Electrochemical device, battery pack and electrical apparatus

Abstract

Disclosed in the present application are an electrochemical device, a battery pack and an electrical apparatus. The electrochemical device comprises a casing and an electrode assembly accommodated in the casing; the electrode assembly comprises a first electrode sheet, a second electrode sheet and a separator, the first electrode sheet, the separator and the second electrode sheet being stacked and wound in a winding direction; the first electrode sheet comprises a first current collector and a first active substance arranged on the first current collector; the first current collector comprises a first main body area and a first empty foil area, the first active substance being arranged in the first main body area; the electrochemical device is configured to: in response to placing the electrochemical device having a SOC of 100% in a first ambient temperature for a first duration, perform a discharge operation at a first discharge rate in the first ambient temperature, and keep the discharge operation until the SOC of the electrochemical device is 90%, the minimum voltage value of the electrochemical device being greater than or equal to 2V, the first ambient temperature being -20℃-0℃, the first duration being greater than or equal to 6 hours, and the first discharge rate being greater than or equal to 10C.

Description

Electrochemical devices, battery packs, and electrical equipment

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application 202311828008.2, 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] A rechargeable electrochemical device is one that can be recharged to activate its active materials after discharge, allowing for continued use. Rechargeable electrochemical devices, such as rechargeable batteries, are widely used in electronic devices such as mobile phones, laptops, and drones.

[0005] As electrochemical devices become increasingly widely used, electronic devices are increasingly demanding low-temperature performance. Improving the discharge performance of electrochemical devices in low-temperature environments has always been a research direction in the industry. Summary of the Invention

[0006] The present application provides an electrochemical device, a battery pack, and an electrical device, which can improve the discharge performance of the electrochemical device in a low-temperature environment.

[0007] 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 polarities of the first electrode sheet and the second electrode sheet are opposite, and the first electrode sheet, the diaphragm, and the second electrode sheet are stacked and wound along a winding direction. The first electrode sheet comprises a first current collector and a first active material disposed on the first current collector, the first current collector comprising a first main body region and a first hollow foil region, the first active material being disposed in the first main body region, and the arrangement direction of the first main body region and the first hollow foil region being perpendicular to the winding direction. The portion of the first hollow foil region away from the first main body region forms a first flattened region.

[0008] The electrochemical device is configured to: in response to the electrochemical device at 100% SOC being placed at a first ambient temperature for a first time, at the first ambient temperature, perform a discharge operation at a first discharge rate, continue the discharge operation until the SOC of the electrochemical device reaches 90%, and the minimum voltage value of the electrochemical device is greater than or equal to 2V; wherein the first ambient temperature is -20°C to 0°C, the first time is greater than or equal to 6 hours, and the first discharge rate is greater than or equal to 10C.

[0009] After being left in a low-temperature environment of -20°C to 0°C for a first period of time, the electrochemical device can still discharge at a relatively high discharge rate, thereby improving the applicability of the electrochemical device in low-temperature environments. During the initial discharge phase of the electrochemical device in a low-temperature environment, a large voltage drop may occur. In the embodiment of the present application, at the first ambient temperature, the electrochemical device performs a discharge operation at a first discharge rate. During the continuous discharge operation from 100% SOC to 90% SOC, the electrochemical device can maintain a voltage of not less than 2V, thereby enabling continuous discharge to the outside and improving the discharge performance of the electrochemical device in low-temperature environments.

[0010] 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, wherein the mass percentage of the lithium hexafluorophosphate is 12%-16% and the mass percentage of the fluoroethylene carbonate is 0.8%-1.5% based on the mass of the electrolyte.

[0011] Fluoroethylene carbonate, as an electrolyte additive, is beneficial to improving the performance of the SEI film, forming a tight structural layer without increasing impedance, preventing further decomposition of the electrolyte, and improving the low-temperature performance of the electrolyte.

[0012] In one or more of the above optional embodiments, a first notch is provided at a corner of an outer end of the first hollow foil region along the winding direction. The first notch has a dimension La along the length of the unfolded first electrode sheet; and a dimension W1 along the width of the unfolded first electrode sheet. La and W1 satisfy the following relationship: 0.2 ≤ La / W1 ≤ 4.

[0013] After the first empty foil area is flattened to form the first flattened area, an insulating member can be attached to the periphery of the first flattened area; by setting the first incision, the risk of the insulating member being punctured due to the sharp corner at the end of the first empty foil area being too large can be reduced, which is beneficial to reducing the use of insulating members and improving energy density.

[0014] 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.

[0015] 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.

[0016] In one or more of the above optional embodiments, the first incision is a rectangular incision, a triangular incision or an arc-shaped incision.

[0017] In one or more of the above optional embodiments, the first time is less than or equal to 10 hours.

[0018] In one or more of the above optional embodiments, the first time is 7 hours, 8 hours or 9 hours.

[0019] In one or more of the above optional embodiments, the first discharge rate is less than or equal to 17.5C.

[0020] In one or more optional embodiments above, the first ambient temperature is 0° C., and the first discharge rate is 10° C.-20° C. The electrochemical device can discharge at 10° C.-20° C. at a temperature of 0° C., and has good low-temperature discharge performance.

[0021] In one or more optional embodiments above, the minimum voltage is greater than or equal to 2.5 V, and the first discharge rate is 10 C-20 C. During the initial discharge phase of the electrochemical device at 0° C., a higher voltage can be maintained.

[0022] In one or more of the above optional embodiments, the minimum voltage is greater than or equal to 3V, and the first discharge rate is 10C-20C. The electrochemical device can maintain a higher voltage during the initial discharge phase at 0°C. In a low-temperature environment, reducing the discharge rate can increase the minimum voltage of the electrochemical device during the initial discharge phase.

[0023] In one or more optional embodiments above, the first ambient temperature is -10° C., and the first discharge rate is 10 C-17.5 C. The electrochemical device can discharge at 10 C-17.5 C at a temperature of -10° C., and has good low-temperature discharge performance.

[0024] In one or more optional embodiments above, the lowest voltage is greater than or equal to 2.5 V. The electrochemical device has a higher voltage during the initial discharge phase at a low temperature of -10°C.

[0025] In one or more of the above optional embodiments, the minimum voltage is greater than or equal to 3V, and the first discharge rate is 10C-12.5C. The electrochemical device can maintain a higher voltage during the initial discharge phase at -10°C. In a low-temperature environment, reducing the discharge rate can increase the minimum voltage of the electrochemical device during the initial discharge phase.

[0026] In one or more optional embodiments above, the first ambient temperature is -20° C., and the first discharge rate is 10 C-17.5 C. The electrochemical device can discharge at 10 C-17.5 C at a temperature of -20° C., and has good low-temperature discharge performance.

[0027] In one or more optional embodiments above, the minimum voltage is greater than or equal to 2.5 V, and the first discharge rate is 10 C-12 C. The electrochemical device can maintain a higher voltage during the initial discharge phase at -20°C.

[0028] In one or more optional embodiments above, the electrochemical device is further configured: in response to the electrochemical device at 100% SOC continuously discharging to 0% SOC at a first discharge rate at a first ambient temperature, the ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 80%.

[0029] In the above embodiment, the electrochemical device can have a higher discharge capacity when discharged at a high rate of 10C or higher in a low temperature environment of -20°C to 0°C, thereby being able to provide more electrical energy to electrical equipment in a low temperature environment.

[0030] In one or more optional embodiments above, the electrochemical device is further configured as follows: in response to the electrochemical device at 100% SOC continuously discharging to 0% SOC at a first discharge rate at a first ambient temperature, 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%; the first discharge rate is 10C-17.5C.

[0031] In the above embodiment, the electrochemical device can have a higher discharge capacity when discharged at a high rate of 10C-17.5C in a low temperature environment of -20°C-0°C, thereby being able to provide more electrical energy to electrical equipment in a low temperature environment.

[0032] In one or more of the above optional embodiments, along the length direction of the unfolded first electrode sheet, the size of the first hollow foil area is L1, and the size of the first main area is L2, where L1 and L2 satisfy the following relationship: 0.8≤L1 / L2≤1. The first hollow foil area has a large flow area. When the electrochemical device is discharged at a high rate in a low temperature environment, a large current can pass through the first hollow foil area, thereby reducing heat generation in the first hollow foil area and lowering the risk of the first hollow foil area fusing.

[0033] In one or more of the above optional embodiments, the first empty foil area includes a plurality of first sub-electrode tabs, which are separated and arranged along the length direction of the unfolded first pole piece. During the flattening process, each first sub-electrode tab is more easily bent and deformed, thereby reducing stress during the flattening process.

[0034] In one or more of the above optional embodiments, along the length direction of the unfolded first electrode sheet, the minimum spacing D between adjacent first sub-electrode tabs is 0 mm to 66 mm. Limiting D to 0 mm to 66 mm facilitates electrolyte infiltration when separating adjacent first sub-electrode tabs and reduces loss of flow area in the first empty foil region.

[0035] In one or more optional embodiments above, the first empty foil region includes a first tab region, a second tab region, and a third tab region arranged along the length direction of the first pole piece after unfolding, and each of the first tab region, the second tab region, and the third tab region includes at least two first sub-tabs. Along the length direction of the first pole piece after unfolding, the minimum spacing between adjacent first sub-tabs in the first tab region is d1, the minimum spacing between adjacent first sub-tabs in the second tab region is d2, and the minimum spacing between adjacent first sub-tabs in the third tab region is d3, and d1, d2, and d3 satisfy: d2 < d1, d2 < d3. The electrochemical device also includes a current collecting disc housed in the housing, and the current collecting disc is welded to the second tab region.

[0036] The spacing between adjacent first sub-tabs in the second tab region is smaller. After flattening the first empty foil region, the second tab region becomes denser, resulting in higher weld strength between the second tab region and the current collector plate, and a lower risk of cold welds. The first and third tab regions do not need to be welded to the current collector plate. Larger gaps can exist between the first sub-tabs in the first tab region and between the first sub-tabs in the third tab region, facilitating electrolyte infiltration into the electrode assembly.

[0037] In one or more optional embodiments above, the first empty foil region includes a first tab region, a second tab region, and a third tab region arranged along the length direction of the first tab after the tab is unfolded. Each of the first tab region and the third tab region includes at least two first sub-tabs, and the second tab region includes one first sub-tab. Along the length direction of the first tab after the tab is unfolded, the size of the first sub-tab of the second tab region is larger than the size of the first sub-tab of the first tab region, and the size of the first sub-tab of the second tab region is larger than the size of the first sub-tab of the third tab region. The electrochemical device also includes a current collecting disc housed in the housing, the current collecting disc being welded to the second tab region.

[0038] The first sub-tabs in the second tab region are arranged continuously and are of larger size. After the first empty foil region is flattened, the second tab region becomes denser, and the weld strength between the second tab region and the current collector plate is higher, reducing the risk of cold welds. The first and third tab regions do not need to be welded to the current collector plate. Larger gaps can be provided between the first sub-tabs in the first tab region and between the first sub-tabs in the third tab region, thereby facilitating electrolyte infiltration into the electrode assembly.

[0039] In one or more optional embodiments above, along the length direction of the unfolded first pole piece, the size of the first sub-pole lug in the second pole lug region is 0.6m-1.1m, which can increase the flow area and connection strength between the second pole lug region and the current collecting disk.

[0040] 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.

[0041] Limiting 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. Limiting W1 / W2 to less than or equal to 0.1 allows for more space for the first active material, reducing energy density loss. When flattening the first hollow foil area, it will bend and deform; a W1 / W2 ratio of 0.05 or greater reduces the stress on the first active material during flattening, reducing the risk of deformation and powder loss.

[0042] In one or more optional embodiments above, 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 positive electrode sheet includes a positive electrode active material, a positive electrode active material including a positive electrode active material, a binder and a conductive agent, and the positive electrode active material includes Li 1+a Ni x1 Co y1 Mn z1 O2 or Li 1+a Ni x2 Co y2 Al z2 At least one of O2. 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.

[0043] In one or more of the above optional embodiments, x1 and x2 are both greater than or equal to 0.9.

[0044] In one or more optional embodiments above, 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 negative electrode sheet includes a negative electrode active substance, the negative electrode active substance includes a negative electrode active material, and the negative electrode active material includes artificial graphite and / or natural graphite.

[0045] In one or more of the above optional embodiments, the electrochemical device includes a cylindrical battery cell having a diameter of 17 mm to 22 mm and a height of 64 mm to 72 mm. Cylindrical battery cells have a mature production process, a high product yield, and good heat dissipation performance.

[0046] In one or more optional embodiments above, the cylindrical battery cell is an 18650 battery cell or a 21700 battery cell.

[0047] 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 (mOhm). The electrochemical device has a smaller DC resistance in a low-temperature environment, thereby reducing energy loss of the electrochemical device at low temperatures and improving discharge performance of the electrochemical device in a low-temperature environment.

[0048] In one or more of the above optional embodiments, the rated capacity of the electrochemical device is 2500 mAh to 4500 mAh. The electrochemical device has a higher capacity, thereby increasing the battery life of the electrical device and improving the user experience.

[0049] In one or more of the above optional embodiments, when the electrochemical device is at the first ambient temperature and is discharged at a rate of 0.2C, the volumetric energy density (VED) of the electrochemical device is ≥ 558Wh / L. The electrochemical device has a higher volumetric energy density in a low-temperature environment, thereby improving the battery life of the electrical device and the user experience.

[0050] In one or more optional embodiments above, when the electrochemical device is at the first ambient temperature and the electrochemical device is discharged at a rate of 0.2C, the volume energy density VED of the electrochemical device is ≥603Wh / L.

[0051] 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.

[0052] 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.

[0053] In one or more of the above optional embodiments, one battery module includes 5 electrochemical devices or 6 electrochemical devices.

[0054] In a second aspect, an embodiment of the present application further provides an electrical device, which includes a battery pack provided according to any embodiment of the first aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] 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.

[0056] FIG1 is a schematic structural diagram of an electrochemical device provided in some embodiments of the present application;

[0057] FIG2 is a schematic diagram of an explosion of the electrochemical device shown in FIG1 ;

[0058] FIG3 is a front view schematic diagram of an electrode assembly of an electrochemical device provided in some embodiments of the present application;

[0059] FIG4 is a schematic top view of the electrode assembly shown in FIG3 ;

[0060] FIG5 is a schematic cross-sectional view taken along the AA direction in FIG3 ;

[0061] 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;

[0062] FIG7 is a schematic cross-sectional view taken along the BB direction in FIG6 ;

[0063] FIG8 is a partial cross-sectional schematic diagram of an electrode tab of an electrochemical device provided in some embodiments of the present application;

[0064] FIG9 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;

[0065] FIG10 is an enlarged schematic diagram of the circle frame of FIG9;

[0066] FIG11 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;

[0067] FIG12 is a schematic diagram of a first electrode sheet of an electrochemical device in an expanded state provided in some further embodiments of the present application;

[0068] FIG13 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;

[0069] FIG14 is a schematic diagram of a first electrode sheet of an electrochemical device in an unfolded state provided in some further embodiments of the present application;

[0070] FIG15 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;

[0071] FIG16 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;

[0072] FIG17 is a schematic top view of an electrode assembly provided in some other embodiments of the present application, wherein the first hollow foil area is not flattened;

[0073] FIG18 is a schematic diagram of the first electrode piece of the electrode assembly shown in FIG17 in an unfolded state;

[0074] FIG19 is a schematic top view of an electrode assembly provided in some other embodiments of the present application, wherein the first hollow foil area is not flattened;

[0075] FIG20 is a schematic diagram of the first electrode piece of the electrode assembly shown in FIG19 in an unfolded state;

[0076] FIG21 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;

[0077] FIG22 is a schematic cross-sectional view taken along the CC direction of FIG21;

[0078] FIG23 is a schematic diagram of a second electrode sheet of an electrochemical device in an unfolded state provided by other embodiments of the present application;

[0079] FIG24 is a schematic diagram of a battery pack provided in some embodiments of the present application;

[0080] FIG25 is a schematic diagram of an electrical device provided by some embodiments of the present application;

[0081] FIG26 is a schematic diagram showing discharge performance of electrochemical devices provided by some embodiments of the present application at different discharge rates at 0° C.;

[0082] FIG27 is a schematic diagram of the discharge performance of FIG26 between 100% SOC and 90% SOC;

[0083] FIG28 is a schematic diagram of the discharge performance of the electrochemical device of FIG26 at a discharge rate of 20C;

[0084] FIG29 is a schematic diagram showing the discharge performance of electrochemical devices provided by some embodiments of the present application at different discharge rates at -10°C;

[0085] FIG30 is a schematic diagram of the discharge performance of FIG29 between 100% SOC and 90% SOC;

[0086] FIG31 is a schematic diagram of the discharge performance of the electrochemical device of FIG29 at a discharge rate of 17.5C;

[0087] FIG32 is a schematic diagram showing the discharge performance of electrochemical devices provided by some embodiments of the present application at different discharge rates at -20°C;

[0088] FIG33 is a schematic diagram of the discharge performance of FIG32 between 100% SOC and 90% SOC;

[0089] FIG34 is a schematic diagram of the discharge performance of the electrochemical device of FIG32 at a discharge rate of 17.5C.

[0090] The reference numerals are as follows: DETAILED DESCRIPTION

[0091] 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.

[0092] 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.

[0093] 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.

[0094] 1 to 8 , 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.

[0095] 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.

[0096] In some embodiments, the electrochemical device 1000 includes a housing 2 and an electrode assembly 1 accommodated in the housing 2 .

[0097] 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.

[0098] 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.

[0099] Optionally, the electrode assembly 1 further includes a separator 13 disposed between the positive electrode sheet and the negative electrode sheet, the separator 13 insulating the first electrode sheet 11 from the second electrode sheet 12. The separator 13 can reduce the risk of short circuit between the positive and negative electrode sheets while allowing active ions to pass through.

[0100] One or more electrode assemblies 1 can be accommodated in the housing 2 .

[0101] In some embodiments, the electrode assembly 1 may be a wound structure, a laminated structure, or other structures.

[0102] In some embodiments, the shape of the electrode assembly 1 can be cylindrical, flat, or polygonal.

[0103] 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).

[0104] 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.

[0105] 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.

[0106] The cover plate 5 can be connected to the housing 2 by welding, bonding, clamping or other methods.

[0107] 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.

[0108] In some embodiments, the electrochemical device 1000 further includes an electrode terminal 3 , which is disposed on the cover plate 5 .

[0109] 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.

[0110] 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.

[0111] 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 .

[0112] 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.

[0113] 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 .

[0114] 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 .

[0115] 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.

[0116] 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.

[0117] 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 .

[0118] 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 .

[0119] 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.

[0120] 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.

[0121] In some embodiments, the portion of the first hollow foil region 111b away from the first main region 111a forms the first flattened region 111c. For example, as shown in FIG6 , the portion of the first hollow foil region 111b located above the dotted line is used to form the first flattened region 111c.

[0122] 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.

[0123] 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 .

[0124] In some embodiments, the electrochemical device 1000 is configured to: in response to the electrochemical device 1000 having a 100% SOC being placed at a first ambient temperature for a first time, the electrochemical device 1000 performs a discharge operation at a first discharge rate at the first ambient temperature, and the discharge operation continues until the SOC of the electrochemical device 1000 reaches 90% and the lowest voltage of the electrochemical device 1000 is greater than or equal to 2 V. The first ambient temperature is between -20°C and 0°C, the first time is greater than or equal to 6 hours, and the first discharge rate is greater than or equal to 10C.

[0125] In the embodiments of the present application, SOC (State of charge) refers to the state of charge of an electrochemical device.

[0126] 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.

[0127] 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.

[0128] For example, the charge and discharge process of the electrochemical device can be tested by a battery tester (Neware CT-4016-5V-100A).

[0129] 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.

[0130] 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.

[0131] 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 an SOC of 100%.

[0132] 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.

[0133] 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.

[0134] Exemplarily, the electrochemical device being at a 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 a SOC of 0%.

[0135] 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.

[0136] Exemplarily, charge rate = current / rated capacity; discharge rate = current / rated capacity.

[0137] For example, the rated capacity of the electrochemical device is 4000 mAh. During a constant current charging operation at 0.5 C, the charging current is 4000×0.5 mA. During a constant current discharging operation at 0.2 C, the discharging current is 4000×0.2 mA.

[0138] The first ambient temperature is a constant temperature. Exemplarily, the electrochemical device is placed in a constant temperature box (Coming EH-1000) at a constant temperature of -20°C, and after standing for a first time, the electrochemical device performs a discharge operation at a first discharge rate at -20°C. Exemplarily, the electrochemical device is placed in a constant temperature box (Coming EH-1000) at a constant temperature of -10°C, and after standing for a first time, the electrochemical device performs a discharge operation at a first discharge rate at -10°C. Exemplarily, the electrochemical device is placed in a constant temperature box (Coming EH-1000) at a constant temperature of 0°C, and after standing for a first time, the electrochemical device performs a discharge operation at a first discharge rate at 0°C.

[0139] As an example, the first ambient temperature may be -20°C, -18°C, -15°C, -12°C, -10°C, -8°C, -5°C, -2°C or 0°C.

[0140] As an example, the first time may be 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0141] As an example, the first discharge rate may be 10C, 12C, 13C, 15C, 16C, 17.5C, 18C, or 20C.

[0142] Exemplarily, the lowest voltage value of the electrochemical device 1000 may refer to the lowest value of the terminal voltage of the electrochemical device 1000 .

[0143] After being left in a low-temperature environment of -20°C to 0°C for a first period of time, the electrochemical device of the embodiment of the present application can still discharge at a relatively high discharge rate, thereby improving the applicability of the electrochemical device in low-temperature environments. During the initial discharge phase of the electrochemical device in a low-temperature environment, a large voltage drop may occur. In the embodiment of the present application, at the first ambient temperature, the electrochemical device performs a discharge operation at a first discharge rate. During the continuous discharge operation from 100% SOC to 90% SOC, the electrochemical device can maintain a voltage of not less than 2V, thereby enabling continuous discharge to the outside, thereby improving the discharge performance of the electrochemical device in low-temperature environments.

[0144] 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.

[0145] 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%.

[0146] 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 low-temperature performance of the electrolyte.

[0147] In some embodiments, the first time is less than or equal to 10 hours.

[0148] In some embodiments, the first time is 7 hours, 8 hours, or 9 hours.

[0149] The electrochemical device of the embodiment of the present application is placed in a low-temperature environment of -20°C to 0°C for more than 6 hours, and the temperature inside and outside the electrochemical device is substantially consistent with the temperature of the low-temperature environment.

[0150] In some embodiments, the first discharge rate is less than or equal to 17.5C.

[0151] In some embodiments, the first ambient temperature is 0° C., the first discharge rate is 10° C.-20° C., the first time is greater than or equal to 6 hours, and the minimum voltage is greater than or equal to 2 V. Optionally, the first time is 6 hours-10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0152] During the process of continuously discharging the electrochemical device with 100% SOC at 10C-20C to 90% SOC at 0°C, the lowest voltage of the electrochemical device is greater than or equal to 2V.

[0153] The electrochemical device of the embodiment of the present application can discharge at 10C-20C at a temperature of 0°C, and has good low-temperature discharge performance.

[0154] In some embodiments, the first ambient temperature is 0° C., the first time is greater than or equal to 6 hours, the first discharge rate is 10C-20C, and the minimum voltage is greater than or equal to 2.5 V. Optionally, the first time is 6 hours to 10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0155] During the process of continuously discharging the electrochemical device with 100% SOC at 10C-20C to 90% SOC at 0°C, the lowest voltage of the electrochemical device is greater than or equal to 2.5V.

[0156] The electrochemical device of the embodiment of the present application can maintain a higher voltage during the initial discharge stage in an environment of 0°C.

[0157] In some embodiments, the first ambient temperature is 0° C., the first time is greater than or equal to 6 hours, the first discharge rate is 10C-20C, and the minimum voltage is greater than or equal to 3 V. Optionally, the first time is 6 hours to 10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0158] During the process of continuously discharging the electrochemical device with 100% SOC at 10C-20C to 90% SOC at 0°C, the lowest voltage of the electrochemical device is greater than or equal to 3V.

[0159] The electrochemical device of the embodiment of the present application can maintain a higher voltage during the initial discharge stage at 0° C. In a low temperature environment, reducing the discharge rate can increase the lowest voltage of the electrochemical device during the initial discharge stage.

[0160] In some embodiments, the first ambient temperature is -10°C, the first discharge rate is 10C-17.5C, the first time is greater than or equal to 6 hours, and the minimum voltage is greater than or equal to 2 V. Optionally, the first time is 6 hours-10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0161] The electrochemical device of the embodiment of the present application can discharge at 10C-17.5C at a temperature of -10°C, and has good low-temperature discharge performance.

[0162] In some embodiments, the first ambient temperature is -10°C, the first time is greater than or equal to 6 hours, the first discharge rate is 10C-17.5C, and the minimum voltage is greater than or equal to 2.5 V. Optionally, the first time is 6 hours to 10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0163] The electrochemical device of the embodiment of the present application has a higher voltage in the initial discharge stage in a low temperature environment of -10°C.

[0164] In some embodiments, the first ambient temperature is -10°C, the first time is greater than or equal to 6 hours, the first discharge rate is 10C-12.5C, and the minimum voltage is greater than or equal to 3 V. Optionally, the first time is 6 hours to 10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0165] The electrochemical device of the embodiment of the present application can maintain a higher voltage during the initial discharge stage at -10° C. In a low temperature environment, reducing the discharge rate can increase the lowest voltage of the electrochemical device during the initial discharge stage.

[0166] In some embodiments, the first ambient temperature is -20°C, the first time is greater than or equal to 6 hours, the first discharge rate is 10C-17.5C, and the minimum voltage is greater than or equal to 2 V. Optionally, the first time is 6 hours to 10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0167] The electrochemical device of the embodiment of the present application can discharge at 10C-17.5C at a temperature of -20°C, and has good low-temperature discharge performance.

[0168] In some embodiments, the first ambient temperature is -20°C, the first time is greater than or equal to 6 hours, the first discharge rate is 10C-12C, and the minimum voltage is greater than or equal to 2.5 V. Optionally, the first time is 6 hours to 10 hours, for example, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours.

[0169] The electrochemical device of the embodiment of the present application can maintain a higher voltage during the initial discharge stage in an environment of -20°C.

[0170] In some embodiments, the electrochemical device 1000 is further configured such that, in response to the electrochemical device at 100% SOC continuously discharging to 0% SOC at a first discharge rate at a first ambient temperature, a ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 80%.

[0171] The present application can have a higher discharge capacity in a low temperature environment of -20°C-0°C and at a high rate of 10C or more, thereby being able to provide more electrical energy to electrical equipment in a low temperature environment.

[0172] In some embodiments, the electrochemical device 1000 is further configured such that, in response to the electrochemical device 1000 at 100% SOC being continuously discharged at 10C-17.5C to 0% SOC at a first ambient temperature, a 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%.

[0173] The present application can have a higher discharge capacity under a low temperature environment of -20°C-0°C and a high rate discharge of 10C-17.5C, thereby being able to provide more electrical energy to electrical equipment in a low temperature environment.

[0174] 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.

[0175] In some embodiments, along the length direction X of the unfolded first electrode 11 , L1 is the maximum size of the first empty foil area 111 b .

[0176] Exemplarily, unfolding the first electrode sheet 11 may involve unfolding the first electrode sheet 11 into a flat sheet-like structure. Accordingly, the first current collector 111 is flattened as a whole, and the first flattened region is also flattened. The first hollow foil region 111b has a large flow area. When the electrochemical device 1000 is discharged at a high rate in a low-temperature environment, a large current can flow through the first hollow foil region 111b, thereby reducing heat generation in the first hollow foil region 111b and lowering the risk of melting the first hollow foil region 111b.

[0177] Alternatively, L1 / L2 may be 0.8, 0.85, 0.9, 0.95 or 1.

[0178] 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.

[0179] 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.

[0180] 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.

[0181] 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.

[0182] 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.

[0183] Alternatively, W1 / W2 may be 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1.

[0184] In some embodiments, the electrode assembly further includes an insulating sheet attached to the outer periphery of the first flattened area 111 c.

[0185] 9 and 10 , 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.

[0186] 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.

[0187] After the first empty foil area 111b is flattened to form the first flattened area 111c, an insulating member can be attached to the periphery of the first flattened area 111c; by providing the first incision G1, the risk of the insulating member being punctured due to the sharp corner at the end of the first empty foil area 111b being too large can be reduced, which is beneficial to reducing the use of insulating members and improving energy density.

[0188] 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.

[0189] 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.

[0190] In some embodiments, the size of the first cutout G1 along the length direction X of the unfolded first electrode 11 is La, and the size of the first empty foil area 111b along the width direction Y of the unfolded first electrode 11 is W1. La and W1 satisfy: 0.2≤La / W1≤4.

[0191] 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.

[0192] 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.

[0193] In some embodiments, 0.5≤La / W1≤2.

[0194] In some embodiments, along the width direction Y of the unfolded first pole piece 11 , the size of the first cutout G1 is W3 , and W3 and W1 satisfy the following: 0.2≤W3 / W1≤1.

[0195] 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.

[0196] Optionally, W3 / W1 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.

[0197] In some embodiments, the first incision G1 and the second incision G2 have the same shape and size.

[0198] In some embodiments, the first cutout G1 may be formed by chamfering a corner of the first empty foil area 111 b .

[0199] 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.

[0200] 11 , 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.

[0201] 12 , in some embodiments, the first cutout G1 may be a rectangular cutout.

[0202] In some embodiments, referring to FIG. 13 , 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.

[0203] 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.

[0204] 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.

[0205] 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.

[0206] 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.

[0207] 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.

[0208] 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.

[0209] 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 .

[0210] 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 FIG13 , there are four first sub-tabs 1111, and L3 = K1 + K2 + K3 + K4.

[0211] The plurality of first sub-tabs 1111 have a large flow area, which can reduce heat generation of the first sub-tabs 1111 and lower the risk of melting of the first sub-tabs 1111 when the electrochemical device 1000 is discharged at a high rate in a low temperature environment.

[0212] Alternatively, L3 / L2 may be 0.8, 0.85, 0.9, 0.95 or 1.

[0213] In some embodiments, 0.9≤L3 / L2≤0.95.

[0214] 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.

[0215] 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.

[0216] 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 .

[0217] 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.

[0218] 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.

[0219] 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 .

[0220] 14 , in some embodiments, along the length direction X after the first electrode 11 is unfolded, the inner end E1 of the first hollow 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.

[0221] 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.

[0222] 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 in a low temperature environment.

[0223] In some embodiments, D1 / L2 may be 0.05, 0.1, 0.15, or 0.18.

[0224] In some embodiments, 0.05≤D1 / L2≤0.1 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 be discharged at a high rate in a low temperature environment.

[0225] 15 , 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.

[0226] 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 in low temperature environments.

[0227] In some embodiments, D2 / L2 may be 0.05, 0.1, 0.15, or 0.18.

[0228] In some embodiments, 0.05≤D2 / L2≤0.1 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 be discharged at a high rate in a low temperature environment.

[0229] In some embodiments, referring to Figure 16, 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 outer end E2 of the first empty foil area 111b and the outer end E4 of the first main area 111a are separated by a second distance D2. 0<(D1+D2) / L2<0.2, D1>0, D2>0.

[0230] Optionally, 0.05≤(D1+D2) / L2≤0.1.

[0231] 2 , 17 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.

[0232] 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 .

[0233] 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.

[0234] 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.

[0235] 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.

[0236] 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.

[0237] 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.

[0238] 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.

[0239] 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.

[0240] 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.

[0241] In some embodiments, referring to Figures 19 and 20, 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.

[0242] 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.

[0243] 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.

[0244] 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.

[0245] 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.

[0246] 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 .

[0247] 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 .

[0248] 21 and 22 , 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 .

[0249] 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 .

[0250] 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.

[0251] 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.

[0252] 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 .

[0253] 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.

[0254] 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.

[0255] 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.

[0256] 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.

[0257] 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 .

[0258] In some embodiments, along the length direction X' of the unfolded second electrode 12, the size of the second hollow foil area 121b is L4, and the size of the second main body area 121a is L5. L4 and L5 satisfy: 0.8≤L4 / L5≤1.

[0259] In some embodiments, along the length direction X′ of the unfolded second electrode 12 , L4 is the maximum size of the second empty foil region 121 b .

[0260] The second empty foil area 121b has a larger flow area. When the electrochemical device 1000 is discharged at a high rate in a low temperature environment, a larger current can pass through the second empty foil area 121b, thereby reducing the heat generated by the second empty foil area 121b and reducing the risk of the second empty foil area 121b fusing.

[0261] Optionally, L4 / L5 may be 0.8, 0.85, 0.9, 0.95 or 1.

[0262] In some embodiments, 0.9≤L4 / L5≤0.95, which can further improve the flow capacity of the second empty foil area 121b, and on the premise that the second empty foil area 121b meets the flow capacity, reduce the size of the second empty foil area 121b, reduce the space and weight occupied by the second empty foil area 121b, and improve the energy density.

[0263] 23 , in some embodiments, the second empty foil region 121 b includes a plurality of second sub-electrode tabs 1211 , and the plurality of second sub-electrode tabs 1211 are separately disposed along the length direction X′ of the unfolded second electrode sheet 12 .

[0264] In some embodiments, along the length direction X' of the unfolded second pole piece 12, the sum of the dimensions of the plurality of second sub-electrode tabs 1211 is L6, the dimension of the second main body region 121a is L5, and L6 and L5 satisfy: 0.8≤L6 / L5≤1. Optionally, 0.9≤L6 / L5≤0.95.

[0265] In some embodiments, along the length direction X′ of the unfolded second pole piece 12 , L6 is the sum of the minimum dimensions of the plurality of second sub-pole tabs 1211 .

[0266] For example, along the length direction X' after the second pole piece 12 is unfolded, the minimum dimensions of the n second sub-pole tabs 1211 are J1, J2, ..., Jn, respectively, where n is a positive integer greater than 1, and L6 = J1 + J2 + ... + Jn. For example, as shown in FIG23 , there are four second sub-pole tabs 1211, and L6 = J1 + J2 + J3 + J4.

[0267] In some embodiments, along the length direction X′ of the unfolded second pole piece 12 , the minimum distance D5 between adjacent second sub-pole tabs 1211 is 0 mm-66 mm.

[0268] In some embodiments, along the length direction X' after the second electrode 12 is unfolded, the inner end of the second hollow foil area 121b and the inner end of the second main area 121a are separated by a third distance D3, and the size of the second main area 121a is L5. 0<D3 / L5<0.2.

[0269] In some embodiments, 0.05≤D3 / L5≤0.1.

[0270] In some embodiments, along the length direction X' after the second electrode 12 is unfolded, the outer end of the second hollow foil region 121b and the outer end of the second main region 121a are separated by a fourth distance D4, and the size of the second main region 121a is L5. 0<D4 / L5<0.2. Optionally, 0.05≤D4 / L5≤0.1.

[0271] In some embodiments, along the length direction X' after the second electrode sheet 12 is unfolded, the inner end of the second hollow foil area 121b and the inner end of the second main body area 121a are separated by a third distance D3, and the outer end of the second hollow foil area 121b and the outer end of the second main body area 121a are separated by a fourth distance D4. 0<(D3+D4) / L4<0.2, D3>0, D4>0. Optionally, 0.05≤(D3+D4) / L5≤0.1.

[0272] 21 to 23 , in some embodiments, along the width direction Y′ after the second electrode sheet 12 is unfolded, the size of the second empty foil area 121 b is W4 , the total size of the second current collector 121 is W5 , and W4 and W5 satisfy: 0.05≤W4 / W5≤0.1.

[0273] Setting W4 / W5 to be greater than or equal to 0.05 allows the second hollow foil area 121b to have a larger width, facilitating connection between the second hollow foil area 121b and other conductive structures. Setting W4 / W5 to be less than or equal to 0.1 allows more space to be reserved for the second active material 122, reducing energy density loss.

[0274] In addition, when the second empty foil area 121b is flattened, the second empty foil area 121b will bend and deform; in the embodiment of the present application, W4 / W5 is greater than or equal to 0.05 to reduce the force on the second active material 122 during flattening, thereby reducing the risk of deformation and powder loss of the second active material 122.

[0275] Alternatively, W4 / W5 may be 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1.

[0276] In some embodiments, the second pole piece 12 may also have the same structure as the first pole piece 11 shown in Figures 9-20.

[0277] 3 to 8, in some embodiments, one of the first electrode sheet 11 and the second electrode sheet 12 is a positive electrode sheet, and the other is a negative electrode sheet. The positive electrode sheet includes a positive electrode active material, which includes a positive electrode active material, a binder, and a conductive agent. The positive electrode active material includes Li 1+a Nix1 Co y1 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.

[0278] In some examples, the first electrode 11 is a positive electrode, and the first active material 112 is a positive electrode active material; in other examples, the second electrode 12 is a positive electrode, and the second active material 122 is a positive electrode active material.

[0279] In some embodiments, x1 and x2 are both greater than or equal to 0.9.

[0280] 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.

[0281] In some embodiments, the adhesive includes at least one of polyacrylic acid (PAA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or polyamide (PA).

[0282] 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.

[0283] 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%.

[0284] In some embodiments, one of the first electrode sheet 11 and the second electrode sheet 12 is a positive electrode sheet, and the other is a negative electrode sheet. The negative electrode sheet includes a negative electrode active material, which includes a negative electrode active material, and the negative electrode active material includes at least one of artificial graphite and / or natural graphite.

[0285] 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.

[0286] 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.

[0287] 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.

[0288] In some embodiments, the electrochemical device 1000 is an 18650 battery cell or a 21700 battery cell.

[0289] In some embodiments, at the first ambient temperature, the direct current resistance of the electrochemical device 1000 is less than or equal to 10 milliohms.

[0290] For example, the DC resistance of the electrochemical device 1000 is tested as follows:

[0291] 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;

[0292] Standing at the first ambient temperature for 6 hours;

[0293] 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;

[0294] The DC resistance of the electrochemical device is (V1-V2) / (i2-i1).

[0295] The electrochemical device 1000 of the present application has a smaller DC resistance in a low-temperature environment, thereby reducing the energy loss of the electrochemical device 1000 in a low-temperature environment and improving the discharge performance of the electrochemical device 1000 in a low-temperature environment.

[0296] In some embodiments, the electrochemical device has a rated capacity of 2500-4500 milliampere hours (mAh). Alternatively, the electrochemical device has a rated capacity of 2500 milliampere hours (mAh), 2600 milliampere hours (mAh), 2700 milliampere hours (mAh), 2800 milliampere hours (mAh), 2900 milliampere hours (mAh), 3000 milliampere hours (mAh), 3100 milliampere hours (mAh), 3200 milliampere hours (mAh), 3300 milliampere hours (mAh), 3400 milliampere hours (mAh), 3500 milliampere hours (mAh), 3600 milliampere hours (mAh), 3700 milliampere hours (mAh), 3800 milliampere hours (mAh), 3900 milliampere hours (mAh), 4000 milliampere hours (mAh), 4100 milliampere hours (mAh), 4200 milliampere hours (mAh), 4300 milliampere hours (mAh), 4400 milliampere hours (mAh), or 4500 milliampere hours (mAh).

[0297] In some embodiments, when the electrochemical device 1000 is at a first ambient temperature and the electrochemical device 1000 is discharged at a rate of 0.2C, the volumetric energy density VED of the electrochemical device is ≥558Wh / L.

[0298] For example, when the electrochemical device is at a first ambient temperature and the electrochemical device 1000 is discharged at a rate of 0.2C, the discharge energy E of the electrochemical device is obtained by testing with a battery tester (Neware CT-4016-5V-100A) during the process of discharging the electrochemical device 1000 from 100% SOC to 0% SOC. Alternatively, the battery tester (Neware CT-4016-5V-100A) measures the discharge capacity of the electrochemical device under the aforementioned conditions, where E = discharge capacity × platform voltage of the electrochemical device. For example, the platform voltage of a 21700 battery cell may be 3.69V.

[0299] For example, taking a cylindrical cell as an example, the volume of the cylindrical cell can be obtained by measuring the diameter φ and height H of the cylindrical cell. The diameter φ of the cylindrical cell is the diameter of the smallest circumscribed circle of the radial section of the cylindrical cell, and the height H of the cylindrical cell is the maximum axial dimension of the cylindrical cell. The volume V of the cylindrical cell is π*φ 2 *H / 4.

[0300] For example, the volume V of an 18650 cell can be π×9 2 ×65mm 3 The volume V of 21700 battery cell can be π×10.5 2 ×70mm 3 .

[0301] VED of an electrochemical device = E / V.

[0302] The electrochemical device of the embodiment of the present application has a higher volume energy density in a low-temperature environment, thereby increasing the battery life of the electrical device 4000 and improving the user experience.

[0303] In some embodiments, when the electrochemical device 1000 is at a first ambient temperature and the electrochemical device 1000 is discharged at a rate of 0.2C, the volumetric energy density VED of the electrochemical device is ≥603Wh / L.

[0304] 24 , the present application further provides a battery pack 3000 , which includes the electrochemical device 1000 provided in any of the aforementioned embodiments.

[0305] 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.

[0306] Connecting multiple electrochemical devices 1000 in series can increase the output voltage of the battery pack.

[0307] 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.

[0308] 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.

[0309] In some embodiments, one battery module 2000 includes five electrochemical devices 1000 or six electrochemical devices 1000 .

[0310] In some embodiments, the number of battery modules 2000 is 2 or 3.

[0311] In some embodiments, the battery pack further includes a box 2100 , and the battery module 2000 is accommodated in the box 2100 .

[0312] 25 , 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 .

[0313] 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.

[0314] In some embodiments, embodiments of the present application provide an electrochemical device comprising a housing and an electrode assembly housed in the housing.

[0315] The electrode assembly includes a first electrode plate, a second electrode plate, and a separator. The first electrode plate is a positive electrode plate, and the second electrode plate is a negative electrode plate. The separator insulates the first electrode plate and the second electrode plate.

[0316] Example 1

[0317] Fabrication of electrochemical devices.

[0318] <Production of positive electrode sheet>

[0319] 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.

[0320] For example, referring to FIG13 , the positive electrode sheet has a structure similar to that of the first electrode sheet. Specifically, L2 is 1.36m, there are 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 1.1m. The distance between two adjacent first sub-electrode tabs is equal, D is 20mm, and along the length direction X after the first electrode sheet is unfolded, 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 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, and W1 is 4mm.

[0321] <Preparation of negative electrode sheet>

[0322] 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.

[0323] For example, referring to Figures 22 and 23 , the negative electrode sheet has a similar structure to the second electrode sheet. Specifically, L5 is 1.464m, and there are 10 second sub-electrode tabs, all of which are identical in size. The total length L6 (J1+J2+…+J10) of the 10 second sub-electrode tabs is 1.2m. The spacing D5 between adjacent second sub-electrode tabs is equal, D5 being 20mm. Along the length direction X' of the unfolded second electrode sheet 12, the inner end of the second hollow foil region and the inner end of the second main body region are separated by a third distance D3 of 42mm, and the outer end of the second hollow foil region and the outer end of the second main body region are separated by a fourth distance D4 of 42mm. W5 is 64.1mm, and W4 is 4mm.

[0324] <Preparation of Separator>

[0325] 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.

[0326] <Preparation of Electrolyte>

[0327] 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.

[0328] <Preparation of Electrochemical Device>

[0329] 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.

[0330] According to the above method, three electrochemical devices were prepared and numbered as U1, U2, and U3 respectively.

[0331] Electrochemical device testing methods

[0332] The three electrochemical devices were tested according to the following steps using a battery tester (Neware CT-4016-5V-100A).

[0333] (1) After standing for 120 minutes in a 25°C constant temperature box (Coming EH-1000), the three electrochemical devices (U1, U2, and U3) were charged to 100% SOC. Specifically, at a constant temperature of 25°C, each 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.

[0334] (2) After standing at a constant temperature of 25°C for 120 minutes, the three electrochemical devices at 100% SOC were discharged at a constant current of 0.2C to the discharge cutoff voltage of the electrochemical device (2.5V). The discharge capacity, which is the rated capacity of each electrochemical device, was tested. The devices were then charged at a constant current of 0.5C to the charge cutoff voltage of the electrochemical device (4.2V). The devices were then charged at a constant voltage of 0.05C at the charge cutoff voltage, at which point each electrochemical device was at 100% SOC.

[0335] (III) The three electrochemical devices at 100% SOC were placed in thermostats (Coming EH-1000) at different temperatures and allowed to stand for 6 hours. They were then discharged at the same temperature at a current i1 corresponding to a 0.1C rate for 10 seconds, and the voltage V1 was measured. They were then discharged at a current i2 corresponding to a 1C rate for 1 second, and the voltage V2 was measured. The DC resistance of the electrochemical device is (V1-V2) / (i2-i1). Electrochemical device U1 was tested in a thermostat at 0°C, electrochemical device U2 was tested in a thermostat at -10°C, and electrochemical device U3 was tested in a thermostat at -20°C.

[0336] (4) The three electrochemical devices tested for DC resistance were allowed to stand at a constant temperature of 25°C for 120 min, then discharged at a constant current of 0.5C to the discharge cutoff voltage (2.5V) of the electrochemical device, 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 point the electrochemical device was at 100% SOC;

[0337] (V) The three electrochemical devices at 100% SOC were placed in thermostats (Keming EH-1000) at different temperatures and left to stand for 6 hours. The corresponding ambient temperatures of the electrochemical devices are shown in Table 1.

[0338] (6) Maintaining the temperature in the constant temperature box, the three electrochemical devices were discharged at a discharge rate of 0.2 C until the three electrochemical devices were discharged to the discharge cutoff voltage (2.5 V). During the discharge process, the discharge parameters of each electrochemical device were recorded.

[0339] (VII) The electrochemical device after step (VI) was allowed to stand at a constant temperature of 25°C for 120 min, and 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 0.05C at the charge cut-off voltage, at which time the electrochemical device was at 100% SOC; the three electrochemical devices at 100% SOC were placed in thermostats (Coming EH-1000) at different temperatures and allowed to stand for 6 hours, and then discharged at other rates at the same temperature until the electrochemical device was discharged to the discharge cut-off voltage (2.5V).

[0340] (8) Repeat step (7), change the discharge rate, and record the discharge parameters of each electrochemical device.

[0341] Among them, the discharge ambient temperature, discharge rate, minimum voltage of 100% SOC-90% SOC, discharge capacity of 100% SOC-0% SOC, rated capacity, DC resistance at the discharge ambient temperature, and volume energy density at the discharge ambient temperature of each electrochemical device are shown in Table 1.

[0342] Table 1

[0343] The “ / ” in the table indicates that the electrochemical device is discharged at a 0.2C rate in step (six). After the volume energy density is calculated, the volume energy density at other discharge rates is not calculated.

[0344] 26 to 28 show discharge performance curves of the electrochemical device U1 at 0°C, FIG. 29 to FIG. 31 show discharge performance curves of the electrochemical device U2 at -10°C, and FIG. 32 to FIG. 34 show discharge performance curves of the electrochemical device U2 at -20°C.

[0345] Referring to Table 1 and Figures 26 to 34, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 6 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices maintained a voltage of at least 2V, enabling continuous discharge.

[0346] Note that in Figures 26 to 34, the electrochemical device achieves 0% SOC at each discharge rate when discharged to the cutoff voltage. Figures 26 to 34 are based on a 0.2C discharge rate, integrating the discharge performance curves at multiple rates.

[0347] Taking Figure 26 as an example, the horizontal axis of Figure 26 is based on the discharge capacity at a rate of 0.2C at 0°C to the cutoff voltage (2.5V), and is arranged in reverse order. The discharge capacity at other rates is divided by the discharge capacity at 0.2C, and then arranged in reverse order to obtain Figure 26. For example, the discharge capacity of the electrochemical device U1 at a rate of 0.2C at 0°C is 4113mAh. When the horizontal axis is 90%, the SOC of the electrochemical device U1 is 90%, the remaining capacity of the electrochemical device U1 is 4113mAh×90%, and the capacity released by the electrochemical device U1 is 4113mAh×10%; the discharge capacity of the electrochemical device U1 at a rate of 3C at 0°C is 3631mAh. Then when the horizontal axis is 90%, the SOC of the electrochemical device U1 is 90%×(3631 / 4113)=79%, the remaining capacity of the electrochemical device U1 is 3631mAh×79%, and the capacity released by the electrochemical device U1 is 3631mAh×21%.

[0348] FIG. 27 to FIG. 34 also integrate multiple discharge performance curves in the above manner.

[0349] Specifically, referring to Table 1 and Figures 26 to 28 , the electrochemical device U1 can still discharge normally after being left at rest for 6 hours at 0°C, and can still discharge at a high rate of no less than 10C. It should be noted that in Figures 26 and 27 , the 10C discharge performance curve is nearly identical to the 12C discharge performance curve.

[0350] At an ambient temperature of 0°C, discharging at 0.2C-20C from 100% SOC to 90% SOC, the electrochemical device U1 can maintain a voltage of no less than 2.5V, thereby enabling continuous discharge. The electrochemical device of the present embodiment has good discharge performance at 0°C.

[0351] At an ambient temperature of 0°C, discharging at 0.2C-20C from 100% SOC to 90% SOC, the electrochemical device U1 can maintain a voltage of no less than 3V, thereby enabling continuous discharge. The electrochemical device of the present embodiment has good discharge performance at 0°C.

[0352] When discharged at a discharge rate of 10C-20C to a discharge cut-off voltage (e.g., 2.5V) at 0°C, the discharge capacity of the electrochemical device can exceed 80% of the rated capacity. When discharged at a discharge rate of 10C-20C to a discharge cut-off voltage (e.g., 2.5V) at 0°C, the discharge capacity of the electrochemical device can exceed 95% of the rated capacity. The electrochemical device of the embodiment of the present application can have a higher discharge capacity at 0°C, thereby being able to provide more electrical energy to electrical equipment in a low-temperature environment.

[0353] When the electrochemical device U1 is discharged at 5C-20C in an environment of 0°C, the discharge capacity can exceed 90% of the rated capacity.

[0354] When the electrochemical device is at 0° C. and discharged at a rate of 0.2 C, the volume energy density VED of the electrochemical device is ≥ 600 Wh / L. The electrochemical device of the embodiment of the present application has a high energy density in a low temperature environment.

[0355] Referring to Table 1 and Figures 29 to 31 , the electrochemical device U2 can still discharge normally after being left at rest for 6 hours in an environment of -10°C, and can still discharge at a high rate of not less than 10C.

[0356] At an ambient temperature of -10°C, during discharge at 0.2C-17.5C from 100% SOC to 90% SOC, the electrochemical device U2 can maintain a voltage of no less than 2.5V, thereby enabling continuous discharge to the outside. The electrochemical device of the embodiment of the present application has good discharge performance in an environment of -10°C. In particular, at an ambient temperature of -10°C, during discharge at 10C-12.5C from 100% SOC to 90% SOC, the electrochemical device U2 can maintain a voltage of no less than 3V.

[0357] When discharged at a discharge rate of 10C-17.5C to a discharge cutoff voltage (e.g., 2.5V) at -10°C, the discharge capacity of the electrochemical device U2 can exceed 90% of the rated capacity. The electrochemical device of the embodiment of the present application can have a higher discharge capacity at -10°C, thereby being able to provide more power to electrical equipment in low-temperature environments.

[0358] When the electrochemical device is at -10°C and discharged at a rate of 0.2C, the volume energy density VED of the electrochemical device is ≥600Wh / L. The electrochemical device of the embodiment of the present application has a high energy density in an environment of -10°C.

[0359] The discharge capacity of the electrochemical device U2 at 12.5C-17.5C in a -10°C environment is greater than the discharge capacity of the electrochemical device U2 at 0.2C in a -10°C environment. In a low temperature environment, increasing the discharge rate of the electrochemical device can increase the discharge capacity of the electrochemical device.

[0360] Referring to Table 1 and Figures 32 to 34, the electrochemical device U3 can still discharge normally after being left at rest for 6 hours in an environment of -20°C, and can still discharge at a high rate of not less than 10C.

[0361] At an ambient temperature of -20°C, discharging at a rate of 0.2C-17.5C from 100% SOC to 90% SOC, the electrochemical device can maintain a voltage of no less than 2V, thereby enabling continuous discharge. The electrochemical device of the present embodiment has good discharge performance in an environment of -20°C.

[0362] At an ambient temperature of -20°C, during discharge at 3C-12C from 100% SOC to 90% SOC, the electrochemical device U3 can maintain a voltage of not less than 2.5V, thereby enabling continuous discharge to the outside.

[0363] When discharged at a discharge rate of 0.2-17.5C to a discharge cut-off voltage (e.g., 2.5V) at -20°C, the discharge capacity of the electrochemical device can exceed 80% of the rated capacity. When discharged at a discharge rate of 5C-17.5C to a discharge cut-off voltage (e.g., 2.5V) at -20°C, the discharge capacity of the electrochemical device can exceed 90% of the rated capacity. The electrochemical device of the embodiment of the present application can have a higher discharge capacity at -20°C, thereby being able to provide more electrical energy to electrical equipment in a low-temperature environment.

[0364] At -20°C, when the electrochemical device U3 is able to discharge at 17.5C, at the beginning of discharge, the minimum voltage can be seen to exceed 2V, and at the end of discharge, the discharge is cut off at 2.5V.

[0365] The discharge capacity of the electrochemical device U3 at 8C-17.5C in a -20°C environment is greater than the discharge capacity of the electrochemical device U3 at 0.2C in a -20°C environment. In low temperature environments, increasing the discharge rate of the electrochemical device can increase the discharge capacity of the electrochemical device.

[0366] Example 2

[0367] Three other electrochemical devices U4, U5, and U6 were manufactured according to the electrochemical device manufacturing method of Example 1.

[0368] Electrochemical devices U4, U5, and U6 were tested according to the electrochemical device testing method of Example 1. The difference between Example 2 and Example 1 is that in steps (3), (5), and (7) of the test, the electrochemical device was left to stand in a constant temperature box (Coming EH-1000) for 8 hours.

[0369] The test conditions and test results of each electrochemical device in Example 2 are shown in Table 2.

[0370] Table 2

[0371] Referring to Table 2, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 8 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices were able to maintain a voltage of at least 2V, enabling continuous discharge.

[0372] After standing at an ambient temperature of 0° C. for 8 hours, the electrochemical device U4 can maintain a voltage of not less than 3V during a discharge at 0.2C-20C from 100% SOC to 90% SOC.

[0373] After standing for 8 hours at 0°C, the electrochemical device can achieve a discharge capacity exceeding 80% of its rated capacity when discharged at a discharge rate of 0.2C-20C to a discharge cutoff voltage (e.g., 2.5V). Electrochemical device U4 can achieve a discharge capacity exceeding 90% of its rated capacity when discharged at a rate of 5C-20C at 0°C.

[0374] After standing at a temperature of -10°C for 8 hours, the electrochemical device U5 was able to maintain a voltage of no less than 2.5 V during a discharge at a rate of 0.2C-17.5C from 100% SOC to 90% SOC. After standing at a temperature of -10°C for 8 hours, the electrochemical device U5 was able to maintain a voltage of no less than 3 V during a discharge at a rate of 10C-12.5C from 100% SOC to 90% SOC.

[0375] When discharged at a discharge rate of 10C-17.5C to a discharge cutoff voltage (eg, 2.5V) in a -10°C environment, the discharge capacity of the electrochemical device U5 may exceed 90% of the rated capacity.

[0376] After standing for 8 hours at a temperature of -20°C, the electrochemical device U6 was able to maintain a voltage of no less than 2V during discharge from 100% SOC to 90% SOC at a rate of 0.2C-17.5C, thus enabling continuous discharge. The electrochemical device of the present embodiment exhibited good discharge performance at -20°C.

[0377] At an ambient temperature of -20°C, during discharge at 3C-12C from 100% SOC to 90% SOC, the electrochemical device U6 can maintain a voltage of not less than 2.5V, thereby enabling continuous external discharge.

[0378] When discharged at a discharge rate of 0.2-17.5C to a discharge cutoff voltage (e.g., 2.5V) at -20°C, the discharge capacity of the electrochemical device can exceed 80% of the rated capacity. When discharged at a discharge rate of 5C-17.5C to a discharge cutoff voltage (e.g., 2.5V) at -20°C, the discharge capacity of the electrochemical device can exceed 90% of the rated capacity.

[0379] Example 3

[0380] Three more electrochemical devices U7, U8, and U9 were manufactured according to the electrochemical device manufacturing method of Example 1.

[0381] Electrochemical devices U7, U8, and U9 were tested according to the electrochemical device testing method of Example 1. The difference between Example 3 and Example 1 is that in steps (3), (5), and (7) of the test, the electrochemical device was left to stand in a constant temperature box (Coming EH-1000) for 10 hours.

[0382] The test conditions and test results of each electrochemical device in Example 3 are shown in Table 3.

[0383] Table 3

[0384] Referring to Table 3, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 10 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices maintained a voltage of at least 2V, enabling continuous discharge.

[0385] After standing at an ambient temperature of 0° C. for 10 hours, the electrochemical device U7 can maintain a voltage of not less than 3V during the process of discharging from 100% SOC to 90% SOC at 0.2C-20C.

[0386] After standing at an ambient temperature of -10°C for 10 hours, the electrochemical device U8 can maintain a voltage of not less than 3V during the process of discharging at 10C-12.5C from 100% SOC to 90% SOC.

[0387] After standing at an ambient temperature of -20°C for 10 hours, the electrochemical device U9 can maintain a voltage of not less than 2.5V during the process of discharging at 3C-12C from 100% SOC to 90% SOC.

[0388] Example 4

[0389] Fabrication of electrochemical devices.

[0390] <Production of positive electrode sheet>

[0391] Lithium nickel cobalt manganese oxide NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 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.

[0392] Exemplarily, the positive electrode plate has a structure similar to that of the first electrode plate. Specifically, referring to FIG6 , L1 = L2 = 1.36 m, W2 is 63.2 mm, and W1 is 4 mm.

[0393] <Production of negative electrode sheet>

[0394] The negative electrode active materials (artificial graphite and natural graphite, the mass ratio of artificial graphite to natural graphite is 30%:70%), conductive carbon black, styrene butadiene rubber (SBR, weight average molecular weight of 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.

[0395] Exemplarily, the negative electrode plate has a similar structure to the second electrode plate. Specifically, referring to FIG21 , L4 = L5 = 1.464 m, W5 is 64.1 mm, and W4 is 4 mm.

[0396] <Preparation of Separator>

[0397] Same as Example 1.

[0398] <Preparation of Electrolyte>

[0399] Same as Example 1.

[0400] <Preparation of Electrochemical Device>

[0401] Same as Example 1.

[0402] According to the above method, three electrochemical devices were prepared, and the three electrochemical devices were numbered U10, U11 and U12 respectively.

[0403] Electrochemical devices U10, U11, and U12 were tested using the same electrochemical device testing method as in Example 1. The test conditions and test results for each electrochemical device in Example 4 are shown in Table 4.

[0404] Table 4

[0405] Referring to Table 4, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 6 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices maintained a voltage of at least 2V, enabling continuous discharge.

[0406] After standing at an ambient temperature of 0° C. for 6 hours, the electrochemical device U10 can maintain a voltage of not less than 3V during the process of discharging from 100% SOC to 90% SOC at 0.2C-20C.

[0407] After standing at an ambient temperature of -10°C for 6 hours, the electrochemical device U11 was able to maintain a voltage of not less than 3V during the process of discharging at 10C-12.5C from 100% SOC to 90% SOC.

[0408] After standing at an ambient temperature of -20°C for 6 hours, the electrochemical device U12 can maintain a voltage of not less than 2.5V during the process of discharging at 3C-12C from 100% SOC to 90% SOC.

[0409] Comparative Example 1

[0410] Three INR21700-40T cells from the same batch were sampled, numbered U1', U2', and U3'. The same electrochemical device testing method as in Example 1 was used to test cells U1', U2', and U3'. The test conditions and results for each cell in Comparative Example 1 are shown in Table 5.

[0411] Table 5

[0412] Referring to Table 5, in Comparative Example 1, when the battery cell is discharged at a 9C rate from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the battery cell voltage drops below 2V, resulting in insufficient external voltage supply. Referring to Examples 1-4 and Comparative Example 1, the present embodiment can discharge at a rate of 10C or higher in a low-temperature environment, demonstrating excellent low-temperature discharge performance.

[0413] Example 5

[0414] <Production of positive electrode sheet>

[0415] Lithium nickel cobalt manganese oxide Ni95 (LiNi 0.95 Co 0.01 Mn 0.04 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.

[0416] Exemplarily, the positive electrode plate has a similar structure to the first electrode plate. Specifically, referring to Figure 13 , L2 is 1.36m, and there are five first sub-electrode tabs, all of which are identical in size. The total length L3 (K1+K2+K3+K4+K5) of the five first sub-electrode tabs is 1.1m. The distance between adjacent first sub-electrode tabs is equal, D is 65mm; D1=D2=0mm. W2 is 63.2mm, and W1 is 4mm.

[0417] <Preparation of negative electrode sheet>

[0418] Natural 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.

[0419] Exemplarily, the negative electrode has a similar structure to the second electrode. Specifically, referring to Figures 22 and 23 , L5 is 1.464m. There are five second sub-electrode tabs, all of which are identical in size. The total length L6 (J1+J2+J3+J4+J5) of the five second sub-electrode tabs is 1.2m. The distance D5 between adjacent second sub-electrode tabs is equal, D5 being 66mm; D3 = D4 = 0mm. W5 is 64.1mm, and W4 is 4mm.

[0420] <Preparation of Separator>

[0421] Same as Example 1.

[0422] <Preparation of Electrolyte>

[0423] Same as Example 1.

[0424] <Preparation of Electrochemical Device>

[0425] Same as Example 1.

[0426] According to the above scheme, three electrochemical devices were prepared, and the three electrochemical devices were numbered U13, U14 and U15 respectively.

[0427] Electrochemical devices U13, U14, and U15 were tested using the same electrochemical device testing method as in Example 1. The test conditions and test results for each electrochemical device in Example 5 are shown in Table 6.

[0428] Table 6

[0429] Referring to Table 6, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 6 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices were able to maintain a voltage of at least 2V, enabling continuous discharge.

[0430] After standing at an ambient temperature of 0° C. for 6 hours, the electrochemical device U13 can maintain a voltage of not less than 3V during the process of discharging at 0.2C-20C from 100% SOC to 90% SOC.

[0431] After standing at an ambient temperature of -10°C for 6 hours, the electrochemical device U14 can maintain a voltage of not less than 3V during the process of discharging at 10C-12.5C from 100% SOC to 90% SOC.

[0432] After standing at an ambient temperature of -20°C for 6 hours, the electrochemical device U15 can maintain a voltage of not less than 2.5V during the process of discharging at 3C-12C from 100% SOC to 90% SOC.

[0433] Example 6

[0434] <Production of positive electrode sheet>

[0435] The difference from Example 1 lies in the size and distribution of the first sub-pole lugs. Specifically, in a similar structure as shown in Figure 18, the L2 of the first main region is 1.36m, with a total of 10 first sub-pole lugs, all of which are of the same size, and the total length L3 (K1+K2+…+K10) of the 10 first sub-pole lugs is 1.1m. The Z1 region includes three first sub-pole lugs, each with a spacing of d1=40mm; the Z3 region includes three first sub-pole lugs, each with a spacing of d3=40mm; the Z2 region includes four first sub-pole lugs, each with a spacing of d2=20mm; the spacing between the Z2 region and the Z1 region is 20mm, and the spacing between the Z2 region and the Z3 region is 20mm.

[0436] <Preparation of negative electrode sheet>

[0437] The difference from Example 1 lies in the size and distribution of the second sub-pole ears. Specifically, the negative electrode plate has a similar structure as shown in Figure 23, and the second electrode plate of Figure 23 may also have a Z1 zone, a Z2 zone, and a Z3 zone as shown in Figure 18. The length of the second main area is 1.464m, with a total of 10 second sub-pole ears. The 10 second sub-pole ears have the same size, and the total length L6 (J1+J2+...+J10) of the 10 second sub-pole ears is 1.2m. The Z1 zone includes 3 second sub-pole ears with a spacing of d1=40mm, the Z3 zone includes 3 second sub-pole ears with a spacing of d3=40mm, and the Z2 zone includes 4 second sub-pole ears with a spacing of d2=20.8mm. The spacing between the Z2 zone and the Z1 zone is 20.8mm, and the spacing between the Z2 zone and the Z3 zone is 20.8mm.

[0438] <Preparation of Separator>

[0439] Same as Example 1.

[0440] <Preparation of Electrolyte>

[0441] Same as Example 1.

[0442] <Preparation of Electrochemical Device>

[0443] Same as Example 1.

[0444] According to the above method, three electrochemical devices were prepared, and the three electrochemical devices were numbered U16, U17 and U18 respectively.

[0445] Electrochemical devices U16, U17, and U18 were tested using the same electrochemical device testing method as in Example 1. The test conditions and test results for each electrochemical device in Example 6 are shown in Table 7.

[0446] Table 7

[0447] Referring to Table 7, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 6 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices were able to maintain a voltage of at least 2V, enabling continuous discharge.

[0448] After standing for 6 hours at an ambient temperature of 0°C, the electrochemical device U16 can maintain a voltage of not less than 3V during the process of discharging from 100% SOC to 90% SOC at 0.2C-20C.

[0449] After standing at an ambient temperature of -10°C for 6 hours, the electrochemical device U17 was able to maintain a voltage of not less than 3V during the process of discharging at 10C-12.5C from 100% SOC to 90% SOC.

[0450] After standing for 6 hours at an ambient temperature of -20°C, the electrochemical device U18 was able to maintain a voltage of not less than 2.5V during the process of discharging at 3C-12C from 100% SOC to 90% SOC.

[0451] Example 7

[0452] <Production of positive electrode sheet>

[0453] The difference from Example 1 lies in the size and distribution of the first sub-pole lugs. Specifically, in a similar structure as shown in Figure 20, the L2 of the first main body area is 1.36m, there are 5 first sub-pole lugs, and the total length L3 (K1+K2+...+K5) of the 5 first sub-pole lugs is 1.1m. The Z1 area includes 2 first sub-pole lugs with a spacing of d1=65mm, and the Z3 area includes 2 first sub-pole lugs with a spacing of d3=65mm. The first sub-pole lugs in the Z1 and Z3 areas are the same size. The Z2 area includes a first sub-pole lug with a size of 1m. The spacing between the Z2 area and the Z1 area is 65mm, and the spacing between the Z2 area and the Z3 area is 65mm.

[0454] <Preparation of negative electrode sheet>

[0455] The difference from Example 1 lies in the size and distribution of the second sub-pole ears. Specifically, the structure of the negative electrode plate is similar to the structure of the second electrode plate in Figure 23. The second electrode plate in Figure 23 may also have a Z1 zone, a Z2 zone, and a Z3 zone as shown in Figure 20. The length of the second main body area is 1.464m, with a total of 5 second sub-pole ears, and the total length L6 (J1+J2+...+J5) of the 5 second sub-pole ears is 1.2m. The Z1 zone includes 2 second sub-pole ears with a spacing of d1=66mm, and the Z3 zone includes 2 second sub-pole ears with a spacing of d3=66mm. The sizes of the second sub-pole ears in the Z1 zone and the Z3 zone are the same. The Z2 zone includes a second sub-pole ear with a size of 1.1m. The spacing between the Z2 zone and the Z1 zone is 66mm, and the spacing between the Z2 zone and the Z3 zone is 66mm.

[0456] <Preparation of Separator>

[0457] Same as Example 1.

[0458] <Preparation of Electrolyte>

[0459] Same as Example 1.

[0460] <Preparation of Electrochemical Device>

[0461] Same as Example 1.

[0462] According to the above method, three electrochemical devices were prepared, and the three electrochemical devices were numbered U19, U20 and U21 respectively.

[0463] Electrochemical devices U19, U20, and U21 were tested using the same electrochemical device testing method as in Example 1. The test conditions and test results for each electrochemical device in Example 6 are shown in Table 8.

[0464] Table 8

[0465] Referring to Table 8, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 6 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices maintained a voltage of at least 2V, enabling continuous discharge.

[0466] After standing for 6 hours at an ambient temperature of 0°C, the electrochemical device U19 was able to maintain a voltage of not less than 3V during the process of discharging from 100% SOC to 90% SOC at 0.2C-20C.

[0467] After standing at an ambient temperature of -10°C for 6 hours, the electrochemical device U20 can maintain a voltage of not less than 3V during the process of discharging at 10C-12.5C from 100% SOC to 90% SOC.

[0468] After standing at an ambient temperature of -20°C for 6 hours, the electrochemical device U21 was able to maintain a voltage of not less than 2.5V during the process of discharging at 3C-12C from 100% SOC to 90% SOC.

[0469] Example 8

[0470] <Production of positive electrode sheet>

[0471] The difference from Example 1 is that the first empty foil area is continuous and has a cutout. Specifically, referring to Figures 9 and 10, L1 = L2 = 1.36 m. The first empty foil area is provided with identical triangular cutouts at both the outer and inner corners along the winding direction, where La = W1 = 4 mm, W3 = 0.5 mm, and W1 = 2 mm.

[0472] <Preparation of negative electrode sheet>

[0473] The difference from Example 1 is that the second hollow foil area is continuous and has a cutout. Referring to Figure 21 , L4 = L5 = 1.464 m. The outer and inner corners of the second hollow foil area along the winding direction are both provided with triangular cutouts, as shown in Figure 9 . The cutouts for the negative electrode sheet are the same shape and size as those for the positive electrode sheet.

[0474] <Preparation of Separator>

[0475] Same as Example 1.

[0476] <Preparation of Electrolyte>

[0477] Same as Example 1.

[0478] <Preparation of Electrochemical Device>

[0479] Same as Example 1.

[0480] According to the above method, three electrochemical devices were prepared, and the three electrochemical devices were numbered U22, U23 and U24 respectively.

[0481] Electrochemical devices U22, U23, and U24 were tested using the same electrochemical device testing method as in Example 1. The test conditions and test results for each electrochemical device in Example 8 are shown in Table 9.

[0482] Table 9

[0483] Referring to Table 9, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 6 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices were able to maintain a voltage of at least 2V, enabling continuous discharge.

[0484] The embodiment of the present application reduces the amount of insulating components used by providing the cutouts, thereby increasing the energy density of the electrochemical device.

[0485] Example 9

[0486] The electrochemical device was fabricated as follows.

[0487] <Production of positive electrode sheet>

[0488] 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.

[0489] Exemplarily, the positive electrode plate has a structure similar to that of the first electrode plate. Specifically, referring to FIG13 , L2 is 0.92 m, there are 10 first sub-electrode tabs in total, and the 10 first sub-electrode tabs have the same size. The total length L3 (K1+K2+…+K10) of the 10 first sub-electrode tabs is 0.8 m. The spacing between two adjacent first sub-electrode tabs is equal, D is 10 mm. Along the length direction X after the first electrode plate is unfolded, 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 15 mm, 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 15 mm. W2 is 59 mm, and W1 is 4 mm.

[0490] <Preparation of negative electrode sheet>

[0491] 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.

[0492] Exemplarily, the negative electrode sheet has a similar structure to the second electrode sheet. Specifically, referring to Figures 22 and 23 , L5 is 1.02m. There are 10 second sub-electrode tabs, all of which are identical in size. The total length L6 (J1+J2+…+J10) of the 10 second sub-electrode tabs is 0.9m. The spacing D5 between adjacent second sub-electrode tabs is equal, at 10mm. Along the unfolded length direction X' of the second electrode sheet 12, the inner end of the second hollow foil region and the inner end of the second main body region are separated by a third distance D3 of 15mm, and the outer end of the second hollow foil region and the outer end of the second main body region are separated by a fourth distance D4 of 15mm. W5 is 60.2mm, and W4 is 4mm.

[0493] <Preparation of Separator>

[0494] 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.

[0495] <Preparation of Electrolyte>

[0496] 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.

[0497] <Preparation of Electrochemical Device>

[0498] 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.

[0499] According to the above method, three electrochemical devices were prepared and numbered as U25, U26, and U27, respectively.

[0500] Then, the three electrochemical devices were tested according to the following steps. The testing process was carried out using a battery tester (Neware Electronics Co. Ltd, China).

[0501] (1) After standing for 120 min in a 25°C constant temperature box (Coming EH-1000), the three electrochemical devices were charged to 100% SOC. Specifically, at a constant temperature of 25°C, each 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.

[0502] (2) After standing at a constant temperature of 25°C for 120 minutes, the three electrochemical devices at 100% SOC were discharged at a constant current of 0.2C to the discharge cutoff voltage of the electrochemical device (2.5V). The discharge capacity, which is the rated capacity of each electrochemical device, was tested. The devices were then charged at a constant current of 0.5C to the charge cutoff voltage of the electrochemical device (4.2V). The devices were then charged at a constant voltage of 0.05C at the charge cutoff voltage, at which point each electrochemical device was at 100% SOC.

[0503] (III) The three electrochemical devices at 100% SOC were placed in thermostats (Coming EH-1000) at different temperatures and allowed to stand for 6 hours. They were then discharged at the ambient temperature at a current i1 corresponding to a 0.1C rate for 10 seconds, and the voltage V1 was measured. They were then discharged at a current i2 corresponding to a 1C rate for 1 second, and the voltage V2 was measured. The DC resistance of the electrochemical device is (V1-V2) / (i2-i1). Electrochemical device U25 was tested in a thermostat at 0°C, electrochemical device U26 was tested in a thermostat at -10°C, and electrochemical device U27 was tested in a thermostat at -20°C.

[0504] (4) The electrochemical device tested for DC resistance was allowed to stand at a constant temperature of 25°C for 120 min, 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 0.05C at the charge cut-off voltage, at which point the electrochemical device was at 100% SOC;

[0505] (V) The three electrochemical devices at 100% SOC were placed in thermostats (Coming EH-1000) at different temperatures and left to stand for 6 hours. The corresponding ambient temperatures for each electrochemical device are shown in Table 10.

[0506] (6) Maintaining the temperature in the constant temperature box, the three electrochemical devices were discharged at a discharge rate of 0.2 C until the three electrochemical devices were discharged to the discharge cutoff voltage (2.5 V). During the discharge process, the discharge parameters of each electrochemical device were recorded.

[0507] (VII) The electrochemical device after step (VI) was allowed to stand at a constant temperature of 25°C for 120 min, and 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 0.05C at the charge cut-off voltage, at which time the electrochemical device was at 100% SOC; the three electrochemical devices at 100% SOC were placed in thermostats (Coming EH-1000) at different temperatures and allowed to stand for 6 hours, and then discharged at other rates at the same temperature until the electrochemical device was discharged to the discharge cut-off voltage (2.5V).

[0508] (8) Repeat step (7), change the discharge rate, and record the discharge parameters of each electrochemical device.

[0509] Among them, the discharge ambient temperature, discharge rate, minimum voltage of 100% SOC-90% SOC, discharge capacity of 100% SOC-0% SOC, rated capacity, DC resistance at the discharge ambient temperature, and volume energy density at the discharge ambient temperature of each electrochemical device are shown in Table 10.

[0510] Table 10

[0511] Referring to Table 10, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 6 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices maintained a voltage of at least 2V, enabling continuous discharge.

[0512] Specifically, referring to Table 10, the electrochemical device U25 can still discharge normally after being left at rest for 6 hours in an environment of 0° C., and can still discharge at a high rate of not less than 10C.

[0513] At an ambient temperature of 0°C, discharging at 0.2C-20C from 100% SOC to 90% SOC, the electrochemical device U25 can maintain a voltage of no less than 3V, thereby enabling continuous discharge. The electrochemical device of the present embodiment has good discharge performance at 0°C.

[0514] When discharged at a discharge rate of 10C-20C to a discharge cutoff voltage (eg, 2.5V) at 0°C, the discharge capacity of the electrochemical device U25 may exceed 90% of the rated capacity.

[0515] When the electrochemical device is at 0° C. and discharged at a rate of 0.2 C, the volume energy density VED of the electrochemical device is ≥ 670 Wh / L. The electrochemical device of the embodiment of the present application has a high energy density in a low temperature environment.

[0516] Referring to Table 10, the electrochemical device U26 can still discharge normally after being left at rest for 6 hours in an environment of -10°C, and can still discharge at a high rate of not less than 10C.

[0517] At an ambient temperature of -10°C, during discharge at 0.2C-17.5C, from 100% SOC to 90% SOC, the electrochemical device U26 can maintain a voltage of not less than 2.5V, thereby enabling continuous discharge to the outside. The electrochemical device of the embodiment of the present application has good discharge performance in an environment of -10°C. In particular, at an ambient temperature of -10°C, during discharge at 10C-12.5C, from 100% SOC to 90% SOC, the electrochemical device U26 can maintain a voltage of not less than 3V.

[0518] When discharged at a discharge rate of 10C-17.5C to a discharge cutoff voltage (eg, 2.5V) in a -10°C environment, the discharge capacity of the electrochemical device U26 may exceed 90% of the rated capacity.

[0519] When the electrochemical device is at -10°C and discharged at a rate of 0.2C, the volume energy density VED of the electrochemical device is ≥640Wh / L. The electrochemical device of the embodiment of the present application has a high energy density at -10°C.

[0520] Referring to Table 10, the electrochemical device U27 can still discharge normally after being left at rest for 6 hours in an environment of -20°C, and can still discharge at a high rate of not less than 10C.

[0521] At an ambient temperature of -20°C, discharging at a rate of 0.2C-17.5C from 100% SOC to 90% SOC, the electrochemical device can maintain a voltage of no less than 2V, thereby enabling continuous discharge. The electrochemical device of the embodiment of the present application has good discharge performance in an environment of -20°C.

[0522] At an ambient temperature of -20°C, during discharge at 3C-12C from 100% SOC to 90% SOC, the electrochemical device U27 can maintain a voltage of not less than 2.5V, thereby enabling continuous discharge to the outside.

[0523] When discharged at a discharge rate of 0.2-17.5C to a discharge cutoff voltage (e.g., 2.5V) at -20°C, the discharge capacity of the electrochemical device can exceed 80% of the rated capacity. When discharged at a discharge rate of 5C-17.5C to a discharge cutoff voltage (e.g., 2.5V) at -20°C, the discharge capacity of the electrochemical device can exceed 90% of the rated capacity.

[0524] Example 10

[0525] Three more electrochemical devices U28, U29, and U30 were manufactured according to the electrochemical device manufacturing method of Example 9.

[0526] Electrochemical devices U28, U29, and U30 were tested using the same electrochemical device testing method as in Example 9. Example 10 differs from Example 9 in that, in steps (3), (5), and (7), the electrochemical devices were left in a thermostat (Keming EH-1000) for 8 hours. The test conditions and results for each electrochemical device in Example 10 are shown in Table 11.

[0527] Table 11

[0528] Referring to Table 11, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 8 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices maintained a voltage of at least 2V, enabling continuous discharge.

[0529] After standing at an ambient temperature of 0°C for 8 hours, the electrochemical device U28 was discharged at 0.2C-20C from 100% SOC to 90% SOC, and the electrochemical device U31 was able to maintain a voltage of not less than 3V.

[0530] After standing at an ambient temperature of -10°C for 8 hours, the electrochemical device U32 was able to maintain a voltage of not less than 3V during the process of discharging the electrochemical device U29 at 10C-12.5C from 100% SOC to 90% SOC.

[0531] After standing at an ambient temperature of -20°C for 8 hours, the electrochemical device U33 was able to maintain a voltage of not less than 2.5V during the process of the electrochemical device U30 being discharged at 3C-12C from 100% SOC to 90% SOC.

[0532] Example 11

[0533] Three more electrochemical devices U31 , U32 , and U33 were manufactured according to the electrochemical device manufacturing method of Example 9.

[0534] Electrochemical devices U31, U32, and U33 were tested using the same electrochemical device testing method as in Example 9. Example 11 differs from Example 9 in that, in steps (3), (5), and (7), the electrochemical devices were left in a thermostat (Keming EH-1000) for 10 hours. The test conditions and results for each electrochemical device in Example 11 are shown in Table 12.

[0535] Table 12

[0536] Referring to Table 12, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 10 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices maintained a voltage of at least 2V, enabling continuous discharge.

[0537] After standing at an ambient temperature of 0°C for 10 hours, the electrochemical device U31 can maintain a voltage of not less than 3V during the process of discharging from 100% SOC to 90% SOC at 0.2C-20C.

[0538] After standing for 10 hours at an ambient temperature of -10°C, the electrochemical device U32 can maintain a voltage of not less than 3V during the process of discharging at 10C-12.5C from 100% SOC to 90% SOC.

[0539] After standing for 10 hours at an ambient temperature of -20°C, the electrochemical device U33 was able to maintain a voltage of not less than 2.5V during the process of discharging at 3C-12C and discharging from 100% SOC to 90% SOC.

[0540] Example 12

[0541] <Production of positive electrode sheet>

[0542] The difference from Example 9 is the length of the first empty foil area and the selection of the positive electrode active material. Specifically, referring to Figure 6, the first empty foil area is set continuously, L2 is 0.92m, L1=L2, L3=L2. W2 is 59mm, W1 is 4mm. The positive electrode active material is NCM811 (LiNi 0.8 Co 0.1 Mn 0.1 O2).

[0543] <Preparation of negative electrode sheet>

[0544] The differences from Example 9 lie in the length of the second hollow foil area and the choice of negative electrode active material. Specifically, referring to Figure 21 , the second main body area is 1.02m long, and the second hollow foil area is 1.02m long. W5 is 60.2mm, and W4 is 4mm. The negative electrode active materials are artificial graphite and natural graphite, with a mass ratio of 30% to 70%.

[0545] <Preparation of Separator>

[0546] Same as Example 9.

[0547] <Preparation of Electrolyte>

[0548] Same as Example 9.

[0549] <Preparation of Electrochemical Device>

[0550] Same as Example 9.

[0551] According to the above method, three electrochemical devices were prepared, and the three electrochemical devices were numbered U34, U35 and U36 respectively.

[0552] Electrochemical devices U34, U35, and U36 were tested using the same electrochemical device testing method as in Example 9. The test conditions and test results for each electrochemical device in Example 12 are shown in Table 13.

[0553] Table 13

[0554] Referring to Table 13, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 6 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices maintained a voltage of at least 2V, enabling continuous discharge.

[0555] After standing for 6 hours at an ambient temperature of 0°C, the electrochemical device U34 was able to maintain a voltage of not less than 3V during the process of discharging from 100% SOC to 90% SOC at 0.2C-20C.

[0556] After standing at an ambient temperature of -10°C for 6 hours, the electrochemical device U34 was able to maintain a voltage of not less than 3V during the process of discharging the electrochemical device U35 at 10C-12.5C from 100% SOC to 90% SOC.

[0557] After standing at an ambient temperature of -20°C for 6 hours, the electrochemical device U12 was able to maintain a voltage of not less than 2.5V during the process of the electrochemical device U36 being discharged at 3C-12C from 100% SOC to 90% SOC.

[0558] Comparative Example 2

[0559] Three INR18650-25R cells from the same batch were sampled, numbered U4', U5', and U6'. Cells U4', U5', and U6' were tested using the same electrochemical device testing method as in Example 9. The test conditions and results for each cell in Comparative Example 1 are shown in Table 14.

[0560] Table 14

[0561] Referring to Table 14, in Comparative Example 2, when the battery cell is discharged at a 9C rate from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the battery cell voltage drops below 2V, resulting in insufficient external voltage supply. Referring to Examples 9-12 and Comparative Example 2, the present embodiment can discharge at a rate of 10C or higher in a low-temperature environment, demonstrating excellent low-temperature discharge performance.

[0562] Example 13

[0563] <Production of positive electrode sheet>

[0564] The difference from Example 9 lies in the selection of the first sub-electrode tab and the selection of the positive electrode active material. Specifically, the positive electrode active material is Ni95 (LiNi 0.95 Co 0.01 Mn 0.04 Referring to FIG13 , the positive electrode sheet has five first sub-electrode tabs, all of which have the same size. The total length L3 (K1+K2+K3+K4+K5) of the five first sub-electrode tabs is 0.8 m. The distance D between two adjacent first sub-electrode tabs is equal, D is 30 mm, and D1=D2=0 mm.

[0565] <Preparation of negative electrode sheet>

[0566] The difference from Example 9 lies in the selection of the second sub-tab and the choice of negative electrode active material. Specifically, natural graphite is selected as the negative electrode active material. Referring to Figure 23, the negative electrode plate has five second sub-tabs, all of which are identical in size. The total length L6 (J1+J2+J3+J4+J5) of the five second sub-tabs is 0.9m. The distance D5 between adjacent second sub-tabs is equal, D5 being 30mm; D3 = D4 = 0mm.

[0567] <Preparation of Separator>

[0568] Same as Example 9.

[0569] <Preparation of Electrolyte>

[0570] Same as Example 9.

[0571] <Preparation of Electrochemical Device>

[0572] Same as Example 9.

[0573] Three electrochemical devices were prepared using the above method. These devices were numbered U37, U38, and U39. The same electrochemical device testing method as in Example 9 was used to test these devices. The test conditions and results for each electrochemical device in Example 13 are shown in Table 15.

[0574] Table 15

[0575] Referring to Table 15, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 6 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices maintained a voltage of at least 2V, enabling continuous discharge.

[0576] After standing for 6 hours at an ambient temperature of 0°C, the electrochemical device U37 was able to maintain a voltage of not less than 3V during the process of discharging at 0.2C-20C and discharging from 100% SOC to 90% SOC.

[0577] After standing for 6 hours at an ambient temperature of -10°C, the electrochemical device U38 was able to maintain a voltage of not less than 3V during the process of discharging at 10C-12.5C from 100% SOC to 90% SOC.

[0578] After standing for 6 hours at an ambient temperature of -20°C, the electrochemical device U39 was able to maintain a voltage of not less than 2.5V during the process of discharging at 3C-12C and discharging from 100% SOC to 90% SOC.

[0579] Example 14

[0580] <Production of positive electrode sheet>

[0581] The difference from Example 9 lies in the size and distribution of the first sub-electrode lugs. Specifically, in a similar structure as shown in Figure 18, the L2 of the first main region is 0.92m, with a total of 10 first sub-electrode lugs, all of which are of the same size, and the total length L3 (K1+K2+…+K10) of the 10 first sub-electrode lugs is 0.8m. The Z1 region includes three first sub-electrode lugs, each with a spacing of d1=17.5mm, the Z3 region includes three first sub-electrode lugs, each with a spacing of d3=17.5mm, and the Z2 region includes four first sub-electrode lugs, each with a spacing of d2=10mm. The spacing between the Z2 region and the Z1 region is 10mm, and the spacing between the Z2 region and the Z3 region is 10mm.

[0582] <Preparation of negative electrode sheet>

[0583] The difference from Example 9 lies in the size and distribution of the second sub-pole ears. Specifically, the negative electrode plate has a similar structure as shown in Figure 23, and the second electrode plate of Figure 23 may also have a Z1 region, a Z2 region, and a Z3 region as shown in Figure 18. The length of the second main region is 1.02m, with a total of 10 second sub-pole ears. The 10 second sub-pole ears have the same size, and the total length L6 (J1+J2+...+J10) of the 10 second sub-pole ears is 0.9m. The Z1 region includes 3 second sub-pole ears with a spacing of d1=17.5mm, the Z3 region includes 3 second sub-pole ears with a spacing of d3=17.5mm, and the Z2 region includes 4 second sub-pole ears with a spacing of d2=10mm. The spacing between the Z2 region and the Z1 region is 10mm, and the spacing between the Z2 region and the Z3 region is 10mm.

[0584] <Preparation of Separator>

[0585] Same as Example 9.

[0586] <Preparation of Electrolyte>

[0587] Same as Example 9.

[0588] <Preparation of Electrochemical Device>

[0589] Same as Example 9.

[0590] According to the above method, three electrochemical devices were prepared, and the three electrochemical devices were numbered U40, U41 and U42 respectively.

[0591] Electrochemical devices U40, U41, and U42 were tested using the same electrochemical device testing method as in Example 9. The test conditions and test results for each electrochemical device in Example 14 are shown in Table 16.

[0592] Table 16

[0593] Referring to Table 16, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 6 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices maintained a voltage of at least 2V, enabling continuous discharge.

[0594] After standing at an ambient temperature of 0° C. for 6 hours, the electrochemical device U40 can maintain a voltage of not less than 3V during the process of discharging from 100% SOC to 90% SOC at 0.2C-20C.

[0595] After standing at an ambient temperature of -10°C for 6 hours, the electrochemical device U41 was able to maintain a voltage of not less than 3V during the process of discharging at 10C-12.5C from 100% SOC to 90% SOC.

[0596] After standing at an ambient temperature of -20°C for 6 hours, the electrochemical device U42 can maintain a voltage of not less than 2.5V during the process of discharging at 3C-12C from 100% SOC to 90% SOC.

[0597] Example 15

[0598] <Production of positive electrode sheet>

[0599] The difference from Example 9 lies in the size and distribution of the first sub-pole ears. Specifically, in a similar structure as shown in Figure 20, the L2 of the first main body area is 0.92m, there are 5 first sub-pole ears in total, and the total length L3 (K1+K2+...+K5) of the 5 first sub-pole ears is 0.8m. The Z1 area includes 2 first sub-pole ears with a spacing of d1=30mm, and the Z3 area includes 2 first sub-pole ears with a spacing of d3=30mm. The sizes of the first sub-pole ears in the Z1 area and the Z3 area are the same. The Z2 area includes a first sub-pole ear with a size of 0.6m. The spacing between the Z2 area and the Z1 area is 30mm, and the spacing between the Z2 area and the Z3 area is 30mm. W2 is 59mm and W1 is 4mm.

[0600] <Preparation of negative electrode sheet>

[0601] The difference from Example 9 lies in the size and distribution of the second sub-pole ears. Specifically, the structure of the negative electrode plate is similar to the structure of the second electrode plate in Figure 23. The second electrode plate in Figure 23 may also have a Z1 zone, a Z2 zone, and a Z3 zone as shown in Figure 20. The length of the second main area is 1.02m, with a total of 5 second sub-pole ears, and the total length L6 (J1+J2+...+J5) of the 5 second sub-pole ears is 0.9m. The Z1 zone includes 2 second sub-pole ears with a spacing of d1=30mm, and the Z3 zone includes 2 second sub-pole ears with a spacing of d3=30mm. The sizes of the second sub-pole ears in the Z1 zone and the Z3 zone are the same. The Z2 zone includes a second sub-pole ear with a size of 0.7m. The spacing between the Z2 zone and the Z1 zone is 30mm, and the spacing between the Z2 zone and the Z3 zone is 30mm.

[0602] <Preparation of Separator>

[0603] Same as Example 9.

[0604] <Preparation of Electrolyte>

[0605] Same as Example 9.

[0606] <Preparation of Electrochemical Device>

[0607] Same as Example 9.

[0608] According to the above method, three electrochemical devices were prepared, and the three electrochemical devices were numbered U43, U44 and U45 respectively.

[0609] Electrochemical devices U43, U44, and U45 were tested using the same electrochemical device testing method as in Example 9. The test conditions and test results for each electrochemical device in Example 15 are shown in Table 17.

[0610] Table 17

[0611] Referring to Table 17, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 6 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices maintained a voltage of at least 2V, enabling continuous discharge.

[0612] After standing at an ambient temperature of 0°C for 6 hours, the electrochemical device U43 can maintain a voltage of not less than 3V during the process of discharging from 100% SOC to 90% SOC at 0.2C-20C.

[0613] After standing at an ambient temperature of -10°C for 6 hours, the electrochemical device U44 can maintain a voltage of not less than 3V during the process of discharging at 10C-12.5C from 100% SOC to 90% SOC.

[0614] After standing at an ambient temperature of -20°C for 6 hours, the electrochemical device U45 can maintain a voltage of not less than 2.5V during the process of discharging at 3C-12C from 100% SOC to 90% SOC.

[0615] Example 16

[0616] <Production of positive electrode sheet>

[0617] The difference from Example 9 is that the first empty foil area is continuous and has a cutout. Specifically, referring to Figures 9 and 10, L1 = L2 = 0.92m. The first empty foil area has identical triangular cutouts at both the outer and inner corners along the winding direction, with La = W1 = 4mm, W3 = 0.5mm, and W1 = 2mm.

[0618] <Preparation of negative electrode sheet>

[0619] The difference from Example 9 is that the second hollow foil area is continuous and has a cutout. Specifically, referring to Figure 21 , L4 = L5 = 1.02 m. The outer and inner corners of the second hollow foil area along the winding direction are both provided with triangular cutouts, as shown in Figure 9 . The cutouts for the negative electrode sheet are identical in shape and size to those for the positive electrode sheet.

[0620] <Preparation of Separator>

[0621] Same as Example 9.

[0622] <Preparation of Electrolyte>

[0623] Same as Example 9.

[0624] <Preparation of Electrochemical Device>

[0625] Same as Example 9.

[0626] According to the above method, three electrochemical devices were prepared. The three electrochemical devices were numbered U46, U47 and U48 respectively.

[0627] Electrochemical devices U46, U47, and U48 were tested using the same electrochemical device testing method as in Example 9. The test conditions and test results for each electrochemical device in Example 8 are shown in Table 18.

[0628] Table 18

[0629] Referring to Table 18, the three electrochemical devices were able to discharge at a high rate even after being stored in a low-temperature environment of -20°C to 0°C for 6 hours. During the high-rate discharge from 100% SOC to 90% SOC in a low-temperature environment of -20°C to 0°C, the three electrochemical devices maintained a voltage of at least 2V, enabling continuous discharge.

[0630] The embodiment of the present application reduces the amount of insulating components used by providing the cutouts, thereby increasing the energy density of the electrochemical device.

Claims

1. An electrochemical device, comprising a housing and an electrode assembly accommodated in the housing; The electrode assembly includes a first pole piece, a second pole piece and a separator. The polarities of the first pole piece and the second pole piece are opposite. The first pole piece, the separator and the second pole piece are laminated and wound along the winding direction; The first pole piece 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, A part of the first empty foil region away from the first main region forms a first flattened region; The electrochemical device is configured to: In response to the electrochemical device at 100% SOC being placed at a first ambient temperature for a first time, at the first ambient temperature, the electrochemical device performs a discharge operation at a first discharge rate, and continues the discharge operation until the SOC of the electrochemical device is 90%, and the minimum voltage value of the electrochemical device is greater than or equal to 2V; Among them, The first ambient temperature is -20°C - 0°C, the first time is greater than or equal to 6 hours, and the first discharge rate is greater than or equal to 10C.

2. The electrochemical device according to claim 1, further 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%.

3. The electrochemical device according to claim 1 or 2, wherein A first cut is provided at a corner of the outer end of the first empty foil region along the winding direction; Along the length direction of the first pole piece after being unfolded, the size of the first cut is La; along the width direction of the first pole piece after being unfolded, the size of the first empty foil region is W1; La and W1 satisfy: 0.2 ≤ La / W1 ≤ 4.

4. The electrochemical device according to claim 3, wherein, Along the width direction of the first pole piece after being unfolded, the size of the first cut is W3; W3 and W1 satisfy: 0.2 ≤ W3 / W1 ≤ 1.

5. The electrochemical device according to claim 3 or 4, wherein, The first cut is a rectangular cut, a triangular cut or an arc cut.

6. The electrochemical device according to any one of claims 1-5, wherein, The first time is less than or equal to 10 hours.

7. The electrochemical device according to claim 6, wherein, The first time is 7 hours, 8 hours or 9 hours.

8. The electrochemical device according to any one of claims 1-7, wherein, The first discharge rate is less than or equal to 17.5C.

9. The electrochemical device according to any one of claims 1-7, wherein, The first ambient temperature is 0°C, and the first discharge rate is 10C - 20C.

10. The electrochemical device according to claim 9, wherein, The minimum voltage is greater than or equal to 2.5V, and the first discharge rate is 10C - 20C.

11. The electrochemical device according to claim 9, wherein, The minimum voltage is greater than or equal to 3V, and the first discharge rate is 10C - 20C.

12. The electrochemical device according to any one of claims 1-7, wherein, The first ambient temperature is -10°C, and the first discharge rate is 10C - 17.5C.

13. The electrochemical device according to claim 12, wherein, The minimum voltage is greater than or equal to 2.5V.

14. The electrochemical device according to claim 12, wherein, The minimum voltage is greater than or equal to 3V, and the first discharge rate is 10C - 12.5C.

15. The electrochemical device according to any one of claims 1-7, wherein, The first ambient temperature is -20°C, and the first discharge rate is 10C - 17.5C.

16. The electrochemical device according to claim 15, wherein, The minimum voltage is greater than or equal to 2.5V, and the first discharge rate is 10C - 12C.

17. The electrochemical device according to any one of claims 1-16, wherein, the electrochemical device is further configured: in response to the electrochemical device at 100% SOC discharging continuously at the first discharge rate to 0% SOC at the first ambient temperature, the ratio of the discharge capacity of the electrochemical device to the rated capacity of the electrochemical device is greater than or equal to 80%.

18. The electrochemical device according to claim 17, wherein, the electrochemical device is further configured: in response to the electrochemical device at 100% SOC discharging continuously at the first discharge rate to 0% SOC at the first ambient temperature, 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%; the first discharge rate is 10C - 17.5C.

19. The electrochemical device according to any one of claims 1-18, wherein, Along the length direction after the first pole piece is unfolded, the size of the first empty foil area is L1, and the size of the first main body area is L2, and L1 and L2 satisfy: 0.8 ≤ L1 / L2 ≤ 1.

20. The electrochemical device according to any one of claims 1-18, wherein, The first empty foil area includes a plurality of first sub-tab ears, and along the length direction after the first pole piece is unfolded, the plurality of first sub-tab ears are separately arranged.

21. The electrochemical device according to claim 20, wherein, Along the length direction after the first pole piece is unfolded, the minimum distance D between adjacent first sub-tab ears is 0 mm - 66 mm.

22. The electrochemical device according to claim 20, wherein, The first empty foil area includes a first tab ear area, a second tab ear area, and a third tab ear area arranged along the length direction after the first pole piece is unfolded, and each of the first tab ear area, the second tab ear area, and the third tab ear area includes at least two of the first sub-tab ears; Along the length direction after the first pole piece is unfolded, the minimum distance between adjacent first sub-tab ears in the first tab ear area is d1, the minimum distance between adjacent first sub-tab ears in the second tab ear area is d2, and the minimum distance between adjacent first sub-tab ears in the third tab ear area is d3, and d1, d2, and d3 satisfy: d2 < d1, d2 < d3; The electrochemical device further includes a current collector plate accommodated in the housing, and the current collector plate is welded to the second tab ear area.

23. The electrochemical device according to claim 20, wherein, The first empty foil area includes a first tab ear area, a second tab ear area, and a third tab ear area arranged along the length direction after the first pole piece is unfolded, and each of the first tab ear area and the third tab ear area includes at least two of the first sub-tab ears, and the second tab ear area includes one of the first sub-tab ears; Along the length direction after the first pole piece is unfolded, the size of the first sub-tab ear in the second tab ear area is greater than the size of the first sub-tab ear in the first tab ear area, and the size of the first sub-tab ear in the second tab ear area is greater than the size of the first sub-tab ear in the third tab ear area; The electrochemical device further includes a current collector plate accommodated in the housing, and the current collector plate is welded to the second tab ear area.

24. The electrochemical device according to claim 23, wherein, Along the length direction after the first pole piece is unfolded, the size of the first sub-tab ear in the second tab ear area is 0.6 m - 1.1 m.

25. The electrochemical device according to any one of claims 1-24, wherein, In the width direction of the first pole piece after unfolding, the size of the first empty foil area is W1, and the total size of the first current collector is W2. W1 and W2 satisfy: 0.05 ≤ W1 / W2 ≤ 0.

1.

26. The electrochemical device according to any one of claims 1-25, wherein, One of the first pole piece and the second pole piece is a positive pole piece, and the other is a negative pole piece; The positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes a positive electrode active material, a binder, and a conductive agent. The positive electrode active material includes at least one of Li 1+a Ni x1 Co y1 Mn z1 O2 or Li 1+a Ni x2 Co y2 Al z2 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; -0.05 ≤ a ≤ 0.

2.

27. The electrochemical device according to claim 26, wherein, Both x1 and x2 are greater than or equal to 0.

9.

28. The electrochemical device according to any one of claims 1-27, wherein, One of the first pole piece and the second pole piece is a positive pole piece, and the other is a negative pole piece; The negative pole piece includes a negative active material, the negative active material includes a negative active material, and the negative active material includes artificial graphite and / or natural graphite.

29. The electrochemical device according to any one of claims 1-28, including a cylindrical battery cell, the diameter of the cylindrical battery cell being 17 mm - 22 mm, and the height of the cylindrical battery cell being 64 mm - 72 mm.

30. The electrochemical device according to claim 29, wherein, The cylindrical battery cell is a 18650 type battery cell or a 21700 type battery cell.

31. The electrochemical device according to any one of claims 1-30, wherein, At the first ambient temperature, the DC resistance of the electrochemical device is less than or equal to 10 mΩ.

32. The electrochemical device according to any one of claims 1-31, wherein, The rated capacity of the electrochemical device is 2500 mAh - 4500 mAh.

33. The electrochemical device according to any one of claims 1-32, wherein, When the electrochemical device is at the first ambient temperature and the electrochemical device discharges at a rate of 0.2C, the volume energy density VED of the electrochemical device ≥ 558 Wh / L.

34. The electrochemical device according to claim 33, wherein, When the electrochemical device is at the first ambient temperature and the electrochemical device discharges at a rate of 0.2C, the volume energy density VED of the electrochemical device ≥ 603 Wh / L.

35. A battery pack, including the electrochemical device according to any one of claims 1-34.

36. The battery pack according to claim 35, including 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.

37. An electrical device, including the battery pack according to any one of claims 35 or 36.

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