Lithium ion secondary battery structure and lithium ion secondary battery module comprising same

Abstract

The invention provides a lithium ion secondary battery structure and a lithium ion secondary battery module comprising the same, and relates to the technical field of lithium ion batteries. The battery structure comprises a first electrode unit and a second electrode unit which are stacked in the thickness direction of the battery, a negative electrode of the first electrode unit adopts a metal current collector to guarantee high conductivity and long cycle stability, and a negative electrode of the second electrode unit adopts a polymer-based composite current collector with metal coatings on two sides to provide thermal runaway fusing protection. And the outermost layer of the whole battery pack is the second electrode unit, so that safe starting priority is realized. According to the battery structure, conductivity and cycling stability are guaranteed through the first electrode unit, and thermal runaway early fusing and current blocking are realized through the second electrode unit, so that the effects of synergistically improving the safety and the output performance of the battery and prolonging the cycle life of the battery are realized; the problems that in the prior art, a composite current collector causes internal resistance increase, and circulation attenuation and essential safety deficiency of a metal current collector are difficult to consider are effectively relieved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and in particular to a lithium-ion secondary battery structure and a lithium-ion secondary battery module comprising the same. Background Technology

[0002] With technological advancements, rechargeable batteries have been widely used in portable electronic devices (such as mobile phones, digital cameras, and laptops), electric vehicles, electric bicycles, and other transportation sectors, and are showing great promise in energy storage systems. In new energy vehicles and energy storage systems, the market demand for high power output and low internal resistance in battery cells continues to increase.

[0003] Currently, the conventional manufacturing process of lithium-ion secondary batteries includes: coating a slurry containing electrode active materials onto an electrode current collector, drying, rolling, die-cutting, and winding (or stacking) to form an electrode; then assembling the positive electrode, negative electrode, and separator into an electrode assembly, injecting electrolyte, and encapsulating it in a battery casing to form a complete cell.

[0004] Currently, copper foil and aluminum foil are commonly used materials for electrode current collectors. Among them, copper foil is generally used as the current collector for the negative electrode. However, traditional metal current collectors pose safety hazards: when an internal short circuit occurs in the battery, the aluminum positive electrode current collector may come into direct contact with the negative electrode active material (such as lithium metal or lithium carbon material), triggering a violent exothermic reaction, and even causing a fire or explosion.

[0005] To improve safety, researchers are exploring the use of composite current collectors to replace traditional metal current collectors. These composite conductive current collectors are made by depositing a metal layer (such as copper) onto a polymer film, such as polyester (PET), as the substrate. In the event of localized overheating, the polymer substrate of this type of current collector can melt and shrink, cutting off the current path and thus suppressing the spread of thermal runaway.

[0006] However, in practical applications, it has been found that such composite current collectors not only have increased resistance, but also significantly increase the total resistance of the short-circuit loop when a short circuit occurs in contact with the negative electrode active material. Although this phenomenon is theoretically beneficial for limiting short-circuit current, it may delay the response of the protection circuit in safety verification. More seriously, the increase in the ohmic internal resistance of the entire battery pack leads to a decrease in rate performance, increased polarization, shortened cycle life, and a significant deterioration in output characteristics.

[0007] Therefore, there is an urgent need to develop a novel electrode structure that maintains high structural stability and good processability while taking into account intrinsic safety characteristics and excellent electrochemical output performance.

[0008] In view of this, the present invention is hereby proposed. Summary of the Invention

[0009] The primary objective of this invention is to provide a lithium-ion secondary battery structure that has the advantage of synergistically leveraging the output characteristics of a metal current collector and the safety function of a composite current collector, effectively balancing the battery's safety performance, output characteristics, and cycle life.

[0010] The second objective of this invention is to provide a lithium-ion secondary battery module.

[0011] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: This invention provides a lithium-ion secondary battery structure, the battery structure comprising: a first electrode unit and a second electrode unit, wherein both the first electrode unit and the second electrode unit independently include a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; wherein: The negative electrode of the first electrode unit is referred to as the negative electrode of the first electrode unit, and the negative electrode of the first electrode unit uses a metal current collector; The negative electrode of the second electrode unit is referred to as the negative electrode of the second electrode unit, and the negative electrode of the second electrode unit uses a composite current collector; the composite current collector is composed of a polymer substrate and metal plating layers located on both sides of the polymer substrate; The first electrode unit and the second electrode unit are stacked along the thickness direction of the battery, a separator is provided between the positive electrode and the negative electrode, and the outermost layer of the battery structure is the second electrode unit.

[0012] Furthermore, the ratio of the first electrode unit to the second electrode unit in the entire battery pack is 10:1 to 1:10, preferably 3:1 to 1:3.

[0013] Furthermore, the first electrode unit and the second electrode unit are arranged and stacked in a periodic sequence along the thickness direction of the battery. The periodic sequence arrangement includes one of the following: BABAB, BAAABB, BAAABAAAB, BABB, BABBB, BABBBB, BABABB, and BABBBBB, where A is the first electrode unit and B is the second electrode unit.

[0014] Furthermore, the surface of the metal current collector substrate of the first electrode unit has a protrusion and depression structure; Preferably, the metal current collector substrate is selected from one of copper foil, aluminum foil, stainless steel foil, nickel foil, titanium foil, silver foil, and aluminum-cadmium alloy foil.

[0015] Furthermore, the polymer substrate of the composite current collector in the second electrode unit is selected from at least one of polyethylene terephthalate substrate, polyethylene terephthalate substrate, polyethylene terephthalate substrate, and polyethylene naphthalate substrate.

[0016] Furthermore, the composite current collector of the second electrode unit leaves a blank in the tab region to form the tab of the second electrode unit; The metal current collector of the first electrode unit leaves a blank in the tab region to form the tab of the first electrode unit; The length of the first electrode unit tab is greater than the length of the second electrode unit tab.

[0017] Furthermore, the length of the first electrode unit tab is 10-20 mm longer than the length of the second electrode unit tab.

[0018] Furthermore, the battery structure also includes a negative electrode tab integrated welding structure and a positive electrode tab integrated welding structure, wherein: The integrated welding structure of the negative electrode tab includes a first welding area and a second welding area; The first welding area is formed by arranging and welding the second electrode unit tab and the first electrode unit tab side by side; The second welding area is obtained by welding the redundant section of the first electrode unit tab corresponding to the length difference between the first electrode unit tab and the second electrode unit tab as a conductive bridging path. The positive electrode tab integrated welding structure includes a third welding area, which is formed by welding the positive electrodes of the first electrode unit and the second electrode unit arranged side by side.

[0019] Furthermore, the width of the conductive bridging path in the second welding area is 50-70% of the width of the negative electrode metal current collector tab.

[0020] The present invention provides a lithium-ion secondary battery module, the module comprising multiple lithium-ion secondary battery structures as described above, and a module frame for fixing and electrically connecting the multiple lithium-ion secondary battery structures. In this system, the negative electrode tabs of each lithium-ion secondary battery structure are welded together and connected to the same external negative electrode busbar, and the positive electrode tabs are connected together to the same external positive electrode busbar.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a lithium-ion secondary battery structure, comprising: a first electrode unit and a second electrode unit, wherein each of the first and second electrode units independently includes a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes; wherein: the negative electrode of the first electrode unit uses a metal current collector, and the negative electrode of the second electrode unit uses a composite current collector, and the first and second electrode units are stacked along the thickness direction of the battery to form a lithium-ion secondary battery structure. The battery structure described in this application uses an alternating stacking structure of the first and second electrode units, wherein the negative electrode of the first electrode unit uses a metal current collector to ensure high conductivity and long cycle stability, and the negative electrode of the second electrode unit uses a polymer-based composite current collector with metal coatings on both sides to provide safety protection. This synergistic effect of the output characteristics of the metal current collector and the safety function of the composite current collector in the entire battery pack effectively balances the battery's safety performance, output characteristics, and cycle life.

[0022] The present invention also provides a lithium-ion secondary battery module, which includes multiple lithium-ion secondary battery structures as described above, and is fixed and electrically connected to them by a module frame; the negative electrode tabs of each battery structure are integrated and welded together to the same external negative electrode busbar, and the positive electrode tabs are also connected together to the same external positive electrode busbar; the lithium-ion secondary battery module realizes stable structural integration and balanced current output among multiple units, thereby improving the energy density and system reliability of the overall module. Attached Figure Description

[0023] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the structure of the first electrode unit and the second electrode unit provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the stacked structure of the first electrode unit and the second electrode unit provided in Embodiment 1 of the present invention; Figure 3 This is a schematic diagram showing the relationship between the lengths of the negative electrode tabs of the first electrode unit and the second electrode unit provided in Embodiment 1 of the present invention; Figure 4 This is a schematic diagram of the electrode tab welding structure of the lithium-ion secondary battery provided in Embodiment 1 of the present invention.

[0025] Icons: 100 - First electrode unit negative electrode; 110 - Metal current collector; 120 - Negative electrode active material layer; 200 - Positive electrode; 210 - Positive electrode substrate; 220 - Positive electrode active material layer; 300 - Separator; 400 - Second electrode unit negative electrode; 410 - Composite current collector; 411 - Polymer substrate; 412 - Metal plating; 413 - Second electrode unit tab; 111 - First electrode unit tab; 500 - First welding area; 600 - Second welding area; 700 - Third welding area. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to the 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.

[0027] According to one aspect of the present invention, a lithium-ion secondary battery structure is provided, the battery structure comprising: a first electrode unit and a second electrode unit, wherein the first electrode unit and the second electrode unit each independently include a positive electrode 200, a negative electrode, and a separator 300 disposed between the positive electrode 200 and the negative electrode; wherein: The negative electrode of the first electrode unit is denoted as the negative electrode 100 of the first electrode unit, and the negative electrode 100 of the first electrode unit uses a metal current collector 110. The negative electrode of the second electrode unit is designated as the negative electrode of the second electrode unit 400. The negative electrode of the second electrode unit 400 uses a composite current collector 410. The composite current collector 410 is composed of a polymer substrate 411 and a metal plating layer 412 located on both sides of the polymer substrate 411. The first electrode unit and the second electrode unit are stacked along the thickness direction of the battery, a separator 300 is provided between the positive electrode 200 and the negative electrode, and the outermost layer of the battery structure is the second electrode unit.

[0028] The present invention provides a lithium-ion secondary battery structure, the battery structure comprising: a first electrode unit and a second electrode unit, wherein the first electrode unit and the second electrode unit each independently include a positive electrode 200, a negative electrode and a separator 300 disposed between the positive electrode 200 and the negative electrode; wherein: the negative electrode 100 of the first electrode unit uses a metal current collector 110, and the negative electrode 400 of the second electrode unit uses a composite current collector 410, and the first electrode unit and the second electrode unit are stacked along the thickness direction of the battery to form a lithium-ion secondary battery structure.

[0029] The battery structure described above in this invention is configured by alternately stacking first electrode units and second electrode units. The negative electrode 100 of the first electrode unit uses a metal current collector 110 to ensure high conductivity and long cycle stability, while the negative electrode 400 of the second electrode unit uses a polymer-based composite current collector 410 with metal plating layers 412 on both sides to provide safety protection. This allows the output characteristics of the metal current collector 110 and the safety function of the composite current collector 410 to be synergistically utilized in the entire battery pack, effectively balancing the battery's safety performance, output characteristics, and cycle life. Furthermore, the outermost layer of the above periodic arrangement consists of second electrode units, forming an outer layer of protection in the battery thickness direction. This achieves priority blocking of external risks, balances the current path, stabilizes the thermal field distribution, and synergistically improves the overall safety performance and electrochemical consistency.

[0030] In a preferred embodiment of the present invention, the ratio of the first electrode unit to the second electrode unit in the entire battery pack is 10:1 to 1:10; the ratio can be 10:1, 5:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:5 or 1:10, or any achievable ratio between 10:1 and 1:10, such as 7:1, 4:1, 3:2, 1:1.5, 1:2.5, 1:4, etc.

[0031] Preferably, the ratio of the first electrode unit to the second electrode unit in the entire battery pack is 3:1 to 1:3.

[0032] In a preferred embodiment of the present invention, the first electrode unit and the second electrode unit are periodically arranged and stacked along the thickness direction of the battery; The periodic sequence arrangement includes one of the following: BABAB, BAAABB, BAAABAAAB, BABB, BABBB, BABBBB, BABABB, and BABBBBB, where A is the first electrode unit and B is the second electrode unit.

[0033] As a preferred embodiment, the above-mentioned periodic arrangement is beneficial to uniformly distribute the metal current collector 110 unit and the composite current collector 410 unit in the thickness direction of the battery, thereby balancing the current path, stabilizing the thermal field distribution, and synergistically improving the overall safety performance and electrochemical consistency.

[0034] In a preferred embodiment of the present invention, the metal current collector 110 substrate surface of the first electrode unit has a raised and recessed structure, which can enhance the interfacial bonding strength between it and the active material layer, thereby suppressing interfacial peeling during charging and discharging, and improving the stability and cycle reliability of the electrode structure.

[0035] In the above preferred embodiment, the metal current collector 110 substrate is selected from one of copper foil, aluminum foil, stainless steel foil, nickel foil, titanium foil, silver foil, and aluminum-cadmium alloy foil; In a preferred embodiment of the present invention, the polymer substrate 411 of the composite current collector 410 in the second electrode unit is selected from at least one of polyethylene terephthalate substrate, propylene terephthalate substrate, butylene terephthalate substrate, and polyethylene naphthalate substrate.

[0036] In a preferred embodiment of the present invention, the composite current collector 410 of the second electrode unit leaves a blank in the tab region (without negative electrode material coating) to form the tab 413 of the second electrode unit. The metal current collector 110 of the first electrode unit leaves a blank in the tab area (without negative electrode material coating) to form the tab 111 of the first electrode unit; The length of the first electrode unit tab 111 is greater than the length of the second electrode unit tab 413.

[0037] In a preferred embodiment, both the composite current collector 410 of the second electrode unit and the metal current collector 110 of the first electrode unit have reserved blanks in the tab area to form their respective tabs, and the tab length of the metal current collector 110 is greater than the tab length of the composite current collector 410. This structure provides the necessary physical basis for the subsequent electrical connection of the metal plating layers 412 on both sides of the composite current collector 410 through redundant segment stacking welding, thereby ensuring the integrity and reliability of the overall conductive path of the negative electrode.

[0038] In the preferred embodiment described above, the length of the first electrode unit tab 111 is 10mm to 20mm longer than the length of the second electrode unit tab 413; the length difference can be 10mm, 12mm, 15mm, 18mm or 20mm, or any value between 10mm and 20mm, such as 11.3mm, 14.7mm, 16.2mm, 19.5mm, etc.

[0039] In a preferred embodiment of the present invention, the battery structure further includes a negative electrode tab integrated welding structure and a positive electrode 200 tab integrated welding structure, wherein: The negative electrode tab integrated welding structure includes a first welding area 500 and a second welding area 600; The first welding area 500 is formed by arranging and welding the second electrode unit tab 413 and the first electrode unit tab 111 side by side. The second welding area 600 is obtained by welding the redundant section of the first electrode unit tab 111 corresponding to the length difference between the first electrode unit tab 111 and the second electrode unit tab 413 as a conductive bridging path. The integrated welding structure of the positive electrode 200 includes a third welding area 700, which is formed by welding the first electrode unit positive electrode 200 and the second electrode unit positive electrode 200 arranged side by side.

[0040] The second welding area 600 is obtained by welding the redundant section of the first electrode unit tab 111 corresponding to the length difference between the first electrode unit tab 111 and the second electrode unit tab 413 as a conductive bridging path, based on the length difference between the first electrode unit tab 111 and the second electrode unit tab 413. Here, the conductive bridge and the conductive bridging path are different representations of the same physical structure in the second welding area, and the solder mark is the process carrier for realizing this conductive structure. The conductive bridge describes the functional attributes of the structure, referring to a bridge-like conductive structure formed through the welding process that can achieve the bridging and conduction of electrical signals or currents. The physical carrier is the solder mark generated during welding, and its essential function is to connect the first electrode unit tab 111 and the second electrode unit tab 413. The metal plating on both sides of the composite current collector of the two electrode units achieves electrical connection, while simultaneously allowing the second electrode unit tab to form a complete, low-resistance conductive loop with the first electrode unit tab. The conductive bridging path describes the physical form and current flow of this structure. It refers to the specific current conduction path when current flows through the conductive bridge, from the metal plating on one side of the composite current collector, through the solder mark, to the metal plating on the other side, and into the overall negative electrode busbar structure. This path has specific dimensional limitations such as width and length (determined by the welding process and the size of the redundant section of the tab). The solder mark is the fusion mark formed by processes such as ultrasonic welding, and it is the physical entity of the conductive bridge. Simply put, the solder mark is the corresponding physical entity, the conductive bridge is the functional definition of this entity, and the conductive bridging path is the current conduction trajectory on this entity. All three point to the same welded structure in the second welding area.

[0041] In a preferred embodiment, the negative electrode tab integrated welding structure of the present invention has a first welding area 500 that rigidly integrates the highly conductive metal current collector 110 tab and the high-safety composite current collector 410 tab at a macroscopic level through side-by-side welding, forming a current-carrying foundation. The second welding area 600 utilizes the inherent length difference between the two to use the redundant section of the metal current collector 110 tab as a controllable conductive bridge, bridging the metal plating layers 412 on both sides of the composite current collector 410. The above-mentioned welding structure of the present invention is not a simple connection, but rather transforms the conductivity advantage of the metal current collector 110 in the battery thickness direction into an active empowerment of the safety function of the composite current collector 410, ensuring low-resistance conduction under normal operating conditions and reliable melting in the event of thermal runaway.

[0042] In the preferred embodiment described above, the width of the conductive bridging path of the second welding area 600 is 50% to 70% of the width of the tab of the negative electrode metal current collector 110; the width can be 50%, 55%, 60%, 65% or 70%, or any value between 50% and 70%, such as 52.3%, 58.7%, 64.1%, 69.5%, etc.

[0043] According to one aspect of the present invention, a lithium-ion secondary battery module is provided, the module comprising a plurality of the above-described lithium-ion secondary battery structures, and a module frame for fixing and electrically connecting the plurality of lithium-ion secondary battery structures. Among them, the negative electrode tabs of each lithium-ion secondary battery structure are welded together and connected to the same external negative electrode busbar, and the positive electrode 200 tabs are connected to the same external positive electrode 200 busbar.

[0044] The present invention also provides a lithium-ion secondary battery module, which includes multiple lithium-ion secondary battery structures as described above, and is fixed and electrically connected to them by a module frame; the negative electrode tabs of each battery structure are integrated and welded together to the same external negative electrode busbar, and the positive electrode tabs 200 are also connected to the same external positive electrode busbar 200; the lithium-ion secondary battery module realizes stable structural integration and balanced current output among multiple units, thereby improving the energy density and system reliability of the overall module.

[0045] The technical solution of the present invention will be further described below with reference to the embodiments.

[0046] Example 1 Figure 1 This is a schematic diagram of the structure of the first electrode unit and the second electrode unit provided in this embodiment; Figure 2 This is a schematic diagram of the stacked structure of the first electrode unit and the second electrode unit provided in this embodiment; Figure 3 This is a schematic diagram showing the relationship between the lengths of the negative electrode tabs of the first electrode unit and the second electrode unit provided in this embodiment. Figure 4 This is a schematic diagram of the electrode tab welding structure of the lithium-ion secondary battery provided in this embodiment.

[0047] See Figures 1-4 A lithium-ion secondary battery structure, the preparation method of which includes the following steps: (1) Electrode unit fabrication: First electrode unit: A negative electrode slurry was prepared by mixing graphite (95 wt%), carbon black (0.5 wt%), styrene-butadiene rubber (SBR) (3 wt%), and carboxymethyl cellulose (CMC) (1.5 wt%). The slurry was coated onto a 6 μm thick copper foil. The surface of the copper foil was etched with a 40% hydrochloric acid system copper chloride etching solution to form a fine raised and recessed structure to enhance the bonding strength with the active material layer. After coating, the foil was dried at 80 °C for 12 h and then rolled until the areal density of the negative electrode active material layer was 18 mg / cm², thus obtaining the first electrode unit negative electrode 100.

[0048] Lithium cobalt oxide (LCO) (97 wt%), carbon black (1 wt%) and polyvinylidene fluoride (PVdF) (2 wt%) were mixed in N-methylpyrrolidone (NMP) solvent to prepare positive electrode 200 slurry; the slurry was coated on a 10 μm thick aluminum foil and dried at 120 ℃ for 8 h to obtain the first electrode unit positive electrode 200.

[0049] Second electrode unit: The same negative electrode slurry as the first electrode unit is coated onto an 8 μm thick composite current collector 410. The composite current collector 410 consists of a polyethylene terephthalate (PET) substrate and copper plating layers on both sides of the substrate, wherein the PET substrate is 6 μm thick and the copper plating layers on both sides are 1 μm thick. A blank area is reserved on the negative electrode side as an electrode tab. After coating the negative electrode active material layer 120, it is dried at 80 °C for 12 h to obtain the negative electrode of the second electrode unit 400.

[0050] Positive electrode 200 and separator 300: The positive electrode 200 is a 10 μm aluminum foil coated with LCO slurry, that is, the positive electrode substrate 210 is aluminum foil and the positive electrode active material layer 220 is LCO slurry; The diaphragm 300 is a 10 μm thick polyolefin-based nonwoven fabric with an SRS material coating on the surface.

[0051] (2) Stacking and welding: Twelve first electrode units and twelve second electrode units are stacked alternately in a periodic sequence “BAAABB” (i.e., each second electrode unit is connected to three first electrode units and two second electrode units in sequence), forming a total of 24 electrode units; a diaphragm 300 is set between each group of positive electrode 200 and negative electrode to form an electrode assembly.

[0052] Perform integrated welding on the negative electrode tab: 1. Arrange each second electrode unit tab 413 and the adjacent first electrode unit tab 111 side by side along the width direction, and form a first welding area 500 by ultrasonic welding (pressure 0.4 MPa, welding time 0.6 s, amplitude 40 μm); 2. Based on the length difference between the first electrode unit tab 111 and the second electrode unit tab 413, the redundant section of the first electrode unit tab 111 corresponding to the length difference is used as a conductive bridging path to weld and obtain the second welding area 600. 3. The first electrode unit positive electrode 200 and the second electrode unit positive electrode 200 arranged side by side are welded to form the third welding area 700.

[0053] (3) Packaging: The welded electrode assembly is placed into an aluminum-plastic film soft-pack shell, and an electrolyte containing 1 mol / L LiPF6 in ethylene carbonate / dimethyl carbonate (volume ratio 1:1) is injected. After vacuum sealing, formation, and aging, a lithium-ion secondary battery structure is obtained.

[0054] Example 2 A lithium-ion secondary battery structure is prepared according to Example 1, the only difference being the stacking ratio and arrangement of the electrode units: Eight first electrode units and sixteen second electrode units are stacked alternately in a periodic sequence “BABABB” to form a total of 24 electrode units; a diaphragm 300 is set between each group of positive electrode 200 and negative electrode to form an electrode assembly.

[0055] Example 3 A lithium-ion secondary battery structure is prepared using a method essentially the same as in Example 1, differing only in the stacking ratio and arrangement of the electrode units: Four first electrode units and 20 second electrode units are stacked alternately in a periodic sequence “BABBBB” to form a total of 24 electrode units; a diaphragm 300 is set between each group of positive electrode 200 and negative electrode to form an electrode assembly.

[0056] Comparative Example 1 A lithium-ion secondary battery structure is prepared using a method essentially the same as in Example 1, differing only in the stacking ratio and arrangement of the electrode units: Twenty first electrode units and four second electrode units are stacked alternately in a periodic sequence “AAAAAB” (i.e., every five first electrode units are followed by one second electrode unit), forming a total of 24 electrode units; a diaphragm 300 is set between each group of positive electrode 200 and negative electrode to form an electrode assembly.

[0057] Comparative Example 2 A lithium-ion secondary battery structure is prepared using a method essentially the same as in Example 1, differing only in the stacking ratio and arrangement of the electrode units: Four first electrode units and 20 second electrode units are stacked alternately in a periodic sequence “ABBBBB” (i.e., each first electrode unit is followed by five second electrode units), forming a total of 24 electrode units; a diaphragm 300 is set between each group of positive electrode 200 and negative electrode to form an electrode assembly.

[0058] Comparative Example 3 A lithium-ion secondary battery structure is prepared in a manner that is basically the same as that in Example 1, except that it does not include a second electrode unit and the entire battery consists of 24 first electrode units.

[0059] Comparative Example 4 A lithium-ion secondary battery structure is prepared in a manner that is basically the same as that in Example 1, except that it does not include a first electrode unit and the entire battery consists of 24 second electrode units.

[0060] Experimental Example 1 To evaluate the performance of the lithium-ion secondary battery structures in the examples and comparative examples, the following experiments were conducted: (1) Initial resistance: The AC impedance of the secondary battery structure was measured at a frequency of 10 kHz; (2) Cycle life performance evaluation: Initial charge-discharge tests (single cycle) were performed on the secondary battery structure under room temperature conditions. During the charging phase, the battery was charged at a constant current rate of 1C to 50% capacity, followed by constant current and constant voltage charging at a rate of 0.7C to 100% capacity. The discharging phase was performed at a rate of 0.7C at 3.0V. After 300 charge-discharge cycles, the capacity retention rate was calculated using the following formula: Capacity retention rate (%) = (Discharge capacity during 300 charge-discharge cycles / Discharge capacity during 1 charge-discharge cycle) × 100%.

[0061] (3) Stability Test: A cylindrical rod with a diameter of 200 mm is placed on the secondary battery structure and dropped freely from a height of 600 mm to impact the battery. If the battery meets the NF (no fire) and NE (no explosion) conditions, it is considered qualified. The pass rate (%) is calculated based on the total number of tests. The evaluation statistics are shown in Table 1.

[0062] Table 1:

[0063] Note: In the stability test, 10 samples are selected for each test, meaning that 90% means that 9 out of 10 samples pass the stability test.

[0064] As shown in Table 1, the lithium-ion secondary battery structures of Examples 1-3 of the present invention all exhibit substantial improvements in safety, electrochemical performance, and cycle life. In terms of safety: all examples (with a pass rate of 90-100%) were significantly better than Comparative Example 3 (40%) with an all-metal structure, and significantly better than Comparative Example 1 (70%) with a similar proportion of the second electrode unit but without the "outermost layer is B" configuration, which confirms the effective suppression of thermal runaway propagation by the outer composite current collector 410 unit. In terms of electrochemical performance: the initial resistance of Examples 1-3 (13.9-15.8 mΩ) is much lower than that of Comparative Example 4 (24.5 mΩ) with a fully composite structure, and is also better than that of Comparative Example 2 (18.9 mΩ) with a higher proportion of the second electrode unit, indicating that the "length difference driven redundant bridging welding" effectively ensures the low resistance conduction of the double-sided coating of the composite current collector 410. Regarding cycle life: The capacity retention rates of Examples 1-3 (91.8-94.8%) not only comprehensively surpass those of Comparative Example 4 (79.9%) with the all-composite structure, but also for the first time surpass those of Comparative Example 3 (92.3%) with the all-metal structure, proving that the present invention has successfully overcome the performance degradation problem caused by the composite current collector 410 while maintaining high safety.

[0065] In summary, this invention, through the periodic stacking configuration of the first electrode unit and the second electrode unit in the battery thickness direction and the integrated welding structure of the negative electrode tab, breaks through the long-standing technical bottleneck of lithium-ion batteries in terms of "safety, performance and lifespan" at the single-cell level, and achieves the organic unity of intrinsic safety and high output characteristics.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A lithium-ion secondary battery structure, characterized in that, include: A first electrode unit and a second electrode unit, each of which independently includes a positive electrode (200), a negative electrode, and a diaphragm (300) disposed between the positive electrode (200) and the negative electrode; wherein: The negative electrode of the first electrode unit is referred to as the negative electrode of the first electrode unit (100), and the negative electrode of the first electrode unit (100) uses a metal current collector (110). The negative electrode of the second electrode unit is referred to as the negative electrode of the second electrode unit (400), and the negative electrode of the second electrode unit (400) uses a composite current collector (410); the composite current collector (410) is composed of a polymer substrate (411) and metal plating layers (412) located on both sides of the polymer substrate (411); The first electrode unit and the second electrode unit are stacked along the thickness direction of the battery, a separator (300) is provided between the positive electrode (200) and the negative electrode, and the outermost layer of the battery structure is the second electrode unit.

2. The lithium-ion secondary battery structure according to claim 1, characterized in that, The ratio of the first electrode unit to the second electrode unit in the entire battery pack is 10:1 to 1:10, preferably 3:1 to 1:

3.

3. The lithium-ion secondary battery structure according to claim 1, characterized in that, The first electrode unit and the second electrode unit are arranged and stacked in a periodic sequence along the thickness direction of the battery; The periodic sequence arrangement includes one of the following: BABAB, BAAABB, BAAABAAAB, BABB, BABBB, BABBBB, BABABB, and BABBBBB, where A is the first electrode unit and B is the second electrode unit.

4. The lithium-ion secondary battery structure according to claim 1, characterized in that, The metal current collector (110) substrate surface of the first electrode unit has a protrusion and depression structure; Preferably, the substrate of the metal current collector (110) is selected from one of copper foil, aluminum foil, stainless steel foil, nickel foil, titanium foil, silver foil, and aluminum-cadmium alloy foil.

5. The lithium-ion secondary battery structure according to claim 1, characterized in that, The polymer substrate (411) of the composite current collector (410) in the second electrode unit is selected from at least one of polyethylene terephthalate substrate, propylene terephthalate substrate, butylene terephthalate substrate, and polyethylene naphthalate substrate.

6. The lithium-ion secondary battery structure according to claim 1, characterized in that, The composite current collector (410) of the second electrode unit leaves a blank in the tab area to form the tab (413) of the second electrode unit. The metal current collector (110) of the first electrode unit leaves a blank in the tab area to form the tab (111) of the first electrode unit. The length of the first electrode unit tab (111) is greater than the length of the second electrode unit tab (413).

7. The lithium-ion secondary battery structure according to claim 6, characterized in that, The length of the first electrode unit tab (111) is 10-20 mm longer than the length of the second electrode unit tab (413).

8. The lithium-ion secondary battery structure according to claim 6, characterized in that, The battery structure also includes a negative electrode tab integrated welding structure and a positive electrode (200) tab integrated welding structure, wherein: The negative electrode tab integrated welding structure includes a first welding area (500) and a second welding area (600); The first welding area (500) is formed by arranging and welding the second electrode unit tab (413) and the first electrode unit tab (111) side by side; The second welding area (600) is obtained by welding the redundant section of the first electrode unit tab (111) corresponding to the length difference between the first electrode unit tab (111) and the second electrode unit tab (413) as a conductive bridging path. The positive electrode (200) tab integrated welding structure includes a third welding area (700), which is formed by welding the first electrode unit positive electrode (200) and the second electrode unit positive electrode (200) arranged side by side.

9. The lithium-ion secondary battery structure according to claim 8, characterized in that, The width of the conductive bridging path in the second welding area (600) is 50-70% of the width of the tab of the negative electrode metal current collector (110).

10. A lithium-ion secondary battery module, characterized in that, The module includes multiple lithium-ion secondary battery structures as described in any one of claims 1 to 9, and a module frame for fixing and electrically connecting multiple lithium-ion secondary battery structures. Among them, the negative electrode tabs of each lithium-ion secondary battery structure are connected to the same external negative electrode busbar after welding, and the positive electrode (200) tabs are connected to the same external positive electrode (200) busbar.

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