Electrochemical apparatus, battery pack and electrical device

Abstract

The application discloses an electrochemical apparatus, a battery pack and an electric device. The electrochemical apparatus comprises a housing, an electrode terminal, an electrode assembly, a current cut-off apparatus and an electrolyte. The electrode terminal is arranged on the housing. The electrode assembly and the electrolyte are accommodated in the housing. The current cut-off apparatus is connected to the electrode terminal and the electrode assembly. The electrolyte comprises lithium hexafluorophosphate and fluoroethylene carbonate. In the charging process in a high-temperature environment and in a large-rate discharge process, the electrochemical apparatus is not prone to generating gas, can endure harsh charging and discharging environments, and has good cycle performance and cycle life.

Description

Electrochemical devices, battery packs, and electrical equipment

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202311830520.0, filed on December 27, 2023, entitled “Electrode assembly, battery cell, battery and electrical device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application relates to the field of battery technology, and more particularly, to an electrochemical device, a battery pack, and an electrical device. Background Art

[0004] With the widespread application of electrochemical devices (such as lithium-ion batteries) in various electronic products, users have placed increasingly higher demands on the performance of electrochemical devices. How to improve the cycle life of electrochemical devices has always been a research direction in the industry. Summary of the Invention

[0005] The present application provides an electrochemical device, a battery pack, and electrical equipment, which are beneficial to improving cycle life.

[0006] In a first aspect, embodiments of the present application provide an electrochemical device comprising a housing, electrode terminals, an electrode assembly, a current interruption device, and an electrolyte. The electrode terminals are disposed on the housing, the electrode assembly and the electrolyte are contained within the housing, and the current interruption device is connected to the electrode terminals and the electrode assembly. The electrolyte comprises lithium hexafluorophosphate and fluoroethylene carbonate.

[0007] The electrochemical device is configured as follows:

[0008] i) the electrochemical device performs a first discharge operation: after the electrochemical device is allowed to stand at a first temperature for a first time, a discharge operation is performed at a first discharge rate until the voltage of the electrochemical device reaches a discharge cutoff voltage. The electrochemical device terminates the first discharge operation and stands for a second time;

[0009] ii) the electrochemical device performs a charging operation: after the electrochemical device is allowed to stand at the second temperature for a third time, a charging operation is performed at the first charge rate until the voltage of the electrochemical device reaches the charge cut-off voltage. The electrochemical device continues to perform the charging operation at the charge cut-off voltage, and the charging operation ends after 24 hours;

[0010] iii) the electrochemical device performs a second discharge operation: after the electrochemical device is allowed to stand at the third temperature for a fourth time, the electrochemical device performs a discharge operation at the third temperature at a second discharge rate until the voltage of the electrochemical device reaches a discharge cutoff voltage, thereby ending the second discharge operation;

[0011] iv) the electrochemical device repeatedly performs the second operation and the third operation (m-1) times;

[0012] In response to the electrochemical device performing the i-th operation to the iv-th operation, the current cutoff device cuts off the connection between the electrode terminal and the electrode assembly;

[0013] Among them, the first discharge rate is 0.2C-0.5C, the first charge rate is 2C-3C, and the second discharge rate is 8C to 10C; the first temperature is 15℃-30℃, the second temperature is 55℃-60℃, and the third temperature is 15℃-30℃; the first time is 1 hour-2 hours, the second time is 1 hour-2 hours, the third time is 1 hour-2 hours, and the fourth time is 1 hour-2 hours; m≥50.

[0014] In the embodiments of the present application, the electrolyte is not easily decomposed during long-term charging and high-rate discharge, and the electrochemical device is capable of maintaining connection between the electrode terminals and the electrode assembly when repeating the second and third operations for 50 cycles. The electrochemical device is not easily gassed during charging in a high-temperature environment and during high-rate discharge, can withstand rigorous charging and discharging scenarios, and has good cycle performance and cycle life.

[0015] In one or more of the above optional embodiments, m≥55.

[0016] In one or more of the above optional embodiments, m≥60.

[0017] In one or more of the above optional embodiments, m≥65.

[0018] In one or more of the above optional embodiments, 70≤m≤90.

[0019] In one or more optional embodiments above, the first temperature is 25° C., and / or the third temperature is 25° C. The electrochemical device has better discharge performance under normal temperature environment.

[0020] In one or more of the above optional embodiments, the weight percentage of lithium hexafluorophosphate is 12%-16% and the weight percentage of fluoroethylene carbonate is 0.8%-1.5% based on the mass of the electrolyte. The electrolyte is not easily decomposed during long-term charging and high-rate discharge, and gas generation is slow, thereby improving the cycling performance and cycle life of the electrochemical device.

[0021] In one or more of the above optional embodiments, the electrochemical device further comprises a current collecting disc connected to the electrode assembly. The current cutoff device comprises a connecting plate and a flip plate connected to each other, the connecting plate having a through hole and comprising a first surface and a second surface disposed opposite each other, the first surface of the connecting plate being connected to the current collecting disc, the second surface of the connecting plate being connected to the flip plate, and the flip plate being connected to the electrode terminal. The flip plate is configured to flip relative to the connecting plate to disconnect the electrode terminal from the electrode assembly.

[0022] When the internal gas pressure of the electrochemical device reaches a threshold, the flip plate flips under the action of the internal gas pressure to disconnect the electrode terminal from the electrode assembly, thereby breaking the circuit, delaying the gas production inside the electrochemical device, reducing the risk of explosion of the electrochemical device, and improving the safety of the electrochemical device. The through-hole can provide a channel for gas. When the electrode assembly releases gas, the gas can act on the flip plate through the through-hole, allowing the flip plate to flip in time. During liquid injection, the electrolyte can also pass through the through-hole, improving the injection efficiency of the electrolyte and improving the wettability of the electrode assembly.

[0023] In one or more optional embodiments above, the electrode assembly includes a first electrode sheet, a second electrode sheet, and a separator. The first electrode sheet, the separator, and the second electrode sheet are stacked and wound along a winding direction. One of the first electrode sheet and the second electrode sheet is a positive electrode sheet, and the other is a negative electrode sheet. The first electrode sheet includes a first current collector and a first active material. The first current collector includes a first main body area and a first hollow foil area. The first active material is provided in the first main body area. The arrangement direction of the first main body area and the first hollow foil area is perpendicular to the winding direction. The first hollow foil area includes a first flattened area. The first flattened area is away from the first main body area and is connected to the current cut-off device.

[0024] The first flattened area has a dense end surface, and connecting the first flattened area to the current cut-off device can improve the connection strength between the first flattened area and the current cut-off device.

[0025] In one or more optional embodiments above, along the width direction of the unfolded first electrode sheet, the size of the first empty foil area is W1, the size of the first current collector is W2, and W1 and W2 satisfy: 0.05≤W1 / W2≤0.1.

[0026] Setting W1 / W2 to greater than or equal to 0.05 allows the first hollow foil area to have a larger width, facilitating connection between the first hollow foil area and other conductive structures. Setting W1 / W2 to less than or equal to 0.1 allows more space to be reserved for the first active material, reducing energy density loss.

[0027] In one or more optional embodiments above, along the width direction of the unfolded first pole piece, the size of the first flattened area is W4, and 0.6≤W4 / W1≤0.95.

[0028] Setting W4 / W1 to greater than or equal to 0.6 helps increase the pressure area of ​​the first empty foil area during the flattening process, reducing the axial size of the electrode assembly, improving space utilization, and making the first flattened area more compact. Setting W4 / W1 to less than or equal to 0.95 helps reduce the force transmitted to the first active material during the flattening process, reducing the risk of the first active material falling off.

[0029] In one or more of the above optional embodiments, a first notch is provided at a corner of an outer end of the first empty foil region along the winding direction. The first notch has a dimension La along the length of the unfolded first pole piece. La and W1 satisfy: 0.2≤La / W1≤4.

[0030] Limiting La / W1 to greater than or equal to 0.2 helps reduce the accumulation of empty foil material during the flattening process, lowering the risk of puncturing the insulating member covering the first empty foil area, and improving safety. Limiting La / W1 to less than or equal to 4 helps reduce the impact of the first cut on the flow capacity of the first empty foil area.

[0031] In one or more optional embodiments above, along the width direction of the unfolded first pole piece, the size of the first incision is W3; W3 and W1 satisfy: 0.2≤W3 / W1≤1.

[0032] Setting W3 / W1 to greater than or equal to 0.2 helps reduce the accumulation of empty foil material during the flattening process, lowering the risk of puncturing the insulating member covering the first empty foil area, and improving safety. Setting W3 / W1 to less than or equal to 1 helps reduce the risk of the first incision extending into the first main body area, thereby reducing the loss of the first active material.

[0033] In one or more optional embodiments above, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material, the positive electrode active material is provided on the positive electrode current collector, and the positive electrode active material includes Li 1+a Ni x1 Co y1 Mn z1 O2 or Li 1+a Ni x2 Co y2 Al z2 At least one of O2. x1 and x2 are both greater than or equal to 0.8, y1 and y2 are both greater than 0, z2 and z3 are both greater than 0, x1+y1+z1=1, x2+y2+z2=1, -0.05≤a≤0.2.

[0034] In one or more of the above optional embodiments, x1 and x2 are both greater than or equal to 0.9.

[0035] In one or more optional embodiments above, the negative electrode plate includes a negative electrode current collector and a negative electrode active material, the negative electrode active material is disposed on the negative electrode current collector, and the negative electrode active material includes at least one of artificial graphite or natural graphite.

[0036] In one or more of the above optional embodiments, the rated capacity of the electrochemical device is 2500 mAh to 4500 mAh.

[0037] In one or more of the above optional embodiments, the electrochemical device has an AC internal resistance of less than 6 milliohms. The electrochemical device has a low AC resistance, generates less heat during charging and high-rate discharge, slows electrolyte decomposition, reduces gas production, and improves the cycling performance and cycle life of the electrochemical device.

[0038] In one or more of the above optional embodiments, the electrochemical device is a cylindrical battery cell, which has a mature production process, a high product yield, and good heat dissipation performance.

[0039] In one or more optional embodiments above, the diameter of the cylindrical battery cell is 17 mm-22 mm, and the height of the cylindrical battery cell is 64 mm-72 mm.

[0040] In one or more optional embodiments above, the cylindrical battery cell is an 18650 battery cell or a 21700 battery cell.

[0041] In a second aspect, an embodiment of the present application further provides a battery pack, which includes the electrochemical device provided in any embodiment of the first aspect.

[0042] In one or more of the above optional embodiments, the battery pack includes one battery module or multiple battery modules arranged in parallel, and one battery module includes multiple electrochemical devices arranged in series.

[0043] In a third aspect, an embodiment of the present application further provides an electrical device comprising a battery pack provided in any embodiment of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application.

[0045] FIG1 is a schematic structural diagram of an electrochemical device provided in some embodiments of the present application;

[0046] FIG2 is a schematic cross-sectional view of an electrochemical device provided in some embodiments of the present application;

[0047] FIG3 is an enlarged schematic diagram of the electrochemical device shown in FIG2 at the frame;

[0048] FIG4 is an enlarged schematic diagram of the circle frame in FIG3 ;

[0049] FIG5 is a front view schematic diagram of an electrode assembly of an electrochemical device provided in some embodiments of the present application;

[0050] FIG6 is a schematic top view of the electrode assembly shown in FIG5 ;

[0051] FIG7 is a schematic cross-sectional view taken along the AA direction in FIG5 ;

[0052] FIG8 is a schematic diagram of a first electrode sheet of an electrochemical device in an unfolded state according to some embodiments of the present application;

[0053] FIG9 is a schematic cross-sectional view taken along the BB direction in FIG8 ;

[0054] FIG10 is a partial cross-sectional schematic diagram of a first electrode tab of an electrochemical device provided in some embodiments of the present application;

[0055] FIG11 is a schematic diagram of a first electrode sheet of an electrochemical device in an unfolded state provided by other embodiments of the present application;

[0056] FIG12 is an enlarged schematic diagram of the circle frame of FIG11;

[0057] FIG13 is a schematic diagram of a first electrode sheet of an electrochemical device in an unfolded state provided by yet other embodiments of the present application;

[0058] FIG14 is a schematic diagram of a first electrode sheet of an electrochemical device in an unfolded state provided in some further embodiments of the present application;

[0059] FIG15 is a schematic diagram of a second electrode sheet of an electrochemical device in an expanded state according to some embodiments of the present application;

[0060] FIG16 is a schematic cross-sectional view taken along the CC direction of FIG15;

[0061] FIG17 is a schematic diagram of a battery pack provided in some embodiments of the present application;

[0062] FIG18 is a schematic diagram of an electrical device provided in some embodiments of the present application.

[0063] The reference numerals are as follows: DETAILED DESCRIPTION

[0064] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly described below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0065] The terms "first," "second," and the like in the specification and claims of this application or the accompanying drawings are used to distinguish between different objects, rather than to describe a specific order or a primary-secondary relationship. In the embodiments of this application, the same reference numerals represent the same components, and for the sake of brevity, detailed descriptions of the same components in different embodiments are omitted.

[0066] References to "embodiments" in this application mean that a particular feature, structure, or characteristic described in connection with the embodiment may be included in at least one embodiment of the application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments.

[0067] In the description of this application, it should be noted that, unless otherwise specified or limited, the terms "mounted" and "connected" should be understood broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to direct connections, indirect connections through an intermediate medium, or internal connections between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on specific circumstances.

[0068] In the embodiments of this application, "parallel" includes not only absolute parallelism but also approximately parallelism as commonly understood in engineering practice. Similarly, "perpendicular" also includes not only absolute perpendicularity but also approximately perpendicularity as commonly understood in engineering practice. For example, if the angle between two directions is 85°-90°, they are considered perpendicular; if the angle between two directions is 0°-5°, they are considered parallel.

[0069] 1 to 7 , an embodiment of the present application provides an electrochemical device 1000. The electrochemical device 1000 may be a secondary battery cell, which refers to a battery cell that can be recharged to activate active materials after discharge and continue to be used.

[0070] In some embodiments, the electrochemical device 1000 may be a cylindrical cell, a prismatic cell, or a cell of other shapes. Prismatic cells include square shell cells, blade-shaped cells, and polygonal cells. Polygonal cells may be, for example, hexagonal cells.

[0071] In some embodiments, the electrochemical device 1000 includes an electrode assembly 1 , a housing 2 , and an electrolyte (not shown), wherein the electrode assembly 1 and the electrolyte are contained in the housing 2 .

[0072] One or more electrode assemblies 1 can be accommodated in the housing 2 .

[0073] The electrode assembly 1 may be a wound structure, a laminated structure or other structures.

[0074] The shape of the electrode assembly 1 can be cylindrical, flat, or polygonal.

[0075] In some embodiments, the electrode assembly 1 includes a first electrode sheet 11, a second electrode sheet 12, and a separator 13. One of the first electrode sheet 11 and the second electrode sheet 12 is a positive electrode sheet, and the other is a negative electrode sheet.

[0076] During the charge and discharge process of electrochemical device 1000, active ions (e.g., lithium ions) are intercalated and released between the positive and negative electrode sheets. Separator 13 insulates first electrode sheet 11 from second electrode sheet 12 to reduce the risk of short circuits between the positive and negative electrode sheets, while allowing the active ions to pass through.

[0077] The housing 2 can be a steel shell, an aluminum shell, a stainless steel shell, a copper shell, a plastic shell (such as polypropylene) or a composite metal shell (such as a copper-aluminum composite shell), etc. The housing 2 can be of various shapes and sizes, such as a rectangular parallelepiped or a cylindrical shape.

[0078] In some embodiments, the electrolyte includes lithium hexafluorophosphate (LiPF6) and fluoroethylene carbonate (FEC). FEC, as an electrolyte additive, helps improve the performance of the SEI (solid electrolyte interface) film, forming a dense structure without increasing impedance, preventing further decomposition of the electrolyte, and improving the electrolyte's cycling performance.

[0079] In some embodiments, the electrochemical device 1000 further includes an electrode terminal 3, which is electrically connected to the electrode assembly 1. The electrode terminal 3 can be used to conduct the current generated by the electrode assembly 1, and an external power source can also charge the electrode assembly 1 through the electrode terminal 3.

[0080] In some embodiments, the housing 2 has an opening.

[0081] Optionally, the electrode terminal 3 may cover the opening of the housing 2 and cooperate with the housing 2 to form an internal cavity of the electrochemical device 1000 . The internal cavity may be used to accommodate the electrode assembly 1 , electrolyte, and other components.

[0082] Alternatively, the electrochemical device 1000 further includes a cover plate (not shown), which can cover the opening of the housing 2 and cooperate with the housing 2 to form an internal cavity of the electrochemical device 1000. The electrode terminal 3 can be mounted on the cover plate. For example, the cover plate can be connected to the housing 2 by welding, bonding, clamping, or other means.

[0083] In some embodiments, the electrochemical device 1000 includes an electrode terminal 3, wherein one of the electrode terminal 3 and the housing 2 is electrically connected to the first electrode sheet 11, and the other is electrically connected to the second electrode sheet 12. One of the electrode terminal 3 and the housing 2 serves as the positive electrode of the electrochemical device 1000, and the other serves as the negative electrode of the electrochemical device 1000.

[0084] In other examples, the electrochemical device 1000 includes two electrode terminals 3, which are electrically connected to the first electrode sheet 11 and the second electrode sheet 12. The two electrode terminals 3 are the positive electrode and the negative electrode of the electrochemical device 1000, respectively.

[0085] In some embodiments, the electrochemical device 1000 further includes a current cutoff device 5 , which is connected to the electrode terminal 3 and the electrode assembly 1 .

[0086] The current interruption device 5 can be directly connected to the electrode assembly 1 or indirectly connected to the electrode assembly 1 through other conductive components. The current interruption device 5 can be directly connected to the electrode terminal 3 or indirectly connected to the electrode terminal 3 through other conductive components.

[0087] When the electrochemical device 1000 fails due to overheating, overcharging, short circuit or other reasons, the current cut-off device 5 can be activated to disconnect the electrode terminal 3 and the electrode assembly 1, thereby breaking the circuit inside the electrochemical device 1000 and reducing safety risks.

[0088] For example, the current cutoff device 5 can be activated by pressure. When the electrochemical device 1000 fails due to overheating, overcharging, short circuit, or other reasons, the electrode assembly 1 releases gas. As the gas increases, the pressure inside the housing 2 increases. When the pressure inside the housing 2 reaches a threshold, the current cutoff device 5 cuts off the connection between the electrode terminal 3 and the electrode assembly 1.

[0089] In some embodiments, the electrochemical device 1000 is configured to:

[0090] i) the electrochemical device 1000 performs a first discharge operation: after the electrochemical device 1000 is allowed to stand at a first temperature for a first time, a discharge operation is performed at a first discharge rate until the voltage of the electrochemical device 1000 reaches a discharge cutoff voltage. The electrochemical device 1000 then terminates the first discharge operation and stands for a second time;

[0091] ii) the electrochemical device 1000 performs a charging operation: after the electrochemical device 1000 is allowed to stand at the second temperature for a third time, a charging operation is performed at the first charge rate until the voltage of the electrochemical device 1000 reaches the charge cutoff voltage. The electrochemical device 1000 continues to perform the charging operation at the charge cutoff voltage, and the charging operation is terminated after 24 hours.

[0092] iii) the electrochemical device 1000 performs a second discharge operation: after the electrochemical device 1000 is allowed to stand at the third temperature for a fourth time, the electrochemical device 1000 performs a discharge operation at the third temperature at a second discharge rate until the voltage of the electrochemical device 1000 reaches a discharge cutoff voltage, thereby ending the second discharge operation;

[0093] iv) the electrochemical device 1000 repeatedly performs the charging operation and the second discharging operation (m-1) times;

[0094] In response to the electrochemical device 1000 performing the i-th to iv-th operations, the current cutoff device 5 cuts off the connection between the electrode terminal 3 and the electrode assembly 1 ;

[0095] Among them, the first discharge rate is 0.2C-0.5C, the first charge rate is 2C-3C, and the second discharge rate is 8C to 10C; the first temperature is 15℃-30℃, the second temperature is 55℃-60℃, and the third temperature is 15℃-30℃; the first time is 1 hour-2 hours, the second time is 1 hour-2 hours, the third time is 1 hour-2 hours, and the fourth time is 1 hour-2 hours; m≥50.

[0096] In the embodiment of the present application, the charge and discharge operation of the electrochemical device 1000 is performed within the allowed number of charge and discharge cycles. The allowed number of charge and discharge cycles is obtained from the manufacturer or seller on the label, packaging, user manual, instruction manual, advertisement, marketing or other supporting documents of these products for user reference.

[0097] For example, the discharge cut-off voltage and charge cut-off voltage of the electrochemical device can be obtained from the manufacturer or seller on the label, packaging, user manual, instruction manual, advertisement, marketing, or other supporting documents of these products for user reference. The advertised voltage may include a numerical voltage value, or other words, phrases, alphanumeric character combinations, icons, or symbols that indicate to the user how the electrochemical device works.

[0098] For example, the electrochemical device 1000 may be an 18650 battery cell or a 21700 battery cell. The discharge cut-off voltage of the 18650 battery cell may be 2.5 V, and the charge cut-off voltage may be 4.2 V. The discharge cut-off voltage of the 21700 battery cell may be 2.5 V, and the charge cut-off voltage may be 4.2 V.

[0099] For example, the electrochemical device being at 100% SOC may mean that: at 25° C., the electrochemical device is discharged at a constant current of 0.5C to the discharge cut-off voltage of the electrochemical device, then charged at a constant current of 0.5C to the charge cut-off voltage of the electrochemical device, and then charged at a constant voltage of 0.05C at the charge cut-off voltage, at which time the electrochemical device is at 100% SOC.

[0100] Exemplarily, the electrochemical device being at an SOC of 0% means that the electrochemical device is discharged at a constant current rate to a discharge cut-off voltage of the electrochemical device, at which time the electrochemical device is at an SOC of 0%.

[0101] For example, the charge and discharge process of the electrochemical device can be tested by a battery tester (Neware CT-4016-5V-100A).

[0102] For example, for an electrochemical device at an early stage of a cycle, when its load reaches the rated capacity of the electrochemical device, the electrochemical device can also be considered to be at 100% SOC.

[0103] For example, the rated capacity of an electrochemical device can be considered as follows: when an electrochemical device at 100% SOC is discharged at a constant current rate of 0.2C at 25°C to 0% SOC, the discharged capacity is the rated capacity.

[0104] For example, the rated capacity of the electrochemical device can be obtained from the manufacturer or seller on the label, packaging, user manual, instruction manual, advertisement, marketing or other supporting documents of these products for user reference. The rated capacity may include a number, or other words, phrases, alphanumeric character combinations, icons or symbols that indicate to the user how the electrochemical device works.

[0105] For example, the electrochemical device may be an 18650 battery cell or a 21700 battery cell. For example, the rated capacity of the 18650 battery cell may be 2500 mAh, 3000 mAh, 3500 mAh, or 4000 mAh, and the rated capacity of the 21700 battery cell may be 3500 mAh, 4000 mAh, 4500 mAh, or 5000 mAh.

[0106] The electrochemical device at 100% SOC was discharged at a constant current rate of 0.2C to 30% SOC at 25°C. The internal resistance was measured using an internal resistance tester (HIOKI BT3563) set to a frequency of 1 kHz.

[0107] Exemplarily, discharge rate = current / rated capacity. Exemplarily, the discharge rate is the rate at which an electrochemical device or battery pack discharges its total storage capacity expressed in Ah or mAh. Exemplarily, a 1C rate means that all stored energy is utilized in 1 hour; a 0.5C rate means that all stored energy is utilized in 2 hours; and a 10C rate means that all stored energy is utilized in 0.1 hours.

[0108] For example, if the discharge rate is xC, the time it takes for the electrochemical device to discharge from 100% SOC to 0% SOC is t, where t is equal to 1 / x hours.

[0109] Exemplarily, charge rate = current / rated capacity. Exemplarily, when the rated capacity of the electrochemical device is 4000 mAh, during a charging operation performed at a 2C charge rate, the charging current is 4000×2 mAh.

[0110] As an example, the first discharge rate is 0.2C, 0.3C, 0.4C or 0.5C.

[0111] As an example, the first charging rate is 2C, 2.5C or 3C.

[0112] As an example, the second discharge rate is 8C, 9C or 10C.

[0113] As an example, the first temperature, the second temperature, and the third temperature may all be the temperature of the environment in which the electrochemical device 1000 is located when performing charge and discharge operations. The first temperature, the second temperature, and the third temperature may all be a constant temperature environment.

[0114] As an example, the electrochemical device 1000 performs the i-th operation to the iv-th operation in a constant temperature chamber (Comin EH-1000).

[0115] As an example, the first temperature is 15°C, 20°C, 25°C or 30°C.

[0116] As an example, the second temperature is 55°C, 56°C, 57°C, 58°C, 59°C or 60°C.

[0117] As an example, the third temperature is 15°C, 20°C, 25°C or 30°C.

[0118] As an example, the first time is 1 hour, 1.5 hours or 2 hours.

[0119] As an example, the second time is 1 hour, 1.5 hours or 2 hours.

[0120] As an example, the third time is 1 hour, 1.5 hours or 2 hours.

[0121] As an example, the fourth time is 1 hour, 1.5 hours or 2 hours.

[0122] m≥50. Exemplarily, when the current cutoff device is actuated and cuts off the connection between the electrode terminal and the electrode assembly, the electrochemical device 1000 repeatedly performs the ii-th operation and the iii-th operation a number of times greater than or equal to 50.

[0123] When the electrochemical device 1000 performs the second operation, it is charged for an extended period in a high-temperature environment. During extended charging, the electrolyte may decompose and generate gas. When the electrochemical device 1000 performs the third operation, it is discharged at a high rate. During high-rate discharge, the internal temperature of the electrochemical device 1000 is likely to rise, and the electrolyte may also decompose and generate gas.

[0124] In the embodiment of the present application, the electrolyte is not easily decomposed during long-term charging and high-rate discharge. The electrochemical device 1000 can maintain the connection between the electrode terminal 3 and the electrode assembly 1 when the second and third operations are repeated for 50 cycles. The electrochemical device 1000 of the embodiment of the present application is not easily gassed during charging in a high-temperature environment and during high-rate discharge. It can withstand rigorous charging and discharging scenarios and has good cycle performance and cycle life.

[0125] In some embodiments, m≥55. The electrochemical device 1000 can maintain the connection between the electrode terminal 3 and the electrode assembly 1 when the ii-th operation and the iii-th operation are repeatedly performed for 55 cycles, and has good cycle performance and cycle life.

[0126] In some embodiments, m≥60. The electrochemical device 1000 can maintain the connection between the electrode terminal 3 and the electrode assembly 1 when the ii-th operation and the iii-th operation are repeatedly performed for 60 cycles, and has better cycle performance and cycle life.

[0127] In some embodiments, m≥65. The electrochemical device 1000 can maintain the connection between the electrode terminal 3 and the electrode assembly 1 when the ii-th operation and the iii-th operation are repeatedly performed for 65 cycles, and has good cycle performance and cycle life.

[0128] In some embodiments, 70≤m≤90. The electrochemical device 1000 can maintain the connection between the electrode terminal 3 and the electrode assembly 1 when the ii-th operation and the iii-th operation are repeatedly performed for 90 cycles, and has good cycle performance and cycle life.

[0129] In some embodiments, the first temperature is 25° C. The electrochemical device 1000 has better discharge performance under normal temperature.

[0130] In some embodiments, the third temperature is 25° C. The electrochemical device 1000 has better discharge performance under normal temperature.

[0131] In some embodiments, the first temperature is 25° C., and the third temperature is 25° C. The electrochemical device 1000 has better discharge performance under normal temperature conditions.

[0132] In some embodiments, based on the mass of the electrolyte, the mass percentage of lithium hexafluorophosphate is 12%-16%, and the mass percentage of fluoroethylene carbonate is 0.8%-1.5%.

[0133] As an example, the mass percentage of lithium hexafluorophosphate is 12%, 13%, 14%, 15% or 16% based on the mass of the electrolyte.

[0134] As an example, the mass percentage of fluoroethylene carbonate is 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4% or 1.5% based on the mass of the electrolyte.

[0135] The embodiments of the present application can slow down the decomposition of the electrolyte during long-term charging and high-rate discharge, thereby reducing gas production.

[0136] In some embodiments, the electrolyte further comprises a solvent. Exemplarily, the electrolyte solvent is a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC:EMC mass ratio = 70:30). The solute is lithium hexafluorophosphate (LiPF6), and the additive is fluoroethylene carbonate (FEC). Optionally, based on the mass of the electrolyte, the mass percentage of LiPF6 is 15%, and the mass percentage of FEC is 1%.

[0137] In some embodiments, the electrochemical device 1000 further includes a current collecting disc 4 connected to the electrode assembly 1. The current cutoff device 5 includes a connecting plate 51 and a flip plate 52 connected to each other. The connecting plate 51 has a through hole 511 and includes a first surface 512 and a second surface 513 disposed opposite each other. The first surface 512 of the connecting plate 51 is connected to the current collecting disc 4, and the second surface 513 of the connecting plate 51 is connected to the flip plate 52. The flip plate 52 is connected to the electrode terminal 3. The flip plate 52 is configured to flip relative to the connecting plate 51 to disconnect the electrode terminal 3 from the electrode assembly 1.

[0138] When the internal gas pressure of the electrochemical device 1000 reaches a threshold, the flip plate 52 flips under the action of the internal gas pressure to disconnect the electrode terminal 3 from the electrode assembly 1, thereby breaking the circuit, delaying the gas production inside the electrochemical device 1000, reducing the risk of explosion of the electrochemical device 1000, and improving the safety of the electrochemical device 1000. The through hole 511 can provide a channel for gas. When the electrode assembly 1 releases gas, the gas can act on the flip plate 52 through the through hole 511, allowing the flip plate 52 to flip in time. During liquid injection, the electrolyte can also pass through the through hole 511, improving the injection efficiency of the electrolyte and improving the wettability of the electrode assembly 1.

[0139] In some embodiments, the current collecting plate 4 may be bent into a C-shape or an S-shape. The bent current collecting plate 4 may apply elastic force to the electrode assembly 1 to reduce vibration of the electrode assembly 1 when the electrochemical device 1000 is subjected to external impact.

[0140] In some alternative embodiments, the collecting plate 4 may also be a flat plate structure.

[0141] In some embodiments, the connecting plate 51 is a flat plate structure. The first surface 512 and the second surface 513 can both be planes and are disposed opposite to each other along the thickness direction of the connecting plate 51 .

[0142] In some embodiments, the flip sheet 52 and the current collecting plate 4 are respectively located on both sides of the connecting plate 51 .

[0143] In some embodiments, the flip sheet 52 has a convex structure protruding toward the connecting plate 51, with the top of the convex structure abutting and connecting with the connecting plate 51. The convex structure can flip away from the connecting plate 51 when the pressure applied reaches a threshold.

[0144] In some embodiments, the connecting plate 51 includes an annular first weak portion 514 , the portion of the connecting plate 51 surrounded by the first weak portion 514 is connected to the flip sheet 52 , and the portion of the connecting plate 51 surrounding the first weak portion 514 is connected to the collecting plate 4 .

[0145] When the internal air pressure of the electrochemical device 1000 reaches a threshold value, the flip sheet 52 flips under the action of the internal air pressure and breaks the first weak portion 514 , and the connecting plate 51 is separated into two parts, one part is fixed to the collecting plate 4 , and the other part flips along with the flip sheet 52 , thereby disconnecting the electrode terminal 3 from the electrode assembly 1 .

[0146] In some embodiments, the first weak portion 514 may be formed by opening an annular groove on the connecting plate 51 .

[0147] In some embodiments, the flip sheet 52 includes a ring-shaped second weak portion 521 , and the portion of the flip sheet 52 surrounded by the second weak portion 521 is connected to the connecting plate 51 .

[0148] By providing the second weak portion 521 , the flipping piece 52 can be guided to flip, thereby reducing the difficulty of flipping the flipping piece 52 .

[0149] In some embodiments, the second weak portion 521 may be formed by opening an annular groove on the flip sheet 52 .

[0150] In some embodiments, the first pole piece 11, the separator 13, and the second pole piece 12 are stacked and wound along a winding direction V. The winding direction V may be the direction in which the second pole piece 12, the separator 13, and the first pole piece 11 are wound from the inside to the outside. For example, as shown in FIG7 , the winding direction V is clockwise.

[0151] In some embodiments, after the electrode assembly 1 is wound, a central hole 10c is formed in the middle.

[0152] 5 to 10 , in some embodiments, the first electrode 11 includes a first current collector 111 and a first active material 112 disposed on the first current collector 111 .

[0153] For example, the first current collector 111 may have two opposite surfaces in its thickness direction, and the first active material 112 may be disposed on either or both of the two opposite surfaces of the first current collector 111 .

[0154] In some embodiments, the first current collector 111 may be made of metal foil, such as stainless steel foil, copper foil, aluminum foil, nickel foil, etc.

[0155] In some embodiments, the first electrode sheet 11 is a positive electrode sheet, the first current collector 111 is a positive electrode current collector, and the first active material 112 is a positive electrode active material. In other embodiments, the first electrode sheet 11 is a negative electrode sheet, the first current collector 111 is a negative electrode current collector, and the first active material 112 is a negative electrode active material.

[0156] In some embodiments, the first current collector 111 includes a first main region 111a and a first empty foil region 111b, the first active material 112 is disposed in the first main region 111a, and the arrangement direction of the first main region 111a and the first empty foil region 111b is perpendicular to the winding direction V.

[0157] Exemplarily, the arrangement direction of the first main body region 111 a and the first empty foil region 111 b is parallel to the winding axial direction P of the electrode assembly 1 .

[0158] At least one surface of the first main body region 111 a is coated with the first active material 112 . Both surfaces of the first blank foil region 111 b are not coated with the first active material 112 .

[0159] Part of the first hollow foil region 111b may be provided with other coatings that do not contain active materials, such as an insulating coating. Of course, both surfaces of at least part of the first hollow foil region 111b are exposed and not covered by other coatings. The exposed area of ​​the first hollow foil region 111b can serve as the first tab 10a of the electrode assembly 1, which can conduct current from the electrode assembly 1.

[0160] Exemplarily, after the first electrode sheet 11 is unfolded, the arrangement direction of the first main body region 111 a and the first hollow foil region 111 b is parallel to the width direction Y of the first electrode sheet.

[0161] In some embodiments, the first empty foil region 111b includes a first crumpled region 111c, which is away from the first main region 111a. In other words, the first crumpled region 111c is formed at the end of the first empty foil region 111b away from the first main region 111a.

[0162] Exemplarily, as shown in FIG8 , a portion of the first empty foil area 111 b located above the dotted line is used to form the first flattened area 111 c .

[0163] After the electrode assembly 1 is wound, the first empty foil area 111b is wound and roughly forms a columnar structure. The external tooling can apply external force to the first empty foil area 111b along the circumference of the columnar structure to cause the first empty foil area 111b to bend and deform, thereby making the two radially adjacent layers of the first empty foil area 111b more compact and forming a first flattened area 111c.

[0164] In some embodiments, the first flattened area 111 c is connected to the current cut-off device 5 . Exemplarily, the first flattened area 111 c is connected to the current cut-off device 5 through the current collecting plate 4 .

[0165] In some embodiments, the first flattened area 111 c forms a dense end surface, and the collecting plate 4 abuts against the first flattened area 111 c.

[0166] In some embodiments, the first flattened area 111c is welded to the current collecting plate 4. The first flattened area 111c has a dense end surface. Welding the first flattened area 111c to the current collecting plate 4 can reduce the risk of cold welding, improve welding strength, and reduce the risk of burning the diaphragm 13 due to laser leakage, thereby improving safety.

[0167] In some embodiments, along the length direction X after the first electrode 11 is unfolded, the size of the first hollow foil area 111b is L1, and the size of the first main body area 111a is L2. L1 and L2 satisfy: 0.8≤L1 / L2≤1.

[0168] L1 is the maximum size of the first hollow foil area 111b after unfolding along the length direction X of the unfolded first electrode sheet 11. Exemplarily, the unfolding of the first electrode sheet 11 may be to unfold the first electrode sheet 11 into a flat sheet structure, and correspondingly, the first flattened area 111c is also flattened.

[0169] The first empty foil area 111b has a large flow area. When the electrochemical device 1000 discharges at a high rate, a large current can pass through the first empty foil area 111b, thereby reducing heat generation in the first empty foil area 111b and lowering the risk of the first empty foil area 111b fusing.

[0170] The first hollow foil region 111b has a large flow area. When the electrochemical device 1000 performs the third operation, the temperature rise of the first hollow foil region 111b is relatively low, thereby slowing down the decomposition of the electrolyte and reducing gas production. The electrochemical device 1000 of the present embodiment is not prone to gas production during high-rate discharge, can withstand rigorous charge and discharge scenarios, and has good cycle performance and cycle life.

[0171] Alternatively, L1 / L2 may be 0.8, 0.85, 0.9, 0.95 or 1.

[0172] In some embodiments, 0.9≤L1 / L2≤0.95, which can further improve the flow capacity of the first empty foil area 111b, and on the premise that the first empty foil area 111b meets the flow capacity, reduce the size of the first empty foil area 111b, reduce the space and weight occupied by the first empty foil area 111b, improve the energy density, and facilitate the infiltration of the electrolyte.

[0173] In some embodiments, the first hollow foil region 111b is continuously disposed and wound into multiple turns along the winding direction V. The continuous winding of the first hollow foil region 111b can increase the overall strength of the first hollow foil region 111b. The overall continuity of the first hollow foil region 111b allows current to be transmitted across different regions of the first hollow foil region 111b, thereby improving the current consistency of the first electrode 11.

[0174] In some embodiments, along the width direction Y of the unfolded first electrode sheet 11 , the size of the first empty foil area 111 b is W1 , the size of the first current collector 111 is W2 , and W1 and W2 satisfy: 0.05≤W1 / W2≤0.1.

[0175] Setting W1 / W2 to be greater than or equal to 0.05 allows the first hollow foil area 111b to have a larger width, facilitating connection between the first hollow foil area 111b and other conductive structures. Setting W1 / W2 to be less than or equal to 0.1 allows more space to be reserved for the first active material 112, reducing energy density loss.

[0176] In addition, when the first empty foil area 111b is flattened, the first empty foil area 111b will bend and deform; in the embodiment of the present application, W1 / W2 is greater than or equal to 0.05 to reduce the force on the first active material 112 during flattening, thereby reducing the risk of deformation and powder loss of the first active material 112.

[0177] Alternatively, W1 / W2 may be 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1.

[0178] In some embodiments, along the width direction Y of the unfolded first electrode sheet 11 , the size of the first flattened area 111 c is W4 , and 0.6≤W4 / W1≤0.95.

[0179] Setting W4 / W1 to greater than or equal to 0.6 can increase the pressure area of ​​the first hollow foil region 111b during the flattening process, reduce the axial size of the electrode assembly 1, improve space utilization, and make the first flattened region 111c more compact. Setting W4 / W1 to less than or equal to 0.95 can reduce the force transmitted to the first active material 112 during the flattening process, reducing the risk of the first active material 112 falling off.

[0180] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material, the positive electrode active material is disposed on the positive electrode current collector, and the positive electrode active material includes Li 1+a Ni x1 Co y1 Mn z1 O2 or Li 1+a Ni x2 Co y2 Al z2 At least one of O2. x1 and x2 are both greater than or equal to 0.8, y1 and y2 are both greater than 0, z2 and z3 are both greater than 0, x1+y1+z1=1, x2+y2+z2=1, -0.05≤a≤0.2.

[0181] Illustratively, the first electrode sheet 11 is a positive electrode sheet, the first current collector 111 is a positive electrode current collector, and the first active material 112 is a positive electrode active material.

[0182] In some embodiments, in some embodiments, x1 and x2 are both greater than or equal to 0.9.

[0183] In some embodiments, the positive electrode active material includes LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.91 Co 0.04 Mn 0.05 O2、LiNi 0.92 Co 0.03 Mn 0.05 O2、LiNi 0.93 Co 0.02 Mn 0.05 O2、LiNi 0.94 Co 0.01 Mn 0.05 O2、LiNi 0.95 Co 0.01 Mn 0.04 O2、LiNi 0.8 Co 0.1 Al 0.1 O2、LiNi 0.91 Co 0.04 Al 0.05O2、LiNi 0.92 Co 0.03 Al 0.05 O2、LiNi 0.93 Co 0.02 Al 0.05 O2、LiNi 0.94 Co 0.01 Al 0.05 O2、LiNi 0.95 Co 0.01 Al 0.04 At least one of O2.

[0184] In some embodiments, the positive electrode active material further includes a positive electrode active material, a binder and a conductive agent, and the positive electrode active material includes Li 1+a Ni x1 Co y1 Mn z1 O2 or Li 1+a Ni x2 Co y2 Al z2 At least one of O2.

[0185] In some embodiments, the adhesive includes at least one of polyacrylic acid (PAA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or polyamide (PA).

[0186] In some embodiments, the conductive agent includes at least one of acetylene black, conductive carbon black, carbon nanotubes, carbon fibers, flake graphite, Ketjen black, or graphene.

[0187] In some embodiments, in the positive electrode active material, the mass percentage of the positive electrode active material is 90%-98%, the mass percentage of the binder is 1.25%-5%, and the mass percentage of the conductive agent is 0.75%-5%.

[0188] In an alternative embodiment, the first electrode 11 may also be a negative electrode.

[0189] In some embodiments, the electrode assembly further includes an insulating sheet (not shown), which is attached to the outer periphery of the first flattened area 111 c.

[0190] 11 and 12 , in some embodiments, a first cutout G1 is provided at a corner of an outer end of the first empty foil region 111 b along the winding direction V.

[0191] Exemplarily, the first cutout G1 is located at one end of the first empty foil area 111 b along the length direction X after the first electrode sheet 11 is unfolded.

[0192] After the first empty foil area 111b is flattened to form the first flattened area 111c, an insulating member can be attached to the periphery of the first flattened area 111c; by providing the first incision G1, the risk of the insulating member being punctured due to the sharp corner at the end of the first empty foil area 111b being too large can be reduced, which is beneficial to reducing the use of insulating members and improving energy density.

[0193] In some embodiments, a second cutout G2 is provided at a corner of an inner end of the first empty foil region 111 b along the winding direction V.

[0194] Exemplarily, the first notch G1 and the second notch G2 are respectively located at two ends of the first empty foil area 111 b along the length direction X after the first electrode sheet 11 is unfolded.

[0195] In some embodiments, along the length direction X of the unfolded first pole piece 11 , the size of the first cutout G1 is La. La and W1 satisfy: 0.2≤La / W1≤4.

[0196] Limiting La / W1 to greater than or equal to 0.2 can reduce the accumulation of empty foil material during the flattening process, lowering the risk of puncturing the insulating member covering the first empty foil area 111b, and improving safety. Limiting La / W1 to less than or equal to 4 can reduce the impact of the first cutout G1 on the flow capacity of the first empty foil area 111b.

[0197] Optionally, La / W1 is 0.2, 0.3, 0.5, 0.8, 1.0, 1.5, 1.8, 2, 2.5, 3, 3.5 or 4.

[0198] In some embodiments, 0.5≤La / W1≤2.

[0199] In some embodiments, along the width direction Y of the unfolded first pole piece 11 , the size of the first cutout G1 is W3 , and W3 and W1 satisfy the following: 0.2≤W3 / W1≤1.

[0200] Setting W3 / W1 to greater than or equal to 0.2 can reduce the accumulation of empty foil material during the flattening process, lowering the risk of puncturing the insulating member covering the first empty foil region 111b, thereby improving safety. Setting W3 / W1 to less than or equal to 1 can reduce the risk of the first incision G1 extending into the first main region 111a, thereby reducing the loss of the first active material 112.

[0201] Optionally, W3 / W1 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.

[0202] In some embodiments, the first incision G1 and the second incision G2 have the same shape and size.

[0203] In some embodiments, the first cutout G1 may be formed by chamfering a corner of the first empty foil area 111 b .

[0204] In some embodiments, the first cutout G1 may be a triangular cutout. For example, the triangular cutout may be formed by chamfering the first empty foil region 111 b.

[0205] 13 , in some embodiments, the first cutout G1 may be an arc-shaped cutout. For example, the arc-shaped cutout may be formed by rounding the first empty foil region 111 b.

[0206] 14 , in some embodiments, the first cutout G1 may be a rectangular cutout.

[0207] 15 and 16 , in some embodiments, the second electrode 12 includes a second current collector 121 and a second active material 122 disposed on the second current collector 121 .

[0208] For example, the second current collector 121 may have two opposite surfaces in its thickness direction, and the second active material 122 may be disposed on either or both of the two opposite surfaces of the second current collector 121 .

[0209] In some embodiments, the second current collector 121 may be made of metal foil, such as stainless steel foil, copper foil, aluminum foil, nickel foil, etc.

[0210] In some embodiments, the second current collector 121 includes a second main region 121a and a second hollow foil region 121b, and the second active material 122 is disposed in the second main region 121a. The second main region 121a and the second hollow foil region 121b are arranged perpendicular to the winding direction V.

[0211] At least one surface of the second main body region 121 a is coated with the second active material 122 . Both surfaces of the second blank foil region 121 b are not coated with the second active material 122 .

[0212] Part of the second hollow foil region 121b may be provided with other coatings that do not contain active materials, such as an insulating coating. Of course, both surfaces of at least part of the second hollow foil region 121b are exposed, not covered by other coatings. The exposed area of ​​the second hollow foil region 121b can serve as the second tab 10b of the electrode assembly 1, which can conduct current from the electrode assembly 1.

[0213] Exemplarily, the arrangement direction of the second main body region 121 a and the second hollow foil region 121 b is parallel to the width direction Y′ of the second pole piece 12 after it is unfolded.

[0214] In some embodiments, the end of the second hollow foil region 121 b away from the second main body region 121 a is flattened to form a second flattened region.

[0215] After the electrode assembly 1 is wound, the second empty foil area 121b is wound and roughly forms a columnar structure. The external tooling can apply external force to the second empty foil area 121b along the circumference of the columnar structure to cause the second empty foil area 121b to bend and deform, thereby making the two radially adjacent layers of the second empty foil area 121b more compact and forming a second flattened area.

[0216] The second flattened area forms a dense end surface, thereby facilitating connection with other conductive structures, such as welding with the collecting plate 4 or the housing 2 .

[0217] In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material. The negative electrode active material is disposed on the negative electrode current collector, and the negative electrode active material includes at least one of artificial graphite or natural graphite.

[0218] As an example, the second electrode sheet 12 is a negative electrode sheet, and correspondingly, the second current collector 121 is a negative electrode current collector, and the second active material 122 is a negative electrode active material.

[0219] In some embodiments, the negative electrode active material also includes a binder and a conductive agent.

[0220] In some embodiments, the rated capacity of the electrochemical device 1000 is 2500 mAh to 4500 mAh. For example, the rated capacity of the electrochemical device 1000 is 2500 mAh, 2600 mAh, 2700 mAh, 2800 mAh, 2900 mAh, 3000 mAh, 3100 mAh, 3200 mAh, 3300 mAh, 3400 mAh, 3500 mAh, 3600 mAh, 3700 mAh, 3800 mAh, 3900 mAh, 4000 mAh, 4100 mAh, 4200 mAh, 4300 mAh, 4400 mAh, or 4500 mAh.

[0221] In some embodiments, the AC internal resistance of the electrochemical device 1000 is less than 6 milliohms (mΩ).

[0222] In some embodiments, the AC internal resistance of the electrochemical device 1000 is less than 3 milliohms (mΩ).

[0223] The electrochemical device 1000 of the present application has a smaller AC resistance, thereby reducing the heat generated by the electrochemical device 1000 during charging and high-rate discharge, slowing down the decomposition of the electrolyte, reducing gas production, and improving the cycle performance and cycle life of the electrochemical device 1000.

[0224] In some embodiments, the electrochemical device 1000 is a cylindrical battery cell, which has a mature production process, high product yield, and good heat dissipation performance.

[0225] In some embodiments, the diameter of the cylindrical battery cell is 17 mm to 22 mm. Optionally, the diameter of the cylindrical battery cell is 17 mm, 18 mm, 19 mm, 20 mm, 21 mm, or 22 mm.

[0226] In some embodiments, the height of the cylindrical battery cell is 64 mm to 72 mm. Optionally, the height of the cylindrical battery cell is 64 mm, 65 mm, 66 mm, 67 mm, 68 mm, 69 mm, 70 mm, 71 mm, or 72 mm.

[0227] In some embodiments, the cylindrical battery cell is an 18650 battery cell or a 21700 battery cell.

[0228] 17 , the present application further provides a battery pack 3000 , which includes the electrochemical device 1000 provided in any of the aforementioned embodiments.

[0229] In some embodiments, the battery pack 3000 includes one battery module 2000 or multiple battery modules 2000 arranged in parallel, and one battery module 2000 includes multiple electrochemical devices 1000 arranged in series.

[0230] Connecting multiple electrochemical devices 1000 in series can increase the output voltage of the battery pack.

[0231] For example, the number of battery modules 2000 in the battery pack 3000 may be 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0232] The number of electrochemical devices 1000 included in a battery module 2000 may be 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0233] In some embodiments, one battery module 2000 includes five electrochemical devices 1000 or six electrochemical devices 1000 .

[0234] In some embodiments, the number of battery modules 2000 is 2 or 3.

[0235] In some embodiments, the battery pack further includes a box 2100 , and the battery module 2000 is accommodated in the box 2100 .

[0236] 18 , the present application further provides an electric device 4000 , which includes the battery pack 3000 provided in any of the aforementioned embodiments. The battery pack 3000 can provide power for the operation of the electric device 4000 .

[0237] The electrical device 4000 in the embodiments of the present application may be a portable device, a laptop computer, an electric toy, a drone, a power tool, an energy storage system, and the like. Power tools include metal cutting power tools and cleaning tools, such as electric drills, electric wrenches, vacuum cleaners, and robot vacuums. The embodiments of the present application do not impose any particular restrictions on the aforementioned electrical devices.

[0238] In some embodiments, the present application provides an electrochemical device comprising a housing and an electrode assembly housed in the housing.

[0239] The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, and the separator insulates the positive electrode sheet and the negative electrode sheet.

[0240] Example 1

[0241] Fabrication of electrochemical devices.

[0242] <Production of positive electrode sheet>

[0243] Lithium nickel cobalt manganese oxide Ni91 (LiNi 0.91 Co 0.04 Mn 0.05 O2), polyvinylidene fluoride (PVDF, weight average molecular weight 7×10 6 ), conductive carbon black were mixed in a mass ratio of 95.8:2.8:1.4, N-methylpyrrolidone (NMP) was added as a solvent, and stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 75wt% and a uniform system. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 13μm, and dried at 90°C to obtain a positive electrode sheet with a single-sided coating of positive electrode active material (the unit area coating weight of the positive electrode active material on one side of the positive electrode sheet is 217mg / 1540.25mm 2 ). Then, repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with positive electrode active material coated on both sides. Then, cold press and cut the sheet to obtain a positive electrode sheet for use.

[0244] For example, referring to Figures 8 and 9 , the positive electrode sheet adopts a structure similar to the first electrode sheet. Specifically, L1 = L2 = 1.36m, W2 is 63.2mm, W1 is 4mm, and W4 is 3.2mm.

[0245] <Preparation of negative electrode sheet>

[0246] Artificial graphite, conductive carbon black, styrene-butadiene rubber (SBR, weight average molecular weight 5×10 6) were mixed in a mass ratio of 97.4:1.4:1.2, and then deionized water was added as a solvent and stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry with a solid content of 51wt% and a uniform system. The negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 8mm and dried at 90°C to obtain a negative electrode sheet with a single-sided coating of a negative electrode active material layer (the unit area coating weight of the negative electrode active material on one side of the negative electrode sheet was 113mg / 1540.25mm 2 ). Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. Then, the negative electrode sheet is cold pressed and cut into pieces for use.

[0247] For example, referring to Figures 8 and 9 , the negative electrode plate adopts a structure similar to the first electrode plate. Specifically, L1 = L2 = 1.464 mm, W2 is 64.1 mm, W1 is 4 mm, and W4 is 3.2 mm.

[0248] <Preparation of Separator>

[0249] An aluminum oxide coating is provided on one surface of a base film to prepare a diaphragm, wherein the base film is a polyethylene base film with a thickness of 9 μm and the aluminum oxide coating has a thickness of 2 μm.

[0250] <Preparation of Electrolyte>

[0251] In an environment with a water content of less than 10 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 70:30 to obtain a non-aqueous organic solvent. Lithium hexafluorophosphate (LiPF6) and an additive, fluoroethylene carbonate (FEC), are then added to the non-aqueous organic solvent, dissolved, and mixed uniformly to obtain an electrolyte. The electrolyte comprises 15% by mass of LiPF6, 1% by mass of fluoroethylene carbonate, and the remainder is the non-aqueous organic solvent.

[0252] <Preparation of Electrochemical Device>

[0253] The negative electrode sheet, separator, and positive electrode sheet prepared above are stacked and wound in sequence to form an electrode assembly with a wound structure. The electrode assembly is then installed in an aluminum shell and undergoes a series of processes including rolling, liquid injection, formation, degassing, and shaping to form an electrochemical device. The electrochemical device is a 21700 lithium-ion cell with a diameter of 21mm. The formation process is as follows: at 25°C, the electrochemical device is charged at a constant current of 0.02C to 3.3V, and then at a constant current of 0.1C to 3.6V.

[0254] According to the above method, an electrochemical device was prepared.

[0255] Electrochemical device testing

[0256] The electrochemical device was tested according to the following steps. The test process was carried out using a battery tester (Neware CT-4016-5V-100A).

[0257] Rated capacity test:

[0258] The electrochemical device was placed in a thermostat (Keming EH-1000) at 25°C for 1 hour. At a constant temperature of 25°C, the electrochemical device was discharged at a constant current of 0.5C to the discharge cut-off voltage (2.5V) of the electrochemical device. Then, the device was charged at a constant current of 0.5C to the charge cut-off voltage (4.2V) of the electrochemical device. Then, the device was charged at a constant voltage of the charge cut-off voltage to 0.05C, at which point the electrochemical device was at 100% SOC. The electrochemical device at 100% SOC was discharged at a constant current of 0.2C to the discharge cut-off voltage (2.5V) of the electrochemical device, and the discharge capacity was tested, which was the rated capacity of the electrochemical device.

[0259] AC internal resistance test:

[0260] The electrochemical device tested for rated capacity was charged at 0.5C constant current to the charge cut-off voltage of the electrochemical device at 25°C, and then charged at the charge cut-off voltage to 0.05C constant voltage, at which time the electrochemical device was at 100% SOC;

[0261] The electrochemical device at 100% SOC was allowed to stand at 25° C. for 1 hour, and then discharged at a constant current of 0.2 C to 30% SOC of the electrochemical device. The internal resistance tester (HIOKI BT3563) was set to 1 kHz for testing to obtain the AC internal resistance value.

[0262] Cycle test:

[0263] i) the electrochemical device 1000 performs a first discharge operation: after the electrochemical device 1000 is allowed to stand at a first temperature for a first time, a discharge operation is performed at a first discharge rate until the voltage of the electrochemical device 1000 reaches a discharge cutoff voltage. The electrochemical device 1000 then terminates the first discharge operation and stands for a second time;

[0264] ii) the electrochemical device 1000 performs a charging operation: after the electrochemical device 1000 is allowed to stand at the second temperature for a third time, a charging operation is performed at the first charge rate until the voltage of the electrochemical device 1000 reaches the charge cutoff voltage. The electrochemical device 1000 continues to perform the charging operation at the charge cutoff voltage, and the charging operation is terminated after 24 hours.

[0265] iii) the electrochemical device 1000 performs a second discharge operation: after the electrochemical device 1000 is allowed to stand at the third temperature for a fourth time, the electrochemical device 1000 performs a discharge operation at the third temperature at a second discharge rate until the voltage of the electrochemical device 1000 reaches a discharge cutoff voltage, thereby ending the second discharge operation;

[0266] iv) The electrochemical device 1000 repeatedly performs the ii-th operation and the iii-th operation until the current cut-off device 5 cuts off the connection between the electrode terminal 3 and the electrode assembly 1; when the current cut-off device 5 cuts off the connection between the electrode terminal 3 and the electrode assembly 1, the number of cycles m of repeatedly performing the ii-th operation and the iii-th operation is recorded.

[0267] Among them, the first discharge rate is 0.2C, the first charge rate is 2C, and the second discharge rate is 8C; the first temperature is 25°C, the second temperature is 55°C, and the third temperature is 25°C; the first time is 2 hours, the second time is 2 hours, the third time is 2 hours, and the fourth time is 2 hours.

[0268] Example 2:

[0269] The method for manufacturing the electrochemical device of Example 2 is the same as the method for manufacturing the electrochemical device of Example 1.

[0270] The electrochemical device testing method of Example 2 differs from the electrochemical device testing method of Example 1 in that the first discharge rate is 0.5C.

[0271] Example 3:

[0272] The method for manufacturing the electrochemical device of Example 3 is the same as the method for manufacturing the electrochemical device of Example 1.

[0273] The electrochemical device testing method of Example 3 differs from the electrochemical device testing method of Example 1 in that the first charging rate is 2.5C.

[0274] Embodiment 4:

[0275] The method for manufacturing the electrochemical device of Example 4 is the same as the method for manufacturing the electrochemical device of Example 1.

[0276] The electrochemical device testing method of Example 4 differs from the electrochemical device testing method of Example 1 in that the first charging rate is 3C.

[0277] Example 5:

[0278] The method for manufacturing the electrochemical device of Example 5 is the same as the method for manufacturing the electrochemical device of Example 1.

[0279] The electrochemical device testing method of Example 5 differs from the electrochemical device testing method of Example 1 in that the second discharge rate is 9C.

[0280] Example 6:

[0281] The method for manufacturing the electrochemical device of Example 6 is the same as the method for manufacturing the electrochemical device of Example 1.

[0282] The electrochemical device testing method of Example 6 differs from the electrochemical device testing method of Example 1 in that the second discharge rate is 10C.

[0283] Example 7:

[0284] The method for manufacturing the electrochemical device of Example 7 is the same as the method for manufacturing the electrochemical device of Example 1.

[0285] The electrochemical device testing method of Example 7 differs from the electrochemical device testing method of Example 1 in that the second temperature is 60°C.

[0286] Example 8:

[0287] The method for manufacturing the electrochemical device of Example 8 is the same as the method for manufacturing the electrochemical device of Example 1.

[0288] The electrochemical device testing method of Example 8 differs from the electrochemical device testing method of Example 1 in that the second temperature is 60° C. and the second discharge rate is 10C.

[0289] Example 9:

[0290] The method for manufacturing the electrochemical device of Example 9 is the same as the method for manufacturing the electrochemical device of Example 1.

[0291] The electrochemical device testing method of Example 9 differs from the electrochemical device testing method of Example 1 in that the first time, the second time, the third time, and the fourth time are all one hour.

[0292] Embodiment 10:

[0293] The method for manufacturing the electrochemical device of Example 10 is the same as the method for manufacturing the electrochemical device of Example 1.

[0294] The electrochemical device testing method of Example 10 differs from the electrochemical device testing method of Example 1 in that both the first temperature and the third temperature are 15°C.

[0295] Example 11:

[0296] The method for manufacturing the electrochemical device of Example 11 is the same as the method for manufacturing the electrochemical device of Example 1.

[0297] The electrochemical device testing method of Example 11 differs from the electrochemical device testing method of Example 1 in that both the first temperature and the third temperature are 30°C.

[0298] Example 12:

[0299] Fabrication of electrochemical devices

[0300] <Production of positive electrode sheet>

[0301] The difference from Example 1 is that the positive electrode sheet adopts the structure of the first electrode sheet shown in Figures 11 and 12. Specifically, referring to Figures 11 and 12, L1 = L2 = 1.36m, W2 is 63.2mm, W1 is 4mm, and W4 is 3.2mm. The first empty foil area of ​​the positive electrode sheet is provided with identical triangular cutouts at both the outer and inner corners along the winding direction, where La = W1 = 4mm, W3 = 0.5, and W1 = 2mm.

[0302] <Preparation of negative electrode sheet>

[0303] The difference from Example 1 is that the negative electrode sheet adopts the structure of the first electrode sheet shown in Figures 11 and 12. Referring to Figures 11 and 12, L1 = L2 = 1.464m, W2 is 64.1mm, W1 is 4mm, and W4 is 3.2mm. The first empty foil area of ​​the negative electrode sheet is provided with identical triangular cutouts at both the outer and inner corners along the winding direction, where La = W1 = 4mm, W3 = 0.5, and W1 = 2mm. The cutouts of the negative electrode sheet are identical in shape and size to those of the positive electrode sheet.

[0304] <Preparation of Separator>

[0305] Same as Example 1.

[0306] <Preparation of Electrolyte>

[0307] Same as Example 1.

[0308] <Preparation of Electrochemical Device>

[0309] Same as Example 1.

[0310] According to the above method, an electrochemical device was prepared.

[0311] The electrochemical device testing method of Example 12 is the same as the electrochemical device testing method of Example 1.

[0312] Example 13:

[0313] The difference between the manufacturing method of the electrochemical device of Example 13 and the manufacturing method of the electrochemical device of Example 1 is that the positive electrode active material of the positive electrode sheet of Example 13 is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0314] The electrochemical device testing method of Example 13 is the same as the electrochemical device testing method of Example 1.

[0315] Example 14:

[0316] The difference between the manufacturing method of the electrochemical device of Example 14 and the manufacturing method of the electrochemical device of Example 1 is that the positive electrode active material of the positive electrode sheet of Example 14 is LiNi 0.95 Co 0.01 Mn 0.04 O2.

[0317] The electrochemical device testing method of Example 14 is the same as the electrochemical device testing method of Example 1.

[0318] Comparative Example 1:

[0319] INR21700-40T (21700 battery cell);

[0320] The testing method of Comparative Example 1 is the same as the testing method of the electrochemical device of Example 1.

[0321] Comparative Example 2:

[0322] INR21700-40T (21700 battery cell);

[0323] The difference between the test method of Comparative Example 1 and the electrochemical device test method of Example 1 is that the second temperature is 60°C.

[0324] Example 15:

[0325] <Production of positive electrode sheet>

[0326] Lithium nickel cobalt manganese oxide Ni91 (LiNi 0.91 Co 0.04 Mn 0.05 O2), polyvinylidene fluoride (PVDF, weight average molecular weight 7×10 6), conductive carbon black according to the mass ratio of 96:2:2, N-methylpyrrolidone (NMP) was added as a solvent, and stirred evenly under the action of a vacuum mixer to obtain a positive electrode slurry with a solid content of 75wt% and a uniform system. The positive electrode slurry was evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12μm, and dried at 90°C to obtain a positive electrode sheet with a single-sided coating of positive electrode active material (the unit area coating weight of the positive electrode active material on one side of the positive electrode sheet is 198mg / 1540.25mm 2 ). Then, repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with positive electrode active material coated on both sides. Then, cold press and cut the sheet to obtain a positive electrode sheet for use.

[0327] For example, referring to Figures 8 and 9 , the positive electrode sheet adopts a structure similar to the first electrode sheet. Specifically, L1 = L2 = 0.92 mm, W2 is 59 mm, W1 is 4 mm, and W4 is 3.2 mm.

[0328] <Preparation of negative electrode sheet>

[0329] Artificial graphite, conductive carbon black, styrene-butadiene rubber (SBR, weight average molecular weight 5×10 6 ) were mixed in a mass ratio of 97.5:1.3:1.2, and then deionized water was added as a solvent and stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry with a solid content of 51wt% and a uniform system. The negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 8mm and dried at 90°C to obtain a negative electrode sheet with a single-sided coating of a negative electrode active material layer (the coating weight per unit area of ​​the negative electrode active material on one side of the negative electrode sheet was 103mg / 1540.25mm 2 ). Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. Then, the negative electrode sheet is cold pressed and cut into pieces for use.

[0330] For example, referring to Figures 8 and 9 , the negative electrode sheet adopts a structure similar to the first electrode sheet. Specifically, L1 = L2 = 1.02m, W2 is 60.2mm, W1 is 4mm, and W4 is 3.2mm.

[0331] <Preparation of Separator>

[0332] An aluminum oxide coating is provided on one surface of a base film to prepare a diaphragm, wherein the base film is a polyethylene base film with a thickness of 8 μm and the aluminum oxide coating has a thickness of 2 μm.

[0333] <Preparation of Electrolyte>

[0334] In an environment with a water content of less than 10 ppm, ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of 70:30 to obtain a non-aqueous organic solvent. Lithium hexafluorophosphate (LiPF6) and an additive, fluoroethylene carbonate (FEC), are then added to the non-aqueous organic solvent, dissolved, and mixed uniformly to obtain an electrolyte. The electrolyte comprises 15% by mass of LiPF6, 1% by mass of fluoroethylene carbonate, and the remainder is the non-aqueous organic solvent.

[0335] <Preparation of Electrochemical Device>

[0336] The negative electrode sheet, separator, and positive electrode sheet prepared above are stacked and wound in sequence to form an electrode assembly with a wound structure. The electrode assembly is then installed in an aluminum shell and undergoes a series of processes including rolling, liquid injection, formation, degassing, and shaping to form an electrochemical device. The electrochemical device is an 18650 lithium-ion cell with an 18mm diameter. The formation process is as follows: at 25°C, the electrochemical device is charged at a constant current of 0.02C to 3.3V, and then at a constant current of 0.1C to 3.6V.

[0337] According to the above method, an electrochemical device was prepared.

[0338] Electrochemical device testing

[0339] The electrochemical device was tested according to the following steps. The test process was carried out using a battery tester (Neware Electronics Co. Ltd, China).

[0340] Rated capacity test:

[0341] The electrochemical device was placed in a thermostat (Keming EH-1000) at 25°C for 1 hour. At a constant temperature of 25°C, the electrochemical device was discharged at a constant current of 0.5C to the discharge cut-off voltage (2.5V) of the electrochemical device. Then, the device was charged at a constant current of 0.5C to the charge cut-off voltage (4.2V) of the electrochemical device. Then, the device was charged at a constant voltage of the charge cut-off voltage to 0.05C, at which point the electrochemical device was at 100% SOC. The electrochemical device at 100% SOC was discharged at a constant current of 0.2C to the discharge cut-off voltage (2.5V) of the electrochemical device, and the discharge capacity was tested, which was the rated capacity of the electrochemical device.

[0342] AC internal resistance test:

[0343] The electrochemical device tested for rated capacity was charged at 0.5C constant current to the charge cut-off voltage of the electrochemical device at 25°C, and then charged at the charge cut-off voltage to 0.05C constant voltage, at which time the electrochemical device was at 100% SOC;

[0344] The electrochemical device at 100% SOC was allowed to stand at 25° C. for 1 hour, and then discharged at a constant current of 0.2 C to 30% SOC of the electrochemical device. The internal resistance tester (HIOKI BT3563) was set to 1 kHz for testing to obtain the AC internal resistance value.

[0345] Cycle test:

[0346] i) the electrochemical device 1000 performs a first discharge operation: after the electrochemical device 1000 is allowed to stand at a first temperature for a first time, a discharge operation is performed at a first discharge rate until the voltage of the electrochemical device 1000 reaches a discharge cutoff voltage. The electrochemical device 1000 then terminates the first discharge operation and stands for a second time;

[0347] ii) the electrochemical device 1000 performs a charging operation: after the electrochemical device 1000 is allowed to stand at the second temperature for a third time, a charging operation is performed at the first charge rate until the voltage of the electrochemical device 1000 reaches the charge cutoff voltage. The electrochemical device 1000 continues to perform the charging operation at the charge cutoff voltage, and the charging operation is terminated after 24 hours.

[0348] iii) the electrochemical device 1000 performs a second discharge operation: after the electrochemical device 1000 is allowed to stand at the third temperature for a fourth time, the electrochemical device 1000 performs a discharge operation at the third temperature at a second discharge rate until the voltage of the electrochemical device 1000 reaches a discharge cutoff voltage, thereby ending the second discharge operation;

[0349] iv) The electrochemical device 1000 repeatedly performs the ii-th operation and the iii-th operation until the current cut-off device 5 cuts off the connection between the electrode terminal 3 and the electrode assembly 1; when the current cut-off device 5 cuts off the connection between the electrode terminal 3 and the electrode assembly 1, the number of cycles m of repeatedly performing the ii-th operation and the iii-th operation is recorded.

[0350] Among them, the first discharge rate is 0.2C, the first charge rate is 2C, and the second discharge rate is 8C; the first temperature is 25°C, the second temperature is 55°C, and the third temperature is 25°C; the first time is 2 hours, the second time is 2 hours, the third time is 2 hours, and the fourth time is 2 hours.

[0351] Example 16:

[0352] The method for manufacturing the electrochemical device of Example 16 is the same as the method for manufacturing the electrochemical device of Example 15.

[0353] The electrochemical device testing method of Example 16 differs from the electrochemical device testing method of Example 15 in that the first discharge rate is 0.5C.

[0354] Example 17:

[0355] The method for manufacturing the electrochemical device of Example 17 is the same as the method for manufacturing the electrochemical device of Example 15.

[0356] The electrochemical device testing method of Example 17 differs from the electrochemical device testing method of Example 15 in that the first charging rate is 2.5C.

[0357] Example 18:

[0358] The method for manufacturing the electrochemical device of Example 18 is the same as the method for manufacturing the electrochemical device of Example 15.

[0359] The electrochemical device testing method of Example 18 differs from the electrochemical device testing method of Example 15 in that the first charging rate is 3C.

[0360] Example 19:

[0361] The method for manufacturing the electrochemical device of Example 19 is the same as the method for manufacturing the electrochemical device of Example 15.

[0362] The electrochemical device testing method of Example 19 differs from the electrochemical device testing method of Example 15 in that the second discharge rate is 9C.

[0363] Example 20:

[0364] The method for manufacturing the electrochemical device of Example 20 is the same as the method for manufacturing the electrochemical device of Example 15.

[0365] The electrochemical device testing method of Example 20 differs from the electrochemical device testing method of Example 15 in that the second discharge rate is 10C.

[0366] Example 21:

[0367] The method for manufacturing the electrochemical device of Example 21 is the same as the method for manufacturing the electrochemical device of Example 15.

[0368] The electrochemical device testing method of Example 21 differs from the electrochemical device testing method of Example 15 in that: the second temperature is 60°C.

[0369] Example 22:

[0370] The method for manufacturing the electrochemical device of Example 22 is the same as the method for manufacturing the electrochemical device of Example 15.

[0371] The electrochemical device testing method of Example 22 differs from the electrochemical device testing method of Example 15 in that: the second temperature is 60° C., and the second discharge rate is 10C.

[0372] Example 23:

[0373] The method for manufacturing the electrochemical device of Example 23 is the same as the method for manufacturing the electrochemical device of Example 15.

[0374] The electrochemical device testing method of Example 23 differs from the electrochemical device testing method of Example 15 in that the first time, the second time, the third time, and the fourth time are all one hour.

[0375] Example 24:

[0376] The method for manufacturing the electrochemical device of Example 24 is the same as the method for manufacturing the electrochemical device of Example 15.

[0377] The electrochemical device testing method of Example 24 differs from the electrochemical device testing method of Example 15 in that both the first temperature and the third temperature are 15°C.

[0378] Example 25:

[0379] The method for manufacturing the electrochemical device of Example 25 is the same as the method for manufacturing the electrochemical device of Example 15.

[0380] The electrochemical device testing method of Example 25 differs from the electrochemical device testing method of Example 15 in that the first temperature and the third temperature are both 30°C.

[0381] Example 26:

[0382] Fabrication of electrochemical devices

[0383] <Production of positive electrode sheet>

[0384] The difference from Example 15 is that the positive electrode sheet adopts the structure of the first electrode sheet shown in Figures 11 and 12. Specifically, referring to Figures 11 and 12, L1 = L2 = 0.92m, W2 is 59mm, W1 is 4mm, and W4 is 3.2mm. The first empty foil area of ​​the positive electrode sheet is provided with identical triangular cutouts at both the outer and inner corners along the winding direction, where La = W1 = 4mm, W3 = 0.5mm, and W1 = 2mm.

[0385] <Preparation of negative electrode sheet>

[0386] The difference from Example 15 is that the negative electrode sheet adopts the structure of the first electrode sheet shown in Figures 11 and 12. Referring to Figures 11 and 12, L1 = L2 = 1.02m, W2 is 60.2mm, W1 is 4mm, and W4 is 3.2mm. The outer and inner corners of the second hollow foil area of ​​the negative electrode sheet along the winding direction are both provided with identical triangular cutouts, where La = W1 = 4mm, W3 = 0.5, and W1 = 2mm. The cutouts of the negative electrode sheet are the same shape and size as those of the positive electrode sheet.

[0387] <Preparation of Separator>

[0388] Same as Example 1.

[0389] <Preparation of Electrolyte>

[0390] Same as Example 1.

[0391] <Preparation of Electrochemical Device>

[0392] Same as Example 1.

[0393] According to the above method, an electrochemical device was prepared.

[0394] The electrochemical device testing method of Example 26 is the same as the electrochemical device testing method of Example 15.

[0395] Example 27:

[0396] The difference between the manufacturing method of the electrochemical device of Example 27 and the manufacturing method of the electrochemical device of Example 15 is that the positive electrode active material of the positive electrode sheet of Example 27 is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0397] The electrochemical device testing method of Example 27 is the same as the electrochemical device testing method of Example 15.

[0398] Example 28:

[0399] The difference between the manufacturing method of the electrochemical device of Example 28 and the manufacturing method of the electrochemical device of Example 15 is that the positive electrode active material of the positive electrode sheet of Example 28 is LiNi 0.95 Co 0.01 Mn 0.04 O2.

[0400] The electrochemical device testing method of Example 28 is the same as the electrochemical device testing method of Example 15.

[0401] Comparative Example 3:

[0402] INR18650-25R, (18650 battery cell);

[0403] The testing method of Comparative Example 3 is the same as the testing method of the electrochemical device of Example 15.

[0404] Comparative Example 4:

[0405] INR18650-25R, (18650 battery cell);

[0406] The difference between the test method of Comparative Example 4 and the electrochemical device test method of Example 15 is that the second temperature is 60°C.

[0407] The test conditions and test results of Examples 1-28 and Comparative Examples 1-4 are shown in Table 1.

[0408] Referring to Table 1, compared with the battery cells of Comparative Examples 1-4, the electrochemical devices of Examples 1-28 can repeatedly perform the second operation and the third operation more times, can also withstand harsh charge and discharge scenarios, and have better cycle performance and cycle life.

[0409] The electrochemical devices of Examples 1-28 can repeatedly perform the ii-th operation and the iii-th operation for more than 60 cycles, and have good cycle performance and cycle life.

[0410] The electrochemical devices of Examples 1-28 have a smaller AC resistance, thereby reducing the heat generated by the electrochemical devices during charging and high-rate discharge, slowing down the decomposition of the electrolyte, reducing gas production, and improving the cycle performance and cycle life of the electrochemical devices.

[0411] With reference to Examples 1, 3, 4 or Examples 15, 17, and 18, when the electrochemical device is charged for a long time in a high-temperature environment, reducing the charge rate can delay gas production and improve the cycle performance and cycle life of the electrochemical device.

[0412] With reference to Examples 1, 10, 11 or Examples 15, 24, 25, when the electrochemical device is discharged at a high rate, lowering the external ambient temperature can accelerate the heat dissipation of the electrochemical device, reduce the heat dissipation of the electrochemical device, reduce gas production, and delay the activation of the current cut-off device.

[0413] With reference to Examples 1 and 9 or Examples 15 and 23, the electrochemical device is left to stand in an environment for more than 1 hour, and the temperature inside and outside the electrochemical device is substantially consistent with the temperature of the environment.

[0414] With reference to Examples 13 and 14, reducing the nickel content in the positive electrode material can reduce gas generation during charging of the electrochemical device in a high-temperature environment and during high-rate discharge.

Claims

1. An electrochemical device, comprising a housing, an electrode terminal, an electrode assembly, a current cut-off device, and an electrolyte; The electrode terminal is disposed on the housing, the electrode assembly and the electrolyte are accommodated in the housing, and the current cut-off device is connected to the electrode terminal and the electrode assembly; The electrolyte comprises lithium hexafluorophosphate and fluoroethylene carbonate; The electrochemical device is configured to: i) The electrochemical device performs a first discharge operation: after the electrochemical device stands at a first temperature for a first time, it performs a discharge operation at a first discharge rate until the voltage of the electrochemical device reaches a discharge cut-off voltage, and the electrochemical device ends the first discharge operation and stands for a second time; ii) The electrochemical device performs a charging operation: after the electrochemical device stands at a second temperature for a third time, it performs a charging operation at a first charging rate until the voltage of the electrochemical device reaches a charging cut-off voltage, and the electrochemical device continues to perform the charging operation at the charging cut-off voltage, and the charging operation ends after 24 hours; iii) The electrochemical device performs a second discharge operation: after the electrochemical device stands at a third temperature for a fourth time, the electrochemical device performs a discharge operation at a second discharge rate at the third temperature until the voltage of the electrochemical device reaches the discharge cut-off voltage, and the electrochemical device ends the second discharge operation; iv) The electrochemical device repeats the operations of ii) and iii) for (m - 1) times; In response to the electrochemical device performing the operations of i) to iv), the current cut-off device cuts off the connection between the electrode terminal and the electrode assembly; Wherein, the first discharge rate is 0.2C - 0.5C, the first charging rate is 2C - 3C, and the second discharge rate is 8C to 10C; The first temperature is 15°C - 30°C, the second temperature is 55°C - 60°C, and the third temperature is 15°C - 30°C; The first time is 1 hour - 2 hours, the second time is 1 hour - 2 hours, the third time is 1 hour - 2 hours, and the fourth time is 1 hour - 2 hours; m≥50。 2. The electrochemical device according to claim 1, wherein, m≥55。 3. The electrochemical device according to claim 2, wherein, m≥60。 4. The electrochemical device according to claim 3, wherein, m≥65。 5. The electrochemical device according to claim 4, wherein, 70≤m≤90。 6. The electrochemical device according to any one of claims 1-5, wherein, The first temperature is 25°C, and / or the third temperature is 25°C.

7. The electrochemical device according to any one of claims 1-6, wherein, Based on the mass of the electrolyte, the mass percentage content of lithium hexafluorophosphate is 12% - 16%, and the mass percentage content of fluoroethylene carbonate is 0.8% - 1.5%.

8. The electrochemical device according to any one of claims 1 - 7, comprising a current collector plate connected to the electrode assembly; The current cut-off device comprises a connecting plate and a flipping piece connected to each other. The connecting plate is provided with a through hole and comprises a first surface and a second surface arranged oppositely. The first surface of the connecting plate is connected to the current collector plate, the second surface of the connecting plate is connected to the flipping piece, and the flipping piece is connected to the electrode terminal; The flipping piece is configured to be able to flip relative to the connecting plate so as to disconnect the electrode terminal from the electrode assembly.

9. The electrochemical device according to any one of claims 1-8, wherein, the electrode assembly includes a first electrode tab, a second electrode tab and a separator, the first electrode tab, the separator and the second electrode tab are laminated and wound along the winding direction, and one of the first electrode tab and the second electrode tab is a positive electrode tab and the other is a negative electrode tab; the first electrode tab includes a first current collector and a first active material, the first current collector includes a first main region and a first empty foil region, the first active material is disposed in the first main region, and the arrangement direction of the first main region and the first empty foil region is perpendicular to the winding direction; the first empty foil region includes a first flattened region, the first flattened region is away from the first main region and connected to the current cut-off device.

10. The electrochemical device according to claim 9, wherein, Along the width direction of the first electrode tab after unfolding, the size of the first empty foil region is W1, the size of the first current collector is W2, and W1 and W2 satisfy: 0.05≤W1 / W2≤0.

1.

11. The electrochemical device according to claim 10, wherein, Along the width direction of the first electrode tab after unfolding, the size of the first flattened region is W4, and 0.6≤W4 / W1≤0.

95.

12. The electrochemical device according to claim 10 or 11, wherein, A first cut is provided at the corner of the outer end of the first empty foil region along the winding direction; Along the length direction of the first electrode tab after unfolding, the size of the first cut is La; wherein, La and W1 satisfy: 0.2≤La / W1≤4.

13. The electrochemical device according to claim 12, wherein, Along the width direction of the first electrode tab after unfolding, the size of the first cut is W3; W3 and W1 satisfy: 0.2≤W3 / W1≤1.

14. The electrochemical device according to any one of claims 9-13, wherein, The positive electrode plate includes a positive current collector and a positive active material, the positive active material is disposed on the positive current collector, and the positive active material includes Li 1+a Ni x1 Co y1 Mn z1 O2 or Li 1+a Ni x2 Co y2 Al z2 at least one of O2; wherein, both x1 and x2 are greater than or equal to 0.8, both y1 and y2 are greater than 0, both z2 and z3 are greater than 0, x1 + y1 + z1 = 1, x2 + y2 + z2 = 1, and -0.05≤a≤0.

2.

15. The electrochemical device according to claim 14, wherein, Both x1 and x2 are greater than or equal to 0.

9.

16. The electrochemical device according to any one of claims 9-15, wherein, the negative electrode tab includes a negative current collector and a negative active material, the negative active material is disposed on the negative current collector, and the negative active material includes at least one of artificial graphite and natural graphite.

17. The electrochemical device according to any one of claims 1-16, wherein, The rated capacity of the electrochemical device is 2500 mAh - 4500 mAh.

18. The electrochemical device according to any one of claims 1-17, wherein, The AC internal resistance of the electrochemical device is less than 6 mΩ.

19. The electrochemical device according to any one of claims 1-18, wherein, The electrochemical device is a cylindrical battery cell; wherein, the diameter of the cylindrical battery cell is 17 mm - 22 mm, and the height of the cylindrical battery cell is 64 mm - 72 mm.

20. The electrochemical device according to claim 19, wherein, The cylindrical battery cell is a 18650 type battery cell or a 21700 type battery cell.

21. A battery pack, comprising the electrochemical device according to any one of claims 1-20.

22. The battery pack according to claim 21, comprising one battery module or a plurality of the battery modules arranged in parallel, and one battery module includes a plurality of the electrochemical devices arranged in series.

23. An electrical equipment, comprising the battery pack according to claim 21 or 22.

Images