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

Abstract

The application provides a lithium ion battery, comprising: an electrode assembly and an electrolyte; the electrode assembly comprises a negative electrode sheet, a separator and a positive electrode sheet, and is wound into a winding structure along a winding direction; the winding structure comprises a circular-arc-shaped bending part, and the circular-arc-shaped bending part at least comprises: a first bending part and a second bending part; a corner lithium precipitation coefficient β of the lithium ion battery satisfies 0.015 ≤ β = R / (R+L) ≤ 0.95, R is the minimum radius of curvature of the convex surface of the negative current collector of the first bending part, L is the shortest distance between the convex surface of the negative current collector of the first bending part and the concave surface of the positive current collector of the second bending part, the electrolyte contains fluorosulfonate and / or difluorophosphate substances, and the mass percentage content w% of the fluorosulfonate and / or difluorophosphate substances in the electrolyte and the corner lithium precipitation coefficient β satisfy 0.01 ≤ w*β ≤ 20. According to the lithium ion battery, high energy density and the problem of negative electrode lithium precipitation under high energy density can be considered.

Description

Technical Field

[0001] This application relates to the field of electrochemical batteries, and in particular to lithium-ion batteries, battery modules, battery packs, and electrical devices. Background Technology

[0002] Lithium-ion batteries have become the most popular energy storage system due to their high operating potential, long lifespan, and environmental friendliness, and are now widely used in pure electric vehicles, hybrid electric vehicles, smart grids, and other fields. However, the current range of lithium-ion batteries is insufficient to meet people's higher demands. To alleviate people's "range anxiety" regarding electric vehicles, there is an urgent need to develop lithium-ion batteries with higher energy density.

[0003] However, for wound-type lithium-ion batteries, as the energy density of the designed battery increases, lithium plating is also prone to occur at the winding corners of the negative electrode. As lithium dendrites continue to form, the separator is punctured, causing a short circuit and reducing battery safety performance.

[0004] This demonstrates that improving the energy density of wound batteries and preventing lithium plating are contradictory. Therefore, there is an urgent need to design and develop a lithium-ion battery that combines high energy density with effective prevention of lithium plating. Summary of the Invention

[0005] This application was made to solve the problems existing in the prior art. The purpose of this application is to develop and design a lithium-ion battery that can significantly improve the energy density of the wound structure battery, while preventing the corner lithium deposition phenomenon of the negative electrode sheet under high energy density, and improving the electrochemical performance and safety performance of the battery.

[0006] To achieve the above objectives, this application provides a lithium-ion battery, comprising: an electrode assembly; and an electrolyte for wetting the electrode assembly; wherein,

[0007] The electrode assembly includes a negative electrode, a separator, and a positive electrode. The negative electrode, the separator, and the positive electrode are wound together in a winding direction to form a wound structure, which includes an arc-shaped bend.

[0008] The arc-shaped bend includes at least: a first bend and a second bend.

[0009] The first bending portion is the innermost arc-shaped bending portion formed by winding the negative electrode sheet. The first bending portion includes a negative electrode current collector and a negative electrode material layer located at least on the convex surface of the negative electrode current collector.

[0010] The second bend is located outside the first bend and adjacent to the first bend through the separator. The second bend includes a positive current collector and a positive electrode material layer located at least on the concave surface of the positive current collector.

[0011] Let β be the corner lithium deposition coefficient of the lithium-ion battery, then β satisfies the following equation I.

[0012] β=R / (R+L) Equation I,

[0013] And 0.015≤β≤0.95, where,

[0014] R is the minimum radius of curvature of the convex surface of the negative electrode current collector in the first bend.

[0015] L is the shortest distance between the convex surface of the negative current collector in the first bend and the concave surface of the positive current collector in the second bend.

[0016] The electrolyte contains fluorosulfonates and / or difluorophosphates, and,

[0017] The mass percentage w% of the fluorosulfonate and / or difluorophosphate in the electrolyte and the corner lithium deposition coefficient β satisfy the following formula II.

[0018] 0.01≤w×β≤20 Equation II.

[0019] When w and β of a lithium-ion battery meet the above conditions, the designed and developed lithium-ion battery can simultaneously take into account both high energy density and lithium deposition on the convex surface of the negative electrode under high energy density, thereby improving the electrochemical performance and safety performance of the battery.

[0020] For the lithium-ion battery of this application, it is preferable that 0.2 ≤ w × β ≤ 5. When w and β satisfy this condition, the energy density of the battery can be further improved and the lithium deposition on the negative electrode convex surface can be mitigated.

[0021] For the lithium-ion battery of this application, 0.15 ≤ β ≤ 0.8 is preferred. When β is controlled within the given range, the energy density of the battery and the lithium deposition on the negative electrode convex surface can be further improved.

[0022] For the lithium-ion battery of this application, the range of R is 2μm to 5000μm, and preferably 50μm to 500μm. When R is controlled within the given range, the energy density of the battery and the lithium deposition on the negative electrode convex surface can be further improved.

[0023] For the lithium-ion battery of this application, L ranges from 20 μm to 900 μm, with a preferred range of 50 μm to 500 μm. When L is controlled within the given range, the energy density, negative electrode convex lithium plating, and power performance (lower battery internal resistance) of the battery can be further improved.

[0024] For the lithium-ion battery of this application, the structural formula of the fluorosulfonate is (FSO3). x M x+ M x+ Selected from Li + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Al 3+ Fe 2+ Fe 3+ Ni 2+ and Ni 3+ One or more of them,

[0025] The structural formula of the difluorophosphate is (F₂PO₂). y M y+ M y+ Selected from Li + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Al 3+ Fe 2+ Fe 3+ Ni 2+ and Ni 3+ One or more of them.

[0026] For the lithium-ion battery of this application, the mass percentage w% of the fluorosulfonate and / or difluorophosphate substances in the electrolyte ranges from 0.02% to 25%, preferably from 0.02% to 20%, more preferably from 0.05% to 10%, and even more preferably from 0.1% to 5%. When w is controlled within the given range, the energy density, negative electrode convex lithium plating, and power performance (lower battery internal resistance) of the battery can be further improved.

[0027] For the lithium-ion battery of this application, the electrolyte preferably further comprises fluoroethylene carbonate. This further improves the battery's room-temperature and high-temperature cycling performance.

[0028] For the lithium-ion battery of this application, the porosity of the negative electrode material layer is 20% to 50%, and can be further selected as 30% to 50%. This allows for further improvement in the battery's energy density and lithium deposition on the negative electrode convex surface.

[0029] This application also provides a battery module, characterized in that it includes the lithium-ion battery of this application.

[0030] This application also provides a battery pack, characterized in that it includes one or more of the lithium-ion batteries or battery modules of this application.

[0031] This application also provides an electrical device, characterized in that it includes one or more of the lithium-ion battery, battery module, or battery pack of this application.

[0032] [Invention Effects]

[0033] The lithium-ion battery obtained according to this application not only improves the battery's energy density but also alleviates lithium plating in high-energy-density batteries. In other words, according to this invention, a high-energy-density wound lithium-ion battery that suppresses lithium plating at the innermost negative electrode's convex corner can be obtained. Although the lithium-ion battery of this application has a high-energy-density wound structure, by possessing the aforementioned specific technical features, it can suppress lithium plating at the innermost negative electrode's convex corner, thereby suppressing abnormal capacity utilization and further improving the safety of the lithium-ion battery.

[0034] It should be understood here that the above general description and the following detailed description are merely exemplary and do not limit this application. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the arc-shaped bend of the electrode assembly of a lithium-ion battery according to one embodiment of this application.

[0036] Figure 2 This is a schematic diagram of a lithium-ion battery according to one embodiment of this application.

[0037] Figure 3 yes Figure 1 An exploded view of a lithium-ion battery according to an embodiment of this application is shown.

[0038] Figure 4 This is a schematic diagram of a battery module according to one embodiment of this application.

[0039] Figure 5 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0040] Figure 6 yes Figure 5An exploded view of a battery pack according to one embodiment of this application is shown.

[0041] Figure 7 This is a schematic diagram of a device using a lithium-ion battery as a power source according to one embodiment of this application.

[0042] Explanation of reference numerals in the attached figures:

[0043] 1 battery pack

[0044] 2 upper box

[0045] 3 lower cabinets

[0046] 4 battery modules

[0047] 5 Lithium-ion batteries

[0048] 51 housing

[0049] 52 Electrode Assembly

[0050] 53 Top Cover Assembly

[0051] 6. Arc-shaped bend

[0052] 61 Separating Membrane

[0053] 62 Negative Electrode Current Collector

[0054] 62a and 62b anode material layers

[0055] 63 Positive Current Collector

[0056] 63a and 63b cathode material layers Detailed Implementation

[0057] The present application will now be further described in conjunction with the accompanying drawings and embodiments.

[0058] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the lithium-ion battery, battery module, battery pack, and device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0059] For the sake of brevity, this application specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0060] In this application, the outer surface of the negative electrode current collector is referred to as the "convex surface of the negative electrode current collector," that is, the "convex surface of the negative electrode current collector" is the surface of the negative electrode current collector away from the winding center. In this application, the inner surface of the negative electrode current collector is referred to as the "concave surface of the negative electrode current collector," that is, the "concave surface of the negative electrode current collector" is the surface of the negative electrode current collector closer to the winding center.

[0061] In this application, the outer surface of the positive current collector is referred to as the "convex surface of the positive current collector," that is, the "convex surface of the positive current collector" is the surface of the positive current collector away from the winding center. In this application, the inner surface of the positive current collector is referred to as the "concave surface of the positive current collector," that is, the "concave surface of the positive current collector" is the surface of the positive current collector closer to the winding center.

[0062] As described above, in this application, for ease of explanation, the surfaces of the "positive electrode", "negative electrode", "current collector" and "separator" located in the arc-shaped bend are referred to as "concave surface" on the inner side, i.e. the side closer to the winding center, and "convex surface" on the outer side, i.e. the side farther from the winding center.

[0063] This application relates to a high-energy-density, non-lithium-plating wound lithium-ion battery.

[0064] For wound lithium-ion batteries, there is a wound structure arranged from the inside out in the order of negative electrode-separator-positive electrode-separator-negative electrode-separator-positive electrode. This wound structure has unavoidable arc-shaped bends (at both ends of the wound structure). Therefore, in these arc-shaped bends, for each pair of negative electrodes and the positive electrode adjacent to the convex surface of the negative electrode, the radius of curvature of the convex surface of the negative electrode is greater than the radius of curvature of the concave surface of the positive electrode adjacent to it. That is, the length of the concave surface of the positive electrode is longer than the length of the corresponding convex surface of the negative electrode. Thus, when the capacity of the positive and negative electrode materials per unit area is consistent, the capacity of the negative electrode will be lower than that of the positive electrode in the arc-shaped bend. As a result, the negative electrode material cannot fully accept the lithium ions migrating from the positive electrode during charging. These excess lithium ions "accumulate" on the surface of the negative electrode. As the battery charges, these "accumulated" lithium ions gain electrons to form lithium metal and gradually deposit into lithium dendrites (i.e., corner lithium deposition). The formed lithium dendrites can easily penetrate the separator, causing a short circuit between the positive and negative electrodes, leading to battery thermal runaway and posing a safety hazard.

[0065] To increase the energy density of wound lithium-ion batteries, the inventors of this application discovered that increasing the coating thickness of the positive and negative electrode materials and reducing the number of initial empty turns of the separator are effective and feasible solutions. However, through extensive experiments, the inventors found that the greater the coating thickness of the positive and negative electrode materials on the positive and negative electrode sheets and the fewer the initial empty turns of the separator, the more severe the lithium plating phenomenon is on the negative electrode sheet (especially the innermost negative electrode sheet) in the arc-shaped bend. Therefore, in wound lithium-ion batteries, increasing energy density by increasing active materials and preventing lithium plating are contradictory; that is, increasing the battery's energy density will deteriorate the battery's safety performance.

[0066] Based on this, this application designs and develops a lithium-ion battery with high energy density and no lithium plating by comprehensively controlling various aspects such as the winding structure itself, electrode coating thickness, and electrolyte composition. The lithium-ion battery of this application has excellent electrochemical and safety performance. Furthermore, the theoretical formula proposed in this application is not limited to the design of a single battery structure; it also applies when the shape of the battery or the winding method of the bare cells is changed due to other requirements.

[0067] [Lithium-ion battery]

[0068] This application provides a lithium-ion battery, comprising: an electrode assembly; and an electrolyte for wetting the electrode assembly; wherein,

[0069] The electrode assembly includes a negative electrode, a separator, and a positive electrode. The negative electrode, the separator, and the positive electrode are wound together in a winding direction to form a wound structure, which includes an arc-shaped bend.

[0070] The arc-shaped bend includes at least: a first bend and a second bend.

[0071] The first bending portion is the innermost arc-shaped bending portion formed by winding the negative electrode sheet. The first bending portion includes a negative electrode current collector and a negative electrode material layer located at least on the convex surface of the negative electrode current collector.

[0072] The second bend is located outside the first bend and adjacent to the first bend through the separator. The second bend includes a positive current collector and a positive electrode material layer located at least on the concave surface of the positive current collector.

[0073] Let β be the corner lithium deposition coefficient of the lithium-ion battery, then β satisfies the following equation I.

[0074] β=R / (R+L) Equation I,

[0075] And 0.015≤β≤0.95, where,

[0076] R is the minimum radius of curvature of the convex surface of the negative electrode current collector in the first bend.

[0077] L is the shortest distance between the convex surface of the negative current collector in the first bend and the concave surface of the positive current collector in the second bend.

[0078] The electrolyte contains fluorosulfonates and / or difluorophosphates, and,

[0079] The mass percentage w% of the fluorosulfonate and / or difluorophosphate in the electrolyte and the corner lithium deposition coefficient β satisfy the following formula II.

[0080] 0.01≤w×β≤20 Equation II.

[0081] The lithium-ion battery of this application refers to a wound lithium-ion battery, wherein the wound structure is an electrode assembly formed by winding the positive and negative electrode sheets from the inside out in the order of negative electrode-separator-positive electrode-separator-negative electrode-separator-positive electrode through a winding process.

[0082] Figure 1 This is a schematic diagram of the arc-shaped bend (i.e., the corner of the winding structure) of the electrode assembly of a lithium-ion battery according to one embodiment of this application. Figure 1 As shown, the electrode assembly of this application includes a negative electrode sheet, a separator, and a positive electrode sheet. The negative electrode sheet, the separator, and the positive electrode sheet are wound into a winding structure along the winding direction. The winding structure includes an arc-shaped bend, and the arc-shaped bend includes at least a first bend and a second bend.

[0083] The first bend is the innermost arc-shaped bend (6) formed by winding the negative electrode sheet. The first bend includes a negative current collector (62) and a negative electrode material layer (62a) located at least on the convex surface of the negative current collector. The second bend is located outside the first bend and adjacent to the first bend through the separator (61). The second bend includes a positive current collector (63) and a positive electrode material layer (63a) located at least on the concave surface of the positive current collector.

[0084] The negative electrode current collector may also have a negative electrode material layer located on a concave surface (62b).

[0085] The positive electrode current collector may also have a positive electrode material layer located on the convex surface (63b).

[0086] In the lithium-ion battery of this application, when the negative electrode sheet is produced by a coating process, the capacity of the negative electrode sheet is usually designed to fully accept lithium ions from the positive electrode. However, after the positive electrode, negative electrode, and separator are wound together, for a pair of adjacent negative and positive electrode sheets separated by the separator, the arc length of the convex surface of the negative electrode is shorter than the arc length of the concave surface of the positive electrode at the arc-shaped bend. This makes it impossible for the negative electrode sheet to fully accept lithium ions from the positive electrode sheet, and thus severe lithium plating is very likely to occur at the arc-shaped bend, thereby deteriorating the safety and electrochemical performance of the battery.

[0087] In the design and development of the lithium-ion battery of this application, the inventors discovered that if lithium plating does not occur on the innermost negative electrode convex surface of the arc-shaped bend, then lithium plating will not occur on the other outer negative electrode convex surfaces. Therefore, by comprehensively controlling the minimum radius of curvature R of the negative electrode current collector in the first bend and the shortest distance L between the convex surface of the negative electrode current collector in the first bend and the concave surface of the positive electrode current collector in the second bend, the inventors determined the corner lithium plating coefficient β, which is closely related to high energy density and negative electrode lithium plating. The specific influence of β, R, and L on the energy density and corner lithium plating of the lithium-ion battery of this application is analyzed as follows:

[0088] Regarding the corner lithium plating coefficient β, β comprehensively characterizes the combined influence of R and L on the energy density and corner lithium plating of lithium-ion batteries. Since the arc length of the convex surface of the negative electrode current collector and the arc length of the concave surface of the positive electrode current collector are proportional to the curvature of their substrate surfaces, the smaller β is, the shorter the arc length of the convex surface of the negative electrode current collector relative to its adjacent concave surface of the positive electrode current collector, and the easier it is for lithium to plating. Therefore, β actually characterizes the overall lithium plating risk of high-energy-density batteries.

[0089] In this application, considering both reducing lithium plating at the arc-shaped bends and maintaining high battery energy density, the β range is 0.015 ≤ β ≤ 0.95. Lithium-ion batteries within this range achieve high energy density without lithium plating on the convex negative electrode surface at the arc-shaped bends. When the β value is less than 0.015, i.e., in the initial stage of the actual winding process, the number of empty turns of the separator is too small. Although this allows for more winding space for the positive and negative electrode sheets that are beneficial to improving battery energy density, it also results in the arc length of the convex negative electrode current collector at the first bend being shorter than the arc length of the concave positive electrode current collector at the adjacent second bend. This significantly increases the risk of severe lithium plating on the convex negative electrode surface. Conversely, when the β value is greater than 0.95, although lithium plating on the convex negative electrode surface does not occur, the excessively high β value results in a loss of winding space for the positive and negative electrode sheets that are beneficial to improving battery energy density, thus significantly reducing the battery energy density.

[0090] Based on the above discussion of β, the inventors of this application, through extensive experiments, discovered that when a battery assembly satisfying 0.015≤β≤0.95 is paired with a specific electrolyte, the risk of lithium plating on the negative electrode convex surface of the high-energy-density lithium-ion battery of this application can be significantly reduced. A smaller β indicates that the negative electrode convex surface in the arc-shaped bend is shorter than the corresponding positive electrode concave surface. During charging, more lithium ions will accumulate on the negative electrode convex surface, exacerbating lithium dendrite formation. This necessitates higher levels of fluorosulfonate and difluorophosphate additives to enhance the migration ability of lithium ions at the negative electrode interface and improve lithium plating on the negative electrode convex surface. Through extensive research, the inventors of this application discovered that the relationship between the content (w%) of the lithium plating-improving additives fluorosulfonate and / or difluorophosphate in the electrolyte and the lithium plating coefficient β at the innermost corner has a significant impact on the battery's volumetric energy density, lithium plating at the negative electrode convex corner, and battery internal resistance. When the mass content w% of the additive in the electrolyte and the lithium plating coefficient β at the innermost corner satisfy the relationship 0.01≤w×β≤20, it can ensure that the battery has a high energy density and also alleviate the lithium plating on the negative electrode convex surface.

[0091] Therefore, applying electrolytes containing additives such as fluorosulfonate and / or difluorophosphate to inhibit lithium plating to lithium-ion batteries, and more specifically, applying them to high-energy-density batteries with a large active material layer thickness and a small innermost radius of curvature, can solve the problem of the difficulty in achieving both high energy density and corner lithium plating.

[0092] In some implementations, optionally, 0.02 ≤ w × β ≤ 5.

[0093] When w×β is in the range of 0.02 to 5, the high-energy-density lithium-ion batteries developed and designed will not exhibit lithium plating at all, and even gray spots will not appear on the negative electrode surface.

[0094] In some implementations, optionally, 0.15 ≤ β ≤ 0.8.

[0095] When β is in the range of 0.15 to 0.8, it can be guaranteed that the developed and designed batteries will not experience lithium plating while maintaining high energy density.

[0096] In some implementations, R can optionally range from 2 μm to 5000 μm, or optionally from 50 μm to 500 μm.

[0097] In some implementations, L may optionally range from 20 μm to 900 μm, or optionally from 50 μm to 500 μm.

[0098] This application allows w×β to be adjusted to an appropriate value by adjusting w% and / or β. Furthermore, regarding β, as mentioned above, since β = R / (R+L), an appropriate β value can be obtained by adjusting R and / or L.

[0099] Regarding the R value, R is the minimum radius of curvature of the convex surface of the negative electrode current collector in the first bend. The R value can be increased by emptying the separator or the negative electrode sheet (for cylindrical batteries, the R value can also be increased by increasing the volume of the central cavity).

[0100] From the perspective of improving battery energy density and reducing lithium plating on the convex negative electrode, the range of R is 2μm to 5000μm, preferably 50μm to 500μm. For a battery of the same volume, the smaller the R value, the higher the volumetric energy density; the larger the R value, the larger the proportion of inactive space and the lower the volumetric energy density. When the R value is less than 2μm, current winding technology cannot achieve the required size, and lithium plating on the convex negative electrode is also relatively severe. Conversely, when the R value exceeds 5000μm, the battery energy density cannot meet the shipping requirements.

[0101] Regarding the value of L, L is the shortest distance between the convex surface of the negative current collector in the first bend and the concave surface of the positive current collector in the second bend. The physical meaning of L is the sum of the thickness of the negative active material layer on the convex surface of the negative current collector in the first bend, the thickness of the separator, and the thickness of the positive active material layer on the concave surface of the positive current collector in the second bend. However, in reality, since the thickness of our separator is negligible compared to the other two thicknesses, for a tightly wound battery structure, the value of L actually represents the sum of the thickness of the negative active material layer on the convex surface of the negative current collector in the first bend and the thickness of the positive active material layer on the concave surface of the positive current collector in the second bend. Therefore, the value of L has a significant impact on the battery energy density.

[0102] From the perspective of improving battery energy density and reducing lithium plating on the convex surface of the negative electrode, the range of L is 20μm to 900μm, preferably 50μm to 500μm. When L is less than 20μm, the battery volumetric energy density is low. Conversely, when L exceeds 900μm, the thickness of both the positive and negative electrode active layers is too thick, resulting in a long lithium-ion migration path. This not only prevents lithium ions from the positive electrode from quickly embedding into the negative electrode active layer, increasing the risk of lithium plating, but also causes high battery polarization, leading to high internal resistance.

[0103] In some embodiments, the fluorosulfonate may optionally have the structural formula (FSO3). x M x+ M x+ Selected from Li + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Al 3+ Fe 2+ Fe 3+ Ni 2+ and Ni 3+ One or more of the following, the structural formula of difluorophosphate is (F₂PO₂). y M y+ M y+ Selected from Li + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Al 3+ Fe 2+ Fe 3+ Ni 2+ and Ni 3+ One or more of them.

[0104] Regarding the reason why this type of electrolyte and its specific component content can suppress lithium plating on the convex surface of the negative electrode at high energy density, the inventors of this application speculate as follows:

[0105] In electrode assemblies, the innermost negative electrode convex surface has a higher risk of lithium plating, and increasing the coating thickness further exacerbates this problem. By adding specific fluorosulfonates and / or difluorophosphates as inorganic additives to the electrolyte, the microstructure of the SEI film formed on the negative electrode surface can be improved, resulting in an SEI film with an intercalated inorganic-organic network. The improved SEI film exhibits high lithium-ion conductivity, allowing lithium ions that gradually accumulate on the negative electrode convex surface to migrate promptly to the main surface of the negative electrode sheet under the influence of an electric field, such as areas outside the arc-shaped bends, rather than "accumulating" on the negative electrode convex surface. This results in more uniform lithium intercalation throughout the negative electrode, effectively suppressing the formation of lithium dendrites on the negative electrode convex surface.

[0106] Regarding the reason why the SEI film with interlocked inorganic and organic networks is more advantageous in suppressing lithium plating on the convex surface of the negative electrode under high energy density, the inventors of this application speculate as follows:

[0107] During formation, fluorosulfonates and difluorophosphates are reduced on the negative electrode surface, forming a low-resistance SEI film. This low-resistance SEI film originates from two aspects: firstly, the inorganic products of fluorosulfonates or difluorophosphates have excellent lithium-ion conductivity, thus enhancing the lithium-ion transport capacity of the SEI; secondly, an inorganic-rich SEI is thinner and more stable, reducing the path of lithium ions across the SEI. Due to the low-resistance SEI film, unacceptable lithium rapidly migrates to areas not yet fully intercalated under the influence of the electric field, resulting in uniform lithium intercalation throughout the negative electrode and suppressing lithium plating.

[0108] Therefore, applying electrolytes containing additives such as fluorosulfonate and / or difluorophosphate to inhibit lithium plating to lithium-ion batteries, and more specifically, applying them to high-energy-density batteries with a large active material layer thickness and a small innermost radius of curvature, can solve the problem of the difficulty in achieving both high energy density and corner lithium plating.

[0109] In some embodiments, optionally, the mass percentage (w%) of fluorosulfonates and / or difluorophosphates in the electrolyte ranges from 0.02% to 25%, preferably from 0.02% to 20%, more preferably from 0.05% to 10%, and even more preferably from 0.1% to 5%.

[0110] The inventors of this application discovered in actual research that adding too much fluorosulfonate and / or difluorophosphate additives to the electrolyte increases the electrolyte viscosity, deteriorates the electrolyte conductivity, and leads to an increase in the battery's internal resistance; conversely, too little fluorosulfonate and / or difluorophosphate additives cannot suppress lithium plating on the negative electrode's convex surface.

[0111] In some embodiments, the electrolyte may optionally further comprise fluoroethylene carbonate (FEC) and / or 1,3-propanesulfonate lactone (PS), wherein the mass percentage of fluoroethylene carbonate and / or 1,3-propanesulfonate lactone in the electrolyte is 0.01% to 15%, optionally 0.05% to 5%, and further optionally 0.1% to 2%.

[0112] The inventors of this application have also discovered that adding FEC and / or PS to the electrolyte containing fluorosulfonate and difluorophosphate further enhances the stability of the negative electrode interface, thereby further improving both room temperature and high temperature cycling performance. Furthermore, the improvement in battery cycle performance is more significant when the content of FEC and / or PS in the electrolyte is between 0.01% and 15%. However, when the content of fluoroethylene carbonate and / or 1,3-propanesulfonate lactone is high, fluoroethylene carbonate and / or 1,3-propanesulfonate lactone are easily oxidized and form a film on the positive electrode at high temperatures, leading to increased polarization of the positive electrode, which is detrimental to the high-temperature cycling performance of the lithium-ion battery.

[0113] In the lithium-ion battery described in this application, the electrolyte includes a lithium salt. There are no particular limitations on the type of lithium salt, and it can be selected according to actual needs. Specifically, the lithium salt can be selected from LiN(C) m F 2m+1 SO2)(C n F 2n+1 The combination of one or more of the following: SO2, LiPF6, LiBF4, LiBOB, LiAsF6, Li(CF3SO2)2N, LiCF3SO3, and LiClO4, wherein m and n are natural numbers, for example, 1 to 5.

[0114] In the lithium-ion battery described in this application, the electrolyte contains an organic solvent. There are no particular limitations on the type of organic solvent; it can be selected according to actual needs. Specifically, the organic solvent may include one or more selected from various chain carbonates, cyclic carbonates, and carboxylic acid esters. There are no specific limitations on the types of chain carbonates, cyclic carbonates, and carboxylic acid esters; they can be selected according to actual needs. Preferably, the organic solvent may also include one or more selected from diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, ethylene carbonate, propylene carbonate, butenyl carbonate, γ-butyrolactone, methyl formate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl propionate, and tetrahydrofuran.

[0115] The content of organic solvents in the electrolyte can be appropriately adjusted according to the mass percentage (w%) of the aforementioned fluorosulfonates and / or difluorophosphates.

[0116] In the lithium-ion battery described in this application, the electrolyte may further contain other additives. These other additives can be appropriately selected according to specific purposes, and for example, may be selected from at least one of the following: sulfate ester compounds, sulfite ester compounds, disulfonic acid compounds, nitrile compounds, aromatic compounds, isocyanate compounds, phosphonitrile compounds, cyclic anhydride compounds, phosphite ester compounds, phosphate ester compounds, borate ester compounds, and carboxylic acid ester compounds. The content of these other additives in the electrolyte is 0.01% to 10%, preferably 0.1% to 5%, and more preferably 0.1% to 2%.

[0117] In some embodiments, the porosity of the negative electrode material layer is optionally 20% to 50%, and more preferably 30% to 50%.

[0118] In the lithium-ion battery of this application, the porosity of the negative electrode active layer is 20%–50%. While maintaining a relatively high energy density in the lithium-ion battery, a higher porosity in the negative electrode material layer allows lithium migrating from the positive electrode to the negative electrode during charging to rapidly migrate into the interior of the negative electrode active layer, thus mitigating lithium deposition on the negative electrode surface. However, this reduces the volumetric energy density of the electrode assembly. By limiting the porosity of the negative electrode active layer to 20%–50%, both lithium deposition on the negative electrode convex surface and a high volumetric energy density of the battery can be achieved. The porosity of the negative electrode active layer can be modulated by using negative electrode materials of different particle sizes and cold-pressing the negative electrode sheets under different pressures.

[0119] In the lithium-ion battery described in this application, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer disposed on the negative electrode current collector and including a negative electrode active material. The negative electrode material layer can be disposed on one of the two surfaces of the negative electrode current collector, or it can be disposed on both surfaces of the negative electrode current collector. In the lithium-ion battery described in this application, preferably, the negative electrode sheet includes a negative electrode current collector and negative electrode active layers respectively located on the two surfaces of the negative electrode current collector. After winding, the negative electrode material layers on the two surfaces of the negative electrode current collector become negative electrode material layers located on the concave surface (i.e., the inner side) and convex surface (i.e., the outer side) of the negative electrode current collector.

[0120] The type of negative electrode active material contained in the negative electrode active layer is not specifically limited. Conventional negative electrode active materials in the field of lithium batteries can be used, such as graphite, soft carbon, hard carbon, mesophase carbon microspheres, carbon fiber, carbon nanotubes, elemental silicon, silicon oxide, silicon-carbon composites, and lithium titanate, or one or more of these.

[0121] In the lithium-ion battery of this application, the negative electrode active layer may further include a conductive agent and a binder. The type and content of the conductive agent and binder are not specifically limited; they can be the types and contents commonly used in the negative electrode material layer of lithium batteries, and can be selected according to actual needs.

[0122] In addition, the type of negative electrode current collector in the lithium battery of this application is not specifically limited. It can be a negative electrode current collector commonly used in lithium batteries, or it can be selected according to actual needs.

[0123] In the lithium-ion battery described in this application, the positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on the positive current collector and including a positive electrode active material. The positive electrode material layer may be disposed on one of the two surfaces of the positive current collector, or it may be disposed on both surfaces of the positive current collector. In the lithium-ion battery described in this application, preferably, the positive electrode sheet includes a positive current collector and positive electrode material layers respectively located on the two surfaces of the positive current collector. After winding, the positive electrode material layers on the two surfaces of the positive current collector become positive electrode material layers located on the concave surface (i.e., the inner side) and convex surface (i.e., the outer side) of the positive current collector.

[0124] In the lithium-ion battery of this application, the positive electrode active material included in the positive electrode material layer is selected from materials capable of extracting and inserting lithium ions. Specifically, the positive electrode active material can be selected from one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and compounds obtained by adding other transition metals or non-transition metals to the above compounds. However, this application is not limited to these materials, and conventional positive electrode active materials in the field of lithium batteries can also be used.

[0125] In the lithium-ion battery described in this application, the positive electrode material layer may further include a conductive agent and a binder. The type and content of the conductive agent and binder are not specifically limited; they can be the types and contents commonly used in the positive electrode material layer of lithium batteries, and can be selected according to actual needs.

[0126] In addition, the type of positive electrode current collector in the lithium battery of this application is not specifically limited. It can be the positive electrode current collector commonly used in lithium batteries, or it can be selected according to actual needs.

[0127] In the lithium-ion battery described in this application, a separator is disposed between the positive electrode and the negative electrode to provide isolation. The type of separator is not specifically limited; it can be any type of separator material used in existing batteries. Examples include films made of polyethylene, polypropylene, polyvinylidene fluoride, and their multilayer composite films, but it is not limited to these.

[0128] This application does not impose any particular limitation on the shape of the lithium-ion battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 2 This is an example of a square-structured lithium-ion battery 5.

[0129] In some implementations, refer to Figure 3 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. Positive electrode sheets, negative electrode sheets, and a separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The lithium-ion battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0130] In addition, the lithium-ion battery, battery module, battery pack and device of this application will be described below with appropriate reference to the accompanying drawings.

[0131] [Battery Module]

[0132] In some embodiments, the lithium-ion battery of the first aspect of this application can be assembled into a battery module. The number of lithium-ion batteries contained in the battery module can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery module.

[0133] Figure 4 This is battery module 4, used as an example. (See reference...) Figure 4 In battery module 4, multiple lithium-ion batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple lithium-ion batteries 5 can be fixed in place using fasteners.

[0134] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple lithium-ion batteries 5 are housed.

[0135] [Battery Pack]

[0136] In some embodiments, the battery modules of this application can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0137] Figure 5 and Figure 6 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0138] [Electrical appliances]

[0139] In addition, this application also provides an electrical device, which includes one or more of the lithium-ion battery, battery module, or battery pack provided in this application. The lithium-ion battery, battery module, or battery pack can be used as a power source for the device or as an energy storage unit for the device. The device can be, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0140] As the electrical device, a lithium-ion battery, battery module, or battery pack can be selected according to its usage requirements.

[0141] Figure 7 This is an example device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the device's requirements for high power and high energy density lithium-ion batteries, a battery pack or battery module can be used.

[0142] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use lithium-ion batteries as their power source.

[0143] Example

[0144] The present application is further illustrated below with reference to embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present application.

[0145] The lithium-ion batteries in the examples and comparative examples were prepared according to the following method:

[0146] (1) Preparation of positive electrode sheet

[0147] LiNi, the positive electrode active material 0.8 Mn 0.1 Co 0.1 O2, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) are dissolved in N-methylpyrrolidone (NMP) at a weight ratio of 94:3:3 and thoroughly mixed to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated onto a positive electrode current collector, followed by drying, cold pressing, and slitting to obtain the positive electrode sheet. Different thicknesses of positive electrode sheets can be obtained by adjusting the coating weight of the positive electrode slurry.

[0148] (2) Preparation of negative electrode sheet

[0149] A negative electrode slurry was prepared by dissolving artificial graphite (active material), acetylene black (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC) (thickener) in deionized water at a weight ratio of 95:2:2:1. The slurry was then uniformly mixed with deionized water to form a negative electrode slurry. This slurry was then uniformly coated onto a copper foil current collector, dried, and the resulting negative electrode film was cold-pressed and slit to obtain the negative electrode sheet. Different thicknesses of negative electrode sheets can be obtained by adjusting the coating weight of the negative electrode slurry.

[0150] (3) Preparation of the separating membrane

[0151] The separator used in this application is a polyethylene film.

[0152] (4) Electrode assembly fabrication

[0153] Example 1-1:

[0154] The negative electrode copper foil substrate is 2μm thick, and the negative electrode material layer coated on it is 66μm thick. Only the convex side of the innermost ring is coated with negative electrode material, while the other areas are coated on both sides. The positive electrode aluminum foil substrate is 13μm thick, and a positive electrode material layer with a thickness of 62μm is coated on both sides. The separator is 7μm thick. Finally, the components are wound together in the following order from the inside out: negative electrode, separator, positive electrode, separator, resulting in an electrode assembly with R = 2μm and L = 135μm.

[0155] Examples 1-2:

[0156] The negative electrode copper foil substrate is 5 μm thick, and the negative electrode material layer coated on it is 66 μm thick. Only the convex side of the innermost ring is coated with negative electrode material, while the other areas are coated on both sides. The positive electrode aluminum foil substrate is 13 μm thick, and a positive electrode material layer with a thickness of 62 μm is coated on both sides. The separator is 7 μm thick. Finally, the components are wound together in the following order from the inside out: negative electrode, separator, positive electrode, separator, resulting in an electrode assembly with R = 5 μm and L = 135 μm.

[0157] Examples 1-3:

[0158] The negative electrode copper foil substrate is 4 μm thick, and the negative electrode material layer coated on it is 66 μm thick. Only the convex side of the innermost ring is coated with negative electrode material, while the other areas are coated on both sides. The positive electrode aluminum foil substrate is 13 μm thick, and a positive electrode material layer with a thickness of 62 μm is coated on both sides. The separator is 7 μm thick. The separator is first wound once, then inserted into the negative electrode, followed by the positive electrode, and then wound together to obtain an electrode assembly with R = 25 μm and L = 135 μm.

[0159] Examples 1-4:

[0160] The negative electrode copper foil substrate is 8 μm thick, and the negative electrode material layer coated on it is 66 μm thick. Only the convex side of the innermost ring is coated with negative electrode material, while the other areas are coated on both sides. The positive electrode aluminum foil substrate is 13 μm thick, and a positive electrode material layer with a thickness of 62 μm is coated on both sides. The separator is 7 μm thick. The separator is first wound three times, then inserted into the negative electrode, followed by the positive electrode, and then wound together to obtain an electrode assembly with R = 50 μm and L = 135 μm.

[0161] Examples 1-5:

[0162] The negative electrode copper foil substrate is 8 μm thick, with a 66 μm thick negative electrode material layer coated on both sides; the positive electrode aluminum foil substrate is 13 μm thick, with a 62 μm thick positive electrode material layer coated on both sides; the separator is 7 μm thick. The separator is first wound once, then inserted into the negative electrode, followed by the positive electrode, and then wound together to obtain an electrode assembly with R = 95 μm and L = 135 μm.

[0163] Examples 1-6:

[0164] The negative electrode copper foil substrate is 8 μm thick, and the negative electrode material layer coated on it is 66 μm thick. Only the convex side of the innermost ring is coated with negative electrode material, while the other areas are coated on both sides. The positive electrode aluminum foil substrate is 13 μm thick, and a positive electrode material layer with a thickness of 62 μm is coated on both sides. The separator is 7 μm thick. The separator is first wound 13 times, then inserted into the negative electrode, followed by the positive electrode, and then wound together to obtain an electrode assembly with R = 190 μm and L = 135 μm.

[0165] Examples 1-7:

[0166] The negative electrode copper foil substrate is 7μm thick, with a 66μm thick negative electrode material layer coated on both sides; the positive electrode aluminum foil substrate is 13μm thick, with a 62μm thick positive electrode material layer coated on both sides; the separator is 7μm thick. The separator is first wound 8 turns, then inserted into the negative electrode and wound 3 turns, followed by the positive electrode and wound together, resulting in an electrode assembly with R = 500μm and L = 135μm.

[0167] Examples 1-8:

[0168] The negative electrode copper foil substrate is 7 μm thick, with a 66 μm thick negative electrode material layer coated on both sides; the positive electrode aluminum foil substrate is 13 μm thick, with a 62 μm thick positive electrode material layer coated on both sides; the separator is 7 μm thick. The separator is first wound 6 turns, then inserted into the negative electrode and wound 4 turns, followed by the positive electrode and wound together, resulting in an electrode assembly with R = 780 μm and L = 135 μm.

[0169] Examples 1-9:

[0170] The negative electrode copper foil substrate is 7 μm thick, with a 66 μm thick negative electrode material layer coated on both sides; the positive electrode aluminum foil substrate is 13 μm thick, with a 62 μm thick positive electrode material layer coated on both sides; the separator is 7 μm thick. The separator is first wound 3 times, then inserted into the negative electrode and wound 9 times, followed by the positive electrode and wound together, resulting in an electrode assembly with R = 1500 μm and L = 135 μm.

[0171] Examples 1-10:

[0172] The negative electrode copper foil substrate is 9 μm thick, with a 100 μm thick negative electrode material layer coated on both sides; the positive electrode aluminum foil substrate is 13 μm thick, with a 93 μm thick positive electrode material layer coated on both sides; the separator is 7 μm thick. The separator is first wound 15 turns, then inserted into the negative electrode and wound 12 turns, followed by the positive electrode and wound together, resulting in an electrode assembly with R = 3000 μm and L = 200 μm.

[0173] Examples 1-11:

[0174] The negative electrode copper foil substrate is 9 μm thick, with a negative electrode material layer of 151 μm thickness coated on both sides; the positive electrode aluminum foil substrate is 13 μm thick, with a positive electrode material layer of 142 μm thickness coated on both sides; the separator is 7 μm thick. The separator is first wound 20 times, then inserted into the negative electrode and wound 14 times, followed by the positive electrode and wound together, resulting in an electrode assembly with R = 5000 μm and L = 300 μm.

[0175] Example 2-1:

[0176] The negative electrode copper foil substrate is 7 μm thick, with a negative electrode material layer of 2.6 μm thickness coated on both sides; the positive electrode aluminum foil substrate is 13 μm thick, with a positive electrode material layer of 2.4 μm thickness coated on both sides; the separator is 5 μm thick. The separator is first wound 8 times, then inserted into the negative electrode, followed by the positive electrode, and wound together to obtain an electrode assembly with R = 95 μm and L = 10 μm.

[0177] Example 2-2:

[0178] The negative electrode copper foil substrate is 10 μm thick, with a negative electrode material layer of 6.7 μm thickness coated on both sides; the positive electrode aluminum foil substrate is 13 μm thick, with a positive electrode material layer of 6.3 μm thickness coated on both sides; the separator is 7 μm thick. The separator is first wound 5 times, then inserted into the negative electrode, followed by the positive electrode, and then wound together to obtain an electrode assembly with R = 95 μm and L = 20 μm.

[0179] Examples 2-3:

[0180] The negative electrode copper foil substrate is 10 μm thick, with a 22 μm thick negative electrode material layer coated on both sides; the positive electrode aluminum foil substrate is 13 μm thick, with a 21 μm thick positive electrode material layer coated on both sides; the separator is 7 μm thick. The separator is first wound 4 turns, then inserted into the negative electrode, followed by the positive electrode, and wound together to obtain an electrode assembly with R = 95 μm and L = 50 μm.

[0181] Examples 2-4:

[0182] The negative electrode copper foil substrate is 12μm thick, with a negative electrode material layer of 48μm thickness coated on both sides; the positive electrode aluminum foil substrate is 13μm thick, with a positive electrode material layer of 45μm thickness coated on both sides; the separator is 7μm thick. The separator is first wound twice, then inserted into the negative electrode, followed by the positive electrode and wound together, resulting in an electrode assembly with R = 95μm and L = 100μm.

[0183] Examples 2-5:

[0184] Electrode assemblies were prepared in the same manner as in Examples 1-5.

[0185] Examples 2-6:

[0186] The negative electrode copper foil substrate is 5 μm thick, and the negative electrode material layer coated on it is 94.4 μm thick. Only the convex side of the innermost ring is coated with negative electrode material, while the other areas are coated on both sides. The positive electrode aluminum foil substrate is 13 μm thick, and a positive electrode material layer with a thickness of 88.6 μm is coated on both sides. The separator is 7 μm thick. The separator is first wound 6 times, then inserted into the negative electrode, followed by the positive electrode, and then wound together to obtain an electrode assembly with R = 95 μm and L = 190 μm.

[0187] Examples 2-7:

[0188] The negative electrode copper foil substrate is 5 μm thick, and the negative electrode material layer coated on it is 120 μm thick. Only the convex side of the innermost ring is coated with negative electrode material, while the other areas are coated on both sides. The positive electrode aluminum foil substrate is 13 μm thick, and a positive electrode material layer with a thickness of 113 μm is coated on both sides. The separator is 7 μm thick. The separator is first wound 6 times, then inserted into the negative electrode, followed by the positive electrode, and then wound together to obtain an electrode assembly with R = 95 μm and L = 240 μm.

[0189] Examples 2-8:

[0190] The negative electrode copper foil substrate is 5 μm thick, and the negative electrode material layer coated on it is 228 μm thick. Only the convex side of the innermost ring is coated with negative electrode material, while the other areas are coated on both sides. The positive electrode aluminum foil substrate is 13 μm thick, and a positive electrode material layer with a thickness of 216 μm is coated on both sides. The separator is 7 μm thick. The separator is first wound 6 times, then inserted into the negative electrode, followed by the positive electrode, and then wound together to obtain an electrode assembly with R = 95 μm and L = 450 μm.

[0191] Examples 2-9:

[0192] The negative electrode copper foil substrate is 5 μm thick, and the negative electrode material layer coated on it is 254 μm thick. Only the convex side of the innermost ring is coated with negative electrode material, while the other areas are coated on both sides. The positive electrode aluminum foil substrate is 13 μm thick, and a positive electrode material layer with a thickness of 239 μm is coated on both sides. The separator is 7 μm thick. The separator is first wound 6 times, then inserted into the negative electrode, followed by the positive electrode, and then wound together to obtain an electrode assembly with R = 95 μm and L = 500 μm.

[0193] Example 2-10:

[0194] The negative electrode copper foil substrate is 5 μm thick, and the negative electrode material layer coated on it is 460 μm thick. Only the convex side of the innermost ring is coated with negative electrode material, while the other areas are coated on both sides. The positive electrode aluminum foil substrate is 13 μm thick, and a positive electrode material layer with a thickness of 433 μm is coated on both sides. The separator is 7 μm thick. The separator is first wound 6 times, then inserted into the negative electrode, followed by the positive electrode, and then wound together to obtain an electrode assembly with R = 95 μm and L = 900 μm.

[0195] Example 2-11:

[0196] The negative electrode copper foil substrate is 5 μm thick, and the negative electrode material layer coated on it is 564 μm thick. Only the convex side of the innermost ring is coated with negative electrode material, while the other areas are coated on both sides. The positive electrode aluminum foil substrate is 13 μm thick, and a positive electrode material layer with a thickness of 529 μm is coated on both sides. The separator is 7 μm thick. The separator is first wound 6 times, then inserted into the negative electrode, followed by the positive electrode, and then wound together to obtain an electrode assembly with R = 95 μm and L = 1100 μm.

[0197] Examples 3-1 to 3-10:

[0198] Electrode assemblies were prepared in the same manner as in Examples 1-5.

[0199] Example 3-11:

[0200] The negative electrode copper foil substrate is 5 μm thick, with a negative electrode material layer of 27.3 μm thickness coated on both sides; the positive electrode aluminum foil substrate is 13 μm thick, with a positive electrode material layer of 25.7 μm thickness coated on both sides; the separator is 7 μm thick. The separator is first wound 4 turns, then inserted into the negative electrode, followed by the positive electrode, and wound together to obtain an electrode assembly with R = 95 μm and L = 60 μm.

[0201] Example 3-12:

[0202] The negative electrode copper foil substrate is 8μm thick, with a negative electrode material layer of 38μm thickness coated on both sides; the positive electrode aluminum foil substrate is 13μm thick, with a positive electrode material layer of 35μm thickness coated on both sides; the separator is 7μm thick. The separator is first wound 4 turns, then inserted into the negative electrode and wound 4 turns, followed by the positive electrode and wound together, resulting in an electrode assembly with R = 500μm and L = 80μm.

[0203] Example 3-13:

[0204] The negative electrode copper foil substrate is 7 μm thick, with a 100 μm thick negative electrode material layer coated on both sides; the positive electrode aluminum foil substrate is 13 μm thick, with a 93 μm thick positive electrode material layer coated on both sides; the separator is 7 μm thick. The separator is first wound 9 turns, then inserted into the negative electrode and wound 17 turns, followed by the positive electrode and wound together, resulting in an electrode assembly with R = 4000 μm and L = 200 μm.

[0205] Example 3-14:

[0206] The electrode assembly was prepared in the same manner as in Examples 3-13.

[0207] Examples 4-1 to 4-15:

[0208] Electrode assemblies were prepared in the same manner as in Examples 1-5.

[0209] Examples 5-1 to 5-7:

[0210] Electrode assemblies were prepared in the same manner as in Examples 1-5.

[0211] Comparative Example 1:

[0212] The negative electrode copper foil substrate is 5 μm thick, and the negative electrode material layer coated on it is 73 μm thick. Only the convex side of the innermost ring is coated with negative electrode material, while the other areas are coated on both sides. The positive electrode aluminum foil substrate is 13 μm thick, and a positive electrode material layer with a thickness of 55 μm is coated on both sides. The separator is 7 μm thick. Finally, the negative electrode, separator, and positive electrode are wound together in the order from the inside out to obtain the electrode assembly of Comparative Example 1.

[0213] Comparative Example 2:

[0214] The negative electrode copper foil substrate is 8 μm thick, with a negative electrode material layer of 73 μm thickness coated on both sides; the positive electrode aluminum foil substrate is 13 μm thick, with a positive electrode material layer of 55 μm thickness coated on both sides; the separator is 7 μm thick. The separator is first wound once, then inserted into the negative and positive electrodes and wound together, finally obtaining the electrode assembly of Comparative Example 2.

[0215] Comparative Example 3:

[0216] The negative electrode copper foil substrate is 8 μm thick, with a negative electrode material layer of 73 μm thickness coated on both sides; the positive electrode aluminum foil substrate is 13 μm thick, with a positive electrode material layer of 55 μm thickness coated on both sides; the separator is 7 μm thick. First, the separator is wound once, then inserted into the negative electrode and wound 6 times, then inserted into the positive electrode and wound together, finally obtaining the electrode assembly of Comparative Example 3.

[0217] Comparative Example 4:

[0218] The negative electrode copper foil substrate is 8 μm thick, with a negative electrode material layer of 30 μm thickness coated on both sides; the positive electrode aluminum foil substrate is 13 μm thick, with a positive electrode material layer of 23 μm thickness coated on both sides; the separator is 7 μm thick. The separator is first wound 4 turns, then inserted into the negative and positive electrodes and wound together, finally obtaining the electrode assembly of Comparative Example 4.

[0219] Comparative Example 5:

[0220] The negative electrode copper foil substrate is 8 μm thick, and the negative electrode material layer coated on it is 218.5 μm thick. Only the convex side of the innermost ring is coated with negative electrode material, while the other areas are coated on both sides. The positive electrode aluminum foil substrate is 13 μm thick, and a positive electrode material layer with a thickness of 164.5 μm is coated on both sides. The separator is 7.2 μm thick. The separator is first wound 6 times, then inserted into the negative and positive electrodes and wound together, finally obtaining the electrode assembly of Comparative Example 5.

[0221] (5) Preparation of electrolyte

[0222] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), organic solvent EC / EMC is mixed evenly at a volume ratio of 3 / 7. 12.5% ​​of LiPF6 lithium salt is added and dissolved in the organic solvent. Add the additives shown in the table, stir evenly, and the corresponding electrolyte is obtained.

[0223] (6) Preparation of lithium-ion batteries

[0224] The electrode assembly is placed in the battery casing, dried, and then injected with electrolyte. The lithium-ion battery is then produced through processes such as formation and settling.

[0225] The following describes the testing process for the relevant parameters of the electrode assembly.

[0226] [1] Method for determining the minimum radius of curvature R (μm) of the convex surface of the negative electrode current collector in the first bend.

[0227] X-ray computed tomography (CT) analysis of the battery was performed according to ISO 15708:22, "Non-destructive testing - Radiation methods - Computed tomography," using a Waygate Technologies nanomelx neo 180 instrument. First, the electrode assembly was fixed on a high-precision CNC programmable sample scanning stage. Then, the instrument was turned on, and two-dimensional projections were acquired using Phoenix Datos X Acquisition software. After the two-dimensional projection acquisition was completed, geometric correction was performed, followed by three-dimensional volume reconstruction. This non-destructively obtained the three-dimensional structure of the battery cell assembly. Then, CAD software was used to measure the radius of curvature of the innermost negative electrode convex substrate surface, and the minimum value R was taken.

[0228] [2] The shortest distance L (μm) between the convex surface of the negative current collector in the first bend and the concave surface of the positive current collector in the second bend.

[0229] The electrode assembly was disassembled, and then the thicknesses H2 and H3 of the negative electrode and current collector were measured using a micrometer. The thicknesses H4 and H5 of the positive electrode and current collector, as well as the thickness of the separator, were measured. The thickness of the separator was calculated using the formula L(μm)=(H2-H3+H4-H5) / 2+H6.

[0230] [3] Porosity of the negative electrode active layer

[0231] The negative electrode active layer was punched into small circular pieces with a diameter of 10 cm. The thickness was measured using a micrometer, and the apparent volume V1 was calculated. Then, referring to GB / T 24586-2009, the true volume V2 was measured using a true density meter (AccuPyc 1340). A certain mass of sample was weighed and placed in the true density meter. The testing system was sealed, and nitrogen gas was introduced according to the program. By detecting the gas pressure in the sample chamber and the expansion chamber, the instrument automatically calculated the true volume V2 according to Bohr's Law. Porosity = (V1-V2) / V1*100%.

[0232] The testing methods for lithium-ion batteries will be explained next.

[0233] [1] Lithium deposition on the negative electrode convex surface in the first bend

[0234] After formation, the battery is charged at 25°C with a constant current of 1.5C to 4.2V, then charged at a constant voltage of 4.2V until the current is less than 0.05C, and then discharged at 1C to 2.8V. After 20 cycles, it is charged at a constant current of 1.5C to 4.2V, and then charged at a constant voltage of 4.2V until the current is less than 0.05C to obtain a fully charged battery.

[0235] After the battery has been cycled 20 times, disassemble it and observe the lithium plating on the innermost (outermost) negative electrode convex surface. Record the observations in the "Lithium Plating on Negative Electrode Convex Surface" column of the table below.

[0236] The evaluation criteria after observation are as follows.

[0237] No lithium deposition: The fully charged negative electrode surface in the corner area is golden yellow. When wiped with a dust-free paper, there is no gray metallic lithium powder on the paper.

[0238] Slight lithium plating: The fully charged negative electrode surface in the corner area is dark yellow. When wiped with lint-free paper, gray metallic lithium powder is found on the paper.

[0239] Gray spots: The corner area has localized gray spots on the fully charged negative electrode surface, with no golden yellow showing through.

[0240] Severe lithium plating: The entire surface of the fully charged negative electrode in the corner area is gray, with no golden yellow showing through.

[0241] In this application, the preferred order of lithium plating on the convex surface of the negative electrode is no lithium plating > gray spots > slight lithium plating > severe lithium plating.

[0242] [2] Volumetric energy density

[0243] At 25℃, a lithium-ion battery is charged at a constant current of 1C to 4.2V, then charged at a constant voltage of 4.2V until the current is less than 0.05C, and then discharged at 0.33C to 2.8V, yielding the discharge energy Q. The length, width, and height of the cell casing are measured using vernier calipers to calculate the volume V. The volumetric energy density is calculated as Q / V. The unit of volumetric energy density is Wh / L. -1 .

[0244] [3] Battery internal resistance

[0245] At 25°C, the lithium-ion battery was charged at a constant current of 1C to 4.2V, then charged at a constant voltage of 4.2V until the current was less than 0.05C, and then discharged at 1C for 30 minutes, adjusting the cell's charge to 50% SOC. Then, the positive and negative probes of a TH2523A AC internal resistance tester were connected to the positive and negative terminals of the battery, and the battery's internal resistance value was read using the tester.

[0246] [4] Battery room temperature cycle performance test

[0247] At 25°C, the lithium-ion battery is charged at a constant current of 1C to 4.2V, then charged at a constant voltage of 4.2V until the current is less than 0.05C, and then discharged at a constant current of 1C to 2.8V. This constitutes one charge-discharge cycle. This charging and discharging process is repeated, and the capacity retention rate of the lithium-ion battery after 1000 cycles is calculated.

[0248] The capacity retention rate (%) of a lithium-ion battery after 1000 cycles at 25°C = (discharge capacity of the 1000th cycle / discharge capacity of the first cycle) × 100%.

[0249] [5] Battery high-temperature cycling performance test

[0250] At 45°C, the lithium-ion battery is charged at a constant current of 1C to 4.2V, then charged at a constant voltage of 4.2V until the current is less than 0.05C, and then discharged at a constant current of 1C to 2.8V. This constitutes one charge-discharge cycle. This charging and discharging process is repeated, and the capacity retention rate of the lithium-ion battery after 800 cycles is calculated.

[0251] The capacity retention rate (%) of a lithium-ion battery after 1000 cycles at 45℃ = (discharge capacity of the 800th cycle / discharge capacity of the first cycle) × 100%.

[0252]

[0253] The following can be seen from Table 1.

[0254] As can be seen from Examples 1-1 to 1-11, the volumetric energy density of the lithium-ion battery decreases with increasing R value. Therefore, to obtain a battery with high energy density, the R value cannot be too large. Conversely, with decreasing R value, slight lithium plating occurs on the negative electrode convex surface in the first bend. Therefore, the R value cannot be too small either. The preferred R value is 2μm to 5000μm, more preferably 50μm to 500μm. Within this range, both high energy density and severe lithium plating can be ensured in the lithium-ion battery.

[0255] As shown in Table 1, compared with the examples, the lithium plating and energy density of all comparative examples could not be improved simultaneously.

[0256] Compared to Examples 1-2, the only difference in Comparative Example 1 is that the electrolyte does not contain fluorosulfonate / difluorophosphate, i.e., the mass percentage (w%) of fluorosulfonate / difluorophosphate in the electrolyte is 0. As a result, in the evaluation of "lithium deposition at the corner of the negative electrode film", Comparative Example 1 is rated as "severe lithium deposition", and compared to the "slight lithium deposition" of Examples 1-2, it cannot achieve a good effect in suppressing corner lithium deposition.

[0257] Comparing Comparative Examples 1 through 3, it can be seen that, similarly, when the electrolyte does not contain fluorosulfonate and / or difluorophosphate, Comparative Example 2 significantly increased the β value by reducing the L value. The evaluation result for "lithium deposition at the corner of the negative electrode film" in Comparative Example 2 was "slight lithium deposition," indicating that "corner lithium deposition" was improved to some extent. However, since Comparative Example 2 achieved the increase in the β value by reducing L, its "volume energy density" was lower compared to Comparative Example 1 and Comparative Document 3.

[0258] As can be seen from Comparative Example 4, if the R value or β value is too low, the evaluation result of "lithium deposition at the corner of the negative electrode film" is "severe lithium deposition", and the effect of suppressing corner lithium deposition cannot be obtained well.

[0259] As can be seen from Comparative Example 5, if the R value is too large, the volumetric energy density will decrease too much and will not meet the "high energy density" requirement of lithium-ion batteries.

[0260]

[0261] Table 2 shows that if the L value is too small, the volumetric energy density of the lithium battery is too low; as the L value increases, the volumetric energy density of the lithium battery increases; on the other hand, if the L value is too large, slight lithium plating occurs at the corners of the negative electrode film, and the internal resistance of the battery is too high. The data in the table indicate that the preferred L value is 20 μm to 900 μm, and more preferably 50 μm to 500 μm.

[0262] More specifically, as shown in Example 2-1, if the L value is too small, the volumetric energy density of the lithium battery will be too low due to the thinness of the positive electrode active layer and the negative electrode active layer. As shown in Example 2-11, if the L value is too large, the thickness of the positive electrode active layer and the negative electrode active layer will be too thick, the lithium ion migration path will be long, slight lithium plating will occur at the corner of the negative electrode film, and the internal resistance of the battery will be too large. As shown in Examples 2-2 to 2-10, the L value is preferably 20μm to 900μm, and more preferably 50μm to 500μm.

[0263]

[0264] The following information can be obtained from Table 3.

[0265] As can be seen from Examples 3-1 to 3-13, adding fluorosulfonate and / or difluorophosphate to the electrolyte can improve the effect of suppressing lithium plating at corners.

[0266] Examples 3-1 to 3-10 show that increasing the mass percentage w% of fluorosulfonate and / or difluorophosphate in the electrolyte (i.e., increasing the w value) leads to an increase in the battery's internal resistance. Furthermore, Examples 3-14 show that if the mass percentage w% of fluorosulfonate and / or difluorophosphate in the electrolyte is too low, the effect of suppressing corner lithium plating is not significant.

[0267] As can be seen from Examples 3-1 to 3-14 in Table 3, in this invention, the w% of fluorosulfonate and / or difluorophosphate is 0.02% to 25%, preferably 0.02% to 20%, more preferably 0.5% to 10%, and even more preferably 0.1% to 5%. Furthermore, a comparison of Examples 3-9 and 3-11 in Table 3 shows that reducing the L value can also reduce the battery's internal resistance.

[0268]

[0269] The following can be seen from Table 4.

[0270] Examples 4-7 to 4-15: Adding fluoroethylene carbonate and / or 1,3-propanesulfonate lactone to an electrolyte containing fluorosulfonate and / or difluorophosphate can further improve the high and low temperature cycling performance of lithium-ion batteries.

[0271] In this application, when fluoroethylene carbonate and / or 1,3-propanesulfonate lactone are added to an electrolyte containing fluorosulfonate and / or difluorophosphate, from the viewpoint of improving battery cycle performance, the mass percentage of fluoroethylene carbonate and / or 1,3-propanesulfonate lactone in the electrolyte is 0.01% to 15%, preferably 0.05% to 5%, and more preferably 0.1% to 2%.

[0272]

[0273] Table 5 shows that, while maintaining a relatively high energy density (560–580 Wh / L), lithium-ion batteries… -1 Under the premise of considering the lithium deposition situation on the negative electrode convex surface in the first bending part, the porosity of the negative electrode material layer can preferably be 20% to 50%, more preferably 30% to 50%.

[0274] In summary, as shown in Tables 1 (Examples 1-1 to 1-11), 2 (Examples 2-1 to 2-11), 3 (Examples 3-1 to 3-14), 4 (Examples 4-1 to 4-15), and 5 (Examples 5-1 to 5-7), when the mass percentage w of fluorosulfonate and / or difluorophosphate in the electrolyte is multiplied by the innermost corner lithium deposition coefficient β, which is between 0.01 and 20, especially within the range of 0.05 to 10, both high energy density and sufficient additives to suppress lithium deposition at the negative electrode convex corner can be ensured. Simultaneously, when the amount of fluorosulfonate and / or difluorophosphate is appropriate, good internal resistance at room temperature is ensured for the lithium-ion battery.

[0275] It should be noted that this application is not limited to the above-described embodiments. The embodiments within the scope of this application are obviously not exhaustive; the above embodiments are merely illustrative. Embodiments with the same essential structure and achieving the same effects as the technical concept within the scope of this application are all included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing embodiments by combining some of the constituent elements, are also included within the scope of this application without departing from the spirit of this application.

Claims

1. A lithium-ion battery, characterized in that, include: Electrode assembly and electrolyte for wetting the electrode assembly; wherein, The electrode assembly includes a negative electrode, a separator, and a positive electrode. The negative electrode, the separator, and the positive electrode are wound together in a winding direction to form a wound structure, which includes an arc-shaped bend. The arc-shaped bend includes at least: a first bend and a second bend. The first bending portion is the innermost arc-shaped bending portion formed by winding the negative electrode sheet. The first bending portion includes a negative electrode current collector and a negative electrode material layer located at least on the convex surface of the negative electrode current collector. The second bend is located outside the first bend and adjacent to the first bend through the separator. The second bend includes a positive current collector and a positive electrode material layer located at least on the concave surface of the positive current collector. Let β be the corner lithium deposition coefficient of the lithium-ion battery, then β satisfies the following equation I. β=R / (R+L) Equation I, And 0.015≤β≤0.66, where, R is the minimum radius of curvature of the convex surface of the negative electrode current collector in the first bend. L is the shortest distance between the convex surface of the negative current collector in the first bend and the concave surface of the positive current collector in the second bend. The electrolyte contains fluorosulfonates and / or difluorophosphates, and, The mass percentage w% of the fluorosulfonate and / or difluorophosphate in the electrolyte and the corner lithium deposition coefficient β satisfy the following formula II. 0.01≤w×β≤20 Equation II.

2. The lithium-ion battery according to claim 1, characterized in that, 0.02≤w×β≤5。 3. The lithium-ion battery according to claim 1 or 2, characterized in that, 0.15≤β≤0.61。 4. The lithium-ion battery according to claim 1, characterized in that, The range of R is 2μm to 5000μm.

5. The lithium-ion battery according to claim 4, characterized in that, The range of R is 50μm to 500μm.

6. The lithium-ion battery according to claim 1, characterized in that, The range of L is 20μm to 900μm.

7. The lithium-ion battery according to claim 6, characterized in that, The range of L is 50μm to 500μm.

8. The lithium-ion battery according to claim 1, characterized in that, The structural formula of the fluorosulfonate is (FSO3). x M x + M x+ Selected from Li + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Al 3+ Fe 2+ Fe 3+ Ni 2+ and Ni 3+ One or more of them, The structural formula of the difluorophosphate is (F₂PO₂). y M y+ M y+ Selected from Li + Na + K + 、Rb + Cs + Mg 2+ Ca 2+ Ba 2+ Al 3+ Fe 2+ Fe 3+ Ni 2+ and Ni 3+ One or more of them.

9. The lithium-ion battery according to claim 1, characterized in that, The mass percentage (w%) of the fluorosulfonate and / or difluorophosphate substances in the electrolyte ranges from 0.02% to 25%.

10. The lithium-ion battery according to claim 9, characterized in that, The mass percentage (w%) of the fluorosulfonate and / or difluorophosphate substances in the electrolyte ranges from 0.02% to 20%.

11. The lithium-ion battery according to claim 10, characterized in that, The mass percentage (w%) of the fluorosulfonate and / or difluorophosphate substances in the electrolyte ranges from 0.05% to 10%.

12. The lithium-ion battery according to claim 11, characterized in that, The mass percentage (w%) of the fluorosulfonate and / or difluorophosphate substances in the electrolyte ranges from 0.1% to 5%.

13. The lithium-ion battery according to claim 1, characterized in that, The electrolyte further comprises fluoroethylene carbonate and / or 1,3-propanesulfonate lactone, wherein the fluoroethylene carbonate and / or 1,3-propanesulfonate lactone constitute 0.01% to 15% by mass in the electrolyte.

14. The lithium-ion battery according to claim 13, characterized in that, The mass percentage of the fluoroethylene carbonate and / or 1,3-propanesulfonate lactone in the electrolyte is 0.05% to 5%.

15. The lithium-ion battery according to claim 14, characterized in that, The fluoroethylene carbonate and / or 1,3-propanesulfonate lactone have a mass percentage content of 0.1% to 2% in the electrolyte.

16. The lithium-ion battery according to claim 1, characterized in that, The porosity of the negative electrode material layer is 20% to 50%.

17. The lithium-ion battery according to claim 16, characterized in that, The porosity of the negative electrode material layer is 30% to 50%.

18. A battery module, characterized in that, The lithium-ion battery includes any one of claims 1 to 17.

19. A battery pack, characterized in that, It includes one or more of the lithium-ion batteries selected from any one of claims 1 to 17 or the battery module described in claim 18.

20. An electrical device, characterized in that, It includes one or more of the lithium-ion battery selected from any one of claims 1 to 17, the battery module of claim 18, or the battery pack of claim 19.

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