An electric cell and battery

Abstract

The application relates to the technical field of batteries, in particular to a battery cell and a battery comprising the same. The battery cell comprises a positive electrode sheet, a diaphragm and a negative electrode sheet, the diaphragm is located between the positive electrode sheet and the negative electrode sheet, the diaphragm comprises a base material and a rubber coating layer, the rubber coating layer is located on both sides of the base material or on one side of the base material close to the positive electrode sheet, the battery cell comprises a flat area and a bending area, the diaphragm corresponding to the flat area comprises a first area and a second area, the second area is an area where the diaphragm and the positive electrode sheet are projected and overlapped, the first area is an area where the diaphragm and the positive electrode sheet are projected and not overlapped, the thickness of the rubber coating layer in the first area is H1, the thickness of the rubber coating layer in the second area is H2, and the battery cell satisfies the following relationship: 1 < H1 / H2 <= 10. The battery has high cycle stability and good high-low temperature performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of battery, in particular to a battery cell and a battery comprising the same. BACKGROUND

[0002] In recent years, lithium ion batteries have been widely used in the fields of smart phones, tablet computers, power tools, energy storage and electric vehicles. With the wide application of lithium ion batteries, consumers' demand for the service life and application environment of lithium ion batteries is increasing, which requires lithium ion batteries to have good cycle performance while considering high and low temperature performance.

[0003] At present, lithium ion batteries have the problem of short service life during use. For example, the capacity of the battery decays rapidly after a period of use, and the battery cannot be charged and discharged, or even a serious safety accident occurs, such as fire or explosion. SUMMARY

[0004] It is found through research that the main reason for the cycle life problem of the battery is that the residual electrolyte is insufficient during the cycle process, causing ion breakage at local positions in the battery, which cannot effectively shuttle lithium ions between the positive and negative electrodes.

[0005] In order to overcome the above technical problems existing in the prior art, the present application provides a battery cell and a battery comprising the same. The battery cell of the present application controls the thickness ratio of the glue layer in the flat area, improves the retention rate of the electrolyte, and at the same time shortens the distance between the positive and negative electrodes, thereby improving the long cycle performance of the battery.

[0006] The first aspect of the present application provides a battery cell, wherein the battery cell comprises a positive electrode sheet, a separator and a negative electrode sheet, the separator is located between the positive electrode sheet and the negative electrode sheet, the separator comprises a substrate and a glue layer, the glue layer is located on both sides of the substrate or on one side of the substrate close to the positive electrode sheet, the battery cell comprises a flat area and a bending area, the separator corresponding to the flat area comprises a first area and a second area, the second area is an area where the separator and the positive electrode sheet are projected and overlapped, the first area is an area where the separator and the positive electrode sheet are projected and not overlapped, the thickness of the glue layer in the first area is H1, the thickness of the glue layer in the second area is H2, and the battery cell satisfies the following relationship: 1

[0007] The second aspect of the present application provides a battery, comprising the battery cell of the first aspect of the present application.

[0008] Compared with the prior art, the present application has at least the following advantages:

[0009] By setting the adhesive layer on at least one side of the base material of the diaphragm close to the positive electrode sheet, and by controlling the ratio of the thickness of the adhesive layer in the first region to the thickness of the adhesive layer in the second region in the flat area of the battery cell, the retention of electrolyte in the diaphragm can be improved, the retention rate of electrolyte in the battery can be improved, and the distance between the positive and negative electrode sheets can be reduced, thereby shortening the path length of ion intercalation and deintercalation, and further improving the long cycle performance of the battery and prolonging the cycle life of the battery.

[0010] Other features and advantages of the present application will be described in detail in the following detailed description.

[0011] The endpoints of the ranges and any values described herein are not limited to the precise values stated. The ranges and values should be construed to be approximations that allow for significant variation. Various ranges of values are stated in terms of being wider than the ranges and endpoints. For example, a range of 2 to 10 can include from 3 to 7, 4 to 6, or 4 to 5, etc. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 The structure of the un-wound battery cell of the present application is shown.

[0013] Figure 2 The structure of the battery of the wound battery cell of the present application is shown.

[0014] Figure 3 The structure of the diaphragm corresponding to the flat area of the wound battery cell of the present application is shown. Figure 2 The structure of the diaphragm corresponding to the flat area of the wound battery cell of the present application is shown.

[0015] Figure 4 The structure of the diaphragm corresponding to the flat area of the wound battery cell of the present application is shown. Figure 2 The structure of the diaphragm corresponding to the flat area of the wound battery cell of the present application is shown.

[0016] Figure 5 The structure of the diaphragm corresponding to the flat area of the wound battery cell of the present application is shown.

[0017] Figure 6 The SEM of the diaphragm corresponding to the flat area of the wound battery cell of the present application is shown.

[0018] Figure 7 The SEM of the diaphragm corresponding to the flat area of the wound battery cell of the present application is shown. DETAILED DESCRIPTION

[0019] The specific embodiments of the present application are described in detail below. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the application, are given by way of illustration only, and not by way of limitation. Herein, the data ranges include the endpoints unless specifically stated otherwise.

[0020] It should be noted that the "first", "second" and the like in the present application are only used to distinguish different substances or use methods, and do not represent the difference in order.

[0021] The first aspect of the present application provides an electric core, wherein the electric core comprises a positive electrode sheet, a diaphragm and a negative electrode sheet, the diaphragm is located between the positive electrode sheet and the negative electrode sheet, the diaphragm comprises a base material and a rubber coating layer, the rubber coating layer is located on both sides of the base material or on the side of the base material close to the positive electrode sheet, the electric core comprises a flat area and a bending area, the diaphragm corresponding to the flat area comprises a first area and a second area, the second area is an area where the diaphragm and the positive electrode sheet project overlap, and the first area is an area where the diaphragm and the positive electrode sheet project do not overlap, the thickness of the rubber coating layer in the first area is H1, the thickness of the rubber coating layer in the second area is H2, and the electric core satisfies the following relationship: 1

[0022] The electric core can satisfy: 1

[0023] In the present application, the thickness of the rubber coating layer is the average thickness, and the specific test method is: in the SEM image of the diaphragm, in the interval of 400 μm x 500 μm, the average value of the thickness of the rubber coating layer with a diameter of more than 2 μm.

[0024] As shown in Figure 1 , the diaphragm 1 is located between the positive electrode sheet 2 and the negative electrode sheet 3, the diaphragm 1 comprises a base material 11 and a rubber coating layer 12, and the rubber coating layer 12 is located on both sides of the base material 11 or on the side of the base material 11 close to the positive electrode sheet 2.

[0025] As shown in Figure 2 , the battery can include a height H, a width W and a thickness T. It can be understood that in the structure of the electric core, the diaphragm is located between the positive electrode sheet and the negative electrode sheet, and the diaphragm serves to isolate the positive and negative electrode sheets, the starting point of the electric core is S, S is the starting point position of the positive electrode sheet, and the positions of the positive electrode sheet, the diaphragm and the negative electrode sheet at S can be aligned (as shown in Figure 4 , the positions of the positive electrode sheet and the negative electrode sheet at S are aligned), or can not be aligned (as shown in Figure 3 , the positions of the positive electrode sheet and the negative electrode sheet at S are not aligned), that is, the starting positions of the positive electrode sheet and the negative electrode sheet can be the same or different.

[0026] In the present application, the electric core comprises a bending area and a flat area, and the diaphragm comprises an area corresponding to the bending area of the electric core and an area corresponding to the flat area of the electric core. In the structure of the electric core, the flat area is an area that is not bent, as shown in Figure 3 and Figure 4The region between the middle line MN and the middle part of the line OP is a flat region, which is a region without bending, as shown in Figure 3 and Figure 4 The region to the left of the middle line MN and to the right of the line OP is a bending region, which is a region where bending occurs.

[0027] In the present application, in the height H direction of the battery cell, the height of the diaphragm is greater than the height of the positive plate, as shown in Figure 5 As shown in the figure, in the height H direction of the battery cell, the projection of the diaphragm located in the first region 1111 on the positive plate 2 does not overlap the positive plate 2, and the projection of the diaphragm located in the second region 1112 on the positive plate 2 overlaps the positive plate 2.

[0028] By arranging the glue layer at least on the side of the diaphragm substrate close to the positive plate, and by controlling the ratio of the thickness of the glue layer in the first region to the thickness of the glue layer in the second region in the flat region, the present application can form a "groove" in the flat region that can hold a certain amount of electrolyte, thereby increasing the retention of electrolyte in the diaphragm, improving the retention rate of electrolyte in the battery, and overcoming the problem of broken bridge caused by insufficient electrolyte, while also reducing the distance between the positive and negative plates, thereby shortening the path length of ion insertion and extraction, thereby improving the long cycle performance of the battery and prolonging the cycle life of the battery.

[0029] In the present application, by arranging the glue layer at least on the side of the diaphragm substrate close to the positive plate, and by controlling the ratio of the thickness of the glue layer in the first region to the thickness of the glue layer in the second region in the flat region, the present application can form a "groove" in the flat region that can hold a certain amount of electrolyte, thereby increasing the retention of electrolyte in the diaphragm, improving the retention rate of electrolyte in the battery, and overcoming the problem of broken bridge caused by insufficient electrolyte, while also reducing the distance between the positive and negative plates, thereby shortening the path length of ion insertion and extraction, thereby improving the long cycle performance of the battery and prolonging the cycle life of the battery.

[0030] The glue layer can be located on both sides of the substrate or on the side of the substrate close to the positive plate.

[0031] In an example, the glue layer is located on the side of the substrate close to the positive plate.

[0032] As shown in Figure 1As shown, the adhesive layer 12 is located on the side of the substrate 11 close to the positive electrode sheet 2, i.e., the positive electrode sheet 2 directly contacts the adhesive layer 12, while the side of the substrate 11 away from the positive electrode sheet 2 (i.e., the side close to the negative electrode sheet 3) can directly contact the negative electrode sheet 3. At this time, the battery can still solve the problem of shortening of the battery cycle life caused by insufficient residual electrolyte, achieve the effect of improving the cycle stability of the battery and prolonging the cycle life of the battery, and because the substrate of the separator close to the negative electrode sheet directly contacts the negative electrode sheet, the possibility of blockage of the separator channel can be reduced, the ion transmission of the negative electrode side separator is more smooth, and the negative electrode has good adhesion. In addition, the cost of the battery can be reduced because only one side of the substrate of the separator is coated with the adhesive layer.

[0033] In an example, the battery cell satisfies the following relationship: 1.5≤H1 / H2≤5.

[0034] In an example, H1 is 0.5 μm-5 μm (e.g., 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm).

[0035] In an example, H2 is 0.2 μm-3 μm (e.g., 0.2 μm, 0.5 μm, 1 μm, 2 μm, 3 μm).

[0036] In an example, the battery cell satisfies the following relationship: 1

[0037] In an example, the heat shrinkage rate of the separator at 130°C is ≤5%. The test method of the heat shrinkage rate is as follows: take a separator sample with an area of 15 cm*15 cm, and punch two holes with a diameter of 0.5 mm at a distance of 10 cm along the length direction of the separator, place the sample in an oven at 130±2°C for 1 h, the distance between the two holes before baking is L1, the distance between the two holes after baking is L2, and the heat shrinkage rate=(L1-L2) / L1*100%. Controlling the heat shrinkage rate of the separator within the above range can effectively block the contact between the positive and negative electrodes of the battery when the battery is placed in a high-temperature environment, reduce the risk of short circuit of the positive and negative electrodes, and thus improve the high-temperature safety performance of the battery.

[0038] In an example, the coverage area of the adhesive layer in the flat area accounts for 10%-40% (e.g., 10%, 15%, 20%, 25%, 30%, 35%, or 40%) of the area of the flat area (see Figure 6Research has revealed that factors contributing to battery cycle life issues include swelling of the adhesive layer on the separator surface in relation to the electrolyte, which blocks the separator channels and hinders ion transport, leading to severe capacity decay in later stages of cycling. Therefore, by controlling the coverage area of ​​the adhesive layer in the flat region, the swelling of the adhesive layer on the separator surface and the blockage of the separator channels can be mitigated, allowing for smooth ion transport and thus improving battery cycle performance.

[0039] In one example, based on the area of ​​the bending region, the coverage area A% of the adhesive layer located in the bending region is 5%-30% (e.g., 5%, 10%, 15%, 20%, 25%, or 30%) (see [reference]). Figure 7 ).

[0040] Research has found that lithium plating in bending areas is a contributing factor to battery cycle life issues, leading to a decrease in cycle capacity and consequently affecting cycle performance and safety. Therefore, controlling the coverage area of ​​the adhesive layer in the bending area can improve lithium plating, thereby enhancing battery safety. Furthermore, it can mitigate the swelling of the adhesive layer on the separator surface and the battery, preventing blockage of separator channels and allowing for smooth ion transport, thus improving battery cycle performance.

[0041] In one example, the coverage area of ​​the adhesive layer is 5%-40% (e.g., 5%, 10%, 15%, 20%, 25%, 30%, 35% or 40%), based on the area of ​​the diaphragm.

[0042] In one example, based on the area of ​​the bending region, the coverage area A% of the adhesive layer in the bending region is 5%-30%, and based on the area of ​​the straight region, the coverage area B% of the adhesive layer in the straight region is 10%-40%, and based on the area of ​​the separator, the coverage area of ​​the adhesive layer is 5%-40%. By simultaneously controlling the coverage area percentages of the adhesive layer in the bending region, the straight region, and the separator, the swelling of the adhesive layer on the separator surface and the battery, which could block the separator channels, can be further improved, thereby allowing ion transport to proceed smoothly and improving the cycle performance of the battery.

[0043] In one instance, such as Figure 1 As shown, the adhesive layer 12 includes a polymer 121, which includes primary particles and secondary particles, wherein the secondary particles are formed by the accumulation of primary particles.

[0044] In an example, the primary particles have a median particle size Dv50 of 100 nm to 300 nm (e.g., 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, or 300 nm).

[0045] In an example, the secondary particles have a median particle size Dv50 of 0.1 pm to 100 pm (e.g., 0.1 pm, 0.5 pm, 1 pm, 5 pm, 10 pm, 20 pm, 30 pm, 40 pm, 50 pm, 60 pm, 70 pm, 80 pm, 90 pm, or 100 pm).

[0046] In an example, the secondary particles have a median particle size Dv50 of 1 pm to 50 pm.

[0047] In the present application, the median particle size Dv50 can be obtained by a laser particle size analyzer test.

[0048] In an example, the primary particles have a mean particle size of 100 nm to 300 nm (e.g., 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, or 300 nm).

[0049] In an example, the secondary particles have a mean particle size of 0.1 pm to 100 pm (e.g., 0.1 pm, 0.5 pm, 1 pm, 5 pm, 10 pm, 20 pm, 30 pm, 40 pm, 50 pm, 60 pm, 70 pm, 80 pm, 90 pm, or 100 pm).

[0050] In an example, the secondary particles have a mean particle size of 1 pm to 50 pm.

[0051] In the present application, the average particle diameter can be tested by observing the surface of the porous layer at a magnification of 500,000 times using an electron beam radiation type scanning electron microscope (S-3400N manufactured by Hitachi, Ltd.). The image size at this time is 2.5 μm x 1.8 μm. Note that the number of pixels is 1,280 pixels x 960 pixels, and the size of 1 pixel is 2 nm x 1.9 nm. For the average particle diameter, the smallest square or rectangle that completely encloses one particle is drawn on the obtained image, that is, a square or rectangle in which the end of the particle is in contact with the four sides of the square or rectangle is drawn, and in the case of a square, the length of one side is set as the particle diameter, and in the case of a rectangle, the length of the long side (major axis diameter) is set as the particle diameter. For any 81 particles, the particle diameter of each is measured, and the number average thereof is set as the average particle diameter. Note that in the case where more than 81 particles are observed in the photographed image, the number average of the particle diameters of any 81 particles in the image is set as the average particle diameter, and in the case where 81 particles are not observed in the image, a plurality of images are photographed, and the number average of the particle diameters of 81 particles in total is set as the average particle diameter.

[0052] In an example, the polymer comprises one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylonitrile, polymethyl methacrylate, and polyacrylic acid.

[0053] In an example, the weight content of the polymer is 80 wt% to 95 wt% (e.g., 80 wt%, 82 wt%, 85 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, or 95 wt%) based on the total weight of the gum layer.

[0054] In an example, the weight content of the polymer is 85 wt% to 94 wt% based on the total weight of the gum layer.

[0055] In an example, the gum layer comprises a first binder and a thickening agent.

[0056] In an example, the weight content of the first binder is 1 wt% to 15 wt% (e.g., 1 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt%, 10 wt%, 11 wt%, 13 wt%, or 15 wt%) and the weight content of the thickening agent is 1 wt% to 5 wt% (e.g., 1 wt%, 2 wt%, 3 wt%, 4 wt%, or 5 wt%) based on the total weight of the gum layer.

[0057] In an example, the gum layer comprises a first binder and a thickening agent, the weight content of the first binder is 3 wt% to 12 wt% and the weight content of the thickening agent is 1.5 wt% to 4.5 wt% based on the total weight of the gum layer.

[0058] In an example, the first binder includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, polyacrylonitrile, poly(methyl) methacrylate, aramid resin, poly(meth)acrylic acid, styrene butadiene rubber (SBR), polyvinyl alcohol, polyvinyl acetate, and carboxyethyl cellulose.

[0059] In an example, the thickening agent includes one or more of carboxymethyl cellulose (CMC), sodium carboxymethyl cellulose (CMC-Na), and lithium carboxymethyl cellulose (CMC-Li).

[0060] In an example, the substrate includes one or more of polyethylene, polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, poly(p-phenylene), polynaphthalene, polyimide, polyamide, aramid, and poly(p-phenylene benzobisoxazole).

[0061] In an example, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer located on one or both sides of the positive electrode current collector, the positive electrode active material layer including a positive electrode active substance, a positive electrode conductive agent, and a positive electrode binder.

[0062] In an example, the positive electrode sheet includes a positive electrode active material layer including a positive electrode active substance, the positive electrode active substance including a ternary material with or without a doping coating treatment, a lithium iron phosphate with or without a doping coating treatment, wherein the doping element includes one or more of Al, Mg, Mn, Cr, Ti, V, and Zr.

[0063] In an example, the positive electrode active substance has a median particle size Dv50 of 0.3-5 μm (e.g., 0.3 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, or 5 μm).

[0064] In an example, the average particle size of the primary particles is D1, the average particle size of the secondary particles is D2, the median particle size Dv50 of the positive electrode active material is D3, and the battery cell satisfies the following relationship: 0.1≤D1 / D3≤1 (e.g., 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1), and / or, 1≤D2 / D3≤20 (e.g., 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20). Controlling the average particle size D1 of the primary particles to be less than or equal to the median particle size Dv50 of the positive electrode active material can cause the primary particles to be embedded between the particles of the positive electrode active material, thereby improving the adhesion between the adhesive layer and the positive electrode active material layer through riveting force. Controlling the average particle size D2 of the secondary particles to be greater than or equal to the median particle size Dv50 of the positive electrode active material can cause the secondary particles not to be completely embedded between the particles of the positive electrode active material, thereby increasing the contact area between the adhesive layer and the positive electrode active material layer, improving the adhesion between the adhesive layer and the positive electrode active material layer through chemical bonds between the adhesive layer and the positive electrode active material layer, and improving the interface stability of the separator and the positive electrode sheet, thereby reducing the side effects on the positive electrode side and improving the long cycle performance of the battery.

[0065] In an example, the battery cell satisfies the following relationship: 0.2≤D1 / D3≤0.8, and / or, 1.2≤D2 / D3≤15.

[0066] In an example, the average particle size of the primary particles is 100 nm-300 nm, the average particle size of the secondary particles is 0.1 μm-100 μm, and the median particle size Dv50 of the positive electrode active material is 0.3 μm-5 μm. The average particle size of the primary particles is D1, the average particle size of the secondary particles is D2, and the median particle size Dv50 of the positive electrode active material is D3. The battery cell satisfies the following relationship: 0.1≤D1 / D3≤1, and / or, 1≤D2 / D3≤20.

[0067] In an example, the positive electrode conductive agent includes one or more of acetylene black, ketjen black, carbon fiber, carbon nanotube, and graphene.

[0068] In an example, the positive electrode binder includes one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene, polyimide, polyacrylic acid, and polyacrylonitrile.

[0069] In one example, based on the total weight of the positive electrode active material layer, the weight content of the positive electrode active material is 85wt%-99wt% (e.g., 85wt%, 87wt%, 90wt%, 92wt%, 95wt%, 97wt%, or 99wt%), the weight content of the positive electrode conductive agent is 0.5wt%-8wt% (e.g., 0.5wt%, 1wt%, 3wt%, 5wt%, or 8wt%), and the weight content of the binder is 0.5wt%-7wt% (e.g., 0.5wt%, 1wt%, 3wt%, 5wt%, or 7wt%).

[0070] In one example, the positive current collector includes one or more of aluminum foil and composite aluminum foil.

[0071] In one example, the diaphragm 1 includes a heat-resistant layer 13 located between the substrate 11 and the adhesive layer 12.

[0072] like Figure 1 As shown, the separator 1 includes a substrate 11 and an adhesive layer 12 located on the side of the substrate 11 near the positive electrode 2, and a heat-resistant layer 13 located between the substrate 11 and the adhesive layer 12. It can be understood that the substrate 11 and the positive electrode 2 are connected by the adhesive layer 12 and the heat-resistant layer 13, wherein the adhesive layer 12 is in direct contact with the positive electrode 2, and the substrate 11 is in direct contact with the negative electrode 3.

[0073] In one example, the heat-resistant layer comprises heat-resistant particles with a median particle size Dv50 of 0.5 μm to 2 μm (e.g., 0.5 μm, 1 μm, 1.5 μm, or 2 μm).

[0074] In one example, the heat-resistant particles include one or more of alumina, boehmite, magnesium oxide, magnesium hydroxide, barium sulfate, barium titanate, zinc oxide, calcium oxide, silicon dioxide, silicon carbide, and nickel oxide. By controlling the specific selection of heat-resistant particles, the heat resistance of the separator can be controlled, thereby enabling the battery to still prevent contact between the positive and negative electrodes at high temperatures, thus improving the high-temperature safety performance of the battery.

[0075] In one example, the heat-resistant layer includes a second adhesive.

[0076] In one example, the second adhesive comprises one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polyimide, polyacrylonitrile, poly(meth)acrylate, aramid resin, poly(meth)acrylic acid, styrene-butadiene rubber (SBR), polyvinyl alcohol, polyvinyl acetate, and carboxyethyl cellulose.

[0077] In one example, the weight content of the heat-resistant particles is 50wt%-99wt% (e.g., 50wt%, 55wt%, 60wt%, 65wt%, 70wt%, 75wt%, 80wt%, 85wt%, 90wt%, 95wt% or 99wt%) and the weight content of the second binder is 1wt-50wt% (e.g., 1wt%, 5wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt% or 50wt%) based on the total weight of the heat-resistant layer.

[0078] In one example, the weight content of the heat-resistant particles is 80wt%-97wt% and the weight content of the second binder is 3wt%-20wt% based on the total weight of the heat-resistant layer.

[0079] In one example, the adhesion between the separator and the positive electrode sheet is 2N / m-10N / m (e.g., 2N / m, 3N / m, 4N / m, 5N / m, 6N / m, 7N / m, 8N / m, 9N / m or 10N / m).

[0080] In one example, the adhesive layer in the separator is located on the side of the substrate close to the positive electrode sheet, the substrate in the separator directly contacts the negative electrode sheet, and the adhesion between the separator and the negative electrode sheet is 0.5N / m-5N / m (e.g., 0.5N / m, 1N / m, 2N / m, 3N / m, 4N / m or 5N / m). By applying ultra-high pressure to the wound core after winding, specifically, the wound core is pressed at a pressure of 3MPa-10MPa (e.g., 3MPa, 4MPa, 5MPa, 6MPa, 7MPa, 8MPa, 9MPa or 10MPa) for 1min-20min (e.g., 1min, 3min, 5min, 8min, 10min, 13min, 15min, 18min or 20min), part of the negative electrode active material (the negative electrode active material directly contacting the substrate in the separator) is embedded into the separator (substrate) under the ultra-high pressure, so that the negative electrode sheet and the separator have a certain adhesion, ensuring the interface stability of the separator and the negative electrode sheet, thereby making the battery have good long cycle performance.

[0081] When the substrate in the separator directly contacts the negative electrode sheet, the separator (substrate) and the negative electrode sheet can still have the adhesion in the above range, thereby ensuring the interface stability of the separator and the negative electrode sheet and improving the long cycle performance of the battery, although there is no adhesive layer between the separator and the negative electrode sheet.

[0082] The second aspect of the present application provides a battery comprising the core of the first aspect of the present application.

[0083] In an example, the battery includes an electrolyte.

[0084] In an example, the electrolyte includes vinyl carbonate and / or vinylene carbonate, the weight content of the vinylene carbonate is Cwt%, the weight content of the vinyl carbonate is Dwt%, and the battery satisfies: 0.001≤C / (B / A)≤0.1, and / or, 1≤D / C≤10.

[0085] It is found through research that the reason causing the battery cycle life problem also includes that the electrolyte design and the swelling of the separator glue are too large, causing the separator to be seriously blocked; in addition, the lithium precipitation in the bending area is also an important factor causing the battery cycle capacity attenuation, thereby affecting the battery cycle performance. Based on this, by controlling the relationship between the coverage area ratio of the glue layer in the flat area, the coverage area ratio of the glue layer in the bending area, and the weight content of the vinylene carbonate in the electrolyte, and / or, controlling the weight content ratio of the vinyl carbonate and the vinylene carbonate in the electrolyte, the swelling effect of the electrolyte on the glue layer in the separator can be reduced, and the lithium precipitation problem in the bending area can also be improved, thereby improving the cycle performance and safety performance of the battery.

[0086] In an example, the electrolyte includes vinyl carbonate and vinylene carbonate, the weight content of the vinylene carbonate is Cwt%, the weight content of the vinyl carbonate is Dwt%, and the battery satisfies: 0.001≤C / (100*(B / A))≤0.1, and / or, 1≤D / C≤10.

[0087] In an example, Cwt% is 0.1wt%-10wt% (for example, 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt% or 10wt%). When the content of vinylene carbonate (VC) in the electrolyte is less than 0.1wt%, the electrolyte dynamics is slightly poor due to the too low VC content, affecting the low temperature performance of the battery; when the VC content in the electrolyte is greater than 10wt%, the polymer in the separator glue layer is too large due to the too high VC content, thereby increasing the coverage of the separator glue layer and affecting the transmission of lithium ions in the separator, affecting the long cycle performance of the battery.

[0088] In an example, Cwt% is 1wt%-8wt%.

[0089] In an example, Dwt% is 5wt%-25wt% (for example, 5wt%, 10wt%, 15wt%, 20wt% or 25wt%).

[0090] In an example, Dwt% is 7wt%-20wt%.

[0091] In an example, the proportion of the area of the adhesive layer located in the bending area to the area of the bending area is A%, and the proportion of the area of the adhesive layer located in the flat area to the area of the flat area is B%, the proportion of the weight of the adhesive layer located in the bending area to the total weight of the electrolyte is Cwt%, and the proportion of the weight of the adhesive layer located in the flat area to the total weight of the electrolyte is Dwt%, and the battery satisfies: 0.001≤C / (100*(B / A))≤0.1, and / or, 1≤D / C≤10.

[0092] In an example, the electrolyte includes a lithium salt, EMC, EA, and LIFSi.

[0093] In an example, the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium perchlorate.

[0094] In an example, the weight content of the lithium salt is 1wt%-20wt% (e.g., 1wt%, 5wt%, 10wt%, 15wt%, or 20wt%) based on the total weight of the electrolyte, the weight content of the EMC is 10wt%-70wt% (e.g., 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, or 70wt%) based on the total weight of the electrolyte, the weight content of the EA is 10wt%-70wt% (e.g., 10wt%, 20wt%, 30wt%, 40wt%, 50wt%, 60wt%, or 70wt%) based on the total weight of the electrolyte, and the weight content of the LIFSi is 1wt%-20wt% (e.g., 1wt%, 5wt%, 10wt%, 15wt%, or 20wt%) based on the total weight of the electrolyte.

[0095] In an example, the weight content of the lithium salt is 5wt%-15wt% based on the total weight of the electrolyte, the weight content of the EMC is 15wt%-50wt% based on the total weight of the electrolyte, the weight content of the EA is 15wt%-50wt% based on the total weight of the electrolyte, and the weight content of the LIFSi is 5wt%-15wt% based on the total weight of the electrolyte.

[0096] In an example, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer located on one side or both sides of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active substance, a negative electrode conductive agent, and a negative electrode binder.

[0097] In an example, the negative electrode active substance includes one or more of graphite, hard carbon, SiOx / C, and Si / C graphite composite.

[0098] In an example, the graphite includes one or more of artificial graphite and natural graphite.

[0099] In an example, the negative electrode conductive agent includes one or more of conductive carbon black (SP), acetylene black, ketjen black, carbon fiber, carbon nanotube, and graphene.

[0100] In an example, the carbon nanotube includes one or more of single-walled carbon nanotube and multi-walled carbon nanotube.

[0101] In an example, the negative electrode binder includes one or more of styrene butadiene rubber (SBR), PAA, sodium carboxymethyl cellulose (CMC-Na), lithium carboxymethyl cellulose (CMC-Li), PVDF, and PTFE.

[0102] In an example, the weight content of the negative electrode active material is 80 wt% to 99 wt% (e.g., 80 wt%, 85 wt%, 90 wt%, 95 wt%, or 99 wt%), the weight content of the negative electrode conductive agent is 0.5 wt% to 10 wt% (e.g., 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%), and the weight content of the negative electrode binder is 0.5 wt% to 10 wt% (e.g., 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, or 10 wt%) based on the total weight of the negative electrode active material layer.

[0103] In an example, the battery is a lithium ion battery.

[0104] In an example, the battery is a lithium ion secondary battery.

[0105] The present application will be described in detail below through examples. The examples described in the present application are only a part of the examples of the present application, but not all of the examples. Based on the examples in the present application, all other examples obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present application.

[0106] The following examples are used to illustrate the battery of the present application.

[0107] Example 1

[0108] (1) Preparation of the positive electrode sheet

[0109] The positive active material (lithium iron phosphate (LFP) doped with titanium and vanadium), the positive electrode binder (polyvinylidene fluoride (PVDF)), and the positive electrode conductive agent (acetylene black) are mixed in a weight ratio of 96.5:1.5:2.0, N-methyl pyrrolidone (NMP) is added, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is uniformly coated on both sides of an aluminum foil with a thickness of 10 μm; the coated aluminum foil is baked in an oven with five different temperature gradients (95℃±5℃, 100℃±5℃, 103℃±5℃, 100℃±5℃, 95℃±5℃), and then dried in an oven at 120℃ for 8 h, followed by rolling and slitting to obtain the required positive electrode sheet.

[0110] (2) Preparation of the negative electrode sheet

[0111] The negative active material (artificial graphite), the negative electrode conductive agent (0.2 parts by weight of single-walled carbon nanotubes (SWCNT) and 1 part by weight of conductive carbon black (SP)), and the negative electrode binder (1 part by weight of sodium carboxymethyl cellulose (CMC-Na) and 2.5 parts by weight of styrene-butadiene rubber (SBR)) are mixed in a weight ratio of 95.3:1.2:3.5, a slurry is prepared by a wet process (water is added to the mixture formed above, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a negative electrode slurry with uniform fluidity), and the slurry is coated on both sides of the negative electrode current collector (copper foil), followed by drying (temperature: 85℃, time: 5 h), rolling, and die cutting to obtain the negative electrode sheet.

[0112] (3) Preparation of the electrolyte

[0113] In an argon-filled glove box (moisture <10 ppm, oxygen <1 ppm), 36 parts by weight of methyl ethyl carbonate (EMC), 27 parts by weight of ethyl acetate (EA), and 13.5 parts by weight of ethylene carbonate (EC) are mixed uniformly to obtain a mixed solution 1, 4.5 parts by weight of VC is added to the mixed solution 1 to obtain a mixed solution 2, 6.5 parts by weight of LiFSi and 12.5 parts by weight of lithium hexafluorophosphate are slowly added to the mixed solution 2, and stirring is performed uniformly to obtain a non-aqueous electrolyte.

[0114] (4) Preparation of the separator

[0115] The heat-resistant particles (aluminum oxide, 95 parts by weight) and the second binder (poly(meth)acrylic acid, 5 parts by weight) are mixed to form solution A.

[0116] The polymer (polyvinylidene fluoride-hexafluoropropylene copolymer, 92 parts by weight), the first binder (poly(meth)acrylic acid, 4 parts by weight), and the thickening agent (sodium carboxymethyl cellulose, 4 parts by weight) are mixed to form solution B.

[0117] Solution A is coated on one side of the substrate (PE) with a thickness of 7 μm by means of gravure roll coating, and after drying, a 2 μm heat-resistant layer is obtained, which is referred to as separator C;

[0118] Solution B is coated on the heat-resistant layer side of separator C by means of spray coating, and after drying, a 2 μm heat-resistant layer and a 2 μm adhesive layer are obtained, which is referred to as separator D; the surface of one side of the substrate of the separator has a heat-resistant layer and an adhesive layer, and the heat-resistant layer is located between the substrate and the adhesive layer, and the other side is not coated with a heat-resistant layer and an adhesive layer.

[0119] (5) Preparation of lithium ion battery

[0120] The positive electrode sheet of step (1), the separator of step (4), and the negative electrode sheet of step (2) are wound to obtain a bare battery without liquid injection, wherein the adhesive layer of the separator is in direct contact with the positive electrode sheet, and the substrate (the side not coated with a heat-resistant layer and an adhesive layer) is in direct contact with the negative electrode sheet, and a 5 MPa pressure is applied to the wound core for 10 min; the bare battery is placed in an outer packaging foil, and the electrolyte of step (3) is injected into the dried bare battery, and after vacuum packaging, standing, formation, shaping, sorting, and other processes, the desired lithium ion battery is obtained.

[0121] Example 2

[0122] Example 1 is referred to, except that the values of the parameters are changed, and the specific values are shown in Table 1-1 and Table 1-2.

[0123] Example 3

[0124] Example 1 is referred to, except that the values of the parameters are changed, and the specific values are shown in Table 1-1 and Table 1-2.

[0125] Example 4 group

[0126] This group of examples is used to illustrate the effect of changing H1 / H2.

[0127] This group of examples refers to Example 1, except that H1 / H2 is changed, and the specific values are shown in Table 1-1 and Table 1-2.

[0128] Example 5 group

[0129] This group of examples is used to illustrate the effect of changing the coverage area ratio of the adhesive layer.

[0130] This group of examples refers to Example 1, except that the coverage area ratio of the adhesive layer is changed, and the specific values are shown in Table 1-1 and Table 1-2.

[0131] Example 6 group

[0132] This group of examples is used to illustrate the effect of changing the weight content of the polymer in the adhesive layer.

[0133] This group of examples was conducted according to Example 1, except that the weight content of the polymer in the adhesive layer was changed, see Table 1-1 and Table 1-2.

[0134] Example 7 group

[0135] This group of examples was conducted to show the effect of changing D1 and / or D2 and / or D3.

[0136] This group of examples was conducted according to Example 1, except that D1 and / or D2 and / or D3 were changed, see Table 1-1 and Table 1-2.

[0137] Example 8 group

[0138] This group of examples was conducted to show the effect of changing Cwt%.

[0139] This group of examples was conducted according to Example 1, except that Cwt% was changed, see Table 1-1 and Table 1-2.

[0140] Example 9 group

[0141] This group of examples was conducted to show the effect of changing Dwt%.

[0142] This group of examples was conducted according to Example 1, except that Dwt% was changed, see Table 1-1 and Table 1-2.

[0143] Example 10 group

[0144] This group of examples was conducted to show the effect of changing C / (100*(B / A)).

[0145] This group of examples was conducted according to Example 1, except that C / (100*(B / A)) was changed, see Table 1-1 and Table 1-2.

[0146] Example 11

[0147] This group of examples was conducted according to Example 1, except that both sides of the substrate of the separator were coated with a heat resistant layer and an adhesive layer, see Table 1-1 and Table 1-2.

[0148] Comparative Example 1

[0149] This group of examples was conducted according to Example 1, except that no adhesive layer was coated, see Table 1-1 and Table 1-2.

[0150] Comparative Example 2

[0151] This group of examples was conducted according to Example 1, except that H1 and / or H2 were changed so that H1 / H2 > 10, see Table 1-1 and Table 1-2.

[0152] Comparative Example 3

[0153] Refer to Example 1, except that H1 and / or H2 are changed to make H1 / H2 < 1, see Table 1-1 and Table 1-2.

[0154] Comparative Example 4

[0155] Refer to Example 1, except that H1 and / or H2 are changed to make H1 / H2 = 1, see Table 1-1 and Table 1-2.

[0156] Table 1-1

[0157]

[0158]

[0159]

[0160] * means the same as Example 1; - means not present.

[0161] Table 1-2

[0162]

[0163]

[0164]

[0165] * means the same as Example 1;

[0166] - means not present.

[0167] Test Example

[0168] The lithium ion batteries obtained in the examples and comparative examples were tested as follows:

[0169] (1) -20℃ cycle test

[0170] The lithium ion battery was placed in an environment of (-20±2)℃, and rested for 2-3 hours, when the battery body reached (25±2)℃, the battery was charged at 1C constant current with a cutoff current of 0.05C, after the battery was fully charged, it was rested for 5 min, then discharged at 1C constant current to a cutoff voltage of 3.0V, the highest discharge capacity of the first 3 cycles was recorded as the initial capacity Q, when the cycle reached 10 times, the discharge capacity of the last cycle Q1 was recorded, the capacity retention rate (%) = Q1 / Q x 100%, the results were recorded in Table 2.

[0171] (2) 25℃ cycle test

[0172] The lithium ion battery was placed in an environment of (25±2) °C, and was allowed to stand for 2-3 hours. When the battery body reached (25±2) °C, the battery was charged at 3C constant current with a cut-off current of 0.05C. After the battery was fully charged, it was allowed to stand for 5 min, and then was discharged at 3C constant current to a cut-off voltage of 3.0V. The highest discharge capacity of the first 3 cycles was recorded as the initial capacity Q. When the cycle reached 1000 times, the discharge capacity of the last cycle was recorded as Q1, and the capacity retention rate (%) = Q1 / Q x 100%. The results were recorded in Table 2.

[0173] (3) 130 °C thermal shock test

[0174] The lithium ion battery was heated in a convection air oven at an initial temperature of (25±3) °C, with a temperature change rate of (5±2) °C / min, and was heated to (130±2) °C. After maintaining for 60 min, the test was ended. The state of the battery was recorded. If no explosion and / or fire occurred for 15 batteries of each sample, it was indicated as “pass”. If explosion or fire occurred, it was indicated as “fail”. The results were expressed as “pass times / 15”. For example, “15 / 15” indicated that all passed, and “10 / 15” indicated that 10 batteries of 15 batteries failed. The results were recorded in Table 2.

[0175] Table 2

[0176]

[0177]

[0178] The battery prepared in Comparative Example 1 had a cycle capacity retention rate of 70% after 500 cycles when subjected to the 25 °C cycle capacity retention test. Thereafter, the cycle capacity retention rate of the battery rapidly decreased, and the 1000 cycle test could not be completed.

[0179] The battery prepared in Comparative Example 3 had a cycle capacity retention rate of 70% after 300 cycles when subjected to the 25 °C cycle capacity retention test. Thereafter, the cycle capacity retention rate of the battery rapidly decreased, and the 1000 cycle test could not be completed.

[0180] As can be seen from Table 2, it can be seen from the comparative examples and the examples that, by providing a gum coating layer on the side of the base material of the separator close to the positive electrode sheet, and by controlling the ratio of the thickness of the gum coating layer in the first region to the thickness of the gum coating layer in the second region in the flat area, the cycle stability and safety performance of the battery are improved, and the service life of the battery is prolonged.

[0181] The preferred embodiments of the present application are described in detail above, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including that each technical feature is combined in any other suitable manner. These simple modifications and combinations should also be considered as disclosed by the present application and fall within the protection scope of the present application.

Claims

1. A battery cell, characterized in that, The battery cell includes a positive electrode, a separator, and a negative electrode. The separator is located between the positive electrode and the negative electrode. The separator includes a substrate and a coating layer. The coating layer is located on both sides of the substrate or on the side of the substrate closer to the positive electrode. The battery cell includes a flat region and a bent region. The separator includes a first region and a second region corresponding to the flat region. The second region is the region where the projection of the separator overlaps with that of the positive electrode. The first region is the region where the projection of the separator does not overlap with that of the positive electrode. The thickness of the coating layer in the first region is H1, and the thickness of the coating layer in the second region is H2. Then the battery cell satisfies the following relationship: 1 < H1 / H2 ≤ 10.

2. The battery cell according to claim 1, wherein, The battery cell satisfies the following relationship: 1.5≤H1 / H2≤5; And / or, H1 is 0.5μm-5μm; And / or, H2 is 0.2μm-3μm; And / or, the adhesive layer is located on the side of the substrate closer to the positive electrode sheet; And / or, the diaphragm has a thermal shrinkage rate of ≤5% at 130°C.

3. The battery cell according to claim 2, wherein, Based on the area of ​​the diaphragm, the coverage area of ​​the adhesive layer is 5%-40%; And / or, based on the area of ​​the bending zone, the coverage area A% of the adhesive layer in the bending zone is 5%-30%; And / or, based on the area of ​​the flat area, the coverage area of ​​the adhesive layer located in the flat area is 10%-40%.

4. The battery cell according to any one of claims 1-3, wherein, The coating layer includes a polymer, which includes primary particles and secondary particles; And / or, the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes a positive electrode active substance, the positive electrode active substance includes ternary materials that have been or have not been doped and coated, and lithium iron phosphate that has been or has not been doped and coated, wherein the doped elements include one or more of Al, Mg, Mn, Cr, Ti, V and Zr.

5. The battery cell according to claim 4, wherein, The average particle size of the primary particles is D1, the average particle size of the secondary particles is D2, and the median particle size Dv50 of the positive electrode active material is D3. Then, the battery cell satisfies the following relationship: 0.1≤D1 / D3≤1, and / or, 1≤D2 / D3≤20. And / or, based on the total weight of the adhesive layer, the polymer content is 80wt%-95wt%; And / or, the polymer includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylonitrile, polymethyl methacrylate and polyacrylic acid; And / or, the average particle size of the primary particles is 100nm-300nm; And / or, the average particle size of the secondary particles is 0.1 μm-100 μm; And / or, the median particle size Dv50 of the positive electrode active material is 0.3 μm-5 μm.

6. The battery cell according to any one of claims 1-3, wherein, The diaphragm includes a heat-resistant layer, which is located between the substrate and the adhesive layer; Preferably, the heat-resistant layer comprises heat-resistant particles, and the median particle size Dv50 of the heat-resistant particles is 0.5μm-2μm; Preferably, the heat-resistant particles include one or more of alumina, boehmite, magnesium oxide, magnesium hydroxide, barium sulfate, barium titanate, zinc oxide, calcium oxide, silicon dioxide, silicon carbide, and nickel oxide.

7. The battery cell according to claim 6, wherein, The adhesive layer includes a first adhesive and a thickener. Based on the total weight of the adhesive layer, the weight content of the first adhesive is 1wt%-15wt%, and the weight content of the thickener is 1wt%-5wt%. And / or, the heat-resistant layer includes a second binder, wherein the weight content of the heat-resistant particles is 50wt%-99wt% based on the total weight of the heat-resistant layer, and the weight content of the second binder is 1wt%-50wt%.

8. A battery, characterized in that, The battery comprises the cell according to any one of claims 1-7.

9. The battery according to claim 8, wherein, The battery includes an electrolyte comprising ethylene carbonate and / or vinylene carbonate. Based on the total weight of the electrolyte, the weight content of vinylene carbonate is Cwt%, and the weight content of ethylene carbonate is Dwt%. Then the battery satisfies: 0.001≤C / (100*(B / A))≤0.1, and / or, 1≤D / C≤10.

10. The battery according to claim 9, wherein, The electrolyte includes ethylene carbonate and vinylene carbonate; And / or, Cwt% is 0.1wt%-10wt%; And / or, Dwt% is 5wt%-25wt%.

Images