Secondary battery electrode, secondary battery, and manufacturing method

Abstract

The application provides a secondary battery electrode, a secondary battery and a preparation method. The secondary battery electrode comprises a current collector and an active material coated on the surface of the current collector, and the active material comprises, in parts by weight, 90-98 parts of an electrode active material, 0.1-7 parts of a multifunctional composite agent and 1-5 parts of a binder. The multifunctional composite agent comprises a porous insulating oxide, a carbon-based conductive agent and a first dispersion medium; the carbon-based conductive agent accounts for 0 wt.%-0.1 wt.% of the total weight percentage of the active material, and the porous insulating oxide serves as a main skeleton to dominate ion transmission. The weight of all components is calculated according to dry matter.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a secondary battery electrode, a secondary battery, and a method for preparing them. Background Technology

[0002] Currently, commercially available lithium-ion batteries typically employ carbon materials such as carbon black and carbon nanotubes to construct a continuous electronic conductive network to ensure the battery's charge transfer efficiency. However, this design based on continuous carbon networks has inherent safety flaws that are difficult to avoid. When the battery is subjected to abuse conditions such as puncture or crushing, causing an internal short circuit, the low-resistance continuous carbon network will rapidly form a highly efficient discharge channel, generating an extremely large short-circuit current. This will then trigger a severe Joule heating effect and quickly initiate a chain thermal runaway reaction, ultimately leading to serious safety accidents such as battery fires and explosions.

[0003] To address these issues, related technologies attempt to modify carbon-based conductive networks by introducing porous oxides. For example, patent CN120600814A discloses a "carbon black + mesoporous" method. One approach involves a composite conductive agent consisting of carbon black and mesoporous alumina (1:1). The mesoporous alumina serves as an auxiliary component of the conductive network, while carbon black is the primary conductive component. This approach aims to improve the performance of the anode material. Patent CN120280449A proposes a "pore-forming and then filling" method using porous particles. This involves first creating mechanical / laser-generated pores (10–500 μm) in the active layer, then filling these pores with porous particles. These porous particles fill the macroscopic pores, providing support, liquid retention, and acting as ion channels. As a multifunctional composite agent, they form a "three-dimensional interconnected pore framework," replacing the carbon conductive network. However, both approaches retain the continuous carbon network as the main electron transport backbone, using only oxides as auxiliary ion channels. Such approaches cannot eliminate low-resistance discharge paths during internal short circuits and are essentially "passive safety" improvements, failing to address the root cause of thermal runaway.

[0004] Another patent, WO2024199328A1, discloses a method for preparing battery electrodes by adding inorganic porous materials. Its technical solution still uses carbon-based conductive agents (the conductive agents account for 0.1% to 5% of the total mass of the negative electrode active material layer) as the main body for electron transport, and inorganic porous materials are only used as auxiliary additives. The final technical effect focuses on improving the rate performance of the battery, but does not improve the thermal runaway problem caused by short circuits in the battery.

[0005] Another patent, CN116632156A, discloses a negative electrode sheet, a wound battery cell, a lithium-ion battery, and a method for preparing the same. Although the mass percentages of active material, conductive agent, binder, and porous liquid-absorbing molecules such as alumina in the second active material layer are (95-98.5%):(0-2.0%):(0.5-2.5%):(0.1-2.0%), as described in its specification, conductive carbon black is a product of the thermal decomposition of small-particle carbon and hydrocarbons. It has a small particle size, large specific surface area, and high structure, occupying a larger volume fraction in the polymer, which is beneficial for forming a conductive network and thus achieving better conductivity. Furthermore, its first active material layer does not contain porous liquid-absorbing molecules; therefore, the main conductive network is still composed of carbon-based conductive agents. The content of carbon-based conductive agents in each embodiment is also higher than 0.1%.

[0006] In summary, existing technical solutions either rely on the main architecture of carbon-based conductive networks or focus on improving battery rate performance, but neither has achieved the technical goal of "blocking internal short-circuit discharge channels and suppressing thermal runaway from the source". Summary of the Invention

[0007] The purpose of this invention is to provide a secondary battery electrode, a secondary battery, and a preparation method that no longer uses a carbon-based conductive network as the main structure.

[0008] To address the aforementioned technical problems, the present invention provides a secondary battery electrode, comprising a current collector and an active material coated on the surface of the current collector, wherein the active material comprises, by weight:

[0009] Electrode active material: 90-98 parts;

[0010] Multifunctional composite agent: 0.1 parts to 7 parts; wherein the multifunctional composite agent includes: porous insulating oxide, carbon-based conductive agent, and a first dispersion medium; the carbon-based conductive agent accounts for 0 wt.%-0.1 wt.% of the total weight of the active material, and the mass ratio of the dry powder in the porous insulating oxide, carbon-based conductive agent, and first dispersion medium is (1-5):(0-0.1):(0-2), wherein the porous insulating oxide serves as the main framework to dominate ion transport;

[0011] Binder: 1 to 5 parts; the binder content here includes the content of the first dispersion medium of the multifunctional composite agent mentioned above;

[0012] All components are weighed on a dry matter basis. For example, when calculating the weight parts, the weight of the solvent is not included in the first dispersion medium, and the weight of the solvent used to swell the binder is not included when calculating the weight of the binder.

[0013] Optionally, the solid content of the multifunctional compound is 18 wt.%-24 wt.%, for example, it can be 20 wt.%.

[0014] Optionally, the solvent can be water, or NMP solvent (NMP or water). The amount of NMP or water added is adjusted according to the target solid content (usually 50%~52% for the negative electrode and 58%~60% for the positive electrode) to ensure that each layer of slurry has good rheological properties and coating adaptability.

[0015] Alternatively, the carbon-based conductive agent can be Super P, acetylene black, Ketjen black ECP-300J, conductive graphite KS-6, or fiber conductive agents such as CNT and VGCF.

[0016] Because lithium-ion transport exhibits a significant gradient along the electrode thickness, the central region of the electrode (i.e., the middle part away from the separator and current collector) typically becomes a bottleneck for ion diffusion, exhibiting the lowest ion flux and the most severe concentration polarization. To fully leverage the effectiveness of porous insulating oxides in constructing local ion transport channels and stabilizing interfaces, their content needs to be enriched in the central part of the electrode structure. This allows for targeted enhancement of the ion conductivity network in the weakest region of ion transport, thereby improving the overall rate performance of the electrode. Optionally, the active material has at least three layers, from top to bottom: a surface layer, an intermediate layer, and a bottom layer. The bottom layer is closest to the current collector. The porous insulating oxide content in the intermediate layer accounts for 60 wt.%-70 wt.% of the sum of the porous insulating oxide contents in all active material layers, which can be considered a fixed content. The bottom and surface layers are configured with lower contents to match the ion concentration gradient within the electrode, achieving "on-demand" ion transport enhancement.

[0017] Optionally, the adhesive content in the bottom layer is greater than or equal to the adhesive content in the intermediate layer, and the adhesive content in the bottom layer is greater than or equal to the adhesive content in the top layer.

[0018] Optionally, the content of electrode active material in the surface layer is greater than or equal to the content of electrode active material in the intermediate layer, and the content of electrode active material in the surface layer is greater than or equal to the content of electrode active material in the bottom layer.

[0019] Optionally, the content of the multifunctional composite agent in the intermediate layer is greater than or equal to the content of the multifunctional composite agent in the surface layer, and the content of the multifunctional composite agent in the intermediate layer is greater than or equal to the content of the multifunctional composite agent in the bottom layer.

[0020] Optionally, guided by high electrochemical activity, the surface layer comprises, by weight: 94 to 98 parts of electrode active material; 0.1 to 4 parts of multifunctional composite agent; and 1 to 3 parts of binder. This ensures necessary mechanical strength while maximizing the reactivity of the surface area, which is beneficial for electrolyte wetting and rapid charge / discharge performance.

[0021] Optionally, the intermediate layer is located in the central region along the thickness direction of the electrode and comprises, by weight: 92 to 96 parts of electrode active material; 1 to 7 parts of multifunctional composite agent; and 1 to 3 parts of binder. This high-content porous insulating oxide is enriched in the central region of the electrode where ion transport is slowest, enhancing the local ion conductivity of the central part of the electrode—the region with the slowest ion transport—alleviating concentration polarization, and improving the utilization rate of the electrode's active material.

[0022] Optionally, the bottom layer comprises, by weight: 92 to 96 parts of electrode active material; 0.1 to 4 parts of multifunctional composite agent; and 3 to 5 parts of binder. The multifunctional composite agent content is low, while the binder content is high, such as increasing the PVDF or CMC proportion by 10% to 30%. This aims to significantly enhance the adhesion between the active material and the foil current collector by increasing the binder proportion, effectively suppressing electrode peeling caused by volume changes or stress accumulation during long-term battery cycling.

[0023] Optionally, the porous insulating oxide is selected from any one or more combinations of porous alumina, porous silica, and porous zirconium oxide.

[0024] Optionally, the porous insulating oxide has a specific surface area ≥ 50 m² / g, a porosity of 5%-40%, and a pore size distribution of 2nm-500 nm. Among them, the porous insulating oxide with a pore size distribution of 2nm-50 nm accounts for 50%-100% or even 90%-100% of all porous insulating oxides.

[0025] Furthermore, the specific surface area of ​​the porous insulating oxide is >100 m² / g, and the porous insulating oxide can be mesoporous Al₂O₃.

[0026] Optionally, the electrode active material is either a positive electrode active material or a negative electrode active material. The positive electrode active material is selected from any one or more combinations of lithium cobalt oxide, lithium iron phosphate, ternary materials, and lithium-rich manganese-based materials. The negative electrode active material is selected from any one or more combinations of graphite, hard carbon, silicon-based materials, silicon-carbon composite materials, and metallic lithium. The ternary material can be NCM / NCA.

[0027] Optionally, the first dispersion medium is CMC adhesive, PVDF adhesive, or PAA (polyacrylic acid) adhesive, and the binder is selected from any one or more combinations of styrene-butadiene rubber, PVDF, CMC, and PAA. The secondary battery electrode also includes a second dispersion medium, which is CMC adhesive, PVDF adhesive, or PAA adhesive.

[0028] Optionally, the current collector for the positive electrode can be aluminum foil, and the current collector for the negative electrode can be copper foil.

[0029] The present invention also provides a secondary battery, comprising any of the secondary battery electrodes as described above and a separator for stacking the secondary battery electrodes.

[0030] The present invention also provides a method for preparing any of the secondary battery electrodes described above, comprising:

[0031] Preparation of the multifunctional composite agent S1: Porous insulating oxide is added to a first dispersion medium, and a carbon-based conductive agent, accounting for 0 wt.%-0.1 wt.% of the total weight of the active material, is added. Shear dispersion is then performed to form a gel-like multifunctional composite agent. Optionally, the carbon-based conductive agent may be omitted, or, to prevent localized electronic insulation, it may be added at 0.05 wt.%-0.1 wt.% of the total weight of the active material.

[0032] Preparation of active materials S2: Add the multifunctional composite agent obtained in S1, electrode active material and binder, and perform shear dispersion to form a slurry of active materials;

[0033] Electrode preparation S3: The slurry obtained in S2 is coated onto the current collector and then heated and dried to cure.

[0034] This preparation method only requires coating and molding, without the need for post-processing such as pore creation or filling.

[0035] Optionally, the preparation of the multifunctional composite agent S1 includes:

[0036] S11: Add the pre-prepared first dispersion medium into the dispersion equipment, the volume of which is about 60% to 70% of the total volume of the dispersion equipment.

[0037] S12: Slowly add porous insulating oxide powder while stirring at low speed (approximately 200 rpm - 800 rpm) to avoid dust and local agglomeration.

[0038] S13: After feeding, let it stand and moisten for 5 to 10 minutes.

[0039] S14: Start the dispersion equipment and perform high-speed (2000rpm~4000rpm) shear dispersion for 20 min~40 min to form a gel-like multifunctional composite agent; observe the slurry state during the process: it gradually changes from a turbid suspension to a homogeneous, particle-free, and well-flowing gel-like dispersion.

[0040] Optionally, in S2, a first slurry, a second slurry, and a third slurry are prepared according to a surface layer, an intermediate layer, and a bottom layer, respectively. The first slurry comprises, by weight, 94 to 98 parts of electrode active material; 0.1 to 4 parts of multifunctional composite agent; and 1 to 3 parts of binder. The second slurry comprises, by weight, 92 to 96 parts of electrode active material; 1 to 7 parts of multifunctional composite agent; and 1 to 3 parts of binder. The third slurry comprises, by weight, 92 to 96 parts of electrode active material; 0.1 to 4 parts of multifunctional composite agent; and 3 to 5 parts of binder.

[0041] In S3, the coating is applied in the order of base layer, intermediate layer and top layer. Each layer is dried independently and cooled to room temperature before the next layer is applied.

[0042] Optionally, in S3, when preparing the positive electrode, the total coating density of the positive electrode is calculated as 145 g / m²~155 g / m² based on the dry film, wherein the coating density of the bottom layer is in the range of 35 g / m²~40 g / m², the coating density of the middle layer is in the range of 75 g / m²~80 g / m², and the coating density of the surface layer is in the range of 35 g / m²~40 g / m².

[0043] When preparing the negative electrode, the total coating density of the negative electrode is calculated based on the dry film as 77 g / m²~83 g / m², of which the coating density of the bottom layer ranges from 18 g / m² to 21 g / m², the coating density of the middle layer ranges from 40 g / m² to 43 g / m², and the coating density of the surface layer ranges from 18 g / m² to 21 g / m².

[0044] The total coating density can be the sum of the coating densities of each layer.

[0045] Optionally, S2 includes:

[0046] S21: Add the multifunctional composite agent obtained in S1 to the second dispersion medium or the adhesive solution formed by the binder;

[0047] S22: Add electrode active material and perform shear dispersion; and

[0048] S23: When the second dispersion medium is used in S21, a binder is added to obtain a slurry.

[0049] The present invention also provides a method for preparing any of the secondary batteries described above, comprising: a method for preparing any of the secondary battery electrodes described above; stacking electrode sheets and separators to form an electrode core; and encapsulating the electrode core to form a battery cell.

[0050] Existing technologies primarily employ traditional carbon conductive networks. However, the inventors discovered that carbon materials, widely used in electrode systems, suffer from numerous unresolved technical defects that severely limit battery rate performance, cycle stability, and safety. Firstly, carbon materials have a limited functional dimension, making it difficult to collaboratively address the ion transport bottleneck. Carbon materials can only construct electron transport paths and cannot facilitate ion migration between electrode particles. With the development of high-energy-density thick electrode technology, the diffusion resistance of ions in the electrolyte within the electrode pores has gradually become a core factor restricting battery rate performance; simultaneously, the presence of carbon materials may also block ion channels, further exacerbating the problem of hindered ion transport.

[0051] Secondly, carbon materials can cause interfacial chemical instability, which in turn induces side reactions and lithium dendrite growth. On the positive electrode side, when the battery is at a high operating potential greater than 3.8V, violent interfacial side reactions can easily occur between the carbon materials and the electrolyte, causing electrolyte oxidation and decomposition, increased battery impedance, and rapid capacity decay. On the negative electrode side, an unstable solid electrolyte interfacial film is easily formed under low potential conditions, and due to uneven ion transport, lithium dendrite growth can be further induced. Lithium dendrites are the direct cause of puncturing the battery separator and causing internal short circuits in the battery.

[0052] Third, carbon materials pose an inherent safety risk; they can act as an "explosive fuse" during internal short circuits in the battery, which is the most fatal and common defect in existing technologies. When an internal short circuit occurs in the battery due to abuse conditions such as puncture or crushing, the positive and negative electrodes can be directly connected through a carbon-based conductive network; based on Joule's law (P=I... 2 The extremely low resistance of the carbon-based network causes a sharp increase in short-circuit current, resulting in a huge instantaneous peak heating power and rapidly triggering a chain reaction of thermal runaway. Therefore, the carbon-based network in the electrode not only fails to provide safety protection but also exacerbates the thermal runaway process, becoming a "catalyst" and "accelerant" for thermal runaway.

[0053] To address the aforementioned issues, the inventors have also attempted improvements such as coating the surface of positive electrode particles and applying ceramic coatings to the separator. However, these solutions are all localized and passive protection strategies. They cannot construct efficient ion transport channels on the macroscopic three-dimensional scale of the electrode, nor can they fundamentally change the inherent property of the electrode body to actively exacerbate thermal runaway under abuse conditions.

[0054] Ultimately, the inventors overcame the technical bias that traditional carbon conductive networks could only be used as the primary method, while porous insulating oxides could only be used as an auxiliary method. They adopted a method of replacing traditional carbon conductive networks with porous insulating oxides, eliminating low-resistance discharge channels during internal short circuits at the source, thus achieving intrinsic safety improvements. This led to the first proposal of the "low-conductivity network" electrode design concept. A novel "ion-dominant, electron-assisted" transport system was constructed: porous oxides form a three-dimensional interconnected mesoporous network, serving as efficient ion channels; electron conduction relies on the conductivity of the active material itself or trace amounts of conductive agents, forming discontinuous, high-resistance electronic paths that meet usage requirements under normal operating conditions and effectively limit current during short circuits. By abandoning traditional carbon-based conductive networks and introducing porous insulating oxides with three-dimensional interconnected channels as the functional framework of the electrode, the risk of internal short-circuit thermal runaway is significantly suppressed while ensuring necessary electron / ion co-transport, and rate performance and cycle stability are simultaneously improved.

[0055] In traditional electrodes, the continuous carbon network has extremely low resistance (approximately 0.8Ω for the positive electrode and only 0.02Ω for the negative electrode). Once an internal short circuit occurs (such as due to needle penetration or dendrite penetration), a low-resistance discharge circuit is formed, generating a very large short-circuit current I=V / R. According to Joule's law, P=I... 2 R, although R is small, but I 2 The growth is more dramatic, resulting in extremely high instantaneous power P (up to several kilowatts) and extremely high instantaneous heat generation, which rapidly ignites the electrolyte.

[0056] By introducing a high-resistivity porous insulating oxide, the electron transport path is "disrupted," significantly increasing the overall electrode resistance (up to 2Ω for the positive electrode, a 2.5-fold increase; and 0.06Ω for the negative electrode, a 3-fold increase). Although the resistance R increases, more importantly, it limits the maximum short-circuit current I. max .

[0057] Secondly, the porous oxide framework has high mechanical strength (Mohs hardness ≥8), which can serve as a "rigid support" to inhibit the pulverization and shedding of active materials during cycling; its chemical inertness avoids side reactions of carbon materials at high / low potentials (such as electrolyte oxidation and excessive SEI growth), reducing the accumulation of interfacial impedance; for large-volume expansion systems such as silicon-based anodes, its nanopores can accommodate some of the expansion stress and alleviate electrode cracking.

[0058] Furthermore, as an option, porous insulating oxides (such as mesoporous oxides) It possesses a high specific surface area (>100 m² / g) and a three-dimensional interconnected mesoporous structure (pore size 2nm~50 nm), which can adsorb and enrich the electrolyte, forming an "ion buffer pool"; it constructs a low-torsion ion channel that spans the electrode thickness, shortening the... Diffusion pathways; improved wettability of the active material / electrolyte interface, reducing interfacial charge transfer impedance. The kinetics have shifted from traditional reliance on carbon networks and the tendency for thick electrodes to polarize easily to ion channel optimization, significantly reducing the cell's line impedance. Attached Figure Description

[0059] Figure 1 This is the SEM image provided in Embodiment 1 of the present invention;

[0060] Figure 2 This is a schematic diagram of the structure of the active material in this invention and the prior art;

[0061] Figure 3 These are temperature comparison curves from safety experiments provided in the embodiments and comparative embodiments of this invention;

[0062] Figure 4 These are the cyclic curves provided in the embodiments and comparative embodiments of this invention;

[0063] Figure 5 These are the surface temperature curves of the extrusion test cell provided in the embodiments and comparative embodiments of the present invention. Detailed Implementation

[0064] The specific embodiments of the present invention will be described in further detail below with reference to examples. These examples are used to illustrate the present invention, but are not intended to limit the scope of the invention.

[0065] Unless otherwise specified, all references in the following examples are by weight.

[0066] Example 1

[0067] This embodiment provides a preparation method, including:

[0068] Preparation of multifunctional composite agents:

[0069] S11: Add the pre-prepared CMC aqueous solution (containing 2.0 parts of CMC dry powder) or PVDF / NMP adhesive solution (containing 8–10 parts of dry powder) to the Primix dispersion equipment, with the volume accounting for approximately 60% to 70% of the total volume of the Primix dispersion equipment.

[0070] S12: Add porous insulating oxide powder slowly in proportion while stirring at low speed (500 rpm) to avoid dust and local agglomeration.

[0071] S13: After feeding, let stand and moisten for 5 minutes.

[0072] S14: Start the Primix equipment for high-speed shear dispersion to form a gel-like multifunctional composite agent; the high-speed shear dispersion speed is 3000 rpm and the dispersion time is 30 min. During the process, observe the state of the slurry: it gradually changes from a turbid suspension to a homogeneous, particle-free, and free-flowing gel-like dispersion.

[0073] Preparation of negative electrode sheet:

[0074] S21: Sodium carboxymethyl cellulose (CMC) is added to deionized water, fully swollen and gelled in a double planetary mixer to form a homogeneous gel solution to obtain the second dispersion medium; the gel solution of the prepared multifunctional composite agent is added and mixed evenly.

[0075] S22: Slowly add the negative electrode active material to achieve high shear dispersion;

[0076] S23: Finally, add styrene-butadiene rubber (SBR) emulsion as an elastic binder, and continue stirring until the slurry is homogeneous and stable to obtain the final negative electrode slurry.

[0077] In S2, the negative electrode slurry is divided into at least three types, which are respectively made into the first slurry, the second slurry, and the third slurry according to the surface layer, the middle layer, and the bottom layer.

[0078] The first slurry comprises, by weight: 97 parts of electrode active material; 0.5 parts of multifunctional composite agent; and 2.5 parts of binder; the coating density of the surface layer ranges from 19.5 g / m².

[0079] The second slurry comprises, by weight: 96 parts of electrode active material; 1.5 parts of multifunctional composite agent; and 2.5 parts of binder; the coating density of the intermediate layer is 41 g / m².

[0080] The third slurry comprises, by weight: 95 parts of electrode active material; 0.5 parts of multifunctional composite agent; and 4.5 parts of binder; the coating density of the underlayer is 19.5 g / m².

[0081] S3: Coating is performed sequentially in the order of base layer, intermediate layer, and top layer. Each layer is dried independently and cooled to room temperature before the next layer is applied. A step-by-step three-coating-baking process is adopted to sequentially construct the base layer, intermediate layer, and top layer on the current collector. The slurry components of each layer are specifically designed to achieve synergistic improvement in adhesion enhancement, ion transport optimization, and electrochemical performance.

[0082] More specifically: After each coating layer is applied, it is immediately placed in an oven for independent drying and curing (e.g., 80℃~120℃, 2min~5min). Only after the layer is completely dry and cooled is the next layer applied. Each layer is dried independently and cooled to room temperature before the next layer is applied, avoiding interlayer cracking caused by thermal stress. This process involves three coatings and three baking cycles: bottom layer → intermediate layer → surface layer, ultimately forming a gradient composite electrode with a clear structure and well-defined functional zones. Double-sided coating is performed after single-sided coating.

[0083] S4: The coated electrode sheet is compacted according to the design requirements through a rolling process to control the electrode porosity, thickness and areal density, and ensure that it has good electronic conductivity and ion transport performance.

[0084] The final negative electrode sheet contains 0 parts carbon-based conductive agent, 1 part mesoporous alumina, 96 parts total active material, 3 parts total binder, and a total coating density of 80 g / m² on one side. 2 The SEM image of the negative electrode is shown below. Figure 1 As shown, the red arrow indicates mesoporous alumina.

[0085] Preparation of the positive electrode sheet:

[0086] The differences between this and the preparation process of the negative electrode sheet mentioned above will be explained:

[0087] The positive electrode slurry prepared in S2 is an NMP oil-based system;

[0088] S2 specifically includes:

[0089] S21: Add polyvinylidene fluoride (PVDF) to N-methylpyrrolidone (NMP), swell fully under stirring conditions, and apply as a glue to form an adhesive solution;

[0090] S22: Add multifunctional composite adhesive (composed of porous insulating oxide, trace carbon-based conductive agent (optional) and PVDF / NMP carrier); add positive electrode active material (such as NCM, LFP, etc.) in batches for high-energy dispersion to ensure no agglomeration; stir until the slurry is uniform and the viscosity is stable to obtain the basic positive electrode slurry.

[0091] S3: Based on dry film calculations, the coating density range for the bottom layer is 35g / m²~40g / m², the coating density range for the middle layer is 75g / m²~80g / m², and the coating density range for the top layer is 35g / m²~40g / m².

[0092] The final positive electrode sheet contains 0 parts carbon-based conductive agent, 1 part mesoporous alumina, 97 parts total active material, 2 parts total binder, and a total coating density of 150 g / m² on one side. 2 .

[0093] Cell manufacturing:

[0094] S5: The positive and negative electrode sheets are precisely cut into single electrode sheets through the die-cutting process, and the size and alignment accuracy meet the requirements of the stacking process.

[0095] S6: Using a Z-shaped stacking process, the positive electrode sheet, the negative electrode sheet, and the separator obtained above are automatically stacked in an alternating sequence of "separator-negative electrode-separator-positive electrode" to form a compact and uniform stacked electrode core, which effectively improves volume utilization and reduces internal resistance.

[0096] S7: The assembly process then begins, where the stacked electrode cores are installed into an aluminum-plastic film housing. After being sealed by the top and side seals and the liquid injection port, a fixed amount of electrolyte is injected. The cores then undergo key electrochemical treatment steps such as formation, aging, and capacity testing to finally produce a high-performance soft-pack lithium-ion cell.

[0097] Example 2

[0098] The difference from Example 1 is that,

[0099] The final negative electrode sheet contains 0.05 parts carbon-based conductive agent, 0.95 parts mesoporous alumina, 96 parts total active material, and 3 parts total binder, with a total coating density of 80 g / m² on one side. 2 .

[0100] The final positive electrode sheet is composed of a total active material containing 0.05 parts carbon-based conductive agent, 0.95 parts mesoporous alumina, 97 parts total active material, and 2 parts total binder, with a total coating density of 150 g / m² on one side. 2 .

[0101] Example 3

[0102] The difference from Example 1 is that,

[0103] The final negative electrode sheet contains 0.1 parts carbon-based conductive agent, 0.9 parts mesoporous alumina, 96 parts total active material, 3 parts total binder, and a total coating density of 80 g / m² on one side. 2 .

[0104] The final positive electrode sheet is composed of a total active material containing 0.1 parts carbon-based conductive agent, 0.9 parts mesoporous alumina, 97 parts total active material, and 2 parts total binder, with a total coating density of 150 g / m² on one side. 2 .

[0105] Example 4

[0106] The difference from Example 1 is that the porous insulating oxide is porous silicon dioxide. The total coating density of the positive electrode is 155 g / m² on one side.2 The total coating density of the negative electrode is 83 g / m² on one side. 2 .

[0107] Example 5

[0108] The difference from Example 1 is that the porous insulating oxide is porous zirconium oxide. The total coating density of the positive electrode is 145 g / m² on one side. 2 The total coating density of the negative electrode is 77 g / m² on one side. 2 .

[0109] Example 6

[0110] The difference from Example 1 is that the total active material in the final negative electrode sheet contains 0.05 parts carbon-based conductive agent, 4.95 parts mesoporous alumina, 93 parts total active material, 2 parts total binder, and a total coating density of 80 g / m² per side. 2 .

[0111] The final positive electrode sheet is composed of a total active material containing 0.05 parts carbon-based conductive agent, 4.95 parts mesoporous alumina, 93 parts total active material, and 2 parts total binder, with a total coating density of 150 g / m² on one side. 2 .

[0112] Example 7

[0113] The difference from Example 1 is that the total active material in the final negative electrode sheet contains 0.05 parts carbon-based conductive agent, 4.95 parts mesoporous alumina, 90 parts total active material, 5 parts total binder, and a total coating surface density of 80 g / m² per side. 2 .

[0114] The final positive electrode sheet is composed of a total active material containing 0.05 parts carbon-based conductive agent, 4.95 parts mesoporous alumina, 90 parts total active material, and 5 parts total binder, with a total coating density of 150 g / m² on one side. 2 .

[0115] Example 8

[0116] The difference from Example 1 is that the negative electrode slurry has three layers, but the content of each layer is the same. This means that the porous insulating oxide content in the middle layer accounts for about 33 wt.% of the sum of the porous insulating oxide contents of all active material layers. The total content of each component is the same as in Example 1, and the total coating surface density is 80 g / m² on one side. 2 .

[0117] The positive electrode slurry consists of three layers, but the content of each layer is the same. This means that the porous insulating oxide content in the middle layer accounts for approximately 33 wt.% of the sum of the porous insulating oxide contents of all active material layers. The total component content is the same as in Example 1, and the total coating density is 150 g / m² on one side. 2 .

[0118] Example 9

[0119] The difference from Example 1 is that the negative electrode slurry is a single layer without a three-layer gradient. The total content of each component is the same as in Example 1, and the total coating surface density is 80 g / m² on one side. 2 .

[0120] The positive electrode slurry is a single layer without a three-layer gradient. The total content of each component is the same as in Example 1, and the total coating surface density is 150 g / m² on one side. 2 .

[0121] Example 10

[0122] The difference from Example 1 is that,

[0123] The final negative electrode sheet is identical to the negative electrode sheet of Example 1. The final positive electrode sheet is a single-layer coating without gradient. The total active material in the electrode sheet contains 1 part carbon-based conductive agent, 0 parts mesoporous alumina, 97 parts total active material, and 2 parts total binder. The total coating surface density is 150 g / m² on one side. 2 .

[0124] Example 11

[0125] The final positive electrode sheet is identical to the positive electrode sheet of Example 1. The final negative electrode sheet is composed of a total active material containing 1 part carbon-based conductive agent, 0 parts mesoporous alumina, 96 parts total active material, 3 parts total binder, and a total coating surface density of 80 g / m² on one side. 2 .

[0126] Comparative Example 1

[0127] The difference from Example 1 is that,

[0128] The final negative electrode sheet contains 1 part carbon-based conductive agent, 0 parts mesoporous alumina, 96 parts total active material, 3 parts total binder, and a total coating density of 80 g / m² on one side. 2 .

[0129] The final positive electrode sheet is composed of a total active material, containing 1 part carbon-based conductive agent, 0 parts mesoporous alumina, 97 parts total active material, 2 parts total binder, and a total coating surface density of 150 g / m² on one side. 2 .

[0130] Comparative Example 2

[0131] The difference from Example 1 is that,

[0132] The final negative electrode sheet contains 0.2 parts carbon-based conductive agent, 0.8 parts mesoporous alumina, 96 parts total active material, 3 parts total binder, and a total coating density of 80 g / m² on one side. 2 .

[0133] The final positive electrode sheet is composed of a total active material containing 0.2 parts carbon-based conductive agent, 0.8 parts mesoporous alumina, 97 parts total active material, and 2 parts total binder, with a total coating density of 150 g / m² on one side. 2 .

[0134] Comparative Example 3

[0135] The difference from Example 1 is that,

[0136] The final negative electrode sheet contains 0.5 parts carbon-based conductive agent, 0.5 parts mesoporous alumina, 96 parts total active material, 3 parts total binder, and a total coating density of 80 g / m² on one side. 2 .

[0137] The final positive electrode sheet is composed of a total active material, containing 0.5 parts carbon-based conductive agent, 0.5 parts mesoporous alumina, 97 parts total active material, and 2 parts total binder, with a total coating density of 150 g / m² on one side. 2 .

[0138] test:

[0139] The electrode impedance in the above embodiments and comparative examples was tested using the ROCK TH2523 film impedance testing system. The specific testing steps were as follows: After coating, the electrode was rolled to the specified thickness, cut into 4*4cm pieces, placed in the film impedance testing system, and after clicking start, the system applied pressure to the electrode at a set pressure of 750N. After the pressure stabilized, the electrode impedance value was read. The test results are shown in Table 1.

[0140] The battery cells in the above embodiments and comparative examples were subjected to safety tests using the ARC test method and the continuous extrusion test method.

[0141] The ARC test employs an accelerating calorimeter, a highly sensitive adiabatic calorimeter, to measure parameters such as heat release, temperature change rate, and pressure change during sample heating under near-adiabatic conditions. The test principle of ARC is based on a "Heat-Wait-Search" (HWS) mode, which includes:

[0142] 1. Heating: Heat the sample to the set temperature.

[0143] 2. Wait: Allow the sample to reach thermal equilibrium with the environment.

[0144] 3. Search: Monitor whether the sample exhibits spontaneous heating (temperature rise rate exceeds a threshold, such as 0.02 ℃ / min).

[0145] Once spontaneous heating is detected, the system switches to adiabatic tracking mode, no longer actively heating, but following the sample's own temperature rise, recording temperature (T), temperature rise rate (dT / dt), pressure (P), and time (t) until thermal runaway occurs.

[0146] The method used in this test was: initial temperature 50℃, temperature increment 5℃, scanning temperature (0.02℃ / min), thermal runaway rate (1℃ / s), cutoff temperature 500℃, step length 15min, search time 5min, and cooling to room temperature 25℃.

[0147] The test results are shown in Table 2. T1: Self-exothermic onset temperature; T2: Thermal runaway trigger temperature; T3: Maximum adiabatic temperature rise. Temperature comparison curves are shown below. Figure 3 As shown.

[0148] The continuous extrusion test method is carried out according to the following steps:

[0149] a) The test subject is a fully charged battery cell;

[0150] b) The compression directions are perpendicular to the x, y, and z directions of the battery (the x-axis is the direction of vehicle travel, and the y-axis is a horizontal direction perpendicular to the direction of travel). A semi-cylinder with a radius of 75 mm and a length greater than the size of the battery being compressed is used, and compression is applied at a speed not exceeding 2 mm / s. The deformation is increased in increments of 5% of the battery's deformation, and each increment is maintained for 10 minutes. Compression is stopped when one of the following conditions is met:

[0151] — Thermal runaway occurred;

[0152] —A fire or explosion occurred;

[0153] —The voltage reaches 0 V;

[0154] —The extrusion pressure reaches 500 kN.

[0155] c) After completing the above test steps, observe for 1 hour at the test environment temperature. This test is conducted in the Z-axis direction.

[0156] Test results are as follows Figure 5 As shown.

[0157] The capacity retention rate of the cells in the above embodiments and comparative examples was tested. The test method was as follows: For the rate charging test, the fully charged cell was discharged at a 1C rate to 2V in a constant temperature chamber at 25℃, rested for 30 minutes, then charged at a constant current and constant voltage at a 1C rate to the cutoff voltage of 3.65V (this step represents the full charge capacity), rested for 30 minutes, discharged at 1C, and rested for 30 minutes. For constant current charging, the charging rates were adjusted to 1C, 1.5C, and 2C. The capacity retention rate at each charging rate was obtained based on the ratio of the charged capacity to the full charge capacity. The measured results are shown in the table: In the LFP system, the 2C fast charging capacity retention rate increased from 70% in Comparative Example 1 to 91.2% in Example 6 (an increase of 21%). This indicates that the 2C capacity retention rate of the LFP electrode increased from 70% to 91.2% due to the low-torsion ion channels constructed by the porous oxide. Although the electronic resistance increased, the ion transport gain dominated.

[0158] The battery cells from Example 1 and Comparative Example 1 were subjected to a cycle capacity retention test. The test method was as follows: the battery cells were placed in a constant temperature chamber at 45°C, discharged at a constant current of 1C to 2.5V, rested for 30 minutes, charged at a constant current and constant voltage of 1C to 3.65V, and rested for 30 minutes. This constituted one cycle. The discharge capacity of the first cycle was recorded as the initial capacity; the ratio of the discharge capacity to the initial capacity was recorded as the capacity retention rate. The test results are shown below. Figure 4 As shown.

[0159] Comparison diagrams of the structures of the examples and embodiments are shown below. Figure 2 As shown, instead of the traditional carbon-based conductive network, a porous insulating oxide with three-dimensional interconnected channels is introduced as the electrode functional framework. While ensuring the necessary electron / ion co-transmission, the risk of internal short-circuit thermal runaway is significantly suppressed, and the rate performance and cycle stability are improved simultaneously.

[0160] As shown in Table 1, the impedance of the negative electrode gradually increases with the increase of the proportion of mesoporous alumina. When the carbon-based conductive agent increases by more than 0.1 parts, the conductive agent directly forms a conductive network, and the increase in electrode impedance is not significant. When the carbon-based conductive agent increases by less than 0.1 parts, the electrode impedance will increase significantly.

[0161] The security test results show that, Figure 5 As shown, under continuous extrusion conditions, the temperature of the battery cell in Comparative Example 1 rapidly rises to >150°C, accompanied by intense smoke; the battery cell in Example 1 of this invention has a maximum temperature of <50°C, with no open flame or smoke. Figure 3The ARC experiment quantitatively demonstrated that, compared to the comparative example, the embodiment exhibited higher self-exothermic initiation and trigger temperatures (T1, T2) and a lower thermal runaway peak temperature (T3), indicating a more stable chemical system, less prone to thermal runaway, and significantly reduced risk. Therefore, by increasing the local resistance at the short-circuit point, the rate of thermal runaway energy release is effectively reduced, achieving the intrinsic safety objective of "no ignition, no explosion" in extreme safety tests.

[0162] Figure 4 The measured results show that the capacity retention rate of Example 1 after 1200 cycles reached 90%, Example 2 88.5%, Example 7 90%, and Example 8 88%, all of which are better than the 87% of Comparative Example 1. This demonstrates that the long-term cycling capacity retention rate of the porous oxide system is significantly better than that of the base carbon-containing system.

[0163] Table 1 Impedance data for each embodiment and comparative example.

[0164] Negative electrode impedance / Ω Positive electrode impedance / Ω Example 1 0.06 1.8 Example 2 0.057 1.62 Example 3 0.055 1.51 Example 4 0.061 1.79 Example 5 0.059 1.79 Example 6 0.076 1.97 Example 7 0.085 2.01 Example 8 0.061 1.76 Example 9 0.059 1.77 Example 10 0.06 0.81 Example 11 0.019 1.79 Comparative Example 1 0.02 0.8 Comparative Example 2 0.025 0.95 Comparative Example 3 0.022 0.92

[0165] Table 2 Temperature data for each embodiment and comparative example.

[0166] / T1 / ℃ T2 / ℃ T3 / ℃ Example 1 135 249 347.9 Example 2 133 247 350 Example 3 129 246 352 Example 4 136 251 360 Example 5 134 249 361 Example 6 142 257 336 Example 7 141 256 339 Example 8 134 247 344 Example 9 134 246 347 Example 10 133 245 356 Example 11 107 232 390 Comparative Example 1 105 230 392.3 Comparative Example 2 110 233 386 Comparative Example 3 108 231 390

[0167] Table 3. Data on charging capacity retention in various embodiments and comparative examples.

[0168] / 2C charging capacity retention rate Example 1 90.0% Example 2 88.5% Example 3 86.0% Example 4 88.9% Example 5 89.2% Example 6 91.2% Example 7 90.3% Example 8 81.5% Example 9 80.7% Example 10 87.0% Example 11 72.3% Comparative Example 1 70.0% Comparative Example 2 70.4% Comparative Example 3 71.7%

[0169] The abbreviations and full names in Chinese and English are shown in the table below.

[0170]

[0171] Although the present invention has been disclosed above by way of preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make some modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the scope of protection claimed in the claims.

Claims

1. A secondary battery electrode, characterized in that, It includes a current collector and an active material coated on the surface of the current collector, wherein the active material comprises, by weight: Electrode active material: 90-98 parts; Multifunctional composite agent: 0.1 parts to 7 parts; wherein the multifunctional composite agent comprises: porous insulating oxide, carbon-based conductive agent, and a first dispersion medium; the carbon-based conductive agent accounts for 0 wt.% to 0.1 wt.% of the total amount of the active material, and the mass ratio of the dry powder in the porous insulating oxide, carbon-based conductive agent, and first dispersion medium is (1-5):(0-0.1):(0-2); the porous insulating oxide serves as the main framework to dominate ion transport; The adhesive, including the first dispersion medium, wherein the total amount of the adhesive is 1 part to 5 parts; All components are weighed on a dry matter basis.

2. The secondary battery electrode according to claim 1, characterized in that, The active material has at least three layers, which include a surface layer, an intermediate layer and a bottom layer from top to bottom. The bottom layer is located closest to the current collector. The porous insulating oxide content in the intermediate layer accounts for 60 wt.%-70 wt.% of the sum of the porous insulating oxide contents of all active material layers.

3. The secondary battery electrode according to claim 2, characterized in that, The adhesive content in the bottom layer is greater than or equal to the adhesive content in the intermediate layer, and the adhesive content in the bottom layer is greater than or equal to the adhesive content in the top layer.

4. The secondary battery electrode according to claim 2, characterized in that, The content of electrode active material in the surface layer is greater than or equal to the content of electrode active material in the intermediate layer, and the content of electrode active material in the surface layer is greater than or equal to the content of electrode active material in the bottom layer.

5. The secondary battery electrode according to claim 2, characterized in that, The content of the multifunctional composite agent in the intermediate layer is greater than or equal to the content of the multifunctional composite agent in the surface layer, and the content of the multifunctional composite agent in the intermediate layer is greater than or equal to the content of the multifunctional composite agent in the bottom layer.

6. The secondary battery electrode according to any one of claims 2 to 5, characterized in that, The surface layer comprises, by weight: 94 to 98 parts of electrode active material; 0.1 to 4 parts of multifunctional composite agent; and 1 to 3 parts of binder. The intermediate layer comprises, by weight: 92 to 96 parts of electrode active material; 1 to 7 parts of multifunctional composite agent; 1 to 3 parts of binder; and The bottom layer comprises, by weight: 92 to 96 parts of electrode active material; 0.1 to 4 parts of multifunctional composite agent; and 3 to 5 parts of binder.

7. The secondary battery electrode according to any one of claims 1 to 5, characterized in that, The porous insulating oxide is selected from any one or more combinations of porous alumina, porous silica, and porous zirconium oxide; The porous insulating oxide has a specific surface area ≥ 50 m² / g, a porosity of 5%-40%, and a pore size distribution of 2 nm to 500 nm, wherein the porous insulating oxide with a pore size distribution of 2 nm to 50 nm accounts for 50%-100% of all porous insulating oxides.

8. The secondary battery electrode according to claim 7, characterized in that, The specific surface area of ​​the porous insulating oxide is ≥ 100 m² / g.

9. The secondary battery electrode according to any one of claims 1 to 5, characterized in that, The electrode active material is either a positive electrode active material or a negative electrode active material. The positive electrode active material is selected from any one or more combinations of lithium cobalt oxide, lithium iron phosphate, ternary materials, and lithium-rich manganese-based materials. The negative electrode active material is selected from any one or more combinations of graphite, hard carbon, silicon-based materials, silicon-carbon composite materials, and metallic lithium.

10. The secondary battery electrode according to any one of claims 1 to 5, characterized in that, The first dispersion medium is CMC adhesive, PVDF adhesive, or PAA adhesive, and the binder is selected from any one or more combinations of styrene-butadiene rubber, PVDF, CMC, and PAA. The secondary battery electrode also includes a second dispersion medium, which is CMC adhesive, PVDF adhesive, or PAA adhesive.

11. A secondary battery, characterized in that, include: The secondary battery electrode according to any one of claims 1 to 10, The separator stacked with the electrodes of the secondary battery.

12. A method for preparing a secondary battery electrode according to any one of claims 1 to 10, characterized in that, include: Preparation of multifunctional composite agent S1: The porous insulating oxide is added to the first dispersion medium, and a carbon-based conductive agent of 0 wt.%-0.1 wt.% of the total weight of the active material is added, and shear dispersion is performed to form a gel-like multifunctional composite agent; Preparation of active material S2: The multifunctional composite agent obtained in S1, the electrode active material and the binder are added and sheared and dispersed to form a slurry of active material; Electrode preparation S3: The slurry obtained in S2 is coated onto the current collector and then heated and dried to cure.

13. A method for preparing a secondary battery electrode according to claim 12, characterized in that, In step S2, a first slurry, a second slurry, and a third slurry are prepared according to a surface layer, an intermediate layer, and a bottom layer, respectively. The first slurry comprises, by weight, 94 to 98 parts of electrode active material, 0.1 to 4 parts of multifunctional composite agent, and 1 to 3 parts of binder. The second slurry comprises, by weight, 92 to 96 parts of electrode active material, 1 to 7 parts of multifunctional composite agent, and 1 to 3 parts of binder. The third slurry comprises, by weight, 92 to 96 parts of electrode active material, 0.1 to 4 parts of multifunctional composite agent, and 3 to 5 parts of binder. In step S3, the coating is applied sequentially in the order of bottom layer, intermediate layer and top layer. Each layer is dried independently and cooled to room temperature before the next layer is applied.

14. A method for preparing a secondary battery electrode according to claim 13, characterized in that, In S3, when preparing the positive electrode, the total coating density of the positive electrode is calculated as 145 g / m²~155 g / m² based on the dry film, wherein the coating density of the bottom layer is 35 g / m²~40 g / m², the coating density of the middle layer is 75 g / m²~80 g / m², and the coating density of the surface layer is 35 g / m²~40 g / m². When preparing the negative electrode, the total coating density of the negative electrode is calculated based on the dry film as 77 g / m²~83 g / m², of which the coating density of the bottom layer ranges from 18 g / m² to 21 g / m², the coating density of the middle layer ranges from 40 g / m² to 43 g / m², and the coating density of the surface layer ranges from 18 g / m² to 21 g / m².

15. A method for preparing a secondary battery electrode according to claim 13, characterized in that, S2 includes: S21: Add the multifunctional composite agent obtained in S1 to the second dispersion medium or the adhesive solution formed by the binder; S22: Add electrode active material and perform shear dispersion; and S23: When the second dispersion medium is used in S21, a binder is added to obtain a slurry.

16. A method for preparing a secondary battery according to claim 11, characterized in that, include: A method for preparing a secondary battery electrode according to any one of claims 12-15; Electrode sheets and diaphragms are stacked to form the electrode core; and The electrode core is packaged to form a battery cell.

Images