Negative electrode sheet, preparation method therefor, lithium-ion battery, and electrical device

Abstract

A negative electrode sheet, a preparation method therefor, a lithium-ion battery, and an electrical device. The electrical device comprises a lithium-ion battery, and the lithium-ion battery comprises a negative electrode sheet. The negative electrode sheet comprises a current collector, and a negative electrode active material layer disposed on a surface of the current collector, an active material in the negative electrode active material layer comprising a silicon-based material. The surface of the side of the negative electrode active material layer away from the current collector is provided with holes, the holes extending into the interior of the negative electrode active material layer.

Description

Negative electrode sheet, preparation method thereof, lithium ion battery and electric device

[0001] Cross-reference to related applications

[0002] The present disclosure claims priority to the Chinese patent application No. 202410869630.6, filed on June 30, 2024, and entitled "A negative electrode sheet, preparation method thereof, and lithium ion battery and electric device", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure belongs to the field of lithium batteries, and in particular, relates to a negative electrode sheet, a preparation method thereof, and a lithium ion battery and an electric device. BACKGROUND

[0004] As a lithium ion battery negative active material, silicon-based material has a much higher lithium storage capacity than graphite (its room temperature theoretical capacity is as high as 3580 m·Ah / g), and also has a good electronic channel, a small strain, and an environment that promotes stable growth of SEI film, and is expected to replace graphite as the next generation of high-energy-density lithium ion battery negative active material. However, silicon-based materials also have many problems. During the cycle process, the silicon particles are repeatedly expanded and contracted, and the silicon particles are subjected to a large stress, resulting in silicon particle pulverization, shedding, and electrochemical performance failure, thereby requiring continuous growth of the silicon particle surface solid electrolyte layer (SEI), which irreversibly consumes electrolyte and lithium source from the positive electrode, ultimately affecting the cycle life of the battery. SUMMARY

[0005] The purpose of the present disclosure is to solve the problem of active material pulverization and shedding caused by the volume expansion effect of the negative electrode sheet, and further improve the problem of reduced battery cycle stability caused by the continuous growth of the SEI film on the surface of the negative electrode sheet.

[0006] To achieve the above purpose, the first aspect of the present disclosure provides a negative electrode sheet, which comprises a current collector, and further comprises a negative active material layer arranged on the surface of the current collector, wherein the active material in the negative active material layer comprises a silicon-based material; a hole is arranged on the side surface of the negative active material layer away from the current collector, and the hole extends to the inside of the negative active material layer.

[0007] Optionally, the depth of the hole is 20-50 μm; and / or the diameter of the hole is 10-50 μm.

[0008] Optionally, the minimum distance between any two adjacent holes on the side surface of the negative active material layer away from the current collector is 10-50 μm.

[0009] Optionally, the negative active material layer has pores, and a porosity of the pores is 20% to 40%.

[0010] Optionally, the negative electrode sheet further comprises a protective layer laminated on a surface of the negative active material layer away from the current collector; and the protective layer is provided with through holes corresponding to the holes.

[0011] Optionally, the thickness of the protective layer is 0.02 to 5 μm.

[0012] Optionally, the areal density of the protective layer is 1.5 to 10 g / m 2 .

[0013] Optionally, the material of the protective layer comprises a high polymer.

[0014] Optionally, the material of the protective layer comprises a high polymer and a lithium salt; and the mass ratio of the high polymer to the lithium salt is 1 to 5:1.

[0015] Optionally, the high polymer is selected from at least one of PEO, PVA, PVDF-HFP, PAN, PMMA, PET and PVCA.

[0016] Optionally, the lithium salt is selected from at least one of lithium perchlorate, lithium nitrate, lithium aluminum titanium phosphate, lithium bisfluoromethanesulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium lanthanum zirconium oxide, lithium sulfide and lithium hexafluorophosphate; and optionally, the protective layer further comprises Al2O3 and / or SiO2.

[0017] Optionally, pores in a region of the negative active material layer close to the protective layer are filled with the material of the protective layer, and pores in a region of the negative active material layer close to the current collector do not contain the material of the protective layer.

[0018] Optionally, the silicon-based material is selected from at least one of silicon, silicon monoxide, silicon-carbon composite material and silicon-iron composite material.

[0019] Optionally, the active material further comprises a lithium-based material; and the lithium-based material is selected from at least one of lithium boron alloy, lithium magnesium alloy, lithium aluminum alloy, lithium tin alloy, lithium germanium alloy, lithium gallium alloy, lithium indium alloy, lithium antimony alloy, lithium indium alloy, lithium zinc alloy, lithium lead alloy and lithium bismuth alloy.

[0020] Optionally, the active material further comprises graphite; and the mass percentage of the graphite in the active material is 5 to 20 wt% based on the total weight of the active material.

[0021] Optionally, the negative active material layer further comprises a conductive agent and a binder; and a mass ratio of the silicon-based material, the conductive agent and the binder is 5-8:0.5-2:1.

[0022] A second aspect of the present disclosure provides a method for preparing a negative electrode sheet, comprising the following steps:

[0023] applying a negative electrode slurry to a side surface of a current collector to obtain a current collector coated with the negative electrode slurry; an active material in the negative electrode slurry comprises a silicon-based material;

[0024] performing first drying and rolling on the current collector coated with the negative electrode slurry in sequence to form a negative active material layer on the current collector;

[0025] forming a hole on a surface of the negative active material layer away from the current collector, and the hole extends to an inside of the negative active material layer.

[0026] Optionally, a depth of the hole is 20-50 μm; and / or, a diameter of the hole is 10-50 μm.

[0027] Optionally, a minimum spacing between any two adjacent holes on a surface of the negative active material layer away from the current collector is 10-50 μm.

[0028] Optionally, the method further comprises: before forming the hole on the surface of the negative active material layer away from the current collector, applying a protective layer slurry on the surface of the negative active material layer away from the current collector, and performing second drying on the electrode after applying the protective layer slurry to form a protective layer on the surface of the negative active material layer, to obtain a negative electrode sheet with the protective layer.

[0029] Optionally, the method further comprises: perforating the negative electrode sheet with the protective layer, the hole extending from a surface of the protective layer to the negative active material layer to form a through hole in the protective layer and the hole in the negative active material layer.

[0030] Optionally, the negative active material layer has pores, and the protective layer slurry penetrates into the pores.

[0031] A third aspect of the present disclosure provides a negative electrode sheet prepared by the method provided in the second aspect of the present disclosure.

[0032] A fourth aspect of the present disclosure provides a lithium ion battery comprising any one of the negative electrode sheets provided in the first aspect of the present disclosure or the third aspect of the present disclosure.

[0033] The fifth aspect of the present disclosure provides a power utilization device, which comprises any one of the lithium ion batteries provided in the fourth aspect of the present disclosure.

[0034] Other features and advantages of the present disclosure will be described in detail in the following detailed description.

[0035] Through the above technical solution, the negative electrode active material layer of the present disclosure is provided with holes, which can increase the surface area of the negative electrode active material layer on the one hand, and the current density is lower compared with the negative electrode active material layer without holes, which is beneficial to the uniform deposition of lithium, thereby helping to relieve the expansion of the electrode sheet; on the other hand, the holes provided in the present disclosure can form a strong electric potential in the negative electrode active material layer, and lithium will preferentially deposit at the site with higher electric potential (i.e. the side of the hole close to the current collector), so lithium will preferentially deposit in the hole to avoid the pulverization of the silicon-based material caused by the reaction of all lithium ions with silicon, thereby improving the cycle performance of the battery. BRIEF DESCRIPTION OF DRAWINGS

[0036] The accompanying drawings are included to provide a further understanding of the present disclosure and constitute a part of the specification, and together with the following detailed description, serve to explain the present disclosure but do not constitute a limitation thereof. In the drawings:

[0037] FIG. 1 is a structural schematic diagram of a negative electrode sheet provided in Embodiment 1 of the present disclosure.

[0038] FIG. 2 is a structural schematic diagram of a negative electrode sheet provided in Embodiment 11 of the present disclosure.

[0039] FIG. 3 is an SEM diagram of the negative electrode sheet provided in Embodiment 11 of the present disclosure after punching.

[0040] FIG. 4 is an SEM diagram of the negative electrode sheet provided in Embodiment 11 of the present disclosure at different SOCs.

[0041] Legend of reference signs: 210, current collector; 220, negative electrode active material layer; 221, hole; 230, protective layer; 231, through hole. DETAILED DESCRIPTION

[0042] The specific embodiments of the present disclosure are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0043] The first aspect of the present disclosure provides a negative electrode sheet, as shown in FIG. 1, which comprises a current collector 210 and a negative electrode active material layer 220 provided on the surface of the current collector 210, and the active material in the negative electrode active material layer 220 comprises a silicon-based material; a hole 221 is provided on the side surface of the negative electrode active material layer 220 away from the current collector 210, and the hole extends to the inside of the negative electrode active material layer.

[0044] In the present disclosure, the active material in the negative electrode active material layer is a silicon-based material, which has a lithium affinity. The holes provided in the present disclosure can form a stronger electric potential in the negative electrode active material layer, and lithium will preferentially deposit at the site with a higher electric potential (the lithium hole is close to the side of the current collector), so lithium will preferentially deposit in the hole to avoid the pulverization of the silicon-based material caused by the reaction of all lithium ions with silicon, thereby improving the cycle performance of the battery. In addition, the holes provided on the negative electrode active material layer can increase the surface area of the negative electrode active material layer. Compared with the negative electrode active material layer without holes, the battery has a lower current density, which is conducive to the uniform deposition of lithium and provides expansion space for the silicon-based material in the direction parallel to the current collector, thereby relieving the expansion pressure of the negative electrode sheet in the direction perpendicular to the current collector.

[0045] In the present disclosure, the field effect exhibited by the silicon-based material at the hole has a synergistic effect with the diameter and depth of the hole. If the diameter of the hole is larger, the field effect is weakened. Therefore, the diameter of the hole is preferably 10-50 μm, for example, it can be 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 40 μm, 45 μm, 50 μm or any value within the aforementioned range.

[0046] If the depth of the hole is deeper, the field strength at the bottom of the hole is difficult to affect the deposition of lithium ions. Therefore, in order to facilitate the capture of lithium ions, the depth of the hole is preferably 20-50 μm, for example, it can be 20 μm, 25 μm, 30 μm, 37 μm, 40 μm, 45 μm, 50 μm or any value within the aforementioned range.

[0047] In order to make the negative electrode active material layer have a suitable surface area and at the same time facilitate the improvement of the energy density of the negative electrode sheet, the minimum spacing between any two adjacent holes is preferably 10-50 μm, for example, it can be 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 40 μm, 45 μm, 50 μm or any value within the aforementioned range.

[0048] In some preferred embodiments of the present disclosure, the holes are ordered 3D structures, and the holes are arranged in an array on the negative electrode active material layer.

[0049] In the present disclosure, the negative electrode active material layer has a porous structure and has pores with a porosity of 20-40%.

[0050] In some preferred embodiments of the present disclosure, referring to FIG. 2, the negative electrode sheet comprises a current collector 210 and a negative active material layer 220 stacked on one side surface of the current collector 210, and further comprises a protective layer 230 arranged on the side surface of the negative active material layer 220 away from the current collector 210; and the protective layer 230 is provided with through holes 231 corresponding to the holes 221, so as to facilitate the deposition of lithium in the holes or the holes and the through holes.

[0051] In order to prevent the protective layer from being too thick to affect the performance of the electrode, the thickness of the protective layer is 0.02-5 μm, for example, 0.02 μm, 0.1 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm or any value within the above range.

[0052] The addition of the protective layer on the surface of the negative active material layer makes it more difficult for lithium ions to deposit on the surface of the negative electrode sheet from the perspective of kinetics, and the appropriate thickness of the protective layer also enables the negative electrode sheet to have a suitable energy density. If the thickness of the protective layer is too small, it is difficult to form a three-dimensional structure with the current collector, which is lithium-deficient on the surface and lithium-rich inside, and thus the deposition of lithium ions is obviously dispersed; if the thickness of the protective layer is too large, it will increase the volume of the battery and adversely affect the volume expansion of the negative electrode, and also reduce the performance of the battery.

[0053] Specifically, the calculation formula of the designed thickness of the protective layer is: designed thickness of the protective layer = (thickness of the electrode - thickness of the current collector) x porosity of the negative active material layer x filling percentage (generally calculated as 50%) x area of the negative active material layer.

[0054] In the formula, the areal density of the protective layer is 1.5-10 g / m 2 .

[0055] In the formula, the material of the protective layer can be a high molecular polymer, and the higher affinity of silicon-based materials to lithium than the high molecular polymer enables lithium to bypass the protective layer and preferentially deposit on the silicon-based material. In order to make the protective layer have a higher lithium ion conductivity, the high molecular polymer can be at least one of polyethylene oxide (PEO), polyvinyl alcohol (PVA), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET) and polyvinyl chloride acetate (PVCA).

[0056] In some preferred embodiments of the present disclosure, the protective layer comprises a high-molecular polymer and a lithium salt to better conduct lithium ions. Specifically, the mass ratio of the high-molecular polymer to the lithium salt is 1-5:1. Specifically, the lithium salt can be at least one of lithium perchlorate, lithium nitrate, lithium aluminum titanium phosphate (LATP), lithium bisfluoromethanesulfonimide (LiFSI), lithium bis-trifluoromethanesulfonimide (LiTFSI), lithium lanthanum zirconium oxide (LLZO), lithium sulfide, and lithium hexafluorophosphate.

[0057] Optionally, the protective layer further comprises Al2O3 and / or SiO2 with high lithium ion conductivity.

[0058] In the present disclosure, since the negative electrode active material layer has pores, the slurry of the protective layer also penetrates into the pores, the pores in the region of the negative electrode active material layer close to the side of the protective layer are filled with the material of the protective layer, the pores in the region of the negative electrode active material layer close to the side of the current collector do not contain the material of the protective layer, and the content of the material of the protective layer in the pores of the negative electrode active material layer gradually decreases from the protective layer to the current collector.

[0059] Since the protective layer has weak lithium affinity and the silicon-based material has strong lithium affinity, by creating ordered deposition sites on the negative electrode active material layer and the protective layer (lithium ions preferentially deposit into the material layer through the pores), the lithium ion deposition current can be uniformly dispersed to alleviate the risk of lithium dendrite formation caused by lithium ion deposition aggregation.

[0060] In the present disclosure, the silicon-based material in the negative electrode active material layer can be at least one of silicon, silicon monoxide, silicon-carbon composite material, and silicon-iron composite material, which has lithium affinity and is suitable for use as a negative electrode sheet. The silicon-based material is used as a lithium storage material and is accompanied by a small amount of lithium precipitation to form a negative electrode sheet with high energy density.

[0061] In some specific embodiments of the present disclosure, the lithium-based material is selected from at least one of lithium boron alloy, lithium magnesium alloy, lithium aluminum alloy, lithium tin alloy, lithium germanium alloy, lithium gallium alloy, lithium indium alloy, lithium antimony alloy, lithium indium alloy, lithium zinc alloy, lithium lead alloy, and lithium bismuth alloy.

[0062] The active material further comprises graphite, and the mass percentage of the graphite in the active material is 5-20wt% based on the total weight of the active material.

[0063] In some embodiments of the present disclosure, the negative electrode active material layer further comprises a conductive agent and a binder; to improve the performance of the negative electrode, the mass ratio of the silicon-based material, the conductive agent, and the binder is 5-8:0.5-2:1.

[0064] The second aspect of the present disclosure provides a method for preparing a negative electrode sheet, comprising the following steps:

[0065] applying a negative electrode slurry to one side surface of the current collector to obtain a current collector coated with the negative electrode slurry; the active material in the negative electrode slurry comprises a silicon-based material;

[0066] sequentially performing first drying and rolling on the current collector coated with the negative electrode slurry to form a negative electrode active material layer on the current collector;

[0067] forming holes on the surface of the negative electrode active material layer away from the current collector, and the holes extend to the inside of the negative electrode active material layer.

[0068] By providing holes on the negative electrode active material layer, expansion space can be provided for the silicon-based material in the direction parallel to the current collector, thereby relieving the expansion pressure of the negative electrode in the direction perpendicular to the current collector and improving the cycle stability of the electrode.

[0069] In order to enable the field effect of the silicon-based material at the holes to affect lithium ions, in some embodiments of the present disclosure, the depth of the holes is 20-50 μm; and / or the diameter of the holes is 10-50 μm.

[0070] In order to enable the negative electrode sheet to have a high enough energy density, the minimum distance between any two adjacent holes on the surface of the negative electrode active material layer away from the current collector is 10-50 μm.

[0071] In some embodiments of the present disclosure, the method further comprises: before forming the holes on the surface of the negative electrode active material layer away from the current collector, applying a protective layer slurry on the surface of the negative electrode active material layer away from the current collector, and performing second drying on the electrode after applying the protective layer slurry to form a protective layer on the surface of the negative electrode active material layer, thereby obtaining a negative electrode sheet with a protective layer.

[0072] The above method further comprises: perforating the negative electrode sheet with the protective layer, the holes extending from the surface of the protective layer to the negative electrode active material layer to form through holes in the protective layer and the holes in the negative electrode active material layer. After forming the protective layer on the negative electrode active material layer, perforation is performed, such as laser perforation. The protective layer material can absorb part of the laser energy to protect the current collector substrate from being damaged by the laser, while also inhibiting the waste splashing caused by laser perforation.

[0073] In the negative electrode active material layer, there are pores, and the protective layer slurry penetrates into the pores.

[0074] In some embodiments of the present disclosure, the protective layer slurry comprises a high molecular polymer and a solvent, and the mass ratio of the high molecular polymer to the solvent in the protective layer slurry is 0.5-1.5:1. The high molecular polymer is preferably a high molecular material with poor affinity to lithium, and specifically, the high molecular polymer is selected from at least one of polyethylene oxide (PEO), polyvinyl alcohol (PVA), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), polyethylene terephthalate (PET), and polyvinyl chloride acetate (PVCA). In some preferred embodiments of the present disclosure, the high molecular polymer is PEO with a molecular weight of 30W.

[0075] In some embodiments of the present disclosure, the protective layer slurry further comprises a lithium salt; and the mass ratio of the high molecular polymer, the lithium salt, and the solvent is 0.006-0.03:0.006:1.

[0076] Specifically, the lithium salt can be at least one of lithium perchlorate, lithium nitrate, lithium aluminum titanium phosphate, lithium bisfluoromethanesulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium lanthanum zirconium oxide, lithium sulfide, and lithium hexafluorophosphate, which have high ion conductivity; and the solvent is selected from at least one of DME, DMF, and NMP to form a protective layer slurry suitable for coating.

[0077] In the active material, the lithium-based material has a lithium affinity, and the lithium-based material can be at least one of lithium boron alloy, lithium magnesium alloy, lithium aluminum alloy, lithium tin alloy, lithium germanium alloy, lithium gallium alloy, lithium indium alloy, lithium antimony alloy, lithium indium alloy, lithium zinc alloy, lithium lead alloy, and lithium bismuth alloy.

[0078] In the active material, the lithium-based material has a lithium affinity, and the lithium-based material can be at least one of lithium boron alloy, lithium magnesium alloy, lithium aluminum alloy, lithium tin alloy, lithium germanium alloy, lithium gallium alloy, lithium indium alloy, lithium antimony alloy, lithium indium alloy, lithium zinc alloy, lithium lead alloy, and lithium bismuth alloy.

[0079] In some embodiments of the present disclosure, the negative electrode slurry further comprises a conductive agent and a binder; and to improve the stability of the electrode structure and the performance of the battery, the mass ratio of the silicon-based material, the conductive agent, and the binder is 5-8:0.5-2:1.

[0080] In some embodiments of the present disclosure, the punching method comprises laser punching or mechanical punching. The size of the hole formed by laser punching can be accurately controlled by adjusting the parameters of laser punching. Mechanical punching can also be used to form ordered holes on the negative electrode sheet, and preferably, a physical hole pressing method is used to manufacture the holes to reduce the material loss of the electrode sheet and avoid the influence of excessive material loss on the energy density of the electrode sheet.

[0081] The third aspect of the present disclosure also provides a negative plate prepared by the above method.

[0082] The present disclosure also provides a lithium ion battery comprising any one of the negative plates provided by the first aspect of the present disclosure.

[0083] The present disclosure also provides an electrical device, such as an electric tool, a digital product, a mobile phone, a notebook computer, an electric vehicle, etc., comprising the lithium ion battery described above.

[0084] The present disclosure is further illustrated in detail by the following examples. The raw materials used in the examples can be obtained by commercial channels.

[0085] Example 1

[0086] This example is used to illustrate the preparation method of the negative plate provided by the present disclosure, which comprises the following steps:

[0087] (1) Silicon, conductive carbon black and binder polyacrylic acid (PAA) are added into water in a mass ratio of 8:1:1 and stirred uniformly to obtain a negative electrode slurry;

[0088] (2) The negative electrode slurry is uniformly coated on one side surface of a copper foil current collector to form a negative electrode slurry layer, which is dried and rolled to form a negative electrode active material layer on the copper foil; the thickness of the negative electrode active material layer is 58 μm; the coating surface density of the negative electrode active material layer is 2 g / m 2 ;

[0089] (3) The negative electrode active material layer is subjected to laser drilling, wherein the laser drilling conditions include a frequency of 50 kHz, a power of 120 W and a scanning speed of 15000 mm / s; the average diameter of the holes formed by laser drilling is 30 μm, the hole depth is 37 μm, and the hole spacing between adjacent two holes is 35 μm. The obtained lithium ion battery negative plate is marked as M1.

[0090] Example 2

[0091] The preparation method of the negative plate in this example is carried out with reference to Example 1, and the difference between this example and Example 1 is that:

[0092] In step (3), the average diameter of the holes formed by laser drilling of the negative electrode active material layer is 5 μm, the hole depth is 37 μm, and the hole spacing between adjacent two holes is 35 μm. The obtained lithium ion battery negative plate is marked as M2.

[0093] Example 3

[0094] The preparation method of the negative plate in this example is carried out with reference to Example 1, and the difference between this example and Example 1 is that:

[0095] The average diameter of the holes formed by laser drilling in the negative active material layer in step (3) is 10 μm, the hole depth is 37 μm, and the hole spacing between adjacent two holes is 35 μm. The obtained lithium ion battery negative plate is marked as M3.

[0096] Example 4

[0097] The preparation method of the negative plate in this example is carried out with reference to Example 1, and the difference from Example 1 is that:

[0098] The average diameter of the holes formed by laser drilling in the negative active material layer in step (3) is 50 μm, the hole depth is 37 μm, and the hole spacing between adjacent two holes is 35 μm. The obtained lithium ion battery negative plate is marked as M4.

[0099] Example 5

[0100] The preparation method of the negative plate in this example is carried out with reference to Example 1, and the difference from Example 1 is that:

[0101] The average diameter of the holes formed by laser drilling in the negative active material layer in step (3) is 60 μm, the hole depth is 37 μm, and the hole spacing between adjacent two holes is 35 μm. The obtained lithium ion battery negative plate is marked as M5.

[0102] Example 6

[0103] The preparation method of the negative plate in this example is carried out with reference to Example 1, and the difference from Example 1 is that:

[0104] The average diameter of the holes formed by laser drilling in the negative active material layer in step (3) is 30 μm, the hole depth is 10 μm, and the hole spacing between adjacent two holes is 35 μm. The obtained lithium ion battery negative plate is marked as M6.

[0105] Example 7

[0106] The preparation method of the negative plate in this example is carried out with reference to Example 1, and the difference from Example 1 is that:

[0107] The average diameter of the holes formed by laser drilling in the negative active material layer in step (3) is 30 μm, the hole depth is 20 μm, and the hole spacing between adjacent two holes is 35 μm. The obtained lithium ion battery negative plate is marked as M7.

[0108] Example 8

[0109] The preparation method of the negative plate in this example is carried out with reference to Example 1, and the difference from Example 1 is that:

[0110] The average diameter of the holes formed by laser drilling in the negative active material layer in step (3) is 30 μm, the hole depth is 50 μm, and the hole spacing between adjacent two holes is 35 μm. The obtained lithium ion battery negative plate is marked as M8.

[0111] Example 9

[0112] The preparation method of the negative plate in this example is carried out with reference to Example 1, and the difference between this example and Example 1 is that:

[0113] The average diameter of the holes formed by laser drilling in the negative active material layer in step (3) is 30 μm, the hole depth is 37 μm, and the hole spacing between adjacent two holes is 10 μm. The obtained lithium ion battery negative plate is marked as M9.

[0114] Example 10

[0115] The preparation method of the negative plate in this example is carried out with reference to Example 1, and the difference between this example and Example 1 is that:

[0116] The average diameter of the holes formed by laser drilling in the negative active material layer in step (3) is 30 μm, the hole depth is 37 μm, and the hole spacing between adjacent two holes is 50 μm. The obtained lithium ion battery negative plate is marked as M10.

[0117] Example 11

[0118] The difference between this example and Example 1 is that a step of preparing a protective layer is added, specifically:

[0119] (3) The polyethylene oxide (PEO) solution (the mass ratio of PEO and N-N dimethylformamide DMF is 3:100, and the molecular weight of PEO is 30W) is added into the lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) solution (the mass ratio of PEO and LiTFSI is 1:5), and stirred uniformly to obtain a protective layer slurry; then the protective layer slurry is coated on the surface of the negative active material layer away from the copper foil current collector, the doctor blade thickness is 30 μm, and the protective layer is formed on the negative active material layer after drying, thereby obtaining a negative plate with a protective layer.

[0120] (4) The negative plate is laser drilled, wherein the laser drilling conditions include: a frequency of 50 kHz, a power of 120 W, and a scanning speed of 15000 mm / s; the average diameter of the holes formed by laser drilling is 30 μm, the hole depth is 37 μm, and the hole spacing between adjacent two holes is 35 μm. The obtained lithium ion battery negative plate is marked as M11.

[0121] The actual thickness of the protective layer formed on the surface of the negative plate is 2 μm, and the area density of the protective layer is 5 g / m 2The thickness of the protective layer is calculated using the following formula:

[0122] The thickness of the protective layer = thickness of the pole piece after the protective layer is applied (60 μm) - thickness of the pole piece without the protective layer (58 μm).

[0123] In addition, after the protective layer slurry is applied to the surface of the negative pole piece, it will penetrate into the pores of the negative pole piece. The penetrated slurry will form a layer of penetrated slurry with a concentration gradient distribution in the negative active material layer.

[0124] The picture of the negative pole piece after laser drilling in this embodiment is shown in Figure 3.

[0125] Example 12

[0126] The preparation method of the negative pole piece in this embodiment is carried out with reference to Example 11, and the difference from Example 11 is that:

[0127] The thickness of the protective layer is 0.02 μm. The obtained lithium ion battery negative pole piece is marked as M12.

[0128] Example 13

[0129] The preparation method of the negative pole piece in this embodiment is carried out with reference to Example 11, and the difference from Example 11 is that:

[0130] The thickness of the protective layer is 0.1 μm. The obtained lithium ion battery negative pole piece is marked as M13.

[0131] Example 14

[0132] The preparation method of the negative pole piece in this embodiment is carried out with reference to Example 11, and the difference from Example 11 is that:

[0133] The thickness of the protective layer is 1 μm. The obtained lithium ion battery negative pole piece is marked as M14.

[0134] Example 15

[0135] The preparation method of the negative pole piece in this embodiment is carried out with reference to Example 11, and the difference from Example 11 is that:

[0136] The thickness of the protective layer is 5 μm. The obtained lithium ion battery negative pole piece is marked as M15.

[0137] Example 16

[0138] The preparation method of the negative pole piece in this embodiment is carried out with reference to Example 11, and the difference from Example 11 is that:

[0139] The thickness of the protective layer is 7 μm. The obtained lithium ion battery negative pole piece is marked as M16.

[0140] Example 17

[0141] The preparation method of the negative electrode sheet in this example was carried out with reference to Example 11, which was different from Example 11 in that:

[0142] The protective layer slurry did not contain lithium salt, i.e., a polyethylene oxide (PEO) solution (the mass ratio of PEO and N-N dimethylformamide DMF was 3:100, and the molecular weight of PEO was 30W) was directly used as the protective layer slurry.

[0143] The obtained lithium ion battery negative electrode sheet was marked as M17.

[0144] Comparative Example 1

[0145] The preparation method of the negative electrode sheet in this example was carried out with reference to Example 11, which was different from Example 11 in that:

[0146] The negative active material layer was not punched. The obtained lithium ion battery negative electrode sheet was marked as D1.

[0147] Battery preparation:

[0148] The positive active material NCM622, the binder PVDF, acetylene black and carbon fiber were mixed in a mass ratio of 960:30:5:5 to prepare an NCM positive electrode sheet.

[0149] The lithium battery negative electrode sheets prepared in Examples 1-17 and Comparative Examples 1-2 and the separator and the NCM positive electrode sheet were alternately stacked to obtain a bare cell, the bare cell was placed in an aluminum plastic film outer packaging body, electrolyte was injected, and then vacuum sealed; then the obtained cell was placed at 60°C for 48h, and then pressure formation was carried out at 45°C, and then secondary packaging, degassing and capacity distribution were carried out to obtain a lithium ion battery.

[0150] The electrolyte comprises the following components: N,N-dimethylacetamide (DME) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) in a volume ratio of 2:8; and lithium bisfluorosulfonylimide salt (LiFSI) with a molar concentration of 1.3mol / L.

[0151] The obtained lithium ion batteries were respectively marked as B1-B18.

[0152] Performance test

[0153] Test Example 1

[0154] The lithium ion batteries prepared in Examples 1-17 and Comparative Example 1 were subjected to charge-discharge cycle tests, and the test steps were as follows:

[0155] The batteries prepared from Examples 1-17 and Comparative Example 1 were subjected to formation treatment, i.e. constant current charging to 4.2V at a current density of 0.05C, then constant current discharging to 2.5V at a current density of 0.05C, and so on for three times, so as to achieve the purpose of formation.

[0156] Battery charge-discharge cycle test: at 25℃, the battery was charged at a current density of 0.5C to 4.2V, and the cutoff current was 0.05C; then the battery was discharged at a current density of 0.5C to 2.5V, and so on for one cycle. The maximum cycle number at which the battery capacity remained 80% was recorded.

[0157] The test results are shown in Table 1.

[0158] Table 1

[0159] As can be seen from the above table, the cycle stability of the battery prepared by the negative active material layer provided with holes is obviously enhanced.

[0160] Test Example 2

[0161] The lithium ion battery B11 prepared by using the lithium ion battery negative plate M11 was cycled, and the battery was disassembled at different SOC (state of charge available in the battery, 0% when the battery is not charged, and 100% when the battery is fully charged) (SOC was 0%, 50%, and 100%, respectively), and the lithium ion battery negative plate was observed under different SOC conditions by scanning electron microscopy, and the SEM image is shown in FIG. 4, and then the site selection of lithium deposition was observed.

[0162] As can be seen from FIG. 4, as the SOC increases, lithium tends to deposit in the holes of the negative plate, and finally reaches a saturated state, and the surface of the battery is smooth.

[0163] The preferred embodiments of the present disclosure are described in detail above with reference to the accompanying drawings, but the present disclosure is not limited to the specific details in the above-described embodiments. Within the technical concept of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.

[0164] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction, and in order to avoid unnecessary repetition, the present disclosure will not further describe various possible combinations.

Claims

1. A negative electrode sheet comprising a current collector (210), characterized by, Also included are: a negative active material layer (220) disposed on a surface of the current collector (210); the active material in the negative active material layer (220) includes a silicon-based material; the negative active material layer (220) is provided with a hole (221) on a side surface away from the current collector (210), and the hole (221) extends to the inside of the negative active material layer (220).

2. The negative electrode sheet according to claim 1, wherein The depth of the hole (221) is 20-50 μm; and / or, The diameter of the hole (221) is 10-50 μm.

3. The negative electrode sheet according to claim 1 or 2, wherein The minimum distance between any two adjacent holes (221) on the side surface of the negative active material layer (220) away from the current collector (210) is 10-50 μm.

4. The negative electrode sheet according to any one of claims 1 to 3, wherein The negative active material layer (220) has pores, and the porosity of the pores is 20-40%.

5. The negative electrode sheet according to any one of claims 1 to 4, wherein The negative electrode sheet further includes a protective layer (230) stacked on the side surface of the negative active material layer (220) away from the current collector (210); and the protective layer (230) is provided with a through hole (231) corresponding to the hole (221).

6. The negative electrode sheet according to claim 5, wherein The thickness of the protective layer (230) is 0.02-5 μm.

7. The negative electrode sheet according to claim 5 or 6, wherein The surface density of the protective layer (230) is 1.5-10 g / m 2 .

8. The negative electrode sheet according to any one of claims 5 to 7, wherein The material of the protective layer includes a high polymer.

9. The negative electrode sheet according to any one of claims 5 to 7, wherein The material of the protective layer includes a high polymer and a lithium salt; the mass ratio of the high polymer to the lithium salt is 1-5:

1.

10. The negative electrode sheet according to claim 8 or 9, wherein The high polymer is selected from at least one of PEO, PVA, PVDF-HFP, PAN, PMMA, PET and PVCA.

11. The negative electrode sheet according to claim 9 or 10, wherein The lithium salt is selected from at least one of lithium perchlorate, lithium nitrate, lithium aluminum titanium phosphate, lithium bisfluoromethane sulfonimide, lithium bis-trifluoromethane sulfonimide, lithium lanthanum zirconium oxide, lithium sulfide and lithium hexafluorophosphate; Optionally, the protective layer further includes Al2O3 and / or SiO2.

12. The negative electrode sheet according to any one of claims 5 to 11, wherein The pores in the region of the negative active material layer close to the side of the protective layer are filled with the material of the protective layer, and the pores in the region of the negative active material layer close to the side of the current collector do not contain the material of the protective layer.

13. The negative electrode sheet according to any one of claims 1 to 12, wherein The silicon-based material is selected from at least one of silicon, silicon monoxide, silicon-carbon composite material and silicon-iron composite material.

14. The negative electrode sheet according to any one of claims 1 to 12, wherein The active material further includes a lithium-based material; the lithium-based material includes at least one of lithium boron alloy, lithium magnesium alloy, lithium aluminum alloy, lithium tin alloy, lithium germanium alloy, lithium gallium alloy, lithium indium alloy, lithium antimony alloy, lithium indium alloy, lithium zinc alloy, lithium lead alloy and lithium bismuth alloy.

15. The negative electrode sheet according to any one of claims 1 to 12, wherein The active material further includes graphite; The mass percentage of graphite in the active material is 5-20 wt% based on the total weight of the active material.

16. The negative electrode sheet according to claim 1 to 12, wherein The negative active material layer further includes a conductive agent and a binder; The mass ratio of the silicon-based material, the conductive agent and the binder is 5-8:0.5-2:

1.

17. A method for producing a negative electrode sheet, characterized by The method includes the following steps: coating a negative electrode slurry to one side surface of a current collector to obtain a current collector coated with a negative electrode slurry; the active material in the negative electrode slurry includes a silicon-based material; sequentially performing first drying and rolling on the current collector coated with the negative electrode slurry to form a negative active material layer on the current collector; A hole is formed on the surface of the negative electrode active material layer away from the current collector, and the hole extends to the inside of the negative electrode active material layer.

18. The method of claim 17, wherein, The depth of the hole is 20-50 μm; and / or, The diameter of the hole is 10-50 μm.

19. The method of claim 17 or 18, wherein, The minimum distance between any two adjacent holes on the surface of the negative electrode active material layer away from the current collector is 10-50 μm.

20. The method of any one of claims 17-19, wherein, The method further comprises: Before forming the hole on the surface of the negative electrode active material layer away from the current collector, a protective layer slurry is coated on the surface of the negative electrode active material layer away from the current collector, and the electrode after coating the protective layer slurry is subjected to a second drying to form a protective layer on the surface of the negative electrode active material layer, thereby obtaining a negative electrode sheet with a protective layer.

21. The method of claim 20, wherein, The method further comprises: punching the negative electrode sheet with a protective layer, the hole extending from the surface of the protective layer to the negative electrode active material layer to form a through hole in the protective layer and the hole in the negative electrode active material layer.

22. The method of claim 20, wherein, The negative electrode active material layer has pores, and the protective layer slurry penetrates into the pores.

23. A negative electrode sheet prepared by the method according to any one of claims 17-22.

24. A lithium-ion battery, characterized by, The lithium ion battery comprises the negative electrode sheet according to any one of claims 1-16 or claim 23.

25. An electrical device, comprising: The electric device comprises the lithium ion battery according to claim 24.

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