CN116190777A - Cellulose-based eutectic gel electrolyte, preparation method and application thereof - Google Patents

Cellulose-based eutectic gel electrolyte, preparation method and application thereof Download PDF

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CN116190777A
CN116190777A CN202211644526.4A CN202211644526A CN116190777A CN 116190777 A CN116190777 A CN 116190777A CN 202211644526 A CN202211644526 A CN 202211644526A CN 116190777 A CN116190777 A CN 116190777A
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cellulose
eutectic
electrolyte
lithium
gel electrolyte
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王世力
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Chongqing Talent New Energy Co 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
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0565—Polymeric materials, e.g. gel-type or solid-type
    • 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
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • 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
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0085—Immobilising or gelification of electrolyte
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
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    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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Abstract

The invention discloses a cellulose-based eutectic gel electrolyte, a preparation method and application thereof. The preparation method comprises the following steps: dissolving lithium salt in a eutectic organic solvent to obtain a eutectic electrolyte; wherein the eutectic organic solvent is a single solvent; and (2) adding cellulose into the eutectic electrolyte to obtain the cellulose-based eutectic gel electrolyte. The preparation method of the cellulose-based eutectic gel electrolyte is simple, the preparation process does not involve polymerization and crosslinking reaction, and the reaction condition is at room temperature and in a dry environment. Moreover, the eutectic gel electrolyte based on cellulose has higher lithium salt dissolution capacity, improves the conductivity of the electrolyte and reduces the interface impedance of the electrolyte and the negative electrode.

Description

Cellulose-based eutectic gel electrolyte, preparation method and application thereof
Technical Field
The invention belongs to the field of lithium ion batteries, and particularly relates to a cellulose-based eutectic gel electrolyte, a preparation method and application thereof.
Background
Among the many chemical sources, lithium ion batteries are certainly the most developed. The traditional lithium ion battery mainly uses nonaqueous organic liquid as electrolyte, and the liquid electrolyte not only can provide high enough ionic conductivity, but also provides excellent interface contact, so that the internal resistance of the battery is greatly reduced.
With the increase of energy density, the safety of the battery is a main focus, and the liquid electrolyte also presents some defects in the use process, so that the commercial liquid battery is extremely easy to cause fire burning or even explosion under the extreme conditions of short circuit, overcharge, high heat, external extrusion and the like of the battery due to the use of the organic solvent. Particularly, when the negative electrode adopts lithium metal with high specific capacity, the liquid electrolyte is easy to react with the lithium metal, is easy to leak, is inflammable and explosive, has poor safety and other problems, so that the further development of the lithium battery is limited. Therefore, reducing the use of organic electrolytes, even replacing the use of liquid electrolytes, is the most promising solution to address high energy density systems and to improve battery safety.
In order to reduce the amount of organic solvent used in the electrolyte, researchers have proposed a technical route for polymer electrolytes. All solid polymer electrolytes, gel polymer electrolytes, and the like can be classified according to the morphology of the polymer electrolyte. The all-solid-state polymer electrolyte mainly comprises a polymer and lithium salt, and is difficult to meet the actual requirements due to the defects of low ionic conductivity at room temperature, large interface contact resistance and the like. The gel polymer electrolyte is mainly formed by introducing a plasticizer with small molecular weight to reduce the glass transition temperature of the polymer and reduce the polymerization strength of chains. Compared with all-solid polymer electrolyte, the gel electrolyte has higher room temperature conductivity, and in addition, due to the advantages of softness and the like, the contact of an interface is improved, and the internal resistance of the battery is reduced. Meanwhile, the gel electrolyte has the advantages that the use amount of the organic solvent is small or the gel electrolyte does not contain the organic solvent, so that the compatibility with lithium metal is greatly improved compared with the current commercial liquid electrolyte, and the safety of the high-energy-density lithium metal battery is greatly improved.
Currently, the most used are polyethylene oxide (PEO), polyacrylonitrile (PAA), vinylidene fluoride (PVDF) based and their copolymer based polymer electrolytes in gel state. Although the gel polymer electrolyte has better battery performance and safety stability, the gel polymer electrolyte belongs to non-renewable resources due to the fact that raw materials of the gel polymer electrolyte are petrochemical industry, fossil minerals and the like.
Therefore, there is a clear prospect in searching for a gel state polymer electrolyte raw material which is wide in reserves, renewable and free from environmental pollution and preparing a high-performance gel state polymer electrolyte.
Disclosure of Invention
In view of the above problems in the prior art, it is an object of the present invention to provide a cellulose-based eutectic gel electrolyte, a method for preparing the same and applications thereof.
In order to achieve the above purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method for preparing a cellulose-based eutectic gel electrolyte, the method comprising:
dissolving lithium salt in a eutectic organic solvent to obtain a eutectic electrolyte;
wherein the eutectic organic solvent is a single solvent;
and (2) adding cellulose into the eutectic electrolyte to obtain the cellulose-based eutectic gel electrolyte.
In the present invention, the eutectic organic solvent means that the melting point of the other component can be lowered when the organic solvent is mixed with the other component.
The following preferred technical solutions are used as the present invention, but not as limitations on the technical solutions provided by the present invention, and the technical objects and advantageous effects of the present invention can be better achieved and achieved by the following preferred technical solutions.
Preferably, the lithium salt of step (1) comprises lithium hexafluorophosphate (LiPF) 6 ) Lithium perchlorate (LiClO) 4 ) At least one of lithium bis (trifluorosulfonimide) (LiTFSI), lithium bis (fluorosulfonimide) (LiWSI), and lithium bis (oxalato) borate (LiBOB), preferably including lithium bis (trifluorosulfonimide).
Preferably, the lithium salt of step (1) comprises 10% -65% of the total mass of the eutectic electrolyte.
Preferably, the eutectic organic solvent in the step (1) is selected from any one of an ester solvent, a sulfone solvent, a nitrile solvent and an amide solvent.
Preferably, the ester solvent includes any one of Ethylene Carbonate (EC), propylene Carbonate (PC) or fluoroethylene carbonate (FEC).
Preferably, the sulfone-based solvent comprises Sulfolane (SL).
Preferably, the nitrile solvent comprises Succinonitrile (SN).
Preferably, the eutectic organic solvent of step (1) comprises 35% -90% of the total mass of the eutectic electrolyte, such as 30%, 38%, 42%, 45%, 47%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% or 90%, etc.
As a preferable technical scheme of the method, the cellulose is cellulose with high substitution degree, and the substitution degree is 1.5-3.5.
Preferably, the cellulose includes at least one of hydroxyalkyl cellulose, carboxymethyl cellulose (CMC), ethyl Cellulose (EC), and polyanionic cellulose (PAC).
Preferably, the hydroxyalkyl cellulose is at least one selected from hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose (HPMC).
Preferably, the cellulose is selected from at least one of hydroxyethyl cellulose and carboxymethyl cellulose.
Preferably, the cellulose is added in an amount of 8% -25% of the mass of the eutectic electrolyte.
Preferably, the mixture formed is stirred after the addition of the cellulose.
As a preferred technical scheme of the method of the present invention, the preparation method further comprises: adding a lithium salt additive to the eutectic electrolyte after step (1) and before step (2) to form a deep eutectic electrolyte; or alternatively, the process may be performed,
after the cellulose is added in step (2), adding a lithium salt additive to the cellulose-containing eutectic electrolyte to obtain the cellulose-based eutectic gel electrolyte.
Preferably, the lithium salt additive includes at least one of lithium 4, 5-dicyano-2-trifluoromethyl imidazole (LiTDI), lithium difluorooxalato borate (LiODFB), lithium difluorophosphate (LiDFP), and lithium bisoxalato phosphate (LiDFOP).
Preferably, the lithium salt additive comprises 0.1-3%, e.g. 0.1%, 0.2%, 0.5%, 0.7%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.6% or 3% etc., preferably 0.5-2% of the mass of the deep eutectic electrolyte.
As a preferred embodiment of the method of the present invention, the preparation method comprises:
dissolving lithium salt in a eutectic organic solvent to obtain a eutectic electrolyte (EEs for short);
wherein the eutectic organic solvent is a single solvent;
adding a lithium salt additive into the eutectic electrolyte to form deep eutectic electrolyte (DEEs for short);
and (2) adding cellulose into the deep eutectic electrolyte to obtain the eutectic gel electrolyte based on cellulose.
In a second aspect, the present invention provides a cellulose-based eutectic gel electrolyte prepared by the preparation method of the first aspect.
In a third aspect, the present invention provides a cellulose-based eutectic gel electrolyte membrane produced by drying the cellulose-based eutectic gel electrolyte of the second aspect.
Preferably, the mass of the cellulose-based eutectic gel electrolyte membrane accounts for 8-20% of the weight of the cellulose-based eutectic gel electrolyte.
Preferably, the drying mode is drying.
Preferably, the temperature of the drying is 45-80 ℃; the drying time is 0.5-4 hours.
In a fourth aspect, the present invention provides a pole piece, the surface of which is coated with the cellulose-based eutectic gel electrolyte of the second aspect and dried, or,
the surface of the pole piece is provided with the cellulose-based eutectic gel electrolyte membrane in the third aspect.
In a fifth aspect, the present invention provides a battery comprising the pole piece of the fourth aspect.
In one embodiment, the battery includes a positive electrode, a negative electrode, and the above-described cellulose-based eutectic gel electrolyte, which is compounded on the surface of the pole piece in the form of a film.
Preferably, the battery is a quasi-solid state lithium metal battery.
Compared with the prior art, the invention has the following beneficial effects:
the preparation method of the cellulose-based eutectic gel electrolyte is simple, the preparation process does not involve polymerization and crosslinking reaction, and the reaction condition is at room temperature and in a dry environment. Moreover, the eutectic gel electrolyte based on cellulose has higher lithium salt dissolution capacity, improves the conductivity of the electrolyte, and reduces the interface impedance of the electrolyte and a negative electrode (such as a lithium metal negative electrode).
Because the single solvent is adopted as the eutectic organic solvent in the preparation process of the cellulose-based eutectic gel electrolyte, the single solvent can obviously reduce the probability of side reaction between the electrolyte and lithium metal when applied to a quasi-solid lithium metal battery, thereby improving the performance of the lithium metal battery.
Detailed Description
The technical scheme of the invention is further described by the following specific embodiments.
The present invention provides in one embodiment a method of preparing a cellulose-based eutectic gel electrolyte, the method comprising:
dissolving lithium salt in a eutectic organic solvent to obtain a eutectic electrolyte;
wherein the eutectic organic solvent is a single solvent;
and (2) adding cellulose into the eutectic electrolyte to obtain the cellulose-based eutectic gel electrolyte.
Cellulose has a plurality of advantages when used for preparing gel polymer electrolyte, and is used as a degradable, nontoxic, low-cost and raw material source-rich material. According to the method provided by the embodiment of the invention, the lithium salt is dissolved in the single solvent of the eutectic organic solvent in advance, and then the cellulose is added into the single solvent, so that the advantage of the cellulose can be achieved under the condition of ensuring the maximum solubility of the lithium salt, and the high-performance cellulose-based eutectic gel electrolyte can be obtained.
The preparation method of the cellulose-based eutectic gel electrolyte provided by the embodiment of the invention is simple, the preparation process does not involve polymerization and crosslinking reaction, and the reaction condition is at room temperature and in a dry environment. Moreover, the eutectic gel electrolyte based on cellulose has higher lithium salt solubility, so that the conductivity of the electrolyte is improved, and the interface impedance between the electrolyte and a negative electrode (such as a lithium metal negative electrode) is reduced.
Meanwhile, in one embodiment of the invention, the single solvent is selected for preparing the eutectic electrolyte, so that the probability of the reaction between the electrolyte and the lithium metal can be reduced, because the more the solvent components are, the more water and impurities of each solvent are difficult to control compared with one component, and the problem can be avoided to a certain extent by adopting the single solvent.
In one embodiment, the lithium salt of step (1) comprises lithium hexafluorophosphate (LiPF) 6 ) Lithium perchlorate (LiClO) 4 ) At least one of lithium bis (trifluorosulfonimide) (LiTFSI), lithium bis (fluorosulfonimide) (LiWSI), and lithium bis (oxalato) borate (LiBOB), preferably including lithium bis (trifluorosulfonimide).
In one embodiment, the lithium salt of step (1) comprises 10% -65%, e.g., 10%, 12%, 15%, 17%, 20%, 25%, 30%, 32%, 35%, 38%, 40%, 45%, 50%, 55%, 60%, 65%, etc., of the total mass of the eutectic electrolyte. If the mass ratio of the lithium salt is too low, the conductivity of the cellulose-based eutectic gel electrolyte may be reduced; if the mass ratio of the lithium salt is too high, the solubility of the lithium salt is affected.
In one embodiment, the eutectic organic solvent of step (1) has a dielectric constant greater than 30. Under these conditions, the eutectic organic solvent can rapidly dissolve more lithium salt.
In one embodiment, the co-crystal organic solvent of step (1) is selected from any one of an ester solvent, a sulfone solvent, a nitrile solvent, or an amide solvent.
In one embodiment, the ester solvent includes any one of Ethylene Carbonate (EC), propylene Carbonate (PC) or fluoroethylene carbonate (FEC).
In one embodiment, the sulfone-based solvent comprises Sulfolane (SL).
In one embodiment, the nitrile solvent comprises Succinonitrile (SN).
In one embodiment, the eutectic organic solvent of step (1) comprises 35% -90%, e.g., 30%, 38%, 42%, 45%, 47%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, etc., of the total mass of the eutectic electrolyte. If the amount of the eutectic organic solvent is too small, the amount of the dissolved lithium salt is too small, which affects the conductivity of the final electrolyte, and if the amount of the eutectic organic solvent is too large, the solvent is wasted, and the cost is increased.
In one embodiment, the cellulose of step (2) is a small molecular weight cellulose having a molecular weight of 150-20000, e.g. 150, 200, 300, 400, 500, 600, 800, 1000, 1200, 1400, 1500, 1700, 2000, 2200, 2500, 2700, 3000, 3300, 3600, 3800, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000, 9500, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, etc. Through selecting small molecular weight cellulose, the cellulose can be mixed with electrolyte without heating to form gel electrolyte, and meanwhile, the prepared electrolyte can contain a certain solvent, thereby being helpful for improving the conductivity of the gel electrolyte.
In one embodiment, the cellulose is a high degree of substitution cellulose having a degree of substitution of 1.5 to 3.5, for example 1.5, 1.6, 1.8, 2.0, 2.1, 2.3, 2.5, 2.7, 2.8, 3.0, 3.2, 3.3, 3.4, or 3.5, etc., preferably 1.5 to 2.8. Cellulose with high substitution degree, such as at least one of hydroxyethyl cellulose and carboxymethyl cellulose, has high dielectric constant and good compatibility with organic solvents, increases solubility of lithium salt, improves room temperature conductivity, reduces battery polarization, has good compatibility with lithium metal, and inhibits nonuniform deposition of lithium. In one embodiment, the cellulose includes at least one of hydroxyalkyl cellulose, carboxymethyl cellulose (CMC), ethyl Cellulose (EC), and polyanionic cellulose (PAC).
In one embodiment, the hydroxyalkyl cellulose is at least one selected from hydroxyethyl cellulose (HEC), hydroxypropyl cellulose (HPC), hydroxypropyl methylcellulose (HPMC).
In one embodiment, the cellulose is selected from at least one of hydroxyethyl cellulose and carboxymethyl cellulose.
In one embodiment, the cellulose is added in an amount of 8% -25%, such as 8%, 10%, 12%, 15%, 18%, 20%, 21%, 22%, 23%, 24% or 25% and the like, preferably 11% -21% of the mass of the eutectic electrolyte. Note that, in the mass ratio here, if the eutectic electrolyte is modified before cellulose is added, the modified eutectic electrolyte is used as a reference. When the addition amount of cellulose is too large, the viscosity of the electrolyte is increased, the diffusion rate of lithium ions is reduced, and when the addition amount of cellulose is too low, the solvent in the electrolyte is increased, and the side reaction with lithium metal is increased, so that the exertion of the material capacity is reduced.
In one embodiment, the mixture formed is stirred after the addition of the cellulose.
In one embodiment, the method further comprises: adding a lithium salt additive to the eutectic electrolyte after step (1) and before step (2) to form a deep eutectic electrolyte; or alternatively, the process may be performed,
after the cellulose is added in step (2), adding a lithium salt additive to the cellulose-containing eutectic electrolyte to obtain the cellulose-based eutectic gel electrolyte.
By adding the lithium salt additive in the preparation process, the ion conductivity of the electrolyte can be further increased, and the performance of the cellulose-based eutectic gel electrolyte is further improved.
According to one embodiment of the invention, the lithium salt additive is added into the eutectic electrolyte after the step (1) and before the step (2), so that the solvent structure in the electrolyte is further optimized, the conductivity of lithium ions in the electrolyte is improved, the desolvation rate of the lithium ions is also improved, the rate capability of the battery is improved, and the effect of better optimizing the performance is achieved. However, if a lithium salt additive is added to the eutectic electrolyte containing cellulose after the cellulose is added in step (2), there is a possibility that dissolution of the lithium salt additive is affected due to formation of the gel electrolyte, which is disadvantageous for dissolution of the lithium salt additive.
In one embodiment, the lithium salt additive is a lithium salt additive containing a large anion.
In one embodiment, the macroanion comprises any one of oxalate, dioate or sulfonyl.
In one embodiment, the lithium salt additive containing a large anion includes at least one of lithium 4, 5-dicyano-2-trifluoromethylimidazole (LiTDI), lithium difluorooxalato borate (LiODFB), lithium difluorophosphate (LiDFP), and lithium bisoxalato phosphate (LiDFOP).
In one embodiment, the lithium salt additive comprises 0.1-3%, such as 0.1%, 0.2%, 0.5%, 0.7%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.3%, 2.6% or 3% and the like, preferably 0.5-2% of the mass of the deep eutectic electrolyte.
In one embodiment, the method of making comprises:
dissolving lithium salt in a eutectic organic solvent to obtain a eutectic electrolyte;
wherein the eutectic organic solvent is a single solvent;
adding a lithium salt additive into the eutectic electrolyte to form a deep eutectic electrolyte;
and (2) adding cellulose into the deep eutectic electrolyte to obtain the eutectic gel electrolyte based on cellulose. In another embodiment, the invention provides a cellulose-based eutectic gel electrolyte prepared by the preparation method provided in one embodiment.
In yet another embodiment, the present invention provides a cellulose-based eutectic gel electrolyte membrane prepared by drying the cellulose-based eutectic gel electrolyte provided in one of the above embodiments.
In one embodiment, the mass of the cellulose-based eutectic gel electrolyte membrane is 8-20%, such as 8%, 10%, 12%, 14%, 15%, 18%, 20%, etc., by weight of the cellulose-based eutectic gel electrolyte.
In one embodiment, the drying is by baking.
In one embodiment, the temperature of the drying is 45 ℃ to 80 ℃, such as 45 ℃, 50 ℃, 55 ℃, 60 ℃, 65 ℃, 70 ℃, 75 ℃, 80 ℃, or the like; the drying time is 0.5 hours to 4 hours, for example, 0.5 hours, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours, 4 hours, or the like.
In yet another embodiment, the invention provides a pole piece having a surface coated with the cellulose-based eutectic gel electrolyte provided in one of the embodiments above and dried, or,
the surface of the pole piece is placed with the cellulose-based eutectic gel electrolyte membrane provided in one embodiment.
In the embodiment of the invention, the cellulose-based eutectic gel electrolyte prepared in the embodiment can be directly coated on the surface of the pole piece, and the pole piece with the cellulose-based eutectic gel electrolyte membrane is formed after drying. The cellulose-based eutectic gel electrolyte prepared in the above embodiment may be dried to form a film, or the cellulose-based eutectic gel electrolyte film provided in the above embodiment may be directly used, and then the film and the negative electrode may be put together for use.
In the embodiment of the present invention, the drying method is not limited, and may be, for example, drying.
The pole piece in the embodiment of the invention can be a negative pole or a positive pole.
In yet another embodiment of the present invention, a battery is provided, which includes the pole piece provided in one embodiment described above.
In one embodiment, the battery comprises a positive electrode, a negative electrode and the cellulose-based eutectic gel electrolyte, wherein the cellulose-based eutectic gel electrolyte is compounded on the surface of a pole piece in a film mode, and the pole piece can be the positive electrode, the negative electrode, the positive electrode and the negative electrode.
In one embodiment, the positive electrode adopts the electrode plate, and the negative electrode is a lithium metal negative electrode.
In one embodiment, the battery is a quasi-solid state lithium metal battery.
In the liquid battery in the prior art, as the liquid electrolyte has various solvents, the probability of side reactions between the liquid electrolyte and lithium metal is much higher, and the eutectic organic solvent selected in one embodiment of the invention is a single solvent, so that the probability of side reactions between the electrolyte and lithium metal can be obviously reduced when the eutectic organic solvent is applied to a quasi-solid lithium metal battery, thereby improving the performance of the lithium metal battery.
The technical solution of the present invention will be further described by specific examples, and it should be clear that all examples are only preferred embodiments of the present invention, but not limited to the present invention. It will be apparent to those skilled in the art that any relevant changes and modifications may be made in the invention without departing from the spirit or scope of the invention.
Example 1
The present example provides a method for preparing a cellulose-based eutectic gel electrolyte in a glove box (water oxygen values of less than 0.01 ppm) or in a dry room (dew point of less than-60 ℃) environment, comprising the steps of:
(1) Preparation of Eutectic Electrolyte (EEs):
mixing battery-level PC and LiTFSI according to a mass ratio of 5:4, and dissolving to obtain Eutectic Electrolyte (EEs);
(2) Preparation of Deep Eutectic Electrolytes (DEEs):
the eutectic electrolyte was then optimized and a large anion lithium salt additive LiODFB was added to the eutectic electrolyte in an amount of 0.5% by mass of EEs to obtain Deep Eutectic Electrolytes (DEEs).
(3) Preparation of cellulose-based eutectic gel electrolytes (GEEs):
HEC with a degree of substitution of 2.0 is added to the deep eutectic electrolyte, where DEEs: HEC (mass ratio) =91:10, and stirring to obtain a eutectic gel electrolyte.
(4) Preparation of a cellulose-based gel electrolyte membrane:
the obtained eutectic gel electrolyte was placed in a mold having a diameter of 14mm, and vacuum-dried at 50 ℃ to a cellulose-based gel electrolyte membrane.
The embodiment also provides a method for preparing the pole piece and the lithium metal battery by adopting the cellulose-based gel electrolyte membrane, which specifically comprises the following steps:
preparing a gel electrolyte pole piece:
lithium cobaltate, conductive agent Super-P, polyvinylidene fluoride (PVDF) and Carbon Nanotubes (CNTs) were mixed according to 96.7:1.3:1.8: and (3) uniformly stirring the mixture according to the mass ratio of 0.2, adding NMP to adjust the viscosity to 4200cp, and obtaining stable lithium cobaltate slurry, coating one side of the slurry on the surface of an aluminum foil with the diameter of 10 micrometers, drying and rolling the slurry to obtain a positive plate, uniformly coating GEEs prepared in the step (3) on the surface of the positive plate by using a 25 micrometer scraper, and drying the positive plate at a low temperature to obtain the gel electrolyte pole plate.
Preparation of lithium metal battery:
assembling the positive plate, the gel electrolyte membrane and the lithium metal plate into a CR2032 type button cell in a glove box; or assembling the gel electrolyte pole piece, the diaphragm and the lithium metal sheet into another type of lithium metal battery in sequence.
Examples 2 to 6 and comparative examples 1 to 3
The preparation methods of examples 2 to 6 were the same as in example 1, except that the kinds and amounts of the respective components of the electrolyte were different, and the specific electrolyte compositions are shown in Table 1.
Comparative examples 1 to 3 are electrolyte solutions of conventional liquid lithium metal batteries, and the battery preparation process comprises assembling a positive electrode, an electrolyte, a diaphragm and a lithium sheet into a CR2032 button battery, wherein the electrolyte is respectively dripped on the pole piece and the diaphragm, and the composition of the electrolyte is shown in Table 1.
TABLE 1
Figure BDA0004009185460000131
Example 7
The difference from example 1 is that the addition amount of LiODFB in step (2) was 0.05%.
Example 8
The difference from example 1 is that the addition amount of LiODFB in step (2) was 3.2%.
Example 9
The difference from example 1 is that in step (3), DEEs: HEC (mass ratio) =93:8, calculated to be added to 8% of DEEs.
Example 10
The difference from example 1 is that in step (3), DEEs: HEC (mass ratio) =76:25, calculated to be 25% of DEEs.
Example 11
The difference from example 1 is that in step (3), DEEs: HEC (mass ratio) =84:17, calculated to be 16.8% of DEEs.
Performance test:
test analysis was performed on button cells assembled in examples 1 to 11 and comparative examples 1 to 3:
first, all assembled button cells were allowed to stand at 25 ℃ for 12 hours to wet, ensuring sufficient contact between the electrode sheet and electrolyte. After the completion of standing, gram capacity exertion of each sample cell was tested.
The test temperature is 25 ℃ + -2 ℃ or 45 ℃ + -2 ℃.
The test procedure was: the current of 0.1C is charged to 3.5V, then the constant current and the constant voltage are charged to 4.4V at 0.2C current, the current is 0.02C, the rest is carried out for 5min, and the constant current is discharged to 3.0V at the rate of 0.2C.
The test results of each sample battery are counted respectively, the same system tests 3 batteries respectively to ensure the stability of the test results, and the test results of 3 batteries are averaged and recorded in table 1.
TABLE 2
Figure BDA0004009185460000141
Figure BDA0004009185460000151
Analysis:
the eutectic gel electrolyte of the cellulose provided by the invention is applied to a lithium metal button cell, has a capacity exertion of materials in the liquid electrolyte which is not much different from that of materials in the lithium metal button cell from the aspect of the capacity exertion of materials, particularly, the capacity exertion of the battery at 45 ℃ in a gel electrolyte system is improved by more than 4mAh/g compared with the capacity exertion at 25 ℃ in a high-temperature environment, and is higher than that of the liquid electrolyte (about 3 mAh/g) provided in comparative examples 1-3, so that the gel electrolyte has better performance in the aspect of high-temperature performance.
At the same time, different examples also reflect that different components and different contents have different effects on the battery performance. For example, examples 7 and 8 exhibited significantly lower material capacities than examples 1-6 and comparative examples, and it was also seen that when the amount of lithium salt additive was greater than 3% and less than 0.1%, negative effects were instead provided on cell performance, and we analyzed that too little amount of lithium salt additive did not function to increase conductivity, while too high an amount we analyzed that the lithium salt additive did not completely dissociate, resulting in a decrease in ionic conductivity, increased interfacial resistance between the electrode sheet and electrolyte, and affected material capacity performance. As another example, the material capacity exertion of examples 9 and 10 is also significantly lower than examples 1-6, and we analyze that when the amount of cellulose is too large, the viscosity of the electrolyte is increased, the diffusion rate of lithium ions is reduced, and when the amount of cellulose is too low, the solvent in the electrolyte is increased, and the side reaction with lithium metal is increased, so that the exertion of the material capacity is reduced.
In summary, the invention provides a simple preparation method of the cellulose-based eutectic gel electrolyte, which has more excellent use performance at high temperature, and is expected to become a promising quasi-solid electrolyte through optimizing the preparation process.
The applicant states that the detailed method of the present invention is illustrated by the above examples, but the present invention is not limited to the detailed method described above, i.e. it does not mean that the present invention must be practiced in dependence upon the detailed method described above. It should be apparent to those skilled in the art that any modification of the present invention, equivalent substitution of raw materials for the product of the present invention, addition of auxiliary components, selection of specific modes, etc., falls within the scope of the present invention and the scope of disclosure.

Claims (10)

1. A method for preparing a cellulose-based eutectic gel electrolyte, the method comprising:
dissolving lithium salt in a eutectic organic solvent to obtain a eutectic electrolyte;
wherein the eutectic organic solvent is a single solvent;
and (2) adding cellulose into the eutectic electrolyte to obtain the cellulose-based eutectic gel electrolyte.
2. The method of claim 1, wherein the lithium salt of step (1) comprises at least one of lithium hexafluorophosphate, lithium perchlorate, lithium bis (trifluorosulfonimide), lithium bis (fluorosulfonimide) and lithium bis (oxalato) borate, preferably comprises lithium bis (trifluorosulfonimide);
preferably, the lithium salt of step (1) comprises 10% -65% of the total mass of the eutectic electrolyte;
preferably, the eutectic organic solvent in the step (1) is any one of an ester solvent, a sulfone solvent, a nitrile solvent or an amide solvent;
preferably, the ester solvent includes any one of ethylene carbonate, propylene carbonate or fluoroethylene carbonate;
preferably, the sulfone-based solvent comprises sulfolane;
preferably, the nitrile solvent comprises succinonitrile;
preferably, the eutectic organic solvent of step (1) comprises 35% -90% of the total mass of the eutectic electrolyte.
3. The preparation method according to claim 1 or 2, wherein the cellulose is a cellulose with a high degree of substitution, the degree of substitution being 1.5-3.5, preferably 1.5-2.8;
preferably, the cellulose comprises at least one of hydroxyalkyl cellulose, carboxymethyl cellulose, ethyl cellulose and polyanionic cellulose;
preferably, the hydroxyalkyl cellulose is at least one selected from hydroxyethyl cellulose, hydroxypropyl cellulose and hydroxypropyl methyl cellulose;
preferably, the cellulose is selected from at least one of hydroxyethyl cellulose and carboxymethyl cellulose;
preferably, the cellulose is added in an amount of 8% -25% by mass of the eutectic electrolyte, preferably 11% -21%;
preferably, the mixture formed is stirred after the addition of the cellulose.
4. A method of preparation according to any one of claims 1 to 3, further comprising: adding a lithium salt additive to the eutectic electrolyte after step (1) and before step (2) to form a deep eutectic electrolyte; or alternatively, the process may be performed,
after the cellulose is added in step (2), adding a lithium salt additive to the cellulose-containing eutectic electrolyte to obtain the cellulose-based eutectic gel electrolyte.
5. The method of preparing according to claim 4, wherein the lithium salt additive comprises at least one of lithium 4, 5-dicyano-2-trifluoromethylimidazole, lithium difluorooxalato borate, lithium difluorophosphate and lithium bisoxalato phosphate;
preferably, the lithium salt additive comprises 0.1% -3%, preferably 0.5% -2% of the mass of the deep eutectic electrolyte.
6. The method of any one of claims 1-5, wherein the method of preparation comprises:
dissolving lithium salt in a eutectic organic solvent to obtain a eutectic electrolyte;
wherein the eutectic organic solvent is a single solvent;
adding a lithium salt additive into the eutectic electrolyte to form a deep eutectic electrolyte;
and (2) adding cellulose into the deep eutectic electrolyte to obtain the eutectic gel electrolyte based on cellulose.
7. A cellulose-based eutectic gel electrolyte, characterized in that it is prepared by the preparation method according to any one of claims 1 to 6.
8. A cellulose-based eutectic gel electrolyte membrane, characterized in that the cellulose-based eutectic gel electrolyte membrane is produced by drying the cellulose-based eutectic gel electrolyte of claim 7;
preferably, the mass of the cellulose-based eutectic gel electrolyte membrane accounts for 8% -20% of the weight of the cellulose-based eutectic gel electrolyte;
preferably, the drying mode is drying;
preferably, the temperature of the drying is 45-80 ℃, and the time of the drying is 0.5-4 hours.
9. A pole piece, characterized in that the surface of the pole piece is coated with the cellulose-based eutectic gel electrolyte according to claim 7 and dried, or,
the surface of the pole piece is placed with the cellulose-based eutectic gel electrolyte membrane of claim 8.
10. A battery comprising the pole piece of claim 9;
preferably, the battery is a quasi-solid state lithium metal battery.
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