A winding cell, a battery and an energy storage device

Abstract

The present application relates to a kind of winding electric core, battery and energy storage device, for solving the technical problem that existing winding electric core is prone to lithium precipitation in circular arc area, thereby leading to battery capacity attenuation and there is certain security risk.The winding electric core provided by the present application includes positive pole piece, diaphragm and negative pole piece, the positive pole piece, the diaphragm and the negative pole piece are laminated and wound to form the winding electric core, the positive pole piece includes positive pole current collector and positive pole active coating coated on the surface of the positive pole current collector, the negative pole piece includes negative pole current collector, the negative pole current collector includes oppositely arranged first surface and second surface, the first surface is coated with first negative pole active coating, the second surface is coated with second negative pole active coating, the design value of the NP ratio of the first negative pole active coating and the positive pole active coating on its opposite side is a, the design value of the NP ratio of the second negative pole active coating and the positive pole active coating on its opposite side is b, wherein a>b.

Description

Technical Field

[0001] This invention relates to the field of battery manufacturing technology, and in particular to a wound cell, a battery, and an energy storage device. Background Technology

[0002] Wound cells are widely used in prismatic and pouch lithium-ion batteries due to their mature technology and high efficiency. However, the structure of a wound cell consists of flat and arc-shaped regions. In the arc-shaped region, due to the difference in the paths of the inner and outer rings, the arc lengths of the positive and negative electrode plates are not equal. Specifically, for the same arc-shaped region, the arc length of the outer electrode (positive electrode plate) is greater than that of the inner electrode (negative electrode plate). This means that in the arc-shaped region, the area of ​​the positive electrode plate corresponding to a unit arc length of negative electrode plate is larger than that in the flat region.

[0003] Currently, to ensure battery safety and prevent lithium plating, wound cell designs typically require a negative-to-positive capacity ratio (NP ratio) greater than 1, meaning the negative electrode has a slightly excess capacity. Conventional designs employ a uniform areal capacity design across the entire negative electrode sheet, resulting in a uniform average NP ratio (e.g., 1.1) for the cell. However, this uniform design ignores the spatial non-uniformity introduced by the wound structure. In the curved region, due to the aforementioned geometric effects, the actual local negative electrode capacity available for receiving lithium ions is relatively insufficient, causing the effective local NP ratio in this region to be lower than the cell's average NP ratio. Especially under harsh conditions such as high-rate charging and low-temperature charging, lithium ions preferentially deposit on the negative electrode surface in the curved region, forming lithium dendrites. Lithium plating not only leads to capacity decay but also poses serious safety hazards.

[0004] Therefore, finding a technical solution that can solve the above-mentioned technical problems has become an important research topic for those skilled in the art. Summary of the Invention

[0005] The purpose of this invention is to provide a wound battery cell, a battery, and an energy storage device to solve the technical problem that existing wound battery cells are prone to lithium plating in the arc area, which leads to battery capacity decay and certain safety hazards.

[0006] To achieve this objective, the present invention adopts the following technical solution: This invention provides a wound battery cell, comprising a positive electrode, a separator, and a negative electrode. The positive electrode, the separator, and the negative electrode are stacked and wound to form the wound battery cell. The positive electrode includes a positive current collector and a positive active coating coated on the surface of the positive current collector. The negative electrode includes a negative current collector, which includes a first surface and a second surface disposed opposite to each other. The first surface is coated with a first negative active coating, and the second surface is coated with a second negative active coating. The designed NP ratio of the first negative active coating to the positive active coating on its opposite side is a, and the designed NP ratio of the second negative active coating to the positive active coating on its opposite side is b, wherein a > b.

[0007] Optionally, a and b also satisfy the following relationship: a=(1.03~1.08)*b, 1.07 ≤ b ≤1.14.

[0008] Optionally, along the thickness direction of the negative electrode current collector, the first end of the first negative electrode active coating is aligned with the first end of the second negative electrode active coating; Along the length direction of the negative electrode current collector, the length of the first negative electrode active coating is greater than the length of the second negative electrode active coating.

[0009] Optionally, the negative electrode active material in the first negative electrode active coating and the second negative electrode active coating is graphite, wherein the graphite has a Dv50 of 9~15μm and a BET of 0.5~1.5μm. 2 / g.

[0010] Optionally, the positive electrode active coating contains a positive electrode active material, the positive electrode active material includes Ni, and the mass ratio of Ni in the positive electrode active material is 35~42%wt.

[0011] Optionally, the Dv50 of the positive electrode active material is 3~6 μm, and the BET of the positive electrode active material is 0.5~1.5 μm. 2 / g.

[0012] Optionally, the positive electrode active material is a ternary material.

[0013] Optionally, the first negative electrode active coating and the second negative electrode active coating have the same coating thickness.

[0014] The present invention provides a battery comprising the above-described wound cell.

[0015] The present invention provides an energy storage device, including the battery described above.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: In the wound cell of the present invention, the design value of the NP ratio of the first negative electrode active coating to the positive electrode active coating on its opposite side is a, and the design value of the NP ratio of the second negative electrode active coating to the positive electrode active coating on its opposite side is b. A and b are differentiated so that a > b. Under this design, the amount of active material coated in the first negative electrode active coating increases, which can effectively improve the local negative electrode capacity for receiving lithium ions in the arc region of the wound cell. This makes the NP ratio of the arc region closer to the average NP ratio of the wound cell, thereby resulting in less lithium plating in the arc region of the wound cell compared to existing wound cells, or even no lithium plating at all. This slows down the capacity decay of the battery and gives the battery a longer service life, lower thickness expansion, and higher safety performance. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the cross-sectional structure of the negative electrode sheet in a wound battery cell provided in an embodiment of the present invention.

[0019] Illustration: Negative electrode current collector 1; First negative electrode active coating 2; Second negative electrode active coating 3. Detailed Implementation

[0020] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0021] On one hand, the present invention provides a wound battery cell, including a positive electrode sheet, a separator, and a negative electrode sheet. The positive electrode sheet, the separator, and the negative electrode sheet are stacked and wound to form the wound battery cell. The positive electrode sheet includes a positive current collector and a positive active coating coated on the surface of the positive current collector. The negative electrode sheet includes a negative current collector, which includes a first surface and a second surface disposed opposite to each other. The first surface is coated with a first negative active coating, and the second surface is coated with a second negative active coating. The design value of the NP ratio of the first negative active coating to the positive active coating on its opposite side is a, and the design value of the NP ratio of the second negative active coating to the positive active coating on its opposite side is b, wherein a > b.

[0022] It should be noted that in existing wound cells, the radius of curvature of the arc region of the positive and negative electrode sheets increases with the number of layers. This results in a positive electrode sheet with a larger radius of curvature corresponding to a negative electrode sheet with a smaller radius of curvature. The actual local negative electrode capacity that can be used to receive lithium ions is relatively insufficient, which leads to the local effective NP ratio of the arc region being lower than the average NP ratio of the cell.

[0023] Based on the above, the wound cell of the present invention has a designed NP ratio of the first negative electrode active coating to the positive electrode active coating on its opposite side as value a, and a designed NP ratio of the second negative electrode active coating to the positive electrode active coating on its opposite side as value b. Furthermore, a and b are differentiated to ensure that a > b. Under this design, the amount of active material coated in the first negative electrode active coating increases, effectively improving the local negative electrode capacity for receiving lithium ions in the arc region of the wound cell. This makes the NP ratio in the arc region closer to the average NP ratio of the wound cell, resulting in less lithium plating or no lithium plating in the arc region of the wound cell compared to existing wound cells. This slows down battery capacity decay and gives the battery a longer lifespan, lower thickness expansion, and higher safety performance.

[0024] Furthermore, in the wound battery cell of the present invention, a and b also satisfy the following relationship: a=(1.03~1.08)*b, 1.07 ≤ b ≤1.14.

[0025] It should be noted that the above design precisely limits the ratio of a to b and the range of b values. Specifically, limiting a to (1.03~1.08)*b ensures the appropriateness of the differentiated design. When a = 1.03*b or less, the problem can theoretically be solved, but in practice, there are tolerances in the coating process of the first negative electrode active coating. If the difference is too small, it is difficult to achieve the coating. When a = 1.08*b or more, the lithium plating problem can also be solved, but more first negative electrode active coating will result in a thicker negative electrode sheet, which will reduce energy density. In addition, an excessively high NP ratio will cause more lithium ions in the positive electrode to be inserted into the negative electrode. At this time, the potential of the positive electrode will be higher, which will oxidize the electrolyte and pose a risk of gas generation. Therefore, by limiting a as described above, the technical effect can be optimized.

[0026] Meanwhile, a safety benchmark is set for the second negative electrode active coating by limiting 1.07 ≤ b ≤ 1.14, ensuring that the NP ratio on this side is also greater than 1, leaving sufficient safety margin to prevent the risk of lithium plating in any area. This numerical range is a performance-safety balance point verified by a large number of experiments, achieving optimal safety protection while ensuring high energy density of the whole cell.

[0027] Furthermore, in the wound cell of the present invention, along the thickness direction of the negative electrode current collector, the first end of the first negative electrode active coating is aligned with the first end of the second negative electrode active coating; Along the length direction of the negative electrode current collector, the length of the first negative electrode active coating is greater than the length of the second negative electrode active coating.

[0028] It should be noted that in the above design, alignment along the thickness direction facilitates the cutting and winding alignment of the electrode sheets, ensuring manufacturing precision. However, the first negative electrode active coating is longer than the second negative electrode active coating along its length. This means that after winding, the longer first negative electrode active coating will be more distributed in the "head" or "tail" regions where there are more winding turns and a more pronounced arc effect. This asymmetric coating method allows for precise placement of the high NP ratio first negative electrode active coating in areas with large winding arcs and significant differences in the inner and outer winding paths of the wound cell. This achieves the most effective local capacity replenishment with the most economical material usage, further optimizing the suppression of lithium plating.

[0029] Furthermore, in the wound battery cell of the present invention, the negative electrode active material in the first negative electrode active coating and the second negative electrode active coating is graphite, wherein the Dv50 of the graphite is 9~15μm and the BET (specific surface area) of the graphite is 0.5~1.5m². 2 / g.

[0030] It should be noted that the physical parameters of the graphite used as the negative electrode active material are limited. Dv50 is medium-sized graphite with a particle size of 9–15 μm, which ensures both high tap density and volumetric energy density, while also providing good ion and electron transport pathways. BET (specific surface area) is 0.5–1.5 m². 2 The specific surface area range per gram is crucial: too low a BET (specific surface area) leads to insufficient reactivity, affecting rate performance; too high a BET exacerbates side reactions, increases initial irreversible capacity loss, and affects electrolyte retention. Graphite within this optimized range, in synergy with a differentiated NP ratio design, can provide sufficient and rapid lithium-ion insertion capability while maintaining electrode structure stability and low side reaction activity, thereby improving safety without compromising battery cycle life and efficiency.

[0031] Furthermore, in the wound battery cell of the present invention, the positive electrode active coating contains a positive electrode active material, which is a ternary material.

[0032] It should be noted that in the above design, the ternary material contains Ni, Co, Mn or Ni, Co, Al, specifically lithium nickel cobalt manganese oxide or lithium nickel cobalt aluminum oxide. Limiting the positive electrode active material to ternary materials is the key to realizing high energy density batteries.

[0033] Specifically, in the above design, Ni accounts for 35~42%wt of the total positive electrode active material. This range of design can meet the requirements of most existing ternary positive electrode material systems.

[0034] The positive electrode active material has a Dv50 of 3~6 μm and a BET (specific surface area) of 0.5~1.5 m². 2 / g.

[0035] It should be noted that the above design limits the particle size and specific surface area of ​​the positive electrode active material to optimize the kinetic performance on the positive electrode side, synergizing with the optimization on the negative electrode side. A finer particle size of 3~6μm (Dv50) helps shorten the lithium-ion diffusion path and improve rate performance. A BET (specific surface area) of 0.5~1.5m² is also beneficial. 2 The appropriate specific surface area per g ensures a sufficient reaction interface while avoiding side reactions caused by excessive active surface.

[0036] Furthermore, in the wound cell of the present invention, the coating thickness of the first negative electrode active coating and the second negative electrode active coating are the same.

[0037] It should be noted that limiting the coating thickness on both sides to the same level simplifies the process control of the coating procedure. Differentiation can be achieved simply by adjusting the slurry delivery rate or coating speed, without needing to change the coating mold or adjust the electrode rolling process. This design achieves significant technical benefits while minimizing the cost and complexity of modifying existing production processes, thus improving the feasibility and industrialization feasibility of this invention.

[0038] Secondly, the present invention provides a battery comprising the aforementioned wound cell.

[0039] It should be noted that in the battery of the present invention, the NP ratio a of the first negative electrode active coating of the wound cell and the NP ratio b of the second negative electrode active coating of the wound cell are designed differently, so that a > b. This can effectively improve the local negative electrode capacity for receiving lithium ions in the arc region of the wound cell, so that the NP ratio of the arc region is closer to the average NP ratio of the wound cell. This makes the lithium plating in the arc region of the wound cell less severe or even non-existent compared to existing wound cells, thereby slowing down the capacity decay of the battery and giving the battery a longer service life, lower thickness expansion and higher safety performance.

[0040] Thirdly, the present invention provides an energy storage device comprising the aforementioned battery.

[0041] It should be noted that the energy storage device of the present invention can be a battery pack, etc., and this embodiment does not limit it.

[0042] In the energy storage device of the present invention, the NP ratio a of the wound cell in the first negative electrode active coating and the NP ratio b of the wound cell in the second negative electrode active coating are differentiated so that a > b. This can effectively improve the local negative electrode capacity for receiving lithium ions in the arc region of the wound cell, so that the NP ratio of the arc region is closer to the average NP ratio of the wound cell. This makes the lithium plating in the arc region of the wound cell less severe or even non-existent compared to existing wound cells, thereby slowing down the capacity decay of the battery and giving the battery a longer service life, lower thickness expansion and higher safety performance.

[0043] The above is a detailed description of a wound cell, battery, and energy storage device provided by the present invention. The performance of the battery with the wound cell will be tested below with multiple embodiments and comparative examples to verify the technical effect of the present invention.

[0044] First, the battery is manufactured according to the specific parameters of the wound cell shown in Table 1 below, as well as the comparative examples. The specific manufacturing process is as follows: Preparation of positive electrode sheet The positive electrode active material lithium nickel manganese oxide, the positive electrode conductive agent acetylene black (SuperP), polyvinylidene fluoride (PVDF) binder, and carbon nanotubes (CNT) are mixed evenly in a mass ratio of 97:1.5:1.0:0.5, and then evenly dispersed with 1-methyl-2-pyrrolidone (NMP) to form a uniform positive electrode slurry. The mixed positive electrode slurry is coated on both sides of an aluminum foil current collector, and then baked, rolled, and cut into sheets to obtain the positive electrode sheet.

[0045] Preparation of negative electrode sheet The negative electrode active material graphite, thickener CMC and negative electrode binder SBR are mixed evenly in a mass ratio of 97:1.5:1.5 and then evenly dispersed with deionized water to form a uniform negative electrode slurry. The mixed slurry is coated on both sides of the copper foil current collector, and then baked, rolled, and cut into sheets to obtain the negative electrode sheet. Manufacturing of lithium-ion batteries The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator in the middle of the positive and negative electrode. After winding and welding the tabs, a bare cell is obtained. The bare cell is placed in an aluminum-plastic film for liquid injection and encapsulation to obtain a lithium-ion battery.

[0046] The specific testing method is as follows: The battery prepared above was charged at a constant current and constant voltage of 0.5C to 4.4V, cut off at 0.05C, allowed to stand for 10 minutes, discharged at a constant current of 0.5C to 3.0V, cycled at room temperature for 600 cycles, and the thickness was measured after cycling. Then, it was fully charged and disassembled to observe the interface of the negative electrode. The test results are shown in Table 2: Table 1 Table 2 in conclusion: By designing the NP ratio of the active coatings on both sides of the wound cell negative electrode with a > b, the problem of local capacity deficiency and lithium plating caused by the difference in geometric path in the arc region was successfully solved. Experimental data confirms that when the parameters are strictly controlled within the range of a = (1.03~1.08)*b and 1.07≤b≤1.14 (as in Examples 1-6), no obvious lithium plating occurs in the arc region, the energy retention rate is high, the thickness expansion is low, and the battery does not exhibit lithium plating after 600 cycles, with an energy retention rate of over 82% and a thickness expansion rate of less than 9%, resulting in optimal overall performance.

[0047] Comparative Examples 1, 2, 4, and 5: Severe lithium plating leads to loss of active lithium, reduced energy retention, and localized cell arching and significant thickness expansion. Comparative Example 3: No lithium plating, but the NP is too high, resulting in energy density loss and increased positive electrode pressure. Therefore, it can be concluded that any design deviating from this range (such as Comparative Examples 1-5) will result in problems such as lithium plating, capacity decay, energy density loss, or accelerated expansion, especially when a≤b. This indicates that the parameter range defined by this invention is the key to achieving high-safety, long-life batteries.

[0048] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A wound battery cell, comprising a positive electrode, a separator, and a negative electrode, wherein the positive electrode, the separator, and the negative electrode are stacked and wound to form the wound battery cell, wherein the positive electrode comprises a positive current collector and a positive active coating coated on the surface of the positive current collector, characterized in that, The negative electrode sheet includes a negative current collector, which includes a first surface and a second surface disposed opposite to each other. The first surface is coated with a first negative active coating, and the second surface is coated with a second negative active coating. The design value of the NP ratio of the first negative active coating to the positive active coating on its opposite side is a, and the design value of the NP ratio of the second negative active coating to the positive active coating on its opposite side is b, wherein a > b.

2. The wound battery cell according to claim 1, characterized in that, a and b also satisfy the following relationship: a=(1.03~1.08)*b, 1.07 ≤ b ≤1.

14.

3. The wound battery cell according to claim 1, characterized in that, Along the thickness direction of the negative electrode current collector, the first end of the first negative electrode active coating is aligned with the first end of the second negative electrode active coating; Along the length direction of the negative electrode current collector, the length of the first negative electrode active coating is greater than the length of the second negative electrode active coating.

4. The wound battery cell according to claim 1, characterized in that, The negative electrode active material in both the first and second negative electrode active coatings is graphite, wherein the graphite has a Dv50 of 9~15μm and a BET of 0.5~1.5μm. 2 / g.

5. The wound battery cell according to claim 1, characterized in that, The positive electrode active coating contains a positive electrode active material, which includes Ni, and the mass ratio of Ni in the positive electrode active material is 35~42%wt.

6. The wound battery cell according to claim 5, characterized in that, The positive electrode active material has a Dv50 of 3~6μm and a BET of 0.5~1.5μm. 2 / g.

7. The wound battery cell according to claim 5, characterized in that, The positive electrode active material is a ternary material.

8. The wound battery cell according to claim 1, characterized in that, The first negative electrode active coating has the same coating thickness as the second negative electrode active coating.

9. A battery, characterized in that, Including the wound battery cell as described in any one of claims 1 to 8.

10. An energy storage device, characterized in that, Includes the battery as described in claim 9.

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