Electrochemical apparatus, battery pack and electrical device

Abstract

Disclosed in the present application are an electrochemical apparatus, a battery pack and an electrical device. The electrochemical apparatus comprises a housing and an electrode assembly accommodated in the housing. The electrode assembly comprises a first electrode sheet, a second electrode sheet and a separator, wherein the first electrode sheet, the separator and the second electrode sheet are laminated and are wound in a winding direction, and one of the first electrode sheet and the second electrode sheet is a positive electrode sheet, and the other one is a negative electrode sheet. The first electrode sheet comprises a first current collector and a first active substance provided on the first current collector, the first current collector comprising a first main body region and a first blank foil region, the first active substance being provided in the first main body region, and the arrangement direction of the first main body region and the first blank foil region being perpendicular to the winding direction. The first blank foil region comprises a first rolled flat region, the first rolled flat region being far away from the first main body region. The electrochemical apparatus is provided with the first rolled flat region, so that the current-carrying capability can be increased, and the energy loss is reduced when the electrochemical apparatus discharges at a high rate of 15C-20C, thus allowing the electrochemical apparatus to have a higher discharge capacity.

Description

Electrochemical devices, battery packs, and electrical equipment

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202311828023.7, filed on December 27, 2023, entitled “Electrochemical device, battery pack, and electrical equipment,” 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 discharge performance 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 an electrical device, which can improve discharge performance.

[0006] In a first aspect, an embodiment of the present application provides an electrochemical device comprising a housing and an electrode assembly housed within the housing. The electrode assembly comprises a first electrode sheet, a second electrode sheet, and a diaphragm, wherein the first electrode sheet, the diaphragm, and the second electrode sheet are stacked and wound along a winding direction, wherein 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 comprises a first current collector and a first active material disposed on the first current collector, wherein the first current collector comprises a first main body region and a first hollow foil region, wherein the first active material is disposed in the first main body region, and the arrangement direction of the first main body region and the first hollow foil region is perpendicular to the winding direction. The first hollow foil region comprises a first flattened region, which is away from the first main body region.

[0007] The electrochemical device is configured as follows:

[0008] In response to the electrochemical device having a 100% SOC, performing a discharge operation at a first discharge rate at a first ambient temperature, continuing the discharge operation until the SOC of the electrochemical device reaches 0%, and a ratio of a discharge capacity of the electrochemical device to a rated capacity of the electrochemical device is greater than or equal to 90%;

[0009] The first ambient temperature is 22° C.-28° C., and the first discharge rate is in the range of 15° C.-20° C.

[0010] By setting the first flattening zone, the electrochemical device can increase the overcurrent capacity, the electrochemical device has a small resistance, and when discharged at a high rate of 15C-20C, the temperature rise of the electrochemical device is low, which is beneficial to reducing energy loss, thereby enabling the electrochemical device to have a higher discharge capacity, provide more electrical energy for electrical equipment, and improve the discharge performance of the electrochemical device.

[0011] In one or more of the above optional embodiments, the ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 95%. The electrochemical device can have a higher discharge capacity when discharged at a high rate of 15C-20C, providing more electrical energy to electrical equipment.

[0012] In one or more of the above optional embodiments, the ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 98%. The electrochemical device can have a higher discharge capacity when discharged at a high rate of 15C-20C, providing more electrical energy to electrical equipment.

[0013] In one or more of the above optional embodiments, the first discharge rate is within the range of 17.5C-20C. When discharging at a high rate of 17.5C-20C, the ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 99%, thereby providing more electrical energy for electrical equipment.

[0014] In one or more of the above optional embodiments, the first ambient temperature is 25°C.

[0015] In one or more optional embodiments above, along the width direction of the unfolded first pole piece, the size of the first empty foil area is W1, the total size of the first current collector is W2, and W1 and W2 satisfy: 0.05≤W1 / W2≤0.1.

[0016] 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. This also reduces the stress on the first active material during flattening, lowering the risk of deformation and powder loss. Setting W1 / W2 to less than or equal to 0.1 allows more space for the first active material, reducing energy density loss.

[0017] 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.

[0018] Setting W4 / W1 to greater than or equal to 0.6 can increase the pressure area of ​​the first empty foil area during the flattening process, reduce the axial size of the electrode assembly, improve space utilization, and make the first flattened area more compact. Setting W4 / W1 to less than or equal to 0.95 can reduce the force transmitted to the first active material during the flattening process, reducing the risk of the first active material falling off.

[0019] In one or more optional embodiments above, a first cutout is provided at a corner of an outer end of the first empty foil region along the winding direction; along the length direction of the unfolded first electrode sheet, the size of the first cutout is La. La and W1 satisfy: 0.2≤La / W1≤4.

[0020] 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, and improving safety. Limiting La / W1 to less than or equal to 4 can reduce the impact of the first cut on the flow capacity of the first empty foil area.

[0021] 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.

[0022] 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 area, thereby improving safety. Setting W3 / W1 to less than or equal to 1 can reduce the risk of the first incision extending into the first main body area, thereby minimizing loss of the first active material.

[0023] In one or more optional embodiments above, along the length direction of the unfolded first electrode sheet, the size of the first empty foil area is L1, the size of the first main body area is L2, and L1 and L2 satisfy: 0.8≤L1 / L2≤1.

[0024] The first empty foil area has a large flow area. When the electrochemical device discharges at a high rate, a large current can pass through the first empty foil area, thereby reducing heat generation in the first empty foil area and reducing the risk of the first empty foil area fusing.

[0025] In one or more optional embodiments above, the electrochemical device further comprises an insulating member, which surrounds the outside of the first flattened zone, and an overlapping area is provided at the surrounding interface of the insulating member, which avoids the outer end of the first flattened zone along the winding direction.

[0026] The insulating sheet can separate the first flattened area from the housing to reduce the risk of short circuits. It can also gather the first flattened area from the periphery, reducing the risk of it spreading out. The outer end of the first flattened area along the winding direction does not overlap with the overlapping area, alleviating the problem of increased radial dimension and reduced energy density caused by the increased thickness after overlap.

[0027] In one or more optional embodiments above, the electrochemical device further includes a first electrode terminal provided on the housing and a current collecting disk connecting the first flattened area and the first electrode terminal, wherein the current collecting disk is provided with a through hole.

[0028] The first flattened area has a dense end surface, and connecting the first flattened area to the current collecting plate can improve the connection strength. During the injection process, the electrolyte can pass through the through-holes and infiltrate the electrode assembly, improving wettability. When an electrochemical device fails due to overheating, overcharging, short circuit, or other reasons, the electrode assembly will release gas; the through-holes provide a channel for the gas to be quickly discharged to the outside of the electrochemical device, reducing the risk of explosion.

[0029] 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.

[0030] In one or more of the above optional embodiments, x1 and x2 are both greater than or equal to 0.9.

[0031] In one or more optional embodiments above, the negative electrode plate includes a negative electrode current collector and a negative electrode active material, and the negative electrode active material includes artificial graphite and / or natural graphite.

[0032] In one or more of the above optional embodiments, the electrochemical device further comprises an electrolyte contained within the housing. The electrolyte comprises lithium hexafluorophosphate and fluoroethylene carbonate, with the weight percentage of lithium hexafluorophosphate being 12%-16% and the weight percentage of fluoroethylene carbonate being 0.8%-1.5% based on the mass of the electrolyte. Fluoroethylene carbonate, as an electrolyte additive, is beneficial for improving the performance of the SEI film, forming a compact structural layer without increasing impedance, preventing further decomposition of the electrolyte, and improving the discharge performance of the electrochemical device.

[0033] In one or more of the above optional embodiments, the electrochemical device includes a cylindrical battery cell, which has a mature production process, a high product yield, and good heat dissipation performance.

[0034] 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.

[0035] In one or more optional embodiments above, the cylindrical battery cell is an 18650 battery cell or a 21700 battery cell.

[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, at the first ambient temperature, the DC resistance of the electrochemical device is less than or equal to 10 milliohms. The electrochemical device has a low DC resistance, and the electrochemical device has a low temperature rise during high-rate discharge, which helps reduce energy loss, increase the discharge capacity of the electrochemical device, and improve the discharge performance of the electrochemical device.

[0038] In a second aspect, an embodiment of the present application further provides a battery pack, which includes an electrochemical device provided according to any embodiment of the first aspect.

[0039] 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.

[0040] In a third aspect, an embodiment of the present application further provides an electrical device comprising a battery pack provided according to any embodiment of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] 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.

[0042] FIG1 is a schematic structural diagram of an electrochemical device provided in some embodiments of the present application;

[0043] FIG2 is a schematic diagram of an explosion of the electrochemical device shown in FIG1 ;

[0044] FIG3 is a front view schematic diagram of an electrode assembly of an electrochemical device provided in some embodiments of the present application;

[0045] FIG4 is a schematic top view of the electrode assembly shown in FIG3 ;

[0046] FIG5 is a schematic cross-sectional view taken along the AA direction in FIG3 ;

[0047] FIG6 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;

[0048] FIG7 is a schematic cross-sectional view taken along the BB direction in FIG6 ;

[0049] FIG8 is a partial cross-sectional schematic diagram of a first flattened area, a current collecting plate, and an insulating member of a battery cell provided in some embodiments of the present application;

[0050] FIG9 is a partial cross-sectional schematic diagram of a first flattened area and an insulating member of a battery cell provided in some embodiments of the present application;

[0051] FIG10 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;

[0052] FIG11 is an enlarged schematic diagram of the circle frame of FIG10;

[0053] FIG12 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;

[0054] FIG13 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;

[0055] FIG14 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] FIG15 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;

[0057] FIG16 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] FIG17 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;

[0059] FIG18 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;

[0060] FIG19 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;

[0061] FIG20 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;

[0062] FIG21 is a schematic cross-sectional view taken along the CC direction of FIG20;

[0063] FIG22 is a schematic diagram of a battery pack provided in some embodiments of the present application;

[0064] FIG23 is a schematic diagram of an electrical device provided by some embodiments of the present application;

[0065] FIG24 is a schematic diagram showing discharge performance of electrochemical devices according to some embodiments of the present application at different discharge rates;

[0066] FIG25 is a partial schematic diagram of FIG24.

[0067] The reference numerals are as follows: DETAILED DESCRIPTION

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 1 to 9 , 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.

[0072] 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.

[0073] In some embodiments, the electrochemical device 1000 includes a housing 2 and an electrode assembly 1 accommodated in the housing 2 .

[0074] The electrode assembly 1 includes a first electrode plate 11 and a second electrode plate 12 with opposite polarities. One of the first electrode plate 11 and the second electrode plate 12 is a positive electrode plate, and the other is a negative electrode plate.

[0075] During the charge and discharge process of the electrochemical device 1000 , active ions (eg, lithium ions) are intercalated and deintercalated between the positive electrode and the negative electrode.

[0076] Optionally, the electrode assembly 1 further includes a separator 13 disposed between the first electrode 11 and the second electrode 12. The separator 13 insulates the first electrode 11 from the second electrode 12. The separator 13 can reduce the risk of short circuit between the positive and negative electrodes while allowing active ions to pass through.

[0077] One or more electrode assemblies 1 can be accommodated in the housing 2 .

[0078] In some embodiments, the electrode assembly 1 may be a wound structure, a laminated structure, or other structures.

[0079] In some embodiments, the shape of the electrode assembly 1 can be cylindrical, flat, or polygonal.

[0080] In some embodiments, the housing 2 is used to encapsulate the electrode assembly 1 and components such as the electrolyte. The housing 2 can be a steel housing, an aluminum housing, a plastic housing (such as polypropylene), or a composite metal housing (such as a copper-aluminum composite housing 2).

[0081] In some embodiments, the electrochemical device 1000 further includes a cover plate 5. The housing 2 has an opening, and the cover plate 5 is used to cover the opening. The housing 2 and the cover plate 5 cooperate to form an internal cavity of the electrochemical device 1000. The formed internal cavity can be used to accommodate the electrode assembly 1, the electrolyte, and other components.

[0082] The housing 2 can be of various shapes and sizes, such as a rectangular parallelepiped or a cylindrical shape. The housing 2 can be made of various materials, such as, but not limited to, copper, iron, aluminum, stainless steel, aluminum alloy, etc.

[0083] The cover plate 5 can be connected to the housing 2 by welding, bonding, clamping or other methods.

[0084] In some embodiments, the housing 2 may be a structure with one side open, and the cover plate 5 is provided as one and covers the housing 2. In other embodiments, two cover plates 5 are provided, and the two cover plates 5 cover the two openings of the housing 2 respectively.

[0085] In some embodiments, the electrochemical device 1000 further includes an electrode terminal 3 , which is disposed on the cover plate 5 .

[0086] In some examples, 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.

[0087] 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.

[0088] In some embodiments, the electrochemical device 1000 further includes a current collecting plate 4 , which connects the electrode terminal 3 and the electrode assembly 1 . Exemplarily, the current collecting plate 4 connects the electrode terminal 3 and the first electrode sheet 11 .

[0089] 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 FIG5 , the winding direction V is clockwise.

[0090] 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 .

[0091] 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 .

[0092] 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.

[0093] 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.

[0094] 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 .

[0095] 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 .

[0096] 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.

[0097] 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.

[0098] In some embodiments, the first empty foil region 111b includes a first crumpled region 111c, which is away from the first main region 111a. For example, as shown in FIG6 , the portion of the first empty foil region 111b located above the dotted line is used to form the first crumpled region 111c.

[0099] 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.

[0100] The first flattened area 111 c forms a dense end surface, thereby facilitating connection with other conductive structures, such as welding with the current collecting plate 4 .

[0101] In some embodiments, the electrochemical device 1000 is configured to: in response to the electrochemical device 1000 having a 100% SOC at a first ambient temperature, perform a discharge operation at a first discharge rate, continue the discharge operation until the SOC of the electrochemical device 1000 reaches 0%, and the ratio of the discharge capacity of the electrochemical device 1000 to the rated capacity of the electrochemical device 1000 is greater than or equal to 80%. The first ambient temperature is 22-28°C, and the first discharge rate is within the range of 15°C-20°C.

[0102] In the embodiments of the present application, SOC (State of charge) refers to the state of charge of an electrochemical device.

[0103] 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.

[0104] 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.

[0105] For example, the charge and discharge process of the electrochemical device can be tested by a battery tester (Neware CT-4016-5V-100A).

[0106] 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.

[0107] For example, the electrochemical device 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.

[0108] 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.

[0109] 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.

[0110] 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%.

[0111] 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.

[0112] For example, the rated capacity of the 18650 battery cell can be 2500 mAh, 2600 mAh, 2700 mAh, 2800 mAh, 2900 mAh, 3000 mAh, 3100 mAh, 3200 mAh, 3300 mAh, 3400 mAh, and 3500 mAh. For example, the rated capacity of the 21700 battery cell can be 3500 mAh, 3600 mAh, 3700 mAh, 3800 mAh, 3900 mAh, 4000 mAh, 4100 mAh, 4200 mAh, 4300 mAh, 4400 mAh, and 4500 mAh.

[0113] 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.

[0114] 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.

[0115] 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 0.5C charge rate, the charging current is 4000×0.5 mAh.

[0116] The discharge capacity of the electrochemical device 1000 can be measured using a battery tester (Neware CT-4016-5V-100A). For example, a discharge operation is performed at a first discharge rate until the SOC of the electrochemical device 1000 reaches 0%. The duration of the discharge operation is t, the current corresponding to the first discharge rate is i, and the discharge capacity can be t×i.

[0117] As an example, the first ambient temperature is a constant temperature. For example, the electrochemical device 1000 may be operated in a constant temperature box (Comin EH-1000).

[0118] As an example, the first ambient temperature may be 22°C, 23°C, 24°C, 25°C, 26°C, 27°C or 28°C.

[0119] As an example, the first discharge rate may be 15C, 16C, 17C, 17.5C, 18C, 19C, or 20C.

[0120] The embodiment of the present application increases the overcurrent capacity by setting the first flattening zone, and the resistance of the electrochemical device is small. When discharging at a high rate of 15C-20C, the temperature rise of the electrochemical device is low, which is beneficial to reducing energy loss, thereby enabling the electrochemical device to have a higher discharge capacity, provide more electrical energy for electrical equipment, and improve the discharge performance of the electrochemical device.

[0121] In some embodiments, the ratio of the discharge capacity of the electrochemical device 1000 to the rated capacity of the electrochemical device 1000 is greater than or equal to 90%. The electrochemical device 1000 can have a higher discharge capacity when discharged at a high rate of 15C-20C, providing more power to electrical devices.

[0122] In some embodiments, the ratio of the discharge capacity of the electrochemical device 1000 to the rated capacity of the electrochemical device 1000 is greater than or equal to 95%. The electrochemical device 1000 can have a higher discharge capacity when discharged at a high rate of 15C-20C, providing more power to electrical devices.

[0123] In some embodiments, the ratio of the discharge capacity of the electrochemical device 1000 to the rated capacity of the electrochemical device 1000 is greater than or equal to 98%. The electrochemical device 1000 can have a higher discharge capacity when discharged at a high rate of 15C-20C, providing more power to electrical devices.

[0124] In some embodiments, the first discharge rate is in the range of 17.5 C-20 C. When discharging at a high rate of 17.5 C-20 C, the ratio of the discharge capacity of the electrochemical device 1000 to the rated capacity of the electrochemical device 1000 is greater than or equal to 99%, thereby providing more electrical energy for electrical equipment.

[0125] In some embodiments, the first ambient temperature is 25°C.

[0126] 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 Coy1 Mn z1 O2 or Li 1+a Ni x2 Co y2 Al z2 At least one of O2. Wherein, 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.

[0127] In some embodiments, x1 and x2 are both greater than or equal to 0.9.

[0128] 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 0.05 O2、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.

[0129] In some embodiments, the positive electrode active material 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 Li1+a Ni x2 Co y2 Al z2 At least one of O2.

[0130] In some embodiments, the adhesive includes at least one of polyacrylic acid (PAA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or polyamide (PA).

[0131] 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.

[0132] 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%.

[0133] In some embodiments, 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 artificial graphite and / or natural graphite.

[0134] In some embodiments, the negative electrode active material also includes a binder and a conductive agent.

[0135] 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.

[0136] In some embodiments, the electrochemical device 1000 further includes an electrolyte contained in the housing 2. The electrolyte includes lithium hexafluorophosphate (LiPF6) and fluoroethylene carbonate (FEC), wherein the mass percentage of lithium hexafluorophosphate is 12%-16% and the mass percentage of fluoroethylene carbonate is 0.8%-1.5% based on the mass of the electrolyte.

[0137] The electrolyte also includes 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%.

[0138] As an electrolyte additive, FEC is beneficial to improving the performance of the SEI film, forming a tight structural layer without increasing the impedance, preventing further decomposition of the electrolyte, and improving the discharge performance of the electrochemical device.

[0139] 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.

[0140] 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.

[0141] 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.

[0142] In some embodiments, the electrochemical device 1000 is an 18650 battery cell or a 21700 battery cell.

[0143] In some embodiments, the rated capacity of the electrochemical device 1000 is 2500 mAh to 4500 mAh. Optionally, the rated capacity of the electrochemical device 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.

[0144] In some embodiments, at the first ambient temperature, the DC resistance of the electrochemical device 1000 is less than or equal to 10 milliohms.

[0145] For example, the DC resistance of the electrochemical device 1000 is tested as follows:

[0146] At 25° C., the electrochemical device is discharged at a constant current of 0.5 C to a discharge cutoff voltage of the electrochemical device, then charged at a constant current of 0.5 C to a charge cutoff voltage of the electrochemical device, and then charged at a constant voltage of the charge cutoff voltage to 0.05 C, at which point the electrochemical device is at 100% SOC;

[0147] Standing at the first ambient temperature for 2 hours;

[0148] At the first ambient temperature, discharge the battery with a current i1 corresponding to a 0.1C rate for 10 seconds, and measure a voltage V1; then discharge the battery with a current i2 corresponding to a 1C rate for 1 second, and measure a voltage V2;

[0149] The DC resistance of the electrochemical device is (V1-V2) / (i2-i1).

[0150] The electrochemical device 1000 of the present application has a relatively small DC resistance. The temperature rise of the electrochemical device 1000 is relatively low during high-rate discharge, which is beneficial for reducing energy loss, increasing the discharge capacity of the electrochemical device, and improving the discharge performance of the electrochemical device.

[0151] 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 total size of the first current collector 111 is W2 , and W1 and W2 satisfy: 0.05≤W1 / W2≤0.1.

[0152] 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.

[0153] 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.

[0154] Alternatively, W1 / W2 may be 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1.

[0155] 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.

[0156] 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.

[0157] Optionally, W4 / W1 is 0.6, 0.7, 0.8, 0.9 or 0.95.

[0158] 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.

[0159] Along the length direction X of the first electrode 11 after it is unfolded, L1 is the maximum size of the first empty foil area 111 b after it is unfolded.

[0160] Exemplarily, unfolding the first pole piece 11 may be unfolding the first pole piece 11 into a flat sheet structure, and correspondingly, the first flattened area 111 c is also flattened.

[0161] 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.

[0162] Alternatively, L1 / L2 may be 0.8, 0.85, 0.9, 0.95 or 1.

[0163] 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.

[0164] 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.

[0165] In some embodiments, the electrochemical device 1000 further includes a current collecting plate 4 , which connects the electrode terminal 3 and the electrode assembly 1 . Exemplarily, the current collecting plate 4 connects the electrode terminal 3 and the first electrode sheet 11 .

[0166] In some embodiments, the electrochemical device 1000 further includes an electrode terminal 3 disposed on the housing 2 and a current collecting plate 4 connecting the first flattened area 111 c and the electrode terminal 3 .

[0167] The first flattened area 111 c has a dense end surface, and the connection strength can be improved by connecting the first flattened area 111 c to the collecting plate 4 .

[0168] In some embodiments, the current collecting plate 4 is welded to the first flattened area 111 c. The embodiments of the present application 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.

[0169] In some embodiments, the current collecting plate 4 is provided with through-holes 41. During the injection process, the electrolyte can pass through the through-holes 41 and soak into the electrode assembly 1, improving wettability. If the electrochemical device 1000 fails due to overheating, overcharging, short circuiting, or other reasons, the electrode assembly 1 will release gas. The through-holes 41 provide a channel for the gas to be quickly discharged to the outside of the electrochemical device, reducing the risk of explosion.

[0170] In some embodiments, the electrochemical device 1000 further includes an insulating member 6 , which surrounds the outer side of the first flattened region 111 c .

[0171] The insulating sheet 6 can separate the first flattened area 111c from the housing 2 to reduce the risk of short circuit. The insulating sheet 6 can also gather the first flattened area 111c from the periphery to reduce the risk of the first flattened area 111c spreading out.

[0172] In some embodiments, the insulating member 6 surrounds at least one circle of the first flattened area 111 c .

[0173] In some embodiments, an overlapping region 61 is provided at the surrounding interface of the insulating member 6. The insulating member 61 can be connected at the overlapping region 61 to reduce the risk of the insulating member 6 falling off from the first flattened area 111c.

[0174] In some embodiments, the insulating member 6 is bonded in the overlapping region 61 .

[0175] In some embodiments, the insulating member 6 comprises adhesive tape.

[0176] In some embodiments, the overlapping region 61 avoids the outer end of the first flattened region 111 c along the winding direction V. For example, in the radial direction of the first flattened region 111 c, the outer end of the first flattened region 111 c along the winding direction does not overlap with the overlapping region 61, thereby alleviating the problem of increased radial dimension and reduced energy density caused by increased thickness after overlap.

[0177] When connecting the insulating member 6, the overlapping area 61 needs to be squeezed from the outside. The overlapping area 61 is kept away from the outer end of the first flattened area 111c, which helps to reduce the problem of lithium deposition caused by the outer end of the first flattened area 111c being squeezed when the electrochemical device expands.

[0178] 10 and 11 , 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.

[0179] 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.

[0180] After the first empty foil area 111b is flattened to form the first flattened area 111c, the insulating member 6 can be attached to the periphery of the first flattened area 111c; by setting the first incision G1, the risk of the outer end of the first empty foil area 111b being too sharp and puncturing the insulating member 6 can be reduced, which is beneficial to reducing the use of the insulating member 6 and improving the energy density.

[0181] 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.

[0182] 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.

[0183] 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.

[0184] 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.

[0185] 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.

[0186] In some embodiments, 0.5≤La / W1≤2.

[0187] In some embodiments, along the width direction Y of the unfolded first pole piece 11 , the size of the first cutout G1 is W3 ; W3 and W1 satisfy the following: 0.2≤W3 / W1≤1.

[0188] 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.

[0189] Optionally, W3 / W1 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.

[0190] In some embodiments, the first incision G1 and the second incision G2 have the same shape and size.

[0191] In some embodiments, the first cutout G1 may be formed by chamfering a corner of the first empty foil area 111 b .

[0192] 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.

[0193] 12 , 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.

[0194] 13 , in some embodiments, the first cutout G1 may be a rectangular cutout.

[0195] In some embodiments, referring to FIG. 14 , the first empty foil region 111 b includes a plurality of first sub-electrode tabs 1111 , and the plurality of first sub-electrode tabs 1111 are separately arranged along the length direction X after the first electrode sheet 11 is unfolded.

[0196] The plurality of first sub-electrode tabs 1111 are separately arranged. During the flattening process, each first sub-electrode tab 1111 is more easily bent and deformed, thereby reducing stress during the flattening process.

[0197] The plurality of first sub-tabs 1111 are discontinuous along the winding direction V. Adjacent first sub-tabs 1111 may or may not be in contact with each other in the winding direction V.

[0198] In some embodiments, along the length direction X of the unfolded first pole piece 11 , the minimum distance D between adjacent first sub-pole tabs 1111 is 0 mm-66 mm.

[0199] Alternatively, D may be 0 mm, 1 mm, 5 mm, 8 mm, 10 mm, 20 mm, 30 mm, 40 mm, 50 mm, 60 mm, or 66 mm.

[0200] In the embodiment of the present application, D is limited to 0 mm-66 mm, which can facilitate the infiltration of the electrolyte while separating the adjacent first sub-electrode tabs 1111 and reduce the loss of the flow area of ​​the first empty foil region 111 b.

[0201] In some embodiments, along the length direction X after the first pole piece 11 is unfolded, the sum of the sizes of the plurality of first sub-pole tabs 1111 is L3, the size of the first main region 111 a is L2, and L3 and L2 satisfy: 0.8≤L3 / L2≤1.

[0202] In some embodiments, along the length direction X of the unfolded first pole piece 11 , L3 is the sum of the minimum dimensions of the plurality of first sub-pole tabs 1111 .

[0203] Exemplarily, the minimum dimensions of the n first sub-tabs 1111 along the length direction X after the first pole piece is unfolded are K1, K2, ..., Kn, respectively, where n is a positive integer greater than 1, and L3 = K1 + K2 + ... + Kn. For example, as shown in FIG14 , there are four first sub-tabs 1111, and L3 = K1 + K2 + K3 + K4.

[0204] The multiple first sub-tabs 1111 have a large flow area, which can reduce the heat generated by the first sub-tabs 1111 and the risk of the first sub-tabs 1111 fusing when the electrochemical device 1000 discharges at a high rate.

[0205] Alternatively, L3 / L2 may be 0.8, 0.85, 0.9, 0.95 or 1.

[0206] In some embodiments, 0.9≤L3 / L2≤0.95.

[0207] The embodiment of the present application can increase the flow capacity of the first sub-electrode tab 1111 and reserve more gaps between adjacent first sub-electrode tabs 1111, thereby reducing the resistance of the first sub-electrode tab 1111 during the flattening process and facilitating the infiltration of the electrolyte.

[0208] In some embodiments, the number of the first sub-tabs 1111 is greater than or equal to 4. For example, the number of the first sub-tabs 1111 is 4, 5, 6, 8, 10, 12, 15, 18, or 20.

[0209] Under the premise that the sum L3 of the plurality of first sub-electrode tabs 1111 is constant, the resistance to flattening of a single first sub-electrode tab 1111 is reduced by increasing the number of the first sub-electrode tabs 1111 .

[0210] In some embodiments, along the length direction X of the unfolded first pole piece 11 , the plurality of first sub-pole tabs 1111 are arranged at equal intervals.

[0211] In some embodiments, along the length direction X after the first pole piece 11 is unfolded, the sizes of the plurality of first sub-pole tabs 1111 are the same.

[0212] In some embodiments, the first empty foil region 111 b further includes a transition portion (not shown), which is continuously arranged along the winding direction V and connects the first main body region 111 a and the plurality of first sub-tabs 1111 .

[0213] In some embodiments, along the length direction X of the unfolded first pole piece 11 , the size of the transition portion is equal to the size of the first main body region 111 a .

[0214] 16 , in some embodiments, along the length direction X after the first electrode 11 is unfolded, the inner end E1 of the first empty foil area 111b and the inner end E3 of the first main area 111a are separated by a first distance D1, and the size of the first main area 111a is L2. 0<D1 / L2<0.2.

[0215] After winding, the electrode assembly 1 forms a central hole 10c. During liquid injection, the central hole 10c serves as a liquid injection channel. In this embodiment, D1 / L2 is set to be greater than 0 to increase the distance between the first hollow foil area 111b and the central hole 10c, reducing the risk of the first hollow foil area 111b obstructing the central hole 10c during the flattening process.

[0216] In the embodiment of the present application, D1 / L2 is set to be less than 0.2, which can reduce the loss of the current capacity of the first empty foil area 111 b and enable the electrochemical device 1000 to discharge at a high rate.

[0217] In some embodiments, D1 / L2 may be 0.05, 0.1, 0.15, or 0.18.

[0218] In some embodiments, 0.05≤D1 / L2≤0.1, which can reduce the resistance to flattening the first empty foil area 111b, improve the wettability of the electrolyte, and reduce the loss of the current capacity of the first empty foil area 111b, so that the electrochemical device 1000 can discharge at a high rate.

[0219] 16 , in some embodiments, along the length direction X after the first electrode 11 is unfolded, the outer end E2 of the first empty foil area 111 b and the outer end E4 of the first main area 111 a are separated by a second distance D2, and the size of the first main area 111 a is L2, 0<D2 / L2<0.2.

[0220] In this embodiment of the present application, D2 / L2 is set to be greater than 0, which can reduce the outer diameter of the cylindrical structure formed by the winding of the first hollow foil area 111b, making it easier for external tooling to flatten the first hollow foil area 111b from the outside. In this embodiment of the present application, D2 / L2 is set to be less than 0.2, which can reduce the loss of the flow capacity of the first hollow foil area 111b, enabling the electrochemical device 1000 to discharge at a high rate.

[0221] In some embodiments, D2 / L2 may be 0.05, 0.1, 0.15, or 0.18.

[0222] In some embodiments, 0.05≤D2 / L2≤0.1, which can reduce the resistance to flattening the first empty foil area 111b, improve the wettability of the electrolyte, and reduce the loss of the current capacity of the first empty foil area 111b, so that the electrochemical device 1000 can discharge at a high rate.

[0223] In some embodiments, referring to Figure 17, along the length direction X after the first electrode 11 is unfolded, the inner end E1 of the first empty foil area 111b and the inner end E3 of the first main body area 111a are separated by a first distance D1, and the outer end E2 of the first empty foil area 111b and the outer end E4 of the first main body area 111a are separated by a second distance D2. 0<(D1+D2) / L2<0.2, D1>0, D2>0.

[0224] Optionally, 0.05≤(D1+D2) / L2≤0.1.

[0225] 2 and 18 , in some embodiments, the first empty foil area 111b includes a first pole lug area Z1, a second pole lug area Z2, and a third pole lug area Z3 arranged along the length direction X after the first pole piece 11 is unfolded, and each of the first pole lug area Z1, the second pole lug area Z2, and the third pole lug area Z3 includes at least two first sub-pole lugs 1111.

[0226] Exemplarily, the first tab region Z1 is close to the inner end E3 of the first main body region 111 a , and the third tab region Z3 is close to the outer end E4 of the first main body region 111 a .

[0227] In some embodiments, along the length direction X after the first electrode sheet 11 is unfolded, the minimum spacing between adjacent first sub-electrode tabs 1111 in the first electrode tab region Z1 is d1, the minimum spacing between adjacent first sub-electrode tabs 1111 in the second electrode tab region Z2 is d2, and the minimum spacing between adjacent first sub-electrode tabs 1111 in the third electrode tab region Z3 is d3, where d1, d2, and d3 satisfy the following: d2 < d1, d2 < d3. The electrochemical device 1000 also includes a current collecting plate 4 housed in the housing 2, and the current collecting plate 4 is welded to the second electrode tab region Z2.

[0228] Illustratively, along the length direction X after the first pole piece 11 is unfolded, the minimum distance between the first sub-pole lug 1111 in the first pole lug region Z1 and the first sub-pole lug 1111 in the second pole lug region Z2 can be flexibly set as needed, for example, can be d1.

[0229] Illustratively, along the length direction X after the first pole piece 11 is unfolded, the minimum distance between the first sub-pole lug 1111 in the third pole lug zone Z3 and the first sub-pole lug 1111 in the second pole lug zone Z2 can be flexibly set as needed, for example, can be d3.

[0230] The spacing between adjacent first sub-tabs 1111 in the second tab region Z2 is smaller. After flattening the first hollow foil region 111b, the second tab region Z2 becomes denser, and the weld strength between the second tab region Z2 and the current collector plate 4 is higher, reducing the risk of a cold weld. The first tab region Z1 and the third tab region Z3 do not need to be welded to the current collector plate 4. A larger gap can be provided between the first sub-tabs 1111 in the first tab region Z1 and the first sub-tabs 1111 in the third tab region Z3. This facilitates the infiltration of the electrolyte into the electrode assembly 1.

[0231] In some embodiments, d1≤d3. The third tab zone Z3 is closer to the outer ring, the first empty foil zone 111b of the outer ring has a larger circumference, and the first sub-tabs 1111 of the third tab zone Z3 may have a larger gap.

[0232] In some embodiments, d2 is 0 mm to 20 mm. Alternatively, d2 is 0 mm, 3 mm, 5 mm, 10 mm, 15 mm or 20 mm.

[0233] In some embodiments, along the length direction X after the first pole piece 11 is unfolded, the size of the second pole tab region Z2 is 0.6m-1.1m, that is, the sum of the sizes of the multiple first sub-pole tabs 1111 in the second pole tab region Z2 is 0.6m-1.1m.

[0234] The embodiment of the present application can increase the flow area and connection strength between the second tab zone Z2 and the current collecting disk 4.

[0235] In some embodiments, referring to FIG. 19 , the first empty foil region 111b includes a first tab region Z1, a second tab region Z2, and a third tab region Z3 arranged along the length direction X after the first tab 11 is unfolded. Each of the first tab region Z1 and the third tab region Z3 includes at least two first sub-tabs 1111, and the second tab region Z2 includes one first sub-tab 1111. Along the length direction X after the first tab 11 is unfolded, the size of the first sub-tab 1111 in the second tab region Z2 is larger than the size of the first sub-tab 1111 in the first tab region Z1, and the size of the first sub-tab 1111 in the second tab region Z2 is larger than the size of the first sub-tab 1111 in the third tab region Z3. The electrochemical device 1000 also includes a current collecting plate 4 housed in the housing 2, and the current collecting plate 4 is welded to the second tab region Z2.

[0236] The first sub-tabs 1111 of the second tab region Z2 are arranged continuously and have larger dimensions. After the first hollow foil region 111b is flattened, the second tab region Z2 becomes more compact, and the weld strength between the second tab region Z2 and the current collecting plate 4 is higher, reducing the risk of a cold weld. The first tab region Z1 and the third tab region Z3 do not need to be welded to the current collecting plate 4. Large gaps can be provided between the first sub-tabs 1111 of the first tab region Z1 and the first sub-tabs 1111 of the third tab region Z3. This facilitates the infiltration of the electrolyte into the electrode assembly.

[0237] In some embodiments, along the length direction X of the unfolded first pole piece 11, the dimension Kz of the first sub-tab 1111 of the second tab region Z2 is 0.6m-1.1m. Optionally, Kz is 0.6m, 0.7m, 0.8m, 0.9m, 1.0m or 1.1m.

[0238] For example, Kz may be the minimum dimension of the first sub-tab 1111 in the second tab region Z2 along the length direction X after the first pole piece is unfolded.

[0239] The embodiment of the present application can increase the flow area and connection strength between the second tab zone Z2 and the current collecting disk 4.

[0240] In some embodiments, the size Kz of the first sub-tab 1111 in the second tab region Z2 is greater than the sum of the sizes of the plurality of first sub-tabs 1111 in the first tab region Z1 .

[0241] In some embodiments, the size Kz of the first sub-tab 1111 in the second tab zone Z2 is greater than the sum of the sizes of the plurality of first sub-tabs 1111 in the third tab zone Z3 .

[0242] 20 and 21 , 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 .

[0243] 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 .

[0244] 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.

[0245] 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.

[0246] 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 .

[0247] 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.

[0248] 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.

[0249] In some embodiments, the portion 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.

[0250] 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.

[0251] 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 .

[0252] In some embodiments, the second electrode sheet 12 is a negative electrode sheet. Correspondingly, the second current collector 121 is a negative electrode current collector, and the second active material 122 is a negative electrode active material.

[0253] 22 , the present application further provides a battery pack 3000 , which includes the electrochemical device 1000 provided in any of the aforementioned embodiments.

[0254] 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.

[0255] Connecting multiple electrochemical devices 1000 in series can increase the output voltage of the battery pack.

[0256] 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.

[0257] 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.

[0258] In some embodiments, one battery module 2000 includes five electrochemical devices 1000 or six electrochemical devices 1000 .

[0259] In some embodiments, the number of battery modules 2000 is 2 or 3.

[0260] In some embodiments, the battery pack further includes a box 2100 , and the battery module 2000 is accommodated in the box 2100 .

[0261] 23 , 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 .

[0262] 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.

[0263] In some embodiments, embodiments of the present application provide an electrochemical device comprising a housing and an electrode assembly housed in the housing.

[0264] 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.

[0265] Example 1

[0266] Fabrication of electrochemical devices.

[0267] <Production of positive electrode sheet>

[0268] 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.

[0269] For example, referring to Figures 6 and 7 , 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.

[0270] <Preparation of negative electrode sheet>

[0271] 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 8μm 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.

[0272] For example, referring to Figures 6 and 7 , 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.

[0273] <Preparation of Separator>

[0274] 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.

[0275] <Preparation of Electrolyte>

[0276] 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.

[0277] <Preparation of Electrochemical Device>

[0278] 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.

[0279] According to the above method, an electrochemical device was prepared.

[0280] Electrochemical device testing methods

[0281] 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).

[0282] (1) The electrochemical device was placed in a 25°C constant temperature box (Coming EH-1000) for 2 hours and charged to 100% SOC. Specifically, 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 charged at a constant current of 0.5C to the charge cut-off voltage (4.2V) of the electrochemical device, and then charged at a constant voltage of the charge cut-off voltage to 0.05C, at which point the electrochemical device was at 100% SOC.

[0283] (2) After standing in a constant temperature box (Coming EH-1000) at 25°C for 2 hours, the electrochemical device at 100% SOC was discharged at a constant current of 0.2C to the discharge cut-off voltage of the electrochemical device (2.5V). The discharge capacity was measured, which was the rated capacity of the electrochemical device. The device was then charged at a constant current of 0.5C to the charge cut-off voltage (4.2V) of the electrochemical device. The device was then charged at a constant voltage of 0.05C at the charge cut-off voltage, at which point the device was at 100% SOC.

[0284] (3) The electrochemical device at 100% SOC was placed in a 25°C constant temperature box (Coming EH-1000) and allowed to stand for 2 hours. The device was then discharged at the same temperature with a current i1 corresponding to a 0.1C rate for 10 seconds, and the voltage V1 was measured. The device was then discharged with a current i2 corresponding to a 1C rate for 1 second, and the voltage V2 was measured. The DC resistance of the electrochemical device was (V1-V2) / (i2-i1).

[0285] (IV) The electrochemical device after the DC resistance test was placed in a 25°C constant temperature box (Coming EH-1000) for 2 hours, then discharged at a constant current of 0.5C to the discharge cut-off voltage (2.5V) of the electrochemical device, then charged at a constant current of 0.5C to the charge cut-off voltage (4.2V) of the electrochemical device, and then charged at a constant voltage of the charge cut-off voltage to 0.05C, at which time the electrochemical device was at 100% SOC.

[0286] (5) The electrochemical device at 100% SOC was placed in a 25°C thermostat (Coming EH-1000) for 2 hours. The temperature in the thermostat was then maintained while the device was discharged at a 5C discharge rate until it reached a cutoff voltage (2.5V). During the discharge process, the discharge parameters of the device were recorded.

[0287] (6) The electrochemical device after step (5) was placed in a 25°C constant temperature box (Coming EH-1000) for 2 hours, and then charged at a constant current of 0.5C to the charge cutoff voltage (4.2V) of the electrochemical device, and then charged at a constant voltage of 0.05C at the charge cutoff voltage, at which time the electrochemical device was at 100% SOC.

[0288] (7) Repeat steps (5) and (6), change the discharge rate in step (5), and record the discharge parameters of the electrochemical device.

[0289] The ambient temperature, discharge rate, and corresponding discharge capacity, rated capacity, and DC resistance of the electrochemical device are shown in Table 1.

[0290] Table 1

[0291] Referring to Table 1, Figures 24 and 25, the electrochemical device of Example 1 exhibits low energy loss during discharge at high rates of 15C-20C. The ratio of the electrochemical device's discharge capacity to its rated capacity is greater than or equal to 99%, enabling it to provide more power to electrical equipment. When discharged at a high rate of 15C, the electrochemical device can achieve a discharge capacity that reaches or even exceeds its rated capacity.

[0292] The internal resistance of the electrochemical device of Example 1 is only 6 milliohms (mΩ), and the energy loss during the high rate discharge process of 15C-20C is small, thereby increasing the discharge capacity of the electrochemical device and improving the discharge performance of the electrochemical device.

[0293] Example 2

[0294] The difference between the manufacturing method of the electrochemical device of Example 2 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 2 is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0295] The electrochemical device testing method of Example 2 is the same as the electrochemical device testing method of Example 1.

[0296] The ambient temperature, discharge rate, and corresponding discharge capacity, rated capacity, DC resistance, and other parameters of the electrochemical device of Example 2 are shown in Table 2.

[0297] Table 2

[0298] Referring to Table 2, the electrochemical device of Example 2 has low energy loss when discharged at a high rate of 15C-20C, and the ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 99%, which can provide more electrical energy for electrical equipment.

[0299] Example 3

[0300] The difference between the manufacturing method of the electrochemical device of Example 3 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 3 is LiNi 0.95 Co 0.01 Mn 0.04 O2.

[0301] The electrochemical device testing method of Example 3 is the same as the electrochemical device testing method of Example 1.

[0302] The ambient temperature, discharge rate, and corresponding discharge capacity, rated capacity, DC resistance, and other parameters of the electrochemical device of Example 3 are shown in Table 3.

[0303] Table 3

[0304] Referring to Table 3, the electrochemical device of Example 3 has low energy loss when discharged at a high rate of 15C-20C, and the ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 99%, which can provide more electrical energy for electrical equipment.

[0305] Example 4

[0306] Fabrication of electrochemical devices.

[0307] <Production of positive electrode sheet>

[0308] The difference from Example 1 is that the positive electrode sheet adopts the structure of the first electrode sheet shown in Figures 10 and 11. Specifically, referring to Figures 10 and 11, L1 = L2 = 1.36m, W2 is 63.2mm, W1 is 4mm, and W4 is 3.2mm. The first bare foil region has identical triangular cutouts at both the outer and inner corners along the winding direction, where La = W1 = 4mm, W3 = 0.5mm, and W1 = 2mm.

[0309] <Preparation of negative electrode sheet>

[0310] The difference from Example 1 is that the negative electrode sheet adopts the structure of the first electrode sheet shown in Figures 10 and 11. Referring to Figures 10 and 11, L1 = L2 = 1.464m, W2 is 64.1mm, W1 is 4mm, and W4 is 3.2mm. The first empty foil area has identical triangular cutouts at both the outer and inner corners along the winding direction, where La = W1 = 4mm, W3 = 0.5mm, and W1 = 2mm. The cutouts for the negative electrode sheet are identical in shape and size to those for the positive electrode sheet.

[0311] <Preparation of Separator>

[0312] Same as Example 1.

[0313] <Preparation of Electrolyte>

[0314] Same as Example 1.

[0315] <Preparation of Electrochemical Device>

[0316] Same as Example 1.

[0317] According to the above method, an electrochemical device was prepared.

[0318] The electrochemical device testing method of Example 4 is the same as the electrochemical device testing method of Example 1.

[0319] The ambient temperature, discharge rate, and corresponding discharge capacity, rated capacity, DC resistance, and other parameters of the electrochemical device of Example 4 are shown in Table 4.

[0320] Table 4

[0321] Referring to Table 4, the electrochemical device of Example 4 has low energy loss when discharged at a high rate of 15C-20C, and the ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 99%, which can provide more electrical energy for electrical equipment.

[0322] Example 5

[0323] Fabrication of electrochemical devices.

[0324] <Production of positive electrode sheet>

[0325] The difference from Example 1 is that the positive electrode plate adopts the structure of the first electrode plate shown in Figure 14. Specifically, referring to Figure 14, L2=1.36m. The first electrode plate includes a total of 10 first sub-electrode ears, and the 10 first sub-electrode ears have the same size. The total length L3 (K1+K2+...+K10) of the 10 first sub-electrode ears is 1.1m. The distance between two adjacent first sub-electrode ears is equal, D is 20mm, and along the length direction of the first electrode plate after unfolding, the inner end of the first hollow foil area and the inner end of the first main body area are separated by a distance D1 of 40mm, and the outer end of the first hollow foil area and the outer end of the first main body area are separated by a second distance D2 of 40mm. W2 is 63.2mm, W1 is 4mm, and W4 is 3.2mm.

[0326] <Preparation of negative electrode sheet>

[0327] The difference from Example 1 is that the negative electrode plate adopts the structure of the first electrode plate shown in Figure 14. Referring to Figure 14, L2 is 1.464m. The first electrode plate includes a total of 10 first sub-pole ears, and the 10 first sub-pole ears have the same size. The total length L3 (K1+K2+...+K10) of the 10 first sub-pole ears is 1.2m; the distance between two adjacent first sub-pole ears is equal, D is 20mm, and along the length direction of the unfolded first electrode plate, the inner end of the first empty foil area and the inner end of the first main body area are separated by a first distance D1 of 42mm, and the outer end of the first empty foil area and the outer end of the first main body area are separated by a second distance D2 of 42mm. W2 is 64.1mm, W1 is 4mm, and W4 is 3.2mm.

[0328] <Preparation of Separator>

[0329] Same as Example 1.

[0330] <Preparation of Electrolyte>

[0331] Same as Example 1.

[0332] <Preparation of Electrochemical Device>

[0333] Same as Example 1.

[0334] According to the above method, an electrochemical device was prepared.

[0335] The electrochemical device testing method of Example 5 is the same as the electrochemical device testing method of Example 1.

[0336] The ambient temperature, discharge rate, and corresponding discharge capacity, rated capacity, DC resistance, and other parameters of the electrochemical device of Example 5 are shown in Table 5.

[0337] Table 5

[0338] Referring to Table 5, the electrochemical device of Example 5 has low energy loss when discharged at a high rate of 15C-20C, and the ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 99%, which can provide more electrical energy for electrical equipment.

[0339] Comparative Example 1

[0340] INR21700-40T (21700 battery cell)

[0341] The test method of the INR21700-40T battery cell of Comparative Example 1 is the same as the test method of the electrochemical device of Example 1.

[0342] The ambient temperature, discharge rate, and corresponding discharge capacity, rated capacity, DC resistance, and other parameters of the INR21700-40T battery cell of Comparative Example 1 are shown in Table 6.

[0343] Table 6

[0344] Referring to Tables 1 to 6, compared with the INR21700-40T battery cell, the electrochemical devices of Examples 1 to 5 have lower energy loss and higher discharge capacity when discharged at a high rate of 15C-20C.

[0345] Referring to Table 6, when discharging an INR21700-40T cell at a 20C rate, the cell's current interrupt device (CID) activates and disconnects the discharge circuit, allowing the INR21700-40T cell to release only a portion of its capacity. For example, a battery tester (Neware CT-4016-5V-100A) can measure the capacity released from 100% SOC to the moment the CID activates, which is 2643 mAh in Table 6.

[0346] Referring to Table 6, when the INR21700-40T battery cell is discharged at a rate of 15C-20C, the internal temperature of the battery cell is relatively high, which has a significant impact on the performance of the electrolyte, affecting the discharge performance and discharge capacity.

[0347] Example 6

[0348] Fabrication of electrochemical devices.

[0349] <Production of positive electrode sheet>

[0350] 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.

[0351] For example, referring to Figures 6 and 7 , 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.

[0352] <Preparation of negative electrode sheet>

[0353] 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 8μm 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 is 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.

[0354] For example, referring to Figures 6 and 7 , 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.

[0355] <Preparation of Separator>

[0356] 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.

[0357] <Preparation of Electrolyte>

[0358] 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.

[0359] <Preparation of Electrochemical Device>

[0360] 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.

[0361] According to the above method, an electrochemical device was prepared.

[0362] Electrochemical device testing methods

[0363] 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).

[0364] (1) The electrochemical device was placed in a 25°C constant temperature box (Coming EH-1000) for 2 hours and charged to 100% SOC. Specifically, 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 charged at a constant current of 0.5C to the charge cut-off voltage (4.2V) of the electrochemical device, and then charged at a constant voltage of the charge cut-off voltage to 0.05C, at which point the electrochemical device was at 100% SOC.

[0365] (2) After standing in a constant temperature box (Coming EH-1000) at 25°C for 2 hours, the electrochemical device at 100% SOC was discharged at a constant current of 0.2C to the discharge cut-off voltage of the electrochemical device (2.5V). The discharge capacity was measured, which was the rated capacity of the electrochemical device. The device was then charged at a constant current of 0.5C to the charge cut-off voltage (4.2V) of the electrochemical device. The device was then charged at a constant voltage of 0.05C at the charge cut-off voltage, at which point the device was at 100% SOC.

[0366] (3) The electrochemical device at 100% SOC was placed in a 25°C constant temperature box (Coming EH-1000) and allowed to stand for 2 hours. The device was then discharged at the same temperature with a current i1 corresponding to a 0.1C rate for 10 seconds, and the voltage V1 was measured. The device was then discharged with a current i2 corresponding to a 1C rate for 1 second, and the voltage V2 was measured. The DC resistance of the electrochemical device was (V1-V2) / (i2-i1).

[0367] (IV) The electrochemical device after the DC resistance test was placed in a 25°C constant temperature box (Coming EH-1000) for 2 hours, then discharged at a constant current of 0.5C to the discharge cut-off voltage (2.5V) of the electrochemical device, then charged at a constant current of 0.5C to the charge cut-off voltage (4.2V) of the electrochemical device, and then charged at a constant voltage of the charge cut-off voltage to 0.05C, at which time the electrochemical device was at 100% SOC.

[0368] (5) The electrochemical device at 100% SOC was placed in a 25°C thermostat (Coming EH-1000) for 2 hours. The temperature in the thermostat was then maintained while the device was discharged at a 5C discharge rate until it reached a cutoff voltage (2.5V). During the discharge process, the discharge parameters of the device were recorded.

[0369] (6) The electrochemical device after step (5) was placed in a 25°C constant temperature box (Coming EH-1000) for 2 hours, and then charged at a constant current of 0.5C to the charge cutoff voltage (4.2V) of the electrochemical device, and then charged at a constant voltage of 0.05C at the charge cutoff voltage, at which time the electrochemical device was at 100% SOC.

[0370] (7) Repeat steps (5) and (6), change the discharge rate in step (5), and record the discharge parameters of the electrochemical device.

[0371] Among them, the ambient temperature, discharge rate and corresponding discharge capacity, rated capacity, DC resistance and other parameters of the electrochemical device are shown in Table 7.

[0372] Table 7

[0373] Referring to Table 7, the electrochemical device of Example 6 exhibits low energy loss during discharge at a high rate of 15C-20C. The ratio of the electrochemical device's discharge capacity to its rated capacity is greater than or equal to 99%, enabling it to provide more power to electrical equipment. When discharged at a high rate of 15C, the electrochemical device can achieve a discharge capacity that reaches or even exceeds its rated capacity.

[0374] The internal resistance of the electrochemical device of Example 6 is 8.5 milliohms (mΩ), and the energy loss during the high-rate discharge process of 15C-20C is small, thereby increasing the discharge capacity of the electrochemical device and improving the discharge performance of the electrochemical device.

[0375] Example 7

[0376] The difference between the manufacturing method of the electrochemical device of Example 7 and the manufacturing method of the electrochemical device of Example 6 is that the positive electrode active material of the positive electrode sheet of Example 7 is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0377] The electrochemical device testing method of Example 7 is the same as the electrochemical device testing method of Example 6.

[0378] The ambient temperature, discharge rate, and corresponding discharge capacity, rated capacity, DC resistance, and other parameters of the electrochemical device of Example 7 are shown in Table 8.

[0379] Table 8

[0380] Referring to Table 8, the electrochemical device of Example 7 has low energy loss when discharged at a high rate of 15C-20C, and the ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 99%, which can provide more electrical energy for electrical equipment.

[0381] Example 8

[0382] The difference between the manufacturing method of the electrochemical device of Example 8 and the manufacturing method of the electrochemical device of Example 6 is that the positive electrode active material of the positive electrode sheet of Example 8 is LiNi 0.95 Co 0.01 Mn 0.04 O2.

[0383] The electrochemical device testing method of Example 8 is the same as the electrochemical device testing method of Example 6.

[0384] The ambient temperature, discharge rate, and corresponding discharge capacity, rated capacity, DC resistance, and other parameters of the electrochemical device of Example 8 are shown in Table 9.

[0385] Table 9

[0386] Referring to Table 9, the electrochemical device of Example 8 has low energy loss when discharged at a high rate of 15C-20C, and the ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 99%, which can provide more electrical energy for electrical equipment.

[0387] Example 9

[0388] Fabrication of electrochemical devices.

[0389] <Production of positive electrode sheet>

[0390] The difference from Example 6 is that the positive electrode sheet adopts the structure of the first electrode sheet shown in Figures 10 and 11. Specifically, referring to Figures 10 and 11, L1 = L2 = 0.92m. W2 is 59mm, W1 is 4mm, and W4 is 3.2mm. The first empty foil area has identical triangular cutouts at both the outer and inner corners along the winding direction, where La = W1 = 4mm, W3 = 0.5mm, and W1 = 2mm.

[0391] <Preparation of negative electrode sheet>

[0392] The difference from Example 6 is that the negative electrode sheet adopts the structure of the first electrode sheet shown in Figures 10 and 11. Referring to Figures 10 and 11, L1 = L2 = 1.02m, W2 is 60.2mm, W1 is 4mm, and W4 is 3.2mm. The first empty foil area has identical triangular cutouts at both the outer and inner corners along the winding direction, where La = W1 = 4mm, W3 = 0.5mm, and W1 = 2mm. The cutouts for the negative electrode sheet are identical in shape and size to those for the positive electrode sheet.

[0393] <Preparation of Separator>

[0394] Same as Example 6.

[0395] <Preparation of Electrolyte>

[0396] Same as Example 6.

[0397] <Preparation of Electrochemical Device>

[0398] Same as Example 6.

[0399] According to the above method, an electrochemical device was prepared.

[0400] The electrochemical device testing method of Example 9 is the same as the electrochemical device testing method of Example 6.

[0401] The ambient temperature, discharge rate, and corresponding discharge capacity, rated capacity, DC resistance, and other parameters of the electrochemical device of Example 9 are shown in Table 10.

[0402] Table 10

[0403] Referring to Table 10, the electrochemical device of Example 9 has low energy loss when discharged at a high rate of 15C-20C, and the ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 99%, which can provide more electrical energy for electrical equipment.

[0404] Example 10

[0405] Fabrication of electrochemical devices.

[0406] <Production of positive electrode sheet>

[0407] The difference from Example 1 is that the positive electrode sheet adopts the structure of the first electrode sheet shown in Figure 14. Specifically, referring to Figure 14, L2 is 0.92m, the first electrode sheet includes a total of 10 first sub-electrode tabs, and the 10 first sub-electrode tabs are of the same size. The total length L3 (K1+K2+…+K10) of the 10 first sub-electrode tabs is 0.8m. The spacing between two adjacent first sub-electrode tabs is equal, D is 10mm. Along the length direction of the unfolded first electrode sheet, the inner end of the first hollow foil area and the inner end of the first main body area are separated by a first distance D1 of 15mm, and the outer end of the first hollow foil area and the outer end of the first main body area are separated by a second distance D2 of 15mm. W2 is 59mm, W1 is 4mm, and W4 is 3.2mm.

[0408] <Preparation of negative electrode sheet>

[0409] The difference from Example 1 is that the negative electrode plate adopts the structure of the first electrode plate shown in Figure 14. Referring to Figure 14, L2 is 1.02m, and the first electrode plate includes 10 first sub-electrode tabs, all of which are identical in size. The total length L3 (K1+K2+…+K10) of the 10 first sub-electrode tabs is 0.9m. The spacing D between adjacent first sub-electrode tabs is equal, D is 10mm. Along the length direction of the unfolded first electrode plate, the inner end of the first hollow foil area and the inner end of the first main body area are separated by a first distance D1 of 15mm, and the outer end of the first hollow foil area and the outer end of the first main body area are separated by a second distance D2 of 15mm. W2 is 60.2mm, W1 is 4mm, and W4 is 3.2mm.

[0410] <Preparation of Separator>

[0411] Same as Example 6.

[0412] <Preparation of Electrolyte>

[0413] Same as Example 6.

[0414] <Preparation of Electrochemical Device>

[0415] Same as Example 6.

[0416] According to the above method, an electrochemical device was prepared.

[0417] The electrochemical device testing method of Example 10 is the same as the electrochemical device testing method of Example 6.

[0418] The ambient temperature, discharge rate, and corresponding discharge capacity, rated capacity, DC resistance, and other parameters of the electrochemical device of Example 10 are shown in Table 11.

[0419] Table 11

[0420] Referring to Table 11, the electrochemical device of Example 10 has low energy loss when discharged at a high rate of 15C-20C, and the ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 99%, which can provide more electrical energy for electrical equipment.

[0421] Comparative Example 2

[0422] INR18650-25R (18650 battery cell);

[0423] The test method of the INR18650-25R battery cell of Comparative Example 2 is the same as the test method of the electrochemical device of Example 6.

[0424] The ambient temperature, discharge rate, and corresponding discharge capacity, rated capacity, DC resistance, and other parameters of the INR18650-25R battery cell of Comparative Example 2 are shown in Table 12.

[0425] Table 12

[0426] Referring to Tables 7 to 12, compared with the INR18650-25R battery cell, the electrochemical devices of Examples 6 to 10 have lower energy loss and higher discharge capacity when discharged at a high rate of 15C to 20C.

[0427] Referring to Table 12, when discharging an INR18650-25R cell at a 20C rate, the cell's current interrupt device (CID) activates and disconnects the discharge circuit, allowing the INR18650-25R cell to release only a portion of its capacity. For example, a battery tester (Neware CT-4016-5V-100A) can measure the capacity released from 100% SOC to the moment the CID activates, which is 2063 mAh as shown in Table 6.

[0428] Referring to Table 12, when the INR18650-25R battery cell is discharged at a rate of 15C-20C, the internal temperature of the battery cell is relatively high, which has a significant impact on the performance of the electrolyte, affecting the discharge performance and discharge capacity.

Claims

1. An electrochemical device, comprising a housing and an electrode assembly accommodated in the housing, 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 a winding direction. 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 disposed on the first current collector. 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. 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, and the first flattened region is away from the first main region; The electrochemical device is configured to: In response to the electrochemical device at 100% SOC at a first ambient temperature, performing a discharge operation at a first discharge rate, and continuing the discharge operation until the SOC of the electrochemical device is 0%, the ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 90%; Among them, The first ambient temperature is 22°C - 28°C, and the first discharge rate is in the range of 15C - 20C.

2. The electrochemical device according to claim 1, wherein, The ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 95%.

3. The electrochemical device according to claim 2, wherein, The ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 98%.

4. The electrochemical device according to any one of claims 1 to 3, wherein, The first discharge rate is in the range of 17.5C - 20C.

5. The electrochemical device according to any one of claims 1-4, wherein, The first ambient temperature is 25°C.

6. The electrochemical device according to any one of claims 1-5, wherein, Along the width direction of the first electrode tab after unfolding, the size of the first empty foil region is W1, and the total size of the first current collector is W2. W1 and W2 satisfy: 0.05 ≤ W1 / W2 ≤ 0.

1.

7. The electrochemical device according to claim 6, 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.

8. The electrochemical device according to claim 6 or 7, 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; La and W1 satisfy: 0.2 ≤ La / W1 ≤ 4.

9. The electrochemical device according to claim 8, 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.

10. The electrochemical device according to any one of claims 1-9, wherein, Along the length direction of the first electrode tab after unfolding, the size of the first empty foil region is L1, and the size of the first main region is L2. L1 and L2 satisfy: 0.8 ≤ L1 / L2 ≤ 1.

11. The electrochemical device according to any one of claims 1 - 10, comprising an insulating member. The insulating member surrounds the outside of the first flattened region, and an overlapping region is provided at the surrounding interface of the insulating member, and the overlapping region avoids the outer end of the first flattened region along the winding direction.

12. The electrochemical device according to any one of claims 1 - 11, comprising a first electrode terminal provided on the housing and a current collecting plate connecting the first flattened region and the first electrode terminal. The current collecting plate is provided with a through hole.

13. The electrochemical device according to any one of claims 1-12, 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.

14. The electrochemical device according to claim 13, wherein, Both x1 and x2 are greater than or equal to 0.

9.

15. The electrochemical device according to any one of claims 1-14, wherein, The negative electrode tab includes a negative electrode current collector and a negative electrode active material, and the negative electrode active material includes artificial graphite and / or natural graphite.

16. The electrochemical device according to any one of claims 1-15, comprising an electrolyte accommodated in the housing; The electrolyte includes lithium hexafluorophosphate and fluoroethylene carbonate. 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%.

17. The electrochemical device according to any one of claims 1-16, comprising a cylindrical battery cell, 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.

18. The electrochemical device according to claim 17, wherein, The cylindrical battery cell is a 18650-type battery cell or a 21700-type battery cell.

19. The electrochemical device according to any one of claims 1-18, wherein, The rated capacity of the electrochemical device is 2500 mAh - 4500 mAh.

20. The electrochemical device according to any one of claims 1-19, wherein, At the first ambient temperature, the DC resistance of the electrochemical device is less than or equal to 10 mΩ.

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 device, comprising the battery pack according to any one of claims 21-22.

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