Lithium supplementing material, preparation method thereof, positive electrode sheet and secondary battery

Abstract

A lithium replenishment material and its preparation method, a positive electrode sheet, and a secondary battery are disclosed. The lithium replenishment material includes a core; the core includes a lithium-rich compound doped with element A, which is a metallic element; the core also includes ion vacancies formed by element A replacing the metallic element in the lithium-rich compound; ion vacancies are formed by doping element A into the core of the lithium replenishment material; oxygen generated during charging is adsorbed by the ion vacancies, and the oxygen is converted into lattice oxygen during discharging, thus suppressing the generation of gas in the secondary battery during operation; at the same time, the doped element A can also regulate the electronic structure in the lithium replenishment material, improve its electronic conductivity, reduce the decomposition potential and interface resistance of the lithium replenishment material, thereby improving the lithium-ion transport rate.

Description

Technical Field

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

[0002] During the first charge and discharge process of a lithium-ion battery, a large amount of solid electrolyte interface film is generated on the surface of the negative electrode, which consumes the limited lithium ions and electrolyte in the battery, causing irreversible capacity loss, reducing the energy density of the lithium-ion secondary battery and the charge and discharge efficiency of the electrode material, and limiting the application of lithium-ion batteries.

[0003] In existing technologies, lithium-ion batteries compensate for the initial irreversible capacity loss by adding lithium-ion replenishing materials to the cathode material. However, existing lithium-ion replenishing materials tend to generate gas during the first charge, which further leads to a continuous decline in the lifespan of the lithium-ion battery during cycling and may cause safety issues.

[0004] Therefore, there is an urgent need to develop a cathode lithium replenishment material that can replenish lithium in lithium-ion cathode materials while suppressing gas production. Summary of the Invention

[0005] The purpose of this application is to provide a lithium supplement material and its preparation method, a positive electrode sheet, and a secondary battery.

[0006] This application provides the following technical solution:

[0007] In a first aspect, this application provides a lithium replenishment material, which includes a core comprising a lithium-rich compound doped with element A, wherein element A is a metallic element; the core also includes ion vacancies formed by the substitution of the metallic element in the lithium-rich compound by element A.

[0008] This application involves doping the core of a lithium replenishment material with element A, which replaces some of the metal elements in the lithium-rich compound. This allows ion vacancies to form within the core of the material. These ion vacancies can adsorb oxygen generated by the lithium-rich compound during charging and convert it into lattice oxygen during discharging. This prevents oxygen generated in the lithium replenishment material from escaping from the core and reacting with the electrolyte, thus suppressing gas generation during battery operation. Simultaneously, the doped element A can also regulate the electronic structure of the lithium replenishment material, increasing its electronic conductivity, reducing its decomposition potential and interfacial resistance, thereby improving the lithium-ion transport rate. Therefore, the lithium replenishment material provided in this application combines the advantages of low gas production and good lithium replenishment effect, showing promising application prospects.

[0009] In one embodiment, the number of ion vacancies near the outer surface of the core is greater than the number of ion vacancies near the core. The advantage of having a greater number of ion vacancies near the outer surface is that more ion vacancies are placed in locations where oxygen is more easily formed and released, thereby utilizing these ion vacancies to adsorb the generated oxygen and preventing oxygen from escaping from the core.

[0010] In one embodiment, the lithium-rich compound has the structural formula including Li x0 M y O z and Li x1 A x2 M y O z Where M is a transition metal element, 1 < x0 ≤ 10, 1 < x1 < 10, 0 < x2 ≤ 2, x0 = x1 + x2, 0 < y ≤ 6, 0 < z ≤ 13; and / or, lithium-rich compounds include those doped with element A whose ionic radius is greater than or equal to that of element M, and whose ionic radius is less than or equal to that of element Li.

[0011] In one embodiment, the lithium-rich compound has the structural formula including Li x M y0 O z and Li x M y1 A y2 O z Where M is a transition metal element, 1 < x ≤ 10, 0 < y0 ≤ 6, 0 < y1 < 6, 0 < y2 ≤ 1.2, y0 = y1 + y2, 0 < z ≤ 13; and / or, lithium-rich compounds include those doped with element A whose ionic radius is less than or equal to that of element M.

[0012] In one embodiment, the ionic radius of element A is less than or equal to the ionic radius of element M. Since element A is suitable for replacing the original position of element M, selecting element A with a smaller ionic radius than element M for doping increases the doping rate of element A (a higher content of element A per unit volume). This makes it easier to utilize the ion vacancies generated by element A to adsorb more oxygen, thereby further reducing oxygen release. Simultaneously, the increased content of A ions (element A) in the core enhances the structural stability of the core; understandably, the increased number of ions per unit volume results in a more stable overall structure for the lithium supplementation material.

[0013] In one embodiment, the lithium replenishment material satisfies the ratio m1:m2:m3 = 100:(0.1~20):(0.1~25), where m1 is the molar amount of the lithium-rich compound, m2 is the molar amount of element A near the core, and m3 is the molar amount of element A near the outer surface of the core. Satisfying this ratio ensures that the content of element A in the lithium replenishment material is moderate, thus forming sufficient ion vacancies while also ensuring that the lithium replenishment material has a sufficient lithium content. Furthermore, satisfying this ratio also ensures that the number of ion vacancies on the core surface always exceeds the number of ion vacancies in the bulk phase.

[0014] In one embodiment, the element A near the core is designated as element A1, and the element A near the outer surface of the core is designated as element A2. The elements A1 and A2 may be the same or different. By doping the core with two or more metal elements, not only can the structural stability and purity of the lithium replenishment material be improved, but the lithium-ion transport rate within the material can also be increased.

[0015] In one embodiment, the lithium replenishment material further includes a coating layer covering the outer surface of the core. The coating layer is a metal compound layer and includes the element A. By providing a coating layer of a metal compound containing element A, not only can more element A be provided to the core to form ion vacancies, but the formed coating layer also helps to reduce the erosion of the core by external moisture and reduce the reaction between lithium-rich compounds and external moisture.

[0016] In one embodiment, the particle size D50 of the lithium replenishment material is 0.5 μm to 100 μm;

[0017] In one embodiment, the specific surface area of ​​the lithium replenishing material is 0.1 m². 2 / g~60m 2 / g.

[0018] Secondly, this application provides a method for preparing a lithium replenishing material, comprising: mixing an M source and a Li source and sintering them to obtain a lithium replenishing material, wherein the M source and the Li source react to generate a lithium-rich compound; mixing the lithium replenishing material and an A source in a mass ratio and sintering them to obtain a lithium replenishing material doped with element A, wherein element A is a metallic element.

[0019] Thirdly, this application also provides a positive electrode sheet, the positive electrode sheet comprising a current collector and an active material layer disposed on the current collector, the active material layer comprising a positive electrode material and a lithium supplement material as described in any one of the embodiments of the first aspect, or the active material layer comprising a lithium supplement material obtained by a method for preparing a positive electrode material and a lithium supplement material as described in any one of the embodiments of the second aspect.

[0020] Fourthly, this application also provides a secondary battery, the secondary battery comprising a negative electrode, a separator, and the positive electrode described in the third aspect. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0022] Figure 1 This is a schematic cross-sectional view of the lithium replenishment material in one embodiment;

[0023] Figure 2 This is a schematic cross-sectional view of the lithium replenishment material in another embodiment;

[0024] Figure 3 This is a flowchart of a method for preparing a lithium-supplementing material in one embodiment;

[0025] Figure 4 This is a flowchart of a method for preparing lithium-supplementing materials in another embodiment;

[0026] Figure 5 This is a flowchart of a method for preparing lithium-supplementing materials in another embodiment;

[0027] Figure 6 The graph shows the gas production rate measured in the lithium-ion batteries assembled from Examples 1-6 and Comparative Example 1. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0029] It should be noted that when a component is said to be "fixed" to another component, it can be directly on the other component or it can be in a middle component. When a component is said to be "connected" to another component, it can be directly connected to the other component or it may be in a middle component.

[0030] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in this application's specification is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used in this application includes any and all combinations of one or more of the associated listed items.

[0031] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0032] Firstly, this application provides a lithium supplementation material, please refer to... Figure 1 The lithium replenishment material includes a core 10; the core 10 includes a lithium-rich compound, which is doped with element A, which is a metal element; the core 10 also includes ion vacancies 11, which are formed by replacing the metal element in the lithium-rich compound with element A.

[0033] Specifically, the core 10 of the lithium replenishment material can mainly be composed of lithium-rich compounds. These lithium-rich compounds are the core of the lithium replenishment material, providing lithium ions, and their structural formula is not specifically limited. Optionally, the core 10 can be spherical, near-spherical, or other irregular shapes. By adding lithium-rich compounds as the lithium replenishment material to the electrode core 10, it acts as a "sacrificial agent" during the first charging cycle, releasing as many lithium ions as possible at once to replenish the irreversible lithium ions consumed in the formation of the SEI film at the negative electrode. This maintains an ample supply of lithium ions within the battery system, improving the battery's initial efficiency and overall electrochemical performance.

[0034] In one embodiment, the lithium-rich compound has the structural formula Li x M y O z Wherein, 1 < x ≤ 10, 0 < y ≤ 6, 0 < z ≤ 13; M is a transition metal element, specifically, element M can be one or more of Ni, Co, Fe, Cu, Mg, Mn, Cr, Zn, Ti, Zr, etc. In specific embodiments, the lithium-rich compound can be Li5FeO4, Li6MnO4, Li6CoO4, Li6ZnO4, Li2NiO2, Li2CuO2, Li2CoO2, Li2MnO2, Li2Ni 0.5 Mn 1.5 O4, Li2Ni 0.5 Cu 0.5 At least one of O2, etc. It should be noted that some of the above-mentioned lithium-rich compounds can be directly used as lithium-rich cathode materials, such as Li2NiO2, Li2CuO2, Li2CoO2, Li2MnO2, and Li2Ni. 0.5Mn 1.5 O4.

[0035] Optionally, the lithium-rich compound is doped with element A, which is a metallic element. Element A can be one or more of the following: Ni, Mo, Co, Fe, Cu, Mg, Mn, Cr, Zn, Ti, Zr, Hf, Nb, Ta, and Ge. Element A specifically replaces some of the metallic elements (such as Li and / or M) in the lithium-rich compound. For example, in a lithium-rich compound with the structural formula Li₂NiO₂, element A can be Mo, which can replace the original Ni element, thus forming a Mo-doped lithium-rich compound.

[0036] The core 10 also includes ion vacancies 11, which are formed by the substitution of elements in the lithium-rich compound by element A. Understandably, when the valence state of the doped element A is different from that of the metal element in the lithium-rich compound, ion vacancies 11 will be generated in the lithium replenishment material due to the valence state imbalance.

[0037] For example, the structural formula of a lithium-rich compound is Li₂NiO₂, where element A can be element Mo, which can replace the original Ni element, thus forming a Mo-doped lithium-rich compound; since the nickel ion in the lithium-rich compound is divalent (Ni... 2+ Molybdenum ions are hexavalent (Mo). 6+ However, due to insufficient oxygen ions to balance the doped ions (A element), ion vacancies 11 are formed inside the core 10. Ion vacancies 11 can adsorb oxygen generated by the lithium-rich compound itself during charging and convert oxygen into lattice oxygen during discharging. This prevents oxygen generated in the lithium replenishment material from escaping from the core 10, avoiding the reaction of oxygen escaping from the core 10 with the electrolyte, thereby suppressing the generation of gas in the secondary battery during operation.

[0038] This application involves doping the core 10 of a lithium replenishment material with element A, thereby replacing some of the metal elements in the lithium-rich compound. This allows ion vacancies 11 to form within the core 10. These ion vacancies 11 can adsorb oxygen generated by the lithium-rich compound during charging and convert it into lattice oxygen during discharge. This prevents oxygen generated in the lithium replenishment material from escaping from the core 10, avoiding reactions between the escaping oxygen and the electrolyte, thus suppressing gas generation during battery operation. Simultaneously, the doped element A can regulate the electronic structure of the lithium replenishment material, increasing its electronic conductivity, reducing its decomposition potential and interfacial resistance, thereby improving the lithium-ion transport rate. Therefore, the lithium replenishment material provided in this application combines the advantages of low gas production and good lithium replenishment effect, showing promising application prospects.

[0039] The core 10 can be spherical or ellipsoidal in shape, and can include a surface layer and a bulk phase. The surface layer can be the outer surface of the core 10, and the bulk phase can be the portion extending inward from the outer surface. It is understood that "surface layer" and "bulk phase" are merely terms describing the specific structural relationship of the core 10; the surface layer and bulk phase are connected and there is no clear dividing line to distinguish them. In the following text, the surface layer refers to the portion of the core 10 near the outer surface, and the bulk phase refers to the portion of the core 10 near the core.

[0040] For example, the radius of the core is R, and the portion from the core to the outer surface with a radius of (9 / 10)*R to (4 / 5)*R is the bulk phase, with the remaining portion being the surface layer. See the detailed description for reference. Figure 1 In the diagram, the area outside the dashed line represents the surface layer, and the area inside the dashed line represents the bulk layer. It should be noted that since there is no clear boundary between the surface and bulk layers within the kernel, the dashed lines in the diagram are for illustrative purposes only and do not represent that the actual kernel structure is two layers.

[0041] In one embodiment, along the direction from the core of the core 10 outwards, the number of ion vacancies 11 near the outer surface of the core 10 is greater than the number of ion vacancies 11 near the core of the core 10. Based on the above-described surface layer and bulk phase, the number of ion vacancies 11 located on the surface layer of the core 10 is greater, while the number of ion vacancies 11 located on the bulk phase (near the core) is less. Optionally, the ion vacancies 11 located on the bulk phase are uniformly distributed (i.e., the number of ion vacancies at each point on the bulk phase is the same), and the number of ion vacancies 11 located on the surface layer is greater than the number of ion vacancies 11 located on the bulk phase.

[0042] Understandably, since most existing lithium replenishment materials are spherical, the closer to the outer surface, the easier it is for lattice oxygen to escape after combining and forming oxygen (the closer to the outer surface, the shorter the path for oxygen to escape, thus reducing the difficulty of oxygen formation and escape). The advantage of having a larger number of ion vacancies 11 near the outer surface of the core 10 is that more ion vacancies 11 are placed in locations where oxygen is more easily formed and escaped, thereby utilizing the ion vacancies 11 to adsorb the generated oxygen and preventing oxygen from escaping from the core 10.

[0043] Optionally, a core 10 with a greater number of surface ion vacancies 11 than bulk ion vacancies 11 can be prepared by a two-stage doping method. For example, when preparing lithium-rich compounds using Li and M sources, an A source (i.e., an A element precursor) can be pre-added to the precursor to ensure a uniform A element distribution within the prepared lithium-replenishing material; this step is the first doping. Then, the prepared lithium-replenishing material is mixed and sintered again with the A source. Since the lithium-replenishing material is now formed, A element can only be doped by penetrating inward from the outer surface of the lithium-replenishing material, thus allowing for the doping of more A element in the surface layer; this step is the second doping.

[0044] In one implementation method, please refer to Figure 1 The number of ion vacancies 11 gradually increases along the direction from the core of the core 10 to the outer surface. Preferably, the number of ion vacancies 11 increases in a gradient along the direction from the core of the core 10 to the outer surface. For example, when the core 10 of the lithium-supplementing material is spherical, the number of ion vacancies 11 increases with the increase of radius from the center of the sphere to the outer surface. Furthermore, the number of ion vacancies 11 reaches its maximum at the outer surface of the core 10.

[0045] In one embodiment, element A is doped at the Li site in the lithium-rich compound, and element A has a different valence state than element Li; and / or, element A is doped at the M site in the lithium-rich compound, and element A has a different valence state than element M.

[0046] Specifically, element A is doped in small amounts in the lithium-rich compound, so the doping of element A in this application differs from that in existing ternary or multi-element lithium-supplementing materials. In existing technologies, ternary or multi-element lithium-supplementing materials are materials in which transition metal elements are combined in a certain proportion and sintered with lithium elements to form materials with internal valence equilibrium, lacking a structure with ion vacancies.

[0047] Therefore, when element A is used as a small dopant, it can be doped at the Li site and / or the M site in the lithium-rich compound. For example, in a lithium-rich compound with the structural formula Li₂NiO₂, element A can be Mo, and Mo can be doped at the Ni site. In other embodiments, element A doped at the Li site can be Cu. 2+ Mg 2+ Zr 4+ Zn 2+ Hf 4+ And so on. It is understandable that element A, whether doped at the Li site or the M site, should be different from the doped element and have a different valence state.

[0048] Optionally, the lithium-rich compound can be doped with two types of aluminum (A), namely A1 and A2. Furthermore, the doping positions of A1 and A2 elements are different. For example, in a lithium-rich compound with the structural formula Li2NiO2, A1 can be Mg, and A2 can be Mo. Mg can be doped at the Li site, and Mo can be doped at the Ni site. By doping the lithium-rich compound with two different metal elements, the structural stability and purity of the lithium-replenishing material can be improved, while simultaneously increasing the lithium-ion transport rate within the material.

[0049] In one embodiment, the lithium-rich compound has the structural formula including Li x M y0 O z and Li x M y1 A y2 O z 1 < x ≤ 10, 0 < y0 ≤ 6, 0 < y1 < 6, 0 < y2 ≤ 1.2, y0 = y1 + y2, 0 < z ≤ 13. Specifically, this application adds a small amount of element A into the core through doping and uses element A to replace part of the element M. Therefore, at least two lithium-rich compound structures will appear in the core, namely, the undoped lithium-rich compound (Li... x M y0 O z ) and lithium-rich compounds with doping (Li x M y1 A y2 O z ).

[0050] In one embodiment, the lithium-rich compound includes an ionic dopant of element A with an ionic radius less than or equal to that of element M. For example, the lithium-rich compound has the structural formula Li₂NiO₂, and Ni... 2+ The ionic radius is 0.069 nm, and the doped Mo 6+ The ionic radius is 0.059 nm.

[0051] Understandably, since element A is suitable for replacing the original position of element M, using element A, with an ionic radius smaller than that of element M, for doping increases the doping rate of element A (a higher content of element A per unit volume). This makes it easier to utilize the ion vacancies created by element A to adsorb more oxygen, thereby further reducing oxygen release. Simultaneously, the increased content of A ions (element A) in the core enhances the structural stability of the core; understandably, the increased number of ions per unit volume results in a more stable overall structure for the lithium supplementation material.

[0052] In one embodiment, the lithium-rich compound has the structural formula including Li x0M y O z and Li x1 A x2 M y O z 1 < x0 ≤ 10, 1 < x1 < 10, 0 < x2 ≤ 2, x0 = x1 + x2, 0 < y ≤ 6, 0 < z ≤ 13. Specifically, this application adds a small amount of element A into the core through doping and uses element A to replace part of the element Li. Therefore, at least two lithium-rich compound structures will appear in the core, namely, the undoped lithium-rich compound (Li... x0 M y O z ) and lithium-rich compounds with doping (Li x1 A x2 M y O z ).

[0053] In one embodiment, the lithium-rich compound includes an ionic radius of element A that is greater than or equal to the ionic radius of element M, and an ionic radius of element A that is less than or equal to the ionic radius of element Li. Specifically, when the ionic radius of element A is greater than the ionic radius of element M, element A cannot be doped into the M site, so it can be doped into the Li site.

[0054] In one embodiment, the lithium replenishment material satisfies m1:m2:m3 = 100:(0.1~20):(0.1~25), where m1 is the molar amount of the lithium-rich compound, m2 is the molar amount of element A near the core, and m3 is the molar amount of element A near the outer surface of the core.

[0055] Specifically, the ratio of m1:m2:m3 can be, but is not limited to, 100:0.1:0.5, 100:0.5:1, 100:0.5:5, 100:1:2, 100:1:10, 100:3:5, 100:5:10, 100:10:20, 100:10:25, 100:15:20, and 100:20:25. Meeting these ratios ensures that the content of element A in the lithium supplement material is appropriate, creating enough ion vacancies while also ensuring sufficient lithium content. Furthermore, meeting these ratios ensures that the number of ion vacancies on the core surface layer always exceeds the number of ion vacancies in the bulk phase.

[0056] When the doping amount of element A in the lithium replenishment material is less than the above-mentioned proportion (either in the surface layer or bulk phase), the insufficient doping of element A results in fewer ion vacancies in the lithium replenishment material, leading to fewer sites for oxygen adsorption and a greater amount of oxygen removal, thus failing to effectively suppress gas production. When the doping amount of element A in the lithium replenishment material is greater than the above-mentioned proportion (either in the surface layer or bulk phase), the lithium content in the lithium replenishment material decreases, which is detrimental to achieving efficient lithium replenishment.

[0057] In one implementation method, please refer to Figure 2 The ion vacancies include cation vacancies 111 and anion vacancies 112. Specifically, based on the above embodiments, it is known that the doped element A should have a different valence state than the replaced element M. Therefore, the selection of element A has two possibilities: 1) the valence state of the A ion (element A) is higher than that of the M ion (element); 2) the valence state of the A ion (element A) is lower than that of the M ion (element).

[0058] Therefore, in this application, the ion vacancy formed when the valence state of A ion (A element) is higher than that of M ion (element) is called cation vacancy 111; and the ion vacancy formed when the valence state of A ion (A element) is lower than that of M ion (element) is called anion vacancy 112.

[0059] For example, the structural formula of a lithium-rich compound is Li5FeO4, where element A can be Mo, and Mo is doped at the Fe site. Since the iron ion is in the trivalent state (Fe... 3+ Molybdenum ions are in a positive hexavalent oxidation state (Mo). 6+ Therefore, the ion vacancy formed in the core 10 is a cation vacancy 111.

[0060] Optionally, the lithium-rich compound has the structural formula Li5FeO4, where element A can be Ni, and Ni is doped at the Fe site. Since the iron ion is in the trivalent state (Fe... 3+ Nickel ions are divalent (Ni...) 2+ Therefore, the ion vacancy formed in kernel 10 is anion vacancy 112.

[0061] Therefore, the ion vacancies formed in the core 10 can be either cation vacancies 111 or anion vacancies 112. Of course, if the core 10 is doped with two different elements, the core 10 can contain either cation vacancies 111 or anion vacancies 112.

[0062] By forming cation vacancies 111 in the core 10, the binding energy between metal ions and oxygen ions can be enhanced, thereby reducing lattice distortion; by forming anion vacancies 112 in the core 10, not only can the adsorption force on lattice oxygen be improved, preventing lattice oxygen from combining to form oxygen and being released, but the electronic conductivity of the lithium supplement material can also be improved.

[0063] In one embodiment, the ratio R of the number of cation vacancies 111 to the number of anion vacancies 112 satisfies: 1 ≤ R ≤ 20. By controlling the number of cation vacancies 111 to be no less than the number of anion vacancies 112, oxygen can be adsorbed using cation vacancies 111, while further reducing lattice distortion in the lithium replenishment material and ensuring the structural stability of the lithium replenishment material.

[0064] In one implementation, the A element near the core of the kernel 10 is called the A1 element, and the A element near the outer surface of the kernel 10 is called the A2 element. The A1 element and the A2 element may be the same or different.

[0065] Specifically, the lithium-rich compound can be doped with two or more types of element A, namely element A1 and element A2. Furthermore, the doping locations of element A1 and element A2 are different. Element A1 can be doped in the bulk phase, while element A2 can be doped in the surface layer.

[0066] Preferably, the A1 and A2 elements are different. For example, in the lithium-rich compound with the structural formula Li2NiO2, the A1 element can be Co, and the A2 element can be Mo. The Co element can be doped in the bulk phase, and the Mo element can be doped in the surface layer.

[0067] By doping the core 10 with two or more metal elements, not only can the structural stability and purity of the lithium replenishment material be improved, but the lithium ion transport rate in the lithium replenishment material can also be increased.

[0068] In one embodiment, the lithium replenishment material further includes a coating layer 20, which coats the outer surface of the core 10. The coating layer 20 is a metal compound layer and includes element A. Specifically, the coating layer 20 may be composed of a metal compound, and the metal element in the metal compound is element A. The metal compound includes, but is not limited to, at least one of oxides, hydroxides, chlorides, carbonates, sulfates, nitrates, and oxalates.

[0069] The role of the metal compound layer can be to provide the doped alumina (A) element to the core 10. For example, after the core 10 is prepared (at which point the core 10 may contain a small amount of A), the metal compound containing A is then sintered together with the core 10, so that the metal compound can cover the outer surface of the core 10 to form a coating layer 20. The A element in the coating layer 20 can penetrate into the core 10 (from the outer surface of the core 10 towards the core), thereby further doping the core 10 with more A element to form more ion vacancies.

[0070] Understandably, since the A element in the coating layer 20 permeates from the outer surface of the core 10 towards the core, there is more A element on the outer surface of the core 10 compared to the core of the core 10. As a result, the number of ion vacancies near the outer surface of the core 10 is greater than the number of ion vacancies near the core of the core 10.

[0071] By setting a coating layer 20 of a metal compound containing element A, not only can more element A be provided to the core 10 to form ion vacancies, but the coating layer 20 also helps to reduce the corrosion of the core 10 by external water vapor and reduce the reaction between lithium-rich compounds and external water vapor.

[0072] In one embodiment, the doped element A also reacts with the lithium source on the core surface to generate a lithium-ion conductor material, thereby reducing the residual alkalinity value of the lithium replenishment material surface. Specifically, after the core is prepared, a small amount of lithium source may not have fully participated in the reaction and remain on the outer surface of the core. In the prior art, a small amount of unreacted lithium source will form residual alkali (lithium carbonate) during the discharge process of the lithium replenishment material. The surface alkalinity mainly affects electrochemical performance by increasing irreversible capacity loss and deteriorating cycle performance. In addition, the residual alkali on the surface decomposes into gas under high voltage, which is also one of the main causes of gas expansion in secondary batteries, thus posing a safety hazard.

[0073] This application involves applying a coating layer of a metal compound containing element A to the outer surface of the core. This allows element A to react with the lithium source on the core surface, generating a lithium-ion conductor material. This not only reduces residual alkali on the core surface but also provides a barrier against external moisture.

[0074] In one embodiment, the particle size D50 of the lithium replenishing material is 0.5 μm to 100 μm. Specifically, the particle size D50 of the lithium replenishing material can be, but is not limited to, 0.5 μm, 1 μm, 2 μm, 5 μm, 10 μm, 15 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm.

[0075] In one embodiment, the specific surface area of ​​the lithium replenishing material is 0.1 m². 2 / g~60m 2 / g. Specifically, the specific surface area of ​​the lithium-supplementing material can be, but is not limited to, 0.1m². 2 / g, 0.2m 2 / g, 0.5m 2 / g, 1m 2 / g、3m 2 / g、5m 2 / g, 10m 2 / g、20m 2 / g、30m 2 / g、40m 2 / g, 50m 2 / g、60m 2 / g.

[0076] In one embodiment, the lithium replenishment material further includes a carbon layer, an ion conductor layer, or a phosphate layer, wherein the carbon layer, ion conductor layer, or phosphate layer is coated on the outer surface of the coating layer.

[0077] Secondly, this application also provides a method for preparing a lithium-supplementing material, please refer to... Figure 3 Specifically, it is used in the preparation of the lithium supplementation material in the first aspect. Its preparation method includes the following steps:

[0078] Step S10: Mix the M source and the Li source and sinter to obtain a lithium supplement material. The M source and the Li source react to generate a lithium-rich compound.

[0079] Step S20: The lithium replenishment material and the A source are mixed and sintered according to the mass ratio to obtain the lithium replenishment material doped with element A, where element A is a metallic element.

[0080] Specifically, in steps S10 and S20, source A and source M are two different metal compounds. Source A is the metal compound containing element A that was doped in the first aspect, and source M is the compound that constitutes the lithium-rich compound Li. x M y O z The precursor.

[0081] Optionally, source A and source M can be at least one of oxides, hydroxides, chlorides, carbonates, sulfates, nitrates, and oxalates.

[0082] Optionally, in step S10, the M source and the Li source are sintered under a protective atmosphere. The protective atmosphere includes at least one of nitrogen, argon, and helium. The sintering temperature is 600℃~900℃, and the sintering time is 6h~24h.

[0083] Optionally, in step S20, the lithium replenishment material and source A are sintered under a protective atmosphere. The protective atmosphere includes at least one of nitrogen, argon, and helium. The sintering temperature is 350℃~800℃, and the sintering time is 2h~8h.

[0084] Understandably, the lithium replenishment material obtained after step S10 should have a stable structure with lithium-rich compounds. Therefore, in step S20, the A source should cover the outer surface of the lithium replenishment material in the form of a coating, and the A element should gradually penetrate into the core of the lithium replenishment material during the sintering process.

[0085] The lithium replenishment material prepared by the above method not only has ion vacancies formed by doping with element A, but also has a large number of ion vacancies on its surface, which is more conducive to adsorbing oxygen generated on the surface.

[0086] In one embodiment, a small amount of element A may be pre-doped into the lithium-supplementing material in step S10. Please refer to [reference needed]. Figure 4 The specific steps are as follows:

[0087] Step S11: Mix source A and source M in a mass ratio and sinter to obtain source M doped with element A, where element A is a metallic element.

[0088] In step S12, the M source and Li source with A element doping are mixed and sintered to obtain a lithium supplement material. The M source and Li source react to generate a lithium-rich compound.

[0089] Step S30: The lithium replenishment material and the A source are mixed in a mass ratio and sintered to obtain a lithium replenishment material doped with element A.

[0090] Understandably, the mass ratio of source A is less than that of source M, so element A exists in source M as a dopant, thus forming source M doped with element A. Furthermore, since element A and element M have different valence states, source M obtained in step S11 has a vacancy structure (i.e., ion vacancies in the first aspect).

[0091] Optionally, in step S11, source A and source M are sintered under a protective atmosphere. The protective atmosphere includes at least one of nitrogen, argon, and helium. The sintering temperature is 400℃~700℃, and the sintering time is 3h~7h.

[0092] Optionally, in step S12, the Li source specifically includes at least one of lithium oxide, lithium hydroxide, lithium carbonate, lithium oxalate, and lithium sulfate.

[0093] After completing step S12, element A from source M exists in the lithium replenishment material as a dopant. Furthermore, since element A has a different valence state than both element M and element Li, the lithium replenishment material obtained in step S30 has ion vacancies.

[0094] Optionally, in step S12, the M source and the Li source are sintered under a protective atmosphere. The protective atmosphere includes at least one of nitrogen, argon, and helium. The sintering temperature is 600℃~900℃, and the sintering time is 6h~24h.

[0095] In other embodiments, this application also provides another method for preparing lithium-supplementing materials, please refer to... Figure 5 Specifically, it is used in the preparation of the lithium supplementation material in the first aspect. Its preparation method includes the following steps:

[0096] Step S10': Mix the A source, M source and Li source in the mass ratio and sinter to obtain the A-doped lithium supplement material.

[0097] Step S20': The lithium replenishment material and source A are mixed in a mass ratio and then sintered a second time.

[0098] Optionally, in step S10', the A source, M source, and Li source are sintered under a protective atmosphere. The protective atmosphere includes at least one of nitrogen, argon, and helium. The sintering temperature is 600℃~900℃, and the sintering time is 6h~24h.

[0099] The lithium replenishment material prepared by the method provided in this application has simple processing steps and low cost. Furthermore, by doping the core of the lithium replenishment material with element A to form ion vacancies, these ion vacancies can adsorb oxygen generated by the lithium-rich compound itself during charging and convert it into lattice oxygen during discharge. This prevents oxygen generated in the lithium replenishment material from escaping from the core, avoiding reaction between the escaping oxygen and the electrolyte, thereby suppressing gas generation in the secondary battery during operation. Simultaneously, the doped element A can also regulate the electronic structure of the lithium replenishment material, improving its electronic conductivity, reducing the decomposition potential and interfacial resistance, thereby increasing the lithium-ion transport rate. Therefore, the lithium replenishment material provided in this application combines the advantages of low gas production and good lithium replenishment effect, showing promising application prospects.

[0100] Thirdly, this application also provides a positive electrode sheet, which includes a current collector and an active material layer disposed on the current collector. The active material layer includes a positive electrode material and a lithium replenishment material as described in the first aspect, or the active material layer includes a lithium replenishment material obtained by a method for preparing a positive electrode material and a lithium replenishment material as described in the second aspect. The positive electrode sheet provided by this application, because it contains the aforementioned lithium replenishment material, and this lithium replenishment material can provide compensation for the active lithium ions consumed during the first charge of the battery due to the formation of the SEI film, effectively maintains the specific capacity of the positive electrode sheet and improves the capacity retention rate of the positive electrode sheet.

[0101] In one embodiment, the positive electrode sheet includes a positive current collector, and a positive active layer is formed on the positive current collector. The positive active layer includes components such as a positive electrode material, a conductive agent, and a binder. This application does not specifically limit these materials, and appropriate materials can be selected according to actual application requirements. The positive current collector includes, but is not limited to, any one of copper foil and aluminum foil. The positive active material can be a phosphate positive active material or a ternary positive active material. In specific embodiments, it includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, lithium fluorinated vanadium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide. The conductive agent includes one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes, and the content of the conductive agent in the positive active layer is 3wt% to 5wt%. The types of binders include one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethylcellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivatives, and the content of the binder in the positive electrode active layer is 2wt% to 4wt%.

[0102] In one embodiment, the content of the lithium replenishing material in the positive electrode material can be controlled at 1% to 6% of the mass of the positive electrode active material. This ratio can precisely compensate for the loss of active lithium during the first charge of the battery. If the amount of lithium replenishing material added to the positive electrode is too low, the lost active lithium in the positive electrode material cannot be fully replenished, which is not conducive to improving the energy density and capacity retention of the battery. If the amount of lithium replenishing material added to the positive electrode material is too high, it may cause severe lithium plating on the negative electrode and increase costs. In some specific embodiments, the mass percentage of the lithium replenishing material in the positive electrode material can be 1%, 2%, 4%, 6%, etc.

[0103] Fourthly, this application also provides a secondary battery, which includes a negative electrode, a separator, and the aforementioned positive electrode. The positive electrode is coated with the aforementioned lithium-replenishing material, or the secondary battery includes the aforementioned lithium-replenishing material, or the secondary battery includes the lithium-replenishing material obtained by the aforementioned preparation method. Based on the excellent lithium-replenishing performance and low gas production characteristics of the lithium-replenishing material in the embodiments of this application, the secondary battery of this application is endowed with excellent electrochemical performance and safety performance.

[0104] The technical solution of the present invention will be described in detail below through specific embodiments.

[0105] Example 1

[0106] This embodiment provides a lithium-rich material and its preparation method, the lithium-rich material comprising a core. The lithium-rich compound has the structural formula Li₂NiO₂, and is doped with Co and Mo elements.

[0107] Co is doped in the bulk phase of the core (near the core), and Mo is doped in the surface layer of the core (near the outer surface). The molar ratio of lithium-rich compound, Co, and Mo is 100:2:5.

[0108] Ni in lithium-rich compounds 2+ The ionic radius is 0.069 nm, Co 3+ The ionic radius is 0.061 nm, Mo 6+ The ionic radius is 0.059 nm.

[0109] The preparation method of this lithium supplement material includes the following steps:

[0110] (1) Nickel hydroxide and cobalt trioxide were sintered at 500°C for 3 hours under a nitrogen atmosphere in a molar ratio of 1:0.01 to obtain a nickel source containing vacancy structures.

[0111] (2) Add lithium hydroxide to the nickel source in (1) and mix well. The molar ratio of nickel source to lithium hydroxide is 1:2. Sinter at 750°C for 6 hours under nitrogen atmosphere to obtain a lithium supplement material containing ion vacancies in the bulk phase.

[0112] (3) Add molybdenum trioxide to the lithium replenishing material in (2) and mix well. The molar ratio of lithium replenishing material to molybdenum trioxide is 1:0.05. Sinter at 450°C for 4 hours under nitrogen atmosphere to obtain a lithium replenishing material containing ion vacancies in both the bulk phase and the surface layer.

[0113] The lithium replenishment material has a D50 particle size of 4.56 μm and a BET specific surface area of ​​2.61 m². 2 / g.

[0114] Example 2

[0115] The lithium replenishment material provided in this embodiment differs from the lithium replenishment material in Embodiment 1 only in that the doping elements in both the bulk core and the surface layer are Zr elements.

[0116] Example 3

[0117] The lithium replenishment material provided in this embodiment differs from the lithium replenishment material in Example 1 only in that the doping elements in both the bulk core and the surface layer are Co.

[0118] Example 4

[0119] The lithium replenishment material provided in this embodiment differs from the lithium replenishment material in Embodiment 1 only in that the bulk doping element of the core is Zr, and the doping element of the surface layer is Mo.

[0120] Example 5

[0121] The lithium replenishment material provided in this embodiment differs from the lithium replenishment material in Example 1 only in that the molar ratio of lithium-rich compound, bulk Co element, and surface Mo element is 100:4:10.

[0122] Example 6

[0123] The lithium replenishment material provided in this embodiment differs from the lithium replenishment material in Example 1 only in that the molar ratio of lithium-rich compound, bulk Co element, and surface Mo element is 100:5:2.

[0124] Comparative Example 1

[0125] The lithium replenishment material provided in this comparative example differs from the lithium replenishment material in Example 1 only in that the lithium-rich compound Li2NiO2 does not contain any doping elements or ion vacancies.

[0126] The lithium replenishment materials provided in Examples 1 to 6 above, and the lithium replenishment material provided in Comparative Example 1, were respectively assembled into positive electrodes and lithium-ion batteries according to the following methods:

[0127] Positive electrode: The lithium supplement material, SP and PVDF are mixed in a mass ratio of 90:4:6 to form a positive electrode slurry. The positive electrode slurry is coated on the surface of aluminum foil, vacuum dried at 110°C overnight, and rolled to obtain a positive electrode sheet.

[0128] Negative electrode: Lithium foil;

[0129] 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.

[0130] Diaphragm: Polypropylene microporous diaphragm;

[0131] Lithium-ion battery assembly: Assemble button-type lithium-ion full cells in an inert atmosphere glove box according to the assembly sequence of graphite negative electrode sheet - separator - electrolyte - positive electrode sheet.

[0132] The electrochemical performance of each lithium-ion battery assembled in the above lithium-ion battery examples was tested under the following conditions:

[0133] Constant current and constant voltage charging, first charge / discharge voltage 2.5-4.3V, current 0.1C, cut-off current 0.01C.

[0134] The initial gas production test involved assembling a lithium-ion battery using a mold battery, followed by constant current and constant voltage charging. The initial charge / discharge voltage was 2.5-4.3V, the current was 0.1C, and the cutoff current was 0.01C. The gas from the mold battery was then introduced into a differential electrochemical mass spectrometer for testing.

[0135] The test results of the aforementioned lithium replenishment materials and lithium-ion batteries are shown in Table 1 below. Figure 6 The table below shows the gas production rate measured in the lithium-ion batteries assembled by Examples 1-6 and Comparative Example 1. The gas production of each example and comparative example is obtained by area integration of their respective time-gas production rate curves.

[0136] Table 1 Performance Test Results

[0137]

[0138] As can be seen from Tables 1-6 of Examples 1-6 and Comparative Example 1, the types and proportions of bulk and surface dopants in the lithium-rich material Li₂NiO₂ significantly affect the initial charge capacity, initial discharge capacity, and gas production of the optimized lithium replenishment material. This is because the doped lithium replenishment material contains vacancy structures, which can adsorb gas and effectively suppress gas production; at the same time, the number of external vacancies has a significant impact on gas production. Furthermore, since the dopants do not participate in charging and discharging, they have a slight impact on the capacity of the lithium replenishment material.

[0139] As can be seen from the results of Examples 1-4 in Table 1, the types of bulk and surface dopants have a significant impact on the gas production results. In Example 1, the bulk Co... 3+ and surface Mo 6+ The doping in Example 2 is bulk Zr. 4+ and surface Zr 4+ In Example 3, the doping is bulk Co. 3+ and surface Co 3+ The amount of gas produced in the three embodiments satisfies the following order: Embodiment 3 > Embodiment 2 > Embodiment 1.

[0140] The reason for the above results is that the greater the difference in valence state between the doping element and the element at the doping site, the more vacancies are formed. At the same time, compared with the core position, the closer the lattice oxygen is to the outer surface, the easier it is to escape after the oxygen is combined (the closer to the outer surface, the shorter the path of oxygen escape, so the difficulty of oxygen formation and escape is reduced). Therefore, the number of surface vacancies has a significant effect on gas production.

[0141] In Example 1, Co 3+ Mo 6+ All are doped at nickel sites, Zr in Example 2 4+ Co is doped at lithium sites. In Example 3, Co was used alone. 3+ In Example 2, the number of surface vacancies is significantly less than in Examples 1 and 2. Although the number of bulk vacancies in Example 2 is slightly greater than in Example 1, the number of surface vacancies is slightly less than in Example 1, resulting in a slightly higher gas production rate. Furthermore, because both the bulk and surface doping in Example 2 occurs at lithium sites, the capacity is somewhat reduced.

[0142] As can be seen from the results of Examples 1 and 4 in Table 1, in Example 4, bulk Zr4 was used. + and surface Mo 6+ The doping of this material results in a greater number of vacancies generated in the bulk phase compared to Example 1, thus providing a better gas generation suppression effect.

[0143] As can be seen from Examples 1, 5 and 6 in Table 1, when the proportion of doping elements in the bulk phase and the surface layer is further increased, the gas production of the lithium replenishment material is further suppressed. However, the doping elements will occupy the weight of the lithium replenishment material, and since the doping elements do not participate in charging and discharging, the initial charge / discharge capacity will be significantly reduced.

[0144] In Examples 1 and 6, after changing the bulk phase and the number of surface vacancies, it can be seen that the gas production in Example 6 is significantly increased. This is because, compared to the core position, the closer to the outer surface, the easier it is for lattice oxygen to combine and form oxygen gas, and the effect of the number of surface vacancies on gas production is significantly greater than that of the bulk phase.

[0145] In the description of the embodiments of this application, it should be noted that the orientation or positional relationship of the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and other indicators are based on the orientation or positional relationship of the drawings, and are only for the convenience of describing this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0146] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art will understand that all or part of the processes for implementing the above embodiments and equivalent variations made in accordance with the claims of this application are still within the scope of this application.

Claims

1. A lithium supplementation material, characterized in that, include: The core includes a lithium-rich compound, wherein the lithium-rich compound is doped with element A, wherein element A is a metallic element; The core also includes ion vacancies, which are formed by the substitution of metal elements in the lithium-rich compound by the A element. The structural formula of the lithium-rich compound includes Li x M y0 O z and Li x M y1 A y2 O z wherein M is a transition metal element, 1 The ion vacancies include cation vacancies and anion vacancies, and the ratio R of the number of cation vacancies to the number of anion vacancies satisfies: 1≤R≤20; wherein, the cation vacancy is an ion vacancy formed by the valence state of element A being higher than that of element M, and the anion vacancy is an ion vacancy formed by the valence state of element A being lower than that of element M.

2. The lithium replenishment material according to claim 1, characterized in that, Along the direction from the core of the core to the outer surface, the number of ion vacancies near the outer surface of the core is greater than the number of ion vacancies near the core of the core.

3. The lithium replenishment material according to claim 1, characterized in that, The ionic radius of element A in lithium-rich compounds is less than or equal to the ionic radius of element M.

4. The lithium replenishment material according to claim 1, characterized in that, The lithium replenishment material satisfies m1:m2:m3=100:(0.1~20):(0.1~25), where m1 is the molar amount of the lithium-rich compound, m2 is the molar amount of element A near the core, and m3 is the molar amount of element A near the outer surface of the core.

5. The lithium replenishment material according to claim 1, characterized in that, The A element located near the core of the kernel is called the A1 element, and the A element located near the outer surface of the kernel is called the A2 element. The A1 element and the A2 element may be the same or different.

6. The lithium replenishment material according to claim 1, characterized in that, The lithium replenishment material also includes a coating layer, which covers the outer surface of the core. The coating layer is a metal compound layer and includes the A element.

7. The lithium replenishment material according to claim 1, characterized in that, The particle size D50 of the lithium supplementing material is 0.5 μm to 100 μm; and / or, the specific surface area of the lithium supplementing material is 0.1 m 2 / g to 60 m 2 / g.

8. A method for preparing a lithium-supplementing material, characterized in that, The preparation method is used to prepare the lithium supplementation material according to any one of claims 1-7, and the preparation method includes: The M source and the Li source are mixed and sintered to obtain a lithium supplement material, wherein the M source and the Li source react to generate a lithium-rich compound; The lithium replenishing material and the A source are mixed in a certain mass ratio and sintered to obtain a lithium replenishing material doped with element A, wherein element A is a metallic element.

9. A positive electrode sheet, characterized in that, The positive electrode includes a current collector and an active material layer disposed on the current collector, the active material layer including a positive electrode material and a lithium supplement material as described in any one of claims 1-7; or, the active material layer includes a positive electrode material and a lithium supplement material obtained by the preparation method of the lithium supplement material as described in claim 8.

10. A secondary battery, characterized in that, The secondary battery includes a negative electrode, a separator, and a positive electrode as described in claim 9.

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