A current collector-free pole piece and battery

Abstract

The application relates to the technical field of batteries, and discloses a current collector-free pole piece and a battery; the current collector-free pole piece comprises an active layer, a conductive layer and a tab leading-out part, the conductive layer is arranged on the surface of the active layer, and the tab leading-out part is arranged on the conductive layer; the conductive layer is sequentially divided into first, second and third conductive layers along the tab leading-out direction, and the thicknesses of the three satisfy d1 < d2 <= d3. According to the application, the thickness gradient of the conductive layer is used to construct a step-shaped space to accommodate the thickness of the tab leading-out part, the structure gap is gentle to disperse stress, the risk of bending and fracture of the connection part of the tab leading-out part is reduced, the mechanical constraint of the edge region of the pole piece is enhanced, the edge material dropping is inhibited, and therefore the manufacturing yield, the cycle performance and the rate performance of the battery are improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more specifically, to a current collector-free electrode and battery. Background Technology

[0002] In conventional lithium-ion battery construction, active materials are typically coated onto metal foil (such as copper or aluminum foil). While this metal foil acts as a current collector, providing conductivity and load-bearing capacity, its own mass is significant and it lacks lithium storage capacity, limiting further improvements in battery energy density. If the aforementioned metal current collector is omitted and a self-supporting, current-free electrode is directly formed, not only can the additional mass burden from the inactive metal foil be eliminated to improve energy density, but the physical barrier of the metal layer between the two active materials can also be eliminated. This facilitates the direct migration of lithium ions in the thickness direction, improving the battery's fast-charging capability.

[0003] However, the lack of a current collector-free electrode results in insufficient overall mechanical strength due to the absence of a mechanical support framework provided by a metal current collector. Especially at the end edge of the electrode where the tab leads are located inside the electrode, and in the edge area of ​​the electrode, the active layer is more prone to cracking or material loss during battery manufacturing or use due to structural differences or uneven stress distribution. Summary of the Invention

[0004] In view of this, the present invention aims to at least partially solve one of the technical problems in the related art. To this end, the present invention provides a current collector-free electrode and battery. By providing a conductive layer on the surface of the active layer, the loss of electrode electronic conductivity due to the removal of the metal current collector is effectively compensated. Furthermore, the conductive layer is designed in zones to control the thickness relationship of each region, thereby improving the electrode's conductivity while also considering mechanical strength and energy density.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows: According to one aspect of the present invention, a current collectorless electrode sheet is provided, comprising an active layer, a conductive layer and a tab lead-out portion connected to the conductive layer, wherein the conductive layer is disposed on at least one surface in the thickness direction of the active layer, and the tab lead-out portion is disposed on the side surface of the conductive layer opposite to the active layer. The conductive layer includes a first conductive layer, a second conductive layer, and a third conductive layer arranged along the extension direction of the tab lead-out portion. The first conductive layer is located in the orthogonal projection region of the tab lead-out portion on the active layer along the thickness direction. The third conductive layer is located in the edge region away from the tab lead-out portion. The second conductive layer is located between the first conductive layer and the third conductive layer, and its two ends are respectively connected to the first conductive layer and the third conductive layer. The thickness of the first conductive layer is d1 in μm, the thickness of the second conductive layer is d2 in μm, and the thickness of the third conductive layer is d3 in μm, satisfying: d1 < d2 ≤ d3.

[0006] In some of these implementations, d2 and d3 satisfy the condition: d2 < d3.

[0007] In some of these embodiments, the thickness of the tab lead-out portion is D, in μm, which satisfies: 0.5×(D+d1)≤d2.

[0008] In some of these implementations, d3 satisfies: 0.8×(D+d1)≤d3≤D+d1.

[0009] In some of these implementations, d1 satisfies: 0.5μm≤d1≤2μm.

[0010] In some of these implementations, d2 satisfies: 1.5μm≤d2≤5μm.

[0011] In some of these implementations, d3 satisfies: 3μm≤d3≤8μm.

[0012] In some of these implementations, D satisfies: 3μm≤D≤6μm.

[0013] In some embodiments, the first conductive layer is composed of a first conductive agent and a first adhesive, the second conductive layer is composed of a second conductive agent and a second adhesive, and the third conductive layer is composed of a third conductive agent and a third adhesive; based on the total mass of the first conductive layer, the mass content of the first conductive agent is W1; based on the total mass of the second conductive layer, the mass content of the second conductive agent is W2; based on the total mass of the third conductive layer, the mass content of the third conductive agent is W3; satisfying: W1 > W2 > W3.

[0014] In some of these implementations, W1 satisfies: 50% ≤ W1 ≤ 60%.

[0015] In some of these implementations, W2 satisfies: 40% ≤ W2 ≤ 50%.

[0016] In some of these implementations, W3 satisfies: 30% ≤ W3 ≤ 40%.

[0017] In some embodiments, the first conductive agent comprises a first zero-dimensional conductive material and a first one-dimensional conductive material, with the mass content of the first one-dimensional conductive material being K1 based on the total mass of the first conductive agent; the second conductive agent comprises a second zero-dimensional conductive material and a second one-dimensional conductive material, with the mass content of the second one-dimensional conductive material being K2 based on the total mass of the second conductive agent; the third conductive agent comprises a third zero-dimensional conductive material and a third one-dimensional conductive material, with the mass content of the third one-dimensional conductive material being K3 based on the total mass of the third conductive agent; satisfying: K1 > K2 > K3.

[0018] In some of these implementations, K1 satisfies: 40% ≤ K1 ≤ 50%.

[0019] In some of these implementations, K2 satisfies: 20% ≤ K2 ≤ 30%.

[0020] In some of these implementations, K3 satisfies: 0% ≤ K3 ≤ 10%.

[0021] In some embodiments, the first zero-dimensional conductive material, the second zero-dimensional conductive material, and the third zero-dimensional conductive material each independently include at least one of carbon black and metal powder; the first one-dimensional conductive material, the second one-dimensional conductive material, and the third one-dimensional conductive material each independently include at least one of carbon nanotubes, carbon nanofibers, metal nanowires, and conductive polymer nanofibers; the first binder, the second binder, and the third binder each independently include at least one of polyvinylidene fluoride, a modified polyvinylidene fluoride, polyacrylate, and a modified polyacrylate.

[0022] In some embodiments, the active layer includes an active substance, a fourth binder, and a fourth conductive agent, and the thickness of the active layer is 60 μm to 100 μm; based on the total mass of the active layer, the mass content of the fourth binder is 1.5% to 3%, and the mass content of the fourth conductive agent is 1% to 2%.

[0023] In some embodiments, the active material includes at least one of carbon materials and carbon-coated silicon materials; the fourth binder includes at least one of polyacrylic acid, modified polyacrylic acid, styrene-butadiene rubber, and modified styrene-butadiene rubber; and the fourth conductive agent includes at least one of carbon black and metal powder.

[0024] According to another aspect of the present invention, the present invention provides a battery comprising a current collector-free electrode as described in any of the above-described technical solutions.

[0025] Implementing the technical solution of the present invention has at least the following beneficial effects: 1. By setting a conductive layer on the surface of the active layer, the loss of electrode electronic conductivity due to the removal of the metal current collector is effectively compensated, the overall internal resistance of the current collector-free electrode is reduced, thereby improving the rate performance of the battery using this electrode.

[0026] 2. This invention divides the conductive layer into a first conductive layer, a second conductive layer, and a third conductive layer, defining a relationship of d1 < d2 ≤ d3. This results in a controllable thickness difference between the second and third conductive layers relative to the first conductive layer in the extension direction of the tab lead. This thickness difference creates a stepped space that smoothly transitions from the surface of the first conductive layer to the surfaces of the second and third conductive layers. When the electrode and the tab lead are stacked and hot-pressed, this stepped space provides sufficient space to accommodate the thickness of the tab lead. This makes the thickness transition of the electrode at the termination edge of the tab lead smoother, effectively reducing the structural discontinuity caused by the introduction of the tab lead, dispersing the concentrated stress in this area during battery manufacturing or use, reducing the risk of bending and breakage of the active layer, and improving the stability of the conductive connection between the tab lead and the active layer. Furthermore, because the first conductive layer is relatively thin, it mitigates the adverse effects on the overall energy density of the battery caused by the conductive layer.

[0027] 3. By setting the third conductive layer located in the edge region of the electrode to its maximum thickness, the present invention enhances the mechanical binding strength of the electrode edge region, improves the adhesion stability of the edge active layer, and thus suppresses the occurrence of edge material loss.

[0028] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0029] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0030] Figure 1 This is a schematic diagram of a current collector-free electrode provided in an embodiment of the present invention.

[0031] Explanation of reference numerals in the attached figures: 1. Electrode lead-out section; 2. Active layer; 3. Conductive layer; 31. First conductive layer; 32. Second conductive layer; 33. Third conductive layer.

[0032] The accompanying drawings have illustrated specific embodiments of the invention, which will be described in more detail below. These drawings and descriptions are not intended to limit the scope of the invention in any way, but rather to illustrate the concept of the invention to those skilled in the art through reference to particular embodiments. Detailed Implementation

[0033] The present application will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0034] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0035] In the description of this application, "same chemical composition" should be interpreted broadly, that is, the main components of the two have the same chemical composition, or the two have substantially the same chemical composition, but may have errors or impurities within the acceptable range that can be understood by those skilled in the art.

[0036] In the description of this application, "A and / or B" can include any of the cases of A alone, B alone, or A and B, where A and B are merely examples and can be any technical feature connected by "and / or" in this application.

[0037] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0038] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0039] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0040] Unless otherwise specified, all steps of the present invention may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order; for example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0041] Currently, to improve battery energy density and fast charging capabilities, existing technologies have proposed solutions that eliminate the need for metal current collectors and directly form self-supporting electrode sheets without current collectors. However, due to the lack of a mechanically supporting framework provided by the metal current collector, the overall mechanical strength of the electrode sheet without current collectors is significantly insufficient.

[0042] During the actual research and development process, the inventors of this application discovered that, in order to compensate for the loss of electrode electronic conductivity due to the removal of the metal current collector, a conductive layer needs to be set on the surface of the active layer, and the current is conducted out through the tab lead-out portion. However, when the tab lead-out portion is laminated and connected to the electrode, due to the certain thickness of the tab lead-out portion itself, the active layer of the electrode is prone to cracking in the root region where the thickness of the tab lead-out portion disappears during the hot pressing process of battery manufacturing. At the same time, in the edge region of the electrode far from the tab lead-out portion, the active layer in this region is relatively weakly mechanically constrained, and cracking or material loss of the active layer is prone to occur during battery manufacturing or use, further affecting the manufacturing yield and reliability of the current collector-free electrode.

[0043] According to one aspect of the present invention, a current collectorless electrode sheet is provided, comprising an active layer, a conductive layer, and a tab lead-out portion connected to the conductive layer. The conductive layer is disposed on at least one surface of the active layer in the thickness direction, and the tab lead-out portion is disposed on the surface of the conductive layer opposite to the active layer. The conductive layer includes a first conductive layer, a second conductive layer, and a third conductive layer arranged along the extension direction of the tab lead-out portion. The first conductive layer is located within the orthographic projection region of the tab lead-out portion onto the active layer in the thickness direction. The third conductive layer is located in an edge region away from the tab lead-out portion. In this invention, the edge region refers to the edge region of the active layer on the side opposite to the tab lead-out portion in the extension direction of the tab lead-out portion. The second conductive layer is located between the first and third conductive layers, and both ends of the second conductive layer are respectively connected to the first and third conductive layers. The thickness of the first conductive layer is d1, the thickness of the second conductive layer is d2, and the thickness of the third conductive layer is d3, all in μm, and the thicknesses of the three conductive layers satisfy: d1 < d2 ≤ d3. See details below. Figure 1 As shown, Figure 1 This is a schematic diagram of a current collectorless electrode provided in an embodiment of the present invention, wherein 1 is the electrode lead-out part, 2 is the active layer, 3 is the conductive layer, 31 is the first conductive layer, 32 is the second conductive layer, and 33 is the third conductive layer.

[0044] In this invention, the current collector-less electrode eliminates the need for a metal current collector, and the active layer and conductive layer form a self-supporting structure. The conductive layer compensates for electronic conductivity, and the tab lead-out portion is used to guide current out of the electrode. Based on this, by dividing the conductive layer into a first conductive layer, a second conductive layer, and a third conductive layer, and defining the relationship d1 < d2 ≤ d3, a controllable thickness difference is formed between the second and third conductive layers relative to the first conductive layer in the extension direction of the tab lead-out portion. This thickness difference constructs a stepped space that smoothly transitions from the surface of the first conductive layer to the surfaces of the second and third conductive layers. When the electrode and the tab lead-out portion are stacked and hot-pressed, this stepped space provides room for the thickness of the tab lead-out portion, making the thickness transition of the electrode at the termination edge of the tab lead-out portion more gradual. This effectively reduces the structural discontinuity caused by the introduction of the tab lead-out portion, thereby dispersing the concentrated stress in this area and reducing the risk of bending and breakage of the active layer. Simultaneously, the thinner first conductive layer reduces the adverse effects on the overall energy density of the battery caused by the conductive layer. The third conductive layer has the largest thickness, which enhances the mechanical binding strength of the electrode edge area and reduces the probability of edge chipping.

[0045] In a specific embodiment of the present invention, the thickness d2 of the second conductive layer and the thickness d3 of the third conductive layer further satisfy d2 < d3. Thus, a thickness difference is formed between the second and third conductive layers, which facilitates the formation of tiny gaps between the conductive layer in the corresponding region of the second conductive layer and adjacent electrodes, thereby improving the battery's electrolyte retention capacity and enhancing its long-cycle performance.

[0046] In a specific embodiment of the present invention, the tab lead-out portion is used to connect the conductive layer and the battery terminal, thereby realizing the output of the electrode current. The tab lead-out portion is disposed on the side surface of the conductive layer opposite to the active layer. In the electrode stack structure, the tab lead-out portion is sandwiched between two adjacent electrode sheets without current collectors and is connected to the conductive layer by hot pressing. The thickness D of the tab lead-out portion is preferably 3μm~6μm, specifically it can be: 3μm, 3.3μm, 4.1μm, 4.7μm, 5.6μm, 6μm, or any value between two of these. By controlling D within the above range, the present invention can control the structural discontinuity introduced by the tab lead-out portion inside the electrode sheet while ensuring the conductive cross-sectional area and mechanical strength of the tab lead-out portion.

[0047] In a specific embodiment of the present invention, the tab lead-out portion has a thickness D, in μm. The thickness d2 of the second conductive layer satisfies 0.5×(D+d1)≤d2. When d2 is less than 0.5×(D+d1), the thickness of the second conductive layer is too small, making it difficult to provide sufficient thickness compensation for the end edge of the tab lead-out portion located inside the electrode, and the electrode is at risk of collapse and breakage in the corresponding region of the second conductive layer. Therefore, by controlling d2 to satisfy the above range, the mechanical support strength of the electrode in the corresponding region of the second conductive layer can be improved, reducing the risk of collapse and breakage in the middle.

[0048] In a specific embodiment of the present invention, the thickness d3 of the third conductive layer satisfies 0.8×(D+d1)≤d3≤D+d1. When d3 is less than 0.8×(D+d1), the thickness of the third conductive layer is too small, resulting in insufficient mechanical binding strength at the electrode edge, which can easily lead to material loss due to insufficient edge adhesion. When d3 is greater than D+d1, the thickness of the third conductive layer is too large, which will reduce the energy density of the battery. Therefore, by controlling d3 to meet the above range, the mechanical binding strength at the electrode edge can be improved while maintaining the energy density of the battery.

[0049] In a specific embodiment of the present invention, the thickness d1 of the first conductive layer is preferably 0.5 μm to 2 μm, specifically 0.5 μm, 0.7 μm, 1.2 μm, 1.3 μm, 1.7 μm, 1.9 μm, 2 μm, or any value between two of these. By controlling d1 within the above range, the present invention can reduce manufacturing difficulty and mitigate the adverse effects on battery energy density caused by the presence of the first conductive layer.

[0050] In a specific embodiment of the present invention, the thickness d2 of the second conductive layer is preferably 1.5 μm to 5 μm, specifically 1.5 μm, 1.7 μm, 2.3 μm, 2.8 μm, 3.1 μm, 3.6 μm, 4.2 μm, 4.8 μm, 5 μm, or any value between two of these. By controlling d2 within the above range, the present invention can improve the mechanical support strength of the electrode in the corresponding region of the second conductive layer and provide suitable electrolyte storage space, thereby further improving the long-cycle performance of the battery.

[0051] In a specific embodiment of the present invention, the thickness d3 of the third conductive layer is preferably 3μm to 8μm, specifically 3μm, 3.2μm, 4.5μm, 5.1μm, 5.8μm, 6.3μm, 7.6μm, 8μm, or any value between two of these. By controlling d3 within the above range, the present invention can improve the mechanical binding strength of the electrode edge region while maintaining the energy density of the battery.

[0052] In a specific embodiment of the present invention, the first conductive layer is composed of a first conductive agent and a first adhesive, the second conductive layer is composed of a second conductive agent and a second adhesive, and the third conductive layer is composed of a third conductive agent and a third adhesive. Based on the total mass of the first conductive layer, the mass content of the first conductive agent is W1. Based on the total mass of the second conductive layer, the mass content of the second conductive agent is W2. Based on the total mass of the third conductive layer, the mass content of the third conductive agent is W3. The conductive agent contents of the three conductive layers satisfy the following order: W1 > W2 > W3.

[0053] Because the current density is higher near the tab lead during charging and discharging, and decreases towards the direction away from the tab lead, controlling the conductive agent content to decrease gradually from the first conductive layer to the third conductive layer can match the current density distribution, which is beneficial to improving the battery's dynamic performance. Simultaneously, the third conductive layer has the highest binder content, which helps enhance the adhesion of the conductive layer to the electrode edge area and further suppresses edge shedding. The second conductive layer has the second highest binder content, which helps improve the liquid retention capacity in this area.

[0054] In a specific embodiment of the present invention, W1 is preferably 50% to 60%, specifically 50%, 51%, 53%, 54%, 58%, 59%, 60%, or any value between two of these. By controlling W1 within the above range, the present invention can improve the current-carrying capacity of the first conductive layer while reducing the risk of conductive layer detachment.

[0055] In a specific embodiment of the present invention, W2 is preferably 40% to 50%, specifically 40%, 41%, 43%, 44%, 48%, 49%, 50%, or any value between two of these. By controlling W2 within the above range, the present invention ensures that the second conductive layer has sufficient conductivity while retaining an appropriate amount of binder to maintain the structural stability of the conductive layer in this region. This facilitates the formation of tiny voids in the corresponding region of the second conductive layer that can store electrolyte, thereby improving the battery's electrolyte retention capacity and long-cycle performance.

[0056] In a specific embodiment of the present invention, W3 is preferably 30% to 40%, specifically 30%, 31%, 33%, 35%, 38%, 39%, 40%, or any value between two of these. By controlling W3 within the above range, the present invention can improve the current-carrying capacity of the third conductive layer, while enhancing the adhesion stability of the electrode edge region and suppressing edge shedding.

[0057] In a specific embodiment of the present invention, the first conductive agent includes a first zero-dimensional conductive material and a first one-dimensional conductive material, with the mass content of the first one-dimensional conductive material being K1 based on the total mass of the first conductive agent. The second conductive agent includes a second zero-dimensional conductive material and a second one-dimensional conductive material, with the mass content of the second one-dimensional conductive material being K2 based on the total mass of the second conductive agent. The third conductive agent includes a third zero-dimensional conductive material and a third one-dimensional conductive material, with the mass content of the third one-dimensional conductive material being K3 based on the total mass of the third conductive agent. The content of the one-dimensional conductive material in the total mass of the conductive agent in the three conductive layers satisfies the following order: K1 > K2 > K3.

[0058] Zero-dimensional conductive materials refer to conductive materials in which the conductive particles are all on the nanometer to micrometer scale in all three dimensions. The first zero-dimensional conductive material, the second zero-dimensional conductive material, and the third zero-dimensional conductive material each independently include at least one of carbon black and metal powder.

[0059] One-dimensional conductive materials refer to fibrous or tubular conductive materials whose conductive particles are nanoscale in two dimensions and micrometer scale in one dimension. First-dimensional conductive materials, second-dimensional conductive materials, and third-dimensional conductive materials each independently include at least one of carbon nanotubes, carbon nanofibers, metal nanowires, and conductive polymer nanofibers.

[0060] A conductive network composed of both one-dimensional and zero-dimensional conductive materials is more complete and has stronger conductivity than a conductive network composed only of zero-dimensional conductive materials. By controlling K1 > K2 > K3, the first conductive layer has the highest proportion of one-dimensional conductive material, which can form an optimal conductive network in the area covered by the tab lead-out part with the highest current density, thus improving the dynamic performance of the battery.

[0061] In a specific embodiment of the present invention, K1 satisfies 40% ≤ K1 ≤ 50%. When K1 is less than 40%, the proportion of one-dimensional conductive material in the first conductive layer is too low, resulting in insufficient integrity of the conductive network. When K1 is greater than 50%, the proportion of one-dimensional conductive material in the first conductive layer is too high. Since one-dimensional conductive materials typically have a large specific surface area, they consume more active lithium, which is detrimental to further improving the cycle performance of the battery. Therefore, by controlling K1 within the range of 40% to 50%, the conductivity of the first conductive layer can be improved, while reducing the adverse effects on cycle performance. For example, K1 can be 40%, 41%, 43%, 45%, 46%, 49%, 50%, or a value within any two of the above values.

[0062] In a specific embodiment of the present invention, K2 satisfies 20% ≤ K2 ≤ 30%. When K2 is less than 20%, the proportion of one-dimensional conductive material in the second conductive layer is too low, resulting in insufficient integrity of the conductive network. When K2 is greater than 30%, the proportion of one-dimensional conductive material is too high. Furthermore, the gap between the two opposing second conductive layers stores electrolyte, making side reactions more likely and consuming excessive active lithium, which is detrimental to further improvement of cycle performance. Therefore, by controlling K2 within the range of 20% to 30%, the conductivity of the second conductive layer can be improved while reducing the adverse effects on cycle performance. For example, K2 can be 20%, 21%, 22%, 25%, 27%, 28%, 30%, or a value within any two of the above ranges.

[0063] In a specific embodiment of the present invention, K3 satisfies 0% ≤ K3 ≤ 10%. By controlling K3 within the range of 0% to 10%, the conductivity requirements of the third conductive layer can be met while reducing the amount of one-dimensional conductive material, thereby reducing the manufacturing cost of the electrode. For example, K3 can be 0%, 1%, 4%, 5%, 8%, 10%, or a value within any two of the above values.

[0064] In a specific embodiment of the present invention, the first adhesive, the second adhesive, and the third adhesive each independently include at least one of polyvinylidene fluoride and its modified forms, and polyacrylate and its modified forms. The aforementioned adhesives are thermoplastic and can soften and flow during hot pressing, thereby achieving an adhesive connection between the conductive layer and the tab lead-out portion. After hot pressing, the aforementioned adhesives are re-cured to maintain the connection strength between the conductive layer and the tab lead-out portion.

[0065] In a specific embodiment of the present invention, the active layer includes an active material, a fourth binder, and a fourth conductive agent. The thickness of the active layer is preferably 60 μm to 100 μm, specifically 60 μm, 67 μm, 73 μm, 77 μm, 85 μm, 94 μm, 100 μm, or any value between two of these. Due to the relatively large thickness of the active layer, to ensure the bonding strength between the active layer particles, the mass content of the fourth binder, based on the total mass of the active layer, is preferably 1.5% to 3%, specifically 1.5%, 1.7%, 2.2%, 2.4%, 2.7%, 3%, or any value between two of these. When the content of the fourth binder is less than 1.5%, the bonding between the active layer particles is insufficient, easily leading to processing problems such as powder shedding. When the content of the fourth binder is greater than 3%, it will reduce the energy density of the battery. Meanwhile, to ensure sufficient conductive pathways between the active material particles, the mass content of the fourth conductive agent is preferably 1% to 2% based on the total mass of the active layer, specifically 1%, 1.1%, 1.4%, 1.5%, 1.8%, 2%, or any value between two of these. By controlling the active layer thickness, the content of the fourth binder, and the content of the fourth conductive agent within the above ranges, this invention can further improve the structural strength of the electrode and enhance the cycle performance and rate performance of the battery.

[0066] In a specific embodiment of the present invention, the active material includes at least one of carbon materials and carbon-coated silicon materials. The fourth binder includes at least one of polyacrylic acid and its modified forms, and styrene-butadiene rubber and its modified forms. The fourth conductive agent includes at least one of carbon black and metal powder.

[0067] According to another aspect of the present invention, a battery is provided, comprising a current collector-less electrode sheet as described in any of the above embodiments. In this invention, the current collector-less electrode sheet can be used as either a positive or negative electrode sheet, and those skilled in the art can choose according to actual needs. When the current collector-less electrode sheet is used as a negative electrode sheet, the battery further includes a positive electrode sheet and a separator; when the current collector-less electrode sheet is used as a positive electrode sheet, the battery further includes a negative electrode sheet and a separator. Due to the use of the current collector-less electrode sheet in the above embodiments of this application, the battery exhibits improved structural strength, cycle performance, and rate performance.

[0068] The present application will be described in detail below with reference to the accompanying drawings and embodiments. However, the implementation and protection of the present invention are not limited thereto. The following embodiments are only some embodiments of the present application and are not intended to limit the present application. Where specific techniques or conditions are not specified in the embodiments, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0069] Example 1 (1) Preparation of current collector-less negative electrode: 94.5 wt% artificial graphite, 2 wt% SBR, 2 wt% SP, and 1.5 wt% CMC were added to a certain amount of deionized water and stirred continuously until homogeneous to obtain a negative electrode slurry. The negative electrode slurry was then uniformly coated onto a glass plate using a coating machine to a thickness of 100 μm, and after high-temperature drying, an active layer was formed.

[0070] The first conductive layer slurry is formulated with 24.75 wt% carbon nanotubes, 30.25 wt% carbon black (SP), and 45 wt% PVDF. Carbon nanotubes, SP, and PVDF are added to a certain amount of NMP according to the above mass ratio and mixed evenly to obtain the first conductive layer slurry.

[0071] The second conductive layer slurry is formulated with 11.25 wt% carbon nanotubes, 33.75 wt% SP, and 55 wt% PVDF. Carbon nanotubes, SP, and PVDF are added to a certain amount of NMP according to the above mass ratio and mixed thoroughly to obtain the second conductive layer slurry.

[0072] The third conductive layer slurry is formulated with 1.75 wt% carbon nanotubes, 33.25 wt% SP, and 65 wt% PVDF. Carbon nanotubes, SP, and PVDF are added to a certain amount of NMP according to the above mass ratio and mixed thoroughly to obtain the third conductive layer slurry.

[0073] The first, second, and third conductive layer slurries are coated onto the surface of the active layer in sections. After high-temperature drying, they are removed from the glass plate to obtain a single current collector-free electrode. The coating thickness of the first conductive layer is 1 μm, the second conductive layer is 3 μm, and the third conductive layer is 5 μm. Two of the above-mentioned current collector-free electrode sheets are taken, and a tab with a thickness of 4.5 μm is sandwiched between the two current collector-free electrode sheets, with the tab facing the surface of the two current collector-free electrode sheets coated with the first conductive layer. The sheets are then pressed to a thickness of 65 μm using a roller press to obtain a current collector-free negative electrode. In the first conductive layer, the conductive agent content W1 is 55%, and the one-dimensional conductive material content K1 is 45%; in the second conductive layer, the conductive agent content W2 is 45%, and the one-dimensional conductive material content K2 is 25%; in the third conductive layer, the conductive agent content W3 is 35%, and the one-dimensional conductive material content K3 is 5%.

[0074] (2) Preparation of the positive electrode: 96.8 wt% lithium iron phosphate, 2 wt% PVDF, 1 wt% SP and 0.2 wt% PVP were added to a certain amount of NMP and continuously stirred until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was uniformly coated onto an aluminum foil current collector using a coating machine, with a coating thickness of 130 μm on the aluminum foil current collector side. After high-temperature drying, it was pressed to a thickness of 75 μm using a roller press to obtain the positive electrode sheet.

[0075] (3) Electrolyte preparation: EC, EMC, and DMC were mixed uniformly in a volume ratio of 1:1:1 to form a solvent. 1 mol / L LiPF6 was then dissolved in the solvent to obtain the electrolyte.

[0076] (4) Battery assembly: The above-mentioned current collector-free negative electrode, positive electrode and separator are assembled into a core, wherein the separator is a polypropylene porous separator. After encapsulation, the above-mentioned electrolyte is injected, and after formation and capacity testing, a battery is obtained.

[0077] In the context of this specification, including the following embodiments and comparative examples, tests were conducted in the following manner: (1) The test method for 5C energy retention is as follows: the battery is left to stand at 25℃ for 1 hour, charged at 1C constant current to 3.65V, charged at constant voltage to current ≤0.05C; discharged at 1C constant current to 2.5V, and marked with energy E1; charged at 1C constant current to 3.65V, charged at constant voltage to current ≤0.05C; discharged at 5C constant current to 2.5V, and marked with energy E2; the 5C energy retention rate of the battery is calculated by E2 / E1×100%.

[0078] (2) The test method for cycle performance is as follows: the battery is placed at 25℃ for 1 hour, charged at 1C constant current to 3.65V, charged at constant voltage to current ≤0.05C; discharged at 1C constant current to 2.5V; the constant current discharge capacity of each time is recorded and marked as Q1 to Qn respectively; the capacity retention rate is calculated by dividing the constant current discharge capacity of each time by the first discharge capacity: Rn=Qn / Q1×100%; the last cycle when the capacity retention rate is ≥80% is taken as the cycle number.

[0079] The test results are shown in Table 1 below.

[0080] Example 2 The preparation method provided in Example 1 is used, with the only difference being that the coating thickness of the first conductive layer is 0.5 μm, the coating thickness of the second conductive layer is 2.5 μm, and the coating thickness of the third conductive layer is 4.5 μm.

[0081] Example 3 The preparation method provided in Example 1 is used, with the only difference being that the coating thickness of the first conductive layer is 2 μm, the coating thickness of the second conductive layer is 4 μm, and the coating thickness of the third conductive layer is 6 μm.

[0082] Example 4 The preparation method provided in Example 1 is adopted, with the only difference being that the mass ratio of carbon nanotubes, SP and binder in the first conductive layer slurry is 27:33:40, so that the conductive agent content W1 in the first conductive layer is 60% and the proportion of one-dimensional conductive material K1 is 50%.

[0083] Example 5 The preparation method provided in Example 1 is adopted, with the only difference being that the mass ratio of carbon nanotubes, SP and binder in the first conductive layer slurry is 20:30:50, so that the conductive agent content W1 in the first conductive layer is 50% and the proportion of one-dimensional conductive material K1 is 40%.

[0084] Example 6 The preparation method provided in Example 1 is adopted, with the only difference being that the mass ratio of carbon nanotubes, SP and binder in the second conductive layer slurry is 15:35:50, so that the content of conductive agent W2 in the second conductive layer is 50% and the proportion of one-dimensional conductive material K2 is 30%.

[0085] Example 7 The preparation method provided in Example 1 is adopted, with the only difference being that the mass ratio of carbon nanotubes, SP and binder in the second conductive layer slurry is 8:32:60, so that the content of conductive agent W2 in the second conductive layer is 40% and the proportion of one-dimensional conductive material K2 is 20%.

[0086] Example 8 The preparation method provided in Example 1 is adopted, with the only difference being that the mass ratio of carbon nanotubes, SP and binder in the third conductive layer slurry is 4:36:60, so that the content of conductive agent W3 in the third conductive layer is 40% and the proportion of one-dimensional conductive material K3 is 10%.

[0087] Example 9 The preparation method provided in Example 1 is adopted, with the only difference being that the mass ratio of carbon nanotubes, SP and binder in the third conductive layer slurry is 0:30:70, so that the content of conductive agent W3 in the third conductive layer is 30% and the proportion of one-dimensional conductive material K3 is 0%.

[0088] Example 10 The preparation method provided in Example 1 is used, with the only difference being that the coating thickness of the first conductive layer is 0.3 μm.

[0089] Example 11 The preparation method provided in Example 1 is used, with the only difference being that the coating thickness of the first conductive layer is 2.2 μm and the coating thickness of the third conductive layer is 6 μm.

[0090] Example 12 The preparation method provided in Example 1 is adopted, with the only difference being that the mass ratio of carbon nanotubes, SP and binder in the first conductive layer slurry is 15.75:29.25:55, so that the conductive agent content W1 in the first conductive layer is 45% and the proportion of one-dimensional conductive material K1 is 35%.

[0091] Example 13 The preparation method provided in Example 1 is adopted, with the only difference being that the mass ratio of carbon nanotubes, SP and binder in the first conductive layer slurry is 35.75:29.25:35, so that the conductive agent content W1 in the first conductive layer is 65% and the proportion of one-dimensional conductive material K1 is 55%.

[0092] Example 14 The preparation method provided in Example 1 is adopted, with the only difference being that the mass ratio of carbon nanotubes, SP and binder in the second conductive layer slurry is 5.25:29.75:65, so that the conductive agent content W2 in the second conductive layer is 35% and the proportion of one-dimensional conductive material K2 is 15%.

[0093] Example 15 The preparation method provided in Example 1 is adopted, with the only difference being that the mass ratio of carbon nanotubes, SP and binder in the second conductive layer slurry is 19.25:35.75:45, so that the conductive agent content W2 in the second conductive layer is 55% and the proportion of one-dimensional conductive material K2 is 35%.

[0094] Example 16 The preparation method provided in Example 1 is used, with the only difference being that the coating thickness of the third conductive layer is 8.5 μm.

[0095] Example 17 The preparation method provided in Example 1 is adopted, with the only difference being that the mass ratio of carbon nanotubes, SP and binder in the third conductive layer slurry is 0:20:80, so that the content of conductive agent W3 in the third conductive layer is 20% and the proportion of one-dimensional conductive material K3 is 0%.

[0096] Example 18 The preparation method provided in Example 1 is adopted, with the only difference being that the mass ratio of carbon nanotubes, SP and binder in the third conductive layer slurry is 6.75:38.25:55, so that the conductive agent content W3 in the third conductive layer is 45% and the proportion of one-dimensional conductive material K3 is 15%.

[0097] Comparative Example 1 The preparation method provided in Example 1 is used, with the only difference being that the coating thickness of the second conductive layer is 1 μm.

[0098] Comparative Example 2 The preparation method provided in Example 1 is used, with the only difference being that the coating thickness of the second conductive layer is 6 μm.

[0099] Comparative Example 3 The preparation method provided in Example 1 is used, with the only difference being that the coating thickness of the third conductive layer is 2.5 μm.

[0100] Table 1 Test results of the examples and comparative examples It should be noted that in Example 10, d1 was 0.3 μm, which increased the difficulty of the coating process, resulting in missed coating or over-coating, and no valid test data was obtained; in Example 16, d3 was 8.5 μm, and large-area cracks appeared on the electrode, and no valid test data was obtained; in Comparative Example 1, d2 was 1 μm, which did not satisfy d1 < d2, and large-area cracks appeared on the electrode; in Comparative Example 2, d2 was 6 μm, which did not satisfy d2 ≤ d3, and the electrode tab lead-out part fell off; in Comparative Example 3, d3 was 2.5 μm, which did not satisfy d2 ≤ d3, and the electrode end edge lost material, and no valid test data was obtained in any of these cases.

[0101] As shown in Table 1, in Comparative Example 1, d2 is 1 μm, which does not satisfy d1 < d2. The excessive thickness difference between the first and second conductive layers leads to large-area cracks in the electrode sheet after rolling. In Comparative Example 2, d2 is 6 μm, which does not satisfy d2 ≤ d3. The thickness of the second conductive layer is greater than that of the third conductive layer, creating a gap between the tab lead-out portion and the first conductive layer, causing the tab lead-out portion to detach. In Comparative Example 3, d3 is 2.5 μm, which does not satisfy d2 ≤ d3. The thickness of the third conductive layer is too small, resulting in poor surface adhesion between the two electrode sheets without current collectors after rolling, leading to edge chipping. These results indicate that controlling the relationship d1 < d2 ≤ d3 plays a crucial role in maintaining the structural integrity of the electrode sheet.

[0102] It is worth noting that in Example 10, d1 is 0.3 μm, which is lower than the lower limit of the preferred range. During the coating process, incomplete or over-coating occurred, increasing the manufacturing difficulty and making it impossible to obtain effective electrical performance data. In Example 11, d1 is 2.2 μm, which is higher than the upper limit of the preferred range. Its 5C energy retention rate is improved compared to Example 1, but due to the increased total amount of conductive agent and increased consumption of active lithium, its cycle performance is significantly lower than that of Example 1. In Example 12, W1 and K1 are lower than the preferred range. The content of conductive agent and the proportion of one-dimensional conductive material in the first conductive layer are low, resulting in insufficient integrity of the conductive network. Therefore, its 5C energy retention rate is significantly lower than that of Example 1. In Example 13, W1 and K1 are higher than the preferred range. The total amount of conductive agent and the proportion of one-dimensional conductive material in the first conductive layer are too high, increasing the specific surface area and increasing the consumption of active lithium. Therefore, its cycle performance is significantly lower than that of Example 1. In Example 16, d3 is 8.5 μm, which is higher than the upper limit of the preferred range. Large-area cracks appear on the electrode, making it impossible to obtain effective electrical performance data. In Example 17, W3 is below the preferred range, the content of conductive agent in the third conductive layer is too low, and the current carrying capacity is insufficient. Therefore, its 5C energy retention rate is significantly lower than that of Example 1. In Example 18, W3 and K3 are above the preferred range, the total amount of conductive agent and the proportion of one-dimensional conductive material in the third conductive layer are too high, and the consumption of active lithium increases. Therefore, its cycle performance is significantly lower than that of Example 1.

[0103] The parts of this invention not described in detail are techniques known to those skilled in the art.

[0104] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0105] In the foregoing description of this specification, references to terms such as "one embodiment," "another embodiment," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment is included in at least one embodiment of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples, without contradiction. Additionally, it should be noted that in this specification, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features.

[0106] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A current collector-free electrode, characterized in that, It includes an active layer, a conductive layer, and a tab lead-out portion connected to the conductive layer. The conductive layer is disposed on at least one surface in the thickness direction of the active layer, and the tab lead-out portion is disposed on the side surface of the conductive layer opposite to the active layer. The conductive layer includes a first conductive layer, a second conductive layer, and a third conductive layer arranged along the extension direction of the tab lead-out portion. The first conductive layer is located in the orthogonal projection region of the tab lead-out portion on the active layer along the thickness direction. The third conductive layer is located in the edge region away from the tab lead-out portion. The second conductive layer is located between the first conductive layer and the third conductive layer, and its two ends are respectively connected to the first conductive layer and the third conductive layer. The thickness of the first conductive layer is d1 in μm, the thickness of the second conductive layer is d2 in μm, and the thickness of the third conductive layer is d3 in μm, satisfying: d1 < d2 ≤ d3.

2. The current collector-free electrode according to claim 1, characterized in that, The condition d2 and d3 satisfy: d2 < d3; And / or, the thickness of the electrode lead-out portion is D, in μm, satisfying: 0.5×(D+d1)≤d2; And / or, 0.8×(D+d1)≤d3≤D+d1.

3. The current collector-free electrode according to claim 2, characterized in that, The d1 satisfies: 0.5μm≤d1≤2μm; And / or, the d2 satisfies: 1.5μm≤d2≤5μm; And / or, the d3 satisfies: 3μm≤d3≤8μm; And / or, the D satisfies: 3μm≤D≤6μm.

4. The current collector-free electrode according to any one of claims 1 to 3, characterized in that, The first conductive layer is composed of a first conductive agent and a first adhesive, the second conductive layer is composed of a second conductive agent and a second adhesive, and the third conductive layer is composed of a third conductive agent and a third adhesive; based on the total mass of the first conductive layer, the mass content of the first conductive agent is W1; Based on the total mass of the second conductive layer, the mass content of the second conductive agent is W2; Based on the total mass of the third conductive layer, the mass content of the third conductive agent is W3; The following condition must be met: W1 > W2 > W3.

5. The current collector-free electrode according to claim 4, characterized in that, The condition W1 satisfies: 50% ≤ W1 ≤ 60%; And / or, W2 satisfies: 40% ≤ W2 ≤ 50%; And / or, W3 satisfies: 30% ≤ W3 ≤ 40%.

6. The current collector-free electrode according to claim 4, characterized in that, The first conductive agent comprises a first zero-dimensional conductive material and a first one-dimensional conductive material, with the mass content of the first one-dimensional conductive material being K1 based on the total mass of the first conductive agent; the second conductive agent comprises a second zero-dimensional conductive material and a second one-dimensional conductive material, with the mass content of the second one-dimensional conductive material being K2 based on the total mass of the second conductive agent; the third conductive agent comprises a third zero-dimensional conductive material and a third one-dimensional conductive material, with the mass content of the third one-dimensional conductive material being K3 based on the total mass of the third conductive agent. The following condition must be met: K1 > K2 > K3.

7. The current collector-free electrode according to claim 6, characterized in that, The condition K1 satisfies: 40%≤K1≤50%; And / or, K2 satisfies: 20% ≤ K2 ≤ 30%; And / or, K3 satisfies: 0%≤K2≤10%.

8. The current collector-free electrode according to claim 6, characterized in that, The first zero-dimensional conductive material, the second zero-dimensional conductive material, and the third zero-dimensional conductive material each independently include at least one of carbon black and metal powder; the first one-dimensional conductive material, the second one-dimensional conductive material, and the third one-dimensional conductive material each independently include at least one of carbon nanotubes, carbon nanofibers, metal nanowires, and conductive polymer nanofibers; the first binder, the second binder, and the third binder each independently include at least one of polyvinylidene fluoride, modified polyvinylidene fluoride, polyacrylate, and modified polyacrylate.

9. The current collectorless electrode sheet according to any one of claims 1 to 8, characterized in that, The active layer comprises an active substance, a fourth binder, and a fourth conductive agent, and the thickness of the active layer is 60 μm to 100 μm; based on the total mass of the active layer, the mass content of the fourth binder is 1.5% to 3%, and the mass content of the fourth conductive agent is 1% to 2%. The active material includes at least one of carbon materials and carbon-coated silicon materials; the fourth binder includes at least one of polyacrylic acid, modified polyacrylic acid, styrene-butadiene rubber, and modified styrene-butadiene rubber; the fourth conductive agent includes at least one of carbon black and metal powder.

10. A battery, characterized in that, Includes the current collectorless electrode as described in any one of claims 1 to 9.

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