CN114649563A

CN114649563A - Electrochemical device and electricity utilization device

Info

Publication number: CN114649563A
Application number: CN202210345000.XA
Authority: CN
Inventors: 魏红梅; 郑碧珠; 胡乔舒
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2022-03-31
Filing date: 2022-03-31
Publication date: 2022-06-21

Abstract

The application discloses an electrochemical device and a power utilization device. The electrochemical device includes an electrode assembly, a heating member, and tabs. The heating member is disposed in the electrode assembly, and the heating member includes a heating wire and a first insulating layer. The heating wire and the electrode assembly are connected with the tabs. The first insulating layer includes a first sub-insulating layer and a second sub-insulating layer. The first sub-insulating layer is attached to the surface of the heating wire. The second sub-insulating layer is connected to the first sub-insulating layer in a surrounding manner. In the first direction, the total thickness T1 of the first sub-insulating layer, the thickness T2 of the heating wire, and the thickness T3 of the second sub-insulating layer satisfy: 0 μm T1+ T2-T3 < 20 μm, wherein the first direction is a thickness direction of the electrode assembly. Based on this, can improve the whole roughness of heating member, and then can reduce the anchor clamps and become the interface contact that the pole piece leads to because of the pressurized insufficiency constantly worsens, forms the condition of educing lithium easily.

Description

Electrochemical device and electricity utilization device

Technical Field

The present application relates to the field of battery technologies, and in particular, to a battery and a power consumption device.

Background

The charging speed of the electrochemical device is related to the temperature of the electrochemical device under the influence of the characteristics of the active material of the electrochemical device, and the temperature needs to be controlled within a reasonable range to ensure that the charging speed of the electrochemical device is maintained in a normal state. The charging temperature range of the common electrochemical device is 0-45 ℃, and the discharging temperature range is-20-60 ℃. When the electrochemical device is in a low temperature environment (e.g., below-20 ℃) for a long time, it is hardly operable to the outside, which greatly limits the range of the application environment of the electric device to which the electrochemical device is applied. Therefore, the low-temperature normal operation of the electrochemical device can be realized by the built-in heating sheet. However, the arrangement of the heating sheet inside the electrochemical device may cause the thickness of the electrochemical device to be non-uniform. Particularly, the pole piece region corresponding to the heating plate is easy to generate the lithium precipitation phenomenon caused by poor interface contact in the high-rate charging and discharging process.

Disclosure of Invention

The present application provides an electrochemical device and an electric device, which can improve the situation that lithium is easy to be separated out in the charging and discharging process of the electrochemical device.

A first aspect of the present application provides an electrochemical device. The electrochemical device includes an electrode assembly, a heating member, and tabs. The heating member is disposed in the electrode assembly, and the heating member includes a heating wire and a first insulating layer. The heating wire and the electrode assembly are connected with the tabs. The first insulating layer includes a first sub-insulating layer and a second sub-insulating layer. The first sub-insulating layer is attached to the surface of the heating wire. The second sub-insulating layer is connected to the first sub-insulating layer in a surrounding manner. In the first direction, a thickness T1 of the first sub-insulating layer, a thickness T2 of the heating wire, and a thickness T3 of the second sub-insulating layer satisfy: 0 μm ≦ T1+ T2-T3 < 20 μm, where the total thickness T1 of the first sub-insulating layer 211 is T1a + T1 b. Wherein the first direction is a thickness direction of the electrode assembly. Based on this, can improve the whole roughness of heating member, and then can reduce the anchor clamps and become the interface contact that the pole piece leads to because of the pressurized insufficiency constantly worsens, forms the condition of educing lithium easily.

In some optional embodiments, a ratio of the total thickness T1 of the first sub insulating layer to the thickness T3 of the second sub insulating layer is 10% to 80%.

In some optional embodiments, the electrode assembly includes a positive electrode tab, a negative electrode tab, and a separator separating the positive electrode tab and the negative electrode tab, which are sequentially stacked and wound. 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 the winding direction of the electrode assembly, the first straight section and the second straight section are oppositely arranged, the first bent section and the second bent section are oppositely arranged, and the heating element is arranged between the first straight section and the second straight section. Because the heating member has certain rigidity, put the heating member here, can improve electrode assembly's overall structure intensity on the one hand, on the other hand the area of contact of heating member and electrode assembly is bigger, and then promotes the heating efficiency of heating member.

In some optional embodiments, in the third direction, a distance S1 between one end of the heating wire close to the first bend section and the first bend section satisfies: s1 is more than or equal to 2mm and less than or equal to 5 mm. And the distance S2 between one end of the heating wire close to the second bending section and the second bending section satisfies the following conditions: s2 is more than or equal to 2mm and less than or equal to 5mm, wherein the third direction is perpendicular to the first direction. This has the advantage that the deterioration of the interface of the first or second bending section due to bending of the edge of the heating wire can be reduced.

In some optional embodiments, projections of the positive electrode tab, the negative electrode tab, and the separator film along the first direction have an overlapping region. Along the first direction, the ratio of the projection area of the heating element in the overlapping region to the area of the overlapping region is 60-98%. By such arrangement, the heating efficiency of the heating element can be maintained within a preferable range.

In some optional embodiments, the electrochemical device comprises a tab. The tabs are respectively connected with the electrode assembly and the heating wire. The heating element further includes a second insulating layer. The second insulating layer is arranged on the surface, deviating from the heating wire, of the first insulating layer. The second insulating layer is connected to the electrode assembly. In the first direction, the thickness T4 of the electrochemical device at the part where the tab is located and the thickness T5 of the electrochemical device at the part where the second insulation layer is located satisfy: t5 is more than or equal to 95 percent of T4. Like this, promoted electrochemical device's whole roughness for electrochemical device is all atress even in each region of formation in-process, in anchor clamps formation technology, reduces because of the condition that each region worsens because of the interface that the atress inequality caused.

In some optional embodiments, the second insulating layer is integrally connected with the first insulating layer. Therefore, the connection between the first insulating layer and the second insulating layer is more stable, and the risk of safety failure caused by direct contact of the heating wire and the pole piece is further reduced.

In some optional embodiments, the first and second insulating layers comprise a fibrous material having a high compression ratio. The fiber material comprises at least one of polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyphenyl ether, polypropylene carbonate, polyethylene oxide, polyimide, polyamide and derivatives thereof.

In some optional embodiments, the first insulating layer comprises a fibrous material. The fiber material comprises at least one of vinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyphenyl ether, polypropylene carbonate, polyethylene oxide, polyimide, polyamide and derivatives thereof.

In some optional embodiments, the first insulating layer comprises at least one of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyetheretherketone, polyimide, polyamide, polyethylene glycol, polyamideimide, polycarbonate, cyclic polyolefin, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, poly (vinylidene fluoride-hexafluoropropylene), poly (vinylidene fluoride-co-chlorotrifluoroethylene), silicone, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyethernitrile, polyurethane, polyphenylene oxide, polyester, polysulfone, and derivatives thereof.

In some optional embodiments, the first insulating layer comprises at least one of an epoxy glue, a polyurethane glue, an amino resin glue, a phenolic resin glue, an acrylic resin glue, a furan resin glue, a resorcinol-formaldehyde resin glue, a xylene-formaldehyde resin glue, an unsaturated polyester glue, a composite resin glue, a polyimide glue, a urea-formaldehyde resin glue, a hot-melt glue strip, a glue strip, an EVA hot-melt glue, a rubber hot-melt glue, a polypropylene, a polyester, a polyamide, a polyurethane hot-melt glue, a styrene hot-melt glue, a new hot-melt glue, a polyethylene and an ethylene copolymer hot-melt glue.

In a second aspect, the present application provides an electric device comprising an electrochemical device as described above.

Further features of the present application and advantages thereof will become apparent from the following detailed description of exemplary embodiments thereof, which is to be read in connection with the accompanying drawings.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. Throughout the drawings, like elements or portions are generally identified by like reference numerals. In the drawings, elements or portions are not necessarily drawn to scale.

Fig. 1 is a schematic structural diagram of an electric device according to an embodiment of the present disclosure;

fig. 2 is a schematic view illustrating the construction of an electrode assembly and a heating element in the electrochemical device shown in fig. 1;

FIG. 3 is a cross-sectional view A-A of FIG. 2;

FIG. 4 is a schematic structural view of the heating sheet of FIG. 2;

FIG. 5 is a cross-sectional view taken along line B-B of FIG. 4;

FIG. 6 is another schematic view of the heating plate of FIG. 2;

fig. 7 is another structural view illustrating an electrode assembly and a heating element in the electrochemical device shown in fig. 1;

fig. 8 is a cross-sectional view of C-C in fig. 7.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments. The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the application, its application, or uses. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application without any creative effort belong to the protection scope of the present application.

Techniques, methods, and apparatus known to those of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the specification where appropriate.

In the description of the present application, it should be noted that the orientation or positional relationship indicated by the orientation words such as "front, back, up, down, left, right", "lateral, vertical, horizontal" and "top, bottom", etc., are usually based on the orientation or positional relationship shown in the drawings, and are only for convenience of description and simplicity of description, and in the case of not making a reverse description, these orientation words do not indicate and imply that the device or element being referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore, should not be construed as limiting the scope of the present application; the terms "inner and outer" refer to the inner and outer relative to the profile of the respective component itself.

Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity, and should be interpreted flexibly to include not only the numerical values explicitly recited as the limits of the range, but also to include all the individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly recited.

In the description of the present application, it should be noted that the terms "first", "second", etc. are used to define the components, and are only used for convenience of distinguishing the corresponding components, and if not otherwise stated, the terms have no special meaning, and thus, should not be construed as limiting the scope of the present application.

The electrochemical device disclosed in the present application is suitable for an electric device to which the electrochemical device is applied. Therefore, the situation of lithium precipitation in the conventional electrochemical device can be improved, so that the safety performance of the electrochemical device is improved. It is to be understood that the electric device according to the embodiment of the present application is not particularly limited. The power consumption device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an electric car, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, and a lithium ion capacitor.

Fig. 1 shows a schematic structural diagram of an electrical consumer. The electrochemical device 01 is arranged in the power utilization device, and the electrochemical device 01 provides electric energy or stores the electric energy for the power utilization device, so that the power utilization requirement when the power utilization device is used is met. It is to be understood that the electrochemical device 01 according to the embodiment of the present application may be variously classified. For example, the electrochemical device 01 may include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. Alternatively, the electrochemical device 01 is a lithium secondary battery including 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, the following embodiments are each illustrated with the electrochemical device 01 being a lithium ion secondary battery.

Referring to fig. 1 in conjunction with fig. 2 and 3, fig. 2 is a schematic view illustrating an electrode assembly and a heating member of the electrochemical device of fig. 1. Fig. 3 is a cross-sectional view a-a of fig. 2. The electrochemical device 01 includes a case (not shown), an electrode assembly 1, a heating element 2, and tabs (not shown). The shell is an installation supporting structure of the structures. The casing is provided with a cavity, and the cavity is used for accommodating the electrode assembly 1 so as to protect the electrode assembly 1. The electrode assembly 1 is a component of the electrochemical device 01 that performs a charge and discharge function. The electrode assembly 1 is accommodated in the cavity, and the electrode assembly 1 comprises a positive electrode plate, a negative electrode plate and an isolating membrane for separating the positive electrode plate from the negative electrode plate. The heating member is in contact with at least one of the positive electrode tab and the negative electrode tab. The electrode tabs are respectively connected with the electrode assembly 1 and the heating element, penetrate through the shell and are exposed out of the shell to form connecting terminals, and the connecting terminals are used for being electrically communicated with the outside. The tab connected to the positive electrode tab 11 of the electrode assembly 1 is referred to as a positive electrode tab. Accordingly, the portion of the positive tab that is led out of the case and is used for electrical connection with the outside is called a positive terminal. The tab connected to the negative electrode tab of the electrode assembly 1 is referred to as a negative tab. Accordingly, the portion of the negative electrode tab that is drawn out of the case and is used for electrical connection with the outside is referred to as a negative electrode terminal. When the electrochemical device is electrically conducted with the outside, current flows through the heating element through the tabs, and the heating element starts to heat and provides heat for an electrode assembly and electrolyte of the electrochemical device, so that the migration rate of lithium ions is maintained in a better range. When the temperature of the electrochemical device rises to exceed the threshold value, the connection between the outside and the electrochemical device is disconnected, and the heating element stops heating.

In order to be able to describe the orientations clearly in the following, the directions are defined by using the coordinate system in fig. 2. As shown in fig. 2, the coordinate axis X is a thickness direction of the electrode assembly, and in some embodiments of the present application, may be a direction in which the first straight section 1a and the second straight section 1c of the electrode assembly 1 are oppositely disposed. The coordinate axis Y represents a length direction of the electrode assembly, and may be a protruding direction of the positive electrode tab or the negative electrode tab in some embodiments of the present application. The coordinate axis Z represents a width direction of the electrode assembly, and in some embodiments, may also be a direction in which the first bent section 1b and the second bent section 1d of the electrode assembly 1 are oppositely disposed. The first direction, the second direction and the third direction are mutually vertical pairwise.

Based on the above orientation definitions, the following explains the illustrated embodiments with reference to the drawings, and explains the specific structure of the electrode assembly 1. And terms used below such as "upper", "lower", "top", "bottom", etc., which indicate orientation or positional relationship, are all relative to the second direction Y. For simplicity of description, the electrode assembly 1 disclosed in the present application is exemplified by a wound electrode assembly, i.e., a positive electrode tab, a separator, and a negative electrode tab are sequentially stacked and wound to form a flat wound structure.

Please continue with the example shown in fig. 3. The electrode assembly may include a first straight section 1a, a first bent section 1b, a second straight section 1c, and a second bent section 1 d. The first flat section 1a, the first bent section 1b, the second flat section 1c, and the second bent section 1d are sequentially distributed in the winding direction of the electrode assembly 1. First flat straight section 1a and second flat straight section 1c set up relatively, and first kinked section 1b and second kinked section 1d set up relatively, and the both ends of first kinked section 1b are connected with the one end of first flat straight section 1a and the one end of second flat straight section 1c respectively, and the both ends of second kinked section 1d are connected with the other end of first flat straight section 1a and second flat straight section 1c respectively. The first straight section 1a is a portion between a first bent point and a second non-bent point of the electrode assembly 1. The second straight section 1c is a portion between the point where the electrode assembly 1 is bent for the second time and the point where the electrode assembly is not bent for the first time. The first bent section 1b is a portion between a point where the electrode assembly 1 is bent for the first time and a point where the electrode assembly is not bent for the first time. The second bending section 1d is a portion between a point where the electrode assembly 1 is bent a second time and a point where the electrode assembly is not bent a second time.

Referring to fig. 3 in combination with fig. 4 and fig. 5, fig. 4 is a schematic structural view of the heating element 2 in fig. 2, and fig. 5 is a cross-sectional view of B-B in fig. 4. The heating member 2 is located between the first and second straight sections 1a and 1c on the innermost side of the electrode assembly. The heating member 2 includes a heating wire 21 and a first insulating layer 22. The first insulating layer 22 covers the outer surface of the heating wire 21 and forms an integral structure with the heating wire 21. Specifically, the heating wire 21 has a serpentine structure formed by alternately bending and folding forward and backward as viewed in the first direction X. One end of the heating wire 21 is electrically connected with the positive tab, and the other end of the heating wire 21 is electrically connected with the negative tab. The first insulating layer 22 includes a first sub-insulating layer 221 and a second sub-insulating layer 222. The first sub-insulating layer 221 is a portion of the first insulating layer 22 attached to the surface of the heating wire 21. The second sub-insulating layer 222 is the remaining part of the first insulating layer 22 surrounding the first sub-insulating layer 221, i.e., the second sub-insulating layer 222 is the part of the first insulating layer 22 between two adjacent parts of the heating wire 21 and the part of the first insulating layer 22 at the edge of the heating wire 21. The first sub-insulating layer 221 and the second sub-insulating layer 222 do not overlap with each other along the first direction X. And the total thickness T1 of the first sub-insulating layer 221, the thickness T2 of the heating wire 21, and the thickness T3 of the second sub-insulating layer 222 satisfy: 0 μm ≦ T1+ T2-T3 < 20 μm, where the total thickness T1 of the first sub-insulating layer 211 is T1a + T1 b. Based on this, can improve the whole roughness of heating member 2, and then can reduce the anchor clamps and become the interface contact that the pole piece leads to because of the insufficient pressure constantly worsens, forms the condition of educing lithium easily. This will be described in more detail later in connection with the lithium extraction window test of the electrochemical device. Further, the ratio of the total thickness T1 of the first sub-insulating layer 221 to the thickness T3 of the second sub-insulating layer 222 is 10% to 80%. The advantage of this arrangement is that the joint between the first sub-insulating layer 221 and the second sub-insulating layer 222 can be smoothly transitioned, so as to reduce the interface deterioration caused by uneven stress on the pole piece region corresponding to the joint.

It is to be understood that the shape of the heating wire 21 is not particularly limited in the embodiments disclosed in the present application. For example, the shape of the heating wire 21 may be a zigzag shape, a water wave shape, or a cosine wave shape.

The material of the heater wire 21 is not particularly limited. For example, the heating wire 21 may be at least one of a metal material, a carbon-based conductive material, a metal oxide, or a conductive polymer material. Specifically, the metallic material may include, but is not limited to, at least one of nickel, titanium, copper, gold, silver, platinum, iron, cobalt, chromium, tungsten, molybdenum, aluminum, magnesium, potassium, sodium, calcium, strontium, barium, silicon, germanium, antimony, lead, indium, zinc, and combinations (alloys) thereof. The carbon-based conductive material includes at least one of carbon black, graphite, graphene, carbon fiber, single-walled carbon nanotubes, or multi-walled carbon nanotubes. The conductive polymer material comprises at least one of polyacetylene, polypyrrole, polythiophene, polyparaphenylene, polyphenylacetylene, polyaniline or doped polymer materials thereof, and the dopant in the doped polymer material comprises at least one of chlorine, iodine, bromine, iodine chloride, iodine bromide, iodine fluoride, phosphorus pentafluoride, hydrofluoric acid, hydrochloric acid, nitric acid, sulfuric acid, perchloric acid, molybdenum pentafluoride, tungsten pentafluoride, titanium tetrachloride, zirconium tetrachloride, ferric chloride or tin tetraiodide.

In addition, the material of the first insulating layer 22 is not particularly limited. For example, the first insulating layer 22 is at least one of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyetheretherketone, polyimide, polyamide, polyethylene glycol, polyamideimide, polycarbonate, cyclic polyolefin, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, poly (vinylidene fluoride-hexafluoropropylene), poly (vinylidene fluoride-co-chlorotrifluoroethylene), silicone, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene oxide, polyester, polysulfone, and derivatives thereof. Alternatively, the thickness T1 of the first sub-insulating layer 221 is 5 μm to 30 μm and the thickness T3 of the second sub-insulating layer 222 is 15 μm to 60 μm along the first direction X. This has the advantage that the first insulating layer 22 still has a good structural strength while saving space occupied by the heating element 2 and increasing the energy density of the electrochemical device. Illustratively, the thickness T1 of the first sub-insulating layer 221 is 10 μm. The thickness T3 of the second sub-insulating layer 222 was 30 μm.

Of course, the first insulating layer 22 may also be at least one of an epoxy resin adhesive, a polyurethane adhesive, an amino resin adhesive, a phenolic resin adhesive, an acrylic resin adhesive, a furan resin adhesive, a resorcinol-formaldehyde resin adhesive, a xylene-formaldehyde resin adhesive, an unsaturated polyester adhesive, a composite resin adhesive, a polyimide adhesive, a urea-formaldehyde resin adhesive, a hot-melt adhesive tape, a colloidal particle, an adhesive powder, an EVA hot-melt adhesive, a rubber hot-melt adhesive, polyacrylic acid, polyester, polyamide, a polyurethane hot-melt adhesive, a styrene hot-melt adhesive, a novel hot-melt adhesive, polyethylene, and an ethylene copolymer hot-melt adhesive. Specifically, the first sub-insulating layer and the second sub-insulating layer may be made of glue with different compression ratios. For example, the first sub-insulating layer may use glue having a compression ratio larger than that of the second sub-insulating layer, and the second sub-insulating layer may use glue having a compression ratio smaller than that of the first sub-insulating layer. The compression ratio of the glue adopted by the first sub-insulating layer and the compression ratio of the glue adopted by the second sub-insulating layer both range from 10% to 80%. Alternatively, the thickness T1 of the first sub-insulating layer 221 is 3 μm to 25 μm and the thickness T3 of the second sub-insulating layer 222 is 20 μm to 50 μm along the first direction X. Illustratively, the thickness T1 of the first sub-insulating layer 221 is 5 μm. The thickness T3 of the second sub-insulating layer 222 was 25 μm.

Of course, the first insulating layer 22 may also be a fibrous material (Nanofiber). The fiber material can be at least one of vinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyphenyl ether, polypropylene carbonate, polyethylene oxide, polyimide, polyamide and derivatives thereof. Optionally, the individual fiber diameter of the fiber material is less than or equal to 300 nm.

Referring to the example shown in fig. 6, fig. 6 is another schematic structural diagram of the heating sheet in fig. 2. Along the third direction Z, a distance S1 between one end of the heating wire 21 close to the first bending section 1b and the first bending section 1b satisfies: s1 is more than or equal to 2mm and less than or equal to 5 mm. And the distance S2 between the end of the heating wire 21 close to the second bending section 1d and the second bending section 1d satisfies: s2 is more than or equal to 2mm and less than or equal to 5 mm. S1 and S2 both fall within this range, and thus, the interface deterioration of the first bent section 1b and the second bent section 1d of the electrode assembly 1 due to the bending tendency with a small pitch, and the interface deterioration of the pole piece region adjacent to the edge of the heater wire 21 due to uneven pressure, can be reduced.

Further, the projections of the positive electrode tab, the negative electrode tab and the separator in the first direction have an overlapping region (not shown). In the first direction, the ratio of the projected area of the heating member 2 in the overlapping region to the projected area of the overlapping region is 60% to 98%. The advantage of this arrangement is that the situation that when the heating member 2 and the electrode assembly 1 are simultaneously electrically conducted with the outside, the heating member 1 is in contact with the negative electrode plate or the positive electrode plate and is short-circuited is reduced. In addition, the heating member 2 can be sufficiently contacted with the surface of the electrode assembly 1 within this numerical range, thereby improving the heating efficiency of the heating member 1. Illustratively, the ratio of the projected area of the heating member 1 in the overlapping region to the projected area of the overlapping region in the first direction X is 90%. It should be noted that, in the second direction Y, the width of the negative electrode tab of the electrode assembly 1 is generally larger than the width of the positive electrode tab. In other words, one end of the negative electrode plate usually extends out of the positive electrode plate, because the negative electrode plate needs to leave a residual cavity for lithium ions of the positive electrode plate to be inserted, the occurrence of the situation that lithium is easily separated from the edge of the negative electrode plate is reduced. In addition, the width of the isolation film is usually larger than that of the negative pole piece, so that the situation that the positive pole piece and the negative pole piece are in direct contact and short circuit can be reduced.

Referring to the examples shown in fig. 7 and 8 together, fig. 7 is another structural view illustrating an electrode assembly and a heating element in the electrochemical device shown in fig. 1. Fig. 8 is a cross-sectional view of C-C in fig. 7. The heating element 2 further comprises a second insulating layer 23. A second insulating layer 23 is provided on the surface of the first insulating layer 22 facing away from the heating wire 21, the second insulating layer 23 being connected to the electrode assembly 1. Along the first direction X, the thickness T4 of the part of the electrochemical device 01 where the tabs are located and the thickness T5 of the part of the electrochemical device where the second insulating layer is located satisfy: t5 is more than or equal to 95 percent of T4.

Specifically, the electrode assembly 1 has a plurality of recessed regions (not shown) with different thicknesses. For example, along the second direction Y, the thickness of the part of the electrochemical device 01 where the tab is located is greater than the thickness of the part of the electrochemical device 01 adjacent to the tab, that is, the part of the electrochemical device 01 adjacent to the tab has a recessed area, and the second insulating layer 23 may be disposed in the area of the heating element 2 corresponding to the recessed area, so that the overall thickness of the part of the electrochemical device is substantially the same as the thickness of the part of the electrochemical device 01 where the tab is located, that is, along the second direction Y, the thickness difference between the part of the electrochemical device 01 where the tab is located and the part of the electrochemical device 01 adjacent to the tab is reduced, thereby reducing the interface deterioration caused by uneven stress at the transition portion between the two transition portions.

Similarly, along the third direction, the thickness of the electrochemical device 01 where the winding start end and the winding end of the double-sided area of the pole piece are located is smaller than that of the part of the electrochemical device 01 where the pole tab is located, that is, the electrochemical device 01 where the winding start end and the winding end of the double-sided area of the pole piece are located has a recessed area, and the second insulating layer 23 can be arranged in the area of the heating element 2 corresponding to the recessed area, so that the overall thickness of the part of the electrochemical device 01 is substantially the same as that of the part of the electrochemical device 01 where the pole tab is located, that is, along the third direction, the thickness of the part of the electrochemical device 01 where the pole tab is located and that of the electrochemical device 01 where the winding start end and the winding end of the double-sided area of the pole piece are located are shortened, thereby achieving the similar effects described above.

In summary, the second insulating layers corresponding to the recessed regions may be disposed in the recessed regions at different positions of the electrochemical device 01, so that the overall thickness of the electrochemical device 01 at different positions is substantially the same as that of the electrochemical device at the tab along the first direction X, thereby improving the interface degradation caused by the uneven stress at different positions of the electrochemical device 01 in the clamp formation process. 700g of the thickness of the part of the electrochemical device where the electrode lug is located can be applied to the surface of the electrochemical device, and the thickness can be measured by PPG. The thickness of the portion of the electrochemical device where the recessed region is located can be measured at the MMC. This will be described in more detail later in connection with the lithium extraction window test of electrochemical device 01. It is to be understood that, in the embodiments disclosed in the present application, the material of the second insulating layer 23 is not particularly limited. For example, the first insulating layer 22 and the second insulating layer 23 can be made of high compression ratio fiber materials, and in this case, the first insulating layer 22 and the second insulating layer 23 are different parts of a unitary structure. The high compression ratio is a fiber material with a thickness compression ratio of more than 1.5 along the first direction X, and the spun fiber material has a thickness ranging from 15 μm to 100 μm after spinning. And the thickness after compression is 5-60 μm. Of course, the second insulating layer 23 may be made of a material other than the spun fiber material used for the first insulating layer 22, and will not be described in detail.

The present application will be described in further detail with reference to specific examples.

Example 1

(1) Production of heating elements

The metal sheet was laser-cut into its surface into loops as shown in fig. 5 to obtain a heating wire. And then the first insulating layer made of polypropylene (PP) is hot-pressed to be compounded with the first insulating layer to form the heating element.

(2) Preparation of positive pole piece

The positive electrode active material lithium cobaltate (LiCoO)₂) Mixing conductive carbon black (Super P) and polyvinylidene fluoride (PVDF) according to the weight ratio of 97.5:1.0:1.5, adding N-methylpyrrolidone (NMP) as a solvent, preparing into slurry with the solid content of 0.75, and uniformly stirring. The slurry is evenly coated on a positive current collector, and the weight of positive active substances on the pole piece is 180g/m². Drying at 90 deg.C to finish the single-side coating of the positive pole piece, and finishing the coating of the other side by the same method. After coating, the positive active material layer of the pole piece is cold-pressed to 4.1g/cm³And then carrying out auxiliary processes such as tab welding, gummed paper pasting and the like to compact the density, thereby completing the whole preparation process of the double-sided coated positive pole piece.

(3) Preparation of negative pole piece

Mixing Graphite (Graphite) as a negative active material, conductive carbon black (Super P) and Styrene Butadiene Rubber (SBR) according to a weight ratio of 96:1.5:2.5, and adding deionized water (H)₂O) is used as a solvent, and is prepared into slurry with solid content of 0.7 and is stirred uniformly. The slurry is evenly coated on a negative current collector, and the weight of negative active substances on a pole piece is 95g/m². Drying at 110 ℃ to finish the single-side coating of the negative pole piece of the pole piece, and finishing the coating of the other side by the same method. After coating, the negative active material layer of the pole piece was cold pressed to a compacted density of 1.7g/cm 3. And then carrying out auxiliary processes such as tab welding, gummed paper pasting and the like, thus completing the whole preparation process of the double-coated negative pole piece.

(4) Preparation of the electrolyte

In a dry argon atmosphere, organic solvents of Ethylene Carbonate (EC), Ethyl Methyl Carbonate (EMC) and diethyl carbonate (DEC) were first mixed in a mass ratio of EC: EMC: DEC: 30:50:20, and then lithium salt lithium hexafluorophosphate (LiPF) was added to the organic solvent₆) Dissolved and mixed uniformly to obtain an electrolyte with the lithium salt concentration of 1.15M.

(5) Preparation of electrochemical devices

Polyethylene (PE) with the thickness of 15 mu m is selected as an isolating film, the prepared positive pole piece, the isolating film and the heating piece are fixed on a structure formed by the negative pole piece, and are sequentially overlapped and wound into a battery cell, and the heating piece is positioned at the winding center of the electrode assembly. And (3) after top sealing and side sealing, injecting liquid into the battery cell, forming the battery cell after liquid injection (charging to 3.3V at a constant current of 0.02C, and then charging to 3.6V at a constant current of 0.1C), and finally obtaining the electrochemical device.

(6) The test temperatures were 10 ℃ respectively, and the electrochemical devices fabricated in each example and each comparative example were charged to 4.4V at a constant current of 1.5C, charged at a constant voltage of 0.05C, and discharged to 3.0V at 0.5C after standing for 5 min. And then carrying out 1.5C charging/0.5C discharging cycle test, carrying out 300 cycles of cycle, then carrying out disassembly observation on the lithium separation phenomenon after full charging at 1.5C. And (3) judging the lithium analysis degree according to the ratio of the area of fully charged electrode plate for lithium analysis (gray) to the area of the whole electrode plate: < 3% is slightly delithiated; 3-5% of the total amount is lithium precipitation; severe lithium evolution was > 5%.

Example 2

The difference from example 1 is that: the thickness of the second sub-insulating layer increases and the thickness of the heating wire decreases.

Example 3

The difference from example 1 is that: the thickness of the heating wire is reduced.

Example 4

The difference from example 1 is that: the first insulating layer is made of PP glue.

Example 5

The difference from example 1 is that: the first insulating layer is made of PPA glue.

Comparative example 1

The difference from example 1 is that: the first insulating layer is made of a PE film, and the thickness of the first sub-insulating layer is increased.

The parameter settings and test results of examples 1-5 and comparative example 1 are shown in Table 1.

TABLE 1

Example 6:

the difference from example 1 is that: the first insulating layer is made of a high compression ratio spun fiber material.

Example 7:

the difference from example 6 is that: the thickness of the first insulating layer is reduced and the compression ratio of the first sub-insulating layer and the compression ratio of the second sub-insulating layer are both lowered.

The parameter settings and test results of examples 6 and 7 and comparative example 1 are shown in Table 2.

TABLE 2

Example 7:

the difference from example 1 is that: the first insulating layer is made of a high-compression-ratio spinning fiber material, and the overall thickness difference of the battery is reduced by adding the second insulating layer.

Example 8:

the difference from example 7 is that: the thickness and compression ratio of the first sub-insulating layer are both reduced, the thickness of the second sub-insulating layer is increased, but the compression ratio is reduced, and the difference in the overall thickness of the battery is further reduced.

The parameter settings and test results of the above examples 7 and 8 and comparative examples are shown in Table 3.

TABLE 3

As can be seen from the data of examples 1 to 9 and comparative example 1, compared with the case of encapsulating the heating wire by using the first insulating layer having the same thickness, the area between two adjacent portions of the heating wire which is not uniformly pressed and the edge portion of the heating wire in the embodiment of the present application are encapsulated by using the insulating layer having a larger thickness, so that the overall flatness of the heating member is higher, and further, the pressing of the heating member can be more uniform, thereby reducing the situation that the interface contact of the pole piece is continuously deteriorated due to insufficient pressing when the jig is formed, and the lithium deposition is easily caused.

Furthermore, the second insulating layer is arranged on the surface of the first insulating layer and is arranged in each concave area of the electrode assembly, so that the overall flatness of the electrode assembly is higher, the electrode assembly is pressed more uniformly, the problem that when the clamp is formed, the interface contact of each area of the electrochemical device is continuously worsened due to insufficient pressing, and lithium precipitation is easily caused is further reduced.

The above description is only an example of the present application and is not intended to limit the scope of the present application, and all modifications of equivalent structures and equivalent processes, which are made by the contents of the specification and the drawings, or which are directly or indirectly applied to other related technical fields, are intended to be included within the scope of the present application.

Claims

1. An electrochemical device, comprising an electrode assembly and a heating element, wherein the heating element is disposed in the electrode assembly, the heating element comprises a heating wire and a first insulating layer, wherein the first insulating layer comprises a first sub-insulating layer and a second sub-insulating layer, the first sub-insulating layer is attached to the surface of the heating wire, the second sub-insulating layer is connected around the first sub-insulating layer, along a first direction, the total thickness T1 of the first sub-insulating layer, the thickness T2 of the heating wire and the thickness T3 of the second sub-insulating layer satisfy: 0 μm ≦ T1+ T2-T3 < 20 μm, wherein the first direction is a thickness direction of the electrode assembly.

2. The electrochemical device as claimed in claim 1, wherein a ratio of the total thickness T1 of the first sub insulating layer to the thickness T3 of the second sub insulating layer is 10-80%.

3. The electrochemical device according to claim 2, wherein the electrode assembly comprises 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, the separator, and the negative electrode sheet being stacked and wound in this order;

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 the winding direction of the electrode assembly, the first straight section and the second straight section are oppositely arranged, the first bent section and the second bent section are oppositely arranged, and the heating element is connected between the first straight section and the second straight section.

4. The electrochemical device according to claim 3, wherein, in the third direction, a spacing S1 between one end of the heating wire facing the first bend and the first bend satisfies: s1 is more than or equal to 2mm and less than or equal to 5 mm; and

the distance S2 between one end of the heating wire facing the second bending section and the second bending section satisfies that: s2 is more than or equal to 2mm and less than or equal to 5mm, wherein the third direction is perpendicular to the first direction.

5. The electrochemical device according to claim 3, wherein projections of the positive electrode tab, the negative electrode tab, and the separator film along the first direction have an overlapping region;

along the first direction, the ratio of the projection area of the heating element in the overlapping region to the area of the overlapping region is 60-98%.

6. The electrochemical device according to any one of claims 1 to 5, comprising tabs respectively connected to the electrode assembly and the heating wire;

the heating element further comprises a second insulating layer, the second insulating layer is arranged on the surface, away from the heating wire, of the first insulating layer, and the second insulating layer is connected with the electrode assembly;

in the first direction, the thickness T4 of the electrochemical device at the part where the tab is located and the thickness T5 of the electrochemical device at the part where the second insulation layer is located satisfy: t5 is more than or equal to 95 percent of T4.

7. The electrochemical device according to claim 6, wherein the second insulating layer is integrally connected to the first insulating layer.

8. The electrochemical device of claim 7, wherein said first and second insulating layers comprise a fibrous material having a high compression ratio, said fibrous material comprising:

at least one of polyvinylidene fluoride-hexafluoropropylene, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polyphenylene oxide, polypropylene carbonate, polyethylene oxide, polyimide, polyamide and derivatives thereof.

9. The electrochemical device of any one of claims 1-5, wherein said first insulating layer comprises a fibrous material comprising:

10. The electrochemical device according to any one of claims 1 to 5, wherein the first insulating layer comprises:

at least one of polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyetheretherketone, polyimide, polyamide, polyethylene glycol, polyamideimide, polycarbonate, cyclic polyolefin, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene naphthalene, polyvinylidene fluoride, polyethylene naphthalate, polypropylene carbonate, poly (vinylidene fluoride-hexafluoropropylene), poly (vinylidene fluoride-co-chlorotrifluoroethylene), silicone, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyethernitrile, polyurethane, polyphenylene oxide, polyester, polysulfone, and derivatives thereof; or

At least one of epoxy resin glue, polyurethane glue, amino resin glue, phenolic resin glue, acrylic resin glue, furan resin glue, resorcinol-formaldehyde resin glue, xylene-formaldehyde resin glue, unsaturated polyester glue, composite resin glue, polyimide glue, urea-formaldehyde resin glue, hot-melt adhesive tape, colloidal particle, adhesive powder, EVA hot melt adhesive, rubber hot melt adhesive, polypropylene, polyester, polyamide, polyurethane hot melt adhesive, styrene hot melt adhesive, novel hot melt adhesive, polyethylene and ethylene copolymer hot melt adhesive.

11. An electric device comprising the electrochemical device according to any one of claims 1 to 10.