Electrochemical device and electronic device

Abstract

An electrochemical device comprises a bipolar current collector, the bipolar current collector is connected with an outer package in a sealed mode, independent cavities are formed in the two sides of the bipolar current collector respectively, each cavity comprises an electrode assembly and electrolyte, and at least one surface of the bipolar current collector comprises electrode active materials. The adjacent electrode assemblies are connected in series. According to the electrochemical device, the safety of the electrochemical device can be improved; and the electrode active material on the surface of the bipolar current collector also participates in the reaction process in the electrochemical device, so that the electrochemical device realizes high-voltage output and has relatively high energy density.

Description

[0001] This application is a divisional application with application number 202080053225.7, application date June 30, 2020, and invention name “An electrochemical device and an electronic device”. Technical Field

[0002] The present invention relates to the field of electrochemistry, and in particular to an electrochemical device and an electronic device comprising the electrochemical device. Background Art

[0003] In the existing lithium-ion battery system, due to the limited voltage difference between the positive and negative electrode materials, the limited anti-oxidation and reduction capacity of the electrolyte, etc., the open circuit voltage of the battery is difficult to exceed 5V. However, in the actual use of batteries, there are many scenarios where voltages exceeding 5V are required, such as electric vehicles (EV), power tools (PT), energy storage systems (ESS), etc. Even in the mobile phone market, in order to meet the needs of fast charging, the open circuit voltage of the battery cell needs to be increased. At present, the method of connecting multiple batteries in series is generally used to increase the output voltage, but there are many problems with multiple batteries in series, such as: the capacity difference between individual batteries leads to a low overall energy density; the series connection uses wires and contact resistance to introduce additional electronic resistance, resulting in heat and waste of energy; the higher the voltage, the more individual batteries are required, which increases the difficulty of battery management. In order to solve the above problems, the concept of high-output voltage battery was proposed, which uses the internal series connection of the battery to achieve high voltage output of a single battery, reduce the total heat generated by the battery, and reduce the temperature rise during use.

[0004] The series battery in the prior art is to directly connect two batteries in series in the same packaging bag, without ion insulation between the two series batteries. If the battery voltage increases, the electrolyte will be decomposed under high voltage conditions, which will cause the battery to fail. In addition, the two batteries will have an internal short circuit due to the voltage difference between the pole pieces, which will also cause the battery to fail. For the above reasons, the solutions currently proposed are only applicable to solid electrolyte batteries. However, mainstream lithium batteries use liquid electrolytes, so the above solutions are difficult to promote. Summary of the invention

[0005] The purpose of the present application is to provide an electrochemical device that achieves high voltage output and has high energy density.

[0006] The first aspect of the present application provides an electrochemical device, comprising a bipolar current collector, the bipolar current collector is sealed and connected to an outer package, and separate cavities are formed on both sides of the bipolar current collector. An electrode assembly and an electrolyte are encapsulated in each cavity. An electrode active material is provided on at least one surface of the bipolar current collector. The electrode assemblies in adjacent cavities are connected in series.

[0007] In some embodiments of the first aspect of the present application, the cavity is a sealed cavity.

[0008] In some embodiments of the first aspect of the present application, an electrode active material is provided on the first surface of the bipolar current collector. The polarity of the electrode active material is opposite to the polarity of the outermost electrode sheet of the adjacent electrode assembly. A separator is provided between the outermost electrode sheet and the bipolar current collector. The second surface of the bipolar current collector is electrically insulated from the adjacent electrode assembly.

[0009] In some embodiments of the first aspect of the present application, a tab is disposed on the bipolar current collector, and the tab is connected in parallel with a tab of the same polarity in an electrode assembly adjacent to the first surface.

[0010] In some embodiments of the present application, the bipolar current collector has a thickness of 6 μm to 100 μm, preferably 10 μm to 55 μm.

[0011] In some embodiments of the present application, the bipolar current collector has a thickness of 10 μm to 40 μm, preferably 20 μm to 30 μm.

[0012] In some embodiments of the first aspect of the present application, an electrode active material is provided on the first surface of the bipolar current collector, and the electrode active material has an opposite polarity to the outermost electrode plate of an adjacent electrode assembly. The second surface of the bipolar current collector is electrically connected to the current collector of the outermost electrode plate of the adjacent electrode assembly, and the polarity of the electrode plate adjacent to the second surface is opposite to the polarity of the electrode active material on the first surface.

[0013] In some embodiments of the first aspect of the present application, the two surfaces of the bipolar current collector are respectively provided with electrode active materials of different polarities, the outermost electrode sheet of the electrode assembly adjacent to each surface has a different polarity from the electrode active material on the surface, and a separator is provided between the outermost electrode sheet of the electrode assembly and the bipolar current collector.

[0014] In some embodiments of the first aspect of the present application, the electrochemical device is provided with two electrode tabs with opposite polarities, and the electrode assembly of the electrochemical device is connected in series between the two electrode tabs.

[0015] In some embodiments of the first aspect of the present application, each of the electrode assemblies is provided with two electrode tabs with opposite polarities, and one of the electrode tabs is connected in series with a electrode tab with opposite polarity of an adjacent electrode assembly.

[0016] In some embodiments of the first aspect of the present application, a pole ear is further provided on the bipolar current collector for detecting the operating status of the electrode assemblies on both sides thereof.

[0017] In some embodiments of the first aspect of the present application, a tab is further provided on the bipolar current collector, and the tab is connected to tabs that connect the electrode assemblies on both sides of the bipolar current collector in series.

[0018] A second aspect of the present application provides an electronic device, which includes the electrochemical device provided by the first aspect of the present application.

[0019] The electrochemical device provided by the present application has a bipolar current collector that not only has a physical isolation effect, but also completely isolates the electrode assemblies on both sides of the bipolar current collector to form an independent sealed cavity, thereby ensuring the normal operation of the electrochemical device and improving the safety of the electrochemical device; and the electrode active materials on the surface of the bipolar current collector also participate in the electrochemical reaction process in the electrochemical device, so that the electrochemical device achieves high voltage output and has a high energy density. At the same time, the bipolar current collector is sealed and connected to the outer packaging, so a liquid electrolyte can be used, thereby meeting the needs of the market. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention and the technical solutions of the prior art, the following briefly introduces the drawings required for use in the embodiments and the prior art. Obviously, the drawings described below are only some embodiments of the present invention, not all embodiments.

[0021] Figure 1 A schematic diagram of an electrochemical device in one embodiment of the present application;

[0022] Figure 2 A partial schematic cross-sectional view of the internal structure of an electrochemical device in one embodiment of the present application;

[0023] Figure 3 A partial schematic cross-sectional view of the internal structure of an electrochemical device in another embodiment of the present application;

[0024] Figure 4 A schematic diagram of an electrochemical device in another embodiment of the present application;

[0025] Figure 5 A partial schematic cross-sectional view of the internal structure of an electrochemical device in another embodiment of the present application;

[0026] Figure 6 This is a schematic diagram of a bipolar current collector structure in one embodiment of the present application.

[0027] Reference numerals:

[0028] 1. Bipolar current collector; 2. Electrode assembly; 201. Electrode assembly; 202. Electrode assembly; 3. Outer packaging; 4. Bipolar current collector tab; 5. Positive electrode tab; 6. Negative electrode tab; 7. Positive electrode active material; 8. Negative electrode active material; 9. Diaphragm; 10. Positive electrode collector; 11. Negative electrode collector; 12. Sealing area. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them.

[0030] The electrochemical device of the present application can be any electrochemical device known to those skilled in the art, such as a lithium-ion battery, a sodium-ion battery, a magnesium-ion battery, a supercapacitor, etc., and the following description is made using a lithium-ion battery as an example. Those skilled in the art should understand that the following description is only for illustrative purposes and does not limit the scope of protection of the present application.

[0031] The present application provides an electrochemical device, which includes a bipolar current collector, which is sealed and connected to an outer package, and independent sealed cavities are formed on both sides of the bipolar current collector, each sealed cavity encapsulates an electrode assembly and an electrolyte, and an electrode active material is provided on at least one surface of the bipolar current collector, and the electrode assemblies in adjacent sealed cavities are connected in series.

[0032] Figure 1 An embodiment of the present application is shown, which includes a bipolar current collector 1, which is sealed and connected to an outer package 3, and independent cavities are formed on both sides of the bipolar current collector 1, each cavity contains an electrode assembly 2 and an electrolyte, and at least one surface of the bipolar current collector 1 contains an electrode active material, and adjacent electrode assemblies 2 are connected in series.

[0033] The cavity is a sealed cavity.

[0034] The bipolar current collector in the present application refers to a current collector whose two sides can be coated with active materials of different polarities at the same time, and which has the characteristics of both a positive electrode current collector and a negative electrode current collector.

[0035] In some embodiments of the present application, the bipolar current collector is sealed and connected to the outer package, and independent sealed cavities are formed on both sides of the bipolar current collector. The electrode assemblies and electrolyte on both sides of the bipolar current collector are completely separated, which can not only ensure the normal operation of the electrode assemblies on both sides, but also the good sealing is conducive to improving the safety of the electrochemical device. In addition, the bipolar current collector has the characteristics of electronic conduction and ion insulation, which can avoid internal short circuits, high-voltage decomposition of electrolytes, and short circuits within electrode assemblies. Electrode active materials are provided on at least one surface of the bipolar current collector. The presence of the electrode active materials enables the bipolar current collector to participate in the electrochemical reaction of the electrochemical device, which can effectively improve the energy density of the electrochemical device. Adjacent electrode assemblies connected in series can achieve high voltage output, thereby meeting the needs of the existing market.

[0036] In some embodiments of the present application, an electrode active material is provided on the first surface of the bipolar current collector, and the electrode active material has an opposite polarity to the outermost electrode sheet of the adjacent electrode assembly, and a separator is provided between the outermost electrode sheet and the bipolar current collector; the second surface of the bipolar current collector is electrically insulated from the adjacent electrode assembly. In this embodiment, the first surface of the bipolar current collector and the outermost electrode sheet of the adjacent electrode assembly constitute an electrochemical unit, participate in the charge and discharge process of the electrochemical device, and improve the energy density of the electrochemical device.

[0037] In some embodiments of the present application, a tab is provided on the bipolar current collector, and the tab is connected in parallel with a tab of the same polarity in an electrode assembly adjacent to the first surface. In this embodiment, the tab is connected in parallel and then connected in series with an electrode assembly adjacent to the second surface of the bipolar current collector, thereby providing a high output voltage.

[0038] Figure 2 An embodiment of the present application is shown, wherein the bipolar current collector 1 is provided with a positive electrode active material 7 on the a surface, and has no electrode active material on the b surface. The outermost layer of the electrode assembly 201 adjacent to the a surface is provided with a negative electrode active material 8, and the outermost layer of the electrode assembly 202 adjacent to the b surface is provided with a separator 9. The bipolar current collector 1 is provided with a pole ear 4 (such as Figure 1As shown in FIG. 1 ), the tab 4 of the bipolar current collector 1 is connected to the positive tab of the electrode assembly 201 on the side adjacent to the a-face of the bipolar current collector to form a parallel connection, and then connected to the negative tab of the electrode assembly 202 to form a series connection, thereby realizing the series connection of the electrode assemblies 201 and 202. It can be understood by those skilled in the art that the positive electrode active material on the a-face of the bipolar current collector may also be a negative electrode active material. In this case, the outermost layer of the electrode assembly 201 adjacent to the a-face contains a positive electrode active material, and the tab of the bipolar current collector is connected to the negative electrode tab of the electrode assembly 201 to form a parallel connection, and then connected to the positive electrode tab of the electrode assembly 202 to form a series connection.

[0039] In some embodiments of the present application, an electrode active material is disposed on the first surface of the bipolar current collector, the electrode active material has a polarity opposite to that of the outermost electrode sheet of an adjacent electrode assembly, and a separator is provided between the outermost electrode sheet and the bipolar current collector; the second surface of the bipolar current collector is electrically connected to the collector of the outermost electrode sheet of an adjacent electrode assembly, and the polarity of the outermost electrode sheet of the adjacent electrode assembly on the second surface is opposite to that of the electrode active material on the first surface.

[0040] In some embodiments of the present application, the bipolar current collector may not have pole ears. In this case, the electrode assemblies on both sides of the bipolar current collector are directly connected in series internally through the bipolar current collector. The electrochemical device may only have two pole ears with opposite polarities, wherein all the electrode assemblies are connected in series between the two pole ears with opposite polarities through the bipolar current collector.

[0041] In some embodiments of the present application, the bipolar current collector may also lead out a pole ear, which is connected to the pole ear of the same polarity on the electrode assembly on the side where the bipolar current collector is provided with the electrode active material to form a parallel connection, and then connected to the pole ear of the opposite polarity on the electrode assembly on the other side to form a series connection. At this time, the two electrode assemblies can be connected in series through the inside of the bipolar current collector and through the outside of the pole ear. In addition, the pole ear of the bipolar current collector may not be connected to the pole ear of the electrode assembly and is only used to monitor the voltage of the electrochemical device.

[0042] Figure 3An embodiment of the present application is shown, wherein the a-side of the bipolar current collector contains negative electrode active material 8, and the b-side of the bipolar current collector 1 has no electrode active material. The outermost layer of the electrode assembly 201 adjacent to the a-side of the bipolar current collector 1 is provided with positive electrode active material 7, and the outermost layer of the electrode assembly 202 adjacent to the b-side of the bipolar current collector 1 is a positive electrode collector 10, and the positive electrode collector 10 is electrically connected to the b-side of the bipolar current collector 1. The electrode assembly 201 and the electrode assembly 202 can be directly connected in series through the bipolar current collector 1, and the positive electrode tab of the electrode assembly 201 and the negative electrode tab of the electrode assembly 202 are led out as the charging and discharging electrode tabs of the electrochemical device. In some embodiments of the present application, a tab is provided on the bipolar current collector, and the tab is connected to the negative electrode tab of the electrode assembly 201 to form a parallel connection, and then connected to the positive electrode tab of the electrode assembly 202 to form a series connection. At this time, the two electrode assemblies are connected in series both through the inside of the bipolar current collector and through the outside of the tab. In addition, the tabs on the bipolar current collector may not be connected to the tabs of the electrode assembly and may only be used to monitor the voltage of the electrochemical device.

[0043] Those skilled in the art can understand that the negative electrode active material on the a-side of the bipolar current collector can also be a positive electrode active material. In this case, the outermost layer of the electrode assembly 201 adjacent to the a-side is provided with the negative electrode active material, and the outermost layer of the electrode assembly 202 adjacent to the b-side of the bipolar current collector 1 is the negative electrode current collector. The electrode assembly 201 and the electrode assembly 202 can be directly connected in series through the bipolar current collector 1.

[0044] In some embodiments of the present application, the two surfaces of the bipolar current collector are respectively provided with electrode active materials of different polarities, the outermost electrode sheet of the electrode assembly adjacent to each surface has a different polarity from the electrode active material on the surface, and a separator is provided between the outermost electrode sheet of the electrode assembly and the bipolar current collector. The two surfaces of the bipolar current collector are respectively provided with electrode active materials of different polarities, and the two surfaces respectively form an electrochemical unit with the outermost electrode sheet of the adjacent electrode assembly, further improving the energy density of the battery.

[0045] The electrode assemblies on both sides of the bipolar current collector can be directly connected in series internally through the bipolar current collector, or can be simultaneously connected in series internally and externally through the bipolar current collector and two pole ears with opposite polarities.

[0046] Figure 5An embodiment of the present application is shown, wherein the a-surface of the bipolar current collector 1 is provided with a positive electrode active material 7, the b-surface of the bipolar current collector 1 is provided with a negative electrode active material 8, the outermost electrode sheet of the electrode assembly 201 adjacent to the a-surface of the bipolar current collector 1 comprises the negative electrode active material 8, and the outermost electrode sheet of the electrode assembly 202 adjacent to the b-surface of the bipolar current collector 1 comprises the positive electrode active material 7. The electrode assembly 201 and the electrode assembly 202 can be directly connected in series internally through the bipolar current collector 1, and the negative electrode tab of the electrode assembly 201 and the positive electrode tab of the electrode assembly 202 are drawn out as the output tabs of the electrochemical device.

[0047] In some embodiments of the present application, the bipolar current collector has a positive electrode active material on its a surface and a negative electrode active material on its b surface. The outermost electrode sheet of the electrode assembly 201 adjacent to the a surface contains the negative electrode active material, and the outermost electrode sheet of the electrode assembly 202 adjacent to the b surface contains the positive electrode active material. All the tabs of the electrode assemblies 201 and 202 are drawn out, and the positive tab of the electrode assembly 201 and the negative tab of the electrode assembly 202 are connected in series. The electrode assemblies 201 and 202 are not only connected in series internally through the bipolar current collector, but also connected in series externally through the tabs. The negative tab of the electrode assembly 201 and the positive tab of the electrode assembly 202 are output tabs of the electrochemical device, such as Figure 4 shown.

[0048] In some embodiments of the present application, the two surfaces of the bipolar current collector are respectively provided with electrode active materials of different polarities, and a tab is provided on the bipolar current collector, and the tab can be used to monitor the voltage of the electrochemical device, or to insulate the tab. The tab can also be connected to the tabs that connect the electrode assemblies on both sides of the bipolar current collector in series.

[0049] In some embodiments of the present application, there is no particular restriction on the bipolar current collector, as long as electrode active materials with different polarities can be set on its two surfaces. Generally, the bipolar current collector needs to have anti-oxidation and reduction properties and can be stably present in the electrolyte, for example, the bipolar current collector includes a metal bipolar current collector or a composite bipolar current collector. The metal bipolar current collector includes at least one of a copper-aluminum composite current collector, stainless steel, Ni, Ti, Ag, Au, Pt, etc.

[0050] The composite bipolar current collector is not particularly limited. For example, a composite bipolar current collector includes a metal and a polymer, wherein the metal is disposed on the surface of the polymer, and the metals on the two surfaces may be the same or different, and the metals on the two surfaces are electrically connected. In the present application, the metal is not particularly limited as long as the purpose of the present application can be achieved. For example, the metal includes two of Cu, Al, Ni, Ti, Ag, Au, Pt, etc. In the present application, the polymer is not particularly limited as long as the purpose of the present application can be achieved, for example, 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 resin, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene ether, polysulfone or at least one of the derivatives of the above substances.

[0051] Another composite bipolar current collector includes a one-dimensional or two-dimensional conductive material and a polymer, wherein the conductive material is embedded in the polymer at a certain angle (e.g., 0° to 30°) to achieve conductivity in the thickness direction. The conductive material includes at least one of a carbon material or a metal material. The carbon material includes at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon fibers, conductive carbon black, fullerenes, conductive graphite, or graphene. The metal material includes at least one of Ni, Ti, Ag, Au, Pt, or stainless steel and its alloys. The polymer includes 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 resin, vinylon, polypropylene, polyethylene, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene ether, polysulfone or at least one of the derivatives of the above substances.

[0052] In some embodiments of the present application, the thickness of the bipolar current collector is 6μm to 100μm, preferably 10μm to 55μm. In some embodiments of the present application, the thickness of the bipolar current collector is 10μm to 40μm, preferably 20μm to 30μm. The bipolar current collector not only has the characteristics of ion insulation, but also should have a certain mechanical strength. Therefore, if the bipolar current collector is too thin, the mechanical strength is poor, which is easy to cause damage and affect the performance and even safety of the electrochemical device. If it is too thick, it will affect the conduction of electrons and reduce the energy density of the electrochemical device, so that the performance of the electrochemical device is limited. The electronic resistivity of the bipolar current collector in the Z direction is 1×10 -11 to 30 Ω·cm, preferably 1×10 -5 The resistance value is preferably 0.01 to 0.10 Ω·cm, more preferably 0.01 to 0.10 Ω·cm.

[0053] When the electrode active material on the surface of the bipolar current collector is a positive electrode active material, the thickness of the positive electrode active material is 30 to 120 μm; when the electrode active material on the surface of the bipolar current collector is a negative electrode active material, the thickness of the negative electrode active material is 30 to 120 μm. The surface of the bipolar current collector contains electrode active materials, which can participate in the reaction process in the electrochemical device, not only to increase the output voltage, but also to increase the energy density of the electrochemical device. In the present application, if the thickness of the electrode active material is too thin, the coating surface will be uneven due to the particle size of the product, and the energy that the coated material can exert is low. If the thickness of the electrode active material is too thick, it will affect the electrochemical reaction activity of the battery cell. Therefore, selecting the electrode active material of the above thickness is more conducive to achieving high voltage output while having a higher energy density.

[0054] In some embodiments of the present application, Figure 6 As shown, the bipolar current collector 1 further includes a sealing region 12, which is located at the edges of the bipolar current collector 1. The sealing region also includes a sealing material, which includes at least one of polypropylene, anhydride-modified polypropylene, polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-vinyl alcohol copolymer, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyamide, polyester, amorphous α-olefin copolymer and its derivatives. The above sealing material can be more effectively sealed and connected with the outer package, thereby helping to improve the safety of the electrochemical device.

[0055] In the present application, there is no particular restriction on the sealing method between the bipolar current collector and the outer package, and any sealing method known in the art can be used. For example, a typical method is to set a sealing material around the edges of the bipolar current collector and perform heat-pressing sealing with the outer package to form a sealing area in the contact area between the sealing material and the outer package. During the hot pressing and sealing process, the polymer material in the sealing area is fused with the polymer material in the inner layer of the outer package. In the present application, there is no particular restriction on the size of the sealing area, as long as the purpose of the present application can be achieved. For example, the seal thickness T (unit: mm) and the seal width W (unit: mm) of the sealing area satisfy 0.01≤T / W≤0.05. The ratio of T / W within the above range can ensure good sealing of the battery and improve the service life of the battery. When T / W is too small, the seal thickness may be insufficient, the sealing effect is poor, and the environmental stability of the battery is reduced. For example, water vapor in the environment can easily penetrate into the battery, causing the water content in the battery to increase, the electrolyte to decompose, and the battery life to be reduced. When the T / W ratio is too large, the seal width W may be too small, and there is also a poor sealing effect, which leads to a reduction in the environmental stability of the battery. For example, water vapor in the environment can easily penetrate into the battery, causing the water content in the battery to increase, the electrolyte to decompose, and other problems, which reduce the battery life. In this application, the seal thickness and seal width are not particularly limited, as long as the purpose of the present invention can be achieved. For example, the seal width is preferably 1mm to 7mm.

[0056] In the sealing process of the present application, the polymer material in the outer packaging and the polymer material in the sealing material are sealed together by heat pressing. Therefore, the seal thickness includes the thickness after the polymer material in the sealing material and the polymer material in the inner layer of the outer packaging are fused. The seal width refers to the width of the sealed area formed by the polymer material in the sealing material and the polymer material in the inner layer of the outer packaging after heat pressing and sealing.

[0057] In some embodiments of the present application, the electrolyte includes one of a gel state, a solid state and a liquid state. In the present application, the electrolyte is not particularly limited, as long as the purpose of the present application can be achieved. In some embodiments of the present application, the structure of the electrode assembly includes a winding structure or a laminate structure. The battery assemblies connected in series may have the same structure or different structures.

[0058] In some embodiments of the present application, the structure of the electrode assembly is a winding structure, and the electrode assembly includes a single pole ear or multiple pole ears. The electrode assembly includes a single pole ear, which is a positive pole ear and a negative pole ear respectively drawn from the positive pole sheet and the negative pole sheet. The electrode assembly includes multiple pole ears, which can be a positive pole ear and a negative pole ear respectively drawn from each circle of the positive pole sheet and the negative pole sheet, or a positive pole ear and a negative pole ear respectively drawn from two or more circles of the positive pole sheet and the negative pole sheet. Finally, an electrode assembly with a winding structure includes multiple groups of positive pole ears and negative pole ears, and then the pole ear leads are transferred by transfer welding.

[0059] In some embodiments of the present application, the structure of the electrode assembly is a stacked structure, and the electrode assembly includes multiple pole tabs, which can be a positive pole tab and a negative pole tab respectively led out from each layer of the positive pole sheet and the negative pole sheet. Finally, an electrode assembly with a stacked structure contains multiple groups of positive pole tabs and negative pole tabs, and then the pole tab leads are transferred by adapter welding.

[0060] In the present application, the welding method is not particularly limited as long as the purpose of the present application can be achieved, for example, laser welding, ultrasonic welding or resistance welding.

[0061] In some embodiments of the present application, the series-connected tabs are stacked or staggered in the thickness direction of the electrochemical device. The present application has no particular restrictions on the distribution of the tabs, as long as the purpose of the present application can be achieved. In practical applications, the distribution of the tabs can be adjusted according to demand.

[0062] The electrode assembly mentioned in the present application may be an electrode assembly including a positive electrode sheet, a negative electrode sheet and a separator, and the above electrode assembly is used as an example for description. Those skilled in the art should understand that the following description is only for illustration and does not limit the scope of protection of the present application.

[0063] In some embodiments of the present application, the positive electrode sheet is not particularly limited, as long as the purpose of the present application can be achieved. For example, the positive electrode sheet generally includes a positive current collector and a positive active material. In the present application, the positive current collector is not particularly limited, and can be any positive current collector known in the art, such as copper foil, aluminum foil, aluminum alloy foil, and composite current collector. The positive active material is not particularly limited, and can be any positive active material of the prior art, for example, the positive active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, or lithium manganese iron phosphate. In the present application, the thickness of the positive current collector and the positive active material is not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness of the positive current collector is 8-12 μm, and the thickness of the positive active material is 30-120 μm.

[0064] In some preferred embodiments of the present application, the positive electrode sheet may further include a conductive layer, and the conductive layer is located between the positive electrode current collector and the positive electrode active material layer. The composition of the conductive layer is not particularly limited, and may be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder.

[0065] In some embodiments of the present application, the negative electrode sheet is not particularly limited, as long as the purpose of the present application can be achieved. For example, the negative electrode sheet generally includes a negative electrode current collector and a negative electrode active material. In the present application, the negative electrode current collector is not particularly limited, and any negative electrode current collector known in the art can be used, such as copper foil, aluminum foil, aluminum alloy foil, and composite current collector. The negative electrode active material is not particularly limited, and any negative electrode active material known in the art can be used. For example, it can include at least one of artificial graphite, natural graphite, mesophase carbon microspheres, silicon, silicon carbon, silicon oxides, soft carbon, hard carbon, lithium titanate, or niobium titanate. In the present application, the thickness of the negative electrode current collector and the negative electrode active material is not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness of the negative electrode current collector is 6-10 μm, and the thickness of the negative electrode active material is 30-120 μm.

[0066] In some preferred embodiments of the present application, the negative electrode plate may further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode active material layer. The composition of the conductive layer is not particularly limited, and may be a conductive layer commonly used in the art. The conductive layer includes a conductive agent and a binder.

[0067] The conductive agent described above is not particularly limited, and any conductive agent known in the art can be used, as long as the purpose of the present application can be achieved. For example, the conductive agent can include at least one of conductive carbon black (Super P), carbon nanotubes (CNTs), carbon fiber or graphene. The adhesive described above is not particularly limited, and any adhesive known in the art can be used, as long as the purpose of the present application can be achieved. For example, the adhesive can include at least one of styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE) or sodium carboxymethyl cellulose (CMC-Na).

[0068] In some embodiments of the present application, the diaphragm is not particularly limited as long as the purpose of the present application can be achieved. For example, the thickness of the diaphragm can be 5-15 μm, and the diaphragm can include a polymer or inorganic material formed by a material that stabilizes the electrolyte of the present application. In the present application, the diaphragm can also be referred to as an isolation membrane.

[0069] For example, the diaphragm may include a substrate layer and a surface treatment layer. The substrate layer may be a nonwoven fabric, a film or a composite film having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide. Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance.

[0070] For example, the inorganic layer includes inorganic particles and a binder, and the inorganic particles are not particularly limited, for example, they can be selected from at least one of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is not particularly limited, for example, it can be selected from one or more combinations of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylic acid salt, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

[0071] The tabs mentioned in this application refer to metal conductors drawn from the positive electrode sheet or the negative electrode sheet, which are used to connect other parts of the electrochemical device in series or in parallel. The positive tabs are drawn from the positive electrode sheet, and the negative tabs are drawn from the negative electrode sheet.

[0072] The electrolyte described in the present application may contain a lithium salt and a non-aqueous solvent. In the present application, the lithium salt is not particularly limited, and any lithium salt known in the art can be used, as long as the purpose of the present application can be achieved. For example, the lithium salt may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3 or LiPO2F2. For example, LiPF6 can be selected as the lithium salt. In the present application, the non-aqueous solvent is not particularly limited, as long as the purpose of the present application can be achieved. For example, the non-aqueous solvent may include at least one of a carbonate compound, a carboxylate compound, an ether compound, a nitrile compound, and other organic solvents.

[0073] For example, the carbonate compound may include at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethyl methyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, and trifluoromethylethylene carbonate.

[0074] The present application has no special restrictions on the outer packaging, as long as the purpose of the present application can be achieved. For example, the outer packaging may include an inner layer and an outer layer, and the inner layer is sealed and connected to the bipolar current collector, so the material of the inner layer may include a polymer material, thereby achieving a good sealing effect; at the same time, the combination of the inner layer and the outer layer can effectively protect the internal structure of the electrochemical device. In the present application, there is no special restriction on the material of the inner layer, as long as the purpose of the present application can be achieved. For example, the material of the inner layer includes at least one of polypropylene, polyester, parahydroxybenzaldehyde, polyamide, polyphenylene ether, polyurethane, etc. In the present application, there is no special restriction on the material of the outer layer, as long as the purpose of the present application can be achieved. For example, the material of the outer layer includes at least one of aluminum foil, aluminum oxide layer, silicon nitride layer, etc.

[0075] There is no special limitation on the thickness of the outer package in the present application, as long as the purpose of the present application can be achieved. For example, the thickness of the outer package is 60 to 200 μm, and the outer package of the above thickness can effectively protect the internal structure of the electrochemical device.

[0076] The present application has no particular restrictions on the sealing connection method between the bipolar current collector and the outer packaging, as long as the purpose of the present application can be achieved. For example, the sealing method includes one of hot pressing, glue sealing, and welding. In the present application, the hot pressing conditions are not particularly limited, as long as the purpose of the present application can be achieved. For example, for the polypropylene inner layer material, the hot pressing temperature is 150-220°C and the hot pressing pressure is 0.1-0.6MPa.

[0077] The present application also provides an electronic device, which includes an electrochemical device provided in the present application. The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. For example, the display device includes but is not limited to a laptop computer, a pen-input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0078] The method for preparing the electrochemical device of the present application is not particularly limited, and any method known in the art may be used. For example, in one embodiment, the present application may be prepared by the following preparation method:

[0079] (1) Preparation of negative electrode sheet: The negative electrode active material and solvent are mixed into a slurry and stirred evenly. The slurry is evenly coated on the negative electrode sheet and dried to obtain a single-sided coated negative electrode sheet. The above steps are repeated on the other surface of the negative electrode sheet to obtain a double-sided coated negative electrode sheet. Then, the negative electrode sheet is cut for standby use.

[0080] (2) Preparation of positive electrode sheet: The positive electrode active material and solvent are mixed into a slurry and stirred evenly. The slurry is evenly coated on the positive electrode sheet and dried to obtain a single-sided coated positive electrode sheet. The above steps are repeated on the other surface of the positive electrode sheet to obtain a double-sided coated positive electrode sheet. Then, the positive electrode sheet is cut for standby use.

[0081] (3) Preparation of electrolyte: The lithium salt and the non-aqueous solvent are mixed and stirred uniformly to obtain an electrolyte containing lithium salt.

[0082] (4) Preparation of electrode assemblies: stack the double-sided coated negative electrode sheet, the separator, and the double-sided coated positive electrode sheet in sequence and fix the layers together for use, each electrode assembly comprising a positive electrode tab and / or a negative electrode tab; repeating the above steps can obtain multiple electrode assemblies; the structure of the electrode assembly can be a winding structure or a laminated structure.

[0083] (5) Preparation of bipolar current collector: coating a positive electrode active material or a negative electrode active material on one surface of the bipolar current collector and drying it, and leading out a tab; or coating a positive electrode active material and a negative electrode active material on both surfaces of the bipolar current collector and drying them, leading out a tab or not leading out a tab. The thickness of the positive electrode active material and the negative electrode active material on the surface of the bipolar current collector is the same as the thickness on the positive electrode sheet and the negative electrode sheet, respectively.

[0084] (6) Assembly of the electrode assembly: The outer package is placed in an assembly fixture, and then the electrode assembly and the bipolar current collector are spaced apart, with the outer package adjacent to the electrode assembly, and finally sealed to obtain an assembled electrode assembly.

[0085] (7) Liquid injection packaging: The electrolyte is injected into each cavity of the assembled electrode assembly separately, and all the tabs of the electrode assembly are led out of the aluminum-plastic film for subsequent processing.

[0086] (8.1) Connecting the electrode assemblies in series: welding the positive electrode tab of one electrode assembly to the negative electrode tab of another electrode assembly to connect the two electrode assemblies in series, and repeating the above steps to complete the assembly of the electrochemical device; or

[0087] (8.2) Connecting the electrode assemblies in series: Connect the tabs of the bipolar current collector in parallel with the tabs of the same polarity of the adjacent electrode assembly, and then weld the positive and negative tabs of the two electrode assemblies together to achieve series connection between the two electrode assemblies. Repeat the above steps to complete the assembly of the electrochemical device.

[0088] In the above preparation process, the connection method of the electrode assembly can be selected from the connection method in (8.1) or the connection method in (8.2) according to different implementation methods in the specification.

[0089] The electrochemical device provided in the present application may include two electrode assemblies or three or more electrode assemblies. The preparation method of the electrochemical device containing two electrode assemblies or three or more electrode assemblies can refer to the preparation method of the above-mentioned electrochemical device. The electrochemical device containing three or more electrode assemblies is also within the protection scope defined by the claims of the present application.

[0090] The terms used in this application are generally commonly used by those skilled in the art. If there is any inconsistency with the commonly used terms, the terms in this application shall prevail. In this application, unless otherwise specified, "%" and "part" are based on weight.

[0091] Test method:

[0092] Battery Energy Density

[0093] The electrochemical device was left at room temperature for 30 minutes, and then charged at a constant current of 0.05C charging rate to a voltage of 4.4V (rated voltage), and then discharged at a rate of 0.05C to 3.0V, and the above charge / discharge steps were repeated for 3 cycles to complete the formation of the electrochemical device to be tested. After the formation of the electrochemical device was completed, it was charged at a constant current of 0.1C charging rate to a voltage of 4.4V, and then discharged at a discharge rate of 0.1C to 3.0V, and its discharge capacity was recorded, and then its energy density at 0.1C discharge was calculated:

[0094] Energy density (Wh / L) = discharge capacity (Wh) / electrochemical device volume size (L).

[0095] Lithium-ion battery self-discharge rate K:

[0096] The lithium-ion battery was discharged at a current of 0.5C to 3.0V, and then left to stand for 5 minutes. Then, the lithium-ion battery was charged at a constant current of 0.5C to 3.85V, and then charged at a constant voltage of 3.85V to a current of 0.05C, and left to stand for two days in an environment of 25℃±5℃, and the voltage OCV1 at this time was tested and recorded. Then, the lithium-ion battery was left to stand for two days in an environment of 25℃±5℃, and the voltage OCV2 at this time was tested and recorded, and the K value was obtained by the following formula: K (mV / h) = (OCV2-OCV1) / 48h-OCV1.

[0097] Discharge temperature rise:

[0098] The test temperature is 25℃. A temperature probe is bonded to the center of the cell surface to monitor the temperature of the cell body, and foam is wrapped on the cell surface to weaken the heat exchange between the cell and the contact. The test process is as follows: discharge at a constant current of 0.2C to 6V (6V for series cells) or 3V (3V for a single cell in the comparison example, the same below), then charge at 05C cross current to 8.4V or 4.2V, charge at 02C to 8.9V or 4.45V, and let stand for 120min until the center temperature of the cell drops to room temperature 25℃. Use the same power ~15W to discharge and monitor the temperature rise of the cell body during the discharge process.

[0099] Nail penetration test:

[0100] The electrochemical device to be tested is charged at a constant current of 0.05 C to a voltage of 4.45 V (rated voltage of comparative example 1) or 8.90 V (other comparative examples and all embodiments), and then charged at a constant voltage to a current of 0.025C (cut-off current) to fully charge the battery, and record the appearance of the electrochemical device before the test. The electrochemical device is subjected to a nail penetration test in a 25°C environment, with a steel nail diameter of 4 mm and a penetration speed of 30 mm / s. The nail penetration positions are located 15 mm from the edge of the positive pole tab electrode assembly and 15 mm from the edge of the negative pole tab electrode assembly, respectively. The test is stopped after 3.5 minutes or the surface temperature of the electrode assembly drops to 50°C. Ten cells are grouped together to observe the battery status during the test, and the battery is judged as not burning or exploding.

[0101] AC impedance test:

[0102] The test was carried out using an internal resistance meter, and the excitation signal for the electrochemical device was 1KHz, 10mA.

[0103] Embodiment 1:

[0104] (1) Preparation of negative electrode sheet: Mix the negative electrode active materials artificial graphite, conductive carbon black (Super P), and styrene-butadiene rubber (SBR) in a weight ratio of 96:1.5:2.5, add deionized water as a solvent, prepare a slurry with a solid content of 70wt%, and stir evenly. The slurry is evenly coated on one surface of a negative electrode current collector copper foil with a thickness of 10μm, and dried at 110°C to obtain a negative electrode sheet with a coating thickness of 150μm and a single-sided negative electrode active material layer. Repeat the above steps on the other surface of the negative electrode sheet to obtain a negative electrode sheet with a double-sided negative electrode active material layer. Then, cut the negative electrode sheet into a size of 41mm×61mm for standby use.

[0105] (2) Preparation of positive electrode sheet: Mix the positive electrode active materials lithium cobalt oxide (LiCoO2), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) in a weight ratio of 97.5:1.0:1.5, add N-methylpyrrolidone (NMP) as a solvent, prepare a slurry with a solid content of 75wt%, and stir evenly. The slurry is evenly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12μm, and dried at 90°C to obtain a positive electrode sheet with a positive electrode active material layer thickness of 100μm. Repeat the above steps on the other surface of the positive electrode current collector aluminum foil to obtain a positive electrode sheet with a positive electrode active material layer coated on both sides. Then, the positive electrode sheet is cut into a specification of 38mm×58mm for standby use.

[0106] (3) Preparation of electrolyte: In a dry argon atmosphere, organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed at a mass ratio of EC:EMC:DEC = 30:50:20. Then, lithium salt lithium hexafluorophosphate (LiPF6) was added to the organic solvent to dissolve and mix well to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0107] (4) Preparation of electrode assembly A: The separator, double-sided coated negative electrode sheet, separator, and double-sided coated positive electrode sheet are stacked in sequence to form a laminate, and then the four corners of the entire laminate structure are fixed for use. Among them, the electrode assembly A includes a positive electrode tab and a negative electrode tab, and the separator is a polyethylene (PE) film with a thickness of 15 μm.

[0108] (5) Preparation of electrode assembly B: The double-sided coated negative electrode sheet, the separator, the double-sided coated positive electrode sheet, and the separator are stacked in sequence to form a laminate, and then the four corners of the entire laminate structure are fixed for use. Among them, electrode assembly B includes a positive electrode tab and a negative electrode tab, and the separator is a polyethylene (PE) film with a thickness of 15 μm.

[0109] (6) Preparation of bipolar current collector: A CuAl composite current collector with a thickness of 30 μm is used as the bipolar current collector. The slurry of the negative electrode active material in step (1) is evenly coated on one surface of the CuAl composite current collector and dried at 110°C to obtain a negative electrode active material layer with a thickness of 150 μm. Then, the slurry of the positive electrode active material in step (2) is evenly coated on the other surface of the CuAl composite current collector and dried at 90°C to obtain a positive electrode active material layer with a thickness of 100 μm. The sealing area of ​​the bipolar current collector contains a sealing material polypropylene (PP), and the thickness of the polypropylene sealing material is 20 μm and the width is 3 mm. The sealing area is not coated with electrode active material.

[0110] (7) Assembly of electrode assembly A: Place the aluminum-plastic film with the holes punched out in an assembly fixture with the holes facing upward, place the electrode assembly A in the holes with the separator side facing upward, and then place the bipolar current collector with the positive electrode active material side facing downward on the electrode assembly A so that the active material coating areas correspond to each other. The positive electrode active material of the bipolar current collector is separated from the active material of the negative electrode plate by the separator, and external force is applied to compact the semi-finished product.

[0111] (8) Assembly of electrode assembly B: Place the semi-finished product in an assembly fixture, with the side of the bipolar current collector provided with the negative electrode active material facing upward, and place the separator side of electrode assembly B facing downward on the bipolar current collector so that the active material coating areas correspond, apply external force to compact, and then cover the aluminum-plastic film formed by punching with the pit side facing downward on electrode assembly B, and heat-seal the surroundings by hot pressing to obtain an assembled electrode assembly. The hot pressing temperature is 185°C, the hot pressing pressure is 0.5MPa, the width of the sealing area is 2mm, and the thickness of the sealing area is 0.03mm.

[0112] (9) Liquid injection packaging: The electrolyte is injected into the two cavities of the assembled electrode assembly separately, and all the tabs of the electrode assemblies A and B are led out of the aluminum-plastic film for subsequent processing.

[0113] (10) Connection of electrode assemblies in series: The positive electrode tab of electrode assembly A and the negative electrode tab of electrode assembly B are connected together by laser welding to achieve series connection between electrode assemblies A and B. The battery assembly is then completed.

[0114] Example 2

[0115] The bipolar current collector is a composite bipolar current collector, that is, a film made by inserting conductive carbon fibers into a PE matrix, and the rest is the same as in Example 1.

[0116] Example 3

[0117] The bipolar current collector is a stainless steel metal foil, and the rest is the same as in Example 1.

[0118] Example 4

[0119] The bipolar current collector is a composite bipolar current collector, which is a thin film made by inserting conductive carbon fibers into a PE matrix, and has a thickness of 6 μm. The rest is the same as in Example 1.

[0120] Example 5

[0121] The bipolar current collector is a composite bipolar current collector, which is a thin film made by inserting conductive carbon fibers into a PE matrix, and has a thickness of 100 μm. The rest is the same as in Example 1.

[0122] Example 6

[0123] The bipolar current collector is a composite bipolar current collector, which is a thin film made by inserting conductive carbon fibers into a PE matrix, with a thickness of 55 μm. The rest is the same as in Example 1.

[0124] Example 7

[0125] Except for leading out a tab on the bipolar current collector, the rest is the same as that of Example 1. The tab is used to detect the voltage of the electrochemical device.

[0126] Example 8

[0127] The bipolar current collector is a composite bipolar current collector, which is a film made by inserting conductive carbon fibers into a PE matrix. The rest is the same as Example 7.

[0128] Example 9

[0129] The bipolar current collector is a stainless steel metal foil, and the rest is the same as Example 7.

[0130] Example 10

[0131] The preparation steps (1) to (4) are the same as those in Example 1.

[0132] (5) Preparation of electrode assembly B: The separator, double-sided coated negative electrode sheet, separator, double-sided coated positive electrode sheet, and separator are stacked in sequence to form a laminate, and then the four corners of the entire laminate structure are fixed for use. Among them, the electrode assembly B includes a positive electrode tab and a negative electrode tab, and the separator is a polyethylene (PE) film with a thickness of 15.

[0133] (6) Preparation of electrode assembly C: Double-sided coated negative electrode sheet, separator, double-sided coated positive electrode sheet, and separator are stacked in sequence to form a laminate, and then the four corners of the entire laminate structure are fixed for use. Among them, electrode assembly C includes a positive electrode tab and a negative electrode tab, and the separator is a polyethylene (PE) film with a thickness of 15.

[0134] (7) Preparation of bipolar current collector I and bipolar current collector II: A composite bipolar current collector is used as the bipolar current collector, which is a film made of conductive carbon fiber inserted into a PE matrix with a thickness of 30 μm. The slurry of the negative electrode active material in step (1) is evenly coated on one surface of the composite bipolar current collector and dried at 110°C to obtain a negative electrode active material layer with a thickness of 150 μm. Then, the slurry of the positive electrode active material in step (2) is evenly coated on the other surface of the composite bipolar current collector and dried at 90°C to obtain a positive electrode active material layer with a thickness of 100 μm. Among them, the bipolar current collector sealing area contains a sealing material polypropylene (PP), and the thickness of the polypropylene sealing material is 20 μm and the width is 3 mm. Among them, the sealing area is not coated with electrode active material.

[0135] (8) Assembly of electrode assembly A: Place the aluminum-plastic film with the holes punched out, with the holes facing upward, and place the electrode assembly A in the holes with the separator side facing upward. Then place the bipolar current collector I with the positive electrode active material side facing downward on the electrode assembly A so that the active material coating areas correspond to each other. Apply external force to compact the semi-finished product.

[0136] (9) Assembly of electrode assembly B: Place the semi-finished assembly in an assembly fixture, with the negative electrode active material side of the bipolar current collector I facing upward, and the separator side of the electrode assembly B close to the positive electrode plate facing downward, and place it on the bipolar current collector I so that the active material coating areas correspond, and apply external force to compact it to obtain the semi-finished assembly 2.

[0137] (10) Assembly of electrode assembly C: Place the semi-finished assembly in an assembly fixture, with the separator side of electrode assembly B close to the negative electrode plate facing upward, and the positive electrode active material side of bipolar current collector II facing downward, and place it on electrode assembly B. Then place electrode assembly C with the separator side facing downward on bipolar current collector II, so that the active material coating areas correspond, apply external force to press tightly, and then place the aluminum-plastic film with cavities formed on electrode assembly C, and heat-seal it around by hot pressing to obtain an assembled electrode assembly. The hot pressing temperature is 185°C, the hot pressing pressure is 0.5MPa, the width of the sealing area is 2mm, and the thickness of the sealing area is 0.03mm.

[0138] (11) Liquid injection packaging: The electrolyte is injected into the three cavities of the assembled electrode assembly separately, and all the tabs of the electrode assemblies A, B, and C are led out of the aluminum-plastic film for subsequent processing.

[0139] (12) Connection of electrode assemblies in series: The positive electrode tab of electrode assembly A and the negative electrode tab of electrode assembly B are connected together by laser welding to realize the series connection between electrode assemblies A and B. The positive electrode tab of electrode assembly B and the negative electrode tab of electrode assembly C are connected together by laser welding to realize the series connection between electrode assemblies B and C. The battery assembly is completed.

[0140] Embodiment 11

[0141] The preparation steps (1) to (4) are the same as those in Example 1.

[0142] (5) Preparation of electrode assembly B: The separator, double-sided coated negative electrode sheet, separator, and double-sided coated positive electrode sheet are stacked in sequence to form a laminate, and then the four corners of the entire laminate structure are fixed for use. Among them, electrode assembly B includes a positive electrode tab and a negative electrode tab, and the separator is a polyethylene (PE) film with a thickness of 15 μm.

[0143] (6) Preparation of bipolar current collector: A composite bipolar current collector is used as the bipolar current collector, which is a film made of conductive carbon fiber inserted into a PE matrix with a thickness of 30 μm. The slurry of the positive electrode active material in step (2) is evenly coated on one surface of the composite bipolar current collector and dried at 90°C to obtain a positive electrode active material layer with a thickness of 100 μm. At the same time, a pole ear is led out from the bipolar current collector for standby use. Among them, the outer contour sealing area of ​​the bipolar current collector contains a sealing material polypropylene (PP), the thickness of the polypropylene is 20 μm, the coating width is 3 mm, and the electrode active material is not coated in the outer contour sealing area.

[0144] (7) Assembly of electrode assembly A: Place the aluminum-plastic film with the holes punched out, with the holes facing upward, and place the electrode assembly A in the holes with the separator side facing upward. Then place the bipolar current collector with the positive electrode active material side facing downward on the electrode assembly A so that the active material coating areas correspond to each other, and apply external force to compact it to obtain the assembled semi-finished product.

[0145] (8) Assembly of electrode assembly B: Place the semi-finished product in an assembly fixture, with the side of the bipolar current collector without electrode active material facing upward, and place the separator side of electrode assembly B facing downward on the bipolar current collector so that it is aligned with the edges of the semi-finished product, apply external force to press tightly, and then cover the aluminum-plastic film with the pitted surface facing downward on electrode assembly B, and heat-seal the surroundings by hot pressing to obtain an assembled electrode assembly. The hot pressing temperature is 185°C, the hot pressing pressure is 0.5MPa, the width of the sealing area is 2mm, and the thickness of the sealing area is 0.03mm.

[0146] (9) Liquid injection packaging: The electrolyte is injected into the two cavities of the assembled electrode assembly separately, and all the tabs of the electrode assemblies A and B and the tabs of the bipolar current collector are led out of the aluminum-plastic film for subsequent processing.

[0147] (10) Connection of electrode assemblies in series: The positive electrode tab of electrode assembly A and the tab of the bipolar current collector are connected together by laser welding, and then the negative electrode tab of electrode assembly B is connected to them by laser welding to achieve series connection between electrode assemblies A and B. The battery assembly is completed.

[0148] Example 12

[0149] The preparation steps (1) to (3) are the same as those in Example 1.

[0150] (4) Preparation of electrode assembly A: The separator, double-sided coated negative electrode plate, separator, and double-sided coated positive electrode plate are stacked in sequence to form a laminate, and then the four corners of the entire laminate structure are fixed for use. Among them, the electrode assembly A includes a positive electrode tab, and the separator is a polyethylene (PE) film with a thickness of 15 μm.

[0151] (5) Preparation of electrode assembly B: The single-sided coated negative electrode sheet, the separator, and the double-sided coated positive electrode sheet are stacked in sequence to form a laminate, and the uncoated negative electrode sheet is placed outward, and then the four corners of the entire laminate structure are fixed for use. Among them, electrode assembly B includes a negative electrode tab, and the separator is a polyethylene (PE) film with a thickness of 15μm.

[0152] (6) Preparation of bipolar current collector: A composite bipolar current collector is used as the bipolar current collector, which is a film made of a PE matrix with conductive carbon fibers inserted therein, with a thickness of 30 μm. The slurry of the positive electrode active material in step (2) is evenly coated on one surface of the composite bipolar current collector and dried at 90°C to obtain a positive electrode active material layer with a thickness of 100 μm. The outer contour sealing area of ​​the bipolar current collector contains a sealing material polypropylene (PP), the thickness of the sealing material polypropylene is 20 μm, the width is 3 mm, and the electrode active material is not coated on the outer contour sealing area.

[0153] (7) Assembly of electrode assembly A: Place the aluminum-plastic film with the holes punched out, with the holes facing upward, and place the electrode assembly A in the holes with the separator side facing upward. Then place the bipolar current collector with the side containing the positive electrode active material facing downward on the electrode assembly A so that the active material coating areas correspond to each other, and apply external force to compact it to obtain the assembled semi-finished product.

[0154] (8) Assembly of electrode assembly B: Place the semi-finished product in the assembly fixture, with the side of the bipolar current collector that does not contain the electrode active material facing upward, and place the uncoated side of the negative electrode sheet of electrode assembly B facing downward on the bipolar current collector so that it is aligned with the edges of the semi-finished product, apply external force to press tightly, and then cover the aluminum-plastic film formed by punching with the pit side facing downward on the electrode assembly B, and heat-seal the surroundings by hot pressing to obtain an assembled electrode assembly. The hot pressing temperature is 185°C, the hot pressing pressure is 0.5MPa, the width of the sealing area is 2mm, and the thickness of the sealing area is 0.03mm.

[0155] (9) Liquid injection packaging: The electrolyte is injected into the two cavities of the assembled electrode assembly separately, and the positive electrode tab of electrode assembly A and the negative electrode tab of electrode assembly B are led out of the aluminum-plastic film for subsequent processing.

[0156] (10) The electrode assemblies are connected in series: The negative electrode tab of electrode assembly B contacts the uncoated surface of the bipolar current collector and forms an electrical connection, thereby realizing the series connection between electrode assemblies A and B. The positive electrode tab of electrode assembly A and the negative electrode tab of electrode assembly B are output tabs, and the battery assembly is completed.

[0157] Example 13

[0158] The preparation steps (1) to (5) are the same as those in Example 1.

[0159] (6) Preparation of bipolar current collector: A composite bipolar current collector is used as the bipolar current collector, that is, a film made of conductive carbon fiber inserted into a PE matrix with a thickness of 30 μm. The slurry of the positive electrode active material in step (2) is evenly coated on one surface of the composite bipolar current collector and dried at 90°C to obtain a positive electrode active material layer with a thickness of 100 μm. At the same time, a pole ear is led out from the bipolar current collector for standby use. Among them, the outer contour sealing area of ​​the bipolar current collector contains a sealing material polypropylene (PP), the thickness of the sealing material polypropylene is 20 μm, the width is 3 mm, and the electrode active material is not coated on the outer contour sealing area.

[0160] (7) Assembly of electrode assembly A: Place the aluminum-plastic film with the holes punched out, with the holes facing upward, and place the electrode assembly A in the holes with the separator side facing upward. Then place the bipolar current collector with the side containing the positive electrode active material facing downward on the electrode assembly A so that the active material coating areas correspond to each other, and apply external force to compact it to obtain the assembled semi-finished product.

[0161] (8) Assembly of electrode assembly B: Place the semi-finished product in an assembly fixture, with the side of the bipolar current collector that does not contain electrode active materials facing upward, and place the uncoated side of the negative electrode sheet of electrode assembly B facing downward on the bipolar current collector so that it is aligned with the edges of the semi-finished product, apply external force to press tightly, and then cover the aluminum-plastic film formed by punching with the pit side facing downward on electrode assembly B, and heat-seal the surroundings by hot pressing to obtain an assembled electrode assembly. The hot pressing temperature is 185°C, the hot pressing pressure is 0.5Mpa, the width of the sealing area is 2mm, and the thickness of the sealing area is 0.03mm.

[0162] (9) Liquid injection packaging: The electrolyte is injected into the two cavities of the assembled electrode assembly separately, and all the tabs of the electrode assemblies A and B are led out of the aluminum-plastic film for subsequent processing.

[0163] (10) Connection of electrode assemblies in series: The negative electrode tab of electrode assembly A and the positive electrode tab of electrode assembly B are connected together by laser welding to realize the series connection between electrode assemblies A and B. The tab of the bipolar current collector is used to monitor the voltage of the electrochemical device. The battery assembly is completed.

[0164] Embodiment 14

[0165] The thickness of the bipolar current collector is 10 μm, and the rest is the same as in Example 1.

[0166] Embodiment 15

[0167] The thickness of the bipolar current collector is 40 μm, and the rest is the same as in Example 1.

[0168] Example 16

[0169] The thickness of the bipolar current collector is 25 μm, and the rest is the same as in Example 1.

[0170] Embodiment 17

[0171] (1) Preparation of negative electrode sheet: The negative electrode sheet was cut into a size of 41 mm×550 mm for later use, and the rest was the same as in Example 1.

[0172] (2) Preparation of positive electrode sheet: The positive electrode sheet was cut into a size of 35 mm×547 mm for later use. The rest of the process was the same as in Example 1.

[0173] (3) Preparation of electrolyte: In a dry argon atmosphere, organic solvents ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) were first mixed at a mass ratio of EC:EMC:DEC = 30:50:20. Then, lithium salt lithium hexafluorophosphate (LiPF6) was added to the organic solvent to dissolve and mix well to obtain an electrolyte with a lithium salt concentration of 1.15 mol / L.

[0174] (4) Preparation of electrode assembly A and electrode assembly B: stack the separator, double-sided coated negative electrode sheet, separator, and double-sided coated positive electrode sheet, and then wind them from one end to finally form a roll core with the negative electrode sheet placed on the outermost side. Each electrode assembly includes a positive electrode tab and a negative electrode tab, and the separator is a polyethylene (PE) film with a thickness of 15 μm.

[0175] (5) Preparation of bipolar current collector: A copper-aluminum composite current collector with a thickness of 30 μm is used as the bipolar current collector. The slurry of the negative electrode active material in step (1) is evenly coated on one surface of the copper-aluminum composite current collector and dried at 110°C to obtain a negative electrode active material layer with a thickness of 150 μm. Then, the slurry of the positive electrode active material in step (2) is evenly coated on the other surface of the copper-aluminum composite current collector and dried at 90°C to obtain a positive electrode active material layer with a thickness of 100 μm. The sealing area of ​​the bipolar current collector contains a sealing material polypropylene (PP), and the thickness of the sealing material polypropylene is 20 μm and the width is 3 mm. The sealing area is not coated with electrode active material.

[0176] (6) Assembly of electrode assembly A: Place the aluminum-plastic film with holes punched and formed into it in an assembly fixture with the holes facing upward, and place the electrode assembly A in the holes. Then, place the bipolar current collector with the side containing the positive electrode active material facing downward on the electrode assembly A so that the active material coating areas correspond to each other, and apply external force to compact it to obtain an assembled semi-finished product.

[0177] (7) Assembly of electrode assembly B: Place the semi-finished assembly in an assembly fixture, with the side of the bipolar current collector containing the negative electrode active material facing upwards, place electrode assembly B on the bipolar current collector, and the separator of electrode assembly B close to the positive electrode sheet is adjacent to the bipolar current collector, so that the active material coating area corresponds, apply external force to press, and then cover the aluminum-plastic film with the pitted surface facing downwards on electrode assembly B, and heat-seal all around by hot pressing to obtain an assembled electrode assembly. The hot pressing temperature is 185°C, the hot pressing pressure is 0.5MPa, the width of the sealing area is 2mm, and the thickness of the sealing area is 0.03mm.

[0178] (8) Liquid injection packaging: The electrolyte is injected into the two cavities of the assembled electrode assembly separately, and all the tabs of the electrode assemblies A and B are led out of the aluminum-plastic film for subsequent processing.

[0179] (9) Connection of electrode assemblies in series: The positive electrode tab of electrode assembly A and the negative electrode tab of electrode assembly B are connected together by laser welding to achieve series connection between electrode assemblies A and B. The battery assembly is then completed.

[0180] Comparative Example 1

[0181] The bipolar current collector is replaced with a separator, which adopts a composite PP structure, including two surface layers and one middle layer, the surface layer has a melting point of 140°C, the middle is an ion insulating layer, the melting point is 165°C, and the thickness of the separator is 50 μm. The rest is the same as Example 1.

[0182] Comparative Example 2

[0183] The preparation steps (1) to (3) are the same as those in Example 1.

[0184] (4) Preparation of electrode assembly A and electrode assembly B: Double-sided coated negative electrode sheet, separator, and double-sided coated positive electrode sheet are stacked in sequence to form a laminate, and then the four corners of the entire laminate structure are fixed for use. Each electrode assembly includes a positive electrode tab and a negative electrode tab. Among them, the separator uses a polyethylene (PE) film with a thickness of 15 μm.

[0185] (5) Liquid injection packaging: The electrode assemblies A and B are packaged with aluminum foil respectively, and then the packages are sealed on all sides. The electrolyte is injected into the sealed cavities where the electrode assemblies A and B are located, and they are charged (charged to 3.3V at a constant current of 0.02C, and then charged to 3.6V at a constant current of 0.1C). All the tabs of the electrode assemblies A and B are then led out of the aluminum-plastic film.

[0186] (6) Series connection: stack electrode assembly A and electrode assembly B in the thickness direction, and weld the positive electrode tab of electrode assembly A and the negative electrode tab of electrode assembly B together by laser welding to achieve series conduction. Then, pack the main body of the electrode assembly together with the outer shell, and the battery assembly is completed.

[0187] The data and test results of each embodiment and comparative example are shown in Table 1.

[0188] Table 1

[0189] Note: The electrode assembly A tailing structure and the electrode assembly B tailing structure refer to the structures of electrode assembly A and electrode assembly B adjacent to the bipolar current collector, respectively.

[0190] It can be seen from the above examples that the use of bipolar current collectors can increase the energy density by about 2% compared to insulating separators. Therefore, the use of bipolar current collectors as separators between series-connected electrode assemblies not only improves the output voltage and reduces the charging temperature rise, but also increases the current density of the battery, which has very good industrial applicability. When using metal bipolar current collectors, the battery charging temperature rise is small, which should be due to the metal bipolar current collector's ability to conduct heat to the outer packaging.

[0191] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An electrochemical device, comprising a bipolar current collector, the bipolar current collector is sealed and connected to an outer package to form a sealing area, the seal thickness T and the seal width W of the sealing area satisfy 0.01≤T / W≤0.05, and separate cavities are formed on both sides of the bipolar current collector, each cavity encapsulates an electrode assembly and an electrolyte, at least one surface of the bipolar current collector is provided with an electrode active material, and the electrode assemblies in adjacent cavities are connected in series; in, The first surface of the bipolar current collector is provided with an electrode active material, the polarity of the electrode active material is opposite to the polarity of the outermost electrode plate of the adjacent electrode assembly, and a separator is provided between the outermost electrode plate and the bipolar current collector; the second surface of the bipolar current collector is not provided with an electrode active material, and a separator is provided between the second surface of the bipolar current collector and the adjacent electrode assembly; the bipolar current collector is provided with a pole ear, and the pole ear is connected in parallel with the pole ear of the same polarity in the electrode assembly adjacent to the first surface; or, An electrode active material is provided on the first surface of the bipolar current collector, and the polarity of the electrode active material is opposite to the polarity of the outermost electrode plate of the adjacent electrode assembly, and a separator is provided between the outermost electrode plate and the bipolar current collector; the second surface of the bipolar current collector is electrically connected to the current collector of the outermost electrode plate of the adjacent electrode assembly, and the polarity of the outermost electrode plate of the electrode assembly adjacent to the second surface is opposite to the polarity of the electrode active material on the first surface; a pole ear is provided on the bipolar current collector, and the pole ear is connected in parallel with the pole ears of the same polarity in the electrode assembly adjacent to the first surface.

2. An electrochemical device, comprising a bipolar current collector, the bipolar current collector is sealed and connected to an outer package to form a sealing area, the seal thickness T and the seal width W of the sealing area satisfy 0.01≤T / W≤0.05, and separate cavities are formed on both sides of the bipolar current collector, each cavity encapsulates an electrode assembly and an electrolyte, an electrode active material is provided on at least one surface of the bipolar current collector, and the electrode assemblies in adjacent cavities are connected in series; The two surfaces of the bipolar current collector are respectively provided with electrode active materials of different polarities, the outermost electrode sheet of the electrode assembly adjacent to each surface has a different polarity from the electrode active material on the surface, and a separator is provided between the outermost electrode sheet of the electrode assembly and the bipolar current collector; The bipolar current collector is provided with pole ears for monitoring the operating status of the electrode assemblies on both sides thereof.

3. An electrochemical device, comprising a bipolar current collector, the bipolar current collector is sealed and connected to an outer package to form a sealing area, the seal thickness T and the seal width W of the sealing area satisfy 0.01≤T / W≤0.05, and separate cavities are formed on both sides of the bipolar current collector, each cavity encapsulates an electrode assembly and an electrolyte, an electrode active material is provided on at least one surface of the bipolar current collector, and the electrode assemblies in adjacent cavities are connected in series; The two surfaces of the bipolar current collector are respectively provided with electrode active materials of different polarities, the outermost electrode sheet of the electrode assembly adjacent to each surface has a different polarity from the electrode active material on the surface, and a separator is provided between the outermost electrode sheet of the electrode assembly and the bipolar current collector; Each of the electrode assemblies is provided with two electrode tabs of opposite polarity, wherein one electrode tab is connected in series with the electrode tab of opposite polarity of an adjacent electrode assembly; The bipolar current collector is also provided with a tab, and the tab is connected to the tabs that connect the electrode assemblies on both sides of the bipolar current collector in series.

4. The electrochemical device according to claim 1, wherein The bipolar current collector is selected from a metal bipolar current collector or a composite bipolar current collector.

5. The electrochemical device according to claim 4, wherein: The metal bipolar current collector includes any one of stainless steel, Ni, Ti, Ag, Au, and Pt bipolar current collectors, and the composite bipolar current collector includes any one of copper-aluminum composite current collectors and polymer-metal composite current collectors.

6. The electrochemical device according to claim 1, wherein The bipolar current collector has a thickness of 6 to 100 μm.

7. The electrochemical device according to claim 1, wherein: The electrode active material includes a positive electrode active material or a negative electrode active material, the positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium cobalt oxide, lithium manganese oxide, lithium iron manganese phosphate or lithium titanate, and the negative electrode active material includes at least one of artificial graphite, natural graphite, mesophase carbon microbeads, soft carbon, hard carbon, silicon, silicon carbon and lithium titanate.

8. The electrochemical device according to claim 1, wherein The bipolar current collector also includes a sealing area, which is located at the edges of the bipolar current collector. The sealing area contains a sealing material, and the sealing material includes at least one of polypropylene, anhydride-modified polypropylene, polyethylene, ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ethylene-acrylic acid copolymer, ethylene-vinyl alcohol copolymer, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyamide, polyester, amorphous α-olefin copolymer and its derivatives.

9. The electrochemical device according to claim 1, wherein: The electrolyte includes one of a gel state, a solid state and a liquid state.

10. The electrochemical device according to claim 1, wherein The cavity is a sealed cavity.

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

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