Pole piece and battery cell

Abstract

The utility model provides a pole piece and a battery cell, the pole piece comprises a current collector and an active material layer, and the active material layer is arranged on at least one side of the current collector; the active material layer sequentially comprises a first region, a second region and a third region along the first direction; the first region is located on one side of the active material layer close to the current collector, and the second region is located on one side of the first region away from the current collector; the third region is located on one side of the second region away from the first region; and the section porosity of the first region is smaller than that of the second region, so that the energy density of the battery cell and the stability of the battery cell during high-temperature storage and circulation are improved.

Description

Technical Field

[0001] The utility model relates to the technical field of batteries, in particular to a pole piece and a battery core. Background Art

[0002] Currently, lithium-ion batteries are widely used not only in portable electronic devices such as mobile phones and laptops, but also in electric equipment such as electric vehicles and electric bicycles.

[0003] As the requirements for electronic products and new energy vehicles become higher and higher, users' performance requirements for lithium-ion batteries are also getting higher and higher. Among them, the energy density of the battery cell, the stability of the battery cell during high-temperature storage and cycling are all important performance indicators of the battery. How to balance the energy density, high-temperature storage of the battery cell and the stability during cycling has become the focus of attention. Utility Model Content

[0004] In view of this, an embodiment of the utility model provides a pole piece and a battery cell, so as to take into account the energy density of the battery cell, the stability of the battery cell during high temperature storage and cycling.

[0005] In a first aspect, the utility model provides a pole piece, comprising a current collector and an active material layer, wherein the active material layer is arranged on at least one side of the current collector;

[0006] The active material layer includes a first region, a second region and a third region in sequence along a first direction; the first region is located on a side of the active material layer close to the current collector, the second region is located on a side of the first region away from the current collector; the third region is located on a side of the second region away from the first region;

[0007] The cross-sectional porosity of the first region is smaller than the cross-sectional porosity of the second region.

[0008] The pole piece provided by the utility model increases the bonding strength between the active material particles in the first zone and the second zone by making the cross-sectional porosity of the active material layer smaller than the cross-sectional porosity of the second zone, thereby restraining the physical rebound and electrochemical rebound of the active material particles, thereby improving the volume energy density of the battery cell using the pole piece, improving the energy density of the corresponding battery, and improving the conductivity of the battery cell during charging and discharging, reducing the internal resistance of the battery, and improving the charging and discharging performance of the battery. In addition, since the cross-sectional porosity of the first zone is smaller than that of the second zone, the bonding strength between the current collector and the first zone can be increased, that is, the peeling force between the active material layer and the current collector is increased, thereby improving the problem of active material shedding and large expansion of the pole piece during the cycle process, and improving the stability of the battery cell during circulation and high-temperature storage.

[0009] Optionally, the cross-sectional porosity of the third zone is smaller than the cross-sectional porosity of the second zone.

[0010] Optionally, the thickness of the first region ranges from 1 / 10 to 3 / 10 of the total thickness of the active material layer;

[0011] The thickness of the second region ranges from 2 / 5 to 4 / 5 of the total thickness of the active material layer;

[0012] The thickness of the third region ranges from 1 / 10 to 3 / 10 of the total thickness of the active material layer.

[0013] Optionally, a hole is provided on a side of the third zone facing away from the first zone, and the hole extends toward the second zone.

[0014] Optionally, a ratio of a size of the hole along a thickness direction of the third zone to a thickness of the third zone is in a range of 20% to 100%.

[0015] Optionally, the cross-sectional porosity of the first region, the cross-sectional porosity of the second region and the cross-sectional porosity of the third region satisfy: (a+c) / 2≤b;

[0016] Wherein, a is the cross-sectional porosity of the first zone, b is the cross-sectional porosity of the second zone, and c is the cross-sectional porosity of the third zone.

[0017] Optionally, the cross-sectional porosity of the first zone is 5% to 40%;

[0018] and / or, the cross-sectional porosity of the second zone is 7% to 60%;

[0019] And / or, the cross-sectional porosity of the third zone is 5% to 40%.

[0020] Optionally, the peeling force between the first region and the current collector is greater than or equal to 5N.

[0021] Optionally, the ratio of the peeling force between the first region and the current collector to the cross-sectional porosity of the first region is in the range of 10-300.

[0022] In a second aspect, the utility model provides a battery cell, comprising a first pole piece, a second pole piece, and a diaphragm disposed between the first pole piece and the second pole piece, wherein the first pole piece and the second pole piece have opposite polarities;

[0023] At least one of the first pole piece and the second pole piece is the pole piece as described above.

[0024] The battery cell provided by the utility model increases the bonding strength between the active material particles in the first and second regions of the entire region by making the cross-sectional porosity of the first region in the active material layer of the pole piece smaller than the cross-sectional porosity of the second region, thereby restraining the physical rebound and electrochemical rebound of the active material particles, thereby increasing the volume energy density of the battery cell using the pole piece, increasing the energy density of the corresponding battery, and increasing the conductivity of the battery cell during charging and discharging, reducing the internal resistance of the battery, and improving the charging and discharging performance of the battery. In addition, since the cross-sectional porosity of the first region is smaller than that of the second region, the bonding strength between the current collector and the first region can be increased, that is, the peeling force between the active material layer and the current collector is increased, thereby improving the problem of active material shedding and large expansion of the pole piece during the cycle process, and improving the stability of the battery cell during circulation and high-temperature storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The figure shows a cross-sectional structure diagram of a pole piece provided by an embodiment of the utility model. Figure 1 ;

[0026] Figure 2 The figure shows a cross-sectional structure diagram of a pole piece provided by an embodiment of the utility model. Figure 2 ;

[0027] Figure 3 Shown is a SEM800x electron microscope image of a pole piece provided by an embodiment of the utility model;

[0028] Figure 4 Shown is a SEM2kx electron microscope image of an active material layer provided in one embodiment of the utility model;

[0029] Figure 5 The figure shows a SEM electron microscope image of a pole piece provided by an embodiment of the utility model after a hole is punched in the third area.

[0030] Among them, 100, pole piece; 1, current collector; 2, active material layer; 20, pores; 21, first zone; 22, second zone; 23, third zone. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the utility model to clearly and completely describe the technical solutions in the embodiments of the utility model. Obviously, the described embodiments are only part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0032] Reference Figures 1 to 5As shown, an embodiment of the present invention provides a pole piece 100 , including a current collector 1 and an active material layer 2 , wherein the active material layer 2 is disposed on at least one side of the current collector 1 .

[0033] Specifically, the current collector 1 has two opposite sides, and the two opposite sides are used to coat the active material layer 2. In specific implementation, refer to Figure 1 As shown, it is possible to only have one side of the current collector 1 (for example Figure 1 The active material layer 2 is arranged on the upper side of the current collector 1 to form a single-sided electrode. Of course, in other implementations, the active material layer 2 can also be arranged only on the lower side of the current collector 1. Figure 2 As shown, active material layers 2 may also be provided on both sides (upper side and lower side) of the current collector 1 to form a double-sided electrode sheet.

[0034] For the active material layer 2 disposed on either side of the current collector 1, the active material layer 2 includes a first region 21, a second region 22 and a third region 23 in sequence along a first direction. The first direction here may be the thickness direction of the active material layer 2, such as Figures 1 to 3 The first direction may be the hh direction of the active material layer 2; the first direction may be the width direction or the length direction of the active material layer 2.

[0035] The first region 21 is located on the side of the active material layer 2 close to the current collector 1 , the second region 22 is located on the side of the first region 21 away from the current collector 1 , and the third region 23 is located on the side of the second region 22 away from the first region 21 , that is, the second region 22 is located between the first region 21 and the third region 23 .

[0036] The cross-sectional porosity of the first region 21 is smaller than the cross-sectional porosity of the second region 22 .

[0037] In the present application, “cross-sectional porosity” refers to the cross-sectional porosity of the active material layer 2 in a section (ie, cross section) perpendicular to the current collector 1 .

[0038] For example, Figure 2 Taking the active material layer 2 located on the upper side of the current collector 1 as an example, in the active material layer 2 on this side, the cross-sectional porosity of the first region 21 is the percentage of the pore area of ​​the cross-sectional area of ​​the first region 21 located on the upper side in the direction perpendicular to the current collector 1 to the total area of ​​the cross-sectional area of ​​the first region 21 located on the upper side in the direction perpendicular to the current collector 1. The pore 20 refers to the particle spacing in each region.

[0039] In specific implementation, the porosity of the cross-sections of different regions of the active material layer 2 can be tested as follows:

[0040] For example, select the active material layer 2 test area of ​​1000μm×Aμm, count all the pores between particles in the cross section at A=10μm and A>10μm, obtain photos with obvious brightness and darkness of particles and pores through maps test, and then use image software to process the electrode to obtain the cross-sectional porosity.

[0041] In some embodiments, the electrode sheet 100 may be a negative electrode sheet. In this case, the current collector 1 may be, for example, copper foil, and the material of the active material layer 2 may be, for example, graphite, silicon-based, or other negative electrode active materials. This embodiment does not specifically limit the specific materials of the current collector 1 and the active material layer 2, and they may be selected according to actual needs.

[0042] Of course, in other embodiments, the electrode sheet 100 may also be a positive electrode sheet. In this case, the current collector 1 may be, for example, aluminum foil, and the material of the active material layer 2 may be, for example, a ternary material or positive electrode active materials such as lithium iron phosphate.

[0043] By making the cross-sectional porosity of the first region 21 of the active material layer 2 smaller than the cross-sectional porosity of the second region 22, the bonding strength between the active material particles in the entire region of at least the first region 21 and the second region 22 is increased, thereby restraining the physical rebound and electrochemical rebound of the active material particles, thereby improving the volume energy density of the battery cell using the electrode 100, improving the energy density of the corresponding battery, and improving the conductivity of the battery cell during charge and discharge, reducing the internal resistance of the battery, thereby improving the charge and discharge performance of the battery.

[0044] In addition, since the cross-sectional porosity of the first region 21 is smaller than that of the second region 22, the bonding strength between the current collector 1 and the first region 21 can be increased, that is, the peeling force between the active material layer 2 and the current collector 1 is increased, thereby improving the problem of active material shedding and large expansion of the electrode piece 100 during the cycle process, and improving the stability of the battery cell using the electrode piece 100 during cycling and high-temperature storage.

[0045] Continue to refer to Figures 1 to 4 As shown, in some embodiments, the cross-sectional porosity of the third region 23 is less than the cross-sectional porosity of the second region 22 .

[0046] That is, in the active material layer 2 located on one side of the current collector 1 , the cross-sectional porosity of the first region 21 close to the current collector 1 and the third region 23 relatively far from the current collector 1 are both smaller than the cross-sectional porosity of the second region 22 located in the middle.

[0047] In this way, by making the cross-sectional porosity of the third region 23 smaller than the cross-sectional porosity of the second region 22, it is helpful to reduce the contact area between the third region 23 and the electrolyte, thereby reducing the instability of the electrode during use and the excessive reaction speed, which leads to problems such as reduced initial charging efficiency of the battery. In addition, since the cross-sectional porosity of the third region 23 is also reduced relative to the cross-sectional porosity of the second region 22, the volume energy density of the battery cell is further improved, and the energy density of the battery is further improved. At the same time, such a setting further improves the conductivity of the battery cell during charging and discharging, reduces the electron and ion transmission path inside the battery, reduces the internal resistance of the battery, and improves the energy conversion efficiency of the battery, thereby improving the electrochemical reaction rate of the electrode material, thereby improving the discharge performance and charging rate of the battery, and will not affect the bonding strength between the first region 21 and the current collector 1.

[0048] Considering the above cross-sectional porosity distribution of the first region 21, the second region 22 and the third region 23, in order to ensure that the electrolyte and lithium ions can smoothly enter the active material layer 2 and avoid battery failure, the following are combined: Figures 1 to 3 As shown, in some embodiments, the thickness L1 of the first region 21 can be set to 1 / 10 to 3 / 10 of the total thickness L of the active material layer 2, the thickness L2 of the second region 22 can be set to 2 / 5 to 4 / 5 of the total thickness L of the active material layer 2, and the thickness L3 of the third region 23 can be set to 1 / 10 to 3 / 10 of the total thickness L of the active material layer 2.

[0049] It should be noted that the total thickness L of the active material layer 2 here refers to the active material layer 2 on one side of the current collector 1 (for example Figure 1 The active material layer on the upper side of the middle current collector 1, such as Figure 2 The active material layer 2 on the upper side of the current collector 1 or the active material layer 2 on the lower side of the current collector 1, such as Figure 3 The ratio of each region to the total thickness of the active material layer is the ratio of the first region 21, the second region 22, and the third region 23 to the total thickness L of the active material layer 2 on the side thereof.

[0050] Specifically, the thickness L1 of the first region 21 can be set to 3 / 10 of the total thickness L of the active material layer 2 on that side, the thickness L2 of the second region 22 can be set to 2 / 5 of the total thickness L of the active material layer 2 on that side, and the thickness L3 of the third region 23 can be set to 3 / 10 of the total thickness L of the active material layer 2 on that side. For example, when the electrode 100 is a negative electrode, the compaction density PD of the active material layer 2 here is g / cm 3 Specifically, the following relationship is satisfied: 1.4g / cm 3 ≤PD≤1.85g / cm 3 .

[0051] Reference Figure 3 As shown, exemplarily, the total thickness L of the active material layer 2 on one side of the current collector 1 is 52.7 μm, wherein the thickness L1 of the first region 21 is 15.8 μm, the thickness L2 of the second region 22 is 21.1 μm, and the thickness L3 of the third region 23 is 15.8 μm.

[0052] For another example, the thickness of the first region 21 and the third region 23 each accounts for 1 / 5 of the total thickness of the active material layer 2 on that side, and the thickness of the second region 22 accounts for 3 / 5 of the total thickness of the active material layer 2 .

[0053] That is to say, on the basis that the cross-sectional porosity of the first zone 21 and the third zone 23 is smaller than the cross-sectional porosity of the second zone 22, the thickness of the second zone 22 with relatively larger cross-sectional porosity is larger than the thickness of the first zone 21 and the thickness of the second zone 22, thereby effectively ensuring that the electrolyte and lithium ions can enter the active material layer 2 more smoothly, avoiding battery failure and the like.

[0054] It should be noted that the thickness of each of the above-mentioned regions refers to the thickness of each region in the electrode sheet 100 corresponding to the battery after the battery is formed.

[0055] In addition, illustratively, the thickness of the current collector 1 can be set to, for example, 5.36 μm. The thickness of the current collector 1 is not particularly limited in this embodiment and can be adjusted according to actual needs.

[0056] Through specific experiments, this embodiment sets the cross-sectional porosity distribution of the active material layer 2 as above, which can increase the peeling force between the active material layer 2 and the current collector 1 to greater than or equal to 5N, thereby effectively preventing the active material from falling off and expanding.

[0057] In some embodiments, the ratio of the peeling force between the first region 21 and the current collector 1 to the cross-sectional porosity of the first region 21 in the active material layer 2 can be between 10 and 300 to better ensure the bonding strength between the first region 21 and the current collector 1 .

[0058] For example, the cross-sectional porosity of the first region 21 is 5%, the peeling force between the first region 21 and the current collector 1 is 15N, and the ratio of the peeling force between the first region 21 and the current collector 1 to the cross-sectional porosity of the first region 21 in the active material layer 2 is 300.

[0059] For another example, the cross-sectional porosity of the first region 21 is 40%, the peeling force between the active material layer 2 and the current collector 1 is 5N, and the ratio of the peeling force between the first region 21 and the current collector 1 to the cross-sectional porosity of the first region 21 in the active material layer 2 is 12.5.

[0060] For another example, the cross-sectional porosity of the first region 21 is 20%, the peeling force between the active material layer 2 and the current collector 1 is 10N, and the ratio of the peeling force between the first region 21 and the current collector 1 to the cross-sectional porosity of the first region 21 in the active material layer 2 is 50.

[0061] In some embodiments, the cross-sectional porosity of the first region 21, the cross-sectional porosity of the second region 22, and the cross-sectional porosity of the third region 23 satisfy the following relationship:

[0062] (a+c) / 2≤b;

[0063] Wherein, a is the cross-sectional porosity of the first zone 21 , b is the cross-sectional porosity of the second zone 22 , and c is the cross-sectional porosity of the third zone 23 .

[0064] This setting can further improve the volume energy density, conductivity, and stability of the battery during high-temperature storage and cycling.

[0065] In some embodiments, the cross-sectional porosity of the first zone 21 may be set between 5% and 40%, the cross-sectional porosity of the second zone 22 may be set between 7% and 60%, and the cross-sectional porosity of the third zone 23 may be set between 5% and 40%.

[0066] Since the cross-sectional porosity of the third region 23 is smaller than that of the second region 22, the instability and over-fast reaction speed of the electrode during use can be reduced, and the volume energy density of the battery cell is increased. At the same time, in order to take into account the wettability of the electrolyte to ensure good ion transmission and battery cell liquid retention, the third region 23 is preferably a plurality of electrodes. Figure 5 As shown, in some embodiments, a hole is provided on a side of the third region 23 facing away from the first region 21 , and the hole extends toward the second region 22 .

[0067] By providing the openings in the third area 23, the electrolyte infiltration and ion transmission rate can be accelerated, the rate performance of the battery can be improved, and the liquid retention of the battery cell can be increased, thereby improving the cycle performance of the battery. That is, such a setting reduces the instability and excessive reaction speed of the electrode during use, and improves the volume energy density of the battery cell to a certain extent, while also taking into account the good transmission of ions and the liquid retention of the battery cell.

[0068] For example, when the electrode sheet 100 is a negative electrode sheet, the surface density of the active material layer 2 before rolling is 0.05 mg / mm 2 Up to 0.150mg / mm 2 The compacted density PD of the active material layer 2 after roller pressing is g / cm 3 Specifically, it can satisfy the following relationship: 1.4g / cm 3 ≤PD≤1.85g / cm3 .

[0069] In some embodiments, the holes are specifically arranged in the thickness direction ( Figures 1 to 3 The dimension in the hh direction is not greater than the thickness of the third area 23. That is to say, the perforated area is within the third area 23 and does not involve the second area 22, thereby improving the electrolyte infiltration rate, ion transfer rate and battery cell liquid retention while not affecting the energy density of the second area 22, thereby further ensuring the energy density of the battery.

[0070] The hole may be arranged perpendicular to the third area 23, that is, the axial direction of the hole may be consistent with the thickness direction of the third area 23. Alternatively, the hole may be opened obliquely relative to the thickness direction of the third area 23, that is, there is an angle between the axial direction of the hole and the thickness direction of the third area 23.

[0071] For example, the size of the hole along the thickness direction of the third region 23 can be set between 2 μm and 20 μm, such as 2 μm, 5 μm, 10 μm, 15 μm, and 20 μm.

[0072] In some embodiments, the ratio of the size of the hole in the thickness direction of the third region 23 to the thickness of the third region 23 can be between 20% and 100%. That is, the perforated area is within the third region 23 and does not involve the second region 22, thereby improving the electrolyte infiltration rate, ion transfer rate and battery cell liquid retention while not affecting the energy density of the second region 22, thereby further ensuring the energy density of the battery.

[0073] For example, when the thickness of the third region 23 is 15.8 μm, the size of the hole along the thickness direction of the third region 23 can be set to 3.16 μm, 10 μm, 15 μm, and 15.8 μm, which can be adjusted according to actual needs.

[0074] In specific implementation, laser scribing can be used to punch holes in the surface layer of the third zone 23. Exemplarily, the parameters can be set as follows: the punching power is 0.2W to 2kW, and the punching speed is 10m / min to 40m / min. The depth of the holes in the active material layer 2 can be effectively controlled by laser scribing, and the weight loss rate and electrical properties of the electrode 100 can be effectively controlled. Especially for fast-charging system cells such as 5C and 7C or negative electrode sheets PD>1.76g / cm 3 The battery cell combined with laser scribing technology can improve the electrolyte infiltration rate, battery cell liquid retention and ion transmission rate.

[0075] Of course, in other implementations, holes may be opened in the third area 23 by mechanical bonding or other methods.

[0076] The present invention also provides a battery cell, comprising a first pole piece, a second pole piece and a diaphragm disposed between the first pole piece and the second pole piece, wherein the first pole piece and the second pole piece have opposite polarities, for example, the first pole piece is a positive pole piece and the second pole piece is a negative pole piece.

[0077] Among them, at least one of the positive electrode sheet and the negative electrode sheet has the same structure and implementation principle as the electrode sheet 100 provided in the above embodiment, and can bring the same or similar technical effects, which will not be described one by one here, and the details can be referred to the description of the above embodiment.

[0078] The present invention also provides a battery, comprising a battery cell, a shell and an electrolyte, wherein the battery cell is located in the shell, and the electrolyte is injected into the shell in which the battery cell is installed.

[0079] The battery may be, for example, a lithium-ion battery.

[0080] Among them, the structure and implementation principle of the battery cell are the same as the battery cell provided in the above embodiment, and can bring the same or similar technical effects, which will not be described one by one here, and the details can be referred to the description of the above embodiment.

[0081] The present invention is further described below by taking the electrode sheet 100 as a negative electrode sheet as an example:

[0082] 1) Select a negative electrode active material, such as graphite, and coat it on a copper foil current collector to form a negative electrode active material layer on the copper foil current collector, thereby forming a negative electrode sheet.

[0083] The surface density of the negative electrode active material layer is, for example, 0.05 mg / mm 2 ~0.150mg / mm 2 .

[0084] 2) The negative electrode sheet is subjected to high temperature roll pressing, wherein the third region 23 is in contact with the roller during the rolling process.

[0085] Exemplarily, in this process, for example, the rolling temperature is controlled between 60° C. and 120° C., and the rolling speed is controlled between 10 m / min and 40 m / min.

[0086] By high-temperature rolling, the cross-sectional porosity of the negative electrode sheet in the thickness direction can be effectively controlled, especially the cross-sectional porosity of the surface layer (third region 23) and the bottom layer (first region 21) of the electrode sheet 100 is significantly reduced compared with the middle layer (second region 22).

[0087] The compaction density of the negative electrode active material layer after the negative electrode sheet is rolled is PD g / cm 3 Satisfy the relationship: 1.40g / cm 3 ≤PD≤1.85g / cm 3 .

[0088] 3) After obtaining the well-rolled negative electrode sheet, use a laser scribing device (such as a continuous laser) to punch holes on the surface of the electrode sheet 100.

[0089] Specifically, the parameters can be set as follows: punching power is 0.2W to 2kW, and punching speed is 10m / min to 40m / min.

[0090] 4) Take the punched electrode sheet and the normally coated and rolled positive electrode sheet and the separator (for example, a PE porous polymer film can be selected as the separator), wind them together, place them in an aluminum-plastic film, and then inject liquid, let them stand, form them, divide the capacity, measure the K value (the voltage drop of the battery per unit time), and package them into lithium-ion secondary batteries.

[0091] 5) Measure the cross-sectional porosity of the electrode piece 100 of the battery cell.

[0092] For the qualified battery cells, some of them are discharged with a small current to 3.0V, and then disassembled to obtain negative electrode sheets with good appearance.

[0093] A small piece of the obtained electrode was taken for cross-sectional CP (argon ion polishing) sample preparation, and then a scanning electron microscope (SEM) was used to take a cross-sectional view of the electrode 100 at 800x and 2.0kx magnifications (refer to Figure 3 and Figure 4 , Figure 3 This is an electron microscope image at 800x magnification. Figure 4 is an electron microscope image at a magnification of 2.0kx), the thickness value and pore distribution map of the active material layer 2 on one side of the electrode can be obtained.

[0094] Then modify the redundant areas of the image (foil, blank, etc.), and adjust the threshold size by using CCD image processing software, and analyze the thickness of the first area 21, the second area 22, and the third area 23 in the thickness direction of the electrode 100 (the threshold value must remain consistent). Three different positions on the same electrode 100 need to be tested and calculated to obtain the cross-sectional porosity of the three different areas in the final thickness direction.

[0095] 6) Measure the peeling force between the active material layer of the negative electrode sheet of the battery cell and the current collector 1.

[0096] For the qualified battery cells, some of them were discharged with a small current to 3.0V, and then disassembled to obtain negative electrode sheets with good appearance.

[0097] Then, a universal testing machine was used to test the peeling force between the active material layer 2 and the current collector 1 .

[0098] In this article, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, or it can be indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to the specific circumstances. In addition, the orientation or position relationship indicated by the terms "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are based on the orientation or position relationship shown in the accompanying drawings, which is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0099] In this article, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprises", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprising a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0100] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A pole piece, characterized in that: It includes a current collector and an active material layer, wherein the active material layer is arranged on at least one side of the current collector; The active material layer includes a first region, a second region and a third region in sequence along a first direction; the first region is located on a side of the active material layer close to the current collector, the second region is located on a side of the first region away from the current collector; the third region is located on a side of the second region away from the first region; The cross-sectional porosity of the first region is smaller than the cross-sectional porosity of the second region.

2. The pole piece according to claim 1, characterized in that: The cross-sectional porosity of the third region is smaller than the cross-sectional porosity of the second region.

3. The pole piece according to claim 2, characterized in that: The thickness of the first region ranges from 1 / 10 to 3 / 10 of the total thickness of the active material layer; The thickness of the second region ranges from 2 / 5 to 4 / 5 of the total thickness of the active material layer; The thickness of the third region ranges from 1 / 10 to 3 / 10 of the total thickness of the active material layer.

4. The pole piece according to claim 2, characterized in that: A hole is provided on a side of the third zone facing away from the first zone, and the hole extends toward the second zone.

5. The pole piece according to claim 4, characterized in that: The ratio of the size of the hole along the thickness direction of the third region to the thickness of the third region is in the range of 20% to 100%.

6. The pole piece according to any one of claims 1 to 5, characterized in that: The cross-sectional porosity of the first region, the cross-sectional porosity of the second region, and the cross-sectional porosity of the third region satisfy: (a+c) / 2≤b; Wherein, a is the cross-sectional porosity of the first zone, b is the cross-sectional porosity of the second zone, and c is the cross-sectional porosity of the third zone.

7. The pole piece according to any one of claims 1 to 5, characterized in that: The cross-sectional porosity of the first zone is 5% to 40%; and / or, the cross-sectional porosity of the second zone is 7% to 60%; And / or, the cross-sectional porosity of the third zone is 5% to 40%.

8. The pole piece according to any one of claims 1 to 5, characterized in that: The peeling force between the first region and the current collector is greater than or equal to 5N.

9. The pole piece according to any one of claims 1 to 5, characterized in that: The ratio of the peeling force between the first region and the current collector to the cross-sectional porosity of the first region is in the range of 10 to 300.

10. A battery cell, characterized in that: It comprises a first pole piece, a second pole piece and a diaphragm arranged between the first pole piece and the second pole piece, wherein the first pole piece and the second pole piece have opposite polarities; At least one of the first pole piece and the second pole piece is the pole piece according to any one of claims 1 to 9.

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