Secondary battery and electronic device

Abstract

The invention provides a secondary battery and an electronic device, the secondary battery comprises an electrode assembly of a winding structure, the electrode assembly comprises a positive pole piece, a negative pole piece and a diaphragm, the diaphragm comprises a base film and a bonding layer coated on at least one surface of the base film, and the base film comprises plane areas and corner areas which are continuously and alternately arranged along the winding direction of the diaphragm; the bonding layer comprises a first bonding layer and a second bonding layer, the first bonding layer is arranged in the plane area of the base film, the second bonding layer is arranged in the corner area of the base film, the bonding force of the first bonding layer is FA N / 15mm, the bonding force of the second bonding layer is FB N / 15mm, and FB is larger than FA. By regulating and controlling the secondary battery to meet the characteristics, the gap between the corner region of the diaphragm of the secondary battery and the pole piece can be reduced, so that the problem of lithium precipitation in the corner region of the secondary battery in a full charge state is well relieved, and the cycle performance of the secondary battery is improved.

Description

Technical Field

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

[0002] As the rate performance of lithium-ion batteries improves, the amount of gas generated during the formation of square soft-pack lithium-ion batteries with wound structure increases during high-rate fast charging cycles. Large gaps are prone to appear at the corners, and there are also problems such as poor electrolyte wetting and poor contact between the separator and the electrode at the corners, which can lead to lithium plating. This increases the risk of lithium-ion batteries experiencing capacity drops and short circuits during cycling.

[0003] At present, a single high-adhesion separator is usually used or the tension between the electrode and the separator is increased during the winding process to reduce the gap between the electrodes. However, high-adhesion separators are usually more expensive to manufacture and the process is more complicated. Furthermore, there is a limited range to which the tension between the electrode and the separator can be increased. Excessive tension can easily lead to problems such as separator wrinkling and electrode breakage. Summary of the Invention

[0004] The purpose of this application is to provide a secondary battery and electronic device that reduces the gap between the separator corner area and the electrode in the secondary battery, improves the wetting of the electrode in the corner area, and better alleviates the problem of lithium plating in the corner area of ​​the secondary battery under full charge, so as to improve the cycle performance and safety performance of the secondary battery.

[0005] It should be noted that while this application uses lithium-ion batteries as an example of secondary batteries to explain the invention, the secondary batteries in this application are not limited to lithium-ion batteries. The specific technical solution is as follows:

[0006] A first aspect of this application provides a secondary battery comprising a wound electrode assembly, the electrode assembly including a positive electrode, a negative electrode, and a separator. The separator includes a base film and an adhesive layer coated on at least one surface of the base film. Along the winding direction of the separator, the base film includes continuously alternating planar regions and corner regions. The adhesive layer includes a first adhesive layer and a second adhesive layer, the first adhesive layer being disposed in the planar region of the base film, and the second adhesive layer being disposed in the corner region of the base film. The adhesive force of the first adhesive layer is F. A N / 15mm, the adhesion strength of the second adhesive layer is F B N / 15mm, F B >F AThe second adhesive layer has stronger adhesion than the first adhesive layer, with even greater adhesion at the corners of the separator. This facilitates better connection between the separator and the electrode at the corners, ensuring good contact between them. It reduces the likelihood of voids formed in the corners due to gas generation during electrode assembly formation, preventing gas accumulation and improving electrolyte wetting in the corners during cycling. Using a high-adhesion second adhesive layer in the corners reduces the possibility of secondary battery expansion due to gas generation, improving battery safety. It also reduces the risk of purple or black spots appearing on the negative electrode during formation due to larger voids. Furthermore, it reduces the likelihood of lithium plating in the corners during later stages of battery cycling, improving overall battery cycle performance. Therefore, when the separator in the electrode assembly meets the above characteristics, a second adhesive layer with high adhesion is set in the corner area to reduce the gap between the corner area of ​​the secondary battery separator and the electrode, thereby reducing the generation of purple or black spots on the negative electrode and effectively alleviating the problem of lithium plating in the corner area of ​​the secondary battery under full charge, thus improving the cycle performance and safety performance of the secondary battery.

[0007] In one or more embodiments of this application, 2≤F B ≤5, 1≤F A ≤2. By adjusting the secondary battery to meet the above characteristics, the first adhesive layer and the second adhesive layer have suitable adhesive forces. Specifically, when the adhesive forces of the first adhesive layer and the second adhesive layer are within the above range, the adhesive force of the second adhesive layer is greater than that of the first adhesive layer. The adhesive force in the corner area of ​​the separator is greater, which is conducive to better connection between the separator and the electrode, reduces the voids generated in the corner area due to gas production, makes it less likely for gas to accumulate in the corner area, improves the situation of poor electrolyte wetting in the corner area during the electrode assembly cycle, and at the same time helps to reduce the risk of purple spots or black spots on the negative electrode during the formation process due to large voids, and reduces the possibility of lithium plating in the corner area in the later stage of the secondary battery cycle, thereby improving the cycle performance and safety performance of the secondary battery.

[0008] In one or more embodiments of this application, the first adhesive layer includes a first adhesive, which includes at least one of alumina-polyvinylidene fluoride composite adhesive, alumina-styrene-butadiene rubber composite adhesive, polymethyl methacrylate, polyvinyl alcohol, or sodium carboxymethyl cellulose. Based on the mass of the first adhesive layer, the mass percentage content of the first adhesive is M1, where 15% ≤ M1 ≤ 45%. The second adhesive layer includes a second adhesive, which includes at least one of polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene. Based on the mass of the second adhesive layer, the mass percentage content of the second adhesive is M2, where 55% ≤ M2 ≤ 65%. By adjusting the secondary battery to meet the above characteristics, and by selecting suitable first and second adhesives with appropriate mass percentages for the first and second adhesive layers, it is beneficial to ensure that the first and second adhesive layers have appropriate adhesion, thus effectively mitigating the situation where excessive adhesive leads to increased membrane interfacial impedance and reduced cycle life of the secondary battery. Specifically, the adhesion force of the second adhesive layer is greater than that of the first adhesive layer. The adhesion force in the corner area of ​​the secondary battery separator is relatively large, which helps to reduce the gap between the corner area of ​​the secondary battery separator and the electrode, improve the wetting of the electrode at the corner, reduce the generation of purple or black spots on the negative electrode, and better alleviate the problem of lithium plating in the corner area of ​​the secondary battery under full charge, thereby improving the cycle performance and safety performance of the secondary battery.

[0009] In one or more embodiments of this application, the electrode assembly includes N turns, where 9 ≤ N ≤ 100. In any turn of the electrode assembly, the width of the negative electrode formed by winding along the width direction of the electrode assembly is W1 μm, the width of the planar region of the base film is W2 μm, and the thickness of the negative electrode formed by winding along the thickness direction of the electrode assembly is D1 μm, where W2 < W1 - D1. By adjusting the secondary battery to meet the above characteristics, the planar region of the base film has a suitable width, which is smaller than the difference between the width and thickness of the negative electrode. That is, the width of the planar region in this turn of the base film is smaller than the width of the corresponding area of ​​the negative electrode, thus the corner region of the base film has a suitable width. This is beneficial for better covering the area on the negative electrode corresponding to the corner region of the base film, improving the adhesion between the separator and the electrode, improving the wetting effect of the negative electrode at the corner, and better reducing the gap between the corner region of the secondary battery separator and the electrode, reducing the generation of purple or black spots on the negative electrode, thereby improving the cycle performance of the secondary battery.

[0010] In one or more embodiments of this application, 3≤D1≤300. By adjusting the thickness of any single turn of the negative electrode assembly within the scope of this application, on the one hand, the negative electrode has a suitable thickness, which is beneficial for the negative electrode to have suitable charge transport performance and suitable internal resistance, and better reduces the risk of lithium-ion transport efficiency being affected by excessive thickness of the negative electrode; on the other hand, it is beneficial for the wound electrode assembly to have a suitable thickness, which is better reduced for the risk of encapsulation performance being affected by excessive thickness of a single turn of the negative electrode after winding, thereby improving the cycle performance of the secondary battery.

[0011] In one or more embodiments of this application, starting from the beginning of the separator winding, the second adhesive layer is only disposed in the corner region of the base film from the N / 3th turn to the Nth turn along the winding direction of the separator. Specifically, as the number of turns of the electrode assembly increases, the thickness of the electrode assembly increases, and the corner region also increases accordingly. Correspondingly, the possibility of voids being generated due to gas production during the secondary battery formation process is also greater. By disposing of the second adhesive layer in the corner region of the base film from the N / 3th turn to the Nth turn, the corner region can be better matched, the adhesion between the separator and the electrode in the corner region can be better improved, the voids between the corner region of the secondary battery separator and the electrode can be better reduced, and the generation of purple spots or black spots on the negative electrode can be reduced, thereby improving the cycle performance of the secondary battery.

[0012] In one or more embodiments of this application, in any ring of electrode assembly, along the width direction of the electrode assembly, the width of any corner region of the base film is W3 μm, where W3 > D1 / 2. After the secondary battery is formed, in any ring of electrode assembly, the width of the corner region of the base film is greater than half the thickness of the negative electrode sheet of that ring. By adjusting the width of the corner region to meet the above characteristics, the corner region has a suitable width. Specifically, the width of the corner region is greater than the width of the corresponding area of ​​the negative electrode sheet, which is beneficial to better cover the area on the negative electrode sheet corresponding to the corner region of the base film, better improve the adhesion between the separator and the electrode sheet in the corner region, improve the wetting of the negative electrode sheet at the corner, better reduce the gap between the corner region of the secondary battery separator and the electrode sheet, reduce the generation of purple spots or black spots on the negative electrode sheet, thereby improving the cycle performance of the secondary battery.

[0013] In one or more embodiments of this application, the widths of any two planar regions of the base membrane are equal. By adjusting the secondary battery to meet the above characteristics, the equal widths of any two planar regions on the base membrane are beneficial for optimizing production steps and improving the manufacturability of the separator.

[0014] In one or more embodiments of this application, an adhesive layer is disposed on one surface of the base film along the thickness direction of the separator, with the base film surface having the adhesive layer facing the negative electrode. During secondary battery cycling, lithium plating typically occurs on the surface of the negative electrode. By adjusting the secondary battery to meet the above-mentioned characteristics, the second adhesive layer corresponds to the negative electrode, which helps to better cover the area on the negative electrode corresponding to the corner region of the base film, better improves the adhesion between the separator and the electrode in the corner region, improves the wetting of the negative electrode at the corner, better reduces the gap between the secondary battery separator corner region and the electrode, reduces the generation of purple or black spots on the negative electrode, thereby improving the cycle performance of the secondary battery.

[0015] A second aspect of this application provides an electronic device that includes the secondary battery found in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance.

[0016] The beneficial effects of this application are:

[0017] This application provides a secondary battery and an electronic device. The secondary battery includes a wound electrode assembly, which includes a positive electrode, a negative electrode, and a separator. The separator includes a base film and an adhesive layer coated on at least one surface of the base film. Along the winding direction of the separator, the base film includes continuously alternating planar regions and corner regions. The adhesive layer includes a first adhesive layer and a second adhesive layer. The first adhesive layer is disposed in the planar region of the base film, and the second adhesive layer is disposed in the corner region of the base film. The adhesive force of the first adhesive layer is F. A N / 15mm, the adhesion strength of the second adhesive layer is F B N / 15mm, F B >F A By adjusting the secondary battery to meet the above characteristics, the gap between the secondary battery separator corner region and the electrode can be reduced, thereby effectively alleviating the problem of lithium plating in the corner region of the secondary battery under full charge and improving the cycle performance of the secondary battery.

[0018] Of course, implementing any product or method of this application does not necessarily require achieving all of the advantages described above at the same time. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other embodiments can be obtained based on these accompanying drawings.

[0020] Figure 1 This is a schematic diagram of the winding structure formed by the electrode assembly in some embodiments of this application;

[0021] Figure 2This is a schematic diagram of the winding structure of one of the electrode components in some embodiments of this application;

[0022] In the figure, electrode assembly 001; positive electrode 10; positive current collector 11; positive electrode material layer 12; negative electrode 20; negative current collector 21; negative electrode material layer 22; separator 30; base film 31; first adhesive layer 32; second adhesive layer 33; planar region 301; corner region 302. Detailed Implementation

[0023] The technical solutions of this application will be clearly and completely described below with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. All other embodiments obtained by those skilled in the art based on this application are within the scope of protection of this application.

[0024] It should be noted that, in the specific embodiments of this application, a lithium-ion battery is used as an example of a secondary battery to explain this application; however, the secondary battery in this application is not limited to lithium-ion batteries. The specific technical solution is as follows:

[0025] This application provides a secondary battery comprising a wound electrode assembly, the electrode assembly including a positive electrode, a negative electrode, and a separator. The separator includes a base film and an adhesive layer coated on at least one surface of the base film. Along the winding direction of the separator, the base film includes continuously alternating planar regions and corner regions. The adhesive layer includes a first adhesive layer and a second adhesive layer. The first adhesive layer is disposed in the planar region of the base film, and the second adhesive layer is disposed in the corner region of the base film. The adhesive force of the first adhesive layer is F. A N / 15mm, the adhesion strength of the second adhesive layer is F B N / 15mm, F B >F A .

[0026] The winding direction of the electrode assembly is defined as the W direction. For example, as shown... Figure 1 As shown, the electrode assembly 001 includes a positive electrode 10, a negative electrode 20, and a separator 30. The positive electrode 10 includes a positive current collector 11 and a positive electrode material layer 12 disposed on two surfaces of the positive current collector 11. The negative electrode 20 includes a negative current collector 21 and a negative electrode material layer 22 disposed on two surfaces of the negative current collector 21. The separator 30 includes a base film 31 and a first adhesive layer 32 disposed on two surfaces of the planar region 301 and a second adhesive layer 33 disposed on two surfaces of the corner region 302 on the base film 31.

[0027] With the widespread adoption of wound lithium-ion batteries, improving their cycle performance and safety has become increasingly important. Due to their unique structure, wound batteries contain planar areas and corner areas formed by the winding process. During the formation of the secondary battery, as gas production increases, the voids in the corner areas also increase. On one hand, increased voids in the corner areas can lead to poorer contact between the electrodes and the separator, increasing the risk of lithium plating. On the other hand, excessive residual reactant gases in the corner areas can cause poor electrolyte wetting of the electrode components during secondary battery cycling, resulting in purple or black spots. Further lithium plating can occur under full charge conditions during cycling, increasing the probability of reduced cycle capacity, lithium plating, purple spots on the electrodes, and short circuits. This application provides a secondary battery including a wound electrode assembly. The separator of the electrode assembly is designed such that, along the winding direction of the separator, continuously alternating planar regions and corner regions are pre-planned on a base film. A first adhesive layer is formed in the planar regions of the base film, and a second adhesive layer is formed in the corner regions of the base film. The adhesive force of the first adhesive layer is F. A N / 15mm, the adhesion strength of the second adhesive layer is F B N / 15mm, F B >F A Due to the adhesive force F of the second adhesive layer B Greater than the first adhesive layer F A The second adhesive layer has stronger adhesion than the first adhesive layer, with even greater adhesion at the corners of the separator. This facilitates better connection between the separator and the electrode at the corners, ensuring good contact between them. It reduces the likelihood of voids formed in the corners due to gas generation during electrode assembly formation, preventing gas accumulation and improving electrolyte wetting in the corners during cycling. Using a high-adhesion second adhesive layer in the corners reduces the possibility of secondary battery expansion due to gas generation, improving battery safety. It also reduces the risk of purple or black spots appearing on the negative electrode during formation due to larger voids. Furthermore, it reduces the likelihood of lithium plating in the corners during later stages of battery cycling, improving overall battery cycle performance. Therefore, when the separator in the electrode assembly meets the above characteristics, a second adhesive layer with high adhesion is set in the corner area to reduce the gap between the corner area of ​​the secondary battery separator and the electrode, thereby reducing the generation of purple or black spots on the negative electrode and effectively alleviating the problem of lithium plating in the corner area of ​​the secondary battery under full charge, thus improving the cycle performance and safety performance of the secondary battery.

[0028] In one or more embodiments of this application, 2≤F B ≤5. For example, F BThe value of F can be 2, 2.1, 2.3, 2.5, 2.7, 2.9, 3, 3.1, 3.3, 3.5, 3.7, 3.9, 4, 4.5, 5, or a range consisting of any two of the above values. B The value range of can be 2 to 5, 2.1 to 4.5, 2.3 to 4, 2.5 to 3.9, 2.7 to 3.7, and all ranges and subranges thereof. 1 ≤ F A ≤2. For example, F A The value of F can be 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, or a range consisting of any two of the above values. A The value range can be 1 to 2, 1.1 to 1.9, 1.2 to 1.8, 1.3 to 1.7, 1.4 to 1.6, and all of these ranges and sub-ranges. By adjusting the secondary battery to meet the above characteristics, the first adhesive layer and the second adhesive layer have suitable adhesive forces. Specifically, when the adhesive forces of the first adhesive layer and the second adhesive layer are within the above ranges, the adhesive force of the second adhesive layer is greater than that of the first adhesive layer. The adhesive force in the corner area of ​​the separator is greater, which is beneficial for better connection between the separator and the electrode, reducing the voids generated in the corner area due to gas production, making it less likely for gas to accumulate in the corner area, improving the situation of poor electrolyte wetting in the corner area during the electrode assembly cycle, and at the same time, helping to reduce the risk of purple spots or black spots on the negative electrode during the formation process due to large voids, reducing the possibility of lithium plating in the corner area in the later stage of the secondary battery cycle, thereby improving the cycle performance and safety performance of the secondary battery.

[0029] In one or more embodiments of this application, the first adhesive layer includes a first adhesive, which includes at least one of alumina-polyvinylidene fluoride composite adhesive, alumina-styrene-butadiene rubber composite adhesive, polymethyl methacrylate, polyvinyl alcohol, or sodium carboxymethyl cellulose. Based on the mass of the first adhesive layer, the mass percentage of the first adhesive is M1, where 15% ≤ M1 ≤ 45%. For example, the value of M1 can be 15%, 17.5%, 20%, 22.5%, 25%, 27.5%, 30%, 32.5%, 35%, 37.5%, 40%, 42.5%, 45%, or a range consisting of any two of the above values. The range of M1 can be 15% to 45%, 17.5% to 42.5%, 20% to 40%, 22.5% to 37.5%, 25% to 35%, and all ranges and sub-ranges thereof. The second adhesive layer includes a second adhesive, which includes at least one of polyvinylidene fluoride (PVDF) or PVDF-hexafluoropropylene. Based on the mass of the second adhesive layer, the mass percentage of the second adhesive is M2, where 55% ≤ M2 ≤ 65%. For example, the value of M2 can be 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, or a range of any two of the above values. The range of M2 can be 55% to 65%, 56% to 64%, 57% to 63%, 58% to 62%, 59% to 61%, and all ranges and sub-ranges thereof. By adjusting the secondary battery to meet the above characteristics, and by selecting suitable first and second adhesives with appropriate mass percentages for the first and second adhesive layers, it is beneficial to ensure that the first and second adhesive layers have suitable adhesion, thus effectively mitigating the situation where excessive adhesive leads to increased membrane interfacial impedance and reduced cycle life of the secondary battery. Specifically, the adhesion force of the second adhesive layer is greater than that of the first adhesive layer. The adhesion force in the corner area of ​​the secondary battery separator is relatively large, which helps to reduce the gap between the corner area of ​​the secondary battery separator and the electrode, improve the wetting of the electrode at the corner, reduce the generation of purple or black spots on the negative electrode, and better alleviate the problem of lithium plating in the corner area of ​​the secondary battery under full charge, thereby improving the cycle performance and safety performance of the secondary battery.

[0030] In one or more embodiments of this application, the first adhesive layer further includes an inorganic filler and a first additive. The inorganic filler may include at least one of alumina, silica, or zirconium oxide. The first additive includes at least one of acetylated tributyl citrate, polyethylene glycol, or triphenyl phosphate. Based on the mass of the first adhesive layer, the mass percentage of the inorganic filler may be 45% to 83%, and the mass percentage of the first additive may be 2% to 10%.

[0031] In one or more embodiments of this application, the second adhesive layer further includes an inorganic filler and a second additive. The inorganic filler may include at least one of alumina, silica, or zirconium oxide. The second additive may include at least one of benzoic acid ester, epoxidized soybean oil, tricresyl phosphate, polysiloxane derivative, or fatty alcohol polyoxyethylene ether. Based on the mass of the second adhesive layer, the mass percentage of the inorganic filler may be 25% to 43%, and the mass percentage of the second additive may be 2% to 10%.

[0032] In one or more embodiments of this application, the electrode assembly includes N turns, where 9 ≤ N ≤ 100. For example, the value of N can be 9, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or a range consisting of any two of the above values. The range of N can be 9 to 100, 10 to 90, 20 to 80, 30 to 70, 40 to 60, and all such ranges and sub-ranges. In any turn of the electrode assembly, along the width direction of the electrode assembly, the width of the negative electrode sheet formed by winding is W1 μm, the width of the planar region of the base film is W2 μm, and along the thickness direction of the electrode assembly, the thickness of the negative electrode sheet formed by winding is D1 μm, where W2 < W1 - D1. Specifically, as... Figure 2 As shown, the thickness of the wound negative electrode 20 is D1 along the thickness direction Z, the width of the wound negative electrode 20 is W1 along the width direction Y, the width of the planar region 301 on the base film 31 is W2, and the width of the corner region 302 is W3. After the secondary battery is formed, the difference between the width and thickness of the negative electrode sheet in any ring of electrode assembly can be considered as the width of the negative electrode sheet relative to the planar area of ​​the base film in that ring. By adjusting the secondary battery to meet the above characteristics, the planar area of ​​the base film has a suitable width, which is smaller than the difference between the width and thickness of the negative electrode sheet. That is, the width of the planar area in the base film ring is smaller than the width of the corresponding area of ​​the negative electrode sheet. Thus, the corner area of ​​the base film has a suitable width, which is beneficial to better cover the area of ​​the negative electrode sheet corresponding to the corner area of ​​the base film, improve the adhesion between the separator and the electrode sheet, improve the wetting effect of the negative electrode sheet at the corner, better reduce the gap between the corner area of ​​the secondary battery separator and the electrode sheet, reduce the generation of purple spots or black spots on the negative electrode sheet, and thus improve the cycle performance of the secondary battery.

[0033] In this application, along the thickness direction of the wound electrode assembly, the electrode assembly is formed by stacking and winding a separator, a negative electrode sheet, a separator, and a positive electrode sheet sequentially from the winding center outwards. Therefore, an electrode assembly with N turns is prepared by winding the aforementioned stacked separator, negative electrode sheet, separator, and positive electrode sheet N times. In the following embodiments and tests, the separator referred to is the separator near the winding center along the thickness direction of the electrode assembly.

[0034] In one or more embodiments of this application, 3 ≤ D1 ≤ 300. For example, the value of D1 can be 3, 5, 10, 30, 50, 70, 90, 100, 150, 200, 250, 300, or a range consisting of any two of the above values. The value range of D1 can be 3 to 300, 5 to 250, 10 to 200, 30 to 150, 50 to 100, 70 to 90, and all such ranges and sub-ranges. By adjusting the thickness of any single turn of the negative electrode sheet within the scope of this application, on the one hand, the negative electrode sheet has a suitable thickness, which is beneficial for the negative electrode sheet to have suitable charge transport performance and suitable internal resistance, and better reduces the risk of lithium-ion transport efficiency being affected by excessive thickness of the negative electrode sheet; on the other hand, it is beneficial for the wound electrode assembly to have a suitable thickness, which is better reduced the risk of encapsulation performance being affected by excessive thickness of a single turn of the wound negative electrode sheet, thereby improving the cycle performance of the secondary battery.

[0035] In one or more embodiments of this application, 35 ≤ W1 ≤ 165. For example, the value of W1 can be 35, 40, 45, 50, 55, 60, 80, 100, 120, 140, 160, 165, or a range consisting of any two of the above values. The range of W1 can be 35 to 165, 40 to 160, 45 to 140, 50 to 120, 55 to 100, and all such ranges and sub-ranges. By adjusting the value of W1 within the above range, the negative electrode sheet in any loop electrode assembly has a suitable width, which is beneficial for the negative electrode sheet to have suitable charge transport performance and suitable internal resistance, while also ensuring the fabrication feasibility of the negative electrode sheet, thereby improving the cycle performance of the secondary battery.

[0036] In one or more embodiments of this application, 30 ≤ W2 ≤ 150. For example, the value of W2 can be 30, 35, 40, 45, 50, 70, 90, 100, 110, 130, 140, 150, or a range consisting of any two of the above values. The value range of W2 can be 35 to 150, 35 to 140, 40 to 130, 45 to 110, 50 to 100, and all such ranges and sub-ranges. By adjusting the value of W2 within the above range, the base film plane region in any ring electrode assembly has a suitable width, which is beneficial for synergistic effect with the corner region. This ensures that the width of the corner region covers the corresponding area on the negative electrode sheet, improves the wetting of the negative electrode sheet at the corner, better fills the gap between the corner region of the secondary battery separator and the electrode sheet, reduces the generation of purple or black spots on the negative electrode sheet, and thus improves the cycle performance of the secondary battery.

[0037] In one or more embodiments of this application, starting from the beginning of the separator winding, the second adhesive layer is only disposed in the corner region of the base film from the N / 3th turn to the Nth turn along the winding direction of the separator. Specifically, as the number of turns of the electrode assembly increases, the thickness of the electrode assembly increases, and the corner region also increases accordingly. Correspondingly, the possibility of voids being generated due to gas production during the secondary battery formation process is also greater. By disposing of the second adhesive layer in the corner region of the base film from the N / 3th turn to the Nth turn, the corner region can be better matched, the adhesion between the separator and the electrode in the corner region can be better improved, the voids between the corner region of the secondary battery separator and the electrode can be better reduced, and the generation of purple spots or black spots on the negative electrode can be reduced, thereby improving the cycle performance of the secondary battery.

[0038] In one or more embodiments of this application, in any ring of electrode assembly, along the width direction of the electrode assembly, the width of any corner region of the base film is W3 μm, where W3 > D1 / 2. After the secondary battery is formed, in any ring of electrode assembly, the width of the corner region of the base film is greater than half the thickness of the negative electrode sheet of that ring. By adjusting the width of the corner region to meet the above characteristics, the corner region has a suitable width. Specifically, the width of the corner region is greater than the width of the corresponding area of ​​the negative electrode sheet, which is beneficial to better cover the area on the negative electrode sheet corresponding to the corner region of the base film, better improve the adhesion between the separator and the electrode sheet in the corner region, improve the wetting of the negative electrode sheet at the corner, better reduce the gap between the corner region of the secondary battery separator and the electrode sheet, reduce the generation of purple spots or black spots on the negative electrode sheet, thereby improving the cycle performance of the secondary battery.

[0039] In one or more embodiments of this application, the widths of any two planar regions of the base membrane are equal. By adjusting the secondary battery to meet the above characteristics, the equal widths of any two planar regions on the base membrane are beneficial for optimizing production steps and improving the manufacturability of the separator.

[0040] In one or more embodiments of this application, an adhesive layer is disposed on one surface of the base film along the thickness direction of the separator, with the base film surface having the adhesive layer facing the negative electrode. During secondary battery cycling, lithium plating typically occurs on the surface of the negative electrode. By adjusting the secondary battery to meet the above-mentioned characteristics, the second adhesive layer corresponds to the negative electrode, which helps to better cover the area on the negative electrode corresponding to the corner region of the base film, better improves the adhesion between the separator and the electrode in the corner region, improves the wetting of the negative electrode at the corner, better reduces the gap between the secondary battery separator corner region and the electrode, reduces the generation of purple or black spots on the negative electrode, thereby improving the cycle performance of the secondary battery.

[0041] In this application, the adhesive strength of the first adhesive layer can be controlled by adjusting the mass percentage content of the first adhesive and / or the coating weight of the first adhesive layer. For example, under the same conditions, as M1 increases, F... A Increase; M1 decreases, FA Reduce; increase the coating weight of the first adhesive layer, F A Increase; the coating weight of the first adhesive layer decreases, F A Decrease.

[0042] In this application, the adhesive strength of the second adhesive layer can be controlled by adjusting the mass percentage content of the second adhesive and / or the coating weight of the second adhesive layer. For example, under the same conditions, as M2 increases, F... B Increase; M2 decreases, F B Reduce; increase the coating weight of the second adhesive layer, F B Increase; the coating weight of the second adhesive layer decreases, F B Decrease.

[0043] In this application, the value of D1 can be adjusted by regulating the thickness of the positive electrode, negative electrode, and separator, or the winding gap in the electrode assembly. For example, under the same conditions, increasing the thickness of the positive electrode increases D1; ​​decreasing the thickness of the positive electrode decreases D1; ​​increasing the thickness of the negative electrode increases D1; ​​decreasing the thickness of the negative electrode decreases D1; ​​increasing the thickness of the separator increases D1; ​​decreasing the thickness of the separator decreases D1.

[0044] In this application, the size of the winding gap in the electrode assembly can be adjusted by regulating the winding tension of the diaphragm and the electrode sheet. For example, under the same conditions, increasing the winding tension increases the gap in the electrode assembly, while decreasing the winding tension decreases the gap in the electrode assembly.

[0045] This application does not impose any particular restrictions on the preparation method of the diaphragm, as long as the purpose of this application can be achieved. For example, the diaphragm can be prepared by the following method: (1) Mix the first binder, inorganic filler and first additive in proportion and add solvent, stir evenly to obtain the first adhesive layer slurry; mix the second binder, inorganic filler and second additive in proportion and add solvent, stir evenly to obtain the second adhesive layer slurry. (2) Take the base film, and alternately set the planar area and corner area along the winding direction of the base film. Coat the first adhesive layer slurry on one surface of the planar area of ​​the base film, and coat the second adhesive layer slurry on the same surface of the corner area of ​​the base film. After drying, a diaphragm with the first adhesive layer and the second adhesive layer coated on one side is obtained; (3) Repeat the above steps on the other surface of the planar area and the corner area of ​​the base film to obtain a finished diaphragm with the first adhesive layer and the second adhesive layer coated on both sides.

[0046] In one or more embodiments of this application, the coating weight of the first adhesive layer is X mg / 5000 mm. 20 < X ​​≤ 230. For example, the value of X can be 0.1, 1, 5, 10, 30, 50, 70, 90, 100, 150, 200, 230, or any two of the above values. The range of X can be 0.1 to 230, 1 to 200, 5 to 150, 10 to 100, 30 to 90, and all of these ranges and sub-ranges. By adjusting the coating weight of the first adhesive layer within the above range, the first adhesive layer has suitable adhesive force, which is beneficial to better increase the adhesion between the electrode and the separator in the corner area of ​​the separator, and better reduce the risk of partial deformation and void formation due to insufficient adhesive force during the electrode assembly production process. This further alleviates the problem of purple spots or lithium plating on the electrode due to voids in the corner area during the formation and cycling of the secondary battery, thereby improving the cycle performance and safety performance of the secondary battery.

[0047] In one or more embodiments of this application, the coating weight of the second adhesive layer is Y mg / 5000mm. 2 60≤Y≤320. For example, the value of Y can be 60, 80, 100, 110, 130, 150, 170, 190, 200, 250, 300, 320, or any two of the above values. The range of Y values ​​can be 60 to 320, 80 to 300, 100, 5 to 250, 110 to 200, 130 to 190, and all of these ranges and sub-ranges. By adjusting the coating weight of the second adhesive layer within the above range, it is beneficial for the second adhesive layer to have suitable adhesion, further distinguishing it from the first adhesive layer. The adhesion force in the corner area of ​​the secondary battery separator is relatively large, which helps to reduce the gap between the corner area of ​​the secondary battery separator and the electrode, improve the wetting of the electrode at the corner, reduce the generation of purple or black spots on the negative electrode, and better alleviate the problem of lithium plating in the corner area of ​​the secondary battery under full charge, thereby improving the cycle performance and safety performance of the secondary battery.

[0048] In this application, "a material layer disposed on at least one surface of the current collector" means that the material layer can be disposed on one surface of the current collector along its own thickness direction, or on two surfaces of the current collector along its own thickness direction. It should be noted that the "surface" here can be the entire area of ​​the current collector surface or a part of the current collector surface. This application has no particular limitation, as long as the purpose of this application can be achieved.

[0049] This application does not impose any particular restrictions on the positive electrode current collector, as long as it can achieve the purpose of this application. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector).

[0050] The positive electrode material layer includes a positive electrode active material. This application does not impose any particular restrictions on the positive electrode active material, as long as it can achieve the purpose of this application. For example, the positive electrode active material may include, but is not limited to, lithium nickel cobalt manganese oxide (e.g., NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium-rich manganese-based materials, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0051] The positive electrode material layer may also include a conductive agent and a binder. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, the binder may include at least one of polyacrylate, polyimide, polyamide, polyamide-imide, polyvinylidene fluoride, polystyrene-butadiene copolymer (styrene-butadiene rubber), sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, potassium carboxymethyl cellulose, sodium carboxymethyl cellulose, or potassium carboxymethyl cellulose. The conductive agent may include at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, or graphene. The conductive carbon black may be at least one of acetylene black, Super P, or Ketjen black. The carbon nanotubes may be at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes. The carbon fibers may be at least one of vapor-grown carbon fibers (VGCF) or carbon nanofibers. This application does not impose any particular restrictions on the mass ratio of the positive electrode active material, conductive agent, and binder in the positive electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0052] Optionally, the positive electrode may further include a conductive layer located between the positive current collector and the positive electrode material layer. The composition of the conductive layer is not particularly limited and can be any conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0053] This application does not impose any particular restrictions on the negative electrode current collector, as long as it can achieve the purpose of this application. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. For example, the composite current collector may be lithium copper composite current collector, carbon copper composite current collector, nickel copper composite current collector, titanium copper composite current collector, etc.

[0054] The negative electrode material layer includes a negative electrode active material. This application does not impose any particular limitation on the negative electrode active material, as long as it can achieve the purpose of this application. For example, the negative electrode active material may include, but is not limited to, natural graphite, artificial graphite, mesophase micro carbon spheres, hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Or at least one of Li-Al alloys.

[0055] The negative electrode material layer may also include a conductive agent and a binder. This application does not impose any particular restrictions on the types of conductive agents and binders, as long as they achieve the purpose of this application. For example, it may be at least one of the aforementioned conductive agents and binders. This application does not impose any particular restrictions on the mass ratio of the negative electrode active material, conductive agent, and binder in the negative electrode material layer. Those skilled in the art can select according to actual needs, as long as the purpose of this application is achieved.

[0056] Optionally, the negative electrode sheet may further include a conductive layer located between the negative electrode current collector and the negative electrode material layer. This application does not impose any particular limitation on the composition of the conductive layer, which can be a conductive layer commonly used in the art. For example, the conductive layer may include a conductive agent and a binder. This application does not impose any particular limitation on the conductive agent and binder in the conductive layer; for example, it can be at least one of the aforementioned conductive agents and binders.

[0057] This application does not impose any particular limitation on the type of base membrane, as long as it can achieve the purpose of this application. For example, the base membrane can be a nonwoven fabric or composite membrane with a porous structure, and the material of the base membrane can include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane can be used.

[0058] In this application, the secondary battery also includes an electrolyte, which includes lithium salts and non-aqueous solvents.

[0059] This application does not impose any particular limitation on the lithium salt, as long as it achieves the purpose of this application. For example, the lithium salt may 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. This application also does not impose any particular limitation on the content of the lithium salt in the electrolyte, as long as it achieves the purpose of this application.

[0060] This application does not impose any particular restrictions on non-aqueous solvents, as long as they can achieve the purpose of this application. For example, non-aqueous solvents may include, but are not limited to, at least one of carbonate compounds, carboxylic acid ester compounds, ether compounds, or other organic solvents.

[0061] The aforementioned carbonate compounds may include, but are not limited to, at least one of chain carbonate compounds, cyclic carbonate compounds, or fluorocarbonate compounds. The aforementioned chain carbonate compounds may include, but are 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 aforementioned cyclic carbonates may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butyl carbonate (BC), or vinyl ethylene carbonate (VEC). Fluorocarbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethylethylene carbonate. The aforementioned carboxylic acid ester compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolactone, valproic acid lactone, or caprolactone. The aforementioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. Other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolium ketone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate. This application does not impose any particular limitation on the content of non-aqueous solvents in the electrolyte, as long as the purpose of this application is achieved.

[0062] The secondary battery of this application also includes a packaging bag for containing the positive electrode, separator, negative electrode, and electrolyte, as well as other components known in the art for secondary batteries. This application does not limit the aforementioned other components. This application does not have any particular limitation on the packaging bag; it can be any packaging bag known in the art, as long as it can achieve the purpose of this application.

[0063] This application does not impose any particular limitation on the type of secondary battery, which may include any device in which an electrochemical reaction occurs. In this application, the secondary battery may include, but is not limited to: lithium metal secondary batteries, lithium-ion secondary batteries (lithium-ion batteries), lithium polymer secondary batteries, or lithium-ion polymer secondary batteries (lithium-ion polymer batteries), etc.

[0064] The preparation process of the secondary battery described in this application is well known to those skilled in the art, and this application does not impose any particular limitations. For example, it may include, but is not limited to, the following steps: stacking a separator, a negative electrode sheet, a separator, and a positive electrode sheet in sequence, and performing operations such as winding and folding as needed to obtain a wound electrode assembly; placing the electrode assembly in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the secondary battery. Furthermore, overcurrent protection components, conductive plates, etc., may be placed in the packaging bag as needed to prevent pressure rise and overcharging / discharging inside the secondary battery.

[0065] A second aspect of this application provides an electronic device that includes the secondary battery found in any of the foregoing embodiments. Therefore, the electronic device provided by this application has good performance.

[0066] This application does not specifically limit the type of electronic device; it can be any electronic device known in the prior art. In one or more embodiments of this application, the electronic device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0067] Example

[0068] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below. Furthermore, unless otherwise specified, "parts" and "%" are quality standards.

[0069] Test methods and equipment:

[0070] Electrode assembly sampling:

[0071] At 25°C, the lithium-ion battery was charged to 3.6V at a constant current of 0.3C, then charged to 0.05C at a constant voltage of 3.6V until the current cutoff was reached. After standing for 15 minutes, it was discharged to 2.0V at a constant current of 0.3C. Subsequently, the discharged lithium-ion battery was disassembled under an argon atmosphere, the electrode assembly was removed, and the electrode assembly was soaked in dimethyl carbonate solvent for 2 hours and dried at 60°C for 1 hour to obtain the electrode assembly.

[0072] W1, W2, W3, D1 tests

[0073] Along the thickness direction of the electrode assembly, the electrode assembly was photographed using a scanning electron microscope (SEM). Along the width direction of the electrode assembly, after removing the Nth to N-1th turns of the electrode assembly, the N-2th turn of the core was prepared. The width of the sample was directly measured using vernier calipers to obtain W1. The thickness of the sample was directly measured using a PPG battery thickness gauge under a pressure of 20 kg to obtain D1.

[0074] Disassemble the N-2 ring electrode assembly to obtain the diaphragm. Attach one side of the diaphragm to a smooth steel plate and the other side with adhesive tape. Fix one end of the adhesive tape to a tensile testing machine. Set the speed to 10 mm / min and pull the adhesive tape 180° straight using the tensile testing machine. Read the adhesive force when the adhesive tape is stretched and record the force-displacement curve. Measure the two adjacent abrupt change points of the adhesive force. The sample movement distance at this point is taken as W2, and W3 = W1 - W2.

[0075] Test of adhesion strength of first adhesive layer and second adhesive layer

[0076] The electrode assembly was disassembled to obtain the diaphragm. After scraping off the coating on any surface of the diaphragm, samples were taken from the corner area and the planar area. The side containing the base film of the planar area sample and the corner area sample were respectively pasted onto a smooth steel plate, and the other side was glued with adhesive tape. One end of the adhesive tape was fixed to a tensile testing machine. The speed was set to 10 mm / min, and the adhesive tape was pulled straight by the tensile testing machine at 180°. The adhesive force when the adhesive tape was stretched was read, and the force-displacement curve was recorded. After exporting the data, it was divided by the width of the adhesive tape to calculate the adhesive force of the first adhesive layer and the adhesive force of the second adhesive layer (N / 15mm).

[0077] Purple spot test

[0078] After placing the lithium-ion battery in a 45℃ environment for 60 minutes, charge it to 3.6V at a constant current of 1C, then charge it to the cutoff current of 0.05C at a constant voltage of 3.6V, let it stand for 5 minutes, and then discharge it to 2.5V at a constant current of 1C, and let it stand for 5 minutes. This process is considered one cycle. Repeat the above cycle with the lithium-ion battery. After the 100th cycle, disassemble the lithium-ion battery to obtain the positive and negative electrode sheets. Soak the positive and negative electrode sheets in dimethyl carbonate solvent for 2 hours and dry them at 60℃ for 1 hour to obtain the positive and negative electrode sheets. Use a scanning electron microscope (SEM) to photograph the positive and negative electrode sheets and observe whether purple spots appear on the surface of the electrode sheets.

[0079] Lithium plating test

[0080] After placing the lithium-ion battery in a 15°C environment for 60 minutes, charge it to 3.6V at a constant current of 1C, then charge it to 0.05C at a constant voltage of 3.6V until the cutoff current is reached. Let it rest for 5 minutes, then discharge it to 2.5V at a constant current of 1C and let it rest for 5 minutes. This process is considered one cycle. Repeat the above cycle for the lithium-ion battery. After the 10th cycle, disassemble the lithium-ion battery to obtain the negative electrode. Observe the lithium deposition state on the surface of the negative electrode material layer. The non-lithium-deposited area on the surface of the negative electrode material layer is golden yellow, and the lithium-deposited area is grayish white. Measure the lithium deposition area on the surface of the negative electrode material layer in the planar area and the corner area. For each example and comparative example, the lithium deposition state of the negative electrode material layer surface in 10 groups of lithium-ion batteries is statistically analyzed, and the average value is calculated to obtain the percentage of lithium deposition area to evaluate the lithium deposition state of the negative electrode material layer.

[0081] The criteria for judging the lithium plating state on the surface of the negative electrode material layer are as follows: lithium plating area less than or equal to 1% is no lithium plating, lithium plating area greater than 1% and less than or equal to 3% is slight lithium plating, lithium plating area greater than 3% and less than or equal to 5% is moderate lithium plating, and lithium plating area greater than 5% is severe lithium plating.

[0082] Cyclic capacity retention test:

[0083] At 45℃, the lithium-ion battery was charged at a constant current of 0.5C to 3.6V, then charged at a constant voltage of 3.6V to 0.05C, allowed to rest for 5 minutes, and then discharged at a constant current of 1C to 2.5V, allowed to rest for 5 minutes. This constitutes one charge-discharge cycle, and the discharge capacity of each cycle was recorded. The lithium-ion battery was subjected to 1000 cycles under the above conditions, and the discharge capacity was measured after each cycle. Cycle capacity retention (%) = (Capacity after 1000 discharge cycles / First discharge cycle capacity) × 100%.

[0084] Thickness expansion rate test:

[0085] In an environment of 25℃, the lithium-ion battery was charged to 3.6V at a constant current of 0.5C, and then charged to 0.05C at a constant voltage of 3.6V to achieve a fully charged state. The thickness of the lithium-ion battery before storage was measured. Then, the fully charged lithium-ion battery was placed in an 80℃ oven for 108 hours, and its thickness after storage was measured. The high-temperature thickness expansion rate of the lithium-ion battery was calculated using the following formula:

[0086] Thickness expansion rate (%) = ((thickness after storage - thickness before storage) / thickness before storage) × 100%.

[0087] Example 1

[0088] <Preparation of the positive electrode>

[0089] Lithium iron phosphate (LiFePO4, Dv50=12μm), the positive electrode active material, polyvinylidene fluoride (PVDF), the positive electrode binder, and Super P, were added to N-methylpyrrolidone (NMP) at a solid mass ratio of 95:2.5:2.5 and mixed evenly under vacuum stirring to obtain a positive electrode material slurry with a solid content of 60wt%. The positive electrode material slurry was then uniformly coated onto one surface of a 13μm thick aluminum foil for the positive electrode current collector and dried at 80℃ for 1 hour to obtain a positive electrode sheet with a single-sided coating of the positive electrode material layer. The single-sided coating weight of the positive electrode material layer was 300mg / 1540.25mm. 2 Then, the above steps are repeated on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode material. After cold pressing, cutting, and welding of tabs, a positive electrode sheet with a size of 7600mm×64mm is obtained. The thickness of the single-sided positive electrode material layer is 43.5μm, and the thickness of the prepared positive electrode sheet is 100μm.

[0090] <Preparation of Negative Electrode Sheets>

[0091] Artificial graphite (negative electrode active material), styrene-butadiene rubber (binder), and acetylene black (conductive agent) were mixed in a mass ratio of 97.4:1.4:1.2. Deionized water was added as a solvent to prepare a slurry with a solid content of 45 wt%. The slurry was stirred evenly in a vacuum mixer to obtain the negative electrode slurry. The negative electrode slurry was uniformly coated onto one surface of a 6 μm thick copper foil used as a negative electrode current collector. The foil was dried at 120°C for 1 hour to obtain a negative electrode sheet with a single-sided coating of negative electrode material. The coating weight of the negative electrode material layer was 230 mg / 1540 mm². 2The above steps are then repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of negative electrode material. After drying at 120℃, it is cold-pressed, then cut and welded with tabs to obtain a negative electrode sheet with dimensions of 7842mm×67mm for later use. The thickness of the single-sided negative electrode material layer is 72μm, and the thickness of the prepared negative electrode sheet is 150μm.

[0092] <Preparation of the diaphragm>

[0093] The first adhesive polyvinyl alcohol, inorganic filler alumina and the first additive polyethylene glycol are mixed in a mass ratio of 30:62:8, NMP solvent is added, and the mixture is stirred evenly under vacuum to obtain the first adhesive layer slurry.

[0094] The second adhesive polyvinylidene fluoride, inorganic filler alumina, second additive tricresyl phosphate, and second additive fatty alcohol polyoxyethylene ether are mixed in a mass ratio of 60:30:5:5, and NMP solvent is added. After vacuum stirring, the second adhesive layer slurry is obtained.

[0095] A 5μm thick polyethylene base film is used as the base film for the diaphragm. Planar regions and corner regions are alternately formed on the base film along its width. The width of each planar region is 100μm, and the width of each corner region is 15μm. A first adhesive layer slurry is coated on the planar regions at a coating weight of 65mg / 5000mm². 2 The second adhesive layer slurry applied to the corner area has a coating weight of 84 mg / 5000 mm. 2 After drying, a diaphragm is obtained.

[0096] <Preparation of Electrolyte>

[0097] In an environment with a water content of less than 10 ppm, dimethyl carbonate, diethyl carbonate, and ethylene carbonate were mixed in a mass ratio of 1:1:1 to obtain an organic solvent. Then, the electrolyte salt LiPF6 was added to the organic solvent and mixed thoroughly to obtain the electrolyte. Based on the mass of the electrolyte, the electrolyte salt comprised 12.5% ​​by mass, with the remainder being the organic solvent.

[0098] <Preparation of Lithium-ion Batteries>

[0099] The prepared positive electrode, separator, and negative electrode are stacked in the order of separator, negative electrode, separator, and positive electrode, with the separator positioned between the positive and negative electrodes to provide insulation. The electrode assembly is then wound with 100 turns. The electrode assembly is placed in an aluminum-plastic film packaging bag and dehydrated at 80°C. The prepared electrolyte is then injected, followed by vacuum sealing, settling, formation, degassing, and edge trimming to obtain a lithium-ion battery. The formation upper limit voltage is 3.6V, the formation temperature is 70°C, and the formation settling time is 2 hours.

[0100] Examples 2 to 9

[0101] Except for adjusting the relevant preparation parameters according to Table 1, the rest is the same as in Example 1. Specifically, when the mass percentage of the first adhesive in the first adhesive layer changes, the mass percentage of the first additive in the first adhesive layer remains unchanged, while the mass percentage of the inorganic filler alumina changes accordingly; when the mass percentage of the second adhesive changes, the mass percentage of the second additive in the second adhesive layer remains unchanged, while the mass percentage of the inorganic filler alumina changes accordingly.

[0102] Examples 10 to 12

[0103] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0104] Example 13

[0105] Except for adjusting the number of winding turns to 9 in <Preparation of Lithium-ion Battery>, adjusting the size of the positive electrode to 1080mm×64mm in <Preparation of Positive Electrode>, and adjusting the size of the negative electrode to 1290mm×67mm in <Preparation of Negative Electrode>, the rest is the same as in Example 1.

[0106] Example 14

[0107] Except for adjusting the number of winding turns to 100 in <Preparation of Lithium-ion Battery>, adjusting the size of the positive electrode to 12600mm×64mm in <Preparation of Positive Electrode>, and adjusting the size of the negative electrode to 12842mm×67mm in <Preparation of Negative Electrode>, the rest is the same as in Example 1.

[0108] Examples 15 to 16

[0109] Except for adjusting the relevant preparation parameters according to Table 1, everything else is the same as in Example 1.

[0110] Example 17

[0111] Except for adjusting the alternating arrangement of the first and second adhesive layers in the first 20 turns of the electrode assembly in the <Preparation of the Separator> section to only the second coating layer, the rest is the same as in Example 1.

[0112] Example 18

[0113] Except that in the <Preparation of the Separator>, the first adhesive layer and the second adhesive layer are alternately provided only on the side of the separator facing the negative electrode sheet, and only the second coating layer is provided on the other side, the rest is the same as in Example 1.

[0114] Comparative Example 1

[0115] Except for the use of a 5 μm thick porous polyethylene film (provided by Celgard) as the separator in the <Separator Preparation> section, the rest is the same as in Example 1.

[0116] Comparative Example 2

[0117] Except for coating the planar area with a second adhesive layer and coating the corner area with a first adhesive layer in the <Preparation of the diaphragm>, the rest is the same as in Example 1.

[0118] Table 1

[0119] Note: In Table 1, " / " indicates that the corresponding preparation parameter or substance does not exist; M1 represents the mass percentage content of the first binder; M2 represents the mass percentage content of the second binder; F A F represents the adhesive strength of the first adhesive layer. B W1 represents the adhesion strength of the second adhesive layer; W2 represents the width of the planar area; W3 represents the width of the corner area; W1 represents the width of the negative electrode in the 57th turn of the electrode assembly; N represents the number of turns of the electrode assembly.

[0120] As can be seen from Examples 1 to 18 and Comparative Examples 1 to 2, by setting planar regions and corner regions that satisfy the characteristics of this application in the separator and adjusting the adhesion of the first adhesive layer and the second adhesive layer within the range of this application, the lithium-ion battery has a lower lithium plating rate and a higher cycle capacity retention rate, indicating that the lithium plating resistance and cycle performance of the embodiments of this application are good. Comparative Example 1 uses a conventional separator, and the secondary battery showed purple spots during cycling, significant lithium plating in the later stage of cycling, and had a poor cycle capacity retention rate and a high thickness expansion rate; in Comparative Example 2, the adhesion force of the first adhesive layer is greater than that of the second adhesive layer, and the adhesion force of the planar region is greater than that of the corner region, which cannot fill the gaps in the corner region well. The secondary battery showed purple spots during cycling, severe lithium plating in the later stage of cycling, and had a poor cycle capacity retention rate and a high thickness expansion rate. This indicates that embodiments that do not meet the requirements of this application have poor cycle performance and safety performance, while embodiments of this application, while reducing the possibility of purple spots, have a lower lithium plating rate and a higher cycle capacity retention rate, and a lower thickness expansion rate, indicating that embodiments that meet the features of this application improve the cycle performance and safety performance of lithium-ion batteries.

[0121] As can be seen from Examples 1 to 9, the adhesive strength of the first adhesive layer and the adhesive strength of the second adhesive layer affect the cycle performance and safety performance of the secondary battery. When adjusting F... A and F BWhen the value is within the range of this application, it reduces the voids generated in the corner area due to gas production, making it less likely for gas to accumulate in the corner area. This reduces the possibility of purple spots, while also resulting in a lower lithium plating rate, a higher cycle capacity retention rate, and a lower thickness expansion rate. This indicates that the embodiments provided in this application are beneficial for enhancing the safety performance and improving the cycle performance of secondary batteries.

[0122] As can be seen from Examples 1 to 12, the type and mass percentage of the first and second binders affect the cycle performance and safety performance of the secondary battery. When the type and mass percentage of the first and second binders are controlled within the scope of this application, the first and second adhesive layers have suitable adhesive strength, which helps to reduce the gap between the secondary battery separator corner area and the electrode, thereby improving the electrode wetting at the corner. This reduces the likelihood of purple spots, while also exhibiting a lower lithium plating rate, a higher cycle capacity retention rate, and a lower thickness expansion rate. This indicates that the embodiments provided in this application are beneficial for enhancing the safety performance and improving the cycle performance of the secondary battery.

[0123] As can be seen from Examples 1, 13, and 14, the number of turns of the electrode assembly affects the cycle performance and safety performance of the secondary battery. When the number of turns of the electrode assembly is adjusted within the range of this application, the secondary battery has a suitable energy density. Specifically, when the number of turns of the electrode assembly is small, the energy density of the secondary battery is low, and the cycle capacity retention rate is low; when the number of turns of the electrode assembly is large, the capacity loss during cycling is high, and the cycle capacity retention rate is low. This indicates that the embodiments provided in this application are beneficial for enhancing the safety performance and improving the cycle performance of the secondary battery.

[0124] As can be seen from Examples 1 and 15, the width and thickness of the negative electrode sheet and the width of the planar region in any loop electrode assembly affect the cycle performance and safety performance of the secondary battery. When the above values ​​are adjusted to satisfy W2 < W1 - D1, the planar region of the base film has a suitable width, which is smaller than the difference between the width and thickness of the negative electrode sheet. Thus, the corner region of the base film has a suitable width, which is beneficial for better covering the area on the negative electrode sheet corresponding to the corner region of the base film, improving the adhesion of the corner region, reducing the gap between the corner region of the secondary battery separator and the electrode sheet, thereby improving the wetting of the negative electrode sheet at the corner. While reducing the formation of purple spots or black spots on the electrode sheet, it has a lower lithium plating rate and a higher cycle capacity retention rate, indicating that the embodiments provided in this application are beneficial for enhancing the safety performance and improving the cycle performance of the secondary battery.

[0125] As can be seen from Examples 1 and 16, the width of the corner region and the thickness of the negative electrode sheet in any ring of electrode assembly affect the cycle performance and safety performance of the secondary battery. When the above values ​​are adjusted to satisfy W3 > D1 / 2, the width of the corner region of the base film is greater than half the thickness of the negative electrode sheet of that ring. This is beneficial for better covering the area on the negative electrode sheet corresponding to the corner region of the base film, improving the adhesion of the corner region, reducing the gap between the corner region of the secondary battery separator and the electrode sheet, thereby improving the wetting of the negative electrode sheet at the corner. While reducing the formation of purple spots or black spots on the electrode sheet, it has a lower lithium plating rate and a higher cycle capacity retention rate, indicating that the embodiments provided in this application are beneficial for enhancing the safety performance and improving the cycle performance of the secondary battery.

[0126] As can be seen from Examples 1 and 17, the number of winding turns of the separator coating affects the cycle performance and safety performance of the secondary battery. Along the winding direction of the separator, the thickness of the electrode assembly increases, and the corner area also increases accordingly. This increases the likelihood of voids being generated during the secondary battery formation process due to gas production. When the second adhesive layer is only placed in the corner area of ​​the base film from the N / 3rd to the Nth turn, it can better match the corner area and effectively reduce the void between the secondary battery separator corner area and the electrode. This reduces the formation of purple or black spots on the negative electrode while exhibiting a lower lithium plating rate and a higher cycle capacity retention rate. This indicates that the embodiments provided in this application are beneficial for enhancing the safety performance and improving the cycle performance of the secondary battery.

[0127] As can be seen from Examples 1 and 18, the location of the separator coating affects the cycle performance and safety performance of the secondary battery. When the separator coating is only disposed on one surface of the base film along the thickness direction of the separator, and the coated base film surface faces the negative electrode, during the cycle of the secondary battery, the second coating corresponds to the negative electrode, which is beneficial for better covering the area on the negative electrode corresponding to the corner area of ​​the base film, improving the wetting of the negative electrode at the corner, and better reducing the gap between the corner area of ​​the secondary battery separator and the electrode. While reducing the formation of purple or black spots on the negative electrode, it also has a lower lithium plating rate and a higher cycle capacity retention rate, indicating that the embodiments provided in this application are beneficial for enhancing the safety performance and improving the cycle performance of the secondary battery.

[0128] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, or article that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, or article.

[0129] The above description is only a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A secondary battery comprising an electrode assembly of a jelly-roll structure, the electrode assembly comprising a positive electrode sheet, a negative electrode sheet, and a separator, the separator comprising a base film and a bonding layer coated on at least one surface of the base film, the base film comprising planar regions and corner regions continuously and alternately arranged in a winding direction of the separator; the bonding layer comprising a first bonding layer and a second bonding layer, the first bonding layer being arranged at the planar regions of the base film, the second bonding layer being arranged at the corner regions of the base film, the first bonding layer having a bonding force of F A N / 15 mm, the second bonding layer having a bonding force of F B N / 15 mm, F B > F A .

2. The secondary battery according to claim 1, wherein 2≤F B ≤5, 1≤F A ≤2.

3. The secondary battery according to claim 1, wherein The first adhesive layer includes a first adhesive including at least one of an alumina-polyvinylidene fluoride composite adhesive, an alumina-styrene butadiene rubber composite adhesive, polymethyl methacrylate, polyvinyl alcohol, or sodium carboxymethyl cellulose, a mass percentage of the first adhesive being M1 based on a mass of the first adhesive layer, 15%≤M1≤45%; The second adhesive layer includes a second adhesive including at least one of polyvinylidene fluoride or polyvinylidene fluoride-hexafluoropropylene, a mass percentage of the second adhesive being M2 based on a mass of the second adhesive layer, 55%≤M2≤65%.

4. The secondary battery according to claim 1, wherein The electrode assembly includes N turns, 9≤N≤100; in any turn of the electrode assembly, a width of the negative electrode tab formed by winding in a width direction of the electrode assembly is W1 mm, a width of the planar region of the base film is W2 mm, and a thickness of the negative electrode tab formed by winding in a thickness direction of the electrode assembly is D1 mm, W2 < W1-D1.

5. The secondary battery according to claim 4, wherein 3≤D1≤300。 6. The secondary battery according to claim 4, wherein The second adhesive layer is disposed only on the corner region of the base film from the N / 3th turn to the Nth turn in a winding direction of the separator from a winding start end of the separator.

7. The secondary battery according to claim 4, wherein In any turn of the electrode assembly, a width of any one corner region of the base film in the width direction of the electrode assembly is W3 mm, W3 > D1 / 2.

8. The secondary battery according to claim 4, wherein The widths of any two planar regions of the base film are equal.

9. The secondary battery according to claim 1, wherein The adhesive layer is disposed on one surface of the base film in the thickness direction of the separator, and the surface of the base film on which the adhesive layer is disposed faces the negative electrode tab. 10.An electronic device including the secondary battery of any one of claims 1 to 9.

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