Composite positive electrode active material, secondary battery and electric device

Abstract

The invention provides a composite positive electrode active material, a secondary battery and an electric device, and belongs to the technical field of batteries. The composite positive electrode active material comprises a positive electrode active material, a passivation layer and a solid electrolyte layer, wherein the passivation layer and the solid electrolyte layer coat the surface of the positive electrode active material; the passivation layer is positioned between the positive electrode active material and the solid electrolyte layer; the passivation layer comprises a passivation material and metal ions; the solid electrolyte layer includes a porous solid electrolyte. The surface of the positive electrode active material is coated with the passivation layer and the solid electrolyte layer, so that the manganese dissolution amount of the composite positive electrode active material is reduced, and the cycle performance of the secondary battery is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, specifically to a composite positive electrode active material, a secondary battery, and an electrical device. Background Technology

[0002] With the rapid development of electric vehicles and renewable energy storage systems, the performance improvement of secondary batteries, as key energy storage devices, has become particularly important. Among the many components of secondary batteries, the characteristics of the positive electrode active material directly affect the battery's energy density, cycle life, and safety. Lithium manganese oxide, in particular, faces problems such as manganese dissolution and structural phase transitions during practical use, severely impacting its cycle life and stability. During the charging and discharging process of secondary batteries, corrosive substances such as HF in the electrolyte can erode the surface of lithium manganese oxide, leading to the degradation of Mn²⁺. + Dissolution occurs; at the same time, the stress generated inside lithium manganese oxide will cause lattice distortion and crack formation, further accelerating the dissolution of manganese and the destruction of the structure, resulting in rapid degradation of the secondary battery performance. Summary of the Invention

[0003] The purpose of this application is to overcome the shortcomings of the prior art and provide a composite positive electrode active material, a secondary battery, and an electrical device.

[0004] To achieve the above objectives, the technical solution adopted in this application is as follows: In the first aspect of this application, a composite positive electrode active material is provided, the composite positive electrode active material comprising a positive electrode active material and a passivation layer and a solid electrolyte layer coated on the surface of the positive electrode active material, wherein the passivation layer is located between the positive electrode active material and the solid electrolyte layer; The passivation layer comprises a passivation material and metal ions; The solid electrolyte layer includes a porous solid electrolyte; The passivation material includes at least one of cyclodextrin, cyclodextrin derivatives, metal oxides, metal hydroxides, polymers, ion exchange materials, nanomaterials, and metal-organic frameworks.

[0005] In some embodiments, the thickness of the passivation layer is 5-50 nm.

[0006] In some embodiments, the substituents of the cyclodextrin include at least one of sulfonic acid groups and amino groups.

[0007] In some embodiments, the degree of substitution of the cyclodextrin is 0.5-3.0.

[0008] In some embodiments, the metal ions include Ag. + Cu + Cu 2+ Zn 2+ Fe3+ At least one of them.

[0009] In some embodiments, the molar ratio of the passivating material to the metal ions is (1:1) to (2:1).

[0010] In some embodiments, the passivation material has a mass percentage of 1-5%, based on a composite positive electrode active material mass percentage of 100%.

[0011] In some embodiments, the porosity of the porous solid electrolyte is 30-50%.

[0012] In some embodiments, the pore size of the porous solid electrolyte is 50-2000 nm.

[0013] In some embodiments, the porous solid electrolyte includes at least one of lithium aluminate, lithium niobate, lithium titanate, lithium borate, lithium metaborate, lithium zirconate, lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium titanium aluminum phosphate, and lithium phosphorus oxynitride.

[0014] In some embodiments, the porous solid electrolyte further includes a silane coupling agent.

[0015] In some embodiments, the positive electrode active material includes at least one of lithium manganese oxide, modified lithium manganese oxide, and lithium manganese iron phosphate.

[0016] In some embodiments, the average particle size of the positive electrode active material is 0.5-5 μm.

[0017] A second aspect of this application provides a secondary battery, including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer including the composite positive active material.

[0018] In some embodiments, the positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer disposed on the surface of the positive electrode current collector, wherein the first positive electrode active layer is located between the positive electrode current collector and the second positive electrode active layer; The first positive electrode active layer includes a first composite positive electrode active material, and the second positive electrode active layer includes a second composite positive electrode active material. With the mass percentage of the first positive electrode active layer being 100%, the mass percentage of the first composite positive electrode active material is denoted as A1. With the mass percentage of the second positive electrode active layer being 100%, the mass percentage of the second composite positive electrode active material is denoted as A2; A1 and A2 satisfy: A1 <A2。

[0019] A third aspect of this application provides an electrical device including the aforementioned secondary battery.

[0020] Compared with the prior art, the beneficial effects of this application are as follows: the passivation layer of the composite positive electrode active material of this application can effectively block Mn 2+ The dissolution pathway significantly improves the structural stability and cycle life of the composite cathode active material. The porous solid electrolyte in the solid electrolyte layer reduces the contact between the cathode active material and the electrolyte, thus reducing the erosion of the cathode active material by the electrolyte; the porous structure of the porous solid electrolyte provides abundant transport channels for lithium ions, improving the ionic conductivity of the composite cathode active material. Detailed Implementation

[0021] To facilitate understanding of this application, a more complete description will be provided below. However, 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.

[0022] As used in this article: "Prepared from" is synonymous with "comprising". The terms "comprising", "including", "having", "containing", or any other variations thereof as used herein are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0023] The conjunction "composed of..." excludes any unspecified elements, steps, or components. If used in a claim, this phrase makes the claim closed, excluding materials other than those described, except for associated conventional impurities. When the phrase "composed of..." appears in a clause of the body of a claim rather than immediately following it, it limits only the elements described in that clause; other elements are not excluded from the claim as a whole.

[0024] When a quantity, concentration, or other value or parameter is expressed as a range, a preferred range, or a range defined by a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether the range is disclosed individually. For example, when the range “1-5” is disclosed, the described range should be interpreted as including ranges “1-4”, “1-3”, “1-2”, “1-2 and 4-5”, “1-3 and 5”, etc. When numerical ranges are described herein, unless otherwise stated, the range is intended to include its endpoints and all integers and fractions within that range.

[0025] In these embodiments, unless otherwise specified, the portions and percentages are all by weight.

[0026] "Parts by mass" refers to the basic unit of measurement that expresses the mass ratio of multiple components. One part can represent any unit mass, such as 1g or 2.689g. If we say that component A has 'a' parts by mass and component B has 'b' parts by mass, it means that the mass ratio of component A to component B is a:b. It is important to understand that, unlike mass percentage content, the sum of the mass parts of all components is not limited to 100 parts.

[0027] "And / or" is used to indicate that one or both of the described situations may occur, for example, A and / or B includes (A and B) and (A or B).

[0028] In a first aspect, this application provides a composite positive electrode active material, the composite positive electrode active material comprising a positive electrode active material and a passivation layer and a solid electrolyte layer coated on the surface of the positive electrode active material, the passivation layer being located between the positive electrode active material and the solid electrolyte layer; The passivation layer comprises a passivation material and metal ions; The solid electrolyte layer includes a porous solid electrolyte; The passivation material includes at least one of cyclodextrin, cyclodextrin derivatives, metal oxides, metal hydroxides, polymers, ion exchange materials, nanomaterials, and metal-organic frameworks.

[0029] The passivation layer of the composite positive electrode active material in this application can effectively block Mn. 2+ The dissolution pathway significantly improves the structural stability and cycle life of the composite cathode active material. The porous solid electrolyte in the solid electrolyte layer reduces the contact between the cathode active material and the electrolyte, thus reducing the erosion of the cathode active material by the electrolyte; the porous structure of the porous solid electrolyte provides abundant transport channels for lithium ions, improving the ionic conductivity of the composite cathode active material.

[0030] Understandably, in one embodiment, when the passivating material includes cyclodextrin, firstly, the cyclodextrin forms a complex with the metal ions, inhibiting manganese dissolution. The mechanism is that the hydrophobic cavities of the cyclodextrin selectively coat metal ions (such as Mn). 2+ This reduces the solubility of Mn in the electrolyte through coordination or physical adsorption. Specifically, positive electrode materials (such as manganese-based oxides) may experience reduced solubility in the electrolyte during cycling due to Mn. 2+ Dissolution can lead to capacity decay or side reactions. Cyclodextrins react with Mn... 2+Firstly, cyclodextrins can reduce the activity of the passivation layer, thereby inhibiting dissolution and improving the cycle stability of the battery. Secondly, cyclodextrins can act as structural stabilizers for the passivation layer: they may enhance the mechanical strength and density of the passivation layer through intermolecular hydrogen bonds or synergistic effects with metal ions, preventing interfacial side reactions between the solid electrolyte layer and the cathode material. Thirdly, cyclodextrins can regulate the interfacial properties of the solid electrolyte layer: their hydrophobicity or hydrophilicity modulates the interfacial compatibility of the solid electrolyte layer, reducing interfacial impedance and improving ion transport efficiency.

[0031] Specifically, the cyclodextrin includes at least one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin. For example, in one embodiment, the cyclodextrin includes β-cyclodextrin, which is composed of 7 glucose units, i.e., the degree of polymerization of the cyclodextrin is 7. The inner diameter of the β-cyclodextrin is 0.7 nm, which has better inclusion efficiency and adsorption capacity for metal ions. The degree of polymerization of the cyclodextrin is around 7, which helps the cavity size of the cyclodextrin to match the metal ions, thereby improving the adsorption capacity of the cyclodextrin for metal ions.

[0032] Specifically, the cyclodextrin derivatives include hydroxypropyl-β-cyclodextrin, and the cyclodextrin derivatives may have higher water solubility or binding ability with metal ions.

[0033] It is understood that, in one embodiment, the metal oxide includes at least one of aluminum oxide, titanium dioxide, and zirconium dioxide; the metal hydroxide includes at least one of zinc hydroxide (Zn(OH)2), aluminum hydroxide (Al(OH)3), aluminum hydroxide containing hydroxyl oxide (AlOOH), copper hydroxide (Cu(OH)2), basic copper carbonate (Cu2(OH)2CO3), and magnesium hydroxide (Mg(OH)2); the metal oxide and / or metal hydroxide inhibit the dissolution of metal ions through a physical barrier effect, or react with Mn 2+ A surface reaction occurs to form a stable compound.

[0034] It is understood that, in one embodiment, the polymer includes at least one of polyvinyl alcohol (PVA) and polyacrylic acid (PAA), and the polymer binds to metal ions through hydrogen bonding or electrostatic interaction, or forms a dense layer to block the dissolution of metal ions.

[0035] It is understood that, in one embodiment, the ion exchange material includes at least one of phosphate, zeolite, and ion exchange resin; the ion exchange material captures Mn through ion exchange. 2+ This reduces its concentration in the electrolyte.

[0036] It is understood that, in one embodiment, the carbon nanomaterial includes at least one of graphene, carbon nanotubes, and MXene; the carbon nanomaterial stabilizes the surface of the positive electrode active material through physical adsorption or electron transfer, and inhibits the dissolution of metal ions.

[0037] It is understood that, in one embodiment, the metal-organic framework includes at least one of ZIF-8 and Zn-MOFs; the metal-organic framework is connected to Mn through a porous structure and metal nodes. 2+ Complexation, while providing structural stability.

[0038] In some embodiments, the thickness of the passivation layer is 5-50 nm; for example, it can be a range of one or any combination of two of the following: 5 nm, 7 nm, 10 nm, 13 nm, 15 nm, 18 nm, 20 nm, 22 nm, 25 nm, 28 nm, 30 nm, 32 nm, 35 nm, 37 nm, 40 nm, 43 nm, 45 nm, 48 nm, and 50 nm.

[0039] In this application, when the thickness of the passivation layer is within the above-mentioned range, it is beneficial to improve the self-healing ability and ion transport balance of the passivation layer; when the thickness of the passivation layer is greater than or equal to 5 nm, the self-healing ability of the passivation layer is stronger, which helps to block Mn. 2+ The dissolution of the passivation layer; when the thickness of the passivation layer is less than or equal to 50 nm, it helps to reduce the electrode impedance of the composite positive electrode active material and improve the ion diffusion rate.

[0040] Specifically, the passivation layer is typically a nanometer to micrometer-scale interface modification layer, containing cyclodextrin, metal ions (such as Ag), etc. + Li + Passivation layers (such as those for substrates and coordination complexes) typically range in thickness from 5 to 50 nm. Several common and feasible methods can be used to test the thickness of the passivation layer, with the specific method chosen based on the actual thickness of the passivation layer, its bonding state with the substrate, and its conductivity. I. Scanning Electron Microscopy (SEM) Cross-Sectional Observation Method – Applicable to micrometer-scale or relatively thick nanometer-scale passivation layers (≥50 nm). By preparing a sample cross-section containing the passivation layer, the interface between the passivation layer and the substrate (such as cathode materials or porous solid electrolytes) can be observed using high-resolution imaging (secondary electron imaging or backscattered electron imaging) of SEM, and the thickness can be directly measured.

[0041] II. Transmission Electron Microscopy (TEM) High-Resolution Cross-Sectional Observation Method – Suitable for Nanoscale Thin Passivation Layers (≤100 nm, especially 10~50 nm). TEM resolution can reach 0.1~0.2 nm, allowing direct observation of the microstructure of nanoscale passivation layers (such as whether they are uniform and whether they form a continuous interface with the substrate), and precise measurement of thickness through high-resolution images.

[0042] In some embodiments, the substituents of the cyclodextrin include at least one of sulfonic acid groups and amino groups.

[0043] In this application, cyclodextrins including sulfonic acid groups and / or amino groups can enhance the electrostatic adsorption force of cyclodextrins on the surface of the positive electrode active material and improve the bonding strength between the passivation layer and the positive electrode active material.

[0044] In some embodiments, the degree of substitution of the cyclodextrin is 0.5-3.0, for example, it can be a range of one or any two of 0.5, 0.7, 0.9, 1.1, 1.3, 1.5, 1.7, 1.9, 2, 2.2, 2.4, 2.6, 2.8, and 3.

[0045] In this application, the degree of substitution of cyclodextrin affects its water solubility and its complexing ability with metal ions. A degree of substitution within the aforementioned range is beneficial for improving both the water solubility and the complexing ability of cyclodextrin with metal ions. For example, in one embodiment, when the degree of substitution of cyclodextrin is 1.5-2.5, not only is the dispersibility of cyclodextrin in polar solvents guaranteed, but it also allows for the formation of stable complexes with metal ions through the polyhydroxy sites of the cyclodextrin.

[0046] Specifically, the degree of substitution (DS) of cyclodextrin can be obtained through the following test method: I. Nuclear Magnetic Resonance Spectroscopy (NMR). This method utilizes nuclear magnetic resonance (e.g., ¹H NMR, ¹³C NMR) to detect the integral area ratio of the characteristic proton (or carbon) peaks of the cyclodextrin skeleton to the characteristic proton (or carbon) peaks of the substituents, and then quantitatively calculates the degree of substitution. This method requires no standards, can directly distinguish signals through differences in chemical shifts, and has high accuracy (error ≤ 0.1%). It is suitable for organically substituted cyclodextrins such as methylated, ethylated, hydroxypropylated, and acylated ones (e.g., in metal ion coordination complexes of β-cyclodextrin, it is also applicable if the substituents contain organic groups).

[0047] II. Chemical titration method – applicable to substituted cyclodextrins containing ionizable groups (such as carboxyl groups and sulfonic acid groups).

[0048] If the substituents of cyclodextrin are ionizable functional groups (such as carboxymethyl (-CH2COOH), sulfonic acid group (-SO3H), etc.), the total content of functional groups can be determined by acid-base titration and then converted into the degree of substitution. Taking carboxymethyl cyclodextrin (CM-CD) as an example, the carboxyl group (-COOH) can react quantitatively with NaOH, and the total number of carboxyl groups can be calculated by the volume of NaOH consumed, thus obtaining the DS.

[0049] III. Elemental analysis method – applicable to substituted cyclodextrins containing characteristic elements (such as N, S, Cl, and metal ions).

[0050] If the substituent contains a characteristic element not present in the cyclodextrin skeleton (such as N in amino substitution, Cl in chloroethyl substitution, or Ag) + (e.g., metal ions) can be determined by measuring the mass fraction of the element using an elemental analyzer, and then the DS can be calculated by combining the proportion of the element in the substituents.

[0051] In some embodiments, the metal ions include Ag. + Cu + Cu 2+ Zn 2+ Fe 3+ At least one of them.

[0052] Specifically, through Ag + Redox reaction forms a self-healing layer; Cu + and / or Cu 2+ : Through Cu + →The oxidation reaction of Cu2O forms a protective barrier, suitable for high-voltage environments (above 4.3V); Zn 2+ A Zn(OH)₂ gel-like passivation film is formed, which has a strong adsorption capacity for HF and reduces the acidic corrosion effect of the electrolyte on the positive electrode active material; Fe 3+ : via Fe 3+ → The transformation of Fe2O3 forms a highly stable oxide layer, improving high-temperature cycling performance.

[0053] In some embodiments, the molar ratio of the passivating material to the metal ions is (1:1) to (2:1), for example, it can be a range of values ​​consisting of one or any two of 1:1, 1.1:1, 1.2:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.7:1, 1.8:1, 1.9:1, and 2:1.

[0054] In some embodiments, with the mass percentage of the composite positive electrode active material being 100%, the mass percentage of the passivation material is 1-5%, for example, it can be a range of one or any two of 1%, 1.2%, 1.5%, 1.7%, 2%, 2%, 3%, 3.5%, 4%, 4.3%, 4.5%, 4.8%, and 5%.

[0055] In some embodiments, the porous solid electrolyte has an ionic conductivity ≥ 5 × 10⁻⁶ at 25°C. -4 S / cm; can effectively reduce interface impedance.

[0056] In some embodiments, the porosity of the porous solid electrolyte is 30-50%, for example, it can be a range of one or any combination of 30%, 32%, 34%, 36%, 38%, 40%, 42%, 44%, 46%, 48%, 50%.

[0057] In this application, when the porosity of the porous solid electrolyte is 30-50%, the compressive strength of the composite positive electrode active material can reach 30-80 MPa, which can both support the composite positive electrode active material and facilitate lithium ion penetration.

[0058] Specifically, the porosity of porous solid electrolytes can be obtained by testing the following methods: 1. Gas adsorption method (BET method) Specific surface area and pore structure (e.g., micropores, mesopores) are calculated by measuring the amount of gas (e.g., nitrogen) adsorbed on the material surface. Porosity can be estimated by combining specific surface area with material density. This method is applicable to microporous and mesoporous materials, but its applicability to non-porous materials or macroporous structures should be noted. After sample degassing, adsorption isotherms are measured at liquid nitrogen temperature. Specific surface area is calculated using the BET formula, and porosity is then calculated by combining this with density.

[0059] 2. Mercury Intrusion Porosimetry (MIP) Mercury is injected into the pores of a material under high pressure, and the pore size distribution and total porosity are determined by the relationship between pressure and pore size. This method is applicable to mesopores (2-300 nm) and macropores (>300 nm), but may not be suitable for materials that are easily oxidized or react with mercury.

[0060] Specifically, testing methods for composite positive electrode active materials include direct compression methods and indirect inference methods. The direct compression method involves directly applying pressure to the powder sample and measuring its compressive strength. This method is intuitive, simple, and easy to operate, and is suitable for testing most powder materials. The indirect inference method involves measuring certain physical properties of the powder material, such as particle size and density, to indirectly calculate its compressive strength. This method is suitable for testing powder materials under specific conditions, such as certain special powders or powders that are difficult to compress directly.

[0061] In some embodiments, the porous solid electrolyte has a pore size of 50-2000 nm, for example, it can be a range of one or any two of 50 nm, 100 nm, 300 nm, 500 nm, 700 nm, 900 nm, 1000 nm, 1200 nm, 1400 nm, 1600 nm, 1800 nm, and 2000 nm; and an average particle size of 1-10 μm, for example, it can be a range of one or any two of 1 μm, 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 9.5 μm, and 10 μm.

[0062] In this application, the pore size of the porous solid electrolyte is within the above-mentioned range, which helps active ions (e.g., for lithium-ion batteries, the active ions are lithium ions) to embed in the pores of the porous solid electrolyte, thus enriching the transport channels of active ions.

[0063] Specifically, in this application, the pore size of the porous solid electrolyte can be obtained by X-ray computed tomography (X-CT) testing, which includes the following steps: X-ray scanning of samples generates three-dimensional images, allowing direct analysis of pore morphology, pore size, and connectivity. This method is applicable to materials with any pore size range (especially suitable for large pores and complex three-dimensional structures). Steps: After sample fixation, multi-angle X-ray imaging is performed. Three-dimensional tomographic images are generated using image reconstruction techniques. Pore regions are segmented using image processing software (such as Avizo and ImageJ), and pore size distribution is calculated.

[0064] In some embodiments, the porous solid electrolyte includes at least one of lithium aluminate, lithium niobate, lithium titanate, lithium borate, lithium metaborate, lithium zirconate, lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium titanium aluminum phosphate, and lithium phosphorus oxynitride.

[0065] In some embodiments, the method for preparing porous solid electrolytes includes the following steps: A mixture of a solid electrolyte and a pore-forming agent with an average particle size of 50-100 μm is sintered at a temperature of 800-1200 °C to obtain a porous solid electrolyte.

[0066] This application adjusts the pore size and porosity of porous solid electrolytes by changing the type of pore-forming agent, average particle size, and sintering temperature.

[0067] Specifically, based on the mass of the solid electrolyte, the mass percentage of the pore-forming agent is 10% to 70%; for example, it can be a range of one or any two of 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, and 70%.

[0068] Those skilled in the art can adjust the mass percentage content of the pore-forming agent according to the porosity of the porous solid electrolyte. Specifically, based on the mass of the solid electrolyte, when the mass percentage content of the pore-forming agent is 10-30%, the porosity of the porous solid electrolyte is 20-40%; when the mass percentage content of the pore-forming agent is 30-50%, the porosity of the porous solid electrolyte is 40-60%; and when the mass percentage content of the pore-forming agent is 40-70%, the porosity of the porous solid electrolyte is 60-80%.

[0069] The mass percentage of pore-forming agent affects pore size, but the relationship is not direct and linear. When the average particle size of the pore-forming agent is fixed and uniformly dispersed: the mass percentage of the pore-forming agent mainly affects the "pore connectivity," with a smaller impact on pore size, but it may indirectly lead to a slight increase in pore size. When the mass percentage of the pore-forming agent is 10-30%, the pore-forming agent particles are dispersed and isolated, with large distances between them, forming mostly "isolated pores" (pores that are not connected to each other), and the pore size is close to the particle size of the pore-forming agent itself (e.g., 5μm pore-forming agent → pore size ≈ 4~6μm, due to slight shrinkage caused by the matrix material). When the mass percentage of the pore-forming agent is 30-70%, the distance between the pore-forming agent particles decreases, and they begin to contact or partially overlap each other. The pores formed are connected through the "gap between the pore-forming agent particles." At this time, the pore size of a single pore is still close to the particle size of the pore-forming agent, but the particles may aggregate to form "composite pores" (multiple small pores connected to form larger pores), resulting in a wider overall pore size distribution (e.g., a pore that was originally 5μm may become a connected pore of 8~10μm).

[0070] When the mass percentage of the pore-forming agent is greater than 50% and the dispersion is uneven, it may lead to "abnormal macropores" with a significant increase in pore size. If the amount of pore-forming agent exceeds the encapsulation capacity of the matrix material, or if the dispersion is uneven during mixing (such as local aggregation of pore-forming agent), a "pore-forming agent enrichment zone" will be formed: a large number of pore-forming agent particles are stacked in this zone. After removal, the pores left behind have no matrix skeleton support and are prone to merging and collapse, forming "macropores" (even exceeding 10 μm) that are much larger than the particle size of the pore-forming agent.

[0071] When the pore-forming agent is a "soluble / decomposable small molecule", the mass percentage of the pore-forming agent has a weak effect on the pore size. If the pore-forming agent is a small molecule without a fixed form (such as PEG-400, citric acid, rather than particulate), its function is to form pores by "occupying space + later volatilization / dissolution". In this case, the pore size is mainly determined by the diffusion ability of the small molecule in the matrix and its compatibility with the matrix. The mass percentage of the pore-forming agent only affects the porosity and has a small effect on the pore size (for example, if the amount of PEG-400 increases from 20% to 50%, the pore size may always remain at 0.1~0.5μm, and only the porosity increases from 25% to 55%).

[0072] Specifically, the sintering time is 0.5 to 24 h, for example, it can be a range of one or any two of 0.5 h, 1 h, 3 h, 5 h, 7 h, 9 h, 11 h, 13 h, 15 h, 17 h, 19 h, 20 h, 22 h, and 24 h.

[0073] Specifically, inorganic electrolytes require a longer densification time (1~12h) due to the high temperature, while organic-inorganic composite electrolytes have a shorter time (0.5~5h) due to the limited heat resistance of the organic phase.

[0074] Sintering time affects pore size, but its effect needs to be judged in combination with the degree of removal of pore-forming agent and the degree of densification of matrix skeleton. The core rule is: within the critical range of "complete removal of pore-forming agent and no over-sintering of matrix", pore size first stabilizes / slightly increases with time, and after exceeding the critical time, pore size decreases or even pore structure collapses.

[0075] If the sintering time is insufficient, the pore-forming agent cannot be completely decomposed / volatilized (e.g., particulate pore-forming agent is not completely removed, or small molecule pore-forming agent remains in the matrix), which will result in "the space occupied by the pore-forming agent not being completely released". The pores formed will be blocked by the residual substances, and the final pore size will be smaller than the target value. Furthermore, due to the uneven amount of residue, the pore size distribution will become wider.

[0076] When enough time is available for the pore-forming agent to be completely removed (e.g., pore-forming agent decomposition residue <1% in inorganic systems, no pore-forming agent residue in composite systems), and the matrix has only completed "preliminary skeleton formation" (bonding between particles but no excessive growth), the pore size is mainly determined by the size of the pore-forming agent itself and is evenly distributed. At this time, time has little effect on the pore size, and the pore size is only slightly smaller than the particle size of the pore-forming agent due to slight shrinkage of the matrix (usually shrinking by 5% to 10%).

[0077] If the sintering time exceeds the "minimum time required for the stability of the matrix framework", the matrix will undergo "over-sintering" at high temperature: inorganic particles continue to diffuse and grains grow, causing the gaps (i.e., pores) in the framework to be squeezed; or the organic phase in the composite system is degraded by heat for a long time, loses its binding force on the inorganic particles, the framework support decreases, the pores merge and collapse, and the pore size is significantly reduced, or even some pores disappear.

[0078] Specifically, the solid electrolyte includes at least one of lithium aluminate, lithium niobate, lithium titanate, lithium borate, lithium metaborate, lithium zirconate, lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium titanium aluminum phosphate, and lithium phosphorus oxygen nitrogen.

[0079] Specifically, the pore-forming agent includes inorganic pore-forming agents and / or organic pore-forming agents; specifically, the inorganic pore-forming agent includes at least one of ammonium bicarbonate (NH4HCO3), ammonium carbonate [(NH4)2CO3], ammonium chloride (NH4Cl), sodium chloride (NaCl), coal powder, and carbon powder; the organic pore-forming agent includes at least one of polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), urea, and starch.

[0080] In some embodiments, the surface of the porous solid electrolyte is provided with a silane coupling agent.

[0081] In this application, a porous solid electrolyte with a silane coupling agent on its surface is provided. One end of the silane coupling agent (e.g., the epoxy group of KH560) forms a covalent bond with a group (e.g., hydroxyl group) on the surface of the porous solid electrolyte, and the other end (e.g., alkoxy group) can bind with the hydroxyl group or modified group (e.g., sulfonic acid group, amino group) of β-cyclodextrin through hydrogen bonding or chemical adsorption. This enhances the interfacial bonding strength between the porous solid electrolyte and the passivation layer, further improves the structural stability of the composite positive electrode active material, reduces interfacial peeling caused by volume changes during cycling, and reduces interfacial impedance.

[0082] Specifically, the silane coupling agent includes at least one of KH550, KH560, KH570, KH172, and KH173.

[0083] Specifically, the preparation method of a porous solid electrolyte with a silane coupling agent on its surface includes the following steps: A porous solid electrolyte is dispersed in a solvent, a silane coupling agent is added, and the mixture is stirred at 60-80°C for 2-4 hours. After centrifugation and drying, a porous solid electrolyte with a silane coupling agent on its surface is obtained.

[0084] Specifically, the mass of the silane coupling agent is 1 to 3% of the mass of the porous solid electrolyte, for example, it can be a range of one or any two of 1%, 1.2%, 1.5%, 1.7%, 2%, 2.3%, 2.5%, 2.8%, and 3%.

[0085] Specifically, the solvent is at least one of ethanol and water.

[0086] In some embodiments, the positive electrode active material includes at least one of lithium manganese oxide, modified lithium manganese oxide, and lithium iron manganese phosphate.

[0087] Modified lithium manganese oxide includes at least one of lithium-rich manganese-based materials and lithium nickel cobalt manganese oxide; the chemical formula of the lithium-rich manganese-based material is γLi₂MnO₃·(1-γ)LiGO₂, 0<γ<1, and G is a transition metal such as nickel, cobalt, or iron; the chemical formula of lithium nickel cobalt manganese oxide is LiNi x1 Coy1 Mn 1-x1-y1-z1 M1 z1 O₂, where 0.5 ≤ x1 ≤ 0.8, 0.1 ≤ y1 ≤ 0.3, 0.1 ≤ z1 ≤ 0.3, x1 + y1 + z1 ≤ 1, 1 - x1 - y1 - z1 > 0, M1 includes at least one of In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, Cr. For example, lithium nickel cobalt manganese oxide includes at least one of NCM811, NCM622, NCM523, NCM111. It can also be understood that the chemical formula of lithium manganese iron phosphate is Li x2 Mn y2 Fe 1-y2 M2 z2 a compound of PO₄, where 0.9 ≤ x2 ≤ 1.1, 0 < y2 < 1, 0 ≤ z2 ≤ 0.05, and M2 includes at least one of In, La, Zr, Ce, W, Al, Ti, Sr, Mg, Sb, V, Zn, Cu, Cr.

[0088] In some embodiments, the average particle size of the positive electrode active material is 0.5 - 5 μm. For example, it can be one of 0.5 μm, 0.7 μm, 0.9 μm, 1.1 μm, 1.3 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.2 μm, 4.4 μm, 4.6 μm, 4.8 μm, 5 μm or a range value composed of any two of them.

[0089] Specifically, the average particle size of the positive electrode active material can be obtained by scanning electron microscopy (SEM) combined with image analysis testing: Principle: Observe the surface morphology of the sample through SEM, and use image processing software (such as ImageJ) to count the particle size. Scope of application: Applicable to particles from micrometer to nanometer scale (high-resolution SEM is required). Steps: After the sample is gold-plated or conductively treated, SEM imaging is performed. Mark the particles with software and measure the diameter, and calculate the average particle size (such as number-average particle size, volume-average particle size).

[0090] In some embodiments, the preparation method of the composite positive electrode active material includes the following steps: Prepare the passivation layer: Disperse the positive electrode active material in deionized water, then add β-cyclodextrin solution, stir evenly, and then add a solution containing metal ions, react to obtain a positive electrode active material@passivation layer composite material; Prepare the composite positive electrode active material: Mix the porous solid electrolyte and the positive electrode active material@passivation layer composite material evenly to obtain the composite positive electrode active material.

[0091] Specifically, the mass ratio of the porous solid electrolyte and the positive electrode active material@passivation layer composite material is (1:1) to (1:3), for example, it can be one of 1:1, 1:1.5, 1:2, 1:2.5, 1:3 or any combination of two of them.

[0092] Specifically, the molar concentration of the β-cyclodextrin solution is 0.1-0.5 mol / L, for example, it can be a range of one or any combination of 0.1 mol / L, 0.15 mol / L, 0.2 mol / L, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L.

[0093] Specifically, the reaction time is 2-6 hours, for example, it can be a range of 2 hours, 3 hours, 4 hours, 5 hours, 6 hours or any combination of both.

[0094] In this application, the thickness of the passivation layer can be changed by adjusting the molar concentration of the β-cyclodextrin solution and the reaction time. For example, by reacting a β-cyclodextrin solution with a molar concentration of 0.3 mol / L for 4 hours, the thickness of the passivation layer obtained is 20 nm.

[0095] Specifically, during the preparation of the passivation layer, ultrasonic-assisted dispersion can be used in the reaction process. Ultrasonic-assisted dispersion can promote the diffusion of metal ions into the cavity of β-cyclodextrin, thereby increasing the saturation efficiency of metal ions from 65% to 85%.

[0096] Specifically, the power of the ultrasound is 100-300W, for example, it can be one or any combination of 100W, 150W, 200W, 250W, 300W.

[0097] Specifically, the solution containing metal ions can be prepared using methods known in the art, such as adding a metal element compound to deionized water and dispersing it evenly to obtain a solution containing metal ions; furthermore, the metal element compound may include at least one of metal nitrates, metal sulfates, and metal chlorides.

[0098] Specifically, in the process of preparing composite positive electrode active materials, the mixing method is planetary ball milling. Planetary ball milling can achieve nanoscale dispersion of positive electrode active material@passivation layer composite material and porous solid electrolyte, avoiding local agglomeration that leads to ion transport bottlenecks.

[0099] Specifically, the rotational speed of the planetary ball mill is 300-500 rpm, for example, it can be one or any combination of 300 rpm, 350 rpm, 400 rpm, 450 rpm, 500 rpm; the time is 4-6 h, for example, it can be one or any combination of 4 h, 4.5 h, 5 h, 5.5 h, 6 h.

[0100] Specifically, nanoscale dispersion refers to a dispersion of ≤15%, which can be a range of values ​​consisting of one or any combination of 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, and 15%.

[0101] Specifically, the method for testing dispersion is as follows: X-ray computed tomography (X-CT) Principle: X-ray scanning of the sample generates a three-dimensional image, allowing analysis of the spatial distribution of particles within the matrix. Applications: Suitable for three-dimensional structural analysis (e.g., composite materials, porous materials, particle-filled systems).

[0102] Procedure: After sample fixation, multi-angle X-ray imaging is performed. A three-dimensional tomographic image is generated using image reconstruction technology. Particle regions are segmented using software (such as Avizo), and dispersion parameters (such as interparticle spacing and distribution density) are calculated.

[0103] A second aspect of this application provides a secondary battery, including a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer including the composite positive active material.

[0104] In some embodiments, the positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer disposed on the surface of the positive electrode current collector, wherein the first positive electrode active layer is located between the positive electrode current collector and the second positive electrode active layer; The first positive electrode active layer includes a first composite positive electrode active material, and the second positive electrode active layer includes a second composite positive electrode active material. With the mass percentage of the first positive electrode active layer being 100%, the mass percentage of the first composite positive electrode active material is denoted as A1. With the mass percentage of the second positive electrode active layer being 100%, the mass percentage of the second composite positive electrode active material is denoted as A2; A1 and A2 satisfy: A1 <A2。

[0105] In this application, in the thickness direction of the positive electrode sheet, the mass percentage of the second composite positive electrode active material in the second active layer is greater than the mass percentage of the first composite positive electrode active material in the first active layer, which can form a gradient structure of "strong surface repair - high internal capacity", which can preferentially protect the area in contact with the electrolyte and improve the overall performance of the secondary battery.

[0106] Specifically, based on the thickness of the positive electrode active layer, the thickness percentage of the second positive electrode active layer is 15-20%; for example, it can be a range of one or any two of 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20%.

[0107] Specifically, the compaction density of the positive electrode sheet is 3-3.5 g / cm³. 3 For example, it could be 3g / cm 3 3.1 g / cm 3 3.2g / cm 3 3.3 g / cm 3 3.4 g / cm 3 3.5 g / cm 3 The range of values ​​consisting of one or any two of them.

[0108] In this application, the compaction density of the positive electrode sheet is within the above-mentioned range, which can balance the ion transport path and the loading of the positive electrode active material, thereby improving the volumetric energy density of the positive electrode sheet.

[0109] In addition to the aforementioned composite positive electrode active materials, the positive electrode active layer in this application may also include positive electrode active materials conventionally used in the art, such as, but not limited to, at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, lithium titanate, lithium vanadium phosphate, lithium cobalt phosphate, lithium manganese phosphate, lithium iron silicate, lithium vanadium silicate, lithium cobalt silicate, and lithium manganese silicate. The chemical formula of the lithium-rich manganese-based material is γLi2MnO3·(1-γ)LiGO2, where 0 < γ < 1, and G is a transition metal such as nickel, cobalt, or iron. In some embodiments, lithium nickel cobalt manganese oxide includes at least one of NCM901, NCM712, NCM811, NCM622, NCM523, and NCM111. In this application, the surface of the positive electrode active material may be coated with a substance of a different composition. Exemplarily, the coated substance may include, but is not limited to, at least one of the following: aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, aluminum sulfate, lithium carbonate, calcium carbonate, magnesium carbonate, and carbon. By coating the surface of the positive electrode active material with the aforementioned substances, the oxidation reaction of the electrolyte on the surface of the positive electrode active material can be suppressed, thereby improving the service life of the electrochemical device.

[0110] In some embodiments, the positive electrode active layer further includes at least one of a conductive agent, a binder, and a thickener. This application does not particularly limit the conductive agent and binder, as long as they can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of carbon-based materials, metal-based materials, and conductive polymers. In some embodiments, the carbon-based materials may include, but are not limited to, at least one of graphite, carbon black, acetylene black, Super-P, Ketjen black, carbon fiber, carbon nanotubes, graphene, and amorphous carbon. In some embodiments, the metal-based materials may include, but are not limited to, at least one of metal powder and metal fibers, and the metal may include, but is not limited to, at least one of copper, nickel, aluminum, and silver. In some embodiments, the conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polythiophene, polypyrrole, polyaniline, polyacetylene, and poly(p-phenylene). For example, the binder may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, polyacrylic acid, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon. For another example, the thickener may include, but is not limited to, at least one of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts.

[0111] This application does not impose any particular limitation on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of aluminum foil, aluminum alloy foil, composite current collector, carbon cloth, and carbon paper. In some embodiments, the composite current collector may include, but is not limited to, an aluminum-carbon composite current collector.

[0112] In some embodiments, the method for preparing the positive electrode sheet is a method known in the art for preparing positive electrode sheets that can be used in secondary batteries. For example, the positive electrode sheet can be obtained by mixing the components of the positive electrode active layer [including the positive electrode active material, and optionally a conductive agent, binder, and thickener, etc.] in a solvent, and heating it as needed before using the thickener to prepare a positive electrode slurry, and coating and / or spraying the positive electrode slurry onto a positive electrode current collector. In some embodiments, the solvent may include, but is not limited to, at least one of water, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, trimethyl phosphate, acetone, and dipropylene glycol dimethyl ether.

[0113] In some embodiments, the negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector.

[0114] This application does not impose any particular limitation on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of copper foil, aluminum foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, and composite current collectors. In some embodiments, the composite current collector may include, but is not limited to, at least one of carbon copper composite current collectors, nickel copper composite current collectors, and titanium copper composite current collectors.

[0115] In some embodiments, the negative electrode active layer includes a negative electrode active material. This application does not particularly limit the negative electrode active material, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of graphite, hard carbon, soft carbon, silicon carbide, silicon suboxide, lithium metal, lithium titanate, metal alloys, metal sulfides, and graphene. Metal alloys include, but are not limited to, at least one of Li-Sn alloys, Li-Sn-O alloys, and Li-Al alloys. Silicon suboxide is SiO₂. x (0.5 <x<1.6)。

[0116] In some embodiments, the negative electrode active layer further includes at least one of a conductive agent, a binder, and a thickener. This application does not impose particular limitations on the conductive agent and binder, as long as they can achieve the purpose of this application. For example, the conductive agent may include, but is not limited to, at least one of metal-based materials and conductive polymers. In some embodiments, the metal-based material may include, but is not limited to, at least one of metal powder and metal fibers, and the metal may include, but is not limited to, at least one of copper, nickel, aluminum, and silver. In some embodiments, the conductive polymer may include, but is not limited to, at least one of polyphenylene derivatives, polythiophene, polypyrrole, polyaniline, polyacetylene, poly(p-phenylene), and polyfluorene. For example, the binder may include, but is not limited to, at least one of polyvinyl alcohol, hydroxypropyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, polyacrylic acid, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, and nylon. For example, thickeners may include, but are not limited to, at least one of carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, and their salts.

[0117] In some embodiments, the negative electrode sheet has a structure known in the art that can be used as a negative electrode sheet in secondary batteries.

[0118] In some embodiments, the method for preparing the negative electrode sheet is a method known in the art for preparing negative electrode sheets that can be used in secondary batteries. For example, the negative electrode sheet can be obtained by mixing the components of the negative electrode active layer (including the negative electrode active material, and optionally a conductive agent, binder, and thickener, etc.) in a solvent, and heating the mixture before using the thickener as needed to prepare a negative electrode slurry, and coating and / or spraying the negative electrode slurry onto a negative electrode current collector. In some embodiments, the solvent may include, but is not limited to, at least one of water, N-methylpyrrolidone, dimethylformamide, dimethylacetamide, dimethyl sulfoxide, trimethyl phosphate, acetone, and dipropylene glycol dimethyl ether.

[0119] This application does not impose any particular restrictions on the electrolyte, as long as it can achieve the purpose of this application. The electrolyte used in this application can be any electrolyte known in the prior art. For example, electrolytes can be divided into aqueous electrolytes and non-aqueous electrolytes. Compared with aqueous electrolytes, secondary batteries using non-aqueous electrolytes can operate in a wider voltage window, thereby achieving higher energy density.

[0120] In some embodiments, the non-aqueous electrolyte includes organic solvents and electrolytes.

[0121] In some embodiments, this application does not particularly limit the organic solvent, as long as it can achieve the purpose of this application. The organic solvent used in this application can be an organic solvent known in the prior art. For example, the organic solvent can include, but is not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, and other organic solvents. Among them, carbonate compounds can include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, and fluorinated carbonate compounds. Chain carbonate compounds can include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and methyl ethyl carbonate (EMC). Cyclic carbonates can include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate. Carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, and caprolactone. The ether compound may include, but is not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran. Other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,3-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, and trioctyl phosphate.

[0122] In some embodiments, the electrolyte may include, but is not limited to, at least one of inorganic lithium salts, fluorine-containing organic lithium salts, and lithium salts containing dicarboxylic acid complexes. The inorganic lithium salt may include, but is not limited to, at least one of LiClO4, LiAsF6, LiPF6, LiBF4, LiSbF6, LiSO3F, LiPO2F2, and LiN(FSO2)2. Fluorinated organic lithium salts may include, but are not limited to, at least one of LiCF3SO3, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, cyclic 1,3-hexafluoropropane disulfonylimide lithium, cyclic 1,2-tetrafluoroethane disulfonylimide lithium, LiPF4(CF3)2, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2)3, LiPF4(CF3SO2)2, LiPF4(C2F5)2, LiPF4(C2F5SO2)2, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, and LiBF2(C2F5SO2)2. Lithium salts containing dicarboxylic acid complexes may include, but are not limited to, at least one of lithium bis(oxalate)borate, lithium difluorooxalateborate [LiBF2(C2O4)], lithium tri(oxalate)phosphate, lithium difluorobis(oxalate)phosphate, and lithium tetrafluoro(oxalate)phosphate.

[0123] In some embodiments, the mass percentage of the electrolyte is 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 12.5%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, or 30%, based on the mass of the electrolyte.

[0124] In some embodiments, the non-aqueous electrolyte also includes additives.

[0125] In some embodiments, this application does not particularly limit the additives used, as long as they can achieve the purpose of this application. The additives used in this application can be additives known in the prior art. For example, the additives can include, but are not limited to, at least one of polynitrile compounds, sulfur-containing additives, fluoroethylene carbonate (FEC), 1,3-propanesulfonyl lactone (PS), and 1,4-butanesulfonyl lactone. Among them, the polynitrile compounds include at least one of dinitrile compounds and trinitrile compounds. Dinitrile compounds are compounds containing two cyano groups (-CN), and may include, but are not limited to, malononitrile, succinic anionyl nitrile, glutaronitrile, adiponitrile, heptacyanide, caprylic anionyl nitrile, nonadionitrile, decanonitrile, methylmalononitrile, ethylmalononitrile, isopropylmalononitrile, tert-butylmalononitrile, methylsuccinic anionyl nitrile, 2-methyleneglutaronitrile, 1,4-dicyano-3-butene, 2,2-dimethylsuccinic anionyl nitrile, 2,3-dimethylsuccinic anionyl nitrile, 2,3,3-trimethylsuccinic anionyl nitrile, 2,2,3,3-tetramethylsuccinic anionyl nitrile, 2,3-diethyl-2,3-dimethylsuccinic anionyl nitrile, 2,2-diethyl-3,3-dimethylsuccinic anionyl nitrile, dicyclohexyl-1,1-dicarboxynitrile, dicyclohexyl-2,2-dicarboxynitrile, dicyclohexyl-3 3-Dicarboxylonite, 2,5-Dimethyl-2,5-hexanedicarboxylonite, 2,3-Diisobutyl-2,3-dimethylbutanedilonite, 2,2-Diisobutyl-3,3-dimethylbutanedilonite, 2-Methylglutaronilonite, 2,3-Dimethylglutaronilonite, 2,4-Dimethylglutaronilonite, 2,2,3,3-Tetramethylglutaronilonite, 2,2,4,4-Tetramethylglutaronilonite, 2,2,3,4-Tetramethylglutaronilonite, 2,3,3,4-Tetramethylglutaronilonite, 1,4-Dicyanopentane, 2,6-Dicyanopentane, 2,7-Dicyanopentane, 2,8-Dicyanopennonane, 1,6-Dicyanopentane, 1,2-Dicyanobenzene, 1,3-Dicyanopenzene, 1,4-Dicyanopenzene, 3,3'- At least one of (ethylenedioxy)dipropionitrile, 3,3'-(ethylenedisulfide)dipropionitrile, 1,4-dicyano-2-butene, and trans-butenedionitrile. Trinitrile compounds are compounds containing three cyano groups (-CN).

[0126] In some embodiments, the electrolyte preparation method is a method known in the art for preparing electrolytes that can be used in electrochemical devices (including batteries). For example, the electrolyte can be obtained by mixing the components of the electrolyte [including organic solvents, electrolytes, and optional additives, etc.].

[0127] A separator is disposed between the positive and negative electrode plates to prevent internal short circuits in the secondary battery, allowing electrolyte ions to pass freely without affecting the electrochemical charging and discharging process. This application does not impose any particular limitation on the separator, as long as it achieves the purpose of this application. The separator used in this application can be any separator known in the prior art. For example, the type of separator can include, but is not limited to, at least one of woven membranes, nonwoven membranes, microporous membranes, composite membranes, rolled membranes, and spun membranes. The material of the separator can include, but is not limited to, at least one of polyethylene (PE), polyolefins (PO) mainly composed of polypropylene (PP), polyester, cellulose, polyimide (PI), polyamide (PA), spandex, and aramid. Polyester can include, but is not limited to, polyethylene terephthalate (PET) film.

[0128] In some embodiments, the diaphragm includes a substrate layer. The substrate layer may include, but is not limited to, at least one of a nonwoven fabric, membrane, or composite membrane having a porous structure. The material of the substrate layer may include, but is not limited to, at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. In some embodiments, the substrate layer may include, but is not limited to, at least one of a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane.

[0129] In some embodiments, the separator further includes a surface treatment layer disposed on at least one surface of the substrate layer. The surface treatment layer may include, but is not limited to, at least one of a polymer layer, an inorganic layer, and a layer formed by a mixture of polymers and inorganic substances. The polymer layer includes polymers. This application does not particularly limit the polymer, as long as it achieves the purpose of this application. For example, the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymers, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene). The inorganic layer includes inorganic particles and a binder. This application does not particularly limit the inorganic particles and binder, as long as it achieves the purpose of this application. For example, the inorganic particles may include, but are not limited to, at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. As another example, the binder may include, but is not limited to, at least one of the binders used in the above-mentioned positive or negative electrode active layers.

[0130] In some embodiments, the present application does not have a particular limitation on the thickness of the diaphragm, as long as the purpose of the present application can be achieved. For example, the thickness of the diaphragm is 3 μm to 20 μm.

[0131] The methods for preparing secondary batteries are well known to those skilled in the art. This application does not impose any particular limitation on the preparation method of secondary batteries, as long as it can achieve the purpose of this application. For example, the preparation method of secondary batteries may include, but is not limited to, the following steps: stacking positive electrode sheets, separators, and negative electrode sheets in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly into an aluminum-plastic film; injecting electrolyte into the aluminum-plastic film and sealing it to obtain a secondary battery; or stacking positive electrode sheets, separators, and negative electrode sheets in sequence, and then fixing the four corners of the entire stacked structure with tape to obtain a stacked electrode assembly; placing the electrode assembly into an aluminum-plastic film; injecting electrolyte into the aluminum-plastic film and sealing it to obtain a secondary battery. In addition, overcurrent protection elements, conductive plates, etc., can also be placed in the aluminum-plastic film as needed to prevent the internal pressure of the secondary battery from rising and overcharging / discharging.

[0132] A third aspect of this application provides an electrical device including the aforementioned secondary battery.

[0133] This application does not impose any particular limitation on the electrical device used, as long as it can achieve the purpose of this application. The electrical device used in this application can be any electrical device known in the prior art. For example, the electrical device can include, but is not limited to, at least one of the following: laptop computer, pen input computer, mobile computer, e-book player, portable telephone, portable fax machine, portable copier, portable printer, over-ear stereo headphones, video recorder, LCD TV, portable cleaner, portable CD player, mini CD, transceiver, electronic notebook, calculator, memory card, portable recorder, radio, backup power supply, motor, automobile, motorcycle, electric bicycle, bicycle, lighting fixture, toy, game console, clock, power tool, flashlight, camera, large household rechargeable secondary battery, and lithium-ion capacitor.

[0134] Examples 1-16 A series of composite positive electrode active materials were prepared. Taking Example 1 as an example, the preparation method of the composite positive electrode active material includes the following steps: Preparation of porous solid electrolytes: Li 1.3 Al 0.3 Ti 1.7 A mixture of (PO4)3 and starch with an average particle size of 100 nm was sintered at 1150 °C for 6 h to obtain a porous solid electrolyte; wherein, the mass of starch was Li 1.3 Al 0.3 Ti 1.7 (PO4)3 15% by mass; the porous solid electrolyte has an ionic conductivity of 8 × 10⁻⁶. -4 S / cm, porosity 40%, pore size 100nm, average particle size 3μm; Preparation of passivation layer: 10g of lithium manganate with an average particle size of 2μm was dispersed in 200mL of deionized water, and then 100mL of 0.3mol / L sulfonyl-β-cyclodextrin solution (with a degree of substitution of 2 for sulfonyl) was added. After sonication at 200W for 4h, 50mL of 0.2mol / L silver nitrate solution was added, and after sonication at 200W for 4h, lithium manganate@passivation layer composite material was obtained. Preparation of composite positive electrode active material: Porous solid electrolyte and lithium manganese oxide@passivation layer composite material were added to a planetary ball mill at a mass ratio of 2:1 and ball milled at 400 rpm for 5 hours to obtain composite positive electrode active material.

[0135] It should be noted that, in the embodiments of this application, the pore size of the porous solid electrolyte can be adjusted by regulating the average particle size of the starch and the sintering temperature; for example, when using starch with a larger particle size (e.g., 50-100 μm) as a pore-forming agent, the pore size formed after sintering is usually larger than that of samples with smaller particle size starch (e.g., 10-20 μm); while a lower sintering temperature (e.g., 800-900℃) can retain more of the original pore structure, while a high temperature (e.g., above 1200℃) may cause the pore size to shrink or the pores to merge due to particle sintering; The porosity of porous solid electrolytes can be adjusted by regulating the amount of starch added, sintering time, and the type of pore-forming agent. For example, increasing the amount of starch added (e.g., 10%-30 wt%) can significantly improve the porosity, but excessive addition may lead to a decrease in structural strength. Extending the sintering time (e.g., 2-5 h) may promote the homogenization of pores, while using different pore-forming agents (e.g., cellulose, polyvinyl alcohol) can regulate the connectivity and distribution of pores. The average particle size of porous solid electrolytes can be adjusted by regulating the starch pretreatment method (such as ball milling or ultrasonic dispersion) and the sintering atmosphere; for example, ball milling starch particles to a finer particle size (such as 5-10 μm) can refine the grain size of the electrolyte substrate; sintering in an inert atmosphere (such as argon) can reduce grain growth, thereby reducing the average particle size, while an oxidizing atmosphere may promote grain coarsening. The preparation method of porous solid electrolyte with silane coupling agent on the surface is as follows: the porous solid electrolyte is dispersed in water, a silane coupling agent is added, and the mixture is stirred at 70°C for 3 hours. After centrifugation and drying, a porous solid electrolyte with silane coupling agent on the surface is obtained; the mass of the silane coupling agent is 2% of the mass of the porous solid electrolyte. The thickness of the passivation layer of the composite positive electrode active material can be adjusted by regulating the molar concentration of the β-cyclodextrin solution and the reaction time. For example, when the concentration of the β-cyclodextrin solution increases from 0.1 M to 0.5 M, the passivation layer thickness increases significantly. Extending the reaction time (e.g., 1-4 h) can make the passivation layer denser, but excessively long reaction time may lead to over-coating and reduce the electrochemical activity of the material. The metal ions in the passivation layer can be controlled by changing the types of metal ions added.

[0136] The porous solid electrolytes lithium aluminate and lithium lanthanum zirconium oxide in Examples 15 and 16 have ionic conductivity of 10⁻⁻⁶. 6 S / cm, 6mS / cm.

[0137] Example 17 This embodiment provides a composite positive electrode active material, which differs from Example 1 except that alumina is used instead of sulfobutyl-β-cyclodextrin in the preparation of the passivation layer. Otherwise, it is the same as Example 1.

[0138] Example 18 This embodiment provides a composite positive electrode active material, which differs from Example 1 except that polyvinyl alcohol is used instead of sulfobutyl-β-cyclodextrin in the preparation of the passivation layer. Otherwise, it is the same as Example 1.

[0139] Example 19 This embodiment provides a composite positive electrode active material, which differs from Example 1 except that zeolite is used to replace sulfobutyl-β-cyclodextrin in the preparation of the passivation layer. Otherwise, it is the same as Example 1.

[0140] Example 20 This embodiment provides a composite positive electrode active material, which differs from Example 1 except that graphene is used to replace sulfonyl-β-cyclodextrin in the preparation of the passivation layer. Otherwise, it is the same as Example 1.

[0141] Example 21 This embodiment provides a composite positive electrode active material, which differs from Example 1 except that ZIF-8 is used instead of sulfobutyl-β-cyclodextrin in the preparation of the passivation layer. Otherwise, it is the same as Example 1.

[0142] Comparative Example 1 The preparation method of this comparative composite positive electrode active material includes the following steps: 10g of lithium manganese oxide with an average particle size of 2μm was dispersed in 200mL of deionized water, and then 100mL of a 0.3mol / L sulfonyl-β-cyclodextrin solution (sulfonyl substitution degree of 2) was added. After sonication at 200W for 4h, 50mL of a 0.2mol / L silver nitrate solution was added, and the mixture was sonicated at 200W for 4h to obtain the composite positive electrode active material. That is, compared with Example 1, the surface of the positive electrode active material in Comparative Example 1 only has a passivation layer.

[0143] Comparative Example 2 The preparation method of this comparative composite positive electrode active material includes the following steps: Preparation of porous solid electrolytes: Li 1.3 Al 0.3 Ti 1.7 A mixture of (PO4)3 and starch with an average particle size of 100 nm was sintered at 1150 °C for 6 h to obtain a porous solid electrolyte; wherein, the mass of starch was Li 1.3 Al 0.3 Ti 1.7 (PO4)3 15% by mass; the porous solid electrolyte has an ionic conductivity of 8 × 10⁻⁶. -4 S / cm, porosity 40%, pore size 100nm, average particle size 3μm; Preparation of composite positive electrode active material: Porous solid electrolyte and lithium manganese oxide were added to a planetary ball mill at a mass ratio of 2:1 and ball milled at 400 rpm for 5 hours to obtain composite positive electrode active material. That is, compared with Example 1, the surface of the positive electrode active material in Comparative Example 2 only has a solid electrolyte layer.

[0144] Comparative Example 3 The preparation method of this comparative composite positive electrode active material includes the following steps: Preparation of porous solid electrolytes: Li 1.3 Al 0.3 Ti 1.7 A mixture of (PO4)3 and starch with an average particle size of 100 nm was sintered at 1150 °C for 6 h to obtain a porous solid electrolyte; wherein, the mass of starch was Li 1.3 Al 0.3 Ti 1.7 (PO4)3 15% by mass; the porous solid electrolyte has an ionic conductivity of 8 × 10⁻⁶. -4 S / cm, porosity 40%, pore size 100nm, average particle size 3μm; Preparation of solid electrolyte layer: Porous solid electrolyte and lithium manganese oxide were added to a planetary ball mill at a mass ratio of 2:1 and ball milled at 400 rpm for 5 hours to obtain lithium manganese oxide@solid electrolyte layer composite material. Preparation of composite positive electrode active material: 10g of lithium manganese oxide@solid electrolyte layer composite material was dispersed in 200mL of deionized water, and then 100mL of 0.3mol / L sulfonyl-β-cyclodextrin solution (sulfonyl substitution degree of 2) was added. After ultrasonication at 200W for 4h, 50mL of 0.2mol / L silver nitrate solution was added, and after ultrasonication at 200W for 4h, the composite positive electrode active material was obtained.

[0145] The positive electrode active materials prepared in the above examples and comparative examples were used to prepare secondary batteries, and the performance of the secondary batteries was tested. Specifically, compared with Example 1, the surface of the positive electrode active material in Comparative Example 3 was sequentially provided with a solid electrolyte layer and a passivation layer.

[0146] Comparative Example 4 The difference between Comparative Example 4 and Example 1 lies in the preparation of the positive electrode sheet; the positive active material in the positive electrode sheet of Comparative Example 4 is lithium manganese oxide. The rest is the same as Comparative Example 1, and will not be repeated here.

[0147] The composite positive electrode active materials of Examples 1-21 and Comparative Examples 1-4, and some performance parameters of the positive electrode active materials are shown in Table 1.

[0148] Table 1 Note: A represents β-cyclodextrin, and B represents metal ions.

[0149] Examples 1-21 and Comparative Examples 1-3 Preparation of secondary batteries <Preparation of Positive Electrode> The composite positive electrode active materials prepared in Examples 1-21 and Comparative Examples 1-3 were mixed with the binder polyvinylidene fluoride and the conductive agent acetylene black at a mass ratio of 85:7.5:7.5, respectively. N-methylpyrrolidone (NMP) was added, and the mixture was stirred evenly under vacuum to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto an aluminum foil with a thickness of 16 μm. The electrode sheet coated with the positive electrode slurry was dried, cold-pressed, and slit to obtain a positive electrode sheet with a size of 700 mm * 120 mm, wherein the thickness of the positive electrode active layer was 80 μm, and the compaction density of the positive electrode sheet was 3.2 g / cm³. 3 .

[0150] <Preparation of Negative Electrode Sheets> Hard carbon, a negative electrode active material, sodium carboxymethyl cellulose, a thickener, styrene-butadiene rubber, and acetylene black, a conductive agent, were mixed in a mass ratio of 95.7:0.8:2.5:1. Deionized water was added, and the mixture was stirred in a vacuum mixer to obtain a negative electrode slurry. The negative electrode slurry was uniformly coated onto a copper foil with a thickness of 8 μm. The coated electrode was dried, cold-pressed, and slit to obtain a negative electrode sheet, wherein the thickness of the negative electrode active layer was 110 μm.

[0151] <Preparation of Electrolyte> At room temperature, in a glove box filled with argon (H2O < 1 ppm, O2 < 1 ppm), ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate were mixed uniformly in a volume ratio of 1:2:1, and water was removed using a 4 Å molecular sieve to obtain a mixed solvent. Lithium salt LiPF6 was added to a mixed solvent and mixed thoroughly to obtain an electrolyte; wherein the mass concentration of LiPF6 was 1 mol / L.

[0152] <Preparation of Secondary Batteries> The prepared positive electrode, separator (12μm thick polypropylene separator), and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrode. After winding, hot pressing and shaping, and welding of the tabs, a bare cell is obtained. The bare cell is placed in an outer packaging aluminum-plastic film and baked in an oven at 85±10℃ for 24 hours. The electrolyte prepared above is injected into the dried battery, and the battery is allowed to stand, form, and be capacity tested to complete the preparation of the secondary battery.

[0153] Example 22 The difference between Example 22 and Example 1 lies in the preparation of the positive electrode sheet; the preparation of the positive electrode sheet in this example includes the following steps: The composite positive electrode active material prepared in Example 1 above was mixed with the binder polyvinylidene fluoride and the conductive agent acetylene black at a mass ratio of 90:7.5:2.5. N-methylpyrrolidone (NMP) was added and the mixture was stirred evenly under the action of a vacuum mixer to obtain the first positive electrode slurry. The composite positive electrode active material prepared in Example 1 above was mixed with the binder polyvinylidene fluoride and the conductive agent acetylene black at a mass ratio of 80:12.5:7.5. N-methylpyrrolidone (NMP) was added and the mixture was stirred evenly under the action of a vacuum mixer to obtain the second positive electrode slurry. A double-layer extrusion method was used to simultaneously coat a first positive electrode slurry and a second positive electrode slurry onto an aluminum foil with a thickness of 16 μm. The electrode sheet coated with the first and second positive electrode slurries was then dried, cold-pressed, and slit to obtain a 700 mm * 120 mm positive electrode sheet. The thickness of the positive electrode active layer was 85 μm, the thickness of the first positive electrode active layer was 40 μm, and the thickness of the second positive electrode active layer was 45 μm. The compaction density of the positive electrode sheet was 3.2 g / cm³.3 .

[0154] Example 23 The difference between Example 23 and Example 1 lies in the preparation of the positive electrode sheet; the preparation of the positive electrode sheet in this example includes the following steps: The composite positive electrode active material prepared in Example 1 above was mixed with the binder polyvinylidene fluoride and the conductive agent acetylene black at a mass ratio of 80:12.5:7.5. N-methylpyrrolidone (NMP) was added and the mixture was stirred evenly under the action of a vacuum mixer to obtain the first positive electrode slurry. The composite positive electrode active material prepared in Example 1 above was mixed with the binder polyvinylidene fluoride and the conductive agent acetylene black at a mass ratio of 90:7.5:2.5. N-methylpyrrolidone (NMP) was added and the mixture was stirred evenly under the action of a vacuum mixer to obtain the second positive electrode slurry. A double-layer extrusion process was used to simultaneously coat a first positive electrode slurry and a second positive electrode slurry onto an aluminum foil with a thickness of 16 μm. The electrode sheet coated with the first and second positive electrode slurries was then dried, cold-pressed, and slit to obtain a 700 mm * 120 mm positive electrode sheet. The thickness of the positive electrode active layer was 80 μm, the thickness of the first positive electrode active layer was 40 μm, and the thickness of the second positive electrode active layer was 45 μm. The compaction density of the positive electrode sheet was 3.2 g / cm³. 3 .

[0155] Performance testing (1) Cyclic performance: At 55℃, the secondary battery was charged to 4.35V at a current density of 1C, and then discharged to 2.5V at a current density of 1C. The discharge capacity during the discharge process was Q1. The same battery was cycled under the following conditions: 1C charging and 1C discharging rate, voltage range of 2.5V~4.35V. The discharge capacity after 500 cycles was Q2, and the capacity retention rate after 500 cycles = Q2 / Q1×100%; (2) Manganese leaching amount: Sample pretreatment: Remove the electrolyte from the secondary battery and filter to remove particulate matter; Acid digestion: Disassemble the positive electrode to obtain the positive active layer, and digest the positive active layer with nitric acid to obtain the sample solution to be tested.

[0156] Preparation of standard curve: Prepare Mn standard solutions of known concentrations (e.g., 0.1-10 mg / L), measure the emission spectral intensity of the Mn standard solutions on an inductively coupled plasma optical emission spectrometer (ICP-OES), and plot a standard curve; Sample determination: The emission intensity of Mn in the sample solution was detected by ICP-OES, and the concentration of Mn in the sample was calculated by using a standard curve, which is the amount of manganese leached out.

[0157] The test results are shown in Table 2.

[0158] Table 2 As can be seen from the experimental data in Table 2, the manganese leaching amount of the composite positive electrode active material of this application is ≤0.46mg / g, and the capacity retention rate of the prepared secondary battery after 500 cycles is >67%.

[0159] The experimental data from Examples 1-4 show that when the passivation layer thickness is 20-40 nm, the manganese leaching amount of the obtained composite positive electrode active material is ≤0.42 mg / g, and the capacity retention rate of the prepared secondary battery after 500 cycles is ≥72.5%. This indicates that when the passivation layer thickness is 20-40 nm, the composite positive electrode active material can improve the cycle performance of the secondary battery.

[0160] The experimental data from Comparative Example 1 and Examples 5-7 show that when the degree of substitution of β-cyclodextrin is 1.5-2, the manganese leaching amount of the obtained composite positive electrode active material is ≤0.40mg / g, and the capacity retention rate of the prepared secondary battery after 500 cycles is ≥73%. This indicates that when the degree of substitution of β-cyclodextrin is 1.5-2, the composite positive electrode active material can improve the cycle performance of the secondary battery.

[0161] The experimental data from Comparative Example 1 and Examples 8-11 show that when the pore size of the porous solid electrolyte is ≤500nm, the manganese dissolution of the obtained composite positive electrode active material is ≤0.46mg / g, and the capacity retention rate of the prepared secondary battery after 500 cycles is ≥70%. When the pore size of the porous solid electrolyte is ≤500nm, the composite positive electrode active material can improve the cycle performance of the secondary battery.

[0162] The experimental data from Comparative Example 1 and Examples 12-14 show that when the porous solid electrolyte includes a silane coupling agent, the manganese leaching amount of the resulting composite positive electrode active material is ≤0.28mg / g, and the capacity retention rate of the prepared secondary battery after 500 cycles is ≥80%. This indicates that when a silane coupling agent is provided on the surface of the porous solid electrolyte, the composite positive electrode active material can significantly improve the cycle performance of the secondary battery.

[0163] Comparative Example 1 and Examples 22-23 show that when the mass percentage of the composite positive electrode active material in the first positive electrode active layer is lower than that in the second positive electrode active layer, the manganese leaching amount of the resulting composite positive electrode active material is ≤0.19mg / g, and the capacity retention rate of the prepared secondary battery after 500 cycles is ≥78%. This indicates that when the mass percentage of the composite positive electrode active material in the first positive electrode active layer is lower than that in the second positive electrode active layer, the composite positive electrode active material can improve the cycle performance of the secondary battery.

[0164] Comparative Examples 1 and 1-4 show that, without at least one of the passivation layer or solid electrolyte layer, the manganese leaching amount of the resulting composite positive electrode active material is ≥0.46 mg / g, and the capacity retention rate of the prepared secondary battery after 500 cycles is ≤71%. This indicates that the absence of at least one of the passivation layer or solid electrolyte layer will lead to a significant decrease in the cycle performance of the secondary battery.

[0165] Finally, it should be noted that the above embodiments are used to illustrate the technical solutions of this application and not to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A composite positive electrode active material, characterized in that, The composite positive electrode active material includes a positive electrode active material, a passivation layer and a solid electrolyte layer coated on the surface of the positive electrode active material, wherein the passivation layer is located between the positive electrode active material and the solid electrolyte layer; The passivation layer comprises a passivation material and metal ions; The solid electrolyte layer includes a porous solid electrolyte; The passivation material includes at least one of cyclodextrin, cyclodextrin derivatives, metal oxides, metal hydroxides, polymers, ion exchange materials, carbon nanomaterials, and metal-organic frameworks.

2. The composite positive electrode active material as described in claim 1, characterized in that, The thickness of the passivation layer is 5-50 nm.

3. The composite positive electrode active material as described in claim 1, characterized in that, The substituents of the cyclodextrin include at least one of sulfonic acid groups and amino groups; And / or, the degree of substitution of the cyclodextrin is 0.5-3.0; And / or, the metal ions include Ag + Cu + Cu 2+ Zn 2+ Fe 3+ At least one of them.

4. The composite positive electrode active material as described in claim 1, characterized in that, The molar ratio of the passivating material to the metal ions is (1:1) to (2:1). And / or, based on the mass percentage of the composite positive electrode active material being 100%, the mass percentage of the passivation material is 1-5%.

5. The composite positive electrode active material as described in claim 1, characterized in that, The porosity of the porous solid electrolyte is 30-50%; And / or, the pore size of the porous solid electrolyte is 50-2000 nm; And / or, the porous solid electrolyte includes at least one of lithium aluminate, lithium niobate, lithium titanate, lithium borate, lithium metaborate, lithium zirconate, lithium lanthanum zirconium oxide, lithium lanthanum titanium oxide, lithium titanium aluminum phosphate, and lithium phosphorus oxynitride.

6. The composite positive electrode active material as described in claim 1, characterized in that, The surface of the porous solid electrolyte is provided with a silane coupling agent.

7. The composite positive electrode active material as described in claim 1, characterized in that, The positive electrode active material includes at least one of lithium manganese oxide, modified lithium manganese oxide, and lithium iron manganese phosphate. And / or, the average particle size of the positive electrode active material is 0.5-5 μm.

8. A secondary battery, characterized in that, The positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer comprising a composite positive active material as described in any one of claims 1-7.

9. The secondary battery as described in claim 8, characterized in that, The positive electrode active layer includes a first positive electrode active layer and a second positive electrode active layer disposed on the surface of the positive electrode current collector, wherein the first positive electrode active layer is located between the positive electrode current collector and the second positive electrode active layer; The first positive electrode active layer includes a first composite positive electrode active material, and the second positive electrode active layer includes a second composite positive electrode active material. With the mass percentage of the first positive electrode active layer being 100%, the mass percentage of the first composite positive electrode active material is denoted as A1. With the mass percentage of the second positive electrode active layer being 100%, the mass percentage of the second composite positive electrode active material is denoted as A2; A1 and A2 satisfy: A1 <A2。 10. An electrical device, characterized in that, Includes the secondary battery as described in claim 9.

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