A composite lithium supplement material and its preparation method and application

Abstract

The present application proposes a composite lithium-supplementing material and a preparation method and application thereof, wherein the composite lithium-supplementing material comprises a lithium-rich core and an amino acid substance, wherein the lithium-rich core comprises a lithium-containing compound, and the amino acid substance is bound to the outer layer or / and the interior of the lithium-rich core. The composite lithium-supplementing material of the present application, by binding the amino acid substance to the lithium-rich core, can react with the oxygen species generated by the lithium-rich core and the residual alkali, thereby inhibiting the reaction of the oxygen species with the electrolyte, achieving the effect of inhibiting gas production, thereby achieving the purpose of improving the electrochemical performance and safety performance of the material.

Description

Technical Field

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

[0002] During the first charge and discharge process of a lithium-ion battery, a large amount of solid electrolyte interface film will be produced on the surface of the negative electrode of the battery, which consumes the limited lithium ions and electrolyte in the battery, causing irreversible capacity loss, reducing the energy density of the lithium-ion secondary battery and reducing the charge and discharge efficiency of the electrode material, limiting the application of lithium-ion batteries. In the prior art, the first irreversible capacity loss of a lithium battery can be effectively compensated by adding lithium-supplementing materials to the positive electrode material. However, the existing lithium-supplementing materials still have the problem of negative electrode transition metal ion deposition, and are prone to produce gas during the first charging process. The residual alkali substances on the surface may react with the electrolyte under high temperature conditions to generate gas substances such as carbon dioxide, resulting in increased battery gas production or increased battery impedance, and ultimately causing a decrease in battery performance.

[0003] Therefore, it is very necessary to develop a lithium-supplementing material that can prevent the deposition of transition metal ions at the negative electrode of the battery and improve the problems of gas production and high residual alkalinity on the surface interface of the lithium-supplementing material. Summary of the invention

[0004] In view of this, one purpose of the present application is to provide a composite lithium supplement material, in which amino acid substances are combined with a lithium-rich core. The amino acid substances can not only act as chelating agents to coordinate with transition metal ions dissolved in positive electrode materials and lithium supplement materials to prevent them from depositing on the negative electrode, but also react with oxygen species to inhibit the side reaction of oxygen species with electrolyte to produce gas, thereby achieving the purpose of improving the electrochemical performance of the composite lithium supplement material.

[0005] Another object of the present application is to provide a method for preparing a composite lithium supplement material.

[0006] Another object of the present application is to provide a positive electrode.

[0007] Another object of the present application is to provide a secondary battery.

[0008] To achieve the above-mentioned purpose, the first embodiment of the present application proposes a composite lithium supplement material, comprising:

[0009] a lithium-rich core, including a lithium-containing compound;

[0010] Amino acid substances are combined with the outer layer and / or the interior of the lithium-rich core.

[0011] In some embodiments of the present application, the amino acid substance includes one or more of reducing amino acids and polymers of reducing amino acids.

[0012] In some embodiments of the present application, the reducing amino acids and polymers thereof include one or more of arginine, threonine, proline, serine, cysteine ​​and polymers thereof.

[0013] In some embodiments of the present application, the composite lithium-supplementing material further includes a first coating material, and the first coating material is coated on the outer surface layer of the lithium-rich core.

[0014] In some embodiments of the present application, the first coating material is continuously coated on the outer surface of the lithium-rich core, and at least a portion of the amino acid substance is coated on the outer surface of the first coating material as the second coating material.

[0015] In some embodiments of the present application, the first coating material is discontinuously coated on the outer surface of the lithium-rich core, part of the amino acid substance is coated on the outer surface of the first coating material as the second coating material, and part of the amino acid substance is doped in the lithium-rich core.

[0016] In some embodiments of the present application, the first coating material is a carbon material, and the mass ratio of the lithium-containing compound, the first coating material, and all amino acid substances is 100:0.1-5:0.1-10.

[0017] In some embodiments of the present application, the thickness of the first coating layer formed by the first coating material and the second coating layer formed by the amino acid substance are both 1-100 nm.

[0018] In some embodiments of the present application, the lithium-containing compound includes a general structural formula of Li 1+x A y O z Or / and the general structural formula is Li w O r material; wherein 0.3﹤x﹤10, 0﹤y﹤6, 0﹤z﹤13, and A is selected from at least one of Fe, Ni, Mn, Co, Cu, Zn, Si, Sn, Al, Zr, and Ge elements, 1≤w≤2, and 1≤r≤2.

[0019] In some embodiments of the present application, the median particle size of the lithium-rich core is 0.5-20 μm.

[0020] In some embodiments of the present application, the median particle size of the amino acid substance is 0.05-10 μm.

[0021] In some embodiments of the present application, the median particle size of the composite lithium supplement material is 1-45 μm.

[0022] In some embodiments of the present application, the BET specific surface area of ​​the lithium-rich core is 0.5-50 m 2 / g.

[0023] In some embodiments of the present application, the residual alkalinity of the composite lithium supplementing material is less than 5 wt %.

[0024] To achieve the above-mentioned purpose, the second embodiment of the present application proposes a method for preparing a composite lithium supplement material, comprising:

[0025] After the lithium-rich core and the amino acid substance are mixed, a first sintering is performed at 100-300° C. in a first inert atmosphere to obtain the composite lithium supplement material.

[0026] In some embodiments of the present application, the method for preparing the composite lithium-supplementing material also includes: before mixing the lithium-rich core with the amino acid substance, first mixing the lithium-rich core with the source material of the first coating material, performing a second sintering in a second inert atmosphere to obtain a lithium-rich core coated with the first coating material, and the first sintering temperature is lower than the second sintering temperature.

[0027] To achieve the above objectives, a third aspect of the present application provides a positive electrode, including the composite lithium replenishing material of the embodiment of the present application or a composite lithium replenishing material prepared by the preparation method of the composite lithium replenishing material of the embodiment of the present application.

[0028] To achieve the above-mentioned purpose, a fourth aspect of the present application provides a secondary battery, comprising a positive electrode, a negative electrode and a separator, wherein the positive electrode is the positive electrode of the embodiment of the present application.

[0029] The composite lithium supplement material of the embodiment of the present application can bring the following beneficial effects:

[0030] 1. Amino acid substances are combined with the lithium-rich core. Amino acid substances can act as chelating agents to coordinate with transition metal ions dissolved in the positive electrode material and lithium supplement material to prevent them from depositing on the negative electrode, thereby achieving the purpose of improving the electrochemical performance of the composite lithium supplement material.

[0031] 2. Amino acid substances Select reducing amino acids and their polymers to react with the lithium-rich core and oxygen species produced by residual alkali, thereby inhibiting the reaction of oxygen species with the electrolyte, achieving the effect of inhibiting gas production, thereby achieving the purpose of further improving the electrochemical properties and safety performance of the material.

[0032] 3. The first coating material and the amino acid substance are sequentially arranged outside the lithium-rich core to form a double-layer coating structure, which has the following functions:

[0033] (1) It can reduce the residual alkali value on the surface of the material;

[0034] (2) Inhibiting the gelation phenomenon during the preparation of slurry of composite lithium supplement materials;

[0035] (3) It can isolate the water in the air from corroding the lithium-rich core material, improve the stability of the composite lithium-supplementing material in the air, make it not require a harsh operating environment, and facilitate large-scale production.

[0036] 4. The first coating material can improve the conductivity of the composite lithium supplement material.

[0037] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the following description of the embodiments in conjunction with the accompanying drawings, in which:

[0039] Figure 1 The figure is a schematic diagram of a simple structure of a composite lithium supplement material according to an embodiment of the present application.

[0040] Figure 2 Schematic diagram of the simple structure of a composite lithium supplement material according to another embodiment of the present application.

[0041] Figure 3 Schematic diagram of the simple structure of a composite lithium supplement material according to another embodiment of the present application.

[0042] Figure 4 Schematic diagram of the simple structure of a composite lithium supplement material according to another embodiment of the present application.

[0043] Figure 5 Schematic diagram of the simple structure of a composite lithium supplement material according to another embodiment of the present application.

[0044] Reference numerals:

[0045] 1-lithium-rich core; 2-amino acid substance; 3-first coating material. DETAILED DESCRIPTION

[0046] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, but cannot be understood as limiting the present application.

[0047] Throughout the application, the disclosure of numerical ranges includes all values ​​within the entire range and disclosure of further subdivided ranges, including endpoints and subranges given within those ranges.

[0048] In the application, the raw materials, equipment, etc. involved, unless otherwise specified, are all raw materials and equipment that can be produced through commercial channels or known methods; the methods involved, unless otherwise specified, are all conventional methods.

[0049] A composite lithium supplement material according to an embodiment of the present application is described below with reference to the accompanying drawings.

[0050] The composite lithium supplement material of the embodiment of the present application includes a lithium-rich core 1 and an amino acid substance 2. The lithium-rich core 1 includes a lithium-containing compound; the amino acid substance 2 can be completely combined with the outer layer of the lithium-rich core 1 (such as Figure 1 As shown), they can also be all combined inside the lithium-rich core 1 (as shown Figure 2 As shown), it can also be partially combined with the outer layer of the lithium-rich core 1 and partially combined with the interior of the lithium-rich core 1 (as shown Figure 3 shown).

[0051] It can be understood that the "combination" in the present application can be coating, blending, etc., depending on the relative position of the amino acid substance and the lithium-rich core. For example, when the amino acid substance is completely combined with the outer layer of the lithium-rich core 1, the "combination" here can be coating, and specifically the amino acid substance can be discontinuously or continuously coated on the outer surface of the lithium-rich core; when the amino acid substance is completely combined with the inside of the lithium-rich core, or partially combined with the outer layer of the lithium-rich core and partially combined with the inside of the lithium-rich core, the "combination" can be blending, and the specific blending method can be uniform blending or non-uniform blending.

[0052] The composite lithium-supplementing material of the embodiment of the present application combines amino acid substances with the lithium-rich core. The amino acid substances can act as chelating agents to coordinate with transition metal ions dissolved in the positive electrode material and the lithium-supplementing material to prevent them from being deposited on the negative electrode, thereby achieving the purpose of improving the electrochemical performance of the composite lithium-supplementing material.

[0053] It should be noted that in the present application, the reaction of oxygen species with the electrolyte does not necessarily produce only oxygen, but more likely other gases, such as methane, ethane, ethylene, CO, CO2, etc. Most of the oxygen should be produced by the decomposition of the lithium-rich core material.

[0054] In addition, it should be noted that in the present application, when the amino acid substance is partially bound to the outer surface of the lithium-rich core and partially bound to the interior of the lithium-rich core 1, the mass ratio of the amino acid substance bound to the interior of the lithium-rich core to the amino acid substance bound to the outer surface of the lithium-rich core is not limited and can be any ratio.

[0055] In some embodiments of the present application, the amino acid substances include, but are not limited to, one or more of reducing amino acids and polymers of reducing amino acids. Among them: reducing amino acids and their polymers include, but are not limited to, one or more of arginine, threonine, proline, serine, cysteine ​​and their polymers. The amino acid substances are selected from reducing amino acids and their polymers, which can not only coordinate with the transition metal ions dissolved in the positive electrode material and the lithium supplement material to prevent their deposition on the negative electrode, but also react with the oxygen species produced by the lithium-rich core and the residual alkali, thereby inhibiting the reaction of the oxygen species with the electrolyte, thereby achieving the effect of inhibiting the gas production of lithium-ion batteries.

[0056] In some embodiments of the present application, the median particle size (D50) of the amino acid substance is 0.05-10 μm, including but not limited to 0.05 μm, 0.1 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm or 10 μm, etc. The median particle size of the amino acid substance within the above range can better combine with the lithium-rich core; if it is less than 0.05 μm, the dispersion is poor and it is easy to agglomerate; if it is greater than 10 μm, the contact area with the lithium-rich core is reduced, which is not conducive to inhibiting the oxygen species generated by the lithium-rich core.

[0057] In some embodiments of the present application, when the composite lithium supplement material contains only a lithium-rich core and amino acid substances, the mass ratio of the lithium-rich core and the amino acid substances is 100:(0.2-15), including but not limited to 100:0.2, 100:1, 100:2, 100:3, 100:4, 100:5, 100:6, 100:7, 100:8, 100:9, 100:10, 100:11, 100:12, 100:13, 100:14 or 100:15, etc. When the composite lithium supplement material contains only a lithium-rich core and amino acid substances, the mass ratio of the lithium-rich core and the amino acid substances is within the above range, which can ensure the lithium supplement amount of the lithium-rich core while playing a role in inhibiting oxygen species; if the mass ratio is too small, the effect of inhibiting oxygen species cannot be achieved; if the mass ratio is too large, the lithium supplement amount of the lithium-rich core will be reduced.

[0058] In some embodiments of the present application, when the composite lithium supplement material contains only a lithium-rich core and amino acid substances, and the amino acid substances are all bound to the surface of the lithium-rich core in the form of coating, the thickness of the amino acid substances as a coating layer is 2-200nm, including but not limited to 2nm, 50nm, 100nm, 150nm or 200nm, etc. When the composite lithium supplement material contains only a lithium-rich core and amino acid substances, and the amino acid substances are all bound to the surface of the lithium-rich core in the form of coating, the thickness of the amino acid substances as a coating layer is within the above range, the coating layer has good stability and can ensure the timely release of active lithium; if it is less than 2nm, the coating layer has weak stability; if it is greater than 200nm, it affects the timely release of active lithium and increases battery impedance.

[0059] In the present application, the lithium-containing compound is a material that easily generates gas during the initial charging process and the residual alkaline substances present on the surface may react with the electrolyte under high temperature to generate gaseous substances such as carbon dioxide.

[0060] In some embodiments of the present application, the lithium-containing compound includes a general structural formula of Li 1+x A y O z material, wherein 0.3﹤x﹤10, 0﹤y﹤6, 0﹤z﹤13, and A is selected from at least one of Fe, Ni, Mn, Co, Cu, Zn, Si, Sn, Al, Zr, and Ge elements. As a non-limiting example, the value of x includes but is not limited to 0.4, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 9.9, the value of y includes but is not limited to 0.1, 1, 2, 3, 4, 5, or 5.9, and the value of z includes but is not limited to 0.1, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, or 12.9. When the values ​​of x, y, and z are within the above ranges, respectively, the lithium-replenishing performance of the lithium-containing compound can be fully exerted; if the values ​​exceed the above ranges, the lithium-replenishing effect of the lithium-containing compound is weak and the impedance is large. As a possible example, the lithium-rich core is a general structural formula of Li 1+x A y O z When the lithium-containing compound is used, the lithium-containing compound is selected from one or more of Li5FeO4, Li6CoO4, Li6MnO4, Li8ZrO6, Li2CoO2, Li2MnO2, and Li2NiO2.

[0061] In some other embodiments of the present application, the lithium-containing compound includes a general structural formula of Li w O rMaterials, wherein 1≤w≤2, 1≤r≤2. As non-limiting examples, the value of w includes but is not limited to 1, 1.2, 1.5, 1.8 or 2, and the value of r includes but is not limited to 1, 1.2, 1.5, 1.8 or 2. If the values ​​of w and r are within the above ranges, the lithium-replenishing performance of the lithium-containing compound can be fully exerted; if the values ​​are beyond the above ranges, the lithium-replenishing effect of the lithium-containing compound is weak and the impedance is large. As a possible example, the general structural formula is Li w O r The material is selected from one or more of Li2O, Li2O2, etc.

[0062] In some other embodiments of the present application, the lithium-rich core is the above-mentioned structural formula Li 1+x A y O z The lithium-containing compound and the general structural formula Li w O r A mixture of materials.

[0063] In some embodiments of the present application, the median particle size (D50) of the lithium-rich core is 0.5-20 μm, including but not limited to 0.5 μm, 1 μm, 5 μm, 10 μm, 15 μm or 20 μm, etc. When the median particle size of the lithium-rich core is within the above range, its dispersibility in the slurry is good, and it does not affect the electronic conduction and ion conduction of the pole piece, and can ensure the electrical performance of the lithium-ion secondary battery; when it is less than 0.5 μm, it is not conducive to its dispersion in the slurry; when it is greater than 20 μm, it will affect the electronic conduction and ion conduction of the pole piece, thereby affecting the electrical performance of the lithium-ion secondary battery.

[0064] In some embodiments of the present application, the BET specific surface area of ​​the lithium-rich core is 0.5-50 m 2 / g, including but not limited to 0.5m 2 / g, 1m 2 / g, 10m 2 / g, 20m 2 / g, 25m 2 / g, 30m 2 / g, 40m 2 / g or 50m 2 / g, etc.

[0065] In some embodiments of the present application, Figure 4 and Figure 5As shown, the composite lithium-supplementing material also includes a first coating material 3, which is coated on the outer layer of the lithium-rich core 1. The first coating material can improve the conductivity of the composite lithium-supplementing material, which is beneficial to reduce the impedance inside the electrode; at the same time, during the release process of the lithium-rich core as a "sacrifice" and after the release, the first coating material can also be reused to play an auxiliary role as a conductive agent inside the positive electrode. As a non-limiting example, the first coating material in the present application includes at least one of a carbon material, a conductive polymer or a conductive oxide. Among them, the carbon material may include but is not limited to one or more of amorphous carbon, carbon nanotubes, graphite, carbon black, graphene, etc. The conductive oxide may include but is not limited to one or more of In2O3, ZnO, SnO2. By adjusting the material of the electronic conductor encapsulation layer, its electronic conductivity can be further improved. Conductive polymers may include but are not limited to [C6H7O6Na] n Organic polymers with the structure [C6H7O2(OH)2OCH2COONa] n Organic polymers with [C3H4O2] n Organic polymers with the structure [C3H3O2M a ] n Organic polymers with the structure [C3H3N] n An organic polymer with the structure [CH2CF2] n One or more of an organic polymer having a [NHCO] structure, an organic polymer having an imide ring [CONCO] structure on the main chain, and polyvinyl pyrrolidone, wherein M a Alkali metal elements. In some embodiments, the polymer includes one or more of polyvinylidene fluoride, sodium alginate, sodium carboxymethyl cellulose, polyacrylic acid, polyacrylic acid salt, polyacrylonitrile, polyamide, polyimide, polyvinyl pyrrolidone, polyethylene oxide (PEO), polypyrrole (PPy), polytetrafluoroethylene (PTFE), and polyurethane (PU). In other embodiments, the polymer includes one or more of sodium carboxymethyl cellulose and polyacrylic acid. Sodium carboxymethyl cellulose and polyacrylic acid are two-dimensional surface polymers with good bonding effects, which can effectively coat the core of manganese-based lithium supplement materials, thereby avoiding contact between the core of the composite lithium supplement material and the air, and improving the stability of the composite lithium supplement material. In the embodiment of the present application, the molecular weight of the polymer is greater than or equal to 100,000. The molecular weight of the polymer can be specifically but not limited to 100,000, 150,000, 200,000, 300,000, 500,000 or 1 million. The larger the molecular weight of the polymer, the higher the density and structural strength of the polymer layer, and the more conducive to the protection of the core 10.

[0066] In some embodiments of the present application, the first coating material 3 is continuously coated on the outer surface of the lithium-rich core 1, and at least part of the amino acid substance 2 is coated on the outer surface of the first coating material 3 as the second coating material. It should be noted that in this case of the present application, the amino acid substance 2 as the second coating material can be continuously coated on the outer surface of the first coating material, or can be non-continuously coated on the outer surface of the first coating material 3. As a possible example, Figure 4 As shown, the first coating material 3 is continuously coated on the outer surface of the lithium-rich core 1, and all the amino acid substances 2 are continuously coated on the outer surface of the first coating material 3 as the second coating material. In this way, the first coating material and the amino acid substance together constitute a double-layer coating structure of the lithium-rich core, which can isolate the corrosion of the lithium-rich core material by water in the air, improve the stability of the composite lithium supplement material in the air, and make it not require a harsh operating environment, which is conducive to large-scale production. It is particularly important to explain that at this time, when the first coating material is continuously coated on the core material, and all the amino acid substances 2 are also continuously coated on the first coating layer as the second coating material, the compactness of the first coating material can also alleviate the impact of a large number of oxygen species on the second coating material, thereby inhibiting gas production. As another possible example, the first coating material 3 is continuously coated on the outer surface of the lithium-rich core 1, and part of the amino acid substance 2 is continuously or discontinuously coated on the outer surface of the first coating material 3 as the second coating material, and another part of the amino acid substance 2 can be doped in the lithium-rich core 1. It should be noted that the mass ratio of the amino acid substance mixed in the lithium-rich core and the amino acid substance as the second coating material is (0.1-5): (90-99.1), including but not limited to 0.1:90, 0.1:99.1, 5:90, 5:99.1 or 2.5:94.5. When appropriate amino acid substances are doped in the lithium-rich core, these amino acid substances can adsorb oxygen species produced by the lithium-rich core material to prevent the amino acid substances in the coating layer from being unable to suppress the generation of oxygen species when the lithium-rich core material releases too many oxygen species. If the amino acid substance in the lithium-rich core is too low, it will not play a role in suppressing the impact of a large amount of oxygen species on the coating layer; if the amino acid substance in the lithium-rich core is too much, the volume of the lithium-rich core unit cell will increase, affecting the stability of the structure of the lithium-rich core material.

[0067] In other embodiments of the present application, Figure 5As shown, the first coating material 3 is non-continuously coated on the outer surface of the lithium-rich core 1, part of the amino acid substance 2 is coated on the outer surface of the first coating material 3 as the second coating material, and part of the amino acid substance is doped in the lithium-rich core 1. It should be noted that the mass ratio of the amino acid substance mixed in the lithium-rich core and the amino acid substance as the second coating material is (0.1-5): (90-99.1), including but not limited to 0.1:90, 0.1:99.1, 5:90, 5:99.1 or 2.5:94.5. When appropriate amino acid substances are doped in the lithium-rich core, these amino acid substances can absorb oxygen species generated by the lithium-rich core material to prevent the amino acid substances in the coating layer from being unable to suppress the generation of oxygen species when the lithium-rich core material releases too many oxygen species. If the amino acid substance in the lithium-rich core is too low, it will not play a role in suppressing the impact of a large amount of oxygen species on the coating layer; if the amino acid substance in the lithium-rich core is too much, the volume of the lithium-rich core unit cell will increase, affecting the stability of the structure of the lithium-rich core material. It should also be noted that this situation in the present application has a better technical effect than the aforementioned situation of "the first coating material 3 is continuously coated on the outer surface of the lithium-rich core 1, and at least part of the amino acid substance 2 is coated on the outer surface of the first coating material 3 as the second coating material". Because the amino acid substance in the outer layer enters the lithium-rich core material through heat treatment, the amino acid substance can be distributed not only in the inner core and the outer layer, but also continuously distributed in the middle area. This gradient distribution structure is more conducive to inhibiting the generation of gas.

[0068] In some embodiments of the present application, when the first coating material is a carbon material, the mass ratio of the lithium-containing compound, the first coating material, and all amino acid substances is 100:0.1-5:0.1-10, including but not limited to 100:0.1:0.1, 100:0.1:10, 100:5:0.1, 100:5:10, 100:1:0.1, 100:2.5:0.1, 100:2.5:5 or 100:2.5:10, etc. When the first coating material is a carbon material, the mass ratio of the lithium-containing compound, the first coating material, and all amino acid substances is within the above range, and the lithium-containing compound, the first coating material, and all amino acid substances can fully exert their respective effects; if the first coating material and the amino acid substance are used in too much amount, the coating layer on the surface of the material will be too thick or even the coating will agglomerate, which will affect the reaction process kinetics of the composite lithium supplement material, thereby affecting the performance of the composite lithium supplement material; if the first coating material and the amino acid substance are used in too little amount, it is difficult to achieve the coating effect.

[0069] In some embodiments of the present application, the thickness of the first coating layer formed by the first coating material and the second coating layer formed by the amino acid substance are both 1-100nm, including but not limited to 1nm, 10nm, 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm or 100nm, etc. When the thickness of the first coating layer and the second coating layer is within the above range, the lithium-containing compound, the first coating layer, and the second coating layer can give full play to their respective effects; if the thickness of the first coating layer and the second coating layer is too large, the coating layer on the surface of the material will be too thick or even the coating will agglomerate, which will affect the reaction process kinetics of the composite lithium supplement material, thereby affecting the performance of the composite lithium supplement material; if the thickness of the first coating layer and the second coating layer is too small, it is difficult to achieve the coating effect.

[0070] It should be noted that, in the present application, the thickness of the first coating layer formed by the first coating material and the second coating layer formed by the amino acid substance may be the same or different.

[0071] In some embodiments of the present application, the median particle size of the composite lithium supplement material is 1-45 μm, including but not limited to 1 μm, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm or 45 μm, etc. The median particle size of the composite lithium supplement material is within the above range; if it is less than 1 μm, it is not conducive to dispersion in the positive electrode slurry; if it is greater than 45 μm, it will affect the electronic conduction and ion conduction of the positive electrode sheet, thereby affecting the electrical performance of the lithium ion secondary battery.

[0072] In some embodiments of the present application, the residual alkalinity of the composite lithium supplement material is lower than 5wt%, including but not limited to 0.01wt%, 0.1wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt% or 4.5wt%, etc. The lower the residual alkalinity of the composite lithium supplement material, the better, which can improve the surface stability and structural stability of the composite lithium supplement material; if the residual alkalinity of the composite lithium supplement material is too large, it will have the opposite effect, and at the same time, it will cause a gelation reaction when the slurry is prepared, reducing the number of lithium ions released by the composite lithium supplement material.

[0073] The preparation method of the composite lithium-supplementing material of the embodiment of the present application comprises: mixing the lithium-rich core with the amino acid substance, and then performing a first sintering at 100-300° C. in a first inert atmosphere to obtain the composite lithium-supplementing material.

[0074] In some embodiments of the present application, the temperature of the first sintering includes but is not limited to 100°C, 150°C, 200°C, 250°C or 300°C, etc. The temperature of the first sintering is within the above range, which can ensure that the amino acid substance has a good binding force with the lithium-rich core and the effect of inhibiting gas production; if it is lower than 100°C, the binding force between the amino acid substance and the lithium-rich core is weak; if it is higher than 300°C, the amino acid substance is carbonized and the effect of inhibiting gas production cannot be achieved.

[0075] In some embodiments of the present application, the first sintering time is 1-6 hours, including but not limited to 1 hour, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours, etc. The first sintering time is within the above range; if it is less than 1 hour, if the amino acid substance is combined with the outer surface of the lithium-rich core in the form of a coating, the coating will be uneven; if it is higher than 6 hours, unnecessary side reactions will occur.

[0076] In some embodiments of the present application, the first inert atmosphere includes, but is not limited to, one or more of argon, nitrogen, helium, and neon.

[0077] In the present application, the lithium-rich core is a lithium-containing compound, which can be obtained through commercial channels or made in-house. In some embodiments of the present application, the lithium-containing compound includes a general structural formula of Li 1+x A y O z The material, wherein 0.3﹤x﹤10, 0﹤y﹤6, 0﹤z﹤13, A is selected from at least one of Fe, Ni, Mn, Co, Cu, Zn, Si, Sn, Al, Zr, and Ge. The preparation method of the lithium-rich core is: after the A source and the lithium source are uniformly mixed in molar ratio, sintering at 650-900℃ in an inert atmosphere for 4-10h, a lithium-rich core having a general structural formula of Li 1+x A y O z The lithium-containing compound. The source of A includes but is not limited to at least one of the sulfate, carbonate, acetate, oxide, hydroxide, etc. of element A, and the lithium source includes but is not limited to one or more of lithium oxide, lithium hydroxide, lithium oxalate, lithium sulfate, lithium carbonate, etc. The general structural formula is Li 1+x A y O z In the preparation process of the lithium-containing compound, the sintering temperature includes but is not limited to 650°C, 700°C, 750°C, 800°C, 850°C or 900°C, and the sintering time includes but is not limited to 4h, 5h, 6h, 7h, 8h, 9h or 10h. The general structural formula is Li 1+x A y O z In the preparation process of the lithium-containing compound, the sintering temperature and sintering time are within the above range, and a high-purity lithium-containing compound with a general structural formula of Li 1+x Ay O z Lithium-containing compound core material.

[0078] In some embodiments of the present application, the general structural formula is Li 1+x A y O z In the preparation process of the lithium-containing compound, the mixing method of source A and the lithium source includes but is not limited to mixing using one or both of a ball mill, a fusion machine or a dual-motion mixer.

[0079] In some other embodiments of the present application, when the composite lithium-supplementing material also contains a first coating material, the preparation method of the composite lithium-supplementing material includes: before mixing the lithium-rich core with the amino acid substance, first mixing the lithium-rich core with the source material of the first coating material, and performing a second sintering in a second inert atmosphere to obtain the lithium-rich core coated with the first coating material. After that, the lithium-rich core coated with the first coating material is mixed with the amino acid substance, and the aforementioned first sintering is performed in the first inert atmosphere to obtain the composite lithium-supplementing material.

[0080] In some embodiments of the present application, when the first coating material is a carbon material, the source material of the first coating material includes but is not limited to one or more of glucose, asphalt, sucrose, fructose, polyvinyl pyrrolidone (PVP), etc.; when the first coating material is a conductive polymer or a conductive oxide, the source material of the first coating material includes but is not limited to at least one of hard carbon, soft carbon, carbon black, graphite, and graphene.

[0081] In some embodiments of the present application, the second sintering temperature is higher than the first sintering temperature. As a non-limiting example, the temperature of the second sintering is 500-800°C, including but not limited to 500°C, 550°C, 600°C, 650°C, 700°C, 750°C or 800°C, etc. When the temperature of the second sintering is within the above range, a carbon material with higher purity can be obtained with moderate energy consumption; if it is lower than 500°C, a carbon material with higher purity cannot be sintered, and the interaction with the lithium-rich core is weak; if it is higher than 800°C, energy consumption is increased.

[0082] In some embodiments of the present application, the second sintering time is 2-6 hours, including but not limited to 2 hours, 3 hours, 4 hours, 5 hours or 6 hours, etc. The second sintering time is within the above range; if it is less than 2 hours, if the electronic conductor encapsulation layer is combined with the outer surface of the lithium-rich core in the form of a coating, the coating will be uneven; if it is higher than 6 hours, unnecessary side reactions will occur.

[0083] In some embodiments of the present application, the second inert atmosphere includes, but is not limited to, one or more of argon, nitrogen, helium, and neon.

[0084] In some embodiments of the present application, the general structural formula is Li 1+x A y O z In the preparation process of the lithium-containing compound, the sintering, the first sintering and the second sintering can be carried out in any one of a rotary furnace, a rotary furnace, a box furnace, a tubular furnace, a roller kiln, a push plate kiln or a fluidized bed.

[0085] In the preparation method of the composite lithium supplement material of the embodiment of the present application, when the composite lithium supplement material also contains the first coating material, a dry mixing technology is used to successively add a certain amount of the source material of the first coating material and the amino acid substance into the lithium-rich core material, and after mixing evenly, high and low temperature sintering are performed respectively to obtain a composite lithium supplement material with a double coating layer structure. The method is simple in process and easy to operate.

[0086] The positive electrode of the embodiment of the present application includes the composite lithium-replenishing material of the embodiment of the present application or the composite lithium-replenishing material prepared by the preparation method of the composite lithium-replenishing material of the embodiment of the present application.

[0087] In some embodiments of the present application, the content of the composite lithium supplement material accounts for 0.5-15wt% of the entire positive electrode. As a non-limiting example, the content of the composite lithium supplement material accounts for 3wt%, 6wt%, 9wt%, 12wt% or 15wt% of the entire positive electrode. When the content of the composite lithium supplement material accounts for the mass percentage of the entire positive electrode within the above range, the amount of lithium supplement is moderate, which can improve the energy density of the lithium-ion battery; if it is lower than 0.5wt%, the amount of lithium supplement is low, and the effect of improving the energy density of the lithium-ion battery cannot be achieved; if it is higher than 15wt%, the proportion of the positive electrode material in the lithium-ion battery is affected, and the effect of improving the energy density of the lithium-ion battery cannot be achieved.

[0088] In some embodiments of the present application, in addition to the composite lithium supplement material, the positive electrode may also include a positive electrode active material, and at least one of a positive electrode conductor and a positive electrode binder. The positive electrode active material includes but is not limited to one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, lithium fluorinated vanadium phosphate, lithium titanate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminum oxide. The positive electrode active material is capable of lithium insertion and extraction, alloying and dealloying, or plating and stripping. The positive electrode conductor includes but is not limited to one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes. Adding a positive electrode conductor to the positive electrode material can enhance the conductivity of the electrode material layer, improve the conductivity of the lithium supplement material, and facilitate the transmission of electrons and ions. The positive electrode binder includes but is not limited to one or more of polyvinylidene fluoride (PVDF), sodium alginate, sodium carboxymethyl cellulose, and polyacrylic acid.

[0089] In some embodiments of the present application, the positive electrode also includes a current collector, which can be selected to include aluminum or any other suitable conductive metal foil (such as solid or mesh or covered foil) known to those skilled in the art, a metal grid or screen, or a porous metal. In some variations, the surface of the current collector may include a metal foil that has been surface treated (e.g., carbon coated and / or etched).

[0090] The secondary battery of the embodiment of the present application comprises a positive electrode, a negative electrode and a separator, wherein the positive electrode is the positive electrode of the embodiment of the present application.

[0091] In some embodiments of the present application, the positive electrode sheet, the separator and the negative electrode sheet can be processed by a lamination process or a winding process to form a secondary battery. It should be noted that the secondary battery of the embodiment of the present application includes but is not limited to a lithium-ion battery.

[0092] The secondary battery of the embodiment of the present application can be widely used in the fields of new energy vehicles, aerospace, electronic products, etc.

[0093] Certain features of the present technology are further illustrated in the following non-limiting examples.

[0094] 1. Examples and Comparative Examples

[0095] Example 1

[0096] like Figure 3 As shown, the composite lithium supplement material of this embodiment includes a lithium-rich core 1, an amino acid substance 2 and a first coating material 3. The first coating material 3 is continuously coated on the outer surface of the lithium-rich core 1, and the amino acid substance 2 is continuously coated on the outer surface of the first coating material 3. The first coating material 3 and the amino acid substance 2 constitute a double-layer coating structure of the lithium-rich core 1. The mass percentage ratio of the lithium-rich core 1, the first coating material 3 and the amino acid substance is 100:0.1:0.1. The lithium-rich core 1 is a lithium-containing compound Li5FeO4, with a median particle size (D50) of 2.16μm and a BET specific surface area of ​​4.32m 2 / g; the first coating material 3 is made of hard carbon, and the thickness of the first coating layer formed by it is 5nm; the amino acid substance 2 is arginine, and the median particle size (D50) is 0.5μm, and the thickness of the second coating layer formed by the amino acid substance 2 is 4nm. The median particle size of the composite lithium supplement material of this embodiment is 3.45μm, and the residual alkalinity is 1.02wt%.

[0097] The method for preparing the composite lithium supplement material of the embodiment of the present application comprises the following steps:

[0098] S1. Preparation of lithium-rich core: Iron oxide and lithium hydroxide were uniformly mixed in a ball mill at a molar ratio of 0.5:5 (ball milling rate was 1000 r / min, ball milling time was 6 h), and then sintered at 850° C. for 10 h under nitrogen atmosphere to obtain Li5FeO4 lithium-containing metal compound.

[0099] S2. Prepare a lithium-rich core coated with a first coating material: mix the Li5FeO4 lithium-containing compound and glucose in a mass ratio of 5:0.005 in a ball mill (the ball milling rate is 700 r / min, and the ball milling time is 1 h), and then sinter at 600°C for 2 h under a nitrogen atmosphere to obtain a lithium-rich core coated with the first coating material.

[0100] S3. Preparation of composite lithium supplement material: Take 3 g of the lithium-rich core coated with the first coating material prepared in step S2, add 0.003 g of arginine, mix evenly in a ball mill (ball milling rate of 350 r / min, ball milling time of 2 h), and then sinter at 150° C. for 1 h in a nitrogen atmosphere to obtain a composite lithium supplement material.

[0101] The positive electrode of this embodiment includes a positive electrode current collector and a positive electrode material coated on the surface of the positive electrode current collector, wherein the positive electrode current collector is aluminum foil, and the positive electrode material includes the following components in parts by weight: 93 parts of lithium iron phosphate, a positive electrode active material, 2 parts of the composite lithium supplement material of this embodiment, 2 parts of the positive electrode conductive agent Super P, and 3 parts of the positive electrode binder polyvinylidene fluoride.

[0102] The secondary battery of this embodiment includes a positive electrode, a negative electrode, a separator stacked between the positive electrode and the negative electrode, and an electrolyte, wherein: the positive electrode is the positive electrode of this embodiment; the negative electrode includes a negative electrode current collector and a negative electrode material coated on the surface of the negative electrode current collector, the negative electrode current collector is a copper foil, and the negative electrode material includes the following components in parts by weight: 95 parts of graphite as a negative electrode active material, 2 parts of Super P as a negative electrode conductive agent, 0.5 parts of carboxymethyl cellulose (CMC) as a thickener, and 2.5 parts of styrene-butadiene rubber (SBR) as a negative electrode binder; the separator adopts a polyethylene (PE) microporous separator; the electrolyte includes ethylene carbonate (EC), ethyl methyl carbonate (DEC) and LiPF6, wherein the volume ratio of ethylene carbonate (EC) to ethyl methyl carbonate (DEC) is 3:7, and the concentration of LiPF6 is 1 mol / L.

[0103] The method for preparing the secondary battery of this embodiment comprises the following steps:

[0104] 1) Preparation of positive electrode: N-methylpyrrolidone, lithium iron phosphate, composite lithium supplement material, conductive agent Super P and polyvinylidene fluoride were mixed in a mass ratio of 100:93:2:2:3, and the positive electrode slurry was obtained by ball milling. The ball milling time was 60 min and the rotation speed was 30 Hz. The positive electrode slurry was coated on the surface of aluminum foil, rolled, and vacuum dried at 100°C overnight to obtain a positive electrode sheet.

[0105] 2) Preparation of negative electrode: negative electrode active material (graphite), conductive agent (conductive carbon black, Super P), thickener (carboxymethyl cellulose, CMC), binder (styrene butadiene rubber, SBR) are placed in deionized water at a mass ratio of 95:2:0.5:2.5 and mixed evenly to form negative electrode slurry, and the negative electrode slurry is coated on the surface of the current collector copper foil. After drying-rolling-secondary drying process, the negative electrode sheet is obtained.

[0106] 3) Preparation of electrolyte: Ethylene carbonate (EC) and ethyl methyl carbonate (DEC) were mixed in a volume ratio of 3:7, and LiPF6 was added to form an electrolyte, and the concentration of LiPF6 was 1 mol / L.

[0107] 4) Secondary battery (lithium-ion battery) assembly: A lithium-ion battery is assembled in an argon inert atmosphere glove box in the order of negative electrode-diaphragm-electrolyte-positive electrode.

[0108] Example 2

[0109] This embodiment is basically the same as Embodiment 1, except that:

[0110] In the composite lithium supplement material, the first coating material 3 and the amino acid substance 2 constitute a double-layer coating structure of the lithium-rich core 1, and the mass percentage ratio of the lithium-rich core 1, the first coating material 3 and the amino acid substance 2 is 100:2:5. The thickness of the first coating layer formed by the first coating material 3 is 10nm; the amino acid substance 2 is threonine, and the thickness of the second coating layer formed by it is 6nm. The median particle size (D50) of the composite lithium supplement material of this embodiment is 4.15μm, and the residual alkalinity is 0.02wt%.

[0111] In the preparation method of amino acid composite lithium supplement material, in step S2, the Li5FeO4 lithium-containing compound and glucose are in a mass ratio of 5:0.01; in step S3, 3g of the lithium-rich core coated with the first coating material prepared in step S2 is taken and 0.15g of threonine is added.

[0112] Example 3

[0113] This embodiment is basically the same as Embodiment 1, except that:

[0114] In the composite lithium supplement material, the first coating material 3 and the amino acid substance 2 constitute a double-layer coating structure of the lithium-rich core 1, and the mass percentage ratio of the lithium-rich core 1, the first coating material 3 and the amino acid substance 2 is 100:5:10. The thickness of the first coating layer formed by the first coating material 3 is 15nm; the amino acid substance 2 is threonine, and the thickness of the second coating layer formed by it is 10nm. The median particle size (D50) of the composite lithium supplement material of this embodiment is 5.20μm, and the residual alkalinity is 0.01wt%.

[0115] In the preparation method of the composite lithium supplement material, in step S2, the Li5FeO4 lithium-containing compound and glucose are in a mass ratio of 5:0.25; in step S3, 3g of the lithium-rich core coated with the first coating material prepared in step S2 is taken and 0.3g of threonine is added.

[0116] Example 4

[0117] This embodiment is basically the same as Embodiment 1, except that:

[0118] like Figure 5 As shown, in the composite lithium supplement material, the first coating material 3 is completely discontinuously coated on the surface of the lithium-rich core 1, 98wt% of the amino acid substance 2 is coated on the outer surface of the first coating material 3 as the second coating material, and 2wt% of the amino acid substance 2 is doped into the lithium-rich core 1.

[0119] The thickness of the first coating layer formed by the first coating material 3 is 4.3nm; the amino acid substance 2 is arginine, and its median particle size (D50) is 0.5μm, and the thickness of the second coating layer formed by the amino acid substance as the second coating material is 3.5nm. The median particle size of the composite lithium supplement material of this embodiment is 4.18μm, and the residual alkalinity is 2.15wt%.

[0120] In the preparation method of the composite lithium supplement material: the sintering temperature of step S2 is 500°C.

[0121] Example 5

[0122] This embodiment is basically the same as Embodiment 1, except that:

[0123] In composite lithium supplement materials, such as Figure 1 As shown, there is no first coating material, and the amino acid substance 2 is directly and continuously coated on the outer surface of the lithium-rich core 1, and the thickness of the coating layer formed by the amino acid substance 2 is 5.2nm. The median particle size (D50) of the composite lithium supplement material of this embodiment is 1.05μm, and the residual alkalinity is 3.01wt%.

[0124] The preparation method of the composite lithium supplementing material does not include step S2. In step S3, the lithium-rich core prepared in step S1 is directly sintered together with arginine.

[0125] Example 6

[0126] This embodiment is basically the same as Embodiment 1, except that:

[0127] In the composite lithium supplement material, the amino acid substance 2 is a mixture of proline and serine in a mass ratio of 1:1, and the coating thickness of the second coating layer formed by the amino acid substance 2 is 5.25nm. The median particle size (D50) of the composite lithium supplement material of this embodiment is 1.26μm, and the residual alkalinity is 3.35wt%.

[0128] In the preparation method of the composite lithium supplement material, in step S3, the amino acid substance components are proline and serine.

[0129] Example 7

[0130] This embodiment is basically the same as Embodiment 1, except that:

[0131] Composite lithium supplement materials, such as Figure 2 As shown, there is no first coating material, and the amino acid substances are all mixed in the lithium-rich core. The median particle size (D50) of the composite lithium-supplementing material of this embodiment is 3.92 μm, and the residual alkalinity is 4.91 wt %.

[0132] The preparation method of the composite lithium supplement material does not include step S2. In step S3, the lithium-rich core prepared in step S1 is directly sintered with arginine, and the sintering temperature is 300° C. and the sintering time is 1 hour.

[0133] Comparative Example 1

[0134] This comparative example is basically the same as Example 1, except that:

[0135] The lithium supplement material does not contain a first coating material and amino acid substances.

[0136] Comparative Example 2

[0137] This comparative example is basically the same as Example 1, except that:

[0138] In the preparation method of the composite lithium supplement material, the "sintering at 150° C. for 1 h in a nitrogen atmosphere" in step S3 is replaced by "carbonization treatment at 700° C. for 1 h in a nitrogen atmosphere".

[0139] Comparative Example 3

[0140] This comparative example is basically the same as Example 1, except that:

[0141] In the preparation method of the composite lithium supplement material, the sintering temperature in step S3 is set to 95°C.

[0142] 2. Performance Test

[0143] 1. Test methods

[0144] (1) Residual alkali value

[0145] The test method for residual alkali is:

[0146] Weigh 5g of the composite lithium supplement material of Examples 1-7 and Comparative Examples 1-3 respectively, add 50mL of ultrapure water freed of carbon dioxide and dissolve in a beaker, ultrasonically oscillate the sample for 5min at an ultrasonic frequency of 5KHz and a power of 50w, and stir every 1min during the ultrasonic oscillation; then, filter the mixed solution obtained by ultrasonic oscillation into a 100ml volumetric flask with quantitative filter paper, fix the volume, and record the volume of the filtrate. Finally, take the above sample solution, titrate it with a standard hydrochloric acid solution, and record the volumes V1 and V2 of the consumed standard hydrochloric acid solution, where V1 is the volume of the standard hydrochloric acid solution consumed by titration to the first jump point; V2 is the volume of the standard hydrochloric acid solution consumed by titration from the first jump point to the second jump point. Calculate OH- and CO3 according to formula (1) and formula (2) respectively. 2- Residual alkali value:

[0147]

[0148]

[0149] In formula (1) and / or formula (2):

[0150] m——actual mass of the sample, g;

[0151] c——Concentration of hydrochloric acid standard solution, 12 mol / L;

[0152] V1——The volume of hydrochloric acid standard solution consumed in titration to the first jump point, mL;

[0153] V2——The volume of hydrochloric acid standard solution consumed in titration from the first jump point to the second jump point, mL;

[0154] V3——filtrate volume, mL;

[0155] V4——volume of filtrate after constant volume, 100ml;

[0156] w(OH - )——OH - Residual alkali value, wt%;

[0157] w(CO3 2- )——CO3 2-Residual alkali value, wt%.

[0158] (2) Stability

[0159] The method for judging stability is: when preparing slurry examples 1-7 and comparative examples 1-3, observe whether a jelly-like state appears; if so, it is judged that a gel phenomenon occurs and the slurry stability is poor; if not, it indicates that the gel phenomenon is suppressed and the slurry stability is good.

[0160] (3) Electrochemical performance

[0161] The lithium ion batteries of the embodiment and the comparative example were placed at room temperature (25° C.) for 6 hours and then subjected to charge and discharge tests. The charge and discharge voltage was 2.0-4.3V. The initial gas production and initial charging capacity were tested at 0.2C and 1C, respectively.

[0162] 2. Test results

[0163] The residual alkali value and stability test results of the embodiments and comparative examples are shown in Table 1.

[0164] Table 1 Residual alkali value and stability test results of the embodiments and comparative examples

[0165]

[0166] It can be seen from Table 1 that the residual alkali value on the surface of the composite lithium-replenishing material of the embodiment of the present application is relatively low. Therefore, when preparing the slurry, it is found that there is no jelly state in the slurry containing the composite lithium-replenishing material of the embodiment of the present application, while the comparative example is the opposite.

[0167] The electrochemical performance test results of the lithium ion batteries of the embodiments and comparative examples are shown in Table 2.

[0168] Table 2 Electrochemical performance test results of lithium ion batteries of embodiments and comparative examples

[0169]

[0170]

[0171] It can be seen from Table 2 that the initial gas production of the lithium-ion battery prepared by the composite lithium-supplement material of the embodiment of the present application is much lower than the initial gas production of the lithium-ion battery prepared by the composite lithium-supplement material of the comparative example, and from the data in the embodiment, it can be found that when the gas production in the lithium-ion battery is low, its initial charging capacity will be improved; when the rate is increased, the gas production of the lithium-ion battery prepared by the composite lithium-supplement material of the embodiment of the present application increases less, while the gas production of the lithium-ion battery in the comparative example increases more, indicating that the use of amino acids can significantly inhibit the gas production of the composite lithium-supplement material. Specifically, we can observe from Examples 1-3 that the content of the first coating material and the amino acid substance in the composite lithium supplement material of the present application is not the more the better, but the right amount, in order to effectively exert the effect of the composite lithium supplement material; in Examples 1 and 4, because the second coating material, i.e., the amino acid substance, is combined with the inner core in a different manner, the electrochemical properties of the lithium ion battery prepared by using these two materials will also change, but both can improve the performance of the lithium ion battery; in Examples 5 and 7, because the first coating material is not contained, the first charge specific capacity will be low, but its capacity is higher than that in the comparative example. In the comparative example, because the comparative example 1 does not contain the first coating material and the amino acid substance, the first charge capacity is lower than the first charge capacity in other comparative examples, and the gas production is higher than that in other comparative examples.

[0172] In summary, the composite lithium-supplementing material containing the first coating material and amino acid substances can improve the conductivity of the material, reduce the residual alkali value on the surface of the material, inhibit the gelation phenomenon in the process of preparing the slurry of the composite lithium-supplementing material, and inhibit the generation of gas, thereby improving the electrochemical properties and safety performance of lithium-ion batteries.

[0173] In the present application, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0174] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A composite lithium supplement material, characterized in that: It includes a lithium-rich core, an amino acid substance and a first coating material; The lithium-rich core comprises a lithium-containing compound; the lithium-containing compound comprises a general structural formula of Li 1+x A y O z Or / and the general structural formula is Li w O r A material; wherein 0.3﹤x﹤10, 0﹤y﹤6, 0﹤z﹤13, the A is selected from at least one of Fe, Ni, Mn, Co, Cu, Zn, Si, Sn, Al, Zr, Ge, 1≤w≤2, 1≤r≤2; The composite lithium supplement material further includes a first coating material; the first coating material is continuously coated on the outer surface of the lithium-rich core, and at least part of the amino acid substance is coated on the outer surface of the first coating material as a second coating material; Alternatively, the first coating material is discontinuously coated on the outer surface of the lithium-rich core, part of the amino acid substance is coated on the outer surface of the first coating material as the second coating material, and part of the amino acid substance is doped into the lithium-rich core; the first coating material is a carbon material.

2. The composite lithium supplement material according to claim 1, characterized in that: The amino acid substances include one or more of reducing amino acids and polymers of reducing amino acids.

3. The composite lithium supplement material according to claim 2, characterized in that: The reducing amino acids and polymers thereof include one or more of arginine, threonine, proline, serine, cysteine ​​and polymers thereof.

4. The composite lithium supplement material according to claim 1, characterized in that: The mass ratio of the lithium-containing compound, the first coating material, and all amino acid substances is 100:0.1-5:0.1-10; And / or, the thickness of the first coating layer formed by the first coating material and the second coating layer formed by the amino acid substance are both 1-100 nm.

5. The composite lithium supplement material according to any one of claims 1 to 4, characterized in that: The median particle size of the lithium-rich core is 0.5-20 μm; and / or, the median particle size of the amino acid substance is 0.05-10 μm; And / or, the median particle size of the composite lithium supplement material is 1-45 μm; And / or, the BET specific surface area of ​​the lithium-rich core is 0.5-50m 2 / g; And / or, the residual alkalinity of the composite lithium supplement material is lower than 5wt%.

6. A method for preparing the composite lithium supplement material according to any one of claims 1 to 5, characterized in that: include: After the lithium-rich core and the amino acid substance are mixed, a first sintering is performed in a first inert atmosphere to obtain the composite lithium supplement material.

7. The method for preparing the composite lithium supplement material according to claim 6, characterized in that: Also includes: Before mixing the lithium-rich core with the amino acid substance, the lithium-rich core is first mixed with the source material of the first coating material, and a second sintering is performed in a second inert atmosphere to obtain a lithium-rich core coated with the first coating material, and the first sintering temperature is lower than the second sintering temperature.

8. A positive electrode, characterized in that The invention comprises the composite lithium supplement material as claimed in any one of claims 1 to 5 or the composite lithium supplement material prepared by the preparation method as claimed in claim 6 or 7.

9. A secondary battery comprising a positive electrode, a negative electrode and a separator, characterized in that: The positive electrode is the positive electrode as claimed in claim 8.

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