Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device. In the secondary battery, a plurality of second electrode assemblies are arranged on two sides of a first electrode assembly, a first positive pole piece in the first electrode assembly comprises a first positive pole material layer, and a first negative pole piece in the first electrode assembly comprises a first negative pole material layer; a second positive pole piece in the second electrode assembly comprises a second positive pole material layer, and a second negative pole piece in the second electrode assembly comprises a second negative pole material layer. The coating weight CW1 of the first positive electrode material layer, the coating weight CW2 of the second positive electrode material layer, the coating weight CW3 of the first negative electrode material layer, the coating weight CW4 of the second negative electrode material layer, the compaction density PD1 of the first negative electrode material layer and the compaction density PD2 of the second negative electrode material layer are regulated and controlled; according to the present invention, the performance uniformity of different positions of the secondary battery can be improved according to the type or the mass percentage content of the first negative electrode material layer or the type or the mass percentage content of the negative electrode active material in the first negative electrode material layer and the second negative electrode material layer, such that the secondary battery has high energy density and good cycle performance.

Description

Technical Field

[0001] The present application relates to the field of electrochemical technology, and in particular to a secondary battery and an electronic device. Background Art

[0002] Secondary batteries, such as lithium-ion batteries, have increasingly higher market requirements for energy density and cost. In the prior art, energy density is increased by increasing coating weight and compaction density, but these methods will lead to poor power performance and cycle performance. The prior art reduces the preparation cost of lithium-ion batteries by introducing natural graphite, but natural graphite expands greatly and has poor cycle performance. At the same time, due to the inconsistent heat dissipation and pressure conditions at different positions in the lithium-ion battery pack, there will be differences in performance at different positions, resulting in poor performance (such as cycle performance) of the entire lithium-ion battery pack.

[0003] Therefore, it is necessary to provide a lithium ion battery with uniform performance at different positions so that it has high energy density and good cycle performance. Summary of the invention

[0004] The purpose of this application is to provide a secondary battery and an electronic device, which can improve the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance. The specific technical solution is as follows:

[0005] The first aspect of the present application provides a secondary battery, comprising an electrode assembly, the electrode assembly comprising at least one first electrode assembly and a plurality of second electrode assemblies, wherein the plurality of second electrode assemblies are arranged on both sides of the first electrode assembly along the thickness direction of the secondary battery; the first electrode assembly comprises a first positive electrode plate and a first negative electrode plate, the first positive electrode plate comprises a first positive electrode collector and a first positive electrode material layer arranged on at least one surface of the first positive electrode collector, the first negative electrode plate comprises a first negative electrode collector and a first negative electrode material layer arranged on at least one surface of the first negative electrode collector; the second electrode assembly comprises a second positive electrode plate and a second negative electrode plate, the second positive electrode plate comprises a second positive electrode collector and a second positive electrode material layer arranged on at least one surface of the second positive electrode collector, the second negative electrode plate comprises a second negative electrode collector and a second negative electrode material layer arranged on at least one surface of the second negative electrode collector; wherein the secondary battery satisfies at least one of the following characteristics: (1) the coating weight of the first positive electrode material layer is CW1 mg / cm 2 The coating weight of the second positive electrode material layer is CW2 mg / cm 2 , CW1<CW2; (2) the coating weight of the first negative electrode material layer is CW3 mg / cm 2 The coating weight of the second negative electrode material layer is CW4 mg / cm 2, CW3<CW4; (3) the compaction density of the first negative electrode material layer is PD1 g / cm 3 The compaction density of the second negative electrode material layer is PD2 g / cm 3 , PD1>PD2; (4) the types of negative electrode active materials or the mass percentage of each negative electrode active material in the first negative electrode material layer and the second negative electrode material layer are different. The secondary battery meets the above characteristics, which can improve the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0006] In one or more embodiments of the present application, the secondary battery satisfies at least one of the following characteristics: (1) 8≤CW1≤25, 10≤CW2≤30; (2) 3.7≤CW3≤11.5, 4.7≤CW4≤14.1; (3) 1≤CW2-CW1≤5; (4) 0.6≤CW4-CW3≤2.4; (5) 1.0≤PD1≤1.8, 0.6≤PD2≤1.7; (6) 0.1≤PD1-PD2≤0.3. The secondary battery satisfies the above characteristics, can balance the temperature difference at different positions of the electrode assembly, reduce the cyclic expansion of the first electrode assembly, and improve the energy density of the secondary battery, which is conducive to improving the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0007] In one or more embodiments of the present application, the electrode assembly further includes a plurality of third electrode assemblies, wherein the second electrode assembly is disposed between the first electrode assembly and the third electrode assembly along the thickness direction of the secondary battery, and the outermost side of the electrode assembly is the third electrode assembly; the third electrode assembly includes a third positive electrode sheet and a third negative electrode sheet, the third positive electrode sheet includes a third positive electrode collector and a third positive electrode material layer disposed on at least one surface of the third positive electrode collector, and the third negative electrode sheet includes a third negative electrode collector and a third negative electrode material layer disposed on at least one surface of the third negative electrode collector; wherein the secondary battery satisfies at least one of the following characteristics: (1) the coating weight of the third positive electrode material layer is CW5 mg / cm 2 , CW1<CW2<CW5; (2) the coating weight of the third negative electrode material layer is CW6 mg / cm 2 , CW3<CW4<CW6; (3) the compaction density of the third negative electrode material layer is PD3 g / cm 3 , PD1>PD2>PD3; (4) the type of negative electrode active material or the mass percentage of each negative electrode active material in the third negative electrode material layer is different from that in the first negative electrode material layer and the second negative electrode material layer. The secondary battery meets the above characteristics, which is conducive to further improving the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0008] In one or more embodiments of the present application, the secondary battery satisfies at least one of the following characteristics: (1) 12≤CW5≤35, 5.5≤CW6≤16.1; (2) 0.5≤PD3≤1.6. The secondary battery satisfies the above characteristics, which is conducive to further improving the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0009] In one or more embodiments of the present application, the first negative electrode material layer includes a first negative electrode active material, the first negative electrode active material includes a first carbon material, and the mass percentage of the first carbon material is G1% based on the mass of the first negative electrode material layer; the second negative electrode material layer includes a second negative electrode active material, the second negative electrode active material includes a second carbon material, and the mass percentage of the second carbon material is G2% based on the mass of the second negative electrode material layer, G1>G2. By regulating G1 and G2 to satisfy the above relationship, it is beneficial to improve the performance uniformity of different positions of the secondary battery so that the secondary battery has high energy density and good cycle performance while reducing the preparation cost of the secondary battery.

[0010] In one or more embodiments of the present application, 10≤G1≤50, 0≤G2≤15. By regulating G1 and G2 to satisfy the above relationship, it is beneficial to improve the performance uniformity of different positions of the secondary battery so that the secondary battery has high energy density and good cycle performance while reducing the preparation cost of the secondary battery.

[0011] In one or more embodiments of the present application, 5≤G1-G2≤15. By adjusting the value of G1-G2 within the scope of the present application, it is beneficial to improve the performance uniformity of different positions of the secondary battery so that the secondary battery has high energy density and good cycle performance, while further reducing the preparation cost of the secondary battery.

[0012] In one or more embodiments of the present application, the third negative electrode material layer includes a third negative electrode active material, the third negative electrode active material includes a third carbon material, and based on the mass of the third negative electrode material layer, the mass percentage of the third carbon material is G3%, G1>G2>G3, 0≤G3≤10. By adjusting the value of G3 to satisfy the above relationship, it is beneficial to improve the performance uniformity of different positions of the secondary battery so that the secondary battery has high energy density and good cycle performance, while further reducing the preparation cost of the secondary battery.

[0013] In one or more embodiments of the present application, the first carbon material, the second carbon material and the third carbon material each independently include at least one of natural graphite, soft carbon or hard carbon. The selection of the first carbon material, the second carbon material and the third carbon material is conducive to improving the performance uniformity of different positions of the secondary battery so that the secondary battery has high energy density and good cycle performance, while reducing the preparation cost of the secondary battery.

[0014] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the above embodiments. The secondary battery provided by the present application has good performance uniformity at different positions, and also has high energy density and good cycle performance, so that the electronic device provided by the present application has a long service life and good performance.

[0015] Beneficial effects of this application:

[0016] The present application provides a secondary battery and an electronic device. The secondary battery includes an electrode assembly, the electrode assembly includes at least one first electrode assembly and a plurality of second electrode assemblies, and along the thickness direction of the secondary battery, the plurality of second electrode assemblies are arranged on both sides of the first electrode assembly; the first electrode assembly includes a first positive electrode plate and a first negative electrode plate, the first positive electrode plate includes a first positive electrode collector and a first positive electrode material layer arranged on at least one surface of the first positive electrode collector, and the first negative electrode plate includes a first negative electrode collector and a first negative electrode material layer arranged on at least one surface of the first negative electrode collector; the second electrode assembly includes a second positive electrode plate and a second negative electrode plate, the second positive electrode plate includes a second positive electrode collector and a second positive electrode material layer arranged on at least one surface of the second positive electrode collector, and the second negative electrode plate includes a second negative electrode collector and a second negative electrode material layer arranged on at least one surface of the second negative electrode collector; wherein the secondary battery satisfies at least one of the following characteristics: (1) the coating weight of the first positive electrode material layer is CW1 mg / cm 2 The coating weight of the second positive electrode material layer is CW2 mg / cm 2 , CW1<CW2; (2) the coating weight of the first negative electrode material layer is CW3 mg / cm 2 The coating weight of the second negative electrode material layer is CW4 mg / cm 2 , CW3<CW4; (3) the compaction density of the first negative electrode material layer is PD1 g / cm 3 The compaction density of the second negative electrode material layer is PD2 g / cm 3, PD1>PD2; (4) the types of negative electrode active materials or the mass percentage of each negative electrode active material in the first negative electrode material layer and the second negative electrode material layer are different. The secondary battery meets the above characteristics, which can improve the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0017] Of course, implementing any product or method of the present application does not necessarily require achieving all of the advantages described above at the same time. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and for ordinary technicians in this field, other embodiments can also be obtained based on these drawings.

[0019] Figure 1 This is a schematic diagram of the structure of an electrode assembly along its thickness direction according to an embodiment of the present application;

[0020] Figure 2 This is a schematic structural diagram of an electrode assembly along its thickness direction according to another embodiment of the present application;

[0021] Figure 3 This is a schematic structural diagram of an electrode assembly along its thickness direction according to another embodiment of the present application;

[0022] Figure 4 This is a schematic structural diagram of an electrode assembly along its thickness direction according to another embodiment of the present application;

[0023] Reference numerals: electrode assembly 100 , first electrode assembly 110 , first positive electrode sheet 111 , first negative electrode sheet 112 , separator 113 , second electrode assembly 120 , second positive electrode sheet 121 , second negative electrode sheet 122 , third electrode assembly 130 . DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those skilled in the art based on the present application belong to the scope of protection of the present application.

[0025] It should be noted that in the specific implementation manner of the present application, the present application is explained by taking a lithium-ion battery as an example of a secondary battery, but the secondary battery of the present application is not limited to a lithium-ion battery.

[0026] In the secondary batteries of the prior art, multiple electrode assemblies usually adopt the same design. When the thickness of the secondary battery is large, due to the inconsistent heat dissipation and pressure conditions at different positions, the temperature and pressure of the electrode assemblies at different positions are different during the charging and discharging process, resulting in poor performance uniformity of the secondary battery at different positions, thereby affecting the cycle performance of the secondary battery.

[0027] Based on this, the first aspect of the present application provides a secondary battery, including an electrode assembly, the electrode assembly including at least one first electrode assembly and a plurality of second electrode assemblies, and along the thickness direction of the secondary battery, the plurality of second electrode assemblies are arranged on both sides of the first electrode assembly; the first electrode assembly includes a first positive electrode plate and a first negative electrode plate, the first positive electrode plate includes a first positive electrode collector and a first positive electrode material layer arranged on at least one surface of the first positive electrode collector, and the first negative electrode plate includes a first negative electrode collector and a first negative electrode material layer arranged on at least one surface of the first negative electrode collector; the second electrode assembly includes a second positive electrode plate and a second negative electrode plate, the second positive electrode plate includes a second positive electrode collector and a second positive electrode material layer arranged on at least one surface of the second positive electrode collector, and the second negative electrode plate includes a second negative electrode collector and a second negative electrode material layer arranged on at least one surface of the second negative electrode collector. The secondary battery satisfies at least one of the following characteristics: (1) the coating weight of the first positive electrode material layer is CW1 mg / cm 2 The coating weight of the second positive electrode material layer is CW2 mg / cm 2 , CW1<CW2; (2) the coating weight of the first negative electrode material layer is CW3 mg / cm 2 The coating weight of the second negative electrode material layer is CW4 mg / cm 2 , CW3<CW4; (3) the compaction density of the first negative electrode material layer is PD1g / cm 3 The compaction density of the second negative electrode material layer is PD2 g / cm 3 , PD1>PD2; (4) the types of negative electrode active materials or the mass percentage of each negative electrode active material in the first negative electrode material layer and the second negative electrode material layer are different.

[0028] The inventors have found that different designs of electrode assemblies usually affect the performance of secondary batteries. For example, when the positive electrode material layer and / or the negative electrode material layer adopts a high coating weight, although the secondary battery has a high energy density, the temperature and heat generation are high due to the increase in impedance, and the kinetic performance is poor, thereby affecting the cycle performance of the secondary battery; when the negative electrode material layer adopts a high compaction density, although the secondary battery has a high energy density, the probability of the negative electrode active material particles being broken increases, and the side reactions between the electrolyte and the negative electrode active material increase, resulting in poor cycle performance of the secondary battery; when the negative electrode active material is selected from natural graphite, although the secondary battery has a low preparation cost, due to the more structural defects in natural graphite and the smaller interlayer spacing, the cycle expansion performance of the secondary battery is poor. Based on this, the present application can give play to the performance advantages of different designs by designing different electrode assemblies at different positions, improve the performance uniformity of different positions of the secondary battery, and make it have good cycle performance while having high energy density.

[0029] In one or more embodiments of the present application, the coating weight of the first positive electrode material layer is CW1 mg / cm 2 The coating weight of the second positive electrode material layer is CW2 mg / cm 2 , CW1<CW2. Compared with the second electrode assemblies located on both sides of the secondary battery, the first electrode assembly at the middle position is usually more difficult to dissipate heat. The secondary battery meets the above characteristics, and the coating weight of the first positive electrode material layer is lower than that of the second positive electrode material layer, which can reduce the heat generation of the first electrode assembly, balance the temperature difference at different positions of the electrode assembly, reduce the difference in the attenuation rate of the electrode assembly at different positions, make the electrochemical reaction rate of the electrode assembly at different positions the same, reduce the probability of early termination of the secondary battery cycle, thereby improving the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance. If CW1≥CW2, the first electrode assembly will generate too much heat, the temperature difference at different positions of the electrode assembly will be too large, and the difference in the electrochemical reaction rate will be too large, thereby affecting the performance uniformity and cycle performance of different positions of the secondary battery.

[0030] In one or more embodiments of the present application, the coating weight of the first negative electrode material layer is CW3 mg / cm 2 The coating weight of the second negative electrode material layer is CW4 mg / cm 2, CW3<CW4. Compared with the second electrode assemblies located on both sides of the secondary battery, the first electrode assembly at the middle position is usually more difficult to dissipate heat. The secondary battery meets the above characteristics, and the coating weight of the first negative electrode material layer is lower than that of the second negative electrode material layer, which can reduce the heat generation of the first electrode assembly, balance the temperature difference at different positions of the electrode assembly, reduce the difference in the attenuation rate of the electrode assembly at different positions, make the electrochemical reaction rate of the electrode assembly at different positions the same, reduce the probability of early termination of the secondary battery cycle, thereby improving the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance. If CW3≥CW4, the first electrode assembly will generate too much heat, the temperature difference at different positions of the electrode assembly will be too large, and the difference in the electrochemical reaction rate will be too large, thereby affecting the performance uniformity and cycle performance of different positions of the secondary battery.

[0031] In one or more embodiments of the present application, the compaction density of the first negative electrode material layer is PD1 g / cm 3 The compaction density of the second negative electrode material layer is PD2 g / cm 3 , PD1>PD2. Compared with the second electrode assemblies located on both sides of the secondary battery, the first electrode assembly at the middle position is usually subjected to greater pressure. The secondary battery meets the above characteristics, and the compaction density of the first negative electrode material layer is greater than that of the second negative electrode material layer. The pressure of the second electrode assemblies on both sides can be used to reduce the cyclic expansion of the first electrode assembly, so that the expansion consistency of each electrode assembly in the secondary battery is better, and the energy density of the secondary battery can also be improved, thereby improving the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance. If PD1≤PD2, the energy density of the secondary battery will be reduced, the cyclic expansion of the second electrode assembly will be aggravated, and the expansion difference of the electrode assemblies at different positions will increase, thereby affecting the performance uniformity, energy density and cycle performance of the secondary battery.

[0032] In one or more embodiments of the present application, the type of negative electrode active material or the mass percentage of each negative electrode active material in the first negative electrode material layer and the second negative electrode material layer is different. The secondary battery meets the above characteristics, the design of the negative electrode active material in the first negative electrode material layer and the second negative electrode material layer is different, the first negative electrode material layer located in the middle of the secondary battery can use a negative electrode active material with a lower cost, or the mass percentage of the negative electrode active material with a lower cost can be higher, so as to reduce the preparation cost of the secondary battery, and at the same time, the pressure of the second electrode assembly on both sides can be used to reduce the cycle expansion of the first electrode assembly caused by the use of the negative electrode active material with a lower cost, and improve the cycle and expansion performance of the first electrode assembly at the middle position, thereby improving the performance uniformity of different positions of the secondary battery so that the secondary battery has high energy density and good cycle performance while reducing the preparation cost of the secondary battery. If the type and mass percentage of the negative electrode active material in the first negative electrode material layer and the second negative electrode material layer are the same, the preparation cost of the secondary battery is high.

[0033] Therefore, the present application satisfies the above characteristics by regulating at least one of the relationship between CW1 and CW2, CW3 and CW4, PD1 and PD2, the type of negative electrode active materials in the first negative electrode material layer and the second negative electrode material layer, or the mass percentage of each negative electrode active material, so as to improve the performance uniformity of the secondary battery at different positions, so that the secondary battery has good cycle performance while having high energy density. In the present application, the coating weight refers to the single-sided coating weight. Characteristics such as CW1<CW2, CW3<CW4, PD1>PD2, the type or mass percentage of negative electrode active materials in the first negative electrode material layer and the second negative electrode material can be arbitrarily combined. The secondary battery satisfies at least one of the above characteristics, and the implementation methods covered by the above combination are all within the protection scope of the present application.

[0034] For ease of understanding, in this application, the thickness direction of the electrode assembly is taken as the Y direction. It should be understood that the above definition of the direction is for the purpose of convenient description of this application. Figure 1As shown, along the thickness direction of the electrode assembly 100, two second electrode assemblies 120 are arranged on both sides of the first electrode assembly 110. The first electrode assembly 110 includes a first positive electrode sheet 111 and a first negative electrode sheet 112, the first positive electrode sheet 111 includes a first positive electrode collector and a first positive electrode material layer arranged on at least one surface of the first positive electrode collector, and the first negative electrode sheet 112 includes a first negative electrode collector and a first negative electrode material layer arranged on at least one surface of the first negative electrode collector; the second electrode assembly 120 includes a second positive electrode sheet 121 and a second negative electrode sheet 122, the second positive electrode sheet 121 includes a second positive electrode collector and a second positive electrode material layer arranged on at least one surface of the second positive electrode collector, and the second negative electrode sheet 122 includes a second negative electrode collector and a second negative electrode material layer arranged on at least one surface of the second negative electrode collector. A separator 113 is disposed between the first positive electrode sheet 111 and the first negative electrode sheet 112 , between the first positive electrode sheet 111 and the second negative electrode sheet 122 , between the first negative electrode sheet 112 and the second positive electrode sheet 121 , and between the second positive electrode sheet 121 and the second negative electrode sheet 122 .

[0035] In the present application, the first positive electrode material layer can be arranged on one surface of the first positive electrode collector along its thickness direction, or on two surfaces of the first positive electrode collector along its thickness direction; the first negative electrode material layer can be arranged on one surface of the first negative electrode collector along its thickness direction, or on two surfaces of the first negative electrode collector along its thickness direction. The second positive electrode material layer can be arranged on one surface of the second positive electrode collector along its thickness direction, or on two surfaces of the second positive electrode collector along its thickness direction; the second negative electrode material layer can be arranged on one surface of the second negative electrode collector along its thickness direction, or on two surfaces of the second negative electrode collector along its thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the first positive electrode collector, the first negative electrode collector, the second positive electrode collector or the second negative electrode collector, or it can be a partial area of ​​the surface. This application is not particularly limited, as long as the purpose of this application can be achieved.

[0036] In one or more embodiments of the present application, 8≤CW1≤25, 10≤CW2≤30. Exemplarily, the value of CW1 can be 8, 10, 12, 15, 17, 20, 23, 25 or a range consisting of any two of the above values, and the value of CW2 can be 10, 13, 15, 18, 20, 22, 25, 27, 30 or a range consisting of any two of the above values. By regulating the values ​​of CW1 and CW2 within the scope of the present application, the heat generation of the first electrode assembly can be reduced, the temperature difference at different positions of the electrode assembly can be balanced, and the energy density of the secondary battery can be improved, which is beneficial to improve the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0037] In one or more embodiments of the present application, 1≤CW2-CW1≤5. Exemplarily, the value of CW2-CW1 can be 1, 1.5, 2, 2.4, 3, 3.6, 4, 4.5, 5, or a range consisting of any two of the above values. By regulating the value of CW2-CW1 within the scope of the present application, the heat generation of the first electrode assembly can be further reduced, and the temperature difference at different positions of the electrode assembly can be balanced, which is conducive to further improving the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0038] In one or more embodiments of the present application, 3.7≤CW3≤11.5, 4.7≤CW4≤14.1. Exemplarily, the value of CW3 can be 3.7, 4, 5, 6, 7, 8, 9, 10, 11.5 or a range consisting of any two of the above values, and the value of CW4 can be 4.7, 5, 7, 8, 9, 10, 11, 12, 13, 14.1 or a range consisting of any two of the above values. By regulating the values ​​of CW3 and CW4 within the scope of the present application, the heat generation of the first electrode assembly can be reduced, the temperature difference at different positions of the electrode assembly can be balanced, and the energy density of the secondary battery can be improved at the same time, which is beneficial to improve the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0039] In one or more embodiments of the present application, 0.6≤CW4-CW3≤2.4. Exemplarily, the value of CW4-CW3 can be 0.6, 1, 1.3, 1.7, 1.9, 2, 2.1, 2.3, 2.4 or a range consisting of any two of the above values. By regulating the value of CW4-CW3 within the scope of the present application, the heat generation of the first electrode assembly can be further reduced, and the temperature difference at different positions of the electrode assembly can be balanced, which is conducive to further improving the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0040] In one or more embodiments of the present application, 1.0≤PD1≤1.8, 0.6≤PD2≤1.7. Exemplarily, the value of PD1 can be 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8 or a range consisting of any two of the above values, and the value of PD2 can be 0.6, 0.8, 1.0, 1.1, 1.2, 1.4, 1.5, 1.6, 1.7 or a range consisting of any two of the above values. By regulating the values ​​of PD1 and PD2 within the scope of the present application, the pressure of the second electrode assembly on both sides can be utilized to reduce the cyclic expansion of the first electrode assembly, and the energy density of the secondary battery can also be increased, which is beneficial to improve the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0041] In one or more embodiments of the present application, 0.1≤PD1-PD2≤0.3. Exemplarily, the value of PD1-PD2 can be 0.1, 0.13, 0.15, 0.18, 0.2, 0.22, 0.25, 0.27, 0.3 or a range consisting of any two of the above values. By regulating the value of PD1-PD2 within the scope of the present application, the pressure of the second electrode assembly on both sides can be utilized to further reduce the cyclic expansion of the first electrode assembly, and at the same time, the energy density of the secondary battery can be increased, which is conducive to further improving the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0042] In the present application, a plurality of second electrode assemblies are arranged on both sides of the first electrode assembly, the number of electrode assemblies is N, the number of first electrode assemblies is N1, the number of second electrode assemblies is N2, N≥3, N1≥1, N2≥2. The upper limits of N, N1 and N2 may not be particularly required, and may be adjusted according to the heat dissipation conditions of the secondary battery, the temperature difference and pressure difference at different positions, the cycle performance requirements, etc. For example, the value of N may be 3, 4, 5, 6, 7, 8, 9, 10, 12 or a range consisting of any two of the above values, the value of N1 may be 1, 2, 3, 4, 5, 6 or a range consisting of any two of the above values, and the value of N2 may be 2, 3, 4, 5, 6 or a range consisting of any two of the above values. It is understood that the polarity of the outermost pole pieces of the two adjacent electrode assemblies is the same; or when the polarity of the outermost pole pieces of the two adjacent electrode assemblies is different, the outermost circle of at least one of the electrode assemblies is a diaphragm to avoid short-circuit connection between the two electrode assemblies.

[0043] The present application has no particular limitation on the arrangement of the first electrode assembly and the second electrode assembly in the electrode assembly, as long as the purpose of the present application can be achieved. For example, in some embodiments, Figure 1 As shown, N=3, N1=1, N2=2, and along the thickness direction of the electrode assembly 100, a second electrode assembly 120 is distributed on both sides of a first electrode assembly 110. In other embodiments, such as Figure 2 As shown, N=5, N1=1, N2=4, and along the thickness direction of the electrode assembly 100, two second electrode assemblies 120 are distributed on both sides of a first electrode assembly 110. In some other embodiments, as Figure 3 As shown, N=5, N1=3, N2=2, and along the thickness direction of the electrode assembly 100, three first electrode assemblies 110 are sequentially distributed between the two second electrode assemblies 120.

[0044] In one or more embodiments of the present application, the electrode assembly also includes multiple third electrode assemblies, along the thickness direction of the secondary battery, the second electrode assembly is arranged between the first electrode assembly and the third electrode assembly, and the outermost side of the electrode assembly is the third electrode assembly; the third electrode assembly includes a third positive electrode plate and a third negative electrode plate, the third positive electrode plate includes a third positive electrode collector and a third positive electrode material layer arranged on at least one surface of the third positive electrode collector, and the third negative electrode plate includes a third negative electrode collector and a third negative electrode material layer arranged on at least one surface of the third negative electrode collector.

[0045] In one or more embodiments of the present application, the coating weight of the third positive electrode material layer is CW5 mg / cm 2 , CW1<CW2<CW5. By adjusting CW1, CW2 and CW5 to satisfy the above relationship, the heat generation of the first electrode assembly and the second electrode assembly can be further reduced, the temperature difference at different positions of the electrode assembly can be balanced, and the energy density of the secondary battery can be improved, which is conducive to further improving the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0046] In one or more embodiments of the present application, the coating weight of the third negative electrode material layer is CW6 mg / cm 2 , CW3<CW4<CW6. By adjusting CW3, CW4 and CW6 to satisfy the above relationship, the heat generation of the first electrode assembly and the second electrode assembly can be further reduced, the temperature difference at different positions of the electrode assembly can be balanced, and the energy density of the secondary battery can be improved, which is conducive to further improving the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0047] In one or more embodiments of the present application, the compaction density of the third negative electrode material layer is PD3 g / cm 3, PD1>PD2>PD3. By adjusting PD1, PD2 and PD3 to satisfy the above relationship, the pressure of the second electrode assembly and the third electrode assembly can be used to reduce the cyclic expansion of the first electrode assembly, and the pressure of the third electrode assembly can be used to reduce the cyclic expansion of the second electrode assembly. At the same time, the energy density of the secondary battery can be further improved, which is conducive to further improving the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0048] In one or more embodiments of the present application, the type of negative electrode active material or the mass percentage of each negative electrode active material in the third negative electrode material layer is different from that in the first negative electrode material layer and the second negative electrode material layer. The third negative electrode material layer satisfies the above characteristics, and the design of the negative electrode active material in the third negative electrode material layer is different from that in the first negative electrode material layer and the second negative electrode material layer. The first negative electrode material layer and the second negative electrode material layer can use negative electrode active materials with lower cost, or the mass percentage of negative electrode active materials with lower cost can be higher, so as to further reduce the preparation cost of the secondary battery, and at the same time, the pressure of the second electrode assembly and the third electrode assembly on both sides can be used to reduce the cyclic expansion of the first electrode assembly, and the pressure of the third electrode assembly on both sides can be used to reduce the cyclic expansion of the second electrode assembly, so as to improve the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance, and further reduce the preparation cost of the secondary battery.

[0049] In the present application, characteristics such as CW1<CW2<CW5, CW3<CW4<CW6, PD1>PD2>PD3, the type or mass percentage of the negative electrode active material in the third negative electrode material layer, etc. can be combined arbitrarily. The secondary battery satisfies at least one of the above characteristics, and the implementation methods covered by the above combination are all within the protection scope of the present application.

[0050] In one or more embodiments of the present application, 12≤CW5≤35, 5.5≤CW6≤16.1. Exemplarily, the value of CW5 can be 12, 15, 18, 20, 22, 25, 28, 30, 35 or a range consisting of any two of the above values, and the value of CW6 can be 5.5, 6, 8, 9, 10, 11, 12, 13, 14, 15, 16.1 or a range consisting of any two of the above values. By regulating the values ​​of CW5 and CW6 within the scope of the present application, the heat generation of the first electrode assembly and the second electrode assembly can be further reduced, the temperature difference at different positions of the electrode assembly can be balanced, and the energy density of the secondary battery can be improved at the same time, which is conducive to further improving the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0051] In one or more embodiments of the present application, 0.5≤PD3≤1.6. Exemplarily, the value of PD3 can be 0.5, 0.8, 1.0, 1.2, 1.4, 1.6 or a range consisting of any two of the above values. By regulating the value of PD3 within the scope of the present application, the pressure of the second electrode assembly and the third electrode assembly can be used to reduce the cyclic expansion of the first electrode assembly, and the pressure of the third electrode assembly can be used to reduce the cyclic expansion of the second electrode assembly. At the same time, the energy density of the secondary battery can be further improved, which is conducive to further improving the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance.

[0052] The present application has no particular restrictions on the method of regulating the compaction density PD1 of the first negative electrode material layer, the compaction density PD2 of the second negative electrode material layer, and the compaction density PD3 of the third negative electrode material layer, as long as the purpose of the present application can be achieved. For example, PD1 can be regulated by regulating the cold pressing pressure of the first negative electrode material layer, PD2 can be regulated by regulating the cold pressing pressure of the second negative electrode material layer, and PD3 can be regulated by regulating the cold pressing pressure of the third negative electrode material layer. When other conditions remain unchanged, the cold pressing pressure of the first negative electrode material layer increases, and PD1 increases; the cold pressing pressure of the first negative electrode material layer decreases, and PD1 decreases. When other conditions remain unchanged, the cold pressing pressure of the second negative electrode material layer increases, and PD2 increases; the cold pressing pressure of the second negative electrode material layer decreases, and PD2 decreases. When other conditions remain unchanged, the cold pressing pressure of the third negative electrode material layer increases, and PD3 increases; the cold pressing pressure of the third negative electrode material layer decreases, and PD3 decreases.

[0053] In the present application, the second electrode assembly is disposed between the first electrode assembly and the third electrode assembly, and the outermost electrode assembly is the third electrode assembly, and the number of the third electrode assemblies is N3, where N3 ≥ 2. There is no special requirement for the upper limit of N3, and it can be adjusted according to the heat dissipation conditions of the secondary battery, the temperature difference and pressure difference at different positions, the cycle performance requirements, etc. For example, the value of N3 can be 2, 3, 4, 5, 6, or a range consisting of any two of the above values.

[0054] The present application has no particular restrictions on the arrangement of the first electrode assembly, the second electrode assembly, and the third electrode assembly in the electrode assembly, as long as the purpose of the present application can be achieved. For example, in some embodiments, Figure 4 As shown, N=5, N1=1, N2=2, N3=2, and along the thickness direction of the electrode assembly 100, a second electrode assembly 120 and a third electrode assembly 130 are sequentially distributed on both sides of a first electrode assembly 110.

[0055] In one or more embodiments of the present application, the first negative electrode material layer includes a first negative electrode active material, the first negative electrode active material includes a first carbon material, and the mass percentage of the first carbon material is G1% based on the mass of the first negative electrode material layer; the second negative electrode material layer includes a second negative electrode active material, the second negative electrode active material includes a second carbon material, and the mass percentage of the second carbon material is G2% based on the mass of the second negative electrode material layer, G1>G2. The cost of the first carbon material and the second carbon material is relatively low. By adjusting G1 and G2 to meet the above relationship, the mass percentage of the first carbon material in the first negative electrode material layer is higher, which can reduce the preparation cost of the secondary battery. At the same time, the pressure of the second electrode assembly on both sides can be used to reduce the cyclic expansion of the first electrode assembly caused by the use of more first carbon material, which is conducive to improving the performance uniformity of different positions of the secondary battery so that the secondary battery has high energy density and good cycle performance while reducing the preparation cost of the secondary battery.

[0056] In one or more embodiments of the present application, 10≤G1≤50, 0≤G2≤15. Exemplarily, the value of G1 can be 10, 15, 20, 24, 30, 36, 40, 45, 50 or a range consisting of any two of the above values, and the value of G2 can be 0, 2, 4, 6, 8, 10, 12, 15 or a range consisting of any two of the above values. By regulating G1 and G2 to satisfy the above relationship, the preparation cost of the secondary battery can be further reduced, and at the same time, the pressure of the second electrode assembly on both sides can be utilized to reduce the cyclic expansion of the first electrode assembly caused by the use of more first carbon material, thereby facilitating the improvement of the performance uniformity of different positions of the secondary battery so that the secondary battery has high energy density and good cycle performance while further reducing the preparation cost of the secondary battery.

[0057] In one or more embodiments of the present application, 5≤G1-G2≤15. Exemplarily, the value of G1-G2 can be 5, 7, 10, 12, 15 or a range consisting of any two of the above values. By regulating the value of G1-G2 within the scope of the present application, the preparation cost of the secondary battery can be further reduced, and at the same time, the pressure of the second electrode assembly on both sides can be utilized to reduce the cyclic expansion of the first electrode assembly caused by the use of more first carbon material, which is beneficial to improve the performance uniformity of different positions of the secondary battery so that the secondary battery has high energy density and good cycle performance, while further reducing the preparation cost of the secondary battery.

[0058] In one or more embodiments of the present application, the third negative electrode material layer includes a third negative electrode active material, the third negative electrode active material includes a third carbon material, and based on the mass of the third negative electrode material layer, the mass percentage of the third carbon material is G3%, G1>G2>G3, 0≤G3≤10. Exemplarily, the value of G3 can be 0, 2, 4, 5, 6, 8, 10 or a range consisting of any two of the above values. The cost of the third carbon material is relatively low. By adjusting the value of G3 to satisfy the above relationship, the mass percentage of the third carbon material in the third negative electrode material layer is lower, which can further reduce the preparation cost of the secondary battery. At the same time, the pressure of the second electrode assembly and the third electrode assembly on both sides can be used to reduce the cyclic expansion of the first electrode assembly, and the pressure of the third electrode assembly on both sides can be used to reduce the cyclic expansion of the second electrode assembly, so as to improve the performance uniformity of different positions of the secondary battery, so that the secondary battery has high energy density and good cycle performance, while further reducing the preparation cost of the secondary battery.

[0059] In one or more embodiments of the present application, the first carbon material, the second carbon material and the third carbon material each independently include at least one of natural graphite, soft carbon or hard carbon. The selection of the first carbon material, the second carbon material and the third carbon material has a low cost, which is conducive to improving the performance uniformity of different positions of the secondary battery so that the secondary battery has a high energy density and good cycle performance, while reducing the preparation cost of the secondary battery.

[0060] In the present application, the first negative electrode material layer includes a first negative electrode active material, the first negative electrode active material includes a first carbon material, and also includes a first artificial graphite. The first negative electrode material layer may also include a first negative electrode binder, or the first negative electrode material layer may also include a first negative electrode binder and a first negative electrode conductor and / or a first thickener. Based on the mass of the first negative electrode material layer, the mass percentage of the first artificial graphite may be 40% to 80%, the mass percentage of the first negative electrode binder may be 0.1% to 4%, the mass percentage of the first negative electrode conductor may be 0% to 4%, and the mass percentage of the first thickener may be 0% to 3%.

[0061] In the present application, the second negative electrode material layer includes a second negative electrode active material, the second negative electrode active material includes a second carbon material, and also includes a second artificial graphite. The second negative electrode material layer may also include a second negative electrode binder, or the second negative electrode material layer may also include a second negative electrode binder and a second negative electrode conductor and / or a second thickener. Based on the mass of the second negative electrode material layer, the mass percentage of the second artificial graphite may be 75% to 90%, the mass percentage of the second negative electrode binder may be 0.1% to 4%, the mass percentage of the second negative electrode conductor may be 0% to 4%, and the mass percentage of the second thickener may be 0% to 3%.

[0062] In the present application, the third negative electrode material layer includes a third negative electrode active material, the third negative electrode active material includes a third carbon material, and also includes a third artificial graphite. The third negative electrode material layer may also include a third negative electrode binder, or the third negative electrode material layer may also include a third negative electrode binder and a third negative electrode conductor and / or a third thickener. Based on the mass of the third negative electrode material layer, the mass percentage of the third artificial graphite may be 80% to 90%, the mass percentage of the third negative electrode binder may be 0.1% to 4%, the mass percentage of the third negative electrode conductor may be 0% to 4%, and the mass percentage of the third thickener may be 0% to 3%.

[0063] The present application has no particular restrictions on the types of the first negative electrode binder, the second negative electrode binder, the third negative electrode binder, the first negative electrode conductive agent, the second negative electrode conductive agent and the third negative electrode conductive agent, as long as the purpose of the present application can be achieved. For example, the first negative electrode binder, the second negative electrode binder and the third negative electrode binder can each independently include but are not limited to at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, polyamide-imide, styrene-butadiene rubber or polyvinylidene fluoride. For example, the first negative electrode conductive agent, the second negative electrode conductive agent and the third negative electrode conductive agent can each independently include but are not limited to at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials or conductive polymers, and conductive carbon black can include but are not limited to at least one of acetylene black or Ketjen black. The above-mentioned carbon nanotubes can include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers can include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano carbon fibers. The above-mentioned metal material may include but is not limited to metal powder and / or metal fiber. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymer may include but is not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole. The present application has no particular restrictions on the types of the first thickener, the second thickener and the third thickener, as long as the purpose of the present application can be achieved. For example, the first thickener, the second thickener and the third thickener may each independently include but is not limited to at least one of sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.

[0064] The present application has no particular restrictions on the first negative electrode current collector, the second negative electrode current collector, and the third negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the first negative electrode current collector, the second negative electrode current collector, and the third negative electrode current collector can each independently include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector (for example, lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.). The present application has no particular restrictions on the thickness of the first negative electrode current collector, the second negative electrode current collector, and the third negative electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the first negative electrode current collector, the second negative electrode current collector, and the third negative electrode current collector can each independently be 4 μm to 20 μm.

[0065] The present application has no particular restrictions on the first positive electrode current collector, the second positive electrode current collector, and the third positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the first positive electrode current collector, the second positive electrode current collector, and the third positive electrode current collector can each independently include aluminum foil, aluminum alloy foil, or a composite current collector (such as an aluminum-carbon composite current collector). The present application has no particular restrictions on the thickness of the first positive electrode current collector, the second positive electrode current collector, and the third positive electrode current collector, as long as the purpose of the present application can be achieved. For example, the thickness of the first positive electrode current collector, the second positive electrode current collector, and the third positive electrode current collector can each independently be 6 μm to 16 μm.

[0066] The first positive electrode material layer of the present application includes a first positive electrode active material, the second positive electrode material layer includes a second positive electrode active material, and the third positive electrode material layer includes a third positive electrode active material. The first positive electrode active material, the second positive electrode active material, and the third positive electrode active material include substances that can reversibly embed and extract active ions such as lithium ions. The first positive electrode material layer, the second positive electrode material layer, and the third positive electrode material layer can each independently be one or more layers, and each layer in the multilayer positive electrode material layer can contain the same or different positive electrode active materials. The present application has no special restrictions on the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material, as long as the purpose of the present application can be achieved. For example, the first positive electrode active material, the second positive electrode active material, and the third positive electrode active material can each independently include but are not limited to lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium iron manganese phosphate or lithium titanate. The above-mentioned lithium nickel cobalt manganese oxide may include LiNi 0.95 Co 0.03 Mn 0.02 O2(Ni95),LiNi 0.91 Co 0.03 Mn 0.06 O2(Ni91), LiNi 0.8 Co 0.1 Mn0.1 O2(NCM811), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523) or LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 At least one of O2 (NCM111). The first positive electrode material layer of the present application also includes a first positive electrode conductor and a first positive electrode binder, the second positive electrode material layer also includes a second positive electrode conductor and a second positive electrode binder, and the third positive electrode material layer also includes a third positive electrode conductor and a third positive electrode binder. The present application has no special restrictions on the first positive electrode conductor, the second positive electrode conductor, and the third positive electrode conductor, as long as the purpose of the present application can be achieved. For example, the first positive electrode conductor, the second positive electrode conductor, and the third positive electrode conductor can each independently include at least one of the above-mentioned first negative electrode conductors. The present application has no special restrictions on the first positive electrode binder, the second positive electrode binder, and the third positive electrode binder, as long as the purpose of the present application can be achieved. For example, the first positive electrode binder, the second positive electrode binder, and the third positive electrode binder can each independently include at least one of the above-mentioned first negative electrode binders. The present application has no particular restrictions on the mass ratio of the first positive electrode active material, the first positive electrode conductor, and the first positive electrode binder in the first positive electrode material layer, the mass ratio of the second positive electrode active material, the second positive electrode conductor, and the second positive electrode binder in the second positive electrode material layer, and the mass ratio of the third positive electrode active material, the third positive electrode conductor, and the third positive electrode binder in the third positive electrode material layer. Those skilled in the art can choose according to actual needs as long as the purpose of the present application can be achieved.

[0067] The present application has no particular limitation on the compaction density of the first positive electrode material layer, the second positive electrode material layer, and the third positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the compaction density of the first positive electrode material layer, the second positive electrode material layer, and the third positive electrode material layer can be 1 g / cm 3 Up to 5g / cm 3 .

[0068] In the present application, the secondary battery also includes an electrolyte. The electrolyte includes a lithium salt. The present application does not particularly limit the type of lithium salt. Lithium salts known in the art can be used. For example, the lithium salt may include but is not limited to lithium hexafluorophosphate (LiPF6), lithium bistrifluoromethanesulfonyl imide (LiN(CF3SO2)2, LiTFSI), lithium bis(fluorosulfonyl) imide (Li(N(SO2F)2), LiFSI), lithium difluorophosphate (LiPO2F2), lithium bis(oxalate borate) (LiB(C2O4)2, LiBOB) or lithium difluorooxalate borate (LiBF2(C2O4), LiDFOB). The present application does not particularly limit the mass percentage of lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. The electrolyte also includes a non-aqueous organic solvent. The present application does not particularly limit the non-aqueous organic solvent, as long as the purpose of the present application can be achieved. For example, the non-aqueous organic solvent may include at least one of a carbonate compound, a carboxylate compound, an ether compound or other organic solvents. The above-mentioned carbonate compound may include but is not limited to at least one of a linear carbonate compound, a cyclic carbonate compound or a fluorinated carbonate compound. The above-mentioned linear carbonate compound may include but is not limited to at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC) or ethyl methyl carbonate (EMC). The above-mentioned cyclic carbonate compound may include but is not limited to at least one of ethylene carbonate (EC), vinylene carbonate, propylene carbonate (PC), butylene carbonate (BC) or vinyl ethylene carbonate (VEC). The above-mentioned fluorinated carbonate compound may include but is not limited to fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate or trifluoromethylethylene carbonate. The above-mentioned carboxylate compound may include but is not limited to at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate or propyl propionate. The above-mentioned ether compound may include but is not limited to at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran or tetrahydrofuran. The above-mentioned other organic solvents may include, but are not limited to, at least one of 1,3-propanesultone, dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate or phosphate ester.The present application has no particular limitation on the mass percentage of the non-aqueous organic solvent in the electrolyte, as long as the purpose of the present application can be achieved.

[0069] In the present application, the secondary battery also includes a diaphragm. The diaphragm is used to separate the positive electrode plate and the negative electrode plate, prevent the internal short circuit of the secondary battery, allow the electrolyte ions to pass freely, and do not affect the electrochemical charge and discharge process. The present application has no special restrictions on the diaphragm, as long as the purpose of the present application can be achieved. For example, the material of the diaphragm may include but is not limited to polyethylene (PE), polypropylene (PP)-based polyolefins (PO), polyesters (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid; the type of diaphragm may include at least one of a woven membrane, a non-woven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.

[0070] In the present application, the diaphragm may include a substrate and a surface treatment layer. The substrate may be a non-woven fabric or a composite film having a porous structure, and the material of the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. For example, the inorganic layer includes inorganic particles and a diaphragm binder, and the present application has no particular restrictions on the above-mentioned inorganic particles, for example, it may include at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide or barium sulfate. The present application has no particular restrictions on the above-mentioned diaphragm binder, for example, it may be at least one of the above-mentioned first negative electrode binders. The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride or vinylidene fluoride-hexafluoropropylene copolymer.

[0071] In the present application, the secondary battery also includes a packaging bag for containing a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte, as well as other components known in the art in the secondary battery, and the present application does not limit the above other components. The present application does not specifically limit the packaging bag, and it can be a packaging bag known in the art, as long as it can achieve the purpose of the present application.

[0072] The present application does not particularly limit the type of secondary battery, which may include any device that undergoes an electrochemical reaction. In the present application, the secondary battery may include, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery or a lithium ion polymer secondary battery (lithium ion polymer battery), etc.

[0073] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and there is no particular limitation in the present application. For example, in some embodiments, the preparation of the secondary battery may include but is not limited to the following steps: stacking the first positive electrode sheet, the separator and the first negative electrode sheet in sequence, and winding, folding and other operations as needed to obtain the first electrode assembly of the winding structure; stacking the second positive electrode sheet, the separator and the second negative electrode sheet in sequence, and winding, folding and other operations as needed to obtain the second electrode assembly of the winding structure. Put the second electrode assembly, the first electrode assembly and the second electrode assembly into the packaging bag in the order of the second electrode assembly, inject the electrolyte into the packaging bag and seal it to obtain a secondary battery. In other embodiments, the preparation of the secondary battery may include but is not limited to the following steps: stacking the first positive electrode sheet, the separator and the first negative electrode sheet in sequence to obtain the first electrode assembly; stacking the second positive electrode sheet, the separator and the second negative electrode sheet in sequence to obtain the second electrode assembly. The second electrode assembly, the first electrode assembly, and the second electrode assembly are stacked in order, and then the four corners of the entire stacked structure are fixed with tape to obtain an electrode assembly of the stacked structure, and the electrode assembly is placed in a packaging bag, and the electrolyte is injected into the packaging bag and sealed to obtain a secondary battery. In addition, an overcurrent protection element, a guide plate, etc. can also be placed in the packaging bag as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0074] The second aspect of the present application provides an electronic device, which includes the secondary battery in any of the above embodiments. The secondary battery provided by the present application has good performance uniformity at different positions, and also has high energy density and good cycle performance, so that the electronic device provided by the present application has a long service life and good performance.

[0075] The present application does not particularly limit the type of electronic device, which can be any electronic device known in the prior art. In some embodiments, the electronic device can include but is not limited to a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0076] Example

[0077] The following examples and comparative examples are given to more specifically describe the embodiments of the present application. Various tests and evaluations were performed according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0078] Test methods and equipment:

[0079] Coat Weight Test

[0080] After the lithium-ion battery is discharged to 2.5V at a constant current of 0.5C, it is disassembled to obtain a first positive electrode sheet, a first negative electrode sheet, a second positive electrode sheet, a second negative electrode sheet, or a third positive electrode sheet and a third negative electrode sheet. After cleaning the above-mentioned electrodes with dimethyl carbonate (DMC), they are dried at 60°C. A 1cm×1cm test sample is punched out at any position on both sides of the first positive electrode sheet coated with the first positive electrode material layer, and its mass is weighed, recorded as m1 mg. Then the first positive electrode material layer on both sides of the test sample is peeled off, and the mass of the first positive electrode current collector is weighed, recorded as m2 mg. The coating weight CW1 of the first positive electrode material layer is calculated by the following formula: CW1=(m1-m2) / 2, unit is mg / cm 2 Using the same method, the coating weight CW2 of the second positive electrode material layer, the coating weight CW3 of the first negative electrode material layer, the coating weight CW4 of the second negative electrode material layer, the coating weight CW5 of the third positive electrode material layer, and the coating weight CW6 of the third negative electrode material layer are measured respectively.

[0081] Compacted density test

[0082] After the lithium-ion battery is discharged to 2.5V at a constant current of 0.5C, it is disassembled to obtain the first negative electrode plate, the second negative electrode plate, or the third negative electrode plate. After the above-mentioned plates are cleaned with dimethyl carbonate (DMC), they are dried at 60°C. A 1cm×1cm test sample is punched out at any position where the first negative electrode material layer is coated on the first negative electrode plate, and its mass is weighed, recorded as m3 mg, and its thickness is tested, recorded as h1μm. Then the first negative electrode material layer of the test sample is peeled off, and the mass of the first negative electrode current collector is weighed, recorded as m4 mg, and its thickness is tested, recorded as h2μm. The compaction density PD1 of the first negative electrode material layer is calculated by the following formula: PD1=(m3-m4)×10 / (h1-h2), unit is g / cm 3 The same method is used to measure the compaction density PD2 of the second negative electrode material layer and the compaction density PD3 of the third negative electrode material layer.

[0083] Energy density test

[0084] At 25°C, the lithium-ion battery was charged at a constant current of 0.2C to a voltage of 4.30V, charged at a constant voltage of 4.30V to a current of 0.05C, and then left to stand for 5 minutes, and then discharged at a constant current of 0.2C to a voltage of 2.5V, and left to stand for 5 minutes. The discharge energy at this time was tested and recorded by a battery tester (Neware CTE-4016-5V-200A), which was recorded as the energy E of the lithium-ion battery, and the mass of the lithium-ion battery was measured and recorded as m. The energy density of the lithium-ion battery was calculated by the following formula: Energy density (Wh / kg) = E / m.

[0085] Cycle performance test

[0086] At 25°C, charge the lithium-ion battery to 4.30V at 1.0C constant current, charge to 0.05C at 4.30V constant voltage (this state is the full charge state), let stand for 10 minutes, then discharge to 2.5V at 4.0C constant current, let stand for 15 minutes. The above is a charge and discharge cycle. Follow the above steps for 500 cycles, record the first cycle discharge capacity as the initial capacity Q0, and the 500th cycle lithium-ion battery discharge capacity as Q1. The 500th cycle capacity retention rate of the lithium-ion battery is calculated by the following formula: Cycle capacity retention rate (%) = Q1 / Q0×100%.

[0087] The lithium-ion battery is placed in a 25°C environment, discharged to 2.5V at a constant current of 4.0C, left to stand for 15 minutes, and then charged to 3.60V at a constant current of 1.0C. At this time, the state of charge (SOC) of the lithium-ion battery is 50% SOC, that is, half-charged. At this time, the initial thickness of the lithium-ion battery is tested, which is recorded as T0. According to the above charge and discharge cycle steps, the thickness of the lithium-ion battery in the fully charged state is tested for 500 cycles, which is recorded as T1. The cycle expansion rate of the lithium-ion battery at the 500th cycle is calculated by the following formula: Cycle expansion rate (%) = (T1-T0) / T0×100%.

[0088] Discharge temperature difference test

[0089] The temperature-sensitive wires are respectively attached to the center point of the plane composed of the length direction and the width direction on the outside of the lithium-ion battery (testing the temperature of the second electrode assembly or the third electrode assembly) and the center point of the plane composed of the width direction and the thickness direction (testing the temperature of the first electrode assembly).

[0090] At 25°C, the lithium-ion battery was charged to 4.30V at a constant current of 1.0C, charged to 0.05C at a constant voltage of 4.30V, and left to stand for 10 minutes, and then discharged to 2.5V at a constant current of 4.0C and left to stand for 15 minutes. The temperature difference between the first electrode assembly at the highest temperature point and the second electrode assembly or the third electrode assembly on both sides during the discharge process was recorded to obtain the discharge temperature difference of the lithium-ion battery.

[0091] Example 1-1

[0092] <Preparation of the First Positive Electrode Sheet>

[0093] The first positive electrode active material is lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2), the first positive electrode conductive agent conductive carbon black (Super P), and the first positive electrode binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97:2:1, and N-methylpyrrolidone (NMP) is added as a solvent, and the mixture is stirred and mixed to obtain a first positive electrode slurry, wherein the solid content of the first positive electrode slurry is 75wt%. The first positive electrode slurry is evenly coated on one surface of the first positive electrode current collector aluminum foil with a thickness of 6μm, and dried at 120°C for 1h to obtain a first positive electrode sheet coated with a first positive electrode material layer on one side. Repeat the above steps on the other surface of the aluminum foil to obtain a first positive electrode sheet coated with a first positive electrode material layer on both sides. Dry under vacuum conditions at 120°C for 1h, and then after cold pressing, cutting, and slitting, a first positive electrode sheet with a specification of 50mm×80mm is obtained. Among them, the coating weight CW1 of the first positive electrode material layer after drying is shown in Table 1, and the compaction density of the first positive electrode material layer is 3.5g / cm3 .

[0094] <Preparation of the First Negative Electrode Sheet>

[0095] The first carbon material natural graphite, the first artificial graphite, and the first negative electrode binder styrene-butadiene rubber (SBR) are mixed in a weight ratio of 15:83:2, and deionized water is added as a solvent, and the mixture is stirred and mixed to obtain a first negative electrode slurry, wherein the solid content of the first negative electrode slurry is 45wt%. The first negative electrode slurry is evenly coated on one surface of the first negative electrode current collector copper foil with a thickness of 10μm, and dried at 120°C for 1h to obtain a first negative electrode sheet coated with a first negative electrode material layer on one side. Repeat the above steps on the other surface of the copper foil to obtain a first negative electrode sheet coated with a first negative electrode material layer on both sides. After drying at 120°C for 1h, cold pressing, cutting, and slitting, a first negative electrode sheet with a specification of 50mm×80mm is obtained. Among them, the coating weight CW3 of the first negative electrode material layer after drying is shown in Table 1, and the compaction density PD1 of the first negative electrode material layer is 1.7g / cm 3 .

[0096] <Preparation of the Second Positive Electrode Sheet>

[0097] The second positive electrode active material is lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1 O2), the second positive electrode conductive agent conductive carbon black (Super P), and the second positive electrode binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97:2:1, and N-methylpyrrolidone (NMP) is added as a solvent, and the mixture is stirred and mixed to obtain a second positive electrode slurry, wherein the solid content of the second positive electrode slurry is 75wt%. The second positive electrode slurry is evenly coated on one surface of the second positive electrode current collector aluminum foil with a thickness of 6μm, and dried at 120°C for 1h to obtain a second positive electrode sheet coated with a second positive electrode material layer on one side. Repeat the above steps on the other surface of the aluminum foil to obtain a second positive electrode sheet coated with a second positive electrode material layer on both sides. Dry under vacuum conditions at 120°C for 1h, and then after cold pressing, cutting and slitting, a second positive electrode sheet with a specification of 50mm×80mm is obtained. Among them, the coating weight CW2 of the second positive electrode material layer after drying is shown in Table 1, and the compaction density of the second positive electrode material layer is 3.5g / cm 3 .

[0098] <Preparation of the Second Negative Electrode Sheet>

[0099] The second carbon material natural graphite, the second artificial graphite, and the second negative electrode binder styrene-butadiene rubber (SBR) were mixed in a weight ratio of 15:83:2, and deionized water was added as a solvent, and the mixture was stirred and mixed to obtain a second negative electrode slurry, wherein the solid content of the second negative electrode slurry was 45wt%. The second negative electrode slurry was evenly coated on one surface of the second negative electrode current collector copper foil with a thickness of 10μm, and dried at 120°C for 1h to obtain a second negative electrode sheet coated with a second negative electrode material layer on one side. Repeat the above steps on the other surface of the copper foil to obtain a second negative electrode sheet coated with a second negative electrode material layer on both sides. After drying at 120°C for 1h, cold pressing, cutting, and slitting, a second negative electrode sheet with a specification of 50mm×80mm was obtained. Among them, the coating weight CW4 of the second negative electrode material layer after drying is shown in Table 1, and the compaction density PD2 of the second negative electrode material layer is 1.7g / cm 3 .

[0100] <Preparation of Electrolyte>

[0101] In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were mixed at a weight ratio of 20:30:40:10 to obtain a base solvent, and then lithium salt lithium hexafluorophosphate (LiPF6) was added and mixed evenly to obtain an electrolyte. Based on the mass of the electrolyte, the mass percentage of lithium salt LiPF6 was 12.5%, and the remainder was the base solvent.

[0102] <Preparation of Separator>

[0103] A porous polyethylene film with a thickness of 7 μm (provided by Celgard Company) was used as a separator.

[0104] <Preparation of lithium-ion batteries>

[0105] The first positive electrode sheet, the separator, and the first negative electrode sheet prepared above are alternately stacked, wherein the first positive electrode sheet has 20 layers, the separator has 39 layers, and the second negative electrode sheet has 20 layers, to obtain the first electrode assembly. The second positive electrode sheet, the separator, and the second negative electrode sheet prepared above are alternately stacked, wherein the second positive electrode sheet has 20 layers, the separator has 41 layers, and the second negative electrode sheet has 20 layers, to obtain the second electrode assembly. The second electrode assembly, the first electrode assembly, and the second electrode assembly are stacked in the order of the second electrode assembly, the first electrode assembly, and the second electrode assembly, and then the four corners of the entire laminate structure are fixed to obtain the electrode assembly of the laminate structure. After welding the pole ear, the electrode assembly is placed in an aluminum-plastic film packaging bag, and the electrolyte is injected after drying. The amount of electrolyte injection is 9g. After vacuum packaging, standing, formation (the upper limit voltage of formation is 4.30V, the formation temperature is 70°C, and the formation standing time is 2h), degassing, and trimming processes, a lithium-ion battery is obtained.

[0106] Example 1-2 to Example 1-8

[0107] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1. Among them, when the values ​​of CW1, CW2, CW3, and CW4 change, the volume of the prepared lithium-ion battery remains unchanged, and the number of layers of the first positive electrode sheet, the first negative electrode sheet, the second positive electrode sheet, the second negative electrode sheet, and the separator changes accordingly.

[0108] Example 2-1 to Example 2-7

[0109] In addition to adjusting the relevant preparation parameters according to Table 2, CW1 = CW2 = 13 mg / cm 2 , CW3=CW4=6mg / cm 2 Other than that, the rest is the same as Example 1-1. PD1 is regulated by regulating the cold pressing pressure of the first negative electrode material layer, and PD2 is regulated by regulating the cold pressing pressure of the second negative electrode material layer.

[0110] Example 3-1 to Example 3-7

[0111] In addition to adjusting the relevant preparation parameters according to Table 3, CW1 = CW2 = 13 mg / cm 2 , CW3=CW4=6mg / cm 2 Except for the above, the rest is the same as Example 1-1. When the mass percentage of the first carbon material natural graphite changes by G1%, the mass percentage of the first artificial graphite changes accordingly, and the mass percentage of the first negative electrode binder remains unchanged; when the mass percentage of the second carbon material natural graphite changes by G2%, the mass percentage of the second artificial graphite changes accordingly, and the mass percentage of the second negative electrode binder remains unchanged.

[0112] Example 4-1

[0113] Except for adding the following <Preparation of the third positive electrode sheet>, <Preparation of the third negative electrode sheet>, and <Preparation of the lithium-ion battery> using the following preparation method, the rest is the same as Example 1-1.

[0114] <Preparation of the Third Positive Electrode Sheet>

[0115] The third positive electrode active material is lithium nickel cobalt manganese oxide (LiNi 0.8 Co 0.1 Mn 0.1O2), the third positive electrode conductive agent conductive carbon black (Super P), and the third positive electrode binder polyvinylidene fluoride (PVDF) are mixed in a weight ratio of 97:2:1, and N-methylpyrrolidone (NMP) is added as a solvent, and the mixture is stirred and mixed to obtain a third positive electrode slurry, wherein the solid content of the third positive electrode slurry is 75wt%. The third positive electrode slurry is evenly coated on one surface of the third positive electrode current collector aluminum foil with a thickness of 6μm, and dried at 120°C for 1h to obtain a third positive electrode sheet coated with a third positive electrode material layer on one side. Repeat the above steps on the other surface of the aluminum foil to obtain a third positive electrode sheet coated with a third positive electrode material layer on both sides. Dry under vacuum conditions at 120°C for 1h, and then after cold pressing, cutting, and slitting, a third positive electrode sheet with a specification of 50mm×80mm is obtained. Among them, the coating weight CW5 of the third positive electrode material layer after drying is shown in Table 4, and the compaction density of the third positive electrode material layer is 3.5g / cm 3 .

[0116] <Preparation of the Third Negative Electrode Sheet>

[0117] The third carbon material natural graphite, the third artificial graphite, and the third negative electrode binder styrene-butadiene rubber (SBR) are mixed in a weight ratio of 15:83:2, and deionized water is added as a solvent, and the mixture is stirred and mixed to obtain a third negative electrode slurry, wherein the solid content of the third negative electrode slurry is 45wt%. The third negative electrode slurry is evenly coated on one surface of the third negative electrode current collector copper foil with a thickness of 10μm, and dried at 120°C for 1h to obtain a third negative electrode sheet coated with a third negative electrode material layer on one side. Repeat the above steps on the other surface of the copper foil to obtain a third negative electrode sheet coated with a third negative electrode material layer on both sides. After drying at 120°C for 1h, cold pressing, cutting, and slitting, a third negative electrode sheet with a specification of 50mm×80mm is obtained. Among them, the coating weight CW6 of the third negative electrode material layer after drying is shown in Table 4, and the compaction density PD3 of the third negative electrode material layer is 1.7g / cm 3 .

[0118] <Preparation of lithium-ion batteries>

[0119] The first positive electrode sheet, separator, and first negative electrode sheet prepared above are alternately stacked, wherein the first positive electrode sheet has 20 layers, the separator has 39 layers, and the second negative electrode sheet has 20 layers, to obtain the first electrode assembly. The second positive electrode sheet, separator, and second negative electrode sheet prepared above are alternately stacked, wherein the second positive electrode sheet has 20 layers, the separator has 40 layers, and the second negative electrode sheet has 20 layers, to obtain the second electrode assembly. The third positive electrode sheet, separator, and third negative electrode sheet prepared above are alternately stacked, wherein the third positive electrode sheet has 20 layers, the separator has 41 layers, and the third negative electrode sheet has 20 layers, to obtain the third electrode assembly. The third electrode assembly, the second electrode assembly, the first electrode assembly, the second electrode assembly, and the third electrode assembly are stacked in order, and then the four corners of the entire laminate structure are fixed to obtain the electrode assembly of the laminate structure. After welding the pole ears, the electrode assembly is placed in an aluminum-plastic film packaging bag, and the electrolyte is injected after drying. The injection amount of the electrolyte is 13g. The lithium-ion battery is obtained through vacuum packaging, standing, forming (the upper limit voltage of formation is 4.30V, the forming temperature is 70°C, and the forming standing time is 2h), degassing, and trimming processes.

[0120] Example 4-2

[0121] Except for adjusting the relevant preparation parameters according to Table 4, the values ​​of CW1, CW2, CW3, CW4, PD1, PD2, G1, and G2 are the same as those of Example 1-7, and the rest are the same as Example 4-1. Among them, when the values ​​of CW5 and CW6 change, the volume of the prepared lithium-ion battery remains unchanged, and the number of layers of the third positive electrode sheet, the third negative electrode sheet, and the separator changes accordingly.

[0122] Example 4-3 to Example 4-4

[0123] Except for adjusting the relevant preparation parameters according to Table 4, the rest is the same as Example 4-1. Among them, when the values ​​of CW5 and CW6 change, the volume of the prepared lithium-ion battery remains unchanged, and the number of layers of the third positive electrode sheet, the third negative electrode sheet, and the separator changes accordingly.

[0124] Example 4-5 to Example 4-7

[0125] Except for adjusting the relevant preparation parameters according to Table 4, the values ​​of CW1, CW2, CW3, CW4, PD1, PD2, G1, and G2 are the same as those of Example 2-1, and the rest are the same as Example 4-1. Among them, PD3 is regulated by regulating the cold pressing pressure of the third negative electrode material layer.

[0126] Embodiment 4-8

[0127] Except for adjusting the relevant preparation parameters according to Table 4, the values ​​of CW1, CW2, CW3, CW4, PD1, PD2, G1, and G2 are the same as those of Example 2-7, and the rest are the same as Example 4-1. Among them, PD3 is regulated by regulating the cold pressing pressure of the third negative electrode material layer.

[0128] Example 4-9 to Example 4-11

[0129] Except for adjusting the relevant preparation parameters according to Table 4, the values ​​of CW1, CW2, CW3, CW4, PD1, PD2, G1, and G2 are the same as those of Example 3-1, and the rest are the same as those of Example 4-1. Among them, when the mass percentage of the third carbon material natural graphite G3% changes, the mass percentage of the third artificial graphite changes accordingly, and the mass percentage of the third negative electrode binder remains unchanged.

[0130] Embodiment 4-12

[0131] Except for adjusting the relevant preparation parameters according to Table 4, the values ​​of CW1, CW2, CW3, CW4, PD1, PD2, G1, and G2 are the same as those of Example 3-6, and the rest are the same as Example 4-1. Among them, when the mass percentage of the third carbon material natural graphite G3% changes, the mass percentage of the third artificial graphite changes accordingly, and the mass percentage of the third negative electrode binder remains unchanged.

[0132] Comparative Example 1-1 to Comparative Example 1-3

[0133] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1. Among them, when the values ​​of CW1, CW2, CW3, and CW4 change, the volume of the prepared lithium-ion battery remains unchanged, and the number of layers of the first positive electrode sheet, the first negative electrode sheet, the second positive electrode sheet, the second negative electrode sheet, and the separator changes accordingly.

[0134] Comparative Example 2-1 to Comparative Example 2-2

[0135] In addition to adjusting the relevant preparation parameters according to Table 2, CW1 = CW2 = 13 mg / cm 2 , CW3=CW4=6mg / cm 2 Other than that, the rest is the same as Example 1-1. PD1 is regulated by regulating the cold pressing pressure of the first negative electrode material layer, and PD2 is regulated by regulating the cold pressing pressure of the second negative electrode material layer.

[0136] Comparative Example 3-1 to Comparative Example 3-2

[0137] In addition to adjusting the relevant preparation parameters according to Table 3, CW1 = CW2 = 13 mg / cm 2 , CW3=CW4=6mg / cm 2Except for the above, the rest is the same as Example 1-1. When the mass percentage of the first carbon material natural graphite changes by G1%, the mass percentage of the first artificial graphite changes accordingly, and the mass percentage of the first negative electrode binder remains unchanged; when the mass percentage of the second carbon material natural graphite changes by G2%, the mass percentage of the second artificial graphite changes accordingly, and the mass percentage of the second negative electrode binder remains unchanged.

[0138] Comparative Example 4-1

[0139] Except for adjusting the relevant preparation parameters according to Table 4, the values ​​of CW1, CW2, CW3, CW4, PD1, PD2, G1, and G2 are the same as those of Comparative Example 1-1, and the rest are the same as those of Example 4-1. Among them, when the values ​​of CW5 and CW6 change, the volume of the prepared lithium-ion battery remains unchanged, and the number of layers of the third positive electrode sheet, the third negative electrode sheet, and the separator changes accordingly.

[0140] The preparation parameters and performance parameters of each embodiment and comparative example are shown in Tables 1 to 4.

[0141] Table 1

[0142]

[0143] Note: In Examples 1-1 to 1-8 and Comparative Examples 1-1 to 1-3, PD1 = PD2 = 1.7 g / cm 3 , G1=G2=15%.

[0144] Table 2

[0145]

[0146]

[0147] Note: In Examples 2-1 to 2-7 and Comparative Examples 2-1 to 2-2, CW1 = CW2 = 13 mg / cm 2 , CW3=CW4=6mg / cm 2 , G1=G2=15%.

[0148] Table 3

[0149]

[0150] Note: In Examples 3-1 to 3-7 and Comparative Examples 3-1 to 3-2, CW1 = CW2 = 13 mg / cm 2 , CW3=CW4=6mg / cm 2 , PD1=PD2=1.7g / cm 3 .

[0151] It can be seen from Examples 1-1 to 1-8, Examples 2-1 to 2-7, Examples 3-1 to 3-7, Comparative Examples 1-1 to 1-3, Comparative Examples 2-1 to 2-2, and Comparative Examples 3-1 to 3-2 that the present application designs the structure of the electrode assembly, and regulates at least one of the relationship between CW1 and CW2, CW3 and CW4, PD1 and PD2, and the type or mass percentage of the negative electrode active materials in the first negative electrode material layer and the second negative electrode material layer within the scope of the present application. The energy density and cycle capacity retention rate of the lithium ion battery are high, and the cycle expansion rate and discharge temperature difference are small, indicating that the lithium ion battery has a high energy density, good cycle performance and performance uniformity at different positions, and the above performance can be taken into account. However, for the lithium-ion batteries of Comparative Examples 1-1 to 1-3, Comparative Examples 2-1 to 2-2, and Comparative Examples 3-1 to 3-2, the types or mass percentage relationships of the negative electrode active materials in CW1 and CW2, CW3 and CW4, PD1 and PD2, and the first negative electrode material layer and the second negative electrode material layer are not within the scope of the present application, and the lithium-ion batteries cannot simultaneously have high energy density and cycle capacity retention rate, small cycle expansion rate and discharge temperature difference, indicating that the lithium-ion batteries cannot simultaneously take into account energy density, cycle performance and performance uniformity at different positions.

[0152] The values ​​of CW1, CW2 and CW2-CW1 usually affect the energy density, cycle performance and performance uniformity of different positions of the lithium-ion battery. It can be seen from Example 1-1 to Example 1-4, Comparative Example 1-1 and Comparative Example 1-3 that when the values ​​of CW1, CW2 and CW2-CW1 are within the scope of this application, the energy density of the lithium-ion battery is high and the discharge temperature difference is small, indicating that the energy density and performance uniformity of the lithium-ion battery at different positions are improved on the basis of good cycle performance. It can be seen from Example 1-1, Example 1-5 to Example 1-6 and Comparative Example 1-2 that when the values ​​of CW1, CW2 and CW2-CW1 are within the scope of this application, the cycle capacity retention rate of the lithium-ion battery is high, the cycle expansion rate and the discharge temperature difference are small, indicating that the cycle performance and performance uniformity of the lithium-ion battery at different positions are improved on the basis of higher energy density. From Examples 1-7 and Comparative Examples 1-1 to 1-3, it can be seen that when the values ​​of CW1, CW2 and CW2-CW1 are within the range of this application, the cycle capacity retention rate of the lithium-ion battery is high, the cycle expansion rate and the discharge temperature difference are small, indicating that the cycle performance and the performance uniformity of different positions of the lithium-ion battery are improved on the basis of having a higher energy density. From Examples 1-8 and Comparative Examples 1-1 to 1-3, it can be seen that when the values ​​of CW1, CW2 and CW2-CW1 are within the range of this application, the energy density of the lithium-ion battery is high and the discharge temperature difference is small, indicating that the energy density and the performance uniformity of different positions of the lithium-ion battery are improved on the basis of having good cycle performance.

[0153] The values ​​of CW3, CW4 and CW4-CW3 usually affect the energy density, cycle performance and performance uniformity of different positions of the lithium-ion battery. It can be seen from Example 1-1 to Example 1-4, Comparative Example 1-1 and Comparative Example 1-3 that when the values ​​of CW3, CW4 and CW4-CW3 are within the scope of this application, the energy density of the lithium-ion battery is high and the discharge temperature difference is small, indicating that the energy density and performance uniformity of the lithium-ion battery at different positions are improved on the basis of good cycle performance. It can be seen from Example 1-1, Example 1-5 to Example 1-6 and Comparative Example 1-2 that when the values ​​of CW3, CW4 and CW4-CW3 are within the scope of this application, the cycle capacity retention rate of the lithium-ion battery is high, the cycle expansion rate and the discharge temperature difference are small, indicating that the cycle performance and performance uniformity of the lithium-ion battery at different positions are improved on the basis of higher energy density. From Examples 1-7 and Comparative Examples 1-1 to 1-3, it can be seen that when the values ​​of CW3, CW4 and CW4-CW3 are within the range of this application, the cycle capacity retention rate of the lithium-ion battery is high, the cycle expansion rate and the discharge temperature difference are small, indicating that the cycle performance and the performance uniformity of different positions of the lithium-ion battery are improved on the basis of having a higher energy density. From Examples 1-8 and Comparative Examples 1-1 to 1-3, it can be seen that when the values ​​of CW3, CW4 and CW4-CW3 are within the range of this application, the energy density of the lithium-ion battery is high and the discharge temperature difference is small, indicating that the energy density and the performance uniformity of different positions of the lithium-ion battery are improved on the basis of having good cycle performance.

[0154] The values ​​of PD1, PD2 and PD1-PD2 usually affect the energy density, cycle performance and performance uniformity of different positions of the lithium-ion battery. It can be seen from Example 2-1 to Example 2-3 and Comparative Example 1-1 that when the values ​​of PD1, PD2 and PD1-PD2 are within the scope of this application, the cycle capacity retention rate of the lithium-ion battery is high, the cycle expansion rate and the discharge temperature difference are small, indicating that the cycle performance and performance uniformity of different positions of the lithium-ion battery are improved on the basis of having a higher energy density. It can be seen from Example 2-1, Example 2-4 to Example 2-5 and Comparative Example 2-1 that when the values ​​of PD1, PD2 and PD1-PD2 are within the scope of this application, the energy density of the lithium-ion battery is high, indicating that the energy density of the lithium-ion battery is improved on the basis of having good cycle performance and performance uniformity at different positions. From Example 2-6, Comparative Example 1-1, Comparative Example 2-1 to Comparative Example 2-2, it can be seen that when the values ​​of PD1, PD2 and PD1-PD2 are within the range of this application, the cycle capacity retention rate of the lithium-ion battery is high, the cycle expansion rate and the discharge temperature difference are small, indicating that the cycle performance and the performance uniformity at different positions of the lithium-ion battery are improved on the basis of having a higher energy density. From Example 2-7, Comparative Example 1-1, Comparative Example 2-1 to Comparative Example 2-2, it can be seen that when the values ​​of PD1, PD2 and PD1-PD2 are within the range of this application, the energy density of the lithium-ion battery is high, indicating that the energy density of the lithium-ion battery is improved on the basis of having good cycle performance and performance uniformity at different positions.

[0155] The values ​​of G1, G2 and G1-G2 usually affect the energy density, cycle performance and performance uniformity of different positions of the lithium-ion battery. It can be seen from Example 3-1 to Example 3-3, Comparative Example 1-1 and Comparative Example 3-2 that when the values ​​of G1, G2 and G1-G2 are within the scope of this application, the cycle capacity retention rate of the lithium-ion battery is high, the cycle expansion rate and the discharge temperature difference are small, indicating that the cycle performance and performance uniformity of the lithium-ion battery at different positions are improved on the basis of having a higher energy density. It can be seen from Example 3-1, Example 3-4 to Example 3-5 and Comparative Example 3-1 that when the values ​​of G1, G2 and G1-G2 are within the scope of this application, the energy density of the lithium-ion battery is high and the discharge temperature difference is small, indicating that the energy density and performance uniformity of the lithium-ion battery at different positions are improved on the basis of having good cycle performance. It can be seen from Example 3-6 to Example 3-7 and Comparative Example 1-1 that when the values ​​of G1, G2 and G1-G2 are within the range of this application, the energy density of the lithium-ion battery is high and the discharge temperature difference is small, indicating that the energy density and performance uniformity of the lithium-ion battery at different positions are improved on the basis of good cycle performance.

[0156] Table 4

[0157]

[0158]

[0159] The values ​​of CW5 and CW6 usually affect the energy density, cycle performance and performance uniformity of different positions of the lithium-ion battery. From Example 4-1 to Example 4-4 and Comparative Example 4-1, it can be seen that when the values ​​of CW5 and CW6 are within the range of this application, the energy density of the lithium-ion battery is high and the discharge temperature difference is small, indicating that the energy density and performance uniformity of different positions of the lithium-ion battery are improved on the basis of good cycle performance.

[0160] The value of PD3 usually affects the energy density, cycle performance and performance uniformity of different positions of the lithium-ion battery. It can be seen from Examples 4-5 to 4-8 and Comparative Example 4-1 that when the value of PD3 is within the range of this application, the cycle capacity retention rate of the lithium-ion battery is high, the cycle expansion rate and the discharge temperature difference are small, indicating that the cycle performance and performance uniformity of different positions of the lithium-ion battery are improved on the basis of having a higher energy density.

[0161] The value of G3 usually affects the energy density, cycle performance and performance uniformity of different positions of the lithium-ion battery. It can be seen from Examples 4-9 to 4-12 and Comparative Example 4-1 that when the value of G3 is within the range of this application, the cycle capacity retention rate of the lithium-ion battery is high, the cycle expansion rate and the discharge temperature difference are small, indicating that the cycle performance and performance uniformity of different positions of the lithium-ion battery are improved on the basis of having a higher energy density.

[0162] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method or article.

[0163] Each embodiment in this specification is described in a related manner, and the same or similar parts between the embodiments can be referenced to each other, and each embodiment focuses on the differences from other embodiments.

[0164] The above description is only a preferred embodiment of the present application and is not intended to limit the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A secondary battery, comprising an electrode assembly, wherein the electrode assembly comprises at least one first electrode assembly and a plurality of second electrode assemblies, wherein the plurality of second electrode assemblies are arranged on both sides of the first electrode assembly along a thickness direction of the secondary battery; The first electrode assembly includes a first positive electrode sheet and a first negative electrode sheet, the first positive electrode sheet includes a first positive electrode collector and a first positive electrode material layer disposed on at least one surface of the first positive electrode collector, and the first negative electrode sheet includes a first negative electrode collector and a first negative electrode material layer disposed on at least one surface of the first negative electrode collector; The second electrode assembly includes a second positive electrode sheet and a second negative electrode sheet, the second positive electrode sheet includes a second positive electrode collector and a second positive electrode material layer disposed on at least one surface of the second positive electrode collector, and the second negative electrode sheet includes a second negative electrode collector and a second negative electrode material layer disposed on at least one surface of the second negative electrode collector; in, The secondary battery satisfies at least one of the following characteristics: (1) The coating weight of the first positive electrode material layer is CW1 mg / cm 2 The coating weight of the second positive electrode material layer is CW2 mg / cm 2 , CW1<CW2; (2) The coating weight of the first negative electrode material layer is CW3 mg / cm 2 The coating weight of the second negative electrode material layer is CW4 mg / cm 2 , CW3<CW4; (3) The compaction density of the first negative electrode material layer is PD1 g / cm 3 The compaction density of the second negative electrode material layer is PD2 g / cm 3 , PD1>PD2; (4) The types of negative electrode active materials or the mass percentage of each negative electrode active material in the first negative electrode material layer and the second negative electrode material layer are different.

2. The secondary battery according to claim 1, wherein The secondary battery satisfies at least one of the following characteristics: (1) 8≤CW1≤25, 10≤CW2≤30; (2) 3.7≤CW3≤11.5, 4.7≤CW4≤14.1; (3)1≤CW2-CW1≤5; (4) 0.6≤CW4-CW3≤2.4; (5) 1.0≤PD1≤1.8, 0.6≤PD2≤1.7; (6)0.1≤PD1-PD2≤0.

3.

3. The secondary battery according to claim 1 or 2, wherein: The electrode assembly further includes a plurality of third electrode assemblies, wherein along the thickness direction of the secondary battery, the second electrode assembly is disposed between the first electrode assembly and the third electrode assembly, and the outermost side of the electrode assembly is the third electrode assembly; The third electrode assembly includes a third positive electrode sheet and a third negative electrode sheet, wherein the third positive electrode sheet includes a third positive electrode collector and a third positive electrode material layer disposed on at least one surface of the third positive electrode collector, and the third negative electrode sheet includes a third negative electrode collector and a third negative electrode material layer disposed on at least one surface of the third negative electrode collector; The secondary battery satisfies at least one of the following characteristics: (1) The coating weight of the third positive electrode material layer is CW5 mg / cm 2 , CW1<CW2<CW5; (2) The coating weight of the third negative electrode material layer is CW6 mg / cm 2 , CW3<CW4<CW6; (3) The compaction density of the third negative electrode material layer is PD3 g / cm 3 , PD1>PD2>PD3; (4) The type of negative electrode active material or the mass percentage of each negative electrode active material in the third negative electrode material layer is different from that in the first negative electrode material layer and the second negative electrode material layer.

4. The secondary battery according to claim 3, wherein The secondary battery satisfies at least one of the following characteristics: (1) 12 ≤ CW5 ≤ 35, 5.5 ≤ CW6 ≤ 16.1; (2)0.5≤PD3≤1.

6.

5. The secondary battery according to any one of claims 1 to 4, wherein The first negative electrode material layer includes a first negative electrode active material, the first negative electrode active material includes a first carbon material, and based on the mass of the first negative electrode material layer, the mass percentage of the first carbon material is G1%; The second negative electrode material layer includes a second negative electrode active material, the second negative electrode active material includes a second carbon material, and based on the mass of the second negative electrode material layer, the mass percentage of the second carbon material is G2%, G1>G2.

6. The secondary battery according to claim 5, wherein 10≤G1≤50, 0≤G2≤15.

7. The secondary battery according to claim 5 or 6, wherein: 5≤G1-G2≤15.

8. The secondary battery according to any one of claims 5 to 7, wherein The third negative electrode material layer includes a third negative electrode active material, and the third negative electrode active material includes a third carbon material. Based on the mass of the third negative electrode material layer, the mass percentage of the third carbon material is G3%, G1>G2>G3, and 0≤G3≤10.

9. The secondary battery according to any one of claims 5 to 8, wherein The first carbon material, the second carbon material, and the third carbon material each independently include at least one of natural graphite, soft carbon, or hard carbon. 10 . An electronic device comprising the secondary battery according to claim 1 .

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