Positive electrode material and preparation method thereof, positive plate and lithium ion battery

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a positive electrode material and a preparation method thereof, a positive plate and a lithium ion battery. The preparation method of the positive electrode material comprises the following steps: S1, mixing a lithium cobalt oxide, nickel cobalt lithium manganate ternary material and a primary sintering coating material, carrying out primary sintering, and crushing; wherein the mass ratio of the lithium cobalt oxide to the nickel cobalt lithium manganate ternary material is (1: 9)-(9: 1); the primary firing coating accounts for 0.01-0.5 wt% of the total mass of the lithium cobalt oxide and nickel cobalt lithium manganate ternary material, and the primary firing coating is a metal oxide; and S2, mixing the material obtained in the step S1 with a secondary sintering coating material, and performing secondary sintering to obtain the positive electrode material, wherein the secondary sintering coating accounts for 0.02-1wt% of the total mass of the lithium cobalt oxide and nickel cobalt lithium manganate ternary material, and the secondary sintering coating is metal fluoride and / or metal phosphate. With the adoption of the mode, the lithium ion battery can be used under high voltage, and has relatively high thermal stability and excellent cycle performance.

Description

Technical Field

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

[0002] In recent years, with the advancement of science and technology, lithium-ion secondary batteries have gradually occupied most of the battery industry market with their unique advantages of high capacity, long cycle life, no memory effect, high energy density, clean and pollution-free. Among the raw material costs of lithium-ion batteries, the proportion of lithium cobalt oxide positive electrode active materials is the largest, reaching more than 40% of the total. With the gradual reduction of cobalt resources and the continuous rise in prices, the cost and selling price of lithium-ion batteries will further increase. At the same time, the high-voltage lithium cobalt oxide is extremely unstable at high temperatures, which easily causes oxygen precipitation and cobalt dissolution, resulting in serious attenuation of storage capacity.

[0003] At present, the structural stability of nickel-cobalt-manganese-oxide ternary materials is significantly better than that of lithium cobalt oxide, and has better high-temperature storage performance. However, under high voltage, the structure of ternary materials is unstable during the charge and discharge process. Although the thermal stability of the composite material is effectively improved by mixing ternary materials with lithium cobalt oxide materials, the cycle also decays quickly. Summary of the invention

[0004] The present invention provides a positive electrode material and a preparation method thereof, a positive electrode sheet and a lithium ion battery, which can be used at a high voltage and have high thermal stability and excellent cycle performance.

[0005] In order to solve the above technical problems, a technical solution adopted by the present invention is: to provide a method for preparing a positive electrode material, comprising the following steps:

[0006] Step S1: mixing, sintering and crushing lithium cobalt oxide, nickel cobalt lithium manganese oxide ternary material and a sintered coating; wherein the mass ratio of the lithium cobalt oxide to the nickel cobalt lithium manganese oxide ternary material is (1:9) to (9:1); the sintered coating accounts for 0.01-0.5wt% of the total mass of the lithium cobalt oxide and the nickel cobalt lithium manganese oxide ternary material, and the sintered coating is a metal oxide;

[0007] Step S2: Mixing the material obtained in step S1 with the di-sintered coating and performing secondary sintering to obtain the positive electrode material; wherein the di-sintered coating accounts for 0.02-1wt% of the total mass of the lithium cobalt oxide and the nickel cobalt manganese oxide ternary material, and the di-sintered coating is a metal fluoride and / or a metal phosphate.

[0008] According to an embodiment of the present invention, the primary sintering temperature is 700-900° C., the heating rate is 3-5° C. / min, and the sintering time is 0.5-6 h.

[0009] According to one embodiment of the present invention, the secondary sintering temperature is 400-700° C., the heating rate is 3-5° C. / min, and the sintering time is 0.5-6 h.

[0010] According to an embodiment of the present invention, the sintered coating is one or more of Al2O3, TiO2, ZrO2 and MgO2.

[0011] According to one embodiment of the present invention, the di-sintered coating is one or more of AlF3, LiF, MgF2, AlPO4 and Li3PO4.

[0012] According to one embodiment of the present invention, the chemical formula of the nickel-cobalt-lithium-manganese oxide ternary material is Li(Ni x Co y Mn 1-x-y )O2, where 0.3≤x≤0.9, 0.1≤y≤0.4.

[0013] According to one embodiment of the present invention, the chemical formula of the lithium cobalt oxide is Li a Co 1-b M b O2, wherein M is one or more of Mg, Al, Zr, La, Y, Mn, Ni, 0.95≤a≤1.05, 0≤b≤0.1.

[0014] In order to solve the above technical problem, another technical solution adopted by the present invention is: to provide a positive electrode material, including: prepared by the positive electrode material preparation method.

[0015] In order to solve the above technical problems, another technical solution adopted by the present invention is: to provide a positive electrode sheet, the positive electrode sheet comprises: a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer comprises the positive electrode material.

[0016] In order to solve the above technical problem, another technical solution adopted by the present invention is: to provide a lithium ion battery, wherein the lithium ion battery comprises the above positive electrode sheet.

[0017] The beneficial effects of the present invention are as follows: a method for preparing a positive electrode material comprises the following steps: step S1: mixing, sintering and crushing lithium cobalt oxide, a nickel cobalt manganese oxide ternary material and a sintered coating; wherein the mass ratio of the lithium cobalt oxide to the nickel cobalt manganese oxide ternary material is (1:9) to (9:1); the sintered coating accounts for 0.01-0.5wt% of the total mass of the lithium cobalt oxide and the nickel cobalt manganese oxide ternary material, and the sintered coating is a metal oxide; step S2: mixing the material obtained in step S1 with the sintered coating and sintering for a second time to obtain the positive electrode material; wherein the sintered coating accounts for 0.02-1wt% of the total mass of the lithium cobalt oxide and the nickel cobalt manganese oxide ternary material, and the sintered coating is a metal fluoride and / or a metal phosphate; through the first sintering co-coating and the second sintering co-coating, it can be used at high voltage and has high thermal stability and excellent cycle performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of a process for preparing a positive electrode material according to an embodiment of the present invention. DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0020] The terms "first", "second" and "third" in the present invention are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. Thus, the features defined as "first", "second" and "third" can explicitly or implicitly include at least one of the features. In the description of the present invention, the meaning of "multiple" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined. All directional indications (such as up, down, left, right, front, back...) in the embodiments of the present invention are only used to explain the relative position relationship, movement, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication also changes accordingly. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but optionally also includes steps or units that are not listed, or optionally also includes other steps or units inherent to these processes, methods, products or devices.

[0021] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present invention. The appearance of the phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0022] Figure 1 FIG. 1 is a flow chart of a method for preparing a positive electrode material according to an embodiment of the present invention. It should be noted that the method of the present invention is not limited to the method of preparing a positive electrode material according to an embodiment of the present invention if the results are substantially the same. Figure 1 The process sequence shown is limited. Figure 1 As shown, the method comprises the steps of:

[0023] Step S1: mixing, sintering and crushing lithium cobalt oxide, nickel cobalt lithium manganese oxide ternary materials and a sintered coating; wherein the mass ratio of lithium cobalt oxide and nickel cobalt lithium manganese oxide ternary materials is (1:9) to (9:1); the sintered coating accounts for 0.01-0.5wt% of the total mass of the lithium cobalt oxide and nickel cobalt lithium manganese oxide ternary materials, and the sintered coating is a metal oxide.

[0024] In step S1, the primary sintering temperature is 700-900°C, the heating rate is 3-5°C / min, and the sintering time is 0.5-6h. Exemplarily, the primary sintering temperature is 750°C, 850°C, 700°C or 800°C; the heating rate is 3°C / min, 4°C / min or 5°C / min; and the sintering time is 0.5h, 1h, 2h, 3h, 4h, 5h or 6h.

[0025] Preferably, the mass ratio of lithium cobalt oxide and nickel cobalt lithium manganese oxide ternary material is (2:8) to (8:2). Exemplarily, the mass ratio of lithium cobalt oxide and nickel cobalt lithium manganese oxide ternary material is 2:8, 3:7, 4:6, 5:5, 6:4, 7:3 or 8:2.

[0026] Preferably, the median particle size D50 of the nickel-cobalt-manganese-oxide lithium ternary material is 3 to 13 μm. The general chemical formula of the nickel-cobalt-manganese-oxide lithium ternary material is Li(Ni x Co y Mn 1-x-y )O2, wherein 0.3≤x≤0.9, 0.1≤y≤0.4. Exemplarily, the chemical formula of the nickel cobalt manganese oxide ternary material is Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2、Li(Ni 0.5 Co 0.3 Mn 0.2 )O2、Li(Ni 0.6 Co0.2 Mn 0.2 )O2、Li(Ni 0.7 Co 0.1 Mn 0.2 )O2、Li(Ni 0.8 Co 0.1 Mn 0.1 )O2 or Li(Ni 0.9 Co 0.05 Mn 0.05 )O2.

[0027] Preferably, the median particle size D50 of lithium cobalt oxide is 5 to 19 μm. The general chemical formula of lithium cobalt oxide is Li a Co 1-b M b O2, wherein M is one or more of Mg, Al, Zr, La, Y, Mn, Ni, 0.95≤a≤1.05, 0≤b≤0.1.

[0028] Preferably, the calcined coating is a metal oxide selected from one or more of Al2O3, TiO2, ZrO2 and MgO2. The thickness of the coating layer formed by the calcined coating is 5-30nm.

[0029] Step S2: Mixing the material obtained in step S1 with the di-sintered coating and performing secondary sintering to obtain a positive electrode material; wherein the di-sintered coating accounts for 0.02-1wt% of the total mass of the lithium cobalt oxide and nickel cobalt manganese oxide ternary material, and the di-sintered coating is a metal fluoride and / or a metal phosphate.

[0030] In step S2, the secondary sintering temperature is 400-700°C, the heating rate is 3-5°C / min, and the sintering time is 0.5-6h. Exemplarily, the secondary sintering temperature is 400°C, 500°C, 600°C or 700°C; the heating rate is 3°C / min, 4°C / min or 5°C / min, and the sintering time is 0.5h, 1h, 2h, 3h, 4h, 5h or 6h.

[0031] Preferably, the di-sintered coating is a metal fluoride selected from one or more of AlF3, LiF and MgF2, and the di-sintered coating is a metal phosphate selected from one or two of AlPO4 and Li3PO4. The thickness of the coating layer formed by the di-sintered coating is 10-30 nm.

[0032] The preparation method of the positive electrode material of one embodiment of the present invention can be used at high voltage through primary sintering co-coating and secondary sintering co-coating, and has high thermal stability and excellent cycle performance, low cost, simple synthesis process, and is suitable for large-scale production.

[0033] The embodiment of the present invention further provides a positive electrode material, which is prepared by the above-mentioned preparation method of the positive electrode material. The positive electrode material can be used at high voltage through primary sintering co-coating and secondary sintering co-coating, i.e., secondary coating, and has high thermal stability and excellent cycle performance.

[0034] The embodiment of the present invention further provides a positive electrode sheet, which includes: a positive electrode current collector and a positive electrode active material layer, wherein the positive electrode active material layer includes the above-mentioned positive electrode material. The positive electrode material can be used at high voltage through primary sintering co-coating and secondary sintering co-coating, and has high thermal stability and excellent cycle performance.

[0035] The embodiment of the present invention further provides a lithium ion battery, which comprises the above-mentioned positive electrode sheet, negative electrode sheet, a separator arranged between the positive electrode sheet and the negative electrode sheet, and an electrolyte. The charging cut-off voltage of the lithium ion battery is 4.45-4.53V relative to the graphite negative electrode. The lithium ion battery can be used at high voltage and has high thermal stability and excellent cycle performance.

[0036] The preparation process of the lithium-ion battery is as follows: artificial graphite negative electrode active material, styrene diene rubber, sodium hydroxymethyl cellulose and conductive carbon black are mixed in a weight ratio of 94%:3%:2%:1%, the mixture is dispersed in water, and a negative electrode slurry is obtained by double planetary mixing; the negative electrode slurry is coated on a copper current collector, followed by roll pressing and drying to obtain a negative electrode sheet.

[0037] The above positive electrode material is used as a positive electrode active material and is mixed with conductive carbon black and polyvinylidene fluoride binder in a weight ratio of 95%:2.5%:2.5% to obtain a positive electrode slurry by dispersion. The positive electrode slurry is coated on an aluminum foil current collector and rolled to obtain a positive electrode sheet.

[0038] The positive electrode sheet, the negative electrode sheet and the separator are assembled into a lithium-ion battery, and a non-aqueous electrolyte is injected. The non-aqueous electrolyte used is a conventional electrolyte known in the art, and the solvent contains ethylene carbonate, diethyl carbonate, propylene carbonate, fluoroethylene carbonate, etc. The separator used is a commercial separator known in the art and available for purchase.

[0039] Example 1

[0040] Step S1: physically mix lithium cobalt oxide, nickel cobalt lithium manganese oxide ternary material and a sintered coating, place in a muffle furnace, heat to 850°C at a heating rate of 5°C / min, keep warm for 3h, and after sintering, grind with a ball mill at a ball milling speed of 300r / min and a ball milling time of 30min to obtain a 1500ppm metal oxide coated material with a coating layer thickness of 30nm; wherein the mass ratio of lithium cobalt oxide to nickel cobalt lithium manganese oxide ternary material is 7.5:2.5, the median particle size D50 of lithium cobalt oxide is 5μm, and the nickel cobalt lithium manganese oxide ternary material is Li(Ni 0.5 Co 0.3 Mn 0.2 )O2, and the sintered coating is 500ppm each of Al2O3, TiO2, and ZrO2.

[0041] Step S2: The material obtained in step S1 is mixed with 1000ppm of LiF di-sintered coating and placed in a muffle furnace, heated to 500°C at a heating rate of 5°C / min, and kept warm for 3h. After sintering, a positive electrode material coated with 1500ppm of fluoride oxide is obtained, and the thickness of the coating layer is 20nm.

[0042] Example 2

[0043] The difference from Example 1 is that the nickel-cobalt-lithium-manganese oxide ternary material uses Li(Ni 0.7 Co 0.1 Mn 0.2 )O2.

[0044] Example 3

[0045] The difference from Example 1 is that the nickel-cobalt-lithium-manganese oxide ternary material uses Li(Ni 0.8 Co 0.1 Mn 0.1 )O2.

[0046] Comparative Example 1

[0047] The difference from Example 1 is that pure lithium cobalt oxide is not coated.

[0048] Comparative Example 2

[0049] The difference from Example 1 is that the lithium cobalt oxide composite nickel cobalt lithium manganese oxide ternary material is not coated, and the nickel cobalt lithium manganese oxide ternary material adopts Li (Ni 0.5 Co 0.3 Mn 0.2 )O2.

[0050] Comparative Example 3

[0051] The difference from Example 1 is that the lithium cobalt oxide and the nickel cobalt lithium manganese oxide ternary material are coated once, and the nickel cobalt lithium manganese oxide ternary material adopts Li (Ni 0.5 Co 0.3 Mn 0.2 )O2.

[0052] test

[0053] Lithium-ion batteries were prepared using the positive electrode materials prepared in the above Examples 1-3 and Comparative Examples 1-3, and the prepared lithium-ion batteries were subjected to capacity tests, cycle retention rate tests, and storage capacity retention rate tests, respectively. The test results are shown in Table 1.

[0054] Capacity test: The lithium-ion batteries obtained in Examples 1-10 and Comparative Examples 1-2 were respectively tested for their specific capacity at the first discharge at a current of 0.1C in the voltage range of 3-4.5V.

[0055] Cycle retention rate test: The lithium-ion batteries obtained in Examples 1-10 and Comparative Examples 1-2 were subjected to charge and discharge cycles of 500 times at a charge and discharge rate of 1C in the voltage range of 3-4.5V and 45°C, respectively. The cycle discharge capacity was recorded and divided by the discharge capacity of the first cycle to obtain the capacity retention rate, i.e., the cycle retention rate.

[0056] Storage capacity retention rate test: The lithium-ion batteries obtained in Examples 1-10 and Comparative Examples 1-2 were fully charged at a charge and discharge rate of 1C within a voltage range of 3-4.5V, and placed at 45°C for 30 days. The discharge capacity on the 30th day was recorded and divided by the discharge capacity on the 1st day to obtain the capacity retention rate, i.e., the storage capacity retention rate.

[0057] Table 1: Performance data of lithium-ion batteries prepared in various embodiments and comparative examples.

[0058] Capacity / mA·h / g Cycle retention rate / % Storage capacity retention rate / % Example 1 204 84.5 92 Example 2 210 82 91.4 Example 3 214 81.2 90.5 Comparative Example 1 195 85 65 Comparative Example 2 205 60 85 Comparative Example 3 207 80 90

[0059] Description of the characterization results of the lithium-ion batteries prepared in the above Examples 1-3 and Comparative Examples 1-3: Compared with simple physical mixing, the primary coating is beneficial to improving the storage performance while improving the cycle capacity, and the secondary coating further improves the interface stability of the composite material, thereby further improving the cycle performance and storage performance of the storage material. In addition, when used in combination with high-nickel materials, the higher the capacity, the lower the storage and cycle performance, and the user can choose according to the use requirements and scenarios. The positive electrode material of Examples 1-3 of the present invention is a mixture of lithium cobalt oxide and nickel cobalt manganese oxide ternary materials, and is formed by secondary coating. At a voltage of 3-4.5V, the capacity is greater than 200mA·h / g, the cycle retention rate is greater than 81%, and the storage capacity retention rate is greater than 90%, indicating that the positive electrode material has higher cycle stability, better storage performance and energy density when used at high voltage (3-4.5V), and has low cost, simple synthesis process, and is suitable for large-scale production. It can solve the current problem of mixing ternary materials with lithium cobalt oxide materials at high voltage, although it effectively improves the thermal stability of the composite material, but the cycle also decays faster.

[0060] The above are only implementation modes of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a positive electrode material, characterized in that: The following steps are involved: Step S1: mixing, sintering and crushing lithium cobalt oxide, nickel cobalt lithium manganese oxide ternary material and a sintered coating; wherein the mass ratio of the lithium cobalt oxide to the nickel cobalt lithium manganese oxide ternary material is (1:9) to (9:1); the sintered coating accounts for 0.01-0.5wt% of the total mass of the lithium cobalt oxide and the nickel cobalt lithium manganese oxide ternary material, and the sintered coating is a metal oxide; Step S2: Mixing the material obtained in step S1 with the di-sintered coating and performing secondary sintering to obtain the positive electrode material; wherein the di-sintered coating accounts for 0.02-1wt% of the total mass of the lithium cobalt oxide and the nickel cobalt manganese oxide ternary material, and the di-sintered coating is a metal fluoride and / or a metal phosphate.

2. The method for preparing the positive electrode material according to claim 1, characterized in that: The primary sintering temperature is 700-900° C., the heating rate is 3-5° C. / min, and the sintering time is 0.5-6h.

3. The method for preparing the positive electrode material according to claim 1, characterized in that: The secondary sintering temperature is 400-700° C., the heating rate is 3-5° C. / min, and the sintering time is 0.5-6h.

4. The method for preparing the positive electrode material according to claim 1, characterized in that: The sintered coating is one or more of Al2O3, TiO2, ZrO2 and MgO2.

5. The method for preparing the positive electrode material according to claim 1, characterized in that: The di-sintered coating is one or more of AlF3, LiF, MgF2, AlPO4 and Li3PO4.

6. The method for preparing the positive electrode material according to claim 1, characterized in that: The general chemical formula of the nickel-cobalt-lithium-manganese oxide ternary material is Li(Ni x Co y Mn 1-x-y )O2, where 0.3≤x≤0.9, 0.1≤y≤0.

4.

7. The method for preparing the positive electrode material according to claim 1, characterized in that: The general chemical formula of the lithium cobalt oxide is Li a Co 1-b M b O2, wherein M is one or more of Mg, Al, Zr, La, Y, Mn, Ni, 0.95≤a≤1.05, 0≤b≤0.

1.

8. A positive electrode material, characterized in that The cathode material is prepared by the method for preparing the cathode material according to any one of claims 1 to 7.

9. A positive electrode sheet, characterized in that: The positive electrode sheet comprises: a positive electrode current collector and a positive electrode active material layer, and the positive electrode active material layer comprises the positive electrode material according to claim 8.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises the positive electrode sheet as claimed in claim 9.

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