Composite positive electrode lithium supplementing additive, preparation method and application thereof

Abstract

The application discloses a composite positive electrode lithium supplement additive and a preparation method and application thereof. The composite positive electrode lithium supplement additive comprises a core and a functional encapsulation layer coated on the core, the core comprises a positive electrode lithium supplement material, and the functional encapsulation layer contains an oxygen absorber. The composite positive electrode lithium supplement additive can effectively remove active oxygen and inhibit gas production reactions caused by the active oxygen, thereby inhibiting the gas production of a battery containing the composite positive electrode lithium supplement additive during charging and discharging, effectively improving the safety of the battery, and having good lithium supplement effect and processing performance. The preparation method of the composite positive electrode lithium supplement additive can ensure that the prepared composite positive electrode lithium supplement additive has stable structure and electrochemical performance, and has high efficiency and low production cost.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of secondary batteries, and particularly relates to a composite positive electrode lithium supplement additive as well as a preparation method and application thereof. BACKGROUND

[0002] Lithium ion batteries are considered to be one of the most promising energy sources due to their high working voltage and energy density, relatively small self-discharge level, no memory effect, no pollution of heavy metal elements such as lead and cadmium, and super-long cycle life, and are widely used in electric vehicles, electric tools, mobile electronic consumer goods, energy storage and many other aspects.

[0003] Although lithium ion batteries have many advantages, during the first charging process of lithium ion batteries, the formation of a solid-state electrolyte film (SEI film) on the surface of the negative electrode usually accompanies, and this process consumes a large amount of Li + , which means that part of the Li + released from the positive electrode material is irreversibly consumed, and the reversible capacity of the battery cell is reduced.

[0004] The negative electrode material, especially the silicon-based negative electrode material, further consumes Li + , causing lithium loss of the positive electrode material and reducing the first coulomb efficiency and capacity of the lithium ion battery. For example, in a lithium ion battery system using a graphite negative electrode, about 10% of the lithium source is consumed during the first charging. When high-capacity negative electrode materials such as alloy-based (silicon, tin, etc.), oxide-based (silicon oxide, tin oxide) and amorphous carbon negative electrodes are used, the consumption of positive electrode lithium sources will be further aggravated.

[0005] In recent years, positive electrode lithium supplement additives have attracted much attention because they can make up for the irreversible capacity loss caused by the formation of SEI film during the first charging process of lithium ion batteries, and are one of the key technologies for further improving the performance of lithium ion batteries, and have broad market application and development prospects. However, it is found in research and practical application that the use of existing lithium supplement additives also leads to an increase in the gas production of lithium ion batteries during the formation stage, which can cause the internal expansion of the sealed battery system, and cause the volume expansion and safety problems of the battery.

[0006] Currently, the research on positive electrode lithium supplementing additive is still in the initial stage, and there is no stable and mature product formed. The mechanism of gas generation of lithium supplementing additive has not been clearly and systematically studied. For traditional lithium ion batteries, the decomposition of SEI film, the decomposition of electrolyte, the reaction of negative active material and binder, etc. can easily lead to the generation of gas, and these reactions often do not occur independently, and multiple reactions may occur at the same time. In order to solve the above problems of lithium ion battery gas generation, the currently used methods are to add acid anhydride compounds, cyclic esters such as γ-butyrolactone, and polynitrile compounds as additives into the electrolyte to form positive and negative electrode protection films to inhibit gas generation. However, these measures often have problems such as poor ion conductivity of the protection film, increased impedance, unstable positive and negative electrode protection film, etc. Therefore, how to effectively improve the gas generation problem caused by the use of positive electrode lithium supplementing additive without affecting other performances of the battery is a problem that needs to be solved at present, which has a great influence on the improvement of the performance of lithium ion battery. SUMMARY

[0007] The present application aims to overcome the above-mentioned deficiencies of the prior art, and provides a composite positive electrode lithium supplementing additive and a preparation method thereof, to solve the technical problem that the existing positive electrode lithium supplementing additive cannot inhibit the gas generation of the battery.

[0008] Another object of the present application is to provide a positive electrode and a secondary battery containing the same, to solve the technical problem that the existing secondary battery is prone to gas generation, resulting in unsatisfactory safety.

[0009] In order to achieve the above-mentioned application purposes, the first aspect of the present application provides a composite positive electrode lithium supplementing additive. The composite positive electrode lithium supplementing additive of the present application comprises a core and a functional encapsulation layer encapsulating the core, the core comprises a positive electrode lithium supplementing material, and the functional encapsulation layer contains an oxygen absorber.

[0010] Further, the functional encapsulation layer forms a first oxygen absorber encapsulation layer encapsulating the core.

[0011] Or further, the functional encapsulation layer comprises a dense functional encapsulation layer encapsulating the core, and the oxygen absorber is doped in the dense functional encapsulation layer.

[0012] Or further, the functional encapsulation layer comprises a dense functional encapsulation layer encapsulating the core, and the oxygen absorber forms a second oxygen absorber encapsulation layer encapsulating the dense functional encapsulation layer.

[0013] Still further, the dense functional encapsulation layer comprises an ionic conductivity encapsulation layer and / or an electronic conductivity encapsulation layer, and the ionic conductivity encapsulation layer or the electronic conductivity encapsulation layer encapsulates the core.

[0014] Still further, the thickness of any one of the first oxygen absorber encapsulation layer and the second oxygen absorber encapsulation layer is 2-100 nm.

[0015] Specifically, the material of the electronic conductivity encapsulation layer comprises at least one of carbon material, conductive oxide, and conductive organic matter.

[0016] Specifically, the material of the ionic conductivity encapsulation layer can comprise at least one of perovskite type, NASICON type, and garnet type.

[0017] Specifically, the functional encapsulation layer comprises an electronic conductivity encapsulation layer, the electronic conductivity encapsulation layer encapsulates the core, and the oxygen-consuming agent forms a second oxygen-consuming encapsulation layer and encapsulates the electronic conductivity encapsulation layer; wherein the electronic conductivity encapsulation layer is a carbon layer.

[0018] Further, the active oxygen content in the composite positive electrode lithium supplement additive is not higher than 5%.

[0019] Further, the weight content of the oxygen-consuming agent in the composite positive electrode lithium supplement additive is 0.1%-10%.

[0020] Further, the oxygen-consuming agent comprises at least one of polyphenol type oxygen-consuming agent, hindered phenol type oxygen-consuming agent, hindered amine type oxygen-consuming agent, L-ascorbic acid, melatonin, and zinc dialkyldithiophosphate.

[0021] Specifically, the polyphenol type oxygen-consuming agent comprises at least one of tert-butyl hydroquinone, tea polyphenol, etc.

[0022] Specifically, the hindered phenol type comprises at least one of 2,6-di-tert-butyl-p-cresol, antioxidant 1076, antioxidant 1010, tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, etc.

[0023] Specifically, the hindered amine type comprises N,N'-diphenyl-p-phenylenediamine.

[0024] In a second aspect, the application provides a preparation method of the composite positive electrode lithium supplement additive.

[0025] The functional encapsulation layer is formed on the surface of the positive electrode lithium supplement material particles, and the functional encapsulation layer encapsulates the positive electrode lithium supplement material particles, and the functional encapsulation layer contains the oxygen-consuming agent.

[0026] Further, the method for forming the functional encapsulation layer on the surface of the positive electrode lithium supplement material particles comprises the following steps:

[0027] The oxygen-consuming agent and the positive electrode lithium supplement material particles are subjected to a first mixing treatment, so that the oxygen-consuming agent forms a third oxygen-consuming encapsulation layer on the surface of the positive electrode lithium supplement material particles.

[0028] Or further, the method for forming the functional encapsulation layer on the surface of the positive electrode lithium supplement material particles comprises the following steps:

[0029] The oxygen-consuming agent is mixed with the material for forming the dense functional encapsulation layer to form a mixture, and the mixture is mixed with the positive electrode lithium supplement material particles to form the functional encapsulation layer on the surface of the positive electrode lithium supplement material particles.

[0030] Further, the method for forming the functional encapsation layer on the surface of the positive electrode lithium supplement material particles comprises the following steps:

[0031] The material for forming the dense functional encapsation layer is first mixed with the positive electrode lithium supplement material particles to form a dense functional encapsation layer on the surface of the positive electrode lithium supplement material particles, and then the oxygen-consuming agent is mixed with the dense functional encapsation layer to form a fourth oxygen-consuming coating layer on the surface of the dense functional encapsation layer.

[0032] In a third aspect, the present application provides a positive electrode lithium supplement additive. The positive electrode lithium supplement additive of the present application comprises the composite positive electrode lithium supplement additive of the present application or the composite positive electrode lithium supplement additive prepared by the preparation method of the composite positive electrode lithium supplement additive of the present application, and further comprises other lithium supplement additives and / or auxiliary agents.

[0033] In a fourth aspect, the present application provides a positive electrode. The positive electrode of the present application comprises a current collector and a positive electrode active layer combined on the surface of the current collector, wherein the positive electrode active layer comprises a positive electrode active material, a lithium supplement additive, a binder and a conductive agent; and the lithium supplement additive is the composite positive electrode lithium supplement additive of the present application or the composite positive electrode lithium supplement additive prepared by the preparation method of the composite positive electrode lithium supplement additive of the present application or the positive electrode lithium supplement additive of the present application.

[0034] Further, the composite positive electrode lithium supplement additive accounts for 0.5%-10% of the mass percentage of the positive electrode active material.

[0035] In a fifth aspect, the present application provides a secondary battery. The secondary battery of the present application comprises a positive electrode sheet, and the positive electrode sheet is the positive electrode of the present application.

[0036] Compared with the prior art, the present application has the following technical effects:

[0037] The functional encapsulation layer of the composite positive electrode lithium supplementing additive of the present application contains an oxygen consumer, which can effectively remove active oxygen, including the active oxygen in the core and in the charging and discharging process, and inhibit the gas production reaction caused by the active oxygen, thereby inhibiting the gas production of the battery containing the composite positive electrode lithium supplementing additive of the present application in the charging and discharging process, and effectively improving the safety of the battery. In addition, the functional encapsulation layer encapsulates the lithium-rich core, which isolates the core from the outside world, avoids the contact between the core and the outside world such as moisture and carbon dioxide, ensures the stability of the core, and endows the composite positive electrode lithium supplementing additive with excellent lithium supplementing effect and processability, and good storage property. Secondly, the core of the composite positive electrode lithium supplementing additive of the present application contains a positive electrode lithium supplementing material, which endows the composite positive electrode lithium supplementing additive of the present application with the ability to provide abundant lithium, so that it can be used as a "sacrificial agent" in the first charging process to release all lithium ions at one time, thereby improving the initial efficiency and overall electrochemical performance of the battery.

[0038] The preparation method of the composite positive electrode lithium supplementing additive of the present application can effectively prepare the composite positive electrode lithium supplementing additive with core-shell structure, and the shell is rich in oxygen consumer, thereby ensuring that the prepared composite positive electrode lithium supplementing additive has the functions of removing active oxygen and inhibiting battery gas production, and has excellent lithium supplementing effect and processability. In addition, the preparation method of the composite positive electrode lithium supplementing additive can ensure that the prepared composite positive electrode lithium supplementing additive has stable structure and electrochemical performance, and has high efficiency and saves production cost.

[0039] The positive electrode lithium supplementing additive of the present application can remove active oxygen and inhibit the gas production reaction caused by active oxygen, thereby inhibiting the gas production of the battery in the charging and discharging process, and effectively improving the initial efficiency and safety of the battery.

[0040] The positive electrode of the present application contains the composite positive electrode lithium supplementing additive of the present application, and therefore the positive electrode active layer of the positive electrode has the function of inhibiting gas production, thereby improving the safety performance of the battery. In addition, it is rich in lithium, and has high initial coulomb efficiency and excellent other electrochemical performance.

[0041] The secondary battery of the present application contains the electrode sheet of the present application, and therefore the lithium ion battery of the present application has excellent initial coulomb efficiency, battery capacity and cycle performance, low gas production, high safety, long service life and stable electrochemical performance. BRIEF DESCRIPTION OF DRAWINGS

[0042] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0043] Figure 1 This is a schematic diagram of the structure of the composite cathode lithium supplementation additive in the embodiments of this application;

[0044] Figure 2 for Figure 1 The diagram shows a structural schematic of one type of composite cathode lithium supplementation additive.

[0045] Figure 3 for Figure 1 The diagram shows another structural schematic of a composite cathode lithium supplement additive.

[0046] Figure 4 for Figure 1 The diagram shows the third structure of the composite cathode lithium supplement additive. Detailed Implementation

[0047] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0048] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0049] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0050] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0051] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0052] The weight of the related components mentioned in the embodiment specification of the present application can not only refer to the specific content of each component, but also represent the proportional relationship between the weights of each component. Therefore, as long as the content of the related components in the embodiment specification of the present application is enlarged or reduced in proportion, it is within the scope disclosed in the embodiment specification of the present application. Specifically, the mass mentioned in the embodiment specification of the present application can be μg, mg, g, kg, and other mass units commonly known in the chemical industry.

[0053] The terms "first", "second" are only used for descriptive purposes and are used to distinguish objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features. For example, without departing from the scope of the present application, the first XX can also be referred to as the second XX, and similarly, the second XX can also be referred to as the first XX. Therefore, the features defined with "first", "second" can explicitly or implicitly include one or more of the features.

[0054] In a first aspect, the present application provides a composite positive electrode lithium supplement additive. The composite positive electrode lithium supplement additive of the present application comprises a core and a functional encapsulation layer coated on the core, that is, the composite positive electrode lithium supplement additive of the present application is a core-shell structure. As shown in the embodiment, the structure of the composite positive electrode lithium supplement additive of the present application comprises a core 10 and a functional encapsulation layer 20 coated on the core 10. Figures 1 to 4

[0055] Among them, the core 10 comprises a positive electrode lithium supplement material, that is, in the composite positive electrode lithium supplement additive of the present application, the core 10 is a lithium source for supplementing lithium. Since the core 10 is rich in lithium, when the composite positive electrode lithium supplement additive of the present application is added to the electrode, it can act as a "sacrificial agent" during the first charging process, and release all the lithium ions contained in the composite positive electrode lithium supplement additive at one time to supplement the irreversible lithium ions consumed by the formation of SEI film in the negative electrode.

[0056] At the same time, the positive electrode lithium supplement material contained in the core 10 can be a conventional lithium supplement material or a newly developed lithium supplement material. Based on the function of the composite positive electrode lithium supplement additive of the present application, the positive electrode lithium supplement material in the embodiment is a reverse fluorite structure lithium supplement material. The reverse fluorite structure lithium supplement material thus endows the positive electrode lithium supplement material with a one-way capacity characteristic, which can effectively de-lithiate during the first charging process and will not cause lithium ions to re-embed into the lithium supplement material during discharging, thereby ensuring the lithium supplement effect of the present application.

[0057] The positive electrode lithium supplement material contained in the core 10 can be a ternary lithium supplement material or a binary lithium supplement material. As shown in the embodiment, the positive electrode lithium supplement material is L x M​y N z O q Wherein, L in the molecular formula is Li or / and a mixture of Li and at least one of K and Na, not exceeding 30%; M includes at least one of Fe, Co, Mn, Al, Ni, and Si; N includes at least one of Fe, Co, Mn, Al, Ni, Si, or other equivalent or different valence metal elements; O is oxygen; x is 2-6, further 4-6; y is 0.7-1.0; z is 0-0.3, further 0.01-0.3; q is 2-5, further 4-5. In a further embodiment, the molecular formula L... x M y N z O q The total molar ratio of L to M and N in the formula is 4-7:1, specifically 4:1, 5:1, 6:1, 7:1, etc., which are typical but not limited to new molar ratios. Based on the molecular formula L... x M y N z O q In specific embodiments, the positive electrode lithium replenishment material can be Li2NiO2, Li5FeO4, Li6MnO4, or Li5Fe 0.98 Al 0.02 At least one of O4, Li2MnO2, and Li2CoO2. These cathode lithium replenishment materials are rich in lithium and can release lithium ions during the first charge cycle to effectively replenish lithium. When the cathode lithium replenishment material has an anti-fluorite structure, it can also improve the unidirectional capacity characteristics of the cathode lithium replenishment material, thereby ensuring the lithium replenishment effect of the lithium replenishment additive in this application.

[0058] In this embodiment, the core 10 can be at least one of primary particles and secondary particles, specifically, the core 10 contains at least one of primary particles and secondary particles formed from the cathode lithium supplementation material. In this embodiment, the particle size of the core 10 can be 0.2 μm-20 μm. For example, when the core 10 is a primary particle, the primary particle size, i.e., the particle size distribution of the core 10, is 0.2 μm-4 μm; when the core 10 is a secondary particle, the secondary particle size, i.e., the particle size distribution of the core 10, is 0.4 μm-20 μm. Here, secondary particles refer to agglomerated particles formed by the aggregation of one or more primary particles. By controlling the particle morphology and particle size of the core 10, while providing abundant lithium ions, the processability of the composite cathode lithium supplementation additive in the preparation of lithium battery slurry is also improved. Furthermore, a smaller primary particle size allows for the extraction of more lithium.

[0059] In addition, although the positive electrode lithium supplement material contained in the core 10 in each of the above embodiments is rich in lithium, it is found in research that it generally contains active oxygen and residual alkali and other components. Among them, the presence of active oxygen causes the battery to have the problem of increased gas production in the formation stage in use. The residual alkali contained therein causes it to be unstable in the presence of water and carbon dioxide, and it is prone to react with water and carbon dioxide, thereby reducing the lithium supplement effect of the positive electrode lithium supplement additive, further reducing its processing performance and storage performance, thereby increasing its processing and application cost, such as causing the slurry containing the positive electrode lithium supplement material contained in the core 10 to have a dramatic increase in viscosity during processing, quickly gelling and losing fluidity, thereby unable to be processed subsequently. Therefore, on the basis of the core 10 in each of the above embodiments, the functional packaging layer 20 containing the composite positive electrode lithium supplement additive in each of the above embodiments is coated on the core 10 to form a complete coating layer, as shown in Figure 1 The functional packaging layer 20 contains an oxygen absorber. In this way, the functional packaging layer 20 can effectively remove active oxygen in the core, inhibit the active oxygen from causing a gas production reaction, thereby being able to inhibit the battery containing the composite positive electrode lithium supplement additive from producing gas during charging and discharging, and effectively improving the safety of the battery. On the other hand, the functional packaging layer 20 acts as a barrier layer to isolate the core 10 from the outside world, avoiding the contact between the core and external factors such as moisture and carbon dioxide, ensuring the stability of the positive electrode lithium supplement material contained in the core 10 and thereby endowing the composite positive electrode lithium supplement additive with excellent lithium supplement effect, processability and storage performance.

[0060] Among them, the oxygen absorber can exist in the functional packaging layer 20 in at least the following ways:

[0061] In the embodiment, as shown in Figure 2 The functional packaging layer 20 is a first oxygen absorber coating layer 21 formed by the oxygen absorber, and the first oxygen absorber coating layer 21 coats the core 10. That is, the oxygen absorber is the material of the functional packaging layer 20, and forms a coating layer to coat the core 10. The first oxygen absorber coating layer 21 directly coats the core 10, fully playing the above-mentioned role of the oxygen absorber to inhibit the gas production reaction caused by active oxygen and other easy-gas components. In the embodiment, the thickness of the first oxygen absorber coating layer 21 can be controlled to be 2-100 nm.

[0062] In another embodiment, as shown in Figure 3As shown, the functional encapsulation layer 20 includes a dense functional encapsulation layer 22, the dense functional encapsulation layer 22 encapsulates the core 10, and the oxygen absorber is doped in the dense functional encapsulation layer 22. By doping the oxygen absorber in the dense functional encapsulation layer 22, the above-mentioned effects of the oxygen absorber are fully exerted, and the gas generation reaction caused by the active oxygen and other easy-gas-generating components is inhibited. At the same time, the dense functional encapsulation layer 22 can play a protective role of isolating the environment, improve the lithium supplement effect of the positive electrode lithium supplement material in the core 10, and improve the processing performance and storage performance of the composite positive electrode lithium supplement additive of the embodiment. In the embodiment, the thickness of the dense functional encapsulation layer 22 can be controlled to be 2 nm-100 nm.

[0063] In still another embodiment, as shown in the figure, Figure 4 As shown, the functional encapsulation layer 20 includes a dense functional encapsulation layer 22, the dense functional encapsulation layer 22 encapsulates the core 10, and the oxygen absorber is doped in the dense functional encapsulation layer 22. By doping the oxygen absorber in the dense functional encapsulation layer 22, the above-mentioned effects of the oxygen absorber are fully exerted, and the gas generation reaction caused by the active oxygen and other easy-gas-generating components is inhibited. At the same time, the dense functional encapsulation layer 22 can play a protective role of isolating the environment, improve the lithium supplement effect of the positive electrode lithium supplement material in the core 10, and improve the processing performance and storage performance of the composite positive electrode lithium supplement additive of the embodiment. In the embodiment, the thickness of the dense functional encapsulation layer 22 can be controlled to be 2 nm-100 nm.

[0064] In the functional encapsulation layer 20 of each of the above embodiments, the content of the oxygen absorber can be controlled to be 0.1%-10% by weight in the composite positive electrode lithium supplement additive, and can be specifically 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, etc. typical but non-limiting content. In another embodiment, the oxygen absorber is at least one of a polyphenol type oxygen absorber, a hindered phenol type oxygen absorber, a hindered amine type oxygen absorber, and other types of oxygen absorbers. In a specific embodiment, the polyphenol type oxygen absorber can include at least one of tert-butyl hydroquinone, tea polyphenol, etc., the hindered phenol type can include at least one of 2,6-di-tert-butyl-p-cresol, antioxidant 1076, antioxidant 1010, tris(3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate, etc., the hindered amine type can include but not limited to N,N'-diphenyl-p-phenylenediamine, and the other type of oxygen absorber can include at least one of L-ascorbic acid, melatonin, and zinc dialkyldithiophosphate. By controlling and optimizing the type and content of the oxygen absorber in the functional encapsulation layer 20, i.e., the composite positive electrode lithium supplement additive, the active oxygen in the core 10 is removed by the oxygen absorber, and the gas generation reaction caused by the active oxygen is further inhibited, thereby further effectively improving the safety of the battery.

[0065] In the embodiments of the functional encapsulation layer 20 of the composite positive electrode lithium supplementing additive, when the functional encapsulation layer 20 contains the dense functional encapsulation layer 22, in the embodiments, the dense functional encapsulation layer 22 includes an ion conductivity encapsulation layer or an electron conductivity encapsulation layer, or a composite encapsulation layer of the ion conductivity encapsulation layer and the electron conductivity encapsulation layer. The ion conductivity encapsulation layer or the electron conductivity encapsulation layer encapsulates the core 10, and when the dense functional encapsulation layer 22 includes the composite encapsulation layer of the ion conductivity encapsulation layer and the electron conductivity encapsulation layer, the ion conductivity encapsulation layer or the electron conductivity encapsulation layer encapsulates the core 10, and the remaining functional layer encapsulates the outer surface. By adding the ion conductivity encapsulation layer, the ion conductivity and the density of the dense functional encapsulation layer 22 can be effectively enhanced, so that the ion conductivity of the composite positive electrode lithium supplementing additive is enhanced, the lithium ion transport out of the core is facilitated, and the lithium supplementing effect is enhanced. Meanwhile, after the core 10 releases the lithium ion as a “sacrifice”, the ion conductivity encapsulation layer can be used again to assist the ion transport in the electrode. By adding the electron conductivity encapsulation layer, the electron conductivity and the density of the dense functional encapsulation layer 22 can be enhanced, so that the electron conductivity of the composite positive electrode lithium supplementing additive is enhanced, and the impedance in the electrode is reduced; meanwhile, during the release of the core 10 as a “sacrifice” and after the release, the electron conductivity encapsulation layer can be used again to assist the electron conductivity agent in the electrode.

[0066] When the dense functional encapsulation layer 22 contains the composite layer of the ion conductivity encapsulation layer and the electron conductivity encapsulation layer, the electron conductivity encapsulation layer and the ion conductivity encapsulation layer can also have a synergistic effect of density, so that the density of the dense functional encapsulation layer 22 is improved, and the ion and electron conductivity performance is improved. When the dense functional encapsulation layer 22 contains the composite layer of the ion conductivity encapsulation layer and the electron conductivity encapsulation layer, the ion conductivity encapsulation layer and the electron conductivity encapsulation layer can not be densely encapsulated, but the composite layer formed by the combination of the two is densely encapsulated.

[0067] In the embodiments, the material of the ion conductivity encapsulation layer can include at least one of a perovskite type, a NASICON type, and a garnet type. In specific embodiments, the perovskite type includes Li 3x La 2 / 3-x TiO3(LLTO), specifically Li 0.5 La 0.5 TiO3, Li 0.33 La 0.57 TiO3, Li 0.29 La 0.57 TiO3, Li 0.33 Ba 0.25 La 0.39 TiO3, (Li 0.33 La 0.56 1.005 Ti​0.99 Al 0.01 O3, Li 0.5 La 0.5 Ti 0.95 Zr 0.05 O3, NASICON type such as but not limited to Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP), garnet type including Li7La3Zr2O 12 (LLZO), Li 6.4 La3Zr 1.4 Ta 0·6 O 12 , Li 6.5 La3Zr 1.5 Ta 0.5 O 12 At least one of the above. By selecting the material of the ionically conductive encapsulation layer, the ionic conductivity of the ionically conductive encapsulation layer can be further improved. Of course, the thickness of the ionically conductive encapsulation layer, or further the electronically conductive encapsulation layer, can also be adjusted to optimize the densification of the functional encapsulation layer 22 and to adjust the path of ion transport.

[0068] In embodiments, the material of the electronically conductive encapsulation layer can include at least one of a carbon material, a conductive oxide, a conductive organic material. In specific embodiments, when the material of the electronically conductive encapsulation layer is a carbon material, the carbon material can include at least one of amorphous carbon, carbon nanotube, graphite, carbon black, graphene, etc. In other specific embodiments, when the material of the electronically conductive encapsulation layer is a conductive oxide, the conductive oxide can include at least one of In2O3, ZnO, SnO2. The conductive organic material can be a conductive polymer, etc. By adjusting the material of the electronically conductive encapsulation layer, or further the content, the electronic conductivity of the electronically conductive encapsulation layer can be further improved.

[0069] Based on the structure of the functional encapsulation layer 20 and the types of materials contained in each layer, in specific embodiments, the functional encapsulation layer 20 includes an electronically conductive encapsulation layer, the electronically conductive encapsulation layer coats the core, and the oxygen-consuming agent forms a second oxygen-consuming coating layer 23 and coats the electronically conductive encapsulation layer; wherein the electronically conductive encapsulation layer is a carbon layer.

[0070] In addition, based on the structure and components of the composite positive electrode lithium supplement additive in the above embodiments, the composite positive electrode lithium supplement additive of the embodiments of the present application not only provides abundant lithium, but also effectively removes active oxygen in the core and in the charging and discharging process, inhibits the active oxygen from triggering a gas production reaction, thereby effectively inhibiting the amount of gas produced by the battery during the charging and discharging process, effectively improving the safety of the battery. At the same time, it also has excellent lithium supplement effect and processability, and good storage property.

[0071] It is detected that the active oxygen content of the composite positive electrode lithium supplement additive is low, for example, the active oxygen content of the composite positive electrode lithium supplement additive is not more than 5%, and even can be controlled to 0. The active oxygen content can be measured by potassium permanganate titration method, and the test principle is as follows:

[0072] Active oxygen [O2 - ] will react with potassium permanganate (purple black) under acidic conditions to generate O 2 and colorless Mn 2+ , and the reaction equation is shown as formula (1), so the active oxygen content in the measured substance can be titrated by using the potassium permanganate standard solution, and the titration end point is the appearance of the non-retracted light pink. The chemical reaction formula is shown as formula (1):

[0073] 5[O2 - ]+MnO4 - +8H + →5O2↑+Mn 2+ +4H2O Formula (1)

[0074] In a second aspect, the embodiment of the present application also provides a preparation method of the composite positive electrode lithium supplement additive. The preparation method of the composite positive electrode lithium supplement additive includes the following steps:

[0075] A functional encapsulation layer is formed on the surface of the positive electrode lithium supplement material particles, and the functional encapsulation layer covers the positive electrode lithium supplement material particles, and the functional encapsulation layer contains an oxygen absorber.

[0076] The positive electrode lithium supplement material particles in step S01 are the particles in the core 10 of the composite positive electrode lithium supplement additive. Therefore, the positive electrode lithium supplement material contained therein is the positive electrode lithium supplement material contained in the core 10 of the composite positive electrode lithium supplement additive. The functional encapsulation layer in step S01 is the functional encapsulation layer 20 of the composite positive electrode lithium supplement additive, and the functional encapsulation layer contains an oxygen absorber, as described above. Therefore, the materials, structures and thicknesses of the positive electrode lithium supplement material particles and the functional encapsulation layer in step S01 are the materials, structures and thicknesses of the core 10 and the functional encapsulation layer 20 of the composite positive electrode lithium supplement additive. In order to save space, the positive electrode lithium supplement material and the functional encapsulation layer in step S01 will not be described again.

[0077] In addition, the positive electrode lithium supplement material can be prepared according to the preparation method of each positive electrode lithium supplement material.

[0078] In the embodiment, the method for forming the functional encapsulation layer on the surface of the positive electrode lithium supplement material particles in step S01 can be flexibly controlled according to the structure of the functional encapsulation layer 20 of the composite positive electrode lithium supplement additive, for example, when the functional encapsulation layer 20 is as Figure 2When the first oxygen-consuming coating layer 21 is shown, the method for forming a functional encapsulation layer on the surface of particles containing positive electrode lithium replenishment material includes the following steps:

[0079] The oxygen-consuming agent is first mixed with particles containing positive electrode lithium replenishment material, so that the oxygen-consuming agent forms a third oxygen-consuming coating layer on the surface of the particles containing positive electrode lithium replenishment material.

[0080] Among them, the mixing treatment of oxygen-consuming agent and positive electrode lithium replenishment material particles can be carried out by first preparing the oxygen-consuming agent into a solution and then mixing it with the positive electrode lithium replenishment material particles to form a mixture, or by directly mixing the oxygen-consuming agent with the positive electrode lithium replenishment material particles and then preparing a slurry.

[0081] The first mixing process can be any mixing method that enables the oxygen-consuming agent to form a uniform coating layer on the surface of the positive electrode lithium replenishment material particles, such as, but not limited to, stirring, ball milling, etc.

[0082] If the functional encapsulation layer 20 is as follows Figure 3 The method for forming a functional encapsulation layer on the surface of positive electrode lithium replenishment material particles when the oxygen-consuming agent shown is doped in the dense functional encapsulation layer 22 includes the following steps:

[0083] The oxygen-consuming agent is mixed with the material forming a dense functional encapsulation layer in a second process to form a mixture; then the mixture is mixed with particles containing positive electrode lithium replenishment material in a third process, so that the mixture forms a functional encapsulation layer on the surface of the particles containing positive electrode lithium replenishment material.

[0084] The second mixing process can be any mixing method that allows the oxygen-consuming agent to form a mixture with the material forming the dense functional encapsulation layer and ensures the uniform dispersion of the oxygen-consuming agent, such as, but not limited to, stirring and ball milling. Since the oxygen-consuming agent forms a mixture with the material forming the dense functional encapsulation layer, the stability of the oxygen-consuming agent and the material forming the dense functional encapsulation layer should be compatible, such as thermal stability. That is, during the process of forming the functional encapsulation layer on the surface of the positive electrode lithium-filling material particles, the stability of the oxygen-consuming agent must be guaranteed to ensure its inhibition of reactive oxygen species activity. In the embodiments, the oxygen-consuming agent is based on the oxygen-consuming agent described above, and the material forming the dense functional encapsulation layer includes conductive organic materials, metal oxides, non-metal oxides, etc.

[0085] The third mixing process has the same purpose and method as the first mixing process, and any mixing method that can enable the mixture to form a uniform coating layer on the surface of the positive electrode lithium replenishment material particles is acceptable.

[0086] Among them, the oxygen-consuming agent and the positive electrode lithium replenishment material particles form such as Figure 3 The method shown can involve first mixing the oxygen-consuming agent with the encapsulation layer material, then heat-treating it to form a composite, and finally mixing it with lithium replenishment material particles.

[0087] As shown in the following, when the functional encapsulating layer 20 is formed as a second oxygen-consuming coating layer 23 by using an oxygen-consuming agent to coat the dense functional encapsulating layer 22, the method for forming the functional encapsulating layer on the surface of the positive electrode lithium supplement material-containing particle includes the following steps: Figure 4

[0088] The material for forming the dense functional encapsulating layer is first mixed with the oxygen-consuming agent to form a fourth oxygen-consuming coating layer on the surface of the dense functional encapsulating layer.

[0089] The method for forming the dense functional encapsulating layer on the surface of the positive electrode lithium supplement material-containing particle can be determined according to the characteristics of the material for forming the dense functional encapsulating layer. For example, the material for forming the dense functional encapsulating layer can be prepared into a slurry and then mixed with the positive electrode lithium supplement material-containing particle, or further sintering treatment can be performed, or the material for forming the dense functional encapsulating layer can be deposited to form the coating layer. For example, when the material for forming the dense functional encapsulating layer is a conductive organic material, the conductive organic material is prepared into a slurry and then mixed with the positive electrode lithium supplement material-containing particle to form a conductive organic material coating layer on the surface of the positive electrode lithium supplement material-containing particle. Alternatively, the organic material coating layer can be carbonized to form a carbon coating layer in situ on the surface of the positive electrode lithium supplement material-containing particle. Alternatively, when the material for forming the dense functional encapsulating layer is a conductive oxide, a conductive oxide precursor slurry is mixed with the positive electrode lithium supplement material-containing particle to form a precursor coating layer on the surface of the positive electrode lithium supplement material-containing particle, and then sintering treatment is performed to form an oxide coating layer. The method for forming the second oxygen-consuming coating layer on the surface of the dense functional encapsulating layer can refer to the method for forming the first oxygen-consuming coating layer to form the second oxygen-consuming coating layer to coat the dense functional encapsulating layer.

[0090] Therefore, the above-mentioned preparation method of the composite positive electrode lithium supplement additive can effectively prepare the composite positive electrode lithium supplement additive with the core-shell structure according to the embodiments of the present application, so as to ensure that the prepared composite positive electrode lithium supplement additive has the functions of scavenging active oxygen and inhibiting gas production, has excellent lithium supplement effect and good processing performance. In addition, the preparation method of the composite positive electrode lithium supplement additive can ensure that the structure and electrochemical performance of the prepared composite positive electrode lithium supplement additive are stable, and the efficiency is high and the production cost is saved.

[0091] In a third aspect, the embodiments of the present application further provide a positive electrode lithium supplement additive. The positive electrode lithium supplement additive according to the embodiments of the present application contains the composite positive electrode lithium supplement additive according to the above embodiments of the present application. Of course, the positive electrode lithium supplement additive according to the embodiments of the present application can also contain other lithium supplement additives and / or auxiliary agents. Since the positive electrode lithium supplement additive according to the embodiments of the present application contains the composite positive electrode lithium supplement additive according to the above embodiments of the present application, the positive electrode lithium supplement additive can scavenge active oxygen and inhibit the active oxygen from triggering a gas production reaction, so as to inhibit the gas production amount of the battery containing the positive electrode lithium supplement additive according to the embodiments of the present application during the charging and discharging process, and effectively improve the initial efficiency and safety of the battery.​

[0092] In a fourth aspect, the embodiments of the present application further provide a positive electrode. The positive electrode of the embodiments of the present application comprises a positive electrode current collector and a positive electrode active layer combined on the surface of the positive electrode current collector.

[0093] In the positive electrode, the positive electrode current collector can be, but is not limited to, any one of a copper foil and an aluminum foil.

[0094] The positive electrode active layer of the positive electrode comprises a positive electrode active material, a lithium supplementing additive, a binder, and a conductive agent, etc.

[0095] In the positive electrode active layer, the lithium supplementing additive is the composite positive electrode lithium supplementing additive of the embodiments of the present application or the positive electrode lithium supplementing additive. Since the positive electrode of the embodiments of the present application contains the composite positive electrode lithium supplementing additive of the embodiments of the present application, the positive electrode of the embodiments of the present application can inhibit gas production and lithium supplementing effect, effectively improve the safety performance of the battery, has high first coulomb efficiency, and has excellent other electrochemical performance. Desirably, the composite positive electrode lithium supplementing additive of the embodiments of the present application and the positive electrode of the embodiments of the present application are stored in a dry and oxygen-free environment, such as a vacuum environment, to maximize the electrochemical performance of the composite positive electrode lithium supplementing additive of the embodiments of the present application and the positive electrode of the embodiments of the present application. In the embodiments, the mass percentage of the composite positive electrode lithium supplementing additive in the positive electrode active material is controlled to be 0.5% to 10%.

[0096] The positive electrode active material in the positive electrode active layer can be a positive electrode material in the field of lithium ion batteries. For example, the positive electrode active material can comprise one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadium oxyphosphate, fluorinated lithium vanadium phosphate, lithium titanate, lithium nickel manganate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminum.

[0097] In the embodiments, the content of the binder in the positive electrode active layer can be 2wt% to 4wt%. In specific embodiments, the content of the binder can be 2wt%, 3wt%, 4wt%, etc., which are typical but not limiting contents. In specific embodiments, the binder comprises one or more of polyvinylidene fluoride, soluble polytetrafluoroethylene, styrene butadiene rubber, hydroxypropyl methyl cellulose, methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives.

[0098] In the embodiments, the content of the conductive agent in the positive electrode active layer can be 3wt% to 5wt%. In specific embodiments, the content of the conductive agent can be 3wt%, 4wt%, 5wt%, etc., which are typical but not limiting contents. In specific embodiments, the conductive agent comprises one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotube.

[0099] In the embodiment, the preparation process of the positive electrode can be as follows: mixing the positive electrode active material, the lithium supplement additive, the conductive agent and the binder to obtain an electrode slurry, coating the electrode slurry on a current collector, and performing drying, rolling, die cutting and other steps to obtain the positive electrode sheet.

[0100] In a fifth aspect, the embodiments of the present application also provide a secondary battery. The secondary battery of the embodiments of the present application comprises necessary components such as a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, and of course, other necessary or auxiliary components. Among them, the positive electrode sheet is the positive electrode described above, that is, the positive electrode active layer contained in the positive electrode sheet contains the composite positive electrode lithium supplement additive of the embodiments of the present application described above. Since the secondary battery of the embodiments of the present application contains the composite positive electrode lithium supplement additive of the embodiments of the present application described above, based on the composite positive electrode lithium supplement additive, the secondary battery of the present application has excellent first coulomb efficiency, high energy density and cycle performance, high capacity retention rate, long service life, low gas production, high safety and stable electrochemical performance.

[0101] In addition, the lithium battery of the embodiments of the present application can be a lithium ion battery or a lithium metal battery.

[0102] The composite positive electrode lithium supplement additive, the preparation method and application thereof and the like of the embodiments of the present application are illustrated by a plurality of specific embodiments as follows.

[0103] 1. Composite positive electrode lithium supplement additive and preparation method thereof

[0104] Embodiment A1

[0105] The embodiments provide a composite positive electrode lithium supplement additive and a preparation method thereof. The composite positive electrode lithium supplement additive comprises a Li5FeO4 positive electrode lithium supplement material as a core and a functional encapsulation layer covering the core, wherein the carbon layer is an intermediate layer in the functional encapsulation layer, and the t-butyl hydroquinone oxygen absorber is an outer layer.

[0106] The preparation method of the composite positive electrode lithium supplement additive of the embodiments comprises the following steps:

[0107] S1. Preparation of a positive electrode lithium supplement material: according to the ratio of Li: Fe = 5.1:1, a certain amount of lithium oxide and ferric oxide is weighed, and after being fully mixed, Li5FeO4 material is obtained by sintering at 800℃ for 10h under an argon atmosphere.

[0108] S2. Preparation of a functional encapsulation layer: 5wt% of citric acid is added to the Li5FeO4 lithium supplement material prepared in S1, and after being fully mixed by ball milling, the functional encapsulation layer is formed on the surface of the lithium supplement material by sintering at 550℃ for 4h under an argon atmosphere, and then 3wt% of t-butyl hydroquinone oxygen absorber is added, and after being mixed uniformly, sintering at 200℃ for 3h under argon.

[0109] The D50 of the composite positive electrode lithium supplement additive is 0.78 μm, the BET specific surface area is 0.35 m2 / g, the active oxygen content is 0.60%, and the thickness of the functional encapsulation layer is about 10 nm. 2 / g, the active oxygen content is 0.60%, and the thickness of the functional encapsulation layer is about 10 nm.

[0110] Example A2

[0111] The present example provides a composite positive electrode lithium supplement additive and a preparation method thereof. The composite positive electrode lithium supplement additive comprises a Li5FeO4 positive electrode lithium supplement material as a core and a functional encapsulation layer encapsulating the core, wherein the carbon layer is an intermediate layer in the functional encapsulation layer, and the tea polyphenol oxygen absorber is an outer layer.

[0112] The preparation method of the composite positive electrode lithium supplement additive of the present example is the same as that of Example 1, except that the oxygen absorber is tea polyphenol.

[0113] The D50 of the composite positive electrode lithium supplement additive is 0.76 μm, the BET specific surface area is 0.35 m2 / g, the active oxygen content is 0.83%, and the thickness of the functional encapsulation layer is about 10 nm. 2 / g, the active oxygen content is 0.60%, and the thickness of the functional encapsulation layer is about 10 nm.

[0114] Example A3

[0115] The present example provides a composite positive electrode lithium supplement additive and a preparation method thereof. The composite positive electrode lithium supplement additive comprises a Li5FeO4 positive electrode lithium supplement material as a core and a functional encapsulation layer encapsulating the core, wherein the carbon layer is an intermediate layer in the functional encapsulation layer, and the tea polyphenol oxygen absorber is an outer layer.

[0116] The preparation method of the composite positive electrode lithium supplement additive of the present example is the same as that of Example 1, except that the oxygen absorber is tea polyphenol.

[0117] The D50 of the composite positive electrode lithium supplement additive is 0.76 μm, the BET specific surface area is 0.35 m2 / g, the active oxygen content is 0.83%, and the thickness of the functional encapsulation layer is about 10 nm. 2 / g, the active oxygen content is 0.60%, and the thickness of the functional encapsulation layer is about 10 nm.

[0118] Example A4

[0119] The present example provides a composite positive electrode lithium supplement additive and a preparation method thereof. The composite positive electrode lithium supplement additive comprises a Li5FeO4 positive electrode lithium supplement material as a core and a functional encapsulation layer encapsulating the core, wherein the carbon layer is an intermediate layer in the functional encapsulation layer, and the tea polyphenol oxygen absorber is an outer layer.

[0120] The preparation method of the composite positive electrode lithium supplement additive of the present example comprises the following steps:

[0121] S1. Preparation of the positive electrode lithium supplement material: according to the ratio of Li:Mn = 6.2:1, a certain amount of lithium oxide and manganese oxide was weighed and mixed, and then sintered at 750°C for 6h under argon atmosphere to obtain Li6MnO4 material;

[0122] S2. Preparation of the functional encapsulation layer: 5wt% of citric acid was added to the Li6MnO4 lithium supplement material prepared in S1, and then ball-milled to mix thoroughly. Then, the mixture was sintered at 550°C for 4h under argon atmosphere, and then 3wt% of t-butyl hydroquinone oxygen absorber was added and mixed uniformly, and then sintered at 200°C for 3h under argon to form a functional encapsulation layer on the surface of the lithium supplement material.

[0123] It was measured that the D50 of the composite positive electrode lithium supplement additive was 0.76μm, the BET specific surface area was 0.37m 2 / g, the active oxygen content was 1.02%, and the thickness of the functional encapsulation layer was about 10nm.

[0124] Example A5

[0125] The present example provides a composite positive electrode lithium supplement additive and a preparation method thereof. The composite positive electrode lithium supplement additive comprises a Li2NiO2 positive electrode lithium supplement material as a core and a functional encapsulation layer covering the core, wherein the carbon layer is the intermediate layer in the functional encapsulation layer, and the t-butyl hydroquinone oxygen absorber is the outer layer.

[0126] The preparation method of the composite positive electrode lithium supplement additive of the present example comprises the following steps:

[0127] S1. Preparation of the positive electrode lithium supplement material: according to the ratio of Li:Ni = 2.2:1, a certain amount of lithium oxide and nickel oxide was weighed and mixed, and then sintered at 700°C for 8h under argon atmosphere to obtain Li2NiO2 material;

[0128] S2. Preparation of the functional encapsulation layer: 5wt% of citric acid was added to the Li2NiO2 lithium supplement material prepared in S1, and then ball-milled to mix thoroughly. Then, the mixture was sintered at 520°C for 4h under argon atmosphere, and then 3wt% of t-butyl hydroquinone oxygen absorber was added and mixed uniformly, and then sintered at 200°C for 3h under argon to form a functional encapsulation layer on the surface of the lithium supplement material.

[0129] It was measured that the D50 of the composite positive electrode lithium supplement additive was 0.71μm, the BET specific surface area was 0.41m 2 / g, the active oxygen content was 0.90%, and the thickness of the functional encapsulation layer was about 10nm.

[0130] Example A6

[0131] The embodiment provides a composite positive electrode lithium supplement additive and a preparation method thereof. The composite positive electrode lithium supplement additive comprises a Li2NiO2 positive electrode lithium supplement material as a core and a functional encapsulation layer for coating the core, wherein the carbon layer is an intermediate layer in the functional encapsulation layer, and the N,N'-diphenyl-p-phenylenediamine oxygen absorber is an outer layer.

[0132] The preparation method of the composite positive electrode lithium supplement additive in the embodiment comprises the following steps:

[0133] S1. Preparation of the positive electrode lithium supplement material: according to the ratio of Li:Ni=2.2:1, a certain amount of lithium oxide and nickel oxide is weighed, mixed sufficiently, sintered at 700 DEG C for 8h under an argon atmosphere to obtain a Li2NiO2 material;

[0134] S2. Preparation of the functional encapsulation layer: 5wt% of citric acid is added to the Li2NiO2 lithium supplement material prepared in S1, ball-milled to mix sufficiently, sintered at 520 DEG C for 4h under an argon atmosphere, and then 3wt% of N,N'-diphenyl-p-phenylenediamine oxygen absorber is added, mixed uniformly, and sintered at 200 DEG C for 3h under an argon atmosphere to form a functional encapsulation layer on the surface of the lithium supplement material.

[0135] It is measured that the D50 of the composite positive electrode lithium supplement additive is 0.71 μm, the BET specific surface area is 0.41 m 2 / g, the active oxygen content is 1.63%, and the thickness of the functional encapsulation layer is about 10 nm.

[0136] Comparative Example A1

[0137] A core-shell structure Li5FeO4 positive electrode lithium supplement additive is provided, which is different from Comparative Examples A1-A3 in that the functional encapsulation layer does not contain an oxygen absorber.

[0138] Comparative Example A2

[0139] A core-shell structure Li6MnO4 positive electrode lithium supplement additive is provided, which is different from Comparative Example A4 in that the functional encapsulation layer does not contain an oxygen absorber.

[0140] Comparative Example A3

[0141] A core-shell structure Li2NiO2 positive electrode lithium supplement additive is provided, which is different from Comparative Example A5 in that the functional encapsulation layer does not contain an oxygen absorber.

[0142] 2. Lithium ion battery embodiment:

[0143] The lithium ion batteries in Embodiments A1 to A6 and Comparative Examples A1 to A3 are respectively provided. Each lithium ion battery is assembled into a partial lithium ion battery according to the following method:

[0144] 1) Positive electrode sheet:

[0145] The positive electrode lithium supplement additives provided in Examples A1 to A6 and Comparative Examples A1 to A3, respectively, were used as the positive electrode lithium supplement additives of lithium ion battery Examples B1 to B6 and Comparative Examples B1 to B3. Under the same conditions, they were mixed in the ratio of NMP: LiFePO4: positive electrode lithium supplement additive: Super P: PVDF at a mass ratio of 100:93:2:2:3 by ball milling for 60 min at a rotation speed of 30 Hz. After homogenization-coating-drying-cutting, the positive electrode sheet was prepared. The positive electrode sheet was baked in a vacuum oven at 100°C to remove trace water.

[0146] 2) Negative electrode sheet: The negative electrode active material graphite, conductive agent Super P, thickening agent carboxymethyl cellulose (CMC), and binder styrene-butadiene rubber (SBR) were mixed uniformly in deionized water to prepare a negative electrode slurry, wherein the mass ratio of graphite: Super P: CMC: SBR was 95:2:0.5:2.5. The negative electrode slurry was coated on the current collector copper foil, and after drying-rolling-secondary drying, the negative electrode sheet was prepared.

[0147] 3) Separator: A polyethylene (PE) separator was used.

[0148] 4) Electrolyte: The electrolyte was a 1 mol / L LiPF6 solution, and the solvent was composed of EC (ethylene carbonate) and DEC (diethyl carbonate) at a volume ratio of 1:1.

[0149] 5) Assembly of secondary battery:

[0150] The above positive electrode sheet, negative electrode sheet, electrolyte, and separator were assembled into a lithium ion soft package battery according to the requirements of lithium ion battery assembly.

[0151] 3. Performance test of lithium ion battery:

[0152] The lithium ion batteries of each example and comparative example assembled in Section 5) were subjected to the following performance tests:

[0153] Normal temperature cycle test: The battery was placed at 25°C, and the charge and discharge cycles were carried out using a 1C current in the charge and discharge voltage range of 3.0-4.4V. The initial thickness T0 and initial capacity Q0 were recorded, and the thickness T1 and capacity Q1 were recorded after 300 cycles. The thickness change rate and capacity retention rate of the battery after 300 cycles at normal temperature were calculated by the following formula:

[0154] Normal temperature cycle 300 cycles thickness change rate (%) = (T1-T0) / T0x100%;

[0155] Room temperature cycle 300 cycles capacity retention rate (%) = Q1 / Q0 x 100%.

[0156] High temperature cycle test: under high temperature 45℃, using 1C current to charge and discharge in the charge and discharge voltage range of 3.0-4.4V, recording the initial thickness T2 and the initial capacity Q2, the thickness T3 and the capacity Q3 after 300 cycles, and calculating the thickness change rate and the capacity retention rate of the battery under high temperature (45℃) cycle 300 cycles by the following formula:

[0157] High temperature (45℃) cycle 300 cycles thickness change rate (%) = (T3-T2) / T2 x 100%;

[0158] High temperature (45℃) cycle 300 cycles capacity retention rate (%) = Q3 / Q2 x 100%.

[0159] The relevant performance test results are shown in Table 1 as follows:

[0160] Table 1 Performance test results

[0161]

[0162] From the test results in Table 1, it can be seen that in the lithium ion batteries of Examples B1-B6, the thickness change rate under room temperature / high temperature (45℃) cycle 300 cycles is significantly smaller than that of Comparative Examples B1-B3, and the capacity retention rate (%) under room temperature / high temperature (45℃) cycle 300 cycles is significantly higher than that of Comparative Examples B1-B3. It is shown that the battery of the composite positive electrode lithium supplement additive of the application can inhibit gas production during charging and discharging, effectively improve the safety performance of the battery, and also improve the cycle performance of the battery. It also shows that the addition of different oxygen consumption agents in Examples B1-B6, especially B1, B2 and B3, does not affect the performance of the lithium supplement agent, and has the characteristics of good compatibility. At the same time, by comparing Comparative Examples B1, B2 and B3 with Examples B1-B6, especially B1, B4 and B5, it is found that the application of oxygen consumption agent to other lithium supplement additives also does not affect the performance of the lithium supplement agent.

[0163] Further comparison of the thickness change rate of lithium ion batteries under room temperature / high temperature (45℃) cycle 300 cycles of Examples B1-B5 and Example B6 shows that the thickness change rate of lithium ion batteries of Examples B1-B5 and Example B6 is also significantly smaller than that of Example B6, reaching a significant difference, and the capacity retention rate (%) under room temperature / high temperature (45℃) cycle 300 cycles is significantly higher than that of Example B6, also reaching a significant difference.

[0164] Therefore, it is illustrated that the composite lithium supplement additive has the universality. In summary, the lithium ion battery using the composite positive electrode material can inhibit the gas production in the charging and discharging process, has high capacity retention rate, and has high safety performance.

[0165] The above embodiments only express several embodiments of the application, and the description is more specific and detailed, but it cannot be understood as the limitation of the patent scope of the application. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the application, several modifications and improvements can be made, which belong to the protection scope of the application. Therefore, the protection scope of the patent of the application should be subject to the appended claims.

Claims

1. A composite positive electrode lithium supplementing additive comprising a core and a functional encapsulation layer coated on the core, characterized in that: The core comprises a positive electrode lithium supplementing material, and the functional encapsulation layer contains an oxygen consumption agent; The functional encapsulation layer forms a first oxygen consumption coating layer for the oxygen consumption agent, and encapsulates the core; or The functional encapsulation layer comprises a dense functional encapsulation layer, the dense functional encapsulation layer encapsulates the core, and the oxygen consumption agent is doped in the dense functional encapsulation layer; or The functional encapsulation layer comprises a dense functional encapsulation layer, the dense functional encapsulation layer encapsulates the core, and the oxygen consumption agent forms a second oxygen consumption coating layer and encapsulates the dense functional encapsulation layer; The active oxygen content of the composite positive electrode lithium supplementing additive is not higher than 5%; the weight content of the oxygen consumption agent in the composite positive electrode lithium supplementing additive is 0.1%-10%; and the oxygen consumption agent comprises at least one of a polyphenol type oxygen consumption agent, L-ascorbic acid, melatonin, and zinc dialkyldithiophosphate. The dense functional encapsulation layer comprises an ion conductivity encapsulation layer and / or an electron conductivity encapsulation layer, and the ion conductivity encapsulation layer or the electron conductivity encapsulation layer encapsulates the core; and / or The thickness of any one of the first oxygen consumption coating layer and the second oxygen consumption coating layer is 2 nm-100 nm. 2.The composite positive electrode lithium supplementing additive of claim 1, characterized in that: The material of the electron conductivity encapsulation layer comprises at least one of a carbon material, a conductive oxide, and a conductive organic material; and / or The material of the ion conductivity encapsulation layer can comprise at least one of a perovskite type, a NASICON type, and a garnet type. 3.The composite positive electrode lithium supplementing additive of claim 2, characterized in that: The functional encapsulation layer comprises an electron conductivity encapsulation layer, the electron conductivity encapsulation layer encapsulates the core, the oxygen consumption agent forms the second oxygen consumption coating layer and encapsulates the electron conductivity encapsulation layer; and the electron conductivity encapsulation layer is a carbon layer. The polyphenol type oxygen consumption agent comprises at least one of a tert-butyl hydroquinone and tea polyphenol. 4.The composite positive electrode lithium supplementing additive of claim 1, characterized in that: The method comprises the following steps: 5.The composite positive electrode lithium supplementing additive of claim 1, characterized in that: A functional encapsulation layer is formed on the surface of the positive electrode lithium supplementing material particles, and the functional encapsulation layer encapsulates the positive electrode lithium supplementing material particles and contains an oxygen consumption agent; 6. A method for preparing a composite anode lithium supplement additive, characterized in that: The method for forming the functional encapsulation layer on the surface of the positive electrode lithium supplementing material particles comprises the following steps: The oxygen consumption agent is subjected to first mixing treatment with the positive electrode lithium supplementing material particles, so that the oxygen consumption agent forms a third oxygen consumption coating layer on the surface of the positive electrode lithium supplementing material particles; Or The oxygen consumption agent is subjected to second mixing treatment with a material for forming a dense functional encapsulation layer to form a mixture, and the mixture is subjected to third mixing treatment with the positive electrode lithium supplementing material particles, so that the mixture forms the functional encapsulation layer on the surface of the positive electrode lithium supplementing material particles; Or The material for forming a dense functional encapsulation layer is first formed into a dense functional encapsulation layer on the surface of the positive electrode lithium supplementing material particles, and then subjected to fourth mixing treatment with the oxygen consumption agent to form a fourth oxygen consumption coating layer on the surface of the dense functional encapsulation layer. The composite positive electrode lithium supplementing additive of any one of claims 1-5 or prepared by the method of claim 6 further comprises other lithium supplementing additives and / or auxiliary agents. ​ 7. A positive electrode lithium supplementing additive, characterized by: ​ 8. A positive electrode, characterized by: The positive electrode active material comprises a current collector and a positive electrode active layer combined on the surface of the current collector, wherein the positive electrode active layer comprises a positive electrode active material, a lithium supplementing additive, a binder and a conductive agent; wherein the lithium supplementing additive is the composite positive electrode lithium supplementing additive according to any one of claims 1-5 or the composite positive electrode lithium supplementing additive prepared by the preparation method according to claim 6 or the positive electrode lithium supplementing additive according to claim 7.

9. The positive electrode according to claim 8, characterized by: The composite positive electrode lithium supplementing additive accounts for 0.5%-10% of the mass percentage of the positive electrode active material.

10. A secondary battery comprising a positive electrode, characterized by: The positive electrode is the positive electrode according to any one of claims 8-9.

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