WO2023164914A1

WO2023164914A1 - Electrochemical device and electronic device

Info

Publication number: WO2023164914A1
Application number: PCT/CN2022/079189
Authority: WO
Inventors: 郝慧; 刘道林; 何平
Original assignee: 宁德新能源科技有限公司
Priority date: 2022-03-04
Filing date: 2022-03-04
Publication date: 2023-09-07
Also published as: CN116830341A

Abstract

An electrochemical device, comprising a casing and a first electrode assembly and a second electrode assembly that are disposed in the casing. The first electrode assembly and the second electrode assembly are in series connection, and satisfy the following relationship: formula (I), wherein C1 represents the capacity of the first electrode assembly, and C2 represents the capacity of the second electrode assembly. An electronic device, comprising an electrochemical device.

Description

Electrochemical devices and electronic devices

technical field

The present application relates to the field of energy storage, in particular to an electrochemical device and an electronic device.

Background technique

In the existing lithium-ion battery system, due to the limited voltage difference between the positive electrode material and the negative electrode material, and the limited anti-oxidation and reduction ability of the electrolyte, it is difficult for the open circuit voltage of the battery to exceed 5V. However, in the actual use of the battery, there are many scenarios that require a voltage exceeding 5V, such as electric vehicles, electric tools, and energy storage systems. Even in the mobile phone market, in order to meet the needs of fast charging, it is necessary to increase the open circuit voltage of the battery. At present, the method of connecting multiple lithium-ion batteries in series is generally used to increase the output voltage, but there are many problems in series connection of multiple lithium-ion batteries, such as: the wires and contact resistances used in series introduce additional electronic resistance, resulting in waste of heat and affecting battery life. ; The higher the voltage, the more lithium-ion batteries are needed, 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 electrode assemblies to achieve high voltage output of a single battery, reduces the total heat production of the battery, and reduces the temperature rise during use. However, due to the inherent defects of the series connection of high output voltage batteries, the premature degradation of one of the electrode components will lead to a sharp decline in the cycle performance of the high output voltage battery as a whole. Therefore, the cycle performance of high output voltage batteries needs to be further improved.

Contents of the invention

In view of the above-mentioned problems in the prior art, the present application provides an electrochemical device and an electronic device including the electrochemical device, so as to improve the cycle performance of the internal series-connected electrochemical devices.

In a first aspect, the present application provides an electrochemical device, which includes a casing and a first electrode assembly and a second electrode assembly disposed in the casing, the first electrode assembly and the second electrode assembly are connected in series, and satisfy The following relational formula:

Wherein, C1 represents the capacity of the first electrode assembly, and C2 represents the capacity of the second electrode assembly.

The inventors of the present application have found through research that: the capacity difference between individual electrode assemblies, on the one hand, has an important impact on the cycle performance of the internal series high output voltage battery, through the capacity C1 of the first electrode assembly and the capacity of the second electrode assembly C2 satisfies the above relational expression. During the series charge and discharge process, the potential levels between the first electrode assembly and the second electrode assembly can tend to be consistent, reducing the risk of overcharging and/or overdischarging of one of the electrode assemblies, thereby Inhibit the premature deterioration of one of the electrode components and improve the cycle performance of the internal series high output voltage battery; on the other hand, the capacity difference between individual electrode components also affects the actual performance of the internal series high output voltage battery. Capacity level, through the capacity C1 of the first electrode assembly and the capacity C2 of the second electrode assembly satisfying the above relationship, in the process of series discharge, the capacities of the first electrode assembly and the second electrode assembly can be effectively exerted, which is conducive to improving Energy density of electrochemical devices.

According to some embodiments of the present application, the first electrode assembly includes a first negative electrode sheet and a first positive electrode sheet, and the first negative electrode sheet includes a first negative electrode current collector and a first negative electrode current collector on the surface of the first negative electrode current collector. A negative electrode active material layer, the first positive electrode sheet includes a first positive electrode current collector and a first positive electrode active material layer positioned on the surface of the first positive electrode current collector, the area of the first positive electrode active material layer is Sc1, The area of the first negative electrode active material layer is Sa1, the first positive pole piece with a test area of Stc1 is taken, and lithium metal is used as a counter electrode to assemble a button-type half-cell, and the test area is the capacity of the first positive pole piece of Stc1 is Ctc1; get the first negative pole piece that test area is Sta1, take lithium metal as counter electrode and assemble into button type half cell, the capacity of the first negative pole piece that test area is Sta1 is Cta1; CB1=(Cta1×Sa1/ Sta1)/(Ctc1×Sc1/Stc1).

The second electrode assembly includes a second negative pole piece and a second positive pole piece, the second negative pole piece includes a second negative current collector and a second negative active material layer positioned on the surface of the second negative current collector, the second positive pole The sheet includes a second positive electrode current collector and a second positive electrode active material layer positioned on the surface of the second positive electrode current collector, the area of the second positive electrode active material layer is Sc2, the area of the second negative electrode active material layer is Sa2, and the test area is Stc2 The second positive pole piece is assembled into a button-type half-cell with lithium metal as the counter electrode, and the capacity of the second positive pole piece whose test area is Stc2 is Ctc2; the second negative pole piece whose test area is Sta2 is To assemble the electrode into a button-type half-cell, the capacity of the second negative pole sheet whose test area is Sta2 is Cta2; CB2=(Cta2*Sa2/Sta2)/(Ctc2*Sc2/Stc2).

Wherein, the first electrode assembly and the second electrode assembly also satisfy the following relationship:

By satisfying the above relationship between CB1 and CB2, the first electrode assembly and the second electrode assembly form a solid electrolyte interface film in the formation stage, and the lithium content consumed in the positive electrode piece matches, which can reduce the subsequent series charging. During the discharge process, the risk of excessively high potential of the positive pole piece in a certain electrode assembly inhibits the destruction of the positive active material in the positive pole piece and the solid electrolyte interfacial film structure, thereby improving the cycle performance of the internal series high output voltage battery.

According to some embodiments of the present application, the first electrode assembly and the second electrode assembly also satisfy the following relationship:

Among them, W1 represents the coating weight of the first negative electrode active material layer, the unit is mg/1540.25mm ² ; W2 represents the coating weight of the second negative electrode active material layer, the unit is mg/1540.25mm ² , CB1 and CB2 are as above definition. By W1, W2, CB1 and CB2 satisfying the above relationship, the reversible capacity corresponding to the negative electrode active material layer of the same area in the first electrode assembly and the second electrode assembly can be matched, and the adaptability of each electrode assembly to the charge and discharge rate can be made It is relatively consistent, thereby further improving the cycle performance of the internal series high output voltage battery.

According to some embodiments of the present application, the first electrode assembly and the second electrode assembly satisfy the following relationship:

Wherein, W1 represents the coating weight of the first negative electrode active material layer, the unit is mg/1540.25mm ² ; W2 represents the coating weight of the second negative electrode active material layer, the unit is mg/1540.25mm ² ; CB1 and CB2 are as above definition.

According to some embodiments of the present application, the electrochemical device satisfies at least one of the following conditions (i) and (ii): (i) the value range of CB1 is 0.7 to 1.1; (ii) the value range of CB2 0.7 to 1.1. The value range of CB1 and/or CB2 is within the above range, and the capacity of the positive and negative electrodes in the first electrode assembly and/or the second electrode assembly is relatively matched. On the one hand, it can reduce the positive electrode activity caused by the high potential of the positive electrode during the charge and discharge process. The risk of damage to the material structure can improve the cycle performance of the battery; on the other hand, it can also reduce the risk of lithium deposition on the negative electrode during charging and discharging, and improve the safety performance of the battery.

According to some embodiments of the present application, the electrochemical device satisfies at least one of the following conditions (iii) and (iv): (iii) the value range of W1 is 100mg/1540.25mm ² to 200mg/1540.25mm ² ; (iv) The value range of W2 is 100mg/1540.25mm ² to 200mg/1540.25mm ² .

According to some embodiments of the present application, the electrochemical device further includes a separator located between the first electrode assembly and the second electrode assembly.

According to some embodiments of the present application, the spacer includes a substrate layer and an encapsulation layer located on the surface of the substrate layer, and the material of the substrate layer includes at least one of metal, carbon material or first polymer; the material of the encapsulation layer includes second polymer.

According to some embodiments of the present application, the metal used as the material of the substrate layer includes Ni, Ti, Cu, Ag, Au, Pt, Fe, Co, Cr, W, Mo, Al, Mg, K, Na, Ca, Sr, At least one of Ba, Si, Ge, Sb, Pb, In, Zn, stainless steel, and combinations or alloys thereof.

According to some embodiments of the present application, the carbon material used as the material of the substrate layer includes at least one of carbon felt, carbon film, carbon black, acetylene black, fullerene, conductive graphite film or graphene film.

According to some embodiments of the present application, the first polymer used as the material of the substrate layer includes polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyether Etherketone, polyimide, polyamide, polyethylene glycol, polyamideimide, polycarbonate, cyclic polyolefin, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene Naphthalene, polyvinylidene fluoride, polypropylene carbonate, poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-chlorotrifluoroethylene), silicone, vinylon, polypropylene, Anhydride-modified polypropylene, polyethylene, ethylene-propylene copolymer, polyvinyl chloride, polystyrene, polyethernitrile, polyurethane, polyphenylene ether, polyester, polysulfone, amorphous alpha-olefin copolymer, or the above at least one of the derivatives.

According to some embodiments of the present application, the second polymer used as the material of the encapsulation layer includes: polypropylene, anhydride-modified polypropylene, polyethylene, ethylene-propylene copolymer, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane , polyamide, polyester, amorphous α-olefin copolymer or at least one of the derivatives of the above substances.

In a second aspect, the present application provides an electronic device, which includes the electrochemical device described in the first aspect of the present application.

The present application limits the capacity, CB value, coating weight W and the relationship between each electrode assembly in the internal series electrochemical device, which can significantly improve the cycle performance of the internal series electrochemical device.

Description of drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Apparently, the drawings in the following description are only some embodiments of the present application.

Figure 1 is a schematic diagram of an electrochemical device according to some embodiments of the present application.

The reference signs are as follows:

001: Electrochemical device

11: Electrode assembly A

12: Electrode assembly B

20: Isolation piece

41: upper packaging shell

42: the lower packaging shell.

Detailed ways

The present application will be further elaborated below in combination with specific embodiments. It should be understood that these specific implementations are only used to illustrate the present application, not to limit the present application.

The present application provides an electrochemical device, which includes a casing and a first electrode assembly and a second electrode assembly disposed in the casing, the first electrode assembly and the second electrode assembly are connected in series, and satisfy the following relationship:

The inventors of the present application have found through research that: the capacity difference between individual electrode assemblies has an important impact on the cycle performance of the internal series high output voltage battery, by making the capacity C1 of the first electrode assembly and the capacity C2 of the second electrode assembly satisfy According to the above relationship, during the series charge and discharge process, the potential levels between the first electrode assembly and the second electrode assembly can tend to be consistent, reducing the risk of overcharging and/or overdischarging of one of the electrode assemblies, thereby inhibiting the Premature degradation of a certain electrode assembly can not only improve the cycle performance of the internal series high output voltage battery, but also reduce the expansion rate of the internal series high output voltage battery. In some embodiments,

9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.25%. In some embodiments,

The range of value is 0.01% to 9.5%, specifically, it can be 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.25%.

According to some embodiments of the present application, the first electrode assembly includes a first negative pole piece and a first positive pole piece. The first negative pole piece includes a first negative current collector and a first negative active material layer positioned on the surface of the first negative current collector, and the first positive pole piece includes a first positive current collector and a first negative active material layer positioned on the surface of the first positive current collector. A positive electrode active material layer. The area of the first positive electrode active material layer is Sc1, the area of the first negative electrode active material layer is Sa1, and the first positive pole piece with the test area of Stc1 is taken, and the lithium metal is assembled into a button-type half-cell as the counter electrode, and the test area is The capacity of the first positive pole piece of Stc1 is Ctc1; take the first negative pole piece with the test area of Sta1, and use lithium metal as the counter electrode to assemble into a button-type half-cell, and the capacity of the first negative pole piece with the test area of Sta1 is Cta1; CB1=(Cta1*Sa1/Sta1)/(Ctc1*Sc1/Stc1).

According to some embodiments of the present application, the second electrode assembly includes a second negative pole piece and a second positive pole piece, and the second negative pole piece includes a second negative current collector and a second negative active material on the surface of the second negative current collector The second positive electrode sheet includes a second positive electrode current collector and a second positive electrode active material layer on the surface of the second positive electrode current collector. The area of the second positive electrode active material layer is Sc2, and the area of the second negative electrode active material layer is Sa2, get the second positive electrode sheet that test area is Stc2, take lithium metal as counter electrode and assemble into button type half cell, test area is The capacity of the second positive pole piece of Stc2 is Ctc2; Get the second negative pole piece that test area is Sta2, take lithium metal as counter electrode and assemble into button type half cell, the capacity of the second negative pole piece that test area is Sta2 is Cta2; CB2=(Cta2*Sa2/Sta2)/(Ctc2*Sc2/Stc2).

In some embodiments,

12%, 10%, 9.5%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.25%. In some embodiments,

The range of value is 0.01% to 10%, specifically, it can be 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.25%.

In some embodiments,

16%, 14%, 12%, 10%, 9.5%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.25%. In some embodiments,

Wherein, W1 represents the coating weight of the first negative electrode active material layer, the unit is mg/1540.25mm ² ; W2 represents the coating weight of the second negative electrode active material layer, the unit is mg/1540.25mm ² ; CB1 and CB2 are as above definition. In some embodiments,

16%, 14%, 12%, 10%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, or 0.25%. In some embodiments,

The value range is 0.01% to 8%, specifically, it can be 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% or 0.25%.

According to some embodiments of the present application, the electrochemical device satisfies at least one of the following conditions (i) and (ii): (i) the value range of CB1 is 0.7 to 1.1, specifically 0.7, 0.75, 0.8 , 0.85, 0.9, 0.95, 1.0, 1.05 or 1.1; (ii) The value range of CB2 is 0.7 to 1.1, specifically 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.05 or 1.1. The value range of CB1 and/or CB2 is within the above range, and the capacity of the positive and negative electrodes in the first electrode assembly and/or the second electrode assembly is relatively matched. On the one hand, it can reduce the positive electrode activity caused by the high potential of the positive electrode during the charge and discharge process. The risk of damage to the material structure can improve the cycle performance of the battery; on the other hand, it can also reduce the risk of lithium deposition on the negative electrode during charging and discharging, and improve the safety performance of the battery.

According to some embodiments of the present application, the spacer includes a substrate layer and an encapsulation layer located on the surface of the substrate layer, and the material of the substrate layer includes at least one of metal, carbon material or first polymer; the material of the encapsulation layer includes second polymer. In some embodiments of the present application, the encapsulation layer can be disposed on both sides of the ion insulating layer, the encapsulation layer is disposed on the peripheral edge of the surface of the ion insulating layer or on the entire surface thereof, and the encapsulation layer is used to insulate the ion The layers are hermetically connected to the housing.

In some embodiments of the present application, the structures of the first electrode assembly and the second electrode assembly include at least one of a wound structure and a laminated structure.

In this application, the connection is made through the tabs provided on the first electrode assembly and the tabs provided on the second electrode assembly. There is no particular limitation on the connection method of the two tabs, as long as the purpose of this application can be achieved. For example, solder connections. There is no particular limitation on the manner of the above welding connection, as long as the purpose of the present application can be achieved. For example, laser welding, ultrasonic welding or resistance welding, etc. The tab mentioned in this application refers to the metal conductor drawn out from the positive pole piece or the negative pole piece. The positive pole lug is drawn from the positive pole piece, and the negative pole lug is drawn from the negative pole piece.

In the present application, the thicknesses of the first and second electrode assemblies are not particularly limited, as long as the purpose of the present application can be achieved.

In some embodiments of the present application, the first positive electrode piece and the second positive electrode piece are not particularly limited, as long as the purpose of the present application can be achieved. For example, the first positive pole piece and the second positive pole piece generally include a positive current collector and a positive active material. In the present application, the positive current collector is not particularly limited, and may be any positive current collector known in the art, such as copper foil, aluminum foil, aluminum alloy foil, composite current collector, and the like. The positive electrode active material is not particularly limited, and can be any positive electrode active material in the prior art. For example, the positive electrode active material includes nickel-cobalt lithium manganate, nickel-cobalt lithium aluminate, lithium iron phosphate, lithium cobaltate, manganic acid At least one of lithium or lithium manganese iron phosphate. In the present application, the thicknesses of the positive electrode current collector and the positive electrode active material layer are not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness of the positive electrode current collector is 8 μm to 12 μm, and the thickness of the positive electrode active material layer is 30 μm to 120 μm.

In some preferred embodiments of the present application, the first positive electrode sheet and the second 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 commonly used conductive layer in the field. The conductive layer includes a conductive agent and an adhesive.

In some embodiments of the present application, the first negative pole piece and the second negative pole piece are not particularly limited, as long as the purpose of the present application can be achieved. For example, the first negative electrode sheet and the second negative electrode sheet generally include 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 collectors. The negative active material is not particularly limited, and any negative active material known in the art can be used. For example, at least one of graphite, mesocarbon microspheres, silicon, silicon carbon, silicon oxide, soft carbon, hard carbon, lithium titanate, or niobium titanate may be included. In the present application, the thickness of the negative electrode current collector and the negative electrode active material layer 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 μm to 10 μm, and the thickness of the negative electrode active material is 30 μm to 120 μm.

In some preferred embodiments of the present application, the first negative electrode sheet and the second negative electrode sheet 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 commonly used conductive layer in the field. The conductive layer includes a conductive agent and an adhesive.

The conductive agent mentioned 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 may include at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, or graphene, among others. The above-mentioned adhesive 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 may include polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), polytetrafluoroethylene (PTFE), or sodium carboxymethylcellulose (CMC-Na), etc. at least one of the

In some embodiments of the present application, the separator is not particularly limited, as long as the purpose of the present application can be achieved. For example, the thickness of the separator may be 5 μm to 15 μm, and the separator may include a polymer or an inorganic substance formed of a material stable to the electrolyte of the present application, or the like. In the present application, the separator may also be referred to as a separator.

For example, a separator may include a substrate layer and a surface treatment layer. The substrate layer can be a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer can include at least one of polyethylene, polypropylene, polyethylene terephthalate and polyimide . Optionally, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite film may be used. Optionally, at least one surface of the substrate layer is provided with a surface treatment layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic material.

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 aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium oxide, nickel oxide , zinc oxide, calcium oxide, zirconia, 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 polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinyl pyrene One or a combination of rolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer comprises a polymer, and the polymer material includes polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly( at least one of vinylidene fluoride-hexafluoropropylene).

According to an embodiment of the present application, the electrochemical device further includes an electrolytic solution. The electrolytic solution mentioned in this 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, lithium salts may include LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiClO ₄ , LiB(C ₆ H ₅ ) ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN(SO ₂ CF ₃ ) ₂ , LiC(SO ₂ At least one of CF ₃ ) 3 or LiPO ₂ F ₂ . For example, LiPF ₆ may 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 nonaqueous solvent may include at least one of carbonate compounds, carboxylate compounds, ether compounds, nitrile compounds, and other organic solvents.

For example, the carbonate compound may include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), methyl ethyl carbonate Carbonate (MEC), Ethylene Carbonate (EC), Propylene Carbonate (PC), Butylene Carbonate (BC), Vinyl Ethylene Carbonate (VEC), Fluoroethylene Carbonate (FEC), Carbonic Acid 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- At least one of 2-methylethylene carbonate and trifluoromethylethylene carbonate.

The present application has no special limitation on the casing, as long as the purpose of the present application can be achieved. The casing includes at least one of an aluminum-plastic film, an aluminum shell, a steel shell, and a plastic shell. For example, the housing can include an inner layer and an outer layer, and the inner layer is sealed and connected with the separator, so the material of the inner layer can include a polymer material to achieve a good sealing effect; at the same time, the combination of the inner layer and the outer layer can effectively protect Internal structure of an electrochemical device. In the present application, the material of the inner layer is not particularly limited, as long as the purpose of the application can be achieved, for example, the material of the inner layer includes polypropylene, polyester, p-hydroxybenzaldehyde, polyamide, polyphenylene ether, polyurethane at least one of these. In the present application, the material of the outer layer is not particularly limited, as long as the purpose of the 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 and the like.

In this application, there is no special limitation on the thickness of the casing, as long as the purpose of this application can be achieved. For example, the casing has a thickness of 60 μm to 500 μm, preferably 60 μm to 300 μm, more preferably 60 μm to 200 μm, and the above thickness of the casing can effectively protect the internal structure of the electrochemical device.

The present application has no special limitation on the sealing connection method between the spacer and the housing, 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 this application, the hot-pressing conditions are not particularly limited, as long as the purpose of this application can be achieved, for example, for the polypropylene inner layer material, the hot-pressing temperature is 150°C to 220°C, and the hot-pressing pressure is 0.1Mpa to 0.6 MPa.

In some embodiments of the present application, the structure of the electrode assembly is a wound structure, and the electrode assembly includes a single tab or multiple tabs. The electrode assembly includes a monopole lug, and a positive pole lug and a negative pole lug are led out from the positive pole piece and the negative pole piece respectively. The electrode assembly includes multiple tabs, one positive tab and one negative tab can be drawn from each circle of positive pole pieces and negative pole pieces, or two or more circles of positive pole pieces and negative pole pieces can be drawn out. One positive pole tab and one negative pole tab are led out respectively, and finally an electrode assembly with a winding structure includes multiple sets of positive pole tabs and negative pole tabs, and then the tab leads are transferred through transfer welding.

In some embodiments of the present application, the structure of the electrode assembly is a stacked sheet structure, and the electrode assembly includes multiple tabs, which may be a positive tab and a negative tab respectively drawn from each layer of positive pole pieces and negative pole pieces. Ears, the final electrode assembly of a laminated structure includes multiple sets of positive and negative pole tabs, and then the tab leads are transferred through transfer welding.

The electrochemical device provided in the present application may contain two electrode assemblies, or may contain 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 electrochemical device. Electrochemical devices comprising three or more electrode assemblies are also within the scope of protection defined by the claims of the present application.

The present application also provides an electronic device, which includes the electrochemical device provided in the present application. The electronic device in this application is not particularly limited, and it may be any electronic device known in the prior art. Examples of electronic devices include, but are not limited to, notebook computers, pen-based computers, mobile computers, e-book players, cellular phones, portable fax machines, portable copiers, portable printers, headsets, VCRs, LCD televisions, portable Cleaners, portable CD players, mini discs, transceivers, electronic organizers, calculators, memory cards, portable recorders, radios, backup power supplies, electric motors, automobiles, motorcycles, power-assisted bicycles, bicycles, lighting appliances, toys, game consoles , clocks, electric tools, flashlights, cameras, large household batteries and lithium-ion capacitors, etc.

Test Methods

Coating Weight Test Method:

1. Preparation before the test: Turn on the analytical balance, confirm that the balance is in a balanced state, and adjust to zero.

2. Making samples: cut out the pole piece sample with standard tools (area 1540.25mm ² ), put it on a balance and weigh it, and record it as m1; then clean the active material layer on the pole piece sample, dry it and put it on the balance Weigh the mass on the top, record it as m2,

3. Coating weight calculation:

If the pole piece sample is a pole piece coated with an active material layer on one side, the coating weight = m1-m2;

If the pole piece sample is a pole piece coated with active material layers on both sides, the coating weight=(m1-m2)/2.

CB value test method:

Take a positive pole piece with a test area of Stc, assemble it into a button half-cell with lithium metal as the counter electrode, and test the capacity of the positive pole piece as Ctc; take a negative pole piece with a test area of Sta, and use lithium metal as the counter electrode Assembled into a button-type half-battery, the capacity of the negative pole piece tested is Cta; the total positive pole piece area of the battery is Sa, and the total negative pole piece area is Sc, then, CB=(Cta×Sa/Sta)/(Ctc ×Sc/Stc). Wherein, the voltage test range of the negative pole piece is 2V-0.005V, and the voltage test range of the positive pole piece is 2.5V-4.5V.

500 cycle cycle capacity retention rate and thickness expansion rate test method:

1. At 25±3°C, 2C CC (cross current) charging to 8.4V, CV (constant voltage) charging, the cut-off current is 1.0C, 1.0C CC charging to 8.8V, CV charging, the cut-off current is 0.05C, and finally 1.0C CC discharge to 6.0V, record the discharge capacity of the battery as C'; and use a micrometer to measure the thickness of the battery at this time as h1;

2. According to the charging and discharging steps in step 1, charge and discharge the battery for 500 cycles, record the discharge capacity of the 500th cycle as C"; and measure the thickness of the battery at this time with a micrometer as h2;

3. Calculation of capacity retention rate and thickness expansion rate:

Capacity retention = C”/C’×100%

Thickness expansion rate=(h2-h1)/h1×100%.

Examples and comparative examples

Example 1:

(1) Preparation of the negative pole piece: mix the negative active material 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, and prepare A slurry with a solid content of 70wt%, and stirred evenly. The slurry was uniformly coated on one surface of a negative electrode current collector copper foil with a thickness of 10 μm, and dried at 110° C. to obtain a negative electrode sheet with a coating thickness of 150 μm coated on one side with a negative electrode active material layer. The above steps are repeated on the other surface of the negative electrode sheet to obtain a negative electrode sheet coated with negative electrode active material layers on both sides. Then, the negative electrode sheet was cut into a size of 41 mm×61 mm for use.

(2) Preparation of the positive pole piece: the positive active material lithium cobaltate (LiCoO ₂ ), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were mixed according to the weight ratio of 97.5:1.0:1.5, and N - Using methylpyrrolidone (NMP) as a solvent, prepare a slurry with a solid content of 75 wt%, and stir evenly. The slurry was uniformly coated on one surface of a positive electrode current collector aluminum foil with a thickness of 12 μm, and dried at 90° C. to obtain a positive electrode sheet with a positive electrode active material layer thickness of 100 μm. On the other surface of the positive electrode current collector aluminum foil, the above steps were repeated to obtain a positive electrode sheet coated with a positive electrode active material layer on both sides. Then, cut the positive electrode sheet into a size of 38mm×58mm for use.

(3) Preparation of electrolyte: in a dry argon atmosphere, at first organic solvent ethylene carbonate (EC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC) are mixed with mass ratio EC:EMC:DEC= Mix at 30:50:20, then add lithium salt lithium hexafluorophosphate (LiPF ₆ ) into the organic solvent to dissolve and mix evenly to obtain an electrolyte solution with a lithium salt concentration of 1.15 mol/L.

(4) Preparation of electrode assembly A and electrode assembly B: the separator, the double-sided coated negative electrode sheet, the separator, and the double-sided coated positive electrode sheet are sequentially stacked to form a laminate, and then the four corners of the entire laminate structure are Secure it for later use. Wherein, each electrode assembly includes a positive electrode tab and a negative electrode tab, and a polyethylene (PE) film with a thickness of 15 μm is selected as the separator.

(5) Separator: The overall thickness of the separator is 85 μm, the base material layer is Al, the thickness is 25 μm, the packaging layer on both sides is PP with a melting point of 140 ° C, and the thickness on both sides is 30 μm.

(6) Assembly of electrode assembly A: Place the aluminum-plastic film 1 formed by punching the pit in the assembly jig with the pit face up, place the electrode assembly A in the pit with the diaphragm face up, and then place the separator on the electrode On component A, make the edges aligned, and apply external force to press to obtain the assembled semi-finished product.

(7) Assembly of electrode assembly B: place the assembled semi-finished product in the assembly jig with one side of the separator facing up, place the electrode assembly B diaphragm on the separator so that the edges are aligned, apply external force to compress, and then Cover the electrode assembly B with another punched aluminum-plastic film pit face down, and heat seal around it by hot pressing to obtain an assembled electrode assembly.

(8) Liquid injection encapsulation: separately inject electrolyte solution into the two cavities of the assembled electrode assembly, and lead all the tabs of the electrode assembly A and B out of the aluminum plastic film.

(9) Series connection: The positive electrode tab of the electrode assembly A and the negative electrode tab of the electrode assembly B are welded together by laser welding to realize the series connection, and the battery assembly is completed.

Embodiment 2-23 and comparative example 1

The coating weight and CB value of each electrode assembly in actual production were adjusted, and other conditions were the same as in Example 1.

The test results of Examples 2-23 and Comparative Example 1 are shown in Table 1, wherein,

W1 represents the coating weight of the negative electrode active material layer in the electrode assembly A, and the unit is mg/1540.25mm ² ;

W2 represents the coating weight of the negative electrode active material layer in the electrode assembly B, and the unit is mg/1540.25mm ² ;

CB1 represents the CB value of electrode assembly A;

CB2 represents the CB value of electrode assembly B;

C1 represents the capacity of the electrode assembly A;

C2 represents the capacity of electrode assembly B;

X means

Y means

Z means

Q means

Table 1

It can be seen from the examples and comparative examples in Table 1 that when the two electrode assemblies connected in series internally satisfy the following relationship:

At this time, not only the cycle performance of the battery can be significantly improved, but also the thickness expansion rate of the battery can be significantly reduced.

Further, when satisfying

, the capacity retention rate can reach more than 80%. This is because, through CB1 and CB2 satisfying the above relationship, the first electrode assembly and the second electrode assembly form the solid electrolyte interfacial film in the formation stage, the lithium content consumed in the positive electrode sheet matches, and the lithium content in the positive electrode sheet can be reduced. In the subsequent series charge and discharge process, the risk of the positive electrode sheet potential in a certain electrode assembly being too high can inhibit the destruction of the positive electrode active material in the positive electrode sheet and the solid electrolyte interface film structure, thereby improving the internal series connection of high output voltage batteries. cycle performance.

Furthermore, when the following relationship is satisfied:

, the capacity retention rate can be further improved to more than 85%, and the battery expansion rate can be further reduced to less than 8%; at this time, the reversible capacity corresponding to the same area of the negative electrode active material layer in the first electrode assembly and the second electrode assembly can be Matching can make the adaptability of each electrode assembly to the charge and discharge rate relatively consistent, thereby further improving the cycle performance and safety performance of the internal series high output voltage battery.

Although illustrative embodiments have been shown and described, those skilled in the art should understand that the foregoing embodiments are not to be construed as limitations on the present application, and that changes may be made in the embodiments without departing from the spirit, principle and scope of the application. , substitution and modification.

Claims

An electrochemical device, comprising a casing and a first electrode assembly and a second electrode assembly disposed in the casing, the first electrode assembly and the second electrode assembly are connected in series and satisfy the following relational expression:

Wherein, C1 represents the capacity of the first electrode assembly, and C2 represents the capacity of the second electrode assembly.
The electrochemical device according to claim 1, wherein,

The first electrode assembly includes a first negative pole piece and a first positive pole piece, the first negative pole piece includes a first negative current collector and a first negative active material layer located on the surface of the first negative current collector, The first positive electrode sheet includes a first positive electrode current collector and a first positive electrode active material layer positioned on the surface of the first positive electrode current collector, the area of the first positive electrode active material layer is Sc1, and the first negative electrode is active The area of the material layer is Sa1, the first positive pole piece with a test area of Stc1 is taken, and lithium metal is used as a counter electrode to assemble a button half-cell, and the capacity of the first positive pole piece with a test area of Stc1 is Ctc1 Get the described first negative pole sheet that test area is Sta1, take lithium metal as counter electrode and assemble into button type half cell, the capacity of the described first negative pole sheet that test area is Sta1 is Cta1; CB1=(Cta1× Sa1/Sta1)/(Ctc1×Sc1/Stc1);

The second electrode assembly includes a second negative pole piece and a second positive pole piece, the second negative pole piece includes a second negative current collector and a second negative active material layer located on the surface of the second negative current collector, The second positive electrode sheet includes a second positive electrode current collector and a second positive electrode active material layer positioned on the surface of the second positive electrode current collector, the area of the second positive electrode active material layer is Sc2, and the second negative electrode is active The area of the material layer is Sa2, the second positive pole piece whose test area is Stc2 is taken, and lithium metal is used as a counter electrode to assemble a button half battery, and the capacity of the second positive pole piece whose test area is Stc2 is Ctc2 Get the described second negative pole sheet that test area is Sta2, take lithium metal as counter electrode and assemble into button type half cell, the capacity of the described second negative pole sheet that test area is Sta2 is Cta2; CB2=(Cta2× Sa2/Sta2)/(Ctc2×Sc2/Stc2);

The first electrode assembly and the second electrode assembly satisfy the following relationship:
The electrochemical device according to claim 2, wherein the first electrode assembly and the second electrode assembly satisfy the following relational expression:

Wherein, W1 represents the coating weight of the first negative electrode active material layer, and the unit is mg/1540.25mm 2 ; W2 represents the coating weight of the second negative electrode active material layer, and the unit is mg/1540.25mm 2 .
The electrochemical device according to claim 2, wherein the first electrode assembly and the second electrode assembly satisfy the following relationship:

Wherein, W1 represents the coating weight of the first negative electrode active material layer, and the unit is mg/1540.25mm 2 ; W2 represents the coating weight of the second negative electrode active material layer, and the unit is mg/1540.25mm 2 .
The electrochemical device according to claim 1, wherein the electrochemical device satisfies at least one of the following conditions (i) and (ii):

(i) The value range of CB1 is 0.7 to 1.1;

(ii) The value range of CB2 is from 0.7 to 1.1.
The electrochemical device according to claim 3, wherein the electrochemical device satisfies at least one of the following conditions (iii) and (iv):

(iii) The value range of W1 is 100mg/1540.25mm 2 to 200mg/1540.25mm 2 ;

(iv) The value range of W2 is 100mg/1540.25mm 2 to 200mg/1540.25mm 2 .
The electrochemical device according to any one of claims 1-6, wherein the electrochemical device further comprises a separator located between the first electrode assembly and the second electrode assembly.
The electrochemical device according to claim 7, wherein the separator comprises a base material layer and an encapsulation layer located on the surface of the base material layer, and the material of the base material layer comprises metal, carbon material or a first polymer At least one of them; the material of the encapsulation layer includes the second polymer.
The electrochemical device according to claim 8, wherein,

The metals include Ni, Ti, Cu, Ag, Au, Pt, Fe, Co, Cr, W, Mo, Al, Mg, K, Na, Ca, Sr, Ba, Si, Ge, Sb, Pb, In, At least one of Zn, stainless steel, and combinations or alloys thereof;

The carbon material includes at least one of carbon felt, carbon film, carbon black, acetylene black, fullerene, conductive graphite film or graphene film;

The first polymer includes polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polyether ether ketone, polyimide, polyamide, poly Ethylene glycol, polyamideimide, polycarbonate, cyclic polyolefin, polyphenylene sulfide, polyvinyl acetate, polytetrafluoroethylene, polymethylene naphthalene, polyvinylidene fluoride, polypropylene carbonate Ester, poly(vinylidene fluoride-hexafluoropropylene), poly(vinylidene fluoride-co-chlorotrifluoroethylene), silicone, vinylon, polypropylene, anhydride-modified polypropylene, polyethylene, ethylene-propylene Copolymer, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyphenylene ether, polyester, polysulfone, amorphous α-olefin copolymer or at least one of the above derivatives;

The second polymer includes: polypropylene, anhydride-modified polypropylene, polyethylene, ethylene-propylene copolymer, polyvinyl chloride, polystyrene, polyether nitrile, polyurethane, polyamide, polyester, amorphous alpha - Olefin copolymers or at least one of the above derivatives.
An electronic device comprising the electrochemical device according to any one of claims 1-9.