A pole piece and a method for manufacturing the same

Abstract

The application discloses a kind of pole piece, including current collector and the active material layer of at least one surface of the current collector is arranged;The surface of active material layer is arranged first area and second area;First area is with the center of pole lug as the center of circle, and the radius of X·C is semicircle;First area is provided with first recess, and the ratio of the depth of first recess and the thickness of active material layer is a;X is the width of pole piece, C is the charge rate of battery using pole piece;Second area is the area except first area of pole piece, and second area is provided with second recess, and the ratio of the depth of second recess is b;Wherein, a>b.Compared with prior art, the depth of recess is flexibly adjusted according to the specific position and potential distribution of pole lug, the uniformization of electrode potential distribution is realized, the possibility of uneven deposition of alkali metal ions on electrode surface during charging is reduced, thereby reducing the risk of local lithium precipitation, and then improving the overall kinetic performance of battery, and significantly prolong its cycle life.

Description

TECHNICAL FIELD

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

[0002] With the vigorous 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 construction and manufacturing process of the pole piece have a decisive influence on the overall performance and service life of the battery.

[0003] In the traditional laser punching technology of the pole piece, the punching depth ratio is often set as a fixed value. However, this process does not fully consider the differences in current density distribution and the non-uniformity of potential at different parts of the pole piece during charging. Especially in the area close to the tab of the pole piece, the current density is significantly higher than that in other areas, and the potential is correspondingly reduced. This phenomenon leads to an increase in the risk of local metal precipitation near the tab. Precipitated metal not only reduces the capacity retention rate of the battery, but also may cause internal short circuit, thereby seriously affecting the safety and cycle stability of the battery.

[0004] In view of the above-mentioned defects of the pole piece, it is necessary to provide a technical solution to solve the above-mentioned problems. SUMMARY

[0005] The purpose of the present application is to provide a pole piece and a preparation method thereof. The pole piece automatically and flexibly adjusts the depth of the concave hole according to the specific position and potential distribution of the tab, realizes the uniformization of the electrode potential distribution, and further improves the overall kinetic performance of the battery and significantly prolongs its cycle life.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions:

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

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

[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 tab 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 charge rate of the battery using the pole piece;

[0011] The second region is the region of the pole piece except the first region, and 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] wherein 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 areal density of the active material layer, and k satisfies the relationship: 0 < k ≤ 15 mg / cm 2 .

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

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

[0017] Preferably, the distance between any two adjacent second recesses 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 recess is e, and A and e satisfy the relationship: e = a·A, and e > 0.8 mm.

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

[0020] Preferably, the aperture of the first recess is h, and h satisfies the relationship: 10 μm ≤ h ≤ 200 μm.

[0021] Preferably, the aperture of the second recess is i, and i satisfies the relationship: 10 μm ≤ i ≤ 200 μm.

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

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

[0024] Preferably, h and 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 recesses on the surface of the active material layer to the area of the surface of the first region is D = 1 / 4πh 2 / (C+h) 2 .

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

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

[0028] The application also provides a preparation method of the pole piece, comprising the following steps:

[0029] Step one: mixing an active material, a conductive agent, a binder and a solvent to obtain an active material layer slurry;

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

[0031] Step three: cutting and laser punching the to-be-punched pole piece to obtain the pole piece.

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

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

[0034] The application also provides a secondary battery comprising a diaphragm, an electrolyte, a battery shell and a pole piece, wherein the pole piece is the above-mentioned pole piece.

[0035] The application has the beneficial effects that the application provides a pole piece and a preparation method thereof, the pole piece flexibly adjusts the depth of the recess hole according to the specific position and potential distribution of the tab, realizes the homogenization of the electrode potential distribution, reduces the possibility of uneven deposition of alkali metal ions on the electrode surface during the charging process, thereby reducing the risk of local metal precipitation, further improving the overall kinetic performance of the battery, and significantly prolonging the cycle life. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 FIG. 1 is a structural schematic diagram of a pole piece according to an embodiment of the application.

[0037] Wherein: 1, current collector; 2, active material layer; 21, first region; 211, first recess hole; 22, second region; 221, second recess hole; 3, tab. DETAILED DESCRIPTION

[0038] In order to make the technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below in conjunction with specific embodiments. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative efforts fall within the scope of the present application.

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

[0040] The pole piece is provided with a tab 3;

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

[0042] The first area 21 is a semicircle with the center of the tab 3 as the center and a radius of X·C; the first area 21 is provided with a first recess hole 211, and the ratio of the depth of the first recess 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 charge rate of the battery using the pole piece;

[0043] The second area 22 is the area of the pole piece except the first area 21, and the second area 22 is provided with a second recess hole 221, and the ratio of the depth of the second recess hole 221 to the thickness of the active material layer 2 is b;

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

[0045] The pole piece automatically and flexibly adjusts the depth of the recess hole according to the specific position and potential distribution of the tab 3; the current density of the first area 21 is larger, and the first recess hole 211 with a deeper setting is used, which is beneficial to realize the uniformization of the electrode potential distribution, reduce the possibility of uneven deposition of alkali metal ions on the electrode surface during charging, thereby reducing the risk of local lithium precipitation, further improving the overall kinetic performance of the battery, and significantly prolonging the cycle life of the battery.

[0046] The first area 21 is a semicircle with the center of the tab 3 as the center and a radius of X·C, and the electrode potential of this area is higher; C is a compensation coefficient related to the charge rate, which is filled in, thereby reducing the possibility of uneven deposition of lithium ions on the electrode surface during charging; at the same time, too deep holes can be used as heat transfer channels, which are helpful for quickly dissipating the heat generated during charging, thereby reducing the temperature rise of the battery.

[0047] In an embodiment of the present application, a satisfies the relationship: 10%≤a≤50%. The pore depth in this proportion range can ensure that the electrolyte fully wets the surface of the electrode sheet, thereby improving the capacity and energy density of the battery; it is also helpful to build an efficient ion migration network, thereby improving the charge and discharge rate of the battery, in addition, it 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 sheet 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 sheet and the electrolyte may be insufficient, leading to 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 sheet may be damaged, leading to the shedding or failure of the active material, which also reduces the capacity of the battery.

[0049] In an embodiment of the present application, a and b satisfy the relationship: a=b+kC%, wherein k is the area density of the active material layer, and the value range of k is 0 2 When a and b do not satisfy the relationship, there will be a difference in current density distribution and unevenness of potential in different parts of the electrode sheet during charging, which increases the risk of local lithium precipitation near the tab 3, thereby affecting the cycle performance and life of the battery.

[0050] In an embodiment of the present application, C satisfies the relationship: 0

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

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

[0053] If the distance between any two recess holes is too small, a lot of active material will be lost, affecting the capacity of the battery, in addition, the laser punching process is less stable when the punching pitch is too small, and a larger error is easily generated.

[0054] In an embodiment of the present application, the thickness of the pole piece is A, the depth of the first recess 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 pole piece is the highest, the compaction density of the bottom layer is lower, the depth e of the first recess 211 needs to be greater than 0.8mm to ensure that the active material with the highest compaction density on the surface layer of the electrode pole piece is knocked off, so that lithium ions can be embedded from the bottom layer with lower compaction density; if the depth e of the first recess 211 is less than 0.8mm, the effect of kinetic improvement brought by pore making will be lost.

[0055] And / or, the depth of the second recess 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 pole piece is the highest, the compaction density of the bottom layer is lower, the depth f of the second recess 221 needs to be greater than 0.8mm to ensure that the active material with the highest compaction density on the surface layer of the electrode pole piece is knocked off, 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 kinetic improvement brought by pore making will be lost.

[0056] In an embodiment of the present application, the pore diameter of the first recess 211 is h, h satisfies the relationship: 10um<=h<=200um, too many recesses or too large pore diameter will lead to the decrease of the conductivity of the electrode, increase the internal resistance of the battery, and thus generate more heat during the charging process, and exacerbate the problem of temperature rise.

[0057] And / or, the pore diameter of the second recess 221 is i, i satisfies the relationship: 10um<=i<=200um, too many recesses or too large pore diameter will lead to the decrease of the conductivity of the electrode, increase the internal resistance of the battery, and thus generate more heat during the charging process, and exacerbate the problem of temperature rise.

[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 an embodiment of the present application, the ratio D of the total of the projection area of the first recess 211 on the surface of the active material layer 2 to the area of the first area 21 is D=1 / 4pih 2 / (C+h) 2When the total area of the apertures in the total area of the pole piece is too small, although the mechanical integrity of the pole piece can be maintained to a certain extent, the ion diffusion speed in the battery is limited due to insufficient ion transmission channels, so that the charge and discharge performance of the battery cannot be effectively improved, especially in the case of high-rate charge and discharge, polarization may be intensified, internal resistance may be increased, and the like.

[0062] When the total area of the apertures in the total area of the pole piece is too large, the overall structure of the pole piece is excessively damaged, the mechanical strength and stability of the pole piece are reduced, the pole piece may be easily broken or damaged during the assembly and use of the battery, thereby affecting the performance and service life of the battery, and problems such as intensified polarization and increased internal resistance may occur.

[0063] And / or, the ratio E of the sum of the projected areas of the second recesses 221 on the surface of the active material layer 2 to the area of the surface of the second region 22 is E=1 / 4pi 2 / (C+i) 2 , and the influence of an area ratio that is too large or too small is equivalent to the influence of the 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 application further provides a preparation method of the pole piece, comprising the following steps:

[0066] Step one: mixing an active material, a conductive agent, a binder and a solvent to obtain an active material layer 2 slurry;

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

[0068] Step three: cutting and laser punching the to-be-punched pole piece to obtain the pole piece.

[0069] In an embodiment of the application, the laser power of the laser punching 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 punching of the application is formed by adjusting the power of the laser, and the pole piece can be quickly and simply punched and the parameters of the hole can be controlled through the relationship of the application.

[0071] The application further provides a secondary battery comprising a diaphragm, an electrolyte, a battery shell and a pole piece, wherein the pole piece is the above-mentioned pole piece.

[0072] The positive electrode tab includes a positive current collector and a positive active material layer coated on at least one surface of the positive current collector. The positive active material layer can be one or more of, but 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. The positive current collector can be any material suitable for use as a positive current collector in a lithium ion battery, such as, for example, aluminum foil, copper foil, nickel foil, stainless steel, or carbon material.

[0073] The negative electrode tab includes a negative current collector and a negative active material layer coated on at least one surface of the negative current collector. The negative active material layer can be one or more of, but not limited to, graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbead, silicon-based material, tin-based material, lithium titanate, or other metal capable of forming an alloy with lithium.

[0074] The graphite can be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material can be selected from one or more of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon alloy; and the tin-based material can be selected from one or more of elemental tin, tin oxide compound, tin alloy. The negative current collector is generally a structure or component that collects current, and can be any material suitable for use as a negative current collector in a secondary battery, such as, for example, metal foil, and more specifically, but 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. The electrolyte lithium salt can be LiPF6 and / or LiBOB used in a high-temperature electrolyte, at least one of LiBF4, LiBOB, and LiPF6 used in a low-temperature electrolyte, at least one of LiBF4, LiBOB, LiPF6, and LiTFSI used in an overcharge-preventing electrolyte, and at least one of LiClO4, LiAsF6, LiCF3SO3, and LiN(CF3SO2)2. The organic solvent can be cyclic carbonate, including PC and EC, chain carbonate, including DFC, DMC, or EMC, or carboxylic acid ester, including MF, MA, EA, and MP. The additive can be at least one of, but not limited to, film-forming additive, conductive additive, flame-retardant additive, overcharge-preventing additive, additive for controlling H2O and HF content in the electrolyte, additive for improving low-temperature performance, and multifunctional additive.

[0076] The application is further described below by way of specific examples. The following specific embodiments are merely intended to more clearly describe the technical solutions of the application, and cannot be used to limit the protection scope of the application.

[0077] Example 1

[0078] A method for preparing a pole piece:

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

[0080] Step two: coat the active material layer slurry on both surfaces of the current collector 1, dry and roll to obtain a to-be-punched pole piece;

[0081] Step three: cut and laser punch the to-be-punched pole piece, the wavelength of the laser is 1064 nm, and the laser power is set to 50 W;

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

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

[0084] Preparation of a lithium ion battery:

[0085] The separator, negative pole piece and the above positive pole piece are alternately wound and then packaged with an aluminum plastic film to prepare a battery core, which is placed in a battery shell, electrolyte is added, and then sealed to obtain a lithium ion battery. The active material of the positive pole piece 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 prepared by mixing ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate in a mass ratio of 1:2:1. The concentration of the electrolyte is 1 mol / L.

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

[0087] Table 1

[0088]

[0089] Performance test:

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

[0091] The batteries of Examples 1-8 and Comparative Examples 1-6 after cycling were disassembled, and the lithium precipitation of the pole piece was observed, and the test results are shown in Table 2.

[0092] Table 2

[0093]

[0094] According to Table 2, the data comparison of Examples 1-8 and Comparative Examples 1-2 shows that the first area 21 of Comparative Examples 1-2 has lithium precipitation, which further leads to a lower capacity retention rate when the battery is cycled to 500 cycles. This is because the surface of the electrode tab of Comparative Examples 1 and 2 is not provided with recesses with different depths, on the contrary, Examples 1-8 are provided with recesses with different depths, and the first recess 211 is provided with a deeper depth, which is beneficial to the uniformization of the electrode potential distribution, reduces the possibility of uneven deposition of alkali metal ions on the electrode surface during charging, thereby reducing the risk of local lithium precipitation, and further improving the overall kinetic performance of the battery and significantly prolonging its cycle life.

[0095] The data comparison of Examples 1-8 and Comparative Example 3 shows that the first area 21 of Comparative Example 3 has lithium precipitation, which further leads to a lower capacity retention rate when the battery is cycled to 500 cycles. This is because the depth of the first recess 211 provided on the surface of the electrode tab of Comparative Example 3 is less than the depth of the second recess 221; the current in the first area 21 is large, and a deeper recess should be provided. The depth of the first recess 211 of Comparative Example 3 is too small, so the first area 21 of Comparative Example 3 has lithium precipitation.

[0096] The data comparison of Examples 1-8 and Comparative Examples 4-5 shows that the first area 21 of Comparative Example 4 has severe lithium precipitation, which further leads to a lower capacity retention rate when the battery is cycled to 500 cycles. This is because the depth of the first recess 211 provided on the surface of the electrode tab of Comparative Example 4 is too deep, and the depth of the first recess 211 provided on the surface of the electrode tab of Comparative Example 5 exceeds the range, which damages the active material layer 2 on the surface of the electrode tab, leading to the shedding or failure of the active material, and also cannot improve the problem of lithium precipitation in the first area 21, and is suspected to also reduce the capacity of the battery.

[0097] The data comparison of Examples 1-8 and Comparative Example 6 shows that the first area 21 of Comparative Example 6 has severe lithium precipitation, which further leads to a sharp drop in capacity retention rate when the battery is cycled to 500 cycles. This is because the use rate of Comparative Example 6 exceeds the range of the parameter, and under the condition of large charging and discharging rate, the negative electrode cannot embed lithium ions in time, leading to the accumulation of a large amount of lithium ions on the surface of the negative electrode, forming metal lithium deposition, leading to a sharp decrease in 500 cycle retention rate, and seriously affecting the performance and cycle life of the battery.

[0098] Based on the disclosure and teachings of the above specification, those skilled in the art can also make changes and modifications to the above embodiments. Therefore, the present application is not limited to the specific embodiments described above, and any obvious improvements, replacements or modifications made by those skilled in the art based on the present application shall fall within the scope of the present application. In addition, although some specific terms are used in the specification, these terms are only for convenience of description and do not constitute any limitation on the present application.

Claims

1. An electrode sheet, characterized in that, It includes a current collector and an active material layer disposed on at least one surface of the current collector; The electrode sheet is provided with electrode tabs; 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 tab as the center and a radius of X·C; the first region is provided with a first recess, and the ratio of the depth of the first recess to the thickness of the active material layer is a; X is the width of the electrode, and C is the charging rate of the battery using the electrode; The second region is the region of the electrode other than the first region. The second region is provided with a second recess, and the ratio of the depth of the second recess to the thickness of the active material layer is b. Where a and b satisfy the relationship: a > b; The condition 'a' satisfies the following relationship: 10% ≤ a ≤ 50%; The relationship between a and b is: a = b + kC%, where k is the areal density of the active material layer, and the value of k ranges from 0 < k ≤ 15 mg / cm³. 2 ; The C satisfies the relation: 0 < C ≤ 5; The thickness of the electrode is A, and the depth of the first concave hole is e. A and e satisfy the relationship: e = a·A, and e > 0.8 mm. The depth of the second concave hole is f, and A and f satisfy the relationship: f=b·A, and f>0.8mm.

2. The electrode sheet 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 concave holes is d, where d satisfies the relationship: d≥0.8mm.

3. The electrode sheet according to claim 1, characterized in that, The diameter of the first concave hole is h, and h satisfies the relationship: 10μm≤h≤200μm; The diameter of the second concave hole is i, and i satisfies the relationship: 10μm≤i≤200μm; The relationship between e and h is: h = 2.2758e + 32.498; The relationship between f and i is: i = 2.2758f + 32.498; The relationship between h and i is: h = i(2.2758e + 32.498) / (2.2758f + 32.498).

4. The electrode sheet according to claim 3, characterized in that, The ratio of the sum of the projected areas of the first concave holes on the surface of the active material layer to the area of ​​the surface of the first region is D, where D = 1 / 4πh 2 / (C+h) 2 ; The ratio of the sum of the projected areas of the second concave holes on the surface of the active material layer to the area of ​​the second region is E, where E = 1 / 4πi 2 / (C+i) 2 ; The relationship between D and E is: E / D=i 2 (C+h) 2 / (h 2 +(C+i) 2 ).

5. A method for preparing an electrode sheet, applied to the electrode sheet as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: Mix the active material, conductive agent, binder and solvent to obtain the active material layer slurry; Step 2: Coat the active material layer slurry onto at least one surface of the current collector, dry and roll it to obtain the electrode sheet to be drilled; Step 3: Cut the electrode sheet to be drilled into pieces and then laser-drill holes to obtain the electrode sheet.

6. The method for preparing the electrode according to claim 5, characterized in that, In step three, the laser creates a first recessed hole on the surface of the active material layer of the electrode, the depth of the first recessed hole is e, and the laser power for drilling is j, where j satisfies the relationship: e = (j - 38.244) / 115.63; and / or, the laser creates a second recessed hole on the surface of the active material layer of the electrode, the depth of the second recessed hole is f, where j satisfies the relationship: f = (j - 38.244) / 115.63.

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