Double-sided dry electrode and preparation method thereof

Abstract

The invention provides a double-sided dry-method electrode and a preparation method, and relates to the technical field of energy storage device electrode preparation, and the preparation method comprises the following steps: providing and compounding a dry-method pole piece roll and a hollow current collector coiled material, adopting an upper roller and a lower roller during compounding, the surface of the upper roller is provided with raised lines corresponding to the hollow part of a hollow current collector, and the surface of the lower roller is provided with raised lines corresponding to the hollow part of the hollow current collector; the rotating speed of the lower roller is higher than that of the upper roller, and the dry-method pole piece material is pressed into the other surface of the hollow current collector through rolling to form a composite electrode; the composite electrode is subjected to flattening treatment; carrying out thinning treatment on the composite electrode; and rolling the composite electrode to obtain the double-sided dry electrode. The pole piece material penetrates through the two surfaces of the current collector through the composite roller and the roller speed difference, full fibrillation of a PTFE binder under high shear force is achieved, the electrode and the current collector are tightly combined, and an additional bonding layer is not needed; meanwhile, the technological process is simplified, the winding frequency is reduced, raw material waste is reduced, and the final electrode has excellent mechanical strength and electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of energy storage device electrode preparation, and in particular to a double-sided dry electrode and a preparation method thereof. Background Art

[0002] Lithium-ion batteries and supercapacitors are important energy storage devices and are widely used in electronic devices, electric vehicles, and large-scale energy storage systems. Currently, electrode preparation methods are mainly divided into two types: wet process and dry process. The wet process usually uses water or organic solvents such as N-methylpyrrolidone (NMP) to prepare a slurry for coating. This method has the disadvantages of high energy consumption and long drying time. At the same time, the recovery and treatment of organic solvents also increase production costs. In addition, if the solvent is not completely removed, it will cause the battery to swell and its performance to decay too quickly during the cycle, affecting the performance and life of the battery.

[0003] The dry process involves mixing the positive and negative active materials with a polytetrafluoroethylene (PTFE) binder and a conductive agent, then directly rolling them into a self-supporting dry film. This film has certain mechanical tensile properties and good ductility, and will not break or shatter during the continuous rolling process. The resulting film has a uniform thickness and is easy to process. In the dry process, the PTFE binder needs to be fibrillated under shear force to form filamentous fibers, which can then cross-link to form a network structure, bonding the active material and the conductive agent to form a self-supporting film.

[0004] However, the existing dry electrode preparation process still has many technical defects. First, the traditional dry electrode preparation process usually involves first pressing the dry electrode film to a certain thickness through a multi-stage rolling process, and then compounding it with a current collector coated with a conductive adhesive coating. This preparation method has a complicated process and requires repeated winding and unwinding, resulting in serious waste of raw materials. Secondly, in the composite process, if there is no conductive adhesive coating, the bonding between the self-supporting film and the current collector is poor. In extreme cases, the electrode material may fall off the current collector, seriously affecting the overall conductivity of the electrode and battery performance.

[0005] In addition, the current collector used in traditional batteries and capacitors is usually a metal foil (such as copper foil, aluminum foil), which accounts for 10% to 25% of the weight of the entire battery. This design results in a low mass energy density of the battery and reduces the battery's cycle life. Although the main function of the current collector is to collect the current generated by the battery's active materials to form a larger current output, it itself does not participate in the energy storage reaction. Excessive weight share is not conducive to improving the overall performance of the battery.

[0006] Chinese patent CN114335409B discloses a dry electrode, its preparation method, dry cell and battery. It adopts a three-layer composite structure in which the dry electrode membrane is sandwiched between the diaphragm and the current collector. The three layers of material are composited into an integrated dry electrode with a diaphragm by hot rolling. The technical effect achieved is to improve the stacking speed and alignment, and solve the problems of diaphragm shrinkage and electrode misalignment.

[0007] Chinese patent CN111430671B discloses a bipolar pole piece and a preparation method, a lithium-ion battery and a preparation method. It adopts a double-sided electrode structure and uses a two-step rolling process to solve the problem that traditional bipolar pole pieces are difficult to simultaneously meet the required compaction density of the positive and negative electrode material layers. However, it does not solve the problems that the existing dry-process electrodes have poor bonding with the current collectors, the electrode materials are easy to fall off, and the conductivity is affected; the traditional current collectors have a large weight proportion, which affects the battery quality energy density and cycle life. Summary of the Invention

[0008] The purpose of the present invention is to provide a double-sided dry electrode and a preparation method to solve the problems that the existing dry electrode has poor bonding with the current collector, the electrode material is easy to fall off, affecting the conductivity; the traditional current collector has a large weight proportion, affecting the battery quality energy density and cycle life.

[0009] To achieve the above object, the present invention is implemented by the following technical solution: A method for preparing a double-sided dry electrode comprises the following steps:

[0010] S1: Compounding the dry electrode roll and the hollow current collector roll, wherein a compound roller is used for compounding, and the compound roller includes an upper roller and a lower roller, the surface of the upper roller has raised lines corresponding to the hollow part of the hollow current collector, and the rotation speed of the lower roller is faster than the rotation speed of the upper roller, and the material of the dry electrode roll is pressed from the hollow part of the hollow current collector into the other side of the hollow current collector by rolling, thereby forming a composite electrode;

[0011] S2: flattening the composite electrode;

[0012] S3: thinning the composite electrode to obtain a double-sided dry electrode.

[0013] Furthermore, the pattern of the raised lines on the upper roller surface of the composite roller matches the pattern of the hollow portion of the hollow current collector.

[0014] Furthermore: the hollow current collector is a perforated metal foil or a metal mesh.

[0015] Furthermore, the speed difference between the speed of the lower roller and the speed of the upper roller is used to adjust the thickness ratio of the two sides of the composite electrode.

[0016] Furthermore: the rotation speed range of the upper roller is 0.1-10m / s, and the rotation speed range of the lower roller is 0.15-12m / s.

[0017] Furthermore: the thickness of the dry electrode in the dry electrode roll is 20-5000 μm.

[0018] Furthermore: the dry-process electrode in the dry-process electrode roll includes an active material, a conductive agent and a binder, wherein the binder is a fibrillable polymer material.

[0019] Furthermore: the polymer material is polytetrafluoroethylene.

[0020] Furthermore: the active material includes activated carbon, and / or lithium iron phosphate, and / or ternary material, and / or graphite, and / or silicon-carbon material.

[0021] A double-sided dry electrode comprises a first electrode layer, a current collector layer and a second electrode layer, wherein the first electrode layer is located at the top of the current collector layer, the second electrode layer is located at the bottom of the current collector layer, and the current collector layer is a hollow current collector layer filled with electrode material.

[0022] Furthermore: the binder in the first electrode layer and the binder in the second electrode layer form a network structure.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] First, this invention uses a composite roller with a raised surface and a lower roller running faster than the upper roller to press the dry-process electrode material through the hollowed-out current collector onto the other side, forming a tightly bonded double-sided dry-process electrode. Experimental results show that the electrodes prepared using this method achieve a 90° peel strength of 13.7-14.6 N / m, with fracture occurring within the electrode rather than at the interface. This demonstrates a strong bond between the electrode and the current collector, significantly outperforming both conventional methods (only 6.8 N / m) and the conventional adhesive-coated aluminum foil method (11.8 N / m).

[0025] 2. The present invention overturns the traditional dry-process electrode preparation process of "pressing → winding, compounding → winding" and adopts the new process of "compounding → pressing → winding", which significantly reduces the number of winding times and process complexity, reduces raw material waste, and improves production efficiency.

[0026] Third, this invention utilizes the shear force generated by the speed difference between the upper and lower rollers to further promote the fibrillation of the PTFE binder in the dry-process electrode, forming a stronger network structure and enhancing the mechanical strength and bonding of the electrode. This method achieves a tight bond between the electrode and the current collector without the need for an additional adhesive layer, simplifying the process while also improving the electrode's conductivity.

[0027] Fourth, this invention uses a hollowed-out current collector instead of a traditional solid metal foil, effectively reducing the current collector's weight and increasing the overall mass energy density of the battery or capacitor. Since the current collector accounts for 10% to 25% of the weight of a traditional energy storage device, this improvement has a significant effect on increasing the battery's energy density.

[0028] 5. The preparation process of the present invention can be carried out at room temperature without heating, thus reducing energy consumption. At the same time, it has a wide range of applications and can be used for secondary batteries such as lithium-ion batteries, as well as for the preparation of positive and negative electrodes of various energy storage devices such as supercapacitors or lithium-ion capacitors. It has good technical versatility and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A flow chart of a method for preparing a double-sided dry electrode provided by the present invention;

[0030] Figure 2 A schematic diagram of the technical process route of a method for preparing a double-sided dry electrode provided by the present invention;

[0031] Figure 3 A schematic diagram of the composite process of a method for preparing a double-sided dry electrode provided by the present invention;

[0032] Figure 4 A peel strength test curve of a double-sided dry electrode provided by the present invention;

[0033] Figure 5 This is a schematic cross-sectional view of a double-sided dry electrode provided by the present invention.

[0034] In the picture:

[0035] 1. Dry-process electrode roll; 2. Hollow current collector roll; 3. Upper roller; 4. Lower roller; 5. Flattening roller; 6. Double-sided dry-process electrode roll; 7. First electrode layer; 8. Current collector layer; 9. Second electrode layer; 10. Dry-process electrode layer; 20. Hollow current collector layer. DETAILED DESCRIPTION

[0036] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0037] 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.

[0038] like Figure 1 As shown: The present invention provides a method for preparing a double-sided dry electrode, comprising the following steps:

[0039] S1: Compounding the dry electrode roll 1 and the hollow current collector roll, wherein a compound roller is used for compounding, and the compound roller includes an upper roller 3 and a lower roller 4, the surface of the upper roller 3 has raised lines corresponding to the hollow part of the hollow current collector, and the rotation speed of the lower roller 4 is faster than the rotation speed of the upper roller 3, and the material of the dry electrode roll 1 is pressed from the hollow part of the hollow current collector into the other side of the hollow current collector by rolling, thereby forming a composite electrode;

[0040] S2: flattening the composite electrode;

[0041] S3: thinning the composite electrode to obtain a double-sided dry electrode.

[0042] According to a specific embodiment of the present invention, the pattern of the raised lines on the surface of the upper roller 3 of the composite roller matches the pattern of the hollow portion of the hollow current collector, and the hollow current collector is a perforated metal foil or metal mesh.

[0043] According to a specific embodiment of the present invention, the speed difference between the speed of the lower roller 4 and the speed of the upper roller 3 is used to adjust the thickness ratio of the two sides of the composite electrode, the speed range of the upper roller 3 is 0.1-10m / s, and the speed range of the lower roller 4 is 0.15-12m / s.

[0044] According to a specific embodiment of the present invention, the thickness of the dry electrode in the dry electrode roll 1 is 20-5000 μm, and the dry electrode in the dry electrode roll 1 includes an active substance, a conductive agent and a binder, wherein the binder is a fibrillable polymer material, and the polymer material is polytetrafluoroethylene.

[0045] According to a specific embodiment of the present invention, the active material includes activated carbon, and / or lithium iron phosphate, and / or ternary material, and / or graphite, and / or silicon-carbon material.

[0046] A double-sided dry electrode includes a first electrode layer 7, a current collector layer 8 and a second electrode layer 9. The first electrode layer 7 is located at the top of the current collector layer 8, and the second electrode layer 9 is located at the bottom of the current collector layer 8. The current collector layer 8 is formed by filling the hollow part of the hollow current collector layer 20 with the electrode material.

[0047] According to a specific embodiment of the present invention, the binder in the first electrode layer 7 and the binder in the second electrode layer 9 form a network structure.

[0048] The following is explained through specific examples.

[0049] Example 1

[0050] like Figure 1-Figure 2 As shown, the method for preparing a double-sided dry electrode in this embodiment includes the following steps:

[0051] First, a dry-process electrode roll 1 and a hollow current collector roll 2 are provided. The thickness range of the dry-process electrode roll 1 is 20-5000μm, of which 20μm is the minimum thickness of the electrode roll that can be rolled up and down. The electrode roll is prone to breakage if the thickness is less than this; 5000μm is the maximum thickness of the electrode material that can be formed into sheets by the dry process. The preferred thickness range is 300-800μm. The initial dry-process electrode roll 1 thickness does not need to be the final electrode thickness. The hollow area ratio of the hollow current collector is greater than 0 and less than 1, and can be a perforated metal foil or metal mesh.

[0052] The dry electrode in the dry electrode roll 1 includes an active substance, a conductive agent and a binder, wherein the binder is a fibrillable polymer material, the polymer material is polytetrafluoroethylene, and the active substance is selected from activated carbon, and / or lithium iron phosphate, and / or ternary material, and / or graphite, and / or silicon-carbon material.

[0053] Then, the dry electrode roll 1 and the hollow current collector roll 2 are combined by a rolling process. Figure 3 As shown, during the composite process, the surface of the upper roller 3 has raised patterns that match the pattern of the hollowed-out portion of the hollowed-out current collector layer 20, and the size of the raised patterns is smaller than the size of the hollowed-out portion of the hollowed-out current collector layer 20. In the rolling zone, the dry-process electrode layer 10 can be pressed to the other side of the hollowed-out current collector layer 20. The rotation speed of the upper roller 3 ranges from 0.1 to 10 m / s, and the rotation speed of the lower roller 4 ranges from 0.15 to 12 m / s. The speed of the lower roller 4 is faster than that of the upper roller 3 so that the electrode material rolled through the hollowed-out portion of the hollowed-out current collector layer 20 can be evenly covered on the second side of the hollowed-out current collector layer 20. The speed difference between the upper and lower rollers can be used to adjust the thickness ratio of each side of the final electrode. There are no special requirements for the material of the upper and lower rollers. Through this specially designed composite process, the electrode material in the dry-process electrode layer 10 will be pressed into the other side through the hollowed-out portion of the hollowed-out current collector layer 20 under the action of roller pressure to form a double-sided electrode.

[0054] The surface of the composite electrode is not flat, so it needs to enter the flattening roller 5 for flattening process. According to the actual situation, the corresponding multi-stage rolling can achieve the ideal flatness.

[0055] After the flattening process, if the electrode needs to be further thinned, it can continue to enter the multi-stage rolling process for thinning until the required thickness is reached.

[0056] Finally, the electrode pressed to a suitable thickness is rolled up to obtain a double-sided dry electrode roll 6, thereby completing the preparation of the double-sided dry electrode.

[0057] like Figure 5 As shown, it is a schematic cross-sectional view of a double-sided dry electrode, comprising a first electrode layer 7, a second electrode layer 9 and a current collector layer 8, wherein the first electrode layer 7 and the second electrode layer 9 are electrode layers formed by electrode materials, and the middle layer is the current collector layer 8 in which the hollow part of the hollow current collector layer 20 is filled with electrode materials. The black lines in the figure represent the network structure formed by the binder of the electrode material in the double-sided dry electrode after fibrillation, which enhances the mechanical strength and bonding of the double-sided dry electrode structure.

[0058] It should be noted that the upper roller 3 of the laminating roller has protrusions. The pattern of these protrusions must match the hollowed-out portion of the hollowed-out current collector layer 20, but they are smaller in size. For example, if the hollowed-out portion of the current collector is a 1mm x 1mm square array, the protrusions on the upper roller 3 are preferably a 0.8mm x 0.8mm square array. The lower roller 4 of the laminating roller must run faster than the upper roller 3, and a flattening step is required after the laminating process.

[0059] Compared with the traditional dry electrode preparation method, the preparation method of the present invention has the following advantages:

[0060] First, a process route of first compounding and then pressing and winding was adopted, replacing the traditional steps of pressing → winding and compounding → winding, greatly simplifying the process flow; after multi-stage rolling, the active material and the current collector are tightly combined without the need for an additional adhesive layer, which not only improves the overall energy density of the battery, but also facilitates the design of the tabs.

[0061] Secondly, after the electrode and the current collector enter the roller gap, the electrode material undergoes strong deformation due to the extrusion of the two rollers (the upper roller 3 has a protrusion, and the lower roller 4 is faster than the upper roller 3). The electrode material passes through the hollow part and enters the other side of the hollow current collector layer 20. At the same time, due to the roller speed difference between the two rollers, a high shear force is applied to the electrode material, which triggers the fibrillation of the PTFE binder in the electrode, forming a network structure, enhancing the mechanical strength and bonding of the dry electrode. The subsequent rolling process also provides high shear force for the dry electrode, further enhancing the strength of the dry electrode and improving its bonding.

[0062] In addition, the use of hollow current collectors reduces the weight of the electrode and increases the energy density. The composite process can be achieved at room temperature without heating. This technology has a wide range of applications and can be used for secondary batteries such as lithium-ion batteries, as well as for the preparation of positive and negative electrodes of energy storage devices such as supercapacitors or lithium-ion capacitors.

[0063] Finally, the electrode prepared by this method is tightly bonded to the current collector without the need for an additional adhesive layer, and is significantly superior to the traditional method in peel strength testing.

[0064] The following is further described through specific peel strength test examples and comparative examples. The following table is a table of peel strength test results of different examples and comparative examples.

[0065]

[0066]

[0067] Example 2

[0068] Dry-process electrode roll 1 is an activated carbon roll with a weight ratio of activated carbon (YP-50, Kuraray Co): conductive carbon black (Super P): PTFE = 92:5:3. After thorough mixing, the powders are rolled on an open mill into a 0.8mm thick sheet, which is then rolled up for later use. The current collector roll is a commercial stainless steel mesh with 300-mesh square holes and a thickness of 135±2μm. The two rolls are laminated together. The top roller (3) of the lamination roll features a raised dot pattern, with the dot size and spacing matching the hollowed-out portion of the current collector. The bottom roller (4) of the lamination roll is a flat steel roll. The roll gap is adjusted to 600μm, with the top roller (3) rotating at 3m / min and the bottom roller (4) rotating at 3.5m / min. After lamination, the material undergoes thickness measurement, tension adjustment, and deflection correction before passing through flattening roller (5). It then passes through a multi-stage roller with gaps of 500μm, 400μm, and 300μm for thinning. During the last rolling, the excess material edge is cut off and then rolled.

[0069] Take a 150mm×20mm sample electrode composite film and firmly fix it in the center of the steel plate of the lower fixture of the peel tester. Take a 3M tape, fix the upper end in the chuck of the upper fixture, and stick the lower end to the 10×20mm area on the surface of the sample electrode. The tape should be at 90° to the sample. The test results are as follows: Figure 4 As shown, the average peel strength in the stable stage is 13.7N / m, and the curve stabilizes in the middle and late stages, indicating uniform bonding. Observation shows that the fracture surface is internal to the electrode layer, rather than separation between the electrode and the current collector, indicating good bonding between the electrode and the current collector.

[0070] Example 3

[0071] Dry-process electrode roll 1 is a lithium iron phosphate coil, with lithium iron phosphate (D50 = 800nm): conductive carbon black (Super P): PTFE = 92:5:3 (weight ratio). After the above powder ratio is fully mixed, it is rolled into a 0.6mm thick sheet on an open mill and rolled up for use. The current collector coil is a perforated aluminum foil (opening rate 40%, pore size 0.5mm, thickness 0.045mm). The two coils are compounded, and the roller pattern of the composite roller (top roller 3) is a raised dot array, the dot size and spacing of which match the hollowed-out portion of the current collector. The composite roller (bottom roller 4) is a flat steel roller. The roller gap is adjusted to 600μm, the rotation speed of the top roller 3 is 1m / min, and the rotation speed of the bottom roller 4 is 1.2m / min. The composite material is thickness measured, tension adjusted, and corrected before passing through the flattening roller 5. After that, it sequentially enters a multi-stage roller with a roller gap of 500μm, 400μm, 350μm, and 300μm for thinning. During the last rolling, the excess material edge is cut off and then rolled up. Then the sample is taken for peeling test, and the test method is the same as that in Example 2. The average peel strength is measured to be 14.5N / m. After observation, the fracture surface is a fracture inside the pole piece, rather than a fracture separated from the pole piece and the current collector, which proves that the pole piece and the current collector are well bonded.

[0072] Example 4

[0073] Dry-process electrode roll 1 is a lithium iron phosphate / activated carbon hybrid roll. The weight ratio of lithium iron phosphate (D50 = 800nm): activated carbon (YP-50, Kuraray Co): conductive carbon black (Super P): PTFE is 28:64:5:3. After thorough mixing, the powders are rolled on an open mill into a 0.6mm thick sheet, which is then rolled up for later use. The current collector roll is a perforated aluminum foil (40% porosity, 0.5mm pore size, 0.045mm thickness). The two rolls are laminated together. The lamination roller (top roller 3) features a raised dot pattern, with the dot size and spacing matching the hollowed-out portion of the current collector. The lamination roller (bottom roller 4) is a flat steel roller. The roll gap is adjusted to 600μm, with the top roller 3 rotating at 2m / min and the bottom roller 4 at 2.3m / min. The laminated material undergoes thickness measurement, tension adjustment, and deflection correction before passing over a flattening roller 5. After that, it sequentially enters a multi-stage roller with a roller gap of 500μm, 400μm, 350μm, and 300μm for thinning. During the last rolling, the excess material edge is cut off and then rolled up. Then the sample is taken for peeling test, and the test method is the same as that in Example 2. The average peel strength is measured to be 14.6N / m. After observation, the fracture surface is a fracture inside the pole piece, rather than a fracture separated from the pole piece and the current collector, which proves that the pole piece and the current collector are well bonded.

[0074] It can be found from Examples 3 and 4 that a lower compounding speed helps to improve the bonding strength. This is because a lower compounding speed can give the material a longer strain time, thereby more fully fibrillating the PTFE binder.

[0075] Comparative Example 1

[0076] The dry electrode roll is the same as that in Example 2. After being rolled into a sheet with a thickness of 0.6 mm, it sequentially enters a multi-stage roller with a roller gap of 500 μm, 400 μm, 350 μm, and 300 μm for thinning, and then is rolled. The current collector roll is a smooth aluminum foil (thickness 25 μm). The above two rolls are compounded. The upper and lower rollers of the compound roller are flat steel rollers with a roller speed of 1 m / min. After compounding, the material is rolled after being compacted by a roller. Then samples are taken for peeling test, and the test method is the same as in Example 2. The average peel strength is measured to be only 6.8 N / m. After observation, the fracture surface is the separation of the pole piece and the current collector, which proves that the bonding between the pole piece and the current collector is poor.

[0077] Comparative Example 2

[0078] The dry-process electrode coils were processed in the same manner as in Comparative Example 1. The current collector coil was a carbon-coated aluminum foil (30 μm thick). The two coils were then laminated using the same method as in Comparative Example 1. Samples were then taken for peel testing using the same method as in Example 2. The average peel strength was 11.8 N / m. Observation revealed that the fracture surface was primarily internal to the electrode sheet, with a few areas showing separation between the electrode sheet and the current collector, demonstrating uneven bonding between the electrode sheet and the current collector.

[0079] The above embodiments are intended only to illustrate the technical concepts and features of the present invention. Their purpose is to enable those skilled in the art to understand the contents of the present invention and implement them accordingly. They are not intended to limit the scope of protection of the present invention. Any equivalent changes or modifications made in accordance with the spirit of the present invention are intended to be covered by the scope of protection of the present invention.

Claims

1. A method for preparing a double-sided dry electrode, characterized in that: The following steps are involved: S1: Compounding the dry electrode roll and the hollow current collector roll, wherein a compound roller is used for compounding, and the compound roller includes an upper roller and a lower roller, the surface of the upper roller has raised lines corresponding to the hollow part of the hollow current collector, and the rotation speed of the lower roller is faster than the rotation speed of the upper roller, and the material of the dry electrode roll is pressed from the hollow part of the hollow current collector into the other side of the hollow current collector by rolling, thereby forming a composite electrode; S2: flattening the composite electrode; S3: thinning the composite electrode to obtain a double-sided dry electrode.

2. The method for preparing a double-sided dry electrode according to claim 1, characterized in that: The pattern of the raised lines on the upper roller surface of the composite roller matches the pattern of the hollow portion of the hollow current collector.

3. The method for preparing a double-sided dry electrode according to claim 1, wherein: The hollow current collector is a perforated metal foil or a metal mesh.

4. The method for preparing a double-sided dry electrode according to claim 1, wherein: The speed difference between the speed of the lower roller and the speed of the upper roller is used to adjust the thickness ratio of the two sides of the composite electrode.

5. The method for preparing a double-sided dry electrode according to claim 1, wherein: The speed range of the upper roller is 0.1-10m / s, and the speed range of the lower roller is 0.15-12m / s.

6. The method for preparing a double-sided dry electrode according to claim 1, wherein: The thickness of the dry-process electrode in the dry-process electrode roll is 20-5000 μm.

7. The method for preparing a double-sided dry electrode according to claim 1, wherein: The dry-process electrode in the dry-process electrode roll includes an active material, a conductive agent and a binder, wherein the binder is a fibrillable polymer material.

8. The method for preparing a double-sided dry electrode according to claim 7, characterized in that: The polymer material is polytetrafluoroethylene.

9. The method for preparing a double-sided dry electrode according to claim 7, characterized in that: The active material includes activated carbon, and / or lithium iron phosphate, and / or ternary material, and / or graphite, and / or silicon-carbon material.

10. A double-sided dry electrode, characterized in that: It includes a first electrode layer, a current collector layer and a second electrode layer. The first electrode layer is located at the top of the current collector layer, the second electrode layer is located at the bottom of the current collector layer, and the current collector layer is a hollow current collector layer filled with pole piece material.

11. The double-sided dry electrode according to claim 10, characterized in that: The binder in the first electrode layer and the binder in the second electrode layer form a network structure.

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