A secondary battery and an electric device

Abstract

The application provides a secondary battery and a power utilization device. A negative electrode sheet in the secondary battery of the application comprises: a first coating layer arranged on at least one side surface of the current collector, and a second coating layer arranged on the first coating layer; the first coating layer comprises a first silicon negative electrode active material, and the second coating layer comprises a second silicon negative electrode active material; the first silicon negative electrode active material and the second silicon negative electrode active material contain a modified element, the modified element contains elements P, Al and K; and the following relationship is satisfied: the content of the modified element satisfies: P1P2, Al1>Al2, and K1>K2. The application introduces P, Al and K elements into the silicon negative electrode active material, the three modified elements are used together, and meanwhile, through specific design of element distribution in the silicon negative electrode active material, lithium precipitation of the secondary battery can be inhibited, and the service life of the secondary battery is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a secondary battery and an electrical device. Background Technology

[0002] Silicon anodes are prone to defects such as lithium plating and rapid capacity decay during cycling. Disassembly analysis of cycled silicon anode batteries reveals that lithium plating interfaces typically appear after 800–1200 cycles. Current solutions primarily address these issues by reducing anode compaction density, using soft or hard carbon coatings to improve anode kinetics, and optimizing electrolyte formulations. However, batteries obtained through these modifications exhibit increasing polarization and overpotential between the positive and negative electrodes with each cycle, leading to a significant decrease in capacity retention and a substantial shortening of the rechargeable battery's lifespan. Summary of the Invention

[0003] The purpose of this application is to improve the negative electrode plate in order to further improve the service life of secondary batteries and provide a secondary battery with a longer service life.

[0004] To achieve the above objectives, a first aspect of this application provides a secondary battery, including a negative electrode, said negative electrode comprising:

[0005] A current collector; a first coating disposed on at least one side surface of the current collector, and a second coating applied on the first coating;

[0006] The first coating comprises a first silicon anode active material, and the second coating comprises a second silicon anode active material;

[0007] The first silicon anode active material and the second silicon anode active material contain modifying elements, namely, elements P, Al, and K; and satisfy the following relationship:

[0008] The content of the modified elements satisfies: P1<P2,Al1> Al2, K1>K2,

[0009] Wherein, P1, Al1 and K1 represent the contents of elements P, Al and K in the first silicon anode active material, respectively, and P2, Al2 and K2 represent the contents of elements P, Al and K in the second silicon anode active material, respectively.

[0010] As an embodiment of this application, the negative electrode in the secondary battery satisfies: 1000ppm≤P2-P1≤2000ppm.

[0011] As an embodiment of this application, the negative electrode in the secondary battery satisfies: 50ppm≤Al1-Al2≤1000ppm.

[0012] As an embodiment of this application, the negative electrode in the secondary battery satisfies: 50ppm≤K1-K2≤600ppm.

[0013] As an embodiment of this application, the negative electrode in the secondary battery satisfies the following condition: K1 is 500-700 ppm.

[0014] As an embodiment of this application, the negative electrode in the secondary battery satisfies the following condition: K2 is 50 to 500 ppm.

[0015] As an embodiment of this application, the modified elements are distributed on the surface and / or inside the first silicon anode active material or the second silicon anode active material.

[0016] As an embodiment of this application, the negative electrode sheet satisfies: 10mAh / g≤C2-C1≤21mAh / g; where C1mAh / g represents the specific capacity of the first silicon negative electrode active material; and C2mAh / g represents the specific capacity of the second silicon negative electrode active material.

[0017] As an embodiment of this application, the particle size D of the first silicon anode active material is... V50 The particle size D of the second silicon anode active material is 4.0–7.0 μm. V50 The particle size is 4.0–7.0 μm; wherein, the particle size D V50 This indicates the particle size at which the cumulative volume of the material particles reaches 50%, expressed in μm.

[0018] As an embodiment of this application, the negative electrode sheet satisfies: 0.94≤PD2 / PD1≤1.07, PD1 g / cm³ 3 This represents the compaction density of the first coating in the negative electrode sheet, PD2 g / cm³. 3 This indicates the compaction density of the second coating in the negative electrode sheet.

[0019] A second aspect of this application provides an electrical device comprising the secondary battery described in the first aspect of this application.

[0020] Compared with the prior art, the beneficial effects of this application are:

[0021] This application introduces P, Al, and K elements into silicon anode active materials. The three modifying elements are used together. At the same time, by specifically designing the element distribution in the silicon anode active material, the specific capacity and structural stability of the silicon anode material are improved, and polarization is reduced. This improves the capacity retention rate of the silicon anode during cycling, improves the lithium plating interface during cycling, and increases the service life of the secondary battery prepared from it. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the negative electrode sheet in Example 1. Detailed Implementation

[0023] To better illustrate the purpose, technical solution, and advantages of this application, the following description, in conjunction with specific embodiments and accompanying drawings, will further explain this application. However, the embodiments do not limit this application in any way. Unless otherwise specified, the reagents, methods, and equipment used in this application are conventional reagents, methods, and equipment in this technical field. Unless otherwise specified, all reagents and materials used in this application are commercially available.

[0024] An embodiment of this application provides a secondary battery, including a negative electrode sheet, the negative electrode sheet comprising:

[0025] A current collector; a first coating disposed on at least one side surface of the current collector, and a second coating disposed on the first coating;

[0026] The first coating comprises a first silicon anode active material, and the second coating comprises a second silicon anode active material;

[0027] The first silicon anode active material and the second silicon anode active material contain modifying elements, namely, elements P, Al, and K; and satisfy the following relationship:

[0028] The content of the modified elements satisfies: P1<P2,Al1> Al2, K1>K2,

[0029] Wherein, P1, Al1 and K1 represent the contents of elements P, Al and K in the first silicon anode active material, respectively, and P2, Al2 and K2 represent the contents of elements P, Al and K in the second silicon anode active material, respectively.

[0030] The negative electrode sheet of this application introduces P, Al, and K elements into the silicon negative electrode active material, which can improve the interlayer spacing of the silicon negative electrode active material, increase the lithium-ion diffusion coefficient, and reduce polarization. P element can improve the specific capacity of the silicon negative electrode active material, while K and Al elements can improve the structural stability of the silicon negative electrode active material and reduce the free energy of lithium intercalation. The use of these three modifying elements, along with the specific design of the element distribution in the silicon negative electrode active material, improves the specific capacity and structural stability of the silicon negative electrode material while reducing polarization. This, in turn, improves the capacity retention rate of the silicon negative electrode during cycling, improves the lithium plating interface during negative electrode cycling, and extends the lifespan of the secondary battery prepared from it.

[0031] In this application, the modifying elements can be distributed on the surface of the first silicon anode active material or the second silicon anode active material, or they can be distributed inside the first silicon anode active material or the second silicon anode active material. When the modifying elements are distributed on the surface and inside the anode active material, the stability of the anode active material can be optimized, and the anode material can have more electrochemical active sites.

[0032] In the first and second silicon anode active materials of some embodiments of this application, K and Al elements can improve the structural stability of the material and reduce the free energy of lithium intercalation. Simultaneously, K and Al elements loaded into the silicon material can also work together with P element to improve the crystallinity of the material, thereby significantly improving the cycle stability of the battery and extending its lifespan.

[0033] In some embodiments, the following condition is satisfied: 1000ppm ≤ P2 - P1 ≤ 2000ppm. For example, the value of P2 - P1 can be any one of 1000ppm, 1500ppm, or 2000ppm, or a range between any two values. When the above condition is met, the initial discharge capacity and cycle performance of the battery can be further improved.

[0034] In some embodiments, P1 is in the range of 800ppm to 1200ppm. For example, the value of P1 can be any one of 800ppm, 1000ppm, and 1200ppm or a range between any two values.

[0035] In some embodiments, P2 is in the range of 1800ppm to 3200ppm. For example, the value of P2 can be any one of 1800ppm, 2000ppm, 2900ppm, 3000ppm, 3200ppm or a range between any two values.

[0036] In some embodiments, the following condition is satisfied: 50ppm ≤ Al1 - Al2 ≤ 1000ppm; exemplarily, the values ​​of Al1 - Al2 can be any one of 50ppm, 300ppm, 400ppm, 500ppm, 700ppm, 950ppm, or a range between any two values. When the above condition is met, the cycle capacity retention rate of the battery can be further improved.

[0037] In some embodiments, Al1 is in the range of 1000ppm to 1200ppm. For example, the value of Al1 can be any one of 1000ppm, 1050ppm, and 1200ppm or a range between any two values.

[0038] In some embodiments, Al2 is in the range of 100ppm to 950ppm. For example, the value of Al2 can be any one of 100ppm, 300ppm, 500ppm, 700ppm, 800ppm, 950ppm or a range between any two values.

[0039] In some embodiments, the following condition is satisfied: 50ppm ≤ K1-K2 ≤ 600ppm. For example, the values ​​of K1-K2 can be any one of 50ppm, 200ppm, 300ppm, 400ppm, 500ppm, and 600ppm, or a range between any two values. When the above condition is met, the cycle capacity retention rate of the battery can be improved.

[0040] In some embodiments, K1 is in the range of 500ppm to 700ppm. For example, the value of K1 can be any one of 500ppm, 550ppm, and 700ppm or a range between any two values.

[0041] In some embodiments, K2 is in the range of 50ppm to 500ppm. For example, the value of K2 can be any one of 50ppm, 100ppm, 200ppm, 300ppm, and 450ppm, or a range between any two values.

[0042] In some embodiments, the negative electrode sheet satisfies: 0.94 ≤ PD2 / PD1 ≤ 1.07, more preferably 1.0 ≤ PD2 / PD1 ≤ 1.07. Exemplarily, the value of PD2 / PD1 can be any one of 0.94, 0.97, 1.00, 1.03, 1.07, or a range between any two values. PD1 g / cm³ 3 This represents the compaction density of the first coating in the negative electrode sheet, PD2 g / cm³. 3 This indicates the compaction density of the second coating in the negative electrode sheet. When PD2 / PD1 is within the above range, it can improve the cycle capacity retention rate of the battery.

[0043] In some embodiments, PD1 is at 1.5 g / cm³. 3 ~1.6g / cm 3 Within the range, for example, the value of PD1 can be 1.5 g / cm³. 3 1.6g / cm 3 The range of values ​​between any one or any two values ​​in the range.

[0044] In some embodiments, PD2 is at 1.5 g / cm³. 3 ~1.6g / cm 3 Within this range, for example, the value of PD2 can be 1.5 g / cm³. 31.55g / cm 3 1.6g / cm 3 The range of values ​​between any one or any two values ​​in the range.

[0045] In some embodiments, PD1 is 1.5 g / cm³. 3 PD2 is 1.55 g / cm³ 3 This can improve the battery's cycle capacity retention rate.

[0046] In some embodiments, the negative electrode sheet satisfies the following conditions: 10 mAh / g ≤ C2-C1 ≤ 21 mAh / g; more preferably, 15 mAh / g ≤ C2-C1 ≤ 20 mAh / g. Exemplarily, the values ​​of C2-C1 can be any one of 10 mAh / g, 11 mAh / g, 14 mAh / g, 15 mAh / g, 20 mAh / g, or 21 mAh / g, or a range between any two values. Wherein, C1 mAh / g represents the specific capacity of the first silicon negative electrode active material; C2 mAh / g represents the specific capacity of the second silicon negative electrode active material. When the above conditions are met, the cycle capacity retention rate of the battery can be improved.

[0047] In some embodiments, C1 is in the range of 1400mAh / g to 1415mAh / g. For example, the value of C1 can be any one of 1408mAh / g, 1409mAh / g, 1410mAh / g, 1412mAh / g, 1413mAh / g, and 1415mAh / g, or a range between any two values.

[0048] In some embodiments, C2 is in the range of 1415 mAh / g to 1432 mAh / g. For example, the value of C2 can be any one of 1418 mAh / g, 1420 mAh / g, 1423 mAh / g, 1424 mAh / g, 1425 mAh / g, 1430 mAh / g, 1432 mAh / g, or a range between any two values.

[0049] In some embodiments, C1 is 1420 mAh / g and C2 is 1425 mAh / g, which can improve lithium plating on the negative electrode and thus further improve the cycle capacity retention of the battery. In some embodiments, the particle size D of the first silicon negative electrode active material is... V50 The particle size is 4.0–7.0 μm. For example, the particle size D of the first silicon anode active material is… V50 It can take any one of the values ​​of 4μm, 5μm, 6μm, and 7μm, or a range between any two values.

[0050] In some embodiments, the particle size D of the second silicon anode active material V50The particle size is 4.0–7.0 μm. For example, the particle size D of the second silicon anode active material... V50 It can take any one of the values ​​of 4μm, 5μm, 6μm, and 7μm, or a range between any two values.

[0051] In this application, the particle size D V50 This indicates the particle size at which the cumulative volume of the material particles reaches 50%, expressed in μm.

[0052] When the particle size of the silicon anode active material is within the above range, the compaction density of the coating can be further improved, thereby increasing the battery capacity. At the same time, when the particle size ratio of the two silicon anode active materials is within the above range, a good ion channel can be formed on the basis of a high compaction density, improving the ion transport performance and further improving the cycle capacity retention rate of the battery.

[0053] In some embodiments, the active material in the first and second silicon anode active materials includes at least one of silicon oxide (SiOx, x = 1 or 2), Si alloy, and Si-C. It should be noted that in this application, the silicon anode active material includes both active material and modifying elements.

[0054] In some embodiments, the first and second coatings, in addition to containing silicon anode active materials, also contain conductive agents, binders, and thickeners.

[0055] In this application, the secondary battery further includes a positive electrode, an electrolyte, and a separator.

[0056] In some embodiments, the positive electrode sheet includes a positive current collector and a positive active coating disposed on at least one side of the surface of the positive current collector; the positive active coating includes a positive active material, which includes, but is not limited to, at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium iron phosphate.

[0057] In some embodiments, the positive electrode may further include a conductive agent, a binder, and a thickener.

[0058] The conductive agent includes, but is not limited to, at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene.

[0059] The adhesive includes, but is not limited to, at least one of styrene-butadiene rubber, styrene-acrylic emulsion, polyacrylic acid, and sodium alginate.

[0060] The thickener includes, but is not limited to, at least one of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose.

[0061] This application also protects electrical devices that include the aforementioned secondary batteries.

[0062] The following are specific embodiments of this application, and the technical solutions of this application are further described in conjunction with the embodiments. However, this application is not limited to these embodiments. Unless otherwise specified, the reagents, methods, and equipment used in this application are all conventional reagents, methods, and equipment in this technical field.

[0063] Example 1

[0064] This embodiment provides a secondary battery, the preparation method of which includes the following steps:

[0065] Negative electrode preparation

[0066] The anode active material (a mixture of the first silicon anode active material and graphite in a mass ratio of 10:90), the conductive agent (a mixture of conductive carbon black and carbon nanotubes in a weight ratio of 1:1), the thickener sodium carboxymethyl cellulose, and the binder polyacrylic acid in a mass ratio of 96:1.5:0.5:2 were mixed, deionized water was added, and the first anode slurry was obtained under the action of a vacuum stirrer.

[0067] The negative electrode active material (a mixture of second silicon negative electrode active material and graphite in a mass ratio of 10:90), conductive agent (conductive carbon black and carbon nanotubes mixed in a weight ratio of 1:1), thickener sodium carboxymethyl cellulose, and binder polyacrylic acid in a mass ratio of 96:1.5:0.5:2 are mixed, deionized water is added, and the second negative electrode slurry is obtained under the action of a vacuum stirrer.

[0068] A first negative electrode slurry is uniformly coated on both sides of the copper foil of the negative electrode current collector, forming a first coating on each side. Then, a second negative electrode slurry is coated on top of the first coating to form a second coating. The coated electrode is then transferred to an oven for drying, followed by cold pressing and slitting to obtain the negative electrode sheet. A schematic diagram of the negative electrode sheet is shown below. Figure 1 As shown.

[0069] The first and second silicon anode active materials are obtained by mixing, grinding, and sintering silicon dioxide (or Si-C material) with metal salts of modified elements, such as AlPO4 and K3PO4.

[0070] Other parameters of the negative electrode sheet and silicon negative electrode active material are shown in Table 1 and Table 2.

[0071] Preparation of positive electrode sheet

[0072] The positive electrode active material (high-nickel ternary material, chemical formula LiNi) 0.9 Co 0.05 Mn 0.05O2), binder polyvinylidene fluoride (PVDF), and conductive agent (conductive carbon black and carbon nanotubes mixed in a weight ratio of 1:1) are mixed in a mass ratio of 97:1.5:1.5, and solvent N-methylpyrrolidone is added. Then, the mixture is stirred in a vacuum mixer until the system is homogeneous to obtain the positive electrode slurry. The positive electrode slurry is uniformly coated onto both sides of the positive electrode current collector (carbon-coated aluminum foil). The coated electrode is dried in an oven, and then cold-pressed and slit to obtain the positive electrode sheet.

[0073] Preparation of electrolyte

[0074] The organic solvent is a mixture containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC), wherein the volume ratio of EC, EMC, and DEC is 20:20:60. In an argon-atmosphere glove box with a water content of <10 ppm, thoroughly dried lithium hexafluorophosphate (LiPF6), lithium difluorosulfonyl imide (LiFSI) (mixed in a molar ratio of 1:1), and additives (fluoroethylene carbonate (FEC), tris(trimethylsilyl) phosphate (TMSP), and ethylene sulfate (DTD) mixed in a mass ratio of 1:1:1) are dissolved in the organic solvent and mixed thoroughly to obtain the electrolyte. In this embodiment, the concentration of lithium salt is 1.2 mol / L, and the concentration of additives is 5 wt%.

[0075] Secondary battery assembly

[0076] The positive electrode, separator (PE base film + [ceramic & PVDF coating]), and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. After being wound into a square bare cell, it is installed in a casing, baked at 100°C to remove water, injected with electrolyte, sealed, and then subjected to processes such as standing, hot and cold pressing, formation, and capacity testing to obtain a secondary battery.

[0077] Examples 2-23, Comparative Examples 1-4

[0078] A series of secondary batteries were provided, prepared according to the method of Example 1. The negative electrode sheets differed slightly from those of Example 1, and the differences are detailed in the parameters in Tables 1 and 2. In the silicon negative electrode active materials of Comparative Example 4, neither the first nor the second silicon negative electrode materials were doped with any modifying elements.

[0079] Table 1

[0080]

[0081] Table 2

[0082]

[0083]

[0084] Note: In the table, P1 represents the content of element P in the first silicon anode active material; P2 represents the content of element P in the second silicon anode active material; Al1 represents the content of element Al in the first silicon anode active material; Al2 represents the content of element Al in the second silicon anode active material; K1 represents the content of element K in the first silicon anode active material; K2 represents the content of element K in the second silicon anode active material.

[0085] Performance testing

[0086] The performance of the secondary batteries obtained in the above embodiments and comparative examples was tested, specifically including the following steps:

[0087] (1) Let stand at 45℃ for 30 minutes; (2) Discharge at a constant current of 0.02C to 2.5V; (3) Let stand for 30 minutes; (4) Charge at a constant current of 0.02C to 4.2V, and charge at a constant voltage until the current is 0.05C; (5) Let stand for 30 minutes; (6) Discharge at a constant current of 0.02C to 2.5V; (7) Let stand at 45℃ for 180 minutes; (8) Charge at a constant current of 1C to 4.25V, and charge at a constant voltage until the current is 0.05C; (9) Let stand for 60 minutes; (10) Discharge at a constant current of 1C to 2.5V; (11) Let stand for 120 minutes; record the discharge capacity at this time, which is the initial discharge capacity; (12) Repeat steps (8) to (11) 1500 times, stop the test, and record the discharge capacity at this time.

[0088] Wherein, the capacity retention rate after 1500 cycles (%) = discharge capacity after 1500 cycles / initial discharge capacity * 100%.

[0089] After 1500 cycles, the rechargeable battery was further disassembled to observe whether lithium was deposited on its negative electrode and to calculate the lithium deposition area. The details of the lithium deposition are shown in Table 3.

[0090] Table 3

[0091]

[0092] The results above show that:

[0093] By introducing P, Al, and K elements into silicon anode active materials and using these three modifying elements together, and by specifically designing the element distribution in the silicon anode active materials, the capacity retention rate of silicon anodes during cycling can be significantly improved, the lithium plating interface during anode cycling can be improved, and thus the service life of the secondary batteries prepared from them can be significantly improved.

[0094] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A secondary battery comprising a negative electrode sheet, characterized by, The negative electrode plate comprises: a current collector; a first coating layer arranged on at least one side surface of the current collector, and a second coating layer arranged on the first coating layer; the first coating layer comprises a first silicon negative electrode active material, and the second coating layer comprises a second silicon negative electrode active material; the first silicon negative electrode active material and the second silicon negative electrode active material contain a modified element, the modified element contains elements P, Al and K; and the following relationships are satisfied: the content of the modified element satisfies: P1 P1 is 800 ppm to 1200 ppm; P2 is 1800 ppm to 3200 ppm; Al1 is 1000 ppm to 1200 ppm; Al2 is 100 ppm to 950 ppm; K1 is 500 to 700 ppm; and K2 is 50 to 500 ppm; wherein P1, Al1 and K1 respectively represent the content of elements P, Al and K in the first silicon negative electrode active material, and P2, Al2 and K2 respectively represent the content of elements P, Al and K in the second silicon negative electrode active material.

2. The secondary battery according to claim 1, characterized by 1000 ppm≤P2-P1≤2000 ppm is satisfied.

3. The secondary battery according to claim 1, characterized by 50 ppm≤Al1-Al2≤1000 ppm is satisfied.

4. The secondary battery according to claim 1, characterized by 50 ppm≤K1-K2≤600 ppm is satisfied.

5. The secondary battery according to claim 1, characterized by the modified element is distributed on the surface and / or inside of the first silicon negative electrode active material or the second silicon negative electrode active material.

6. The secondary battery according to claim 1, characterized by the negative electrode plate satisfies 10 mAh / g≤C2-C1≤21 mAh / g; C1 mAh / g represents the gram capacity of the first silicon negative electrode active material; C2 mAh / g represents the gram capacity of the second silicon negative electrode active material.

7. The secondary battery according to claim 1, characterized by The negative electrode sheet satisfies: 0.94 ≤ PD2 / PD1 ≤ 1.07, PD1 g / cm 3 represents the compacted density of the first coating in the negative electrode sheet, PD2 g / cm 3 represents the compacted density of the second coating in the negative electrode sheet.

8. The secondary battery according to claim 1, characterized by The particle size D of the first silicon negative electrode active material is 4.0 to 7.0 μm V50 The particle size D of the second silicon negative electrode active material is 4.0 to 7.0 μm V50 The particle size D of the second silicon negative electrode active material is 4.0 to 7.0 μm wherein the particle size D V50 The volume cumulative 50% corresponds to the particle size of the material particles, and the unit is μm.

9. An electrical device, characterized by a secondary battery comprising any one of claims 1 to 8.

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