Lithium-replenishing material, preparation method therefor, and use thereof

Abstract

A lithium-replenishing material, comprising: a lithium-replenishing agent core (1); and a first shell layer (2) and a second shell layer (3) sequentially disposed outward from a surface of the lithium-replenishing agent core (1); the first shell layer (2) comprises a carbon material, and the second shell layer (3) comprises a MOF material. By coating the lithium-replenishing agent core (1) with the first shell layer (2) and the second shell layer (3), the energy density and cycling performance of a lithium battery are improved.

Description

A lithium supplement material, its preparation method and application

[0001] This application claims priority to Chinese Patent Application No. 202411915604.9, filed with the Chinese Patent Office on December 24, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of lithium-ion battery technology, and in particular to a lithium replenishment material, its preparation method, and its application. Background Technology

[0003] As lithium-ion batteries are used more and more in the field of electric vehicles, the performance requirements for lithium batteries are also increasing. Lithium iron phosphate batteries are gradually gaining attention due to their advantages such as long life and high safety performance. However, lithium iron phosphate batteries also have certain disadvantages, namely, their energy density is relatively low, with the energy density of a single cell generally only around 160Wh / kg.

[0004] To address the above issues, pre-lithiation technology is currently widely used to improve the energy density of lithium iron phosphate batteries. By selecting appropriate lithium replenishment materials, the energy density of a single cell can be increased to 170Wh / kg, or even 180Wh / kg. Pre-lithiation technology mainly involves two methods: positive electrode lithium replenishment and negative electrode lithium replenishment. However, negative electrode lithium replenishment poses significant safety risks and is difficult to process. Therefore, in practical applications, positive electrode lithium replenishment is generally preferred to improve the energy density of lithium iron phosphate batteries. Specifically, positive electrode lithium replenishment typically involves adding an appropriate amount of lithium replenishment material during the homogenization process of the positive electrode active material, resulting in a positive electrode active material containing lithium replenishment material. During charging, these excess lithium elements are extracted from the positive electrode active material and embedded into the negative electrode, thereby replenishing the irreversible capacity during the first charge and discharge cycle. Technical issues

[0005] However, due to the high residual alkali content of the lithium replenishment material, it is easy to react with carbon dioxide and water in the air to generate hydroxide ions, which in turn react with the binder in the positive electrode active material, causing the positive electrode active material to gel during the homogenization process. This reduces the electronic conductivity of the lithium replenishment material and is not conducive to improving the energy density and cycle performance of lithium batteries. Technical solutions

[0006] In order to avoid gelation after the lithium supplement material is added to the positive electrode active material and to improve the electronic conductivity of the lithium supplement material, this application provides a lithium supplement material, its preparation method and application.

[0007] In a first aspect, this application provides a lithium replenishment material, which adopts the following technical solution:

[0008] A lithium replenishing material includes a lithium replenishing core and a first shell and a second shell sequentially disposed on a surface away from the lithium replenishing core; the first shell includes a carbon material and the second shell includes a MOF material.

[0009] Secondly, this application provides a method for preparing a lithium supplement material, which adopts the following technical solution:

[0010] A method for preparing a lithium supplement material includes the following steps:

[0011] Step 1: Mix the lithium source, iron source and carbon source, add water, and grind to obtain a pre-ground slurry;

[0012] Step 2: Granulate the pre-ground slurry to obtain the first precursor;

[0013] Step 3: Spray the first precursor with atomized MOF material and dry it to obtain the second precursor;

[0014] Step four: calcining the second precursor to obtain the lithium-supplemented material.

[0015] Thirdly, this application provides a positive electrode sheet, which adopts the following technical solution:

[0016] A positive electrode sheet includes a positive current collector and a positive active material layer located on the surface of the positive current collector. The positive active material layer includes a positive electrode material, which includes a lithium supplement material as provided in the first aspect of this application or a lithium supplement material prepared in the second aspect.

[0017] Fourthly, this application provides a lithium-ion battery, which adopts the following technical solution:

[0018] A method for preparing a lithium-ion battery includes a negative electrode, a separator, an electrolyte, and a positive electrode as provided in the third aspect of this application. Beneficial effects

[0019] First, this application coats the surface of the lithium replenisher core with carbon material. The carbon source is then subjected to high-temperature treatment under oxygen-deficient conditions to form a network of amorphous carbon, thereby creating a first shell layer composed of amorphous carbon layers on the surface of the lithium replenisher core. This first shell layer is tightly bonded to the lithium replenisher core, has a uniform coating thickness, a smooth coating, and is not easily detached. While isolating the lithium replenisher core from carbon dioxide and water in the external air, it also forms an overall conductive network layer, significantly improving the electronic conductivity of the lithium replenishing material. Second, the amorphous carbon layer in the first shell layer has a strong bond with the MOF material, thereby improving the coating stability of the first and second shell layers. Furthermore, it effectively inhibits crystal growth of particles during high-temperature treatment and suppresses particle agglomeration. First, aggregation facilitates the formation of uniform and controllable micron- or nano-sized particles, thereby reducing the migration paths of electrons and lithium ions and improving the lithium replenishment performance and electrochemical performance of the lithium replenishment material. Second, the framework structure of the MOF material in the second shell can construct a regular and ordered pore structure, which is conducive to the migration of ions and electrons. Moreover, this framework structure can alleviate the volume expansion of the positive electrode during the use of lithium batteries and improve the cycle performance of lithium batteries. More importantly, the MOF material in the second shell can actively capture carbon dioxide in the external environment and "fix" it in its metal structure framework, further isolating the lithium replenishment core from the reaction of carbon dioxide and water in the external environment, significantly improving the cycle performance of lithium batteries. Attached Figure Description

[0020] Figure 1 is a schematic diagram of the particle structure of the lithium replenishment material of this application.

[0021] In the diagram: 1. Lithium replenisher core; 2. First shell layer; 3. Second shell layer. Embodiments of the present invention

[0022] Unless otherwise stated, all numerical values ​​for the amounts of expressed components, reaction conditions, etc., used in the specification and claims are to be understood as being modified by the term "about". Therefore, unless otherwise indicated, the numerical parameters set forth herein are approximate values ​​that can be varied to obtain the desired performance.

[0023] The word “and / or” as used in this article refers to one or all of the elements mentioned.

[0024] The terms "include" and "contain" as used in this article cover both cases where only the mentioned elements exist and cases where other unmentioned elements exist in addition to the mentioned elements.

[0025] All percentages in this application are weight percentages unless otherwise stated.

[0026] Unless otherwise stated, the terms “a,” “an,” “an,” and “the” as used in this specification are intended to include “at least one” or “one or more.” For example, “a component” refers to one or more components, and therefore more than one component may be considered and may be employed or used in the implementation of the described embodiments.

[0027] In a first aspect, this application provides a lithium replenishment material, which adopts the following technical solution:

[0028] A lithium-supplementing material includes a lithium-supplementing core and a first shell and a second shell sequentially disposed on a surface away from the lithium-supplementing core; the first shell comprises a carbon material, and the second shell comprises a MOF material. MOF materials, also known as metal-organic framework materials, are a class of compounds that form one-dimensional, two-dimensional, or three-dimensional structures by coordination of metal ions or metal clusters with organic ligands.

[0029] In this application, the lithium replenishing agent core is coated with a first shell and a second shell, which significantly improves the chemical stability of the lithium replenishing material without reducing its conductivity due to the isolation effect of the coating layer. This allows the lithium replenishing performance of the lithium replenishing material to be maintained for a long time, thereby improving the energy density and cycle performance of the lithium battery.

[0030] Optionally, the particle size D50 of the lithium replenishment material is 5-15μm, for example, it can be 5μm, 7μm, 9μm, 10μm, 11μm, 13μm, 15μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] The lithium replenishment material prepared in this application has regular ion and electron transport channels, which significantly improves the stability of the lithium replenishment material while improving its ionic conductivity.

[0032] Optionally, the thickness of the first shell layer is 1-10 nm, for example, it can be 1 nm, 3 nm, 5 nm, 6 nm, 8 nm, 9 nm, or 10 nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Optionally, the thickness of the second shell is 10-50nm, for example, it can be 10nm, 18nm, 25nm, 32nm, 38nm, 45nm, or 50nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0034] By controlling the thickness of the first and second shells, the MOF material in the second shell has a more regular crystal structure and pores suitable for lithium-ion and electron transport compared to the amorphous carbon in the first shell. Therefore, when the thickness of the second shell is higher, the ion transport performance and electronic conduction performance of the lithium-ion battery can be significantly improved, thereby improving the conductivity of the lithium battery.

[0035] Optionally, the MOF material includes any one of Al-MOF, Nb-MOF, Ti-MOF, and Mg-MOF.

[0036] Optionally, the lithium replenishing agent core includes at least one of lithium iron ferrite, lithium nickel ferrite, lithium manganese nickel oxide, and lithium nickel iron oxide.

[0037] Secondly, this application provides a method for preparing a lithium supplement material, which adopts the following technical solution:

[0038] A method for preparing a lithium supplement material includes the following steps:

[0039] Step 1: Mix the lithium source, iron source, and carbon source, add water, and grind to obtain a pre-ground slurry. The molar ratio of lithium, iron, and carbon in the pre-ground slurry is (5.5-7):1:(3-4), for example, it can be 5.5:1:3, 5.5:1:4, 7:1:3, 7:1:4, 6:1:3.5, 6:1:3, 6:1:4, but is not limited to the listed ratios; other unlisted ratios within the range are also applicable. The particle size D50 of the particles in the pre-ground slurry is 0.2-1μm, for example, it can be... The micrometer diameter is 0.2μm, 0.3μm, 0.5μm, 0.7μm, 0.8μm, 0.9μm, or 1μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable. The lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, and lithium acetate. The iron source includes at least one of ferric sulfate, ferric phosphate, and ferric oxide. The carbon source includes at least one of polyethylene glycol (PEG), lactose, and fructose. The mixing method includes any one or a combination of several of the following: ball milling, grinding, spraying, stirring, and ultrasonication.

[0040] Step 2: Granulate the pre-ground slurry to obtain the first precursor; the particle size D50 of the first precursor is 1-10 μm, for example, it can be 1 μm, 3 μm, 4 μm, 5 μm, 7 μm, 8 μm, 10 μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable; the particle size D50 of the first precursor is 5-6 μm, for example, it can be 5 μm, 5.2 μm, 5.4 μm, 5.5 μm, 5.7 μm, 5.9 μm, 6 μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0041] Step 3: Spray the first precursor with the atomized MOF material and dry it to obtain the second precursor. The drying temperature in Step 3 is 70-105℃, for example, it can be 70℃, 75℃, 80℃, 85℃, 90℃, 100℃, 105℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0042] Step four involves calcining the second precursor to obtain the lithium-replenishing material. During the calcination process in step four, the temperature is increased at a rate of 2-10℃ / min, for example, 2℃, 3℃, 5℃, 7℃, 8℃, 9℃, or 10℃, but not limited to the listed values. Other unlisted values ​​within the range are also applicable. The lithium-replenishing material is obtained by isothermal calcination at 500-800℃ for 10-18 hours. For example, the calcination temperature can be 500℃, 600℃, 650℃, 700℃, or 800℃, and the calcination time can be 10 hours, 12 hours, 14 hours, 15 hours, 17 hours, or 18 hours, but not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0043] In step one of this application, a carbon source is added during the preparation of the pre-grinding slurry. The carbon source can be uniformly dispersed in the first precursor obtained from the pre-grinding slurry. During the subsequent sintering process, the carbon source can act as a barrier between particles, thereby slowing down the growth of primary particles and preventing the growth of large single crystal particles, which is beneficial to improving the conductivity of the material.

[0044] In step three, the preparation of the atomized MOF material includes the following steps: mixing the MOF material and ethanol and grinding them to obtain MOF slurry. The solid content of the MOF slurry is 1%-10%, for example, it can be 1%, 3%, 5%, 6%, 8%, 10%, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0045] This application improves the uniformity of MOF slurry coating on the surface of the first shell by controlling the solid content of the MOF slurry, and improves the bonding tightness between the second shell and the first layer, thereby enhancing the stability and electronic conductivity of the lithium supplementation material.

[0046] The particle size D50 of MOF materials is 5-15nm, for example, it can be 5nm, 7nm, 8nm, 10nm, 11nm, 13nm, 15nm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0047] This application improves the ability of MOF materials to capture carbon dioxide from the external environment by adjusting the particle size of MOF materials and the specific surface area of ​​MOF materials, thereby avoiding the reaction between the lithium replenishment core and carbon dioxide in the external environment.

[0048] Thirdly, this application provides a positive electrode sheet, which adopts the following technical solution:

[0049] A positive electrode sheet includes a positive current collector and a positive active material layer located on the surface of the positive current collector. The positive active material layer includes a positive electrode material, which includes a lithium supplement material as provided in the first aspect of this application or a lithium supplement material prepared in the second aspect.

[0050] Positive electrode materials include positive electrode active materials, conductive agents, binders, and lithium supplementation materials.

[0051] The lithium replenishment material of this application can alleviate the expansion of the active material in the positive electrode during use, reduce the water absorption of the positive electrode active material containing the lithium replenishment material, reduce the irreversible capacity loss of the positive electrode during use, significantly improve the stability of the positive electrode, and thus improve the cycle performance of the lithium battery.

[0052] The mass percentage of lithium supplementation material in the cathode material is 0.5%-5%, for example, it can be 0.5%, 1%, 2%, 2.5%, 3%, 4%, 5%, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0053] The lithium replenishing material prepared in this application has excellent electronic conductivity and long-lasting lithium replenishment properties, and its mass proportion in the positive electrode active material is relatively low compared with conventional lithium replenishing materials in the field, thereby reducing costs.

[0054] Fourthly, this application provides a lithium-ion battery, which adopts the following technical solution:

[0055] A method for preparing a lithium-ion battery includes a negative electrode, a separator, an electrolyte, and a positive electrode as provided in the third aspect of this application.

[0056] Example 1

[0057] 1. A lithium supplement material

[0058] The lithium replenishment material in this embodiment was prepared using the following steps:

[0059] Step 1: Lithium carbonate, iron phosphate, and glucose are mixed and stirred in a molar ratio of lithium:iron:carbon = 6:1:3.5. Water is added and the mixture is ground to obtain a pre-ground slurry. The particle size D50 of the pre-ground slurry is 0.8 μm.

[0060] Step 2: Granulate the pre-ground slurry obtained in Step 1 to obtain the first precursor;

[0061] Step 3: Nb-MOF material with a particle size D50 of 10 nm is mixed with ethanol to obtain Nb-MOF slurry with a solid content of 5%. The obtained Nb-MOF slurry is sprayed onto the first precursor and dried at 90 °C to obtain the second precursor.

[0062] Step four: The second precursor obtained in step three is placed in a calcination furnace and heated to 700°C at a rate of 6°C / min, and calcined at a constant temperature for 14 hours to obtain a lithium supplement material with a particle size D50 of 10 μm. The thickness of the first shell layer in the lithium supplement material is 5 nm, and the thickness of the second shell layer is 30 nm.

[0063] 2. Preparation of the positive electrode sheet

[0064] The positive electrode slurry was prepared as follows: lithium iron phosphate positive electrode active material, conductive agent acetylene black, binder PVDF, and the prepared lithium supplement material were added to a vacuum mixer at a mass ratio of 96.5:0.5:1:2 and mixed. Then, solvent NMP was added to the mixed slurry, and the slurry was stirred until homogeneous under vacuum, thereby obtaining the positive electrode slurry of this embodiment. The obtained positive electrode slurry was uniformly coated on both surfaces of the positive electrode current collector aluminum foil, air-dried at room temperature, and then transferred to an oven for further drying. After drying in the oven, a positive electrode sheet semi-finished product was obtained. Then, the positive electrode sheet semi-finished product was cold-pressed and cut to obtain the positive electrode sheet to be assembled.

[0065] 3. Preparation of negative electrode sheet

[0066] The negative electrode slurry was prepared as follows: artificial graphite, conductive agent acetylene black, thickener CMC, and binder SBR were added to a vacuum mixer in a mass ratio of 96.4:1:1.2:1.4 and mixed. Then, deionized water was added to the resulting mixture and the mixture was stirred in a vacuum mixer until it became homogeneous, thus obtaining the negative electrode slurry of this embodiment.

[0067] The obtained negative electrode slurry is uniformly coated on both surfaces of the negative electrode current collector copper foil, air-dried at room temperature, and then transferred to an oven for further drying. After drying in the oven, a negative electrode semi-finished product is obtained. Then, the negative electrode semi-finished product is cold-pressed and cut to obtain the negative electrode sheet to be assembled.

[0068] 4. Preparation of lithium batteries

[0069] Commercially available polyethylene film is used as the separator for lithium-ion batteries, and a commercially available electrolyte suitable for 4.2V (upper charging voltage) battery systems is used as the electrolyte. The prepared positive and negative electrode sheets are wound together with the separator to obtain bare cells. The bare cells are then packaged, injected with electrolyte, left to stand, formed, and tested for capacity to obtain the finished battery.

[0070] Example 2

[0071] 1. A lithium supplement material

[0072] The lithium replenishment material in this embodiment was prepared using the following steps:

[0073] Step 1: Lithium nitrate, iron oxide and starch are mixed and stirred in a molar ratio of lithium:iron:carbon = 5.5:1:4. Water is added and the mixture is ground to obtain a pre-ground slurry. The particle size D50 of the pre-ground slurry is 1.0 μm.

[0074] Step 2: Granulate the pre-ground slurry obtained in Step 1 to obtain the first precursor;

[0075] Step 3: Mix Ti-MOF material with a particle size D50 of 5 nm with ethanol to obtain Ti-MOF slurry with a solid content of 10%. Spray the obtained Ti-MOF slurry onto the first precursor and dry it at 105°C to obtain the second precursor.

[0076] Step four: The second precursor obtained in step three is placed in a calcination furnace and heated to 500°C at a rate of 10°C / min, and calcined at a constant temperature for 18 hours to obtain a lithium supplement material with a particle size D50 of 5 μm. The thickness of the first shell layer in the lithium supplement material is 1.5 nm, and the thickness of the second shell layer is 10 nm.

[0077] 2. Preparation of the positive electrode sheet

[0078] The positive electrode slurry was prepared as follows: Lithium iron phosphate positive electrode active material, conductive agent acetylene black, binder PVDF, and the prepared lithium supplement material were added to a vacuum mixer at a mass ratio of 94:0.5:1:4.5 and mixed. Then, NMP solvent was added to the mixed slurry, and the mixture was stirred until homogeneous under vacuum, thus obtaining the positive electrode slurry of this embodiment. The obtained positive electrode slurry was uniformly coated onto both surfaces of the positive electrode current collector aluminum foil, air-dried at room temperature, and then transferred to an oven for further drying. After drying in the oven, a semi-finished positive electrode sheet was obtained. The semi-finished positive electrode sheet was then cold-pressed and slit to obtain the positive electrode sheet to be assembled.

[0079] 3. Preparation of negative electrode sheet

[0080] The preparation of the negative electrode in this embodiment is consistent with that in Example 1.

[0081] 4. Preparation of lithium batteries

[0082] The preparation of the lithium battery in this embodiment is consistent with that in Example 1.

[0083] Example 3

[0084] 1. A lithium supplement material

[0085] The lithium replenishment material in this embodiment was prepared using the following steps:

[0086] Step 1: Lithium acetate, ferric sulfate and glucose are mixed and stirred in a molar ratio of lithium:iron:carbon = 7:1:3. Water is added and the mixture is ground to obtain a pre-ground slurry. The particle size D50 of the pre-ground slurry is 0.2μm.

[0087] Step 2: Granulate the pre-ground slurry obtained in Step 1 to obtain the first precursor;

[0088] Step 3: Mix Mg-MOF material with a particle size D50 of 15 nm with ethanol to obtain Mg-MOF slurry with a solid content of 1%. Spray the obtained Mg-MOF slurry onto the first precursor and dry it at 70°C to obtain the second precursor.

[0089] Step four: The second precursor obtained in step three is placed in a calcination furnace and heated to 800°C at a rate of 2°C / min, and calcined at a constant temperature for 10 hours to obtain a lithium supplement material with a particle size D50 of 15 μm. The thickness of the first shell layer in the lithium supplement material is 10 nm, and the thickness of the second shell layer is 50 nm.

[0090] 2. Preparation of the positive electrode sheet

[0091] The positive electrode slurry was prepared as follows: lithium iron phosphate positive electrode active material, conductive agent acetylene black, binder PVDF, and the prepared lithium supplement material were added to a vacuum mixer at a mass ratio of 96.5:1.5:1:1 and mixed. Then, solvent NMP was added to the mixed slurry, and the slurry was stirred until homogeneous under vacuum, thus obtaining the positive electrode slurry of this embodiment. The obtained positive electrode slurry was uniformly coated on both surfaces of the positive electrode current collector aluminum foil, air-dried at room temperature, and then transferred to an oven for further drying. After drying in the oven, a positive electrode sheet semi-finished product was obtained. Then, the positive electrode sheet semi-finished product was cold-pressed and cut to obtain the positive electrode sheet to be assembled.

[0092] 3. Preparation of negative electrode sheet

[0093] The preparation of the negative electrode in this embodiment is consistent with that in Example 1.

[0094] 4. Preparation of lithium batteries

[0095] The preparation of the lithium battery in this embodiment is consistent with that in Example 1.

[0096] Example 4

[0097] The difference between this embodiment and Embodiment 1 is that the particle size D50 of the lithium replenishment material is 2 μm; the other steps and parameter settings are consistent with Embodiment 1.

[0098] Example 5

[0099] The difference between this embodiment and Embodiment 1 is that the particle size D50 of the lithium replenishment material is 20 μm; all other steps and parameter settings are consistent with Embodiment 1.

[0100] Example 6

[0101] The difference between this embodiment and Embodiment 1 is that, in the process of preparing the lithium supplement material, the solid content of the MOF slurry used in step three is 0.3%; the rest are consistent with Embodiment 1.

[0102] Example 7

[0103] The difference between this embodiment and Embodiment 1 is that the solid content of the MOF slurry used in step three of the preparation of the lithium supplement material is 13%; the rest are consistent with Embodiment 1.

[0104] Example 8

[0105] The difference between this embodiment and Embodiment 1 is that the particle size D50 of the MOF material is 40 nm during the preparation of the lithium supplementation material; the rest are consistent with Embodiment 1.

[0106] Example 9

[0107] The difference between this embodiment and Embodiment 1 is that the thickness of the first shell layer in the lithium replenishment material is 0.1 nm; the other steps and parameter settings are consistent with Embodiment 1.

[0108] Example 10

[0109] The difference between this embodiment and Embodiment 1 is that the thickness of the second shell layer in the lithium replenishment material is 5 nm; all other steps and parameter settings are consistent with Embodiment 1.

[0110] Comparative Example 1

[0111] The difference between this comparative example and Example 1 lies in the preparation of the lithium replenishing material. The specific steps for preparing the lithium replenishing material are as follows:

[0112] Step 1: Disperse lithium hydroxide and nickel sulfate in deionized water. After they are completely dissolved, add sucrose to obtain a mixed solution. The molar ratio of lithium to iron to carbon in the mixed solution is 5.5-7:1:3-4.

[0113] Step 2: Stir the solution obtained in Step 1 at 80°C to form a sol;

[0114] Step 3: The sol obtained in Step 2 is spray-dried to obtain precursor powder. The obtained precursor powder is calcined in an inert atmosphere for 10 hours and then cooled in the furnace to obtain a core-shell structure of lithium-rich oxide Li2NiO2 / C with Li2NiO2 as the core and carbon material as the shell. The particle size D50 of the lithium-rich oxide Li2NiO2 / C is 10 μm, and the shell thickness is 50 nm.

[0115] Comparative Example 2

[0116] The difference between this comparative example and Example 1 is that the lithium replenishment material contains only a second shell layer; the remaining steps and parameter settings are consistent with Example 1.

[0117] Comparative Example 3

[0118] The difference between this comparative example and Example 1 is that the lithium replenishment material contains only the first shell layer; the remaining steps and parameter settings are consistent with Example 1.

[0119] Comparative Example 4

[0120] The difference between this comparative example and Example 1 is that an equal weight of conventional positive electrode lithium replenishing agent was used instead of the lithium replenishing material in Example 1 during the preparation of the positive electrode sheet; the remaining steps and parameter settings are consistent with Example 1.

[0121] Detection methods

[0122] I. Particle size testing of lithium supplementation materials

[0123] The particle size of the lithium supplement materials prepared in Examples 1-10 and Comparative Examples 1-4 was tested. The specific test methods are as follows: the powder particle size D50 and particle size concentration were tested by a Malvern laser particle size analyzer. D50 is the particle size corresponding to the cumulative particle size distribution percentage reaching 50%. The test data are recorded in Table 1.

[0124] II. Coating Thickness Test

[0125] The thickness of the first and second shells of the lithium-supplementing materials prepared in Examples 1-10 and Comparative Examples 1-4 was tested by TEM. The test method is as follows: (1) The lithium-supplementing material samples prepared in Examples 1-10 and Comparative Examples 1-4 were dispersed by ultrasonic vibration to remove soft agglomerates, and then dispersed in water or other solvents to prepare a sample suspension; (2) A copper mesh covered with a carbon film or other polymer film was taken, and the required amount was taken from the prepared sample suspension or piped onto the copper mesh. After being dried with filter paper or air-dried, it was placed on the sample stage for testing; (3) In a representative In areas with narrow size distribution and good dispersion, photographs are taken, and the size of the lithium-replenishing material with complete morphology is arbitrarily selected and measured. After the pre-grinding slurry is dried, the size of the lithium-replenishing material core is measured by TEM and recorded as d1. After the first precursor is obtained, the size of the first precursor is measured by TEM and recorded as d2. After the lithium-replenishing material is obtained, the size of the lithium-replenishing material is measured by TEM and recorded as d3. Then, the formula for calculating the thickness h1 of the first shell is: h1=d2-d1, and the formula for calculating the thickness h2 of the second shell is: h2=d3-d2.

[0126] III. Lithium Battery Energy Density Test

[0127] The energy density of the ion batteries prepared in Examples 1-10 and Comparative Examples 1-4 was tested according to the national standard GB / T31486-2015 "Electrical Performance Requirements and Test Methods for Power Batteries for Electric Vehicles".

[0128] IV. Lithium-ion battery cycle performance test

[0129] The lithium-ion batteries prepared in Examples 1-10 and Comparative Examples 1-4 were placed in an oven at a constant temperature of 25°C and charged to 4.20V at a constant current of 1C. Then, the constant voltage charging current was reduced to 0.05C, and the batteries were left to stand for 10 minutes. Subsequently, they were discharged to 2.5V at a constant current of 1C. This cycle was repeated until the capacity was less than 80% of the initial capacity (cycle cutoff condition). The number of cycles at this point was recorded in Table 1.

[0130] Table 1

[0131]

[0132] Based on Examples 1-3, Comparative Examples 1-4, and Table 1, it can be seen that the lithium replenishment material with a double-layer core-shell structure prepared in this application can significantly improve the energy density and cycle performance of lithium batteries after being added to the positive electrode active material. This is because the lithium replenishment material of this application can isolate carbon dioxide and water in the external environment, improve the stability of the lithium replenishment material, and prevent residual alkali from reacting with carbon dioxide and water to cause gel formation in the positive electrode active material, which would affect the adhesion stability of the positive electrode active material on the surface of the positive electrode current collector. This allows the lithium replenishment material to maintain its lithium replenishment performance for a long time, thereby improving the energy density and cycle performance of lithium batteries. Furthermore, the core-shell structure of this application can construct a pore structure that facilitates the passage of ions and electrons, significantly improving the electronic conductivity of the lithium replenishment material and further improving the cycle performance of lithium batteries.

[0133] Combining Examples 1, 4-5, and Table 1, it can be seen that the cycle performance of the lithium battery slightly decreases when the particle size of the lithium replenishing material is too large or too small. This is because when the particle size of the lithium replenishing material is too small, it is easy for the material to agglomerate in the positive electrode active material, and the thickness of the first shell layer and the second shell layer is uneven, which is not conducive to the construction of a conductive network structure that is uniformly distributed on the surface of the lithium replenishing agent core. When the particle size of the lithium replenishing material is too large, it increases the migration path of ions and electrons, thereby increasing the internal resistance of the lithium battery, which is not conducive to improving the cycle performance of the lithium battery.

[0134] Combining Examples 1, 6-8, and Table 1, it can be seen that when the solid content of the MOF slurry is too low or too high, or when the particle size D50 of the MOF material is too large, the cycle performance of the lithium battery decreases slightly. This is because both excessively high and low solid content of the MOF slurry and excessively large particle size D50 of the MOF material have negative effects.

[0135] It is not conducive to the formation of a uniform thickness of the second shell, affects the pore structure of the MOF material in the second shell, is not conducive to the conduction of ions and electrons, and thus reduces the cycle performance of lithium batteries.

[0136] Based on Examples 1, 9-10 and Table 1, it can be seen that when the thickness of the first shell layer is too small, the bonding degree between the second shell layer and the first shell layer is low, which is not conducive to the coating stability of the shell structure and affects the cycle stability of the lithium battery. When the thickness of the second shell layer is too small, it will not be conducive to improving the electronic conduction of the lithium replenishment material and reducing the electrochemical performance of the lithium battery.

Claims

1. A lithium replenishing material, comprising a lithium replenishing agent core and a first shell and a second shell sequentially disposed on a surface away from the lithium replenishing agent core; the first shell comprising a carbon material and the second shell comprising a MOF material.

2. The lithium replenishment material according to claim 1, wherein, The particle size D50 of the lithium replenishment material is 5-15 μm.

3. A lithium replenishment material according to any one of claims 1-2, wherein, The thickness of the first shell layer is 1-10 nm.

4. A lithium replenishment material according to any one of claims 1-3, wherein, The thickness of the second shell is 10-50 nm.

5. A lithium replenishment material according to any one of claims 1-4, wherein, The MOF material includes any one of Al-MOF, Nb-MOF, Ti-MOF, and Mg-MOF.

6. A lithium replenishment material according to any one of claims 1-5, wherein, The lithium replenishing agent core includes at least one of lithium iron ferrite, lithium nickel ferrite, lithium manganese nickel oxide, and lithium nickel iron oxide.

7. A method for preparing the lithium-supplementing material according to any one of claims 1-6, comprising the following steps: Step 1: Mix lithium source, iron source and carbon source, add water, and grind to obtain pre-ground slurry; Step 2: Granulate the pre-ground slurry to obtain the first precursor; Step 3: Spray the first precursor with atomized MOF material and dry to obtain the second precursor; Step four: calcining the second precursor to obtain the lithium-supplementing material.

8. The method for preparing a lithium-supplementing material according to claim 7, wherein, In step three, the preparation of the atomized MOF material includes the following steps: mixing the MOF material with ethanol and grinding it to obtain a MOF slurry, wherein the solid content of the MOF slurry is 1%-10%.

9. A method for preparing a lithium-supplementing material according to claim 8, wherein, The particle size D50 of the MOF material is 5-15 nm.

10. A positive electrode sheet comprising a positive current collector and a positive active material layer located on the surface of the positive current collector, the positive active material layer comprising a positive electrode material, the positive electrode material comprising a lithium supplementing material as described in any one of claims 1-9.

11. A positive electrode according to claim 10, wherein, The lithium supplement material accounts for 0.5%-5% of the mass of the cathode material.

12. A lithium-ion battery, comprising a negative electrode, a separator, an electrolyte, and a positive electrode as described in any one of claims 10-11.

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