Positive pole piece, preparation method thereof and lithium ion battery

Abstract

The invention discloses a positive pole piece, a preparation method thereof and a lithium ion battery, and belongs to the technical field of new energy materials. According to the invention, by optimizing the particle size matching and adding proportion of the main active material and the auxiliary nanoparticles in the positive electrode active material layer and combining the synergistic effect of the solid electrolyte and the conductive agent in the bottom coating layer, the synergistic improvement of high energy density and high safety is realized; the specific particle size range of the main active material ensures high compaction density and lithium ion diffusion efficiency, and the auxiliary nanoparticles significantly reduce the porosity of the pole piece through a grading filling effect, enhance mechanical strength and thermal stability, and effectively inhibit microcrack propagation and thermal runaway under abuse working conditions of needling, extrusion and the like. And a bifunctional network formed by the solid electrolyte with high ionic conductivity in the bottom coating and the conductive agent further reduces the interface impedance and disperses local heat, so that the technical problems of poor mechanical property and high thermal runaway risk of the traditional high-nickel positive pole piece are solved.

Description

Technical Field

[0001] This invention relates to the field of new energy materials technology, specifically to a positive electrode sheet, its preparation method, and a lithium-ion battery. Background Technology

[0002] The widespread application of high-energy-density lithium-ion batteries in electric vehicles and energy storage has made their safety under extreme abuse conditions such as needle penetration, external short circuits, and extrusion increasingly prominent. While existing layered metal oxide cathode materials (such as high-nickel NCM and NCA) can improve energy density, their large particle size and brittleness make them prone to microcrack propagation and structural collapse under mechanical and thermal shock. During needle penetration or extrusion, the active layer of the cathode is easily pulverized and detached, inducing current collector exposure, runaway electron / ion transport, and violent exothermic reactions. Traditional cathode electrode interfaces have limited buffering and barrier capabilities, making it difficult to dissipate heat during internal short circuits, easily triggering thermal runaway chain reactions. Existing technologies improve safety through single methods such as surface coating and inorganic coatings, but these have shortcomings such as easy cracking of the coating layer and increased interfacial impedance, making it difficult to address various abuse scenarios. How to improve the structural integrity and thermal stability of the electrode without sacrificing energy density has become a core bottleneck restricting the development of high-safety lithium batteries. Summary of the Invention

[0003] The main objective of this invention is to propose a positive electrode sheet, its preparation method, and a lithium-ion battery, in order to solve the technical problems of limited interface buffering and barrier capabilities of traditional positive electrode sheets in the prior art, difficulty in dispersing heat during internal short circuits, and easy triggering of thermal runaway chain reactions.

[0004] To achieve the above objectives, the present invention proposes a positive electrode sheet, comprising an aluminum current collector, a base coating, and a positive electrode active material layer coated on the surface of the base coating; the positive electrode active material layer is composed of a main active material and auxiliary nanoparticles, wherein the main active material is a layered metal oxide; the auxiliary nanoparticles are selected from at least one of phosphates, oxides, and nitrides; the D50 particle size of the main active material is 7-12 μm, and the D50 particle size of the auxiliary nanoparticles is 200-300 nm.

[0005] Based on the above technical solutions, preferably, the ratio of the D50 particle size of the auxiliary nanoparticles to the D50 particle size of the main active material is 0.02-0.04.

[0006] Based on the above technical solutions, preferably, the amount of auxiliary nanoparticles added is 3-6 wt% of the mass of the main active material.

[0007] Based on the above technical solutions, preferably, the auxiliary nanoparticles are at least one of lithium phosphate (Li3PO4), aluminum phosphate (AlPO4), lithium vanadium phosphate (Li3V2(PO4)3), aluminum oxide (Al2O3), silicon dioxide (SiO2), titanium dioxide (TiO2), boron nitride (BN), and aluminum nitride (AlN).

[0008] Based on the above technical solutions, preferably, the base coating comprises inorganic components and a binder; the inorganic components consist of a solid electrolyte and a conductive agent; the solid electrolyte comprises at least one of lithium aluminum titanium phosphate, lithium lanthanum zirconium titanium oxide, and lithium lanthanum zirconium oxide; the conductive agent in the base coating is selected from carbon black and / or carbon nanotubes; and the binder is at least one of polyvinylidene fluoride, polyacrylic acid, and polyimide.

[0009] Based on the above technical solutions, preferably, the mass ratio of inorganic components to binder in the base coating is 8-10:1.

[0010] Based on the above technical solution, preferably, the layered metal oxide is LiNi. x Co y Mn z O2 or LiNi x Co y Al z O2, where x≥0.4, x+y+z=1.

[0011] Based on the above technical solutions, preferably, in the spherical indentation test, the critical failure displacement of the positive electrode sheet is 10-15 μm.

[0012] The present invention also provides a lithium-ion battery, wherein the lithium-ion battery includes the above-mentioned positive electrode sheet.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: 1) This invention provides a positive electrode sheet, its preparation method, and a lithium-ion battery. By optimizing the particle size matching and addition ratio of the main active material and auxiliary nanoparticles in the positive electrode active material layer, combined with the synergistic effect of the solid electrolyte and conductive agent in the undercoat layer, a synergistic improvement in high energy density and high safety is achieved. The specific particle size range of the main active material ensures high compaction density and lithium-ion diffusion efficiency, while the auxiliary nanoparticles significantly reduce the porosity of the electrode sheet through the gradation filling effect, enhancing mechanical strength and thermal stability, and effectively suppressing microcrack propagation and thermal runaway under abuse conditions such as needle penetration and extrusion. The bifunctional network formed by the high ionic conductivity solid electrolyte and conductive agent in the undercoat layer further reduces interfacial impedance and disperses local heat, solving the technical problems of poor mechanical properties and high risk of thermal runaway in traditional high-nickel positive electrode sheets. 2) The auxiliary nanoparticles of this invention are preferably made of materials such as lithium phosphate, alumina, or aluminum nitride. Lithium phosphate can provide additional lithium-ion transport channels, alumina can remove HF from the electrolyte, and aluminum nitride can accelerate heat diffusion through high thermal conductivity, further optimizing thermal safety. The bottom coating adopts an inorganic component / organic binder mass ratio of 8-10:1, which maintains the mechanical integrity of the electrode while ensuring ion / electron conduction, so that the critical failure displacement reaches 10-15μm, significantly improving the electrode processing performance and cycle stability. Through multi-scale synergistic regulation, while maintaining the high energy density advantage of high-nickel cathode, the safety and fast charging performance of the battery are comprehensively improved, which has important industrial application value. Detailed Implementation

[0014] To avoid unnecessary details, unless otherwise specified, all items used in the following examples are commercially available products, and all methods used are conventional methods unless otherwise specified.

[0015] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0016] This invention proposes a positive electrode sheet, comprising an aluminum current collector, a base coating, and a positive electrode active material layer coated on the surface of the base coating; the positive electrode active material layer is composed of a main active material and auxiliary nanoparticles, wherein the main active material is a layered metal oxide; the auxiliary nanoparticles are selected from at least one of phosphates, oxides, and nitrides; the main active material has a D50 particle size of 7-12 μm, denoted as D50 positive electrode; the auxiliary nanoparticles have a D50 particle size of 200-300 nm, denoted as D50 auxiliary.

[0017] This invention achieves a synergistic improvement in high energy density and high safety by setting a special positive electrode active material layer on the surface of the base coating. This particle size range ensures that the material has high compaction density and volumetric energy density, while avoiding the problems of excessively long lithium-ion diffusion paths and poor high-rate performance caused by excessively large particles. At the same time, the main active material and auxiliary nanoparticles in this particle size range form an optimal graded packing effect, which significantly reduces the porosity of the electrode, not only improving the structural stability of the active layer, but also effectively suppressing particle breakage and microcrack propagation, thus achieving both high capacity utilization and long cycle life.

[0018] Optionally, the ratio of the D50 particle size of the auxiliary nanoparticles to the D50 particle size of the main active material is 0.02-0.04.

[0019] This specific ratio follows the principle of closest packing of particle size distribution, ensuring that auxiliary nanoparticles can precisely fill the intergranular voids constructed by the micron-sized main active material. This avoids both excessively large particles that could stretch the main material and reduce compaction density, and excessively small particles that could lead to agglomeration and increased side reactions. At this golden ratio, the auxiliary particles not only increase the overall density of the electrode but also construct a highly efficient short-range conductive network, significantly reducing interparticle contact resistance and effectively dispersing the expansion stress of the main material as mechanical buffer sites. This synergistically improves the battery's volumetric energy density, rate performance, and long-cycle stability.

[0020] Optionally, the amount of auxiliary nanoparticles added is 3-6 wt% of the total mass of the positive electrode active material layer; this ratio is key to balancing energy density and safety performance: if the content is too low, it is difficult to form an effective mechanical buffer and physical barrier network, and it cannot fully suppress crack propagation; if the content is too high, it will sacrifice battery capacity and increase interfacial impedance. This specific amount of addition ensures that the nanoparticles are fully filled and uniformly dispersed in the gaps between the main materials, maximizing their structural enhancement and thermal stability effects, while also ensuring a high proportion of the main active material, achieving the best balance between high specific capacity, low polarization, and excellent safety.

[0021] Optionally, the auxiliary nanoparticles are at least one of lithium phosphate (Li3PO4), aluminum phosphate (AlPO4), lithium vanadium phosphate (Li3V2(PO4)3), aluminum oxide (Al2O3), silicon dioxide (SiO2), titanium dioxide (TiO2), boron nitride (BN), and aluminum nitride (AlN). Among them, phosphate nanoparticles not only have excellent thermal stability but also provide additional lithium-ion transport channels and reduce polarization; oxide nanoparticles, as chemical inert barriers, can effectively remove trace amounts of HF in the electrolyte and inhibit interfacial side reactions and metal dissolution; nitride nanoparticles have excellent thermal conductivity, which helps to evenly dissipate heat from the electrode. The introduction of these materials significantly enhances the heat resistance, chemical stability, and mechanical strength of the electrode, thereby greatly improving the safety performance and cycle life of the battery.

[0022] Optionally, the base coating comprises an inorganic component and a binder; the inorganic component consists of a solid electrolyte and a conductive agent; the solid electrolyte comprises at least one of lithium aluminum titanium phosphate (LATP), lithium lanthanum zirconium titanium oxide (LLZTO), and lithium lanthanum zirconium oxide (LLZO); the conductive agent in the base coating is selected from carbon black (SP) and / or carbon nanotubes (CNT); and the binder is at least one of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), and polyimide (PI).

[0023] This invention introduces a composite inorganic component of solid electrolyte (LATP / LLZTO, etc.) and conductive agent (SP / CNT) into the undercoat layer, constructing a dual-functional interface layer with both high ionic and electronic conductivity. The solid electrolyte provides a rapid transport channel for lithium ions, significantly reducing interfacial impedance and polarization; the conductive agent ensures contact between the current collector and the active layer; and in conjunction with a high-strength binder (PVDF, etc.), this undercoat layer not only greatly enhances electrode adhesion and prevents delamination, but its highly thermally stable inorganic components also act as a thermal barrier under abuse conditions, delaying thermal runaway and significantly improving battery rate performance and safety.

[0024] Optionally, the mass ratio of inorganic components to binder in the base coating is 8-10:1. This ratio ensures that the solid electrolyte and conductive agent form a continuous and dense functional network, maximizing ion and electron transport efficiency and significantly reducing interfacial impedance and polarization. At the same time, the high content of inorganic components constructs a robust thermal barrier, greatly improving the resistance to thermal shock, and retaining the minimum binder content required to maintain the flexibility of the coating. This effectively avoids the increase in impedance caused by excessive binder or the brittle cracking and peeling of the coating caused by insufficient binder, achieving a balance between excellent electrochemical performance and processing stability.

[0025] Optionally, the layered metal oxide is LiNi. x Co y Mn z O2 or LiNi x Co y Al z O2, where x≥0.4, x+y+z=1. This layered metal oxide is a high-nickel ternary material with high specific capacity and high energy density, but its thermal stability is relatively poor under abuse conditions such as needle punching or extrusion, requiring a dielectric hard barrier layer to improve its safety performance.

[0026] Optionally, in the spherical indentation test, the critical failure displacement of the positive electrode sheet is 10-15 μm. The positive electrode sheet prepared by this invention has a high critical failure displacement, indicating that there is a very strong bonding force between the active layer and the current collector, and the coating itself has good ductility, which can effectively adapt to the mechanical stress of the battery during winding, stamping and other processing, avoid powder shedding or brittle fracture, and can fully buffer the internal stress generated by the repeated expansion / contraction of the active particles during charging and discharging, preventing the electrode sheet from peeling or the propagation of microcracks, so that the prepared battery has overall structural integrity and long cycle life.

[0027] This invention also provides a method for preparing a positive electrode sheet, comprising the following steps: a) Pretreated aluminum foil is obtained by pre-treating aluminum foil using an alkaline washing + acid washing process; b) After the solid electrolyte, conductive agent and binder are mixed evenly, they are added to the solvent and dispersed at high speed to obtain the base coating slurry; c) Using a slot coating process, the base coating slurry is evenly coated on both sides of the pretreated aluminum foil, and after drying and curing, an aluminum current collector coated with the base coating is obtained. d) Take the positive electrode active material, conductive carbon black, carbon nanotubes, polyvinylidene fluoride and auxiliary nanoparticles and stir them thoroughly in the solvent system to obtain the positive electrode coating material. Then coat the positive electrode coating material onto the pretreated aluminum foil, and after drying and cold pressing, obtain the positive electrode sheet.

[0028] The present invention also provides a lithium-ion battery comprising the positive electrode sheet as described above.

[0029] Specifically, the secondary battery includes a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode includes a negative current collector copper foil and a negative electrode coating material coated on both sides of the copper foil. Calculated by mass percentage, the negative electrode coating material includes 10.0% deposited silicon carbon, 76.0% graphite, 0.75% of the conductive agent, 0.75% conductive carbon black, 1.0% thickener sodium carboxymethyl cellulose (CMC), 0.75% binder polyacrylic acid (PAA), and 0.75% binder styrene-butadiene rubber (SBR). The compaction density of the negative electrode is 1.5 g / cm3.

[0030] A membrane with high porosity (~40%) was selected. The thickness of the PE base membrane in the membrane was 9 μm, the thickness of the ceramic coating on both sides of the base membrane was 1.0 μm, and the thickness of the PVDF coating was 1.0 μm.

[0031] The electrolyte includes lithium hexafluorophosphate (LiPF6), and organic solvents such as ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), ethylene sulfate (DTD), and vinylene carbonate (VC).

[0032] After the positive and negative electrode sheets are rolled and slit, they are wound together with the separator according to a set process to form a 21700 cylindrical battery core. Subsequently, the battery core is fixed to a pre-made connecting piece by welding and then installed into a metal battery casing. After completing key processes such as electrolyte injection, sealing, and formation, the lithium-ion battery described in Example 1 is obtained. This lithium-ion battery uses a cylindrical casing with an external dimension of 21.0 mm in diameter and 70.0 mm in length, conforming to the 21700 standard specification.

[0033] The technical solution of the present invention will be further explained and illustrated below through specific embodiments.

[0034] Example 1 This embodiment discloses a positive electrode sheet and a lithium-ion battery, and its preparation method includes the following steps: 1. Preparation method of primer current collector a) Pretreatment of aluminum current collector Aluminum foil with a thickness of about 8μm was selected, and the surface oil and oxide layer were removed by alkaline washing + acid washing process: first, it was soaked in 5% NaOH solution for 30s (25℃), then neutralized with 10% HNO3 solution for 30s, and finally rinsed with deionized water until neutral, and dried in a vacuum drying oven at 80℃ for 2h for later use.

[0035] b) Preparation of the base coating slurry Solid electrolyte LLZTO, conductive agent SWCNT and binder PVDF were mixed at a mass percentage of 45:45:10 (the mass ratio of inorganic components to binder was 9:1), and added to N-methylpyrrolidone (NMP) solvent with a solid content of 40wt%. The mixture was dispersed for 30 minutes using a high-speed disperser (3000rpm) to form a uniform slurry without agglomeration.

[0036] c) Primer coating A slot coating process was used to uniformly coat the slurry onto both sides of the pretreated aluminum foil. The wet film thickness was calculated based on the target thickness of the base coating after drying (0.5 μm) and the solid content of the slurry (when the solid content is 30%, the wet film thickness = target dry film thickness / 0.3, i.e., 1.7 μm). The sample was then placed in a vacuum oven at 100℃ for 30 min to dry and cure, forming a dense and strong adhesive layer. The total thickness of the aluminum current collector after the base coating was 9 μm.

[0037] 2. Method for manufacturing positive electrode plates Take the positive electrode active material (Li1Ni) 0.8 Co 0.1 Mn 0.1 O2 (D50 9.5 μm), conductive carbon black, carbon nanotubes, polyvinylidene fluoride (PVDF), and auxiliary nanoparticles lithium phosphate (Li3PO4, D50 250 nm) were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 92:1:1:2:4 (the mass of the auxiliary nanoparticles was 4.3% of the active main material; the D50 auxiliary / D50 positive ratio was 0.026) to obtain the positive electrode coating material. This positive electrode coating material was then coated onto the aforementioned coated aluminum foil. After drying and cold pressing, the positive electrode sheet was obtained with a compaction density of 3.6 g / cm³. 3 .

[0038] 3. Negative electrode manufacturing method The negative electrode sheet includes a copper foil current collector and a negative electrode coating material coated on both sides of the current collector. The negative electrode coating material includes 20.0 wt% deposited silicon carbon, 76.0 wt% graphite, 0.5 wt% single-walled carbon nanotubes (SWCNTs), 0.9 wt% conductive carbon black, 1.0 wt% sodium carboxymethyl cellulose, 0.8 wt% polyacrylic acid, and 0.8 wt% styrene-butadiene rubber. These substances are added to deionized water and stirred to form the negative electrode coating material. The negative electrode coating material is then coated on both sides of the current collector. After drying and cold pressing, the negative electrode sheet is formed with a compaction density of 1.55 g / cm³. 3 .

[0039] 4. Preparation of electrolyte An electrolyte was prepared by mixing lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC) in a mass percentage ratio of 16.0:22.0:52.0:5.0:5.0.

[0040] 5. Diaphragm A membrane with high porosity (~40%) was selected. The thickness of the PE base membrane in the membrane was 9 μm, the thickness of the ceramic coating on both sides of the base membrane was 1.0 μm, and the thickness of the PVDF coating was 1.0 μm.

[0041] 6. Assembly of lithium-ion batteries After the positive and negative electrode sheets are rolled and slit, they are wound together with the separator according to a set process to form a 21700 cylindrical battery core. Subsequently, the battery core is fixed to a pre-made connecting piece by welding and then installed into a metal battery casing. After completing key processes such as electrolyte injection, sealing, and formation, the lithium-ion battery described in Example 1 is obtained. This lithium-ion battery uses a cylindrical casing with an external dimension of 21.0 mm in diameter and 70.0 mm in length, conforming to the 21700 standard specification.

[0042] Example 2 The difference between this embodiment and Embodiment 1 is that the active material Li1Ni in the positive electrode sheet... 0.8 Co 0.1 Mn 0.1 The D50 particle size of O2 is 7.0 μm, the D50 auxiliary / D50 positive ratio is 0.036, and all other parameters are the same as in Example 1.

[0043] Example 3 The difference between this embodiment and Embodiment 1 is that the active material Li1Ni in the positive electrode sheet... 0.8 Co 0.1 Mn 0.1The D50 particle size of O2 is 12.0 μm, the D50 auxiliary / D50 positive ratio is 0.021, and all other parameters are the same as in Example 1.

[0044] Example 4 The difference between this embodiment and Embodiment 1 is that the D50 particle size of the auxiliary nanoparticles Li3PO4 in the positive electrode is 201 nm, and the D50 auxiliary / D50 positive electrode ratio is 0.021. All other aspects are the same as in Embodiment 1.

[0045] Example 5 The difference between this embodiment and Embodiment 1 is that the D50 particle size of the auxiliary nanoparticles Li3PO4 in the positive electrode is 299 nm, and the D50 auxiliary / D50 positive electrode ratio is 0.031. All other aspects are the same as in Embodiment 1.

[0046] Example 6 The difference between this embodiment and Embodiment 1 is that the auxiliary nanoparticles in the positive electrode sheet account for 3.2 wt% of the mass percentage of the main active material (Li1Ni). 0.8 Co 0.1 Mn 0.1 The mass ratio of O2, conductive carbon black, carbon nanotubes, polyvinylidene fluoride (PVDF), and auxiliary nanoparticle lithium phosphate (Li3PO4) was 95:1:1:2:1. All other components were the same as in Example 1.

[0047] Example 7 The difference between this embodiment and Embodiment 1 is that the auxiliary nanoparticles in the positive electrode sheet account for 5.5 wt% of the mass percentage of the positive electrode active material (Li1Ni). 0.8 Co 0.1 Mn 0.1 The mass ratio of O2, conductive carbon black, carbon nanotubes, polyvinylidene fluoride (PVDF), and auxiliary nanoparticle lithium phosphate (Li3PO4) is 91:1:1:2:5. All other components are the same as in Example 1.

[0048] Example 8 The difference between this embodiment and Embodiment 1 is that the auxiliary nanoparticles in the positive electrode sheet are aluminum oxide (Al2O3), while all other aspects are the same as in Embodiment 1.

[0049] Example 9 The difference between this embodiment and Embodiment 1 is that the auxiliary nanoparticles in the positive electrode are aluminum nitride (AlN), while all other aspects are the same as in Embodiment 1.

[0050] Example 10 The difference between this embodiment and Embodiment 1 is that the solid electrolyte type in the undercoat is LATP, while all other aspects are the same as in Embodiment 1.

[0051] Example 11 The difference between this embodiment and Embodiment 1 is that the solid electrolyte in the undercoat is LLZO, while all other aspects are the same as in Embodiment 1.

[0052] Example 12 The difference between this embodiment and Embodiment 1 is that the mass ratio of inorganic (solid electrolyte + conductive agent) to organic (binder) components in the base coating is 8:1, while all other aspects are the same as in Embodiment 1.

[0053] Example 13 The difference between this embodiment and Embodiment 1 is that the mass ratio of inorganic (solid electrolyte + conductive agent) to organic (binder) components in the base coating is 10:1, while all other aspects are the same as in Embodiment 1.

[0054] Comparative Example 1 The difference between this comparative example and Example 1 is that the active material Li1Ni in the positive electrode sheet... 0.8 Co 0.1 Mn 0.1 The D50 particle size of O2 is 4.0 μm, the D50 auxiliary / D50 positive ratio is 0.063, and all other parameters are the same as in Example 1.

[0055] Comparative Example 2 The difference between this comparative example and Example 1 is that the active material Li1Ni in the positive electrode sheet... 0.8 Co 0.1 Mn 0.1 The D50 particle size of O2 is 15.0 μm, the D50 auxiliary / D50 positive ratio is 0.017, and all other parameters are the same as in Example 1.

[0056] Comparative Example 3 The difference between this comparative example and Example 1 is that the D50 particle size of the auxiliary nanoparticles Li3PO4 in the positive electrode is 150 nm, and the D50 auxiliary / D50 positive electrode ratio is 0.016. All other aspects are the same as in Example 1.

[0057] Comparative Example 4 The difference between this comparative example and Example 1 is that the D50 particle size of the auxiliary nanoparticles Li3PO4 in the positive electrode is 350 nm, and the D50 auxiliary / D50 positive electrode ratio is 0.037. All other aspects are the same as in Example 1.

[0058] Comparative Example 5 The difference between this embodiment and Embodiment 1 is that the auxiliary nanoparticles in the positive electrode sheet account for 1.1 wt% of the mass percentage of the main active material (Li1Ni). 0.8 Co 0.1 Mn 0.1The mass ratio of O2, conductive carbon black, carbon nanotubes, polyvinylidene fluoride (PVDF), and auxiliary nanoparticle lithium phosphate (Li3PO4) was 95:1:1:2:1. All other components were the same as in Example 1.

[0059] Comparative Example 6 The difference between this embodiment and Embodiment 1 is that the auxiliary nanoparticles in the positive electrode sheet account for 7.8 wt% of the mass percentage of the main active material (Li1Ni). 0.8 Co 0.1 Mn 0.1 The mass ratio of O2, conductive carbon black, carbon nanotubes, polyvinylidene fluoride (PVDF), and auxiliary nanoparticle lithium phosphate (Li3PO4) was 89:1:1:2:7. All other components were the same as in Example 1.

[0060] Comparative Example 7 The difference between this embodiment and Embodiment 1 is that the auxiliary nanoparticles in the positive electrode sheet are aluminum phosphate (AlPO4), while all other aspects are the same as in Embodiment 1.

[0061] Comparative Example 8 The difference between this embodiment and Embodiment 1 is that the auxiliary nanoparticles in the positive electrode sheet are titanium dioxide (TiO2), while all other aspects are the same as in Embodiment 1.

[0062] Comparative Example 9 The difference between this embodiment and Embodiment 1 is that the auxiliary nanoparticles in the positive electrode are boron nitride (BN), while all other aspects are the same as in Embodiment 1.

[0063] Comparative Example 10 The difference between this embodiment and Embodiment 1 is that there is no solid electrolyte in the base coating, and the inorganic components are all conductive agent SWCNT. Everything else is the same as in Embodiment 1.

[0064] Comparative Example 11 The difference between this embodiment and Embodiment 1 is that the mass ratio of inorganic (solid electrolyte + conductive agent) to organic (binder) components in the base coating is 12:1, while all other aspects are the same as in Embodiment 1.

[0065] Comparative Example 12 The difference between this embodiment and Embodiment 1 is that the mass ratio of inorganic (solid electrolyte + conductive agent) to organic (binder) components in the base coating is 6:1, while all other aspects are the same as in Embodiment 1.

[0066] Performance testing Methods for determining the size of active particles and auxiliary nanoparticles: Take a small amount of powder and spread it evenly on conductive tape. Then, take clear particle images of at least 5 different regions under a scanning electron microscope (SEM). Import the images using ImageJ or Nanomeasure software, calibrate the scale, and manually or automatically measure the projected diameter of more than 200 particles. Arrange the data in ascending order and plot the cumulative distribution curve. Take the particle size value corresponding to 50% of the cumulative percentage as D50. At the same time, it is necessary to exclude the interference data of obvious agglomerates to ensure accuracy.

[0067] Method for determining the mass ratio of inorganic to organic components in the bottom coating of the positive electrode: This method involves sampling and vacuum drying the bottom coating powder of the positive electrode sheet, then using a thermogravimetric analyzer (TGA) to test it up to 800℃ in an air atmosphere at a heating rate of 10℃ / min. The method utilizes the difference in thermal stability between the organic component (binder) which completely decomposes at 300~600℃ and the inorganic component (solid electrolyte + conductive agent) which remains stable above 600℃. The mass loss of the organic component (morganic) and the residual mass of the inorganic component (minorganic) are recorded, and the mass ratio between the two is calculated as R = minorganic / morganic.

[0068] Positive electrode sheet spherical indentation test method: Take the prepared positive electrode sheet and cut it into 10mm×10mm square samples. Dry it in a vacuum drying oven at 60℃ for 12h to remove residual solvent. Fix the sample on the stage of the indenter and use a 50μm diameter tungsten carbide spherical indenter. Set the loading rate to 10μm / min and apply vertical loading to the sample surface at room temperature (25℃) without humidity control. Record the displacement (μm) of the indenter and the corresponding loading force (mN) in real time during the loading process. When the force-displacement curve shows an obvious "plateau region" or "slope change" (indicating that cracks have appeared inside the positive electrode material layer or that it has peeled off from the current collector), the displacement value at this time is the critical failure displacement.

[0069] 70% Deformation Extrusion Test: After charging the lithium-ion battery to 100% state of charge, it is placed horizontally on a compression test platform. A cylindrical steel rod with a diameter of 32mm is used as the compression head, and compression force is applied to the battery thickness at a rate of 10mm / min. Simultaneously, a displacement sensor monitors the battery thickness change in real time. Compression is stopped immediately when the battery deformation reaches 70% of its original thickness. The requirements are: no fire, no explosion, and a maximum battery temperature <100℃.

[0070] 15mΩ external short-circuit test: The external short-circuit test method for the lithium-ion battery is as follows: First, charge the cell at a constant current of 1C to the rated voltage (e.g., 4.2V), then charge at a constant voltage until the charging current is ≤0.1C, and record the initial internal resistance and voltage; subsequently, use a 10mΩ low-resistance wire to directly connect the positive and negative terminals of the battery to trigger a short circuit; the test is conducted at 25℃. Passing requirements: no fire, no explosion, and a maximum battery temperature <80℃.

[0071] Needle prick test experiment: The battery to be tested was fully charged to 100% SOC and placed in a 25℃ environment for 2 hours to stabilize. Then, the battery was fixed on an insulating clamp, ensuring that its positive and negative terminals were horizontal. Using a 3mm diameter stainless steel needle, perpendicular to the battery surface and along the direction between the positive and negative terminals, the needle was inserted into the battery at a constant speed of 10±1mm / s until it was completely penetrated (the penetration depth should exceed 90% of the battery thickness). After insertion, the needle was kept still, and the battery status was continuously observed for 5 minutes. Any abnormal phenomena such as fire, explosion, or smoke were recorded, and temperature changes were monitored using a thermocouple attached to the battery surface.

[0072] 25℃ Rate Charging Performance Test Method: The lithium battery was discharged to 2.5V and placed in a 25℃ constant temperature chamber for 6 hours, and then tested according to the following steps: (1) Under 1C conditions, constant current and constant voltage charging to 4.2V, cutoff current is 0.1C, and stand for 30 minutes. The capacity of constant current charging to 4.2V is Q1 (constant current segment capacity). (2) Discharge under constant current at 1C until 2.5V cutoff, with a cutoff current of 0.1C, and let stand for 30 minutes; (3) Under 6C conditions, constant current and constant voltage charging to 4.2V, the cutoff current is 0.1C, and it is left to stand for 30 minutes. The capacity meter that is constant current charged to 4.2V is Q6. (4) Discharge under constant current at 1C until 2.5V cutoff, with a cutoff current of 0.1C, and let stand for 30 minutes; The calculation method for the 6C charging capacity retention rate of a lithium battery at 25℃ is: Q1 / Q6×100.

[0073] The test results are shown in Tables 1-7.

[0074] Table 1 Table 1 shows the battery performance under the combination of positive electrode active main material D50 particle size (7.0~12.0μm) and auxiliary nanoparticles with a fixed D50 particle size of 250nm: the smaller the main material D50 (e.g., Example 2, 7.0μm), the higher the 6C charging capacity retention rate (71.9%), but the slightly higher needle penetration temperature (93.5℃); the larger the main material D50 (e.g., Example 3, 12.0μm), the lower the 6C capacity retention rate (68.6%), but the lower the needle penetration temperature (80.5℃). All examples passed the needle penetration, extrusion, and short circuit tests. The mechanism is as follows: the auxiliary nanoparticles (250nm) enhance the mechanical strength of the electrode through the filling effect, and work synergistically with the bottom coating to buffer mechanical impact, ensuring the safety test is passed; reducing the main material D50 improves Li⁺ insertion / extraction kinetics (fast charging performance), but the finer particles lead to stress concentration, causing the needle penetration temperature to rise; increasing the main material D50 prolongs the Li⁺ insertion / extraction time. + The diffusion path (decreases with fast charging) is observed, but the particle mechanical strength is higher, crack propagation resistance is increased, and the needle penetration temperature is reduced, verifying that... With the D50 auxiliary / D50 positive electrode in the range of 0.02~0.04, adjusting the D50 of the main material can achieve a balance between energy density and fast charging performance under safe redundancy.

[0075] Table 2 Table 2 shows the battery performance of auxiliary nanoparticles with D50 (201~299nm) and corresponding particle size ratio (0.021~0.031): All examples passed the needle penetration, 70% deformation extrusion and 15mΩ short circuit tests, and the 6C charging capacity retention rate reached 67.5%~70.6%, and the highest needle penetration temperature was ≤83.4℃. The mechanism is as follows: When the auxiliary nanoparticles D50 are in the range of 200~300nm, the particle size ratio (0.021~0.031) formed with the positive electrode main material is in the optimal range (0.02~0.04) defined by the invention. This enhances the mechanical strength of the electrode through the particle filling effect (suppressing the pulverization and shedding of the active layer under needle punching / extrusion) and maintains the continuity of the ion transport channel (ensuring 6C fast charging performance). Among them, the 250nm auxiliary particles (Example 1) have better matching with the main material in terms of particle size, achieving the optimal balance between capacity retention (70.6%) and thermal safety (81.0℃). The 201nm (Example 4) and 299nm (Example 5) particles, due to their smaller or larger particle size, respectively lead to a slight increase in interfacial impedance (slight decrease in capacity retention) or a slightly weaker mechanical buffer (slight increase in needle punching temperature), but neither of them exceeds the safety threshold. This verifies that the auxiliary nanoparticles D50 can stably achieve synergistic optimization of mechanical enhancement and electrochemical performance in the range of 200~300nm.

[0076] Table 3 Table 3 shows the effect of the percentage of auxiliary nanoparticles in the positive electrode active material (3.2%~5.5%) on battery performance: all examples passed the needle penetration, 70% deformation extrusion and 15mΩ short circuit tests, the 6C charging capacity retention rate was 67.4%~71.5%, and the highest needle penetration temperature was ≤93.2℃. The mechanism is as follows: the mass ratio of auxiliary nanoparticles directly regulates the mechanical strength and ion transport efficiency of the electrode. When the mass ratio is 3.2% (Example 6), the mechanical enhancement effect is limited due to the small amount added (the needle penetration temperature rises to 93.2℃), but the ion diffusion is less hindered and the capacity retention rate is optimal (71.5%). When the mass ratio is 5.5% (Example 7), the mechanical enhancement is sufficient (the needle penetration temperature drops to 82.1℃), but the excessive particles lead to a slight increase in interfacial impedance and a slight decrease in capacity retention rate (67.4%). When the mass ratio is 4.3% (Example 1), it is in the optimal range (3%~5%) defined by the invention. Through the synergistic effect of "appropriate filling to enhance mechanical strength + non-blocking of ion channels", the optimal balance between capacity retention rate (70.6%) and thermal safety (81.0℃) is achieved, which verifies that the mass ratio of auxiliary nanoparticles in the range of 3%~5% can stably balance mechanical protection and electrochemical performance.

[0077] Table 4 Table 4 shows the impact of three auxiliary nanoparticles—lithium phosphate (Li3PO4), aluminum oxide (Al2O3), and aluminum nitride (AlN)—on battery performance: All examples underwent needle penetration, 70% deformation extrusion, and 15mΩ short-circuit tests. The 6C charging capacity retention rate was 68.7%~70.6%, and the highest needle penetration temperature was ≤82.6℃. Mechanistically, all three ensure safety through mechanical enhancement, but differences in material properties lead to performance differentiation—lithium phosphate, due to its lithium content promoting ion conduction, has the best capacity retention rate (70.6%) and balanced thermal safety (81.0℃); aluminum oxide has high mechanical strength but strong electrochemical inertness, resulting in a slightly lower capacity retention rate (69.4%) and a slightly higher needle penetration temperature (82.6℃); aluminum nitride, with its high thermal conductivity, rapidly disperses heat, resulting in the lowest needle penetration temperature (80.6℃), but its interfacial impedance leads to a slightly lower capacity retention rate (68.7%). This verifies that ceramic auxiliary nanoparticles can be selected according to different needs: lithium phosphate is chosen for fast charging, while aluminum nitride is chosen for thermal safety.

[0078] Table 5 Table 5 shows the impact of LLZTO, LATP, and LLZO solid electrolytes in the undercoat on battery performance: All examples underwent needle penetration, 70% deformation extrusion, and 15mΩ short-circuit tests. The 6C charging capacity retention rate was 68.9%–70.6%. During the needle penetration test, LATP reached a maximum surface temperature of 96.9℃, while LLZTO and LLZO both reached approximately 81℃. Mechanistically, the core difference among the three stems from the synergistic effect of ionic conductivity, chemical stability, and thermo / mechanical properties of the solid electrolytes—LLZTO, due to the introduction of lattice defects from titanium doping, enhances ionic conductivity (promoting fast charging), while its garnet-type structure imparts excellent mechanical strength (suppressing lithium dendrites and needle penetration). The garnet structure ensures optimal capacity retention (70.6%) and thermal stability (rapid dissipation of local heat), thus achieving a balance between thermal safety (81.0℃). Although LATP has high ionic conductivity, its poor chemical stability (easily reacts with the lithium anode to form a high-resistivity interface layer) and low thermal conductivity (making it difficult for Joule heat to diffuse during needle penetration) result in a slight decrease in capacity retention (69.3%) and a sharp increase in surface temperature (96.9℃). LLZO has slightly lower ionic conductivity than LLZTO (due to the lack of titanium doping defect regulation), so its capacity retention is slightly lower (68.9%). However, its garnet structure still ensures excellent mechanical strength and thermal stability, so its needle penetration temperature is close to that of LLZTO (81.7℃).

[0079] Table 6 Table 6 shows the effect of the inorganic / organic mass ratio (8:1, 9:1, 10:1) in the undercoat on battery performance. All examples underwent nail penetration, 70% deformation extrusion, and 15mΩ short-circuit tests. The 6C charging capacity retention rate was 67.9%~73.4%, and the highest surface temperature of the battery during the nail penetration test was 79.6℃~98.6℃. The core mechanism is the synergistic effect of the inorganic phase (providing mechanical support and ion conduction channels) and the organic phase (ensuring electrode flexibility and interfacial contact) in the undercoat. When the mass ratio is 9:1 (Example 1), the two... To achieve the optimal balance, the capacity retention rate (70.6%) and thermal safety (81.0℃) are best balanced. When the mass ratio is 8:1 (Example 10), the proportion of organic phase is too high. Although the needle penetration temperature decreases slightly (79.6℃), the capacity retention rate drops to 67.9%. When the mass ratio is 10:1 (Example 11), the proportion of inorganic phase is too high. The capacity retention rate increases to 73.4%, but the increased brittleness of the electrode leads to a sharp increase in the needle penetration temperature (98.6℃). Finally, it is verified that the inorganic / organic mass ratio of the undercoat needs to be controlled at around 9:1 to balance fast charging performance and safety performance.

[0080] Table 7 Table 7, through a comparison of Example 1 (the optimal solution) and 12 comparative examples, reveals the key impacts of the positive electrode active material particle size, auxiliary nanoparticle parameters (particle size / addition amount / type), and undercoating configuration on battery performance: Example 1, due to its optimal parameters, achieved a 6C capacity retention rate of 70.6% and passed the full safety test (needle penetration temperature 81.0℃); however, when the variables deviated, the performance significantly differentiated—if the positive electrode active material D50 was too small (4.0μm, Comparative Example 1), although the capacity was improved (73.9%), it caused serious safety failures (failure to pass needle penetration / extrusion / short circuit, temperature 456℃), while if it was too large (15.0μm)... In Comparative Example 2, the capacity dropped sharply (59.8%). Excessively large D50 of auxiliary nanoparticles (350nm, Comparative Example 4), insufficient addition (1.1%, Comparative Example 5), or inappropriate type (aluminum phosphate, Comparative Example 7) all led to failure in the safety test. Conversely, excessively small D50 (150nm, Comparative Example 3), excessive addition (7.8%, Comparative Example 6), or the use of titanium dioxide / boron nitride (Comparative Examples 8 / 9) resulted in reduced capacity. The absence of a solid electrolyte in the undercoat (Comparative Example 10) and an imbalance in the inorganic-organic ratio (12:1 / 6:1, Comparative Examples 11 / 12) respectively caused safety failure or capacity reduction. Ultimately, it was verified that only through the synergistic regulation of various parameters (such as cathode D50 compatibility, reasonable auxiliary nanoparticle D50 / addition amount / type, and appropriate undercoat configuration) can the optimal balance between battery capacity retention and safety performance be achieved.

[0081] The above are merely preferred embodiments of the present invention and do not limit the patent scope of the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the patent protection scope of the present invention.

Claims

1. A positive electrode plate, characterized in that, The device includes an aluminum current collector, a base coating, and a positive electrode active material layer coated on the surface of the base coating. The positive electrode active material layer is composed of a main active material and auxiliary nanoparticles. The main active material is a layered metal oxide. The auxiliary nanoparticles are selected from at least one of phosphates, oxides, and nitrides. The D50 particle size of the main active material is 7-12 μm, and the D50 particle size of the auxiliary nanoparticles is 200-300 nm.

2. The positive electrode sheet according to claim 1, characterized in that: The ratio of the D50 particle size of the auxiliary nanoparticles to the D50 particle size of the main active material is 0.02-0.

04.

3. The positive electrode sheet according to claim 1, characterized in that: The amount of auxiliary nanoparticles added is 3-6 wt% of the mass of the main active material.

4. The positive electrode sheet according to claim 1, characterized in that: The auxiliary nanoparticles are at least one of lithium phosphate, aluminum phosphate, lithium vanadium phosphate, aluminum oxide, silicon dioxide, titanium dioxide, boron nitride, and aluminum nitride.

5. The positive electrode sheet according to claim 4, characterized in that: The auxiliary nanoparticles are at least one of lithium phosphate, aluminum oxide, and aluminum nitride.

6. The positive electrode sheet according to claim 1, characterized in that: The base coating comprises inorganic components and a binder; the inorganic components consist of a solid electrolyte and a conductive agent; the solid electrolyte comprises at least one of lithium aluminum titanium phosphate, lithium lanthanum zirconium titanium oxide, and lithium lanthanum zirconium oxide; the conductive agent in the base coating is selected from carbon black and / or carbon nanotubes; the binder is at least one of polyvinylidene fluoride, polyacrylic acid, and polyimide.

7. The positive electrode sheet according to claim 6, characterized in that: The mass ratio of inorganic components to binder in the base coating is 8-10:

1.

8. The positive electrode sheet according to claim 1, characterized in that: The layered metal oxide is LiNi x Co y Mn z O2 or LiNi x Co y Al z O2, where x≥0.4, x+y+z=1.

9. The positive electrode sheet according to any one of claims 1-8, characterized in that: In the spherical indentation test, the critical failure displacement of the positive electrode sheet is 10-15 μm.

10. A lithium-ion battery, characterized in that, The lithium-ion battery includes a positive electrode as described in any one of claims 1-8.

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