CN114420933A

CN114420933A - Negative electrode, electrochemical device, and electronic device

Info

Publication number: CN114420933A
Application number: CN202210050506.8A
Authority: CN
Inventors: 蒋欣; 王慧鑫
Original assignee: Dongguan Poweramp Technology Ltd
Current assignee: Dongguan Poweramp Technology Ltd
Priority date: 2022-01-17
Filing date: 2022-01-17
Publication date: 2022-04-29

Abstract

The present application relates to a negative electrode, an electrochemical device, and an electronic device. The negative electrode provided by the application comprises a current collector and a negative active material layer located on the current collector, wherein the negative active material layer comprises a negative active material and a polythiophene compound, and the mass percentage of the polythiophene compound is 0.05-5% based on the total mass of the negative active material layer. The negative electrode has good electronic and ionic conductivity, can effectively expand a charging window when used for an electrochemical device, and shows good electrochemical performance.

Description

Negative electrode, electrochemical device, and electronic device

Technical Field

The application belongs to the technical field of batteries, and particularly relates to a negative electrode, an electrochemical device comprising the negative electrode and an electronic device.

Background

With the continuous development of lithium batteries, people experience and pursue higher and higher for electronic products such as mobile phones, notebooks and unmanned aerial vehicles, and transportation means such as electric bicycles, electric motorcycles and electric automobiles. Particularly, with the introduction of the fast-filling products, the expectation of the users for the fast-filling products is stronger. However, the dynamic performance of the conventional lithium battery is limited by the intrinsic characteristics of a chemical system, and is represented by the fact that a charging window is narrowed, and lithium precipitation occurs during high-rate charging, so that a bottleneck exists in quick charging, and particularly for high-endurance products, a thick coating design is usually adopted for realizing higher energy density, so that the improvement of the dynamic performance is more difficult.

Disclosure of Invention

Aiming at the defects of the prior art, the application provides the cathode which has good electronic and ionic conductivity, is used for an electrochemical device to effectively expand a charging window and shows good electrochemical performance. The present application also provides an electrochemical device and an electronic device comprising the anode.

In a first aspect, the present application provides a negative electrode, including a current collector and a negative active material layer on the current collector, wherein the negative active material layer includes a negative active material and a polythiophene compound, and the mass percentage of the polythiophene compound is 0.05% to 5% based on the total mass of the negative active material layer. The cathode provided by the application has better ionic and electronic conductivity and shows good dynamic performance. The polythiophene compound is used as an electron relay body to play a role in electron transfer, can effectively balance electron and ion transmission rates, and avoids the precipitation of lithium ions on the surface of a negative electrode due to overhigh local current density under high multiplying power, so that the charging window of an electrochemical device is expanded.

In the application, the content of the polythiophene compound has an important influence on the performance of the prepared negative electrode, if the content is too small, the improvement effect on the charging window of the electrochemical device is not significant, and if the content is too large, the cycle performance of the electrochemical device is obviously reduced. According to some embodiments of the present application, the mass percentage content of the polythiophene compound is 0.05%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 5%, or any value therebetween, based on the total mass of the anode active material layer. According to some embodiments of the present application, the mass percentage of the polythiophene compound is 0.1% to 2% based on the total mass of the anode active material layer.

According to some embodiments of the present application, the polythiophene compound has a structural unit represented by formula a below:

in the formula A, R₁And R₂Each independently selected from hydrogen, halogen, optionally substituted C1 to C18 alkyl or optionally substituted C1 to C18 alkoxy, or R₁And R₂Are each selected from optionally substituted C1 to C18 alkylene groups, or optionally substituted C1 to C18 alkylene groups in which one or more carbon atoms are substituted by one or more identical or different heteroatoms selected from O and S. According to some embodiments of the application, the halogen is selected from Cl, Br or I.

According to some embodiments of the application, R in formula A₁And R₂Each selected from C1 to C8 dioxyalkylene, optionally substituted C1 to C8 oxathioalkylene, or optionally substituted C1 to C8 dithioalkylene, or optionally substituted C1 to C8 alkylidene wherein at least one carbon atom is optionally substituted with a heteroatom selected from O and S.

According to some embodiments of the present application, the negative electrode active material layer further includes an ionic liquid, and the ionic liquid is contained in an amount of 0.01% to 10% by mass based on the total mass of the negative electrode active material layer. In some embodiments of the present application, the mass percentage of the ionic liquid is 0.01%, 0.05%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, and any value therebetween, based on the total mass of the anode active material layer. According to some embodiments of the present application, the ionic liquid is contained in an amount of 0.1% to 2% by mass based on the total mass of the anode active material layer.

According to some embodiments of the present application, the ionic liquid comprises at least one of an imidazole-based ionic liquid, a pyrrole-based ionic liquid, or a pyridine-based ionic liquid. According to some embodiments of the present application, imidazole-based ionic liquids include, but are not limited to, 1-butyl-3-methylimidazolium hexafluorophosphate ([ Bmim [ ])][PF₆]) 1-butyl-3-methylImidazole tetrafluoroborate ([ Bmim)][BF₄]) Or 1-methylimidazolium tetrafluoroborate ([ Hmim ]][BF₄]) At least one of (1). According to some embodiments of the present application, the pyrrole-based ionic liquids include, but are not limited to, N-methyl-N-propylpyrroleditrifluoromethylsulfonyl ([ PYR)₁₃]TFSI). According to some embodiments of the present application, the pyridine-based ionic liquid includes, but is not limited to, 1-butyl-4-methylpyridine bis (trifluoromethylsulfonyl) imide ([ BMPy)]TFSI)。

According to some embodiments of the present application, the mass ratio of the polythiophene compound to the ionic liquid is (0.01-500): 1. according to some embodiments of the application, the mass ratio of polythiophene compound to ionic liquid is 0.01: 1. 0.05: 1. 0.1: 1. 0.5: 1. 1: 1. 5: 1. 10: 1. 50: 1. 100, and (2) a step of: 1. 500: 1 and any value in between. According to some embodiments of the present application, the mass ratio of the polythiophene compound to the ionic liquid is (0.05-10): 1. according to some embodiments of the present application, the mass ratio of the polythiophene compound to the ionic liquid is (0.1-5): 1.

according to some embodiments of the present application, the polythiophene compound is obtained by polymerizing a thiophene monomer in the presence of an ionic liquid. In this application, the polythiophene compounds have a chimerism in the range of-3.1 eV to-3.4 eV and a lowest unoccupied orbital LUMO in the range of-1.4 eV to-3.04 eV.

According to some embodiments of the present application, the negative active material layer is obtained by coating a slurry including a negative active material, a thiophene monomer, an ionic liquid, a binder, and a conductive agent on a current collector.

According to some embodiments of the present application, the polythiophene compound is added by adding a thiophene monomer and an ionic liquid to the negative electrode formulation and is polymerized in situ in the formation stage. Compared with other negative electrode material additives, the thiophene monomer is uniformly dispersed on the surface of the negative electrode active material in a solution mode, and the polythiophene compound is formed in an in-situ polymerization mode, so that the coating effect is more uniform compared with other solid phase additives. More importantly, the polythiophene coating layer is used as an electron relay, and can transfer excessive electrons to play a role of a buffer layer when charged at a high rate, namely when the current density is overlarge, so that the diffusion rate of lithium ions is close to that of electrons, and the condition that the lithium ions accept the electrons to be separated out on the surface is avoided.

The negative electrode of the present application can be prepared by a method known in the art. According to some embodiments of the present application, a method of preparing a negative electrode includes the steps of: s1: mixing the ionic liquid with an organic solvent to obtain a solution 1; preferably, the volume ratio of the ionic liquid to the organic solvent is 1: (5-15); s2: dissolving a thiophene monomer in the solution 1 to obtain a solution 2; preferably, the concentration of thiophene monomer in solution 1 is 0.5mol/L to 5 mol/L; s3: mixing and dispersing a negative electrode active material, a conductive agent, a binder and other optional additives in a mixed solvent comprising the solution 2 and water to obtain slurry; s4: and coating the slurry on a current collector, drying and carrying out cold pressing to obtain the cathode. The reaction conditions of the cathode preparation are easy to control, the process is mature, the synthesized cathode has good electron and ion conducting performance, the structure is relatively stable, and the electrochemical performance of the battery can be effectively improved.

According to some embodiments of the present application, the thiophene monomer has the formula

In which R is₃And R₄Each independently selected from hydrogen, halogen, optionally substituted C1 to C18 alkyl or optionally substituted C1 to C18 alkoxy, or R₃And R₄Are each selected from optionally substituted C1 to C18 alkylene groups, or optionally substituted C1 to C18 alkylene groups in which one or more carbon atoms are substituted by one or more identical or different heteroatoms selected from O and S. According to some embodiments of the application, the halogen is selected from Cl, Br or I. According to some embodiments of the present application, the thiophene monomer includes at least one of 3-methylthiophene, 3-butylthiophene, 3-bromothiophene, or 3-methoxythiophene.

According to some embodiments of the present application, the thiophene monomer and the ionic liquid are used in a ratio of 1: 5 (g: mL) to 5: 1 (g: mL). According to some embodiments of the present application, the thiophene monomer and the ionic liquid are used in a ratio of 1: 5 (g: mL), 1: 4 (g: mL), 1: 3 and any value therebetween (g: mL), 1: 2 (g: mL), 1: 1 (g: mL), 2: 1 (g: mL), 3: 1 (g: mL), 4: 1 (g: mL), 5: 1 (g: mL). According to some embodiments of the present application, the thiophene monomer and the ionic liquid are used in a ratio of 1: 2 (g: mL) to 2: 1 (g: mL).

According to some embodiments of the present application, the negative active material includes at least one of soft carbon, hard carbon, artificial graphite, or natural graphite.

A second aspect of the present application provides an electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte, the negative electrode comprising the negative electrode according to the first aspect.

A third aspect of the present application provides an electronic device comprising an electrochemical device according to the second aspect of the present application.

The prior art mostly solves the problems of narrow charging window during quick charging and lithium separation during high-rate charging from the aspects of design, materials or chemical systems and the like. From the aspect of design, the dynamic performance deficiency is mainly compensated by losing energy density (such as reducing coating weight), and the scheme can only be used for temporary solution but not for permanent solution, and has great influence on the long endurance experience of users; from the aspect of materials, the dynamic performance of graphite can be improved by coating the graphite or improving the OI value and the like, but the scheme can only carry out special optimization treatment on certain materials and does not have universality; from the aspect of a chemical system, the dynamic performance of the system is usually improved by increasing more conductive agents or reducing film forming additives in electrolyte, and the like, and the scheme can increase the consumption of active lithium in the system to compensate the dynamic performance in a mode of losing the service life of the battery.

Compared with the prior art, the negative electrode pole piece has good electronic and ionic conductivity and good electrochemical performance, excessive electrons can be transferred by the polythiophene compound during high-rate charging, the buffer layer effect is achieved, the diffusion rate of lithium ions is close to that of electrons, the situation that the lithium ions are subjected to electron precipitation on the surface is avoided, and the charging window of an electrochemical device is effectively expanded.

Drawings

Fig. 1 is an SEM image of the negative electrode prepared according to example 1 of the present application.

Detailed Description

To make the purpose, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be clearly and completely described below with reference to the embodiments, and it is obvious that the described embodiments are a part of the embodiments of the present application, and not all of the embodiments. The embodiments described herein are illustrative and are provided to provide a basic understanding of the present application. The embodiments of the present application should not be construed as limiting the present application.

For the sake of brevity, only some numerical ranges are specifically disclosed herein. However, any lower limit may be combined with any upper limit to form ranges not explicitly recited; and any lower limit may be combined with any other lower limit to form a range not explicitly recited, and similarly any upper limit may be combined with any other upper limit to form a range not explicitly recited. Furthermore, each separately disclosed point or individual value may itself, as a lower or upper limit, be combined with any other point or individual value or with other lower or upper limits to form ranges not explicitly recited.

In the description herein, "above" and "below" include the present numbers unless otherwise specified.

Unless otherwise indicated, terms used in the present application have well-known meanings that are commonly understood by those skilled in the art. Unless otherwise indicated, the numerical values of the parameters mentioned in the present application can be measured by various measurement methods commonly used in the art (for example, the test can be performed according to the methods given in the examples of the present application).

A list of items to which the term "at least one of," "at least one of," or other similar term is connected may imply any combination of the listed items. For example, if items a and B are listed, the phrase "at least one of a and B" means a only; only B; or A and B. In another example, if items A, B and C are listed, the phrase "at least one of A, B and C" means a only; or only B; only C; a and B (excluding C); a and C (excluding B); b and C (excluding A); or A, B and C. Item A may comprise a single component or multiple components. Item B may comprise a single component or multiple components. Item C may comprise a single component or multiple components.

A first and a negative electrode

The negative electrode comprises a current collector and a negative active material layer located on the current collector, wherein the negative active material layer comprises a negative active material and a polythiophene compound, and the mass percentage of the polythiophene compound is 0.05% -5% based on the total mass of the negative active material layer. The cathode provided by the application has better ionic and electronic conductivity and shows good dynamic performance. The polythiophene compound is used as an electron relay body to play a role in electron transfer, can effectively balance electron and ion transmission rates, and avoids the precipitation of lithium ions on the surface of a negative electrode due to overhigh local current density under high multiplying power, so that the charging window of an electrochemical device is expanded.

in the formula A, R₁And R₂Each independently selected from hydrogen, halogen, optionally substitutedC1 to C18 alkyl or optionally substituted C1 to C18 alkoxy, or R₁And R₂Are each selected from optionally substituted C1 to C18 alkylene groups, or optionally substituted C1 to C18 alkylene groups in which one or more carbon atoms are substituted by one or more identical or different heteroatoms selected from O and S. According to some embodiments of the application, the halogen is selected from Cl, Br or I.

According to some embodiments of the present application, the ionic liquid comprises at least one of an imidazole-based ionic liquid, a pyrrole-based ionic liquid, or a pyridine-based ionic liquid. According to some embodiments of the present application, imidazole-based ionic liquids include, but are not limited to, 1-butyl-3-methylimidazolium hexafluorophosphate ([ Bmim [ ])][PF₆]) 1-butyl-3-methylimidazolium tetrafluoroborate ([ Bmim)][BF₄]) Or 1-methylimidazolium tetrafluoroborate ([ Hmim ]][BF₄]) At least one of (1). According to some embodiments of the present application, the pyrrole-based ionic liquids include, but are not limited to, N-methyl-N-propylpyrroleditrifluoromethylsulfonyl ([ PYR)₁₃]TFSI). According to some embodiments of the present application, the pyridine-based ionic liquid includes, but is not limited to, 1-butyl-4-methylpyridineBis (trifluoromethylsulfonyl) imide ([ BMPy)]TFSI)。

According to some embodiments of the present application, the negative active material includes, but is not limited to: at least one of soft carbon, hard carbon, artificial graphite, or natural graphite.

According to some embodiments of the present application, the conductive agent includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. According to some embodiments of the present application, the carbon-based material is selected from carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. According to some embodiments of the present application, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum or silver. According to some embodiments of the present application, the conductive polymer is a polyphenylene derivative.

According to some embodiments of the present application, the binder includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or the like.

According to some embodiments of the present application, a current collector comprises: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with a conductive metal, or any combination thereof.

Two, electrochemical device

An electrochemical device includes a positive electrode, a negative electrode, a separator, and an electrolyte. The negative electrode in the electrochemical device of the present application includes the negative electrode of the present application.

Materials, compositions, and methods of making positive electrodes useful in embodiments of the present application include any of the techniques disclosed in the prior art. According to some embodiments of the present application, a positive electrode includes a current collector and a positive active material layer on the current collector. According to some embodiments of the present application, the positive active material includes, but is not limited to: olivine-structured materials such as lithium iron manganese phosphate, lithium iron phosphate, and lithium manganese phosphate, ternary-structured materials such as NCM811, NCM622, NCM523, and NCM333, lithium cobaltate materials, lithium manganate materials, and other metal oxides capable of releasing lithium. According to some embodiments of the present application, the positive electrode active material layer further includes a binder, and optionally includes a conductive material. The binder improves the binding of the positive electrode active material particles to each other, and also improves the binding of the positive electrode active material to the current collector.

According to some embodiments of the present application, the binder for the positive active material layer includes, but is not limited to: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1, 1-difluoroethylene, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, or the like.

According to some embodiments of the present application, the conductive material for the positive electrode active material layer includes, but is not limited to: carbon-based materials, metal-based materials, conductive polymers, and mixtures thereof. According to some embodiments of the present application, the carbon-based material is selected from carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. According to some embodiments of the present application, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum or silver. According to some embodiments of the present application, the conductive polymer is a polyphenylene derivative.

According to some embodiments of the present application, a current collector that may be used for a positive electrode may include, but is not limited to: aluminum.

The positive electrode may be prepared by a preparation method well known in the art. For example, the positive electrode can be obtained by: the active material, the conductive material, and the binder are mixed in a solvent to prepare an active material composition, and the active material composition is coated on a current collector. According to some embodiments of the present application, the solvent may include, but is not limited to: n-methyl pyrrolidone.

The electrolyte that may be used in the embodiments of the present application may be an electrolyte known in the art. According to some embodiments of the present application, the electrolyte includes an organic solvent, a lithium salt, and an additive. Organic of the electrolyte according to the present applicationThe solvent may be any organic solvent known in the art that can act as a solvent for the electrolyte. The electrolyte used in the electrolyte according to the present application is not limited, and may be any electrolyte known in the art. The additive of the electrolyte according to the present application may be any additive known in the art as an additive of electrolytes. According to some embodiments of the present application, the organic solvent includes, but is not limited to: at least one of Ethylene Carbonate (EC), Propylene Carbonate (PC), diethyl carbonate (DEC), Ethyl Methyl Carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate, methyl acetate, or ethyl propionate. According to some embodiments of the present application, the lithium salt comprises at least one of an organic lithium salt or an inorganic lithium salt. According to some embodiments of the present application, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF)₆) Lithium tetrafluoroborate (LiBF)₄) Lithium difluorophosphate (LiPO)₂F₂) Lithium bis (trifluoromethanesulfonylimide) LiN (CF)₃SO₂)₂(LiTFSI), lithium bis (fluorosulfonyl) imide Li (N (SO)₂F)₂) (LiFSI), lithium bis (oxalato) borate LiB (C)₂O₄)₂(LiBOB), lithium difluoro (oxalato) borate LiBF₂(C₂O₄) (LiDFOB), phosphorus pentafluoride, lithium perchlorate, lithium hexafluoroarsenate, trimethyl lithium, or lithium chloride. According to some embodiments of the present application, the concentration of the lithium salt in the electrolyte is: 0.5 to 3mol/L, 0.5 to 2mol/L, or 0.8 to 1.5 mol/L.

According to some embodiments of the present application, an electrochemical device of the present application is provided with a separator between a positive electrode and a negative electrode to prevent a short circuit. The material and shape of the separation film used in the electrochemical device of the present application are not particularly limited, and may be any of the techniques disclosed in the prior art. According to some embodiments of the present application, the separator includes a polymer or inorganic substance formed of a material stable to the electrolyte of the present application, or the like.

For example, the release film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film with a porous structure, and the material of the substrate layer is at least one selected from polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide or aramid fiber. Specifically, a polypropylene porous film, a polyethylene porous film, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite film can be used. The base material layer can be one layer or a plurality of layers, when the base material layer is a plurality of layers, the compositions of the polymers of different base material layers can be the same or different, and the weight average molecular weights are different; when the substrate layer is a multilayer, the polymers of different substrate layers have different closed cell temperatures.

According to some embodiments of the present application, a surface treatment layer is disposed on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance.

The inorganic layer comprises inorganic particles and a binder, wherein the inorganic particles are selected from one or more of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium oxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate. The binder is selected from one or a combination of more of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer comprises a polymer, and the material of the polymer comprises at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride or poly (vinylidene fluoride-hexafluoropropylene).

According to some embodiments of the present application, the electrochemical device of the present application includes, but is not limited to: all kinds of primary batteries, secondary batteries, fuel cells, solar cells or capacitors. According to some embodiments of the present application, the electrochemical device is a lithium secondary battery. According to some embodiments of the present application, the lithium secondary battery includes, but is not limited to: a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery.

Electronic device

The present application provides an electronic device comprising an electrochemical device according to the second aspect of the present application.

According to some embodiments of the present application, the electronic device includes, but is not limited to: a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a cellular phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting apparatus, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large-sized household battery or a lithium ion capacitor, and the like.

In order that the present application may be more readily understood, the present application will now be described in detail with reference to the following examples, which are intended to be illustrative only and are not intended to limit the scope of the application.

Test method

1. SEM/EDS testing

And carrying out SEM/EDS test on the prepared negative pole piece. SEM and EDS mainly utilize focused electron beams to excite the surface of a sample to generate secondary information such as secondary electrons, backscattered electrons, characteristic X rays and the like, and the secondary information is collected and detected to be used for analyzing the micro-morphology and the micro-area components of the surface of the sample. SEM test conditions: the working distance is 5-30mm, the aperture of the objective lens is 100-200 μm, and the accelerating power supply is 2-20 kV.

2. Capacity testing

5 prepared batteries are respectively charged at normal temperature with constant current of 0.2C multiplying power until the voltage reaches 4.2V, and further charged at constant voltage of 4.2V until the current is lower than 0.05C, so that the batteries are in a full charge state of 4.2V. The discharge was then stopped at a constant current at 0.2C rate until the voltage was 2.8V and the discharge capacity was recorded.

3. Low temperature Performance test

The prepared lithium ion battery is repeatedly charged and discharged through the following steps, the discharge capacity retention rate of the lithium ion battery is calculated, and after the last charging is finished, the battery is disassembled to observe and record the lithium precipitation state of the negative electrode.

First, in an environment of-20 ℃, first charge and discharge were performed, constant-current and constant-voltage charge was performed at a charge current of x C (i.e., a current value at which the theoretical capacity was completely discharged within 1/x h) until the upper limit voltage was 4.2V, and then constant-current discharge was performed at a discharge current of 1C until the final voltage was 2.8V, and the discharge capacity of the first cycle was recorded.

The low-temperature capacity retention rate (discharge capacity at the first cycle/discharge capacity at room temperature) × 100%.

Next, the charge and discharge cycles were continued for 10 times under the above conditions, and after the 11 th cycle charging was completed, the battery was disassembled, and the state of lithium deposition on the surface of the negative electrode was observed and recorded, and the low-temperature charging ability of the battery having no lithium deposition on the negative electrode was recorded as x C.

Example 1

1. Preparation of the negative electrode

(1) Firstly, ionic liquid [ Bmim ]][PF₆]And ethylene carbonate in a volume ratio of 1: 10 to obtain a solution 1;

(2) dissolving 10g of 3-methylthiophene in 100ml of solution 1 to obtain 1mol/L of solution 2 of 3-methylthiophene monomer;

(3) mixing graphite serving as a negative electrode active material, acetylene black serving as a conductive agent, Styrene Butadiene Rubber (SBR) serving as a binder and sodium carboxymethyl cellulose (CMC) serving as a thickening agent according to a weight ratio of 95: 2: 1, and mixing the graphite and the solution 2 according to a mass ratio of 5: 95 adding the solution 2, namely the mass ratio of the 3-methylthiophene monomer to the graphite is 0.5: and 95, taking deionized water as a solvent, preparing slurry with the solid content of 70%, uniformly stirring, uniformly coating the slurry on one surface of a copper foil with the thickness of 10 microns, drying at 110 ℃, cold-pressing to obtain a negative pole piece with the coating thickness of 150 microns and a single-side coated negative active material layer, and repeating the coating steps on the other surface of the negative pole piece to obtain the negative pole piece with the double-side coated negative active material layer. Cutting the negative pole piece into a size of 74mm multiplied by 867mm, and welding a pole lug for later use.

2. Preparation of the Positive electrode

Preparing active material nickel cobalt lithium manganate, conductive agent acetylene black and binder polyvinylidene fluoride (PVDF) according to a weight ratio of 95: 3: 2, fully stirring and uniformly mixing in an N-methyl pyrrolidone solvent system, coating on an aluminum foil, drying, and performing cold pressing to obtain the positive pole piece.

3. Isolation film

A PE porous polymer film (7 μm) was used as a separator.

4. Preparation of the electrolyte

Under the environment that the water content is less than 10ppm, non-aqueous organic solvents such as Ethylene Carbonate (EC), diethyl carbonate (DEC), Propylene Carbonate (PC), Propyl Propionate (PP) and Vinylene Carbonate (VC) are mixed according to the mass ratio of 20: 30: 20: 28: 2 mixing and then adding lithium hexafluorophosphate (LiPF) to the non-aqueous organic solvent₆) Dissolving and mixing uniformly to obtain electrolyte, wherein the LiPF is₆The mass ratio of the organic solvent to the non-aqueous organic solvent is 8: 92.

5. preparation of lithium batteries

And stacking the positive pole piece, the isolating film and the negative pole piece in sequence to enable the isolating film to be positioned between the cathode and the anode to play an isolating role, and winding to obtain the bare cell. And placing the bare cell in an outer package, dehydrating at 80 ℃, injecting the prepared electrolyte, and performing vacuum packaging, standing, formation, shaping and other processes to obtain the lithium ion battery.

The negative electrode sheet prepared in example 1 was subjected to SEM and EDS tests, the SEM image is shown in fig. 1, and the EDS test results are shown in table 1.

TABLE 1

Element(s)	The weight percentage is%	Atom percent%
			C	50.97	59.68
O	35.33	31.05
			F	10.62	7.86
Na	0.14	0.08
			P	2.47	1.12
S	0.47	0.21

Comparative example 1

Solution 2 is not added in the preparation process of the negative pole piece, and other manufacturing processes and battery processes of the pole piece are the same as those of the embodiment 1.

Comparative example 2

The solution 1 with the same proportion is added in the preparation process of the negative pole piece, and other manufacturing processes and battery processes of the pole piece are the same as those of the embodiment 1.

Comparative example 3

Dissolving 10g of 3-methylthiophene in 100ml of ethylene carbonate to obtain a solution 3 of 1mol/L of 3-methylthiophene monomer; solution 3 with the same proportion as solution 2 is added in the preparation process of the negative pole piece, and other manufacturing processes and battery processes of the pole piece are the same as those of the embodiment 1.

Example 2

Preparing a negative pole piece according to the same method as the embodiment 1, and controlling the mass ratio of the 3-methylthiophene monomer to the graphite to be 0.05: 95.

example 3

Preparing a negative pole piece according to the same method as the embodiment 1, and controlling the mass ratio of the 3-methylthiophene monomer to the graphite to be 0.1: 95.

example 4

Preparing a negative pole piece according to the same method as the embodiment 1, and controlling the mass ratio of the 3-methylthiophene monomer to the graphite to be 0.25: 95.

example 5

Preparing a negative pole piece according to the same method as the embodiment 1, and controlling the mass ratio of the 3-methylthiophene monomer to the graphite to be 1: 95.

example 6

Preparing a negative pole piece according to the same method as the embodiment 1, and controlling the mass ratio of the 3-methylthiophene monomer to the graphite to be 2: 95.

example 7

Preparing a negative pole piece according to the same method as the embodiment 1, and controlling the mass ratio of the 3-methylthiophene monomer to the graphite to be 5: 95.

example 8

The ionic liquid in the solution 1 is [ Bmim ]][BF₄]Other manufacturing processes and battery processes of the pole piece are the same as those of the embodiment 1.

Example 9

The ionic liquid in solution 1 is [ Hmim ]][BF₄]Other manufacturing processes and battery processes of the pole piece are the same as those of the embodiment 1.

Example 10

The ionic liquid in the solution 1 is [ PYR₁₃]The TFSI, other fabrication processes of the pole piece and the battery process are the same as in example 1.

Example 11

The ionic liquid in the solution 1 is [ BMPy ] TFSI, and other manufacturing processes and battery processes of the pole piece are the same as those in the embodiment 1.

Example 12

And 3-butylthiophene is dissolved in the solution 1 to obtain a 1 mol/L3-butylthiophene monomer solution 2, and other manufacturing processes and battery processes of the pole piece are the same as those in the embodiment 1.

Example 13

And 3-octyl thiophene is dissolved in the solution 1 to obtain a 1 mol/L3-octyl thiophene monomer solution 2, and other manufacturing processes and battery processes of the pole piece are the same as those of the embodiment 1.

Example 14

3-bromothiophene is dissolved in the solution 1 to obtain a 1 mol/L3-bromothiophene monomer solution 2, and other manufacturing processes and battery processes of the pole piece are the same as those of the embodiment 1.

Example 15

And 3-methoxythiophene is dissolved in the solution 1 to obtain a 1 mol/L3-methoxythiophene monomer solution 2, and other manufacturing processes and battery processes of the pole piece are the same as those in the embodiment 1.

Example 16

A negative electrode sheet was prepared in the same manner as in example 1, wherein the ionic liquid [ Bmim ] in the solution 1 was controlled][PF₆]And ethylene carbonate in a ratio of 1: 1 and mixing.

Example 17

A negative electrode sheet was prepared in the same manner as in example 1, wherein the ionic liquid [ Bmim ] in the solution 1 was controlled][PF₆]And ethylene carbonate in a ratio of 1: 4, mixing.

Example 18

A negative electrode sheet was prepared in the same manner as in example 1, wherein the ionic liquid [ Bmim ] in the solution 1 was controlled][PF₆]And ethylene carbonate in a ratio of 1: 19, and mixing.

Example 19

A negative electrode sheet was prepared in the same manner as in example 1, wherein the ionic liquid [ Bmim ] in the solution 1 was controlled][PF₆]And ethylene carbonate in a ratio of 1: 49 are mixed.

Example 20

In the preparation of the negative electrode, the negative active material graphite, the conductive agent acetylene black, the binder Styrene Butadiene Rubber (SBR), the thickening agent sodium carboxymethylcellulose (CMC) and polythiophene (which is sodium carboxymethylcellulose) are mixedApplication of 3-methylthiophene in ionic liquid [ Bmim ]][PF₆]Medium polymerization) according to the weight ratio of 95: 2: 1: 0.5, and deionized water is used as a solvent to prepare slurry with the solid content of 70 percent. Other manufacturing processes and battery processes of the pole piece are the same as those of the embodiment 1.

TABLE 2

According to table 2, it is apparent from the test results of comparative examples 1 to 2 and examples 1 to 7 that the low-temperature performance of the battery with the polythiophene electronic relay added to the negative electrode is greatly improved, the improvement of the low-temperature charging capability of the battery gradually increases with the increase of the content, the low-temperature capacity retention rate is also continuously improved, but when the content is too high, the improvement effect is no longer obvious, and the low-temperature performance shows a decreasing trend. When the content of polythiophene is less than 0.1%, the effect of improving low-temperature performance is remarkably reduced due to an excessively small content. The mass content of polythiophene is further preferably 0.1% to 2.0%.

The results of the comparative example 3 and the example 1 show that the ionic liquid is mainly used as a solvent of a thiophene monomer and a polythiophene in-situ polymerization reaction auxiliary agent, and when the ionic liquid is not added, the thiophene monomer is difficult to polymerize to form intermediate polythiophene, so that the obvious electronic intermediate effect is avoided, and the low-temperature performance is not obviously improved.

The results of comparative examples 1 to 2 and example 1 show that the addition of the ionic liquid may block the original partial lithium deintercalation channel of graphite, and the low-temperature capacity retention rate is rather reduced. Therefore, the addition of a proper amount of polythiophene electronic relay can ensure the improvement of low-temperature performance, and the battery cannot cause the blockage of a normal graphite lithium-releasing and-inserting channel due to the residual of the ionic liquid caused by the excessive addition of the ionic liquid, so that the improvement of the low-temperature performance is not obvious.

Comparison of the results of example 1 and examples 8 to 15 shows that different ionic liquids and different thiophene monomers have different degrees of improvement in low temperature performance, [ Bmim ]][BF₄]Is favorable for improving the polymerization efficiency of thiophene monomers, has more obvious effect of improving the low-temperature performance, and the [ Hmin][BF₄]The melting point is higher (55 ℃), the monomer solubility is poorer, the electrochemical in-situ polymerization efficiency is reduced, and the improvement effect is weakened. Pyridine ionic liquids can also have the same effect, but because the melting point of the ionic liquids is higher, the solubility of monomers is poorer, and the improvement effect is weakened. Although the piperidine ionic liquid has a low melting point, the piperidine ionic liquid has a relatively high boiling point, is difficult to volatilize after being formed at a high temperature, has a large amount of residues in the battery, and has poor cycle performance. For thiophene monomers, the longer the alkyl chain in the monomer is, the lower the polymerization efficiency is, but the conductivity of polymerized polythiophene is enhanced, so that although the improvement effect of low-temperature charging capability is slightly poor, the capacity retention rate is higher, when the alkyl chain is too long, the polymerization efficiency is obviously reduced, the conductivity improvement is no longer dominant, and the low-temperature charging capability and the capacity retention rate are both reduced. When the thiophene monomer uses a strong electron-withdrawing group (e.g., the thiophene monomer substituted by bromine in example 14), the polymerization potential is increased, the polymerization efficiency is reduced, and the improvement effect is deteriorated due to the influence of the electronic effect, while when the electron-donating group (e.g., the thiophene monomer substituted by alkoxy in example 15) is used, the polymerization potential is reduced, the stability of the polymer is effectively improved, and the low-temperature charging capability and the capacity retention rate are remarkably improved.

Comparison of the results of example 1 and examples 16 to 19 shows that the thiophene monomer and the ionic liquid have different ratios, and the improvement effect is different, because a proper amount of the ionic liquid can perform the functions of promoting dissolution and catalyzing the thiophene monomer, and the ionic liquid residue can also cause the blockage of a normal graphite lithium-releasing channel, so that if the ionic liquid is added in a large amount, the ionic liquid residue can reduce the improvement effect on the battery, and if the ionic liquid is insufficient, the polymerization effect of the thiophene monomer can be influenced, and the actual improvement effect is reduced. Therefore, the content of the thiophene monomer and the ionic liquid is controlled to be more remarkable than that in the range of the application, and the low-temperature charging capacity and the capacity retention rate of the battery are improved.

Comparison of the results of example 1 and example 20 shows that the low-temperature performance improvement effect of the battery is more remarkable when the polythiophene compound generated in situ by the thiophene monomer is added.

It should be noted that the above-mentioned embodiments are only for explaining the present application and do not constitute any limitation to the present application. The present application has been described with reference to exemplary embodiments, but the words which have been used herein are words of description and illustration, rather than words of limitation. Modifications may be made to the present application as specified within the scope of the claims of the present application and modifications may be made to the present application without departing from the scope and spirit of the present application. Although the present application has been described herein with reference to particular means, materials and embodiments, the present application is not intended to be limited to the particulars disclosed herein, but rather the present application extends to all other methods and applications having the same functionality.

Claims

1. A negative electrode comprising a current collector and a negative active material layer on the current collector, wherein the negative active material layer comprises a negative active material and a polythiophene compound, and the mass percentage of the polythiophene compound is 0.05% to 5% based on the total mass of the negative active material layer.

2. The negative electrode according to claim 1, wherein the polythiophene compound is contained in an amount of 0.1 to 2% by mass based on the total mass of the negative electrode active material layer.

3. The anode according to claim 1, wherein the polythiophene compound has a structural unit represented by formula a below:

in the formula A, R₁And R₂Each independently selected from hydrogen, halogen, optionally substituted C1 to C18 alkyl or optionally substituted C1 to C18 alkoxy, or

R₁And R₂Are each selected from optionally substituted C1 to C18 alkylene groups, or optionally substituted C1 to C18 alkylene groups in which one or more carbon atoms are substituted by one or more identical or different heteroatoms selected from O and S.

4. The negative electrode of claim 3, wherein R in formula A₁And R₂Each selected from C1 to C8 dioxyalkylene, optionally substituted C1 to C8 oxathioalkylene, or optionally substituted C1 to C8 dithioalkylene, or optionally substituted C1 to C8 alkylidene wherein at least one carbon atom is optionally substituted with a heteroatom selected from O and S.

5. The negative electrode according to claim 1, wherein the negative electrode active material layer further comprises an ionic liquid, and the ionic liquid is contained in an amount of 0.01 to 10% by mass based on the total mass of the negative electrode active material layer.

6. The negative electrode of claim 5, wherein the ionic liquid comprises at least one of an imidazole-based ionic liquid, a pyrrole-based ionic liquid, or a pyridine-based ionic liquid.

7. The negative electrode of claim 6, wherein the imidazole-based ionic liquid comprises at least one of 1-butyl-3-methylimidazole hexafluorophosphate, 1-butyl-3-methylimidazole tetrafluoroborate, or 1-methylimidazole tetrafluoroborate, wherein the pyrrole-based ionic liquid comprises N-methyl-N-propyl pyrrole bis (trifluoromethylsulfonyl) imide, and wherein the pyridine-based ionic liquid comprises 1-butyl-4-methylpyridine bis (trifluoromethylsulfonyl) imide.

8. The negative electrode according to claim 5, wherein the mass ratio of the polythiophene compound to the ionic liquid is (0.01-500): 1.

9. an electrochemical device comprising a positive electrode, a negative electrode, a separator, and an electrolyte, the negative electrode comprising the negative electrode according to any one of claims 1 to 8.

10. An electronic device comprising the electrochemical device of claim 9.