A battery

Abstract

The application provides a battery, which comprises a film shell, an electrode assembly arranged in the film shell and an electrolyte, the electrode assembly comprises a positive electrode sheet, a diaphragm and a negative electrode sheet arranged in sequence, a first bottom coating layer is introduced into the first positive electrode sheet, and a second bottom coating layer is introduced into the second positive electrode sheet, the thickness relationship of the first bottom coating layer, the second bottom coating layer, the first positive electrode current collector and the second positive electrode current collector is limited to satisfy 0.2<= (H1-H2) / (B1-B2) <=0.5, and the content of 1,3-propane sulfone lactone in the electrolyte is between 0.1-6%, so that the transition metal ion dissolution caused by the excessively high local current density of the first positive electrode sheet and the purple stain problem of the corresponding negative electrode of the first positive electrode sheet can be effectively inhibited, and the cycle capacity retention rate of the battery can be significantly improved.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and more particularly to a battery. Background Technology

[0002] Stacked batteries are widely used in scenarios with extremely high requirements for energy density and safety due to their high volume utilization, low internal resistance and good heat dissipation performance, such as high-end consumer electronics (such as smartphones and laptops), electric vehicles (such as new energy vehicles) and energy storage systems (such as grid-scale energy storage).

[0003] In traditional stacked battery structures, the outermost electrode is usually a single-sided positive electrode, meaning that the positive active material is only coated on the side with the positive current collector. This structural asymmetry leads to an inherently higher current density for the single-sided positive electrode. The high current density will accelerate side reactions (such as excessive delithiation of the positive active material and dissolution of transition metal ions) and electrolyte consumption, resulting in the region being the first to run out of electrolyte in the later stages of cycling. This reduces the ion transport rate, and under high charging current, purple spots appear on the negative electrode surface corresponding to the single-sided positive electrode, degrading the cycle performance of the battery. Summary of the Invention

[0004] This invention provides a battery that can effectively suppress the dissolution of transition metal ions caused by excessively high local current density on the positive electrode single-sided sheet and the purple spot problem on the corresponding negative electrode, thereby significantly improving the cycle performance of the battery.

[0005] In related technologies, in traditional stacked battery structures, the outermost electrode is typically a single-sided positive electrode, meaning the positive active material is coated only on the side of the positive current collector. The inner electrodes are double-sided positive electrodes, meaning the positive active material is coated on both sides of the positive current collector. However, this invention has found that this design leads to rapid performance degradation in stacked batteries during cycling, especially in the later stages of cycling. Disassembling a stacked battery revealed "purple spots" on the negative electrode region opposite the single-sided positive electrode, accompanied by significant electrolyte consumption and the dissolution and deposition of transition metal ions (such as cobalt ions) from the positive electrode to the negative electrode. The reason for this is likely that only one side of the single-sided positive electrode participates in the reaction, resulting in a low active material loading per unit area. The positive electrode has a higher reaction interface, allowing it to withstand a much higher local current density than the double-sided positive electrode at the same current. This high current density accelerates side reactions (such as excessive delithiation of the positive electrode active material and dissolution of transition metal ions) and electrolyte consumption, leading to liquid shortage in this area during the later stages of cycling. This reduces the ion transport rate, and purple spots appear on the negative electrode surface corresponding to the single-sided positive electrode at high charging current. On the other hand, since the single-sided positive electrode only has an active layer on one side, the surface stress of the electrode is different, causing curling. Furthermore, the single-sided positive electrode is not completely bound in the direction of the battery tab extension. With repeated expansion and contraction during cycling, delamination between the single-sided positive electrode and the negative electrode is likely to occur. As the electrolyte is gradually consumed, this area will eventually also be liquid shortage, making the purple spot problem on the surface of the negative electrode more severe.

[0006] Designing the current collector thickness of the single-sided positive electrode sheet to be higher than that of the double-sided positive electrode sheet can effectively improve the curling of the single-sided positive electrode sheet. However, this invention found that excessive current collector thickness of the single-sided positive electrode sheet will increase the asymmetry of the electrode structure of the stacked battery, resulting in a higher local current density of the single-sided positive electrode sheet under the same total current. This causes the potential of the single-sided positive electrode sheet to rise too high at the end of charging, thereby triggering a series of the above-mentioned side reactions, which in turn aggravates the problem of purple spots appearing on the corresponding negative electrode during cycling.

[0007] Therefore, in order to achieve electrochemical environmental balance between single-sided and double-sided cells and suppress the above-mentioned failure modes from the root, it is urgent to design a stacked cell that is designed for the special working environment of the positive electrode single-sided cell.

[0008] Based on the above, this application provides the following technical solution:

[0009] In detail: The present invention provides a battery including a membrane housing, an electrode assembly and an electrolyte disposed within the membrane housing, the electrode assembly including a positive electrode, a separator and a negative electrode stacked sequentially, wherein the positive electrode includes at least one first positive electrode (single-sided positive electrode) and at least one second positive electrode (double-sided positive electrode), the first positive electrode being located on the outermost side of the electrode assembly, the first positive electrode including a first positive current collector, the first positive current collector including a first surface and a second surface disposed opposite to each other along its thickness direction, the first surface having a first positive active layer and a first base layer stacked thereon, the first base layer being located between the first surface and the first positive active layer, the first surface being away from the membrane housing, the second surface being close to the membrane housing, the thickness of the first base layer being H1 in μm, and the thickness of the first positive current collector being B1 in μm;

[0010] The second positive electrode includes a second positive current collector and a second positive active layer and a second base coating layer stacked on both sides of the second positive current collector. The second base coating layer is located between the second positive current collector and the second positive active layer. The thickness of the second base coating layer is H2 in μm, and the thickness of the second positive current collector is B2 in μm.

[0011] The electrolyte comprises 1,3-propanesulfonate lactone, wherein the mass percentage of 1,3-propanesulfonate lactone in the electrolyte is 0.1 wt%-6 wt%.

[0012] The battery satisfies the following condition: 0.2≤(H1-H2) / (B1-B2)≤0.5.

[0013] By employing the above technical solution, the present invention has at least the following advantages compared with the prior art:

[0014] The battery provided by this invention introduces a first undercoat layer in the first positive electrode and a second undercoat layer in the second positive electrode. By limiting the thickness relationship of the first undercoat layer, the second undercoat layer, the first positive current collector, and the second positive current collector to satisfy: 0.2 ≤ (H1-H2) / (B1-B2) ≤ 0.5, and the content of 1,3-propanesulfonate lactone in the electrolyte, the dissolution of transition metal ions caused by excessively high local current density in the first positive electrode and the purple spot problem appearing on the corresponding negative electrode of the first positive electrode can be effectively suppressed, thereby significantly improving its cycle stability. The main reason for this is that satisfying the above relationship indicates that the thickness of the first positive current collector is greater than that of the second positive current collector. Fluid thickness helps improve the curling problem of the first positive electrode, but it may also exacerbate the asymmetry of the battery electrode structure, leading to a higher current density in the first positive electrode. Therefore, controlling the ratio between the thickness difference (H1-H2) of the first and second undercoating layers and the thickness difference (B1-B2) of the first and second positive current collectors, utilizing the high impedance characteristics of the undercoating layer, can increase the impedance of the first positive electrode and reduce its overpotential. Controlling the ratio between 0.2 and 0.5 ensures that the impedance increment corresponding to the thickening of the first positive electrode foil is controlled within the optimal range, thereby making the current distribution on the electrode surface more uniform and avoiding excessive current concentration in local areas. Simultaneously, the introduction of 1,3-propanesulfonate lactone into the electrolyte and controlling its content within the above range can effectively passivate the positive electrode surface, reduce the dissolution of transition metal ions, and synergistically improve purple spots with the above relationship, ensuring the cycle stability of the stacked battery. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of the first positive electrode sheet according to a specific embodiment of the present invention.

[0016] Wherein, 1-first positive current collector, 2-first base coating, 3-first positive active layer.

[0017] Figure 2 This is a schematic diagram of the structure of the second positive electrode sheet according to a specific embodiment of the present invention.

[0018] Among them, 4-second positive current collector, 5-second bottom coating, 6-second positive active layer.

[0019] Figure 3 This is a schematic diagram of the structure of the first positive electrode sheet according to a specific embodiment of the present invention.

[0020] Among them, 1-first positive current collector, 2-first base coating, 3-first positive active layer, 7-third base coating, 8-fourth base coating.

[0021] Figure 4 This is a schematic diagram of the structure of the first positive electrode sheet according to a specific embodiment of the present invention.

[0022] Wherein, 9-protrusion, 10-recess, 11-second surface, 12-first surface, R1-diameter of the protrusion, R2-distance between the centers of two adjacent protrusions, and h-height of the protrusion. Detailed Implementation

[0023] To enable those skilled in the art to better understand the present invention, the present invention will be further described in detail below. The specific embodiments listed below are merely descriptions of the principles and features of the present invention, and the examples are only for explaining the present invention and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] In this application, the terms "first" and "second" are used for descriptive purposes only, to distinguish objects, such as substances, from one another, and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. For example, without departing from the scope of the embodiments of this application, "first XX" may also be referred to as "second XX," and similarly, "second XX" may also be referred to as "first XX." Thus, features defined with "first" and "second" may explicitly or implicitly include one or more of that feature.

[0025] In this application, references to "an embodiment," "an example," or "an example" mean that a specific feature, structure, or characteristic described in connection with that embodiment, example, or example is included in at least one embodiment of the invention. Therefore, the phrases "an embodiment," "an example," "an example," "an example," or "an example" appearing in various places throughout the specification do not necessarily refer to the same embodiment or example. Furthermore, specific features, structures, or characteristics can be combined in one or more embodiments or examples in any suitable combination and / or sub-combination.

[0026] This invention provides a battery, including a membrane housing, an electrode assembly disposed within the membrane housing, and an electrolyte. The electrode assembly includes a positive electrode, a separator, and a negative electrode stacked sequentially. The positive electrode includes at least one first positive electrode and at least one second positive electrode, with the first positive electrode located on the outermost side of the electrode assembly. (See also...) Figure 1 The first positive electrode includes a first positive current collector 1. The first positive current collector includes a first surface and a second surface disposed opposite to each other along its thickness direction. A first positive active layer 3 and a first base coating 2 are stacked on the first surface. The first base coating 2 is located between the first surface 1 and the first positive active layer 3. The first surface is away from the membrane shell, and the second surface is close to the membrane shell. The thickness of the first base coating is H1 in μm, and the thickness of the first positive current collector is B1 in μm.

[0027] See Figure 2 The second positive electrode includes a second positive current collector 4 and a second positive active layer 6 and a second base layer 5 stacked on both sides of the second positive current collector. The second base layer 5 is located between the second positive current collector 4 and the second positive active layer 6. The thickness of the second base layer 5 is H2 in μm, and the thickness of the second positive current collector is B2 in μm.

[0028] The electrolyte includes 1,3-propanesulfonate lactone (PS), which accounts for 0.1 wt%–6 wt% of the electrolyte by mass.

[0029] Among them, the battery satisfies: 0.2≤(H1-H2) / (B1-B2)≤0.5.

[0030] The battery provided by this invention introduces a first undercoat layer in the first positive electrode and a second undercoat layer in the second positive electrode. It employs a differentiated design approach for the first and second undercoat layers, the first positive electrode current collector, and the second positive electrode current collector. Furthermore, it introduces 1,3-propanesulfonate lactone into the electrolyte and controls its content. This effectively suppresses interfacial side reactions caused by excessively high local current density in the first positive electrode, the dissolution of transition metal ions, and the purple spot problem on the corresponding negative electrode of the first positive electrode. This significantly improves the cycle stability of the stacked battery. The main reasons include: firstly, ensuring that the stacked battery satisfies: 0.2 ≤ (H1 - H2) / (B1-B2)≤0.5 indicates that the thickness of the first positive current collector is greater than that of the second positive current collector. This helps to improve the curling problem of the first positive electrode sheet and makes better contact between the first positive electrode sheet and the separator / negative electrode sheet interface. However, it may also increase the asymmetry of the electrode structure of the stacked battery, resulting in a higher current density of the first positive electrode sheet. Therefore, the formula sets the ratio between the thickness difference (H1-H2) of the first and second bottom coating layers and the thickness difference (B1-B2) of the first and second positive current collectors. By utilizing the high impedance characteristics of the bottom coating layer, the impedance of the first positive electrode sheet can be increased, its overpotential reduced, and its ratio controlled within the range of 0.2-0.5. The thickness of the first positive electrode foil can be controlled within the optimal range to ensure that the impedance increment corresponding to the thickening of the first positive electrode foil is within the optimal range. This results in a more uniform current distribution on the electrode surface, avoiding excessive current concentration in local areas and thus improving the purple spot problem on the negative electrode surface corresponding to the first positive electrode. If (H1-H2) / (B1-B2) is less than 0.2, it means that the impedance compensation of the undercoating layer is insufficient and cannot offset the local high current density effect caused by the asymmetry of the first positive electrode structure and the thick current collector. At the end of charging, the potential of the first positive electrode remains too high, and the purple spots cannot be eliminated. If (H1-H2) / (B1-B2) is greater than 0.5, it means that the undercoating layer has been introduced... Excessive impedance compensation of the coating, although reducing the potential of the first positive electrode, will lead to an increase in the overall internal resistance of the battery and a deterioration in the rate performance of the battery. Furthermore, the first positive electrode is prone to thermal aging due to excessive Joule heating. Therefore, controlling the ratio of (H1-H2) to (B1-B2) within the above range can effectively suppress the problem of excessively high local current density of the first positive electrode and balance the stability of the first positive electrode. On the other hand, introducing 1,3-propanesulfonate lactone into the electrolyte of the battery and controlling its content can effectively passivate the positive electrode surface and reduce the dissolution of transition metal ions. This, together with the above relationship, can improve the purple spot problem and thus ensure the cycle stability of the stacked battery.

[0031] By way of example and not limitation, in some embodiments, the thickness of the undercoat (H1, H2) and the current collector thickness (B1, B2) of the first and second positive electrodes can be measured by scanning electron microscopy (SEM).

[0032] In the present invention, the mass content of 1,3 - propane sultone in the electrolyte can be obtained by conventional testing methods in the art, such as by gas chromatography or gas chromatography - mass spectrometry.

[0033] In some embodiments, the membrane housing is an aluminum - plastic shell membrane.

[0034] Exemplary but not limiting, the mass proportion of 1,3 - propane sultone in the electrolyte is any value among 0.1 wt%, 0.2 wt%, 0.5 wt%, 0.8 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, 5.0 wt%, 5.5 wt%, 6.0 wt%, etc. or the range composed of any two of them.

[0035] Exemplary but not limiting, (H1 - H2) / (B1 - B2) is any value among 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, etc. or the range composed of any two of them.

[0036] In some embodiments, 1μm ≤ H1 ≤ 5μm.

[0037] Among them, the first bottom coating serves as a transition layer between the first current collector and the first positive electrode active layer. Controlling the thickness of the bottom coating within the above range can ensure that the first bottom coating can form a continuous and dense barrier layer, providing sufficient impedance to inhibit the local current concentration caused by the structural asymmetry and thick current collector of the first positive electrode sheet, and ensuring that the compensation effect does not fail due to coating defects. If H1 > 5μm, the ohmic polarization caused by the overly thick first bottom coating increases excessively, deteriorating the rate performance; if H1 is less than 1μm, it is difficult for the first bottom coating to form a continuous and dense electron - conduction barrier layer, and defects such as uneven thickness are likely to occur during coating, and it cannot effectively inhibit the problem of overly high local current density caused by the structural asymmetry and relatively thick current collector of the first positive electrode sheet.

[0038] Exemplary but not limiting, H1 is any value among 1.0μm, 1.2μm, 1.5μm, 1.8μm, 2.0μm, 2.2μm, 2.5μm, 2.8μm, 3.0μm, 3.2μm, 3.5μm, 3.8μm, 4.0μm, 4.2μm, 4.5μm, 4.8μm, 5.0μm, etc. or the range composed of any two of them.

[0039] In some embodiments, 0μm < H2 ≤ 4μm.

[0040] Controlling the thickness of the second undercoat layer within the aforementioned range ensures a reasonable thickness difference between the first and second undercoats. This prevents excessive differences in interface performance between the two electrodes due to the undercoat layer being applied only to one side of the first positive electrode, allowing impedance compensation to be directed towards the first positive electrode. It also prevents the control effect on the local current density of the first positive electrode from being weakened by similar thicknesses of the two undercoats or by an excessively thick second undercoat layer. On the other hand, since the second positive electrode has a double-sided coating structure and its current distribution is relatively uniform, an excessively thick undercoat layer (exceeding 4μm) would unnecessarily increase ohmic polarization inside the battery, especially exacerbating energy loss and heat generation during high-current charging and discharging, potentially lowering the overall rate performance and cycle stability of the battery. Therefore, setting H2 within the aforementioned range ensures that the first positive electrode can obtain sufficient impedance compensation through a thicker undercoat layer to eliminate negative electrode purple spots and suppress side reactions, while avoiding sacrificing the battery's kinetic performance due to an excessively thick undercoat layer on the internal electrodes. This achieves a balance between structural asymmetry compensation and overall internal resistance optimization in stacked batteries.

[0041] By way of example and not limitation, H2 is any value or a range of any two of the following: 0.1μm, 0.2μm, 0.3μm, 0.5μm, 0.8μm, 1.0μm, 1.2μm, 1.5μm, 1.8μm, 2.0μm, 2.2μm, 2.5μm, 2.8μm, 3.0μm, 3.2μm, 3.5μm, 3.8μm, 4.0μm.

[0042] In some implementations, 10μm≤B1≤30μm.

[0043] By way of example and not limitation, B1 is any value or a range of any two of the following: 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, 30μm.

[0044] In some implementations, 6μm≤B2≤15μm.

[0045] By way of example and not limitation, B2 is any value or a range of any two of the following: 6.0μm, 6.5μm, 7.0μm, 7.5μm, 8.0μm, 8.5μm, 9.0μm, 9.5μm, 10.0μm, 10.5μm, 11.0μm, 11.5μm, 12.0μm, 12.5μm, 13.0μm, 13.5μm, 14.0μm, 14.5μm, 15.0μm.

[0046] In some implementations, 4μm≤(B1-B2)≤20μm.

[0047] By way of example and not limitation, B1-B2 is any value or a range of any two of the following: 4.0μm, 5.0μm, 5.5μm, 6.0μm, 6.5μm, 7.0μm, 7.5μm, 8.0μm, 8.5μm, 9.0μm, 9.5μm, 10.0μm, 10.5μm, 11.0μm, 11.5μm, 12.0μm, 12.5μm, 13.0μm, 13.5μm, 14.0μm, 14.5μm, 15.0μm, 15.5μm, 16.0μm, 16.5μm, 17.0μm, 17.5μm, 18.0μm, 18.5μm, 19.0μm, 19.5μm, 20.0μm.

[0048] In this invention, controlling the thickness B1 of the first positive current collector, the thickness B2 of the second positive current collector, or the thickness difference (B1-B2) between the first and second positive current collectors within the aforementioned range ensures, on the one hand, that the first positive current collector possesses sufficient mechanical strength to mitigate the curling problem of the outermost single-sided electrode, enabling effective interfacial contact between it and the separator and negative electrode. On the other hand, controlling the upper limit of B1 to 30 μm further prevents excessive structural asymmetry caused by an excessively thick first positive current collector, preventing a sharp increase in local current density in the first positive electrode due to excessive foil thickness, thereby providing a controllable window for impedance compensation of the undercoating layer. If B1 is less than 10 μm, the improvement in the curling problem of the outermost single-sided electrode is limited. Since the single-sided positive electrode is not fully bound in the electrode tab extension direction of the battery, repeated expansion and contraction during cycling easily leads to delamination between the single-sided positive electrode and the negative electrode. As the electrolyte is gradually consumed, this area will eventually lack electrolyte, and the purple spot problem on the surface of the negative electrode will also be only partially improved. Appropriately thinning the second positive current collector and controlling B2 within the aforementioned range helps reduce the volume and mass ratio of inactive materials inside the cell, thereby increasing energy density. Furthermore, limiting the thickness to 4μm ≤ (B1-B2) ≤ 20μm ensures good anti-bending capability of the first positive electrode sheet while creating impedance compensation that matches the thickness difference of the bottom coating. This more effectively suppresses the local current density of the first positive electrode sheet, avoiding problems such as increased side reactions, increased internal resistance, and process reliability issues caused by insufficient or excessive impedance compensation.

[0049] In some embodiments, the first positive electrode active layer includes: a first positive electrode active material, a third conductive agent, and a fifth binder; the second positive electrode active layer includes: a second positive electrode active material, a fourth conductive agent, and a sixth binder; wherein the first positive electrode active material and the second positive electrode active material can be selected from commonly used positive electrode active materials in the art, such as each independently including one or more of: lithium cobalt oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese phosphate, and lithium iron phosphate; lithium manganese oxide can be selected from LiMnO2 and LiMn2O4; lithium nickel cobalt manganese oxide can be selected from LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 One or more of O2. The third and fourth conductive agents can be selected from conductive agents commonly used in the art, such as one or more of conductive carbon black, carbon nanotubes, graphene, and vapor-grown carbon fibers, each independently selected. The fifth and sixth binders can be selected from binders commonly used in the art, such as one or more of polyvinylidene fluoride, styrene-butadiene rubber latex, sodium carboxymethyl cellulose, polyacrylic acid, polyurethane, polyamide, polyvinyl alcohol, polyethyleneimine, and polyimide, each independently selected.

[0050] In some embodiments, the first primer layer includes a first adhesive, wherein the mass percentage of the first adhesive based on the total mass of the first primer layer is W1.

[0051] The second base coat includes a second adhesive, and based on the mass of the second base coat, the mass percentage of the second adhesive is W2, where W1 and W2 satisfy: 0 wt% ≤ (W1-W2) ≤ 4 wt%.

[0052] Among them, W1 and W2 satisfy the above relationship, which can ensure that the first base coating has a high impedance, thereby increasing the impedance of the first positive electrode to further improve the purple spot problem.

[0053] In some implementations, 0.5wt% ≤ W1 ≤ 35wt%, and 0.5wt% ≤ W2 ≤ 35wt%.

[0054] By controlling W1 and W2 within the above range, it can be ensured that the impedance of the first positive electrode is higher than that of the second positive electrode, thereby improving the current density difference between the first and second positive electrodes, reducing electrolyte consumption, and further improving purple spots. At the same time, it can also avoid excessive binder content, which would lead to excessively low porosity in the undercoat layer and degrade the rate performance of the battery.

[0055] By way of example and not limitation, W1 and W2 are each independently any value or a range of any two of the following: 0.5wt%, 1wt%, 2wt%, 3wt%, 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, 25wt%, 28wt%, 30wt%, 32wt%, 35wt%.

[0056] In some embodiments, the first adhesive and the second adhesive each independently comprise one or more of polyvinylidene fluoride, styrene-butadiene rubber latex, sodium carboxymethyl cellulose, polyacrylic acid, polyurethane, polyamide, polyvinyl alcohol, polyethyleneimine, and polyimide.

[0057] Since the content of the conductive agent in the base coating affects the electronic conductivity of the base coating, the content of the conductive agent directly affects the impedance compensation of the positive electrode. In some embodiments, the first base coating includes a first conductive agent, the second base coating includes a second conductive agent, and the mass percentage of the first conductive agent is D1 based on the mass of the first base coating, and the mass percentage of the second conductive agent is D2 based on the mass of the second base coating, where D1≤D2.

[0058] Among them, D1 and D2 satisfy the above relationship, which can ensure that the electronic resistance of the first positive electrode is high, thereby increasing the electron transport impedance from the first current collector to the first positive electrode active layer and generating higher ohmic polarization in the early stage of charging. This is beneficial to reduce the current density of the first positive electrode and thus further suppress side reactions.

[0059] In some implementations, 0.2wt% ≤D1 ≤ 5.0wt%, 0.2wt% ≤D2 ≤ 5.0wt%.

[0060] By controlling D1 and D2 within the aforementioned range, it is possible to ensure that the impedance of the first positive electrode is higher than that of the second positive electrode, thereby improving the current density difference between the first and second positive electrodes. This allows the first undercoat to generate appropriate ohmic polarization in the early stages of charging, effectively reducing the actual voltage plateau of the first positive electrode and preventing it from entering the excessive delithiation potential range too early, thus suppressing transition metal dissolution and electrolyte side reactions. At the same time, controlling the conductive agent content of the second undercoat to 0.2wt%-5.0wt% ensures that the internal second positive electrode maintains low resistance characteristics to bear the main capacity contribution.

[0061] By way of example and not limitation, D1 is any value or a range of any two of the following: 0.2wt%, 0.3wt%, 0.5wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2.0wt%, 2.2wt%, 2.5wt%, 2.8wt%, 3.0wt%, 3.2wt%, 3.5wt%, 3.8wt%, 4.0wt%, 4.2wt%, 4.5wt%, 4.8wt%, 5.0wt%. D2 is any value or a range of any two of the following: 0.2wt%, 0.3wt%, 0.5wt%, 0.8wt%, 1.0wt%, 1.2wt%, 1.5wt%, 1.8wt%, 2.0wt%, 2.2wt%, 2.5wt%, 2.8wt%, 3.0wt%, 3.2wt%, 3.5wt%, 3.8wt%, 4.0wt%, 4.2wt%, 4.5wt%, 4.8wt%, 5.0wt%.

[0062] In some embodiments, the first conductive agent and the second conductive agent each independently include one or more of conductive carbon black, carbon nanotubes, graphene, and vapor-grown carbon fibers.

[0063] Small-diameter inorganic particles have a higher specific surface area, allowing them to form a denser packing structure in the coating. Furthermore, they have more contact points and smaller pore sizes, resulting in a more tortuous diffusion path for lithium ions in the undercoat, thus reducing ionic conductivity. Using smaller-diameter inorganic particles in the first undercoat improves its ion transport impedance. Additionally, using smaller inorganic particles in the first undercoat ensures more uniform contact with the active material layer, avoiding localized current hotspots. Therefore, in some embodiments, the first undercoat further includes first inorganic particles, and the second undercoat further includes second inorganic particles. The median particle size D501 of the first inorganic particles and the median particle size D502 of the second inorganic particles satisfy the following relationship: D501 ≤ D502.

[0064] The first bottom coating of the first positive electrode in the above embodiment uses small-diameter first inorganic particles, which can effectively slow down the delithiation rate of the first positive electrode in the early stage of charging, and prevent it from entering the excessive delithiation potential range too early, thereby further suppressing the dissolution of transition metals and interfacial side reactions. At the same time, the small-diameter first inorganic particles help to make the surface of the first bottom coating smoother, making its interfacial contact with the positive electrode active layer more uniform, thereby reducing the hot spot area formed by excessively high local current density, and further reducing the risk of inducing purple spots on the negative electrode.

[0065] The aforementioned D501 refers to the particle size value corresponding to 50% (by volume) of the cumulative particle size distribution curve of inorganic particles, which is generally obtained by laser diffraction particle size distribution instrument.

[0066] In some implementations, 0.1 μm ≤ D501 ≤ 1 μm, and / or, 0.2 μm ≤ D502 ≤ 2 μm.

[0067] The above embodiments limit D501 to a particle size range of 0.1μm to 1μm, which allows the first undercoat to form a denser particle packing structure. This makes the diffusion path of lithium ions in the first undercoat more tortuous, thereby increasing the ion transport impedance of the first positive electrode, slowing down its delithiation rate in the early stages of charging, preventing premature entry into the excessive delithiation potential range, and suppressing transition metal dissolution and interfacial side reactions. At the same time, this particle size range ensures that the surface of the first undercoat is smooth and uniform, forming a tight and uniform interfacial contact with the first positive electrode active layer, eliminating hot spots caused by excessively high local current density. Controlling D502 to a range of 0.2μm to 2μm allows for the selection of larger particle sizes to maintain a lower ion transport impedance in the second undercoat, ensuring that the internal bifacial electrode contributes the main capacity contribution with efficient kinetics. Furthermore, the difference in particle size between D501 and D501 creates a gradient match in ion transport capabilities between the inner and outer electrodes, further optimizing the interfacial stability and cycle life of the stacked battery.

[0068] By way of example and not limitation, D501 can be any value or any combination of two of the following: 0.1μm, 0.12μm, 0.15μm, 0.18μm, 0.2μm, 0.22μm, 0.25μm, 0.28μm, 0.3μm, 0.35μm, 0.4μm, 0.45μm, 0.5μm, 0.55μm, 0.6μm, 0.65μm, 0.7μm, 0.75μm, 0.8μm, 0.85μm, 0.9μm, 0.95μm, 1.0μm. The range of values; D502 is any value or a range of any two of the following: 0.2μm, 0.22μm, 0.25μm, 0.28μm, 0.3μm, 0.35μm, 0.4μm, 0.45μm, 0.5μm, 0.6μm, 0.7μm, 0.8μm, 0.9μm, 1.0μm, 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm.

[0069] In some embodiments, the first inorganic particle and the second inorganic particle each independently comprise one or more of the following: metal oxide, metal hydroxide, metal carbide, metal nitride, and metal boride.

[0070] The aforementioned inorganic particles all possess high electrochemical inertness and corrosion resistance, and can form a stable physical barrier on the surface of the current collector, effectively preventing electrolyte erosion.

[0071] Examples of metal oxides include aluminum oxide (Al₂O₃), titanium dioxide (TiO₂), zirconium oxide (TiO₂), silicon dioxide (SiO₂), manganese oxide (MnO₂), magnesium oxide (MgO), and nickel oxide (NiO). Examples of metal hydroxides include aluminum hydroxide (AlOOH), boehmite (γ-AlOOH), and magnesium hydroxide (Mg(OH)₂). Examples of metal nitrides include titanium nitride (TiN), boron nitride (BN), and aluminum nitride (AlN). Magnesium nitride (Mg3N2), silicon nitride (Si3N4), etc.; as metal carbides, examples include: silicon carbide (SiC), boron carbide (B4C), titanium carbide (TiC), tungsten carbide (WC), etc.; as metal borides, examples include: titanium boride (TiB2), zirconium boride (ZrB2), tungsten boride (WB2), molybdenum boride (MoB2), etc., preferably containing at least one of Al2O3, AlOOH, TiO2, ZrO2, SiO2, MnO2, MgO, Si3N4, BN.

[0072] In some embodiments, the first inorganic particle and the second inorganic particle are made of the same material. By using inorganic particles of the same material, the above embodiments ensure that the intrinsic conductivity and interface stability of different undercoating layers of different positive electrode sheets remain consistent, avoiding the impact of uncontrollable variables introduced by intrinsic material differences on the cycle performance of the stacked battery.

[0073] In some implementations, see Figure 3 The first positive electrode also includes a third coating 7, which is located on the surface of the first positive electrode active layer 3 away from the first base coating 2; the third coating 7 includes a third binder and third inorganic particles.

[0074] The first positive electrode sheet can be further improved by designing a third coating, thereby further reducing its local current density and avoiding the accelerated consumption of electrolyte due to excessive current density, thus improving the problem of purple spots on the negative electrode. On the other hand, when the separator undergoes thermal shrinkage, it can effectively isolate the direct contact between the positive and negative electrodes, prevent internal short circuits, and thus improve the thermal safety performance of the battery under abuse conditions.

[0075] In some implementations, the mass percentage of the third inorganic particles is 50 wt%-95 wt% based on the mass of the third coating.

[0076] The aforementioned proportion of the third inorganic particles ensures that they form a continuous and dense inorganic particle skeleton in the third coating. This can effectively increase the impedance of the first positive electrode to reduce the local current density, and also provide a reliable physical barrier at high temperatures, thereby preventing internal short circuits caused by thermal shrinkage of the separator.

[0077] By way of example and not limitation, based on the mass percentage of the third inorganic particles, the mass percentage of the third inorganic particles is any value or a range of any two of the following: 50 wt%, 55 wt%, 60 wt%, 65 wt%, 70 wt%, 75 wt%, 80 wt%, 85 wt%, 90 wt%, 95 wt%.

[0078] In some embodiments, the third inorganic particle includes one or more of metal oxides, metal hydroxides, metal carbides, metal nitrides, and metal borides.

[0079] The aforementioned third inorganic particles all share common advantages such as high melting point, corrosion resistance, and electrochemical inertness. They can form a stable inorganic framework on the surface of the first positive electrode, which can effectively increase the impedance of the first positive electrode to reduce the local current density, and maintain the structural integrity during the thermal shrinkage of the separator, preventing direct contact between the positive and negative electrodes.

[0080] In some embodiments, the third adhesive includes one or more of polyvinylidene fluoride, styrene-butadiene rubber latex, sodium carboxymethyl cellulose, polyacrylic acid, polyurethane, polyamide, polyvinyl alcohol, polyethyleneimine, and polyimide.

[0081] The third binder enables the third coating to adhere firmly to the surface of the first positive electrode active layer, while working together with inorganic particles to build a stable interface protective layer, continuously enhancing impedance and homogenizing current.

[0082] In some embodiments, the thickness of the third coating is 0.5 μm to 5 μm.

[0083] The third coating within this thickness range ensures that the coating forms a continuous and dense inorganic framework, further improving the impedance of the first positive electrode to reduce local current density, and blocking the risk of short circuits caused by thermal shrinkage of the separator at high temperatures.

[0084] By way of example and not limitation, the thickness of the third coating is any value or a range of any two of the following: 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4.0 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5.0 μm.

[0085] In some implementations, see Figure 3 The first positive electrode also includes a fourth coating 8, which is located on the second surface of the first positive current collector. The fourth coating 8 includes a fourth binder and a fourth inorganic particle.

[0086] Among them, the fourth inorganic particles in the fourth coating can further increase the impedance of the first positive electrode, thereby further reducing the local current density and suppressing the problems of transition metal dissolution and negative electrode purple spots caused by the concentration of current density; at the same time, the mechanical strength of the fourth coating itself and its tight bonding with the first current collector can further offset the curling stress caused by the structural asymmetry of the first positive electrode, suppress the edge warping and folding deformation of the first positive current collector, thereby further improving the purple spots.

[0087] In some implementations, the mass percentage of the fourth inorganic particles is 50 wt%-95 wt% based on the mass of the fourth coating.

[0088] By way of example and not limitation, based on the mass of the fourth coating, the mass percentage of the fourth inorganic particles is any value or a range of any two of the following: 50 wt%, 52 wt%, 55 wt%, 58 wt%, 60 wt%, 62 wt%, 65 wt%, 68 wt%, 70 wt%, 72 wt%, 75 wt%, 78 wt%, 80 wt%, 82 wt%, 85 wt%, 88 wt%, 90 wt%, 92 wt%, 95 wt%.

[0089] The above-mentioned mass percentage of the fourth inorganic particles ensures that they form a continuous and dense inorganic framework in the fourth coating, which can effectively increase the impedance of the first positive electrode to reduce the local current density, and enhance the mechanical strength of the fourth coating to counteract the curling stress of the first positive electrode.

[0090] In some embodiments, the fourth inorganic particle includes one or more of metal oxides, metal hydroxides, metal carbides, metal nitrides, and metal borides.

[0091] The aforementioned fourth inorganic particles all possess excellent electrochemical inertness and high resistance characteristics, which help to increase the surface impedance of the exposed side of the fourth inorganic particles to reduce local current density; at the same time, their high hardness and structural rigidity can further enhance the ability of the first positive electrode to resist curling stress and further suppress the warping deformation of the first positive electrode.

[0092] In some embodiments, the fourth adhesive includes one or more of polyvinylidene fluoride, styrene-butadiene rubber latex, sodium carboxymethyl cellulose, polyacrylic acid, polyurethane, polyamide, polyvinyl alcohol, polyethyleneimine, and polyimide.

[0093] In some embodiments, the thickness of the fourth coating is 0.5 μm to 5 μm.

[0094] The fourth coating with the above thickness range can effectively increase the impedance of the second surface on the exposed side of the first positive electrode, thereby further reducing the local current density of the first positive electrode, while providing sufficient mechanical strength to counteract the curling stress of the first positive electrode.

[0095] By way of example and not limitation, the thickness of the fourth coating is any value or a range of any two of the following: 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2.0 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3.0 μm, 3.2 μm, 3.5 μm, 3.8 μm, 4.0 μm, 4.2 μm, 4.5 μm, 4.8 μm, 5.0 μm.

[0096] In some embodiments, the negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one side surface of the negative current collector. The negative active layer includes a silicon-carbon composite material, and the silicon content is 2 wt%-50 wt% based on the mass of the negative active layer.

[0097] With the silicon content of the negative electrode active layer within the above range, the capacity of the negative electrode sheet can be maintained at a high level, while its volume expansion stress is within the range that the first and second positive electrode sheets can effectively buffer and constrain, thus ensuring both the cycle stability and high energy density of the stacked battery.

[0098] In some specific embodiments, the method for testing the mass content of silicon is as follows: After discharging the battery to 0% SOC, the negative electrode sheet is disassembled and removed. It is then soaked in dimethyl carbonate (DMC) solvent for 12 hours, followed by rinsing with DMC solvent to remove lithium salts adhering to the negative electrode sheet. After drying, the negative electrode sheet is subjected to high-temperature treatment at 400°C in an inert atmosphere for 2 hours (e.g., in a tube furnace under nitrogen or argon atmosphere). The negative electrode active layer can then be peeled off from the negative electrode current collector, and the negative electrode active layer is collected as a test sample. Using a thermogravimetric analyzer (e.g., a TGA 550 thermogravimetric analyzer), the sample amount is 5mg-15mg. Under an air or oxygen atmosphere, the temperature is increased from room temperature (25°C) to 900°C at a rate of 10°C / min, and held at 900°C for 40 minutes. This allows the non-silicon components in the negative electrode active layer to volatilize while the silicon is fully oxidized to silicon dioxide. The remaining substance is the ash of the negative electrode active layer. The mass content of silicon in the negative electrode active layer can be calculated based on the mass of the ash. The calculation formula is as follows: Si content in the negative electrode active layer = 7 × mass of ash / (15 × mass of test sample).

[0099] By way of example and not limitation, the mass content of silicon is any value or a range of any two of the following: 2 wt%, 3 wt%, 5 wt%, 8 wt%, 10 wt%, 12 wt%, 15 wt%, 18 wt%, 20 wt%, 22 wt%, 25 wt%, 28 wt%, 30 wt%, 32 wt%, 35 wt%, 38 wt%, 40 wt%, 42 wt%, 45 wt%, 48 wt%, 50 wt%.

[0100] In some embodiments, the sphericity of the silicon-carbon composite material is greater than or equal to 0.85.

[0101] Among them, the silicon-carbon composite material with the above sphericity has a smooth particle surface and few defects. During the repeated volume expansion of the material, the stress distribution is uniform, which can effectively inhibit particle breakage and new surface exposure, reduce electrolyte consumption and side reactions, and further inhibit the formation of purple spots.

[0102] By way of example and not limitation, the sphericity of the silicon-carbon composite material is any value or a range of any two of the following: 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99.

[0103] In some embodiments, the silicon-carbon composite material includes a porous carbon matrix and silicon particles distributed in the pores of the porous carbon matrix. At least a portion of the outer surface of the porous carbon matrix is ​​provided with an amorphous carbon coating layer, the thickness of which is 2 nm to 20 nm.

[0104] Amorphous carbon coatings, acting as an outer surface protective barrier, can effectively reduce side reaction consumption. Furthermore, amorphous carbon coatings with a thickness of 2nm-20nm can reduce interfacial impedance and inhibit the deposition of transition metal ions on the negative electrode surface, thereby further improving the purple spot problem.

[0105] It should be noted that the silicon-carbon composite material in this invention is prepared by vapor deposition, in which silicon particles (by introducing silane gas into a fluidized bed reactor) are deposited into a porous carbon matrix (using methods well known to those skilled in the art).

[0106] By way of example and not limitation, the thickness of the amorphous carbon coating is any value or a range of any two of the following: 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm.

[0107] In some embodiments, the Dv50 of the silicon-carbon composite material is 5.5 μm-12.5 μm, preferably 6.5 μm-10 μm.

[0108] By controlling the Dv50 of the silicon-carbon composite material within the above range, side reactions can be kept at a low level through a suitable specific surface area, while ensuring that the silicon-carbon composite material particles have sufficient compressive strength to withstand mechanical stress during cycling. This allows it to work synergistically with the positive electrode to jointly suppress transition metal deposition and purple spots caused by the degradation of the negative electrode interface. For example, the Dv50 of the silicon-carbon composite material can be any value or a range between 5.5 μm, 6.5 μm, 7.5 μm, 8.5 μm, 9.5 μm, 10 μm, 10.5 μm, 11.5 μm, and 12.5 μm.

[0109] The Dv50 of the aforementioned silicon-carbon composite material refers to the particle size value corresponding to 50% (by volume) of the cumulative particle size distribution curve of the silicon-carbon composite material, which is generally obtained by laser diffraction particle size distribution instrument.

[0110] In some embodiments, the negative electrode active layer includes, in addition to a silicon-carbon composite material, a conductive agent, a binder, and a dispersant. Exemplarily, the conductive agent may be selected from at least one of carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, and graphene; the binder may be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate; and the dispersant may be selected from at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium dodecyl sulfate.

[0111] In some implementations, reference Figure 4 The first positive electrode includes multiple protrusions 9 and multiple recesses 10 corresponding to the multiple protrusions; Reference Figure 1 The protrusion 9 protrudes from the second surface 11 toward the membrane shell, and the recess 10 is recessed from the first surface 12 toward the second surface 11.

[0112] The orthographic projection area of ​​the multiple protrusions 9 on the plane where the second surface 11 is located is S1, and the orthographic projection area of ​​the first positive electrode plate on the plane where the second surface is located is S2; wherein, S1 and S2 satisfy: 0.2≤S1 / S2≤0.7.

[0113] In this first positive electrode sheet, the first current collector has a positive electrode active layer on only one side, which is subject to curling stress. By setting multiple protrusions and corresponding recesses on its surface, the curling problem can be solved, the manufacturing capability can be improved, and the purple spot problem caused by positive electrode sheet stress during cycling can be further alleviated. Controlling S1 and S2 to satisfy: 0.2≤S1 / S2≤0.7 can ensure both the structural stability and anti-curling ability of the first current collector. If S1 / S2 is too large, it may cause wrinkling and cracking of the current collector area corresponding to the electrode sheet embossing protrusion area, degrading the cycle performance of the cell. If S1 / S2 is too small, the improvement of the curling problem is not obvious.

[0114] By way of example and not limitation, S1 / S2 is any value or a range of any two of the following: 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.62, 0.65, 0.68, 0.70.

[0115] In some embodiments, the diameter of the protrusion (refer to...) Figure 1 R1) is 0.5mm-8mm.

[0116] When the diameter of the protrusion is within the aforementioned range, it can better alleviate the bending stress of the first positive electrode. For example, the diameter of the protrusion is any value or a range of any two of the following: 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, 5.0 mm, 5.5 mm, 6.0 mm, 6.5 mm, 7.0 mm, 7.5 mm, 8.0 mm.

[0117] In some embodiments, the distance between the centers of the circumcircles of the orthographic projections of any two adjacent protrusions on the second surface is 4mm-15mm.

[0118] refer to Figure 1 When the protrusion is semi-circular, the distance between the centers of the circumcircles of the orthographic projections of two adjacent protrusions on the second surface is equal to the distance R2 between the centers of the two adjacent protrusions.

[0119] The above embodiments can limit the density of the protrusions by limiting the distance between the centers of the circumcircles of the orthographic projections of any two adjacent protrusions on the second surface. Protrusions with an appropriate density can ensure the structural stability and anti-curling ability of the first current collector.

[0120] In some specific embodiments, the distance between the centers of the circumcircles of the orthographic projections of any two adjacent protrusions on the second surface is 5mm-10mm.

[0121] For example, the distance between the centers of the circumcircles of the orthographic projections of any two adjacent protrusions on the second surface is any value or a range of any two of the following: 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm, 15 mm.

[0122] In some implementations, the height (h) of the protrusion is 2μm-40μm.

[0123] The protrusions of the above height can more effectively alleviate bending stress while ensuring the structural stability of the first positive electrode. In some specific embodiments, the height of the protrusions is 2μm-30μm.

[0124] For example, the height (h) of the protrusion is any value or a range of any two of the following: 2μm, 5μm, 8μm, 10μm, 12μm, 15μm, 18μm, 20μm, 22μm, 25μm, 28μm, 30μm, 32μm, 35μm, 38μm, 40μm.

[0125] In some embodiments, the stacked battery further includes an electrolyte comprising a lithium salt and a solvent. The lithium salt serves as an ion source and can be a lithium salt known in the art for use in battery electrolytes. Exemplarily, the lithium salt can be lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroantimonyate (LiSbF6), lithium difluorophosphate (LiPF2O2), lithium 4,5-dicyano-2-trifluoromethylimidazolium (LiDTI), lithium dioxoborate (LiBOB), lithium trifluoromethanesulfonate (LiTFS), lithium bis(malonic acid)borate (LiBMB), lithium difluorooxalate borate (LiDFOB), etc. The lithium borate (LiBDFMB), lithium borate (LiMOB), lithium borate (LiDFMOB), lithium tri(oxalate) phosphate (LiTOP), lithium tri(difluoromalonic acid) phosphate (LiTDFMP), lithium tetrafluorooxalate phosphate (LiTFOP), lithium difluorodioxalate phosphate (LiDFOP), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium (fluorosulfonyl)(trifluoromethanesulfonyl)imide (LiN(SO2F)(SO2CF3)), lithium nitrate (LiNO3), and lithium fluoride (LiF). For example, the organic solvent may be at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butenyl 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).

[0126] In some embodiments, the above-mentioned positive electrode, separator and negative electrode can be stacked in sequence to obtain a battery cell; the battery cell is placed in a battery packaging shell (such as an aluminum-plastic film shell), electrolyte is injected into the outer packaging and sealed to prepare the stacked battery of the present invention.

[0127] The present invention will be further described below with reference to specific embodiments:

[0128] Example 1

[0129] The fabrication method of the stacked battery in this example includes the following steps:

[0130] (1) Preparation of positive electrode:

[0131] Preparation of the first positive electrode: Boehmite (D501 of 0.5 μm), carbon black, and polyacrylic acid (PAA) were placed in deionized water at a mass ratio of 88.5:1.5:10 to form a first base coating slurry. The first base coating slurry was coated onto one side of the aluminum foil of the first positive electrode current collector using a zebra coating method. The thickness of the aluminum foil was 10 μm, thus obtaining the first positive electrode current collector containing the first base coating. Lithium cobalt oxide, a conductive agent (conductive carbon black to carbon nanotubes at a mass ratio of 99.35:0.65), and polyvinylidene fluoride (PVDF) were placed in N-methylpyrrolidone (NMP) at a mass ratio of 97.85:0.65:1.5 and stirred evenly to obtain the first positive electrode. A positive electrode slurry; the first positive electrode slurry is uniformly coated on the surface of the first base coating layer away from the first positive electrode current collector using a zebra coating method, and then dried, rolled, and die-cut to obtain a first positive electrode sheet. The first positive electrode sheet includes a first positive electrode active layer and a first base coating layer, with the first base coating layer located between the first positive electrode current collector and the first positive electrode active layer; protrusions are provided on the first positive electrode sheet prepared above, specifically including: rolling the prepared first positive electrode sheet with a concave-convex roller to form specific protrusions on the electrode sheet surface (wherein, S1 / S2 is 0.4, the diameter of the protrusion is 2mm, the distance between the centers of adjacent protrusions is 10mm, and the height of the protrusion is 12µm).

[0132] Preparation of the second positive electrode sheet: Boehmite (D502 of 1.0 μm), carbon black, and PAA binder are placed in deionized water at a mass ratio of 90.5:3.5:6 ​​to form a second base coating slurry. The second base coating slurry is coated on both sides of the aluminum foil of the second positive electrode current collector in a zebra coating manner to obtain a second positive electrode current collector containing the second base coating. Lithium cobalt oxide, conductive agent (conductive carbon black and carbon nanotubes in a mass ratio of 99.35:0.65), and PVDF are placed in NMP at a mass ratio of 97.85:0.65:1.5 and stirred evenly to obtain a second positive electrode slurry. The second positive electrode slurry is uniformly coated on the surface of the second base coating away from the second positive electrode current collector in a zebra coating manner. After drying, rolling, and die-cutting, the second positive electrode sheet is obtained.

[0133] (2) Preparation of negative electrode:

[0134] A mixture of artificial graphite and silicon carbon (with a mass ratio of 70:30, a sphericity of silicon carbon greater than 0.9, Dv50 = 7.5 μm, and an amorphous carbon coating thickness of 10 nm), carbon nanotubes, styrene-butadiene rubber, sodium carboxymethyl cellulose, and polyacrylic acid (PAA) in a mass ratio of 96.1:0.5:2.1:0.2:1.1 is placed in deionized water. The above slurry is stirred evenly to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated on both sides of the negative electrode current collector, and then dried, rolled, and die-cut to obtain a negative electrode sheet.

[0135] (3) Diaphragm:

[0136] An 8μm thick substrate is used, with a ceramic layer coated on one side of the substrate and an adhesive layer coated on the other side of both the ceramic layer and the substrate. The substrate is composed of PE, the ceramic layer includes alumina, and the adhesive layer is PVDF.

[0137] (4) Preparation of electrolyte:

[0138] In an argon-filled glove box (moisture < 1 ppm, oxygen < 1 ppm), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC) were mixed thoroughly in a volume ratio of 1:2:3:4 to obtain an organic solvent. Then, lithium hexafluorophosphate (14% by weight of the total electrolyte), fluoroethylene carbonate (FEC) (15% by weight of the total electrolyte), and 1,3-propanesulfonate lactone (2% by weight of the total electrolyte) were added to the organic solvent. After stirring thoroughly, the electrolyte was obtained.

[0139] (5) Assemble the battery:

[0140] The prepared first positive electrode, second positive electrode, negative electrode, and separator are stacked in the following order to form an electrode assembly: the outermost electrode is the first positive electrode, and the middle electrodes are arranged in the following cycle: separator, negative electrode, second positive electrode, to obtain a bare cell; tabs are soldered onto the bare cell to obtain a stacked cell; the obtained cell is then placed into a size-matched aluminum-plastic film (i.e., a film shell) and sealed; the electrolyte prepared above is injected under vacuum conditions and vacuum sealed; and the battery is obtained through standing, formation, and sorting processes. The protrusions extend from the second surface of the first positive current collector towards the film shell.

[0141] The preparation methods of Examples 2-15 are the same as those of Example 1, except that the thicknesses of the first base coating, the second base coating, the first positive current collector, and the second positive current collector are changed.

[0142] The preparation methods of Examples 16-17 are the same as those of Example 1, except that the content of 1,3-propanesulfonate lactone in the electrolyte is changed.

[0143] The preparation methods of Examples 18-23 are the same as those of Example 1, except that the contents of the adhesive and conductive agent in the first and second base coatings are changed.

[0144] The preparation methods of Examples 24-28 are the same as those of Example 1, except that the median particle size of the first inorganic particles in the first base coating and the second inorganic particles in the second base coating are changed.

[0145] Example 29

[0146] The only difference from the stacked battery in Example 1 is that the first positive electrode sheet further includes a third coating and a fourth coating, and the parameters of the protrusion are: S1 / S2=0.2, protrusion diameter=0.5mm, distance between the centers of adjacent protrusions=4mm, and protrusion height=2µm; based on the mass of the negative electrode active layer, the silicon content is 2%, the sphericity is 0.85, Dv50=5.5μm, and the thickness of the amorphous carbon coating layer is 2nm;

[0147] The difference between the preparation method of the third coating and Example 1 is that: after the first positive electrode slurry is coated and dried, boehmite and PAA are placed in deionized water at a mass ratio of 50%:50% to form the third coating slurry, wherein the D501 of the boehmite is the same as that of the first base coating. The third coating slurry is coated on the surface of the first positive electrode active layer away from the first base coating in a zebra coating manner and dried. Then, the fourth coating slurry is prepared with the same ratio as the third coating slurry. The fourth coating slurry is coated on the side of the first positive electrode current collector that is not coated with the first positive electrode slurry and then dried. Other operations are the same as in Example 1.

[0148] Example 30

[0149] The only difference from the stacked battery in Example 1 is that the first positive electrode sheet further includes a third coating and a fourth coating, and the parameters of the protrusion are: S1 / S2=0.7, protrusion diameter=8mm, distance between the centers of adjacent protrusions=15mm, and protrusion height=40µm; based on the mass of the negative electrode active layer, the silicon content is 50%, the sphericity is 0.9, Dv50=12.5μm, and the thickness of the amorphous carbon coating layer is 20nm.

[0150] The difference between the preparation method of the third coating and that of Example 1 is as follows: After the first positive electrode slurry is coated and dried, boehmite and PAA are placed in deionized water at a mass ratio of 95%:5% to form the third coating slurry, with the boehmite having the same D501 as the first coating. The third coating slurry is coated on the surface of the first positive electrode active layer away from the first base coating layer in a zebra coating manner and dried. Then, a fourth coating slurry is prepared with the same proportion as the third coating slurry and coated on the side of the first positive electrode current collector that is not coated with the first positive electrode slurry. Then, it is dried. All other operations are the same as in Example 1.

[0151] The preparation methods of Comparative Examples 1-2 were the same as those in Example 1, except that the thicknesses of the first base coating, the second base coating, the first positive current collector, and the second positive current collector were changed.

[0152] The preparation methods for Comparative Examples 3-5 were the same as those in Example 1, except that the content of 1,3-propanesulfonate lactone in the electrolyte was changed.

[0153] Test case

[0154] The following performance characteristics of the stacked solar cells prepared in the above embodiments and comparative examples were tested:

[0155] 1. Degree of purple spots:

[0156] The batteries prepared in the examples and comparative examples were subjected to purple spot testing. The specific testing methods are as follows:

[0157] The battery was subjected to a 25°C room temperature cycle test. The room temperature cycle test regime was as follows: charge at 2.0C to 4.1V, charge at 1.8C to 4.3V, charge at 1C to 4.4V, charge at 0.5C to 4.53V, stop at 0.05C, rest for 5 minutes, discharge at 0.7C to 3V, and repeat this cycle 600 times. The fully charged battery with 600T of cycle time was disassembled to observe the degree of purple spots. The purple spot area was used to judge: 0% purple spot area was no purple spot (level 0), purple spot area less than 5% was very slight purple spot (level 1), purple spot area between 5% and 10% was slight purple spot (level 2), purple spot area between 10% and 20% was purple spot (level 3), purple spot area between 20% and 50% was severe purple spot (level 4), and purple spot area greater than 50% was very severe purple spot (level 5).

[0158] 2. Dissolved transition metal content: Discharge the stacked battery after the above cycle. The battery needs to be empty. Then disassemble it and take the negative electrode powder to test ICP and Co ion content.

[0159] 3. Cycle retention test, including the following process: (1) Each stacked battery is left to stand at 25℃±2℃ for 5 minutes, and discharged at 0.2C to the lower limit voltage (3V); (2) The lithium-ion battery is left to stand at 25℃±2℃ for 5 minutes, discharged at 0.7C to 3V, and the discharge capacity at this time is measured as X1. After standing for 5 minutes, it is charged at 2.0C to 4.37V, 1.8C to 4.37V, 1C to 4.53V, 0.5C to 4.58V, cut off at 0.05C, left to stand for 5 minutes, and discharged at 0.7C to 3V. This is repeated 600 times. The discharge capacity when discharged at 0.7C to 3V is recorded as X2 when the 600th cycle is completed.

[0160] The battery's cycle capacity retention rate is calculated as (X2 / X1) × 100%.

[0161] The test results are shown in Table 2.

[0162] Table 1:

[0163]

[0164] Table 2:

[0165]

[0166] As shown in Table 2, compared with Comparative Examples 1-5, the batteries of Examples 1-30, by introducing a first undercoat layer in the first positive electrode and a second undercoat layer in the second positive electrode, and by limiting the thickness relationship of the first undercoat layer, the second undercoat layer, the first positive current collector, and the second positive current collector to satisfy: 0.2≤(H1-H2) / (B1-B2)≤0.5, and by keeping the content of 1,3-propanesulfonate lactone in the electrolyte between 0.1-6%, can effectively suppress the dissolution of transition metal ions caused by excessively high local current density in the first positive electrode and the purple spot problem on the corresponding negative electrode of the first positive electrode, thereby significantly improving the cycle capacity retention rate of the battery.

[0167] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A battery, characterized in that, The device includes a membrane housing, an electrode assembly disposed within the membrane housing, and an electrolyte. The electrode assembly includes a positive electrode, a separator, and a negative electrode stacked sequentially. The positive electrode includes at least one first positive electrode and at least one second positive electrode. The first positive electrode is located on the outermost side of the electrode assembly and includes a first positive current collector. The first positive current collector includes a first surface and a second surface disposed opposite to each other along its thickness direction. A first positive active layer and a first base layer are stacked on the first surface. The first base layer is located between the first surface and the first positive active layer. The first surface is away from the membrane housing, and the second surface is close to the membrane housing. The thickness of the first base layer is H1 (in μm), and the thickness of the first positive current collector is B1 (in μm). The second positive electrode includes a second positive current collector and a second positive active layer and a second base coating layer stacked on both sides of the second positive current collector. The second base coating layer is located between the second positive current collector and the second positive active layer. The thickness of the second base coating layer is H2 in μm, and the thickness of the second positive current collector is B2 in μm. The electrolyte comprises 1,3-propanesulfonate lactone, wherein the mass percentage of 1,3-propanesulfonate lactone in the electrolyte is 0.1 wt%-6 wt%. The battery satisfies the following condition: 0.2≤(H1-H2) / (B1-B2)≤0.

5.

2. The battery according to claim 1, characterized in that, 1μm≤H1≤5μm; And / or, 0μm <H2≤4μm; And / or, 10μm≤B1≤30μm; And / or, 6μm≤B2≤15μm; And / or, 4μm≤(B1-B2)≤20μm.

3. The battery according to claim 1 or 2, characterized in that, The first base layer includes a first adhesive, and the mass percentage of the first adhesive based on the total mass of the first base layer is W1. The second primer layer includes a second adhesive, and based on the mass of the second primer layer, the mass percentage of the second adhesive is W2, where W1 and W2 satisfy: 0 wt% ≤ (W1-W2) ≤ 4 wt%; Preferably, 0.5wt% ≤ W1 ≤ 35wt%, 0.5wt% ≤ W2 ≤ 35wt%; Preferably, the first adhesive and the second adhesive each independently comprise one or more of polyvinylidene fluoride, styrene-butadiene rubber latex, sodium carboxymethyl cellulose, polyacrylic acid, polyurethane, polyamide, polyvinyl alcohol, polyethyleneimine, and polyimide.

4. The battery according to any one of claims 1-3, characterized in that, The first base coating includes a first conductive agent, and the second base coating includes a second conductive agent. Based on the mass of the first base coating, the mass percentage of the first conductive agent is D1, and based on the mass of the second base coating, the mass percentage of the second conductive agent is D2, where D1 ≤ D2. Preferably, 0.2wt% ≤ D1 ≤ 5.0wt%, 0.2wt% ≤ D2 ≤ 5.0wt%; Preferably, the first conductive agent and the second conductive agent each independently comprise one or more of conductive carbon black, carbon nanotubes, graphene, and vapor-grown carbon fibers.

5. The battery according to claim 3 or 4, characterized in that, The first base coating further includes first inorganic particles, and the second base coating further includes second inorganic particles. The median particle size D501 of the first inorganic particles and the median particle size D502 of the second inorganic particles satisfy the following relationship: D501 ≤ D502. Preferably, 0.1μm ≤ D501 ≤ 1μm, and / or 0.2μm ≤ D502 ≤ 2μm.

6. The battery according to claim 5, characterized in that, The first inorganic particle and the second inorganic particle each independently comprise one or more of the following: metal oxide, metal hydroxide, metal carbide, metal nitride, and metal boride; Preferably, the first inorganic particle and the second inorganic particle are made of the same material.

7. The battery according to any one of claims 1-6, characterized in that, The first positive electrode further includes a third coating layer, which is located on the surface of the first positive electrode active layer opposite to the first base coating layer; the third coating layer includes a third binder and third inorganic particles; Preferably, based on the mass of the third coating, the mass percentage of the third inorganic particles is 50 wt%-95 wt%; Preferably, the third inorganic particle comprises one or more of metal oxides, metal hydroxides, metal carbides, metal nitrides, and metal borides; Preferably, the third adhesive comprises one or more of polyvinylidene fluoride, styrene-butadiene rubber latex, sodium carboxymethyl cellulose, polyacrylic acid, polyurethane, polyamide, polyvinyl alcohol, polyethyleneimine, and polyimide; Preferably, the thickness of the third coating is 0.5μm-5μm.

8. The battery according to any one of claims 1-7, characterized in that, The first positive electrode further includes a fourth coating, which is located on the second surface of the first positive electrode current collector, and the fourth coating includes a fourth binder and a fourth inorganic particle; Preferably, based on the mass of the fourth coating, the mass percentage of the fourth inorganic particles is 50 wt%-95 wt%. Preferably, the fourth inorganic particle comprises one or more of metal oxides, metal hydroxides, metal carbides, metal nitrides, and metal borides; Preferably, the fourth adhesive comprises one or more of polyvinylidene fluoride, styrene-butadiene rubber latex, sodium carboxymethyl cellulose, polyacrylic acid, polyurethane, polyamide, polyvinyl alcohol, polyethyleneimine, and polyimide. Preferably, the thickness of the fourth coating is 0.5μm-5μm.

9. The battery according to any one of claims 1-8, characterized in that, The negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on at least one surface of the negative electrode current collector. The negative electrode active layer is composed of a silicon-carbon composite material, and the silicon content is 2 wt%-50 wt% based on the mass of the negative electrode active layer. Preferably, the sphericity of the silicon-carbon composite material is greater than or equal to 0.85; Preferably, the silicon-carbon composite material comprises a porous carbon matrix and silicon particles distributed in the pores of the porous carbon matrix, wherein at least a portion of the outer surface of the porous carbon matrix is ​​provided with an amorphous carbon coating layer, and the thickness of the amorphous carbon coating layer is 2nm-20nm. Preferably, the Dv50 of the silicon-carbon composite material is 5.5μm-12.5μm, and more preferably 6.5μm-10μm.

10. The battery according to any one of claims 1-9, characterized in that, The first positive electrode includes a plurality of protrusions and a plurality of recesses corresponding to the plurality of protrusions; the protrusions protrude from the second surface toward the membrane shell, and the recesses are recessed from the first surface toward the second surface; The orthographic projection area of ​​the plurality of protrusions on the plane of the second surface is S1, and the orthographic projection area of ​​the first positive electrode sheet on the plane of the second surface is S2; Where S1 and S2 satisfy: 0.2≤S1 / S2≤0.7; Preferably, the diameter of the protrusion is 0.5mm-8mm; Preferably, the distance between the centers of the circumcircles of the orthographic projections of any two adjacent protrusions onto the second surface is 4mm-15mm, more preferably 5mm-10mm; Preferably, the height of the protrusion is 2μm-40μm, more preferably 2μm-30μm.

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