Winding battery cell suitable for cylindrical battery, preparation method of winding battery cell and cylindrical battery applying winding battery cell

Abstract

The invention provides a winding battery cell suitable for a cylindrical battery, a preparation method of the winding battery cell and the cylindrical battery applying the winding battery cell. The winding cell comprises a pole piece, the pole piece comprises a composite current collector, two surfaces of the composite current collector are respectively provided with a positive active material layer and a negative active material layer, and the surface of the positive active material layer or the negative active material layer is provided with an electronic insulating layer; the composite current collector comprises a base film, and a positive electrode current collection layer and a negative electrode current collection layer which are respectively arranged on two surfaces of the base film; the positive electrode current collection layer is compounded with the positive electrode active material layer, and the negative electrode current collection layer is compounded with the negative electrode active material layer; the wound battery cell is obtained by winding a pole piece in the direction that the negative electrode side faces inwards and the positive electrode side faces outwards; and the outer side of the pole piece positioned on the outermost circle of the winding battery cell does not contain the positive active material layer. Through the design, the energy density and the safety performance of the winding battery cell provided by the invention are improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, specifically to a wound cell suitable for cylindrical batteries, a method for preparing the same, and a cylindrical battery using the wound cell. Background Technology

[0002] Lithium-ion batteries possess advantages such as high energy density and long cycle life, and are widely used in various fields including portable electronic devices, power tools, energy storage, and electric vehicles. With the widespread application of lithium-ion batteries, higher demands are being placed on their energy density.

[0003] Currently, the cell structure of lithium-ion batteries is mostly stacked, wound, or Z-shaped. Regardless of the structure, the basic interface structure is a uniform and regular distribution of negative electrode, separator, and positive electrode. Both the positive and negative electrode sheets in this structure contain current collectors, and the positive and negative electrode sheets must be separated by a separator, resulting in a thicker cell and a lower energy density.

[0004] Existing wound battery cells typically consist of a positive electrode sheet, a negative electrode sheet, and two separators wound together. The positive electrode sheet comprises a positive current collector and positive active material layers coated on both sides of the current collector. The negative electrode sheet also comprises a positive current collector and positive active material layers coated on both sides of the current collector. The main function of the separators is to separate the positive and negative electrodes, preventing them from contacting and causing a short circuit. Simultaneously, the separators act as channels for lithium ion transport between the positive and negative electrodes, enabling rapid lithium ion conduction during charging and discharging. These wound battery cells have a large number of layers and are relatively thick, resulting in lower energy density, which cannot meet market demands. Furthermore, wound battery cells experience temperature increases due to abnormal use such as punctures, compression, and impacts. Conventional separators can thermally shrink at high temperatures, causing short circuits at the contact of the positive and negative electrodes, thus reducing the safety performance of the battery cell. Summary of the Invention

[0005] To address the issues of energy density and safety performance in existing battery cells consisting of a single positive electrode, a single negative electrode, and two separators, and to improve the energy density and safety performance of wound battery cells, this invention proposes a wound battery cell suitable for cylindrical batteries, its preparation method, and a cylindrical battery using this wound battery cell.

[0006] According to a first aspect of the present invention, a wound cell suitable for cylindrical batteries is provided. The wound cell includes an electrode sheet, the electrode sheet including a composite current collector, a positive electrode active material layer being disposed on one surface of the composite current collector and a negative electrode active material layer being disposed on the other surface, and an electronic insulating layer being disposed on the surface of either the positive electrode active material layer or the negative electrode active material layer; the composite current collector includes a base film, a positive electrode current collector layer and a negative electrode current collector layer, a positive electrode current collector layer being disposed on one surface of the base film and a negative electrode current collector layer being disposed on the other surface; the positive electrode current collector layer is composite with the positive electrode active material layer, and the negative electrode current collector layer is composite with the negative electrode active material layer; the side of the electrode sheet containing the positive electrode active material layer is designated as the positive electrode side, and the side of the electrode sheet containing the negative electrode active material layer is designated as the negative electrode side, and the wound cell is obtained by winding the electrode sheet in a direction with the negative electrode side facing inward and the positive electrode side facing outward; the outermost layer of the electrode sheet located on the outermost ring of the wound cell does not contain a positive electrode active material layer.

[0007] The wound battery cell provided by this invention integrates positive and negative active materials simultaneously in the composite current collector of the electrode sheet by designing the electrode sheet structure. Specifically, a positive active material layer is coated on one side of the composite current collector, and a negative active material layer is coated on the other side. The positive and negative active material layers are separated by an electronic insulating layer. Firstly, compared to conventional wound battery cells containing two electrodes and two separators, the wound battery cell provided by this invention has adjacent turns of electrodes with the positive and negative sides facing each other, which not only reduces the number of electrode layers and one electronic insulating layer in the wound battery cell, but also... The use of insulating film increases the energy density of wound cells and avoids the problem of short circuits caused by thermal shrinkage at high temperatures, which occurs when using conventional separators. Secondly, it greatly reduces the complexity of material management during the manufacturing process of wound cells, lowers the difficulty of controlling processing parameters such as the alignment of various materials during the winding process, and reduces the product scrap rate caused by processing errors such as misalignment between positive and negative electrode sheets during the winding process, thus improving the product yield and production efficiency of wound cells. Thirdly, the electrode sheets adopt a design where a positive current collector layer is provided on one surface of the base film and a negative current collector layer is provided on the other surface. The composite current collector of the layer can further reduce the risk of short circuit between the positive and negative electrodes when the wound cell is subjected to external forces such as puncture and collision. Fourth, compared with conventional wound cells containing two electrode sheets, coating the positive electrode active material layer and the negative electrode active material layer on both sides of the same electrode sheet can avoid the risk of lithium plating caused by the misalignment of the positive and negative electrode sheets due to expansion during use, thus improving the cycle life of the wound cell. Fifth, the wound cell is wound from the electrode sheet inward from the negative electrode side and outward from the positive electrode side, and the outermost electrode sheet of the wound cell does not contain the positive electrode active material layer. The outer electrode and its adjacent inner electrode are concentric circles. The radius of the outer electrode in the concentric circle of the wound cell is larger than that of the inner electrode. Therefore, within any central angle range of the concentric circles, the length of the outer electrode is slightly larger than that of the inner electrode to ensure that the wound cell is always negative-wrapped-positive. That is, the negative active material layer always wraps the positive active material layer in the concentric circle. When lithium ions escape from the positive active material layer and reach the negative active material layer, they can be embedded in the negative active material layer in time instead of being deposited on the surface of the negative active material layer. This reduces the risk of lithium plating on the negative electrode of the battery using this wound cell and improves the safety performance of the battery.

[0008] If the battery cell is wound with the electrodes inward from the positive electrode side and outward from the negative electrode side, the radius of the outer electrode in the concentric circle of the battery cell is larger than that of the inner electrode. Therefore, within any central angle range of the concentric circle, the length of the outer electrode is slightly larger than that of the inner electrode. The concentric circle of the battery cell is always positive-enveloping-negative, that is, the positive active material layer always envelops the negative active material layer. When lithium ions escape from the positive active material layer and reach the negative active material layer, they are difficult to embed into the negative active material layer in time, resulting in lithium plating on the negative electrode of the battery using this wound battery cell.

[0009] If a positive active material layer is provided on the outer side of the outermost electrode of the wound cell, then there is no negative active material layer opposite to the positive active material layer on the outermost electrode of the wound cell. After lithium ions are extracted from the positive active material layer, they are difficult to embed into the negative active material layer, which will eventually lead to lithium plating.

[0010] Preferably, the negative electrode active material layer extends beyond the positive electrode active material layer on both sides in the width direction, and the negative electrode active material layer extends beyond the positive electrode active material layer at both ends in the winding direction.

[0011] By extending the negative electrode active material layer beyond the positive electrode active material layer in both width and winding direction, the negative electrode active material layer can always cover the positive electrode active material layer, reducing the risk of lithium plating.

[0012] Preferably, the outermost electrode of the outermost ring of the wound cell does not contain a positive current collector layer.

[0013] By exposing the base film on the outermost side of the electrode sheet located on the outermost ring of the wound cell, when the wound cell provided by the present invention is applied to a cylindrical battery, the exposed base film can serve as an insulating structure between the wound cell and the battery casing, replacing the conventional mylar film, reducing the material usage in the cylindrical battery manufacturing process, increasing the energy density of the cylindrical battery, and improving the production efficiency of the cylindrical battery.

[0014] Preferably, the electronic insulating layer has a porous structure, and the porosity of the electronic insulating layer is 10-80%.

[0015] Preferably, the electronic insulating layer contains a sulfide solid electrolyte Li3PS4 and a binder styrene-butadiene rubber.

[0016] Preferably, the electronic insulating layer is composite with the negative electrode active material layer, and the electronic insulating layer completely covers the negative electrode active material layer.

[0017] By assembling an electronic insulating layer onto the negative electrode active material layer and ensuring that the electronic insulating layer completely covers the negative electrode active material layer, the actual ratio of negative electrode capacity to positive electrode capacity (N / P ratio) can be guaranteed to be close to the designed theoretical N / P ratio. This reduces the risk of lithium plating during cycling, thereby improving the safety performance of batteries using this wound cell. If the electronic insulating layer does not completely cover the negative electrode active material layer, the actual N / P ratio will be too low, and lithium plating will occur on the electrode during cycling. The deposition of lithium metal can easily form lithium dendrites, which can pierce the base film in the composite current collector, thus affecting the safety performance of batteries using this wound cell.

[0018] Preferably, the thickness of the positive electrode active material layer is ≥150μm.

[0019] Existing technologies improve battery energy density by fabricating thick electrodes (i.e., increasing the areal density of the surface active material in the current collector). The thickness of the positive electrode active material layer is designed to be over 150 μm when the electrode is discharged. In the wound cell of this cylindrical battery, the problem of the actual N / P ratio differing from the designed N / P ratio due to circumferential differences is more severe. The wound cell for cylindrical batteries provided by this invention is obtained by winding the electrode inward from the negative electrode side and outward from the positive electrode side, and the outermost electrode of the wound cell does not contain a positive electrode active material layer. Through the above design, the wound cell for cylindrical batteries provided by this invention can also be adapted to thick electrode technology, and can effectively solve the problems caused by the aforementioned thick electrode design.

[0020] Preferably, the base film is made of a high molecular polymer material.

[0021] Preferably, both the positive electrode current collector layer and the negative electrode current collector layer are metal layers.

[0022] Preferably, the thickness of the base film is h1, the thickness of the positive electrode current collector layer is h2, and the thickness of the negative electrode current collector layer is h3. h1, h2, and h3 satisfy the condition that h1 > h2 and h1 > h3.

[0023] The composite current collector in the electrode sheet of the wound cell uses a polymer material base film, and the thickness of the base film and the positive and negative electrode current collector layers are controlled within the above-mentioned range. This can reduce the unit volume weight of the composite current collector and further improve the energy density of the battery using this wound cell.

[0024] According to a second aspect of the present invention, a method for preparing a wound cell suitable for cylindrical batteries is provided, comprising the following steps:

[0025] S1. A positive current collector layer is composited on one surface of the base film, and a negative current collector layer is composited on the other surface to obtain a composite current collector;

[0026] S2. A positive electrode active material layer is composited on the surface of the positive electrode current collector layer of the composite current collector, and a negative electrode active material layer is composited on the surface of the negative electrode current collector layer of the composite current collector.

[0027] S3. An electronic insulating layer is composited on the surface of the positive electrode active material layer or the negative electrode active material layer to obtain an electrode sheet, wherein the side of the electrode sheet containing the positive electrode active material layer is the positive electrode side, and the side containing the negative electrode active material layer is the negative electrode side.

[0028] S4. The electrode sheet is wound in the direction of negative electrode side inward and positive electrode side outward to obtain a wound battery cell;

[0029] Among them, the outermost electrode sheet located on the outermost ring of the wound cell does not have a composite positive electrode active material layer.

[0030] Preferably, in S1, the positive electrode current collector layer and the negative electrode current collector layer are formed on the base film by one or more of the following methods: electroplating, chemical plating, magnetron sputtering, and vapor deposition.

[0031] According to a third aspect of the present invention, a cylindrical battery is provided, the cylindrical battery comprising the above-described wound cell suitable for cylindrical batteries or a wound cell prepared by the above-described method for preparing wound cells suitable for cylindrical batteries.

[0032] Applying the wound cell provided by this invention to cylindrical batteries can improve the energy density, cycle life, and safety performance of cylindrical batteries. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of the wound battery cell provided in Example 1.

[0034] The attached figures are labeled as follows: 1 composite current collector, 2 base film, 3 positive electrode current collector layer, 4 negative electrode current collector layer, 5 positive electrode active material layer, 6 negative electrode active material layer, and 7 electronic insulating layer. Detailed Implementation

[0035] The technical features of the technical solution provided by the present invention will be further clearly and completely described below with reference to specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] Example 1

[0037] A cylindrical battery includes a wound cell and a conventional lithium battery electrolyte. A portion of the wound cell's structure is shown below. Figure 1As shown, the wound battery cell includes an electrode sheet, which includes a composite current collector 1. A positive electrode active material layer 5 is disposed on one surface of the composite current collector, and a negative electrode active material layer 6 is disposed on the other surface. An electronic insulating layer 7 is disposed on the surface of the negative electrode active material layer 6, and the electronic insulating layer 7 completely covers the negative electrode active material layer 6. The composite current collector 1 includes a base film 2, a positive electrode current collector layer 3, and a negative electrode current collector layer 4. The positive electrode current collector layer 3 is disposed on one surface of the base film 2, and the negative electrode current collector layer 4 is disposed on the other surface. The positive electrode current collector layer 3 and the positive electrode active material layer 5 are composite... The negative electrode current collector layer 4 is combined with the negative electrode active material layer 6; the side of the electrode sheet containing the positive electrode active material layer 5 is the positive electrode side, and the side of the electrode sheet containing the negative electrode active material layer 6 is the negative electrode side. The wound cell is obtained by winding the electrode sheet in the direction of negative electrode side inward and positive electrode side outward; the outermost electrode sheet of the wound cell does not contain the positive electrode active material layer 5 and the positive electrode current collector layer 3; the negative electrode active material layer 6 extends beyond the positive electrode active material layer 5 on both sides in the width direction, and extends beyond the positive electrode active material layer 5 at both ends in the winding direction.

[0038] The wound battery cell provided in this embodiment is prepared through the following steps:

[0039] S1. A 1μm thick aluminum metal layer is laminated on one surface of a 6μm thick PET film (base film 2) to form a positive current collector layer 3, and a 1μm thick copper metal layer is laminated on the other surface to form a negative current collector layer 4, thus obtaining a composite current collector 1.

[0040] S2. The positive electrode active material LiNi 0.96 Co 0.02 Mn 0.02 O2, conductive agent (super P + single-walled carbon nanotubes, mass ratio 1:1), and binder polyvinylidene fluoride are mixed at a dry basis mass ratio of 96:2:2, and then N-methylpyrrolidone (NMP) solvent is added and mixed evenly. The amount of NMP solvent added is adjusted so that the viscosity of the positive electrode slurry is 3000-10000 mPa·s at a rotation speed of 12 rpm. The negative electrode active material artificial graphite, conductive agent super P, and binder (styrene-butadiene rubber and sodium carboxymethyl cellulose, mass ratio 1:1) are mixed at a mass ratio of 95:1:4, and then pure water solvent is added and mixed evenly to obtain the negative electrode slurry. The above positive electrode slurry is coated on the surface of the positive electrode current collector layer 3 of the composite current collector 1, and then dried and rolled to form a positive electrode active material layer 5 with a thickness of 140 μm. The above negative electrode slurry is coated on the surface of the negative electrode current collector layer 4 of the composite current collector 1, and then dried and rolled to form a negative electrode active material layer 6 with a thickness of 65 μm.

[0041] S3. The sulfide solid electrolyte Li3PS4 and the binder styrene-butadiene rubber were mixed in the solvent tetrahydrofuran (THF) at a weight ratio of 98:2 to prepare an electrolyte slurry. The slurry was coated on the glass surface, dried at 60°C, and then pressed at 50°C and 250MPa for 2 minutes to obtain a solid electrolyte film with a thickness of 40μm, namely the electronic insulating layer 7.

[0042] An electrode sheet is prepared by laminating the above-mentioned electronic insulating layer 7 onto the surface of the negative electrode active material layer 6, wherein the side of the electrode sheet containing the positive electrode active material layer 5 is the positive electrode side, and the side containing the negative electrode active material layer 6 is the negative electrode side.

[0043] S4. The electrode sheet is wound in a circular motion with the negative side facing inward and the positive side facing outward, for a total of 50 turns. The innermost circle has a radius of 3mm, thus producing a wound battery cell.

[0044] Example 2

[0045] This embodiment provides a cylindrical battery. Compared with Embodiment 1, the difference in structure is that the outermost electrode of the wound cell contains a positive current collector layer but does not contain a positive active material layer. Apart from the above differences, the materials, formulation ratios, and preparation operations used in this embodiment are strictly consistent with those in Embodiment 1.

[0046] Example 3

[0047] This embodiment provides a cylindrical battery. Compared with Embodiment 1, the difference in structure is: (1) an electronic insulating layer is provided on the surface of the positive electrode active material layer of the wound cell, and the electronic insulating layer completely covers the positive electrode active material layer; (2) in the preparation step S3 of the wound cell, an electronic insulating layer is composited on the surface of the positive electrode active material layer. Apart from the above differences, the materials, formulation ratios, and preparation operations used in this embodiment are strictly consistent with those in Embodiment 1.

[0048] Example 4

[0049] This embodiment provides a cylindrical battery. Compared with Embodiment 1, the difference in structure is that in step S1 of preparing the wound cell, the thickness of the positive electrode current collector layer is 180 mm and the thickness of the negative electrode current collector layer is 90 mm; in step S4 of preparing the wound cell, the number of winding turns is 38. Apart from the above differences, the materials, formulation ratios, and preparation operations used in this embodiment are strictly consistent with those in Embodiment 1.

[0050] Comparative Example 1

[0051] This comparative example provides a cylindrical battery, which differs from Example 1 in that the method for preparing the wound battery cell is different.

[0052] The wound battery cell used in this comparative example includes a positive electrode and a negative electrode, and its preparation method includes the following steps:

[0053] Preparation of positive electrode sheet: A metal layer (aluminum layer) with a thickness of 16μm was selected as the positive electrode current collector layer; the same formula as in Example 1 was used to prepare the positive electrode slurry and coated on both surfaces of the positive electrode current collector layer, and then dried and rolled to obtain the positive electrode sheet.

[0054] Preparation of negative electrode sheet: Select a metal layer (copper layer) with a thickness of 10μm to form a negative electrode current collector layer; select the same formula as in Example 1 to prepare a negative electrode slurry and coat it on both surfaces of the negative electrode current collector layer, dry and roll press to obtain a negative electrode sheet.

[0055] Select the same electronic insulating layer as in Example 1, and stack one negative electrode, one electronic insulating layer, one positive electrode, and one electronic insulating layer in sequence, and wind them with the negative electrode on the outside and the positive electrode on the inside to obtain a wound battery cell.

[0056] In step S4 of the winding cell preparation, the negative electrode is pre-wound 1 turn, then the positive electrode is wound 24.5 turns, and the negative electrode is wound 25.5 turns.

[0057] Apart from the differences mentioned above, the materials, formulation ratios, and preparation procedures used in this comparative example are strictly consistent with those in Example 1.

[0058] Comparative Example 2

[0059] This comparative example provides a cylindrical battery. Compared with Example 1, the difference in structure is: (1) the wound cell is obtained by winding the electrode sheet in a direction with the positive electrode side facing inward and the negative electrode side facing outward. The outermost electrode sheet of the wound cell does not contain a negative electrode active material layer and a negative electrode current collector layer; (2) in the preparation step S4 of the wound cell, the electrode sheet is wound in a direction with the positive electrode side facing inward and the negative electrode side facing outward to obtain the wound cell. Apart from the above differences, the materials, formulation ratios and preparation operations used in this comparative example are strictly consistent with those in Example 1.

[0060] Comparative Example 3

[0061] This comparative example provides a square battery. Compared with Example 1, the difference in construction is that in step S4 of the winding cell preparation, the electrode sheets are wound in a racetrack shape with the negative electrode side facing inward and the positive electrode side facing outward. A core hole with a major diameter of 12.8 mm and a minor diameter of 2.5 mm is left at the innermost winding, and a total of 32 turns are made. Then, the core is hot-pressed on both sides in a direction parallel to the major diameter to make the electrode sheets on both sides of the inner ring adhere together, eliminating the core hole and obtaining a flat core. Apart from the above differences, the materials, formulation ratios, and preparation operations used in this comparative example are strictly consistent with those in Example 1.

[0062] Comparative Example 4

[0063] This comparative example provides a square battery. Compared with Comparative Example 3, the difference in its structure is: (1) the wound cell is obtained by winding the electrode sheet in a direction with the positive electrode side facing inward and the negative electrode side facing outward. The outermost electrode sheet of the wound cell does not contain a negative electrode active material layer and a negative electrode current collector layer; (2) in the preparation step S4 of the wound cell, the electrode sheet is wound in a direction with the positive electrode side facing inward and the negative electrode side facing outward to obtain the wound cell. Apart from the above differences, the materials, formula ratios and preparation operations used in this comparative example are strictly consistent with those of Comparative Example 3.

[0064] Comparative Example 5

[0065] This comparative example provides a cylindrical battery, which differs from Comparative Example 2 in that: (1) the thickness of the positive electrode active material layer is 180 μm and the thickness of the negative electrode active material layer is 90 μm; (2) in the preparation step S4 of the winding cell, it is wound 38 times.

[0066] Apart from the differences mentioned above, the materials, formulation ratios, and preparation procedures used in this comparative example are strictly consistent with those in Comparative Example 2.

[0067] Test case

[0068] 1. Participants

[0069] This test example uses the batteries prepared in Examples 1-4 and Comparative Examples 1-5 as test subjects to conduct relevant performance tests.

[0070] 2. Test Content

[0071] (1) Energy density

[0072] At 25°C, the batteries prepared in Examples 1-4 and Comparative Examples 1-5 were charged and discharged for the first time at a current of 0.33C (i.e., the current value at which the theoretical capacity is completely discharged within 3 hours). The charging was constant current and constant voltage charging, with a termination voltage of 4.2V, a cutoff current of 0.05C, and a discharge termination voltage of 3.0V. After the batteries were left to rest for 24 hours, a charge and discharge test was performed under the same conditions. Constant current and constant voltage charging was performed at a current of 1C, with a termination voltage of 4.2V and a cutoff current of 0.05C. Discharge was performed at a current of 1C, with a discharge termination voltage of 3.0V. The cell discharge capacity C0 was recorded, and the corresponding cell weight W0 was measured. The battery weight energy density = discharge capacity C0 / cell weight W0.

[0073] (2) Cyclic performance

[0074] At 25°C, the batteries prepared in Examples 1-4 and Comparative Examples 1-5 were charged and discharged for the first time at a current of 0.33C (i.e., the current value at which the theoretical capacity is completely discharged within 3 hours). The charging was constant current and constant voltage charging, with a termination voltage of 4.2V, a cutoff current of 0.05C, and a discharge termination voltage of 3.0V. After the batteries were left to rest for 24 hours, a charge-discharge test was performed under the same conditions. Constant current and constant voltage charging was performed at a current of 1C, with a termination voltage of 4.2V and a cutoff current of 0.05C. Discharge was performed at a current of 1C, with a discharge termination voltage of 3.0V. The cell BOL (Before of life), i.e., the discharge capacity Cb at the first cycle, was recorded. Then, cycle life testing was performed under the test conditions of room temperature, 1C / 1C cycling, with a voltage range of 3.0-4.2V, and a 5-minute rest in between. The discharge capacity Ce was recorded during the cycle. The ratio of Ce to Cb is the cycle capacity retention rate, which is used to determine the degree of cycle life decay.

[0075] (3) Lithium plating

[0076] At 25°C, the batteries prepared in Examples 1-4 and Comparative Examples 1-5 were subjected to the above-mentioned cycle performance test. After 500 cycles, they were fully charged, i.e., charged with a constant current and constant voltage at a current of 0.5C, with a termination voltage of 4.2V and a cutoff current of 0.05C. The batteries were then disassembled in a disassembly chamber. The outermost negative electrode ring with the positive electrode opposite the negative electrode ring was selected. The un-lithiated area was golden yellow, and the lithium-plated area was purple or black. The surface lithium-plated area was photographed using a CCD camera to read the ratio of the lithium-plated area to the area of ​​the negative electrode ring.

[0077] (4) Puncture test

[0078] The mechanical piercing method uses a steel needle with a diameter of 8mm, which is pierced into the center of the side of the experimental sample battery at a speed of 25mm / s. A temperature monitoring point is set at 1.5cm away from the piercing point of the sample battery. The temperature change of the battery within 2 hours after the steel needle comes into contact with the battery is detected and read in real time by a temperature sensor.

[0079] 3. Experimental Results

[0080] Table 1. Test results of relevant battery performance.

[0081]

[0082]

[0083] The relevant performance test results of the batteries prepared in Examples 1-4 and Comparative Examples 1-5 are shown in Table 1.

[0084] Compared to Comparative Example 1, the cylindrical batteries provided in Examples 1-4 exhibit superior energy density and cycle performance. Furthermore, their lithium plating area and maximum temperature rise rate after puncture are lower than those in Comparative Example 1. This is primarily because, compared to the conventional wound cell in Comparative Example 1, which contains two electrodes and two separators, the wound cells in Examples 1-4 integrate both positive and negative electrode active materials within the composite current collector of the electrodes. This reduces the number of electrode layers and the use of an electronic insulating film, thereby increasing the energy density of the wound cell. It also avoids the problem of short circuits caused by thermal shrinkage at high temperatures during conventional separator use. Additionally, coating the positive and negative electrode active material layers on both sides of the same electrode prevents misalignment of the positive and negative electrodes due to expansion during use. The risk of lithium plating is reduced, and the cycle life of the wound cell is improved. The wound cell is wound with the electrode sheets inward from the negative electrode side and outward from the positive electrode side. The outermost electrode sheet of the wound cell does not contain a positive electrode active material layer. Each electrode sheet and its adjacent inner electrode sheet are concentric circles. The radius of the outer electrode sheet in the concentric circle of the wound cell is larger than that of the inner electrode sheet. Therefore, within any central angle range of the concentric circles, the length of the outer electrode sheet is slightly larger than that of the inner electrode sheet to ensure that the wound cell is always negative-encased positive. That is, the negative electrode active material layer always covers the positive electrode active material layer in the concentric circles. When lithium ions escape from the positive electrode active material layer and reach the negative electrode active material layer, they can be embedded in the negative electrode active material layer in time instead of being deposited on the surface of the negative electrode active material layer. This reduces the risk of lithium plating on the negative electrode of the batteries provided in Examples 1 to 4 and improves the safety performance of the battery.

[0085] Compared to Example 1, the electronic insulation layer of the cylindrical battery cell provided in Example 3 is located on the positive electrode side. The maximum temperature rise rate after battery puncture is comparable to that of Example 1, and the cycle performance is lower than that of Example 1. The lithium plating area ratio is higher than that of Example 1. This is mainly because the electronic insulation layer of the cylindrical battery cell provided in Example 3 is located on the positive electrode side. During battery cycling, the solvent in the electronic insulation layer may evaporate, causing the size of the electronic insulation layer to decrease. At this time, the electronic insulation layer may not be able to completely cover the active material layer on the positive electrode side, resulting in fewer effective ion transport paths, which in turn leads to a decrease in battery cycle performance, an increase in lithium plating, and even a risk of internal short circuit. Example 4... The thickness of the negative electrode active material layer and the positive electrode active material layer in the wound cell of the supplied cylindrical battery is relatively large, at 90μm and 180μm respectively. The test results show that the lithium plating area accounts for only 0.9%. The above results indirectly indicate that the problem of the difference between the actual N / P ratio and the designed N / P ratio caused by the circumferential difference in the wound cell of the cylindrical battery due to the thick electrode is more serious. The wound cell of the cylindrical battery provided in Example 4 is obtained by winding the electrode sheet in the direction of negative electrode side inward and positive electrode side outward. The outer side of the electrode sheet located on the outermost ring of the wound cell does not contain the positive electrode active material layer. It is also suitable for thick electrode technology and can effectively solve the problems caused by the thick electrode design mentioned above.

[0086] Compared to Example 1, the cylindrical battery cell provided in Comparative Example 2 is obtained by winding the electrode sheets in a direction with the positive electrode side facing inward and the negative electrode side facing outward. Test results show that the cycle performance of the cylindrical battery in Comparative Example 2 is significantly lower than that in Example 1, and the lithium plating area ratio is significantly higher. This is mainly because the cylindrical battery cell in Comparative Example 2 is wound by winding the electrode sheets in a direction with the positive electrode side facing inward and the negative electrode side facing outward. In the concentric circles of the wound cell, the radius of the outer electrode sheet is larger than that of the inner electrode sheet. Therefore, within any central angle range of the concentric circles, the length of the outer electrode sheet is slightly larger than that of the inner electrode sheet. The concentric circles of the wound cell always have a positive-to-negative overlap, meaning the positive electrode active material layer initially... The negative electrode active material layer is ultimately wrapped around the positive electrode active material layer. When lithium ions escape from the positive electrode active material layer and reach the negative electrode active material layer, they cannot be embedded in the negative electrode active material layer in time. This leads to lithium plating on the negative electrode of the battery using this wound cell, which significantly reduces the cycle performance of the battery. Compared with Comparative Example 2, the thickness of the negative electrode active material layer and the positive electrode active material layer in the wound cell of the cylindrical battery provided by Comparative Example 5 are both larger than those of Comparative Example 2, at 90μm and 180μm respectively. The lithium plating area of ​​the battery is also higher. This indicates that when the wound cell is obtained by winding the electrode sheet in the direction of positive electrode side inward and negative electrode side outward, the lithium plating situation of the battery with thick electrode structure is more serious.

[0087] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention, but such modifications or substitutions are all within the scope of protection of the present invention.

Claims

1. A wound cell suitable for cylindrical batteries, characterized in that: The wound cell includes an electrode sheet, the electrode sheet includes a composite current collector, one surface of the composite current collector is provided with a positive active material layer, the other surface is provided with a negative active material layer, and the surface of the positive active material layer or the negative active material layer is provided with an electronic insulating layer. The composite current collector includes a base film, a positive current collector layer, and a negative current collector layer. The positive current collector layer is provided on one surface of the base film, and the negative current collector layer is provided on the other surface. The positive electrode current collector layer is composited with the positive electrode active material layer, and the negative electrode current collector layer is composited with the negative electrode active material layer; The side of the electrode containing the positive electrode active material layer is designated as the positive electrode side, and the side of the electrode containing the negative electrode active material layer is designated as the negative electrode side. The wound cell is obtained by winding the electrode in a direction where the negative electrode side faces inward and the positive electrode side faces outward. The outer side of the electrode sheet located on the outermost ring of the wound cell does not contain the positive electrode active material layer.

2. The wound cell suitable for cylindrical batteries as described in claim 1, characterized in that: The negative electrode active material layer extends beyond the positive electrode active material layer on both sides in the width direction, and the negative electrode active material layer extends beyond the positive electrode active material layer at both ends in the winding direction.

3. The wound cell suitable for cylindrical batteries as described in claim 1, characterized in that: The outer side of the electrode located on the outermost ring of the wound cell does not contain the positive electrode current collector layer.

4. The wound cell suitable for cylindrical batteries as described in claim 1, characterized in that: The electronic insulating layer has a porous structure, and the porosity of the electronic insulating layer is 10-80%.

5. The wound cell suitable for cylindrical batteries as described in claim 1, characterized in that: The electronic insulating layer is composite with the negative electrode active material layer, and the electronic insulating layer completely covers the negative electrode active material layer.

6. The wound cell suitable for cylindrical batteries as described in claim 1, characterized in that: The thickness of the positive electrode active material layer is ≥150μm.

7. The wound cell suitable for cylindrical batteries as described in claim 1, characterized in that: The base film is made of a high molecular polymer material; Both the positive electrode current collector layer and the negative electrode current collector layer are metal layers.

8. A method for preparing a wound cell suitable for cylindrical batteries, characterized in that, Includes the following steps: S1. A positive current collector layer is composited on one surface of the base film, and a negative current collector layer is composited on the other surface to obtain a composite current collector; S2. A positive electrode active material layer is laminated on the surface of the positive electrode current collector layer of the composite current collector, and a negative electrode active material layer is laminated on the surface of the negative electrode current collector layer of the composite current collector; S3. An electronic insulating layer is laminated onto the surface of the positive electrode active material layer or the negative electrode active material layer to obtain an electrode sheet, wherein the side of the electrode sheet containing the positive electrode active material layer is the positive electrode side, and the side containing the negative electrode active material layer is the negative electrode side. S4. The electrode sheet is wound in a direction with the negative electrode side facing inward and the positive electrode side facing outward to obtain the wound battery cell; The outer side of the electrode sheet located on the outermost ring of the wound cell does not have the positive electrode active material layer laminated.

9. The method for preparing a wound cell suitable for cylindrical batteries as described in claim 8, characterized in that: In S1, the positive electrode current collector layer and the negative electrode current collector layer are formed on the base film by one or more of the following methods: electroplating, chemical plating, magnetron sputtering, and vapor deposition.

10. A cylindrical battery, characterized in that: The cylindrical battery includes a wound cell suitable for cylindrical batteries as described in any one of claims 1 to 7, or a wound cell prepared using the method for preparing a wound cell suitable for cylindrical batteries as described in any one of claims 8 to 9.

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