Lithium battery electrode, preparation method thereof and lithium ion battery

Abstract

The invention relates to the technical field of lithium batteries, in particular to a lithium battery electrode, a preparation method thereof and a lithium ion battery. The electrode comprises a current collector and a composite coating on the current collector, wherein the coating is formed by combining an interface function layer on the outer side and a current collector function layer on the inner side through a middle area with continuous transition of components and structures. Wherein the interface function layer adopts an active substance with an average particle size D50 of 1-5 [mu] m and contains a conductive agent accounting for 4-8% of the dry weight; and the current collector functional layer adopts an active substance with an average particle size D50 of 8-15 [mu] m, and the mass ratio of the active substance is not less than 94%. The preparation method comprises the following steps: sequentially coating the first slurry and the second slurry by using a coating die head to form a composite wet film, and then drying and rolling. According to the invention, by constructing a continuous gradient structure, an interlayer clear interface is effectively eliminated, the ion diffusion and electron conduction capabilities of the electrode are synergistically improved, and the rate capability and the cycling stability are remarkably improved while the high energy density is maintained.

Description

Technical Field

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

[0002] With the increasing demands on battery performance from electric vehicles and high-end energy storage systems, developing lithium-ion batteries that combine high energy density and high power density has become a core challenge for the industry. Currently, the most direct technical approach to improving battery energy density is to increase electrode thickness and active material loading, but this inevitably lengthens the transport paths of ions and electrons within the electrode. During high-current charging and discharging, severe concentration polarization and electrochemical polarization occur inside the electrode, especially in areas far from the separator and current collector, leading to a sharp decrease in effective capacity, voltage plateau decay, increased heat generation, and rapid deterioration of cycle life. The thick electrode effect has become a fundamental bottleneck restricting the coexistence of fast charging and high energy density in batteries.

[0003] To address this issue, existing technologies often seek breakthroughs in material modification (such as synthesizing highly conductive active materials) or electrolyte optimization. However, these methods often only bring marginal improvements and may introduce new problems related to cost, stability, or safety. From the perspective of the electrode structure itself, traditional homogeneous coating designs have inherent limitations in principle: their single component and pore distribution cannot simultaneously meet the differentiated requirements of the electrode surface layer (requiring rapid ion response) and the underlying layer (requiring high capacity storage) for microstructure and conduction networks.

[0004] Therefore, it is of great significance to construct a lithium battery electrode that can fundamentally coordinate the ion transport dynamics and electron conduction network inside a thick electrode and effectively improve the long-term cycling stability. Summary of the Invention

[0005] The purpose of this invention is to overcome the severe polarization effect caused by excessively long ion / electron transport paths in traditional thick electrodes, and the shortcomings of homogeneous electrode structures in synergistically optimizing rapid ion response and high capacity storage. This invention provides a lithium-ion battery electrode, its preparation method, and a lithium-ion battery. The invention offers a gradient functionalized electrode, constructing a composite coating on the current collector consisting of an outer interface functional layer and an inner current collector functional layer, forming an intermediate region with a continuous transition in composition and structure between the two layers. By controlling the particle size and material ratio of the active material in the coating, the prepared electrode significantly improves the battery's power density and long-cycle stability while maintaining high electrode capacity and energy density.

[0006] A first aspect of the present invention provides a lithium battery electrode, including a current collector and a composite coating disposed on the current collector; the composite coating is composed of an outer interface functional layer and an inner current collector functional layer in the thickness direction, and an intermediate region with continuous transition of composition and structure is formed between the two layers.

[0007] The interface functional layer comprises a first active material with an average particle size D50 of 1-5 μm and a first conductive agent accounting for 4%-8% of the dry weight of the interface functional layer. The current collector functional layer contains a second active material with an average particle size D50 of 8-15 μm, and the second active material accounts for no less than 94% of the dry weight of the current collector functional layer.

[0008] This invention provides a lithium battery electrode, comprising a current collector and a composite coating disposed on the current collector. The composite coating consists of an outer interfacial functional layer and an inner current collector functional layer in the thickness direction, with a continuous transition in composition and structure between the two layers. The interfacial functional layer contains a first active material with an average particle size D50 of 1-5 μm and a first conductive agent comprising 4%-8% of the dry weight of the interfacial functional layer. The current collector functional layer contains a second active material with an average particle size D50 of 8-15 μm, and the second active material comprises at least 94% of the dry weight of the current collector functional layer. This invention uses a small-particle-size active material and a high content of conductive agent as the interfacial functional layer to optimize transport, and a large-particle-size active material and a high proportion of active material as the current collector functional layer to ensure energy storage. The continuous gradient transition fundamentally eliminates the clear physical interface between layers, not only promoting smooth lithium-ion diffusion and reducing concentration polarization, but also reducing overall impedance through the optimized conductive network and particle size distribution. The electrode significantly improves rate performance and cycle stability while maintaining high energy density. After 500 cycles at 3C, the gradient electrode retains a capacity of over 93.2%, achieving unexpected results.

[0009] Furthermore, the interface functional layer is formed by coating and drying a first slurry, wherein the solid content of the first slurry is 45%-55%; and / or, the current collector functional layer is formed by coating and drying a second slurry, wherein the solid content of the second slurry is 60%-70%.

[0010] Furthermore, the viscosity of the first slurry is 3000-6000 mPa·s, and / or the viscosity of the second slurry is 8000-15000 mPa·s.

[0011] Furthermore, the solid components of the first slurry, by mass percentage, include: First active substance: 90%-94%, First conductive agent: 4%-8%, First adhesive: 2%-3%.

[0012] Furthermore, the solid components of the second slurry, by mass percentage, include: Second active substance: 96%-98%, Second conductive agent: 1%-2.5%, Second adhesive: 0.5%-1.5%.

[0013] Furthermore, the first active material is at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium-rich manganese-based lithium; the second active material is at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium-rich manganese-based lithium; and / or, the first conductive agent is at least one of carbon nanotubes, graphene, carbon fibers, and conductive carbon black, and the second conductive agent is at least one of conductive carbon black, acetylene black, and Ketjen black; and / or, the first binder is at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylate, styrene-butadiene rubber, and sodium carboxymethyl cellulose, and the second binder is at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylate, styrene-butadiene rubber, and sodium carboxymethyl cellulose.

[0014] Furthermore, the mass ratio of the first slurry to the second slurry is 1:0.8-1.2.

[0015] A second aspect of the present invention provides a method for preparing a lithium battery electrode as described above, comprising the following steps: Using a coating die, the second slurry is coated onto the current collector to form a bottom wet film; The first slurry is applied onto the underlying wet film; Drying process; The dried electrode sheets are then rolled.

[0016] This invention provides a method for preparing a lithium battery electrode, comprising the following steps: using a coating die to coat a second slurry onto a current collector to form a bottom wet film; coating a first slurry onto the bottom wet film; drying; and rolling the dried electrode sheet. This method is simple to operate and easy to control.

[0017] In some embodiments, the coating die can be a single-channel coating die or a dual-channel coating die. When using a single-channel coating die, the first slurry is coated through a single channel, the channel is cleaned, and then the second slurry is coated through the same single channel. When using a dual-channel coating die, the first slurry is coated through a first single channel, and then the second slurry is coated through a second channel. In some embodiments, while the first slurry is being coated, the second slurry is prepared in the second channel, initially blocked by the die's structure. After the first slurry is coated, the blockage is removed, and the second slurry is then fed in for coating. The dual-channel coating die has higher coating efficiency.

[0018] Furthermore, the drying process is a gradient drying, comprising: first drying in a first temperature zone at a temperature of 70-90℃ and a wind speed of 8-15 m / s, and then drying in a second temperature zone at a temperature of 100-130℃ and a wind speed of 3-8 m / s.

[0019] Furthermore, after rolling, the compacted density of the electrode sheet is 2.4-3.2 g / cm³. 3 .

[0020] A third aspect of the present invention provides a lithium-ion battery, comprising a lithium battery electrode as described above or a lithium battery electrode prepared by the preparation method described above.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides a lithium battery electrode, comprising a current collector and a composite coating disposed on the current collector; the composite coating consists of an outer interface functional layer and an inner current collector functional layer in the thickness direction, with a continuous transition in composition and structure between the two layers; wherein, the interface functional layer comprises a first active material with an average particle size D50 of 1-5 μm and a first conductive agent accounting for 4%-8% of the dry weight of the interface functional layer; the current collector functional layer comprises a second active material with an average particle size D50 of 8-15 μm, and the second active material accounts for not less than 94% of the dry weight of the current collector functional layer. This invention uses small-particle-size active material and high-content conductive agent as the interface functional layer to optimize transport, and large-particle-size active material and high-activity material as the current collector functional layer to ensure energy storage. The continuous gradient transition fundamentally eliminates the clear physical interface between layers, which not only promotes the smooth diffusion of lithium ions and reduces concentration polarization, but also reduces the overall impedance through the optimized conductive network and particle size distribution. The electrode significantly improves rate performance and cycle stability while maintaining high energy density. After 500 cycles at 3C, the gradient electrode retains a capacity of over 93.2%, achieving unexpected results.

[0022] 2. This invention provides a method for preparing a lithium battery electrode, comprising the following steps: using a coating die to coat a second slurry onto a current collector to form a bottom wet film; coating a first slurry onto the bottom wet film; drying; and rolling the dried electrode sheet. This method is simple to operate and easy to control. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the structure of a gradient functionalized lithium battery electrode provided in an embodiment of the present invention.

[0024] Figure 2 This is a scanning electron microscope (SEM) image of the cross-section of the gradient functionalized electrode prepared in Example 1 of the present invention.

[0025] Figure 3 This is a comparison curve of the cycling performance of the electrodes prepared in Example 1 and Comparative Example 1 at a 3C rate.

[0026] Figure 4 Voltage plateau curves for the batteries prepared in Example 1 and Comparative Example 1. Detailed Implementation

[0027] The present invention will now be described in further detail with reference to specific embodiments. However, this should not be construed as limiting the scope of the present invention to the following embodiments; all technologies implemented based on the content of the present invention fall within the scope of the present invention.

[0028] With the increasing demands on battery performance from electric vehicles and high-end energy storage systems, developing lithium-ion batteries that combine high energy density and high power density has become a core challenge for the industry. Currently, the most direct technical approach to improving battery energy density is to increase electrode thickness and active material loading, but this inevitably lengthens the transport paths of ions and electrons within the electrode. During high-current charging and discharging, severe concentration polarization and electrochemical polarization occur inside the electrode, especially in areas far from the separator and current collector, leading to a sharp decrease in effective capacity, voltage plateau decay, increased heat generation, and rapid deterioration of cycle life. The thick electrode effect has become a fundamental bottleneck restricting the coexistence of fast charging and high energy density in batteries.

[0029] A first aspect of a specific embodiment of the present invention provides a lithium battery electrode, including a current collector and a composite coating disposed on the current collector; the composite coating consists of an outer interface functional layer and an inner current collector functional layer in the thickness direction, with an intermediate region of continuous transition in composition and structure formed between the two layers; as shown... Figure 1 As shown.

[0030] The interface functional layer contains a first active material with an average particle size D50 of 1-5 μm and a first conductive agent accounting for 4%-8% of the dry weight of the interface functional layer. For example, the first conductive agent accounting for 4%, 5%, 6%, 7%, and 8% of the dry weight of the interface functional layer can achieve good results.

[0031] The current collector functional layer contains a second active material with an average particle size D50 of 8-15 μm, and the second active material accounts for no less than 94% of the dry weight of the current collector functional layer. For example, when the second active material accounts for 94%, 95%, 96%, 97%, or 98% of the dry weight of the current collector functional layer, the prepared electrode can achieve good, stable, and controllable electrochemical performance.

[0032] This invention uses small-particle-size active materials and high-content conductive agents as the interface functional layer to optimize transport, and large-particle-size active materials and a high proportion of active materials as the current collector functional layer to ensure energy storage. The continuous gradient transition fundamentally eliminates the clear physical interface between layers, which not only promotes smooth lithium-ion diffusion and reduces concentration polarization, but also reduces the overall impedance through the optimized conductive network and particle size distribution. While maintaining high energy density, the electrode significantly improves rate performance and cycle stability. After 500 cycles at 3C, this gradient electrode achieves a capacity retention of over 93.2%, yielding unexpected results.

[0033] The key to the formation of the intermediate region with a continuous transition in composition and structure described in this invention lies in the specific differences between the first and second slurries in terms of viscosity, solid content, and solvent compatibility. When the first slurry is coated onto the undried wet film of the second slurry, selective solvent diffusion occurs from the surface inwards at the contact interface, causing the solid particles (active material, conductive agent) to rearrange in the interface region. Subsequent gradient drying solidification results in a microscopically formed transition region with a continuous and gradual change in composition, particle size, and porosity without a clear interface. This structure effectively reduces the diffusion barrier of lithium ions between layers and the contact resistance of electronic conduction, which is crucial for synergistically improving the performance of thick electrodes.

[0034] In some embodiments, the interface functional layer is formed by coating and drying a first slurry, wherein the solid content of the first slurry is 45%-55%; and / or, the current collector functional layer is formed by coating and drying a second slurry, wherein the solid content of the second slurry is 60%-70%.

[0035] In some embodiments, the viscosity of the first slurry is 3000-6000 mPa·s, and / or the viscosity of the second slurry is 8000-15000 mPa·s.

[0036] In some embodiments, the solid component of the first slurry comprises, by mass percentage: First active substance: 90%-94%, First conductive agent: 4%-8%, First adhesive: 2%-3%.

[0037] In some embodiments, the solid component of the second slurry comprises, by mass percentage: Second active substance: 96%-98%, Second conductive agent: 1%-2.5%, Second adhesive: 0.5%-1.5%.

[0038] In some embodiments, the first active material is at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium-rich manganese-based lithium; the second active material is at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium-rich manganese-based lithium.

[0039] And / or, the first conductive agent is at least one of carbon nanotubes, graphene, carbon fiber, and conductive carbon black, and the second conductive agent is at least one of conductive carbon black, acetylene black, and Ketjen black.

[0040] And / or, the first adhesive is at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylate, styrene-butadiene rubber, and sodium carboxymethyl cellulose, and the second adhesive is at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylate, styrene-butadiene rubber, and sodium carboxymethyl cellulose.

[0041] In some embodiments, the mass ratio of the first slurry to the second slurry is 1:0.8-1.2.

[0042] The second aspect of this embodiment provides a method for preparing a lithium battery electrode as described above, including the following steps: Using a coating die, the second slurry is coated onto the current collector to form a bottom wet film; The first slurry is applied onto the underlying wet film; Drying process; The dried electrode sheets are then rolled.

[0043] Using a coating die, a second slurry is coated onto the current collector to form a bottom wet film; a first slurry is coated onto the bottom wet film; drying is performed; and the dried electrode is rolled. This method is simple to operate and easy to control.

[0044] In some embodiments, the coating die head can be a single-channel coating die head or a dual-channel coating die head; when using a single-channel coating die head, the second slurry is coated through a single channel, the channel is cleaned, and the first slurry is coated through a single channel.

[0045] When using a dual-channel coating die head, the second slurry is coated through the first single channel, and then the first slurry is coated through the second channel.

[0046] In some embodiments, when the second slurry is applied, the first slurry is prepared in the second channel and initially blocked by the die head structure. After the second slurry is applied, the blockage is removed, and the first slurry is then applied. The dual-channel coating die head has higher coating efficiency.

[0047] During the coating process, the second and first wet films of the coating material undergo solvent interdiffusion at the contact interface and are subsequently cured together during gradient drying. This creates a natural intermediate region between the two layers where the composition and structure transition continuously, rather than a clear physical interface.

[0048] In one or more embodiments, the coating speed is 15-25 m / min, and the total thickness of the resulting composite wet film is 250-350 μm.

[0049] In some embodiments, the drying process is gradient drying, comprising: first drying in a first temperature zone at a temperature of 70-90°C and a wind speed of 8-15 m / s, and then drying in a second temperature zone at a temperature of 100-130°C and a wind speed of 3-8 m / s.

[0050] In some embodiments, after rolling, the compacted density of the electrode sheet is 2.4-3.2 g / cm³. 3 Studies have found that compaction density is a key factor affecting the electrochemical performance of electrodes; both excessively low and excessively high compaction densities will significantly reduce electrochemical performance.

[0051] The third aspect of this embodiment provides a lithium-ion battery, including a lithium battery electrode as described above or a lithium battery electrode prepared by the preparation method described above.

[0052] To better understand the technical solutions of the above embodiments, a more detailed implementation process is provided for further explanation: The average particle size D50 of the active material described in this invention refers to the value measured after dispersion using a laser particle size analyzer in accordance with the GB / T 19077-2016 standard.

[0053] Example 1 1. Slurry preparation First slurry (interfacial functional layer): Nickel-cobalt-manganese NCM811 (D50=3μm), Super P, single-walled carbon nanotubes (SWCNT), and polyvinylidene fluoride (PVDF) are mixed in N-methylpyrrolidone (NMP) at a weight ratio of 92.5:4.5:1.0:2.0, and the solid content is adjusted to 50% and the viscosity to 4500 mPa·s.

[0054] Second slurry (current collector functional layer): NCM811 (D50=12μm), Super P and PVDF are mixed in NMP at a weight ratio of 96.5:2.0:1.5, and the solid content is adjusted to 65% and the viscosity to 12000 mPa·s.

[0055] 2. Co-extrusion coating Using a dual-channel coating die, the second slurry is first coated onto the aluminum foil current collector to form a bottom wet film. Then, while the bottom wet film is still wet, the first slurry is immediately coated onto it through the second channel. The mass ratio of the first slurry to the second slurry is 1:1. The coating speed is set to 20 m / min, and the total wet film thickness is 300 μm, applied to the aluminum foil.

[0056] 3. Gradient drying The oven is divided into four sections, with temperature / wind speed settings as follows: 80℃ / 12 m / s, 95℃ / 8 m / s, 110℃ / 5 m / s, and 120℃ / 3 m / s.

[0057] 4. Roller pressing After drying, the electrode sheets are compacted to 3.0 g / cm³ using a double roller press. 3 .

[0058] Example 2 First slurry (interfacial functional layer): NCM811 (D50=4μm), Super P, single-walled carbon nanotubes (SWCNT), and polyvinylidene fluoride (PVDF) are mixed in N-methylpyrrolidone (NMP) at a weight ratio of 92.5:4.5:1.0:2.0, and the solid content is adjusted to 50% and the viscosity to 4500 mPa·s.

[0059] Second slurry (current collector functional layer): NCM811 (D50=11.5μm), Super P and PVDF are mixed in NMP at a weight ratio of 96.5:2.0:1.5, and the solid content is adjusted to 65% and the viscosity to 12000 mPa·s.

[0060] 2. Co-extrusion coating Using a dual-channel coating die, the second slurry is first coated onto the aluminum foil current collector to form a bottom wet film. Then, while the bottom wet film is still wet, the first slurry is immediately coated onto it through the second channel. The mass ratio of the first slurry to the second slurry is 1:1. The coating speed is set to 20 m / min, and the total wet film thickness is 300 μm, applied to the aluminum foil.

[0061] 3. Gradient drying The oven is divided into four sections, with temperature / wind speed settings as follows: 80℃ / 12 m / s, 95℃ / 8 m / s, 110℃ / 5 m / s, and 120℃ / 3 m / s.

[0062] 4. Roller pressing After drying, the electrode sheets are compacted to 3.2 g / cm³ using a roller press. 3 .

[0063] Example 3 First slurry (interfacial functional layer): NCM811 (D50=4μm), Super P, single-walled carbon nanotubes (SWCNT), and polyvinylidene fluoride (PVDF) are mixed in N-methylpyrrolidone (NMP) at a weight ratio of 92.5:4.5:1.0:2.0, and the solid content is adjusted to 52% and the viscosity to 5000 mPa·s.

[0064] Second slurry (current collector functional layer): NCM811 (D50=11.5μm), Super P and PVDF are mixed in NMP at a weight ratio of 96.5:2.0:1.5, and the solid content is adjusted to 63% and the viscosity to 10000 mPa·s.

[0065] 2. Co-extrusion coating Using a coating die with dual channels, the second slurry is first coated onto the aluminum foil current collector to form a bottom wet film. Then, while the bottom wet film is still wet, the first slurry is immediately coated onto it through the second channel. The mass ratio of the first slurry to the second slurry is 1:1.2. The coating speed is set to 20 m / min, and the total wet film thickness is 340 μm, coated onto the aluminum foil.

[0066] 3. Gradient drying The oven is divided into four sections, with temperature / wind speed settings as follows: 80℃ / 12 m / s, 95℃ / 8 m / s, 110℃ / 5 m / s, and 120℃ / 3 m / s.

[0067] 4. Roller pressing After drying, the electrode sheets are compacted to 3.0 g / cm³ using a double roller press. 3 .

[0068] Example 4 First slurry (interfacial functional layer): NCM811 (D50=4μm), Super P, single-walled carbon nanotubes (SWCNT), and polyvinylidene fluoride (PVDF) are mixed in N-methylpyrrolidone (NMP) at a weight ratio of 92.5:4.5:1.0:2.0, and the solid content is adjusted to 53% and the viscosity to 4500 mPa·s.

[0069] Second slurry (current collector functional layer): NCM811 (D50=11.5μm), Super P and PVDF are mixed in NMP at a weight ratio of 96.5:2.0:1.5, and the solid content is adjusted to 63% and the viscosity to 12000 mPa·s.

[0070] 2. Co-extrusion coating Using a coating die with dual channels, the second slurry is first coated onto the aluminum foil current collector to form a bottom wet film. Then, while the bottom wet film is still wet, the first slurry is immediately coated onto it through the second channel. The mass ratio of the first slurry to the second slurry is 1:0.8. The coating speed is set to 20 m / min, and the total wet film thickness is 300 μm, applied to the aluminum foil.

[0071] 3. Gradient drying The oven is divided into four sections, with temperature / wind speed settings as follows: 80℃ / 15 m / s, 90℃ / 12 m / s, 105℃ / 6 m / s, and 120℃ / 3 m / s.

[0072] 4. Roller pressing After drying, the electrode sheets are compacted to 3.1 g / cm³ using a double roller press. 3 .

[0073] Example 5 First slurry (interfacial functional layer): NCM811 (D50=3μm), Super P, single-walled carbon nanotubes (SWCNT), and polyvinylidene fluoride (PVDF) are mixed in N-methylpyrrolidone (NMP) at a weight ratio of 92.5:4.5:1.0:2.0, and the solid content is adjusted to 50% and the viscosity to 4500 mPa·s.

[0074] Second slurry (current collector functional layer): NCM811 (D50=12μm), Super P and PVDF are mixed in NMP at a weight ratio of 96.5:2.0:1.5, and the solid content is adjusted to 65% and the viscosity to 12000 mPa·s.

[0075] 2. Co-extrusion coating Using a coating die with dual channels, the second slurry is first coated onto the aluminum foil current collector to form a bottom wet film. Then, while the bottom wet film is still wet, the first slurry is immediately coated onto it through the second channel. The mass ratio of the first slurry to the second slurry is 1:1. The coating speed is set to 18 m / min, and the total wet film thickness is 280 μm, which is applied to the aluminum foil.

[0076] 3. Gradient drying The oven is divided into four sections, with temperature / wind speed settings as follows: 80℃ / 12 m / s, 95℃ / 8 m / s, 110℃ / 5 m / s, and 120℃ / 3 m / s.

[0077] 4. Roller pressing After drying, the electrode sheets are compacted to 2.9 g / cm³ using a double roller press. 3 .

[0078] Comparative Example 1 Traditional homogeneous thick electrode A homogeneous slurry (NCM811 D50=8μm) with the same total solids content and total active substance loading as in Example 1 was used for single-layer coating, drying and rolling, while other conditions remained the same as in Example 1.

[0079] Comparative Example 2 In Comparative Example 2, the active material NCM811 in the first slurry (interfacial functional layer) was replaced with D50=8μm (i.e., the same particle size as the second slurry) instead of D50=3μm in Example 1.

[0080] The other components of the first slurry (92.5% active material, 4.5% Super P, 1.0% SWCNT, 2.0% PVDF) and solid content (50%) and viscosity (4500 mPa·s) remained unchanged.

[0081] The formulation and process of the second slurry (current collector functional layer) are exactly the same as those in Example 1.

[0082] Comparative Example 3 Comparative Example 3 adjusted the formulation of the first slurry (interfacial functional layer) to: NCM811 (D50=3μm) 95.5%, SuperP 2.0%, SWCNT 0.5%, PVDF 2.0%. At this time, the total content of conductive agent was 2.5% (dry material ratio).

[0083] The amount of solvent was adjusted so that the solid content of the first slurry remained at 50%, and the viscosity was controlled at around 4500 mPa·s by adjusting the dispersion process.

[0084] The formulation and process of the second slurry (current collector functional layer) are exactly the same as those in Example 1.

[0085] Comparative Example 4 Comparative Example 4 swaps the roles of the first slurry and the second slurry in Example 1.

[0086] That is: the first slurry (applied to the outside) adopts the second slurry formulation of Example 1 (NCM811 D50=12μm, content 96.5%, Super P 2.0%, PVDF 1.5%, solid content 65%, viscosity 12000 mPa·s).

[0087] The second slurry (applied to the inner side) uses the first slurry formulation of Example 1 (NCM811 D50=3μm, content 92.5%, Super P 4.5%, SWCNT 1.0%, PVDF 2.0%, solid content 50%, viscosity 4500 mPa·s).

[0088] Test Example 1 The electrodes prepared in Examples 1-5 and Comparative Examples 1-4 were assembled into coin cells or pouch cells and subjected to 3C high-rate cycling tests. Meanwhile, the AC impedance data obtained by EIS testing are shown in Table 1.

[0089] Figure 2 The image shows a scanning electron microscope (SEM) image of the cross-section of the gradient functionalized electrode prepared in Example 1.

[0090] like Figure 3 and Figure 4 As shown, the comparison curves and voltage plateau curves of the batteries prepared in Example 1 and Comparative Example 1 at 3C rate are presented respectively. Figure 4 Among these, with similar capacities, Example 1 has a smaller polarization platform.

[0091] Table 1

[0092] The above results fully demonstrate that the gradient functionalized electrode and its multilayer co-extrusion preparation method provided by the present invention can effectively coordinate the ion and electron transport inside the thick electrode, and significantly improve the rate performance and long cycle stability of the battery while maintaining high energy density. Moreover, the process is simple and suitable for mass production.

[0093] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A lithium battery electrode, characterized in that, Includes a current collector and a composite coating disposed on the current collector; The composite coating consists of an outer interface functional layer and an inner current collector functional layer in the thickness direction, with an intermediate region between the interface functional layer and the current collector functional layer forming a continuous transition in composition and structure. in, The interface functional layer contains a first active material with an average particle size D50 of 1-5 μm, and a first conductive agent accounting for 4%-8% of the dry weight of the interface functional layer. The current collector functional layer contains a second active material with an average particle size D50 of 8-15 μm, and the second active material accounts for no less than 94% of the dry weight of the current collector functional layer.

2. The lithium battery electrode according to claim 1, characterized in that, The interface functional layer is formed by coating and drying a first slurry, wherein the solid content of the first slurry is 45%-55%. And / or, The current collector functional layer is formed by coating and drying a second slurry, wherein the solid content of the second slurry is 60%-70%.

3. The lithium battery electrode according to claim 2, characterized in that, The viscosity of the first slurry is 3000-6000 mPa·s, and / or the viscosity of the second slurry is 8000-15000 mPa·s.

4. The lithium battery electrode according to claim 2, characterized in that, The solid components of the first slurry, by mass percentage, include: First active substance: 90%-94%, First conductive agent: 4%-8%, First adhesive: 2%-3%.

5. The lithium battery electrode according to claim 2, characterized in that, The solid components of the second slurry, by mass percentage, include: Second active substance: 96%-98%, Second conductive agent: 1%-2.5%, Second adhesive: 0.5%-1.5%.

6. The lithium battery electrode according to claim 4 or 5, characterized in that, The first active material is at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium-rich manganese-based lithium. The second active material is at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium-rich manganese-based lithium. And / or, The first conductive agent is at least one of carbon nanotubes, graphene, carbon fiber, and conductive carbon black. The second conductive agent is at least one of conductive carbon black, acetylene black, and Ketjen black; And / or, The first binder is at least one selected from polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylate, styrene-butadiene rubber, and sodium carboxymethyl cellulose. The second binder is at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyacrylate, styrene-butadiene rubber, and sodium carboxymethyl cellulose.

7. The method for preparing a lithium battery electrode according to any one of claims 1-6, characterized in that, Includes the following steps: Using a coating die, the second slurry is coated onto the current collector to form a bottom wet film; The first slurry is applied onto the underlying wet film; Drying process; The dried electrode sheets are then rolled.

8. The preparation method according to claim 7, characterized in that, The drying process is a gradient drying process, which includes: first drying in a first temperature zone at a temperature of 70-90℃ and a wind speed of 8-15 m / s, and then drying in a second temperature zone at a temperature of 100-130℃ and a wind speed of 3-8 m / s.

9. The preparation method according to claim 8, characterized in that, After rolling, the compacted density of the electrode sheet is 2.4-3.2 g / cm³. 3 .

10. A lithium-ion battery, characterized in that, The lithium battery electrode includes the lithium battery electrode as described in any one of claims 1-6 or the lithium battery electrode prepared by the preparation method as described in any one of claims 7-9.

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