Electrode assembly and battery

Abstract

The invention discloses an electrode assembly and a battery. The electrode assembly comprises a positive pole piece, a negative pole piece and an isolating membrane arranged between the positive pole piece and the negative pole piece, the positive pole piece, the negative pole piece and the isolating membrane are wound for multiple circles to form an electrode main body, and the electrode main body comprises a straight part and corner parts arranged at two opposite ends of the straight part; the positive pole piece is provided with a plurality of first convex parts arranged corresponding to the corner parts, and the height Hm (mu m) of the first convex parts in the thickness direction of the positive pole piece meets the condition that 15 < = Hm < = 80; the negative electrode piece comprises a negative electrode active material layer, the negative electrode active material layer comprises silicon material particles, based on the total weight of the negative electrode active material layer, the weight percentage A of the silicon material particles is greater than or equal to 5 and less than or equal to 50, and the average particle size Da (mu m) of the silicon material particles is greater than or equal to 1 and less than or equal to 30. Under the condition that the first convex part has higher supporting height, the interface problem of the corner part of the electrode assembly can be improved, and meanwhile, the problems of poor hipot test, poor K value, overheating, ignition and the like of the battery are improved.

Description

Technical Field

[0001] This application relates to the technical field of batteries, and particularly to an electrode assembly and a battery. Background Art

[0002] At present, the improvement of the specific capacity of graphite in the negative electrode of the lithium battery industry has entered a bottleneck. For the improvement of the energy density of lithium-ion batteries, silicon-containing materials are currently the focus of industry research. The theoretical specific capacity of silicon is as high as 4200 mAh / g, which is 10 times that of graphite. Currently, silicon-containing materials are ideal graphite replacement materials. However, the biggest challenge faced by silicon-containing materials at present is the swelling problem during the cycling process. When silicon reacts with Li + to generate Li x Si, the volume expands by up to 320%. The high volume expansion of silicon-containing materials will cause excessive extrusion at the corners of wound batteries, resulting in the inability of the electrolyte to be transported to the battery corners, and then triggering the problem of purple spot lithium deposition at the corners and the battery cycle performance degradation. Summary of the Invention

[0003] The inventors found that the expansion of silicon-containing materials easily causes extrusion between the layers of the electrode assembly. Especially during the charge and discharge process of the battery, the expansion and extrusion of the electrode assembly will be further aggravated, resulting in insufficient electrolyte between the layers of the electrode assembly, poor wetting, and easy occurrence of interface deterioration.

[0004] The embodiments of this application provide an electrode assembly and a battery, which can improve the problem that the expansion of silicon-containing materials easily causes the deterioration of the electrode sheet interface.

[0005] In a first aspect, the embodiments of this application provide an electrode assembly. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet. The positive electrode sheet, the negative electrode sheet, and the separator are wound multiple times to form an electrode body. The electrode body includes a flat part and corner parts disposed at opposite ends of the flat part. Multiple first protrusions are provided at the corner part of the positive electrode sheet. Along the thickness direction of the positive electrode sheet, the height of the first protrusion is Hm (μm), and Hm satisfies: 15 ≤ Hm ≤ 80. The negative electrode sheet includes a negative electrode active material layer, and the negative electrode active material layer includes silicon material particles. Based on the total weight of the negative electrode active material layer, the weight percentage content of the silicon material particles is A (%), and A satisfies: 5 ≤ A ≤ 50. The average particle diameter Da (μm) of the silicon material particles satisfies: 1 ≤ Da ≤ 30. The silicon material particles in this application can be pure silicon particles or silicon-containing particles with a carbon material as the skeleton.

[0006] Based on the above embodiments, by matching the particle size Da of the silicon material particles in the negative electrode sheet, the weight percentage A of the silicon material particles, and the height Hm of the first convex portion of the positive electrode sheet, the force exerted by the overall volume expansion of the negative active material layer of the negative electrode sheet on the first convex portion of the positive electrode sheet is made appropriate. When the first convex portion has an appropriate support height, the interface problem at the corner portion of the electrode assembly is improved, and at the same time, problems such as poor hipot test, poor K value, overheating, and ignition of the battery are improved.

[0007] In some embodiments, A satisfies: 5 ≤ A ≤ 20.

[0008] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive active material layer provided on the surface of the positive electrode current collector. The coating weight per unit area of the positive active material layer is CW1 (mg / 1540.25mm 2 ), and CW1 satisfies: 150 ≤ CW1 ≤ 400.

[0009] In some embodiments, CW1 satisfies: 150 ≤ CW1 ≤ 250, and the negative electrode sheet satisfies one of the following conditions:

[0010] (1) 10 < Da ≤ 20, 5 ≤ A ≤ 50, 15 ≤ Hm ≤ 60;

[0011] (2) 5 < Da ≤ 10, 5 ≤ A ≤ 40, 17 ≤ Hm ≤ 80;

[0012] (3) 1 ≤ Da ≤ 5, 5 ≤ A ≤ 23, 25 ≤ Hm ≤ 80.

[0013] In some embodiments, CW1 satisfies: 250 < CW1 ≤ 400, and the negative electrode sheet satisfies one of the following conditions:

[0014] (1) 10 < Da ≤ 20, 5 ≤ A ≤ 50, 25 ≤ Hm ≤ 70;

[0015] (2) 5 < Da ≤ 10, 5 ≤ A ≤ 40, 27 ≤ Hm ≤ 80;

[0016] (3) 1 ≤ Da ≤ 5, 5 ≤ A ≤ 20, 35 ≤ Hm ≤ 80.

[0017] Based on the above embodiments, different CW1 of the positive active material layer are matched with different heights of the first convex portion, and the weight percentage A of the silicon material particles and the average particle size Da of the silicon material particles of the negative active material layer are matched to reduce the damage of the expansion of the negative active material layer to the positive electrode sheet, thereby optimizing the manufacturing process and safety of the battery.

[0018] In some embodiments, the silicon material particles are spherical silicon material particles.

[0019] In some embodiments, the sphericity of the silicon material particles is S, and S satisfies: 0.7 ≤ S ≤ 1.

[0020] Based on the above embodiments, the outer surface of the silicon material particles is regular, which facilitates the matching of the silicon material particles with the first convex part of the positive electrode tab. When the silicon material particles expand, the extrusion damage to the first convex part is small, preventing the hard and overly sharp surface of the silicon material particles from piercing the separator or the positive electrode active material layer.

[0021] In some embodiments, the straight part has a first thickness L1 in the first direction;

[0022] Two corner parts are respectively arranged at opposite ends of the straight part in a second direction perpendicular to the first direction, and the corner part has a second thickness L2 in the second direction;

[0023] Each turn of the electrode tab includes two straight sections arranged opposite to each other in the first direction and two corner sections respectively arranged at both ends of the straight sections in the second direction;

[0024] The electrode tab has a finishing end corresponding to the straight section of the outermost turn of the electrode tab. All the straight sections and the finishing end arranged in layers in the first direction form a straight part; the first thickness L1 is the thickness of the straight part passing through the finishing end in the first direction; all the corner sections on the same side of the straight section in the second direction form a corner part, and the second thickness L2 is the thickness of the corner part passing through the midpoint of the line connecting the two ends of the innermost corner section in the second direction; the electrode assembly satisfies at least one of the following conditions:

[0025] (1) The number of winding turns of the electrode tab of the electrode body is even, and L1 and L2 satisfy: 2.0 ≤ L1 / L2 ≤ 2.2;

[0026] (2) The number of winding turns of the electrode tab of the electrode body is odd, and L1 and L2 satisfy: 2.0 ≤ L1 / L2 ≤ 2.4.

[0027] Based on the above embodiments, the electrode assembly has appropriate stress inside, which can better buffer the extrusion of the negative electrode active material layer on the separator and the positive electrode tab when the negative electrode active material layer expands, thereby reducing the probability of damage to the negative electrode active material layer, the positive electrode active material layer and the separator. When the electrode assembly is used in a battery, the use safety of the battery is improved.

[0028] In some embodiments, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes silicon material particles;

[0029] The negative electrode active material further includes at least one of silicon carbide, silicon oxide, graphite, and hard carbon.

[0030] In some embodiments, the negative electrode active material includes graphite, and the specific capacity of the graphite is ρ (mAh / g), where ρ satisfies: 350 ≤ ρ ≤ 370 mAh / g, and the OI value of the graphite satisfies: 6 ≤ OI ≤ 18.

[0031] Based on the above embodiments, by selecting the OI value of the graphite within the range satisfying the above conditional formula, the hard expansion of the graphite can be within a reasonable range, while not deteriorating the extension of the negative electrode tab in the length and width directions, so as to process convex portions on the negative electrode tab, and at the same time reduce the extrusion damage of the negative electrode tab to the positive electrode tab.

[0032] In some embodiments, the positive electrode tab includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode binder;

[0033] Based on the total weight of the positive electrode active material layer, the weight percentage content of the positive electrode binder is B, where 0.2% ≤ B ≤ 2.4%.

[0034] Based on the above embodiments, the bonding effect of the positive electrode binder is good, so that the positive electrode active material at the processed first convex portion has good morphological stability, is not prone to generating microcracks, and when the positive electrode active material is subjected to the acting force of the expansion and extrusion of the negative electrode active material layer, the positive electrode active material layer can still have good stability and is not easily extruded and deformed or chipped.

[0035] In a second aspect, an embodiment of the present application provides a battery, including an outer package and the electrode assembly as described above, and the electrode assembly is disposed in the internal space of the outer package.

[0036] Based on the electrode assembly and battery of the embodiments of the present application, by selecting silicon material particles with appropriate content and appropriate average particle size, the silicon material particles can reduce the damage to the separator during battery preparation processes such as electrode winding and formation hot pressing. During the process of embossing the electrode, when convex portions are formed on the electrode, some microcracks may be caused. Since the silicon material particles are relatively hard materials, when a certain pressure is applied to the electrode assembly during battery preparation, the microcracks generated on the surface of the positive electrode are likely to damage the separator, and there is also a risk that the silicon material may pierce the separator. When the average particle size and content of the selected silicon material particles are appropriate, the silicon material particles on the negative electrode can effectively reduce the number of microcracks formed, further reducing the damage to the separator. In addition, when the selected silicon material particles are spherical, the silicon material particles can better improve the number of microcracks formed and reduce the damage to the separator. Among them, since the silicon material particles will also expand, when the silicon material particles exist in the negative active material and expand, it will cause extrusion to the positive electrode, especially having a greater impact on the first convex portion of the positive electrode. The main factors affecting the hard expansion of the silicon material particles are the size of the average particle size Da of the silicon material particles and the content of the silicon material particles. With the same content, the larger the average particle size Da, the smaller the cyclic hard expansion. With the same average particle size Da, the greater the content of the silicon material particles, the greater the cyclic hard expansion. In addition, if the height Hm of the first convex portion of the positive electrode is too large, the gap between the electrodes during the cycle is large, and purple spot ion bridge-breaking problems are likely to occur in the later stage of the cycle. If Hm is too small, the hard expansion during the cycle causes extrusion at the corner, resulting in the inability to replenish the electrolyte, and lithium plating at the corner is likely to occur. By matching the average particle size Da of the silicon material particles, the weight percentage content A of the silicon material particles of the negative electrode and the height Hm of the first convex portion of the positive electrode in the embodiments of the present application, the force exerted by the overall volume expansion of the negative active material layer of the negative electrode on the first convex portion of the positive electrode is appropriate. Under the condition that the first convex portion has a higher support height, the interface problem of the corner part of the electrode assembly is improved, and at the same time, problems such as poor hipot test, poor K value, overheating, and ignition of the battery are improved.

[0037] In addition, the corner ion transport is also affected by the coating weight CW1 of the positive active material layer of the positive electrode. The greater the coating weight CW1, the more ions are transported per unit area, and the more timely the electrolyte replenishment is required, and the greater the convex point height Hm should be. By further selecting the coating weight CW1 of the positive electrode, the force exerted by the overall volume expansion of the negative active material layer of the negative electrode on the first convex portion of the positive electrode is appropriate, further improving the interface problem of the corner part of the electrode assembly and improving problems such as poor hipot test, poor K value, overheating, and ignition of the battery. Description of the Drawings

[0038] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those skilled in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0039] Figure 1 It is a front view structural schematic diagram of a pole piece in an unfolded state according to an embodiment of the present application;

[0040] Figure 2 It is a cross-sectional structural schematic diagram of an electrode assembly according to an embodiment of the present application;

[0041] Figure 3 It is a partial cross-sectional structural schematic diagram of a pole piece with a convex portion according to an embodiment of the present application.

[0042] Reference numerals:

[0043] 20, electrode body; 201, straight portion; 202, corner portion; 21, straight section; 22, corner section; 50, separator film;

[0044] 300, pole piece; 311, convex portion; 311a, first convex portion;

[0045] 410, positive pole piece; 420, negative pole piece;

[0046] X, length direction; Y, width direction; Z, thickness direction. Detailed implementation manners

[0047] In order to make the objectives, technical solutions and advantages of the present application more clear and understandable, the following further details the present application in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0048] The inventor found that when a bump structure is introduced into the pole piece, these bump structures will play a supporting role during the winding process of the pole piece, increasing the interlayer gap of the pole piece and being able to improve the corner extrusion problem caused by the expansion of the silicon-containing material. Among them, there are currently the following problems in forming a bump structure on the silicon-containing pole piece by mechanical pressure: 1) Mechanical pressure causes an increase in pole piece material chipping; 2) Mechanical pressure causes an increase in the extension of the current collector of the pole piece, and even a problem of current collector cracks; 3) The silicon-containing material itself has a hard nature and many sharp points. During the winding process, hot pressing is likely to pierce the separator film, and when further pressed in other processes of battery processing, combined with the pole piece having a bump structure, there are risks such as an increase in hipot test (dielectric withstand voltage test) failure, an increase in K value failure, overheating, and ignition.

[0049] Based on this, embodiments of the present application provide an electrode assembly and a battery. The structure of the electrode assembly is designed to effectively improve the problems of electrolyte infiltration and electrode sheet interface caused by the expansion of silicon-containing materials.

[0050] The battery provided by the embodiments of the present application includes an outer package, an electrode assembly disposed in the inner space of the outer package, and an electrolyte filled in the inner space of the outer package. The electrode assembly includes two electrode sheets with opposite polarities and a separator. As Figure 1 shown, it is a schematic front view structure diagram of the electrode sheet 300 in an unfolded state according to an embodiment of the present application. The electrode sheet 300 has a length direction X, a width direction Y, and a thickness direction Z that are perpendicular to each other in pairs. The length direction X, the width direction Y, and the thickness direction Z of the two electrode sheets 300 with opposite polarities of the electrode assembly are the same. As Figure 2 shown, the separator 50 is disposed between the two electrode sheets 300 with opposite polarities in the thickness direction Z of the electrode sheet 300. One of the two electrode sheets 300 with opposite polarities is a positive electrode sheet 410, and the other is a negative electrode sheet 420. The separator 50 has insulation properties and is used to separate the positive electrode sheet 410 and the negative electrode sheet 420 to prevent the positive electrode sheet 410 and the negative electrode sheet 420 from being short-circuited. The silicon material particles in the present application can be spherical with different sphericities (different aspect ratios) or irregularly shaped silicon material particles. The silicon material particles in the present application can be pure silicon particles or silicon-containing particles with a carbon material as the skeleton.

[0051] As Figure 2 shown, the separator 50 and the two electrode sheets 300 are wound around multiple turns along the length direction X of the electrode sheet 300 to form an electrode body 20. The length direction X of the electrode sheet 300 is the winding direction of the electrode sheet 300. The electrode body 20 is flat. The electrode body 20 includes a straight part 201 and two corner parts 202. The two corner parts 202 are respectively disposed at opposite ends of the straight part 201. Specifically, each turn of the electrode sheet 300 of the electrode body 20 includes two straight segments 21 and two corner segments 22. The two straight segments 21 are arranged side by side in a direction perpendicular to the plane of the straight segment 21, and the two corner segments 22 are arranged opposite to each other along the plane of the straight segment 21. That is, the two straight segments 21 and the two corner segments 22 are connected end to end in sequence. The electrode body 20 has a finishing end, and the finishing end is formed by a part of the straight segment 21 of the outermost turn of the electrode sheet 300. All the straight segments 21, the finishing end, and the separator 50 sandwiched between adjacent two straight segments 21 that are stacked in a direction perpendicular to the plane of the straight segment 21 together form the straight part 201; all the corner segments 22 located on the same side of the straight segment 21 in a direction parallel to the plane of the straight segment 21 and the separator 50 sandwiched between adjacent two corner segments 22 together form the corner part 202.

[0052] In the embodiments of the present application, any one of the two electrode plates (the positive electrode plate 410 and the negative electrode plate 420) may be provided with a convex portion 311. Specifically, the electrode plate includes a current collector and an active material layer, the active material layer and the current collector are stacked along the thickness direction Z of the electrode plate 300, and the active material layer is provided on the surface of the current collector. Among them, the convex portion 311 is formed by the convexity of a part of the current collector and a part of the active material layer along the thickness direction Z of the electrode plate 300 toward the same side of the electrode plate 300. As Figure 1 shown, the convex portion 311 is provided in the convex point area on the surface of the active material layer facing away from the current collector, and there is a distance between the convex point area and the edge of the surface of the active material layer. After two electrode plates 300 with opposite polarities and the separator 50 are wound multiple times to form the electrode body 20, the convex portion 311 contacts the separator 50 to provide support for the separator 50. When the electrode body 20 expands, the convex portion 311 can still support the separator 50. The contact area between the convex portion 311 and the separator 50 is small, so that there is a space between the part of the electrode plate 300 corresponding to the convex point area 310 and the separator 50 for accommodating the electrolyte, preventing abnormal situations such as insufficient electrolyte and poor wetting between the electrode plate 300 and the separator 50 due to expansion extrusion.

[0053] The electrode plate 300 has a plurality of convex portions 311, and at least one of the straight section 21 and the corner section 22 has a convex portion 311. Optionally, all the convex portions 311 provided on a single electrode plate 300 protrude toward the same side of the electrode plate 300 in the thickness direction Z of the electrode plate 300. For example, when both the straight section 21 and the corner section 22 have convex portions 311, the convex portion 311 provided on the straight section 21 and the convex portion 311 provided on the corner section 22 both protrude toward the side of the winding center of the electrode body 20; or, the convex portion 311 provided on the straight section 21 and the convex portion 311 provided on the corner section 22 both protrude toward the side away from the winding center of the electrode body 20. Optionally, some of the convex portions 311 provided on a single electrode plate 300 protrude toward one side of the electrode plate 300 in the thickness direction Z of the electrode plate 300, and the other part of the convex portions 311 protrude toward the other side of the electrode plate 300 in the thickness direction Z of the electrode plate 300. For example, the convex portion 311 provided on the straight section 21 protrudes toward the side of the winding center of the electrode body 20, and the convex portion 311 provided on the corner section 22 protrudes toward the side away from the winding center of the electrode body 20; or, the convex portion 311 provided on the straight section 21 protrudes toward the side away from the winding center of the electrode body 20, and the convex portion 311 provided on the corner section 22 protrudes toward the side of the winding center of the electrode body 20.

[0054] The above is only an exemplary introduction, and the present application does not limit the orientation of the convex portions 311 of each electrode plate 300, and can be specifically selected according to actual needs.

[0055] Among them, the current collector of the positive electrode plate 410 is the positive current collector, and the active material layer is the positive active material layer; the current collector of the negative electrode plate 420 is the negative current collector, and the active material layer is the negative active material layer. The negative active material layer includes a negative active material, and the negative active material includes a silicon-containing material. When the silicon-containing material expands, in addition to the fact that the negative active material layer is easily damaged due to internal stress inside the negative electrode plate 420, it is also likely to cause extrusion on the separator 50 and the positive electrode plate 410. Especially when the positive electrode plate 410 has a convex portion 311, when the silicon-containing material expands and extrudes the positive electrode plate 410, it is likely to cause deformation or damage at the convex portion 311. In addition, the positive electrode plate 410, the negative electrode plate 420, and the separator 50 are wound multiple times to form an electrode body. The electrode body includes a flat portion and corner portions provided at opposite ends of the flat portion. When the positive electrode plate 410 is provided with a convex portion 311 (i.e., the first convex portion 311a described later) corresponding to the corner portion, since the convex portion 311 provided corresponding to the corner portion already bears a large interlayer extrusion force, when the silicon-containing material contained in the negative active material layer expands, the extrusion on the positive electrode plate 410 corresponding to the corner portion will be further strengthened, resulting in the convex portion 311 corresponding to the corner portion of the positive electrode plate 410 being more easily extruded and deformed.

[0056] As Figure 2 and Figure 3 shown, the convex portion 311 of the positive electrode plate 410 includes a plurality of first convex portions 311a provided corresponding to the corner portion. Along the thickness direction of the positive electrode plate 410, the height of the first convex portion 311a is Hm, and Hm satisfies: 15 μm ≤ Hm ≤ 80 μm. In this height range, the first convex portion 311a can provide support for the separator 50 and the negative electrode plate 420 at the corner portion, improving the electrolyte infiltration effect. Preferably, 20 μm ≤ Hm ≤ 55 μm. Among them, the silicon-containing material included in the negative active material is silicon material particles. Based on the total weight of the negative active material layer, the weight percentage content of the silicon material particles is A, and A satisfies: 1% ≤ A ≤ 50%. Preferably, 5% ≤ A ≤ 20%. The average particle diameter Da of the silicon material particles satisfies: 1 μm ≤ Da ≤ 30 μm. Preferably, 5 μm ≤ Da ≤ 20 μm.

[0057] In the embodiments of the present application, by selecting silicon material particles with appropriate average particle size and in an appropriate range, the silicon material particles can reduce the damage to the separator 50 due to the expansion of the silicon material particles. Among them, the larger the average particle size Da of the silicon material particles, the smaller the expansion rate of the silicon material particles, and the smaller the extrusion of the corner part caused by the expansion of the silicon material particles. By matching the average particle size Da of the silicon material particles, the weight percentage content A of the silicon material particles in the negative electrode plate 420, and the height Hm of the first convex part 311a of the positive electrode plate 410, the acting force of the overall volume expansion of the negative active material layer of the negative electrode plate 420 on the first convex part 311a of the positive electrode plate 410 is appropriate. In the case where the first convex part 311a has a higher support height, it has good structural stability at the same time, so as to stably play a supporting role, improve the interface problem of the corner part of the electrode assembly, and further improve problems such as hipot test failure, K value failure, overheating, and ignition of the battery. When the selected silicon material particles are spherical, the damage to the separator 50 can be further reduced, and the regular spherical shape and smooth surface can play a more stable supporting role, improve the interface problem of the corner part of the electrode assembly, and further improve problems such as hipot test failure, K value failure, overheating, and ignition of the battery.

[0058] In the embodiments of the present application, the negative electrode plate 420 may also have a convex part 311. Some parts of the negative current collector and some parts of the negative active material layer need to be extended and deformed to form the convex part 311. When the negative active material layer extends, the particle size of the silicon material particles easily affects the morphological stability of the negative active material layer at the convex part 311. For example, if the particle size of the silicon material particles is too large, there is a risk of microcracks or powder falling off in the negative active material layer at the convex part 311, which affects the yield rate during the battery winding process and the safety of the battery. In addition, the content of the silicon material particles will also have a greater impact on the overall volume expansion rate of the negative active material layer. By selecting the average particle size Da of the silicon material particles to satisfy 1μm ≤ Da ≤ 30μm, and selecting the weight percentage content A of the silicon material particles to satisfy 5% ≤ A ≤ 50%, a convex part 311 with better morphology can be processed on the negative electrode plate 420, and abnormal conditions such as microcracks, powder falling off, or piercing of the diaphragm are not likely to occur in the negative active material layer, improving the yield rate during the winding process. When the negative electrode plate 420 is used in a battery, the battery can have good use safety. When A is greater than 50%, the content of the silicon material particles is too large, which easily leads to too large an overall volume expansion rate of the negative active material layer. When the average particle size Da of the silicon material particles is greater than 30μm, the particle size of the silicon material particles is too large, which is not conducive to the formation of the convex part 311, and it is also easy to cause risks such as microcracks or powder falling off in the negative active material layer. Moreover, the hardness of the silicon material particles is relatively large. When the silicon material particles expand, a too large average particle size Da of the silicon material particles is more likely to cause damage to the positive electrode plate 410 due to extrusion.

[0059] In some embodiments, the positive electrode sheet 410 includes a positive electrode current collector and a positive electrode active material layer provided on the surface of the positive electrode current collector. The coating weight per unit area of the positive electrode active material layer is CW1, and CW1 satisfies: 150 mg / 1540.25 mm 2 ≤ CW1 ≤ 400 mg / 1540.25 mm 2 , for example, CW1 can be 150 mg / 1540.25 mm 2 、200 mg / 1540.25 mm 2 、300 mg / 1540.25 mm 2 、350 mg / 1540.25 mm 2 、400 mg / 1540.25 mm 2 Or any range of the above two. By selecting the coating weight CW1 per unit area of the active material layer within the above range, the positive electrode sheet 410 has a suitable electrolyte infiltration effect, and it is convenient to control the thickness of the positive electrode active material layer within a suitable range. Furthermore, when the first convex portion 311a is formed by convexity on the positive electrode sheet 410, microcracks are not easily generated in the positive electrode active material layer, and abnormal conditions such as powder falling and piercing of the separator film 50 are not likely to occur in the positive electrode active material layer.

[0060] It can be understood that for the positive electrode sheet 410 with a lower CW1, the thickness of the positive electrode active material layer is smaller, and for the positive electrode sheet 410 with a higher CW1, the thickness of the positive electrode active material layer is larger. When the first convex portion 311a of the positive electrode sheet 410 is generated, stress and plastic deformation are generated on the positive electrode sheet 410. At this time, the positive electrode sheet 410 undergoes extension. The higher the height Hm of the first convex portion 311a, the greater its elongation rate, and the greater the damage to the positive electrode sheet 410, and it is easier to generate microcracks on the surface of the positive electrode active material layer, and risks such as powder falling and piercing of the separator membrane occur, affecting the yield rate and battery safety during the winding process. Moreover, when the positive electrode sheet 410 is subjected to the expansion and extrusion force of the negative electrode active material layer, not only is the first convex portion 311a of the positive electrode sheet 410 prone to deformation, but also if the thickness of the positive electrode active material layer does not match the content and particle size of the silicon material particles, the positive electrode active material layer is easily damaged by extrusion. Therefore, for different CW1 of the positive electrode active material layer, not only different heights of the first convex portion 311a need to be matched, but also the weight percentage A of the silicon material particles and the average particle size Da of the silicon material particles of the negative electrode active material layer need to be matched to reduce the damage to the positive electrode sheet 410 caused by the expansion of the negative electrode active material layer, thereby optimizing the manufacturing process and safety of the battery.

[0061] In some embodiments, CW1 satisfies: 150 mg / 1540.25 mm 2 ≤ CW1 ≤ 250 mg / 1540.25 mm 2, that is, when the coating weight CW1 per unit area of the positive electrode active material layer is low, the negative electrode sheet 420 satisfies one of the following conditions:

[0062] (1) 10 μm < Da ≤ 20 μm, 5% ≤ A ≤ 50%, 15 μm ≤ Hm ≤ 60 μm.

[0063] (2) 5 μm < Da ≤ 10 μm, 5% ≤ A ≤ 40%, 17 μm ≤ Hm ≤ 80 μm.

[0064] (3) 1 μm ≤ Da ≤ 5 μm, 5% ≤ A ≤ 23%, 25 μm ≤ Hm ≤ 80 μm.

[0065] In some embodiments, CW1 satisfies: 250 mg / 1540.25 mm 2 <CW1 ≤ 400 mg / 1540.25 mm 2 , that is, when the coating weight CW1 per unit area of the positive electrode active material layer is high, the negative electrode sheet 420 satisfies one of the following conditions:

[0066] (1) 10 μm < Da ≤ 20 μm, 5% ≤ A ≤ 50%, 25 μm < Hm ≤ 70 μm.

[0067] (2) 5 μm < Da ≤ 10 μm, 5% ≤ A ≤ 40%, 27 μm < Hm ≤ 80 μm.

[0068] (3) 1 μm ≤ Da ≤ 5 μm, 5% ≤ A ≤ 20%, 35 μm ≤ Hm ≤ 80 μm.

[0069] In this application, by selecting silicon material particles in the negative electrode active material layer and matching the particle size and content of the silicon material particles, for the positive electrode sheet 410 having the first convex portion 311a, at the coating weight CW1 per unit area corresponding to the positive electrode active material layer, it is possible to achieve a more appropriate height of the first convex portion 311a while reducing the damage to the positive electrode sheet 410, preventing microcracks from occurring in the positive electrode active material layer of the positive electrode sheet 410, having no side effects on the processing process, and thus not affecting its safety performance at the battery level. At the same time, the electrolyte infiltration is improved, and the charge and discharge cycle performance of the battery is improved.

[0070] Among them, the positive electrode sheet 410 has a plurality of second convex portions corresponding to the flat portion. Along the thickness direction of the positive electrode sheet 410, the height of the second convex portion is Hn, the diameter of the inner surface of the first convex portion 311a is Rm, and the diameter of the inner surface of the second convex portion is Rn. The electrode assembly further satisfies at least one of the following conditions:

[0071] (1) 5 μm ≤ Hn ≤ 40 μm.

[0072] (2) 1.5 ≤ Hm / Hn ≤ 5.

[0073] (3) 0.3 mm ≤ Rm ≤ 10 mm.

[0074] (4) Rm = Rn.

[0075] In some embodiments, the sphericity of the silicon material particles is S, satisfying: 0.7 ≤ S ≤ 1. For example, S can be 0.70, 0.74, 0.80, 0.88, 0.90, 0.96, 1.0 or any range between the two. The sphericity of the silicon material particles is the ratio of the surface area of a sphere with the same volume as the silicon material particles to the surface area of the silicon material particles. By selecting the sphericity of the silicon material particles to satisfy the range of the above conditional formula in the embodiments of the present application, the appearance of the silicon material particles is regular, which is convenient for the silicon material particles to match with the first convex portion 311a of the positive electrode tab 410. When the silicon material particles expand, the extrusion damage to the first convex portion 311a is small, preventing the silicon material particles with high hardness and overly sharp surfaces from piercing the separator 50 or the positive electrode active material layer. Moreover, by using silicon material particles with a relatively high sphericity S, it is convenient to prevent microcracks from appearing in the negative electrode active material layer when processing the convex portion 311 on the negative electrode tab 420. Therefore, considering the dual effects on the positive electrode tab 410 and the negative electrode tab 420, using the above silicon material particles with a relatively high sphericity can effectively improve the problems of rapid power loss of the battery and excessive voltage drop during long-term storage.

[0076] As Figure 2 shown, the straight portion of the electrode body 20 has a first thickness L1 in the first direction; two corner portions are respectively provided at opposite ends of the straight portion in a second direction perpendicular to the first direction, and the corner portion has a second thickness L2 in the second direction; each turn of the tab includes two straight segments 21 arranged opposite to each other in the first direction and two corner segments 22 respectively provided at both ends of the straight segment 21 in the second direction; the tab 300 has a finishing end corresponding to the straight segment 21 of the outermost turn of the tab 300, and all the straight segments 21 and the finishing end stacked in the first direction form the straight portion; the first thickness L1 is the thickness of the straight portion passing through the finishing end in the first direction; all the corner segments 22 on the same side of the straight segment 21 in the second direction form the corner portion, and the second thickness L2 is the thickness of the corner portion passing through the midpoint of the line connecting both ends of the innermost corner segment 22 in the second direction.

[0077] In some embodiments, the electrode assembly satisfies at least one of the following conditions:

[0078] (1) The number of winding turns of the tabs of the electrode body is even, and L1 and L2 satisfy: 2.0 ≤ L1 / L2 ≤ 2.2.

[0079] (2) The number of winding turns of the tabs of the electrode body is odd, and L1 and L2 satisfy: 2.0 ≤ L1 / L2 ≤ 2.4.

[0080] By selecting the first thickness L1 of the flat part and the second thickness L2 of the corner part to satisfy the range of the above conditional formula, a suitable stress is provided inside the electrode assembly, which can better buffer the extrusion of the negative electrode active material layer on the separator and the positive electrode plate 410 when the negative electrode active material layer expands, thereby reducing the probability of damage to the negative electrode active material layer, the positive electrode active material layer and the separator. When the electrode assembly is used in a battery, the safety of battery use is improved.

[0081] In the embodiments of the present application, in addition to silicon material particles, the negative electrode active material may further include at least one of silicon carbide, silicon oxide, graphite, and hard carbon. Compared with other Si materials, spherical Si has the best comprehensive performance in terms of cycling and swelling.

[0082] When the negative electrode active material includes graphite, graphite will also expand by a certain volume. However, compared with silicon material particles, the expansion rate of graphite is smaller, and the hardness of graphite is lower, so the damage of graphite expansion to the separator and the positive electrode plate 410 is relatively small. In some embodiments, based on the total weight of the negative electrode active material layer, the weight percentage content of graphite is C, and 50% ≤ B ≤ 95%, which is convenient for the cooperation of graphite and silicon material particles. While the battery has a higher energy density, the negative electrode active material layer has a suitable expansion rate, reducing the damage of the negative electrode active material layer to the positive electrode plate 410.

[0083] In some embodiments, the specific capacity of graphite is ρ, and ρ satisfies: 350 mAh / g ≤ ρ ≤ 370 mAh / g. For example, ρ can be 350 mAh / g, 355 mAh / g, 358 mAh / g, 362 mAh / g, 366 mAh / g, 370 mAh / g or any range between the two. By selecting the negative electrode active material to further include graphite with the above specific capacity range, the battery has a higher energy density.

[0084] The OI value (On-Island value) of graphite reflects the insertion and extraction rate of lithium ions on the surface of graphite, which is an important basis for evaluating the performance of graphite. In some embodiments, the OI value of graphite satisfies: 6 ≤ OI ≤ 18. For example, the OI value can be 6, 7, 8, 9, 10, 11, 12, 14, 16, 18 or any range between the two. By selecting the OI value of graphite to satisfy the range of the above conditional formula, the hard expansion of graphite can be within a reasonable range, and at the same time, the extension of the negative electrode plate 420 in its length and width directions is not deteriorated, so that convex portions can be processed on the negative electrode plate 420, while reducing the extrusion damage of the negative electrode plate 420 to the positive electrode plate 410.

[0085] The positive electrode active material layer includes a positive electrode active material. In the embodiments of the present application, the type of the positive electrode active material is not limited, and any material that can be used as a positive electrode active material in the art is applicable to the present application. In some embodiments, the positive electrode active material includes at least one of lithium cobalt oxide material LiCoO2 (LCO), ternary material, and lithium iron phosphate material.

[0086] Exemplarily, the positive electrode active material includes LiCoO2, LiNiO2, LiMn2O4, LiCo 1-y M y O2, LiNi 1-y M y O2, LiMn 2-y M y O4, LiNi x Co y Mn z M 1-x-y-z O2, where M is selected from at least one of Fe, Co, Ni, Mn, Mg, Cu, Zn, Al, Sn, B, Ga, Cr, Sr, V, or Ti, and 0 ≤ y ≤ 1, 0 ≤ x ≤ 1, 0 ≤ z ≤ 1, and x + y + z ≤ 1.

[0087] The positive electrode active material layer further includes a positive electrode binder. The positive electrode binder is mixed with the positive electrode active material. The positive electrode binder bonds the positive electrode active material, and the positive electrode binder located in the inner layer also bonds to the positive electrode current collector, so that the entire positive electrode active material can stably adhere to the surface of the positive electrode current collector. It can be understood that different contents of the positive electrode active material or different contents of the positive electrode binder result in different stresses and plastic deformation capabilities on the positive electrode tab 410. The higher the content of the positive electrode active material, the lower the content of the positive electrode binder, and the higher the risk of powder shedding in the positive electrode active material layer during the manufacturing of the convex portion 311.

[0088] In some embodiments, based on the total weight of the positive electrode active material layer, the weight percentage content of the positive electrode binder is B, 0.2% ≤ B ≤ 2.4%. For example, B can be 0.2%, 0.8%, 1.2%, 1.6%, 2.0%, 2.2%, 2.4%, or any range between the above two values. By selecting the content of the positive electrode binder within the above range, the bonding effect of the positive electrode binder is good, so that the positive electrode active material at the first convex portion 311a processed has good morphological stability and is not prone to generating microcracks. Moreover, when the positive electrode active material is subjected to the expansion and extrusion force of the negative electrode active material layer, the positive electrode active material layer can still have good stability and is not easily squeezed and deformed or chipped.

[0089] There is no particular limitation on the cathode binder in the embodiments of the present application, and various materials known to those skilled in the art that can be used as cathode binders are applicable to the present application. Exemplarily, the cathode binder may include at least one of a copolymer of vinylidene fluoride - hexafluoropropylene, a styrene - acrylate copolymer, a styrene - butadiene copolymer, a polyamide, a polyacrylonitrile, a polyacrylate, a polyacrylate salt, sodium carboxymethyl cellulose, a polyvinyl acetate, a polyvinylpyrrolidone, a polyethylene ether, a polymethyl methacrylate, a polytetrafluoroethylene, or a polyhexafluoropropylene.

[0090] The cathode active material layer further includes a conductive agent. Exemplarily, the conductive agent in the cathode active material layer may include at least one of conductive carbon black, acetylene black, Ketjen black, flake graphite, graphene, carbon nanotubes, or carbon fibers.

[0091] There is no particular limitation on the cathode current collector in the embodiments of the present application, and various materials known to those skilled in the art that can be used as cathode current collectors are applicable to the present application. Exemplarily, an aluminum foil may be used as the cathode current collector. Of course, other commonly used cathode current collectors in the art may also be used. The thickness of the cathode current collector may be from 1 μm to 200 μm. The cathode active material layer may be disposed on one surface or opposite two surfaces of the cathode current collector. Further, in the thickness direction Z of the cathode electrode sheet 410, the cathode active material layer may be coated only on a partial area of the cathode current collector, and the thickness of the cathode active material layer may be from 10 μm to 500 μm.

[0092] There is no particular limitation on the material of the anode current collector in the embodiments of the present application, and various materials known to those skilled in the art that can be used as anode current collectors are applicable to the present application. Exemplarily, the anode current collector may be at least one of a copper foil, an aluminum foil, a nickel foil, or a carbon - based current collector; the thickness of the anode current collector may be from 1 μm to 200 μm. The anode active material layer may be disposed on one surface or opposite two surfaces of the anode current collector. Further, in the thickness direction Z of the anode electrode sheet 420, the anode active material layer may be coated only on a partial area of the anode current collector. Exemplarily, the thickness of the anode active material layer may be from 10 μm to 500 μm.

[0093] The anode active material layer may further include a conductive agent. Exemplarily, the conductive agent in the anode active material layer may include at least one of carbon black, acetylene black, Ketjen black, graphene, carbon nanotubes, carbon fibers, or carbon nanowires. Among them, the anode active material layer may further include an anode binder, and the anode binder may include at least one of carboxymethyl cellulose CMC, polyacrylate salts, polyacrylates, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, epoxy resin, polyester resin, polyurethane resin, or polyfluorene.

[0094] There are no particular restrictions on the separator 50 in the embodiments of the present application, and various materials known to those skilled in the art that can be used as the separator 50 are applicable to the present application. Exemplarily, the separator 50 includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, polyethylene includes at least one selected from high-density polyethylene, low-density polyethylene, or ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene have a good effect on preventing short circuits and can improve the stability of the electrode assembly through the shut-off effect. The thickness of the separator 50 is in the range of about 3 μm to 500 μm.

[0095] The electrode assembly in the embodiments of the present application further includes a positive electrode tab and a negative electrode tab. The positive electrode tab is provided on the positive electrode plate 410, and the negative electrode tab is provided on the negative electrode plate 420. There are no particular restrictions on the positive electrode tab and the negative electrode tab in the embodiments of the present application, and various materials known to those skilled in the art that can be used as the positive electrode tab and the negative electrode tab are applicable to the present application.

[0096] There are no particular restrictions on the electrolyte in the embodiments of the present application, and various materials known to those skilled in the art that can be used as the electrolyte are applicable to the present application. The electrolyte includes a lithium salt and a non-aqueous organic solvent.

[0097] Exemplarily, the lithium salt includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium nitrate, or lithium methyl sulfite.

[0098] Exemplarily, the non-aqueous organic solvent may further include at least one of a carboxylic acid ester compound, an ether compound, or other organic solvents. The above-mentioned carbonate compound may include, but is not limited to, at least one of a chain carbonate compound and a cyclic carbonate compound. The above-mentioned chain carbonate compound may include, but is not limited to, at least one of dipropyl carbonate (DPC) or ethyl methyl carbonate (EMC). The above-mentioned cyclic carbonate compound may include, but is not limited to, at least one of butylene carbonate (BC) or vinylene ethylene carbonate (VEC). The above-mentioned carboxylic acid ester compound may include, but is not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, or propyl propionate. The above-mentioned ether compound may include, but is not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The above-mentioned other organic solvents may include, but is not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, or phosphate esters. The present application does not particularly limit the mass percentage content of the non-aqueous organic solvent in the electrolyte, as long as the object of the present application can be achieved. For example, based on the total mass of the electrolyte, the mass percentage content of the non-aqueous organic solvent is 10% to 70%.

[0099] The present application does not particularly limit the battery packaging bag, and it can be a packaging bag well-known in the art, as long as the object of the present application can be achieved.

[0100] The present application does not particularly limit the type of battery, and it may include any device that undergoes an electrochemical reaction. In the present application, the battery may include, but is not limited to: lithium metal batteries, lithium ion batteries, lithium polymer batteries, or lithium ion polymer batteries, etc.

[0101] The preparation process of the battery of the present application is well-known to those skilled in the art, and the present application has no special limitations. For example, it may include, but is not limited to, the following steps: after installing the positive electrode tab on the positive electrode plate 410 and the negative electrode tab on the negative electrode plate 420, stacking the positive electrode plate 410, the separator, and the negative electrode plate 420 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 the electrolyte into the packaging bag and sealing it to obtain the battery.

[0102] The battery of the present application can be used in electrical devices. There is no particular limitation on the type of electrical device, and it can be any electrical device known in the prior art. In some embodiments, the electrical device may include, but is not limited to, laptop computers, pen-input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, liquid crystal televisions, hand-held cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, automobiles, motorcycles, motorized bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household storage batteries, and lithium-ion capacitors, etc.

[0103] Taking a lithium-ion battery as an example and in combination with specific embodiments, the present application will be further elaborated below. It should be understood that these embodiments are only used to illustrate the present application and not to limit the scope of the present application.

[0104] The following methods are used to test the performance of the lithium-ion battery in the embodiments and comparative examples of the present application:

[0105] (1) Test method for cycle capacity retention rate of 25°C / 45°C 5C charge / 0.7C discharge

[0106] In an environment of 25°C / 45°C, the lithium-ion battery is charged at a constant current of 5C until the full charge voltage (the maximum voltage designed for the lithium-ion battery is 4.5V), then charged at a constant voltage at the maximum voltage until the current is 0.02C, and then discharged at a constant current of 0.7C until the final voltage is 3.0V. Record the discharge capacity of the first cycle. Then repeat the above steps for charge and discharge cycles, and record the discharge capacity of the lithium-ion battery for each charge and discharge cycle.

[0107] Cycle capacity retention rate of 25°C / 45°C 5C charge / 0.7C discharge = (discharge capacity of the Nth cycle / discharge capacity of the first cycle) × 100%.

[0108] The number of cycles with a 25°C / 45°C 5C cycle capacity ≤ 80% is: the number of charge and discharge cycles when the cycle capacity retention rate is 80%.

[0109] (2) Test method for liquid retention

[0110] During the assembly process of the lithium-ion battery, after drying in a vacuum oven at 85°C for 12 hours to remove moisture, the weight of the dry battery before injection is counted and recorded as w1; after obtaining the lithium-ion battery through processes such as vacuum packaging, standing, formation, capacity measurement, degassing, and edge cutting, the weight of the lithium-ion battery is counted and recorded as w2.

[0111] Retention volume = (w2 - w1) / w1 × 100%.

[0112] (3) Test method for wetting improvement effect

[0113] Cut the electrode sheet into a standard size of 10 mm × 10 mm. Drop 5 μL of electrolyte on the surface of the electrode sheet, observe the diffusion rate and wetting area of the electrolyte, measure the contact angle of the electrolyte on the surface of the electrode sheet using a contact angle measuring instrument, and evaluate the wettability of the electrode sheet based on the diffusion rate and contact angle of the electrolyte. The faster the diffusion rate and the smaller the contact angle, the better the wettability.

[0114] Among them, the contact angle range is 0° to 30°, the surface wetting effect level is "high", the contact angle range is 30° to 60°, the surface wetting effect level is "medium", and the contact angle range of 60° to 90° indicates that the wetting effect level is "low".

[0115] (4) Test method for the morphology of the active material layer

[0116] Cut the positive electrode sheet into a standard size of 10 mm × 10 mm and place it in the sample chamber of a scanning electron microscope (SEM). Observe the surface morphology of the electrode sheet using a scanning electron microscope (SEM).

[0117] If the surface of the positive electrode sheet is smooth, complete, and free of cracks, there is no powder shedding. If the number of pits per square centimeter on the surface of the positive electrode sheet is less than or equal to 3, it indicates that the integrity of the positive electrode sheet has been damaged, which belongs to mild powder shedding. If the number of pits per square centimeter on the surface of the positive electrode sheet is greater than 3, it indicates that the positive electrode sheet has been severely damaged, which belongs to severe powder shedding.

[0118] (5) Test method for the average particle size Da of silicon material particles

[0119] Export the SEM image (backscattered condition, distinguishing Si and graphite) of the second material layer taken as a common image format (such as JPEG), and use image analysis software (such as ImageJ) to process and analyze the image. The image magnification is 5000X, the number of test particles is 35, and the calibration scale: in the image analysis software, calibrate the scale of the image according to the magnification of the SEM. For example, if the magnification of the SEM is 10,000 times and 100 pixels in the image correspond to 1 micron, then the size of each pixel is 0.01 micron. Manually or automatically mark the particles in the image. Measure the diameter or equivalent diameter of each particle (when the particle is of an irregular shape, the equivalent diameter in this application is defined as the longest distance formed between two points of the particle), record the size data of all particles, and calculate the average particle size Da of this application.

[0120] (6) Test method for the coating weight per unit area of the active material layer

[0121] Take a pole piece with a certain area and cut it into circular pieces with an area of 15.4025 cm 2 using a punching machine. After deducting the weight of the current collector, the coating weight per unit area of the active material layer can be obtained.

[0122] (7) Sphericity test method for silicon material particles:

[0123] Use the laser diffraction method to test the sphericity of spherical silicon material particles: Disperse the silicon material particles in water to form a stable suspension. Use a laser light source to irradiate the sample, collect the intensity of the scattered light through detectors at multiple angles, calculate the particle size distribution using Mie scattering theory, analyze and fit the data through software, and generate a sphericity distribution map.

[0124] (8) Weight percentage test method for silicon material particles:

[0125] Discharge the negative electrode pole piece at 0.1C to 3.0V and then process it to obtain the negative electrode pole piece. Determine the element distribution by scanning electron microscopy (SEM), and use energy-dispersive X-ray spectroscopy analysis to test the content of silicon elements. The test area is 5 places, calculate the average mass of silicon elements, and the mass of silicon material particles is twice the mass of silicon elements.

[0126] (9) Test method for the height Hm of the convex part 311

[0127] Charge the lithium-ion battery at a constant current of 0.5C to 4.5V, charge it at a constant voltage of 4.5V to 0.05C, let it stand for 5 min, then discharge it at a constant current of 0.5C to 3.0V, disassemble the lithium-ion battery, and take out the positive electrode pole piece with the positive electrode material layer set on the surface.

[0128] Perform plasma longitudinal cutting on the positive electrode pole pieces of the examples and comparative examples along the thickness direction to obtain a flat cross-section. Characterize the cross-section using a Philips XL-30 type field emission scanning electron microscope (SEM) at a magnification of 300 times, measure the vertical height from the bottom to the top of the convex point, measure the heights of five convex points and take the average value as Hm.

[0129] (10) Hard expansion test method for the battery cell

[0130] For a fresh battery, use a micrometer to measure the thickness at the Al tab position, measure 3 points, record the values, and take the average value and record it as T0. Perform charge and discharge processing on the battery cell, use a charging process of 0.7C to 4.5V and a discharging process of 0.5C to 3V. Measure the full charge thickness every 50 cycles and at the end of the battery cell cycle. The method is the same as above, record the thicknesses T1, T2... Tn. The calculation formula for the hard expansion rate is: Hard expansion rate = Tn / T0 - 1.

[0131] (11) K - value testing method

[0132] After the battery cells are produced, use an open - circuit voltage tester to first measure the open - circuit voltage OCV1 of the battery cells. After an interval of 48 h, re - measure the open - circuit voltage OCV2 of the battery cells. The K - value = (OCV1 - OCV2) mV / 48 h. The K - value can characterize the self - discharge performance of the battery cells. When the K - value is larger, it means that the battery discharges quickly, that is, the battery's power drops quickly when it is in a static state. When the K - value is smaller, it means that the battery discharges slowly and the battery has good stability, that is, the battery's power drops slowly when it is in a static state.

[0133] Example 1 - 1

[0134] (1) Preparation of the positive electrode plate

[0135] Mix the positive electrode active material LiCoO2, the positive electrode conductive agent conductive carbon black (Super P), and the positive electrode binder polyvinylidene fluoride (PVDF, Mw = 7×10 6 ) in a mass ratio of 96:2:2, add N - methylpyrrolidone (NMP) as a solvent, and stir evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 75 wt%. Uniformly coat the positive electrode slurry on one surface of a positive electrode current collector aluminum foil with a thickness of 10 μm, dry it at 85 °C, and cold - press it to obtain a positive electrode plate with a single - sided coated positive electrode active material layer with a thickness of 50 μm. Then, repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode plate with a double - sided coated positive electrode active material layer. After cutting, obtain a positive electrode plate with a specification of 74 mm×851 mm for use.

[0136] Among them, the compaction density of the positive electrode active material layer is 4.23 g / cm 3 , and the coating weight CW1 per unit area of the positive electrode active material layer is 150 mg / 1540.25 cm 2 .

[0137] (2) Preparation of the negative electrode plate

[0138] Mix the negative electrode active material graphite, the negative electrode active material spherical silicon material particles (sphericity is 0.8), the negative electrode conductive agent carbon nanotubes (CNT), and the thickening agent carboxymethyl cellulose (CMC - Na, Mw = 7×10 5) The negative electrode binder polyacrylamide (PAA) is mixed in a mass ratio of (0.285:0.665:0.05:0.05:4), and then deionized water is added as a solvent and stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry with a solid content of 50 wt%. The negative electrode slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 12 μm, dried at 85°C, and cold-pressed to obtain a negative electrode sheet with a single-sided coated negative electrode active material layer with a thickness of 60 μm. Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coated negative electrode active material layer. After cutting, a negative electrode sheet with a specification of 76 mm × 867 mm is obtained for use.

[0139] Among them, the tap density of the negative electrode active material layer is 1.75 g / cm 3 , the weight percentage content A of the silicon material particles is 30%, the average particle diameter Da of the silicon material particles is 20 μm, and the sphericity S of the silicon material particles is 0.8.

[0140] (3) Preparation of the separator

[0141] A polyethylene (PE) porous membrane with a thickness of 5 μm is used.

[0142] (4) Preparation of the electrolyte

[0143] In a glove box under an argon atmosphere with a water content of less than 10 ppm, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) are mixed in a mass ratio of 1:1:2 to obtain a basic solvent, and then lithium hexafluorophosphate (LiPF6) is dissolved in the above basic solvent to obtain an electrolyte. Among them, based on the total mass of the electrolyte, the mass percentage content of LiPF6 is 12.5%.

[0144] (5) Assembly of the lithium-ion battery

[0145] The positive electrode tab, an aluminum tab, is installed in the edge area of the positive electrode sheet 410 by rolling, the protective glue is pasted on the edge area of the positive electrode sheet 410, and the negative electrode tab, a nickel tab, is installed in the edge area of the negative electrode sheet 420 by rolling.

[0146] The positive electrode sheet 410 with the positive electrode tab installed, the separator 50, and the negative electrode sheet 420 with the negative electrode tab installed are stacked in sequence, and the separator 50 is placed in the middle of the positive electrode sheet 410 and the negative electrode sheet 420 to play a separating role, and then wound to obtain the electrode body 20. The electrode assembly is placed in an outer packaging aluminum-plastic film, dried in a vacuum oven at 85°C for 12 h to remove moisture, then the electrolyte is injected, and after vacuum packaging, standing, formation (constant current charging at 0.2°C to 3.5 V, and then constant current charging at 1C to 3.9 V), capacity measurement, degassing, trimming and other processes, a lithium-ion battery is obtained.

[0147] In Example 1-1, the positive electrode sheet has a convex portion 311. The convex portion 311 is roll-pressed in the convex point area of the positive electrode sheet by means of roll pressing, and Figure 1 the shown electrode sheet 300 is used as the positive electrode sheet. In the wound electrode body 20, each corner section 21 and straight section 22 of the electrode sheet 300 in each turn have a convex portion 311. Among them, the ratio of the height Hm of the first convex portion 311a to the height Hn of the second convex portion is: Hm / Hn = 2.

[0148] In Examples 1-2 to 1-44, 1-46, and Comparative Examples 1-1 to 1-9, except that in the preparation of the positive electrode sheet, the height of the first convex portion 311a and the coating weight CW1 per unit area of the positive electrode active material layer are adjusted according to Table 1, and in the preparation of the negative electrode sheet, the content A of the silicon material particles and the average particle diameter Da of the silicon material particles are adjusted according to Table 1, the rest are the same as in Example 1-1.

[0149] Example 1-45, which does not contain spherical silicon. Based on the total mass of the negative electrode active material layer, the content of irregularly shaped silicon material particles accounts for 30%, and the rest are the same as in Example 1-1.

[0150] The parameters of the lithium-ion batteries and the performance test results of the lithium-ion batteries in Examples 1-1 to 1-46 and Comparative Examples 1-1 to 1-9 are shown in Table 1.

[0151] Table 1

[0152]

[0153]

[0154] It can be seen from Examples 1-1 to 1-46 and Comparative Examples 1-1 to 1-9 in Table 1 that when the coating weight CW1 per unit area of the positive electrode active material layer satisfies 150 mg / 1540.25 mm 2 ≤CW1≤250 mg / 1540.25 mm 2When the height Hm of the first convex portion of the positive electrode sheet satisfies 5 μm ≤ Hm ≤ 80 μm, and the weight percentage content A of the silicon material particles in the negative electrode sheet satisfies 0% ≤ A ≤ 50%, and the average particle diameter Da of the silicon material particles satisfies 1 μm ≤ Da ≤ 20 μm, the various performances of the lithium-ion battery are good. Among them, when A is greater than 50%, the charge-discharge cycle performance of the lithium-ion battery decreases significantly. This is because the silicon content is too high, the cyclic expansion is large, the corner is severely extruded, and the electrolyte cannot be replenished in time during the cycle, resulting in liquid shortage. Due to the limited tensile performance of the aluminum foil in the cathode, Hm cannot be further widened. When the average particle diameter Da of the silicon material particles is greater than 20 μm, the material particles are likely to be too large, and the poor kinetics leads to poor charge-discharge cycle performance of the battery.

[0155] Among them, according to Examples 1-1 to 1-15 and Examples 1-41 to 1-43 in Table 1, it can be seen that the average particle diameter Da of the silicon material particles satisfies 10 μm < Da ≤ 20 μm, the weight percentage content A of the silicon material particles satisfies 5% ≤ A ≤ 50%, and the height Hm of the first convex portion 311a of the positive electrode sheet 410 satisfies 15 μm ≤ Hm ≤ 60 μm, and the various performances of the lithium-ion battery are good. Preferably, according to Examples 1-6 to 1-12, it can be seen that the weight percentage content A of the silicon material particles satisfies 30% ≤ A ≤ 50%, and the wetting improvement effect of the electrolyte is better. This is because as the silicon content increases, more corner extrusion occurs, the larger Hm is, the larger the interlayer gap gap created by the corner is, and the more the corner is improved during the cycle.

[0156] According to Examples 1-16 to 1-27 in Table 1, it can be seen that the average particle diameter Da of the silicon material particles satisfies 5 μm < Da ≤ 10 μm, the weight percentage content A of the silicon material particles satisfies 5% ≤ A ≤ 40%, and the height Hm of the first convex portion 311a of the positive electrode sheet 410 satisfies 17 μm ≤ Hm ≤ 80 μm, and the various performances of the lithium-ion battery are good.

[0157] According to Examples 1-29 to 1-46 in Table 1, it can be seen that the average particle diameter Da of the silicon material particles satisfies 1 μm ≤ Da ≤ 5 μm, the weight percentage content A of the silicon material particles satisfies 5% ≤ A ≤ 23%, and the height Hm of the first convex portion 311a of the positive electrode sheet 410 satisfies 25 μm ≤ Hm ≤ 80 μm, and the various performances of the lithium-ion battery are good.

[0158] Examples 2-1 to 2-38 and Comparative Examples 2-1 to 2-5 are the same as Example 2-1, except that in the preparation of the positive electrode sheet, the height of the first convex portion 311a and the coating weight CW1 per unit area of the positive electrode active material layer are adjusted as shown in Table 2, and in the preparation of the negative electrode sheet, the content A of the silicon material particles and the average particle diameter Da of the silicon material particles are adjusted as shown in Table 2.

[0159] The parameters of the lithium-ion batteries of Examples 2-1 to 2-38 and Comparative Examples 2-1 to 2-5 and the performance test results of the lithium-ion batteries are shown in Table 2.

[0160] Table 2

[0161]

[0162]

[0163] It can be seen from Examples 2-1 to 2-38 and Comparative Examples 2-1 to 2-5 in Table 2 that, similarly, when the coating weight CW1 per unit area of the positive electrode active material layer satisfies 250 mg / 1540.25 mm 2 <CW1 ≤ 400 mg / 1540.25 mm 2 and the height Hm of the first convex portion of the positive electrode sheet satisfies 5 μm ≤ Hm ≤ 80 μm, and the weight percentage content A of the silicon material particles in the negative electrode sheet satisfies 0% ≤ A ≤ 50% and the average particle diameter Da of the silicon material particles satisfies 1 μm ≤ average particle diameter Da ≤ 30 μm, the various performances of the lithium-ion battery are good.

[0164] Moreover, it can be seen from Examples 2-1 to 2-14 in Table 2 that the average particle diameter Da of the silicon material particles satisfies 10 μm < average particle diameter Da ≤ 20 μm, the weight percentage content A of the silicon material particles satisfies 5% ≤ A ≤ 50%, and the height Hm of the first convex portion 311a of the positive electrode sheet 410 satisfies 25 μm ≤ Hm ≤ 70 μm, and the various performances of the lithium-ion battery are good.

[0165] It can be seen from Examples 2-15 to 2-26 in Table 2 that the average particle diameter Da of the silicon material particles satisfies 5 μm < average particle diameter Da ≤ 10 μm, the weight percentage content A of the silicon material particles satisfies 5% ≤ A ≤ 40%, and the height Hm of the first convex portion 311a of the positive electrode sheet 410 satisfies 27 μm ≤ Hm ≤ 80 μm, and the various performances of the lithium-ion battery are good.

[0166] As can be seen from Examples 2-27 to 2-38 in Table 2, the average particle size Da of the silicon material particles satisfies 1 μm ≤ average particle size Da ≤ 5 μm, the weight percentage content A of the silicon material particles satisfies 5% ≤ A ≤ 20%, and the height Hm of the first convex portion 311a of the positive electrode tab 410 satisfies 35 μm ≤ Hm ≤ 80 μm, and the various performances of the lithium-ion battery are good.

[0167] Examples 3-1 to 3-20 are the same as Examples 1-7 except that in the preparation of the negative electrode tab, other types of negative electrode active materials in addition to the silicon material particles are added as shown in Table 3.

[0168] The parameters of the lithium-ion batteries of Examples 3-1 to 3-20 and the performance test results of the lithium-ion batteries are shown in Table 3.

[0169] Example 3-21 uses irregular silicon carbide, and the rest is the same as Example 1-7.

[0170] Table 3

[0171]

[0172]

[0173] As can be seen from Examples 3-1 to 3-6, the specific capacity per gram of graphite is ρ, and 350 mAh / g ≤ ρ ≤ 370 mAh / g, which has a good improvement effect on the cycle and wetting of the battery.

[0174] As can be seen from Examples 3-7 to 3-13, the OI value of graphite satisfies 6 ≤ OI ≤ 18, which has a good improvement effect on the charge and discharge cycle performance of the battery. The larger the OI value, the greater the hard expansion of the battery cell, the more serious the extrusion at the corners, and the worse the wetting. The smaller the IO value, the smaller the hard expansion of the battery cell, but the negative electrode tab has poor extension in its width direction and length direction, resulting in easy deformation of the electrical main body after winding, and thus easy deterioration of the charge and discharge cycle performance of the battery.

[0175] As can be seen from Examples 3-14 to 3-15 and Example 3-21 in Table 3, adding irregularly shaped silicon carbide and silicon oxide can improve the energy density of the battery, but the comprehensive performance is slightly worse than that of spherical Si. This is mainly because the silicon material particles have stronger ability to resist stress expansion during the silicon cycle, which can further improve the energy density of the battery. Hard carbon can improve the hard expansion of the battery cell, but the capacity decays rapidly during the cycle.

[0176] It can be seen from Examples 3-13 and Examples 3-16 to 3-20 that when the content of the positive electrode binder satisfies 0.2% ≤ B ≤ 2.4%, it has a good improvement effect on the cycle of the battery. The lower the binder content, the worse the extensibility, the more difficult it is to form corner intermittence during the processing, the worse the infiltration, and the worse the cycle. The higher the binder content, the better the extensibility, and the easier it is to form corner gaps. However, when the binder content exceeds a certain range, the cathode kinetics is poor and the cycle deteriorates.

[0177] Examples 4-1 to 4-4 are the same as Examples 1-7 except that the sphericity of the silicon material particles is adjusted as shown in Table 4 during the preparation of the negative electrode sheet.

[0178] The parameters of the lithium-ion batteries of Examples 4-1 to 4-4 and the performance test results of the lithium-ion batteries are shown in Table 4.

[0179] Table 4

[0180]

[0181]

[0182] It can be seen from Examples 4-1 to 4-4 that by selecting the sphericity S of the silicon material particles to satisfy 0.7 ≤ S ≤ 1, the appearance of the silicon material particles is regular, preventing the silicon material particles with large hardness and overly sharp surfaces from piercing the separator 50. Moreover, by using silicon material particles with a higher sphericity S, the above-mentioned silicon material particles with a higher sphericity can effectively improve the problems of poor battery K value, fast power loss, and excessive voltage drop during long-term storage. At the same time, the electrolyte infiltration effect of the battery is better, improving the cycle performance of the battery at normal temperature and high temperature.

[0183] In the drawings of this embodiment, the same or similar reference numerals correspond to the same or similar components; in the description of this application, it should be understood that if there are terms such as "upper", "lower", "left", "right", etc. indicating the orientation or positional relationship, they are based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, the terms describing the positional relationship in the drawings are only for illustrative purposes and cannot be understood as a limitation of this patent. For those of ordinary skill in the art, the specific meanings of the above terms can be understood according to specific circumstances.

[0184] The above are only the preferred embodiments of this application and are not used to limit this application. Any modifications, equivalent replacements, and improvements made within the spirit and principle of this application shall be included in the protection scope of this application.

Claims

1. An electrode assembly, characterized in that: It includes a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet, the negative electrode sheet, and the separator are wound multiple times to form an electrode body, and the electrode body includes a straight portion and corner portions disposed at opposite ends of the straight portion; The corner portion of the positive electrode sheet is provided with a plurality of first protrusions, and along the thickness direction of the positive electrode sheet, the height of the first protrusion is Hm (μm), and Hm satisfies: 15≤Hm≤80; The negative electrode plate includes a negative electrode active material layer, and the negative electrode active material layer includes silicon material particles. Based on the total weight of the negative electrode active material layer, the weight percentage of the silicon material particles is A (%), A satisfies: 5≤A≤50, and the average particle size Da (μm) of the silicon material particles satisfies: 1≤Da≤30.

2. The electrode assembly according to claim 1, characterized in that: A satisfies: 5≤A≤20.

3. The electrode assembly according to claim 1, characterized in that: The positive electrode sheet comprises a positive electrode current collector and a positive electrode active material layer disposed on the surface of the positive electrode current collector, wherein the coating weight per unit area of ​​the positive electrode active material layer is CW1 (mg / 1540.25mm 2 ), CW1 satisfies: 150≤CW1≤400.

4. The electrode assembly according to claim 3, characterized in that: CW1 satisfies: 150≤CW1≤250, and the negative electrode plate satisfies one of the following conditions: (1) 10<Da≤20, 5≤A≤50, 15≤Hm≤60; (2) 5<Da≤10, 5≤A≤40, 17≤Hm≤80; (3)1≤Da≤5,5≤A≤23,25≤Hm≤80.

5. The electrode assembly according to claim 3, characterized in that: CW1 satisfies: 250<CW1≤400, and the negative electrode sheet satisfies one of the following conditions: (1) 10<Da≤20, 5≤A≤50, 25≤Hm≤70; (2) 5<Da≤10, 5≤A≤40, 27≤Hm≤80; (3)1≤Da≤5, 5≤A≤20, 35≤Hm≤80.

6. The electrode assembly according to any one of claims 1 to 5, characterized in that: The silicon material particles are spherical silicon, and the sphericity of the silicon material particles is S, where S satisfies: 0.7≤S≤1.

7. The electrode assembly according to any one of claims 1 to 5, characterized in that: The straight portion has a first thickness L1 in the first direction; The two corner portions are arranged at opposite ends of the straight portion in a second direction perpendicular to the first direction, and the corner portions have a second thickness L2 in the second direction; Each circle of the pole piece comprises two straight sections arranged opposite to each other along the first direction, and two corner sections arranged at both ends of the straight section along the second direction; The pole piece has a tail end arranged corresponding to the straight segment of the pole piece of the outermost circle, and all the straight segments and the tail end stacked in the first direction form the straight portion; the first thickness L1 is the thickness of the straight portion passing the tail end in the first direction; all the corner segments located on the same side of the straight segment in the second direction form a corner portion, and the second thickness L2 is the thickness of the corner portion passing the midpoint of the line connecting the two ends of one of the innermost corner segments in the second direction; the electrode assembly satisfies at least one of the following conditions: (1) The number of winding turns of the electrode sheet of the electrode body is an even number, and L1 and L2 satisfy: 2.0≤L1 / L2≤2.2; (2) The number of winding turns of the pole piece of the electrode body is an odd number, and L1 and L2 satisfy: 2.0≤L1 / L2≤2.

4.

8. The electrode assembly according to any one of claims 1 to 5, characterized in that: The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes the silicon material particles; The negative electrode active material further includes at least one of silicon carbide, silicon oxide, graphite, and hard carbon.

9. The electrode assembly according to claim 7, characterized in that: The negative electrode active material includes graphite, the gram capacity of the graphite is ρ (mAh / g), ρ satisfies: 350≤ρ≤370mAh / g, and the OI value of the graphite satisfies: 6≤OI≤18.

10. The electrode assembly according to any one of claims 1 to 5, characterized in that: The positive electrode sheet includes a positive electrode active material layer, and the positive electrode active material layer includes a positive electrode binder; Based on the total weight of the positive electrode active material layer, the weight percentage of the positive electrode binder is B, and 0.2%≤B≤2.4%.

11. A battery, characterized in that: include: shell; and, The electrode assembly according to any one of claims 1-10, wherein the electrode assembly is arranged in the internal space of the shell.

Images