Current collector, electrode sheet, and electrochemical device

Abstract

This application discloses a current collector, an electrode, and an electrochemical device. The current collector includes a first conductive layer, a first support layer, a second conductive layer, a second support layer, and a third conductive layer stacked sequentially along the thickness direction. The first conductive layer has a plurality of first countersunk holes on its surface opposite to the first support layer, the first countersunk holes penetrating the first support layer and extending at least partially to the second conductive layer. The third conductive layer has a plurality of second countersunk holes on its surface opposite to the second support layer, the second countersunk holes penetrating the second support layer and extending at least partially to the second conductive layer. The first countersunk holes are not connected to the second countersunk holes. This application utilizes the mechanical strength of the support layer to suppress structural deformation caused by the volume expansion and contraction of the electrode material during charging and discharging, avoiding the interlayer delamination problem caused by insufficient bonding strength between a single support layer and the conductive layer in traditional three-layer composite current collectors. Furthermore, the three conductive layers construct a three-dimensional conductive network, significantly reducing the overall resistivity of the current collector and improving the uniformity of current conduction.

Description

Technical Field

[0001] This application relates to the field of electrochemical devices, and in particular to a current collector, an electrode, and an electrochemical device. Background Technology

[0002] In the battery field, current collectors are key components that determine battery energy density, cycle life, and safety performance. Traditional metal foil current collectors, due to their high density and susceptibility to lithium plating and short circuits, are unable to meet the demands of new energy vehicles, energy storage power stations, and other applications for lightweight and high-safety batteries. As a result, composite current collectors have become a core research and development direction in the industry.

[0003] To achieve lightweighting and reduce metal usage, existing current collectors adopt a three-layer composite structure of metal-polymer-metal. By replacing part of the metal with polymer substrates (such as PET and PP), the areal density of the current collector can be reduced to achieve the goal of lightweighting, and the flexibility of polymer materials can be used to improve processing performance.

[0004] However, this structure has the following drawbacks when adapted to high-performance electrode materials such as silicon-carbon anodes: Due to the lithium storage mechanism, the volume expansion rate of silicon-carbon anodes often exceeds 300% during charge and discharge, and the repeated expansion and contraction processes cause continuous and severe impacts on the interface between the current collector and the active material. Furthermore, the low bonding strength between the metal layer and the polymer layer in the three-layer structure makes them susceptible to interlayer delamination under expansion forces, directly leading to a sharp drop in the conductivity of the current collector and a surge in the battery's internal resistance, thus affecting the battery's safety and cycle performance. Utility Model Content

[0005] The main purpose of this application is to propose a current collector, electrode, and electrochemical device, which aims to solve the technical problem that existing current collectors have weak bonding between the metal layer and the polymer layer, making them susceptible to interlayer peeling due to expansion forces, resulting in decreased conductivity and increased internal resistance.

[0006] To achieve the above objectives, this application proposes a current collector, comprising a first conductive layer, a first support layer, a second conductive layer, a second support layer, and a third conductive layer stacked sequentially along the thickness direction;

[0007] The first conductive layer has a plurality of first countersunk holes on its surface away from the first support layer. The first countersunk holes penetrate the first support layer and extend at least partially to the second conductive layer.

[0008] The third conductive layer has a plurality of second countersunk holes on its surface away from the second support layer. The second countersunk holes penetrate the second support layer and extend at least partially into the second conductive layer.

[0009] The first countersunk hole is not connected to the second countersunk hole.

[0010] In some embodiments, the projection area of ​​the first countersunk hole in the thickness direction of the current collector is offset from the projection area of ​​the second countersunk hole in the thickness direction of the current collector.

[0011] In some embodiments, the first countersunk hole and the second countersunk hole are alternately spaced along the length direction of the current collector.

[0012] In some embodiments, the minimum distance between the first countersunk hole and the second countersunk hole is D, and the diameters of both the first and second countersunk holes are Φ, satisfying the following relationship:

[0013] D>max{2Φ,6T1,6T2};

[0014] Wherein, 40μm≤Φ≤200μm, T1 is the thickness of the first support layer, and T2 is the thickness of the second support layer.

[0015] In some embodiments, the inner walls of the first and / or second countersunk holes are coated with a gel layer.

[0016] In some embodiments, the depth of the first countersunk hole is H1, and the depth of the second countersunk hole is H2, respectively satisfying the following relationships:

[0017] H1 = T1 + T3 + T4 - δ;

[0018] H2 = T2 + T4 + T5 - δ;

[0019] Where 0um < δ ≤ 0.5um, T1 is the thickness of the first support layer, T2 is the thickness of the second support layer, T3 is the thickness of the first conductive layer, T4 is the thickness of the second conductive layer, and T5 is the thickness of the third conductive layer.

[0020] In some embodiments, the diameter of the first countersunk hole and / or the second countersunk hole is 40um-200um.

[0021] In some embodiments, the pore density of the first countersunk hole and / or the second countersunk hole is 5 pores / mm. 2 -100 pieces / mm 2 The pore density is any 1 mm of the current collector surface. 2 The number of the first countersunk holes or the second countersunk holes within the area.

[0022] This application also provides an electrode sheet, comprising:

[0023] current collector;

[0024] An active material layer is coated on at least one side surface of the current collector.

[0025] This application also provides an electrochemical device, including a cathode electrode, an anode electrode, and a diaphragm, wherein the diaphragm is disposed between the cathode electrode and the anode electrode.

[0026] The current collector of this application adopts a five-layer composite structure design consisting of a first conductive layer, a first support layer, a second conductive layer, a second support layer, and a third conductive layer. With the double support layer as the core framework, it not only uses the mechanical strength of the support layer to suppress the structural deformation caused by the volume expansion and contraction of the electrode material (such as silicon-carbon anode) during charging and discharging, but also avoids the interlayer delamination problem caused by insufficient bonding strength between the single support layer and the conductive layer in traditional three-layer composite current collectors. Furthermore, the conductive layers symmetrically distributed on both sides of the double support layer form a three-dimensional conductive network, which significantly reduces the overall resistivity of the current collector and improves the uniformity of current conduction. At the same time, the first countersunk hole opened on the surface of the first conductive layer away from the surface of the first support layer penetrates the first support layer and extends at least partially to the second conductive layer, and the second countersunk hole opened on the surface of the third conductive layer away from the surface of the second support layer penetrates the second support layer and extends at least partially to the second conductive layer. The first countersunk hole is not connected to the second countersunk hole. This countersunk hole design allows the electrode active material to be embedded into the current collector through the countersunk hole, increasing the contact area between the active material and the conductive layer, strengthening the interfacial bonding stability, and reducing the risk of active material detachment. On the other hand, it provides a buffer space for the volume expansion of the electrode, mitigating the impact of the expansion force on the current collector structure. In addition, the non-connected first and second countersunk holes can prevent current from directly passing through the support layer and forming a short circuit channel, ensuring that the conductive path is conducted in an orderly manner along the conductive layer. This helps to reduce safety hazards such as short circuits and overheating caused by current collector problems during battery use, and further improves the cycle performance and safety performance of the current collector. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the structure of a current collector according to an embodiment of this application.

[0028] Explanation of icon numbers:

[0029] 100 current collector 10 First conductive layer 20 First support layer 30 Second conductive layer 40 Second support layer 50 Third conductive layer 60 First countersunk hole 70 Second countersunk hole X Thickness direction Y Length direction

[0030] The realization of the purpose, functional features and advantages of this utility model will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0031] The solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments in this application, and not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0032] It should be noted that all directional indicators (such as up, down, left, right, front, back, etc.) in the embodiments of this application are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indicator will also change accordingly.

[0033] It should also be noted that when a component is described as "fixed to" or "set on" another component, it can be directly on the other component or there may be an intervening component present. When a component is described as "connected to" another component, it can be directly connected to the other component or there may be an intervening component present.

[0034] Furthermore, the use of terms such as "first" and "second" in this application is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed in this application.

[0035] Please refer to Figure 1 One embodiment of this application proposes a current collector 100, which includes a first conductive layer 10, a first support layer 20, a second conductive layer 30, a second support layer 40 and a third conductive layer 50 stacked sequentially along the thickness direction X.

[0036] The first conductive layer 10 has a plurality of first countersunk holes 60 on its surface away from the first support layer 20. The first countersunk holes 60 penetrate the first support layer 20 and extend at least partially to the second conductive layer 30.

[0037] The third conductive layer 50 has a plurality of second countersunk holes 70 on its surface opposite to the second support layer 40. The second countersunk holes 70 penetrate the second support layer 40 and extend at least partially to the second conductive layer 30.

[0038] The first countersunk hole 60 is not connected to the second countersunk hole 70.

[0039] In this embodiment, the first conductive layer 10, the second conductive layer 30 and the third conductive layer 50 constitute a three-level current conduction path. The first conductive layer 10 directly contacts the active material to collect electrons generated by the chemical reaction. The second conductive layer 30 receives and transfers the current to avoid transmission interruption. The third conductive layer 50 finally gathers the current to the external electrode.

[0040] The first support layer 20 and the second support layer 40 serve a dual function of structural support and isolation protection. On the one hand, they provide mechanical support for the first conductive layer 10 and the second conductive layer 30, resisting the stress caused by volume changes during the charging and discharging of the active material and preventing deformation and damage to the conductive layer. On the other hand, they separate adjacent conductive layers through physical isolation to avoid the risk of short circuit caused by direct contact. At the same time, the support layer allows the countersunk hole to penetrate and works in conjunction with the conductive layer, which not only ensures the increased contact area of ​​the countersunk hole with the active material, but also maintains the overall structural stability of the current collector 100, achieving dual optimization of current conduction efficiency and structural reliability.

[0041] The first countersunk hole 60 is formed on the surface of the first conductive layer 10 opposite to the first support layer 20, and extends at least partially through the first support layer 20 to the second conductive layer 30. The second countersunk hole 70 is formed on the surface of the third conductive layer 50 opposite to the second support layer 40, and extends at least partially through the second support layer 40 to the second conductive layer 30. The presence of these countersunk holes increases the contact area between the current collector 100 and the active material, allowing the active material to better bond with the current collector 100. During battery charging and discharging, when the active material undergoes volume changes, the structure around the countersunk holes can buffer the stress caused by these changes to a certain extent, reducing damage to the overall structure of the current collector 100. At the same time, the presence of the countersunk holes can also form a special current transmission path inside the current collector 100, allowing electrons to directly penetrate the three conductive layers along the hole walls without relying on interlayer indirect conduction, significantly reducing the surface resistance and thus improving current transmission efficiency.

[0042] In this current collector 100, the conductive layer material is mainly a metal with high conductivity, good ductility, and chemical stability. In addition to copper, aluminum, nickel, or metal alloys such as copper-nickel alloys or copper-silver alloys can also be used. Graphene, carbon nanotubes, and other carbon-based conductive materials can also be composited on the surface of the metal layer. The support layer material focuses on mechanical strength, resistance to electrolyte corrosion, and lightweight characteristics. In addition to commonly used polyethylene terephthalate (PET), polypropylene (PP), polyimide (PI), or composite polymer materials such as PET / PP blends can also be used. Of course, this is only an example and is not intended to limit the scope of this application.

[0043] The current collector 100 of this application adopts a five-layer composite structure design consisting of a first conductive layer 10, a first support layer 20, a second conductive layer 30, a second support layer 40, and a third conductive layer 50. With the double support layer as the core framework, it not only uses the mechanical strength of the support layer to suppress the structural deformation caused by the volume expansion and contraction of the electrode material (such as silicon-carbon anode) during charging and discharging, but also avoids the interlayer delamination problem caused by insufficient bonding strength between the single support layer and the conductive layer in the traditional three-layer composite current collector 100. Furthermore, it constructs a three-dimensional conductive network through the conductive layers symmetrically distributed on both sides of the double support layer, which significantly reduces the overall resistivity of the current collector 100 and improves the uniformity of current conduction.

[0044] Meanwhile, the first countersunk hole 60 opened on the surface of the first conductive layer 10 away from the surface of the first support layer 20 penetrates the first support layer 20 and extends at least partially to the second conductive layer 30. The second countersunk hole 70 opened on the surface of the third conductive layer 50 away from the surface of the second support layer 40 penetrates the second support layer 40 and extends at least partially to the second conductive layer 30. The first countersunk hole 60 is not connected to the second countersunk hole 70. This countersunk hole design allows the electrode active material to be embedded into the current collector 100 through the countersunk hole, increasing the contact area between the active material and the conductive layer, strengthening the interfacial bonding stability, and reducing the risk of active material falling off. On the other hand, it can provide a buffer space for the expansion of the electrode volume and alleviate the impact of the expansion force on the structure of the current collector 100.

[0045] In addition, the non-connected first countersunk hole 60 and second countersunk hole 70 can prevent current from directly passing through the support layer to form a short circuit channel, ensuring that the conductive path is conducted in an orderly manner along the conductive layer. This helps to reduce safety hazards such as short circuits and overheating caused by current collector 100 during battery use, and further improves the cycle performance and safety performance of current collector 100.

[0046] In some embodiments, the projection area of ​​the first countersunk hole 60 in the thickness direction X of the current collector 100 is offset from the projection area of ​​the second countersunk hole 70 in the thickness direction X of the current collector 100.

[0047] Since the opening of the countersunk hole will damage the integrity of the material in the corresponding area, if the projection overlaps, the second conductive layer 30 in the middle will form a superimposed weak area of ​​double openings. During the charging and discharging of the battery, the stress generated by the repeated expansion of the silicon-carbon negative electrode is easily concentrated in this weak area, leading to interlayer peeling or conductive layer breakage.

[0048] In this embodiment, by staggering the projection areas of the first countersunk hole 60 and the second countersunk hole 70 in the same thickness direction X of the current collector 100, stress can be distributed to different areas of the current collector 100, avoiding stress overload in a single area and ensuring the overall structural strength. Furthermore, the staggered projection areas make the electron-ion transport channels corresponding to the first countersunk hole 60 and the second countersunk hole 70 spatially complementary. This avoids local current / ion congestion caused by channel overlap and allows the distributed channels to cover the entire current collector 100, ensuring uniform vertical electron conduction and three-dimensional ion diffusion throughout the entire current collector 100, further optimizing transport efficiency and reaction consistency.

[0049] In some embodiments, the first countersunk hole 60 and the second countersunk hole 70 are alternately spaced along the length direction Y of the current collector 100.

[0050] During battery assembly and charging / discharging, the current collector 100 is prone to longitudinal tensile and compressive stress in the length direction Y due to electrode winding or expansion of active material. If the countersunk hole is concentrated along the length direction Y, the stress will be superimposed in the concentrated area, causing local structural deformation.

[0051] In this embodiment, the alternating arrangement of the first countersunk hole 60 and the second countersunk hole 70 along the length Y of the current collector 100 ensures a uniform distribution of countersunk holes in the length Y direction. This allows for linear stress dispersion along the longitudinal direction, preventing stress overload at a single location and ensuring the structural integrity of the current collector 100 in the length Y direction. Furthermore, the alternating countersunk hole layout forms a continuous and uninterrupted electron-ion transport channel in the length Y direction. Each first countersunk hole 60 and its adjacent second countersunk hole 70 form a transport unit. Through the alternating connection between units, continuous coverage of vertical electron conduction and three-dimensional ion diffusion in the length Y direction is achieved, avoiding transport blind spots caused by uneven distribution of countersunk holes and further improving the overall transport efficiency of the current collector 100.

[0052] In some embodiments, the minimum distance between the first countersunk hole 60 and the second countersunk hole 70 is D, and the diameters of both the first countersunk hole 60 and the second countersunk hole 70 are Φ, satisfying the following relationship:

[0053] D>max{2Φ,6T1,6T2};

[0054] Wherein, 40μm≤Φ≤200μm, T1 is the thickness of the first support layer 20, and T2 is the thickness of the second support layer 40.

[0055] In this embodiment, the minimum distance D between the first countersunk hole 60 and the second countersunk hole 70 satisfies D>max{2Φ,6T1,6T2}, and the structural safety threshold is achieved through quantitative constraints.

[0056] Specifically, this relation constructs a protective boundary from three aspects:

[0057] Firstly, the constraint of D>2Φ can prevent the material width between adjacent countersunk holes from being insufficient due to the small spacing, thus preventing the stress generated by the volume change of the active material during battery charging and discharging from concentrating in the weak area between the holes, which could cause the conductive layer to break or the support layer to tear.

[0058] Secondly, the design of D>6T1, combined with the material mechanical properties of the first support layer 20 (such as PET, PP), ensures that the effective load-bearing width of the support layer between the countersinks is sufficient to resist the expansion deformation during the lateral wetting of the electrolyte and the compressive stress transmitted by the conductive layer, thus maintaining the structural integrity of the support layer.

[0059] Thirdly, D>6T2 similarly ensures the load-bearing capacity of the second support layer 40, avoiding the delamination of the current collector 100 layers due to damage to the support layer.

[0060] The lower limit of 40μm≤Φ ensures the effective cross-sectional area of ​​the vertical electron-ion transport channel, avoiding electron congestion and ion migration obstruction due to excessively small aperture. The upper limit of Φ≤200μm controls the area occupied by the pores on the surface of the current collector 100, ensuring that the conductive layer (such as Cu, Al) retains a sufficient effective conductive area, avoiding the increase in surface resistance due to insufficient conductive area, and ultimately achieving a quantitative balance between structural stability and transport efficiency.

[0061] This embodiment provides a clear numerical design standard for countersunk hole layout through this relationship, eliminating the need for experience-based judgment. The minimum safety clearance D can be accurately calculated based on the actual parameters of the first support layer 20 (T1), the thickness of the second support layer 40 (T2), and the countersunk hole diameter (Φ). For example, when T1 = 10 μm, T2 = 20 μm, and Φ = 100 μm, D must be greater than max{200 μm, 60 μm, 120 μm}, i.e., D > 200 μm. This accurately avoids structural risks associated with different specifications of current collectors 100, ensuring that the current collector 100 can stably withstand stress impacts under different support layer materials and different hole diameter designs.

[0062] Furthermore, the formula can be adapted to support layer materials of different thicknesses (such as PET and PI with T1 = 5μm-30μm) and different pore size requirements (such as laser drilling specifications of 40μm-200μm). There is no need to redesign the overall structure due to adjustments in the support layer or pore size. Only the spacing D needs to be updated by calculating the formula, which greatly improves the adaptability of the current collector 100 to different battery models (such as cylindrical, square, and pouch batteries).

[0063] In some embodiments, the inner walls of the first countersunk hole 60 and / or the second countersunk hole 70 are coated with a gel layer.

[0064] In this embodiment, the gel layer (such as polyvinylidene fluoride-hexafluoropropylene gel, lithium bis(trifluoromethanesulfonyl)imide gel) has high ionic conductivity and good electrolyte adsorption capacity: on the one hand, the gel layer can adsorb and store electrolyte, forming a stable ion transport medium layer on the inner wall of the sink hole, filling the micro gaps that may exist on the inner wall of the sink hole, avoiding ion transport blind zones caused by unevenness of the inner wall, and making the transmission of electrons and ions in the sink hole channel more continuous; on the other hand, the three-dimensional network structure of the gel layer can guide the directional migration of ions, reduce the disordered diffusion of ions in the sink hole, and further improve the ion transport efficiency by combining the original vertical channel advantage of the sink hole, especially suitable for the rapid ion migration requirements in high-rate charge and discharge scenarios.

[0065] Furthermore, the gel layer can play a role in interface buffering and corrosion barrier: Firstly, when the volume of the active material repeatedly expands during battery charging and discharging, the elastic properties of the gel layer can buffer the mechanical impact between the inner wall of the sump and the active material and electrolyte, reduce material loss caused by stress friction on the inner wall of the sump, and prevent microcracks from appearing in the conductive layer (such as the Cu layer); Secondly, the gel layer can form a dense protective film on the inner wall of the sump, preventing corrosive components in the electrolyte from directly contacting the conductive layer, reducing the corrosion rate of the conductive layer, maintaining the conductivity stability of the sump channel, and extending the service life of the current collector.

[0066] In some embodiments, the depth of the first countersunk hole 60 is H1, and the depth of the second countersunk hole 70 is H2, respectively satisfying the following relationships:

[0067] H1 = T1 + T3 + T4 - δ;

[0068] H2 = T2 + T4 + T5 - δ;

[0069] Where 0um < δ ≤ 0.5um, T1 is the thickness of the first support layer 20, T2 is the thickness of the second support layer 40, T3 is the thickness of the first conductive layer 10, T4 is the thickness of the second conductive layer 30, and T5 is the thickness of the third conductive layer 50.

[0070] In this embodiment, the calculation formula for the depth H1 of the first countersunk hole 60 is based on the total thickness of the first conductive layer 10 (T3), the first support layer 20 (T1), and the second conductive layer 30 (T4). Through the design of "total thickness - δ", it is ensured that the first countersunk hole 60 can penetrate the first conductive layer 10 and the first support layer 20 and extend into the interior of the second conductive layer 30. This avoids the first conductive layer 10 and the second conductive layer 30 from not being able to form a conductive connection through the hole wall due to insufficient countersunk hole depth. At the same time, the small margin of δ (0um < δ ≤ 0.5um) prevents the countersunk hole from penetrating the second conductive layer 30 excessively, ensuring the structural integrity of the second conductive layer 30 and maintaining its conductive transfer function between the upper and lower layers.

[0071] Similarly, H2 uses the total thickness of the second support layer 40 (T2), the second conductive layer 30 (T4), and the third conductive layer 50 (T5) as a reference, and ensures that the second countersunk hole 70 penetrates the third conductive layer 50 and the second support layer 40 and extends to the second conductive layer 30 through "total thickness - δ", so as to achieve conductive connection between the third conductive layer 50 and the second conductive layer 30, while avoiding the breakdown of the second conductive layer 30.

[0072] This embodiment uses the quantitative formulas H1 and H2 to precisely design the counterbore depth based on the actual thickness (T1-T5) of each material layer, ensuring that the first conductive layer 10 and the second conductive layer 30, as well as the third conductive layer 50 and the second conductive layer 30, can form a stable conductive connection through the counterbore wall. This avoids interlayer conductivity interruption due to insufficient counterbore depth, or excessive damage to the second conductive layer 30 due to excessive depth, thereby improving the overall conductivity stability of the current collector 100.

[0073] In some embodiments, the diameter of the first countersunk hole 60 and / or the second countersunk hole 70 is 40um-200um.

[0074] The 40µm lower limit of the pore size design can ensure the effective migration space of ions in the sink hole channel: During the charging and discharging of the battery, the electrolyte needs to carry ions through the sink hole to achieve three-dimensional diffusion. If the pore size is less than 40µm, the electrolyte flow cross section in the sink hole will be too narrow, and ion migration will be prone to congestion. Especially in high-rate charging and discharging scenarios, the supply and demand of ions cannot be matched, which may lead to battery capacity decay or charging and discharging efficiency reduction.

[0075] The constraint of an upper limit of 200um for the aperture is to avoid excessive occupation of the surface area of ​​the current collector 100 by the aperture. Since the conductive layer (such as Cu layer, Al layer) of the current collector 100 needs to retain a sufficient effective area to realize electron collection and transport, if the aperture exceeds 200um, it will lead to a significant reduction in the effective conductive area of ​​the conductive layer and an increase in the surface resistance, which will affect the overall conductivity. Therefore, the aperture of 40um-200um provides sufficient and not excessive channel space for ion migration, which can avoid ion congestion caused by small aperture and prevent the waste of conductive area caused by large aperture. It can maintain the stability of ion transport rate under different charge and discharge rate scenarios.

[0076] In a wound battery cell, there are a tab region, a corner region and a center region. The aperture of the first countersunk hole 60 and / or the second countersunk hole 70 can be limited to 40μm≤Φ1≤100μm, 100μm≤Φ2≤140μm and 140μm≤Φ3≤200μm in the tab region, corner region and center region, respectively.

[0077] The tab region, as the core node for current collection and discharge in the battery cell, has a significantly higher current density than other regions. This makes it prone to lithium plating due to electron accumulation rates far exceeding ion migration rates and resulting in insufficient local ion supply. By limiting the aperture size (Φ1) to 40μm-100μm, densely arranged pores can be arranged within the limited space of the tab region, maximizing the number of ion transport channels, rapidly replenishing the ion demand under high current density, and balancing electron and ion transport rates.

[0078] Due to the cell winding process, the corner area has the dual problems of uneven current distribution and stress concentration. The current density is between that of the tab area and the center area. Therefore, Φ2 is limited to a medium aperture of 100μm-140μm. This can ensure the ion transport capacity to cope with local current peaks, while avoiding excessive density of small apertures that will aggravate the structural stress in the corner area.

[0079] The central region has the lowest current density and a moderate demand for ion transport. By limiting Φ3 to a large aperture of 140μm-200μm, the basic ion transport requirements can be met while reducing the area occupied by the pores on the effective area of ​​the conductive layer, maintaining the overall low surface resistivity of the current collector 100, and avoiding redundant loss of conductivity performance.

[0080] In some embodiments, the pore density of the first countersunk hole 60 and / or the second countersunk hole 70 is 5 pores / mm². 2 -100 pieces / mm 2 The pore density is 1 mm on any surface of the current collector 100. 2 The number of the first countersunk hole 60 or the second countersunk hole 70 in the area.

[0081] In this embodiment, the lower limit of the pore density is 5 pores / mm. 2 Ensuring basic ion transport requirements: During battery charging and discharging, the electrolyte needs to form a three-dimensional diffusion network through the pores. If the number of pores per unit area is too small (less than 5 pores / mm), 2 This can lead to insufficient ion transport channels, especially in medium-rate charge and discharge scenarios. The ion migration rate cannot match the electron conduction rate, which can easily cause local ion shortages and affect the battery's charge and discharge efficiency.

[0082] The upper limit for pore density is 100 pores / mm². 2 The constraints prevent excessive apertures from damaging the structure of the current collector 100. Since the conductive layer (e.g., Cu layer, Al layer) and the support layer (e.g., PET layer, PP layer) of the current collector 100 need to maintain a sufficient continuous area to preserve mechanical strength and conductive continuity, if the number of countersunk holes per unit area is too large (exceeding 100 holes / mm), it will damage the structure. 2 This can lead to excessive fragmentation of the material between holes, which not only reduces the tensile and bending resistance of the current collector 100, but may also cause an increase in surface resistance due to excessive reduction of the effective conductive area of ​​the conductive layer, thus affecting the overall conductivity.

[0083] In a wound battery cell, which includes a tab region, a corner region, and a center region, the pore density of the first countersunk hole 60 and / or the second countersunk hole 70 can be limited to 20≤ρ1≤100 holes / mm in the tab region, corner region, and center region, respectively. 2 10≤ρ2≤40 pieces / mm 2 5≤ρ3≤20 pieces / mm 2 .

[0084] The tab region, as the sole node for current collection and conduction in the wound cell, has a much higher current density than other regions. Electrons accumulate in large numbers here, making it prone to localized ion shortages due to delayed ion migration, thus leading to lithium plating. ρ1 is limited to 20-100 ions / mm. 2 Its high density allows for the construction of sufficient ion transport channels within a limited area of ​​the tab region, rapidly replenishing the ion demand under high current, balancing the electron-ion transport rate, and suppressing the risk of lithium plating from the root.

[0085] The corner area is the core bending region of the wound battery cell. Due to the winding structure, the current is prone to local unevenness. Moreover, this area simultaneously bears the bending stress during the winding process and the expansion stress of the active material during charging and discharging. Therefore, ρ2 is limited to 10-40 cells / mm. 2 The medium density allows for the use of an appropriate number of ion channels to address uneven current distribution while avoiding the exacerbation of structural fragility in corner areas by high-density openings.

[0086] The central region, located inside the wound cell, has the lowest current density and a moderate ion transport requirement, limiting ρ3 to 5-20 ions / mm. 2 The low density maximizes the effective area of ​​the conductive layer, maintains the overall low surface resistance of the current collector 100, and avoids excessive openings that weaken the structural stability of the central region under winding compression.

[0087] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and do not limit the scope of the present invention.

[0088] This embodiment provides a current collector 100 and a wound battery cell based on the current collector 100. The specific fabrication process and parameters are as follows:

[0089] 1. Preparation of current collector 100:

[0090] Insulating polymer PET is selected as the substrate for the support layer, and Cu is selected as the substrate for the conductive layer. The thickness of the first support layer 20 and the second support layer 40 is set to 3.0 μm, the thickness of the first conductive layer 10 and the third conductive layer 50 is set to 1.5 μm, and the thickness of the second conductive layer 30 is set to 1.0 μm.

[0091] A Cu conductive layer is formed on both sides of the insulating polymer PET by magnetron sputtering and copper sulfate electrolyte electroplating. Finally, a five-layer composite structure is obtained by adjusting the hot pressing temperature (130℃, lower than the glass transition temperature of PET) and pressure using a hot pressing laminating machine.

[0092] 2. Laser drilling

[0093] Front-side drilling: Using an ultraviolet laser system in conjunction with CCD visual positioning technology, the first conductive layer 10 is divided into sections for drilling to form the first countersunk hole 60. The hole diameter and hole density are set according to the requirements of the cell area (tab area, corner area, center area).

[0094] Reverse drilling: Flip the current collector 100 and use the light transmission signal of the hole already drilled on the front as the positioning reference to drill a hole on one side of the third conductive layer 50 to form the second countersunk hole 70.

[0095] 3. Functional treatment of pore walls

[0096] First, the current collector 100 after drilling was activated using an atmospheric pressure plasma device to reduce the contact angle of the hole wall to 25° to improve wettability. Then, a gel layer was coated. Using a microgravure coating process, 8 wt% of PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer) and 2 wt% of LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) were added to an acetone / DMF (N,N-dimethylformamide) mixed solvent (7:3) and coated onto the hole wall. After thermal drying at 120°C to evaporate the solvent, a gel layer with a thickness of 1.5 μm was obtained.

[0097] 4. Manufacturing of positive and negative electrode plates and wound battery cells

[0098] The positive electrode and negative electrode are composed of the current collector 100 prepared above and the electrode active slurry coated on the surface. The positive electrode active material used is one or more of the following composite materials: lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, nickel cobalt manganese ternary material, and lithium iron phosphate. The active material LiCoO2, conductive agent acetylene black, conductive carbon nanotubes, and binder polyvinylidene fluoride (PVDF) are fully dispersed and uniformly coated on the aluminum current collector 100 in an N-methylpyrrolidone solvent system at a weight ratio of 98.2:0.5:0.3:1.0, and then cold-pressed and slit to obtain the positive electrode.

[0099] The active material used in the negative electrode is one or more of graphite, graphite-silicon carbon material, and hard carbon material. The negative electrode active material, conductive agent, and binder are mixed in a weight ratio of 90.23:0.5:2.3, fully dispersed and uniformly dispersed in a deionized water solvent system, coated onto Cu composite current collector 100, and then cold-pressed and slit to obtain the negative electrode sheet.

[0100] A ceramic mixture is coated onto the PE surface to serve as a release film.

[0101] Ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and propyl propionate (PP) were mixed in a volume ratio of 1:1:4:4. Then, fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent at a ratio of 1 mol / L to prepare an electrolyte.

[0102] A wound battery cell is prepared by taking the above positive electrode sheet, separator, and negative electrode sheet through steps such as winding, top-side sealing, liquid injection, formation, and secondary sealing.

[0103] The above-mentioned wound battery cell is divided into several embodiments and comparative examples. The design parameters of the specific embodiments and comparative examples are shown in Table 1 below:

[0104]

[0105] Table 1

[0106] 5. Cell performance testing

[0107] Performance tests were conducted on the cells listed in Table 1 above. Five parallel samples were set up for each test group, and the average value of the results was taken.

[0108] (1) Cyclic performance test: Under 25℃ environment, charging and discharging were performed according to the following method. The cells were charged to 4.10V at a 2.5C rate stepwise, then charged to 4.20V at a 2.5C rate, to 4.30V at a 1.5C rate, and to 4.53V at a 1.0C rate. Then, they were discharged to 3.0V at a 0.7C rate, and the cycle was repeated 500 times. The cycle capacity retention rate and cycle expansion retention rate were obtained. Among them, the cycle capacity retention rate = (discharge capacity of the 500th cycle / discharge capacity of the first cycle) × 100%; the cycle expansion retention rate = (thickness of the 500th cycle - initial half-cell thickness) / initial half-cell thickness * 100%; initial half-cell thickness: charged at a constant current of 0.5C to 3.9V and then constant voltage to 0.02C. The thickness of all cells was tested using 600PPG.

[0109] (2) Corner lithium plating level test: After the parallel samples of the battery cells obtained from each embodiment and comparative example are cycled in step 1), the cells are disassembled, the encapsulation film is removed, the cells are unwound along the winding direction, the separator and the electrode are separated, and the interface of the negative electrode is observed. If there is no lithium plating, it is marked as level 0; if there is point-like lithium plating, it is marked as level 1; if there is linear lithium plating but it is not continuous, it is marked as level 2; if there is linear lithium plating and it is continuous, it is marked as level 3. There are 5 parallel samples in each group of tests, and the highest level among the samples is counted.

[0110] (3) Cell breakage test: After cycling, the cells are characterized by CT to observe the breakage of the electrodes and the number of breaks.

[0111] (4) Electrode film surface resistance: After the negative electrode is coated and dried, the electrode is punched into a circle and the film resistance of the electrode is tested.

[0112] (5) Tab temperature rise: The test was conducted at an ambient temperature of 25℃±5℃. The temperature rise test location was the tab position. The specific steps are as follows:

[0113] 1) Let it sit: 5 minutes;

[0114] 2) Discharge at a constant current of 0.7C with a cutoff voltage of 3.0V;

[0115] 3) Let it sit: 30 minutes;

[0116] 4) Charge at a constant current rate of 3C, with a cutoff voltage of 4.25V and a charging time of 1.5min;

[0117] 5) Charge at a constant current rate of 2.65C, cutoff voltage of 4.25V, for 2.0min;

[0118] 6) Charge at a constant current rate of 2.3C, with a cutoff voltage of 4.33V;

[0119] 7) Charge at a constant current rate of 1.7C, with a cutoff voltage of 4.35V;

[0120] 8) Charge at a constant current rate of 1.5C, with a cutoff voltage of 4.53V;

[0121] 9) Charge at a constant current and constant voltage of 1.3C to 4.58V, with a cut-off rate of 0.25C;

[0122] 10) Let it sit: 5 minutes;

[0123] 11) Repeat steps 2)-10) a total of 2 times;

[0124] 12) Let it sit: 5 minutes;

[0125] 13) End.

[0126] The performance of the battery cells in all the embodiments and comparative examples in Table 1 above was tested, and the test results are shown in Table 2 below.

[0127]

[0128] Table 2

[0129] In Example 1, the five-layer composite structure of this application is shown, in which the first and second submerged holes are not connected. In contrast, the current collectors in Comparative Examples 1-2 have through holes, meaning that the first submerged hole is connected to the corresponding second submerged hole. This results in the absence of ion transport channels and insufficient stress buffering: ions cannot be quickly replenished under high current in the tab region, and the lithium plating level reaches level 3 (the most severe); there is no buffer space for changes in the volume of the active material, the cycle expansion retention rate is 10.4%, and the number of electrode breakages is 3.

[0130] Therefore, as can be seen from the comparison between Example 1 and Comparative Examples 1 and 2, the design of the first and second countersinks of the current collector in this application being non-connected can ensure orderly ion transport and effective stress buffering, thus giving full play to the isolation and protection of the double support layer and the three-dimensional transport advantages of the conductive layer, thereby meeting the requirements of high cycle stability of the battery cell.

[0131] Among them, when 0 < δ ≤ 0.5 μm (Example 1, δ = 0.3 μm), the electrode film resistance is as low as 45 mΩ, the capacity retention rate after 500 cycles is 92.3%, the corner lithium plating level is 0 (no lithium plating), and the electrode breakage number is 0; while in Comparative Example 3 (δ = 0): the small δ causes the through-hole to penetrate the second conductive layer excessively, destroying its conductive transfer function, the film resistance rises to 71 mΩ, the capacity retention rate drops to 88.3%, the lithium plating level rises to 2 (linear discontinuous lithium plating), and the electrode breakage number reaches 2; in Comparative Example 4 (δ = 1 μm): the large δ causes the through-hole to not extend sufficiently to the second conductive layer, the interlayer conductivity is interrupted, the film resistance further rises to 4 mΩ, the capacity retention rate is only 78.3%, the lithium plating level is 2, and the electrode breakage number is 2.

[0132] Therefore, as can be seen from the comparison between Example 1 and Comparative Examples 3 and 4, δ needs to be strictly controlled within 0 < δ ≤ 0.5 μm. Within this range, stable interlayer conductivity and the integrity of the second conductive layer structure can be achieved simultaneously, which is the basis for the low resistance and high cycle stability of the battery cell.

[0133] In Example 1, D1 = 160 μm, D2 = 240 μm, and D3 = 320 μm (all satisfying "D > 2Φ", such as when Φ1 = 80 μm, 2Φ = 160 μm, and D1 = 160 μm is close to the upper limit), the corresponding cell cycle expansion retention rate is only 6.9% (one of the lowest values), and there is no electrode breakage; while in Comparative Example 5, D1 = 60 μm < 2Φ1 = 60 μm, Φ1 = 30 μm, D is too small, which leads to fragmentation of the inter-pore material, the membrane resistance soars to 98 mΩ (the highest among all samples), the cycle capacity retention rate is only 76.1%, and the expansion retention rate is 11.1%; in Comparative Example 7, D1 = 80 μm < 2Φ1 = 160 μm, Φ1 = 80 μm, D does not satisfy "D > 2Φ", the membrane resistance is 85 mΩ, the capacity retention rate is 75% (the lowest value), and the number of electrode breaks is 3.

[0134] Therefore, as can be seen from the comparison between Example 1 and Comparative Examples 5 and 7, D must strictly follow the relationship D>max{2Φ,6T1,6T2}. This constraint can effectively avoid stress concentration between holes, maintain the stability of the current collector structure, and thus reduce the cell expansion rate and fracture risk.

[0135] In Examples 1-5, Φ1 (tab region, 40-100μm), Φ2 (corner region, 100-140μm), and Φ3 (central region, 140-200μm) conform to the logic of "small aperture in the tab region (dense channels for ion replenishment) and large aperture in the central region (maintaining conductive area)". All examples showed no lithium plating (level 0), and the membrane resistance was 45-61mΩ. However, in Comparative Example 5 (Φ1 = 30μm < 40μm lower limit): the tab region aperture was too small, resulting in insufficient ion channels, ion congestion under high current, lithium plating level 3, and capacity retention of 76.1%; in Comparative Example 6 (Φ3 = 250μm > 200μm upper limit): the central region aperture was too large, reducing the effective area of ​​the conductive layer, resulting in a membrane resistance of 89mΩ, a capacity retention of 79.2%, and lithium plating level 3.

[0136] Therefore, as can be seen from the comparison between Examples 1-5 and Comparative Examples 5 and 6, Φ needs to be designed according to "40-100μm in the tab area, 100-140μm in the corner area, and 140-200μm in the center area". This range can match the current and stress characteristics of different areas and avoid lithium plating and increased resistance.

[0137] Among them, ρ1 (20-100 pieces / mm) in Examples 1-5 2 ), ρ2 (10-40 pieces / mm) 2 ), ρ3 (5-20 pieces / mm) 2 It meets regional requirements, with a diaphragm resistance of 45-61 mΩ and an expansion retention rate of 6.9-9.2%. Comparative Example 8 (ρ1 = 30 pieces / mm) 2 <20 pieces / mm 2 Lower limit): Insufficient pore density in the tab region, few ion channels, lithium plating grade 3, expansion retention rate 12.3% (maximum value, stress cannot be buffered); Comparative example 9 (ρ2 = 50 pores / mm) 2 >40 pieces / mm 2 Upper limit, ρ3 = 30 pieces / mm 2 >20 pieces / mm 2 Upper limit): The pore density in the corner and central areas is too high, the structure is excessively weakened, the number of electrode breaks is 3, and the capacity retention rate is 74.5%.

[0138] Therefore, a comparison between Examples 1-5 and Comparative Examples 8 and 9 shows that ρ needs to be calculated according to "20-100 tabs / mm". 2 10-40 corner sections / mm 2 5-20 per mm in the central area 2 The design allows this range to balance between "sufficient ion channels" and "structural strength".

[0139] In Example 1, the pore walls were coated with a gel layer, while in Comparative Example 10, no gel layer was used. Although δ, D, Φ, and ρ all met the design constraints, the electrode film resistance (70 mΩ) was significantly higher than that of Example 1 (45 mΩ), the capacity retention rate after 500 cycles (86.2%) was lower than that of Example 1 (92.3%), and the corner lithium plating grade increased to level 3 (level 0 in Example 1).

[0140] Therefore, as can be seen from the comparison between Example 1 and Comparative Example 10, coating the pore wall with a gel layer can achieve "high-efficiency ion transport + interface buffer protection", thus achieving the comprehensive performance goals of low resistance, high cycle stability and no lithium plating.

[0141] This application also provides an electrode sheet, including a current collector 100 as described above and an active material layer, wherein the active material layer is coated on at least one side surface of the current collector 100. Since the electrode sheet adopts all the technical solutions of all the embodiments of the current collector 100 described above, the electrode sheet of this utility model also possesses at least all the beneficial effects brought about by the technical solutions of the above embodiments, which will not be elaborated upon here.

[0142] This application also provides an electrochemical device, including a cathode electrode, an anode electrode, and a separator, wherein the separator is disposed between the cathode electrode and the anode electrode, and the cathode electrode and / or the anode electrode are electrodes as described above. This electrochemical device can be a lithium secondary battery, including a lithium metal secondary battery, a lithium-ion secondary battery, a lithium polymer secondary battery, or a lithium-ion polymer secondary battery. This electrochemical device can possess all the technical features and corresponding beneficial effects of the aforementioned electrodes, which will not be elaborated further here.

[0143] The above are only some or preferred embodiments of this application. Neither the text nor the drawings should limit the scope of protection of this application. All equivalent structural transformations made using the content of this application's specification and drawings under the overall concept of this application, or direct / indirect applications in other related technical fields, are included within the scope of protection of this application.

Claims

1. A current collector, characterized in that, It includes a first conductive layer, a first support layer, a second conductive layer, a second support layer, and a third conductive layer that are stacked sequentially along the thickness direction; The first conductive layer has a plurality of first countersunk holes on its surface away from the first support layer. The first countersunk holes penetrate the first support layer and extend at least partially to the second conductive layer. The third conductive layer has a plurality of second countersunk holes on its surface away from the second support layer. The second countersunk holes penetrate the second support layer and extend at least partially into the second conductive layer. The first countersunk hole is not connected to the second countersunk hole.

2. The current collector according to claim 1, characterized in that, The projection area of ​​the first countersunk hole in the thickness direction of the current collector is offset from the projection area of ​​the second countersunk hole in the thickness direction of the current collector.

3. The current collector according to claim 1, characterized in that, The first countersunk hole and the second countersunk hole are alternately spaced along the length of the current collector.

4. The current collector according to claim 3, characterized in that, The minimum distance between the first countersunk hole and the second countersunk hole is D, and the diameters of both the first and second countersunk holes are Φ, satisfying the following relationship: D>max{2Φ,6T1,6T2}; Wherein, 40μm≤Φ≤200μm, T1 is the thickness of the first support layer, and T2 is the thickness of the second support layer.

5. The current collector according to any one of claims 1 to 4, characterized in that, The inner walls of the first and / or second countersunk holes are coated with a gel layer.

6. The current collector according to any one of claims 1 to 4, characterized in that, The depth of the first countersunk hole is H1, and the depth of the second countersunk hole is H2, which respectively satisfy the following relationships: H1 = T1 + T3 + T4 - δ; H2 = T2 + T4 + T5 - δ; Where 0um < δ ≤ 0.5um, T1 is the thickness of the first support layer, T2 is the thickness of the second support layer, T3 is the thickness of the first conductive layer, T4 is the thickness of the second conductive layer, and T5 is the thickness of the third conductive layer.

7. The current collector according to any one of claims 1 to 4, characterized in that, The diameter of the first countersunk hole and / or the second countersunk hole is 40um-200um.

8. The current collector according to any one of claims 1 to 4, characterized in that, The pore density of the first countersunk hole and / or the second countersunk hole is 5 pores / mm. 2 -100 pieces / mm 2 The pore density is any 1 mm of the current collector surface. 2 The number of the first countersunk holes or the second countersunk holes within the area.

9. An electrode sheet, characterized in that, include: The current collector as described in any one of claims 1 to 8; An active material layer is coated on at least one side surface of the current collector.

10. An electrochemical device, characterized in that, It includes a cathode electrode, an anode electrode, and a diaphragm, wherein the diaphragm is disposed between the cathode electrode and the anode electrode, and the cathode electrode and / or the anode electrode are electrodes as described in claim 9.

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