Positive electrode material, positive electrode plate containing positive electrode material and electrochemical device

Abstract

The invention relates to the field of electrochemistry, and particularly discloses a positive electrode material, a positive electrode plate containing the positive electrode material and an electrochemical device. The positive electrode material comprises a lithium-rich manganese-based positive electrode material and a coating layer existing on the lithium-rich manganese-based positive electrode material, the coating layer is an MOF structure layer containing C, N and O elements, and is formed by mixing the lithium-rich manganese-based positive electrode material with an organic ligand and coordinating the organic ligand with metal ions on the surface of the lithium-rich manganese-based positive electrode material by adopting a low-pressure vapor deposition method. When the positive electrode material is applied to a battery system, the structural stability of the material can be greatly improved, direct contact between the positive electrode material and an electrolyte is reduced through the surface coating layer, side reactions in the battery charging and discharging process are inhibited, gas production is inhibited, and the cycle performance is further improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electrochemistry, and more particularly, to a positive electrode material, a positive electrode tab comprising the material, and an electrochemical device. BACKGROUND

[0002] Among all the commercialized positive electrode materials at present, the lithium-rich manganese-based positive electrode material is an ideal positive electrode material for high-energy-density batteries, and exhibits excellent electrochemical performance under conventional voltage conditions. Meanwhile, the lithium-rich manganese-based positive electrode material is a low-cobalt / low-nickel high-manganese material, greatly reduces the dependence on resources such as cobalt and nickel, is the most competitive positive electrode material for power lithium-ion batteries at present, and has great development potential. However, there are still many problems to be solved for such a material, such as low first coulomb efficiency, voltage decay and energy density reduction during the cycle process. Such a positive electrode material has more side reactions with electrolyte under the environment of high-voltage use, and produces gas seriously, which affects the battery performance and has a great safety hazard. At present, in order to improve the cycle performance and safety of the lithium-rich manganese-based positive electrode material, various means are generally used for modification treatment in the industry. Common methods include surface coating, doping, and morphology control of the material. Among them, the surface coating technology forms a protective layer on the lithium-rich manganese-based positive electrode material to inhibit the occurrence of side reactions. However, the surface coating layer in the prior art usually has the problem of insufficient stability. The traditional coating layer is difficult to effectively inhibit the release of oxygen and the dissolution of metal ions during the electrochemical cycle process, especially under high-voltage and high-temperature conditions, the coating layer is easy to crack or fall off, resulting in that the cycle performance and safety of the electrochemical device still cannot meet the high-performance requirements.

[0003] Therefore, it is urgent to develop a new lithium-rich manganese-based positive electrode material and coating technology to solve the above problems. SUMMARY

[0004] In order to solve the above technical problems, the present application provides a positive electrode material, a positive electrode tab comprising the material, and an electrochemical device.

[0005] The present application provides the following technical solutions:

[0006] In a first aspect, the present application provides a positive electrode material, comprising a lithium-rich manganese-based positive electrode material, and a coating layer existing on the lithium-rich manganese-based positive electrode material, wherein the thickness of the coating layer is 10 nm to 20 nm.

[0007] The coating layer is a MOF structure layer containing C, N, and O elements, which is formed by mixing the lithium-rich manganese-based positive electrode material with an organic ligand and using a low-pressure vapor deposition method to make the organic ligand coordinate with metal ions on the surface of the lithium-rich manganese-based positive electrode material.

[0008] Further, the structure of the above lithium-rich manganese-based positive electrode material is xLi2MnO3·(1-x)LiNi y Co z Mn w O2, wherein 0 < x < 1, y + z + w = 1, 0 ≤ y ≤ 1.0, 0.13 ≤ z ≤ 1.0, and 0 ≤ w ≤ 1.0. These materials combine the MOF structure of the coating layer, which can effectively inhibit the release of oxygen and the dissolution of metal ions, thereby improving the cycle performance and safety of the electrochemical device. In addition, by selecting the above specific type of lithium-rich manganese-based positive electrode material, the comprehensive performance of the material can be further optimized while maintaining high energy density, so that the electrochemical device exhibits more stable characteristics during long cycle.

[0009] Further, the above organic ligand is an aromatic or heterocyclic compound containing a polydentate coordination group selected from carboxyl, amino, hydroxyl, or a nitrogen-containing heterocycle, and an aromatic or heterocyclic skeleton selected from a benzene ring, a naphthalene ring, or an imidazole ring.

[0010] Further, the above organic ligand is one or more of terephthalic acid, trimesic acid, 2-amino isophthalic acid, 2-methyl imidazole, or N-methyl imidazole.

[0011] By adopting the above technical solution, the organic ligand is selected as an aromatic or heterocyclic compound containing a polydentate coordination group, which can form a stable coordination structure with the metal ions on the surface of the lithium-rich manganese-based positive electrode material, thereby enhancing the bonding force of the coating layer to the material surface. Among them, carboxyl, amino, hydroxyl, or nitrogen-containing heterocycle as a coordination group can effectively promote the occurrence of coordination reaction, improve the uniformity and density of the coating layer. At the same time, the benzene ring, naphthalene ring or imidazole ring as the aromatic or heterocyclic skeleton endows the organic ligand with good thermal stability and chemical stability, further improving the protection effect of the coating layer on the positive electrode material, thereby effectively inhibiting the release of oxygen and the dissolution of metal ions during the cycle, improving the cycle performance and safety of the electrochemical device.

[0012] Further, the mass ratio of the above lithium-rich manganese-based positive electrode material and the organic ligand when mixed is 1:2-10.

[0013] By adopting the above technical solution, the lithium-rich manganese-based positive electrode material and the organic ligand are mixed in a specific mass ratio range, which can be fully coordinated to form a coating layer with a MOF structure.

[0014] Further, the process parameters of the above low-pressure vapor deposition method are as follows:

[0015] The vacuum condition is 100-150 Pa, the temperature is 120-250℃, and the reaction time is 12-20h.

[0016] Further, the average particle size D50 of the positive electrode material is 10-20 μm.

[0017] In a second aspect, the application provides a preparation method of the positive electrode material, which comprises: mixing a proper amount of lithium-rich manganese-based positive electrode material with a proper amount of organic ligand, the mass ratio of the lithium-rich manganese-based positive electrode material to the organic ligand being 1:2-10, heating at 120-250 ℃ under a vacuum condition of 100-150 Pa, and reacting for 12-20 h to obtain the positive electrode material.

[0018] In a third aspect, the application provides a positive electrode tab comprising the positive electrode material.

[0019] In a fourth aspect, the application provides an electrochemical device comprising: the positive electrode tab, a negative electrode tab, a separator, and an electrolyte.

[0020] In summary, the application has the following advantages:

[0021] 1. The positive electrode material provided by the application takes lithium-rich manganese-based positive electrode material as the core, and the structural formula of the material is xLi2MnO3·(1-x)LiNi y Co z Mn w O2, wherein 0

[0022] 2. The aromatic or heterocyclic compound containing polydentate coordination groups used as the organic ligand in the application can form stable metal-organic framework materials with the metal ions on the surface of the lithium-rich manganese-based positive electrode material. Such coordination structure effectively improves the stability and uniformity of the coating layer, thereby further inhibiting the release of oxygen and the dissolution of metal ions of the positive electrode material during the cycle process. At the same time, due to the presence of polydentate coordination groups, the weather resistance and anti-hydration performance of the coating layer are also significantly improved, so that the stability of the positive electrode material is enhanced, and the overall energy density, cycle performance and safety of the electrochemical device are improved.

[0023] 3. The coating layer is prepared by low-pressure vapor deposition in the application, and the organic ligand and the metal ions on the surface of the lithium-rich manganese-based positive electrode material form a combination through coordination, which has strong binding force and high interface stability, can maintain good protection effect during long-term cycle process, and improve the cycle performance of the electrochemical device. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 is a TEM picture of the positive electrode material provided in Example 4 of the application;

[0025] Figure 2 is the XRD pattern of the positive electrode material corresponding to Example 4 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0026] The embodiments of the present application will be described in detail below with examples, but those skilled in the art will understand that the following examples are only for illustration of the present application and should not be regarded as limiting the scope of the present application, and the specific conditions not noted in the examples are carried out according to the conventional conditions or the conditions recommended by the manufacturer, and the reagents or instruments not noted the manufacturer are all conventional products that can be purchased on the market.

[0027] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are only for illustration and explanation of the present application, and are not intended to limit the present application.

[0028] Example 1

[0029] The present embodiment provides a positive electrode material, and a preparation method thereof comprises:

[0030] (1) 0.2Li2MnO3·0.8LiNi 0.13 Co 0.13 Mn 0.54 O2 is a lithium-rich manganese-based positive electrode material, and 2-methylimidazole is an organic ligand, 0.2Li2MnO3·0.8LiNi 0.13 Co 0.13 Mn 0.54 O2 and 2-methylimidazole are mixed in a mass ratio of 1:5 to obtain a mixture;

[0031] (2) The obtained mixture is subjected to low-pressure vapor deposition under vacuum conditions of 100 Pa, the temperature is 140℃, and the deposition time is 15h to obtain a coated positive electrode material.

[0032] Example 2

[0033] The difference between the present embodiment and Example 1 is that the low-pressure vapor deposition time is 18h.

[0034] Example 3

[0035] The difference between the present embodiment and Example 1 is that the low-pressure vapor deposition temperature is 150℃.

[0036] Example 4

[0037] The difference between the present embodiment and Example 1 is that the low-pressure vapor deposition temperature is 150℃ and the time is 18h.

[0038] Example 5

[0039] The difference between this embodiment and embodiment 4 is that the mass ratio of 0.2Li2MnO3·0.8LiNi 0.13 Co 0.13 Mn 0.54 The mass ratio of O2 to 2-methylimidazole is 1:1.5.

[0040] Example 6

[0041] The difference between this embodiment and embodiment 4 is that the mass ratio of 0.2Li2MnO3·0.8LiNi 0.13 Co 0.13 Mn 0.54 The mass ratio of O2 to 2-methylimidazole is 1:10.

[0042] Comparative Example 1

[0043] 0.2Li2MnO3·0.8LiNi 0.13 Co 0.13 Mn 0.54 O2 is directly used as a positive electrode material without coating.

[0044] Comparative Example 2

[0045] The difference between this comparative example and embodiment 4 is that the mass ratio of 0.2Li2MnO3·0.8LiNi 0.13 Co 0.13 Mn 0.54 The mass ratio of O2 to 2-methylimidazole is 1:12.

[0046] Comparative Example 3

[0047] The difference between this comparative example and embodiment 4 is that the temperature of low-pressure vapor deposition is 260°C.

[0048] Comparative Example 4

[0049] The difference between this comparative example and embodiment 1 is that the temperature of low-pressure vapor deposition is 110°C, and the time is 20h.

[0050] Performance detection test

[0051] I. Assembling half-cell electrochemical performance test

[0052] (1) Assembling a button-type half-cell

[0053] Positive electrode sheet: after the positive electrode material, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are fully stirred, mixed, and uniformly mixed in an N-methylpyrrolidone solvent system according to a weight ratio of 96.8:1.5:1.7, the mixture is coated on an Al foil, dried, and cold-pressed to obtain a positive electrode sheet.

[0054] Negative electrode sheet: lithium sheet with a diameter of 16 mm.

[0055] Separator: PP porous polymer film as a separator

[0056] Electrolyte: 1M LiPF6 in EC: EMC: DMC = 1:1:1 (Vol%)

[0057] Lithium ion battery assembly: assemble the lithium ion battery in the inert glove box according to the assembly order of lithium metal sheet-separator-electrolyte-positive electrode sheet.

[0058] (2) The assembled lithium ion battery was subjected to electrochemical performance test at a voltage interval of 2.0-4.8V and a current density of 0.1C, and the results are shown in Table 1 (material physical properties and electrochemical performance):

[0059] Table 1

[0060]

[0061] II. Full battery electrochemical performance test

[0062] (1) Assemble soft package cell:

[0063] Positive electrode sheet: after the positive electrode material, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are fully stirred and mixed uniformly in the N-methyl pyrrolidone solvent system according to the weight ratio of 96.8:1.5:1.7, they are coated on Al foil, dried, and cold pressed to obtain the positive electrode sheet.

[0064] Negative electrode sheet: after the active material artificial graphite, conductive agent Super P, binder styrene-butadiene rubber (SBR), and thickening agent sodium carbon methyl cellulose (CMC) are fully stirred and mixed uniformly in the deionized water solvent system according to the weight ratio of 95.5:1.5:1.2:1.8, they are coated on Cu foil, dried, and cold pressed to obtain the negative electrode sheet.

[0065] Separator: PP porous polymer film as a separator

[0066] Electrolyte: 1M LiPF6 in EC: EMC: DMC = 1:1:1 (Vol%)

[0067] Stack the positive electrode sheet, separator, and negative electrode sheet in order, with the separator in the middle of the anode and cathode to play a separating role, to obtain a bare cell. Place the bare cell in an outer package, inject the prepared base electrolyte, and go through the processes of vacuum packaging, standing, formation (charge to 4.75V at 0.1C constant current), capacity test, etc. to obtain a lithium ion battery.

[0068] The obtained lithium ion battery was subjected to electrochemical cycle test at a voltage range of 2.0-4.75 V and a current density of 0.1 C, and the performance of each battery after 500 cycles was as shown in Table 2 (material physical properties and battery performance).

[0069] Table 2

[0070]

[0071] As can be seen from Table 1 and Table 2:

[0072] The lithium-rich manganese-based positive electrode material provided by the embodiments 1-6 exhibits excellent specific capacity and capacity retention rate. The soft-pack battery assembled also exhibits excellent cycle performance, and the battery does not have swelling, and the transition metal ion dissolution amount is low.

[0073] As can be seen from the embodiments 1-6 and the comparative examples 1-3, the MOF structure coating layer provided by the application can effectively inhibit the dissolution of metal ions and the release of oxygen, thereby improving the cycle performance and safety performance of the battery.

[0074] As can be seen from the embodiments 4-6 and the comparative example 2, when the mass ratio of transition metal oxide to organic ligand is 1:2-10, the coating effect is best, and when the proportion of organic ligand is too high, the preparation cost is increased, and the thickness of the coating layer is also increased, thereby reducing the specific discharge capacity of the lithium-rich manganese-based positive electrode material.

[0075] As can be seen from the embodiments 1-4 and the comparative examples 3 and 4, during the low-pressure vapor deposition process, the temperature and time parameters of the low-pressure vapor deposition have a significant influence on the performance of the lithium-rich manganese-based positive electrode material. When the temperature is too high or too low, the thickness of the coating layer is not suitable, thereby reducing the coating effect.

[0076] The positive electrode material provided by the application includes a lithium-rich manganese-based positive electrode material and a coating layer existing on the lithium-rich manganese-based positive electrode material; the coating layer is a MOF structure layer containing C, N and O elements, which is formed by mixing the lithium-rich manganese-based positive electrode material with an organic ligand and using a low-pressure vapor deposition method to make the organic ligand coordinate with the metal ions on the surface of the lithium-rich manganese-based positive electrode material. When the positive electrode material is applied in a battery system, the material structure stability can be greatly improved, and the surface coating layer reduces the direct contact between the positive electrode material and the electrolyte, thereby inhibiting the occurrence of side reactions during the charging and discharging process of the battery, inhibiting gas production, and further improving the cycle performance.

[0077] The specific embodiments are merely an explanation of the application, and are not a limitation of the application. Those skilled in the art can make modifications to the embodiments without creative contribution after reading the specification, as long as the modifications are within the scope of the claims of the application.

Claims

1. A positive electrode material, characterized in that The invention comprises a lithium-rich manganese-based positive electrode material and a coating layer on the lithium-rich manganese-based positive electrode material, wherein the thickness of the coating layer is 10 nm to 20 nm; The coating layer is a MOF structure layer containing C, N, and O elements, which is formed by mixing a lithium-rich manganese-based positive electrode material with an organic ligand and using a low-pressure vapor deposition method to coordinate the organic ligand with the metal ions on the surface of the lithium-rich manganese-based positive electrode material.

2. The positive electrode material according to claim 1, characterized in that The structural formula of the lithium-rich manganese-based positive electrode material is xLi2MnO3·(1-x)LiNi y Co z Mn w O2, where 0<x<1, y+z+w=1, 0≤y≤1.0, 0.13≤z≤1.0, 0≤w≤1.

0.

3. The positive electrode material according to claim 1, characterized in that The organic ligand is an aromatic or heterocyclic compound containing a multidentate ligand group, the multidentate ligand group is selected from carboxyl, amino, hydroxyl or nitrogen-containing heterocycle, and the aromatic or heterocyclic skeleton is selected from benzene ring, naphthalene ring or imidazole ring.

4. The positive electrode material according to claim 3, characterized in that The organic ligand is one or more of terephthalic acid, trimesic acid, 2-aminoisophthalic acid, 2-methylimidazole or N-methylimidazole.

5. The positive electrode material according to claim 1, characterized in that In the process of forming the coating layer, the lithium-rich manganese-based positive electrode material and the organic ligand are mixed in a mass ratio of 1:2 to 10.

6. The positive electrode material according to claim 1, characterized in that The process parameters of the low pressure vapor deposition method are: Vacuum conditions are 100-150 Pa, temperature is 120℃-250℃, and reaction time is 12-20h.

7. The positive electrode material according to any one of claims 1 to 6, characterized in that The average particle size D50 of the positive electrode material is 10 μm to 20 μm.

8. A method for preparing the positive electrode material according to any one of claims 1 to 7, characterized in that: It includes: An appropriate amount of the lithium-rich manganese-based positive electrode material is mixed with an appropriate amount of organic ligand, the mass ratio of the lithium-rich manganese-based positive electrode material to the organic ligand being 1:2-10, and the mixture is heated at 120°C-250°C under vacuum conditions of 100-150Pa and reacted for 12-20h to obtain the positive electrode material.

9. A positive electrode plate, characterized in that: It comprises the positive electrode material according to any one of claims 1 to 8.

10. An electrochemical device, characterized in that It includes: A positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; wherein the positive electrode sheet is the positive electrode sheet according to claim 9.

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