Battery cell and lithium ion battery

Abstract

The application relates to the technical field of batteries, and provides a battery cell and a lithium ion battery. The battery cell comprises a positive plate, a diaphragm and a silicon-containing negative plate which are laminated and wound. The positive plate comprises a double-coated area and a single-coated area; a first circular arc segment, a first straight segment, a second circular arc segment, a second straight segment, a third circular arc segment and a third straight segment are sequentially connected along a winding tail end to a winding head end of the positive plate; the battery cell comprises a first conductive adhesive paper, the first conductive adhesive paper is arranged on a positive current collector and covers the third circular arc segment, and the two ends of the first conductive adhesive paper extend to the second straight segment and the third straight segment along the winding tail end and the winding head end of the positive plate respectively; the mass ratio of conductive particles to the total mass of the adhesive layer of the first conductive adhesive paper is Psi1; the thickness of the single-coated area is h1; Psi1 and h1 satisfy 30 <= h1 / Psi1 <= 2000; the first conductive adhesive paper can maintain a conductive path when the positive plate at the bonding position is broken, and does not affect the capacity and performance of the battery.

Description

TECHNICAL FIELD

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

[0002] With the rapid development of the new energy industry, the demand for high energy density of lithium ion batteries is increasing, and the traditional graphite negative electrode has been difficult to meet the urgent demand of the market for higher energy density. Using other negative electrodes becomes a choice, and silicon-based negative electrodes become the only choice with the advantage of high theoretical capacity. Under this background, silicon-based negative electrodes have become an ideal choice for improving the energy density of batteries due to their excellent theoretical capacity advantage. However, the silicon negative electrode has brought severe challenges to the performance and safety of the battery due to its significant volume expansion characteristics. For the winding structure of the battery cell, the outermost circle arc area of the winding cell is prone to breakage due to the existence of bending stress and extrusion stress, especially for the winding cell with a silicon negative electrode. As a result, the capacity and cycle performance of the winding cell are deteriorated, and there is a great safety risk accordingly. Therefore, how to reduce the risk of electrode fracture without affecting the capacity and performance of the battery cell is an important problem to be solved at present. SUMMARY

[0003] The present application aims to overcome the above-mentioned problems existing in the prior art, and provides a battery cell and a lithium ion battery. The present application pastes a first conductive adhesive paper at the easy fracture position of the positive electrode sheet, and by controlling the ratio of the thickness of the single-sided coating area of the positive electrode sheet to the content of conductive particles in the adhesive layer of the first conductive adhesive paper, the positive electrode sheet with different thicknesses can be matched with the first conductive adhesive paper with corresponding conductive properties, so that the first conductive adhesive paper can still maintain the conductive path when the positive electrode sheet breaks, and at the same time, it can also avoid the situation that too many conductive particles make the positive electrode at the fracture position lithium speed too fast, which is unbalanced with the lithium intercalation speed of the negative electrode, and easily causes lithium dendrite to cause battery short circuit; it can also prevent too many conductive particles from being precipitated from the adhesive layer and reacting with lithium ions or electrolyte to produce gas, thereby ensuring the capacity of the battery and improving the cycle performance of the battery.

[0004] In order to achieve the above-mentioned purpose, the first aspect of the present application provides a battery cell, which comprises a positive electrode sheet, a separator and a negative electrode sheet stacked and wound; the negative electrode sheet comprises a negative electrode active material, and the negative electrode active material comprises a silicon-based material.

[0005] The positive electrode sheet comprises a positive electrode current collector, a first positive electrode active layer and a second positive electrode active layer, along a first direction Z, the positive electrode current collector has oppositely arranged first and second surfaces, the first positive electrode active layer is arranged on the first surface, and the second positive electrode active layer is arranged on the second surface, the positive electrode sheet comprises a double-sided coating area and a single-sided coating area along a winding direction, a tail end of the first positive electrode active layer exceeds a tail end of the second positive electrode active layer, and the part of the first positive electrode active layer exceeding the second positive electrode active layer is the single-sided coating area.

[0006] The electric core comprises a flat area and a circular arc area connected with the flat area; the positive electrode sheet comprises a first circular arc segment, a second circular arc segment and a third circular arc segment located in the circular arc area, and a first flat segment, a second flat segment and a third flat segment located in the flat area, the first circular arc segment and the second circular arc segment are located at the outermost side of the electric core, along a direction from a winding tail end to a winding head end of the positive electrode sheet, the first circular arc segment is sequentially connected with the first flat segment, the second circular arc segment, the second flat segment, the third circular arc segment and the third flat segment, and the first flat segment, the second circular arc segment, the second flat segment and the third circular arc segment are located in the single-sided coating area.

[0007] The electric core comprises a first conductive adhesive paper, the first conductive adhesive paper is arranged on the positive electrode current collector and covers the third circular arc segment, and two ends of the first conductive adhesive paper extend to the second flat segment and the third flat segment along the winding tail end and the winding head end of the positive electrode sheet respectively.

[0008] The first conductive adhesive paper comprises an adhesive layer, and the adhesive layer comprises conductive particles; the mass percentage of the conductive particles in the first conductive adhesive paper is Ψ1% based on the total mass of the adhesive layer of the first conductive adhesive paper; the thickness of the single-sided coating area is h1 μm; and Ψ1 and h1 satisfy: 30≤h1 / Ψ1≤2000.

[0009] The second aspect of the present application provides a lithium ion battery comprising the electric core of the first aspect of the present application.

[0010] The present application has the following beneficial effects by adopting the above technical solutions:

[0011] The application can ensure that the positive plate of different thickness matches the first conductive adhesive paper with corresponding conductive performance, so that the first conductive adhesive paper can still maintain the conductive path when the positive plate is broken, and also can avoid that too many conductive particles make the positive plate at the broken position too fast to be delithiated, and the speed of delithiation is unbalanced with the speed of lithium intercalation of the negative plate, which is easy to cause lithium dendrite to cause battery short circuit; and can also prevent too many conductive particles from being precipitated from the adhesive layer to have a lithium reaction with lithium ions or a side reaction with electrolyte to produce gas, thereby ensuring the capacity of the battery and improving the cycle performance of the battery.

[0012] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as exactly that endpoint. Any values that fall within the range, including the upper and lower limits, are contemplated as if they were specifically and individually recited herein. Ranges are understood to be shorthand for describing each and every value and sub-range falling within the range. Any reference to the term "about" includes an exact value, unless the context clearly indicates otherwise. In this application, the singular forms also include the plural unless the context clearly indicates otherwise. Throughout this application, the term "comprising" or grammatical variations thereof is used in the sense of "including" but also includes "consisting only of". BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 A schematic diagram of a positive plate in an example of the application is shown.

[0014] Figure 2 A schematic diagram of a positive plate in another example of the application is shown.

[0015] Figure 3 A schematic diagram of a battery cell in an example of the application is shown.

[0016] Figure 4 A schematic diagram of a battery cell in another example of the application is shown.

[0017] Figure 5 An X-ray diffraction pattern of the first conductive adhesive paper in an example of the application is shown.

[0018] Reference signs: 100 - positive current collector; 101 - first positive active layer; 102 - second positive active layer; 103 - positive plate; 104 - double-sided coating area; 105 - single-sided coating area; 106 - first conductive adhesive paper; 107 - second conductive adhesive paper; 108 - third adhesive paper; 109 - first circular arc segment; 110 - first straight segment; 111 - second circular arc segment; 112 - second straight segment; 113 - third circular arc segment; 114 - third straight segment; 115 - fourth straight segment; 116 - fourth adhesive paper. DETAILED DESCRIPTION

[0019] The specific embodiments of the present application are described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and explanatory and are not intended to limit the present application.

[0020] Unless otherwise defined, all scientific and technical terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0021] It should be noted that in the present application, the formula related to Ψ1 and Ψ2 is calculated by substituting the corresponding decimal value of Ψ1 and Ψ2 into the formula. For example, when calculating the formula h1 / Ψ1, when Ψ1 is equal to 5, substitute Ψ1 with 0.05 into the formula to calculate the value of h1 / Ψ1. Specific examples are as follows: when h1 is equal to 40 μm and Ψ1 is equal to 5, substitute Ψ1 with 0.05 into the formula to calculate h1 / Ψ1, h1 / Ψ1 = 40 / 0.05 = 800; for example, the mass percentage of silicon element η is 10 based on the total mass of the negative active material, and Ψ1 is 40, then Ψ1 / η = 0.4 / 0.1 = 4; for example, the thermal conductivity K1 of the first conductive adhesive paper is 7 W / (m·k), and Ψ1 is 20%, then K1 / Ψ1 = 7 / 0.2 = 35.

[0022] The first aspect of the present application provides an electric core, comprising a positive electrode sheet, a separator and a negative electrode sheet stacked and wound; the negative electrode sheet comprises a negative active material, and the negative active material comprises a silicon-based material; for easy understanding, the structure is referenced to the schematic diagram of the positive electrode sheet shown in Figure 1 It can be seen from Figure 1 that the positive electrode sheet 103 comprises a positive current collector 100, a first positive active layer 101 and a second positive active layer 102, along the first direction Z, the positive current collector 100 has oppositely arranged first and second surfaces, the first positive active layer 101 is arranged on the first surface, and the second positive active layer 102 is arranged on the second surface, the positive electrode sheet comprises a double-sided coating area 104 and a single-sided coating area 105 along the winding direction, the tail end of the first positive active layer 101 exceeds the tail end of the second positive active layer 102, and the part of the first positive active layer 101 exceeding the second positive active layer 102 is the single-sided coating area 105; the structure is referenced to the schematic diagram of the electric core shown in Figure 3 It can be seen from Figure 3As can be seen from the figure, the battery cell comprises a flat area and an arc area connected with the flat area; the positive plate comprises a first arc segment 109, a second arc segment 111 and a third arc segment 113 located in the arc area, and a first flat segment 110, a second flat segment 112 and a third flat segment 114 located in the flat area, the first arc segment 109 and the second arc segment 111 are located at the outermost side of the battery cell, along the direction from the winding tail end to the winding head end of the positive plate, the first arc segment 109 is sequentially connected with the first flat segment 110, the second arc segment 111, the second flat segment 112, the third arc segment 113 and the third flat segment 114, in addition, the other end of the first arc segment 109 is connected with one end of a fourth flat segment 115, and the other end of the fourth flat segment 115 is overlapped on the second flat segment 112. The first flat segment 110, the second arc segment 111, the second flat segment 112 and the third arc segment 113 are located in the single-side coating area; the battery cell comprises a first conductive adhesive paper, referring to Figure 1 and Figure 3 As can be seen from the figure, the first conductive adhesive paper 106 is arranged on the positive current collector 100 and covers the third arc segment 113, and the two ends of the first conductive adhesive paper 106 extend to the second flat segment 112 and the third flat segment 114 along the winding tail end and winding head end direction of the positive plate respectively; the first conductive adhesive paper comprises an adhesive layer, and the adhesive layer comprises conductive particles; the mass fraction of the conductive particles in the first conductive adhesive paper is Ψ1% based on the total mass of the adhesive layer of the first conductive adhesive paper; the thickness of the single-side coating area is h1μm; Ψ1 and h1 satisfy: 30≤h1 / Ψ1≤2000.

[0023] In the present application, the double-side coating area refers to the area where the positive active layer is arranged on both sides of the positive plate in the thickness direction, and the single-side coating area refers to the area where the positive active layer is arranged on only one side of the positive plate in the thickness direction, and the thickness of the single-side coating area is the sum of the thickness of the single-side active layer (i.e. the first positive active layer) and the thickness of the positive current collector.

[0024] Due to the structural characteristics of the winding type battery cell, the positive plate has a single-sided coating area and a double-sided coating area, and a single-double-sided junction transitioning from the double-sided coating area to the single-sided coating area. Due to the thickness difference of the positive plate on both sides of the single-double-sided junction, overpressure of the positive current collector near the single-double-sided junction occurs during rolling, which causes the positive current collector near the single-double-sided junction to be easily damaged. Further, due to the fact that the silicon-containing negative electrode in the battery cell has a large volume expansion during the charge and discharge cycle, the stress on both sides of the junction line between the single-sided coating area and the double-sided coating area is uneven (only one side of the positive plate in the single-sided area undergoes charge and discharge, while both sides of the positive plate in the double-sided area undergo charge and discharge), which further aggravates the extrusion of the positive current collector near the single-double-sided junction transitioning from the double-sided coating area to the single-sided coating area, and eventually causes the positive current collector to break.

[0025] Based on the above findings, the inventors of the present application have conducted a large number of targeted researches, and have found that the first conductive adhesive paper is attached to the position where the positive plate is most prone to breakage, and the adhesive layer of the first conductive adhesive paper contains conductive particles, which can form a conductive network in the first conductive adhesive paper, and the content of the conductive particles directly affects the conductivity of the first conductive adhesive paper, the more the content of the conductive particles, the stronger the conductivity of the first conductive adhesive paper. The positive plate is one of the main places for battery electrochemical reaction, and the thickness of the positive plate directly affects the reaction rate and the complexity of the reaction path, when positive plates of different thicknesses break, the conductivity of the conductive adhesive paper is also different, in order to ensure that the electron can still be effectively transmitted through the first conductive adhesive paper after the positive plate breaks, it is necessary to change the number of conductive particles in the first conductive adhesive paper, control the density and connectivity of the conductive network in the first conductive adhesive paper, so that the conductivity of the first conductive adhesive paper is similar to or slightly greater than the conductivity of the positive plate of different thicknesses, thereby avoiding the obstruction of the conductive path at the first conductive adhesive paper when the positive plate breaks, while ensuring that the lithium ion is normally deintercalated at the broken positive plate. Since the first conductive adhesive paper is mainly attached to the single-sided coating area of the positive plate, when the ratio of the thickness of the single-sided coating area to the content of the conductive particles in the adhesive layer of the first conductive adhesive paper satisfies the above range, the present application can ensure that the positive plate of different thicknesses matches the first conductive adhesive paper with corresponding conductivity, and the first conductive adhesive paper can still maintain the conductive path when the positive plate breaks, without affecting the capacity and performance of the battery. At the same time, one end of the first conductive adhesive paper extends to the third flat section along the winding head end direction of the positive plate, and the other end of the first conductive adhesive paper extends to the second flat section along the winding tail end direction, which can completely cover the single-sided coating area and the junction position between the single-sided coating area and the double-sided coating area, and at least part of the two ends of the first conductive adhesive paper is located in the flat section of the battery cell, so that even if the circular arc area has excessive expansion stress, the part of the first conductive adhesive paper located in the flat section can still interact with the first conductive adhesive paper, ensuring that the first conductive adhesive paper is not easily detached.

[0026] In the present application, the mass ratio of the conductive particles of the first conductive adhesive paper (Ψ1%) to the thickness of the single-side coating area (h1μm) satisfies: 30≤h1 / Ψ1≤2000, for example, h1 / Ψ1 can be 30, 40, 50, 100, 500, 1000, 1500, 2000 or any value within the range formed by any two of the above values, and preferably 30≤h1 / Ψ1≤800. When h1 / Ψ1 satisfies the above range, the problem of mismatch between the content of conductive particles in the adhesive layer of the first conductive adhesive paper and the thickness of the single-side coating area can be avoided. For example, when the thickness of the single-side coating area is constant, if h1 / Ψ1>2000, it indicates that the content of conductive particles in the adhesive layer of the first conductive adhesive paper is too low, and the first conductive adhesive paper cannot guarantee the electronic conduction at the breaking position, so that the lithium ions near the breaking position cannot be deintercalated at a normal speed through the first conductive adhesive paper, reducing the dynamic performance of the positive active material and the energy density of the battery. When the thickness of the single-side coating area is constant, if h1 / Ψ1<30, it indicates that the content of conductive particles in the adhesive layer of the first conductive adhesive paper is too high, which will make the deintercalation speed of the positive active material near the breaking position too fast, while the intercalation speed of the negative active material remains unchanged, so that the lithium ions near the breaking position are precipitated at the corresponding negative electrode, which will cause lithium dendrites to precipitate and pierce the separator, causing short circuit of the battery. On the other hand, too many conductive particles may also precipitate from the adhesive layer, and the precipitated conductive particles may react with the lithium ions deintercalated from the positive electrode, causing the part of the material to be unable to undergo normal charge and discharge reactions, resulting in waste of the positive electrode material and reduction of the capacity of the battery. In addition, during the cycle process, the precipitated conductive particles may also react with the electrolyte to produce gas, causing the electrochemical reaction to be unable to proceed normally, deteriorating the cycle performance of the battery, and in severe cases, causing the battery to fail.

[0027] For example, the content of conductive particles in the adhesive layer of the conductive adhesive paper can be tested by high-precision microscope technology and image processing technology, which can include the following steps: ① sample preparation: place the sample to be tested on the stage of the microscope, adjust the microscope to an appropriate magnification to ensure that the conductive particles can be clearly observed. ② image acquisition: use the image system of the microscope to capture the image of the conductive particles. ③ image processing: process and analyze the collected image. Identify and count the conductive particles through edge detection, threshold segmentation and other techniques. ④ content calculation: count and analyze the number of conductive particles in the image through image processing software, and calculate the content of conductive particles according to the area or volume of the sample. ⑤ data verification: in order to ensure the accuracy of the results, the same batch of samples can be tested multiple times, and the average value and standard deviation can be calculated.

[0028] The thickness of the first conductive adhesive paper and / or the second conductive adhesive paper can be tested by a thickness measuring device such as a scanning electron microscope.

[0029] In some embodiments, the electric core comprises a second conductive adhesive paper, for the convenience of understanding, the structure of the electric core is referred to as Figure 3 As shown in the schematic diagram of the electric core, the second conductive adhesive paper 107 is arranged on the positive current collector 100 and covers the second arc segment 111, and the two ends of the second conductive adhesive paper 107 extend to the first flat segment 110 and the second flat segment 112 along the winding tail end and the winding head end direction of the positive plate respectively; the second conductive adhesive paper 107 comprises an adhesive layer, and the adhesive layer comprises conductive particles; the mass fraction of the conductive particles in the second conductive adhesive paper is Ψ2% based on the total mass of the adhesive layer of the second conductive adhesive paper; Ψ2 and h1 satisfy: 30≤h1 / Ψ2≤2000, for example, the value of h1 / Ψ2 can be 30, 40, 50, 100, 500, 1000, 1500, 2000 or any point value in the range composed of any two of the above point values, preferably 30≤h1 / Ψ2≤800.

[0030] The inventors of the present application further found that in the winding type electric core adopting the outer wrapping structure of the positive plate, in the positive plate, in addition to the positive current collector in the step region of the transition from the double-sided coating region to the single-sided coating region, the positive current collector in the arc region of the outermost circle of the positive plate (i.e. the second arc segment and the third arc segment) and the connection between the arc region and the flat region (including the connection between the second arc segment and the first flat segment and the second flat segment, and the connection between the third arc segment and the second flat segment and the third flat segment) is also prone to fracture. Specifically, unlike the flat region, due to the structural characteristics, the expansion force received during the battery cycle process cannot be effectively released outward, and the expansion stress of the inner circle of the electric core is superimposed layer by layer on the arc (i.e. the second arc segment and the third arc segment) of the outermost circle of the electric core, resulting in a greater outward expansion pressure at the second arc segment and the third arc segment, and at the same time, since the second arc segment and the third arc segment correspond to the single-sided coating region of the positive plate, only one side undergoes the charging and discharging reaction, the stress on the inner and outer sides is uneven, making the arc region and the connection between the arc and the flat segment more prone to fracture of the positive plate. The two ends of the second conductive adhesive paper extend to the first flat segment and the second flat segment along the winding tail end and the winding head end direction of the positive plate respectively. The first conductive adhesive paper and the second conductive adhesive paper can cover the positive plate in the arc region of the outermost circle of the electric core and the connection between the arc region and the flat region, which can further reduce the risk of fracture of the positive plate of the electric core. At the same time, by further controlling the mass fraction of the conductive particles in the adhesive layer of the second conductive adhesive paper and the thickness of the single-sided coating region to satisfy the above range, even if the positive plate at the bonding position of the second conductive adhesive paper breaks, the second conductive adhesive paper can also form a conductive path, so that the broken positive plate can still play a capacity, thereby not affecting the capacity and performance of the battery.

[0031] In some embodiments, at least part of the first conductive adhesive paper and the second conductive adhesive paper are arranged on the surface of the positive current collector in the single-sided coating area without the positive active layer.

[0032] In some embodiments, the thickness (h1) of the single-sided coating area satisfies: 25 μm≤h1≤100 μm. Since the first conductive adhesive paper and the second conductive adhesive paper are mainly located in the single-sided coating area of the positive electrode sheet, in order to ensure that the first conductive adhesive paper and the second conductive adhesive paper can still form a good conductive path at the single-sided coating area when the positive current collector in the single-sided coating area is broken, the present application further controls the thickness of the single-sided coating area to satisfy the above range, which can avoid that the thickness of the single-sided coating area is too thick, the battery internal resistance is increased, and the cycle performance and cycle life of the battery are reduced. At the same time, the thickness of the single-sided coating area being too thick will lead to too long lithium ion diffusion path, which is easy to cause battery capacity attenuation; the thickness of the single-sided coating area being too thin will also cause insufficient battery capacity and reduced battery cycle performance; at the same time, the thickness of the single-sided coating area is ensured to be within a suitable range, so that the conductive capacity of the first conductive adhesive paper and the second conductive adhesive paper matches the normal lithium extraction rate of the positive electrode sheet.

[0033] In some embodiments, the mass percentage of the silicon element is η%, based on the total mass of the negative electrode active material, and Ψ1 and η satisfy: 0.2≤Ψ1 / η≤40. For example, the value of Ψ1 / η can be 0.2, 0.5, 0.8, 1, 5, 10, 12, 15, 20, 23, 28, 30, 32, 35, 40, or any point value in the range composed of any two of the above point values.

[0034] In some embodiments, Ψ2 and η satisfy: 0.2≤Ψ2 / η≤40. For example, the value of Ψ2 / η can be 0.2, 0.5, 0.8, 1, 5, 12, 15, 10, 20, 23, 28, 30, 32, 35, 40, or any point value in the range composed of any two of the above point values.

[0035] In some embodiments, the mass percentage of the silicon element is η%, based on the total mass of the negative electrode active material, and satisfies: 1≤η≤50. For example, the mass percentage of the silicon element can be 1%, 1.5%, 2%, 5%, 10%, 15%, 20%, 25%, 30%, 34%, 38%, 40%, 45%, 50%, or any point value in the range composed of any two of the above point values.

[0036] In the present application, the negative active material includes a silicon-based material. Although the negative electrode containing silicon can improve the energy density of the battery, the higher the content of silicon element in the negative active material, the greater the stress generated by the expansion of the negative electrode sheet, and the greater the risk of fracture and the degree of fracture damage of the outer arc region (second and third arc segments) of the positive electrode sheet. By controlling the ratio of the content of conductive particles in the first and / or second conductive adhesive paper to the mass percentage of silicon element to meet the above range, the content of silicon element in the negative active material can be avoided to be too high, the stress generated by the expansion of the negative electrode is too large, the degree of fracture of the positive electrode sheet is too heavy, which exceeds the range that the first and / or second conductive adhesive paper can bear, and the conductive performance of the first and / or second conductive adhesive paper is insufficient to maintain the original electron conduction of the positive electrode sheet, resulting in a decrease in the conduction and deintercalation rate of electrons and lithium ions, so that the battery cannot be fully charged within the specified time, the charging time of the battery is increased, the charging efficiency of the battery is reduced, in addition, the content of silicon element in the negative active material is too high, which may cause the fracture damage of the outer arc region (second and third arc segments) of the positive electrode sheet to be more serious, leading to uneven electrochemical reaction of the battery, and further leading to local overheating, affecting the safety of the battery.

[0037] Exemplarily, the test method of the mass percentage of silicon element can be tested by thermogravimetric analysis, for example, using Shimadzu DTG-60 thermal gravimetric analyzer for testing, test conditions: sample amount 5 mg, air as atmosphere, heating rate 10 ℃ / min from room temperature to 900 ℃ and constant temperature for 40 min. The relationship between the mass percentage of silicon element (x) and the final weight residue percentage (y) of the whole test is: x = 7y / 15.

[0038] In some embodiments, the silicon-based material includes at least one of elemental silicon, silicon carbon, silicon oxygen and silicon alloy.

[0039] In some embodiments, the mass percentage of conductive particles in the first conductive adhesive paper (Ψ1%) is 5≤Ψ1≤85, for example, the mass percentage of conductive particles in the first conductive adhesive paper can be 5%, 8%, 10%, 15%, 20%, 24%, 35%, 40%, 43%, 55%, 60%, 70%, 75%, 80%, 85% or any point value in the range consisting of any two of the above point values.

[0040] In some embodiments, the mass ratio of the conductive particles in the second conductive adhesive paper is (Ψ2%) and satisfies 5≤Ψ2≤85, for example, the mass ratio of the conductive particles in the second conductive adhesive paper can be 5%, 8%, 10%, 15%, 20%, 24%, 35%, 40%, 43%, 55%, 60%, 70%, 75%, 80%, 85%, or any value within the range defined by any two of the above values.

[0041] In the present application, the content of the conductive particles in the adhesive layer of the first conductive adhesive paper and / or the second conductive adhesive paper is kept within the above range, which can avoid the risk of precipitation of the conductive particles when the content of the conductive particles is too high. On the one hand, the precipitation of the conductive particles increases the risk of short circuit of the battery. On the other hand, the precipitated conductive particles may react with lithium ions released from the positive electrode sheet, resulting in a decrease in the capacity of the battery. In addition, the precipitated conductive particles may also react with the electrolyte to produce gas, resulting in a decrease in the cycle performance of the battery.

[0042] In some embodiments, the thermal conductivity of the first conductive adhesive paper is K1 W / (m·k), Ψ1 and K1 satisfy 15≤K1 / Ψ1≤40, and the value of K1 / Ψ1 may, for example, be 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 36, 37, 38, 39, 40, or any value within the range defined by any two of the above values.

[0043] In some embodiments, the thermal conductivity of the second conductive adhesive paper is K2 W / (m·k), Ψ2 and K2 satisfy 15≤K2 / Ψ2≤40, and the value of K2 / Ψ2 may, for example, be 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 36, 37, 38, 39, 40, or any value within the range defined by any two of the above values.

[0044] In some embodiments, the thermal conductivity of the first conductive adhesive paper (K1 W / (m·k)) satisfies 2≤K1≤32, and the thermal conductivity of the first conductive adhesive paper may, for example, be 2W / (m·k), 4W / (m·k), 6W / (m·k), 8W / (m·k), 10W / (m·k), 15W / (m·k), 20W / (m·k), 25W / (m·k), 30W / (m·k), 32W / (m·k), or any value within the range defined by any two of the above values.

[0045] In some embodiments, the second conductive adhesive paper has a thermal conductivity (K2 W / (m·k)) that satisfies: 2≤K2≤32. The thermal conductivity of the second conductive adhesive paper may, for example, be 2 W / (m·k), 4 W / (m·k), 6 W / (m·k), 8 W / (m·k), 10 W / (m·k), 15 W / (m·k), 20 W / (m·k), 25 W / (m·k), 30 W / (m·k), 32 W / (m·k), or any value in the range defined by any two of the aforementioned values.

[0046] In the present application, the first conductive adhesive paper and / or the second conductive adhesive paper has better thermal conductivity than ordinary insulating adhesive paper. The more conductive particles in the adhesive layer of the first conductive adhesive paper and / or the second conductive adhesive paper, the better the thermal conductivity of the first conductive adhesive paper and / or the second conductive adhesive paper. After the positive electrode sheet is broken, the internal resistance of the battery increases. At this time, more heat is generated at the broken position of the positive electrode sheet. After the battery is charged and discharged (especially at a large rate), the first conductive adhesive paper and / or the second conductive adhesive paper at the broken position of the positive electrode sheet will overheat. If the electrical conductivity and thermal conductivity of the first conductive adhesive paper and / or the second conductive adhesive paper are poor (the poorer the electrical conductivity of the first conductive adhesive paper and / or the second conductive adhesive paper, the greater the resistance of the first conductive adhesive paper and / or the second conductive adhesive paper, and the higher the overheat; the poorer the thermal conductivity of the first conductive adhesive paper and / or the second conductive adhesive paper, the easier it is to accumulate heat), the first conductive adhesive paper and / or the second conductive adhesive paper is prone to have a high temperature, which reduces the stability of the adhesive layer of the first conductive adhesive paper and / or the second conductive adhesive paper, and causes physical or chemical changes, such as decomposition or phase change of the adhesive layer due to high temperature, resulting in that the electrical conductivity of the first conductive adhesive paper and / or the second conductive adhesive paper cannot be normally played, and further leading to the decline of the capacity and performance of the battery.

[0047] For example, the test method for the thermal conductivity of the first conductive adhesive paper and / or the second conductive adhesive paper is as follows: ① sample preparation: prepare a conductive adhesive paper sample. ② test equipment: use a thermal conductivity test device that can accurately measure the heat transfer of the sample along the heat flow direction under a certain temperature gradient. ③ set the temperature gradient: during the test, a stable temperature gradient is obtained by setting temperature controllers on both sides of the sample. ④ test: under the temperature gradient, record the heat flow and temperature difference through the sample, and calculate the thermal conductivity. ⑤ data recording and analysis: record the thermal conductivity data obtained during the test. ⑥ repeated test: in order to ensure the accuracy of the results, the same batch of samples can be tested repeatedly.

[0048] In some embodiments, the electrical resistance of the first conductive adhesive paper is denoted as R1 Ω, the electrical resistance of the single-sided coated area is denoted as R ^ Ω, and the electrical resistance (R1) of the first conductive adhesive paper and the electrical resistance (R ^ ) of the single-sided coated area satisfy: R1≤R ^ .

[0049] In some embodiments, the resistance of the second conductive adhesive paper is denoted as R2Ω, the resistance (R2) of the second conductive adhesive paper and the resistance (R ^ ) satisfy: R2≤R ^ .

[0050] The resistance R1 of the first conductive adhesive paper, the resistance R2 of the second conductive adhesive paper and the resistance R^ of the single-sided coating area can be obtained by methods conventional in the art, for example, using a two-probe resistance meter.

[0051] In the present application, the first conductive adhesive paper and / or the second conductive adhesive paper can form a conductive path in the case of fracture of the positive electrode sheet at the bonding site. By further limiting the resistance of the first conductive adhesive paper and / or the second conductive adhesive paper to be ≤ the resistance of the single-sided coating area in the positive electrode sheet, it can be ensured that the electronic conduction and lithium ion deintercalation rate at the fracture site of the positive electrode sheet are not affected. If the resistance of the first conductive adhesive paper and / or the second conductive adhesive paper at the fracture site of the positive electrode sheet is greater than the resistance of the positive electrode sheet, the conductive performance of the first conductive adhesive paper and / or the second conductive adhesive paper is poorer than that of the positive electrode sheet. When the positive electrode sheet fractures, the first conductive adhesive paper and / or the second conductive adhesive paper cannot exhibit the same or better conductive performance as the positive electrode sheet, thereby affecting the electronic conduction of the overall battery cell, reducing the capacity of the battery, and degrading the cycle performance of the battery.

[0052] In some embodiments, the resistance (R1) of the first conductive adhesive paper and the thickness (h1) of the single-sided coating area satisfy: 1

[0053] In some embodiments, the resistance (R2) of the second conductive adhesive paper and the thickness (h1) of the single-sided coating area satisfy: 1

[0054] If the components and manufacturing process of the electrode are the same, under the same compaction conditions, assuming that the resistivity p of the coating is the same and the area (S) of the electrode test sample is also the same, then the relationship between the thickness (H) of the electrode and the resistance R AM of the electrode is: R AM= p x H / S. As can be seen from the above formula, the greater the thickness of the electrode, the greater the resistance of the electrode. Therefore, the thicker the positive plate, the greater the resistance, and the poorer the conductive effect. The conductive performance of the first conductive adhesive paper and / or the second conductive adhesive paper can be relatively reduced to a level comparable to that of the positive plate, and the content of conductive particles in the corresponding first conductive adhesive paper and / or second conductive adhesive paper can be correspondingly reduced. The less the content of conductive particles in the first conductive adhesive paper and / or the second conductive adhesive paper, the more difficult it is for the adhesive layer of the first conductive adhesive paper and / or the second conductive adhesive paper to precipitate conductive particles. Therefore, by limiting the ratio of the resistance of the first conductive adhesive paper and / or the resistance of the second conductive adhesive paper to the thickness of the single-side coated area in the positive plate to satisfy the above range, the application can reduce the risk of short circuit of the battery and avoid the problems of battery capacity reduction and battery cycle performance reduction caused by precipitation of conductive particles.

[0055] In some embodiments, the positive plate further comprises a positive current collector empty foil area, which is connected to the single-side coated area along the winding direction, and at least part of the positive current collector empty foil area is located in the first circular arc segment. The battery cell further comprises a third adhesive paper, one end of which is bonded to the first positive active layer of the single-side coated area, and the other end of which is bonded to the positive current collector empty foil area. The bonding force of the first conductive adhesive paper is greater than or equal to the bonding force of the third adhesive paper, and / or the bonding force of the second conductive adhesive paper is greater than or equal to the bonding force of the third adhesive paper.

[0056] In the application, the third adhesive paper is a tailing insulating adhesive paper of the positive plate or a tailing adhesive paper of the battery cell (the third adhesive paper is not conductive), and the tailing insulating adhesive paper of the positive plate is used as an example for description. Figure 3 When the third adhesive paper is the tailing insulating adhesive paper of the positive plate, the third adhesive paper 108 exceeds the tail end of the negative plate at the tail end of the positive empty foil area, which can effectively block the burrs at the tail end of the negative plate, prevent abnormal self-discharge, heating and explosion inside the battery, and ensure the safety and stability of the battery. On the other hand, when the tail end of the positive plate exceeds the tail end of the corresponding negative plate, the third adhesive paper pasted at the tail end of the positive plate can reduce the risk of short circuit caused by misalignment of the tail ends of the positive and negative plates, and plays a good insulating and isolating role. When the third adhesive paper is the tailing adhesive paper of the battery cell, the third adhesive paper is located at the tailing position of the battery cell, which can bind the structure of the battery cell and ensure that the overall structure of the battery cell will not be loose.

[0057] In the present application, the adhesion of the first conductive adhesive paper, the adhesion of the second conductive adhesive paper and the adhesion of the third adhesive paper are all represented as the adhesion between the corresponding adhesive paper and the positive electrode current collector, the adhesion of the first conductive adhesive paper is limited to be greater than or equal to the adhesion of the third adhesive paper, and / or the adhesion of the second conductive adhesive paper is limited to be greater than or equal to the adhesion of the third adhesive paper, so as to ensure that the first conductive adhesive paper and / or the second conductive adhesive paper has high adhesion performance. On the one hand, the first conductive adhesive paper and / or the second conductive adhesive paper can be ensured not to be separated from the positive electrode sheet in the electrolyte environment; on the other hand, the high adhesion performance of the first conductive adhesive paper and / or the second conductive adhesive paper can also inhibit the fracture of the positive electrode sheet at the bonding position of the first conductive adhesive paper and / or the second conductive adhesive paper to a certain extent.

[0058] The adhesion of the first conductive adhesive paper, the adhesion of the second conductive adhesive paper and the adhesion of the third adhesive paper can be measured by a peel strength test method: under the condition of (25±1)℃ and relative humidity of (50±5)%, the adhesive paper sample is pasted on a metal plate (which is made of the same material as the positive electrode current collector, for example, aluminum), the metal plate is fixed on one clamp of a tensile testing machine, the other clamp of the testing machine clamps the free end of the adhesive paper sample at an angle of 180° with the metal plate, and the peel strength of the adhesive paper sample is calculated by measuring the tensile force and the peel speed of the adhesive paper sample at a uniform speed of (5.0±0.2)mm / s.

[0059] In some embodiments, the insulating adhesive paper comprises rubber adhesive paper, acrylic adhesive paper, polypropylene adhesive paper or SIS (Styrene-Isoprene-Styrene) adhesive paper, etc.

[0060] In some embodiments, the first conductive adhesive paper at one end of the second flat section and the second conductive adhesive paper at one end of the second flat section can be connected or not connected.

[0061] Figure 3 The schematic diagram of the battery cell in one example of the present application is shown in FIG. 1, from which it can be seen that the first conductive adhesive paper 106 at one end of the second flat section 112 is not connected with the second conductive adhesive paper 107 at one end of the second flat section 112. Figure 3 The schematic diagram of the battery cell in one example of the present application is shown in FIG. 1, from which it can be seen that the first conductive adhesive paper 106 at one end of the second flat section 112 is not connected with the second conductive adhesive paper 107 at one end of the second flat section 112.

[0062] Figure 4 The schematic diagram of the battery cell in one example of the present application is shown in FIG. 1, from which it can be seen that the first conductive adhesive paper 106 at one end of the second flat section 112 is not connected with the second conductive adhesive paper 107 at one end of the second flat section 112. Figure 4 The schematic diagram of the battery cell in one example of the present application is shown in FIG. 1, from which it can be seen that the first conductive adhesive paper 106 at one end of the second flat section 112 is not connected with the second conductive adhesive paper 107 at one end of the second flat section 112.

[0063] In some embodiments, the total length of the first conductive adhesive paper and the second conductive adhesive paper along the winding direction is denoted as W1 mm, the total length of the second circular arc segment and the third circular arc segment is denoted as W2 mm, and the total length of the first flat segment and the second flat segment is denoted as W3 mm; W1, W2, and W3 satisfy: W2 + 4 mm ≤ W1 ≤ W2 + W3; when the total length of the first conductive adhesive paper and the second conductive adhesive paper is at the lower limit of the above range, the adhesive positions of the first conductive adhesive paper and the second conductive adhesive paper cover the second circular arc region and the third circular arc region on the left and right sides of the core, and the length of the second flat segment and the third flat segment covered by the first conductive adhesive paper is not less than 4 mm in combination with the length of the first flat segment and the second flat segment covered by the second conductive adhesive paper, as shown in FIG. 15; when the total length of the first conductive adhesive paper and the second conductive adhesive paper is at the upper limit of the above range, the effect is equivalent to that the single-sided coating region in the positive plate is entirely covered by the first conductive adhesive paper and the second conductive adhesive paper, as shown in FIG. 16. By further limiting the total length of the first conductive adhesive paper and the second conductive adhesive paper within the above range, the present application can ensure that the first conductive adhesive paper and the second conductive adhesive paper completely protect the position of the positive plate in the core that is prone to breakage, while ensuring that the first conductive adhesive paper and the second conductive adhesive paper exceed the outermost circular arc region and are partially located in the flat region connected to the outermost circular arc region, thereby ensuring the bonding reliability of the first conductive adhesive paper and the second conductive adhesive paper, so that the first conductive adhesive paper and the second conductive adhesive paper better play the role of electronic conduction after the positive plate breaks, and maintain a smooth conductive path, thereby not affecting the capacity and performance of the battery. Figure 3 Figure 4

[0064] In some embodiments, the projection of the first conductive adhesive paper on the positive plate along the winding direction can also be discontinuous, but should at least cover the stepped region where the double-sided coating region of the positive plate transitions to the single-sided coating region, as shown in FIG. 17. Figure 2

[0065] In some embodiments, when the second conductive adhesive paper exists in the core, the projection of the second conductive adhesive paper on the positive plate along the winding direction can be continuous or discontinuous; when the projection of the second conductive adhesive paper on the positive plate is discontinuous, the second conductive adhesive paper at least covers the junction region of the first flat segment and the second circular arc segment, part of the second circular arc segment, and the junction region of the second circular arc segment and the second flat segment.

[0066] ​​​In some embodiments, along the width direction of the positive electrode sheet, the width of the first conductive adhesive paper is denoted as L1 mm, the width of the second conductive adhesive paper is denoted as L2 mm, and the width of the positive electrode sheet is denoted as L mm, L1 and L satisfy: L1≤L, and / or, L2 and L satisfy: L2≤L. Controlling the width of the first conductive adhesive paper and / or the second conductive adhesive paper to be less than or equal to the width of the positive electrode sheet can prevent the first conductive adhesive paper and / or the second conductive adhesive paper from contacting the edge of the negative electrode sheet, thereby preventing short circuit of the battery.

[0067] In some embodiments, the thickness of the first conductive adhesive paper is 0.012 mm-0.2 mm, for example, can be 0.012 mm, 0.015 mm, 0.02 mm, 0.04 mm, 0.06 mm, 0.08 mm, 0.1 mm, 0.15 mm, 0.2 mm, or any point value in the range consisting of any two of the above point values.

[0068] In some embodiments, the thickness of the second conductive adhesive paper is 0.012 mm-0.2 mm, for example, can be 0.012 mm, 0.015 mm, 0.02 mm, 0.04 mm, 0.06 mm, 0.08 mm, 0.1 mm, 0.15 mm, 0.2 mm, or any point value in the range consisting of any two of the above point values.

[0069] Controlling the thickness of the first conductive adhesive paper and / or the second conductive adhesive paper within the above range can ensure that the first conductive adhesive paper and / or the second conductive adhesive paper has sufficient conductivity, and at the same time, the first conductive adhesive paper and / or the second conductive adhesive paper has a certain strength, good flexibility and operability, facilitating the adhesion with the positive electrode sheet. In addition, due to the certain strength of the first conductive adhesive paper and / or the second conductive adhesive paper, it can also be ensured that the first conductive adhesive paper and / or the second conductive adhesive paper will not be easily damaged due to bending or battery expansion during use.

[0070] In some embodiments, the junction of the double-sided coating area and the single-sided coating area is denoted as the positive electrode sheet single-double junction, the projection of the first conductive adhesive paper on the positive electrode sheet is located at the positive electrode sheet single-double junction and the part of the double-sided coating area is a porous area, and the porous area comprises a porous structure; the porous structure satisfies at least one of the following conditions:

[0071] (a) the pore size of the porous structure is denoted as a mm, a satisfies: 0.05≤a≤3;

[0072] (b) the inter-pore distance of the porous structure is denoted as b mm, b satisfies: 0.1≤b≤4;

[0073] (c) the porosity of the porous area is denoted as c%, c satisfies: 25≤c≤80.

[0074] The pore size of the porous structure may be, for example, 0.05 mm, 0.1 mm, 0.5 mm, 1 mm, 2 mm, 3 mm, or any value within a range defined by any two of the above values.

[0075] The inter-pore distance of the porous structure may be, for example, 0.1 mm, 0.3 mm, 0.5 mm, 0.8 mm, 1 mm, 2 mm, 3 mm, 4 mm, or any value within a range defined by any two of the above values.

[0076] The porosity of the porous region may be, for example, 25%, 30%, 40%, 50%, 60%, 70%, 80%, or any value within a range defined by any two of the above values.

[0077] In the present application, the first conductive adhesive paper may also be provided with a through hole at a position where the first conductive adhesive paper is attached to the double-sided coating region, so that the first conductive adhesive paper has a porous structure. The smaller the pore size and inter-pore distance of the porous structure, the higher the porosity of the porous region, and the stronger the ion penetration ability. The porous structure can promote the transmission of lithium ions in the double-sided coating region, improve the utilization rate of the positive active material, and improve the energy density of the battery.

[0078] In some embodiments, the conductive particles of the first conductive adhesive paper and the conductive particles of the second conductive adhesive paper each independently comprise at least one of a conductive metal material, a conductive non-metal material, and a conductive compound.

[0079] In some embodiments, the conductive metal material comprises at least one of aluminum, copper, nickel, gold, silver, zinc, and iron.

[0080] In some embodiments, the conductive non-metal material comprises a carbon material; the carbon material may be, for example, selected from at least one of conductive carbon black, conductive graphite, carbon nanotubes, and graphene.

[0081] Graphite material typically exists at around 2θ = 26.5° (002) peak. As shown in FIG. 1, the X-ray diffraction (XRD) spectrum of the first conductive adhesive paper in an example of the present application shows a sharp peak near 26.5°, which can prove the presence of graphite material (conductive carbon black) in the first conductive adhesive paper, which can be distinguished from the polymer carbon chain present in other components of the first conductive adhesive paper. Figure 5

[0082] ​In some embodiments, the conductive particles in the first conductive adhesive paper have a particle size of 2-30 μm, for example, 2 μm, 6 μm, 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or any value within the range defined by any two of the above values; and / or the conductive particles in the second conductive adhesive paper have a particle size of 2-30 μm, for example, 2 μm, 6 μm, 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, or any value within the range defined by any two of the above values. Controlling the particle size of the conductive particles in the first conductive adhesive paper and / or the second conductive adhesive paper to be within the above range can avoid the following problems. If the particle size of the conductive particles is too large, the contact area between the particles will decrease, resulting in poor conduction, increased resistance, and reduced conductivity of the first conductive adhesive paper and / or the second conductive adhesive paper. If the particle size of the conductive particles is too small, although a smaller particle size can help form a more compact conductive network, a too small particle size can result in a too small contact area between the conductive particles, unstable conduction, and deterioration of the conductivity of the first conductive adhesive paper and / or the second conductive adhesive paper. In addition, a too small particle size can also increase the difficulty and cost of production.

[0083] In the present application, the method for testing the particle size of the conductive particles includes the following steps: using a laser particle size analyzer to test, mixing the conductive adhesive paper sample with a dispersion medium, setting parameters such as stirring speed, refractive index of the dispersion medium, and refractive index of the particles, starting the test program, generating measurement data, and then obtaining the particle size of the conductive particles.

[0084] In some embodiments, the first conductive adhesive paper and the second conductive adhesive paper each independently further include a substrate layer, and the adhesive layer is arranged on at least one surface of the substrate layer.

[0085] In some embodiments, the adhesive layer of the first conductive adhesive paper and the adhesive layer of the second conductive adhesive paper each independently further include an adhesive and an auxiliary agent.

[0086] In some embodiments, the adhesive includes at least one of an epoxy resin, an acrylate resin, a polyvinyl chloride, a silicone resin, a polyimide resin, a phenolic resin, a polyurethane, and a pyridine.

[0087] In some embodiments, the auxiliary agent includes at least one of a crosslinking agent (such as acrylamide), a coupling agent (such as silane, phosphate, borate, etc.), a preservative (such as a mildew-resistant agent, an antibacterial agent), a toughening agent (such as nitrile rubber, epoxy resin, chlorinated polyethylene, polyvinyl butyral, etc.), and a thixotropic agent (such as polyamide wax, organic bentonite, fumed silica, hydrogenated castor oil, etc.).

[0088] In some embodiments, the single-double surface junction is located at the third straight section, and the distance between the intersection point of the third circular arc section and the third straight section and the projection point of the single-double surface junction on the third straight section is 0 mm-10 mm, for example, it can be 0 mm, 1 mm, 2 mm, 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm or any point value in the range formed by any two of the above point values. If the distance < 0 mm, it means that the step region of the transition from the double-sided coating area of the positive plate to the single-sided coating area is located on the third circular arc section outside the positive plate of the battery cell, and the existence of the step region will occupy additional space, so that the width of the battery cell in the cross section increases, the increase of the width of the battery cell will change the shape and size of the circular arc interface, which may be not conducive to the current distribution and heat management inside the battery, resulting in the decrease of the energy density of the battery. At the same time, since the step region is located at the outer third circular arc section, the positive current collector of the step region is more prone to breakage, which is also not conducive to the improvement of the positive plate breakage problem; if the distance > 10 mm, the far single-double surface junction position means that the end part of the battery cell is far away, which may cause the battery cell to fail to maintain uniform flatness during winding; the far end part of the battery cell may cause uneven distribution of positive and negative materials in the battery, thereby reducing the utilization rate of these materials. The decrease of the flatness of the battery cell and the decrease of the utilization rate of the positive and negative electrodes will further reduce the energy density of the battery.

[0089] The second aspect of the present application provides a lithium ion battery comprising the battery cell of the first aspect of the present application.

[0090] In some embodiments, the first positive active layer and the second positive active layer each independently comprises the following mass percentage of components: 90wt%-99.4wt% of positive active material, 0.3wt%-5wt% of conductive agent, 0.3wt%-5wt% of binder.

[0091] In some embodiments, the negative plate comprises a negative current collector and a negative active material layer arranged on at least one side surface of the negative current collector, and the negative active material layer comprises the following mass percentage of components: 90wt%-99.4wt% of negative active material, 0.2wt%-5wt% of conductive agent, 0.4wt%-5wt% of binder.

[0092] In some embodiments, the conductive agent includes but is not limited to one or more of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, and metal powder.

[0093] In some embodiments, the binder includes, but is not limited to, one or more of styrene butadiene rubber emulsion, polytetrafluoroethylene emulsion, sodium carboxymethyl cellulose, sodium alginate, polyvinyl alcohol, polyacrylic acid, lithium polyacrylate, sodium polyacrylate, and carboxylated chitosan.

[0094] In some embodiments, the lithium ion battery includes a non-aqueous electrolyte.

[0095] In some embodiments, the lithium ion battery includes a separator. In the present application, the type of the separator is not specifically limited, and for example, a conventional lithium ion battery separator can be used, including but not limited to a woven film, a non-woven film (non-woven fabric), a microporous film, a composite film, a separator paper, a calendered film, a polyethylene microporous film, a polypropylene microporous film, and the like.

[0096] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application.

[0097] The materials, reagents, and the like used in the following examples are commercially available unless otherwise specified.

[0098] The present application will be described in detail below in conjunction with specific examples, which are used for understanding rather than limiting the present application.

[0099] Example 1

[0100] The battery is prepared according to the following method:

[0101] (1) Preparation of a positive electrode sheet

[0102] Lithium cobaltate, an electrically conductive agent acetylene black, and a binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97.6:1.4:1.2, and then N-methyl pyrrolidone (NMP) is added and stirred under the action of a vacuum stirrer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is uniformly coated on the surface of an aluminum foil, dried, rolled, and cut to obtain a positive electrode sheet including a positive electrode active layer, the positive electrode sheet including a double-coated area and a single-coated area, the thickness h1 of the single-coated area being 50 μm, and the width L of the positive electrode sheet being 66.5 mm. A first conductive adhesive paper and a second conductive adhesive paper are attached, and the total length (W1) of the first conductive adhesive paper and the second conductive adhesive paper is (the total length W2 of the second circular arc segment and the third circular arc segment + 4) mm.

[0103] In the first conductive adhesive paper, the proportion of conductive particles in the adhesive layer is 45%, the conductive particles are conductive carbon black, the particle size of the conductive particles is 15 μm, the binder is epoxy resin, the additive is peroxysilane coupling agent, the bonding force is 0.03 kgf / mm, the thickness is 0.1 mm, and the width L1 is 66 mm. The first conductive adhesive paper has a porous area, the pore size a of the porous structure is 0.05 mm, the pore spacing b of the porous structure is 0.1 mm, and the porosity c of the porous area is 80%. The second conductive adhesive paper has the same parameters as the first conductive adhesive paper.

[0104] (2) Preparation of negative electrode sheet

[0105] The negative electrode active material (95% graphite and 5% SiC), a styrene-butadiene rubber (SBR) binder, a carbon nanotube conductive agent, and carboxymethyl cellulose (CMC) are mixed in a mass ratio of 97.2:2.4:0.05:0.35 to prepare an active layer slurry. The slurry is coated on both surfaces of a copper foil, and then dried, rolled, and cut to obtain a negative electrode sheet including a negative electrode active layer. The mass proportion of the silicon element is η, which is 20%.

[0106] (3) Preparation of electrolyte

[0107] The electrolyte includes ethylene carbonate (EC), propylene carbonate (PC), polypropylene (PP), lithium hexafluorophosphate (LiPF6), fluoroethylene carbonate (FEC), and polystyrene (PS). The mass ratio of EC, PC, PP, LiPF6, FEC, and PS is 12:12:47:15:10:4.

[0108] (4) Preparation of battery

[0109] The positive electrode sheet prepared in step (1), the separator, and the negative electrode sheet prepared in step (2) are wound to form a roll core, and a third adhesive paper (insulating adhesive paper) is attached. After injecting the electrolyte of step (2), the battery is formed, sorted, and tested for OCV to obtain the battery.

[0110] The attachment positions of the first conductive adhesive paper and the second conductive adhesive paper and the third adhesive paper are shown in, for example, Figure 3 The bonding force of the third adhesive paper is 0.02 kgf / mm.

[0111] Example 2

[0112] Example 2 refers to the preparation of the battery according to Example 1, except that:

[0113] In the first conductive adhesive paper, the proportion of conductive particles in the adhesive layer is 85%, the conductive particles are graphene, the particle size of the conductive particles is 30 μm, the binder is organic silicone resin, and the bonding force is 0.025 kgf / mm. The second conductive adhesive paper has the same parameters as the first conductive adhesive paper.

[0114] The total length (W1) of the first conductive adhesive paper and the second conductive adhesive paper is (the total length W2 of the second circular arc segment and the third circular arc segment + the total length W3 of the first straight segment and the second straight segment) mm, and the attachment position of the first conductive adhesive paper and the second conductive adhesive paper is, for example Figure 4 as shown.

[0115] The thickness h1 of the single-sided coating area in the positive electrode sheet is 25.5 μm.

[0116] The mass percentage η of the silicon element in the negative electrode sheet is 50%.

[0117] Example 3

[0118] Example 3 refers to the preparation of the battery in Example 1, except that:

[0119] In the first conductive adhesive paper, the proportion of conductive particles in the adhesive layer is 5%, and the conductive particles are aluminum; the particle size of the conductive particles is 2 μm; the binder is polyurethane; the bonding force is 0.04 kgf / mm; and the parameters of the second conductive adhesive paper are the same as those of the first conductive adhesive paper.

[0120] The thickness h1 of the single-sided coating area in the positive electrode sheet is 25 μm.

[0121] The mass percentage η of the silicon element in the negative electrode sheet is 1%.

[0122] Example 4

[0123] Example 4 refers to the preparation of the battery in Example 1, except that, in Example 4, only the first conductive adhesive paper is pasted.

[0124] Example 5 group

[0125] Example 5 group refers to the preparation of the battery in Example 1, except that:

[0126] Example 5a: In the first conductive adhesive paper, the proportion of conductive particles in the adhesive layer is 90%, which is beyond the protection scope in the present application; and the parameters of the second conductive adhesive paper are the same as those of the first conductive adhesive paper.

[0127] Example 5b: In the first conductive adhesive paper, the proportion of conductive particles in the adhesive layer is 4.2%, which is beyond the protection scope in the present application; and the parameters of the second conductive adhesive paper are the same as those of the first conductive adhesive paper.

[0128] Example 6

[0129] Example 6 refers to the preparation of the battery in Example 1, except that, in the negative electrode sheet, the mass percentage η of the silicon element is 60%, which is beyond the protection scope in the present application.

[0130] Example 7

[0131] Example 7 The battery was prepared according to Example 1, except that the parameters of the porous area of the first conductive adhesive paper were different, specifically, the pore size a of the porous structure was 3.5 mm, the pore spacing b of the porous structure was 5 mm, and the porosity c of the porous area was 20%, which was beyond the protection scope of the present application.

[0132] Example 8

[0133] Example 8 The battery was prepared according to Example 1, except that the adhesion of the first conductive adhesive paper was 0.01 kgf / mm, which was lower than the adhesion of the third adhesive paper (the adhesion of the third adhesive paper in Example 1 was 0.02 kgf / mm); the parameters of the second conductive adhesive paper were the same as those of the first conductive adhesive paper.

[0134] Example 9 group

[0135] The purpose of the setting of the Example 9 group was to verify the influence of the value of Ψ1 / η and Ψ2 / η on the performance of the battery.

[0136] Example 9a: Example 9a was prepared according to Example 2, except that the mass percentage of silicon element η was 2.2%.

[0137] Example 9b: Example 9b was prepared according to Example 2, except that the mass percentage of silicon element η was 1.5%.

[0138] Example 9c: Example 9b was prepared according to Example 3, except that the mass percentage of silicon element η was 40%.

[0139] Example 10

[0140] Example 7 The battery was prepared according to Example 3, except that in the positive electrode sheet, the thickness h1 of the single-sided coating area was 20 μm.

[0141] Comparative Example 1

[0142] Comparative Example 1 The battery was prepared according to Example 1, except that the first conductive adhesive paper and the second conductive adhesive paper were not attached in Comparative Example 1.

[0143] Comparative Example 2

[0144] Comparative Example 2 The battery was prepared according to Example 1, except that in Comparative Example 2, ordinary insulating adhesive paper (acrylic adhesive paper) was attached at the positions of the first conductive adhesive paper and the second conductive adhesive paper in the original Example 1.

[0145] Comparative Example 3 group

[0146] Comparative Example 3a: The preparation of the battery was carried out according to Reference Example 5a, except that the thickness of the single-coated area in the positive electrode sheet was 25.5 μm.

[0147] Comparative Example 3b: The preparation of the battery was carried out according to Reference Example 5b, except that the thickness of the single-coated area in the positive electrode sheet was 100 μm.

[0148] The relevant parameters involved in the formula calculation in each of the examples and comparative examples are recorded in Table 1.

[0149] Table 1

[0150]

[0151] Note: "*" indicates that the corresponding parameter in the example or comparative example is the same as that in Example 1-1. " / " indicates that the corresponding parameter is not tested. In each of the examples and comparative examples involving the second conductive adhesive paper, the parameters of the second conductive adhesive paper are the same as those of the first conductive adhesive paper.

[0152] Parameter Test

[0153] i) At 25°C, the battery was subjected to charge-discharge cycle test at 4.2C charge rate, 0.7C discharge rate, and 3.0V-4.53V voltage window (using Blue Electric test equipment), for 1000 cycles, using the discharge capacity of the 1st cycle C1and the discharge capacity of the 1000th cycle C1000. 1000 The capacity retention rate was calculated: C1000 / C1x 100%. 1000

[0154] ii) During the cycle, it was monitored whether the battery was short-circuited (100 batteries were tested), and the short-circuit rate was calculated.

[0155] iii) After the cycle in i), the battery was disassembled, and it was observed whether the current collector (from the single-coated area and the double-coated area junction to the winding tail end) was broken.

[0156] Table 2

[0157]

[0158] Note: The batteries prepared in each of the examples and comparative examples were all broken at the second and third circular arc sections during the cycle test.

[0159] ​As can be seen from Table 2, compared with the comparative examples, the battery of the present application pastes the conductive adhesive paper at the easy-to-break position of the positive plate, ensures that the positive plates of different thicknesses match the first conductive adhesive paper with corresponding conductive properties, and enables the first conductive adhesive paper to maintain the conductive path when the positive plate breaks, thereby improving the capacity retention rate of the battery. Moreover, the battery of the comparative example breaks the current collector during the cycle process, and the burr generated by the breaking of the current collector can pierce the separator, thereby causing the battery to short circuit. After the battery of the present application is pasted with the conductive adhesive paper, the short circuit rate is significantly lower than that of the battery of the comparative example.

[0160] It should be noted that in this document, the terms "comprise", "comprising", or any other variant thereof are intended to cover non-exclusive inclusions, such that processes, methods, articles, or apparatuses that comprise a list of elements are not limited to those elements, but can also include other elements not expressly listed, or inherent to such processes, methods, articles, or apparatuses. Without more limitations, the element defined by the phrase "comprising a" does not exclude the presence of additional identical elements in the process, method, article, or apparatus that includes the element. In addition, it should be noted that the scope of the methods and apparatuses in the embodiments of the present application is not limited to performing functions in the order shown or discussed, but can also include performing functions in a substantially simultaneous manner or in reverse order, for example, the described methods can be performed in an order different from that described, and various steps can be added, omitted, or combined. In addition, features described with reference to certain examples can be combined in other examples.

[0161] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Any modification, equivalent replacement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. An electric cell, characterized by, The positive electrode sheet, the separator, and the negative electrode sheet are arranged in a stacked winding manner; the negative electrode sheet comprises a negative electrode active material, and the negative electrode active material comprises a silicon-based material; The positive electrode sheet comprises a positive electrode current collector, a first positive electrode active layer, and a second positive electrode active layer; along a first direction Z, the positive electrode current collector has oppositely arranged first and second surfaces, the first positive electrode active layer is arranged on the first surface, and the second positive electrode active layer is arranged on the second surface; along a winding direction, the positive electrode sheet comprises a double-sided coating region and a single-sided coating region; a tail end of the first positive electrode active layer is beyond a tail end of the second positive electrode active layer, and a portion of the first positive electrode active layer beyond the second positive electrode active layer is the single-sided coating region; The battery cell comprises a flat region and a circular arc region connected to the flat region; the positive electrode sheet comprises a first circular arc segment, a second circular arc segment, and a third circular arc segment located in the circular arc region, and a first flat segment, a second flat segment, and a third flat segment located in the flat region; the first circular arc segment and the second circular arc segment are located on the outermost side of the battery cell; along a direction from a winding tail end to a winding head end of the positive electrode sheet, the first circular arc segment is sequentially connected to the first flat segment, the second circular arc segment, the second flat segment, the third circular arc segment, and the third flat segment; the first flat segment, the second circular arc segment, the second flat segment, and the third circular arc segment are located in the single-sided coating region; The battery cell comprises a first conductive adhesive paper, which is arranged on the positive electrode current collector and covers the third circular arc segment; two ends of the first conductive adhesive paper extend to the second flat segment and the third flat segment along the winding tail end and the winding head end of the positive electrode sheet, respectively; The first conductive adhesive paper comprises a glue layer, and the glue layer comprises conductive particles; The mass percentage of the conductive particles in the first conductive adhesive paper is Ψ1 % based on the total mass of the glue layer of the first conductive adhesive paper; the thickness of the single-sided coating region is h1 μm; Ψ1 and h1 satisfy 30≤h1 / (Ψ1 %)≤2000; h1 satisfies 25 μm≤h1≤100 μm; Ψ1 satisfies 5≤Ψ1≤85; the mass percentage of silicon in the negative electrode active material is η % based on the total mass of the negative electrode active material; and η satisfies 1≤η≤50.

2. The electric cell of claim 1, wherein, The battery cell comprises a second conductive adhesive paper, which is arranged on the positive electrode current collector and covers the second circular arc segment; two ends of the second conductive adhesive paper extend to the first flat segment and the second flat segment along the winding tail end and the winding head end of the positive electrode sheet, respectively; The second conductive adhesive paper comprises a glue layer, and the glue layer comprises conductive particles; The mass percentage of the conductive particles in the second conductive adhesive paper is Ψ2 % based on the total mass of the glue layer of the second conductive adhesive paper; Ψ2 and h1 satisfy 30≤h1 / (Ψ2 %)≤2000; and Ψ2 satisfies 5≤Ψ2≤85.

3. The electric cell of claim 2, wherein, Ψ1 and h1 satisfy 30≤h1 / (Ψ1 %)≤800; and Ψ2 and h1 satisfy 30≤h1 / (Ψ2 %)≤800.

4. The cell of claim 2, wherein, Ψ1 and η satisfy 0.2≤(Ψ1 %) / η≤40.

5. The electric cell of claim 4, wherein, Ψ2 and η satisfy: 0.2≤(Ψ2 %) / η≤40.

6. The electric cell of claim 2, wherein, The thermal conductivity of the first conductive adhesive paper is denoted as K1 W / (m·k), and the thermal conductivity of the second conductive adhesive paper is denoted as K2 W / (m·k); Ψ1 and K1 satisfy: 15≤K1 / (Ψ1 %)≤40, and Ψ2 and K2 satisfy: 15≤K2 / (Ψ2 %)≤40. K1 satisfies: 2≤K1≤32; and K2 satisfies: 2≤K2≤32.

7. The electric cell of claim 2, wherein, The resistance of the first conductive adhesive paper is denoted as R1 Ω, the resistance of the second conductive adhesive paper is denoted as R2 Ω, and the resistance of the single-side coating area is denoted as R ^ Ω; R1 and R ^ satisfy: R1≤R ^ , R2 and R ^ satisfy: R2≤R ^ .

8. The electric cell of claim 6, wherein, R1 and h1 satisfy: 1<R1 / h1<35, and R2 and h1 satisfy: 1<R2 / h1<35.

9. The electric cell of claim 2, wherein, The positive electrode sheet further comprises a positive electrode current collector empty foil area, which is connected to the single-sided coating area along the winding direction, and at least part of the positive electrode current collector empty foil area is located in the first circular arc segment; the battery cell further comprises a third adhesive paper, one end of which is bonded to the first positive electrode active layer of the single-sided coating area, and the other end of which is bonded to the positive electrode current collector empty foil area; the bonding force of the first conductive adhesive paper is greater than or equal to the bonding force of the third adhesive paper, and / or the bonding force of the second conductive adhesive paper is greater than or equal to the bonding force of the third adhesive paper.

10. The cell of claim 1 or 2, wherein, The first conductive adhesive paper at one end of the second flat segment and the second conductive adhesive paper at one end of the second flat segment can be connected or not connected.

11. The cell of claim 1 or 2, wherein, The total length of the first conductive adhesive paper and the second conductive adhesive paper along the winding direction is denoted as W1 mm, the total length of the second circular arc segment and the third circular arc segment is denoted as W2 mm, and the total length of the first flat segment and the second flat segment is denoted as W3 mm; W1, W2, and W3 satisfy: W2+4 mm≤W1≤W2+W3. And / or, along the width direction of the positive electrode sheet, the width of the first conductive adhesive paper is denoted as L1 mm, the width of the second conductive adhesive paper is denoted as L2 mm, and the width of the positive electrode sheet is denoted as L mm; L1 and L satisfy: L1≤L, and / or L2 and L satisfy: L2≤L. And / or, the thickness of the first conductive adhesive paper is 0.012 mm-0.2 mm. And / or, the thickness of the second conductive adhesive paper is 0.012 mm-0.2 mm.

12. The electric cell of claim 2, wherein, The conductive particles of the first conductive adhesive paper and the conductive particles of the second conductive adhesive paper each independently comprise at least one of a conductive metal material, a conductive non-metal material, and a conductive compound. And / or, the particle size of the conductive particles of the first conductive adhesive paper is 2 μm-30 μm, and / or the particle size of the conductive particles of the second conductive adhesive paper is 2 μm-30 μm. And / or, the first conductive adhesive paper and the second conductive adhesive paper each independently further comprise a substrate layer, and the adhesive layer is arranged on at least one side of the substrate layer. And / or, the adhesive layer of the first conductive adhesive paper and the adhesive layer of the second conductive adhesive paper each independently further comprise an adhesive and an auxiliary agent.

13. The electric cell of claim 12, wherein, The conductive metal material comprises at least one of aluminum, copper, nickel, gold, silver, zinc, and iron.

14. The electric cell of claim 12, wherein, The conductive non-metal material comprises a carbon material; the carbon material comprises at least one of conductive carbon, conductive graphite, and carbon nanotubes.

15. The electrically charged cell of claim 2, wherein, The first conductive adhesive paper is located in a part of the double-coated area as a porous area, and the porous area comprises a porous structure; the porous structure satisfies at least one of the following conditions: (a) a pore diameter of the porous structure is denoted as a mm, and a satisfies: 0.05≤a≤3; (b) a pore spacing of the porous structure is denoted as b mm, and b satisfies: 0.1≤b≤4; (c) a porosity of the porous area is denoted as c %, and c satisfies: 25≤c≤80.

16. A lithium-ion battery, characterized by, An electric core comprising any one of claims 1-15.

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