Pole core and secondary battery

Abstract

In order to overcome the problem that the existing battery is difficult to consider low production cost, high energy density and high safety performance, the application provides an electrode core, which satisfies the following conditions: 2<=N<=500, 0.5<=T1<=50, 50<=T2<=500, 5.5<=L1<100, 5<L1'<100; wherein N is the number of layers of the bipolar electrode sheet on the cross section of the electrode core; T1 is the thickness of a single diaphragm, in units of mu m; T2 is the thickness of a single bipolar electrode sheet, in units of mu m; L1 is the width of the first blank area, in units of mm; L1' is the width of the second blank area, in units of mm. Meanwhile, the application also discloses a secondary battery comprising the above-mentioned electrode core.

Description

Technical Field

[0001] This invention belongs to the field of energy storage electronic components technology, specifically relating to an electrode core and a secondary battery. Background Technology

[0002] Against the backdrop of the rapid development of the new energy industry, lithium batteries, with their advantages of high capacity and long cycle life, have been widely used in electric vehicles, energy storage systems, portable electronic devices, and other fields. In the current mainstream lithium battery manufacturing process, the core components of the cell are the positive electrode, negative electrode, separator, and electrolyte. Among these, the preparation of the electrode is the key step that determines the performance, cost, and production efficiency of lithium batteries.

[0003] In existing technologies, the positive and negative electrodes of lithium batteries need to be manufactured using two separate production systems. The positive electrode typically uses aluminum foil as the current collector, and the positive active material (such as ternary materials, lithium iron phosphate, etc.), binder, and conductive agent are mixed in a certain proportion to form a slurry, which is then processed through coating, rolling, and slitting. The negative electrode uses copper foil as the current collector, and a similar process is used to process the negative active material (such as graphite, silicon-based materials, etc.). This "separate manufacturing" model has the following significant drawbacks:

[0004] Firstly, the investment cost of production equipment is high. Due to the significant differences in process parameters such as slurry formulation, coating thickness, drying temperature, and rolling strength between positive and negative electrode sheets, production equipment cannot be shared. Enterprises need to purchase core equipment such as coating machines, rolling presses, slitting machines, and slurry mixing tanks separately, resulting in a substantial increase in the total investment in equipment.

[0005] Secondly, production efficiency is low. Two independent production lines require separate operating teams, logistics systems, and quality inspection processes, leading to complex production scheduling and poor workflow coordination. For example, positive and negative electrode sheets need to be stacked with the separator in a specific order; if the production rhythm cannot be perfectly matched, one production line may experience a shutdown due to material shortages.

[0006] Third, material costs remain high. Positive electrode aluminum foil and negative electrode copper foil, as the core substrates of the electrode sheets, account for a significant portion of the electrode sheet material costs. As a highly conductive metal material, the market price of copper foil is significantly affected by fluctuations in copper prices; the continuous rise in copper prices in recent years has led to a continuous increase in the cost of negative electrode sheet materials. Although aluminum foil is relatively inexpensive, it requires high purity and thickness uniformity, making its procurement costs considerable.

[0007] Fourth, the improvement of battery energy density is limited. Pure metal foil (copper foil density is approximately 8.96 g / cm³, aluminum foil density is approximately 2.7 g / cm³) 3 The weight of the battery cell accounts for 8%-12% of the total weight of the battery cell, and its high density characteristics make it difficult to break through the bottleneck of the battery cell's mass energy density.

[0008] A composite current collector technology is currently available. This composite current collector uses polymer materials (such as PET, PP, PI, etc.) as the core substrate. Through processes such as vacuum coating, electroplating, and magnetron sputtering, copper or aluminum layers are deposited on both sides of the polymer substrate, thereby combining the lightweight characteristics of polymer materials with the electrical conductivity of metallic materials.

[0009] From the perspective of application effects, composite current collectors have indeed achieved technological breakthroughs in some fields: In terms of material costs, since the price of polymer substrates is much lower than that of pure copper foil and pure aluminum foil, and the thickness of the metal coating can be controlled at 1 / 3 to 1 / 2 of that of traditional pure metal foils, the amount of precious metals such as copper and aluminum used is greatly reduced, which can reduce material costs by 15% to 25% compared with traditional current collectors; In terms of weight control, the low density of polymer substrates (density is usually 1.0-1.4 g / cm³) makes the overall weight of composite current collectors 30% to 50% lighter than that of pure metal foils of the same size, which can increase the mass energy density of the battery cell by 5% to 8%, thus alleviating the weight bottleneck of traditional lithium batteries to a certain extent.

[0010] However, this type of composite current collector still has significant technical limitations and fails to fundamentally solve the core pain points in lithium battery production: On the one hand, composite current collectors have not broken through the limitations of the independent production model of positive and negative electrodes, and the problems of high equipment investment costs and low assembly efficiency still exist. On the other hand, as a new type of current collector structure, composite current collectors have a significant short-circuit safety risk. Specifically, this manifests in the following ways: First, the interfacial bonding force between the polymer substrate and the metal coating is weak. Under the mechanical stress of processes such as electrode coating and rolling, the metal coating is prone to peeling and cracking, and the detached metal debris may puncture the separator, causing an internal short circuit. Second, the heat resistance of the polymer substrate is lower than that of metal materials. When the battery experiences thermal runaway in its early stages, the polymer substrate is prone to softening and melting, leading to deformation and misalignment of the metal layers on both sides, forming local conductive channels and exacerbating the short-circuit risk. Third, the composite current collector is relatively thin. During electrode processing and battery assembly, if it is subjected to external impact or puncture by burrs, the coating is easily damaged, which can lead to a direct contact short circuit between the positive and negative electrodes. Summary of the Invention

[0011] To address the problem that existing batteries struggle to balance low production costs, high energy density, and high safety performance, this invention provides a core and a secondary battery.

[0012] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0013] On one hand, the present invention provides an electrode core comprising a plurality of bipolar electrodes and a plurality of separators. The plurality of bipolar electrodes are stacked sequentially, and the separators are disposed between adjacent bipolar electrodes. Each bipolar electrode comprises a composite current collector, a positive electrode material layer, and a negative electrode material layer. The composite current collector comprises a polymer layer, a first conductive layer, and a second conductive layer. The first conductive layer is located on one side surface of the polymer layer, and a first blank area is disposed between one end of the polymer layer and one end of the first conductive layer. The second conductive layer is located on the other side surface of the polymer layer, and a second blank area is disposed between the other end of the polymer layer and one end of the second conductive layer. The negative electrode material layer is located on the first conductive layer, and the positive electrode material layer is located on the second conductive layer. The electrode core satisfies the following conditions:

[0014] , And 2≤N≤500, 0.5≤T1≤50, 50≤T2≤500, 5.5≤L1<100, 5<L1'≤100;

[0015] Where N is the number of layers of bipolar electrodes on the cross-section of the electrode core;

[0016] T1 is the thickness of a single diaphragm, in μm;

[0017] T2 is the thickness of a single bipolar electrode, in μm;

[0018] L1 is the width of the first blank area, in mm;

[0019] L1' is the width of the second blank area, in mm.

[0020] Optionally, the electrode core satisfies the following conditions:

[0021] , .

[0022] Optionally, the number N of bipolar electrode layers on the core cross-section is 10 ≤ N ≤ 400; and / or,

[0023] The thickness T1 of a single diaphragm is 2.5 ≤ T1 ≤ 30; and / or,

[0024] The thickness T2 of a single bipolar electrode is 100 ≤ T2 ≤ 350; and / or,

[0025] The width L1 of the first blank area is 10.5 ≤ L1 < 75; and / or,

[0026] The width L1' of the second blank area is 10 < L1' ≤ 75.

[0027] Optionally, a first empty foil area is provided between one end of the first conductive layer and one end of the negative electrode material layer, and the width L2 of the first empty foil area is 0~5mm; a second empty foil area is provided between the other end of the first conductive layer and the other end of the negative electrode material layer; the width L3 of the second empty foil area and the width L1' of the second empty area satisfy: 5≤L3<L1'≤100.

[0028] Optionally, a third empty foil region is provided between one end of the second conductive layer and one end of the positive electrode material layer, and the width L2' of the third empty foil region is 0~5mm; a fourth empty foil region is provided between the other end of the second conductive layer and the other end of the positive electrode material layer; the width L3' of the fourth empty foil region and the width L1 of the first empty region satisfy 5.5≤L1<L3'≤100.

[0029] Optionally, the thickness of the composite current collector is 0.12~40μm.

[0030] Optionally, the thickness of the polymer layer is 0.1~30 μm.

[0031] Optionally, the thickness of the first conductive layer is 0.01~5.0 μm, and the thickness of the second conductive layer is 0.01~5.0 μm.

[0032] Optionally, the first conductive layer is a copper layer and the second conductive layer is an aluminum layer.

[0033] Optionally, both the first conductive layer and the second conductive layer are aluminum layers.

[0034] Optionally, on the other side surface of the polymer layer, the second conductive layer covers the area corresponding to the second blank area, and multiple second conductive layers are stacked in the corresponding area of ​​the second blank area for welding with the epitaxial positive electrode;

[0035] On one side surface of the polymer layer, the first conductive layer covers the area corresponding to the first blank area, and multiple first conductive layers are stacked in the corresponding area of ​​the first blank area for welding with the epitaxial negative electrode.

[0036] In another aspect, the present invention provides a secondary battery, including the electrode core as described above.

[0037] According to the electrode core provided by the present invention, a first conductive layer and a second conductive layer are respectively disposed on both sides of the polymer layer, resulting in a lightweight composite current collector with relatively low overall cost. By disposing a first blank area and a second blank area at different ends on both sides of the polymer layer, the first conductive layer and the second conductive layer are staggered and avoid each other, giving the bipolar electrode a structure with tabs on both sides. Based on this, a positive electrode material layer and a negative electrode material layer are respectively coated on both sides of the composite current collector, so that the battery production process only needs to produce one type of electrode, thereby greatly simplifying production, reducing equipment investment, and improving production efficiency.

[0038] Furthermore, addressing the challenge of balancing high energy density and high safety performance in composite current collector batteries, the inventors, based on the electrode core structure provided by this invention, conducted experiments with different parameters. They discovered that different numbers and thicknesses of bipolar electrodes, different thicknesses of separators, and different widths of the first and second blanking regions have a significant correlation with the energy density and short-circuit risk of the final secondary battery, especially regarding its resistance to mechanical shock. Further extensive experiments and data fitting revealed that when the number of bipolar electrode layers N, the separator thickness T1, the bipolar electrode thickness T2, the width of the first blanking region L1, and the width of the second blanking region L1' on the electrode core cross-section meet certain conditions... , When 2≤N≤500, 0.5≤T1≤50, 50≤T2≤500, 5.5≤L1<100, and 5<L1'≤100, the resulting secondary battery can have higher safety performance while having higher energy density. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the structure of the electrode core provided by the present invention;

[0040] Figure 2 This is a schematic diagram of the structure of the bipolar electrode provided by the present invention.

[0041] The reference numerals in the accompanying drawings are as follows:

[0042] 1. Bipolar electrode; 11. Composite current collector; 111. Polymer layer; 1111. First blank area; 1112. Second blank area; 112. First conductive layer; 1121. First empty foil area; 1122. Second empty foil area; 113. Second conductive layer; 1131. Third empty foil area; 1132. Fourth empty foil area; 12. Negative electrode material layer; 13. Positive electrode material layer; 2. Separator. Detailed Implementation

[0043] To make the technical problems solved, the technical solutions, and the beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0044] In the description of this invention, "the number N of bipolar electrode layers on the electrode core cross-section" refers to the number of bipolar electrode layers on the cross-section passing through the central axis of the electrode core. Specifically, when the electrode core is a stacked structure, the number N of bipolar electrode layers on the electrode core cross-section is the number of stacked bipolar electrode layers; when the electrode core is a wound structure, with the winding axis of the electrode core as the central axis, the number of bipolar electrode layers on the cross-section passing through the central axis of the electrode core is the number N of bipolar electrode layers on the electrode core cross-section.

[0045] See Figure 1 and Figure 2 As shown, an embodiment of the present invention provides an electrode core, including a plurality of bipolar electrodes 1 and a plurality of separators 2. The plurality of bipolar electrodes 1 are stacked sequentially, and the separators 2 are disposed between adjacent bipolar electrodes 1. Each bipolar electrode 1 includes a composite current collector 11, a positive electrode material layer 13, and a negative electrode material layer 12. The composite current collector 11 includes a polymer layer 111, a first conductive layer 112, and a second conductive layer 113. The first conductive layer 112 is located on one side surface of the polymer layer 111, and a first blank area 1111 is provided between one end of the polymer layer 111 and one end of the first conductive layer 112. The first blank area 1111 is the polymer layer 112. The exposed area on the sublayer 111, with one end of the polymer layer 111 flush with the other end of the first conductive layer 112; the second conductive layer 113 is located on the other side surface of the polymer layer 111, and a second blank area 1112 is provided between the other end of the polymer layer 111 and one end of the second conductive layer 113, the second blank area 1112 being the exposed area on the polymer layer 111, with one end of the polymer layer 111 flush with the other end of the second conductive layer 113; the negative electrode material layer 12 is located on the first conductive layer 112, and the positive electrode material layer 13 is located on the second conductive layer 113, the electrode core satisfying the following conditions:

[0046] , And 2≤N≤500, 0.5≤T1≤50, 50≤T2≤500, 5.5≤L1<100, 5<L1'≤100;

[0047] Where N is the number of layers of bipolar electrodes on the cross-section of the electrode core;

[0048] T1 is the thickness of a single diaphragm, in μm;

[0049] T2 is the thickness of a single bipolar electrode, in μm;

[0050] L1 is the width of the first blank area, in mm;

[0051] L1' is the width of the second blank area, in mm.

[0052] By setting a first conductive layer 112 and a second conductive layer 113 on both sides of the polymer layer 111, a lightweight composite current collector 11 with relatively low overall cost is obtained. By setting a first blank area 1111 and a second blank area 1112 at different ends on both sides of the polymer layer 111, the first conductive layer 112 and the second conductive layer 113 are staggered and avoid each other, and the bipolar electrode 1 has the structural feature of tabs on both sides. On this basis, the positive electrode material layer 13 and the negative electrode material layer 12 are respectively coated on both sides of the composite current collector 11, so that only one type of electrode needs to be produced in the battery production process, thereby greatly simplifying production, reducing equipment investment, and improving production efficiency.

[0053] Furthermore, addressing the issue of balancing high energy density and high safety performance in composite current collector 11 batteries, the inventors conducted experiments with different parameters based on the core structure provided by this invention. They discovered that different numbers and thicknesses of bipolar electrodes 1, different thicknesses of separators 2, and different widths of the first blank area 1111 and the second blank area 1112 have a significant correlation with the energy density and short-circuit risk of the final secondary battery, especially regarding the mechanical shock resistance of the secondary battery. Further experiments and data fitting revealed that when the number of bipolar electrode layers N, the thickness T1 of separator 2, the thickness T2 of bipolar electrode 1, the width L1 of the first blank area 1111, and the width L1' of the second blank area 1112 on the core cross-section meet certain conditions... , When 2≤N≤500, 0.5≤T1≤50, 50≤T2≤500, 5.5≤L1<100, and 5<L1'≤100, the resulting secondary battery can have higher safety performance while having higher energy density.

[0054] In a preferred embodiment, the electrode core satisfies the following conditions:

[0055] , .

[0056] When the number of bipolar electrode layers N, the thickness T1 of separator 2, the thickness T2 of bipolar electrode 1, the width L1 of the first blank area 1111, and the width L1' of the second blank area 1112 on the electrode core cross section further meet the above conditions, it is beneficial to further reduce the short circuit risk of the secondary battery and improve the energy density of the secondary battery.

[0057] In some embodiments, the number N of bipolar electrode layers on the core cross section can be 2, 28, 54, 81, 107, 133, 159, 185, 212, 238, 264, 290, 317, 343, 369, 395, 421, 448, 474, 500 or a range of two of these.

[0058] In a preferred embodiment, the number N of bipolar electrode layers on the core cross-section is 10≤N≤400.

[0059] In some embodiments, the thickness T1 of a single diaphragm 2 can be 0.5 μm, 3.1 μm, 5.7 μm, 8.3 μm, 10.9 μm, 13.5 μm, 16.1 μm, 18.7 μm, 21.3 μm, 23.9 μm, 26.6 μm, 29.2 μm, 31.8 μm, 34.4 μm, 37.0 μm, 39.6 μm, 42.2 μm, 44.8 μm, 47.4 μm, 50.0 μm, or a range between two of these.

[0060] In a preferred embodiment, the thickness T1 of a single diaphragm 2 is 2.5 ≤ T1 ≤ 30.

[0061] In some embodiments, the thickness T2 of a single bipolar electrode 1 can be 50 μm, 74 μm, 97 μm, 121 μm, 145 μm, 168 μm, 192 μm, 216 μm, 239 μm, 263 μm, 287 μm, 311 μm, 334 μm, 358 μm, 382 μm, 405 μm, 429 μm, 453 μm, 476 μm, 500 μm, or a range between two of these.

[0062] In a preferred embodiment, the thickness T2 of a single bipolar electrode 1 is 100≤T2≤350.

[0063] In some embodiments, the first blank area 1111 is a strip-shaped region extending along one end edge of the polymer layer 111, and the second blank area 1112 is a strip-shaped region extending along the other end edge of the polymer layer 111.

[0064] In the description of this invention, the "first blank area 1111" is defined by one end of the polymer layer 111 and one end of the first conductive layer 112, and the "width L1 of the first blank area 1111" refers to the distance between one end of the polymer layer 111 and one end of the first conductive layer 112; the "width L1' of the second blank area 1112", the "width L2 of the first blank foil area 1121", the "width L3 of the second blank foil area 1122", the "width L2' of the third blank foil area 1131" and the "width L3' of the fourth blank foil area 1132" can be understood in this definition.

[0065] In some embodiments, the width L1 of the first blank area 1111 can be 5.5mm, 10.5mm, 15.5mm, 20.5mm, 25.5mm, 30.5mm, 35.5mm, 40.5mm, 45.5mm, 50.5mm, 55.5mm, 60.5mm, 65.5mm, 70.5mm, 75.5mm, 80.5mm, 85.5mm, 90.5mm, 95.0mm, 99.0mm, or a range between two of these.

[0066] In a preferred embodiment, the width L1 of the first blank area 1111 is 10.5 ≤ L1 < 75.

[0067] In some embodiments, the width L1' of the second blank area 1112 can be 5.5mm, 10.5mm, 15.5mm, 20.5mm, 25.5mm, 30.5mm, 35.5mm, 40.5mm, 45.5mm, 50.5mm, 55.5mm, 60.5mm, 65.5mm, 70.5mm, 75.5mm, 80.5mm, 85.5mm, 90.5mm, 95.0mm, 100.0mm, or a range between two of these.

[0068] In a preferred embodiment, the width L1' of the second blank area 1112 is 10 < L1' ≤ 75.

[0069] In some embodiments, in two adjacent bipolar electrodes 1, the positive electrode material layer 13 of one bipolar electrode 1 is opposite to the negative electrode material layer 12 of the other bipolar electrode 1, and the separator 2 is disposed between the positive electrode material layer 13 and the negative electrode material layer 12.

[0070] In some embodiments, the projection of the negative electrode material layer 12 onto the polymer layer 111 lies within the projection area of ​​the first conductive layer 112 onto the polymer layer 111. The projection of the positive electrode material layer 13 onto the polymer layer 111 lies within the projection area of ​​the second conductive layer 113 onto the polymer layer 111.

[0071] In some embodiments, a first empty foil region 1121 is provided between one end of the first conductive layer 112 and one end of the negative electrode material layer 12, and the width L2 of the first empty foil region 1121 is 0~5mm; a second empty foil region 1122 is provided between the other end of the first conductive layer 112 and the other end of the negative electrode material layer 12; the first empty foil region 1121 and the second empty foil region 1122 are both exposed areas of the first conductive layer 112, and the width L3 of the second empty foil region 1122 and the width L1' of the second empty region 1112 satisfy: 5≤L3<L1'≤100.

[0072] By controlling the width L3 of the second empty foil region 1122 and the width L1' of the second blank region 1112 to satisfy 5≤L3<L1'≤100, on the one hand, sufficient space is ensured for subsequent welding operations of the negative electrode post, ensuring the stability of the welding effect and avoiding impedance problems caused by poor welding. On the other hand, it is beneficial to ensure that the edge of the negative electrode material layer 12 can cover the edge of the positive electrode material layer 13 when multiple bipolar electrode sheets 1 are stacked, thereby ensuring that lithium ions extracted from the positive electrode material layer 13 can be uniformly deposited in the negative electrode material layer 12, reducing the risk of lithium plating due to edge effects.

[0073] In some embodiments, a third empty foil region 1131 is provided between one end of the second conductive layer 113 and one end of the positive electrode material layer 13, and the width L2' of the third empty foil region 1131 is 0~5mm; a fourth empty foil region 1132 is provided between the other end of the second conductive layer 113 and the other end of the positive electrode material layer 13; the third empty foil region 1131 and the fourth empty foil region 1132 are both exposed areas of the second conductive layer 113, and the width L3' of the fourth empty foil region 1132 and the width L1 of the first blank region 1111 satisfy 5.5≤L1<L3'≤100.

[0074] By controlling the width L3' of the fourth empty foil region 1132 and the width L1 of the first blank region 1111 to satisfy 5.5≤L1<L3'≤100, on the one hand, sufficient space is ensured for subsequent positive electrode post welding operations, ensuring the stability of the welding effect and avoiding impedance problems caused by poor welding. On the other hand, it is beneficial to ensure that the edge of the negative electrode material layer 12 can cover the edge of the positive electrode material layer 13 when multiple bipolar electrode sheets 1 are stacked, thereby ensuring that lithium ions extracted from the positive electrode material layer 13 can be uniformly deposited in the negative electrode material layer 12, reducing the risk of lithium plating due to edge effects.

[0075] In some embodiments, the thickness of the composite current collector 11 is 0.12~40μm.

[0076] In some embodiments, the thickness of the polymer layer is 0.1~30 μm.

[0077] In some embodiments, the thickness of the first conductive layer 112 is 0.01~5.0 μm, and the thickness of the second conductive layer 113 is 0.01~5.0 μm.

[0078] In some embodiments, the polymer layer 111 includes one or more of polyethylene, polyethylene terephthalate, polyimide, polypropylene, polyethylene, polyamide, polyphenylene sulfide, and polyethylene naphthalate.

[0079] In some embodiments, the first conductive layer 112 and the second conductive layer 113 each independently comprise one or more of a metallic material, a carbon material, and a conductive polymer. The metallic material comprises one or more of copper, aluminum, gold, silver, iron, nickel, and zinc. The carbon material comprises one or more of graphene, amorphous carbon, carbon nanotubes, and carbon fibers. The conductive polymer comprises one or more of polyaniline, polythiophene, polyphenylene sulfide, polyacetylene, and polystyrene sulfonate.

[0080] In some embodiments, when the electrode core is applied to a lithium-ion battery, the first conductive layer 112 is a copper layer and the second conductive layer 113 is an aluminum layer.

[0081] In some embodiments, when the electrode core is applied to a sodium-ion battery, both the first conductive layer 112 and the second conductive layer 113 are aluminum layers.

[0082] The copper layer comprises elemental copper or a copper alloy; the aluminum layer comprises elemental aluminum or an aluminum alloy.

[0083] In some embodiments, a positive electrode post and a negative electrode post are also included. On the other side surface of the polymer layer 111, the second conductive layer 113 covers the area corresponding to the second blank area 1112. After multiple second conductive layers 113 are stacked in the corresponding area of ​​the second blank area 1112, they are used for welding with the epitaxial positive electrode.

[0084] On one side surface of the polymer layer 111, the first conductive layer 112 covers the area corresponding to the first blank area 1111, and multiple first conductive layers 112 are stacked in the corresponding area of ​​the first blank area 1111 for welding with the epitaxial negative electrode.

[0085] Another embodiment of the present invention provides a secondary battery comprising the electrode core as described above.

[0086] By employing the electrode core described above, equipment and material costs can be significantly reduced, production and assembly efficiency improved, safety performance such as short-circuit resistance enhanced, and mass energy density and electrochemical stability increased. Compared to secondary batteries using traditional electrode sheets or existing composite current collector electrode cores, this secondary battery exhibits superior overall performance and significantly enhances its market competitiveness in fields such as electric vehicles and energy storage systems.

[0087] In some embodiments, the secondary battery is a lithium-ion battery or a sodium-ion battery.

[0088] The present invention will be further illustrated by the following examples.

[0089] Table 1

[0090]

[0091] Example 1

[0092] This embodiment illustrates the lithium-ion battery and its preparation method disclosed in this invention, including the following operations:

[0093] PET with a thickness d of 4.4 μm was selected as the insulating polymer layer. On one side of the polymer layer, a first conductive layer of copper with a total thickness of 1 μm was obtained by magnetron sputtering followed by aqueous solution electroplating. A first blank area with a width of 35 mm was set between one end of the polymer layer and one end of the first conductive layer. On the other side of the polymer layer, a second conductive layer of aluminum with a thickness of 1 μm was formed by vacuum evaporation. A second blank area with an exposed width of 38 mm was set between the other end of the polymer layer and one end of the second conductive layer. The first blank area and the second blank area of ​​the polymer layer were not at the same end, resulting in a composite current collector.

[0094] Graphite was selected as the negative electrode active material. Graphite was mixed with a conductive agent, binder and solvent to obtain a uniform mixture, which was then formulated into a negative electrode slurry. The negative electrode slurry was coated on one side of the composite current collector with the first conductive layer. After baking, an electrode sheet coated with a negative electrode material layer was obtained. The negative electrode material layer did not completely cover the first conductive layer. A first empty foil area was set between one end of the first conductive layer and one end of the negative electrode material layer. The width of the first empty foil area L2 was 1 mm. A second empty foil area was set between the other end of the first conductive layer and the other end of the negative electrode material layer. The width of the second empty foil area L3 was 37 mm.

[0095] Lithium iron phosphate was selected as the positive electrode active material. Lithium iron phosphate was mixed evenly with conductive agent, binder and solvent to prepare positive electrode slurry. The positive electrode slurry was coated on the side of the composite current collector with the second conductive layer. After baking, a bipolar electrode sheet coated with positive electrode material layer was obtained. The positive electrode material layer did not completely cover the second conductive layer. A third empty foil area was set between one end of the second conductive layer and one end of the positive electrode material layer. The width of the third empty foil area L2' was 1 mm. A fourth empty foil area was set between the other end of the second conductive layer and the other end of the positive electrode material layer. The width of the fourth empty foil area L3' was 37 mm.

[0096] The baked bipolar electrode sheet is rolled to obtain a thickness T2 of 160 μm;

[0097] Select a diaphragm thickness T1 of 14µm;

[0098] The bipolar electrode sheet and the diaphragm are stacked after rolling to obtain the electrode core. The cross-section of the electrode core contains 120 layers of bipolar electrode sheets, N. The positive electrode tab and the negative electrode tab are distributed on both sides of the electrode core.

[0099] The obtained electrode core is then placed into a casing, baked, injected with electrolyte, aged, formed, aged, and tested for capacity to obtain a lithium-ion battery.

[0100] Examples 2-10

[0101] Examples 2-10 illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences:

[0102] The number of bipolar electrode layers N, the thickness of the diaphragm T1, the thickness of the bipolar electrode T2, the width of the first blank area L1, the width of the second blank area L1', the width of the second empty foil area L3, and the width of the fourth empty foil area L3' on the cross-section of the electrode core are shown in Examples 2 to 10 in Table 1.

[0103] Comparative Examples 1-8

[0104] Comparative Examples 1-8 are used to compare and illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operation steps in Example 1, with the following differences:

[0105] The number of bipolar electrode layers N, the thickness of the diaphragm T1, the thickness of the bipolar electrode T2, the width of the first blank area L1, the width of the second blank area L1', the width of the second empty foil area L3, and the width of the fourth empty foil area L3' on the cross-section of the electrode core are shown in Comparative Examples 1 to 8 in Table 1.

[0106] Performance testing

[0107] The lithium-ion batteries prepared above were subjected to the following performance tests:

[0108] 1. Compression Test: After fully charging the battery, fix it on the compression test equipment and compress it along the direction parallel to the line connecting the positive and negative electrodes, at the middle position of the battery width. The compression column is a semi-cylinder with a radius of 75mm, and the length of the semi-cylinder is greater than the length of the battery. The compression speed is no more than 2mm / s. When the battery deformation reaches 30% or the compression force reaches 1000 times the weight of the battery, stop the compression. Hold the current position for 10 minutes and then stop the test. Observe for 60 minutes to see if the battery smokes, catches fire, explodes, or other phenomena. If not, dissect the battery to observe whether the electrode plates inside the core have burned or other thermal runaway phenomena. If any of the above phenomena occur, it means that the battery has failed. The number of failed batteries divided by the total number of test batteries is recorded as the compression failure ratio φ_compression.

[0109] 2. Energy density test: Charge the battery at a constant current and constant voltage of 0.5C to 3.65V, cut off the current at 0.05C to fully charge, and then discharge the battery at 0.5C to 2.5V. Record the discharge energy of the battery. Divide the obtained discharge energy by the mass or volume of the battery to obtain the mass or volumetric energy density.

[0110] The test results are entered into Table 2.

[0111] Table 2

[0112]

[0113] A comparison of the test results of Examples 1-10 and Comparative Examples 1-8 shows that Examples 1-10 meet the conditions defined in the invention. , Furthermore, 2≤N≤500, 0.5≤T1≤50, 50≤T2≤500, 5.5≤L1<100, 5<L1'≤100 (including the numerical ranges of the number of layers N, separator thickness T1, electrode thickness T2, blank area width L1 / L1', and the core proportional relationship), its overall performance is excellent: the extrusion failure rate is at a low level, both mass energy density and volumetric energy density remain at high values, and no lithium plating phenomenon occurs, demonstrating a good synergy between safety performance, energy density, and production and processing stability; while proportions 1 to 8 do not meet these requirements. , The occurrence of one or more problems, such as a significantly high rate of extrusion failure and extremely low energy density, indicates that the parameter conditions defined in this invention are necessary for achieving low battery failure, high energy density, high safety, and good processing performance.

[0114] Table 3

[0115]

[0116] Examples 11-16

[0117] Examples 11-16 illustrate the lithium-ion battery and its preparation method disclosed in this invention, including most of the operational steps in Example 1, with the following differences:

[0118] The number of bipolar electrode layers N, the thickness of the separator T1, the thickness of the bipolar electrode T2, the width of the first blank area L1, the width of the second blank area L1', the width of the second empty foil area L3, and the width of the fourth empty foil area L3' on the cross-section of the electrode core are shown in Examples 11 to 16 in Table 3.

[0119] Performance testing

[0120] The lithium-ion batteries obtained in Examples 1-16 were disassembled, and the positive and negative electrodes were removed for observation of lithium deposition. The lithium deposition on the surface of the negative electrode is recorded in Table 4:

[0121] Table 4

[0122]

[0123] A comparison of the test results of Examples 1-10 and Examples 11-16 shows that Examples 1-10 satisfy the size relationships of 5≤L3<L1'≤100 and 5.5≤L1<L3'≤100, and no lithium plating occurs, with normal performance such as energy density. Examples 11-16, however, do not satisfy these size relationships and all exhibit lithium plating at the electrode edges. This indicates that satisfying the conditions 5≤L3<L1'≤100 and 5.5≤L1<L3'≤100 helps to avoid lithium plating in the battery and ensures normal energy output.

[0124] 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, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An electrode core, characterized in that, The device comprises multiple bipolar electrodes and multiple separators. The multiple bipolar electrodes are stacked sequentially, and a separator is disposed between two adjacent bipolar electrodes. Each bipolar electrode includes a composite current collector, a positive electrode material layer, and a negative electrode material layer. The composite current collector includes a polymer layer, a first conductive layer, and a second conductive layer. The first conductive layer is located on one side surface of the polymer layer, and a first blank area is provided between one end of the polymer layer and one end of the first conductive layer. The second conductive layer is located on the other side surface of the polymer layer, and a second blank area is provided between the other end of the polymer layer and one end of the second conductive layer. The negative electrode material layer is located on the first conductive layer, and the positive electrode material layer is located on the second conductive layer. The electrode core satisfies the following conditions: , And 2≤N≤500, 0.5≤T1≤50, 50≤T2≤500, 5.5≤L1<100, 5<L1'≤100; Where N is the number of layers of bipolar electrodes on the cross-section of the electrode core; T1 is the thickness of a single diaphragm, in μm; T2 is the thickness of a single bipolar electrode, in μm; L1 is the width of the first blank area, in mm; L1' is the width of the second blank area, in mm; A first empty foil area is provided between one end of the first conductive layer and one end of the negative electrode material layer, and the width L2 of the first empty foil area is 0~5mm; a second empty foil area is provided between the other end of the first conductive layer and the other end of the negative electrode material layer; the width L3 of the second empty foil area and the width L1' of the second empty area satisfy: 5≤L3<L1'≤100; A third empty foil region is provided between one end of the second conductive layer and one end of the positive electrode material layer, and the width L2' of the third empty foil region is 0~5mm; a fourth empty foil region is provided between the other end of the second conductive layer and the other end of the positive electrode material layer; the width L3' of the fourth empty foil region and the width L1 of the first empty region satisfy 5.5≤L1<L3'≤100.

2. The electrode core according to claim 1, characterized in that, The electrode core satisfies the following conditions: ， 。 3. The electrode core according to claim 1, characterized in that, The number of bipolar electrode layers N on the core cross-section is 10 ≤ N ≤ 400; and / or, The thickness T1 of a single diaphragm is 2.5 ≤ T1 ≤ 30; and / or, The thickness T2 of a single bipolar electrode is 100 ≤ T2 ≤ 350; and / or, The width L1 of the first blank area is 10.5 ≤ L1 < 75; and / or, The width L1' of the second blank area is 10 < L1' ≤ 75.

4. The electrode core according to claim 1, characterized in that, The thickness of the composite current collector is 0.12~40μm.

5. The electrode core according to claim 1, characterized in that, The thickness of the polymer layer is 0.1~30μm.

6. The electrode core according to claim 1, characterized in that, The thickness of the first conductive layer is 0.01~5.0μm, and the thickness of the second conductive layer is 0.01~5.0μm.

7. The electrode core according to claim 1, characterized in that, The first conductive layer is a copper layer, and the second conductive layer is an aluminum layer.

8. The electrode core according to claim 1, characterized in that, Both the first conductive layer and the second conductive layer are aluminum layers.

9. The electrode core according to claim 1, characterized in that, On the other side surface of the polymer layer, the second conductive layer covers the area corresponding to the second blank area, and multiple second conductive layers are stacked in the corresponding area of ​​the second blank area for welding with the epitaxial positive electrode; On one side surface of the polymer layer, the first conductive layer covers the area corresponding to the first blank area, and multiple first conductive layers are stacked in the corresponding area of ​​the first blank area for welding with the epitaxial negative electrode.

10. A secondary battery, characterized in that, Includes the electrode core as described in any one of claims 1 to 9.

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