Battery cell and lithium ion battery

Abstract

The invention 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-sided coating area and a single-sided coating area; a first arc section, a first straight section, a second arc section, a second straight section, a third arc section and a third straight section which are connected in sequence are arranged from the winding tail end to the winding head end of the positive plate; the battery cell comprises first conductive adhesive paper, the first conductive adhesive paper is arranged on the positive current collector and covers the third arc section, and the two ends of the first conductive adhesive paper extend to the second straight section and the third straight section along the winding tail end and the winding head end of the positive plate respectively; based on the total mass of the first conductive adhesive paper layer, the mass ratio of the conductive particles is Psi 1; the thickness of the single-side coating area is h1; psi 1 and h1 satisfy 30 < = h1 / psi < = 2000, and the first conductive adhesive paper can maintain a conductive path when the positive plate at the adhesion position is broken, so that the capacity and the performance of the battery are not influenced.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a battery cell and a lithium-ion battery. Background Art

[0002] With the rapid development of the new energy industry, the demand for high energy density of lithium-ion batteries is increasing, and traditional graphite negative electrodes can no longer meet the market's urgent demand for higher energy density. Using other negative electrodes has become an option, and silicon-based negative electrodes have become the only choice with their high theoretical capacity. In this context, silicon-based negative electrodes have become an ideal choice for improving battery energy density due to their excellent theoretical capacity advantages. However, silicon negative electrodes pose severe challenges to battery performance and safety due to their significant volume expansion characteristics. For cells with a wound structure, due to the existence of bending stress and extrusion force in the arc area of ​​the winding core, the pole piece in the outermost arc area of ​​the wound cell, especially the wound cell with silicon negative electrode, is easy to break after multiple charge and discharge. As a result, the capacity and cycle performance of the wound cell deteriorate, and there is a correspondingly large safety risk. Therefore, how to reduce the risk of pole piece breakage without affecting the capacity and performance of the cell is an important problem that needs to be solved urgently. Summary of the invention

[0003] The purpose of the present invention is to overcome the above-mentioned problems existing in the prior art, and provide a battery cell and a lithium-ion battery. The present invention pastes a first conductive adhesive tape at the part of the positive electrode sheet that is easy to break, and by controlling the ratio of the thickness of the single-sided coating area of ​​the positive electrode sheet to the content of the conductive particles in the adhesive layer of the first conductive adhesive tape, it can ensure that the positive electrode sheets of different thicknesses match the first conductive adhesive tape with corresponding conductive properties, so that the first conductive adhesive tape can still maintain a conductive path when the positive electrode sheet breaks, and at the same time, it can also avoid that too many conductive particles make the positive electrode de-lithiation speed at the break position too fast, which is unbalanced with the negative electrode lithium insertion speed, and easily induces lithium dendrites to cause battery short circuit; it can also prevent too many conductive particles from precipitating from the adhesive layer to react with lithium ions or produce gas by side reaction with the electrolyte, thereby ensuring the capacity of the battery and improving the cycle performance of the battery.

[0004] In order to achieve the above-mentioned object, the first aspect of the present invention provides a battery cell, comprising 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 a first surface and a second surface arranged opposite to each other, 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, the tail end of the first positive electrode active layer exceeds the tail end of the second positive electrode active layer, and the portion of the first positive electrode active layer exceeding the second positive electrode active layer is the single-sided coating area;

[0006] The battery cell comprises a straight area and an arc area connected to the straight area; the positive electrode sheet comprises a first arc segment, a second arc segment and a third arc segment located in the arc area, and a first straight segment, a second straight segment and a third straight segment located in the straight area, the first arc segment and the second arc segment are both 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 electrode sheet, the first arc segment is connected with the first straight segment, the second arc segment, the second straight segment, the third arc segment and the third straight segment in sequence, and the first straight segment, the second arc segment, the second straight segment and the third arc segment are all located in the single-sided coating area;

[0007] The battery cell comprises a first conductive adhesive paper, which is arranged on the positive electrode current collector and covers the third arc segment, and two ends of the first conductive adhesive paper extend to the second straight segment and the third straight segment respectively along the winding tail end and the winding head end of the positive electrode sheet;

[0008] The first conductive adhesive paper includes an adhesive layer, and the adhesive layer includes conductive particles; based on the total mass of the adhesive layer of the first conductive adhesive paper, the mass proportion of the conductive particles of the first conductive adhesive paper is Ψ1%; the thickness of the single-sided coating area is h1μm; Ψ1 and h1 satisfy: 30≤h1 / Ψ1≤2000.

[0009] A second aspect of the present invention provides a lithium ion battery, wherein the lithium ion battery comprises the battery cell described in the first aspect of the present invention.

[0010] The present invention adopts the above technical solution to achieve the following beneficial effects:

[0011] The present invention can ensure that positive electrode sheets of different thicknesses match the first conductive adhesive paper with corresponding conductive properties by pasting the first conductive adhesive paper at the easily broken part of the positive electrode sheet and controlling the ratio of the thickness of the single-sided coating area of ​​the positive electrode sheet to the conductive particle content in the adhesive layer of the first conductive adhesive paper, so that the first conductive adhesive paper can still maintain a conductive path when the positive electrode sheet breaks. At the same time, it can also avoid that too many conductive particles cause the positive electrode to de-lithium too quickly at the broken part, which is unbalanced with the negative electrode lithium insertion speed and easily induces lithium dendrites to cause battery short circuit; it can also prevent too many conductive particles from precipitating from the adhesive layer to react with lithium ions to generate lithium or to react with the electrolyte to generate gas, thereby ensuring the capacity of the battery and improving the cycle performance of the battery.

[0012] The endpoints and any values ​​of the range disclosed in this article are not limited to the precise range or value, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the 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 as specifically disclosed in this article. Herein, in the absence of special instructions, data ranges include endpoints. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Shown is a schematic diagram of a positive electrode sheet in an example of the present invention.

[0014] Figure 2 Shown is a schematic diagram of a positive electrode sheet in another embodiment of the present invention.

[0015] Figure 3 FIG. 4 is a schematic diagram of a battery cell in an embodiment of the present invention.

[0016] Figure 4 Shown is a schematic diagram of a battery cell in another embodiment of the present invention.

[0017] Figure 5 Shown is an X-ray diffraction pattern of the first conductive adhesive tape in an example of the present invention.

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

[0019] 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 used to limit the present invention.

[0020] Unless otherwise defined, all scientific and technical terms used in the present invention have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention relates.

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

[0022] The first aspect of the present invention provides a battery cell, comprising 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; for ease of understanding, the structure is referred to as Figure 1 The schematic diagram of the positive electrode sheet is shown in Figure 1 It can be seen that the positive electrode sheet 103 includes a positive electrode current collector 100, a first positive electrode active layer 101 and a second positive electrode active layer 102. Along the first direction Z, the positive electrode current collector 100 has a first surface and a second surface arranged opposite to each other, the first positive electrode active layer 101 is arranged on the first surface, and the second positive electrode active layer 102 is arranged on the second surface. The positive electrode sheet includes a double-sided coating area 104 and a single-sided coating area 105 along the winding direction. The tail end of the first positive electrode active layer 101 exceeds the tail end of the second positive electrode active layer 102, and the portion of the first positive electrode active layer 101 exceeding the second positive electrode active layer 102 is the single-sided coating area 105; structure reference Figure 3 The schematic diagram of the battery cell shown is Figure 3It can be seen that the battery cell includes a straight area and an arc area connected to the straight area; the positive electrode sheet includes a first arc segment 109, a second arc segment 111 and a third arc segment 113 located in the arc area, and a first straight segment 110, a second straight segment 112 and a third straight segment 114 located in the straight area. The first arc segment 109 and the second arc segment 111 are both 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 electrode sheet, the first arc segment 109 is connected to the first straight segment 110, the second arc segment 111, the second straight segment 112, the third arc segment 113 and the third straight segment 114 in sequence. In addition, the other end of the first arc segment 109 is connected to one end of the fourth straight segment 115, and the other end of the fourth straight segment 115 is overlapped on the second straight segment 112. The first straight section 110, the second arc section 111, the second straight section 112 and the third arc section 113 are all located in the single-sided coating area; the battery cell includes a first conductive adhesive tape, Figure 1 and Figure 3 As can be seen from the figure, the first conductive adhesive paper 106 is arranged on the positive electrode 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 straight segment 112 and the third straight segment 114 along the winding tail end and the winding head end of the positive electrode sheet respectively; the first conductive adhesive paper includes an adhesive layer, and the adhesive layer includes conductive particles; based on the total mass of the adhesive layer of the first conductive adhesive paper, the mass proportion of the conductive particles of the first conductive adhesive paper is Ψ1%; the thickness of the single-sided coating area is h1μm; Ψ1 and h1 satisfy: 30≤h1 / Ψ1≤2000.

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

[0024] Due to the structural characteristics of the wound battery cell, the positive electrode sheet has a single-sided coating area and a double-sided coating area, as well as a single-sided and double-sided interface where the double-sided coating area transitions to the single-sided coating area. Due to the thickness difference of the positive electrode sheet on both sides of the single-sided and double-sided interface, the positive electrode collector near the single-sided and double-sided interface will be over-pressured during rolling, which will easily damage the positive electrode collector near the single-sided and double-sided interface. Furthermore, since the silicon-containing negative electrode in the battery cell has a large volume expansion during the charge and discharge cycle, the forces on both sides of the interface between the single-sided coating area and the double-sided coating area are uneven (only one side of the positive electrode sheet in the single-sided area is charged and discharged, while both sides of the positive electrode sheet in the double-sided area are charged and discharged), the squeezing effect on the positive electrode collector near the single-sided and double-sided interface where the double-sided coating area transitions to the single-sided coating area will be further aggravated, eventually causing the positive electrode collector to break.

[0025] Based on the above findings, the inventors of the present invention have conducted a large number of targeted studies, where the first conductive adhesive paper is attached to the part where the positive electrode sheet is extremely easy to break. There are conductive particles in the adhesive layer of the first conductive adhesive paper, and the conductive particles can form a conductive network in the first conductive adhesive paper. 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 electrode sheet is one of the main places for the electrochemical reaction of the battery. The thickness of the positive electrode sheet directly affects the reaction rate and the complexity of the reaction path. When the positive electrode sheets of different thicknesses are broken, the conductivity requirements of the conductive adhesive paper are also different. In order to ensure that the electrons can still be effectively transmitted through the first conductive adhesive paper after the electrode sheet is broken, 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 electrode sheet of different thicknesses, thereby avoiding the conductive path being blocked at the first conductive adhesive paper when the positive electrode sheet is broken, and at the same time ensuring that the lithium ions are deintercalated at a normal speed at the electrode sheet break. Since the first conductive adhesive paper is mainly attached to the single-sided coating area of ​​the positive electrode sheet, the present invention can ensure that the positive electrode sheets of different thicknesses match the first conductive adhesive paper with corresponding conductive properties by controlling 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 to meet the above range. When the positive electrode sheet breaks, the first conductive adhesive paper can still maintain a conductive path, 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 straight section along the winding head end direction of the positive electrode sheet, and the other end of the first conductive adhesive paper extends to the second straight section along the winding tail end direction. In this way, on the one hand, the first conductive adhesive paper can completely cover the single-sided coating area that is easy to break and the junction position of the single-sided coating area and the double-sided coating area. On the other hand, the two ends of the first conductive adhesive paper are at least partially located in the straight section of the battery cell. Even if the expansion stress of the arc area is too large, the part of the first conductive adhesive paper located in the straight section can still interact with the first conductive adhesive paper to ensure that the first conductive adhesive paper is not easy to fall off.

[0026] In the present invention, based on the total mass of the first conductive adhesive paper layer, the mass proportion of the conductive particles of the first conductive adhesive paper (Ψ1%) and the thickness of the single-sided coating area (h1μm) satisfy: 30≤h1 / Ψ1≤2000, and the value of h1 / Ψ1 can be, for example, 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 / Ψ1≤800. When h1 / Ψ1 satisfies the above range, the mismatch problem between the conductive particle content in the adhesive layer of the first conductive adhesive paper and the thickness of the single-sided coating area can be avoided. For example, when the thickness of the single-sided coating area is constant, when h1 / Ψ1>2000, it indicates that the conductive particle content in the adhesive layer of the first conductive adhesive paper is too little, and the first conductive adhesive paper cannot ensure the electronic conduction at the fracture position, so that the lithium ions near the fracture position cannot be deintercalated at a normal speed through the first conductive adhesive paper, reducing the power performance of the positive electrode active material and reducing the energy density of the battery; when the thickness of the single-sided coating area is constant, when h1 / Ψ1<30, it indicates that the conductive particle content in the adhesive layer of the first conductive adhesive paper is too much, which will cause the lithium ions near the fracture position to be deintercalated at a normal speed. The positive electrode active material removes lithium ions too quickly, while the negative electrode active material inserts lithium at a constant rate, causing the lithium ions near the fracture site to precipitate at the corresponding negative electrode, which will cause lithium dendrites to puncture the diaphragm and cause a short circuit in the battery. On the other hand, too many conductive particles may precipitate from the glue layer, and the precipitated conductive particles may react with the lithium ions released from the positive electrode to undergo a lithium reaction, resulting in the inability of this part of the material to undergo normal charge and discharge reactions, causing a waste of positive electrode materials and reducing the capacity of the battery. In addition, during the cycle process, the conductive particles may react with the electrolyte to produce gas after precipitation, resulting in the inability of the electrochemical reaction to proceed normally, deteriorating the cycle performance of the battery, and in severe cases, causing battery failure.

[0027] Exemplarily, the content of conductive particles in the adhesive layer of conductive adhesive tape can be tested by high-precision microscopy technology and image processing technology, which may include the following steps: ① Sample preparation: Place the sample to be tested on the workbench of the microscope and 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 images. Conductive particles are identified and counted through edge detection, threshold segmentation and other technologies. ④ Content calculation: The number of conductive particles in the image is counted and analyzed by image processing software, and the content of the conductive particles is calculated based on 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 and standard deviation can be calculated.

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

[0029] In some embodiments, the battery cell includes a second conductive adhesive tape. For ease of understanding, the battery cell structure is referred to as Figure 3 The schematic diagram of the battery cell shown in the figure, the second conductive adhesive paper 107 is arranged on the positive electrode 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 straight segment 110 and the second straight segment 112 respectively along the winding tail end and the winding head end direction of the positive electrode sheet; the second conductive adhesive paper 107 includes an adhesive layer, and the adhesive layer includes conductive particles; based on the total mass of the adhesive layer of the second conductive adhesive paper, the mass proportion of the conductive particles of the second conductive adhesive paper is Ψ2%; Ψ2 and h1 satisfy: 30≤h1 / Ψ2≤2000, the value of h1 / Ψ2 can be, for example, 30, 40, 50, 100, 500, 1000, 1500, 2000 or any point value in the range composed of the above two point values, preferably 30≤h1 / Ψ2≤800.

[0030] The inventors of the present invention further discovered that, in a wound battery cell with a positive electrode sheet outsourcing structure, in the positive electrode sheet, in addition to the positive electrode collector located in the step area where the double-sided coating area transitions to the single-sided coating area, which is prone to breakage, the positive electrode collector in the arc area of ​​the positive electrode sheet in the outermost circle of the battery cell (i.e., the second arc segment and the third arc segment) and the connection between the outermost arc area and the straight area (including the connection between the second arc segment and the first straight segment and the second straight segment, and the connection between the third arc segment and the second straight segment and the third straight segment) are also prone to breakage. Specifically, unlike the straight area, the arc area cannot effectively release the expansion force during the battery cycle due to its structural characteristics. The expansion stress of the inner circle of the battery cell is superimposed on the arc of the outermost circle of the battery cell (i.e., the second arc segment and the third arc segment), so that the second arc segment and the third arc segment generate a greater extrusion force that expands outward. At the same time, since the second arc segment and the third arc segment correspond to the single-sided coating area of ​​the positive electrode sheet, only one side undergoes charging and discharging reactions, and the forces on the inside and outside are uneven, making it easier for the positive electrode sheet to break near the arc of this area and the connection between the arc and the straight section. The two ends of the second conductive adhesive tape of the present invention extend to the first straight section and the second straight section respectively along the winding tail end and the winding head end of the positive electrode sheet. The first conductive adhesive tape and the second conductive adhesive tape can cover the arc area of ​​the positive electrode sheet of the outermost circle of the battery cell and the positive electrode sheet at the connection between the outermost arc area and the straight area, which can further reduce the risk of fracture of the positive electrode sheet of the battery cell. At the same time, the mass ratio of the conductive particles in the second conductive tape layer and the thickness of the single-sided coating area are further controlled to meet the above range. Even if the positive electrode sheet is broken at the bonding point of the second conductive tape, the second conductive tape can form a conductive path, so that the broken positive electrode sheet can still exert its capacity as usual, thereby not affecting the capacity and performance of the battery.

[0031] In some embodiments, at least parts of the first conductive paper and the second conductive paper are disposed on the surface of the positive electrode current collector in the single-sided coating area where the positive electrode active layer is not disposed.

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

[0033] In some embodiments, based on the total mass of the negative electrode active material, the mass proportion of silicon element is recorded as η%, Ψ1 and η satisfy: 0.2≤Ψ1 / η≤40, and the value of Ψ1 / η can be, for example, 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, and the value of Ψ2 / η can be, for example, 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 consisting of any two of the above point values.

[0035] In some embodiments, based on the total mass of the negative electrode active material, the mass proportion (η%) of the silicon element satisfies: 1≤η≤50, and the mass proportion of the silicon element can be, for example, 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 invention, the negative electrode active material includes a silicon-based material. Although the silicon-containing negative electrode can improve the energy density of the battery, the higher the content of silicon in the negative electrode active material, the greater the stress generated by the expansion of the negative electrode sheet, and the risk of fracture of the outer arc area (the second arc segment and the third arc segment) of the positive electrode sheet and the degree of fracture damage will also be greater. By controlling the ratio of the content of conductive particles in the first conductive tape and / or the second conductive tape to the mass proportion of silicon to meet the above range, it is possible to avoid excessive silicon content in the negative electrode active material, excessive stress caused by negative electrode expansion, and excessive fracture of the positive electrode sheet, which exceeds the range that the first conductive tape and / or the second conductive tape can bear. The conductivity of the first conductive tape and / or the second conductive tape is insufficient to maintain the electronic conduction of the original positive electrode sheet, resulting in a decrease in the conduction and deintercalation rate of electrons and lithium ions, making it impossible for the battery to be fully charged within the specified time, increasing the charging time of the battery and reducing the charging efficiency of the battery. In addition, too high a silicon content in the negative electrode active material may cause the fracture and damage of the outer arc area (the second arc segment and the third arc segment) of the positive electrode sheet to increase, resulting in uneven electrochemical reaction of the battery, and then causing local overheating, affecting battery safety.

[0037] For example, the test method of the mass percentage of silicon element can be tested by thermogravimetric analysis, for example, using Shimadzu DTG-60 thermogravimetric analyzer for testing, and the test conditions are: sample amount 5 mg, air as atmosphere, heating rate 10°C / min from room temperature to 900°C and constant temperature for 40 minutes. The relationship between the mass percentage of silicon element (x) and the final weight residual percentage (y) of the entire 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, based on the total mass of the adhesive layer of the first conductive adhesive paper, the mass proportion of the conductive particles of the first conductive adhesive paper (Ψ1%) satisfies: 5≤Ψ1≤85. The mass proportion of the conductive particles of the first conductive adhesive paper can be, for example, 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, based on the total mass of the adhesive layer of the second conductive adhesive paper, the mass proportion of the conductive particles of the second conductive adhesive paper is (Ψ2%), which satisfies: 5≤Ψ2≤85. The mass proportion of the conductive particles of the second conductive adhesive paper can be, for example, 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.

[0041] In the present invention, the conductive particle content in the first conductive adhesive tape and / or the second conductive adhesive tape adhesive layer is maintained within the above range, which can avoid the risk of conductive particle precipitation when the conductive particle content is too high. The precipitation of conductive particles will increase the risk of battery short circuit on the one hand; on the other hand, the precipitated conductive particles may react with the lithium ions released from the positive electrode sheet to undergo lithiumization reaction, resulting in the inability of the positive electrode sheet to perform charge and discharge reactions, and the battery capacity is reduced; furthermore, the precipitated conductive particles may also react with the electrolyte to produce gas as a side reaction, resulting in reduced cycle performance of the battery.

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

[0043] In some embodiments, the thermal conductivity of the second conductive tape is recorded as K2 W / (m·k), Ψ2 and K2 satisfy: 15≤K2 / Ψ2≤40, and the value of K2 / Ψ2 can be, for example, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 36, 37, 38, 39, 40 or any point value in the range consisting of any two of the above point values.

[0044] In some embodiments, the thermal conductivity of the first conductive adhesive paper (K1 W / (m·k)) satisfies: 2≤K1≤32. The thermal conductivity of the first conductive adhesive paper can be, for example, 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 point value in the range consisting of any two of the above point values.

[0045] In some embodiments, the thermal conductivity (K2 W / (m·k)) of the second conductive adhesive tape satisfies: 2≤K2≤32. The thermal conductivity of the second conductive adhesive tape may be, for example, 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 point value in the range consisting of any two of the above point values.

[0046] In the present invention, the thermal conductivity of the first conductive adhesive paper and / or the second conductive adhesive paper is better than that of common insulating adhesive paper in the art. The more conductive particles there are 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 breaks, the internal resistance of the battery will increase. At this time, more heat is generated at the broken position of the positive electrode sheet. After the battery is charged and discharged (especially high-rate charge and discharge), the first conductive tape and / or the second conductive tape at the broken position of the positive electrode sheet will overcurrent and generate heat. If the conductivity and thermal conductivity of the first conductive tape and / or the second conductive tape are poor (the worse the conductivity of the first conductive tape and / or the second conductive tape, the greater the resistance of the first conductive tape and / or the second conductive tape, and the higher the overcurrent heat generation; the worse the thermal conductivity of the first conductive tape and / or the second conductive tape, the easier it is for heat to accumulate), it is easy for excessive heat to reduce the stability of the adhesive layer of the first conductive tape and / or the second conductive tape, and cause physical or chemical changes, such as decomposition or phase change of the adhesive layer due to high temperature, resulting in the first conductive tape and / or the second conductive tape. The conductive performance cannot be normally exerted, thereby causing a decrease in battery capacity and performance.

[0047] Exemplarily, the test method for the thermal conductivity of the first conductive tape and / or the second conductive tape is as follows: ① Sample preparation: prepare a conductive tape sample. ② Test equipment: Use thermal conductivity test equipment, which should be able to 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 Conduct the 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 multiple times.

[0048] In some embodiments, the resistance of the first conductive adhesive tape is denoted as R1Ω, and the resistance of the single-sided coating area is denoted as R ^ Ω, the resistance of the first conductive adhesive tape (R1) and the resistance of the single-sided coating area (R ^ ) satisfies: R1≤R ^ .

[0049] In some embodiments, the resistance of the second conductive adhesive tape is recorded as R2Ω, and the resistance of the second conductive adhesive tape (R2) and the resistance of the single-sided coating area (R ^ ) satisfies: R2≤R ^ .

[0050] The resistance R1 of the first conductive paper, the resistance R2 of the second conductive paper, and the resistance R2 of the single-sided coated area can be measured by conventional methods in the art, such as using a two-probe resistance meter.

[0051] In the present invention, the first conductive tape and / or the second conductive tape can form a conductive path when the positive electrode sheet is broken at the bonding position. By further limiting the resistance of the first conductive tape and / or the second conductive tape to ≤ 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 break of the positive electrode sheet are not affected. If the resistance of the first conductive tape and / or the second conductive tape at the break of the positive electrode sheet is greater than the resistance of the positive electrode sheet, the conductivity of the first conductive tape and / or the second conductive tape is worse than that of the positive electrode sheet. When the positive electrode sheet is broken, the first conductive tape and / or the second conductive tape cannot exert the same or better conductivity as the positive electrode sheet, thereby affecting the electronic conductivity of the overall battery cell, reducing the capacity of the battery, and reducing the cycle performance of the battery.

[0052] In some embodiments, the resistance (R1) of the first conductive adhesive tape and the thickness (h1) of the single-sided coating area satisfy: 1<R1 / h1<35, and the value of R1 / h2 can be, for example, 1.1, 2, 3, 5, 10, 20, 27, 30, 34.9 or any point value in the range formed by any two of the above point values, preferably 3≤R1 / h1≤27.

[0053] In some embodiments, the resistance (R2) of the second conductive adhesive tape and the thickness (h1) of the single-sided coating area satisfy: 1<R2 / h1<35, and the value of R2 / h1 can be, for example, 1.1, 2, 3, 5, 10, 20, 27, 30, 34.9 or any point value in the range formed by any two of the above point values, preferably 3≤R1 / h1≤27.

[0054] If the electrode components and manufacturing process are the same, under the same compaction conditions, assuming that the resistivity ρ of the coating is the same, and the area (S) of the electrode test sample is also the same, then the thickness (H) and resistance R of the electrode are AM The relationship is: R AM=ρ×H / S. It can be seen from the above formula that the greater the thickness of the electrode, the greater the electrode resistance. Therefore, the thicker the positive electrode sheet, the greater the resistance and the worse the conductive effect. The conductivity of the first conductive adhesive paper and / or the second conductive adhesive paper can be relatively reduced to a level equivalent to that of the positive electrode sheet, and the corresponding conductive particle content in the first conductive adhesive paper and / or the second conductive adhesive paper can be reduced accordingly. The less the conductive particle content of the first conductive adhesive paper and / or the second conductive adhesive paper, the less likely it is for the adhesive layer of the first conductive adhesive paper and / or the second conductive adhesive paper to precipitate conductive particles. Therefore, the present invention reduces the risk of battery short circuit and avoids the problem of battery capacity reduction and battery cycle performance reduction due to the precipitation of conductive particles 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-sided coating area in the positive electrode sheet to meet the above range.

[0055] In some embodiments, the positive electrode sheet also includes a positive electrode collector empty foil area, and along the winding direction, the positive electrode collector empty foil area is connected to the single-sided coating area, and at least part of the positive electrode collector empty foil area is located in the first arc segment. The battery cell also includes a third adhesive paper, one end of the third adhesive paper is bonded to the first positive electrode active layer of the single-sided coating area, and the other end of the third adhesive paper is bonded to the positive electrode collector empty foil area, the bonding strength of the first conductive adhesive paper is ≥ the bonding strength of the third adhesive paper, and / or the bonding strength of the second conductive adhesive paper is ≥ the bonding strength of the third adhesive paper.

[0056] In the present invention, the third adhesive tape is the final insulating adhesive tape of the positive electrode sheet or the final adhesive tape of the battery cell (the third adhesive tape is non-conductive), refer to Figure 3 When the third adhesive tape is the insulating adhesive tape for the positive electrode sheet, the third adhesive tape 108 exceeds the tail end of the negative electrode sheet at the tail end of the positive electrode empty foil area, which can effectively block the burrs at the tail end of the negative electrode sheet, prevent abnormal self-discharge, heat 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 electrode sheet exceeds the tail end of the corresponding negative electrode sheet, sticking the third adhesive tape on the tail end of the positive electrode sheet can reduce the risk of short circuit caused by the uneven tail ends of the positive and negative electrode sheets, and play a good role in insulation isolation. When the third adhesive tape is the finishing tape for the battery cell, the third adhesive tape is located at the tail position of the battery cell, which can restrain the structure of the battery cell and ensure that the overall structure of the battery cell will not be loose.

[0057] In the present invention, the bonding force of the first conductive paper, the bonding force of the second conductive paper, and the bonding force of the third conductive paper are all expressed as the bonding force between the corresponding adhesive paper and the positive electrode current collector. The bonding force of the first conductive paper is defined as ≥ the bonding force of the third conductive paper, and / or the bonding force of the second conductive paper is ≥ the bonding force of the third conductive paper, which can ensure that the first conductive paper and / or the second conductive paper have high bonding performance. On the one hand, it can ensure that the first conductive paper and / or the second conductive paper do not separate from the positive electrode sheet in the electrolyte environment; on the other hand, the high bonding performance of the first conductive paper and / or the second conductive paper can also inhibit the breakage of the positive electrode sheet at the bonding point of the first conductive paper and / or the second conductive paper to a certain extent.

[0058] The bonding strength of the first conductive tape, the bonding strength of the second conductive tape and the bonding strength of the third tape can be measured by a peel strength test method: under the conditions of (25±1)°C and a relative humidity of (50±5)%, the tape sample is adhered to a metal plate (the same material as the positive electrode current collector, such as aluminum), the metal plate is fixed on a clamp of a tensile testing machine, and the other clamp of the testing machine clamps the free end of the tape sample at an angle of 180° to the metal plate, and moves at a constant speed of (5.0±0.2) mm / s, and the tensile force and peeling speed of the tape sample are measured to calculate the peel strength of the tape sample.

[0059] In some embodiments, the insulating tape includes: rubber tape, acrylic tape, polypropylene tape or SIS (Styrene-Isoprene-Styrene, styrene-isoprene-styrene) tape, etc.

[0060] In some embodiments, the first conductive adhesive tape at one end of the second straight section and the second conductive adhesive tape at one end of the second straight section may be connected or not connected.

[0061] Figure 3 The schematic diagram of the battery cell in one embodiment of the present invention is shown in FIG. Figure 3 It can be seen from the figure that the first conductive adhesive tape 106 at one end of the second straight section 112 is not connected to the second conductive adhesive tape 107 at one end of the second straight section 112 .

[0062] Figure 4 The schematic diagram of the battery cell in one embodiment of the present invention is shown in FIG. Figure 4 It can be seen from the figure that the first conductive adhesive tape 106 is connected to the second conductive adhesive tape 107 at one end of the second straight section 112 .

[0063] In some embodiments, along the winding direction, the total length of the first conductive adhesive tape and the second conductive adhesive tape is recorded as W1 mm, the total length of the second arc segment and the third arc segment is recorded as W2 mm, and the total length of the first straight segment and the second straight segment is recorded as W3 mm; W1, W2, and W3 satisfy: W2+4mm≤W1≤W2+W3; when the total length of the first conductive adhesive tape and the second conductive adhesive tape is at the lower limit of the above range, the adhesive positions of the first conductive adhesive tape and the second conductive adhesive tape cover the second arc area and the third arc area on the left and right sides of the winding core, and the sum of the length of the first conductive adhesive tape covering the second straight segment and the third straight segment and the length of the second conductive adhesive tape covering the first straight segment and the second straight segment is not less than 4 mm, such as Figure 3 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 area in the positive electrode sheet is completely covered by the first conductive adhesive paper and the second conductive adhesive paper, such as Figure 4 As shown. The present invention further limits the total length of the first conductive tape and the second conductive tape to be within the above range, so as to ensure that the first conductive tape and the second conductive tape completely protect the position of the positive electrode sheet in the battery cell that is easy to break, and at the same time ensure that the first conductive tape and the second conductive tape exceed the outermost circular arc area and are partially located in the straight area connected to the outermost circular arc area, so as to ensure the bonding reliability of the first conductive tape and the second conductive tape, so as to better play the role of the first conductive tape and the second conductive tape in electronic conduction after the positive electrode sheet breaks, maintain a smooth conductive path, and thus do not affect the capacity and performance of the battery.

[0064] In some embodiments, along the winding direction, the projection of the first conductive adhesive tape on the positive electrode sheet may also be discontinuous, but should at least cover the step area where the double-sided coating area in the positive electrode sheet transitions to the single-sided coating area, such as Figure 2 shown.

[0065] In some embodiments, when there is a second conductive tape in the battery cell, the projection of the second conductive tape on the positive electrode sheet may be continuous or discontinuous along the winding direction; when the projection of the second conductive tape on the positive electrode sheet is discontinuous, the second conductive tape at least covers the junction area between the first straight segment and the second arc segment, a partial area of ​​the second arc segment, and the junction area between the second arc segment and the second straight segment.

[0066] In some embodiments, along the width direction of the positive electrode sheet, the width of the first conductive adhesive paper is recorded as L1 mm, the width of the second conductive adhesive paper is recorded as L2 mm, the width of the positive electrode sheet is recorded 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 and causing a short circuit in the battery.

[0067] In some embodiments, the thickness of the first conductive adhesive paper is 0.012 mm-0.2 mm, for example, it 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, it 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 paper and / or the second conductive paper within the above range can ensure that the first conductive paper and / or the second conductive paper have sufficient conductivity, and can also maintain the first conductive paper and / or the second conductive paper with a certain strength, good flexibility and operability, so as to facilitate lamination with the positive electrode sheet. In addition, since the first conductive paper and / or the second conductive paper have a certain strength, it can also be ensured that they 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 recorded as the single-sided and double-sided junction of the positive electrode sheet, and the projection of the first conductive adhesive tape on the positive electrode sheet located at the single-sided and double-sided junction of the positive electrode sheet and the double-sided coating area is a porous area, and the porous area includes 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, where a satisfies: 0.05≤a≤3;

[0072] (b) The pore spacing of the porous structure is denoted as b mm, where b satisfies: 0.1≤b≤4;

[0073] (c) The porosity of the porous region is denoted as c%, where 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 in a range consisting of any two of the above values.

[0075] The pore spacing of the porous structure can 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 point value in the range consisting of any two of the above point values.

[0076] The porosity of the porous zone may be, for example, 25%, 30%, 40%, 50%, 60%, 70%, 80% or any value in the range consisting of any two of the above values.

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

[0078] In some embodiments, the conductive particles of the first conductive adhesive tape and the conductive particles of the second conductive adhesive tape each independently include 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 includes at least one of aluminum, copper, nickel, gold, silver, zinc, and iron.

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

[0081] Graphite materials usually have a (002) peak at around 2θ=26.5°. Figure 5 The figure shows the X-ray diffraction (XRD) spectrum of the first conductive adhesive paper in an example of the present invention. The conductive particles of the first conductive adhesive paper contain conductive carbon black. In the XRD spectrum, there is an obvious 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 chains present in other components of the first conductive adhesive paper.

[0082] In some embodiments, the particle size of the conductive particles of the first conductive adhesive paper is 2μm-30μm, for example, it can be 2μm, 6μm, 8μm, 10μm, 15μm, 20μm, 25μm, 30μm or any point value in the range composed of any two of the above point values, and / or the particle size of the conductive particles of the second conductive adhesive paper is 2μm-30μm, for example, it can be 2μm, 6μm, 8μm, 10μm, 15μm, 20μm, 25μm, 30μm or any point value in the range composed of any two of the above point values. Controlling the particle size of the conductive particles in the first conductive paper and / or the second conductive paper to meet the above range can avoid the particle size of the conductive particles being too large, which will reduce the contact point area between the particles, resulting in a poor conductive path, increased resistance, and reduced conductivity of the first conductive paper and / or the second conductive paper; avoid the particle size of the conductive particles being too small. Although a smaller particle size is conducive to forming a denser conductive network, an excessively small particle size may result in an excessively small contact point area between the conductive particles, unstable conductivity, and deterioration of the conductive performance of the first conductive paper and / or the second conductive paper. In addition, an excessively small particle size may also increase production difficulty and cost.

[0083] In the present invention, the testing method of the particle size of the conductive particles comprises the following steps: using a laser particle size analyzer for testing, mixing a conductive adhesive tape sample with a dispersion medium, setting parameters such as stirring speed, the refractive index of the dispersion medium and the refractive index of the particles, starting a 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 further independently include a substrate layer, and the adhesive layer is disposed on a surface of at least one side 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 further independently include an adhesive and an auxiliary agent.

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

[0087] In some embodiments, the auxiliary agent includes at least one of a cross-linking agent (such as acrylamide, etc.), a coupling agent (such as silane, phosphate, borate, etc.), a preservative (such as a mildew inhibitor, 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-sided and double-sided intersection is located in the third straight segment. Taking the intersection of the third arc segment and the third straight segment as the starting point, along the direction from the winding tail end to the winding head end of the positive electrode sheet, the distance between the intersection of the third arc segment and the third straight segment and the projection point of the single-sided and double-sided intersection on the third straight segment is 0mm-10mm, for example, it can be 0mm, 1mm, 2mm, 3mm, 4mm, 5mm, 6mm, 7mm, 8mm, 9mm, 10mm or any point value in the range composed of any two of the above point values. If the distance is less than 0mm, it means that the step area where the double-sided coating area of ​​the positive electrode sheet transitions to the single-sided coating area is located on the third arc segment outside the positive electrode sheet of the battery cell. The existence of the step area will occupy additional space, increasing the width of the battery cell on the cross section. The increase in the width of the battery cell will change the shape and size of the arc interface, which may be detrimental to the current distribution and heat management inside the battery, resulting in a decrease in the battery energy density. At the same time, since the step area is in the third arc segment of the outer circle, the positive electrode current collector in the step area is more likely to break, which is not conducive to improving the problem of positive electrode sheet breakage. If the distance is greater than 10mm, the farther single-sided and double-sided interface position means that the distance between the end of the battery cell is farther, which may cause the battery cell to be unable to maintain uniform flatness during the winding process. The farther the end of the battery cell is, the uneven distribution of positive and negative electrode materials in the battery may reduce the utilization rate of these materials. The decrease in the flatness of the battery cell and the decrease in the utilization rate of the positive and negative electrodes will further reduce the energy density of the battery.

[0089] A second aspect of the present invention provides a lithium ion battery, wherein the lithium ion battery comprises the battery cell described in the first aspect of the present invention.

[0090] In some embodiments, the first positive electrode active layer and the second positive electrode active layer each independently include the following components in percentage by weight: 90 wt % to 99.4 wt % of positive electrode active material, 0.3 wt % to 5 wt % of conductive agent, and 0.3 wt % to 5 wt % of binder.

[0091] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector, wherein the negative electrode active material layer includes the following components in percentage by weight: 90wt%-99.4wt% of negative electrode active material, 0.2wt%-5wt% of conductive agent, and 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 nanotubes, and metal powder.

[0093] In some embodiments, the binder includes but is not limited to one or more of styrene-butadiene rubber latex, polytetrafluoroethylene latex, 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 invention, the type of the separator is not specifically limited, for example, conventional lithium ion battery separators in the art can be selected, including but not limited to woven membranes, non-woven membranes (non-woven fabrics), microporous membranes, composite membranes, separator paper, rolled membranes, polyethylene microporous membranes, polypropylene microporous membranes, etc.

[0096] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0097] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0098] The present invention is described in detail below in conjunction with specific embodiments, which are used to understand but not to limit the present invention.

[0099] Example 1

[0100] Prepare the battery as follows:

[0101] (1) Preparation of positive electrode sheet

[0102] The positive electrode active material lithium cobalt oxide, the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 97.6:1.4:1.2, and then N-methylpyrrolidone (NMP) is added and stirred under the action of a vacuum mixer until the mixed system becomes a positive electrode slurry with uniform fluidity; the positive electrode slurry is evenly coated on the surface of the aluminum foil, and after drying, rolling and cutting, a positive electrode sheet including a positive electrode active layer is obtained, the positive electrode sheet includes a double-sided coating area and a single-sided coating area, the thickness h1 of the single-sided coating area is 50μm, and the width L of the positive electrode sheet is 66.5mm. The first conductive adhesive tape and the second conductive adhesive tape are attached, and the total length of the first conductive adhesive tape and the second conductive adhesive tape (W1) = (the total length of the second arc segment and the third arc segment W2+4) mm;

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

[0104] (2) Preparation of negative electrode sheet

[0105] The negative electrode active material (95% graphite and 5% SiC), styrene-butadiene rubber (SBR) binder, 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, and the slurry is coated on both surfaces of a copper foil. After drying, rolling, and slitting, a negative electrode sheet including a negative electrode active layer is obtained; wherein the mass proportion of silicon element is η 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 batteries

[0109] The positive electrode sheet and the separator prepared in step (1) and the negative electrode sheet prepared in step (2) are wound to form a winding core, and a third adhesive tape (insulating adhesive tape) is pasted; after injecting the electrolyte of step (2), the battery is formed, sorted, and OCV tested to obtain a battery.

[0110] The attachment positions of the first conductive adhesive tape, the second conductive adhesive tape and the third conductive adhesive tape are as follows: Figure 3 The bonding force of the third adhesive tape is 0.02kgf / mm.

[0111] Example 2

[0112] Example 2 The battery was prepared according to Example 1, except that:

[0113] In the first conductive adhesive tape: the conductive particles account for 85% of the adhesive layer, and the conductive particles are graphene; the particle size of the conductive particles is 30 μm; the adhesive is silicone resin; the bonding force is 0.025 kgf / mm; the parameters of the second conductive adhesive tape are the same as those of the first conductive adhesive tape.

[0114] The total length of the first conductive adhesive tape and the second conductive adhesive tape (W1) = (the total length of the second arc segment and the third arc segment W2 + the total length of the first straight segment and the second straight segment W3) mm. The attachment positions of the first conductive adhesive tape and the second conductive adhesive tape are as follows. Figure 4 shown.

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

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

[0117] Example 3

[0118] Example 3 The battery was prepared according to Example 1, except that:

[0119] In the first conductive adhesive tape: 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 adhesive is polyurethane; the bonding force is 0.04 kgf / mm; and the parameters of the second conductive adhesive tape are the same as those of the first conductive adhesive tape.

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

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

[0122] Example 4

[0123] Example 4 The battery was prepared by referring to Example 1, except that, in Example 4, only the first conductive tape was pasted.

[0124] Example 5 Group

[0125] Example 5 The battery was prepared in the same manner as in Example 1, except that:

[0126] Embodiment 5a: In the first conductive adhesive paper, the conductive particles account for 90% of the adhesive layer, which exceeds the protection scope of the present invention; various parameters of the second conductive adhesive paper are the same as those of the first conductive adhesive paper.

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

[0128] Example 6

[0129] Example 6 The battery is prepared with reference to Example 1, except that the mass proportion of silicon element in the negative electrode sheet is η, which is 60%, exceeding the protection scope of the present invention.

[0130] Example 7

[0131] Example 7 prepares a battery with reference to Example 1, except that the parameters of the porous area of ​​the first conductive adhesive paper are different, specifically, the pore size a of the porous structure is 3.5 mm, the pore spacing b of the porous structure is 5 mm, and the porosity c of the porous area is 20%, which exceeds the protection scope of the present invention.

[0132] Example 8

[0133] Example 8 prepares a battery with reference to Example 1, except that the bonding force of the first conductive tape is 0.01 kgf / mm, which is lower than the bonding force of the third tape (the bonding force of the third tape in Example 1 is 0.02 kgf / mm); the parameters of the second conductive tape are the same as those of the first conductive tape.

[0134] Example 9 Group

[0135] The purpose of setting up the Example 9 group is to verify the influence of the values ​​of Ψ1 / η and Ψ2 / η on the battery performance.

[0136] Example 9a: Example 9a is carried out with reference to Example 2, except that the mass percentage of silicon element η is 2.2%.

[0137] Example 9b: Example 9b is carried out with reference to Example 2, except that the mass percentage of silicon element η is 1.5%.

[0138] Example 9c: Example 9b is carried out with reference to Example 3, except that the mass proportion of silicon element η is 40%.

[0139] Example 10

[0140] Example 7 A battery was prepared with reference 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 A battery was prepared with reference to Example 1, except that the first conductive tape and the second conductive tape were not attached in Comparative Example 1.

[0143] Comparative Example 2

[0144] Comparative Example 2 prepared a battery with reference to Example 1, except that in Comparative Example 2, ordinary insulating tape (acrylic tape) was attached to the first conductive tape and the second conductive tape in Example 1.

[0145] Comparative Example 3

[0146] Comparative Example 3a: A battery was prepared by referring to Example 5a, except that the thickness of the single-sided coating area in the positive electrode sheet was 25.5 μm.

[0147] Comparative Example 3b: A battery was prepared with reference to Example 5b, except that the thickness of the single-sided coating area in the positive electrode sheet was 100 μm.

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

[0149] Table 1

[0150]

[0151] Note: "*" indicates that the corresponding parameter in the embodiment or comparative example is the same as that in embodiment 1-1. " / " indicates that the corresponding parameter is not tested. In each embodiment and comparative example 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 tested for charge and discharge cycles at a 4.2C charge rate, a 0.7C discharge rate, and a voltage window of 3.0V-4.53V (using a blue power test device). The cycle was repeated for 1000 cycles, using the first cycle discharge capacity C1 and the 1000th cycle discharge capacity C 1000 Calculate the capacity retention rate: C 1000 / C1×100%.

[0154] ii) During the cycling process, monitor whether the battery is short-circuited (test 100 batteries) and calculate the short-circuit rate.

[0155] iii) After completing the cycle in i), the battery is disassembled to observe whether the current collector (the portion from the boundary between the single-sided coating area and the double-sided coating area to the winding tail end) is broken.

[0156] Table 2

[0157]

[0158] Note: In the battery prepared in each embodiment and comparative example, the positive electrode current collector broke at the second arc segment and the third arc segment during the cycle test.

[0159] As can be seen from Table 2, compared with the comparative example, the battery of the present invention has a conductive adhesive tape pasted on the part of the positive electrode sheet that is easy to break, ensuring that the positive electrode sheets of different thicknesses match the first conductive adhesive tape with corresponding conductive properties, so that the first conductive adhesive tape can still maintain a conductive path when the positive electrode sheet breaks, thereby improving the capacity retention rate of the battery. In addition, the battery of the comparative example has a current collector that breaks during the cycle process, and the burrs generated by the current collector breakage will pierce the diaphragm, thereby causing the battery to short-circuit. After the conductive adhesive tape is pasted on the battery of the present invention, the short-circuit rate is significantly lower than that of the battery of the comparative example.

[0160] It should be noted that, in this article, the terms "comprise", "include" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise one..." do not exclude the presence of other identical elements in the process, method, article or device including the element. In addition, it should be pointed out that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in reverse order according to the functions involved, for example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0161] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A battery cell, characterized in that: It comprises a positive electrode sheet, a separator and a negative electrode sheet which are stacked and wound; 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 a first surface and a second surface arranged opposite to each other, 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, the tail end of the first positive electrode active layer exceeds the tail end of the second positive electrode active layer, and the portion of the first positive electrode active layer exceeding the second positive electrode active layer is the single-sided coating area; The battery cell comprises a straight area and an arc area connected to the straight area; the positive electrode sheet comprises a first arc segment, a second arc segment and a third arc segment located in the arc area, and a first straight segment, a second straight segment and a third straight segment located in the straight area, the first arc segment and the second arc segment are both 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 electrode sheet, the first arc segment is connected with the first straight segment, the second arc segment, the second straight segment, the third arc segment and the third straight segment in sequence, and the first straight segment, the second arc segment, the second straight segment and the third arc segment are all located in the single-sided coating area; The battery cell comprises a first conductive adhesive paper, which is arranged on the positive electrode current collector and covers the third arc segment, and two ends of the first conductive adhesive paper extend to the second straight segment and the third straight segment respectively along the winding tail end and the winding head end of the positive electrode sheet; The first conductive adhesive paper includes an adhesive layer, and the adhesive layer includes conductive particles; Based on the total mass of the adhesive layer of the first conductive adhesive paper, the mass proportion of the conductive particles of the first conductive adhesive paper is Ψ1%; the thickness of the single-sided coating area is h1 μm; Ψ1 and h1 satisfy: 30≤h1 / Ψ1≤2000.

2. The battery cell according to claim 1, characterized in that: The battery cell includes a second conductive adhesive paper, which is arranged on the positive electrode current collector and covers the second arc segment, and two ends of the second conductive adhesive paper extend to the first straight segment and the second straight segment respectively along the winding tail end and the winding head end of the positive electrode sheet; The second conductive adhesive paper comprises an adhesive layer, and the adhesive layer comprises conductive particles; Based on the total mass of the adhesive layer of the second conductive adhesive paper, the mass proportion of the conductive particles of the second conductive adhesive paper is Ψ2%; Ψ2 and h1 satisfy: 30≤h1 / Ψ2≤2000.

3. The battery cell according to claim 2, characterized in that: Ψ1 and h1 satisfy: 30≤h1 / Ψ1≤800; and / or, Ψ2 and h1 satisfy: 30≤h1 / Ψ2≤800; And / or, h1 satisfies: 25μm≤h1≤100μm.

4. The battery cell according to claim 2, characterized in that: Based on the total mass of the negative electrode active material, the mass proportion of silicon is recorded as η%, and Ψ1 and η satisfy: 0.2≤Ψ1 / η≤40; and / or, Ψ2 and η satisfy: 0.2≤Ψ2 / η≤40; and / or, η satisfies: 1≤η≤50; and / or, Ψ1 satisfies: 5≤Ψ1≤85; And / or, Ψ2 satisfies: 5≤Ψ2≤85.

5. The battery cell according to claim 2, characterized in that: The thermal conductivity of the first conductive adhesive tape is recorded as K1 W / (m·k), and the thermal conductivity of the second conductive adhesive tape is recorded as K2 W / (m·k); Ψ1 and K1 satisfy: 15≤K1 / Ψ1≤40, and / or, Ψ2 and K2 satisfy: 15≤K2 / Ψ2≤40; And / or, K1 satisfies: 2≤K1≤32; And / or, K2 satisfies: 2≤K2≤32.

6. The battery cell according to claim 2, characterized in that: The resistance of the first conductive adhesive tape is recorded as R1Ω, the resistance of the second conductive adhesive tape is recorded as R2Ω, and the resistance of the single-sided coating area is recorded as R ^ Ω; R1 and R ^ Satisfies: R1≤R ^ , and / or, R2 and R ^ Satisfy: R2≤R ^ ; And / or, R1 and h1 satisfy: 1<R1 / h1<35, and / or, R2 and h1 satisfy: 1<R2 / h1<35.

7. The battery cell according to claim 2, characterized in that: The positive electrode sheet also includes a positive electrode 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 collector empty foil area is located in the first arc segment. The battery cell also includes a third adhesive paper, one end of the third adhesive paper is bonded to the first positive electrode active layer of the single-sided coating area, and the other end of the third adhesive paper is bonded to the positive electrode collector empty foil area, the bonding strength of the first conductive adhesive paper is ≥ the bonding strength of the third adhesive paper, and / or the bonding strength of the second conductive adhesive paper is ≥ the bonding strength of the third adhesive paper.

8. The battery cell according to claim 1 or 2, characterized in that: The first conductive adhesive tape at one end of the second straight section may be connected to or not connected to the second conductive adhesive tape at one end of the second straight section.

9. The battery cell according to claim 1 or 2, characterized in that: Along the winding direction, the total length of the first conductive adhesive tape and the second conductive adhesive tape is recorded as W1 mm, the total length of the second arc segment and the third arc segment is recorded as W2 mm, and the total length of the first straight segment and the second straight segment is recorded as W3 mm; W1, W2, W3 meet the following conditions: W2+4mm≤W1≤W2+W3; And / or, along the width direction of the positive electrode sheet, the width of the first conductive adhesive paper is recorded as L1 mm, the width of the second conductive adhesive paper is recorded as L2 mm, the width of the positive electrode sheet is recorded 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.

10. The battery cell according to claim 2, characterized in that: The conductive particles of the first conductive adhesive paper and the conductive particles of the second conductive adhesive paper each independently include at least one of a conductive metal material, a conductive non-metal material and a conductive compound; Preferably, the conductive metal material includes at least one of aluminum, copper, nickel, gold, silver, zinc, and iron; Preferably, the conductive non-metallic material includes a carbon material; the carbon material includes at least one of conductive carbon, conductive graphite, and carbon nanotubes; 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 further independently include a substrate layer, and the adhesive layer is disposed on a surface of 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 further independently include an adhesive and an auxiliary agent.

11. The battery cell according to claim 2, characterized in that: The portion of the first conductive adhesive paper located in the double-sided coating area is a porous area, and the porous area includes a porous structure; the porous structure satisfies at least one of the following conditions: (a) The pore size of the porous structure is denoted as a mm, where a satisfies: 0.05≤a≤3; (b) The pore spacing of the porous structure is denoted as b mm, where b satisfies: 0.1≤b≤4; (c) The porosity of the porous region is denoted as c%, where c satisfies: 25≤c≤80.

12. A lithium ion battery, characterized in that: A battery cell comprising the battery cell described in any one of claims 1 to 11.

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