Pole piece and preparation method thereof

Abstract

The invention discloses a pole piece which comprises a current collector and an active material layer arranged on at least one surface of the current collector, a first region and a second region are arranged on the surface of the active material layer; the first area is a semicircle which takes the center of the tab as a circle center and has a radius of X.C; the first area is provided with a first concave hole, and the ratio of the depth of the first concave hole to the thickness of the active material layer is a; x is the width of the pole piece, and C is the charging rate of the battery using the pole piece; the second area is the area, except the first area, of the pole piece, the second area is provided with a second concave hole, and the depth ratio of the second concave hole is b; wherein a is greater than b. Compared with the prior art, the pole piece flexibly adjusts the depth of the concave hole according to the specific position of the tab and potential distribution, realizes homogenization of electrode potential distribution, and reduces the possibility of non-uniform deposition of alkali metal ions on the surface of the electrode in the charging process, so that the risk of local lithium precipitation is reduced, the overall dynamic performance of the battery is improved, and the service life of the battery is prolonged. And the cycle life is obviously prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to a pole piece and a preparation method thereof. Background Art

[0002] With the booming development of the electric vehicle industry and the widespread popularity of mobile electronic devices, the performance requirements for lithium-ion batteries are becoming increasingly stringent. As an indispensable component in the structure of secondary batteries, the structure of the pole piece and its manufacturing process have a decisive influence on the overall performance and service life of the battery.

[0003] In traditional pole piece laser drilling technology, the drilling depth ratio is often set to a fixed value. However, this process method fails to fully consider the differences in current density distribution in various parts of the pole piece and the non-uniformity of potential during charging. Especially in the area of ​​the pole piece close to the pole ear, the current density is significantly higher than other areas, and the potential is correspondingly reduced. This phenomenon leads to an increased risk of local metal precipitation near the pole ear. The precipitated metal will not only reduce the capacity retention rate of the battery, but may also cause internal short circuits, which will seriously affect the safety and cycle stability of the battery.

[0004] In view of the above-mentioned defects of the current pole pieces, it is indeed necessary to provide a technical solution to solve the above-mentioned problems. Summary of the invention

[0005] The purpose of the present invention is to provide a pole piece and a preparation method thereof, wherein the pole piece automatically and flexibly adjusts the depth of the recessed hole according to the specific position and potential distribution of the pole ear, thereby achieving uniform electrode potential distribution, thereby improving the overall dynamic performance of the battery and significantly extending its cycle life.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A pole piece, comprising a current collector and an active material layer disposed on at least one surface of the current collector;

[0008] The pole piece is provided with a pole ear;

[0009] The surface of the active material layer is provided with a first region and a second region;

[0010] The first region is a semicircle with the center of the pole ear as the center and a radius of X*C; the first region is provided with a first concave hole, and the ratio of the depth of the first concave hole to the thickness of the active material layer is a; X is the width of the pole piece, and C is the charging rate of the battery using the pole piece;

[0011] The second region is a region of the pole piece other than the first region, the second region is provided with a second concave hole, and the ratio of the depth of the second concave hole to the thickness of the active material layer is b;

[0012] Among them, a and b satisfy the relationship: a>b.

[0013] Preferably, a satisfies the relationship: 10%≤a≤50%.

[0014] Preferably, a and b satisfy the relationship: a=b+kC%, wherein k is the surface density of the active material layer, and the value range of k is 0<k≤15mg / cm 2 .

[0015] Preferably, C satisfies the relationship: 0<C≤5.

[0016] Preferably, the distance between any two adjacent first concave holes is c, and c satisfies the relationship: c≥0.8 mm;

[0017] Preferably, the distance between any two adjacent second recessed holes is d, and d satisfies the relationship: d≥0.8 mm.

[0018] Preferably, the thickness of the pole piece is A, the depth of the first concave hole is e, and A and e satisfy the relationship: e=a·A, and e>0.8mm;

[0019] And / or, the depth of the second concave hole is f, and A and f satisfy the relationship: f=b·A, and f>0.8 mm.

[0020] Preferably, the aperture of the first concave hole is h, and h satisfies the relationship: 10 μm≤h≤200 μm;

[0021] Preferably, the aperture of the second concave hole is i, and i satisfies the relationship: 10 μm≤i≤200 μm;

[0022] Preferably, the e and h satisfy the relationship: h=2.2758e+32.498;

[0023] Preferably, the f and the i satisfy the relationship: i=2.2758f+32.498;

[0024] Preferably, the h and the i satisfy the relationship: h=i(2.2758e+32.498) / (2.2758f+32.498).

[0025] Preferably, the ratio D of the sum of the projected areas of the first concave holes on the surface of the active material layer to the surface area of ​​the first region is D=1 / 4πh 2 / (C+h) 2 ;

[0026] Preferably, the ratio E of the sum of the projected areas of the second concave holes on the surface of the active material layer to the surface area of ​​the second region is E=1 / 4πi 2 / (C+i) 2 ;

[0027] Preferably, the D and E satisfy the relationship: E / D=i 2 (C+h) 2 / (h 2 +(C+i) 2 ).

[0028] The present invention also provides a method for preparing a pole piece, comprising the following steps:

[0029] Step 1: Mixing active material, conductive agent, binder and solvent to obtain active material layer slurry;

[0030] Step 2: coating the active material layer slurry on at least one surface of the current collector, drying, and rolling to obtain a pole piece to be punched;

[0031] Step 3: Cut the electrode to be punched and perform laser punching to obtain the electrode.

[0032] Preferably, the laser power of the laser drilling is j, and j satisfies the relationship: e=(j-38.244) / 115.63;

[0033] And / or, j satisfies the relationship: f = (j-38.244) / 115.63.

[0034] The present invention also provides a secondary battery, comprising a diaphragm, an electrolyte, a battery casing and a pole piece, wherein the pole piece is the pole piece mentioned above.

[0035] The beneficial effects of the present invention are as follows: the present invention provides an electrode piece and a preparation method thereof, wherein the electrode piece flexibly adjusts the depth of the recessed hole according to the specific position and potential distribution of the electrode ear, thereby achieving uniform electrode potential distribution, reducing the possibility of uneven deposition of alkali metal ions on the electrode surface during charging, thereby reducing the risk of local metal precipitation, thereby improving the overall dynamic performance of the battery and significantly extending its cycle life. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagram of the structure of a pole piece according to an embodiment of the present invention.

[0037] Among them: 1. current collector; 2. active material layer; 21. first region; 211. first concave hole; 22. second region; 221. second concave hole; 3. pole ear. DETAILED DESCRIPTION

[0038] In order to make the technical solutions and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0039] According to a first aspect of the present invention, the present invention provides a pole piece, comprising a current collector 1 and an active material layer 2 disposed on at least one surface of the current collector 1;

[0040] A pole ear 3 is provided on the pole piece;

[0041] The surface of the active material layer 2 is provided with a first region 21 and a second region 22;

[0042] The first region 21 is a semicircle with the center of the pole ear 3 as the center and a radius of X·C; the first region 21 is provided with a first concave hole 211, and the ratio of the depth of the first concave hole 211 to the thickness of the active material layer 2 is a; X is the width of the pole piece, and C is the charging rate of the battery using the pole piece;

[0043] The second region 22 is the region of the pole piece other than the first region 21. The second region 22 is provided with a second concave hole 221. The ratio of the depth of the second concave hole 221 to the thickness of the active material layer 2 is b.

[0044] Among them, a and b satisfy the relationship: a>b.

[0045] The electrode piece automatically and flexibly adjusts the depth of the recess according to the specific position and potential distribution of the electrode ear 3; the current density in the first area 21 is relatively large, and a deeper first recess 211 is used, which is conducive to achieving uniform electrode potential distribution and reducing the possibility of uneven deposition of alkali metal ions on the electrode surface during charging, thereby reducing the risk of local lithium precipitation, thereby improving the overall dynamic performance of the battery and significantly extending its cycle life.

[0046] The first region 21 is a semicircle with the center of the tab 3 as the center and a radius of X·C. The electrode potential in this region is relatively high, and C is filled in as a compensation coefficient related to the charging rate, thereby reducing the possibility of uneven lithium ion deposition on the electrode surface during the charging process; at the same time, too many deep holes can serve as heat transfer channels, which help to quickly dissipate the heat generated during the charging process, thereby reducing the temperature rise of the battery.

[0047] In one embodiment of the present invention, a satisfies the relationship: 10%≤a≤50%. The pore depth within this ratio range can ensure that the electrolyte fully infiltrates the surface of the electrode, thereby improving the capacity and energy density of the battery; it also helps to build an efficient ion migration network, thereby improving the charge and discharge rate of the battery, and can also alleviate the volume effect of the active material of the electrode during the charge and discharge cycle, prevent the destruction of the electrode structure, and thus improve the cycle stability of the battery.

[0048] In addition, when the pore depth is too shallow, the contact area between the electrode and the electrolyte may be insufficient, resulting in insufficient electrochemical reaction, thereby reducing the capacity and energy density of the battery; when the pore depth is too deep, the active material layer 2 on the surface of the electrode may be damaged, causing the active material to fall off or fail, which will also reduce the capacity of the battery.

[0049] In one embodiment of the present invention, a and b satisfy the relationship: a=b+kC%, wherein k is the surface density of the active material layer, and the value range of k is 0<k≤15mg / cm 2 When a and b do not satisfy the relationship, differences in current density distribution and potential non-uniformity will occur in various parts of the electrode during charging. This phenomenon leads to an increase in the risk of local lithium deposition near the electrode tab 3, which in turn affects the cycle performance and life of the battery.

[0050] In one embodiment of the present invention, C satisfies the relationship: 0<C≤5. In daily use, the common usage rate range is 0-5C. If the battery cell rate is greater than 5C and a hole-making process is performed, the presence of the holes will reduce the conductivity of the electrode and increase the internal resistance of the battery cell. Excessively high charging rates will aggravate the temperature rise problem of the battery cell.

[0051] In one embodiment of the present invention, the distance between any two adjacent first recessed holes 211 is c, and c satisfies the relationship: c ≥ 0.8 mm;

[0052] And / or, the distance between any two adjacent second recessed holes 221 is d, and d satisfies the relationship: d≥0.8 mm.

[0053] If the distance between any two recessed holes is too small, more active materials will be lost, affecting the capacity of the battery. In addition, when the spacing between holes in the laser drilling process is too small, the recessed holes are less stable and prone to large errors.

[0054] In one embodiment of the present invention, the thickness of the electrode sheet is A, the depth of the first concave hole 211 is e, A and e satisfy the relationship: e=a·A, and e>0.8mm. The compaction density of the active material on the surface of the conventional electrode sheet is the highest, and the compaction density of the bottom layer is relatively low. The depth e of the first concave hole 211 needs to be greater than 0.8mm to ensure that the active material with the highest compaction density on the surface of the electrode sheet is knocked off, so that lithium ions can be embedded from the bottom layer with a relatively low compaction density. If the depth e of the first concave hole 211 is less than 0.8mm, the effect of the dynamic improvement brought by the pore formation will be lost.

[0055] And / or, the depth of the second recessed hole 221 is f, A and f satisfy the relationship: f=b·A, and f>0.8mm. The compaction density of the active material on the surface of the conventional electrode plate is the highest, and the compaction density of the bottom layer is lower. The depth f of the second recessed hole 221 needs to be greater than 0.8mm to ensure that the active material with the highest compaction density on the surface of the electrode plate is knocked out, so that lithium ions can be embedded from the bottom layer with lower compaction density; if the depth f is less than 0.8mm, the effect of dynamic improvement brought by pore creation will be lost.

[0056] In one embodiment of the present invention, the aperture of the first recessed hole 211 is h, and h satisfies the relationship: 10μm≤h≤200μm. Too many recessed holes or too large an aperture will cause the conductivity of the electrode to decrease and increase the internal resistance of the battery, thereby generating more heat during the charging process and exacerbating the temperature rise problem.

[0057] And / or, the aperture of the second recessed hole 221 is i, i satisfies the relationship: 10μm≤i≤200μm. Too many recessed holes or too large an aperture will cause the conductivity of the electrode to decrease, increase the internal resistance of the battery, and thus generate more heat during the charging process, exacerbating the temperature rise problem.

[0058] And / or, e and h satisfy the relationship: h=2.2758e+32.498;

[0059] And / or, f and i satisfy the relationship: i=2.2758f+32.498;

[0060] And / or, h and i satisfy the relationship: h=i(2.2758e+32.498) / (2.2758f+32.498).

[0061] In one embodiment of the present invention, the ratio D of the sum of the projected areas of the first recessed holes 211 on the surface of the active material layer 2 to the surface area of ​​the first region 21 is D=1 / 4πh 2 / (C+h) 2When the total area of ​​the electrode occupied by the aperture is too small, although the mechanical integrity of the electrode can be maintained to a certain extent, the insufficient ion transmission channel will limit the ion diffusion rate inside the battery, making it impossible to effectively improve the battery's charge and discharge performance, especially in the case of high-rate charge and discharge, polarization may be aggravated, internal resistance may increase, and other problems may occur;

[0062] When the total area of ​​the electrode occupied by the aperture is too large, the overall structure of the electrode will be excessively damaged, reducing the mechanical strength and stability of the electrode. This may cause the electrode to break or be damaged easily during the assembly and use of the battery, thereby affecting the performance and life of the battery. Problems such as intensified polarization and increased internal resistance may also occur.

[0063] Or, the ratio E of the sum of the projected areas of the second recessed holes 221 on the surface of the active material layer 2 to the surface area of ​​the second region 22 is E=1 / 4πi 2 / (C+i) 2 , the influence of too large or too small area ratio is equivalent to the influence of parameter D;

[0064] And or, D and E satisfy the relationship: E / D=i 2 (C+h) 2 / (h 2 +(C+i) 2 ).

[0065] The present invention also provides a method for preparing a pole piece, comprising the following steps:

[0066] Step 1: Mixing active material, conductive agent, binder and solvent to obtain active material layer 2 slurry;

[0067] Step 2: coating the active material layer 2 slurry on at least one surface of the current collector 1, drying and rolling to obtain a pole piece to be punched;

[0068] Step 3: Cut the electrode to be punched and perform laser punching to obtain the electrode.

[0069] In one embodiment of the present invention, the laser power of the laser drilling is j, and j satisfies the relationship: e=(j-38.244) / 115.63;

[0070] And / or, j satisfies the relationship: f=(j-38.244) / 115.63. The hole depth of the laser drilling of the present application is formed by adjusting the power of the laser, and the relationship of the present invention can be used to quickly and easily drill holes in the pole piece and control the parameters of the hole.

[0071] The present invention also provides a secondary battery, comprising a diaphragm, an electrolyte, a battery casing and a pole piece, wherein the pole piece is the pole piece mentioned above.

[0072] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on at least one surface of the positive electrode current collector, and the positive electrode active material layer may include but is not limited to lithium cobalt dioxide, lithium nickel oxide, lithium nickel cobalt manganese oxide, lithium iron phosphorus oxide, lithium cobalt oxide and lithium iron phosphate, etc. The positive electrode current collector may be any material suitable for use as a positive electrode current collector for lithium-ion batteries in the art, for example, aluminum foil, copper foil, nickel foil, stainless steel or carbon material.

[0073] The negative electrode plate includes a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode active material layer can be one or more of graphite, soft carbon, hard carbon, carbon fiber, mesophase carbon microspheres, silicon-based materials, tin-based materials, lithium titanate or other metals that can form alloys with lithium.

[0074] The graphite may be selected from one or more of artificial graphite, natural graphite and modified graphite; the silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites and silicon alloys; the tin-based material may be selected from one or more of elemental tin, tin oxide compounds and tin alloys. The negative electrode current collector is usually a structure or part for collecting current. The negative electrode current collector may be any material suitable for use as a negative electrode current collector for secondary batteries in the art. For example, the negative electrode current collector may include but is not limited to metal foil, and more specifically may include but is not limited to copper foil.

[0075] The secondary battery also includes an electrolyte, which includes an organic solvent, an electrolyte lithium salt and an additive. Among them, the electrolyte lithium salt can be LiPF6 and / or LiBOB used in high-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, and LiPF6 used in low-temperature electrolytes; it can also be at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in anti-overcharge electrolytes; it can also be at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be a cyclic carbonate, including PC and EC; it can also be a chain carbonate, including DFC, DMC, or EMC; it can also be a carboxylic acid ester, including MF, MA, EA, MP, etc. The additives include but are not limited to at least one of film-forming additives, conductive additives, flame retardant additives, anti-overcharge additives, additives for controlling the content of H2O and HF in the electrolyte, additives for improving low-temperature performance, and multifunctional additives.

[0076] The present invention is further described below by means of specific embodiments. The following specific embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0077] Example 1

[0078] A method for preparing a pole piece:

[0079] Step 1: mixing lithium cobalt oxide, carbon black, polyvinylidene fluoride and a solvent to obtain an active material layer slurry;

[0080] Step 2: coating the active material layer slurry on the two surfaces of the current collector 1, drying and rolling to obtain the electrode sheet to be punched;

[0081] Step 3: Cut the electrode to be punched and perform laser drilling. The wavelength of the laser is 1064nm and the laser power is set to 50W.

[0082] Among them, the pole piece width X is 20mm, C is 2, and k is 10mg / cm 2 ; Set the radius of the first area 21 to 40 mm.

[0083] The ratio of the depth of the first concave hole 211 to the thickness of the active material layer 2 is a, a=30%; the ratio of the depth of the second concave hole 221 to the thickness of the active material layer 2 is b, b=20%.

[0084] Preparation of lithium-ion batteries:

[0085] The separator, the negative electrode sheet and the positive electrode sheet are interlaced and then packaged with an aluminum-plastic film to prepare a battery cell, which is placed in a battery shell, an electrolyte is added, and then sealed to obtain a lithium-ion battery. Among them, the active material of the positive electrode sheet is lithium iron phosphate; the separator is a polyethylene-ceramic composite separator; the electrolyte salt of the electrolyte is lithium hexafluorophosphate, and the solvent is ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate in a mass ratio of 1:2:1, and the electrolyte concentration is 1 mol / L.

[0086] Table 1 shows the experimental parameters of Examples 1 to 8 and Comparative Examples 1 to 6, and the rest are the same as the examples and will not be repeated here.

[0087] Table 1

[0088]

[0089] Performance Test:

[0090] The batteries of Examples 1 to 8 and Comparative Examples 1 to 6 were subjected to electrochemical performance tests, and the test results are shown in Table 2;

[0091] The batteries of Examples 1 to 8 and Comparative Examples 1 to 6 were disassembled after cycling to observe the lithium deposition on the electrodes. The test results are shown in Table 2.

[0092] Table 2

[0093]

[0094] According to Table 2, a comparison of the data of Examples 1 to 8 and Comparative Examples 1 to 2 shows that lithium deposition occurs in the first region 21 of Comparative Examples 1 to 2, which results in a low capacity retention rate after 500 cycles of the battery. This is because the electrode surfaces of Comparative Examples 1 and 2 are not provided with concave holes of different hole depths. On the contrary, Examples 1 to 8 are provided with concave holes of different hole depths, and a deeper first concave hole 211 is provided, which is conducive to achieving uniform electrode potential distribution and reducing the possibility of uneven deposition of alkali metal ions on the electrode surface during charging, thereby reducing the risk of local lithium deposition, thereby improving the overall dynamic performance of the battery and significantly extending its cycle life.

[0095] A comparison of the data of Examples 1 to 8 and Comparative Example 3 shows that lithium deposition occurs in the first region 21 of Comparative Example 3, which results in a low capacity retention rate after 500 cycles of the battery. This is because the depth of the first recessed hole 211 arranged on the surface of the electrode of Comparative Example 3 is smaller than the depth of the second recessed hole 221. The current in the first region 21 is relatively large, and deeper recessed holes should be arranged. The depth of the first recessed hole 211 of Comparative Example 3 is too small, so lithium deposition occurs in the first region 21 of Comparative Example 3.

[0096] Comparison of the data of Examples 1 to 8 and Comparative Examples 4 to 5 shows that the first region 21 of Comparative Example 4 has serious lithium deposition, which results in a low capacity retention rate after 500 cycles of the battery. This is because the depth of the first concave hole 211 set on the surface of the pole piece of Comparative Example 4 is too deep and the depth of the first concave hole 211 set on the surface of the pole piece of Comparative Example 5 exceeds the range, which destroys the active material layer 2 on the surface of the pole piece, causing the active material to fall off or fail. At the same time, it is also impossible to improve the problem of lithium deposition in the first region 21, and it is speculated that the capacity of the battery will also be reduced.

[0097] Comparison of the data of Examples 1 to 8 and Comparative Example 6 shows that the first region 21 of Comparative Example 6 has serious lithium deposition, which leads to a drop in the capacity retention rate of the battery after 500 cycles. This is because the usage rate of Comparative Example 6 exceeds the parameter range. Under excessive charge and discharge rates, the negative electrode has no time to embed lithium ions, resulting in a large amount of lithium ions accumulating on the surface of the negative electrode to form metal lithium deposition, resulting in a sharp drop in the 500-cycle retention rate, which seriously affects the performance and cycle life of the battery.

[0098] According to the disclosure and teaching of the above description, those skilled in the art to which the present invention belongs can also change and modify the above embodiment. Therefore, the present invention is not limited to the above specific embodiment, and any obvious improvement, replacement or modification made by those skilled in the art on the basis of the present invention belongs to the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for the convenience of description and do not constitute any limitation to the present invention.

Claims

1. A pole piece, characterized in that: comprising a current collector and an active material layer disposed on at least one surface of the current collector; The pole piece is provided with a pole ear; The surface of the active material layer is provided with a first region and a second region; The first region is a semicircle with the center of the pole ear as the center and a radius of X·C; the first region is provided with a first concave hole, and the ratio of the depth of the first concave hole to the thickness of the active material layer is a; X is the width of the pole piece, and C is the charging rate of the battery using the pole piece; The second region is a region of the pole piece other than the first region, the second region is provided with a second concave hole, and the ratio of the depth of the second concave hole to the thickness of the active material layer is b; Among them, a and b satisfy the relationship: a>b.

2. The pole piece according to claim 1, characterized in that: The a satisfies the relationship: 10%≤a≤50%.

3. The pole piece according to claim 1 or 2, characterized in that: The a and b satisfy the relationship: a=b+kC%, wherein k is the surface density of the active material layer, and the value range of k is 0<k≤15 mg / cm 2 .

4. The pole piece according to claim 1, characterized in that: The C satisfies the relationship: 0<C≤5.

5. The pole piece according to claim 1, characterized in that: The distance between any two adjacent first concave holes is c, and c satisfies the relationship: c≥0.8mm; And / or, the distance between any two adjacent second recessed holes is d, and d satisfies the relationship: d≥0.8 mm.

6. The pole piece according to claim 1, characterized in that: The thickness of the pole piece is A, the depth of the first concave hole is e, and A and e satisfy the relationship: e=a·A, and e>0.8mm; And / or, the depth of the second concave hole is f, A and foot are related by the formula: f=b·A, and f>0.8mm.

7. The pole piece according to claim 6, characterized in that: The aperture of the first concave hole is h, and h satisfies the relationship: 10 μm≤h≤200 μm; And / or, the aperture of the second concave hole is i, i satisfies the relationship: 10 μm≤i≤200 μm; And / or, the e and h satisfy the relationship: h=2.2758e+32.498; And / or, said f and said i satisfy the relationship: i=2.2758f+32.498; And / or, the h and the i satisfy the relationship: h=i(2.2758e+32.498) / (2.2758f+32.498).

8. The pole piece according to claim 7, characterized in that: The ratio D of the sum of the projected areas of the first concave holes on the surface of the active material layer to the surface area of ​​the first region is D=1 / 4πh 2 / (C+h) 2 ; Or, the ratio E of the sum of the projected areas of the second concave holes on the surface of the active material layer to the surface area of ​​the second region is E=1 / 4πi 2 / (C+i) 2 ; And or, the D and the E satisfy the relationship: E / D = i 2 (C+h) 2 / (h 2 +(C+i) 2 ).

9. A method for preparing a pole piece, characterized in that: The following steps are involved: Step 1: Mixing active material, conductive agent, binder and solvent to obtain active material layer slurry; Step 2: coating the active material layer slurry on at least one surface of the current collector, drying, and rolling to obtain a pole piece to be punched; Step 3: Cut the electrode to be punched and perform laser punching to obtain the electrode.

10. The method for preparing a pole piece according to claim 9, characterized in that: The laser power of the laser drilling is j, and j satisfies the relationship: e=(j-38.244) / 115.63; And / or, j satisfies the relationship: f = (j-38.244) / 115.63.

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