Lithium-ion secondary battery and electrical device

Abstract

A lithium-ion secondary battery and an electrical device, relating to the technical field of batteries. The lithium-ion secondary battery comprises a positive electrode sheet and a negative electrode sheet. The ratio of the capacity per unit area of the negative electrode sheet to the capacity per unit area of the positive electrode sheet is 1.13-1.5. The negative electrode sheet comprises a negative electrode active material layer, and the negative electrode active material layer comprises graphite and a silicon-based material. In the negative electrode sheet, the ratio of the delithiation capacity within a potential range of 0.5 V to 2 V relative to lithium to the total delithiation capacity is 4-16%. The technical solution of the present application helps improve the fast charging performance and cycling performance of high-energy-density lithium-ion secondary batteries.

Description

Lithium-ion secondary batteries and electrical appliances Cross-references to related applications

[0001] This application claims priority to Chinese Patent Application No. 202510374310.8, filed on March 27, 2025, entitled “Lithium-ion Secondary Battery, Electrical Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, and more specifically, to a lithium-ion secondary battery and an electrical device. Background Technology

[0003] With increasing environmental pollution, the new energy industry is attracting more and more attention. Within the new energy industry, battery technology is a crucial factor in its development.

[0004] The development of battery technology requires consideration of various design factors, such as energy density, cycle performance, lifespan, capacity, fast charging performance, and reliability. Improving the fast charging and cycle performance of high-energy-density lithium-ion rechargeable batteries is a pressing technical challenge. Summary of the Invention

[0005] This application is made in view of the above-mentioned issues, and its purpose is to provide a lithium-ion secondary battery and an electrical device that are beneficial to improving the fast charging performance and cycle performance of high-energy-density lithium-ion secondary batteries.

[0006] In a first aspect, a lithium-ion secondary battery is provided, comprising: a positive electrode and a negative electrode, wherein the ratio of the capacity per unit area of ​​the negative electrode to the capacity per unit area of ​​the positive electrode is 1.13-1.5; the negative electrode includes a negative electrode active material layer, wherein the negative electrode active material layer includes graphite and silicon-based materials; and in the negative electrode, the ratio of the amount of lithium delithiation within the lithium potential range of 0.5V to 2V to the total amount of lithium delithiation is 4% to 16%.

[0007] In this embodiment, setting the ratio of the capacity per unit area of ​​the negative electrode to that of the positive electrode to be 1.13-1.5 is beneficial for improving the fast-charging and cycle performance of the lithium-ion secondary battery. When the ratio is greater than or equal to 1.13, the capacity per unit area of ​​the negative electrode is higher, which helps to provide more space for lithium-ion insertion, reducing the deposition of lithium-ions on the surface of the negative electrode, preventing side reactions, and reducing the fast-charging performance of the lithium-ion secondary battery. When the ratio is less than or equal to 1.5, the content of silicon-based material in the negative electrode active material layer can be controlled, reducing the impact of silicon-based material expansion and improving the cycle performance of the lithium-ion secondary battery. The negative electrode active material layer includes graphite and silicon-based materials. The silicon-based materials have a higher specific capacity, which is beneficial for increasing the capacity per unit area of ​​the negative electrode sheet without increasing the amount of negative electrode active material added or the coating weight and thickness. This allows the negative electrode sheet to achieve a capacity per unit area that is 1.13-1.5 times that of the positive electrode sheet, increasing the lithium intercalation space and improving the fast-charging performance of high-energy-density lithium-ion secondary batteries. When the ratio of lithium delithiation in the 0.5V–2V range to the total lithium delithiation is greater than or equal to 4%, it is beneficial for improving the fast-charging performance of lithium-ion secondary batteries. When the ratio is less than or equal to 16%, it can reduce the risk of excessive lithium ion deintercalation and deintercalation, volume expansion and particle breakage of silicon-based materials, and SEI oxidation decomposition in the 0.5V–2V range, thus improving the cycle performance of lithium-ion secondary batteries. Therefore, the technical solution of this application embodiment is beneficial to improving the fast charging performance and cycle performance of high energy density lithium-ion secondary batteries.

[0008] In some embodiments, the capacity per unit area of ​​the negative electrode sheet is 3.15 mAh / cm². 2 -5.61mAh / cm 2 The capacity per unit area of ​​the positive electrode is 2.75 mAh / cm². 2 -3.75mAh / cm 2 .

[0009] In this embodiment, the capacity per unit area of ​​the negative electrode and the capacity per unit area of ​​the positive electrode respectively meet the above-mentioned ranges. This is beneficial for achieving a capacity per unit area of ​​1.13-1.5 times that of the positive electrode, increasing the lithium intercalation space of the negative electrode, and thus improving the fast-charging performance of the lithium-ion secondary battery. The capacity per unit area of ​​the negative electrode is greater than or equal to 3.15 mAh / cm². 2The capacity per unit area of ​​the positive electrode is greater than or equal to 2.75 mAh / cm². 2 This allows for a higher ratio of the capacity per unit area of ​​the negative electrode to that of the positive electrode, while maintaining a lower amount of silicon-based material, thus improving the fast-charging performance of lithium-ion secondary batteries; when the capacity per unit area of ​​the negative electrode is less than or equal to 5.61 mAh / cm². 2 The capacity per unit area of ​​the positive electrode is less than or equal to 3.75 mAh / cm². 2 This is beneficial for increasing the ratio of the capacity per unit area of ​​the negative electrode to the capacity per unit area of ​​the positive electrode when the amount of high silicon-based materials is added, thereby improving the fast charging performance and cycle performance of lithium-ion secondary batteries.

[0010] In some embodiments, the specific capacity of the silicon-based material is 800 mAh / g to 2300 mAh / g.

[0011] In this embodiment, the specific capacity of the silicon-based material meets the above-mentioned range, which is beneficial to improving the specific capacity of the negative electrode sheet, achieving a ratio of the capacity per unit area of ​​the negative electrode sheet to the capacity per unit area of ​​the positive electrode sheet of 1.13-1.5, and thus improving the fast-charging performance and cycle performance of high-energy-density lithium-ion secondary batteries. When the specific capacity of the silicon-based material is greater than or equal to 800 mAh / g, it is beneficial to improve the capacity per unit area of ​​the negative electrode sheet, achieving a ratio of the capacity per unit area of ​​the negative electrode sheet to the capacity per unit area of ​​the positive electrode sheet of 1.13-1.5. When the specific capacity of the silicon-based material is less than or equal to 2300 mAh / g, it is beneficial to reduce the risk of increased expansion of the negative electrode sheet caused by silicon being exposed on the surface of porous carbon, thus reducing the expansion of the negative electrode sheet and improving the cycle life of the lithium-ion secondary battery.

[0012] In some embodiments, based on the total mass of the negative electrode active material layer, the mass content A of the silicon-based material satisfies: 1 wt.% to 12 wt.%.

[0013] In this embodiment, by setting the mass content of silicon-based material to meet the above-mentioned range, the silicon-based material has a higher specific capacity. This is beneficial for increasing the capacity per unit area of ​​the negative electrode sheet without increasing the coating weight and coating thickness, thereby improving the energy density and cycle stability of the lithium-ion secondary battery. This, in turn, is beneficial for improving the fast-charging and cycle performance of the lithium-ion secondary battery. When the mass content of silicon-based material is greater than or equal to 1 wt.%, it is beneficial for improving the energy density and fast-charging performance of the lithium-ion secondary battery; when the mass content of silicon-based material is less than or equal to 12 wt.%, it can reduce the expansion risk caused by silicon-based material and improve the cycle performance of the lithium-ion secondary battery.

[0014] In some embodiments, the positive electrode sheet includes a positive electrode active material, which includes a lithium phosphate.

[0015] In this embodiment, lithium phosphate has high structural stability. By including lithium phosphate in the positive electrode active material, it is beneficial to improve the cycle performance of lithium-ion secondary batteries.

[0016] In some embodiments, the surface of the silicon-based material has a coating layer comprising carbon. This coating layer protects the silicon-carbon particles, reduces contact between water and pure silicon during preparation, lowers reaction risks, and improves the stability of the negative electrode slurry. Simultaneously, the coating layer reduces contact between the silicon-based material and the electrolyte, minimizing side reactions and improving the cycle life of the secondary battery.

[0017] In some embodiments, the silicon-based material includes at least one of elemental silicon, silicon-oxygen materials, and silicon-carbon materials. This allows for the selection of a suitable silicon-based material based on specific conditions. The aforementioned silicon-based materials are beneficial for improving the specific capacity of the negative electrode and increasing the energy density of lithium-ion secondary batteries.

[0018] In some embodiments, the silicon-carbon material comprises porous carbon having a pore structure in which silicon is disposed.

[0019] In this embodiment, porous carbon has a high specific surface area and a large number of pore structures. Silicon is deposited in the pores of the porous carbon, which can disperse silicon particles, improve the particle integrity of silicon-carbon materials, and have a certain binding effect on silicon particles, reducing direct contact between silicon particles, thereby reducing the degree of silicon expansion. This helps to reduce the risk of aggravated side reactions caused by the expansion of silicon-carbon materials.

[0020] In some embodiments, in the negative electrode, the ratio of the amount of lithium removed in the lithium potential range of 0.5V to 2V to the total amount of lithium removed is 7% to 15%.

[0021] In this embodiment, the appropriate amount of lithium ions intercalated in the negative electrode sheet is beneficial to improving the fast-charging performance of the lithium-ion secondary battery. When the ratio of the amount of lithium delithiation in the 0.5V to 2V range to the total amount of lithium delithiation is greater than or equal to 7%, the amount of lithium delithiation in the 0.5V to 2V range is relatively high, thus improving the fast-charging performance of the lithium-ion secondary battery. When the ratio of the amount of lithium delithiation in the 0.5V to 2V range to the total amount of lithium delithiation is less than or equal to 15%, excessive intercalation and deintercalation of lithium ions in the 0.5V to 2V range can be reduced, reducing the risk of volume expansion and particle breakage of silicon-based materials, thereby improving the fast-charging performance and cycle performance of the lithium-ion secondary battery.

[0022] In some embodiments, the specific capacity of the silicon-carbon material is 1400 mAh / g to 2000 mAh / g.

[0023] In this embodiment, the specific capacity of the silicon-carbon material is greater than or equal to 1400 mAh / g, which is beneficial to improving the energy density of the secondary battery. Furthermore, the silicon-carbon material has suitable strength, which helps to reduce the risk of exacerbating side reactions caused by the breakage of the silicon-carbon material, thereby improving the cycle life of the secondary battery. When the specific capacity of the silicon-carbon material is less than or equal to 2000 mAh / g, it helps to reduce the risk of increased expansion of the negative electrode caused by silicon being exposed on the surface of porous carbon, thus reducing the expansion of the negative electrode and improving the cycle life of the secondary battery.

[0024] In a second aspect, an electrical device is provided, comprising a lithium-ion secondary battery according to the first aspect and any of the embodiments thereof. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the embodiments of this application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on the drawings without creative effort.

[0026] Figure 1 is a SEM image of the negative electrode sheet according to an embodiment of this application;

[0027] Figure 2 is a schematic diagram of the structure of a battery cell according to an embodiment of this application;

[0028] Figure 3 is a schematic diagram of the structure of a battery device according to an embodiment of this application;

[0029] Figure 4 is a schematic diagram of an electrical device according to an embodiment of this application;

[0030] Figure 5 is a schematic diagram of an electrical device according to another embodiment of this application.

[0031] Reference numerals: 3: battery cell; 30: casing; 31: housing; 313: pressure relief mechanism; 32: end cap; 322: electrode terminal; 33: electrode assembly; 331: tab; 34: connecting member; 10: battery device; 11: housing; 111: first housing section; 112: second housing section; 1: vehicle; 4: controller; 5: motor; 2: energy storage device. Detailed Implementation

[0032] Embodiments of the secondary battery and power-consuming device of this application have been described in detail with appropriate reference to the accompanying drawings, but 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.

[0033] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0034] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0035] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0036] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the method may also include step (c), indicating that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0037] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0038] The embodiments of this application will be described next.

[0039] The development of battery technology must consider multiple design factors simultaneously, such as energy density, cycle life, discharge capacity, fast charging performance, and reliability. Among these, the active materials in the negative and positive electrode sheets are crucial for the fast charging performance of lithium-ion rechargeable batteries. To achieve the high energy density required for lithium-ion rechargeable batteries, high-density active materials can be selected, or the mass content of the active material can be increased to improve the energy density. For example, in lithium-ion rechargeable batteries containing lithium phosphate, increasing the mass content of the positive electrode active material is necessary to achieve high energy density. However, this increases the coating thickness of the positive electrode sheet, reduces lithium-ion transport efficiency, and consequently lowers the fast charging performance of the lithium-ion rechargeable battery.

[0040] In some processing methods, the fast-charging performance of lithium-ion batteries is improved by reducing the weight and thickness of the active material layers in the positive and negative electrode sheets, thereby shortening the lithium-ion transport distance, or by simultaneously reducing the compaction density and increasing the porosity of both positive and negative electrode sheets. In other processing methods, the fast-charging performance of lithium-ion batteries is improved by increasing the charging temperature. However, reducing the thickness of the active material layer, the content of active material per unit area, and the coating weight will lead to a decrease in the thickness or compaction density of the active material layer, resulting in a decrease in the energy density of the lithium-ion battery. To maintain the total capacity of the lithium-ion battery, the electrode area needs to be increased. An increased electrode area means more current collectors and separators are required, leading to an increase in the manufacturing cost of lithium-ion batteries. Although increasing the charging temperature can improve the fast-charging performance of lithium-ion batteries, high temperatures may accelerate electrolyte decomposition and cause side reactions, leading to battery capacity decay and shortened cycle life, thus reducing the battery's cycle performance.

[0041] In view of this, embodiments of this application provide a lithium-ion secondary battery, comprising: a positive electrode and a negative electrode, wherein the ratio of the capacity per unit area of ​​the negative electrode to the capacity per unit area of ​​the positive electrode is 1.13-1.5; the negative electrode includes a negative electrode active material layer, which includes graphite and silicon-based materials; in the negative electrode, the ratio of the amount of lithium delithiation within the lithium potential range of 0.5V to 2V to the total amount of lithium delithiation is 4% to 16%. By setting the ratio of the capacity per unit area of ​​the negative electrode to the capacity per unit area of ​​the positive electrode to 1.13-1.5, it is beneficial to improve the fast-charging performance and cycle performance of the lithium-ion secondary battery. When the ratio of the capacity per unit area of ​​the negative electrode to that of the positive electrode is greater than or equal to 1.13, the higher capacity per unit area of ​​the negative electrode provides more space for lithium-ion intercalation, reducing lithium-ion deposition on the negative electrode surface, side reactions, and the resulting decrease in fast-charging performance of the lithium-ion rechargeable battery. When the ratio is less than or equal to 1.5, the content of silicon-based materials in the negative electrode active material layer can be controlled, reducing the impact of silicon-based material expansion and improving the cycle performance of the lithium-ion rechargeable battery. The negative electrode active material layer includes graphite and silicon-based materials. The higher specific capacity of silicon-based materials allows for an increase in the capacity per unit area of ​​the negative electrode without increasing the amount of negative active material added or the coating weight and thickness of the negative electrode. This facilitates achieving a capacity per unit area of ​​the negative electrode that is 1.13-1.5 times that of the positive electrode, increasing the lithium intercalation space of the negative electrode and improving the fast-charging performance of high-energy-density lithium-ion rechargeable batteries. When the ratio of lithium delithiation in the 0.5V–2V range to the total lithium delithiation is greater than or equal to 4%, it is beneficial to improve the fast-charging performance of lithium-ion secondary batteries. When the ratio of lithium delithiation in the 0.5V–2V range to the total lithium delithiation is less than or equal to 16%, it can reduce the risk of excessive lithium-ion intercalation / deintercalation, volume expansion and particle breakage of silicon-based materials, and SEI oxidation decomposition in the 0.5V–2V range, thereby improving the cycle performance of lithium-ion secondary batteries. Therefore, the technical solution of the embodiments of this application is beneficial to improving the fast-charging performance and cycle performance of high-energy-density lithium-ion secondary batteries.

[0042] It should be understood that the “intercalation” process mentioned in this application refers to the process in which lithium ions are intercalated into the positive or negative electrode active material due to an electrochemical reaction, and the “extraction” or “deintercalation” process mentioned in this application refers to the process in which lithium ions are extracted from the positive or negative electrode active material due to an electrochemical reaction.

[0043] It should be understood that the lithium-ion secondary battery in this application can be a battery pack or a single battery cell. Typically, a single battery cell includes a positive electrode, a negative electrode, an electrolyte, and a separator. The following section describes the lithium-ion secondary battery provided in this application and its various components.

[0044] [Lithium-ion rechargeable battery]

[0045] This application provides a lithium-ion secondary battery, including a positive electrode and a negative electrode. The ratio of the capacity per unit area of ​​the negative electrode to the capacity per unit area of ​​the positive electrode is 1.13-1.5. The negative electrode includes a negative active material layer, which includes graphite and silicon-based materials. In the negative electrode, the ratio of the amount of lithium delithiation in the lithium potential range of 0.5V to 2V to the total amount of lithium delithiation is 4% to 16%.

[0046] Specifically, the ratio of the capacity per unit area of ​​the negative electrode to the capacity per unit area of ​​the positive electrode can be 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19, 1.20, 1.21, 1.22, 1.23, 1.24, 1.25, 1.26, 1.27, 1.28, 1.29, 1.30, 1.31, 1.32, 1.33, 1.34, 1.35, 1.36, 1.37, 1.38, 1.39, 1.40, 1.41, 1.42, 1.43, 1.44, 1.45, 1.46, 1.47, 1.48, 1.49, 1.5, or any value within any two of the above ranges.

[0047] The percentage of lithium removed in the 0.5V to 2V range can be 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.2%, 10.8%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, or any value within any two of the above ranges.

[0048] In the above embodiments, setting the ratio of the capacity per unit area of ​​the negative electrode to that of the positive electrode to be 1.13-1.5 is beneficial to improving the fast-charging performance and cycle performance of the lithium-ion secondary battery. When the ratio of the capacity per unit area of ​​the negative electrode to that of the positive electrode is greater than or equal to 1.13, the capacity per unit area of ​​the negative electrode is higher, which is beneficial to providing more space for lithium-ion insertion, reducing the deposition of lithium-ions on the surface of the negative electrode, the occurrence of side reactions, and the reduction of fast-charging performance of the lithium-ion secondary battery. When the ratio of the capacity per unit area of ​​the negative electrode to that of the positive electrode is less than or equal to 1.5, the content of silicon-based material in the negative electrode active material layer can be controlled, reducing the impact of silicon-based material expansion, which is beneficial to improving the cycle performance of the lithium-ion secondary battery. The negative electrode active material layer includes graphite and silicon-based materials. The silicon-based materials have a higher specific capacity, which is beneficial for increasing the capacity per unit area of ​​the negative electrode sheet without increasing the amount of negative electrode active material added or the coating weight and thickness. This allows the negative electrode sheet to achieve a capacity per unit area that is 1.13-1.5 times that of the positive electrode sheet, increasing the lithium intercalation space and improving the fast-charging performance of high-energy-density lithium-ion secondary batteries. When the ratio of lithium delithiation in the 0.5V–2V range to the total lithium delithiation is greater than or equal to 4%, it is beneficial for improving the fast-charging performance of lithium-ion secondary batteries. When the ratio is less than or equal to 16%, it can reduce the risk of excessive lithium ion deintercalation and deintercalation, volume expansion and particle breakage of silicon-based materials, and SEI oxidation decomposition in the 0.5V–2V range, thus improving the cycle performance of lithium-ion secondary batteries.

[0049] Figure 1 is a SEM image of a negative electrode sheet according to an embodiment of this application. For example, as shown in Figure 1, the negative electrode active material layer includes graphite and silicon-based materials.

[0050] Graphite can include at least one of natural graphite and artificial graphite.

[0051] Lithium potential refers to the potential relative to the lithium electrode. For example, in a coin cell consisting of a negative electrode and a lithium plate, the lithium potential refers to the potential of the negative electrode relative to the lithium plate. The negative electrode has different lithium potentials at different charge / discharge stages.

[0052] Lithium stripping capacity refers to the capacity generated by the removal of lithium ions from the negative electrode active material during discharge within a specific potential range. For example, within a specific potential range, it refers to the capacity generated by the removal of lithium ions from the negative electrode active material during the discharge of a lithium-ion secondary battery. For example, in the embodiments of this application, lithium stripping capacity in the 0.5V to 2V range can refer to the capacity generated by the removal of lithium ions within the 0.5V to 2V range; total lithium stripping capacity can refer to the total capacity generated by the removal of lithium ions from the negative electrode within the 0V to 2V range.

[0053] In some possible implementations, the capacity per unit area of ​​the negative electrode is 3.15 mAh / cm². 2 -5.61mAh / cm 2 The capacity per unit area of ​​the positive electrode is 2.75 mAh / cm². 2 -3.75mAh / cm 2 .

[0054] The capacity per unit area of ​​the negative electrode sheet can be 3.15 mg / cm². 2 3.5 mg / cm 2 4.0 mg / cm 2 4.15 mg / cm 2 4.5 mg / cm 2 5.0 mg / cm 2 5.15 mg / cm 2 5.5 mg / cm 2 5.61 mg / cm 2 Or any value within any two of the above numerical ranges; the capacity per unit area of ​​the positive electrode can be 2.75 mg / cm². 2 3.0 mg / cm 2 3.15 mg / cm 2 3.55 mg / cm 2 3.75 mg / cm 2 , or any value within any two of the above numerical ranges.

[0055] In the above embodiments, the capacity per unit area of ​​the negative electrode and the capacity per unit area of ​​the positive electrode respectively meet the aforementioned ranges. This is beneficial for achieving a capacity per unit area of ​​1.13-1.5 times that of the positive electrode, increasing the lithium intercalation space of the negative electrode, and thus improving the fast-charging performance of the lithium-ion secondary battery. The capacity per unit area of ​​the negative electrode is greater than or equal to 3.15 mAh / cm². 2 The capacity per unit area of ​​the positive electrode is greater than or equal to 2.75 mAh / cm². 2This allows for a higher ratio of the capacity per unit area of ​​the negative electrode to that of the positive electrode, while maintaining a lower amount of silicon-based material, thus improving the fast-charging performance of lithium-ion secondary batteries; when the capacity per unit area of ​​the negative electrode is less than or equal to 5.61 mAh / cm². 2 The capacity per unit area of ​​the positive electrode is less than or equal to 3.75 mAh / cm². 2 This is beneficial for increasing the ratio of the capacity per unit area of ​​the negative electrode to the capacity per unit area of ​​the positive electrode when the amount of high silicon-based materials is added, thereby improving the fast charging performance and cycle performance of lithium-ion secondary batteries.

[0056] In some possible implementations, the specific capacity of silicon-based materials ranges from 800 mAh / g to 2300 mAh / g.

[0057] The specific capacity of silicon-based materials can be 800mAh / g, 900mAh / g, 1000mAh / g, 1100mAh / g, 1200mAh / g, 1300mAh / g, 1400mAh / g, 1500mAh / g, 1600mAh / g, 1700mAh / g, 1800mAh / g, 1900mAh / g, 2000mAh / g, 2100mAh / g, 2200mAh / g, 2300mAh / g, or any value within any two of the above ranges.

[0058] In the above embodiments, the specific capacity of the silicon-based material meets the aforementioned range, which is beneficial for improving the specific capacity of the negative electrode sheet, achieving a ratio of the capacity per unit area of ​​the negative electrode sheet to the capacity per unit area of ​​the positive electrode sheet of 1.13-1.5, and thus improving the fast-charging performance and cycle performance of high-energy-density lithium-ion secondary batteries. A specific capacity of silicon-based material greater than or equal to 800 mAh / g is beneficial for improving the capacity per unit area of ​​the negative electrode sheet, achieving a ratio of the capacity per unit area of ​​the negative electrode sheet to the capacity per unit area of ​​the positive electrode sheet of 1.13-1.5. When the specific capacity of the silicon-based material is less than or equal to 2300 mAh / g, it helps reduce the risk of increased expansion of the negative electrode sheet caused by silicon being exposed on the surface of porous carbon, thus reducing the expansion of the negative electrode sheet and improving the cycle life of the lithium-ion secondary battery.

[0059] In some possible implementations, based on the total mass of the negative electrode active material layer, the mass content A of the silicon-based material satisfies: 1 wt.% to 12 wt.%.

[0060] Based on the total mass of the negative electrode active material layer, the mass content A of the silicon-based material can be 1 wt.t%, 2 wt.t%, 3 wt.t%, 4 wt.t%, 5 wt.t%, 6 wt.t%, 7 wt.t%, 8 wt.t%, 9 wt.t%, 10 wt.t%, 11 wt.t%, 12 wt.t%, or any value within any two of the above ranges.

[0061] In the above embodiments, by setting the mass content of silicon-based material to meet the aforementioned range, the silicon-based material has a higher specific capacity. This is beneficial for increasing the capacity per unit area of ​​the negative electrode sheet without increasing the coating weight and coating thickness, thereby improving the energy density and cycle stability of the lithium-ion secondary battery. This, in turn, is beneficial for improving the fast-charging and cycle performance of the lithium-ion secondary battery. When the mass content of silicon-based material is greater than or equal to 1 wt.%, it is beneficial for improving the energy density and fast-charging performance of the lithium-ion secondary battery; when the mass content of silicon-based material is less than or equal to 12 wt.%, it can reduce the expansion risk caused by silicon-based material and improve the cycle performance of the lithium-ion secondary battery.

[0062] In some possible implementations, the positive electrode includes a positive active material, which includes a lithium phosphate.

[0063] Lithium-containing phosphates refer to phosphates with an olivine structure, such as lithium iron phosphate, lithium manganese iron phosphate, and lithium manganese phosphate. Lithium-containing phosphates include transition metals, such as iron and manganese. Lithium-containing phosphates can also be modified by doping or surface coating to improve their performance. For example, the surface of lithium-containing phosphates can be coated with carbon materials, thereby improving the conductivity of the positive electrode active material.

[0064] In this embodiment, the positive electrode active material includes lithium-containing phosphates. Lithium iron phosphates and other lithium-containing phosphates have high structural stability, which is beneficial to improving the cycle performance of lithium-ion secondary batteries.

[0065] In some possible implementations, the surface of the silicon-based material has a coating layer, which includes carbon elements. The coating layer protects the silicon-carbon particles, reduces the contact between water and pure silicon during the preparation process, lowers the reaction risk, and improves the stability of the negative electrode slurry. At the same time, the coating layer can reduce the contact between the silicon-based material and the electrolyte, reduce side reactions, and improve the cycle performance of the secondary battery.

[0066] When observing silicon-carbon materials (e.g., using SEM), the coating layer on the surface of the silicon-carbon material can be observed. Furthermore, combined with EDS analysis, it can be determined that the coating layer contains carbon elements.

[0067] In some possible implementations, the silicon-based material can include one or more of elemental silicon, silicon-oxygen materials, and silicon-carbon materials. This allows for the selection of a suitable silicon-based material based on specific requirements. The aforementioned silicon-based materials are beneficial for increasing the specific capacity of the negative electrode and improving the fast-charging performance of lithium-ion secondary batteries.

[0068] In some possible implementations, silicon-carbon materials include porous carbon with a pore structure in which silicon is incorporated.

[0069] Porous carbon can refer to materials with a carbon matrix and a porous structure within the matrix. Silicon in silicon-carbon materials is deposited within the porous structure of porous carbon. Porous carbon can be one or more types of porous hard carbon or porous soft carbon. As an example, porous carbon is porous hard carbon.

[0070] As an example, SEM and EDS can be combined to observe silicon-carbon materials. SEM can be used to observe the pore structure of porous carbon with carbon as the matrix, while EDS can be used to analyze the distribution of silicon in the pores of the carbon matrix.

[0071] As an example, silicon-carbon materials can be prepared by vapor deposition. Vapor deposition can include depositing silicon into the porous structure of porous carbon using at least one of chemical vapor deposition (CVD) and physical vapor deposition (PVD). For example, by using CVD, the distribution and content of silicon in the pores can be adjusted by controlling the deposition temperature, gas flow rate, and deposition time, resulting in a silicon-carbon material with silicon uniformly distributed in the porous structure of the carbon.

[0072] In the above embodiments, porous carbon has a high specific surface area and a large number of pore structures. Silicon is distributed in the pores of the porous carbon, which can disperse silicon particles, improve the particle integrity of silicon-carbon materials, and have a certain binding effect on silicon particles, reducing direct contact between silicon particles, thereby reducing the degree of silicon expansion. This helps to reduce the risk of aggravated side reactions caused by the expansion of silicon-carbon materials.

[0073] In some possible implementations, the ratio of lithium delithiation in the 0.5V–2V lithium potential range to the total lithium delithiation in the negative electrode is 7%–15%. This ensures an appropriate amount of lithium ions intercalated in the negative electrode, which is beneficial for improving the fast-charging performance of lithium-ion rechargeable batteries. When the ratio of lithium delithiation in the 0.5V–2V lithium potential range to the total lithium delithiation is greater than or equal to 7%, the high lithium delithiation in this range further improves the fast-charging performance of the lithium-ion rechargeable battery. When the ratio is less than or equal to 15%, excessive lithium ion intercalation / deintercalation in the 0.5V–2V range can be reduced, decreasing the risk of volume expansion and particle breakage of silicon-based materials, thereby improving the fast-charging and cycle performance of lithium-ion rechargeable batteries.

[0074] In some possible implementations, the specific capacity of silicon-carbon materials ranges from 1400 mAh / g to 2000 mAh / g.

[0075] The specific capacity of silicon-carbon materials can be 1400mAh / g, 1500mAh / g, 1600mAh / g, 1700mAh / g, 1800mAh / g, 1900mAh / g, 2000mAh / g or any value within the above range.

[0076] In the above embodiments, the specific capacity of the silicon-carbon material is greater than or equal to 1400 mAh / g, which is beneficial to improving the energy density of the secondary battery. Furthermore, the silicon-carbon material has suitable strength, which helps to reduce the risk of exacerbating side reactions caused by the breakage of the silicon-carbon material, thereby improving the cycle life of the secondary battery. When the specific capacity of the silicon-carbon material is less than or equal to 2000 mAh / g, it helps to reduce the risk of increased expansion of the negative electrode sheet caused by silicon being exposed on the surface of porous carbon, thus reducing the expansion of the negative electrode sheet and improving the cycle life of the secondary battery.

[0077] In some possible implementations, the volume average particle size Dv50 of the negative electrode active material of the negative electrode sheet satisfies: 8μm≤Dv50≤15μm.

[0078] The volume average particle size (Dv50) of a material represents the particle size corresponding to a cumulative volume distribution percentage of 50%. The volume average particle size of the negative electrode active material refers to the volume average particle size of the mixture of graphite and silicon-based materials.

[0079] The volume average particle size Dv50 of the negative electrode active material can be 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, or any value within the above two ranges.

[0080] In the above embodiments, when the volume average particle size Dv50 of the negative electrode active material is greater than or equal to 8 μm, the negative electrode active material has a suitable specific surface area, which is beneficial to reducing lithium ion consumption and thus improving the cycle performance of the secondary battery. When the volume average particle size Dv50 of the negative electrode active material is less than or equal to 15 μm, it is beneficial to reduce the kinetic resistance of lithium ion embedding in the negative electrode active material and improve the fast charging performance of the lithium-ion secondary battery. In addition, when the volume average particle size Dv50 of the negative electrode active material is less than or equal to 15 μm, it is also beneficial to uniformly disperse the silicon-based material particles in the negative electrode active material. The gaps between the particles are beneficial to provide expansion space for the silicon-based material, reducing the risk of severe expansion in some areas, thus improving the cycle performance of the lithium-ion secondary battery.

[0081] [Positive electrode plate]

[0082] The positive electrode includes a positive current collector and a positive active material layer disposed on at least one side surface of the positive current collector.

[0083] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive active material layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0084] As an example, the positive electrode current collector can be a metal foil, a foamed metal, or a composite current collector. For example, as a metal foil, it can be silver-treated aluminum or stainless steel, stainless steel, copper, aluminum, nickel, carbon electrode, carbon, nickel, or titanium, etc. Foamed metal can be foamed nickel, foamed copper, foamed aluminum, foamed alloy, or foamed carbon, etc. Composite current collectors can include a polymer material base layer and a metal layer. Composite current collectors can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0085] In some embodiments, the positive electrode active material layer includes a positive electrode active material. Optionally, the positive electrode active material may include positive electrode active materials known in the art for use in batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as positive electrode active materials for batteries may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides may include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0086] In some embodiments, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0087] In some embodiments, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0088] In some embodiments, the positive electrode sheet can be prepared by forming a positive electrode slurry using the components described above. For example, the positive electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., N-methylpyrrolidone) to form the positive electrode slurry. The positive electrode slurry is then coated onto a positive electrode current collector, and after drying, cold pressing, and other processes, the positive electrode sheet is obtained.

[0089] [Negative electrode plate]

[0090] The negative electrode includes a negative current collector and a negative active material layer disposed on the negative current collector. The negative active material layer includes a negative active material, which may include silicon-based materials in any of the above possible embodiments or implementations.

[0091] The negative electrode current collector can be a metal foil or a composite negative electrode current collector. The negative electrode current collector can be copper foil. Composite negative electrode current collectors can be formed by depositing metallic materials (copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys, etc.) onto a polymer substrate (such as polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0092] The negative electrode active material may be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, etc. The negative electrode active material may also include a mixture of graphite and silicon-based materials, tin-based materials, and lithium titanate, etc.; the silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys; the tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys.

[0093] The negative electrode active material layer may also optionally include a binder. As an example, the binder may include one or more of styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), water-soluble unsaturated resin SR-1B, waterborne acrylic resins (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0094] The negative electrode active material layer may optionally include a conductive agent. The conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0095] In one embodiment, the negative electrode sheet can be prepared by forming a negative electrode slurry using the components described above. For example, the negative electrode active material, conductive agent, binder, and any other components are dispersed in a solvent (e.g., deionized water) to form the negative electrode slurry. The negative electrode slurry is then coated onto a negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode sheet is obtained.

[0096] [Electrolytes]

[0097] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, semi-solid, or fully solid.

[0098] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0099] For lithium-ion battery cells, the electrolyte salt may include one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, and lithium tetrafluorooxalate phosphate.

[0100] For lithium-ion battery cells, the solvent may include one or more of the following: ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0101] In some embodiments, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0102] This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. The electrolyte can be liquid, semi-solid, or solid.

[0103] [Isolation membrane]

[0104] The separator is a membrane. This application does not have any particular restrictions on the type of separator. Any well-known porous separator with good chemical and mechanical stability can be selected.

[0105] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0106] Positive electrode, negative electrode and separator can be made into electrode assembly by winding process or stacking process.

[0107] [Battery cell]

[0108] In some embodiments, the lithium-ion secondary battery can be a single battery cell.

[0109] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. Figure 2 is a schematic diagram of the structure of a battery cell according to an embodiment of this application. For example, as shown in Figure 2, the battery cell 3 is a square battery cell. The battery cell 3 includes a housing 30 and an electrode assembly 33 disposed in the housing 30. The housing 30 includes a shell 31 and an end cap 32, which is used to cover the opening of the shell 31.

[0110] The electrode assembly 33 can be manufactured from a positive electrode, a negative electrode, and a separator through a winding process or a stacking process. The electrode assembly 33 may include an electrode assembly body and tabs 331 extending from the electrode assembly body.

[0111] The end cap 32 includes electrode terminals 322, as shown in Figure 2. The end cap 32 includes two electrode terminals 322, one of which is a positive electrode terminal and the other is a negative electrode terminal.

[0112] The battery cell 3 also includes a connecting member 34 for connecting the tab 331 and the electrode terminal 322 of the electrode assembly 33. For example, one connecting member 34 is used to connect the tab of the positive electrode and the positive electrode terminal, and another connecting member 34 is used to connect the tab of the negative electrode and the negative electrode terminal.

[0113] In some embodiments, the battery cell 3 includes a pressure relief mechanism 313 for releasing substances inside the battery cell 3 when thermal runaway occurs, thereby reducing the risk caused by the failure to release the emissions from the battery cell 3 in a timely manner.

[0114] In some embodiments, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0115] [Battery Device]

[0116] In some embodiments, the lithium-ion secondary battery is a battery device, which includes one or more battery cells.

[0117] Figure 3 is a schematic diagram of the structure of a battery device according to an embodiment of this application. For example, as shown in Figure 3, the battery device 10 is a battery pack. The battery pack may include a housing and multiple battery cells housed in the housing, and the multiple battery cells are connected in series, parallel, or mixed connection. The battery cells can be directly assembled into a battery pack, or they can be first assembled into battery modules, and then multiple battery modules are assembled into a battery pack.

[0118] The battery device 10 may further include a housing 11, which has a hollow interior and houses multiple battery cells 3. For example, multiple battery cells 3 may be connected in parallel, series, or a combination thereof and then placed inside the housing 11. The housing 11 may include a first housing portion 111 and a second housing portion 112, which are fitted together to form the housing 11. The shapes of the first housing portion 111 and the second housing portion 112 may be determined by the shape of the components housed inside, for example, by the shape of the combination of multiple battery cells 3 housed inside. At least one of the first housing portion 111 and the second housing portion 112 may have an opening. For example, as shown in Figure 3, the first housing portion 111 and the second housing portion 112 can both be hollow cuboids with one open side each. The openings of the first housing portion 111 and the second housing portion 112 are opposite to each other, and the first housing portion 111 and the second housing portion 112 are interlocked to form a housing 11 with a closed cavity, which can be used to accommodate multiple battery cells 3. The multiple battery cells 3 are connected in parallel, series, or mixed and placed inside the housing 11 formed by the interlocking of the first housing portion 111 and the second housing portion 112.

[0119] For example, unlike what is shown in Figure 3, only one of the first housing portion 111 and the second housing portion 112 may be a hollow cuboid with an opening, while the other is plate-shaped to cover the opening. Taking the second housing portion 112 as a hollow cuboid with one opening, and the first housing portion 111 as a plate-shaped example, then the first housing portion 111 covers the opening of the second housing portion 112 to form a housing 11 with a closed chamber, which can be used to accommodate multiple battery cells 3.

[0120] In some embodiments, the battery device 10 may further include other components. For example, the battery device 10 may further include a busbar component, which can be used to realize electrical connections between multiple battery cells 3, such as in parallel, series, or mixed connections. Specifically, the busbar component can realize electrical connections between battery cells 3 by connecting to the electrode terminals of the battery cells 3; or, the busbar component can also realize electrical connections between battery cells 3 by connecting to other components of the battery cells 3. The busbar component can be fixed to corresponding components of the battery cells 3 by welding, for example, by welding to electrode terminals, sealing structures, or housings, etc., and the embodiments of this application are not limited thereto.

[0121] The battery cells 3 can be directly assembled into the battery device 10, or they can be first assembled into battery modules, and then multiple battery modules can be assembled into the battery device 10.

[0122] In some embodiments, the battery device 10 may be located in an energy storage device. The energy storage device includes an energy storage container, an energy storage cabinet, etc.

[0123] [Electrical appliances]

[0124] This includes at least one of the lithium-ion secondary batteries, battery modules, or battery packs provided in this application. The lithium-ion battery, battery module, or battery pack can be used as a power source for an electrical device or as an energy storage unit for that device. Electrical devices can include, but are 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.

[0125] As an electrical device, lithium-ion secondary batteries, battery modules, or battery packs can be selected according to their usage requirements.

[0126] Electrical devices can include vehicles, mobile phones, portable devices, laptops, ships, spacecraft, electric toys, and power tools, etc. Vehicles can be gasoline-powered cars, natural gas-powered cars, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. This application does not impose any special limitations on the above-mentioned electrical devices.

[0127] Figure 4 is a schematic diagram of an electrical device according to an embodiment of this application. As shown in Figure 4, this application provides an electrical device, which can be a vehicle 1, and includes the lithium-ion secondary battery in the above embodiment.

[0128] Vehicle 1 can be a gasoline-powered vehicle, a natural gas-powered vehicle, or a new energy vehicle. New energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc. A motor 5, a controller 4, and a battery device 10 can be installed inside vehicle 1. The controller 4 controls the battery device 10 to supply power to the motor 5. For example, the battery device 10 can be installed under, at the front, or at the rear of vehicle 1. The battery device 10 can be used to power vehicle 1; for example, it can serve as the operating power source for the vehicle 1's electrical system, such as meeting the power requirements for starting, navigation, and operation. In another embodiment of this application, the battery device 10 can not only serve as the operating power source for vehicle 1 but also as the driving power source, replacing or partially replacing gasoline or natural gas to provide driving power to vehicle 1.

[0129] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a lithium-ion rechargeable battery as their power source.

[0130] Figure 5 is a schematic diagram of an electrical device according to another embodiment of this application. As shown in Figure 5, this application provides an electrical device, which is an energy storage device 2, and the energy storage device 2 may include multiple battery devices 10. The energy storage device 2 can be applied to a power storage station to store and release electrical energy.

[0131] Alternatively, the electrical device may also be an energy storage device, a lighting device, a spacecraft, etc., as is the case in the embodiments of this application.

[0132] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0133] [Example]

[0134] Example 1

[0135] (1) Preparation of positive electrode sheet

[0136] Lithium iron phosphate (LiFePO4) as the positive electrode active material, acetylene black as the conductive agent, and polyvinylidene fluoride (PVDF) as the binder were mixed at a mass ratio of 97.9:0.5:1.6. N-methylpyrrolidone (NMP) as the solvent was added, and the mixture was stirred under vacuum until homogeneous to obtain a positive electrode slurry. The positive electrode slurry was then uniformly coated onto both surfaces of the positive electrode current collector aluminum foil. After drying, the foil underwent cold pressing, edge trimming, cutting, and slitting processes to obtain the positive electrode sheet. The capacity per unit volume of the positive electrode sheet was 3.11 mAh / cm².

[0137] (2) Preparation of negative electrode sheet

[0138] Preparation of silicon-carbon materials: First, silicon-carbon materials are subjected to vapor phase deposition treatment. An appropriate amount of porous carbon is weighed and placed in a rotary kiln. Under argon protection, the temperature is heated to 500℃ and held for 2 hours to desorb the air adsorbed in the porous carbon. A mixture of silane and argon (volume ratio of silane to argon 1:4) is introduced into the rotary kiln at a flow rate of 4L / min, maintaining a slight positive pressure of 200Pa. The rotary kiln is rotated at a frequency of 20Hz to obtain silicon-carbon particles. The temperature of the rotary kiln is raised to 600℃, and a mixture of acetylene and argon is introduced at a flow rate of 3L / min. The rotary kiln is rotated at a frequency of 20Hz, and the silicon-carbon particles are then coated. After natural cooling, the silicon-carbon materials are obtained by passing them through a 200-mesh sieve.

[0139] Preparation of negative electrode sheet: The negative electrode active material, conductive agent carbon black, thickener sodium carboxymethyl cellulose (CMC), binder styrene-butadiene rubber (SBR), and single-arm carbon nanotubes are mixed in a weight ratio of 96.9:0.5:1:1.5:0.1 and dissolved in deionized water to prepare a negative electrode slurry. The negative electrode slurry is obtained under the action of a vacuum stirrer. Then, the negative electrode slurry is coated on both surfaces of the negative electrode current collector copper foil. After drying, it is subjected to cold pressing, edge trimming, cutting, and slitting processes to obtain the negative electrode sheet.

[0140] The negative electrode active materials include silicon carbide and artificial graphite. Based on the total mass of the negative electrode active materials, the mass content of silicon carbide is 3.5%, and the mass content of artificial graphite is 96.5%. The volume average particle size (Dv50) of silicon carbide is 9 μm, and the volume average particle size (Dv50) of artificial graphite is 14 μm. The specific capacity of silicon carbide is 1600 mAh / g. The capacity per unit volume of the negative electrode sheet is 3.67 mAh / cm³. 2 .

[0141] In the negative electrode, the proportion of lithium delithiation in the range of 0.5V to 2V accounts for 7% of the total lithium delithiation.

[0142] (3) Preparation of the separating membrane

[0143] Porous polyethylene film is used as the separator.

[0144] (4) Preparation of electrolyte

[0145] The organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 3:3:4 to obtain a mixed solvent. Then, fully dried lithium salt (LiPF6) was dissolved in the above mixed solvent at a ratio of 1 mol / L, and 3% fluoroethylene carbonate (FEC) was added to obtain the electrolyte.

[0146] (5) Preparation of secondary battery cells

[0147] The positive electrode, separator, and negative electrode are prepared in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrodes are then wound and hot-pressed to form an electrode assembly. The electrode assembly is then welded to the end cap and placed in a square aluminum shell. After vacuum drying, the electrolyte is injected, followed by standing, formation testing, aging, and capacity testing. Finally, a secondary battery cell with a volume of 0.411L is obtained.

[0148] The preparation methods of the secondary battery cells in Examples 2-8 are basically the same as those in Example 1, except that the relevant parameters of the silicon-based material are adjusted.

[0149] Examples 2-4

[0150] The difference between Examples 2-4 and Example 1 lies in the following: the amount of silicon-based material added was changed, the ratio of the capacity per unit area of ​​the negative electrode to the capacity per unit area of ​​the positive electrode was different, and the ratio of the amount of lithium delithiation in the lithium potential range of 0.5V to 2V to the total amount of lithium delithiation was different. Specific parameters are detailed in Table 1.

[0151] Examples 5-6

[0152] The difference between Examples 5-6 and Example 1 is that the specific capacity of the silicon-based material was changed, the ratio of the capacity per unit area of ​​the negative electrode to the capacity per unit area of ​​the positive electrode was different, and the ratio of the amount of lithium delithiation in the lithium potential range of 0.5V to 2V to the total amount of lithium delithiation was different.

[0153] Examples 7-8

[0154] The difference between Examples 7-8 and Example 1 is that the capacity per unit area of ​​the positive electrode and the capacity per unit area of ​​the negative electrode are different. See Table 1 for specific parameters.

[0155] Comparative Example 1

[0156] The difference between Comparative Example 1 and Example 1 is that the ratio of the capacity per unit area of ​​the negative electrode to the capacity per unit area of ​​the positive electrode is less than 1.13, and the percentage of delithiation in the 0.5V to 2V range is less than 4%. Specific parameters are detailed in Table 1.

[0157] Comparative Example 2

[0158] The difference between Comparative Example 2 and Example 1 is that the ratio of the capacity per unit area of ​​the negative electrode to the capacity per unit area of ​​the positive electrode is greater than 1.5, and the proportion of delithiation in the 0.5V to 2V range is greater than 16%. Specific parameters are detailed in Table 1.

[0159] Table 1 shows the specific parameters of Examples 1-8 and Comparative Examples 1-2.

[0160] Table 1. Specific parameters of the embodiments and comparative examples.

[0161] Table 2 Test results of the examples and comparative examples

[0162] In Table 1, A represents the total mass of silicon-based materials based on the negative electrode active material layer; in Table 2, T represents the charging time of a single secondary battery cell.

[0163] Examples 1-8 and Comparative Examples 1-2 and their test results are explained below:

[0164] Based on Examples 1-4 and Comparative Examples 1 and 2, it can be seen that the fast charging time of the secondary battery cells in Examples 1-4 decreased from 13.7 min and 14.0 min in Comparative Examples 1 and 2 to 11.4 min, 12.5 min, 10.1 min, and 8.5 min, respectively. The cycle capacity retention increased from 82.2% to 92.3%, 92.1%, 91.5%, and 90.2%, respectively. The highest energy density in Examples 1-4 was 397 Wh / L, and the lowest was 391 Wh / L, both higher than the energy densities in Comparative Examples 1 and 2. By setting the ratio of the capacity per unit area of ​​the negative electrode to the capacity per unit area of ​​the positive electrode to 1.13-1.5, it is beneficial to improve the fast charging performance and cycle performance of the lithium-ion secondary battery. The negative electrode active material layer includes graphite and silicon-based materials. Silicon-based materials have a higher specific capacity, which is beneficial for increasing the capacity per unit area of ​​the negative electrode sheet without increasing the amount of negative electrode active material added or the coating weight and thickness. This allows the negative electrode sheet to achieve a capacity per unit area that is 1.13-1.5 times that of the positive electrode sheet, increasing the lithium intercalation space of the negative electrode sheet and improving the fast-charging performance of high-energy-density lithium-ion secondary batteries. When the ratio of lithium delithiation in the lithium potential range of 0.5V to 2V is 4% to 16% of the total delithiation, it is beneficial for improving the fast-charging and cycle performance of lithium-ion secondary batteries.

[0165] Compared to Examples 1-3 and Comparative Example 1, the cycle capacity retention rate of Example 4 was 90.2%, which is because the amount of silicon-based material added in Example 4 was higher, and the silicon-based material expanded during cycling, but it was still higher than 82.2% in Comparative Example 2.

[0166] As can be seen from Examples 5 and 6, the fast charging time of the secondary battery cells in Examples 5 and 6 was reduced from 13.7 min and 14.0 min in Comparative Examples 1 and 2 to 12.9 min and 11.6 min, respectively, without a decrease in cycle capacity retention. The highest energy density was 394 Wh / L, which is higher than that in Comparative Examples 1 and 2. By setting the specific capacity of the silicon-based material to 800 mAh / g to 2300 mAh / g, the specific capacity of the silicon-based material meets the above range, which is beneficial to improving the specific capacity of the negative electrode sheet. This achieves a ratio of the capacity per unit area of ​​the negative electrode sheet to the capacity per unit area of ​​the positive electrode sheet of 1.13-1.5, which is beneficial to improving the fast charging performance and cycle performance of high-energy-density lithium-ion secondary batteries.

[0167] As can be seen from Examples 1-6 and Comparative Examples 1 and 2, by setting the mass content A of silicon-based material to be 1wt.% to 12wt.%, the capacity per unit area of ​​the negative electrode sheet is increased, the energy density and cycle stability of the lithium-ion secondary battery are improved, which is beneficial to improving the fast charging performance and cycle performance of high-energy-density lithium-ion secondary batteries.

[0168] Based on Examples 7 and 8, as well as Comparative Examples 1 and 2, the capacity per unit area of ​​the negative electrode sheet is 3.15 mAh / cm². 2 ~5.61mAh / cm 2 The capacity per unit area of ​​the positive electrode is 2.75 mAh / cm². 2 ~3.75mAh / cm 2 The fast charging times in Examples 7 and 8 were 8.1 min and 12.8 min, respectively, which were shorter than those in Comparative Examples 1 and 2. The cycle capacity retention rates were 93% and 91.8%, respectively, and the energy densities were 389 Wh / L and 401 Wh / L, respectively, which were higher than those in Comparative Examples 1 and 2. By satisfying the above-mentioned ranges for the capacity per unit area of ​​the negative electrode and the positive electrode, it is beneficial to achieve a capacity per unit area of ​​1.13-1.5 times that of the positive electrode, thereby increasing the lithium intercalation space of the negative electrode and thus improving the fast charging performance of the lithium-ion secondary battery.

[0169] As can be seen from Examples 1-8, the positive electrode active material includes lithium phosphate, which has high structural stability and is beneficial to improving the cycle performance of lithium-ion secondary batteries.

[0170] The following is a brief description of the testing methods for the physicochemical and performance parameters involved in the embodiments of this application. It should be understood that the following testing methods are only examples, and other testing methods known in the art can also be used for testing.

[0171] (1) Testing of the specific capacity of the negative electrode active material layer

[0172] At 25°C, the secondary battery is discharged at a rate of 0.05C to 2V and disassembled to obtain the negative electrode sheet. The negative electrode sheet is then cut into small discs of a specific area (the weight of the discs and the current collector is measured using a 5-digit high-precision electronic balance; the weight of the active layer W is obtained by subtracting the weight of the current collector from the weight of the discs) and assembled with lithium sheets to form a coin cell. At 25°C, it is discharged at a constant current of 200µA to 0.005V, and then charged at a constant current of 200µA to 2.0V. The charging capacity (Ctotal) of the lithium potential in the 0.005V–2V range is calculated as follows: Specific capacity of the negative electrode active material layer = Ctotal / W.

[0173] (2) Testing of capacity per unit area

[0174] As an example, the capacity per unit area of ​​the negative electrode and the capacity per unit area of ​​the positive electrode can be measured in the following ways.

[0175] At 25°C, the secondary battery was discharged to 2V at a rate of 0.05C and then disassembled to obtain the positive electrode and the negative electrode.

[0176] The negative electrode sheet is cut into small circular pieces with an area of ​​S and assembled with lithium sheets to form a coin cell. At 25°C, the coin cell is discharged to 0.005V with a constant current of 200uA, and then charged to 2.0V with a constant current of 200uA. The charging capacity (Cnegative) of the lithium potential in the range of 0.005V to 2V is recorded. The capacity per unit area of ​​the negative electrode sheet = Cnegative / S.

[0177] The positive electrode is cut into small circular pieces with an area of ​​S and assembled with lithium sheets to form a coin cell. At 25°C, the coin cell is charged to 3.65V with a constant current of 200uA, and then discharged to 2V with a constant current of 200uA. The total discharge capacity is Cpositive, and the capacity per unit area of ​​the positive electrode is Cpositive / S.

[0178] As another example, when the positive active material in the positive electrode is a ternary material, at 25°C, the coin cell assembled in the above manner is charged to 4.3V with a constant current of 200uA, and then discharged to 2.5V with a constant current of 200uA. The total discharge capacity is Cpositive, and the unit area capacity of the positive electrode is Cpositive / S.

[0179] (3) Testing of delithiation amount (ρ) within the voltage range of 0.5V-2V

[0180] As an example, the amount of delithiation and the total amount of delithiation can be measured in the following ways.

[0181] At 25°C, the secondary battery was discharged at a rate of 0.05C to 2V and disassembled to obtain the negative electrode. The negative electrode was then cut to a specific size and assembled with lithium sheets to form a coin cell. The coin cell was discharged at a constant current of 200µA to 0.005V, and then charged at a constant current of 200µA to 2.0V. During this process, the charging capacity with respect to the lithium potential in the range of 0.5V to 2V was recorded, denoted as the amount of lithium delithiation in the range of 0.5V to 2V (C1). The total amount of lithium delithiation was the charging capacity with respect to the lithium potential in the range of 0.005V to 2V (Ctotal), where ρ = C1 / Ctotal.

[0182] (4) Testing the energy density of a single secondary battery cell

[0183] Secondary battery cells were prepared using negative electrode active materials, and the secondary battery cells were tested.

[0184] The volumetric energy density of a secondary battery cell = energy of the battery cell / volume of the battery cell.

[0185] As an example, the energy density of a secondary battery cell is measured as follows: At 25°C, the battery cell is charged and discharged within a voltage range of 2V-3.65V using a current density of 0.33C. After three cycles, the energy of the third discharge cycle is recorded as the energy of the secondary battery cell. The unit of energy for a secondary battery cell is Wh, and the unit of capacity is Ah.

[0186] (5) Cyclic performance test

[0187] As an example, at 25°C, a single secondary battery cell is discharged to 10% SOC using a current density of 0.33C. The cell is then charged to 100% SOC (state of charge) at a constant current of 0.33C. This cycle is repeated 9 times. On the 10th cycle, the cell is discharged to 0% SOC. The discharge capacity on the 10th cycle is recorded as the initial capacity C0 of the secondary battery cell. The capacity decay of the cell is then tested. The capacity of the cell after 1000 charge-discharge cycles is recorded as C1. The capacity retention rate of the cell after 1000 cycles is calculated as C1 / C0 × 100%. A higher cycle capacity retention rate indicates better cycle performance of the secondary battery cell.

[0188] (6) Charging time test

[0189] The above-mentioned negative electrode active material was used to prepare a secondary battery cell containing a third electrode, and the secondary battery cell was subjected to three-electrode testing.

[0190] Using an ultra-high precision blue electric current tester or an electrochemical workstation, the secondary battery cell was charged at a constant current of 0.33C to 3.65V at 25℃, then charged at a constant voltage to a current of 0.05C. After standing for 10 minutes, the secondary battery cell was discharged at a constant current of 0.33C to 2V, and its actual discharge capacity was recorded as C0.

[0191] At 25℃, the secondary battery cells were charged at a constant current rate of 0.33C for 90 minutes to adjust the SOC of the cells to 50%. Then, the three electrodes were connected to the positive electrode and charged at a constant current rate of 0.0001C for 2 hours. After resting for 1 minute, the three electrodes were connected to the negative electrode and charged at a constant current rate of 0.0001C for 2 hours. The above is the lithium plating process for the three electrodes. After lithium plating, the potential of the three electrodes and the negative electrode is between 40-400mV.

[0192] Then, the secondary battery cells were sequentially charged at constant currents of 0.8C0, 1.0C0, 1.5C0, 2.0C0, 2.5C0, 3.0C0, 3.5C0, and 4.0C0 until the positive and negative electrode potentials reached 3.65V or the cutoff potential of 0V between the negative electrode and the three electrodes (whichever comes first). After each charge, the cells were discharged to 2V at 0.33C0. The state of charge was recorded at different charging rates until 10%, 20%, 30%, 40%, 50%, 60%, 70%, and 80% SOC. The negative electrode potential corresponding to the state of charge (SOC) is plotted, and the charging rate-negative electrode potential curves are drawn for different SOC states. After linear fitting, the charging rate corresponding to the negative electrode potential of 0V under different SOC states is obtained. This charging rate is the charging window under that SOC state, denoted as C10%SOC, C20%SOC, C30%SOC, C40%SOC, C50%SOC, C60%SOC, C70%SOC, and C80%SOC, respectively. According to the formula (60 / C20%SOC+60 / C30%SOC+60 / C40%SOC+60 / C50%SOC+60 / C60%SOC+60 / C70%SOC+60 / C80%SOC)×10%, the charging time T of the secondary battery cell from 10%SOC to 80%SOC (under the premise that the secondary battery cell does not plaque lithium) is obtained, in min. The shorter the charging time, the better the fast charging performance of the secondary battery cell.

[0193] (7) Test method for volumetric particle size distribution

[0194] The fully loaded negative electrode sheet is placed in deionized water to separate it from the negative electrode current collector. After washing and filtering three times, the active material particles are dried. The particle size distribution of the powder is then tested using the laser particle size distribution method, referring to the document GB / T 19077-2016 / ISO 13320:2009.

[0195] As an example, the volumetric particle size distribution of the negative electrode active material can be determined using a particle size analyzer-laser diffraction method. Specifically, it can be measured according to the manufacturer's instructions using a laser diffraction scattering particle size analyzer, referring to standard GB / T19077-2016. For instance, the negative electrode sheet, after being fully loaded, is placed in deionized water to separate it from the negative electrode current collector. After three water washes, filtration, and drying, the negative electrode active material particles are obtained as a sample. The average volumetric particle size of the sample is tested using a Malvern 3000 (MasterSizer 3000) laser particle size analyzer. Take an appropriate amount of the sample to be tested (the sample concentration should be 8-12% opacity), add 20 ml of deionized water, and simultaneously incubate for 5 minutes (53 kHz / 120 W) to ensure complete dispersion of the sample. Then, the sample is measured according to the standard GB / T19077-2016 / ISO 13320:2009. It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples. Embodiments with the same structure and function as the technical concept as described in this application are all included within the scope of this application. Furthermore, various modifications conceivable to the embodiments by those skilled in the art, and other methods of constructing embodiments by combining some of the constituent elements, are also included within the scope of this application without departing from its intent.

Claims

1. A lithium-ion secondary battery, characterized in that, include: The positive electrode and the negative electrode, wherein the ratio of the capacity per unit area of ​​the negative electrode to the capacity per unit area of ​​the positive electrode is 1.13-1.5; The negative electrode sheet includes a negative electrode active material layer, which includes graphite and silicon-based materials; In the negative electrode, the ratio of the amount of lithium delithiation to the total amount of lithium delithiation in the lithium potential range of 0.5V to 2V is 4%-16%.

2. The lithium-ion secondary battery according to claim 1, characterized by The negative electrode has a capacity of 3.15 mAh / cm² per unit area. 2 -5.61mAh / cm 2 The capacity per unit area of ​​the positive electrode is 2.75 mAh / cm². 2 -3.75mAh / cm 2 .

3. The lithium-ion secondary battery according to claim 1 or 2, characterized by The specific capacity of the silicon-based material is 800mAh / g to 2300mAh / g.

4. The lithium-ion secondary battery according to any one of claims 1 to 3, characterized by Based on the total mass of the negative electrode active material layer, the mass content A of the silicon-based material satisfies: 1 wt.% to 12 wt.%.

5. The lithium-ion secondary battery according to any one of claims 1-4, characterized in that, The positive electrode sheet includes a positive active material, which includes a lithium phosphate.

6. The lithium-ion secondary battery according to any one of claims 1-5, characterized in that, The surface of the silicon-based material has a coating layer, which includes carbon elements.

7. The lithium-ion secondary battery according to any one of claims 1-6, characterized in that, The silicon-based material includes at least one of elemental silicon, silicon-oxygen materials, and silicon-carbon materials.

8. The lithium-ion secondary battery according to any one of claims 1-7, characterized in that, The silicon-carbon material includes porous carbon, which has a pore structure and contains silicon.

9. The lithium-ion secondary battery according to any one of claims 1-8, characterized in that, In the negative electrode, the ratio of the amount of lithium removed in the lithium potential range of 0.5V to 2V to the total amount of lithium removed is 7% to 15%.

10. The lithium-ion secondary battery according to any one of claims 1-9, characterized in that, The specific capacity of the silicon-based material is 1400mAh / g to 2000mAh / g.

11. An electrical appliance, characterized in that, Including the lithium-ion secondary battery according to any one of claims 1-10.

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