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

Abstract

The invention relates to the field of electrochemistry, and particularly discloses a positive electrode lithium supplementing material, a positive electrode plate containing the material and an electrochemical device. The positive electrode lithium supplementing material comprises an inner core of a lithium-rich transition metal oxide and a coating layer existing on the inner core, and the coating layer is an MOF structure layer with the thickness of 1nm-20nm. When the positive electrode lithium supplement material is applied to a positive electrode plate, the supplement of active lithium can be realized, and the long cycle life of an electrochemical device is effectively prolonged. Moreover, the coating layer on the surface of the positive electrode lithium supplement material can effectively inhibit oxygen release and metal ion dissolution in the circulation process, and effectively improve the gas production problem in the circulation process of an electrochemical device, thereby improving the safety performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemistry, and more specifically, to a positive electrode lithium supplement material, a positive electrode sheet containing the material, and an electrochemical device. Background Art

[0002] With the rapid development of energy storage technology, lithium-ion batteries, as the mainstream energy storage device, have expanded their application from portable electronic devices to electric vehicles and large-scale energy storage systems. The market has placed increasingly higher demands on the energy density, cycle performance, kinetic performance, and safety of lithium-ion batteries. During the initial charge and discharge process of lithium-ion batteries, an SEI film forms at the interface of the negative electrode material. This process inevitably consumes some active lithium ions, resulting in irreversible capacity loss, thereby reducing the overall energy density of the battery. To improve battery performance, lithium replenishment technology has become a research hotspot. Among them, lithium-rich transition metal oxides are widely used in lithium replenishment materials due to their high specific capacity and simple preparation process, effectively improving the energy density of lithium-ion secondary batteries.

[0003] In the existing technology, in order to solve the problems of stability of lithium-supplementing materials in air and side reactions during the circulation process, they are usually modified by coating. Common coating methods include inorganic material coating, organic material coating, and composite material coating. Inorganic material coating mainly forms a protective layer through oxides, phosphates, etc.; organic material coating uses polymers or carbon materials for surface modification; composite material coating combines the advantages of inorganic and organic materials, aiming to achieve multiple performance improvements at the same time. In addition, there are technical means to further optimize the coating effect by regulating the thickness of the coating layer and adjusting the composition of the coating material.

[0004] However, existing coating methods still have certain limitations and cannot completely solve the problems of gassing and metal ion dissolution caused by lithium-ion materials during battery cell cycling. These problems seriously affect the energy density, cycling performance, and safety of lithium-ion batteries. Therefore, it is necessary to develop a new type of positive electrode lithium-ion material and its coating technology to overcome the shortcomings of existing technologies. Summary of the Invention

[0005] In order to solve the above technical problems, the present application provides a positive electrode lithium supplement material, a positive electrode plate containing the material, and an electrochemical device.

[0006] This application adopts the following technical solutions: In a first aspect, the present application provides a positive electrode lithium supplement material, which includes a core of a lithium-rich transition metal oxide and a coating layer present on the core; The coating layer is a MOF structure layer with a thickness of 1nm to 20nm, which is formed by mixing a lithium-rich transition metal oxide 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 transition metal oxide material.

[0007] Furthermore, the organic ligand is an aromatic or heterocyclic compound containing a multidentate ligand group, wherein 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.

[0008] Furthermore, the organic ligand is one or more of terephthalic acid, trimesic acid, 2-aminoisophthalic acid, 2-methylimidazole or N-methylimidazole.

[0009] Furthermore, the mass ratio of the coating layer in the positive electrode lithium supplement material is 1% to 10%. In the process of forming the coating layer, the mass ratio of the lithium-rich transition metal oxide material and the organic ligand when mixed is 1:0.5-5.

[0010] By adopting the above technical solution, lithium-rich transition metal oxide materials are mixed with organic ligands in a specific mass ratio, and the coating layer occupies 1% to 10% of the mass ratio of the positive electrode lithium supplement material. The thickness and uniformity of the coating layer can be precisely controlled. This not only effectively suppresses oxygen release and metal ion dissolution during electrochemical cycling, but also significantly reduces the occurrence of gas production problems, thereby improving the safety and cycling performance of electrochemical devices.

[0011] Furthermore, the process parameters of the low pressure vapor deposition method are: Vacuum conditions are 100-150 Pa, temperature is 120°C-250°C, and reaction time is 4-12h.

[0012] Furthermore, the lithium-rich transition metal oxide includes one or a combination of two or more of lithium nickelate, lithium cobaltate, lithium ferrite, lithium manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum oxide or lithium-rich manganese-based materials.

[0013] Furthermore, the specific surface area of the coating layer is 10m 2 / g~100m 2 / g, and a thickness of 1nm to 20nm; the average particle size D50 of the positive electrode lithium supplement material is 3μm to 20μm.

[0014] By adopting the above technical solution, the thickness of the coating layer is controlled to be 1nm~20nm and the specific surface area is controlled to be 10m 2 / g~100m 2 / g range, it can effectively form protection for the lithium-rich transition metal oxide core, preventing oxygen release and metal ion dissolution during the battery cell cycle, thereby suppressing gas production and improving the safety of electrochemical devices. At the same time, the average particle size D50 of the positive electrode lithium supplement material is controlled within the range of 3μm to 20μm, which helps to optimize the material's packing density and interface stability, further improving the energy density and cycle performance of the electrochemical device.

[0015] In the second aspect, the present application provides a method for preparing the above-mentioned positive electrode lithium-replenishing material, which comprises: mixing an appropriate amount of the lithium-rich transition metal oxide material with an appropriate amount of organic ligand, wherein the mass ratio of the lithium-rich transition metal oxide material to the organic ligand is 1:0.5~5, heating at 120℃~250℃ under vacuum conditions of 100~150Pa, reacting for 4-12h, and obtaining the lithium-replenishing positive electrode material.

[0016] In a third aspect, the present application provides a positive electrode plate comprising the above-mentioned positive electrode lithium supplement material.

[0017] In a fourth aspect, the present application provides an electrochemical device comprising: a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte.

[0018] In summary, this application has the following beneficial effects: 1. The lithium-rich transition metal oxide core of the positive electrode lithium-supplementing material provided herein can provide a high specific capacity, effectively replenishing the active lithium lost due to SEI film formation during the initial charge and discharge process of lithium-ion batteries, thereby improving the energy density and cycle life of electrochemical devices. The coating layer, made of a material with a MOF structure and having a thickness ranging from 1nm to 20nm, can significantly inhibit oxygen release and metal ion dissolution during electrochemical cycling, thereby reducing gassing and improving the safety and cycle stability of the electrochemical device.

[0019] 2. This application uses aromatic or heterocyclic compounds containing multidentate ligands as organic ligands, which can form stable metal-organic framework materials with metal ions on the surface of lithium-rich transition metal oxide materials. This coordination structure effectively improves the stability and uniformity of the coating layer, thereby further suppressing the oxygen release and metal ion dissolution of the positive electrode lithium supplement material during the cycle. At the same time, due to the presence of multidentate ligands, the weather resistance and deliquescence resistance of the coating layer are also significantly improved, which enhances the stability of the positive electrode lithium supplement material and thereby improves the overall energy density, cycle performance and safety of the electrochemical device.

[0020] 3. This application adopts low-pressure vapor deposition method to prepare the coating layer. The coordination effect between the organic ligand and the metal ions on the surface of the core further enhances the stability of the coating layer, avoiding the problem of traditional coating layer breaking due to volume change during electrochemical cycling, thereby effectively improving the cycling performance of the electrochemical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a TEM image of the positive electrode lithium supplement material provided in Example 4 of the present application. DETAILED DESCRIPTION

[0022] The embodiments of the present invention will be described in detail below with reference to the examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Specific conditions not specified in the examples are carried out according to conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used without indicating the manufacturer are all conventional products that can be purchased commercially.

[0023] The following is a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention.

[0024] Example 1 This embodiment provides a positive electrode lithium supplement material, and the preparation method thereof includes: S1: Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 is used as a lithium-rich transition metal oxide material, and 2-methylimidazole is used as an organic ligand to convert Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 and 2-methylimidazole are mixed in a mass ratio of 1:2 to obtain a mixed material; S2: The obtained mixed material is subjected to low-pressure vapor deposition under vacuum conditions of 100 Pa, a temperature of 140° C., and a deposition time of 4 hours to obtain a lithium-supplementing positive electrode material.

[0025] Example 2 The difference between this embodiment and embodiment 1 is that the time of low-pressure vapor deposition is 8 hours.

[0026] Example 3 The difference between this embodiment and embodiment 1 is that the temperature of low-pressure vapor deposition is 150°C.

[0027] Example 4 The difference between this embodiment and embodiment 1 is that the temperature of low-pressure vapor deposition is 150° C. and the time is 8 hours.

[0028] Example 5 The difference between this embodiment and embodiment 1 is that: Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 The mass ratio of O2 to 2-methylimidazole is 1:0.5.

[0029] Example 6 The difference between this embodiment and embodiment 1 is that: Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 The mass ratio of O2 to 2-methylimidazole is 1:5.

[0030] Example 7 The difference between this embodiment and embodiment 1 is that terephthalic acid is used as the organic ligand.

[0031] Example 8 The difference between this embodiment and embodiment 1 is that 2-aminoisophthalic acid is used as the organic ligand.

[0032] Comparative Example 1 Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 is directly used as the positive electrode material without coating.

[0033] Comparative Example 2 The commercial cathode lithium supplement material 1 purchased is Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 is the core and has a carbon coating.

[0034] Comparative Example 3 The commercial cathode lithium supplement material 2 purchased is Li 1.2 Mn 0.54 Ni 0.13 Co 0.13 O2 is the core and has a transition metal-doped LiAlO2 coating layer.

[0035] Comparative Example 4 The difference between this comparative example and Example 1 is that: 1.2 Mn 0.54 Ni 0.13 Co 0.13 The mass ratio of O2 to 2-methylimidazole is 1:0.25.

[0036] Comparative Example 5 The difference between this comparative example and Example 1 is that: 1.2 Mn 0.54 Ni 0.13 Co 0.13 The mass ratio of O2 to 2-methylimidazole is 1:6.

[0037] Comparative Example 6 The difference between this comparative example and Example 1 is that the temperature of low-pressure vapor deposition is 260° C. and the time is 4 hours.

[0038] Comparative Example 7 The difference between this comparative example and Example 1 is that the temperature of low-pressure vapor deposition is 110° C. and the time is 10 h.

[0039] Comparative Example 8 The difference between this comparative example and Example 1 is that 2,5-dihydroxyterephthalic acid is used as the organic ligand.

[0040] Performance Testing 1. Assemble half-cell electrochemical performance test: (1) Assembling button half-cell Positive electrode sheet: The positive electrode lithium supplement material provided in the above embodiments and comparative examples, the conductive agent Super P, and the binder polyvinylidene fluoride (PVDF) were thoroughly stirred and mixed in an N-methylpyrrolidone solvent system at a weight ratio of 90:5:5, and then coated on Al foil, dried, and cold pressed to obtain a positive electrode sheet.

[0041] Negative electrode: lithium sheet with a diameter of 16 mm.

[0042] Diaphragm: PP porous polymer film as the separator Electrolyte: 1M LiPF6 in EC:EMC:DMC=1:1:1(Vol%) Lithium-ion battery assembly: Lithium-ion batteries are assembled in an inert glove box in the order of lithium metal sheet-diaphragm-electrolyte-positive electrode sheet.

[0043] 1. The electrochemical performance of the assembled lithium-ion battery was tested at a voltage range of 2.5-4.8V and a current density of 0.1C. The results are shown in Table 1: Table 1. Material properties and electrochemical performance 2. Electrochemical performance test of assembled full battery (1) Assembling soft pack batteries: Positive electrode sheet: The materials provided in the above embodiments and comparative examples are used as positive electrode lithium replenishing materials. The active material composite material (lithium iron phosphate + positive electrode lithium replenishing material, of which the positive electrode lithium replenishing material accounts for 3%), conductive agent Super P, and binder polyvinylidene fluoride (PVDF) are thoroughly stirred and mixed in an N-methylpyrrolidone solvent system at a weight ratio of 94:3:3, and then coated on Al foil, dried, and cold pressed to obtain a positive electrode sheet.

[0044] Negative electrode sheet: The active material artificial graphite, conductive agent Super P, binder styrene-butadiene rubber (SBR), and thickener carbon methyl cellulose sodium (CMC) are thoroughly stirred and mixed in a deionized water solvent system in a weight ratio of 95.5:1.5:1.2:1.8, and then coated on Cu foil, dried, and cold pressed to obtain the negative electrode sheet.

[0045] Diaphragm: PP porous polymer film as the separator Electrolyte: 1M LiPF6 in EC:EMC:DMC=1:1:1(Vol%) The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator positioned between the cathode and anode to provide isolation, to obtain a bare cell. The bare cell is placed in outer packaging and injected with the prepared basic electrolyte. After vacuum packaging, standing, formation (charging at a constant current of 0.02C to 3.5V, then at a constant current of 0.1C to 3.65V), and capacity testing, a lithium-ion battery is obtained.

[0046] 2. The obtained lithium-ion battery was subjected to electrochemical cycling test at a voltage range of 2.5-3.65V, a current density of 0.1C, and a SOH of 80%. The results are shown in Table 2: Table 2. Material properties and battery cell performance It can be seen from Table 1 and Table 2 that: The positive electrode lithium-replenishing materials provided in Examples 1-8 of this application exhibit excellent initial charge gram capacity. This demonstrates that these positive electrode lithium-replenishing materials can compensate for lithium ions consumed by SEI film formation during the battery's initial charge, effectively replenishing active lithium. Furthermore, the soft-pack cells exhibited no bloating, and the total amount of metal ion dissolution was significantly less than that observed in Comparative Examples 1-3.

[0047] Combining Examples 1, 5, and 6 with Comparative Examples 4 and 5, it can be seen that when the mass ratio of transition metal oxide to organic ligand is 1:0.5-5, the initial charge capacity can achieve optimal results. Adding too little organic ligand can affect the performance of the positive electrode lithium supplement material because it fails to form a uniform coating structure, effectively inhibiting oxygen release and metal ion dissolution. For cost considerations, when performance improvement has reached its upper limit, adding too much organic ligand is detrimental to cost control.

[0048] Combining Examples 1-4 with Comparative Examples 6 and 7, it can be seen that the temperature and time parameters of low-pressure vapor deposition during the low-pressure vapor deposition process have a significant impact on the performance of the positive electrode lithium replenishment material. Combining Examples 1, 7-8, and Comparative Example 8, it can be seen that the selection of different organic ligands during the preparation of the positive electrode lithium replenishment material can affect the gas production and total metal ion dissolution of the assembled battery cell.

[0049] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A positive electrode lithium supplement material, characterized in that: The invention comprises a core of a lithium-rich transition metal oxide and a coating layer on the core; The coating layer is a MOF structure layer with a thickness of 1nm to 20nm, which is formed by mixing a lithium-rich transition metal oxide 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 transition metal oxide material.

2. The positive electrode lithium supplement 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.

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

4. The positive electrode lithium supplement material according to claim 1, characterized in that The coating layer accounts for 1% to 10% by mass of the positive electrode lithium supplement material. During the formation of the coating layer, the lithium-rich transition metal oxide material and the organic ligand are mixed in a mass ratio of 1:0.5 to 5.

5. The positive electrode lithium supplement material according to claim 1, characterized in that The process parameters of the low pressure vapor deposition method are: Vacuum conditions are 100~150Pa, temperature is 120℃~250℃, and reaction time is 4-12h.

6. The positive electrode lithium supplement material according to any one of claims 1 to 5, characterized in that: The lithium-rich transition metal oxide includes one or a combination of two or more of lithium nickelate, lithium cobaltate, lithium ferrite, lithium manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum oxide or lithium-rich manganese-based materials.

7. The positive electrode lithium supplement material according to any one of claims 1 to 5, characterized in that: The specific surface area of the coating layer is 10 m 2 / g ~ 100 m 2 / g; the average particle size D50 of the positive electrode lithium supplement material is 3μm~20μm.

8. A method for preparing the positive electrode lithium supplement material according to any one of claims 1 to 7, characterized in that: It includes: An appropriate amount of the lithium-rich transition metal oxide material is mixed with an appropriate amount of organic ligand, where the mass ratio of the lithium-rich transition metal oxide material to the organic ligand is 1:0.5~5. The mixture is heated at 120°C~250°C under vacuum conditions of 100~150Pa and reacted for 4-12h to obtain the lithium-supplemented positive electrode material.

9. A positive electrode plate, characterized in that: It comprises the positive electrode lithium supplement material according to any one of claims 1 to 7.

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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