Secondary battery and electrical equipment

Abstract

The embodiment of the present invention provides a secondary battery and an electrical device, wherein the embodiment of the present invention adds element P and element Al to a double-layer silicon negative electrode material, and controls the mass content of element P in the first negative electrode active material located in the inner layer to be greater than that in the second negative electrode active material located in the outer layer, and the mass content of element Al in the first negative electrode active material located in the inner layer to be less than that in the second negative electrode active material located in the outer layer, so that a synergistic effect can be achieved, a more stable SEI film can be formed on the surface of the negative electrode, and the impedance of lithium ions between the positive and negative electrodes is reduced, thereby improving the high-temperature storage performance of the battery, and its capacity recovery rate is also significantly improved, and the expansion rate can be significantly reduced, thereby solving the problem that the existing battery is prone to swelling during high-temperature storage and has a low capacity recovery rate.

Description

Technical Field

[0001] The present invention relates to the technical field of battery manufacturing, in particular to a secondary battery and electrical equipment. Background Art

[0002] Currently, secondary batteries, especially lithium-ion batteries, have been widely used in various fields due to their many advantages such as high specific energy and cycle life. However, existing lithium-ion batteries, especially lithium-ion batteries with silicon-based materials as negative electrode materials, have problems such as easy swelling during high-temperature storage and low capacity recovery rate. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a secondary battery and an electrical device to solve the problems of the existing lithium-ion batteries being prone to swelling during high-temperature storage and having a low capacity recovery rate.

[0004] In order to solve the above problems, the present invention is achieved through the following technical solutions:

[0005] The present invention proposes a secondary battery, including a negative electrode plate, wherein the negative electrode plate includes a negative electrode collector, a first negative electrode active material layer and a second negative electrode active material layer, the first negative electrode active material layer is arranged on at least one surface of the negative electrode collector, and the second negative electrode active material layer is arranged on the surface of the first negative electrode active material layer; the first negative electrode active material layer includes a first negative electrode active material, the second negative electrode active material layer includes a second negative electrode active material, and the first negative electrode active material and the second negative electrode active material both have element P and element Al; the mass content of element P in the first negative electrode active material is greater than the mass content of element P in the second negative electrode active material; the mass content of element Al in the first negative electrode active material is less than the mass content of element Al in the second negative electrode active material.

[0006] Furthermore, in the secondary battery, the gram capacity of the first negative electrode active material is greater than the gram capacity of the second negative electrode active material.

[0007] Furthermore, in the secondary battery, the gram capacity difference Δq between the first negative electrode active material and the second negative electrode active material satisfies: 10 mAh / g≤Δq≤20 mAh / g.

[0008] Furthermore, in the secondary battery, the difference ΔC1 in mass content of element P between the first negative electrode active material and the second negative electrode active material satisfies: 200 ppm≤ΔC1≤1000 ppm.

[0009] Furthermore, in the secondary battery, the mass content of element P in the first negative electrode active material is 1600-2000 ppm, and the mass content of element P in the second negative electrode active material is 800-1200 ppm.

[0010] Furthermore, in the secondary battery, the difference ΔC2 in mass content of element Al between the second negative electrode active material and the first negative electrode active material satisfies: 100 ppm≤ΔC2≤1000 ppm.

[0011] Furthermore, in the secondary battery, the mass content of the element Al in the first negative electrode active material is 300 to 700 ppm, and the mass content of the element Al in the second negative electrode active material is 800 to 1200 ppm.

[0012] Furthermore, in the secondary battery, the first negative electrode active material and the second negative electrode active material each independently contain at least one element of N, B, Na, Li, V, and Ge.

[0013] Furthermore, in the secondary battery, the first negative electrode active material and the second negative electrode active material both contain elements N, V ​​and Na;

[0014] or the first negative electrode active material and the second negative electrode active material both contain elements Li, B, and Ge;

[0015] Or the first negative electrode active material and the second negative electrode active material both contain N, B, and V elements.

[0016] The present invention further provides an electrical device, which includes the above-mentioned secondary battery, and the secondary battery serves as a power supply for the electrical device.

[0017] Compared with the prior art, the embodiments of the present invention have the following advantages:

[0018] In an embodiment of the present invention, a negative electrode plate in a provided secondary battery includes a negative electrode current collector, a first negative electrode active material layer and a second negative electrode active material layer, wherein the first negative electrode active material layer is arranged on at least one surface of the negative electrode current collector, the second negative electrode active material layer is arranged on the surface of the first negative electrode active material layer, the first negative electrode active material layer includes a first negative electrode active material, the second negative electrode active material layer includes a second negative electrode active material, the first negative electrode active material and the second negative electrode active material both have element P and element Al, and the mass content of element P in the first negative electrode active material is greater than the mass content of element P in the second negative electrode active material, and the mass content of element Al in the first negative electrode active material is less than the mass content of element Al in the second negative electrode active material. Among them, element P can increase the gram capacity of silicon negative electrode materials and improve the transmission rate of lithium ions in the negative electrode materials, element Al can improve the structural stability of the material, the negative electrode material in the upper layer of the negative electrode sheet has a high Al content, which can reduce the dissolution of metal elements at the interface between the negative electrode sheet and the electrolyte, which is beneficial to the stability of the negative electrode sheet during the cycle, and the lower layer of the negative electrode sheet has a high P content, which can make the lower layer of the negative electrode sheet have better lithium affinity and increase the diffusion rate of lithium ions in the lower layer of the negative electrode sheet. In addition, element P and element Al can increase the interlayer spacing and lithium ion diffusion coefficient of silicon negative electrode materials and reduce polarization. The combination of the two modifying elements P and Al to form the above-mentioned negative electrode double-layer structure can play a synergistic role, can form a stable SEI film on the surface of the negative electrode, reduce the impedance of lithium ions between the positive and negative electrodes, thereby improving the high-temperature storage performance of lithium-ion batteries, improving capacity recovery rate, and reducing expansion rate.

[0019] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the structure of a negative electrode plate in a secondary battery provided by an embodiment of the present invention.

[0021] Description of reference numerals:

[0022] 10 - negative electrode plate, 11 - negative electrode current collector, 12 - first negative electrode active material layer, 13 - second negative electrode active material layer. DETAILED DESCRIPTION

[0023] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0024] An embodiment of the present invention provides a secondary battery, such as Figure 1As shown, it includes a negative electrode plate 10, wherein the negative electrode plate 10 includes a negative electrode collector 11, a first negative electrode active material layer 12 and a second negative electrode active material layer 13, the first negative electrode active material layer 12 is arranged on at least one surface of the negative electrode collector 11, and the second negative electrode active material layer 13 is arranged on the surface of the first negative electrode active material layer 12; the first negative electrode active material layer 12 includes a first negative electrode active material, the second negative electrode active material layer 13 includes a second negative electrode active material, and the first negative electrode active material and the second negative electrode active material both have element P and element Al; the mass content of element P in the first negative electrode active material is greater than the mass content of element P in the second negative electrode active material; the mass content of element Al in the first negative electrode active material is less than the mass content of element Al in the second negative electrode active material.

[0025] In this embodiment, element P and element Al are doped in the negative electrode material. Element P and element Al can increase the interlayer spacing and lithium ion diffusion coefficient of the negative electrode material and reduce polarization. Element P can increase the gram capacity of the negative electrode material, while element Al can improve the structural stability of the material. Element P and element Al are added to the negative electrode material, and the mass content of element P in the first negative electrode active material located in the inner layer is controlled to be greater than that of the second negative electrode active material located in the outer layer, and the mass content of element Al in the first negative electrode active material located in the inner layer is controlled to be less than that of the second negative electrode active material located in the outer layer. The negative electrode material in the upper layer of the negative electrode sheet (the second negative electrode active material layer) has a higher element Al content, which can reduce the dissolution of metal elements at the interface between the negative electrode sheet and the electrolyte, which is beneficial to the cycle of the negative electrode sheet. The process is stable and the cycle performance is improved. The lower layer of the negative electrode sheet (the first negative electrode active material layer) has a higher content of element P, which can make the lower layer of the negative electrode sheet have better lithium affinity and increase the diffusion rate of lithium ions in the lower layer of the negative electrode sheet, which is beneficial to improving the rate performance of the battery. At the same time, it also ensures that the battery has a high energy density. The comprehensive use of elements P and Al can play a synergistic role and can form a more stable SEI film on the surface of the negative electrode, reducing the impedance of lithium ions between the positive and negative electrodes, thereby improving the high-temperature storage performance of lithium-ion batteries. In particular, lithium-ion batteries with high-nickel layered ternary as the positive electrode material and silicon-carbon as the negative electrode material not only have improved high-temperature storage performance, but also significantly improved capacity recovery rate, and can significantly reduce the expansion rate.

[0026] Optionally, in one embodiment, in the secondary battery provided by the embodiment of the present invention, the gram capacity of the first negative electrode active material is greater than the gram capacity of the second negative electrode active material. In the embodiment of the present invention, the second negative electrode active material with a smaller gram capacity is arranged on the surface of the first negative electrode active material with a larger gram capacity, and the second negative electrode active material layer including the second negative electrode active material can be used to provide expansion space for the first negative electrode active material layer including the first negative electrode active material while maintaining the overall gram capacity of the battery, thereby reducing the overall expansion rate of the battery.

[0027] Optionally, in a specific embodiment, the gram capacity difference Δq between the first negative electrode active material and the second negative electrode active material satisfies: 10mAh / g≤Δq≤20mAh / g, which can not only solve the problems of easy swelling and low capacity recovery rate of existing lithium-ion batteries during high-temperature storage, but also effectively take into account the overall gram capacity of the battery and ensure the energy density of the battery.

[0028] Optionally, in some embodiments, 12 mAh / g≤Δq≤18 mAh / g; optionally, in some embodiments, 14 mAh / g≤Δq≤16 mAh / g.

[0029] Optionally, in one embodiment, the difference ΔC1 in the mass content of the element P between the first negative electrode active material and the second negative electrode active material satisfies: 200ppm≤ΔC1≤1000ppm. That is, the mass content of the element P in the first negative electrode active material is 200ppm-1000ppm higher than that in the second negative electrode active material, which can significantly improve the high temperature storage performance, reduce the polarization of the battery, and inhibit the battery swelling.

[0030] Optionally, in some embodiments, 300 ppm≤ΔC1≤900 ppm; optionally, in some embodiments, 400 ppm≤ΔC1≤800 ppm; in some embodiments, 600 ppm≤ΔC1≤700 ppm.

[0031] Optionally, in one embodiment, the mass content of element P in the first negative electrode active material is 1600-2000 ppm, and the mass content of element P in the second negative electrode active material is 800-1200 ppm, which can not only improve the high temperature storage performance and reduce the polarization and swelling rate of the battery, but also ensure the gram capacity of the silicon negative electrode material.

[0032] Optionally, in some embodiments, the mass content of element P in the first negative electrode active material is 1700-1900 ppm, and the mass content of element P in the second negative electrode active material is 900-1100 ppm; in some embodiments, the mass content of element P in the first negative electrode active material is 1750-1850 ppm, and the mass content of element P in the second negative electrode active material is 950-1050 ppm.

[0033] Optionally, in one embodiment, the difference ΔC2 in the mass content of element Al between the second negative electrode active material and the first negative electrode active material satisfies: 100ppm≤ΔC2≤1000ppm, that is, the mass content of element Al in the second negative electrode active material is 100ppm~1000ppm higher than that in the first negative electrode active material, which can significantly improve the high temperature storage performance and reduce the polarization and swelling rate of the battery.

[0034] Optionally, in some embodiments, 200ppm≤ΔC2≤900ppm; optionally, in some embodiments, 400ppm≤ΔC2≤700ppm; in some embodiments, 500ppm≤ΔC2≤600ppm.

[0035] Optionally, in one embodiment, the mass content of element Al in the first negative electrode active material is 300-700 ppm, and the mass content of element Al in the second negative electrode active material is 800-1200 ppm, which can further improve the structural stability of the material, improve the high temperature storage performance, and reduce the polarization and swelling rate of the battery.

[0036] Optionally, in some embodiments, the mass content of element Al in the first negative electrode active material is 400-600 ppm, and the mass content of element Al in the second negative electrode active material is 900-1100 ppm; in some embodiments, the mass content of element Al in the first negative electrode active material is 450-550 ppm, and the mass content of element Al in the second negative electrode active material is 950-1050 ppm.

[0037] Optionally, in one embodiment, the first negative electrode active material and the second negative electrode active material are independently selected from at least one of single crystal silicon, silicon-oxygen material, silicon-carbon material, silicon alloy material, soft carbon, hard carbon, and graphite. The above active materials have a high energy density and can effectively increase the capacity of the battery.

[0038] Optionally, in an embodiment of the present invention, the first negative electrode active material and the second negative electrode active material each independently contain at least one element of N, B, Na, Li, V, and Ge. The above elements are doped in the negative electrode material. In some embodiments, the negative electrode material and the material containing the above elements can be sintered at a high temperature to obtain a negative electrode material doped with the above elements.

[0039] Optionally, based on the mass of the first negative electrode active material or the second negative electrode active material, the total mass percentage of at least one element among N, B, Na, Li, V, and Ge is 0.1% to 0.3%, for example, it can be one of 0.1%, 0.12%, 0.15%, 0.18%, 0.2%, 0.25%, 0.3% or any two of the range values.

[0040] Optionally, in one embodiment, the first negative electrode active material and the second negative electrode active material both contain the elements N, V ​​and Na;

[0041] Optionally, the first negative electrode active material and the second negative electrode active material both contain elements Li, B, and Ge.

[0042] Optionally, the first negative electrode active material and the second negative electrode active material both contain N, B, and V elements.

[0043] In the secondary battery provided by the embodiment of the present invention, the negative electrode plate also includes a conductive agent and a binder; optionally, the conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene, and the binder includes a carboxymethyl cellulose-based binder and a resin binder.

[0044] Optionally, in one embodiment, the carboxymethyl cellulose-based binder includes one or more of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose; and / or the resin-based binder includes one or more of styrene rubber, polyacrylic acid, and polyacrylonitrile.

[0045] The secondary battery provided by the embodiment of the present invention further includes a positive electrode plate, a separator and an electrolyte.

[0046] The positive electrode plate includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, and the positive electrode active material can be independently selected from at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate. Optionally, in one embodiment, the positive electrode plate further includes a conductive agent, and the conductive agent can include at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, hard carbon, carbon fiber, and carbon microspheres.

[0047] In some embodiments, the positive electrode sheet is prepared as follows: the components for preparing the positive electrode sheet, such as the positive electrode active material including the positive electrode material, the binder and the conductive agent are dispersed in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; the positive electrode slurry is coated on a positive electrode collector such as aluminum foil; after drying, rolling, die cutting and other processes, the positive electrode sheet can be obtained.

[0048] The electrolyte plays a role in conducting ions between the positive electrode and the negative electrode, and the electrolyte can be liquid, gel or all-solid. In some embodiments, the electrolyte is a liquid electrolyte, and the electrolyte includes an electrolyte salt and a solvent, and the electrolyte salt is a lithium salt.

[0049] In practical applications, the negative electrode sheet, the positive electrode sheet and the separator are wound to obtain a core, the core is packaged to obtain a dry cell, and the dry cell is baked and then injected, formed, sealed and sorted to obtain the above-mentioned secondary battery.

[0050] The present invention further provides an electrical device, which includes the above-mentioned secondary battery, and the secondary battery serves as a power supply for the electrical device.

[0051] For the above-mentioned electrical equipment embodiment, it includes the above-mentioned secondary battery and can achieve the same technical effect. In order to avoid repetition, it will not be described here. For relevant matters, please refer to the partial description of the secondary battery embodiment.

[0052] In order to make the invention purpose, technical scheme and beneficial effect of the present invention clearer, the present invention is further described below in conjunction with embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention.

[0053] Example 1

[0054] (1) Preparation of the first negative electrode slurry:

[0055] The first negative electrode material, graphite, conductive carbon black, carbon nanotubes CNTs, sodium carboxymethyl cellulose CMC, and polyacrylic acid PAA are mixed in a mass ratio of 10:86:1.0:0.5:0.5:2.0 to prepare a first negative electrode slurry;

[0056] Among them, the first negative electrode material is silicon dioxide doped with elements P, Al, N, V ​​and Na, and the mass content of element P in silicon dioxide is 1800ppm, the mass content of element Al is 500ppm, and the mass contents of element N, element V and element Na are 576ppm, 1248ppm and 480ppm respectively.

[0057] (2) Preparation of the Second Negative Electrode Material

[0058] The second negative electrode material, graphite, conductive carbon black, carbon nanotubes CNTs, sodium carboxymethyl cellulose CMC, and polyacrylic acid PAA are mixed in a mass ratio of 10:86:1.0:0.5:0.5:2.0 to prepare a second negative electrode slurry;

[0059] Among them, the second negative electrode material is silicon dioxide doped with elements P, Al, N, V ​​and Na, and the mass content of element P is 1000ppm, the mass content of element Al is 1000ppm, and the mass contents of element N, element V and element Na are 576ppm, 1248ppm and 480ppm respectively.

[0060] (3) Preparation of negative electrode sheet

[0061] The first negative electrode slurry is coated on both sides of the negative electrode collector copper foil to form a first negative electrode active material layer with a total thickness of 50 μm (the first negative electrode active material layer on each side is 25 μm), and then the second negative electrode slurry is coated on the first negative electrode active material layer to form a second negative electrode active material layer with a total thickness of 50 μm (the second negative electrode active material layer on each side is 25 μm), and after high-temperature drying, the layers are rolled and die-cut to obtain negative electrode sheets.

[0062] (4) Preparation of positive electrode sheet

[0063] The mass ratio of LiNi is 95:2:1:2. 0.8 Co 0.1 Mn 0.1 O2, conductive carbon black, carbon nanotubes and polyvinylidene fluoride are mixed to obtain a positive electrode slurry;

[0064] The positive electrode slurry is coated on the aluminum foil by extrusion coating, and after high-temperature drying, it is rolled and die-cut to obtain a positive electrode sheet.

[0065] (5) Preparation of lithium-ion batteries

[0066] A PE ceramic film with polyvinylidene fluoride is used as a separator, the positive electrode plate, the negative electrode plate and the separator are wound and placed in an aluminum-plastic film for packaging, and an electrolyte is injected (lithium hexafluorophosphate is added to a non-aqueous electrolyte solvent prepared by mixing ethylene carbonate and diethyl carbonate in a volume ratio of 30:70 to prepare a 1M lithium hexafluorophosphate non-aqueous electrolyte) to prepare a soft-pack lithium-ion battery.

[0067] Example 2

[0068] The difference between Example 2 and Example 1 is that in step (1), the mass content of element P in the first negative electrode material is 1600 ppm.

[0069] Example 3

[0070] The difference between Example 3 and Example 1 is that in step (1), the mass content of element P in the first negative electrode material is 1688 ppm.

[0071] Example 4

[0072] The difference between Example 4 and Example 1 is that in step (1), the mass content of element P in the first negative electrode material is 2000 ppm.

[0073] Example 5

[0074] The difference between Example 5 and Example 1 is that in step (2), the mass content of element P in the second negative electrode material is 800 ppm.

[0075] Example 6

[0076] The difference between Example 6 and Example 1 is that in step (2), the mass content of element P in the second negative electrode material is 1080 ppm.

[0077] Example 7

[0078] The difference between Example 7 and Example 1 is that in step (2), the mass content of element P in the second negative electrode material is 1200 ppm.

[0079] Example 8

[0080] The difference between Example 8 and Example 1 is that in step (1), the mass content of element Al in the first negative electrode material is 300 ppm.

[0081] Example 9

[0082] The difference between Example 9 and Example 1 is that in step (1), the mass content of element Al in the first negative electrode material is 408 ppm.

[0083] Example 10

[0084] The difference between Example 10 and Example 1 is that in step (1), the mass content of element Al in the first negative electrode material is 700 ppm.

[0085] Embodiment 11

[0086] The difference between Example 11 and Example 1 is that in step (2), the mass content of element Al in the second negative electrode material is 800 ppm.

[0087] Example 12

[0088] The difference between Example 12 and Example 1 is that in step (2), the mass content of element Al in the second negative electrode material is 1080 ppm.

[0089] Embodiment 13

[0090] The difference between Example 13 and Example 1 is that in step (2), the mass content of element Al in the second negative electrode material is 1200 ppm.

[0091] Embodiment 14

[0092] The difference between Example 14 and Example 1 is that in step (3), the total thickness of the first negative electrode active material layer and the second negative electrode active material layer is adjusted to 25 μm.

[0093] Embodiment 15

[0094] The difference between Example 15 and Example 1 is that in step (3), the total thickness of the first negative electrode active material layer and the second negative electrode active material layer is adjusted to 75 μm.

[0095] Example 16

[0096] The difference between Example 16 and Example 1 is that in step (1), the mass contents of element N, element V and element Na in the first negative electrode material are 288 ppm, 624 ppm and 240 ppm respectively;

[0097] In step (2), the mass contents of element N, element V and element Na in the second negative electrode material are 288 ppm, 624 ppm and 240 ppm respectively.

[0098] Embodiment 17

[0099] The difference between Example 17 and Example 1 is that in step (1), the mass contents of element N, element V and element Na in the first negative electrode material are 1152 ppm, 2496 ppm and 960 ppm respectively;

[0100] In step (2), the mass contents of element N, element V and element Na in the second negative electrode material are 1152 ppm, 2496 ppm and 960 ppm respectively.

[0101] Embodiment 18

[0102] The difference between Example 18 and Example 1 is that in step (1), the doping elements of the first negative electrode material include P, Al, Li, B, and Ge, the mass content of the element P is 1800 ppm, the mass content of the element Al is 500 ppm, and the mass contents of the element B, the element Ge, and the element Li are 576 ppm, 480 ppm, and 1248 ppm, respectively;

[0103] In step (2), the doping elements of the second negative electrode material include P, Al, Li, B and Ge, the mass content of element P is 1000ppm, the mass content of element Al is 1000ppm, the mass content of element B, element Ge and element Li are 576ppm, 480ppm and 1248ppm respectively.

[0104] Embodiment 19

[0105] The difference between Example 19 and Example 1 is that in step (1), the doping elements of the first negative electrode material include P, Al, N, B, and V, the mass content of the element P is 1800 ppm, the mass content of the element Al is 500 ppm, and the mass contents of the element N, the element B, and the element V are 576 ppm, 480 ppm, and 1248 ppm, respectively;

[0106] In step (2), the doping elements of the second negative electrode material include P, Al, N, B, and V, and the mass content of the P element is 1000 ppm, the mass content of the Al element is 1000 ppm, and the mass contents of the N element, the B element, and the V element are 576 ppm, 480 ppm, and 1248 ppm, respectively.

[0107] Embodiment 20

[0108] The difference between Example 20 and Example 1 is that the first negative electrode material and the second negative electrode material are only doped with element P and element Al.

[0109] Comparative Example 1

[0110] The difference between Comparative Example 1 and Example 1 is that step (2) is not included, and in step (3), the first negative electrode slurry is coated on the negative electrode collector copper foil to form a first negative electrode active material layer with a thickness of 50 μm, and then the first negative electrode slurry is coated on the first negative electrode active material layer to form a second negative electrode active material layer with a thickness of 50 μm, and after high-temperature drying, the negative electrode sheet is obtained by rolling and die-cutting.

[0111] Comparative Example 2

[0112] The difference between Comparative Example 2 and Example 1 is that no element doping exists in the first negative electrode material and the second negative electrode material.

[0113] The components and parameters of the negative electrode sheets in each embodiment and comparative example are shown in Table 1.

[0114] Table 1

[0115]

[0116]

[0117]

[0118] The batteries prepared in each embodiment were subjected to high temperature capacity recovery performance test and high temperature expansion test, and the test data are shown in Table 2. The specific test method is as follows:

[0119] (1) High temperature capacity recovery performance test: The battery was charged with a current of 1C to a cut-off voltage of 4.2V, placed in a 70°C incubator for 40 days, then discharged with a current of 1C to 2.8V, and the battery capacity C1 was recorded. The battery was then charged with a current of 1C to 4.2V, and finally discharged with a current of 1C to 2.8V, and the battery capacity C2 was recorded. Capacity recovery rate = 100%*C2 / C1.

[0120] (2) High temperature expansion test: Charge the battery at 1C current to a cut-off voltage of 4.2V, and use a PPG thickness tester to test the battery thickness H0. Place the battery in a 70°C incubator for 40 days, and then use a PPG thickness tester to test the battery thickness H1 after placement. The battery storage thickness expansion rate = 100%*(H1-H0) / H0.

[0121] (3) Cycle performance test: The battery is subjected to a charge and discharge cycle test at a current of 1C / 1C with a cut-off voltage of 2.8 to 4.2 until the battery capacity drops to 80% of the initial capacity, and the current cycle number is recorded.

[0122] Table 2

[0123]

[0124] According to the above data, it can be known that setting the negative electrode plate into a double-layer structure, and having both P and Al in the upper and lower layers of the negative electrode plate, and setting the Al element content of the upper layer to be greater than that of the lower layer, and the P element content of the lower layer to be greater than that of the lower layer, is beneficial to improving the cycle performance and storage performance of the battery, and can also inhibit battery expansion.

[0125] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they are aware of the basic creative concept. Therefore, the claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the embodiments of the present invention.

[0126] The secondary battery and electrical equipment provided by the present invention are introduced in detail above. The principle and implementation mode of the present invention are explained by using specific examples in this article. The description of the above embodiments is only used to help understand the method and core idea of ​​the present invention. At the same time, for those skilled in the art, according to the idea of ​​the present invention, there will be changes in the specific implementation mode and application scope. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A secondary battery, comprising a negative electrode plate, characterized in that: The negative electrode sheet comprises a negative electrode current collector, a first negative electrode active material layer and a second negative electrode active material layer, wherein the first negative electrode active material layer is disposed on at least one surface of the negative electrode current collector, and the second negative electrode active material layer is disposed on the surface of the first negative electrode active material layer; The first negative electrode active material layer includes a first negative electrode active material, the second negative electrode active material layer includes a second negative electrode active material, and the first negative electrode active material and the second negative electrode active material both contain element P and element Al; The mass content of the element P in the first negative electrode active material is greater than the mass content of the element P in the second negative electrode active material; the mass content of the element P in the first negative electrode active material is 1600-2000 ppm, and the mass content of the element P in the second negative electrode active material is 800-1200 ppm; The mass content of element Al in the first negative electrode active material is less than the mass content of element Al in the second negative electrode active material; the mass content of element Al in the first negative electrode active material is 300-700 ppm, and the mass content of element Al in the second negative electrode active material is 800-1200 ppm.

2. The secondary battery according to claim 1, characterized in that: The gram capacity of the first negative electrode active material is greater than the gram capacity of the second negative electrode active material.

3. The secondary battery according to claim 1, characterized in that: The gram capacity difference Δq between the first negative electrode active material and the second negative electrode active material satisfies: 10 mAh / g≤Δq≤20 mAh / g.

4. The secondary battery according to claim 1, characterized in that: The difference ΔC1 in mass content of element P between the first negative electrode active material and the second negative electrode active material satisfies: 200 ppm≤ΔC1≤1000 ppm.

5. The secondary battery according to claim 1, characterized in that: The difference ΔC2 in mass content of element Al between the second negative electrode active material and the first negative electrode active material satisfies: 100 ppm≤ΔC2≤1000 ppm.

6. The secondary battery according to claim 1, characterized in that: The first negative electrode active material and the second negative electrode active material each independently contain at least one element selected from the group consisting of N, B, Na, Li, V, and Ge.

7. The secondary battery according to claim 1, characterized in that: Meet one of the following conditions: a. The first negative electrode active material and the second negative electrode active material both contain elements N, V ​​and Na; b. The first negative electrode active material and the second negative electrode active material both contain elements Li, B, and Ge; c. The first negative electrode active material and the second negative electrode active material both contain elements N, B, and V.

8. An electrical device, characterized in that: It comprises the secondary battery according to any one of claims 1 to 7, wherein the secondary battery is used as a power supply for the electrical device.

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