Lithium cobalt oxide, preparation method therefor, and use thereof

Abstract

A lithium cobalt oxide, a preparation method therefor, and a use thereof, relating to the field of lithium ion batteries. The lithium cobalt oxide comprises large particles LicCo1-dMdQeO2-e and small particles LiaCo1-bTbEfO2-f, the M element being a doping element, the Q element being a wrapping element, the T element being a doping element, and the E element being a wrapping element. By matching large and small particles of lithium cobalt oxide, an oxygen reduction reaction between an electrolyte and the surface of a positive electrode material can be inhibited, Co valence state changes in the positive electrode material are inhibited, Co dissolution is reduced, the capacity is increased, and the storage and gas production performance of a lithium cobalt oxide positive electrode material are improved.

Description

A lithium cobalt oxide and its preparation method and application Technical Field

[0001] This article relates to the field of lithium-ion battery technology, and in particular to a lithium cobalt oxide and its preparation method and application. Background Art

[0002] Rechargeable lithium-ion batteries are a new generation of green energy storage batteries, boasting outstanding advantages such as high power density, high voltage, high energy density, no memory effect, stable cycling, and long life. They have been widely used in products such as mobile phones, computers, new energy vehicles, smart networking, and distributed energy storage. There are many types of lithium-ion batteries, primarily composed of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium nickel oxide, lithium nickel cobalt manganese oxide, and lithium cobalt oxide / lithium nickel cobalt manganese oxide composites. Lithium cobalt oxide has the highest theoretical density, resulting in outstanding tap density and compaction density among existing materials in practical applications, leading to its widespread use in the 3C industry. Lithium nickel cobalt manganese oxide has excellent storage and cycling performance and is widely used in the power battery field. Lithium iron phosphate has excellent safety performance and is widely used in the energy storage field.

[0003] Lithium cobalt oxide (LCO) is one of the most ideal cathode materials for the 3C industry. With technological advancements, LCO is becoming a new trend in the power battery sector, placing higher demands on the energy density, storage performance, and cycling performance of LCO batteries. The volumetric energy density of a lithium-ion battery is calculated as discharge capacity × discharge voltage platform × compaction density. Currently, the energy density of LCO batteries can be increased by increasing compaction density and cutoff voltage. Increasing compaction density through particle size grading has reached its limit, leaving little room for improvement. Increasing the cutoff voltage further increases the discharge capacity, but as the charge voltage rises, more lithium ions in the cathode material are extracted from the crystal lattice, causing structural instability. The degree of surface delithiation increases, and the structural phase transition extends from the surface to the particle interior. Due to the significant overlap in the band structures of Co and O, high voltages accelerate Co dissolution and O precipitation, hindering the practical application of high-voltage LCO in power batteries.

[0004] The current mainstream optimization method is to prepare the positive electrode material by doping and coating, and then coating and sintering it under high temperature conditions. The coating material can absorb excess lithium and reduce residual lithium, which helps to improve the high-temperature safety performance of the material and reduce gas production. However, under high voltage conditions, as the number of lithium ions released increases, the valence of cobalt tends to increase, and it is easy to react with the electrolyte, causing Co to dissolve, resulting in capacity decay and deterioration of storage performance, which is not suitable for the field of power batteries. Therefore, it is necessary to provide a lithium-cobalt composite oxide material with few interfacial side reactions, while ensuring capacity at a voltage of 4.50V or even higher, and effectively improving gas production and storage performance.

[0005] Summary of the Invention

[0006] This article provides a lithium cobalt oxide, its preparation method and application. When lithium cobalt oxide is used as a battery material, the battery capacity is guaranteed under high voltage conditions, while effectively improving gas production and storage performance.

[0007] In order to solve the above technical problems, one of the purposes of this paper is to provide a lithium cobalt oxide, including a sintering process with a molar ratio of 1:r to prepare large-particle lithium cobalt oxide and a sintering process to prepare small-particle lithium cobalt oxide, the general formula of which is: Li c Co 1-d M d Q e O 2-e , particle size 17μm≤Dv50≤30μm; the general formula of small particle lithium cobalt oxide is: Li a Co 1-b T b E f O 2-f , particle size 2.5μm≤Dv50≤8μm; among which 0.98≤a≤1.02, 0.45≤b≤0.97, 0.98≤c≤1.01, 0.03≤d≤0.06, 0.001≤e≤0.005, 0.001≤f≤0.005, 0.16≤r≤0.39;

[0008] M and Q are each independently selected from at least one of Mg, Al, Ni, Mn, Y, La, Zr, F, P, B, Ti, Cu, and Na;

[0009] T includes Ni and Mn, and E is selected from at least one of Y, Al, B, Ni, Mn, La, Sr, W, F, Zr, and Na;

[0010] In large-particle lithium cobalt oxide, element M is the doping element added during the first sintering process, and element Q is the encapsulating element added during the second sintering process; in small-particle lithium cobalt oxide, element T is the doping element added during the first sintering process, and element E is the encapsulating element added during the second sintering process.

[0011] This article introduces the M, Q, T, and E elements, among which the M element replaces the Co position or the Li position. When combined with Co, it can inhibit the valence change of Co and the release of Co at the same time. When combined with Li, it can improve the channel and enhance the lithium ion deintercalation ability; the Q element greatly improves the interface stability. The Q element occupies the O position, lowering the overall p-band Fermi level and matching the reduced driving force of carbonate dehydrogenation. In the process of replacing the O position, the Co element is reduced, which increases the energy barrier of electron conduction from the electrolyte, reduces the interface side reaction, and improves gas production; the T element can improve the capacity of the material, and the E element can improve the stability of the structure. Large-particle lithium cobalt oxide and small-particle lithium cobalt oxide are used for grading. The small-particle lithium cobalt oxide can inhibit the oxygen reduction reaction between the electrolyte and the surface of the positive electrode material, inhibit the valence change of Co in the positive electrode material, change the average energy band structure of Co, reduce Co dissolution, and improve the storage and gas production performance of the lithium cobalt oxide positive electrode material.

[0012] In a specific embodiment, the molar ratio of the large-particle lithium cobalt oxide to the small-particle lithium cobalt oxide is 1:r, wherein 0.22≤r≤0.32.

[0013] In this article, when the matching molar ratio of lithium cobalt oxide particle size is limited to the above range, when the r value is greater than 0.32, its cycle performance under high voltage conditions when used as a positive electrode material will tend to decline, and the compaction density will become smaller. When the r value is less than 0.22, its capacity and storage performance under high voltage conditions when used as a positive electrode material will be affected.

[0014] In one embodiment, the lithium cobalt oxide has a layered phase structure.

[0015] In a specific embodiment, the particle morphology of the lithium cobalt oxide is single crystal or quasi-single crystal.

[0016] In a specific embodiment, T further includes at least one selected from Y, Al, B, La, Sr, W, Zr, Na, and F.

[0017] In the general formula of lithium cobalt oxide in this article, when the value of b is greater than 0.5, the residual alkali content of the material increases with the increase of the b value. When the value of b is less than or equal to 0.5, the capacity of the material will show a decreasing trend as the b value decreases. Limiting the b value to the above range can simultaneously meet the effects of low residual alkali and high capacity.

[0018] In one embodiment, Q is selected from at least one of F, P, and B;

[0019] In a specific embodiment, M is selected from at least one of Mg, Al, Ni, Mn, Y, and La;

[0020] In a specific embodiment, T is selected from at least one of Ni, Mn, Sr, and Zr;

[0021] In one embodiment, E is F.

[0022] In order to solve the above technical problems, the second purpose of this article is to provide a method for preparing lithium cobalt oxide, comprising the following steps:

[0023] A Li-containing precursor, a Co-containing precursor and an M-containing element precursor are mixed according to the stoichiometric ratio of the large-particle lithium cobalt oxide general formula, and after sintering, a large-particle primary powder doped with the M element is obtained;

[0024] The large-particle primary powder doped with the M element is mixed with the Q element precursor, and after sintering, the large-particle secondary powder coated with the Q element is obtained;

[0025] A Li-containing precursor, Co and a T element precursor are mixed according to the stoichiometric ratio of the general formula of small-particle lithium cobalt oxide, and after sintering, a T-doped small-particle primary powder is obtained;

[0026] The small-particle primary powder doped with the T element is mixed with the E element precursor, and after sintering, the small-particle secondary powder coated with the E element is obtained;

[0027] The large-particle secondary powder and the small-particle secondary powder are mixed to obtain lithium cobalt oxide.

[0028] In a specific embodiment, the Q element precursor and the E element precursor are each independently selected from at least one of oxides, hydroxides, fluorides, and phosphides.

[0029] In a specific embodiment, the Q element precursor and the E element precursor are at the micro-nano level.

[0030] In a specific embodiment, during the primary sintering process of the large-particle lithium cobalt oxide, the sintering temperature is 900-1100° C., the time is 8-12 hours, and the sintering is carried out in an oxygen-containing atmosphere;

[0031] In a specific embodiment, during the secondary sintering process of the large-particle lithium cobalt oxide, the sintering temperature is 800-1000° C., the time is 8-12 hours, and the sintering is carried out in an oxygen-containing atmosphere;

[0032] In a specific embodiment, during the primary sintering process of the small-particle lithium cobalt oxide, the sintering temperature is 600-1000° C., the time is 8-12 hours, and the sintering is carried out in an oxygen-containing atmosphere;

[0033] In a specific embodiment, during the secondary sintering process of the small-particle lithium cobalt oxide, the sintering temperature is 500-900° C., the sintering time is 8-12 hours, and the sintering is carried out in an oxygen-containing atmosphere.

[0034] In a specific embodiment, when weighing the raw materials in the primary sintering process of large-particle lithium cobalt oxide and small-particle lithium cobalt oxide, the ratio of the sum of the molar amounts of Co, M, T, and E elements to the molar amount of Li element is recorded as m1, that is, [1+(b+f)r] / (a*r+c)=m1, 0.97≤m1≤1.1.

[0035] In a specific embodiment, during the primary sintering process of large-particle lithium cobalt oxide, the molar ratio m2 of Li and Co is adjusted to: 1.0≤m2≤1.12. When the M element replaces the Co position, additional lithium is added according to the Co position. When the M element is +n valence, the molar ratio M:Co=1:(3 / n) is used for lithium addition, and the total amount of lithium added is the sum of m2 and the additional lithium addition amount.

[0036] In a specific embodiment, during the primary sintering process of small-particle lithium cobalt oxide, the molar ratio m3 of Li to Co is adjusted to: 1.02≤m3≤1.1. When the T element replaces the Co position, additional lithium is added according to the Co position. When the T element has a +n valence, the molar ratio T:Co=1:(3 / n) is used for lithium addition; the total amount of lithium added is the sum of m3 and the additional lithium addition amount.

[0037] In a specific embodiment, during the primary sintering process of small-particle lithium cobalt oxide, the Co and T element precursors include at least one of NCM523, NCM622, NCM71515, NCM811, and NCM90505.

[0038] In order to solve the above technical problems, the third purpose of this article provides an application of lithium cobalt oxide in the field of lithium-ion batteries.

[0039] Compared with the existing technology, this article has the following beneficial effects:

[0040] In this paper, large-particle lithium cobalt oxide di-calcined products and small-particle lithium cobalt oxide di-calcined products are matched. The elements of large and small-particle lithium cobalt oxide are prepared by doping and encapsulating. This can inhibit the oxygen reduction reaction between the electrolyte and the surface of the positive electrode material, inhibit the change of Co valence state in the positive electrode material, and at the same time inhibit the release of Co, change the average energy band structure of Co, reduce Co dissolution, improve the channel, enhance the lithium ion deintercalation ability, increase the capacity, and improve the storage and gas production performance of lithium cobalt oxide positive electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] FIG1 is a SEM image of a lithium cobalt oxide in Example 1 of this invention (note: magnified 1000 times, scale bar is 200 μm);

[0042] FIG2 is an SEM image of a lithium cobalt oxide in Example 3 of this invention (note: magnified 1000 times, scale bar is 200 μm);

[0043] FIG3 is a SEM image of a lithium cobalt oxide in Example 8 of this invention (note: magnified 1000 times, scale bar is 200 μm);

[0044] FIG4 is a SEM image of a lithium cobalt oxide in Example 10 of this invention (note: magnified 1000 times, scale bar is 200 μm). DETAILED DESCRIPTION

[0045] The following will be combined with the accompanying drawings to clearly and completely describe the technical solutions in the embodiments of this document. Obviously, the embodiments described are only part of the embodiments of this document, not all of the embodiments. Based on the embodiments of this document, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this document. In the present invention, the ternary precursor adopts an abbreviation form, for example, NCM=523 indicates that the molar ratio of Ni:Co:Mn in the precursor is 0.5:0.22:0.3, NCM=622 indicates that the molar ratio of Ni:Co:Mn in the precursor is 0.6:0.2:0.2, NCM=71515 indicates that the molar ratio of Ni:Co:Mn in the precursor is 0.7:0.15:0.15, NCM=811 indicates that the molar ratio of Ni:Co:Mn in the precursor is 0.8:0.1:0.1, NCM=90505 indicates that the molar ratio of Ni:Co:Mn in the precursor is 0.9:0.05:0.05, and other series are similar. The positive electrode material has consistent inheritance of the precursor element content and ratio. During the sintering process, problems such as lithium volatilization will occur. The total lithium content in the actual production process is greater than the Li / Me content reflected in the chemical formula (Me is the molar ratio of cobalt + other elements replacing Co).

[0046] Example 1

[0047] A lithium cobalt oxide, the chemical formula of which is Li 1.006 Co 0.9689 Mg 0.0045 Al 0.0266 F 0.0016 O 1.9984 0.25Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 , the preparation method comprises the following steps:

[0048] S1, according to the chemical formula Li 1.006 Co 0.9689 Mg 0.0045 Al 0.0266 F 0.0016 O1.9984 Lithium carbonate, Al-doped cobalt oxide, magnesium oxide, and lithium fluoride are weighed in a molar ratio of 1:1, and the lithium carbonate, Al-doped cobalt oxide, and magnesium oxide are placed in a three-dimensional mixing device at a rotation speed of 50 r / min and a mass ratio of the ball material of 1.5:1. The materials are mixed for 3 hours to obtain a mixed powder, and the mixed powder is calcined at a temperature of 1070° C. for 10 hours. After natural cooling and crushing, the powder is pulverized and sieved to obtain a modified lithium cobalt oxide large particle primary powder.

[0049] S2. Mix lithium fluoride and modified lithium cobalt oxide large-particle primary powder, place them in a three-dimensional mixing device, rotate at 50 r / min, and have a mass ratio of 1.5:1 for 3 hours to obtain a mixed powder. Calcining the mixed powder at a temperature of 950° C. for 8 hours, cooling and crushing naturally, and then pulverizing and sieving to obtain large-particle secondary powder with a particle size of Dv50 = 20 μm;

[0050] S3, according to the chemical formula Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 Lithium carbonate, NCM=523 precursor, strontium oxide, zirconium oxide and lithium fluoride raw materials are weighed respectively in a molar ratio, and lithium carbonate, NCM=523 precursor, strontium oxide and zirconium oxide are placed in a three-dimensional mixer at a speed of 50 r / min and a mass ratio of the ball material of 1:1. The three-dimensional mixing is performed for 1.5 hours to obtain a mixed powder, and the mixed powder is calcined at a temperature of 850°C and a calcination time of 8 hours. After natural cooling and sieving, small-particle primary powder is obtained;

[0051] S4. The small particles of primary powder were mixed with lithium fluoride and placed in a three-dimensional mixing device at a speed of 50 r / min, a mass ratio of the ball material of 1.5: 1, and the mixing was performed for 3 hours to obtain a mixed powder. The mixed powder was calcined at a temperature of 800 ° C and kept warm for 8 hours. After natural cooling and crushing, the small particles of secondary powder were crushed and sieved to obtain a particle size of Dv50 = 4.5 μm.

[0052] S5. Place the large-particle secondary powder and the small-particle secondary powder in a three-dimensional mixing device at a mass ratio of 4:1, with a ball-to-material mass ratio of 0.5:1 and a rotation speed of 50 r / min. Mix for 30 minutes and then sieve to obtain Li 1.006 Co 0.9689 Mg 0.0045 Al 0.0266 F 0.0016 O 1.9984 0.25 Li 0.99 Co 0.2Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 .

[0053] Example 2

[0054] A lithium cobalt oxide, the chemical formula of which is Li 1.001 Co 0.968 Mg 0.0044 Al 0.0266 Y 0.001 F 0.0016 O 1.9984 0.25 Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 , the preparation method comprises the following steps:

[0055] S1, according to the chemical formula Li 1.001 Co 0.968 Mg 0.0044 Al 0.0266 Y 0.001 F 0.0016 O 1.9984 Lithium carbonate, Al-doped cobalt oxide, magnesium oxide, yttrium oxide, and lithium fluoride are weighed in a molar ratio, and lithium carbonate, Al-doped cobalt oxide, magnesium oxide, and yttrium oxide are placed in a three-dimensional mixing device at a speed of 50 r / min and a mass ratio of the ball material of 1.5:1. The materials are mixed for 3 hours to obtain a mixed powder, and the mixed powder is calcined at a temperature of 1070° C. and a holding time of 10 hours. After natural cooling and crushing, the powder is pulverized and sieved to obtain a modified lithium cobalt oxide large particle primary powder;

[0056] S2. Mix lithium fluoride and modified lithium cobalt oxide large-particle primary powder, place them in a three-dimensional mixing device, rotate at 50 r / min, and have a mass ratio of 1.5:1 for 3 hours to obtain a mixed powder. Calcining the mixed powder at a temperature of 950° C. for 8 hours, cooling and crushing naturally, and then pulverizing and sieving to obtain large-particle secondary powder with a particle size of Dv50 = 20 μm;

[0057] S3, according to the chemical formula Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984Lithium carbonate, NCM=523 precursor, strontium oxide, zirconium oxide and lithium fluoride raw materials are weighed respectively in a molar ratio, and lithium carbonate, NCM=523 precursor, strontium oxide and zirconium oxide are placed in a three-dimensional mixer at a speed of 50 r / min and a mass ratio of the ball material of 1:1. The three-dimensional mixing is performed for 1.5 hours to obtain a mixed powder, and the mixed powder is calcined at a temperature of 850°C and a calcination time of 8 hours. After natural cooling and sieving, small-particle primary powder is obtained;

[0058] S4. The small particles of primary powder were mixed with lithium fluoride and placed in a three-dimensional mixing device at a speed of 50 r / min, a mass ratio of the ball material of 1.5: 1, and the mixing was performed for 3 hours to obtain a mixed powder. The mixed powder was calcined at a temperature of 800 ° C and kept warm for 8 hours. After natural cooling and crushing, the small particles of secondary powder were crushed and sieved to obtain a particle size of Dv50 = 4.5 μm.

[0059] S5. Place the large-particle secondary powder and the small-particle secondary powder in a three-dimensional mixing device at a mass ratio of 4:1, with a ball-to-material mass ratio of 0.5:1 and a rotation speed of 50 r / min. Mix for 30 minutes and then sieve to obtain Li 1.001 Co 0.968 Mg 0.0044 Al 0.0266 Y 0.001 F 0.0016 O 1.9984 0.25Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 .

[0060] Example 3

[0061] A lithium cobalt oxide, the chemical formula of which is Li 1.001 Co 0.943 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 F 0.0016 O 1.9984 0.25Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 , the preparation method comprises the following steps:

[0062] S1, according to the chemical formula Li 1.001Co 0.943 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 F 0.0016 O 1.9984 Lithium carbonate, Al-doped cobalt oxide, magnesium oxide, nickel oxide, manganese oxide, and lithium fluoride are weighed in a molar ratio, and lithium carbonate, Al-doped cobalt oxide, magnesium oxide, nickel oxide, and manganese oxide are placed in a three-dimensional mixing device at a speed of 50 r / min and a mass ratio of the ball material of 1.5:1. The materials are mixed for 3 hours to obtain a mixed powder, and the mixed powder is calcined at a calcination temperature of 1070° C. for 10 hours. After natural cooling and crushing, the powder is pulverized and sieved to obtain a modified lithium cobalt oxide large particle primary powder;

[0063] S2. Mix lithium fluoride and modified lithium cobalt oxide large-particle primary powder, place them in a three-dimensional mixing device, rotate at 50 r / min, and have a mass ratio of 1.5:1 for 3 hours to obtain a mixed powder. Calcining the mixed powder at a temperature of 950° C. for 8 hours, cooling and crushing naturally, and then pulverizing and sieving to obtain large-particle secondary powder with a particle size of Dv50 = 20 μm;

[0064] S3, according to the chemical formula Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 Lithium carbonate, NCM=523 precursor, strontium oxide, zirconium oxide and lithium fluoride raw materials are weighed respectively in a molar ratio, and lithium carbonate, NCM=523 precursor, strontium oxide and zirconium oxide are placed in a three-dimensional mixer at a speed of 50 r / min and a mass ratio of the ball material of 1:1. The three-dimensional mixing is performed for 1.5 hours to obtain a mixed powder, and the mixed powder is calcined at a temperature of 850°C and a calcination time of 8 hours. After natural cooling and sieving, small-particle primary powder is obtained;

[0065] S4. The small particles of primary powder were mixed with lithium fluoride and placed in a three-dimensional mixing device at a speed of 50 r / min, a mass ratio of the ball material of 1.5: 1, and the mixing was performed for 3 hours to obtain a mixed powder. The mixed powder was calcined at a temperature of 800 ° C and kept warm for 8 hours. After natural cooling and crushing, the small particles of secondary powder were crushed and sieved to obtain a particle size of Dv50 = 4.5 μm.

[0066] S5. Place the large-particle secondary powder and the small-particle secondary powder in a three-dimensional mixing device at a mass ratio of 4:1, with a ball-to-material mass ratio of 0.5:1 and a rotation speed of 50 r / min. Mix for 30 minutes and then sieve to obtain Li 1.001 Co0.943 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 F 0.0016 O 1.9984 0.25Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.002 5Zr 0.0025 F 0.0016 O 1.9984 .

[0067] Example 4

[0068] A lithium cobalt oxide, the chemical formula of which is Li 1.001 Co 0.942 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 Y 0.001 F 0.0016 O 1.9984 0.25 Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 , the preparation method comprises the following steps:

[0069] S1, according to the chemical formula Li 1.001 Co 0.942 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 Y 0.001 F 0.0016 O 1.9984 Lithium carbonate, Al-doped cobalt oxide, magnesium oxide, nickel oxide, manganese oxide, yttrium oxide, and lithium fluoride are weighed in a molar ratio, and lithium carbonate, Al-doped cobalt oxide, magnesium oxide, nickel oxide, manganese oxide, and yttrium oxide are placed in a three-dimensional mixing device at a speed of 50 r / min and a mass ratio of the ball material of 1.5:1. The materials are mixed for 3 hours to obtain a mixed powder, and the mixed powder is calcined at a calcination temperature of 1070° C. for 10 hours. After natural cooling and crushing, the powder is pulverized and sieved to obtain a large-particle primary powder of modified lithium cobalt oxide;

[0070] S2. Mix lithium fluoride and modified lithium cobalt oxide large-particle primary powder, place them in a three-dimensional mixing device, rotate at 50 r / min, and have a mass ratio of 1.5:1 for 3 hours to obtain a mixed powder. Calcining the mixed powder at a temperature of 950° C. for 8 hours, cooling and crushing naturally, and then pulverizing and sieving to obtain large-particle secondary powder with a particle size of Dv50 = 20 μm;

[0071] S3, according to the chemical formula Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 Lithium carbonate, NCM=523 precursor, strontium oxide, zirconium oxide and lithium fluoride raw materials are weighed respectively in a molar ratio, and lithium carbonate, NCM=523 precursor, strontium oxide and zirconium oxide are placed in a three-dimensional mixer at a speed of 50 r / min and a mass ratio of the ball material of 1:1. The three-dimensional mixing is performed for 1.5 hours to obtain a mixed powder, and the mixed powder is calcined at a temperature of 850°C and a calcination time of 8 hours. After natural cooling and sieving, small-particle primary powder is obtained;

[0072] S4. The small particles of primary powder were mixed with lithium fluoride and placed in a three-dimensional mixing device at a speed of 50 r / min, a mass ratio of the ball material of 1.5: 1, and the mixing was performed for 3 hours to obtain a mixed powder. The mixed powder was calcined at a temperature of 800 ° C and kept warm for 8 hours. After natural cooling and crushing, the small particles of secondary powder were crushed and sieved to obtain a particle size of Dv50 = 4.5 μm.

[0073] S5. Place the large-particle secondary powder and the small-particle secondary powder in a three-dimensional mixing device at a mass ratio of 4:1, with a ball-to-material mass ratio of 0.5:1 and a rotation speed of 50 r / min. Mix for 30 minutes and then sieve to obtain Li 1.001 Co 0.942 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 Y 0.001 F 0.0016 O 1.9984 0.25Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 .

[0074] Example 5

[0075] A lithium cobalt oxide, the chemical formula of which is Li 1.001 Co 0.942 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 Y 0.0007 La 0.0003 F 0.0016 O 1.9984 0.25 Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 , the preparation method comprises the following steps:

[0076] S1, according to the chemical formula Li 1.001 Co 0.942 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 Y 0.0007 La 0.0003 F 0.0016 O 1.9984 Lithium carbonate, Al-doped cobalt oxide, magnesium oxide, nickel oxide, manganese oxide, yttrium oxide, lanthanum oxide, and lithium fluoride are weighed in a molar ratio, and lithium carbonate, Al-doped cobalt oxide, magnesium oxide, nickel oxide, manganese oxide, yttrium oxide, and lanthanum oxide are placed in a three-dimensional mixing device at a speed of 50 r / min and a mass ratio of the ball material of 1.5:1. The materials are mixed for 3 hours to obtain a mixed powder, and the mixed powder is calcined at a calcination temperature of 1070° C. for 10 hours. After natural cooling and crushing, the powder is pulverized and sieved to obtain a modified lithium cobalt oxide large-particle primary powder.

[0077] S2. Mix lithium fluoride and modified lithium cobalt oxide large-particle primary powder, place them in a three-dimensional mixing device, rotate at 50 r / min, and have a mass ratio of 1.5:1 for 3 hours to obtain a mixed powder. Calcining the mixed powder at a temperature of 950° C. for 8 hours, cooling and crushing naturally, and then pulverizing and sieving to obtain large-particle secondary powder with a particle size of Dv50 = 20 μm;

[0078] S3, according to the chemical formula Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984Lithium carbonate, NCM=523 precursor, strontium oxide, zirconium oxide and lithium fluoride raw materials are weighed respectively in a molar ratio, and lithium carbonate, NCM=523 precursor, strontium oxide and zirconium oxide are placed in a three-dimensional mixer at a speed of 50 r / min and a mass ratio of the ball material of 1:1. The three-dimensional mixing is performed for 1.5 hours to obtain a mixed powder, and the mixed powder is calcined at a temperature of 850°C and a calcination time of 8 hours. After natural cooling and sieving, small-particle primary powder is obtained;

[0079] S4. The small-particle primary powder was mixed with lithium fluoride and placed in a three-dimensional mixing device at a speed of 50 r / min, a mass ratio of the ball material of 1.5:1, and the mixture was mixed for 3 hours to obtain a mixed powder. The mixed powder was calcined at a temperature of 800 ° C and kept warm for 8 hours. After natural cooling and crushing, the small-particle secondary powder was crushed and sieved to obtain a particle size of Dv50 = 4.5 μm.

[0080] S5. Place the large-particle secondary powder and the small-particle secondary powder in a three-dimensional mixing device at a mass ratio of 4:1, with a ball-to-material mass ratio of 0.5:1 and a rotation speed of 50 r / min. Mix for 30 minutes and then sieve to obtain Li 1.001 Co 0.942 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 Y 0.0007 La 0.0003 F 0.0016 O 1.9984 0.25Li 0.99 Co 0.2 Ni 0.4 95 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 .

[0081] Example 6

[0082] A lithium cobalt oxide, wherein each step and the components and process parameters applicable to each step in the preparation method are the same as those in Example 3, except that in S3, the NCM=523 precursor is replaced by the NCM=622 precursor, and the chemical formula thereof is Li 1.001 Co 0.943 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 F 0.0016 O 1.9984 0.25 Li 0.99 Co 0.2 Ni 0.595 Mn0.2 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 .

[0083] Example 7

[0084] A lithium cobalt oxide, wherein each step and the components and process parameters applicable to each step in the preparation method are the same as those in Example 3, except that in S3, the NCM=523 precursor is replaced by the NCM=71515 precursor, and its chemical formula is Li 1.001 Co 0.943 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 F 0.0016 O 1.9984 0.25 Li 0.99 Co 0.15 Ni 0.695 Mn 0.15 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 .

[0085] Example 8

[0086] A lithium cobalt oxide, wherein each step and the components and process parameters applicable to each step in the preparation method are the same as those in Example 3, except that in S3, the NCM=523 precursor is replaced by the NCM=811 precursor, and its chemical formula is Li 1.001 Co 0.943 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 F 0.0016 O 1.9984 0.25 Li 0.99 Co 0.1 Ni 0.795 Mn 0.1 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 .

[0087] Example 9

[0088] A lithium cobalt oxide, wherein each step and the components and process parameters applicable to each step in the preparation method are the same as those in Example 3, except that in S3, the NCM=523 precursor is replaced by the NCM=90505 precursor, and its chemical formula is Li 1.001 Co0.943 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 F 0.0016 O 1.9984 0.25 Li 0.99 Co 0.05 Ni 0.895 Mn 0.05 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 .

[0089] Example 10

[0090] A lithium cobalt oxide, wherein each step and the components and process parameters applicable to each step in the preparation method are the same as those in Example 3, except that the chemical formula of the lithium cobalt oxide is Li 1.001 Co 0.943 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 F 0.0016 O 1.9984 ·(7 / 18)Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 In S5, the mass ratio of large-particle secondary powder to small-particle secondary powder is 7:18.

[0091] Example 11

[0092] A lithium cobalt oxide, wherein each step and the components and process parameters applicable to each step in the preparation method are the same as those in Example 3, except that the chemical formula of the lithium cobalt oxide is Li 1.001 Co 0.943 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 F 0.0016 O 1.9984 ·(4 / 21)Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984In S5, the mass ratio of large-particle secondary powder to small-particle secondary powder is 4:21.

[0093] Example 12

[0094] A lithium cobalt oxide, wherein each step, components applicable to each step, and process parameters in its preparation method are the same as those in Example 3, except that in S2, the large-particle secondary powder has a particle size Dv50 of 30 μm.

[0095] Example 13

[0096] A lithium cobalt oxide, wherein each step, components applicable to each step, and process parameters in its preparation method are the same as those in Example 3, except that, in S4, the particle size of the small particle secondary powder Dv50=8 μm.

[0097] Comparative Example 1

[0098] A lithium cobalt oxide, wherein each step and the components and process parameters applicable to each step in the preparation method are the same as those in Example 1, except that the chemical formula of the lithium cobalt oxide is Li 1.006 Co 0.9689 Mg 0.0045 Al 0.0266 F 0.0016 O 1.9984 0.25 Li 0.99 Co 0.995 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 , in S3, the small particles use cobalt trioxide precursor.

[0099] Comparative Example 2

[0100] A lithium cobalt oxide, wherein each step and the components and process parameters applicable to each step in the preparation method are the same as those in Example 2, except that the chemical formula of the lithium cobalt oxide is Li 1.001 Co 0.968 Mg 0.0044 Al 0.0266 Y 0.001 F 0.0016 O 1.9984 0.25 Li 0.99 Co 0.995 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 , in S3, the small particles use cobalt trioxide precursor.

[0101] Comparative Example 3

[0102] A lithium cobalt oxide, wherein each step and the components and process parameters applicable to each step in the preparation method are the same as those in Example 3, except that the chemical formula of the lithium cobalt oxide is Li 1.001 Co 0.943 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 F 0.0016 O 1.9984 0.25Li 0.99 Co 0.995 Sr 0.0025 Zr 0.0025 F 0. 0016 O 1.9984 , in S3, the small particles use cobalt trioxide precursor.

[0103] Comparative Example 4

[0104] A lithium cobalt oxide, wherein each step and the components and process parameters applicable to each step in the preparation method are the same as those in Example 4, except that the chemical formula of the lithium cobalt oxide is Li 1.001 Co 0.942 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 Y 0.001 F 0.0016 O 1.9984 0.25Li 0.99 Co 0.995 Sr 0.0025 Zr 0.0 025 F 0.0016 O 1.9984 , in S3, the small particles use cobalt trioxide precursor.

[0105] Comparative Example 5

[0106] A lithium cobalt oxide, wherein each step and the components and process parameters applicable to each step in the preparation method are the same as those in Example 5, except that the chemical formula of the lithium cobalt oxide is Li 1.001 Co 0.942 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 Y 0.0007 La 0.0003 F 0.0016 O 1.9984 0.25Li 0.99 Co 0.995 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 , in S3, the small particles use cobalt trioxide precursor.

[0107] Comparative Example 6

[0108] A lithium cobalt oxide, the chemical formula of which is Li 1.001 Co 0.943 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 F 0.0016 O 1.9984 0.25 Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 , the preparation method comprises the following steps:

[0109] S1, according to the chemical formula Li 1.001 Co 0.943 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 F 0.0016 O 1.9984 Lithium carbonate, Al-doped cobalt oxide, magnesium oxide, nickel oxide, manganese oxide, and lithium fluoride were weighed in a molar ratio, and lithium carbonate, Al-doped cobalt oxide, magnesium oxide, nickel oxide, manganese oxide, and lithium fluoride were placed in a three-dimensional mixing device at a speed of 50 r / min and a mass ratio of the balls of 1.5:1. The materials were mixed for 3 hours to obtain a mixed powder, and the mixed powder was calcined at a temperature of 1070° C. for 10 hours. After natural cooling and crushing, the modified lithium cobalt oxide large-particle primary powder was crushed and sieved to obtain a particle size Dv50=20 μm.

[0110] S2, according to the chemical formula Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984Lithium carbonate, NCM=523 precursor, strontium oxide, zirconium oxide, and lithium fluoride raw materials were weighed in a molar ratio, and lithium carbonate, NCM=523 precursor, strontium oxide, zirconium oxide, and lithium fluoride were placed in a three-dimensional mixer at a speed of 50 r / min and a mass ratio of the ball materials of 1:1. The three-dimensional mixing was performed for 1.5 hours to obtain a mixed powder. The mixed powder was calcined at a temperature of 850°C for 8 hours. After natural cooling and sieving, a small particle primary powder was obtained with a particle size Dv50=4.5 μm.

[0111] S3. Place the large-particle primary powder and the small-particle primary powder in a three-dimensional mixing device at a mass ratio of 4:1, with a ball-to-material mass ratio of 0.5:1 and a rotation speed of 50 r / min. Mix for 30 minutes and then sieve to obtain Li 1.001 Co 0.943 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 F 0.0016 O 1.9984 0.25Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.002 5Zr 0.0025 F 0.0016 O 1.9984 .

[0112] Comparative Example 7

[0113] A lithium cobalt oxide, wherein each step and the components and process parameters applicable to each step in the preparation method are the same as those in Example 3, except that the chemical formula of the lithium cobalt oxide is Li 0.93 Co 0.943 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 F 0.0016 O 1.9984 0.25Li 0.90 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 .

[0114] Comparative Example 8

[0115] A lithium cobalt oxide, wherein each step and the components and process parameters applicable to each step in the preparation method are the same as those in Example 3, except that the chemical formula of the lithium cobalt oxide is Li 1.001 Co0.843 Mg 0.0044 Al 0.0266 Ni 0.038 Mn 0.088 F 0.0016 O 1.9984 0.25Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.002 5Zr 0.0025 F 0.0016 O 1.9984 .

[0116] Comparative Example 9

[0117] A lithium cobalt oxide, wherein each step and the components and process parameters applicable to each step in the preparation method are the same as those in Example 3, except that the chemical formula is Li 1.001 Co 0.943 Mg 0.0044 Al 0.0266 Ni 0.008 Mn 0.018 F 0.0016 O 1.9984 The preparation method and particle size are the same as those of the large-particle secondary powder in Example 3.

[0118] Comparative Example 10

[0119] A lithium cobalt oxide, wherein each step and the components and process parameters applicable to each step in the preparation method are the same as those in Example 3, except that the chemical formula is Li 0.99 Co 0.2 Ni 0.495 Mn 0.3 Sr 0.0025 Zr 0.0025 F 0.0016 O 1.9984 The preparation method and particle size are the same as those of the small particle secondary powder in Example 3.

[0120] Performance testing

[0121] 1. The lithium cobalt oxides obtained in the above embodiments or comparative examples were used as positive electrode materials to prepare lithium ion batteries: lithium cobalt oxide, SP (conductive agent), and PVDF (binder) were mixed in a mass ratio of 92:4:4, NMP (N-methylpyrrolidone) was added, and the mixture was stirred to form a slurry, which was applied on an aluminum foil and dried at 80°C to form a positive electrode sheet; graphite, SP (conductive agent), binder, and dispersant were mixed in a mass ratio of 96.5:1.5:1.5:1.5, a solvent (H2O) was added, and the mixture was stirred to form a slurry, which was applied on an aluminum foil and dried at 80°C to form a negative electrode sheet; the positive electrode sheet, negative electrode, electrolyte, and diaphragm were used as raw materials to assemble a soft-pack battery.

[0122] 2. Capacity test: Take 4 of the soft-pack batteries prepared above as parallel samples, form them, divide the capacity, and then charge them at a constant current of 0.2C rate to a V1 voltage of 4.48V at room temperature of 25°C. Then charge them under V1 constant voltage conditions until the current is lower than 0.05C, so that they are in a V1 full charge state. Then, discharge them at a constant current of 0.2C rate to V2 = 3.0V to obtain the discharge capacity. The discharge gram capacity at 0.2C rate is obtained by the following calculation formula: discharge gram capacity = discharge capacity / mass of positive electrode material. The results are shown in Table 1 below.

[0123] 3. Gas production and storage test: The soft-pack battery obtained above was tested and stored at 45°C, 3.0-4.48V / 1.0C. The higher the data, the better the storage. At the same time, the storage gas production performance was tested at 70°C for 60 days or 120 days. The lower the data, the better the gas production. The test results are shown in Table 1 below.

[0124] Table 1 - Performance test results of examples and comparative examples

[0125] Combining the performance test results of Examples 1-5 and Comparative Examples 1-5 in Table 1, it can be seen that the sample capacity of Examples 3-5 is higher than that of Examples 1-2, indicating that large-particle lithium cobalt oxide doped with nickel and manganese has a capacity-enhancing effect. In addition, by comparing Examples 1-5 and Comparative Examples 1-5, it can be seen that small-particle lithium cobalt oxide doped with nickel and manganese has a capacity-enhancing effect. Doped nickel can replace the position of cobalt, and the layered structure remains unchanged. The capacity is significantly improved by matching large and small particles of lithium cobalt oxide. Generally, cobalt and oxygen have some band structure overlap, and trivalent cobalt is easily oxidized to tetravalent cobalt under high voltage, which leads to The cobalt is dissolved and the interface side reaction is aggravated, which makes the storage and gas production significantly deteriorate. By comparing Example 1-2 and Comparative Example 1-2, it can be seen that the nickel-manganese doping in the small particles improves the band structure of cobalt in the pure cobalt system, reduces the overlap of the cobalt and oxygen band structures, reduces cobalt dissolution, thereby reducing the interface side reaction, improving the interface stability, and improving the gas production and storage performance. By comparing Example 3-5 and Comparative Example 3-5, it can be seen that after the large particles and small particles are doped with nickel-manganese, the large and small particles simultaneously change the band structure of cobalt, and at the same time improve the band structure stability of the large and small particles, and the gas production and energy storage performance are significantly improved.

[0126] Combining the performance test results of Example 3 and Comparative Example 6 in Table 1, it can be seen that after the elements in the large and small particles of lithium cobalt oxide are prepared by doping in a single sintering process, the capacity of Comparative Example 6 has a slight downward trend, and its gas production and energy storage performance are poor. However, Example 3 of the present application uses lithium fluoride as the encapsulating element in the second sintering process, which can ensure the capacity while effectively improving the gas production and energy storage performance.

[0127] Combining the performance test results of Example 3 and Comparative Example 7 in Table 1, it can be seen that the lithium content of Comparative Example 7 is lower than that of Example 3. Controlling the excess lithium during the sintering process can promote particle growth, promote the full growth of particles, eliminate secondary grain boundaries between particles, compensate for lithium loss during the sintering process, and improve capacity, storage, and gas production performance.

[0128] Combining the performance test results of Example 3 and Comparative Example 8 in Table 1, it can be seen that the large particles in Comparative Example 8 reduce the cobalt content and increase the nickel and manganese content, resulting in the large particles being difficult to grow and easy to produce polycrystalline, resulting in deterioration of storage and gas production.

[0129] Combining the performance test results of Example 3 and Comparative Examples 9-10 in Table 1, it can be seen that the lithium cobalt oxide prepared from large particles alone leads to a decrease in compaction density, capacity, and cycle when used in batteries. Although the gas production is improved, the overall performance deteriorates; the lithium cobalt oxide prepared from small particles alone improves the capacity when used in batteries, but the compaction density is reduced, the capacity is increased, the cycle is reduced, and the gas production deteriorates significantly.

[0130] Combining the performance test results of Examples 3 and 6-9 in Table 1, it can be seen that on the basis of the same large particles, small particles are prepared using ternary precursors with different nickel and manganese contents. As the nickel and manganese production increases, the storage and gas production gradually deteriorate. When the small particles are prepared using NCM=90505, the gas production performance is significantly improved. This is because, based on the higher nickel content, the small particles have higher residual lithium, and the graded samples have higher total residual lithium. Under high voltage, the interfacial side reactions are more intense, and the interfacial side reactions exceed the positive effect of inhibiting cobalt dissolution, resulting in a significant increase in gas production.

[0131] Combining the performance test results of Example 3 and Examples 10-11 in Table 1, it can be seen that increasing the content of small particles improves storage and worsens gas production. The transmission path of small-particle lithium is shorter, which is conducive to lithium ion deintercalation and storage improvement. However, as the number of small particles increases, BET increases, the contact area between the interface and the electrolyte increases, and gas production worsens; increasing the proportion of large particles reduces BET, reduces the contact area between the interface and the electrolyte, improves gas production, increases the lithium ion transmission path, and worsens storage. Controlling the matching of large and small particle lithium cobalt oxides can simultaneously ensure that gas production and energy storage performance are at a high level.

[0132] Combining the performance test results of Example 3 and Examples 12-13 in Table 1, it can be seen that if the particle size of large-particle lithium cobalt oxide is too large, the capacity will decrease. If the particle size of small-particle lithium cobalt oxide is too large, the capacity and storage will be affected, and there will be a decrease.

[0133] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this document. It should be understood that the above descriptions are merely specific embodiments of this document and are not intended to limit the scope of protection of this document. In particular, it should be noted that any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of this document by those skilled in the art should be included within the scope of protection of this document.

Claims

1. A lithium cobalt oxide, characterized in that The invention comprises a sintering process with a molar ratio of 1:r to prepare large-particle lithium cobalt oxide and a sintering process to prepare small-particle lithium cobalt oxide. The general formula of the large-particle lithium cobalt oxide is: Li c Co 1-d M d Q e O 2-e , particle size 17μm≤Dv50≤30μm; the general formula of small particle lithium cobalt oxide is: Li a Co 1-b T b E f O 2-f , particle size 2.5μm≤Dv50≤8μm; among which 0.98≤a≤1.02, 0.45≤b≤0.95, 0.98≤c≤1.01, 0.03≤d≤0.06, 0.001≤e≤0.005, 0.001≤f≤0.005, 0.16≤r≤0.39; M and Q are each independently selected from at least one of Mg, Al, Ni, Mn, Y, La, Zr, F, P, B, Ti, Cu, and Na; T includes Ni and Mn, and E is selected from at least one of Y, Al, B, Ni, Mn, La, Sr, W, Zr, Na, and F; In large-particle lithium cobalt oxide, element M is a doping element added during the first sintering process, and element Q is an encapsulating element added during the second sintering process; in small-particle lithium cobalt oxide, element T is a doping element added during the first sintering process, and element E is an encapsulating element added during the second sintering process.

2. A lithium cobalt oxide according to claim 1, characterized in that: The molar ratio of the large-particle lithium cobalt oxide to the small-particle lithium cobalt oxide is 1:r, wherein 0.22≤r≤0.

32.

3. The lithium cobalt oxide according to claim 1, characterized in that: The lithium cobalt oxide has a layered phase structure.

4. The lithium cobalt oxide according to claim 1, characterized in that: The particle morphology of the lithium cobalt oxide is in a single crystal state or a quasi-single crystal state.

5. The lithium cobalt oxide according to claim 1, characterized in that: T also includes at least one selected from Y, Al, B, La, Sr, W, Zr, Na, and F.

6. The lithium cobalt oxide according to claim 1, characterized in that: Satisfy at least one of the following a)-d): a) Q is selected from at least one of F, P, and B; b) M is selected from at least one of Mg, Al, Ni, Mn, Y and La; c) T is selected from at least one of Ni, Mn, Sr and Zr; d)E is F.

7. A method for preparing lithium cobalt oxide according to any one of claims 1 to 6, characterized in that: The following steps are involved: A Li-containing precursor, a Co precursor and an M-element precursor are mixed according to the stoichiometric ratio of the general formula of large-particle lithium cobalt oxide, and a large-particle primary powder doped with the M element is obtained after a single sintering; The large-particle primary powder doped with the M element is mixed with the Q element precursor, and the large-particle secondary powder coated with the Q element is obtained after secondary sintering; A Li-containing precursor, Co and T element precursor are mixed according to the stoichiometric ratio of the general formula of small-particle lithium cobalt oxide, and a small-particle primary powder doped with T element is obtained after a single sintering; The small-particle primary powder doped with the T element is mixed with the E element precursor, and the secondary powder of the small-particle secondary powder coated with the E element is obtained after secondary sintering; The large-particle secondary powder and the small-particle secondary powder are mixed to obtain lithium cobalt oxide.

8. The method for preparing lithium cobalt oxide according to claim 7, characterized in that: The Q element precursor and the E element precursor are each independently selected from at least one of oxides, hydroxides, fluorides, and phosphides.

9. The method for preparing lithium cobalt oxide according to claim 7, characterized in that: The Q element precursor and the E element precursor are at micro-nano level.

10. The method for preparing lithium cobalt oxide according to claim 7, characterized in that: Satisfy at least one of the following a)-d): a) During the primary sintering process of the large-particle lithium cobalt oxide, the sintering temperature is 900-1100°C, the time is 8-12 hours, and the sintering is carried out in an oxygen-containing atmosphere; b) During the secondary sintering process of the large-particle lithium cobalt oxide, the sintering temperature is 800-1000°C, the time is 8-12h, and the sintering is carried out in an oxygen-containing atmosphere; c) During the primary sintering process of the small-particle lithium cobalt oxide, the sintering temperature is 600-1000° C., the time is 8-12 hours, and the sintering is carried out in an oxygen-containing atmosphere; d) During the secondary sintering of small-particle lithium cobalt oxide, the sintering temperature is 500-900°C and the time is 8-12h, sintering in an oxygen-containing atmosphere.

11. The lithium cobalt oxide according to claim 7, characterized in that: When weighing the raw materials during the primary sintering process of large-particle lithium cobalt oxide and small-particle lithium cobalt oxide, the ratio of the sum of the molar amounts of added Co, M, T, and E elements to the molar amount of Li element is recorded as m1, that is, [1+(b+f)r] / (a*r+c)=m1, 0.97≤m1≤1.

1.

12. The method for preparing lithium cobalt oxide according to claim 7, characterized in that: During the primary sintering process of large-particle lithium cobalt oxide, the molar ratio of Li to Co, m2, is adjusted to: 1.0≤m2≤1.

12. When the M element replaces the Co position, additional lithium is added according to the Co position. When the M element is +n valence, the molar ratio M:Co=1:(3 / n) lithium is added, and the total amount of lithium added is the sum of m2 and the additional lithium added.

13. The method for preparing lithium cobalt oxide according to claim 7, characterized in that: During the primary sintering process of small-particle lithium cobalt oxide, the molar ratio m3 of Li and Co is adjusted to: 1.02≤m3≤1.

1. When the T element replaces the Co position, additional lithium is added according to the Co position. When the T element is +n valence, the molar ratio T:Co=1:(3 / n) lithium is added; the total amount of lithium added is the sum of m3 and the additional lithium added.

14. The method for preparing lithium cobalt oxide according to claim 7, characterized in that: In the primary sintering process of small-particle lithium cobalt oxide, the Co and T element precursors include at least one of NCM523, NCM622, NCM71515, NCM811, and NCM90505.

15. Use of the lithium cobalt oxide according to any one of claims 1 to 14 in the field of lithium ion batteries.

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