Electrochemical apparatus, electrical device, and preparation method for electrochemical apparatus

Abstract

An electrochemical apparatus, an electrical device, and a preparation method for the electrochemical apparatus. The electrochemical apparatus comprises an electrode assembly, the electrode assembly comprising a pole piece assembly, a first tab and a second tab, and the pole piece assembly comprising a first pole piece and a second pole piece. The first pole piece comprises a first current collector and a first active material layer, a first area of a winding tail section of the first current collector being connected to the first tab, and the first current collector comprising a first coating area and a first section located at the winding tail section. The second pole piece comprises a second current collector and a second active material layer, a second area of a winding tail section of the second current collector being connected to the second tab, and the second current collector comprising a second coating area, and a second section located at the winding tail section. The sum of the equivalent magnetic field intensity of the first current collector F1 and the sum of the equivalent magnetic field intensity of the second current collector F2 satisfy the formula: |F1-F2|≤4×10-5; thus, the axial magnetic field of an end surface of a winding structure can be better reduced, and interference of the electrochemical apparatus on the electrical device can be reduced.

Description

Electrochemical device, electrical equipment, and method for preparing electrochemical device Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to an electrochemical device, an electrical equipment, and a method for preparing the electrochemical device. Background Art

[0002] Due to the unique spiral involute structure of wound batteries, a strong axial magnetic field is generated at the end faces of the wound structure. This can significantly interfere with electrical devices such as Bluetooth headsets, affecting their normal operation. Therefore, how to reduce the axial magnetic field of wound batteries has become an urgent problem.

[0003] Summary of the Invention

[0004] In view of this, the present application provides an electrochemical device to reduce the axial magnetic field of a wound structure battery, thereby reducing the interference of the electrochemical device on electrical equipment.

[0005] In a first aspect, the present application provides an electrochemical device comprising a housing and an electrode assembly. The electrode assembly is housed in the housing and includes a pole piece assembly, a first tab, and a second tab. The pole piece assembly comprises a first pole piece and a second pole piece arranged in a wound manner. The first pole piece comprises a first current collector and a first active material layer; the second pole piece comprises a second current collector and a second active material layer; the winding start section of the second active material layer is located outside the winding start section of the pole piece assembly relative to the winding start section of the first active material layer. The first tab is connected to a first region of the winding end section of the first current collector. The second tab is connected to a second region of the winding end section of the second current collector. Along the winding direction of the pole piece assembly from the inside to the outside, the first region extends beyond the second region. The first active material layer comprises a first active region, which is the region of the first active material layer opposite the second active material layer. The total length of the first active region along the winding direction of the pole piece assembly from the inside to the outside is L1 mm. The first current collector comprises a first coating region, which is disposed on the surface of the first coating region. The second active material layer includes a second effective area, which is the area in the second active material layer opposite to the first active material layer. Along the winding direction of the pole piece assembly from the inside to the outside, the total length of the second effective area is L2mm; the second current collector includes a second coating area, and the second effective area is arranged on the surface of the second coating area. Along the winding direction of the pole piece assembly from the inside to the outside, the first coating area includes a first starting end and a first end, and the second coating area includes a second starting end and a second end. The first current collector includes a first section from the first end to the center of the first area. The length of the first section is S1mm, the winding angle of the first section is α1°, and the number of winding turns of the first section is C. 10 =α1 / 360, the winding radius R of the first section 10 mm=S1 / (2π×C10 ); The second current collector optionally includes a second segment from the second end to the center of the second region, the length of the second segment is S2mm, the winding angle of the second segment is α2°, the number of winding turns of the second segment is C 20 =α2 / 360, the winding radius R of the second section 20 mm=S2 / (2π×C 20 ).

[0006] Along the winding direction of the pole piece assembly from inside to outside, the number of winding turns of the first coating area and the second coating area is n, and the winding radius of the first coating area of ​​the i-th turn is R 1i mm, the winding radius of the second coating area of ​​the i-th circle is R 2i mm, the length of the first effective area in the i-th circle is l 1i mm, the proportion of the first effective area in the i-th circle X 1i =l 1i / L1; the length of the second effective area in the i-th circle is l 2i mm, the proportion of the second effective area in the i-th circle X 2i =l 2i / L2. Equivalent current intensity λ of the i-th circle in the first coating area 1i =X 11 +…+X 1(i-1) +0.5X 1i , the equivalent current intensity λ of the i-th circle in the second coating area 2i =X 21 +…+X 2(i-1) +0.5X 2i The equivalent magnetic field strength of the i-th circle in the first coating area is λ 1i ×f(R 1i ), the equivalent magnetic field strength of the first section is C 10 ×f(R 10 ), the equivalent magnetic field strength of the i-th circle in the second coating area is λ 2i ×f(R 2i ), the equivalent magnetic field strength of the second section is C 20 ×f(R 20 ). Where, f(R)=0.000016866R 4 -0.0002591R 3 +0.001204R 2 -0.00198162R+0.0018255. The sum of the equivalent magnetic field strength of the first current collector is F1, F1=C 10 ×f(R 10 )+λ 11 ×f(R 11 )+λ 12 ×f(R 12 )+…λ 1n×f(R 1n The sum of the equivalent magnetic field strength of the second current collector is F2, F2 = C 20 ×f(R 20 )+λ 21 ×f(R 21 )+λ 22 ×f(R 22 )+…λ 2n ×f(R 2n ), satisfying: |F1-F2|≤4×10 -5 .

[0007] The inventors of this application have discovered through research that, due to the special structure of the spiral involute of the pole piece assembly of the winding structure, the winding radius of the first pole piece on the inner side of the winding and the second pole piece on the outer side of the winding are different under the same number of turns, which makes the magnetic field strength generated by the first pole piece and the second pole piece in the axial direction with the same number of turns different. At the same time, since the effective current in the same pole piece gradually increases from the inside to the outside, the difference in the axial magnetic field strength generated by the first pole piece and the second pole piece in each circle from the inside to the outside continues to increase, thereby accumulating a strong axial magnetic field on the end face of the pole piece assembly. This application extends the effective length of the first pole piece located on the inner side of the winding, and controls the length of the first region to exceed the second region until the sum of the equivalent magnetic field strength of the first current collector F1 and the sum of the equivalent magnetic field strength of the second current collector F2 satisfy: |F1-F2|≤4×10 -5 When the electrode assembly discharges and generates current, the magnetic field generated by the portion of the first pole piece that extends beyond the second area can better offset the axial magnetic field generated by the spiral involute structure, thereby better reducing the axial magnetic field at the end face of the winding structure, and thus helping to reduce the interference of the electrochemical device on electrical equipment.

[0008] In some embodiments, |F1-F2|≤3×10 -5 In this way, the axial magnetic field at the end face of the winding structure can be further reduced, thereby further reducing the interference to electrical equipment.

[0009] In some embodiments, the first region extends beyond the second region by less than one turn along the winding direction of the pole piece assembly from the inside out. This helps reduce the length of the first current collector extension, thereby reducing the risk of the first current collector extending too long and being easily misaligned, causing a short circuit.

[0010] In some embodiments, the first electrode is a negative electrode and the second electrode is a positive electrode. In the opposite direction of winding the electrode assembly from the inside out, the first active material layer's winding start section extends beyond the second active material layer's winding start section, and / or in the direction of winding the electrode assembly from the inside out, the first active material layer's winding end section extends beyond the second active material layer's winding end section. This helps reduce the risk of lithium plating and improves the safety of the electrochemical device.

[0011] In some embodiments, the shell includes a first shell portion and a second shell portion with different polarities, the first shell portion includes a top wall, a bottom wall and a side wall, the second shell portion includes a pole, the top wall is provided with a through hole, and the pole is provided in the through hole, so that it is beneficial to lead out the polarity of the electrode assembly in the shell.

[0012] In some embodiments, along the winding direction of the pole piece assembly from the inside out, the winding tail of the first current collector also includes a blank section extending beyond the first region and not provided with the first active material layer on its surface. This blank section covers the winding tail of the second current collector. This blank section of the first current collector is provided between the winding tail of the second current collector and the first shell, thereby enhancing the isolation between the second current collector and the first shell and reducing the risk of short circuits caused by direct contact between the second current collector and the first shell.

[0013] In some embodiments, the first tab includes a first connecting portion and a first bend, the first connecting portion being connected to the first region, and the first bend including a third region connected to the first shell. The electrochemical device also includes a first connector located outside the shell, the first connector including a first end and a second end, the first end being connected to the first shell, and the second end including a fourth region for connection to an external load. The angle between a ray from the center of the third region to the center of the first region and a ray from the center of the third region to the center of the fourth region is θ1, satisfying θ1 ≤ 45°. This helps reduce the impact of current passing through the first bend on the axial magnetic field, thereby further reducing interference with electrical equipment.

[0014] In some embodiments, the second tab includes a second connecting portion and a second bend, the second connecting portion being connected to the second region, the second bend including a fifth region connected to the second shell; the electrochemical device further includes a second connector located outside the shell, the second connector including a third end and a fourth end, the third end being connected to the second shell, the fourth end including a sixth region for connection to an external load, and the angle between a ray from the center of the fifth region to the center of the second region and a ray from the center of the fifth region to the center of the sixth region being θ2, such that θ2 ≤ 45°. This helps reduce the impact of current passing through the second bend on the axial magnetic field, thereby further reducing interference with electrical equipment.

[0015] In some embodiments, the electrode assembly further includes a first diaphragm, which is disposed between the first electrode and the second electrode. The first diaphragm extends beyond the first electrode along the winding direction of the electrode assembly from the inside out. Thus, the first electrode's winding end is covered by the first diaphragm, which helps reduce the risk of direct contact between the first and second electrode sheets.

[0016] In some embodiments, the electrode assembly further includes a second diaphragm disposed between the first electrode and the second electrode. The second diaphragm extends beyond the second electrode along the winding direction of the electrode assembly from the inside out. This allows the second diaphragm to cover the winding end of the second electrode, thereby reducing the risk of direct contact between the second electrode and the first electrode or the housing.

[0017] In some embodiments, the electrochemical device further includes an insulating member disposed between the housing and the pole piece assembly, thereby reducing the risk of direct contact between the pole piece assembly and the housing, thereby reducing the risk of internal short circuits in the electrochemical device.

[0018] In a second aspect, the present application further provides an electrical device comprising the electrochemical device of any of the above embodiments. The electrochemical device of the above embodiments has a reduced axial magnetic field, which reduces electromagnetic interference to the electrical device, thereby improving the reliability of the electrical device.

[0019] In a third aspect, the present application provides a method for preparing an electrochemical device. The electrochemical device includes a housing and an electrode assembly. The electrode assembly is housed in the housing and includes a pole piece assembly, a first tab, and a second tab. The pole piece assembly includes a first pole piece and a second pole piece arranged in a wound manner. The first pole piece includes a first current collector and a first active material layer; the second pole piece includes a second current collector and a second active material layer; the winding start section of the second active material layer is located outside the winding start section of the pole piece assembly relative to the winding start section of the first active material layer. The first tab is connected to a first region of the winding end section of the first current collector. The second tab is connected to a second region of the winding end section of the second current collector. Along the winding direction of the pole piece assembly from the inside to the outside, the first region extends beyond the second region. The first active material layer includes a first active region, which is the region of the first active material layer opposite the second active material layer. The total length of the first active region along the winding direction of the pole piece assembly is L1 mm. The first current collector includes a first coating region, which is disposed on the surface of the first coating region. The second active material layer includes a second active area, which is the area of ​​the second active material layer opposite the first active material layer. Along the winding direction of the pole piece assembly from the inside to the outside, the total length of the second active area is L2mm. The second current collector includes a second coating area, and the second active area is located on the surface of the second coating area. Along the winding direction of the pole piece assembly from the inside to the outside, the first coating area includes a first starting end and a first ending end, and the second coating area includes a second starting end and a second ending end. The first current collector includes a first section from the first ending end to the center of the first area, with a length of S1mm. The second current collector optionally includes a second section from the second ending end to the center of the second area, with a length of S2mm.

[0020] Along the winding direction of the pole piece assembly from inside to outside, the number of winding turns of the first coating area and the second coating area is n, and the winding radius of the first coating area of ​​the i-th turn is R 1i mm, the winding radius of the second coating area of ​​the i-th circle is R 2i mm, the length of the first effective area in the i-th circle is l 1i mm, the proportion of the first effective area in the i-th circle X 1i =l 1i / L1; the length of the second effective area in the i-th circle is l 2i mm, the proportion of the second effective area in the i-th circle X 2i =l 2i / L2. Equivalent current intensity λ of the i-th circle in the first coating area 1i =X 11 +…+X 1(i-1) +0.5X 1i , the equivalent current intensity λ of the i-th circle in the second coating area 2i =X 21 +…+X 2(i-1) +0.5X2i .

[0021] According to the equivalent current intensity λ of the i-th circle in the first coating area 1i The equivalent magnetic field strength generated by the i-th circle in the first coating area is calculated, and the sum of the equivalent magnetic field strengths generated by the first coating area is calculated; and the equivalent current strength λ of the i-th circle in the second coating area is calculated based on the equivalent magnetic field strength generated by the i-th circle in the first coating area. 2i The equivalent magnetic field strength generated by the i-th circle in the second coating area is used to calculate the sum of the equivalent magnetic field strengths generated by the second coating area; based on the difference between the sum of the equivalent magnetic field strengths generated by the first coating area and the sum of the equivalent magnetic field strengths generated by the second coating area, the length S1mm of the first segment is determined to be greater than the length S2mm of the second segment so that the difference between the sum F1 of the equivalent magnetic field strengths generated by the first current collector and the sum F2 of the equivalent magnetic field strengths generated by the second current collector is smaller.

[0022] By comprehensively considering the difference in the winding radius of each turn in the first current collector and the second current collector and the current size, an optimal value of the length S1mm of the first segment is selected to be greater than the length S2mm of the second segment. This ensures that the difference between the sum of the equivalent magnetic field intensities F1 generated by the first current collector and the sum of the equivalent magnetic field intensities F2 generated by the second current collector is small, thereby conveniently preparing an electrochemical device that has less interference with electrical equipment.

[0023] In some embodiments, according to f(R)=0.000016866R 4 -0.0002591R 3 +0.001204R 2 -0.00198162R+0.0018255, calculate the equivalent magnetic field strength generated by the i-th circle in the first coating area as λ 1i ×f(R 1i ), the equivalent magnetic field strength generated by the i-th circle in the second coating area is λ 2i ×f(R 2i ).

[0024] In some embodiments, the step of calculating the equivalent magnetic field strength of the first segment and the equivalent magnetic field strength of the second segment is further included, wherein the winding angle of the first segment is α1°, the number of winding turns of the first segment is C 10 =α1 / 360, the winding radius R of the first section 10 mm=S1 / (2π×C 10 ), the winding angle of the second section is α2°, and the number of winding turns of the second section is C 20 =α2 / 360, the winding radius R of the second section 20 mm=S2 / (2π×C 20 ); the equivalent magnetic field strength of the first section is C 10 ×f(R10 ), the equivalent magnetic field strength of the second section is C 20 ×f(R 20 ); then F1=C 10 ×f(R 10 )+λ 11 ×f(R 11 )+λ 12 ×f(R 12 )+…λ 1n ×f(R 1n ); F2=C 20 ×f(R 20 )+λ 21 ×f(R 21 )+λ 22 ×f(R 22 )+…λ 2n ×f(R 2n ); Determine the value of the length of the first segment S1mm greater than the length of the second segment S2mm so that F1 and F2 satisfy: |F1-F2|≤4×10 -5 . BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG1 is a schematic diagram of an electrical device provided in an embodiment of the present application.

[0026] FIG2 is a schematic structural diagram of an electrochemical device provided in one embodiment of the present application.

[0027] FIG3 is a cross-sectional view of the electrochemical device in FIG2 .

[0028] FIG4 is a schematic structural diagram of an electrode assembly provided in one embodiment of the present application.

[0029] FIG5 is a schematic diagram of the winding of a pole piece assembly provided in one embodiment of the present application.

[0030] FIG6 is a schematic diagram of the winding of a pole piece assembly provided in another embodiment of the present application.

[0031] FIG7 is a schematic structural diagram of an electrode assembly and a first connecting member provided in one embodiment of the present application.

[0032] FIG8 is a schematic structural diagram of an electrode assembly and a second connecting member provided in one embodiment of the present application.

[0033] Description of Main Component Symbols Electrochemical Device 100 Housing 10 First Shell 11 Accommodating Space 11a Top Wall 111 Through Hole 1111 Bottom Wall 112 Side Wall 113 Second Shell 12 Mounting Portion 121 Lead-Out Portion 122 Electrode Assembly 20 Pole Sheet Assembly 21 First End Surface 21a Second End Surface 21b First Pole Sheet 211 First Current Collector 2111 First Region 211a Blank Section 211b First Coating Area 211c First Starting End 211d First End 211e First Section 211f Third Coating Area 211g Fourth Coating Area 211h First Active Material Layer 2112 First Active Area 2113 First Inactive Area 2114 Second Inactive Area 2115 Second Pole Sheet212 Second current collector 2121 Second region 212a Second coating region 212b Second starting end 212c Second end 212d Second segment 212e Second active material layer 2122 Second effective region 2123 First electrode tab 22 First connecting portion 221 First bent portion 222 Third region 222a Second electrode tab 23 Second connecting portion 231 Second bent portion 232 Fifth region 232a First separator 24 Second separator 25 First connector 30 First end 31 Second end 32 Fourth region 321 Second connector 40 Third end 41 Fourth end 42 Sixth region 421 Sealing member 50 Winding center B Width direction of first electrode sheet X Winding direction of electrode sheet assembly from inside to outside C Device body 200Electrical equipment 1000 DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments.

[0035] It should be noted that, in this application, "region center" refers to the center of gravity of the planar shape of the region when the region is a continuous entity. It is understood that the center of gravity of a planar shape can be determined by the hanging method: suspend the planar shape with a thin wire, draw a straight line vertically from the starting point of the thin wire, suspend the planar shape again with a different endpoint from the first, and draw another straight line using the same method. The intersection of the two straight lines is the center of gravity of the planar shape. When the region is composed of multiple discrete regions, the center of the region is the center of the minimum circumscribed circle containing the multiple discrete regions. It is understood that the minimum circumscribed circle is the circle with the smallest radius that contains the multiple discrete regions.

[0036] It will be understood that when a component is referred to as being "connected to" another component, it may be directly connected to the other component or there may be an intervening component. When a component is referred to as being "disposed on" another component, it may be directly disposed on the other component or there may be an intervening component. The terms "top," "bottom," and similar expressions used herein are for illustrative purposes only.

[0037] The terms "first", "second", etc. are only used to distinguish different objects and cannot be understood as indicating or implying relative importance or implying the quantity, specific order or primary and secondary relationship of the technical features indicated.

[0038] The term "parallel" is used to describe an ideal state between two components. In actual production or use, two components can be approximately parallel. Two components described as "parallel" do not necessarily need to be absolutely straight lines or planes; they can be roughly straight lines or planes. From a macroscopic perspective, a component is considered "straight" or "planar" if its overall extension is a straight line or plane.

[0039] It should be understood that the sizes and thicknesses of the components shown in the drawings are for better understanding and more convenient description, and the present application is not limited to the sizes and thicknesses shown in the drawings.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application.

[0041] The following will describe some embodiments of the present application in conjunction with the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0042] Referring to FIG. 1 , an embodiment of the present application provides an electrical device 1000 , which includes an electrochemical device 100 .

[0043] In some embodiments, referring to FIG. 1 , the power-consuming device 1000 further includes a device body 200 , and the electrochemical device 100 is installed in the device body 200 to supply power to the device body 200 .

[0044] In some embodiments, the power-consuming device 1000 may be a Bluetooth headset, a Bluetooth speaker, a mobile phone, a laptop computer, a tablet computer, an e-book player, an electric toy, a game console, a video recorder, a portable recorder, a radio, a smart watch, a lighting lamp, or a calculator, etc., which are not listed here one by one.

[0045] In some embodiments, referring to Figures 2 and 3, an electrochemical device 100 includes a housing 10 and an electrode assembly 20, wherein the electrode assembly 20 is accommodated in the housing 10. The electrode assembly 20 includes a pole piece assembly 21, a first pole tab 22, and a second pole tab 23. The first pole tab 22 is connected to the pole piece assembly 21, and the second pole tab 23 is connected to the pole piece assembly 21.

[0046] In some embodiments, referring to Figures 4 and 5 , the electrode assembly 21 includes a first electrode 211 and a second electrode 212 that are wound together. Along the width direction of the first electrode 211, the wound electrode assembly 21 includes a first end face 21a and a second end face 21b that are opposed to each other. The first electrode 211 has a first polarity, and the second electrode 212 has a second polarity, where the first polarity and the second polarity are different. For example, the first electrode 211 is a negative electrode, and the second electrode 212 is a positive electrode; in another example, the first electrode 211 is a positive electrode, and the second electrode 212 is a negative electrode.

[0047] 4 and 5 , in some embodiments, the first electrode piece 211 is connected to the first electrode tab 22 so that the first electrode tab 22 has a first polarity, and the second electrode piece 212 is connected to the second electrode tab 23 so that the second electrode tab 23 has a second polarity.

[0048] In some embodiments, referring to FIG5 , the first electrode 211 includes a first current collector 2111 and a first active material layer 2112 ; the second electrode 212 includes a second current collector 2121 and a second active material layer 2122 ; the winding starting section of the second active material layer 2122 is located on the winding outside of the electrode assembly 21 relative to the winding starting section of the first active material layer 2112 .

[0049] The first current collector 2111 and the second current collector 2121 may be metal layers. As an illustrative example, the first electrode sheet 211 is a negative electrode sheet, and the first current collector 2111 may be a metal layer including at least one of copper, nickel, tantalum, titanium, etc., such as copper foil. The first active material layer 2112 includes a negative electrode active material, which may include at least one of graphite, hard carbon, soft carbon, silicon, silicon oxide material, silicon carbon material, etc. The second electrode sheet 212 is a positive electrode sheet, and the second current collector 2121 may be a metal layer including at least one of aluminum, nickel, tantalum, titanium, etc., such as aluminum foil. The first active material layer 2112 includes a positive electrode active material, which may include at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese iron phosphate, or lithium manganese oxide.

[0050] Continuing to refer to Figures 4 and 5, the first current collector 2111 is connected to the first electrode tab 22 and includes a first region 211a connected to the first electrode tab 22. The first region 211a is located at the end of the winding of the first current collector 2111. It can be understood that the first region 211a is the region where the first current collector 2111 and the first electrode tab 22 are connected. The second current collector 2121 is connected to the second electrode tab 23 and includes a second region 212a connected to the second electrode tab 23. The second region 212a is located at the end of the winding of the second current collector 2121. It can be understood that the second region 212a is the region where the second current collector 2121 and the second electrode tab 23 are connected. Along the winding direction C of the electrode assembly 21 from the inside to the outside, the first region 211a extends beyond the second region 212a.

[0051] Continuing with FIG5 , the first active material layer 2112 includes a first active area 2113, wherein the first active area 2113 is the region of the first active material layer 2112 opposite the second active material layer 2122. Along the winding direction C from the inside to the outside of the electrode assembly 21, the total length of the first active area 2113 is L1 mm. The total length of the first active area 2113 is the sum of the lengths of the first active areas 2113 located on two opposing surfaces of the first current collector 2111. It is understood that the surface of the innermost circle of the first current collector 2111 facing the winding center B may be provided with the first active material layer 2112, but since the opposite side does not have the second active material layer 2122, it is not the first active area 2113. The first current collector 2111 also includes a first coating area 211c, and the first active area 2113 is provided on the surface of the first coating area 211c. The second active material layer 2122 includes a second active area 2123, which is the region of the second active material layer 2122 opposite the first active material layer 2112. Along the winding direction C from the inside to the outside of the pole piece assembly 21, the total length of the second active area 2123 is L2 mm. The total length of the second active area 2123 is the sum of the lengths of the second active areas 2123 located on two opposing surfaces of the second current collector 2121. The second current collector 2121 also includes a second coating area 212b, and the second active area 2123 is located on the surface of the second coating area 212b.

[0052] It can be understood that the first coating region 211 c and the first region 211 a are different regions of the first current collector 2111 , and the second coating region 212 b and the second region 212 a are different regions of the second current collector 2121 .

[0053] Continuing to refer to FIG5 , along the winding direction C from the inside to the outside of the electrode assembly 21, the first coating area 211c includes a first starting end 211d and a first end 211e, and the second coating area 212b includes a second starting end 212c and a second end 212d. The first current collector 2111 includes a first section 211f from the first end 211e to the center of the first region 211a. The length of the first section 211f is S1mm, the winding angle of the first section 211f is α1°, and the number of winding turns of the first section 211f is C. 10 =α1 / 360, the winding radius R of the first section 211f 10 mm=S1 / (2π×C 10 The second current collector 2121 optionally includes a second segment 212e extending from the second end 212d to the center of the second region 212a. The length of the second segment 212e is S2 mm, the winding angle of the second segment 212e is α2°, and the number of winding turns of the second segment 212e is C. 20 =α2 / 360, the winding radius R of the second section 212e 20mm=S2 / (2π×C 20 ).

[0054] Among them, along the winding direction C from the inside to the outside of the pole piece assembly 21, the number of winding turns of the first coating area 211c and the second coating area 212b is n, and the winding radius of the first coating area 211c of the i-th turn is R 1i mm, the winding radius of the second coating area 212b of the i-th circle is R 2i mm.

[0055] It can be understood that the winding length of the first coating area 211c of the i-th circle is L 1i mm, the winding angle of the first coating area 211c of the i-th circle is β i °, then the number of turns of the first coating area 211c of the i-th turn is C 1i =β i / 360, the winding radius R of the first coating area 211c of the i-th circle 1i mm=L 1i / (2π×C 1i The winding length of the second coating area 212b of the i-th circle is L 2i mm, the winding angle of the second coating area 212b of the i-th circle is γ i °, then the number of turns of the second coating area 212b of the i-th turn is C 2i =γ i / 360, the winding radius R of the second coating area 212b of the i-th circle 2i mm=L 2i / (2π×C 2i ).

[0056] The length of the first valid area 2113 in the i-th circle is l 1i mm, the proportion of the first effective area 2113 in the i-th circle X 1i =l 1i / L1; the length of the second effective area 2123 in the i-th circle is l 2i mm, the proportion of the second effective area 2123 in the i-th circle X 2i =l 2i / L2. The equivalent current intensity λ of the i-th circle in the first coating area 211c 1i =X 11 +…+X 1(i-1) +0.5X 1i , the equivalent current intensity λ of the i-th circle in the second coating area 212b 2i =X 21 +…+X 2(i-1) +0.5X 2i , understandably, with λ 1i For example, the above recursive formula should be understood as the equivalent current intensity λ of the first circle in the first coating area 211c11 =0.5X 11 , the equivalent current intensity λ of the second circle 12 =X 11 +0.5X 12 , the equivalent current intensity λ of the third circle 13 =X 11 +X 12 +0.5X 13 , and so on, λ 2i The same relationship as above is also followed and will not be elaborated here.

[0057] The inventors of this application have discovered that the winding radius of each turn in the pole piece has a significant impact on the magnetic field generated at the winding end face. Taking the electrical device 1000 as a Bluetooth headset as an example, the first pole piece 211 and the second pole piece 212 with different winding radii in the winding structure pole piece assembly 21 generate different magnetic fields in the Bluetooth headset voice coil. Taking the first pole piece 211 as an example, the Biot-Saffar law is used to calculate the average magnetic field strength in the Bluetooth headset voice coil when the first pole pieces 211 with different winding radii pass a unit current (1A). The relationship between the calculated magnetic field strength and the winding radius of the first pole piece 211 is shown in Table 1 below:

[0058] Table 1: Relationship between the winding radius of the first pole piece 211 of the i-th circle and the magnetic field strength

[0059] The winding radius of the first pole piece 211 of the i-th circle in Table 1 and the magnetic field strength of the first pole piece 211 of the i-th circle are fitted and calculated to obtain the relationship: f(R)=0.000016866R 4 -0.0002591R 3 +0.001204R 2 Of course, the relationship between the winding radius of the i-th circle of the second pole piece 212 and the magnetic field strength of the i-th circle of the second pole piece 212 also conforms to the above relationship, which will not be repeated here.

[0060] It can be concluded that the equivalent magnetic field strength of the i-th circle in the first coating area 211c is λ 1i ×f(R 1i ), the equivalent magnetic field strength of the first segment 211f is C 10 ×f(R 10 ), the equivalent magnetic field strength of the i-th circle in the second coating area 212b is λ 2i ×f(R 2i ), the equivalent magnetic field strength of the second segment 212e is C 20 ×f(R 20 ). Then the sum of the equivalent magnetic field strength of the first current collector 2111 is F1=C10 ×f(R 10 )+λ 11 ×f(R 11 )+λ 12 ×f(R 12 )+…λ 1n ×f(R 1n ); the sum of the equivalent magnetic field strength of the second current collector 2121 is F2 = C 20 ×f(R 20 )+λ 21 ×f(R 21 )+λ 22 ×f(R 22 )+…λ 2n ×f(R 2n ); satisfy: |F1-F2|≤4×10 -5 .

[0061] The present invention extends the effective length of the first pole piece 211 located inside the winding so that the first region 211a extends beyond the second region 212a, and controls the length of the first region 211a extending beyond the second region 212a until the sum of the equivalent magnetic field strength F1 of the first current collector 2111 and the sum of the equivalent magnetic field strength F2 of the second current collector 2121 satisfy the following: |F1-F2|≤4×10 -5 When the electrode assembly 20 discharges and generates current, the magnetic field generated by the portion of the first pole piece 211 that extends beyond the second region 212a can better offset the axial magnetic field generated by the spiral involute structure, thereby better reducing the axial magnetic field at the end face of the winding structure, and thus helping to reduce the interference of the electrochemical device 100 on the electrical equipment 1000.

[0062] It can be understood that the second current collector 2121 optionally includes the second segment 212e, which can be understood to include two solutions: one solution is that the second current collector 2121 includes the second segment 212e, and the other solution is that the second current collector 2121 does not include the second segment 212e, that is, the second region 212a and the second coating region 212b are connected along the winding direction from the inside to the outside of the pole piece assembly 21. In the embodiment where the second current collector 2121 includes the second segment 212e, S2>0, and in the embodiment where the second current collector 2121 does not include the second segment 212e, S2=0.

[0063] In addition, it can be understood that the surface of the first segment 211f or the second segment 212e may be partially or fully coated with an active material layer. For example, when the first electrode 211 is a negative electrode, the surface of the first segment 211f may be partially or fully coated with a negative electrode active material layer. Since there is no corresponding positive electrode active material layer on the opposite side, no effective current is generated during the discharge process. Moreover, since the negative electrode active material layer exceeds the positive electrode active material layer in the winding direction, the risk of lithium plating during the charging process can be reduced, thereby improving the safety of the electrochemical device 100.

[0064] It can be understood that when F2>F1, and the difference between the two is large, the effective length of the first pole piece 211 can be extended, that is, the length of the first region 211a beyond the second region 212a can be extended. Preferably, the extended length of the first pole piece 211 is D1=2π×R1×(F2-F1) / f(R1), where R1 is the distance between the center of the first region 211a and the winding center B of the pole piece assembly 21. At this time, when observing along the width direction X of the first pole piece 211, the angle of rotation of the ray from the winding center B of the pole piece assembly 21 to the center of the first region 211a along the winding direction C from the inside to the outside of the pole piece assembly 21 is θ1'=360°×D1 / 2πR1.

[0065] When F2 is less than F1, and the difference between the two is large, the effective length of the second pole piece 212 can be extended, that is, the length by which the first region 211a extends beyond the second region 212a can be shortened. Preferably, the extended length of the second pole piece 212 is D2 = 2π × R2 × (F1-F2) / f(R2), where R2 is the distance from the center of the second region 212a to the winding center B of the pole piece assembly 21. At this time, when observed along the width direction of the second pole piece 212, the angle of rotation of the ray from the winding center B of the pole piece assembly 21 to the center of the second region 212a along the winding direction C from the inside to the outside of the pole piece assembly 21 is θ2' = 360° × D2 / 2πR2.

[0066] In some embodiments, |F1-F2|≤3×10 -5 In this way, the axial magnetic field at the end face of the winding structure can be further reduced, thereby further reducing the interference to the electrical equipment 1000.

[0067] As an illustrative example, the value of |F1-F2| may be 4×10 -5 , 3.6×10 -5 , 3.5×10 -5 , 3.2×10 -5 , 3×10 -5 , 2.8×10 -5 , 2.5×10 -5 , 2×10 -5 , 1.5×10 -5 , 1×10-5 , 5×10 -6 , 1×10 -6 , 5×10 -7 , 2×10 -7 , 0 or a range consisting of any two of the above.

[0068] In some embodiments, referring to FIG. 3 , the housing 10 includes a first housing portion 11 and a second housing portion 12 . The first housing portion 11 and the second housing portion 12 have different polarities and are insulated from each other.

[0069] In some embodiments, referring to Figures 3 to 5 , the first electrode piece 211 is connected to the first electrode tab 22, which is connected to the first shell 11, so that the first electrode tab 22 and the first shell 11 have a first polarity. The second electrode piece 212 is connected to the second electrode tab 23, which is connected to the second shell 12, so that the second electrode tab 23 and the second shell 12 have a second polarity.

[0070] In some embodiments, referring to FIG3 , the first shell portion 11 includes a top wall 111, a bottom wall 112, and side walls 113. The side walls 113 are located between the top wall 111 and the bottom wall 112. The top wall 111 and the bottom wall 112 are both connected to the side walls 113, and enclose a receiving space 11a for accommodating the electrode assembly 20. The first shell portion 11 can protect the electrode assembly 20 and reduce the risk of external impact to the electrode assembly 20.

[0071] In some embodiments, referring to FIG. 3 , the second shell portion 12 includes a pole, and a through hole 1111 is defined in the top wall 111 . The pole is disposed in the through hole 1111 and is insulated and connected to the top wall 111 .

[0072] In some embodiments, referring to FIG3 , the electrode post includes a mounting portion 121 and a lead portion 122. The mounting portion 121 is located within the accommodating space 11a and connected to the electrode assembly 20. The mounting portion 121 is also insulated from the top wall 111. The lead portion 122 is disposed through the through hole 1111 and is at least partially exposed outside the accommodating space 11a.

[0073] In some embodiments, referring to FIG. 3 , the electrochemical device 100 further includes a sealing member 50 . The sealing member 50 is disposed between the top wall 111 and the mounting portion 121 to insulate and seal the mounting portion 121 from the top wall 111 .

[0074] In some embodiments, the seal 50 may be a sealant.

[0075] In some embodiments, the pole can be made of a conductive metal such as copper, aluminum, nickel, or iron. The pole can be in the shape of a column, a hemisphere, a sheet, or a combination thereof, and is not specifically limited here.

[0076] In some embodiments, as shown in FIG5 , along the winding direction C of the pole piece assembly 21 from the inside out, the first region 211a extends beyond the second region 212a by less than one turn. This helps reduce the extended length of the first current collector 2111, thereby reducing the risk of the first current collector 2111 extending too long and becoming misaligned, causing a short circuit.

[0077] In some embodiments, please refer to Figure 5, the first electrode 211 is a negative electrode, the second electrode 212 is a positive electrode, and the winding starting section of the first active material layer 2112 exceeds the winding starting section of the second active material layer 2122 in the opposite direction of the winding direction C from the inside to the outside of the electrode assembly 21, and\or the winding end section of the first active material layer 2112 exceeds the winding end section of the second active material layer 2122 along the winding direction C from the inside to the outside of the electrode assembly 21. Accordingly, the first current collector 2111 further includes a third coating area 211g and / or a fourth coating area 211h. The portion where the winding start section of the first active material layer 2112 extends beyond the winding start section of the second active material layer 2122 is a first inactive area 2114, and the portion where the winding end section of the first active material layer 2112 extends beyond the winding end section of the second active material layer 2122 is a second inactive area 2115. The first inactive area 2114 is provided on the surface of the third coating area 211g, and the second inactive area 2115 is provided on the surface of the fourth coating area 211h. This helps reduce the risk of lithium plating and improves the safety of the electrochemical device 100. It can be understood that the first section 211f includes the fourth coating area 211h.

[0078] In some embodiments, referring to FIG6 , along the winding direction of the pole piece assembly 21 from the inside out, the winding tail section of the first current collector 2111 further includes a blank section 211b extending beyond the first region 211a and not provided with the first active material layer 2112 on its surface. The blank section 211b covers the winding tail section of the second current collector 2121. This arrangement provides the blank section 211b of the first current collector 2111 between the winding tail section of the second current collector 2121 and the first shell 11, thereby enhancing the isolation between the second current collector 2121 and the first shell 11, thereby reducing the risk of a short circuit caused by direct contact between the second current collector 2121 and the first shell 11.

[0079] In some embodiments, referring to Figures 4 and 7 , the first tab 22 includes a first connecting portion 221 and a first bent portion 222. The first connecting portion 221 is connected to the first region 211a, and the first bent portion 222 includes a third region 222a connected to the first shell 11. The electrochemical device 100 also includes a first connector 30 located outside the shell 10. The first connector 30 includes a first end 31 and a second end 32. The first end 31 is connected to the first shell 11, and the second end 32 includes a fourth region 321 for connecting to an external load. The angle θ1 between a ray from the center of the third region 222a to the center of the first region 211a and a ray from the center of the third region 222a to the center of the fourth region 321 is θ1, satisfying θ1 ≤ 45°. This helps reduce the impact of current passing through the first bent portion 222 on the axial magnetic field, thereby further reducing interference with the electrical device 1000.

[0080] It is understood that the first region 211a generally has a specific planar shape. When the planar shape of the first region 211a is a continuous entity, the center of the first region 211a is defined as the center of gravity of the planar shape of the first region 211a. The center of gravity of the planar shape can be determined by the suspension method. When the first region 211a is composed of multiple discrete regions (for example, the first current collector 2111 and the first connecting portion 221 are connected by multiple discrete point-shaped regions), the center of the first region 211a is defined as the center of the smallest circumscribed circle containing the multiple discrete regions. The method for determining the center of the third region 222a and the center of the fourth region 321 is the same as the method for determining the center of the first region 211a and will not be repeated here.

[0081] In some embodiments, please refer to Figure 4, the first bending portion 222 is bent toward the first end surface 21a of the pole piece assembly 21, and along the width direction of the first pole piece 211, the first bending portion 222 is located on one side of the pole piece assembly 21, and the first bending portion 222 is connected to the first shell portion 11.

[0082] In some embodiments, referring to FIG. 4 , the first bent portion 222 extends in a direction parallel to the first end surface 21 a .

[0083] In some embodiments, referring to Figures 4 and 8 , the second tab 23 includes a second connecting portion 231 and a second bent portion 232. The second connecting portion 231 is connected to the second region 212a. The second bent portion 232 includes a fifth region 232a connected to the second shell 12. The electrochemical device 100 also includes a second connector 40 located outside the housing 10. The second connector 40 includes a third end 41 and a fourth end 42. The third end 41 is connected to the second shell 12. The fourth end 42 includes a sixth region 421 for connecting to an external load. The angle θ2 between a ray from the center of the fifth region 232a to the center of the second region 212a and a ray from the center of the fifth region 232a to the center of the sixth region 421 is such that θ2 ≤ 45°. This helps reduce the impact of current passing through the second bent portion 232 on the axial magnetic field, thereby further reducing interference with the electrical device 1000. The method for determining the center of the second region 212a, the center of the fifth region 232a, and the center of the sixth region 421 is the same as the method for determining the center of the first region 211a, and will not be repeated here.

[0084] In some embodiments, please refer to Figure 4, the second bending portion 232 is bent toward the second end surface 21b of the pole piece assembly 21, and along the width direction of the first pole piece 211, the second bending portion 232 is located on the side of the pole piece assembly 21 away from the first bending portion 222, and the second bending portion 232 is connected to the second shell portion 12.

[0085] In some embodiments, referring to FIG. 4 , the second bent portion 232 extends in a direction parallel to the second end surface 21 b .

[0086] In some embodiments, referring to Figures 5 and 6, the pole piece assembly 21 further includes a first diaphragm 24, which is disposed between the first pole piece 211 and the second pole piece 212. Along the winding direction of the pole piece assembly 21 from the inside to the outside, the winding tail section of the first diaphragm 24 exceeds the first pole piece 211, so that the winding tail end of the first pole piece 211 is covered by the first diaphragm 24, which helps to reduce the risk of direct contact between the first pole piece 211 and the second pole piece 212.

[0087] In some embodiments, referring to Figures 5 and 6, the pole piece assembly 21 further includes a second diaphragm 25, which is disposed between the first pole piece 211 and the second pole piece 212. Along the winding direction of the pole piece assembly 21 from the inside to the outside, the winding tail section of the second diaphragm 25 exceeds the second pole piece 212, allowing the winding tail section of the second pole piece 212 to be covered by the second diaphragm 25, which helps to reduce the risk of direct contact between the second pole piece 212 and the first pole piece 211 or the shell 10.

[0088] In some embodiments, along the winding direction from the inside to the outside of the pole piece assembly 21, the winding tail sections of the first diaphragm 24 and / or the second diaphragm 25 are fixed to the main body of the pole piece assembly 21 by gluing with adhesive tape, which helps to reduce the risk of curling of the winding tail sections of the first diaphragm 24 and / or the second diaphragm 25.

[0089] 5 and 6 , the second electrode piece 212 is located between the first diaphragm 24 and the second diaphragm 25. In other embodiments, the first electrode piece 211 is located between the first diaphragm 24 and the second diaphragm 25.

[0090] In some embodiments, the first diaphragm 24 and the second diaphragm 25 can be made of materials such as polyethylene (PE) or polypropylene (PP), and are used to isolate the first electrode piece 211 from the second electrode piece 212 .

[0091] In some embodiments, the electrochemical device 100 further includes an insulating member (not shown) disposed between the housing 10 and the electrode assembly 21. This helps reduce the risk of direct contact between the electrode assembly 21 and the housing 10, thereby reducing the risk of internal short circuits in the electrochemical device 100.

[0092] In order to verify the control of the length of the first region 211a of the electrochemical device 100 of the present application beyond the second region 212a, and to meet the condition: |F1-F2|≤4×10 -5 To investigate the effect of canceling the magnetic field generated in the axial direction, the following experiment was conducted. First, the magnetic field strengths of different turns of the first pole piece 211 and the magnetic field strengths of different turns of the second pole piece 212 in an electrochemical device 100 were measured, and then multiple comparison experiments were performed to verify the results.

[0093] Taking a cylindrical battery with a wound structure as an example, the cylindrical battery is assembled in a Bluetooth headset. The first pole piece 211 is the negative pole piece, and the second pole piece 212 is the positive pole piece. The first pole piece 211 and the second pole piece 212 are both 21.25 turns, the first coating area 211c and the second coating area 212b are both 21 turns, and the first section 211f and the second section 212e are both 0.25 turns (because there is no active material layer on the surface of the two, the distance is very close, and the magnetic field generated can be approximately offset). The spacing between the current collectors of the first coating area 211c and the second coating area 212b is 86μm. The equivalent current intensity in the first section 211f and the second section 212e is 1A. The calculation of the magnetic field strength of the second coating area 212b in the second pole piece 212 is as shown in Table 2 below:

[0094] Table 2: Magnetic field strength of different turns of the second pole piece 212

[0095] The magnetic field strength of the first pole piece 211 is calculated as shown in Table 3:

[0096] Table 3: Magnetic field strength of different turns of the first pole piece 211

[0097] According to the comparison of the magnetic field strength of the first pole piece 211 and the magnetic field strength of the second pole piece 212 in Tables 2 and 3 above, it can be seen that the length of the first pole piece 211 needs to be extended to reduce the axial magnetic field. According to the formula, the length of the first pole piece 211 that needs to be extended is preferably D1 = 2π × R1 × (F2-F1) / f(R1) = 2 × 3.14 × 5 × (0.006409-0.006345) / 0.0001711 = 11.745 mm, where R1 is the distance from the center of the first region 211a to the winding center B, which is approximately equal to the winding radius of the outermost circle of the second coating area 212b, which is 5 mm. The angle that the ray from the winding center B of the pole piece assembly 21 to the center of the first region 211a rotates from the position before the extension of the first pole piece 211 to the position after the extension of the first pole piece 211 is θ1' = 360° × D1 / 2πR1 = 134.5°.

[0098] To verify the demagnetizing effect of the extension of the first pole piece 211 on the axial magnetic field in the above embodiment, batteries with different extension lengths D1 of the first pole piece 211 were manufactured and passed with a current of 40 mA to conduct the following comparative test. The test results are shown in Table 4 below:

[0099] Table 4: Magnetic field strength of batteries with different extension lengths D1

[0100] Referring to Table 4, when the length D1 of the extended first pole piece 211 is 5.2-18.3 mm, the angle θ1′ of the ray from the winding center B of the pole piece assembly 21 to the center of the first region 211a from the position before the extension of the first pole piece 211 to the position after the extension of the first pole piece 211 is 60°-210°, so that |F1-F2|≤4×10 -5 When , the axial magnetic field of the electrode assembly 20 is extremely small.

[0101] Further, referring to Table 4, satisfying |F1-F2|≤3×10 -5 When the axial magnetic field at the end face of the winding structure is reduced, the interference to the electrical equipment 1000 can be further reduced.

[0102] In addition, those skilled in the art should recognize that the above embodiments are only used to illustrate the present application and are not used to limit the present application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present application should be included in the scope of protection of the present application.

Claims

1. An electrochemical device, characterized in that: include: case; An electrode assembly is housed in the housing, and the electrode assembly comprises: A pole piece assembly, comprising a first pole piece and a second pole piece arranged in a wound state, wherein the first pole piece comprises a first current collector and a first active material layer; the second pole piece comprises a second current collector and a second active material layer; a winding start section of the second active material layer is located outside the winding of the pole piece assembly relative to a winding start section of the first active material layer; A first electrode tab, the first electrode tab being connected to a first region of a winding tail section of the first current collector; A second electrode tab, the second electrode tab being connected to a second region of the second current collector winding tail section; Along the winding direction of the pole piece assembly from inside to outside, the first area exceeds the second area; The first active material layer includes a first effective area, wherein the first effective area is an area of ​​the first active material layer opposite to the second active material layer, and along the winding direction of the pole piece assembly from inside to outside, the total length of the first effective area is L1mm; the first current collector includes a first coating area, and the first effective area is provided on the surface of the first coating area; The second active material layer includes a second effective area, wherein the second effective area is an area of ​​the second active material layer opposite to the first active material layer, and along the winding direction of the pole piece assembly from inside to outside, the total length of the second effective area is L2mm; the second current collector includes a second coating area, and the second effective area is provided on the surface of the second coating area; Along the winding direction of the pole piece assembly from inside to outside, the first coating area includes a first starting end and a first end, and the second coating area includes a second starting end and a second end; The first current collector includes a first section from the first end to the center of the first region, the length of the first section is S1 mm, the winding angle of the first section is α1°, and the number of winding turns of the first section is C 10 =α1 / 360, the winding radius R of the first section 10 mm = S1 / (2π×C 10 ); the second current collector optionally includes a second section from the second end to the center of the second region, the length of the second section is S2mm, the winding angle of the second section is α2°, and the number of winding turns of the second section is C 20 =α2 / 360, the winding radius R of the second section 20 mm = S2 / (2π×C 20 ); Among them, along the winding direction of the pole piece assembly from inside to outside, the number of windings of the first coating area and the second coating area is n, and the winding radius of the first coating area in the i-th circle is R 1i mm, the winding radius of the second coating zone in the i-th circle is R 2i mm; the length of the first effective area in the i-th circle is l 1i mm, the proportion of the first effective area in the i-th circle is X 1i = l 1i / L1; the length of the second effective area in the i-th circle is l 2i mm, the proportion of the second effective area in the i-th circle is X 2i = l 2i / L2; The equivalent current intensity λ of the i-th circle in the first coating area 1i =X 11 +…+X 1(i-1) +0.5X 1i , the equivalent current intensity λ of the i-th circle in the second coating area 2i =X 21 +…+X 2(i-1) +0.5X 2i ; The equivalent magnetic field strength of the i-th circle in the first coating area is λ 1i ×f(R 1i ), the equivalent magnetic field strength of the first section is C 10 ×f(R 10 ), the equivalent magnetic field strength of the i-th circle in the second coating area is λ 2i ×f(R 2i ), the equivalent magnetic field strength of the second section is C 20 ×f(R 20 ); Where, f(R) = 0.000016866R 4 -0.0002591R 3 +0.001204R 2 -0.00198162R+0.0018255; The sum of the equivalent magnetic field strengths of the first current collector is F1, F1=C 10 ×f(R 10 )+λ 11 ×f(R 11 )+λ 12 ×f(R 12 )+…λ 1n ×f(R 1n ); The sum of the equivalent magnetic field strength of the second current collector is F2, F2=C 20 ×f(R 20 )+λ 21 ×f(R 21 )+λ 22 ×f(R 22 )+…λ 2n ×f(R 2n ); Satisfy: |F1-F2|≤4×10 -5 .

2. The electrochemical device according to claim 1, characterized in that Satisfy |F1-F2|≤3×10 -5 .

3. The electrochemical device according to claim 1, characterized in that Along the winding direction of the pole piece assembly from inside to outside, the winding length of the first region beyond the second region is less than one turn.

4. The electrochemical device according to claim 1, characterized in that The first pole piece is a negative pole piece, and the second pole piece is a positive pole piece, satisfying at least one of the following conditions: (1) In the opposite direction of the winding direction of the electrode assembly from inside to outside, the winding start section of the first active material layer exceeds the winding start section of the second active material layer; (2) Along the winding direction of the pole piece assembly from inside to outside, the winding tail section of the first active material layer exceeds the winding tail section of the second active material layer.

5. The electrochemical device according to claim 1, characterized in that The shell comprises a first shell portion and a second shell portion with different polarities, the first shell portion comprises a top wall, a bottom wall and a side wall, the second shell portion comprises a pole, the top wall is provided with a through hole, and the pole is arranged in the through hole.

6. The electrochemical device according to claim 5, characterized in that Along the winding direction of the pole piece assembly from inside to outside, the winding tail section of the first current collector also includes a blank section that exceeds the first region and has no first active material layer on the surface, and the blank section covers the winding tail section of the second current collector.

7. The electrochemical device according to claim 5, characterized in that At least one of the following conditions is met: (1) The first electrode tab includes a first connecting portion and a first bending portion, wherein the first connecting portion is connected to the first region, and the first bending portion includes a third region connected to the first shell; the electrochemical device further includes a first connecting member, wherein the first connecting member is located outside the shell, and the first connecting member includes a first end and a second end, wherein the first end is connected to the first shell, and the second end includes a fourth region for connecting to an external load, and an angle between a ray from the center of the third region to the center of the first region and a ray from the center of the third region to the center of the fourth region is θ1, satisfying θ1≤45°; (2) The second electrode tab includes a second connecting portion and a second bending portion, the second connecting portion is connected to the second region, and the second bending portion includes a fifth region connected to the second shell; the electrochemical device also includes a second connecting member, the second connecting member is located outside the shell, the second connecting member includes a third end and a fourth end, the third end is connected to the second shell, and the fourth end includes a sixth region for connecting to an external load, and the angle between the ray from the center of the fifth region to the center of the second region and the ray from the center of the fifth region to the center of the sixth region is θ2, satisfying θ2≤45°.

8. The electrochemical device according to claim 1, characterized in that At least one of the following conditions is met: (1) The pole piece assembly further includes a first diaphragm, the first diaphragm is disposed between the first pole piece and the second pole piece, and along the winding direction of the pole piece assembly from inside to outside, the winding tail section of the first diaphragm exceeds the first pole piece; (2) The pole piece assembly further includes a second diaphragm, which is disposed between the first pole piece and the second pole piece, and along the winding direction of the pole piece assembly from inside to outside, the winding tail section of the second diaphragm exceeds the second pole piece.

9. The electrochemical device according to any one of claims 1 to 8, characterized in that: The electrochemical device further includes an insulating member disposed between the housing and the pole piece assembly.

10. An electrical device, characterized in that: An electrochemical device comprising any one of claims 1 to 9.

11. A method for preparing an electrochemical device, the electrochemical device comprising: case; An electrode assembly is housed in the housing, and the electrode assembly comprises: A pole piece assembly, comprising a first pole piece and a second pole piece arranged in a wound state, wherein the first pole piece comprises a first current collector and a first active material layer; the second pole piece comprises a second current collector and a second active material layer; a winding start section of the second active material layer is located outside the winding of the pole piece assembly relative to a winding start section of the first active material layer; A first electrode tab, the first electrode tab being connected to a first region of a winding tail section of the first current collector; A second electrode tab, the second electrode tab being connected to a second region of the second current collector winding tail section; Along the winding direction of the pole piece assembly from inside to outside, the first area exceeds the second area; The first active material layer includes a first effective area, wherein the first effective area is an area of ​​the first active material layer opposite to the second active material layer, and is located along the pole piece assembly from the inner side to the outer side. In the winding direction outside, the total length of the first effective area is L1 mm; the first current collector includes a first coating area, and the first effective area is arranged on the surface of the first coating area; The second active material layer includes a second effective area, wherein the second effective area is an area of ​​the second active material layer opposite to the first active material layer, and along the winding direction of the pole piece assembly from inside to outside, the total length of the second effective area is L2mm; the second current collector includes a second coating area, and the second effective area is provided on the surface of the second coating area; Along the winding direction of the pole piece assembly from inside to outside, the first coating area includes a first starting end and a first end, and the second coating area includes a second starting end and a second end; The first current collector includes a first section from the first end to the center of the first region, and the length of the first section is S1 mm; the second current collector optionally includes a second section from the second end to the center of the second region, and the length of the second section is S2 mm; Among them, along the winding direction of the pole piece assembly from inside to outside, the number of windings of the first coating area and the second coating area is n, and the winding radius of the first coating area in the i-th circle is R 1i mm, the winding radius of the second coating zone in the i-th circle is R 2i mm; the length of the first effective area in the i-th circle is l 1i mm, the proportion of the first effective area in the i-th circle is X 1i = l 1i / L1; the length of the second effective area in the i-th circle is l 2i mm, the proportion of the second effective area in the i-th circle is X 2i = l 2i / L2; The equivalent current intensity λ of the i-th circle in the first coating area 1i =X 11 +…+X 1(i-1) +0.5X 1i , the equivalent current intensity λ of the i-th circle in the second coating area 2i =X 21 +…+X 2(i-1) +0.5X 2i ; It is characterized in that, according to the equivalent current intensity λ of the i-th circle in the first coating area 1i The equivalent magnetic field strength generated by the i-th circle in the first coating area is calculated, and the sum of the equivalent magnetic field strengths generated by the first coating area is calculated; and the equivalent current strength λ of the i-th circle in the second coating area is calculated according to the equivalent magnetic field strength generated by the i-th circle in the first coating area. 2i The equivalent magnetic field strength generated by the i-th circle in the second coating area is used to calculate the sum of the equivalent magnetic field strengths generated by the second coating area; based on the difference between the sum of the equivalent magnetic field strengths generated by the first coating area and the sum of the equivalent magnetic field strengths generated by the second coating area, the length S1mm of the first segment is determined to be greater than the length S2mm of the second segment so that the difference between the sum F1 of the equivalent magnetic field strengths generated by the first current collector and the sum F2 of the equivalent magnetic field strengths generated by the second current collector is smaller.

12. The preparation method according to claim 11, characterized in that: According to f(R)=0.000016866R 4 -0.0002591R 3 +0.001204R 2 -0.00198162R+0.0018255, the equivalent magnetic field strength generated by the i-th circle in the first coating area is calculated as λ 1i ×f(R 1i ), the equivalent magnetic field strength generated by the i-th circle in the second coating area is λ 2i ×f(R 2i ).

13. The preparation method according to claim 12, characterized in that: The method further includes calculating the equivalent magnetic field strength of the first segment and the equivalent magnetic field strength of the second segment, wherein the winding angle of the first segment is α1°, the number of winding turns of the first segment is C 10 =α1 / 360, the winding radius R of the first section 10 mm = S1 / (2π×C 10 ), the winding angle of the second section is α2°, and the number of winding turns of the second section is C 20 =α2 / 360, the winding radius R of the second section 20 mm = S2 / (2π×C 20 ); The equivalent magnetic field strength of the first section is C 10 ×f(R 10 ), the equivalent magnetic field strength of the second section is C 20 ×f(R 20 ); then F1=C 10 ×f(R 10 )+λ 11 ×f(R 11 )+λ 12 ×f(R 12 )+…λ 1n ×f(R 1n ); F2=C 20 ×f(R 20 )+λ 21 ×f(R21)+λ 22 ×f(R 22 )+…λ 2n ×f(R 2n ); Determine that the length S1mm of the first segment is greater than the length S2mm of the second segment so that F1 and F2 satisfy: |F1-F2|≤4×10 -5 .

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