Composite lithium supplementing material and preparation method thereof, positive electrode material and secondary battery

Abstract

The invention discloses a composite lithium supplementing material and a preparation method thereof, a positive electrode material and a secondary battery. The composite lithium supplementing material comprises a lithium-rich material and a catalytic core, wherein the specific surface area of the catalytic core is 50-120 m < 2 > / g; the lithium-rich material grows on the outer surface layer of the catalytic core in situ, and the lithium-rich material is tightly stacked on the outer surface layer of the catalytic core. The specific surface area of the catalytic core is 50m < 2 > / g to 120m < 2 > / g and is far larger than that of a catalyst in the prior art, so that more surface active sites are exposed on the surface of the catalytic core, a lithium-rich material can be in full contact with the active sites of the catalytic core, and the catalytic efficiency of the catalytic core is increased; moreover, the lithium-rich material grows on the outer surface layer of the catalytic core in situ, so that the connection strength of the lithium-rich material and the catalytic core is increased, and active sites on the surface of the catalytic core can be covered as many as possible, thereby maintaining the catalytic activity of the catalytic core and avoiding the reduction of the catalytic performance of the catalytic core.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a composite lithium supplement material and a preparation method thereof, a positive electrode material and a secondary battery. Background Art

[0002] With the rapid development of electric vehicles and electrochemical energy storage, traditional lithium-ion batteries are unable to meet the growing demand for energy density. In practical applications, simply increasing the energy density of the cathode has limited effect on the actual application of the full battery, because in the initial cycle, the Coulombic efficiency (CE) of the anode is much lower than that of the cathode. For the negative electrode, the irreversible loss of lithium is caused by the formation of a solid electrolyte interface (SEI) and metallic lithium plating. Therefore, the development of pre-lithiation technology to compensate for the loss of active lithium is the key to improving the energy density of the full battery.

[0003] Positive electrode lithium replenishment is a method of replenishing lithium by adding an additional lithium source to the positive electrode active material. However, the current lithium replenishment materials have the problem of high delithiation voltage, which makes it impossible for the lithium replenishment materials to fully release lithium ions under low voltage conditions. Therefore, metal catalysts are added to the existing lithium replenishment materials to reduce the delithiation potential of lithium-rich materials in the lithium replenishment materials. However, after the metal catalyst and the lithium-rich material are simply mixed, the contact points between the metal catalyst and the lithium-rich material are limited due to the low specific surface area of ​​the metal catalyst, so the catalytic effect of the metal catalyst is limited. In addition, the surface of the metal catalyst is covered by the solid product initially deposited, which significantly deteriorates the subsequent catalytic activity, resulting in a limited decrease in the delithiation voltage of the lithium replenishment material. Therefore, how to provide a lithium-rich material that effectively reduces the delithiation voltage has become the key. Summary of the invention

[0004] The purpose of the present application is to provide a composite lithium supplement material and a preparation method thereof, a positive electrode material and a secondary battery, so as to solve the problem of high decomposition voltage of lithium-rich materials.

[0005] To achieve the purpose of this application, this application provides the following technical solutions:

[0006] In a first aspect, the present invention provides a composite lithium supplement material, comprising a lithium-rich material and a catalytic core, wherein the specific surface area of ​​the catalytic core is 50 m 2 / g~120m 2 / g; the lithium-rich material is in-situ grown on the outer layer of the catalytic core, and the lithium-rich material is tightly stacked on the outer layer of the catalytic core.

[0007] The present invention provides a composite lithium-supplementing material composed of a catalytic core with a large specific surface area and a lithium-rich material. The specific surface area of ​​the catalytic core is 50 m 2 / g~120m 2 / g, and its specific surface area far exceeds that of the catalysts in the prior art, so that more surface active sites are exposed on the surface of the catalytic core, the lithium-rich material can fully contact with the active sites of the catalytic core, and the catalytic efficiency of the catalytic core is increased; moreover, the lithium-rich material is in situ grown on the outer layer of the catalytic core, so that the connection strength between the lithium-rich material and the catalytic core is increased, and the active sites on the surface of the catalytic core can be covered as much as possible, thereby maintaining the catalytic activity of the catalytic core and avoiding the catalytic performance of the catalytic core from decreasing.

[0008] In one embodiment, the catalytic core has a plurality of grooves, and the lithium-rich material is filled in the grooves.

[0009] In one embodiment, the catalytic core includes an inner core and a plurality of branches, wherein the branches are connected to the inner core, the grooves are formed between the plurality of branches, and the branches extend in a direction away from the inner core to be exposed to the external environment.

[0010] In one embodiment, the composite lithium-supplementing material further includes a carbon material, and the carbon material is combined on the outer surface of the lithium-rich material and the catalytic core.

[0011] In one embodiment, the carbon material includes carbon nanotubes, and the carbon nanotubes are in-situ grown on the branches exposed to the external environment.

[0012] In one embodiment, the particle size of the catalytic core is 0.6 μm to 1.2 μm.

[0013] In one embodiment, the groove width of the catalytic core is 30nm to 100nm.

[0014] In one embodiment, the specific surface area of ​​the catalytic core is 50 m 2 / g~120m 2 / g.

[0015] In one embodiment, the catalytic core includes one or more of metal carbides, metal sulfides, and metal oxides.

[0016] In one embodiment, the catalytic core is at least one of a dandelion shape, a pine needle shape, and a fluff ball shape.

[0017] In one embodiment, the catalytic core accounts for 5% to 15% of the mass of the composite lithium supplement material.

[0018] In one embodiment, the particle size of the composite lithium supplement material is 0.6 μm to 1.5 μm.

[0019] In a second aspect, the present invention also provides a method for preparing a composite lithium supplement material, comprising: preparing a catalyst precursor into a catalytic core, wherein the specific surface area of ​​the catalytic core is 50 m 2 / g~120m 2 / g; mixing the lithium-rich material with the catalytic core so that the lithium-rich material is in-situ grown on the outer layer of the catalytic core.

[0020] In one embodiment, the lithium-rich material and the catalytic core are stacked to form a stacking material, a carbon source is mixed with the stacking material, and the carbon source etches the outer surface of the stacking material so that the branches of the catalytic core are exposed to the external environment; the stacking material loaded with the carbon source is sintered, and the carbon source is converted into a carbon material, and the carbon material is coated on the outer surface of the stacking material.

[0021] In a third aspect, the present invention further provides a positive electrode material, which includes a positive electrode active material and a lithium supplement material, wherein the lithium supplement material includes the composite lithium supplement material described in the first aspect, or the positive electrode material includes the composite lithium supplement material obtained by the preparation method of the composite lithium supplement material described in the second aspect.

[0022] In a fourth aspect, the present invention further provides a secondary battery, comprising a positive electrode, a negative electrode and an electrolyte arranged between the positive electrode and the negative electrode, wherein the positive electrode comprises the positive electrode material described in the third aspect; the electrolyte may be liquid or solid, and if a liquid electrolyte is used, a diaphragm is required for use. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the implementation methods of the present application or the technical solutions in the prior art, the drawings required for use in the implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some implementation methods of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1 is a schematic structural diagram of a lithium supplement material according to an embodiment;

[0025] Figure 2 is a schematic structural diagram of a catalytic core of one embodiment;

[0026] Figure 3 is a schematic diagram of a preparation process of a lithium supplement material according to an embodiment;

[0027] Figure 4 is a schematic diagram of a preparation process of a catalytic core according to an embodiment;

[0028] Figure 5is a schematic diagram of a preparation process of a catalytic core according to another embodiment;

[0029] Figure 6 is a schematic diagram of a preparation process of a lithium supplement material according to another embodiment;

[0030] Figure 7 is a schematic diagram of an etching reaction in one embodiment;

[0031] Figure 8 is a SEM image of the composite lithium supplement material provided in Example 1;

[0032] Fig. 9 is a SEM image of the composite lithium supplement material provided in Example 13;

[0033] Fig.10 This is a SEM image of the composite lithium supplement material provided in Example 15. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0035] 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 there can be a central component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there can be a central component at the same time.

[0036] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used in this application and in the specification are only for the purpose of describing specific embodiments and are not intended to limit this application. The term "and / or" used in this application includes any and all combinations of one or more of the related listed items.

[0037] In conjunction with the accompanying drawings, some embodiments of the present application are described in detail below. In the absence of conflict, the following embodiments and features in the embodiments can be combined with each other.

[0038] The present invention provides a composite lithium supplement material, please refer to Figure 1 and Figure 2 , including lithium-rich material and catalytic core, the specific surface area of ​​the catalytic core is 50m 2 / g~120m 2 / g; the lithium-rich material is in-situ grown on the outer layer of the catalytic core, and the lithium-rich material is densely stacked on the outer layer of the catalytic core.

[0039] The lithium-rich material 10 is the main body for lithium supplementation, which can contribute a large amount of lithium ions. During the first charging process, the lithium in the lithium-rich material 10 can be released and migrated to the negative electrode of the battery to offset the irreversible lithium loss caused by the formation of the SEI film, thereby increasing the total capacity and energy density of the battery. However, most of the existing high-capacity lithium-rich materials 10 have problems with poor conductivity and high detachment potential, which makes the lithium-rich material 10 unable to match most commercial positive electrode materials, which greatly hinders its commercial application. Therefore, how to solve the high detachment potential and poor conductivity of the lithium-rich material 10 has become the key.

[0040] In one embodiment, the chemical formula of the lithium-rich material 10 is Li x C y O z , where 0<x≤2,y> 0, z>0. In some embodiments of the present application, the lithium-rich material 10 can be one or more of Li2CO3, Li2C3O3, Li2C4O4, Li2C6O6, Li2C3O5, Li2C2O4 and Li2C4O6. It can be understood that such lithium-rich materials 10 have a relatively high theoretical capacity (for example, the theoretical capacity of Li2CO3 can reach 725 mAhg -1 , the theoretical capacity of Li2C6O6 can also reach 294mAhg -1 ) and good air stability, it is considered to be an attractive cathode pre-lithiation additive. However, it has a high delithiation potential (>4.7V), which cannot match most commercial cathode voltage systems, and its poor conductivity greatly hinders its commercial application.

[0041] In one embodiment, the lithium-rich material 10 also includes other lithium-supplementing materials with higher decomposition voltages, mainly including lithium-supplementing materials with a delithiation potential of more than 4V, such as Li2O (delithiation potential 4.5V), Li2O2 (delithiation potential 4.3V), LiOH (delithiation potential 4.8V), Li4SiO4 (delithiation potential 4.5V), Li3PO4 (delithiation potential exceeding 4V), and Li5FeO4 (delithiation potential 4V). These lithium-rich materials 10 also have a higher capacity, but these lithium-rich materials 10 require a higher charging voltage for delithiation, and there is a technical problem of high platform voltage. At the same time, the higher voltage also causes the lithium-rich material 10 to produce oxygen when the lithium-ion battery is charged and discharged for the first time. The generated oxygen is further oxidized to cause oxidative decomposition of the electrolyte, thereby reducing the safety and performance of the lithium-ion battery. These lithium-rich materials 10 with higher decomposition voltages are also difficult to compound with conventional positive electrode materials (such as lithium iron phosphate with a delithiation potential of about 3.5V), which limits the wide application of lithium-supplementing materials.

[0042] Furthermore, the catalytic core 20 includes a catalytic material, which has a catalytic effect and is used to catalytically reduce the delithiation potential of the lithium-rich material 10. It should be explained that among the existing commercial lithium-rich materials 10, most of the lithium-rich materials 10 have a relatively high capacity, but because the delithiation potential of the lithium-rich material 10 does not match the voltage of the existing commercial positive electrode materials, the lithium-rich material 10 cannot fully release its capacity during use. Therefore, by adding a catalytic material to the lithium-supplementing material to reduce the activation energy of the reaction and increase the reaction rate. The addition of the catalytic material can reduce the delithiation potential of the lithium-rich material 10 to varying degrees, so that it can match the existing commercial positive electrode materials.

[0043] In one embodiment, the catalytic material includes one or more of metal carbides, metal sulfides, and metal oxides. In a specific embodiment, the catalytic material includes metal carbides, and the metal carbides may be nickel carbide, iron carbide, titanium carbide, etc. In other embodiments, the catalytic material includes metal sulfides, metal oxides, etc., and may be copper oxide, zinc oxide, cobalt sulfide, nickel sulfide, etc.

[0044] In one embodiment, the specific surface area of ​​the catalytic core 20 is 50 m 2 / g~120m 2 Optionally, the specific surface area of ​​the catalytic core 20 may be 50 m 2 / g, 60m 2 / g, 70m 2 / g, 80m 2 / g, 90m 2 / g、100m 2 / g, 110m 2 / g, 120m 2 / g.

[0045] When the specific surface area of ​​the catalytic core 20 is within the above range, the loading amount of the lithium-rich material 10 on the catalytic core 20 can be increased, thereby increasing the lithium replenishment capacity of the composite lithium replenishing material. When the specific surface area of ​​the catalytic core 20 is less than the above range, the loading amount of the lithium-rich material 10 is small, resulting in limited improvement in the lithium replenishment capacity of the composite lithium replenishing material, and the effect of the catalytic core 20 is relatively weak; when the specific surface area of ​​the catalytic core 20 is greater than the above range, it is difficult for the catalytic core 20 to suppress the lattice volume expansion of the composite lithium replenishing material.

[0046] It should be noted that the specific surface area of ​​catalysts in the prior art is mostly concentrated around 40 m 2 / g~80m 2 / g. Therefore, the specific surface area of ​​the catalyst in the prior art is relatively small, which makes it difficult for the catalyst in the prior art to load sufficient lithium-rich materials. In addition, the specific surface area of ​​the existing catalyst is relatively low, which limits the contact points between the catalyst and the lithium-rich material, so the catalytic effect of the catalyst is limited, and the surface of the catalyst is covered by the solid product initially deposited, thereby significantly deteriorating the subsequent catalytic activity, resulting in a limited decrease in the de-lithiation voltage of the lithium-supplementing material.

[0047] Therefore, the present invention provides a composite lithium supplement material composed of a catalytic core 20 with a large specific surface area and a lithium-rich material 10. The specific surface area of ​​the catalytic core 20 is 50 m 2 / g~120m 2 / g, and its specific surface area far exceeds that of the catalysts in the prior art, so that more surface active sites are exposed on the surface of the catalytic core 20, the lithium-rich material 10 can fully contact with the active sites of the catalytic core 20, and the catalytic efficiency of the catalytic core 20 is increased; moreover, the lithium-rich material 10 is in situ grown on the outer layer of the catalytic core 20, so that the connection strength between the lithium-rich material 10 and the catalytic core 20 is increased, and the active sites on the surface of the catalytic core 20 can be covered as much as possible, thereby maintaining the catalytic activity of the catalytic core 20 and avoiding the catalytic performance of the catalytic core 20 from decreasing.

[0048] In one embodiment, the catalytic core 20 has a plurality of grooves, and the lithium-rich material 10 is in-situ grown on the outer surface of the catalytic core 20 and fills the grooves, so that the catalytic core 20 becomes the main body of the lithium-rich material 10. The structure formed thereby includes but is not limited to a spherical shape, a polyhedron shape, etc. The grooves on the catalytic core 20 increase its own specific surface area, the surface active sites on the catalytic core 20 are exposed, and the lithium-rich material 10 is tightly stacked at the active position, thereby increasing the catalytic activity of the catalytic core 20 to the lithium-rich material 10. The catalytic core 20 is composed of a core and many radially arranged branches, and grooves are formed between the branches. The precursor solution of the lithium-rich material 10 grows by heterogeneous nucleation and crystallization on the surface of the catalytic core 20, and accumulates and fills the grooves.

[0049] The present invention forms a tightly stacked material by opening grooves on the catalytic core 20 and allowing the lithium-rich material 10 to grow in situ on the outer surface of the catalytic core 20 and fill the grooves. The composite lithium-supplementing material has the following advantages: the grooves on the catalytic core 20 increase its own specific surface area, thereby exposing more surface active sites, and the contact area between the lithium-rich material 10 filled in the grooves and the catalytic core 20 is increased, thereby improving the catalytic effect of the catalytic core 20 on the lithium-rich material 10.

[0050] In one implementation, please refer to Figure 1 and Figure 2 The catalytic core 20 includes an inner core 21 and a plurality of branches 22, wherein the branches 22 are connected to the inner core 21, and grooves are formed between the plurality of branches 22, and the branches 22 extend in a direction away from the inner core to be exposed to the external environment. Optionally, the catalytic core 20 is at least one of a dandelion shape, a pine needle shape, and a plush ball shape.

[0051] In a specific embodiment, the inner core 21 and the branches 22 together form the catalytic core 20 into a dandelion-shaped or sea urchin-shaped structure. The advantages of the catalytic core 20 of this structure include: 1) compared with the current spherical catalytic material, the dandelion-shaped or sea urchin-shaped catalytic core 20 has a larger molecular gap and accommodation space under the same volume, and can load more lithium-rich materials 10, thereby increasing the lithium replenishment capacity of the lithium replenishment material under unit volume; 2) the dandelion-shaped or sea urchin-shaped catalytic core 20 has a larger specific surface area, which increases the contact area between the catalytic core 20 and the lithium-rich material 10, thereby improving the catalytic performance of the catalytic core 20.

[0052] It is understandable that the lithium-rich material 10 can be coated on the outer surface of the core 21 and the branches 22 to form a lithium-rich layer coating the catalytic core 20; the lithium-rich material 10 is uniformly coated on the outer surface of the catalytic core 20 to form a dense and stable coated lithium-rich layer. It should be explained that the lithium-rich material 10 is accumulated in the grooves between the branches 22, and the branches 22 pass through the lithium-rich layer to be exposed to the external environment.

[0053] In one embodiment, the catalytic core 20 further includes a growth end 23 , which is connected to an end of the branch 22 away from the core 21 , and the growth end 23 is exposed to the external environment.

[0054] In one embodiment, the growth end 23 exposed to the external environment may be a sheet structure, or a ball structure or a wire structure.

[0055] In one embodiment, the growth end 23 is hexagonal, and along the radial direction of the core 21 , the orthographic projection of the growth end 23 on the core 21 covers the orthographic projection of the branch 22 on the core 21 .

[0056] It can be understood that the diameter of the growth end 23 is larger than the diameter of the branch 22, so that the growth end 23 has a larger surface area; the growth end 23 with a larger surface area can combine more carbon materials 30; the carbon material 30 is connected to the catalytic core 20 as a conductive network to improve the conductivity of the composite lithium supplement material.

[0057] In a specific embodiment, the metal compounds aggregate to form the inner core 21; the branches 22 and the growth ends 23 grow radially outward along the inner core 21 to form the branches 22 and the growth ends 23; in the crystal structure of the metal compound, the face-centered cubic phase is stable, so densely packed hexagons are formed in the macroscopic view, and finally a hexagonal growth end 23 is formed.

[0058] In one implementation, please refer to Figure 1 The composite lithium supplement material also includes a carbon material 30 , which is combined on the outer surfaces of the lithium-rich material 10 and the catalytic core 20 .

[0059] Specifically, the lithium-rich material 10 and the catalytic core 20 are closely stacked to form a stacked material. A carbon material 30 is connected to the outer surface of the stacked material. In a specific embodiment, the carbon material 30 can be coated on the outer surface of the stacked material to form a carbon coating layer; in other embodiments, the carbon material 30 can be only combined with the branches 22 of the catalytic core 20 exposed to the outside. It can be understood that the carbon material 30 is mainly connected to the catalytic core 20, and the carbon material 30 combined with the catalytic core 20 serves as a conductive circuit, wherein a single catalytic core 20 is combined with multiple carbon materials 30, and multiple carbon materials 30 and the catalytic core 20 form multiple conductive circuits, and multiple conductive circuits thereby form a conductive network, thereby improving the conductivity of the composite lithium supplement material.

[0060] In a specific embodiment, the carbon material 30 is not selectively attached to the catalytic core 20, that is, the carbon material 30 will not only be attached to the catalytic core 20 exposed to the external environment, but the carbon material 30 will also be combined with the lithium-rich material 10, thereby forming a structure in which the carbon coating layer is coated on the outer surface of the stacked material. It can be understood that part of the carbon coating layer is coated on the lithium-rich material 10, and another part of the carbon coating layer is coated on the catalytic core; the carbon coating layer combined on the branch 22 serves as a conductive line, so that a conductive network is formed between the catalytic cores 20 through the carbon material 30, thereby improving the conductivity of the composite lithium supplement material. Optionally, the carbon material includes at least one of carbon nanotubes, graphene oxide, fullerenes and their derivatives, and carbon yne.

[0061] The purpose of setting a carbon coating layer on the outer surface of the composite lithium-supplementing material is to: 1) improve the conductivity of the composite lithium-supplementing material and increase the lithium ion transmission rate; 2) coat the stacked material to inhibit the lattice volume expansion of the lithium-rich material 10; 3) reduce the erosion of the lithium-rich material 10 by external water vapor.

[0062] In one embodiment, the carbon material 30 includes carbon nanotubes, which are in-situ grown on the branches 22 exposed to the external environment.

[0063] Specifically, since the branches 22 (or the growth ends 23) are exposed to the external environment, the carbon material 30 combined with the branches 22 is catalytically grown, so that carbon nanotubes 31 are in-situ grown on the branches 22. The in-situ grown carbon nanotubes 31 are connected to the catalytic core 20 as conductive lines, and multiple in-situ grown carbon nanotubes 31 are interconnected with multiple catalytic cores 20, and are interwoven in the composite lithium supplement material to form a conductive network structure.

[0064] The advantages of in-situ growth of carbon nanotubes on a catalytic core 20 exposed to the external environment are: 1) forming an effective conductive network to improve the overall conductivity of the composite lithium supplement material; 2) the in-situ grown carbon nanotubes can directly contact the catalytic core 20, preventing the surface of the catalytic core 20 from being covered by the initially deposited solid products, thereby avoiding a decrease in catalytic activity; 3) obtaining carbon nanotubes directly on the catalytic core 20 by in-situ growth can reduce interface defects between the catalytic core 20 and the carbon nanotubes, and can also adjust the growth environment to precisely control the size, shape and arrangement of the carbon nanotubes.

[0065] In one embodiment, the particle size of the catalytic core 20 is 0.6 μm to 1.2 μm. Optionally, the particle size of the catalytic core 20 may be 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, or 1.2 μm.

[0066] When the particle size of the catalytic core 20 is within the above range, it can ensure that the catalytic core 20 has a high catalytic performance, and can also reduce the difficulty of preparing the catalytic core 20 and avoid the agglomeration of the catalytic core 20. When the particle size of the catalytic core 20 is smaller than the above range, the difficulty of preparing the catalytic core 20 increases, and the agglomeration of the catalytic core 20 is serious, which affects the performance of its catalytic performance; when the particle size of the catalytic core 20 is larger than the above range, the catalytic performance of the catalytic core is reduced.

[0067] In one embodiment, the groove width of the catalytic core 20 is 30nm to 100nm (the distance between the tops of the branches is used as the width). Optionally, the groove width of the catalytic core 20 can be 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, or 100nm.

[0068] When the groove width of the catalytic core 20 is within the above range, the loading amount of the lithium-rich material 10 on the catalytic core 20 can be increased, thereby increasing the lithium replenishment capacity of the composite lithium replenishment material. When the groove width is less than the above range, the branches are dense and the groove is too narrow, the loading amount of the lithium-rich material 10 is small, resulting in limited improvement in the lithium replenishment capacity of the composite lithium replenishment material, and the effect of the catalytic core 20 is weak; when the groove width is greater than the above range, the branches are sparse, and it is difficult for the branches to cooperate with the carbon material 30 to form a rich conductive network.

[0069] In one embodiment, the length of the carbon nanotube is 50 nm to 100 nm. Optionally, the length of the carbon nanotube can be 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, or 100 nm.

[0070] When the length of the carbon nanotubes is within the above range, it can be ensured that the carbon nanotubes can connect two adjacent catalytic cores 20, thereby providing higher conductivity. When the length of the carbon nanotubes is less than the above range, the carbon nanotubes are shorter, resulting in the inability to construct a conductive circuit between the catalytic cores 20, and the inability to form a conductive network in the composite lithium-supplementing material, thereby reducing the conductivity of the composite lithium-supplementing material. When the length of the carbon nanotubes is greater than the above range, the carbon nanotubes are too long, resulting in an increase in the conduction path of electrons in the carbon nanotubes, which is not conducive to improving the conductive efficiency of the lithium-supplementing material, and the carbon nanotubes are too long, resulting in reduced mechanical properties of the carbon nanotubes, which are easy to break, resulting in the inability of the conductive circuits to connect to form a conductive network.

[0071] In one embodiment, the diameter of the carbon nanotube is 3 nm to 5 nm. Optionally, the diameter of the carbon nanotube can be 3 nm, 3.5 nm, 4 nm, 4.5 nm, or 5 nm.

[0072] When the diameter of the carbon nanotubes is within the above range, it can ensure that the carbon nanotubes have a larger specific surface area, thereby providing higher conductivity and higher strength. When the diameter of the carbon nanotubes is smaller than the above range, the carbon nanotubes are thinner, resulting in poor strength of the carbon nanotubes and easy breakage and slag. When the diameter of the carbon nanotubes is larger than the above range, the carbon nanotubes are thicker, resulting in a decrease in the specific surface area of ​​the carbon nanotubes, which is not conducive to improving conductivity.

[0073] In one embodiment, the mass proportion of the catalytic core in the composite lithium supplement material is 5% to 15%, and the mass proportion of the carbon nanotube in the composite lithium supplement material is less than or equal to 5%. Optionally, the mass proportion of the catalytic core in the composite lithium supplement material can be 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%. The mass proportion of the carbon nanotube in the composite lithium supplement material can be 0%, 1%, 2%, 3%, 4%, 5%.

[0074] When the mass ratio of the three materials is within the above range, the lithium replenishing capacity of the composite lithium replenishing material can be ensured, and the catalytic effect of the catalytic core 20 can be fully exerted, and the conductivity of the composite lithium replenishing material can be ensured, and the delithiation potential of the composite lithium replenishing material can be reduced. When the mass ratio of the carbon material 30 is less than the above range, the carbon material 30 is too little to form a sufficient conductive network, resulting in poor conductivity of the composite lithium replenishing material. When the mass ratio of the catalytic core 20 is less than the above range, the catalytic effect is poor, resulting in the incompatibility of the decomposition potential of the composite lithium replenishing material with the working voltage of the actual battery system. When the mass ratio of the above two materials is greater than the above range, the proportion of the lithium-rich material 10 will be further reduced, and the lithium-rich material 10 will find it difficult to exert more battery capacity, resulting in a decrease in the energy density of the battery.

[0075] In one embodiment, the particle size of the composite lithium supplement material is 0.6 μm to 1.5 μm. Optionally, the particle size of the composite lithium supplement material can be 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, or 1.5 μm.

[0076] When the particle size of the composite lithium supplement material is within the above range, the composite lithium supplement material can be matched with the positive electrode active material, and the lithium removal efficiency of the composite lithium supplement material can be improved. When the particle size of the composite lithium supplement material is smaller than the above range, the difficulty of preparing the catalytic core 20 increases, and the material is easy to accumulate and agglomerate. When the particle size of the composite lithium supplement material is larger than the above range, the composite lithium supplement material is not easy to match the positive electrode active material, and the lithium removal efficiency is reduced.

[0077] In one embodiment, the present invention also provides a method for preparing a composite lithium supplement material, please refer to Figure 3 , including the following steps:

[0078] Step S10, preparing a catalyst precursor into a catalytic core, wherein the specific surface area of ​​the catalytic core is 50 m 2 / g~120m 2 / g.

[0079] Step S20, mixing the lithium-rich material with the catalytic core, so that the lithium-rich material is in-situ grown on the outer surface of the catalytic core.

[0080] In the specific embodiment, please refer to Figure 4 Step S10, preparing the catalyst precursor into a catalytic core, specifically comprising:

[0081] Step S11, dispersing the catalyst material precursor in the solvent A, and stirring the mixture sufficiently to allow the catalyst material precursor and the solvent A to react sufficiently, thereby obtaining a mixed solution A.

[0082] Step S12, degassing the mixed solution A, and then backfilling it with a chemically stable gas to obtain a mixed solution B.

[0083] Step S13, heating the mixed solution B to obtain a mixed solution C.

[0084] Step S14, extracting the catalytic core in the mixed solution C.

[0085] Optionally, in step S11, solvent A is a mixed solution of oleylamine and 1-octadecene; and the catalytic material precursor is nickel acetylacetonate.

[0086] Optionally, in step S11, the catalytic material precursor and solvent A may be stirred evenly at room temperature until a mixed solution A is formed, wherein the stirring time may be 6 h to 12 h.

[0087] Optionally, in step S12, the degassing temperature is 60°C and the degassing time is 2 hours.

[0088] Optionally, in step S12, the chemically stable gas may be nitrogen, helium and argon.

[0089] Optionally, in step S13, the mixed solution B is heated, including a first step of heating and a second step of heating. The first step of heating is heated to 230°C at a rate of 15°C / min; the first step of heating is heated at 230°C for 90 minutes.

[0090] Optionally, in step S14, the catalytic core in the mixed liquid C is extracted, specifically by cooling the mixed liquid C to reduce the solubility of the catalytic core in the mixed liquid C; then centrifugally collecting to obtain a solid material; and vacuum drying the solid material to obtain the catalytic core; wherein the vacuum drying temperature can be 40°C to 100°C.

[0091] In the specific embodiment, please refer to Figure 5 Step S20, mixing the lithium-rich material with the catalytic core so that the lithium-rich material grows in situ on the outer surface of the catalytic core. Specifically comprising:

[0092] Step S21, preparing solution A.

[0093] Step S22, adding the catalytic core obtained in step S14 into solution A, stirring sufficiently, and adding dropwise solvent B to obtain a mixed solution D.

[0094] Step S23, collecting the substrate to obtain a stacking material.

[0095] Optionally, in step S21, solution A is a lithium carbonate solution with a mass concentration of 5%-10%.

[0096] Optionally, in step S22, 100 mL of the lithium carbonate solution prepared in step S21 is taken and mixed with 0.5 g to 0.1 g of the catalytic core obtained in step S14.

[0097] Optionally, in step S22, solvent B is ethanol. 20 mL of ethanol is added to the lithium carbonate solution at a drop rate of 0.125 mL / min-0.25 mL / min. The lithium carbonate solution is heated to 80° C. at a heating rate of 0.5° C. / min-1° C. / min. The stirring rate is 400 r / min.

[0098] Optionally, in step S23, the mixed solution D obtained in step S22 is kept warm for 30 minutes, the liquid is quickly filtered, and vacuum dried at 120° C. for 5 hours to obtain a stacking material.

[0099] In one implementation, please refer to Figure 3 The preparation method of the composite lithium supplement material also includes the following steps:

[0100] Step S30, mixing the carbon source with the stacking material, and the carbon source etches the outer surface of the stacking material so that the branches of the catalytic core are exposed to the external environment.

[0101] Step S40, sintering the deposited material loaded with the carbon source, converting the carbon source into a carbon material, and the carbon material is coated on the outer surface of the deposited material.

[0102] In the specific embodiment, please refer to Figure 6 and Figure 7 Step S30, mixing the carbon source with the stacking material, and etching the outer surface of the stacking material with the carbon source, so that the branches of the catalytic core are exposed to the external environment. Specifically comprising:

[0103] Step S31, adding a carbon source to react with the deposition material.

[0104] Step S32, purifying to obtain modified material.

[0105] Optionally, in step S31, the carbon source material is ethylene carbonate. The addition of ethylene carbonate can react with lithium carbonate on the outer surface of the stacking material, and after the ring-opening polymerization of ethylene carbonate, ether oxygen oligomers with ion transport properties are generated.

[0106] Optionally, in step S31, ethylene carbonate is added dropwise to completely cover the deposited material powder, and after soaking for 10 seconds, the liquid is pumped away, and the operation is repeated 3-10 times to control the etching depth.

[0107] Optionally, in step S32, vacuum drying is performed at 80°C to obtain a modified material.

[0108] In a specific embodiment, in step S40, 10% argon hydrogen gas is introduced, and the modified material is heated to 700°C at a rate of 5°C / min in a tube furnace and kept warm for 30 minutes. Through the high-temperature reducing atmosphere, the catalytic core continues to grow, and the ether oxygen oligomers are converted into carbon materials; in a specific embodiment, the reducing atmosphere helps Ni3C to reduce the Ni element, and the Ni element catalyzes the in-situ growth of carbon nanotubes, and the in-situ growth is uniaxial epitaxial growth.

[0109] The preparation method of the composite lithium-supplementing material provided by the present invention synthesizes a catalytic core through a chemical reaction, mixes a lithium-rich material with the catalytic core, and forms a structure in which the lithium-rich material is filled in the catalytic core; the method grows the lithium-rich material in situ in the catalytic core, and the contact area between the lithium-rich material and the catalytic core is increased, thereby improving the catalytic effect of the catalytic core on the lithium-rich material; and the connection strength between the lithium-rich material and the catalytic core is increased, and the surface active sites of the catalytic core are fully covered, thereby maintaining the catalytic activity of the catalytic core and avoiding a decrease in the catalytic performance of the catalytic core.

[0110] Furthermore, the present invention also adds a carbon source to the stacked material to etch the outer surface of the stacked material so that part of the outer surface of the catalytic core is exposed to the external environment; after sintering, part of the carbon source is converted into carbon material, and the carbon material is combined with the catalytic core exposed to the external environment; the composite lithium-supplementing material obtained by this method maintains the catalytic activity of the catalytic core, and the delithiation voltage of the lithium-rich material is significantly reduced; moreover, the carbon material connects the catalytic core as a conductive network, and the composite lithium-supplementing material has excellent conductive properties.

[0111] In one embodiment, the present invention further provides a positive electrode material, the positive electrode material includes a positive electrode active material and a lithium supplement material. The lithium supplement material includes the composite lithium supplement material provided in the above embodiment. Optionally, the positive electrode active material can be a phosphate positive electrode active material and a ternary positive electrode active material, and in a specific embodiment, includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium fluorinated vanadium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0112] In one embodiment, the content of the composite lithium-supplementing 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 just make up for the loss of active lithium in the battery during the first charging process. If the amount of composite lithium-supplementing material added to the positive electrode material is too low, the active lithium lost in the positive electrode active material cannot be fully replenished, which is not conducive to improving the energy density and capacity retention rate of the battery. If the amount of composite lithium-supplementing material added to the positive electrode active material is too high, the original reversible capacity will be occupied and the cost will be increased. In some specific embodiments, in the positive electrode material, the mass percentage of the composite lithium-supplementing material can be 1%, 2%, 4%, 6%, etc.

[0113] In one embodiment, the present invention further provides a positive electrode plate, the positive electrode plate includes a current collector and an active material layer disposed on the current collector, the active material layer includes the composite lithium supplement material of any one of the above embodiments. Or the active material layer includes the composite lithium supplement material obtained by the preparation method of the composite lithium supplement material in the above embodiments.

[0114] In one embodiment, the positive electrode sheet includes a positive current collector, and the positive current collector has a positive active layer, and the positive active layer includes components such as positive active materials, composite lithium supplement materials, conductive agents, and binders. The present invention does not specifically limit these materials, and suitable 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 3wt% to 5wt%. The types of binders include polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivatives, and the content of the binder in the positive active layer is 2wt% to 4wt%.

[0115] In one embodiment, the present invention also provides a secondary battery, including a positive electrode, a negative electrode, a separator and an electrolyte, wherein the separator is arranged between the positive electrode and the negative electrode, the positive electrode, the negative electrode and the separator are arranged in the electrolyte, and the negative electrode includes the negative electrode plate provided in the above embodiment. Optionally, the electrolyte includes a liquid electrolyte or a solid electrolyte. During the battery charge and discharge process, the active positive electrode ions are embedded and removed back and forth between the positive electrode and the negative electrode. The electrolyte plays a role in conducting positive electrode ions between the positive electrode and the negative electrode. The separator is arranged between the positive electrode and the negative electrode, mainly playing a role in preventing the positive and negative electrodes from short-circuiting, while allowing the positive electrode ions to pass through.

[0116] The technical solution of the present invention is described in detail below through specific embodiments.

[0117] Example 1

[0118] This embodiment provides a composite lithium supplement material. The composite lithium supplement material includes a lithium-rich material (Li2CO3), a catalytic core (Ni3C) and a carbon material.

[0119] The catalytic core includes an inner core and branches, with grooves formed between the branches; Li2CO3 grows in situ on the outer layer of the catalytic core and fills the grooves. Carbon material is coated on the outer surface of Li2CO3, and carbon nanotubes grow on the branches exposed to the outside. Please refer to Figure 8 .

[0120] Among them, the particle size of Ni3C is 0.6μm; the width of the groove is 100nm, and the specific surface area of ​​Ni3C is 50m 2 / g; the length of the carbon nanotube is 70nm; the diameter of the carbon nanotube is 4nm; the mass ratio of Li2CO3, Ni3C and carbon nanotube is 90:7:3; the particle size of the composite lithium supplement material is 0.8μm.

[0121] The preparation method of the composite lithium supplement material comprises the following steps:

[0122] (1) Preparation of catalytic core: 0.5 g of nickel acetylacetonate was dissolved in a mixture of oleylamine and 1-octadecene, degassed at 60° C. for 2 hours, and then backfilled with nitrogen. The mixture was heated to 230° C. at a rate of 15° C. / min. The mixture was heated at 230° C. for 90 minutes, then cooled and centrifuged to remove the waste liquid, and vacuum dried to obtain a catalytic core having a core, branches, and growth end structure.

[0123] (2) Lithium carbonate recrystallization grows on the catalytic core: control the temperature at about 0℃-10℃ in an ice bath, the mass concentration of lithium carbonate is 5%-10%, add 0.5g-0.1g nickel carbide to 100ml lithium carbonate solution, and stir at 400r / min. Control the heating rate to slowly rise to 80℃ at 0.5-1℃ / min, and add 20ml of ethanol at a dropping rate of 0.125mL / min-0.25mL / min. After the reaction is completed, stop stirring, keep warm for 30min, quickly filter the liquid, and collect the substrate. After vacuum drying at 120℃ for 5h, a lithium carbonate-coated catalytic core is obtained.

[0124] (3) Ethylene carbonate surface etching: Spread the dried lithium carbonate-coated catalytic core powder on filter paper, add ethylene carbonate dropwise until the powder is completely covered, soak for 10 seconds, remove the liquid, and repeat the operation 3-10 times to control the etching depth. Dry at 80°C in a vacuum oven to obtain the etched modified material.

[0125] (4) In situ growth of carbon nanotubes: The etched modified material powder is transferred to a tubular furnace, 10% argon hydrogen gas is introduced, the temperature is raised to 700°C at a rate of 5°C / min, and the temperature is kept at this temperature for 30 minutes. The etching exposes the top hexahedron of the catalytic material through the high-temperature reducing atmosphere, and the ether oxygen oligomers are converted into carbon materials. The reducing atmosphere helps Ni3C to reduce Ni element, and Ni element catalyzes the growth of carbon nanotubes, and the growth is uniaxial epitaxial.

[0126] Example 2

[0127] This embodiment provides a composite lithium supplement material. The difference between this embodiment 2 and embodiment 1 is that the specific surface area of ​​the catalytic core is 60m 2 / g.

[0128] Among them, the particle size of Ni3C is 0.7μm; the width of the groove is 90nm, and the specific surface area of ​​Ni3C is 60m 2 / g; the length of the carbon nanotube is 70nm; the diameter of the carbon nanotube is 4nm; the mass ratio of Li2CO3, Ni3C and carbon nanotube is 90:7:3; the particle size of the composite lithium supplement material is 0.9μm.

[0129] The difference between the preparation method of the composite lithium supplement material and that of Example 1 is that:

[0130] (1) Preparation of the catalytic core: 0.5 g of nickel acetylacetonate was dissolved in a mixture of oleylamine and 1-octadecene, degassed at 60°C for 2 hours, and then backfilled with nitrogen. Heated to 240°C at a rate of 15°C / min. Heated at 240°C for 90 minutes.

[0131] Then the waste liquid is removed by cooling and centrifugation, and vacuum drying is performed to obtain a catalytic core having a structure of an inner core, branches and a growth end.

[0132] Example 3

[0133] This embodiment provides a composite lithium supplement material. The difference between this embodiment 3 and embodiment 1 is that the specific surface area of ​​the catalytic core is 70m 2 / g.

[0134] Among them, the particle size of Ni3C is 0.8μm; the width of the groove is 80nm, and the specific surface area of ​​Ni3C is 70m 2 / g; the length of the carbon nanotube is 70nm; the diameter of the carbon nanotube is 4nm; the mass ratio of Li2CO3, Ni3C and carbon nanotube is 90:7:3; the particle size of the composite lithium supplement material is 1μm.

[0135] The difference between the preparation method of the composite lithium supplement material and that of Example 1 is that:

[0136] (1) Preparation of the catalytic core: 0.5 g of nickel acetylacetonate was dissolved in a mixture of oleylamine and 1-octadecene, degassed at 60°C for 2 hours, and then backfilled with nitrogen. Heated to 250°C at a rate of 15°C / min. Heated at 250°C for 90 minutes.

[0137] Then the waste liquid is removed by cooling and centrifugation, and vacuum drying is performed to obtain a catalytic core having a structure of an inner core, branches and a growth end.

[0138] Example 4

[0139] This embodiment provides a composite lithium supplement material. The difference between this embodiment 4 and embodiment 1 is that the specific surface area of ​​the catalytic core is 80m 2 / g.

[0140] Among them, the particle size of Ni3C is 0.9μm; the width of the groove is 70nm, and the specific surface area of ​​Ni3C is 80m 2 / g; the length of the carbon nanotube is 70nm; the diameter of the carbon nanotube is 4nm; the mass ratio of Li2CO3, Ni3C and carbon nanotube is 90:7:3; the particle size of the composite lithium supplement material is 1.1μm.

[0141] The difference between the preparation method of the composite lithium supplement material and that of Example 1 is that:

[0142] (1) Preparation of the catalytic core: 0.5 g of nickel acetylacetonate was dissolved in a mixture of oleylamine and 1-octadecene, degassed at 60°C for 2 hours, and then backfilled with nitrogen. Heated to 260°C at a rate of 15°C / min. Heated at 260°C for 90 minutes.

[0143] Then the waste liquid is removed by cooling and centrifugation, and vacuum drying is performed to obtain a catalytic core having a structure of an inner core, branches and a growth end.

[0144] Example 5

[0145] This embodiment provides a composite lithium supplement material. The difference between this embodiment 5 and embodiment 1 is that the specific surface area of ​​the catalytic core is 90m 2 / g.

[0146] The particle size of Ni3C is 1 μm, the width of the groove is 60 nm, and the specific surface area of ​​Ni3C is 90 m 2 / g; the length of the carbon nanotube is 70nm; the diameter of the carbon nanotube is 4nm; the mass ratio of Li2CO3, Ni3C and carbon nanotube is 90:7:3; the particle size of the composite lithium supplement material is 1.2μm.

[0147] The difference between the preparation method of the composite lithium supplement material and that of Example 1 is that:

[0148] (1) Preparation of the catalytic core: 0.5 g of nickel acetylacetonate was dissolved in a mixture of oleylamine and 1-octadecene, degassed at 60°C for 2 hours, and then backfilled with nitrogen. Heated to 270°C at a rate of 15°C / min. Heated at 270°C for 90 minutes.

[0149] Then the waste liquid is removed by cooling and centrifugation, and vacuum drying is performed to obtain a catalytic core having a structure of an inner core, branches and a growth end.

[0150] Example 6

[0151] This embodiment provides a composite lithium supplement material. The difference between this embodiment 6 and embodiment 1 is that the specific surface area of ​​the catalytic core is 100m 2 / g.

[0152] The particle size of Ni3C is 1.1 μm, the width of the groove is 50 nm, and the specific surface area of ​​Ni3C is 100 m 2 / g; the length of the carbon nanotube is 70nm; the diameter of the carbon nanotube is 4nm; the mass ratio of Li2CO3, Ni3C and carbon nanotube is 90:7:3; the particle size of the composite lithium supplement material is 1.3μm.

[0153] The difference between the preparation method of the composite lithium supplement material and that of Example 1 is that:

[0154] (1) Preparation of the catalytic core: 0.5 g of nickel acetylacetonate was dissolved in a mixture of oleylamine and 1-octadecene, degassed at 60°C for 2 hours, and then backfilled with nitrogen. Heated to 280°C at a rate of 15°C / min. Heated at 280°C for 90 minutes.

[0155] Then the waste liquid is removed by cooling and centrifugation, and vacuum drying is performed to obtain a catalytic core having a structure of an inner core, branches and a growth end.

[0156] Example 7

[0157] This embodiment provides a composite lithium supplement material. The difference between this embodiment 7 and embodiment 1 is that the specific surface area of ​​the catalytic core is 110m 2 / g.

[0158] Among them, the particle size of Ni3C is 1.15μm; the width of the groove is 40nm, and the specific surface area of ​​Ni3C is 110m 2 / g; the length of the carbon nanotube is 70nm; the diameter of the carbon nanotube is 4nm; the mass ratio of Li2CO3, Ni3C and carbon nanotube is 90:7:3; the particle size of the composite lithium supplement material is 1.35μm.

[0159] The difference between the preparation method of the composite lithium supplement material and that of Example 1 is that:

[0160] (1) Preparation of the catalytic core: 0.5 g of nickel acetylacetonate was dissolved in a mixture of oleylamine and 1-octadecene, degassed at 60°C for 2 hours, and then backfilled with nitrogen. Heated to 290°C at a rate of 15°C / min. Heated at 290°C for 90 minutes.

[0161] Then the waste liquid is removed by cooling and centrifugation, and vacuum drying is performed to obtain a catalytic core having a structure of an inner core, branches and a growth end.

[0162] Example 8

[0163] This embodiment provides a composite lithium supplement material. The difference between this embodiment 8 and embodiment 1 is that the specific surface area of ​​the catalytic core is 120m 2 / g.

[0164] Among them, the particle size of Ni3C is 1.2μm; the width of the groove is 30nm, and the specific surface area of ​​Ni3C is 120m 2 / g; the length of the carbon nanotube is 70nm; the diameter of the carbon nanotube is 4nm; the mass ratio of Li2CO3, Ni3C and carbon nanotube is 90:7:3; the particle size of the composite lithium supplement material is 1.4μm.

[0165] The difference between the preparation method of the composite lithium supplement material and that of Example 1 is that:

[0166] (1) Preparation of the catalytic core: 0.5 g of nickel acetylacetonate was dissolved in a mixture of oleylamine and 1-octadecene, degassed at 60°C for 2 hours, and then backfilled with nitrogen. The mixture was heated to 300°C at a rate of 15°C / min. The mixture was heated at 300°C for 90 minutes.

[0167] Then the waste liquid is removed by cooling and centrifugation, and vacuum drying is performed to obtain a catalytic core having a structure of an inner core, branches and a growth end.

[0168] Example 9

[0169] This embodiment provides a composite lithium supplement material. The difference between this embodiment 9 and embodiment 1 is that carbon nanotubes are directly added, and carbon nanotubes are not grown in situ on the catalytic core, that is, the catalytic core is not etched by ethylene carbonate to expose branches.

[0170] Among them, the particle size of Ni3C is 0.6μm; the width of the groove is 100nm, and the specific surface area of ​​Ni3C is 50m 2 / g; the length of the carbon nanotube is 70nm; the diameter of the carbon nanotube is 4nm; the mass ratio of Li2CO3, Ni3C and carbon nanotube is 90:7:3; the particle size of the composite lithium supplement material is 0.65μm.

[0171] The difference between the preparation method of the composite lithium supplement material and that of Example 1 is that:

[0172] (3) Commercial carbon nanotube compounding: Commercial carbon nanotubes are added to the material at a total weight of 3%, and the mixture is evenly mixed by high-speed ball milling to obtain a composite lithium supplement material.

[0173] Example 10

[0174] This embodiment provides a composite lithium supplement material. The difference between this embodiment 10 and embodiment 4 is that carbon nanotubes are directly added without in-situ growth of carbon nanotubes on the catalytic core, that is, the catalytic core is not etched by ethylene carbonate to expose branches.

[0175] Among them, the particle size of Ni3C is 0.9μm; the width of the groove is 70nm, and the specific surface area of ​​Ni3C is 80m 2 / g; the length of the carbon nanotube is 70nm; the diameter of the carbon nanotube is 4nm; the mass ratio of Li2CO3, Ni3C and carbon nanotube is 90:7:3; the particle size of the composite lithium supplement material is 0.95μm.

[0176] The difference between the preparation method of the composite lithium supplement material and that of Example 1 is that:

[0177] (3) Carbon nanotube compounding: Commercial carbon nanotubes are added to the material at a total weight of 3%, and the mixture is evenly mixed by high-speed ball milling to obtain a composite lithium supplement material.

[0178] Embodiment 11

[0179] This embodiment provides a composite lithium supplement material. The difference between this embodiment 11 and embodiment 1 is that the length of the carbon nanotube is 50nm, and the diameter of the carbon nanotube is 3nm.

[0180] Among them, the particle size of Ni3C is 0.6μm; the width of the groove is 100nm, and the specific surface area of ​​Ni3C is 50m 2 / g; the length of the carbon nanotube is 50nm; the diameter of the carbon nanotube is 3nm; the mass ratio of Li2CO3, Ni3C and carbon nanotube is 90:7:3; the particle size of the composite lithium supplement material is 0.76μm.

[0181] The difference between the preparation method of the composite lithium supplement material and that of Example 1 is that:

[0182] (4) In-situ growth of carbon nanotubes: The etched modified material powder is transferred to a tubular furnace, 10% argon hydrogen gas is introduced, the temperature is raised to 680°C at a rate of 5°C / min, and the temperature is kept for 30 minutes. The high-temperature reducing atmosphere allows the top hexahedron of the catalytic material to be exposed due to etching, and the ether oxygen oligomers are converted into carbon materials. The reducing atmosphere helps Ni3C to reduce Ni element, and Ni element catalyzes the growth of carbon nanotubes, and the growth is uniaxial epitaxial.

[0183] Example 12

[0184] This embodiment provides a composite lithium supplement material. The difference between this embodiment 12 and embodiment 1 is that the length of the carbon nanotube is 100 nm and the diameter of the carbon nanotube is 5 nm.

[0185] Among them, the particle size of Ni3C is 0.6μm; the width of the groove is 100nm, the specific surface area of ​​Ni3C is 50m2 / g; the length of the carbon nanotube is 100nm; the diameter of the carbon nanotube is 5nm; the mass ratio of Li2CO3, Ni3C and carbon nanotube is 90:7:3; the particle size of the composite lithium supplement material is 0.86μm.

[0186] The difference between the preparation method of the composite lithium supplement material and that of Example 1 is that:

[0187] (4) In-situ growth of carbon nanotubes: The etched modified material powder is transferred to a tubular furnace, 10% argon hydrogen gas is introduced, the temperature is raised to 750°C at a rate of 5°C / min, and the temperature is kept at this temperature for 30 minutes. The high-temperature reducing atmosphere allows the top hexahedron of the catalytic material to be exposed due to etching, and the ether oxygen oligomers are converted into carbon materials. The reducing atmosphere helps Ni3C to reduce Ni element, and Ni element catalyzes the growth of carbon nanotubes in a uniaxial epitaxial manner.

[0188] Example 13

[0189] This embodiment provides a composite lithium supplement material. The difference between this embodiment 13 and embodiment 1 is that the mass ratio of Li2CO3, Ni3C and carbon nanotubes is 94:5:1. Fig. 9 .

[0190] Among them, the particle size of Ni3C is 0.6μm; the width of the groove is 100nm, and the specific surface area of ​​Ni3C is 50m 2 / g; the length of the carbon nanotube is 70nm; the diameter of the carbon nanotube is 4nm; the mass ratio of Li2CO3, Ni3C and carbon nanotube is 94:5:1; the particle size of the composite lithium supplement material is 0.8μm.

[0191] The difference between the preparation method of the composite lithium supplement material and that of Example 1 is that:

[0192] (4) Surface etching with ethylene carbonate: Spread the dried lithium carbonate-coated catalytic core powder on filter paper, add ethylene carbonate dropwise until the powder is completely covered, soak for 10 seconds, remove the liquid, and etch once. Dry under vacuum at 80°C to obtain the etched modified material.

[0193] Embodiment 14

[0194] This embodiment provides a composite lithium supplement material. The difference between this embodiment 14 and embodiment 1 is that the mass ratio of Li2CO3, Ni3C and carbon nanotubes is 80:15:5.

[0195] Among them, the particle size of Ni3C is 0.6μm; the width of the groove is 100nm, and the specific surface area of ​​Ni3C is 50m 2 / g; the length of the carbon nanotube is 70nm; the diameter of the carbon nanotube is 4nm; the mass ratio of Li2CO3, Ni3C and carbon nanotube is 80:15:5; the particle size of the composite lithium supplement material is 0.8μm.

[0196] The difference between the preparation method of the composite lithium supplement material and that of Example 1 is that:

[0197] (4) Ethylene carbonate surface etching: Spread the dried lithium carbonate-coated catalytic core powder on filter paper, add ethylene carbonate dropwise until the powder is completely covered, soak for 10 seconds, remove the liquid, and etch 10 times. Dry under vacuum at 80°C to obtain the etched modified material.

[0198] Embodiment 15

[0199] This embodiment provides a composite lithium supplement material. The difference between this embodiment 15 and embodiment 1 is that the particle size of the composite lithium supplement material is 0.6 μm. Fig.10 .

[0200] Among them, the particle size of Ni3C is 0.6μm; the width of the groove is 100nm, and the specific surface area of ​​Ni3C is 50m 2 / g; the mass ratio of Li2CO3, Ni3C and carbon nanotubes is 85:15:0; the particle size of the composite lithium supplement material is 0.6μm.

[0201] The difference between the preparation method of the composite lithium supplement material and that of Example 1 is that:

[0202] Steps (3) and (4) are not performed.

[0203] Example 16

[0204] This embodiment provides a composite lithium supplement material. The difference between this embodiment 16 and embodiment 8 is that the particle size of the composite lithium supplement material is 1.5 μm.

[0205] Among them, the particle size of Ni3C is 1.2μm; the width of the groove is 30nm, and the specific surface area of ​​Ni3C is 120m 2 / g; the length of the carbon nanotube is 100nm; the diameter of the carbon nanotube is 5nm; the mass ratio of Li2CO3, Ni3C and carbon nanotube is 90:7:3; the particle size of the composite lithium supplement material is 1.5μm.

[0206] Embodiment 17

[0207] This embodiment provides a composite lithium supplement material. The difference between this embodiment 17 and embodiment 1 is that the catalytic core is molybdenum carbide.

[0208] Embodiment 18

[0209] This embodiment provides a composite lithium supplement material. The difference between this embodiment 18 and embodiment 1 is that the lithium-rich material is Li

[0210] 2C2O4 lithium oxalate.

[0211] Comparative Example 1

[0212] This comparative example provides a lithium-rich material (Li2CO3).

[0213] Comparative Example 2

[0214] This comparative example provides a composite lithium supplement material, which comprises a simple mixture of Li2CO3 and Ni3C.

[0215] Comparative Example 3

[0216] This comparative example provides a composite lithium supplement material, which comprises a simple mixture of Li2CO3, Ni3C and carbon nanotubes.

[0217] The negative electrode material parameters provided by Examples 1 to 18 and Comparative Examples 1 to 3 are shown in Table 1:

[0218] Table 1 Negative electrode material parameters provided in Examples and Comparative Examples

[0219]

[0220] In Table 1, parameter A is the particle size of the catalytic core, parameter B is the width of the groove, parameter C is the specific surface area of ​​the catalytic core, parameter D is the length of the carbon nanotube, parameter E is the diameter of the carbon nanotube, parameter F is the mass ratio of the lithium-rich material, the catalytic core and the carbon material, and parameter G is the particle size of the composite lithium-supplementing material.

[0221] The composite lithium supplement material provided in the above examples 1-18 and the lithium supplement material provided in comparative examples 1-3 are respectively assembled into positive electrode sheets and lithium ion batteries according to the following methods:

[0222] Positive electrode sheet: The lithium supplement material, SP and PVDF are mixed in a mass ratio of 90:4:6 to prepare 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;

[0223] Negative electrode: lithium sheet;

[0224] Electrolyte: Ethylene carbonate and ethyl methyl carbonate were mixed in a volume ratio of 3:7, and LiPF6 was added to form an electrolyte. The concentration of LiPF6 was 1 mol / L.

[0225] Diaphragm: Polypropylene microporous separator;

[0226] Lithium-ion battery assembly: Assemble button-type lithium-ion half cells in an inert atmosphere glove box in the order of negative electrode sheet - separator - electrolyte - positive electrode sheet.

[0227] The electrochemical performance of each lithium-ion battery assembled in the above lithium-ion battery embodiment was tested under the following test conditions:

[0228] The battery was charged at a rate of 0.1C with a cut-off voltage of 4.7V. The battery was charged at a constant voltage of 4.7V. After the charging process was completed, the battery was allowed to stand for 10 minutes and then discharged at a rate of 0.1C with a cut-off voltage of 2.5V. The charging platform was observed during the charging process to obtain the delithiation potential of the lithium supplement material.

[0229] The test results of the above lithium supplement materials and lithium batteries are shown in Table 2 below:

[0230] Table 2. Formation test results of the assembled batteries of the examples and comparative examples

[0231]

[0232]

[0233] It can be seen from the test results of the embodiments and comparative examples in Table 2 that the detachment point of the composite lithium supplement material provided by the present invention is lower than that of the common lithium-rich material (lithium carbonate) in the prior art. The delithiation potential of the material in the comparative example is higher than 4.3V when used as a positive electrode, and higher than 4.5V when the positive electrode LFP is compounded, and an effective lithium supplement effect cannot be produced. At the same time, the lithium supplement capacity of the embodiments can reach 400mAh / g, and is close to the initial charging capacity, indicating that the capacity of the composite lithium supplement material is fully released, so the performance of the composite lithium supplement material provided by the present invention is greatly improved compared with the prior art.

[0234] It can be seen from the test results of Examples 1 to 8 in Table 2 that catalytic cores with different surface parameters can be obtained by changing the preparation temperature of the catalytic core. As the temperature increases, the number of branches of the catalytic core increases and the length grows, so the groove width of the catalytic core decreases, the particle size of the catalytic core increases, and the specific surface area of ​​the catalytic core increases. The higher contact specific surface promotes its catalysis of lithium-rich materials, thereby reducing the delithiation energy barrier and promoting the release of capacity.

[0235] From the test results of Example 1, Example 9 and Example 10 in Table 2, it can be seen that carbon nanotubes are directly added, and carbon nanotubes are not grown in situ on the catalytic core, that is, the catalytic core is not etched by ethylene carbonate to expose branches. Although carbon nanotubes can improve the conductivity of the composite lithium supplement material, they are not in contact with the core branches, and only form a certain conductive film layer on the surface of the material, which has a relatively limited gain in material performance. In addition, the direct mixing of carbon nanotubes in Example 9 cannot directly increase the radial length of the particles. Therefore, the present invention can further improve the conductivity of the composite lithium supplement material by growing carbon materials outside the catalytic core.

[0236] It can be seen from the test results of Example 1, Example 11 and Example 12 in Table 2 that the performance of the composite lithium supplement material can be adjusted by adjusting the preparation conditions of the carbon nanotubes and controlling their length. The test results show that the longer the length of the carbon nanotubes, the more it can promote the release of material capacity, because sufficiently long carbon nanotubes are more likely to contact each other to form an integrated conductive network.

[0237] It can be seen from the test results of Example 1 and Example 13-Example 16 in Table 2 that the etching depth can be controlled by the number of etching times of vinyl carbonate, and whether the branch endpoints of the catalytic core are exposed can also be controlled, thereby adjusting the proportions of suitable lithium-rich materials, catalytic cores and carbon materials to maximize the material performance. If the lithium-rich material content is too high, the contact with the catalyst is insufficient, making it difficult to reduce the delithiation potential. If the lithium-rich material content is too low, the lithium replenishment capacity cannot be taken into account. If the catalytic core content is too high, a certain capacity share is sacrificed, and it is also easy to produce side reactions at high potentials. If the catalytic core content is too low, the catalytic effect cannot be guaranteed. The appropriate carbon material content can ensure moderate conductivity.

[0238] It can be seen from the test results of Example 1, Example 17 and Example 18 in Table 2 that the solution provided by the present invention can also be applied to other types of catalytic cores and lithium-rich materials, indicating that the solution provided by the present invention has good universality, can be applied to large-scale mass production, and has high commercial value.

[0239] In the description of the embodiments of the present application, it should be noted that the orientation or positional relationship of terms such as "center", "up", "down", "left", "right", "vertical", "horizontal", "inside" and "outside" are based on the orientation or positional relationship described in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0240] What is disclosed above is only a preferred embodiment of the present application, and it certainly cannot be used to limit the scope of rights of the present application. Ordinary technicians in this field can understand that all or part of the processes of implementing the above embodiment and equivalent changes made according to the claims of the present application are still within the scope covered by the present application.

Claims

1. A composite lithium supplement material, characterized in that: The invention comprises a lithium-rich material and a catalytic core, wherein the specific surface area of ​​the catalytic core is 50 m 2 / g~120m 2 / g; the lithium-rich material is in-situ grown on the outer layer of the catalytic core, and the lithium-rich material is tightly stacked on the outer layer of the catalytic core.

2. The composite lithium supplement material according to claim 1, characterized in that: The catalytic core is provided with a plurality of grooves, and the lithium-rich material is filled in the grooves.

3. The composite lithium supplement material according to claim 2, characterized in that: The catalytic core includes an inner core and a plurality of branches, wherein the branches are connected to the inner core, grooves are formed between the plurality of branches, and the branches extend in a direction away from the inner core to be exposed to the external environment.

4. The composite lithium supplement material according to claim 3, characterized in that: The composite lithium-supplementing material further includes a carbon material, which is combined on the outer surfaces of the lithium-rich material and the catalytic core.

5. The composite lithium supplement material according to claim 4, characterized in that: The carbon material includes carbon nanotubes, and the carbon nanotubes are in-situ grown on the branches exposed to the external environment.

6. The composite lithium supplement material according to any one of claims 1 to 5, characterized in that: The particle size of the catalytic core is 0.6 μm to 1.2 μm; and / or The groove width of the catalytic core is 30nm to 100nm; and / or The catalytic core comprises one or more of metal carbides, metal sulfides, and metal oxides; and / or The catalytic core is at least one of a dandelion shape, a pine needle shape, and a plush ball shape; and / or The mass proportion of the catalytic core in the composite lithium supplement material is 5% to 15%; and / or The particle size of the composite lithium supplement material is 0.6 μm to 1.5 μm.

7. A method for preparing a composite lithium supplement material, characterized in that: include: The catalyst precursor is made into a catalytic core, and the specific surface area of ​​the catalytic core is 50m 2 / g~120m 2 / g; A lithium-rich material is mixed with the catalytic core so that the lithium-rich material is in-situ grown on the outer surface of the catalytic core.

8. The preparation method according to claim 7, characterized in that: The preparation method further comprises: The lithium-rich material and the catalytic core are stacked to form a stacking material, a carbon source is mixed with the stacking material, and the carbon source etches the outer surface of the stacking material so that the branches of the catalytic core are exposed to the external environment; The stacked material loaded with the carbon source is sintered, and the carbon source is converted into a carbon material, and the carbon material is coated on the outer surface of the stacked material.

9. A positive electrode material, characterized in that: The positive electrode material includes an active material and a composite lithium-replenishing material, and the composite lithium-replenishing material includes the composite lithium-replenishing material according to any one of claims 1 to 6, or includes a composite lithium-replenishing material obtained by the preparation method of the composite lithium-replenishing material according to claim 7 or 8.

10. A secondary battery, characterized in that: The invention comprises a positive electrode, a negative electrode and an electrolyte arranged between the positive electrode and the negative electrode, wherein the positive electrode comprises the positive electrode material as claimed in claim 9.

Images