Lithium supplement material and preparation method thereof, positive electrode material and secondary battery

Abstract

The lithium supplementing material comprises a first lithium-rich material and a second lithium-rich material which are connected with each other, the chemical formula of the lithium supplementing material comprises LiaMbOc, M is Fe and / or Co, a is greater than or equal to 1 and less than or equal to 8, b is greater than 0 and c is greater than 7, the chemical formula of the second lithium-rich material comprises Li < 2 + x > NiO < 2 + y, x is greater than or equal to-0.5 and less than or equal to 0.5, and y is greater than or equal to 0 and less than 0.3; the particle size of the first lithium-rich material is smaller than that of the second lithium-rich material. The lithium supplementing material provided by the invention has relatively low gas production rate and relatively high electrochemical performance.

Description

Technical Field

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

[0002] Rechargeable lithium-ion batteries (LIBs) are widely used as the core power of portable electronic devices and electric vehicles due to their long life and high energy density. As the electric vehicle market continues to develop, high energy density LIBs are used to improve mileage. However, traditional graphite anode LIBs consume active lithium to form a solid electrolyte interface (SEI), resulting in permanent lithium loss in the first cycle. The irreversible loss of active lithium inevitably reduces the capacity and energy density, which is not conducive to meeting the emerging high energy density requirements.

[0003] Positive electrode lithium replenishment is a method of replenishing lithium by adding additional lithium sources to the positive electrode active material. In the prior art, in order to increase the lithium replenishment capacity of the lithium replenishment material, two different lithium-rich materials are usually simply physically mixed to obtain a lithium replenishment material with a higher lithium replenishment capacity. However, simple physical mixing cannot guarantee that the two lithium-rich materials are completely evenly distributed. Factors such as density differences, particle size, and static electricity during the mixing process can easily lead to component segregation. The gas production of the lithium replenishment material during the formation and aging stages increases, thereby making the composite effect of the two lithium-rich materials worse. Summary of the invention

[0004] The purpose of the present invention is to provide a lithium supplement material and a preparation method thereof, a positive electrode material and a secondary battery, so as to solve the problem that the compounding effect of the lithium supplement material is deteriorated due to mixing uniformity and segregation.

[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 lithium supplement material, comprising a first lithium-rich material and a second lithium-rich material connected to each other, wherein the chemical formula of the first lithium-rich material comprises Li a M b O c , wherein M is Fe and / or Co, and 1≤a≤8, 0<b, 0<c<7, and the chemical formula of the second lithium-rich material includes Li 2+x NiO 2+y , wherein, -0.5≤x≤0.5, 0≤y<0.3; the particle size of the first lithium-rich material is smaller than the particle size of the second lithium-rich material.

[0007] In one embodiment, the particle size of the first lithium-rich material is 3 μm to 15 μm.

[0008] In one embodiment, the particle size of the second lithium-rich material is 8 μm to 20 μm.

[0009] In one embodiment, the mass ratio of the first lithium-rich material to the second lithium-rich material is (1-10):1.

[0010] In one embodiment, there are multiple particles of the first lithium-rich material, and the multiple particles of the first lithium-rich material are distributed around the particles of the second lithium-rich material. The first lithium-rich material and the second lithium-rich material together constitute secondary particles.

[0011] In one embodiment, the lithium-supplementing material also includes a functional material, part of which is coated on the outer layer of the first lithium-rich material, and / or part of which is coated on the outer layer of the second lithium-rich material; and / or part of which is filled in the gap between the first lithium-rich material and the second lithium-rich material.

[0012] In one embodiment, the functional material includes a polar group, and the polar group forms a coordination bond with the transition metal element in the first lithium-rich material and the nickel element in the second lithium-rich material.

[0013] In one embodiment, the functional material includes one or more of triethanolamine, triethylamine, p-phenylenediamine, tetrabutyl titanate, 2,6-di-tert-butyl-4-methylphenol, phosphite, poly-{[6-[(1,1,3,3,-tetramethylbutyl)-amino]1,3,5,-triazine-2,4-diyl][(2,2,6,6-tetramethylpiperidinyl)-imino]-1,6-hexanediyl-[(2,2,6,6-tetramethylpiperidinyl)-imino]}, poly{(6-morpholinyl-5-triazine-2,4-diyl)(2,2,6,6-tetramethylpiperidinyl)iminohexamethylene[(2,2,6,6-tetramethylpiperidinyl)-imino]}.

[0014] In one embodiment, the polar group includes one or more of a hydroxyl group, an amine group, an ester group, a phenyl group, a piperidinyl group, an imino group, a morpholinyl group, and a triazine group.

[0015] In one embodiment, the functional material accounts for 0.5% to 10% by mass of the lithium supplementing material.

[0016] In a second aspect, the present invention further provides a method for preparing a lithium-supplementing material, comprising: providing a first lithium-rich material and a second lithium-rich material, wherein the chemical formula of the first lithium-rich material includes Li a M b O c , wherein M is Fe and / or Co, and 1≤a≤8, 0<b, 0<c<7, and the chemical formula of the second lithium-rich material includes Li2+x NiO 2+y , wherein -0.5≤x≤0.5, 0≤y<0.3; the first lithium-rich material and the second lithium-rich material are uniformly mixed and dried so that the first lithium-rich material is connected to the second lithium-rich material, and the particle size of the first lithium-rich material is smaller than the particle size of the second lithium-rich material.

[0017] 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 is the lithium supplement material described in the first aspect, or the positive electrode material includes a lithium supplement material obtained by the preparation method of the lithium supplement material described in the second aspect.

[0018] In a fourth aspect, the present invention further provides a secondary battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode and the negative electrode are arranged in the electrolyte, and the positive electrode comprises the positive electrode material described in the third aspect.

[0019] In one embodiment, the gas production of the secondary battery during formation is 15 mL to 30 mL, and the gas production of the secondary battery after aging at 45° C. for 48 hours is 0.1 mL to 2.5 mL.

[0020] The present invention mixes two different first lithium-rich materials and second lithium-rich materials, and utilizes the surface catalytic effect of the second lithium-rich material containing nickel elements, so that the gas generation reaction of the first lithium-rich material in the formation stage is more complete, and at the same time, the second lithium-rich material can inhibit the side reaction between the first lithium-rich material and the electrolyte to a certain extent, thereby significantly reducing the gas production of the first lithium-rich material in the subsequent aging and storage stages, preventing the safety problems caused by battery flatulence, and improving the capacity and cycle performance of the battery; in addition, the first lithium-rich material and the second lithium-rich material can increase the contact area between the first lithium-rich material and the second lithium-rich material through the adaptation of the particle size, ensuring that more of the first lithium-rich material can fully contact the second lithium-rich material, thereby utilizing the second lithium-rich material to catalyze the first lithium-rich material, and improve the catalytic efficiency, promote the complete reaction of the first lithium-rich material, and make the reaction of the entire electrode more uniform. In addition, the uniformly distributed small-size particles can reduce the agglomeration of large-size particles, maintain the pore structure of the electrode material, and facilitate the penetration of the electrolyte and the migration of ions. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] 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.

[0022] Figure 1 is a schematic diagram of a lithium supplement material interface in one embodiment;

[0023] Figure 2 The present invention is a flow chart of a method for preparing lithium supplement materials according to an embodiment of the present invention. DETAILED DESCRIPTION

[0024] 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.

[0025] 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.

[0026] 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.

[0027] The present invention provides a lithium supplement material, please refer to Figure 1 , including a first lithium-rich material 10 and a second lithium-rich material 20 connected to each other, the first lithium-rich material 10 includes a first transition metal element, the second lithium-rich material 20 includes a nickel element, the first transition metal element and the nickel element are different, and the particle size of the first lithium-rich material 10 is smaller than the particle size of the second lithium-rich material 20.

[0028] The first lithium-rich material 10 may be composed of a first transition metal element, a lithium element, and an oxygen element. The chemical formula of the first lithium-rich material 10 may include Li a M b O c , wherein M is Fe and / or Co, and 1≤a≤8, 0<b, 0<c<7, and M is the first transition metal element.

[0029] The second lithium-rich material 20 may include lithium-rich nickel oxide, the chemical formula of which includes Li 2+x NiO 2+y, wherein -0.5≤x≤0.5, 0≤y<0.3. In a specific embodiment, the second lithium-rich material 20 may include Li2NiO2 (LNO for short); or the second lithium-rich material includes a lithium-rich nickel-based material, such as lithium-rich nickel oxide doped with other transition metals.

[0030] In other embodiments, the first lithium-rich material 10 may also be a doped structure, the chemical formula of which includes Li a M b1 N b2 O c , wherein M is Fe and / or Co, N is at least one element selected from Ni, Mn, Cu, Zn, Cr, Zr, Sb, Ti, V, Mo, and Sn, 1≤a≤8, 0<b1+b2, b2<b1, 0<c<7, and M is the first transition metal element. In a specific embodiment, the first lithium-rich material 10 may be lithium-rich iron oxide (Li5FeO4), lithium-rich cobalt oxide (Li6CoO4), or the first lithium-rich material 10 may be a lithium-rich iron-based material or a lithium-rich cobalt-based material, such as Li 4.985 Fe 0.967 Al 0.03 O 3.988 、Li6Co 0.98 Ni 0.02 O4, Li8ZrO6.

[0031] In a specific embodiment, the first lithium-rich material 10 and the second lithium-rich material 20 are both granular structures, such as Figure 1 As shown, the particles of the first lithium-rich material 10 and the particles of the second lithium-rich material 20 are connected together to form secondary particles. The first lithium-rich material 10 and the second lithium-rich material 20 can be formed separately and then combined together by physical mixing.

[0032] Therefore, it should be understood that the first lithium-rich material 10 and the second lithium-rich material 20 need to be distinguished from the simple nickel-doped lithium-rich material (e.g., Li6Co 0.98 Ni 0.02 O4), the first lithium-rich material 10 and the second lithium-rich material 20 have independent elemental compositions and crystal configurations, and the two are directly or indirectly connected together by physical contact. There is no mutually doped component in the crystal structure of the first lithium-rich material 10 and the second lithium-rich material 20.

[0033] The transition metal lithium-rich material (first lithium-rich material 10) and the nickel-based lithium-rich material (second lithium-rich material 20) are directly added to the positive electrode material of the battery by physical mixing. This method is simple and easy to implement, and can achieve a certain degree of gas production inhibition effect. However, in the prior art, the simple physical mixing of the transition metal lithium-rich material (first lithium-rich material 10) and the nickel-based lithium-rich material (second lithium-rich material 20) cannot guarantee that the two are completely evenly distributed. Factors such as density differences, particle size, and static electricity during the mixing process can easily lead to component segregation; in a specific embodiment, the uneven dispersion of the two will lead to uneven material capacity and gas production, affecting the NP ratio design and gas production design of battery preparation, and increasing the defective rate after use; for example, too much second lithium-rich material 20 will lead to low capacity, affecting the lithium supplement effect of the lithium supplement agent, and too little second lithium-rich material 20 will lead to too high capacity, the negative electrode is prone to lithium precipitation, and the second lithium-rich material 20 is affected. Reduce the gas production effect, and under the same battery preparation conditions, it is easy to bulge. At the same time, the mixed materials may separate during transportation and storage due to vibration, pressure changes, etc., which reduces the uniformity of the lithium supplement and the overall performance of the battery. Therefore, the present invention further solves the problem of matching the first lithium-rich material 10 and the second lithium-rich material 20.

[0034] In one implementation, please refer to Figure 1 The particle size of the first lithium-rich material 10 provided in the present invention is different from the particle size of the second lithium-rich material 20, and the particle size of the first lithium-rich material 10 is smaller than the particle size of the second lithium-rich material 20. In this way, the small particles and large particles of the first lithium-rich material 10 and the second lithium-rich material 20 are matched.

[0035] The present invention mixes two different first lithium-rich materials 10 and second lithium-rich materials 20, and utilizes the surface catalytic effect of the second lithium-rich material 20 containing nickel elements, so that the gas generation reaction of the first lithium-rich material 10 in the formation stage is more complete. At the same time, the second lithium-rich material 20 can inhibit the side reaction between the first lithium-rich material 10 and the electrolyte to a certain extent, thereby significantly reducing the gas generation of the first lithium-rich material 10 in the subsequent aging and storage stages, preventing the safety problems caused by battery flatulence, and improving the capacity and cycle performance of the battery. In addition, the first lithium-rich material 10 and the second lithium-rich material 20Through the adaptation of the size of the particles, the first lithium-rich material 10 and the second lithium-rich material 20 both have better fluidity, and the first lithium-rich material 10 is not easy to agglomerate, so that the first lithium-rich material 10 is easier to be evenly dispersed around the second lithium-rich material 20, thereby increasing the contact area between the first lithium-rich material 10 and the second lithium-rich material 20, ensuring that more of the first lithium-rich material 10 can fully contact the second lithium-rich material 20, using the second lithium-rich material 20 to catalyze the first lithium-rich material 10, and improve the catalytic efficiency, promote the complete reaction of the first lithium-rich material 10, and make the reaction of the entire electrode more uniform. In addition, the uniformly distributed small-size particles can reduce the agglomeration of large-size particles, maintain the pore structure of the electrode material, and facilitate the penetration of the electrolyte and the migration of ions.

[0036] In one embodiment, the particle size of the first lithium-rich material 10 is 3 μm to 15 μm. Optionally, the particle size of the first lithium-rich material 10 can be 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, or 15 μm.

[0037] When the particle size of the first lithium-rich material 10 is within the above range, it can ensure that the first lithium-rich material 10 and the second lithium-rich material 20 are compatible, and the first lithium-rich material 10 within the particle size range can fully release the capacity, and the preparation difficulty of the first lithium-rich material 10 is relatively low. When the particle size of the first lithium-rich material 10 is larger than the range, the corresponding particle size of the second lithium-rich material 20 is larger, which is not only not conducive to capacity release, but also causes the compaction density of the positive electrode to decrease. When the particle size of the first lithium-rich material 10 is smaller than the range, the preparation difficulty of the first lithium-rich material 10 increases, and the first lithium-rich material 10 itself is severely agglomerated, and it is not easy to disperse and adapt to the second lithium-rich material 20.

[0038] In one embodiment, the particle size of the second lithium-rich material 20 is 8 μm to 20 μm. Optionally, the particle size of the second lithium-rich material 20 can be 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm.

[0039] The particle size of the second lithium-rich material 20 is within the above range, which can ensure that the first lithium-rich material 10 and the second lithium-rich material 20 are compatible, and the second lithium-rich material 20 within the particle size range can fully release the capacity, and the preparation difficulty of the second lithium-rich material 20 is relatively low. When the particle size of the second lithium-rich material 20 is larger than the range, it is not conducive to the release of its own capacity, and it will also cause the compaction density of the positive electrode to decrease. When the particle size of the second lithium-rich material 20 is smaller than the range, the corresponding particle size of the first lithium-rich material 10 is smaller, and the preparation difficulty of the first lithium-rich material 10 increases.

[0040] In one embodiment, the mass ratio of the first lithium-rich material 10 to the second lithium-rich material 20 is (1-10): 1. Optionally, the mass ratio of the first lithium-rich material 10 to the second lithium-rich material 20 may be 1:1, 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1.

[0041] The mass ratio of the first lithium-rich material 10 to the second lithium-rich material 20 is within the above range, which can ensure that the lithium-supplementing material has a higher capacity. Because the first lithium-rich material 10 is the main component that provides lithium ions, it is necessary to ensure that the components of the first lithium-rich material 10 are not less than the second lithium-rich material 20. When the mass ratio of the first lithium-rich material 10 is less than the above range, the capacity of the lithium-supplementing material is reduced. When the mass ratio of the first lithium-rich material is greater than the above range, the catalytic effect of the second lithium-rich material 20 on the first lithium-rich material 10 becomes worse, which is not conducive to controlling the gas production.

[0042] In one implementation, please refer to Figure 1 There are multiple particles of the first lithium-rich material 10, and the multiple particles of the first lithium-rich material 10 are distributed on the periphery of the particles of the second lithium-rich material 20. The first lithium-rich material 10 and the second lithium-rich material 20 together constitute secondary particles.

[0043] Specifically, the positive electrode active layer of the positive electrode may include a plurality of secondary particles composed of a first lithium-rich material 10 and a second lithium-rich material 20. Each secondary particle includes at least one particle of the second lithium-rich material 20 and a plurality of particles of the first lithium-rich material 10. The particles of the first lithium-rich material 10 are distributed in a star-shaped manner around the particles of the second lithium-rich material 20, such as Figure 1 shown.

[0044] In a specific embodiment, the secondary particles include two or more particles of the second lithium-rich material 20, and there is a first pore between the adjacent particles of the second lithium-rich material 20, and the first lithium-rich material 10 is filled in the first pore; and a second pore is formed between the first lithium-rich material 10 and the second lithium-rich material 20, and the second pore is smaller than the first pore. It can be understood that the first lithium-rich material 10 is filled in the first pore, thereby reducing the size of the first pore, and dividing the first pore to form at least one second pore, so the second pore is smaller than the first pore.

[0045] The present invention can provide a better catalytic effect by distributing the particles of the first lithium-rich material 10 on the periphery of the second lithium-rich material 20; and through the space around the second lithium-rich material 20, a high compaction density of the lithium-supplementing material is achieved, thereby increasing the capacity of the lithium-supplementing material; at the same time, the pores between the first lithium-rich material 10 and the second lithium-rich material 20 can increase the wettability of the electrolyte to the material, thereby improving the ion deintercalation efficiency.

[0046] In one implementation, please refer to Figure 1 The lithium-supplementing material also includes a functional material 30. The first lithium-rich material 10 is connected to the second lithium-rich material 20 through the functional material 30. The functional material 30 can be an organic chelating agent. It should be explained that chelating agents are a class of chemical species that can form a stable ring structure with metal ions. They generally contain organic ligands and form a stable chelate ring with metal ions through coordinating atoms such as oxygen, nitrogen, sulfur, etc. The functional material 30 can include three types of substances: organic small molecules, organic macromolecules, and polymers.

[0047] It is understandable that one side of the functional material 30 can be firmly connected to the first lithium-rich material 10 or the second lithium-rich material 20, and the other side can be connected to the second lithium-rich material 20 and the first lithium-rich material 10. Of course, in other embodiments, the particles of the first lithium-rich material 10 can also be connected through the functional material 30.

[0048] The present invention performs surface modification on the first lithium-rich material 10 and the second lithium-rich material 20 through the functional material 30, so that the first lithium-rich material 10 and the second lithium-rich material 20 are connected through the functional material 30, which can enhance the interaction between the two and form a more stable composite material.

[0049] In one embodiment, part of the functional material 30 is coated on the outer layer of the first lithium-rich material 10, and / or, part of the functional material 30 is coated on the outer layer of the second lithium-rich material 20; and / or, part of the functional material 30 is filled in the gap between the first lithium-rich material 10 and the second lithium-rich material 20.

[0050] Specifically, Figure 1As shown, the functional material 30 can be coated on the outer layer of the first lithium-rich material 10, thereby achieving surface modification of the first lithium-rich material 10; then, part of the functional material 30 can also be coated on the outer layer of the second lithium-rich material 20, thereby achieving surface modification of the second lithium-rich material 20; the first lithium-rich material 10 and the second lithium-rich material 20 after surface modification are connected. The advantage of this structure is that the functional material 30 also forms a coating layer, which can not only connect the first lithium-rich material 10 and the second lithium-rich material 20, but also isolate the external water vapor from corroding the lithium-rich material. In other embodiments, such as Figure 1 As shown, the functional material 30 is filled between the gap between the first lithium-rich material 10 and the second lithium-rich material 20 , so as to improve the connection strength between the first lithium-rich material 10 and the second lithium-rich material 20 .

[0051] In one embodiment, the functional material 30 includes a polar group, and the polar group forms a coordination bond with the first transition metal element and the nickel element. Specifically, the functional material 30 with a specific coordination function that can be synthesized by molecular design can form a coordination bond with the transition metal ions (the first transition metal element and the nickel element) through the polar groups on its side chain or main chain, thereby enhancing its binding with the first transition metal element and the nickel element.

[0052] The functional material 30 is connected to the first lithium-rich material 10 and the second lithium-rich material 20 respectively. The polar groups on the functional material 30 are similar to pliers that firmly combine with the first transition metal element and the nickel element, thereby forming a connecting bridge between the first lithium-rich material 10 and the second lithium-rich material 20.

[0053] The present invention forms coordination bonds with transition metal elements through the polar groups on the functional material 30, and utilizes the high bond energy characteristics of the coordination bonds to make it difficult to separate the first lithium-rich material 10 and the second lithium-rich material 20, and the two are connected more closely, thereby further enhancing the catalytic performance of the second lithium-rich material 20 on the first lithium-rich material 10, reducing the risk of segregation of the mixed product during storage and transportation, and enhancing the uniformity and stability of the first lithium-rich material 10 and the second lithium-rich material 20; and, during the battery charging process, the strong coordination effect formed by the functional material 30 and the metal ions in the lithium-rich material can promote the firm bonding between the lithium-rich materials, and this firm bonding helps the second lithium-rich material 20 to efficiently catalyze the first lithium-rich material 10 to reduce gas production, and reduce the possibility of side reactions between the first lithium-rich material 10 and the electrolyte.

[0054] In one embodiment, the functional material 30 includes one or more of triethanolamine, triethylamine, p-phenylenediamine, tetrabutyl titanate, 2,6-di-tert-butyl-4-methylphenol, phosphite, poly-{[6-[(1,1,3,3,-tetramethylbutyl)-amino]1,3,5,-triazine-2,4-diyl][(2,2,6,6-tetramethylpiperidinyl)-imino]-1,6-hexanediyl-[(2,2,6,6-tetramethylpiperidinyl)-imino]}, poly{(6-morpholinyl-5-triazine-2,4-diyl)(2,2,6,6-tetramethylpiperidinyl)iminohexamethylene[(2,2,6,6-tetramethylpiperidinyl)-imino]}.

[0055] In one embodiment, the polar group includes one or more of a hydroxyl group (-OH), a carboxyl group (-COOH), an amine group (-NH2), an ester group (-COOR), a phenyl group, a piperidinyl group, an imino group, a morpholinyl group, and a triazine group. Specifically, the polar group may also include a nitro group (-NO2), a dimethylamine group (CH3-N-CH3), a carbonyl group (-CO-), an aldehyde group (-CHO), a thiol group (-SH), an amide group (-NHCO-), and the like. Among them, the nitro group is a strong electron-withdrawing group, which can significantly increase the polarity of the functional material 30 and adsorb transition metal elements in the lithium-rich material. The nitrogen atoms in the amine group and the dimethylamine carry lone pairs of electrons and can form dipoles, so they have a certain polarity. Ester groups, carbonyl groups, carboxyl groups, aldehyde groups, and amide groups have polarity because of the difference in electronegativity between the carbon-oxygen double bond and the oxygen atom. The sulfur atom in the thiol carries a lone pair of electrons and can form a dipole, so it has a certain polarity. The oxygen atom in the hydroxyl group has a lone pair of electrons, and there is a difference in electronegativity between the oxygen and hydrogen atoms, so it has a certain polarity.

[0056] In one embodiment, the mass proportion of the functional material 30 in the lithium supplement material is 0.5% to 10%. Optionally, the mass proportion of the functional material 30 in the lithium supplement material can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%.

[0057] When the mass proportion of the functional material 30 in the lithium-supplementing material is within the above range, the connection strength between the first lithium-rich material 10 and the second lithium-rich material 20 can be ensured, as well as the lithium-supplementing capacity of the lithium-supplementing material. When the mass proportion of the functional material 30 in the lithium-supplementing material is less than the above range, the connection effect contributed by the functional material 30 is weak, and part of the first lithium-rich material 10 and the second lithium-rich material 20 may not be connected through the functional material 30. When the mass proportion of the functional material 30 in the lithium-supplementing material is greater than the above range, since the functional material 30 does not contribute lithium ions, the lithium-supplementing capacity of the lithium-supplementing material of the same mass will decrease.

[0058] In one embodiment, the present invention also provides a method for preparing a lithium supplement material, please refer to Figure 2 ,include:

[0059] Step S10, providing a first lithium-rich material and a second lithium-rich material, respectively, wherein the chemical formula of the first lithium-rich material includes Li a M b O c , wherein M is Fe and / or Co, and 1≤a≤8, 0<b, 0<c<7, and the chemical formula of the second lithium-rich material includes Li 2+ x NiO 2+y , where -0.5≤x≤0.5, 0≤y<0.3.

[0060] Step S20, uniformly mixing and drying the first lithium-rich material and the second lithium-rich material, so that the first lithium-rich material is connected to the second lithium-rich material, and the particle size of the first lithium-rich material is smaller than that of the second lithium-rich material.

[0061] In one embodiment, step S20 also includes adding a functional material while mixing the first lithium-rich material and the second lithium-rich material, specifically including: uniformly mixing and drying the first lithium-rich material, the second lithium-rich material and the functional material so that the first lithium-rich material is connected to the second lithium-rich material through the functional material.

[0062] The preparation method of the lithium-supplementing material provided by the present invention can increase the contact area between the first lithium-rich material and the second lithium-rich material by uniformly mixing the two, and the mixing method of matching the large and small particle sizes improves the mixing uniformity, while improving the stability during transportation and storage, and inhibiting the segregation of the two components.

[0063] In addition, the preparation method of the lithium-supplementing material provided by the present invention also adds functional materials during the preparation process, and the surfaces of the first lithium-rich material and the second lithium-rich material are modified by the functional materials, so that the first lithium-rich material and the second lithium-rich material are connected by the functional materials, which can enhance the interaction between the two and form a more stable composite material.

[0064] 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 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 vanadium phosphate fluoride, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0065] In one embodiment, the content of 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 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 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 lithium-supplementing material can be 1%, 2%, 4%, 6%, etc.

[0066] 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 lithium supplement material of any one of the above embodiments. Or the active material layer includes the lithium supplement material obtained by the preparation method of the lithium supplement material in the above embodiments.

[0067] In one embodiment, the positive electrode sheet includes a positive electrode current collector, and the positive electrode current collector has a positive electrode active layer, and the positive electrode active layer includes components such as positive electrode active materials, 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 electrode 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 electrode 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 electrode active layer is 2wt% to 4wt%.

[0068] 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.

[0069] In one embodiment, the gas production of the secondary battery is 15 mL to 30 mL, and the gas production of the secondary battery after aging at 45° C. for 48 hours is 0.1 mL to 2.5 mL. Optionally, the gas production of the secondary battery can be 15 mL, 20 mL, 25 mL, or 30 mL, and the gas production of the secondary battery after aging at 45° C. for 48 hours can be 0.1 mL, 0.5 mL, 1 mL, 1.5 mL, 2 mL, or 2.5 mL.

[0070] The technical solution of the present invention is described in detail below through specific embodiments.

[0071] Example 1

[0072] This embodiment provides a lithium supplement material. The lithium supplement material includes a first lithium-rich material (Li5FeO4), a second lithium-rich material (Li2NiO2) and a functional material (poly{(6-morpholinyl-5-triazine-2,4-diyl)(2,2,6,6-tetramethylpiperidinyl)iminohexamethylene[(2,2,6,6-tetramethylpiperidinyl)-imino]}), and Li5FeO4 is connected to Li2NiO2 through the functional material.

[0073] Among them, the particle size of Li5FeO4 is 9μm, and the particle size of Li2NiO2 is 14μm. The mass ratio of Li5FeO4 and Li2NiO2 is 4:1, and multiple Li5FeO4 particles are distributed on the periphery of Li2NiO2. The mass proportion of functional materials in lithium supplement materials is 0.5%.

[0074] The preparation method of the lithium supplement material comprises the following steps:

[0075] 1) Provide a first lithium-rich material and a second lithium-rich material respectively.

[0076] 2) The first lithium-rich material, the second lithium-rich material and the functional material are uniformly mixed at a temperature of 60° C. to 100° C. for 1 hour, and sieved so that the first lithium-rich material is connected to the second lithium-rich material through the functional material.

[0077] Example 2

[0078] This embodiment provides a lithium supplement material. The difference between this embodiment and embodiment 1 is that the particle size of Li5FeO4 is 9 μm, and the particle size of Li2NiO2 is 11 μm.

[0079] Example 3

[0080] This embodiment provides a lithium supplement material. The difference between this embodiment and embodiment 1 is that the particle size of Li5FeO4 is 3 μm, and the particle size of Li2NiO2 is 8 μm.

[0081] Example 4

[0082] This embodiment provides a lithium supplement material. The difference between this embodiment and embodiment 1 is that the functional material is poly-{[6-[(1,1,3,3,-tetramethylbutyl)-amino]1,3,5,-triazine-2,4-diyl][(2,2,6,6-tetramethylpiperidinyl)-imino]-1,6-hexanediyl-[(2,2,6,6-tetramethylpiperidinyl)-imino]}.

[0083] Example 5

[0084] This embodiment provides a lithium supplement material. The difference between this embodiment and embodiment 1 is that the functional material is p-phenylenediamine.

[0085] Example 6

[0086] This embodiment provides a lithium supplement material. The difference between this embodiment and embodiment 1 is that the mass proportion of the functional material in the lithium supplement material is 1%.

[0087] Example 7

[0088] This embodiment provides a lithium supplement material. The difference between this embodiment and embodiment 1 is that the weight proportion of the functional material in the lithium supplement material is 5%.

[0089] Example 8

[0090] This embodiment provides a lithium supplement material. The difference between this embodiment and embodiment 1 is that the weight proportion of the functional material in the lithium supplement material is 10%.

[0091] Example 9

[0092] This embodiment provides a lithium supplement material. The difference between this embodiment and embodiment 1 is that the first lithium-rich material is Li6CoO4.

[0093] Example 10

[0094] This embodiment provides a lithium supplement material. The difference between this embodiment and embodiment 1 is that the first lithium-rich material is Li6CoO4, and the functional material is poly-{[6-[(1,1,3,3,-tetramethylbutyl)-amino]1,3,5,-triazine-2,4-diyl][(2,2,6,6-tetramethylpiperidinyl)-imino]-1,6-hexanediyl-[(2,2,6,6-tetramethylpiperidinyl)-imino]}.

[0095] Embodiment 11

[0096] This embodiment provides a lithium supplement material. The difference between this embodiment and embodiment 1 is that the first lithium-rich material is Li6CoO4 and the functional material is p-phenylenediamine.

[0097] Example 12

[0098] This embodiment provides a lithium supplement material. The difference between this embodiment and embodiment 1 is that the first lithium-rich material is Li6CoO4, and no functional material is added.

[0099] Comparative Example 1

[0100] This comparative example provides a lithium supplement material. The difference between this comparative example and Example 1 is that only the first lithium-rich material (Li5FeO4) is used, and no second lithium-rich material and functional material are compounded.

[0101] Comparative Example 2

[0102] This comparative example provides a lithium supplement material. The difference between this comparative example and Example 1 is that the particle size of Li5FeO4 is 15 μm, and the particle size of Li2NiO2 is 8 μm.

[0103] Comparative Example 3

[0104] This comparative example provides a lithium supplement material. The difference between this comparative example and Example 1 is that the particle size of Li5FeO4 is 15 μm, the particle size of Li2NiO2 is 8 μm, and there is no compound functional material.

[0105] Comparative Example 4

[0106] This comparative example provides a lithium supplement material. The difference between this comparative example and Example 1 is that only the first lithium-rich material (Li6CoO4) is used, and no second lithium-rich material and functional material are compounded.

[0107] The parameters of the lithium supplement materials provided by Examples 1 to 12 and Comparative Examples 1 to 4 are shown in Table 1:

[0108] Table 1 Parameters of lithium supplement materials provided in Examples and Comparative Examples

[0109]

[0110]

[0111] The lithium supplement materials provided in the above-mentioned Examples 1 to 12 and the lithium supplement materials provided in Comparative Examples 1 to 4 are assembled into positive electrode sheets and lithium-ion batteries according to the following method:

[0112] (1) Preparation of positive electrode sheet: Lithium iron phosphate (LFP, LiFePO4), lithium supplement material, polyvinylidene fluoride and carbon nanotubes were mixed in a mass ratio of 93.5:2.5:1.5:2.5, and N-methylpyrrolidone was added to the slurry and then coated on aluminum foil (aluminum foil roll with a thickness of 13 μm and a width of 220 mm). The surface density of the coating was about 15 mg / cm 2 ~20mg / cm 2 , and after drying, the positive electrode sheet is obtained.

[0113] (2) Preparation of negative electrode sheet

[0114] Graphite, binder, dispersant and conductive agent were mixed in a mass ratio of 96.6:1.8:1:0.6 to obtain graphite slurry, and the graphite slurry was evenly coated on copper foil (copper foil roll with a thickness of 12 μm and a width of 222 mm). The surface density of the coating was about 8 mg / cm 2 , and after drying, the negative electrode sheet is obtained.

[0115] (3) Preparation of LFP lithium-ion batteries

[0116] The obtained negative electrode sheet and positive electrode sheet are assembled, injected and formed into a battery. The designed charging N / P ratio of the lithium-ion battery is about 1.07. The LFP lithium-ion battery is prepared according to the lithium-ion battery preparation method. Specific steps: The obtained electrode sheet roll is rolled to obtain positive and negative electrode sheets with a certain compaction density (the positive electrode sheet has a compaction density of 2.45g / cm 3 , the compaction density of the negative electrode is 1.6g / cm 3 , and then the electrode pieces are cut and laser die-cut. The obtained positive and negative electrode pieces are stacked to assemble the battery cell, with 25 layers of stacking, then put into the shell, dried, and finally filled with electrolyte, with an injection coefficient of 3.5g / Ah. The obtained lithium-ion battery is then divided into capacity and tested.

[0117] (4) Formation and aging

[0118] The electrochemical performance of each lithium-ion battery assembled in the above lithium-ion battery embodiment was tested under the following test conditions:

[0119] (a) Forming at 45℃, the process steps are as follows:

[0120] 1. 0.1C constant current charging to 3.2V;

[0121] 2. 0.2C constant current charging to 3.4V;

[0122] 3. 0.33C constant current and constant voltage charging to 3.55V, cut-off current 0.05C;

[0123] 4. 0.05C constant current charging to 4.05V;

[0124] 5. 0.02C constant current charge to 4.05V;

[0125] 6. Charge at 0.01C constant current to 4.05V.

[0126] (b) The battery volume V1 is tested by the water displacement method.

[0127] (c) Vacuum exhaust for 8 seconds and heat seal at 195℃ for 5 seconds.

[0128] (d) The volume V2 after exhaust is tested by drainage method, and the gas production V is obtained. 化成 =V1-V2.

[0129] (e) High temperature aging at 45°C for 48 h.

[0130] (f) Drainage method to test the cell volume V3 and obtain the aging gas production V 老化 =V3-V2.

[0131] Among them, in the process of assembling into the positive electrode plate, the lithium supplement material provided in the embodiment and the comparative example needs to be placed under vibration conditions for 8 hours. After vibration, the upper layer of lithium supplement material is taken to prepare a lithium-ion battery, and then its capacity and aging gas production data are evaluated. It should be explained that the vibration test is to simulate the situation of the material during long-term storage and freight; in order to demonstrate its uniformity and stability; after vibration, the material is prone to stratification, and the actual values ​​of the first lithium-rich material and the second lithium-rich material in the upper and lower layers will be different from the designed values ​​in the embodiment, which will not only affect the uniformity of the material, but also cause the actual gas production to be different from the designed gas production, and affect the capacity deviation caused by the different lithium supplements required by the battery design. At the same time, a comparative example 5 without vibration testing is provided, and the lithium supplement material in comparative example 5 is the same as that in embodiment 1, with the only difference that the material in comparative example 5 is not subjected to vibration testing.

[0132] The test results of the above lithium supplement materials and lithium batteries are shown in Table 2 below:

[0133] Table 2. Formation test results of the assembled batteries of the examples and comparative examples

[0134]

[0135]

[0136] It can be seen from the test results of Examples 1 to 12 and Comparative Examples 1 and 4 in Table 1 that the present application can substantially reduce the gas production of the battery during the formation stage and the aging stage of the battery by compounding the first lithium-rich material and LNO and controlling the particle size of the first lithium-rich material to be smaller than the particle size of LNO.

[0137] From the test results of Examples 1 to 3 in Table 1, it can be seen that by reducing the particle size of LNO and always controlling the particle size of LNO to be larger than the particle size of the first lithium-rich material, the gas production in the formation stage can be always controlled within a smaller range. In addition, due to the reduction in the particle size of LNO, stratification will occur in the lithium-supplementing material under vibration conditions, causing LNO to be more easily deposited on the lower part of the lithium-supplementing material during the vibration process, thereby increasing the gas production in the aging stage.

[0138] From the test results of Example 1 and Examples 4 to 8 in Table 1, it can be seen that the solution of the present application can be applied to other functional materials. And the capacity and gas production of the lithium supplement material can be controlled by adjusting the proportion of the functional material.

[0139] From the test results of Example 1 and Example 9-Example 12 in Table 1, it can be seen that the solution of the present application can be applied to other lithium-rich materials (such as Li6CoO4, LCO). It should be noted that since LCO has a higher lithium replenishment capacity, the solution using LCO will obtain a higher lithium replenishment capacity than the solution using Li5FeO4. However, from the results of the vertical comparison (Example 9-Example 12 and Comparative Example 4), it can be seen that the solution provided by the present application can significantly solve the problem of gas production. At the same time, the addition of functional materials also has an impact on the gas production.

[0140] From the test results of Example 1 and Comparative Example 5 in Table 1, it can be seen that the vibration test simulates the situation of materials in long-term storage and freight, and will not affect the capacity of the lithium supplement material provided by the present application. In addition, the solution provided by the present application can be applied to the situation of materials in long-term storage and freight, and reduce the gas production in the formation and aging stages.

[0141] 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.

[0142] 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 lithium supplement material, It is characterized in that The invention comprises a first lithium-rich material and a second lithium-rich material connected to each other, wherein the chemical formula of the first lithium-rich material comprises Li a M b O c , wherein M is Fe and / or Co, and 1≤a≤8, 0<b, 0<c<7, and the chemical formula of the second lithium-rich material includes Li 2+x NiO 2+y , wherein, -0.5≤x≤0.5, 0≤y<0.3; the particle size of the first lithium-rich material is smaller than the particle size of the second lithium-rich material.

2. The lithium supplement material according to claim 1, It is characterized in that The particle size of the first lithium-rich material is 3 μm to 15 μm; and / or The particle size of the second lithium-rich material is 8 μm to 20 μm; and / or The mass ratio of the first lithium-rich material to the second lithium-rich material is (1-10):

1.

3. The lithium supplement material according to claim 1, It is characterized in that There are a plurality of particles of the first lithium-rich material, and the plurality of particles of the first lithium-rich material are distributed around particles of the second lithium-rich material. The first lithium-rich material and the second lithium-rich material together constitute secondary particles.

4. The lithium supplement material according to any one of claims 1 to 3, It is characterized in that The lithium-supplementing material further includes a functional material, part of which is coated on the outer surface of the first lithium-rich material, and / or part of which is coated on the outer surface of the second lithium-rich material; And / or, part of the functional material is filled in the gap between the first lithium-rich material and the second lithium-rich material.

5. The lithium supplement material according to claim 4, It is characterized in that The functional material includes a polar group, and the polar group forms a coordination bond with the transition metal element in the first lithium-rich material and the nickel element in the second lithium-rich material; and / or, The polar group includes one or more of a hydroxyl group, an amine group, an ester group, a phenyl group, a piperidinyl group, an imino group, a morpholinyl group, and a triazine group.

6. The lithium supplement material according to claim 4, It is characterized in that The functional material comprises one or more of triethanolamine, triethylamine, p-phenylenediamine, tetrabutyl titanate, 2,6-di-tert-butyl-4-methylphenol, phosphite, poly-{[6-[(1,1,3,3,-tetramethylbutyl)-amino]1,3,5,-triazine-2,4-diyl][(2,2,6,6-tetramethylpiperidinyl)-imino]-1,6-hexanediyl-[(2,2,6,6-tetramethylpiperidinyl)-imino]}, poly{(6-morpholinyl-5-triazine-2,4-diyl)(2,2,6,6-tetramethylpiperidinyl)iminohexamethylene[(2,2,6,6-tetramethylpiperidinyl)-imino]}; and / or The functional material accounts for 0.5% to 10% by weight of the lithium supplement material.

7. A method for preparing a lithium supplement material, It is characterized in that include: A first lithium-rich material and a second lithium-rich material are provided respectively, wherein the chemical formula of the first lithium-rich material includes Li a M b O c , wherein M is Fe and / or Co, and 1≤a≤8, 0<b, 0<c<7, and the chemical formula of the second lithium-rich material includes Li 2+x NiO 2+y , where -0.5≤x≤0.5, 0≤y<0.3; The first lithium-rich material and the second lithium-rich material are uniformly mixed and dried so that the first lithium-rich material is connected to the second lithium-rich material, and the particle size of the first lithium-rich material is smaller than that of the second lithium-rich material.

8. A positive electrode material, It is characterized in that The positive electrode material comprises an active material and the lithium supplement material according to any one of claims 1 to 6, or comprises a lithium supplement material obtained by the preparation method of the lithium supplement material according to claim 7.

9. A secondary battery, It is characterized in that The invention comprises a positive electrode, a negative electrode and an electrolyte, wherein the positive electrode and the negative electrode are arranged in the electrolyte, and the positive electrode comprises the positive electrode material according to claim 8.

10. The secondary battery according to claim 9, It is characterized in that The gas production of the secondary battery during formation is 15 mL to 30 mL, and the gas production of the secondary battery after aging at 45° C. for 48 hours is 0.1 mL to 2.5 mL.

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