Positive electrode material, secondary battery and electric device

Abstract

A positive electrode material of the present application comprises an inner core and a coating layer arranged on the outer surface of the inner core, wherein the inner core comprises a ternary positive electrode active material, and the coating layer comprises a graft polymer, a dielectric material and a lithium salt. The main chain of the graft polymer comprises a conductive polymer, and the conductive polymer comprises at least one of a styrene-butadiene-styrene block copolymer, a nitrile rubber and a styrene-isoprene-styrene copolymer. The side chain of the graft polymer comprises at least one of polyparaphenylene, polypyrrole, polythiophene, polydiacetylene and polyaniline.

Description

Positive electrode materials, secondary batteries and electrical devices

[0001] Cross-reference to related applications

[0002] This application claims priority to Chinese invention patent application CN202411611357.3, filed on November 11, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of battery technology, specifically to a positive electrode material, a secondary battery, and an electrical device. Background Technology

[0004] Secondary batteries, especially lithium-ion batteries, have certain safety issues. Fires and explosions of lithium-ion batteries occur frequently. All-solid-state batteries replace the flammable, explosive, and volatile electrolyte in lithium-ion batteries with a non-flammable solid electrolyte, significantly improving battery safety.

[0005] Currently, solid electrolytes mainly include oxides, sulfides, and polymers. Sulfide solid electrolytes have attracted widespread attention due to their high ionic conductivity and moderate mechanical properties. However, sulfide solid electrolytes have a narrow electrochemical window, and when matched with ternary cathode materials, severe interfacial side reactions and the formation of space charge layers can occur. Furthermore, the cathode undergoes volume changes during cycling, leading to particle breakage and detachment from the solid electrolyte.

[0006] Therefore, this application is submitted. Summary of the Invention

[0007] This application provides a positive electrode material, a secondary battery, and an electrical device.

[0008] A first aspect of this application provides a cathode material, including a core and a coating layer disposed on the outer surface of the core. The core includes a ternary cathode active material, and the coating layer includes a graft polymer, a dielectric material, and a lithium salt. The main chain of the graft polymer includes at least one of styrene-butadiene-styrene block copolymer, nitrile rubber, and styrene-isoprene-styrene copolymer. The side chains of the graft polymer include a conductive polymer, which includes at least one of poly(p-phenylene), polypyrrole, polythiophene, polyacetylene, and polyaniline.

[0009] In some embodiments, the thickness of the coating layer is 20–100 nm.

[0010] In some embodiments, the mass of the coating layer accounts for 1 to 2% of the total mass of the cathode material.

[0011] In some embodiments, the weight-average molecular weight of the conductive polymer is 5,000 to 20,000.

[0012] In some embodiments, the grafting rate of the grafted polymer is 1 to 5%.

[0013] In some embodiments, the grafted polymer in the coating layer comprises 60-70% by mass.

[0014] In some embodiments, the dielectric material content of the coating layer is 10-20% by mass.

[0015] In some embodiments, the lithium salt content in the coating layer is 10-20% by mass.

[0016] In some embodiments, the dielectric material includes at least one of BaTiO3, LiNbO3, and NaNbO3.

[0017] In some embodiments, the lithium salt includes at least one of LiPF6, LiClO4, LiTFSI, LiFSI, and LiBOB.

[0018] In some embodiments, the ternary cathode active material comprises Li a Ni b Co c X d M e Compounds of O2, wherein 0.9 ≤ a ≤ 1.1, 0.6 ≤ b < 1, 0 <c<0.4,0<d<0.4,0≤e≤0.1,b+c+d+e=1;

[0019] X includes at least one of Mn and Al; M includes at least one of Zr, Zn, Cu, Cr, Mg, Fe, V, W, Y, Nb, Ti, In, La, Ce, Sr, Sb, and B.

[0020] A second aspect of this application provides a secondary battery including a positive electrode sheet containing the aforementioned positive electrode material.

[0021] A third aspect of this application provides an electrical device including the aforementioned secondary battery, wherein the secondary battery serves as a power supply for the electrical device.

[0022] The beneficial effects of this application are as follows: This application provides a coating layer comprising a grafted polymer, a dielectric material, and a lithium salt on the surface of the ternary cathode active material. The grafted polymer exhibits excellent compatibility with the sulfide electrolyte material, effectively improving not only the electron transport rate but also the contact between the cathode material and the sulfide electrolyte. The dielectric material promotes lithium salt dissociation by forming a built-in electric field within the coating layer, thereby increasing the ionic conductivity of the coating layer. The coating layer simultaneously possesses high ionic conductivity, high electronic conductivity, and flexibility, which is beneficial for improving ion and electron transport rates. Furthermore, it effectively suppresses interfacial side reactions, improves the electrochemical stability between the cathode material and the sulfide electrolyte, prevents cathode material breakage, enhances the contact between the cathode material and the electrolyte material, and prevents detachment from the solid electrolyte, thereby effectively improving the coulombic efficiency and cycle performance of the secondary battery. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0024] In this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0025] In this application, numerical ranges are referred to as continuous unless otherwise specified, and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Furthermore, when the range refers to integers, it includes every integer between the minimum and maximum values ​​of the range. Additionally, when multiple ranges are provided to describe a feature or characteristic, the ranges may be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges to which they are incorporated.

[0026] Unless otherwise specified, all reagents or instruments used in this application are commercially available products.

[0027] This application provides a cathode material, including a core and a coating layer disposed on the outer surface of the core. The core includes a ternary cathode active material, and the coating layer includes a grafted polymer, a dielectric material, and a lithium salt.

[0028] The main chain of the grafted polymer includes at least one of styrene-butadiene-styrene block copolymer (SBS), nitrile rubber (NBR), and styrene-isoprene-styrene copolymer (SIS). The side chains of the grafted polymer include conductive polymers, which include at least one of poly(p-phenylene), polypyrrole, polythiophene, polyacetylene, and polyaniline.

[0029] This application provides a coating layer comprising a grafted polymer, a dielectric material, and a lithium salt on the surface of the ternary cathode active material. The grafted polymer exhibits excellent compatibility with the sulfide electrolyte material, effectively improving both electron transport rate and the contact between the cathode material and the sulfide electrolyte. The dielectric material, by creating a built-in electric field within the coating layer, promotes lithium salt dissociation, thereby increasing the ionic conductivity of the coating layer. The coating layer simultaneously possesses high ionic conductivity, high electronic conductivity, and flexibility, which are beneficial for enhancing ion and electron transport rates. Furthermore, it effectively suppresses interfacial side reactions, improves the electrochemical stability between the cathode material and the sulfide electrolyte, prevents cathode material breakage, enhances the contact between the cathode material and the electrolyte material, and prevents detachment from the solid electrolyte, thereby effectively improving the coulombic efficiency and cycle performance of the secondary battery.

[0030] In some embodiments, the thickness of the coating layer is 20 to 100 nm, for example, it can be a range of 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm or any two of these values. When the thickness of the coating layer is within this range, it provides good protection for the ternary positive electrode active material of the core, improves the stability of the material, and can obtain a coating layer with better blocking effect and kinetic effect.

[0031] The thickness of the coating layer is a well-known concept in the art and can be tested using instruments and methods known in the art. For example, it can be analyzed and tested using a transmission electron microscope (TEM) to obtain TEM images. Then, the thickness at multiple (e.g., more than 30) different locations on the TEM images is measured, and the average value is taken as the thickness of the coating layer.

[0032] In some embodiments, the mass of the coating layer accounts for 1 to 2% of the total mass of the cathode material. For example, it can be 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or any two of these values. When the mass of the coating layer is within this range, it is beneficial to improve the transport rate of ions and electrons, ensure that active ions can migrate smoothly into and out of the coating layer, better improve ionic conductivity and electronic conductivity, better protect the core material, improve the stability between the cathode material and the sulfide electrolyte, and thus further improve coulombic efficiency and cycle performance.

[0033] In some implementations, the mass of the coating layer relative to the total mass of the cathode material can be determined using well-known methods, such as thermogravimetric analysis (TG). Since the cathode material and the coating layer material have different thermal decomposition temperatures, the coating layer and the cathode material will exhibit weight reduction at different temperatures during thermogravimetric testing, thereby characterizing the mass percentage of the coating layer.

[0034] In some embodiments, the thickness of the coating layer is controlled by adjusting the solid content of the slurry prepared with the grafted polymer, dielectric material, and lithium salt solvent.

[0035] In some embodiments, the weight-average molecular weight of the conductive polymer is 5,000 to 20,000, for example, it can be a range of 5,000, 6,000, 8,000, 10,000, 12,000, 14,000, 15,000, 16,000, 18,000, 20,000 or any two of these values. When the molecular weight of the conductive polymer is within this range, it ensures high ionic conductivity and high electronic conductivity while having good flexibility and being able to better suppress the breakage of the positive electrode material particles, improve its interfacial contact effect with the electrolyte material, and prevent the positive electrode material from separating from the electrolyte material, thereby further improving coulombic efficiency and cycle performance.

[0036] In some embodiments, the grafting rate of the grafted polymer is 1 to 5%, for example, it can be 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or any two of these values. When the grafting rate of the grafted polymer is within this range, the grafted polymer has better flexibility and electronic conductivity, which can effectively reduce the volume expansion rate of the cathode material during charging and discharging, thereby further improving coulombic efficiency and cycle performance.

[0037] In some embodiments, the mass percentage of the grafted polymer in the coating layer is 60-70%, for example, it can be 60%, 62%, 64%, 65%, 66%, 68%, 70%, or any two of these values. When the mass percentage of the grafted polymer is within this range, the coating layer can better balance flexibility and ionic and electronic conductivity, thereby further improving coulombic efficiency and cycle performance.

[0038] In some embodiments, the mass percentage of dielectric material in the coating layer is 10-20%, for example, it can be 10%, 12%, 14%, 15%, 16%, 18%, 20%, or any two of these values. When the mass percentage of dielectric material is within this range, the dielectric material promotes the dissociation of lithium salt by forming an internal electric field, further improving the ionic conductivity of the coating layer, thereby further improving the coulombic efficiency and cycle performance.

[0039] In some embodiments, the mass percentage of lithium salt in the coating layer is 10-20%, for example, it can be 10%, 12%, 14%, 15%, 16%, 18%, 20% or any two of these values. When the mass percentage of lithium salt is within this range, it can better promote the ion transport rate, improve ionic conductivity and electronic conductivity, thereby further improving coulombic efficiency and cycle performance.

[0040] In some embodiments, the positive electrode material satisfies at least one of the following (I) to (III):

[0041] (I) The grafted polymer in the coating layer has a mass percentage of 60-70%;

[0042] (II) The mass percentage of the dielectric material in the coating layer is 10-20%;

[0043] (III) The mass percentage of lithium salt in the coating layer is 10-20%.

[0044] The mass percentage content of grafted polymers, dielectric materials, and / or lithium salts in the coating layer can be detected using conventional methods in the art. For example, in some embodiments, a detection method including the following steps can be employed: The positive electrode sheet is removed from the secondary battery, then soaked in NMP, filtered, and dried to obtain the positive electrode material. Infrared spectroscopy is then used to test the positive electrode material to identify the groups in the grafted polymer and the lithium salt in the coating layer. X-ray photoelectron spectroscopy (XPS) is then used to test the positive electrode material to analyze the dielectric material in the coating layer. Finally, time-of-flight secondary ion mass spectrometry (TOS-SIMS) is performed to perform quantitative analysis based on the fragment peak information of the grafted polymer, lithium salt, and dielectric material.

[0045] In some embodiments, the dielectric material includes at least one of BaTiO3, LiNbO3, and NaNbO3.

[0046] In some embodiments, the lithium salt includes at least one of LiPF6, LiClO4, LiTFSI, LiFSI, and LiBOB.

[0047] In some embodiments, the dielectric material includes at least one of BaTiO3, LiNbO3, and NaNbO3; and / or the lithium salt includes at least one of LiPF6, LiClO4, LiTFSI, LiFSI, and LiBOB.

[0048] In some embodiments, the ternary cathode active material comprises Li a Ni b Co c X d M e Compounds of O2, wherein 0.9 ≤ a ≤ 1.1, 0.6 ≤ b < 1, 0 <c<0.4,0<d<0.4,0≤e≤0.1,b+c+d+e=1;

[0049] X includes at least one of Mn and Al; M includes at least one of Zr, Zn, Cu, Cr, Mg, Fe, V, W, Y, Nb, Ti, In, La, Ce, Sr, Sb, and B.

[0050] While meeting the limitations of this application regarding the grafted polymer, the grafted polymer can be obtained by purchasing commercially available products or prepared by conventional methods. In some embodiments, the preparation method of the grafted polymer includes the following steps:

[0051] The main-chain polymer and grafted monomer were placed in a three-necked flask, toluene solution was added, followed by acetone solution containing the initiator. The mixture was magnetically stirred, heated to 60–80 °C, and subjected to a protective nitrogen atmosphere for constant temperature reaction. After the reaction was complete, anhydrous ethanol was added, producing a white flocculent precipitate. The solvent was removed by rotary evaporation, and the product was dried under vacuum to obtain a white solid product. Finally, the product was purified using a Soxhlet extractor to obtain the grafted polymer.

[0052] In some embodiments, the grafting monomer includes at least one of p-benzene, pyrrole, thiophene, diacetylene, and aniline.

[0053] In some embodiments, the grafting rate of the grafted polymer is calculated as (total mass of the grafted polymer - amount of main chain polymer added) / amount of main chain polymer added × 100%. The grafting rate of the grafted polymer can be controlled by controlling the amount of main chain polymer and grafting monomer added.

[0054] In some embodiments, the mass ratio of the main-chain polymer to the grafted monomer is (99:1) to (90:10).

[0055] In some embodiments, the initiator includes at least one selected from benzoyl peroxide, azobisisobutyronitrile, azobisisoheptanenitrile, dimethyl azobisisobutyrate, and azobisisopropylimidazoline hydrochloride.

[0056] It should be noted that this application does not impose any particular limitation on the amount of initiator added, as long as it is sufficient to initiate the reaction. For example, the initiator is 0.01% to 1% of the main chain polymer, such as 0.01%, 0.02%, 0.05%, 0.08%, 0.1%, 0.2%, 0.4%, 0.5%, 0.6%, 0.8%, 1%, or any two of these values.

[0057] While meeting the limitations of this application regarding the cathode material, the cathode material can be prepared using conventional methods. In some embodiments, the preparation method of the cathode material includes the following steps: preparing a slurry from graft polymer, dielectric material, and lithium salt using a solvent; adding the ternary cathode material to the slurry; stirring until homogeneous; and drying to obtain the cathode material.

[0058] In some embodiments, the solvent includes at least one selected from toluene, xylene, acetone, ethanol, methanol, N,N-dimethylformamide, acetonitrile, dimethyl sulfoxide, sulfolane, tetrahydrofuran, 2-methyltetrahydrofuran, ethylidene nitrate, ethylene carbonate, 1,4-butyrolactone, and dimethylacetamide.

[0059] In some embodiments, the solid content of the slurry is 1 to 60%, for example, it can be 1%, 2%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any two of these values.

[0060] Some embodiments of this application provide a secondary battery including a positive electrode sheet, the positive electrode sheet comprising the positive electrode material described above.

[0061] In some embodiments, the positive electrode further includes a sulfide solid electrolyte and a conductive agent.

[0062] In some embodiments, the sulfide solid electrolyte includes Li 10 GeP2S 12 Li7P3S 11 Li6PS5Cl, Li 5.5 PS 4.5 Cl 1.5 At least one of Li3PS4.

[0063] In some embodiments, the conductive agent includes one or more of vapor-grown carbon fiber (VGCF), acetylene black (AB), carbon nanotubes (CNT), and carbon black (superP).

[0064] In some embodiments, the secondary battery further includes a negative electrode.

[0065] In some embodiments, the negative electrode sheet includes one or more of lithium sheets, indium sheets, and LiIn alloy sheets.

[0066] In some embodiments, the secondary battery further includes a solid electrolyte located between the positive electrode and the negative electrode.

[0067] In some embodiments, the solid electrolyte includes Li 10 GeP2S 12 Li7P3S 11 Li6PS5Cl, Li 5.5 PS 4.5 Cl 1.5 At least one of Li3PS4.

[0068] In some embodiments, the secondary battery may include an outer packaging that can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0069] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. In some embodiments, the outer packaging of the secondary battery can also be a soft pack, such as a pouch-type soft pack. In some embodiments, the material of the soft pack can be plastic, and non-limiting examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0070] This application does not impose any particular restrictions on the shape of the secondary battery; in some embodiments, it can be cylindrical, square, or any other arbitrary shape.

[0071] Some embodiments of this application provide an electrical device including the secondary battery described above, wherein the secondary battery serves as the power supply for the electrical device.

[0072] For example, the aforementioned electrical devices may include mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc., but are not limited thereto.

[0073] The present application is further illustrated below with specific embodiments:

[0074] Example 1

[0075] The preparation of a secondary battery includes the following steps:

[0076] (1) Preparation of the grafted polymer: SBS and pyrrole were placed in a three-necked flask at a mass ratio of 95:5. Toluene solution was added, followed by an acetone solution containing 0.5% benzoyl peroxide (BPO) as the initiator, based on the total amount of SBS. The mixture was magnetically stirred, heated to 70°C, and subjected to a protective N2 atmosphere for constant temperature reaction. After the reaction was complete, anhydrous ethanol was added, resulting in a white flocculent precipitate. The solvent was removed by rotary evaporation, and the product was dried under vacuum at 60°C to obtain a white solid product. Finally, the product was purified using a Soxhlet extractor to obtain the grafted polymer (SBS-grafted polypyrrole polymer, grafting rate 3%).

[0077] (2) Preparation of positive electrode material: SBS-grafted polypyrrole polymer (grafting rate 3%), BaTiO3, and LiTFSI were added to xylene solution in a mass ratio of 60:20:20 and stirred for 6 hours. LiNi 0.8 Co 0.1 Mn 0.1 O2 (i.e., NCM811) is added to the above mixed solution, LiNi 0.8 Co 0.1 Mn 0.1 The mass ratio of O2 to solute (i.e. coating material) in the mixed solution is 1:100. After stirring for 12 hours, the solvent is dried to obtain the positive electrode material.

[0078] (3) The above-prepared cathode material, Li6PS5Cl solid electrolyte and VGCF are mixed in a planetary ball mill at a weight ratio of 80:19:1 to obtain composite cathode powder.

[0079] (4) Secondary battery assembly and testing: Li6PS5Cl solid electrolyte was added to the mold battery, and then a pressure of 30MPa was applied for pre-pressing. Subsequently, the composite cathode powder prepared above was added to one side of the electrolyte, and an indium sheet (100μm) and a lithium sheet (30μm) were added to the other side. Then, a pressure of 400MPa was applied to complete the assembly of the entire secondary battery.

[0080] The preparation methods of the secondary batteries in Examples 2-21 and Comparative Examples 1-4 are basically the same as those in Example 1, with the parameters changed as detailed in Table 1. It should be noted that, unless otherwise specified, all variables in the examples listed in Table 1 are single-factor variables.

[0081] Examples 2-5

[0082] The difference between Examples 2-5 and Example 1 is that Examples 2-5 adjust the thickness and mass percentage of the coating layer by adjusting the amount of mixed solution and NCM811 added in step (2).

[0083] Examples 6-9

[0084] The difference between Examples 6-9 and Example 1 is that Examples 6-9 adjust the mass percentage content of the grafted polymer, dielectric material, and lithium salt in the coating layer by adjusting the mass ratio of the grafted polymer, dielectric material, and lithium salt.

[0085] Examples 10-13

[0086] The difference between Examples 10-13 and Example 1 is that Examples 10-13 use conductive polymers with different weight-average molecular weights, thereby adjusting the weight-average molecular weight of the conductive polymers.

[0087] Examples 14-17

[0088] The difference between Examples 14-17 and Example 1 is that the grafting rate of the grafted polymer is adjusted by adjusting the amount of SBS and pyrrole in Examples 14-17.

[0089] Examples 18-21

[0090] The difference between Example 18 and Example 1 is that Example 18 uses thiophene instead of pyrrole.

[0091] The difference between Example 19 and Example 1 is that aniline is used instead of pyrrole in Example 19.

[0092] The difference between Example 20 and Example 1 is that Example 20 uses LiNbO3 instead of BaTiO3.

[0093] The difference between Example 21 and Example 1 is that in Example 21, NaNbO3 is used instead of BaTiO3.

[0094] Comparative Example 1

[0095] The preparation of a secondary battery includes the following steps:

[0096] (1) The LiNi obtained above 0.8 Co 0.1 Mn 0.1 O2, Li6PS5Cl solid electrolyte, and VGCF were mixed in a planetary ball mill at a weight ratio of 80:19:1 to obtain composite cathode powder.

[0097] (2) Secondary battery assembly and testing: Li6PS5Cl solid electrolyte was added to the mold battery, and then a pressure of 30MPa was applied for pre-pressing. Subsequently, the composite cathode powder prepared above was added to one side of the electrolyte, and an indium sheet (100μm) and a lithium sheet (30μm) were added to the other side. Then, a pressure of 400MPa was applied to complete the assembly of the entire secondary battery.

[0098] Comparative Example 2

[0099] The preparation of a secondary battery includes the following steps:

[0100] (1) Preparation of cathode material: SBS, BaTiO3, and LiTFSI were added to xylene solution in a mass ratio of 60:20:20 and stirred for 6 hours. LiNi 0.8 Co 0.1 Mn 0.1 O2 is added to the above mixed solution, LiNi 0.8 Co 0.1 Mn 0.1 The mass ratio of O2 to solute in the mixed solution is 1:100. After stirring for 12 hours, the solvent is dried to obtain the positive electrode material.

[0101] (3) The above-prepared cathode material, Li6PS5Cl solid electrolyte and VGCF are mixed in a planetary ball mill at a weight ratio of 80:19:1 to obtain composite cathode powder.

[0102] (4) Secondary battery assembly and testing: Li6PS5Cl solid electrolyte was added to the mold battery, and then a pressure of 30MPa was applied for pre-pressing. Subsequently, the composite cathode powder prepared above was added to one side of the electrolyte, and an indium sheet (100μm) and a lithium sheet (30μm) were added to the other side. Then, a pressure of 400MPa was applied to complete the assembly of the entire secondary battery.

[0103] Comparative Example 3

[0104] The preparation of a secondary battery includes the following steps:

[0105] (1) Preparation of the grafted polymer: SBS and pyrrole were placed in a three-necked flask at a mass ratio of 95:5. Toluene solution was added, followed by an acetone solution containing benzoyl peroxide (BPO, accounting for 0.5% of the total SBS). The mixture was magnetically stirred, heated to 70°C, and subjected to a protective N2 atmosphere for constant temperature reaction. After the reaction was completed, anhydrous ethanol was added, resulting in a white flocculent precipitate. The solvent was removed by rotary evaporation, and the product was dried under vacuum at 60°C to obtain a white solid product. Finally, the product was purified using a Soxhlet extractor to obtain the grafted polymer (SBS grafted polypyrrole polymer, grafting rate 3%).

[0106] (2) Preparation of positive electrode material: SBS-grafted polypyrrole polymer (grafting rate 3%) and LiTFSI were added to xylene solution at a mass ratio of 80:20 and stirred for 6 hours. LiNi 0.8 Co 0.1 Mn 0.1 O2 is added to the above mixed solution, LiNi 0.8 Co 0.1 Mn 0.1 The mass ratio of O2 to solute in the mixed solution is 1:100. After stirring for 12 hours, the solvent is dried to obtain the positive electrode material.

[0107] (3) The above-prepared cathode material, Li6PS5Cl solid electrolyte and VGCF are mixed in a planetary ball mill at a weight ratio of 80:19:1 to obtain composite cathode powder.

[0108] (4) Secondary battery assembly and testing: Li6PS5Cl solid electrolyte was added to the mold battery, and then a pressure of 30MPa was applied for pre-pressing. Subsequently, the composite cathode powder prepared above was added to one side of the electrolyte, and an indium sheet (100μm) and a lithium sheet (30μm) were added to the other side. Then, a pressure of 400MPa was applied to complete the assembly of the entire secondary battery.

[0109] Comparative Example 4

[0110] The preparation of a secondary battery includes the following steps:

[0111] (1) Preparation of the grafted polymer: SBS and pyrrole were placed in a three-necked flask at a mass ratio of 95:5. Toluene solution was added, followed by an acetone solution containing benzoyl peroxide (BPO, accounting for 0.5% of the total SBS). The mixture was magnetically stirred, heated to 70°C, and subjected to a protective N2 atmosphere for constant temperature reaction. After the reaction was completed, anhydrous ethanol was added, resulting in a white flocculent precipitate. The solvent was removed by rotary evaporation, and the product was dried under vacuum at 60°C to obtain a white solid product. Finally, the product was purified using a Soxhlet extractor to obtain the grafted polymer (SBS grafted polypyrrole polymer, grafting rate 3%).

[0112] (2) Preparation of positive electrode material: SBS-grafted polypyrrole polymer (grafting rate 3%) and BaTiO3 were added to xylene solution at a mass ratio of 80:20 and stirred for 6 hours. LiNi 0.8 Co 0.1 Mn 0.1 O2 was added to the above mixed solution and stirred for 12 hours. (LiNi) 0.8 Co 0.1 Mn 0.1 The mass ratio of O2 to solute in the mixed solution is 1:100. The solvent is dried to obtain the positive electrode material.

[0113] (3) The above-prepared cathode material, Li6PS5Cl solid electrolyte and VGCF are mixed in a planetary ball mill at a weight ratio of 80:19:1 to obtain composite cathode powder.

[0114] (4) Secondary battery assembly and testing: Li6PS5Cl solid electrolyte was added to the mold battery, and then a pressure of 30MPa was applied for pre-pressing. Subsequently, the composite cathode powder prepared above was added to one side of the electrolyte, and an indium sheet (100μm) and a lithium sheet (30μm) were added to the other side. Then, a pressure of 400MPa was applied to complete the assembly of the entire secondary battery.

[0115] Table 1 Parameter table for Examples 1-21

[0116] Performance testing

[0117] The Xinwei battery testing system was used, with a voltage range of 3-4.25V. Charge / discharge rate tests included 0.1C, 0.33C, and 0.5C, while cycle performance tests were conducted at a rate of 0.33C.

[0118] Table 2 Performance test results of Examples 1-21 and Comparative Examples 1-4

[0119] As can be seen from Table 1, the cathode material described in this application can significantly improve coulombic efficiency and cycle performance, with a coulombic efficiency ≥74% and a 100-cycle capacity retention rate ≥72%. Because this application provides a coating layer comprising a grafted polymer, a dielectric material, and a lithium salt on the surface of the ternary cathode active material, this coating layer possesses both high ionic and electronic conductivity, effectively suppressing interfacial side reactions, improving the stability of the cathode material, preventing breakage, and ensuring close contact between the cathode material and the electrolyte material, preventing detachment from the solid electrolyte. The conductive polymer has good compatibility with the electrolyte material and good flexibility, effectively improving the electron transport rate. The dielectric material, through the formation of an internal electric field, promotes the lithium salt to increase the ionic conductivity of the coating layer, thereby effectively improving coulombic efficiency and cycle performance.

[0120] Comparing Examples 1 to 5, it can be seen that the coating thickness in the range of 20 to 100 nm has a significant effect. Within this range, the ability to balance ion electron transport rate and suppress side reactions can be well balanced, thereby further improving coulombic efficiency and cycle performance.

[0121] Comparing Examples 1 and 6-9, it can be seen that when the mass ratio of grafted polymer in the coating layer is 60-70%, the mass ratio of dielectric material is 10-20%, and the mass ratio of lithium salt is 10-20%, the effect is significant. Within this range, the ionic conductivity and electronic conductivity of the coating layer are optimal, thereby further improving the coulombic efficiency and cycle performance.

[0122] Comparing Examples 1, 10-13, it can be seen that the preferred range of the weight-average molecular weight of the conductive polymer is 5,000 to 20,000. Within this range, the electronic conductivity of the coating layer is the highest, thereby further improving the coulombic efficiency and cycle performance.

[0123] Comparative Examples 1, 14-17 show that the optimal range of polymer grafting rate is 1-5%. Within this range, the grafted polymer has good compatibility with the electrolyte material, good flexibility, and can effectively improve the electron transport rate, thereby further improving coulombic efficiency and cycle performance.

[0124] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended 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 cathode material, comprising a core and a coating layer disposed on the outer surface of the core, wherein the core comprises a ternary cathode active material, and the coating layer comprises a grafted polymer, a dielectric material, and a lithium salt; The main chain of the grafted polymer includes at least one of styrene-butadiene-styrene block copolymer, nitrile rubber, and styrene-isoprene-styrene copolymer, and the side chain of the grafted polymer includes a conductive polymer, which includes at least one of poly(p-phenylene), polypyrrole, polythiophene, polyacetylene, and polyaniline.

2. The cathode material according to claim 1, wherein, The thickness of the coating layer is 20–100 nm.

3. The cathode material according to claim 1, wherein, The coating layer accounts for 1 to 2% of the total mass of the cathode material.

4. The cathode material according to claim 1, wherein, The weight-average molecular weight of the conductive polymer is 5000 to 20000.

5. The cathode material according to claim 1, wherein, The grafting rate of the grafted polymer is 1-5%.

6. The cathode material according to claim 1, wherein, The grafted polymer in the coating layer has a mass percentage of 60-70%.

7. The cathode material according to claim 1, wherein, The dielectric material in the coating layer has a mass percentage content of 10-20%.

8. The cathode material according to claim 1, wherein, The lithium salt content in the coating layer is 10-20% by mass.

9. The cathode material according to any one of claims 1-8, wherein, The dielectric material includes at least one of BaTiO3, LiNbO3, and NaNbO3.

10. The cathode material according to any one of claims 1-8, wherein, The lithium salt includes at least one of LiPF6, LiClO4, LiTFSI, LiFSI, and LiBOB.

11. The cathode material according to any one of claims 1-8, wherein, The ternary cathode active material includes materials with the molecular formula Li. a Ni b Co c X d M e Compounds of O2, wherein 0.9 ≤ a ≤ 1.1, 0.6 ≤ b < 1, 0 <c<0.4,0<d<0.4,0≤e≤0.1,b+c+d+e=1; X includes at least one of Mn and Al; M includes at least one of Zr, Zn, Cu, Cr, Mg, Fe, V, W, Y, Nb, Ti, In, La, Ce, Sr, Sb, and B.

12. A secondary battery, comprising a positive electrode sheet, wherein the positive electrode sheet comprises the positive electrode material according to any one of claims 1 to 11.

13. An electrical device comprising the secondary battery of claim 11, wherein the secondary battery serves as a power supply for the electrical device.

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