Lithium-ion secondary battery, battery module, battery pack, and electric device

Abstract

The present application relates to the field of electrochemistry, and particularly relates to a lithium ion secondary battery, a battery module, a battery pack and a power utilization device. The present application provides a lithium ion secondary battery, comprising a bare cell accommodating cavity, wherein a bare cell group is arranged in the bare cell accommodating cavity, the bare cell group comprises one or more bare cells A and one or more bare cells B, the bare cell A comprises a first positive pole sheet, the first positive pole sheet comprises a first positive pole active material, the first positive pole active material is selected from single crystal or single crystal-like low-nickel ternary positive pole material A1, the bare cell B comprises a second positive pole sheet, the second positive pole sheet comprises a second positive pole active material and / or a third positive pole active material, the second positive pole active material is selected from polycrystalline high-nickel ternary positive pole material B1, and the third positive pole active material is selected from polycrystalline low-nickel ternary positive pole material B2. The lithium ion battery provided by the present application has excellent cycle, storage, gas production and safety performance under high energy density and high state of charge.

Description

Technical Field

[0001] This invention relates to the field of electrochemistry, and in particular to a lithium-ion secondary battery, battery module, battery pack, and electrical device. Background Technology

[0002] Lithium-ion rechargeable batteries primarily rely on the migration of lithium ions between the positive and negative electrode active materials for charging and discharging. During use, lithium-ion rechargeable batteries provide stable voltage and current, and their operation is environmentally friendly, making them widely used in various electrical devices such as mobile phones, tablets, laptops, electric bicycles, and electric vehicles.

[0003] For high-energy-density, high-voltage lithium-ion batteries, the need to improve their overall performance remains constant. Existing technologies employ structures with multiple different cathode active material sublayers. One sublayer uses a single-crystal or near-single-crystal ternary cathode material, while another sublayer uses a mixture of single-crystal or near-single-crystal and polycrystalline ternary cathode materials. However, such improvements only consider the electrode layer level and have limited impact on improving the overall battery performance. Summary of the Invention

[0004] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide a lithium-ion secondary battery to further improve the overall performance of lithium-ion secondary batteries, such as high energy density, cycle performance, storage performance, gas generation performance, and safety performance.

[0005] To achieve the above and other related objectives, the present invention provides a lithium-ion secondary battery, including a bare cell housing cavity, wherein a bare cell assembly is provided in the bare cell housing cavity, the bare cell assembly including one or more bare cells A and one or more bare cells B, the bare cell A including a first positive electrode plate including a first positive active material, the first positive active material being selected from a single crystal or near-single crystal low-nickel ternary positive electrode material A1, the bare cell B including a second positive electrode plate including a second positive active material and / or a third positive active material, the second positive active material being selected from a polycrystalline high-nickel ternary positive electrode material B1, and the third positive active material being selected from a polycrystalline low-nickel ternary positive electrode material B2. By using a cathode material that combines bare cells containing monocrystalline or near-monocrystalline low-nickel ternary cathode materials with polycrystalline high-nickel ternary cathode materials, the characteristic of polycrystalline high-nickel ternary cathode materials exhibiting significant lattice shrinkage during high SOC (state of charge) delithiation can be better utilized to improve cycle performance. This can effectively enhance the overall performance of lithium-ion secondary batteries, such as high energy density, cycle performance, storage performance, gas generation performance, and safety performance.

[0006] In any embodiment, the molecular formula of the single-crystal or quasi-single-crystal low-nickel ternary cathode material A1 is LiNi

[0008] , x3 , y2 , 1-x3- , x3 , y2 , y2 , 1-x3-y3 , , , 1-x2- , x2 , y3 , y3 , y3 , 1-x2-y2 , x2 Co y1 Mn 1-x1-y1 O2, where 0 < x1 ≤ 0.65, 0 < y1 < 0.35, 0 < 1 - x1 - y1 < 0.35; or, the molecular formula of the single-crystal or quasi-single-crystal low-nickel ternary cathode material A1 is LiNi x1 Co y1 Mn 1-x1-y1 O2, where 0 < x1 ≤ 0.55, 0 < y1 < 0.45, 0 < 1 - x1 - y1 < 0.45. Thus, the single-crystal or quasi-single-crystal ternary cathode material with a lower nickel content ratio in the bare cell A can be combined with the polycrystalline ternary cathode material with a higher nickel content in the bare cell B to improve the comprehensive performance of the lithium-ion secondary battery.

[0007] In any embodiment, the molecular formula of the polycrystalline high-nickel ternary cathode material B1 is LiNi x2 Co y2 [[ID=第十九]]Mn 1-x2- y2 O2, where 0.7 ≤ x2 < 1, 0 < y2 < 0.3, 0 < 1 - x2 - y2 < 0.3; or, the molecular formula of the polycrystalline high-nickel ternary cathode material B1 is LiNi x2 Co y2 Mn 1-x2-y2 O2, where 0.7 ≤ x2 ≤ 0.8, 0.2 < y2 < 0.3, 0.2 < 1 - x2 - y2 < 0.3. Thus, by introducing a polycrystalline ternary cathode material with a higher nickel content in the bare cell B, it can be combined with the single-crystal or quasi-single-crystal ternary cathode material with a lower nickel content ratio in the bare cell A to improve the comprehensive performance of the lithium-ion secondary battery.

[0008] In any embodiment, the molecular formula of the polycrystalline low-nickel ternary cathode material B2 is LiNi x3 Co y3 Mn 1-x3- y3 O2, where 0 < x3 ≤ 0.65, 0 < y3 < 0.35, 0 < 1 - x3 - y3 < 0.35; or, the molecular formula of the polycrystalline low-nickel ternary cathode material B2 is LiNi x3 Co y3 Mn 1-x3-y3 O2, where 0 < x3 ≤ 0.55, 0 < y3 < 0.45, 0 < 1 - x3 - y3 < 0.45. Thus, a polycrystalline ternary cathode material with a lower nickel content ratio can be introduced into the bare cell B. Although the introduction of this material may lead to a relatively deteriorated gas generation performance, overall, it can improve the comprehensive performance of the lithium-ion secondary battery.

[0009] In any embodiment, the cell volume shrinkage rate of the single-crystal or quasi single-crystal low-nickel ternary cathode material A1 during 100% SOC charging is ≤ 3%; and / or, the cell volume shrinkage rate of the polycrystalline high-nickel ternary cathode material B1 during 100% SOC charging is ≥ 4%; and / or, the cell volume shrinkage rate of the polycrystalline low-nickel ternary cathode material B2 during 100% SOC charging is ≤ 3%. Thus, by selecting the cell volume shrinkage rate during 100% SOC charging, the property of lattice shrinkage of the ternary cathode material at high SOC can be better reflected.

[0010] In any embodiment, compared with the bare cell A, the bare cell B is distributed closer to the outer side of the bare cell group. Thus, placing the bare cell B on the outermost side of the bare cell group is similar to providing a buffer layer to buffer the bare cell A, thereby effectively avoiding the expansion problem caused by the obvious growth trend of the expansion force of the bare cell during the charging process

[0011] In any embodiment, compared with the bare cell B, the bare cell A is distributed closer to the middle of the bare cell group. This is because the bare cells in the middle area of the cell usually have more obvious temperature rise and are more conducive to electrolyte infiltration. Distributing the bare cell A in the middle of the bare cell group can further avoid the situation of large-area lithium deposition of the bare cell A due to large expansion force and insufficient electrolyte infiltration in the middle area.

[0012] In any embodiment, the second positive electrode sheet further includes a fourth positive electrode active material, and the fourth positive electrode active material is selected from a single-crystal or quasi single-crystal low-nickel ternary cathode material A2, and the molecular formula of the single-crystal or quasi single-crystal low-nickel ternary cathode material A2 is LiNi x4 Co y4 Mn 1-x4-y4 O2, where 0 < x4 ≤ 0.65, 0 < y4 < 0.35, 0 < 1 - x4 - y4 < 0.35; or, the second positive electrode sheet further includes a fourth positive electrode active material, and the fourth positive electrode active material is selected from a single-crystal or quasi single-crystal low-nickel ternary cathode material A2, and the molecular formula of the single-crystal or quasi single-crystal low-nickel ternary cathode material A2 is LiNi x4 Co y4 Mn 1-x4-y4 O2, where 0 < x4 ≤ 0.55, 0 < y4 < <0.45, 0 < 1 - x4 - y4 < 0.45. Thus, the single-crystal or quasi single-crystal ternary cathode material with a relatively low nickel content ratio within the above numerical range has good gas production performance, and when combined with the ternary cathode material with a relatively high nickel content in the bare cell B, it can improve the comprehensive performance of the lithium-ion secondary battery.

[0013] In any embodiment, the 100% SOC charging cell volume shrinkage rate of the single-crystal or near-single-crystal low-nickel ternary cathode material A2 is ≤3%. By selecting the 100% SOC charging cell volume shrinkage rate, the lattice shrinkage property of the ternary cathode material at high SOC can be better reflected.

[0014] In any embodiment, the mass ratio k of the total mass of the monocrystalline positive electrode active material to the total mass of the polycrystalline positive electrode active material in the lithium-ion secondary battery is 0.5 to 9. This allows the lithium-ion secondary battery to exhibit better overall performance.

[0015] In any embodiment, the coating amount of the negative electrode in the bare cell A is ≤0.150g / 1540.25mm^2. Therefore, the coating amount of the negative electrode in the bare cell A is within the above range, which is more conducive to improving the negative electrode dynamics and avoiding the occurrence of large-area lithium plating in the bare cell A with obvious expansion growth due to excessive expansion growth and insufficient electrolyte wetting.

[0016] A second aspect of this application provides a battery module including the lithium-ion secondary battery of the first aspect of this application.

[0017] A third aspect of this application provides a battery pack that includes the battery module of the second aspect of this application.

[0018] A fourth aspect of this application provides an electrical device comprising one or more of the following: a lithium-ion secondary battery selected from the second aspect of this application, a battery module selected from the third aspect of this application, or a battery pack selected from the fifth aspect of this application.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The lithium-ion battery provided by this invention includes monocrystalline or near-monocrystalline low-nickel ternary cathode materials and polycrystalline high-nickel ternary cathode materials, each located in different bare cells. By combining bare cells with different cathode systems, the ratio of monocrystalline low-nickel cathode active material to polycrystalline high-nickel cathode active material in the entire battery can be better optimized, thereby obtaining a lithium-ion secondary battery with excellent cycling, storage, gas generation, and safety performance under high energy density and high charge state. Attached Figure Description

[0021] Figure 1 This diagram shows the position of the bare battery cell in the bare battery cell receiving cavity in Embodiment 1 of the present invention.

[0022] Figure 2 This is a schematic diagram of a lithium-ion secondary battery according to one embodiment of this application.

[0023] Figure 3 yes Figure 2An exploded view of a lithium-ion secondary battery according to an embodiment of this application is shown.

[0024] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0025] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0026] Figure 6 yes Figure 5 An exploded view of a battery pack according to one embodiment of this application is shown.

[0027] Figure 7 This is a schematic diagram of a device using a lithium-ion secondary battery as a power source according to an embodiment of this application.

[0028] Figure 8 The diagram shows the cell volume changes of the positive electrode active material in different delithiation states (SOC) of the positive electrode used in one embodiment of this application.

[0029] Figure 9 The diagram shown is a schematic design of a synchrotron radiation in-situ XRD electrolysis cell used in one embodiment of this application.

[0030] Component designation explanation

[0031] 1 Battery Pack

[0032] 2 Upper box

[0033] 3 lower box

[0034] 4 Battery Modules

[0035] 5. Lithium-ion secondary batteries

[0036] 51. Housing

[0037] 52 Electrode Assembly

[0038] 53 Top Cover Assembly Detailed Implementation

[0039] To make the inventive objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to embodiments. Those skilled in the art can easily understand other advantages and effects of this invention from the content disclosed in this specification.

[0040] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated, and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can serve as its own lower or upper limit and be combined with any other point or individual value, or with other lower or upper limits, to form a range not explicitly stated.

[0041] In this description, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more.

[0042] The above description of the invention is not intended to describe every disclosed embodiment or implementation of the invention. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are merely representative and should not be construed as exhaustive.

[0043] Lithium-ion secondary batteries

[0044] In one embodiment of this application, the present invention provides a lithium-ion secondary battery, including a bare cell receiving cavity, wherein a bare cell assembly is provided in the bare cell receiving cavity, the bare cell assembly including one or more bare cells A and one or more bare cells B, bare cell A including a first positive electrode plate, the first positive electrode plate including a first positive active material, the first positive active material being selected from a single crystal or near-single crystal low-nickel ternary positive electrode material A1, bare cell B including a second positive electrode plate, the second positive electrode plate including a second positive active material and / or a third positive active material, the second positive active material being selected from a polycrystalline high-nickel ternary positive electrode material B1, and the third positive active material being selected from a polycrystalline low-nickel ternary positive electrode material B2. Compared to single-crystal or near-single-crystal low-nickel ternary cathode materials, polycrystalline high-nickel ternary cathode materials exhibit a more pronounced lattice contraction effect at high SOCs (e.g., ≥65%, ≥64%, ≥63%, ≥62%, ≥61%, ≥60%, ≥59%, ≥58%, ≥57%, ≥56%, or ≥55%). This effectively mitigates the impact on the negative electrode's stress during charging, reducing the risk of lithium plating due to large expansion forces and the risk of cycle failure due to lithium plating. However, at high SOCs, polycrystalline high-nickel ternary cathode materials face the risk of deteriorated gas production and reduced safety performance, and their storage performance is also significantly worse than that of single-crystal low-nickel materials. The inventors of this application unexpectedly discovered that, compared to physically mixing single-crystal or near-single-crystal low-nickel ternary cathode materials with polycrystalline high-nickel ternary cathode materials in a single bare cell, a cathode material with a mixed combination of single-crystal and polycrystalline materials can better utilize the characteristic of polycrystalline high-nickel ternary cathode materials with significant lattice shrinkage in the high SOC delithiation state to improve cycle life, thereby effectively improving the overall performance of lithium-ion secondary batteries (e.g., cycle life).

[0045] In this application, the single-crystal ternary cathode material generally refers to a ternary cathode material with primary particles that do not exhibit significant agglomeration (the volume distribution of secondary particles formed by a very small amount of agglomeration is <5%). The volume average particle size (D) of the primary particles in the single-crystal ternary cathode material is... V50 The micrometer size (μm) can typically be 1–10 μm, 1–2 μm, 2–3 μm, 3–4 μm, 4–5 μm, 5–6 μm, 6–7 μm, 7–8 μm, 8–9 μm, or 9–10 μm. For example, a single-crystal ternary cathode material can be LiNi. 0.55 Co 0.15 Mn 0.30 O2, LiNi 0.55 Co 0.05 Mn 0.40 O2, LiNi 0.65 Co 0.07 Mn 0.28O2, etc. Ternary cathode materials with a near-single-crystal structure typically refer to ternary cathode materials where the primary particles are slightly agglomerated (the volume distribution of secondary particles formed by agglomeration is 10%–35%). For example, a near-single-crystal structure ternary cathode material could be LiNi. 0.56 Co 0.12 Mn 0.32 O2, etc. Polycrystalline ternary cathode materials refer to materials formed by the agglomeration of primary particles into secondary spherical particles. For example, a polycrystalline ternary cathode material with a relatively high nickel content could be LiNi. 0.70 Co 0.10 Mn 0.20 O2, LiNi 0.80 Co 0.10 Mn 0.10 O2, etc. For example, a polycrystalline ternary cathode material with a relatively low nickel content could be LiNi. 0.56 Co 0.12 Mn 0.32 O2, etc.

[0046] In some embodiments, the positive electrode active material included in the bare cell A may mainly include a first positive electrode active material, which is typically a single-crystal or near-single-crystal low-nickel ternary positive electrode material Al, and its molecular formula may be LiNi. x1 Co y1 Mn 1-x1-y1O2. Among them, x1 can usually satisfy 0<x1≤0.65, 0<x1≤0.05, 0.05≤x1≤0.1, 0.1≤x1≤0.15, 0.15≤x1≤0.2, 0.2≤x1≤0.25, 0.25≤x1≤0.3, 0.3≤x1≤0.35, 0.35≤x1≤0.4, 0.4≤x1≤0.45, 0.45≤x1≤0.5, 0.5≤x1≤0.0.55, 0.55≤x1≤0.6, or 0.6≤x1≤0.65, preferably satisfying 0<x1≤0.55. y1 can typically satisfy 0 < y1 < 0.45, 0 < y1 ≤ 0.05, 0.05 ≤ y1 ≤ 0.1, 0.1 ≤ y1 ≤ 0.15, 0.15 ≤ y1 ≤ 0.2, 0.2 ≤ y1 ≤ 0.25, 0.25 ≤ y1 ≤ 0.3, 0.3 ≤ y1 < 0.35, 0.35 ≤ y1 < 0.4, or 0.4 ≤ y1 < 0.45. Generally speaking, the preferred range of y1 corresponds to the preferred range of x1. When x1 satisfies 0 < x1 ≤ 0.55, y1 can typically satisfy 0 < y1 < 0.45. 1 - x1 - y1 can typically satisfy 0 < 1 - x1 - y1 < 0.45, 0 < 1 - x1 - y ... The preferred range of values ​​for 1-x1-y1 is generally the same as the preferred range of values ​​for x1. When x1 satisfies 0 < x1 ≤ 0.55, 1-x1-y1 can usually satisfy 0 < 1-x1-y1 < 0.45. The lattice shrinkage property of ternary cathode materials at high SOC can be reflected by the nickel content in the material. Generally speaking, the lattice shrinkage effect of single-crystal or near-single-crystal ternary cathode materials with a lower nickel content is relatively less obvious, but the gas generation performance is better. The single-crystal or near-single-crystal ternary cathode material with a lower nickel content in bare cell A can be combined with the polycrystalline ternary cathode material with a higher nickel content in bare cell B to improve the overall performance of lithium-ion secondary batteries.

[0047] In some embodiments, the 100% SOC charging cell volume shrinkage rate of the single-crystal or near-single-crystal low-nickel ternary cathode material A1 is typically ≤3%. The specific measurement method for the 100% SOC charging cell volume shrinkage rate can refer to the measurement method given in the embodiments of this invention. By selecting the 100% SOC charging cell volume shrinkage rate, the lattice shrinkage property of the ternary cathode material at high SOC can be more accurately reflected.

[0048] In some embodiments, the positive electrode active material included in the bare cell B may include a second positive electrode active material, which is typically a polycrystalline high-nickel ternary positive electrode material B1 with the molecular formula LiNix2Co. y2 Mn 1-x2-y2 O2. Among them, x2 can usually satisfy 0.7≤x2<1, 0.7≤x2≤0.75, 0.75≤x2≤0.8, 0.8≤x2≤0.85, 0.85≤x2≤0.9, 0.9≤x2≤0.95, 0.95≤x2<1, and preferably can satisfy 0.7≤x2≤0.8. y² can typically satisfy 0 < y² < 0.3, 0 < y² ≤ 0.05, 0.05 ≤ y² ≤ 0.1, 0.1 ≤ y² ≤ 0.15, 0.15 ≤ y² ≤ 0.2, 0.2 ≤ y² ≤ 0.25, or 0.25 ≤ y² < 0.3. Generally speaking, the preferred range of y² corresponds to the preferred range of x². When x² satisfies 0.7 ≤ x² ≤ 0.8, y² can typically satisfy 0.2 < y² < 0.3. 1 - x² - y² typically satisfies 0 < 1 - x² - y² < 0.3. 0 < 1 - x² - y² ≤ 0.05, 0.05 ≤ 1 - x² - y² ≤ 0.1, 0.1 ≤ 1 - x² - y² ≤ 0.15, 0.15 ≤ 1 - x² - y² ≤ 0.2, 0.2 ≤ 1 - x² - y² ≤ 0.25, or 0.25 ≤ 1 - x² - y² < 0.3. Generally speaking, the preferred range of values ​​for 1 - x² - y² corresponds to the preferred range of values ​​for x². When x² satisfies 0.7 ≤ x² ≤ 0.8, 1 - x² - y² usually satisfies 0.2 < 1 - x² - y² < 0.3. The lattice contraction property of ternary cathode materials at high SOC can be reflected by the nickel content in the material. Generally speaking, polycrystalline ternary cathode materials with a higher nickel content have a more obvious lattice contraction effect, but their gas generation performance will be worse. Introducing polycrystalline ternary cathode materials with a higher nickel content into bare cell B can be combined with monocrystalline or near-monocrystalline ternary cathode materials with a lower nickel content in bare cell A to improve the overall performance of lithium-ion secondary batteries.

[0049] In some implementations, the 100% SOC charge cell volume shrinkage rate of the polycrystalline high-nickel ternary cathode material B1 is typically ≥4%. By selecting the 100% SOC charge cell volume shrinkage rate, the lattice shrinkage property of the ternary cathode material at high SOC can be more accurately reflected.

[0050] In some embodiments, the positive electrode active material included in the bare cell B may include a third positive electrode active material, which is typically a polycrystalline low-nickel ternary positive electrode material B2, and its molecular formula may be LiNi. x3 Co y3 Mn 1-x3-y3O2. Among them, x3 generally satisfies 0 < x3 ≤ 0.65, 0 < x3 ≤ 0.05, 0.05 ≤ x3 ≤ 0.1, 0.1 ≤ x3 ≤ 0.15, 0.15 ≤ x3 ≤ 0.2, 0.2 ≤ x3 ≤ 0.25, 0.25 ≤ x3 ≤ 0.3, 0.3 ≤ x3 ≤ 0.35, 0.35 ≤ x3 ≤ 0.4, 0.4 ≤ x3 ≤ 0.45, 0.45 ≤ x3 ≤ 0.5, 0.5 ≤ x3 ≤ 0.55, 0.55 ≤ x3 ≤ 0.6, or 0.6 ≤ x3 ≤ 0.65, and preferably satisfies 0 < x3 ≤ 0.55. y3 generally satisfies 0 < y3 < 0.45, 0 < y3 ≤ 0.05, 0.05 ≤ y3 ≤ 0.1, 0.1 ≤ y3 ≤ 0.15, 0.15 ≤ y3 ≤ 0.2, 0.2 ≤ y3 ≤ 0.25, 0.25 ≤ y3 ≤ 0.3, 0.3 ≤ y3 < 0.35, 0.35 ≤ y3 < 0.4, or 0.4 ≤ y3 < 0.45. Generally speaking, the preferred value range of y3 corresponds to the preferred value range of x3. When x3 satisfies 0 < x3 ≤ 0.55, y3 generally satisfies 0 < y3 < 0.45. 1 - x3 - y3 generally satisfies 0 < 1 - x3 - y3 < 0.45, 0 < 1 - x3 - y3 ≤ 0.05, 0.05 ≤ 1 - x3 - y3 ≤ 0.1, 0.1 ≤ 1 - x3 - y3 ≤ 0.15, 0.15 ≤ 1 - x3 - y3 ≤ 0.2, 0.2 ≤ 1 - x3 - y3 ≤ 0.25, 0.25 ≤ 1 - x3 - y3 ≤ 0.3, 0.3 ≤ 1 - x3 - y3 < 0.35, 0.35 ≤ 1 - x3 - y3 < 0.4, or 0.4 ≤ 1 - x3 - y3 < 0.45. Generally speaking, the preferred value range of 1 - x3 - y3 corresponds to the preferred value range of x3. When x3 satisfies 0 < x3 ≤ 0.55, 1 - x3 - y3 generally satisfies 0 < 1 - x3 - y3 < 0.45. In the bare cell B, a polycrystalline ternary cathode material with a relatively low nickel content ratio can be introduced. The secondary particles of the polycrystalline ternary cathode material with a relatively low nickel content ratio are relatively easy to break, which can improve the swelling growth during the cycling process. Although the introduction of this material may cause the gas generation performance to deteriorate relatively, overall, it can improve the comprehensive performance of the lithium-ion secondary battery.

[0051] In some embodiments, in the lithium-ion secondary battery, the 100% SOC charging cell volume shrinkage rate of the polycrystalline low-nickel ternary cathode material B2 is generally ≤ 3%. By selecting the 100% SOC charging cell volume shrinkage rate, the property of lattice shrinkage of the ternary cathode material at high SOC can be more accurately reflected.

[0052] In some implementations, bare cell B can be distributed closer to the outer edge of the bare cell group compared to bare cell A, while bare cell A can be distributed closer to the center of the bare cell group compared to bare cell B. This distribution trend can be the overall distribution trend of one or more bare cells A relative to one or more bare cells B, or it can be the individual positional relationship between a single bare cell A and a single bare cell B. Since the polycrystalline high-nickel ternary cathode material B1 included in bare cell B exhibits more significant lattice contraction at high SOC, resulting in a slower increase in bare cell expansion force during charging, while the monocrystalline or near-monocrystalline low-nickel ternary cathode material A1 included in bare cell A shows less significant lattice contraction at high SOC, resulting in a more pronounced increase in bare cell expansion force during charging, placing bare cell B further out of the bare cell group is similar to providing a buffer layer for bare cell A. In addition, since the temperature rise of bare cells in the middle area of ​​the battery cell is usually more obvious, which is more conducive to electrolyte wetting, distributing bare cell A in the middle of the bare cell group can further avoid the occurrence of large-area lithium plating in bare cell A due to large expansion force and insufficient electrolyte wetting in the middle area.

[0053] In some embodiments, the second positive electrode further includes a fourth positive electrode active material, which is selected from a single-crystal or near-single-crystal low-nickel ternary positive electrode material A2. The molecular formula of the single-crystal or near-single-crystal low-nickel ternary positive electrode material A2 can be LiNi. x4 Co y4 Mn 1-x4-y4O2. Among them, x4 can generally satisfy 0 < x4 ≤ 0.65, 0 < x4 ≤ 0.05, 0.05 ≤ x4 ≤ 0.1, 0.1 ≤ x4 ≤ 0.15, 0.15 ≤ x4 ≤ 0.2, 0.2 ≤ x4 ≤ 0.25, 0.25 ≤ x4 ≤ 0.3, 0.3 ≤ x4 ≤ 0.35, 0.35 ≤ x4 ≤ 0.4, 0.4 ≤ x4 ≤ 0.45, 0.45 ≤ x4 ≤ 0.5, 0.5 ≤ x4 ≤ 0.55, 0.55 ≤ x4 ≤ 0.6, or 0.6 ≤ x4 ≤ 0.65. y4 can generally satisfy 0 < y4 < 0.45, 0 < y4 ≤ 0.05, 0.05 ≤ y4 ≤ 0.1, 0.1 ≤ y4 ≤ 0.15, 0.15 ≤ y4 ≤ 0.2, 0.2 ≤ y4 ≤ 0.25, 0.25 ≤ y4 ≤ 0.3, 0.3 ≤ y4 < 0.35, 0.35 ≤ y4 < 0.4, or 0.4 ≤ y4 < 0.45. Generally speaking, the preferred value range of y4 corresponds to the preferred value range of x4. When x4 satisfies 0 < x4 ≤ 0.55, y4 generally satisfies 0 < y4 < 0.45. 1 - x4 - y4 can generally satisfy 0 < 1 - x4 - y4 < 0.45, 0 < 1 - x4 - y4 ≤ 0.05, 0.05 ≤ 1 - x4 - y4 ≤ 0.1, 0.1 ≤ 1 - x4 - y4 ≤ 0.15, 0.15 ≤ 1 - x4 - y4 ≤ 0.2, 0.2 ≤ 1 - x4 - y4 ≤ 0.25, 0.25 ≤ 1 - x4 - y4 ≤ 0.3, 0.3 ≤ 1 - x4 - y4 < 0.35, 0.35 ≤ 1 - x4 - y4 < 0.4, or 0.4 ≤ 1 - x4 - y4 < 0.45. Generally speaking, the preferred value range of 1 - x4 - y4 corresponds to the preferred value range of x4. When x4 satisfies 0 < x4 ≤ 0.55, 1 - x4 - y4 generally satisfies 0 < 1 - x4 - y4 < 0.45. In the bare cell B, a single - crystal or quasi - single - crystal ternary cathode material with a relatively low nickel content ratio can be further introduced. As mentioned above, the lattice contraction effect of the single - crystal or quasi - single - crystal ternary cathode material with a relatively low nickel content ratio is relatively not obvious, but the gas - generating performance is better. When combined with the ternary cathode material with a relatively high nickel content in the bare cell B, the comprehensive performance of the lithium - ion secondary battery can be improved overall. The usage amount of the single - crystal or quasi - single - crystal low - nickel ternary cathode material A2 in the bare cell B can be adjusted and optimized based on the actual performance requirements of the cell. When the gas - generating demand for the bare cell is high, the proportion of the single - crystal or quasi - single - crystal low - nickel ternary cathode material A2 in the bare cell B can be appropriately increased, and the proportion of the polycrystalline high - nickel ternary cathode material B1 can be reduced.

[0054] In some embodiments, the volume shrinkage rate of the single - crystal or quasi - single - crystal low - nickel ternary cathode material A2 during 100% SOC charging is generally ≤ 3%. By selecting the volume shrinkage rate during 100% SOC charging, the property of lattice contraction of the ternary cathode material at high SOC can be more accurately reflected.

[0055] In some embodiments, the mass ratio k of the total mass of monocrystalline positive electrode active material (e.g., including monocrystalline or near-monocrystalline low-nickel ternary positive electrode material A1, monocrystalline or near-monocrystalline low-nickel ternary positive electrode material A2, etc.) to the total mass of polycrystalline positive electrode active material (e.g., including polycrystalline high-nickel ternary positive electrode material B1, polycrystalline low-nickel ternary positive electrode material B2, etc.) in the entire battery system can be 0.5–9, 0.5–1, 1–1.5, 1.5–2, 2–2.5, 2.5–3, 3–3.5, 3.5–4, 4–4.5, 4.5–5, 5–5.5, 5.5–6, 6–6.5, 6.5–7, 7–7.5, 7.5–8, 8–8.5, or 8.5–9. The mass ratio k can usually be adjusted by the ratio of bare cell A to bare cell B, or the ratio of each ternary cathode material included in bare cell A or bare cell B. Generally speaking, when the mass ratio k meets the above range, the lithium-ion secondary battery can have better overall performance. This may be because when the proportion of polycrystalline cathode active material is too high, the gas generation performance of the lithium-ion battery may deteriorate, while when the proportion of polycrystalline cathode active material is too low, the improvement of cycle expansion may not be sufficient. Therefore, in the later stages of battery cycling, due to the large expansion force, lithium deposition in the middle of the bare cell is likely to occur, resulting in a sharp drop in cycle performance.

[0056] In some implementations, the coating amounts of the positive electrodes in bare cell A and bare cell B can be substantially the same or different, and the coating amounts of the negative electrodes in bare cell A and bare cell B can also be substantially the same or different. However, the coating amount of the negative electrode in bare cell A should generally not be too large; for example, the coating amount of the negative electrode in bare cell A can be ≤0.150g / 1540.25mm^2. A relatively small coating amount for the negative electrode in bare cell A is more conducive to improving negative electrode kinetics and preventing large-area lithium plating due to insufficient electrolyte wetting caused by excessive expansion growth in bare cell A. Correspondingly, due to the lattice contraction of the polycrystalline positive electrode material, bare cell B experiences less stress on the negative electrode and will not experience large-area lithium plating due to large expansion forces; therefore, the coating amount of the negative electrode in bare cell B can be relatively larger. Both can be adjusted in combination to meet the overall capacity and energy density requirements of the cell.

[0057] In some embodiments, each ternary cathode material (e.g., single-crystal or near-single-crystal low-nickel ternary cathode material A1, single-crystal or near-single-crystal low-nickel ternary cathode material A2, polycrystalline high-nickel ternary cathode material B1, polycrystalline low-nickel ternary cathode material B2, etc.) can independently be a ternary cathode material that has undergone coating modification. Generally, after appropriate coating modification, the overall performance (e.g., gas generation performance) of the ternary cathode material can usually be improved. However, overall, the lattice shrinkage property of the ternary cathode material at high SOC is still closely related to the nickel content and / or the cell volume shrinkage rate at 100% SOC charging. Suitable methods for coating modification of ternary cathode materials should be known to those skilled in the art. For example, the gas generation performance of the ternary material can be improved by coating lithium iron phosphate nanoparticles on the surface of a high-nickel ternary material.

[0058] Typically, the lithium-ion secondary battery provided in this application may include bare cell A and / or bare cell B, which may include a positive electrode, a negative electrode, an electrolyte, and a separator. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0059] In the lithium-ion secondary battery provided in this application, bare cell A and bare cell B can each independently include the first positive electrode sheet, the second positive electrode sheet, etc., as described above. The positive electrode sheet can generally include a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector. The composition of the positive active material in the positive electrode film layer can be as described above.

[0060] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0061] In the lithium-ion secondary battery provided in this application, the positive electrode current collector can be a metal foil or a composite current collector. For example, aluminum foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0062] The positive electrode film may optionally include a conductive agent. However, there is no specific limitation on the type of conductive agent, and those skilled in the art can select it according to actual needs. As an example, the conductive agent used for the positive electrode film may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0063] In this application, the positive electrode sheet can be prepared according to methods known in the art. As an example, the positive active material, conductive agent and binder of this application can be dispersed in a solvent (e.g., N-methylpyrrolidone (NMP)) to form a uniform positive electrode slurry; the positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode sheet is obtained.

[0064] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0065] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0066] In the lithium-ion secondary battery provided in this application, the negative electrode current collector can be a metal foil or a composite current collector. For example, copper foil can be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector can be formed by forming a metal material (such as copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0067] In the lithium-ion secondary battery provided in this application, the negative electrode film typically comprises a negative electrode active material and optional binders, optional conductive agents, and other optional additives, and is usually formed by coating and drying a negative electrode slurry. The negative electrode slurry coating is typically formed by dispersing the negative electrode active material, optional conductive agents, and binders in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water.

[0068] As an example, the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0069] As an example, the adhesive may be selected from one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0070] Other optional additives include thickeners (such as sodium carboxymethyl cellulose (CMC-Na)).

[0071] In the lithium-ion secondary battery provided in this application, the negative electrode film layer includes, in addition to the negative electrode active material, other commonly used negative electrode active materials. Examples of other commonly used negative electrode active materials include artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys.

[0072] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specifically limit the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions).

[0073] In some embodiments, the electrolyte may be an electrolyte solution, which may include an electrolyte salt and a solvent.

[0074] In some embodiments, the electrolyte salt may be selected from one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0075] In some embodiments, the solvent may be selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0076] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature performance, and additives that improve battery low-temperature performance.

[0077] Lithium-ion secondary batteries using electrolytes, as well as some lithium-ion secondary batteries using solid electrolytes, also include a separator. The separator is disposed between the positive and negative electrodes, serving a separating function. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected. In some embodiments, the separator material can be selected from one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0078] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0079] In some embodiments, the lithium-ion secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0080] In some implementations, the outer packaging of a lithium-ion secondary battery can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of a lithium-ion secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0081] This application does not impose any particular limitation on the shape of the lithium-ion secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured lithium-ion secondary battery.

[0082] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The lithium-ion secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0083] Battery Module

[0084] In some implementations, lithium-ion secondary batteries can be assembled into battery modules, and the number of lithium-ion secondary batteries contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0085] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple lithium-ion secondary batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple lithium-ion secondary batteries 5 can be fixed in place using fasteners.

[0086] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of lithium-ion secondary batteries 5 are received.

[0087] battery pack

[0088] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be selected by those skilled in the art based on the application and capacity of the battery pack.

[0089] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 5 and Figure 6 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0090] Electrical appliances

[0091] In addition, this application also provides an electrical device that may include one or more of the lithium-ion secondary batteries, battery modules, or battery packs provided in this application. The aforementioned lithium-ion secondary batteries, battery modules, or battery packs can be used as a power source for the device or as an energy storage unit for the device. The aforementioned electrical device may be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0092] For the aforementioned electrical devices, lithium-ion secondary batteries, battery modules, or battery packs can be selected according to their usage requirements.

[0093] Figure 7 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of lithium-ion secondary batteries for this device, a battery pack or battery module can be used.

[0094] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use lithium-ion rechargeable batteries as their power source.

[0095] The present application will be further illustrated by the following examples, but these examples do not limit the scope of the present application.

[0096] The main materials and parameters used in this embodiment are as follows:

[0097] Single crystal NCM523 (LiNi) 0.55 Co 0.15 Mn 0.3 O2), 4.35V full battery first discharge capacity ~182mAh / g, 100% SOC cell volume shrinkage rate ~2.27%;

[0098] Polycrystalline NCM712 (LiNi 0.7 Co 0.10 Mn 0.2 O2), 4.35V full battery first discharge capacity ~197mAh / g, 100% SOC cell volume shrinkage rate ~4.04%;

[0099] Polycrystalline NCM523 (LiNi) 0.56 Co 0.12 Mn 0.32O2), 4.35V full battery first discharge capacity ~182mAh / g, 100% SOC cell volume shrinkage rate ~2.30%.

[0100] The active mass ratio k in the entire cell is equal to the mass of monocrystalline positive electrode active material / the mass of polycrystalline positive electrode active material. Monocrystalline positive electrode active material includes monocrystalline NCM523, etc., as mentioned above, and polycrystalline positive electrode active material includes polycrystalline NCM712, polycrystalline NCM523, etc., as mentioned above.

[0101] Example 1

[0102] Preparation of the positive electrode sheet: Ternary positive electrode material, single-crystal NCM523, was used as the positive electrode active material, carbon black as the conductive agent, and polyvinylidene fluoride as the binder, with a mass ratio of 96:2:2. N-methylpyrrolidone was used as the solvent, and the slurry solid content was 64%. After uniform mixing, a positive electrode slurry was formed. This slurry was then uniformly coated onto the positive electrode current collector aluminum foil (double-sided coating). After drying, the foil underwent cold pressing, edge trimming, cutting, and slitting to form the positive electrode sheet. The coating weight on one side of the foil was 0.260 g / 1540.25 mm. 2 (Total mass of mixture, excluding base material).

[0103] Preparation of the negative electrode sheet: Artificial graphite was used as the negative electrode active material, carbon black as the conductive agent, and styrene-butadiene rubber (SBR) (solid content 0.48%) as the binder. Sodium carboxymethyl cellulose was added as a thickener. The mixture was stirred and mixed evenly at a mass ratio of 96.9:0.5:1.5:1.1 to form a negative electrode slurry. The negative electrode slurry was then uniformly coated onto the copper foil of the negative electrode current collector (double-sided coating). After drying, the foil underwent cold pressing, edge trimming, cutting, and slitting to form the negative electrode sheet. The single-sided coating amount of the foil was 0.155 g / 1540.25 mm. 2 (Total mass of mixture, excluding base material).

[0104] Preparation of the separator membrane: A 7μm thick polyethylene film was used as the separator membrane substrate. Then, using a microgravure coating method, an inorganic oxide layer slurry was coated onto one side of the 7μm thick separator membrane substrate (polyethylene). The inorganic oxide layer slurry consisted of inorganic aluminum oxide powder, polyvinylpyrrolidone, and acetone solvent, mixed in a mass ratio of 3:1:6. After oven drying, a separator membrane with a first coating was obtained. Polyvinylidene fluoride (PVDF), acetone solvent, and ethyl acetate were mixed evenly in a mass ratio of 5:40:55 to form a slurry. This slurry was then sprayed onto the separator membrane with the first coating. The second coating had a single-sided thickness of 1μm. After oven drying, the second coating was formed on top of the first coating, resulting in the final separator membrane.

[0105] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. Then, the electrode is wound to obtain bare cell A.

[0106] The preparation process of bare cell B is the same as that of bare cell A, except that the positive electrode active material used is ternary positive electrode material polycrystalline NCM712, and the single-sided weight of the positive electrode coating is 0.257g / 1540.25mm. 2 (Excluding substrate), the single-sided weight of the positive electrode coating is 0.163g / 1540.25mm. 2 (Excluding substrate), and the electrode lengths vary slightly.

[0107] The battery cell assembly process is as follows Figure 1 As shown in the figure, A represents bare cell A, and B represents bare cell B, with an internal volume of 47582 mm². 3 In a rectangular space containing the bare battery cells, bare cell B is placed in outer regions ① and ④, and bare cell A is placed in middle regions ② and ③. The electrolyte composition is 1 mol / L lithium hexafluorophosphate (LiPF6), with ethylene carbonate (EC) and dimethyl carbonate (DMC) as solvents, and the volume ratio of EC to DMC is 9:1. The battery is manufactured through processes such as electrolyte injection, formation, venting, and sealing.

[0108] The active mass ratio k in the entire cell is 1.08.

[0109] Example 2

[0110] The preparation process of the lithium-ion battery is generally the same as in Example 1, except that there is only one bare cell B, which is located in region ④, and the active mass ratio k in the whole cell is 3.44.

[0111] Example 3

[0112] The preparation process of the lithium-ion battery is generally the same as in Example 1, except that the positive electrode active material of the bare cell B is a physical mixture of single crystal NCM523 and polycrystalline NCM712, with a mixing mass ratio of 5:5, and the active mass ratio k in the whole cell is 3.13.

[0113] Example 4

[0114] The preparation process of the lithium-ion battery is generally the same as in Example 1, except that the positive electrode active material of the bare cell B is a physical mixture of single crystal NCM523 and polycrystalline NCM712, with a mixing mass ratio of 7:3, and the active mass ratio k in the whole cell is 5.85.

[0115] Example 5

[0116] The preparation process of the lithium-ion battery is generally the same as in Example 1, except that the positive electrode active material of the bare cell B is polycrystalline Ni55, and the active mass ratio k in the whole cell is 1.00.

[0117] Example 6

[0118] The preparation process of the lithium-ion battery is generally the same as in Example 1, except that the number of layers of the bare cell A is different and the active mass ratio k in the whole cell is 1.07.

[0119] Example 7

[0120] The preparation process of the lithium-ion battery is generally the same as in Example 3, except that the monocrystalline NCM523 in the bare cell B is replaced with polycrystalline NCM523, and the active mass ratio k in the whole cell is 1.06.

[0121] Example 8

[0122] The preparation process of the lithium-ion battery is generally the same as in Example 1, except that bare cell A is placed in the outer regions ① and ④, and bare cell B is placed in the middle regions ② and ③, and the active mass ratio k in the whole cell is 1.08.

[0123] Example 9

[0124] The preparation process of the lithium-ion battery is generally the same as in Example 1, except that the positive electrode active material of the bare cell B is a physical mixture of single crystal NCM523 and polycrystalline NCM712, with a mixing mass ratio of 8:2, and the active mass ratio k in the whole cell is 9.26.

[0125] Example 10

[0126] The preparation process of the lithium-ion battery is generally the same as in Example 1, except that bare cell A is placed in the middle region ②, and bare cell B is placed in the outer regions ①③ and ④, and the active mass ratio k in the whole cell is 0.35.

[0127] Comparative Example 1

[0128] The preparation process of the lithium-ion battery is generally the same as in Example 1, except that all the bare cells are bare cells A.

[0129] Comparative Example 2

[0130] The preparation process of the lithium-ion battery is generally the same as in Example 1, except that all the bare cells are bare cells B.

[0131] Comparative Example 3

[0132] The preparation process of the lithium-ion battery is generally the same as in Example 1, except that all the bare cells are bare cells B, and the positive electrode active material of bare cells B is a physical mixture of single crystal NCM523 and polycrystalline NCM712 with a mixing mass ratio of 5:5.

[0133] The lithium-ion batteries prepared in the examples and comparative examples were subjected to performance tests. The specific measurement methods for each performance test are as follows:

[0134] Cyclic performance test (capacity retention rate 1000 cycles): Under conditions of 25±2℃, an initial pressure of 2000±300N was applied to the battery. The battery was charged to 4.35V using a step-charging strategy, and then discharged to 2.8V at a current of 1C. This cycle was repeated, and the capacity retention rate of the battery after 1000 cycles was recorded. The test results are shown in Table 1.

[0135] Gas generation performance test (70℃, 4.35V, gas generation after 40 days of storage): Before welding the sealing nails during battery manufacturing, a gas-generating cell was created by retaining the battery cell. The manufacturing and testing process for the gas-generating cell is as follows: A gas-generating nail was laser-welded to the injection port. The other end of the gas-generating nail was connected to a plastic hose filled with silicone oil, and the other end of the plastic hose was connected to a pressure gauge. Gas generation test conditions: The battery was initially charged to 4.35V with an initial pressure of 2000±300N and tested in a 70℃ high-temperature furnace (stored for 40 days). The changes in the pressure gauge readings were recorded. The test results are shown in Table 1.

[0136] Battery capacity test: Under conditions of 25±2℃, the battery was discharged to 2.8V at a current of 1 / 3C, then charged to 4.35V at a current of 1 / 3C, and then charged at a constant voltage until the current dropped to 0.05C to complete the full charge. Finally, the battery was discharged to 2.8V at a current of 1 / 3C. The result is the initial battery capacity C0.

[0137] Battery energy density test: During the battery capacity test, the battery is charged from full charge (100% SOC) to full discharge (0% SOC). The discharge voltage-capacity curve is integrated to obtain the total discharge energy of the battery. Battery energy density = total discharge energy of battery / total weight of battery.

[0138] Battery casing thickness margin: For hard-cased cells, this is the thickness of the bare cell after winding / the maximum thickness left inside the casing for the cell, to ensure assembly and allowance for future expansion.

[0139] XRD: X-ray powder crystal diffraction (XRD) is one of the most commonly used characterization techniques for analyzing material structures. The periodic repeating structure of crystals enables them to produce X-ray diffraction effects. The position of the diffracted X-rays is related to the unit cell parameters (unit cell shape and size), i.e., determined by the interplanar spacing; the relative intensity of the diffracted rays is determined by the types, numbers, and arrangement of atoms within the unit cell. X-ray diffraction on specific crystalline materials reflects a specific crystal structure diffraction pattern, thus allowing for the analysis of the material's phase structure. However, powder crystal diffraction suffers from significant peak overlap, making it difficult to separate and obtain precise diffraction intensity values. This results in some loss of structural crystal information, making it challenging to obtain accurate crystal structure data. Hugo M. Rietveld proposed a Rietveld full-spectrum fitting method for correcting crystal structures using full-spectrum fitting of polycrystalline diffraction data. Based on a given initial crystal structure model and parameters, a suitable peak shape function is used to calculate the diffraction pattern. The crystal structure parameters and peak shape parameters are then continuously adjusted using the least squares method to gradually match the calculated spectrum with the experimental spectrum, thereby obtaining the corrected structural parameters. In this application, the data refinement software used was the General Structure Analytic System (GSAS) for Rietveld structure refinement (Toby BHEXPGUI, a graphical user interface for GSAS[J]. Journal of Applied Crystallography, 2001, 34, 210-213).

[0140] Electrochemical in-situ XRD is an important method for testing the structural evolution of materials during charge and discharge processes. In-situ XRD testing typically requires a high-energy synchrotron radiation source. Synchrotron radiation is extremely strong electromagnetic radiation emitted along the tangent of the orbital curve of high-energy charged particles moving at near-light speed in a magnetic field. Synchrotron radiation sources possess characteristics such as wide wavelength range, high collimation, high polarization, high purity, and high brightness. The design of the electrolytic cell for synchrotron radiation in-situ XRD is as follows... Figure 9 As shown, a Kapton membrane was used as the sealing window, and the test mode was transmission mode.

[0141] The synchrotron X-ray diffraction experiments in this application were conducted at the Advanced Light Source 11-ID-D at Argonne National Laboratory in the United States, with an X-ray diffraction wavelength of [wavelength missing].

[0142] During the charging process of the battery (from a fully discharged state of 0% SOC to a fully charged state of 100% SOC), the positive electrode continuously delithiates. For ternary materials, the diffraction peaks of the material can be attributed to the hexagonal layered structure of α-NaFeO2 with the R-3m space group. During the lithium ion delithiation process, the changes in the interplanar spacing of the (003) peak and (110) peak in the XRD pattern represent the changes in the cell parameters c and a. The in-situ battery was subjected to the first charge and discharge cycle to obtain the XRD patterns of the positive electrode in different delithiation states (SOC). The XRD patterns of different delithiation states were refined using GSAS software with Rietveld to obtain the changes in the cell parameters a and c of different delithiation states. The cell volume V = a was calculated using the cell parameters. 2 *c*sin120°, thus the cell volume change of the positive electrode in different lithium-depleted states (SOC) can be obtained (see Figure 8 The initial cell volume V0 is calculated by fitting the XRD pattern of the initially fully lithium-intercalated cathode (corresponding to 0% SOC of the full cell) with Rietveld to obtain the cell parameters c0 and a0. As charging progresses, lithium ions are continuously extracted from the cathode (corresponding to an increase in the SOC of the full cell), resulting in XRD patterns of the cathode at different delithiation states (SOC). Rietveld is then used to fit the cell parameters c and a of the cathode at these different delithiation states, and the cell volume V is calculated. Therefore, the change in cell volume of the cathode at different delithiation states (SOC) can be calculated as (V - V0) / V0. When the cell volume V corresponds to the 100% SOC state of the full cell, the above formula calculates the cell volume shrinkage rate at 100% SOC. SOC: State of Charge, refers to the percentage of remaining battery capacity; 100% is a fully charged state, and 0% is a fully discharged state.

[0143] Table 1

[0145] As can be seen from Table 1 above, the embodiments of this application can achieve better overall performance than the comparative examples, and can avoid the downward trend of lithium-ion batteries or excessive gas production. Specifically, as can be seen from Example 1 compared to Comparative Examples 1 and 2, and Example 3 compared to Comparative Example 3, when different bare positive electrode cells are used in the battery cell, the lithium-ion battery can achieve better overall performance and can avoid the downward trend of lithium-ion batteries or excessive gas production.

[0146] Furthermore, although, as described above, the embodiments of this application can achieve better overall performance than the comparative examples, and can avoid the rapid degradation or excessive gas generation of lithium-ion batteries, it can be seen from Example 1 compared to Example 8 that when the bare cell B, which includes polycrystalline high-nickel material, is placed on the outside of the cell, the lithium-ion battery can achieve better cycle performance. When cycled to 1000 cycles, the capacity retention rate of Example 1 is significantly improved compared to Example 8.

[0147] Compared with Examples 9 and 10, other embodiments show that when the proportion of high-nickel active material is too large, the gas production performance of lithium-ion batteries may deteriorate. When the proportion of high-nickel active material is too small, the improvement of cycle expansion may not be obvious, and the battery may be prone to lithium plating in the middle section of the bare cell due to large expansion force in the later stage of cycle, resulting in a drop in cycle performance.

[0148] As can be seen from Example 7, a polycrystalline ternary cathode material with a low nickel content can be further introduced into bare cell B, which can improve the overall performance of lithium-ion battery. Although the introduction of this material may lead to a relative deterioration in gas generation performance, it can improve the overall performance of lithium-ion secondary battery in combination with the ternary cathode material with a high nickel content in bare cell B.

[0149] As can be seen from Examples 3 and 4, a single-crystal or near-single-crystal ternary cathode material with a low nickel content can be further introduced into the bare cell B, which can improve the overall performance of the lithium-ion battery. While ensuring that the cycle expansion is improved, the gas generation performance will also be better, and the lithium-ion battery has better overall performance when the k value is in a suitable range.

[0150] In summary, this invention effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0151] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A lithium-ion secondary battery, characterized in that, The device includes a bare cell receiving cavity, in which a bare cell assembly is provided. The bare cell assembly includes one or more bare cells A and one or more bare cells B. The bare cell A includes a first positive electrode plate, which includes a first positive active material selected from a single-crystal or near-single-crystal low-nickel ternary positive electrode material A1. The bare cell B includes a second positive electrode plate, which includes a second positive active material and / or a third positive active material selected from a polycrystalline high-nickel ternary positive electrode material B1. The third positive active material is selected from a polycrystalline low-nickel ternary positive electrode material B2.

2. The lithium-ion secondary battery according to claim 1, characterized in that, The molecular formula of the single-crystal or near-single-crystal low-nickel ternary cathode material Al is LiNi. x1 Co y1 Mn 1-x1-y1 O2, where 0 < x1 ≤ 0.65, 0 < y1 < 0.35, and 0 < 1 - x1 - y1 < 0.

35.

3. The lithium-ion secondary battery according to claim 1, characterized in that, The molecular formula of the single-crystal or near-single-crystal low-nickel ternary cathode material Al is LiNi. x1 Co y1 Mn 1-x1-y1 O2, where 0 < x1 ≤ 0.55, 0 < y1 < 0.45, and 0 < 1 - x1 - y1 < 0.

45.

4. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that, The molecular formula of the polycrystalline high-nickel ternary cathode material B1 is LiNi. x2 Co y2 Mn 1-x2-y2 O2, where 0.7≤x2<1, 0<y2<0.3, 0<1-x2-y2<0.

3.

5. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that, The molecular formula of the polycrystalline high-nickel ternary cathode material B1 is LiNi. x2 Co y2 Mn 1-x2-y2 O2, where 0.7≤x2≤0.8, 0.2<y2<0.3, 0.2<1-x2-y2<0.

3.

6. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that, The molecular formula of the polycrystalline low-nickel ternary cathode material B2 is LiNi. x3 Co y3 Mn 1-x3-y3 O2, where 0 <x3≤0.65,0<y3<0.35,0<1-x3-y3<0.35。 7. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that, The molecular formula of the polycrystalline low-nickel ternary cathode material B2 is LiNi. x3 Co y3 Mn 1-x3-y3 O2, where 0 < x3 ≤ 0.55, 0 < y3 < 0.45, and 0 < 1 - x3 - y3 < 0.

45.

8. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that, The single-crystal or near-single-crystal low-nickel ternary cathode material A1 has a 100% SOC charging cell volume shrinkage rate of ≤3%. And / or, the 100% SOC charging cell volume shrinkage rate of the polycrystalline high-nickel ternary cathode material B1 is ≥4%; And / or, the 100% SOC charging cell volume shrinkage rate of the polycrystalline low-nickel ternary cathode material B2 is ≤3%.

9. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that, Compared to bare cell A, bare cell B is located closer to the outer side of the bare cell group.

10. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that, Compared to bare cell B, bare cell A is located closer to the center of the bare cell group.

11. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that, The second positive electrode also includes a fourth positive electrode active material, which is selected from single crystal or near-single crystal low-nickel ternary materials.

12. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that, The second positive electrode also includes a fourth positive electrode active material, which is selected from single-crystal or near-single-crystal low-nickel ternary positive electrode material A2, and the molecular formula of the single-crystal or near-single-crystal low-nickel ternary positive electrode material A2 is LiNi. x4 Co y4 Mn 1-x4- y4 O2, where 0 < x4 ≤ 0.55, 0 < y4 < 0.45, and 0 < 1 - x4 - y4 < 0.

45.

13. The lithium-ion secondary battery according to claim 11, characterized in that, The single-crystal or near-single-crystal low-nickel ternary cathode material A2 has a 100% SOC charging cell volume shrinkage rate of ≤3%.

14. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that, In the lithium-ion secondary battery, the mass ratio k of the total mass of the monocrystalline positive electrode active material to the total mass of the polycrystalline positive electrode active material is 0.5 to 9.

15. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized in that, The coating amount of the negative electrode in the bare cell A is ≤0.150g / 1540.25mm^2.

16. A battery module, characterized in that, Includes the lithium-ion secondary battery as described in any one of claims 1 to 15.

17. A battery pack, characterized in that, Includes the battery module as described in claim 16.

18. An electrical appliance, characterized in that, It includes one or more of the lithium-ion secondary batteries according to any one of claims 1 to 15, the battery module according to claim 16, or the battery pack according to claim 17.

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