Positive electrode material, positive electrode sheet and battery

Abstract

The present disclosure relates to the field of batteries, and specifically relates to a positive electrode material, a positive electrode sheet comprising the positive electrode material, and a battery comprising the positive electrode material. Elements in the positive electrode material at least comprise Co and Ni; and in the positive electrode material, the content of Co is 20-60% based on the total mass of the positive electrode material, and the mass ratio of Co to Ni is (1.1-20):1. The positive electrode material of the present disclosure has good electrochemical performance at a high voltage (4.5 V or higher).

Description

Cathode materials, cathode sheets and batteries Technical Field

[0001] The present disclosure relates to the field of batteries, and in particular to a positive electrode material, a positive electrode sheet comprising the positive electrode material, and a battery comprising the positive electrode material. Background Art

[0002] Lithium-ion batteries (Li-ion batteries) have been widely used in consumer electronics and electric vehicles due to their high energy density, long cycle life, and environmental friendliness. As a crucial component of Li-ion batteries, cathode materials play a crucial role in their performance and cost. Lithium cobalt oxide (LCO) is currently the most widely used cathode material in Li-ion batteries for consumer electronics and electric vehicles, and it has a high cobalt content. However, the growing demand for cathode materials has accelerated the depletion of global cobalt reserves, leading to a supply shortage and a continued rise in cobalt prices. To address this issue, cathode materials with lower cobalt content (e.g., lithium nickel cobalt manganese oxide) are currently being used to reduce dependence on cobalt, thereby significantly reducing the cost of Li-ion batteries. However, current cathode materials with lower cobalt content are not resistant to high voltages, which seriously hinders their application.

[0003] Therefore, it is very important to invent a positive electrode material that is resistant to high voltage and has a low cobalt content.

[0004] Summary of the Invention

[0005] The present invention aims to overcome the problem of prior art cathode materials with low cobalt content being unable to withstand high voltages, and provides a cathode material, a cathode sheet comprising the cathode material, and a battery comprising the cathode material. The cathode material disclosed herein exhibits good electrochemical performance at high voltages (4.5V and above).

[0006] In a first aspect, the present disclosure provides a positive electrode material, wherein the elements in the positive electrode material include at least Co and Ni. In the positive electrode material, based on the total mass of the positive electrode material, the content of the element Co is 20%-60%, and the mass ratio of the element Co to the element Ni is (1.1-20):1.

[0007] A second aspect of the present disclosure provides a positive electrode sheet, which includes the positive electrode material described in the first aspect of the present disclosure.

[0008] A third aspect of the present disclosure provides a battery, which includes the positive electrode material described in the first aspect of the present disclosure and / or the positive electrode sheet described in the second aspect of the present disclosure.

[0009] Through the above technical solution, the present disclosure has at least the following advantages compared with the prior art:

[0010] (1) The cathode material disclosed in the present invention has a lower cobalt content than conventionally used lithium cobalt oxide, which can significantly reduce production costs and has high-voltage resistance;

[0011] (2) The positive electrode material disclosed in the present invention has high-voltage resistance compared to the conventional nickel-cobalt-manganese ternary material.

[0012] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] FIG. 1 shows an embodiment of the present disclosure and a pair of proportional dQ / dV curves.

[0014] FIG2 is a schematic cross-sectional view of a positive electrode sheet in an example of the present disclosure.

[0015] FIG3 shows the XRD curve of the positive electrode material in Example 1 of the present disclosure.

[0016] FIG4 shows an electron microscope image (surface morphology) of the positive electrode material in Example 1 of the present disclosure.

[0017] FIG5 shows an electron microscope image (cross-sectional morphology) of the positive electrode material in Example 1 of the present disclosure.

[0018] FIG6 shows a cross-sectional energy spectrum diagram of the positive electrode material in Example 1 of the present disclosure. DETAILED DESCRIPTION

[0019] The following describes the specific embodiments of the present disclosure in detail. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not intended to limit the present disclosure.

[0020] A first aspect of the present disclosure provides a positive electrode material, wherein the elements in the positive electrode material include at least Co and Ni. In the positive electrode material, based on the total mass of the positive electrode material, the content of the element Co may be 20%-60% (for example, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55% or 60%), and the mass ratio of the element Co to the element Ni may be (1.1-20):1 (for example, 1.1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 11:1, 12:1, 13:1, 14:1, 15:1, 16:1, 17:1, 18:1, 19:1 or 20:1).

[0021] Lithium cobalt oxide is one of the most widely used positive electrode materials. However, cobalt is a scarce resource and its price continues to rise. Therefore, the cost of batteries using lithium cobalt oxide with a cobalt content of approximately 60% as a positive electrode material has also increased accordingly. Lithium nickel cobalt manganese oxide has a lower cobalt content (approximately 6%-21%), which can significantly reduce the manufacturing cost of batteries. However, compared with lithium cobalt oxide, lithium nickel cobalt manganese oxide has a lower voltage, which affects its application. The inventors of the present disclosure have discovered that when the mass ratio of the element Co to the element Ni in the positive electrode material is within a certain range, the high voltage resistance of the positive electrode material can be significantly improved.

[0022] In one embodiment, in the positive electrode material, the content of the element Co is 35%-50% based on the total mass of the positive electrode material, and the mass ratio of the element Co to the element Ni is (2-8):1.

[0023] In the present disclosure, the types of elements in the positive electrode material and the content of each element can be tested by conventional means in the art, such as inductively coupled plasma mass spectrometry (ICP-MS).

[0024] In the present disclosure, the positive electrode material may include a first active material and a second active material.

[0025] The first active material may include a chemical formula of Li x1 Co p Al m M n O2, wherein 0.9≤x1≤1.05 (e.g., x1=0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.01, 1.02, 1.03, 1.04, or 1.05), 0≤m≤0.05 (e.g., m=0, 0.01, 0.02, 0.03, 0.04, or 0.05), 0≤n≤0.01 (e.g., n=0, 0.0005, 0.001 , 0.002, 0.003, 0.004, 0.005, 0.006, 0.007, 0.008, 0.009 or 0.01), 0.94≤p≤1 (for example, p=1, 0.99, 0.98, 0.97, 0.96, 0.95 or 0.94), M is selected from at least one of Mg, Ti, La, Y, Zr, W, Nb, Te, B and Ce, and it can be considered that the values ​​of x1, m, n and p satisfy that the algebraic sum of the valences of the elements in the substance is 0.

[0026] When M is selected from at least two of Mg, Ti, La, Y, Zr, W, Nb, Te, B and Ce, the number of atoms of each element is the same. For example, when M is Mg and Ti, the chemical formula Li x1Co p Al m M n O2 is Li x1 Co p Al m Mg n / 2 Ti n / 2 O2; For example, when M is Mg, Ti and Y, the chemical formula Li x1 Co p Al m M n O2 is Li x1 Co p Al m Mg n / 3 Ti n / 3 Y n / 3 O2.

[0027] In one example, 0.001≤m≤0.01.

[0028] In one example, 0.001≤n≤0.005.

[0029] The second active material may include a chemical formula of Li x2 Ni a Mn b L c O2, wherein 0.9≤x2≤1.05 (e.g., x2=0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, 1.01, 1.02, 1.03, 1.04, or 1.05), 0.5≤a≤0.8 (e.g., a=0.5, 0.55, 0.6, 0.65, 0.7, 0.75, or 0.8), and 0.1≤b ≤0.5 (for example, b=0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5), 0≤c≤0.4 (for example, c=0.4, 0.3, 0.2, 0.1 or 0), L is selected from at least one of Al, Mg, Ti, Zr, P, Te, Nb, W, Mo, Y and Si, and it can be considered that the values ​​of x2, a, b and c satisfy that the algebraic sum of the valences of the elements in the substance is 0.

[0030] When L is selected from at least two of Al, Mg, Ti, Zr, P, Te, Nb, W, Mo, Y and Si, the number of atoms of each element is the same. For example, when L is Al and Mg, the chemical formula Li x2 Ni a Mn b L c O2 is Li x2 Ni a Mn b Alc / 2 Mg c / 2 O2; For example, when L is Al, Mg and Ti, the chemical formula Li x2 Ni a Mn b L c O2 is Li x2 Ni a Mn b Al c / 3 Mg c / 3 Ti c / 3 O2.

[0031] The inventors of the present disclosure have discovered that a and b have specific ranges, which can improve the bulk structural stability and surface structural stability of the positive electrode material while ensuring the gram capacity of the positive electrode material.

[0032] In one example, 0.5≤a≤0.75.

[0033] In one example, 0.5≤a≤0.7.

[0034] In one example, 0.25≤b≤0.5.

[0035] The inventors of the present disclosure have discovered that when the positive electrode material includes the first active material and the second active material, the positive electrode material has high gram capacity and stability while having high voltage resistance.

[0036] The inventors of the present disclosure have discovered that when the chemical formula is Li x2 Ni a Mn b L c When the space group of the O2 substance is R-3m, the gram capacity, stability and high-voltage resistance of the positive electrode material can be further improved.

[0037] In one embodiment, the chemical formula is Li x2 Ni a Mn b L c The space group of O2 is R-3m.

[0038] In one example, the space group of the second active material is R-3m.

[0039] In the present disclosure, the median particle size Dv50 of the first active material may be greater than the median particle size Dv50 of the second active material. The ratio of the median particle size Dv50 of the first active material to the median particle size Dv50 of the second active material may be (2-5):1, for example, 2:1, 2.5:1, 3:1, 3.5:1, 4:1, 4.5:1, or 5:1.

[0040] The inventors of the present disclosure have found that when the ratio of the median particle size Dv50 of the first active material to the median particle size Dv50 of the second active material is within a specific range, a battery including the positive electrode material has higher rate performance and energy density.

[0041] In one example, the ratio of the median particle size Dv50 of the first active material to the median particle size Dv50 of the second active material is (3-4):1.

[0042] In the present disclosure, the median particle size Dv50 of the positive electrode material can be 10μm-23μm, for example, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm or 23μm.

[0043] In one example, the median particle size Dv50 of the positive electrode material is 15 μm-18 μm.

[0044] In the present disclosure, the median particle size Dv50 of the first active material may be 12 μm-25 μm, for example, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm or 25 μm.

[0045] In one example, the median particle size Dv50 of the first active material is 16 μm-20 μm.

[0046] In the present disclosure, the median particle size Dv50 of the second active material may be 2 μm-10 μm, for example, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm.

[0047] In one example, the median particle size Dv50 of the second active material is 4 μm-6 μm.

[0048] In the present disclosure, the mass proportion of the second active material in the positive electrode material may be 10%-50%, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45% or 50%.

[0049] The inventors of the present disclosure have discovered that when the mass proportion of the second active material in the positive electrode material is within a specific range, the positive electrode material can better balance capacity, structural stability, high-voltage resistance, and production cost.

[0050] In one example, the mass proportion of the second active material in the positive electrode material is 20%-40%.

[0051] In the present disclosure, in the XRD pattern of the positive electrode material, there are at least two diffraction peaks in the range of 18.0° - 19.5°.

[0052] In one example, in the XRD pattern of the positive electrode material, there are at least two diffraction peaks in the range of 18.5° - 19.0°.

[0053] In the present disclosure, the angular range of the first diffraction peak among the above two diffraction peaks is 18.5° - 18.75°.

[0054] In one example, the angular range of the first diffraction peak is 18.55° - 18.7°.

[0055] In the present disclosure, the angular range of the second diffraction peak among the above two diffraction peaks is 18.8° - 19.0°.

[0056] In one example, the angular range of the second diffraction peak is 18.85° - 18.9°.

[0057] In the present disclosure, the difference between the angle of the second diffraction peak and the angle of the first diffraction peak is less than 0.5°, such as less than 0.5°, 0.4°, 0.3°, 0.2° or 0.1°.

[0058] In one example, the difference between the angle of the second diffraction peak and the angle of the first diffraction peak is less than 0.3°.

[0059] In one example, the peak intensity of the second diffraction peak is I2, and the peak intensity of the first diffraction peak is I1, and 1 < I2 / I1 < 2.5.

[0060] The inventors of the present disclosure found that when 1 < I2 / I1 < 2.5 in the XRD pattern of the positive electrode material, the crystal structure of the positive electrode material is more stable, and the positive electrode material has more excellent high-voltage resistance performance. At the same time, when the positive electrode material includes a first active material and a second active material, satisfying this peak intensity ratio can better play the advantages of these two materials, improve the synergistic effect, make the structure between these two materials more stable, reduce side reactions, and improve the high-voltage resistance performance of the positive electrode material.

[0061] In the present disclosure, the specific surface area of the positive electrode material can be 0.1 m 2 / g - 0.8 m 2 / g, such as 0.1 m 2 / g, 0.15 m 2 / g, 0.2 m 2 / g, 0.25 m 2 / g, 0.3 m 2 / g, 0.35 m 2 / g, 0.4m 2 / g, 0.45m 2 / g, 0.5m 2 / g, 0.55m 2 / g, 0.6m 2 / g, 0.65m 2 / g, 0.7m 2 / g, 0.75m 2 / g or 0.8m 2 / g.

[0062] The inventors of the present disclosure have discovered that when the specific surface area of ​​the positive electrode material is within a specific range, it is beneficial to improve the wettability of the electrolyte to the positive electrode material, improve the conductivity of lithium ions, and improve the cycle performance of the battery.

[0063] In one embodiment, the specific surface area of ​​the positive electrode material is 0.2 m 2 / g-0.45m 2 / g.

[0064] In the present disclosure, the specific surface area of ​​the first active material may be 0.05 m 2 / g-0.3m 2 / g, for example 0.05m 2 / g, 0.1m 2 / g, 0.15m 2 / g, 0.2m 2 / g, 0.25m 2 / g or 0.3m 2 / g.

[0065] In the present disclosure, the specific surface area of ​​the second active material can be 0.3m 2 / g-1.2m 2 / g, for example 0.3m 2 / g, 0.35m 2 / g, 0.4m 2 / g, 0.45m 2 / g, 0.5m 2 / g, 0.55m 2 / g, 0.6m 2 / g, 0.65m 2 / g, 0.7m 2 / g, 0.75m 2 / g, 0.8m 2 / g, 0.85m 2 / g, 0.9m 2 / g, 0.95m 2 / g、1m 2 / g, 1.05m 2 / g, 1.1m 2 / g, 1.15m 2 / g or 1.2m 2 / g.

[0066] The inventors of the present disclosure have discovered that the specific surface area of ​​the first active material and the specific surface area of ​​the second active material are within a specific range, which can effectively improve the uniformity of the positive electrode material and thereby increase the compaction density of the positive electrode material.

[0067] In one embodiment, the specific surface area of ​​the first active material is 0.1 m 2 / g-0.2m 2 / g.

[0068] In one embodiment, the specific surface area of ​​the second active material is 0.5 m 2 / g-1m 2 / g.

[0069] In the present disclosure, the dQ / dV curve of the positive electrode material has at least two peaks in the range of 3.7V-4.0V (i.e., the charge-discharge curve has two voltage platforms), the first peak is located at 3.7V-3.8V (the first voltage platform is 3.7V-3.8V), and the second peak is located at 3.9V-4.0V (the second voltage platform is 3.9V-4.0V). For example, FIG1 shows the dQ / dV curves of an embodiment of the present disclosure and a comparative example. As can be seen from FIG1 , compared with the comparative example, the dQ / dV curve of the positive electrode material provided by the present disclosure has at least two peaks in the range of 3.7V-4.0V, indicating that the positive electrode material of the present disclosure has a higher specific capacity at the same voltage.

[0070] The cathode material disclosed herein has high gram capacity, high structural stability, high voltage resistance and low cost.

[0071] A second aspect of the present disclosure provides a positive electrode sheet, which includes the positive electrode material described in the first aspect of the present disclosure.

[0072] In the present disclosure, the compaction density of the positive electrode sheet is ≥3g / cm 3 , for example 3g / cm 3 , 3.1g / cm 3 、3.2g / cm 3 , 3.3g / cm 3 、3.4g / cm 3 , 3.5g / cm 3 、3.6g / cm 3 、3.7g / cm 3 、3.8g / cm 3 、3.9g / cm 3 , 4g / cm 3, 4.1g / cm 3 , 4.2g / cm 3 , 4.3g / cm 3 , 4.4g / cm 3 or 4.5g / cm 3 .

[0073] In one embodiment, the compaction density of the positive electrode sheet is 3.5 g / cm 3 -4.5g / cm 3 .

[0074] In one embodiment, the compaction density of the positive electrode sheet is 4.15 g / cm 3 -4.25g / cm 3 Within this range (including both end point values), the energy density of the battery can be improved.

[0075] In the present disclosure, the positive electrode sheet may include a positive electrode current collector and a positive electrode material layer on at least one side of the positive electrode current collector, and the positive electrode material layer may include the positive electrode material. As shown in Figure 2, a cross-sectional schematic diagram of a positive electrode sheet in an example of the present disclosure is shown, wherein Figure 2(a) shows the case where the positive electrode material layer is set on one side; Figures 2(b) and 2(c) show the cases where the positive electrode material layer is set on both sides. In Figure 2(a), the positive electrode sheet includes a positive electrode current collector 1 and a positive electrode material layer 2 on one side of the positive electrode current collector 1; in Figures 2(b) and 2(c), the positive electrode sheet includes a positive electrode current collector 1 and a positive electrode material layer 2 on both sides of the positive electrode current collector 1.

[0076] In the present disclosure, the positive electrode material layer may further include a conductive agent and a binder. The conductive agent may be selected from those commonly used in the art, such as at least one of conductive carbon black, acetylene black, Ketjen black, carbon fiber, graphene, single-walled carbon nanotubes, and multi-walled carbon nanotubes. The binder may be selected from those commonly used in the art, such as at least one of carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyethylene, polyvinyl alcohol, polyvinyl chloride, polyvinylidene fluoride, polyvinyl pyrrolidone, polytetrafluoroethylene, polypropylene, styrene-butadiene rubber, epoxy resin, butadiene rubber binder, and acrylonitrile binder.

[0077] In the present disclosure, based on the total weight of the positive electrode material layer, the content of the positive electrode material may be 80-99 weight % (for example, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98 or 99 weight %), the content of the conductive agent may be 0.5-10 weight % (for example, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 or 0.5 weight %), and the content of the binder may be 0.5-10 weight % (for example, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1 or 0.5 weight %).

[0078] In one example, based on the total weight of the positive electrode material layer, the content of the positive electrode material is 91-97.5 wt %, the content of the conductive agent is 0.5-4 wt %, and the content of the binder is 2-5 wt %.

[0079] A third aspect of the present disclosure provides a battery, which includes the positive electrode material described in the first aspect of the present disclosure and / or the positive electrode sheet described in the second aspect of the present disclosure.

[0080] The inventors of the present disclosure found that the charge cut-off voltage that the battery can withstand changes with the change of the second active material. When 0.5≤a≤0.7, the charge cut-off voltage of the battery can be ≥4.5V; when a>0.7, the charge cut-off voltage of the battery is <4.5V.

[0081] In one example, the battery has a charge cut-off voltage of ≥4.5V.

[0082] The components of the battery other than the positive electrode sheet (such as the negative electrode sheet, the separator and the electrolyte, etc.) can all be conventionally selected in the art.

[0083] In one example, the battery further includes a negative electrode sheet, a separator, and an electrolyte.

[0084] The negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer on at least one side of the negative electrode current collector. The negative electrode active material layer may include a negative electrode active material.

[0085] The negative electrode active material can be a conventional choice in the art. For example, the negative electrode active material includes at least one of natural graphite, artificial graphite, mesophase carbon microsphere graphite, soft carbon, hard carbon, silicon, silicon oxide, silicon carbon and silicon alloy.

[0086] The battery can be assembled in a conventional manner in the art.

[0087] It should be noted that the numerical expressions such as "first" and "second" in this disclosure are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0088] The present disclosure will be described in detail below through examples. The examples described in this disclosure are only a portion of the examples of the present disclosure, not all of the examples. Based on the examples in this disclosure, all other examples obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this disclosure.

[0089] In the following examples, unless otherwise specified, all materials used were commercially available analytical grade.

[0090] Example

[0091] Prepare the battery as follows:

[0092] (1) Preparation of positive electrode sheet

[0093] The positive electrode material (wherein the space group of the second active material is R-3m), polyvinylidene fluoride (PVDF), conductive carbon black SP and carbon nanotubes CNT are mixed in a mass ratio of 96:2:1.5:0.5, and N-methylpyrrolidone (NMP) is added with a solid content of 75wt%. The mixture is stirred in a vacuum mixer to form a positive electrode slurry with uniform fluidity; the above positive electrode slurry is evenly coated on aluminum foil (thickness of 9μm), dried, rolled, slit, and super welded to obtain a positive electrode sheet, wherein the compacted density of the positive electrode sheet is 4.2g / cm 3 ;

[0094] (2) Preparation of negative electrode sheet

[0095] Graphite, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), and acetylene black SP were mixed in a mass ratio of 96.5:1:1:1.5, deionized water was added, and the solid content was 45 wt%, and the mixture was stirred in a vacuum mixer to form a negative electrode slurry with uniform fluidity; the negative electrode slurry was evenly coated on a copper foil (thickness of 6 μm), dried, rolled, slit, and super welded to obtain a negative electrode sheet;

[0096] (3) Preparation of electrolyte

[0097] Ethylene carbonate, propylene carbonate, and diethyl carbonate were mixed in a mass ratio of 1:1:1 as a solvent, and 1 mol / L lithium hexafluorophosphate (LiPF6) was used as a lithium salt;

[0098] (4) Preparation of batteries

[0099] The positive electrode sheet obtained in step (1), the separator (7μm+3μm mixed separator, substrate polypropylene film+PVDF&ceramic mixed coating) and the negative electrode sheet obtained in step (2) are stacked in order, the multi-layer aluminum foil of the positive electrode sheet is transferred to the aluminum tab through the aluminum foil sheet, and the multi-layer copper foil of the negative electrode sheet is transferred to the nickel tab through the copper foil sheet to obtain a multi-tab type battery cell, wherein two layers of separators wrap the negative electrode sheet, and the positive electrode sheet is placed on the separator to ensure that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and the bare battery cell is wound; the bare battery cell is heat-sealed in a shell made of aluminum-plastic film, and the electrolyte obtained in step (3) is injected into the bare battery cell with a moisture value of <200ppm after baking, and a battery is obtained through vacuum packaging, hot and cold pressing plasticization, chemical formation, shaping, sorting and other processes.

[0100] Prepare a button cell battery as follows:

[0101] The positive electrode material, conductive carbon black SP and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 95:2.5:2.5, dispersed with N-methylpyrrolidone (NMP) to form a slurry, coated on the surface of an aluminum foil, and dried at 80°C for 12 hours to obtain a positive electrode sheet. The dried positive electrode sheet was roll-pressed and cut into discs and placed in a glove box for standby use. The above-mentioned positive electrode sheet was used as the positive electrode, metallic lithium was used as the negative electrode, Celgard 2400 (microporous polypropylene membrane) was used as the separator, 1 mol / L LiPF6 and EC:EMC:DMC=1:1:1 were used as the electrolyte, and a 2032-type button battery was assembled.

[0102] The batteries and button cells of the embodiment and the comparative example were prepared according to the above method, except for the positive electrode materials, as shown in Table 1. The specific surface area of ​​the first active material in the embodiment is 0.1 m 2 / g-0.2m 2 / g, and the specific surface area of ​​the second active material is 0.5m 2 / g-1m 2 / g, the specific surface area of ​​the positive electrode material is 0.2m 2 / g-0.45m 2 / g.

[0103] Table 1 shows the chemical formula and particle size parameters of the first active material and the second active material in the examples and comparative examples; Table 2 shows the parameters of the positive electrode material.

[0104] Table 1

[0105] Table 2

[0106] Test Case

[0107] (1) Discharge capacity and rate test

[0108] The button batteries prepared in the examples and comparative examples were charged and discharged at a test temperature of 25°C and a test voltage range of 3.0V-4.5V, wherein the charge rate was 0.1C and the discharge rates were 0.1C, 0.2C, 0.5C, 1C, and 2C, respectively. The test results are recorded in Table 3.

[0109] (2) 25℃ cycle capacity test

[0110] The batteries prepared in the examples and comparative examples were placed in an environment of 25°C ± 2°C:

[0111] 1) Discharge at 0.7C to a lower voltage of 3.0V and let stand for 10 minutes;

[0112] 2) Charge at 2C to the upper limit voltage of 4.5V, stop at 0.05C, and let it stand for 10 minutes;

[0113] 3) 2C discharge to the lower limit voltage of 3.0V, and let it stand for 10 minutes;

[0114] 4) Charge at 2C to an upper voltage of 4.5V, then reduce to 0.05C and let stand for 10 minutes; repeat steps 3) to 4) 800 times;

[0115] Capacity retention rate formula: Capacity retention rate = A2 / A1×100%;

[0116] The first cycle test capacity is recorded as A1, and the test capacity after 800 cycles is recorded as A2. The results are recorded in Table 3.

[0117] (3) 45℃ cycle capacity test

[0118] The batteries prepared in the examples and comparative examples were placed in an environment of 45°C ± 2°C:

[0119] 1) Discharge at 0.7C to a lower voltage of 3.0V and let stand for 10 minutes;

[0120] 2) Charge at 2C to the upper limit voltage of 4.5V, stop at 0.05C, and let it stand for 10 minutes;

[0121] 3) 2C discharge to the lower limit voltage of 3.0V, and let it stand for 10 minutes;

[0122] 4) Charge at 2C to an upper voltage of 4.5V, then reduce to 0.05C and let stand for 10 minutes; repeat steps 3) to 4) 800 times;

[0123] Capacity retention rate formula: Capacity retention rate = A4 / A3×100%;

[0124] The capacity tested in the first cycle is recorded as A3, and the capacity tested after 800 cycles is recorded as A4. The results are recorded in Table 3.

[0125] (4) XRD test

[0126] The positive electrode material of Example 1 was subjected to X-ray diffraction to test the crystal structure of the material. FIG3 is an XRD curve of the positive electrode material of Example 1 of the present disclosure. As can be seen from the figure, there are two diffraction peaks in the range of 18.5°-19.0°. The angle range of the first diffraction peak is 18.55°-18.7°, and the angle range of the second diffraction peak is 18.85°-18.9°; the difference between the angle of the second diffraction peak and the angle of the first diffraction peak is less than 0.3°; <I2 / I1<2.5。

[0127] (5) Electron microscopy test

[0128] The positive electrode material of Example 1 was subjected to a scanning electron microscope (SEM) test to obtain the morphological structure of the material, and the material structure and element distribution of the material were analyzed with a matching X-ray energy spectrometer. As shown in Figure 4, an electron microscope image (surface morphology) of the positive electrode material in Example 1 of the present disclosure is shown in Figure 5. The electron microscope image (cross-sectional morphology) of the positive electrode material in Example 1 of the present disclosure is shown in Figure 6. The cross-sectional energy spectrum of the positive electrode material in Example 1 of the present disclosure is shown. It can be seen from the electron microscope image that the positive electrode material is a combination of large and small particle sizes, wherein the large particle material is nickel-free lithium cobalt oxide, and the small particle material is cobalt-free lithium nickel oxide.

[0129] Table 3

[0130] It can be seen from Table 3 that the battery prepared by the positive electrode material disclosed in the present invention has excellent high voltage resistance performance compared with the comparative example under the premise of reducing the cobalt content.

[0131] The preferred embodiments of the present disclosure are described in detail above, but the present disclosure is not limited thereto. Within the technical concept of the present disclosure, various simple variations of the technical solution of the present disclosure may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed by the present disclosure and fall within the scope of protection of the present disclosure.

Claims

1. A positive electrode material, characterized in that: The elements in the positive electrode material include at least Co and Ni. In the positive electrode material, based on the total mass of the positive electrode material, the content of the element Co is 20%-60%, and the mass ratio of the element Co to the element Ni is (1.1-20):

1.

2. The positive electrode material according to claim 1, wherein In the positive electrode material, the content of the element Co is 35%-50% based on the total mass of the positive electrode material; And / or, the mass ratio of the element Co to the element Ni is (2-8):

1.

3. The positive electrode material according to claim 1 or 2, wherein The positive electrode material includes a first active material and a second active material. The first active material includes a chemical formula of Li x1 Co p Al m M n O2, wherein 0.9≤x1≤1.05, 0≤m≤0.05, 0≤n≤0.01, 0.94≤p≤1, M is selected from at least one of Mg, Ti, La, Y, Zr, W, Nb, Te, B and Ce; the second active material includes a chemical formula of Li x2 Ni a Mn b L c O2, wherein 0.9≤x2≤1.05, 0.5≤a≤0.8, 0.1≤b≤0.5, 0≤c≤0.4, and L is selected from at least one of Al, Mg, Ti, Zr, P, Te, Nb, W, Mo, Y and Si; Preferably, 0.001≤m≤0.01, 0.001≤n≤0.005; Preferably, 0.5≤a≤0.7, 0.25≤b≤0.

5.

4. The positive electrode material according to claim 3, wherein The space group of the second active substance is R-3m; Preferably, the chemical formula is Li x2 Ni a Mn b L c The space group of O2 substance is R-3m.

5. The positive electrode material according to claim 3 or 4, wherein The median particle size Dv50 of the first active substance is greater than the median particle size Dv50 of the second active substance; Preferably, the ratio of the median particle size Dv50 of the first active substance to the median particle size Dv50 of the second active substance is (2-5):1; preferably (3-4):

1.

6. The positive electrode material according to any one of claims 1 to 5, wherein The median particle size Dv50 of the positive electrode material is 10 μm-23 μm, preferably 15 μm-18 μm.

7. The positive electrode material according to any one of claims 3 to 6, wherein The median particle size Dv50 of the first active substance is 12 μm-25 μm; preferably 16 μm-20 μm; And / or, the median particle size Dv50 of the second active substance is 2 μm-10 μm; preferably 4 μm-6 μm.

8. The positive electrode material according to any one of claims 1 to 7, wherein The dQ / dV curve of the positive electrode material has at least two peaks at 3.7V-4.0V, the first peak is located at 3.7V-3.8V, and the second peak is located at 3.9V-4.0V.

9. The positive electrode material according to any one of claims 3 to 8, wherein The mass proportion of the second active material in the positive electrode material is 10%-50%; Preferably, the mass proportion of the second active material in the positive electrode material is 20%-40%.

10. The positive electrode material according to any one of claims 1 to 9, wherein In the XRD spectrum of the positive electrode material, at least two diffraction peaks are included in the range of 18.0°-19.5°; Preferably, in the XRD spectrum of the positive electrode material, at least two diffraction peaks are included in the range of 18.5°-19.0°.

11. The positive electrode material according to claim 10, wherein The angle range of the first diffraction peak of the two diffraction peaks is 18.5°-18.75°; And / or, the angle range of the second diffraction peak of the two diffraction peaks is 18.8°-19.0°.

12. The positive electrode material according to claim 10 or 11, wherein The difference between the angles of the two diffraction peaks is less than 0.5°; And / or, the peak intensity of the second diffraction peak of the two diffraction peaks is I2, and the peak intensity of the second diffraction peak of the two diffraction peaks is I2. The peak intensity of a diffraction peak is I1,1 <I2 / I1<2.5。 13. The positive electrode material according to any one of claims 1 to 12, wherein: The specific surface area of ​​the positive electrode material is 0.1 m 2 / g-0.8m 2 / g; preferably 0.2m 2 / g-0.45m 2 / g; And / or, the specific surface area of ​​the first active material is 0.05m 2 / g-0.3m 2 / g; preferably 0.1m 2 / g-0.2m 2 / g; And / or, the specific surface area of ​​the second active material is 0.3m 2 / g-1.2m 2 / g; preferably 0.5m 2 / g-1m 2 / g.

14. A positive electrode sheet, characterized in that: The positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 13; Preferably, the compaction density of the positive electrode sheet is ≥3g / cm 3 .

15. A battery, characterized in that: The battery comprises the positive electrode material according to any one of claims 1 to 13 and / or the positive electrode sheet according to claim 14; Preferably, the charging cut-off voltage of the battery is ≥4.5V.

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