Positive electrode lithium supplementing additive, preparation method and application thereof

Abstract

The application discloses a positive electrode lithium supplementing additive and a preparation method and application thereof. The positive electrode lithium supplementing additive is of a core-shell structure, the core of the core-shell structure comprises a positive electrode lithium supplementing material, and the coating layer covering the core comprises a polymer containing a piperidyl group. The polymer used in the positive electrode lithium supplementing additive gives the coating layer the functions of inhibiting active oxygen and capturing free radicals generated in the charging and discharging of a lithium ion battery, so that the gas generation amount of the lithium ion battery is obviously reduced in the charging and discharging process, the volume expansion of the lithium ion battery is reduced, the stability and safety of the charging and discharging of the lithium ion battery are effectively improved, the lithium supplementing effect is improved, the preparation method of the positive electrode lithium supplementing additive can guarantee that the structure and electrochemical performance of the prepared positive electrode lithium supplementing additive are stable, the efficiency is high, and the production cost is saved. The positive electrode lithium supplementing additive can be applied to positive electrode plates and secondary batteries.

Description

Technical Field

[0001] This application belongs to the field of secondary batteries, specifically relating to a positive electrode lithium supplementation additive, its preparation method, and its application. Background Technology

[0002] The oil and energy crisis of the 1960s and 70s forced people to search for new alternative energy sources. With increasing awareness of environmental protection and the energy crisis, lithium-ion batteries, due to their high operating voltage and energy density, relatively low self-discharge, lack of memory effect, absence of heavy metal pollution such as lead and cadmium, and ultra-long cycle life, are considered one of the most promising energy sources. Lithium-ion batteries are widely used in electric vehicles, power tools, portable consumer electronics, and energy storage, among other applications.

[0003] Currently, the most commonly used positive electrode materials for lithium-ion batteries include lithium iron phosphate, lithium nickel cobalt manganese (aluminum) oxide ternary materials (commonly known as ternary materials), lithium cobalt oxide, and lithium manganese oxide. The most widely used negative electrode materials are carbon-based graphite materials and silicon-based negative electrode materials. Although lithium-ion batteries have many advantages, during the first charge, a solid electrolyte interphase (SEI) film typically forms on the negative electrode surface. This process consumes a significant amount of Li. + This means that Li is extracted from the cathode material. + Some of the lithium is irreversibly consumed, resulting in a decrease in the reversible specific capacity of the battery cell. The anode material, especially silicon-based anode materials, further consumes Li. + This results in lithium loss from the cathode material, reducing the initial coulombic efficiency and capacity of the lithium-ion battery. For example, in a lithium-ion battery system using a graphite anode, approximately 10% of the lithium source is consumed during the first charge. When using anode materials with high specific capacity, such as alloys (silicon, tin, etc.), oxides (silicon oxide, tin oxide), and amorphous carbon anodes, the consumption of the cathode lithium source will be further aggravated.

[0004] To improve the low coulombic efficiency caused by irreversible losses at the negative electrode, researchers have developed lithium-rich compounds as additives to address the problem of irreversible lithium-ion losses during the first charge and discharge cycle.

[0005] However, research and practical applications have revealed that the use of existing lithium supplementation additives has also led to an increase in gas production during the formation stage of lithium-ion batteries. This can cause gas expansion inside the sealed battery system, resulting in battery volume expansion and safety issues.

[0006] Currently, research on lithium-ion battery additives is still in its initial stages, and stable, mature products have not yet been developed. There are no clear and systematic research results regarding the gas generation mechanism of lithium-ion battery additives. For traditional lithium-ion batteries, reactions such as SEI film decomposition, electrolyte decomposition, and the reaction between the negative electrode active material and the binder easily lead to gas generation. Furthermore, these reactions are often not independent and may occur simultaneously. To address the aforementioned gas generation problem in lithium-ion batteries, current methods include adding acid anhydrides, cyclic esters such as γ-butyrolactone, and polynitrile compounds as additives to the electrolyte to form protective films on both the positive and negative electrodes, thereby suppressing gas generation. However, these measures often suffer from poor ion conductivity of the protective film, increased impedance, and instability of the protective films. Therefore, how to effectively improve the gas generation problem caused by the use of lithium-ion battery additives without affecting other performance characteristics of lithium-ion batteries is a pressing issue that has a significant impact on improving lithium-ion battery performance. Summary of the Invention

[0007] The purpose of this application is to overcome the above-mentioned deficiencies of the prior art and provide a positive electrode lithium replenishment additive and its preparation method to solve the technical problem that existing positive electrode lithium replenishment additives lead to an increase in gas production in lithium-ion batteries.

[0008] Another objective of this application is to provide a positive electrode and a secondary battery containing the electrode to solve the technical problem that the initial coulombic efficiency of existing secondary batteries is improved but the gas production is increased.

[0009] To achieve the aforementioned objectives, a first aspect of this application provides a positive electrode lithium replenishment additive. This positive electrode lithium replenishment additive has a core-shell structure, wherein the core of the core-shell structure comprises a positive electrode lithium replenishment material, and the coating layer encapsulating the core contains a polymer with the following general molecular formula I:

[0010]

[0011] In general formula I, X1, X2, X3, and X4 are each of hydrogen atoms and alkyl groups having 1 to 3 carbon atoms, and R is a polymer chain segment.

[0012] Furthermore, the alkyl group includes any one of methyl, ethyl, propyl, and isopropyl.

[0013] Furthermore, the polymer chain segment includes at least one segment selected from carbon chain polymer chains, heterochain polymer chains, and non-carbon chain polymer chains.

[0014] Furthermore, the piperidine group contained in general formula I is a branched or terminal group.

[0015] Furthermore, the polymer content in the positive electrode lithium supplementation additive is 0.1%-5% by mass.

[0016] Furthermore, X1, X2, X3, and X4 are all methyl groups, and R is one or more of the following: polyolefin, polyacrylate, polymethacrylate, polyester, polyamide, polyurethane, polyether, polysilane, and polysiloxane.

[0017] Specifically, the polymer includes one or more of the following molecular structural formulas I1 to I6:

[0018]

[0019] Furthermore, the coating layer includes a polymer coating layer, and the polymer contained in the polymer coating layer includes polymers.

[0020] Furthermore, positive electrode lithium replenishment materials include positive electrode lithium replenishment materials containing oxygen atoms.

[0021] Furthermore, the coating layer also includes a hydrophobic encapsulation layer, which encapsulates the core, and the polymer coating layer is applied to the surface of the hydrophobic encapsulation layer that is away from the core.

[0022] Furthermore, the hydrophobic encapsulation layer includes at least one of an ion conductor encapsulation layer and an electronic conductor encapsulation layer.

[0023] Furthermore, the hydrophobic encapsulation layer contains a polymer with the molecular structure shown in Formula I.

[0024] A second aspect of this application provides a method for preparing the cathode lithium supplement additive of this application. The method for preparing the cathode lithium supplement additive of this application includes the following steps:

[0025] The positive electrode lithium replenishment material particles are mixed with a solution containing a polymer with the following general molecular structure formula I to form a mixture.

[0026] In a protective atmosphere, the mixture is dried to disperse the polymer on the surface of the positive electrode lithium replenishment material particles, thus obtaining a positive electrode lithium replenishment additive.

[0027]

[0028] In general formula I, X1, X2, X3, and X4 are each of hydrogen atoms and alkyl groups with 1 to 3 carbon atoms, and R is a polymer chain segment.

[0029] Furthermore, the polymer forms a polymer coating layer, which coats the positive electrode lithium replenishment material particles.

[0030] Furthermore, the cathode lithium replenishment material particle raw material includes a core containing the cathode lithium replenishment material and a hydrophobic encapsulation layer covering the core.

[0031] A third aspect of this application provides a positive electrode sheet. The positive electrode sheet includes a positive current collector and a positive active layer bonded to the surface of the positive current collector, wherein the positive active layer contains the positive lithium supplement additive of this application or a positive lithium supplement additive prepared by the method for preparing the positive lithium supplement additive of this application.

[0032] A fourth aspect of this application provides a secondary battery. This application includes a positive electrode and a negative electrode, wherein the positive electrode is the same as the one described in this application.

[0033] Furthermore, the secondary battery retains more than 87% of its capacity after 300 cycles at room temperature.

[0034] Furthermore, the secondary battery retains more than 80% of its capacity after 300 cycles at 45°C.

[0035] Furthermore, the thickness change rate of the secondary battery after 300 cycles at 45°C is less than 15%.

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

[0037] The polymer of general formula I contained in the coating layer of the cathode lithium-ion additive of this application can effectively suppress the generation of active oxygen inside the lithium-ion material on the one hand, and effectively suppress the generation of free radicals during the charging and discharging process of the lithium-ion battery on the other hand, and can effectively capture the free radicals generated during the charging and discharging process of the lithium-ion battery to form stabilizers. Therefore, the polymer of general formula I contained in the cathode lithium-ion additive of this application endows the coating layer with the function of suppressing active oxygen and capturing free radicals generated during the charging and discharging process of the lithium-ion battery, which significantly reduces the amount of gas generated during the charging and discharging process of the lithium-ion battery, reduces the volume expansion of the lithium-ion battery, and thus effectively improves the stability and safety of the charging and discharging of the lithium-ion battery, while improving its lithium-ion replenishment effect.

[0038] The method for preparing the cathode lithium-ion supplement additive in this application can effectively disperse the polymer shown in General Formula I on the surface of the cathode lithium-ion supplement material particles. This endows the prepared cathode lithium-ion supplement additive with the functions of fully exerting lithium-ion supplementation, while also inhibiting reactive oxygen species and capturing free radicals generated during the charging and discharging of lithium-ion batteries, thus significantly reducing gas production during charging and discharging. Furthermore, the preparation method ensures the stability of the structure and electrochemical performance of the prepared cathode lithium-ion supplement additive, and is highly efficient, saving production costs.

[0039] Because the positive electrode sheet of this application contains the positive electrode lithium replenishment additive of this application, the positive electrode lithium replenishment additive contained in the positive electrode sheet of this application can play a lithium replenishment role in the first charging process. At the same time, it can effectively capture and consume harmful groups generated by lithium-ion batteries during charging and discharging, effectively reduce the gas generation phenomenon of lithium-ion batteries during charging and discharging, thereby effectively improving the stability and safety of lithium-ion battery charging and discharging.

[0040] The secondary battery of this application produces little gas during cycling, which can effectively reduce or avoid phenomena such as volume expansion. It has high cycle performance, thus having high safety performance, long working life, high initial coulombic efficiency and secondary battery capacity, and stable electrochemical performance. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the structure of a positive electrode lithium supplement additive according to an embodiment of this application;

[0043] Figure 2 This is another structural schematic diagram of the positive electrode lithium supplementation additive in the embodiments of this application. Detailed Implementation

[0044] To make the technical problems, technical solutions, and beneficial effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0045] In this application, the term "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects have an "or" relationship.

[0046] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c", or "at least one of a, b, and c", can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0047] It should be understood that in the various embodiments of this application, the order of the above processes does not imply the order of execution. Some or all steps may be executed in parallel or sequentially. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0048] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. The singular forms “a,” “the,” and “the” used in the embodiments of this application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0049] The weights of the relevant components mentioned in the embodiments of this application can refer not only to the specific content of each component, but also to the proportional relationship between the weights of the components. Therefore, any scaling up or down of the content of the relevant components according to the embodiments of this application is within the scope disclosed in the embodiments of this application. Specifically, the mass described in the embodiments of this application can be a mass unit known in the chemical industry, such as μg, mg, g, or kg.

[0050] The terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0051] Numerous studies have shown that during the formation of the SEI film in lithium-ion batteries, as well as during charging and discharging, reactions such as SEI film decomposition, electrolyte decomposition, and reactions between the negative electrode active material and the binder often involve the formation of various free radicals. These free radicals can combine with each other or further trigger other chain reactions, ultimately producing gas. When lithium-ion batteries contain lithium replenishment additives, the amount of gas produced during the first charge also increases.

[0052] To address this problem, firstly, embodiments of this application provide a positive electrode lithium replenishment additive. The positive electrode lithium replenishment additive of this application embodiment has a core-shell structure, as shown below... Figure 1 As shown, it includes a core 01 and a coating layer 02 covering the core 01.

[0053] The core 01 includes a positive electrode lithium replenishment material. Thus, the core 01 is rich in lithium, ensuring that the positive electrode lithium replenishment additive in this embodiment can provide abundant lithium. When added to the positive electrode as a positive electrode lithium replenishment additive, it acts as a "sacrificial agent" during the first charging cycle, releasing as many lithium ions as possible at once to replenish the irreversible lithium ions consumed in the formation of the SEI film at the negative electrode, thereby improving the first coulombic efficiency of the lithium-ion battery.

[0054] The cathode lithium replenishment material contained in the core 01 can be a commonly used cathode lithium replenishment material, or a cathode lithium replenishment material modified or altered based on a commonly used cathode lithium replenishment material, or a newly developed cathode lithium replenishment material. In the embodiments of this application, combined with the characteristics of the coating layer 02 described below, it is a cathode lithium replenishment material that is relatively prone to gas generation, such as a cathode lithium replenishment material containing oxygen atoms.

[0055] As in the embodiments, the oxygen-containing cathode lithium replenishment material described above may include L x M y N z O q Li w At least one of O. Wherein, L x M y N z O q In the molecular formula, L represents Li or / and a mixture of Li and at least one of K and Na (not exceeding 30%); M includes at least one of Fe, Co, Ni, Mn, V, Fe-Co, Cu, Mo, Al, Ti, and Mg; N includes at least one of Fe, Co, Mn, Ni, Si, Al, or other equivalent or different valence metals; O represents oxygen; x is 4-6, y is 0.7-1.0, z is 0-0.3, and q is 4-5. Therefore, based on the element type indicated by M, the lithium replenishment material can be at least one of iron-based, manganese-based, or nickel-based lithium materials. When z is zero, the L... x M y N z O q It can be a doped or undoped cathode lithium replenishment material. In a specific embodiment, L x M y N z O q In this case, M is Fe and N is Al. At this time, L... x My N z O q The lithium-rich lithium supplementation material shown can be Li5Fe 0.98 Al 0.02 O4. It can also include, but is not limited to, Li2NiO2, Li5FeO4, LiCoO2, Li2MnO2, LiMn2O4, LiFePO4, etc. Li w In the O molecular formula, O represents oxygen; w is 1.5-3.5. These lithium-rich materials are rich in lithium and can release lithium ions during the first charge cycle, effectively replenishing lithium. When the lithium-rich material has an anti-fluorite structure, it can also improve the unidirectional capacity characteristics of the lithium-rich material, thereby ensuring the lithium-rich effect of the positive electrode lithium-rich additive of this application. When the lithium-rich material contains aluminum doping, Al atoms exist in the form of replacing iron atoms in the lattice. This form of Al atoms can broaden the lithium-ion transport channels and increase the lithium-ion extraction rate. Of course, the core 01 can contain not only positive electrode lithium-rich additives containing oxygen atoms, but also other lithium-rich materials. More importantly, these oxygen-containing positive electrode lithium-rich materials, while fully exerting their lithium-rich effect, can effectively suppress the generation of active oxygen in the lithium-rich material under the action of the coating layer 02 described below, further effectively suppressing gas generation and further improving the lithium-rich effect of the positive electrode lithium-rich additive.

[0056] In the embodiments, the core body 01 can be at least one of primary particles and secondary particles, specifically at least one of primary particles and secondary particles formed by the positive electrode lithium supplementation additive contained in the core body 01. For example, when the core body 01 is a primary particle, the particle size of the primary particles, i.e., the particle size distribution of the core body 01, is 0.01 μm-5.0 μm; when the core body 01 is a secondary particle, the particle size of the secondary particles, i.e., the particle size distribution of the core body 01, is 0.02 μm-20 μm. Here, secondary particles refer to agglomerated particles formed by the aggregation of one or more primary particles. By controlling the morphology and particle size of the core body 01, the overall particle size of the positive electrode lithium supplementation additive in the embodiments of this application can be controlled, and the lithium supplementation effect of the positive electrode lithium supplementation additive can be adjusted.

[0057] The coating layer O2 of the positive electrode lithium supplementation additive in this application embodiment contains a polymer with the following general molecular structure formula I:

[0058]

[0059] In general formula I, X1, X2, X3, and X4 are independently any one of hydrogen atoms and alkyl groups having 1 to 3 carbon atoms, and R is a polymer segment. Since the coating layer 02 of the positive electrode lithium supplement additive in this application contains the polymer shown in general formula I, the coating layer 02 effectively inhibits the generation of reactive oxygen species, thereby effectively suppressing gas production and improving the lithium supplementation effect of the positive electrode lithium supplement additive.

[0060] Because lithium-ion batteries easily generate harmful free radicals during charging and discharging, such as CH3· radicals, acyl radicals, and CH3O· radicals, the polymer shown in Formula I can effectively suppress the generation of free radicals during charging and discharging and effectively capture these free radicals to form stabilizers. For example, the RN-O· radicals in the polymer shown in Formula I couple with CH3· radicals, acyl radicals, and CH3O· radicals to form relatively stable chemical bonds, thus consuming these free radicals. Therefore, the polymer shown in Formula I imparts the effect of inhibiting reactive oxygen species and capturing free radicals generated during charging and discharging of the O2 coating layer, significantly reducing gas production during charging and discharging, reducing the volume expansion of the lithium-ion battery, and thus effectively improving the stability and safety of the lithium-ion battery during charging and discharging, while also improving its lithium replenishment effect.

[0061] In the embodiments, the polymer represented by general formula I has a mass content of 0.1%-5% in the positive electrode lithium supplementation additive of this application. Specifically, it can be a typical but non-limiting content such as 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%. By adjusting the content of this polymer in the positive electrode lithium supplementation additive of this application embodiment, the polymer's role is fully utilized, such as enhancing the role of the O2 coating layer in inhibiting reactive oxygen species and capturing free radicals generated during the charging and discharging of lithium-ion batteries. This results in a significant reduction in gas production during the charging and discharging of lithium-ion batteries and reduces the volume expansion of lithium-ion batteries.

[0062] In the polymer represented by Formula I, the groups X1, X2, X3, and X4 can stabilize the nitroxide radicals contained in the polymer through steric hindrance. In the embodiments, when X1, X2, X3, and X4 are independently alkyl groups with 1 to 3 carbon atoms, the alkyl group can be any one of methyl, ethyl, propyl, isopropyl, etc. These groups can enhance the steric hindrance effect, further improving the stability of the nitroxide radicals.

[0063] In specific embodiments, the piperidine group contained in general formula I, specifically the piperidine group substituted with X1, X2, X3, X4 and containing nitric oxide radicals, can be a branched chain or a terminal group, all of which can exert the functions described above for the polymer.

[0064] The polymer segment R contained in the polymer of Formula I can play a role in film formation and improve the adhesion between the coating layer 02 and the core 01. In the embodiments, the polymer segment R can be at least one segment selected from carbon-chain polymer chains (carbon-chain polymer chains refer to polymer chains whose molecular backbone contains only carbon atoms), hetero-chain polymer chains (hetero-chain polymer chains refer to polymer chains whose molecular backbone contains carbon and other atoms (such as O, N, S, etc.)), and non-carbon-chain polymer chains (non-carbon-chain polymer chains refer to polymer chains whose molecular backbone does not contain carbon atoms). In further embodiments, the polymer segment R can be at least one segment selected from polyolefin segments, polyacrylate segments, polymethacrylate segments, polyester segments, polyamide segments, polyurethane segments, polyether segments, polysilane segments, and polysiloxane segments. These polymer segments can further improve the film-forming properties and other properties of the polymer of Formula I.

[0065] Based on the types of groups represented by X1, X2, X3, X4, and R in general formula I above, in specific embodiments, the polymers represented by general formula I in the above embodiments can be at least polymers represented by the following molecular structural formulas I1 to I6:

[0066]

[0067] In I1, R includes a polyacrylate segment; in I2, R includes a polymethacrylate segment; in I3, R includes a polyallyloxy group; in I4, R includes a polystyrene segment; in I5, R includes a polyester segment; and in I6, R includes a polyamide segment. Furthermore, n in the polymer structures shown in I1 to I6 represents the degree of polymerization of each polymer. This value of n can be a typical degree of polymerization value for the polymer, and can be adjusted according to actual performance requirements.

[0068] All of these can exert the aforementioned effects of polymers, inhibiting reactive oxygen species and capturing free radicals generated during the charging and discharging of lithium-ion batteries, thereby significantly reducing the amount of gas produced during charging and discharging of lithium-ion batteries and reducing the volume expansion of lithium-ion batteries.

[0069] Furthermore, the polymer shown in General Formula I can be prepared using existing methods (such as free radical polymerization, condensation polymerization, esterification, etc.). As in the examples, the preparation method includes: obtaining polymer segments from monomers through free radical polymerization or condensation polymerization; and performing esterification or amidation reactions with small molecules containing piperidine groups on the polymer segments to attach the piperidine structure to the polymer segments, thereby obtaining the polymer shown in General Formula I in each example.

[0070] Based on the embodiments described above, the coating layer 02 includes a polymer coating layer, which comprises the polymer shown in General Formula I. This polymer coating layer can be formed solely by the polymer shown in General Formula I, or it can be a mixture of the polymer shown in General Formula I and other polymers, or it can be a composite polymer coating layer formed by a first polymer coating layer formed solely by the polymer shown in General Formula I and a second polymer coating layer formed by other polymers. Dispersing the polymer shown in General Formula I within the polymer coating layer or forming a polymer coating layer core 01 enhances the ability of the coating layer 02 to suppress reactive oxygen species and capture free radicals generated during the charging and discharging of the lithium-ion battery.

[0071] In a further embodiment of this application, the coating layer 02 of the positive electrode lithium replenishment additive includes the aforementioned polymer coating layer. Furthermore, the coating layer 02 of the positive electrode lithium replenishment additive further includes a hydrophobic encapsulation layer. For example... Figure 2 As shown, the hydrophobic encapsulation layer 21 contained in the coating layer 02 covers the core body 01, and the polymer coating layer 22 covers the surface of the hydrophobic encapsulation layer 21 facing away from the core body 01. The addition of the hydrophobic encapsulation layer 21 to the coating layer 02 allows it to function as an insulating layer, protecting the positive electrode lithium replenishment material contained in the core body 01 from the storage environment, such as preventing contact with adverse factors like moisture and carbon dioxide. This improves the lithium replenishment stability of the positive electrode lithium replenishment material, thereby endowing the core body 01 with high lithium replenishment stability and effect, as well as the storage and processing performance of the positive electrode lithium replenishment additive in this embodiment. Based on the function of the hydrophobic encapsulation layer 21, the material of the hydrophobic encapsulation layer 21 can be a material capable of forming a dense hydrophobic coating layer to effectively ensure the stability of the positive electrode lithium replenishment material contained in the core body 01. The material of the hydrophobic encapsulation layer 21 can also be an ion conductor encapsulation layer that facilitates ion conduction, an electronic conductor encapsulation layer that improves conductivity, or a composite layer structure of an ion conductor encapsulation layer and an electronic conductor encapsulation layer. When the hydrophobic encapsulation layer 21 is a composite layer structure of an ion conductor encapsulation layer and an electronic conductor encapsulation layer, either the ion conductor encapsulation layer or the electronic conductor encapsulation layer can be directly coated on the surface of the aforementioned particulate lithium replenishment material with lithium fluoride bonded to it. The ion conductor encapsulation layer can improve the lithium ion insertion / extraction effect and the ion conductivity of the lithium ions in the lithium replenishment material. The electronic conductor encapsulation layer can improve the electronic conductivity of the lithium replenishment material, enhance its conductivity, and stimulate the specific capacity of the positive electrode lithium replenishment additive, achieving truly efficient lithium replenishment.

[0072] When the hydrophobic encapsulation layer 21 includes an ion conductor encapsulation layer, it improves lithium-ion conductivity. Therefore, the material of this ion conductor encapsulation layer can be a material that promotes improved ion conductivity, such as, but not limited to, at least one of perovskite, NASICON, and garnet types. In a specific embodiment, the perovskite type includes Li... 3x La 2 / 3-x TiO3(LLTO), specifically Li 0.5 La 0.5 TiO3, Li 0.33 La 0.57 TiO3, Li 0.29 La 0.57 TiO3, Li 0.33 Ba 0.25 La 0.39 TiO3, (Li 0.33 La 0.56 ) 1.005 Ti 0.99 Al 0.01 O3, Li 0.5 La 0.5 Ti 0.95 Zr 0.05 At least one of O3, etc., NASICON type such as but not limited to Li 1.4 Al 0.4 Ti 1.6 (PO4)3(LATP), garnet type including Li7La3Zr2O 12 (LLZO), Li 6.4 La3Zr 1.4 Ta 0.6 O 12 Li 6.5 La3Zr 1.5 Ta 0.5 O 12 At least one of the following. By selecting the appropriate material for the ion conductor encapsulation layer, the ionic conductivity of the ion conductor encapsulation layer can be further improved.

[0073] When the hydrophobic encapsulation layer 21 includes an electronic conductor encapsulation layer, this electronic conductor encapsulation layer can enhance the electronic conductivity of the hydrophobic encapsulation layer, thereby enhancing the electronic conductivity of the positive electrode lithium replenishment additive, which is beneficial for reducing the impedance inside the electrode. Simultaneously, during and after the release of the aforementioned particulate lithium replenishment material as a "sacrifice," the electronic conductor encapsulation layer can be reused, acting as an auxiliary conductive agent inside the positive electrode. Furthermore, this electronic conductor encapsulation layer may further enhance the density of the ion conductor encapsulation layer, improving the density of the hydrophobic encapsulation layer, thereby improving the lithium replenishment stability and lithium replenishment effect of the positive electrode lithium replenishment additive. Based on the function of the electronic conductor encapsulation layer, it can be a full or partial encapsulation. In the embodiments, the material of the electronic conductor encapsulation layer includes at least one of carbon materials, conductive oxides, and conductive organic materials. In specific embodiments, when the material of the electronic conductor encapsulation layer is a carbon material, the carbon material includes at least one of amorphous carbon, carbon nanotubes, graphite, carbon black, and graphene. In other specific embodiments, when the material of the electronic conductor encapsulation layer is a conductive oxide, the conductive oxide may include at least one of In₂O₃, ZnO, and SnO₂. The conductive organic material may be a conductive polymer, etc. By adjusting the content and material of the electronic conductor encapsulation layer, its electronic conductivity can be further improved.

[0074] In a further embodiment, such as Figure 2 The thickness of the hydrophobic encapsulation layer 21 shown can be 1-100 nm. This can be adjusted by controlling the thickness of the ion conductor encapsulation layer and the electronic conductor encapsulation layer contained within the hydrophobic encapsulation layer. Controlling the thickness of the hydrophobic encapsulation layer within this range can improve the density of the hydrophobic encapsulation layer, further improving the storage and processing stability of the cathode lithium supplement additive, while also increasing the ionic and / or electronic conductivity of the cathode lithium supplement additive.

[0075] In addition, the hydrophobic encapsulation layer can also include other functional layers as needed, and the types of other functional layers can be flexibly selected according to the requirements.

[0076] In a further embodiment, the hydrophobic encapsulation layer 21 further contains a polymer represented by the general molecular formula I above. By further adding this polymer to the hydrophobic encapsulation layer 21, the polymer and the hydrophobic encapsulation layer 21 can play a hydrophobic barrier role, such as enhancing its barrier effect against water vapor in the production process and environment, improving the storage and processing performance of the positive electrode lithium supplement additive, and further reducing the gas generation phenomenon of the battery to improve safety performance.

[0077] Secondly, this application also provides a method for preparing the aforementioned cathode lithium supplementation additive. The method for preparing the cathode lithium supplementation additive in this application includes the following steps:

[0078] S01: Mix the positive electrode lithium replenishment material particles with a solution containing a polymer as shown in the above general molecular structure formula I to form a mixture.

[0079] S02: In a protective atmosphere, the mixture is dried to disperse the polymer on the surface of the positive electrode lithium replenishment material particles, thus obtaining a positive electrode lithium replenishment additive.

[0080] In step S01, the cathode lithium replenishment material particles are the core material 01 containing the cathode lithium replenishment material that forms the cathode lithium replenishment additive of the above-described embodiment. The type and particle size of these cathode lithium replenishment material particles are the same as those of the cathode lithium replenishment material contained in the core 01 of the cathode lithium replenishment additive of the above-described embodiment. The polymer represented by general formula I is also the polymer with the molecular structure represented by general formula I contained in the coating layer 02 of the above-described cathode lithium replenishment additive. Therefore, to save space, the cathode lithium replenishment material particles will not be described in detail here.

[0081] In the embodiments, when the coating layer O2 contained in the above-mentioned positive electrode lithium supplementation additive contains such as Figure 2 When the hydrophobic encapsulation layer 21 is shown, the positive electrode lithium replenishment material particles in step S01 include a hydrophobic encapsulation layer 21 containing the core 01 contained in the positive electrode lithium replenishment additive of the above-described embodiments and a core 01 covering the core 01. In specific embodiments, the hydrophobic encapsulation layer 21 may be a composite layer containing the ion conductor encapsulation layer or the electronic conductor encapsulation layer or the composite layer of the ion conductor encapsulation layer and the electronic conductor encapsulation layer described above. In addition, the method for forming the hydrophobic encapsulation layer can be selected according to the structure and material of the hydrophobic encapsulation layer 21, and a corresponding or suitable method can be selected.

[0082] In step S01, the positive electrode lithium-ion material particles are mixed with a solution containing the polymer shown in General Formula I. This mixing process ensures that the solution and the positive electrode lithium-ion material particles are uniformly mixed, allowing the solution containing the polymer shown in General Formula I to form a film layer on the surface of the positive electrode lithium-ion material particles. At least, it ensures that the polymer shown in General Formula I is dispersed on the surface of the positive electrode lithium-ion material particles. Therefore, any mixing method that ensures uniform mixing of the positive electrode lithium-ion material particles and the solution is within the scope of the embodiments disclosed in this application, such as, but not limited to, stirring or ball milling.

[0083] In the embodiments, the mixing ratio of the positive electrode lithium replenishment material particles to the solution ensures that the content of the polymer shown in Formula I in the positive electrode lithium replenishment additive prepared in step S02 is 0.1%-5%. In a further embodiment, by controlling the mixing ratio of the positive electrode lithium replenishment material particles to the solution, a polymer coating layer formed by the polymer shown in Formula I is formed on the surface of the positive electrode lithium replenishment material particles, that is, a polymer coating layer formed by the polymer shown in Formula I is formed on the surface of the positive electrode lithium replenishment additive prepared in step S02.

[0084] In a further embodiment, the mass concentration of the polymer represented by General Formula I in the solution in step S01 can be 2%-20%. By controlling the concentration of the polymer represented by General Formula I in the solution, the integrity and uniformity of the wet film formed on the surface of the positive electrode lithium replenishment material particles can be improved, such as forming a complete and uniform wet film. The solvent contained in the solution can be a solvent capable of dispersing the positive electrode lithium replenishment material particles and the polymer represented by General Formula I and ensuring their stable performance. For example, it can be at least one organic solvent selected from methanol, ethanol, n-hexane, cyclohexane, ethyl acetate, toluene, xylene, tetrahydrofuran, N-methylpyrrolidone, N,N-dimethylformamide, etc.

[0085] The drying process in step S02 is to remove the solvent contained in the wet film in step S01. Therefore, on the premise of ensuring the stability of the positive electrode lithium replenishment material particles and the polymer shown in Formula I, any drying process is within the scope of the specification of the embodiments of this application, such as heating drying, vacuum drying or natural air drying.

[0086] In this embodiment, the protective atmosphere is formed by continuously introducing a chemical inert gas. Specifically, the chemical inert gas can be at least one of conventional chemical inert gases, such as Ar, N2, and He.

[0087] Therefore, the above-mentioned method for preparing the cathode lithium replenishment additive can effectively disperse the polymer shown in General Formula I on the surface of the cathode lithium replenishment material particles, thereby enabling the prepared cathode lithium replenishment additive to possess the structural characteristics and corresponding electrochemical properties of the cathode lithium replenishment additive described in this application. For example, the prepared cathode lithium replenishment additive, while fully exerting its lithium replenishment function, also has the function of inhibiting reactive oxygen species and capturing free radicals generated during the charging and discharging of lithium-ion batteries, resulting in a significant reduction in gas production during the charging and discharging of lithium-ion batteries. In addition, the preparation method of the cathode lithium replenishment additive can ensure the stability of the structure and electrochemical performance of the prepared cathode lithium replenishment additive, and is also highly efficient and saves production costs.

[0088] Thirdly, this application also provides a positive electrode sheet. The positive electrode sheet of this application includes a positive electrode current collector and a positive electrode active layer bonded to the surface of the current collector. The positive electrode active layer contains the positive electrode lithium replenishment additive described in the above-described embodiment. Because the positive electrode sheet of this application contains the aforementioned positive electrode lithium replenishment additive, during charging and discharging, the positive electrode lithium replenishment additive plays the aforementioned role, acting as a lithium source and being consumed first as a "sacrificial agent" during the first charge cycle to replenish the irreversible lithium ions consumed in the formation of the SEI film at the negative electrode. This maintains an abundance of lithium ions in the lithium-ion battery system, improving the first-cycle efficiency and overall electrochemical performance of the lithium-ion battery. Furthermore, the electrode sheet exhibits stable quality and a high yield. Simultaneously, it can effectively capture and consume harmful groups generated during the charging and discharging process of the lithium-ion battery, effectively reducing gas generation during charging and discharging, thereby effectively improving the stability and safety of the lithium-ion battery during charging and discharging.

[0089] In one embodiment, the mass content of the positive electrode lithium supplementation additive contained in the positive electrode active layer according to the above-described embodiments can be 0.1wt%-10wt%; preferably, 0.5wt%-5wt%. The positive electrode active layer includes, in addition to the positive electrode lithium supplementation additive, a positive electrode active material, a binder, and a conductive agent. The binder can be a commonly used electrode binder, such as one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan, and chitosan derivatives. In this embodiment, the conductive agent can be a commonly used conductive agent, such as one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60, and carbon nanotubes. The positive electrode active material can be one or more of lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium vanadium oxide phosphate, lithium fluorinated vanadium phosphate, lithium titanate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminum oxide.

[0090] In the embodiments, the positive electrode sheet preparation process can be as follows: mixing positive electrode active material, positive electrode lithium supplementation additive, conductive agent and binder to obtain electrode slurry, coating the positive electrode slurry on the positive electrode current collector, and preparing the positive electrode sheet through steps such as drying, rolling and die cutting.

[0091] Fourthly, this application also provides a secondary battery. The secondary battery of this application includes necessary components such as a positive electrode, a negative electrode, a separator, and an electrolyte, and of course, other necessary or auxiliary components. The positive electrode is the same as the one described in the embodiment of this application.

[0092] Because the secondary battery of this application embodiment contains the positive electrode lithium supplementation additive mentioned in the above application embodiment, the secondary battery of this application embodiment produces less gas during cycling, effectively reducing or avoiding phenomena such as volume expansion. It has high cycle performance, thus exhibiting high safety performance, long service life, high initial coulombic efficiency, high lithium-ion battery capacity, and stable electrochemical performance. As tested, after 300 cycles at room temperature, the capacity retention rate of this secondary battery is still above 87%, and further above 91%. At high temperature, such as 45°C after 300 cycles, the capacity retention rate is still above 80%, and further above 85%, with the battery thickness change rate less than 15%, and further less than 9%. It has excellent cycle performance and high safety.

[0093] The following examples illustrate the positive electrode lithium supplementation additive, its preparation method, and its application, etc.

[0094] 1. Examples of cathode lithium supplementation additives and their preparation methods:

[0095] Examples A1 to A6

[0096] Examples A1 to A6 provide positive electrode lithium replenishment additives, and the components contained in each positive electrode lithium replenishment additive are shown in Table 1 below. Specifically, the positive electrode lithium replenishment additive of Example A1 contains a coating layer formed by the polymer shown in structural formula I1, Example A2 contains a coating layer formed by the polymer shown in structural formula I2, and so on. The content of each component in the positive electrode lithium replenishment additive is shown in Table 1.

[0097] The preparation methods of the positive electrode lithium supplementation additives in each embodiment include the following steps:

[0098] S1.: The positive electrode lithium replenishment material (Li5FeO4) particulate raw material is mixed with a solution containing polymers with molecular structures shown in general formulas I1 to I6 to form a mixture.

[0099] S2: In a protective atmosphere, the mixture is dried so that the polymer is dispersed on the surface of the positive electrode lithium replenishment material particles, thus obtaining a positive electrode lithium replenishment additive.

[0100] Comparative Example A1

[0101] Comparative Example A1 provides a positive electrode lithium replenishment additive. Compared with the positive electrode lithium replenishment additive in Example A1, the positive electrode lithium replenishment material (Li5FeO4) particles in this comparative example are not mixed with polymers of general molecular structures I1 to I6, but are otherwise identical.

[0102] Table 1. Composition of lithium-added additives in the cathodes of each embodiment and comparative example.

[0103]

[0104] 2. Example of a lithium-ion battery:

[0105] Examples B1 to B6 and Comparative Example B1 each provide a lithium-ion battery. Each lithium-ion battery is assembled according to the following method:

[0106] 1) Positive electrode plate:

[0107] The positive electrode lithium replenishment additives provided in Examples A1 to A6 and Comparative Example A1 were used as positive electrode lithium replenishment additives in Examples B1 to B6 and Comparative Example B1, respectively. Under the same conditions, they were mixed in a mass ratio of NMP:LiFePO4:positive electrode lithium replenishment additive:Super P:PVDF of 100:93:2:2:3. The mixing method was ball milling for 60 min at a speed of 30 Hz. After homogenization, coating, drying and cutting, positive electrode sheets were prepared. The positive electrode sheets were baked in a vacuum oven at 100°C to remove trace amounts of water.

[0108] 2) Negative Electrode Sheet: A negative electrode slurry is prepared by uniformly mixing graphite (the negative electrode active material), Super P (the conductive agent), carboxymethyl cellulose (CMC) (the thickener), and styrene-butadiene rubber (SBR) (the binder) in deionized water. The mass ratio of graphite:Super P:CMC:SBR is 95:2:0.5:2.5. The negative electrode slurry is coated onto copper foil (the current collector), and after drying, rolling, and a second drying process, the negative electrode sheet is formed.

[0109] 3) Diaphragm: Polyethylene (PE) diaphragm is used.

[0110] 4) Electrolyte: The electrolyte is a 1 mol / L LiPF6 solution, and the solvent is composed of EC (ethylene carbonate) and DEC (diethyl carbonate) in a volume ratio of 1:1.

[0111] 5) Assembly of secondary batteries:

[0112] The above-mentioned positive electrode, negative electrode, electrolyte and separator are assembled into a lithium-ion pouch battery according to the lithium-ion battery assembly requirements.

[0113] 3. Performance tests related to lithium-ion batteries:

[0114] The lithium-ion batteries assembled in Section 5) for each embodiment and comparative example were subjected to the following performance tests:

[0115] Room temperature cycling test: The battery was placed at 25℃ and charged and discharged at 1C current within the charge-discharge voltage range of 3.0~4.4V. The initial thickness was recorded as T0 and the initial capacity as Q0. The thickness and capacity after 300 cycles were recorded as T1 and Q1. The thickness change rate and capacity retention rate of the battery after 300 cycles at room temperature were calculated using the following formulas:

[0116] Thickness change rate (%) after 300 cycles at room temperature = (T1-T0) / T0 × 100%;

[0117] Capacity retention rate (%) after 300 cycles at room temperature = Q1 / Q0 × 100%.

[0118] High-temperature cycling test: Under high temperature (45℃) conditions, charge-discharge cycles were performed using a 1C current within the charge-discharge voltage range of 3.0–4.4V. The initial thickness was recorded as T2 and the initial capacity as Q2. The thickness and capacity after 300 cycles were recorded as T3 and Q3, respectively. The thickness change rate and capacity retention rate of the battery after 300 cycles at high temperature (45℃) were calculated using the following formulas:

[0119] Thickness change rate (%) after 300 cycles at high temperature (45℃) = (T3-T2) / T2×100%;

[0120] Capacity retention rate (%) after 300 cycles at high temperature (45℃) = Q3 / Q2 × 100%.

[0121] The relevant performance test results are shown in Table 2 below:

[0122] Table 2 Performance Test Results

[0123]

[0124] As can be seen from the test results in Table 2, in the lithium-ion batteries prepared in Examples B1 to B6, after using polymers with structural formulas I1 to I6 as lithium-replenishing additives for the coating layer, the thickness change rate of the lithium-ion battery at room temperature was significantly less than that of the comparative example B1 without a polymer coating layer, indicating a significant reduction in gas production. Furthermore, the capacity retention rate of the examples after 300 cycles was significantly higher than that of the comparative example; similar trends were observed after 300 cycles at high temperature (45%). In summary, the electrolyte additives of this application can suppress gas production during the charge and discharge process of lithium-ion batteries, and their cycle performance is good, thus exhibiting high safety performance and long service life.

[0125] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of this patent application. 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 protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A positive electrode sheet, comprising a positive current collector and a positive active layer bonded to the surface of the positive current collector, characterized in that: The positive electrode active layer contains a positive electrode lithium supplementation additive, and the mass content of the positive electrode lithium supplementation additive in the positive electrode active layer is 0.1wt%~10wt%. The positive electrode lithium supplementation additive has a core-shell structure. The core of the core-shell structure includes a positive electrode lithium supplementation material. The coating layer covering the core includes a polymer coating layer and a hydrophobic encapsulation layer. The hydrophobic encapsulation layer covers the core, and the polymer coating layer covers the surface of the hydrophobic encapsulation layer opposite to the core. The polymer contained in the polymer coating layer includes one or more of the following molecular structural formulas I1~I6: ； The polymer has a mass content of 0.1%-5% in the positive electrode lithium supplementation additive.

2. The positive electrode sheet according to claim 1, characterized in that: The cathode lithium replenishment material includes cathode lithium replenishment materials containing oxygen atoms.

3. The positive electrode sheet according to claim 1 or 2, characterized in that: The hydrophobic encapsulation layer includes at least one of an ion conductor encapsulation layer and an electronic conductor encapsulation layer; and / or The hydrophobic encapsulation layer contains polymers with molecular structural formulas I1 to I6.

4. The positive electrode sheet according to claim 1, characterized in that, The preparation method of the positive electrode lithium supplementation additive includes the following steps: The positive electrode lithium replenishment material particles are mixed with a solution of one or more polymers with molecular structural formulas I1 to I6 to form a mixture. The mixture is dried in a protective atmosphere to disperse the polymer on the surface of the positive electrode lithium replenishment material particles, thereby obtaining a positive electrode lithium replenishment additive.

5. The positive electrode sheet according to claim 4, characterized in that, The polymer forms the polymer coating layer, coating the positive electrode lithium replenishment material particles; and / or The cathode lithium replenishment material particle raw material includes a core containing the cathode lithium replenishment material and a hydrophobic encapsulation layer covering the core.

6. A secondary battery, comprising a positive electrode and a negative electrode, characterized in that: The positive electrode is the positive electrode as described in any one of claims 1 to 5.

7. The secondary battery according to claim 6, characterized in that, The secondary battery retains more than 87% of its capacity after 300 cycles at room temperature; and / or The secondary battery retains more than 80% of its capacity after 300 cycles at 45°C; and / or The thickness change rate of the secondary battery after 300 cycles at 45°C is less than 15%.

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