CN113544881A

CN113544881A - Electrochemical device and electronic device including the same

Info

Publication number: CN113544881A
Application number: CN202080017680.1A
Authority: CN
Inventors: 李大光; 陈茂华; 谢远森
Original assignee: Ningde Amperex Technology Ltd
Current assignee: Ningde Amperex Technology Ltd
Priority date: 2020-09-18
Filing date: 2020-09-18
Publication date: 2021-10-22
Also published as: WO2022056818A1

Abstract

The present application relates to an electrochemical device and an electronic device including the same. The electrochemical device comprises a positive electrode, an isolating membrane and a negative electrode, wherein the negative electrode comprises a negative electrode current collector and a pole piece framework arranged on the surface of the negative electrode current collector, and the pole piece framework comprises a porous carbon material and a fiber reinforcement. The electrochemical device has good product yield and can effectively save the cost of the manufacturing process. Meanwhile, the structured negative electrode adopted by the application can inhibit the generation of lithium dendrite and the volume expansion change of the electrochemical device in the charge-discharge cycle process, and further improve the safety and the cycle performance of the electrochemical device.

Description

Electrochemical device and electronic device including the same

Technical Field

The present disclosure relates to the field of energy storage technologies, and particularly to a structured anode and an electrochemical device and an electronic device including the same.

Background

With the rapid development of mobile electronic technology, the frequency and experience requirements of people using mobile electronic devices such as mobile phones, tablets, notebook computers, unmanned planes, electric vehicles and the like are higher and higher. Therefore, electrochemical devices (e.g., lithium ion batteries) that provide energy sources for electronic devices are required to exhibit higher energy density, greater rate, higher safety, and less capacity fade after repeated charge and discharge processes.

The energy density and cycling performance of an electrochemical device are closely related to its negative electrode material. For example, lithium metal is the metal with the smallest relative atomic mass and the lowest standard electrode potential among all metal elements. The lithium metal is used as the negative electrode of the electrochemical device, and the energy density and the operating voltage of the electrochemical device can be effectively improved. However, the use of a high gram-capacity positive electrode material or negative electrode material (e.g., lithium metal, silicon-based material, etc.) tends to cause partial technical problems in the electrochemical device during charge-discharge cycles or under storage environments, such as increased side reactions with the electrolyte, increased cyclic volume expansion rate, lithium dendrite formation, and the like. Therefore, there is a need for further structural improvements and optimizations of the pole pieces in electrochemical devices.

Disclosure of Invention

The present application provides an electrochemical device and an electronic device including the same in an attempt to solve at least one of the problems existing in the related art to at least some extent.

According to one aspect of the present application, there is provided an electrochemical device comprising a positive electrode, a separator and a negative electrode, wherein the negative electrode comprises a negative electrode current collector and a pole piece skeleton present on a surface of the negative electrode current collector, wherein the pole piece skeleton comprises a porous carbon material and a fiber reinforcement.

The electrochemical device has good product yield and can effectively save the cost of the manufacturing process. Meanwhile, the structured negative electrode adopted by the application can inhibit the generation of lithium dendrite and the volume expansion change of the electrochemical device in the charge-discharge cycle process, and further improve the safety and the cycle performance of the electrochemical device.

According to another aspect of the present application, there is provided an electronic device comprising the electrochemical device described above.

Additional aspects and advantages of embodiments of the present application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of embodiments of the present application.

Drawings

Drawings necessary for describing embodiments of the present application or the prior art will be briefly described below in order to describe the embodiments of the present application.

Fig. 1 is a schematic cross-sectional structure diagram of a pole piece skeleton according to the prior art.

Fig. 2 is a schematic cross-sectional structure diagram of a pole piece skeleton according to the prior art.

Fig. 3 is a schematic sectional structure of a porous carbon material according to the prior art.

Fig. 4 is a schematic cross-sectional view of a pole piece skeleton according to an embodiment of the present application.

Detailed Description

Embodiments of the present application will be described in detail below. Throughout the specification, the same or similar components and components having the same or similar functions are denoted by like reference numerals. The embodiments described herein with respect to the figures are illustrative in nature, are diagrammatic in nature, and are used to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limiting the present application.

In this specification, unless specified or limited otherwise, relative terms such as: terms of "central," "longitudinal," "lateral," "front," "rear," "right," "left," "inner," "outer," "lower," "upper," "horizontal," "vertical," "above," "below," "top," "bottom," and derivatives thereof (e.g., "horizontally," "downwardly," "upwardly," etc.) should be construed to refer to the orientation as then described in the discussion or as shown in the drawing figures. These relative terms are for convenience of description only and do not require that the present application be constructed or operated in a particular orientation.

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

In the detailed description and claims, a list of items connected by the term "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means a only; only B; or A and B. In another example, if items A, B and C are listed, the phrase "at least one of A, B and C" means a only; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item a may comprise a single element or multiple elements. Item B may comprise a single element or multiple elements. Item C may comprise a single element or multiple elements.

In the field of energy storage, in order to pursue electrochemical devices with higher energy density and high power performance, it is necessary to continuously design and develop a positive electrode material and a negative electrode material with high theoretical gram capacity. However, in an electrochemical device using a negative electrode material with a high theoretical gram-volume, the negative electrode material undergoes a series of side reactions with the solvent and lithium salt of the existing organic small-molecule electrolyte system, resulting in low cyclic coulombic efficiency. Meanwhile, in the charging and discharging process, the electrochemical device with higher current density can cause the concentration of lithium ions in the electrolyte to be uneven, and the situation that the deposition distribution of lithium metal is uneven at different positions is generated, so that the phenomenon that the deposition speed of partial areas is too fast can occur on the surface of an electrode plate in the deposition process, and further lithium dendrites with sharp structures are formed. The presence of lithium dendrites can result in a reduction in the deposition density on the surface of the pole piece and reduce the cycle retention of the electrochemical device. In severe cases, the membrane may be punctured to form a short circuit, causing safety problems. In addition, during the charge and discharge cycle, the thickness of the pole piece material structure changes with the deposition and dissociation of lithium metal, and affects the cycle performance and safety performance of the electrochemical device.

Structured negative electrodes are one of the possible solutions to the above-mentioned problems encountered with electrochemical devices employing high energy density or high electrical performance. The main concept of the structured negative electrode is that a porous pole piece framework is arranged on the surface of the negative electrode in a mode of a 3D current collector or a porous material and the like. As shown in fig. 1, by providing the pole piece skeleton 11 on the negative electrode current collector 10, it is theoretically possible to provide sufficient space for lithium metal deposition and control and reduce the volume change of the negative electrode during charge and discharge.

U.S. patent nos.: US2011/0104571a1 proposes a fiber-structured polymer network prepared on a current collector by an electrospinning method and applied to lithium ion secondary batteries, lithium metal batteries and the like as a pole piece skeleton. Further, U.S. patent nos.: US2002/0100725a1 proposes another structured anode for application in a lithium metal battery, the structured anode comprising: (a) the conductive nanofiber is of an integral structure, and the nanofibers are interwoven to form a porous network; (b) micro-or nano-sized lithium metal, lithium alloy, or lithium-containing compound. The battery using the structure has high specific capacity and reversible capacity and long cycle life. However, the pole piece framework formed by stacking the fibers has the problems of low efficiency, high cost, loose structure and the like. As shown in fig. 2, after depositing a certain amount of lithium 22, the whole structure of the electrode sheet frame 21 disposed on the current collector 20 is supported, and cannot improve the volume expansion.

U.S. patent nos.: US20160046491a1 proposes a porous carbon material having both a continuous porous structure and a discontinuous porous structure. The porous carbon material has the advantages of low cost, dense pore size distribution and high controllability, and is an ideal pole piece framework material. However, as shown in fig. 3, there are a large number of pores 33 and cracks 32 between the pores 33 in the porous carbon material 31 on the current collector 30, and the existence of these pores 33 and cracks 32 provides a good propagation space and path for lithium metal deposition and ion passage, but also results in poor strength and flexibility of the porous carbon material. The actions of cutting, laminating, winding and the like of the electrochemical device in the preparation process need certain flexibility of the pole piece material, so that the structure can not be damaged. Meanwhile, the pole piece material also needs to have certain flexibility in the charge-discharge cycle process, so that the influence of volume expansion change can be avoided. Therefore, the structured negative electrode adopting the porous carbon material is very easy to break in the preparation and use processes, and the safety performance and the cycle performance of the electrochemical device are further reduced.

The above U.S. patent nos.: the patent document of US20160046491a1, which is incorporated herein by reference in its entirety, exemplifies several exemplary illustrations of porous carbon materials in the examples of the present application.

According to one aspect of the present application, some embodiments of the present application provide a negative electrode, wherein the negative electrode includes a negative electrode current collector and a pole piece skeleton present at a surface of the negative electrode current collector, and the pole piece skeleton includes a porous carbon material and a fiber reinforcement. The porous carbon material has sufficient structural rigidity (e.g., >200GPa) to maintain a stable morphology and internal space. The flexibility of the pole piece framework can be improved by adding the reinforcement fibers into the porous carbon material, the integrity of the pole piece framework in the using process can be kept, and the cycle performance and the safety performance of the pole piece framework in the cycle process of the electrochemical device are further improved.

Referring to fig. 4, when the electrochemical device is charged or discharged, the pores 43 and cracks 42 in the porous carbon material 41 deposited on the current collector 40 due to lithium metal are accumulated, so that the cracks are propagated to the intersections of the fiber reinforcements 44 and further along the interfaces of the fiber reinforcements 44, thereby causing the fiber reinforcements to break 45 or displace 46. Before and after the displacement of the fiber reinforcement body, the fiber reinforcement body can be debonded from the porous carbon material and generate a new contact surface, so that the work generated by crack propagation is consumed. Second, fiber reinforcement displacement can reduce crack tip stress and slow crack propagation. Therefore, the toughness and the strength of the pole piece framework can be obviously improved.

It should be understood that the pole piece framework in the embodiment of the present application may be disposed on a single surface or disposed on both surfaces of a part or all of the surface of the negative electrode current collector according to actual requirements, without being limited thereto.

In some embodiments, the fiber reinforcement includes at least one of a metallic material and a non-metallic material. It will be appreciated that for the fibre reinforcement to achieve high mechanical properties, a moderate bond strength to the porous carbon material interface is necessary. The interface with weak bonding can not effectively transmit the crack propagation work of the porous carbon material, so that the fiber reinforcement can not fully exert the reinforcing function. Too strong interface bonding can easily cause local stress concentration on the surface of the fiber reinforcement, and crack propagation of the porous carbon material can easily cut off the fiber reinforcement and rapidly propagate along the radial direction of the fiber, so that the pole piece framework can be subjected to brittle fracture under low stress. In the fiber reinforcement, the interface between one or more composite materials of glass fiber materials, carbon fiber materials, metal materials and the like and the porous carbon materials can effectively transfer load and play the role of reinforcing fibers to the maximum extent, and meanwhile, the stress distribution in the pole piece framework can be adjusted through a crack deflection mechanism (namely, cracks are expanded along the axial direction of the interface, and the energy of crack expansion is consumed in a mode of interface debonding or displacement) and the crack expansion is prevented, so that the materials with moderate interface combination generally have higher mechanical properties. In some embodiments, the fiber reinforcement is a glass fiber material, and the glass fiber material has a low manufacturing cost, so that the manufacturing cost of the pole piece framework can be reduced. In other embodiments, the fiber reinforcement is a metal material, and the metal material has better conductivity and ductility, which can effectively improve the conductivity of the negative electrode.

In some embodiments, the metallic material of the fiber reinforcement comprises at least one of the elements Ti, Cr, Fe, Ni, Cu, Mo, Ag. In some embodiments, the fiber reinforcement may be a fiber reinforcement comprising at least one of Ti metal, Cr metal, Fe metal, Ni metal, Cu metal, Mo metal, Ag metal, or alloys thereof.

In some embodiments, the non-metallic material of the fiber reinforcement comprises B, C, MgO, TiO₂、ZrO₂、SiO₂、Al₂O₃、SiC、MgSiO₃、Al₂SiO₅At least one of (1).

In some embodiments, the fiber reinforcement comprises one or more of long fibers, short fibers, and whiskers.

In some embodiments, the fiber reinforcement has a length of 1 μm to 100 mm. In some embodiments, the fiber reinforcement has a length of 3mm to 10 mm. Fiber reinforcement, having a length within the scope of the embodiments of the present application, can be more uniformly dispersed in the pole piece backbone and is less prone to fracture.

In some embodiments, the fiber reinforcement has a diameter of 0.01 μm to 10 μm. In some embodiments, the fiber reinforcement has a diameter of 5 μm to 10 μm. The fiber reinforcement with the diameter within the range of the embodiment has a certain contact area with the porous carbon material and has certain fiber strength.

In some embodiments, the aspect ratio of the fiber reinforcement is from 5 to 1000000. In some embodiments, the aspect ratio of the fiber reinforcement is from 100 to 1000.

In some embodiments, the fiber reinforcement is 5% to 80% by volume in the pole piece backbone. In some embodiments, the fiber reinforcement is 30% to 70% by volume in the pole piece backbone. In some embodiments, the fiber reinforcement is 50% to 60% by volume in the pole piece backbone. When the volume ratio of the fiber reinforcement in the pole piece framework is too large, the fiber reinforcement is easy to be subjected to segregation, and less porous carbon material exists in the aggregation area of the fiber reinforcement, so that defects are formed in the pole piece framework; in contrast, when the volume ratio of the fiber reinforcement in the pole piece frame is too small, the porous carbon material cannot be well dispersed by the fiber reinforcement, stress concentration is easily formed in a local area in the pole piece frame, and cracks are easily induced in the stress concentration area.

In some embodiments, the porosity of the pole piece skeleton is 60% to 80%. The pole piece framework can provide a stable space, for example, when a negative electrode is charged, lithium metal can be deposited in pores of the pole piece framework; during discharging, in the process that the lithium metal deposition of the negative electrode is continuously reduced, the pole piece framework can form a stable structure and an internal space, so that the negative electrode cannot be severely shrunk.

In some embodiments, the average pore size of the backbone of the pole piece is from 2nm to 100 nm. The electrode plate framework has the advantages that the pore diameter distribution of the electrode plate framework is very dense, the uniform conductive channel is provided, the good ion and electron conductivity is realized, the current in the charge-discharge cycle process can be effectively dispersed, the current density in the region is reduced, the more uniform electric field is formed, the uniformity of a lithium deposition structure is improved, and the growth of lithium dendrites is inhibited

In some embodiments, the thickness of the negative electrode is 50 μm to 100 mm. The thickness of the negative electrode is generally the sum of the thickness of the negative current collector and the thickness of the pole piece framework. It should be understood that, in the negative electrode of the present application, the arrangement of the electrode plate framework on the negative electrode current collector may be a single-sided arrangement or a double-sided arrangement, and the thickness of the negative electrode may be adjusted according to the arrangement mode.

In some embodiments, the thickness of the pole piece backbone is 40 μm to 2000 μm. In other embodiments, the thickness of the pole piece backbone is approximately, for example, 40 μm, 50 μm, 100 μm, 150 μm, 200 μm, 250 μm, 500 μm, 1000 μm, 2000 μm, or a range consisting of any two of these values.

In some embodiments, the negative electrode current collector may be a copper foil or a nickel foil, however, other negative electrode current collectors commonly used in the art may be employed without limitation.

In some embodiments, during the preparation of the negative electrode, a negative active material can be further added to the pole piece framework to further improve the electrical performance of the electrochemical device. It is to be understood that the manner of adding the anode active material in the anode of the present application may be a manner commonly used in the art, and for example, the manner of adding the anode active material includes: magnetron sputtering, vacuum evaporation, melting, hot pressing, electrochemistry and the like. In some embodiments, the negative active material is disposed on the electrode sheet frame in the form of a metal sheet, a particle coating, or the like, and disposed in the electrode sheet frame in the form of a deposit by chemical conversion after the electrode assembly is assembled.

In some embodiments, the negative electrode further comprises a negative active material layer disposed on the surface of the pole piece skeleton prior to formation.

In some embodiments, the negative active material comprises lithium metal flakes, lithium metal alloys, nitrides of lithium. In some embodiments, the active material in the further negative electrode tab further comprises a material having a high energy density, for example, a simple substance, an alloy or a compound thereof of silicon, tin, germanium, antimony, bismuth, aluminum.

According to another aspect of the present application, some embodiments of the present application provide an electrochemical device including the anode in the above-described embodiments of the present application. In some embodiments, the electrochemical device is a lithium ion battery. In some embodiments, an electrochemical device includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode.

In some embodiments, the positive electrode includes a positive electrode material and a positive electrode current collector. The positive electrode collector may be an aluminum foil or a nickel foil, however, other positive electrode collectors commonly used in the art may be employed without limitation. It is understood that one skilled in the art can select the cathode material commonly used in the art without limitation according to the actual difference of the reduction potentials of different materials and the electrical performance requirements of the electrochemical device without departing from the spirit of the present application. In some embodiments, the active material in the further positive electrode sheet comprises one or more of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium manganate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, lithium iron phosphate, lithium titanate and a lithium-rich manganese-based material.

In some embodiments, the release film includes, but is not limited to, at least one selected from the group consisting of polyethylene, polypropylene, polyethylene terephthalate, polyimide, and aramid. For example, the polyethylene includes at least one component selected from the group consisting of high density polyethylene, low density polyethylene, and ultra high molecular weight polyethylene. In particular polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of lithium ion batteries by means of a shutdown effect.

The electrochemical device of the present application further includes an electrolyte, which may be one or more of a gel electrolyte, a solid electrolyte, and an electrolytic solution including a lithium salt and a non-aqueous solvent.

In some embodiments, the lithium salt is selected from LiPF₆、LiBF₄、LiAsF₆、LiClO₄、LiB(C₆H₅)₄、LiCH₃SO₃、LiCF₃SO₃、LiN(SO₂CF₃)₂、LiC(SO₂CF₃)₃、LiSiF₆One or more of LiBOB and lithium difluoroborate. For example, the lithium salt is LiPF₆Since it can give high ionic conductivity and improve cycle characteristics.

The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, other organic solvent, or a combination thereof.

The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluoro carbonate compound, or a combination thereof.

Examples of such other organic solvents are dimethylsulfoxide, 1, 2-dioxolane, sulfolane, methyl sulfolane, 1, 3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters and combinations thereof.

In some embodiments, the non-aqueous solvent is selected from the group consisting of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, propylene carbonate, methyl acetate, ethyl propionate, fluoroethylene carbonate, and combinations thereof.

It is to be understood that the methods for preparing the positive electrode, the negative electrode, the separator, and the lithium ion battery in the examples of the present application may be any suitable conventional method in the art according to specific needs without departing from the spirit of the present application, and are not limited thereto. In one embodiment of the method of manufacturing an electrochemical device, the method of manufacturing a lithium ion battery includes: the positive electrode, the separator, and the negative electrode in the above embodiments are sequentially wound into an electrode assembly, the electrode assembly is incorporated into, for example, an aluminum plastic film, and an electrolyte is injected, followed by vacuum packaging, standing, formation, shaping, and the like to obtain a lithium ion battery.

The electrode assembly of the electrochemical device of the present application includes not only the winding type structure, but also, in some embodiments, the button type structure, the lamination structure, and the folding structure.

Although illustrated above as a lithium ion battery, one skilled in the art, after reading this application, will appreciate that the negative electrode of the present application can be used in other suitable electrochemical devices without departing from the spirit of the present application. Such an electrochemical device includes any device in which electrochemical reactions occur, and specific examples thereof include all kinds of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery including a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

According to another aspect of the present application, some embodiments of the present application further provide an electronic device including the electrochemical device in the embodiments of the present application.

The electronic device of the embodiment of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notebook, a calculator, a memory card, a portable recorder, a radio, a backup power source, a motor, an electric vehicle, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.

Examples

The following examples are listed and the electrochemical device (lithium ion battery) thereof is subjected to a volume expansion rate test and a bending strength test respectively to better illustrate the technical solution of the present application. It will be understood by those skilled in the art that the electrochemical devices of the following examples and comparative examples were tested for structural and cycling performance of the structured negative electrode of the present application using half-cell button type cells. In the description that follows, the structured negative electrode of the present application is used as a positive electrode in a button half cell, which is a common measurement method in the art for providing standard samples for volume expansion rate testing and bending strength testing, and does not represent the practical application of the structured negative electrode of the present application in an electrochemical device.

One-button half-cell testing method

Volume expansion rate test:

the length, width and height of the button type lithium ion battery are tested by adopting a ten-thousandth micrometer and converted into volume. The button half-cells of the following examples and comparative examples were placed in an incubator at 25 ℃. + -. 2 ℃ and left to stand for 2 hours at 0.2mA/cm²Charging for 5 hours at constant current to make the SOC reach 100 percent, standing for 15 minutes, and recording the volume of the lithium ion battery when fully charged; then 0.2mA/cm²And discharging for 15 hours at constant current to ensure that the lithium ion battery is completely discharged to 0% SOC, and recording the volume of the lithium ion battery when the lithium ion battery is completely discharged.

And 4 lithium ion batteries are taken for testing each group, and the average value of the volume expansion rate of the lithium ion batteries is calculated.

The volume expansion rate (volume of the lithium ion battery at full charge/volume of the lithium ion battery at discharge-1) × 100%.

And (3) testing the bending strength:

the button half-cells of the following examples were placed in an incubator at 25 ℃. + -. 2 ℃ and left to stand for 2 hours at 0.2mA/cm²Charging for 5 hours at constant current to reach100% SOC and left for 15 minutes. And (3) testing the three-point bending performance of the button lithium ion battery material by adopting an electronic universal material testing machine (INSTRON-5569). The size of the lithium ion battery sample is 60mm multiplied by 10mm multiplied by 2mm, and the span is 40 mm. Other test parameters were as follows: the moving speed of the beam is 2mm/min, the data acquisition rate is 100 points/min, and the diameter of the pressure head is 10 mm. And 4 lithium ion batteries are taken for testing each group, and the average value of the bending strength of the lithium ion batteries is calculated.

Preparing a button half cell:

preparation of negative pole piece

A lithium piece with the diameter of 18mm and the thickness of 0.5mm is used as a negative pole piece.

Preparation of the separator

Polyethylene (PE) film having a thickness of 15 μm was used as the separator.

Preparation of the electrolyte

Lithium hexafluorophosphate was mixed with a nonaqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): 1 by weight) in an environment having a water content of less than 10ppm to prepare an electrolyte solution having a lithium salt (lithium hexafluorophosphate) concentration of 1.0M.

Examples 1 to 1

The pole piece framework is formed by combining carbon fibers (fiber reinforcements) and porous carbon materials, wherein the volume percentage of the fiber reinforcements is 5%, the thickness of the pole piece framework is 50 mu m, the average length of the fiber reinforcements is 3mm, the diameter of the fiber reinforcements is 5 mu m, and the porosity of the pole piece framework is 80%. The pole piece skeleton was placed on a copper foil current collector and cut to form a positive pole piece 18mm in diameter and 60 μm thick. 2430 is selected as the model of the button lithium ion battery, and the button half battery is obtained by sequentially assembling a negative electrode shell, an elastic sheet, a gasket, a negative electrode plate, electrolyte, an isolating membrane, the electrolyte, a positive electrode plate and a positive electrode shell from bottom to top.

Examples 1-2 to 1-9

The same procedure as in example 1-1 was followed, except that the fiber reinforcement was used in the different volume percentages in examples 1-2 to 1-9, see Table 1.

Examples 1-10 to 1-11

The same procedure as in example 1-1 was followed, except that in examples 1-10 to 1-11, the electrode sheet was made of glass fibers and titanium fibers combined with a porous carbon material, wherein the fiber reinforcement was 50% by volume, as shown in Table 1.

Examples 1 to 12 and 1 to 13

The same procedure as in examples 1 to 6 was conducted except that the thickness of the lead frame in examples 1 to 12 and 1 to 13 was 100 μm and 30 μm, respectively, and the thickness of the positive electrode sheet was 110 μm and 40 μm, respectively.

Examples 1 to 14 and 1 to 15

The same procedure was followed as in examples 1-6, except that the porosity of the matrix of the pole piece in examples 1-14 and 1-15 was 70% and 60%, respectively.

Comparative examples 1 to 1

The same preparation method as that of example 1-1 was followed, except that in comparative example 1-1, only the porous carbon material was used as the electrode sheet skeleton, the thickness of the electrode sheet skeleton was 50 μm, and the porosity of the electrode sheet skeleton was 80%.

Comparative examples 1 to 2

The same preparation method as that of example 1-1 was followed, except that the fibrous structure polymer network prepared on the current collector by the electrospinning method in comparative example 1-2 was used as the electrode sheet skeleton. The electrostatic spinning method comprises the following steps: dissolving Polybenzenenitrile (PAN) powder in Dimethylformamide (DMF) according to a mass ratio of 1: 9, stirring for 2 hours to obtain a precursor solution; injecting the precursor solution into an injector, applying voltage on a spray head to start spinning, wherein the voltage is 20kV, and the distance between a collecting plate and the spray head is 15 cm; collecting a fiber structure polymer network through aluminum foil, pre-oxidizing the fiber structure polymer network for 1 hour at 280 ℃ in air, and then sintering the fiber structure polymer network for 1 hour at 800 ℃ to obtain a pole piece framework, wherein the thickness of the pole piece framework is 50 mu m, and the porosity of the pole piece framework is 80%.

Comparative examples 1 to 3

The same procedure as in example 1-1 was followed, except that in comparative examples 1-3, only copper foil having a thickness of 10 μm was used as the positive electrode sheet.

Comparative examples 1 to 4

The same procedure as in comparative examples 1-1 was conducted except that the thickness of the electrode sheet bobbin in comparative examples 1-4 was 30 μm.

The statistics of the negative electrodes of examples 1-1 to 1-15 and comparative examples 1-1 to 1-4 and the results of the lithium ion batteries passing the volume expansion ratio test and the bending strength test are shown in table 1 below.

TABLE 1

As shown in table 1, it can be seen from the comparative examples and comparative examples that, in the lithium ion battery of the embodiment of the present application, by using the pole piece framework including the fiber reinforcement and the porous carbon material, under the condition that other setting parameters are not changed, compared with the comparative examples, the bending strength of the electrode pole piece can be effectively improved, and meanwhile, the volume expansion rate of the lithium ion battery in the charging and discharging processes is greatly improved. Specifically, comparing examples 1-1 to 1-11 with comparative examples 1-1 to 1-4, it can be seen that the lithium ion battery using the electrode plate of the present invention as the positive electrode plate has almost no problem of volume change during the charging and discharging processes, and in contrast, the lithium ion battery of comparative examples 1-2 to 1-4 has a very large volume expansion rate in the absence of effective control of lithium metal deposition. In addition, although the lithium ion battery of comparative example 1-1, which employs the porous carbon material as the backbone of the electrode sheet, has no problem of significant volume change, the bending strength of the electrode sheet of comparative example 1-1 is very low, which means that the structure thereof is easily damaged by external force, resulting in low safety performance.

Comparing examples 1-1, 1-12 and 1-13, it can be seen that increasing the thickness of the pole piece skeleton can further increase the mechanical strength of the membrane, but may cause a loss of energy density due to lithium ion-bundling. Accordingly, reducing the thickness of the electrode sheet frame can reduce the bending strength of the electrode sheet. Meanwhile, as can be seen from comparison of examples 1-13 to 1-15, in the case of depositing the same lithium metal (the same volume energy density), reducing the thickness or porosity of the electrode sheet skeleton may not accommodate deposition of all lithium metal during charging and discharging of the electrode sheet skeleton, thereby causing volume expansion of the lithium ion battery. The lithium ion battery with the thickness and the porosity of the pole piece framework within the range of the embodiment of the application can have higher mechanical strength and lower volume expansion rate.

Method for testing lithium ion battery

Volume expansion rate test:

the length, width and height of the lithium ion battery are tested by ten-thousandth micrometer and converted into volume. The lithium ion full cells of the following examples and comparative examples were left to stand in a thermostat of 25 ℃. + -. 2 ℃ for 2 hours, charged to 4.3V at a rate of 0.1C, then charged at a constant voltage until the current was less than 0.025C, and then discharged at a rate of 0.2C until 3V was cut off, and the above procedure was repeated 2 times for activation. After activation, charging to 4.3V at a rate of 0.2C, then charging to 0.025C at a constant voltage of 4.3V to make the SOC reach 100%, standing for 15 minutes, and recording the volume of the lithium ion battery when fully charged; and discharging to 3V at the rate of 1C, so that the lithium ion battery is completely discharged to 0% SOC, and recording the volume of the lithium ion battery when the lithium ion battery is completely discharged. The number of cycles was read through electrochemical test curves output by LAND or NEWARE.

Preparing a lithium ion battery:

preparation of the Positive electrode

Aluminum foil is used as the positive current collector. Uniformly coating a layer of positive active material slurry on the surface of the aluminum foil, wherein the positive active material slurry comprises the following components: 95.8 wt% of nickel cobalt lithium manganate, 2.8 wt% of polyvinylidene fluoride (PVDF) and 1.4 wt% of conductive carbon black, and drying at 85 ℃. And then, carrying out cold pressing, cutting and slitting on the positive electrode active material layer to prepare the positive electrode. The thickness of the positive electrode was 67 μm.

Preparation of the separator

Polyethylene (PE) film having a thickness of 15 μm was used as the separator.

Preparation of the electrolyte

Example 2-1

The copper foil is used as a negative current collector, a pole piece framework formed by combining carbon fibers (fiber reinforcement) and porous carbon materials is adopted, wherein the volume percentage of the fiber reinforcement is 5%, the thickness of the pole piece framework is 50 mu m, the average length of the fiber reinforcement is 3mm, the diameter of the fiber reinforcement is 5 mu m, and the porosity of the pole piece framework is 80%. And arranging the pole piece framework on a negative current collector, and then cutting pieces and cutting to prepare the negative pole piece with the thickness of 60 mu m. And sequentially stacking the positive electrode, the isolating membrane and the negative electrode into an electrode assembly, packaging the electrode assembly into an aluminum plastic membrane, injecting electrolyte, and then carrying out vacuum packaging, standing, formation, shaping and other processes to obtain the lithium ion battery.

Examples 2-2 to 2-9

The same procedure as in example 2-1 was followed, except that the fiber reinforcement was used in the different volume percentages in examples 2-2 to 2-9, see Table 2.

Examples 2-10 to 2-11

The same procedure as in example 2-1 was followed, except that in examples 2-10 to 2-11, the electrode sheet was made of glass fibers and titanium fibers combined with a porous carbon material, wherein the fiber reinforcement was 50% by volume, as shown in Table 2.

Examples 2 to 12 and 2 to 13

The same procedure was followed as in examples 2-6 except that the thickness of the electrode sheet skeleton was 100 μm and 30 μm and that of the negative electrode sheet was 110 μm and 40 μm in examples 2-12 and 2-13, respectively.

Examples 2 to 14 and 2 to 15

The same procedure was followed as in examples 2-6, except that the porosity of the matrix of the pole piece in examples 2-14 and 2-15 was 70% and 60%, respectively.

Comparative example 2-1

The preparation method is the same as that of the example 2-1, except that only the porous carbon material is used as the pole piece skeleton in the comparative example 2-1, the thickness of the pole piece skeleton is 50 μm, and the porosity of the pole piece skeleton is 80%.

Comparative examples 2 to 2

The preparation method is the same as that of the example 2-1, except that the fiber structure polymer network prepared on the current collector by the electrostatic spinning method in the comparative example 2-2 is used as the pole piece framework. The electrostatic spinning method comprises the following steps: dissolving Polybenzenenitrile (PAN) powder in Dimethylformamide (DMF) according to a mass ratio of 1: 9, stirring for 2 hours to obtain a precursor solution; injecting the precursor solution into an injector, applying voltage on a spray head to start spinning, wherein the voltage is 20kV, and the distance between a collecting plate and the spray head is 15 cm; collecting a fiber structure polymer network through aluminum foil, pre-oxidizing the fiber structure polymer network for 1 hour at 280 ℃ in air, and then sintering the fiber structure polymer network for 1 hour at 800 ℃ to obtain a pole piece framework, wherein the thickness of the pole piece framework is 50 mu m, and the porosity of the pole piece framework is 80%.

Comparative examples 2 to 3

The same procedure as in example 2-1 was conducted except that in comparative examples 2-3, only copper foil having a thickness of 10 μm was used as the positive electrode sheet.

Comparative examples 2 to 4

The same procedure as in comparative example 2-1 was conducted except that the thickness of the electrode sheet bobbin in comparative example 2-4 was 30 μm.

The statistics of the negative electrodes of examples 2-1 to 2-15 and comparative examples 2-1 to 2-4 and the results of the lithium ion batteries passing the volume expansion ratio test and the bending strength test are shown in table 2 below.

TABLE 2

By comparing examples 2-1 to 2-11 with comparative examples 2-1 to 2-4, the structured negative electrode of the present application has better bending strength, and the pole piece frame has higher structural strength. The electrochemical device adopting the structured negative electrode can effectively inhibit the expansion change rate of the electrode assembly and improve the cycle performance of the electrode assembly.

Referring to examples 2-10, the structured negative electrode using glass fiber as the fiber reinforcement can have a certain structural reinforcement effect, and the structured negative electrode has lower raw material cost, which can reduce the manufacturing cost. Referring to examples 2 to 11, the structured negative electrode using titanium fibers as a fiber reinforcement has a lower structural reinforcement effect than carbon fibers, however, the titanium fibers or other metal fibers can improve the structural strength of the structured negative electrode and the electronic conductivity of the pole piece framework thereof, thereby improving the cycle performance of the structured negative electrode.

It can be seen from the comparison of examples 2-12 to 2-15 that the thickness and porosity of the electrode sheet skeleton of the structured negative electrode of the present application have a certain influence on the structural strength and cycle performance of the structured negative electrode. The structured negative electrode in the range of the thickness and the porosity of the pole piece framework provided by the embodiment of the application has the optimal structural strength, and can limit the volume change of an electrochemical device in the circulating process.

Through the comparison between the above embodiments and the comparative example, it can be clearly understood that the electrochemical device of the present application can improve the volume change of the electrochemical device in the charge-discharge cycle process by providing the pole piece skeleton containing the fiber reinforcement and the porous carbon material, and the problem that the pole piece skeleton is fragile can be solved by adding the fiber reinforcement in the porous carbon material. The structured negative electrode can inhibit the volume expansion and the growth of lithium dendrites of the electrochemical device in the charge-discharge cycle process, and can also increase the flexibility and the mechanical strength of the structured negative electrode, thereby improving the cycle performance and the safety performance of the electrochemical device.

Reference throughout this specification to "some embodiments," "one embodiment," "another example," "an example," "a specific example," or "some examples" means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present application. Thus, throughout the specification, descriptions appear, for example: "in some embodiments," "in an embodiment," "in one embodiment," "in another example," "in one example," "in a particular example," or "by example," which do not necessarily refer to the same embodiment or example in this application. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments or examples.

Although illustrative embodiments have been illustrated and described, it will be appreciated by those skilled in the art that the above embodiments are not to be construed as limiting the application and that changes, substitutions and alterations can be made to the embodiments without departing from the spirit, principles and scope of the application.

Claims

1. An electrochemical device, comprising:

a positive electrode;

an isolation film; and

a negative electrode, wherein the negative electrode comprises a negative electrode current collector and a pole piece framework present on a surface of the negative electrode current collector, wherein the pole piece framework comprises a porous carbon material and a fiber reinforcement.

2. The electrochemical device of claim 1, wherein the fiber reinforcement comprises at least one of a metallic material comprising at least one of the elements Ti, Cr, Fe, Ni, Cu, Mo, Ag and a non-metallic material comprising B, C, MgO, TiO₂、ZrO₂、SiO₂、Al₂O₃、SiC、MgSiO₃、Al₂SiO₅At least one of (1).

3. The electrochemical device of claim 1, wherein the fiber reinforcement comprises one or more of long fibers, short fibers, and whiskers.

4. The electrochemical device of claim 1, wherein the fiber reinforcement has a length of 1 μ ι η to 100mm, a diameter of 0.01 μ ι η to 10 μ ι η, and an aspect ratio of 5 to 1000000.

5. The electrochemical device of claim 1, wherein the fiber reinforcement is 5% to 80% by volume in the pole piece backbone.

6. The electrochemical device of claim 1, wherein the porosity of the pole piece skeleton is 60% to 80%.

7. The electrochemical device of claim 1, wherein the average pore size of the pole piece backbone is from 2nm to 100 nm.

8. The electrochemical device of claim 1, wherein the negative electrode has a thickness of 50 μ ι η to 100mm, and the pole piece skeleton has a thickness of 40 μ ι η to 2000 μ ι η.

9. An electronic device comprising the electrochemical device of any one of claims 1 to 8.