Composite lithium supplement agent and preparation method thereof, positive pole piece and battery

Abstract

The invention relates to the technical field of batteries, in particular to a composite lithium supplement agent and a preparation method thereof, a positive pole piece and a battery. The composite lithium supplement agent comprises a core body and a shell covering the surface of the core body, m is one or more of Fe, Co and Ni, x is greater than or equal to 1 and less than or equal to 6, y is greater than or equal to 1 and less than or equal to 6, and z is greater than or equal to 1 and less than or equal to 6; the elementary substances comprise one or more of sulfur elementary substances and iron elementary substances; and the shell comprises lithium titanium aluminum phosphate. The composite lithium supplement agent provided by the invention has good conductivity and air stability and relatively low oxygen generation amount, and is beneficial to improving the charging capacity of the battery.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to composite lithium replenishing agents and their preparation methods, positive electrode sheets, and batteries. Background Technology

[0002] Lithium-ion batteries have been widely used in new energy vehicles, portable electronic devices, energy storage systems and other fields due to their advantages such as high energy density, long cycle life and environmental friendliness.

[0003] During the initial charging of a lithium-ion battery, a solid electrolyte interphase (SEI) film spontaneously forms on the surface of the negative electrode material due to the reduction and decomposition reaction of the electrolyte. This SEI film isolates the continuous reaction between the electrolyte and the negative electrode material, stabilizes the electrode structure, and ensures battery cycle performance, making it a necessary condition for reversible charge-discharge of lithium-ion batteries. However, the formation of the SEI film consumes lithium ions, and the lithium ions involved in the construction of the SEI film originate from the positive electrode material. These lithium ions cannot be extracted and reinserted into the positive electrode to participate in electrochemical reactions during subsequent charge-discharge cycles, leading to an initial irreversible capacity loss in the battery.

[0004] To compensate for the initial loss of lithium ions, a lithium replenishing agent is usually added to the positive or negative electrode material layer. Positive electrode lithium replenishing agents are mainly Li₅FeO₄ and other Li₂... x M y O z Lithium replenishing agents decompose and release lithium during the first charge of a battery to achieve a lithium replenishment effect. However, Li... x M y O z Lithium supplements have poor conductivity; and the high Li content makes them prone to chemical reactions with air during storage, transportation, electrode preparation, and battery assembly, resulting in poor air stability; furthermore, Li x M y O z The oxygen produced during the decomposition of lithium replenishment may cause electrolyte decomposition and even cause battery fire. Summary of the Invention

[0005] Based on this, this application provides a composite lithium replenishing agent and its preparation method, a positive electrode sheet, and a battery. The composite lithium replenishing agent of this application has good conductivity, air stability, and low oxygen generation, and it is beneficial to improve the charging capacity of the battery.

[0006] A first aspect of this application provides a composite lithium replenishing agent, comprising a core and a shell covering the surface of the core;

[0007] The core includes Li x M y O zThe lithium supplement and the element, wherein M is one or more of Fe, Co and Ni, 1≤x≤6, 1≤y≤6, 1≤z≤6; the element includes one or more of sulfur and iron.

[0008] The casing comprises lithium titanium aluminum phosphate.

[0009] In some embodiments, the composite lithium supplement meets one of the following characteristics:

[0010] (1) The core body includes the Li x M y O z The lithium supplement and the elemental iron, wherein the casing comprises the lithium aluminum titanium phosphate;

[0011] (2) The core includes the Li x M y O z The lithium supplement and the elemental sulfur, the casing comprising the lithium titanium aluminum phosphate and the elemental sulfur.

[0012] In some embodiments, the shell further includes glucose. The Li x M y O z The mass ratio of lithium supplement to glucose is 10:(0.1~1.5).

[0013] In some embodiments, the Li x M y O z The mass ratio of lithium supplement to the element is 10:(0.1~1).

[0014] In some embodiments, the Li x M y O z The mass ratio of the lithium supplement to the lithium titanium aluminum phosphate is 10:(0.5~5).

[0015] In some embodiments, the Li x M y O z The lithium replenishing agent is Li5FeO4.

[0016] In some embodiments, the Li x M y O z The average particle size of the lithium supplement is 10 μm to 20 μm.

[0017] In some embodiments, the average particle size of the elemental iron is 200 nm to 400 nm.

[0018] In some embodiments, the average particle size of the lithium titanium aluminum phosphate is 200 nm to 400 nm.

[0019] A second aspect of this application provides a method for preparing a composite lithium supplement, comprising the following steps:

[0020] Li x M y O z The composite lithium supplement is prepared by first fusion coating of a lithium supplement agent, nano-iron powder, and lithium titanium aluminum phosphate under conditions with or without glucose to form a core and a shell covering the outer surface of the core; the core comprises Li x M y O z The lithium supplement and elemental iron are present, and the casing comprises lithium titanium aluminum phosphate.

[0021] Or, Li x M y O z A lithium supplement and lithium aluminum titanium phosphate are subjected to a second fusion coating in the presence or absence of glucose to form a core and a shell covering the outer surface of the core, thus preparing a core-shell intermediate; the core in the core-shell intermediate comprises Li x M y O z A lithium supplement agent, wherein the shell comprises lithium titanium aluminum phosphate; the core-shell intermediate is mixed with sulfur powder, heated until the sulfur powder melts and penetrates into the shell and core to form elemental sulfur, thereby preparing the composite lithium supplement agent.

[0022] Where M is one or more of Fe, Co and Ni, 1≤x≤6, 1≤y≤6, 1≤z≤6.

[0023] In some embodiments, the Li x M y O z The average particle size of the lithium supplement is 10 μm to 20 μm.

[0024] In some embodiments, the average particle size of the nano-iron powder is 200 nm to 400 nm.

[0025] In some embodiments, the average particle size of the lithium titanium aluminum phosphate is 200 nm to 400 nm.

[0026] In some embodiments, the process parameters for the first fusion coating and the second fusion coating each independently include: a temperature of 640°C to 660°C and a rotation speed of 1400 rpm to 1600 rpm.

[0027] In some embodiments, the Li x My O z The lithium supplement is a Li5FeO4 lithium supplement, and the preparation steps of the Li5FeO4 lithium supplement include:

[0028] Fe2O3 and Li2O were mixed and ground to prepare a mixture.

[0029] The mixture was sintered in an inert gas atmosphere to prepare the Li5FeO4 lithium supplement.

[0030] In some embodiments, the molar ratio of Fe2O3 to Li2O is 1:(4.5~6).

[0031] In some embodiments, the sintering process parameters include heating to 600°C to 700°C at a heating rate of 4°C / min to 6°C / min.

[0032] In a third aspect, this application provides a positive electrode sheet, comprising a current collector and a positive active material layer loaded on the surface of the current collector, wherein the positive active material layer comprises a positive active material and a lithium supplementing agent;

[0033] The lithium replenishing agent is the composite lithium replenishing agent described in any of the first aspects of this application, or the composite lithium replenishing agent prepared by any of the preparation methods in the second aspect of this application.

[0034] In a fourth aspect, this application provides a battery including the positive electrode sheet described in the third aspect of this application.

[0035] The composite lithium supplement provided in this application has at least the following advantages:

[0036] The composite lithium replenisher provided in this application uses lithium titanium aluminum phosphate as a coating layer. Its three-dimensional lattice channels ensure rapid lithium-ion migration, while the elemental iron or sulfur in the core possesses high electronic conductivity, enabling the construction of continuous electronic pathways within the lithium replenisher. These two elements synergistically improve the overall conductivity of the composite lithium replenisher. The chemical stability of the lithium titanium aluminum phosphate shell physically isolates the lithium ions from the core. x M y O z The lithium supplement reacts with H2O and CO2 in the air, preventing it from absorbing moisture and hydrolyzing, causing lithium source loss, and generating inert impurities, thus giving the composite lithium supplement excellent air stability. Furthermore, elemental iron or sulfur can absorb Li. x M y O z The oxidative decomposition of lithium supplements generates oxygen, thereby reducing the amount of oxygen produced in the battery system. Furthermore, the lithium titanium aluminum phosphate casing can suppress Li... x M y O zThe excessive reaction between the lithium replenishing agent and the electrolyte during the first charge, as well as the reaction between iron ions and the electrolyte, enable the composite lithium replenishing agent provided in this application to balance lithium replenishment efficiency and battery safety.

[0037] Therefore, the composite lithium replenisher of this application has good conductivity, air stability and low oxygen production, and it is beneficial to improve the charging capacity of the battery. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the structure of a composite lithium supplement provided as an example in this application.

[0039] 10. Composite lithium supplement; 110. Core; 120. Shell. Detailed Implementation

[0040] The following detailed description, in conjunction with specific embodiments, provides a more complete and clear account of the composite lithium supplement agent, its preparation method, the positive electrode sheet, and the battery of this application. This application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0041] In this application, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0042] When a range of values ​​is disclosed herein, the range is considered continuous and includes the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. Unless otherwise stated or in case of conflict, the terms or phrases used herein have the following meanings:

[0044] In this application, the terms "multiple", "various", "multiple times", "multi-dimensional", etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more or more.

[0045] In this application, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth," etc., serve only a non-exhaustive enumeration purpose and should be understood not to constitute a closed limitation on quantity.

[0046] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0047] In this application, the terms "combinations thereof", "any combination thereof", and "any combination thereof" include all suitable combinations of any two or more of the listed items.

[0048] In this application, the term "suitable" as used in phrases such as "suitable combination," "suitable method," and "any suitable method" refers to the ability to implement the technical solution of this application, solve the technical problem of this application, and achieve the expected technical effect of this application.

[0049] In this application, terms such as "preferred," "better," "more suitable," and "ideal" are used only to describe implementation methods or embodiments with better effects, and should be understood not to constitute a limitation on the scope of protection of this application.

[0050] In this application, terms such as "further," "even further," and "particularly" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0051] In this application, the terms "optionally," "optionally," and "optional" refer to options that are optional, meaning they can be selected from either "with" or "without." If multiple "optional" options appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" option is independent.

[0052] In this application, numerical intervals (i.e., numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the aforementioned numerical intervals are considered continuous and include the two endpoints (i.e., the minimum and maximum values) of the numerical range, as well as every value between these two endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoint integers of the numerical range, as well as every integer between the two endpoints. In this document, this is equivalent to directly listing every integer. For example, if t is an integer selected from 1 to 10, it means that t is any integer selected from the group of integers consisting of 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Furthermore, when multiple ranges are provided to describe features or characteristics, these ranges can be merged. In other words, unless otherwise specified, the ranges disclosed herein should be understood to include any and all subranges to which they are included.

[0053] Unless otherwise specified, the temperature parameters in this application are permitted to be either constant-temperature treatment or variations within a certain temperature range. It should be understood that the constant-temperature treatment allows temperature fluctuations within the precision range of the instrument control, such as ±5℃, ±4℃, ±3℃, ±2℃, or ±1℃.

[0054] In this application, percentage content refers to mass percentage for solid-liquid mixtures and solid-phase-solid mixtures, and volume percentage for liquid-phase-liquid mixtures, unless otherwise specified.

[0055] In this application, unless otherwise specified, percentage concentrations refer to final concentrations. The final concentration refers to the percentage of the added component in the system after its addition.

[0056] To compensate for the initial loss of lithium ions, a lithium replenishing agent is typically added to either the positive or negative electrode material layer. Lithium foil or lithium silicide powder can be used for negative electrode replenishment; lithium ferrite (Li₅FeO₄) or other lithium-ion replenishing agents can be used for positive electrode replenishment. x M y O z Lithium replenishing agents or over-lithium compounds, etc. For example, Li5FeO4 lithium replenishing agents are typically mixed with the positive electrode active material and then coated onto the current collector. During the first charge of the battery, when the charging voltage reaches a certain value (approximately 3.6V vs. Li), + When the lithium ferrite (Li5FeO4) is above a certain level (e.g., Li3FeO4 is 1 / 2 Li), it undergoes electrochemical decomposition, releasing lithium ions and electrons.

[0057] But Li x M y O z Lithium supplements have poor conductivity; and the high Li content makes them prone to chemical reactions with air during storage, transportation, electrode preparation, and battery assembly, resulting in poor air stability; furthermore, Lix M y O z Oxygen generated during the decomposition of lithium additives may cause electrolyte decomposition and even battery fire. Currently, efforts are being made to improve the lithium content... x M y O z To improve the conductivity and air stability of lithium replenishing agents, carbon coating technology is typically used. However, carbon coating technology cannot shield the electrolyte from the decomposition effect of oxygen.

[0058] Based on this, see Figure 1 In a first aspect, this application provides a composite lithium supplement 10, comprising a core 110 and a shell 120 covering the surface of the core 110. The core 110 comprises Li x M y O z Lithium supplement and elemental. The casing 120 comprises lithium titanium aluminum phosphate. For example, the elemental includes one or more of elemental sulfur and elemental iron.

[0059] Where M is one or more of Fe, Co and Ni, 1≤x≤6, 1≤y≤6, 1≤z≤6.

[0060] The composite lithium replenisher provided in this application uses lithium titanium aluminum phosphate as a coating layer. The three-dimensional lattice channels of lithium titanium aluminum phosphate can ensure rapid lithium-ion migration. At the same time, the elemental iron and sulfur in the core have high electronic conductivity, which helps to build a continuous electronic pathway inside the lithium replenisher. The two work synergistically to improve the overall conductivity of the composite lithium replenisher. In addition, the chemical stability of the lithium titanium aluminum phosphate shell can physically isolate the lithium in the core. x M y O z The lithium supplement reacts with H2O and CO2 in the air, preventing it from absorbing moisture and hydrolyzing, causing lithium source loss, and generating inert impurities, thus giving the composite lithium supplement excellent air stability. Furthermore, elemental iron and sulfur can absorb Li. x M y O z The oxidative decomposition of lithium supplements generates oxygen, thereby reducing the amount of oxygen produced in the battery system. Furthermore, the lithium titanium aluminum phosphate casing can suppress Li... x M y O z The excessive reaction between the lithium replenishing agent and the electrolyte during the first charge, as well as the reaction between iron ions and the electrolyte, enable the composite lithium replenishing agent provided in this application to balance lithium replenishment efficiency and battery safety.

[0061] Therefore, the composite lithium replenisher of this application has good conductivity, air stability and low oxygen production, and it is beneficial to improve the charging capacity of the battery.

[0062] For example, Li x My O z The value of x in lithium supplements includes, but is not limited to, 1, 2, 3, 4, 5, or 6. Li x M y O z The value of y in lithium supplements includes, but is not limited to, 1, 2, 3, 4, 5, or 6. Li x M y O z The value of z in lithium supplements includes, but is not limited to, 1, 2, 3, 4, 5, or 6.

[0063] Lithium aluminum titanium phosphate (LATP) has a NASICON-type crystal structure, which consists of lithium ions (Li). + Aluminum ions (Al) 3+ Titanium ions (Ti) 4 + PO4 3- A three-dimensional network lattice structure formed by ionic bonding.

[0064] Preferably, Li x M y O z The lithium replenisher is Li5FeO4. This application found that using Li5FeO4 as the lithium replenisher in the core results in better compatibility with the elemental material and the casing 120. In this case, the composite lithium replenisher has better conductivity, higher air stability, and lower oxygen production, which is beneficial to improving the charging capacity of the battery.

[0065] In some of these examples, the core 110 includes Li x M y O z Lithium supplement and elemental iron, the casing 120 includes lithium titanium aluminum phosphate.

[0066] In other examples, the core 110 includes Li x M y O z The lithium supplement and elemental sulfur are present in the casing 120, which includes lithium titanium aluminum phosphate and elemental sulfur.

[0067] Understandably, since elemental iron is easily oxidized, it needs to be present in the core 110. Since elemental sulfur is not easily oxidized, it can also be present in the shell 120. Furthermore, since the method of forming elemental sulfur provided in the second aspect of this application is infiltration, some elemental sulfur will also be present in the shell 120.

[0068] In some of these examples, Li x M y O z The mass ratio of lithium supplement to elemental lithium is 10:(0.1~1). Understandably, Li... x M y Oz The mass ratio of lithium supplement to elemental lithium includes, but is not limited to, 10:0.1, 10:0.3, 10:0.4, 10:0.5, 10:0.6, 10:0.7, 10:0.8, 10:0.9, or 10:1, or any two of the above values ​​as endpoints. Further, Li... x M y O z The mass ratio of lithium supplement to elemental lithium is 10:(0.4~0.6). Li x M y O z The mass ratio of lithium supplement to elemental lithium is limited to the above range. This avoids both the problem of excessive oxygen production caused by insufficient elemental lithium content and the problem of decreased battery charging capacity caused by excessive elemental lithium content.

[0069] In some of these examples, Li x M y O z The mass ratio of lithium supplement to lithium aluminum titanium phosphate is 10:(0.5~5). Understandably, Li... x M y O z The mass ratio of lithium supplement to lithium aluminum phosphate includes, but is not limited to, 10:0.5, 10:1, 10:1.5, 10:2, 10:2.5, 10:3, 10:3.5, 10:4, 10:4.5, or 10:5, or any two of the above values ​​as endpoints. Further, Li... x M y O z The mass ratio of lithium supplement to lithium aluminum titanium phosphate is 10:(1.5~2.5). x M y O z When the mass ratio of lithium supplement to lithium titanium aluminum phosphate is within the above range, it avoids both the problem of restricted electron transport caused by excessive lithium titanium aluminum phosphate content and the problem of ineffective Li-isolation caused by insufficient lithium titanium aluminum phosphate content. x M y O z Lithium supplement and air, Li x M y O z The issues of lithium supplements and electrolytes limit the application of Li. x M y O z When the mass ratio of lithium replenisher to lithium titanium aluminum phosphate is within the above range, it is beneficial to improve the charging capacity of the battery.

[0070] In some of these examples, Li x M y O zThe average particle size of the lithium supplement is 10 μm to 20 μm. For example, Li... x M y O z The average particle size of the lithium supplement includes, but is not limited to, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, or 20 μm, or any two of the above values ​​as endpoints. x M y O z The particle size of the lithium supplement is within the above range, which facilitates the composite composition of core components such as elemental iron, and it is compatible with the coating process of lithium titanium aluminum phosphate, which helps to improve the overall performance of the composite lithium supplement.

[0071] In some examples, the average particle size of elemental iron is 200 nm to 400 nm. For example, the average particle size of elemental iron includes, but is not limited to, 200 nm, 220 nm, 230 nm, 240 nm, 260 nm, 280 nm, 300 nm, 320 nm, 340 nm, 360 nm, 380 nm, or 400 nm, or any two of the above values ​​as endpoints. Elemental iron and Li within this particle size range... x M y O z The lithium replenishing agents work synergistically to enable elemental iron to be evenly dispersed in the composite lithium replenishing agent and to build an electron conduction network; at the same time, they can synergistically improve the battery charging capacity.

[0072] In some examples, the average particle size of lithium titanium aluminum phosphate is 200 nm to 400 nm. For example, the average particle size of lithium titanium aluminum phosphate includes, but is not limited to, 200 nm, 220 nm, 230 nm, 240 nm, 260 nm, 280 nm, 300 nm, 320 nm, 340 nm, 360 nm, 380 nm, or 400 nm, or any two of the above values ​​as endpoints. Lithium titanium aluminum phosphate within this particle size range can uniformly coat the core surface to form a dense and thin functional shell, which can efficiently isolate air and electrolyte to ensure the stability of the lithium replenishing agent, provide sufficient channels for lithium-ion transport, and simultaneously adapt to the overall structural compatibility and electrode formability of composite lithium replenishing agents.

[0073] In some of these examples, the shell 120 also includes glucose. Li x M y O z The mass ratio of lithium supplement to glucose is 10:(0.1~1.5). For example, Li... x M y O zThe mass ratio of lithium supplement to glucose includes, but is not limited to, 10:0.1, 10:0.4, 10:0.5, 10:0.6, 10:1, or 10:1.5, or any two of the above values ​​as endpoints. This application has found that including glucose in the casing, in synergy with lithium aluminum titanium phosphate, can further improve the overall conductivity of the composite lithium supplement.

[0074] A second aspect of this application provides a method for preparing a composite lithium supplement, comprising the following steps:

[0075] Li x M y O z A composite lithium supplement is prepared by first fusion coating of a lithium supplement agent, nano-iron powder, and lithium titanium aluminum phosphate under glucose-containing or glucose-free conditions to form a core and a shell coating the outer surface of the core; the core includes Li x M y O z Lithium supplement and elemental iron, the casing includes lithium titanium aluminum phosphate.

[0076] Where M is one or more of Fe, Co and Ni, 1≤x≤6, 1≤y≤6, 1≤z≤6.

[0077] In other examples, the preparation method includes the following steps: [The text abruptly ends here, so the translation stops.] x M y O z A lithium supplement and lithium aluminum titanium phosphate undergo a second fusion coating process with or without glucose to form a core and a shell coating the outer surface of the core, thus preparing a core-shell intermediate; the core in the core-shell intermediate includes Li x M y O z A lithium supplement agent is prepared by mixing a core-shell intermediate with sulfur powder and heating the mixture until the sulfur powder melts and diffuses into the shell and core to form elemental sulfur. In this example, the melting temperature of the sulfur powder is 110℃~130℃.

[0078] In some of these examples, Li x M y O z The mass ratio of lithium supplement to nano iron powder is 10:(0.1~1).

[0079] In some of these examples, Li x M y O z The mass ratio of lithium supplement to sulfur powder is 10:(0.1~1).

[0080] In some of these examples, Li x M y Oz The mass ratio of lithium supplement to lithium aluminum phosphate is 10:(0.5~5).

[0081] In some of these examples, Li x M y O z The mass ratio of lithium supplement to glucose is 10:(0.1~1.5).

[0082] In some of these examples, Li x M y O z The average particle size of the lithium supplement is 10 μm to 20 μm.

[0083] In some of these examples, the average particle size of the nano-iron powder is 200 nm to 400 nm.

[0084] In some of these examples, the average particle size of lithium titanium aluminum phosphate is 200 nm to 400 nm.

[0085] It is understood that the Li described in the second aspect of this application x M y O z The mass ratio and properties of the lithium supplement, nano-iron powder, and lithium titanium aluminum phosphate are the same as those described in the first aspect of this application, and therefore will not be repeated here. It is understood that in this application, nano-iron powder is a raw material, and it is elemental iron in the composite lithium supplement.

[0086] In some examples, the process parameters for the first and second fusion coatings independently include: a temperature of 640°C to 660°C and a rotation speed of 1400 rpm to 1600 rpm. For example, the temperature of the fusion coating includes, but is not limited to, 640°C, 645°C, 650°C, 655°C, or 660°C, or any two of the above values ​​as endpoints. The rotation speed of the fusion coating includes, but is not limited to, 1400 rpm, 1450 rpm, 1500 rpm, 1550 rpm, or 1600 rpm, or any two of the above values ​​as endpoints.

[0087] For example, the equipment used for fusion coating includes, but is not limited to, high-energy fusion coating machines.

[0088] In some of these examples, Li x M y O z The lithium supplement is Li5FeO4. The preparation steps of Li5FeO4 lithium supplement include:

[0089] P10: Fe2O3 and Li2O are mixed and ground to prepare a mixture.

[0090] P20: The mixture is sintered in an inert gas atmosphere to prepare Li5FeO4 lithium supplement.

[0091] To ensure that Fe2O3 and Li2O react completely to form Li5FeO4, in some examples, the molar ratio of Fe2O3 to Li2O in step P10 is 1:(4.5~6). For example, the molar ratio of Fe2O3 to Li2O includes, but is not limited to, 1:4.5, 1:5, 1:5.3, 1:5.4, 1:5.5, 1:5.6, or 1:6, or any two of the above values ​​as endpoints.

[0092] In some examples, in step P20, the sintering process parameters include heating to 600°C to 700°C at a heating rate of 4°C / min to 6°C / min. For example, the sintering equipment includes, but is not limited to, a tube furnace. In some examples, the sintering time is 20h to 30h. Further, the heating rate includes, but is not limited to, 4°C / min, 5°C / min, or 6°C / min, or any two of the above values ​​as endpoints. The temperature after heating includes, but is not limited to, 600°C, 620°C, 640°C, 650°C, 660°C, 680°C, or 700°C, or any two of the above values ​​as endpoints.

[0093] A third aspect of this application provides a positive electrode sheet, comprising a current collector and a positive active material layer loaded on the surface of the current collector, wherein the positive active material layer comprises a positive active material and a lithium replenishing agent; the lithium replenishing agent is a composite lithium replenishing agent according to any of the first aspects of this application, or a composite lithium replenishing agent prepared by any of the preparation methods of the second aspect of this application.

[0094] In some examples, the mass fraction of the composite lithium supplement in the positive electrode active material layer is 1.5% to 3%. For example, the mass fraction of the composite lithium supplement in the positive electrode active material layer includes, but is not limited to, 1.5%, 1.6%, 1.7%, 1.8%, 1.85%, 1.89%, 1.9%, 1.95%, 2%, 2.5%, or 3%, or any two of the above values ​​as endpoints.

[0095] The positive electrode active material layer also includes conductive agents and binders. For example, conductive agents include, but are not limited to, carbon nanotubes and conductive carbon black.

[0096] Furthermore, by mass fraction, the positive electrode active material layer comprises: 93% to 95% positive electrode active material, 1.5% to 3% composite lithium supplement, 1% to 2% conductive agent, and 1.5% to 3% binder.

[0097] In some examples, the positive electrode active material is lithium iron phosphate (LFP). This application found that composite lithium replenishing agents are more compatible with the positive electrode active material LFP. In this case, the composite lithium replenishing agent can replenish the lithium ions required for SEI film formation, and the two have compatible electrochemical windows and no obvious side reactions, which can synergistically ensure the charging capacity of the battery.

[0098] In some examples, this application also provides a method for preparing a positive electrode sheet, comprising the following steps: a1, mixing a positive electrode active material, a composite lithium supplement agent, a conductive agent, and a binder in a solvent to prepare a positive electrode active slurry. a2, coating the positive electrode active material onto the surface of a positive electrode current collector, drying, and then statically pressing to prepare a positive electrode sheet. As a further example, in step a1, the solid content of the positive electrode active slurry is 60%~75%. In step a2, the drying temperature is 115℃~125℃. The drying time is 10h~14h. The static pressing pressure is 8MPa~12MPa. The static pressing time is 3min~6min.

[0099] In a fourth aspect, this application provides a battery including the positive electrode sheet of the third aspect of this application.

[0100] Furthermore, the battery also includes a negative electrode and an electrolyte.

[0101] For example, the negative electrode sheet includes a negative current collector and a negative active material layer disposed on the surface of the negative current collector. As a further example, the negative active material in the negative active material layer is graphite.

[0102] The following detailed embodiments illustrate this application in more detail. It should also be understood that the following embodiments are for further explanation only and should not be construed as limiting the scope of protection of this application. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of this application fall within the scope of protection of this application. The specific process parameters, etc., in the following embodiments are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the range based on the description herein, and are not necessarily limited to the specific values ​​in the embodiments below.

[0103] Example 1

[0104] (1) Preparation of Li5FeO4 lithium supplement: Fe2O3 and Li2O were mixed and ground at a molar ratio of 1:5.5 to prepare a mixture. The mixture was sintered at 650℃ for 24h under a nitrogen atmosphere at a heating rate of 5℃ / min to prepare Li5FeO4 lithium supplement.

[0105] (2) Li5FeO4 lithium supplement (average particle size of 15μm), lithium titanium aluminum phosphate (average particle size of 300nm) and nano iron powder (average particle size of 300nm) were fused and coated in a mass ratio of 10:2:0.5 (using a high-energy fusion coating machine) to form a core and a shell coating the outer surface of the core. The core included Li5FeO4 lithium supplement and elemental iron, and the shell included lithium titanium aluminum phosphate. The parameters for the first fusion coating were: temperature of 650℃, rotation speed of 1500rpm, and time of 10 hours; to prepare a composite lithium supplement.

[0106] Examples 2 to 7

[0107] Examples 2 through 7 are basically the same as Example 1, the main difference being that the mass ratio of Li5FeO4 lithium supplement, lithium titanium aluminum phosphate, and elemental iron in Examples 2 through 7 is different from that in Example 1. The mass ratios of Li5FeO4 lithium supplement, lithium titanium aluminum phosphate, and nano-iron powder / elemental iron in Examples 2 through 7 are shown in Table 1.

[0108] Table 1 Mass ratio of Li5FeO4 lithium supplement, lithium titanium aluminum phosphate, and nano iron powder / elemental iron

[0109]

[0110] Example 8

[0111] (1) Preparation of Li5FeO4 lithium supplement: Fe2O3 and Li2O were mixed and ground at a molar ratio of 1:5.5 to prepare a mixture. The mixture was sintered at 650℃ for 24h under a nitrogen atmosphere at a heating rate of 5℃ / min to prepare Li5FeO4 lithium supplement.

[0112] (2) Li5FeO4 lithium supplement (average particle size of 15μm) and lithium titanium aluminum phosphate (average particle size of 300nm) are fused and coated in a second mass ratio of 10:2 (high-energy fusion coating machine is selected) to form a core and a shell coated on the outer surface of the core. The core includes Li5FeO4 lithium supplement and the shell includes lithium titanium aluminum phosphate. The parameters of the second fusion coating are: temperature of 650℃ and rotation speed of 1500rpm; LATP coated Li5FeO4 powder (core-shell intermediate) is prepared.

[0113] (3) After mixing and grinding the LATP-coated Li5FeO4 powder obtained in the second step with elemental sulfur powder again (the mass ratio of Li5FeO4 and elemental sulfur powder included in the LATP-coated Li5FeO4 powder is 10:1), transfer it to an aluminum-plastic film bag and bake it in a vacuum oven at 120°C for 2 hours to obtain the final product.

[0114] Example 9

[0115] (1) Preparation of Li5FeO4 lithium supplement: Fe2O3 and Li2O were mixed and ground at a molar ratio of 1:5.5 to prepare a mixture. The mixture was sintered at 650℃ for 24h under a nitrogen atmosphere at a heating rate of 5℃ / min to prepare Li5FeO4 lithium supplement.

[0116] (2) Li5FeO4 lithium supplement (average particle size of 15 μm), lithium titanium aluminum phosphate (average particle size of 300 nm), and glucose were fused and coated in a mass ratio of 10:2:0.5 (using a high-energy fusion coating machine) to form a core and a shell coating the outer surface of the core. The core included Li5FeO4 lithium supplement, and the shell included lithium titanium aluminum phosphate and glucose. The parameters for fusion coating were: temperature of 650℃ and rotation speed of 1500 rpm. LATP-coated Li5FeO4 powder (core-shell intermediate) was prepared.

[0117] (3) After mixing and grinding the LATP-coated Li5FeO4 powder obtained in the second step with elemental sulfur powder again (the mass ratio of Li5FeO4 and elemental sulfur powder included in the LATP-coated Li5FeO4 powder is 10:1), transfer it to an aluminum-plastic film bag and bake it in a vacuum oven at 120°C for 2 hours to obtain the final product.

[0118] Example 10

[0119] (1) Preparation of Li5FeO4 lithium supplement: Fe2O3 and Li2O were mixed and ground at a molar ratio of 1:5.5 to prepare a mixture. The mixture was sintered at 650℃ for 24h under a nitrogen atmosphere at a heating rate of 5℃ / min to prepare Li5FeO4 lithium supplement.

[0120] (2) Li5FeO4 lithium supplement (average particle size of 15 μm), lithium titanium aluminum phosphate (average particle size of 300 nm), and glucose are fused and coated in a second mass ratio of 10:2:1 (using a high-energy fusion coating machine) to form a core and a shell coating the outer surface of the core. The core includes Li5FeO4 lithium supplement, and the shell includes lithium titanium aluminum phosphate and glucose. The parameters for the second fusion coating are: temperature of 650℃ and rotation speed of 1500 rpm. LATP-coated Li5FeO4 powder (core-shell intermediate) is prepared.

[0121] (3) After mixing and grinding the LATP-coated Li5FeO4 powder obtained in the second step with elemental sulfur (the mass ratio of Li5FeO4 and elemental sulfur powder included in the LATP-coated Li5FeO4 powder is 10:1), transfer it to an aluminum-plastic film bag and bake it in a vacuum oven at 120°C for 2 hours to obtain the final product.

[0122] Comparative Example 1

[0123] Preparation of composite lithium supplement: Fe2O3 and Li2O were mixed and ground at a molar ratio of 1:5.5, and then sucrose carbon source (0.05 mol) was added to prepare a mixture. The mixture was sintered at 650℃ for 24 h under a nitrogen atmosphere at a heating rate of 5℃ / min to prepare Li5FeO4 composite lithium supplement.

[0124] Test case

[0125] Fabrication of pouch cells:

[0126] (I) Preparation of the positive electrode sheet: The positive electrode active material LFP, the composite lithium supplement agent from the above examples and comparative examples, the conductive agent carbon nanotubes (CNT), the conductive agent conductive carbon black (SP), and the binder PVDF were dissolved in solvent NMP at a mass ratio of 94.61:1.89:1:0.5:2. The mass ratio of positive electrode active material LFP to solvent NMP was 94.61:42. The mixture was stirred at low speed for 24 hours. After stirring until homogeneous, a positive electrode active slurry was prepared. The positive electrode active slurry was coated onto aluminum foil using an adjustable coating applicator and vacuum dried at 120°C for 12 hours. After the temperature dropped to room temperature, it was statically pressed at 10 MPa for 5 minutes. After weighing, it was placed in a glove box for later use to prepare the positive electrode sheet.

[0127] (II) Preparation of the negative electrode sheet: Graphite, conductive carbon black (SP), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were dissolved in deionized water at a mass ratio of 95.2:1.2:1.4:2.2, with a graphite to deionized water mass ratio of 95.2:48. The mixture was stirred at low speed for 10 hours until homogeneous, thus preparing the negative electrode active slurry. The negative electrode active slurry was coated onto copper foil using an adjustable coating applicator and vacuum dried at 80°C for 12 hours. After the temperature dropped to room temperature, it was statically pressed at 10 MPa for 5 minutes, weighed, and placed in a glove box for later use, thus preparing the negative electrode sheet.

[0128] (III) Preparation of electrolyte: Lithium hexafluorophosphate (LiPF6) was added to a mixed solution of dehydrated ethylene carbonate (EC) and ethyl methyl carbonate (EMC), wherein the volume ratio of EC to EMC was 3:7 and the concentration of LiPF6 was 14 wt%. Then, 2 wt% vinylene carbonate (VC) was added and completely dissolved to obtain the electrolyte.

[0129] (iv) Assembly process of soft-pack battery: The positive electrode and negative electrode are separated by a separator to prepare a stacked battery. 4.5g of electrolyte is added dropwise using a pipette, and the battery is left to stand to obtain a soft-pack battery.

[0130] Battery testing: (1) Charging capacity test: Charge the battery to 3.2V with a current of 50mA in an environment of 45℃, and then charge it to 4.2V with a current of 500mA. Record the charging capacity at this time. (2) Gas production test: Place the battery before and after charging into a beaker containing 100mL of water, and measure the height of the gas in the beaker to obtain the gas volume. The corresponding test results are shown in Table 2.

[0131] Table 2 Performance test results in the examples and comparative examples

[0132]

[0133] As can be seen from Tables 1 and 2, the composite lithium replenisher of this application has superior performance compared to the carbon-coated lithium replenisher in Comparative Example 1. It is more conducive to reducing the generation of gases such as oxygen and can improve the charging capacity of the battery.

[0134] Examples 1 through 3 are essentially the same, the main difference being the amount of nano-iron powder added. A comparison of Examples 1 through 3 shows that a slightly lower content of nano-iron powder results in a slightly higher gas production volume; a slightly higher content of nano-iron powder leads to a decrease in battery charging capacity. Examples 1, 4, and 5 are essentially the same, as are Examples 3 and 6, the main difference being the amount of lithium titanium aluminum phosphate added. A comparison of Examples 1, 4, and 5, and Examples 3 and 6, shows that even slight variations in the amount of lithium titanium aluminum phosphate added lead to a decrease in charging capacity. Examples 8 through 10 all use elemental sulfur. The main difference between Examples 8, 9, and 10 is the amount of glucose added; Example 9 has the optimal amount of glucose, resulting in the highest charging capacity. Furthermore, this application also found that when elemental iron is used, the amount of glucose added shows the same trend as with the aforementioned elemental sulfur.

[0135] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0136] The embodiments described above are merely illustrative of several implementation methods of this application, intended to facilitate a detailed understanding of the technical solutions of this application, but should not be construed as limiting the scope of protection of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the scope of protection of this application. It should be understood that technical solutions obtained by those skilled in the art based on the technical solutions provided in this application through logical analysis, reasoning, or limited experimentation are all within the scope of protection of the appended claims. Therefore, the scope of protection of this patent application should be determined by the content of the appended claims, and the specification can be used to interpret the content of the claims.

Claims

1. A composite lithium supplement, characterized in that, It includes a core and a shell covering the surface of the core; The core includes Li x M y O z The lithium supplement and the element, wherein M is one or more of Fe, Co and Ni, 1≤x≤6, 1≤y≤6, 1≤z≤6; the element includes one or more of sulfur and iron. The casing comprises lithium titanium aluminum phosphate.

2. The composite lithium supplement agent according to claim 1, characterized in that, The composite lithium supplement meets one of the following characteristics: (1) The core body includes the Li x M y O z The lithium supplement and the elemental iron, wherein the casing comprises the lithium aluminum titanium phosphate; (2) The core includes the Li x M y O z The lithium supplement and the elemental sulfur, the casing comprising the lithium titanium aluminum phosphate and the elemental sulfur.

3. The composite lithium supplement agent according to claim 1, characterized in that, The shell also includes glucose, the Li x M y O z The mass ratio of lithium supplement to glucose is 10:(0.1~1.5).

4. The composite lithium supplement agent according to any one of claims 1 to 3, characterized in that, The Li x M y O z The mass ratio of lithium supplement to the element is 10:(0.1~1); and / or, The Li x M y O z The mass ratio of the lithium supplement to the lithium aluminum titanium phosphate is 10:(0.5~5); and / or, The Li x M y O z The lithium supplement is Li5FeO4 lithium supplement; and / or, The Li x M y O z The average particle size of the lithium supplement is 10 μm to 20 μm; and / or, The average particle size of the iron element is 200 nm to 400 nm; and / or, The average particle size of the lithium titanium aluminum phosphate is 200nm~400nm.

5. A method for preparing a composite lithium supplement, characterized in that, Includes the following steps: Li x M y O z The composite lithium supplement is prepared by first fusion coating of a lithium supplement agent, nano-iron powder, and lithium titanium aluminum phosphate under conditions with or without glucose to form a core and a shell covering the outer surface of the core; the core comprises Li x M y O z Lithium supplement and elemental iron, wherein the shell comprises lithium aluminum titanium phosphate; Or, Li x M y O z A lithium supplement and lithium aluminum titanium phosphate are subjected to a second fusion coating in the presence or absence of glucose to form a core and a shell covering the outer surface of the core, thus preparing a core-shell intermediate; the core in the core-shell intermediate comprises Li x M y O z A lithium supplement agent, wherein the shell comprises lithium titanium aluminum phosphate; the core-shell intermediate is mixed with sulfur powder, heated until the sulfur powder melts, and diffuses into the shell and core to form elemental sulfur, thereby preparing the composite lithium supplement agent; Where M is one or more of Fe, Co and Ni, 1≤x≤6, 1≤y≤6, 1≤z≤6.

6. The method for preparing the composite lithium supplement according to claim 5, characterized in that, The Li x M y O z The average particle size of the lithium supplement is 10 μm to 20 μm; and / or, The average particle size of the nano-iron powder is 200nm~400nm; and / or, The average particle size of the lithium titanium aluminum phosphate is 200nm~400nm.

7. The method for preparing the composite lithium supplement according to claim 5, characterized in that, The process parameters for the first and second fusion coatings are each independent of the following: Temperature range: 640℃~660℃; Rotation speed range: 1400rpm~1600rpm.

8. The method for preparing the composite lithium supplement according to claim 6 or 7, characterized in that, The Li x M y O z The lithium supplement is a Li5FeO4 lithium supplement, and the preparation steps of the Li5FeO4 lithium supplement include: Fe2O3 and Li2O were mixed and ground to prepare a mixture. The mixture was sintered in an inert gas atmosphere to prepare the Li5FeO4 lithium supplement. Wherein, the molar ratio of Fe2O3 to Li2O is 1:(4.5~6); and / or, The sintering process parameters include: heating to 600℃~700℃ at a heating rate of 4℃ / min~6℃ / min.

9. A positive electrode sheet, characterized in that, It includes a current collector and a positive electrode active material layer loaded on the surface of the current collector, wherein the positive electrode active material layer includes a positive electrode active material and a lithium supplement agent; The lithium replenishing agent is the composite lithium replenishing agent according to any one of claims 1 to 4, or the composite lithium replenishing agent prepared by any one of claims 5 to 8.

10. A battery, characterized in that, Includes the positive electrode sheet as described in claim 9.

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