Positive electrode lithium supplement additive, preparation method thereof, positive electrode sheet, and secondary battery

Abstract

The present application relates to the technical field of lithium-ion batteries, and provides a positive electrode lithium replenishing additive, which includes a core and a shell layer bound to the surface of the core body, the core body includes a first lithium-rich particle, the shell layer includes a second lithium-rich particle, and the particle size of the second lithium-rich particle is smaller than the particle size of the first lithium-rich particle. The positive electrode lithium replenishing additive provided by the present application, the first lithium-rich particles contained in the core body and the second lithium-rich particles contained in the shell layer are both rich in lithium, which can replenish the lithium ions consumed by the battery to form the SEI film during the first charge and discharge process, thereby improving the first efficiency of the battery; and the particle size of the second lithium-rich particles is smaller than that of the first lithium-rich particles. The second lithium-rich particles with a small particle size can form a shell layer with dense grain boundaries, which can effectively inhibit the lattice oxygen of the core body from releasing highly active atomic oxygen, thereby reducing the gas generated by the reaction of the electrolyte. Therefore, the positive electrode lithium replenishing additive has the advantages of low gas production and good lithium replenishment effect, and has good application prospects.

Description

Technical Field

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

[0002] Lithium-ion batteries have the advantages of high operating voltage and energy density, relatively low self-discharge level, ultra-long cycle life, no memory effect, and no pollution from heavy metal elements such as lead and cadmium. They are widely used in many aspects such as electric vehicles, power tools, mobile electronic consumer products and energy storage. However, during the first charging process of lithium-ion batteries, the electrode material and the electrolyte react at the solid-liquid interface to form SEI (solid electrolyte interphase, solid electrolyte) film, which consumes a lot of Li + , so that the Li released from the cathode material + Part of it is irreversibly consumed, which reduces the reversible specific capacity of the battery. Especially for silicon-based negative electrode materials, the Li + It will be further aggravated, causing serious lithium loss in the positive electrode material and reducing the initial coulombic efficiency and capacity of the lithium-ion battery.

[0003] Positive-electrode lithium-supplementing additives can compensate for the irreversible capacity loss caused by the formation of the SEI film during the initial charge of lithium-ion batteries. They are a key technology for improving lithium-ion battery performance, giving them a broad market and development prospects. However, research and practical applications have shown that the use of existing lithium-supplementing additives can lead to high gas production during the formation phase of lithium-ion batteries, causing internal bloating in the sealed battery system, leading to battery volume expansion and safety issues. Summary of the Invention

[0004] The purpose of this application is to provide a positive electrode lithium supplement additive and its preparation method, a positive electrode sheet, and a secondary battery, aiming to solve the problem of large gas production in existing positive electrode lithium supplement additives.

[0005] To achieve the above application objectives, the technical solutions adopted in this application are as follows:

[0006] In a first aspect, the present application provides a positive electrode lithium replenishing additive, which includes a core body and a shell layer bound to the surface of the core body, the core body includes first lithium-rich particles, the shell layer includes second lithium-rich particles, and the particle size of the second lithium-rich particles is smaller than the particle size of the first lithium-rich particles.

[0007] In a second aspect, the present application provides a method for preparing a positive electrode lithium supplement additive, comprising the following steps:

[0008] Providing first lithium-rich particles and second lithium-rich particles;

[0009] mixing the first lithium-rich particles and the second lithium-rich particles to obtain a lithium-rich mixture;

[0010] The lithium-rich mixture is placed in a protective atmosphere and sintered to obtain a positive electrode lithium supplement additive.

[0011] In a third aspect, the present application provides a positive electrode sheet comprising a current collector and a positive electrode material layer bonded to the surface of the current collector, wherein the positive electrode material layer contains the positive electrode lithium replenishing additive provided by the present application, or contains the positive electrode lithium replenishing additive prepared by the preparation method of the positive electrode lithium replenishing additive provided by the present application.

[0012] In a fourth aspect, the present application provides a secondary battery comprising a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet provided in the present application.

[0013] Compared with the prior art, this application has the following beneficial effects:

[0014] The positive electrode lithium supplement additive provided in the first aspect of the present application, because the first lithium-rich particles contained in its core and the second lithium-rich particles contained in its shell are both rich in lithium, can replenish the lithium ions consumed by the formation of the SEI film during the initial charge and discharge process of the battery, and can improve the initial coulombic efficiency of the battery; and the particle size of the second lithium-rich particles is smaller than that of the first lithium-rich particles. The small particle size of the second lithium-rich particles is conducive to the formation of dense grain boundaries. The dense grain boundaries in the shell can not only effectively inhibit the diffusion of oxygen vacancies generated by the release of lattice oxygen during charging of the positive electrode lithium supplement additive to the core, thereby avoiding the release of oxygen caused by the diffusion of oxygen vacancies, but also effectively inhibit the release of lattice oxygen and the escape of highly reactive atomic oxygen, thereby avoiding the redox reaction of highly reactive atomic oxygen with the electrolyte to produce gases such as CO and CO2. Therefore, coating the surface of the core with small-particle-size second lithium-rich particles can form a shell with dense grain boundaries, which can effectively inhibit the release of highly reactive atomic oxygen from the lattice oxygen of the core, thereby reducing the gas generated by the reaction with the electrolyte. Therefore, the positive electrode lithium replenishing additive has the advantages of low gas production and good lithium replenishing effect, and has good application prospects.

[0015] The second aspect of this application provides a method for preparing a positive electrode lithium-replenishing additive. First, a first lithium-rich particle and a second lithium-rich particle are mixed to obtain a lithium-rich mixture. The lithium-rich mixture is then sintered in a protective atmosphere to obtain a positive electrode lithium-replenishing additive in which the second lithium-rich particle is bonded to the surface of the first lithium-rich particle. This method is simple, has an easily controllable process, is low-cost, and is suitable for large-scale mass production. Furthermore, the resulting positive electrode lithium-replenishing additive inhibits the diffusion of surface oxygen vacancies into the core of the lithium-rich material and suppresses gas production.

[0016] The positive electrode sheet provided in the third aspect of the present application contains the positive electrode lithium replenishing additive provided herein, or contains the positive electrode lithium replenishing additive prepared by the preparation method of the positive electrode lithium replenishing additive provided herein. Therefore, the positive electrode active layer of the positive electrode sheet of the present application has the effect of inhibiting gas production, thereby improving the safety performance of the battery. Furthermore, the positive electrode sheet of the present application is rich in lithium, and thus has a high initial coulombic efficiency and other excellent electrochemical properties.

[0017] The secondary battery provided in the fourth aspect of the present application contains the positive electrode provided in the present application. Therefore, the secondary battery of the present application has excellent first coulombic efficiency, battery capacity and cycle performance, and has low gas production, high safety, long life and stable electrochemical performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0019] Figure 1 Schematic diagram of the structure of the positive electrode lithium supplement additive provided in the embodiment of the present application;

[0020] Figure 2 This is a process flow chart of the preparation method of the positive electrode lithium supplement additive provided in the embodiment of the present application;

[0021] in, Figure 1 Reference numerals in the drawings:

[0022] 1-core, 2-shell, 21-second lithium-rich particle, 22-pore. DETAILED DESCRIPTION

[0023] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0024] In this application, the term "and / or" describes the relationship between associated objects, indicating that three possible relationships exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0025] 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 refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0026] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution. Some or all of the steps can 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 the present application.

[0027] The terms used in the embodiments of the present application are for the purpose of describing specific embodiments only and are not intended to limit the present application. The singular forms "a", "an", "the" and "the" used in the embodiments of the present application and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0028] The weights of the relevant components mentioned in the examples of this application may not only refer to the specific content of each component, but also represent the weight ratio between the components. Therefore, as long as the content of the relevant components is proportionally enlarged or reduced according to the examples of this application, it is within the scope disclosed in the examples of this application. Specifically, the mass described in the examples of this application may be a mass unit known in the chemical industry, such as μg, mg, g, kg, etc.

[0029] The terms "first" and "second" are used solely for descriptive purposes to distinguish objects, such as substances, from one another and should not be understood to indicate or imply relative importance or to implicitly specify the quantity of the technical features being referred to. For example, without departing from the scope of the embodiments of this application, a first XX may also be referred to as a second XX, and similarly, a second XX may also be referred to as a first XX. Thus, features defined as "first" or "second" may explicitly or implicitly include one or more of such features.

[0030] The first aspect of the present application provides a positive electrode lithium supplement additive, such as Figure 1 As shown, the positive electrode lithium supplement additive includes a core body 1 and a shell layer 2 bound to the surface of the core body 1, the core body 1 includes first lithium-rich particles, the shell layer 2 includes second lithium-rich particles 21, and the particle size of the second lithium-rich particles 21 is smaller than that of the first lithium-rich particles.

[0031] The positive electrode lithium supplement additive provided in the embodiment of the present application, because the first lithium-rich particles contained in its core and the second lithium-rich particles contained in its shell are both rich in lithium, can replenish the lithium ions consumed by the formation of the SEI film during the first charge and discharge process of the battery, and can improve the first coulombic efficiency of the battery; and the particle size of the second lithium-rich particles is smaller than that of the first lithium-rich particles. The small particle size of the second lithium-rich particles is conducive to the formation of dense grain boundaries. The dense grain boundaries in the shell can not only effectively inhibit the diffusion of oxygen vacancies generated by the release of lattice oxygen during charging of the positive electrode lithium supplement additive to the core, thereby avoiding the release of oxygen caused by the diffusion of oxygen vacancies, but also effectively inhibit the release of lattice oxygen and the escape of highly reactive atomic oxygen, thereby avoiding the redox reaction of highly reactive atomic oxygen with the electrolyte to produce gases such as CO and CO2. Therefore, coating the surface of the core with small-particle-size second lithium-rich particles can form a shell with dense grain boundaries, which can effectively inhibit the release of highly reactive atomic oxygen from the lattice oxygen of the core, thereby reducing the gas generated by the reaction with the electrolyte. Therefore, the positive electrode lithium replenishing additive has the advantages of low gas production and good lithium replenishing effect, and has good application prospects.

[0032] In an embodiment, the core includes a first lithium-rich particle. The core may be composed of a single first lithium-rich particle or may be composed of a plurality of first lithium-rich particles aggregated together. The plurality of particles may refer to two or more first lithium-rich particles.

[0033] In an embodiment, the particle size ratio of the first lithium-rich particles to the second lithium-rich particles is (10-200):1, for example, 10:1, 25:1, 50:1, 75:1, 100:1, 125:1, 150:1, 175:1, and 200:1. Within the particle size ratio range of the first lithium-rich particles and the second lithium-rich particles provided in the embodiments of the present application, not only can the second lithium-rich particles be uniformly attached to the surface of the first lithium-rich particles to form a shell with dense grain boundaries, but the lattice oxygen of the core can also be more effectively suppressed to release highly reactive atomic oxygen, thereby reducing gas production. In addition, the process of dispersing the second lithium-rich particles on the surface of the first lithium-rich particles is simple, easy to implement, and has low production costs, which is conducive to promotion and application.

[0034] In an embodiment, the mass ratio of the first lithium-rich particles and the second lithium-rich particles is 1:(0.01-0.15), for example 1:0.01, 1:0.02, 1:0.03, 1:0.04, 1:0.05, 1:0.06, 1:0.07, 1:0.08, 1:0.09, 1:0.1, 1:0.15. It can be understood that if the mass ratio of the first lithium-rich particles and the second lithium-rich particles is too low, an effective shell layer cannot be formed, and if it is too high, the shell layer is too thick and is not conducive to the delithiation and lithium insertion of the first lithium-rich particles. Within the mass ratio range of the first lithium-rich particles and the second lithium-rich particles provided in the embodiment of the present application, it is beneficial for the second lithium-rich particles to form an effective shell layer on the surface of the first lithium-rich particles, which is beneficial for the first lithium-rich particles to smoothly delithiate and insert lithium, thereby improving the cycle performance and rate performance of the battery.

[0035] In an embodiment, the first lithium-rich particles and / or the second lithium-rich particles include a molecular formula of Li x M y N z O q The material and molecular formula is Li w At least one of the materials of A; It is understood that the first lithium-rich particles include a molecular formula of L x M y N z O q The material and molecular formula is Li w At least one of the materials of A; or the second lithium-rich particles include a molecular formula of L x M y N z O q The material and molecular formula is Li w At least one of the materials of A; or the first lithium-rich particles and the second lithium-rich particles both include a molecular formula of L x M y N z O q The material and molecular formula is Li w At least one of the materials of A. The first lithium-rich particle and the second lithium-rich particle can be the same or different lithium-rich materials; wherein, M includes at least one of Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti and Mg elements, N includes at least one of Fe, Co, Mn, Ni, Si and Al elements, A includes at least one of O and N, and 0<x≤6, 0<y≤1, 0≤z≤2, 0<q≤5, 1≤w≤3. By controlling and optimizing the types of elements represented by M and Q, these elements can form iron-based lithium-supplementing materials, manganese-based lithium-supplementing materials, and nickel-based lithium-supplementing materials with Li elements. For example, the iron-based lithium-supplementing material is Li5Fe 0.98 Al 0.02O4, Li5FeO4; manganese-based lithium supplement materials are Li6MnO4, Li2MnO2, LiMn2O4, Li2Mn2O4; nickel-based lithium supplement materials are Li2NiO2, LiNi 0.5 Mn 1.5 O4、Li2Ni 0.5 Mn 1.5 By controlling and optimizing the types of elements shown in A, these elements can form Li2O, Li2O2, Li3N, etc. with Li element.

[0036] In an embodiment, the first lithium-rich particle and the second lithium-rich particle are made of the same lithium-rich material. For example, the first lithium-rich particle and the second lithium-rich particle are both made of a manganese-based lithium-supplementing material, Li6MnO4; or the first lithium-rich particle and the second lithium-rich particle are both made of an iron-based lithium-supplementing material, Li5FeO4; or the first lithium-rich particle and the second lithium-rich particle are both made of a nickel-based lithium-supplementing material, Li2NiO2.

[0037] In an embodiment, pores 22 are present between the second lithium-rich particles in the shell layer. The pores 22 have a pore diameter of 1 to 200 nm, for example, 1 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 100 nm, 150 nm, or 200 nm. The porosity of the pores 22 is 0.1% to 30%, for example, 0.1%, 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, or 30%. The pores 22 between the second lithium-rich particles facilitate electrolyte infiltration, thereby improving lithium ion conductivity. If the pore size of the pore 22 is too large and the porosity is too high, it is not conducive to the formation of dense grain boundaries, and it is not conducive to suppressing the lattice oxygen of the core body (the first lithium-rich particle) from releasing highly active atomic oxygen, and thus it is not conducive to reducing the electrolyte reaction and gas production. If the pore size of the pore 22 is too small and the porosity is too low, it is not conducive to the infiltration of electrolyte and the transmission of lithium ions. Therefore, within the pore size and porosity range of this embodiment, the second lithium-rich particles can not only form dense grain boundaries, suppress the lattice oxygen of the core body from releasing highly active atomic oxygen, and reduce the electrolyte reaction and gas production, but also can infiltrate the electrolyte, improve the conductivity of lithium ions, and optimize the comprehensive performance of the positive electrode lithium supplement additive.

[0038] In an embodiment, the lithium-rich material Li x M y N z O q In addition, at least one of K and Na elements can be doped, and the molar amount of the doped K and Na elements is less than or equal to 30% of the molar amount of Li. x M y N z O q Doping with alkali metal elements with larger ionic radius such as K and Na can broaden the Li +transmission channel, which is beneficial to Li + Migration in the transmission channel can achieve Li + Rapid insertion and removal are beneficial to improving the electrochemical performance of the battery.

[0039] In the embodiment, the particle size of the first lithium-rich particles satisfies: 0.5 μm ≤ D50 ≤ 30 μm, preferably 2 μm ≤ D50 ≤ 20 μm. The first lithium-rich particles can be at least one of primary particles and secondary particles. x M y N z O q The material forms at least one of primary particles and secondary particles. When the first lithium-rich particle is a primary particle, the particle size of the primary particle is also the particle size of the first lithium-rich particle, and the distribution is 0.5μm to 30μm, preferably 2μm to 20μm. When the first lithium-rich particle is a secondary particle, the particle size of the secondary particle is also the particle size of the first lithium-rich particle, and the distribution is 0.5μm to 30μm, preferably 2μm-20μm. Among them, secondary particles refer to agglomerated particles formed by the aggregation of more than one primary particles. It can be understood that if the particle size of the first lithium-rich particle is too small, the production cost is high, and the dispersion effect is poor during use due to the large specific surface area; when the particle size is too large, the electrode sheet prepared is prone to convex points. This embodiment controls and optimizes the particle size of the first lithium-rich particle, which is conducive to uniform dispersion during homogenization, ensures the quality of the electrode sheet, and enables the core to fully exert its lithium replenishment effect.

[0040] In an embodiment, the particle size of the second lithium-rich particles satisfies: 0.05μm≤D50≤2.0μm, preferably 0.1μm≤D50≤1μm, for example, 0.1μm, 0.2μm, 0.3μm, 0.4μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1μm. Within the particle size range of the second lithium-rich particles provided in the embodiment of the present application, it can ensure that the second lithium-rich particles are uniformly combined on the surface of the lithium-rich core (first lithium-rich particles) to form a shell with dense grain boundaries, which can effectively coat the lithium-rich core, thereby effectively inhibiting the release of highly active atomic oxygen from the lattice oxygen of the lithium-rich core, reducing the reaction of the electrolyte, thereby reducing gas production, and reducing the volume expansion of the battery and safety issues. In addition, dispersing the second lithium-rich particles within this particle size range on the surface of the core also has the advantages of simple process, easy implementation, and low production cost.

[0041] In an embodiment, the thickness of the shell layer is 50 to 500 nm, for example, 50 nm, 75 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, and 500 nm. Within the thickness range of the shell layer provided in the embodiments of the present application, while ensuring smooth lithium removal and lithium insertion of the core body, it can also ensure that the second lithium-rich particles contained in the shell layer form dense grain boundaries, which can effectively cover the core body, thereby effectively inhibiting the release of highly active atomic oxygen from the lattice oxygen of the core body and reducing the gas generated by the reaction of the electrolyte.

[0042] In an embodiment, the positive electrode lithium supplement additive further includes a coating layer coated on the surface of the shell layer, and the material of the coating layer includes a carbon material. For example, the carbon material may include at least one of amorphous carbon, carbon nanotubes, graphite, carbon black, graphene, etc. By selecting the coating layer material, the electronic conductivity of the coating layer can be further improved. The thickness of the coating layer can be adjusted as needed, thereby facilitating electronic conduction while facilitating the stability of the lithium-rich material. In addition, the coating layer may further include other functional layers as needed, and other functional layers can be flexibly selected as needed.

[0043] A second aspect of the present invention provides a method for preparing a positive electrode lithium supplement additive, comprising the following steps:

[0044] S10: providing first lithium-rich particles and second lithium-rich particles;

[0045] S20: mixing the first lithium-rich particles and the second lithium-rich particles to obtain a lithium-rich mixture;

[0046] S30: placing the lithium-rich mixture in a protective atmosphere for sintering to obtain a positive electrode lithium supplement additive.

[0047] The preparation method of the positive electrode lithium-replenishing additive provided in the embodiments of the present application first mixes first and second lithium-rich particles to obtain a lithium-rich mixture, and then sintering the lithium-rich mixture in a protective atmosphere to obtain a positive electrode lithium-replenishing additive in which the second lithium-rich particles are bonded to the surface of the first lithium-rich particles. This preparation method is simple, has an easily controllable process, is low-cost, and is suitable for large-scale mass production. It also ensures that the resulting positive electrode lithium-replenishing additive inhibits the diffusion of surface oxygen vacancies into the core of the lithium-rich material and suppresses gas production.

[0048] In step S10, the materials of the first and second lithium-rich particles are the same as those described above, and are not repeated here. In this embodiment, the first and second lithium-rich particles can be provided in a mass ratio of 1:(0.01-0.1), and the particle size of the second lithium-rich particles is smaller than that of the first lithium-rich particles.

[0049] In the above step S20, the mixing process may be a grinding process. In this embodiment, the first lithium-rich particles and the second lithium-rich particles are ground so that the second lithium-rich particles are uniformly attached to the surface of the first lithium-rich particles to obtain a lithium-rich mixture.

[0050] In step S30, the protective atmosphere can be selected from at least one of argon and nitrogen. Specifically, the lithium-rich mixture can be sintered in an argon atmosphere to obtain a positive electrode lithium-replenishing additive in which the second lithium-rich particles are uniformly dispersed on the surface of the first lithium-rich particles. Alternatively, the lithium-rich mixture can be sintered in a nitrogen atmosphere to obtain a positive electrode lithium-replenishing additive in which the second lithium-rich particles are uniformly dispersed on the surface of the first lithium-rich particles.

[0051] In the embodiment, the sintering temperature is 500-800°C, preferably 600-700°C, and the time is 3-12 hours, preferably 5-10 hours. Within this sintering temperature and time range, the second lithium-rich particles are conducive to melting to form a shell with dense grain boundaries, and are tightly bonded to the surface of the core, so that the shell can effectively inhibit the release of highly active atomic oxygen from the lattice oxygen of the core and reduce the gas production of the electrolyte reaction.

[0052] In a third aspect of an embodiment of the present application, a positive electrode sheet is provided, comprising a current collector and a positive electrode material layer bonded to the surface of the current collector, wherein the positive electrode material layer contains the positive electrode lithium replenishing additive provided in the present application, or contains the positive electrode lithium replenishing additive prepared by the preparation method of the positive electrode lithium replenishing additive provided in the present application.

[0053] The positive electrode sheets provided in the embodiments of the present application contain the positive electrode lithium-replenishing additive provided herein, or contain the positive electrode lithium-replenishing additive prepared by the preparation method of the positive electrode lithium-replenishing additive provided herein. Therefore, the positive electrode active layer of the positive electrode sheets of the present application suppresses gas production, thereby improving battery safety. Furthermore, the positive electrode sheets are rich in lithium, resulting in high initial coulombic efficiency and other excellent electrochemical properties.

[0054] In the embodiments, the positive electrode lithium supplement additive provided in the present application can be used only as an additive in combination with other active materials, or can be used alone as a lithium-rich positive electrode material.

[0055] A fourth aspect of an embodiment of the present application provides a secondary battery, comprising a positive electrode sheet and a negative electrode sheet, wherein the positive electrode sheet is the positive electrode sheet provided in the present application.

[0056] The secondary battery provided in the embodiment of the present application contains the positive electrode provided in the present application. Therefore, the secondary battery of the present application has excellent first coulombic efficiency, battery capacity and cycle performance, and has low gas production, high safety, long life and stable electrochemical performance.

[0057] In the embodiment, since the electrode sheet of the secondary battery of the present application contains a positive electrode lithium replenishing additive, the positive electrode lithium replenishing additive can effectively inhibit the release of highly active atomic oxygen from the lattice oxygen of the core body, reduce the reaction with the electrolyte and reduce the gas production, thereby enabling the first cycle gas production of the secondary battery of the present application to be less than 3 mL / g.

[0058] The following describes the details in conjunction with specific embodiments.

[0059] Example 1

[0060] This embodiment provides a positive electrode lithium supplement additive and a preparation method thereof.

[0061] The positive electrode lithium supplement additive includes a core and a shell layer bound to the surface of the core body, the core body includes a first lithium-rich particle, the shell layer includes a second lithium-rich particle, and the particle size of the second lithium-rich particle is smaller than the particle size of the first lithium-rich particle; wherein, the first lithium-rich particle is Li5FeO4, the second lithium-rich particle is Li5FeO4, the particle size D50 of the first lithium-rich particle is 15.36μm, the particle size D50 of the second lithium-rich particle is 0.156μm, the particle size ratio of the first lithium-rich particle to the second lithium-rich particle is 98:1, and the thickness of the shell layer is 134nm.

[0062] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0063] S10: providing first lithium-rich particles Li5FeO4 with a particle size D50 of approximately 15.36 μm and second lithium-rich particles Li5FeO4 with a particle size D50 of approximately 0.156 μm, according to a mass ratio of the first lithium-rich particles to the second lithium-rich particles of 1:0.03;

[0064] S20: Grinding the first lithium-rich particles Li5FeO4 and the second lithium-rich particles Li5FeO4 to obtain a lithium-rich mixture;

[0065] S30: sintering the lithium-rich mixture in an argon atmosphere at 600° C. for 5 hours to obtain a positive electrode lithium supplement additive.

[0066] Example 2

[0067] This embodiment provides a positive electrode lithium supplement additive and a preparation method thereof.

[0068] The positive electrode lithium supplement additive includes a core and a shell layer bound to the surface of the core body, the core body includes a first lithium-rich particle, the shell layer includes a second lithium-rich particle, and the particle size of the second lithium-rich particle is smaller than the particle size of the first lithium-rich particle; wherein, the first lithium-rich particle is Li5FeO4, the second lithium-rich particle is Li2NiO2, the particle size D50 of the first lithium-rich particle is approximately 15.36μm, the particle size D50 of the second lithium-rich particle is approximately 0.169μm, the particle size ratio of the first lithium-rich particle to the second lithium-rich particle is 91:1, and the thickness of the shell layer is 150nm.

[0069] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0070] S10: providing first lithium-rich particles Li5FeO4 with a particle size D50 of approximately 15.36 μm and second lithium-rich particles Li2NiO2 with a particle size D50 of approximately 0.169 μm, according to a mass ratio of the first lithium-rich particles to the second lithium-rich particles of 1:0.03;

[0071] S20: Grinding the first lithium-rich particles Li5FeO4 and the second lithium-rich particles Li2NiO2 to obtain a lithium-rich mixture;

[0072] S30: sintering the lithium-rich mixture in an argon atmosphere at 600° C. for 5 hours to obtain a positive electrode lithium supplement additive.

[0073] Example 3

[0074] This embodiment provides a positive electrode lithium supplement additive and a preparation method thereof.

[0075] The positive electrode lithium supplement additive includes a core and a shell layer bound to the surface of the core body, the core body includes a first lithium-rich particle, the shell layer includes a second lithium-rich particle, and the particle size of the second lithium-rich particle is smaller than the particle size of the first lithium-rich particle; wherein, the first lithium-rich particle is Li5FeO4, the second lithium-rich particle is Li6MnO4, the particle size D50 of the first lithium-rich particle is approximately 15.36μm, the particle size D50 of the second lithium-rich particle is approximately 0.152μm, the particle size ratio of the first lithium-rich particle to the second lithium-rich particle is 101:1, and the thickness of the shell layer is 138nm.

[0076] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0077] S10: providing first lithium-rich particles Li5FeO4 with a particle size D50 of approximately 15.36 μm and second lithium-rich particles Li6MnO4 with a particle size D50 of approximately 0.152 μm, according to a mass ratio of the first lithium-rich particles to the second lithium-rich particles of 1:0.03;

[0078] S20: Grinding the first lithium-rich particles Li5FeO4 and the second lithium-rich particles Li6MnO4 to obtain a lithium-rich mixture;

[0079] S30: sintering the lithium-rich mixture in an argon atmosphere at 600° C. for 5 hours to obtain a positive electrode lithium supplement additive.

[0080] Example 4

[0081] This embodiment provides a positive electrode lithium supplement additive and a preparation method thereof.

[0082] The positive electrode lithium supplement additive includes a core and a shell layer bound to the surface of the core body, the core body includes a first lithium-rich particle, the shell layer includes a second lithium-rich particle, and the particle size of the second lithium-rich particle is smaller than the particle size of the first lithium-rich particle; wherein, the first lithium-rich particle is Li2O, the second lithium-rich particle is Li2NiO2, the particle size D50 of the first lithium-rich particle is approximately 15.03μm, the particle size D50 of the second lithium-rich particle is approximately 0.148μm, the particle size ratio of the first lithium-rich particle to the second lithium-rich particle is 102:1, and the thickness of the shell layer is 50nm.

[0083] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0084] S10: providing first lithium-rich particles Li2O with a particle size D50 of approximately 15.03 μm and second lithium-rich particles Li2NiO2 with a particle size D50 of approximately 0.148 μm, according to a mass ratio of the first lithium-rich particles to the second lithium-rich particles of 1:0.01;

[0085] S20: mixing the first lithium-rich particles Li2O and the second lithium-rich particles Li5FeO4 and grinding them to obtain a lithium-rich mixture;

[0086] S30: sintering the lithium-rich mixture in an argon atmosphere at 600° C. for 5 hours to obtain a positive electrode lithium supplement additive.

[0087] Example 5

[0088] This embodiment provides a positive electrode lithium supplement additive and a preparation method thereof.

[0089] The positive electrode lithium supplement additive includes a core and a shell layer bonded to the surface of the core body, the core body includes a first lithium-rich particle, the shell layer includes a second lithium-rich particle, and the particle size of the second lithium-rich particle is smaller than that of the first lithium-rich particle; wherein, the first lithium-rich particle is Li2O·Li5FeO4, the second lithium-rich particle is Li6MnO4, the particle size D50 of the first lithium-rich particle is approximately 15.45μm, the particle size D50 of the second lithium-rich particle is approximately 0.152μm, the particle size ratio of the first lithium-rich particle to the second lithium-rich particle is 102:1, and the thickness of the shell layer is 500nm.

[0090] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0091] S10: providing first lithium-rich particles Li2O·Li5FeO4 with a particle size D50 of approximately 15.45 μm and second lithium-rich particles Li6MnO4 with a particle size D50 of approximately 0.152 μm, according to a mass ratio of the first lithium-rich particles to the second lithium-rich particles of 1:0.1;

[0092] S20: Grinding the first lithium-rich particles Li2O·Li5FeO4 and the second lithium-rich particles Li6MnO4 to obtain a lithium-rich mixture;

[0093] S30: sintering the lithium-rich mixture in an argon atmosphere at 600° C. for 5 hours to obtain a positive electrode lithium supplement additive.

[0094] Example 6

[0095] This embodiment provides a positive electrode lithium supplement additive and a preparation method thereof.

[0096] The positive electrode lithium supplement additive includes a core and a shell layer bound to the surface of the core body, the core body includes a first lithium-rich particle, the shell layer includes a second lithium-rich particle, and the particle size of the second lithium-rich particle is smaller than the particle size of the first lithium-rich particle; wherein, the first lithium-rich particle is Li5FeO4, the second lithium-rich particle is Li5FeO4, the particle size D50 of the first lithium-rich particle is approximately 15.41μm, the particle size D50 of the second lithium-rich particle is approximately 1.54μm, the particle size ratio of the first lithium-rich particle to the second lithium-rich particle is 10:1, and the thickness of the shell layer is 297nm.

[0097] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0098] S10: providing first lithium-rich particles Li5FeO4 with a particle size D50 of approximately 15.36 μm and second lithium-rich particles Li5FeO4 with a particle size D50 of approximately 1.54 μm, according to a mass ratio of the first lithium-rich particles to the second lithium-rich particles of 1:0.03;

[0099] S20: Grinding the first lithium-rich particles Li5FeO4 and the second lithium-rich particles Li5FeO4 to obtain a lithium-rich mixture;

[0100] S30: sintering the lithium-rich mixture in an argon atmosphere at 600° C. for 5 hours to obtain a positive electrode lithium supplement additive.

[0101] Example 7

[0102] This embodiment provides a positive electrode lithium supplement additive and a preparation method thereof.

[0103] The positive electrode lithium supplement additive includes a core and a shell layer bound to the surface of the core body, the core body includes a first lithium-rich particle, the shell layer includes a second lithium-rich particle, and the particle size of the second lithium-rich particle is smaller than the particle size of the first lithium-rich particle; wherein, the first lithium-rich particle is Li5FeO4, the second lithium-rich particle is Li5FeO4, the particle size D50 of the first lithium-rich particle is approximately 15.40μm, the particle size D50 of the second lithium-rich particle is approximately 0.077μm, the particle size ratio of the first lithium-rich particle to the second lithium-rich particle is 200:1, and the thickness of the shell layer is 127nm.

[0104] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0105] S10: providing first lithium-rich particles Li5FeO4 with a particle size D50 of approximately 15.40 μm and second lithium-rich particles Li5FeO4 with a particle size D50 of approximately 0.077 μm, according to a mass ratio of the first lithium-rich particles to the second lithium-rich particles of 1:0.03;

[0106] S20: Grinding the first lithium-rich particles Li5FeO4 and the second lithium-rich particles Li5FeO4 to obtain a lithium-rich mixture;

[0107] S30: sintering the lithium-rich mixture in an argon atmosphere at 600° C. for 5 hours to obtain a positive electrode lithium supplement additive.

[0108] Example 8

[0109] This embodiment provides a positive electrode lithium supplement additive and a preparation method thereof.

[0110] The positive electrode lithium supplement additive includes a core and a shell layer bound to the surface of the core body, the core body includes a first lithium-rich particle, the shell layer includes a second lithium-rich particle, and the particle size of the second lithium-rich particle is smaller than the particle size of the first lithium-rich particle; wherein, the first lithium-rich particle is Li5FeO4, the second lithium-rich particle is Li5FeO4, the particle size D50 of the first lithium-rich particle is approximately 0.78μm, the particle size D50 of the second lithium-rich particle is approximately 0.156μm, the particle size ratio of the first lithium-rich particle to the second lithium-rich particle is 5:1, and the thickness of the shell layer is 137nm.

[0111] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0112] S10: providing first lithium-rich particles Li5FeO4 with a particle size D50 of approximately 0.78 μm and second lithium-rich particles Li5FeO4 with a particle size D50 of approximately 0.156 μm, according to a mass ratio of the first lithium-rich particles to the second lithium-rich particles of 1:0.03;

[0113] S20: Grinding the first lithium-rich particles Li5FeO4 and the second lithium-rich particles Li5FeO4 to obtain a lithium-rich mixture;

[0114] S30: sintering the lithium-rich mixture in an argon atmosphere at 600° C. for 5 hours to obtain a positive electrode lithium supplement additive.

[0115] Example 9

[0116] This embodiment provides a positive electrode lithium supplement additive and a preparation method thereof.

[0117] The positive electrode lithium supplement additive includes a core and a shell layer bound to the surface of the core body, the core body includes a first lithium-rich particle, the shell layer includes a second lithium-rich particle, and the particle size of the second lithium-rich particle is smaller than the particle size of the first lithium-rich particle; wherein, the first lithium-rich particle is Li5FeO4, the second lithium-rich particle is Li5FeO4, the particle size D50 of the first lithium-rich particle is approximately 30.00μm, the particle size D50 of the second lithium-rich particle is approximately 0.120μm, the particle size ratio of the first lithium-rich particle to the second lithium-rich particle is 250:1, and the thickness of the shell layer is 122nm.

[0118] The preparation method of the positive electrode lithium supplement additive comprises the following steps:

[0119] S10: providing first lithium-rich particles Li5FeO4 with a particle size D50 of approximately 30.00 μm and second lithium-rich particles Li5FeO4 with a particle size D50 of approximately 0.120 μm, according to a mass ratio of the first lithium-rich particles to the second lithium-rich particles of 1:0.03;

[0120] S20: Grinding the first lithium-rich particles Li5FeO4 and the second lithium-rich particles Li5FeO4 to obtain a lithium-rich mixture;

[0121] S30: sintering the lithium-rich mixture in an argon atmosphere at 600° C. for 5 hours to obtain a positive electrode lithium supplement additive.

[0122] Comparative Example 1

[0123] This comparative example provides a positive electrode lithium supplement additive that is a first lithium-rich particle Li5FeO4. Compared with Examples 1 to 3 and 6 to 9, the positive electrode lithium supplement additive in this comparative example does not contain a shell layer, that is, does not contain a second lithium-rich particle.

[0124] Comparative Example 2

[0125] This comparative example provides a positive electrode lithium supplement additive that is a first lithium-rich particle Li2O. Compared with Example 4, the positive electrode lithium supplement additive in this comparative example does not contain a shell layer, that is, does not contain a second lithium-rich particle.

[0126] Comparative Example 3

[0127] This comparative example provides a positive electrode lithium supplement additive comprising first lithium-rich particles Li2O·Li5FeO4. Compared with Example 5, the positive electrode lithium supplement additive in this comparative example does not contain a shell layer, that is, does not contain second lithium-rich particles.

[0128] Lithium-ion battery examples and comparative examples:

[0129] The positive electrode lithium supplement additives provided in Examples 1 to 9 and the positive electrode lithium supplement additives provided in Comparative Examples 1 to 3 are respectively assembled into positive electrode sheets and lithium-ion batteries according to the following methods:

[0130] Positive electrode: Under the same conditions, N-methylpyrrolidone, lithium iron phosphate, positive electrode lithium supplement additive, conductive agent Super P and polyvinylidene fluoride were mixed in a mass ratio of 100:93:2:2:3 and ball milled to obtain positive electrode slurry. The ball milling time was 60 minutes and the rotation speed was 30Hz. The positive electrode slurry was coated on the surface of aluminum foil, rolled and vacuum dried at 100°C overnight to obtain the positive electrode sheet.

[0131] Negative electrode: The negative electrode active material (graphite), conductive agent (conductive carbon black, Super P), thickener (carboxymethyl cellulose, CMC), and binder (styrene-butadiene rubber, SBR) are placed in deionized water and mixed evenly in a mass ratio of 95:2:0.5:2.5 to form a negative electrode slurry. 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.

[0132] 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. The concentration of LiPF6 was 1 mol / L.

[0133] Diaphragm: Polyethylene (PE) microporous separator;

[0134] Lithium-ion battery assembly: The structure of lithium metal sheet-diaphragm-electrolyte-positive electrode sheet is assembled into a lithium-ion battery in an inert atmosphere glove box.

[0135] Lithium-ion battery related performance test:

[0136] The electrochemical performance of the lithium-ion batteries assembled in the above-described lithium-ion battery examples and comparative examples was tested. The test conditions were: the assembled batteries were charged and discharged at room temperature, with a charge and discharge voltage range of 2.7V to 4.3V. The electrochemical performance of the lithium-ion batteries of Examples 1-9 and Comparative Examples 1-3 is shown in Table 1.

[0137] Table 1

[0138]

[0139] As can be seen from Table 1, the first-cycle gas production of the battery corresponding to the positive electrode lithium replenishing additive provided in Examples 1 to 3, 6 to 9 of the present application is significantly lower than the first-cycle gas production of the battery corresponding to the positive electrode lithium replenishing additive provided in Comparative Example 1; the first-cycle gas production of the battery corresponding to the positive electrode lithium replenishing additive provided in Example 4 of the present application is significantly lower than the first-cycle gas production of the battery corresponding to the positive electrode lithium replenishing additive provided in Comparative Example 2; the first-cycle gas production of the battery corresponding to the positive electrode lithium replenishing additive provided in Example 5 of the present application is significantly lower than the first-cycle gas production of the battery corresponding to the positive electrode lithium replenishing additive provided in Comparative Example 3. This shows that the embodiment of the present application combines second lithium-rich particles with small particle size on the surface of the first lithium-rich particles to form a shell with dense grain boundaries, which can effectively inhibit the diffusion of oxygen vacancies generated by the release of lattice oxygen of the positive electrode lithium replenishing additive to the core during charging, avoids the release of oxygen caused by the diffusion of oxygen vacancies, and effectively inhibits the release of lattice oxygen to escape highly active atomic oxygen, reduces the redox reaction with the electrolyte, and reduces gas production. In addition, the first-cycle gas production of the batteries corresponding to the positive electrode lithium replenishing additives provided in Examples 1 to 7 of the present application is significantly lower than the first-cycle gas production of the batteries corresponding to the positive electrode lithium replenishing additives provided in Examples 8 to 9, indicating that the particle size ratio of the first lithium-rich particles and the second lithium-rich particles in the positive electrode lithium replenishing additives provided in the embodiments of the present application is in the range of (10 to 200): 1, and the second lithium-rich particles can be evenly attached to the surface of the first lithium-rich particles, thereby forming a shell with dense grain boundaries, which can more effectively inhibit the lattice oxygen of the core from releasing highly active atomic oxygen and reducing gas production. Therefore, the embodiments of the present application provide a positive electrode lithium replenishing additive that has the advantages of low gas production and good lithium replenishment effect.

[0140] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. A positive electrode lithium supplement additive, characterized in that: The positive electrode lithium supplement additive includes a core and a shell layer bonded to the surface of the core body, the core body includes a first lithium-rich particle, the shell layer includes a second lithium-rich particle, and the particle size of the second lithium-rich particle is smaller than the particle size of the first lithium-rich particle; the particle size ratio of the first lithium-rich particle to the second lithium-rich particle is (10-200):1; there are pores between the second lithium-rich particles in the shell layer, the pore size of the pores is 1-200 nm, and the porosity of the pores is 0.1%-30%; The first lithium-rich particles and the second lithium-rich particles are made of the same lithium-rich material.

2. The positive electrode lithium supplement additive according to claim 1, characterized in that The mass ratio of the first lithium-rich particles to the second lithium-rich particles is 1:(0.01-0.15).

3. The positive electrode lithium supplement additive according to claim 1, characterized in that The first lithium-rich particles and / or the second lithium-rich particles include a molecular formula of Li x M y N z O q The material and molecular formula is Li w At least one of the materials of A, wherein M includes at least one of Fe, Co, Ni, Mn, V, Cu, Mo, Al, Ti and Mg elements, N includes at least one of Fe, Co, Mn, Ni, Si and Al elements, A includes at least one of O and N, and 0<x≤6, 0<y≤1, 0≤z≤2, 0<q≤5, 1≤w≤3.

4. The positive electrode lithium supplement additive according to any one of claims 1 to 3, characterized in that The particle size of the first lithium-rich particles satisfies: 0.5 μm ≤ D50 ≤ 30 μm; and / or The particle size of the second lithium-rich particles satisfies: 0.05 μm ≤ D50 ≤ 2.0 μm; and / or The thickness of the shell layer is 50 to 500 nm.

5. The positive electrode lithium supplement additive according to any one of claims 1 to 3, characterized in that It also includes a coating layer coated on the surface of the shell layer.

6. A method for preparing the positive electrode lithium supplement additive according to any one of claims 1 to 5, characterized in that: The following steps are involved: Providing the first lithium-rich particles and the second lithium-rich particles; Mixing the first lithium-rich particles and the second lithium-rich particles to obtain a lithium-rich mixture; The lithium-rich mixture is placed in a protective atmosphere and sintered to obtain the positive electrode lithium supplement additive.

7. A positive electrode sheet comprising a current collector and a positive electrode material layer bonded to the surface of the current collector, characterized in that: The positive electrode material layer contains the positive electrode lithium replenishing additive according to any one of claims 1 to 5, or contains the positive electrode lithium replenishing additive prepared by the preparation method of the positive electrode lithium replenishing additive according to claim 6.

8. A secondary battery comprising a positive electrode sheet and a negative electrode sheet, characterized in that: The positive electrode sheet is the positive electrode sheet according to claim 7.

9. The secondary battery according to claim 8, wherein The gas production of the secondary battery in the first cycle is less than 3 mL / g.

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