Composite positive electrode lithium supplement agent, preparation method thereof, positive plate and lithium ion battery

Abstract

The invention discloses a composite positive electrode lithium supplement agent and a preparation method thereof, a positive plate and a lithium ion battery, and belongs to the technical field of lithium ion batteries. The composite positive electrode lithium supplement agent is of a core-shell structure, an internal core body is one of Li2NiO2, Li5FeO4 and Li6CoO4, and an external shell layer is C-coated Li7 / 4Ti5 / 4O3. The preparation method comprises the following steps: co-doping, ball-milling and mixing an internal core material with a lithium source, a titanium source and a carbon source, and calcining in an inert atmosphere to obtain the composite positive electrode lithium supplement agent. The composite positive electrode lithium supplement agent has multiple technical advantages: both the internal core and the external shell have a lithium supplement effect; the external shell layer can effectively isolate the direct contact between the internal main body material and air and inhibit the generation of residual alkali on the surface; and the electronic conductivity of the internal main body material is improved. When the composite positive electrode lithium supplement agent is used for preparing an electrode plate as a lithium ion battery positive electrode, the gas production rate can be reduced, and the energy density, the cycle life and the safety performance of the battery are improved.

Description

Technical Field

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

[0002] With the widespread application of lithium-ion batteries in mobile communications, electric vehicles, energy storage systems and wearable devices, higher requirements are placed on their energy density and cycle life. Studies have shown that the "pre-lithiation" technology can effectively reduce the irreversible lithium loss caused by the formation of the solid electrolyte interface (SEI) film during the first charge, thereby improving the energy density and cycle life of the battery. Pre-lithiation technology includes two methods: negative electrode lithium replenishment and positive electrode lithium replenishment. Negative electrode lithium replenishment involves many methods, such as physical mixing of metallic lithium, vacuum winding lithium plating, self-discharge lithiation, chemical and electrochemical lithiation, etc., but due to technical challenges, such as the use of metallic lithium is incompatible with the production environment, conventional solvents, binders, air contact, and heat treatment processes, its application is limited. Positive electrode lithium replenishment usually adopts an electrochemical method to add a lithium replenisher to the positive electrode, and releases Li through the high-capacity lithium replenisher during the charging process. + , to make up for the irreversible lithium loss caused by the formation of the negative electrode SEI film. In contrast, positive electrode lithium replenishment has a broad industrial application prospect because of its high safety and no need to change the existing production process. However, current positive electrode lithium replenishers, such as Li2NiO2, Li5FeO4, Li6CoO4, etc., generally have problems such as high surface residual alkali, strong interfacial side reactions and poor electronic conductivity. These problems lead to the generation of a large amount of gas and increase the internal resistance of the battery when these positive electrode lithium replenishers are added to lithium-ion batteries, thereby reducing the safety performance and electrochemical performance of the battery, limiting its large-scale application.

[0003] Therefore, there is an urgent need for a composite positive electrode lithium supplement to solve the above problems. Summary of the invention

[0004] One of the purposes of the present invention is to provide a composite positive electrode lithium supplement to solve the problems of existing positive electrode lithium supplements, such as high surface residual alkali, strong interface side reactions, easy generation of a large amount of gas when added to lithium-ion batteries, and poor electronic conductivity;

[0005] The second object of the present invention is to provide a method for preparing a composite positive electrode lithium supplement;

[0006] The third object of the present invention is to provide a positive electrode sheet including a composite positive electrode lithium supplement;

[0007] A fourth object of the present invention is to provide a lithium-ion battery comprising a composite positive electrode lithium replenisher positive electrode sheet.

[0008] The purpose of the present invention can be achieved through the following technical solutions:

[0009] In the first aspect, a composite positive electrode lithium supplement agent is provided, wherein the composite positive electrode lithium supplement agent is a core-shell structure, wherein the internal core is one of Li2NiO2, Li5FeO4, and Li6CoO4, and the external shell is C@Li 7 / 4 Ti 5 / 4 O3(Carbon-coated Li 7 / 4 Ti 5 / 4 O3).

[0010] Further, the mass ratio of the inner core to the outer shell is 1 to 40: 100. In a specific implementation case, the mass ratio of the inner core to the outer shell includes but is not limited to 1: 100, 2.5: 100, 6: 100, 11: 100, 15: 100, 22: 100, 24: 100, 27: 100, 31: 100, 39: 100 or 40: 100.

[0011] Furthermore, in the outer shell, C and Li 7 / 4 Ti 5 / 4 The mass ratio of O3 is 2 to 15:100. In a specific implementation case, C and Li 7 / 4 Ti 5 / 4 The mass ratio of O3 includes, but is not limited to, 2:100, 2.8:100, 3.4:100, 5.7:100, 7.2:100, 9:100, 11.5:100, 13.6:100, 14.7:100 or 15:100.

[0012] In a second aspect, a method for preparing a composite positive electrode lithium supplement comprises the following steps:

[0013] The internal core material is co-doped with a lithium source, a titanium source and a carbon source and mixed by ball milling, and then calcined under an inert atmosphere to obtain a composite positive electrode lithium supplement.

[0014] Furthermore, the lithium source is one or a combination of Li2CO3, LiOH, and Li2O.

[0015] Furthermore, the titanium source is nano-sized TiO2 with a size of 5 to 50 nm. In a specific implementation case, the titanium source is TiO2 with a size of 5 nm, 10 nm, 20 nm, 25 nm, 30 nm, or 50 nm.

[0016] Furthermore, the carbon source is at least one of glucose, lactose, maltose, coke, graphite, and asphalt, and the carbon source participates in the reaction as a reducing agent.

[0017] Furthermore, the inert atmosphere is nitrogen or argon.

[0018] Furthermore, during the ball milling mixing process, the ball milling speed is 50-600 rpm, and the ball milling time is 0.5-8 h. In a specific implementation case, the ball milling speed includes but is not limited to 50 rpm, 120 rpm, 180 rpm, 260 rpm, 350 rpm, 450 rpm, 590 rpm or 600 rpm; the ball milling time includes but is not limited to 0.5 h, 1.1 h, 1.4 h, 1.9 h, 2.8 h, 3.7 h, 4 h, 4.5 h, 5.1 h, 5.9 h, 6.8 h, 7.3 h or 8 h.

[0019] Furthermore, the calcination temperature is 700-1050°C; the calcination time is 4-24h; the temperature is increased at a uniform rate, and the heating rate is 2-5°C / min. In a specific implementation case, the calcination temperature includes but is not limited to 700°C, 730°C, 760°C, 810°C, 850°C, 900°C, 920°C, 980°C, 1030°C or 1050°C, the calcination time includes but is not limited to 4h, 7h, 12h, 15h, 18h, 20h, 24h, and the heating rate includes but is not limited to 2°C / min, 3°C / min, 4°C / min or 5°C / min.

[0020] In a third aspect, a positive electrode sheet comprises a positive electrode material, a conductive agent, a binder and the composite positive electrode lithium replenisher or the composite positive electrode lithium replenisher prepared by the preparation method.

[0021] Furthermore, the positive electrode material is at least one of lithium iron phosphate, lithium iron manganese phosphate, lithium cobalt oxide, lithium nickel manganese oxide, nickel cobalt manganese ternary, and lithium-rich manganese-based positive electrode materials.

[0022] Furthermore, the mass proportion of the composite positive electrode lithium supplement in the positive electrode sheet is 0.1% to 10%. In a specific implementation case, the mass proportion includes but is not limited to 0.1%, 0.2%, 0.5%, 2%, 3%, 4.5%, 6.8%, 7.4%, 8.6%, 9.5% or 10%.

[0023] In a fourth aspect, a lithium-ion battery comprises a negative electrode sheet, a separator, an electrolyte and the positive electrode sheet.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1. The present invention provides a composite positive electrode lithium supplement agent with a core-shell structure, wherein the internal core is one of Li2NiO2, Li5FeO4, and Li6CoO4, and the external shell is C@Li 7 / 4 Ti 5 / 4 O3, and both the inner core and the outer shell have lithium replenishment effects; in addition, C@Li 7 / 4 Ti 5 / 4The O3 outer shell can effectively isolate the internal core material (Li2NiO2, Li5FeO4, Li6CoO4) from direct contact with water vapor, carbon dioxide, etc. in the air, alleviate the formation of residual alkali on the surface, and effectively improve the interface stability. 7 / 4 Ti 5 / 4 The O3 outer shell has a high electronic conductivity, which can further enhance the conductivity of the inner core material.

[0026] 2. The electrode sheet prepared by mixing the prepared composite positive electrode lithium supplement with positive electrode materials, conductive agents, and binders can be used as the positive electrode of lithium-ion batteries, which can effectively reduce gas production and improve battery safety performance; applying it in lithium-ion batteries can effectively improve battery energy density and cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described below in conjunction with the accompanying drawings.

[0028] Figure 1 It is a structural schematic diagram of a composite positive electrode lithium supplement agent of the present invention;

[0029] Figure 2 This is a FESEM (field emission electron microscope) image of the positive electrode lithium supplement prepared in Example 1 of the present invention;

[0030] Figure 1 Medium: 1. One of Li2NiO2, Li5FeO4, Li6CoO4; 2. Li 7 / 4 Ti 5 / 4 O3;3,C. DETAILED DESCRIPTION

[0031] The following will be combined with 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.

[0032] Example 1

[0033] This embodiment provides a composite positive electrode lithium supplement, wherein the composite positive electrode lithium supplement is a core-shell structure, wherein the inner core is Li2NiO2 and the outer shell is C@Li 7 / 4 Ti 5 / 4 O3; the mass ratio of the inner core to the outer shell is 15:100; in the outer shell, C and Li 7 / 4 Ti 5 / 4 The mass ratio of O3 is 5:100;

[0034] The preparation method of the composite positive electrode lithium supplement comprises the following steps:

[0035] The internal core material Li2NiO2 was co-doped with Li2CO3, TiO2 and glucose, ball-milled at 350 rpm for 4 h, and then placed in an argon atmosphere, uniformly heated to 900°C at a heating rate of 3°C / min and sintered for 10 h to obtain a composite positive electrode lithium supplement.

[0036] The structural schematic diagram of the composite positive electrode lithium supplement agent is as follows Figure 1 As shown;

[0037] The FESEM image of the composite positive electrode lithium supplement is as follows: Figure 2 shown.

[0038] Example 2

[0039] This embodiment provides a composite positive electrode lithium supplement, wherein the composite positive electrode lithium supplement is a core-shell structure, wherein the inner core is Li2NiO2 and the outer shell is C@Li 7 / 4 Ti 5 / 4 O3; the mass ratio of the inner core to the outer shell is 10:100; in the outer shell, C and Li 7 / 4 Ti 5 / 4 The mass ratio of O3 is 7:100;

[0040] The preparation method of the composite positive electrode lithium supplement comprises the following steps:

[0041] The internal core material Li2NiO2 was co-doped with LiOH, TiO2 and lactose, ball-milled at 400 rpm for 3 h, and then placed in an argon atmosphere, uniformly heated to 750°C at a heating rate of 2°C / min and sintered for 20 h to obtain a composite positive electrode lithium supplement.

[0042] The structural schematic diagram of the composite positive electrode lithium supplement agent is as follows Figure 1 shown.

[0043] Example 3

[0044] This embodiment provides a composite positive electrode lithium supplement, wherein the composite positive electrode lithium supplement is a core-shell structure, wherein the inner core is Li2NiO2 and the outer shell is C@Li 7 / 4 Ti 5 / 4 O3; the mass ratio of the inner core and the outer shell is 20:100; in the outer shell, C and Li 7 / 4 Ti 5 / 4 The mass ratio of O3 is 9:100;

[0045] The preparation method of the composite positive electrode lithium supplement comprises the following steps:

[0046] The internal core material Li2NiO2 was co-doped with Li2O, TiO2 and asphalt, ball-milled at a speed of 500 rpm for 2 hours, and then placed in an argon atmosphere, uniformly heated to 950°C at a heating rate of 4°C / min and sintered for 8 hours to obtain a composite positive electrode lithium supplement.

[0047] The structural schematic diagram of the composite positive electrode lithium supplement agent is as follows Figure 1 shown.

[0048] Example 4

[0049] This embodiment provides a composite positive electrode lithium supplement, wherein the composite positive electrode lithium supplement is a core-shell structure, wherein the inner core is Li5FeO4 and the outer shell is C@Li 7 / 4 Ti 5 / 4 O3; the mass ratio of the inner core and the outer shell is 22:100; in the outer shell, C and Li 7 / 4 Ti 5 / 4 The mass ratio of O3 is 6:100;

[0050] The preparation method of the composite positive electrode lithium supplement comprises the following steps:

[0051] The internal core material Li5FeO4 was co-doped with Li2CO3, TiO2 and maltose, ball-milled at a speed of 500 rpm for 2 hours, and then placed in an argon atmosphere, uniformly heated to 960°C at a heating rate of 3°C / min and sintered for 12 hours to obtain a composite positive electrode lithium supplement.

[0052] The structural schematic diagram of the composite positive electrode lithium supplement agent is as follows Figure 1 shown.

[0053] Example 5

[0054] This embodiment provides a composite positive electrode lithium supplement, wherein the composite positive electrode lithium supplement is a core-shell structure, wherein the inner core is Li5FeO4 and the outer shell is C@Li 7 / 4 Ti 5 / 4 O3; the mass ratio of the inner core and the outer shell is 8:100; in the outer shell, C and Li 7 / 4 Ti 5 / 4 The mass ratio of O3 is 4:100;

[0055] The preparation method of the composite positive electrode lithium supplement comprises the following steps:

[0056] The internal core material Li5FeO4 was co-doped with LiOH, TiO2 and glucose, ball-milled at a speed of 300 rpm for 6 hours, and then placed in an argon atmosphere, uniformly heated to 920°C at a heating rate of 4°C / min and sintered for 16 hours to obtain a composite positive electrode lithium supplement.

[0057] The structural schematic diagram of the composite positive electrode lithium supplement agent is as follows Figure 1 shown.

[0058] Example 6

[0059] This embodiment provides a composite positive electrode lithium supplement, wherein the composite positive electrode lithium supplement is a core-shell structure, wherein the inner core is Li5FeO4 and the outer shell is C@Li 7 / 4 Ti 5 / 4 O3; the mass ratio of the inner core to the outer shell is 14:100; in the outer shell, C and Li 7 / 4 Ti 5 / 4 The mass ratio of O3 is 8:100;

[0060] The preparation method of the composite positive electrode lithium supplement comprises the following steps:

[0061] The internal core material Li5FeO4 was co-doped with Li2O, TiO2 and glucose, ball-milled at 400 rpm for 4 hours, and then placed in an argon atmosphere, uniformly heated to 1000°C at a heating rate of 5°C / min and sintered for 7 hours to obtain a composite positive electrode lithium supplement.

[0062] The structural schematic diagram of the composite positive electrode lithium supplement agent is as follows Figure 1 shown.

[0063] Example 7

[0064] This embodiment provides a composite positive electrode lithium supplement agent, wherein the composite positive electrode lithium supplement agent is a core-shell structure, wherein the inner core is Li6CoO4 and the outer shell is C@Li 7 / 4 Ti 5 / 4 O3; the mass ratio of the inner core to the outer shell is 15:100; in the outer shell, C and Li 7 / 4 Ti 5 / 4 The mass ratio of O3 is 9:100;

[0065] The preparation method of the composite positive electrode lithium supplement comprises the following steps:

[0066] The internal core material Li6CoO4 was co-doped with Li2CO3, TiO2 and glucose, ball-milled at a speed of 200 rpm for 8 hours, and then placed in an argon atmosphere, uniformly heated to 960°C at a heating rate of 3°C / min and sintered for 8 hours to obtain a composite positive electrode lithium supplement.

[0067] The structural schematic diagram of the composite positive electrode lithium supplement agent is as follows Figure 1 shown.

[0068] Example 8

[0069] This embodiment provides a composite positive electrode lithium supplement agent, wherein the composite positive electrode lithium supplement agent is a core-shell structure, wherein the inner core is Li6CoO4 and the outer shell is C@Li 7 / 4 Ti 5 / 4 O3; the mass ratio of the inner core to the outer shell is 25:100; in the outer shell, C and Li 7 / 4 Ti 5 / 4 The mass ratio of O3 is 15:100;

[0070] The preparation method of the composite positive electrode lithium supplement comprises the following steps:

[0071] The internal core material Li6CoO4 was co-doped with LiOH, TiO2 and lactose, ball-milled at 450 rpm for 4 hours, and then placed in an argon atmosphere, uniformly heated to 750°C at a heating rate of 3°C / min and sintered for 18 hours to obtain a composite positive electrode lithium supplement.

[0072] The structural schematic diagram of the composite positive electrode lithium supplement agent is as follows Figure 1 shown.

[0073] Example 9

[0074] This embodiment provides a composite positive electrode lithium supplement, wherein the composite positive electrode lithium supplement is a core-shell structure, wherein the inner core is Li6CoO4 and the outer shell is C@Li 7 / 4 Ti 5 / 4 O3; the mass ratio of the inner core and the outer shell is 20:100; in the outer shell, C and Li 7 / 4 Ti 5 / 4 The mass ratio of O3 is 5:100;

[0075] The preparation method of the composite positive electrode lithium supplement comprises the following steps:

[0076] The internal core material Li6CoO4 was co-doped with Li2CO3, TiO2 and asphalt, ball-milled at a speed of 300 rpm for 6 hours, and then placed in an argon atmosphere, uniformly heated to 930°C at a heating rate of 4°C / min and sintered for 10 hours to obtain a composite positive electrode lithium supplement.

[0077] The structural schematic diagram of the composite positive electrode lithium supplement agent is as follows Figure 1 shown.

[0078] Comparative Example 1

[0079] This comparative example uses Li2NiO2 as the positive electrode lithium supplement.

[0080] Comparative Example 2

[0081] This comparative example uses Li5FeO4 as the positive electrode lithium supplement.

[0082] Comparative Example 3

[0083] This comparative example uses Li6CoO4 as the positive electrode lithium supplement.

[0084] Preparation Examples 1 to 9:

[0085] Soft pack battery production:

[0086] (1) LiNi 0.8 Co 0.1 Mn 0.1 The O2 positive electrode material and the composite positive electrode lithium supplement prepared in accordance with Examples 1 to 9, the conductive carbon black SP, and the polyvinylidene fluoride PVDF are fully mixed in an N-methylpyrrolidone solvent at a mass ratio of 94:3:1.5:1.5, and the slurry obtained after mixing is applied on an aluminum foil (the coating thickness is 300 μm), and the solvent and moisture are removed by vacuum drying at 80° C., and the positive electrode sheet is obtained by rolling and cutting;

[0087] (2) Artificial graphite, conductive agent SP, binder CMC, and binder SBR were fully mixed in deionized water at a mass ratio of 96:1:1.2:1.8, and the slurry obtained after mixing was applied on copper foil (coating thickness was 140 μm), dried at 80° C. to remove moisture, and negative electrode sheets were prepared by rolling and cutting;

[0088] (3) Assembling the positive and negative electrodes and the separator in step (1) and injecting liquid to obtain the final finished soft-pack battery.

[0089] Comparative Preparation Examples 1 to 3:

[0090] Soft pack battery production:

[0091] (1) LiNi 0.8 Co 0.1 Mn 0.1 The O2 positive electrode material and the positive electrode lithium supplement agent corresponding to comparative examples 1 to 3, conductive carbon black SP, and polyvinylidene fluoride PVDF are fully mixed in an N-methylpyrrolidone solvent at a mass ratio of 94:3:1.5:1.5, and the slurry obtained after mixing is applied on an aluminum foil (the coating thickness is 300 μm), and the solvent and moisture are removed by vacuum drying at 80° C., and the positive electrode sheet is obtained by rolling and cutting;

[0092] Step (2) and step (3) are the same as those in Preparation Examples 1 to 9.

[0093] Comparative Example Preparation Example 4

[0094] Soft pack battery production:

[0095] (1) LiNi 0.8 Co 0.1 Mn0.1 The O2 positive electrode material, conductive carbon black SP, and polyvinylidene fluoride PVDF are fully mixed in an N-methylpyrrolidone solvent at a mass ratio of 97:1.5:1.5, and the slurry obtained after mixing is applied on an aluminum foil (the coating thickness is 300 μm), and the solvent and moisture are removed by vacuum drying at 80°C, and the positive electrode sheet is obtained by rolling and cutting;

[0096] Step (2) and step (3) are the same as those in Preparation Examples 1 to 9.

[0097] Performance Test:

[0098] Test Example 1

[0099] The surface alkali content of the composite positive electrode lithium replenisher in Examples 1 to 9 and the positive electrode lithium replenisher in Comparative Examples 1 to 3 was tested, total alkali (%) = LiOH (%) + Li2CO3 (%); the test results are shown in Table 1:

[0100] Table 1

[0101]

[0102]

[0103] By comparing Examples 1 to 3 with Comparative Example 1, it can be seen that the composite positive electrode lithium replenisher of the present invention can effectively alleviate the generation of residual alkali on the surface.

[0104] By comparing Examples 4 to 6 with Comparative Example 2, it can be seen that the composite positive electrode lithium replenisher of the present invention can effectively alleviate the generation of residual alkali on the surface.

[0105] By comparing Examples 7 to 9 with Comparative Example 3, it can be seen that the composite positive electrode lithium replenisher of the present invention can effectively alleviate the generation of residual alkali on the surface.

[0106] Test Example 2

[0107] The soft-pack batteries assembled with the positive electrode sheets made of the composite positive electrode lithium replenisher in Preparation Examples 1 to 9 and the soft-pack batteries assembled with the positive electrode sheets made without adding the positive electrode lithium replenisher in Comparative Preparation Example 4 were tested for gram capacity, first coulomb efficiency and cycle retention rate. The test results are shown in Table 2:

[0108] Table 2

[0109]

[0110]

[0111] By comparing Preparation Examples 1 to 9 with Comparative Preparation Example 4, it can be seen that the composite positive electrode lithium supplement agent of the present invention can effectively improve the gram capacity and the first coulomb efficiency of the positive electrode material, thereby improving the energy density of the battery and effectively improving the cycle life of the battery.

[0112] Test Example 3

[0113] The gas production of the soft-pack batteries assembled with the positive electrode sheets made of the composite positive electrode lithium replenisher in Preparation Examples 1 to 9 and the soft-pack batteries assembled with the positive electrode sheets made of the positive electrode lithium replenisher in Comparative Preparation Examples 1 to 3 was tested. The test results are shown in Table 3:

[0114] Table 3

[0115] Gas production (mL) Example 1 Preparation Example 1 4.2 Example 2 Preparation Example 2 4.5 Example 3 Preparation Example 3 3.4 Example 4 Preparation Example 4 1.1 Example 5 Preparation Example 5 2.3 Example 6 Preparation Example 6 1.7 Example 7 Preparation Example 7 3.7 Example 8 Preparation Example 8 2.5 Example 9 Preparation Example 9 2.9 Comparative Example 1 Comparative Preparation Example 1 7.8 Comparative Example 2 Comparative Preparation Example 2 3.6 Comparative Example 3 Comparative Preparation Example 3 5.6

[0116] By comparing Preparation Examples 1 to 3 with Comparative Preparation Example 1, it can be seen that the composite positive electrode lithium supplement agent of the present invention can effectively reduce the gas production of the battery and improve the safety performance of the battery.

[0117] By comparing Preparation Examples 4 to 6 with Comparative Preparation Example 2, it can be seen that the composite positive electrode lithium supplement agent of the present invention can effectively reduce the gas production of the battery and improve the safety performance of the battery.

[0118] By comparing Preparation Examples 7 to 9 with Comparative Preparation Example 3, it can be seen that the composite positive electrode lithium supplement agent of the present invention can effectively reduce the gas production of the battery and improve the safety performance of the battery.

[0119] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0120] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A composite positive electrode lithium supplement, characterized in that: The composite positive electrode lithium supplement is a core-shell structure, wherein the inner core is one of Li2NiO2, Li5FeO4, and Li6CoO4, and the outer shell is C@Li 7 / 4 Ti 5 / 4 O3.

2. A composite positive electrode lithium supplement according to claim 1, characterized in that: The mass ratio of the inner core to the outer shell is 1-40:

100.

3. A composite positive electrode lithium supplement according to claim 1, characterized in that: In the outer shell, C and Li 7 / 4Ti 5 / 4 The mass ratio of O3 is 2 to 15:

100.

4. A method for preparing a composite positive electrode lithium supplement as claimed in any one of claims 1 to 3, characterized in that: The following steps are involved: The internal core material is co-doped with a lithium source, a titanium source and a carbon source and mixed by ball milling, and then calcined under an inert atmosphere to obtain a composite positive electrode lithium supplement.

5. A method for preparing a composite positive electrode lithium supplement according to claim 4, characterized in that: The lithium source is one or a combination of Li2CO3, LiOH, and Li2O; and / or, the titanium source is TiO2 with a size of 5 to 50 nm; And / or, the carbon source is at least one of glucose, lactose, maltose, coke, graphite, and asphalt.

6. A method for preparing a composite positive electrode lithium supplement according to claim 4, characterized in that: During the ball milling mixing process, the ball milling speed is 50-600 rpm, and the ball milling time is 0.5-8 h; And / or, the calcination temperature is 700-1050° C., the calcination time is 4-24 hours, and the temperature is increased at a uniform rate of 2-5° C. / min.

7. A positive electrode sheet, characterized in that: The invention comprises a positive electrode material, a conductive agent, a binder and a composite positive electrode lithium supplement agent according to any one of claims 1 to 3, Alternatively, a composite positive electrode lithium supplement prepared by the preparation method according to any one of claims 4 to 6.

8. A positive electrode sheet according to claim 7, characterized in that: The positive electrode material is at least one of lithium iron phosphate, lithium iron manganese phosphate, lithium cobalt oxide, lithium nickel manganese oxide, nickel-cobalt-manganese ternary, and lithium-rich manganese-based positive electrode materials.

9. The positive electrode sheet according to claim 7, characterized in that: The mass proportion of the composite positive electrode lithium supplement in the positive electrode sheet is 0.1% to 10%.

10. A lithium ion battery, characterized in that: The invention comprises a negative electrode sheet, a separator, an electrolyte and the positive electrode sheet according to any one of claims 7 to 9.

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