Composite lithium supplement agent, preparation method thereof and secondary battery

Abstract

The invention relates to a composite lithium supplement agent and a preparation method thereof, and a secondary battery, the composite lithium supplement agent is a core-shell structure, and comprises an inner core and at least two nanometer shell layers; wherein at least one nanometer shell layer comprises a lithium supplementing material, at least one nanometer shell layer further comprises a functional material, and the functional material comprises a conductive material and / or a catalytic material. The composite lithium supplement agent can solve the problems that an existing lithium supplement material is poor in conductivity and high in decomposition voltage platform.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and particularly relates to a composite lithium supplement agent, a preparation method thereof, and a secondary battery. Background Art

[0002] During the first charge and discharge of a liquid lithium-ion battery, the lithium ions released from the positive electrode material react with the electrolyte, and a solid electrolyte interface film (SEI) will be formed on the surface of the negative electrode material. This process will irreversibly consume more than 10% of the lithium source in the positive electrode material, resulting in the Coulombic efficiency of the lithium-ion battery in the first week being lower than 90%, and the active lithium in the positive electrode will also be continuously consumed during the charge and discharge cycle of the lithium-ion battery, leading to a shortened life of the lithium-ion battery.

[0003] In response to this phenomenon, the current solution is to add an appropriate lithium supplement material to the positive electrode active material, and the active lithium released by the decomposition of the lithium supplement material during the battery charging process is used to reduce the lithium loss during the cycle. However, in the prior art, most lithium supplement materials have problems such as poor conductivity or a high decomposition voltage platform. Therefore, how to improve the conductivity of the lithium supplement material or reduce the decomposition voltage of the lithium supplement material has become the key. Summary of the Invention

[0004] The object of the present invention is to provide a composite lithium supplement agent, a preparation method thereof, and a secondary battery, so as to solve the problems of poor conductivity and high decomposition voltage platform of the existing lithium supplement materials.

[0005] To achieve the object of the present invention, the present invention provides the following technical solutions:

[0006] In a first aspect, the present invention provides a composite lithium supplement agent, the composite lithium supplement agent has a core-shell structure, including a core and at least two layers of nano-shells; wherein, at least one of the nano-shells includes a lithium supplement material, and at least one of the nano-shells includes a functional material, and the functional material includes a conductive material and / or a catalytic material.

[0007] In one implementation, the composite lithium supplement agent includes a plurality of sequentially nested cycle units, each of the cycle units includes at least two layers of the nano-shells, and each of the cycle units includes the catalytic material, the lithium supplement material, and the conductive material.

[0008] In one implementation, the plurality of cycle units include a first cycle unit, and the first cycle unit further includes the core. In the first cycle unit, the material density of the core is less than the material density of the nano-shell far from the core; and / or, in at least some of the cycle units, the material density of the nano-shell close to the core is less than the material density of the nano-shell far from the core.

[0009] In one embodiment, the core includes the catalytic material, and the multi-layer nano shell layers include a first nano shell layer and a second nano shell layer nested in sequence. The first nano shell layer includes the lithium supplement material, and the second nano shell layer includes the conductive material.

[0010] In one embodiment, there is also a cavity in the core, and / or there is a cavity between the core and the nano shell layer, and / or there is also a cavity in the nano shell layer, and / or there is a cavity between adjacent two nano shell layers.

[0011] In one embodiment, the chemical formula of the lithium supplement material includes Li x C y O z , where 0 < x ≤ 2, y > 0, z > 0.

[0012] In one embodiment, the conductive material includes one or more of carbon materials, metal materials, and metal carbides.

[0013] In one embodiment, the catalytic material includes one or more of metal oxides, metal carbides, and metal sulfides.

[0014] In one embodiment, the thickness of each nano shell layer is 10 nm to 100 nm.

[0015] In one embodiment, the particle size of the core is 5 nm to 50 nm.

[0016] In one embodiment, the overall particle size of the composite lithium supplement agent is 0.5 μm to 30 μm.

[0017] In one embodiment, the mass ratio of the lithium supplement material, the conductive material, and the catalytic material is 100:(5 - 20):(1 - 20).

[0018] In a second aspect, the present invention provides a preparation method of a composite lithium supplement agent. The preparation method includes: adding a core substrate, a lithium supplement material, and a functional material into a ball milling solvent to obtain a precursor solution; placing the precursor solution in a ball milling device, controlling the rotation speed of the ball milling device to evaporate at least part of the ball milling solvent, and the lithium supplement material and the functional material are respectively formed on the outer layer of the core substrate to obtain the composite lithium supplement agent with a core-shell structure.

[0019] In one embodiment, the adding the core substrate, the lithium supplement material, and the functional material into a solvent to obtain a precursor solution includes: configuring the ball milling solvent by mixing water and an organic solvent according to a mass ratio; mixing the core substrate, the lithium supplement material, and the functional material with different densities into the ball milling solvent to obtain a precursor solution.

[0020] In one embodiment, the precursor solution further includes an organic additive. After the lithium supplement material and the functional material are respectively formed on the outer layer of the core substrate, the method further includes: filtering and drying the crystallized core-shell structure to obtain a first composite lithium supplement agent with a core-shell structure; and calcining the first composite lithium supplement agent to obtain a second composite lithium supplement agent with a core-shell structure and a cavity.

[0021] In a third aspect, the present invention provides a secondary battery, including a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes the composite lithium supplement agent according to any one of the embodiments in the first aspect, or the positive electrode includes the composite lithium supplement agent prepared by the preparation method of the composite lithium supplement agent according to any one of the embodiments in the first aspect.

[0022] In order to solve the above technical problems, the present invention provides a composite lithium supplement agent with a multi-layer core-shell structure. The composite lithium supplement agent includes a core and multiple nano shell layers. The nano shell layers include a lithium supplement material and a functional material, where the functional material can be a conductive material and / or a catalytic material. The core-shell structure has the following advantages: 1) The lithium supplement material is arranged in the nano shell layer, reducing the path of lithium ion insertion and extraction, improving the lithium supplement efficiency, and the nano-scale shell layer also further improves the efficiency of lithium ion insertion and extraction; 2) The functional material can provide a conductive or catalytic effect, thereby improving the conductivity of the lithium supplement material and reducing the decomposition voltage of the lithium supplement material; 3) The thickness of the nano shell layer is relatively thin, ranging from a few nanometers to dozens of nanometers, which can fully release the capacity of the lithium supplement material, and maximize the performance of the functional material. The mass ratio of the regulated functional material is small, increasing the mass ratio of the lithium supplement material; 4) The setting of the multi-layer nano shell layer can achieve the best ratio of the lithium supplement material and the functional material on the basis of realizing a thin shell layer, fully exert the performance of the materials, and also ensure the lithium supplement capacity of the composite lithium supplement agent; 5) The onion-like core-shell structure, each nano shell layer has controllability. The core-shell structure can uniquely adjust the position of each nano shell layer according to the requirements of the use environment. The connection between adjacent nano shell layers is tight, the nano shell layer is not easy to fall off, and the composite lithium supplement agent as a whole is not easy to break, which can significantly reduce the decomposition voltage. Description of the Drawings

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0024] Figure 1 It is a cross-sectional schematic diagram of a composite lithium supplement agent in an embodiment;

[0025] Figure 2 It is a cross-sectional schematic diagram of a circulation unit of a composite lithium supplement in one implementation mode;

[0026] Figure 3 It is a cross-sectional schematic diagram of a composite lithium supplement with a cavity in one implementation mode;

[0027] Figure 4 It is a flowchart of a preparation method of a composite lithium supplement in one implementation mode;

[0028] Figure 5 It is a flowchart of a preparation method of a precursor solution in one implementation mode;

[0029] Figure 6 It is a flowchart of a cavity preparation method of a composite lithium supplement in one implementation mode. Specific implementation mode

[0030] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0031] Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used in the present invention in the specification are only for the purpose of describing specific embodiments, and are not intended to limit the present invention. The term "and / or" used in the present invention includes any and all combinations of one or more of the related listed items.

[0032] It should be noted that the "range" disclosed in the present invention is 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, and the selected lower limit and upper limit define the boundary of a specific range. The range defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 to 120 and 80 to 110 are listed for a specific parameter, ranges of 60 to 110 and 80 to 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, the following ranges are all contemplated: 1 to 3, 1 to 4, 1 to 5, 2 to 3, 2 to 4, and 2 to 5. In the present invention, unless otherwise specified, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where both a and b are real numbers. For example, the numerical range "0 to 5" means that all real numbers between "0 to 5" are fully listed herein, and "0 to 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, the integers 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0033] All steps of the present invention can be carried out sequentially or randomly, and preferably sequentially. For example, the method includes steps (a) and (b), which means that the method can include steps (a) and (b) carried out sequentially, or can also include steps (b) and (a) carried out sequentially. For example, when it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b), and (c), or can also include steps (a), (c), and (b), or can also include steps (c), (a), and (b), etc.

[0034] The following will describe in detail some embodiments of the present invention with reference to the accompanying drawings. Without conflict, the following embodiments and the features in the embodiments can be combined with each other.

[0035] The present invention also provides a composite lithium supplement agent. Please refer to Figures 1-3 .

[0036] In one embodiment, please refer to Figure 1 , the composite lithium supplement agent has a core-shell structure and includes a core 10 and at least two layers of nanoshell layers 20; wherein, at least one layer of the nanoshell layer 20 includes a lithium supplement material 100, and at least one other layer of the nanoshell layer 20 includes a functional material, and the functional material includes a conductive material 300 and / or a catalytic material 200. The composite lithium supplement agent is a core-shell structure with multiple layers of nanoshell layers 20 nested therein, where at least one layer of the multiple layers of nanoshell layers 20 includes a lithium supplement material 100, and the other layer or multiple layers of nanoshell layers 20 include a functional material.

[0037] Specifically, the lithium supplement material 100 is used for lithium supplementation and can contribute a large amount of lithium ions. During the first charging process, lithium (Li) in the lithium supplement material 100 can be released and migrate to the negative electrode of the battery to offset the irreversible lithium loss caused by the formation of the SEI film, thereby improving the total capacity and energy density of the battery. However, in the prior art, most lithium supplement materials 100 have problems such as poor electrical conductivity or high decomposition voltage platform. Therefore, how to improve the electrical conductivity of the lithium supplement material 100 or reduce the decomposition voltage of the lithium supplement material 100 has become the key.

[0038] To solve the above technical problems, the present invention provides a composite lithium supplement agent with a multi-layer core-shell structure. The composite lithium supplement agent is prepared by a liquid-phase ball milling method. By evaporating the solvent during the ball milling process, various materials are precipitated or combined to obtain a composite lithium supplement agent with a multi-layer core-shell structure. The composite lithium supplement agent includes an inner core 10 and multiple nano-shell layers 20. The nano-shell layer 20 includes a lithium supplement material 100 and a functional material, where the functional material can be a conductive material 300 and / or a catalytic material 200. The core-shell structure has the following advantages: 1) The lithium supplement material 100 is arranged in the nano-shell layer 20, reducing the path of lithium ion insertion and extraction, improving the lithium supplementation efficiency, and the nano-scale shell layer further improves the efficiency of lithium ion insertion and extraction; 2) The functional material can play a role in conducting electricity or catalysis, thereby improving the electrical conductivity of the lithium supplement material 100 and reducing the decomposition voltage of the lithium supplement material 100; 3) The thickness of the nano-shell layer 20 is relatively thin, ranging from a few nanometers to dozens of nanometers, which can fully release the capacity of the lithium supplement material 100, and maximize the performance of the functional material. The mass ratio of the functional material is relatively small, increasing the mass ratio of the lithium supplement material 100; 4) The arrangement of the multi-layer nano-shell layer 20 can achieve the best ratio of the lithium supplement material 100 and the functional material on the basis of a thin shell layer, fully exert the performance of the materials, and ensure the lithium supplementation capacity of the composite lithium supplement agent; 5) The onion-like core-shell structure, each nano-shell layer 20 has controllability. The core-shell structure can uniquely adjust the position of each nano-shell layer 20 according to the requirements of the use environment. Moreover, the connection between adjacent nano-shell layers 20 is tight, the nano-shell layer 20 is not easily detached, and the composite lithium supplement agent as a whole is not easily broken, which can significantly reduce the decomposition voltage.

[0039] In one embodiment, the chemical formula of the lithium supplement material 100 includes Li x C y O z , where 0 < x ≤ 2, y > 0, z > 0. In a specific embodiment, the lithium supplement material may include Li 2 C 2 O 4 (lithium oxalate), Li 2 C 3 O3 (Lithium triacid)、Li 2 C 4 O 4 (Lithium butynedioate)、Li 2 C 6 O 6 (Lithium kojate)、Li 2 C 3 O 5 (Lithium pyruvate)、Li 2 C 4 O 6 (Lithium dionesuccinate)、Li 2 C 5 O 5 (Lithium croconate) and lithium triketoglutarate (Li 2 C 5 O 7 ). In other embodiments, the organic lithium supplementing material may further include lithium formate, lithium acetate, lithium propionate, lithium butyrate, lithium isobutyrate, etc.

[0040] In one embodiment, the chemical formula of the lithium supplementing material 100 further includes Li n1 M m1 O u1 , where M is at least one element among Fe, Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, V, Mo, Sn, etc., 1≤n1≤8, 0<m1, 0<u1<7. For example, Li 5 FeO 4 , Li 6 MnO 4 , Li 6 CoO 4 , Li 6 ZnO 4 , Li 2 NiO 2 , Li 2 CuO 2 , Li 2 CoO 2 , Li 2 MnO 2 , Li 2 Ni 0.5 Mn 1.5 O 4 , Li 2 Ni d Cu (1-d) O 2 (0<d<1), etc.

[0041] In one embodiment, the chemical formula of the lithium supplementing material 100 further includes Li n2 Km2 , where K is at least one element among O, S, P, N, F, B, Se, Te, 1 ≤ n2 ≤ 5, 0 < m2. For example, Li 2 O, Li 2 O 2 , Li 3 N, Li 2 S, LiF, Li 3 P, Li 2 at least one of Se.

[0042] In one embodiment, the chemical formula of the lithium supplement material 100 further includes Li 1+n3 A m3 O u3 , where 0 < n3 ≤ 1.2, 1 ≤ m3 < 3, u3 > 0, and A includes at least one of Ni, Fe, Mn, Co, Cr, V, Mo, Ti, Nb, Zr, Cu, Mg. For example, Li 2 CuO 2 , Li 2 NiO 2 , Li 2 MnO 2 at least one of them.

[0043] In one embodiment, the core 10 may include inorganic materials and / or organic materials. Optionally, the core 10 includes but is not limited to metal compounds and / or metal elements; in a specific embodiment, the core 10 includes metal oxides, metal carbides, metal nitrides, etc., such as cobalt oxide, nickel oxide, titanium dioxide, etc. In a specific embodiment, the type of the core 10 and the catalytic material 200 may be the same, and both may be metal compounds. For example, both are metal oxides, and the core 10 also has a catalytic effect.

[0044] In one embodiment, the conductive material 300 includes one or more of carbon materials, metal materials, and metal carbides; the conductive material 300 has the function of conducting electrons or ions. In a specific embodiment, the conductive material 300 may be Ketjen black (KB), graphene, nano-aluminum, nano-cobalt carbide, etc. The catalytic material 200 includes metal compounds and / or metal elements. Optionally, the catalytic material 200 includes one or more of metal oxides, metal carbides, and metal sulfides; the catalytic material 200 has the function of catalyzing the lithium supplement material 100 to reduce the decomposition voltage.

[0045] In one embodiment, when the functional material includes the conductive material 300 and the catalytic material 200, the materials in the three-layer nanoshell 20 can all be different, or the materials in two of the three-layer nanoshells 20 can be the same. When the functional material only includes the conductive material 300 or the catalytic material 200, the materials in two of the three-layer nanoshells 20 can be the same.

[0046] In a specific embodiment, when the functional material only includes the catalytic material 200, the two-layer nanoshell 20 respectively includes the nanoshell 20 of the lithium supplement material 100 and the nanoshell 20 of the catalytic material 200, that is, one of the nanoshells 20 is composed of the lithium supplement material 100, and the other nanoshell 20 is composed of the catalytic material 200. For example, the order of the two-layer nanoshell 20 can include: 1) the nanoshell 20 of the lithium supplement material 100 coats the inner core 10, and the nanoshell 20 of the catalytic material 200 coats the nanoshell 20 of the lithium supplement material 100; 2) the nanoshell 20 of the catalytic material 200 coats the inner core 10, and the nanoshell 20 of the lithium supplement material 100 coats the nanoshell 20 of the catalytic material 200.

[0047] In a specific embodiment, when the functional material only includes the catalytic material 200, the material of the inner core 10 can be a metal compound to provide a catalytic effect. The structure of the composite lithium supplement agent can be that the nanoshell 20 of the lithium supplement material 100 coats the inner core 10 (both are catalytic materials), and the nanoshell 20 of the catalytic material 200 coats the nanoshell 20 of the lithium supplement material 100.

[0048] In a specific embodiment, when the functional material only includes the conductive material 300, the two-layer nanoshell 20 respectively includes the nanoshell 20 of the lithium supplement material 100 and the nanoshell 20 of the conductive material 300, that is, one of the nanoshells 20 is composed of the lithium supplement material 100, and the other nanoshell 20 is composed of the conductive material 300. For example, the order of the two-layer nanoshell 20 can be that the nanoshell 20 of the lithium supplement material 100 coats the inner core 10, and the nanoshell 20 of the conductive material 300 coats the nanoshell 20 of the lithium supplement material 100. Of course, in this embodiment, the inner core 10 can be a metal compound, that is, the inner core 10 acts as the catalytic material 200 to provide a catalytic effect.

[0049] In a specific embodiment, when the functional material only includes the conductive material 300 or the catalytic material 200, the number of the nano-shells 20 can be three or more layers. In the multi-layer nano-shells 20, the nano-shells 20 of any one of the lithium supplementing material 100, the conductive material 300 or the catalytic material 200 may appear repeatedly. It can be understood that in the composite lithium supplementing agent provided by the present application, all the nano-shells 20 are jointly composed of the lithium supplementing material 100 and the functional materials (the catalytic material 200 and the conductive material 300). Therefore, when the composite lithium supplementing agent includes more than three layers of nano-shells 20, the other nano-shells 20 can also be composed of the lithium supplementing material 100 or the functional materials.

[0050] In a specific embodiment, when the functional material includes the conductive material 300 and the catalytic material 200, the three-layer nano-shells 20 respectively include the nano-shell 20 of the lithium supplementing material 100, the nano-shell 20 of the conductive material 300, and the nano-shell 20 of the catalytic material 200; that is, one of the nano-shells 20 is composed of the lithium supplementing material 100, another nano-shell 20 is composed of the conductive material 300, and still another nano-shell 20 is composed of the catalytic material 200. The nesting order of the three-layer nano-shells 20 is not specifically limited.

[0051] In one embodiment, please refer to Figure 1 and Figure 2 , the composite lithium supplementing agent includes a plurality of sequentially nested cyclic units 30. Each cyclic unit 30 includes at least two layers of nano-shells 20, and each cyclic unit 30 includes the catalytic material 200, the lithium supplementing material 100, and the conductive material 300. Specifically, the composite lithium supplementing agent may be composed of the core 10 and at least one cyclic unit 30, wherein the number of nano-shells 20 in each cyclic unit 30 is the same, and each cyclic unit 30 includes the lithium supplementing material 100, the conductive material 300, and the catalytic material 200. Optionally, the adjacent two cyclic units 30 may be directly connected or indirectly connected. It can be understood that the cyclic unit 30 refers to a structure composed of at least two layers of nano-shells 20 that periodically appears in the composite lithium supplementing agent.

[0052] By providing that the composite lithium supplementing agent has a plurality of cyclic units 30 and each cyclic unit 30 includes the same materials, the present invention enables the lithium supplementing material 100 in each cyclic unit 30 to be able to supplement lithium, and can provide conductive and catalytic effects in the corresponding cyclic unit 30, thereby increasing the lithium supplementing ability of the composite lithium supplementing agent.

[0053] In a specific embodiment, the cyclic unit 30 may include three layers of nanoshells 20 connected in sequence. The materials independently included in the three layers of nanoshells 20 may refer to the above-described embodiments and will not be elaborated herein. For example, the composite lithium supplement agent includes adjacent nth cyclic unit and (n + 1)th cyclic unit. Among them, the nth cyclic unit includes a nanoshell 20 of a catalytic material 200, a nanoshell 20 of a lithium supplement material 100, and a nanoshell 20 of a conductive material 300. The (n + 1)th cyclic unit also includes a nanoshell 20 of a catalytic material 200, a nanoshell 20 of a lithium supplement material 100, and a nanoshell 20 of a conductive material 300, and the arrangement order of each nanoshell 20 in the nth cyclic unit and the (n + 1)th cyclic unit is the same.

[0054] In other embodiments, the cyclic unit 30 may include four or more layers of nanoshells 20 connected in sequence, and the arrangement order between the nanoshells 20 composed of different materials in the cyclic unit 30 is not specifically limited. For example, in the cyclic unit 30 with four layers of nanoshells 20, they may be a nanoshell 20 of a lithium supplement material 100, a nanoshell 20 of a catalytic material 200, a nanoshell 20 of a lithium supplement material 100, and a nanoshell 20 of a conductive material 300, respectively.

[0055] In a specific embodiment, the outermost layer of nanoshell 20 in each cyclic unit 30 may be a nanoshell 20 of a conductive material 300. The advantage of this setting is that the outermost layer of the composite lithium supplement agent is the conductive material 300, and the conductive material 300 wraps the catalytic material 200 and the lithium supplement material 100, which can reduce the side reactions generated by the catalytic material 200 during the application of the lithium supplement material 100 and reduce the influence of external environmental factors on the catalytic material 200 and the lithium supplement material 100. In addition, since the outermost layer of each cyclic unit 30 is the conductive material 300 and the conductive material 300 is in contact with the lithium supplement material 100, the lithium ion insertion / extraction efficiency is also correspondingly improved.

[0056] In one embodiment, a plurality of cyclic units 30 include a first cyclic unit, and the first cyclic unit further includes a core 10. In the first cyclic unit, the material density of the core 10 is less than the material density of the nanoshell 20 away from the core 10. Specifically, the first cyclic unit 30 (i.e., the first cyclic unit) in the composite lithium supplement agent may be composed of a core 10 and at least two layers of nanoshells 20. In a specific embodiment, the first cyclic unit includes a core 10 and two layers of nanoshells 20, where the material of the core 10 may be a catalytic material 200, and the two layers of nanoshells 20 include a lithium supplement material 100 and a conductive material 300.

[0057] In one embodiment, in at least part of the cycle unit 30, the material density in the nano-shell layer 20 close to the core 10 is less than the material density in the nano-shell layer 20 far from the core 10. Specifically, the multiple cycle units 30 further include a second cycle unit, a third cycle unit to an nth cycle unit. Among them, in the cycle unit 30, along the direction of nesting outward of the nano-shell layer 20, the density of other materials in the multiple nano-shell layers 20 except the lithium supplement material 100 increases in sequence, so that the density of the outermost nano-shell layer 20 in the cycle unit 30 is the largest.

[0058] In a specific embodiment, the density of the core 10 material is ρ1, the density of the catalytic material 200 is ρ2, and the density of the conductive material 300 is ρ3. The densities of the three materials satisfy: ρ1 ≤ ρ2 < ρ3. In a specific embodiment, the material of the core 10 can be the catalytic material 200, so ρ1 = ρ2. Of course, in the case where the catalytic material 200 includes multiple types, the densities of the multiple catalytic materials 200 can be ρ21, ρ22... ρ2n respectively. In the case where the conductive material 300 includes multiple types, the densities of the multiple conductive materials 300 can be ρ31, ρ32... ρ3m respectively. The arrangement order of the multiple catalytic materials 200 and the multiple catalytic materials 200 in the multi-layer nano-shell layer 20 also conforms to the rule of increasing density in sequence.

[0059] In other embodiments, the densities of the core 10 material, the conductive material 300, and the catalytic material 200 can satisfy: ρ1 < ρ3 < ρ2. Thus, it can be formed that the nano-shell layer 20 of the conductive material 300 wraps around the outer periphery of the core 10, the nano-shell layer 20 of the lithium supplement material 100 wraps around the outer periphery of the nano-shell layer 20 of the conductive material 300, and the nano-shell layer 20 of the catalytic material 200 wraps around the outer periphery of the nano-shell layer 20 of the lithium supplement material 100.

[0060] In one embodiment, please refer to Figure 1 , the core 10 includes the catalytic material 200, and the multi-layer nano-shell layer 20 includes a first nano-shell layer 21 and a second nano-shell layer 22 nested in sequence. The first nano-shell layer 21 includes the lithium supplement material 100, and the second nano-shell layer 22 includes the conductive material 300. Specifically, in the cycle unit 30, it includes a core and two nano-shell layers 20, namely the first nano-shell layer 21 and the second nano-shell layer 22 nested in sequence. The core and the two nano-shell layers 20 can specifically refer to the above method and will not be elaborated here. Wrapping the nano-shell layer 20 of the catalytic material 200 in the corresponding nano-shell layer 20 of the conductive material 300 can reduce the side reactions generated by the catalytic material 200 during the application of the lithium supplement material 100.

[0061] In one implementation, the circulation unit 30 includes three layers of nano-shells 20, and between adjacent circulation units 30, there are nano-shells 20 having a nucleation substrate. Specifically, the material type of the nucleation substrate is the same as that of the inner core 10, that is, at least part of the substrate of the inner core 10 in the preparation method is also used to form the core layer.

[0062] In a specific embodiment, the composite lithium supplement agent includes an inner core 10 and two circulation units 30 (a first circulation unit and a second circulation unit), wherein there is a nano-shell 20 made of the material of the inner core 10 between the first circulation unit and the second circulation unit. Therefore, the composite lithium supplement agent includes an inner core 10, a first nano-shell to a seventh nano-shell, wherein the first nano-shell and the fifth nano-shell include a catalytic material 200, the second nano-shell and the sixth nano-shell include a lithium supplement material 100, the third nano-shell and the seventh nano-shell include a conductive material 300, and the fourth nano-shell includes a substrate made of the same material as the inner core 10.

[0063] In one implementation, the lithium supplement material 100 includes two or more kinds. The two lithium supplement materials 100 are respectively a first lithium supplement material and a second lithium supplement material. The inner core 10 can be a metal compound and has a catalytic effect. The composite lithium supplement agent includes a plurality of circulation units 30. Among them, the first circulation unit includes an inner core 10 with a catalytic effect, two lithium supplement materials 100, and a functional material. It can be understood that the advantage of this core-shell structure is that the material of each layer of nano-shell 20 is designable. Therefore, different lithium supplement materials 100 are arranged in the plurality of nano-shells 20 to realize the combination of multiple lithium supplement materials 100, and the overall performance of the composite lithium supplement agent is improved by combining the advantages of multiple lithium supplement materials 100.

[0064] In a specific embodiment, the composite lithium supplement agent includes an inner core 10, a first nano-shell to a seventh nano-shell, wherein the first nano-shell and the fifth nano-shell include a first lithium supplement material, the second nano-shell and the sixth nano-shell include a catalytic material 200, the third nano-shell and the seventh nano-shell include a second lithium supplement material, and the fourth nano-shell includes a substrate made of the same material as the inner core 10 and all have a catalytic effect.

[0065] In one implementation, please refer to Figure 3, the core 10 also has a cavity 40, and / or, there is a cavity 40 between the core 10 and the nanoshell layer 20, and / or, the nanoshell layer 20 also has a cavity 40, and / or, there is a cavity 40 between adjacent nanoshell layers 20. Specifically, the composite lithium supplement agent can form a cavity 40 inside it by adding an organic substance (i.e., an organic additive) and calcining. It can be understood that based on the process characteristics of liquid-phase self-heating evaporation in the preparation method, the organic additive can be located at any part of the composite lithium supplement agent, so the cavity 40 can be formed in the core 10, in the nanoshell layer 20, or between the core 10 and the nanoshell layer 20. A cavity 40 is formed in the composite lithium supplement agent, and the cavity 40 facilitates the penetration of the electrolyte, making the transmission of lithium ions change from simple solid-phase conduction to multi-layer solid-liquid biphasic conduction, accelerating the transmission of lithium ions, and reducing the overpotential and plateau of the lithium supplement material 100.

[0066] In one embodiment, the thickness of the nanoshell layer 20 is 10 nm to 100 nm. Meeting the thickness of the nanoshell layer 20 within the above range can improve the performance of the lithium supplement material 100 and the functional material, and on the basis of the particle size of the composite conventional material, the number of nanoshell layers 20 can be set as much as possible, thereby improving the capacity of the composite lithium supplement agent. When the thickness of the nanoshell layer 20 is too small, the materials between the nanoshell layers 20 will fuse with each other, resulting in the capacity and performance of the materials being affected. When the thickness of the nanoshell layer 20 is too thick, the nano-effect of the shell layer becomes poor, and the cyclic unit 30 in the structure decreases, making it difficult to exert the performance of the functional material. In a specific embodiment, the thickness of the nanoshell layer 20 can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm.

[0067] In one embodiment, the particle size of the core 10 is 5 nm to 50 nm. Meeting the particle size of the core 10 within the above range can ensure the lithium supplement capacity and thus give full play to the performance of the functional material. When the particle size of the core 10 is too small, the core 10 is not easily dispersed, and its self-aggregation is serious, increasing the preparation difficulty. When the particle size of the core 10 is too large, it occupies the volume of the nanoshell layer 20, resulting in the nanoshell layer 20 being too thin or the number being too small, both of which will affect the performance of the functional material. In a specific embodiment, the particle size of the core 10 can be 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm.

[0068] In one embodiment, the particle size of the composite lithium supplement agent is 0.5 μm to 30 μm. Meeting the particle size of the composite lithium supplement agent within the above range can ensure the number of cycles of the nano-shell layer 20 and ensure the lithium supplement capacity, so as to fully exert the performance of the functional material. When the particle size of the composite lithium supplement agent is too small, the number of nano-shell layers 20 is too small and the number of cycles is too small, resulting in a decrease in the lithium supplement capacity and the performance of the functional material being affected. When the particle size of the composite lithium supplement agent is too large, it is not conducive to the material to fully release its capacity. In a specific embodiment, the particle size of the composite lithium supplement agent can be 0.5 μm, 0.8 μm, 1 μm, 2.5 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm.

[0069] In one embodiment, the mass ratio of the lithium supplement material 100, the conductive material 300 and the catalytic material 200 is 100:(5 - 20):(1 - 20). Meeting the mass ratio of the lithium supplement material 100, the conductive material 300 and the catalytic material 200 within the above range can ensure the lithium supplement capacity, excellent conductivity and low decomposition voltage. When the mass ratio of the conductive material 300 is too small, the overall conductivity of the composite lithium supplement agent will decrease. When the mass ratio of the catalytic material 200 is too small, the catalytic effect of the catalytic material 200 on the lithium supplement material 100 becomes poor, and it is difficult for the lithium supplement material 100 to fully release its capacity. When the mass ratio of the conductive material 300 or the catalytic material 200 is too large, the lithium supplement capacity will decrease. In a specific embodiment, the mass ratio of the lithium supplement material 100, the conductive material 300 and the catalytic material 200 can be 100:5:(1 - 20), 100:10:(1 - 20), 100:15:(1 - 20), 100:20:(1 - 20), 100:(5 - 20):1, 100:(5 - 20):5, 100:(5 - 20):10, 100:(5 - 20):15, 100:(5 - 20):20.

[0070] The present invention provides a preparation method of a composite lithium supplement agent for preparing a composite lithium supplement agent with a core-shell structure having multiple nano-shell layers. Please refer to Figures 4-6 .

[0071] In one embodiment, please refer to Figure 4 , the preparation method of the composite lithium supplement agent specifically includes the following steps:

[0072] Step S10, adding the inner core substrate, the lithium supplement material and the functional material into the ball milling solvent to obtain a precursor solution.

[0073] Step S20, placing the precursor solution in a ball milling device, controlling the rotation speed of the ball milling device to evaporate at least part of the ball milling solvent, and the lithium supplement material and the functional material are respectively formed on the outer layer of the inner core substrate to obtain a composite lithium supplement agent with a core-shell structure.

[0074] In one embodiment, in step S10, the core substrate may include inorganic materials and / or organic materials. Optionally, the core substrate includes, but is not limited to, metal compounds and / or metallic elements; in a specific embodiment, the core substrate includes metal oxides, metal carbides, metal nitrides, etc., such as cobalt oxide, nickel oxide, titanium dioxide, etc. It should be noted that the material type of the core substrate is not specifically limited. The main function of the core substrate is to act as a crystallization nucleus, enabling the lithium supplement material and the functional material to cover the outer surface of the crystallization nucleus.

[0075] In a specific embodiment, in step S10, the core substrate may also be another lithium supplement material, such as an inorganic lithium supplement material. The chemical formula of the lithium supplement material includes Li n1 M m1 O u1 , where M is at least one element among Fe, Ni, Mn, Cu, Zn, Co, Cr, Zr, Sb, Ti, V, Mo, Sn, etc., 1 ≤ n1 ≤ 8, 0 < m1, 0 < u1 < 7. For example, Li 5 FeO 4 , Li 6 MnO 4 , Li 6 CoO 4 , Li 6 ZnO 4 , Li 2 NiO 2 , Li 2 CuO 2 , Li 2 CoO 2 , Li 2 MnO 2 , Li 2 Ni 0.5 Mn 1.5 O 4 , Li 2 Ni d Cu (1-d) O 2 (0 < d < 1), etc. at least one of them. It may also include Li n2 K m2 , where K is at least one element among O, S, P, N, F, B, Se, Te, 1 ≤ n2 ≤ 5, 0 < m2. For example, Li 2 O, Li 2 O 2 , Li 3 N, Li 2 S, LiF, Li 3 P, Li 2 Se, etc. at least one of them. It also includes Li 1+n3 Am3 O u3 , wherein, 0 < n3 ≤ 1.2, 1 ≤ m3 < 3, u3 > 0, and A includes at least one of Ni, Fe, Mn, Co, Cr, V, Mo, Ti, Nb, Zr, Cu, and Mg.

[0076] In one embodiment, in step S10, the lithium supplement material may include an organic lithium supplement material, and the chemical formula of the lithium supplement material includes Li x C y O z , wherein, 0 < x ≤ 2, y > 0, z > 0. In a specific embodiment, the lithium supplement material may include Li 2 C 2 O 4 (lithium oxalate), Li 2 C 3 O 3 (lithium trimesate), Li 2 C 4 O 4 (lithium butynedioate), Li 2 C 6 O 6 (lithium kojate), Li 2 C 3 O 5 (lithium pyruvate), Li 2 C 4 O 6 (lithium diketosuccinate), Li 2 C 5 O 5 (lithium croconate) and lithium triketoglutarate (Li 2 C 5 O 7 ) or one or more of them. In other embodiments, the organic lithium supplement material may further include lithium formate, lithium acetate, lithium propionate, lithium butyrate, lithium isobutyrate, etc. The advantage of using the organic lithium supplement material is that most of the organic lithium supplement materials are soluble and can be attached to the outer surface of the inner core substrate by crystallization.

[0077] In one embodiment, in step S10, the lithium supplement material may further include an inorganic lithium supplement material, and the chemical formula of the inorganic lithium supplement material may refer to that provided in the above embodiment and will not be elaborated here.

[0078] In one embodiment, in step S10, the functional material includes a conductive material and / or a catalytic material, wherein the conductive material has the function of conducting electrons or ions, and the catalytic material has the function of catalyzing the lithium supplement material to reduce the decomposition voltage. Optionally, the conductive material includes one or more of carbon materials, metal oxides, phosphates, electrode materials, solid electrolytes, and conductive polymers; the catalytic material includes metal compounds and / or metal elements.

[0079] It should be noted that the types of the core substrate and the functional material can be the same. For example, both the core substrate and the functional material are inorganic materials. In a specific embodiment, the types of the core substrate and the catalytic material can be the same, and both of them can be metal compounds. For example, both of them are metal oxides. Therefore, the core substrate can also provide a catalytic effect to catalyze the lithium supplement material on its surface to reduce the decomposition voltage.

[0080] In one embodiment, in step S10, the ball milling solvent can be a pure substance of a single solvent, or the ball milling solvent can be a mixture of multiple solvents. In a specific embodiment, the ball milling solvent includes water and / or an organic solvent.

[0081] In a specific embodiment, step S10 includes: configuring the core substrate, the lithium supplement material, and the functional material according to a preset mass ratio, then providing a ball milling solvent, adding the core substrate, the lithium supplement material, and the functional material to the ball milling solvent, and fully stirring the mixed liquid to obtain a precursor solution.

[0082] In one embodiment, in step S20, the ball milling device is a ball mill, and the ball mill includes a ball milling tank and grinding media (ball milling beads). The rotation speed of the ball milling tank is controllable. By controlling the rotation speed of the ball milling, the evaporation rate of the ball milling solvent can be controlled, so that the lithium supplement material and / or the functional material dissolved in the ball milling solvent can precipitate and crystallize.

[0083] In a specific embodiment, step S20 includes: placing the precursor solution in the ball milling tank, controlling the rotation speed of the ball milling tank to control the evaporation rate of the ball milling solvent, so that the lithium supplement material slowly crystallizes preferentially on the surface of the core substrate to form a nano shell layer, and then continuing to control the rotation speed of the ball milling tank and combining with the ball milling beads to make the functional material cover the nano shell layer of the lithium supplement material to form another or multiple nano shell layers, thereby obtaining a composite lithium supplement agent with a core-shell structure.

[0084] It should be noted that the preparation method provided by the present invention prepares each nano shell layer by the asynchronous shell formation method. The asynchronous shell formation means that in the process of preparing a multi-layer nano shell layer, the task of preparing each nano shell layer is independent of the preparation of other nano shell layers, and the arrangement order of multiple different material nano shell layers can be regulated by adjusting process parameters. Compared with the preparation methods of the core-shell structure in the prior art, the preparation method of the present invention has extremely high controllability.

[0085] In addition, the present invention is also different from the ball milling method in the prior art. The ball milling method in the prior art is usually solid-phase mixing, that is, the dry material is put into the ball milling device for solid-state ball milling. The ball milling process does not need to consider the material density and the crystallization of the material; and the wet ball milling in the present invention requires the removal of the solvent during the wet milling process and the control of the evaporation of the solvent to form a core-shell structure. The advantage of this preparation method is that each nanoshell layer is relatively thin and the nanoshell layers are tightly combined.

[0086] The preparation method of the composite lithium supplement provided by the present invention uses a ball milling process and solvent self-evaporation to achieve asynchronous shell formation to prepare an integrated composite lithium supplement. The preparation method has the following advantages:

[0087] 1) The preparation method is simple. The solvent is evaporated by controlling the rotation speed of the ball milling device, so that the lithium supplement material is precipitated and crystallized on the outer layer of the core substrate, and the functional material is mixed on the outer layer of the core substrate by ball milling beads to prepare a composite lithium supplement agent with a core-shell structure having multiple nanoshell layers. The preparation method can optimize the ratio of lithium supplement material and functional material and give full play to the performance of the material.

[0088] 2) An onion-like core-shell structure can be achieved through component regulation. Each nanoshell layer is controllable. The core-shell structure can adjust the position of each nanoshell layer according to the unique requirements of the use environment; and the thickness of each nanoshell layer is relatively thin, ranging from a few nanometers to tens of nanometers.

[0089] 3) The heat generated by the ball mill itself is used to remove the solvent through the synthesis method of self-heating evaporation. On the one hand, the surface energy of the solvent evaporation is reduced, which increases the binding energy between the components and improves the performance of the lithium supplement material. On the other hand, the solvent is removed by the self-heating of the ball mill to achieve composite integration of the components, saving energy and reducing the deterioration of the catalytic material and the stability deterioration caused by the heat generated by the ball mill. In addition, the obtained nanoshells are tightly connected, the nanoshells are not easy to fall off, the composite lithium supplement is intact and not easy to break, and the decomposition voltage can be significantly reduced.

[0090] 4) The asynchronous shell-forming method of liquid phase ball milling reduces the nano-agglomeration of nano-level lithium-supplementing materials and functional materials, maximizes the performance of functional materials, makes the mass proportion of functional materials smaller than that of materials prepared by traditional preparation methods, and increases the mass proportion of lithium-supplementing materials.

[0091] 5) The preparation method is suitable for preparing nanoshells of various different materials; for example, it can be used to prepare different nanoshells from various lithium-supplementing materials. Combining the advantages of various lithium-supplementing materials, nanoshells of various conductive materials can also be prepared, such as electron-conducting nanoshells and ion-conducting nanoshells.

[0092] In one embodiment, please refer to Figure 5 In step S10, adding a core substrate, a lithium supplement material, and a functional material into a ball-milling solvent to obtain a precursor solution, which specifically includes:

[0093] Step S11, configuring a ball-milling solvent by mixing water and an organic solvent according to a mass ratio.

[0094] Step S12, mixing core substrates, lithium supplement materials, and functional materials with different densities into the ball-milling solvent to obtain a precursor solution.

[0095] In one embodiment, in step S11, the ball-milling solvent includes water and at least one organic solvent, where the boiling point of the organic solvent needs to be higher than that of water, and the lithium supplement material can be dissolved in water. In a specific embodiment, the organic solvent includes one or more of propylene carbonate, glycerol, NMP, and benzyl alcohol. Optionally, water and the organic solvent are configured according to a mass ratio, and the mass ratio of water to the organic solvent is 100:(10 - 100).

[0096] In one embodiment, in step S12, the densities of the core substrate, the lithium supplement material, and the functional material are all different. In a specific embodiment, the lithium supplement material is an organic-soluble material, so the densities of the core substrate and the functional material can be different; the density ρ1 of the core substrate, the density ρ2 of the catalytic material, and the density ρ3 of the conductive material satisfy: ρ1 ≤ ρ2 < ρ3. In a specific embodiment, the material of the core 10 can be the catalytic material 200, so ρ1 = ρ2.

[0097] It should be noted that the reason for the formation of the multi-layer nano-shell layer of the present invention according to density is as follows: taking the case where the core substrate and the catalytic material are the same as an example, the present invention controls the evaporation rate of water by controlling the rotation speed of the ball-milling tank. Since the density of the core substrate (catalytic material) is relatively small, it is located at the top layer of the precursor solution compared to the conductive material. During the evaporation of the upper-layer water, the lithium supplement material dissolved in the upper-layer water preferentially precipitates and crystallizes, thereby forming an intermediate including a core and a nano-shell layer of the lithium supplement material. The intermediate sinks to the area of the conductive material located in the lower layer, and then the conductive material is covered on the nano-shell layer of the lithium supplement material through the movement of the ball-milling beads to form a nano-shell layer of the conductive material.

[0098] Further, the preparation method provided by the present invention can also be used to prepare a core-shell structure with multiple nested cyclic units. In a specific embodiment, the first cyclic unit includes a core (catalytic material), a first nano-shell layer (lithium supplement material), and a second nano-shell layer (conductive material); since the content of the conductive material in the lower layer decreases after the conductive material covers the nano-shell layer of the lithium supplement material, the proportion of the catalytic material in the ball-milling solvent increases, and the composite lithium supplement material with the first cyclic unit is distributed to the solution part of the catalytic material. Then, the rotation speed of the ball-milling tank is continuously controlled to evaporate the solvent water and the movement of the ball-milling beads, so that the catalytic material covers the nano-shell layer of the conductive material, forming a nano-shell layer of the catalytic material, and the lithium supplement material precipitates and crystallizes. Therefore, by repeatedly adjusting the drive of the ball-milling device, a core-shell structure with multiple nested cyclic units can be prepared.

[0099] In other embodiments, the lithium supplement material includes a soluble material of the organic system and an insoluble material of the inorganic system, and the density ρ1 of the core substrate, the density ρ2 of the catalytic material, the density ρ3 of the conductive material, and the density ρ4 of the inorganic lithium supplement material satisfy: ρ1 ≤ ρ2 < ρ4 < ρ3. The formation methods of the four materials can refer to the above mechanism and will not be elaborated here. Of course, the formed composite lithium supplement material can include a catalytic material core, an organic lithium supplement material, an inorganic lithium supplement material, and a conductive material from the inside to the outside.

[0100] It can be understood that the preparation method provided by the present invention does not limit the order of the nano-shell layers formed by the lithium supplement material, the conductive material, and the catalytic material. In a specific preparation method, it is also possible to first cover the conductive material (or catalytic material) on the core substrate by the movement of the ball-milling beads, and then use the rotation speed of the ball-milling tank to evaporate water, so that the lithium supplement material precipitates and crystallizes on the functional material.

[0101] In addition, the preparation method provided by the present invention can also be applied to the scheme of simultaneously using multiple conductive materials, multiple catalytic materials, and multiple lithium supplement materials. That is, the composite lithium supplement material includes multiple nano-shell layers, and each of the multiple nano-shell layers independently includes multiple conductive materials, multiple catalytic materials, and multiple lithium supplement materials.

[0102] In one embodiment, the precursor solution further includes an organic additive. Please refer to Figure 6 , in step S20, after the lithium supplement material and the functional material are respectively formed on the outer layer of the core substrate, it further includes:

[0103] Step S21, filtering and drying the crystallized core-shell structure to obtain a first composite lithium supplement agent with a core-shell structure.

[0104] Step S22, performing a calcination treatment on the first composite lithium supplement agent to obtain a second composite lithium supplement agent with a core-shell structure and a cavity.

[0105] In a specific embodiment, in step S10, an organic additive is further added to the ball milling solvent. The organic additive includes a dispersant and a stabilizer. The dispersant is used to disperse materials insoluble in the ball milling solvent, such as the core substrate and the functional material. The stabilizer is used to improve the stability of the materials in the precursor solution. Therefore, the main function of the organic additive is to ensure the uniform dispersion of the core substrate and the functional material, avoid the agglomeration of the two, and improve the uniformity of the formation of the nano shell layer.

[0106] It can be understood that since the organic additive is an organic substance, the organic additive can be decomposed by high-temperature calcination, so that the organic additive originally mixed in the first composite lithium supplementing agent is removed, and cavities are formed in the core or the nano shell layer.

[0107] It should be noted that both the first composite lithium supplementing agent and the second composite lithium supplementing agent are the composite lithium supplementing agents protected by this application. Both of them have the same lithium supplementing effect, and can achieve the effects of exerting the optimal performance of the material, reducing side reactions, increasing the binding energy, and increasing the mass ratio of the lithium supplementing material. Of course, since the second composite lithium supplementing agent forms cavities, which is convenient for the penetration of the electrolyte, the transmission of lithium ions changes from simple solid-phase conduction to multi-layered solid-liquid biphasic conduction, accelerating the transmission of lithium ions and reducing the overpotential and plateau of the lithium supplementing material.

[0108] In the present invention, by adding an organic additive during the preparation process, it can be used to disperse the lithium supplementing material and the functional material, especially to disperse insoluble materials, avoid the agglomeration of the materials, and improve the uniformity of the nano shell layer. Moreover, the organic additive can be removed by high-temperature sintering, so that cavities are formed in the composite lithium supplementing agent. The cavities are convenient for the penetration of the electrolyte, making the transmission of lithium ions change from simple solid-phase conduction to multi-layered solid-liquid biphasic conduction, accelerating the transmission of lithium ions, and reducing the overpotential and plateau of the lithium supplementing material.

[0109] In one embodiment, the present invention further provides a cathode material, which includes a cathode active material and a lithium supplementing agent. The lithium supplementing agent is the composite lithium supplementing agent provided in the above embodiment. Optionally, the cathode active material can be a phosphate cathode active material or a ternary cathode active material. In a specific embodiment, the cathode active material includes one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium fluorovanadate, lithium titanate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate.

[0110] In one embodiment, the content of the composite lithium supplement in the cathode material can be controlled to be 1% to 6% of the mass of the cathode active material. This ratio can exactly compensate for the loss of active lithium during the first charging process of the battery. If the addition amount of the composite lithium supplement in the cathode material is too low, the lost active lithium in the cathode active material cannot be completely replenished, which is not conducive to improving the energy density and capacity retention rate of the battery, etc. If the addition amount of the composite lithium supplement in the cathode active material is too high, it will occupy the original reversible capacity and increase the cost. In some specific embodiments, in the cathode material, the mass percentage content of the composite lithium supplement can be 1%, 2%, 4%, 6%, etc.

[0111] In one embodiment, the present invention also provides a positive electrode plate, which includes a current collector and an active material layer provided on the current collector. The active material layer includes the composite lithium supplement according to any one of the above embodiments. Or the active material layer includes the composite lithium supplement obtained by the preparation method of the composite lithium supplement in the above embodiments.

[0112] In one embodiment, the positive electrode plate includes a positive current collector, and a positive active layer is provided on the positive current collector. The positive active layer includes components such as a positive active material, a composite lithium supplement, a conductive agent, and a binder. The present invention does not make specific limitations on 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 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 3 wt% to 5 wt%. 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 adhesive in the positive active layer is 2 wt% to 4 wt%.

[0113] In one embodiment, the present invention also provides a secondary battery, which includes a negative electrode, a positive electrode, and an electrolyte. Among them, the positive electrode includes the above-mentioned cathode material; the electrolyte can be an electrolyte solution. In this way, the secondary battery further includes a separator provided between the positive electrode plate and the negative electrode plate; or the electrolyte can be a solid electrolyte. In this way, no separator is provided in the secondary battery, and it is replaced by a solid electrolyte.

[0114] The technical solution of the present invention will be described in detail below through specific examples.

[0115] Example 1

[0116] This example provides a composite lithium supplement. The composite lithium supplement includes a core CoO and multiple nano shell layers. The core and the multiple nano shell layers of the composite lithium supplement form multiple cyclic units. Each cyclic unit includes CoO, lithium oxalate (Li2 C 2 O 4 ) and Ketjen black (KB). Among them, the composite lithium supplementing agent also has cavities.

[0117] The thickness of each nano-shell layer is 50 nm, the particle size of the inner core is 20 nm, the particle size of the composite lithium supplementing agent is 5 μm, and the mass ratio of the lithium supplementing material, the conductive material and the catalytic material is 100:15:10.

[0118] The preparation method of the composite lithium supplementing agent includes the following steps:

[0119] (1) Prepare the ball-milling solvent by mixing water and an organic solvent (glycerol) at a mass ratio of 100:40.

[0120] (2) Add the inner core substrate / catalytic material (CoO), lithium oxalate (Li 2 C 2 O 4 ) and the conductive material (KB) into the ball-milling solvent according to the mass ratio to obtain a precursor solution.

[0121] (3) Place the precursor solution in a ball-milling device, control the rotation speed of the ball-milling device to control the evaporation rate of water, and let lithium oxalate slowly crystallize on the surface of the inner core substrate. Then, cover the conductive material on the lithium oxalate crystal layer through the ball-milling beads, and then cover the catalytic material.

[0122] (4) Filter and dry the crystallized material with a core-shell structure, and perform a calcination treatment on the dried material to obtain a composite lithium supplementing agent with a core-shell structure and cavities.

[0123] Example 2

[0124] This example provides a composite lithium supplementing agent. The difference between this example and Example 1 is that each cycle unit includes CoO, lithium oxalate and MnO arranged in sequence 2 .

[0125] Example 3

[0126] This example provides a composite lithium supplementing agent. The difference between this example and Example 1 is that each cycle unit includes nano-aluminum, lithium oxalate and KB arranged in sequence.

[0127] Example 4

[0128] This example provides a composite lithium supplementing agent. The difference between this example and Example 1 is that the inner core is replaced with nano-SiO 2 material; each cycle unit includes CoO, lithium oxalate and KB arranged in sequence.

[0129] Example 5

[0130] This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that each cycle unit includes lithium oxalate, CoO, and MnO arranged in sequence. 2 and KB.

[0131] Embodiment 6

[0132] This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the composite lithium supplement does not have a cavity.

[0133] Embodiment 7

[0134] This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the thickness of the nanoshell layer is 10 nm, and the particle size of the composite lithium supplement is 500 nm.

[0135] Embodiment 8

[0136] This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the thickness of the nanoshell layer is 100 nm, and the particle size of the composite lithium supplement is 30 μm.

[0137] Embodiment 9

[0138] This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the particle size of the core is 5 nm, and the particle size of the composite lithium supplement is 500 nm.

[0139] Embodiment 10

[0140] This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the particle size of the core is 50 nm, and the particle size of the composite lithium supplement is 30 μm.

[0141] Embodiment 11

[0142] This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the mass ratio of the lithium supplement material, the conductive material, and the catalytic material is 100:5:1.

[0143] Embodiment 12

[0144] This embodiment provides a composite lithium supplement. The difference between this embodiment and Embodiment 1 is that the mass ratio of the lithium supplement material, the conductive material, and the catalytic material is 100:20:20.

[0145] Comparative Example 1

[0146] This comparative example provides lithium oxalate.

[0147] Comparative Example 2

[0148] This comparative example provides a composite lithium supplement agent with a core-shell structure. The composite lithium supplement agent includes a lithium oxalate core, a CoO catalytic layer, and a KB conductive layer.

[0149] The parameters of the composite lithium supplement agents provided in Examples 1-12 and Comparative Examples 1-2 are shown in Table 1:

[0150] Table 1 Parameters of the composite lithium supplement agents provided in Examples and Comparative Examples

[0151]

[0152]

[0153] The composite lithium supplement agents provided in Examples 1-12 and Comparative Examples 1-2 above were assembled into positive electrode sheets and lithium-ion batteries respectively according to the following methods:

[0154] Positive electrode sheet: The composite lithium supplement agent, SP, and PVDF were mixed into a positive electrode slurry by homogenization according to a mass ratio of 90:4:6. The positive electrode slurry was coated on the surface of aluminum foil and vacuum dried overnight at 110 °C, and then roll-pressed to obtain the positive electrode sheet;

[0155] Negative electrode sheet: Lithium sheet;

[0156] Electrolyte: Ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7, and LiPF 6 , was added to form an electrolyte, and the concentration of LiPF 6 was 1 mol / L;

[0157] Separator: Polypropylene microporous separator;

[0158] Assembly of lithium-ion battery: A button-type lithium-ion full battery was assembled in an inert atmosphere glove box according to the assembly order of negative electrode sheet - separator - electrolyte - positive electrode sheet.

[0159] 1) The electrochemical performance of each lithium-ion battery assembled in the above lithium-ion battery examples was tested under the following conditions:

[0160] The battery was charged at a rate of 0.1C, and the cut-off voltage was 4.7V; constant voltage charging was carried out at 4.7V; after the charging process was completed, it was left to stand for 10 minutes and then discharged at a rate of 0.1C, and the cut-off voltage was 2.5V; the charging platform was observed during the charging process to obtain the decomposition voltage of the composite lithium supplement agent.

[0161] 2) The gas production of each lithium-ion battery assembled in the above lithium-ion battery examples was tested according to the following method:

[0162] Put the lithium-ion battery that has been charged and discharged into a gas sampling bag. Break open the lithium-ion battery through the device inside the gas sampling bag and release the gas into the gas sampling bag. Then, bring the gas sampling bag into contact with a syringe. Place the gas sampling bag in water and press all the gas into the syringe equipped with a pressure gauge. Adjust the syringe so that the pressure gauge maintains atmospheric pressure, and read the syringe scale to obtain the gas production volume (mL / g) of the lithium-ion battery.

[0163] The test results of the above lithium battery are shown in Table 2 below:

[0164] Table 2. Test results of examples and comparative examples

[0165]

[0166] From the test results of Example 1, Comparative Example 1, and Comparative Example 2 in Table 2, it can be seen that compared with Comparative Example 1, for Example 1, the charge specific capacity of the lithium supplementation material (lithium oxalate) after compounding is significantly improved compared to pure lithium oxalate, and the overpotential and decomposition voltage plateau are significantly decreased. Because after adding the catalytic material and the conductive material, the catalytic material can catalyze the lithium supplementation material to release lithium ions at a lower voltage, reducing the overpotential, indicating that the conductive material reduces the internal impedance of the material. Compared with Comparative Example 2, for Example 1, after fabricating the lithium supplementation material, conductive material, and catalytic material into a unique multi-layer core-shell structure, the electrical properties of the lithium supplementation material can be further improved, the decomposition voltage plateau can be reduced, and the lithium supplementation capacity can be increased. In addition, the gas production of the material can be significantly reduced.

[0167] From the test results of Examples 1 - 3 in Table 2, it can be seen that the solution provided by the present invention can be applied to the case without a conductive material or a catalytic material, and in the case without a catalytic material (Example 3), the solution provided by the present invention can still be used to reduce the gas production of the composite lithium supplementation agent.

[0168] From the test results of Example 1 and Example 4 in Table 2, it can be seen that the inner core provided by the present invention can use other substrates without a catalytic material, and other materials can be used as the crystallization nucleus, so that the lithium supplementation material, catalytic material, and conductive material cover the outer surface of the crystallization nucleus, thereby constructing a unique multi-layer core-shell structure to achieve the purpose of improving the electrical properties of the material and reducing gas production.

[0169] From the test results of Example 1 and Example 5 in Table 2, it can be seen that the number of nano-shell layers in the cycle unit is not limited. Using another catalytic material to construct a cycle unit with four nano-shell layers can not only further improve the electrical properties of the material but also reduce gas production.

[0170] From the test results of Example 1 and Example 6 in Table 2, it can be seen that by constructing a cavity in the composite lithium supplementation agent, the ion conduction speed can be increased.

[0171] As can be seen from the test results of Examples 1, 7 and 8 in Table 2, the thickness of the nano-shell layer and the particle size of the finally formed composite lithium supplement have an impact on the overall performance of the material. By adjusting the thickness of the nano-shell layer and the particle size of the composite lithium supplement within an appropriate range, the electrochemical performance and gas generation amount of the composite lithium supplement can be controlled.

[0172] As can be seen from the test results of Examples 1, 9 and 10 in Table 2, the particle size of the core and the particle size of the finally formed composite lithium supplement have an impact on the overall performance of the material. By adjusting the particle size of the core and the particle size of the composite lithium supplement within an appropriate range, the electrochemical performance and gas generation amount of the composite lithium supplement can be controlled.

[0173] As can be seen from the test results of Examples 1, 11 and 12 in Table 2, the mass ratio of the lithium supplement material, the conductive material and the catalytic material has an impact on the overall performance of the material. By adjusting the mass ratio of the three within an appropriate range, the composite lithium supplement can have a high lithium supplement capacity and a low gas generation amount.

[0174] In the description of the embodiments of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present invention.

[0175] The above-disclosed is only a preferred embodiment of the present invention. Of course, the scope of the rights of the present invention cannot be limited thereby. Those of ordinary skill in the art can understand all or part of the processes of implementing the above embodiments, and the equivalent changes made according to the claims of the present invention still fall within the scope covered by the present invention.

Claims

1. A composite lithium supplement, characterized in that: The composite lithium supplement agent is a core-shell structure, including a core and at least two nanoshell layers; wherein at least one nanoshell layer includes a lithium supplement material, and at least one nanoshell layer includes a functional material, and the functional material includes a conductive material and / or a catalytic material.

2. The composite lithium supplement according to claim 1, characterized in that: The composite lithium supplement agent includes a plurality of sequentially nested circulation units, each of which includes at least two layers of the nanoshell layers, and each of which includes the catalytic material, the lithium supplement material and the conductive material.

3. The composite lithium supplement according to claim 2, characterized in that: The plurality of circulation units include a first circulation unit, the first circulation unit also including the core, in which the material density in the core is less than the material density in the nanoshell layer away from the core; and / or, in at least some of the circulation units, the material density in the nanoshell layer close to the core is less than the material density in the nanoshell layer away from the core.

4. The composite lithium supplement according to any one of claims 1 to 3, characterized in that: The core includes the catalytic material, the multiple nanoshell layers include a first nanoshell layer and a second nanoshell layer nested in sequence, the first nanoshell layer includes the lithium supplement material, and the second nanoshell layer includes the conductive material.

5. The composite lithium supplement according to claim 1, characterized in that: The core further has a cavity, and / or, the core and the nanoshell layer have a cavity, and / or, the nanoshell layer further has a cavity, and / or, two adjacent nanoshell layers have a cavity.

6. The composite lithium supplement according to claim 1, characterized in that: The chemical formula of the lithium supplement material includes Li x C y O z , where 0<x≤2,y> 0, z>0; and / or The conductive material includes one or more of a carbon material, a metal material, and a metal carbide; and / or The catalytic material includes one or more of metal oxides, metal carbides, and metal sulfides; and / or The thickness of each nanoshell layer is 10nm to 100nm; and / or The particle size of the core is 5nm to 50nm; and / or The overall particle size of the composite lithium supplement agent is 0.5 μm to 30 μm; and / or The mass ratio of the lithium supplement material, the conductive material and the catalytic material is 100:(5-20):(1-20).

7. A method for preparing a composite lithium supplement, characterized in that: The preparation method of the composite lithium supplement is used to prepare the composite lithium supplement according to any one of claims 1 to 6, and the preparation method comprises: Adding the core substrate, the lithium supplement material and the functional material into a ball milling solvent to obtain a precursor solution; The precursor solution is placed in a ball milling device, and the rotation speed of the ball milling device is controlled to evaporate at least part of the ball milling solvent. The lithium supplement material and the functional material are respectively formed on the outer layer of the core substrate to obtain the composite lithium supplement agent with a core-shell structure.

8. The preparation method according to claim 7, characterized in that: The method of mixing the core substrate, the lithium supplement material and the functional material into a solvent to obtain a precursor solution comprises: The ball milling solvent is prepared by mixing water and an organic solvent according to a mass ratio; The core substrate, the lithium supplement material and the functional material with different densities are mixed into the ball milling solvent to obtain a precursor solution.

9. The preparation method according to claim 7, characterized in that: The precursor solution also includes an organic additive, and after the lithium supplement material and the functional material are formed on the outer layer of the core substrate respectively, the precursor solution also includes: filtering and drying the crystallized core-shell structure to obtain a first composite lithium supplement agent with a core-shell structure; The first composite lithium supplement agent is calcined to obtain a second composite lithium supplement agent having a core-shell structure and a cavity.

10. A secondary battery, characterized in that: It comprises a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode comprises the composite lithium supplement according to any one of claims 1 to 6, or the positive electrode comprises the composite lithium supplement prepared by the preparation method of the composite lithium supplement according to any one of claims 7 to 9.

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