Positive pole piece and preparation method thereof, lithium ion battery and power utilization device

Abstract

The invention discloses a positive pole piece and a preparation method thereof, a lithium ion battery and an electric device, and belongs to the technical field of new energy materials. By regulating and controlling the compaction density and porosity of the positive pole piece, the excellent volume energy density of the pole piece is guaranteed, a proper ion transmission channel is maintained, particle breakage or electrolyte infiltration difficulty caused by too high compaction is avoided, complementation of the rigidity and toughness of the coating is realized by adopting a mixed binder of PVDF and PAA, and the performance of the positive pole piece is improved. The structural integrity of the pole piece in charge and discharge expansion is guaranteed, interface impedance increase caused by too high adhesion is avoided, and a protective net with both ion conduction and thermal stability is constructed on the premise of not sacrificing energy density in cooperation with the auxiliary nanoparticles with specific content and size, so that the service life of the pole piece is prolonged, and the service life of the pole piece is prolonged. The design is particularly suitable for a high-nickel ternary material system with relatively poor thermal stability, and the technical problem that the rate capability and the safety of a high-nickel battery are difficult to realize is effectively solved.

Description

Technical Field

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

[0002] With the development of electric vehicles and high-energy-density energy storage systems, high-nickel ternary cathode materials (such as NCM811) are widely used due to their high energy density. However, under mechanical abuse conditions such as needle penetration, extrusion, and internal short circuits, high-nickel cathode systems are highly susceptible to low-resistance internal short circuits (aluminum current collector-anode / aluminum current collector-copper foil failure modes) caused by exposure of the cathode current collector aluminum foil. This leads to instantaneous high-current discharge and violent Joule heat release, which can trigger thermal runaway or even combustion and explosion. Although some studies have attempted to improve thermal stability through surface coating and electrolyte additives, these methods cannot fundamentally solve the problem of aluminum foil exposure caused by mechanical failure. In addition, insufficient interfacial adhesion between the aluminum current collector and the cathode active layer is one of the key factors leading to active layer peeling. In traditional direct coating processes, the binder polyvinylidene fluoride (PVDF) is unevenly distributed on the current collector surface, easily forming weak points at the interface and accelerating interlayer separation under mechanical damage. 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. This invention introduces a conductive undercoat between the aluminum current collector and the active layer, and introduces specific auxiliary nanoparticles into the active layer. At the same time, it strictly limits the compaction density and peel strength window of the electrode sheet, thereby achieving synergy between mechanical reinforcement and interfacial adhesion control. This effectively avoids aluminum foil exposure during the needle punching process and significantly improves the safety of the battery.

[0004] To achieve the above objectives, the present invention proposes a positive electrode sheet, comprising a current collector, a base coating, and a positive active material layer coated on the surface of the base coating; the base coating is located between the current collector and the positive active material layer. The compaction density of the positive electrode sheet is 3.3-3.7 g / cm³. 3 ; The porosity of the positive electrode sheet is 18-30%.

[0005] Based on the above technical solutions, preferably, the peel strength of the positive electrode sheet is 15-30 N / m.

[0006] Based on the above technical solution, preferably, the positive electrode active material layer is composed of a main active material and auxiliary nanoparticles; the main active material is a metal oxide; the D90 particle size, D50 particle size, and D10 particle size of the main active material satisfy 0.85 < <1.15.

[0007] Based on the above technical solutions, preferably, the auxiliary nanoparticles are at least one of phosphates, oxides, and nitrides; the mass percentage of the added auxiliary nanoparticles is 2-6 wt%, and the size of the auxiliary nanoparticles is 220-410 nm.

[0008] Based on the above technical solutions, preferably, the base coating includes a conductive agent and a binder; the binder in the base coating is a mixture of polyvinylidene fluoride (PVDF) and polyacrylic acid (PAA).

[0009] Based on the above technical solutions, preferably, the auxiliary nanoparticles are at least one of aluminum oxide, lithium phosphate, silicon dioxide, titanium dioxide, boron nitride, and aluminum nitride.

[0010] Based on the above technical solutions, preferably, the auxiliary nanoparticles are a mixture of aluminum oxide and lithium phosphate.

[0011] Based on the above technical solution, preferably, the metal oxide is LiNi. x Co y Mn z O2, LiNi x Co y Al z At least one of O2, LiCoO2, and LiFePO4, wherein x ≥ 0.3 and x + y + z = 1.

[0012] The present invention also provides a lithium-ion battery comprising the positive electrode sheet as described in any one of claims 1-8.

[0013] The present invention also provides an electrical device comprising the aforementioned lithium-ion battery.

[0014] 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 introducing auxiliary nanomaterials with mechanical reinforcement and adhesion regulation functions into a high-nickel positive electrode slurry, the microstructure and mechanical properties of the positive electrode sheet can be significantly regulated, enhancing the spatial distribution uniformity of the binder, improving the cohesive strength of the active material layer, and increasing the adhesion strength between the active material layer and the aluminum foil. Simultaneously, pre-coating the aluminum current collector surface with a conductive adhesive undercoat further optimizes the interfacial bonding and effectively inhibits active layer peeling. Therefore, when the battery is punctured, the positive electrode material layer can preferentially transfer stress to the aluminum foil and cause it to break, while remaining firmly attached to the current collector surface, effectively preventing aluminum foil exposure. This transforms the originally dangerous aluminum current collector-negative electrode type internal short circuit into a safe positive electrode-negative electrode type internal short circuit, thereby improving the safety of the lithium battery. 2) By controlling the compaction density and porosity of the positive electrode sheet, this invention not only ensures the excellent volumetric energy density of the electrode sheet but also maintains a suitable ion transport channel, avoiding particle breakage or electrolyte wetting difficulties caused by excessive compaction. By using a mixed binder of PVDF and PAA, the rigidity and toughness of the coating are complemented, ensuring the structural integrity of the electrode sheet during charge and discharge expansion while avoiding the increase in interfacial impedance caused by excessive adhesion. In conjunction with auxiliary nanoparticles of specific content (2-6wt%) and size (220-410nm), a protective network with both ion conductivity and thermal stability is constructed without sacrificing energy density. This design is particularly suitable for high-nickel ternary material systems with poor thermal stability, effectively solving the technical problem of balancing rate performance and safety in high-nickel batteries. 3) The lithium-ion battery of the present invention is discharged to 2.5V at 25°C and left to stand for 6 hours, and then charged to 4.2V at constant current with charging rates of 1C and 6C respectively. The corresponding constant current charging capacity is Q1 and Q6, wherein the charging capacity is maintained to satisfy Q6 / Q1≥65%, which ensures the efficient operation of the battery in the rapid energy replenishment scenario; and in the nail penetration test (steel nail diameter 3mm, puncture speed 5mm / s), it does not catch fire or explode, and the highest surface temperature is ≤95°C, which fundamentally suppresses the risk of thermal runaway. Detailed Implementation

[0015] 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.

[0016] 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.

[0017] This invention proposes a positive electrode sheet, comprising a current collector, a base coating, and a positive electrode active material layer coated on the surface of the base coating; the base coating is located between the current collector and the positive electrode active material layer. The compaction density of the positive electrode sheet is 3.3-3.7 g / cm³. 3 ; The porosity of the positive electrode sheet is 18-30%.

[0018] The positive electrode sheet of this invention significantly enhances the interfacial bonding force by introducing a base coating containing conductive agents and binders between the aluminum current collector and the active layer, effectively suppressing the peeling of the active layer and the exposure of the aluminum current collector under mechanical abuse; and by strictly controlling the compaction density to 3.3-3.7 g / cm³.3 With a porosity of 18-30%, the electrode not only ensures excellent volumetric energy density but also maintains suitable ion transport channels, preventing particle breakage or electrolyte wetting difficulties caused by excessive compaction. Furthermore, the phosphate and other auxiliary nanoparticles introduced into the active layer work synergistically with the undercoat to improve the overall structural stability of the electrode and enhance interfacial thermal conductivity. This design effectively prevents severe internal short circuits caused by direct exposure of the current collector under extreme conditions such as needle penetration, significantly improving the safety and rate performance of high-energy-density lithium-ion batteries.

[0019] Optionally, the peel strength of the positive electrode sheet is 15-30 N / m.

[0020] By limiting the peel strength of the positive electrode to 15-30 N / m, an optimal balance between the mechanical stability and electrochemical performance of the electrode is achieved. This strength range ensures that the active material layer adheres tightly to the current collector under extreme conditions such as needle penetration, effectively preventing the exposure of the aluminum current collector due to interlayer peeling and the resulting malignant short circuit between the aluminum and negative electrodes, thereby suppressing thermal runaway. On the other hand, this range avoids the increase in interfacial impedance and the obstruction of ion transport caused by excessive adhesion, preventing the degradation of high-rate charge and discharge performance and ensuring that the battery has both excellent safety and kinetic performance.

[0021] Optionally, the positive electrode active material layer is composed of a main active material and auxiliary nanoparticles; the main active material is a metal oxide; the D90 particle size, D50 particle size, and D10 particle size of the main active material satisfy 0.85 < <1.15.

[0022] By limiting the particle size distribution range of the main active material, the packing method of the active material particles was optimized. This range ensured a reasonable combination of large and small particles, effectively filling the gaps between large particles with small particles, thereby achieving a high compaction density (3.3-3.7 g / cm³) under pressure without damaging the material structure. 3 This significantly improves the volumetric energy density. Simultaneously, this distribution avoids the side reactions caused by excessively large pores due to an overly narrow distribution or excessive fine powder in an overly wide distribution, constructing a uniform and unobstructed ion transport channel, and synergistically improving the battery's cycle stability and rate performance.

[0023] Optionally, the auxiliary nanoparticles are at least one of phosphates, oxides, and nitrides; the mass percentage of the auxiliary nanoparticles added is 2-6 wt%, and the size of the auxiliary nanoparticles is 220-410 nm.

[0024] This invention constructs an optimal microstructure network that balances electron / ion transport and mechanical safety by limiting the type, content, and size of auxiliary nanoparticles. An addition of 2-6 wt% can form an effective physical isolation layer to block short-circuit thermal runaway, while avoiding the reduction in the proportion of active material and the sharp increase in impedance caused by excessive addition. With the selection of particle size of 220-410 nm, it not only optimizes the filling efficiency of particles in the gaps between active layers and enhances structural stability, but also prevents agglomeration caused by excessively small particle size or a reduction in contact points caused by excessively large particle size. Thus, it significantly improves safety while maximizing the energy density and rate performance of the battery.

[0025] Optionally, the primer layer includes a conductive agent and a binder; the binder in the primer layer is a mixture of polyvinylidene fluoride (PVDF) and polyacrylic acid (PAA).

[0026] This invention uses a mixture of PVDF and PAA as the binder for the undercoat, achieving a synergistic enhancement of rigidity and toughness. PAA provides high-strength polar bonding, significantly improving the coating's adhesion to the current collector; while PVDF introduces necessary flexibility, buffering the volume expansion stress during charging and discharging. This composite system not only ensures the electrode has suitable peel strength (approximately 25 N / m), avoiding the problems of excessive brittleness of PAA alone or insufficient adhesion of PVDF, but also effectively reduces interfacial impedance, significantly improving the battery's rate performance and cycle stability.

[0027] Optionally, the auxiliary nanoparticles are at least one of aluminum oxide (Al2O3), lithium phosphate (Li3PO4), silicon dioxide (SiO2), titanium dioxide (TiO2), boron nitride (BN), and aluminum nitride (AlN); more preferably, the auxiliary nanoparticles are a mixture of aluminum oxide and lithium phosphate.

[0028] The aforementioned auxiliary nanoparticles, acting as physical barrier agents, can effectively disperse thermal stress and suppress internal short-circuit current under mechanical abuse. Further optimization of the Al2O3 and Li3PO4 combination leverages the high modulus of Al2O3 to enhance the mechanical stability of the active layer structure and prevent particle breakage; simultaneously, the ionic conductivity of Li3PO4 improves interfacial lithium-ion transport. The synergistic effect of both not only significantly reduces the maximum temperature rise during needle penetration by forming a more robust ceramic armor, greatly improving safety, but also compensates for the increased impedance caused by inert particles, ensuring excellent rate performance and energy retention of the battery.

[0029] Optionally, the metal oxide is LiNi. x Co y Mn z O2, LiNi x Co y Alz At least one of O2, LiCoO2, and LiFePO4, wherein x ≥ 0.3 and x + y + z = 1.

[0030] This invention is applicable to various cathode systems, including high-nickel ternary (x≥0.3), lithium cobalt oxide, and lithium iron phosphate. In particular, it is suitable for high-nickel ternary materials (such as NCM811) that have high energy density but inherently poor thermal stability. The electrode structure design of this invention can effectively make up for their safety shortcomings. Through the synergistic protection of the bottom coating and nanoparticles, even when using high-nickel materials, it can pass the stringent nail penetration test, thus achieving both high energy density and high safety performance, and broadening the flexibility of battery material selection and application scenarios.

[0031] The present invention also provides a positive electrode sheet, the preparation method of which includes the following steps: a) Pretreated aluminum foil is obtained by pre-treating aluminum foil using an alkaline washing + acid washing process; b) After the conductive agent and binder are mixed evenly, they are added to an organic 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, PAA, and auxiliary nanoparticles and mix them thoroughly in a solvent system to obtain a positive electrode coating material. Then, coat the positive electrode coating material onto the pretreated aluminum foil, and after drying and secondary rolling, obtain the positive electrode sheet.

[0032] The present invention also provides a lithium-ion battery, the lithium-ion battery comprising the above-mentioned positive electrode, specifically including a positive electrode, a negative electrode, a separator and an electrolyte.

[0033] 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 deposited silicon carbide, graphite, single-walled carbon nanotubes, conductive carbon black, sodium carboxymethyl cellulose, polyacrylic acid, and styrene-butadiene rubber. The above substances are added to deionized water and stirred to form the negative electrode coating material. Then, the negative electrode coating material is coated on both sides of the current collector. After drying and cold pressing, the negative electrode sheet is formed.

[0034] The electrolyte is prepared as follows: lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC) are mixed evenly to obtain the electrolyte.

[0035] After the positive and negative electrode sheets are rolled and slit, they are wound together with a high-porosity 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.

[0036] The technical solution of the present invention will be further explained and illustrated below through specific embodiments.

[0037] Example 1 This embodiment discloses a positive electrode and a lithium-ion battery, including the following steps: 1. Preparation method of primer current collector a) Pretreatment of aluminum current collector Aluminum foil with a thickness of about 7μm 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 30 seconds (25℃), then neutralized with 10% HNO3 solution for 30 seconds, and finally rinsed with deionized water until neutral, and dried in a vacuum drying oven at 80℃ for 2 hours for later use.

[0038] b) Preparation of the base coating slurry The conductive agent CNT, binder PVDF and PAA were mixed in a mass ratio of 84:8:8 and added to N-methylpyrrolidone (NMP) solvent with a solid content of 30wt%. The mixture was dispersed for 30 minutes using a high-speed disperser (3000rpm) to form a uniform slurry without agglomeration.

[0039] 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 8 μm.

[0040] 2. Method for manufacturing positive electrode plates Take the positive electrode active material (Li1Ni) 0.8 Co 0.1 Mn 0.1O2), conductive carbon black, carbon nanotubes, PVDF, PAA, auxiliary nanoparticles Al2O3 and Li3PO4, mixed thoroughly in an N-methylpyrrolidone solvent system at a mass ratio of 92:1:1:1:1:2:2 (the mass percentage of auxiliary nanoparticles added is 4wt%) to obtain a positive electrode coating material. This positive electrode coating material is then coated onto the aforementioned aluminum foil. After drying, the electrode sheet undergoes a second rolling process: the first pressure is 10 MPa, and the second pressure is 8 MPa, resulting in a positive electrode sheet with a peel strength of 25 N / m and a compaction density of 3.5 g / cm³. 3 The porosity is 24%.

[0041] 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. The above substances are added to deionized water and stirred to form the negative electrode coating material. Then, the negative electrode coating material is coated on both sides of the current collector. After drying and cold pressing, the negative electrode sheet is formed with a compaction density of 1.6 g / cm3.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] The charging characteristics of the lithium-ion battery are as follows: after discharging the lithium-ion battery to 2.5V at 25°C and letting it stand for 6 hours, it is charged to 4.2V at constant current with charging rates of 1C and 6C respectively. The corresponding constant current charging capacities are Q1 and Q6, wherein the charging capacity is maintained to satisfy Q6 / Q1≥65%.

[0046] The lithium-ion battery did not catch fire or explode during the nail penetration test (3mm diameter steel nail, 5mm / s penetration speed), and the highest surface temperature was ≤95℃.

[0047] Example 2 The difference between this embodiment and Embodiment 1 is that the pressure of the first rolling of the positive electrode sheet is 8 MPa, and the pressure of the second rolling is 8 MPa (compacted density is 3.3 g / cm³). 3 (Porosity is 30%), and everything else is the same as in Example 1.

[0048] Example 3 The difference between this embodiment and Embodiment 1 is that the pressure of the first rolling of the positive electrode sheet is 12 MPa, and the pressure of the second rolling is 10 MPa (compacted density is 3.73 g / cm³). 3 (Porosity is 18%), and everything else is the same as in Example 1.

[0049] Example 4 The difference between this embodiment and Embodiment 1 is that the positive electrode active material (Li1Ni) in the positive electrode sheet... 0.8 Co 0.1 Mn 0.1 The mass ratio of O2), conductive carbon black, carbon nanotubes, PVDF, auxiliary nanoparticles Al2O3 and auxiliary nanoparticles Li3PO4 is 92:1:1:2:2:2 (the peeling force of the positive electrode is 16 N / m), and everything else is the same as in Example 1.

[0050] Example 5 The difference between this embodiment and Embodiment 1 is that the positive electrode active material (Li1Ni) in the positive electrode sheet... 0.8 Co 0.1 Mn 0.1 The mass ratio of O2), conductive carbon black, carbon nanotubes, PAA, auxiliary nanoparticles Al2O3 and auxiliary nanoparticles Li3PO4 is 92:1:1:2:2:2 (the peeling force of the positive electrode is 29 N / m), and everything else is the same as in Example 1.

[0051] Example 6 The difference between this embodiment and Embodiment 1 is that the positive electrode active material (Li1Ni) in the positive electrode sheet... 0.8 Co 0.1 Mn 0.1The mass ratio of O2), conductive carbon black, carbon nanotubes, PVDF, PAA and auxiliary nanoparticles Al2O3 is 92:1:1:1:1:4, and all other aspects are the same as in Example 1.

[0052] Example 7 The difference between this embodiment and Embodiment 1 is that the positive electrode active material (Li1Ni) in the positive electrode sheet... 0.8 Co 0.1 Mn 0.1 The mass ratio of O2), conductive carbon black, carbon nanotubes, PVDF, PAA and auxiliary nanoparticles Li3PO4 is 92:1:1:1:1:4, and all other aspects are the same as in Example 1.

[0053] Example 8 The difference between this embodiment and Embodiment 1 is that the positive electrode active material (Li1Ni) in the positive electrode sheet... 0.8 Co 0.1 Mn 0.1 The mass ratio of O2), conductive carbon black, carbon nanotubes, PVDF, PAA, auxiliary nanoparticles Al2O3 and Li3PO4 is 94:1:1:1:1:1:1, and all other aspects are the same as in Example 1.

[0054] Example 9 The difference between this embodiment and Embodiment 1 is that the positive electrode active material (Li1Ni) in the positive electrode sheet... 0.8 Co 0.1 Mn 0.1 The mass ratio of O2), conductive carbon black, carbon nanotubes, PVDF, PAA, auxiliary nanoparticles Al2O3 and Li3PO4 is 90:1:1:1:1:3:3, and all other aspects are the same as in Example 1.

[0055] Comparative Example 1 The difference between this comparative example and Example 1 is that the pressure of the first rolling of the positive electrode sheet is 6 MPa, and the pressure of the second rolling is 6 MPa (compacted density is 3.0 g / cm³). 3 (Porosity 40%), otherwise it is the same as in Example 1.

[0056] Comparative Example 2 The difference between this comparative example and Example 1 is that the pressure of the first rolling of the positive electrode sheet is 14 MPa, and the pressure of the second rolling is 14 MPa (compacted density is 3.85 g / cm³). 3 (Porosity is 10%), and everything else is the same as in Example 1.

[0057] Comparative Example 3 The difference between this embodiment and Embodiment 1 is that the positive electrode active material (Li1Ni) in the positive electrode sheet...0.8 Co 0.1 Mn 0.1 The mass ratio of O2), conductive carbon black, carbon nanotubes, polyimide (PI), auxiliary nanoparticles Al2O3, and auxiliary nanoparticles Li3PO4 is 92:1:1:2:2:2, and all other aspects are the same as in Example 1.

[0058] Comparative Example 4 The difference between this embodiment and Embodiment 1 is that the positive electrode active material (Li1Ni) in the positive electrode sheet... 0.8 Co 0.1 Mn 0.1 The mass ratio of O2), conductive carbon black, carbon nanotubes, PVDF, PAA, and auxiliary nanoparticles SiO2 is 92:1:1:1:1:4, and all other aspects are the same as in Example 1.

[0059] Comparative Example 5 The difference between this embodiment and Embodiment 1 is that the positive electrode active material (Li1Ni) in the positive electrode sheet... 0.8 Co 0.1 Mn 0.1 The mass ratio of O2), conductive carbon black, carbon nanotubes, PVDF, PAA, and auxiliary nanoparticles AlN is 92:1:1:1:1:4, and all other aspects are the same as in Example 1.

[0060] Comparative Example 6 The difference between this embodiment and Embodiment 1 is that the positive electrode active material (Li1Ni) in the positive electrode sheet... 0.8 Co 0.1 Mn 0.1 The mass ratio of O2), conductive carbon black, carbon nanotubes, PVDF, PAA, auxiliary nanoparticles Al2O3 and Li3PO4 is 95.5:1:1:1:1:0.25:0.25, and all other components are the same as in Example 1.

[0061] Comparative Example 7 The difference between this embodiment and Embodiment 1 is that the positive electrode active material (Li1Ni) in the positive electrode sheet... 0.8 Co 0.1 Mn 0.1 The mass ratio of O2), conductive carbon black, carbon nanotubes, PVDF, PAA, auxiliary nanoparticles Al2O3 and Li3PO4 is 85:1:1:1:1:5:5, and all other aspects are the same as in Example 1.

[0062] Performance testing Test method for compaction density of positive electrode sheet: First, the positive electrode sheet, after being washed with dimethyl carbonate and vacuum dried, was cut into nine standard-sized square samples (2.0cm × 2.0cm). Next, the active material on both sides of three of these square samples was removed, and after rinsing with NMP and drying, they were weighed and their average mass M1 was calculated. Simultaneously, the average thickness L1 of the samples was measured using a micrometer. Then, the mass of the remaining three square samples was weighed and their average mass M2 was calculated, and the average thickness L2 of the samples was measured. The compacted density of the positive electrode sheet was calculated. Unit: g / cm 3 .

[0063] Test method for peel force of positive electrode sheet: First, use double-sided tape to fix the strip sample onto a flat, thin steel plate, ensuring the tape is centered on the plate. Then, remove the protective layer of the double-sided tape and attach the exposed aluminum current collector side of the positive electrode sample (one side of which has had the active material and primer removed with a plastic scraper) to the tape. Use a pressure roller to evenly press the strip sample to ensure good adhesion. Next, tear off the unattached end, bend the torn end upwards, and clamp it in the upper fixture of a tensile testing machine for a 180° peel test. Record the tensile force curve. The segment where the tensile force changes by no more than 10% is selected as the stable peel segment. Finally, divide the average tensile force of this segment by the width of the strip sample electrode to calculate the peel strength of the positive electrode. Peel force tests were conducted on the front, middle, and rear segments of the electrode, and the obtained values ​​were recorded as N1, N2, and N3, respectively. Finally, by calculating the arithmetic mean of these values, the average peeling force N of the actual tested positive electrode sheet is obtained (N=(N1+N2+N3) / 3).

[0064] Methods for determining the porosity of positive electrode plates: The positive electrode sample was cut into pieces approximately 2cm in size. 2 A small piece of mercury was weighed, its mass and geometric volume were measured, and then placed into the sample chamber of a high-precision mercury porosimeter. Pressure was gradually applied to allow mercury to penetrate the pores of the electrode, from low pressure to high pressure (e.g., 0.1-60 MPa), and the volume of mercury penetration at each pressure was recorded. The porosity ε was calculated based on the ratio of mercury volume to the total geometric volume of the sample, and pore size distribution information was also obtained. The porosity was calculated using the following formula: in This represents the volume of mercury that seeps in under pressure. This represents the total geometric volume of the electrode.

[0065] 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℃.

[0066] 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.

[0067] 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.

[0068] The specific results are as follows: Table 1 Table 1 shows that when the compaction density of the positive electrode sheet is controlled between 3.3-3.7 g / cm³, 3When the porosity is within the range of 18.0-30.0%, all embodiments successfully passed the needle penetration test and the 70% deformation extrusion test, indicating that the structural design can significantly improve the safety of the battery under mechanical abuse conditions within a wide process window. This demonstrates that by synergistically optimizing the electrode microstructure through nanoscale mechanical reinforcement and bonding control materials, active layer peeling and aluminum foil exposure can be effectively suppressed, thereby reducing the probability of catastrophic internal short circuits. Further analysis shows that the porosity of the positive electrode sheet and the 6C charging capacity retention rate have a certain positive correlation: when the porosity increases from 18.0% to 30.0%, the capacity retention rate increases from 68.6% to 71.5%. This is because higher porosity is beneficial to electrolyte wetting and the construction of lithium-ion transport channels, thereby reducing polarization and improving high-rate kinetic behavior. However, excessively high porosity will weaken the overall mechanical strength and interfacial support capacity of the electrode sheet, so it is necessary to compensate for this through bonding reinforcement and structural control in terms of safety performance. Meanwhile, the highest surface temperature of the battery after needle penetration showed a negative correlation with the density of the electrode: as the compaction density increased from 3.3 g / cm³, the temperature decreased. 3 Increased to 3.7 g / cm³ 3 The porosity decreased from 30.0% to 18.0%, and the highest surface temperature decreased from 93.5℃ to 80.3℃. The fundamental mechanism is that the higher compaction density and lower porosity simultaneously improve the cohesive strength within the active layer and the adhesion strength at the interface with the aluminum foil. During mechanical abuse such as needle punching, it is easier to guide stress to concentrate on the aluminum foil and induce local fracture, rather than the entire active layer peeling off. This avoids large-area exposure of the aluminum current collector, reduces the probability of low-impedance internal short circuits, and ultimately significantly suppresses the intensity of instantaneous heat release.

[0069] Table 2 Table 2 shows that when the peel force of the positive electrode sheet is in the range of 16~29 N / m, all embodiments successfully passed the needle penetration test and the 70% deformation extrusion test. This indicates that within this range, the structural stability and overall safety of the electrode sheet under mechanical abuse conditions can be significantly improved through the rational design of the adhesive system. This demonstrates that the interfacial adhesion performance of the electrode sheet is one of the key structural parameters determining whether the aluminum current collector is exposed and whether it induces a dangerous internal short circuit.

[0070] Further analysis reveals that the peel force of the positive electrode and the 6C charging capacity retention rate are not simply linearly positively correlated. The single PVDF system (Example 4, peel force 16 N / m) suffers from insufficient interfacial adhesion, making it more prone to microcrack propagation and localized debonding during high-rate cycling, leading to instability in the electron / ion transport channels and resulting in the lowest 6C capacity retention rate (66.5%). While the single PAA system (Example 5, peel force 29 N / m) significantly enhances interfacial adhesion strength, its high polar group content easily triggers localized ion migration hindrance and interfacial side reactions, limiting rate performance improvement (69.0%). In contrast, the PAA / PVDF composite system (Example 1), through the synergistic regulation of flexibility and polar groups, maintains a high peel force (25 N / m) while preserving superior charge transport continuity, achieving a 6C capacity retention rate of 70.5% and exhibiting better overall kinetic performance.

[0071] Regarding safety performance, the highest surface temperature of the battery after needle penetration does not exhibit a monotonic relationship with the electrode peel force. When the peel force is too low, the active layer is more likely to peel off completely under needle penetration impact, leading to aluminum foil exposure and the formation of a low-resistance internal short circuit. Conversely, when the peel force is too high, the overall rigidity of the electrode increases, reducing its stress buffering capacity and potentially causing localized stress concentration, which increases the instantaneous heat release rate during needle penetration. Therefore, although Example 5 (peel force 29 N / m) has the highest adhesion, its peak needle penetration temperature is actually higher than that of Examples 1 and 4, demonstrating the potential adverse effects of overly reinforced interfaces under extreme abuse conditions.

[0072] In summary, Example 1 (PAA+PVDF compound system, peel force 25 N / m) achieved a better balance between the highest needle-punching temperature (81.0℃), 6C capacity retention (70.5%), and extrusion safety, indicating that the medium-strength and tough interfacial bonding structure is the optimal design range that simultaneously takes into account high-rate performance and mechanical safety.

[0073] Table 3 Table 3 shows that when different types of auxiliary nanoparticles were introduced into the positive electrode, all examples successfully passed the needle penetration test and the 70% deformation extrusion test, indicating that the introduction of inorganic nanoparticles can improve the overall structural stability and safety of the electrode under mechanical abuse conditions. Further comparison reveals that different nanoparticles have varying effects on rate performance and thermal behavior. Among them, the single Al2O3 system (Example 6), due to its high modulus and inorganic rigidity, significantly enhances the mechanical stability of the electrode, resulting in the lowest maximum surface temperature after needle penetration (76.6℃). However, its contribution to interfacial ion transport and adhesion regulation is limited, leading to a relatively low 6C capacity retention rate (65.4%). The single Li3PO4 system (Example 7) possesses both ion conduction capability and interfacial polarity regulation, thus outperforming the Al2O3 system in rate performance (68.7%). However, its mechanical enhancement ability is relatively limited, and the needle penetration temperature rise is slightly higher (80.6℃). In contrast, the Al2O3 and Li3PO4 composite system (Example 1) achieved the highest 6C capacity retention rate (70.5%) while maintaining a low needle penetration temperature rise (81.0℃) through a synergistic mechanism of mechanical enhancement, interfacial polarity regulation, and ion transport. This demonstrates the advantageous balance between safety and high-rate performance achieved by the synergistic design of multifunctional nanoparticles.

[0074] Table 4 Table 4 shows that when the mass percentage of auxiliary nanoparticles in the positive electrode is in the range of 2.0% to 6.0%, all embodiments can successfully pass the needle penetration test and the 70% deformation extrusion test, indicating that the introduction of nanoparticles within this content range can improve the overall structural stability of the electrode under mechanical abuse conditions.

[0075] Further analysis revealed that the nanoparticle content significantly affected rate performance and needle-punch thermal behavior. When the content was 2.0% (Example 8), the 6C capacity retention rate was the highest (72.3%) due to the relatively small obstruction effect of inorganic particles on ion transport channels. However, its effect on interface enhancement and stress regulation was insufficient, and the highest surface temperature after needle-punching increased significantly (96.9°C), indicating that its ability to suppress dangerous short-circuit heat release was limited.

[0076] When the nanoparticle content is increased to 6.0% (Example 9), the interface strengthening and mechanical support are enhanced. However, the excessive inorganic phase is prone to forming local rigid aggregation areas inside the electrode, which weakens the stress buffering capacity and increases the ion transport impedance. Therefore, its 6C capacity retention rate is not further improved (71.6%), and the needle penetration peak temperature remains at a high level (96.6℃).

[0077] In contrast, Example 1 (4.0%) achieves a better balance between rate performance (70.5%) and safety, with its needle penetration peak temperature significantly reduced to 81.0°C. This indicates that this content can effectively enhance interfacial bonding and stress transfer regulation capabilities without significantly sacrificing kinetic performance, thereby suppressing the occurrence of dangerous short circuits caused by aluminum foil exposure.

[0078] Table 5 Table 5 shows that only Example 1 passed the needle penetration and 70% deformation extrusion tests while simultaneously ensuring high-rate performance and safety against mechanical abuse. This demonstrates that the synergistic solution of structural parameters, interface design, and nano-reinforcement proposed in this invention has irreplaceable systemic advantages.

[0079] Specifically, Comparative Example 1 and Comparative Example 2 correspond to electrode structures that are excessively loose and excessively dense, respectively. Although Comparative Example 1 exhibits a high capacity retention rate (73.8%) at 6C rate, its overall mechanical strength is insufficient due to excessively high porosity (40%). During needle punching, large-area peeling of the active layer and exposure of the aluminum foil easily occur, leading to a low-impedance internal short circuit and a sharp increase in the maximum surface temperature to 476℃. On the other hand, Comparative Example 2, due to excessively high compaction and excessively low porosity (10%), exhibits significantly enhanced electrode brittleness and reduced stress buffering capacity. It also suffers catastrophic failure under needle punching and extrusion conditions, demonstrating the necessity of a reasonable window range for the electrode microstructure.

[0080] Comparative Example 3 uses a single PI adhesive system with a peel strength of only 12 N / m, which is insufficient for interfacial bonding. It is more prone to interlayer separation during needle punching, leading to a dangerous short circuit with exposed aluminum foil, which in turn generates violent exothermic heat (376.4℃). This shows that interfacial bonding strength is one of the key parameters that determines safety.

[0081] Comparative Example 4 uses SiO2 as an auxiliary nanoparticle. Although it improves the rate performance to a certain extent (74.4%), its ability to regulate interface polarity, stress transfer and energy dissipation is limited. It is difficult to effectively guide the aluminum foil to break preferentially, and a high-risk internal short circuit still occurs, causing the needle penetration temperature to soar to 365°C.

[0082] Comparative Examples 5 and 7 represent the scenarios of "safety first, but at the expense of rate capability" and "extreme enhancement," respectively. The AlN system (Comparative Example 5) can suppress local heat accumulation to some extent due to its high rigidity and high thermal conductivity, allowing it to pass the needle penetration and extrusion tests. However, due to its limited support for interfacial chemical regulation and ion migration, the 6C capacity retention rate is significantly reduced (60.5%). When the nanoparticle content is increased to 10.0 wt% (Comparative Example 7), although a strong mechanical framework can be formed to limit catastrophic failure, the excessive inorganic phase significantly hinders ion migration, resulting in a severe deterioration in rate capability (51.3%).

[0083] Comparative Example 6 further shows that when the content of nanoparticles is too low (0.5 wt%), its interface enhancement and stress regulation effects are insufficient, and it cannot prevent the occurrence of exposed internal short circuits in aluminum foil, leading to needle punching failure and high temperature runaway (389℃).

[0084] A comprehensive comparison shows that Example 1, through systematic and coordinated regulation of electrode density, pore structure, interfacial bonding strength, and nanoparticle type and content, ensured a high 6C capacity retention rate (70.5%) while stably controlling the peak needle penetration temperature at 81.0℃ and successfully passing the extrusion test, achieving the optimal balance between high rate performance and high safety.

[0085] In summary, this patent proposes a safety construction strategy for high-nickel cathodes through the coordinated design of electrode microstructure windows, interfacial bonding systems, and multidimensional enhancement by functional nanoparticles. Based on reasonable control of compaction density and porosity, the cohesive strength of the active layer and its interfacial adhesion strength with the aluminum current collector are synergistically improved through a composite binder system and a conductive undercoat. Furthermore, auxiliary nanoparticles with both mechanical support and interfacial control functions are introduced, enabling the electrode to effectively reconstruct the stress transmission path under mechanical abuse conditions such as needle punching and extrusion, thus suppressing active layer peeling and aluminum foil exposure.

[0086] 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, It includes a current collector, a base coating, and a positive electrode active material layer coated on the surface of the base coating; the base coating is located between the current collector and the positive electrode active material layer. The compaction density of the positive electrode sheet is 3.3-3.7 g / cm³. 3 ; The porosity of the positive electrode sheet is 18-30%.

2. The positive electrode sheet according to claim 1, characterized in that: The peel strength of the positive electrode sheet is 15-30 N / m.

3. The positive electrode sheet according to claim 1, characterized in that: The positive electrode active material layer is composed of a main active material and auxiliary nanoparticles; the main active material is a metal oxide; the D90, D50, and D10 particle sizes of the main active material satisfy 0.85 < <1.

15.

4. The positive electrode sheet according to claim 3, characterized in that: The auxiliary nanoparticles are at least one of phosphates, oxides, and nitrides; the mass percentage of the auxiliary nanoparticles added is 2-6 wt%, and the size of the auxiliary nanoparticles is 220-410 nm.

5. The positive electrode sheet according to claim 1, characterized in that: The primer layer includes a conductive agent and a binder; the binder in the primer layer is a mixture of polyvinylidene fluoride (PVDF) and polyacrylic acid (PAA).

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

7. The positive electrode sheet according to claim 6, characterized in that: The auxiliary nanoparticles are a mixture of aluminum oxide and lithium phosphate.

8. The positive electrode sheet according to claim 3, characterized in that: The metal oxide is LiNi. x Co y Mn z O2, LiNi x Co y Al z At least one of O2, LiCoO2, and LiFePO4, wherein x ≥ 0.3 and x + y + z = 1.

9. A lithium-ion battery, characterized in that: The lithium-ion battery includes the positive electrode sheet as described in any one of claims 1-8.

10. An electrical device, characterized in that: Including the lithium-ion battery as described in claim 9.

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