CN114068890B - Composite metal negative electrode, preparation method thereof, secondary battery and terminal - Google Patents
Composite metal negative electrode, preparation method thereof, secondary battery and terminal Download PDFInfo
- Publication number
- CN114068890B CN114068890B CN202010791225.9A CN202010791225A CN114068890B CN 114068890 B CN114068890 B CN 114068890B CN 202010791225 A CN202010791225 A CN 202010791225A CN 114068890 B CN114068890 B CN 114068890B
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- negative electrode
- conductive polymer
- lithium
- metal negative
- protective layer
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Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/362—Composites
- H01M4/366—Composites as layered products
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/04—Construction or manufacture in general
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
- H01M2004/027—Negative electrodes
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
Abstract
The application relates to the technical field of batteries, and provides a composite metal negative electrode, a preparation method thereof, a secondary battery and a terminal. The composite metal negative electrode provided by the application comprises the following components: a metal anode, and a protective layer bonded to at least one side surface of the metal anode, wherein the material of the protective layer comprises a conductive polymer, and the conductive polymer is selected from conductive polymers capable of reversibly doping and dedoping anions. The composite metal negative electrode provided by the application has the advantages that the protective layer can effectively inhibit dendrite growth on the surface of the metal negative electrode in the battery charging process, and the problems of battery safety and service life caused by dendrite are solved from the source.
Description
Technical Field
The application belongs to the technical field of batteries, and particularly relates to a composite metal negative electrode, a preparation method thereof, a secondary battery and a terminal.
Background
With the development of economy and technology, most electronics industries (e.g., portable electronics, unmanned aerial vehicles, electric vehicles) are pressing to demand energy storage devices with higher energy density, higher power density, longer cycle life, and safer. While the energy density of commercial lithium ion batteries using graphite as the negative electrode material has been approaching the upper limit, it has not yet been able to meet the endurance and standby requirements of users for such devices. The metal negative electrode of lithium, sodium, potassium and the like has high theoretical specific capacity and low electrochemical potential, and is a high-energy negative electrode material with wide development prospect. The adoption of the metal cathode can greatly improve the energy density of the secondary battery and remarkably improve the user experience. However, the metal negative electrode has the characteristics of high chemical activity (low coulomb efficiency is caused), dendrite growth (side reaction and potential safety hazard are caused), volume expansion (SEI film is continuously broken and rebuilt) and the like, and the commercialization process of the high-energy-density metal negative electrode battery is hindered.
In the prior art, the safety performance of the metal negative electrode battery can be improved by the following modes:
mode 1, an electrode material having heat-sensitive properties, which includes a core formed of a lithium metal oxide and a shell formed of a polythiophene derivative, and a method for producing the same. The electrode material adopts a thermosensitive material to coat the electrode active material, so that each active particle has a temperature sensitive effect. Therefore, this embodiment can cause an increase in the impedance of the electrode material to block the electronic path and improve the safety of the battery, even when the temperature of the battery increases to the curie temperature of the material. However, it is difficult to uniformly coat each active material during the actual preparation of the electrode material.
In the mode 2, the composite diaphragm and the lithium battery comprising the same, the technology distributes the heat-sensitive material in the diaphragm base layer, and when the temperature of the battery rises, the heat-sensitive material is heated and expands, so that the gap is increased, and the heat dissipation in the battery core is facilitated; meanwhile, the thermosensitive material dispersed in the film base layer can play a role in temperature control and adjustment for a long time, and potential safety hazards caused by overhigh temperature are avoided.
Mode 3, a lithium secondary battery having high stability and superior performance, in which at least one of the positive and negative electrodes contains a PTC material, and when the battery is overheated during overcharge, the PTC material increases in resistance, interrupting current, and preventing explosion of the battery, and a method of manufacturing the same. The technology applies the PTC material to the anode and the cathode of the battery, utilizes the temperature sensitivity characteristic of the PTC material, exerts the function of interrupting current to avoid further reaction, and mainly plays a role in avoiding the safety problem caused by thermal runaway.
Although the three modes can improve the safety performance of the metal negative electrode battery to a certain extent, the methods only remedy the potential safety risk, and can not improve the cycle life and the potential safety hazard of the battery by inhibiting the generation of dendrites of the metal negative electrode from the source.
Disclosure of Invention
The embodiment of the application provides a composite metal negative electrode, a preparation method thereof, a secondary battery and a terminal, and aims to solve the problems that dendrites are easy to generate in the metal negative electrode, so that the battery has short cycle life and potential safety hazard.
In order to achieve the above purpose, the application adopts the following technical scheme:
in a first aspect, an embodiment of the present application provides a composite metal anode, including: a metal negative electrode, and a protective layer bonded to at least one side surface of the metal negative electrode, wherein the material of the protective layer comprises a conductive polymer selected from conductive polymers capable of reversibly doping and dedoping anions.
According to the composite metal negative electrode provided by the embodiment of the application, the protective layer is arranged on the surface of at least one side of the metal negative electrode. The material of the protective layer comprises a conductive polymer capable of reversibly doping and dedoping anions. In this case, the conductive polymer in the protective layer is electrochemically doped oxidatively, doping anions during charging of the battery using the composite metal anode. Since anions are uniformly doped in the conductive polymer, cations can be uniformly deposited on the surface of the composite metal negative electrode, thereby preventing dendrite formation caused by selective deposition of cations on local regions of the metal negative electrode. Thus, the protective layer can solve the problems of battery safety and service life caused by dendrites from the source.
In one possible implementation, the conductive polymer is selected from conductive polymers having heat sensitive properties. In this case, during the charge of the battery, the region where dendrites are located is increased in temperature by local current increase or side reaction, which is higher than that of other regions where dendrites are not formed, under the effect of an electric field. When the temperature of the region where the dendrite is located reaches the thermosensitive critical temperature of the conductive polymer, the thermosensitive property of the conductive polymer is excited, and the conductive polymer changes the spatial conformation and reduces the conjugation degree through dedoping. At this point the resistance of the conductive polymer increases, the conductivity decreases, the resistance to deposition of cations at the tips (dendrite-forming areas) increases, and cations tend to deposit toward non-tips (dendrite-forming other areas) where the resistance is lower. Thus, the dendrite growth can be hindered by the thermosensitive property of the conductive polymer, thereby preventing dendrite growth to some extent to penetrate the separator and cause short circuit of the battery.
In one possible implementation, the conductive polymer is selected from conductive polymers having an impedance that increases with increasing temperature in the range of 50 ℃ to 130 ℃. In this case, in the battery using the composite metal anode as the anode, the conductive polymer in the protective layer has thermal sensitivity in the temperature range of 50-130 ℃, i.e. the conductive polymer can increase the impedance by dedoping anions and changing the spatial configuration thereof in the temperature range so as to adjust the deposition of cations in the non-dendrite region, thereby achieving the purpose of balancing the thickness uniformity of the non-dendrite region and avoiding dendrite growth.
In one possible implementation, the conductive polymer is a homopolymer formed by polymerizing the same structural unit or a copolymer formed by polymerizing different structural units, and the general formula of the structural unit is shown in the following formula (1):
in the formula (1), X is selected from NH, O or S;
R 1 、R 2 each independently selected from any one of hydrogen, halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkenyloxy, haloalkenyloxy, aryl, haloaryl, aryloxy, haloaryloxy. The polymer formed by the structural units shown in the general formula (1) can change the spatial conformation of the conductive polymer by doping anions in the charging process, enhance the planeness of five-membered rings and form a conjugated structure with higher stability and better conductive performance. Therefore, anions are uniformly doped in the conductive polymer, selective deposition of cations is avoided, deposition uniformity of the cations on the surface of the metal negative electrode is improved, and formation probability of dendrites is reduced. Further, the conductive polymer formed by the structural unit represented by the formula (1) has heat sensitivity, and increases in resistance when the temperature is up to its heat sensitive critical temperatureAdding. Therefore, once dendrite is formed on the surface of the composite metal anode, the temperature of the area where the dendrite is located is increased, the conductive polymer of the corresponding area is dedoped with anions, meanwhile, the configuration is converted into a twistable five-membered ring structure (the conjugation degree is reduced), so that the conductivity of the area where the dendrite is located is reduced, and cations are deposited in the non-dendrite area with higher conductivity, and finally, the aim of avoiding the dendrite from growing continuously is achieved.
In one possible implementation, the number of carbon atoms in the alkyl, haloalkyl, alkoxy, haloalkoxy is 1 to 20; the carbon number of the alkenyl, the halogenated alkenyl, the alkenyloxy and the halogenated alkenyloxy is 2-10; the carbon number of the aryl, the halogenated aryl, the aryloxy and the halogenated aryloxy is 6-10. When the number of carbon atoms is within the above range, the resulting conductive polymer has suitable thermosensitive properties.
In one possible implementation, the number of carbon atoms in the alkyl, haloalkyl, alkoxy, haloalkoxy is 1 to 10; the carbon number of the alkenyl, the halogenated alkenyl, the alkenyloxy and the halogenated alkenyloxy is 2-10.
In one possible implementation manner, in the formula (1), the halogen is selected from one of fluorine, chlorine, bromine and iodine; the halogen in the haloalkyl, the haloalkoxy, the haloalkenyl, the haloalkenoxy, the haloaryl and the haloaryloxy is independently selected from at least one of fluorine, chlorine, bromine and iodine.
In one possible implementation manner, the conductive polymer is at least one selected from the compounds (A) to (P) shown in the following structures, wherein the value of n ranges from 10 to 10000, and n 1 +n 2 The values of (2) satisfy the following: n is more than or equal to 10 1 +n 2 ≤10000，
In one possible implementation, the protective layer has a thickness of 1nm-20 μm. Because of the limitation of the conductivity of the conductive polymer, the thickness of the protective layer 11 is not too thick, so that the embodiment of the application can inhibit the growth of dendrites by setting the thickness of the protective layer in the range of 1nm-20 μm, thereby improving the safety performance and the service life of the battery.
In one possible implementation, the protective layer has a thickness of 1 μm to 10 μm. In this case, the protective layer can exert excellent effects of suppressing dendrite formation and suppressing dendrite growth without decreasing the cation transport efficiency.
In one possible implementation, the material of the protective layer further includes a binder, and the protective layer is bonded to at least one side surface of the metal anode through the binder. The adhesive is used for improving the binding force of the conductive polymer on the surface of the metal negative electrode.
In one possible implementation, the mass ratio of the conductive polymer to the binder in the protective layer is 1-100:1. The mass ratio of the conductive polymer to the binder is in the above range, and the binder can improve the binding force of the conductive polymer on the surface of the metal negative electrode. If the content of the binder is too high, the relative content of the conductive polymer is reduced, which weakens the effect of the conductive polymer in inhibiting dendrite formation and dendrite growth, and in addition, the resistance of the protective layer is increased, which is unfavorable for the transmission of cations.
In one possible implementation, the binder is selected from one or more of polyvinylidene fluoride, polymethyl methacrylate, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene, polyacrylonitrile, polyimide, polyethylene glycol, polyethylene oxide, polydopamine, sodium carboxymethyl cellulose/styrene butadiene rubber, polyvinyl alcohol, polyacrylic acid, lithium polyacrylate, polyvinylpyrrolidone, polylactic acid, sodium alginate, poly-p-styrenesulfonic acid, lithium poly-p-styrenesulfonate, and gelatin. The adhesive can improve the binding force of the conductive polymer on the surface of the metal negative electrode, so that the protective layer is firmly bonded on the surface of the metal negative electrode.
In one possible implementation, the metal negative electrode is selected from one or more of a lithium negative electrode, a sodium negative electrode, a potassium negative electrode, a magnesium negative electrode, a zinc negative electrode, and an aluminum negative electrode. In this case, the protective layer is bonded to the surface of the metal anode, wherein the conductive polymer inhibits dendrite formation and growth on the surface of the metal anode.
The lithium negative electrode includes a lithium metal negative electrode and a lithium alloy negative electrode. The lithium negative electrode includes at least one of a lithium metal negative electrode, a lithium sodium alloy negative electrode, a lithium potassium alloy negative electrode, a lithium silicon alloy negative electrode, a lithium tin alloy negative electrode, and a lithium indium alloy negative electrode.
In one possible implementation manner, the composite metal negative electrode further comprises a current collector, the current collector comprises a first surface and a second surface which are arranged in a back-to-back mode, the metal negative electrode is at least combined with the first surface of the current collector, and the protection layer is at least arranged on the surface of the metal negative electrode, which is away from the current collector. Through setting up the electric current collector, can prevent that metal negative pole from taking place to pulverize in the circulation later stage, influence the electrical contact.
In a second aspect, an embodiment of the present application provides a method for preparing a composite metal anode, including the steps of:
obtaining a mixed solution, wherein the mixed solution is obtained by mixing a conductive polymer and an organic solvent, and the conductive polymer is selected from conductive polymers capable of reversibly doping and dedoping anions;
coating the mixed solution on at least one surface of a metal negative electrode to obtain a composite metal negative electrode, wherein the composite metal negative electrode comprises the metal negative electrode and a protective layer combined on at least one side surface of the metal negative electrode; the material of the protective layer includes the conductive polymer.
According to the preparation method of the composite metal negative electrode, the mixed solution containing the conductive polymer is coated on at least one surface of the metal negative electrode, so that the metal negative electrode with the protective layer arranged on at least one side surface of the metal negative electrode can be prepared. The method is simple to operate, easy to control, good in repeatability and convenient for realizing large-scale production; more importantly, the composite metal negative electrode prepared by the method can effectively inhibit the formation and growth of dendrites on the surface of the metal negative electrode in the battery charging process.
In one possible implementation, the mass ratio of the conductive polymer to the organic solvent in the mixed solution is 1:1-100. In this case, the conductive polymer has a proper concentration in the mixed solution, and after the mixed solution is coated on the surface of the metal anode, a protective layer of a proper thickness is formed.
In one possible implementation, the organic solvent is selected from one or more of azomethylpyrrolidone, acetone, acetonitrile, ethanol, dimethyl carbonate, methylethyl carbonate, diethyl carbonate, tetrahydrofuran, dimethyl ether, dimethyl sulfide, 1, 3-dioxolane, 1, 4-dioxane, 1, 2-dimethoxyethane, ethylene glycol dimethyl ether, bis-trifluoroethyl ether, hexafluoroisopropyl methyl ether, hexafluoroisopropyl ethyl ether, perfluorobutyl methyl ether, perfluorobutyl ethyl ether, tetrafluoroethyl tetrafluoropropyl ether, tetrafluoroethyl octafluoropentyl ether. The conductive polymer may or may not be completely dissolved in the organic solvent, and thus, the mixed solution may be a uniform solution or a suspension in the embodiment of the present application.
In one possible implementation, the mass ratio of the conductive polymer to the organic solvent in the mixed solution is 1:1-100; and the organic solvent is selected from one or more of nitrogen methyl pyrrolidone, acetone, acetonitrile, ethanol, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, tetrahydrofuran, dimethyl ether, dimethyl sulfide, 1, 3-dioxolane, 1, 4-dioxane, 1, 2-dimethoxyethane, ethylene glycol dimethyl ether, bis-trifluoroethyl ether, hexafluoroisopropyl methyl ether, hexafluoroisopropyl ethyl ether, perfluorobutyl methyl ether, perfluorobutyl ethyl ether, tetrafluoroethyl tetrafluoropropyl ether and tetrafluoroethyl octafluoropentyl ether. In this case, the conductive polymer has good dispersibility and a proper concentration, and is advantageous in obtaining a protective layer having a uniform thickness and a proper thickness after the surface of the metal anode is coated.
In a third aspect, an embodiment of the present application provides a secondary battery including: the positive electrode and the negative electrode are oppositely arranged, and the diaphragm and the electrolyte are positioned between the positive electrode and the negative electrode; the negative electrode is the composite metal negative electrode according to the first aspect, the protective layer of the composite metal negative electrode is disposed opposite to the positive electrode, and the anions are anions in the electrolyte.
The secondary battery provided by the embodiment of the application has the negative electrode which is the composite metal negative electrode in the first aspect. In this case, when the secondary battery is charged, since the protective layer can inhibit dendrite formation and growth on the surface of the metal negative electrode from the source, the battery safety and life of the secondary battery including the negative electrode are improved.
In a fourth aspect, an embodiment of the present application provides a terminal, including: the secondary battery according to the third aspect, which is used for supplying power to the terminal.
The terminal provided by the embodiment of the application comprises the secondary battery of the third aspect. In this case, when the secondary battery is charged, since the protective layer can inhibit dendrite formation and growth on the surface of the metal negative electrode from the source, the battery safety and life of the secondary battery including the negative electrode are improved.
Drawings
FIG. 1 is a schematic diagram of the dendrite formation mechanism of an unprotected lithium anode provided in the prior art;
fig. 2 is a schematic structural diagram of a composite metal negative electrode provided with a protective layer on one side surface of the metal negative electrode according to an embodiment of the present application;
FIG. 3 is a schematic view of a composite metal negative electrode with protective layers on both side surfaces of the metal negative electrode according to some embodiments of the present application;
FIG. 4 is a schematic diagram of the function of a composite metal anode provided by an embodiment of the present application;
FIG. 5 is a flow chart of a preparation process of a composite metal anode provided by an embodiment of the application;
fig. 6A is a graph of cycle performance of the batteries provided in examples 2, 4, 6, 8, 10 and 1, 2, 3 of the present application;
fig. 6B is a graph of cycle performance of the batteries provided in example 2, example 4, example 6, and comparative example 1 of the present application;
fig. 6C is a graph of cycle performance of the batteries provided in example 8 and comparative example 2 of the present application;
fig. 6D is a graph of cycle performance of the batteries provided in example 10 of the present application and comparative example 3;
fig. 7 is a Scanning Electron Microscope (SEM) photograph of a lithium metal anode protected after 100 weeks of cycling of the secondary battery provided in example 1 of the present application;
Fig. 8 is a Scanning Electron Microscope (SEM) photograph of an unprotected metallic lithium anode after 100 weeks of cycling of some of the cells provided in comparative example 1 of the present application.
Detailed Description
In order to make the technical problems, technical schemes and beneficial effects to be solved more clear, the application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the application.
In the present application, the terminology used in the embodiments of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and/or" describes an association relationship of associated objects, meaning that there may be three relationships, e.g., a and/or B, which may represent: a alone, a and B together, and B alone. Wherein A, B may be singular or plural. The character "/" generally indicates that the front-to-back associated object is a "and" relationship.
The term "at least one" means one or more, and "a plurality" means two or more. "at least one of" or the like means any combination of these items, including any combination of single item(s) or plural items(s). For example, "at least one (individual) of a, b, or c," or "at least one (individual) of a, b, and c," may each represent: a, b, c, a-b (i.e., a and b), a-c, b-c, or a-b-c, wherein a, b, c may be single or multiple, respectively.
As used in this application and the appended claims, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.
The terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying any relative importance or implying any particular order of such items such as materials, interfaces, messages, requests, and terminals. For example, a first surface may also be referred to as a second surface, and similarly, a second surface may also be referred to as a first surface, without departing from the scope of embodiments of the present application. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more such feature.
In the description of the present application, the weight of the related components mentioned may refer not only to the specific content of each component, but also to the proportional relationship between the weights of each component, and thus, it is within the scope of the disclosure of the embodiments of the present application as long as the content of the related components is scaled up or down according to the embodiments of the present application. Specifically, the mass described in the specification of the embodiment of the application can be mass units known in the chemical industry field such as mu g, mg, g, kg.
It should be understood that, in various embodiments of the present application, the sequence number of each process described above does not mean that the execution sequence of some or all of the steps may be executed in parallel or executed sequentially, and the execution sequence of each process should be determined by its functions and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.
Before describing the embodiments of the present application, the following definitions are given for the terms related to the embodiments of the present application:
positive electrode (Cathode): in the primary battery, the device is a power supply, the potential of an electrode from which current flows is higher, and the electrode is a positive electrode, and the positive electrode plays a role in reduction, namely ions or molecules obtain electrons; in the electrolytic cell, the device is an electric appliance, the electrode connected with the positive electrode of the power supply is the positive electrode based on the connected power supply, and at the moment, the positive electrode plays an oxidation role, namely ions or molecules lose electrons.
Negative electrode (Anode): refers to the end of the power supply where the potential (electric potential) is lower. In a primary battery, the potential of an electrode into which current flows is low, and the electrode is a negative electrode, wherein the negative electrode has an oxidation effect, and the electrode is written on the left in a battery reaction; in the electrolytic cell, an electrode connected with a negative electrode of a power supply is a negative electrode, and electrons are obtained from the negative electrode to play a role in reduction. From a physical point of view, the negative electrode is the one from which electrons flow out of the circuit.
Electrolyte (Electrolyte) is a medium between the positive and negative electrodes of the cell and is used to provide ion exchange.
Separator (Separator): and in the electrolytic reaction, the film is used for separating the positive electrode from the negative electrode so as to prevent the contact of the electrodes and the short circuit. In addition, the separator also has a function of allowing electrolyte ions to pass through.
The conductive polymer (Conducting Polymer) is a polymer material with main chain having conjugated main electron system, such as conjugated pi-bond, and capable of being changed from insulating state to conductive state by chemical or electrochemical 'doping'.
PTC is an abbreviation of "Positive Temperature Cofficient", which refers broadly to semiconductor materials or components with a very high positive temperature coefficient, and is commonly referred to as a positive temperature coefficient thermistor, abbreviated as PTC thermistor. PTC has a characteristic that the resistivity increases with an increase in temperature, and in a battery, PTC can improve the safety of the battery in use.
SEI is an abbreviation of "solid electrolyte interphase" and means an interface protective film or a solid electrolyte interface (film), and refers to a passivation film layer having solid electrolyte properties.
EC is an abbreviation of "ethylene carbonate" representing ethylene carbonate.
DMC is an abbreviation for "dimethyl carbonate" and represents dimethyl carbonate.
FEC is an abbreviation for "Fluoroethylene carbonate" and represents fluoroethylene carbonate.
And (3) a secondary battery: (Rechargeable battery) also called a rechargeable battery or a storage battery, means a battery which can be continuously used by activating an active material by charging after discharging the battery.
In connection with fig. 1, a typical operation scenario and failure mechanism will be described using a lithium metal battery with a metal negative electrode as a negative electrode as an example:
the core components of the lithium metal battery mainly comprise a positive electrode, a metal lithium negative electrode, electrolyte and a diaphragm, wherein the diaphragm is arranged between the positive electrode and the negative electrode. When the lithium metal battery is charged, lithium ions are extracted from crystal lattices of the positive electrode material and deposited on the surface of the negative electrode of the metal lithium through electrolyte; when a lithium metal battery discharges, lithium at the negative electrode of the metal lithium loses electrons and is oxidized into lithium ions, and the lithium ions are inserted into the crystal lattice of the positive electrode material through the electrolyte. In the primary charge and discharge process, lithium ions react with a solvent (such as EC/DMC), trace water, HF and the like, and an interface protection film (SEI) is formed on the surface of the electrode.
When the lithium metal battery is stationary, the charge in the electrolyte is uniformly distributed. During charge and discharge cycles, the interfacial protection film is unstable, resulting in direct contact of the exposed metallic lithium with the electrolyte, causing serious side reactions and inducing lithium dendrite formation, thereby reducing coulomb efficiency and causing safety problems. Specifically, in the charging process, under the action of an electric field, the roughness and the non-uniformity of the surface of lithium metal lead to non-uniform current distribution, and lithium ions from a positive electrode are selectively deposited on the surface of the lithium metal to form lithium dendrites. Further, after lithium dendrite formation, lithium ions are preferentially deposited at the tip sites under the effect of the tip effect (negative charges are more densely distributed at the tip), resulting in an increase in current density at the tip sites and localized heat generation (the temperature of the tip region is higher than that of the non-tip region). The newly generated lithium dendrite has large specific surface area and high reaction activity with the electrolyte, so that side reaction between the lithium dendrite and the electrolyte is increased, the coulomb efficiency of the lithium cathode is reduced, and the battery cycle stability is reduced; and the increase of side reaction further generates heat, so that potential safety hazards exist for the battery. Meanwhile, as the lithium dendrite grows continuously, when the lithium dendrite grows to a certain extent, the lithium dendrite penetrates through the diaphragm, so that the battery is short-circuited, the safety problem is further caused, and the service life of the battery is shortened. In addition, lithium dendrites break down during dissolution to form "dead lithium" causing a decrease in the negative electrode capacity.
Research shows that by constructing a stable interface on the surface of the metal negative electrode in a physical or chemical mode, the surface activity of the metal negative electrode can be reduced, and the metal ion flow can be homogenized, so that the growth of dendrites is relieved, and the volume expansion is relieved. However, no stable interface construction scheme which is effective and can realize mass production is found at present.
In view of this, in combination with fig. 2 and 3, a first aspect of the present application provides a composite metal anode, including: a metal anode 10, and a protective layer 11 bonded to at least one side surface of the metal anode 10. The material of the protective layer 11 includes a conductive polymer, and the conductive polymer is selected from conductive polymers capable of reversibly doping and dedoping anions.
It should be appreciated that the metallic negative electrode 10 described above includes a first surface and a second surface. As an example, as shown in fig. 2, the protective layer 11 may be bonded to the first surface or the second surface of the metal anode 10. As another example, as shown in fig. 3, the protective layer 11 may be bonded to the first surface and the second surface of the metal anode 10.
In the composite metal negative electrode provided by the embodiment of the application, the protective layer 11 is arranged on at least one side surface of the metal negative electrode 10. The material of the protective layer 11 comprises a conductive polymer selected from the group consisting of anions capable of being reversibly doped and undoped. In this case, the protective layer 11 can effectively inhibit dendrite growth on the surface of the metal negative electrode during battery charging, and solve the problems of battery safety and life span due to dendrite from the source. With reference to fig. 4, the specific principle is as follows:
In the charging process of the battery using the composite metal anode, the conductive polymer in the protective layer 11 is subjected to electrochemical oxidation doping, and anions are doped. Since anions are uniformly doped in the conductive polymer, cations can be uniformly deposited on the surface of the composite metal anode, thereby preventing dendrite formation by selective deposition of cations on localized areas of the metal anode 10. Thus, the protective layer 11 can solve the problems of safety and life of the battery due to dendrites from the source.
In addition, by adopting the conductive polymer as the protective layer material, a polymer elastic film can be formed on the surface of the metal negative electrode 10, so that the volume expansion of the composite metal negative electrode (the metal negative electrode 10 is mainly referred to in the embodiment of the application) in the circulating process is effectively relieved, the interface of the composite metal negative electrode is stabilized, the side reaction is reduced, and the coulomb efficiency is improved.
In one possible implementation manner, the composite metal anode provided by the embodiment of the application can be used as an anode of a secondary battery. The composition of the composite metal anode is specifically described below.
The metal negative electrode 10 is used as a composite metal negative electrode body, has higher theoretical specific capacity and low electrochemical potential, and provides a material basis for improving the energy density of the secondary battery.
The metal negative electrode 10 is a negative electrode made of a metal. By way of example, the metal negative electrode 10 in the embodiment of the present application is selected from one or more of a lithium negative electrode, a sodium negative electrode, a potassium negative electrode, a magnesium negative electrode, a zinc negative electrode, and an aluminum negative electrode. The lithium negative electrode is a negative electrode made of metal lithium or lithium alloy.
As one possible implementation, the lithium negative electrode includes at least one of a lithium metal negative electrode, a lithium sodium alloy negative electrode, a lithium potassium alloy negative electrode, a lithium silicon alloy negative electrode, a lithium tin alloy negative electrode, and a lithium indium alloy negative electrode.
In the embodiment of the present application, a protective layer 11 containing a conductive polymer is bonded to at least one side surface of the metal negative electrode 10 for preventing dendrite formation of the metal negative electrode 10 during charging. In an embodiment of the present application, the composite metal anode is used as the anode of a secondary battery, and the conductive polymer is reversibly doped and undoped anions derived from anions in the electrolyte of the secondary battery, including but not limited to hexafluorophosphate anions (PF) 6 - ) Hexafluoroarsenate anion (AsF) 6 - ) Perchlorate anions (ClO) 4 - ) Tetrafluoroborate anions (BF) 4 - ) Boron dioxalate anion (BOB) - ) Difluoro-oxalic acid borate anions (DFOB) - ) Bis-fluorosulfonyl imide anions (FSI) - ) Two to threeFluorosulfonimide anions (TFSI) - )。
In one possible implementation, the conductive polymer is selected from conductive polymers having thermal sensitivity, i.e., the conductive polymer used as the protective layer 11 of the embodiment of the present application, causes a chemical or physical change under thermal energy conditions, and its electrical resistance is affected by temperature. In this case, the protective layer 11 can further suppress the growth of dendrites on the surface of the composite metal anode during battery charging. With reference to fig. 4, the specific principle is as follows:
during the charging process, the area where dendrites are located is higher in temperature than other areas where dendrites are not formed due to local current increase or side reaction increase under the action of an electric field. When the temperature of the region where the dendrite is located reaches the thermosensitive critical temperature of the conductive polymer, the thermosensitive property of the conductive polymer is excited, and the conductive polymer changes the spatial conformation and reduces the conjugation degree through dedoping. At this point the resistance of the conductive polymer increases, the conductivity decreases, the resistance to deposition of cations at the tips (dendrite-forming areas) increases, and cations tend to deposit toward non-tips (dendrite-forming other areas) where the resistance is lower. Thus, the dendrite growth can be hindered by the thermosensitive property of the conductive polymer, thereby preventing dendrite growth to some extent to penetrate the separator and cause short circuit of the battery.
In one possible implementation, the conductive polymer is selected from conductive polymers having an impedance that increases with increasing temperature in the range of 50 ℃ to 130 ℃. In this case, in the battery using the above composite metal anode as the anode, the conductive polymer in the protective layer 11 has thermal sensitivity in the range of 50 ℃ to 130 ℃, i.e., the conductive polymer can increase resistance by dedoping anions and changing its spatial configuration in the temperature range to adjust the deposition of cations in the non-dendrite region, thereby achieving the purpose of balancing the non-dendrite region and the thickness uniformity of dendrite region, and finally avoiding dendrite growth. It will be appreciated that the conductive polymer, depending on the specific structural composition, increases resistance to regulate conductivity by dedoping anions and changing its spatial configuration at a certain temperature value in the range of 50-130 ℃. There are differences in the temperatures of different conductive polymers that are dedoped with anions and change the spatial configuration. I.e. the critical temperatures at which the impedance thermosensitive effect occurs differ for different conductive polymers.
In addition, when the conductive polymer with the impedance increased along with the temperature rise is selected in the temperature range of 50-130 ℃, the temperature of the composite metal negative electrode is lower in the initial charge stage of the battery, the conductive polymer exists in a doped anion form, a uniform negative charge interface is provided for the combination of cations on the surface of the composite metal negative electrode, and the regional deposition of the cations on the surface of the composite metal negative electrode is prevented, so that the probability of dendrite formation is reduced from the source; meanwhile, in the middle and later stages of charging, under the condition that dendrites are formed, the temperature of the area where the dendrites are located is increased, and when the temperature is high enough that the conductive polymer is subjected to space configuration change and anions are removed, the impedance of the conductive polymer in the area where the dendrites are located is increased, and the deposition of cations in the dendrite positions is reduced, so that the growth of the dendrites is inhibited. Therefore, the aim of inhibiting dendrite formation and growth is achieved through the double-layer effect of the conductive polymer in different charging periods. If the critical temperature of the conductive polymer is too low (the conductive polymer is too sensitive to temperature), the conductive polymer changes when the ambient temperature slightly fluctuates, which is not beneficial to lithium ion transmission; if the critical temperature of the conductive polymer is too high (the conductive polymer is insensitive to temperature), the heating effect caused by the formation of lithium dendrites cannot be effectively sensed, and the effect of inhibiting the growth of metal negative dendrites in the middle and later stages of charging is not obvious.
In the embodiment of the application, the conductive polymer can be selected from homopolymers polymerized by adopting the same structural units, and can also be selected from copolymers polymerized by adopting different structural units.
In one possible implementation, the general formula of the same or different structural units is shown in formula (1) below:
in the formula (1), X is selected from NH, O or S;
R 1 、R 2 each independently selected from any one of hydrogen, halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkenyloxy, haloalkenyloxy, aryl, haloaryl, aryloxy, haloaryloxy.
In one example, in formula (1), X is NH and the corresponding structural unit has the structure:in another example, in formula (1), X is O and the corresponding structural unit has the structure: />In yet another example, the corresponding X is S and the corresponding structural unit has the structure: />The conductive polymer may be selected from a homopolymer formed of one of the formula (11), the formula (12), and the formula (13); two different structural monomers such as a copolymer formed by the formula (11) and the formula (12), the formula (11) and the formula (13), the formula (12) and the formula (13) can also be adopted; copolymers formed from three structural monomers of formula (11), formula (12) and formula (13) are also possible. It should be noted that when the conductive polymer is a copolymer composed of two different structural monomers or three different structural monomers, the types of substituents in the different structural monomers may be the same or different. R in formula (12) as in the case where the conductive polymer is a copolymer of formula (12) and formula (13) 1 And R in formula (13) 1 May be the same (e.g., H) or different (e.g., R in formula (12) 1 Is H, R in formula (13) 1 Is a haloalkenyl group); likewise, R in formula (12) 2 And R in formula (13) 2 May be the same (e.g., H) or different (e.g., R in formula (12) 2 Is C 6 H 13 R in formula (13) 2 H).
The conductive polymer formed by the structural units shown in the general formula (1) changes the spatial conformation by doping anions in the battery charging process, enhances the planeness of the five-membered ring and forms a conjugated structure with higher stability and better conductive performance. At this time, anions are uniformly doped in the conductive polymer, so that selective deposition of cations is avoided, the deposition uniformity of the cations on the surface of the metal negative electrode is improved, and the formation probability of dendrites is reduced. Further, the conductive polymer formed by the structural unit represented by the formula (1) has heat sensitivity, and the resistance increases when the temperature is as high as its heat sensitive critical temperature. Therefore, once dendrites are formed on the surface of the composite metal anode, the temperature of the area where the dendrites are located is increased, the conductive polymer of the corresponding area is dedoped with anions, and meanwhile, the configuration is converted into a twistable five-membered ring structure (the conjugation degree is reduced), so that the conductivity of the area where the dendrites are located is reduced, cations are deposited in the non-dendrite area with higher conductivity (lower resistance), and finally, the aim of avoiding the dendrites from growing continuously is achieved.
With structural units C 6 H 13 -C 4 H 3 S and anion is TFSI - For example, the structural change after the conductive polymer binds to the anion is shown in the following formula:
in the above formula, the conductive polymer (left formula structure) which is not combined with anions has low conductivity and weaker conductivity; the conductive polymer (right formula structure) combined with anions has high conjugation degree, good conductivity and strong capability of inducing cation combination.
In one possible implementation, in formula (1), the halogen is selected from one of fluorine, chlorine, bromine, iodine.
In one possible implementation, in formula (1), the number of carbon atoms in the alkyl, haloalkyl, alkoxy, haloalkoxy is from 1 to 20. When the number of carbon atoms is within the above range, the resulting conductive polymer has suitable thermosensitive properties.
In one possible implementation, the number of carbon atoms in the alkyl, haloalkyl, alkoxy, haloalkoxy is from 1 to 10.
In one possible implementation, in formula (1), the number of carbon atoms in the alkenyl, haloalkenyl, alkenyloxy, haloalkenyloxy is 2-10. When the number of carbon atoms is within the above range, the resulting conductive polymer has suitable thermosensitive properties.
In one possible implementation, the number of carbon atoms in the alkenyl, haloalkenyl, alkenyloxy, haloalkenyloxy is from 2 to 10.
In one possible implementation, in formula (1), the number of carbon atoms in the aryl, haloaryl, aryloxy, haloaryloxy is 6-20. When the number of carbon atoms is within the above range, the resulting conductive polymer has suitable thermosensitive properties.
In one possible implementation, the number of carbon atoms in the aryl, haloaryl, aryloxy, haloaryloxy groups is from 6 to 10.
In one possible implementation manner, in the formula (1), halogen in the haloalkyl, haloalkoxy, haloalkenyl, haloalkenoxy, haloaryl and haloaryloxy is independently selected from at least one of fluorine, chlorine, bromine and iodine. It is understood that the hydrogen in the alkyl, alkoxy, alkenyl, alkenyloxy, aryl, aryloxy groups in the haloalkyl, haloalkoxy, haloalkenyl, haloalkenyloxy, haloaryl, haloaryloxy groups may be partially or fully halogenated to form the corresponding haloalkyl, haloalkoxy, haloalkenyl, haloalkenyloxy, haloaryl, haloaryloxy groups.
In the above embodiment, in the formula (1), the alkyl group, the haloalkyl group, the alkoxy group, the haloalkoxy group, the alkenyl group, the haloalkenyl group, the alkenyloxy group, the haloalkenyloxy group, the aryl group, the haloaryl group, the aryloxy group, and the haloaryloxy group may be a linear substituent or a substituent having a branched chain.
In one possible implementation manner, the conductive polymer is selected from at least one of the compounds (A) to (P) shown in the following structures, wherein n has a value ranging from 10 to 10000, and n 1 +n 2 The values of (2) satisfy the following: n is more than or equal to 10 1 +n 2 ≤10000；
/>
/>
In one possible implementation, the protective layer 11 in the example of the application consists of a conductive polymer. In this case, the conductive polymer is doped with anions during the charging process, so that cations are regulated and controlled to be uniformly deposited on the surface of the composite metal negative electrode, and dendrite formation is avoided; and regulating and controlling the deposition of cations on the surface of the composite metal anode outside the area where dendrites are located by removing anions, thereby inhibiting the growth of dendrites. In addition, since the liquid crystal display device does not contain other components, the interference of the other components on the regulation and control effect can be avoided.
In one possible implementation, the material of the protective layer 11 in the example of the application also comprises a binder. Wherein, the binder is used for improving the binding force of the conductive polymer on the surface of the metal negative electrode 10, and the protective layer 11 is bound on at least one side surface of the metal negative electrode 10 through the binder. In other words, the protective layer 11 in the above-described composite metal anode includes not only the conductive polymer but also the binder. In one possible embodiment, the material of the protective layer 11 in the example of the application consists of a conductive polymer and a binder.
In one possible implementation, the binder is selected from one or more of polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polytetrafluoroethylene (PTFE), polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), polyacrylonitrile (PAN), polyimide (PI), polyethylene glycol (PEG), polyethylene oxide (PEO), polydopamine (PDA), sodium carboxymethyl cellulose/styrene butadiene rubber (CMC/SBR), polyvinyl alcohol (PVA), polyacrylic acid (PAA), lithium polyacrylate (LiPAA), polyvinylpyrrolidone (PVP), polylactic acid (PLA), sodium Alginate (SA), poly-p-styrenesulfonic acid (PSS), lithium poly-p-styrenesulfonate (lipsp), and gelatin. Wherein the polyvinylidene fluoride-hexafluoropropylene is a copolymer of polyvinylidene fluoride and hexafluoropropylene; the sodium carboxymethyl cellulose/styrene-butadiene rubber is a mixture of sodium carboxymethyl cellulose and styrene-butadiene rubber. The adhesive can improve the binding force of the conductive polymer on the surface of the metal negative electrode, so that the protective layer is firmly bonded on the surface of the metal negative electrode.
In one possible embodiment, the mass ratio of the conductive polymer to the binder in the examples of the present application is 1-100:1. The mass ratio of the conductive polymer to the binder is in the above range, and the binder can improve the binding force of the conductive polymer on the surface of the metal anode 10. If the content of the binder is too high, the relative content of the conductive polymer is reduced, which weakens the effect of the conductive polymer in inhibiting dendrite formation and dendrite growth, and in addition, increases the resistance of the protective layer 11, thereby being unfavorable for the transfer of cations.
As an example, the mass ratio of the conductive polymer to the binder in the embodiments of the present application may be a specific ratio of 100:1, 95:1, 90:1, 85:1, 80:1, 75:1, 70:1, 65:1, 60:1, 55:1, 50:1, 45:1, 40:1, 35:1, 30:1, 25:1, 10:1, 5:1, 2:1, 1:1, etc.
In one possible implementation, the thickness of the protective layer 11 is 1nm-20 μm. Because of the limitation of the conductivity of the conductive polymer, the thickness of the protective layer 11 is not too thick, so that the embodiment of the application can inhibit the growth of dendrites by setting the thickness of the protective layer 11 within the range of 1nm-20 μm, thereby improving the safety performance and the service life of the battery. If the protective layer 11 is too thick, the resistance of the protective layer 11 itself increases, which is rather unfavorable for the transmission of metal ions.
In one possible implementation, the thickness of the protective layer 11 is 1 μm to 10 μm, in which case the protective layer 11 can exert excellent dendrite formation and growth inhibition effects during battery charging without decreasing the cation transport efficiency.
As an example, the thickness of the protective layer 11 in the embodiment of the present application may be specifically 1nm, 5nm, 10nm, 100nm, 200nm, 500nm, 800nm, 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm, 20 μm.
In a possible embodiment, the composite metal negative electrode in the embodiment of the present application further comprises a current collector, the current collector comprising a first surface and a second surface, wherein the metal negative electrode 10 is bonded to at least the first surface of the current collector, and the protective layer 11 is disposed on at least a surface of the side of the metal negative electrode 10 facing away from the current collector. Through setting up the electric current collector, can prevent that metal negative pole from taking place to pulverize in the circulation later stage, influence the electrical contact.
The composite metal anode provided by the embodiment of the application can be prepared by the following method.
As shown in fig. 5, an embodiment of the present application provides a method for preparing a composite metal anode, including the following steps:
s01, obtaining a mixed solution, wherein the mixed solution is obtained by mixing a conductive polymer and an organic solvent, and the conductive polymer is selected from conductive polymers capable of reversibly doping and dedoping anions;
s02, coating a mixed solution on at least one surface of a metal negative electrode to obtain a composite metal negative electrode, wherein the composite metal negative electrode comprises a metal negative electrode and a protective layer combined on at least one side surface of the metal negative electrode; the material of the protective layer comprises the conductive polymer.
According to the preparation method of the composite metal negative electrode, the mixed solution containing the conductive polymer is coated on at least one surface of the metal negative electrode, so that the metal negative electrode with the protective layer arranged on at least one side surface of the metal negative electrode can be prepared. The method is simple to operate, easy to control, good in repeatability and convenient for realizing large-scale production; more importantly, the composite metal negative electrode prepared by the method can effectively inhibit the formation and growth of dendrites on the surface of the metal negative electrode in the battery charging process.
Specifically, in the above step S01, in one possible embodiment, the mixed solution in the example of the present application is obtained by adding the conductive polymer to the organic solvent. As an example, the mixed solution in the embodiment of the present application is obtained by dispersing a conductive polymer in an organic solvent and performing stirring and mixing treatment.
Wherein the conductive polymer is selected from conductive polymers capable of reversibly doping and dedoping anions, the choice of conductive polymer and its optional case are not described here again.
As an example, in one possible embodiment, the organic solvent in the examples of the present application is selected from one or more of the group consisting of azomethylpyrrolidone, acetone, acetonitrile, ethanol, dimethyl carbonate, methylethyl carbonate, diethyl carbonate, tetrahydrofuran, dimethyl ether, dimethyl sulfide, 1, 3-dioxolane, 1, 4-dioxane, 1, 2-dimethoxyethane, ethylene glycol dimethyl ether, bis-trifluoroethyl ether, hexafluoroisopropyl methyl ether, hexafluoroisopropyl ethyl ether, perfluorobutyl methyl ether, perfluorobutyl ethyl ether, tetrafluoroethyl tetrafluoropropyl ether, tetrafluoroethyl octafluoropentyl ether. The above-mentioned organic solvent may be completely dissolved or may not be completely dissolved, and thus, the mixed solution in the embodiment of the present application may be a homogeneous solution or a suspension.
In one possible embodiment, the mass ratio of the conductive polymer to the organic solvent in the examples of the present application is 1:1-100, in which case the conductive polymer has a suitable concentration in the mixed solution, and a protective layer of a suitable thickness is formed after the mixed solution is coated on the surface of the metal anode.
As an example, the mass ratio of the conductive polymer to the organic solvent in the embodiments of the present application is 1:1, 1:2, 1:3, 1:5, 1:10, 1:15, 1:20, 1:25, 1:30, 1:35, 1:40, 1:45, 1:50, 1:55, 1:60, 1:65, 1:70, 1:75, 1:80, 1:85, 1:90, 1:95, 1:100.
In one possible implementation, the mass ratio of the conductive polymer to the organic solvent in the mixed solution is 1:1-100; and the organic solvent is selected from one or more of nitrogen methyl pyrrolidone, acetone, acetonitrile, ethanol, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, tetrahydrofuran, dimethyl ether, dimethyl sulfide, 1, 3-dioxolane, 1, 4-dioxane, 1, 2-dimethoxyethane, ethylene glycol dimethyl ether, bis-trifluoroethyl ether, hexafluoroisopropyl methyl ether, hexafluoroisopropyl ethyl ether, perfluorobutyl methyl ether, perfluorobutyl ethyl ether, tetrafluoroethyl tetrafluoropropyl ether and tetrafluoroethyl octafluoropentyl ether. In this case, the conductive polymer has good dispersibility and a proper concentration, and is advantageous in obtaining a protective layer having a uniform thickness and a proper thickness after the surface of the metal anode is coated.
In one possible embodiment, the mixed solution of the examples of the present application further contains a binder. In other words, the above mixed solution is obtained by mixing the conductive polymer, the binder and the organic solvent. In one possible embodiment, the mixed solution in the examples of the present application is obtained by dispersing the conductive polymer and the binder in an organic solvent and performing a stirring and mixing process.
In one possible implementation, the binder is selected from one or more of polyvinylidene fluoride, polymethyl methacrylate, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene, polyacrylonitrile, polyimide, polyethylene glycol, polyethylene oxide, polydopamine, sodium carboxymethyl cellulose/styrene butadiene rubber, polyvinyl alcohol, polyacrylic acid, lithium polyacrylate, polyvinylpyrrolidone, polylactic acid, sodium alginate, poly-p-styrenesulfonic acid, lithium poly-p-styrenesulfonate, and gelatin. Wherein the polyvinylidene fluoride-hexafluoropropylene is a copolymer of polyvinylidene fluoride and hexafluoropropylene; the sodium carboxymethyl cellulose/styrene-butadiene rubber is a mixture of sodium carboxymethyl cellulose and styrene-butadiene rubber.
In one possible embodiment, the mass ratio of the conductive polymer to the binder in the examples of the present application is 1-100:1.
In step S02, the metal negative electrode is a negative electrode made of a metal. By way of illustration, the metal negative electrode in the embodiments of the present application is selected from one or more of a lithium negative electrode, a sodium negative electrode, a potassium negative electrode, a magnesium negative electrode, a zinc negative electrode, and an aluminum negative electrode. The lithium negative electrode is a negative electrode made of metal lithium or lithium alloy. As one possible implementation, the lithium negative electrode includes at least one of a lithium metal negative electrode, a lithium sodium alloy negative electrode, a lithium potassium alloy negative electrode, a lithium silicon alloy negative electrode, a lithium tin alloy negative electrode, and a lithium indium alloy negative electrode.
It should be appreciated that the metallic negative described above includes a first surface and a second surface. In one example, the mixed solution is coated on the first surface or the second surface of the metal negative electrode, and the protective layer is prepared on the single-side surface of the metal negative electrode. In another example, the mixed solution is coated on the first surface and the second surface of the metal negative electrode, and the protective layers are prepared on both side surfaces of the metal negative electrode.
Means for applying the mixed solution to the surface of the metal negative electrode include, but are not limited to: drop coating, brush coating, roller coating, spray coating, knife coating, dip coating and spin coating. In one possible implementation manner, the mass ratio of the conductive polymer to the organic solvent in the embodiment of the application is 1:1-100, and the time for coating the organic dispersion liquid of the conductive polymer on one side surface of the metal negative electrode is 1 min-12 h, so that the protective layer with the thickness of 1 nm-20 μm is prepared on one side surface of the metal negative electrode. It should be understood that this embodiment is a time for coating the mixed solution on one side surface of the metal negative electrode, and when the protective layers are prepared on both side surfaces of the metal negative electrode, the protective layers on both side surfaces may be realized by simultaneously coating the mixed solution on both side surfaces or sequentially coating the mixed solution, the time being 1min to 12h with reference to the coating time of one side surface. It should be appreciated that in the case where the concentration of the conductive polymer in the mixed solution is determined, the thickness of the protective layer is positively correlated with the coating time.
In one possible implementation, the embodiment of the application coats the mixed solution on at least one side surface of the metal negative electrode, and the mixed solution is carried out at the temperature of-10 ℃ to 50 ℃ so as to prevent the volatilization of the organic solvent in the mixed solution.
In the embodiment of the application, the mixed solution of the conductive polymer is coated on at least one side surface of the metal negative electrode, and the mixed solution can be performed in a drying room or under a protective atmosphere, but is not limited to the above. As one example, the protective atmosphere includes, but is not limited to, a nitrogen atmosphere, an argon atmosphere.
In a third aspect, an embodiment of the present application provides a secondary battery including: the positive electrode, the negative electrode, the diaphragm and the electrolyte are oppositely arranged, and the diaphragm and the electrolyte are positioned between the positive electrode and the negative electrode; the negative electrode is a composite metal negative electrode provided in the first aspect of the embodiment of the application, and the protective layer of the composite metal negative electrode is opposite to the positive electrode.
The embodiment of the application provides a secondary battery, wherein a negative electrode in the secondary battery adopts a composite metal negative electrode, and the composite metal negative electrode comprises a metal negative electrode and a protective layer combined on at least one side surface of the metal negative electrode; the material of the protective layer comprises a conductive polymer, and the conductive polymer is selected from conductive polymers capable of reversibly doping and dedoping anions. Wherein the anions of the conductive polymer that are reversibly doped and undoped are anions in the electrolyte. Illustratively, the anion of the conductive polymer that is reversibly doped and undoped is an anion of an electrolyte in the electrolyte solution; when the solvent in the electrolyte contains anions, the anions of the conductive polymer that are reversibly doped and undoped may also be anions of the solvent in the electrolyte. In this case, the secondary battery can avoid the reaction of cations on the surface of the metal negative electrode to form dendrites during the charging process, and the coulomb efficiency of the battery is reduced; in addition, dendrite growth to contact the positive electrode is avoided, causing safety problems.
It should be noted that, in the secondary battery provided by the present application, the positive electrode is disposed opposite to the protective layer of the composite metal negative electrode. When the composite metal negative electrode is provided with the protective layers on the surfaces of both sides of the metal negative electrode at the same time, the positive electrode is arranged opposite to the protective layer on one side of the composite metal negative electrode at least.
In one possible implementation, the composite metal anode in the embodiment of the present application further includes a current collector, where the current collector includes a first surface and a second surface; the metal negative electrode is at least combined on the first surface of the current collector, and the protective layer is at least arranged on one side surface of the metal negative electrode, which is away from the current collector.
By way of illustration, the metal negative electrode in the embodiments of the present application is selected from one or more of a lithium negative electrode, a sodium negative electrode, a potassium negative electrode, a magnesium negative electrode, a zinc negative electrode, and an aluminum negative electrode. The lithium negative electrode is a negative electrode made of metal lithium or lithium alloy.
As one possible implementation, the lithium negative electrode includes at least one of a lithium metal negative electrode, a lithium sodium alloy negative electrode, a lithium potassium alloy negative electrode, a lithium silicon alloy negative electrode, a lithium tin alloy negative electrode, and a lithium indium alloy negative electrode.
As one possible implementation manner, in an embodiment of the present application, the positive electrode includes a current collector, and a positive electrode material bonded to the current collector, where the positive electrode material includes at least a positive electrode active material. In the embodiments of the present application, the positive electrode active material conventionally used for the secondary battery can be applied to the embodiments of the present application.
As one possible implementation, in an embodiment of the present application, the electrolyte includes an organic solvent and an electrolyte. Because water has certain influence on the formation of SEI of the lithium ion battery and the battery performance, the SEI has the characteristics of reduced battery capacity, shortened discharge time, increased internal resistance, reduced circulating capacity, expanded battery and the like. In some embodiments, the organic solvent may be a non-aqueous organic solvent.
As a possible implementation manner, the electrolyte in the embodiment of the present application may further contain an additive. The additive is mainly used for improving the film forming performance during the first charge and discharge.
In one possible implementation, the separator is disposed between the positive electrode and the protective layer of the composite metal negative electrode.
In a fourth aspect, an embodiment of the present application provides a terminal including the secondary battery of the third aspect, the secondary battery being for supplying power to the terminal. Since the negative electrode of the secondary battery is the composite metal negative electrode provided in the first aspect, the secondary battery of the third aspect is adopted as the terminal of the power supply module, and the safety performance and the service life thereof can be improved accordingly.
The following description is made with reference to specific embodiments.
The following describes in detail, with reference to different examples, a method for manufacturing a composite metal anode and a secondary battery according to an embodiment of the present application.
In example 1, a composite lithium metal negative electrode was prepared by taking a conductive polymer as 3-hexyl-substituted polythiophene, an organic solvent as ethylene glycol dimethyl ether, and a lithium metal negative electrode as an example.
A3-hexyl-substituted polythiophene-protected composite metal lithium anode with thermosensitive properties is prepared by the following steps: dispersing 0.25g of a compound powder represented by the following formula (A) in 10mL of ethylene glycol dimethyl ether in a drying room, and stirring and mixing to form a uniform dispersion; and (3) coating the dispersion liquid on the surface of the metal lithium negative electrode in a dripping mode, wherein the coating (dripping) time is 5min, and after the solvent is evaporated to dryness, a 3-hexyl-substituted polythiophene protective layer with the thickness of 2 mu m is formed on the surface of the metal lithium negative electrode, so that the composite metal lithium negative electrode is obtained.
Example 2A composite metal negative electrode prepared in example 1 was used as a negative electrode, a positive electrode binder was polyvinylidene fluoride, a positive electrode conductive agent was super P, a positive electrode material was lithium cobaltate, a positive electrode current collector was aluminum foil, and an electrolyte was LiPF 6 The organic solvent in the electrolyte is a mixed solvent of EC, DMC and FEC, and the separator is a commercial PE separator as an example, to prepare a lithium secondary battery.
A lithium secondary battery is prepared by the following steps:
(1) And obtaining the positive pole piece.
Wherein, the positive pole piece can be obtained by the following modes: weighing polyvinylidene fluoride (PVDF) with the mass percentage of 2%, super P with 2% conductive agent and 96% lithium cobaltate (LiCoO) 2 ) Adding the mixture into N-methyl pyrrolidone (NMP), fully stirring and uniformly mixing, coating the obtained slurry on an aluminum foil current collector, drying, cold pressing and cutting to obtain the positive electrode plate.
(2) Preparing a battery cell from the positive electrode plate obtained in the step (1), the protective metal lithium negative electrode prepared in the embodiment 1 and the commercial PE diaphragm, packaging by adopting a polymer, and pouring 1.0mol/L LiPF 6 The electrolyte (the weight ratio of the organic solvent EC, DMC, FEC in the electrolyte is 20:50:30) is prepared into the soft-package lithium secondary battery through processes such as formation and the like.
Example 3 a composite lithium metal negative electrode was prepared using polypyrrole as the conductive polymer, azomethine pyrrolidone as the organic solvent, and lithium metal negative electrode as the metal negative electrode.
The polypyrrole-protected composite metal lithium negative electrode with heat-sensitive characteristic is prepared by the following steps: dispersing 0.25g of a compound powder represented by the following formula (B) in 30mL of nitrogen methyl pyrrolidone in a drying room, and stirring and mixing to form a uniform dispersion; and (3) coating the dispersion liquid on the surface of the unprotected metallic lithium negative electrode in a brushing mode, wherein the coating (brushing) time is 10min, and a polypyrrole protective layer with the thickness of 3 mu m is formed on the surface of the metallic lithium negative electrode after the solvent is evaporated to dryness, so that the composite metallic lithium negative electrode is obtained.
Example 4 the composite metal negative electrode prepared in example 3 was a negative electrode, the positive electrode binder was polyvinylidene fluoride, the positive electrode conductive agent was super P, the positive electrode material was lithium cobaltate, the positive electrode current collector was aluminum foil, and the electrolyte was LiPF 6 The organic solvent in the electrolyte is a mixed solvent of EC, DMC and FEC, and the separator is a commercial PE separator as an example, to prepare a lithium secondary battery.
A lithium secondary battery is prepared by the following steps:
(1) And obtaining the positive pole piece. The method is the same as step (1) in example 2, and will not be repeated here.
(2) Preparing a battery cell from the positive electrode plate obtained in the step (1), the protective metal lithium negative electrode prepared in the example 3 and the commercial PE diaphragm, packaging by adopting a polymer, and pouring 1.0mol/L LiPF 6 The electrolyte (in which the weight ratio of the organic solvent EC, DMC, FEC is 20:50:30) is prepared into the soft-package lithium secondary battery through processes such as formation and the like.
Example 5 a composite lithium metal negative electrode was prepared using 3-heptyl substituted polyfuran as the conductive polymer, perfluorobutyl methyl ether as the organic solvent, and lithium metal negative electrode as the metal negative electrode.
A3-heptyl substituted polyfuran-protected composite metal lithium anode with thermosensitive properties is prepared by the following steps: dispersing 0.25g of a compound powder represented by the following formula (C) in 20mL of perfluorobutyl methyl ether in a drying room, and stirring and mixing to form a uniform dispersion; and (3) coating the dispersion liquid on the surface of the metal lithium negative electrode in a spin coating mode, wherein the coating (spin coating) time is 20min, and after the solvent is evaporated to dryness, the surface of the metal lithium negative electrode forms a 3-heptyl substituted polyfuran protective layer with the thickness of 3 mu m, so that the composite metal lithium negative electrode is obtained.
Example 6 Using the composite Metal negative electrode prepared in example 5 as the negative electrode, the Positive electrode binder was polyvinylidene fluoride (PVDF), the positive electrode conductive agent was super P, the positive electrode material was lithium cobalt oxide, the positive electrode current collector was aluminum foil, and the electrolyte was LiPF 6 The organic solvent in the electrolyte is a mixed solvent of EC, DMC and FEC, and the separator is a commercial PE separator as an example, to prepare a lithium secondary battery.
A lithium secondary battery is prepared by the following steps:
(1) And obtaining the positive pole piece. The method is the same as step (1) in example 2, and will not be repeated here.
(2) Preparing a battery cell from the positive electrode plate obtained in the step (1), the protective metal lithium negative electrode prepared in the example 5 and the commercial PE diaphragm, packaging by adopting a polymer, and pouring 1.0mol/L LiPF 6 The electrolyte (in which the weight ratio of the organic solvent EC, DMC, FEC is 20:50:30) is prepared into the soft-package lithium secondary battery through processes such as formation and the like.
In example 7, a composite lithium aluminum alloy negative electrode was prepared using 3-octyl-substituted polythiophene as the conductive polymer, methylethyl carbonate as the organic solvent, and lithium aluminum alloy as the metal negative electrode.
A3-octyl substituted polythiophene-protected composite lithium aluminum alloy negative electrode with thermosensitive characteristics is prepared by the following steps: dispersing 0.25g of a compound powder represented by the following formula (D) in 20mL of ethyl methyl carbonate in a drying room, and stirring and mixing to form a uniform dispersion; and then coating the dispersion liquid on the surface of an unprotected lithium aluminum alloy negative electrode in a blade coating mode, wherein the coating (blade coating) time is 10min, and after the solvent is evaporated to dryness, the surface of the lithium aluminum alloy negative electrode forms a 3-octyl-substituted polythiophene protective layer with the thickness of 2 mu m, so as to obtain the composite lithium aluminum alloy negative electrode.
Example 8A composite Metal negative electrode prepared in example 7 was used as the negative electrode, polyvinylidene fluoride (PVDF) as the positive electrode binder, super P as the positive electrode conductive agent, lithium cobaltate as the positive electrode material, aluminum foil as the positive electrode current collector, and LiPF as the electrolyte 6 The organic solvent in the electrolyte is a mixed solvent of EC, DMC and FEC, and the separator is a commercial PE separator as an example, to prepare a lithium secondary battery.
A lithium secondary battery is prepared by the following steps:
(1) And obtaining the positive pole piece. The method is the same as step (1) in example 2, and will not be repeated here.
(2) Preparing a battery cell from the positive electrode plate obtained in the step (1), the lithium-aluminum alloy-protected negative electrode prepared in the example 7 and the commercial PE diaphragm, packaging by adopting a polymer, and pouring 1.0mol/L LiPF 6 The electrolyte (in which the weight ratio of the organic solvent EC, DMC, FEC is 20:50:30) is prepared into the soft-package lithium secondary battery through processes such as formation and the like.
In example 9, a composite lithium-indium alloy negative electrode was prepared using a conductive polymer of the following formula (E), an organic solvent of tetrahydrofuran, and a metal negative electrode of a lithium-indium alloy negative electrode.
A preparation method of a composite lithium indium alloy negative electrode with thermosensitive characteristics comprises the following steps: dispersing 0.25g of a compound powder represented by the following formula (E) in 25mL of tetrahydrofuran in a drying room, and stirring and mixing to form a uniform dispersion; and then coating the dispersion liquid on the surface of the unprotected lithium-indium alloy negative electrode in a blade coating mode, wherein the coating (dip coating) time is 20min, and the surface of the lithium-indium alloy negative electrode forms a conductive polymer protective layer with the thickness of 1 mu m as shown in formula (E) after the solvent is evaporated to dryness, so as to obtain the composite lithium-indium alloy negative electrode.
Example 10 the composite metal negative electrode prepared in example 9 was used as a negative electrode, the positive electrode binder was polyvinylidene fluoride (PVDF), and the positive electrode conductive agent was superP, the positive electrode material is lithium cobaltate, the positive electrode current collector is aluminum foil, and the electrolyte is LiPF 6 The organic solvent in the electrolyte is a mixed solvent of EC, DMC and FEC, and the separator is a commercial PE separator as an example, to prepare a lithium secondary battery.
A lithium secondary battery is prepared by the following steps:
(1) And obtaining the positive pole piece. The method is the same as step (1) in example 2, and will not be repeated here.
(2) Preparing a battery cell from the positive electrode plate obtained in the step (1), the lithium-indium alloy-protected negative electrode prepared in the example 9 and the commercial PE diaphragm, packaging by adopting a polymer, and pouring 1.0mol/L LiPF 6 The electrolyte (in which the weight ratio of the organic solvent EC, DMC, FEC is 20:50:30) is prepared into the soft-package lithium secondary battery through processes such as formation and the like.
Comparative example 1, lithium metal negative electrode was used as negative electrode, lithium cobalt positive electrode was used as positive electrode, and electrolyte was LiPF 6 The organic solvent in the electrolyte is a mixed solvent of EC, DMC and FEC, and the diaphragm is a commercial PE diaphragm, so that the secondary battery is prepared.
LiCoO 2 A preparation method of the/Li battery comprises the following steps:
making a metal lithium anode, a lithium cobaltate anode and a commercial PE diaphragm into a battery core, packaging by adopting a polymer, and pouring 1.0mol/L LiPF 6 The electrolyte (in which the weight ratio of the organic solvent EC, DMC, FEC is 20:50:30) is prepared into the soft-package lithium secondary battery through processes such as formation and the like.
Comparative example 2, lithium cobalt positive electrode was used as the negative electrode, and LiPF was used as the electrolyte 6 The organic solvent in the electrolyte is a mixed solvent of EC, DMC and FEC, and the diaphragm is a commercial PE diaphragm, so that the secondary battery is prepared.
LiCoO 2 A preparation method of the Li-Al battery comprises the following steps:
making a lithium aluminum alloy cathode, a lithium cobalt oxide anode and a commercial PE diaphragm into a battery core, packaging by adopting a polymer, and pouring 1.0mol/L LiPF 6 The electrolyte (in which the weight ratio of the organic solvent EC, DMC, FEC is 20:50:30) is prepared into the soft-package lithium secondary battery through processes such as formation and the like.
Comparative example 3 lithium cobalt positive electrode was used as the positive electrode, and LiPF was used as the electrolyte 6 The organic solvent in the electrolyte is a mixed solvent of EC, DMC and FEC, and the diaphragm is a commercial PE diaphragm, so that the secondary battery is prepared.
LiCoO 2 A preparation method of the/Li-In battery comprises the following steps:
making a lithium-indium alloy cathode, a lithium cobalt oxide anode and a commercial PE diaphragm into a battery core, packaging by adopting a polymer, and pouring 1.0mol/L LiPF 6 The electrolyte (in which the weight ratio of the organic solvent EC, DMC, FEC is 20:50:30) is prepared into the soft-package lithium secondary battery through processes such as formation and the like.
The secondary batteries provided in examples 2, 4, 6, 8, 10 of the present application and the batteries provided in comparative examples 1, 2, 3 were subjected to electrochemical performance tests, the test methods were subjected to charge and discharge tests according to a 1.0C/1.0C charge and discharge regime, the voltage ranges were 3.0 to 4.5V, and the test results are shown in table 1 and fig. 6A, fig. 6B, fig. 6C, and fig. 6D below. Wherein fig. 6A is a graph of cycle performance of the batteries provided in example 2, example 4, example 6, example 8, comparative example 10 and comparative examples 1, 2, comparative example 3; fig. 6B is a graph of cycle performance of the batteries provided in example 2, example 4, example 6, and comparative example 1; fig. 6C is a graph of cycle performance of the batteries provided in example 8 and comparative example 2; fig. 6D is a graph of cycle performance of the batteries provided in example 10 and comparative example 3.
The negative electrodes of the secondary battery provided in example 6 of the present application and the battery provided in comparative example 1 were scanned with an electron microscope after 100 weeks of cycling, and the electron microscope (SEM) photographs of the negative electrodes of the secondary battery provided in example 6 and the battery provided in comparative example 1 are shown in fig. 7 and 8, respectively.
TABLE 1
| Sequence number | Capacity retention of 50 weeks | 80 week capacity retention | 100 week capacity retention |
| Example 2 | 96.4％ | 94.9％ | 93.6％ |
| Example 4 | 96.9％ | 94.7％ | 92.8％ |
| Example 6 | 95.7％ | 93.4％ | 91.1％ |
| Example 8 | 97.4％ | 95.8％ | 94.5％ |
| Example 10 | 97.5％ | 95.6％ | 94.1％ |
| Comparative example 1 | 92.9％ | 86.8％ | 81.9％ |
| Comparative example 2 | 95.1％ | 90.3％ | 85.9％ |
| Comparative example 3 | 95.5％ | 90.5％ | 86.1％ |
As can be seen from the test results of Table 1 and FIG. 6A, FIG. 6B, FIG. 6C, FIG. 6D, the batteries of examples 2, 4, 6, 8, 10 of the present application provided a capacity retention of more than 90% at 100 weeks, at least 91.1%, higher than that of comparative example 1 2 LiCoO provided in comparative example 2, li cell 2 Li-Al cell and LiCoO provided in comparative example 3 2 Capacity retention after 100 weeks of Li-In cell cycling. This shows that the embodiment of the application adopts the conductive polymer with heat-sensitive property to protect the lithium cathode, and can obviously improve the cycle performance of the battery. This is because a stable protective layer is formed on the surface of a lithium negative electrode protected by a conductive polymer having heat-sensitive properties. In one aspect, the thermally-responsive conductive polymer is electrochemically oxidatively doped (e.g., doped with an anionic PF 6 - ) Promoting the uniform deposition of lithium ions on the surface of the composite lithium cathode and avoiding the growth of lithium dendrites. On the other hand, in the charge and discharge process of the battery, dendrite formation can cause local current to become large or side reaction to increase, so that local temperature is increased, when the temperature reaches the critical temperature of the conductive polymer, the conjugation degree is reduced and the conductive polymer is dedoped, so that impedance is increased, conductivity is reduced, lithium ions are guided to deposit to a non-dendrite area, and continuous growth of lithium dendrites is avoided. In addition, the conductive polymer can form a polymer elastic film, so that the volume expansion of the lithium anode in the circulation process can be effectively relieved, the lithium anode interface is stabilized, the side reaction is reduced, and the coulomb efficiency is improved. The unprotected lithium cathode has no protective layer, and lithium ions Uneven deposition on the surface of the negative electrode causes lithium dendrite growth, and the exposed lithium negative electrode is in direct contact with electrolyte, so that serious side reactions occur, thereby reducing the coulombic efficiency of the lithium negative electrode and having poor battery cycle stability.
Comparing fig. 7 and 8, it can be seen that the surface of the lithium metal negative electrode is complete and no lithium dendrite is generated after the lithium metal negative electrode is protected for 100 weeks in example 2 of the present application, mainly because a stable protective layer is formed on the surface of the lithium metal negative electrode after the lithium metal negative electrode is protected by the conductive polymer having thermal sensitivity, and electrochemical oxidation doping (such as doping anion PF is performed during charging 6 - ) And the uniform deposition of lithium ions on the surface of the composite lithium negative electrode is promoted, the growth of lithium dendrites is avoided, and meanwhile, the polymer elastic membrane can also effectively relieve the volume expansion of the metal lithium negative electrode in the circulation process and stabilize the interface of the metal lithium negative electrode. However, after the unprotected metallic lithium negative electrode in comparative example 1 was cycled for 100 weeks, serious lithium dendrite phenomenon occurred on the surface of the metallic lithium negative electrode, mainly because the unprotected metallic lithium negative electrode formed uneven lithium deposition during the cycle, which easily caused lithium dendrite growth.
Finally, it should be noted that: the present application is not limited to the above embodiments, and any changes or substitutions within the technical scope of the present application should be covered by the scope of the present application. Therefore, the protection scope of the application is subject to the protection scope of the claims.
Claims (12)
1. A composite metal anode, comprising: a metal anode, and a protective layer bonded to at least one side surface of the metal anode, wherein the material of the protective layer comprises a conductive polymer, and the conductive polymer is selected from conductive polymers capable of reversibly doping and dedoping anions;
the conductive polymer is a copolymer formed by at least two structural monomers in the following formulas (11), (12) and (13):
wherein R is 1 、R 2 Each independently selected from any one of hydrogen, halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkenyloxy, haloalkenyloxy, aryl, haloaryl, aryloxy, haloaryloxy, and R in the different structural monomers 1 、R 2 The substituent types are the same or different; the conductive polymer has thermal sensitivity in a temperature range of 50-130 ℃, and the impedance of the conductive polymer is increased along with the rise of temperature by doping and dedoping anions to change the spatial configuration of the conductive polymer in the temperature range.
2. The composite metal anode according to claim 1, wherein the number of carbon atoms in the alkyl group, the haloalkyl group, the alkoxy group, and the haloalkoxy group is 1 to 20;
The carbon number of the alkenyl, the halogenated alkenyl, the alkenyloxy and the halogenated alkenyloxy is 2-10;
the carbon number of the aryl, the halogenated aryl, the aryloxy and the halogenated aryloxy is 6-20.
3. The composite metal anode according to claim 1, wherein the conductive polymer is at least one selected from the group consisting of compounds (E) to (P) represented by the following structures, wherein n has a value in the range of 10 to 10000, n 1 +n 2 The values of (2) satisfy the following: n is more than or equal to 10 1 +n 2 ≤10000，
4. A composite metal negative electrode according to any one of claims 1 to 3, wherein the protective layer has a thickness of 1nm to 20 μm.
5. A composite metal negative electrode according to any one of claims 1 to 3, wherein the material of the protective layer further comprises a binder, and the protective layer is bonded to at least one side surface of the metal negative electrode by the binder.
6. The composite metal negative electrode of claim 5, wherein the mass ratio of the conductive polymer to the binder in the protective layer is 1-100:1.
7. The composite metal negative electrode of any one of claims 1 to 3, 6, wherein the metal negative electrode is selected from one or more of a lithium negative electrode, a sodium negative electrode, a potassium negative electrode, a magnesium negative electrode, a zinc negative electrode, and an aluminum negative electrode.
8. The composite metal negative electrode according to any one of claims 1 to 3 and 6, further comprising a current collector comprising a first surface and a second surface disposed opposite to each other, wherein the metal negative electrode is bonded to at least the first surface of the current collector, and wherein the protective layer is disposed on at least the surface of the metal negative electrode facing away from the current collector.
9. The preparation method of the composite metal negative electrode is characterized by comprising the following steps of:
obtaining a mixed solution, wherein the mixed solution is obtained by mixing a conductive polymer and an organic solvent, and the conductive polymer is selected from conductive polymers capable of reversibly doping and dedoping anions;
coating the mixed solution on at least one surface of a metal negative electrode to obtain a composite metal negative electrode, wherein the composite metal negative electrode comprises the metal negative electrode and a protective layer combined on at least one side surface of the metal negative electrode; the material of the protective layer comprises the conductive polymer;
the conductive polymer is a copolymer formed by at least two structural monomers in the following formulas (11), (12) and (13):
wherein R is 1 、R 2 Each independently selected from any one of hydrogen, halogen, alkyl, haloalkyl, alkoxy, haloalkoxy, alkenyl, haloalkenyl, alkenyloxy, haloalkenyloxy, aryl, haloaryl, aryloxy, haloaryloxy, and R in the different structural monomers 1 、R 2 The substituent types are the same or different; the conductive polymer has thermal sensitivity in a temperature range of 50-130 ℃, and the impedance of the conductive polymer is increased along with the rise of temperature by doping and dedoping anions to change the spatial configuration of the conductive polymer in the temperature range.
10. The method for producing a composite metal anode according to claim 9, wherein the mass ratio of the conductive polymer to the organic solvent in the mixed solution is 1:1-100; and/or the number of the groups of groups,
the organic solvent is selected from one or more of azomethyl pyrrolidone, acetone, acetonitrile, ethanol, dimethyl carbonate, methylethyl carbonate, diethyl carbonate, tetrahydrofuran, dimethyl ether, dimethyl sulfide, 1, 3-dioxolane, 1, 4-dioxane, 1, 2-dimethoxyethane, ethylene glycol dimethyl ether, bis-trifluoroethyl ether, hexafluoroisopropyl methyl ether, hexafluoroisopropyl ethyl ether, perfluorobutyl methyl ether, perfluorobutyl ethyl ether, tetrafluoroethyl tetrafluoropropyl ether and tetrafluoroethyl octafluoropentyl ether.
11. A secondary battery comprising a positive electrode, a negative electrode, a separator, and an electrolyte, wherein the positive electrode and the negative electrode are disposed opposite to each other, and the separator and the electrolyte are disposed between the positive electrode and the negative electrode; wherein the negative electrode is a composite metal negative electrode according to any one of claims 1 to 8 or a composite metal negative electrode prepared by the method according to any one of claims 9 to 10, the protective layer of the composite metal negative electrode is disposed opposite to the positive electrode, and the anion is an anion in the electrolyte.
12. A terminal, comprising: the secondary battery of claim 11 for supplying power to the terminal.
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