CN114068890A

CN114068890A - Composite metal negative electrode, preparation method thereof, secondary battery and terminal

Info

Publication number: CN114068890A
Application number: CN202010791225.9A
Authority: CN
Inventors: 马强; 洪响
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2020-08-07
Filing date: 2020-08-07
Publication date: 2022-02-18
Anticipated expiration: 2040-08-07
Also published as: CN114068890B

Abstract

The application relates to the technical field of batteries, and provides a composite metal cathode, a preparation method of the composite metal cathode, a secondary battery and a terminal. The application provides a composite metal negative electrode, includes: 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 application provides a composite metal negative pole, its protective layer can effectively restrain the growth of metal negative pole surface dendritic crystal among the battery charging process, solves battery safety and life-span problem because dendritic crystal leads to from the source.

Description

Composite metal negative electrode, preparation method thereof, secondary battery and terminal

Technical Field

The application belongs to the technical field of batteries, and particularly relates to a composite metal cathode, a preparation method of the composite metal cathode, a secondary battery and a terminal.

Background

With the development of economy and technology, energy storage devices with higher energy density, higher power density, longer cycle life, and greater safety are urgently needed for most electronic industries (e.g., portable electronic devices, drones, electric vehicles). The energy density of commercial lithium ion batteries using graphite as a negative electrode material is close to the upper limit, but the endurance and standby requirements of users for the above devices cannot be met. The lithium, sodium, potassium and other metal negative electrodes have high theoretical specific capacity and low electrochemical potential, and are high-energy negative electrode materials with wide development prospects. The metal cathode can greatly improve the energy density of the secondary battery, and the user experience is obviously improved. However, the metal negative electrode has the characteristics of high chemical activity (causing low coulombic efficiency), dendritic growth (causing side reactions and potential safety hazards), large volume expansion (continuous fracture and reconstruction of SEI film) 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 cathode battery can be improved in the following ways:

mode 1, an electrode material having thermosensitive characteristics, which includes a core formed of a lithium metal oxide, and a shell formed of a polythiophene derivative, and a method of preparing 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 configuration can increase the resistance of the electrode material to block the electron path and improve the safety of the battery even when the battery temperature rises to the curie temperature of the material. However, in the actual preparation process of the electrode material, it is difficult to achieve uniform coating of each active material.

Mode 2, a composite diaphragm and a lithium battery comprising the same are provided, in the technology, a thermosensitive material is distributed in a diaphragm base layer, and when the temperature of the battery rises, the thermosensitive material is heated to expand, so that gaps are increased, and heat dissipation inside a battery core is facilitated; meanwhile, the thermosensitive material dispersed in the membrane base layer can play a role in temperature control and regulation 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 positive and negative electrodes contains a PTC material, and when the battery is overheated during overcharge, the resistance of the PTC material increases, interrupting the current flow, and preventing explosion of the battery, and a method for manufacturing the same. The technology applies the PTC material to the positive electrode and the negative electrode of the battery, utilizes the temperature sensitivity characteristic of the PTC material, exerts the function of interrupting current to avoid further reaction, and mainly avoids the safety problem caused by thermal runaway.

Although the three modes can improve the safety performance of the metal cathode battery to a certain extent, the methods only remedy potential safety risks, and cannot improve the cycle life and potential safety hazards of the battery by inhibiting dendritic crystal generation of the metal cathode from the source.

Disclosure of Invention

The embodiment of the application provides a composite metal cathode, a preparation method thereof, a secondary battery and a terminal, and aims to solve the problems that a metal cathode is easy to generate dendrite, the cycle life of the battery is short and potential safety hazards exist.

In order to achieve the purpose, the technical scheme is as follows:

in a first aspect, an embodiment of the present application provides a composite metal anode, including: 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.

According to the composite metal negative electrode provided by the embodiment of the application, the protective layer is arranged on at least one side surface of the metal negative electrode. The material of the protective layer includes a conductive polymer capable of reversibly doping and dedoping anions. In this case, the conductive polymer in the protective layer is electrochemically oxidized and doped with anions during charging of the battery using the composite metal negative electrode. Since the anions are uniformly doped in the conductive polymer, the cations can be uniformly deposited on the surface of the composite metal negative electrode, so that the cations are prevented from being selectively deposited in local areas of the metal negative electrode to generate dendrites. Therefore, the protective layer can solve the problems of battery safety and service life caused by dendrite from the source.

In one possible implementation, the conductive polymer is selected from conductive polymers having heat-sensitive properties. In this case, during the charging of the battery, the region where the dendrite is located is increased in temperature due to local current flow or side reactions due to the electric field, which is higher than the temperature of other regions where the dendrite is not formed. When the temperature of the region where the dendrite is located reaches the thermosensitive critical temperature of the conductive polymer, the thermosensitive characteristic of the conductive polymer is excited, and the conductive polymer changes the spatial conformation and reduces the conjugation degree through dedoping. The resistance of the conductive polymer increases, the conductivity decreases, the resistance to deposition of cations at the tip (the region where the dendrite is located) increases, and cations tend to deposit toward the non-tip (the other region where the dendrite is formed) where the resistance is lower. Therefore, the growth of dendrite can be hindered by the heat-sensitive characteristic of the conductive polymer, so that the dendrite is prevented from growing to a certain degree to penetrate through the diaphragm to 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 negative electrode as the negative electrode, the conductive polymer in the protective layer has thermal sensitivity in the range of 50 ℃ to 130 ℃, that is, the conductive polymer can be doped with anions and change the spatial configuration thereof in the temperature range, so as to increase the impedance to adjust the deposition of cations in the non-dendritic region, thereby achieving the purpose of balancing the thickness uniformity of the non-dendritic region and the dendritic region and avoiding the growth of dendritic crystals.

In one possible implementation manner, the conductive polymer is a homopolymer formed by polymerizing the same structural units or a copolymer formed by polymerizing different structural units, and the general formula of the structural units is shown as the following formula (1):

in the formula (1), X is selected from NH, O or S;

R¹、R²each independently selected from any one of hydrogen, halogen, alkyl, halogenated alkyl, alkoxy, halogenated alkoxy, alkenyl, halogenated alkenyl, alkenyloxy, halogenated alkenyloxy, aryl, halogenated aryl, aryloxy and halogenated aryloxy. The general formula of the polymer formed by the structural unit shown as the formula (1),in the charging process, the space conformation of the conductive polymer can be changed by doping anions, the planarity of the five-membered ring is enhanced, and a conjugated structure with higher stability and better conductivity is formed. Therefore, anions are uniformly doped in the conductive polymer, cation selective deposition is avoided, the deposition uniformity of the cations on the surface of the metal cathode is improved, and the formation probability of dendrites is reduced. Further, the conductive polymer formed by the structural unit shown in formula (1) has heat sensitivity, and the resistance is increased when the temperature is higher than the heat sensitive critical temperature. Therefore, once the dendrite is formed on the surface of the composite metal cathode, the temperature of the region where the dendrite is located is increased, the conductive polymer in the corresponding region 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 region where the dendrite is located is reduced, the cations are deposited to a non-dendrite region with higher conductivity, and finally the purpose of avoiding the continuous growth of the dendrite is achieved.

In one possible implementation, the number of carbon atoms in the alkyl group, the haloalkyl group, the alkoxy group, the haloalkoxy group is from 1 to 20; the number of carbon atoms in the alkenyl group, the halogenated alkenyl group, the alkenyloxy group and the halogenated alkenyloxy group is 2-10; the number of carbon atoms in the aryl group, the halogenated aryl group, the aryloxy group, and the halogenated aryloxy group is 6 to 10. When the number of carbon atoms is within the above range, the resulting conductive polymer has suitable heat-sensitive characteristics.

In one possible implementation, the number of carbon atoms in the alkyl group, the haloalkyl group, the alkoxy group, the haloalkoxy group is 1 to 10; the number of carbon atoms in the alkenyl group, the haloalkenyl group, the alkenyloxy group and the haloalkenyloxy group is 2 to 10.

In one possible implementation, in the formula (1), the halogen is selected from one of fluorine, chlorine, bromine and iodine; the halogen in the halogenated alkyl, the halogenated alkoxy, the halogenated alkenyl, the halogenated alkenyloxy, the halogenated aryl and the halogenated aryloxy is independently selected from at least one of fluorine, chlorine, bromine and iodine.

In one possible implementation, the conductive polymerAt least one of a compound (A) to a compound (P) shown in the following structures is selected, wherein the value range of n is 10-10000, and n₁+n₂The value of (A) satisfies: n is more than or equal to 10₁+n₂≤10000，

In one possible implementation, the thickness of the protective layer is 1nm to 20 μm. The thickness of the protective layer 11 should not be too thick due to the limitation of the conductivity of the conductive polymer itself, so the embodiment of the present application sets the thickness of the protective layer within the range of 1nm to 20 μm to inhibit the growth of dendrites, thereby improving the safety performance and the service life of the battery.

In one possible implementation, the thickness of the protective layer is 1 μm to 10 μm. In this case, the protective layer can exert excellent effects of suppressing dendrite formation and suppressing dendrite growth without lowering the cation transport efficiency.

In one possible implementation manner, 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 through the binder. The binder 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 within 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 also increases the resistance of the protective layer, which is not favorable for cation transmission.

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 carboxymethylcellulose/styrene butadiene rubber, polyvinyl alcohol, polyacrylic acid, lithium polyacrylate, polyvinylpyrrolidone, polylactic acid, sodium alginate, poly (p-styrenesulfonic acid), lithium poly (styrene sulfonate), and gelatin. The binding agent can improve the binding force of the conductive polymer on the surface of the metal negative electrode, so that the protective layer is firmly bound on the surface of the metal negative electrode.

In one possible implementation, the metal anode is selected from one or more of a lithium anode, a sodium anode, a potassium anode, a magnesium anode, a zinc anode, and an aluminum anode. In this case, the protective layer is bonded to the surface of the metal negative electrode, and the conductive polymer therein inhibits dendrite formation and growth on the surface of the metal negative electrode.

The lithium negative electrode includes a lithium metal negative electrode and a lithium alloy negative electrode. Illustratively, 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 a possible implementation manner, the composite metal negative electrode further includes a current collector, the current collector includes a first surface and a second surface which are oppositely disposed, the metal negative electrode is at least combined with the first surface of the current collector, and the protective layer is at least disposed on a surface of the metal negative electrode which is deviated from the current collector. Through setting up the mass flow body, can prevent that the pulverization from taking place in the circulation later stage at the metal negative pole, influence the electric contact.

In a second aspect, an embodiment of the present application provides a method for preparing a composite metal anode, including the following steps:

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 cathode to obtain a composite metal cathode, wherein the composite metal cathode comprises the metal cathode and a protective layer combined on at least one side surface of the metal cathode; the material of the protective layer includes the conductive polymer.

According to the preparation method of the composite metal negative electrode provided by the embodiment of the application, 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 charging process of the battery.

In one possible implementation manner, 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 an appropriate concentration in the mixed solution, and after the mixed solution is coated on the surface of the metal negative electrode, a protective layer having an appropriate thickness is formed.

In one possible implementation, the organic solvent is selected from one or more of azomethylpyrrolidone, acetone, acetonitrile, ethanol, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, tetrahydrofuran, dimethyl ether, dimethyl sulfide, 1, 3-dioxolane, 1, 4-dioxan, 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 in the embodiment of the present application may be a uniform solution or a suspension.

In one possible implementation manner, in the mixed solution, the mass ratio of the conductive polymer to the organic solvent is 1: 1-100; and the organic solvent is selected from one or more of azomethylpyrrolidone, acetone, acetonitrile, ethanol, dimethyl carbonate, ethyl methyl 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 appropriate concentration, and after the conductive polymer is coated on the surface of the metal negative electrode, a protective layer with uniform thickness and appropriate thickness can be obtained.

In a third aspect, an embodiment of the present application provides a secondary battery, including: the battery comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, wherein 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; wherein the negative electrode is the composite metal negative electrode of the first aspect, 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.

In the secondary battery provided by the embodiment of the present application, the negative electrode is the composite metal negative electrode of the first aspect. In this case, since the protective layer can suppress the formation and growth of dendrites on the surface of the metal negative electrode from the source when the secondary battery is charged, 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 a third aspect, the secondary battery being used to supply power to the terminal.

The terminal provided by the embodiment of the application comprises the secondary battery of the third aspect. In this case, since the protective layer can suppress the formation and growth of dendrites on the surface of the metal negative electrode from the source when the secondary battery is charged, the battery safety and life of the secondary battery including the negative electrode are improved.

Drawings

FIG. 1 is a schematic diagram of a dendrite formation mechanism of an unprotected lithium negative electrode provided by the prior art;

fig. 2 is a schematic structural diagram of a composite metal anode provided with a protective layer on one side surface of the metal anode according to an embodiment of the present application;

fig. 3 is a schematic structural diagram of a composite metal negative electrode provided with protective layers on both side surfaces of the metal negative electrode according to some embodiments of the present disclosure;

FIG. 4 is a functional diagram of a composite metal negative electrode provided in an embodiment of the present application;

fig. 5 is a flow chart of a process for preparing a composite metal anode provided in an embodiment of the present application;

FIG. 6A is a graph of the cycling performance of the cells provided in examples 2, 4, 6, 8, 10 and 1,2, 3 of the present application;

fig. 6B is a graph showing 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 showing the cycle performance of the batteries provided in example 8 and comparative example 2 of the present application;

FIG. 6D is a graph showing the cycle performance of the batteries provided in example 10 and comparative example 3 of the present application;

fig. 7 is a Scanning Electron Microscope (SEM) photograph of a protected lithium metal negative electrode after the secondary battery provided in example 1 of the present application was cycled for 100 weeks;

fig. 8 is a Scanning Electron Microscope (SEM) photograph of an unprotected lithium metal anode after 100 weeks 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 solutions and advantageous effects to be solved by the present application more clearly apparent, the present application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

In the present application, the terminology used in the embodiments of the present application is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application. The term "and/or" describes an associative relationship of associated objects, meaning that three relationships may exist, e.g., a and/or B, may mean: a is present alone, A and B are present simultaneously, and B is present alone. Wherein A and B can be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "and" relationship.

The term "at least one" means one or more, "a plurality" means two or more. "at least one of the following" or similar expressions refer to any combination of these items, including any combination of the singular or plural items. For example, "at least one (a), b, or c", or "at least one (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, and c may be single or plural, respectively.

As used in the examples of 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" and "second" are used for descriptive purposes only and are used for distinguishing purposes such as substances, interfaces, messages, requests and terminals from one another and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. 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 defined as "first" or "second" may explicitly or implicitly include one or more of that feature.

In the description of the present application, the mentioned weight of the related components may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, therefore, the content of the related components is scaled up or down within the scope disclosed in the embodiment specification of the present application as long as it is scaled up or down according to the embodiment specification of the present application. Specifically, the mass described in the specification of the embodiments of the present application may be a mass unit known in the chemical industry field such as μ g, mg, g, kg, etc.

It should be understood that, in various embodiments of the present application, the sequence numbers of the above-mentioned processes do not mean the execution sequence, 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 function and inherent logic, and should not constitute any limitation to the implementation process of the embodiments of the present application.

Before describing the embodiments of the present application, the terms related to the embodiments of the present application are defined as follows:

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 is a positive electrode, and the positive electrode plays a reducing role, namely ions or molecules obtain electrons; in the electrolytic cell, the device is an electric appliance, an electrode connected with the positive pole of the power supply is the positive pole based on the connected power supply, and at the moment, the positive pole plays an oxidation role, namely ions or molecules lose electrons.

Negative electrode (Anode): refers to the end of the power supply where the potential (potential) is lower. In the primary battery, the electrode potential of the current inflow is lower and is a negative electrode, the negative electrode is an electrode with oxidation, and the battery reaction is written on the left; in the electrolytic cell, the electrode connected to the negative electrode of the power supply is the negative electrode, and at this time, the negative electrode obtains electrons to play a role in reduction. From a physical point of view, the negative electrode is the one from which electrons flow in the circuit.

Electrolyte (Electrolyte) between the positive and negative electrodes of the cell and used to provide a medium for ion exchange.

Separator (Separator): the membrane is used for separating the positive and negative electrodes during the electrolytic reaction so as to prevent the short circuit caused by the contact of the two electrodes. In addition, the separator has a function of allowing electrolyte ions to pass therethrough.

Conductive polymers (conductive polymers) are a class of polymeric materials whose backbone has conjugated main electron systems, such as conjugated pi-bonds, that can be chemically or electrochemically "doped" to change from an insulating state to a conductive state.

PTC is the abbreviation of "Positive Temperature coefficient," and generally refers to a semiconductor material or a component with a large Positive Temperature coefficient, and is usually referred to as a thermistor with a Positive Temperature coefficient, which is abbreviated as PTC thermistor. The PTC has a characteristic in which resistivity increases with an increase in temperature, and the PTC can improve safety in use of the battery in the battery.

SEI is an abbreviation of "solid electrolyte interphase," indicating an interface protective film or a solid electrolyte interface (film), and refers to a passivation film layer having a solid electrolyte property.

EC is an abbreviation for "ethylene carbonate" and represents ethylene carbonate.

DMC is an abbreviation for "dimethyl carbonate" and represents dimethyl carbonate.

FEC is an abbreviation for "Fluoroethylene carbonate" and refers to Fluoroethylene carbonate.

Secondary battery: the Rechargeable battery is also called a Rechargeable battery or a storage battery, and refers to a battery which can be continuously used by activating an active material by means of charging after the battery is discharged.

With reference to fig. 1, a typical working scenario and failure mechanism will be described by taking a lithium metal battery with a metal negative electrode as a negative electrode as an example:

the core components of the lithium metal battery are mainly a positive electrode, a metal lithium negative electrode, an electrolyte and a diaphragm, and 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 anode material and are deposited on the surface of the metal lithium cathode through the electrolyte; when a lithium metal battery is discharged, lithium at the metallic lithium negative electrode loses electrons and is oxidized into lithium ions, and the lithium ions pass through the electrolyte and are inserted into the crystal lattice of the positive electrode material. During the initial charge and discharge, lithium ions react with solvents (e.g., EC/DMC), trace amounts of water, HF, etc., to form an interface protective film (SEI) on the surface of the electrode.

When the lithium metal battery is at rest, 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 severe side reactions and inducing lithium dendrite formation, thereby reducing coulombic efficiency and causing safety problems. Specifically, during charging, under the action of an electric field, the rough and uneven surface of the lithium metal causes uneven current distribution, and lithium ions from the positive electrode are selectively deposited on the surface of the lithium metal to form lithium dendrites. Further, after the formation of lithium dendrites, lithium ions are preferentially deposited at the tip region by the tip effect (negative charges are more densely distributed at the tip), resulting in a higher current density at the tip region and a local heat generation (temperature in the tip region is higher than that in the non-tip region). The specific surface area of the newly generated lithium dendrite is large, and the reactivity with the electrolyte is high, so that the side reaction between the lithium dendrite and the electrolyte is increased, the coulombic efficiency of a lithium cathode is reduced, and the cycling stability of the battery is reduced; and the increase of side reaction further generates heat, so that potential safety hazards exist in the battery. Meanwhile, as the lithium dendrites continuously grow, when the lithium dendrites grow to a certain degree, the lithium dendrites penetrate through the separator, causing a short circuit of the battery, further causing a safety problem, and shortening the service life of the battery. In addition, lithium dendrites crack during the dissolution process to form "dead lithium" causing a decrease in the capacity of the negative electrode.

Researches show that a stable interface is constructed on the surface of the metal cathode in a physical or chemical mode, so that the surface activity of the metal cathode can be reduced, the metal ion flow can be homogenized, the growth of dendrites can be relieved, and the volume expansion can be relieved. However, no stable interface construction scheme which is effective and can realize large-scale production is found at present.

In view of this, with reference to fig. 2 and 3, a first aspect of the embodiments of the present application provides a composite metal anode, including: a metal negative electrode 10, and a protective layer 11 bonded to at least one side surface of the metal negative electrode 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 is to be understood that the above-described metal negative electrode 10 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 negative electrode 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 negative electrode 10.

In the composite metal negative electrode provided in the embodiment of the present application, the protective layer 11 is disposed on at least one side surface of the metal negative electrode 10. The material of the protective layer 11 comprises a material selected from the group of conductive polymers capable of reversibly doping and dedoping anions. Under the condition, the protective layer 11 can effectively inhibit the dendritic crystal growth on the surface of the metal negative electrode in the charging process of the battery, and the problems of the safety and the service life of the battery caused by the dendritic crystal are solved 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 cathode, the conductive polymer in the protective layer 11 is subjected to electrochemical oxidation doping and is doped with anions. Since the anions are uniformly doped in the conductive polymer, the cations can be uniformly deposited on the surface of the composite metal negative electrode, thereby preventing the cations from being selectively deposited in a local region of the metal negative electrode 10 to generate dendrites. Thus, the protective layer 11 can solve the battery safety and life problems due to dendrites from the source.

In addition, the conductive polymer is used as a protective layer material, so that a polymer elastic film can be formed on the surface of the metal negative electrode 10, and the volume expansion of the composite metal negative electrode (mainly the metal negative electrode 10 in the embodiment of the application) in the circulation process is effectively relieved, so that the composite metal negative electrode interface is stabilized, the side reaction is reduced, and the coulomb efficiency is improved.

In one possible implementation manner, the composite metal negative electrode provided in the embodiment of the present application can be used as a negative electrode of a secondary battery. The composition of the composite metal negative electrode will be 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 metal. 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, for example. Here, the lithium negative electrode refers to a negative electrode made of metallic lithium or a 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 surface of the metal negative electrode 10 to prevent dendrite formation of the metal negative electrode 10 during charging. In the embodiment of the application, the composite metal cathode is used as the cathode of the secondary battery and is electrically conductiveThe anion of the compound reversibly dopes and dedopes is derived from anions in the electrolyte of the secondary battery, including but not limited to hexafluorophosphate anion (PF)₆ ^-) Hexafluoroarsenate anion (AsF)₆ ^-) Perchlorate anion (ClO)₄ ^-) Tetrafluoroborate anion (BF)₄ ^-) Bis (oxalato) borate anion (BOB)^-) Difluorooxalato borate anion (DFOB)^-) Bis (fluorosulfonyl) imide anion (FSI)^-) Bis (trifluorosulfonimide) anion (TFSI)^-)。

In one possible implementation, the conductive polymer is selected from conductive polymers having thermal sensitivity, i.e., conductive polymers used as the protective layer 11 of the present embodiment, which cause a chemical or physical change under thermal energy conditions, and the resistance of which 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 negative electrode during the charging of the battery. With reference to fig. 4, the specific principle is as follows:

during charging, under the action of an electric field, the region where the dendrite is located is increased in temperature due to local current or side reactions, which is higher than the temperature of other regions where the dendrite is not formed. When the temperature of the region where the dendrite is located reaches the thermosensitive critical temperature of the conductive polymer, the thermosensitive characteristic of the conductive polymer is excited, and the conductive polymer changes the spatial conformation and reduces the conjugation degree through dedoping. The resistance of the conductive polymer increases, the conductivity decreases, the resistance to deposition of cations at the tip (the region where the dendrite is located) increases, and cations tend to deposit toward the non-tip (the other region where the dendrite is formed) where the resistance is lower. Therefore, the growth of dendrite can be hindered by the heat-sensitive characteristic of the conductive polymer, so that the dendrite is prevented from growing to a certain degree to penetrate through the diaphragm to 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 negative electrode as the negative electrode, the conductive polymer in the protective layer 11 has thermal sensitivity in the range of 50 ℃ to 130 ℃, that is, the conductive polymer can be doped with anions and change the spatial configuration thereof in the temperature range, so as to increase resistance to adjust the deposition of cations in the non-dendritic region, thereby achieving the purpose of balancing the thickness uniformity of the non-dendritic region and the dendritic region, and finally avoiding the growth of dendritic crystals. It should be understood that the conductive polymer can be used to control the conductivity by dedoping anions and changing the spatial configuration thereof to increase the impedance at a certain temperature value within the range of 50 ℃ to 130 ℃ according to a specific structural composition. Different conducting polymers may differ in their temperature at which they are de-doped with anions and change spatial configuration. I.e. there is a difference in the critical temperature at which different conductive polymers develop an impedance thermal response.

In addition, in the embodiment of the application, when the temperature is in the range of 50-130 ℃, and the impedance of the conductive polymer is increased along with the increase of the temperature, the temperature of the composite metal negative electrode is lower in the initial charging period of the battery, the conductive polymer exists in the form of doped anions, 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 dendritic crystal formation is reduced from the source; meanwhile, in the middle and later stages of charging, under the condition that dendritic crystals are formed, the temperature of the area where the dendritic crystals are located is increased, when the temperature is high enough to enable the conductive polymer to generate the change of the spatial configuration and remove anions, the impedance of the conductive polymer in the area where the dendritic crystals are located is increased, the deposition of the cations in the dendritic crystal parts is reduced, and therefore the growth of the dendritic crystals is inhibited. Therefore, the aim of inhibiting the formation and growth of dendrite is achieved by 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 can change due to slight fluctuation of the ambient temperature, and lithium ion transmission is not facilitated; if the critical temperature of the conductive polymer is too high (the conductive polymer is not sensitive to the temperature), the temperature rising effect caused by the formation of lithium dendrites cannot be effectively induced, and the effect of inhibiting the growth of the dendrites of the metal negative electrode in the middle and later charging stages is not obvious.

In the embodiment of the present application, the conductive polymer may be selected from homopolymers formed by polymerizing the same structural units, or may be selected from copolymers formed by polymerizing different structural units.

In one possible implementation, the structural units, which may be the same or different, are of the general formula (1):

in the formula (1), X is selected from NH, O or S;

R¹、R²each independently selected from any one of hydrogen, halogen, alkyl, halogenated alkyl, alkoxy, halogenated alkoxy, alkenyl, halogenated alkenyl, alkenyloxy, halogenated alkenyloxy, aryl, halogenated aryl, aryloxy and halogenated aryloxy.

An example, in formula (1), X is NH, and the structure of the corresponding structural unit is:

in another example, in formula (1), X is O, and the structure of the corresponding structural unit is:

in another example, X is S, and the structure of the corresponding structural unit is:

the conductive polymer can be selected from homopolymers formed by one of the formulas (11), (12) and (13); or two different structural monomers such as a copolymer formed by a formula (11) and a formula (12), a formula (11) and a formula (13), a formula (12) and a formula (13); the copolymer can also be formed by three structural monomers of a formula (11), a formula (12) and a formula (13). 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. For example, when the conductive polymer is a copolymer formed of formula (12) and formula (13), R in formula (12)¹And R in the formula (13)¹May be the same (e.g., all are H) or different (e.g., R in formula (12))¹Is H, formula (13) R in (1)¹Is haloalkenyl); also, R in the formula (12)²And R in the formula (13)²May be the same (e.g., all are H) or different (e.g., R in formula (12))²Is C₆H₁₃R in the formula (13)²Is H).

The conductive polymer formed by the structural unit shown as the general formula (1) changes space conformation by doping anions in the charging process of the battery, enhances the planarity of a five-membered ring, and forms a conjugated structure with higher stability and better conductivity. At the moment, the anions are uniformly doped in the conductive polymer, so that the selective deposition of the cations is avoided, the deposition uniformity of the cations on the surface of the metal cathode is improved, and the formation probability of dendrites is reduced. Further, the conductive polymer formed by the structural unit shown in formula (1) has heat sensitivity, and the resistance is increased when the temperature is higher than the heat sensitive critical temperature. Therefore, once the dendrite is formed on the surface of the composite metal cathode, the temperature of the region where the dendrite is located is increased, the conductive polymer in the corresponding region 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 region where the dendrite is located is reduced, the cations are deposited to a non-dendrite region with higher conductivity (lower resistance), and finally the purpose of avoiding the continuous growth of the dendrite is achieved.

With structural unit as C₆H₁₃-C₄H₃S, anion is TFSI^-For example, the structural change of the conductive polymer after binding anions is shown as follows:

in the above formula, the conductive polymer having no anion bonded (left structure) has low conductivity and weak conductivity; the conductive polymer (right formula structure) after combining with the anion has high conjugation degree, good conductivity and strong capacity of inducing the combination of the cation.

In one possible implementation, in formula (1), the halogen is selected from one of fluorine, chlorine, bromine, and iodine.

In one possible implementation, in formula (1), the number of carbon atoms in the alkyl group, the haloalkyl group, the alkoxy group, and the haloalkoxy group is 1 to 20. When the number of carbon atoms is within the above range, the resulting conductive polymer has suitable heat-sensitive characteristics.

In one possible implementation, the number of carbon atoms in the alkyl, haloalkyl, alkoxy, haloalkoxy groups is from 1 to 10.

In one possible implementation, in formula (1), the number of carbon atoms in the alkenyl group, the haloalkenyl group, the alkenyloxy group, and the haloalkenyloxy group is 2 to 10. When the number of carbon atoms is within the above range, the resulting conductive polymer has suitable heat-sensitive characteristics.

In one possible implementation, the number of carbon atoms in the alkenyl, haloalkenyl, alkenyloxy, haloalkenyloxy group is from 2 to 10.

In one possible implementation, in formula (1), the number of carbon atoms in the aryl group, the halogenated aryl group, the aryloxy group, and the halogenated aryloxy group is 6 to 20. When the number of carbon atoms is within the above range, the resulting conductive polymer has suitable heat-sensitive characteristics.

In one possible implementation, the number of carbon atoms in the aryl, haloaryl, aryloxy, haloaryloxy group is from 6 to 10.

In one possible implementation manner, in formula (1), the halogen in the halogenated alkyl group, the halogenated alkoxy group, the halogenated alkenyl group, the halogenated alkenyloxy group, the halogenated aryl group and the halogenated aryloxy group is independently selected from at least one of fluorine, chlorine, bromine and iodine. It is to be understood that hydrogen of alkyl, alkoxy, alkenyl, alkenyloxy, aryl, aryloxy groups of haloalkyl, haloalkoxy, haloalkenyl, haloalkenyloxy, haloaryl, haloaryloxy groups may be partially halogenated or fully halogenated to form the corresponding haloalkyl, haloalkoxy, haloalkenyl, haloalkenyloxy, haloaryl, haloaryloxy groups.

In the above examples, in 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 linear substituents or substituents having a branched chain.

In one possible implementation mode, the conductive polymer is selected from at least one of a compound (A) to a compound (P) shown in the following structures, wherein the value of n ranges from 10 to 10000, and n₁+n₂The value of (A) satisfies: n is more than or equal to 10₁+n₂≤10000；

In one possible embodiment, the protective layer 11 in the present example is composed of a conductive polymer. Under the condition, the conductive polymer is doped with anions in the charging process, and the cations are regulated and controlled to be uniformly deposited on the surface of the composite metal negative electrode, so that dendritic crystals are prevented from being formed; through doping anion, the deposition of cations on the surface of the composite metal negative electrode outside the region where the dendrite is located is regulated and controlled, so that the growth of the dendrite is inhibited. In addition, because no other components are contained, the interference of other components on the regulation and control effect can be avoided.

In a possible embodiment, the material of the protective layer 11 in the present embodiment further includes a binder. 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 negative electrode includes not only the conductive polymer but also the binder. In one possible embodiment, the material of the protective layer 11 in the present example 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 carboxymethylcellulose/styrene butadiene rubber (CMC/SBR), polyvinyl alcohol (PVA), polyacrylic acid (PAA), lithium polyacrylate (lipa), polyvinylpyrrolidone (PVP), polylactic acid (PLA), Sodium Alginate (SA), poly (styrene-sulfonic acid) (PSS), lithium poly (styrene-sulfonic acid) (LiPSS), and gelatin. Wherein, the polyvinylidene fluoride-hexafluoropropylene is a copolymer of polyvinylidene fluoride and hexafluoropropylene; the sodium carboxymethylcellulose/styrene butadiene rubber is a mixture of sodium carboxymethylcellulose and styrene butadiene rubber. The binding agent can improve the binding force of the conductive polymer on the surface of the metal negative electrode, so that the protective layer is firmly bound 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 to 100: 1. The mass ratio of the conductive polymer to the binder is within the above range, and the binder can improve the binding force of the conductive polymer on the surface of the metal negative electrode 10. If the content of the binder is too high, the relative content of the conductive polymer decreases, which weakens the effect of the conductive polymer in inhibiting dendrite formation and dendrite growth, and also increases the resistance of the protective layer 11, which is not favorable for cation transport.

As an example, the mass ratio of the conductive polymer to the binder in the embodiment of the present application may be 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, and the like.

In a possible implementation, the thickness of the protective layer 11 is between 1nm and 20 μm. The thickness of the protective layer 11 is not too thick due to the limitation of the conductivity of the conductive polymer, so that the embodiment of the application inhibits 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 impedance of the protective layer 11 itself increases, which is not favorable 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 effects of suppressing dendrite formation and suppressing growth during charging of the battery without lowering 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 includes a current collector including 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 one side surface of the metal negative electrode 10 facing away from the current collector. Through setting up the mass flow body, can prevent that the pulverization from taking place in the circulation later stage at the metal negative pole, influence the electric contact.

The composite metal negative electrode 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 the mixed solution on at least one surface of the metal cathode to obtain a composite metal cathode, wherein the composite metal cathode comprises the metal cathode and a protective layer combined on at least one side surface of the metal cathode; the material of the protective layer includes the conductive polymer.

Specifically, in the step S01, the mixed solution in the present example is obtained by adding the conductive polymer to the organic solvent in one possible embodiment. 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 subjecting to a stirring mixing process.

The conductive polymer is selected from the group consisting of a conductive polymer capable of reversibly doping and dedoping anions, and the selection and optional cases of the conductive polymer are not described herein 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 azomethylpyrrolidone, acetone, acetonitrile, ethanol, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, tetrahydrofuran, dimethyl ether, dimethyl sulfide, 1, 3-dioxolane, 1, 4-dioxan, 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 organic solvent may 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 to 100, in which case the conductive polymer has a suitable concentration in the mixed solution, and a protective layer having a suitable thickness is formed after the mixed solution is coated on the surface of the metal negative electrode.

As an example, the mass ratio of the conductive polymer to the organic solvent in the embodiment 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 a possible embodiment, the mixed solution in the examples of the present application further contains a binder. In other words, the 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 subjecting to 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 carboxymethylcellulose/styrene butadiene rubber, polyvinyl alcohol, polyacrylic acid, lithium polyacrylate, polyvinylpyrrolidone, polylactic acid, sodium alginate, poly (p-styrenesulfonic acid), lithium poly (styrene-sulfonic acid), and gelatin. Wherein, the polyvinylidene fluoride-hexafluoropropylene is a copolymer of polyvinylidene fluoride and hexafluoropropylene; the sodium carboxymethylcellulose/styrene butadiene rubber is a mixture of sodium carboxymethylcellulose 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 to 100: 1.

In step S02, the metal negative electrode is a negative electrode made of metal. For example, the metal negative electrode 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. Here, the lithium negative electrode refers to a negative electrode made of metallic lithium or a 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 is to be understood that the metal negative electrode 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 a protective layer is prepared on one 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 protective layers are prepared on both surfaces of the metal negative electrode.

The manner of coating the mixed solution on the surface of the metal negative electrode includes, but is not limited to: drop coating, brush coating, roller coating, spray coating, knife coating, dip coating, spin coating. In one possible implementation manner, the mass ratio of the conductive polymer to the organic solvent in the embodiment of the present application is 1:1-100, and the time for coating the organic dispersion of the conductive polymer on the surface of one side of the metal negative electrode is 1 min-12 h, so that the protective layer with the thickness of 1nm-20 μm is prepared on the surface of one side 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 implemented by coating the mixed solution on both side surfaces simultaneously or sequentially, with reference to the coating time of one side surface being 1min to 12 h. It should be understood that the thickness of the protective layer is positively correlated with the coating time in the case where the concentration of the conductive polymer in the mixed solution is determined.

In one possible implementation manner, the mixed solution is coated on at least one side surface of the metal negative electrode, and the coating is carried out at the temperature of-10 ℃ to 50 ℃ so as to prevent the organic solvent in the mixed solution from volatilizing.

In the embodiment of the present invention, the coating of the mixed solution of the conductive polymer on at least one side surface of the metal negative electrode may be performed in a drying room, or may be performed under a protective atmosphere, but is not limited thereto. As an 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 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 provided in the first aspect of the embodiment of the present application, and the protective layer of the composite metal negative electrode is disposed opposite to the positive electrode.

The embodiment of the application provides a secondary battery, as the negative electrode in the secondary battery adopts a composite metal negative electrode, 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 anion of the conductive polymer reversibly doping and dedoping is an anion in the electrolyte. Illustratively, the anion of the conductive polymer reversibly doping and dedoping is an anion of an electrolyte in the electrolyte; when the solvent in the electrolyte contains anions, the anions to which the conductive polymer reversibly dopes and dedopes may also be the anions of the solvent in the electrolyte. Under the condition, the secondary battery can avoid the reaction of cations on the surface of the metal negative electrode to form dendrites in the charging process, and the coulomb efficiency of the battery is reduced; in addition, the dendritic crystal is prevented from growing to be in contact with the positive electrode, and safety problems are caused.

It should be noted that the present application provides a secondary battery in which the positive electrode is disposed opposite to the protective layer of the composite metal negative electrode. When the protective layers are simultaneously arranged on the surfaces of the two sides of the metal cathode of the composite metal cathode, the anode is at least arranged opposite to the protective layer on one side of the composite metal cathode.

In one possible implementation, the composite metal negative electrode 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 faces away from the current collector.

For example, the metal negative electrode 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. Here, the lithium negative electrode refers to a negative electrode made of metallic lithium or a lithium alloy.

As a possible implementation manner, in the embodiment of the present application, the positive electrode includes a current collector, and a positive electrode material bonded on the current collector, where the positive electrode material includes at least a positive electrode active material. In the examples of the present application, positive electrode active materials conventionally used for secondary batteries can be applied to the examples of the present invention.

As a possible implementation manner, in the embodiment of the present application, the electrolyte includes an organic solvent and an electrolyte. The water has certain influence on the formation of SEI (solid electrolyte interphase) of the lithium ion battery and the performance of the lithium ion battery, and the SEI and the performance are particularly expressed as battery capacity reduction, discharge time reduction, internal resistance increase, cycle capacity attenuation, battery swelling 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 include an additive. The additive is mainly used for improving the film forming property during 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, embodiments of the present application provide a terminal, including the secondary battery of the third aspect, the secondary battery being used 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 used as a terminal of the power supply module, and the safety performance and the service life of the secondary battery can be improved accordingly.

The following description will be given with reference to specific examples.

The following will specifically describe, with reference to various examples, a method for manufacturing a composite metal anode and a secondary battery provided in the embodiments of the present application.

In example 1, a composite lithium metal negative electrode was prepared by using a conductive polymer as 3-hexyl-substituted polythiophene, an organic solvent as ethylene glycol dimethyl ether, and a metal negative electrode as a lithium metal negative electrode.

A composite metal lithium cathode protected by 3-hexyl substituted polythiophene with heat-sensitive characteristic is prepared by the following steps: in a drying room, 0.25g of a compound powder represented by the following formula (A) was dispersed in 10mL of ethylene glycol dimethyl ether, and stirred and mixed to form a uniform dispersion; and (3) coating the dispersion liquid on the surface of the metal lithium cathode 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 cathode, so that the composite metal lithium cathode is obtained.

Example 2, the composite metal negative electrode prepared in example 1 was used as 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 LiPF₆The lithium secondary battery was prepared by using a mixed solvent of EC, DMC and FEC as an organic solvent in the electrolyte, and a commercial PE separator as an example.

A lithium secondary battery, the preparation method of which is as follows:

(1) and obtaining the positive pole piece.

The positive pole piece can be obtained through the following steps: weighing 2% of polyvinylidene fluoride (PVDF), 2% of conductive agent super P and 96% of lithium cobaltate (LiCoO) in percentage by mass₂) Adding the mixture into N-methylpyrrolidone (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 pole piece.

(2) Preparing the positive pole piece obtained in the step (1), the protective metal lithium negative pole prepared in the example 1 and a commercial PE diaphragm into a battery cell, packaging the battery cell by adopting a polymer, and pouring 1.0mol/L LiPF₆ElectrolysisAnd (3) preparing the liquid (in the electrolyte, the weight ratio of organic solvents EC, DMC and FEC is 20:50:30) into the soft package lithium secondary battery through chemical synthesis and other processes.

Example 3, a composite lithium metal negative electrode was prepared by using a conductive polymer as polypyrrole, an organic solvent as nitrogen methyl pyrrolidone, and a metal negative electrode as a lithium metal negative electrode.

A polypyrrole-protected composite metal lithium negative electrode with heat-sensitive characteristics is prepared by the following steps: in a drying room, 0.25g of a compound powder represented by the following formula (B) was dispersed in 30mL of azomethylpyrrolidone, and stirred and mixed to form a uniform dispersion; and (3) coating the dispersion liquid on the surface of an unprotected lithium metal negative electrode in a brush coating mode, wherein the coating (brush coating) time is 10min, and after the solvent is evaporated to dryness, a polypyrrole protective layer with the thickness of 3 mu m is formed on the surface of the lithium metal negative electrode, so that the composite lithium metal negative electrode is obtained.

Example 4, the composite metal negative electrode prepared in example 3 was used as a negative electrode, the positive binder was polyvinylidene fluoride, the positive conductive agent was super P, the positive material was lithium cobaltate, the positive current collector was aluminum foil, and the electrolyte was LiPF₆The lithium secondary battery was prepared by using a mixed solvent of EC, DMC and FEC as an organic solvent in the electrolyte, and a commercial PE separator as an example.

A lithium secondary battery, the preparation method of which is as follows:

(1) and obtaining the positive pole piece. The method is the same as step (1) in example 2, and is not described herein again.

(2) Preparing the positive pole piece obtained in the step (1), the protective metal lithium negative pole prepared in the embodiment 3 and a commercial PE diaphragm into a battery cell, packaging the battery cell by adopting a polymer, and pouring 1.0mol/L LiPF₆And (3) preparing the electrolyte (in the electrolyte, the weight ratio of organic solvents EC, DMC and FEC is 20:50:30) into the soft package lithium secondary battery through chemical synthesis and other processes.

Example 5, a composite metal lithium negative electrode was prepared by using a conductive polymer as 3-heptyl-substituted polyfuran, an organic solvent as perfluorobutyl methyl ether, and a metal negative electrode as a metal lithium negative electrode.

A composite metal lithium negative electrode protected by 3-heptyl substituted polyfuran with heat-sensitive characteristics is prepared by the following steps: in a drying room, 0.25g of a compound powder represented by the following formula (C) was dispersed in 20mL of perfluorobutyl methyl ether, and stirred and mixed to form a uniform dispersion; and (3) coating the dispersion liquid on the surface of the metal lithium cathode in a spin coating mode, wherein the coating (spin coating) time is 20min, and after the solvent is evaporated to dryness, forming a 3-heptyl substituted polyfuran protective layer with the thickness of 3 mu m on the surface of the metal lithium cathode to obtain the composite metal lithium cathode.

Example 6, the composite metal negative electrode prepared in example 5 was used as a negative electrode, the positive binder was polyvinylidene fluoride (PVDF), the positive conductive agent was super P, the positive material was lithium cobaltate, the positive current collector was aluminum foil, and the electrolyte was LiPF₆The lithium secondary battery was prepared by using a mixed solvent of EC, DMC and FEC as an organic solvent in the electrolyte, and a commercial PE separator as an example.

A lithium secondary battery, the preparation method of which is as follows:

(2) Preparing the positive pole piece obtained in the step (1), the protective metal lithium negative pole prepared in the embodiment 5 and a commercial PE diaphragm into a battery cell, packaging the battery cell by adopting a polymer, and pouring 1.0mol/L LiPF₆And (3) preparing the electrolyte (in the electrolyte, the weight ratio of organic solvents EC, DMC and FEC is 20:50:30) into the soft package lithium secondary battery through chemical synthesis and other processes.

Example 7, a composite lithium aluminum alloy negative electrode was prepared by using a conductive polymer of 3-octyl substituted polythiophene, an organic solvent of ethyl methyl carbonate, and a metal negative electrode of a lithium aluminum alloy negative electrode as an example.

A composite lithium-aluminum alloy cathode protected by 3-octyl substituted polythiophene with heat-sensitive characteristics is prepared by the following steps: in a drying room, 0.25g of a compound powder represented by the following formula (D) was dispersed in 20mL of ethyl methyl carbonate, and stirred and mixed to form a uniform dispersion; and then coating the dispersion liquid on the surface of the unprotected lithium-aluminum alloy cathode in a blade coating mode, wherein the coating (blade coating) time is 10min, and after the solvent is evaporated to dryness, a 3-octyl substituted polythiophene protective layer with the thickness of 2 mu m is formed on the surface of the lithium-aluminum alloy cathode, so that the composite lithium-aluminum alloy cathode is obtained.

Example 8, the composite metal negative electrode prepared in example 7 was used as a negative electrode, the positive binder was polyvinylidene fluoride (PVDF), the positive conductive agent was super P, the positive material was lithium cobaltate, the positive current collector was aluminum foil, and the electrolyte was LiPF₆The lithium secondary battery was prepared by using a mixed solvent of EC, DMC and FEC as an organic solvent in the electrolyte, and a commercial PE separator as an example.

A lithium secondary battery, the preparation method of which is as follows:

(2) Preparing the positive pole piece obtained in the step (1), the lithium-aluminum alloy negative pole prepared in the embodiment 7 and the commercial PE diaphragm into a battery cell, packaging the battery cell by adopting a polymer, and pouring 1.0mol/L LiPF₆And (3) preparing the electrolyte (in the electrolyte, the weight ratio of organic solvents EC, DMC and FEC is 20:50:30) into the soft package lithium secondary battery through chemical synthesis and other processes.

Example 9 a composite lithium indium alloy negative electrode was prepared using a conductive polymer of the following formula (E), tetrahydrofuran as an organic solvent, and a lithium indium alloy negative electrode as a metal negative electrode.

A composite lithium indium alloy cathode with heat-sensitive characteristics is prepared by the following steps: in a drying room, 0.25g of a powder of the compound represented by the following formula (E) was dispersed in 25mL of tetrahydrofuran, and stirred and mixed to form a uniform dispersion; and then coating the dispersion liquid on the surface of an unprotected lithium indium alloy cathode in a blade coating mode, wherein the coating (dip-coating) time is 20min, and after the solvent is evaporated to dryness, a conductive polymer protective layer with the thickness of 1 mu m as shown in the formula (E) is formed on the surface of the lithium indium alloy cathode, so that the composite lithium indium alloy cathode is obtained.

Example 10 the composite metal negative electrode prepared in example 9 was used as a negative electrode, the positive binder was polyvinylidene fluoride (PVDF), the positive conductive agent was super P, the positive material was lithium cobaltate, the positive current collector was aluminum foil, and the electrolyte was LiPF₆The lithium secondary battery was prepared by using a mixed solvent of EC, DMC and FEC as an organic solvent in the electrolyte, and a commercial PE separator as an example.

A lithium secondary battery, the preparation method of which is as follows:

(2) Preparing the positive electrode plate obtained in the step (1), the lithium-indium alloy negative electrode prepared in the example 9 and a commercial PE diaphragm into a battery cell, packaging the battery cell by adopting a polymer, and pouring 1.0mol/L LiPF₆And (3) preparing the electrolyte (in the electrolyte, the weight ratio of organic solvents EC, DMC and FEC is 20:50:30) into the soft package lithium secondary battery through chemical synthesis and other processes.

Comparative example 1, the metallic lithium negative electrode was used as the negative electrode, the lithium cobaltate positive electrode was used as the positive electrode, and the electrolyte was LiPF₆The organic solvent in the electrolyte is a mixed solvent of EC, DMC and FEC, and the diaphragm is a commercial PE diaphragm, so as to prepare the secondary battery.

LiCoO (LiCoO)₂The preparation method of the Li battery is as follows:

preparing a battery core from a metallic lithium cathode, a lithium cobaltate anode and a commercial PE diaphragm, packaging by adopting a polymer, and pouring 1.0mol/L LiPF₆And (3) preparing the electrolyte (in the electrolyte, the weight ratio of organic solvents EC, DMC and FEC is 20:50:30) into the soft package lithium secondary battery through chemical synthesis and other processes.

Comparative example 2, the metal lithium aluminum alloy negative electrode was used as the negative electrode, the lithium cobaltate positive electrode was used as the positive electrode, and the electrolyte was LiPF₆The organic solvent in the electrolyte is a mixed solvent of EC, DMC and FEC, and the diaphragm is commercialPE diaphragm, preparing the secondary battery.

LiCoO (LiCoO)₂The preparation method of the/Li-Al battery is as follows:

preparing a lithium-aluminum alloy cathode, a lithium cobaltate anode and a commercial PE diaphragm into a battery cell, packaging by adopting a polymer, and filling 1.0mol/L LiPF₆And (3) preparing the electrolyte (in the electrolyte, the weight ratio of organic solvents EC, DMC and FEC is 20:50:30) into the soft package lithium secondary battery through chemical synthesis and other processes.

Comparative example 3, the metallic lithium indium alloy negative electrode was used as the negative electrode, the lithium cobaltate positive electrode was used as the positive electrode, and the electrolyte was LiPF₆The organic solvent in the electrolyte is a mixed solvent of EC, DMC and FEC, and the diaphragm is a commercial PE diaphragm, so as to prepare the secondary battery.

LiCoO (LiCoO)₂The preparation method of the/Li-In battery comprises the following steps:

preparing a lithium indium alloy cathode, a lithium cobaltate anode and a commercial PE diaphragm into a battery cell, packaging by adopting a polymer, and pouring 1.0mol/L LiPF₆And (3) preparing the electrolyte (in the electrolyte, the weight ratio of organic solvents EC, DMC and FEC is 20:50:30) into the soft package lithium secondary battery through chemical synthesis and other processes.

The secondary batteries provided in examples 2, 4, 6, 8, and 10 of the present application and the batteries provided in comparative examples 1,2, and 3 were subjected to electrochemical performance tests, and the test methods were carried out according to a 1.0C/1.0C charge-discharge regime with a voltage range of 3.0 to 4.5V, with the test results shown in table 1 below and in fig. 6A, 6B, 6C, and 6D. Wherein, fig. 6A is a graph of cycle performance of the batteries provided in examples 2, 4, 6, 8, 10 and 1,2, 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 showing cycle performance of the batteries provided in example 10 and comparative example 3.

The secondary battery provided in example 6 of the present application and the battery provided in comparative example 1 were subjected to scanning of their negative electrodes using an electron microscope after cycling for 100 weeks, and electron microscope (SEM) photographs of the negative electrode of the secondary battery provided in example 6 and the negative electrode of the battery provided in comparative example 1 are shown in fig. 7 and 8, respectively.

TABLE 1

Serial number	Capacity retention at 50 weeks	Capacity retention rate of 80 weeks	Capacity retention rate of 100 weeks
				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 Table 1 and the test results of FIG. 6A, FIG. 6B, FIG. 6C, and FIG. 6D, the batteries of examples 2, 4, 6, 8, and 10 of the present application all provided 100 cycle capacity retention rates greater than 90%, at least 91.1%, which were higher than LiCoO provided in comparative example 1₂LiCoO for Li cell, comparative example 2₂Li-Al cell and LiCoO as provided in comparative example 3₂Capacity retention after 100 cycles of the/Li-In battery. This shows that the example of the present application uses a conductive polymer with a thermal sensitive property to protect a lithium negative electrode, and can significantly improve the cycle performance of the battery. This is because a stable protective layer is formed on the surface of the lithium negative electrode protected with a conductive polymer having a heat-sensitive property. In one aspect, a conductive polymer with heat-sensitive properties is electrochemically oxidatively doped during charging (e.g., doped with an anion PF)₆ ^-) And the uniform deposition of lithium ions on the surface of the composite lithium cathode is promoted, and the growth of lithium dendrites is avoided. On the other hand, in the lithium negative electrode, dendrite formation causes local current increase or side reaction increase during the charge and discharge of the battery, resulting in local current increaseThe temperature rises, when the temperature reaches the critical temperature of the conductive polymer, the conjugation degree is reduced and the doping is removed, so that the impedance is increased, the conductivity is reduced, and lithium ions are guided to deposit to a non-dendritic region at the same time, so that the continuous growth of lithium dendritic crystals is avoided. In addition, the conductive polymer can form a polymer elastic film, so that the volume expansion of the lithium cathode in the circulation process can be effectively relieved, the lithium cathode interface is stabilized, the side reaction is reduced, and the coulomb efficiency is improved. Due to the fact that the unprotected lithium negative electrode is not provided with the protective layer, lithium ions are unevenly deposited on the surface of the negative electrode to cause lithium dendrite growth, and the exposed lithium negative electrode is directly contacted with electrolyte, so that severe side reactions are caused, the coulomb efficiency of the lithium negative electrode is reduced, and the cycling stability of the battery is poor.

Comparing fig. 7 and fig. 8, it can be seen that after the lithium metal negative electrode of example 2 of the present application is protected for 100 cycles, the surface of the lithium metal negative electrode is intact and no lithium dendrite is generated, 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 a conductive polymer with heat-sensitive characteristics, and electrochemical oxidation doping (e.g. doping anion PF) is performed during charging (e.g. doping anion PF)₆ ^-) The lithium ion composite lithium negative electrode promotes the uniform deposition of lithium ions on the surface of the composite lithium negative electrode, avoids the growth of lithium dendrites, 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. After the unprotected lithium metal negative electrode in the comparative example 1 is cycled for 100 weeks, severe lithium dendrite phenomenon appears on the surface of the lithium metal negative electrode, which is mainly because the unprotected lithium metal negative electrode forms uneven lithium deposition in the cycling process and easily causes lithium dendrite growth.

Finally, it should be noted that: the above is only an embodiment of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions within the technical scope of the present disclosure should be covered by the scope of the present application. Therefore, the protection scope of the present application shall be subject to the protection scope of the claims.

Claims

1. A composite metal anode, comprising: 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.

2. The composite metal anode of claim 1, wherein said conductive polymer is selected from the group consisting of conductive polymers having heat sensitive properties.

3. The composite metal anode of claim 2, wherein said conductive polymer is selected from the group consisting of conductive polymers having an impedance that increases with increasing temperature in the range of 50 ℃ to 130 ℃.

4. The composite metal negative electrode according to any one of claims 1 to 3, wherein the conductive polymer is a homopolymer formed by polymerizing the same structural unit or a copolymer formed by polymerizing different structural units, and the structural unit has a general formula represented by the following formula (1):

in the formula (1), X is selected from NH, O or S;

5. The composite metal anode according to claim 4, wherein the number of carbon atoms in the alkyl group, the halogenated alkyl group, the alkoxy group, or the halogenated alkoxy group is 1 to 20;

the number of carbon atoms in the alkenyl group, the halogenated alkenyl group, the alkenyloxy group and the halogenated alkenyloxy group is 2-10;

the number of carbon atoms in the aryl group, the halogenated aryl group, the aryloxy group, and the halogenated aryloxy group is 6 to 20.

6. The composite metal negative electrode according to claim 4, wherein the conductive polymer is at least one selected from a compound (A) to a compound (P) represented by the following structures, wherein n is in a range of 10 to 10000, and n is n₁+n₂The value of (A) satisfies: n is more than or equal to 10₁+n₂≤10000，

7. The composite metal anode according to any of claims 1 to 3, wherein the thickness of the protective layer is 1nm to 20 μm.

8. The composite metal anode of any of claims 1 to 7, 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 anode via the binder.

9. The composite metal anode according to claim 8, wherein a mass ratio of the conductive polymer to the binder in the protective layer is 1 to 100: 1.

10. The composite metal anode of any of claims 1 to 9, wherein the metal anode is selected from one or more of a lithium anode, a sodium anode, a potassium anode, a magnesium anode, a zinc anode, and an aluminum anode.

11. The composite metal anode of any of claims 1 to 9, further comprising a current collector comprising a first surface and a second surface disposed opposite to each other, wherein the metal anode is bonded to at least the first surface of the current collector, and wherein the protective layer is disposed on at least a surface of the metal anode facing away from the current collector.

12. The preparation method of the composite metal negative electrode is characterized by comprising the following steps of:

13. The method for producing a composite metal anode according to claim 12, wherein the mass ratio of the conductive polymer to the organic solvent in the mixed solution is 1:1 to 100; and/or the presence of a gas in the gas,

the organic solvent is selected from one or more of azomethylpyrrolidone, acetone, acetonitrile, ethanol, dimethyl carbonate, ethyl methyl 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.

14. A secondary battery is characterized by comprising a positive electrode, a negative electrode, a diaphragm and electrolyte, wherein 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 composite metal negative electrode according to any one of claims 1 to 13, wherein the negative electrode has a protective layer disposed opposite to the positive electrode, and the anion is an anion in the electrolyte.

15. A terminal, comprising: the secondary battery according to claim 14, which is used to supply power to the terminal.