Roll core structure and lithium ion battery

Abstract

The embodiment of the utility model provides a roll core structure and a lithium ion battery, and relates to the technical field of batteries. The roll core structure comprises a positive plate, a diaphragm and a negative plate which are formed by winding; the negative plate comprises a negative current collector and a negative active layer, the negative plate is provided with a single-sided region and a double-sided region which are connected with each other, one side of the negative current collector in the single-sided region is coated with the negative active layer, two sides of the negative current collector in the double-sided region are coated with the negative active layers, and the single-sided region and the double-sided region are connected to form a junction region; the positive plate comprises a positive current collector and a positive active layer, the positive active layer is provided with a concave region, the concave region is arranged opposite to the junction region, and the positive active layer on one side, facing the junction region, of the concave region is provided with a concave part. According to the roll core structure and the lithium ion battery provided by the embodiment of the utility model, expansion can be effectively relieved, the safety of the lithium ion battery is improved, and the service life of the lithium ion battery is prolonged.

Description

Technical Field

[0001] The utility model relates to the technical field of batteries, in particular to a core structure and a lithium-ion battery. Background Art

[0002] Lithium-ion batteries are favored for their excellent characteristics such as high energy density, long cycle life, and environmental friendliness. With the large-scale application of lithium-ion batteries, continuous exploration and improvement have been carried out on the performance and manufacturing process of lithium-ion batteries, especially the life and safety performance of lithium-ion batteries.

[0003] In the related art, the core structure of a wound lithium-ion battery is formed by stacking a positive electrode sheet, a separator, and a negative electrode sheet together and then winding from the starting end to the ending end. However, local swelling problems occur at the single-sided and double-sided junction of the negative electrode sheet due to local overvoltage, reducing the safety and life of the lithium-ion battery. Summary of the Utility Model

[0004] The embodiment of the utility model provides a core structure and a lithium-ion battery to solve the problem that local swelling problems occur at the single-sided and double-sided junction of the negative electrode sheet due to local overvoltage, reducing the safety and life of the lithium-ion battery.

[0005] On the one hand, the embodiment of the utility model provides a core structure, including a positive electrode sheet, a separator, and a negative electrode sheet, which are stacked and wound;

[0006] The negative electrode sheet includes a negative current collector and a negative active layer. The negative electrode sheet has a single-sided area and a double-sided area connected to each other. The negative active layer is coated on one side of the negative current collector in the single-sided area, and the negative active layer is coated on both sides of the negative current collector in the double-sided area. The single-sided area and the double-sided area intersect to form a junction area;

[0007] The positive electrode sheet includes a positive current collector and a positive active layer. The positive active layer has a concave area. Along the first direction, the concave area is disposed opposite to the junction area, and the positive active layer on the side of the concave area facing the junction area has a concave portion.

[0008] In a possible implementation manner, both the positive electrode sheet and the negative electrode sheet include straight sections and arc sections connected alternately. The junction area is located on the straight section of the negative electrode sheet, and the concave area is located on the straight section of the positive electrode sheet. Along the first direction, the positive active layer on the side of the concave area away from the junction area is provided with the concave portion, and the concave portion includes a hole structure and / or a groove structure.

[0009] In a possible implementation manner, the hole structure includes at least one hole;

[0010] The diameter of the hole is 20um to 200um; and / or,

[0011] In the first direction, the depth of the hole is 1um to 20um.

[0012] In a possible implementation, the hole structure includes a plurality of the holes, and the distance between two adjacent holes is 0mm to 5mm.

[0013] In a possible implementation, the groove structure includes at least one groove, and in the first direction, the depth of the groove is 1um to 20um.

[0014] In a possible implementation, the groove structure includes a plurality of grooves arranged in sequence along the first direction;

[0015] In the second direction, the size of the groove is 1um to 500um, and the distance between two adjacent grooves is 0.1mm to 2mm.

[0016] In a possible implementation, in the winding direction of the core structure, the starting end of the positive electrode sheet is located behind the starting end of the single-sided area;

[0017] The negative electrode sheet further has an empty foil area connected to the single-sided area. The single-sided area includes a paste folding part connected to the empty foil area. In the first direction, the projection of the concave area is located within the projection area of the paste folding part.

[0018] In a possible implementation, the positive electrode sheet has an avoidance area. In the first direction, the projection of the concave area is located within the projection area of the avoidance area. In the width direction of the core structure, the distance between the starting end of the positive electrode active layer and the concave area is 1um to 10mm.

[0019] In a possible implementation, a negative electrode tab is provided on the negative electrode current collector, and a positive electrode tab is provided on the positive electrode current collector;

[0020] In the first direction, the projections of the concave area, the positive electrode tab, and the negative electrode tab do not overlap each other;

[0021] In the second direction, the minimum distance between the concave area and the positive electrode tab is greater than 2mm; and / or,

[0022] In the second direction, the size of the concave area is 1mm to 100mm.

[0023] In a possible implementation, the number of arc segments of the positive electrode sheet is odd. In the first direction, the projection of the concave area does not overlap with the projections of the ending end and the starting end of the end sealant.

[0024] On the other hand, an embodiment of the present utility model provides a lithium-ion battery, including the core structure as described above.

[0025] The embodiment of the present utility model provides a core structure and a lithium-ion battery. Since the positive electrode active layer has a concave area, the concave area is disposed opposite to the junction area, and the concave area and the junction area can be charged and discharged. The positive electrode active layer on the side of the concave area facing the junction area has a concave portion, which can reduce the mechanical strength of the concave area, endow it with elasticity, and effectively relieve the volume expansion caused by the negative overvoltage at the single-sided and double-sided junction of the negative electrode. Therefore, the local expansion caused by the negative overvoltage at the single-sided and double-sided junction of the negative electrode during the charge and discharge process can be effectively relieved, and the safety and life of the lithium-ion battery are improved.

[0026] The positive electrode active layer on the side of the concave area facing the junction area has a concave portion, which can increase the ratio of the capacity of the junction area to the capacity of the concave area, reduce the lithium ions in the concave area, and thus effectively reduce the risk of lithium deposition, improving the safety and life of the lithium-ion battery.

[0027] The positive electrode active layer on the side of the concave area facing the junction area has a concave portion, which can enhance the mass transfer between the junction area and the concave area, reduce the ionic impedance, and shorten the transmission distance of lithium ions.

[0028] The positive electrode active layer on the side of the concave area facing the junction area has a concave portion, which can increase the local electrolyte infiltration effect and speed, as well as increase the liquid storage space and improve the liquid storage capacity, effectively solving the problems of poor electrolyte infiltration at the single-sided and double-sided junction of the negative electrode and insufficient electrolyte in the later stage of cycling, thereby improving the battery cycle life and capacity retention rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions in the embodiments of the present utility model or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present utility model. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0030] Figure 1 It is a schematic structural diagram of a lithium-ion battery provided in Embodiment 1 of the present utility model;

[0031] Figure 2 It is a schematic structural diagram of a negative electrode sheet provided in Embodiment 1 of the present utility model;

[0032] Figure 3 It is a schematic structural diagram of the first positive electrode sheet provided in Embodiment 1 of the present utility model;

[0033] Figure 4is Figure 3 The top view schematic diagram of the positive electrode plate in

[0034] Figure 5 The top view schematic diagram of the second positive electrode plate provided by the first embodiment of the present utility model;

[0035] Figure 6 The structural schematic diagram of the third positive electrode plate provided by the first embodiment of the present utility model;

[0036] Figure 7 is Figure 6 The top view schematic diagram of the positive electrode plate in

[0037] Figure 8 The structural schematic diagram of a lithium-ion battery provided by the second embodiment of the present utility model;

[0038] Figure 9 The structural schematic diagram of a lithium-ion battery provided by the third embodiment of the present utility model.

[0039] Explanation of reference numerals:

[0040] 10 - Positive electrode plate; 101 - End glue;

[0041] 110 - Positive electrode current collector; 120 - Positive electrode active layer;

[0042] 400 - Concave area; 401 - Hole;

[0043] 402 - Groove; 500 - Avoidance area;

[0044] 20 - Negative electrode plate; 210 - Negative electrode current collector;

[0045] 221 - First negative electrode active layer; 222 - Second negative electrode active layer;

[0046] 100 - Single-sided area; 100a - Paste folding part;

[0047] 200 - Double-sided area; 20a - Junction area;

[0048] 300 - Empty foil area; 30 - Negative electrode tab;

[0049] 40 - Positive electrode tab. Detailed implementation manners

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present utility model clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present utility model with reference to the accompanying drawings in the embodiments of the present utility model. Obviously, the described embodiments are some, but not all, of the embodiments of the present utility model. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present utility model without creative efforts shall fall within the protection scope of the present utility model.

[0051] It should be noted that the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, features defined with "first" and "second" may explicitly or implicitly include at least one of such features. In the description of the present utility model, "a plurality of" means at least two, such as two, three, etc., unless otherwise specifically and clearly defined.

[0052] In the present utility model, unless otherwise clearly defined and limited, terms such as "installation", "connection", "fixation", etc. shall be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection, an electrical connection, or communicable with each other; it may be directly connected, or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances.

[0053] In the present utility model, unless otherwise clearly defined and limited, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over", and "on top of" the second feature may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "below", and "beneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0054] In the above description, the description referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" means that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present utility model. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0055] In the related art, due to local overvoltage at the junction of the single and double sides of the negative electrode sheet, local swelling problems occur, reducing the safety and lifespan of the lithium-ion battery. After research by the inventor, it is found that the reason for this problem is that during the rolling of the negative electrode sheet, overvoltage occurs at the junction of the single and double sides of the negative electrode sheet, resulting in obstruction of lithium ions during the charging reaction process and excessive volume expansion.

[0056] To solve the above problems, the core structure and lithium-ion battery provided by the embodiments of the present utility model have a depression in the positive electrode active layer of the area where the junction area between the positive electrode sheet and the negative electrode sheet can be charged and discharged, so that the mechanical strength of the area is reduced, it has elasticity, and the expansion can be effectively alleviated, improving the safety and lifespan of the lithium-ion battery.

[0057] The following will describe in detail the core structure and lithium-ion battery provided by the embodiments of the present utility model with reference to specific embodiments.

[0058] See Figure 1 As shown, the embodiments of the present utility model provide a core structure applied to a lithium-ion battery. The width direction of the core structure is the X-axis direction, and the thickness direction of the core structure is the Y-axis direction.

[0059] The core structure includes a positive electrode sheet 10, a separator, and a negative electrode sheet 20, which are stacked and wound. After stacking the positive electrode sheet 10, the separator, and the negative electrode sheet 20 together in sequence, they are wound from the starting end to the ending end to form a core structure. It should be noted that the starting ends of the positive electrode sheet 10 and the negative electrode sheet 20 are the starting end of the core structure, and the starting end of the core structure is located inside the core structure. The ending ends of the positive electrode sheet 10 and the negative electrode sheet 20 are the ending end of the core structure, and the ending end of the core structure is located outside the core structure. The winding direction of the core structure is the extending direction from the starting end to the ending end of the core structure.

[0060] Figure 2The schematic diagram shows the unrolled wound negative electrode sheet 20. The length direction of the negative electrode sheet 20 is the X1-axis direction, and the thickness direction of the negative electrode sheet 20 is the Y1-axis direction. The X1-axis and the Y1-axis are perpendicular to each other.

[0061] In Figure 2 , one side of the negative electrode sheet 20 in the -X1-axis direction is the left side, and one side of the negative electrode sheet 20 in the +X1-axis direction is the right side. One side of the negative electrode sheet 20 in the -Y1-axis direction is the lower side, and one side of the negative electrode sheet 20 in the +Y1-axis direction is the upper side.

[0062] One end of the left side of the negative electrode sheet 20 is the starting end of the negative electrode sheet 20, and one end of the right side of the negative electrode sheet 20 is the ending end of the negative electrode sheet 20. The negative electrode sheet 20 includes a negative electrode current collector 210 and negative electrode active layers coated on opposite sides in the thickness direction of the negative electrode current collector 210, where Figure 2 the negative electrode active layer on the upper side of the negative electrode current collector 210 in is the first negative electrode active layer 221, and the negative electrode active layer on the lower side of the negative electrode current collector 210 is the second negative electrode active layer 222. After the negative electrode sheet 20 is wound, along the winding direction of the core structure, the starting end of the second negative electrode active layer 222 is located behind the starting end of the first negative electrode active layer 221; that is, in Figure 2 , the starting end of the second negative electrode active layer 222 is located on the right side of the starting end of the first negative electrode active layer 221.

[0063] The negative electrode active layer includes a negative electrode active material, a negative electrode conductive agent, and a negative electrode binder. The negative electrode active material can be graphite or a silicon-based negative electrode material.

[0064] After the negative electrode sheet 20 is wound, along the winding direction of the core structure, the negative electrode sheet 20 includes alternately connected straight sections and arc sections. In the winding direction of the core structure of the negative electrode sheet 20, the straight part is the straight section, and the arc part is the arc section.

[0065] The negative electrode sheet 20 has a connected single-sided area 100 and double-sided area 200. One side of the negative electrode current collector 210 in the single-sided area 100 is coated with a negative electrode active layer, that is, the part of the negative electrode sheet 20 where the negative electrode active layer is provided on only one side is the single-sided area 100. Both sides of the negative electrode current collector 210 in the double-sided area 200 are coated with a negative electrode active layer, that is, the part of the negative electrode sheet 20 where the negative electrode active layer is provided on both sides is the double-sided area 200.

[0066] In Figure 2 , from left to right, the area between the first dashed line and the third dashed line is the single-sided area 100. The area between the third dashed line and the fifth dashed line is the double-sided area 200.

[0067] The single-sided area 100 and the double-sided area 200 meet to form a junction area 20a. The junction area 20a can be understood as the partial areas on both sides of the junction of the single-sided area 100 and the double-sided area 200 where the negative electrode sheet 20 is located in the winding direction of the core structure. In Figure 2 From left to right in, the area between the second dotted line and the fourth dotted line is the junction area 20a. In Figure 1 The part circled by the square box in is the junction area 20a.

[0068] In this embodiment, the junction area 20a can be located on the straight section of the negative electrode sheet 20. In other embodiments, it can also be on the arc section of the negative electrode sheet 20, or can also be on the straight section and the arc section of the negative electrode sheet 20.

[0069] In some examples, in the winding direction of the core structure, the size of the junction area 20a can be 1 mm to 100 mm. A part of the junction area 20a is located in the single-sided area 100, and the other part is located in the double-sided area 200.

[0070] Figure 3 The shown positive electrode sheet 10 is a schematic diagram of the wound positive electrode sheet 10 being unfolded. The length direction of the positive electrode sheet 10 is the X1-axis direction, the thickness direction of the positive electrode sheet 10 is the Y1-axis direction, and the width direction of the positive electrode sheet 10 is the Z1-axis direction (see Figure 4 shown). The X1-axis, Y1-axis, and Z1-axis are perpendicular to each other.

[0071] The positive electrode sheet 10 includes a positive electrode current collector 110 and a positive electrode active layer 120, and the positive electrode active layer 120 is coated on both sides of the positive electrode current collector 120.

[0072] The positive electrode active layer 120 includes a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The positive electrode active material includes at least one of lithium cobaltate, nickel cobalt manganese ternary material, nickel cobalt aluminum ternary material, lithium iron phosphate, lithium-rich manganese-based material, lithium manganese iron phosphate, lithium titanate, lithium nickel manganate, lithium nickelate, lithium manganate, and nickel manganese binary material.

[0073] After the positive electrode sheet 10 is wound, along the winding direction of the core structure, the positive electrode sheet 10 includes alternately connected straight sections and arc sections. In the winding direction of the core structure, the straight part of the positive electrode sheet 10 is the straight section, and the arc part is the arc section.

[0074] The positive electrode active layer 120 has a recessed area 400. In Figure 3 The area between the two dotted lines in is the recessed area 400. In Figure 1 The part circled by the square box in is the recessed area 400.

[0075] Along the first direction, the recessed area 400 is disposed opposite to the junction area 20a. In one embodiment, the first direction can be the thickness direction of the core structure, for example, it can beFigure 1 in the Y direction.

[0076] The concave region 400 and the junction region 20a can be charged and discharged.

[0077] In some examples, in the winding direction of the core structure, the size of the concave region 400 can be 1 mm to 100 mm, that is, in the length direction of the positive electrode sheet 10, the size L1 of the concave region 400 can be 1 mm to 100 mm. If the size L1 of the concave region 400 is less than 1 mm, the change in the mechanical strength of the concave region 400 cannot effectively relieve the volume expansion of the junction region 20a of the negative electrode sheet 20 due to overvoltage. If the size L1 of the concave region 400 is greater than 100 mm, the volume energy density loss of the lithium-ion battery is too high. Thus, by setting the size L1 of the concave region 400 to be 1 mm to 100 mm, the change in the mechanical strength of the concave region 400 can effectively relieve the volume expansion of the junction region 20a of the negative electrode sheet 20 due to overvoltage, and the volume energy density loss of the lithium-ion battery will not be too high.

[0078] Exemplarily, in the winding direction of the core structure, the sizes of the junction region 20a and the concave region 400 can both be 1 mm, 5 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 45 mm, 50 mm, 55 mm, 70 mm, 85 mm, 90 mm, 100 mm, etc. In a specific embodiment, in the winding direction of the core structure, the sizes of the junction region 20a and the concave region 400 can both be 10 mm. Specifically, a part of the junction region 20a located in the single-sided region 100 has a size of 5 mm, and another part located in the double-sided region 200 has a size of 5 mm. Without limitation, a part of the junction region 20a located in the single-sided region 100 can have a size of 3 mm, and another part located in the double-sided region 200 can have a size of 7 mm. This is not limited herein, as long as in the winding direction of the core structure, the sizes of the junction region 20a and / or the concave region 400 are within the above range.

[0079] The positive electrode active layer 120 on the side of the concave region 400 facing the junction region 20a has a concave portion. In some examples, a concave portion can be formed by removing a part of the positive electrode active layer 120 by a laser method or a mechanical method.

[0080] For the core structure provided by the embodiment of the present invention, since the positive electrode sheet 10 has the concave region 400, the concave region 400 and the junction region 20a can be charged and discharged, and the positive electrode active layer 120 on the side of the concave region 400 facing the junction region 20a has a concave portion, the ratio CB of the capacity of the junction region 20a to the capacity of the concave region 400 can be increased, and the lithium ions in the concave region 400 can be reduced, thereby effectively reducing the risk of lithium precipitation and improving the safety and lifespan of the lithium-ion battery.

[0081] In some examples, the positive electrode active material is lithium cobaltate and the negative electrode active material is graphite. When the positive electrode sheet 10 has no concave region 400, the capacity ratio CB of the corresponding parts of the negative electrode sheet 20 and the positive electrode sheet 10 at the position where the junction region 20a is located can be 1.03 to 1.05. When the positive electrode sheet 10 has a concave region 400, the capacity ratio CB of the capacity of the junction region 20a to the capacity of the concave region 400 can increase by 0.05 to 0.3. With such a setting, the lithium ions in the concave region 400 are reduced, thereby effectively reducing the risk of lithium deposition and improving the safety and lifespan of the lithium-ion battery.

[0082] In other examples, the positive electrode active material is a nickel cobalt manganese ternary material or a nickel cobalt aluminum ternary material, and the negative electrode active material is graphite. When the positive electrode sheet 10 has no concave region 400, the capacity ratio CB of the corresponding parts of the negative electrode sheet 20 and the positive electrode sheet 10 at the position where the junction region 20a is located can be 1.05 to 1.25. When the positive electrode sheet 10 has a concave region 400, the capacity ratio CB of the capacity of the junction region 20a to the capacity of the concave region 400 can increase by 0.05 to 0.5. With such a setting, the lithium ions in the concave region 400 are reduced, thereby effectively reducing the risk of lithium deposition and improving the safety and lifespan of the lithium-ion battery.

[0083] The positive electrode active layer 120 on the side of the concave region 400 facing the junction region 20a has a concave portion, which can also reduce the mechanical strength of the concave region 400 and make it elastic, effectively alleviating the volume expansion of the junction region 20a of the negative electrode sheet 20 due to overvoltage. Thus, the excessive expansion of the junction region 20a of the negative electrode sheet 20 caused by overvoltage during the charge and discharge process can be effectively alleviated, improving the safety and lifespan of the lithium-ion battery.

[0084] The positive electrode active layer 120 on the side of the concave region 400 facing the junction region 20a has a concave portion, which can also enhance the mass transfer between the junction region 20a and the concave region 400, reduce the ionic impedance, and shorten the transmission distance of lithium ions.

[0085] The positive electrode active layer 120 on the side of the concave region 400 facing the junction region 20a has a concave portion, which can also increase the local electrolyte infiltration effect and speed, as well as increase the liquid storage space and improve the liquid storage capacity, effectively solving the problems of poor electrolyte infiltration at the junction of the single-sided region 100 and the double-sided region 200 of the negative electrode sheet 20 and insufficient electrolyte in the later stage of cycling. Thus, the battery cycle lifespan and capacity retention rate are improved.

[0086] Compared with the negative electrode using graphite, the negative electrode using a silicon-based negative electrode material has a more serious expansion failure problem in the junction region 20a. By having the concave region 400 on the positive electrode sheet 10, the abnormal overall thickness of the core structure caused by the expansion in the junction region 20a of the negative electrode using a silicon-based negative electrode material can be effectively alleviated.

[0087] In a possible implementation, the junction region 20a is located on the straight section of the negative electrode sheet 20, and the recessed region 400 is located on the straight section of the positive electrode sheet 10.

[0088] Wherein, in the winding direction of the core structure, the size of the junction region 20a can be 1 mm to 100 mm, and the size of the recessed region 400 can be 1 mm to 100 mm, that is, in the second direction, the size of the junction region 20a can be 1 mm to 100 mm, and the size of the recessed region 400 can be 1 mm to 100 mm. In this embodiment, the second direction can be parallel to the width direction of the core structure.

[0089] Along the first direction, the positive electrode active layers 120 on both sides of the recessed region 400 can both have recesses, that is, along the first direction, the positive electrode active layer 120 on the side of the recessed region 400 facing the junction region 20a has a recess, and the positive electrode active layer 120 on the side of the recessed region 400 facing away from the junction region 20a is provided with a recess. With such a setting, an expansion space can be reserved for the recessed region 400.

[0090] In other embodiments, along the first direction, only the positive electrode active layer 120 on the side of the recessed region 400 facing the junction region 20a may have a recess.

[0091] The recess includes a hole structure and / or a groove structure. Specifically, the recess may include a hole structure. Or, it may also include a groove structure. Or, it may further include a hole structure and a groove structure.

[0092] In a possible implementation, the hole structure may include at least one hole 401.

[0093] Wherein, the shape of the hole 401 is not specifically set. Exemplarily, the shape of the hole 401 includes but is not limited to a circle, a square, a triangle, etc.

[0094] The number of the holes 401 is not specifically set. Exemplarily, the number of the holes 401 can be one or multiple.

[0095] In the thickness direction of the positive electrode sheet 10, the depth of the hole 401 is not specifically set. The depth of the hole 401 is less than or equal to the thickness of the positive electrode active layer 120.

[0096] In some examples, refer to Figure 4As shown, the pore structure includes a plurality of pores 401. The shape of the pores 401 is circular. The diameter of the pores 401 can be 20um to 200um. For example, specifically, it can be any value such as 20um, 25um, 30um, 35um, 40um, 50um, 60um, 70um, 80um, 95um, 100um, 120um, 150um, 180um, 200um or a range composed of any two values. With such a setting, on the basis of not affecting the volumetric energy density of the lithium-ion battery, the electrolyte infiltration effect is improved, the transmission distance of lithium ions is shortened, and the risk of poor K value caused by easy edge powder loss due to too large pore diameter is avoided. The K value refers to the voltage drop of the lithium-ion battery per unit time.

[0097] In some examples, in the first direction, the depth of the pores 401 can be 1um to 20um. That is, referring to Figure 4 As shown, in the thickness direction of the positive electrode sheet 10, the depth of the pores can be 1um to 20um. With such a setting, on the basis of not affecting the volumetric energy density of the lithium-ion battery, the electrolyte infiltration effect is improved, and a certain amount of electrolyte can be stored, improving the cycle performance of the battery.

[0098] The plurality of pores 401 of the pore structure are arranged at equal intervals. That is to say, the distance between any two adjacent pores 401 is equal. The distance between two adjacent pores 401 can be 0mm to 5mm. When the distance between two adjacent pores 401 can be 0mm, the two adjacent pores 401 are connected. When the distance between two adjacent pores 401 can be greater than 0mm and less than 5mm, the two adjacent pores 401 are not connected. With such a setting, on the basis of not affecting the volumetric energy density of the lithium-ion battery, the electrolyte infiltration effect is improved, and the transmission distance of lithium ions is shortened.

[0099] The shape of the region surrounded by the plurality of pores 401 of the pore structure includes but is not limited to square, hexagonal, triangular, etc.

[0100] In a possible implementation manner, the groove structure includes at least one groove 402.

[0101] Among them, the shape of the groove 402 is not specifically set. Exemplarily, the cross-sectional shape of the groove 402 includes but is not limited to square, trapezoidal, etc.

[0102] The number of the grooves 402 is not specifically set. Exemplarily, the number of the grooves 402 can be one or multiple.

[0103] In the thickness direction of the positive electrode sheet 10, the depth of the groove 402 is not specifically set. The depth of the groove 402 is less than or equal to the thickness of the positive electrode active layer 120. In some examples, in the thickness direction of the positive electrode sheet 10, the depth H of the groove 402 can be 1um to 20um (see Figure 6as shown).

[0104] In one example, the groove structure includes a plurality of grooves 402 arranged in sequence along the second direction. In one embodiment, the second direction may be parallel to the width direction of the core structure, and the second direction may be perpendicular to the first direction, for example, it may be Figure 1 the X direction in. In other embodiments, the second direction may also have an angle with the width direction of the core structure.

[0105] Figure 5 The schematic diagram shows the unwound positive electrode sheet 10 after winding. In the second direction, the size L2 of the groove 402 may be 1um to 500um, that is, referring to Figure 5 , in the X1-axis direction, the size L2 of the groove 402 may be 1um to 500um. In the second direction, the spacing L3 between two adjacent grooves 402 may be 0.1mm to 2mm, that is, referring to Figure 5 , in the X1-axis direction, the spacing L3 between two adjacent grooves 402 may be 0.1mm to 2mm. With such a setting, on the basis of not affecting the volume energy density of the lithium-ion battery, the electrolyte infiltration effect is improved, and the transmission distance of lithium ions is shortened.

[0106] In some examples, in the third direction, the groove 402 may penetrate the positive electrode active layer 120, that is, in the width direction of the positive electrode sheet 10, the groove 402 penetrates the positive electrode active layer 120. The third direction is parallel to the width direction of the positive electrode sheet 10. The third direction may be perpendicular to the first direction and the second direction. In other embodiments, in the third direction, the groove 402 may also not penetrate the positive electrode active layer 120.

[0107] In another example, referring to 6 and Figure 7 as shown, the groove structure includes a groove 402. The groove 402 may be formed by removing 1um to 20um from the positive electrode active layer 120 in the thickness direction of the positive electrode sheet 10.

[0108] In the third direction, the groove 402 may penetrate the positive electrode active layer 120. In other embodiments, in the third direction, the groove 402 may also not penetrate the positive electrode active layer 120.

[0109] In one possible implementation manner, in the winding direction of the core structure, the starting end of the positive electrode sheet 10 is located behind the starting end of the single-sided area 100.

[0110] Referring to Figure 2 as shown, the negative electrode sheet 20 further has an empty foil area 300 connected to the single-sided area 100. The empty foil area 300 is located inside the core structure.

[0111] Referring to Figure 1As shown, the single-sided area 100 includes a paste-folding portion 100a connected to the empty foil area 300. A part of the paste-folding portion 100a is located on the straight section of the negative electrode sheet 20, and another part of the paste-folding portion 100a is located on the arc section of the negative electrode sheet 20.

[0112] In the first direction, that is, in the thickness direction of the core structure, the projection of the recessed area 400 is located within the projection area of the paste-folding portion 100a. With such a setting, the expansion space reserved for the recessed area 400 can effectively relieve the volume expansion at the paste-folding portion 100a of the negative electrode sheet 20.

[0113] Further, as shown in Figure 1 the positive electrode sheet 10 has an avoidance area 500. The avoidance area 500 is located inside the core structure, and the avoidance area 500 is located on the straight section of the positive electrode sheet 10.

[0114] In Figure 1 the part circled by the square is the avoidance area 500 of the positive electrode sheet 10.

[0115] In the winding direction of the core structure, the positive electrode active layer 120 of the positive electrode sheet 10 is located at the rear side of the avoidance area 500, that is, in the winding direction of the core structure, the starting end of the positive electrode active layer 120 of the positive electrode sheet 10 is located at the rear side of the avoidance area 500. It can be understood that there is no positive electrode active layer 120 in the avoidance area 500 of the positive electrode sheet 10. With such a setting, since there is no positive electrode active layer 120 in the avoidance area 500, a certain amount of free electrolyte is stored in the avoidance area 500.

[0116] In the first direction, that is, in the thickness direction of the core structure, the projection of the recessed area 400 is located within the projection area of the avoidance area 500. With such a setting, it is beneficial to release the free electrolyte in the avoidance area 500 to the recessed area 400 in the later stage of cycling, promote the lithium ion transport in the recessed area 400, and can effectively reduce the risk of lithium deposition at the position of the junction area 20a. In addition, the free electrolyte in the avoidance area 500 can move to the recessed area 400 during the cycling process, form a solid electrolyte interphase (SEI) film on the surface of the recessed area 400, reduce the surface roughness of the recessed area 400, reduce the impedance, avoid the burrs generated in the recessed area 400 from piercing the separator to cause safety problems, and improve the safety of the core structure.

[0117] The positive electrode sheet 10 may not have a positive electrode current collector 110 in the avoidance area 500. It can be understood that in the winding direction of the core structure, the starting end of the positive electrode current collector 110 of the positive electrode sheet 10 is located at the rear side of the avoidance area 500. In other embodiments, the positive electrode sheet 10 may also have a positive electrode current collector 110 in the avoidance area 500.

[0118] The starting end of the positive electrode active layer 120 is located on the straight section of the positive electrode sheet 10.

[0119] In the width direction of the core structure, the distance L4 between the starting end of the positive electrode active layer 120 and the recessed area 400 is 1 um to 10 mm. With such a setting, in the thickness direction of the core structure, it can be ensured that the projection of the recessed area 400 is located within the projection area of the avoidance area 500.

[0120] In a possible implementation manner, a negative electrode tab 30 is provided on the negative electrode current collector 210, and a positive electrode tab 40 is provided on the positive electrode current collector 110.

[0121] Both the negative electrode tab 30 and the positive electrode tab 40 are provided with tab glue, which is used to ensure the sealing between the negative electrode tab 30 and the positive electrode tab 40 and the aluminum-plastic film during the packaging of the lithium-ion battery.

[0122] Exemplarily, in the first direction, that is, in the thickness direction of the core structure, the projections of the recessed area 400, the positive electrode tab 40, and the negative electrode tab 30 do not overlap each other. In some examples, refer to Figure 1 As shown, in the width direction of the core structure, the recessed area 400, the positive electrode tab 40, and the negative electrode tab 30 are arranged in sequence. With such a setting, in the first direction, the recessed area 400 avoids the positive electrode tab 40 and the negative electrode tab 30, so as to avoid introducing a new thickness difference in the core structure due to local swelling or dissolution of the tab glue. It can be understood that the thickness difference of the core structure may refer to the thickness difference that appears in the straight area of the core structure in the first direction, that is, in the thickness direction of the core structure, the straight area of the core structure has different thicknesses at different positions.

[0123] In some examples, in the second direction, that is, in the width direction of the core structure, the minimum distance L5 between the recessed area 400 and the positive electrode tab 40 can be greater than 2 mm. With such a setting, in the thickness direction of the core structure, the recessed area 400 can avoid the positive electrode tab 40.

[0124] In a possible implementation manner, refer to Figure 8 As shown, the number of arc segments of the positive electrode sheet 10 can be odd. Or, refer to Figure 9 As shown, the number of arc segments of the positive electrode sheet 10 can also be even.

[0125] A finishing glue 101 is provided on the empty foil part of the positive electrode sheet 10.

[0126] Exemplarily, refer to Figure 8As shown, the number of arc segments of the positive electrode sheet 10 is odd. In the first direction, that is, in the thickness direction of the core structure, the projections of the recessed areas 400 do not overlap with the projections of the end and start ends of the end sealant 101. It should be noted that the junction corresponding to the recessed area 400 is prone to swelling problems, and the end sealant 101 outside the battery cell is prone to react with the electrolyte in the later stage of cycling, causing the end of the end sealant 101 to swell. With such a setting, when the number of arc segments of the positive electrode sheet 10 is odd, in the thickness direction of the core structure, it is possible to avoid the superposition of the swelling caused by the swelling or dissolution of the end sealant 101 and the swelling of the junction area 20a of the negative electrode sheet 20, resulting in uneven thickness of the core structure, and to avoid the stress concentration of the swelling at the same position, causing abnormal swelling problems of the core structure.

[0127] Among them, in the winding direction of the core structure of the positive electrode sheet 10, the straight part is the straight segment, and the arc part is the arc segment. The end of the end sealant 101 is located at position A, and the start end of the end sealant 101 is located at position B.

[0128] An embodiment of the present invention provides a lithium-ion battery, including a core structure.

[0129] Among them, the core structure in this embodiment has the same structure as the core structure provided in any of the above embodiments, and can bring the same or similar technical effects, which will not be elaborated one by one here, and can be specifically referred to the description of the above embodiments.

[0130] Hereinafter, the lithium-ion battery of the present application will be introduced in detail through specific embodiments, and the specific differences of the following lithium-ion batteries are shown in Table 1.

[0131] Example 1:

[0132] 1. Preparation of the negative electrode sheet 20: Using artificial graphite as the negative electrode active material, graphite, conductive agent and binder are added to the stirring tank according to the mass percentage content of 98.2:0.6:1.2, deionized water solvent is added, and sufficient stirring is carried out, and then passed through a 150-mesh sieve to prepare a negative electrode slurry. The negative electrode slurry is coated on the copper foil by a coater, dried at a temperature of 100°C, and then roll-pressed and slit to finally obtain the negative electrode sheet 20.

[0133] 2. Preparation of the positive electrode sheet 10: Using ternary material as the positive electrode active material, the positive electrode active material, conductive agent and binder are added to the stirring tank according to the mass percentage content of 96.5:2.0:1.5, NMP solvent is added, and sufficient stirring is carried out, and then passed through a 200-mesh sieve to prepare a positive electrode slurry. The positive electrode slurry is coated on the aluminum foil by a coater, and then subjected to drying, roll-pressing and slitting treatments. The corresponding part of the slit part corresponding to the junction area 20a of the negative electrode sheet 20 is laser-drilled to form a recessed area 400, and the distance between two adjacent holes 401 is set to 0.15 mm.

[0134] In the winding direction of the core structure, the size L1 of the recessed area 400 can be 30 mm.

[0135] Measure the diameters of a preset number of holes 401 through a microscope, and then take the average value as 100 μm. The preset number is not specifically limited.

[0136] Measure the depths of a preset number of holes 401 through a microscope, and then take the average value as 5 μm.

[0137] The power of the laser drilling is 85%. After laser drilling, through cleaning and slide preparation, the positive electrode sheet 10 is obtained.

[0138] 3. Separator.

[0139] 4. Assemble the core: Wind the positive electrode sheet 10, negative electrode sheet 20 and separator prepared above together to form a core structure. Subsequently, package it with an aluminum-plastic film, bake to remove moisture, inject electrolyte, and then through processes such as formation and second sealing, a lithium-ion battery is obtained.

[0140] In this embodiment, the ratio CB of the capacity of the junction area 20a to the capacity of the recessed area 400 increases by 0.1.

[0141] Example 2:

[0142] Example 2 is carried out with reference to Example 1. The difference is that the drilling parameters are changed, and the specific parameters are shown in Table 1.

[0143] Example 3:

[0144] Example 3 is carried out with reference to Example 1. The difference is that the CB value is increased by using multiple grooves 402.

[0145] In the second direction, the size L2 of the groove 402 can be 80 μm. The distance L3 between two adjacent grooves 402 can be 0.15 mm. In the thickness direction of the positive electrode sheet 10, measure the depths of a preset number of grooves 402, and then take the average value as 5 μm. The preset number is not specifically limited.

[0146] The specific parameters are shown in Table 1.

[0147] Example 4:

[0148] Example 4 is carried out with reference to Example 1. The difference is that the CB value is increased by using one groove 402.

[0149] In the winding direction of the core structure, the size L1 of the recessed area 400 can be 25 mm.

[0150] In the thickness direction of the positive electrode sheet 10, the depth of the groove 402 can be 2.5 um.

[0151] The specific parameters are shown in Table 1.

[0152] Comparative Example 1:

[0153] Referring to Example 1, the difference is that the positive electrode sheet has no concave area. The remaining steps are the same as those in Example 1.

[0154] Lithium deposition test:

[0155] After the battery has been cycled at room temperature for 100T and 500T, place it in a constant temperature oven at 25°C ± 3°C and let it stand for 2 hours. Charge it at a constant current of 0.5C until the upper limit voltage of the battery's voltage system is reached, with a cut-off current of 0.05C. Then disassemble the fully charged battery in an environment with a temperature of 25°C ± 5°C, a humidity of <10%, and a dew point > -25°C, and observe the state of the negative electrode sheet.

[0156] No abnormality: The surface of the negative electrode sheet is golden yellow. Wipe it with a dust-free paper, and there is no gray metallic lithium powder on the paper.

[0157] Slight lithium deposition: The surface of the negative electrode sheet is dark yellow or partially golden yellow, and the ratio of the lithium deposition area (gray area) of the fully charged negative electrode to the area of the negative electrode active material layer is <5%.

[0158] Severe purple spot lithium deposition: The surface of the negative electrode sheet is dark yellow or partially golden yellow, and the ratio of the lithium deposition area (gray area) of the fully charged negative electrode to the area of the negative electrode active material layer is >5%.

[0159] The specific parameters are shown in Table 1.

[0160] Table 1

[0161]

[0162] It should be noted that "——" in Table 1 means none.

[0163] Table 2: Lithium deposition and swelling conditions at the junction area 20a of the negative electrode sheet during cycling at 25°C

[0164]

[0165] 100T means that the junction area 20a undergoes 100 complete charge-discharge cycles. 500T means that the junction area 20a undergoes 500 complete charge-discharge cycles.

[0166] As can be seen from Table 2, compared with Comparative Example 1, increasing the local CB value in the example can, to a certain extent, improve the lithium deposition problem at the single-sided and double-sided junctions of the negative electrode sheet 20.

[0167] Meanwhile, the expansion space reserved by the hole structure or groove structure for the positive electrode sheet of the core structure can effectively relieve the volume expansion caused by overvoltage at the single-sided and double-sided junction of the negative electrode sheet 20.

[0168] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A core structure, characterized in that, It includes a positive electrode sheet (10), a separator, and a negative electrode sheet (20), and the positive electrode sheet (10), the separator, and the negative electrode sheet (20) are stacked and wound. The negative electrode sheet (20) includes a negative electrode current collector (210) and a negative electrode active layer. The negative electrode sheet (20) has a single-sided area (100) and a double-sided area (200) connected to each other. The negative electrode active layer is coated on one side of the negative electrode current collector (210) in the single-sided area (100), and the negative electrode active layer is coated on both sides of the negative electrode current collector (210) in the double-sided area (200). The single-sided area (100) and the double-sided area (200) intersect to form a junction area (20a). The positive electrode sheet (10) includes a positive electrode current collector (110) and a positive electrode active layer (120). The positive electrode active layer (120) has a recessed area (400). Along a first direction, the recessed area (400) is disposed opposite to the junction area (20a), and the positive electrode active layer (120) on the side of the recessed area (400) facing the junction area (20a) has a concave portion.

2. The core structure according to claim 1, wherein, Both the positive electrode sheet (10) and the negative electrode sheet (20) include straight sections and arc sections connected alternately. The junction area (20a) is located on the straight section of the negative electrode sheet (20), and the recessed area (400) is located on the straight section of the positive electrode sheet (10). Along the first direction, a concave portion is provided on the positive electrode active layer (120) on the side of the recessed area (400) facing away from the junction area (20a). The concave portion includes a hole structure and / or a groove structure.

3. The core structure according to claim 2, characterized in that, The hole structure includes at least one hole (401). The diameter of the hole (401) is 20um to 200um; and / or, In the first direction, the depth of the hole (401) is 1um to 20um.

4. The core structure according to claim 3, characterized in that, The hole structure includes a plurality of the holes (401), and the distance between adjacent two holes (401) is 0mm to 5mm.

5. The core structure according to claim 2, characterized in that, The groove structure includes at least one groove (402). In the first direction, the depth of the groove (402) is 1um to 20um.

6. The core structure according to claim 5, characterized in that, The groove structure includes a plurality of grooves (402) arranged in sequence along a second direction; In the second direction, the size of the groove (402) is 1um to 500um, and the distance between adjacent two grooves (402) is 0.1mm to 2mm.

7. The core structure according to any one of claims 1-6, characterized in that, In the winding direction of the core structure, the starting end of the positive electrode sheet (10) is located behind the starting end of the single-sided area (100). The negative electrode sheet (20) further has a blank foil area (300) connected to the single-sided area (100). The single-sided area (100) includes a paste folding portion (100a) connected to the blank foil area. In the first direction, the projection of the recessed area (400) is located within the projection area of the paste folding portion (100a).

8. The core structure according to claim 7, wherein The positive electrode sheet (10) has an avoidance area (500). In the first direction, the projection of the recessed area (400) is located within the projection area of the avoidance area (500). In the width direction of the core structure, the distance between the starting end of the positive electrode active layer (120) and the recessed area (400) is 1 μm to 10 mm.

9. The core structure according to any one of claims 2-6, characterized in that, A negative electrode tab (30) is provided on the negative electrode current collector (210), and a positive electrode tab (40) is provided on the positive electrode current collector (110); In the first direction, the projections of the recessed area (400), the positive electrode tab (40), and the negative electrode tab (30) do not overlap each other; In the second direction, the minimum distance between the recessed area (400) and the positive electrode tab (40) is greater than 2 mm; and / or, In the second direction, the size of the recessed area (400) is 1 mm to 100 mm.

10. The core structure according to any one of claims 2-6, characterized in that, The number of arc segments of the positive electrode sheet (10) is odd. In the first direction, the projection of the recessed area (400) does not overlap with the projections of the ending end and the starting end of the end sealant (101).

11. A lithium-ion battery, characterized in that, Comprising the core structure according to any one of claims 1-10.

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