Battery cell and battery

Abstract

The invention relates to the technical field of batteries, in particular to a battery cell and a battery comprising the same. The battery cell is formed by laminating and winding electrode assemblies, in the width direction of the battery cell, the battery cell comprises arc areas on the two sides of the battery cell and a straight area in the middle of the battery cell, the electrode assemblies comprise pole pieces and diaphragms, the pole pieces comprise a first pole piece and a second pole piece which are opposite in polarity, and the diaphragms are located between the first pole piece and the second pole piece; the pole piece at the outermost ring in the battery cell is a first pole piece, the first pole piece comprises a double-sided region, a single-sided region and an empty foil region which are adjacent in sequence along the length direction of the first pole piece, the empty foil region comprises a Z-shaped bending part formed by folding at least three layers of current collectors, the Z-shaped bending part is positioned at the outermost ring of the first pole piece, and the battery cell meets the following relational expressions: b is greater than or equal to 2 and less than or equal to 10, and C / D is greater than or equal to 3.5 and less than or equal to 9.4. The battery cell provided by the invention can provide a displacement space for displacement of the outermost pole piece under the action of shear force, so that the problem of breakage or damage of the pole piece is improved and even avoided, and the use performance of the battery is improved.

Description

TECHNICAL FIELD

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

[0002] With the rapid development of lithium ion battery technology, people have higher requirements for the cycle life and safety performance of lithium ion batteries. In order to improve the cycle life and safety performance of lithium ion batteries, on the one hand, the materials such as positive and negative electrode materials, electrolyte types, and separator types constituting the lithium battery need to be optimized and innovated, and on the other hand, the design and optimization of the electrode sheet structure are also crucial to the performance improvement.

[0003] In the cycle process of the winding type lithium ion battery, the electrode sheet will swell, and the swelling of the electrode sheet causes the inner electrode sheet to extrude the outer electrode sheet in the electric core. The extrusion force is transmitted from the inner layer to the outer layer of the electric core, so that the outer layer of the winding type electric core is subjected to a large extrusion force. The electrode sheet at the outermost layer is prone to breakage or damage under the action of the shearing force, especially in the single-coated area, the junction of the single-sided and double-sided active layers of the electrode sheet, and the junction of the active layer and the empty foil area. Once the electrode sheet breaks, the battery resistance increases, the capacity decreases, and the electrode sheet lithium is extracted, and the battery cannot work normally.

[0004] Therefore, it is very important to invent a battery that can improve or even avoid the breakage or damage of the electrode sheet. SUMMARY

[0005] It is found through research that the winding type lithium ion battery is formed by winding the electrode assembly to form an electric core. The circular arc (also called corner) area of the winding type electric core structure itself has a large stress accumulation, which causes extrusion between the electrode sheets. In addition, the positive and negative electrode sheets swell during charging and discharging, which intensifies the extrusion of the inner circle electrode sheet to the outer circle electrode sheet. The extrusion force is transmitted from the inner circle to the outer circle of the electric core. The tail empty foil of the outermost circle electrode sheet is usually fixed by a tailing glue. Due to the lack of displacement space, it is easy to be pulled by the swelling force transmitted from the inside to the outside, and problems such as breakage or damage occur.

[0006] In order to solve the problem that the tail of the electrode sheet in the winding type lithium ion battery is prone to breakage or damage, the present application provides an electric core and a battery comprising the same. When the outer circle electrode sheet is pulled by the swelling force transmitted from the inside to the outside, the electric core of the present application can provide displacement space for the displacement of the outermost circle electrode sheet, and at the same time control the relationship between the weight content of silicon element in the electric core and the active layer of the electrode sheet. The adaptation degree between the swelling generated by the silicon-based material and the displacement space provided by the electric core can be improved, thereby effectively improving or even avoiding the problem of breakage and / or damage of the electrode sheet, and improving the performance of the battery.

[0007] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a battery cell, which is formed by stacking and winding electrode assemblies, the battery cell includes a straight area and arc areas on both sides of the straight area, the electrode assembly includes a pole piece and a diaphragm, the pole piece includes a current collector and an active layer located on both sides of the current collector, the active layer includes a negative electrode active material, the negative electrode active material includes a silicon-based material, the pole piece includes a first pole piece and a second pole piece with opposite polarities, the diaphragm is located between the first pole piece and the second pole piece, and the outermost pole piece in the battery cell is the first pole piece. A pole piece, along the length direction of the first pole piece, the first pole piece includes a double-sided area, a single-sided area and an empty foil area adjacent to each other in sequence, the empty foil area includes a Z-shaped bend portion, the Z-shaped bend portion is located at the outermost circle of the first pole piece, the Z-shaped bend portion includes at least three layers of folded current collectors, and the battery cell satisfies the following relationship: 2≤b≤10, 3.5≤C / D≤9.4, wherein b is the width of the Z-shaped bend portion, the unit is mm, C is the weight content of the silicon element in the active layer, the unit is %, and D is the elongation of the current collector, the unit is %.

[0008] A second aspect of the present invention provides a battery, comprising a housing and the battery cell according to the first aspect of the present invention, wherein the battery cell is located in a receiving space formed by the housing.

[0009] Through the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0010] The outermost circle of the battery cell provided by the present invention includes a Z-shaped bend portion generated by folding the electrode collector. When the electrode expands, the Z-shaped bend portion can provide displacement space for the outermost electrode. At the same time, the relationship between the weight content of the silicon element in the active layer of the electrode, the elongation of the current collector and the components providing the displacement space in the battery cell is controlled, which can improve the adaptability between the expansion generated by the silicon-based material and the displacement space provided by the battery cell. When the electrode expands, the Z-shaped bend portion can provide sufficient buffer space for the displacement of the empty foil at the tail of the battery cell, reduce the extrusion force transmitted to the outer circle electrode, thereby reducing the risk of fracture or damage of the empty foil at the tail of the outer circle electrode, and improve the performance of the battery.

[0011] Other features and advantages of the present invention will be described in detail in the following detailed description.

[0012] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Shown is one of the schematic diagrams of the battery cell of the present invention.

[0014] Figure 2 The figure shows a schematic diagram of the orthographic projection of a battery cell in the height direction in the prior art.

[0015] Figure 3 Shown is one of the schematic diagrams of the orthographic projection of the battery cell of the present invention along the height direction.

[0016] Figure 4 Shown Figure 3 A partial enlarged view of .

[0017] Figure 5 Shown is a schematic cross-sectional view of the first pole piece of the present invention.

[0018] Figure 6 Shown is the second schematic diagram of the orthographic projection of the battery cell of the present invention along the height direction.

[0019] Figure 7 Shown Figure 6 A partial enlarged view of .

[0020] Figure 8 Shown is the second schematic diagram of the battery cell of the present invention.

[0021] Figure 9 Shown is a schematic diagram of the first pole piece of the battery cell of the present invention. DETAILED DESCRIPTION

[0022] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not intended to limit the present invention. In this article, unless otherwise specified, data ranges include endpoints.

[0023] It should be noted that the numerical expressions such as "first" and "second" in the present invention are only used to distinguish different substances or usage methods, and do not represent a difference in order.

[0024] The first aspect of the present invention provides a battery cell, which is formed by stacking and winding electrode assemblies, the battery cell comprising a straight area and arc areas on both sides of the straight area, the electrode assembly comprising a pole piece and a diaphragm, the pole piece comprising a current collector and an active layer on both sides of the current collector, the active layer comprising an active material, the active material being a positive electrode active material or a negative electrode active material, the negative electrode active material comprising a silicon-based material, the pole piece comprising a first pole piece and a second pole piece with opposite polarities, the diaphragm being located between the first pole piece and the second pole piece, the outermost pole piece in the battery cell being the first pole piece, and along the length direction of the first pole piece, the first pole piece comprising a double-sided area, a single-sided area, and a plurality of adjacent double-sided areas. area and an empty foil area, the empty foil area including a Z-shaped bend portion, the Z-shaped bend portion being located at the outermost circle of the first pole piece, the Z-shaped bend portion including at least three layers of the folded current collector, and the battery cell satisfies the following relationship: 2≤b≤10 (b is, for example, 2, 3, 4, 5, 6, 7, 8, 9, 10 or is within the range formed by any two of the above values), 3.5≤C / D≤9.4 (3.5, 4, 5, 6, 7, 8, 9, 9.4 or is within the range formed by any two of the above values), wherein b is the width of the Z-shaped bend portion, in mm, C is the weight content of the silicon element in the active layer, in %, and D is the elongation of the current collector, in %.

[0025] like Figure 2 As shown, the battery cell 1 includes a straight area 12 and arc areas 11 located on both sides of the straight area 12. The arc area 11 is a bent area in the battery cell, and the straight area 12 is an unbent area in the battery cell. Along the width direction Y of the battery cell, the arc area 11 is located on both sides of the battery cell, and the straight area 12 is located in the middle area of ​​the battery cell. The electrode assembly includes an electrode 13 and a diaphragm 14. It can be understood that there are mutually perpendicular height directions G, thickness directions X and width directions Y (such as Figure 1 shown), Figure 2 The figure shows the orthographic projection of the battery cell 1 in the direction perpendicular to the height.

[0026] like Figure 3As shown, the electrode 13 includes a first electrode 131 and a second electrode 132 of opposite polarity. The diaphragm 14 is located between the first electrode 131 and the second electrode 132. The outermost electrode in the battery cell 1 is the first electrode 131. The first electrode 131 can be either a positive electrode or a negative electrode. When the first electrode 131 is a positive electrode, the second electrode 132 is a negative electrode. The active material in the first electrode is a positive electrode active material, the active material in the second electrode is a negative electrode active material, and the outermost electrode in the battery cell 1 is the positive electrode. When the first electrode 131 is a negative electrode, the second electrode 132 is a positive electrode. The active material in the first electrode is a negative electrode active material, the active material in the second electrode is a positive electrode active material, and the outermost electrode in the battery cell 1 is the negative electrode. In the present invention, C represents the weight content of silicon in the active layer, which refers to the weight content of silicon in the active layer comprising silicon-based materials.

[0027] like Figure 5 As shown, along the length direction of the first electrode sheet, the first electrode sheet includes a double-sided region 1311, a single-sided region 1312, and a hollow foil region 1313, which are adjacent to each other in sequence. The hollow foil region 1313 includes a Z-shaped bend 13131. The double-sided region 1311 has an active layer 1315 on both sides of the current collector 1314. The single-sided region 1312 has an active layer 1315 on one side of the current collector 1314. The hollow foil region 1313 has no negative electrode active layer 1315 on either side of the current collector 1314. The length direction N of the first electrode sheet can be the same as the winding direction J of the battery cell.

[0028] In the present invention, the outermost electrode in the battery cell is the first electrode 131, and the Z-shaped bending portion 13131 (such as Figure 3 As shown), and in the length direction N of the first pole piece 131 (the direction J of the battery core winding), the first pole piece 131 includes a double-sided area 1311, a single-sided area 1312 and an empty foil area 1313 (as shown) adjacent to each other in sequence. Figure 5 As shown), it can be understood that the Z-shaped bending portion 1313 is located at the outermost circle of the battery cell, the Z-shaped bending portion 1313 is located at the empty foil area 131, and the empty foil area 1313 is located at the outermost circle of the battery cell. Therefore, in the winding direction J of the battery cell, the empty foil area 1313 is located at the tail end of the battery cell winding, and the double-sided area 1311 is located at the beginning of the battery cell winding.

[0029] In the present invention, the Z-shaped bend portion includes at least three layers of the negative electrode current collector folded. It can be understood that the Z-shaped bend portion is formed by bending the current collector multiple times (≥2 times, for example, 2 times, 3 times, 4 times, 5 times or 6 times). In the Z-shaped bend portion, there are multiple layers of the current collector stacked in the thickness direction X, and the number of layers of the current collector folded in the Z-shaped bend portion is ≥3 (for example, 3, 4, 5, 6 or 7). In the winding direction J of the battery cell, the Z-shaped bend portion includes a first end b2 and a second end b1, and the distance between the first end b2 and the second end b1 is the width b of the Z-shaped bend portion (for example, Figure 4 As shown). The Z-shaped bend is formed by folding (bending) the current collector of the first pole piece, and the Z-shaped bend includes a plurality of bends of the current collector of the first pole piece. The first end b2 and the second end b1 are both bends of the current collector of the first pole piece in the Z-shaped bend, and the first end b2 is the end closest to the single-sided area 1312 among all the bends of the current collector of the first pole piece, and the second end b1 is the end farthest from the single-sided area 1312 among all the bends of the current collector of the first pole piece (as shown). Figure 5 shown).

[0030] In one embodiment, the Z-shaped bend portion includes three layers of the negative electrode current collector (eg Figure 4 shown).

[0031] The electric core of the present application comprises a Z-shaped bending part, which can provide displacement space for the outermost pole piece when the pole piece expands, the Z-shaped bending part is located at the outermost circle of the first pole piece, is formed by folding at least three layers of current collectors of the empty foil area, and has a shape of letter "Z". This unique structure can slide to a certain extent when subjected to the pulling force of the expansion force transmitted from the inside to the outside, which can provide displacement space for the outer circle pole piece, relieve the shear force on the outer circle pole piece, and improve or even avoid the damage or fracture of the outermost circle pole piece. Moreover, it is found through research that, as the weight content of the silicon-based material in the active layer increases, the stress transmitted from the inner circle to the outer circle to the outermost circle becomes larger, resulting in a larger pulling force on the outermost circle pole piece of the electric core. Therefore, by controlling the relationship between the weight content of the silicon-based material in the active layer, the elongation rate of the current collector and the width of the Z-shaped bending part, i.e. controlling the electric core to satisfy the following relationship: 2≤b≤10, 3.5≤C / D≤9.4, the matching degree between the expansion generated by the silicon-based material and the displacement space provided by the electric core can be improved. That is, when the elongation rate D of the current collector reaches the upper limit of the process, and the required weight content C of the silicon element in the active layer of the electric core is larger, the volume expansion of the pole piece will also increase correspondingly during the cycle process, and the expansion force transmitted from the inner circle to the outer circle of the electric core will also increase. At this time, the width b of the Z-shaped bending part is adjusted to satisfy the above relationship, and as the expansion force transmitted from the inner circle to the outer circle increases, the Z-shaped bending part satisfying the above relationship can still slide, and sufficient displacement space is provided for the displacement of the empty foil at the tail of the electric core, so as to reduce the extrusion force transmitted to the outer circle pole piece, thereby reducing the risk of fracture or damage of the empty foil at the tail of the outer circle pole piece, and improving the use performance of the battery.

[0032] In the present application, the weight content C of the silicon element in the active layer can be obtained by using the conventional test method in the art, such as ICP. Specifically, after the lithium ion battery is disassembled, the negative pole piece is taken out, soaked and eluted with dimethyl carbonate, and dried, and then the dried negative pole piece is treated at a high temperature of 400℃ for 2h (such as a tube furnace under nitrogen or argon atmosphere), and the negative active material layer can be peeled off from the current collector, and the negative active material is collected. In the silicon content test, a thermal gravimetric analyzer (such as TGA 550 thermal gravimetric analyzer) is used, the sample amount for testing is 5mg-15mg, and the sample is heated from room temperature to 900℃ at a heating rate of 10℃ / min under air or oxygen atmosphere, and is kept at 900℃ for 40min, so that the non-silicon components in the negative active material layer are volatilized and the silicon is fully oxidized to silicon dioxide. The weight percentage at the end of the whole test process is the ash content of the negative active material layer; the ash content value is divided by the molar mass of silicon dioxide and then multiplied by the molar mass of silicon, and the percentage content of silicon element in the negative active material layer is obtained.

[0033] In the present application, the extension ratio D of the current collector is the extension ratio of the current collector of the first pole piece in the length direction of the first pole piece. The extension ratio of the current collector can be obtained by measuring the extension ratio of the current collector of the empty foil area in the first pole piece, specifically as follows: the extension ratio D of the current collector can be obtained by testing by a method conventional in the art, for example, after discharging the battery to 0% SOC, disassembling and taking out the first pole piece of the outermost circle of the battery cell, taking the current collector of the empty foil area at the tail end of the first pole piece of the outermost circle of the battery cell, soaking in DMC solvent for 12h, and then rinsing with DMC solvent to remove the lithium salt attached on the empty foil area; after drying, using a knife to cut the above-processed empty foil area into a sample with a size of 15mm in the width direction of the current collector and a size exceeding 50mm in the length direction of the current collector; using a WD-D3 electronic universal testing machine (with a precision of 0.5 level and an accuracy of ±1% of the indicated value), setting the gauge length to 50mm and the speed to 50mm / min, and performing tensile test on the above-mentioned sample in the length direction to measure the extension ratio D of the current collector.

[0034] In the present application, by providing a Z-shaped bending part at the tail empty foil area of the outer pole piece of the battery cell, and controlling the relationship between the weight content of silicon element in the active layer, the extension ratio of the current collector and the width of the Z-shaped bending part in the battery cell, compared with the prior art, sufficient displacement space can be provided for the outer pole piece of the battery cell when the battery cell expands, the extrusion force transmitted to the outer pole piece is reduced, thereby reducing the risk of fracture and / or damage of the tail empty foil of the outer pole piece, and improving the use performance of the battery. In order to further improve the effect, one or more of the technical features can be further optimized.

[0035] In some embodiments, the width b of the Z-shaped bending part is 2mm-5mm, for example, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm or within a range consisting of any two of the above values.

[0036] In some embodiments, the weight content C of silicon element in the active layer is 5%-35%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35% or within a range consisting of any two of the above values.

[0037] In some embodiments, the extension ratio D of the current collector is 1.5%-8%, for example, 1.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8% or within a range consisting of any two of the above values.

[0038] In some embodiments, the first electrode sheet is a negative electrode sheet, and the elongation of the current collector is 3.5%-8%, for example, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, or a range between any two of the above values.

[0039] In some embodiments, the first electrode is a positive electrode, and the elongation of the current collector is 1.5%-4%, for example, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, or a range formed by any two of the above values.

[0040] In some embodiments, the Z-shaped bend is located in an arc area or a straight area. Figure 3 As shown, the Z-shaped bending portion 13131 is located in the straight area 12.

[0041] In some embodiments, as Figure 3 As shown, the arc area 11 consists of two fan-shaped areas 111 (such as Figure 3 The Z-shaped bending portion 13131 is located in the fan-shaped area or the straight area 12, wherein the fan-shaped area is half of the arc area.

[0042] In some embodiments, the battery cell satisfies the following relationship: 1.03≤Q=R / (T / 2)≤1.25 (Q=R / (T / 2) is, for example, 1.03, 1.0, 1.1, 1.15, 1.2, 1.22, 1.25 or is within the range of any two of the above values), 4≤C / Q≤28 (C / Q is, for example, 4, 10, 12, 15, 20, 25, 28 or is within the range of any two of the above values), wherein T is the thickness of the battery cell, in mm, and R is the thickness of the arc area, in mm. Wherein, in the thickness direction of the battery cell, the outermost electrode in the straight area includes the electrode on the upper and lower sides, and the thickness T of the battery cell is the vertical distance between the outermost electrode in the straight area in the thickness direction of the battery cell, specifically, the distance between the outer edge line of the outermost electrode in the straight area and the outer edge line of the other outermost electrode opposite in the straight area in the thickness direction X of the battery cell (such as Figure 3 The thickness R of the arc area is the distance between the outermost pole piece and the innermost pole piece of the cell in the same arc area in the width direction of the cell, specifically, the distance between the inner side of the innermost pole piece and the outer side of the outermost pole piece in the same arc area in the width direction of the cell (as shown in FIG. Figure 3 shown).

[0043] Through research, it was found that as the weight content of silicon in the active layer increases, the stress transmitted from the inner ring to the outer ring to the outermost ring becomes greater, resulting in a greater pulling force on the outermost ring electrode of the battery cell, and more buffering displacement required for the tail empty foil. When the battery cell satisfies the above relationship, when the weight content of silicon in the active layer increases, the battery cell of the present invention can still provide sufficient displacement space for the first electrode of the outermost ring, reduce the extrusion force transmitted to the outermost layer, and improve or even avoid the fracture or breakage of the tail of the electrode. When the battery cell satisfies the above relationship, it can provide a suitable gap between the electrodes in the arc area, and provide space for buffering expansion for the coiled core battery containing silicon negative electrode in the width direction of the battery cell, thereby avoiding fracture or breakage of the electrode. At the same time, it can also avoid the gap between the electrodes in the arc area being too large, causing poor adhesion at the interface, and leading to the problem of purple spots on the battery.

[0044] In some embodiments, the battery cell satisfies the following relationship: 0.001≤H1 / L1≤0.023 (H1 / L1 is, for example, 0.001, 0.01, 0.013, 0.016, 0.019, 0.022, 0.023 or is within the range of any two of the above values), wherein H1 is the thickness of the active layer in the single-sided area, and L1 is the length of the empty foil area between the single-sided area and the Z-shaped bending portion along the length direction of the first pole piece (such as Figure 5 Research has found that when the distance between the active layer in the single-sided area and the Z-bend portion is too close, the hollow foil between the active layer in the single-sided area and the Z-bend portion is prone to fracture under the action of shear stress. Therefore, controlling the battery cell to satisfy the above relationship can maintain an appropriate distance between the active layer in the single-sided area and the Z-bend portion. When the battery cell expands, the Z-bend portion provides appropriate displacement while also preventing the hollow foil area from fracture.

[0045] In some embodiments, the thickness H1 of the active layer in the single-sided area is 25 μm-55 μm, for example, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, or within a range formed by any two of the above values.

[0046] In some embodiments, along the length direction of the first pole piece, the length L1 of the empty foil area between the single-sided area and the Z-shaped bending portion is 2mm-35mm, for example, 2mm, 4mm, 6mm, 8mm, 10mm, 15mm, 20mm, 25mm, 30mm, 35mm or within the range of any two of the above values.

[0047] According to a specific embodiment, H1 is 25 μm-55 μm, L1 is 2 mm-35 mm, and the battery cell satisfies the following relationship: 0.001≤H1 / L1≤0.023.

[0048] In some embodiments, the first bend of the Z-shaped bend is bent in a direction away from the battery cell. The first bend is formed by the first bending of the current collector of the first electrode sheet in a direction away from the center of the battery cell (e.g. Figure 4 The bending direction of the Z-shaped bend 13131 is from e2 to e1. ​​The first bending direction of the Z-shaped bend is controlled to bend away from the battery cell. When the battery cell expands, the Z-shaped bend is more likely to expand, further improving the problem of electrode breakage.

[0049] In some embodiments, as Figure 7 As shown, along the winding direction J of the battery cell, the Z-shaped bending portion includes a first end b2 and a second end b1, the first electrode includes a first surface 13132 close to the center of the battery cell and a second surface 13133 away from the center of the battery cell, and the first surface 13132 of the empty foil area includes a first adhesive tape 13134 (as shown in FIG. Figure 7 (shown by the purple dashed line in the middle), the first adhesive tape 13134 includes a third end c1 and a fourth end c2. The third end c1 extends to the junction of the bare foil area and the single-sided area. Along the winding direction of the battery cell, the fourth end c2 extends beyond or does not exceed the second end b1 of the Z-bend portion. This first adhesive tape reduces the friction coefficient of the Z-bend portion and acts as a lubricant. When the battery cell expands, the Z-bend portion expands more easily, providing displacement space and alleviating the expansion force transmitted from the inside out. It also covers the active layer in the single-sided area, preventing burrs on the active layer from piercing the diaphragm.

[0050] In some embodiments, as Figure 3 As shown, the battery cell includes a tab 15 . Along the thickness direction X of the battery cell, the orthographic projection of the tab 15 does not overlap with the orthographic projection of the Z-shaped bending portion 13131 , thereby avoiding affecting the energy density of the battery.

[0051] In some embodiments, as Figure 7 As shown, the second surface 13133 of the single-sided area includes a second adhesive tape 13135, and the second adhesive tape 13135 (such as Figure 7The second adhesive tape is provided on the second surface of the single-sided area to reduce the friction between the Z-bend portion and the current collector. When the battery cell expands, the relative sliding of the first pole piece in the Z-bend portion becomes easier, thereby more effectively dispersing the expansion force and further reducing the risk of fracture or damage to the tail empty foil.

[0052] In some embodiments, as Figure 7 As shown, the fourth end c2 extends beyond the second end b1 of the Z-shaped bending portion 13131 , and at the Z-shaped bending portion 13131 , the first adhesive tape 13134 is folded together with the current collector.

[0053] In some embodiments, as Figure 9 As shown, along the width direction K of the first electrode sheet, both sides of the current collector of the Z-shaped bend include ceramic layers 13136, which are located on the surface of the current collector. Providing a ceramic layer on the surface of the Z-shaped bend can smooth the sharp corners generated by the bend, preventing puncture of the aluminum-plastic film and improving safety.

[0054] In some embodiments, as Figure 9 As shown, along the width direction of the first pole piece, the two side edges of the current collector in the empty foil area include ceramic layers, and the ceramic layers are located on the surface of the current collector.

[0055] In some embodiments, the thickness of the ceramic layer is 6 μm-15 μm, for example, 6 μm, 7.5 μm, 9 μm, 10.5 μm, 12 μm, 13.5 μm, 15 μm, or a range formed by any two of the above values.

[0056] In some embodiments, the silicon-based material includes one or more of a bulk silicon-carbon composite material, a spherical silicon-carbon composite material, a nano silicon-carbon material, and a linear silicon-carbon material.

[0057] In some embodiments, the active material is a negative electrode active material, the active layer including the negative electrode active material is a negative electrode active layer, and the negative electrode active layer further includes a negative electrode conductor and a negative electrode binder.

[0058] In some embodiments, the negative electrode active layer includes a graphite material, a negative electrode conductor, and a negative electrode binder.

[0059] In some embodiments, the graphite material includes artificial graphite and / or natural graphite.

[0060] In some embodiments, the negative electrode conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, conductive graphite, conductive carbon fiber, carbon nanotubes, metal powder, and carbon fiber.

[0061] In some embodiments, the negative electrode binder includes at least one of styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylate lithium (PAALi), polyacrylic acid (PAA), polymethylcellulose sodium (CMC-NA) and polymethylcellulose lithium (CMC-Li).

[0062] In some embodiments, based on the total weight of the negative electrode active layer, the weight content of the graphite material is 45%-94%, the weight content of the negative electrode conductive agent is 0-5%, and the weight content of the negative electrode binder is 0.5%-10%. When the weight content of the negative electrode conductive agent in the negative electrode active layer is 0, it indicates that the negative electrode conductive agent is absent.

[0063] A second aspect of the present invention provides a battery, comprising a housing and the battery cell according to the first aspect of the present invention, wherein the battery cell is located in a receiving space formed by the housing.

[0064] In some embodiments, as Figure 8 As shown, a double-sided hot melt adhesive 16 is arranged between the shell and the battery core, and the position where the double-sided hot melt adhesive 16 is pasted on the outer surface of the battery core is located at the secondary outer circle of the battery core, and the position where the double-sided hot melt adhesive is pasted on the outer surface of the battery core is located in the same plane as the Z-shaped bending portion and does not overlap with the Z-shaped bending portion. The distance between the edge of the Z-shaped bending portion and the edge of the position where the double-sided hot melt adhesive is pasted on the outer surface of the battery core is 2mm-5mm, for example, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm or within the range composed of any two of the above values, so that it can be ensured that the winding core will not be squeezed and deformed due to shaking in the shell, and can also ensure that the Z-shaped bend can be quickly unfolded when the battery core expands, thereby alleviating the expansion force transmitted from the inside to the outside, and effectively avoiding the problem of electrode breakage.

[0065] In the present invention, the secondary outer circle of the battery cell is a circle layer adjacent to the outermost circle of the battery cell along a direction close to the center of the battery cell.

[0066] In some embodiments, the housing is made of aluminum-plastic film.

[0067] In some embodiments, the battery comprises an electrolyte, which is a conventional electrolyte.

[0068] Since the battery of the present application comprises the battery cell of the first aspect of the present application, the risk of fracture or damage of the tab of the battery is reduced, and the use performance of the battery is improved.

[0069] The present application will be described in detail below by way of examples. The examples described in the present application are only a part of the examples of the present application, but not all the examples. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0070] The following examples are used to illustrate the battery cell and battery of the present application.

[0071] Unless otherwise specified, the raw materials and methods for preparing the lithium ion battery described in the present application are all conventional choices in the art.

[0072] The first tab of the battery cell in Example I is a positive tab.

[0073] Example I-1

[0074] (1) Negative tab

[0075] A silicon-based material (spherical silicon-carbon composite material), artificial graphite, polyacrylic acid (PAA), sodium carboxymethyl cellulose, and acetylene black (wherein the weight content of silicon element in the negative active layer is 18.3%, and the weight ratio of artificial graphite, polypropylene, sodium carboxymethyl cellulose, and acetylene black is 96:2.7:0.65:0.65) are added to a vacuum stirrer, and an appropriate amount of deionized water is added at the same time. Under the action of the vacuum stirrer, they are mixed thoroughly until a uniform and flowable negative electrode slurry is formed. The above-mentioned negative electrode slurry is uniformly coated on both sides of the copper foil, and then dried, rolled, and cut to obtain a negative tab.

[0076] (2) Positive tab

[0077] Lithium cobaltate, polyvinylidene fluoride, and carbon nanotubes are added to a vacuum stirrer in a mass ratio of 93:4:3, and an appropriate amount of N-methyl pyrrolidone (NMP) is added at the same time. Under the action of the vacuum stirrer, they are mixed thoroughly until a uniform and flowable positive electrode slurry is formed. The above-mentioned positive electrode slurry is uniformly coated on both sides of the aluminum foil, and then dried, rolled, and cut to obtain a positive tab.

[0078] (3) Separator

[0079] A PP separator is used.

[0080] (4) Electrolyte

[0081] In an argon-filled glove box (moisture <10ppm, oxygen <1ppm), ethylene carbonate (EC), propylene carbonate (PC), and propyl propionate (PP) were mixed in a mass ratio of 2:1.5:2. 14wt.% of LiPF6 based on the total mass of the non-aqueous electrolyte and 20wt.% of ethylene carbonate (FEC) based on the total mass of the non-aqueous electrolyte were slowly added to the mixed solution and stirred to obtain a non-aqueous electrolyte.

[0082] (5) Lithium-ion batteries

[0083] The positive electrode sheet prepared in step (2), the negative electrode sheet prepared in step (3) and the separator prepared in step (4) are wound to obtain a bare battery cell; the bare battery cell is welded with a tab and placed in a battery shell; the electrolyte prepared in step (1) is injected into the dried and qualified battery cell; and a lithium-ion battery is obtained through processes such as standing, aging, formation, exhaust, aging, and sorting. Among them, the first electrode sheet of the outermost circle of the battery cell is the positive electrode sheet, and a Z-shaped bend portion is provided in the empty foil area of ​​the positive electrode sheet, and the number of layers of the positive electrode current collector folded in the Z-shaped bend portion is 3; the width of the Z-shaped bend portion is 3.5 mm (i.e., b is 3.5); the weight content of silicon element in the negative electrode active layer is 18.3% (i.e., C is 18.3); the elongation of the positive electrode current collector is 2.8% (i.e., D is 2.8); C / D=18.3 / 2.8=6.54; the thickness of the active layer in the single-sided area of ​​the positive electrode sheet is 35.3 μm (i.e., H1 is 35.3 μm); along the length direction of the positive electrode sheet, the length of the empty foil area between the single-sided area and the Z-shaped bend portion is 15.3 mm (i.e., L1 is 15.3 mm); H1 / L1=35.3 / 15300=0.0023.

[0084] Example I-2 group

[0085] This set of embodiments is used to illustrate the impact produced when b changes.

[0086] Example I-2a

[0087] The same procedure is carried out as in Example I-1, except that the width of the Z-bend portion is 2.2 mm (ie, b is 2.2).

[0088] Example I-2b

[0089] The same procedure is carried out as in Example I-1, except that the width of the Z-bend portion is 4.8 mm (ie, b is 4.8).

[0090] Example I-2c

[0091] The same procedure is carried out as in Example I-1, except that the width of the Z-bend portion is 9.6 mm (ie, b is 9.6).

[0092] Example 1-3 group

[0093] This set of embodiments is used to illustrate the impact when C / D changes.

[0094] This example group was carried out with reference to Example I-1, except that C and / or D were changed to change C / D, as shown in Table 1.

[0095] Table 1

[0096]

[0097] Example 1-4 group

[0098] This set of examples is used to illustrate the impact when H1 / L1 changes.

[0099] This embodiment group was carried out with reference to embodiment I-1, except that H1 and / or L1 were changed to change H1 / L1, as shown in Table 2.

[0100] Table 2

[0101]

[0102]

[0103] Comparative Example I-1

[0104] The same procedure is carried out as in Example I-1, except that the width of the Z-bend portion is 1 mm (ie, b is 1).

[0105] Comparative Example I-2

[0106] The same procedure is carried out as in Example I-1, except that the width of the Z-bend portion is 12.7 mm (ie, b is 12.7).

[0107] Comparative Example I-3

[0108] The same procedure was followed as in Example I-3a, except that the elongation of the positive electrode current collector was 3.7% (ie, D was 3.7), and C / D = 5.8 / 3.7 = 1.57.

[0109] Comparative Example I-4

[0110] The same procedure was followed as in Example I-1, except that the elongation of the positive electrode current collector was 1.6% (ie, D was 1.6), and C / D = 18.3 / 1.6 = 11.44.

[0111] The first electrode of the battery cell in Example II group is the negative electrode.

[0112] Example II-1

[0113] The reference is made to the example I-1, except that the first pole piece of the outermost circle of the cell is a negative pole piece, a Z-shaped bending part is arranged in the empty foil area of the negative pole piece, the number of layers of the negative pole current collector folded in the Z-shaped bending part is 3; the weight content of silicon element in the negative active layer is 29.7% (i.e. C is 29.7); the elongation of the negative pole current collector is 5.8% (i.e. D is 5.8); C / D = 29.7 / 5.8 = 5.12; the thickness of the active layer in the single-sided area of the negative pole piece is 35.3 μm (i.e. H1 is 35.3 μm); the length of the empty foil area between the single-sided area and the Z-shaped bending part along the length direction of the negative pole piece is 15.3 mm (i.e. L1 is 15.3 mm); H1 / L1 = 35.3 / 15300 = 0.0023.

[0114] Example II-2 group

[0115] This group of examples is used to illustrate the influence caused by the change of C / D.

[0116] The reference is made to the example II-1, except that the change of C / D is caused by changing C and / or D, which is specifically shown in Table 3.

[0117] Table 3

[0118]

[0119] Comparative example II-1

[0120] The reference is made to the example II-2a, except that the elongation of the negative pole current collector is 7.9% (i.e. D is 7.9), C / D = 26.8 / 7.9 = 3.39.

[0121] Comparative example II-2

[0122] The reference is made to the example II-2b, except that the elongation of the negative pole current collector is 3.5% (i.e. D is 3.5), C / D = 34.1 / 3.5 = 9.74.

[0123] Test example

[0124] The batteries prepared in the examples and comparative examples are subjected to the following performance tests, and the test results are shown in Table 4:

[0125] (1) Cycle capacity retention rate / % (environmental test at 25℃, cycle 800 times):

[0126] The batteries are subjected to charge-discharge cycle test at 1.5C charge rate, 0.7C discharge rate, and 3.0V-4.5V voltage window (using Blue Power test equipment), cycle 800 times, and the first discharge capacity C1 and the 800th discharge capacity C800 are used to calculate the capacity retention rate: C800 / C1 x 100%.

[0127] (2) The situation of electrode fracture after cycling:

[0128] The battery was subjected to a charge and discharge cycle test at a 1.5C charge rate, a 0.7C discharge rate, and a voltage window of 3.0V-4.5V (using a blue electric test device). The cycle lasted 800 cycles. After the cycle was completed, the empty foil at the end of the outer ring of the electrode in the battery cell was observed by CT to see if it was broken. If it was broken, it was considered a failure. If it was not broken, it was considered a pass. Ten battery samples were tested for each embodiment and comparative example, and the results were expressed as "number of tests passed / 10". For example, "5 / 10" means that only 5 of the 10 battery samples passed the test.

[0129] Table 4

[0130]

[0131]

[0132] By comparing the test results of the comparative example and the embodiment in Table 4, it can be seen that the fracture of the electrode sheet of the battery in the embodiment is significantly improved after cycling, and the cycle capacity retention rate is significantly improved, indicating that by providing a Z-shaped bend portion in the empty foil area at the tail end of the outer ring electrode sheet of the battery cell, and simultaneously controlling the relationship between the weight content of the silicon element in the active layer in the battery cell, the elongation of the current collector and the width of the Z-shaped bend portion, the risk of fracture and / or damage of the empty foil at the tail end of the outer ring electrode sheet can be reduced, thereby improving the performance of the battery.

[0133] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as the contents disclosed by the present invention and fall within the scope of protection of the present invention.

Claims

1. A battery cell, characterized in that the battery cell is formed by stacking and winding electrode assemblies, the battery cell comprising a straight area and arc areas on both sides of the straight area, the electrode assembly comprising a pole piece and a separator, the pole piece comprising a current collector and an active layer on both sides of the current collector, the active layer comprising a negative electrode active material, the negative electrode active material comprising a silicon-based material, the pole piece comprising a first pole piece and a second pole piece with opposite polarities, the separator being located between the first pole piece and the second pole piece, the pole piece in the outermost circle of the battery cell being the first pole piece, along the length direction of the first pole piece, the first pole piece comprising a double-sided area, a single-sided area and an empty foil area adjacent in sequence, the empty foil area comprising a Z-shaped bend portion, the Z-shaped bend portion being located at the outermost circle of the first pole piece, the Z-shaped bend portion comprising at least three layers of the current collector folded, the battery cell satisfying the following relationship: 2≤b≤10, 3.5≤C / D≤9.4, wherein, b is the width of the Z-shaped bending portion, in mm, C is the weight content of silicon in the active layer, in %, and D is the elongation of the current collector, in %.

2. The battery cell according to claim 1, wherein: The width b of the Z-shaped bending portion is 2mm-5mm; and / or, the weight content C of silicon in the active layer is 5%-35%; And / or, the elongation D of the current collector is 1.5%-8%; And / or, the arc area is composed of two fan-shaped areas, and the Z-shaped bending portion is located in the fan-shaped area or the straight area.

3. The battery cell according to claim 1, wherein: The battery cell satisfies the following relationship: 0.001≤H1 / L1≤0.023, wherein H1 is the thickness of the active layer in the single-sided area, and L1 is the length of the empty foil area between the single-sided area and the Z-shaped bending portion along the length direction of the first pole piece.

4. The battery cell according to claim 3, wherein: The thickness H1 of the active layer in the single-sided area is 25 μm-55 μm.

5. The battery cell according to claim 1, wherein: The first bending direction of the Z-shaped bending portion is bent away from the battery cell; And / or, the silicon-based material includes one or more of a bulk silicon-carbon composite material, a spherical silicon-carbon composite material, a nano silicon-carbon material, and a linear silicon-carbon material.

6. The battery cell according to any one of claims 1 to 4, wherein: Along the winding direction of the battery cell, the Z-shaped bend portion includes a first end and a second end, the first electrode includes a first surface close to the center of the battery cell and a second surface away from the center of the battery cell, the first surface of the empty foil area includes a first adhesive tape, the first adhesive tape includes a third end and a fourth end, the third end extends to the junction of the empty foil area and the single-sided area, and along the winding direction of the battery cell, the fourth end extends to exceed the second end of the Z-shaped bend portion or does not exceed the second end of the Z-shaped bend portion; And / or, the battery cell includes a tab, and along the thickness direction of the battery cell, the orthographic projection of the tab does not overlap with the orthographic projection of the Z-shaped bending portion.

7. The battery cell according to claim 6, wherein: The second surface of the single-sided area includes a second adhesive tape, the second adhesive tape includes a fifth end and a sixth end, the fifth end extends to the junction of the single-sided area and the double-sided area, and along the winding direction of the battery cell, the sixth end extends beyond the second end of the Z-shaped bend portion, and the width of the second adhesive tape is 15μm-35μm; And / or, the fourth end extends beyond the second end of the Z-shaped bending portion, and at the Z-shaped bending portion, the first adhesive tape is folded together with the current collector.

8. The battery cell according to any one of claims 1 to 4, wherein: Along the width direction of the first pole piece, both side edges of the current collector of the Z-shaped bend portion include a ceramic layer, and the ceramic layer is located on the surface of the current collector; Preferably, along the width direction of the first electrode sheet, both side edges of the current collector of the empty foil area include a ceramic layer, and the ceramic layer is located on the surface of the current collector; Preferably, the thickness of the ceramic layer is 6 μm-15 μm.

9. A battery, characterized in that: The battery comprises a housing and the battery cell according to any one of claims 1 to 8, wherein the battery cell is located in a receiving space formed by the housing.

10. The battery according to claim 9, wherein: Double-sided hot melt adhesive is provided between the shell and the battery core, the position where the double-sided hot melt adhesive is attached to the outer surface of the battery core is located on the secondary outer circle of the battery core, the position where the double-sided hot melt adhesive is attached to the outer surface of the battery core is located in the same plane as the Z-shaped bend portion and does not overlap with the Z-shaped bend portion, and the distance between the edge of the Z-shaped bend portion and the edge of the position where the double-sided hot melt adhesive is attached to the outer surface of the battery core is 2 mm to 5 mm; Preferably, the shell is made of aluminum-plastic film.

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