Secondary battery and electric device

Abstract

The invention provides a secondary battery and a power utilization device, the secondary battery comprises N electrode assemblies and a shell for accommodating the N electrode assemblies, N is greater than or equal to 2 and less than or equal to 6, and N is an integer; each electrode assembly comprises a negative electrode plate, the negative electrode plate comprises a negative electrode material layer, the negative electrode material layer of at least one negative electrode plate comprises a silicon material, in the N electrode assemblies, based on the mass of the negative electrode material layer in each electrode assembly, the mass percentage content of the silicon element in the negative electrode material layer in each electrode assembly is Wn, n is greater than or equal to 1 and less than or equal to N, and n is an integer; wherein the maximum value of Wn is defined as Wmax, the minimum value of Wn is defined as Wmin, and Wmax-Wmin is larger than or equal to 1% and smaller than or equal to 40%. The secondary battery provided by the invention is beneficial to considering the dynamic performance, the expansion performance and the energy density.

Description

Technical Field

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

[0002] Secondary batteries, such as lithium-ion batteries, use silicon negative electrode materials with higher energy density than traditional graphite negative electrodes, mainly because the theoretical charge capacity of pure silicon negative electrodes reaches 4200mAh / g, while the theoretical capacity of pure graphite is only 372mAh / g. Therefore, silicon negative electrodes have received more and more attention in high-energy-density lithium-ion batteries. However, the volume change of silicon negative electrodes during charging and discharging will affect the electrical contact of the negative electrodes, which will lead to rapid capacity decay of the battery cells. In addition, silicon negative electrodes have high impedance and are prone to lithium precipitation. This problem becomes more prominent under high-rate discharge.

[0003] At present, the main method is to prepare a hybrid negative electrode by mixing silicon and graphite, taking advantage of the high energy density of silicon, while graphite makes up for the large expansion and poor kinetics of silicon. However, the hybrid negative electrode is more of a compromise between the performance of silicon and graphite, and cannot give full play to the respective advantages of silicon and graphite. As a result, it is difficult for secondary batteries to take into account their kinetic performance, expansion performance and energy density. Summary of the invention

[0004] The purpose of this application is to provide a secondary battery and an electrical device that take into account the dynamic performance, expansion performance and energy density of the secondary battery. The specific technical solution is as follows:

[0005] A first aspect of the present application provides a secondary battery, comprising N electrode assemblies and a shell accommodating the N electrode assemblies, 2≤N≤6, N is an integer; each electrode assembly comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode material layer, the negative electrode material layer of at least one negative electrode sheet comprises a silicon material, and in the N electrode assemblies, based on the mass of the negative electrode material layer in each electrode assembly, the mass percentage of the silicon material in the negative electrode material layer in each electrode assembly is W, ... n , 1≤n≤N, n is an integer; where W n The maximum value in is defined as W max , W n The minimum value of is defined as W min , 1% ≤ W max -W min ≤40%. In some embodiments of the present application, 1%≤W max -W min ≤30%. In some embodiments of the present application, 2%≤W max -W min ≤15%. A secondary battery contains multiple electrode assemblies with different silicon contents, and W max -W minThe above range is met, wherein the electrode assembly with relatively high silicon content can improve the overall energy density of the secondary battery, and the electrode assembly with relatively low silicon content can improve the kinetic performance and expansion performance of the secondary battery. Therefore, the combination of multiple electrode assemblies with different silicon contents is beneficial to taking into account the kinetic performance, expansion performance and energy density of the secondary battery.

[0006] In some embodiments of the present application, 0%≤W n ≤40%. By adjusting W n Within the above range, W can be satisfied max -W min Within the above range, it is beneficial to take into account the dynamic performance, expansion performance and energy density of the secondary battery.

[0007] In some embodiments of the present application, the negative electrode material layer includes at least one of a first binder and / or a second binder, the first binder is selected from at least one of polystyrene butadiene copolymer, carboxymethyl cellulose, and polyvinylidene fluoride, and the second binder is selected from at least one of polyacrylic acid, polyacrylonitrile, polyacrylate, and polyurethane. The first binder has good bonding toughness and low impedance, and the second binder is a high-strength binder. By matching with electrode assemblies containing different contents of silicon materials, the silicon material can be mixed with different materials to better play the respective advantages of different materials, thereby facilitating further consideration of the dynamic performance, expansion performance, and energy density of the secondary battery.

[0008] In some embodiments of the present application, the secondary battery includes a first electrode assembly and a second electrode assembly; the first electrode assembly includes a first negative electrode material layer, the first negative electrode material layer includes a first silicon material and a first binder, and based on the mass of the first negative electrode material layer, the mass percentage of silicon in the first negative electrode material layer is W1; the second electrode assembly includes a second negative electrode material layer, the second negative electrode material layer includes a second silicon material and a second binder, and based on the mass of the second negative electrode material layer, the mass percentage of silicon in the second negative electrode material layer is W2; wherein W1<W2. The content of silicon material in the first electrode assembly and the second electrode assembly is different, and the two are matched with each other, which is conducive to taking into account the dynamic performance, expansion performance and energy density of the secondary battery.

[0009] In some embodiments of the present application, 1%≤W2-W1≤40%. By regulating W2-W1 within the above range, the first electrode assembly improves the kinetic performance and expansion performance of the secondary battery, and the second electrode assembly improves the overall energy density of the secondary battery, so that the first electrode assembly and the second electrode assembly cooperate with each other, which is conducive to taking into account the kinetic performance, expansion performance and energy density of the secondary battery.

[0010] In some embodiments of the present application, the first negative electrode material layer further includes a second binder. Based on the mass of the first negative electrode material layer, the mass percentage of the first binder is C 11 , the mass percentage of the second binder is C 12 The second negative electrode material layer also includes a first binder, based on the mass of the second negative electrode material layer, the mass percentage of the first binder is C 21 , the mass percentage of the second binder is C 22 Among them, C 11 +C 12 <C 21 +C 22 When the contents of the first binder and the second binder in the first negative electrode material layer and the second negative electrode material layer satisfy the above relationship, it is beneficial to further take into account the dynamic performance, expansion performance and energy density of the secondary battery.

[0011] In some embodiments of the present application, the secondary battery satisfies at least one of the following characteristics: (1) 0% ≤ C 21 +C 22 -(C 11 +C 12 )≤13%; (2)1% <C 11 +C 12 ≤10%. The secondary battery satisfies at least one of the above characteristics, which is conducive to further taking into account the dynamic performance, expansion performance and energy density.

[0012] In some embodiments of the present application, C 11 >C 21 , C 22 >C 12 The second negative electrode material layer has a higher silicon content than the first negative electrode material layer, so that the second negative electrode material layer has a higher second binder content, which is conducive to better improving the expansion problem caused by the higher silicon content in the second negative electrode material layer; at the same time, the first negative electrode material layer has a higher first binder content, and the obtained first negative electrode material layer has better dynamic performance, so that the first electrode assembly and the second electrode assembly work together, which is conducive to better taking into account the dynamic performance, expansion performance and energy density of the secondary battery.

[0013] In some embodiments of the present application, the secondary battery satisfies at least one of the following characteristics: (1) 0% ≤ C 11 -C 21 ≤5%;(2)0%≤C 11 ≤5%;(3)0%≤C 22 -C 12 ≤15%; (4) 2% ≤C 22≤15%. The secondary battery satisfies at least one of the above characteristics, which is conducive to further taking into account the dynamic performance, expansion performance and energy density.

[0014] In some embodiments of the present application, the first negative electrode material layer further includes a first carbon material, and the second negative electrode material layer further includes a second carbon material; the first carbon material and the second carbon material each independently include at least one of artificial graphite, natural graphite, hard carbon or soft carbon. On the basis of the first negative electrode material and the second negative electrode material including silicon material, the first negative electrode material layer further includes the first carbon material, and the second negative electrode material layer further includes the second carbon material. In different negative electrode material layers, different contents of silicon material and carbon material are matched with each other, which is conducive to giving play to their respective advantages, thereby facilitating better consideration of the kinetic performance, expansion performance and energy density of the secondary battery.

[0015] In some embodiments of the present application, 3≤N≤6; the secondary battery further includes a shell, the N electrode assemblies include an outer electrode assembly and an inner electrode assembly, and along the stacking direction of the N electrode assemblies, the outer electrode assembly is closer to the shell than the inner electrode assembly; based on the mass of the negative electrode material layer in the outer electrode assembly, the mass percentage of silicon in the negative electrode material layer is Wx, and based on the mass of the negative electrode material layer in the inner electrode assembly, the mass percentage of silicon in the negative electrode material layer is Wy, Wx<Wy. Along the stacking direction of the N electrode assemblies, the problem of greater resistance of the inner electrode assembly due to the high silicon content can be improved, thereby improving the dynamic performance; in addition, the expansion of the inner electrode assembly will be restricted by the outer electrode assemblies on both sides, so that the overall expansion is reduced, which is beneficial to improving the overall expansion performance of the secondary battery. Therefore, the use of the above-mentioned inner electrode assembly and outer electrode assembly is conducive to better taking into account the dynamic performance, expansion performance and energy density of the secondary battery.

[0016] In some embodiments of the present application, the secondary battery further includes a third electrode assembly, and along the stacking direction of the N electrode assemblies, the second electrode assembly is disposed between the first electrode assembly and the third electrode assembly; the third electrode assembly includes a third negative electrode material layer, the third negative electrode material layer includes a third silicon material and a first binder, based on the mass of the third negative electrode material layer, the mass percentage of the silicon element is W3, the mass percentage of the first binder is C 31 ; Among them, W3<W2, C 31 >C 21The second electrode assembly with a higher silicon content is disposed between the first electrode assembly and the third electrode assembly, which can improve the problems of higher impedance and larger expansion caused by the higher silicon content of the second electrode assembly, thereby facilitating further consideration of the dynamic performance, expansion performance and energy density of the secondary battery. In addition, the silicon content of the third electrode assembly is lower than that of the second electrode assembly, and the first binder with better dynamic performance is matched, and its content is higher, which can better consider the dynamic performance of the secondary battery.

[0017] In some embodiments of the present application, the secondary battery satisfies at least one of the following characteristics: (1) 1% ≤ W2-W3 ≤ 40%; (2) 0% ≤ W3 ≤ 39%; (3) 0% ≤ C 31 -C 21 ≤5%;(4)0%≤C 31 ≤5%. The secondary battery satisfies at least one of the above characteristics, which is conducive to further taking into account the dynamic performance, expansion performance and energy density.

[0018] In some embodiments of the present application, the third negative electrode material layer further includes a second binder, and based on the mass of the third negative electrode material layer, the mass percentage of the second binder is C 32 , C 32 <C 22 The second negative electrode material layer has a higher silicon content than the first negative electrode material layer, so that the second negative electrode material layer has a higher second binder content, which is beneficial to better improve the expansion problem caused by the higher silicon content in the second negative electrode material layer, and is beneficial to better balance the dynamic performance, expansion performance and energy density of the secondary battery.

[0019] In some embodiments of the present application, the secondary battery satisfies at least one of the following characteristics: (1) C 31 +C 32 <C 21 +C 22 ; (2) 0% ≤ C 21 +C 22 -(C 31 +C 32 )≤13%; (3)1%<C 31 +C 32 ≤10%;(4)0%≤C 22 -C 32 ≤15%;(5)0%≤C 32 ≤10%. The secondary battery satisfies at least one of the above characteristics, which is conducive to further taking into account the dynamic performance, expansion performance and energy density.

[0020] In some embodiments of the present application, the third negative electrode material layer further includes a third carbon material, and the third carbon material includes at least one of artificial graphite, natural graphite, hard carbon or soft carbon. On the basis of including the silicon material, the third negative electrode material layer further includes a third carbon material. In different negative electrode material layers, different contents of silicon material and carbon material match each other, which is conducive to giving play to their respective advantages, thereby facilitating better consideration of the kinetic performance, expansion performance and energy density of the secondary battery.

[0021] The second aspect of the present application provides an electric device, which includes the secondary battery in any of the aforementioned embodiments, and the obtained electric device has good performance.

[0022] Beneficial effects of this application:

[0023] The present application provides a secondary battery and an electric device, wherein the secondary battery comprises N electrode assemblies and a housing for accommodating the N electrode assemblies. The secondary battery comprises a plurality of electrode assemblies with different silicon contents, and W max -W min The above range is met, wherein the electrode assembly with relatively high silicon content can improve the overall energy density of the secondary battery, and the electrode assembly with relatively low silicon content can improve the kinetic performance and expansion performance of the secondary battery. Therefore, the combination of multiple electrode assemblies with different silicon contents is beneficial to taking into account the kinetic performance, expansion performance and energy density of the secondary battery.

[0024] 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. DETAILED DESCRIPTION

[0025] The technical solutions in the embodiments of the present application are described clearly and completely below. 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.

[0026] The first aspect of the present application provides a secondary battery, comprising N electrode assemblies and a housing for accommodating the N electrode assemblies, 2≤N≤6, N is an integer; for example, N can be 2, 3, 4, 5 or 6. Each electrode assembly comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode material layer, the negative electrode material layer of at least one negative electrode sheet comprises a silicon material, and in the N electrode assemblies, based on the mass of the negative electrode material layer in each electrode assembly, the mass percentage of silicon element in the negative electrode material layer in each electrode assembly is respectively W n , 1≤n≤N, n is an integer; where W n The maximum value in is defined as W max , W n The minimum value of is defined as Wmin , 1% ≤ W max -W min ≤40%. In some embodiments of the present application, 1%≤W max -W min ≤30%. In some embodiments of the present application, 2%≤W max -W min ≤15%. For example, W max -W min It can be 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or a range consisting of any two values ​​therebetween. A secondary battery includes a plurality of electrode assemblies with different silicon contents, and W max -W min The above range is satisfied, wherein the electrode assembly with a relatively high silicon content can improve the overall energy density of the secondary battery, and the electrode assembly with a relatively low silicon content can improve the dynamic performance and expansion performance of the secondary battery, so that the combination of multiple electrode assemblies with different silicon contents is conducive to taking into account the dynamic performance, expansion performance and energy density of the secondary battery. max -W min When the content of silicon material in the multiple electrode assemblies is too small, for example, less than 1%, the content of silicon material in the multiple electrode assemblies is basically the same, and the secondary battery containing a single electrode assembly has the same problem that the dynamic performance, expansion performance and energy density are difficult to take into account. max -W min When it is too large, for example, greater than 40%, the impedance difference between different electrode assemblies is large, and the electrode assembly with relatively low silicon content is prone to self-discharge problems at a lower charge state. In addition, the secondary battery is prone to circular current after being left stationary for a period of time, thereby affecting the capacity retention rate of the secondary battery, so that the energy density of the secondary battery cannot be fully utilized. Therefore, when the secondary battery contains N electrode assemblies and the silicon material content W max -W min Within the above range, the secondary battery can have a balance between dynamic performance, expansion performance and energy density.

[0027] In the present application, "the negative electrode material layer of at least one negative electrode sheet includes silicon material" means that the negative electrode material layer of the negative electrode sheet in at least one electrode assembly includes silicon material. That is, the negative electrode material layer of one electrode assembly may include silicon material, while the negative electrode material layers of the remaining electrode assemblies may not include silicon material; the negative electrode material layers of two or more electrode assemblies may include silicon material, while the negative electrode material layers of the remaining electrode assemblies may not include silicon material; or all electrode assemblies may include silicon material.

[0028] In this application, silicon material refers to a material containing silicon element, and silicon material may include but is not limited to silicon element, silicon oxide material (SiO x , 0<x<2) or at least one of silicon-carbon materials.

[0029] In some embodiments of the present application, 0%≤W n ≤40%. For example, W n It can be 0%, 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or a range consisting of any two values ​​therebetween. n Within the above range, W can be satisfied max -W min Within the above range, it is beneficial to take into account the dynamic performance, expansion performance and energy density of the secondary battery.

[0030] At present, the mixed negative electrode containing both silicon material and graphite not only cannot give full play to the respective advantages of silicon and graphite, but also faces problems in the selection of binders. Under normal circumstances, the binder systems suitable for silicon materials and graphite are different. Silicon materials have large expansion and are more suitable for high-strength binders, but high-strength binders make the negative electrode material layer brittle, easy to crack during processing, and increase impedance. Graphite has small expansion and is more suitable for binders with good bonding toughness. The resulting negative electrode material layer is easy to process and has low impedance, and its dynamics is better than that of high-strength binders. The mixed negative electrode usually selects binders according to the content of silicon materials. Generally speaking, the higher the silicon content, the higher the content of high-strength binders in the system, and the higher the content of high-strength binders, the higher the impedance of the binder. When the type and content of the binder can match the silicon material, it will further affect the performance of graphite. In addition, in the mixed negative electrode, the silicon material itself has high impedance, and the high impedance of the high-strength binder is superimposed, resulting in a further increase in the impedance of the negative electrode material layer in the mixed negative electrode, thereby affecting the dynamic performance of the secondary battery.

[0031] In some embodiments of the present application, the negative electrode material layer includes at least one of a first binder and / or a second binder, the first binder is selected from at least one of polystyrene butadiene copolymer, carboxymethyl cellulose, and polyvinylidene fluoride, and the second binder is selected from at least one of polyacrylic acid, polyacrylonitrile, polyacrylate, and polyurethane. The first binder has good bonding toughness and low impedance, and the second binder is a high-strength binder. By matching with electrode assemblies containing different contents of silicon materials, the silicon material can be mixed with different materials to better play the respective advantages of different materials, thereby facilitating further consideration of the dynamic performance, expansion performance, and energy density of the secondary battery.

[0032] In some embodiments of the present application, when 0%≤W in the negative electrode material layer of the electrode assembly n<2%, the negative electrode material layer may contain only the first binder, and the obtained electrode assembly has good dynamic performance and low expansion. In some embodiments of the present application, when 2%≤W n ≤40% silicon element, the negative electrode material layer contains the second binder and the first binder or does not contain the first binder, that is, the negative electrode material layer includes the first binder and the second binder, or only includes the second binder.

[0033] In some embodiments of the present application, the secondary battery includes a first electrode assembly and a second electrode assembly; the first electrode assembly includes a first negative electrode material layer, the first negative electrode material layer includes a first silicon material and a first binder, and the mass percentage of silicon element is W1 based on the mass of the first negative electrode material layer; the second electrode assembly includes a second negative electrode material layer, the second negative electrode material layer includes a second silicon material and a second binder, and the mass percentage of silicon element is W2 based on the mass of the second negative electrode material layer; wherein W1<W2. The content of silicon material in the first electrode assembly and the second electrode assembly is different, and the two are matched with each other, which is conducive to taking into account the dynamic performance, expansion performance and energy density of the secondary battery.

[0034] In some embodiments of the present application, the first silicon material and the second silicon material are each independently selected from the above silicon materials. It is understandable that the mass percentage content W1 of the silicon element in the first negative electrode material layer varies with the type of the first silicon material and its content in the first negative electrode material layer. The present application has no special restrictions on the mass percentage content W1' of the first silicon material in the first negative electrode material layer, as long as the required W1 can be obtained. The mass percentage content W2 of the silicon element in the second negative electrode material layer varies with the type of the second silicon material and its content in the second negative electrode material layer. The present application has no special restrictions on the mass percentage content W2' of the second silicon material in the second negative electrode material layer, as long as the required W2 can be obtained.

[0035] In some embodiments of the present application, N=2, and the secondary battery includes the first electrode assembly and the second electrode assembly.

[0036] In some embodiments of the present application, 1%≤W2-W1≤40%. For example, W2-W1 can be 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or a range consisting of any two values ​​therebetween. By regulating W2-W1 within the above range, the first electrode assembly improves the kinetic performance and expansion performance of the secondary battery, and the second electrode assembly improves the overall energy density of the secondary battery, so that the first electrode assembly and the second electrode assembly cooperate with each other, which is beneficial to taking into account the kinetic performance, expansion performance and energy density of the secondary battery.

[0037] In some embodiments of the present application, 0%≤W1≤39%. For example, W1 can be 0%, 0.5%, 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 39%, or a range consisting of any two values ​​therebetween. In some embodiments of the present application, 2%≤W2≤40%. For example, W2 can be 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, or a range consisting of any two values ​​therebetween.

[0038] In some embodiments of the present application, 0%≤W1'≤78%. In some embodiments of the present application, 4%≤W2'≤80%.

[0039] In some embodiments of the present application, N=2, 0%≤W1≤39%, 2%≤W2≤40%.

[0040] In some embodiments of the present application, the first negative electrode material layer further includes a second binder. Based on the mass of the first negative electrode material layer, the mass percentage of the first binder is C 11 , the mass percentage of the second binder is C 12 The second negative electrode material layer also includes a first binder, based on the mass of the second negative electrode material layer, the mass percentage of the first binder is C 21 , the mass percentage of the second binder is C 22 Among them, C 11 +C 12 <C 21 +C 22 . The second negative electrode material layer has a higher silicon content than the first negative electrode material layer, so that the total content of the first binder and the second binder in the second negative electrode material layer is higher than that in the first negative electrode material layer, which is conducive to improving the expansion problem caused by the higher silicon content in the second negative electrode material layer; at the same time, the total content of the first binder and the second binder in the first negative electrode material layer is relatively small, that is, the content of inactive substances is relatively small, which is conducive to improving the problem of low energy density caused by the lower silicon content in the first negative electrode material layer. Therefore, when the contents of the first binder and the second binder in the first negative electrode material layer and the second negative electrode material layer meet the above relationship, it is conducive to further taking into account the kinetic performance, expansion performance and energy density of the secondary battery.

[0041] In some embodiments of the present application, the secondary battery satisfies at least one of the following characteristics: (1) 0% ≤ C 21 +C 22 -(C 11 +C 12 )≤13%; (2)1% <C 11 +C 12≤10%. The secondary battery satisfies at least one of the above characteristics, which is conducive to further taking into account the dynamic performance, expansion performance and energy density.

[0042] In some embodiments of the present application, 0%≤C 21 +C 22 -(C 11 +C 12 )≤13%. For example, C 21 +C 22 -(C 11 +C 12 ) can be 0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13% or a range consisting of any two values ​​therebetween. The difference between the sum of the contents of the first binder and the second binder in the first negative electrode material layer and the second negative electrode material layer is within the above range, while improving the expansion problem caused by the higher silicon content in the second negative electrode material layer and the problem of low energy density caused by the lower silicon content in the first negative electrode material layer, the impedance difference between the first negative electrode material layer and the second negative electrode material layer is small, which is beneficial to improving the self-discharge problem in the secondary battery, and the kinetic properties of the first negative electrode material layer and the second negative electrode material layer are closer, which is beneficial to further take into account the kinetic properties, expansion properties and energy density of the secondary battery.

[0043] In some embodiments of the present application, 1% <C 11 +C 12 ≤10%. For example, C 11 +C 12 It can be 1.1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two values ​​therebetween. By regulating the sum of the contents of the first binder and the second binder in the first negative electrode material layer within the above range, the first negative electrode material layer obtained has a lower expansion rate and lower impedance, better kinetic performance, and takes into account the energy density, which is conducive to further taking into account the kinetic performance, expansion performance and energy density of the secondary battery.

[0044] In some embodiments of the present application, 2%≤C 21 +C 22 ≤20%. In some embodiments of the present application, 2%≤C 21 +C 22 ≤15%. For example, C 21 +C 22It can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20% or a range consisting of any two values ​​therebetween.

[0045] In some embodiments of the present application, C 11 >C 21 , C 22 >C 12 The second negative electrode material layer has a higher silicon content than the first negative electrode material layer, so that the second negative electrode material layer has a higher second binder content, which is conducive to better improving the expansion problem caused by the higher silicon content in the second negative electrode material layer; at the same time, the first negative electrode material layer has a higher first binder content, and the obtained first negative electrode material layer has better dynamic performance, so that the first electrode assembly and the second electrode assembly work together, which is conducive to better taking into account the dynamic performance, expansion performance and energy density of the secondary battery.

[0046] In some embodiments of the present application, the secondary battery satisfies at least one of the following characteristics: (1) 0% ≤ C 11 -C 21 ≤5%;(2)0%≤C 11 ≤5%;(3)0%≤C 22 -C 12 ≤15%; (4) 2% ≤C 22 ≤15%. The secondary battery satisfies at least one of the above characteristics, which is conducive to further taking into account the dynamic performance, expansion performance and energy density.

[0047] In some embodiments of the present application, 0%≤C 11 -C 21 ≤5%; for example, C 11 -C 21 It can be 0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range consisting of any two values ​​therebetween. The first negative electrode material layer has less silicon content than the second negative electrode material layer, and the first negative electrode material layer contains more first binder with good kinetic properties. By adjusting C 11 -C 21 Within the above range, it is beneficial to obtain a first negative electrode material layer with good kinetic performance, thereby helping to better balance the kinetic performance, expansion performance and energy density of the secondary battery.

[0048] In some embodiments of the present application, 0%≤C 11 ≤5%; for example, C 11It can be 0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two values ​​therebetween. 11 Within the above range, it is beneficial to obtain a first negative electrode material layer with good kinetic performance, thereby helping to better balance the kinetic performance, expansion performance and energy density of the secondary battery.

[0049] In some embodiments of the present application, 0%≤C 21 ≤5%. For example, C 21 It can be 0%, 1%, 2%, 3%, 4%, 5% or a range consisting of any two values ​​therebetween.

[0050] In some embodiments of the present application, 0%≤C 22 -C 12 ≤15%; for example, C 22 -C 12 It can be 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or a range consisting of any two values ​​therebetween. The second negative electrode material layer has a higher silicon content than the first negative electrode material layer, and the second negative electrode material layer contains more second binder with strong binding properties. By adjusting C 22 -C 12 Within the above range, it is helpful to improve the volume expansion problem caused by the high silicon content of the second material layer, thereby helping to better balance the dynamic performance, expansion performance and energy density of the secondary battery.

[0051] In some embodiments of the present application, 2%≤C 22 ≤15%. For example, C 22 It can be 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or a range consisting of any two values ​​therebetween. 22 Within the above range, it is helpful to improve the volume expansion problem caused by the high silicon content of the second material layer, thereby helping to better balance the dynamic performance, expansion performance and energy density of the secondary battery.

[0052] In some embodiments of the present application, 0%≤C 12 ≤8%. For example, C 12 It can be 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or a range consisting of any two values ​​therebetween.

[0053] In some embodiments of the present application, the first negative electrode material layer further includes a first carbon material, and the second negative electrode material layer further includes a second carbon material; the first carbon material and the second carbon material each independently include at least one of artificial graphite, natural graphite, hard carbon or soft carbon. On the basis of the first negative electrode material and the second negative electrode material including silicon material, the first negative electrode material layer further includes the first carbon material, and the second negative electrode material layer further includes the second carbon material. In different negative electrode material layers, different contents of silicon material and carbon material are matched with each other, which is conducive to giving play to their respective advantages, thereby facilitating better consideration of the kinetic performance, expansion performance and energy density of the secondary battery.

[0054] In some embodiments of the present application, based on the mass of the first negative electrode material layer, the mass percentage of the first carbon material is Z1; based on the mass of the second negative electrode material layer, the mass percentage of the second carbon material is Z2; Z2<Z1. The first negative electrode material layer contains relatively less silicon content, and the first carbon material is relatively more, so that it can match a binder system that is more suitable for the first carbon material, better play the advantages of the first carbon material, and improve the kinetic performance and expansion performance of the secondary battery. The second negative electrode material layer contains relatively more silicon content, and the second carbon material is relatively less, so that it can match a binder system that is more suitable for silicon materials, better play the advantages of silicon materials, and improve the energy density of the secondary battery. Thereby, the problem that silicon and carbon materials in the current mixed negative electrode cannot play their respective advantages is improved, so as to better balance the kinetic performance, expansion performance and energy density of the secondary battery.

[0055] In some embodiments of the present application, 7%≤Z1≤99%, 0%≤Z2≤94%. In some embodiments of the present application, 80%≤Z1≤98%, 40%≤Z2≤94%. In some embodiments of the present application, 50%≤Z1≤95%.

[0056] In some embodiments of the present application, 3≤N≤6; the secondary battery further includes a shell, the N electrode assemblies include an outer electrode assembly and an inner electrode assembly, and along the stacking direction of the N electrode assemblies, the outer electrode assembly is closer to the shell than the inner electrode assembly; based on the mass of the negative electrode material layer in the outer electrode assembly, the mass percentage of silicon element is Wx, based on the mass of the negative electrode material layer in the inner electrode assembly, the mass percentage of silicon element is Wy, Wx<Wy. Along the stacking direction of the N electrode assemblies, during the charging and discharging process, the temperature of the inner electrode assembly will be slightly higher than that of the outer electrode assembly due to poor heat dissipation than the outer electrode assembly, which can improve the problem of greater resistance of the inner electrode assembly due to the high silicon content, thereby improving the dynamic performance; in addition, the silicon content in the inner electrode assembly is high and the expansion is large. When it is placed between the outer electrode assemblies, its expansion will be restricted by the outer electrode assemblies on both sides, thereby reducing the overall expansion, which is conducive to improving the overall expansion performance of the secondary battery. Therefore, the use of the above-mentioned inner electrode assembly and outer electrode assembly is conducive to better taking into account the dynamic performance, expansion performance and energy density of the secondary battery.

[0057] In some embodiments of the present application, the secondary battery includes the first electrode assembly and the second electrode assembly, and the secondary battery also includes a third electrode assembly, along the stacking direction of the N electrode assemblies, the second electrode assembly is arranged between the first electrode assembly and the third electrode assembly; the third electrode assembly includes a third negative electrode material layer, the third negative electrode material layer includes a third silicon material and a first binder, based on the mass of the third negative electrode material layer, the mass percentage of the silicon element is W3, the mass percentage of the first binder is C 31 ; Among them, W3<W2, C 31 >C 21 The second electrode assembly with a higher silicon content is disposed between the first electrode assembly and the third electrode assembly, which can improve the problems of higher impedance and larger expansion caused by the higher silicon content of the second electrode assembly, thereby facilitating further consideration of the dynamic performance, expansion performance and energy density of the secondary battery. In addition, the silicon content of the third electrode assembly is lower than that of the second electrode assembly, and the first binder with better dynamic performance is matched, and its content is higher, which can better consider the dynamic performance of the secondary battery.

[0058] In some embodiments of the present application, the third silicon material is selected from the above silicon materials. It is understandable that the mass percentage content W3 of the silicon element in the third negative electrode material layer varies with the type of the third silicon material and its content in the third negative electrode material layer. The present application has no particular limitation on the mass percentage content W3' of the third silicon material in the third negative electrode material layer, as long as the desired W3 can be obtained.

[0059] In some embodiments of the present application, N=3, and the secondary battery includes the first electrode assembly, the second electrode group, and the third electrode assembly.

[0060] In some embodiments of the present application, the secondary battery includes the above-mentioned first electrode assembly, the above-mentioned second electrode group and the above-mentioned third electrode assembly, and the content of silicon material in the first electrode assembly and the second electrode assembly may be the same or different, as long as the purpose of the present application can be achieved.

[0061] In some embodiments of the present application, the secondary battery satisfies at least one of the following characteristics: (1) 1% ≤ W2-W3 ≤ 40%; (2) 0% ≤ W3 ≤ 39%; (3) 0% ≤ C 31 -C 21 ≤5%;(4)0%≤C 31 ≤5%. The secondary battery satisfies at least one of the above characteristics, which is conducive to further taking into account the dynamic performance, expansion performance and energy density.

[0062] In some embodiments of the present application, 1%≤W2-W3≤40%; for example, W2-W3 can be 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40% or a range consisting of any two values ​​therebetween.

[0063] In some embodiments of the present application, 0%≤W3≤39%; for example, W3 can be 0%, 1%, 2%, 3%, 4%, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 39% or a range consisting of any two values ​​therebetween.

[0064] In some embodiments of the present application, 0%≤W3'≤78%.

[0065] In some embodiments of the present application, N=3, 0%≤W1≤39%, 2%≤W2≤40%, and 0%≤W3≤39%.

[0066] In some embodiments of the present application, 0%≤C 31 -C 21 ≤5%; for example, C 31 -C 21 It can be 0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5% or a range consisting of any two values ​​therebetween. The third negative electrode material layer has less silicon content than the second negative electrode material layer, and the third negative electrode material layer contains more first binder with good kinetic properties. By adjusting C 31 -C 21Within the above range, it is beneficial to obtain a third negative electrode material layer with good kinetic performance, thereby helping to better balance the kinetic performance, expansion performance and energy density of the secondary battery.

[0067] In some embodiments of the present application, 0%≤C 31 ≤5%. For example, C 31 It can be 0%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, or a range consisting of any two values ​​therebetween. 31 Within the above range, it is beneficial to obtain a third negative electrode material layer with good kinetic performance, thereby helping to better balance the kinetic performance, expansion performance and energy density of the secondary battery.

[0068] In some embodiments of the present application, the third negative electrode material layer further includes a second binder, and based on the mass of the third negative electrode material layer, the mass percentage of the second binder is C 32 , C 32 <C 22 The second negative electrode material layer has a higher silicon content than the first negative electrode material layer, so that the second negative electrode material layer has a higher second binder content, which is beneficial to better improve the expansion problem caused by the higher silicon content in the second negative electrode material layer, and is beneficial to better balance the dynamic performance, expansion performance and energy density of the secondary battery.

[0069] In some embodiments of the present application, the secondary battery satisfies at least one of the following characteristics: (1) C 31 +C 32 <C 21 +C 22 ; (2) 0% ≤ C 21 +C 22 -(C 31 +C 32 )≤13%; (3)1%<C 31 +C 32 ≤10%;(4)0%≤C 22 -C 32 ≤15%;(5)0%≤C 32 ≤10%. The secondary battery satisfies at least one of the above characteristics, which is conducive to further taking into account the dynamic performance, expansion performance and energy density.

[0070] In some embodiments of the present application, C 31 +C 32 <C 21 +C 22. The second negative electrode material layer has a higher silicon content than the third negative electrode material layer, so that the total content of the first binder and the second binder in the second negative electrode material layer is higher than that in the third negative electrode material layer, which is conducive to improving the expansion problem caused by the higher silicon content in the second negative electrode material layer; at the same time, the total content of the first binder and the second binder in the third negative electrode material layer is relatively small, that is, the content of inactive substances is relatively small, which is conducive to improving the problem of low energy density caused by the lower silicon content in the third negative electrode material layer. Therefore, when the contents of the first binder and the second binder in the third negative electrode material layer and the second negative electrode material layer meet the above relationship, it is conducive to further taking into account the kinetic performance, expansion performance and energy density of the secondary battery.

[0071] In some embodiments of the present application, 0%≤C 21 +C 22 -(C 31 +C 32 )≤13%; for example, C 21 +C 22 -(C 31 +C 32 ) can be 0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13% or a range consisting of any two values ​​therebetween. The difference between the sum of the contents of the first binder and the second binder in the third negative electrode material layer and the second negative electrode material layer is within the above range, which improves the expansion problem caused by the higher silicon content in the second negative electrode material layer and the problem of low energy density caused by the lower silicon content in the third negative electrode material layer, while making the impedance difference between the third negative electrode material layer and the second negative electrode material layer smaller, thereby helping to improve the self-discharge problem in the secondary battery, and the kinetic properties of the third negative electrode material layer and the second negative electrode material layer are closer, which is conducive to further taking into account the kinetic properties, expansion properties and energy density of the secondary battery.

[0072] In some embodiments of the present application, 1%<C 31 +C 32 ≤10%; for example, C 31 +C 32 It can be 1.1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two values ​​therebetween. By adjusting the sum of the contents of the first binder and the second binder in the third negative electrode material layer within the above range, the third negative electrode material layer obtained has a lower expansion rate and lower impedance, better dynamic performance, and takes into account the energy density, which is conducive to further taking into account the dynamic performance, expansion performance and energy density of the secondary battery.

[0073] In some embodiments of the present application, 0%≤C22 -C 32 ≤15%; for example, C 22 -C 32 It can be 0%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15% or a range consisting of any two values ​​therebetween. The second negative electrode material layer has a higher silicon content than the third negative electrode material layer, and the second negative electrode material layer contains more second binder with strong binding properties. By adjusting C 22 -C 32 Within the above range, it is helpful to improve the volume expansion problem caused by the high silicon content of the second material layer, thereby helping to better balance the dynamic performance, expansion performance and energy density of the secondary battery.

[0074] In some embodiments of the present application, 0%≤C 32 ≤10%. For example, C 32 It can be 0%, 1%, 1.5%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or a range consisting of any two values ​​therebetween. 32 Within the above range, it is beneficial to obtain a third negative electrode material layer that takes both kinetic performance and expansion performance into consideration, thereby helping to better take into consideration the kinetic performance, expansion performance and energy density of the secondary battery.

[0075] In some embodiments of the present application, the third negative electrode material layer further includes a third carbon material, and the third carbon material includes at least one of artificial graphite, natural graphite, hard carbon or soft carbon. On the basis of including the silicon material, the third negative electrode material layer further includes a third carbon material. In different negative electrode material layers, different contents of silicon material and carbon material match each other, which is conducive to giving play to their respective advantages, thereby facilitating better consideration of the kinetic performance, expansion performance and energy density of the secondary battery.

[0076] In some embodiments of the present application, the mass percentage of the first carbon material is Z1; based on the mass of the second negative electrode material layer, the mass percentage of the second carbon material is Z2; based on the mass of the third negative electrode material layer, the mass percentage of the third carbon material is Z3; Z2<Z1, Z2<Z3. The first negative electrode material layer and the third negative electrode material layer contain relatively less silicon content, and the first carbon material or the third carbon material is relatively more, so that a binder system that is more suitable for the first carbon material or the third carbon material can be matched, and the advantages of the first carbon material or the third carbon material can be better exerted, and the kinetic performance and expansion performance of the secondary battery can be improved. The second negative electrode material layer contains relatively more silicon content, and the second carbon material is relatively less, so that a binder system that is more suitable for silicon materials can be matched, and the advantages of silicon materials can be better exerted to improve the energy density of the secondary battery. Thus, the problem that silicon and carbon materials in the current mixed negative electrode cannot exert their respective advantages is improved, so as to better balance the kinetic performance, expansion performance and energy density of the secondary battery.

[0077] In some embodiments of the present application, 7%≤Z3≤99%. In some embodiments of the present application, 80%≤Z3≤98%. In some embodiments of the present application, 50%≤Z3≤95%.

[0078] In some embodiments of the present application, N=4, and the secondary battery includes the first electrode assembly, the second electrode assembly, and the third electrode assembly, wherein there are one first electrode assembly and one third electrode assembly, and there are two second electrode assemblies.

[0079] In some embodiments of the present application, N=5, and the secondary battery includes the above-mentioned first electrode assembly, the above-mentioned second electrode group, and the above-mentioned third electrode assembly, wherein the first electrode assembly and the third electrode assembly are each 1, and the second electrode assembly is 3. The silicon content in the negative electrode material layer of the three second electrode assemblies may be the same or different, but is greater than the silicon content in the negative electrode material layer of the first electrode assembly and the third electrode assembly. In addition, when the silicon content in the negative electrode material layer of the three second electrode assemblies is different, along the stacking direction of the electrode assembly, the electrode assembly with a lower silicon content is closer to the shell.

[0080] In some embodiments of the present application, N=5, and the secondary battery includes the above-mentioned first electrode assembly, the above-mentioned second electrode group, and the above-mentioned third electrode assembly, wherein the first electrode assembly and the third electrode assembly are 2 each, and the second electrode assembly is 1. The silicon content in the negative electrode material layer of the two first electrode assemblies may be the same or different, but both are less than the silicon content in the negative electrode material layer of the second electrode assembly; the silicon content in the negative electrode material layer of the two third electrode assemblies may be the same or different, but both are less than the silicon content in the negative electrode material layer of the second electrode assembly. In addition, when the silicon content in the negative electrode material layer of the two first electrode assemblies is different, along the stacking direction of the electrode assembly, the electrode assembly with a lower silicon content is closer to the shell; when the silicon content in the negative electrode material layer of the two third electrode assemblies is different, along the stacking direction of the electrode assembly, the electrode assembly with a lower silicon content is closer to the shell.

[0081] In some embodiments of the present application, N=6, and the secondary battery includes the above-mentioned first electrode assembly, the above-mentioned second electrode group, and the above-mentioned third electrode assembly, wherein the first electrode assembly, the second electrode group, and the third electrode assembly are 2 each. The silicon content in the negative electrode material layer of the two first electrode assemblies may be the same or different, but both are less than the silicon content in the negative electrode material layer of the second electrode assembly; the silicon content in the negative electrode material layer of the two third electrode assemblies may be the same or different, but both are less than the silicon content in the negative electrode material layer of the second electrode assembly; the silicon content in the negative electrode material layer of the two second electrode assemblies may be the same or different. In addition, when the silicon content in the negative electrode material layer of the two first electrode assemblies is different, along the stacking direction of the electrode assembly, the electrode assembly with a lower silicon content is closer to the shell; when the silicon content in the negative electrode material layer of the two third electrode assemblies is different, along the stacking direction of the electrode assembly, the electrode assembly with a lower silicon content is closer to the shell.

[0082] In some embodiments of the present application, the negative electrode material layer also includes a conductive agent. The application does not particularly limit the type of conductive agent, as long as the purpose of the present application can be achieved. For example, the conductive agent may include but is 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 may include but is not limited to at least one of acetylene black or Ketjen black. The above-mentioned carbon nanotubes may include but are not limited to single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers may include but are not limited to vapor-grown carbon fibers (VGCF) and / or nano-carbon fibers. The above-mentioned metal materials may include but are not limited to metal powders and / or metal fibers. Specifically, the metal may include but is not limited to at least one of copper, nickel, aluminum or silver. The above-mentioned conductive polymers may include but are not limited to at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene or polypyrrole.

[0083] In some embodiments of the present application, based on the mass of the negative electrode material layer, the mass percentage of the conductive agent is 0% to 5%.

[0084] The present application has no particular limitation on the thickness of the negative electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode material layer is 30 μm to 120 μm.

[0085] In the present application, the negative electrode sheet includes a negative electrode current collector and the above-mentioned negative electrode material layer arranged on at least one surface of the negative electrode current collector. Specifically, the negative electrode material layer can be arranged on one surface of the negative electrode current collector along its own thickness direction, or on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the negative electrode current collector, or it can be a partial area of ​​the surface of the negative electrode current collector. This application has no special restrictions, as long as the purpose of this application can be achieved. This application has no special restrictions on the thickness of the negative electrode current collector, as long as the purpose of this application can be achieved. For example, the thickness of the negative electrode current collector is 4μm to 15μm.

[0086] In the present application, each electrode assembly also includes a positive electrode sheet, which includes a positive electrode collector and a positive electrode material layer disposed on at least one surface of the positive electrode collector. The above-mentioned "positive electrode material layer disposed on at least one surface of the positive electrode collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode collector along its own thickness direction, or on two surfaces of the positive electrode collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the surface of the positive electrode collector, or it can be a partial area of ​​the surface of the positive electrode collector. This application has no special restrictions, as long as the purpose of this application can be achieved.

[0087] The present application has no particular limitation on the positive electrode current collector, as long as the purpose of the present application can be achieved. For example, it may include aluminum foil, aluminum alloy foil or a composite current collector (such as an aluminum-carbon composite current collector).

[0088] The positive electrode material layer includes a positive electrode active material. The present application has no particular limitation on the positive electrode active material as long as the purpose of the present application can be achieved. For example, the positive electrode active material may include but is not limited to at least one of lithium nickel cobalt manganese oxide (such as NCM811, NCM622, NCM523, NCM111), 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.

[0089] The positive electrode material layer may also include a conductive agent and a binder. The present application does not particularly limit the types of conductive agents and binders, as long as the purpose of the present application can be achieved. For example, the binder may include but is not limited to polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, styrene-butadiene rubber or at least one of polyvinylidene fluoride. The conductive agent may be at least one of the above conductive agents. The present application does not particularly limit the mass ratio of the positive electrode active material, conductive agent, and binder in the 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. The present application does not particularly limit the mass ratio of the positive electrode active material, conductive agent, and binder in the 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.

[0090] The present application has no particular limitation on the thickness of the positive electrode current collector and the positive electrode material layer, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the positive electrode material layer is 30 μm to 120 μm.

[0091] In the present application, the electrode assembly also includes a diaphragm. The present application has no particular 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 (e.g., polyethylene terephthalate (PET) films), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of diaphragm may include at least one of a woven membrane, a nonwoven membrane, a microporous membrane, a composite membrane, a rolled membrane or a spun membrane.

[0092] In some embodiments of the present application, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, a film or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate or polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0093] Optionally, a surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic layer.

[0094] In some embodiments of the present application, the inorganic layer includes inorganic particles and a binder. The present application is not particularly limited to inorganic particles, such as inorganic particles can 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 is not particularly limited to binders, such as binders can be at least one of the above-mentioned binders. In some embodiments of the present application, the polymer layer includes polymers, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymers, polyacrylic acid, polyacrylates, polyvinyl pyrrolidone, polyvinyl ether or polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0095] In the present application, there is no particular limitation on the thickness of the separator as long as the purpose of the present application can be achieved. For example, the thickness of the separator may be 3 μm to 30 μm.

[0096] In the present application, the shell is used to accommodate the electrode assembly and the electrolyte, as well as other components known in the field of secondary batteries, and the present application does not limit the above-mentioned other components. The present application does not particularly limit the shell, and it can be a shell known in the art, as long as the purpose of the present application can be achieved. For example, the shell can be a hard shell or a flexible shell. The material of the hard shell can be metal, and the present application does not limit the type of metal. A metal hard shell known in the art can be used, as long as the purpose of the present application can be achieved. The flexible shell can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc. The present application does not limit the electrolyte, and an electrolyte known in the art can be used, as long as the purpose of the present application can be achieved.

[0097] 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, the preparation process of the secondary battery may include but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding and other operations as needed to obtain an electrode assembly of a winding structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. Alternatively, stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and then fixing the four corners of the entire laminated structure with tape to obtain an electrode assembly of a laminated structure, placing the electrode assembly in a shell, injecting the electrolyte into the shell and sealing it to obtain a secondary battery. In addition, overcurrent protection elements, guide plates, etc. may also be placed in the shell as needed to prevent the pressure inside the secondary battery from rising and overcharging and discharging.

[0098] In some embodiments of the present application, the secondary battery of the present application may include but is not limited to: a lithium ion secondary battery (lithium ion battery), a lithium polymer secondary battery or a lithium ion polymer secondary battery, etc. In some embodiments of the present application, the secondary battery includes a lithium ion battery.

[0099] The second aspect of the present application provides an electrical device, which includes a secondary battery in any of the foregoing embodiments, and the obtained electrical device has good performance. The present application does not particularly limit the type of electrical device, and it can be used for any electrical device known in the prior art. In some embodiments of the present application, the electrical device may include but is not limited to a computer, a smart phone, a backup power supply, a two-wheeled vehicle, a drone, a power tool or an energy storage device.

[0100] Example

[0101] 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.

[0102] Test methods and equipment:

[0103] In the following test method, the upper limit voltage of charging in the lithium ion battery in the embodiment and the comparative example is 4.25V, and the lower limit voltage of discharging is 2.5V.

[0104] Charging capacity test:

[0105] At an external temperature of 10°C, charge the lithium-ion battery at a rate of 2C to the upper limit voltage, then charge it to 0.05C at the upper limit voltage constant voltage, let it stand for 15 minutes, and then discharge it to the lower limit voltage at a discharge rate of 0.5C, and record the discharge capacity. Repeat the above process 10 times, and use the percentage of the discharge capacity of the 10th cycle to the capacity of the 1st cycle to express the capacity retention rate of 10 cycles, that is, the charging capacity of lithium ions. If the charging kinetics of the lithium-ion battery are poor and lithium is deposited during the charging process, the capacity retention rate will be lower. Therefore, the charging capacity is used to characterize the kinetic performance of the lithium-ion battery.

[0106] High rate discharge capability test:

[0107] Under the external temperature condition of 25℃, charge the lithium-ion battery to the upper limit voltage at a rate of 1C, then charge it to 0.05C at the upper limit voltage, let it stand for 15 minutes, and then discharge it to the lower limit voltage at a discharge rate of 0.2C, and record the discharge capacity C1. Continue to charge the battery cell to the upper limit voltage at a rate of 1C, then charge it to 0.05C at the upper limit voltage, let it stand for 15 minutes, and then discharge it to the lower limit voltage at a discharge rate of 5C, and record the discharge capacity C2. The percentage of the ratio of the 5C capacity of the lithium-ion battery to the 0.2C capacity, that is, C1 / C2×100%, is recorded as the 5C capacity retention rate of the lithium-ion battery, that is, the high-rate discharge capability of the lithium-ion battery. The better the discharge dynamics of the lithium-ion battery, the higher the 5C capacity retention rate.

[0108] Cyclic expansion rate test:

[0109] The lithium-ion battery is charged at a constant current of 1C to the upper limit voltage, and then charged at the upper limit voltage constant voltage until the current drops to 0.05C; the thickness of the tested lithium-ion battery is recorded as the first cycle of lithium-ion battery full charge thickness, and then it is left to stand for 15 minutes; it is then discharged at a constant current of 1C to 2.5V; it is left to stand for 30 minutes, which is a charge and discharge cycle. Under this charge and discharge condition, it is cycled 500 times, and the percentage of the ratio of the lithium-ion battery full charge thickness of the 500th cycle to the lithium-ion battery full charge thickness of the first cycle is recorded as the lithium-ion battery 500 cycle expansion rate.

[0110] Test of Si content in negative electrode material layer:

[0111] The lithium-ion battery is discharged to the lower limit voltage by 0.2C constant current discharge, and the negative electrode sheet is disassembled, washed, and dried. The negative electrode material layer powder on the surface of the negative electrode sheet is taken and its mass is M. 负 , M 负 In volume V 负 The solution was digested in a hydrofluoric acid solution and the silicon concentration in the solution was tested by ICP-AES (inductively coupled atomic emission spectroscopy). 负 , calculate the total mass m of silicon using the concentration and solution volume 负 =n 负 ×V 负 , then the mass percentage of silicon in the negative electrode material layer is m 负 / M 负 × 100%. By testing different negative electrode material layers, W1, W2, and W3 can be calculated.

[0112] Example 1

[0113] <Preparation of positive electrode sheet>

[0114] The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1O2 (NCM811), conductive carbon black (Super P), carbon nanotubes, and binder polyvinylidene fluoride are mixed in a mass ratio of 96:2:0.5:1.5, and N-methylpyrrolidone (NMP) is added as a solvent to prepare a slurry with a solid content of 75wt%. After vacuum stirring, the positive electrode slurry is obtained. The positive electrode slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm, and dried at 120°C to obtain a positive electrode sheet with a single-sided positive electrode material layer. The coating weight of the positive electrode material layer is 220mg / 1540mm 2 Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode material layer on both sides. After drying at 120°C, cold pressing, cutting and welding the tabs, a positive electrode sheet with a specification of 100mm in width and 800mm in length is obtained for standby use. The thickness of the single-sided positive electrode material layer is 42μm.

[0115] <Preparation of the First Negative Electrode Sheet>

[0116] The first silicon material silicon carbon material, the first carbon material artificial graphite, the first binder polystyrene butadiene copolymer, the second binder polyacrylic acid, and the conductive agent are mixed, and deionized water is added as a solvent to prepare a slurry with a solid content of 45wt%. After being stirred evenly by a vacuum mixer, a first negative electrode slurry is obtained. The first negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 8μm, and dried at 120°C to obtain a first negative electrode sheet coated with a first negative electrode material layer on one side, wherein the coating weight of the negative electrode material layer is determined according to the ratio (NP value) of the negative electrode capacity to the positive electrode capacity, and the NP value of the first negative electrode sheet and the positive electrode sheet is 1.1. Then 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, cold pressing is performed, and then cutting and welding of the tabs are performed to obtain a negative electrode sheet with a specification of 103mm in width and 830mm in length for standby use.

[0117] Among them, the mass percentage of silicon element in the silicon-carbon material is 50%; the conductive agent is obtained by mixing Super P and carbon nanotubes in a mass ratio of 4:1; based on the mass of the first negative electrode material layer, the mass percentage of silicon element W1=5%, the mass percentage of the first silicon material W1'=10%, the mass percentage of the first binder C11=2%, the mass percentage of the second binder C12=2%, the mass percentage of the first conductive agent D1=5%, and the mass percentage of the first carbon material=100%-W1'-C11-C12-D1.

[0118] <Preparation of the Second Negative Electrode Sheet>

[0119] The second silicon material silicon carbon material, the second carbon material artificial graphite, the second binder polystyrene butadiene copolymer, the second binder polyacrylic acid, and the conductive agent are mixed, and deionized water is added as a solvent to prepare a slurry with a solid content of 35wt%. After being stirred evenly by a vacuum mixer, a second negative electrode slurry is obtained. The second negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 8μm, and dried at 120°C to obtain a second negative electrode sheet coated with a second negative electrode material layer on one side, wherein the coating weight of the negative electrode material layer is determined according to the ratio of the negative electrode capacity to the positive electrode capacity (NP value), and the NP value of the second negative electrode sheet and the positive electrode sheet is 1.1. Then 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, cold pressing is performed, and then cutting and welding of the pole ears are performed to obtain a negative electrode sheet with a specification of 103mm in width and 830mm in length for standby use.

[0120] Among them, the mass percentage of silicon element in the silicon-carbon material is 50%; the conductive agent is obtained by mixing Super P and carbon nanotubes in a mass ratio of 4:1; based on the mass of the second negative electrode material layer, the mass percentage of silicon element W2=20%, the mass percentage of the second silicon material W1'=40%, the mass percentage of the first binder C21=2%, the mass percentage of the second binder C22=2%, the mass percentage of the second conductive agent D2=5%, and the mass percentage of the second carbon material=100%-W2'-C21-C22-D2.

[0121] <Preparation of the Third Negative Electrode Sheet>

[0122] The preparation is the same as that of the first negative electrode. The mass percentage of silicon in the silicon-carbon material is 50%; the conductive agent is a mixture of Super P and carbon nanotubes at a mass ratio of 4:1; based on the mass of the third negative electrode material layer, the mass percentage of silicon W3 = 5%, the mass percentage of the third silicon material W3' = 10%, the mass percentage of the first binder C31 = 2%, the mass percentage of the second binder C32 = 2%, the mass percentage of the third conductive agent D3 = 5%, and the mass percentage of the second carbon material = 100%-W3'-C31-C32-D3.

[0123] <Preparation of Electrolyte>

[0124] In an environment where the water content is less than 10 ppm, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, and fluoroethylene carbonate are mixed in a mass ratio of 1:1:1:0.5 to obtain an organic solvent, and then electrolyte salt LiPF6 is added to the organic solvent and mixed evenly to obtain an electrolyte solution. Among them, based on the mass of the electrolyte solution, the mass percentage of the electrolyte salt is 12.5%, and the rest is the organic solvent.

[0125] <Diaphragm>

[0126] A porous polyethylene film with a thickness of 9 μm (provided by Celgard Company) was used as a separator.

[0127] <Preparation of First Electrode Assembly>

[0128] The positive electrode sheet, separator, and first negative electrode sheet prepared above are stacked in order, with the separator placed between the positive electrode sheet and the first negative electrode sheet to play an isolating role, and wound to obtain a first electrode assembly. The first electrode assembly has a thickness H1 of 3 mm, a width of 110 mm, and a length of 70 mm.

[0129] <Preparation of Second Electrode Assembly>

[0130] The prepared positive electrode sheet, separator, and second negative electrode sheet are stacked in order, the separator is placed between the positive electrode sheet and the second negative electrode sheet to play a role of isolation, and the second electrode assembly is wound to obtain the second electrode assembly. The thickness H2 of the second electrode assembly is 3 mm, the width is 110 mm, and the length is 70 mm.

[0131] <Preparation of the Third Electrode Assembly>

[0132] The prepared positive electrode sheet, separator, and third negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the third negative electrode sheet to play an isolating role, and the third electrode assembly is wound to obtain the third electrode assembly. The thickness H3 of the third electrode assembly is 3 mm, the width is 110 mm, and the length is 70 mm.

[0133] <Preparation of lithium-ion batteries>

[0134] The first electrode assembly, the second electrode assembly and the third electrode assembly prepared above are placed in an aluminum-plastic film packaging bag, and the second electrode assembly is located between the first electrode assembly and the third electrode assembly, and then the first electrode assembly, the second electrode assembly and the third electrode assembly are connected in parallel, and the water is removed at 80°C, and the prepared electrolyte is injected, and a lithium-ion battery is obtained through vacuum packaging, standing, forming, degassing, trimming and other processes. Among them, the upper limit voltage of the formation is 4.1V, the formation temperature is 70°C, and the formation standing time is 2h.

[0135] Example 2 to Example 18

[0136] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1.

[0137] When the thickness of the first electrode assembly, the second electrode assembly, and the third electrode assembly changes, their width and length remain unchanged. By changing the length of the positive electrode sheet and the negative electrode sheet (that is, the first negative electrode sheet, the second negative electrode sheet, or the third negative electrode sheet), the thickness of each electrode assembly is as shown in Table 1.

[0138] Embodiment 19

[0139] Except for using one first electrode assembly, two second electrode assemblies, and one third electrode assembly to prepare a lithium-ion battery, the rest is the same as Example 1.

[0140] Embodiment 20

[0141] Except that the second binder in the first negative electrode sheet, the second negative electrode sheet or the third negative electrode sheet is replaced with polyurethane, the rest is the same as Example 1.

[0142] Comparative Examples 1 to 5

[0143] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1. Among them, the lithium ion batteries of Comparative Examples 1 to 4 include only one first electrode assembly, and when the thickness of the first electrode assembly changes, its width and length remain unchanged, and the thickness of the first electrode assembly is as shown in Table 1 by changing the length of the positive electrode sheet and the first negative electrode sheet.

[0144] The data of each embodiment and comparative example are shown in Table 1.

[0145]

[0146]

[0147]

[0148] It is understandable that the silicon content per unit weight of lithium-ion batteries is different, and their expansion performance, kinetic performance and energy density are all quite different. Therefore, when the silicon content per unit weight of lithium-ion batteries is the same, similar or equivalent, that is, the weight energy density of the lithium-ion batteries is similar or equivalent, on this basis, the kinetic performance and / or expansion performance of the lithium-ion batteries are improved, which means that the kinetic performance, expansion performance and energy density of the lithium-ion batteries are taken into account. Among them, the silicon content per unit weight of lithium-ion batteries is mainly related to the content of silicon elements in each negative electrode material layer and the thickness of the electrode assembly, that is, related to W1, W2, W3, H1, H2, H3, and the silicon content per unit weight of lithium-ion batteries is defined as (W1×H1+W2×H2+W3×H3) / (H1+H2+H3).

[0149] It can be seen from Examples 1 to 20 and Comparative Examples 1 to 5 that when the silicon content per unit weight of the lithium-ion battery is equal, W max -W min Within the scope of the present application, the obtained lithium-ion battery has both high charging capacity and high-rate discharge capacity, as well as a low 500-cycle expansion rate, while the comparative example cannot take into account the above-mentioned properties at the same time, thus indicating that the secondary battery provided by the present application can take into account dynamic performance, expansion performance and energy density.

[0150] Specifically, as in Example 7, Example 8, Example 13, Example 15, Example 19 and Comparative Example 1, the silicon content per unit weight of the lithium-ion battery is basically the same, that is, the weight energy density is equivalent. At the same time, at least one of the charging capacity and the high-rate discharge capacity of the above embodiments is higher than that of Comparative Example 1, and the 500-cycle expansion ratio of the above embodiments is less than that of Comparative Example 1, that is, when the weight energy density is basically the same, the above embodiments have better kinetic performance and expansion performance than Comparative Example 1, which shows that the secondary battery provided by the present application can take into account kinetic performance, expansion performance and energy density.

[0151] For another example, in Example 1, Example 9, Example 14, Example 16, Example 20, Comparative Example 2 and Comparative Example 3, the silicon content per unit weight of the lithium-ion battery is basically the same, that is, the weight energy density is equivalent. At the same time, at least one of the charging capacity and the high-rate discharge capacity of the above embodiments is higher than that of Comparative Example 2 and Comparative Example 3, and the 500-cycle expansion ratio of the above embodiments is smaller than that of Comparative Example 2 and Comparative Example 3, that is, when the weight energy density is basically the same, the above embodiments have better kinetic performance and expansion performance than Comparative Example 2 and Comparative Example 3, which shows that the secondary battery provided by the present application can take into account kinetic performance, expansion performance and energy density.

[0152] For another example, in Example 11 and Comparative Example 4, the silicon content per unit weight of the lithium-ion battery is basically the same, that is, the weight energy density is equivalent. At the same time, the charging capacity and high-rate discharge capacity of Example 11 are higher than those of Comparative Example 4, and the 500-cycle expansion rate of Example 11 is smaller than that of Comparative Example 4, that is, when the weight energy density is basically the same, Example 11 has better kinetic performance and expansion performance than Comparative Example 4, which shows that the secondary battery provided by the present application can take into account kinetic performance, expansion performance and energy density.

[0153] It can be seen from Examples 1 to 20 that the contents of the first binder and the second binder in each negative electrode material layer are related to the content of the silicon element. When the contents of the first binder and the second binder and the relationship between the contents are within the scope of the present application, the obtained lithium-ion battery has a higher charging capacity and a large-rate discharge capacity, as well as a lower 500-cycle expansion rate. This indicates that when the contents of the first binder and the second binder and the relationship between the contents are within the scope of the present application, the obtained secondary battery can take into account dynamic performance, expansion performance and energy density.

[0154] 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.

[0155] 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 N electrode assemblies and a housing for accommodating the N electrode assemblies, 2≤N≤6, N being an integer; Each of the electrode assemblies comprises a negative electrode sheet, the negative electrode sheet comprises a negative electrode material layer, the negative electrode material layer of at least one of the negative electrode sheets comprises a silicon material, and in the N electrode assemblies, based on the mass of the negative electrode material layer in each of the electrode assemblies, the mass percentage of silicon element in the negative electrode material layer in each of the electrode assemblies is W n , 1≤n≤N, n is an integer; in, The W n The maximum value in is defined as W max , the W n The minimum value of is defined as W min , 1% ≤ W max -W min ≤40%.

2. The secondary battery according to claim 1, wherein 1%≤W max -IN min ≤30%。 3. The secondary battery according to claim 2, wherein: 2%≤W max -IN min ≤15%。 4. The secondary battery according to claim 1, wherein 0％≤W n ≤40％。 5. The secondary battery according to any one of claims 1 to 4, wherein The negative electrode material layer includes at least one of a first binder and / or a second binder, wherein the first binder is selected from at least one of polystyrene butadiene copolymer, carboxymethyl cellulose, and polyvinylidene fluoride, and the second binder is selected from at least one of polyacrylic acid, polyacrylonitrile, polyacrylate, and polyurethane.

6. The secondary battery according to claim 5, wherein The secondary battery includes a first electrode assembly and a second electrode assembly; The first electrode assembly includes a first negative electrode material layer, the first negative electrode material layer includes a first silicon material and the first binder, and based on the mass of the first negative electrode material layer, the mass percentage of silicon element in the first negative electrode material layer is W1; The second electrode assembly includes a second negative electrode material layer, the second negative electrode material layer includes a second silicon material and the second binder, and based on the mass of the second negative electrode material layer, the mass percentage of silicon element in the second negative electrode material layer is W2; Among them, W1<W2.

7. The secondary battery according to claim 6, wherein 1%≤W2-W1≤40%.

8. The secondary battery according to claim 7, wherein The first negative electrode material layer further includes the second binder. Based on the mass of the first negative electrode material layer, the mass percentage of the first binder is C 11 The mass percentage of the second binder is C 12 ; The second negative electrode material layer further includes the first binder. Based on the mass of the second negative electrode material layer, the mass percentage of the first binder is C 21 The mass percentage of the second binder is C 22 ; Among them, C 11 +C 12 <C 21 +C 22 .

9. The secondary battery according to claim 8, which satisfies at least one of the following characteristics: (1) 0%≤C 21 +C 22 -(C 11 +C 12 )≤13%; (2) 1%<C 11 +C 12 ≤10%。 10. The secondary battery according to claim 8, wherein C 11 >C 21 ,C 22 >C 12 。 11. The secondary battery according to claim 10, which satisfies at least one of the following characteristics: (1)0%≤C 11 -C 21 ≤5%; (2)0％≤C 11 ≤5％； (3)0%≤C 22 -C 12 ≤15%; (4)2％≤C 22 ≤15％。 12. The secondary battery according to any one of claims 5 to 11, wherein The first negative electrode material layer further includes a first carbon material, and the second negative electrode material layer further includes a second carbon material; The first carbon material and the second carbon material each independently include at least one of artificial graphite, natural graphite, hard carbon, or soft carbon.

13. The secondary battery according to any one of claims 1 to 4, wherein 3≤N≤6； The secondary battery further includes a shell, the N electrode assemblies include an outer electrode assembly and an inner electrode assembly, and along the stacking direction of the N electrode assemblies, the outer electrode assembly is closer to the shell than the inner electrode assembly; Based on the mass of the negative electrode material layer in the outer electrode assembly, the mass percentage of silicon in the negative electrode material layer is Wx, and based on the mass of the negative electrode material layer in the inner electrode assembly, the mass percentage of silicon in the negative electrode material layer is Wy, Wx<Wy.

14. The secondary battery according to any one of claims 8 to 11, further comprising a third electrode assembly, wherein along the stacking direction of the N electrode assemblies, the second electrode assembly is disposed between the first electrode assembly and the third electrode assembly; The third electrode assembly includes a third negative electrode material layer, the third negative electrode material layer includes a third silicon material and the first binder, based on the mass of the third negative electrode material layer, the mass percentage of silicon element is W3, the mass percentage of the first binder is C 31 ; in, W3<W2,C 31 >C 21 。 15. The secondary battery according to claim 14, which satisfies at least one of the following characteristics: (1) 1% ≤ W2-W3 ≤ 40%; (2)0％≤W3≤39％； (3)0%≤C 31 -C 21 ≤5%; (4)0％≤C 31 ≤5％。 16. The secondary battery according to claim 14 or 15, wherein: The third negative electrode material layer further includes the second binder, and based on the mass of the third negative electrode material layer, the mass percentage of the second binder is C 32 , C 32 <C 22 .

17. The secondary battery according to claim 16, which satisfies at least one of the following characteristics: (1)C 31 +C 32 <C 21 +C 22 ; (2)0%≤C 21 +C 22 -(C 31 +C 32 )≤13%; (3)1%<C 31 +C 32 ≤10%; (4)0%≤C 22 -C 32 ≤15%; (5)0％≤C 32 ≤10％。 18. The secondary battery according to any one of claims 14 to 17, wherein The third negative electrode material layer further includes a third carbon material, and the third carbon material includes at least one of artificial graphite, natural graphite, hard carbon or soft carbon.

19. An electric device comprising the secondary battery according to any one of claims 1 to 18.

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