A lithium ion battery layer oxygen cathode material, a preparation method and application thereof

Abstract

The application belongs to the field of lithium ion batteries, and particularly relates to a lithium ion battery layer oxygen positive electrode material and a preparation method and application thereof. The preparation method of the lithium ion battery layer oxygen positive electrode material comprises uniformly mixing M sources, M' sources and lithium sources, uniformly mixing the obtained mixture, and then high-temperature calcining the mixture in an oxygen-containing gas environment, and then low-temperature calcining the high-temperature calcination product in a fluorine-containing gas environment, wherein the volume fraction of fluorine gas in the fluorine-containing gas is 3% or more, and after the low-temperature calcination is completed, inert gas is introduced and naturally reduced to room temperature to obtain the lithium ion battery layer oxygen positive electrode material. The lithium ion battery layer oxygen positive electrode material obtained by the method can effectively improve the capacity and cycle life of the lithium ion battery.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion batteries, and in particular relates to a lithium-ion battery layer oxygen positive electrode material and a preparation method and application thereof. Background Art

[0002] As one of the four key materials in lithium-ion batteries, cathode materials play a crucial role in their ultimate performance. Element doping is a common method for stabilizing the crystal structure of cathode materials and improving safety. This is typically achieved by adding a small amount of impurity atoms or ions to the cathode material, altering the material's electronic structure, ion diffusion pathways, and crystal stability, thereby improving the capacity and cycle life of lithium-ion batteries.

[0003] For the doping of positive electrode materials, the traditional method is usually to introduce doping elements during the precursor sintering process, or to introduce doping elements after the positive electrode material is formed and then sinter it at high temperature. However, this method usually cannot achieve precise control over the distribution of doping elements, and it is easy for some elements to fail to enter the crystal structure of the material, resulting in the performance of the positive electrode material not meeting expectations or even deteriorating. Summary of the Invention

[0004] The first purpose of the present invention is to overcome the defect that the existing doped positive electrode materials cannot effectively improve the capacity and cycle life of lithium-ion batteries, and to provide a new lithium-ion battery layered oxygen positive electrode material, which can effectively improve the capacity and cycle life of lithium-ion batteries.

[0005] A second object of the present invention is to provide a method for preparing a lithium-ion battery.

[0006] The third object of the present invention is to provide a lithium-ion battery layer oxygen positive electrode material prepared by the above method.

[0007] A fourth object of the present invention is to provide an application of the above-mentioned lithium-ion battery layer oxygen cathode material in lithium-ion batteries.

[0008] Specifically, the lithium-ion battery layer oxygen positive electrode material provided by the present invention includes a substrate, a first region located on the surface of the substrate, and a second region located on the surface of the first region; the chemical formula of the substrate is Li 1+m M a M` b O2, the chemical formula of the first region and the second region is Li 1+m M a M` b O 2-c F c, M is selected from at least one of Ni, Co and Mn, M` is selected from at least one of Al, Mg, Sr, Zr, Ba, Ti, Ca and rare earth elements, a+b=1, 0.9≤a≤1, 0<b≤0.1, -0.05≤m≤0.1, 0<c≤0.1; the matrix does not contain free doping elements M`; the ratio of the atomic concentration of F to the atomic concentration of M` in the first region is smaller than the ratio of the atomic concentration of F to the atomic concentration of M` in the second region, the first region contains a region where the ratio of the atomic concentration of F to the atomic concentration of M` is less than 0.5, and the second region contains a region where the ratio of the atomic concentration of F to the atomic concentration of M` is greater than 1.

[0009] The preparation method of the lithium ion battery layer oxygen positive electrode material provided by the present invention comprises uniformly mixing an M source, an M' source and a lithium source, then subjecting the obtained mixture to high-temperature calcination in an oxygen-containing gas environment, and then subjecting the high-temperature calcination product to low-temperature calcination in a fluorine-containing gas environment, wherein the volume fraction of fluorine gas in the fluorine-containing gas is greater than 3%. After the low-temperature calcination is completed, an inert gas is introduced and the temperature is naturally cooled to room temperature to obtain the lithium ion battery layer oxygen positive electrode material.

[0010] The key to the present invention is to add a low-temperature platform for fluorine-containing gas treatment after the positive electrode material precursor is sintered, and at the same time control the proportion of fluorine gas in the fluorine-containing gas, so that a more electronegative F element can be introduced on the surface of the positive electrode material matrix as a "target point", and the free elements in the matrix that are not doped into the crystal lattice are pulled to the surface of the matrix particles, forming a double metal fluoride coating layer with different F / M' atomic concentration ratios on the surface of the matrix particles. This can not only improve the element utilization rate, reduce the internal defects of the matrix particles, and improve the structural stability and compressive resistance of the material, but also the internal M' element doping of the matrix particles and the double co-coating of the external M' element and F element can synergistically improve the capacity of the lithium-ion battery. At the same time, the formation of the double metal fluoride coating layer with different F / M' atomic concentration ratios can also effectively reduce the side reaction between the material and the electrolyte, reduce the corrosion of the material by trace HF in the battery system, and improve the cycle performance of the material. In addition, the present invention provides F elements through fluorine gas. The content of F elements introduced into the material is controlled by the content of free elements in the material that are not doped into the matrix lattice. Excessive F elements are not introduced. The free elements dispersed in the matrix are attracted by the external fluorine environment and are mostly enriched on the surface of the matrix particles. Therefore, the F content on the surface is relatively high. At the same time, due to the influence of diffusion dynamics, a small amount of F elements will also diffuse into the interior of the matrix particles and combine with the free elements. Therefore, the final state is that the F elements on the surface of the matrix particles are higher than those near the surface. In addition, the method provided by the present invention uses fluorine gas as the doping gas. In addition, no other impurity elements are introduced.

[0011] In a preferred embodiment, the low-temperature calcination method is to introduce inert gas after the high-temperature calcination is completed to evacuate the oxygen-containing gas and reduce the temperature to the low-temperature calcination temperature, and then introduce fluorine-containing gas for low-temperature calcination, that is, a low-temperature platform is added to the cooling section after high-temperature calcination to carry out low-temperature calcination of fluorine-containing gas. At this time, the elements in the matrix particles that are not doped into the crystal lattice are still in an activated state, which is conducive to being drawn to the particle surface by the fluorine element to participate in the fluorination reaction, and the capacity and cycle performance of the material are better. DETAILED DESCRIPTION

[0012] The present invention provides a lithium-ion battery layer oxygen cathode material comprising a substrate, a first region, and a second region. The first region is located on the surface of the substrate, and the second region is located on the surface of the first region. In other words, the substrate surface is sequentially coated with the first and second regions.

[0013] In the present invention, the chemical formula of the matrix is ​​Li 1+m M a M` b O2, the chemical formula of the first region and the second region is Li 1+m M a M` b O 2-c F c, M is selected from at least one of Ni, Co and Mn, M' is selected from at least one of Al, Mg, Sr, Zr, Ba, Ti, Ca and rare earth elements, a+b=1, 0.9≤a≤1, 0<b≤0.1, -0.05≤m≤0.1, 0<c≤0.1. Specifically, the matrix can be at least one of lithium cobalt oxide, ternary materials (nickel cobalt manganese), lithium-rich manganese-based materials and layered lithium manganese oxide. M' is a doping element selected from at least one of Al, Mg, Sr, Zr, Ba, Ti, Ca and rare earth elements, preferably at least one of Mg, Al and Ti. When M' is preferably at least one of Mg, Al and Ti, these elements are more easily drawn to the particle surface when they exist in a free state, which is more conducive to avoiding the generation of defects inside the matrix particles and better improving the cycle stability or rate performance of the material. The term "rare earth elements" includes lanthanides, scandium (Sc) and yttrium (Y). The lanthanide element is selected from at least one of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). a can be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, or any value therebetween. b can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value therebetween. m can be -0.05, -0.04, -0.03, -0.02, -0.01, 0, 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, or any value therebetween. c can be 0.01, 0.02, 0.04, 0.06, 0.08, 0.1, or any value therebetween. Furthermore, the particle size D50 of the matrix is ​​preferably 2 to 20 μm, specifically 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 16 μm, 18 μm, 20 μm, or any value therebetween.

[0014] In the present invention, both the first region and the second region contain F elements and M` elements, and the ratio of the atomic concentration of F to the atomic concentration of M` in the first region is less than the ratio of the atomic concentration of F to the atomic concentration of M` in the second region. The first region contains a region where the ratio of the atomic concentration of F to the atomic concentration of M` is less than 0.5. Preferably, the ratio of the atomic concentration of F to the atomic concentration of M` in the first region is 0.2 to 0.5, specifically 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 or any value therebetween. The second region contains a region where the ratio of the atomic concentration of F to the atomic concentration of M` is greater than 1. Preferably, the ratio of the atomic concentration of F to the atomic concentration of M` in the second region is 1 to 4, specifically 1, 1.5, 2, 2.5, 3, 3.5, 4 or any value therebetween. In addition, the thickness of the first region is preferably 10 to 50 nm, specifically 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or any value therebetween. The thickness of the second region is preferably 2 to 5 nm, specifically 2 nm, 2.5 nm, 3 nm, 3.5 nm, 4 nm, 4.5 nm, 5 nm, or any value therebetween.

[0015] The preparation method of the lithium ion battery layer oxygen positive electrode material provided by the present invention comprises uniformly mixing an M source, an M' source and a lithium source, then subjecting the obtained mixture to high-temperature calcination in an oxygen-containing gas environment, and then subjecting the high-temperature calcination product to low-temperature calcination in a fluorine-containing gas environment, wherein the volume fraction of fluorine gas in the fluorine-containing gas is greater than 3%. After the low-temperature calcination is completed, an inert gas is introduced and the temperature is naturally cooled to room temperature to obtain the lithium ion battery layer oxygen positive electrode material.

[0016] In the present invention, the stoichiometric ratio of the M source, M' source and lithium source is such that the chemical formula of the obtained matrix is ​​Li 1+ m M a M` bO2 is used as the standard, M is selected from at least one of Ni, Co and Mn, M' is selected from at least one of Al, Mg, Sr, Zr, Ba, Ti, Ca and rare earth elements, a+b=1, 0.9≤a≤1, 0<b≤0.1, -0.05≤m≤0.1. M' is a doping element selected from at least one of Al, Mg, Sr, Zr, Ba, Ti, Ca and rare earth elements, preferably at least one of Mg, Al and Ti. The term "rare earth element" includes lanthanides, scandium (Sc) and yttrium (Y). The lanthanide element is selected from at least one of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). a can be 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, or any value therebetween. b can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, or any value therebetween. m can be -0.05, -0.04, -0.03, -0.02, -0.01, 0, 0.01, 0.02, 0.04, 0.06, 0.08, 0.1 or any value therebetween.

[0017] The present invention does not particularly limit the type of M source, and can be any of the existing various substances that can react with the lithium source to form a positive electrode material, for example, it can be selected from at least one of the oxides, hydroxides, oxyhydroxides, carbonates, oxalates, and acetates of M, or the oxides, hydroxides, oxyhydroxides, carbonates, oxalates, and acetates of M' doped with M', specifically, the hydroxides, oxyhydroxides, carbonates, oxalates, and acetates of Ni, the hydroxides, oxyhydroxides, carbonates, oxalates, and acetates of Co, the hydroxides, oxyhydroxides, carbonates, oxalates, and acetates of Mn, the hydroxides, oxyhydroxides, carbonates, oxalates, and acetates of Ni doped with Al, and the hydroxides, oxyhydroxides, carbonates, oxalates, and acetates of Al doped with Al. The hydroxide, oxyhydroxide, carbonate, oxalate, acetate of Co; the hydroxide, oxyhydroxide, carbonate, oxalate, acetate of Al-doped Mn; the hydroxide, oxyhydroxide, carbonate, oxalate, acetate of Mg-doped Ni; the hydroxide, oxyhydroxide, carbonate, oxalate, acetate of Mg-doped Co; the hydroxide, oxyhydroxide, carbonate, oxalate, acetate of Mg-doped Mn; the hydroxide, oxyhydroxide, carbonate, oxalate, acetate of Sr-doped Ni; the hydroxide, oxyhydroxide, carbonate, oxalate, acetate of Sr-doped Co; the hydroxide, oxyhydroxide, carbonate, oxalate, acetate of Sr-doped Mn. hydroxides, oxyhydroxides, carbonates, oxalates, acetates of Zr-doped Ni, hydroxides, oxyhydroxides, carbonates, oxalates, acetates of Zr-doped Co, hydroxides, oxyhydroxides, carbonates, oxalates, acetates of Zr-doped Mn, hydroxides, oxyhydroxides, carbonates, oxalates, acetates of Ba-doped Ni, hydroxides, oxyhydroxides, carbonates, oxalates, acetates of Ba-doped Co, hydroxides, oxyhydroxides, carbonates, oxalates, acetates of Ba-doped Mn, hydroxides, oxyhydroxides, carbonates, oxalates, acetates of Ti-doped Ni, hydroxides, oxyhydroxides, carbonates, oxalates, acetates of Ti-doped Co. at least one of the following: hydroxide, oxyhydroxide, carbonate, oxalate, acetate of Ti-doped Mn, hydroxide, oxyhydroxide, carbonate, oxalate, acetate of Ni doped with Ca, hydroxide, oxyhydroxide, carbonate, oxalate, acetate of Co doped with Ca, hydroxide, oxyhydroxide, carbonate, oxalate, acetate of Mn doped with Ca, hydroxide, oxyhydroxide, carbonate, oxalate, acetate of Ni doped with rare earth elements, hydroxide, oxyhydroxide, carbonate, oxalate, acetate of Co doped with rare earth elements, and hydroxide, oxyhydroxide, carbonate, oxalate, acetate of Mn doped with rare earth elements.

[0018] The present invention does not particularly limit the type of M' source, and can be any of the existing various substances that can be used as doping elements to improve the capacity and cycle performance of lithium-ion batteries. For example, it can be selected from at least one of oxides, carbonates, hydroxides, nitrates, oxalates, chlorides, fluorides, sulfates, and acetates containing M', which can include oxides, carbonates, hydroxides, nitrates, oxalates, chlorides, fluorides, sulfates, and acetates of Al; oxides, carbonates, hydroxides, nitrates, oxalates, chlorides, fluorides, sulfates, and acetates of Mg; oxides, carbonates, hydroxides, nitrates, oxalates, chlorides, fluorides, sulfates, and acetates of Sr; , fluoride, sulfate, acetate, Zr oxide, carbonate, hydroxide, nitrate, oxalate, chloride, fluoride, sulfate, acetate, Ba oxide, carbonate, hydroxide, nitrate, oxalate, chloride, fluoride, sulfate, acetate, Ti oxide, carbonate, hydroxide, nitrate, oxalate, chloride, fluoride, sulfate, acetate, Ca oxide, carbonate, hydroxide, nitrate, oxalate, chloride, fluoride, sulfate, acetate, rare earth element oxide, carbonate, hydroxide, nitrate, oxalate, chloride, fluoride, sulfate, acetate at least one.

[0019] The present invention has no particular limitation on the type of lithium source, and the lithium source may be selected from at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, lithium sulfate and lithium bicarbonate.

[0020] In the present invention, the oxygen-containing gas may be oxygen gas or a mixture of oxygen gas and an inert gas. The oxygen concentration in the oxygen-containing gas is preferably 20 to 100 vol%, specifically 20 vol%, 25 vol%, 30 vol%, 35 vol%, 40 vol%, 45 vol%, 50 vol%, 55 vol%, 60 vol%, 65 vol%, 70 vol%, 75 vol%, 80 vol%, 85 vol%, 90 vol%, 95 vol%, 100 vol%, or any value therebetween.

[0021] In the present invention, the fluorine-containing gas is a mixture of fluorine and an inert gas. The volume fraction of the fluorine gas is 3% or greater, preferably 3% to 10%, and specifically 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value therebetween. When the volume fraction of fluorine in the fluorine-containing gas is less than 3%, the fluorine content is insufficient to completely remove the elements that are not doped into the crystal lattice of the matrix particles, resulting in little change in the material capacity and ineffective improvement in cycling performance.

[0022] In the present invention, the conditions for high-temperature calcination include a temperature preferably of 800-1100°C, such as 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C, 1100°C or any value therebetween; and a time preferably of 6-20h, such as 6h, 8h, 10h, 12h, 14h, 16h, 18h, 20h or any value therebetween.

[0023] In the present invention, the conditions for the low-temperature calcination include a temperature preferably of 500 to 750°C, such as 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or any value therebetween; and a time preferably of 2 to 6 hours, such as 2h, 3h, 4h, 5h, 6h or any value therebetween. In a preferred embodiment, the low-temperature calcination is carried out by introducing an inert gas after the high-temperature calcination is completed, evacuating the oxygen-containing gas and lowering the temperature to the low-temperature calcination temperature, and then introducing a fluorine-containing gas for low-temperature calcination. If the temperature is completely lowered to room temperature and then raised to the calcination temperature required for low-temperature calcination, the elements that are not doped into the matrix lattice will exist in the matrix particles in a relatively stable chemical state. After reheating, these doping elements cannot be fully activated to participate in the fluorination reaction, and the effect is poor. On the contrary, directly adding a low-temperature platform for calcination during the cooling process can pull the undoped elements in the matrix particles to the surface of the matrix particles while they are still in an activated state, giving the material higher capacity and better cycle stability. In addition, the rate of decreasing the calcination temperature from the high temperature to the low temperature is preferably 0.4-5°C / min, specifically 0.4, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5°C / min or any value therebetween.

[0024] In the present invention, the inert gas may be nitrogen and / or argon.

[0025] The present invention also provides a lithium ion battery layer oxygen positive electrode material prepared by the above method.

[0026] In addition, the present invention also provides the use of the above-mentioned lithium ion battery layer oxygen positive electrode material in lithium ion batteries.

[0027] The present invention will be described in detail below through examples.

[0028] Example 1

[0029] According to Li 1.01 Co 0.99 Mg 0.01Cobaltous oxide, magnesium carbonate and lithium carbonate are weighed and mixed evenly in a stoichiometric ratio of O2. The resulting mixture is then calcined at 1000°C for 10 hours in a mixed atmosphere of oxygen and nitrogen (containing 30 vol% oxygen). Nitrogen is introduced to evacuate the oxygen-containing gas and the temperature is lowered to 650°C at a rate of 0.4°C / min. Then, a mixed atmosphere of fluorine and nitrogen (the volume fraction of fluorine is 6%) is introduced and the mixture is calcined for 4 hours. After the calcination is completed, nitrogen is introduced and the mixture is naturally cooled to room temperature. After sieving and powdering, a lithium-ion battery layer oxygen positive electrode material is obtained.

[0030] This lithium-ion battery layered oxygen cathode material includes a substrate, a first region located on the substrate surface, and a second region located on the surface of the first region. Laser particle size analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) revealed that the substrate had a particle size (D50) of 19.4 μm and contained no free dopant element Mg. Both the first and second regions contained F and Mg. The ratio of the atomic concentration of F to the atomic concentration of Mg in the first region was 0.2 to 0.5, while the ratio of the atomic concentration of F to the atomic concentration of Mg in the second region was 1 to 4. The thickness of the first region was 34 to 36 nm, and the thickness of the second region was 3 to 4 nm. Furthermore, XPS was used to measure the atomic concentrations of F and the dopant element Mg at 1 nm and 10 nm from the surface of the material, and the ratios were calculated. The results are shown in Table 1.

[0031] Example 2

[0032] According to Li 1.01 Co 0.99 Mg 0.01 Cobaltous oxide, magnesium carbonate and lithium carbonate are weighed and mixed evenly in a stoichiometric ratio of O2. The resulting mixture is then calcined at 800°C for 20 hours in a mixed atmosphere of oxygen and nitrogen (containing 30 vol% oxygen). Nitrogen is introduced to evacuate the oxygen-containing gas and the temperature is lowered to 500°C at a rate of 5°C / min. Then, a mixed atmosphere of fluorine and nitrogen (the volume fraction of fluorine is 3%) is introduced and the mixture is calcined for 6 hours. After the calcination is completed, nitrogen is introduced and the mixture is naturally cooled to room temperature. After sieving and powdering, a lithium-ion battery layer oxygen positive electrode material is obtained.

[0033] This lithium-ion battery layer oxygen cathode material includes a substrate, a first region located on the substrate surface, and a second region located on the surface of the first region. Laser particle size analysis, SEM, and XPS analysis indicate that the substrate has a particle size (D50) of 16.5 μm and contains no free dopant element Mg. Both the first and second regions contain F and Mg. The ratio of the atomic concentration of F to the atomic concentration of Mg in the first region is 0.2 to 0.5, while the ratio of the atomic concentration of F to the atomic concentration of Mg in the second region is 1 to 4. The thickness of the first region is 30 to 33 nm, and the thickness of the second region is 2.5 to 3.5 nm. Furthermore, XPS was used to measure the atomic concentrations of F and the dopant element Mg at 1 nm and 10 nm from the material surface, and the ratios were calculated. The results are shown in Table 1.

[0034] Example 3

[0035] According to Li 1.01 Co 0.99 Mg 0.01 Cobaltous oxide, magnesium carbonate and lithium carbonate are weighed and mixed evenly in a stoichiometric ratio of O2. The resulting mixture is then calcined at 1000°C for 10 hours in a mixed atmosphere of oxygen and nitrogen (containing 30 vol% oxygen). Nitrogen is introduced to evacuate the oxygen-containing gas and the temperature is lowered to 750°C at a rate of 2°C / min. Then, a mixed atmosphere of fluorine and nitrogen (the volume fraction of fluorine is 10%) is introduced and the mixture is calcined for 2 hours. After the calcination is completed, nitrogen is introduced and the mixture is naturally cooled to room temperature. After sieving and powdering, a lithium-ion battery layer oxygen positive electrode material is obtained.

[0036] This lithium-ion battery layer oxygen cathode material includes a substrate, a first region located on the substrate surface, and a second region located on the surface of the first region. Laser particle size analysis, SEM, XRD, and XPS analysis indicate that the substrate has a particle size (D50) of 11.2 μm and contains no free dopant element Mg. Both the first and second regions contain F and Mg. The ratio of the atomic concentration of F to the atomic concentration of Mg in the first region is 0.2 to 0.5, while the ratio of the atomic concentration of F to the atomic concentration of Mg in the second region is 1 to 4. The thickness of the first region is 35 to 37 nm, and the thickness of the second region is 3.5 to 4.5 nm. Furthermore, XPS was used to measure the atomic concentrations of F and the dopant element Mg at 1 nm and 10 nm from the surface of the material, and the ratios were calculated. The results are shown in Table 1.

[0037] Example 4

[0038] According to LiCo 0.99 Al 0.01O2 stoichiometric ratio of cobalt tetraoxide, aluminum oxide and lithium carbonate are weighed respectively and mixed uniformly, and then the obtained mixture is calcined at 1000℃ for 10h in a mixed atmosphere of oxygen and nitrogen (oxygen content is 30vol%), oxygen-containing gas is exhausted by passing nitrogen, and the temperature is decreased to 650℃ at a rate of 3℃ / min, then a mixed atmosphere of fluorine and nitrogen (volume fraction of fluorine is 6%) is passed in, and calcination is performed for 4h, after the calcination is completed, nitrogen is passed in and the temperature is decreased to room temperature naturally, and after sieving and powdering, a lithium ion battery layer-oxygen positive electrode material is obtained.

[0039] The lithium ion battery layer-oxygen positive electrode material comprises a substrate, a first region on the surface of the substrate, and a second region on the surface of the first region. The results of the laser particle size analyzer, SEM, XRD and XPS show that the particle size D50 of the substrate is 10.5μm, the substrate does not contain free doping elements Al, the first region and the second region both contain F elements and Al elements, the ratio of the atomic concentration of F to the atomic concentration of Al in the first region is 0.2-0.5, the ratio of the atomic concentration of F to the atomic concentration of Al in the second region is 1-4, the thickness of the first region is 46-48nm, and the thickness of the second region is 4-5nm. In addition, the atomic concentrations of F elements and doping elements Al at 1nm and 10nm on the surface of the material are tested by XPS, and the ratio is calculated. The results are shown in Table 1.

[0040] Example 5

[0041] According to Li 0.99 Co 0.99 Ti 0.01 O2 stoichiometric ratio of cobalt tetraoxide, aluminum oxide and lithium carbonate are weighed respectively and mixed uniformly, and then the obtained mixture is calcined at 1000℃ for 10h in a mixed atmosphere of oxygen and nitrogen (oxygen content is 30vol%), oxygen-containing gas is exhausted by passing nitrogen, and the temperature is decreased to 650℃ at a rate of 3℃ / min, then a mixed atmosphere of fluorine and nitrogen (volume fraction of fluorine is 6%) is passed in, and calcination is performed for 4h, after the calcination is completed, nitrogen is passed in and the temperature is decreased to room temperature naturally, and after sieving and powdering, a lithium ion battery layer-oxygen positive electrode material is obtained.

[0042] This lithium-ion battery layered oxygen cathode material includes a substrate, a first region located on the substrate surface, and a second region located on the surface of the first region. Laser particle size analysis, SEM, XRD, and XPS analysis indicate that the substrate has a particle size (D50) of 9.2 μm and contains no free dopant Ti. Both the first and second regions contain fluorine and titanium. The ratio of the atomic concentration of fluorine to the atomic concentration of titanium in the first region is 0.2 to 0.5, while the ratio of the atomic concentration of fluorine to the atomic concentration of titanium in the second region is 1 to 4. The thickness of the first region is 27 to 29 nm, and the thickness of the second region is 2 to 3 nm. Furthermore, XPS was used to measure the atomic concentrations of fluorine and the dopant Ti at 1 nm and 10 nm from the surface of the material, and the ratios were calculated. The results are shown in Table 1.

[0043] Example 6

[0044] The layered oxygen cathode material for lithium-ion batteries was prepared according to the method of Example 1, except that after high-temperature calcination, the material was first cooled to room temperature and then calcined at low temperature. The specific steps are as follows:

[0045] According to Li 1.01 Co 0.99 Mg 0.01 Cobalt trioxide, magnesium carbonate and lithium carbonate were weighed and mixed in a stoichiometric ratio of O2, and the resulting mixture was calcined at 1000 ° C for 10 h in a mixed atmosphere of oxygen and nitrogen (containing 30 vol%), and then naturally cooled to room temperature to obtain the matrix Li 1.01 Co 0.99 Mg 0.01 A mixed atmosphere of fluorine and nitrogen (the volume fraction of fluorine is 6%) is introduced into the substrate, and the temperature is raised to 650°C and calcined for 4 hours. After calcination, nitrogen is introduced and the substrate is naturally cooled to room temperature. The substrate is sieved and powdered to obtain a lithium-ion battery layer oxygen cathode material.

[0046] This lithium-ion battery layered oxygen cathode material includes a substrate, a first region located on the substrate surface, and a second region located on the surface of the first region. Laser particle size analysis, SEM, XRD, and XPS analysis indicate that the substrate has a particle size (D50) of 19.4 μm and contains no free dopant element Mg. Both the first and second regions contain F and Mg. The ratio of the atomic concentration of F to the atomic concentration of Mg in the first region is 0.2 to 0.5, while the ratio of the atomic concentration of F to the atomic concentration of Mg in the second region is 1 to 4. The thickness of the first region is 34 to 36 nm, and the thickness of the second region is 3 to 4 nm. Furthermore, XPS was used to measure the atomic concentrations of F and the dopant element Mg at 1 nm and 10 nm from the material surface, and the ratios were calculated. The results are shown in Table 1.

[0047] Comparative Example 1

[0048] A lithium-ion battery layer oxygen cathode material was prepared according to the method of Example 2, except that the volume fraction of fluorine gas in the mixed atmosphere was reduced to 1%. The remaining conditions were the same as in Example 2 to obtain a lithium-ion battery layer oxygen cathode material, wherein the matrix particles of the lithium-ion battery layer oxygen cathode material contained the doping element Mg.

[0049] Comparative Example 2

[0050] A lithium ion battery layer oxygen cathode material was prepared according to the method of Example 2, except that the mixed gas of fluorine and nitrogen was replaced by nitrogen. The other conditions were the same as in Example 2 to obtain a lithium ion battery layer oxygen cathode material.

[0051] Comparative Example 3

[0052] A lithium-ion battery layer oxygen positive electrode material was prepared according to the method of Example 1, except that the fluorine gas in the mixed atmosphere was replaced by hydrogen fluoride (HF) with the same volume fraction. The other conditions were the same as in Example 1 to obtain a lithium-ion battery layer oxygen positive electrode material. The lithium-ion battery layer oxygen positive electrode material only contained a very thin fluorine-containing layer on the outer surface.

[0053] Comparative Example 4

[0054] A lithium-ion battery layer oxygen positive electrode material was prepared according to the method of Example 1, except that the fluorine gas in the mixed atmosphere was replaced by trifluoromethane (CHF3) in the same volume fraction. The other conditions were the same as in Example 1 to obtain a lithium-ion battery layer oxygen positive electrode material. The lithium-ion battery layer oxygen positive electrode material only contained a very thin fluorine-containing layer on the outer surface.

[0055] Comparative Example 5

[0056] A lithium-ion battery layer oxygen positive electrode material was prepared according to the method of Example 1, except that the fluorine gas in the mixed atmosphere was replaced by hexafluoroethane (C2F6) with the same volume fraction. The other conditions were the same as in Example 1 to obtain a lithium-ion battery layer oxygen positive electrode material. The lithium-ion battery layer oxygen positive electrode material only contained a very thin fluorine-containing layer on the outer surface.

[0057] Comparative Example 6

[0058] A lithium-ion battery layer oxygen positive electrode material was prepared according to the method of Example 1, except that the fluorine gas in the mixed atmosphere was replaced by carbon tetrafluoride (CF4) with the same volume fraction. The other conditions were the same as in Example 1 to obtain a lithium-ion battery layer oxygen positive electrode material. The lithium-ion battery layer oxygen positive electrode material only contained a very thin fluorine-containing layer on the outer surface.

[0059] Comparative Example 7

[0060] A lithium-ion battery layer oxygen cathode material was prepared according to the method of Example 1, except that after high-temperature calcination, the temperature was first cooled to room temperature before low-temperature calcination, and the mixed atmosphere containing fluorine gas was replaced by ammonium fluoride. The specific steps are as follows:

[0061] According to Li 1.01 Co 0.99 Mg 0.01 Cobalt trioxide, magnesium carbonate and lithium carbonate were weighed and mixed in a stoichiometric ratio of O2, and the resulting mixture was calcined at 1000 ° C for 10 h in a mixed atmosphere of oxygen and nitrogen (containing 30 vol%), and then naturally cooled to room temperature to obtain the matrix Li 1.01 Co 0.99 Mg 0.01 The matrix and ammonium fluoride are mixed evenly, and then the temperature is raised to 650°C and calcined for 4 hours. After the calcination is completed, nitrogen is introduced and the temperature is naturally cooled to room temperature. After sieving and powdering, a lithium-ion battery layer oxygen positive electrode material is obtained. The matrix particles of the lithium-ion battery layer oxygen positive electrode material contain the doping element Mg.

[0062] Comparative Example 8

[0063] A lithium-ion battery layer oxygen cathode material was prepared according to the method of Example 2, except that after high-temperature calcination, the temperature was first cooled to room temperature before low-temperature calcination, and the mixed atmosphere containing fluorine gas was replaced by magnesium fluoride. The specific steps are as follows:

[0064] According to Li 1.01 Co 0.99 Mg 0.01 Cobalt trioxide, magnesium carbonate and lithium carbonate were weighed and mixed in a stoichiometric ratio of O2, and the resulting mixture was calcined at 1000 ° C for 10 h in a mixed atmosphere of oxygen and nitrogen (containing 30 vol%), and then naturally cooled to room temperature to obtain the matrix Li 1.01 Co 0.99 Mg 0.01 The matrix and magnesium fluoride are mixed evenly, and then the temperature is raised to 500°C and calcined for 6 hours. After the calcination is completed, nitrogen is introduced and the temperature is naturally cooled to room temperature. After sieving and powdering, a lithium-ion battery layer oxygen positive electrode material is obtained. The matrix particles of the lithium-ion battery layer oxygen positive electrode material contain the doping element Mg.

[0065] Test Case

[0066] The positive electrode materials obtained in the above examples and comparative examples were mixed with conductive carbon and flux PVDF in a weight ratio of 90:5:5 in NMP and then coated on aluminum foil to obtain pole pieces. The pole pieces were dried in a blast oven at 80°C and then placed in a vacuum oven at 120°C to dry overnight. The dried pole pieces were rolled and used as the positive electrode of the battery (with a compaction density of 4.2g / cm 3), lithium metal as the battery negative electrode, a single-layer polyethylene film as the separator, 1M LiPF6-EC-EMC (i.e., the concentration of LiPF6 in EC-EMC solvent is 1M, EC is ethylene carbonate, EMC is methyl ethyl carbonate, and the volume ratio of EC:EMC is 3:7) as the electrolyte, and assembled into a 2032 battery for electrochemical testing.

[0067] (1) Gram capacity: After the unactivated battery was left at 25°C for 6 hours, it was charged at a constant current of 0.1C to a cutoff voltage of 4.6V. It was then charged at a constant voltage to a cutoff current of 0.01C. It was then discharged at a constant current of 0.1C to a cutoff voltage of 3.0V. The gram capacity of the positive electrode material was obtained by dividing the discharge capacity by the mass of the active material (i.e., lithium cobalt oxide positive electrode material). The battery was charged and discharged once more in the same manner, and the battery at this time was regarded as an activated battery. The results are shown in Table 1.

[0068] (2) Cycle Retention: Using activated batteries, charge and discharge cycles were performed 50 times at 45°C, a current density of 0.5C, and a voltage range of 3.0 to 4.6V to examine the capacity retention of the positive electrode material. The results are shown in Table 1.

[0069] (3) Compressive performance: The BET growth rate of the material after compression at 180 MPa is used to characterize the material. A material with a smaller growth rate has better compressive resistance. Using a powder hydraulic press, the powder was recovered after maintaining a pressure of 180 MPa for 30 seconds. The BET growth rate of the material after compression was measured and calculated. The results are shown in Table 1.

[0070]

[0071] It can be seen from the results of Examples 1 to 6 that the method provided by the present invention is used to prepare lithium-ion battery layer oxygen positive electrode materials. The lithium-ion battery layer oxygen positive electrode materials obtained under different fluorine gas treatment conditions and different doping elements not only have high gram capacity and cycle retention rate, but also have good compressive resistance.

[0072] From the comparison between Example 1 and Example 6, it can be seen that when a low-temperature platform is added to the cooling stage after high-temperature calcination to perform low-temperature calcination with fluorine-containing gas, the capacity and cycle performance of the obtained material are better.

[0073] From the comparison between Example 2 and Comparative Example 1, it can be seen that when the fluorine gas volume fraction in the fluorine-containing gas is too low, the fluorine content is insufficient to extract all the elements in the material that are not doped into the crystal lattice, and the material capacity does not change much, but the compressive performance deteriorates significantly and the cycle performance decreases.

[0074] From the comparison between Example 2 and Comparative Example 2, it can be seen that if the fluorination treatment is not performed, the capacity, cycle performance and compressive resistance of the material will be significantly deteriorated.

[0075] From the comparison between Example 1 and Comparative Examples 3 to 6, it can be seen that when other fluorine-containing gases are used instead of fluorine gas, it is difficult to achieve the fluorination effect, and the capacity, cycle performance and compressive resistance of the material are all poor.

[0076] From the comparison between Example 1 and Comparative Example 7, and Example 2 and Comparative Example 8, it can be seen that when fluoride is directly coated on the surface of the base particles, the elements in the material that are not doped into the crystal lattice cannot be drawn to the surface, the compressive properties of the material cannot be improved, and the capacity and cycle performance deteriorate significantly.

[0077] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and purpose of the present invention.

Claims

1. A lithium-ion battery layer oxygen positive electrode material, characterized in that The lithium-ion battery layer oxygen positive electrode material comprises a substrate, a first region located on the surface of the substrate, and a second region located on the surface of the first region; the chemical formula of the substrate is Li 1+m M a M` b O2, the chemical formula of the first region and the second region is Li 1+m M a M` b O 2-c F c , M is selected from at least one of Ni, Co and Mn, M` is selected from at least one of Al, Mg, Sr, Zr, Ba, Ti, Ca and rare earth elements, a+b=1, 0.9≤a≤1, 0<b≤0.1, -0.05≤m≤0.1, 0<c≤0.1; the matrix does not contain free doping elements M`; the ratio of the atomic concentration of F to the atomic concentration of M` in the first region is smaller than the ratio of the atomic concentration of F to the atomic concentration of M` in the second region, the first region contains a region where the ratio of the atomic concentration of F to the atomic concentration of M` is less than 0.5, and the second region contains a region where the ratio of the atomic concentration of F to the atomic concentration of M` is greater than 1; the thickness of the first region is 10~50nm, and the thickness of the second region is 2~5nm.

2. The lithium-ion battery layer oxygen cathode material according to claim 1, characterized in that The ratio of the atomic concentration of F to the atomic concentration of M' in the first region is 0.2-0.5; the ratio of the atomic concentration of F to the atomic concentration of M' in the second region is 1-4.

3. The lithium-ion battery layer oxygen cathode material according to claim 1, characterized in that The particle size D50 of the matrix is ​​2-20 μm.

4. The method for preparing the lithium-ion battery layer oxygen cathode material according to any one of claims 1 to 3, characterized in that: The method comprises uniformly mixing an M source, an M' source and a lithium source, and then performing high-temperature calcination on the obtained mixture in an oxygen-containing gas environment; thereafter, performing low-temperature calcination on the high-temperature calcined product in a fluorine-containing gas environment, wherein the volume fraction of fluorine in the fluorine-containing gas is greater than 3%. After the low-temperature calcination is completed, an inert gas is introduced and the temperature is naturally cooled to room temperature to obtain a lithium-ion battery layer oxygen positive electrode material; the conditions for the high-temperature calcination include a temperature of 800-1100°C and a time of 6-20 hours; and the conditions for the low-temperature calcination include a temperature of 500-750°C and a time of 2-6 hours.

5. The method for preparing the layered oxygen cathode material for lithium-ion batteries according to claim 4, characterized in that: The stoichiometric ratio of the M source, M' source and lithium source is such that the chemical formula of the obtained matrix is ​​Li 1+m M a M` b O2 is used as the basis, M is selected from at least one of Ni, Co and Mn, M' is selected from at least one of Al, Mg, Sr, Zr, Ba, Ti, Ca and rare earth elements, a+b=1, 0.9≤a≤1, 0<b≤0.1, -0.05≤m≤0.

1.

6. The method for preparing the layered oxygen cathode material for lithium-ion batteries according to claim 4, characterized in that: The M source is selected from at least one of oxides, hydroxides, oxyhydroxides, carbonates, oxalates, acetates of M, or oxides, hydroxides, oxyhydroxides, carbonates, oxalates, acetates of M doped with M'.

7. The method for preparing the layered oxygen cathode material for lithium-ion batteries according to claim 4, characterized in that: The M' source is selected from at least one of oxides, carbonates, hydroxides, nitrates, oxalates, chlorides, fluorides, sulfates, and acetates containing M'.

8. The method for preparing the layered oxygen cathode material for lithium-ion batteries according to claim 4, characterized in that: The lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium acetate, lithium nitrate, lithium sulfate and lithium bicarbonate.

9. The method for preparing the layered oxygen cathode material for lithium-ion batteries according to claim 4, characterized in that: The oxygen concentration in the oxygen-containing gas is 20-100 vol%; the volume fraction of fluorine gas in the fluorine-containing gas is 3-10%.

10. The method for preparing the layered oxygen cathode material for lithium-ion batteries according to claim 4, characterized in that: The low-temperature calcination method is to introduce inert gas after the high-temperature calcination is completed to evacuate the oxygen-containing gas and reduce the temperature to the low-temperature calcination temperature, and then introduce fluorine-containing gas to carry out low-temperature calcination.

11. The method for preparing the layered oxygen cathode material for lithium-ion batteries according to claim 4, characterized in that: The rate of decreasing from the high temperature calcination temperature to the low temperature calcination temperature is 0.4~5℃ / min.

12. Use of the lithium ion battery layer oxygen cathode material according to any one of claims 1 to 3 in a lithium ion battery.

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