Lithium supplementing additive, preparation method thereof, positive electrode sheet and lithium ion battery

Abstract

This invention relates to a lithium replenishment additive, its preparation method, a positive electrode sheet, and a lithium-ion battery. The lithium replenishment additive comprises a core and a shell; the core is made of a lithium-rich manganese-based composite material, which includes a lithium-rich manganese-based material matrix and a first solid electrolyte coating layer covering the surface of the lithium-rich manganese-based material matrix; the shell is made of a lithium-rich lithium iron ferrite composite material, which includes a lithium-rich lithium iron ferrite matrix and a second solid electrolyte coating layer covering the surface of the lithium-rich lithium iron ferrite matrix. This invention uses a lithium-rich manganese-based composite material as the core and a lithium-rich lithium iron ferrite composite material as the shell to construct a lithium replenishment additive. This replenishes the active lithium consumed during the initial charge to form the SEI film, while continuously replenishing lithium during subsequent charge and discharge processes, thus improving the battery's cycle performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to lithium replenishment of the positive electrode, and more particularly to a lithium replenishment additive and its preparation method, a positive electrode sheet, and a lithium-ion battery. Background Technology

[0002] The widespread application of lithium-ion batteries in new energy vehicles and energy storage has placed higher demands on their energy density. To compensate for the initial irreversible capacity loss during the first charge and discharge cycle of lithium-ion batteries due to irreversible side reactions such as the formation of a solid electrolyte interphase (SEI) film on the negative electrode surface, and to improve energy density, it is necessary to provide an additional lithium source to the battery system, i.e., lithium replenishment. Lithium replenishment technology is generally divided into negative electrode lithium replenishment and positive electrode lithium replenishment. Negative electrode lithium replenishment typically involves using lithium foil or lithium powder to replenish lithium at the negative electrode, which is not only complex in its preparation process but also poses significant risks. Positive electrode lithium replenishment materials generally employ high-capacity materials. Lithium-rich lithium iron phosphate (Li5FeO4) has attracted widespread attention due to its relatively low production cost and a theoretical specific capacity as high as 867 mAh / g. However, lithium iron ferrite prepared by traditional processes has defects such as poor conductivity, low capacity, and severe gas production. Furthermore, it can only contribute irreversible lithium during the first charge and cannot continuously replenish the active lithium consumed by the repeated rupture and regeneration of the SEI film during subsequent charge and discharge processes.

[0003] CN117558922A discloses a lithium-rich lithium ferrite supplementary material and its preparation method. This lithium-rich lithium ferrite supplementary material comprises doped lithium ferrite and a coral-like carbon-containing coating layer partially or completely covering the surface of the doped lithium ferrite. The coral-like carbon-containing coating layer is obtained by plasma-enhanced chemical vapor deposition (PECVD). The lithium-rich lithium ferrite supplementary material prepared by this invention exhibits good crystallinity and is free of impurities; by partially replacing iron ions in the crystal structure with elements of different valence states and ionic radii, it possesses excellent electrochemical performance; the PECVD-coated carbon layer can improve both the air stability and conductivity of the lithium-rich lithium ferrite material, thus enhancing its performance.

[0004] CN118198536A discloses a lithium-rich lithium ferrite material, comprising core-shell structured particles. Each core-shell particle includes a core, a first coating layer covering the core, and a second coating layer covering the first coating layer. The core is Li5FeO4, the first coating layer is a carbon layer, and the second coating layer is a mixed layer comprising polyethylene oxide and lithium salt. The mass ratio of the first coating layer to the core is (2:100) to (10:100), and the mass ratio of the second coating layer to the core is (3:100) to (13:100). This invention improves the air stability of lithium ferrite materials and also increases the overall ionic conductivity of the electrode.

[0005] CN119905695A discloses a lithium-rich lithium ferrite supplement agent and its synthesis method. The synthesis method involves mixing a solid electrolyte, conductive carbon, and elemental sulfur, followed by low-temperature heat treatment to form a composite mixture. This mixture is then further mixed with lithium-rich lithium ferrite and subjected to low-temperature heat treatment to form a mixed coating layer, thus obtaining the lithium-rich lithium ferrite supplement agent. The sulfur in the mixed coating layer can absorb surface oxygen released during the charging process of lithium-rich lithium ferrite, thereby reducing gas production. The solid electrolyte and conductive carbon can form a conductive network of ions and electrons, avoiding the lithium oxide buildup caused by excessively thick sulfur coating. + Extraction is difficult, leading to a decrease in lithium replenishment capacity. Meanwhile, low-temperature heat treatment allows the melting of elemental sulfur to act as a dispersant and binder, achieving uniform dispersion of the solid electrolyte and conductive carbon, as well as effective coating of the composite mixture. This improves bonding and compatibility, and the resulting mixed coating layer effectively enhances the air stability of the lithium replenishment agent.

[0006] Existing technologies lack a solution to the limitation that lithium-rich lithium iron phosphate (LFP) cannot continuously replenish lithium during subsequent charge-discharge processes after contributing irreversible capacity during the initial charge. Therefore, providing a lithium replenishing additive that can both compensate for the active lithium loss caused by the formation of the SEI film during the initial charge and continuously replenish lithium during subsequent charge-discharge processes is of great significance. Summary of the Invention

[0007] To address the shortcomings of existing technologies, the present invention aims to provide a lithium replenishment additive, its preparation method, a positive electrode sheet, and a lithium-ion battery. The present invention constructs a lithium replenishment additive using a lithium-rich manganese-based composite material as the core and a lithium-rich lithium iron phosphate composite material as the shell. The lithium-rich lithium iron phosphate composite material in the shell contributes to compensate for the irreversible capacity loss during the first charge, making up for the active lithium consumed in the formation of the SEI film during the first charge. The lithium-rich manganese-based composite material in the core continuously replenishes lithium during subsequent charge and discharge processes, improving the battery's cycle performance. Furthermore, by utilizing the synergistic effect of the lithium-rich lithium iron phosphate composite material shell and the lithium-rich manganese-based composite material core, side reactions between the lithium replenishment additive and the electrolyte during formation and subsequent cycling are significantly suppressed, reducing electrolyte consumption and gas generation caused by electrolyte decomposition, thus improving the battery's cycle performance.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a lithium replenishing additive, the lithium replenishing additive comprising a core and a shell; the core is made of a lithium-rich manganese-based composite material, the lithium-rich manganese-based composite material comprising a lithium-rich manganese-based material matrix and a first solid electrolyte coating layer covering the surface of the lithium-rich manganese-based material matrix; the shell is made of a lithium-rich lithium ferrite composite material, the lithium-rich lithium ferrite composite material comprising a lithium-rich lithium ferrite matrix and a second solid electrolyte coating layer covering the surface of the lithium-rich lithium ferrite matrix.

[0010] Lithium-rich lithium iron ferrite (LFP) produces highly oxidizing superoxide dimers during the first charge, which readily undergo nucleophilic reactions with the electrolyte, leading to electrolyte decomposition and gas production. This invention uses a lithium-rich LFP composite material as the outer shell and a lithium-rich manganese-based composite material in its core. Firstly, the transition metal elements in the lithium-rich manganese-based composite material have strong reducing properties, preferentially reducing the superoxide dimers before the electrolyte, thus preemptively consuming the highly oxidizing superoxide dimers and preventing redox reactions with the electrolyte. This reduces electrolyte decomposition and gas production during formation. Secondly, the lithium-rich manganese-based composite material continuously replenishes lithium during subsequent charge and discharge cycles, improving battery cycle performance. Furthermore, placing the lithium-rich manganese-based composite material in the core reduces side reactions between the composite material and the electrolyte during cycling, further enhancing battery cycle performance.

[0011] This invention effectively improves the ionic and electronic conductivity of the lithium iron ferrite matrix and the ionic conductivity of the lithium manganese-based matrix by coating the surfaces of the lithium iron ferrite matrix and the lithium manganese-based matrix with solid electrolyte coating layers, while overcoming the defect of poor air stability of lithium iron ferrite.

[0012] In this invention, the chemical formula of the lithium-rich manganese-based material matrix is ​​Li. 1+x (Nia Co b Mn c D d O2, 0 < x < 0.33, a + b + c + d = 1 - x, D is a doping element, the doping element includes any one or at least two combinations of Al, Mg, La, Ti, and Zr elements, 0.005 ≤ d ≤ 0.05.

[0013] Preferably, in the lithium supplementation additive, the mass ratio of the lithium-rich manganese-based composite material in the core to the lithium-rich lithium iron phosphate composite material in the shell is (0.1~0.2):(0.8~0.9).

[0014] Preferably, the chemical formula of the lithium iron phosphate matrix is ​​Li. 5+i Fe j Al k O4, j+k=1, 0.05≤i≤0.55, 0.7≤j≤1, 0≤k≤0.3.

[0015] Preferably, the material of the first solid electrolyte coating layer includes the first solid electrolyte.

[0016] Preferably, the material of the second solid electrolyte coating layer includes conductive carbon and the second solid electrolyte.

[0017] Preferably, the chemical formulas of the first solid electrolyte and the second solid electrolyte are each independently Li. 1+ m Al m Ti 2-m (PO4)3, 0.2≤m≤0.5.

[0018] Preferably, the conductive carbon includes any one or a combination of at least two of carbon black, graphene, or carbon nanotubes.

[0019] Preferably, in the lithium-rich manganese-based composite material, the mass percentage of the first solid electrolyte is 1 wt.% to 2 wt.%.

[0020] Preferably, in the lithium-rich lithium iron ferrite composite material, the mass percentage of the second solid electrolyte is 0.5 wt.% to 2.5 wt.%.

[0021] Preferably, in the lithium iron ferrite composite material, the mass percentage of conductive carbon is 1 wt.% to 2.5 wt.%.

[0022] Preferably, the D50 particle size of the lithium-rich manganese-based material matrix is ​​8μm~12μm.

[0023] Preferably, the D50 particle size of the lithium iron phosphate matrix is ​​0.8 μm to 2 μm.

[0024] In a second aspect, the present invention provides a method for preparing the lithium supplementation additive as described in the first aspect, the method comprising:

[0025] (1) According to the mass ratio, the lithium-rich manganese-based material matrix and the first solid electrolyte are mixed and sintered to prepare the lithium-rich manganese-based composite material.

[0026] (2) According to the mass ratio, the lithium-rich lithium iron oxide matrix, conductive carbon and the second solid electrolyte are mixed and sintered to prepare the lithium-rich lithium iron oxide composite material.

[0027] (3) Mix the lithium-rich manganese-based composite material and the lithium-rich lithium iron oxide composite material according to the mass ratio, and heat treat to prepare the lithium supplementation additive.

[0028] The order of steps (1) and (2) is not important.

[0029] Preferably, the mixing in steps (1) to (3) each independently comprises solid-phase mixing.

[0030] Preferably, the temperature of the first sintering is 500℃~600℃.

[0031] Preferably, the first sintering time is 5h to 10h.

[0032] Preferably, the second sintering temperature is 400℃~500℃.

[0033] Preferably, the second sintering time is 5h to 10h.

[0034] Preferably, the atmosphere for the first sintering includes air.

[0035] Preferably, the atmosphere for the second sintering includes an inert atmosphere.

[0036] Preferably, the heat treatment temperature is 300℃~400℃.

[0037] Preferably, the heat treatment time is 2h to 5h.

[0038] Preferably, the atmosphere for the heat treatment includes an inert atmosphere.

[0039] Thirdly, the present invention provides a positive electrode sheet comprising the lithium supplementation additive as described in the first aspect.

[0040] Fourthly, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a lithium-replenishing additive as described in the first aspect, or comprising a positive electrode as described in the third aspect.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) This invention uses a lithium-rich manganese-based composite material as the core and a lithium-rich lithium iron phosphate composite material as the shell to construct a lithium replenishing additive. The lithium-rich lithium iron phosphate composite material in the shell can contribute to the irreversible capacity loss during the first charge and compensate for the active lithium consumed by the formation of the SEI film during the first charge. The lithium-rich manganese-based composite material in the core can continuously replenish lithium during subsequent charge and discharge processes, thereby improving the cycle performance of the battery. Furthermore, by utilizing the synergistic cooperation between the lithium-rich lithium iron phosphate composite material shell and the lithium-rich manganese-based composite material core, the side reactions between the lithium replenishing additive and the electrolyte during formation and subsequent cycling are significantly suppressed, reducing electrolyte consumption and gas generation caused by electrolyte decomposition, thereby improving the cycle performance of the battery.

[0043] (2) The present invention effectively improves the ionic conductivity and electronic conductivity of the lithium iron ferrite matrix and the ionic conductivity of the lithium manganese-based material matrix by coating the surface of the lithium iron ferrite matrix and the lithium manganese-based material matrix respectively with solid electrolyte coating layers, while overcoming the defect of poor air stability of lithium iron ferrite. Attached Figure Description

[0044] Figure 1 This is an SEM image of the lithium supplementation additive provided in Example 1.

[0045] Figure 2 Li in Example 1 1.2 Ni 0.13 Co 0.13 Mn 0.53 Al 0.01 SEM image of the O2 matrix.

[0046] Figure 3 This is a SEM image of the lithium-rich manganese-based composite material in Example 1.

[0047] Figure 4 Li in Example 1 5.2 Fe 0.8 Al 0.2 SEM image of the O4 matrix.

[0048] Figure 5 This is a SEM image of the lithium-rich lithium ferrite composite material in Example 1.

[0049] Figure 6 The first charge-discharge curve of the battery prepared with the lithium-replenishing additive provided in Example 1 is shown.

[0050] Figure 7 This is a cycle performance diagram of the battery prepared with the lithium-replenishing additive provided in Example 1.

[0051] Figure 8The first charge-discharge curves of the battery prepared with the lithium-replenishing additive provided in Comparative Example 1 are shown.

[0052] Figure 9 This is a graph showing the cycle performance of the battery prepared with the lithium-replenishing additive provided in Comparative Example 1. Detailed Implementation

[0053] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0054] The "range" disclosed in this invention can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific range. This type of range definition can include or exclude endpoints; any endpoint can be independently included or excluded, and they can be arbitrarily combined, meaning any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for specific parameters, it is understood that ranges of 60~110 and 80~120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this invention, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0" and "5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is described as an integer ≥2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For instance, when a parameter is described as an integer selected from "2~10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0055] In this invention, "a combination of at least two" refers to a quantity greater than or equal to two, unless otherwise specified. For example, "any combination of one or at least two" means one or more or more items. It can be understood that when referring to "a combination of at least two," it refers to any suitable combination of multiple items, that is, a combination of "at least two" items carried out in a manner that does not conflict with and enables the implementation of this invention.

[0056] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0057] The term "embodiment" as used in this invention means that a specific feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of the invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a mutually exclusive, independent, or alternative embodiment. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described in this invention can be combined with other embodiments.

[0058] Those skilled in the art will understand that the order in which the steps are written in the methods of the various embodiments does not imply a strict execution order. The detailed execution order of each step should be determined by its function and possible internal logic. Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, but are preferably performed sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), meaning that step (c) can be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0059] In this invention, open-ended technical features or solutions described using terms such as "comprising" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, A includes a1, a2, and a3. Unless otherwise specified, it may also include other members or exclude additional members. This can be considered as providing both technical features or solutions where "A is composed of a1, a2, and a3" or "A is selected from a1, a2, and a3," and technical features or solutions where "A includes not only a1, a2, and a3, but also other members."

[0060] In this invention, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. These arbitrary and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "A and / or B" represents a group consisting of A, B, and "a combination of A and B". "Containing A and / or B" can mean "containing A, containing B, and containing A and B", or "containing A, containing B, or containing A and B", and can be appropriately understood according to the context.

[0061] In this invention, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," etc., serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on the quantity.

[0062] In this invention, "optional" means that something is optional, that is, it refers to either "with" or "without". If there are multiple "optional" options in a technical solution, unless otherwise specified, and there are no contradictions or mutual constraints, then each "optional" option is independent.

[0063] In this invention, "room temperature" generally refers to 4℃~35℃, and can refer to 20℃±5℃. In some embodiments of this invention, room temperature refers to 20℃~30℃.

[0064] In one specific embodiment, the present invention provides a lithium replenishing additive, the lithium replenishing additive comprising a core and a shell; the core is made of a lithium-rich manganese-based composite material, the lithium-rich manganese-based composite material comprising a lithium-rich manganese-based material matrix and a first solid electrolyte coating layer covering the surface of the lithium-rich manganese-based material matrix; the shell is made of a lithium-rich lithium ferrite composite material, the lithium-rich lithium ferrite composite material comprising a lithium-rich lithium ferrite matrix and a second solid electrolyte coating layer covering the surface of the lithium-rich lithium ferrite matrix.

[0065] Lithium-rich lithium iron phosphate (LFP) produces highly oxidizing superoxide dimers during the first charge, which readily undergo nucleophilic reactions with the electrolyte, leading to electrolyte decomposition and gas production. This invention uses a lithium-rich LFP composite material as the outer shell and a lithium-rich manganese-based composite material in its core. Firstly, the transition metal elements in the lithium-rich manganese-based composite material have strong reducing properties, preferentially reducing the superoxide dimers before the electrolyte, thus preemptively consuming the highly oxidizing superoxide dimers and preventing redox reactions with the electrolyte, thereby reducing electrolyte decomposition and gas production during formation. Secondly, the lithium-rich manganese-based composite material can continuously replenish lithium during subsequent charge and discharge processes, improving battery cycle performance. Furthermore, placing the lithium-rich manganese-based composite material in the core reduces side reactions between the composite material and the electrolyte during cycling, further enhancing battery cycle performance.

[0066] This invention constructs a lithium-replenishing additive using a lithium-rich manganese-based composite material as the core and a lithium-rich lithium iron phosphate composite material as the shell. The lithium-rich lithium iron phosphate composite material in the shell can contribute to the irreversible capacity loss during the first charge, compensating for the active lithium consumed in the formation of the SEI film during the first charge. The lithium-rich manganese-based composite material in the core can continuously replenish lithium during subsequent charge and discharge processes, improving the cycle performance of the battery. Furthermore, by utilizing the synergistic effect of the lithium-rich lithium iron phosphate composite material shell and the lithium-rich manganese-based composite material core, the side reactions between the lithium-replenishing additive and the electrolyte during formation and subsequent cycling are significantly suppressed, reducing electrolyte consumption and gas generation caused by electrolyte decomposition, thereby improving the cycle performance of the battery.

[0067] This invention effectively improves the ionic and electronic conductivity of the lithium iron ferrite matrix and the ionic conductivity of the lithium manganese-based matrix by coating the surfaces of the lithium iron ferrite matrix and the lithium manganese-based matrix with solid electrolyte coating layers, while overcoming the defect of poor air stability of lithium iron ferrite.

[0068] In the lithium replenishment additive provided by this invention, the lithium-rich manganese-based composite material in the core and the lithium-rich lithium iron ferrite composite material in the shell maintain a suitable mass ratio, which can ensure that the lithium-rich lithium iron ferrite composite material forms an intact coating layer on the surface of the lithium-rich manganese-based composite material, thereby reducing the contact between the lithium-rich manganese-based composite material and the electrolyte and giving full play to the role of the lithium-rich manganese-based cathode material in continuous lithium replenishment.

[0069] In this invention, the chemical formula of the lithium-rich manganese-based material matrix is ​​Li. 1+x (Ni a Co b Mn c D d O2, 0 < x < 0.33, for example, it can be 0.1, 0.15, 0.2, 0.25, 0.3 or 0.33, a + b + c + d = 1 - x, D is a dopant element, the dopant element includes any one or at least two combinations of Al, Mg, La, Ti and Zr elements, 0.005 ≤ d ≤ 0.05, for example, it can be 0.005, 0.01, 0.015, 0.02, 0.025, 0.03, 0.035, 0.04, 0.045 or 0.05.

[0070] In some embodiments, the mass ratio of the lithium-rich manganese-based composite material in the core to the lithium-rich lithium iron ferrite composite material in the shell in the lithium supplementation additive is (0.1~0.2):(0.8~0.9), for example, it can be 0.1:0.9, 0.12:0.88, 0.14:0.86, 0.16:0.84, 0.18:0.82 or 0.2:0.8.

[0071] This invention introduces excess lithium into a lithium-rich lithium iron oxide matrix and simultaneously introduces dopant element Al to replace Fe, which helps the lithium-rich lithium iron oxide composite material maintain structural stability during the delithiation process.

[0072] In some embodiments, the chemical formula of the lithium iron phosphate matrix is ​​Li. 5+i Fe j Al k O4, j+k=1, 0.05≤i≤0.55, for example, it can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5 or 0.55, 0.7≤j≤1, for example, it can be 0.7, 0.75, 0.8, 0.85, 0.9, 0.95 or 1, 0≤k≤0.3, for example, it can be 0, 0.05, 0.1, 0.15, 0.2, 0.25 or 0.3.

[0073] In some embodiments, the material of the first solid electrolyte coating layer includes the first solid electrolyte.

[0074] In some embodiments, the material of the second solid electrolyte coating layer includes conductive carbon and the second solid electrolyte.

[0075] This invention utilizes solid electrolyte coating layers to separately coat lithium-rich manganese-based material substrates and lithium-rich lithium iron phosphate substrates, which improves the electronic conductivity, ionic conductivity, and air stability of the lithium-replenishing additive. Specifically, coating the lithium-rich manganese-based material substrate with a first solid electrolyte enhances its ionic conductivity and suppresses side reactions between the substrate and the electrolyte, ensuring continuous capacity delivery during subsequent charge and discharge cycles and improving battery cycle performance. Coating the lithium-rich lithium iron phosphate substrate with a second solid electrolyte and conductive carbon simultaneously effectively improves both its electronic and ionic conductivity, enhances lithium-ion transport rates, and improves interfacial stability.

[0076] In some embodiments, the first solid electrolyte and the second solid electrolyte each have the independent chemical formula Li. 1+m Al m Ti 2-m (PO4)3, 0.2≤m≤0.5, for example, it can be 0.2, 0.25, 0.3, 0.35, 0.4, 0.45 or 0.5.

[0077] In some embodiments, the conductive carbon includes any one or a combination of at least two of carbon black, graphene, or carbon nanotubes.

[0078] In this invention, the coating amount of the solid electrolyte affects the integrity and uniformity of the solid electrolyte coating on the surface of the lithium-rich manganese-based material matrix or the lithium-rich lithium iron ferrite matrix. If the coating amount is too large, the coating layer will be too thick, resulting in an increase in electronic impedance, which is not conducive to electron transport and increases polarization. If the coating amount is too small, it will not be able to fully improve the ionic conductivity of the lithium-rich manganese-based material matrix and the lithium-rich lithium iron ferrite matrix, and it will not be able to effectively improve the air stability of the lithium-rich lithium iron ferrite.

[0079] In some embodiments, the mass percentage of the first solid electrolyte in the lithium-rich manganese-based composite material is 1 wt.% to 2 wt.%, for example, it can be 1 wt.%, 1.2 wt.%, 1.4 wt.%, 1.6 wt.%, 1.8 wt.% or 2 wt.%.

[0080] In some embodiments, the mass percentage of the second solid electrolyte in the lithium-rich lithium iron ferrite composite material is 0.5 wt.% to 2.5 wt.%, for example, it can be 0.5 wt.%, 1 wt.%, 1.5 wt.%, 2 wt.% or 2.5 wt.%.

[0081] In some embodiments, the mass percentage of conductive carbon in the lithium iron ferrite composite material is 1 wt.% to 2.5 wt.%, for example, it can be 1 wt.%, 1.3 wt.%, 1.5 wt.%, 1.7 wt.%, 1.9 wt.%, 2.1 wt.%, 2.3 wt.% or 2.5 wt.%.

[0082] In some embodiments, the D50 particle size of the lithium-rich manganese-based material matrix is ​​8μm to 12μm, for example, it can be 8μm, 9μm, 10μm, 11μm or 12μm.

[0083] In some embodiments, the D50 particle size of the lithium iron phosphate matrix is ​​0.8 μm to 2 μm, for example, it can be 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm or 2 μm.

[0084] In another specific embodiment, the present invention provides a method for preparing the lithium supplementation additive as described in the foregoing specific embodiment, the preparation method comprising:

[0085] (1) According to the mass ratio, the lithium-rich manganese-based material matrix and the first solid electrolyte are mixed and sintered to prepare the lithium-rich manganese-based composite material.

[0086] (2) According to the mass ratio, the lithium-rich lithium iron oxide matrix, conductive carbon and the second solid electrolyte are mixed and sintered to prepare the lithium-rich lithium iron oxide composite material.

[0087] (3) Mix the lithium-rich manganese-based composite material and the lithium-rich lithium iron oxide composite material according to the mass ratio, and heat treat to prepare the lithium supplementation additive.

[0088] The order of steps (1) and (2) is not important.

[0089] In some implementations, the mixing in steps (1) to (3) each independently includes solid-phase mixing.

[0090] In this invention, the temperature of the first sintering affects the crystallinity of the first solid electrolyte, the density of the first solid electrolyte coating layer, and promotes the interfacial reaction between the first solid electrolyte and the lithium-rich manganese-based material matrix, ensuring the formation of a uniform, dense, and continuous nanocrystalline coating layer.

[0091] In some embodiments, the temperature of the first sintering is 500°C to 600°C, for example, it can be 500°C, 510°C, 520°C, 530°C, 540°C, 550°C, 560°C, 570°C, 580°C, 590°C or 600°C.

[0092] In some embodiments, the first sintering time is 5h to 10h, for example, it can be 5h, 6h, 7h, 8h, 9h or 10h.

[0093] In this invention, the temperature of the second sintering affects the crystallinity of the second solid electrolyte, the density of the second solid electrolyte coating layer, and promotes the interfacial reaction between the second solid electrolyte coating layer and the lithium iron phosphate matrix, forming a uniform, dense and continuous nanocrystalline coating layer.

[0094] In some embodiments, the second sintering temperature is 400°C to 500°C, for example, it can be 400°C, 410°C, 420°C, 430°C, 440°C, 450°C, 460°C, 470°C, 480°C, 490°C or 500°C.

[0095] In some embodiments, the second sintering time is 5h to 10h, for example, it can be 5h, 6h, 7h, 8h, 9h or 10h.

[0096] In some embodiments, the atmosphere of the first sintering includes air.

[0097] In some embodiments, the atmosphere for the second sintering includes an inert atmosphere. The inert atmosphere includes nitrogen and / or an inert gas, preferably argon and / or helium.

[0098] In this invention, the temperature of heat treatment affects the density of the lithium iron ferrite composite shell itself, as well as its interfacial reaction with the lithium manganese-based composite core, ensuring that the lithium iron ferrite can form a uniform and dense coating layer.

[0099] In some embodiments, the heat treatment temperature is 300°C to 400°C, for example, it can be 300°C, 310°C, 320°C, 330°C, 340°C, 350°C, 360°C, 370°C, 380°C, 390°C or 400°C.

[0100] In some embodiments, the heat treatment time is 2h to 5h, for example, it can be 2h, 2.5h, 3h, 3.5h, 4h, 4.5h or 5h.

[0101] In some embodiments, the atmosphere for the heat treatment includes an inert atmosphere.

[0102] In this invention, the inert atmosphere includes nitrogen and / or an inert gas, preferably argon and / or helium.

[0103] In yet another embodiment, the present invention provides a positive electrode sheet comprising the lithium supplementation additive as described in the preceding embodiment.

[0104] In another specific embodiment, the present invention provides a lithium-ion battery, the lithium-ion battery comprising a lithium supplementation additive as described in one of the preceding specific embodiments, or comprising a positive electrode sheet as described in yet another specific embodiment.

[0105] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0106] Example 1

[0107] This embodiment provides a lithium replenishment additive, which includes a core and a shell; the core is made of a lithium-rich manganese-based composite material, which includes Li 1.2 Ni 0.13 Co 0.13 Mn 0.53 Al 0.01 O2 matrix and Li 1.2 Ni 0.13 Co 0.13 Mn 0.53 Al 0.01 O2 substrate surface, Li with a mass percentage of 1.6 wt.% 1.3 Al 0.3 Ti 1.7 (PO4)3 coating layer; the Li 1.2 Ni 0.13 Co 0.13Mn 0.53 Al 0.01 The D50 particle size of the O2 matrix is ​​10 μm; the shell material includes lithium iron ferrite composite material, which includes Li... 5.2 Fe 0.8 Al 0.2 O4 matrix, and Li 5.2 Fe 0.8 Al 0.2 The surface of the O4 matrix is ​​composed of Li at a mass percentage of 1.2 wt.%. 1.3 Al 0.3 Ti 1.7 A coating layer consisting of (PO4)3 and carbon black with a mass percentage of 2 wt.%; the Li 5.2 Fe 0.8 Al 0.2 The D50 particle size of the O4 matrix is ​​1.2 μm; in the lithium supplementation additive, the mass ratio of the lithium-rich manganese-based composite material in the core to the lithium-rich lithium iron ferrite composite material in the shell is 0.15:0.85.

[0108] The preparation method of the lithium supplement additive includes:

[0109] (1) According to the mass ratio, solid-phase mixed Li 1.2 Ni 0.13 Co 0.13 Mn 0.53 Al 0.01 O2 matrix and Li 1.3 Al 0.3 Ti 1.7 A lithium-rich manganese-based composite material was prepared by sintering (PO4)3 solid electrolyte at 560°C for 6 hours in air atmosphere.

[0110] (2) According to the mass ratio, solid-phase mixed Li 5.2 Fe 0.8 Al 0.2 O4 matrix, carbon black and Li 1.3 Al 0.3 Ti 1.7 (PO4)3 solid electrolyte was sintered at 420℃ for 5 h under argon atmosphere to prepare lithium-rich lithium ferrite composite material.

[0111] (3) The lithium-rich manganese-based composite material prepared in step (1) and the lithium-rich lithium ferrite composite material prepared in step (2) are mixed according to the mass ratio and heat-treated at 350°C for 3 hours under an argon atmosphere to obtain the lithium supplementation additive.

[0112] In this embodiment, the SEM image of the lithium supplementation additive is as follows: Figure 1As shown, the lithium-rich lithium iron phosphate composite material is observed to coat the surface of the lithium-rich manganese-based composite material. In this embodiment, Li... 1.2 Ni 0.13 Co 0.13 Mn 0.53 Al 0.01 O2 matrix, lithium-rich manganese-based composite materials, Li 5.2 Fe 0.8 Al 0.2 SEM images of the O4 matrix and the lithium iron ferrite composite material are shown below. Figure 2 , Figure 3 , Figure 4 and Figure 5 As shown.

[0113] Example 2

[0114] This embodiment provides a lithium replenishment additive, which includes a core and a shell; the core is made of a lithium-rich manganese-based composite material, which includes Li 1.17 Ni 0.21 Co 0.08 Mn 0.53 Al 0.01 O2 matrix and Li 1.17 Ni 0.21 Co 0.08 Mn 0.53 Al 0.01 O2 substrate surface, Li with a mass percentage of 1 wt.% 1.23 Al 0.23 Ti 1.77 (PO4)3 coating layer; the Li 1.17 Ni 0.21 Co 0.08 Mn 0.53 Al 0.01 The D50 particle size of the O2 matrix is ​​8 μm; the shell material includes lithium iron ferrite composite material, which includes Li... 5.05 Fe 0.7 Al 0.3 O4 matrix and Li coated thereon 5.05 Fe 0.7 Al 0.3 The surface of the O4 substrate is composed of Li at a mass percentage of 0.5 wt.%. 1.23 Al 0.23 Ti 1.77 A coating layer consisting of (PO4)3 and graphene at a mass percentage of 1 wt.%; in the lithium supplementation additive, the mass ratio of the lithium-rich manganese-based composite material in the core to the lithium-rich lithium iron phosphate composite material in the shell is 0.2:0.8; the Li 5.05 Fe0.7 Al 0.3 The D50 particle size of the O4 matrix is ​​0.8 μm.

[0115] The preparation method of the lithium supplement additive includes:

[0116] (1) According to the mass ratio, solid-phase mixed Li 1.17 Ni 0.21 Co 0.08 Mn 0.53 Al 0.01 O2 matrix and Li 1.23 Al 0.23 Ti 1.77 A lithium-rich manganese-based composite material was prepared by sintering (PO4)3 solid electrolyte at 500°C for 5 hours in air atmosphere.

[0117] (2) According to the mass ratio, solid-phase mixed Li 5.05 Fe 0.7 Al 0.3 O4 matrix, graphene and Li 1.23 Al 0.23 Ti 1.77 (PO4)3 solid electrolyte was sintered at 400℃ for 5 h under nitrogen atmosphere to prepare lithium-rich lithium ferrite composite material.

[0118] (3) The lithium-rich manganese-based composite material prepared in step (1) and the lithium-rich lithium ferrite composite material prepared in step (2) are mixed according to the mass ratio and heat-treated at 300°C for 2 hours under a nitrogen atmosphere to obtain the lithium supplementation additive.

[0119] Example 3

[0120] This embodiment provides a lithium replenishment additive, which includes a core and a shell; the core is made of a lithium-rich manganese-based composite material, which includes Li 1.2 Ni 0.13 Co 0.13 Mn 0.52 Al 0.02 O2 matrix and Li 1.2 Ni 0.13 Co 0.13 Mn 0.52 Al 0.02 O2 substrate surface, Li with a mass percentage of 2 wt.% 1.47 Al 0.47 Ti 1.53 (PO4)3 coating layer; the Li 1.2 Ni 0.13 Co 0.13 Mn 0.52 Al0.02 The D50 particle size of the O2 matrix is ​​12 μm; the shell material includes lithium iron ferrite composite material, which includes Li... 5.55 Fe 0.9 Al 0.1 O4 matrix and Li coated thereon 5.55 Fe 0.9 Al 0.1 The surface of the O4 matrix is ​​composed of Li with a mass percentage of 2.5 wt.%. 1.47 Al 0.47 Ti 1.53 A coating layer consisting of (PO4)3 and carbon black with a mass percentage of 2.5 wt.%; in the lithium-supplementing additive, the mass ratio of the lithium-rich manganese-based composite material in the core to the lithium-rich lithium iron phosphate composite material in the shell is 0.1:0.9; the Li 5.55 Fe 0.9 Al 0.1 The D50 particle size of the O4 matrix is ​​2 μm.

[0121] The preparation method of the lithium supplement additive includes:

[0122] (1) According to the mass ratio, solid-phase mixed Li 1.2 Ni 0.13 Co 0.13 Mn 0.52 Al 0.02 O2 matrix and Li 1.47 Al 0.47 Ti 1.53 A lithium-rich manganese-based composite material was prepared by sintering (PO4)3 solid electrolyte at 600℃ for 10 h in air atmosphere.

[0123] (2) According to the mass ratio, solid-phase mixed Li 5.55 Fe 0.9 Al 0.1 O4 matrix, carbon black and Li 1.47 Al 0.47 Ti 1.53 (PO4)3 solid electrolyte was sintered at 500℃ for 10h under argon atmosphere to prepare lithium-rich lithium ferrite composite material.

[0124] (3) The lithium-rich manganese-based composite material prepared in step (1) and the lithium-rich lithium ferrite composite material prepared in step (2) are heat-treated at 400°C for 5 hours under an argon atmosphere according to the mass ratio to obtain the lithium supplementation additive.

[0125] Example 4

[0126] This embodiment provides a lithium supplementation additive, wherein the lithium-rich lithium iron phosphate matrix is ​​Li. 5.55Except for FeO4, everything else is the same as in Example 1.

[0127] Example 5

[0128] This embodiment provides a lithium supplement additive, which is the same as in Example 1 except that the mass ratio of lithium-rich manganese-based composite material in the core to lithium-rich lithium iron ferrite composite material in the shell is 0.25:0.75.

[0129] Example 6

[0130] This embodiment provides a lithium supplement additive, which is the same as in Example 1 except that the mass ratio of lithium-rich manganese-based composite material in the core to lithium-rich lithium iron ferrite composite material in the shell is 0.05:0.95.

[0131] Example 7

[0132] This embodiment provides a lithium supplementation additive, which, in addition to coating the Li... 1.2 Ni 0.13 Co 0.13 Mn 0.53 Al 0.01 Li on the surface of O2 matrix 1.3 Al 0.3 Ti 1.7 Except for the (PO4)3 coating layer having a mass percentage content of 0.5 wt.%, all other aspects are the same as in Example 1.

[0133] Example 8

[0134] This embodiment provides a lithium supplementation additive, which, in addition to coating the Li... 1.2 Ni 0.13 Co 0.13 Mn 0.53 Al 0.01 Li on the surface of O2 matrix 1.3 Al 0.3 Ti 1.7 Except for the (PO4)3 coating layer having a mass percentage content of 2.5 wt.%, all other aspects are the same as in Example 1.

[0135] Example 9

[0136] This embodiment provides a lithium supplementation additive, which, in addition to coating the Li... 5.2 Fe 0.8 Al 0.2 Li on the surface of O4 matrix 1.3 Al 0.3 Ti 1.7 Except for the (PO4)3 coating layer having a mass percentage content of 0.25 wt.%, all other aspects are the same as in Example 1.

[0137] Example 10

[0138] This embodiment provides a lithium supplementation additive, which, in addition to coating the Li... 5.2 Fe 0.8 Al 0.2 Li on the surface of O4 matrix 1.3 Al 0.3 Ti 1.7 Except for the (PO4)3 coating layer having a mass percentage content of 3 wt.%, all other contents are the same as in Example 1.

[0139] Example 11

[0140] This embodiment provides a lithium supplement additive, which is the same as that in Example 1 except that the sintering temperature in step (1) is 450°C.

[0141] Example 12

[0142] This embodiment provides a lithium supplement additive, which is the same as that in Example 1 except that the sintering temperature in step (1) is 650°C.

[0143] Example 13

[0144] This embodiment provides a lithium supplement additive, which is the same as that in Example 1 except that the sintering temperature in step (2) is 350°C.

[0145] Example 14

[0146] This embodiment provides a lithium supplement additive, which is the same as that in Example 1 except that the sintering temperature in step (2) is 550°C.

[0147] Example 15

[0148] This embodiment provides a lithium supplement additive, which is the same as that in Example 1 except that the heat treatment temperature in step (3) is 280°C.

[0149] Example 16

[0150] This embodiment provides a lithium supplement additive, which is the same as that in Example 1 except that the heat treatment temperature in step (3) is 420°C.

[0151] Comparative Example 1

[0152] This comparative example provides a lithium supplementation additive, wherein the lithium supplementation additive is Li5FeO4.

[0153] Comparative Example 2

[0154] This comparative example provides a lithium supplementation additive, which is the lithium-rich lithium ferrite composite material prepared in step (2) of Example 1.

[0155] Comparative Example 3

[0156] This comparative example provides a lithium supplementation additive that, except for the core, only contains Li. 1.2 Ni 0.13 Co 0.13 Mn 0.53 Al 0.01 O2 matrix, shell consists only of Li 5.2 Fe 0.8 Al 0.2 O4 matrix and Li-coated matrix 5.2 Fe 0.8 Al 0.2 The carbon black on the surface of the O4 matrix, except that no solid electrolyte is added in steps (1) and (2), is the same as in Example 1.

[0157] Performance testing:

[0158] The lithium-supplementing additives provided in all the above embodiments and comparative examples were dispersed in NMP with lithium iron phosphate cathode material, conductive carbon black, and polyvinylidene fluoride at a mass ratio of 1.8:88.2:5:5 to prepare a cathode slurry. The cathode slurry was then coated onto the surface of carbon-coated aluminum foil to prepare a cathode sheet. Using graphite as the anode, lithium iron phosphate power-type electrolyte, and a polypropylene separator, a lithium-ion soft-pack battery was assembled, and the battery's electrical performance was tested.

[0159] The pouch cell was charged and discharged once at 0.1C rate within a voltage range of 2V to 4.2V at 25℃. The initial discharge specific capacity and initial efficiency of the battery were tested. Then, the battery was cycled 500 times at 1C rate within a voltage range of 2.3V to 3.75V at 45℃. The cycle capacity retention rate of the battery was tested. The test results are shown in Table 1. The initial charge and discharge curves of the battery prepared with the lithium-replenishing additive provided in Example 1 are shown in Table 1. Figure 6 See the cycle performance diagram. Figure 7 The first charge-discharge curves of the battery prepared with the lithium-replenishing additive provided in Comparative Example 1 are shown below. Figure 8 See the cycle performance diagram. Figure 9 .

[0160] The volume V1 of the lithium-ion pouch battery before the formation process and the volume V2 after the formation process were tested by the water displacement method. The formation process refers to the first charge and discharge of the lithium-ion pouch battery after it is assembled. The volume growth rate was calculated according to V%=(V2-V1) / V1 to characterize the gas production. The test results are shown in Table 1.

[0161] Table 1

[0162]

[0163] In summary, based on the test results of Examples 1 to 3 and Comparative Examples 1 to 3 in Table 1, this invention constructs a lithium replenishing additive using a lithium-rich manganese-based composite material as the core and a lithium-rich lithium iron phosphate composite material as the shell. The lithium-rich lithium iron phosphate composite material in the shell contributes to the irreversible capacity loss during the first charge, compensating for the active lithium consumed in the formation of the SEI film during the first charge. At the same time, the lithium-rich manganese-based composite material in the core can continuously replenish lithium during subsequent charge and discharge processes, improving the cycle performance of the battery. Furthermore, by utilizing the synergistic cooperation between the lithium-rich lithium iron phosphate composite material shell and the lithium-rich manganese-based composite material core, the gas generation caused by the side reaction between the lithium replenishing additive and the electrolyte during the formation process is significantly suppressed, reducing electrolyte consumption and improving the cycle performance of the battery.

[0164] Based on the test results of Examples 1 and 4, the present invention, by performing Al doping on a lithium-rich lithium iron ferrite matrix, helps the lithium-rich lithium iron ferrite composite material maintain structural stability during the delithiation process, improves the material's first efficiency and cycle performance, and reduces gas production.

[0165] Based on the test results of Examples 1, 5, and 6, maintaining a suitable mass ratio between the lithium-rich manganese-based composite material in the core and the lithium-rich lithium iron ferrite composite material in the shell ensures that the lithium-rich lithium iron ferrite composite material forms an intact coating layer on the surface of the lithium-rich manganese-based composite material. This reduces the contact between the lithium-rich manganese-based composite material and the electrolyte, fully leveraging the continuous lithium replenishment function of the lithium-rich manganese-based cathode material. Otherwise, it would be impossible to simultaneously improve the discharge specific capacity, cycle performance, and safety performance of the composite material.

[0166] According to the test results of Examples 1, 7, and 10, if the content of the solid electrolyte coating layer on the surface of the lithium-rich manganese-based material matrix or the lithium-rich lithium iron ferrite matrix is ​​too small, the ionic conductivity of the lithium-rich manganese-based material matrix and the lithium-rich lithium iron ferrite matrix cannot be sufficiently improved, and the air stability of the lithium-rich lithium iron ferrite cannot be effectively improved, which is not conducive to the improvement of cycle performance and the gas production increases significantly. If the content of the solid electrolyte coating layer on the surface of the lithium-rich manganese-based material matrix or the lithium-rich lithium iron ferrite matrix is ​​too large, the coating layer is too thick, which leads to an increase in electronic impedance, which is not conducive to electron transport, increases polarization, is not conducive to the improvement of discharge specific capacity, and continuous lithium replenishment, resulting in a decrease in cycle performance.

[0167] Based on the test results of Examples 1, 11, and 14, in steps (1) and (2), a suitable sintering temperature is more conducive to improving the crystallinity of the solid electrolyte, the density of the solid electrolyte coating layer, and promoting the interfacial reaction between the solid electrolyte and the lithium-rich manganese-based material matrix or the lithium-rich lithium iron ferrite matrix. This ensures the formation of a uniform, dense, and continuous nanocrystalline coating layer, optimizes ionic conductivity, suppresses the occurrence of side reactions between the matrix material and the electrolyte, and improves the air stability of lithium-rich lithium iron ferrite. If the sintering temperature in steps (1) and (2) is too high or too low, it will lead to a decrease in the first-time efficiency of the prepared composite material, a decrease in the discharge specific capacity, a decrease in cycle performance, and a significant increase in gas production.

[0168] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A lithium supplement additive, characterized in that, The lithium supplement additive includes a core and a shell; The core material includes a lithium-rich manganese-based composite material, which includes a lithium-rich manganese-based material matrix and a first solid electrolyte coating layer covering the surface of the lithium-rich manganese-based material matrix. The outer shell is made of lithium-rich lithium iron ferrite composite material, which includes a lithium-rich lithium iron ferrite matrix and a second solid electrolyte coating layer covering the surface of the lithium-rich lithium iron ferrite matrix. In the lithium supplement additive, the mass ratio of the lithium-rich manganese-based composite material in the core to the lithium-rich lithium ferrite composite material in the shell is (0.1~0.2):(0.8~0.9).

2. The lithium supplement additive as described in claim 1, characterized in that, The chemical formula of the lithium-rich lithium iron phosphate matrix is ​​Li 5+ i Fe j Al k O4, j+k=1, 0.05≤i≤0.55, 0.7≤j≤1, 0≤k≤0.3; And / or, the material of the first solid electrolyte coating layer includes the first solid electrolyte; And / or, the material of the second solid electrolyte coating layer includes conductive carbon and the second solid electrolyte.

3. The lithium supplement additive as described in claim 2, characterized in that, The chemical formulas of the first solid electrolyte and the second solid electrolyte are each independently Li. 1+m Al m Ti 2-m (PO4)3, 0.2≤m≤0.5; And / or, the conductive carbon includes any one or a combination of at least two of carbon black, graphene, or carbon nanotubes; And / or, in the lithium-rich manganese-based composite material, the mass percentage of the first solid electrolyte is 1 wt.%~2 wt.%; And / or, in the lithium-rich lithium iron phosphate composite material, the mass percentage of the second solid electrolyte is 0.5 wt.% to 2.5 wt.%; And / or, in the lithium-rich lithium iron ferrite composite material, the mass percentage of conductive carbon is 1 wt.% to 2.5 wt.%; And / or, the D50 particle size of the lithium-rich manganese-based material matrix is ​​8 μm to 12 μm; And / or, the D50 particle size of the lithium iron phosphate matrix is ​​0.8 μm to 2 μm.

4. A method for preparing a lithium supplement additive as described in any one of claims 1 to 3, characterized in that, The preparation method includes: (1) According to the mass ratio, the lithium-rich manganese-based material matrix and the first solid electrolyte are mixed and sintered to prepare the lithium-rich manganese-based composite material. (2) According to the mass ratio, the lithium-rich lithium iron oxide matrix, conductive carbon and the second solid electrolyte are mixed and sintered to prepare the lithium-rich lithium iron oxide composite material. (3) Mix the lithium-rich manganese-based composite material and the lithium-rich lithium iron oxide composite material according to the mass ratio, and heat treat to prepare the lithium supplementation additive. The order of steps (1) and (2) is not important.

5. The preparation method according to claim 4, characterized in that, The mixing described in steps (1) to (3) each independently includes solid-phase mixing.

6. The preparation method according to claim 4, characterized in that, The first sintering temperature is 500℃~600℃; And / or, the first sintering time is 5h~10h; And / or, the second sintering temperature is 400℃~500℃; And / or, the second sintering time is 5h~10h; And / or, the atmosphere of the first sintering includes air; And / or, the atmosphere for the second sintering includes an inert atmosphere.

7. The preparation method according to claim 4, characterized in that, The heat treatment temperature is 300℃~400℃; And / or, the heat treatment time is 2h~5h; And / or, the atmosphere for the heat treatment includes an inert atmosphere.

8. A positive electrode plate, characterized in that, The positive electrode includes the lithium supplementation additive as described in any one of claims 1 to 3.

9. A lithium-ion battery, characterized in that, The lithium-ion battery includes the lithium-replenishing additive as described in any one of claims 1 to 3, or includes the positive electrode as described in claim 8.

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