Lithium supplementation materials and their preparation methods, positive electrode sheets and secondary batteries

Abstract

This application provides a lithium replenishment material and its preparation method, a positive electrode sheet, and a secondary battery. The lithium replenishment material includes a core and a coating layer. The core includes a first lithium-rich compound; the coating layer covers the outer surface of the core and includes a second lithium-rich compound, with the content of the second lithium-rich compound in the coating layer being less than the content of the first lithium-rich compound in the core. The lithium replenishment material provided by this application has a high lithium content in the core and a low lithium content in the coating layer, allowing it to provide a large amount of lithium to ensure its lithium replenishment capability and improve the battery's energy density. Simultaneously, the lithium replenishment material has a low residual alkali value, improving its processing performance and stability.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a lithium replenishment material and its preparation method, a positive electrode sheet, and a secondary battery. Background Technology

[0002] During the initial charge and discharge of batteries such as lithium-ion rechargeable batteries, a large amount of solid electrolyte interphase (SEI) film forms on the surface of the negative electrode. This film consumes the limited lithium ions and electrolyte in the battery, causing irreversible capacity loss and reducing the coulombic efficiency of the lithium-ion rechargeable battery. This directly affects the cycle life and energy density of the battery. Currently, this irreversible capacity loss can be eliminated by lithium replenishment at the positive electrode, improving the battery's energy density and other electrical properties. However, existing lithium replenishment materials suffer from poor chemical stability, low conductivity, and significant residual alkali on the surface, which hinders their industrial production. Summary of the Invention

[0003] This application provides a lithium supplement material and its preparation method, a positive electrode sheet, and a secondary battery.

[0004] In a first aspect, this application provides a lithium replenishment material, the lithium replenishment material comprising a core and a coating layer, the core comprising a first lithium-rich compound; the coating layer covering the outer surface of the core, the coating layer comprising a second lithium-rich compound, and the content of the second lithium-rich compound in the coating layer being less than the content of the first lithium-rich compound in the core.

[0005] In this application, the lithium replenishment material has a high lithium content in its core and a low lithium content in its coating layer, meaning that the lithium content is higher inside and lower outside, exhibiting a gradient distribution structure. On one hand, the lithium replenishment material can provide a large amount of lithium to ensure its replenishment capability and better improve battery energy density. On the other hand, because the outer coating layer of the lithium replenishment material has a lower lithium content, the residual alkalinity on the surface of the material is lower, reducing the phenomenon of slurry gelation during the slurry preparation process, greatly improving its homogenization process, and enhancing the processing performance of the lithium replenishment material. Simultaneously, the lower residual alkalinity reduces side reactions on the surface of the lithium replenishment material, improving its chemical stability.

[0006] In one embodiment, the content of the first lithium-rich compound in the core is 50-90%.

[0007] In one embodiment, the content of the second lithium-rich compound in the coating layer is 10-50%.

[0008] In one embodiment, the content of the second lithium-rich compound in the coating layer gradually decreases in the direction away from the core.

[0009] In one embodiment, the thickness of the coating layer is 1-100 nm.

[0010] In one embodiment, the core further includes a first carbon nanomaterial, at least a portion of which is embedded within the first lithium-rich compound.

[0011] In one embodiment, the coating layer further includes a second carbon nanomaterial, at least a portion of which is embedded within the second lithium-rich compound.

[0012] In one embodiment, the ratio of the sum of the masses of the first carbon nanomaterial and the second carbon nanomaterial to the sum of the masses of the first lithium-rich compound and the second lithium-rich compound is 0.5% to 15%.

[0013] In one embodiment, the first lithium-rich compound and the second lithium-rich compound are both the same lithium metal compound.

[0014] In one embodiment, the first carbon nanomaterial and the second carbon nanomaterial are both the same carbon nanomaterial.

[0015] In one embodiment, the first carbon nanomaterial and the second carbon nanomaterial include at least one of carbon nanotubes, carbon nanofibers, carbon nanospheres, and graphene.

[0016] In one embodiment, both the first carbon nanomaterial and the second carbon nanomaterial are carbon nanotubes, and the aspect ratio of the carbon nanotubes is 7-70.

[0017] In one embodiment, the carbon nanotubes have a diameter of 30-70 nm.

[0018] In one embodiment, the carbon nanotubes have a length of 0.5-2 μm.

[0019] In one embodiment, both the first carbon nanomaterial and the second carbon nanomaterial are carbon nanotubes, with at least one portion of the carbon nanotube embedded in the core and another portion embedded in the coating layer.

[0020] In one embodiment, the lithium-rich material is obtained by lithiation of an intermediate, which is formed by depositing a precursor on a carbon nanomaterial, and the lithiation of the precursor yields the first lithium-rich compound and the second lithium-rich compound.

[0021] In one embodiment, the general structural formula of the first lithium-rich compound and / or the second lithium-rich compound is Li. 1+x A y O zWhere 0 < x < 10, 0 < y < 6, 0 < z < 13, and A is one or more of Ni, Co, Fe, Cu, Mg, Mn, Cr, Zn, Ti, Zr, Nb, and Mo.

[0022] In one embodiment, the particle size of the lithium replenishment material satisfies: 1μm≤D50≤25μm.

[0023] In one embodiment, the specific surface area of ​​the lithium replenishing material is 0.1-25 m². 2 / g.

[0024] In one embodiment, the residual alkali value of the lithium replenishing material is 0%-3%.

[0025] Secondly, this application provides a method for preparing a lithium-supplementing material, the method comprising:

[0026] The first carbon nanomaterial solution and the first precursor solution are added to the reactor, and the pH of the solution in the reactor is adjusted to be alkaline to obtain intermediate I.

[0027] A second carbon nanomaterial solution and a second precursor solution are added to a reactor containing intermediate I, while the pH of the solution in the reactor is adjusted to be alkaline to obtain intermediate II, wherein the concentration of the second precursor solution is less than the concentration of the first precursor solution.

[0028] The intermediate II is mixed with a lithium source and sintered under an inert atmosphere to obtain a lithium-replenishing material.

[0029] Thirdly, this application provides a positive electrode sheet, which includes the lithium replenishing material as described above, or the lithium replenishing material prepared by the method described above.

[0030] Fourthly, this application provides a secondary battery, which includes a negative electrode, a separator, and a positive electrode as described above. Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments of this application will be described below.

[0032] Figure 1 This is a schematic diagram of a lithium replenishment material provided in one embodiment of this application. Detailed Implementation

[0033] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments.

[0034] In this document, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "multiple" means two or more.

[0035] Furthermore, in this article, directional terms such as "upper" and "lower" are defined relative to the orientation of the structure as shown in the attached drawings. It should be understood that these directional terms are relative concepts, used for relative description and clarification, and can change accordingly depending on the orientation of the structure.

[0036] For ease of understanding, the English abbreviations and related technical terms used in the embodiments of this application will be explained and described below.

[0037] SEI membrane: refers to Solid Electrolyte Interphase, i.e., solid electrolyte interface membrane.

[0038] During the first charge and discharge cycle of batteries such as lithium-ion rechargeable batteries, a large amount of solid electrolyte interphase (SEI) film forms on the surface of the negative electrode. This film consumes the limited lithium ions and electrolyte in the battery, resulting in a significant reduction in lithium-ion capacity and causing irreversible capacity loss. During the first discharge, the number of lithium ions extracted from the negative electrode is much smaller than the number extracted from the positive electrode during charging, leading to a decrease in the coulombic efficiency of the lithium-ion rechargeable battery and directly affecting its cycle life and energy density. This problem can usually be addressed by replenishing lithium at the positive electrode to eliminate this irreversible capacity loss and improve the battery's energy density and other electrical properties. However, existing lithium replenishment materials suffer from poor conductivity and low stability, hindering their widespread application and limiting the improvement of lithium-ion rechargeable battery performance.

[0039] This application provides a lithium replenishing material 1, which is applied to the positive electrode of a battery to pre-lithiate the positive electrode, adding lithium to the battery interior to replenish lithium ions before the battery operates. In one embodiment, the lithium replenishing material 1 can be coated onto the outer surface of the battery positive electrode sheet, or it can be embedded into the outer surface of the battery positive electrode sheet. In other embodiments, the lithium replenishing material 1 can be added during the preparation of the battery positive electrode sheet, dispersing it to both the outer surface and interior of the positive electrode sheet.

[0040] Please see Figure 1 , Figure 1This is a schematic diagram of a lithium replenishment material 1 provided according to an embodiment of this application. An embodiment of this application provides a lithium replenishment material 1, which includes a core 10 and a coating layer 20. The core 10 includes a first lithium-rich compound 11, and the coating layer 20 covers the outer surface of the core 10. The coating layer 20 includes a second lithium-rich compound 21, and the content of the second lithium-rich compound 21 in the coating layer 20 is less than the content of the first lithium-rich compound 11 in the core 10.

[0041] Lithium supplement material 1 includes multiple particles. Figure 1 The diagram illustrates one of the particles in the lithium replenishment material 1. In one embodiment, the lithium replenishment material 1 is spherical or nearly spherical. The lithium replenishment material 1 has a core-shell structure, with a coating layer 20 covering the outer surface of the core 10, which isolates the core 10 from the external environment. For example, the coating layer 20 can isolate the core 10 from the electrolyte. In one embodiment, the coating layer 20 can be continuously distributed on the outer surface of the core 10. In one embodiment, the coating layer 20 can be discontinuously and intermittently distributed on the outer surface of the core 10. In one embodiment, the coating layer 20 covers a portion of the outer surface of the core 10. In one embodiment, the coating layer 20 completely covers the outer surface of the core 10, i.e., the coating layer 20 covers the entire outer surface of the core 10.

[0042] Both the first lithium-rich compound 11 and the second lithium-rich compound contain lithium (Li). During the first charge, the lithium (Li) in both compounds is released and migrates to the negative electrode of the battery to offset the irreversible lithium loss caused by the formation of the SEI film, thereby improving the total capacity and energy density of the battery. In one embodiment, the lithium content in the coating layer 20 is less than the lithium content in the core 10. In another embodiment, the density of the second lithium-rich compound 21 in the coating layer 20 is less than the density of the first lithium-rich compound 11 in the core 10.

[0043] The content of the first lithium-rich compound 11 in the core 10 refers to the ratio of the mass of the first lithium-rich compound 11 to the mass of the core 10. The content of the second lithium-rich compound 21 in the coating layer 20 refers to the ratio of the mass of the second lithium-rich compound 21 to the mass of the coating layer 20.

[0044] In this application, the core 10 has a large lithium content, which can release a large number of active lithium ions to replenish the lithium in the battery system. The lithium released from the core 10 is the main lithium source when the lithium replenishment material 1 replenishes the battery. The coating layer 20 is located on the outside of the core 10. The coating layer 20 has a smaller lithium content. While providing a certain amount of lithium ions, it can also reduce the residual alkali value of the lithium replenishment material 1 and improve the processing performance of the lithium replenishment material 1.

[0045] During the preparation of lithium replenishment material 1, to ensure sufficient reaction, an excess of lithium source is generally used. Unreacted raw materials form residual alkali on the surface of lithium replenishment material 1. If the coating layer 20 also contains a large amount of lithium, it will result in a large amount of residual alkali on the outer surface of lithium replenishment material 1. When the residual alkali content of lithium replenishment material 1 is too high, on the one hand, it is prone to gelation of the slurry during the slurry preparation process, resulting in poor slurry fluidity, affecting the coating of the slurry, and thus affecting the processing performance of lithium replenishment material 1. At the same time, it will also increase the internal resistance of the battery, thereby affecting various battery performance aspects. On the other hand, a high residual alkali content makes lithium replenishment material 1 less stable, deteriorates the high-temperature storage performance of the battery, and leads to problems such as gas expansion and performance degradation during battery storage, directly affecting the electrochemical performance of lithium replenishment material 1 and reducing battery safety performance.

[0046] In this application, the core 10 of the lithium replenishment material 1 has a high lithium content, while the coating layer 20 has a low lithium content. This means that the lithium content in the lithium replenishment material 1 is higher inside and lower outside, exhibiting a gradient distribution structure. On one hand, the lithium replenishment material 1 can provide a large amount of lithium to ensure its lithium replenishment capability and better improve battery energy density. On the other hand, because the coating layer 20 on the outside of the lithium replenishment material 1 has a lower residual alkali value, it reduces the phenomenon of slurry gelation during the slurry preparation process, greatly improving its homogenization process and enhancing its processing performance. Simultaneously, the lower residual alkali value reduces side reactions on the surface of the lithium replenishment material 1, improving its stability.

[0047] In one embodiment, the content of the first lithium-rich compound 11 in the core 10 is 50-90%. It is understood that the higher the content of the first lithium-rich compound 11 in the core 10, the more lithium ions the core 10 can provide to offset the irreversible lithium loss caused by the formation of the SEI film. However, too high a content of the first lithium-rich compound 11 may also lead to poor conductivity of the lithium replenishment material 1.

[0048] In this embodiment, by setting the mass percentage of the first lithium-rich compound 11 to the core 10 in the range of 50-90%, not only can the lithium replenishing material 1 have a better lithium replenishing capacity, but other properties such as conductivity of the lithium replenishing material 1 can also be comprehensively improved.

[0049] In one embodiment, the content of the first lithium-rich compound 11 in the core 10 can be 50%, 52%, 55%, 58%, 60%, 63%, 65%, 67%, 70%, 72%, 75%, 78%, 80%, 85%, or 90%.

[0050] In one embodiment, the content of the second lithium-rich compound 21 in the coating layer 20 is 10-50%. It is understood that a higher content of the second lithium-rich compound 21 in the coating layer 20 results in a higher residual alkali value of the lithium replenishment material 1, thereby affecting the processing performance and stability of the lithium replenishment material 1. Conversely, a lower content of the second lithium-rich compound 21 in the coating layer 20, while reducing the residual alkali value of the lithium replenishment material 1, sacrifices some of its lithium replenishment capacity.

[0051] In this application, the content of the second lithium-rich compound 21 in the coating layer 20 is set within a suitable range. On the one hand, the content of the second lithium-rich compound 21 in the coating layer 20 is not too high, resulting in a low residual alkali value of the lithium replenishment material 1, which improves the processing performance and stability of the lithium replenishment material 1. On the other hand, while ensuring that the lithium replenishment material 1 has good processing performance and high stability, the content of the second lithium-rich compound 21 in the coating layer 20 is increased as much as possible so that the lithium replenishment material 1 can provide more lithium ions to offset the irreversible lithium loss caused by the formation of the SEI film, thereby improving the battery energy density.

[0052] In one embodiment, the content of the second lithium-rich compound 21 in the coating layer 20 can be 10%, 15%, 20%, 22%, 25%, 28%, 30%, 33%, 35%, 37%, 40%, 42%, 45%, 48%, or 50%.

[0053] In one embodiment, the coating layer 20 consists of a shell in which the second lithium-rich compound 21 is uniformly distributed.

[0054] In one implementation, the content of the second lithium-rich compound 21 in the coating layer 20 gradually decreases in the direction away from the core 10. That is, along the radial direction of the lithium-supplementing material 1, from the inner surface of the coating layer 20 to the outer surface of the coating layer 20, the content of the second lithium-rich compound 21 gradually decreases. The closer to the outer surface of the lithium-supplementing material 1, the less content of the second lithium-rich compound 21 there is, which can ensure that the lithium-supplementing material 1 has good processing performance and high stability.

[0055] In one embodiment, the coating layer 20 is composed of multiple shell layers, each containing a different content of the second lithium-rich compound 21. The content of the second lithium-rich compound 21 decreases sequentially in the direction away from the core 10. Specifically, the content of the second lithium-rich compound 21 in the shell layers closer to the outer side of the lithium replenishment material 1 is less than the content of the second lithium-rich compound 21 in the shell layers closer to the inner side of the lithium replenishment material 1.

[0056] In one implementation, the thickness of the coating layer 20 is 1-100 nm. The thickness of the coating layer 20 affects the performance of the lithium replenishment material 1. If the coating layer is too thick, the relative volume of the core 10 is small. Since the content of the first lithium-rich compound 11 in the core 10 is greater than the content of the second lithium-rich compound 21 in the coating layer 20, the total number of lithium ions available for offsetting lithium loss in the lithium replenishment material 1 is reduced, thus decreasing the lithium replenishment capacity of the lithium replenishment material 1. If the thickness of the coating layer 20 is too thin, the coating layer 20 is difficult to adhere to the outer surface of the core 10 and is easily damaged, making it difficult for the coating layer 20 to effectively reduce the residual base value of the lithium replenishment material 1.

[0057] In this embodiment, the thickness of the coating layer 20 is limited to the range of 1-100 nm. On the one hand, the relatively large volume of the core 10 ensures that the lithium replenishment material 1 can provide enough lithium ions to offset the irreversible lithium loss caused by the formation of the SEI film, thereby improving the battery energy density. On the other hand, it improves the adhesion between the coating layer 20 and the core 10, allowing the coating layer 20 to better coat the outer surface of the core 10, thereby reducing the residual alkali value of the lithium replenishment material 1 and improving the processing performance and stability of the lithium replenishment material 1.

[0058] In one embodiment, the thickness of the coating layer 20 can be 1nm, 5nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm, 70nm, 75nm, 80nm, 85nm, 90nm, 95nm or 100nm.

[0059] In one implementation, the core 10 further includes a first carbon nanomaterial 12, at least a portion of which is embedded within the first lithium-rich compound 11. The first carbon nanomaterial 12 can improve the conductivity of the lithium-rich material 1, thereby effectively increasing the energy density of the battery. The fact that at least a portion of the first carbon nanomaterial 12 is located within the first lithium-rich compound 11 enhances the bonding ability between the first carbon nanomaterial 12 and the first lithium-rich compound 11, allowing the first carbon nanomaterial 12 to adhere firmly within the first lithium-rich compound 11. The first carbon nanomaterial 12 is not easily peeled off, thus better enhancing the conductivity of the lithium-rich material 1.

[0060] In one embodiment, all of the first carbon nanomaterials 12 are embedded within the first lithium-rich compound 11. Since the first carbon nanomaterials 12 are coated by the first lithium-rich compound 11, they are difficult to peel off from the first lithium-rich compound 11, thus better enhancing the conductivity of the lithium-supplementing material 1.

[0061] In one embodiment, a portion of the first carbon nanomaterial 12 is embedded within the first lithium-rich compound 11, while another portion of the first carbon nanomaterial 12 is located outside the first lithium-rich compound 11. The first carbon nanomaterial 12 connects the interior and exterior of the first lithium-rich compound 11, thereby improving the conductivity of the lithium-supplementing material 1.

[0062] In one embodiment, a portion of the first carbon nanomaterial 12 located outside the first lithium-rich compound 11 is located within the coating layer 20. The first lithium-rich compound 11 connects the first carbon nanomaterial 12 and the coating layer 20, thereby improving the conductivity of the lithium-supplementing material 1 and further enhancing the bonding between the coating layer and the core.

[0063] In one embodiment, a portion of the first carbon nanomaterial 12 located outside the first lithium-rich compound 11 is distributed on the outer surface of the first lithium-rich compound 11.

[0064] In one implementation, the coating layer 20 further includes a second carbon nanomaterial 22, at least a portion of which is embedded within the second lithium-rich compound 21. The second carbon nanomaterial 22 can improve the conductivity of the lithium-rich material 1, thereby effectively increasing the energy density of the battery. The fact that at least a portion of the second carbon nanomaterial 22 is located within the second lithium-rich compound 21 enhances the bonding ability between the second carbon nanomaterial 22 and the second lithium-rich compound 21, allowing the second carbon nanomaterial 22 to adhere firmly within the second lithium-rich compound 21. This prevents the second carbon nanomaterial 22 from being easily peeled off, thus better enhancing the conductivity of the lithium-rich material 1.

[0065] In one embodiment, all of the second carbon nanomaterials 22 are embedded within the second lithium-rich compound 21. Since the second carbon nanomaterials 22 are coated by the second lithium-rich compound 21, they are difficult to peel off from the compound, thus better enhancing the conductivity of the lithium-supplementing material 1.

[0066] In one embodiment, a portion of the second carbon nanomaterial 22 is embedded within the second lithium-rich compound 21, while another portion of the second carbon nanomaterial 22 is located outside the second lithium-rich compound 21. The second carbon nanomaterial 22 connects the interior and exterior of the second lithium-rich compound 21, thereby improving the conductivity of the lithium-supplementing material 1.

[0067] In one embodiment, a portion of the second carbon nanomaterial 22 located outside the second lithium-rich compound 21 is situated within the core 10. The second carbon nanomaterial 22 connects the core 10 and the coating layer 20, thereby improving the conductivity of the lithium-supplementing material 1.

[0068] In one embodiment, a portion of the second carbon nanomaterial 22 located outside the second lithium-rich compound 21 is distributed on the inner surface of the second carbon nanomaterial 22. In another embodiment, a portion of the second carbon nanomaterial 22 located outside the second lithium-rich compound 21 is distributed on the outer surface of the second carbon nanomaterial 22.

[0069] In one implementation, the ratio of the sum of the masses of the first carbon nanomaterial 12 and the second carbon nanomaterial 22 to the sum of the masses of the first lithium-rich compound 11 and the second lithium-rich compound 21 is 0.5% to 15%. The relative content of carbon nanomaterials (i.e., the first carbon nanomaterial 12 and the second carbon nanomaterial 22) and lithium metal compounds (i.e., the first lithium-rich compound 11 and the second lithium-rich compound 21) affects the performance of the lithium replenishment material 1. If the content of carbon nanomaterials is too high, although it can enhance the conductivity of the lithium replenishment material 1, the amount of lithium ions that the lithium replenishment material 1 can provide is reduced, affecting the lithium replenishment capacity of the lithium replenishment material 1. If the content of lithium metal compounds is too high, although it can provide more lithium ions, the conductivity of the lithium replenishment material 1 is poor, reducing the energy density of the battery.

[0070] In this embodiment, the ratio of the sum of the masses of the first carbon nanomaterial 12 and the second carbon nanomaterial 22 to the sum of the masses of the first lithium-rich compound 11 and the second lithium-rich compound 21 is set in the range of 0.5% to 15%. This not only ensures that the lithium replenishment material 1 can provide enough lithium ions to replenish the irreversible lithium loss caused by the formation of the SEI film, but also improves the conductivity of the lithium replenishment material 1.

[0071] In one implementation, the ratio of the sum of the masses of the first carbon nanomaterial 12 and the second carbon nanomaterial 22 to the sum of the masses of the first lithium-rich compound 11 and the second lithium-rich compound 21 can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, or 15%.

[0072] In one implementation, the first lithium-rich compound 11 and the second lithium-rich compound 21 are both the same lithium metal compound. "The same lithium metal compound" means that the type of lithium metal compound is the same; however, the density, content, and other properties of the first lithium-rich compound 11 and the second lithium-rich compound 21 may differ. For example, both the first lithium-rich compound 11 and the second lithium-rich compound 21 are Li₂NiO₂, but the content of the second lithium-rich compound 21 in the coating layer 20 is less than the content of the first lithium-rich compound 11 in the core 10. In this embodiment, the first lithium-rich compound 11 and the second lithium-rich compound 21 use the same lithium metal compound, simplifying the preparation process and facilitating the industrial production of the lithium replenishment material 1.

[0073] In one implementation, the first carbon nanomaterial 12 and the second carbon nanomaterial 22 are both the same carbon nanomaterial. "The same carbon nanomaterial" means that the type of carbon nanomaterial is the same, while other properties such as density and content may differ. For example, both the first carbon nanomaterial 12 and the second carbon nanomaterial 22 are carbon nanotubes, and the content of the second carbon nanomaterial 22 is less than the content of the first carbon nanomaterial 12. In this embodiment, the first carbon nanomaterial 12 and the second carbon nanomaterial 22 use the same carbon nanomaterial, simplifying the preparation process and facilitating the industrial production of the lithium supplement material 1.

[0074] In one implementation, the first carbon nanomaterial 12 includes at least one of carbon nanotubes, carbon nanofibers, carbon nanospheres, and graphene. These types of carbon nanomaterials have stable structures and are not easily stripped, which can better improve the stability of the lithium supplement material 1.

[0075] In one implementation, the second carbon nanomaterial 22 includes at least one of carbon nanotubes, carbon nanofibers, carbon nanospheres, and graphene. These types of carbon nanomaterials have stable structures and are not easily stripped, which can better improve the stability of the lithium supplement material 1.

[0076] In one implementation, both the first carbon nanomaterial 12 and the second carbon nanomaterial 22 are carbon nanotubes. Carbon nanotubes possess excellent electrical conductivity, thereby improving the conductivity of the lithium replenishment material 1. Simultaneously, due to their elongated shape, carbon nanotubes can bind well to the lithium replenishment material 1, enhancing its stability.

[0077] In one implementation, the aspect ratio of the carbon nanotubes is 7-70. The aspect ratio of carbon nanotubes refers to the ratio of the length to the diameter of the carbon nanotube. If the aspect ratio of the carbon nanotubes is too small, it is not conducive to forming a conductive network inside the lithium-rich material 1, and it is not conducive to improving the conductivity of the lithium-rich material 1. If the aspect ratio of the carbon nanotubes is too large, the carbon nanotubes are too long, and it is not easy for the carbon nanotubes to be encapsulated within the first lithium-rich compound 11 and the second lithium-rich compound 21, which increases the difficulty of preparing the lithium-rich material 1.

[0078] In this application, the aspect ratio of carbon nanotubes is set in the range of 7-70. On the one hand, a suitable aspect ratio can improve the conductivity of carbon nanotubes, thereby improving the conductivity of lithium replenishment material 1. On the other hand, a suitable aspect ratio makes it easier for carbon nanotubes to be encapsulated in lithium replenishment material 1, making the preparation process simpler and facilitating the industrial production of lithium replenishment material 1.

[0079] In one embodiment, the aspect ratio of the carbon nanotubes is 7, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65 or 70.

[0080] In one implementation, the carbon nanotubes have a diameter of 30-70 nm. The conductivity of carbon nanotubes is related to their diameter; carbon nanotubes with a suitable diameter have better conductivity, which is more conducive to improving the conductivity of lithium-supplementing material 1.

[0081] In one embodiment, the diameter of the carbon nanotubes is 30nm, 35nm, 40nm, 45nm, 50nm, 55nm, 60nm, 65nm or 70nm.

[0082] In one implementation, the carbon nanotubes have a length of 0.5-2 μm. A length within this range facilitates the formation of a conductive network, thereby improving the conductivity of the lithium-supplementing material 1. Simultaneously, the suitable length of the carbon nanotubes makes the preparation of the lithium-supplementing material 1 easier.

[0083] In one embodiment, the length of the carbon nanotubes is 0.5 μm, 0.55 μm, 0.6 μm, 0.65 μm, 0.7 μm, 0.75 μm, 0.8 μm, 0.85 μm, 0.9 μm, 0.95 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm, 1.9 μm, or 2 μm.

[0084] In one implementation, both the first carbon nanomaterial 12 and the second carbon nanomaterial 22 are carbon nanotubes. At least one carbon nanotube has a portion embedded in the core and another portion embedded in the coating layer. That is, at least one carbon nanotube is simultaneously located in the core 10 and the coating layer 20. The lithium supplement material 1 has multiple carbon nanotubes, some of which are located only in the core 10, and some of which are located only in the coating layer 20. At least one carbon nanotube is simultaneously located in both the core 10 and the coating layer 20. This carbon nanotube connects the core 10 and the coating layer 20, thus improving the conductivity of the lithium supplement material 1.

[0085] In one implementation, the lithium-replenishing material 1 is obtained by lithiation of an intermediate, which is formed by depositing a precursor on a carbon nanomaterial. Lithiation of the precursor yields a first lithium-rich compound 11 and a second lithium-rich compound 21. The precursor can be a metal hydroxide. The intermediate is the carbon nanomaterial after the precursor deposition. Lithiation of the intermediate refers to the reaction of the metal hydroxide in the intermediate with a lithium source to generate a lithium metal compound, which then encapsulates the carbon nanomaterial to form the lithium-replenishing material 1.

[0086] In this application, the precursor grows and deposits continuously with carbon nanomaterials as the core, eventually attaching to the carbon nanomaterials and coating them to form a particulate intermediate. The intermediate is then lithiated to obtain the lithium supplement material 1. This formation method enables the carbon nanomaterials to have high bonding force with both the first lithium-rich compound 11 and the second lithium-rich compound 21, making it less likely for the carbon nanomaterials to fall off, which can better improve the conductivity of the lithium supplement material 1.

[0087] In one implementation, the general structural formula of the first lithium-rich compound 11 is Li 1+x A y O z Where 0 < x < 10, 0 < y < 6, 0 < z < 13, and A is one or more of Ni, Co, Fe, Cu, Mg, Mn, Cr, Zn, Ti, Zr, Nb, and Mo.

[0088] In one embodiment, the first lithium-rich compound 11 is selected from Li8ZrO6, Li5FeO4, Li6MnO4, Li6CoO4, Li2NiO2, Li2CuO2, Li2CoO2, Li2MnO2, Li2Ni 0.5 Mn 1.5 One or more of O4 and Li6ZnO4.

[0089] In one implementation, the general structural formula of the second lithium-rich compound 21 is Li 1+x A y O z Where 0 < x < 10, 0 < y < 6, 0 < z < 13, and A is one or more of Ni, Co, Fe, Cu, Mg, Mn, Cr, Zn, Ti, Zr, Nb, and Mo.

[0090] In one embodiment, the second lithium-rich compound 21 is selected from Li8ZrO6, Li5FeO4, Li6MnO4, Li6CoO4, Li2NiO2, Li2CuO2, Li2CoO2, Li2MnO2, Li2Ni 0.5 Mn 1.5 One or more of O4 and Li6ZnO4.

[0091] In one implementation, the particle size of the lithium replenishment material 1 satisfies the following condition: 1μm ≤ D50 ≤ 25μm. D50 refers to the particle size corresponding to a cumulative particle size distribution percentage of 50% in the lithium replenishment material 1. If the particle size of the lithium replenishment material 1 is too small, it is prone to agglomeration, making it difficult for lithium inside the lithium replenishment material 1 to be extracted when replenishing active lithium to the negative electrode, thus reducing the lithium replenishment effect of the lithium replenishment material 1; while if the particle size of the lithium replenishment material 1 is too large, its dispersibility is poor, which is not conducive to the preparation of the positive electrode sheet.

[0092] In this embodiment, the particle size D50 of the lithium replenishment material 1 is controlled between 1 micrometer and 25 micrometers. This ensures the rapid extraction of lithium ions while also improving the dispersibility of the lithium replenishment material 1, making it easier to use.

[0093] In one embodiment, the particle size D50 of the lithium replenishment material 1 can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, 12.5 μm, 13 μm, 13.5 μm, 14 μm, 14.5 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, or 25 μm.

[0094] In one implementation, the specific surface area of ​​the lithium-supplementing material 1 is 0.1-25 m². 2 / g. In one embodiment, the specific surface area is tested using the BET (Brunauer-Emmett-Teller) specific surface area test method, and the specific surface area is the BET specific surface area. If the specific surface area of ​​the lithium replenishment material 1 is too small, it is not conducive to improving the conductivity and lithium ion extraction and insertion capabilities of the lithium replenishment material 1; if the specific surface area of ​​the lithium replenishment material 1 is too large, the density of the lithium replenishment material 1 is usually low, and the volumetric energy density is low.

[0095] In this embodiment, the specific surface area of ​​the lithium replenishment material 1 is controlled to be between 0.1 and 25 m². 2 Within the range of / g, it can not only improve the conductivity and lithium ion extraction and insertion capabilities of the lithium replenishment material, but also improve the volumetric energy density of lithium replenishment material 1.

[0096] In one embodiment, the specific surface area of ​​the lithium supplement material 1 is 1-10 m². 2 / g.

[0097] In one embodiment, the specific surface area of ​​the lithium replenishing material 1 is 1-4 m². 2 / g.

[0098] In one embodiment, the specific surface area of ​​the lithium-supplementing material can be 0.1 m². 2 / g, 0.2m 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m2 / g, 0.9m 2 / g、1m 2 / g、2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g、9m 2 / g, 10m 2 / g、11m 2 / g、12m 2 / g、13m 2 / g、14m 2 / g, 15m 2 / g, 16m 2 / g、17m 2 / g、18m 2 / g、19m 2 / g、20m 2 / g、21m 2 / g、22m 2 / g、23m 2 / g、24m 2 / g or 25m 2 / g.

[0099] In one implementation, the residual alkali value of lithium replenishment material 1 is 0-3%. The residual alkali value of lithium replenishment material 1 affects its performance. When the residual alkali content of lithium replenishment material 1 is too high, on the one hand, it easily causes gelation of the slurry during the slurry preparation process, resulting in poor slurry flowability, affecting the coating of the slurry, and thus affecting the processing performance of lithium replenishment material 1. At the same time, it also increases the internal resistance of the battery, thereby affecting various battery performance characteristics. On the other hand, a high residual alkali content leads to poor stability of lithium replenishment material 1, deteriorates the high-temperature storage performance of the battery, and causes problems such as gas expansion and performance degradation during battery storage, directly affecting the electrochemical performance of lithium replenishment material 1 and reducing battery safety performance.

[0100] In this application, by reducing the content of the second lithium-rich compound 21 in the coating layer 20, the residual alkali value of the lithium replenishment material 1 is kept in a lower range, thereby improving the processing performance and stability of the lithium replenishment material 1.

[0101] This application provides a method for preparing lithium supplement material 1. The method for preparing lithium supplement material 1 includes steps S1, S2 and S3, as detailed below:

[0102] Step S1: Add the first carbon nanomaterial 12 solution and the first precursor solution to the reactor, and adjust the pH of the solution in the reactor to 9-12 to obtain intermediate I;

[0103] Step S2: The second carbon nanomaterial 22 solution and the second precursor solution are added to the reactor containing intermediate I, and the pH of the solution in the reactor is adjusted to 9-12 to obtain intermediate II. The concentration of the second precursor solution is less than that of the first precursor solution.

[0104] Step S3: Mix intermediate II with lithium source and sinter under an inert atmosphere to obtain lithium supplement material 1.

[0105] In step S1, the first precursor solution is deposited on the first carbon nanomaterial 12 in the form of a first metal hydroxide under alkaline conditions, and intermediate I is the intermediate of the core 10. In step S2, under alkaline conditions, the second precursor solution is co-deposited on intermediate I in the form of a second metal hydroxide and the second carbon nanomaterial 22. Step S2 is used to add an intermediate of the coating layer 20 on the intermediate of the core 10. Intermediate II is the intermediate of the lithium supplement material 1. Since the concentration of the second precursor solution is less than that of the first precursor solution, the content of the second metal hydroxide in the intermediate of the coating layer 20 is less than the content of the first metal hydroxide in the intermediate of the core 10. In step S3, intermediate II is lithiated, that is, the first metal hydroxide and the second metal hydroxide in intermediate II react with the lithium source respectively to generate the first lithium-rich compound 11 and the second lithium-rich compound 21, thereby obtaining the lithium supplement material 1.

[0106] In this embodiment, the concentrations of the first precursor solution and the second precursor solution are adjusted to regulate the content of the first lithium-rich compound 11 in the core 10 and the content of the second lithium-rich compound 21 in the coating layer 20, thereby reducing the residual alkali value of the lithium replenishment material 1. In this application, the first and second metal hydroxides are deposited on the carbon nanomaterials via co-precipitation. This formation method results in high bonding strength between the carbon nanomaterials and both the first and second lithium-rich compounds 11 and 21, making the carbon nanomaterials less prone to detachment and improving the conductivity of the lithium replenishment material 1.

[0107] In one embodiment, the pH of the solution in the reactor is 9-12.

[0108] In one embodiment, the reactor is a ternary reactor.

[0109] In one embodiment, the concentration of the first precursor solution is higher than the concentration of the second precursor solution.

[0110] In one embodiment, the concentration of the first precursor solution is 1-4 mol / L, and the concentration of the second precursor solution is 0.1-1 mol / L.

[0111] In one embodiment, the rate at which the first carbon nanomaterial 12 solution is added to the reactor is 5-50 ml / min, and the rate at which the first precursor solution is added to the reactor is 0.2-1 ml / min.

[0112] In one embodiment, the rate at which the second carbon nanomaterial 22 solution is added to the reactor is 0.1-1 ml / min, and the rate at which the second precursor solution is added to the reactor is 0.2-1 ml / min.

[0113] In one embodiment, the pH of the solution in the reactor is 9-12.

[0114] In one embodiment, the preparation method of lithium supplement material 1 further includes the synthesis of a first carbon nanomaterial 12 solution: the first carbon nanomaterial 12, water, and dispersant are mixed in a mass ratio of (2-11):(1000):(0.4-2.2) to obtain a first carbon nanomaterial 12 solution with a concentration of 2-11 g / L.

[0115] In one embodiment, the preparation method of lithium supplement material 1 further includes the synthesis of a second carbon nanomaterial 22 solution: the second carbon nanomaterial 22, water, and dispersant are mixed in a mass ratio of (0.1-2):(1000):(0.02-4) to obtain a second carbon nanomaterial 22 solution with a concentration of 0.1-2 g / L.

[0116] In one embodiment, the sintering temperature of intermediate II and the lithium source is 700-900°C, and the sintering time is 4-20h.

[0117] In one embodiment, the first precursor solution and the second precursor solution can be at least one of a metal sulfate, carbonate, or chloride.

[0118] In one embodiment, the pH adjusting agent for the solution in the reactor is at least one of ammonia, sodium hydroxide, and potassium hydroxide.

[0119] In one embodiment, the lithium source includes at least one of lithium hydroxide, lithium oxide, lithium oxalate, and lithium carbonate.

[0120] In one embodiment, the inert atmosphere includes one or more of nitrogen, argon, and helium.

[0121] This application provides a positive electrode sheet, which includes the lithium replenishing material 1 as described above, or the lithium replenishing material 1 prepared by the preparation method of the lithium replenishing material 1 as described above.

[0122] This application provides a secondary battery, which includes a negative electrode, a separator, and a positive electrode as described above.

[0123] In one embodiment, the secondary battery is a lithium-ion secondary battery.

[0124] To illustrate the beneficial effects of the method of this application, the following embodiments and comparative examples are also provided.

[0125] Example 1

[0126] This embodiment provides a lithium replenishment material 1, which includes a core and a coating layer. The core includes a first lithium-rich compound 11 and a first carbon nanomaterial 12. The coating layer includes a second lithium-rich compound 21 and a second carbon nanomaterial 22. Both the first lithium-rich compound 11 and the second lithium-rich compound 21 are Li2NiO2, and both the first carbon nanomaterial 12 and the second carbon nanomaterial 22 are carbon nanotubes. The thickness of the coating layer 20 is 10 nm. The content of Li2NiO2 in the core 10 is 90%, and the content of Li2NiO2 in the coating layer 20 is 10%. In the lithium replenishment material, the mass ratio of carbon nanotubes to lithium-rich compound Li2NiO2 is 0.5%.

[0127] The preparation method of lithium supplement material 1 in this embodiment includes the following steps:

[0128] Step 1: Synthesize carbon nanotube solution: Mix carbon nanotubes, water, and sodium dodecyl sulfate at a mass ratio of 5:1000:1 to obtain a high-concentration carbon nanotube solution (i.e., the first carbon nanomaterial 12 solution) with a concentration of 8 g / L; mix carbon nanotubes, water, and sodium dodecyl sulfate at a mass ratio of 1:1000:0.2 to obtain a low-concentration carbon nanotube solution (i.e., the second carbon nanomaterial 22 solution) with a concentration of 1 g / L.

[0129] Step 2: Prepare nickel hydroxide deposited on carbon nanotubes using a co-precipitation method. The high-concentration carbon nanotube solution synthesized in Step 1 is pumped into a ternary reactor at a rate of 5-20 ml / min. Then, a 2 mol / L high-concentration nickel sulfate solution is pumped into the ternary reactor at a rate of 0.2-1 ml / min. Simultaneously, the pH of the solution is adjusted to 9, and high-speed stirring is maintained for a period of time. Then, the low-concentration carbon nanotube solution synthesized in Step 1 is pumped into the ternary reactor at a rate of 0.1-1 ml / min, and a 0.5 mol / L low-concentration nickel sulfate solution is pumped into the ternary reactor at a rate of 0.2-1 ml / min. The pH of the solution is adjusted to 9-12, and high-speed stirring is maintained. This synthesizes a material with a core mainly composed of nickel hydroxide deposited on carbon nanotubes, and a surface with a uniform gradient distribution of nickel hydroxide deposited on carbon nanotubes.

[0130] Step 3: Add lithium source to the material prepared in Step 2 by molar ratio, and sinter at 780℃ for 10h under an inert atmosphere to obtain positive electrode lithium supplement material 1 with Li2NiO2 deposited on carbon nanotubes as the core and Li2NiO2 deposited on carbon nanotubes as the outer surface in a continuous gradient distribution.

[0131] Testing revealed that in lithium replenishment material 1, the D50 particle size was 3.35 μm and the BET specific surface area was 3.5 m². 2 / g.

[0132] Example 2

[0133] The difference from lithium supplement material 1 in Example 1 is that the mass ratio of carbon nanotubes to Li2NiO2 is 15%.

[0134] Example 3

[0135] The difference from the lithium supplement material 1 in Example 1 is that the content of Li2NiO2 in the core 10 is 70% and the content of Li2NiO2 in the coating layer 20 is 30%.

[0136] Example 4

[0137] The difference from the lithium replenishment material 1 in Example 1 is that the thickness of the coating layer 20 is 100 nm.

[0138] Example 5

[0139] The difference between this material and the lithium-supplementing material 1 in Example 1 is that the second carbon nanomaterial 22 is graphite.

[0140] Comparative Example 1

[0141] The difference from Example 1 is that the content of Li2NiO2 in the core 10 in Comparative Example 1 is the same as the content of Li2NiO2 in the coating layer 20.

[0142] The lithium replenishment materials provided in Examples 1-5 and the lithium replenishment material provided in Comparative Example 1 were assembled into positive electrode and lithium-ion battery respectively according to the following methods:

[0143] Positive electrode sheet: The positive electrode lithium supplement material is mixed with lithium manganese iron phosphate at a mass ratio of 5:95 to obtain a mixture. The mixture is then mixed with polyvinylidene fluoride and SP-Li at a mass ratio of 95:3:2 and ball-milled to obtain a positive electrode slurry. The positive electrode slurry is coated on the surface of aluminum foil, rolled, and then vacuum dried at 110°C overnight to obtain the positive electrode sheet.

[0144] Negative electrode: Lithium metal sheet;

[0145] Electrolyte: Ethyl carbonate and ethyl methyl carbonate are mixed in a volume ratio of 3:7, and LiPF6 is added to form an electrolyte with a concentration of 1 mol / L.

[0146] Diaphragm: Polypropylene microporous diaphragm;

[0147] Lithium-ion battery assembly: Lithium-ion batteries are assembled in an inert atmosphere glove box according to the assembly sequence of lithium metal sheet-separator-electrolyte-positive electrode.

[0148] The electrochemical performance of each lithium-ion battery assembled in the above lithium-ion battery examples was tested as shown in Table 1, and the test conditions were as follows:

[0149] Constant current and constant voltage charging, first charge / discharge voltage 2.5-4.3V, current 0.1C, cut-off current 0.01C.

[0150] The relevant performance test results are shown in Table 1 below:

[0151] Table 1 Performance Test Results

[0152]

[0153] As can be seen from the test results of Examples 1-5 and Comparative Example 1 in Table 1, when the Li2NiO2 content in the coating layer is too high, it leads to a decrease in the initial charge specific capacity and initial coulombic efficiency, and also a decrease in the lithium replenishment specific capacity. This is because when the proportion of lithium-rich material in the coating layer is too high, the core Li in Li2NiO2... + The more difficult the extraction, the worse the lithium replenishment effect. In particular, when the Li2NiO2 content in the coating layer is equal to that in the core (Comparative Example 1), the residual alkalinity on the surface of the lithium replenishment material is too high, resulting in relatively poor electrochemical performance.

[0154] Comparing Example 1 and Example 2, it can be seen that when the proportion of carbon nanotubes in the lithium replenishment material is too high, the proportion of Li2NiO2 in the lithium replenishment material will be too low, resulting in a decrease in lithium content and a reduction in lithium replenishment capacity.

[0155] Comparing Examples 1 and 3, it can be seen that when the content of Li2NiO2 in the coating layer increases, the initial coulombic efficiency and capacity retention are not significantly different, but the lithium replenishment capacity and the initial charge capacity decrease.

[0156] Comparing Examples 1 and 4, it can be seen that as the coating thickness increases, the Li in the core lithium replenishment material will increase. + The difficulty in insertion and extraction leads to a decrease in the specific capacity of the first charge, the initial coulombic efficiency, and the specific capacity of the lithium replenishment.

[0157] Comparing Examples 1 and 5, it can be seen that when the carbon material is replaced with graphite, the initial coulombic efficiency and capacity retention rate decrease significantly, but the initial charge capacity and lithium replenishment capacity are not significantly affected.

[0158] The lithium replenishment materials, their preparation methods, positive electrode sheets, and secondary batteries provided in the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and embodiments of this application. The descriptions of the embodiments above are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in specific embodiments and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A lithium supplementation material, characterized in that, The lithium supplementation material includes: The core, including the first lithium-rich compound; A coating layer is applied to the outer surface of the core. The coating layer includes a second lithium-rich compound, and the content of the second lithium-rich compound in the coating layer is less than the content of the first lithium-rich compound in the core. The general structural formula of the first lithium-rich compound and / or the second lithium-rich compound is Li 1+x A y O z Where 0 < x < 10, 0 < y < 6, 0 < z < 13, and A is one or more of Ni, Co, Fe, Cu, Mg, Mn, Cr, Zn, Ti, Zr, Nb, and Mo.

2. The lithium replenishment material according to claim 1, characterized in that, The content of the first lithium-rich compound in the core is 50-90%; and / or The content of the second lithium-rich compound in the coating layer is 10-50%.

3. The lithium replenishment material according to claim 1, characterized in that, In the coating layer, the content of the second lithium-rich compound gradually decreases in the direction away from the core.

4. The lithium replenishment material according to claim 1, characterized in that, The core further includes a first carbon nanomaterial, at least a portion of which is embedded within the first lithium-rich compound; and / or, The coating layer also includes a second carbon nanomaterial, at least a portion of which is embedded within the second lithium-rich compound.

5. The lithium replenishment material according to claim 4, characterized in that, The ratio of the sum of the masses of the first carbon nanomaterial and the second carbon nanomaterial to the sum of the masses of the first lithium-rich compound and the second lithium-rich compound is 0.5% to 15%.

6. The lithium replenishment material according to claim 4, characterized in that, The first lithium-rich compound and the second lithium-rich compound are both the same lithium metal compound; and / or Both the first carbon nanomaterial and the second carbon nanomaterial are the same carbon nanomaterial. and / or The first carbon nanomaterial and the second carbon nanomaterial include at least one of carbon nanotubes, carbon nanofibers, carbon nanospheres and graphene.

7. The lithium replenishment material according to claim 4, characterized in that, Both the first carbon nanomaterial and the second carbon nanomaterial are carbon nanotubes, and the aspect ratio of the carbon nanotubes is 7-70; and / or The carbon nanotubes have a diameter of 30-70 nm; and / or The length of the carbon nanotubes is 0.5-2 μm.

8. The lithium replenishment material according to claim 4, characterized in that, Both the first carbon nanomaterial and the second carbon nanomaterial are carbon nanotubes, with at least one portion of the carbon nanotube embedded in the core and another portion embedded in the coating layer.

9. The lithium replenishment material according to claim 1, characterized in that, The lithium-rich material is obtained by lithiation of an intermediate, which is formed by depositing a precursor on a carbon nanomaterial. The lithiation of the precursor yields the first lithium-rich compound and the second lithium-rich compound.

10. The lithium replenishment material according to claim 1, characterized in that, The thickness of the coating layer is 1-100 nm; and / or The particle size of the lithium supplementation material satisfies: 1μm≤D50≤25μm; and / or The specific surface area of ​​the lithium replenishment material is 0.1-25 m². 2 / g; and / or The residual alkali value of the lithium replenishing material is 0%-3%.

11. A method for preparing a lithium-supplementing material, characterized in that, The preparation method is used to prepare the lithium replenishing material according to any one of claims 1-10, wherein the preparation method of the lithium replenishing material includes: The first carbon nanomaterial solution and the first precursor solution are added to the reactor, and the pH of the solution in the reactor is adjusted to be alkaline to obtain intermediate I. A second carbon nanomaterial solution and a second precursor solution are added to a reactor containing intermediate I, while the pH of the solution in the reactor is adjusted to be alkaline to obtain intermediate II, wherein the concentration of the second precursor solution is less than the concentration of the first precursor solution. The intermediate II is mixed with a lithium source and sintered under an inert atmosphere to obtain a lithium-replenishing material.

12. A positive electrode plate, characterized in that, The positive electrode sheet includes the lithium replenishing material as described in any one of claims 1-10, or the lithium replenishing material prepared by the method for preparing the lithium replenishing material as described in claim 11.

13. A secondary battery, characterized in that, The secondary battery includes a negative electrode, a separator, and a positive electrode as described in claim 12.

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