A secondary battery and an electronic device

Abstract

This application provides a secondary battery and an electronic device. The secondary battery includes an electrode assembly, which includes electrode sheets and a first separator. The electrode sheets include a positive electrode sheet and a negative electrode sheet. The negative electrode sheet includes a negative electrode material layer containing silicon. Based on the mass of the negative electrode material layer, the mass percentage of silicon is W, where W ≥ 3%. The first separator includes a base film, a first ceramic layer, and a second ceramic layer. Along the thickness direction of the first separator, the base film includes a first surface and a second surface. The first surface faces the negative electrode sheet, and the second surface faces the positive electrode sheet. The first ceramic layer is disposed on the first surface, and the second ceramic layer is disposed on the second surface. The thickness of the first ceramic layer is T1 μm, and the thickness of the second ceramic layer is T2 μm, where T1 > T2. This configuration reduces the risk of lithium plating at the negative electrode interface due to insufficient electrolyte and improves the cycle performance of the secondary battery.

Description

A secondary battery and an electronic device TECHNICAL FIELD

[0001] The present application relates to the technical field of electrochemistry, in particular to a secondary battery and an electronic device. BACKGROUND

[0002] Secondary batteries, such as lithium ion batteries, have characteristics such as high specific energy, high working voltage, low self-discharge rate, small size, light weight, etc., and have a wide range of applications in the consumer electronics field.

[0003] With the increasing demand for the energy density of secondary batteries, silicon, as a material with a relatively high gram capacity of 4200 mAh / g, a relatively low cost and an environmentally friendly type, is also increasingly used in the secondary battery system. Due to the ultra-high gram capacity of the current silicon material, the negative electrode material layer containing the silicon material, especially when the proportion of silicon elements in the negative electrode material layer is high, the coating weight during coating is low, only about one fourth of the traditional graphite material, and the thickness is also less than half of the traditional graphite electrode piece. At this time, the negative electrode piece has a relatively poor electrolyte storage capacity, and because the demand for electrolyte of the silicon material is higher than that of the conventional graphite during the secondary battery cycle, the storage capacity of the negative electrode piece containing the silicon material is required to be higher.

[0004] SUMMARY

[0005] The purpose of the present application is to provide a secondary battery and an electronic device to improve the electrolyte storage capacity of the separator facing the negative electrode side, improve the lithium precipitation of the negative electrode interface, and improve the cycle performance of the secondary battery.

[0006] It should be noted that the present application is explained by taking lithium ion batteries as an example of secondary batteries in the summary of the present application, but the secondary batteries of the present application are not limited to lithium ion batteries.

[0007] In the prior art, to solve the problem of the storage of the negative electrode piece containing the silicon material, more electrolyte is retained inside the secondary battery shell to increase the storage capacity of the negative electrode piece. However, the excess electrolyte inside the shell is stored in a free state and cannot be timely supplied and transmitted to the silicon-based material of the negative electrode piece. At this time, the excess free electrolyte increases the sliding property between the layers inside the electrode assembly, affecting the drop performance of the secondary battery. When there is too much excess electrolyte, the secondary battery swells, and the shell may bulge, deform or crack. Based on this, the present application provides a secondary battery that can timely supply electrolyte when the negative electrode piece containing silicon elements needs electrolyte, thereby reducing the risk of ion conduction bridge breakage at the negative electrode interface in the later cycle due to insufficient electrolyte, and the electrolyte cannot be timely supplemented after the SEI film is damaged due to the cycle expansion of silicon particles, the SEI film cannot be regenerated, and further lithium precipitation or cycle diving. The cycle performance of the secondary battery is improved. The specific technical solutions are as follows:

[0008] The first aspect of the present application provides a secondary battery, the secondary battery comprising an electrode assembly, the electrode assembly comprising a pole piece and a first separator, the pole piece comprising a positive pole piece and a negative pole piece, the negative pole piece comprising a negative pole material layer, the negative pole material layer comprising a silicon element, a mass percentage content of the silicon element being W based on a mass of the negative pole material layer, W≥3%. The first separator comprises a base film, a first ceramic layer and a second ceramic layer, the base film comprising a first surface and a second surface along a thickness direction of the first separator, the first surface facing the negative pole piece, the second surface facing the positive pole piece, the first ceramic layer being arranged on the first surface, and the second ceramic layer being arranged on the second surface. A thickness of the first ceramic layer is T1 μm, a thickness of the second ceramic layer is T2 μm, and T1>T2. In the secondary battery containing the silicon element, the ceramic layers on both sides of the separator in the secondary battery are of different thicknesses, so that the ceramic layer on the side of the separator facing the negative pole has a larger thickness, at this time, the ceramic layer with a larger thickness has more inter-particle gaps, the side of the separator facing the negative pole can absorb more electrolyte, and the liquid storage capacity of the side of the separator facing the negative pole is improved, so that the electrolyte can be supplied in time when the negative pole piece containing the silicon element needs electrolyte, the risk of the negative pole interface deterioration caused by insufficient electrolyte is reduced, the risk of the electrolyte being unable to be supplemented in time after the SEI film is destroyed due to the cycle expansion of the silicon particles, and the SEI film being unable to be regenerated, and the risk of lithium precipitation and even cycle diving are reduced, and the cycle performance of the secondary battery is improved.

[0009] In some embodiments of the present application, 3%≤W≤80%. By adjusting the value of W within the above range, the effect of reducing the risk of negative pole interface deterioration caused by insufficient electrolyte is more obvious, and the cycle performance of the secondary battery is further improved.

[0010] In some embodiments of the present application, 1≤T1 / T2≤20, and 0.5≤T1≤5. By adjusting the values of T1 / T2 and T1 within the above range, the mechanical strength of the first separator is considered, the risk of negative pole interface deterioration caused by insufficient electrolyte is reduced, and the cycle performance of the secondary battery is improved.

[0011] In some embodiments of the present application, 0.5T1 / T2≤0.2W×100+0.6≤1.6T1 / T2. By adjusting the value of 0.2W×100+0.6 within the above range, the energy density of the secondary battery is considered, the risk of negative pole interface deterioration caused by insufficient electrolyte is reduced, and the cycle performance of the secondary battery is improved.

[0012] In some embodiments of the present application, 3%≤W≤10%, 1

[0013] In some embodiments of the present application, 10%<W≤30%, 2.5

[0014] In some embodiments of the present application, 30%<W≤80%, 5

[0015] In some embodiments of the present application, the first ceramic layer comprises first ceramic particles, and the second ceramic layer comprises second ceramic particles, and the first ceramic particles and the second ceramic particles are each independently selected from at least one of alumina, magnesia, aluminum hydroxide, magnesium hydroxide, or boehmite. The mass percentage content of the first ceramic particles is 50% to 95% based on the mass of the first ceramic layer, and the mass percentage content of the second ceramic particles is 50% to 95% based on the mass of the second ceramic layer. By selecting the first ceramic particles and the second ceramic particles of the above-mentioned types and regulating the mass percentage content W1 of the first ceramic particles and the mass percentage content W2 of the second ceramic particles within the above-mentioned ranges, the first ceramic layer and the second ceramic layer have good liquid retention capacity and mechanical strength, the risk of deterioration of the negative electrode interface due to insufficient electrolyte is reduced, and the cycle performance of the secondary battery is improved while the safety performance of the secondary battery is taken into account.

[0016] In some embodiments of the present application, the first separator further comprises a first adhesive layer and a second adhesive layer, the first adhesive layer and the first ceramic layer are sequentially stacked on the first surface, and the first ceramic layer is located between the first adhesive layer and the base film; the second adhesive layer and the second ceramic layer are sequentially stacked on the second surface, and the second ceramic layer is located between the second adhesive layer and the base film. The first adhesive layer comprises a first adhesive, and the second adhesive layer comprises a second adhesive, each of the first adhesive and the second adhesive is independently selected from at least one of a styrene-butadiene latex, a styrene-acrylate latex, polymethyl methacrylate, polybutyl methacrylate, polyethyl acrylate, polyvinyl alcohol, ethylene-vinyl acetate copolymer, polyvinyl acetate, polyurethane, polyvinylidene fluoride, or a copolymer of vinylidene fluoride and hexafluoropropylene. By setting the first adhesive layer and the second adhesive layer, and selecting the first adhesive and the second adhesive of the above types, better interface adhesion of the electrode sheet is achieved while the cycle performance is taken into account, thereby improving the safety performance of the secondary battery.

[0017] In some embodiments of the present application, the peeling strength between the first adhesive layer and the negative electrode sheet is 3 N / m to 20 N / m, and the peeling strength between the second adhesive layer and the positive electrode sheet is 5 N / m to 22 N / m. By adjusting the peeling strength F1 between the first adhesive layer and the negative electrode sheet and the peeling strength F2 between the second adhesive layer and the positive electrode sheet within the above range, the first separator has stronger adhesion with the positive electrode sheet than with the negative electrode sheet, thereby strengthening the interface between the first separator and the positive electrode sheet and the interface between the first separator and the negative electrode sheet, facilitating the transmission of lithium ions during the cycle process, and reducing the possibility of the first ceramic layer and / or the second ceramic layer falling off from the base film, thereby further improving the safety performance and cycle performance of the secondary battery.

[0018] In some embodiments of the present application, the electrode assembly is a stacked structure. In some embodiments of the present application, the electrode assembly further comprises a second separator, and the electrode sheet comprises two outer electrode sheets and a plurality of inner electrode sheets, the two outer electrode sheets are located at the outermost two sides of the electrode assembly, the first separator is arranged at least between the outer electrode sheet and the inner electrode sheet adjacent to the outer electrode sheet, and the second separator is arranged between two adjacent inner electrode sheets. In some embodiments of the present application, the number of layers of the first separator is m, and the total number of layers of the first separator and the second separator is n, and 1 / 5≤m / n≤1. By the above arrangement, the risk of lithium precipitation caused by the deterioration of the negative electrode interface due to insufficient electrolyte is reduced, the cycle performance of the secondary battery is improved, the operation difficulty and processing cost in the actual production process are taken into account, and the energy density of the secondary battery is further improved.

[0019] In some embodiments of the present application, the first diaphragm is folded in a Z-shaped structure in the electrode assembly, and the Z-shaped first diaphragm separates the adjacent positive electrode sheet and the negative electrode sheet. Through the above arrangement, the stability of the electrode assembly sheet structure is further improved, and the safety performance of the secondary battery is further improved while improving the cycle performance of the secondary battery.

[0020] The second aspect of the present application provides an electronic device comprising the secondary battery in any of the foregoing embodiments. The secondary battery of the present application has good cycle performance, and therefore the electronic device of the present application has a longer service life.

[0021] The beneficial effects of the embodiments of the present application are as follows:

[0022] The present application provides a secondary battery and an electronic device. In the secondary battery containing silicon elements, the ceramic layers on the two sides of the diaphragm facing the positive and negative electrodes in the secondary battery are of different thicknesses, and the ceramic layer on the negative electrode side of the diaphragm has a larger thickness. At this time, the ceramic layer with a larger thickness has more inter-particle gaps, and the diaphragm facing the negative electrode can absorb more electrolyte, thereby improving the liquid storage capacity of the diaphragm facing the negative electrode. When the negative electrode sheet containing silicon elements needs electrolyte, it can be supplied in time, reducing the risk of broken bridge of ion conduction at the negative electrode interface in the later stage of the cycle due to insufficient electrolyte, and the electrolyte cannot be supplemented in time after the SEI film is destroyed by the cycle expansion of silicon particles, and the SEI film cannot be regenerated, thereby causing lithium precipitation and even cycle diving, thereby improving the cycle performance of the secondary battery. BRIEF DESCRIPTION OF DRAWINGS

[0023] The accompanying drawings, which are included to provide a further understanding of the present application, form a part of the present application and illustrate the illustrative embodiments of the present application and its description, which serve to explain the present application, and do not constitute an improper limitation on the present application.

[0024] FIG. 1 is a partial cross-sectional structure schematic view of the electrode assembly along the thickness direction of the electrode assembly in an embodiment of the present application;

[0025] FIG. 2 is a partial cross-sectional structure schematic view of the electrode assembly along the thickness direction of the electrode assembly in another embodiment of the present application;

[0026] FIG. 3 is a cross-sectional structure schematic view of the secondary battery along the length direction of the secondary battery in another embodiment of the present application;

[0027] FIG. 4 is a cross-sectional structure schematic view of the secondary battery along the length direction of the secondary battery in another embodiment of the present application.

[0028] Reference signs: secondary battery 001; electrode assembly 01; case 02; electrode sheet 10; first separator 20; base film 201; first ceramic layer 202; second ceramic layer 203; first adhesive layer 204; second adhesive layer 205; positive electrode sheet 11; positive electrode current collector 111; positive electrode material layer 112; negative electrode sheet 12; negative electrode current collector 121; negative electrode material layer 122; second separator 21; outer electrode sheet 101; inner electrode sheet 102. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of the present application clearer, the present application will be described in further detail below with reference to the drawings and embodiments. Obviously, the described embodiments are only a 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.

[0030] It should be noted that in the specific embodiments of the present application, lithium ion batteries are taken as examples of secondary batteries to explain the present application, but the secondary batteries of the present application are not limited to lithium ion batteries. The specific technical solutions are as follows:

[0031] The first aspect of the present application provides a secondary battery, the secondary battery comprising an electrode assembly, the electrode assembly comprising an electrode sheet and a first separator, the electrode sheet comprising a positive electrode sheet and a negative electrode sheet, the negative electrode sheet comprising a negative electrode material layer, the negative electrode material layer comprising a silicon element, a mass percentage content of the silicon element being W based on a mass of the negative electrode material layer, and W≥3%. The first separator comprises a base film, a first ceramic layer, and a second ceramic layer, the base film comprising a first surface and a second surface along a thickness direction of the first separator, the first surface facing the negative electrode sheet, and the second surface facing the positive electrode sheet, the first ceramic layer being arranged on the first surface, and the second ceramic layer being arranged on the second surface. A thickness of the first ceramic layer is T1 μm, a thickness of the second ceramic layer is T2 μm, and T1>T2.

[0032] In the present application, the length direction of the electrode assembly in the unfolded state is defined as the X direction, the width direction is defined as the Y direction, and the thickness direction is defined as the Z direction. It can be understood that the length direction, the width direction and the thickness direction of the negative electrode sheet, the positive electrode sheet and the separator in the unfolded state are the same as those of the electrode assembly. Exemplarily, as shown in FIG. 1, the electrode assembly 01 includes a sheet 10 and a first separator 20, the sheet 10 includes a positive electrode sheet 11 and a negative electrode sheet 12, and the negative electrode sheet 12 includes a negative electrode material layer 122. The first separator 20 includes a base film 201, a first ceramic layer 202 and a second ceramic layer 203. In the thickness direction Z of the first separator 20, the base film 201 includes a first surface (not shown in the figure) and a second surface (not shown in the figure), the first surface faces the negative electrode sheet 12, the second surface faces the positive electrode sheet 11, the first ceramic layer 202 is arranged on the first surface, and the second ceramic layer 203 is arranged on the second surface.

[0033] The inventors have found that the ceramic layer of the separator in the prior art is generally designed to be left-right symmetrical, at this time the thickness of the two ceramic layers on the two surfaces of the separator is equal, or only the surface of the separator facing the positive electrode has a ceramic layer, at this time the liquid storage capacity of the surface of the separator facing the negative electrode is poor, and when the negative electrode sheet contains silicon elements, the demand for electrolyte during the cycle of the secondary battery is higher than that of the conventional graphite, and in the later cycle, the interface ion conduction is easily broken due to the lack of electrolyte, and the SEI film of the silicon particles is damaged and cannot be regenerated in time after the cycle expansion, thereby causing lithium precipitation and even cycle diving, affecting the cycle life of the secondary battery and reducing the cycle performance of the secondary battery. In addition, when the two surfaces of the separator in the electrode assembly are coated with a high-thickness ceramic layer, the thickness of the separator is large at this time, which reduces the energy density of the secondary battery; in addition, the separator stores too much electrolyte, and the excess electrolyte in the shell is stored in the form of free state and cannot be supplied and transmitted to the silicon-based material of the negative electrode sheet in time, the excess free electrolyte increases the sliding property between the layers of the electrode assembly, affects the drop performance and safety performance of the secondary battery, and when the excess electrolyte is too much, the secondary battery swells, and the shell may bulge, deform or crack. In the secondary battery containing silicon elements, the present application uses different thickness ceramic layers on the two sides of the separator facing the positive and negative electrodes of the secondary battery, so that the thickness of the ceramic layer on the side of the separator facing the negative electrode is larger, at this time the ceramic layer with larger thickness has more particle gaps, the side of the separator facing the negative electrode can absorb more electrolyte, and the liquid storage capacity of the side of the separator facing the negative electrode is improved, which can supply the electrolyte in time when the negative electrode sheet containing silicon elements needs electrolyte, reduces the risk of breaking the interface ion conduction of the negative electrode in the later cycle due to the lack of electrolyte, and the electrolyte cannot be replenished in time after the SEI film of the silicon particles is damaged by the cycle expansion, and the SEI film cannot be regenerated, thereby causing lithium precipitation and even cycle diving, while taking into account the drop performance and safety performance, the cycle performance of the secondary battery is improved.

[0034] In some embodiments of the present application, 3%≤W≤80%. For example, the value of W can be 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, 52%, 55%, 58%, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, or a range between any two of them. By adjusting the value of W within the above range, the structural stability of the negative electrode sheet during charging and discharging is taken into account, and at the same time, the energy density of the secondary battery is improved. At the same time, the first separator in the secondary battery of the present application can absorb more electrolyte on the side facing the negative electrode, improving the liquid storage capacity of the separator on the side facing the negative electrode, and can supply electrolyte in time when the negative electrode sheet containing silicon elements needs electrolyte. With the increase of the mass percentage of silicon elements, the demand of the negative electrode sheet for electrolyte increases accordingly, therefore, the effect of reducing the risk of broken bridge of ion conduction at the negative electrode interface in the later stage of cycling due to insufficient electrolyte, and the destruction of SEI film after the cyclic expansion of silicon particles, the electrolyte cannot be supplemented in time, and the SEI film cannot be regenerated, thereby leading to lithium precipitation and even cycle diving, is more obvious, further improving the cycle performance of the secondary battery.

[0035] In some embodiments of the present application, 1

[0036] In an embodiment of the present application, 0.025≤T2<5. For example, the value of T2may be 0.025, 0.028, 0.03, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, 0.8, 1, 1.2, 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, 3.2, 3.5, 3.8, 4, 4.2, 4.5, 4.8, 4.9, or a range between any two of them. By regulating the value of T2within the above range, the liquid storage capacity of the first separator facing the negative electrode side is improved, while the liquid storage capacity of the first separator facing the positive electrode side is also considered. When the electrolyte is needed by the positive and negative electrode sheets, it can be supplied in time, reducing the risk of broken ion conduction bridge at the interface of the electrode sheet in the later stage of the cycle due to insufficient electrolyte, and the SEI film being damaged after the cyclic expansion of silicon particles, so that the electrolyte cannot be replenished in time and the SEI film cannot be regenerated, thereby causing lithium precipitation and even cycle diving, improving the cycle performance of the secondary battery.

[0037] In some embodiments of the present application, 0.5T1 / T2≤0.2W×100+0.6≤1.6T1 / T2. For example, the value of (0.2W×100+0.6) / T1 / T2may be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, or a range between any two of them. When the content of silicon element in the negative electrode material layer is relatively high, the demand for electrolyte during the cycle process is correspondingly higher. By regulating the value of 0.2W×100+0.6 within the above range, the negative electrode sheet with different silicon element contents is matched with two ceramic layers with different thickness ratios, so that the content of silicon element and the different thicknesses between different ceramic layers synergize. While considering the mechanical strength of the first separator, the first separator facing the negative electrode side can absorb more electrolyte, improving the liquid storage capacity of the first separator facing the negative electrode side, and supplying the electrolyte in time when the negative electrode sheet containing silicon element needs it. While considering the energy density of the secondary battery, the risk of broken ion conduction bridge at the interface of the electrode sheet in the later stage of the cycle due to insufficient electrolyte, and the electrolyte being unable to be replenished in time after the SEI film is damaged by the cyclic expansion of silicon particles, so that the SEI film cannot be regenerated, thereby causing lithium precipitation and even cycle diving, is reduced, improving the cycle performance of the secondary battery.

[0038] In some embodiments of the present application, 3%≤W≤10%, 1 When 3%≤W≤10%, the value of T1 / T2 can be 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, or a range between any two of them; the value of T1 can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, or a range between any two of them. When 3%≤W≤10%, by regulating the values of T1 / T2 and T1 within the above ranges, the content of silicon element in the negative electrode material layer is relatively low, and the liquid retention capacity of the negative electrode plate is relatively good. The smaller T1 / T2 and T1 make the content of silicon element and the different thicknesses between different ceramic layers synergize, while taking into account the mechanical strength of the first separator, the first separator facing the negative electrode side can absorb more electrolyte, improving the liquid storage capacity of the separator facing the negative electrode side, and providing electrolyte in time when the negative electrode plate containing silicon element needs electrolyte. While taking into account the energy density of the secondary battery, the risk of ion conduction bridge interruption at the interface of the plate after cycling due to insufficient electrolyte, and the destruction of the SEI film after the cycle expansion of the silicon particles, the inability of the electrolyte to supplement in time, and the inability of the SEI film to regenerate, thereby leading to lithium precipitation and even cycle diving, is reduced, and the cycle performance of the secondary battery is improved.

[0039] In some embodiments of the present application, 10% < W≤30%, 2.5 < T1 / T2≤5, 1.5 < T1≤3. For example, when 10% < W≤30%, the value of T1 / T2 can be 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, or a range between any two of them; the value of T1 can be 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, or a range between any two of them. When 10% < W≤30%, by regulating the value of T1 / T2 and T1 within the above range, the content of silicon element in the negative electrode material layer is relatively high, and the demand for electrolyte during the cycle process is correspondingly higher, and the ratio of the thicknesses of different ceramic layers is correspondingly increased, and the thickness of the first ceramic layer is also correspondingly increased, so that the content of silicon element and the different thicknesses between different ceramic layers synergize, the first diaphragm facing the negative electrode side can absorb more electrolyte, further improving the liquid storage capacity of the diaphragm facing the negative electrode side, and can supply in time when the negative electrode sheet containing silicon element needs electrolyte. While taking into account the energy density of the secondary battery, the risk of ion conduction bridge interruption of the sheet interface in the later cycle due to insufficient electrolyte, and the electrolyte cannot be replenished in time after the SEI film is destroyed by the cycle expansion of silicon particles, and the SEI film cannot be regenerated, thereby leading to lithium precipitation and even cycle diving, and the cycle performance of the secondary battery is improved.

[0040] In some embodiments of the present application, 30% < W≤80%, 5 < T1 / T2≤20, 3 < T1≤5. For example, when 30% < W≤80%, the value of T1 / T2 can be 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, or a range between any two of them; the value of T1 can be 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, 4.1, 4.2, 4.3, 4.4, 4.5, 4.6, 4.7, 4.8, 4.9, 5, or a range between any two of them. When 30% < W≤80%, the values of T1 / T2 and T1 are regulated within the above ranges, at this time, the content of silicon element in the negative electrode material layer is high, the ratio of the thickness of the different ceramic layers is large, and the thickness of the first ceramic layer is large, so that the content of silicon element and the different thicknesses between the different ceramic layers synergize, at this time, the demand for electrolyte in the cycle process can be better met, the first diaphragm facing the negative electrode side can absorb more electrolyte, further improving the liquid storage capacity of the diaphragm facing the negative electrode side, and the electrolyte can be supplied in time when the negative electrode sheet containing silicon element needs electrolyte. While taking into account the energy density of the secondary battery, the risk of ion conduction bridge breakage at the interface of the sheet in the later cycle due to insufficient electrolyte, and the inability of the electrolyte to be replenished in time after the SEI film is destroyed by the cycle expansion of the silicon particles, and the inability of the SEI film to be regenerated, thereby leading to lithium precipitation and even cycle diving, is reduced, and the cycle performance of the secondary battery is improved.

[0041] In the present application, the thickness of the first ceramic layer and the thickness of the second ceramic layer can be regulated by means known to those skilled in the art, for example, when the first ceramic layer slurry is coated on the first surface of the base film, the coating amount of the first ceramic layer slurry is increased to increase the thickness of the first ceramic layer on the basis of a certain solid content of the first ceramic layer slurry; when the second ceramic layer slurry is coated on the second surface of the base film, the coating amount of the second ceramic layer slurry is increased to increase the thickness of the second ceramic layer on the basis of a certain solid content of the second ceramic layer slurry, and the present application does not make special limitations as long as the purpose of the present application can be achieved.

[0042] In some embodiments of the present application, the first ceramic layer comprises first ceramic particles, the second ceramic layer comprises second ceramic particles, and the first ceramic particles, the second ceramic particles are each independently selected from at least one of alumina, magnesia, aluminum hydroxide, magnesium hydroxide, or boehmite. The mass percentage content W1 of the first ceramic particles is 50% to 95% based on the mass of the first ceramic layer; for example, the mass percentage content W1 of the first ceramic particles can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or a range formed by any two of them. The mass percentage content W2 of the second ceramic particles is 50% to 95% based on the mass of the second ceramic layer; for example, the mass percentage content W2 of the second ceramic particles can be 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or a range formed by any two of them. By selecting the above types of first ceramic particles and second ceramic particles, and adjusting the mass percentage content W1 of the first ceramic particles and the mass percentage content W2 of the second ceramic particles within the above range, the first ceramic layer and the second ceramic layer have good liquid retention capacity and mechanical strength, the separator can absorb more electrolyte, reducing the risk of interface ion conduction broken bridge in the later stage of the cycle due to insufficient electrolyte, and the electrolyte cannot be supplemented in time after the SEI film is damaged by the cycle expansion of silicon particles, and the SEI film cannot be regenerated, thereby causing lithium precipitation and even cycle diving. While improving the cycle performance of the secondary battery, the safety performance of the secondary battery is also considered.

[0043] In some embodiments of the present application, the first separator further comprises a first adhesive layer and a second adhesive layer, the first adhesive layer and the first ceramic layer are sequentially stacked on the first surface, and the second adhesive layer and the second ceramic layer are sequentially stacked on the second surface. For example, as shown in FIG. 2, the first separator 20 further comprises a first adhesive layer 204 and a second adhesive layer 205, the first adhesive layer 204 and the first ceramic layer 202 are sequentially stacked on the surface of the base film 201 facing the negative electrode tab 12, and the first ceramic layer 202 is located between the first adhesive layer 204 and the base film 201; the second adhesive layer 205 and the second ceramic layer 203 are sequentially stacked on the surface of the base film 201 facing the positive electrode tab 11, and the second ceramic layer 203 is located between the second adhesive layer 205 and the base film 201. The first adhesive layer comprises a first adhesive, and the second adhesive layer comprises a second adhesive, the first adhesive and the second adhesive are each independently selected from at least one of a styrene-butadiene latex, a styrene-acrylate latex, polymethyl methacrylate, polybutyl methacrylate, polyethyl acrylate, polyvinyl alcohol, ethylene-vinyl acetate copolymer, polyvinyl acetate, polyurethane, polyvinylidene fluoride, or a copolymer of vinylidene fluoride and hexafluoropropylene. By arranging the first adhesive layer and the second adhesive layer and selecting the first adhesive and the second adhesive of the above types, the adhesion between the first separator and the positive electrode tab and the adhesion between the first separator and the negative electrode tab can be improved, the interface between the first separator and the positive electrode tab and the interface between the first separator and the negative electrode tab can be strengthened, the transmission of lithium ions can be facilitated, and the possibility of the first ceramic layer and the second ceramic layer falling off can be reduced. When the first separator is applied to a secondary battery, the cycle performance is considered, the tab interface adhesion is better, and the safety performance of the secondary battery is improved.

[0044] In some embodiments of the present application, the peeling strength F1 between the first adhesive layer and the negative electrode sheet is 3 N / m to 20 N / m, and the peeling strength F2 between the second adhesive layer and the positive electrode sheet is 5 N / m to 22 N / m. For example, the peeling strength F1 between the first adhesive layer and the negative electrode sheet can be 3 N / m, 4 N / m, 5 N / m, 6 N / m, 7 N / m, 8 N / m, 9 N / m, 10 N / m, 11 N / m, 12 N / m, 13 N / m, 14 N / m, 15 N / m, 16 N / m, 17 N / m, 18 N / m, 19 N / m, 20 N / m, or a range formed by any two of them; the peeling strength F2 between the second adhesive layer and the positive electrode sheet can be 5 N / m, 6 N / m, 7 N / m, 8 N / m, 9 N / m, 10 N / m, 11 N / m, 12 N / m, 13 N / m, 14 N / m, 15 N / m, 16 N / m, 17 N / m, 18 N / m, 19 N / m, 20 N / m, 21 N / m, 22 N / m, or a range formed by any two of them. By adjusting the peeling strength F1 between the first adhesive layer and the negative electrode sheet and the peeling strength F2 between the second adhesive layer and the positive electrode sheet within the above range, the thickness of the first ceramic layer is greater than that of the second ceramic layer, the first ceramic layer still has more inter-particle gaps, and the first separator has a stronger adhesion with the positive electrode sheet than with the negative electrode sheet, thereby strengthening the interface between the first separator and the positive electrode sheet and the first separator and the negative electrode sheet, facilitating the transmission of lithium ions during the cycle process, and reducing the possibility of the first ceramic layer and / or the second ceramic layer falling off from the base film, thereby further improving the safety performance and cycle performance of the secondary battery.

[0045] In the present application, the peeling strength between the adhesive layer and the electrode sheet is not particularly limited as long as the purpose of the present application can be achieved. For example, the peeling strength between the adhesive layer and the electrode sheet can be adjusted by selecting different types of adhesives, adjusting the coating weight of the adhesive layer, or adjusting the mass percentage of the adhesive in the adhesive layer.

[0046] In some embodiments of the present application, the electrode assembly is a laminated structure. When the electrode assembly is the above structure, since the laminated structure has no interface corner area, the positive and negative electrode plates are uniformly distributed, which is conducive to reducing the excessive corner stress caused by the volume expansion of the negative electrode plate containing silicon elements in the electrode assembly of the winding structure, and thus the overall structure of the electrode assembly is deformed or even the risk of internal tearing of the electrode plate. The first ceramic layer on the side of the first separator facing the negative electrode has a larger thickness, and the side of the first separator facing the negative electrode can absorb more electrolyte, thereby improving the liquid storage capacity of the side of the first separator facing the negative electrode, and when the negative electrode plate containing silicon elements needs electrolyte, it can be supplied in time, thereby reducing the risk of ion conduction bridge breakage at the negative electrode interface in the later stage of the cycle due to insufficient electrolyte, and the electrolyte cannot be supplemented in time after the SEI film is destroyed by the cyclic expansion of silicon particles, the SEI film cannot be regenerated, and thus lithium precipitation and even cycle diving are caused, thereby improving the cycle performance of the secondary battery.

[0047] In some embodiments of the present application, the electrode assembly further comprises a second separator, the electrode plate comprises two outer electrode plates and a plurality of inner electrode plates, the two outer electrode plates are respectively located at the outermost two sides of the electrode assembly, the first separator is arranged at least between the outer electrode plate and the inner electrode plate adjacent to the outer electrode plate, and the second separator is arranged between two adjacent inner electrode plates. For example, as shown in FIG. 3, the electrode assembly 01 further comprises a second separator 21, the electrode plate 10 comprises two outer electrode plates 101 and inner electrode plates 102, the two outer electrode plates 101 are respectively located at the outermost two sides of the electrode assembly 01, the first separator 20 is arranged between the outer electrode plate 101 and the inner electrode plate 102 adjacent to the outer electrode plate 101, and the second separator is arranged between two adjacent inner electrode plates 102. In a conventional laminated electrode assembly, the outer electrode plate has small resistance, large current density, and greater ability to consume and transport electrolyte than the inner electrode plate. Through the above arrangement, while improving the liquid storage capacity of the side of the first separator facing the negative electrode and supplying electrolyte in time when the negative electrode plate containing silicon elements needs electrolyte, the liquid storage capacity of the outer side of the electrode assembly is also improved, thereby reducing the risk of lithium precipitation of the outer electrode plate due to insufficient electrolyte of the outer side of the electrode assembly during the cycle process, and the risk of lithium precipitation and even cycle diving caused by ion conduction bridge breakage at the negative electrode interface in the later stage of the cycle due to insufficient electrolyte, and the electrolyte cannot be supplemented in time after the SEI film is destroyed by the cyclic expansion of silicon particles, the SEI film cannot be regenerated, thereby improving the cycle performance of the secondary battery.

[0048] In some embodiments of the present application, the number of layers of the first separator is m, the total number of layers of the first separator and the second separator is n, and 1 / 5≤m / n≤1. For example, the value of m / n can be 1 / 5, 3 / 10, 2 / 5, 1 / 2, 3 / 5, 7 / 10, 4 / 5, 9 / 10, 1, or a range between any two of the values. By adjusting the value of m / n within the above range, the risk of the electrolyte being unable to supplement in time after the ion conduction bridge of the negative electrode interface is broken due to insufficient electrolyte in the later stage of the cycle, and the SEI film is destroyed by the cycle expansion of the silicon particles, and the SEI film cannot be regenerated, thereby causing lithium precipitation and even cycle diving, is reduced, the cycle performance of the secondary battery is improved, the operation difficulty and processing cost in the actual production process are taken into account, and the energy density of the secondary battery is further improved.

[0049] The second separator of the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the second separator includes a base film. Optionally, the second separator can further include a third ceramic layer, which can be disposed on one surface of the base film or on both surfaces of the base film. The second separator can also be selected from commercially available separators. For example, the second separator can be selected from a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film, etc.

[0050] In some embodiments of the present application, the first separator is in a Z-shaped folded structure in the electrode assembly, and the Z-shaped first separator separates the adjacent positive electrode sheet and the negative electrode sheet. For example, as shown in FIG. 4, the first separator 20 is in a Z-shaped folded structure in the electrode assembly 01, and the Z-shaped first separator 20 separates the adjacent positive electrode sheet 11 and the negative electrode sheet 12. Through the above arrangement, the stability of the electrode assembly sheet structure is further improved, the operation difficulty and processing cost in the actual production process are taken into account, and the sheeting efficiency is higher.

[0051] The material of the base film of the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the material of the base film can include at least one of polyimide, polyamide, polysulfone, polyacrylonitrile, cellulose, polyether ether ketone, polyphenylene sulfide, polyacrylate, polyethylene terephthalate, poly-p-phenylene terephthalamide, polyarylether sulfone ketone, aramid, arnosulfone, or polyolefin, and the polymerized monomer of the polyolefin includes at least one of ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 4-methyl-1-pentene, cyclobutene, cyclopentene, or cyclohexene. In the present application, commercially available base films of desired materials can be selected. The present application is not particularly limited as long as the purpose of the present application can be achieved.

[0052] In an embodiment of the present application, the negative electrode material layer comprises a negative electrode active material, and the negative electrode active material comprises a silicon-based material, and the silicon-based material comprises at least one of a silicon-carbon composite material, a silicon-oxygen composite material, or a pure silicon material. By selecting the above-mentioned silicon-based material, the energy density of the secondary battery is improved while the cycle performance of the secondary battery is taken into account.

[0053] In an embodiment of the present application, the negative electrode active material further comprises at least one of artificial graphite, natural graphite, hard carbon, or MCMB mesophase carbon microbeads. By selecting the above-mentioned negative electrode active material, the structural stability of the negative electrode sheet is improved, so that the volume expansion of the negative electrode sheet in the charging and discharging process is moderate.

[0054] In an embodiment of the present application, the first ceramic layer further comprises a first ceramic layer binder, and the second ceramic layer further comprises a second ceramic layer binder. The present application does not have a particular limitation on the type of the first ceramic layer binder and the second ceramic layer binder, as long as the purpose of the present application can be achieved. For example, the first ceramic layer binder and the second ceramic layer binder are each independently selected from at least one of styrene-butadiene rubber, polyvinyl alcohol, polyvinylidene fluoride, polyacrylic acid, polymethyl methacrylate, polybutyl acrylate, or polyacrylonitrile. In an embodiment of the present application, the mass percentage content of the first ceramic layer binder is 5% to 50% based on the mass of the first ceramic layer; and / or, the mass percentage content of the second ceramic layer binder is 5% to 50% based on the mass of the second ceramic layer.

[0055] In an embodiment of the present application, the first bonding layer can further comprise a first thickening agent, and the second bonding layer can further comprise a second thickening agent. The application of the first thickening agent to the first bonding layer and the second thickening agent to the second bonding layer is beneficial to increase the stability of the first bonding layer slurry and the second bonding layer slurry, and prevent the sedimentation of the components in the first bonding layer slurry and the second bonding layer slurry. The present application does not have a particular limitation on the type of the first thickening agent and the second thickening agent, as long as the purpose of the present application can be achieved. For example, the first thickening agent and the second thickening agent are each independently selected from at least one of hydroxyethyl cellulose, methylhydroxyethyl cellulose, sodium carboxymethyl cellulose, polyacrylamide, or sodium alginate. The present application does not have a particular limitation on the content of the first thickening agent in the first bonding layer and the content of the second thickening agent in the second bonding layer, and a person skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved.

[0056] The preparation method of the first diaphragm is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the preparation method of the first diaphragm includes but is not limited to the following steps: (1) uniformly mixing the first ceramic particles and the first ceramic layer binder in the solvent to obtain a first ceramic layer slurry, and uniformly mixing the second ceramic particles and the second ceramic layer binder in the solvent to obtain a second ceramic layer slurry; (2) coating the first ceramic layer slurry on one surface of the base film, and after drying, forming a first ceramic coating layer on one surface of the base film; (3) coating the second ceramic layer slurry on the other surface of the base film, and after drying, forming a second ceramic coating layer on one surface of the first base film, i.e. obtaining the first diaphragm.

[0057] In another embodiment of the present application, the preparation method of the first diaphragm can include but is not limited to the following steps: (1) uniformly mixing the first ceramic particles and the first ceramic layer binder in the solvent to obtain a first ceramic layer slurry, and uniformly mixing the second ceramic particles and the second ceramic layer binder in the solvent to obtain a second ceramic layer slurry; (2) uniformly mixing the first binder and the first thickening agent to obtain a first adhesive layer slurry, and uniformly mixing the second binder and the second thickening agent to obtain a second adhesive layer slurry; (3) coating the first ceramic layer slurry on one surface of the base film, and after drying, forming a first ceramic layer on one surface of the base film, coating the first adhesive layer slurry on the surface of the first ceramic layer away from the base film, and after drying, obtaining a first ceramic coating layer and a first adhesive layer; (4) coating the second ceramic layer slurry on the other surface of the base film, and after drying, forming a second ceramic layer on one surface of the base film, coating the second adhesive layer slurry on the surface of the second ceramic layer away from the base film, and after drying, obtaining a second ceramic coating layer and a second adhesive layer, i.e. obtaining the first diaphragm.

[0058] The above-mentioned solvent is not limited in the present application, as long as the purpose of the present application can be achieved.

[0059] In the present application, the negative electrode sheet further includes a negative electrode current collector, and the negative electrode material layer is arranged on at least one surface of the negative electrode current collector. The "negative electrode material layer arranged on at least one surface of the negative electrode current collector" means that the negative electrode material layer can be arranged on one surface of the negative electrode current collector along the thickness direction of the negative electrode current collector, or can be arranged on two surfaces of the negative electrode current collector along the thickness direction of the negative electrode current collector. It should be noted that the "surface" here can be the entire area of the surface of the negative electrode current collector, or can be part of the area of the surface of the negative electrode current collector, which is not particularly limited in the present application, as long as the purpose of the present application can be achieved. As shown in FIG. 1, the negative electrode sheet 12 further includes a negative electrode current collector 121, and the negative electrode material layer 122 is arranged on two surfaces of the negative electrode current collector 121 along the thickness direction Z of the negative electrode current collector 121.

[0060] The negative current collector is not particularly limited in the present application, as long as the object of the present application can be achieved, for example, it can include a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a composite current collector, exemplarily, the composite current collector can be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, a titanium-copper composite current collector, or the like. In the present application, the thickness of the negative current collector and the negative material layer is not particularly limited, as long as the object of the present application can be achieved. Optionally, the negative material layer can further include a conductive agent and a negative binder. The type of the conductive agent in the negative material layer is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the conductive agent can include, but is not limited to, at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, a metal material, or a conductive polymer, and the conductive carbon black can include, but is not limited to, at least one of acetylene black or Ketjen black. The above-mentioned carbon nanotubes can include, but are not limited to, single-walled carbon nanotubes and / or multi-walled carbon nanotubes. The above-mentioned carbon fibers can include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or nanocarbon fibers. The above-mentioned metal material can include, but is not limited to, metal powder and / or metal fibers, and specifically, the metal can include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymer can include, but is not limited to, at least one of polyphenylene derivative, polyaniline, polythiophene, polyacetylene, or polypyrrole. The type of the negative binder in the negative material layer is not particularly limited in the present application, as long as the object of the present application can be achieved, for example, the negative binder can include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamide-imide, butadiene-styrene rubber, or polyvinylidene fluoride. Optionally, the negative material layer further includes a thickening agent, and the type of the thickening agent is not particularly limited in the present application, as long as the object of the present application can be achieved. For example, the thickening agent can include at least one of carboxymethyl cellulose or sodium carboxymethyl cellulose. The mass ratio of the negative active material, the conductive agent, the binder, and the thickening agent in the negative material layer is not particularly limited in the present application, and a person skilled in the art can select according to the actual needs, as long as the object of the present application can be achieved.

[0061] The positive electrode tab is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the positive electrode tab includes a positive electrode current collector and a positive electrode material layer disposed on at least one surface of the positive electrode current collector. The "positive electrode material layer disposed on at least one surface of the positive electrode current collector" means that the positive electrode material layer can be disposed on one surface of the positive electrode current collector in the thickness direction of the positive electrode current collector, or can be disposed on both surfaces of the positive electrode current collector in the thickness direction of the positive electrode current collector. It should be noted that the "surface" herein can be the entire area of the surface of the positive electrode current collector, or can be part of the area of the surface of the positive electrode current collector, which is not particularly limited in the present application, as long as the purpose of the present application can be achieved. As shown in FIG. 1, the positive electrode tab 11 includes a positive electrode current collector 111 and a positive electrode material layer 112 disposed on both surfaces of the positive electrode current collector 111 in the thickness direction Z of the positive electrode current collector 111.

[0062] The positive electrode current collector is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the positive electrode current collector can include an aluminum foil, an aluminum alloy foil, or a composite current collector (e.g., an aluminum-carbon composite current collector), etc. The positive electrode material layer of the present application includes a positive electrode active material, and the type of the positive electrode active material is not particularly limited in the present application, as long as the purpose of the present application can be achieved. For example, the positive electrode active material can include at least one of lithium nickel cobalt manganese oxide (LiNi 0.90 Co 0.05 Mn 0.05 O2(NCM955), NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based material, lithium cobaltate (LiCoO2), lithium manganate, lithium manganese iron phosphate, or lithium titanate, etc. In the present application, the positive electrode active material can also include a non-metallic element, for example, the non-metallic element includes at least one of fluorine, phosphorus, boron, chlorine, silicon, or sulfur. In the present application, the thickness of the positive electrode current collector and the positive electrode material layer is not particularly limited, as long as the purpose of the present application can be achieved. In the present application, the positive electrode material layer can also include a positive electrode binder and a conductive agent. The type of the positive electrode binder in the positive electrode material layer is not particularly limited in the present application, as long as the purpose of the present application can be achieved, for example, the positive electrode binder can be the same as the type of the negative electrode binder in the negative electrode material layer described above. The type of the conductive agent in the positive electrode material layer is not particularly limited in the present application, as long as the purpose of the present application can be achieved, for example, the conductive agent can be the same as the type of the conductive agent in the negative electrode material layer described above. The mass ratio of the positive electrode active material, the conductive agent, and the positive electrode binder in the positive electrode material layer is not particularly limited in the present application, which can be selected by a person skilled in the art according to actual needs, as long as the purpose of the present application can be achieved.

[0063] In the present application, the secondary battery further includes an electrolyte including a lithium salt and a non-aqueous solvent. The lithium salt is not particularly limited in the present application as long as the object of the present application is achieved. For example, the lithium salt can include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. The content of the lithium salt in the electrolyte is not particularly limited in the present application as long as the object of the present application is achieved. The non-aqueous solvent is not particularly limited in the present application as long as the object of the present application is achieved, for example, the non-aqueous solvent can include, but is not limited to, at least one of a carbonate compound, a carboxylic acid ester compound, an ether compound, or other organic solvents. The carbonate compound can include, but is not limited to, at least one of a chain carbonate compound, a cyclic carbonate compound, or a fluorinated carbonate compound. The chain carbonate compound can include, but is not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The cyclic carbonate can include, but is not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinyl ethylene carbonate (VEC). The fluorinated carbonate compound can include, but is not limited to, at least one of fluorinated ethylene carbonate (FEC), carbonic acid-1,2-difluoro ethylene ester, carbonic acid-1,1-difluoro ethylene ester, carbonic acid-1,1,2-trifluoro ethylene ester, carbonic acid-1,1,2,2-tetrafluoro ethylene ester, carbonic acid-1-fluoro-2-methyl ethylene ester, carbonic acid-1-fluoro-1-methyl ethylene ester, carbonic acid-1,2-difluoro-1-methyl ethylene ester, carbonic acid-1,1,2-trifluoro-2-methyl ethylene ester, or carbonic acid-trifluoromethyl ethylene ester. The carboxylic acid ester compound can include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valerolactone, or caprolactone. The ether compound can include, but is not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxy ethane, 1,2-diethoxy ethane, 1-ethoxy-1-methoxy ethane, 2-methyl tetrahydrofuran, or tetrahydrofuran. The other organic solvents can include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, methyl sulfolane, methyldicyclohexyl sulfoxide, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. The content of the non-aqueous solvent in the electrolyte is not particularly limited in the present application as long as the object of the present application is achieved.

[0064] Exemplarily, as shown in FIG. 3 and FIG. 4, the secondary battery 001 further comprises a housing 02 for accommodating the positive electrode sheet, the first separator or the first separator and the second separator, the negative electrode sheet, and the electrolyte, and other components known in the art of secondary batteries, which are not limited in the present application. The housing is not particularly limited in the present application, and can be a housing known in the art as long as the purpose of the present application can be achieved. For example, the housing can be a hard-shell housing or a flexible housing. The material of the hard-shell housing can be metal, and the type of metal is not limited in the present application, and a metal hard-shell housing known in the art can be used as long as the purpose of the present application can be achieved. The flexible housing can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0065] The secondary battery of the present application is not particularly limited, and can include any device that undergoes an electrochemical reaction. In some embodiments of the present application, the secondary battery can 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.

[0066] The preparation process of the secondary battery of the present application is well known to those skilled in the art, and the present application is not particularly limited, for example, the preparation process of the secondary battery can include, but is not limited to, the following steps: stacking the positive electrode sheet, the first separator, and the negative electrode sheet in order, and winding, folding, etc. as needed to obtain an electrode assembly with a winding structure, placing the electrode assembly into the housing, injecting the electrolyte into the housing and sealing, to obtain the secondary battery. Alternatively, the positive electrode sheet, the first separator or the first separator and the second separator, and the negative electrode sheet are stacked in order, and then the four corners of the entire stack structure are fixed with adhesive tape to obtain an electrode assembly with a stack structure, the electrode assembly is placed into the housing, the electrolyte is injected into the housing and sealed, to obtain the secondary battery. In addition, the overcurrent prevention element, the guide plate, etc. can also be placed in the housing as needed, so as to prevent the pressure inside the secondary battery from rising, overcharging and discharging.

[0067] The second aspect of the present application provides an electronic device comprising the secondary battery of any of the preceding embodiments. The secondary battery of the present application has good cycle performance, and therefore the electronic device of the present application has a longer service life.

[0068] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the art. For example, the electronic device can include, but is not limited to, a notebook computer, a pen input type computer, a mobile computer, an electronic book player, a portable telephone, a portable facsimile, a portable copying machine, a portable printer, a head-mounted stereo headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable audio recorder, a radio, a backup power supply, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a bicycle, a lighting appliance, a toy, a game machine, a timepiece, an electric tool, a flashlight, a camera, a household large storage battery, and a lithium ion capacitor.

[0069] Embodiment

[0070] Hereinafter, embodiments and comparative examples are cited 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 on a mass basis.

[0071] Test methods and apparatus:

[0072] Sampling method of the first separator:

[0073] The lithium ion battery in the measured example and comparative example was disassembled, and the first separator was taken out, soaked in dimethyl carbonate (DMC) for 20 min to remove electrolyte residues, and then the first separator was placed in an oven, dried at 60°C for 12 h to obtain a first separator sample. The ceramic layer on the surface of the separator facing the negative electrode tab was the first ceramic layer, and the ceramic layer on the surface of the separator facing the positive electrode tab was the second ceramic layer. If an adhesive layer was provided on the surface of the ceramic layer, the adhesive layer provided on the surface of the first ceramic layer was the first adhesive layer, and the adhesive layer provided on the surface of the second ceramic layer was the second adhesive layer.

[0074] Test of the mass percentage content of silicon element:

[0075] The lithium ion battery discharged at 0.5C to 3.0V was disassembled, and the negative electrode tab was taken out, soaked in dimethyl carbonate (DMC) for 20 min, and then rinsed with DMC and acetone in turn. Then the negative electrode tab was placed in an oven and baked at 80°C for 12 hours to obtain a negative electrode tab. The negative electrode tab was placed in a vacuum oven at 100°C for 24 hours, and 1 g of powder sample of the negative electrode material layer on the negative electrode tab was scraped off with a blade, and then the mass percentage content W of silicon element in the negative electrode material layer was tested using an inductively coupled plasma (ICP) analyzer.

[0076] Test of the thickness of the first ceramic layer and the thickness of the second ceramic layer:

[0077] The first separator was subjected to argon ion polishing to obtain a cross section of the first separator. The morphology of the cross section of the first separator along the thickness direction was observed by field emission scanning electron microscopy (Philips, model XL-30), and a scanning electron microscope photograph was taken. The thickness T1 of the first ceramic layer and the thickness T2 of the second ceramic layer were measured by scanning electron microscopy.

[0078] Test of the peeling strength F1 between the first adhesive layer and the negative electrode tab:

[0079] The peeling strength between the first adhesive layer of the first separator and the negative electrode tab was measured using the 180° peeling test standard. The lithium ion batteries in the measured examples and the comparative examples were disassembled, and the positive electrode tab was peeled off. The first separator and the negative electrode tab were soaked in dimethyl carbonate for 20 min to remove the electrolyte. Then, the first separator and the negative electrode tab were cut into samples of 42 mm x 74 mm. The first separator and the negative electrode tab were compounded, and hot pressing was performed using a hot press at a temperature of 85°C, a pressure of 2 MPa, and a time of 70 s. The compounded sample was cut into small strips of 20 mm x 70 mm to obtain test strips for the peeling strength F1. Double-sided tape (NITTO. NO5000NS) of 20 mm x 50 mm was attached to a steel plate, and then the test strips were attached to the double-sided tape with the test surface facing down. A paper tape of 20 mm x 70 mm was connected to one end of the test strip through the double-sided tape, and a small rod with a mass of 2 kg was pushed to roll on the test strip for 8 times to obtain a test sample. The test was performed using a tensile testing machine. The test sample was fixed on the test platform, the paper tape was folded upward by 180°, and was fixed by a clamp. Then, the tensile testing machine started to pull the paper tape at a speed of 50 mm / min, and the test was ended after the first separator and the negative electrode tab on the surface of the double-sided tape were separated. The test data were saved. The peeling strength F1 between the first adhesive layer of the first separator and the negative electrode tab was calculated according to the pulling force and the displacement of the stretching when the first separator and the negative electrode tab were separated, and the unit was N / m.

[0080] Test of the peeling strength F2 between the second adhesive layer and the positive electrode tab:

[0081] The peeling strength between the second adhesive layer of the first separator and the positive electrode tab was measured using the 180° peeling test standard. The lithium ion batteries in the measured examples and the comparative examples were disassembled, and the negative electrode tab was peeled off. The first separator and the positive electrode tab were soaked in dimethyl carbonate for 20 min to remove the electrolyte. Then, the first separator and the positive electrode tab were cut into samples of 42 mm x 74 mm. The first separator and the positive electrode tab were compounded, and hot pressing was performed using a hot press at a temperature of 85°C, a pressure of 2 MPa, and a time of 70 s. The compounded sample was cut into small strips of 20 mm x 70 mm to obtain test strips for the peeling strength F2. Then, the peeling strength F2 between the second adhesive layer of the first separator and the positive electrode tab was measured according to the process of the test of the peeling strength F1 between the first adhesive layer of the first separator and the negative electrode tab, and the unit was N / m.

[0082] Lithium precipitation performance test:

[0083] The lithium ion battery in the examples and comparative examples was placed in a thermostat at 10°C, and after 60 minutes, charged at 2C constant current to 4.45V, charged at 4.45V constant voltage to a current of 0.025C, and after standing for 5 minutes, discharged at 0.5C constant current to 2.75V, which was one cycle. After 100 cycles according to the above charging and discharging process, the lithium ion battery was charged at 2C constant current to 4.45V, charged at 4.45V constant voltage to a current of 0.025C, and after standing for 5 minutes, the lithium ion battery was disassembled, and the negative electrode sheet in the electrode assembly was taken out to observe the lithium precipitation state on the surface of the negative electrode sheet. The area of the negative electrode sheet surface without lithium precipitation was golden yellow, and the area of the lithium precipitation was gray white.

[0084] The judgment standard of the lithium precipitation degree of the lithium ion battery is as follows: the lithium precipitation area is 0% for no lithium precipitation, i.e. the lithium precipitation degree is none, the lithium precipitation area is greater than 0% and less than or equal to 2% for mild lithium precipitation, i.e. the lithium precipitation degree is mild, the lithium precipitation area is greater than 2% and less than or equal to 20% for moderate lithium precipitation, i.e. the lithium precipitation degree is moderate, and the lithium precipitation area is greater than 20% and less than or equal to 100% for severe lithium precipitation, i.e. the lithium precipitation degree is severe, wherein the percentage of the lithium precipitation area is calculated based on the total area of the negative electrode material layer of the negative electrode sheet.

[0085] Cycle performance test:

[0086] The lithium ion battery was placed in a constant temperature test box at 25°C, and after standing for 30 minutes, the lithium ion battery was brought to a constant temperature state at 25°C. Charged at 1C constant current to 4.45V, charged at 4.45V constant voltage to a current of 0.025C, and after standing for 5 minutes, discharged at 0.2C constant current to 2.75V, which was the first cycle. The initial discharge capacity C0 was recorded. The lithium ion battery was cycled according to the above process, and when the cycle reached 500 cycles (cls), the test was stopped, and the discharge capacity after 500 cycles (cls) was recorded as C1. The 500 cls capacity retention rate was calculated as an index for evaluating the cycle performance of the lithium ion battery. 500 cls capacity retention rate (%) = C1 / C0 x 100%.

[0087] The higher the 500 cls capacity retention rate, the better the cycle performance of the lithium ion battery.

[0088] Drop test:

[0089] The lithium ion battery in the examples and comparative examples was placed in a 25°C environment for 30 minutes, and then charged in the following steps: constant current charging to 4.45V at 0.5C, constant voltage charging to 0.025C, standing for 60min, and then testing the voltage of the lithium ion battery before the drop test; the lithium ion battery was loaded into a fixture and dropped freely from a distance of 1.5m from the ground in the following order: head-tail-head right corner-tail right corner-head left corner-tail left corner (angle: 45±15°), repeated for 6 rounds. After the drop test, the lithium ion battery was allowed to stand at room temperature for 24h, and the voltage of the lithium ion battery was measured and recorded. The appearance of the lithium ion battery was checked before and after the test and photographed. The drop test passed the judgment standard: voltage drop <30mV (20 lithium ion batteries were prepared for each example or comparative example and tested, and the number of lithium ion batteries that passed the test was X, and the test pass rate was X / 20x100%).

[0090] The higher the drop test pass rate, the better the drop performance of the lithium ion battery in the group.

[0091] Example 1-1

[0092] <Preparation of the first separator>

[0093] A polyethylene (PE) film with a thickness of 10μm was used as the base film, and the porosity of the first base film was 60%.

[0094] The first ceramic particles boehmite and the first ceramic layer binder polyvinylidene fluoride were mixed in a mass ratio of 85:15, and then deionized water was added. After mixing uniformly, the first ceramic layer slurry was obtained.

[0095] The second ceramic particles boehmite and the second ceramic layer binder polyvinylidene fluoride were mixed in a mass ratio of 85:15, and then deionized water was added. After mixing uniformly, the second ceramic layer slurry was obtained.

[0096] The first ceramic layer slurry was coated on one surface of the base film, and after drying at 60°C, the first ceramic layer was formed on one surface of the first base film; the second ceramic layer slurry was coated on the other surface of the base film, and after drying at 60°C, the second ceramic layer was formed on the other surface of the first base film, i.e., the first separator was prepared.

[0097] Wherein, the mass percentage content W1 of the first ceramic particles is 85% based on the mass of the first ceramic layer; the mass percentage content W2 of the second ceramic particles is 85% based on the mass of the second ceramic layer. The coating weight of the first ceramic layer is 1.5mg / 1540.25mm 2 , and the thickness T1 of the first ceramic layer is 3μm; the coating weight of the second ceramic layer is 0.3mg / 1540.25mm 2 , and the thickness T2 of the second ceramic layer is 0.6μm.

[0098] Preparation of the positive electrode sheet

[0099] The positive electrode active material lithium cobaltate, the conductive agent conductive carbon black and the positive electrode binder polyvinylidene fluoride were mixed in a mass ratio of 97:1.5:1.5, N-methyl pyrrolidone (NMP) was added as a solvent, and the mixture was stirred and mixed uniformly to prepare a positive electrode slurry with a solid content of 75wt%. The positive electrode slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 10μm, and dried at 110℃ to obtain a positive electrode sheet with a single-sided coated positive electrode material layer with a thickness of 55μm. The positive electrode slurry was coated on the other surface of the positive electrode current collector aluminum foil, and after drying, a positive electrode sheet with a total thickness of 120μm was obtained. The coated positive electrode sheet was cold-pressed and then cut into a specification of 70mm×40mm for use. The compaction density of the positive electrode material layer was 4.23g / cm 3 .

[0100] Preparation of the negative electrode sheet

[0101] The negative electrode active material artificial graphite, the silicon-carbon composite material SiC, the conductive agent carbon nanotube and the negative electrode binder polyacrylic acid were mixed in a mass ratio of 51.125:42.875:1:5, and then deionized water was added as a solvent. After stirring and mixing uniformly, a negative electrode slurry with a solid content of 35wt% was obtained. The negative electrode slurry was coated on one surface of a negative electrode current collector copper foil with a thickness of 10μm, and dried at 110℃ to obtain a negative electrode sheet with a negative electrode material layer coated with a thickness of 40μm. The negative electrode slurry was coated on the other surface of the negative electrode current collector copper foil, and after drying, a negative electrode sheet with a total thickness of 90μm was obtained. The coated negative electrode sheet was cold-pressed and then cut into a specification of 74mm×42mm for use. The compaction density of the negative electrode material layer was 1.5g / cm 3 , and the mass percentage of silicon element W was 30% based on the mass of the negative electrode material layer.

[0102] Preparation of the electrolyte

[0103] In a glove box filled with dry argon gas, propylene carbonate (PC), diethyl carbonate (DEC) and ethylene carbonate (EC) were mixed in a mass ratio of 1:1:1 to obtain a base solvent, and then lithium hexafluorophosphate (LiPF6) lithium salt was added to the above base solvent to dissolve and mix uniformly to obtain an electrolyte. The mass percentage of LiPF6 was 4.5% based on the mass of the electrolyte, and the balance was the base solvent.

[0104] Preparation of the lithium ion battery

[0105] The single-sided positive electrode sheet in the preparation of the positive electrode sheet is placed on the outermost side of the electrode assembly as the outermost electrode sheet of the electrode assembly. The remaining positive electrode sheets in the electrode assembly are all double-sided positive electrode sheets.

[0106] The outer positive electrode sheet, the first separator, the outer negative electrode sheet, the first separator, the second outer positive electrode sheet, the first separator, the inner negative electrode sheet, the first separator, the inner positive electrode sheet, the first separator, the inner negative electrode sheet, the first separator, the inner positive electrode sheet, the first separator, the inner negative electrode sheet, the first separator, the inner positive electrode sheet, the first separator, the inner negative electrode sheet, the first separator, the inner positive electrode sheet, the first separator, the inner negative electrode sheet, the first separator, the second outer positive electrode sheet, the first separator, the outer negative electrode sheet, the first separator, the outer positive electrode sheet are sequentially stacked in order, wherein the first separator is continuous and uninterrupted, and has a Z-shaped folding structure in the electrode assembly. Then the four corners of the entire stack structure are fixed with adhesive tape to obtain an electrode assembly with a stack structure. The electrode assembly is placed in an aluminum plastic film packaging bag and dried in a vacuum oven at 80°C for 12 hours to remove water. The above prepared electrolyte is injected, and the lithium ion battery is obtained after vacuum packaging, standing, formation, degassing, and edge cutting processes. The design potential interval of the lithium ion battery is 2.75V to 4.45V.

[0107] Examples 1-2 to 1-15

[0108] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as Example 1-1. When the thickness of the ceramic layer changes, the coating amount of the corresponding ceramic layer slurry is adjusted so that the thickness of the ceramic layer is as shown in Table 1; when the mass percentage of silicon element changes, the mass percentages of the conductive agent carbon nanotube and the negative electrode binder polyacrylic acid remain unchanged, and the mass ratio of artificial graphite and silicon carbon composite SiC is adjusted so that the mass percentage of silicon element is as shown in Table 1. In Example 1-7, Example 1-8 and Example 1-11, the silicon carbon composite SiC is replaced by pure silicon, the mass percentages of the conductive agent carbon nanotube and the negative electrode binder polyacrylic acid remain unchanged, and the mass ratio of artificial graphite and pure silicon is adjusted so that the mass percentage of silicon element is as shown in Table 1.

[0109] Example 1-16

[0110] Except for preparing the first separator according to the following steps, the rest is the same as Example 1-1.

[0111] A polyethylene (PE) film with a thickness of 10μm is used as the base film, and the porosity of the first base film is 60%.

[0112] The first ceramic particles boehmite and the first ceramic layer binder polyvinylidene fluoride are mixed in a mass ratio of 85:15, then solvent deionized water is added, and after uniform mixing, a first ceramic layer slurry is obtained.

[0113] The second ceramic particles boehmite and the second ceramic layer binder polyvinylidene fluoride are mixed in a mass ratio of 85:15, then solvent deionized water is added, and after uniform mixing, a second ceramic layer slurry is obtained.

[0114] The first binder styrene-butadiene emulsion and the first thickening agent sodium carboxymethyl cellulose are mixed in a mass ratio of 98.5:1.5, then solvent deionized water is added, and after uniform mixing, a first adhesive layer slurry is obtained.

[0115] The second binder styrene-butadiene emulsion and the second thickening agent sodium carboxymethyl cellulose are mixed in a mass ratio of 98.5:1.5, then solvent deionized water is added, and after uniform mixing, a second adhesive layer slurry is obtained.

[0116] The first ceramic layer slurry is coated on one surface of the base film, and after drying at 60°C, a first ceramic layer is formed on one surface of the first base film. The first adhesive layer slurry is coated on the surface of the first ceramic layer away from the base film, and after drying at 60°C, a first ceramic coating and a first adhesive layer are obtained. The second ceramic layer slurry is coated on the other surface of the base film, and after drying at 60°C, a second ceramic layer is formed on the other surface of the base film. The second adhesive layer slurry is coated on the surface of the second ceramic layer away from the base film, and after drying at 60°C, a second ceramic coating and a second adhesive layer are obtained, i.e. a first separator is prepared.

[0117] Wherein, the mass percentage content W1 of the first ceramic particles is 85% based on the mass of the first ceramic layer; the mass percentage content W2 of the second ceramic particles is 85% based on the mass of the second ceramic layer. The coating weight of the first ceramic layer is 1.5 mg / 15 40.25 mm 2 , the thickness T1 of the first ceramic layer is 3 μm; the coating weight of the second ceramic layer is 0.3 mg / 15 40.25 mm 2 , the thickness T2 of the second ceramic layer is 0.6 μm; the coating weight of the first adhesive layer is 0.25 mg / 15 40.25 mm 2 , the peeling strength between the first adhesive layer and the negative electrode sheet is 10 N / cm; the coating weight of the second adhesive layer is 0.25 mg / 15 40.25 mm 2 , the peeling strength between the second adhesive layer and the positive electrode sheet is 12 N / cm.

[0118] Examples 1-17 to Example 1-21

[0119] The rest was the same as Example 1-1 except that the relevant preparation parameters were adjusted according to Table 1. Among them, when the type of the binder was unchanged, and the peeling strength between the adhesive layer and the pole piece changed, the coating weight of the corresponding adhesive layer was adjusted so that the peeling strength between the adhesive layer and the pole piece was as shown in Table 1.

[0120] Example 2-1

[0121] The rest was the same as Example 1-1 except that the positive pole piece was cut into a specification of 70 mm x 800 mm in <Preparation of positive pole piece>, the negative pole piece was cut into a specification of 74 mm x 824 mm in <Preparation of negative pole piece>, and the lithium ion battery was prepared according to the following steps.

[0122] <Preparation of lithium ion battery>

[0123] The first separator, the negative pole piece, the first separator, and the positive pole piece prepared above were sequentially stacked in order, ensuring that the first ceramic layer of the first separator faced the negative pole piece, and the second ceramic layer of the first separator faced the positive pole piece, and then wound to obtain an electrode assembly. The electrode assembly was placed in an aluminum plastic film packaging bag, dried, and then injected with the electrolyte prepared above, and then subjected to vacuum packaging, standing, formation, degassing, edge cutting, and other processes to obtain a lithium ion battery.

[0124] Example 2-2

[0125] The rest was the same as Example 1-1 except that the lithium ion battery and the second separator were prepared according to the following steps.

[0126] <Preparation of second separator>

[0127] A polyethylene (PE) film with a thickness of 10 μm was used as the base film, and the porosity of the base film was 60%.

[0128] The ceramic particles boehmite and the ceramic layer binder polyvinylidene fluoride were mixed in a mass ratio of 85:15, and then deionized water was added. After uniform mixing, a third ceramic layer slurry was obtained.

[0129] The third ceramic layer slurry was coated on one surface of the base film, and after drying at 60°C, a third ceramic layer was formed on one surface of the base film; the above operation was repeated on the other surface of the base film, and thus the second separator was prepared.

[0130] Among them, based on the mass of the first ceramic layer, the mass percentage of the ceramic particles was 85%; the coating weight of the ceramic layer was 0.3 mg / 1540.25 mm 2 , and the thickness of the ceramic layer was 0.6 μm.

[0131] <Preparation of lithium ion battery>

[0132] The single-sided positive electrode sheet in the preparation of positive electrode sheet is placed on the outermost side of the electrode assembly as the outermost positive electrode sheet of the electrode assembly. The remaining positive electrode sheets in the electrode assembly are all double-sided positive electrode sheets.

[0133] The outer positive electrode sheet, the first separator, the outer negative electrode sheet, the first separator, the second outer positive electrode sheet, the second separator, the inner negative electrode sheet, the second separator, the inner positive electrode sheet, the second separator, the inner negative electrode sheet, the second separator, the inner positive electrode sheet, the second separator, the inner negative electrode sheet, the second separator, the inner positive electrode sheet, the second separator, the inner negative electrode sheet, the second separator, the inner positive electrode sheet, the second separator, the inner negative electrode sheet, the second separator, the second outer positive electrode sheet, the first separator, the outer negative electrode sheet, the first separator, the outer positive electrode sheet prepared above are sequentially stacked in order. Then the four corners of the entire stack structure are fixed with adhesive tape to obtain an electrode assembly of the stack structure, and the electrode assembly is placed in an aluminum plastic film packaging bag and dried in a vacuum oven at 80°C for 12 hours to remove water. The above prepared electrolyte is injected, and the lithium ion battery is obtained after vacuum packaging, standing, formation, degassing, and edge cutting processes. The design potential interval of the lithium ion battery is 2.75V to 4.45V.

[0134] Example 2-3

[0135] Except for preparing the lithium ion battery according to the following steps, the rest is the same as Example 2-2.

[0136] Preparation of lithium ion battery

[0137] The single-sided positive electrode sheet in the preparation of positive electrode sheet is placed on the outermost side of the electrode assembly as the outermost positive electrode sheet of the electrode assembly. The remaining positive electrode sheets in the electrode assembly are all double-sided positive electrode sheets.

[0138] The outer side positive electrode tab, the first separator, the outer side negative electrode tab, the first separator, the secondary outer side positive electrode tab, the first separator, the inner side negative electrode tab, the first separator, the inner side positive electrode tab, the second separator, the inner side negative electrode tab, the second separator, the inner side positive electrode tab, the second separator, the inner side negative electrode tab, the second separator, the inner side positive electrode tab, the second separator, the inner side negative electrode tab, the second separator, the inner side positive electrode tab, the second separator, the inner side negative electrode tab, the second separator, the inner side positive electrode tab, the first separator, the inner side negative electrode tab, the first separator, the secondary outer side positive electrode tab, the first separator, the outer side negative electrode tab, the first separator, the outer side positive electrode tab prepared above are sequentially stacked in order. Then the four corners of the entire stack structure are fixed with adhesive tape to obtain an electrode assembly of the stack structure. The electrode assembly is placed in an aluminum plastic film packaging bag and dried in a vacuum oven at 80°C for 12 hours to remove water. The electrolyte prepared above is injected, and the lithium ion battery is obtained after vacuum packaging, standing, formation, degassing, and edge cutting processes. The design potential interval of the lithium ion battery is 2.75V to 4.45V.

[0139] Example 2-4

[0140] Except that the first separator is used in the preparation of the lithium ion battery in <Lithium ion battery preparation>, the rest is the same as Example 2-2.

[0141] Comparative Example 1

[0142] Except that the preparation steps of the first ceramic layer are exactly the same as the preparation steps of the second ceramic layer in Example 1-1, the rest is the same as Example 1-1.

[0143] Comparative Example 2

[0144] Except that the preparation steps of the second ceramic layer are exactly the same as the preparation steps of the first ceramic layer in Example 1-1, the rest is the same as Example 1-1.

[0145] Comparative Example 3

[0146] Except that the preparation steps of the first ceramic layer are exactly the same as the preparation steps of the second ceramic layer in Example 1-1, and the preparation steps of the second ceramic layer are exactly the same as the preparation steps of the first ceramic layer in Example 1-1, the rest is the same as Example 1-1.

[0147] The preparation parameters and performance parameters of each example and comparative example are shown in Tables 1 to 2.

[0148] As can be seen from Examples 1-1 to 1-21, Comparative Examples 1 to 3, by adjusting the thickness of the first ceramic layer to be greater than the thickness of the second ceramic layer, the extent of lithium precipitation of the negative electrode tab in the electrode assembly is lighter, the 500 cls capacity retention of the lithium ion battery is improved, and the drop test pass rate is higher, indicating that the lithium ion battery of the present application can reduce the risk of negative electrode interface deterioration caused by insufficient electrolyte, while taking into account the drop performance and safety performance, the lithium ion battery has good cycle performance. The thicknesses of the first ceramic layer and the second ceramic layer of the first separator of the electrode assembly in Comparative Example 1 and Comparative Example 2 are the same; the parameters of the first ceramic layer and the second ceramic layer in Comparative Example 3 are exactly opposite to those of the first ceramic layer and the second ceramic layer in Example 1-1; the extent of lithium precipitation of the negative electrode tab in the lithium ion battery in Comparative Examples 1 to 3 is heavier; the 500 cls capacity retention is lower; and / or, the drop test pass rate is lower. In addition, in Comparative Example 2, because the thicknesses of the first ceramic layer and the second ceramic layer are equal and too large, the energy density of the lithium ion battery will also decrease. However, in the lithium ion batteries in Examples 1-1 to 1-22, the extent of lithium precipitation of the negative electrode tab is lighter, the 500 cls capacity retention is higher, and the drop test pass rate is higher, indicating that the risk of deterioration of the negative electrode tab due to insufficient electrolyte during the cycle process is lower, while taking into account the drop performance and safety performance, the lithium ion battery has good cycle performance.

[0149] The value of W will generally affect the cycle performance of the lithium ion battery. As can be seen from Examples 1-1 to 1-11, when the value of W is within the range of the present application, the extent of lithium precipitation of the negative electrode tab in the lithium ion battery is lighter, the 500 cls capacity retention is higher, and the drop test pass rate is higher, indicating that the risk of deterioration of the negative electrode tab due to insufficient electrolyte during the cycle process is lower, while taking into account the drop performance and safety performance, the lithium ion battery has good cycle performance.

[0150] The values of T1 / T2 and T1 will generally affect the cycle performance of the lithium ion battery. As can be seen from Examples 1-1 to 1-11, when the values of T1 / T2 and T1 are within the range of the present application, the extent of lithium precipitation of the negative electrode tab in the lithium ion battery is lighter, the 500 cls capacity retention is higher, and the drop test pass rate is higher, indicating that the risk of deterioration of the negative electrode tab due to insufficient electrolyte during the cycle process is lower, while taking into account the drop performance and safety performance, the lithium ion battery has good cycle performance. Among them, the values of T1 / T2 and T1 in Example 1-11 are larger, at this time the liquid storage capacity of the separator on the positive electrode side is relatively weak, the liquid storage capacity of the separator on the negative electrode side is relatively strong, and the difference between the liquid storage capacities on both sides is larger, resulting in a decrease in the 500 cls capacity retention of the lithium ion battery, and a larger amount of free electrolyte in the shell, which reduces the drop test pass rate of the lithium ion battery, and the cycle performance and drop performance of the lithium ion battery are affected.

[0151] The correspondence between T1 / T2 and W generally affects the cycle performance of the lithium ion battery. As can be seen from Example 1-1 to Example 1-10, the lithium ion battery has a lighter degree of lithium precipitation of the negative electrode sheet, a higher 500 cls capacity retention rate, and a higher pass rate of drop test, indicating that the risk of deterioration of the negative electrode sheet due to insufficient electrolyte during the cycle process is lower, and the lithium ion battery has good cycle performance while taking into account the drop performance and safety performance. Among them, in Example 1-10, the values of T1 / T2 and T1 are relatively large relative to the value of W, at this time, the liquid storage capacity of the separator on the positive electrode side is relatively weak, and the liquid storage amount on both sides is large, resulting in a decrease in the 500 cls capacity retention rate of the lithium ion battery, and there is more free electrolyte in the shell, which reduces the pass rate of the drop test of the lithium ion battery, and the cycle performance and drop performance of the lithium ion battery are affected.

[0152] The first ceramic particles, the types of the first ceramic particles, and the respective mass percentages generally affect the cycle performance of the lithium ion battery. As can be seen from Example 1-12 to Example 1-15, when the first ceramic particles and the second ceramic particles within the scope of the present application are selected, and the mass percentage of the first ceramic particles and the mass percentage of the second ceramic particles are controlled within the scope of the present application, the lithium ion battery has a lighter degree of lithium precipitation of the negative electrode sheet, a higher 500 cls capacity retention rate, and a higher pass rate of drop test, indicating that the risk of deterioration of the negative electrode sheet due to insufficient electrolyte during the cycle process is lower, and the lithium ion battery has good cycle performance while taking into account the drop performance and safety performance.

[0153] The types of the first binder and the second binder generally affect the cycle performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-16, and Example 1-18, when the first binder and the second binder within the scope of the present application are selected, the lithium ion battery has a lighter degree of lithium precipitation of the negative electrode sheet, a higher 500 cls capacity retention rate, and a higher pass rate of drop test, indicating that the risk of deterioration of the negative electrode sheet due to insufficient electrolyte during the cycle process is lower, and the lithium ion battery has good cycle performance while taking into account the drop performance and safety performance.

[0154] The peeling strength between the first adhesive layer and the negative electrode sheet, and the peeling strength between the second adhesive layer and the positive electrode sheet generally affect the cycle performance of the lithium ion battery. As can be seen from Example 1-1, Example 1-16 to Example 1-21, when the peeling strength between the first adhesive layer and the negative electrode sheet, and the peeling strength between the second adhesive layer and the positive electrode sheet are within the scope of the present application, the degree of lithium precipitation of the negative electrode sheet in the lithium ion battery is lighter, the 500 cls capacity retention is higher, and the drop test pass rate is higher, indicating that the risk of deterioration of the negative electrode sheet due to insufficient electrolyte during the cycle process is lower, and the lithium ion battery has good cycle performance while taking into account the drop performance and safety performance. Among them, the peeling strength between the first adhesive layer and the negative electrode sheet in Example 1-21 is larger, at this time the resistance during the lithium ion transmission process increases, the ion transmission capacity is affected, resulting in a decrease in the 500 cls capacity retention of the lithium ion battery, and the cycle performance of the lithium ion battery is affected.

[0155] Table 2 Note: " / " in Table 2 means no relevant preparation parameters.

[0156] The structure of the electrode assembly generally affects the cycle performance of the lithium ion battery. As can be seen from Example 1-1, Example 2-1 and Example 2-4, when the structure of the electrode assembly meets the present application, the degree of lithium precipitation of the negative electrode sheet in the lithium ion battery is lighter, the 500 cls capacity retention is higher, and the drop test pass rate is higher, indicating that the risk of deterioration of the negative electrode sheet due to insufficient electrolyte during the cycle process is lower, and the lithium ion battery has good cycle performance while taking into account the drop performance and safety performance.

[0157] The value of m / n generally affects the cycle performance of the lithium ion battery. As can be seen from Example 1-1, Example 2-2 and Example 2-4, when the value of m / n meets the present application, the degree of lithium precipitation of the negative electrode sheet in the lithium ion battery is lighter, the 500 cls capacity retention is higher, and the drop test pass rate is higher, indicating that the risk of deterioration of the negative electrode sheet due to insufficient electrolyte during the cycle process is lower, and the lithium ion battery has good cycle performance while taking into account the drop performance and safety performance.

[0158] It should be noted that in this document, relational terms such as first and second and the like can only be used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply that these entities or operations exist in any such actual relationship or order. Moreover, the terms "comprising", "including", or any other variant thereof are intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements does not only include those elements, but also includes other elements not explicitly listed, or further includes elements inherent in such a process, method or article.

[0159] Each of the embodiments in the specification is described in a relevant manner, and the same or similar parts between the embodiments can be referred to each other, and each of the embodiments focuses on the difference from other embodiments.

[0160] The above only describes the preferred embodiments of the present application, and is not used to limit the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A secondary battery, comprising an electrode assembly, the electrode assembly comprising a tab and a first separator, the tab comprising a positive tab and a negative tab, the negative tab comprising a negative material layer, the negative material layer comprising a silicon element, a mass percentage content of the silicon element being W based on a mass of the negative material layer, W ≥ 3%; the first separator comprising a base film, a first ceramic layer and a second ceramic layer, the base film comprising a first surface and a second surface along a thickness direction of the first separator, the first surface facing the negative tab, the second surface facing the positive tab, the first ceramic layer being disposed on the first surface, the second ceramic layer being disposed on the second surface; a thickness of the first ceramic layer being T1 μm, a thickness of the second ceramic layer being T2 μm, T1 > T2.

2. The secondary battery according to claim 1, wherein 3％≤W≤80％。 3. The secondary battery according to claim 1 or 2, wherein 1 < T1 / T2 ≤ 20, 0.5 ≤ T1 ≤ 5.

4. The secondary battery according to claim 3, wherein 0.5T1 / T2 ≤ 0.2W × 100 + 0.6 ≤ 1.6T1 / T2.

5. The secondary battery according to claim 3, wherein 3% ≤ W ≤ 10%, 1 < T1 / T2 ≤ 2.5, 0.5 ≤ T1 ≤ 1.

5.

6. The secondary battery according to claim 3, wherein 10% < W ≤ 30%, 2.5 < T1 / T2 ≤ 5, 1.5 < T1 ≤ 3.

7. The secondary battery according to claim 3, wherein 30% < W ≤ 80%, 5 < T1 / T2 ≤ 20, 3 < T1 ≤ 5.

8. The secondary battery according to any one of claims 1 to 7, wherein the first ceramic layer comprising first ceramic particles, the second ceramic layer comprising second ceramic particles, the first ceramic particles, the second ceramic particles each independently being selected from at least one of alumina, magnesia, aluminum hydroxide, magnesium hydroxide or boehmite; a mass percentage content of the first ceramic particles being 50% to 95% based on a mass of the first ceramic layer; a mass percentage content of the second ceramic particles being 50% to 95% based on a mass of the second ceramic layer.

9. The secondary battery according to any one of claims 1 to 8, wherein the first separator further comprising a first adhesive layer and a second adhesive layer, the first adhesive layer and the first ceramic layer being sequentially laminated on the first surface, the first ceramic layer being between the first adhesive layer and the base film, the second adhesive layer and the second ceramic layer being sequentially laminated on the second surface, the second ceramic layer being between the second adhesive layer and the base film; the first adhesive layer comprising a first adhesive, the second adhesive layer comprising a second adhesive, the first adhesive, the second adhesive each independently being selected from at least one of styrene butadiene latex, styrene acrylic latex, polymethyl methacrylate, polybutyl methacrylate, polyethyl acrylate, polyvinyl alcohol, ethylene-vinyl acetate copolymer, polyvinyl acetate, polyurethane, polyvinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene.

10. The secondary battery according to claim 9, wherein a peeling strength between the first adhesive layer and the negative tab being 3N / m to 20N / m, a peeling strength between the second adhesive layer and the positive tab being 5N / m to 22N / m.

11. The secondary battery according to claim 1, wherein the electrode assembly being a stacked structure.

12. The secondary battery according to claim 11, wherein The electrode assembly further comprises a second separator, the electrode tab comprises two outer electrode tabs and a plurality of inner electrode tabs, the two outer electrode tabs are respectively located at the outermost two sides of the electrode assembly, the first separator is arranged at least between the outer electrode tab and the inner electrode tab adjacent to the outer electrode tab, and the second separator is arranged between two adjacent inner electrode tabs.

13. The secondary battery according to claim 12, wherein The number of layers of the first separator is m, the total number of layers of the first separator and the second separator is n, and 1 / 5≤m / n≤1.

14. The secondary battery according to claim 11, wherein The first separator is folded in a Z-shaped structure in the electrode assembly, and the Z-shaped first separator separates the adjacent positive electrode tab and the negative electrode tab. 15.An electronic device comprising the secondary battery of any one of claims 1 to 14.

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