Electrochemical device and electronic device comprising same

Abstract

The invention discloses an electrochemical device and an electronic device comprising the same, the electrochemical device comprises an aluminum-plastic film layer and a naked cell surrounded by a cavity formed by the aluminum-plastic film layer, the aluminum-plastic film layer sequentially comprises an outer resistance layer, a permeation resistance layer, a first aramid fiber layer and a second aramid fiber layer from outside to inside towards the direction of the naked cell, replacing the second aramid fiber layer with a heat sealing layer at the packaging position; and a third aramid fiber layer is arranged on the surface of the outermost layer of the naked battery cell. The electrochemical device disclosed by the invention has good safety performance and cycle performance and long service life.

Description

Technical Field

[0001] The present invention relates to the field of electrochemical technology, and in particular to an electrochemical device and an electronic device comprising the same. Background Art

[0002] The electrochemical device can be installed in any electronic device to provide energy for the electronic device. Charging devices for household or industrial applications can be connected to the electrochemical device to provide electrical energy for the electronic device.

[0003] With the continuous development of new energy technologies, people have higher and higher requirements for the energy density of electrochemical devices, in the hope that the electrochemical devices used can provide longer endurance after being fully charged. With the continuous iteration and update of technologies that can provide long-lasting endurance, the safety and stability of the electrochemical system of electrochemical devices has gradually decreased. In addition, in the process of continuously improving the energy density of electrochemical devices, the design of electrochemical devices has become more and more extreme, and the utilization rate of space has gradually increased. The safety and stability of electrochemistry are affected by distance. In addition, the cycle performance and isoelectric performance of electrochemical devices are also challenged in the process of improving space utilization. A single solution or improvement of the safety of electrochemical devices or other electrical properties such as their cycle performance cannot meet the increasing requirements for electrochemical devices with high capacity density and high safety.

[0004] Traditional electrochemical devices generally have the following structure: Taking soft-pack batteries as an example, the outermost layer is an aluminum-plastic film formed by a heat-sealing layer including a nylon layer, an aluminum foil layer, and PP as packaging, and the internal bare battery cell is a structure in which a diaphragm, a positive electrode sheet, a diaphragm, and a negative electrode sheet are wound or stacked together. The diaphragm mainly includes: pure PP or PE base film, and a coated diaphragm with a PE base film as the substrate and ceramic or PVDF coated on both sides. The outermost traditional aluminum-plastic film cannot effectively suppress or reduce the risks caused by thermal runaway of the electrochemical device; the traditional diaphragm has no way to prevent or suppress safety risks such as thermal runaway caused by external collisions and punctures. In addition, the structure of the traditional electrochemical device does not have too much space to store electrolytes, and the performance of the electrochemical device such as circulation cannot be guaranteed in the later stages of use. Summary of the invention

[0005] In view of this, the main purpose of the present invention is to provide an electrochemical device and an electronic device including the same, which have good safety performance and cycle performance and a long service life.

[0006] To achieve the above-mentioned invention object, the first aspect of the present invention provides an electrochemical device, comprising an aluminum-plastic film layer and a bare battery cell surrounded by a cavity formed by the aluminum-plastic film layer, wherein the bare battery cell comprises a positive electrode sheet, a separator and a negative electrode sheet stacked in layers, and a separator is arranged between adjacent positive electrode sheets and negative electrode sheets;

[0007] Among them, toward the direction of the bare battery core, the aluminum-plastic film layer includes an outer resistance layer, a barrier layer, a first aramid layer and a second aramid layer from the outside to the inside, and the second aramid layer is replaced with a heat sealing layer at the packaging position; and the outermost surface of the bare battery core has a third aramid layer.

[0008] Furthermore, the outermost layer of the bare battery cell is a separator or a positive electrode sheet without active material.

[0009] Furthermore, the stacking arrangement includes a winding or lamination arrangement, the positive electrode sheet, the separator and the negative electrode sheet arranged in a winding manner form a bare battery cell with a corner, and the surface of the separator of the bare battery cell located at the corner position has a fourth aramid layer.

[0010] Furthermore, the first aramid layer or the second aramid layer is a fiber layer of aramid formula slurry or an aramid modified material layer, and the aramid is selected from one or more of para-aramid and meta-aramid.

[0011] Furthermore, the thickness of the first aramid layer or the second aramid layer is 1-100 μm.

[0012] Furthermore, the third aramid layer or the fourth aramid layer is an aramid stock solution coating layer, and the aramid is selected from one or more of para-aramid and meta-aramid.

[0013] Furthermore, the thickness of the third aramid layer is 1-10 μm.

[0014] Furthermore, the thickness of the fourth aramid layer is 1-5 μm.

[0015] Further, the surface of the diaphragm includes an upper surface and / or a lower surface.

[0016] Furthermore, the third aramid layer or the fourth aramid layer is located on the surface of the base film of the diaphragm, and the thickness of the base film is preferably 4 to 500 μm.

[0017] Furthermore, the width of the heat-sealing layer is 2 mm to 30 mm, and the heat-sealing layer is selected from heat-sealing materials such as polypropylene and polyethylene.

[0018] Furthermore, the material of the outer resistance layer is selected from nylon or PET (polyethylene terephthalate), and the material of the barrier layer is selected from aluminum foil, EVOH (ethylene-vinyl alcohol copolymer) or PVDC (polyvinylidene chloride).

[0019] Furthermore, the cavity formed by the aluminum-plastic film layer of the electrochemical device includes a bare battery cell and an electrolyte, and the electrolyte includes liquid electrolytes such as lithium ions and sodium ions.

[0020] A second aspect of the present invention provides an electronic device comprising the electrochemical device.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] The aluminum-plastic film layer of the present invention includes an outer resistance layer, a barrier layer, a first aramid layer and a second aramid layer from the outside to the inside, and the second aramid layer is replaced with a heat-sealing layer at the packaging position; the arrangement of the first aramid layer and the second aramid layer can improve the safety performance of the electrochemical device, such as the puncture strength and heating performance, and the second aramid layer is replaced at the packaging position and only the heat-sealing layer is arranged for packaging fusion, thereby reducing the overall thickness of the aluminum-plastic film. This structure can further improve the energy density of the electrochemical device. At the same time, the outermost surface of the bare battery core of the present invention has a third aramid layer, and the aramid layer here can not only ensure the heat resistance of the electrochemical device in a high temperature environment, reduce the risk of thermal shrinkage of the diaphragm, but also increase the storage capacity of the electrolyte. Furthermore, for the bare battery cell formed by winding, the present invention arranges a fourth aramid layer on the surface of the diaphragm at the corner position of the bare battery cell. The aramid layer here can ensure that the problem of too little electrolyte at the corner position caused by excessive stress is improved, and can also improve the interface at the corner position. The good electrolyte wettability of aramid can be used to form an electrolyte channel at the corner position, accelerate the electrolyte infiltration, and increase the electrolyte transmission channel.

[0023] Other features and advantages of the present invention will be described in detail through the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention but do not constitute a limitation of the present invention. In the accompanying drawings:

[0025] Figure 1 This is a schematic structural diagram of an electrochemical device according to one embodiment of the present application.

[0026] Figure 2 This is a schematic structural diagram of an electrochemical device according to another embodiment of the present application.

[0027] Figure 3 for Figure 1-2 Schematic diagram of the cross section of the aluminum-plastic film layer at the non-packaging position.

[0028] Figure 4 for Figure 1-2 Schematic diagram of the cross section of the aluminum-plastic film layer at the packaging position.

[0029] Figure 5 for Figure 1-2 Schematic diagram of the cross section of the outermost layer (non-corner position) of the bare battery cell.

[0030] Figure 6 for Figure 2Schematic diagram of the cross section of the bare battery cell at the middle corner.

[0031] The figures are marked as follows: diaphragm 1, negative electrode sheet 2, positive electrode sheet 3, external resistance layer 4, barrier layer 5, first aramid layer 6, second aramid layer 7, heat sealing layer 8, third aramid layer 9, base film 10, glue layer 11, bare cell corner 12, fourth aramid layer 13, ceramic layer 14. DETAILED DESCRIPTION

[0032] The specific implementation of the present invention is described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation described here is only used to illustrate and explain the present invention, and is not used to limit the present invention.

[0033] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance. Among them, the terms "first position" and "second position" are two different positions.

[0034] Unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", and "fixed" should be understood in a broad sense, for example, it can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0035] refer to Figure 1 The present invention provides an electrochemical device, comprising an aluminum-plastic film layer and a bare battery cell surrounded by a cavity formed by the aluminum-plastic film layer, wherein the bare battery cell comprises a positive electrode sheet, a separator and a negative electrode sheet stacked in layers, and a separator is arranged between adjacent positive electrode sheets and negative electrode sheets;

[0036] Among them, toward the direction of the bare battery core, the aluminum-plastic film layer includes an outer resistance layer, a barrier layer, a first aramid layer and a second aramid layer from the outside to the inside, and the second aramid layer is replaced with a heat sealing layer at the packaging position; and the outermost surface of the bare battery core has a third aramid layer.

[0037] In the present invention, the outermost layer of the bare cell is a separator or a positive electrode sheet without an active material. For example, in one embodiment, the outermost layer of the bare cell is a separator (with a third aramid layer on the surface), and the negative electrode sheet, separator, positive electrode sheet, etc. are arranged in sequence inward; in another embodiment, the outermost layer is the positive electrode, but the outermost positive electrode is not coated with an active material, that is, the positive electrode current collector, and is an empty foil, and the third aramid layer is arranged on the surface of the empty foil, and then the separator, negative electrode sheet, separator, positive electrode sheet, etc. are arranged in sequence inward.

[0038] In some embodiments, the bare cell of the electrochemical device is wound or stacked, wherein the wound positive electrode sheet, separator and negative electrode sheet form a bare cell with a corner, and preferably, the surface of the separator at the corner of the bare cell has a fourth aramid layer.

[0039] Preferably, the first aramid layer or the second aramid layer is a fiber layer of aramid formula slurry or a layer of aramid modified material. The properties of the aramid material itself determine its puncture resistance, and it has excellent properties such as high tensile strength, high heat resistance, good wettability, strong bonding force, and high ionic conductivity, which can effectively improve the cycle performance and safety performance of the battery.

[0040] In the present invention, the aramid formula slurry is divided into an aqueous slurry and an oily slurry, the difference being the solvent, the aqueous solvent being water, and the oily solvent being acetone, NMP, etc. In some embodiments, the aramid formula slurry is prepared by adding a solvent, an adhesive, a dispersant, and an additive, etc., to an aramid stock solution. For example, the mass ratio of the dispersant, the additive, the aramid, the solvent, and the adhesive is 0.1-4: 0.1-4: 100: 100-2000: 0.1-20. In some examples, the aramid is selected from one or more of para-aramid and meta-aramid.

[0041] In the present invention, the fiber layer is an aromatic polyamide fiber, which is a linear polymer composed of aromatic groups and amide groups. The aramid modified material layer mainly refers to a composite mixture that uses high-energy physics, coating, fluorination and chemical methods to improve the fiber surface composition and structure or improve the wettability between aramid and matrix resin.

[0042] In the present invention, the materials of the first aramid layer and the second aramid layer can be the same or different. The first aramid layer and the second aramid layer can improve the safety performance of the electrochemical device, such as acupuncture and heating performance, and the second aramid layer is in contact with the electrolyte, and the fiber layer material of the second aramid layer has a pore-forming effect, which can store more electrolyte.

[0043] Preferably, the third aramid layer or the fourth aramid layer is an aramid stock solution coating layer, and the aramid stock solution refers to an aramid monomer solution. In some embodiments, the aramid is selected from one or more of para-aramid and meta-aramid.

[0044] In some embodiments, the third aramid layer and the fourth aramid layer are made of the same material.

[0045] In some embodiments, the material of the outer resistance layer is selected from nylon or PET (polyethylene terephthalate). The outer resistance layer has good impact resistance, puncture resistance, heat resistance, friction resistance and insulation, and is used to protect the internal aluminum foil and other barrier layers from being scratched.

[0046] In some embodiments, the barrier layer is made of aluminum foil, EVOH or PVDC. The barrier layer is used to prevent the intrusion of moisture, oxygen and the like.

[0047] In some embodiments, the thickness of the first aramid layer or the second aramid layer is 1-100 μm.

[0048] In some embodiments, the width of the heat-sealing layer is 2 mm to 30 mm, depending on the size of the area to be sealed, and plays a bonding role when heated during packaging. The heat-sealing layer is selected from heat-sealing materials such as polypropylene and polyethylene. The packaging position replaces the second aramid layer and only the heat-sealing layer is used for packaging fusion. This structure can further improve the energy density of the electrochemical device.

[0049] It is understandable that the outer resistance layer, the barrier layer, the first aramid layer and the second aramid layer (or the heat-sealing layer) can be compounded with each other through an adhesive additive. For details, please refer to conventional bonding methods in the art.

[0050] In the present invention, the surface of the diaphragm includes an upper surface and a lower surface. Preferably, the third aramid layer or the fourth aramid layer can be simultaneously arranged (for example, coated) on both sides of the diaphragm (double-sided coating), i.e., the upper surface and the lower surface, or it can be arranged on only one side (single-sided coating).

[0051] In some embodiments, when the third aramid layer is disposed on both side surfaces of the diaphragm, compared with being disposed on only one side surface, the thickness of the third aramid layer can be reduced or the same.

[0052] In some embodiments, when the fourth aramid layer is disposed on both side surfaces of the diaphragm, compared with being disposed on only one side surface, the thickness of the fourth aramid layer can be reduced or the same.

[0053] In the present invention, the diaphragm includes a base film and a coating disposed on the surface thereof. In some embodiments, the base film includes one of polyethylene, polypropylene, aramid, polyimide, etc. The coating of the diaphragm includes an aqueous coating and an oily coating, such as but not limited to a ceramic coating, polyvinylidene fluoride, aramid, etc. In some embodiments, the coating of the diaphragm located at the outermost layer of the bare cell is the third aramid layer, the coating of the diaphragm at the corner position of the bare cell is the fourth aramid layer, and the coating of the diaphragm at other positions is a non-aramid coating, such as a ceramic coating, which can reduce costs.

[0054] In the present invention, the specific position of setting the third aramid layer or the fourth aramid layer on the diaphragm can be calculated according to the bare cell structure and its position. For example, for a wound bare cell, the third aramid layer is coated on the surface of one end of the diaphragm (as the ending part of the winding, that is, located at the outermost layer of the bare cell), and the fourth aramid layer is coated on the surface of the middle part of the diaphragm (corresponding to the corner position of the bare cell after winding). It can be understood that when there are multiple corners in the bare cell, the fourth aramid layer can be dispersedly set at multiple positions in the middle of the diaphragm.

[0055] Preferably, the length of the third aramid layer is 1-2 times the width of the bare cell; the length of one of the fourth aramid layers is the corner perimeter, and the preferred length is 1-2 times (corner perimeter × number of layers). The longer the length of the third aramid layer or the fourth aramid layer, the better the improvement effect on the safety performance and the cycle life of the electrochemical device, but at the same time it will reduce the energy density. The purpose of selecting a suitable length is to find a balance between energy density and performance according to needs.

[0056] In some embodiments, the base film thickness of the separator is 4-500 μm.

[0057] In some embodiments, the third aramid layer has a thickness of 1-10 μm.

[0058] In some embodiments, the fourth aramid layer has a thickness of 1-5 μm.

[0059] In the present invention, the thicker the first aramid layer, the second aramid layer, the third aramid layer or the fourth aramid layer, the better the safety effect and the effect of extending the life of the electrochemical device, but the lower the energy density of the electrochemical device. The inventors have balanced the requirements of performance improvement and energy density according to actual application scenarios and obtained the above-mentioned suitable thickness of each aramid layer.

[0060] In the electrochemical device of the present invention, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material disposed on the positive electrode current collector.

[0061] The positive electrode current collector may be aluminum foil, or nickel foil, steel mesh, etc. used in electrochemical devices, including but not limited to the aforementioned current collector types. The positive electrode active material is coated on both sides or one side of the positive electrode current collector. In some embodiments, the positive electrode current collector is aluminum foil.

[0062] The positive electrode active material is selected from one or more of lithium cobalt oxide, lithium manganese oxide, nickel cobalt manganese oxide, nickel cobalt aluminum oxide, etc., any one of sodium ion layered oxides, polyanion compounds and Prussian blue compounds, and positive electrode active materials of other liquid electrolyte chemical devices.

[0063] As an example, the positive electrode active material in the lithium-ion battery includes one or more of lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, etc.; the positive electrode active material in the sodium-ion battery includes any one of layered oxides, polyanion compounds and Prussian blue compounds.

[0064] In the present invention, the positive electrode active material further comprises a conductive agent and a binder. As an example, the conductive agent is selected from one or more of conductive carbon black, Ketjen black, KS-6, carbon nanotubes, graphene, etc. The binder may be polyvinylidene fluoride.

[0065] In the electrochemical device of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material disposed on the negative electrode current collector.

[0066] As an example, the negative electrode active material is at least one of graphite, graphene, mesophase carbon microspheres, metallic lithium, metallic sodium, hard carbon, soft carbon, silicon-carbon doping, etc.;

[0067] As an example, the negative electrode current collector includes copper foil and aluminum foil.

[0068] In the present invention, the negative electrode active material also includes a conductive agent and a binder. As an example, the conductive agent is selected from one or more of conductive carbon black, Ketjen black, KS-6, carbon nanotubes, graphene, etc. The binder can use one or more of styrene-butadiene rubber, acrylic acid, polyurethane, etc.

[0069] In the electrochemical device of the present invention, the electrolyte is a liquid electrolyte, the solvent is one or more of carbonate solvents, carboxylate organic solvents, ether organic solvents, N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO) and nitrile organic compounds, and the salt is electrolyte salts such as lithium hexafluorophosphate and sodium hexafluorophosphate.

[0070] Since the present invention still adopts a liquid electrolyte system, lithium ions, sodium ions, etc. can be transmitted through the diaphragm, and the electrolyte channel opened up by the fourth aramid layer at the corner position greatly improves the interface problem of slow infiltration of high energy density electrochemical devices, easy squeezing of electrolyte to other positions, and easy occurrence of electrolyte bridge breakage at the corner position in the late cycle of the electrochemical device.

[0071] In some embodiments, the positive electrode sheet and / or negative electrode sheet of the electrochemical device may be a multi-layer structure formed by winding or stacking, or a single-layer structure in which a single-layer positive electrode sheet, a separator, and a single-layer negative electrode sheet are stacked.

[0072] A second aspect of the present invention provides an electronic device comprising the above electrochemical device, such as a sodium ion battery or a lithium ion battery.

[0073] In some embodiments, taking a lithium-ion battery as an example, a separator, a negative electrode sheet, a separator, and a positive electrode sheet are wound or stacked in sequence to form a bare cell, which is then packaged in an aluminum-plastic film, injected with an electrolyte, formed, and packaged to form a lithium-ion battery. Then, the prepared lithium-ion battery is subjected to a performance test.

[0074] The present invention is further described below in conjunction with embodiments:

[0075] Example 1

[0076] like Figure 1 , 3 -5, an electrochemical device, comprising an outer aluminum-plastic film layer and a bare cell surrounded by the aluminum-plastic film layer, the bare cell comprising a diaphragm 1, a negative electrode sheet 2, a diaphragm 1 and a positive electrode sheet 3 stacked up and down, and a diaphragm 1 is arranged between adjacent negative electrode sheets 2 and positive electrode sheets 3;

[0077] Among them, toward the direction of the bare battery core, the aluminum-plastic film layer includes an outer resistance layer 4 (nylon layer), a barrier layer 5 (aluminum foil layer), a first aramid layer 6 and a second aramid layer 7 from the outside to the inside, and the second aramid layer 7 is replaced with a heat sealing layer 8 (polypropylene layer) at the packaging position. The first aramid layer 6 and the second aramid layer 7 are both made of meta-aramid material, each with a thickness of 10μm. The diaphragm base film is made of PE material, and a third aramid layer 9 is coated on one side of the base film 10 of the outermost diaphragm of the bare battery core. The length is about twice the width of the bare battery core, and the meta-aramid material is used, with a thickness of 3μm. The base film of the diaphragm is coated with a 3μm alumina ceramic layer on one side (on the same side as the third aramid layer), and the other side is coated with a polyvinylidene fluoride adhesive layer 11.

[0078] Figure 5 The cross-sectional schematic diagram of the outermost layer of the bare battery cell is shown. The outermost layer of the bare battery cell is sequentially composed of a diaphragm coated with a third aramid layer, a negative electrode sheet, a diaphragm coated with a ceramic layer, a positive electrode sheet, etc.

[0079] Example 2

[0080] like Figure 2-6 As shown, an electrochemical device comprises an outer aluminum-plastic film layer and a bare battery cell surrounded by the aluminum-plastic film layer, wherein the bare battery cell comprises a wound separator 1, a negative electrode sheet 2, a separator 1 and a positive electrode sheet 3, wherein the separator 1 is arranged between adjacent negative electrode sheets 2 and positive electrode sheets 3;

[0081] Wherein, toward the direction of the bare battery core, the aluminum-plastic film layer includes, from outside to inside, an outer resistance layer 4 (nylon layer), a barrier layer 5 (aluminum foil layer), a first aramid layer 6, and a second aramid layer 7. At the packaging position, the second aramid layer 7 is replaced with a heat-sealing layer 8 (polypropylene layer). Both the first aramid layer 6 and the second aramid layer 7 are made of meta-aramid material, and each has a thickness of 10 μm. The diaphragm base film is made of PE material. A third aramid layer 9 is coated on one side of the base film 10 of the outermost diaphragm of the bare cell. The length is about twice the width of the bare cell. The meta-aramid material is used and the thickness is 3μm. A fourth aramid layer 13 is coated on one side of the base film 10 of the diaphragm at the corner position of the bare cell (for example, the position shown in 12). The total length is the corner circumference × the number of bare cell layers. The meta-aramid material is used and the thickness is 3μm. A 3μm alumina ceramic layer is coated on one side of the base film of the diaphragm at other positions (on the same side as the third aramid layer or the fourth aramid layer), and a polyvinylidene fluoride adhesive layer 11 is coated on the other side.

[0082] Figure 6 The cross-sectional schematic diagram of the bare battery cell at the corner position is shown, and the outermost layers of the bare battery cell are the diaphragm coated with the fourth aramid layer, the negative electrode sheet, the diaphragm coated with the fourth aramid layer, the positive electrode sheet, etc.

[0083] Example 3

[0084] Similar to Example 2, the difference is that: a third aramid layer is coated on both sides of the base film of the outermost separator of the bare cell, with a thickness of 2 μm on each side. Figure 5 The polyvinylidene fluoride adhesive layer 11 is replaced by a third aramid layer; a fourth aramid layer with a thickness of 2 μm is coated on the surface of one side of the base film of the diaphragm at the corner of the bare cell.

[0085] Example 4

[0086] Similar to Example 2, the difference is that: a third aramid layer is coated on both sides of the base film of the outermost separator of the bare cell, with a thickness of 2 μm on each side, and a thickness of 2 μm on each side, that is, Figure 5 The adhesive layer 11 of polyvinylidene fluoride is replaced by the third aramid layer; the fourth aramid layer is coated on both sides of the base film of the diaphragm at the corner of the bare cell, with a thickness of 2 μm each, that is, Figure 6 The polyvinylidene fluoride adhesive layer 11 is replaced by a fourth aramid layer.

[0087] Example 5

[0088] Similar to Example 2, except that the thickness of the second aramid layer is 20 μm.

[0089] Example 6

[0090] Similar to Example 2, except that: the thickness of the second aramid layer is 30 μm.

[0091] Comparative Example 1

[0092] Similar to Example 2, the difference is that the second aramid layer is replaced by a polypropylene coating with a thickness of 20 μm, and the third aramid layer and the fourth aramid layer are replaced by ceramic layers.

[0093] Comparative Example 2

[0094] Similar to Example 2, the difference is that the third aramid layer and the fourth aramid layer are replaced by ceramic layers.

[0095] The following describes the preparation process of the positive electrode sheet, negative electrode sheet, electrolyte and bare cell of the final electrochemical device of the sodium ion battery in this embodiment and the comparative example.

[0096] The positive electrode material, the conductive agent Super P, and the binder polyvinylidene fluoride (PVDF) are stirred in N-methylpyrrolidone (NMP) solvent to form a positive electrode slurry, wherein the positive electrode active material is a layered oxide of sodium ions. The solid content in the positive electrode slurry is 65wt%, and the mass ratio of the positive electrode material, the conductive agent Super P and PVDF in the solid component is 97:1.2:1.8. The positive electrode slurry is evenly coated on the current collector; after drying at high temperature, cold pressing is performed; then trimming, cutting, and striping are performed, and then drying is performed under vacuum conditions at 110°C for 3 hours to form a positive electrode sheet for a sodium ion battery.

[0097] The hard carbon as the negative electrode active material is mixed evenly with the conductive agent Super P, the thickener sodium carboxymethyl cellulose (CMC), the adhesive styrene butadiene rubber (SBR), and the polyacrylic acid adhesive (PAA) in deionized water to prepare the negative electrode slurry. In the negative electrode slurry, the solid content in the negative electrode slurry is 48wt%, and the mass ratio of graphite, conductive agent Super P, CMC, SBR and PAA in the solid component is 95:1.2:1.0:1.3:1.5. The negative electrode slurry is coated on the current collector aluminum foil and dried at 110℃ for 3h to prepare the negative electrode sheet of the sodium ion battery.

[0098] Preparation of electrolyte: In an environment with a water content of less than 20 ppm, sodium hexafluorophosphate is added to a non-aqueous organic solvent. The ratio of the organic solvent in Example 1 is ethylene carbonate (EC): propylene carbonate (PC): dimethyl carbonate (DMC): diethyl carbonate (DEC) = 3:5:1:1.

[0099] Preparation of the separator: The separator base film is polyethylene (PE) with a thickness of 9 μm.

[0100] Preparation of sodium ion battery: The positive electrode sheet, negative electrode sheet and separator prepared above are stacked in order and wound to obtain a bare cell, wherein the outermost layer of the bare cell is a separator (about 0.5 to 2 turns), and the inner layers are the negative electrode sheet, separator and positive electrode sheet. After welding the pole ear, the bare cell is placed in an aluminum plastic film outer package, baked at 90°C for 12 hours to remove moisture, and then the prepared electrolyte is injected into the sodium ion battery. After packaging, high temperature and room temperature standing, formation (0.05C constant current charging to 3.2V, then 0.1C constant current charging to 3.5V, and then 0.5C constant current charging to 4.0V), capacity testing, etc., the preparation of the sodium ion battery is completed (the thickness of the soft pack battery is 4.0mm, the width is 75mm, and the length is 129mm).

[0101] Testing of sodium ion batteries: The testing equipment is to charge the sodium ion battery prepared above at 1C in the range of 1.5-4.0V, leave it for 5 minutes, and then discharge it at 0.2C, 0.5C, and 1C respectively. After each discharge, leave it for 15 minutes to obtain the discharge capacity of the sodium ion battery at different rates.

[0102] Cycle test: Use the 5V 30A charging and discharging equipment model BTS4000 produced by Shenzhen Xinwei Electronics Factory for cycle test. The test temperature is 55℃, and the test method and process are as follows:

[0103] The charging and discharging method adopted is 1C / 1C direct charging, and the charging and discharging voltage range is 1.5V-4.0V. After each step, it is left to stand for 15 minutes. The cycle is terminated when the battery capacity is less than 80%. After the cycle is terminated, the fully charged cell disassembly interface confirms the corner interface.

[0104] The conditions for the puncture test of the electrochemical device for the safety test of the embodiment of the present invention and the comparative example are: the sodium ion battery is fully charged to a voltage of 4.0V, and the voltage of the electrochemical device tested by the multimeter after polarization is eliminated is greater than 3.9V. The ambient temperature of the test is 23±2°C. The sodium ion battery connected to the thermocouple is woven in a fume hood. A rust-free steel needle with a diameter of 8mm is used at a speed of 40mm / s and a penetration force of 180kg. It is penetrated from a direction perpendicular to the electrochemical device, and the steel needle needs to stay in the battery. During the puncture process, it is necessary to puncture the most central position of the surface of the battery cell and keep it for more than 1 minute. If the battery does not catch fire, explode, or smoke, it is considered to have passed the safety puncture test.

[0105] The following table is a summary of the cycle level of the sodium ion batteries made in the above embodiments and comparative examples at 55°C, the interface of the negative electrode at the corner of the bare cell after the cycle, and the pass rate of the electrochemical device for the needle puncture safety test. From the test results, it can be seen that the thickness of the second aramid layer of the aluminum-plastic film increases and the third aramid layer coated on the outermost diaphragm of the bare cell in the electrochemical device is thicker, the pass rate of the needle puncture test is higher, and the cycle performance is better. Compared with the comparative example, whether the corner is coated with aramid and the thickness of the coating is increased, which is beneficial to the improvement of the interface at the corner position and can improve the cycle performance level.

[0106] Table 1. Statistics of the number of cycles, corner interfaces and needle penetration rate of sodium ion battery cycle capacity decay to 80% at 55°C

[0107]

[0108] Obviously, the above embodiments of the present invention are merely examples for clearly explaining the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are within the spirit scope of the present invention.

Claims

1. An electrochemical device, comprising an aluminum-plastic film layer and a bare battery cell surrounded by a cavity formed by the aluminum-plastic film layer, wherein the bare battery cell comprises a stacked positive electrode sheet, a separator and a negative electrode sheet, and a separator is arranged between adjacent positive electrode sheets and negative electrode sheets; characterized in that: Towards the bare battery core, the aluminum-plastic film layer includes an outer resistance layer, a barrier layer, a first aramid layer and a second aramid layer from the outside to the inside, and the second aramid layer is replaced with a heat sealing layer at the packaging position; and the outermost surface of the bare battery core has a third aramid layer.

2. The electrochemical device according to claim 1, characterized in that: The outermost layer of the bare battery cell is a diaphragm or a positive electrode sheet without active material.

3. The electrochemical device according to claim 1, characterized in that: The stacked arrangement includes a winding or lamination arrangement, wherein the positive electrode sheet, the separator and the negative electrode sheet arranged in a winding manner form a bare battery cell with a corner, and the surface of the separator of the bare battery cell located at the corner position has a fourth aramid layer.

4. The electrochemical device according to any one of claims 1 to 3, characterized in that: The first aramid layer or the second aramid layer is a fiber layer of aramid formula slurry or an aramid modified material layer, and the aramid is selected from one or more of para-aramid and meta-aramid.

5. The electrochemical device according to any one of claims 1 to 3, characterized in that: The third aramid layer or the fourth aramid layer is an aramid stock solution coating layer, and is made of an aramid material including para-aramid and meta-aramid.

6. The electrochemical device according to any one of claims 1 to 5, characterized in that: The thickness of the first aramid layer or the second aramid layer is 1 to 100 μm; and / or the thickness of the third aramid layer is 1 to 10 μm; and / or the thickness of the fourth aramid layer is 1 to 5 μm.

7. The electrochemical device according to any one of claims 1 to 6, characterized in that: The membrane surface includes an upper surface and / or a lower surface; preferably, the third aramid layer or the fourth aramid layer is located on the surface of the base film of the membrane, and the thickness of the base film is preferably 4 to 500 μm.

8. The electrochemical device according to claim 1, characterized in that: The material of the outer resistance layer is selected from one or more of nylon and PET; and / or, the material of the barrier layer is selected from one or more of aluminum foil, EVOH and PVDC; and / or, the material of the heat sealing layer is selected from one or more of polypropylene and polyethylene.

9. The electrochemical device according to any one of claims 1 to 8, characterized in that: The cavity formed by the aluminum-plastic film layer of the electrochemical device includes a bare battery cell and an electrolyte, and the electrolyte contains a liquid electrolyte of lithium ions and sodium ions.

10. An electronic device comprising the electrochemical device according to any one of claims 1 to 9.

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