Step special-shaped battery cell, preparation method thereof and step special-shaped lithium ion battery

Abstract

The invention relates to a step special-shaped battery cell and a preparation method thereof and a step special-shaped lithium ion battery, the step special-shaped battery cell comprises a first battery cell unit and a second battery cell unit which are arranged in a stacked mode, and in the length direction and the width direction, the size of the first battery cell unit is larger than that of the second battery cell unit; the first battery cell unit and the second battery cell unit respectively comprise a first positive pole piece, a second positive pole piece, a first negative pole piece, a second negative pole piece and a diaphragm; the first positive pole piece and the second positive pole piece respectively and independently comprise a first positive active material, and the first negative pole piece and the second negative pole piece respectively and independently comprise a first negative active material; the second positive pole piece further comprises a second positive active material, and the second negative pole piece further comprises a second negative active material. According to the step special-shaped battery cell provided by the invention, by adding the high-rate second positive electrode active material and the high-rate second negative electrode active material, the current bearing capacity of the small second battery cell unit is effectively improved, and the current distribution between the small second battery cell unit and the high-rate second negative electrode active material is improved, so that the capacity retention ratio and the safety performance of the step special-shaped battery are greatly improved.

Description

Technical Field

[0001] This invention relates to the field of battery cell manufacturing technology, and in particular to a stepped irregular-shaped battery cell, its manufacturing method, and a stepped irregular-shaped lithium-ion battery. Background Technology

[0002] In the 3C consumer electronics industry, innovative products such as foldable screen phones, curved smartwatches, and uniquely shaped smart glasses are emerging in large numbers. The internal cavities of these devices, needing to accommodate flexible displays and multi-sensor integration, generally exhibit irregular stepped, curved, or irregularly shaped structures. Stepped, irregularly shaped lithium-ion batteries, with their customizable stepped electrode arrangement and casing design, can precisely fill the irregular cavities of devices, increasing energy density by 15% to 20% within the same volume. Therefore, they have become a core solution for battery selection in 3C products in recent years.

[0003] However, while the "irregular structure" of stepped irregular batteries offers advantages in spatial adaptability, it also gives rise to significant current carrying capacity imbalances. Its core structure integrates large and small cell units of different sizes through series or parallel connections (the higher steps correspond to large cells, and the lower steps to small cells). These two types of cells naturally differ in electrode size, heat dissipation conditions, and current carrying paths, resulting in a significant difference in current carrying capacity. During battery cycling, especially in high-rate charging and discharging scenarios (such as 2C fast charging and the high-current discharge of foldable phones during multitasking), current preferentially concentrates in areas with lower resistance. Smaller cell units, due to their smaller electrode area (typically only 30%~60% of that of large cells) and shorter heat dissipation paths (prone to heat accumulation and internal resistance fluctuations), often carry current densities exceeding their design thresholds. Small battery cells operating under overcurrent conditions for extended periods increase the risk of polarization, leading to temperature rise. Furthermore, in the later stages of cycling, this accelerates electrolyte decomposition and SEI film damage, causing an imbalance in the lithium-ion insertion / extraction rate on the negative electrode surface. Excess lithium ions cannot be inserted into the negative electrode lattice in time, resulting in the deposition of lithium dendrites on the negative electrode surface, which seriously threatens the safety and cycle life of the equipment.

[0004] In existing technologies, large and small cells of stepped irregular lithium-ion batteries usually use the same material system, and the capacity is matched only by adjusting the number of layers. However, this still cannot solve the problems of uneven current distribution and long-term overcurrent polarization of small cells.

[0005] Therefore, how to improve the long-term overcurrent polarization of small cells and the uneven current distribution in large and small cells are technical problems that urgently need to be solved. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention provides a stepped irregular-shaped battery cell, its preparation method, and a stepped irregular-shaped lithium-ion battery. By introducing additional high-rate positive and negative active materials into the positive and negative electrode plates of the small second cell unit in the stepped irregular-shaped battery cell, this invention effectively improves the current carrying capacity of the small second cell unit and regulates the uniformity of current distribution between the large first cell unit and the small second cell unit, thereby significantly improving the capacity retention and safety performance of the stepped irregular-shaped battery.

[0007] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a stepped irregularly shaped battery cell, the stepped irregularly shaped battery cell comprising a first battery cell unit and a second battery cell unit stacked together, wherein the size of the first battery cell unit is larger than the size of the second battery cell unit in both the length and width directions of the stepped irregularly shaped battery cell; The first cell unit includes a first positive electrode, a first negative electrode, and a separator; the second cell unit includes a second positive electrode, a second negative electrode, and a separator. The first positive electrode and the second positive electrode each independently include a first positive active material, and the first negative electrode and the second negative electrode each independently include a first negative active material; The second positive electrode also includes a high-rate second positive electrode active material, and the second negative electrode also includes a high-rate second negative electrode active material.

[0008] The high-rate second positive electrode active material of this invention refers to a material with a higher lithium-ion diffusion coefficient and electronic conductivity compared to the first positive electrode active material, specifically supporting stable charge and discharge at a rate of ≥1C. The high-rate second negative electrode active material of this invention refers to a material with a higher lithium-ion diffusion coefficient and electronic conductivity compared to the first negative electrode active material, specifically supporting stable charge and discharge at a rate of ≥5C.

[0009] This invention introduces high-rate positive and negative active materials into the positive and negative electrode plates of the small second cell unit in a stepped irregularly shaped battery cell. The high-rate positive active material has a higher lithium-ion diffusion coefficient and electronic conductivity, while the high-rate negative active material also has a high lithium-ion diffusion coefficient and a low lithium intercalation potential, both exhibiting high structural stability. This effectively improves the current carrying capacity of the small second cell unit; that is, compared to the large first cell unit, the small second cell unit can more easily carry a larger current, avoiding polarization and high temperature phenomena caused by local current overload. It also significantly reduces the impedance of the small second cell unit, narrowing the impedance difference with the large first cell unit, thereby achieving a more uniform current distribution between the first and second cell units and preventing overcurrent lithium deposition in the small cell unit during cycling. Therefore, by introducing additional high-rate positive and negative active materials into the small second cell unit, the capacity retention and safety performance of the stepped irregularly shaped battery can be significantly improved.

[0010] And / or, the first positive electrode active material includes lithium cobalt oxide.

[0011] And / or, the first negative electrode active material includes graphite.

[0012] And / or, the high-rate second positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium iron phosphate.

[0013] And / or, the high-rate second negative electrode active material includes at least one of soft carbon, composite hard carbon, or modified silicon carbon material.

[0014] As a preferred technical solution of the present invention, the modified silicon-carbon material includes carbon-coated silicon-oxygen-graphite composite material and / or carbon-coated nano-silicon-graphite composite material.

[0015] It should be noted that in the carbon-coated silicon-oxygen-graphite composite material and the carbon-coated nano-silicon-graphite composite material of the present invention, the carbon-coated silicon-oxygen and carbon-coated nano-silicon can be a tight core-shell structure in which the carbon material and the silicon-based material are in complete contact, or a yolk-shell structure with a certain buffer space between the carbon material and the silicon-based material. Both are applicable to the present invention, and those skilled in the art can make adaptive selections and adjustments according to actual conditions.

[0016] And / or, the first positive electrode and the second positive electrode each independently include a first conductive agent and a first binder.

[0017] It should be noted that the present invention does not impose specific requirements or special limitations on the types of the first conductive agent and the first binder in the positive electrode sheet. The types of conductive agents and binders conventional in the art are applicable to the present invention, and those skilled in the art can make adaptive selections and adjustments according to actual conditions.

[0018] And / or, the first negative electrode and the second negative electrode each independently include a second conductive agent and a second binder.

[0019] It should be noted that the present invention does not impose specific requirements or special limitations on the types of the second conductive agent and the second binder in the negative electrode sheet. The types of conductive agents and binders conventional in the art are applicable to the present invention, and those skilled in the art can make adaptive selections and adjustments according to actual conditions.

[0020] As a preferred technical solution of the present invention, with the total mass of the second positive electrode active coating in the second positive electrode sheet being 100wt%, the total content of the first positive electrode active material and the second positive electrode active material is 96wt%-98wt%, for example, 96wt%, 96.5wt%, 97wt%, 97.5wt%, or 98wt%, etc. With the total mass of the first positive electrode active material and the second positive electrode active material being 100wt%, the content of the second positive electrode active material is 20wt%-30wt%, for example, 20wt%, 22wt%, 25wt%, 28wt%, or 30wt%, etc., and the content of the first positive electrode active material is 70wt%-80wt%, for example, 70wt%, 72wt%, 75wt%, 78wt%, or 80wt%, etc.

[0021] In this invention, by controlling the content of the second positive electrode active material to be 20wt%-30wt%, a more balanced control of the cell capacity and charging rate of the large first cell unit and the small second cell unit can be achieved. If the content of the second positive electrode active material is too low, the current shunting effect of the small second cell unit will be insignificant, and the large negative electrode of the small second cell unit will result in obvious lithium plating in the first cell unit; if the content of the second positive electrode active material is too high, the cell capacity of the small second cell unit will be too small.

[0022] And / or, based on the total mass of the second positive electrode active coating in the second positive electrode sheet being 100wt%, the content of the first conductive agent is 1wt%-2wt%, for example, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, or 2wt%, etc.

[0023] And / or, based on the total mass of the second positive electrode active coating in the second positive electrode sheet being 100wt%, the content of the first binder is 1wt%-2wt%, for example, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, or 2wt%, etc.

[0024] As a preferred technical solution of the present invention, with the total mass of the second positive electrode active coating in the second negative electrode sheet being 100wt%, the total content of the first negative electrode active material and the second negative electrode active material is 96wt%-98wt%, for example, 96wt%, 96.5wt%, 97wt%, 97.5wt%, or 98wt%, etc. With the total mass of the first negative electrode active material and the second negative electrode active material being 100wt%, the content of the second negative electrode active material is 20wt%-30wt%, for example, 20wt%, 22wt%, 25wt%, 28wt%, or 30wt%, etc., and the content of the first negative electrode active material is 70wt%-80wt%, for example, 70wt%, 72wt%, 75wt%, 78wt%, or 80wt%, etc.

[0025] In this invention, by controlling the content of the second negative electrode active material to be 20wt%-30wt%, a more balanced control of the cell capacity and charging rate of the large first cell unit and the small second cell unit can be achieved. If the content of the second negative electrode active material is too low, the current shunting effect of the small second cell unit will be insignificant, and the negative electrode of the small second cell unit will exhibit obvious lithium plating phenomenon in the larger first cell unit; if the content of the second negative electrode active material is too high, the capacity of the small second cell unit will be too small.

[0026] And / or, based on the total mass of the second negative electrode active coating in the second negative electrode sheet being 100wt%, the content of the second conductive agent is 1wt%-2wt%, such as 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, or 2wt%, etc.

[0027] And / or, based on the total mass of the second negative electrode active coating in the second negative electrode sheet being 100wt%, the content of the second binder is 1wt%-2wt%, for example, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, or 2wt%, etc.

[0028] As a preferred technical solution of the present invention, with the total mass of the first positive electrode active coating in the first positive electrode sheet being 100wt%, the content of the first positive electrode active material is 96wt%-98wt%, such as 96wt%, 96.5wt%, 97wt%, 97.5wt%, or 98wt%.

[0029] And / or, based on the total mass of the first positive electrode active coating in the first positive electrode sheet being 100wt%, the content of the first conductive agent is 1wt%-2wt%, such as 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, or 2wt%, etc.

[0030] And / or, based on the total mass of the first positive electrode active coating in the first positive electrode sheet being 100wt%, the content of the first binder is 1wt%-2wt%, for example, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, or 2wt%, etc.

[0031] And / or, based on the total mass of the first negative electrode active coating in the first negative electrode sheet being 100wt%, the content of the first negative electrode active material is 96wt%-98wt%, such as 96wt%, 96.5wt%, 97wt%, 97.5wt%, or 98wt%.

[0032] And / or, based on the total mass of the first negative electrode active coating in the first negative electrode sheet being 100wt%, the content of the second conductive agent is 1wt%-2wt%, for example, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, or 2wt%, etc.

[0033] And / or, based on the total mass of the first negative electrode active coating in the first negative electrode sheet being 100wt%, the content of the second binder is 1wt%-2wt%, for example, 1wt%, 1.2wt%, 1.5wt%, 1.8wt%, or 2wt%, etc.

[0034] As a preferred embodiment of the present invention, the first positive electrode and the second positive electrode have the same areal density, both being 100 g / m². 2 -240g / m 2 For example, 100g / m 2 120g / m 2 150g / m 2 180g / m 2 200g / m 2 220g / m 2 Or 240g / m 2 wait.

[0035] And / or, the first negative electrode and the second negative electrode have the same areal density, and the areal density of both the first negative electrode and the second negative electrode is 60 g / m³. 2 -170g / m 2 For example, 60g / m 2 80g / m 2 100g / m2 120g / m 2 150g / m 2 Or 170g / m 2 wait.

[0036] And / or, the first positive electrode and the second positive electrode have the same compaction density, both being 3.7 g / cm³. 3 -4.5g / cm 3 For example, 3.7g / cm 3 3.8g / cm 3 3.9g / cm 3 4.0g / cm 3 4.1g / cm 3 4.2g / cm 3 4.3g / cm 3 4.4g / cm 3 Or 4.5g / cm 3 wait.

[0037] And / or, the first negative electrode and the second negative electrode have the same compaction density, and the areal density of both the first negative electrode and the second negative electrode is 1.58 g / cm³. 3 -1.8g / cm 3 For example, 1.58 g / cm³ 3 1.6g / cm 3 1.65g / cm 3 1.7g / cm 3 1.75g / cm 3 Or 1.8g / cm 3 wait.

[0038] As a preferred embodiment of the present invention, both the first battery cell unit and the second battery cell unit are stacked structures, or both the first battery cell unit and the second battery cell unit are wound structures.

[0039] And / or, when both the first cell unit and the second cell unit are stacked structures, the first cell unit includes at least one first positive electrode and at least one first negative electrode, and the second cell unit includes at least one second positive electrode and at least one second negative electrode.

[0040] And / or, the stepped irregular-shaped battery cell further includes a positive electrode tab and a negative electrode tab.

[0041] And / or, the first battery cell unit and the second battery cell unit are aligned at least at one end in the length and width directions, and the common plane of the sidewalls of the aligned ends is denoted as plane A. The positive electrode tab and the negative electrode tab protrude from the outside of the interface between the first battery cell unit and the second battery cell unit in plane A.

[0042] In this invention, the first battery cell unit and the second battery cell unit can be aligned at one end in the length direction, aligned at one end in the width direction, or aligned at one end in the length direction and at one end in the width direction. In this case, there are two A-planes. The positive electrode tab and the negative electrode tab protrude to the outside of the interface between the first battery cell unit and the second battery cell unit in either A-plane.

[0043] And / or, the capacity ratio of the second cell unit to the first cell unit is 0-1, and not 0, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1, etc.

[0044] And / or, the ratio of the electrode active material capacity of the second cell unit to that of the first cell unit is 0-1, and not 0, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.

[0045] And / or, the ratio of the current carrying capacity of the second cell unit to that of the first cell unit is 0-1, and not 0, for example, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.

[0046] And / or, the stepped irregular-shaped battery cell also includes an electrolyte.

[0047] Secondly, the present invention also provides a method for preparing a stepped irregularly shaped battery cell according to the first aspect, the method comprising the following steps: A first positive electrode, a first negative electrode, and a separator are assembled to obtain a first battery cell unit. A second positive electrode, a second negative electrode, and a separator are assembled to obtain a second battery cell unit. The first battery cell unit and the second battery cell unit are stacked to obtain a stepped irregular-shaped battery cell. In both the length and width directions of the stepped irregular-shaped battery cell, the size of the first battery cell unit is larger than the size of the second battery cell unit; The first positive electrode and the second positive electrode each independently include a first positive active material, and the first negative electrode and the second negative electrode each independently include a first negative active material; The second positive electrode also includes a high-rate second positive electrode active material, and the second negative electrode also includes a high-rate second negative electrode active material.

[0048] It should be noted that the assembly methods and structures of the first and second battery cell units in this invention are conventional assembly methods and structures of stacked or wound battery cells in the art. This invention does not impose specific requirements or special limitations, and those skilled in the art can make adaptive selections and adjustments according to actual conditions.

[0049] Thirdly, the present invention also provides a stepped irregular lithium-ion battery, the stepped irregular lithium-ion battery comprising a stepped irregular cell as described in the first aspect, or a stepped irregular cell and a housing prepared by the preparation method described in the second aspect, wherein the stepped irregular cell is encapsulated inside the housing.

[0050] Compared with the prior art, the present invention has at least the following beneficial effects: This invention introduces high-rate positive and negative active materials into the positive and negative electrode plates of the small second cell unit in a stepped irregularly shaped battery cell. The high-rate positive active material has a higher lithium-ion diffusion coefficient and electronic conductivity, while the high-rate negative active material also has a high lithium-ion diffusion coefficient and a low lithium intercalation potential, both exhibiting high structural stability. This effectively improves the current carrying capacity of the small second cell unit; that is, compared to the large first cell unit, the small second cell unit can more easily carry a larger current, avoiding polarization and high temperature phenomena caused by local current overload. It also significantly reduces the impedance of the small second cell unit, narrowing the impedance difference with the large first cell unit, thereby achieving a more uniform current distribution between the first and second cell units and preventing overcurrent lithium deposition in the small cell unit during cycling. Therefore, by introducing additional high-rate positive and negative active materials into the small second cell unit, the capacity retention and safety performance of the stepped irregularly shaped battery can be significantly improved. Attached Figure Description

[0051] Figure 1 This is a top view schematic diagram of the stepped irregular-shaped battery cell provided by the present invention.

[0052] Wherein, 1-first cell unit; 2-second cell unit; L1-length of the first cell unit; L2-length of the second cell unit; W1-width of the first cell unit; W2-width of the second cell unit; 3-positive electrode tab; 4-negative electrode tab. Detailed Implementation

[0053] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0054] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available products or can be prepared by known methods.

[0055] Figure 1 This is a top view of the stepped irregular-shaped battery cell provided by the present invention, including a first battery cell unit 1 and a second battery cell unit 2 stacked together, a positive electrode tab 3 and a negative electrode tab 4. In the length and width directions of the stepped irregular-shaped battery cell, the size of the first battery cell unit 1 is larger than the size of the second battery cell unit 2, that is, the length L1 of the first battery cell unit is larger than the length L2 of the second battery cell unit, and the width W1 of the first battery cell unit is larger than the width W2 of the second battery cell unit. The common plane of the sidewalls of the aligned ends of the first battery cell unit 1 and the second battery cell unit 2 in the length direction is denoted as plane A (not shown in the figure). The positive electrode tab 3 and the negative electrode tab 4 protrude from the outside of the interface between the first battery cell unit 1 and the second battery cell unit 2 in plane A.

[0056] Example 1 This embodiment provides a stepped irregular-shaped battery cell, which includes a first battery cell unit and a second battery cell unit stacked together, as well as a positive electrode tab and a negative electrode tab. The first battery cell unit and the second battery cell unit are stacked structures. In both the length and width directions of the stepped irregular-shaped battery cell, the size of the first battery cell unit is larger than the size of the second battery cell unit. The common plane of the sidewalls of the aligned ends of the first battery cell unit and the second battery cell unit in the length direction is denoted as plane A. The positive electrode tab and the negative electrode tab protrude from the outer side of the interface between the first battery cell unit and the second battery cell unit in plane A.

[0057] The first cell unit includes 18 first positive electrode plates (area density 200g / m³). 2 Compacted density 4.2 g / cm³ 3 ), 17 first negative electrode plates (area density 78g / m²) 2 Compacted density 1.75 g / cm³ 3 The first positive electrode comprises a 10 μm thick aluminum foil and a first positive active coating on one side of the aluminum foil. The first positive active coating comprises 98 wt% lithium cobalt oxide, 1 wt% conductive carbon black, and 1 wt% PVDF binder. The first negative electrode comprises an 8 μm thick copper foil and a first negative active coating on one side of the copper foil. The first negative active coating comprises 98 wt% graphite, 1 wt% conductive carbon black, and 1 wt% SBR-CMC binder (SBR and CMC mass ratio 1:1). The second cell unit includes 12 second positive electrode plates (area density 200g / m²). 2 Compacted density 4.2 g / cm³ 3 ), 11 second negative electrode plates (area density 78g / m²) 2 Compacted density 1.75 g / cm³ 3 ) and diaphragm. The second positive electrode comprises a 10μm thick aluminum foil and a second positive active coating on one side of the aluminum foil. The second positive active coating comprises 98wt% lithium cobalt oxide and NCM523 (wherein, based on a total mass of 100wt% lithium cobalt oxide and NCM523, the content of lithium cobalt oxide is 80wt% and the content of NCM523 is 20wt%), 1wt% conductive carbon black, and 1wt% PVDF binder. The second negative electrode comprises an 8μm thick copper foil and a second negative active coating on one side of the copper foil. The second negative active coating comprises 98wt% graphite and modified silicon-carbon composite material (Shanghai Shanshan Technology Co., Ltd., Si-G100, where, based on a total mass of 100wt% graphite and modified silicon-carbon composite material, the content of graphite is 80wt% and the content of modified silicon-carbon composite material is 20wt%), 1wt% conductive carbon black, and 1wt% SBR-CMC binder (SBR and CMC mass ratio 1:1).

[0058] The capacity ratio of the second cell unit to the first cell unit is 0.6, the capacity ratio of the electrode active material of the second cell unit to the first cell unit is 0.8, and the current carrying capacity ratio of the second cell unit to the first cell unit is 0.98.

[0059] This embodiment provides a method for preparing the stepped irregular-shaped battery cell, the method comprising the following steps: According to the above formula, lithium cobalt oxide, conductive carbon black and PVDF binder are dispersed in NMP to form a slurry, which is then coated onto a 10μm aluminum foil. After drying and rolling, a first positive electrode sheet is obtained. According to the above formula, lithium cobalt oxide, NCM523, conductive carbon black and PVDF binder are dispersed in NMP to form a slurry, which is then coated onto a 10μm aluminum foil. After drying and rolling, a second positive electrode sheet is obtained. According to the above formula, graphite, conductive carbon black, and SBR-CMC binder are dispersed in deionized water to form a slurry, which is then coated onto an 8μm copper foil. After drying and rolling, the first negative electrode sheet is obtained. According to the above formula, graphite, modified silicon-carbon composite material, conductive carbon black, and SBR-CMC binder are dispersed in deionized water to form a slurry, which is then coated onto an 8μm copper foil. After drying and rolling, the second negative electrode sheet is obtained. The first cell unit is obtained by assembling 18 first positive electrode plates, 17 first negative electrode plates and a separator. The second cell unit is obtained by assembling 12 second positive electrode plates, 11 second negative electrode plates and a separator. The first cell unit and the second cell unit are combined by applying double-sided hot melt adhesive, and then injected with electrolyte (1.1mol / L LiPF6-LiFSI (9:1) + EC:EMC=3:7 + 5%FEC + 1%LiBOB) for encapsulation to obtain a stepped irregular cell.

[0060] The stepped irregular-shaped cell provided in this embodiment can be encapsulated in a housing to obtain a stepped irregular-shaped lithium-ion battery.

[0061] Example 2 This embodiment provides a stepped irregular-shaped battery cell, the structure of which is consistent with that of Embodiment 1.

[0062] The first cell unit includes 18 first positive electrode plates (area density 200g / m³). 2 Compacted density 4.2 g / cm³ 3 ), 17 first negative electrode plates (area density 78g / m²) 2 Compacted density 1.75 g / cm³ 3 The first positive electrode comprises a 10 μm thick aluminum foil and a first positive active coating on one side of the aluminum foil. The first positive active coating comprises 96 wt% lithium cobalt oxide, 2 wt% conductive carbon black, and 2 wt% PVDF binder. The first negative electrode comprises an 8 μm thick copper foil and a first negative active coating on one side of the copper foil. The first negative active coating comprises 96 wt% graphite, 2 wt% conductive carbon black, and 2 wt% SBR-CMC binder (SBR and CMC mass ratio 1:1). The second cell unit includes 12 second positive electrode plates (area density 200g / m²). 2 Compacted density 4.2 g / cm³ 3 ), 11 second negative electrode plates (area density 78g / m²) 2 Compacted density 1.75 g / cm³ 3The second positive electrode comprises a 10 μm thick aluminum foil and a second positive active coating on one side of the aluminum foil. The second positive active coating comprises 96 wt% lithium cobalt oxide and lithium manganese oxide (wherein, based on a total mass of 100 wt% lithium cobalt oxide and lithium manganese oxide, the content of lithium cobalt oxide is 75 wt% and the content of lithium manganese oxide is 25 wt%), 2 wt% conductive carbon black, and 2 wt% PVDF binder. The second negative electrode comprises an 8 μm thick copper foil and a second negative active coating on one side of the copper foil. The second negative active coating comprises 96 wt% graphite and carbon nanotube-hard carbon composite material (wherein, in the carbon nanotube-hard carbon composite material, the content of carbon nanotubes is 30 wt% and the content of hard carbon is 70 wt%; based on a total mass of 100 wt% graphite and composite hard carbon, the content of graphite is 75 wt% and the content of composite hard carbon is 25 wt%), 2 wt% conductive carbon black, and 2 wt% SBR-CMC binder.

[0063] The capacity ratio of the second cell unit to the first cell unit is 0.57. In the first cell unit, the capacity ratio of the electrode active material of the second cell unit to the first cell unit is 0.75, and the current carrying capacity ratio of the second cell unit to the first cell unit is 0.97.

[0064] This embodiment provides a method for preparing the stepped irregular battery cell. The difference between this method and Embodiment 1 is that the formulation amounts of the positive and negative electrode sheets in the first and second battery cell units are adjusted adaptively, while the remaining preparation methods and parameters remain the same as in Embodiment 1.

[0065] Example 3 This embodiment provides a stepped irregular-shaped battery cell, the structure of which is consistent with that of Embodiment 1.

[0066] The first cell unit includes 18 first positive electrode plates (area density 200g / m³). 2 Compacted density 4.2 g / cm³ 3 ), 17 first negative electrode plates (area density 78g / m²) 2 Compacted density 1.75 g / cm³ 3 The first positive electrode comprises a 10 μm thick aluminum foil and a first positive active coating on one side of the aluminum foil. The first positive active coating comprises 97 wt% lithium cobalt oxide, 1.5 wt% conductive carbon black, and 1.5 wt% PVDF binder. The first negative electrode comprises an 8 μm thick copper foil and a first negative active coating on one side of the copper foil. The first negative active coating comprises 97 wt% graphite, 1.5 wt% conductive carbon black, and 1.5 wt% SBR-CMC binder (SBR and CMC mass ratio 1:1). The second cell unit includes 12 second positive electrode plates (area density 200g / m²). 2 Compacted density 4.2 g / cm³ 3 ), 11 second negative electrode plates (area density 78g / m²) 2 Compacted density 1.75 g / cm³ 3 The second positive electrode comprises a 10μm thick aluminum foil and a second positive active coating on one side of the aluminum foil. The second positive active coating comprises 97wt% lithium cobalt oxide and lithium iron phosphate (wherein, based on a total mass of 100wt% lithium cobalt oxide and lithium iron phosphate, the content of lithium cobalt oxide is 70wt% and the content of lithium iron phosphate is 30wt%), 1.5wt% conductive carbon black, and 1.5wt% PVDF binder. The second negative electrode comprises an 8μm thick copper foil and a second negative active coating on one side of the copper foil. The second negative active coating comprises 97wt% graphite and soft carbon (wherein, based on a total mass of 100wt% graphite and soft carbon, the content of graphite is 70wt% and the content of soft carbon is 30wt%), 1.5wt% conductive carbon black, and 1.5wt% SBR-CMC binder (SBR and CMC mass ratio 1:1).

[0067] The capacity ratio of the second cell unit to the first cell unit is 0.58. In the first cell unit, the capacity ratio of the electrode active material of the second cell unit to the first cell unit is 0.77, and the current carrying capacity ratio of the second cell unit to the first cell unit is 0.97.

[0068] This embodiment provides a method for preparing the stepped irregular battery cell. The difference between this method and Embodiment 1 is that the formulation amounts of the positive and negative electrode sheets in the first and second battery cell units are adjusted adaptively, while the remaining preparation methods and parameters remain the same as in Embodiment 1.

[0069] Example 4 This embodiment provides a stepped irregular-shaped battery cell. The difference between the stepped irregular-shaped battery cell and Embodiment 1 is that the second positive electrode active coating includes 98wt% lithium cobalt oxide and NCM523 (wherein, based on the total mass of lithium cobalt oxide and NCM523 being 100wt%, the content of lithium cobalt oxide is 85wt% and the content of NCM523 is 15wt%), 1wt% conductive carbon black, and 1wt% PVDF binder. The remaining structure, composition, and parameters are consistent with those of Embodiment 1.

[0070] This embodiment provides a method for preparing the stepped irregular battery cell. The difference between this method and Embodiment 1 is that the formulation amount of the second positive electrode in the second battery cell unit is adjusted adaptively, while the rest of the preparation methods and parameters remain the same as in Embodiment 1.

[0071] Example 5 This embodiment provides a stepped irregular-shaped battery cell. The difference between the stepped irregular-shaped battery cell and Embodiment 1 is that the second positive electrode active coating includes 98wt% lithium cobalt oxide and NCM523 (wherein, based on the total mass of lithium cobalt oxide and NCM523 being 100wt%, the content of lithium cobalt oxide is 65wt% and the content of NCM523 is 35wt%), 1wt% conductive carbon black, and 1wt% PVDF binder. The remaining structure, composition, and parameters are consistent with those of Embodiment 1.

[0072] This embodiment provides a method for preparing the stepped irregular battery cell. The difference between this method and Embodiment 1 is that the formulation amount of the second positive electrode in the second battery cell unit is adjusted adaptively, while the rest of the preparation methods and parameters remain the same as in Embodiment 1.

[0073] Example 6 This embodiment provides a stepped irregular-shaped battery cell. The difference between the stepped irregular-shaped battery cell and Embodiment 1 is that the second negative electrode active coating includes 98 wt% graphite and modified silicon-carbon composite material (wherein, based on the total mass of graphite and modified silicon-carbon composite material being 100 wt%, the content of graphite is 85 wt% and the content of modified silicon-carbon composite material is 15 wt%), 1 wt% conductive carbon black, and 1 wt% SBR-CMC binder. The remaining structure, composition, and parameters are consistent with those of Embodiment 1.

[0074] This embodiment provides a method for preparing the stepped irregular battery cell. The difference between this method and Embodiment 1 is that the formulation amount of the second negative electrode in the second battery cell unit is adjusted adaptively, while the rest of the preparation methods and parameters remain the same as in Embodiment 1.

[0075] Example 7 This embodiment provides a stepped irregular-shaped battery cell. The difference between the stepped irregular-shaped battery cell and Embodiment 1 is that the second negative electrode active coating includes 98 wt% graphite and modified silicon-carbon composite material (wherein, based on the total mass of graphite and modified silicon-carbon composite material being 100 wt%, the content of graphite is 65 wt% and the content of modified silicon-carbon composite material is 35 wt%), 1 wt% conductive carbon black, and 1 wt% SBR-CMC binder. The remaining structure, composition, and parameters are consistent with those of Embodiment 1.

[0076] This embodiment provides a method for preparing the stepped irregular battery cell. The difference between this method and Embodiment 1 is that the formulation amount of the second negative electrode in the second battery cell unit is adjusted adaptively, while the rest of the preparation methods and parameters remain the same as in Embodiment 1.

[0077] Comparative Example 1 This comparative example provides a stepped irregularly shaped battery cell. The difference between the stepped irregularly shaped battery cell and Example 1 is that the addition of NCM523 is omitted in the second positive electrode active coating. It only includes 98wt% lithium cobalt oxide, 1wt% conductive carbon black and 1wt% PVDF binder. The remaining structure, composition and parameters are consistent with Example 1.

[0078] This comparative example provides a method for preparing the stepped irregular battery cell. The difference between this method and Example 1 is that the formulation amount of the second positive electrode in the second battery cell unit is adjusted adaptively, while the rest of the preparation methods and parameters remain the same as in Example 1.

[0079] Comparative Example 2 This comparative example provides a stepped irregularly shaped battery cell. The difference between the stepped irregularly shaped battery cell and Example 1 is that the modified silicon-carbon composite material is omitted in the second negative electrode active coating. It only includes 98 wt% graphite, 1 wt% conductive carbon black and 1 wt% SBR-CMC binder. The remaining structure, composition and parameters are consistent with Example 1.

[0080] This comparative example provides a method for preparing the stepped irregular battery cell. The difference between this method and Example 1 is that the formulation amount of the second negative electrode in the second battery cell unit is adjusted adaptively, while the rest of the preparation methods and parameters remain the same as in Example 1.

[0081] Comparative Example 3 This comparative example provides a stepped irregularly shaped battery cell. The difference between the stepped irregularly shaped battery cell and Example 1 is that the addition of NCM523 is omitted in the second positive electrode active coating, which only includes 98 wt% lithium cobalt oxide, 1 wt% conductive carbon black and 1 wt% PVDF binder. The addition of modified silicon-carbon composite material is omitted in the second negative electrode active coating, which only includes 98 wt% graphite, 1 wt% conductive carbon black and 1 wt% SBR-CMC binder. The remaining structure, composition and parameters are consistent with Example 1.

[0082] This comparative example provides a method for preparing the stepped irregular battery cell. The difference between this method and Example 1 is that the formulation of the second positive electrode and the second negative electrode in the second battery cell unit is adjusted adaptively, while the rest of the preparation methods and parameters remain the same as in Example 1.

[0083] The stepped irregularly shaped cells provided in Examples 1-7 and Comparative Examples 1-3 were charged once using a stepped formation fixture at 80°C, 1MPa, and a stepped charging current of 0.3C+0.5C+1C. After formation, the electrochemical performance was tested under the following test conditions: constant temperature 25°C, constant current charging at 3C to 4.35V, constant current charging at 1.8C to 4.53V, constant current charging at 1.5C to 4.56V, and constant voltage charging to 0.17C. The specific test results are shown in Table 1.

[0084] Table 1 Note: The reduction in lithium plating area of ​​the second cell unit after 600 cycles is a value obtained by comparing the two with that in Comparative Example 3, where no adjustments were made to the positive and negative active materials in the positive and negative electrode sheets.

[0085] The test results show that: (1) As can be seen from Examples 1-3, by introducing additional high-rate positive and negative active materials into the positive and negative electrode plates of the small second cell unit in the stepped irregular battery cell, the present invention can effectively improve the current carrying capacity of the small second cell unit and regulate the uniformity of the current distribution of the large first cell unit and the small second cell unit, thereby significantly improving the capacity retention rate and safety performance of the stepped irregular battery. Specifically, in Examples 1-3, under the same current carrying capacity, compared with Comparative Example 3 where no adjustment was made to the positive and negative active materials in the positive and negative electrode plates, the lithium plating area of ​​the small second cell unit can be reduced by 70%-72.2% after 600 cycles, and the capacity retention rate is 84.3%-85.1% when the entire stepped irregular battery cell cycle is completed.

[0086] (2) As can be seen from Examples 1 and 4-7, by further controlling the content of the second positive electrode active material to 20wt%-30wt% and the content of the second negative electrode active material to 20wt%-30wt%, the present invention can achieve a more balanced control of the cell capacity and charging rate of the large first cell unit and the small second cell unit.

[0087] (3) As can be seen from Example 1 and Comparative Examples 1-2, if the present invention introduces additional high-rate positive active material only in the positive electrode (Comparative Example 2) or only introduces additional high-rate negative active material only in the negative electrode (Comparative Example 1), it cannot effectively reduce the lithium plating area of ​​the second cell unit after 600 cycles, and the capacity retention rate is also significantly reduced when the cycle is completed.

[0088] In summary, by introducing additional high-rate positive and negative active materials into the positive and negative electrode plates of the small second cell unit in the stepped irregular battery cell, this invention can effectively improve the current carrying capacity of the small second cell unit and regulate the uniformity of the current distribution between the large first cell unit and the small second cell unit, thereby significantly improving the capacity retention and safety performance of the stepped irregular battery.

[0089] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A stepped irregular-shaped battery cell, characterized in that, The stepped irregular-shaped battery cell includes a first battery cell unit and a second battery cell unit stacked together. In both the length and width directions of the stepped irregular-shaped battery cell, the size of the first battery cell unit is larger than the size of the second battery cell unit. The first cell unit includes a first positive electrode, a first negative electrode, and a separator; the second cell unit includes a second positive electrode, a second negative electrode, and a separator. The first positive electrode and the second positive electrode each independently include a first positive active material, and the first negative electrode and the second negative electrode each independently include a first negative active material; The second positive electrode also includes a high-rate second positive electrode active material, and the second negative electrode also includes a high-rate second negative electrode active material.

2. The stepped irregular-shaped battery cell according to claim 1, characterized in that, The first positive electrode active material includes lithium cobalt oxide; And / or, the first negative electrode active material includes graphite; And / or, the high-rate second positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium manganese oxide, or lithium iron phosphate; And / or, the high-rate second negative electrode active material includes at least one of soft carbon, composite hard carbon, or modified silicon carbon material.

3. The stepped irregular-shaped battery cell according to claim 1 or 2, characterized in that, The first positive electrode and the second positive electrode each independently include a first conductive agent and a first binder; And / or, the first negative electrode and the second negative electrode each independently include a second conductive agent and a second binder.

4. The stepped irregular-shaped battery cell according to claim 3, characterized in that, Based on a total mass of 100wt% for the second positive electrode active coating in the second positive electrode sheet, the total content of the first positive electrode active material and the second positive electrode active material is 96wt%-98wt%. Based on a total mass of 100wt% for the first positive electrode active material and the second positive electrode active material, the content of the second positive electrode active material is 20wt%-30wt%, and the content of the first positive electrode active material is 70wt%-80wt%. And / or, based on a total mass of 100wt% of the second positive electrode active coating in the second positive electrode sheet, the content of the first conductive agent is 1wt%-2wt%; And / or, based on the total mass of the second positive electrode active coating in the second positive electrode sheet being 100wt%, the content of the first binder is 1wt%-2wt%.

5. The stepped irregular-shaped battery cell according to claim 3 or 4, characterized in that, Based on a total mass of 100wt% for the second negative electrode active coating in the second negative electrode sheet, the total content of the first negative electrode active material and the second negative electrode active material is 96wt%-98wt%. Based on a total mass of 100wt% for the first negative electrode active material and the second negative electrode active material, the content of the second negative electrode active material is 20wt%-30wt%, and the content of the first negative electrode active material is 70wt%-80wt%. And / or, based on a total mass of 100wt% of the second negative electrode active coating in the second negative electrode sheet, the content of the second conductive agent is 1wt%-2wt%; And / or, based on the total mass of the second negative electrode active coating in the second negative electrode sheet being 100wt%, the content of the second binder is 1wt%-2wt%.

6. The stepped irregular-shaped battery cell according to any one of claims 3-5, characterized in that, Based on a total mass of 100wt% for the first positive electrode active coating in the first positive electrode sheet, the content of the first positive electrode active material is 96wt%-98wt%; And / or, based on a total mass of 100wt% of the first positive electrode active coating in the first positive electrode sheet, the content of the first conductive agent is 1wt%-2wt%; And / or, based on a total mass of 100wt% of the first positive electrode active coating in the first positive electrode sheet, the content of the first binder is 1wt%-2wt%; And / or, based on a total mass of 100wt% of the first negative electrode active coating in the first negative electrode sheet, the content of the first negative electrode active material is 96wt%-98wt%; And / or, based on a total mass of 100wt% of the first negative electrode active coating in the first negative electrode sheet, the content of the second conductive agent is 1wt%-2wt%; And / or, based on the total mass of the first negative electrode active coating in the first negative electrode sheet being 100wt%, the content of the second binder is 1wt%-2wt%.

7. The stepped irregular-shaped battery cell according to any one of claims 1-6, characterized in that, The first positive electrode and the second positive electrode have the same areal density, both being 100 g / m³. 2 -240g / m 2 ; And / or, the first negative electrode and the second negative electrode have the same areal density, and the areal density of both the first negative electrode and the second negative electrode is 60 g / m³. 2 -170g / m 2 ; And / or, the first positive electrode and the second positive electrode have the same compaction density, both being 3.7 g / cm³. 3 -4.5g / cm 3 ; And / or, the first negative electrode and the second negative electrode have the same compaction density, both being 1.58 g / cm³. 3 -1.8g / cm 3 .

8. The stepped irregular-shaped battery cell according to any one of claims 1-7, characterized in that, Both the first battery cell unit and the second battery cell unit are stacked structures, or both the first battery cell unit and the second battery cell unit are wound structures; And / or, the capacity ratio of the second cell unit to the first cell unit is 0-1, and not 0; And / or, the ratio of the electrode active material capacity of the second cell unit to that of the first cell unit is 0-1, and not 0; And / or, the ratio of the current carrying capacity of the second cell unit to that of the first cell unit is 0-1, and not 0; And / or, the stepped irregular-shaped battery cell also includes an electrolyte.

9. A method for preparing a stepped irregularly shaped battery cell according to any one of claims 1-8, characterized in that, The preparation method includes the following steps: A first positive electrode, a first negative electrode, and a separator are assembled to obtain a first battery cell unit. A second positive electrode, a second negative electrode, and a separator are assembled to obtain a second battery cell unit. The first battery cell unit and the second battery cell unit are stacked to obtain a stepped irregular-shaped battery cell. In both the length and width directions of the stepped irregular-shaped battery cell, the size of the first battery cell unit is larger than the size of the second battery cell unit; The first positive electrode and the second positive electrode each independently include a first positive active material, and the first negative electrode and the second negative electrode each independently include a first negative active material; The second positive electrode also includes a high-rate second positive electrode active material, and the second negative electrode also includes a high-rate second negative electrode active material.

10. A stepped irregular-shaped lithium-ion battery, characterized in that, The stepped irregular lithium-ion battery includes a stepped irregular cell as described in any one of claims 1-8, or a stepped irregular cell and a housing prepared by the preparation method as described in claim 9, wherein the stepped irregular cell is encapsulated inside the housing.

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