Silicon-containing negative pole piece, secondary battery and electronic device

Abstract

The embodiment of the invention provides a silicon-containing negative pole piece, a secondary battery and an electronic device, the silicon-containing negative pole piece comprises a tab, a negative current collector and an active material layer arranged on at least one surface of the negative current collector, the tab extends out from one end of the negative current collector, and the active material layer is arranged on the other end of the negative current collector. The active material layer has a width in a direction extending along the tab, and the active material layer includes: a first region accounting for 1 / 4-1 / 2 of the width of the active material layer; and a second region occupying 1 / 2-3 / 4 of the width of the active material layer, in which the first region is closer to the tab than the second region, and in which the silicon content of the first region is W1, the silicon content of the second region is W2, and 1.03 < W2 / W1 < 2. According to the silicon-containing negative pole piece provided by the invention, the second region, which is far away from the tab, of the spatial position of the pole piece has relatively high silicon content, and the first region, which is close to the tab, of the spatial position of the pole piece has relatively low silicon content, so that the problem of local lithium precipitation caused by spatial position distribution of an electrolyte is reduced.

Description

Technical Field

[0001] Embodiments of the present application relate to a silicon-containing negative electrode sheet, a secondary battery, and an electronic device. Background Art

[0002] In the new energy sector, lithium-ion batteries are used in modules with a fixed orientation. This results in a cell with a first region closer to the tab and a second region farther away. Under the influence of gravity, the electrolyte distribution in a lithium-ion battery is spatially dependent, with electrolyte concentration in the second region farther away from the tab and electrolyte deficiency in the first region closer to the tab.

[0003] For high energy density lithium-ion batteries, especially ultra-high energy density lithium-ion batteries using high nickel and high silicon systems, in the middle and late stages of their life, as various side reactions occur in the battery cells and the electrolyte is consumed, the battery cells may lack electrolyte. Figure 1 As shown in the figure, the electrolyte shortage in the upper part of the electrode space (the first area closer to the electrode ear) will be more serious. The electrolyte shortage will worsen the dynamics of the battery cell, causing the battery cell to be in a state of low charge when charged at a high rate. Figure 2 Lithium deposition occurs in the shadowed area. This can shorten the life of the battery cell and even pose a safety risk. Summary of the Invention

[0004] In order to solve the problem of lithium plating caused by the spatial distribution of electrolyte during the use of battery cells, especially in the middle and late stages of their life, a lithium-ion battery is designed with a zoned coated negative electrode. A high silicon content design is adopted in the second zone of the battery cell's spatial position (farther away from the bottom of the tab), and a low silicon content design is adopted in the first zone of the battery cell's spatial position (closer to the top of the tab), thereby avoiding the problem of insufficient kinetic lithium plating caused by lack of electrolyte.

[0005] Some embodiments of the present application provide a silicon-containing negative electrode plate, comprising a tab, a negative electrode current collector, and an active material layer arranged on at least one side of the negative electrode current collector, wherein the tab extends from one end of the negative electrode current collector, the active material layer has a width in the direction extending along the tab, and the active material layer comprises: a first region, occupying 1 / 4-1 / 2 of the width of the active material layer; and a second region, occupying 1 / 2-3 / 4 of the width of the active material layer, wherein the first region is closer to the tab than the second region, and wherein, based on the total mass of the first region, the silicon content of the first region is W1, based on the total mass of the second region, the silicon content of the second region is W2, and 1.03<W2 / W1<2.

[0006] In some embodiments, based on the total mass of the active material layer, the total silicon content of the silicon-containing negative electrode plate is W3, wherein 3%≤W3≤20%.

[0007] In some embodiments, 1.1<W2 / W1<1.7.

[0008] In some embodiments, the width of the active material layer is ≥40 mm.

[0009] In some embodiments, the width of the active material layer is ≥60 mm.

[0010] Other embodiments of the present application provide a secondary battery, including: a negative electrode plate, wherein the negative electrode plate is the above-mentioned silicon-containing negative electrode plate.

[0011] In some embodiments, the secondary battery is a soft-pack battery, and the width of the active material layer is ≥40 mm.

[0012] In some embodiments, the width of the active material layer is ≥60 mm.

[0013] In some embodiments, the secondary battery is a square-shell battery, and the width of the active material layer is ≥50 mm.

[0014] In some embodiments, the width of the active material layer is ≥60 mm.

[0015] Still other embodiments of the present application provide an electronic device, characterized by including the aforementioned secondary battery.

[0016] In summary, the silicon-containing negative electrode provided by the present application can improve the problem of local lithium deposition caused by the spatial distribution of the electrolyte. Under the premise of ensuring that the energy density is not reduced (the total content of Si (silicon)-based materials remains unchanged), the Si content can be distributed in the second zone of the spatial position of the electrode (farther away from the bottom of the electrode ear) and the first zone of the spatial position (closer to the top of the electrode ear) (that is, by having a higher silicon content in the second zone of the spatial position of the electrode and a lower silicon content in the first zone of the spatial position), the problem of local lithium deposition caused by the spatial distribution of the electrolyte is reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0017]

[0011] The corresponding aspects of the disclosed embodiments are best understood from the following detailed description when read in conjunction with the accompanying drawings.

[0018] Figure 1 and Figure 2 A secondary battery in the related art is shown.

[0019] Figure 3 and Figure 4 A secondary battery according to some embodiments of the present application is shown.

[0020] Figures 5A to 6B ICP-SEM test images of the secondary battery of Comparative Example 1 and the secondary battery of Example 3 of the present application are shown.

[0021] Figure 7 The cycle performances of the secondary battery of Comparative Example 1 and the secondary battery of Example 3 of the present application are shown. DETAILED DESCRIPTION

[0022] In lithium-ion batteries in the new energy field, the application of silicon-containing negative electrode sheets is becoming more and more widespread. Based on this, some embodiments of the present application provide a silicon-containing negative electrode sheet, which adopts a partitioned design, wherein the second zone that is spatially farther away from the tab has a higher silicon content, and the first zone that is spatially closer to the tab has a lower silicon content. Based on the total mass of the second zone, the silicon content of the high silicon zone of the second zone is recorded as W2, and based on the total mass of the first zone, the silicon content of the low silicon zone of the first zone is recorded as W1, wherein 1.03<W2 / W1<2, and based on the total mass of the active material layer, the total silicon content in the silicon-containing negative electrode sheet is W3, 3%≤W3≤20%. In the present application, if Figure 3 As shown, the active material layer of the silicon-containing negative electrode plate has a width in the direction extending along the tab, and the width of the active material layer is W (i.e., the total width of the active material layer). The second region of the plate is a high-silicon region, and the second region occupies 1 / 2-3 / 4 of the width W of the active material layer. The first region of the plate is a low-silicon region, and the first region occupies 1 / 4-1 / 2 of the width W of the active material layer. The first region of the active material layer closer to the tab is prone to electrolyte deficiency. Setting the first region (such as 1 / 4 to 1 / 3) of the silicon-containing negative electrode plate as a low-silicon region can avoid kinetic insufficient lithium precipitation caused by electrolyte deficiency.

[0023] In some embodiments, the silicon-containing negative electrode sheet can be applied to both prismatic and soft-pack batteries. It should be noted that the electrolyte distribution becomes more pronounced as the width of the silicon-containing negative electrode sheet increases, and when the width reaches a certain level, the problem of uneven electrolyte distribution needs to be addressed. Therefore, when applied to soft-pack batteries, since a thinner active material layer is generally used to improve the power performance and cycle life of the battery, for soft-pack batteries, the width of the active material layer W is ≥ 40 mm, 3% ≤ silicon content ≤ 20%, and optionally, the width of the active material layer W is ≥ 60 mm. Furthermore, when applied to prismatic batteries, since a thicker active material layer is generally used to increase the energy density of the battery, for prismatic batteries, the width of the active material layer W is ≥ 50 mm, 3% ≤ silicon content ≤ 20%, and optionally, the width of the active material layer W is ≥ 60 mm.

[0024] Specifically, some embodiments of the present application provide a silicon-containing negative electrode sheet, such as Figure 3As shown, it includes a tab, a negative electrode current collector and an active material layer arranged on at least one side of the negative electrode current collector, the tab extends from one end of the negative electrode current collector, the active material layer has a width in the direction along the tab and the active material layer includes: a first region, which occupies 1 / 4-1 / 2 of the width W of the active material layer of the silicon-containing negative electrode plate; and a second region, which occupies 1 / 2-3 / 4 of the width W of the active material layer; wherein the first region is closer to the tab of the silicon-containing negative electrode plate than the second region, and wherein, based on the total mass of the first region, the silicon content of the first region is W1, based on the total mass of the second region, the silicon content of the second region is W2, and 1.03<W2 / W1<2, further, 1.1<W2 / W1<1.7, in this application, based on the total mass of the active material layer, the total silicon content of the silicon-containing negative electrode plate is W3, wherein 3%≤W3≤20%. In summary, in this application, as Figure 4 As shown, the silicon-containing negative electrode adopts a low silicon content design in the first area of the electrode, that is, the silicon content is W1, and a high silicon content design is adopted in the second area of the electrode, that is, the silicon content is W2. It should be noted that in this application, the silicon content is the mass ratio of the silicon-based component to the active material component. Silicon is a semiconductor material, and the introduction of silicon-based materials will deteriorate the dynamics of the electrode. Therefore, the dynamics of the second area of the electrode with a high silicon content W2 is poor, while the dynamic performance of the first area of the electrode with a low silicon content W1 design is better. This design can compensate for the lithium plating problem caused by the spatial distribution of the electrolyte.

[0025] In some optional embodiments, the silicon content of 1 / 4-1 / 3 of the width of the active material layer is W1, that is, the first area of the electrode is designed with a low silicon content to compensate for the lithium plating problem caused by the spatial distribution of the electrolyte.

[0026] In some embodiments, the width W of the active material layer of the silicon-containing negative electrode plate is ≥40 mm, optionally ≥60 mm. This is because when the width of the active material layer is small, the electrolyte will not be unevenly distributed due to capillary action.

[0027] Other embodiments of the present application provide a secondary battery and an electronic device including the secondary battery. The secondary battery may include a square-shell battery or a soft-pack battery. As described above, when it is a soft-pack battery, the width W of the active material layer is ≥40 mm, 3% ≤ silicon content ≤ 20%, and optionally, the width W of the active material layer is ≥60 mm. Further, when it is a square-shell battery, the width W of the active material layer is ≥50 mm, 3% ≤ silicon content ≤ 20%, and optionally, the width W of the active material layer is ≥60 mm. The secondary battery includes: a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The separator is arranged between the positive electrode sheet and the negative electrode sheet, and the positive electrode sheet, the negative electrode sheet and the separator are at least partially immersed in the electrolyte. The present invention does not limit the type and shape of the secondary battery. The secondary battery can be a soft-pack battery, a cylindrical battery, a square-shell battery, etc., and can be a square-shell battery or a soft-pack battery. In the following, a soft-pack secondary battery is used as an example for explanation.

[0028] In some embodiments, the negative electrode sheet is the negative electrode sheet described above, comprising a negative electrode current collector supported by first and second negative electrode active materials (as discussed in detail above) on at least one side of the negative electrode current collector. The negative electrode current collector can be made of a foil having good conductivity and mechanical strength, such as nickel, titanium, gold, silver, chromium, molybdenum, copper, stainless steel, or carbon. In addition to foil, the negative electrode current collector can also be in the form of a film, mesh, porous, foam, or non-woven fabric, among other forms, in any one or more combinations thereof. The negative electrode active material is disposed on either or both surfaces of the negative electrode current collector.

[0029] The negative electrode binder can be selected from any one of polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), sodium polyacrylate (PAAS), styrene-butadiene rubber (SBR), or a combination of two or more thereof mixed in any proportion.

[0030] The negative electrode conductive agent can be selected from conductive carbon black (SP), Ketjen black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, porous carbon, carbon nanotubes (CNTs) and single-walled carbon nanotubes (SWCNTs), or a combination of two or more of them mixed in any proportion.

[0031] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode slurry supported on at least one side of the positive electrode current collector. The positive electrode current collector can be made of a foil with good conductivity and mechanical strength, such as aluminum, nickel, titanium, gold, silver, chromium, molybdenum, copper, stainless steel or carbon. In addition to foil, the positive electrode current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam or non-woven fabric. The positive electrode active material is provided on either or both surfaces of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material, a positive electrode binder and a positive electrode conductive agent.

[0032] The positive electrode slurry may include a positive electrode active material selected from a layered structure, a positive electrode binder and a positive electrode conductor, wherein the positive electrode active material includes lithium cobalt oxide (LCO), nickel cobalt manganese lithium oxide (NCM), nickel cobalt aluminum lithium oxide (NCA), etc.; it can also be selected from an olivine structured positive electrode active material, including lithium iron phosphate (LFP), lithium manganese iron phosphate (LFMP), etc.; it can also be selected from a spinel structured positive electrode active material, including lithium manganese oxide (LMO), lithium nickel manganese oxide (LNMO), lithium-rich manganese-based (LMR), etc., or a combination of any two or more of the above positive electrodes.

[0033] The positive electrode binder can be selected from one or more combinations of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyethylene oxide (PEO), polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), etc.

[0034] The positive electrode conductive agent can be selected from one of conductive carbon black (SP), carbon nanotubes (CNTs), single-walled carbon nanotubes (SWCNTs), Ketjen black, acetylene black, graphene, carbon nanotubes, carbon nanofibers, porous carbon, etc., or a combination of two or more of them mixed in any proportion.

[0035] In some embodiments, the separator can be selected from a polyethylene porous film (PE), a polypropylene porous film (PP), and a polyethylene / polypropylene composite porous film (PE / PP / PE).

[0036] The electrolyte soaks into the positive and negative electrodes. During the battery's charge and discharge process, lithium ions are inserted and removed back and forth between the positive and negative electrodes, and the electrolyte acts as a conductor of lithium ions. The electrolyte can be any combination of conventional types in the art.

[0037] In one embodiment, the electrolyte includes an organic solvent and a lithium salt, wherein the organic solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), and ethyl propyl carbonate (EPC). The lithium salt may be selected from one of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiClO4 (lithium perchlorate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(trifluoromethanesulfonyl imide), LiTFSI (lithium bis(trifluoromethanesulfonyl imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalatoborate), LiBOB (lithium dioxalatoborate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorooxalatophosphate), and LiTFOP (lithium tetrafluorooxalatophosphate), or a combination thereof in any proportion. The molar concentration of the lithium salt in the electrolyte is 0.5 mol / L to 2 mol / L.

[0038] The secondary battery is prepared as follows:

[0039] Positive electrode sheet preparation: The positive electrode active material, positive electrode conductive agent, and positive electrode binder are mixed and dispersed in a solvent to form a uniform positive electrode slurry. This positive electrode slurry is evenly coated on the positive electrode current collector, oven-dried, and then cold-pressed and slit to produce the positive electrode sheets. The ratios of the individual components in the positive electrode sheet can be set based on conventional ratios and are not limited here.

[0040] Negative electrode sheet preparation: The negative electrode active material, negative electrode conductive agent, negative electrode binder, and emulsifier are separately dispersed in deionized water to form a uniform negative electrode slurry. The negative electrode slurry is evenly coated on the negative electrode current collector, transferred to an oven for drying, and then cold pressed and cut to obtain the negative electrode sheet. The ratios of the various components in the negative electrode sheet can be set according to conventional ratios and are not limited here.

[0041] Battery Assembly: The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide insulation. The stack is then compacted tightly by hot pressing. The stack is then wrapped in aluminum-plastic film and placed in an aluminum shell. The top cover is welded and the stack is transferred to a vacuum oven for drying. The electrolyte is then injected and sealed. After a series of resting steps, hot and cold pressing, formation, clamping, and capacity grading, the desired secondary battery is finally produced.

[0042] The technical solutions of the present invention are described in detail below through several specific examples and comparative examples. Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available or can be prepared by conventional methods in the art, and the instruments used in the examples are all commercially available.

[0043] Example 1

[0044] (1) Preparation of positive electrode:

[0045] The cathode active material uses eight series and above high nickel ternary cathode materials (LiNi 0.8+x Co y Mn 0.2-x-y , wherein x is 0-0.16), polyvinylidene fluoride (PVDF) is used as an adhesive, one or more of carbon nanotubes (CNTs), conductive carbon black (SP) and single-walled carbon nanotubes (SWCNTs) are used as conductive agents, and N-methylpyrrolidone (NMP) is used as a solvent, wherein the ratio of positive electrode active material: PVDF: conductive agent is 97:1:2. A vacuum mixer is used to stir the positive electrode slurry until it becomes uniform and transparent to obtain a positive electrode slurry. The positive electrode slurry is evenly coated on a 13μm aluminum foil current collector, and the ratio of the coating surface density of the first area to the coating surface density of the second area is 0.95:1.03. Afterwards, it is dried in an oven, and then cold pressed and cut to obtain a positive electrode sheet.

[0046] (2) Preparation of silicon-containing negative electrode sheets:

[0047] Graphite and silicon-based materials (elemental silicon, silicon-carbon materials, silicon dioxide materials) are used as active materials, one or more of polyacrylic acid (PAA), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) are used as binders, and one or more of carbon nanotubes (CNTs), conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) are used as conductive agents. Deionized water is added, wherein the mass ratio of active material, binder, and conductive agent is 96:3:1. In Example 1, the negative electrode slurry is divided into two types: the mass ratio of graphite to silicon-based material in slurry 1 active material is 89:11; the mass ratio of graphite to silicon-based material in slurry 2 active material is 92:8. The negative electrode slurry was evenly coated on a 6μm copper foil current collector. During the coating process, slurry 1 was applied to the second area of the electrode (2 / 3 of the width of the lower active material layer, the width of the active material layer along the direction of the tab extension), while slurry 2 was applied to the first area of the electrode (1 / 3 of the width of the upper active material layer). The silicon content of the first area of the silicon-containing negative electrode was 9.8%, and the silicon content of the second area of the silicon-containing negative electrode was 10.1%. That is, the second area of the silicon-containing negative electrode (2 / 3 of the width of the lower active material layer) was a high-silicon area with a mass ratio of graphite to silicon-carbon material of 89:11; the first area of the silicon-containing negative electrode (1 / 3 of the width of the upper active material layer) was a low-silicon area with a mass ratio of graphite to silicon-carbon material of 92:8. Slurry 1 and slurry 2 had the same coating area density. The CB value (the ratio of the negative electrode capacity per unit area to the positive electrode capacity per unit area) of each part of the battery cell is ensured to be the same. The positive electrode surface density corresponding to the position of slurry 1 and slurry 2 is different. In this embodiment, the silicon-containing negative electrode plate is used to prepare a square shell battery. Therefore, the width W of the active material layer of the silicon-containing negative electrode plate is 55mm, and the total silicon content of the silicon-containing negative electrode plate is 10%. Afterwards, the copper foil current collector coated with the negative electrode slurry is transferred to an oven for drying, and then cold pressed and cut to obtain the negative electrode plate.

[0048] (3) Preparation of electrolyte:

[0049] The organic solvent is a mixture of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), with the volume ratio of EC, EMC, and DEC being 20:20:60. In an argon atmosphere glove box with a water content of <10 ppm, fully dried lithium salt (LiPF6) is dissolved in the organic solvent and mixed thoroughly to obtain an electrolyte solution with a LiPF6 concentration of 1 mol / L.

[0050] (4) Preparation of isolation membrane:

[0051] A 12μm thick polypropylene isolation film was selected.

[0052] (5) Preparation of batteries:

[0053] The positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in sequence, with the separator positioned between the positive and negative sheets to act as a barrier. The stack is then pressed tightly together through hot pressing. The stack is placed in an aluminum shell, the top cover welded, and then transferred to a vacuum oven for drying at 120°C. 2.0g / Ah of electrolyte is injected and sealed. After a series of steps including resting, hot and cold pressing, formation, clamping, and capacity grading, the desired prismatic lithium-ion battery is finally produced.

[0054] Example 2

[0055] The preparation method is consistent with that of Example 1, except that in Example 2, the silicon content of the first region of the silicon-containing negative electrode plate is 9.6%, and the silicon content of the second region of the silicon-containing negative electrode plate is 10.2%.

[0056] Example 3

[0057] The preparation method is consistent with that of Example 1, except that in Example 2, the silicon content of the first region of the silicon-containing negative electrode plate is 9%, and the silicon content of the second region of the silicon-containing negative electrode plate is 10.5%.

[0058] Example 4

[0059] The preparation method is consistent with that of Example 1, except that in Example 2, the silicon content of the first region of the silicon-containing negative electrode plate is 8%, and the silicon content of the second region of the silicon-containing negative electrode plate is 11%.

[0060] Example 5

[0061] The preparation method is consistent with that of Example 1, except that in Example 2, the silicon content of the first region of the silicon-containing negative electrode plate is 7%, and the silicon content of the second region of the silicon-containing negative electrode plate is 11.5%.

[0062] Example 6

[0063] The preparation method is consistent with that of Example 1, except that in Example 6, the silicon content of the first region of the silicon-containing negative electrode plate is 6%, and the silicon content of the second region of the silicon-containing negative electrode plate is 12%.

[0064] Example 7

[0065] The preparation method is consistent with that of Example 1, except that in Example 7, slurry 1 is applied to the second area of the electrode (3 / 4 of the width of the lower active material layer), and slurry 2 is applied to the first area of the electrode (1 / 4 of the width of the upper active material layer). The silicon content of the first area of the silicon-containing negative electrode is 9.8%, and the silicon content of the second area of the silicon-containing negative electrode is 10.1%, that is, the second area of the silicon-containing negative electrode (3 / 4 of the width of the lower active material layer) is a high-silicon area, and the mass ratio of graphite to silicon-carbon material is 89:11; the first area of the silicon-containing negative electrode (1 / 4 of the width of the upper active material layer) is a low-silicon area, and the mass ratio of graphite to silicon-carbon material is 92:8.

[0066] Example 8

[0067] The preparation method is consistent with that of Example 1, except that in Example 7, slurry 1 is applied to the second area of the electrode (1 / 2 of the width of the lower active material layer), and slurry 2 is applied to the first area of the electrode (1 / 2 of the width of the upper active material layer). The silicon content of the first area of the silicon-containing negative electrode is 9.8%, and the silicon content of the second area of the silicon-containing negative electrode is 10.1%. That is, the second area of the silicon-containing negative electrode (1 / 2 of the width of the lower active material layer) is a high-silicon area, and the mass ratio of graphite to silicon-carbon material is 89:11; the first area of the silicon-containing negative electrode (1 / 2 of the width of the upper active material layer) is a low-silicon area, and the mass ratio of graphite to silicon-carbon material is 92:8.

[0068] Example 9

[0069] The preparation method is consistent with that of Example 1, except that in Example 9, the secondary battery prepared is a soft-pack battery. Therefore, the width W of the active material layer of the silicon-containing negative electrode sheet is 45 mm.

[0070] Comparative Example 1

[0071] The preparation method was consistent with that of Example 1, except that in Comparative Example 1, the CB value of the positive electrode sheet was the same as that of Example 1, and the overall areal density of the positive electrode sheet was the same. Furthermore, the ratio of the coating areal density of the positive electrode sheet in Comparative Example 1 to the coating areal density of the first region and the coating areal density of the second region in Example 1 was 1:0.95:1.03. Furthermore, the mass ratio of graphite to silicon-carbon material in the negative electrode active material was 90:10, and the silicon content of the silicon-containing negative electrode sheet was maintained at 10% across the entire width of the active material layer.

[0072] Comparative Example 2

[0073] The preparation method is consistent with that of Example 1, except that in Comparative Example 2, the silicon content of the first region of the silicon-containing negative electrode plate is 12%, and the silicon content of the second region of the silicon-containing negative electrode plate is 9%.

[0074] Comparative Example 3

[0075] The preparation method is consistent with that of Example 1, except that in Comparative Example 3, the silicon content of the first region of the silicon-containing negative electrode plate is 6%, and the silicon content of the second region of the silicon-containing negative electrode plate is 15%.

[0076] In the above-mentioned Examples 1-9 and Comparative Examples 1-3, the CB values of each part of the corresponding secondary batteries remain the same, and the CB values of the secondary batteries of Examples 1-9 and Comparative Examples 1-3 remain the same. In addition, the secondary batteries in the above-mentioned Examples 1-9 and Comparative Examples 1-3 can be subjected to the following performance tests using the following methods:

[0077] Battery testing

[0078] The secondary batteries prepared in Examples 1-9 and Comparative Examples 1-3 were charged and discharged between 2.5 and 4.25V. The specific test process was as follows: Adjust the incubator to 25°C, and then perform the following steps: ① 0-80% SOC with a constant current charge rate of 2C, and 80-100% SOC with a constant current and constant voltage fast charge rate of 0.5C to 4.25V; ② Let it stand for 30 minutes; ③ 0.33C constant current discharge to 2.5V; and ④ Let it stand for 30 minutes. The above four steps complete one cycle. The results are shown in Table 1 below:

[0079] Table 1. Secondary battery performance test results in Examples 1-9 and Comparative Examples 1-3

[0080]

[0081] From the comparison of Examples 1-9 and Comparative Example 1 in Table 1 above, it can be seen that the present application sets the second spatial area of the silicon-containing negative electrode piece as a high silicon area, which occupies a width of 1 / 2W-3 / 4W of the active material layer (the active material layer has a width W in the direction extending along the pole ear), and the first spatial area of the silicon-containing negative electrode piece as a low silicon area, which occupies a width of 1 / 4W-1 / 2W of the active material layer. Since the top of the pole piece is prone to electrolyte deficiency, setting the upper part as a low silicon area can avoid kinetic insufficient lithium precipitation caused by electrolyte deficiency, thereby improving the fast charging life of the corresponding secondary battery. Specifically, Figure 5A and Figure 5B The ICP-SEM (Inductively Coupled Plasma-Scanning Electron Microscope) test results of the silicon-containing negative electrode sheet of Comparative Example 1 corresponding to the low silicon region and high silicon region of the corresponding embodiment are shown, and Figure 6A and Figure 6B The ICP-SEM test results of the low silicon area and high silicon area of the silicon-containing negative electrode plate of Example 3 are shown. Figure 5A and Figure 5BIt can be seen from the figure that lithium deposition occurs in the silicon-containing negative electrode of Comparative Example 1, while Figures 6A to 6B It can be seen that no lithium deposition occurs in the silicon-containing negative electrode plate with low silicon areas and high silicon areas in Example 3, which indicates that the provided silicon-containing negative electrode plate (the second area of the plate spatial position is the high silicon area, and the first area of the plate spatial position is the low silicon area) avoids insufficient kinetics of lithium deposition due to lack of electrolyte. Figure 7 The cycle life of the secondary battery prepared by the silicon-containing negative electrode sheet in Comparative Example 1 and Example 3 is shown. Figure 7 It can be seen that the cycle life of the silicon-containing negative electrode sheet in Comparative Example 1 is 1000 cls, while the cycle life of the silicon-containing negative electrode sheet in Example 3 is 1150 cls, which is significantly higher than the cycle life of Comparative Example 1.

[0082] As can be seen from Examples 1-6 and Comparative Example 3, when the second spatial region of the silicon-containing negative electrode plate is a high-silicon region and the first spatial region of the silicon-containing negative electrode plate is a low-silicon region, 1.03 < W2 / W1 < 2. Within this range, the problem of insufficient kinetic lithium precipitation caused by insufficient electrolyte can be effectively avoided. If it exceeds this range, that is, W2 / W1 < 1, the silicon content in the first region is high and the electrolyte in the first region is insufficient, causing the kinetics of the first region to deteriorate significantly; if W2 / W1 is between 1 and 1.03, the silicon content difference cannot compensate for the corresponding kinetic problem; if W2 / W1 is greater than 2, the silicon content in the second region is too high, which also significantly deteriorates the kinetics. Furthermore, when 1.1 < W2 / W1 < 1.7, the cycle life of the silicon-containing negative electrode plate is above 1100 cls, significantly improving the performance of the secondary battery.

[0083] It can be seen from Examples 7-8 that when the second region (high silicon region) occupies 1 / 2W-3 / 4W of the width of the active material layer and the first region (low silicon region) occupies 1 / 4W-1 / 2W of the width of the active material layer, the performance of the corresponding secondary battery can be improved and the problem of insufficient kinetic lithium precipitation caused by lack of electrolyte can be avoided.

[0084] As can be seen from Examples 1 and 9, the silicon-containing negative electrode plate can be applied to both square-shell batteries and soft-pack batteries. When applied to soft-pack batteries, the width of the active material layer W is ≥ 40 mm, 3% ≤ silicon content ≤ 20%, and optionally, the width of the active material layer W is ≥ 60 mm; when applied to square-shell batteries, the width of the active material layer W is ≥ 50 mm, 3% ≤ silicon content ≤ 20%, and optionally, the width of the active material layer W is ≥ 60 mm. This is because when the plate is too narrow, due to the presence of capillary action, the electrolyte will not be unevenly distributed. Therefore, when the width of the active material layer reaches a certain value, the above-mentioned silicon-containing negative electrode plate can compensate for the lithium plating problem caused by the spatial distribution of the electrolyte.

[0085] Comparing Example 1 with Comparative Example 2, it can be seen that the top of the silicon-containing negative electrode plate (i.e., the first area) is prone to electrolyte deficiency. Setting the first area (such as 1 / 4 to 1 / 3) of the silicon-containing negative electrode plate as a low-silicon area and the second area as a high-silicon area can avoid the kinetic insufficiency of lithium deposition due to electrolyte deficiency. Conversely, if the first area is set as a high-silicon area and the second area is set as a low-silicon area, the kinetic insufficiency of lithium deposition due to electrolyte deficiency cannot be avoided, and since the first area is a high-silicon area, the related lithium deposition phenomenon may be aggravated, thereby deteriorating battery performance.

[0086] The features of several embodiments have been summarized above so that those skilled in the art can better understand aspects of the present invention. Those skilled in the art will appreciate that they can easily use the present invention as a basis to design or modify other processes and structures for implementing the same purpose and / or achieving the same advantages as the embodiments described herein. Those skilled in the art will also appreciate that this equivalent construction does not deviate from the spirit and scope of the present invention, and that they can make various changes, replacements, and modifications herein without departing from the spirit and scope of the present invention.

Claims

1. A silicon-containing negative electrode plate, characterized in that: The invention comprises a tab, a negative electrode current collector, and an active material layer disposed on at least one side of the negative electrode current collector, wherein the tab extends from one end of the negative electrode current collector, wherein the active material layer has a width in a direction along which the tab extends, and the active material layer comprises: The first region occupies 1 / 4 to 1 / 2 of the width of the active material layer; and The second region occupies 1 / 2-3 / 4 of the width of the active material layer, The first region is closer to the tab than the second region, and based on the total mass of the first region, the silicon content of the first region is W1, based on the total mass of the second region, the silicon content of the second region is W2, and 1.03<W2 / W1<2.

2. The silicon-containing negative electrode sheet according to claim 1, characterized in that: Based on the total mass of the active material layer, the total silicon content of the silicon-containing negative electrode plate is W3, wherein 3%≤W3≤20%.

3. The silicon-containing negative electrode plate according to claim 1, characterized in that: 1.1<W2 / W1<1.

7.

4. The silicon-containing negative electrode sheet according to claim 1, characterized in that: The width of the active material layer is ≥40 mm.

5. The silicon-containing negative electrode sheet according to claim 4, characterized in that: The width of the active material layer is ≥60 mm.

6. A secondary battery, characterized in that: include: A negative electrode plate, wherein the negative electrode plate is a silicon-containing negative electrode plate according to any one of claims 1 to 5.

7. The secondary battery according to claim 6, characterized in that The secondary battery is a soft-pack battery, and the width of the active material layer of the negative electrode plate is ≥40 mm.

8. The secondary battery according to claim 6, wherein The secondary battery is a square shell battery, and the width of the active material layer is ≥50 mm.

9. The secondary battery according to claim 7 or 8, characterized in that: The width of the active material layer is ≥60 mm.

10. An electronic device, characterized in that: The invention comprises the secondary battery according to any one of claims 6 to 9.

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