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 lithium battery materials. According to the invention, the technical contradiction that the improvement of high rate performance and the guarantee of safety performance cannot be considered at the same time in the prior art is solved by accurately regulating and controlling the thickness of the aluminum current collector, the thickness of the prime coat, the mass ratio of the composite system binder to the conductive agent to the binder.

Description

A positive electrode sheet, its preparation method, and a lithium-ion battery Technical Field

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

[0002] As lithium-ion batteries develop towards higher specific energy density and high-nickel cathode systems, their safety risks under extreme conditions such as nail penetration, external short circuits, and mechanical extrusion are becoming increasingly prominent. Research indicates that safety failures often first occur at the interface between the current collector and the positive electrode active material layer: under mechanical or high-current impact conditions, this interface is prone to adhesion failure, current density concentration, and localized overheating, which in turn induces aluminum current collector erosion, positive electrode material decomposition, and accelerates thermal runaway propagation. Existing positive electrode sheets typically employ a structure where the aluminum current collector and the positive electrode active material layer are directly bonded. The interface relies primarily on a single binder for mechanical connection, resulting in insufficient continuity of the conductive network at the interface. Furthermore, under pressure or nail penetration conditions, there is a lack of effective stress buffering and current equalization capabilities, making it difficult to simultaneously meet the application requirements of high energy density and high safety. 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 in the prior art where the interface of the positive electrode sheet mainly relies on a single binder to achieve mechanical connection, the continuity of the conductive network at the interface is insufficient, and there is a lack of effective stress buffering and current equalization capabilities under pressure or needle penetration conditions, making it difficult to simultaneously meet the technical requirements of high energy density and high safety.

[0004] To achieve the above objectives, the present invention proposes a positive electrode sheet, comprising an aluminum current collector, a base coating layer, and a positive active material layer coated on the surface of the base coating layer; the base coating layer is located between the aluminum current collector and the positive active material layer, the base coating layer comprises a conductive agent and a binder, and the thickness of the base coating layer is 0.3-3.0 μm, preferably 1.0-3.0 μm.

[0005] Based on the above technical solutions, preferably, the peel strength between the positive electrode active material layer and the base coating layer is >25N / m.

[0006] Based on the above technical solutions, preferably, the thickness of the aluminum current collector is 4-8 μm.

[0007] Based on the above technical solutions, preferably, the base coating includes a conductive agent and a binder, wherein the conductive agent content in the base coating is 70-90wt% and the binder content is 10-30wt%.

[0008] Based on the above technical solutions, preferably, 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 mass of the polyacrylic acid is 45%-55% of the total mass of the adhesive.

[0010] Based on the above technical solutions, preferably, the conductive agent in the base coating is at least one of carbon black, carbon nanotubes, and graphene.

[0011] Based on the above technical solutions, preferably, the conductive agent in the base coating is selected from at least one of carbon black (SP), carbon nanotubes (CNT), and graphene.

[0012] Based on the above technical solutions, preferably, the positive electrode active material layer is composed of a main active material and auxiliary nanoparticles; more preferably, the main active material is a layered metal oxide; even more preferably, the layered metal oxide is LiNi. x Co y Mn z O2 and / or LiNi x Co y Al z O2, where x≥0.3, x+y+z=1).

[0013] The present invention also provides a lithium-ion battery, wherein the lithium-ion battery includes the above-mentioned positive electrode sheet.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention provides a positive electrode sheet and its preparation method and a lithium-ion battery. By introducing an undercoat layer between the aluminum current collector and the positive electrode active material layer, and by precisely limiting parameters such as the thickness of the undercoat layer, the ratio of conductive agent to binder, and the thickness of the aluminum current collector, the technical problem of the prior art in the development of high-energy-density lithium-ion batteries, which is difficult to effectively balance high-rate charging performance and intrinsic safety performance, is effectively solved. This technical solution significantly enhances the mechanical stability and electrochemical stability of the electrode interface without significantly sacrificing the battery energy density and rate performance by optimizing the interface structure. This effectively suppresses the risk of thermal runaway of the battery under puncture, extrusion and short circuit, and comprehensively improves the overall safety of lithium-ion batteries; (2) The base coating of the present invention is composed of a high conductive agent content and a composite binder system. The base coating constructs an efficient and continuous electronic conduction network on the surface of the current collector through a high proportion of conductive agent, which significantly reduces the interfacial contact resistance between the current collector and the active material layer, improves the polarization phenomenon during high-rate charging, improves the capacity retention rate, and can quickly and uniformly conduct current when encountering a large current impact, avoiding hot spots caused by excessive local current density, and fundamentally reducing the probability of triggering thermal runaway. In addition, a composite binder system of polyvinylidene fluoride and polyacrylic acid was adopted. By combining the flexibility of PVDF with the strong hydrogen bonding formed on the PAA and aluminum foil surfaces, a high interfacial bonding force (peel strength >25N / m) was achieved. This effectively suppressed interfacial debonding, crack propagation and heat concentration under conditions of needle penetration, short circuit and extrusion, thereby reducing the risk of thermal runaway triggered on the positive electrode side. While taking into account both lightweight and rate performance, the overall safety of lithium-ion batteries was significantly improved. Detailed Implementation

[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] The present invention provides a positive electrode sheet, comprising an aluminum 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 aluminum current collector and the positive active material layer, the base coating comprises a conductive agent and a binder, and the thickness of the base coating is 0.3-3.0 μm, preferably 1.0-3.0 μm.

[0017] This invention introduces an ultra-thin functional undercoat layer between the aluminum current collector and the positive electrode active material layer, and limits the thickness of the undercoat layer to 1.0-3.0 μm. An excessively thick undercoat layer will increase the interface resistance and reduce the high-rate charging performance, while an excessively thin undercoat layer will not be able to form a complete and dense protective and functional network on the current collector surface due to uneven coverage or defects, which will seriously affect the battery's safety, cycle life and rate performance.

[0018] Optionally, the conductive agent content in the undercoat is 70-90 wt%, and the binder content is 10-30 wt%. By optimizing the content of the conductive agent and binder in the undercoat to this range, an optimal balance between conductivity and adhesion is achieved. The high conductive agent content constructs a highly efficient electronic network, which is the core function ensuring high rate capability and high safety. An appropriate amount of binder provides strong interfacial adhesion, ensuring structural stability and long cycle life of the battery. This precise ratio and synergistic effect fundamentally improves the overall performance of the battery.

[0019] Optionally, the binder in the base coating is a mixture of polyvinylidene fluoride (PVDF) and polyacrylic acid (PAA). The present invention adopts a composite binder system of PVDF and polyacrylic acid, which achieves synergistic optimization of "adhesion strength-conductivity-thermal stability" after the two are combined. This ensures a strong bond between the active layer and the current collector (peel strength > 25 N / m), reduces the risk of short circuit caused by aluminum foil exposure during mechanical abuse, and maintains the interface charge transfer efficiency, thereby reducing capacity loss during high-rate charging.

[0020] Optionally, the mass of the polyacrylic acid is 45%-55% of the total mass of polyvinylidene fluoride and polyacrylic acid; the molecular weight of the polyacrylic acid is 1,250,000, and it is purchased from Sigma-Aldrich. If the proportion of polyacrylic acid is too high, the flexibility of the binder system will decrease; if the proportion of polyacrylic acid is too low, the interfacial hydrogen bonding will be weakened. By controlling the mass of polyacrylic acid within this range, the optimal balance between high-rate performance and thermal runaway risk can be achieved by precisely balancing interfacial bonding and charge transport efficiency.

[0021] Optionally, the thickness of the aluminum current collector is 4-8 μm. A thinner aluminum current collector reduces the resistance of the electron transport path due to its reduced thickness, thereby improving the capacity retention rate during high-rate charging. However, an excessively thin aluminum layer has a limited heat dissipation area, making it difficult for local heat to dissipate quickly during a short circuit, resulting in a sharp rise in surface temperature. While a thicker aluminum current collector has higher mechanical strength and better heat dissipation performance, an excessively thick metal layer increases the internal resistance of the current collector, leading to a decrease in charge transport efficiency at high rates and a corresponding decrease in capacity retention rate. By precisely controlling the thickness of the aluminum current collector, a dynamic balance is achieved between electron conduction efficiency and heat dissipation capacity. This avoids the risk of thermal runaway from an excessively thin current collector and reduces the internal resistance loss from an excessively thick current collector. Therefore, it exhibits superior overall performance in terms of both capacity retention rate and safe temperature.

[0022] Optionally, the peel strength between the positive electrode active material layer and the base coating layer is >25 N / m; during battery manufacturing, it can effectively resist mechanical stress, prevent the active layer from cracking or falling off, and significantly improve product yield. Secondly, during long-term battery cycling, it can effectively buffer the volume change stress caused by lithium insertion and extraction in the active material, maintain the integrity of the interface structure, thereby delaying capacity decay and improving cycle life. More importantly, under abuse conditions such as squeezing and puncture, the strong interfacial bonding force can limit physical damage to local areas, avoid large-area short circuits, and is an important physical guarantee for improving the intrinsic safety of the battery.

[0023] Optionally, the conductive agent in the undercoat is selected from at least one of carbon black (SP), carbon nanotubes (CNT), and graphene.

[0024] Optionally, the positive electrode active material layer is composed of a main active material and auxiliary nanoparticles; more preferably, the main active material is a layered metal oxide; even more preferably, the layered metal oxide is LiNi. x Co y MnzO2 and / or LiNi x Co y Al z O2, where x≥0.3, x+y+z=1).

[0025] Optionally, the auxiliary nanoparticles are aluminum phosphate.

[0026] This invention also provides a method for preparing a positive electrode sheet, comprising the following steps: a) pretreating aluminum foil using an alkaline washing + acid washing process to obtain a pretreated aluminum foil; b) adding conductive agent SWCNT, binder PVDF and PAA to a solvent and dispersing them at high speed to obtain a base coating slurry; c) uniformly coating the base coating slurry onto both sides of the pretreated aluminum foil using a slot coating process, and obtaining an aluminum current collector coated with the base coating after drying and curing; d) thoroughly mixing positive electrode active material, conductive carbon black, carbon nanotubes, polyvinylidene fluoride and auxiliary nanoparticle aluminum phosphate in a solvent system to obtain a positive electrode coating material, and then coating the positive electrode coating material onto the aluminum current collector coated with the base coating, and obtaining a positive electrode sheet after drying and cold pressing.

[0027] Example 1 This example discloses a positive electrode sheet and a lithium-ion battery, including the following steps: a) Pretreatment of aluminum current collector: Select aluminum foil with a thickness of about 7μm, and use alkaline washing + acid washing process to remove surface oil and oxide layer: first soak in 5% NaOH solution for 30s (25℃), then neutralize with 10% HNO3 solution for 30s, finally rinse with deionized water until neutral, and dry in 80℃ vacuum drying oven for 2h for later use.

[0028] b) Preparation of the base coating slurry: The conductive agent single-walled carbon nanotubes (SWCNT), binder PVDF, and PAA were mixed in a mass percentage ratio of 85:7.5:7.5 (PVDF and PAA were 50wt% and 50wt%, respectively). The mixture was added to N-methylpyrrolidone (NMP) solvent with a solid content of 30wt%. The mixture was dispersed for 30 minutes using a high-speed disperser (3000 rpm) to form a uniform, non-agglomerated base coating slurry. c) Application of the base coating: The slit coating process was used to uniformly coat the slurry on both sides of the pretreated aluminum foil. Based on the target thickness of the dried base coating (2.0 μm), the wet film thickness was calculated in combination with the solid content of the slurry (when the solid content is 30%, the wet film thickness = target dry film thickness / 0.3, i.e., 6 μm). The sample was then placed in a vacuum oven at 100℃ for drying and curing for 30 minutes to form a dense and firm adhesive layer. The total thickness of the aluminum current collector after the base coating was 11 μm.

[0029] d) Method for manufacturing positive electrode sheet: Take positive electrode active material (Li1Ni) 0.8 Co 0.1 Mn 0.1 O2), conductive carbon black, carbon nanotubes, polyvinylidene fluoride (PVDF), and auxiliary nanoparticles aluminum phosphate (AlPO4) were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 92:1:1:2:4 to obtain a positive electrode coating material. This positive electrode coating material was then coated onto the aforementioned aluminum foil. After drying and cold pressing, a positive electrode sheet was obtained with a compaction density of 3.6 g / cm³. 3e) Negative Electrode Fabrication 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. 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 f) Electrolyte preparation: Lithium hexafluorophosphate (LiPF6), ethylene carbonate (EC), dimethyl carbonate (DMC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC) were mixed in a mass percentage ratio of 16.0:22.0:52.0:5.0:5.0 to obtain the electrolyte. g) A high-porosity (40%) separator was selected. The thickness of the PE base film in the separator was 9 μm, the thickness of the ceramic coating on both sides of the base film was 1.0 μm, and the thickness of the PVDF coating was 1.0 μm. h) Lithium-ion battery assembly: The positive and negative electrode sheets were rolled and slit, and then wound together with the separator according to the set process to form a 21700 cylindrical battery core. Subsequently, the battery core was fixed to the pre-made connecting piece by welding and installed into a metal battery casing. After completing the key processes such as electrolyte injection, sealing, and formation, the lithium-ion battery described in Example 1 was obtained. The 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.

[0030] Example 2 The difference between this example and Example 1 is that the thickness of the bottom coating on both sides of the aluminum current collector is 1.0 μm, and everything else is the same as in Example 1.

[0031] Example 3 The difference between this example and Example 1 is that the thickness of the bottom coating on both sides of the aluminum current collector is 3.0 μm, and everything else is the same as in Example 1.

[0032] Example 4 The difference between this example and Example 1 is that the mass of PVDF and PAA in the primer adhesive is 45wt% and 55wt% respectively, while all other aspects are the same as in Example 1.

[0033] Example 5 The difference between this example and Example 1 is that the mass of PVDF and PAA in the primer adhesive is 55wt% and 45wt% respectively, while all other aspects are the same as in Example 1.

[0034] Example 6 The difference between this example and Example 1 is that the mass ratio of conductive agent to binder in the base coating is 75:25, while all other aspects are the same as in Example 1.

[0035] Example 7 The difference between this example and Example 1 is that the mass ratio of conductive agent to binder in the base coating is 80:20, while all other aspects are the same as in Example 1.

[0036] Example 8 The difference between this example and Example 1 is that the mass ratio of conductive agent to binder in the base coating is 90:10, while all other aspects are the same as in Example 1.

[0037] Example 9 The difference between this example and Example 1 is that the thickness of the aluminum current collector is 4μm, while all other aspects are the same as in Example 1.

[0038] Example 10 The difference between this example and Example 1 is that the thickness of the aluminum current collector is 5.5 μm, and everything else is the same as in Example 1.

[0039] Example 11 The difference between this example and Example 1 is that the thickness of the aluminum current collector is 8 μm, while all other aspects are the same as in Example 1.

[0040] The difference between Comparative Example 1 and Example 1 is that the thickness of the undercoating on both sides of the aluminum current collector is 0.5 μm, while all other aspects are the same as in Example 1.

[0041] The difference between Comparative Example 2 and Example 1 is that the thickness of the undercoating on both sides of the aluminum current collector is 3.5 μm, while all other aspects are the same as in Example 1.

[0042] The difference between Comparative Example 3 and Example 1 is that the primer adhesive is entirely PVDF, while everything else is the same as in Example 1.

[0043] The difference between Comparative Example 4 and Example 1 is that the primer adhesive is PAA throughout, while everything else is the same as in Example 1.

[0044] The difference between Comparative Example 5 and Example 1 is that the mass ratio of conductive agent to binder in the base coating is 65:35, while all other aspects are the same as in Example 1.

[0045] The difference between Comparative Example 6 and Example 1 is that the mass ratio of conductive agent to binder in the base coating is 95:5, while all other aspects are the same as in Example 1.

[0046] The difference between Comparative Example 7 and Example 1 is that the thickness of the aluminum current collector is 2 μm, while all other aspects are the same as in Example 1.

[0047] The difference between Comparative Example 8 and Example 1 is that the thickness of the aluminum current collector is 10 μm, while all other aspects are the same as in Example 1.

[0048] The difference between Comparative Example 9 and Example 1 is that no base coating is applied to the aluminum current collector; otherwise, they are the same as in Example 1.

[0049] Test method for current collector undercoat thickness: Discharge the lithium-ion battery to 2.5V. Inside a glove box, carefully disassemble the battery and remove the positive electrode from the cylindrical cell. Next, immerse the electrode in dimethyl carbonate for 30 minutes. After removal, wipe the surface to remove residual organic solvents, and repeat this process three times to ensure the removal of all possible impurities and residues. Leave a portion of the positive electrode and allow it to stand in the glove box for 48 hours to ensure complete evaporation of the organic solvents. Fix the dried electrode to the sample stage with conductive adhesive and perform FIB cutting perpendicular to the electrode cross-section (using Ga). + Ion beam (accelerating voltage 30 kV, beam current 10-50 nA). SEM observation was performed at an accelerating voltage of 5 kV. Backscattered electron imaging (BSE) revealed the interlayer structure of the material, showing a significant contrast difference between the aluminum current collector (bright white) and the undercoat (gray / dark gray). During measurement, 5-10 evenly distributed locations were selected in the cross-section. The vertical length was read using the SEM's built-in scale or image analysis software (such as ImageJ), and the average value was taken as the final thickness value. The thickness of the current collector and undercoat was recorded.

[0050] The method for testing the peel strength of the positive electrode sheet is as follows: First, use double-sided tape to fix the strip sample onto a flat, thin steel plate, ensuring the tape is centered on the steel plate. Then, remove the protective layer of the double-sided tape and attach the exposed aluminum current collector side of the strip sample (with the active material and primer removed on one side using a plastic scraper) to the double-sided 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 sheet. Peel strength tests are conducted on the front, middle, and rear segments of the electrode sheet, and the obtained values ​​are 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).

[0051] 70% Deformation Extrusion Test Method: After charging the lithium-ion battery to 100% state of charge, place it horizontally on an extrusion test platform. Use a 32mm diameter cylindrical steel rod as the extrusion head, applying extrusion force along the battery thickness at a rate of 10mm / min. Simultaneously, monitor the battery thickness change in real time using a displacement sensor. Extrusion is stopped immediately when the battery deformation reaches 70% of its original thickness. Passing Requirements: No fire, no explosion, maximum battery temperature <100℃.

[0052] 15mΩ External Short Circuit Test Method: 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 the maximum battery temperature <80℃.

[0053] Needle penetration test method: The battery to be tested is fully charged to 100% SOC and placed in a 25℃ environment for 2 hours to stabilize. Then, the battery is fixed on an insulating clamp, ensuring that its positive and negative terminals are horizontal. Using a 3mm diameter stainless steel needle, perpendicular to the battery surface along the direction between the positive and negative terminals, the needle is inserted into the battery at a constant speed of 10±1mm / s until it is completely penetrated (the penetration depth should exceed 90% of the battery thickness). After insertion, the needle is kept still, and the battery status is continuously observed for 5 minutes. Any abnormal phenomena such as fire, explosion, or smoke are recorded, and temperature changes are monitored using a thermocouple attached to the battery surface.

[0054] 25℃ Rate Charging Performance Test Method: Discharge the lithium battery to 2.5V and place it in a 25℃ constant temperature chamber for 6 hours and test it according to the following steps: (1) Charge it to 4.2V under 1C conditions with constant current and constant voltage, cut off current of 0.1C, and let it stand for 30 minutes. The capacity of the constant current charging to 4.2V is Q1 (constant current capacity); (2) Discharge it to 2.5V under 1C conditions with constant current and cut off current of 0.1C, and let it stand for 30 minutes; (3) Charge it to 4.2V under 6C conditions with constant current and constant voltage, cut off current of 0.1C, and let it stand for 30 minutes. The capacity of the constant current charging to 4.2V is Q6; (4) Discharge it to 2.5V under 1C conditions with constant current and cut off current of 0.1C, and let it stand for 30 minutes; The calculation method for the 6C charging capacity retention rate of the 25℃ lithium battery is: Q1 / Q6×100.

[0055] The test results are shown in Tables 1-5.

[0056] Table 1 Table 1 shows that when the aluminum current collector undercoat thickness is in the range of 1.0-3.0 μm, all embodiments passed the needle penetration, extrusion, and short-circuit tests, indicating that the undercoat technology can effectively improve battery safety. The undercoat thickness is negatively correlated with the 6C charging capacity retention rate (the capacity retention rate decreased from 71.5% to 68.6% when the thickness increased from 1.0 μm to 3.0 μm). This is because an excessively thick undercoat increases interfacial resistance and reduces high-rate charging performance. The highest battery surface temperature after needle penetration is negatively correlated with the undercoat thickness (the highest temperature was 93.5℃ at 1.0 μm, and the lowest was 80.3℃ at 3.0 μm). The mechanism is that a thicker undercoat can more fully enhance the interfacial bonding between the aluminum current collector and the positive electrode active layer, making it easier to guide the aluminum foil to break preferentially rather than be exposed during mechanical abuse, thereby reducing the heat release from dangerous internal short circuits. Overall, an undercoat thickness of 2.0 μm ensures both safety performance and optimal high-rate charging capability.

[0057] Table 2 Table 2 shows that the mass ratio of PVDF to PAA in the aluminum current collector undercoat has a significant regulatory effect on the high-rate charging performance and mechanical abuse safety of the battery. The data indicates that Example 1 (PVDF:PAA = 1:1, PAA accounts for 50%) has the highest 6C charging capacity retention rate (70.5%) and the lowest maximum surface temperature after needle penetration (81.0℃). While Examples 4 (PVDF:PAA = 9:11, PAA accounts for 55%) and 5 (PVDF:PAA = 11:9, PAA accounts for 45%) also passed all safety tests, their 6C capacity retention rates (66.5%, 69.0%) and needle penetration temperatures (82.2℃, 85.4℃) were slightly lower than those of Example 1. Mechanistically, PVDF, as a traditional binder, exhibits good electrochemical stability, but its interfacial adhesion is insufficient when used alone. PAA (polyacrylic acid) can form hydrogen bonds with the hydroxyl groups on the surface of the aluminum current collector through its carboxyl groups, significantly enhancing interfacial adhesion. The combination of the two achieves synergistic optimization of "adhesion, conductivity, and thermal stability"—ensuring a strong bond between the active layer and the current collector (peel strength > 25 N / m), reducing the risk of short circuits caused by aluminum foil exposure during mechanical abuse, and maintaining interfacial charge transport efficiency, thereby reducing capacity loss during high-rate charging. In contrast, when the PAA ratio deviates from 50% (such as 55% in Example 4 or 45% in Example 5), either the excessive PAA ratio leads to a decrease in the flexibility of the binder system (Example 4), or the excessively low PAA ratio weakens the interfacial hydrogen bonding (Example 5), resulting in lower capacity retention and thermal stability compared to a 1:1 ratio. In summary, a PVDF to PAA mass ratio between 9:11 and 11:9 (i.e., PAA accounts for 45%-55%) can simultaneously ensure that the battery passes extreme safety tests such as nail penetration, 70% deformation extrusion, and 15mΩ short circuit. The 1:1 ratio achieves the optimal balance between high-rate performance and thermal runaway risk by precisely balancing interfacial bonding and charge transfer efficiency.

[0058] Table 3 Table 3 shows that the mass ratio of conductive agent to binder in the aluminum current collector undercoat has a significant balancing effect on the high-rate charging performance and mechanical abuse safety of the battery. All examples underwent nail penetration, extrusion, and short-circuit tests. The core difference lies in the trade-off between the 6C charging capacity retention rate and the highest temperature after nail penetration. When the proportion of conductive agent increased from 75% to 90% (mass ratio from 75 / 25 to 90 / 10), the 6C charging capacity retention rate increased from 65.4% to 72.3% (Examples 8 to 10), but the highest surface temperature of the battery after nail penetration increased from 76.6℃ to 96.9℃. The 85 / 15 ratio in Example 1 achieved a balance between performance and safety, with a retention rate of 70.5% and a temperature control of 81.0℃. Mechanistically, the core role of the conductive agent is to construct a continuous conductive network to improve interfacial charge transport efficiency; a higher proportion results in less capacity loss at high rates (6C). The binder, on the other hand, is crucial for ensuring the interfacial bonding strength between the aluminum current collector and the positive electrode active layer. A lower proportion leads to weaker interfacial adhesion, making the active layer more prone to peeling and increasing the risk of aluminum foil exposure during mechanical abuse (needle puncture), resulting in increased heat release (temperature rise) and potentially dangerous internal short circuits. Conversely, while a high binder proportion (e.g., 75 / 25) can enhance interfacial bonding and reduce needle puncture temperature, insufficient conductive agent proportion increases interfacial resistance, leading to decreased capacity retention at high rates. In summary, an 85 / 15 mass ratio achieves optimal high-rate performance through a synergistic balance between conductivity and adhesion, ensuring safety while maintaining optimal high-rate performance.

[0059] Table 4 Table 4 shows that the thickness of the aluminum current collector has a significant inverse correlation with the high-rate charging performance and mechanical abuse safety of the battery. The data indicates that Example 9 (4μm) has the highest 6C charging capacity retention (71.6%), but its highest surface temperature after needle penetration (96.6℃) is significantly higher than other groups. Example 11 (8μm) has the lowest capacity retention (68.7%), but its needle penetration temperature (81.7℃) is relatively controllable. Examples 1 (7μm) and 10 (5.5μm) have intermediate capacity retention (70.5%, 70.9%) and needle penetration temperatures (81.0℃, 87.9℃), and all examples passed needle penetration, 70% deformation extrusion, and 15mΩ short-circuit tests.

[0060] Mechanistically, thinner aluminum current collectors (e.g., 4μm) reduce the resistance of the electron transport path due to their reduced thickness, thereby improving capacity retention during high-rate charging. However, the heat dissipation area of ​​an excessively thin aluminum layer is limited, making it difficult for localized heat to dissipate quickly during a short circuit, leading to a sharp rise in surface temperature. While thicker aluminum current collectors (e.g., 8μm) offer higher mechanical strength and better heat dissipation (lower needle penetration temperature), the excessive metal layer increases the internal resistance of the current collector, resulting in decreased charge transport efficiency at high rates and a consequent reduction in capacity retention. Examples 1 (7μm) and 10 (5.5μm) achieve a dynamic balance between "electron conduction efficiency" and "heat dissipation capacity" through precise thickness control—avoiding the risk of thermal runaway with excessively thin current collectors while reducing the internal resistance loss of excessively thick current collectors. Therefore, they exhibit superior overall performance in terms of both capacity retention and safe temperature.

[0061] Table 5 Table 5 compares the effects of differences in aluminum current collector undercoat thickness, binder type, conductive agent to binder mass ratio, and aluminum current collector thickness on battery performance and safety between Example 1 (optimal solution) and eight comparative examples: Comparative Example 1 (undercoat 0.5 μm), Comparative Example 4 (all PAA binder), Comparative Example 6 (conductive agent / binder 95 / 5), and Comparative Example 7 (current collector 2 μm) had high 6C capacity retention (73.5%~74.4%), but failed the nail penetration / extrusion / short circuit tests and the nail penetration temperature was as high as 365~476℃; Comparative Example 2 (undercoat 3.5 μm), Comparative Example 3 (all PVDF binder), Comparative Example 5 (conductive agent / binder 65 / 35), and Comparative Example 8 (current collector 10 μm) passed the safety test, but the capacity retention was significantly reduced (60.3%~64.5%). Mechanistically, an excessively thin undercoat (0.5μm), poor thermal stability of the binder (all PAA), excessively high proportion of conductive agent (95 / 5), or excessively thin current collector (2μm) can lead to insufficient mechanical strength or lack of thermal stability of the battery. In the event of a short circuit, the electrode structure is prone to failure, resulting in severe thermal runaway. On the other hand, an excessively thick undercoat (3.5μm), poor conductivity of the binder (all PVDF), excessively low proportion of conductive agent (65 / 35), or excessively thick current collector (10μm) can increase the internal resistance of electron transport or reduce the interface contact efficiency, leading to aggravated capacity loss at high rates.

[0062] In summary, this invention solves the technical contradiction in the prior art of being unable to simultaneously achieve high-rate performance improvement and safety performance assurance by precisely controlling the thickness of the aluminum current collector, the base coating parameters, the composite system binder, and the mass ratio of conductive agent to binder.

[0063] 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 an aluminum 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 aluminum current collector and the positive electrode active material layer, and the thickness of the base coating is 0.3-3.0 μm.

2. The positive electrode sheet according to claim 1, characterized in that: The peel strength between the positive electrode active material layer and the base layer is >25 N / m.

3. The positive electrode sheet according to claim 1, characterized in that: The thickness of the aluminum current collector is 4-8 μm.

4. The positive electrode sheet according to claim 1, characterized in that: The base coating includes a conductive agent and a binder, wherein the conductive agent content in the base coating is 70-90 wt% and the binder content is 10-30 wt%.

5. The positive electrode sheet according to claim 1, characterized in that: The binder in the base coating is a mixture of polyvinylidene fluoride and polyacrylic acid.

6. The positive electrode sheet according to claim 5, characterized in that: The mass of the polyacrylic acid is 45%-55% of the total mass of the adhesive.

7. The positive electrode sheet according to claim 1, characterized in that: The conductive agent in the base coating is at least one of carbon black, carbon nanotubes, and graphene.

8. 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.

9. The positive electrode sheet according to claim 8, characterized in that: The main active material is a layered metal oxide.

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

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