CN113330609A - Conductive agent, method for producing same, electrochemical device, and electronic device - Google Patents

Conductive agent, method for producing same, electrochemical device, and electronic device Download PDF

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CN113330609A
CN113330609A CN202080009918.6A CN202080009918A CN113330609A CN 113330609 A CN113330609 A CN 113330609A CN 202080009918 A CN202080009918 A CN 202080009918A CN 113330609 A CN113330609 A CN 113330609A
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carbon
active material
conductive agent
positive electrode
electrode active
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CN113330609B (en
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吴剑
邹邦坤
吕婉婉
屈长明
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Ningde Amperex Technology Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

Provided are a conductive agent, a method of preparing the same, an electrochemical device, and an electronic device. The conductive agent includes: a compound formed of a carbon-based conductive material and a nitrile compound, wherein the nitrile compound is bonded to the carbon-based conductive material. Through bonding the nitrile compound to the carbon-based conductive material, the cyano group of the nitrile compound covers the surface of the carbon-based conductive material and cannot be dissociated into the electrolyte, the reduction reaction of the cyano group at the negative electrode is avoided, and meanwhile, the cyano group on the surface of the conductive agent can be subjected to complexing action with the transition metal atom of the positive electrode active material, so that the dissolution of transition metal ions is reduced, the oxidability of the positive electrode active material is reduced, the oxidation consumption of the electrolyte is reduced, and the high-temperature storage performance and the cycle performance of the electrochemical device are improved.

Description

Conductive agent, method for producing same, electrochemical device, and electronic device
Technical Field
The present disclosure relates to the field of electronic technologies, and in particular, to a conductive agent, a method for preparing the conductive agent, an electrochemical device, and an electronic device.
Background
In the cycle process of an electrochemical device such as a lithium ion battery, transition metal ions in a positive active material of a positive electrode sheet are easily dissolved out, the oxidability of the positive active material is improved, and the high-temperature storage performance and the cycle performance of the electrochemical device are deteriorated.
In order to reduce the dissolution of transition metal ions in the positive electrode active material, some nitrile compounds are added into the electrolyte at present, and the nitrile groups of the nitrile compounds are complexed with transition metal atoms on the surface of the positive electrode active material. However, the nitrile compound free in the electrolyte has a corrosive effect on the copper foil, thereby deteriorating the storage and cycle performance of the electrochemical device.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, the embodiments of the present application bond the nitrile compound with the carbon-based conductive material, and prevent the free nitrile compound from corroding the current collector to deteriorate the storage performance and the cycle performance of the electrochemical device.
Embodiments of the present application provide a conductive agent, including: a compound formed of a carbon-based conductive material and a nitrile compound, wherein the nitrile compound is bonded to the carbon-based conductive material.
In the above conductive agent, a carbon-carbon bond is formed between the carbon-based conductive material and the nitrile compound.
Among the above conductive agents, wherein the conductive agent has a curve obtained by infrared spectroscopy at 2337cm-1～2351cm-1With absorption peaks in between.
In the above conductive agent, the carbon-based conductive material includes at least one of conductive carbon black, ketjen black, acetylene black, conductive graphite, carbon nanotubes, or carbon fibers.
In the above-mentioned conductive agent, the nitrile compound may include at least one of a chain organic nitrile, an organic nitrile containing an aromatic ring or a heteroaromatic ring, or a cyano polymer.
In the above conductive agent, wherein the nitrile compound includes at least one of succinonitrile, adiponitrile, 1, 2-benzenediacetonitrile, 1, 4-benzenediacetonitrile, 1-naphthaleneacetonitrile, 2-naphthaleneacetonitrile, polyacrylonitrile, or polystyrene acrylonitrile.
Embodiments of the present application also provide an electrochemical device, including: the positive pole piece comprises a current collector and a positive active material layer, and the positive active material layer is arranged on the current collector; wherein the positive electrode active material layer includes a positive electrode active material and any one of the above-described conductive agents.
In the electrochemical device, the positive electrode active material includes one or more of lithium cobaltate, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminate, and the mass percentage of the positive electrode active material in the positive electrode active material layer is 95% to 99.5%.
In the electrochemical device, a mole percentage of the nitrile group in the conductive agent to the cobalt element in the positive electrode active material is 0.01% to 5%.
In the above electrochemical device, wherein the positive electrode active material has an absorption peak shift of 0.1eV to 0.45eV of cobalt obtained by an X-ray photoelectron spectroscopy test.
Embodiments of the present application also provide an electronic device including the above electrochemical device.
Embodiments of the present application also provide a method of preparing a conductive agent, including: mixing a carbon-based conductive material with a nitrile compound to obtain a pretreatment mixture; and drying and roasting the pretreated mixture to obtain the conductive agent, wherein the roasting treatment comprises roasting for 1-3 h at the temperature of 300-500 ℃.
According to the method, the carbon-containing conductive material is modified, the cyano group is introduced into the surface of the carbon-containing conductive material, in the positive active material layer, the positive active material is subjected to in-situ protection through the complexation of the cyano group and the transition metal ions, the dissolution of the transition metal ions in the circulation process is reduced, the oxidability of the positive electrode is reduced, and the circulation stability and the high-temperature storage performance of the electrochemical device are further improved.
Drawings
Fig. 1 shows a flowchart of a method for producing a conductive agent.
Fig. 2 is a schematic view of the positive electrode sheet of the present application.
Fig. 3 is a schematic view of an electrode assembly of the electrochemical device of the present application.
Fig. 4 and 5 show scanning electron microscope images of the carbon nanotubes of example 1 of the present application.
Fig. 6 and 7 show scanning electron microscope images of the carbon nanotube of comparative example 1 of the present application.
Fig. 8 shows infrared spectra of carbon nanotubes of example 1 and comparative example 1 of the present application.
Fig. 9 shows electron binding energy maps of cobalt ions of example 1 and comparative example 1 of the present application.
Detailed Description
The following examples are presented to enable those skilled in the art to more fully understand the present application and are not intended to limit the present application in any way.
At present, additives of nitrile compounds such as succinonitrile and adiponitrile are generally added to an electrolyte solution to reduce elution of transition metal ions in a positive electrode active material of an electrochemical device such as a lithium ion battery by complexation of nitrile groups in the nitrile compounds with transition metal atoms on the surface of the positive electrode active material. However, the free nitrile compounds in the electrolyte have a corrosive effect on the copper foil, and the following reactions occur successively: LiPF6+H2O→POF3+LiF+2HF，2H++CuOX→H2O+Cu2+，Cun++2CN-R+nPF6 -→Cu(CN-R)2PF6/Cu(CN-R)2(PF6)2，Cun++n F-→CuFn(slightly soluble), Cun++n PF6 -→Cu(PF6)n↓，Cun++ne-→ Cu ↓ (negative pole table)Surface reduction precipitation). The precipitation of copper on the negative electrode causes black spots at the negative electrode interface, and lithium cannot be inserted into the black spots, which deteriorates the storage performance and cycle performance of the electrochemical device.
This application is through processes such as flooding, stoving, high temperature calcination of carbon base conducting material and nitrile compound solution for carbon base conducting material bonds to nitrile compound, and the cyano-group covers in carbon base conducting material's surface and can not dissociate to electrolyte, and then has avoided the cyano-group to take place reduction reaction at the negative pole, improves positive pole protection effect. When the modified conductive agent is used as the positive electrode conductive agent, the cyano-group on the surface of the conductive agent can be complexed with the transition metal atom of the positive electrode active material, so that the dissolution of transition metal ions is reduced, the oxidability of the positive electrode active material is reduced, the oxidation consumption of the electrolyte is reduced, and the high-temperature storage performance and the cycle performance of the electrochemical device are improved.
Some embodiments of the present application provide a conductive agent including a compound formed of a carbon-based conductive material and a nitrile compound, wherein the nitrile compound is bonded to the carbon-based conductive material. Through bonding the nitrile compound to the carbon-based conductive material, the cyano group of the nitrile compound covers the surface of the carbon-based conductive material and cannot be dissociated into the electrolyte, the reduction reaction of the cyano group at the negative electrode is avoided, and meanwhile, the cyano group on the surface of the conductive agent can be subjected to complexing action with the transition metal atom of the positive electrode active material, so that the dissolution of transition metal ions is reduced, the oxidability of the positive electrode active material is reduced, the oxidation consumption of the electrolyte is reduced, and the high-temperature storage performance and the cycle performance of the electrochemical device are improved.
In some embodiments, the carbon-based conductive material comprises at least one of conductive carbon black, ketjen black, acetylene black, conductive graphite, carbon nanotubes, or carbon fibers. In some embodiments, the nitrile compound includes at least one of a chain organonitrile, an aromatic or heteroaromatic-containing organonitrile, or a cyano polymer. In some embodiments, the nitrile compound comprises at least one of succinonitrile, adiponitrile, 1, 2-benzenediacetonitrile, 1, 4-benzenediacetonitrile, 1-naphthaleneacetonitrile, 2-naphthaleneacetonitrile, polyacrylonitrile, or polystyrene acrylonitrile. In some embodiments, a carbon-carbon bond is formed between the carbon-based conductive material and the nitrile compound.
As shown in fig. 1, a flow chart of a method for preparing a conductive agent is shown. The preparation method comprises the step 101 of mixing the carbon-based conductive material with the nitrile compound to completely impregnate the carbon-based conductive material to obtain a pretreatment mixture. In some embodiments, the method for preparing the conductive agent further includes step 102, drying and baking the pre-treated mixture to obtain the conductive agent. In some embodiments, the drying process may remove moisture from the pre-treatment mixture slurry. In some embodiments, the firing treatment comprises firing at a temperature of 300 ℃ to 500 ℃ for 1h to 3 h. In some embodiments, the firing treatment is performed in an inert atmosphere. The preparation method is simple to operate, and the modification of the carbon-based conductive material by using the nitrile compound is easy to realize.
Some embodiments of the present application provide an electrochemical device including a positive electrode sheet including a current collector and a positive active material layer disposed on the current collector. As shown in fig. 2, in some embodiments, the positive electrode active material layer 2 is disposed on the current collector 1. It should be understood that although the positive electrode active material layer 2 is illustrated in fig. 2 as being located on one side of the current collector 1, this is merely exemplary and the positive electrode active material layer 2 may be located on both sides of the current collector 1. In some embodiments, the positive electrode current collector 1 may be an Al foil, but other positive electrode current collectors commonly used in the art may be used. In some embodiments, the positive electrode active material layer may be coated only on a partial area of the positive electrode collector. In some embodiments, the positive electrode active material layer 2 includes a positive electrode active material and any one of the above-described conductive agents.
In some embodiments, the positive active material comprises one or more of lithium cobaltate, lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminate, and the mass percentage of the positive active material in the positive active material layer is 95-99.5%. In some embodiments, the positive electrode active material layer further includes a binder, and the binder in the positive electrode active material layer may include at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride-hexafluoropropylene, a styrene-acrylate copolymer, a styrene-butadiene copolymer, a polyamide, polyacrylonitrile, a polyacrylate, a polyacrylic acid, a polyacrylate, sodium carboxymethyl cellulose, polyvinyl acetate, polyvinylpyrrolidone, a polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, or polyhexafluoropropylene.
In some embodiments, the mole percentage of the nitrile groups in the conductive agent to the cobalt element in the positive active material is 0.01% to 5%. If the nitrile group content in the conductive agent is too small, it cannot be sufficiently complexed with the cobalt element in the positive electrode active material. If the nitrile group content in the conductive agent is too much, redundant nitrile groups cannot be complexed with cobalt elements, namely, the function of preventing cobalt atoms from dissolving out cannot be achieved, and meanwhile, too many nitrile compounds bonded with the carbon-based conductive material can reduce the conductivity of the conductive agent, so that the cycle performance of an electrochemical device is influenced.
In some embodiments, the electrochemical device further comprises a separator and a negative electrode tab. As shown in fig. 3, the separator 11 is disposed between the positive electrode tab 10 and the negative electrode tab 12. In some embodiments, the negative electrode tab includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector. In some embodiments, the negative active material layer is disposed on one or both sides of the negative current collector. In some embodiments, the negative electrode current collector may employ at least one of a copper foil, an aluminum foil, a nickel foil, or a carbon-based current collector. In some embodiments, the negative active material layer may include a negative active material including at least one of a silicon-based material, a carbon material, lithium titanate, or niobium titanate, and a binder. In some embodiments, the silicon-based material comprises at least one of silicon, silicon oxygen, silicon carbon, or a silicon alloy. In some embodiments, the carbon material in the negative electrode active material layer includes at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, or hard carbon. In some embodiments, the negative active material layer further includes a conductive agent therein, and the conductive agent may include at least one of conductive carbon black, lamellar graphite, graphene, carbon nanotubes, or carbon fibers. In some embodiments, the binder in the negative active material layer may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinyl pyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, poly styrene-butadiene rubber, epoxy resin, polyester resin, polyurethane resin, or polyfluorene. It should be understood that the above disclosed materials are merely exemplary, and any suitable material may be employed for the anode active material layer.
In some embodiments, the separator 11 comprises at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. For example, the polyethylene includes at least one selected from high density polyethylene, low density polyethylene, or ultra high molecular weight polyethylene. Particularly polyethylene and polypropylene, which have a good effect on preventing short circuits and can improve the stability of the battery through a shutdown effect. In some embodiments, the thickness of the separator is in the range of about 5 μm to 500 μm.
In some embodiments, the surface of the separator may further include a porous layer disposed on at least one surface of the separator, the porous layer including inorganic particles selected from alumina (Al) and a binder2O3) Silicon oxide (SiO)2) Magnesium oxide (MgO), titanium oxide (TiO)2) Hafnium oxide (HfO)2) Tin oxide (SnO)2) Cerium oxide (CeO)2) Nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO)2) Yttrium oxide (Y)2O3) At least one of silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. In some embodiments, the pores of the separator have a diameter in the range of about 0.01 μm to 1 μm. The binder is at least one selected from polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene or polyhexafluoropropylene. The porous layer on the surface of the isolating membrane can improve the heat resistance, the oxidation resistance and the electrolyte infiltration performance of the isolating membrane and enhance the adhesion between the isolating membrane and the pole piece.
In some embodiments of the present application, the electrode assembly of the electrochemical device is a wound electrode assembly or a stacked electrode assembly.
In some embodiments, the electrochemical device comprises a lithium ion battery, but the application is not so limited. In some embodiments, the electrochemical device may further include an electrolyte. In some embodiments, the electrolyte includes, but is not limited to, at least two of dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), Ethylene Carbonate (EC), Propylene Carbonate (PC), Propyl Propionate (PP). In addition, the electrolyte may additionally include at least one of Vinylene Carbonate (VC), fluoroethylene carbonate (FEC), or dinitrile compounds as an electrolyte additive. In some embodiments, the electrolyte further comprises a lithium salt.
In some embodiments of the present application, taking a lithium ion battery as an example, a positive electrode plate, a separator, and a negative electrode plate are sequentially wound or stacked to form an electrode member, and then the electrode member is placed in, for example, an aluminum plastic film for packaging, and an electrolyte is injected into the electrode member for formation and packaging, so as to form the lithium ion battery. And then, performing performance test and cycle test on the prepared lithium ion battery.
Those skilled in the art will appreciate that the above-described methods of making electrochemical devices (e.g., lithium ion batteries) are merely examples. Other methods commonly used in the art may be employed without departing from the disclosure herein.
Embodiments of the present application also provide an electronic device including the electrochemical device described above. The electronic device of the embodiment of the present application is not particularly limited, and may be any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a notebook computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable facsimile machine, a portable copier, a portable printer, a headphone, a video recorder, a liquid crystal television, a handheld cleaner, a portable CD player, a mini-disc, a transceiver, an electronic organizer, a calculator, a memory card, a portable recorder, a radio, a backup power source, an electric motor, an automobile, a motorcycle, a power-assisted bicycle, a lighting fixture, a toy, a game machine, a clock, an electric tool, a flashlight, a camera, a large household battery, a lithium ion capacitor, and the like.
In the following, some specific examples and comparative examples are listed to better illustrate the present application, wherein a lithium ion battery is taken as an example.
Example 1
Preparing a positive electrode conductive agent: preparing a succinonitrile aqueous solution with the mass fraction of 20%, and uniformly stirring and mixing 2g of battery-grade commercial carbon nano tube and 6g of the succinonitrile aqueous solution in a beaker to obtain a carbon nano tube conductive agent pretreatment substance; drying the pretreatment substance of the carbon nano tube conductive agent at 80 ℃ for 12h to remove the moisture in the pretreatment substance; and putting the dried material into a tubular furnace, introducing inert protective gas such as nitrogen or helium, and roasting for 2 hours at 400 ℃ to obtain the nitrile-based modified carbon nanotube.
Preparing a positive pole piece: mixing lithium cobaltate, the prepared nitrile-based modified carbon nanotube conductive agent and polyvinylidene fluoride according to the weight ratio of 94: 3: 3 in the proportion of N-methylpyrrolidone (NMP) solution to form positive electrode slurry. The method comprises the steps of coating anode slurry on an anode current collector by using an aluminum foil as the anode current collector, drying, cold pressing and cutting to obtain an anode piece, wherein the anode compaction density in the cold pressing process is 4.1g/cm3。
Preparing a negative pole piece: mixing artificial graphite, acetylene black, styrene butadiene rubber and sodium carboxymethylcellulose in a weight ratio of 96: 1: 1.5: the ratio of 1.5 is dissolved in deionized water to form cathode slurry. And (3) adopting copper foil with the thickness of 10 mu m as a negative current collector, coating the negative slurry on the negative current collector, and drying, cold pressing and cutting to obtain the negative pole piece.
Preparing an isolating membrane: dissolving polyvinylidene fluoride in water, forming uniform slurry through mechanical stirring, coating the slurry on the two side surfaces of a porous base material (polyethylene) coated with ceramic coatings on the two sides, and drying to form an isolating membrane.
Preparing an electrolyte: under the environment that the water content is less than 10ppm, lithium hexafluorophosphate and a nonaqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): Propylene Carbonate (PC): Propyl Propionate (PP): Vinylene Carbonate (VC): 20; 30; 20; 28; 2) are mixed according to the weight ratio of 8: 92 are formulated to form an electrolyte.
Preparing a lithium ion battery: and sequentially 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 positive pole piece and the negative pole piece to play an isolating role, and winding to obtain the electrode assembly. And (3) placing the electrode assembly in an outer packaging aluminum-plastic film, dehydrating at 80 ℃, injecting the electrolyte, packaging, and performing technological processes such as formation, degassing, edge cutting and the like to obtain the lithium ion battery.
Examples 2 to 17 and comparative examples 1 to 5 were modified based on the procedure of example 1, and the modified parameters were as shown in table 1 below, wherein the mole percentage of the nitrile groups to the cobalt atoms in the positive electrode active material was adjusted by controlling the amount of the succinonitrile added.
The cycle performance and storage expansion ratio test method of the present application is described below.
And (3) testing the cycle performance:
the lithium ion battery is placed in a thermostat with the temperature of 45 +/-2 ℃ for standing for 2 hours, and is charged to 4.48V at the rate of 1C, and then is charged to 0.05C at the constant voltage of 4.48V. And then, discharging to 3.0V at a rate of 1C to perform a cycle performance test, wherein the corresponding cycle times are parameters for evaluating the cycle performance of the lithium ion battery when the capacity of the lithium ion battery is reduced to 80% of the initial capacity.
And (3) testing the storage expansion rate:
the lithium ion battery is placed in a thermostat at 25 +/-2 ℃ for standing for 2 hours, is charged to 4.48V at a constant current of 1C multiplying power, is charged to 0.05C at a constant voltage of 4.48V, and is stored in the thermostat at 80 +/-2 ℃ for 7 hours. After high-temperature storage, the thickness of the high-temperature storage lithium ion battery is tested by using a thickness measuring device, and the thickness change after high-temperature storage is recorded. And 4 lithium ion batteries are taken in each group, the average value is taken, and the high-temperature storage expansion rate of the lithium ion batteries is calculated.
The high-temperature storage expansion ratio (thickness of the lithium ion battery after high-temperature storage/thickness of the lithium ion battery after formation-1) × 100%.
Table 1 shows the respective parameters and evaluation results of examples and comparative examples.
TABLE 1
Figure BDA0003169542790000091
Figure BDA0003169542790000101
As can be seen from comparison of example 1 and comparative example 1, comparison example 2 and comparative example 4, or comparison example 3 and comparative example 5, the cycle performance and the storage expansion rate of the lithium ion battery are improved by bonding a nitrile compound to a carbon-based conductive material. The cyano group of the nitrile compound covers the surface of the carbon-based conductive material and cannot be dissociated into the electrolyte, so that the reduction reaction of the cyano group at a negative electrode is avoided, and the cyano group on the surface of the conductive agent can be complexed with a transition metal atom of a positive electrode active material, so that the dissolution of transition metal ions is reduced, the oxidability of the positive electrode active material is reduced, the oxidation consumption of the electrolyte is reduced, and the high-temperature storage performance and the cycle performance of an electrochemical device are improved.
Fig. 4 and 5 show scanning electron microscope images of the carbon nanotubes of example 1 of the present application. Fig. 6 and 7 show scanning electron microscope images of the carbon nanotube of comparative example 1 of the present application. As can be seen from fig. 4 to 7, the nitrile compound treatment has no significant effect on the morphology of the carbon nanotubes.
Fig. 8 shows infrared spectra of carbon nanotubes of example 1 and comparative example 1 of the present application. As shown in FIG. 8, the carbon nanotubes were 2345cm after nitrile group compound treatment-1Obvious absorption peaks appear around the position, which are characteristic infrared absorption peaks of N-H. The carbon nano tube before the nitrile compound treatment has no absorption peak at the position, and the nitrile compound has no N-H bond (NC-C-C-CN). Therefore, the nitrile compound can effectively generate bonding effect with the carbon nano tube, so that the carbon nano tube is provided with nitrile functional groups.The action mechanism of other nitrile compounds is the same, and the nitrile compounds can be bonded with the carbon-based conductive material.
Fig. 9 shows electron binding energy maps of cobalt ions of example 1 and comparative example 1 of the present application. As shown in FIG. 9, before the nitrile compound treatment (comparative example 1), Co shows absorption peaks at 780.07eV and 794.77eV, and after the nitrile compound treatment (example 1), the Co absorption peaks shift to 779.73eV and 794.43eV respectively, which shows that after bonding, the nitrile group in the conductive agent can effectively complex cobalt ions and reduce the oxidation of the cobalt ions.
Comparing examples 1 and 4 to 7, it can be seen that the type of the carbon-based conductive material has a certain influence on the cycle performance and the storage expansion rate of the lithium ion battery, but the difference is not great.
It is understood from comparison between examples 1 and 8 to 11 that the kind of the nitrile compound has a certain influence on the cycle performance and the storage expansion ratio of the lithium ion battery, but the difference is not so great.
As can be seen from comparison between examples 1 and 12 to 15, when the molar percentage of the nitrile group in the conductive agent to the cobalt element in the positive electrode active material is 0.01% to 5%, the cycle performance of the lithium ion battery is first enhanced and then decreased, and the storage expansion rate of the lithium ion battery is first decreased and then increased, with the increase in the molar percentage.
As is clear from comparison between example 16 and comparative example 2 or between comparative example 17 and comparative example 3, when a certain amount of the nitrile compound is contained in the electrolytic solution, the cycle performance and the storage expansion rate of the lithium ion battery can be improved by bonding the nitrile compound to the carbon-based conductive material. It is understood from comparative examples 16 to 17 that the cycle performance and the storage expansion ratio of the lithium ion battery can be improved to some extent when the mass content of the nitrile compound in the electrolyte is increased from 5% to 10%.
According to the preparation method, the nitrile compounds are bonded on the carbon-based conductive material, the cobalt element dissolution of the anode active material in the circulation and storage processes under a high-voltage (>4.2V) system can be improved, and the circulation stability and the high-temperature storage performance of the electrochemical device are improved.
The above description is only a preferred embodiment of the application and is illustrative of the principles of the technology employed. It will be appreciated by those skilled in the art that the scope of the disclosure herein is not limited to the particular combination of features described above, but also encompasses other arrangements formed by any combination of the above features or their equivalents without departing from the spirit of the disclosure. For example, the above features and the technical features having similar functions disclosed in the present application are mutually replaced to form the technical solution.

Claims (12)

1. An electrically conductive agent, comprising:
a compound formed of a carbon-based conductive material and a nitrile compound, wherein the nitrile compound is bonded to the carbon-based conductive material.
2. The conductive agent according to claim 1, wherein a carbon-carbon bond is formed between the carbon-based conductive material and the nitrile compound.
3. The conductive agent according to claim 1, wherein the curve obtained by infrared spectroscopy is 2337cm-1～2351cm-1With absorption peaks in between.
4. The conductive agent according to claim 1, wherein the carbon-based conductive material comprises at least one of conductive carbon black, ketjen black, acetylene black, conductive graphite, carbon nanotubes, or carbon fibers.
5. The conductive agent according to claim 1, wherein the nitrile compound includes at least one of a chain organic nitrile, an organic nitrile containing an aromatic ring or a heteroaromatic ring, or a cyano polymer.
6. The conductive agent according to claim 1, wherein the nitrile compound comprises at least one of succinonitrile, adiponitrile, 1, 2-benzenediacetonitrile, 1, 4-benzenediacetonitrile, 1-naphthaleneacetonitrile, 2-naphthaleneacetonitrile, polyacrylonitrile, or polystyrene acrylonitrile.
7. An electrochemical device, comprising:
the positive pole piece comprises a current collector and a positive active material layer, and the positive active material layer is arranged on the current collector;
wherein the positive electrode active material layer includes a positive electrode active material and the conductive agent according to any one of claims 1 to 6.
8. The electrochemical device according to claim 7, wherein the positive electrode active material includes one or more of lithium cobaltate, lithium nickel cobalt manganese oxide, and lithium nickel cobalt aluminate, and the positive electrode active material is included in the positive electrode active material layer in an amount of 95 to 99.5% by mass.
9. The electrochemical device according to claim 7, wherein a mole percentage of the nitrile group in the conductive agent to the cobalt element in the positive electrode active material is 0.01% to 5%.
10. The electrochemical device according to claim 8, wherein the absorption peak of cobalt of the positive electrode active material obtained by an X-ray photoelectron spectroscopy test is shifted by 0.1eV to 0.45 eV.
11. An electronic device comprising the electrochemical device according to any one of claims 7 to 10.
12. A method of making a conductive agent comprising:
mixing a carbon-based conductive material with a nitrile compound to obtain a pretreatment mixture;
drying and roasting the pretreated mixture to obtain the conductive agent,
wherein the roasting treatment comprises roasting at 300-500 ℃ for 1-3 h.
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