit of 1 nm, 1.5 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, 7.5 nm, 10 nm, 12.5 nm, 15 nm, 17.5 nm, 20 nm, 22.5 nm, 25 nm, 27.5 nm, 30 nm, 32.5 nm, 35 nm, 37.5 nm, 40 nm, 42.5 nm, 45 nm, 47.5 nm, 50 nm, 100 nm, or 125 nm, and an upper limit of 250 nm, 225 nm, 200 nm, 175 nm, 150 nm, 145 nm, 140 nm, 135 nm, or 130 nm.

[0077] Specifically, the thickness of the sacrificial layer can be within the following ranges: 1nm-250nm, 1nm-225nm, 1nm-200nm, 1nm-175nm, 1nm-150nm, 1nm-130nm, 5nm-250nm, 5nm-225nm, 5nm-200nm, 5nm-175nm, 5nm-150nm, 5nm-130nm, 25nm-250nm, 25nm-225nm, 25nm-200nm, 25nm-175nm, 25nm-150nm, 25nm-130nm, 50 nm-250nm, 50nm-225nm, 50nm-200nm, 50nm-175nm, 50nm-150nm, 50nm-130nm, 100nm-250nm, 100nm-225nm, 100nm-200nm, 100n m-175nm, 100nm-150nm, 100nm-130nm, 125nm-250nm, 125nm-225nm, 125nm-200nm, 125nm-175nm, 125nm-150nm, or 125nm-130nm.

[0078] According to another typical embodiment of the present invention, a method for preparing a composite positive electrode active material is provided, comprising the following steps: Step S1-1, mixing a hydrogen fluoride barrier layer precursor material with active material particles to obtain a first mixture, calcining the first mixture at a temperature range of 250°C to 350°C for 2 to 4 hours, crushing the calcined product and sieving it through a 200-mesh to 400-mesh sieve to obtain a hydrogen fluoride barrier layer coated product, wherein the hydrogen fluoride barrier layer precursor material comprises any one or any combination of elemental Nb, Ba, Zr, Mn, Ca, Mg, Al and their oxides, fluorides, borates, sulfates, and phosphates; and Step S2-1, mixing a physical barrier layer precursor material with the hydrogen fluoride barrier layer coated product to obtain a second mixture, calcining the second mixture at a temperature range of 500°C to 600°C for 2 to 4 hours, crushing the calcined product and sieving it through a 200-mesh to 400-mesh sieve to obtain the composite positive electrode active material.

[0079] The positive electrode active material prepared using this method comprises a three-layer structure: a core layer, a physical barrier layer, and a hydrogen fluoride barrier layer. Due to calcination at 500°C to 600°C for 2 to 4 hours, the physical barrier layer has a dense structure, effectively preventing hydrogen fluoride penetration. The hydrogen fluoride barrier layer is formed by sintering precursor materials containing elemental Nb, Ba, Zr, Mn, Ca, Mg, and Al, and their oxides, fluorides, borates, sulfates, and phosphates, or any combination thereof. Therefore, the composite positive electrode active material prepared using the method of this application effectively prevents contact between hydrogen fluoride and the positive electrode active material while overcoming the problem of increased impedance in existing composite positive electrode active materials. Thus, it not only maintains good power discharge capability of the battery but also effectively suppresses impedance growth. In a preferred embodiment, the hydrogen fluoride barrier layer precursor material comprises elemental Nb, Mg, Zr, Mn, and Al, and their oxides, fluorides, borates, sulfates, and phosphates, or any combination thereof.

[0080] According to another typical embodiment of the present invention, a method for preparing a composite positive electrode active material is provided, comprising: step S1-2, mixing a sacrificial layer precursor material with active material particles to obtain a first mixture, calcining the first mixture at a temperature range of 250°C to 350°C for 2 to 4 hours, crushing the calcined product and sieving it through a 200-mesh to 400-mesh sieve to obtain a first coated product, wherein the sacrificial layer precursor material comprises any one or any combination of elemental Ti, Al, Mg, Zr, Sr, Zn, Sc, W and their oxides, fluorides, and borates; step S2-2, mixing a hydrogen fluoride barrier layer precursor material with the first coated product to obtain a second mixture, and then... The two mixtures are calcined at a temperature range of 250°C to 350°C for 2 to 4 hours. The calcined product is crushed and sieved through a 200-400 mesh sieve to obtain the second coated product. The hydrogen fluoride barrier layer precursor material includes any one or any combination of elemental Nb, Ba, Zr, Mn, Ca, Mg, and Al, as well as their oxides, fluorides, borates, sulfates, and phosphates. In step S3-2, the physical barrier layer precursor material is mixed with the second coated product to obtain a third mixture. The third mixture is calcined at a temperature range of 500°C to 600°C for 2 to 4 hours. The calcined product is crushed and sieved through a 200-400 mesh sieve to obtain the composite positive electrode active material. In a preferred embodiment, the sacrificial layer precursor material comprises any one or any combination of elemental Ti, Al, Mg, Zr, W, their oxides, fluorides, and borates, and the hydrogen fluoride barrier layer precursor material comprises any one or any combination of elemental Nb, Mg, Zr, Mn, Al, their oxides, fluorides, borates, sulfates, and phosphates.

[0081] The positive electrode active material prepared using this method comprises a four-layer structure: a core layer, a sacrificial layer, a physical barrier layer, and a hydrogen fluoride barrier layer. The sacrificial layer is prepared from a precursor material containing any one or any combination of elemental Ti, Al, Mg, Zr, Sr, Zn, Sc, and W, as well as their oxides, fluorides, and borates. Therefore, before hydrogen fluoride comes into contact with and reacts with the positive electrode active material in the core layer, the sacrificial layer can react with hydrogen fluoride, thus preventing the corrosion of the positive electrode active material by hydrogen fluoride. Due to calcination at 500°C to 600°C for 2 to 4 hours, the physical barrier layer has a dense structure, effectively preventing the penetration of hydrogen fluoride. The hydrogen fluoride barrier layer is sintered from precursor materials comprising any one or any combination of elemental Nb, Ba, Zr, Mn, Ca, Mg, and Al, as well as their oxides, fluorides, borates, sulfates, and phosphates. Therefore, the composite positive electrode active material prepared using the method of this application effectively prevents hydrogen fluoride from contacting the positive electrode active material while overcoming the problem of increased impedance in existing composite positive electrode active materials. Thus, it not only maintains the battery's good power discharge capability but also effectively suppresses the battery's impedance growth.

[0082] In some embodiments of this application, the sacrificial layer precursor material includes, but is not limited to, any one or any combination thereof of the following: elemental Ti, Al, Mg, Zr, Sr, Zn, and Sc; and MgO, ZrO2, Mg(BO3)2, AlF3, Sr2Mg(BO3)4, TaBO4, ZnO, Sc2O3, Ti(BO3)4, Al(BO3)3, TiO2, Al2O3, MgO, and MgF2. In a preferred embodiment, the sacrificial layer precursor material includes, but is not limited to, any one or any combination thereof of the following: elemental Ti, Al, Mg, Zr, and W; and MgO, ZrO2, Mg(BO3)2, AlF3, and Al2O3. In a more preferred embodiment, the sacrificial layer precursor material includes, but is not limited to, any one or any combination thereof of the following: elemental Ti, Al, and W; and MgO, ZrO2, Mg(BO3)2, and Al2O3.

[0083] In some embodiments of this application, the precursor materials for the hydrogen fluoride barrier layer include, but are not limited to, any one or any combination thereof of the following: elemental Nb, Ba, Zr, Mn, and Ca, and NbBO4, BaSO4, ZrP2O7, Mn2PO4F, CaSn4(PO4)6, MgF2, NbO2, ZrO2, and MnO2. In preferred embodiments, the precursor materials for the hydrogen fluoride barrier layer include, but are not limited to, any one or any combination thereof of the following: elemental Nb, Mg, Zr, Mn, and Al, and MgF2, NbBO4, Mn2PO4F, ZrP2O7, Al2O3, MgO, ZrO2, and Mg(BO3)2. In more preferred embodiments, the precursor materials for the hydrogen fluoride barrier layer include, but are not limited to, any one or any combination thereof of the following: elemental Nb, and MgF2, NbBO4, and Mn2PO4F.

[0084] In some embodiments of this application, the sacrificial layer precursor material comprises a first sacrificial layer precursor material, a second sacrificial layer precursor material, and an optional third sacrificial layer precursor material, wherein the first sacrificial layer precursor material, the second sacrificial layer precursor material, and the third sacrificial layer precursor material are different from each other, and wherein the amount of the first sacrificial layer precursor material and the amount of the second sacrificial layer precursor material are each in the range of 20 parts by weight to 70 parts by weight, and the amount of the optional third sacrificial layer precursor material is in the range of 0 parts by weight to 50 parts by weight, such that the first sacrificial layer precursor material, the second sacrificial layer precursor material, and the optional third sacrificial layer precursor material constitute 100 parts by weight of the sacrificial layer precursor material.

[0085] In some preferred embodiments, the hydrogen fluoride barrier layer precursor material comprises only one hydrogen fluoride barrier layer precursor substance. In other preferred embodiments, the hydrogen fluoride barrier layer precursor material comprises a first hydrogen fluoride barrier layer precursor substance and a second hydrogen fluoride barrier layer precursor substance, wherein the amounts of the first and second hydrogen fluoride barrier layer precursor substances are in the range of 30 parts by weight to 70 parts by weight, such that the first and second hydrogen fluoride barrier layer precursor substances constitute 100 parts by weight of the hydrogen fluoride barrier layer precursor material.

[0086] In some embodiments of this application, the physical barrier layer precursor material comprises any one or any combination of elemental Ta, W, Hf, Zr, Nb, Sc, Zn, Al, their oxides, and phosphates; preferably, the physical barrier layer precursor material comprises a first physical barrier layer precursor material, a second physical barrier layer precursor material, and an optional third physical barrier layer precursor material, wherein the first physical barrier layer precursor material, the second physical barrier layer precursor material, and the optional third physical barrier layer precursor material are different from each other.

[0087] In some embodiments of this application, the physical barrier layer precursor materials include, but are not limited to, any one or any combination thereof of the following: elemental Ta, W, Hf, Zr, Nb, Sc, Zn, and Al, and Al2O3, ZrO2, AlPO4, W(PO4)2, Zr3(PO4)4, ZnO, NbO2, WO3, and Ta2O5. In preferred embodiments, the physical barrier layer precursor materials include, but are not limited to, any one or any combination thereof of the following: elemental W, Zr, Al, Sc, Nb, Zn, and Ta, and Al2O3, ZrO2, and AlPO4. In more preferred embodiments, the physical barrier layer precursor materials include, but are not limited to, any one or any combination thereof of the following: elemental W, Zr, and Sc, and Al2O3, ZrO2, and AlPO4.

[0088] In some preferred embodiments of this application, the physical barrier layer precursor material comprises a first physical barrier layer precursor substance and a second physical barrier layer precursor substance, wherein the amounts of the first physical barrier layer precursor substance and the second physical barrier layer precursor substance are respectively in the range of 20 parts by weight to 70 parts by weight, and the amount of the optional third physical barrier layer precursor substance is in the range of 0 parts by weight to 50 parts by weight, such that the first physical barrier layer precursor substance, the second physical barrier layer precursor substance and the optional third physical barrier layer precursor substance constitute 100 parts by weight of physical barrier layer precursor material.

[0089] According to another typical embodiment of the present invention, a positive electrode sheet for a lithium-ion secondary battery is provided, which comprises the composite positive electrode active material of the present invention. Because it comprises the composite positive electrode active material of the present invention, the positive electrode sheet for the lithium-ion secondary battery of the present invention can effectively prevent hydrogen fluoride from contacting and reacting with the positive electrode active material, inhibit the dissolution of metals in the positive electrode active material, and ensure the stability of the crystal structure in the bulk phase of the positive electrode active material. This allows the lithium-ion secondary battery containing it to maintain good power discharge capability after multiple cycles and suppresses battery gas generation at high temperatures.

[0090] According to another typical embodiment of the present invention, a lithium-ion secondary battery is provided, comprising: a positive electrode, a negative electrode, and a separator, wherein the positive electrode comprises the composite positive electrode active material of the present invention. When comprising the composite positive electrode active material of the present invention, the lithium-ion secondary battery of the present invention effectively avoids the corrosion of the positive electrode material by hydrogen fluoride, maintains good power discharge capability, reduces impedance after multiple cycles, and suppresses battery gas generation at high temperatures.

[0091] The present invention will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed by the present invention.

[0092] Example 1

[0093] Preparation of composite positive electrode active materials

[0094] Weigh out 8.4g of Ti (first sacrificial layer precursor), 8.4g of Al (second sacrificial layer precursor), and 8.4g of MgO (third sacrificial layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the sacrificial layer precursor material. Add 25.0g of the sacrificial layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the sacrificial layer precursor material is 2.5% (wt / wt) of the weight of the main phase (lithium nickel cobalt manganese oxide). Place the mixed material in a calcination furnace and calcine at approximately 300°C for 2 hours. Remove the calcined product, crush it using a crusher, and then sieve it through a 200-mesh sieve to obtain the first coated product (positive electrode active material coated with a sacrificial layer).

[0095] Weigh 25.0g of the first hydrogen fluoride barrier layer precursor material, elemental Nb, and 25.0g of the second hydrogen fluoride barrier layer precursor material, MgF2, in a weight ratio of 1:1, and mix them thoroughly to obtain the hydrogen fluoride barrier layer precursor material. Add 50.0g of the hydrogen fluoride barrier layer precursor material and 1050.0g of the first coating product to a mixer and mix thoroughly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide). Place the mixed material in a calcination furnace and calcine at approximately 350°C for 2 hours. Remove the calcined product, crush it using a crusher, and then sieve it through a 200-mesh sieve to obtain the second coating product (positive electrode active material coated with a sacrificial layer and a hydrogen fluoride barrier layer).

[0096] Weigh out 16.7g of elemental W (first physical barrier layer precursor), 16.7g of elemental Zr (second physical barrier layer precursor), and 16.7g of Al₂O₃ (third physical barrier layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the physical barrier layer precursor material. Add 50.0g of the physical barrier layer precursor material and 1100.0g of the second coating product to a mixer and mix thoroughly, wherein the weight of the physical barrier layer precursor material is 5% (wt / wt) of the weight of the bulk phase. Place the mixed material in a calcining furnace and calcine at approximately 550°C for 2 hours. Remove the calcined product, crush it using a crusher, and then sieve it through a 200-mesh sieve to obtain the composite positive electrode active material.

[0097] Preparation of lithium-ion secondary batteries

[0098] Preparation of positive electrode

[0099] 92.0 g of composite positive electrode active material, 5.0 g of graphite conductive agent, and 3.0 g of polyvinylidene fluoride binder were mixed to obtain a positive electrode mixture, which was then dispersed in 33.0 g of N-methylpyrrolidone to obtain a positive electrode mixture slurry. Subsequently, the positive electrode mixture slurry was coated onto aluminum foil to obtain a positive electrode current collector. The positive electrode current collector was dried, and a positive electrode sheet was formed using a stamping process.

[0100] Preparation of negative electrode

[0101] 97.0g of graphite powder, 2.0g of styrene-butadiene rubber, and 1.0g of carboxymethyl cellulose were added to an appropriate amount of water and stirred to form a negative electrode slurry. The obtained negative electrode slurry was then uniformly coated onto copper foil to obtain a negative electrode current collector. The negative electrode current collector was dried and formed into a negative electrode sheet using a stamping process.

[0102] Preparation of electrolyte

[0103] An electrolyte was prepared by mixing 15.0 g of ethylene carbonate, 70.0 g of dimethyl carbonate and 15.0 g of lithium hexafluorophosphate.

[0104] Battery assembly

[0105] CR2016 coin cells were assembled in a dry laboratory. The positive electrode sheet prepared in the above steps was used as the positive electrode, and the negative electrode sheet was used as the negative electrode. The positive electrode, negative electrode, separator, and coin cell casing were assembled and electrolyte was injected. After assembly, the cells were left to age for approximately 24 hours to obtain a lithium nickel cobalt manganese oxide coin cell.

[0106] Example 2

[0107] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 1, with the difference being:

[0108] Weigh out 8.4g of Ti (first sacrificial layer precursor), 8.4g of Al (second sacrificial layer precursor), and 8.4g of MgO (third sacrificial layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the sacrificial layer precursor material. Add 25.0g of the sacrificial layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the sacrificial layer precursor material is 2.5% (wt / wt) of the bulk phase (lithium nickel cobalt manganese oxide).

[0109] Weigh 50.0 g of the first hydrogen fluoride barrier layer precursor material, elemental Nb, and 50.0 g of the second hydrogen fluoride barrier layer precursor material, MgF2, in a weight ratio of 1:1, and mix them thoroughly to obtain the hydrogen fluoride barrier layer precursor material. Add 100.0 g of the hydrogen fluoride barrier layer precursor material and 1025.0 g of the first coating product to a mixer and mix thoroughly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 10% (wt / wt) of the host phase (lithium nickel cobalt manganese oxide).

[0110] Weigh out 8.4g of elemental W (first physical barrier layer precursor), 8.4g of elemental Zr (second physical barrier layer precursor), and 8.4g of Al₂O₃ (third physical barrier layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the physical barrier layer precursor material. Add 25.0g of the physical barrier layer precursor material and 1125.0g of the second coating product to a mixer and mix thoroughly, wherein the weight of the physical barrier layer precursor material is 2.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0111] Example 3

[0112] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 1, with the difference being:

[0113] Weigh out 16.7g of Ti (first sacrificial layer precursor), 16.7g of Al (second sacrificial layer precursor), and 16.7g of MgO (third sacrificial layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the sacrificial layer precursor material. Add 50.0g of the sacrificial layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the sacrificial layer precursor material is 5wt% (wt / wt) of the weight of the main phase (lithium nickel cobalt manganese oxide).

[0114] Weigh 25.0 g of the first hydrogen fluoride barrier layer precursor material, elemental Nb, and 25.0 g of the second hydrogen fluoride barrier layer precursor material, MgF2, in a weight ratio of 1:1, and mix them thoroughly to obtain the hydrogen fluoride barrier layer precursor material. Add 50.0 g of the hydrogen fluoride barrier layer precursor material and 1050.0 g of the first coating product to a mixer and mix thoroughly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 5 wt% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0115] Weigh out 8.4g of elemental W (first physical barrier layer precursor), 8.4g of elemental Zr (second physical barrier layer precursor), and 8.4g of Al₂O₃ (third physical barrier layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the physical barrier layer precursor material. Add 25.0g of the physical barrier layer precursor material and 1100.0g of the second coating product to a mixer and mix thoroughly, wherein the weight of the physical barrier layer precursor material is 2.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0116] Example 4

[0117] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 1, with the difference being:

[0118] Weigh out 8.4g of Ti (first sacrificial layer precursor), 8.4g of Al (second sacrificial layer precursor), and 8.4g of MgO (third sacrificial layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the sacrificial layer precursor material. Add 25.0g of the sacrificial layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the sacrificial layer precursor material is 2.5% (wt / wt) of the weight of the main phase (lithium nickel cobalt manganese oxide).

[0119] Weigh 25.0 g of the first hydrogen fluoride barrier layer precursor material, elemental Nb, and 25.0 g of the second hydrogen fluoride barrier layer precursor material, MgF2, in a weight ratio of 1:1, and mix them thoroughly to obtain the hydrogen fluoride barrier layer precursor material. Add 50.0 g of the hydrogen fluoride barrier layer precursor material and 1025.0 g of the first coating product to a mixer and mix thoroughly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0120] Weigh out 0.067g of elemental W (first physical barrier layer precursor), 0.067g of elemental Zr (second physical barrier layer precursor), and 0.067g of Al₂O₃ (third physical barrier layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the physical barrier layer precursor material. Add 0.2g of the physical barrier layer precursor material and 1075.0g of the second coating product to a mixer and mix thoroughly, wherein the weight of the physical barrier layer precursor material is 0.02% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0121] Example 5

[0122] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 1, with the difference being:

[0123] Weigh out 8.4g of Ti (first sacrificial layer precursor), 8.4g of Al (second sacrificial layer precursor), and 8.4g of MgO (third sacrificial layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the sacrificial layer precursor material. Add 25.0g of the sacrificial layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the sacrificial layer precursor material is 2.5% (wt / wt) of the weight of the main phase (lithium nickel cobalt manganese oxide).

[0124] Weigh 0.1g of the first hydrogen fluoride barrier layer precursor material, elemental Nb, and 0.1g of the second hydrogen fluoride barrier layer precursor material, MgF2, in a weight ratio of 1:1, and mix them thoroughly to obtain the hydrogen fluoride barrier layer precursor material. Add 0.2g of the hydrogen fluoride barrier layer precursor material and 1025.0g of the first coating product to a mixer and mix thoroughly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 0.02% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0125] Weigh out 8.4g of elemental W (first physical barrier layer precursor), 8.4g of elemental Zr (second physical barrier layer precursor), and 8.4g of Al₂O₃ (third physical barrier layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the physical barrier layer precursor material. Add 25.0g of the physical barrier layer precursor material and 1025.2g of the second coating product to a mixer and mix thoroughly, wherein the weight of the physical barrier layer precursor material is 2.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0126] Example 6

[0127] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 1, with the difference being:

[0128] Weigh out 0.067g of Ti (first sacrificial layer precursor), 0.067g of Al (second sacrificial layer precursor), and 0.067g of MgO (third sacrificial layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the sacrificial layer precursor material. Add 0.2g of the sacrificial layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the sacrificial layer precursor material is 0.02% (wt / wt) of the weight of the main phase (lithium nickel cobalt manganese oxide).

[0129] Weigh 25.0 g of the first hydrogen fluoride barrier layer precursor material, elemental Nb, and 25.0 g of the second hydrogen fluoride barrier layer precursor material, MgF2, in a weight ratio of 1:1, and mix them thoroughly to obtain the hydrogen fluoride barrier layer precursor material. Add 50.0 g of the hydrogen fluoride barrier layer precursor material and 1000.2 g of the first coating product to a mixer and mix thoroughly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0130] Weigh out 8.4g of elemental W (first physical barrier layer precursor), 8.4g of elemental Zr (second physical barrier layer precursor), and 8.4g of Al₂O₃ (third physical barrier layer precursor), with a weight ratio of 1:1:1, and mix thoroughly to obtain the physical barrier layer precursor material. Add 25.0g of the physical barrier layer precursor material and 1050.2g of the second coating product to a mixer and mix thoroughly, wherein the weight of the physical barrier layer precursor material is 2.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0131] Example 7

[0132] Preparation of composite positive electrode active materials

[0133] Weigh 25.0g of the first hydrogen fluoride barrier layer precursor material, elemental Nb, and 25.0g of the second hydrogen fluoride barrier layer precursor material, MgF2, in a weight ratio of 1:1, and mix them thoroughly to obtain the hydrogen fluoride barrier layer precursor material. Add 50.0g of the hydrogen fluoride barrier layer precursor material and 1050.0g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the main phase (lithium nickel cobalt manganese oxide). Place the mixed material in a calcination furnace and calcine at approximately 350°C for 2 hours. Remove the calcined product, crush it using a crusher, and then sieve it through a 200-mesh sieve to obtain the hydrogen fluoride barrier layer coated product (positive electrode active material coated with a hydrogen fluoride barrier layer).

[0134] Weigh out 8.4g of elemental W (first physical barrier layer precursor), 8.4g of elemental Zr (second physical barrier layer precursor), and 8.4g of Al₂O₃ (third physical barrier layer precursor), and mix them evenly to obtain the physical barrier layer precursor material. Add 25.0g of the physical barrier layer precursor material and 1050.0g of the hydrogen fluoride barrier layer coating product to a mixer and mix evenly, wherein the weight of the physical barrier layer precursor material is 2.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide). Place the mixed material in a calcination furnace and calcine at approximately 550°C for 2 hours. Remove the calcined product, crush it using a crusher, and then sieve it through a 200-mesh sieve to obtain the composite positive electrode active material.

[0135] Lithium-ion secondary batteries were prepared using the same method as in Example 1.

[0136] Example 8

[0137] Preparation of composite positive electrode active materials

[0138] Weigh 25.0 g of ZrO2 as the sacrificial layer precursor material. Add 25.0 g of the sacrificial layer precursor material and 1000.0 g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly. The weight of the sacrificial layer precursor material is 2.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide). Place the mixed material in a calcination furnace and calcine at approximately 300°C for 2 hours. Remove the calcined product, crush it using a crusher, and then sieve it through a 200-mesh sieve to obtain the first coated product (positive electrode active material coated with a sacrificial layer).

[0139] Weigh 50.0 g of MgF2 as the precursor material for the hydrogen fluoride barrier layer. Add 50.0 g of the hydrogen fluoride barrier layer precursor material and 1025.0 g of the first coating product to a mixer and mix thoroughly. Place the mixed material in a calcination furnace, wherein the weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide), and calcine at approximately 350°C for 2 hours. Remove the calcined product, crush it using a crusher, and then sieve it through a 200-mesh sieve to obtain the second coating product (positive electrode active material coated with a sacrificial layer and a hydrogen fluoride barrier layer).

[0140] Weigh 12.5g of the first physical barrier layer precursor material Sc and 12.5g of the second physical barrier layer precursor material ZrO2, and mix them evenly to obtain the physical barrier layer precursor material. Add 25.0g of the physical barrier layer precursor material and 1075.0g of the second coating product to a mixer and mix evenly, wherein the weight of the physical barrier layer precursor material is 2.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide). Place the mixed material in a calcination furnace and calcine at approximately 550°C for 2 hours. Remove the calcined product, crush it using a crusher, and then sieve it through a 200-mesh sieve to obtain the composite positive electrode active material.

[0141] Lithium-ion secondary batteries were prepared using the same method as in Example 1.

[0142] Example 9

[0143] Preparation of composite positive electrode active materials

[0144] Weigh 25.0 g of Mg(BO3)2 as the sacrificial layer precursor material. Mix 25.0 g of the sacrificial layer precursor material with 1000.0 g of lithium nickel cobalt manganese oxide in a mixer until homogeneous, wherein the weight of the sacrificial layer precursor material is 2.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide). Place the mixed material in a calcining furnace and calcine at approximately 300°C for 2 hours. Remove the calcined product, crush it using a crusher, and then sieve it through a 200-mesh sieve to obtain the first coated product.

[0145] Weigh 50.0 g of NbBO4 as the precursor material for the hydrogen fluoride barrier layer. Add 50.0 g of the hydrogen fluoride barrier layer precursor material and 1025.0 g of the first coating product to a mixer and mix thoroughly. The weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide). Place the mixed material in a calcining furnace and calcine at approximately 350°C for 2 hours. Remove the calcined product, crush it using a crusher, and then sieve it through a 200-mesh sieve to obtain the second coating product.

[0146] 25.0 g of elemental Nb was weighed as the precursor material for the physical barrier layer. The 25.0 g of the physical barrier layer precursor material and 1075.0 g of the second coating product were added to a mixer and mixed thoroughly. The weight of the physical barrier layer precursor material was 2.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide). The mixed material was placed in a calcining furnace and calcined at approximately 550°C for 2 hours. The calcined product was removed, crushed using a crusher, and then sieved through a 200-mesh sieve to obtain the composite positive electrode active material.

[0147] Lithium-ion secondary batteries were prepared using the same method as in Example 1.

[0148] Example 10

[0149] Preparation of composite positive electrode active materials

[0150] Weigh 12.5g of elemental W and 12.5g of AlF3 and mix them thoroughly as the sacrificial layer precursor material. Add 25.0g of the sacrificial layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the sacrificial layer precursor material is 2.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide). Place the mixed material in a calcining furnace and calcine at approximately 300°C for 2 hours. Remove the calcined product, crush it using a crusher, and then sieve it through a 200-mesh sieve to obtain the first coated product.

[0151] 50.0 g of ZrP₂O₇ was weighed as the precursor material for the hydrogen fluoride barrier layer. The 50.0 g of the hydrogen fluoride barrier layer precursor material and 1025.0 g of the first coating product were added to a mixer and mixed thoroughly. The weight of the hydrogen fluoride barrier layer precursor material was 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide). The mixed material was placed in a calcining furnace and calcined at approximately 350°C for 2 hours. The calcined product was removed, crushed using a crusher, and then sieved through a 200-mesh sieve to obtain the second coating product.

[0152] 25.0 g of Zn was weighed as the physical barrier layer precursor material. The 25.0 g of physical barrier layer precursor material and 1075.0 g of the second coating product were added to a mixer and mixed thoroughly. The weight of the physical barrier layer precursor material was 2.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide). The mixed material was placed in a calcining furnace and calcined at approximately 550°C for 2 hours. The calcined product was removed, crushed using a crusher, and then sieved through a 200-mesh sieve to obtain the composite positive electrode active material.

[0153] Lithium-ion secondary batteries were prepared using the same method as in Example 1.

[0154] Example 11

[0155] Preparation of composite positive electrode active materials

[0156] Weigh 25.0 g of Al₂O₃ as the sacrificial layer precursor material. Add 25.0 g of the sacrificial layer precursor material and 1000.0 g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly. The weight of the sacrificial layer precursor material is 2.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide). Place the mixed material in a calcining furnace and calcine at approximately 300°C for 2 hours. Remove the calcined product, crush it using a crusher, and then sieve it through a 200-mesh sieve to obtain the first coated product.

[0157] 50.0 g of Mn2PO4F was weighed as the precursor material for the hydrogen fluoride barrier layer. The 50.0 g of the hydrogen fluoride barrier layer precursor material and 1025.0 g of the first coating product were added to a mixer and mixed thoroughly. The weight of the hydrogen fluoride barrier layer precursor material was 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide). The mixed material was placed in a calcining furnace and calcined at approximately 350°C for 2 hours. The calcined product was removed, crushed using a crusher, and then sieved through a 200-mesh sieve to obtain the second coating product.

[0158] 25.0 g of AlPO4 was weighed as the precursor material for the physical barrier layer. The 25.0 g of the physical barrier layer precursor material and 1075.0 g of the second coating product were added to a mixer and mixed thoroughly. The weight of the physical barrier layer precursor material was 2.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide). The mixed material was placed in a calcining furnace and calcined at approximately 550°C for 2 hours. The calcined product was removed, crushed using a crusher, and then sieved through a 200-mesh sieve to obtain the composite positive electrode active material.

[0159] Lithium-ion secondary batteries were prepared using the same method as in Example 1.

[0160] Example 12

[0161] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 7, with the difference being:

[0162] Weigh 50.0g of Al2O3 as the precursor material for the hydrogen fluoride barrier layer. Add 50.0g of the hydrogen fluoride barrier layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix evenly. The weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0163] Weigh 50.0g of elemental Ta as the precursor material for the physical barrier layer. Add 50.0g of the physical barrier layer precursor material and 1050.0g of the hydrogen fluoride barrier layer coating product to a mixer and mix evenly. The weight of the physical barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0164] Example 13

[0165] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 7, with the difference being:

[0166] Weigh 50.0g of MgO as the precursor material for the hydrogen fluoride barrier layer. Add 50.0g of the hydrogen fluoride barrier layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix evenly. The weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the main phase (lithium nickel cobalt manganese oxide).

[0167] Weigh 50.0g of elemental Zr as the precursor material for the physical barrier layer. Add 50.0g of the physical barrier layer precursor material and 1050.0g of the hydrogen fluoride barrier layer coating product to a mixer and mix evenly. The weight of the physical barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0168] Example 14

[0169] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 7, with the difference being:

[0170] Weigh 50.0 g of ZrO2 as the precursor material for the hydrogen fluoride barrier layer. Add 50.0 g of the hydrogen fluoride barrier layer precursor material and 1000.0 g of lithium nickel cobalt manganese oxide to a mixer and mix evenly. The weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0171] Weigh 50.0g of elemental Al as the precursor material for the physical barrier layer. Add 50.0g of the physical barrier layer precursor material and 1050.0g of the hydrogen fluoride barrier layer coating product to a mixer and mix evenly. The weight of the physical barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0172] Example 15

[0173] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 7, with the difference being:

[0174] Weigh 25.0 g of Al2O3 and 25.0 g of MgO and mix them evenly as the precursor material for the hydrogen fluoride barrier layer. Add 50.0 g of the hydrogen fluoride barrier layer precursor material and 1000.0 g of lithium nickel cobalt manganese oxide to a mixer and mix evenly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0175] Weigh 25.0g of elemental Ta and 25.0g of elemental Zr, and mix them evenly as the physical barrier layer precursor material. Add 50.0g of the physical barrier layer precursor material and 1050.0g of the hydrogen fluoride barrier layer coating product to a mixer and mix evenly, wherein the weight of the physical barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0176] Example 16

[0177] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 7, with the difference being:

[0178] Weigh 25.0 g of ZrO2 and 25.0 g of Mg(BO3)2 and mix them evenly as the precursor material for the hydrogen fluoride barrier layer. Add 50.0 g of the hydrogen fluoride barrier layer precursor material and 1000.0 g of lithium nickel cobalt manganese oxide to a mixer and mix evenly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0179] Weigh 25.0 g of elemental Al and 25.0 g of elemental Nb, and mix them evenly as the physical barrier layer precursor material. Add 50.0 g of the physical barrier layer precursor material and 1050.0 g of the hydrogen fluoride barrier layer coating product to a mixer and mix evenly, wherein the weight of the physical barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0180] Example 17

[0181] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 7, with the difference being:

[0182] Weigh 16.7 g of elemental Nb and 33.3 g of MgF2 and mix them thoroughly as the precursor material for the hydrogen fluoride barrier layer, wherein the weight ratio of the two precursor materials is 1:2. Add 50.0 g of the hydrogen fluoride barrier layer precursor material and 1000.0 g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0183] Weigh out 12.5g of elemental W, 25.0g of elemental Zr, and 12.5g of Al₂O₃, and mix them evenly as the physical barrier layer precursor materials. The weight ratio of the three physical barrier layer precursor materials is 1:2:1. Add 50.0g of the physical barrier layer precursor materials and 1050.0g of the hydrogen fluoride barrier layer coating product to a mixer and mix evenly. The weight of the physical barrier layer precursor materials is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0184] Example 18

[0185] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 7, with the difference being:

[0186] Weigh 33.3 g of elemental Nb and 16.7 g of MgF2 and mix them thoroughly as the precursor material for the hydrogen fluoride barrier layer, wherein the weight ratio of the two precursor materials is 2:1. Add 50.0 g of the hydrogen fluoride barrier layer precursor material and 1000.0 g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0187] Weigh out 12.5g of elemental W, 12.5g of elemental Zr, and 25.0g of Al₂O₃, and mix them evenly as the physical barrier layer precursor materials. The weight ratio of the three physical barrier layer precursor materials is 1:1:2. Add 50.0g of the physical barrier layer precursor materials and 1050.0g of the hydrogen fluoride barrier layer coating product to a mixer and mix evenly. The weight of the physical barrier layer precursor materials is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0188] Example 19

[0189] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 1, with the difference being:

[0190] Weigh out 12.5g of Ti (first sacrificial layer precursor), 25.0g of Al (second sacrificial layer precursor), and 12.5g of MgO (third sacrificial layer precursor), with a weight ratio of 1:2:1, and mix them thoroughly to obtain the sacrificial layer precursor material. Add 50.0g of the sacrificial layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the sacrificial layer precursor material is 5% (wt / wt) of the weight of the main phase (lithium nickel cobalt manganese oxide).

[0191] Weigh 16.7g of the first hydrogen fluoride barrier layer precursor material, elemental Nb, and 33.3g of the second hydrogen fluoride barrier layer precursor material, MgF2, with a weight ratio of 1:2. Mix them thoroughly to obtain the hydrogen fluoride barrier layer precursor material. Add 50.0g of the hydrogen fluoride barrier layer precursor material and 1050.0g of the first coating product to a mixer and mix thoroughly. The weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0192] Weigh 12.5g of elemental W (first physical barrier layer precursor), 25.0g of elemental Zr (second physical barrier layer precursor), and 12.5g of Al₂O₃ (third physical barrier layer precursor), with a weight ratio of 1:2:1, and mix them thoroughly to obtain the physical barrier layer precursor material. Add 50.0g of the physical barrier layer precursor material and 1100.0g of the second coating product to a mixer and mix thoroughly, wherein the weight of the physical barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0193] Example 20

[0194] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 1, with the difference being:

[0195] Weigh 12.5g of Ti (first sacrificial layer precursor), 12.5g of Al (second sacrificial layer precursor), and 25.0g of MgO (third sacrificial layer precursor), with a weight ratio of 1:1:2, and mix them thoroughly to obtain the sacrificial layer precursor material. Add 50.0g of the sacrificial layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the sacrificial layer precursor material is 5% (wt / wt) of the weight of the main phase (lithium nickel cobalt manganese oxide).

[0196] Weigh 33.3g of the first hydrogen fluoride barrier layer precursor material, elemental Nb, and 16.7g of the second hydrogen fluoride barrier layer precursor material, MgF2, with a weight ratio of 2:1. Mix them thoroughly to obtain the hydrogen fluoride barrier layer precursor material. Add 50.0g of the hydrogen fluoride barrier layer precursor material and 1050.0g of the first coating product to a mixer and mix thoroughly. The weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0197] Weigh 12.5g of elemental W (first physical barrier layer precursor), 12.5g of elemental Zr (second physical barrier layer precursor), and 25.0g of Al₂O₃ (third physical barrier layer precursor), with a weight ratio of 1:1:2, and mix them thoroughly to obtain the physical barrier layer precursor material. Add 50.0g of the physical barrier layer precursor material and 1100.0g of the second coating product to a mixer and mix thoroughly, wherein the weight of the physical barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0198] Example 21

[0199] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 1, with the difference being:

[0200] Weigh out 11.67g of Ti (first sacrificial layer precursor), 11.67g of Al (second sacrificial layer precursor), and 11.67g of MgO (third sacrificial layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the sacrificial layer precursor material. Add 35.0g of the sacrificial layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the sacrificial layer precursor material is 3.5% (wt / wt) of the weight of the main phase (lithium nickel cobalt manganese oxide).

[0201] Weigh 37.5g of the first hydrogen fluoride barrier layer precursor material, elemental Nb, and 37.5g of the second hydrogen fluoride barrier layer precursor material, MgF2, in a weight ratio of 1:1, and mix them thoroughly to obtain the hydrogen fluoride barrier layer precursor material. Add 75.0g of the hydrogen fluoride barrier layer precursor material and 1035.0g of the first coating product to a mixer and mix thoroughly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 7.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0202] Weigh out 11.67g of elemental W (first physical barrier layer precursor), 11.67g of elemental Zr (second physical barrier layer precursor), and 11.67g of Al₂O₃ (third physical barrier layer precursor), with a weight ratio of 1:1:1, and mix thoroughly to obtain the physical barrier layer precursor material. Add 35.0g of the physical barrier layer precursor material and 1110.0g of the second coating product to a mixer and mix thoroughly, wherein the weight of the physical barrier layer precursor material is 3.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0203] Example 22

[0204] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 1, with the difference being:

[0205] Weigh out 6.67g of Ti (first sacrificial layer precursor), 6.67g of Al (second sacrificial layer precursor), and 6.67g of MgO (third sacrificial layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the sacrificial layer precursor material. Add 20.0g of the sacrificial layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the sacrificial layer precursor material is 2% (wt / wt) of the weight of the main phase (lithium nickel cobalt manganese oxide).

[0206] Weigh 10.0 g of the first hydrogen fluoride barrier layer precursor material, elemental Nb, and 10.0 g of the second hydrogen fluoride barrier layer precursor material, MgF2, in a weight ratio of 1:1, and mix them thoroughly to obtain the hydrogen fluoride barrier layer precursor material. Add 20.0 g of the hydrogen fluoride barrier layer precursor material and 1020.0 g of the first coating product to a mixer and mix thoroughly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 2% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0207] Weigh out 3.33g of elemental W (first physical barrier layer precursor), 3.33g of elemental Zr (second physical barrier layer precursor), and 3.33g of Al₂O₃ (third physical barrier layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the physical barrier layer precursor material. Add 10.0g of the physical barrier layer precursor material and 1040.0g of the second coating product to a mixer and mix thoroughly, wherein the weight of the physical barrier layer precursor material is 1% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0208] Comparative Example 1

[0209] Preparation of composite positive electrode active materials

[0210] Weigh 25.0g of Al2O3 and 1000.0g of lithium nickel cobalt manganese oxide and add them to a mixer, mixing thoroughly. Place the mixture in a calcining furnace and calcine at approximately 300°C for 2 hours. Remove the calcined product, crush it using a crusher, and then sieve it through a 200-mesh sieve to obtain the first coated product.

[0211] Weigh 50.0g of ZnO and 1025.0g of the first coating product and add them to a mixer and mix thoroughly. Place the mixture in a calcining furnace and calcine at approximately 350°C for 2 hours. Remove the calcined product, crush it using a crusher, and then sieve it through a 200-mesh sieve to obtain the second coating product.

[0212] Weigh 25.0g of Al2O3 and 1075.0g of the second coating product and add them to a mixer to mix evenly. Place the mixed material in a calcination furnace and calcine at approximately 550℃ for 2 hours. Remove the calcined product, crush it using a crusher, and then sieve it through a 200-mesh sieve to obtain the composite positive electrode active material.

[0213] Lithium-ion secondary batteries were prepared using the same method as in Example 1.

[0214] Comparative Example 2

[0215] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 7, with the difference being:

[0216] Weigh 50.0g of MgO as the precursor material for the hydrogen fluoride barrier layer. Add 50.0g of the hydrogen fluoride barrier layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix evenly. The weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the main phase (lithium nickel cobalt manganese oxide).

[0217] Weigh out 0.033 g of elemental W, 0.033 g of elemental Zr, and 0.033 g of Al₂O₃, and mix them evenly as the physical barrier layer precursor materials. The weight ratio of the three physical barrier layer precursor materials is 1:1:1. Add 0.1 g of the physical barrier layer precursor material and 1050.0 g of the hydrogen fluoride barrier layer coating product to a mixer and mix evenly. The weight of the physical barrier layer precursor material is 0.01% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0218] Comparative Example 3

[0219] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 7, with the difference being:

[0220] Weigh 50.0g of MgO as the precursor material for the hydrogen fluoride barrier layer. Add 50.0g of the hydrogen fluoride barrier layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix evenly. The weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the main phase (lithium nickel cobalt manganese oxide).

[0221] Weigh out 25.0 g of elemental W, 25.0 g of elemental Zr, and 25.0 g of Al₂O₃, and mix them evenly as the physical barrier layer precursor materials. The weight ratio of the three physical barrier layer precursor materials is 1:1:1. Add 75.0 g of the physical barrier layer precursor materials and 1050.0 g of the hydrogen fluoride barrier layer coating product to a mixer and mix evenly. The weight of the physical barrier layer precursor materials is 7.5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0222] Comparative Example 4

[0223] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 7, with the difference being:

[0224] Weigh 0.05 g of elemental Nb and 0.05 g of MgF2, and mix them evenly as the precursor material for the hydrogen fluoride barrier layer, wherein the weight ratio of the two hydrogen fluoride barrier layer precursor materials is 1:1. Add 0.1 g of the hydrogen fluoride barrier layer precursor material and 1000.0 g of lithium nickel cobalt manganese oxide to a mixer and mix evenly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 0.01% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0225] Weigh out 16.7 g of elemental W, 16.7 g of elemental Zr, and 16.7 g of Al₂O₃, and mix them evenly as the physical barrier layer precursor materials. The weight ratio of the three physical barrier layer precursor materials is 1:1:1. Add 50.0 g of the physical barrier layer precursor materials and 1000.1 g of the hydrogen fluoride barrier layer coating product to a mixer and mix evenly. The weight of the physical barrier layer precursor materials is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0226] Comparative Example 5

[0227] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 7, with the difference being:

[0228] Weigh 60.0 g of elemental Nb and 60.0 g of MgF2 and mix them evenly as the precursor material for the hydrogen fluoride barrier layer, wherein the weight ratio of the two hydrogen fluoride barrier layer precursor materials is 1:1. Add 120.0 g of the hydrogen fluoride barrier layer precursor material and 1000.0 g of lithium nickel cobalt manganese oxide to a mixer and mix evenly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 12% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0229] Weigh out 16.7g of elemental W, 16.7g of elemental Zr, and 16.7g of Al₂O₃, and mix them evenly as the physical barrier layer precursor materials. The weight ratio of the three physical barrier layer precursor materials is 1:1:1. Add 50.0g of the physical barrier layer precursor materials and 1120.0g of the hydrogen fluoride barrier layer coating product to a mixer and mix evenly. The weight of the physical barrier layer precursor materials is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0230] Comparative Example 6

[0231] The composite positive electrode active material and lithium-ion secondary battery were prepared in the same manner as in Example 1, with the difference being:

[0232] Weigh out 0.033g of Ti (first sacrificial layer precursor), 0.033g of Al (second sacrificial layer precursor), and 0.033g of MgO (third sacrificial layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the sacrificial layer precursor material. Add 0.1g of the sacrificial layer precursor material and 1000.0g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the sacrificial layer precursor material is 0.01% (wt / wt) of the weight of the main phase (lithium nickel cobalt manganese oxide).

[0233] Weigh 25.0 g of the first hydrogen fluoride barrier layer precursor material, elemental Nb, and 25.0 g of the second hydrogen fluoride barrier layer precursor material, MgF2, in a weight ratio of 1:1, and mix them thoroughly to obtain the hydrogen fluoride barrier layer precursor material. Add 50.0 g of the hydrogen fluoride barrier layer precursor material and 1000.1 g of the first coating product to a mixer and mix thoroughly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0234] Weigh out 16.7g of elemental W (first physical barrier layer precursor), 16.7g of elemental Zr (second physical barrier layer precursor), and 16.7g of Al₂O₃ (third physical barrier layer precursor), with a weight ratio of 1:1:1, and mix thoroughly to obtain the physical barrier layer precursor material. Add 50.0g of the physical barrier layer precursor material and 1050.1g of the second coating product to a mixer and mix thoroughly, wherein the weight of the physical barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0235] Comparative Example 7

[0236] Weigh out 25.0 g of Ti (first sacrificial layer precursor), 25.0 g of Al (second sacrificial layer precursor), and 25.0 g of MgO (third sacrificial layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the sacrificial layer precursor material. Add 75.0 g of the sacrificial layer precursor material and 1000.0 g of lithium nickel cobalt manganese oxide to a mixer and mix thoroughly, wherein the weight of the sacrificial layer precursor material is 7.5% (wt / wt) of the weight of the main phase (lithium nickel cobalt manganese oxide).

[0237] Weigh 25.0 g of the first hydrogen fluoride barrier layer precursor material, elemental Nb, and 25.0 g of the second hydrogen fluoride barrier layer precursor material, MgF2, in a weight ratio of 1:1, and mix them thoroughly to obtain the hydrogen fluoride barrier layer precursor material. Add 50.0 g of the hydrogen fluoride barrier layer precursor material and 1050.0 g of the first coating product to a mixer and mix thoroughly, wherein the weight of the hydrogen fluoride barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0238] Weigh out 16.7g of elemental W (first physical barrier layer precursor), 16.7g of elemental Zr (second physical barrier layer precursor), and 16.7g of Al₂O₃ (third physical barrier layer precursor), with a weight ratio of 1:1:1, and mix them thoroughly to obtain the physical barrier layer precursor material. Add 50.0g of the physical barrier layer precursor material and 1100.0g of the second coating product to a mixer and mix thoroughly, wherein the weight of the physical barrier layer precursor material is 5% (wt / wt) of the weight of the host phase (lithium nickel cobalt manganese oxide).

[0239] Comparative Example 8

[0240] No coating treatment is applied to the positive electrode active material (lithium nickel cobalt manganese oxide).

[0241] Lithium-ion secondary batteries were prepared using the same method as in Example 1.

[0242] Battery performance testing

[0243] Determination of capacity retention

[0244] The capacity retention rates of the lithium-ion secondary batteries produced in the various embodiments and comparative examples described above were measured as follows. First, the batteries were charged under the conditions of an ambient temperature of 23°C, a charging voltage of 4.35V, a charging current of 0.5mA, and a charging time of 10 hours. Then, they were discharged under the conditions of a discharging current of 2.5mA and a termination voltage of 3.0V, and the initial discharge capacity (discharge capacity of the first cycle) was measured. Next, repeated charging and discharging were performed under the conditions of an ambient temperature of 23°C, a charging voltage of 4.35V, a charging current of 0.5mA, and a charging time of 10 hours, and under the conditions of a discharging current of 2.5mA and a termination voltage of 3.0V. Subsequently, the discharge capacity of the 100th cycle was measured. Then, based on the following formula, the capacity retention rate (%) after 100 cycles was calculated using the discharge capacity of the first cycle and the discharge capacity of the 100th cycle.

[0245] Capacity retention rate [%] after 100 cycles = (Discharge capacity of the 100th cycle / Discharge capacity of the 1st cycle) × 100

[0246] Impedance measurement

[0247] The lithium-ion secondary battery was kept at 60°C and charged once at 0.5C, and the initial impedance value of the battery was determined. 100 charge-discharge cycles were performed at 60°C, and the final impedance value of the battery was measured at the end. The impedance growth rate (%) of the battery was calculated using the following formula.

[0248] Impedance growth rate (%) = (Final impedance value - Initial impedance value) / Initial impedance value × 100

[0249] Measurement of the thickness of composite positive electrode active material

[0250] For the first time, XPS depth etching method was used to measure film thickness. If the measured film thickness is in the range of 1-10 μm, the measurement result is retained. If the measured film thickness is greater than 10 μm, field emission scanning electron microscopy is used for measurement, and the film thickness greater than 10 μm is retained.

[0251] Table 1 shows the evaluation results of lithium-ion secondary batteries made from the composite positive electrode active material of the present invention in various comparative examples and embodiments.

[0252] Table 1

[0253]

[0254]

[0255] Note: The layer thickness in Comparative Example 1 in the table above only represents the thickness of the three layers at the corresponding positions, and does not indicate that the three layers in Comparative Example 1 can function as the sacrificial layer, hydrogen fluoride barrier layer and physical barrier layer of the present invention.

[0256] The experimental results above show that the above embodiments of the present invention achieve the following technical effects: By comparing the results of Examples 1-22 with Comparative Example 8 (without any treatment of the positive electrode active material), it can be seen that after using the composite positive electrode active material of this application, the contact and reaction between hydrogen fluoride and the positive electrode active material are effectively prevented, the dissolution of metals in the positive electrode active material is suppressed, and the stability of the crystal structure in the bulk phase of the positive electrode active material is ensured. As a result, the lithium-ion secondary battery containing it can still maintain a good cycle retention rate after multiple cycles, and has a low initial impedance value, and the growth of impedance is suppressed.

[0257] A comparison of the results of Example 7 and Comparative Example 3 shows that when the thickness of the physical barrier layer is greater than the thickness defined in this application, although the impedance growth rate increases by 100%, the initial impedance value and the final impedance value are much higher than the experimental results of Example 7 due to the excessive thickness of the physical barrier layer. At the same time, compared with the results of Comparative Example 3, the capacity and cycle retention rate of Example 7 are also significantly increased.

[0258] A comparison of the results of Example 7 and Comparative Example 2 shows that when the thickness of the physical barrier layer is less than the thickness defined in this application, and the initial impedance values ​​are similar, the final impedance value of Comparative Example 2 is much greater than that of Example 7, and the impedance growth rate reaches 150%. At the same time, the cycle retention rate of Comparative Example 2 is also less than that of Example 7.

[0259] A comparison of the results of Example 7 and Comparative Example 5 shows that when the thickness of the hydrogen fluoride barrier layer is greater than the thickness defined in this application, the capacity of Comparative Example 5 is close to that of Example 7. However, the initial impedance value, final impedance value, and impedance growth rate of Example 7 are all much smaller than those of Comparative Example 5. Meanwhile, Example 7 achieves a better cycle retention rate.

[0260] A comparison of the results of Example 7 and Comparative Example 4 shows that when the thickness of the hydrogen fluoride barrier layer is less than the thickness defined in this application, with an initial impedance value of 10Ω, the final impedance value of Example 7 is only 20Ω, which is much smaller than the result of Comparative Example 4, thus achieving a reduction in the impedance growth rate. Furthermore, compared to Comparative Example 4, Example 7 achieves excellent cycle retention.

[0261] A comparison of the results of Example 1 and Comparative Example 7 shows that when the thickness of the sacrificial layer is greater than the thickness defined in this application, although the impedance growth rate of Comparative Example 7 is lower than that of Example 1, its final impedance value (31.52Ω) also shows a non-structural result because the initial impedance value (16Ω) of Comparative Example 7 is much higher than that of Example 1.

[0262] A comparison of the results of Example 1 and Comparative Example 6 shows that when the thickness of the sacrificial layer is less than the thickness defined in this application, the cycle retention rate of Comparative Example 6 shows an unacceptable decrease (81%).

[0263] Furthermore, the results of Examples 7, 12-18 and Comparative Example 8 show that even with only a physical barrier layer and a hydrogen fluoride barrier layer, it is possible to effectively increase the cycle retention rate and reduce the impedance growth rate.

[0264] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite positive electrode active material, characterized in that, include: The core layer contains the positive electrode active material; A hydrogen fluoride barrier layer covering the core layer, the hydrogen fluoride barrier layer comprising one or any combination of the following substances: NbBO4, BaSO4, ZrP2O7, Mn2PO4F, CaSn4(PO4)6, Nb3(PO4)5, Nb(BO3)3, Zr(BO3)4 or Mn(BO3)4. A physical barrier layer, covering the hydrogen fluoride barrier layer; as well as A sacrificial layer is disposed between the core layer and the hydrogen fluoride barrier layer; the sacrificial layer comprises one or any combination of the following substances: Ti(BO3)4, Al(BO3)3, Zr(BO3)4, SrB4O7, Zn(BO3)2, Sc(BO3)3, Mg(BO3)2, Sr2Mg(BO3)4, and TaBO4.

2. The composite positive electrode active material according to claim 1, characterized in that, Based on 100 parts by weight of the core layer, the hydrogen fluoride barrier layer is in the range of 0.02 to 10 parts by weight.

3. The composite positive electrode active material according to claim 2, characterized in that, Based on 100 parts by weight of the core layer, the hydrogen fluoride barrier layer is in the range of 5 to 10 parts by weight.

4. The composite positive electrode active material according to claim 1, characterized in that, The thickness of the hydrogen fluoride barrier layer is in the range of 1 to 500 nm.

5. The composite positive electrode active material according to claim 4, characterized in that, The thickness of the hydrogen fluoride barrier layer is in the range of 50 to 500 nm.

6. The composite positive electrode active material according to claim 4, characterized in that, The thickness of the hydrogen fluoride barrier layer is in the range of 250 to 500 nm.

7. The composite positive electrode active material according to claim 1, characterized in that, The physical barrier layer comprises a substance consisting of any one or any combination of Ta, W, Hf, Zr, Nb, Sc, Zn, and Al, and any one or any combination of O and P.

8. The composite positive electrode active material according to claim 7, characterized in that, The physical barrier layer comprises a substance consisting of any one or any combination of Ta, W, Zr, Nb, Sc, Zn, and Al, and any one or any combination of O and P.

9. The composite positive electrode active material according to claim 1, characterized in that, Based on 100 parts by weight of the core layer, the physical barrier layer is in the range of 0.02 to 5 parts by weight.

10. The composite positive electrode active material according to claim 9, characterized in that, Based on 100 parts by weight of the core layer, the physical barrier layer is in the range of 0.02 to 2.5 parts by weight.

11. The composite positive electrode active material according to claim 1, characterized in that, The thickness of the physical barrier layer is in the range of 1 to 250 nm.

12. The composite positive electrode active material according to claim 11, characterized in that, The thickness of the physical barrier layer is in the range of 1 to 125 nm.

13. The composite positive electrode active material according to claim 11, characterized in that, The thickness of the physical barrier layer is in the range of 25 to 125 nm.

14. The composite positive electrode active material according to claim 1, characterized in that, The positive electrode active material comprises a general formula LiCo. 1-α M α Lithium cobalt oxide with O2, general formula LiNi 1-x-y Co x Mn y Lithium nickel cobalt manganese oxide (O2) and LiNi 1-x- y Co x Al y O2 is any one or any combination of lithium nickel cobalt aluminum oxide, wherein 0 < α ≤ 0.2, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1 and 0 ≤ x + y ≤ 1, and M is selected from any one or any combination of alkaline earth metal elements and transition metal elements, such that the sum of the valence states of the above general formula compound is zero.

15. The composite positive electrode active material according to claim 1, characterized in that, The sacrificial layer is in the range of 0.02 to 5 parts by weight, based on 100 parts by weight of the core layer.

16. The composite positive electrode active material according to claim 15, characterized in that, Based on 100 parts by weight of the core layer, the sacrificial layer is in the range of 2.5 to 5 parts by weight.

17. The composite positive electrode active material according to claim 1, characterized in that, The thickness of the sacrificial layer is in the range of 1 to 250 nm.

18. The composite positive electrode active material according to claim 17, characterized in that, The thickness of the sacrificial layer is in the range of 25 to 250 nm.

19. The composite positive electrode active material according to claim 17, characterized in that, The thickness of the sacrificial layer is in the range of 125 to 250 nm.

20. A method for preparing composite positive electrode active materials, characterized in that, include: Step S1-2: The sacrificial layer precursor material is mixed with active material particles to obtain a first mixture. The first mixture is calcined at a temperature range of 250°C to 350°C for 2 to 4 hours. The calcined product is crushed and sieved through a 200-mesh to 400-mesh sieve to obtain a first coated product. The first coated product is a positive electrode active material coated with a sacrificial layer. The sacrificial layer precursor material includes any one or any combination of Ti(BO3)4, Al(BO3)3, Zr(BO3)4, SrB4O7, Zn(BO3)2, Sc(BO3)3, Mg(BO3)2, Sr2Mg(BO3)4, and TaBO4. Step S2-2: The hydrogen fluoride barrier layer precursor material is mixed with the first coating product to obtain a second mixture. The second mixture is calcined at a temperature range of 250°C to 350°C for 2 to 4 hours. The calcined product is crushed and sieved through a 200-400 mesh sieve to obtain the second coating product. The hydrogen fluoride barrier layer precursor material comprises any one or any combination of NbBO4, BaSO4, ZrP2O7, Mn2PO4F, CaSn4(PO4)6, Nb3(PO4)5, Nb(BO3)3, Zr(BO3)4, or Mn(BO3)4. Step S3-2: Mix the physical barrier layer precursor material with the second coating product to obtain a third mixture. Calcinate the third mixture at a temperature range of 500°C to 600°C for 2 to 4 hours. Crush the calcined product and sieve it through a 200-mesh to 400-mesh sieve to obtain the composite positive electrode active material.

21. The method according to claim 20, characterized in that, The sacrificial layer precursor material comprises a first sacrificial layer precursor material, a second sacrificial layer precursor material, and an optional third sacrificial layer precursor material, wherein the first sacrificial layer precursor material, the second sacrificial layer precursor material, and the optional third sacrificial layer precursor material are different from each other, and wherein the amounts of the first sacrificial layer precursor material and the second sacrificial layer precursor material are each in the range of 20 parts by weight to 70 parts by weight, and the amount of the optional third sacrificial layer precursor material is in the range of 0 parts by weight to 50 parts by weight, such that the first sacrificial layer precursor material, the second sacrificial layer precursor material, and the optional third sacrificial layer precursor material constitute 100 parts by weight of the sacrificial layer precursor material.

22. The method according to claim 20, characterized in that, The hydrogen fluoride barrier layer precursor material comprises a first hydrogen fluoride barrier layer precursor material and a second hydrogen fluoride barrier layer precursor material, wherein the first hydrogen fluoride barrier layer precursor material and the second hydrogen fluoride barrier layer precursor material are different from each other, and wherein the amounts of the first hydrogen fluoride barrier layer precursor material and the second hydrogen fluoride barrier layer precursor material are in the range of 30 parts by weight to 70 parts by weight, such that the first hydrogen fluoride barrier layer precursor material and the second hydrogen fluoride barrier layer precursor material constitute 100 parts by weight of the hydrogen fluoride barrier layer precursor material.

23. The method according to claim 20, characterized in that, The physical barrier layer precursor material comprises any one or any combination of elemental Ta, W, Hf, Zr, Nb, Sc, Zn, Al, their oxides, and phosphates.

24. The method according to claim 23, characterized in that, The physical barrier layer precursor material comprises a first physical barrier layer precursor material, a second physical barrier layer precursor material, and an optional third physical barrier layer precursor material, wherein the first physical barrier layer precursor material, the second physical barrier layer precursor material, and the optional third physical barrier layer precursor material are different from each other, and wherein the amounts of the first physical barrier layer precursor material and the second physical barrier layer precursor material are each in the range of 20 parts by weight to 70 parts by weight, and the amount of the optional third physical barrier layer precursor material is in the range of 0 parts by weight to 50 parts by weight, such that the first physical barrier layer precursor material, the second physical barrier layer precursor material, and the optional third physical barrier layer precursor material constitute 100 parts by weight of the physical barrier layer precursor material.

25. A positive electrode sheet for a lithium-ion secondary battery, characterized in that, The composite positive electrode active material comprising any one of claims 1 to 19.

26. A lithium-ion secondary battery, comprising: Positive electrode plate, Negative electrode, and Diaphragm, Its features are, The positive electrode sheet comprises the composite positive electrode active material according to any one of claims 1 to 19.

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