Electrochemical apparatus, battery pack and electrical device

Abstract

The application discloses an electrochemical apparatus, a battery pack and an electric device. The electrochemical device comprises a housing and an electrode assembly accommodated in the housing. The electrode assembly comprises a first pole piece, a second pole piece and a separator. The first pole piece, the separator and the second pole piece are stacked and wound in a winding direction. One of the first pole piece and the second pole piece is a positive pole piece, and the other one is a negative pole piece. The negative pole piece comprises a negative electrode current collector and a negative electrode active substance. The negative electrode active substance is arranged on the negative electrode current collector. The negative electrode active substance comprises artificial graphite and / or natural graphite. The electrochemical apparatus has high charging capacity in a constant-current charging operation stage, which is beneficial to improving the charging efficiency and shortening the charging time.

Description

Electrochemical devices, battery packs, and electrical equipment

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202311827964.9, filed on December 27, 2023, entitled “Electrochemical device, battery pack, and electrical equipment,” the entire contents of which are incorporated herein by reference. Technical Field

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

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

[0005] The present application provides an electrochemical device, a battery pack, and an electrical device, which are conducive to improving charging efficiency.

[0006] In a first aspect, embodiments of the present application provide 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 separator, wherein the first electrode sheet, the separator, and the second electrode sheet are stacked and wound along a winding direction, wherein one of the first electrode sheet and the second electrode sheet is a positive electrode sheet and the other is a negative electrode sheet. The negative electrode sheet comprises a negative electrode current collector and a negative electrode active material, wherein the negative electrode active material is disposed on the negative electrode current collector and comprises artificial graphite and / or natural graphite.

[0007] The electrochemical device is configured as follows:

[0008] The electrochemical device is placed in a first ambient temperature and allowed to stand for a first period of time, and then subjected to a constant current charging operation at a first charging rate. The constant current charging operation is performed from a discharge cut-off voltage of the electrochemical device until the voltage of the electrochemical device reaches a charge cut-off voltage.

[0009] The electrochemical device performs a constant voltage charging operation at a first ambient temperature from a charge cutoff voltage until the constant voltage charging operation has a second charge rate;

[0010] In response to the constant current charging operation and the constant voltage charging operation, the charge capacity of the electrochemical device in the constant current charging operation is C1, and the charge capacity of the electrochemical device in the constant voltage charging operation is C2;

[0011] Among them, 0.87≤C1 / (C1+C2)≤0.93, the first charging rate is 2C to 3C, the second charging rate is 0.05C, the first time is 1 hour to 2 hours, and the first ambient temperature is 25℃ to 45℃.

[0012] The charging current of the electrochemical device during the constant current charging operation phase is greater than the charging current of the electrochemical device during the constant voltage charging operation phase, and the charging rate of the electrochemical device during the constant current charging operation phase is faster. The embodiments of the present application have a higher charging capacity during the constant current charging operation phase, which is conducive to improving charging efficiency and shortening charging time.

[0013] In one or more of the above optional embodiments, 0.91≤C1 / (C1+C2)≤0.93.

[0014] In one or more optional embodiments above, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material, the positive electrode active material is provided on the positive electrode current collector, and the positive electrode active material includes Li 1+a Ni x1 Co y1 Mn z1 O2 or Li 1+a Ni x2 Co y2 Al z2 At least one of O2. x1 and x2 are both greater than or equal to 0.8, y1 and y2 are both greater than 0, z2 and z3 are both greater than 0, x1+y1+z1=1, x2+y2+z2=1, -0.05≤a≤0.2.

[0015] In one or more of the above optional embodiments, x1 and x2 are both greater than or equal to 0.9.

[0016] In one or more of the above optional embodiments, the first electrode sheet includes a first current collector and a first active material. The first current collector includes a first main body region and a first hollow foil region. The first active material is disposed in the first main body region, and the first main body region and the first hollow foil region are arranged perpendicular to the winding direction. The first hollow foil region includes a first flattened region, which is distal to the first main body region. The first flattened region forms a dense end face, thereby facilitating connection with other conductive structures.

[0017] In one or more optional embodiments above, along the width direction of the unfolded first electrode sheet, the size of the first empty foil area is W1, the size of the first current collector is W2, and W1 and W2 satisfy: 0.05≤W1 / W2≤0.1.

[0018] Setting W1 / W2 to greater than or equal to 0.05 allows the first hollow foil area to have a larger width, facilitating connection between the first hollow foil area and other conductive structures. This also helps reduce the stress on the first active material during flattening, lowering the risk of deformation and powder loss. Setting W1 / W2 to less than or equal to 0.1 allows more space for the first active material, helping to reduce energy density loss.

[0019] 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.

[0020] Limiting La / W1 to greater than or equal to 0.2 helps reduce the accumulation of empty foil material during the flattening process, lowering the risk of puncturing the insulating member covering the first empty foil area, and improving safety. Limiting La / W1 to less than or equal to 4 helps reduce the impact of the first cut on the flow capacity of the first empty foil area.

[0021] In one or more optional embodiments above, along the width direction of the unfolded first pole piece, the size of the first incision is W3. W3 and W1 satisfy: 0.2≤W3 / W1≤1.

[0022] Setting W3 / W1 to greater than or equal to 0.2 helps reduce the accumulation of empty foil material during the flattening process, lowering the risk of puncturing the insulating member covering the first empty foil area, and improving safety. Setting W3 / W1 to less than or equal to 1 helps reduce the risk of the first incision extending into the first main body area, thereby reducing the loss of the first active material.

[0023] In one or more optional embodiments above, along the width direction of the unfolded first pole piece, the size of the first flattened area is W4, and 0.6≤W4 / W1≤0.95.

[0024] Setting W4 / W1 to greater than or equal to 0.6 helps increase the pressure area of ​​the first empty foil area during the flattening process, reducing the axial size of the electrode assembly, improving space utilization, and making the first flattened area more compact. Setting W4 / W1 to less than or equal to 0.95 helps reduce the force transmitted to the first active material during the flattening process, reducing the risk of the first active material falling off.

[0025] In one or more of the above optional embodiments, the electrochemical device further includes electrode terminals disposed on the housing and a current collecting disk connected to the electrode terminals, the current collecting disk being welded to the first flattened region. The first flattened region has a dense end surface, and welding the first flattened region to the current collecting disk helps reduce the risk of cold welds, improve weld strength, and reduce the risk of diaphragm burns due to laser leakage, thereby improving safety.

[0026] In one or more of the above optional embodiments, the electrochemical device includes a cylindrical battery cell, which has a mature production process, a high product yield, and good heat dissipation performance.

[0027] In one or more optional embodiments above, the diameter of the cylindrical battery cell is 17 mm-22 mm, and the height of the cylindrical battery cell is 64 mm-72 mm.

[0028] In one or more optional embodiments above, the cylindrical battery cell is an 18650 battery cell or a 21700 battery cell.

[0029] In one or more of the above optional embodiments, the rated capacity of the electrochemical device is 2500 mAh to 4500 mAh.

[0030] In one or more of the above optional embodiments, the AC internal resistance of the electrochemical device is less than 6 milliohms. The electrochemical device has a smaller AC resistance, thereby reducing heat generation during charging and improving charging efficiency and performance of the electrochemical device.

[0031] In a second aspect, the present application further provides a battery pack, which includes the electrochemical device provided in any embodiment of the first aspect.

[0032] 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.

[0033] In a third aspect, the present application further provides an electrical device comprising a battery pack provided in any embodiment of the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] 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.

[0035] FIG1 is a schematic structural diagram of an electrochemical device provided in some embodiments of the present application;

[0036] FIG2 is a schematic diagram of an explosion of the electrochemical device shown in FIG1 ;

[0037] FIG3 is a front view schematic diagram of an electrode assembly of an electrochemical device provided in some embodiments of the present application;

[0038] FIG4 is a schematic top view of the electrode assembly shown in FIG3 ;

[0039] FIG5 is a schematic cross-sectional view taken along the AA direction in FIG3 ;

[0040] 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;

[0041] FIG7 is a schematic cross-sectional view taken along the BB direction in FIG6 ;

[0042] FIG8 is a partial cross-sectional schematic diagram of a first electrode tab of an electrochemical device provided in some embodiments of the present application;

[0043] 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;

[0044] FIG10 is an enlarged schematic diagram of the circle frame of FIG9;

[0045] 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;

[0046] 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;

[0047] FIG13 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;

[0048] FIG14 is a schematic cross-sectional view taken along the CC direction of FIG13;

[0049] FIG15 is a schematic diagram of a battery pack provided in some embodiments of the present application;

[0050] FIG16 is a schematic diagram of an electrical device provided by some embodiments of the present application;

[0051] Figure 17 is a schematic diagram of the charging performance of Example 1, Comparative Example 1, and Comparative Example 2 of the present application.

[0052] The reference numerals are as follows: DETAILED DESCRIPTION

[0053] 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 conjunction 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] In some embodiments, the electrochemical device 1000 includes a housing 2 and an electrode assembly 1 accommodated in the housing 2 .

[0059] The electrode assembly 1 includes a first electrode sheet 11, a second electrode sheet 12, and a separator 13. One of the first electrode sheet 11 and the second electrode sheet 12 is a positive electrode sheet, and the other is a negative electrode sheet.

[0060] During the charge and discharge process of electrochemical device 1000, active ions (e.g., lithium ions) are intercalated and released between the positive and negative electrode sheets. Separator 13 insulates first electrode sheet 11 from second electrode sheet 12 to reduce the risk of short circuits between the positive and negative electrode sheets, while allowing the active ions to pass through.

[0061] One or more electrode assemblies 1 can be accommodated in the housing 2 .

[0062] In some embodiments, the electrode assembly 1 may be a wound structure, a laminated structure, or other structures.

[0063] In some embodiments, the shape of the electrode assembly 1 can be cylindrical, flat, or polygonal.

[0064] 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).

[0065] 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.

[0066] 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.

[0067] The cover plate 5 can be connected to the housing 2 by welding, bonding, clamping or other methods.

[0068] 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.

[0069] In some embodiments, the electrochemical device 1000 further includes an electrode terminal 3 , which is disposed on the cover plate 5 .

[0070] 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.

[0071] 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.

[0072] 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 .

[0073] 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.

[0074] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode active material. The negative electrode active material is disposed on the negative electrode current collector, and the negative electrode active material includes artificial graphite and / or natural graphite.

[0075] In some embodiments, the electrochemical device 1000 is configured to:

[0076] The electrochemical device 1000 is placed in a first ambient temperature and allowed to stand for a first period of time, and then subjected to a constant current charging operation at a first charge rate. The electrochemical device 1000 is subjected to the constant current charging operation from a discharge cut-off voltage until the voltage of the electrochemical device 1000 reaches a charge cut-off voltage.

[0077] The electrochemical device 1000 performs a constant voltage charging operation at a first ambient temperature from a charge cutoff voltage until the constant voltage charging operation has a second charge rate;

[0078] In response to the constant current charging operation and the constant voltage charging operation, the charge capacity of the electrochemical device 1000 in the constant current charging operation is C1, and the charge capacity of the electrochemical device 1000 in the constant voltage charging operation is C2;

[0079] Among them, 0.87≤C1 / (C1+C2)≤0.93, the first charging rate is 2C to 3C, the second charging rate is 0.05C, the first time is 1 hour to 2 hours, and the first ambient temperature is 25℃ to 45℃.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] Exemplarily, charge rate = current / rated capacity; discharge rate = current / rated capacity.

[0084] 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.

[0085] 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.

[0086] For example, the electrochemical device may be an 18650 battery cell or a 21700 battery cell. For example, the rated capacity of the 18650 battery cell may be 2500 mAh, 3000 mAh, 3500 mAh, or 4000 mAh, and the rated capacity of the 21700 battery cell may be 3500 mAh, 4000 mAh, 4500 mAh, or 5000 mAh.

[0087] For example, the rated capacity of the electrochemical device is 4000 mAh. During a constant current charging operation at 2C, the charging current is 4000 × 2 mA; during a constant current charging operation at 3C, the charging current is 4000 × 3 mA. During a constant voltage charging operation with a second charge rate, the charging current is 4000 × 0.05 mA.

[0088] Exemplarily, an electrochemical device at 100% SOC means that: at 25° C., the electrochemical device is discharged at a constant current of 0.5 C to the discharge cut-off voltage of the electrochemical device, then charged at a constant current of 0.5 C to the charge cut-off voltage of the electrochemical device, and then charged at a constant voltage of the charge cut-off voltage to 0.05 C, at which time the electrochemical device is at 100% SOC.

[0089] 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%.

[0090] For example, the charge and discharge process of the electrochemical device can be tested by a battery tester (Neware CT-4016-5V-100A).

[0091] For example, when the electrochemical device 1000 is subjected to a constant current charging operation at a first charge rate after being left at a first ambient temperature for a first period of time, the charging current is i1. The time at which the electrochemical device 1000 begins the constant current charging operation from the discharge cutoff voltage is t0, and the time at which the voltage of the electrochemical device 1000 reaches the charge cutoff voltage is t1. C1 = i1 × (t1 - t0).

[0092] The moment when the electrochemical device 1000 performs constant voltage charging until the charging rate reaches the second charging rate is t2. During constant voltage charging, the charging current i2 changes with time t, and the charging current i2 = f(t), t1≤t≤t2.

[0093] For example,

[0094] The first ambient temperature is a constant temperature. For example, the electrochemical device is placed in a constant temperature box (Keming EH-1000) at a constant temperature of 25°C to perform constant current charging and constant voltage charging operations. For example, the electrochemical device is placed in a constant temperature box (Keming EH-1000) at a constant temperature of 35°C to perform constant current charging and constant voltage charging operations. For example, the electrochemical device is placed in a constant temperature box (Keming EH-1000) at a constant temperature of 45°C to perform constant current charging and constant voltage charging operations.

[0095] As an example, the first ambient temperature may be 25°C, 28°C, 30°C, 35°C, 38°C, 40°C, 42°C or 45°C.

[0096] As an example, C1 / (C1+C2) may be 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, or 0.93.

[0097] As an example, the first time may be 1 hour, 1.5 hours, or 2 hours.

[0098] The charging current of the electrochemical device during the constant current charging operation phase is greater than the charging current of the electrochemical device during the constant voltage charging operation phase, and the charging rate of the electrochemical device during the constant current charging operation phase is faster. The embodiments of the present application have a higher charging capacity during the constant current charging operation phase, which is conducive to improving charging efficiency and shortening charging time.

[0099] In some embodiments, the first ambient temperature is 25°C.

[0100] In some embodiments, the electrochemical device 1000 performs a constant voltage charging operation at a charge cutoff voltage at an ambient temperature of 25° C. When the electrochemical device 1000 is charged to a second charge rate in the constant voltage charging operation, the electrochemical device 100 is at a SOC (State of Charge) of 100%.

[0101] In some embodiments, 0.91≤C1 / (C1+C2)≤0.93.

[0102] In some embodiments, the first charging rate is 2C, and C1 / (C1+C2)≥0.91. When the first charging rate is relatively small, more capacity can be charged during the constant current charging operation phase.

[0103] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material, the positive electrode active material is disposed on the positive electrode current collector, and the positive electrode active material includes Li 1+a Ni x1 Co y1 Mn z1 O2 or Li 1+a Ni x2 Co y2 Al z2 At least one of O2. 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.

[0104] In some embodiments, x1 and x2 are both greater than or equal to 0.9.

[0105] 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 0.05O2、LiNi 0.94 Co 0.01 Al 0.05 O2、LiNi 0.95 Co 0.01 Al 0.04 At least one of O2.

[0106] In some embodiments, the positive electrode active material includes a positive electrode active material, a binder and a conductive agent, and the positive electrode active material includes Li 1+a Ni x1 Co y1 Mn z1 O2 or Li 1+a Ni x2 Co y2 Al z2 At least one of O2.

[0107] In some embodiments, the adhesive includes at least one of polyacrylic acid (PAA), polyacrylonitrile (PAN), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), or polyamide (PA).

[0108] 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.

[0109] 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%.

[0110] In some embodiments, the negative electrode active material also includes a binder and a conductive agent.

[0111] 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.

[0112] 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%.

[0113] 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.

[0114] In some embodiments, after the electrode assembly 1 is wound, a central hole 10c is formed in the middle.

[0115] In some embodiments, the first electrode 11 includes a first current collector 111 and a first active material 112 .

[0116] 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 .

[0117] 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.

[0118] In some embodiments, the first electrode sheet 11 is a positive electrode sheet, the first current collector 111 is a positive electrode current collector, and the first active material 112 is a positive electrode active material. In other embodiments, the first electrode sheet 11 is a negative electrode sheet, the first current collector 111 is a negative electrode current collector, and the first active material 112 is a negative electrode active material.

[0119] 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.

[0120] 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 .

[0121] 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 .

[0122] 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.

[0123] 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.

[0124] In some embodiments, the first empty foil region 111b includes a first crumpled region 111c. The first crumpled region 111c is away from the first main region 111a. In other words, the first crumpled region 111c is formed at the end of the first empty foil region 111b away from the first main region 111a.

[0125] Exemplarily, as shown in FIG6 , a portion of the first empty foil area 111 b located above the dotted line is used to form the first flattened area 111 c .

[0126] 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.

[0127] 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 .

[0128] 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.

[0129] L1 is the maximum size of the first hollow foil area 111b after unfolding along the length direction X of the unfolded first electrode sheet 11. Exemplarily, the unfolding of the first electrode sheet 11 may be to unfold the first electrode sheet 11 into a flat sheet structure, and correspondingly, the first flattened area 111c is also flattened.

[0130] The first empty foil area 111b has a large flow area. When the electrochemical device 1000 is charged or discharged at a high rate, a large current can pass through the first empty foil area 111b, thereby reducing heat generation in the first empty foil area 111b and reducing the risk of the first empty foil area 111b fusing.

[0131] Alternatively, L1 / L2 may be 0.8, 0.85, 0.9, 0.95 or 1.

[0132] 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.

[0133] 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.

[0134] In some embodiments, along the width direction Y of the unfolded first electrode sheet 11 , the size of the first empty foil area 111 b is W1 , the size of the first current collector 111 is W2 , and W1 and W2 satisfy: 0.05≤W1 / W2≤0.1.

[0135] 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 helps reserve more space for the first active material 112, reducing energy density loss.

[0136] 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.

[0137] Alternatively, W1 / W2 may be 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1.

[0138] In some embodiments, along the width direction Y of the unfolded first electrode sheet 11 , the size of the first flattened area 111 c is W4 , and 0.6≤W4 / W1≤0.95.

[0139] Setting W4 / W1 to greater than or equal to 0.6 helps increase the pressure area of ​​the first hollow foil region 111b during the flattening process, reduces the axial size of the electrode assembly 1, improves space utilization, and makes the first flattened region 111c more compact. Setting W4 / W1 to less than or equal to 0.95 helps reduce the force transmitted to the first active material 112 during the flattening process, reducing the risk of the first active material 112 falling off.

[0140] In some embodiments, the electrochemical device 1000 further includes an electrode terminal 3 disposed on the housing 2 and a current collecting plate 4 connected to the electrode terminal 3. The current collecting plate 4 is welded to the first flattened region 111c. The first flattened region 111c has a dense end surface. Welding the first flattened region 111c to the current collecting plate 4 helps reduce the risk of cold welds, improves weld strength, and reduces the risk of burning the diaphragm 13 due to laser leakage, thereby improving safety.

[0141] In some embodiments, the electrode assembly further includes an insulating sheet attached to the outer periphery of the first flattened area 111 c.

[0142] 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.

[0143] 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.

[0144] 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.

[0145] In some embodiments, a second cutout G2 is provided at a corner of the inner end of the first empty foil region 111 b along the winding direction V.

[0146] 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.

[0147] 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.

[0148] Limiting La / W1 to greater than or equal to 0.2 helps reduce the accumulation of empty foil material during the flattening process, lowering the risk of puncturing the insulating member covering the first empty foil area 111b, and improving safety. Limiting La / W1 to less than or equal to 4 helps reduce the impact of the first cutout G1 on the flow capacity of the first empty foil area 111b.

[0149] 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.

[0150] In some embodiments, 0.5≤La / W1≤2.

[0151] 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.

[0152] Setting W3 / W1 to greater than or equal to 0.2 helps reduce the accumulation of empty foil material during the flattening process, reduces the risk of puncturing the insulating member covering the first empty foil region 111b, and improves safety. Setting W3 / W1 to less than or equal to 1 helps reduce the risk of the first incision G1 extending into the first main region 111a, reducing the loss of the first active material 112.

[0153] Optionally, W3 / W1 is 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1.

[0154] In some embodiments, the first incision G1 and the second incision G2 have the same shape and size.

[0155] In some embodiments, the first cutout G1 may be formed by chamfering a corner of the first empty foil area 111 b .

[0156] 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.

[0157] 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.

[0158] 12 , in some embodiments, the first cutout G1 may be a rectangular cutout.

[0159] 13 and 14 , 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 .

[0160] 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 .

[0161] 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.

[0162] 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.

[0163] At least one surface of the second main body region 121a is coated with the second active material 122. Both surfaces of the second blank foil region 121b are not coated with the second active material 122.

[0164] 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.

[0165] 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.

[0166] In some embodiments, the end of the second hollow foil region 121 b away from the second main body region 121 a is flattened to form a second flattened region.

[0167] 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.

[0168] 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 .

[0169] 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.

[0170] 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.

[0171] 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.

[0172] In some embodiments, the cylindrical battery cell is an 18650 battery cell or a 21700 battery cell.

[0173] In some embodiments, the rated capacity of the electrochemical device 1000 is 2500 mAh to 4500 mAh. For example, the rated capacity of the electrochemical device 1000 is 2500 mAh, 2700 mAh, 2800 mAh, 3000 mAh, 3300 mAh, 3500 mAh, 3800 mAh, 4000 mAh, 4100 mAh, 4200 mAh, 4300 mAh, 4400 mAh, or 4500 mAh.

[0174] In some embodiments, the AC internal resistance of the electrochemical device 1000 is less than 6 milliohms (mΩ).

[0175] In some embodiments, the AC internal resistance of the electrochemical device 1000 is 5.5 mΩ, 5 mΩ, 4.5 mΩ, 4 mΩ, 3.5 mΩ, 3 mΩ, 2.5 mΩ, 2 mΩ, 1.5 mΩ, or 1 mΩ.

[0176] AC resistance test method:

[0177] The electrochemical device at 100% SOC was discharged at a constant current rate of 0.2C at 25°C until the SOC of the electrochemical device reached 30%. The resistance value was measured using an internal resistance tester (HIOKI BT3563) set at a frequency of 1 kHz.

[0178] The electrochemical device 1000 of the present application has a relatively small AC resistance, thereby reducing heat generation of the electrochemical device 1000 during charging and improving the charging efficiency and charging performance of the electrochemical device 1000 .

[0179] 15 , the present application further provides a battery pack 3000 , which includes the electrochemical device 1000 provided in any of the aforementioned embodiments.

[0180] 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.

[0181] Connecting multiple electrochemical devices 1000 in series can increase the output voltage of the battery pack.

[0182] 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.

[0183] 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.

[0184] In some embodiments, one battery module 2000 includes five electrochemical devices 1000 or six electrochemical devices 1000 .

[0185] In some embodiments, the number of battery modules 2000 is 2 or 3.

[0186] In some embodiments, the battery pack further includes a box 2100 , and the battery module 2000 is accommodated in the box 2100 .

[0187] 16 , 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 .

[0188] 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.

[0189] In some embodiments, embodiments of the present application provide an electrochemical device comprising a housing and an electrode assembly housed in the housing.

[0190] The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, and the separator insulates the positive electrode sheet and the negative electrode sheet.

[0191] Example 1

[0192] Fabrication of electrochemical devices.

[0193] <Production of positive electrode sheet>

[0194] 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.

[0195] For example, referring to Figures 6 and 7 , the positive electrode sheet adopts a structure similar to the first electrode sheet. Specifically, L1 = L2 = 1.36m, W2 is 63.2mm, W1 is 4mm, and W4 is 3.2mm.

[0196] <Preparation of negative electrode sheet>

[0197] Artificial graphite, conductive carbon black, styrene-butadiene rubber (SBR, weight average molecular weight 5×10 6 ) were mixed in a mass ratio of 97.4:1.4:1.2, and then deionized water was added as a solvent and stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry with a solid content of 51wt% and a uniform system. The negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 8mm and dried at 90°C to obtain a negative electrode sheet with a single-sided coating of a negative electrode active material layer (the unit area coating weight of the negative electrode active material on one side of the negative electrode sheet was 113mg / 1540.25mm 2 ). Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. Then, the negative electrode sheet is cold pressed and cut into pieces for use.

[0198] For example, referring to Figures 6 and 7 , the negative electrode plate adopts a structure similar to the first electrode plate. Specifically, L1 = L2 = 1.464 mm, W2 is 64.1 mm, W1 is 4 mm, and W4 is 3.2 mm.

[0199] <Preparation of Separator>

[0200] 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.

[0201] <Preparation of Electrolyte>

[0202] 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.

[0203] <Preparation of Electrochemical Device>

[0204] 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.

[0205] According to the above method, an electrochemical device was prepared.

[0206] Electrochemical device testing methods

[0207] The electrochemical device was tested according to the following steps. The test process was carried out using a battery tester (Neware CT-4016-5V-100A).

[0208] Rated capacity test:

[0209] The electrochemical device was placed in a thermostat (Keming EH-1000) at 25°C for 1 hour. At a constant temperature of 25°C, the electrochemical device was discharged at a constant current of 0.5C to the discharge cut-off voltage (2.5V) of the electrochemical device. Then, it was charged at a constant current of 0.5C to the charge cut-off voltage (4.2V) of the electrochemical device. Then, it was charged at a constant voltage of the charge cut-off voltage to 0.05C, at which point the electrochemical device was at 100% SOC. The electrochemical device at 100% SOC was discharged at a constant current of 0.2C to the discharge cut-off voltage (2.5V) of the electrochemical device, and the discharge capacity was tested, which was the rated capacity of the electrochemical device.

[0210] AC internal resistance test:

[0211] After testing the rated capacity of the electrochemical device, the device was charged at a constant current of 0.5C to the device's charge cutoff voltage (4.2V). The device was then charged at a constant voltage of 0.05C, at which point the device reached 100% SOC. The device was then discharged at a constant current of 0.2C at 25°C to a SOC of 30%. The internal resistance value was measured using an internal resistance tester (HIOKI BT3563) at a frequency of 1 kHz.

[0212] The electrochemical device after the AC internal resistance test was discharged at a constant current of 0.2 C at 25° C. to the discharge cut-off voltage of the electrochemical device.

[0213] Constant current charging operation: The electrochemical device discharged to the discharge cut-off voltage was left to stand at 25°C for 1 hour, and a constant current charging operation was performed at a first charge rate of 2C. The electrochemical device was constantly charged from the discharge cut-off voltage (2.5V) to the charge cut-off voltage (4.2V);

[0214] Constant voltage charging operation: At 25° C., the electrochemical device, which was charged at a constant current to a charge cutoff voltage, was subjected to a constant voltage charging operation until the second charge rate of the electrochemical device reached 0.05C.

[0215] The charging capacity C1 of the constant current charging operation and the charging capacity C2 of the constant voltage charging operation are read by a battery tester.

[0216] Example 2:

[0217] The method for manufacturing the electrochemical device of Example 2 is the same as the method for manufacturing the electrochemical device of Example 1.

[0218] The electrochemical device testing method of Example 2 differs from the electrochemical device testing method of Example 1 in that the temperature during the constant current charging operation and the temperature during the constant voltage charging operation are both 45°C.

[0219] Example 3:

[0220] The method for manufacturing the electrochemical device of Example 3 is the same as the method for manufacturing the electrochemical device of Example 1.

[0221] The electrochemical device testing method of Example 3 differs from the electrochemical device testing method of Example 1 in that the charging rate in the constant current charging operation is 3C.

[0222] Embodiment 4:

[0223] Fabrication of electrochemical devices.

[0224] <Production of positive electrode sheet>

[0225] The difference from Example 1 is that the positive electrode sheet adopts the structure of the first electrode sheet shown in Figures 9 and 10. Specifically, referring to Figures 9 and 10, L1 = L2 = 1.36m, W2 is 63.2mm, W1 is 4mm, and W4 is 3.2mm. The first bare foil region has identical triangular cutouts at both the outer and inner corners along the winding direction, where La = W1 = 4mm, W3 = 0.5mm, and W1 = 2mm.

[0226] <Preparation of negative electrode sheet>

[0227] The difference from Example 1 is that the negative electrode sheet adopts the structure of the first electrode sheet shown in Figures 9 and 10. Referring to Figures 9 and 10, L1 = L2 = 1.464m, W2 is 64.1mm, W1 is 4mm, and W4 is 3.2mm. The first empty foil area has identical triangular cutouts at both the outer and inner corners along the winding direction, where La = W1 = 4mm, W3 = 0.5mm, and W1 = 2mm. The cutouts for the negative electrode sheet are identical in shape and size to those for the positive electrode sheet.

[0228] <Preparation of Separator>

[0229] Same as Example 1.

[0230] <Preparation of Electrolyte>

[0231] Same as Example 1.

[0232] <Preparation of Electrochemical Device>

[0233] Same as Example 1.

[0234] According to the above method, an electrochemical device was prepared.

[0235] The electrochemical device testing method of Example 4 is the same as the electrochemical device testing method of Example 1.

[0236] Example 5:

[0237] The difference between the manufacturing method of the electrochemical device of Example 5 and the manufacturing method of the electrochemical device of Example 1 is that the positive electrode active material of the positive electrode sheet of Example 5 is LiNi 0.95 Co 0.01 Mn 0.04 O2.

[0238] The electrochemical device testing method of Example 5 is the same as the electrochemical device testing method of Example 1.

[0239] Example 6:

[0240] The difference between the manufacturing method of the electrochemical device of Example 6 and the manufacturing method of the electrochemical device of Example 1 is that the positive electrode active material of the positive electrode sheet of Example 6 is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0241] The electrochemical device testing method of Example 6 is the same as the electrochemical device testing method of Example 1.

[0242] Example 7:

[0243] The difference between the manufacturing method of the electrochemical device of Example 7 and the manufacturing method of the electrochemical device of Example 1 is that the negative electrode active material of the negative electrode plate of Example 7 uses artificial graphite and natural graphite, and the weight ratio of artificial graphite to natural graphite is 7:3.

[0244] The electrochemical device testing method of Example 7 is the same as the electrochemical device testing method of Example 1.

[0245] Example 8:

[0246] The difference between the manufacturing method of the electrochemical device of Example 8 and the manufacturing method of the electrochemical device of Example 1 is that the negative electrode active material of the negative electrode sheet of Example 8 is natural graphite.

[0247] The electrochemical device testing method of Example 8 is the same as the electrochemical device testing method of Example 1.

[0248] Comparative Example 1: INR21700-40T (21700 battery cell)

[0249] The testing method of Comparative Example 1 is the same as the testing method of the electrochemical device of Example 1.

[0250] Comparative Example 2: VTC6A (21700 battery cell)

[0251] The testing method of Comparative Example 2 is the same as the testing method of the electrochemical device in Example 1.

[0252] Example 9:

[0253] <Production of positive electrode sheet>

[0254] 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.

[0255] 6 and 7 , the positive electrode sheet adopts a structure similar to the first electrode sheet. Specifically, L1 = L2 = 0.92 mm, W2 is 59 mm, W1 is 4 mm, and W4 is 3.2 mm.

[0256] <Preparation of negative electrode sheet>

[0257] Artificial graphite, conductive carbon black, styrene-butadiene rubber (SBR, weight average molecular weight 5×10 6) were mixed in a mass ratio of 97.5:1.3:1.2, and then deionized water was added as a solvent and stirred evenly under the action of a vacuum mixer to obtain a negative electrode slurry with a solid content of 51wt% and a uniform system. The negative electrode slurry was evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 8mm and dried at 90°C to obtain a negative electrode sheet with a single-sided coating of a negative electrode active material layer (the coating weight per unit area of ​​the negative electrode active material on one side of the negative electrode sheet was 103mg / 1540.25mm 2 ). Then, the above steps are repeated on the other surface of the copper foil to obtain a negative electrode sheet coated with a negative electrode active material layer on both sides. Then, the negative electrode sheet is cold pressed and cut into pieces for use.

[0258] For example, referring to Figures 6 and 7 , the negative electrode sheet adopts a structure similar to the first electrode sheet. Specifically, L1 = L2 = 1.02m, W2 is 60.2mm, W1 is 4mm, and W4 is 3.2mm.

[0259] <Preparation of Separator>

[0260] 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.

[0261] <Preparation of Electrolyte>

[0262] 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.

[0263] <Preparation of Electrochemical Device>

[0264] 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.

[0265] According to the above method, an electrochemical device was prepared.

[0266] Then, the electrochemical device was tested according to the following steps. The testing process was performed using a battery tester (Neware Electronics Co. Ltd, China).

[0267] Electrochemical device testing methods

[0268] The electrochemical device was tested according to the following steps. The test process was carried out using a battery tester (Neware CT-4016-5V-100A).

[0269] Rated capacity test:

[0270] The electrochemical device was placed in a thermostat (Keming EH-1000) at 25°C for 1 hour. At a constant temperature of 25°C, the electrochemical device was discharged at a constant current of 0.5C to the discharge cut-off voltage (2.5V) of the electrochemical device. Then, it was charged at a constant current of 0.5C to the charge cut-off voltage (4.2V) of the electrochemical device. Then, it was charged at a constant voltage of the charge cut-off voltage to 0.05C, at which point the electrochemical device was at 100% SOC. The electrochemical device at 100% SOC was discharged at a constant current of 0.2C to the discharge cut-off voltage (2.5V) of the electrochemical device, and the discharge capacity was tested, which was the rated capacity of the electrochemical device.

[0271] AC internal resistance test:

[0272] After testing the rated capacity of the electrochemical device, the device was charged at a constant current of 0.5C to the device's charge cutoff voltage (4.2V). The device was then charged at a constant voltage of 0.05C, at which point the device reached 100% SOC. The device was then discharged at a constant current of 0.2C at 25°C to a SOC of 30%. The internal resistance tester was set to a frequency of 1 kHz to obtain the AC internal resistance value.

[0273] The electrochemical device after the AC internal resistance test was discharged at a constant current of 0.2 C at 25° C. to the discharge cut-off voltage of the electrochemical device.

[0274] Constant current charging operation: The electrochemical device discharged to the discharge cut-off voltage was left to stand at 25°C for 1 hour, and a constant current charging operation was performed at a first charge rate of 2C. The electrochemical device was constantly charged from the discharge cut-off voltage (2.5V) to the charge cut-off voltage (4.2V);

[0275] Constant voltage charging operation: At 25° C., the electrochemical device, which was charged at a constant current to a charge cutoff voltage, was subjected to a constant voltage charging operation until the second charge rate of the electrochemical device reached 0.05C.

[0276] The charging capacity C1 of the constant current charging operation and the charging capacity C2 of the constant voltage charging operation are read by a battery tester.

[0277] Embodiment 10:

[0278] The method for manufacturing the electrochemical device of Example 10 is the same as the method for manufacturing the electrochemical device of Example 9.

[0279] The electrochemical device testing method of Example 10 differs from the electrochemical device testing method of Example 9 in that the temperature during the constant current charging operation and the temperature during the constant voltage charging operation are both 45°C.

[0280] Example 11:

[0281] The method for manufacturing the electrochemical device of Example 11 is the same as the method for manufacturing the electrochemical device of Example 9.

[0282] The electrochemical device testing method of Example 11 differs from the electrochemical device testing method of Example 9 in that the charging rate in the constant current charging operation is 3C.

[0283] Example 12:

[0284] Fabrication of electrochemical devices.

[0285] <Production of positive electrode sheet>

[0286] The difference from Example 9 is that the positive electrode sheet adopts the structure of the first electrode sheet shown in Figures 9 and 10. Specifically, referring to Figures 9 and 10, L1 = L2 = 0.92m, W2 is 59mm, W1 is 4mm, and W4 is 3.2mm. The first bare foil region has identical triangular cutouts at both the outer and inner corners along the winding direction, where La = W1 = 4mm, W3 = 0.5mm, and W1 = 2mm.

[0287] <Preparation of negative electrode sheet>

[0288] The difference from Example 9 is that the negative electrode sheet adopts the structure of the first electrode sheet shown in Figures 9 and 10. Referring to Figures 9 and 10, L1 = L2 = 1.02m, W2 is 60.2mm, W1 is 4mm, and W4 is 3.2mm. The first empty foil area has identical triangular cutouts at both the outer and inner corners along the winding direction, where La = W1 = 4mm, W3 = 0.5mm, and W1 = 2mm. The cutouts for the negative electrode sheet are identical in shape and size to those for the positive electrode sheet.

[0289] <Preparation of Separator>

[0290] Same as Example 9.

[0291] <Preparation of Electrolyte>

[0292] Same as Example 9.

[0293] <Preparation of Electrochemical Device>

[0294] Same as Example 9.

[0295] According to the above method, an electrochemical device was prepared.

[0296] The electrochemical device testing method of Example 12 is the same as the electrochemical device testing method of Example 9.

[0297] Example 13:

[0298] The difference between the manufacturing method of the electrochemical device of Example 13 and the manufacturing method of the electrochemical device of Example 9 is that the positive electrode active material of the positive electrode sheet of Example 13 is LiNi 0.95 Co 0.01 Mn 0.04 O2.

[0299] The electrochemical device testing method of Example 13 is the same as the electrochemical device testing method of Example 9.

[0300] Example 14:

[0301] The difference between the manufacturing method of the electrochemical device of Example 14 and the manufacturing method of the electrochemical device of Example 9 is that the positive electrode active material of the positive electrode sheet of Example 14 is LiNi 0.8 Co 0.1 Mn 0.1 O2.

[0302] The electrochemical device testing method of Example 14 is the same as the electrochemical device testing method of Example 9.

[0303] Example 15:

[0304] The difference between the manufacturing method of the electrochemical device of Example 15 and the manufacturing method of the electrochemical device of Example 9 is that the negative electrode active material of the negative electrode plate of Example 15 uses artificial graphite and natural graphite, and the weight ratio of artificial graphite to natural graphite is 7:3.

[0305] The electrochemical device testing method of Example 15 is the same as the electrochemical device testing method of Example 9.

[0306] Example 16:

[0307] The difference between the manufacturing method of the electrochemical device of Example 16 and the manufacturing method of the electrochemical device of Example 9 is that the negative electrode active material of the negative electrode plate of Example 16 is natural graphite.

[0308] The electrochemical device testing method of Example 16 is the same as the electrochemical device testing method of Example 9.

[0309] Comparative Example 3: INR18650-25R (18650 battery cell)

[0310] The testing method of Comparative Example 3 is the same as the testing method of the electrochemical device of Example 9.

[0311] Comparative Example 4: 30Q (18650 battery cell)

[0312] The testing method of Comparative Example 4 is the same as the testing method of the electrochemical device of Example 9.

[0313] The test conditions and test results of Examples 1-16 and Comparative Examples 1-4 are shown in Table 1.

[0314] With reference to Examples 1-8 and Comparative Examples 1-2, the present application can increase the charging capacity C1 of the electrochemical device during the constant current charging operation stage, thereby improving the charging efficiency and shortening the charging time.

[0315] The electrochemical device of the present application has a relatively small AC internal resistance, which is beneficial for improving charging efficiency and charging performance.

[0316] With reference to Examples 9-16 and Comparative Examples 3-4, the present application can increase the charging capacity C1 of the electrochemical device during the constant current charging operation stage, thereby improving the charging efficiency and shortening the charging time.

[0317] The electrochemical device of the present application has a relatively small AC internal resistance, which is beneficial for improving charging efficiency and charging performance.

[0318] Referring to Examples 1-16, C1 / (C1+C2) is greater than 87%, and the electrochemical device of the present application can have a higher charging efficiency.

[0319] With reference to Examples 1-2 or 9-10, appropriately increasing the ambient temperature during charging can increase the charging capacity C1 of the electrochemical device during the constant current charging operation stage.

[0320] Referring to Example 1, Comparative Example 1, Comparative Example 2 and Figure 17, the electrochemical device of Example 1 can extend the duration of the constant current charging operation phase and shorten the duration of the constant voltage charging operation phase. At the same charge rate, the time for the electrochemical device to reach 100% SOC is shortened.

Claims

1. An electrochemical device, comprising a housing and an electrode assembly accommodated in the housing; The electrode assembly includes a first electrode tab, a second electrode tab, and a separator. The first electrode tab, the separator, and the second electrode tab are laminated and wound along a winding direction. One of the first electrode tab and the second electrode tab is a positive electrode tab, and the other is a negative electrode tab; The negative electrode tab includes a negative current collector and a negative active material. The negative active material is disposed on the negative current collector, and the negative active material includes artificial graphite and / or natural graphite; The electrochemical device is configured to: When the electrochemical device is at a first ambient temperature and stands for a first time, a constant current charging operation is performed at a first charging rate. The electrochemical device performs the constant current charging operation from a discharge cut-off voltage until the voltage of the electrochemical device reaches a charging cut-off voltage; When the electrochemical device is at the first ambient temperature, a constant voltage charging operation is performed from the charging cut-off voltage until the constant voltage charging operation has a second charging rate; In response to the constant current charging operation and the constant voltage charging operation, the charging capacity of the electrochemical device in the constant current charging operation is C1, and the charging capacity of the electrochemical device in the constant voltage charging operation is C2; Among them, 0.87 ≤ C1 / (C1 + C2) ≤ 0.93, the first charging rate is 2C to 3C, the second charging rate is 0.05C, the first time is 1 hour to 2 hours, and the first ambient temperature is 25°C to 45°C.

2. The electrochemical device according to claim 1, wherein, 0.91 ≤ C1 / (C1 + C2) ≤ 0.

93.

3. The electrochemical device according to claim 1 or 2, wherein, The positive electrode plate includes a positive current collector and a positive active material, the positive active material is disposed on the positive current collector, and the positive active material includes Li 1+a Ni x1 Co y1 Mn z1 O2 or Li 1+a Ni x2 Co y2 Al z2 at least one of O2; Wherein, both x1 and x2 are greater than or equal to 0.8, both y1 and y2 are greater than 0, both z2 and z3 are greater than 0, x1 + y1 + z1 = 1, x2 + y2 + z2 = 1, -0.05 ≤ a ≤ 0.

2.

4. The electrochemical device according to claim 3, wherein, Both x1 and x2 are greater than or equal to 0.

9.

5. The electrochemical device according to any one of claims 1-4, wherein, The first electrode tab includes a first current collector and a first active material. The first current collector includes a first main region and a first empty foil region. The first active material is disposed on the first main region, and the arrangement direction of the first main region and the first empty foil region is perpendicular to the winding direction; The first empty foil region includes a first flattened region, and the first flattened region is away from the first main region.

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

1.

7. The electrochemical device according to claim 5 or 6, 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 electrode tab after unfolding, the size of the first cut is La; along the width direction of the first electrode tab after unfolding, the size of the first empty foil region is W1; La and W1 satisfy: 0.2 ≤ La / W1 ≤ 4.

8. The electrochemical device according to claim 7, wherein, Along the width direction of the first electrode tab after unfolding, the size of the first cut is W3; W3 and W1 satisfy: 0.2 ≤ W3 / W1 ≤ 1.

9. The electrochemical device according to any one of claims 5-8, wherein, Along the width direction after the first pole piece is unfolded, the size of the first flattening area is W4, and 0.6 ≤ W4 / W1 ≤ 0.

95.

10. The electrochemical device according to any one of claims 5-9, wherein, The electrochemical device further includes an electrode terminal disposed on the housing and a current collector plate connected to the electrode terminal, and the current collector plate is welded to the first flattening area.

11. The electrochemical device according to any one of claims 1-10, comprising a cylindrical battery cell; The diameter of the cylindrical battery cell is 17 mm - 22 mm, and the height of the cylindrical battery cell is 64 mm - 72 mm.

12. The electrochemical device according to claim 11, wherein, The cylindrical battery cell is a 18650-type battery cell or a 21700-type battery cell.

13. The electrochemical device according to any one of claims 1-12, wherein, The rated capacity of the electrochemical device is 2500 mAh - 4500 mAh.

14. The electrochemical device according to claims 1-13, wherein, The AC internal resistance of the electrochemical device is less than 6 mΩ.

15. A battery pack, comprising the electrochemical device according to any one of claims 1-14.

16. The battery pack according to claim 15, comprising one battery module or a plurality of the battery modules arranged in parallel, and one battery module comprises a plurality of the electrochemical devices arranged in series.

17. An electrical equipment, comprising the battery pack according to claim 15 or 16.

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