Multi-layer electrode with tree-shaped pore channel structure and preparation method of multi-layer electrode

Abstract

The invention relates to the technical field of lithium ion battery materials, in particular to a multi-layer electrode with a tree-shaped pore channel structure and a preparation method of the multi-layer electrode. The multi-layer electrode comprises a plurality of electrode layers with hierarchical pore structures, and the porosity in each electrode layer is increased layer by layer from the current collector side to the diaphragm side; the multi-layer electrode is provided with a vertical main pore channel in the direction perpendicular to each electrode layer, and the main pore channel is combined with the hierarchical pore channel structure to form a tree-shaped pore channel structure. According to the invention, synergistic conduction is realized through graded pore channel design, on the basis that a main pore channel is constructed through laser ablation in the direction perpendicular to the surface of the thick electrode, an auxiliary pore channel is constructed through additive pore forming in the direction parallel to the thick electrode, a tree-shaped ion transmission channel is formed, and the main pore channel relieves concentration polarization of the thick electrode in the thickness direction; the auxiliary hole channel promotes ions to be transmitted from the channel to the electrode body, the ion diffusion path is remarkably shortened, and the blank of current horizontal direction ion transmission research is filled.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion battery materials, and in particular to a multilayer electrode with a tree-like pore structure and a preparation method thereof. Background Art

[0002] With the rapid development of new energy vehicles and large-scale energy storage markets, the demand for high energy density and high power density of lithium-ion batteries is increasing. In recent years, thick electrode technology has become a research hotspot. Thick electrodes increase the active material loading (greater than 40 mg cm -2 , much higher than the 10-15 mg cm of traditional electrodes -2 ), significantly reducing the proportion of inactive substances, thereby achieving higher energy density at the single cell level. For example, in the positive electrode material, the use of thick electrodes can increase the energy density of lithium iron phosphate batteries from about 180Wh kg -1 Increased to 220Wh kg -1 The above shows that the ternary thick electrode system is expected to exceed 300Wh kg -1 , which is of great significance to improving the endurance of electric vehicles.

[0003] However, the large-scale application of thick electrodes still faces many challenges. As the thickness of the electrode increases, the diffusion path of lithium ions becomes longer, resulting in increased polarization of the electrode and slow reaction kinetics, which in turn affects the rate performance and cycle life of the battery. Secondly, the traditional coating method for preparing thick electrodes is prone to cracking or falling off from the current collector due to uneven stress distribution during the drying and rolling process, reducing the mechanical stability and electrochemical performance of the electrode. In addition, the high surface density of thick electrodes may hinder the wettability of the electrolyte, resulting in low utilization of active materials inside the electrode, further reducing the reaction kinetics of the battery.

[0004] At present, the strategy for improving the polarity of thick electrodes is mainly optimized from multiple aspects such as material system, electrode structure and preparation process. In terms of materials, special conductive agents, binders, current collectors, etc. are used to achieve efficient ion and electron transport. For example, high-conductivity additives (such as carbon nanotubes, graphene or superconducting carbon black) are used to improve electron transport. In terms of structural design, vertically arranged pores (such as 3D printing) are constructed to optimize the ion transport path. In terms of preparation process, new preparation methods such as template method, dry electrode, freeze-drying method, etc. provide new ideas for the preparation of thick electrodes. However, the disordered pore structure prepared by the conventional preparation process has defects such as poor pore connectivity and uneven pore size distribution, and the pores constructed by 3D printing and laser ablation can only alleviate the lithium ion transport in the vertical direction. The ion transport from the channel to the electrode body has not been effectively improved, and it is difficult to achieve effective electron / ion transport. The limitations of the existing preparation methods have caused it to remain in the laboratory stage. Therefore, it is of great significance to develop a thick electrode preparation method that can accurately control the pore structure. Summary of the Invention

[0005] The present invention provides a multilayer electrode with a tree-like pore structure and a preparation method thereof. The purpose is to solve the problems that the pores constructed by the electrode preparation method in the prior art are mostly disorderly distributed, have poor connectivity, and are difficult to improve the ion transmission from the channels to the electrode body. This method is widely applicable to the preparation of thick electrodes of different systems.

[0006] To achieve the above objectives, the present invention provides a multilayer electrode having a tree-like pore structure, wherein the multilayer electrode comprises multiple electrode layers having a hierarchical pore structure, wherein the porosity of each electrode layer increases layer by layer from the current collector side to the separator side;

[0007] The multi-layer electrode is provided with vertical main channels perpendicular to each electrode layer, and the main channels are combined with the hierarchical channel structure to form a tree-like channel structure.

[0008] By designing a hierarchical pore structure, a thick electrode with a tree-like pore structure and gradient pore characteristics is constructed to systematically optimize the mass transfer process within the electrode. This structural design can optimize electrolyte wetting behavior, systematically shorten the horizontal and vertical transmission paths of lithium ions, and form a multi-level three-dimensional transmission network based on the transmission mechanism at different locations on the electrode to enhance the transmission dynamics and thus improve electrode performance.

[0009] The tree-like pore structure of the present invention has the following characteristics:

[0010] 1) The porosity distribution in the vertical direction of the electrode presents a gradient change;

[0011] 2) A network of interconnected branch channels in the horizontal direction;

[0012] 3) The main pores that penetrate the thickness of the electrode and the gradient branch pores form a three-dimensional interconnected ion transmission channel.

[0013] Preferably, the electrode layer of the multi-layer electrode comprises 2-4 layers.

[0014] Preferably, the vertical main channel is a tapered through hole that penetrates the multi-layer electrode, the pore diameter gradually increases from the side close to the current collector to the diaphragm side, and the porosity increases by 2-5% layer by layer. The pore diameter closest to the diaphragm side is 10-20 μm, and the pore diameter closest to the current collector side is 0.1-5 μm; the pore spacing ranges from 50 to 150 μm.

[0015] Preferably, the total thickness of the electrode layer of the multilayer electrode is 200-800 μm, and the surface loading is 40-200 mg cm -2 .

[0016] Preferably, the raw materials of the electrode layer include electrode active material, pore-forming agent, conductive agent and binder, wherein the electrode active material component includes at least one of lithium manganese oxide, lithium iron phosphate, ternary material or lithium cobalt oxide, the conductive agent includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, Super P, Ketjen black or acetylene black, and the added amount is 1wt% to 8wt% of the total solid content of the raw material; the binder is polytetrafluoroethylene, and the added amount is 1wt% to 5wt% of the total solid content of the raw material; the pore-forming agent is polyethylene glycol, and the added amount is 1wt% to 4wt% of the total solid content of the raw material, and the added amount increases with each electrode layer from the current collector side to the diaphragm side.

[0017] More preferably, the pore-forming agent is PEG6000.

[0018] Preferably, the amount of the pore-forming agent added is increased by 1 wt% to 2 wt% per electrode layer from the side close to the current collector to the side close to the separator.

[0019] In this invention, by regulating the proportion of pore-forming agents added to each electrode layer, the porosity distribution of different layers can be precisely controlled. Specifically, a gradient design strategy is employed to adjust the pore-forming agent content in different electrode layers to prepare electrode layers with differentiated porosities. These electrode layers with different porosities are then assembled through a lamination process to ultimately form a thick electrode precursor with a porosity gradient characteristic. The resulting thick electrode can be over 1 mm thick.

[0020] Under the same technical concept, the present invention also provides a method for preparing a multilayer electrode having a tree-like pore structure, comprising the following steps:

[0021] (1) The electrode active material, pore-forming agent, conductive agent, and binder are mixed in proportion by high-speed shear dry mixing under a protective atmosphere, and the mixed mixture is subjected to repeated film-forming and stretching and folding steps at room temperature for multiple times to prepare a self-supporting electrode;

[0022] (2) Repeat step (1) to prepare self-supporting electrodes with different pore-forming agent contents, and assemble the multilayer self-supporting electrodes onto the current collector in the order of pore-forming agent content from low to high by a lamination process to obtain a multilayer electrode precursor;

[0023] (3) The multilayer electrode precursor obtained in step (2) is laser ablated to form vertical main channels, and the pore-forming agent is removed by heat treatment to obtain horizontal secondary channels, which are combined with the vertical main channels to form a tree-like channel structure.

[0024] The present invention adds a pore-forming agent, fibrillates it and causes it to volatilize to form small horizontal channels, and then constructs vertical main channels through laser ablation. The channel morphology is precisely controlled by parameter regulation to form a tree-like channel structure, thereby optimizing electron transmission, ion diffusion and electrolyte wettability in multiple dimensions in horizontal and vertical directions, thereby improving the electrochemical performance of thick electrodes.

[0025] Preferably, the protective atmosphere in step (1) is at least one of argon, nitrogen or other protective gases; the high-speed shearing equipment is at least one of a homogenizer, a high-speed disperser or a fiberizing grinder, the rotation speed is not less than 1000 rpm, and the mixing time is not less than 30 min.

[0026] Preferably, the rolling method in step (1) is at least one of repeatedly rolling on a stainless steel plate using a glass rod or repeatedly rolling using a rolling device; the density of the self-supporting electrode is 2.0 to 3.9 g cm -3 .

[0027] Preferably, the heat treatment in step (3) includes vacuum drying in a heat treatment environment at 120-200° C. for 1-5 hours.

[0028] The above scheme of the present invention has the following beneficial effects: (1) The present invention achieves cooperative conduction through hierarchical channel design. Laser ablation is based on constructing main channels in the vertical direction of the thick electrode surface and constructing secondary channels in the direction parallel to the thick electrode to form a tree-like ion transmission channel. The main channels alleviate the concentration polarization of the thick electrode along the thickness direction, and the secondary channels promote the transmission of ions from the channels to the electrode body, significantly shortening the ion diffusion path, filling the gap in the current research on horizontal ion transmission.

[0029] (2) The present invention achieves directional design of the electrode pore gradient by precisely controlling the morphological characteristics (including but not limited to grain size and geometry) of the pore-forming agent content and its addition ratio, thereby enabling precise control of key parameters such as pore size and branching density. Furthermore, laser ablation is combined to construct a through-hole main pore in the vertical direction of the electrode, thereby forming a tree-like pore structure with the following characteristics.

[0030] Other beneficial effects of the present invention will be described in detail in the subsequent specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 1 is the charge-discharge curve of the multilayer electrode with a tree-like pore structure in Example 1 of the present application;

[0032] Figure 2 0.5C cycle performance curve of the multilayer electrode with a tree-like pore structure in Example 1 of the present application;

[0033] Figure 3 This is a picture of the pole piece that was laser ablated in the vertical direction. DETAILED DESCRIPTION

[0034] To make the technical problems, technical solutions, and advantages to be solved by the present invention more clear, the following is a detailed description with reference to the accompanying drawings and specific embodiments. It is obvious that the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0035] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0036] In the description of the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to a locking connection, a detachable connection, or an integral connection; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0037] In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0038] A method for preparing a multilayer electrode having a tree-like pore structure comprises the following steps:

[0039] (1) The electrode active material, pore-forming agent, conductive agent, and binder are dry-mixed under a protective atmosphere by high-speed shearing to fiberize the binder and pore-forming agent. The uniformly mixed mixture is rolled into a film at room temperature, stretched, folded in half, and repeatedly rolled multiple times until it becomes a dense, self-supporting electrode. The electrode active material includes at least one of lithium manganese oxide, lithium cobalt oxide, lithium iron phosphate, or a ternary material, preferably lithium iron phosphate; the pore-forming agent is PEG6000; the conductive agent includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, Super P, Ketjen black, or acetylene black, preferably carbon nanotubes; and the binder is PTFE.

[0040] (2) Electrode layers with different porosities are prepared by adjusting the amount of pore-forming agent added. These electrode layers with different porosities are then assembled onto the current collector through a lamination process, ultimately forming a thick electrode precursor with pore gradient characteristics. The precursor is laser ablated to form vertical main pores. The pore-forming agent content in the electrode layer increases from the current collector side to the diaphragm side, and the porosity increases by 2-5% layer by layer. The holes formed by laser ablation perpendicular to the electrode surface are tapered through-holes that penetrate the electrode, with a pore pitch of 50-150 μm. The pore diameter closest to the current collector is 10-20 μm, and the pore diameter closest to the diaphragm is 0.1-5 μm. The pore diameter gradually increases from the current collector side to the diaphragm side.

[0041] (3) The laser-ablated electrode is heat-treated to remove the pore-forming agent, thereby obtaining horizontal secondary channels, which are combined with vertical primary channels to form a tree-like channel structure. The heat treatment is performed by vacuum drying at 150°C ± 10°C / 2h in a heat treatment environment.

[0042] It should be noted that the described embodiments are intended to facilitate understanding of the present invention and do not have any limiting effect on the present invention.

[0043] Example 1:

[0044] This embodiment provides a multilayer electrode with a tree-like pore structure. The multilayer electrode comprises multiple electrode layers with a hierarchical pore structure. The porosity of each electrode layer increases gradually from the current collector side to the separator side. The multilayer electrode comprises four electrode layers. From the current collector side to the separator side, the first electrode layer has a porosity of 30%, and the porosity of each subsequent electrode layer increases by 5%. The vertical main pores are tapered through-holes that extend through the multilayer electrode. The electrode layer closest to the separator has a porosity of 30% and a pore pitch of 85 μm. The pore diameter gradually increases from the current collector side to the separator side, with the pore diameter closest to the separator being 15 μm and the pore diameter closest to the current collector being 5 μm.

[0045] The multilayer electrode is provided with vertical main channels perpendicular to each electrode layer, and the main channels are combined with the hierarchical channel structure to form a tree-like channel structure.

[0046] The method for preparing a multilayer electrode having a tree-like pore structure provided in this embodiment specifically includes:

[0047] (1) Four portions of 0.291 g of lithium iron phosphate, 0.003 g of carbon nanotubes, and 0.006 g of PTFE were accurately weighed and mixed. 1.0 wt%, 2.0 wt%, 3.0 wt%, and 4.0 wt% of PEG6000 were added to the four mixtures, respectively. The four mixtures were sheared and mixed at 1000 rpm in an argon atmosphere for 30 min to fiberize the binder and pore-forming agent. The mixed mixture was rolled into a film at room temperature, stretched, folded, and repeatedly rolled several times until it became a dense self-supporting electrode. The density of the self-supporting electrode was 2.65 g cm -3 ; The electrode surface loading is 200 mg cm -2 ;

[0048] (2) Four layers of electrodes with different PEG6000 contents were rolled and overlapped to obtain a self-supporting thick electrode layer, with the layer with a high pore-forming agent content on the diaphragm side. The pore-forming agent content of the electrode gradually decreased from the diaphragm side to the current collector side, thereby obtaining a multilayer electrode precursor.

[0049] (3) The obtained multilayer electrode precursor was laser ablated to form vertical channels with an aperture of 15 μm and a pore pitch of 85 μm. The laser ablated electrode was vacuum dried at 150 °C for 2 h to remove PEG6000, thereby obtaining horizontal secondary channels. Combined with the vertical main channels, a thick electrode with a hierarchical tree-like channel structure was obtained.

[0050] Example 2:

[0051] This embodiment provides a multilayer electrode with a tree-like pore structure. The multilayer electrode comprises multiple electrode layers with a hierarchical pore structure. The porosity of each electrode layer increases gradually from the current collector side to the separator side. The multilayer electrode comprises three electrode layers. From the current collector side to the separator side, the first electrode layer has a porosity of 35%, and the porosity increases by 5% layer by layer thereafter. The vertical main pores are tapered through-holes that extend through the multilayer electrode. The pore pitch is 85 μm, and the pore diameter gradually increases from the current collector side to the separator side, with the pore diameter closest to the separator being approximately 15 μm and the pore diameter closest to the current collector being 5 μm.

[0052] The multilayer electrode is provided with vertical main channels perpendicular to each electrode layer, and the main channels are combined with the hierarchical channel structure to form a tree-like channel structure.

[0053] The method for preparing a multilayer electrode having a tree-like pore structure provided in this embodiment specifically includes:

[0054] (1) Accurately weigh three portions of 0.388g lithium iron phosphate, 0.004g carbon nanotubes, and 0.008g PTFE, and then add 2.0wt%, 3.0wt%, and 4.0wt% of PEG6000 to the three portions of the mixture, respectively. The three portions of the mixture are shear-mixed at 1000rpm for 30min under an argon atmosphere to fiberize the binder and pore-forming agent. The mixed mixture is rolled into a film at room temperature, stretched, folded, and repeatedly rolled multiple times until it becomes a dense self-supporting electrode.

[0055] (2) Three layers of electrodes with different PEG6000 contents are rolled and overlapped to obtain a self-supporting thick electrode layer, with the layer with a high pore-forming agent content on the diaphragm side, and the pore-forming agent content of the electrode gradually decreases from the diaphragm side to the current collector side, to obtain a multilayer electrode precursor;

[0056] (3) The obtained multilayer electrode precursor was laser ablated to form vertical channels with an aperture of 15 μm and a pore pitch of 85 μm. The laser ablated electrode was vacuum dried at 150 °C for 2 h to remove PEG6000, thereby obtaining horizontal secondary channels. Combined with the vertical main channels, a thick electrode with a hierarchical tree-like channel structure was obtained.

[0057] Example 3:

[0058] This embodiment provides a multilayer electrode with a tree-like pore structure. The multilayer electrode comprises multiple electrode layers with a hierarchical pore structure, with the porosity of each electrode layer increasing from the current collector side to the separator side. The multilayer electrode comprises two electrode layers, with the first electrode layer having a porosity of 35% and the porosity increasing by 5% layer by layer from the current collector side to the separator side. The vertical main pores are tapered through-holes running through the multilayer electrode, with a pore pitch of 85 μm. The pore diameter gradually increases from the current collector side to the separator side, with the pore diameter closest to the separator being 15 μm and the pore diameter closest to the current collector being 5 μm.

[0059] The multilayer electrode is provided with vertical main channels perpendicular to each electrode layer, and the main channels are combined with the hierarchical channel structure to form a tree-like channel structure.

[0060] The method for preparing a multilayer electrode having a tree-like pore structure provided in this embodiment specifically includes:

[0061] (1) Accurately weigh two portions of 0.582g lithium iron phosphate, 0.006g carbon nanotubes, and 0.012g PTFE, and then add 2.0wt% and 4.0wt% of PEG6000 to the two mixtures, respectively. The two mixtures are shear-mixed at 1000rpm in an argon atmosphere for 30min to fiberize the binder and pore-forming agent. The mixed mixture is rolled into a film at room temperature, stretched, folded, and repeatedly rolled several times until it becomes a dense self-supporting electrode.

[0062] (2) Two layers of electrodes with different PEG6000 contents are rolled and overlapped to obtain a self-supporting thick electrode layer, with the layer with a higher pore-forming agent content on the diaphragm side, and the pore-forming agent content of the electrode gradually decreases from the diaphragm side to the current collector side, to obtain a multilayer electrode precursor;

[0063] (3) The obtained multilayer electrode precursor was laser ablated to form vertical channels with an aperture of 15 μm and a pore pitch of 85 μm. The laser ablated electrode was vacuum dried at 150 °C for 2 h to remove PEG6000, thereby obtaining horizontal secondary channels. Combined with the vertical main channels, a thick electrode with a hierarchical tree-like channel structure was obtained.

[0064] Example 4:

[0065] The difference between this embodiment and embodiment 1 is that the added amount of PEG6000 is 4.0 wt %. The other aspects are the same as those in embodiment 1.

[0066] Example 5:

[0067] The difference between this embodiment and embodiment 1 is that the added amount of PEG6000 is 1.0 wt %. The other aspects are the same as those in embodiment 1.

[0068] Comparative Example 1:

[0069] 1.164g lithium iron phosphate, 0.012g carbon nanotubes and 0.0024g PTFE were accurately weighed and mixed, and then high-speed shear mixing was carried out at 1000rpm in an argon atmosphere for 30 minutes to fiberize the binder. The evenly mixed mixture was rolled into a film at room temperature, stretched and folded in half, and then repeatedly rolled several times until it became a dense self-supporting electrode. The obtained self-supporting electrode was laser ablated to form vertical channels with an aperture of 15μm and a hole spacing of 85μm to obtain a thick electrode with a vertical channel structure.

[0070] Comparative Example 2:

[0071] Accurately weigh 1.164g lithium iron phosphate, 0.012g carbon nanotubes, and 0.0024g PTFE, mix them, add 3.0wt% PEG6000, and high-speed shear mixing at 1000rpm under argon atmosphere for 30min to fiberize the binder and pore-forming agent. The evenly mixed mixture is rolled into a film at room temperature, stretched and folded in half, and repeatedly rolled several times until it becomes a dense self-supporting electrode. The electrode is vacuum dried at 150°C for 2h to remove PEG6000, obtaining a thick electrode with a horizontal pore structure.

[0072] Comparative Example 3:

[0073] Accurately weigh 1.164g of lithium iron phosphate, 0.012g of carbon nanotubes, and 0.0024g of PTFE and mix them at high speed for 30 minutes to fiberize the binder. The evenly mixed mixture is rolled into a film at room temperature, stretched, folded in half, and repeatedly rolled multiple times until it becomes a dense self-supporting electrode to obtain a thick electrode.

[0074] Electrochemical performance testing and analysis:

[0075] Charge and Discharge Performance Test: The battery was electrochemically tested in a constant current charge and discharge mode at room temperature (25°C) using a test cabinet with a voltage range of 2.5 to 4.2 V. The battery was activated by charging and discharging three times at a rate of 0.1 C before cycle or rate performance testing. Cyclic performance testing was then conducted at 0.5 C.

[0076] Rate performance test: The battery was cycled 5 times at 0.1, 0.2, 0.5, 1, 2, and 0.1C rates for rate performance test.

[0077] Comparative Example 4:

[0078] This comparative example provides a thick electrode with a tree-like pore structure. The thick electrode has one electrode layer, and the vertical main pores are conical through holes that penetrate the multi-layer electrodes. The pore pitch is 85 μm, and the pore diameter gradually increases from the side close to the diaphragm to the current collector side. The pore diameter on the current collector side is 15 μm, and that on the diaphragm side is 5 μm.

[0079] The electrode is provided with a vertical main channel in a direction perpendicular to the electrode layer, and the main channel is combined with the hierarchical channel structure to form a tree-like channel structure.

[0080] The method for preparing a thick electrode having a tree-like pore structure provided in this embodiment specifically includes:

[0081] (1) Accurately weigh 1.164 g of lithium iron phosphate, 0.012 g of carbon nanotubes, and 0.0024 g of PTFE, and then add 3.0 wt% of PEG6000. The mixture is sheared and mixed at 1000 rpm for 30 min under an argon atmosphere. The high-speed shearing equipment is at least one of a homogenizer, a high-speed disperser, or a fiberizing grinder to fiberize the binder and the pore-forming agent. The mixed mixture is rolled into a film at room temperature, stretched, folded, and repeatedly rolled multiple times until it becomes a dense self-supporting electrode. The density of the self-supporting electrode is 2.65 g cm -3 , the electrode surface loading is 40 mg cm -2 .

[0082] (2) assembling the prepared self-supporting electrode onto a current collector to obtain an electrode precursor;

[0083] (3) The obtained electrode precursor was laser ablated to form vertical channels with an aperture of 15 μm and a pore pitch of 85 μm. The laser ablated electrode was vacuum dried at 150 °C for 2 h to remove PEG6000, thereby obtaining horizontal secondary channels. Combined with the vertical main channels, a thick electrode with a tree-like channel structure was obtained.

[0084] Table 1 Performance comparison between traditional thick electrodes and dendritic channel electrodes in Examples 1-5

[0085]

[0086] Table 2 Electrochemical performance test data of the embodiments and comparative examples

[0087]

[0088] Electrochemical test analysis: The electrodes of the embodiment and the comparative example were assembled into half-cells and subjected to electrochemical performance tests. The results showed that the four-layer electrode with different porosities exhibited the highest initial reversible capacity of 159.88 mAh g at 0.5C. -1 Thanks to the high specific surface area formed by the porosity, it is conducive to electrolyte infiltration, thereby optimizing the lithium ion transmission path. After 100 cycles at 0.5C, the capacity retention rate is as high as 99.5%, and it has good rate performance. Figure 1 is the charge and discharge curve, Figure 2 The results of the 0.5C cycle performance show that the electrochemical performance is much better than that of comparative example 1 (only laser drilling) and comparative example 2 (only adding pore-forming agent). Figure 3The conical pore microstructure formed by laser ablation of a conventional electrode is shown in planar SEM images. The pores are neatly arranged, with no evidence of residual material accumulation around the openings due to laser ablation. Cross-sectional SEM images show good pore verticality, with the pores farther from the current collector having a larger diameter than those closer to the current collector. The pore walls are smooth, indicating that laser ablation does not damage the electrode structure. In summary, the present invention demonstrates a feasible method for preparing a multilayer electrode with a tree-like pore structure, and the resulting electrode exhibits high capacity and cycling stability.

[0089] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A multilayer electrode having a tree-like pore structure, characterized in that: The multilayer electrode comprises multiple electrode layers with a hierarchical pore structure, wherein the porosity of each electrode layer increases layer by layer in the order from the current collector side to the separator side; The multi-layer electrode is provided with vertical main channels perpendicular to each electrode layer, and the main channels are combined with the hierarchical channel structure to form a tree-like channel structure.

2. The multilayer electrode according to claim 1, wherein The electrode layers of the multi-layer electrode include 2-4 layers.

3. The multilayer electrode according to claim 1, wherein The vertical main channel is a tapered through hole that penetrates the multi-layer electrode. The pore diameter gradually increases from the side close to the current collector to the diaphragm side, and the porosity increases by 2-5% layer by layer. The pore diameter closest to the diaphragm side is 10-20μm, and the pore diameter closest to the current collector side is 0.1-5μm; the pore spacing ranges from 50 to 150μm.

4. The multilayer electrode according to claim 1, wherein The total thickness of the electrode layer of the multilayer electrode is 200-800 μm, and the surface loading is 40-200 mg cm -2 .

5. The multilayer electrode according to claim 1, wherein The raw materials of the electrode layer include electrode active material, pore-forming agent, conductive agent and binder, wherein the electrode active material component includes at least one of lithium manganate, lithium iron phosphate, ternary material or lithium cobalt oxide, the conductive agent includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, Super P, Ketjen black or acetylene black, and the added amount is 1wt% to 8wt% of the total solid content of the raw materials; the binder is polytetrafluoroethylene, and the added amount is 1wt% to 5wt% of the total solid content of the raw materials; the pore-forming agent is polyethylene glycol, and the added amount is 1wt% to 4wt% of the total solid content of the raw materials, and the added amount increases with each electrode layer from the current collector side to the diaphragm side.

6. The multilayer electrode according to claim 5, wherein The amount of the pore-forming agent added is 1 wt% to 2 wt% per electrode layer from the side close to the current collector to the side of the separator.

7. A method for preparing a multilayer electrode having a tree-like pore structure, characterized in that: The following steps are involved: (1) The electrode active material, pore-forming agent, conductive agent, and binder are mixed in proportion by high-speed shear dry mixing under a protective atmosphere, and the mixed mixture is subjected to repeated film-forming and stretching and folding steps at room temperature for multiple times to prepare a self-supporting electrode; (2) Repeat step (1) to prepare self-supporting electrodes with different pore-forming agent contents, and assemble the multilayer self-supporting electrodes onto the current collector in the order of pore-forming agent content from low to high by a lamination process to obtain a multilayer electrode precursor; (3) The multilayer electrode precursor obtained in step (2) is laser ablated to form vertical main channels, and the pore-forming agent is removed by heat treatment to obtain horizontal secondary channels, which are combined with the vertical main channels to form a tree-like channel structure.

8. The method for preparing a multilayer electrode according to claim 7, wherein: The protective atmosphere in step (1) is at least one of argon, nitrogen or other protective gases; the high-speed shearing equipment is at least one of a homogenizer, a high-speed disperser or a fiberizing grinder, the rotation speed is not less than 1000 rpm, and the mixing time is not less than 30 min.

9. The method for preparing a multilayer electrode according to claim 7, wherein: The rolling method in step (1) is at least one of repeatedly rolling on a stainless steel plate using a glass rod or repeatedly rolling using a rolling device, and the density of the self-supporting electrode is 2.0 to 3.9 g cm -3 .

10. The method for preparing a multilayer electrode according to claim 7, wherein: The heat treatment comprises vacuum drying in a heat treatment environment of 120-200° C. for 1-5 hours.

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