Electrochemical devices and electronic devices

Abstract

The present application discloses an electrochemical device and an electronic device, the electrochemical device electrode assembly, the electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator separating the positive electrode sheet and the negative electrode sheet. The positive electrode sheet includes a positive current collector, a positive active material layer and an inactive material layer. The positive active material layer is formed on the surface of the positive current collector, and the inactive material layer is formed on the surface of the positive active material layer away from the positive current collector. Along the first direction, the thickness of the inactive material layer is 1 micron to 20 microns, wherein the first direction is the thickness direction of the positive current collector. And the diffusion rate of lithium ions in the inactive material layer is less than the diffusion rate in the positive active material layer. In the above manner, the present application can reduce the current density of the region when the electrochemical device is charged, so as to facilitate the improvement of the charge and discharge rate of the electrochemical device.

Description

Technical Field

[0001] The present application relates to the field of energy storage technology, and in particular to an electrochemical device and an electronic device. Background Art

[0002] When charging an electrochemical device, the positive electrode loses electrons, and lithium ions can be deintercalated from the lattice of the positive electrode active material layer. After that, the lithium ions migrate to the negative electrode through the isolation membrane and embed into the holes of the negative electrode active material layer. At the same time, electrons also reach the negative electrode through the external circuit, and the electrons obtained by the negative electrode combine with the embedded lithium ions to form a lithium-carbon intercalation compound. The opposite process occurs when the electrochemical device is discharged.

[0003] At present, as the kinetic performance of electrochemical devices continues to improve, their charge and discharge rates are getting higher and higher. During high-rate charge and discharge cycles, the lithium ion concentration in the electrolyte is prone to unevenness, and there is uneven deposition of lithium metal at different locations. Reflected on the anode of the electrode assembly, some areas on the surface of the anode pole piece will have a deposition rate that is too fast, and then lithium dendrites with sharp structures will be formed. The presence of lithium dendrites can easily pierce the isolation membrane to form a short circuit, which is not conducive to the improvement of the charge and discharge rate of the electrochemical device. Summary of the invention

[0004] One purpose of the present application is to provide an electrochemical device to improve the situation where the electrode of the electrochemical device is prone to lithium deposition.

[0005] The present application provides an electrochemical device, which includes an electrode assembly, wherein the electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator separating the positive electrode sheet and the negative electrode sheet. The positive electrode sheet includes a positive current collector, a positive active material layer, and an inactive material layer. The positive active material layer is formed on the surface of the positive current collector, and the inactive material layer is formed on the surface of the positive active material layer away from the positive current collector. Along the first direction, the thickness of the inactive material layer is 1 micron-20 microns, wherein the first direction is the thickness direction of the positive current collector. And the diffusion rate of lithium ions in the inactive material layer is less than the diffusion rate in the positive active material layer. The advantage of such a setting is that the diffusion rate of lithium ions in the region of the positive active material layer corresponding to the inactive material layer can be reduced, thereby reducing the current density of the region when the electrochemical device is charged, and then optimizing the lithium insertion uniformity of the negative electrode sheet corresponding to the inactive material layer, so as to facilitate the improvement of the charge and discharge rate of the electrochemical device.

[0006] In some optional embodiments, the positive electrode sheet has a first part, a second part and a third part, and along the second direction, the first part is connected to one end of the second part, and the third part is connected to the other end of the second part. Wherein, the second direction is perpendicular to the first direction, and the second direction is the width direction of the positive electrode collector. The inactive material layer includes a first inactive material layer, and the first inactive material layer is arranged in the first part and / or the third part. In order to slow down the lithium ion release rate of the positive electrode active material layer of the first part and the third part, thereby reducing the lithium precipitation phenomenon in the area of ​​the negative electrode sheet corresponding to the first part and the third part.

[0007] In some optional embodiments, along the second direction, the ratio of the width of the first inactive material layer to the width of the positive electrode current collector is 0.01%-30%, so as to save coating costs.

[0008] In some optional embodiments, the positive electrode sheet, the separator and the negative electrode sheet are stacked and wound in sequence to form the electrode assembly. The positive electrode sheet includes a first blank area, a first double-sided area, a first single-sided area and a second blank area. Along the winding direction, the first double-sided area has a winding start end close to the winding center and a winding end end away from the winding center. The first blank area is connected to the winding start end. The first single-sided area is connected to the winding end end. The second blank area is connected to one end of the first single-sided area away from the winding end end. The inactive material layer includes a second inactive material layer, and the second inactive material layer is arranged at least one of the winding start end, the winding end end and one end of the first single-sided area away from the winding end end, so as to slow down the lithium ion release speed of the positive active material layer corresponding thereto, thereby reducing the lithium deposition phenomenon in the negative electrode sheet and its corresponding area.

[0009] In some optional embodiments, along the third direction, the width of the second inactive material layer is 1 micron-30 microns. The third direction, the second direction and the first direction are perpendicular to each other. The width of the second inactive material layer is limited to this numerical range, which has a good effect of slowing down the speed of lithium ion escape and is conducive to saving coating costs.

[0010] In some optional embodiments, the negative electrode plate has a second single-sided area. The inactive material layer includes a third inactive material layer. The third inactive material layer is arranged in the first double-sided area of ​​the positive electrode plate corresponding to the second single-sided area to slow down the lithium ion release rate of the positive electrode active material layer corresponding thereto, thereby reducing the lithium deposition phenomenon in the negative electrode plate and the corresponding area.

[0011] In some optional embodiments, the positive electrode sheet is provided with a first groove, and the bottom of the first groove exposes the positive current collector. The electrochemical device includes a positive electrode ear and a first adhesive. A portion of the positive electrode ear is accommodated in the first groove and connected to the positive current collector. The first adhesive is fixed to the positive electrode sheet and covers the first groove. The inactive material layer includes a fourth inactive material layer. The fourth inactive material layer is arranged around the periphery of the first adhesive.

[0012] In some optional embodiments, the electrochemical device further includes a negative electrode ear and a second adhesive. A portion of the negative electrode ear is connected to the negative electrode current collector. The positive electrode plate is also provided with a second groove corresponding to the negative electrode ear. The bottom of the second groove exposes the positive electrode current collector, and the second adhesive is fixed to the positive electrode plate and covers the second groove. The inactive material layer includes a fifth inactive material layer. The fifth inactive material layer is arranged around the periphery of the second adhesive.

[0013] The positive electrode plate is provided with a groove, and the bottom of the groove exposes the positive electrode current collector. One end of the positive electrode ear is received in the groove and connected to the positive electrode current collector. The electrochemical device also includes an adhesive. The adhesive is fixed to the positive electrode plate and covers the groove. The inactive material layer also includes a fifth inactive material layer. The fifth inactive material layer is arranged around the periphery of the adhesive.

[0014] In some optional embodiments, the electrode assembly includes a first straight section, a first bent section, a second straight section, and a second bent section connected in sequence along the winding direction. The first straight section is arranged opposite to the second straight section, and the first bent section is arranged opposite to the second bent section. The inactive material layer also includes a sixth inactive material layer. The sixth inactive material layer is arranged in the first bent section and / or the second bent section.

[0015] Another technical solution adopted by the present application is to provide an electronic device, including the electrochemical device described above.

[0016] The beneficial effect of the present application is that the inactive material layer is formed on the surface of the positive electrode active material layer, that is, the inactive material layer is formed on the surface of the positive electrode active material layer, and the diffusion rate of lithium ions in the inactive material layer is less than the diffusion rate of lithium ions in the positive electrode active material layer, so that the rate of lithium ion release in the positive electrode active material layer can be slowed down. In other words, part of the lithium compound in the positive electrode active material layer corresponding to the inactive material layer does not form lithium ions, and the total amount of lithium embedded in the negative electrode active material layer corresponding to the inactive material layer in the same time is reduced, which reduces the phenomenon of excessively fast deposition rate in the negative electrode active material layer region corresponding to the inactive material layer, thereby improving the situation of easy lithium precipitation in the electrochemical device. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without paying creative work.

[0018] Figure 1 A schematic diagram of the structure of a mobile phone provided in one embodiment of the present application;

[0019] Figure 2 for Figure 1 A schematic diagram of the structure of an electrode assembly in an electrochemical device when it is wound and not coated with an inactive material layer;

[0020] Figure 3 for Figure 2 A partial schematic diagram showing a first double-sided region or a first single-sided region of a positive electrode sheet in an electrode assembly in an unwound state;

[0021] Figure 4 for Figure 3 A cross-sectional view of the positive electrode sheet shown along a first direction;

[0022] Figure 5 for Figure 3 Another cross-sectional view of the positive electrode sheet shown along the first direction;

[0023] Figure 6 for Figure 2 A partial schematic diagram of the winding start end of the first double-sided area of ​​the positive electrode sheet in the electrode assembly is shown;

[0024] Figure 7 for Figure 6 A cross-sectional view of the winding start end of the first double-sided area along the first direction;

[0025] Figure 8 for Figure 6Another cross-sectional view of the winding starting end of the first double-sided area along the third direction;

[0026] Fig. 9 for Figure 2 A partial schematic diagram of a first double-sided region of a positive electrode sheet and a second single-sided region of a negative electrode sheet corresponding to the first double-sided region of the positive electrode sheet in an electrode assembly is shown;

[0027] Fig.10 for Figure 2 The schematic diagram of the structure shows that the positive electrode plate in the electrode assembly is provided with a first groove and a second groove. DETAILED DESCRIPTION

[0028] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. The description of at least one exemplary embodiment below is actually only illustrative and is by no means intended to limit the present application and its application or use. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without carrying out creative work are within the scope of protection of this application.

[0029] Technologies, methods, and apparatus known to ordinary technicians in the relevant field may not be discussed in detail, but where appropriate, such technologies, methods, and apparatus should be considered part of the authorization specification.

[0030] In the description of the present application, it should be noted that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present application and simplifying the description. Unless otherwise stated, these directional words do not indicate or imply that the devices or elements referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present application. The directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

[0031] In addition, sometimes amounts, ratios and other numerical values ​​are presented in range format herein. It should be understood that such range format is for convenience and brevity, and should be flexibly understood to include not only the numerical values ​​explicitly indicated as range limits, but also all individual numerical values ​​or sub-ranges included within the range, as if each numerical value and sub-range were explicitly specified.

[0032] In the description of the present application, it should be noted that the use of terms such as "first" and "second" to limit components is merely to facilitate the distinction between corresponding components. Unless otherwise stated, the above terms have no special meaning and therefore cannot be understood as limiting the scope of protection of the present application.

[0033] The electrochemical device disclosed in the present application is suitable for electronic devices using the electrochemical device. In this way, the situation of local lithium precipitation in the existing electrochemical device can be improved to enhance the safety performance of the electrochemical device. It is understandable that the electronic device of the embodiment of the present application is not specifically limited. The above-mentioned electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini CD, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an electric car, a car, a motorcycle, a power bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium ion capacitor. However, for the sake of simplicity of description, the following embodiments are all illustrated by taking the electronic device as a mobile phone.

[0034] See also Figure 1 The example shown, Figure 1 A schematic diagram of the structure of a mobile phone is shown. The above-mentioned electrochemical device 01 is installed inside the mobile phone, and the electrochemical device 01 provides electrical energy or stores electrical energy for the mobile phone to meet the power demand when the mobile phone is used. It can be understood that the types of electrochemical devices 01 in the embodiments of the present application can actually be diverse. For example, the electrochemical device 01 can include all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. Optionally, the electrochemical device 01 is a lithium secondary battery, which includes a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery or a lithium ion polymer secondary battery. For the sake of simplicity of description, the following embodiments are all illustrated by taking the electrochemical device 01 as a lithium ion secondary battery.

[0035] Please combine Figure 2 See also Figure 1 The example shown, Figure 2 for Figure 1The schematic diagram of the structure of the electrode assembly 1 in the electrochemical device 01 shown. The electrochemical device 01 includes a shell (not shown), an electrode assembly 1 and a pole ear (not shown). The shell is a mounting support structure for the electrode assembly 1. The shell is provided with a cavity, and the cavity is used to accommodate the electrode assembly 1 to protect the electrode assembly 1. The electrode assembly 1 is a component for the electrochemical device 01 to realize the charging and discharging function. The electrode assembly 1 is accommodated in the cavity, and the electrode assembly 1 includes a positive electrode sheet 11, a negative electrode sheet 13 and a separator 12 separating the positive electrode sheet 11 and the negative electrode sheet 13. The pole ear is connected to the electrode assembly 1, and the pole ear passes through the shell and is exposed outside the shell to form a connection terminal, which is used for electrical conduction with the outside. Among them, the pole ear connected to the positive pole sheet 11 of the electrode assembly 1 is called the positive pole ear. Correspondingly, the part of the positive pole ear that is led out of the shell and used for electrical connection with the outside is called the positive terminal. The pole ear connected to the negative pole sheet 13 of the electrode assembly 1 is called the negative pole ear. Correspondingly, the part of the negative electrode ear that is led out of the shell and used for electrical connection with the outside world is called the negative terminal.

[0036] For the positive electrode sheet 11, please refer to Figure 3 The example shown, Figure 3 This is a schematic diagram of the structure of the electrode assembly 1 provided in one embodiment of the present application. The positive electrode plate 11 includes a positive current collector 111, a positive active material layer 112 and an inactive material layer. The positive active material layer 112 is formed on the surface of the positive current collector 111, and the inactive material layer is formed on the surface of the positive active material layer 112 away from the positive current collector 111. Specifically, the positive active material layer 112 may be formed on the surface of one side of the positive current collector 111, or may be formed on the two surfaces on the opposite sides of the positive current collector 111. When the positive active material layer 112 is formed on the two surfaces on the opposite sides of the positive current collector 111, the inactive material layer may be formed only on the surface of the positive active material layer 112 on one side of the positive current collector 111, or the inactive material layers may also be formed on the surfaces of the two positive active material layers 112 on the opposite sides of the positive current collector 111, respectively, which is not specifically limited in the embodiments disclosed in the present application.

[0037] Among them, the positive electrode current collector 111 is not only a bearing structure for the positive electrode active material layer 112 and the inactive material layer, but also a conductive structure for the positive electrode sheet 11. The positive electrode current collector 111 may be connected to the positive electrode ear to output or input electrons to the outside. Specifically, the positive electrode current collector 111 is made of a metal material. The metal material may include at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Co, Cr, W, Mo, Al, Mg, K, Na, Ca, Sr, Ba, Si, Ge, Sb, Pb, In, Zn and a combination (alloy) thereof. Exemplarily, the positive electrode current collector 111 may be made of copper foil.

[0038] The positive electrode active material layer 112 is a layered structure formed by a slurry composed of a positive electrode active material on the surface of the positive electrode current collector 111. The layered structure has lithium ion conductivity, and even if the positive electrode active material and the solid electrolyte are in contact, the shape can be maintained without flowing. The positive electrode active material is a substance that can perform an electrode reaction by inserting / detaching (inserting / removing) lithium ions relative to the interlayer.

[0039] Optionally, the positive electrode active material may be LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O 2 、LiCoO 2 、LiNiO 2 、LiMn 2 O 4 、LiCoMnO 4 , Li 2 NiMn 3 O 8 Lithium metal oxides such as LiFePO 4 、LiMnPO 4 、LiNiPO 4 、LiCoPO 4 , Li 3 Fe 2 (PO 4 ) 3 and Li 3 V 2 (PO 4 ) 3 etc. Lithium metal phosphate. It is understood that, as the material constituting the positive electrode active material layer 112, in addition to the positive electrode active material, it may also include but is not limited to a conductive aid, a sintering aid, a binder, etc. Among them, the conductive aid may have conductivity. For example, carbon black such as acetylene black, Ketjen black, carbon fiber, carbon nanotube, carbon nanofiber and graphene. The sintering aid may have catalytic properties. For example, ceramics. The binder may have adhesive properties. For example, at least one of the polymer materials of polyvinylidene fluoride, copolymer of vinylidene fluoride-fluorinated olefin, polyvinyl pyrrolidone, polyacrylonitrile, polymethyl acrylate, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene-butadiene rubber, polyurethane, fluorinated rubber or polyvinyl alcohol. Adding the above substances to the positive electrode active material can reduce the adhesion after the slurry is coated to improve the processability of the slurry.

[0040] The inactive material layer is a layered structure formed by a slurry composed of inactive materials on the surface of the positive active material layer 112 away from the positive current collector 111. The layered structure has lithium ion conductivity, and even if the inactive material contacts the solid electrolyte, it can maintain its shape without flowing. The inactive material is a solid electrolyte that basically does not contain positive active materials and negative active materials. Here, "basically does not contain positive active materials and negative active materials" means that there is no problem such as short circuit between the inactive material layer and the positive active material layer 112 without having positive active materials and negative active materials. Exemplarily, the solid electrolyte is an oxide solid electrolyte or a sulfide solid electrolyte. It can be understood that as a material constituting the inactive material layer, in addition to the solid electrolyte, it can also include but is not limited to a conductive aid, a sintering aid, and a binder. The conductive aid, the sintering aid, and the adhesive can use the conductive aid, the sintering aid, and the adhesive mentioned about the positive active material layer 112.

[0041] It should be noted that the difference between the positive electrode active material layer 112 and the inactive material layer disclosed in the present application is not only that the materials used in the two are different. It is more that the diffusion rate of lithium ions in the inactive material layer is less than the diffusion rate of lithium ions in the positive electrode active material layer 112. Here, the diffusion rate of lithium ions in the inactive material layer refers to the ease of lithium ions passing from the side of the inactive material layer close to the positive electrode active material layer 112 to the side of the inactive material layer away from the positive electrode active material layer 112. The diffusion rate of lithium ions in the positive electrode active material layer 112 refers to the ease of lithium ions passing from the side of the positive electrode active material layer 112 close to the positive electrode current collector 111 to the side of the positive electrode active material layer 112 away from the positive electrode current collector 111. It can be considered that the contribution is mainly made by the solid electrolyte in the positive electrode active material layer 112 and the inactive material layer.

[0042] Specifically, the vertical distance between the surface of the inactive material layer facing away from the positive electrode active material layer 112 and the surface of the inactive material layer in contact with the positive electrode active material layer 112 is 1 micron to 20 microns. The advantage of this arrangement is that it can reduce the diffusion rate of lithium ions in the positive electrode active material layer 112 region corresponding to the inactive material layer, thereby reducing the current density of the region when the electrochemical device 01 is charged, and then optimize the lithium insertion uniformity of the negative electrode plate 13 corresponding to the inactive material layer, so as to facilitate the improvement of the charge and discharge rate of the electrochemical device 01. This point will be explained in more detail later in conjunction with the lithium precipitation window test of the electrochemical device 01.

[0043] Furthermore, the vertical distance between the surface of the inactive material layer facing away from the positive active material layer 112 and the surface of the positive active material layer 112 in contact with the positive current collector 111 is equal to the vertical distance between the two opposite sides of the positive active material layer 112 that do not correspond to the inactive material layer. In this way, while reducing the current density of the region when the electrochemical device 01 is charged, the occupied space of the inactive material layer can also be improved, which is beneficial to improving the energy density of the electrochemical device 01. Of course, the vertical distance between the surface of the inactive material layer facing away from the positive active material layer 112 and the surface of the positive active material layer 112 in contact with the positive current collector 111 is greater or less than the vertical distance between the two opposite sides of the positive active material layer 112 that do not correspond to the inactive material layer 1131, which is not specifically limited in this application.

[0044] Optionally, the combined impedance of the positive electrode active material layer 112 and the inactive material layer is greater than the impedance of the positive electrode active material layer 112 , so as to further improve the charge and discharge rate of the electrochemical device 01 .

[0045] The separator 12 is a microporous or porous film that isolates electrons and conducts ions, and has the ability to retain electrolyte. The separator 12 is disposed between the positive electrode sheet 11 and the negative electrode sheet 13, and does not contact the positive electrode active material layer 112 and the negative electrode sheet 13, so as to prevent the positive electrode sheet 11 and the negative electrode sheet 13 with different polarities from contacting and short-circuiting. Of course, the separator 12 may also contact at least a portion of the positive electrode active material layer 112 and the negative electrode sheet 13.

[0046] The separator 12 may include a substrate and a porous layer. The porous layer is formed on at least one surface of the substrate, and the porous layer can improve the heat resistance, oxidation resistance and electrolyte wetting performance of the substrate, and enhance the adhesion between the separator 12 and the positive electrode sheet 11 or the negative electrode sheet 13.

[0047] The substrate may be a nonwoven fabric, a film or a composite film having a porous structure, and the substrate may include at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. For example, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used.

[0048] The porous layer can be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. The polymer layer includes at least one polymer of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride, and poly (vinylidene fluoride-hexafluoropropylene). The inorganic layer includes inorganic particles and a binder, and the inorganic particles are selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylic acid ester, polyacrylic acid, polyacrylic acid salt, polyvinylidene pyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene.

[0049] For the above-mentioned negative electrode sheet 13, the negative electrode sheet 13 includes a negative electrode current collector 131 and a negative electrode active material layer 132. The negative electrode active material layer 132 is formed on the surface of the negative electrode current collector 131. Specifically, the negative electrode active material layer 132 can be formed on the surface of one side of the negative electrode current collector 131, and can also be formed on the two opposite surfaces of the negative electrode current collector 131. It is not specifically limited in the embodiments disclosed in the present application.

[0050] Among them, the negative electrode current collector 131 is not only a bearing structure of the negative electrode active material layer 132, but also a conductive structure of the negative electrode sheet 13. The negative electrode current collector 131 can be connected to the negative electrode ear to output or input electrons to the outside. Specifically, the negative electrode current collector 131 is made of a metal material. The metal material may include at least one of Ni, Ti, Cu, Ag, Au, Pt, Fe, Co, Cr, W, Mo, Al, Mg, K, Na, Ca, Sr, Ba, Si, Ge, Sb, Pb, In, Zn and a combination (alloy) thereof. Exemplarily, the negative electrode current collector 131 may be made of aluminum foil.

[0051] The negative electrode active material layer 132 is a layered structure formed on the surface of the negative electrode current collector 131 by a slurry composed of a negative electrode active material. The layered structure has lithium ion conductivity, and even if the negative electrode active material contacts the solid electrolyte, it can maintain its shape without flowing. The negative electrode active material is a material that can release lithium ions when the electrochemical device 01 is discharged and optionally absorb lithium ions when the electrochemical device 01 is charged. Optionally, the negative electrode active material may include carbon materials such as graphite and hard carbon, or Si, Si alloy and Li 4 Ti 5 O 12It is understood that, in addition to the negative electrode active material, the material constituting the negative electrode active material layer 132 may also include, but is not limited to, a conductive aid, a sintering aid, a binder, etc. The conductive aid, sintering aid, and binder may be the conductive aid, sintering aid, and binder mentioned for the positive electrode active material layer 112.

[0052] When the electrochemical device 01 is discharged, the positive electrode current collector 111 can collect the electrons generated when the positive electrode active material layer 112, the negative electrode active material layer 132 and the electrolyte of the electrochemical device 01 undergo an electrochemical reaction together and conduct them to the positive terminal through the positive electrode ear. Similarly, the negative electrode current collector 131 can collect the electrons generated when the negative electrode active material layer 132, the positive electrode active material layer 112 and the electrolyte undergo an electrochemical reaction together and conduct them to the negative terminal through the negative electrode ear to output electrical energy to the outside. The electron conduction path when the electrochemical device 01 is charged is the opposite, so as to convert the external input electrical energy into chemical energy. By forming an inactive material layer on the surface of the positive electrode active material layer 112, that is, forming an inactive material layer on the surface of the positive electrode active material layer, and the diffusion rate of lithium ions in the inactive material layer is less than the diffusion rate of lithium ions in the positive electrode active material layer 112, the release rate of lithium ions in the positive electrode active material layer 112 can be slowed down. In other words, part of the lithium compounds in the positive electrode active material layer 112 corresponding to the inactive material layer do not form lithium ions, and the total amount of lithium embedded in the negative electrode active material layer 132 corresponding to the inactive material layer is reduced in the same period of time, thereby reducing the phenomenon of excessive deposition speed in the negative electrode active material layer 132 area corresponding to the inactive material layer, thereby improving the situation of easy lithium precipitation in the electrochemical device 01.

[0053] In order to clearly describe each direction in the following, we use Figure 2-10 The coordinate system in defines the directions. Figure 2 As shown, the coordinate axis X represents the thickness direction of the positive electrode current collector 111. In some embodiments of the present application, it may be the direction in which the first straight section 1a and the second straight section 1c of the electrode assembly 1 are arranged relative to each other. The coordinate axis Y represents the width direction of the positive electrode current collector 111. In some embodiments of the present application, it may be the extension direction of the positive electrode ear or the negative electrode ear. The coordinate axis Z represents the length direction of the positive electrode current collector 111. In some embodiments of the application, it may be the direction in which the first bent section 1b and the second bent section 1d of the electrode assembly 1 are arranged relative to each other. Among them, the first direction, the second direction and the third direction are perpendicular to each other.

[0054] Based on the above-mentioned orientation definition, the specific structure of the above-mentioned electrode assembly 1 is described below with reference to the illustrated embodiment of the accompanying drawings. And the nouns such as "upper", "lower", "top", and "bottom" used below to indicate orientation or positional relationship are all relative to the second direction Y. It should be noted that the electrode assembly 1 disclosed in the present application is illustrated by a wound electrode assembly, that is, the positive electrode sheet 11, the separator 12, and the negative electrode sheet 13 are stacked and wound in sequence to form a flat winding structure. Compared with the laminated electrode assembly 1, the wound electrode assembly 1 has the same partial structure as the laminated electrode assembly 1, so the following partial description can also be applied to the laminated electrode assembly 1.

[0055] like Figure 2 As shown, the electrode assembly 1 may include a first straight section 1a, a first bent section 1b, a second straight section 1c, and a second bent section 1d. The first straight section 1a, the first bent section 1b, the second straight section 1c, and the second bent section 1d are sequentially distributed along the winding direction of the electrode assembly 1. The first straight section 1a and the second straight section 1c are arranged opposite to each other, and the first bent section 1b and the second bent section 1d are arranged opposite to each other. The two ends of the first bent section 1b are respectively connected to one end of the first straight section 1a and one end of the second straight section 1c, and the two ends of the second bent section 1d are respectively connected to the other ends of the first straight section 1a and the second straight section 1c. Among them, the first straight section 1a is the portion between the site where the electrode assembly 1 is bent for the first time and the site where it is not bent for the second time. The second straight section 1c is the portion between the site where the electrode assembly 1 is bent for the second time and the site where it is not bent for the first time. The first bent section 1b is the portion between the site where the electrode assembly 1 is bent for the first time and the site where it is not bent for the first time. The second bending section 1d is the portion between the location where the electrode assembly 1 is bent for the second time and the location where it is not bent for the second time.

[0056] For the aforementioned positive electrode sheet 11, the positive electrode sheet 11 may include a first blank area 11a, a first double-sided area 11b, a first single-sided area 11c, and a second blank area 11d. Along the winding direction of the electrode assembly 1, the first double-sided area 11b has a winding start end close to the winding center and a winding end end away from the winding center. The first blank area 11a is located at the innermost side of the electrode assembly 1, and the first blank area 11a is connected to the winding start end of the first double-sided area 11b. The first single-sided area 11c is connected to the winding end end of the first double-sided area 11b, and the second blank area 11d is located at the outermost side of the electrode assembly 1, and the second blank area 11d is connected to the first single-sided area 11c. The first blank area 11a and the second blank area 11d are the parts of the positive electrode current collector 111 that are opposite to each other along the first direction X and are not coated with the positive electrode active material layer 112. The first double-sided area 11b is the part of the positive electrode current collector 111 that is opposite to each other along the first direction X and is coated with the positive electrode active material layer 112. The first single-sided area 11c is a portion of the positive electrode current collector 111 where the positive electrode active material layer 112 is coated on one surface along the first direction X. For example, the positive electrode active material layer 112 may be coated on the surface of the positive electrode current collector 111 facing the winding center. It should be noted that although the first blank area 11a, the second double-sided area 13c, the first single-sided area 11c, and the second blank area 11d of the positive electrode sheet 11 are separated by dotted lines in the figure, there may actually be no interface, and the positive electrode sheet 11 may be continuous as a whole.

[0057] For the first double-sided area 11b and the first single-sided area 11c, please refer to Figure 3 In the example shown, both the first double-sided area 11b and the first single-sided area 11c have a first portion 114, a second portion 115 and a third portion 116. Along the second direction Y, the first portion 114 is connected to one end of the second portion 115, and the third portion 116 is connected to the other end of the second portion 115. Among them, the first portion 114 is the portion of the first double-sided area 11b and the first single-sided area 11c close to the bottom of the electrode assembly 1, and the third portion 116 is the portion of the first double-sided area 11b and the first single-sided area 11c close to the top of the electrode assembly 1. It should be noted that although the first portion 114, the second portion 115 and the third portion 116 of the first double-sided area 11b and the first single-sided area 11c are separated by dotted lines in the figure, there may actually be no interface, and the first double-sided area 11b and the first single-sided area 11c may be continuous as a whole.

[0058] For the aforementioned negative electrode sheet 13, the negative electrode sheet 13 may include a third blank area 13a, a second single-sided area 13b, and a second double-sided area 13c. Along the winding direction of the electrode assembly 1, the second single-sided area 13b has a winding start end close to the winding center and a winding end end away from the winding center. The third blank area 13a is located at the innermost side of the electrode assembly 1, and the third blank area 13a is arranged opposite to at least part of the first blank area 11a of the positive electrode sheet 11, and the third blank area 13a is connected to the winding start end of the second single-sided area 13b. The second double-sided area 13c is located at the outermost side of the electrode assembly 1, and the second double-sided area 13c is arranged opposite to at least part of the second single-sided area 13b of the positive electrode sheet 11, and the second double-sided area 13c is connected to the winding end end of the second single-sided area 13b. Among them, the third blank area 13a is the part where both surfaces of the negative electrode current collector 131 opposite to each other along the first direction X are coated with the negative active material layer 132. The second single-sided area 13b is a portion where the negative electrode active material layer 132 is coated on one of the surfaces of the negative electrode current collector 131 opposite to each other along the first direction X. For example, the negative electrode active material layer 132 may be coated on the surface of the negative electrode current collector 131 away from the winding center. The second double-sided area 13c is a portion where the negative electrode active material layer 132 is coated on the two surfaces of the negative electrode current collector 131 opposite to each other along the first direction X. It should be noted that although the third blank area 13a, the second single-sided area 13b, and the second double-sided area 13c of the negative electrode sheet 13 are separated by dotted lines in the figure, there may actually be no interface, and the negative electrode sheet 13 may be continuous as a whole.

[0059] In the present application, the first portion 114 and / or the third portion 116 of the positive electrode sheet 11 are in full contact with the electrolyte of the electrochemical device 01. Compared with the second portion 115 of the positive electrode sheet 11, the first portion 114 and the third portion 116 of the positive electrode sheet 11 have smaller concentration polarization, that is, the lithium ion extraction and migration speed of the first portion 114 and the third portion 116 are faster, so that the lithium embedding capacity of the region of the negative electrode sheet 13 corresponding to the first portion 114 and the third portion 116 is limited, which ultimately leads to lithium deposition in this region of the negative electrode sheet 13. Based on this, an inactive material layer can be coated on the first portion 114 and / or the third portion 116 of the positive electrode sheet 11 to slow down the lithium ion extraction speed of the positive electrode active material layer 112 of the first portion 114 and / or the third portion 116. Please combine Figure 4 See also Figure 3In the example shown, the inactive material layer may include a first inactive material layer 1131, and the first inactive material layer 1131 is formed on the first portion 114 and the third portion 116 of the positive electrode plate 11. It can be understood that the coating position of the first inactive material layer is not limited to this. For example, the first inactive material layer 1131 may be formed on at least one of the first portion 114 of the first single-sided area 11c, the third portion 116 of the first single-sided area 11c, the first portion 114 of the first double-sided area 11b, and the third portion 116 of the first double-sided area 11b.

[0060] Since the first part 114 or the second part 115 of the positive electrode sheet 11 to the third part 116 of the positive electrode sheet 11 are all in insufficient contact with the electrolyte of the electrochemical device 01, in other words, the closer the first part 114 or the second part 115 is to the third part 116 of the positive electrode sheet 11, the less lithium deposition there is. Figure 5 See also Figure 3 In the example shown, when the first part 114 and the third part 116 of the positive electrode sheet 11 are coated with the first inactive material layer 1131, the cross-sectional area of ​​the first inactive material layer 1131 formed in the first part 114 gradually decreases along the second direction Y. And the cross-sectional area of ​​the first inactive material layer 1131 formed in the third part 116 gradually decreases in the opposite direction of the second direction Y. In this way, the diffusion rate of lithium ions in each region of the first part 114 and the third part 116 of the positive electrode sheet 11 is roughly the same, so as to further improve the charge and discharge rate of the electrochemical device 01. It can be understood that, in the direction close to the third part 116, the cross-sectional area of ​​one of the first inactive material layer 1131 formed in the first part 114 and the first inactive material layer 1131 formed in the third part 116 gradually decreases, and the cross-sectional area of ​​the other can remain unchanged. Alternatively, the cross-sectional areas of the first inactive material layer 1131 formed in the first portion 114 and the first inactive material layer 1131 formed in the third portion 116 may remain unchanged, which is not specifically limited in the present application.

[0061] It should be noted that in the electrochemical device 01 disclosed in the present application, along the second direction Y, the ratio of the distance between the two ends of the first inactive material layer 1131 to the distance between the two ends of the positive electrode current collector 111 is 0.01%-30%, that is, the ratio of the width of the first inactive material layer 1131 to the width of the positive electrode current collector 111 is 0.01%-30%. If the ratio is less than 0.01%, the coverage area of ​​the first inactive material layer 1131 is too small, which is not conducive to slowing down the lithium ion release rate of the positive electrode active material layer 112 of the first part 114 and the second part 115. If the ratio is greater than 30%, the coverage area of ​​the first inactive material layer 1131 is too large, which affects the lithium ion release rate of the first inactive material layer 1131 of the entire positive electrode sheet 11, and is not conducive to improving the charge and discharge rate of the electrochemical device 01.

[0062] In some embodiments, when the positive electrode sheet 11 is subjected to a rolling process, the surface tension of the slurry containing the positive electrode active material causes the slurry to migrate to the first blank area 11a, the first single-sided area 11c, and the second blank area 11d of the positive electrode sheet 11, and form a thick edge after drying. Since the thick edge will form a stress concentration point inside the electrochemical device 01, lithium deposition is likely to occur there. Based on this, an inactive material layer can be coated again on the surface of the positive electrode sheet 11 coated with the positive electrode active material layer 112 to slow down the rate of lithium ion release at the thick edge. Please refer to the following reference for details. Figure 6-8 In the example shown, the inactive material layer further includes a second inactive material layer 1132. The second inactive material layer 1132 may be formed at least one of the winding start end of the first double-sided area 11b, the winding end end of the first double-sided area 11b, and an end of the first single-sided area 11c away from the first double-sided area 11b. Further, along the third direction Z, the width of the second inactive material layer 1132 is 1 micron to 30 microns.

[0063] See also Fig. 9 In the example shown, the negative electrode ear is connected to the third blank area 13a of the negative electrode plate 13. Since the third blank area 13a is connected to the second single-sided area 13b, that is, the second single-sided area 13b is close to the ear, this will cause the current density through the second single-sided area 13b to be larger, so that the polarization degree of the second single-sided area 13b is greater, and the second single-sided area 13b is prone to lithium precipitation. Therefore, an inactive material layer can be coated on the surface of the positive electrode plate 11 facing the second single-sided area 13b to reduce the polarization degree of the second single-sided area 13b. Specifically, the inactive material layer also includes a third inactive material layer 1133. The third inactive material layer 1133 is formed in the first double-sided area 11b of the positive electrode plate 11 corresponding to the second single-sided area 13b of the negative electrode plate 13.

[0064] See also Fig.10In the example shown, the positive electrode plate 11 is provided with a first groove (not shown), and the bottom of the first groove exposes the positive current collector 111. One end of the positive electrode ear is accommodated in the first groove and connected to the positive current collector 111. The electrochemical device also includes a first adhesive 2. The first adhesive 2 is fixed to the positive electrode plate 11 and covers the first groove. The inactive material layer includes a fourth inactive material layer 1134, and the fourth inactive material layer 1134 is arranged around the periphery of the first adhesive 2. During the charge and discharge cycle of the electrochemical device, the current density at the positive electrode ear is large, so that the electrolyte concentration polarization of this part is large, and the first adhesive 2 cannot block the diffusion path of the active lithium covered in the first adhesive 2, and the portion corresponding to the positive electrode ear is also a groove, that is, there is not enough space to embed the active lithium of the positive active material layer 112 and precipitate lithium. Therefore, the fourth inactive material layer 1134 can be coated on the periphery of the first adhesive member 2. In the same time, the total amount of active lithium in the negative electrode active material layer corresponding to the positive electrode tab is reduced by delaying the diffusion rate of active lithium in the positive electrode active material layer 112 corresponding to the fourth inactive material layer 1134, so as to improve the lithium precipitation phenomenon at the positive electrode tab. Exemplarily, the first adhesive member 2 includes but is not limited to insulating tape.

[0065] Furthermore, the positive electrode plate 11 is also provided with a second groove (not shown) corresponding to the negative electrode ear, and the bottom of the second groove exposes the negative electrode collector 131. The electrochemical device also includes a second adhesive 3. The second adhesive 3 is fixed to the positive electrode plate 11 and covers the second groove. The inactive material layer also includes a fifth inactive material layer 1135, and the fifth inactive material layer 1135 is arranged around the periphery of the second adhesive 3. Similar to the aforementioned cause of lithium precipitation, the fifth inactive material layer 1135 can be coated on the periphery of the second adhesive 3 to improve the lithium precipitation phenomenon at the second groove. Exemplarily, the second adhesive 3 includes but is not limited to insulating tape.

[0066] In some embodiments, since the bending part of the pole piece of the wound electrode assembly 1 constitutes a stress concentration point, the bending part of the pole piece is more prone to lithium deposition. Therefore, an inactive material layer can be coated at the bending part of the pole piece to slow down the lithium ion release rate at the bending part of the pole piece. Exemplarily, the inactive material layer also includes a sixth inactive material layer (not shown). The sixth inactive material layer is arranged in the first bending section 1b and / or the second bending section 1d of the positive electrode pole piece 11, that is, the sixth inactive material layer is arranged in at least one of the first bending section 1b of the first double-sided area 11b, the second bending section 1d of the first double-sided area 11b, the first bending section 1b of the first single-sided area 11c, and the second bending section 1d of the first single-sided area 11c.

[0067] Some specific embodiments and comparative examples are listed below to better illustrate the present application, wherein a lithium ion electrochemical device is used as an example.

[0068] Example 1

[0069] Preparation of positive electrode sheet: Lithium cobalt oxide, conductive agent and binder polyvinylidene fluoride (PVDF) are dissolved in N-methylpyrrolidone (NMP) solution in a mass ratio of 97.2:1.5:1.3 to prepare positive electrode active material layer slurry. Pass through a 200-mesh sieve to prepare positive electrode active material layer slurry with a solid content of 70%-75%. Aluminum foil is used as the positive electrode current collector, and a coating machine is used to apply the positive electrode active material layer slurry to the surface of the positive electrode current collector with a coating thickness of 90 microns. The width of the electrode sheet is 70 mm and the length of the electrode sheet is 1400 mm. The binder polyvinylidene fluoride (PVDF) and the conductive agent are dissolved in N-methylpyrrolidone (NMP) solution in a ratio of 6:4 to prepare an inactive material layer slurry with a solid content of 5%. The inactive material layer is coated on the first and third parts of the electrode, with a coating width of 5 mm, a coating thickness of 1 μm, and a coating length equal to the positive electrode active material layer. After drying at 120°C, cold pressing, and slitting, the positive electrode is obtained.

[0070] Preparation of negative electrode sheet: Graphite, conductive agent and binder sodium carboxymethyl cellulose are dissolved in N-methylpyrrolidone (NMP) solution at a mass ratio of 97:1.5:1.5 to prepare negative electrode active material layer slurry. Pass through a 200-mesh sieve to prepare negative electrode active material layer slurry with a solid content of 40%-45%. Copper foil is used as the second current collector, and the negative electrode active material layer slurry is coated on the second current collector. After drying at 80°C, cold pressing and slitting, the negative electrode sheet is obtained.

[0071] Preparation of isolation film: The substrate of the isolation film is 8 μm thick polyethylene (PE), and a 2 μm alumina ceramic layer is coated on each surface of the opposite side of the substrate. Finally, 2.5 mg / cm 2 The binder polyvinylidene fluoride (PVDF) is dried.

[0072] Preparation of electrolyte: In an environment with a water content of less than 10 ppm, lithium hexafluorophosphate and a non-aqueous organic solvent (propylene carbonate (PC): ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC) = 1:1:0.5:1, weight ratio) are prepared into a basic electrolyte, and LiPF is added. 6 Mix well to obtain electrolyte, in which LiPF 6 The concentration is 1 mol / L.

[0073] Preparation of electrochemical device: stack the positive electrode sheet, separator, and negative electrode sheet in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, and wind them to obtain an electrode assembly. Place the electrode assembly in an outer packaging aluminum plastic film, remove moisture at 80°C, inject the above electrolyte and package, and obtain a lithium-ion battery through a process of formation, degassing, trimming, etc.

[0074] Other embodiments and comparative examples are based on the steps of embodiment 1 with parameter changes, and the specific changed parameters are as follows.

[0075] In Comparative Example 1, the positive electrode sheet is not coated with an inactive material layer. In the comparative example and Examples 2-6, the 12°C lithium precipitation window of each positive electrode sheet is different, and the 12°C lithium precipitation window of each positive electrode sheet can be changed by adjusting the thickness of the inactive material layer. In Examples 7-10, the 12°C lithium precipitation window of each positive electrode sheet is different, and the 12°C lithium precipitation window of each positive electrode sheet can be changed by adjusting the coating position of the inactive material layer.

[0076] The thickness of the inactive material layer of the positive electrode sheet is analyzed below in combination with experimental data.

[0077] Lithium deposition window test: First discharge the electrochemical device to a full discharge state, then set a specific temperature (for example, 12°C), and perform conventional charging (constant current + constant voltage) at different rates, such as 1C, 1.1C, 1.2C, etc., according to the design of the electrochemical device, that is, charge to the battery cut-off voltage at a specific rate, then charge at a constant voltage to 0.025C cut-off charging, and fully discharge at 0.5C after charging. The above charge and discharge process is repeated for 10 cycles. Finally, the electrochemical device is disassembled after full charge to observe whether the negative electrode plate is lithium deposited. The maximum current without lithium deposition (no white spots on the surface of the negative electrode plate) is defined as the maximum non-lithium deposition rate of the battery, which is the lithium deposition window.

[0078] Energy density test:

[0079] Battery energy density: The electrochemical device to be tested is placed in a 25°C environment for 3 hours, and then charged at a constant current rate of 0.5C until the voltage reaches the rated voltage. Then, it is charged at a constant voltage until the charge and discharge rate reaches 0.025C, and the charging is stopped. The electrochemical device to be tested is placed for 5 minutes. After that, the battery is discharged to 3.0V at a rate of 0.2C, and the electrochemical device to be tested is placed for 5 minutes. Finally, the discharge capacity is taken as the actual battery capacity C of the battery. The length, width, and thickness of the test electrochemical device are L, W, and T, respectively. The discharge platform voltage of the battery is U, and the energy density of the battery is VED = C×U / (L×W×T), where the unit of the battery capacity C is mA·h, the unit of the platform voltage U is V, and the unit of the length, width, and thickness (L, W, T) is cm.

[0080] Table 1 shows various parameters and evaluation results of corresponding Examples 1 to 11 and Comparative Example 1.

[0081]

[0082]

[0083] By comparing Example 1 with Comparative Example 1, it can be seen that after forming the inactive material layer with this thickness, the charging capacity of the electrochemical device is improved, while the energy density of the electrochemical device remains basically unchanged.

[0084] By comparing Examples 1-6, it can be seen that as the thickness of the inactive material layer increases, the charging capacity of the electrochemical device first increases and then decreases, and the energy density of the electrochemical device continues to decrease.

[0085] By comparing Example 6, Comparative Example 2 and Comparative Example 1, it can be seen that as the thickness of the inactive material layer continues to increase, the charging capacity of the electrochemical device is not as good as the charging capacity when the inactive material layer is not formed.

[0086] By comparing Example 1 with Examples 7 / 8 / 9 / 10, it can be seen that the thickness of the inactive material layer remains unchanged, and adjusting the coating position of the inactive material layer is beneficial to improving the charging capacity of the electrochemical device, while the energy density of the electrochemical device remains basically unchanged.

[0087] The above description is only an implementation method of the present application, and does not limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. An electrochemical device, comprising an electrode assembly, wherein the electrode assembly comprises a positive electrode sheet, a negative electrode sheet, and a separator separating the positive electrode sheet from the negative electrode sheet, wherein: The positive electrode sheet comprises a positive electrode current collector, a positive electrode active material layer and an inactive material layer, wherein the positive electrode active material layer is formed on the surface of the positive electrode current collector, the inactive material layer is formed on the surface of the positive electrode active material layer away from the positive electrode current collector, the inactive material layer is a layered structure formed by a slurry composed of an inactive material on the surface of the positive electrode active material layer away from the positive electrode current collector, the layered structure has lithium ion conductivity, the inactive material is a solid electrolyte that does not contain a positive electrode active material and a negative electrode active material, and along a first direction, the thickness of the inactive material layer is 1 micron-20 microns, wherein the first direction is the thickness direction of the positive electrode current collector, and the diffusion rate of lithium ions in the inactive material layer is less than the diffusion rate in the positive electrode active material layer; The positive electrode sheet has a first part, a second part and a third part, along a second direction, the first part is connected to one end of the second part, and the third part is connected to the other end of the second part, wherein the second direction is perpendicular to the first direction, and the second direction is the width direction of the positive electrode current collector; The inactive material layer includes a first inactive material layer, and the first inactive material layer is arranged on the first part and / or the third part; The cross-sectional area of ​​the first inactive material layer formed in the first portion gradually decreases along the direction from the first portion to the second portion, and the cross-sectional area of ​​the first inactive material layer formed in the third portion gradually decreases along the direction from the third portion to the second portion.

2. The electrochemical device according to claim 1, characterized in that Along the second direction, a ratio of a width of the first inactive material layer on the first portion or the third portion to a width of the positive electrode current collector is 0.01%-30%.

3. The electrochemical device according to claim 1, characterized in that The positive electrode sheet, the separator and the negative electrode sheet are stacked and wound in sequence to form the electrode assembly; The positive electrode sheet comprises a first blank area, a first double-sided area, a first single-sided area, and a second blank area. Along the winding direction, the first double-sided area has a winding start end close to the winding center and a winding end end far away from the winding center. The first blank area is connected to the winding start end, the first single-sided area is connected to the winding end end, and the second blank area is connected to an end of the first single-sided area far away from the winding end end. The inactive material layer includes a second inactive material layer, and the second inactive material layer is disposed at at least one of the winding starting end, the winding ending end, and an end of the first single-sided region away from the winding ending end.

4. The electrochemical device according to claim 3, characterized in that Along the third direction, the length of the second inactive material layer is 1 micrometer to 30 micrometers, wherein the third direction, the second direction and the first direction are perpendicular to each other.

5. The electrochemical device according to claim 3, characterized in that The negative electrode plate has a second single-sided area; The inactive material layer includes a third inactive material layer, and the third inactive material layer is arranged in the first double-sided area of ​​the positive electrode sheet corresponding to the second single-sided area.

6. The electrochemical device according to claim 1, characterized in that The positive electrode plate is provided with a first groove, and the bottom of the first groove exposes the positive electrode current collector; The electrochemical device comprises a positive electrode tab and a first adhesive, a portion of the positive electrode tab is received in a first groove and connected to the positive electrode current collector, and the first adhesive is fixed to the positive electrode plate and covers the first groove; The inactive material layer includes a fourth inactive material layer, and the fourth inactive material layer is disposed around the periphery of the first adhesive component.

7. The electrochemical device according to claim 1, characterized in that The electrochemical device further comprises a negative electrode tab and a second adhesive, wherein a portion of the negative electrode tab is connected to the negative electrode current collector; The positive electrode sheet is provided with a second groove corresponding to the negative electrode ear, the bottom of the second groove exposes the positive electrode collector, and the second adhesive is fixed to the positive electrode collector and covers the second groove; The inactive material layer includes a fifth inactive material layer, and the fifth inactive material layer is disposed around the periphery of the second adhesive component.

8. The electrochemical device according to claim 1, characterized in that The electrode assembly comprises a first straight section, a first bent section, a second straight section and a second bent section which are sequentially connected along a winding direction, wherein the first straight section is arranged opposite to the second straight section, and the first bent section is arranged opposite to the second bent section; The inactive material layer further includes a sixth inactive material layer, and the sixth inactive material layer is arranged in the first bending section and / or the second bending section.

9. An electronic device, characterized in that: Comprising the electrochemical device according to any one of claims 1 to 8.

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