CN113258140B - Lithium secondary battery electrolyte and preparation method and application thereof - Google Patents

Lithium secondary battery electrolyte and preparation method and application thereof Download PDF

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CN113258140B
CN113258140B CN202110768080.5A CN202110768080A CN113258140B CN 113258140 B CN113258140 B CN 113258140B CN 202110768080 A CN202110768080 A CN 202110768080A CN 113258140 B CN113258140 B CN 113258140B
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electrolyte
secondary battery
lithium secondary
nitrate
lithium
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CN113258140A (en
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李金熠
田一帆
鲁卓雅
程晓彦
岳风树
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Beijing One Gold 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
    • 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
    • H01M10/0566—Liquid materials
    • H01M10/0569—Liquid materials characterised by the solvents
    • 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
    • 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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    • 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
    • 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
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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
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    • H01M2300/0017—Non-aqueous electrolytes
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    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
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Abstract

The invention provides a lithium secondary battery electrolyte and a preparation method and application thereof, belonging to the technical field of batteries. The electrolyte of the lithium secondary battery comprises a conventional commercial ester electrolyte additive and a cosolvent, wherein the additive is nitrate and can participate in the formation of an interface layer so as to improve the overall performance of the battery; the cosolvent comprises a boron trifluoride-based complex, so that the nitrate can be dissolved in an ester solvent, and the application range of the nitrate additive is widened. The lithium secondary battery electrolyte shows high reversible specific capacity and excellent cycling stability when matched with a metal lithium battery assembled by a conventional NCM ternary material and a silicon-based negative electrode lithium ion battery, and is a practical electrolyte which can be suitable for a novel high-specific-energy lithium secondary battery system.

Description

Lithium secondary battery electrolyte and preparation method and application thereof
Technical Field
The invention belongs to the technical field of batteries, and particularly relates to a lithium secondary battery electrolyte and a preparation method and application thereof.
Background
As a new green energy storage device, lithium secondary batteries have great diversity in the fields of 3C consumer electronics, electric vehicles, and the like due to their advantages of higher operating voltage, large specific capacity, longer cycle life, lower self-discharge rate, and the like. With the continuous development of these applications and the escalation of social demands, higher requirements are put on various performance indexes, especially energy density and cycle life, of the lithium secondary battery.
Since most of the commonly used negative electrodes have extremely low working potentials, the negative electrode at the working potential directly reacts with the electrolyte in the process of formation of the battery, so that the consumption of electrons and the generation of byproducts are caused. The byproducts are continuously accumulated on the surface of the negative electrode to form a compact film, namely a solid electrolyte layer (SEI), so that the blocking of electron transmission is finally realized, and lithium ions can be conducted, thereby providing possibility for the stable circulation of the battery. In order to realize the generation of compact SEI, the components of the electrolyte are reasonably designed, and the types, structures and appearances of products formed on the surface of the negative electrode are controllably adjusted.
The main component of the SEI on the surface of the negative electrode is from the electrolyte. In order to form a more stable SEI to prevent side reactions from occurring on the surface of a negative electrode in direct contact with an electrolyte, many research works have proposed various additives to modify the SEI, wherein the commonly used additives include fluoroethylene carbonate (FEC), Vinylene Carbonate (VC), nitrate, etc., wherein the introduction of nitrate represented by lithium nitrate induces the formation of Li-rich nitrate3The stable SEI of N can improve the cycle performance, so that the N is widely used for a metal lithium battery system.
In addition, it is proposed to use a silicon-based negative electrode material with a higher theoretical specific capacity to replace the traditional graphite negative electrode material (the theoretical capacity of silicon is 3579mAh/g and the theoretical capacity of graphite is 372mAh/g at normal temperature), but the silicon-based negative electrode material has lower conductivity and faces serious volume expansion problems. On one hand, the contact between the negative active material and the current collector is poor, and on the other hand, the solid electrolyte interface layer on the surface of the negative electrode is cracked and regrown in the alloying expansion process, so that the side reactions are increased, the coulombic efficiency is reduced, and the cycle performance of the silicon-based negative electrode battery is seriously reduced.
The current commercial electrolyte is mainly an ester electrolyte based on Ethylene Carbonate (EC), and the electrolyte shows better film forming property compared with Propylene Carbonate (PC) to a graphite cathode in the early period, so that the problem of solvent molecule co-intercalation is avoided, and the lithium ion battery based on the graphite cathode can be widely researched and applied by stable circulation, and has better anode oxidation resistance compared with an ether electrolyte commonly used in the research field. But it cannot dissolve nitrate becauseThis failure to form Li-rich3SEI of N to achieve further improvement of stability.
Disclosure of Invention
In order to overcome the problems, the invention provides an electrolyte of a lithium secondary battery and applies the electrolyte to the lithium secondary battery. The electrolyte of the lithium secondary battery provided by the invention can enable the nitrate additive to be fully dissolved in the ester electrolyte, and effectively form a stable SEI film on the surface of the negative electrode, so that the whole battery system is promoted to show higher coulombic efficiency and longer cycle life in the circulating process, the reversible capacity is improved to a certain extent, the energy density of an energy storage system can be effectively improved, and the electrolyte of the lithium secondary battery has a better application prospect.
In order to achieve the purpose, the invention adopts the following technical scheme:
a first object of the present invention is to provide an electrolyte for a lithium secondary battery, comprising: a base electrolyte, a nitrate additive and a cosolvent; the base electrolyte comprises a lithium salt and an ester solvent, and an optional base electrolyte additive, wherein the cosolvent comprises a boron trifluoride-based complex, and the boron trifluoride-based complex is at least one of compounds shown in a formula (i), a formula (ii) or a formula (iii):
Figure 204510DEST_PATH_IMAGE001
wherein, in the formula (i), R1、R2Each independently is any one of C1-C50 alkyl, C3-C50 cycloalkyl, C2-C50 alkenyl or C6-C50 aryl;
R1、R2any of the above hydrogen atoms may be optionally substituted; or, R1And R2Forming a saturated or unsaturated ring, any hydrogen atom on said ring being optionally substituted;
in the formula (ii), R3、R4Each independently is any one of C1-C50 alkyl, C3-C50 cycloalkyl, C2-C50 alkenyl or C6-C50 aryl, and any hydrogen atom on R3 and R4 is optionally takenGeneration;
in the formula (iii), D is a nitrogen atom or a phosphorus atom, R5、R6、R7Each independently is any one of C1-C50 alkyl, C3-C50 cycloalkyl, C2-C50 alkenyl or C6-C50 aryl;
R5、R6、R7any of the above hydrogen atoms may be optionally substituted;
the concentration of the nitrate additive in the electrolyte of the lithium secondary battery is 0.01-0.5M, and the concentration of the corresponding cosolvent is 0.01-0.5M; the molar ratio of the nitrate additive to the cosolvent is 2: (1-2).
In a preferred embodiment of the present invention, the boron trifluoride complex comprises: one or more of boron trifluoride diethyl etherate complex, boron trifluoride dimethyl carbonate complex, boron trifluoride diethyl carbonate complex or boron trifluoride ethyl methyl carbonate complex.
In a preferred embodiment of the present invention, the nitrate additive comprises: one or more of lithium nitrate, magnesium nitrate, silver nitrate, sodium nitrate, potassium nitrate, zinc nitrate or calcium nitrate.
In a preferred technical scheme of the invention, the cosolvent further comprises a salicylate compound;
the salicylate compound comprises one or more of methyl salicylate, ethyl salicylate, propyl salicylate, butyl salicylate, benzyl salicylate, phenethyl salicylate or phenylpropyl salicylate;
the molar ratio of the boron trifluoride-based complex to the salicylate compound is 2: (1-2).
In a preferred embodiment of the present invention, the ester solvent includes: one or more of ethylene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl propyl carbonate or ethyl propyl carbonate.
In a preferred embodiment of the present invention, the lithium salt includes: LiPF6、LiAsF6、LiCF3SO3、LiN(CF3SO2)2、LiBF6、LiSbF6、LiN(C2F5SO2)2、LiAlO4、LiAlCl4、LiSO3CF3Or LiClO4One or more of the above;
the concentration of lithium salt in the basic electrolyte is 0.1M-5M.
In a preferred embodiment of the present invention, the base electrolyte additive includes: one or more of fluoroethylene carbonate and vinylene carbonate;
the content of the basic electrolyte additive accounts for 0-20% of the mass or volume of the lithium secondary battery electrolyte. Preferably 5-20%.
The second object of the present invention is to provide a method for preparing the above electrolyte for a lithium secondary battery, comprising the steps of:
a) in an inert environment, introducing lithium salt and optional basic electrolyte additive into an ester solvent, and fully mixing until the mixture is stable and clear to obtain basic electrolyte for later use;
b) in an inert environment, introducing a nitrate additive into a basic electrolyte, fully mixing until the nitrate additive is fully dispersed, and then introducing a cosolvent, fully mixing until the nitrate additive is fully clarified, thereby obtaining the electrolyte of the lithium secondary battery.
A third object of the present invention is to provide a lithium secondary battery comprising the above lithium secondary battery electrolyte.
A fourth object of the present invention is to provide a lithium secondary battery having an application in the field of 2C electronic products or electric vehicles. The 3C electronic products are the general names of computer, communication and consumer electronic products, and are also called "information appliances".
The invention provides an electrolyte for assisting in dissolving nitrate by a cosolvent, wherein the cosolvent comprises a boron trifluoride complex which can be coordinated with nitrate to dissolve the nitrate in an ester electrolyte, and further forms a firm and stable SEI film in the formation process of a battery. When the electrolyte disclosed by the invention is used with a metal lithium battery assembled by a conventional NCM ternary material, the electrolyte can stably exist on the surface of a negative electrode so as to avoid the situation that the electrolyte is in direct contact with the electrode, the occurrence of side reactions is relieved, the coulombic efficiency is improved, and the cycle performance of the battery is further improved.
Drawings
FIG. 1 is an optical photograph of an electrolyte for a lithium secondary battery prepared in example 1 of the present invention;
FIG. 2 is an optical photograph of an electrolyte for a lithium secondary battery according to comparative example 2 of the present invention;
fig. 3 is an N1 s narrow spectrum of an X-ray photoelectron spectrum of an SEI formed on the surface of a lithium metal negative electrode by the lithium secondary battery electrolyte prepared in example 1 of the present invention;
FIG. 4 is a narrow spectrum of an X-ray photoelectron spectrum N1 s of SEI formed on the surface of a lithium metal negative electrode in the electrolyte of a lithium secondary battery according to comparative example 1 of the present invention;
FIG. 5 is a charge-discharge curve of the electrolyte of the lithium secondary battery prepared in example 1 of the present invention in combination with an NCM811 metal lithium battery;
fig. 6 is a charge-discharge curve of the lithium secondary battery electrolyte prepared in example 14 of the present invention in combination with a silicon-based negative electrode battery.
Detailed Description
In order to further the understanding of the present patent, the following sections will be provided to further explain the principle, content and result of the invention in connection with specific examples. It should be noted that the following cases are merely examples of specific descriptions, which are only used for explaining the terms in the invention, and do not constitute any limitation to the scope of the invention.
As used herein, the terms "comprises," "comprising," "includes," "including," and any variations thereof, are intended to cover non-exclusive inclusions.
When a range, preferred range, or a list of upper preferable values and lower preferable values is used to frame a range of values for an amount, concentration, or other parameter, this is to be understood as specifically disclosing combinations of any ratio of the selected parameter within the range (including upper and lower values), regardless of whether ranges are separately disclosed.
The feature technologies referred to in the present invention may be combined with each other as long as they do not conflict with each other.
According to a first aspect of the present invention, there is provided a lithium secondary battery electrolyte comprising: a base electrolyte, a nitrate additive and a cosolvent;
the basic electrolyte comprises a lithium salt and an ester solvent, and an optional basic electrolyte additive;
lithium salts include, but are not limited to, LiPF6、LiAsF6、LiCF3SO3、LiN(CF3SO2)2、LiBF6、LiSbF6、LiN(C2F5SO2)2、LiAlO4、LiAlCl4、LiSO3CF3Or LiClO4。
Preferably, the concentration of the lithium salt is 0.1M to 5M, such as 0.5M, 1M, 1.5M, 2M, 2.5M, 3M, 3.5M, 4M, 4.5M or 5M, based on the base electrolyte.
Ester solvents include, but are not limited to, Ethylene Carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), Ethyl Methyl Carbonate (EMC), propyl methyl carbonate (MPC), and propyl ethyl carbonate (EPC), among others.
The base electrolyte additive is an optional component including, but not limited to, fluoroethylene carbonate (FEC), Vinylene Carbonate (VC), and the like.
The content of the base electrolyte additive is 0 to 20% (mass fraction or volume fraction) based on the total electrolyte (lithium secondary battery electrolyte), for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 12%, 15%, 16%, 18%, 20%.
The nitrate additive is ANO3Wherein a is a common metal cation including, but not limited to, including lithium nitrate, magnesium nitrate, silver nitrate, sodium nitrate, potassium nitrate, zinc nitrate, or calcium nitrate.
The cosolvent comprises boron trifluoride complex, and the boron trifluoride complex is at least one of compounds shown as a formula (i), a formula (ii) or a formula (iii):
Figure 78269DEST_PATH_IMAGE002
wherein, in the formula (i), R1、R2Each independently is any one of C1-C50 alkyl, C3-C50 cycloalkyl, C2-C50 alkenyl or C6-C50 aryl;
R1、R2any of the above hydrogen atoms may be optionally substituted; or, R1And R2Forming a saturated or unsaturated ring, any hydrogen atom on said ring being optionally substituted;
in the formula (ii), R3、R4Each independently is any one of C1-C50 alkyl, C3-C50 cycloalkyl, C2-C50 alkenyl or C6-C50 aryl, and any hydrogen atom on R3 and R4 is optionally substituted;
in the formula (iii), D is a nitrogen atom or a phosphorus atom, R5、R6、R7Each independently is any one of C1-C50 alkyl, C3-C50 cycloalkyl, C2-C50 alkenyl or C6-C50 aryl;
R5、R6、R7any of the above hydrogen atoms may be optionally substituted.
In a preferred embodiment, the boron trifluoride-based complex comprises: one or more of boron trifluoride diethyl etherate complex, boron trifluoride dimethyl carbonate complex, boron trifluoride diethyl carbonate complex and boron trifluoride ethyl methyl carbonate complex.
It is noted that the molar concentration of the nitrate additive in the electrolyte is less than or equal to the molar concentration of the co-solvent. The concentration of the nitrate in the electrolyte of the lithium secondary battery is 0.01 to 0.5M (e.g., 0.05M, 0.1M, 0.15M, 0.2M, 0.25M, 0.3M, 0.35M, 0.4M, 0.5M), and the concentration of the corresponding cosolvent is 0.01 to 0.5M (e.g., 0.05M, 0.1M, 0.15M, 0.2M, 0.25M, 0.3M, 0.35M, 0.4M, 0.5M).
The principle of the invention is that boron trifluoride released by boron trifluoride complex is coordinated with nitrate dissociated by nitrate, when the molar concentration of boron trifluoride complex and nitrate is 2: (1-2) nitric acid can be usedThe radicals are completely coordinated with boron trifluoride and the complex exists stably, so that the nitrate is dissolved in an assistant manner, and Li is generated in the reaction process of a battery3The stable SEI of N can improve the capacity exertion and the cycling stability of the battery. Higher molar concentrations of nitrate relative to boron trifluoride complex result in incomplete dissolution, while too low a concentration results in unnecessary waste. The concentration is not suitable and stable SEI can not be formed so as to improve the capacity exertion and the cycling stability of the battery.
As a preferred embodiment, the cosolvent further comprises a salicylate compound; the molar ratio of the boron trifluoride complex to the salicylate compound is 2: (1-2).
The salicylate compound includes but is not limited to one or more of methyl salicylate, ethyl salicylate, propyl salicylate, butyl salicylate, benzyl salicylate, phenethyl salicylate or phenylpropyl salicylate.
Tests show that the boron trifluoride complex and the salicylate compound are matched according to a certain proportion, so that the dissolution of nitrate can be accelerated, and the capacity and the cycle performance of the battery can be further improved. This is probably because both boron trifluoride and salicylate are coordinated with nitrate, and the addition of salicylate accelerates the progress of the coordination reaction of boron trifluoride with nitrate.
According to a second aspect of the present invention, there is provided a method for preparing the electrolyte for a lithium secondary battery, specifically as follows:
1. fully stirring and mixing the solvents in an argon environment to obtain a mixed ester solvent;
2. in an argon environment, lithium salt and conventional additives are introduced into the mixed ester solvent, and then fully stirred and mixed until the mixed ester solvent is stable and clear, so that a basic electrolyte is obtained for later use;
3. in an argon environment, the nitrate additive is introduced into the basic electrolyte, fully stirred and mixed until the nitrate additive is fully dispersed, and then the boron trifluoride complex is introduced and fully stirred until the nitrate additive is fully clarified.
Step 1 the solvent comprises any one selected from the group consisting of: ethylene Carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), Ethyl Methyl Carbonate (EMC), propyl methyl carbonate (MPC), and propyl ethyl carbonate (EPC), or a mixture of two or more thereof.
Step 2 the lithium salt comprises any one selected from the group consisting of: LiPF6、LiAsF6、LiCF3SO3、 LiN(CF3SO2)2、LiBF6、LiSbF6、LiN(C2F5SO2)2、LiAlO4、LiAlCl4、 LiSO3CF3And LiClO4Or a mixture of two or more thereof.
The conventional additives in step 2 comprise fluoroethylene carbonate (FEC) and Vinylene Carbonate (VC).
And 2, the concentration of lithium salt in the basic electrolyte is 0.1-5M.
And 2, the content of the conventional additive in the solvent in the basic electrolyte accounts for 0-20% of the mass or volume of the total electrolyte.
The concentration of the nitrate in the electrolyte in the step 3 is 0.01 to 0.5M, preferably 0.01 to 0.1, more preferably 0.05 to 0.1M, and the concentration of the corresponding boron trifluoride complex or boron trifluoride complex and salicylate-based compound is 0.01 to 0.5M, preferably 0.05 to 0.2.
According to a third aspect of the present invention, there is provided a lithium secondary battery comprising the above-described lithium secondary battery electrolyte.
According to a fourth aspect of the present invention, there is provided a use of a lithium secondary battery in the field of consumer electronics or electric vehicles.
The invention is further illustrated by the following examples. The materials in the examples are prepared according to known methods or are directly commercially available, unless otherwise specified.
Example 1
A preparation method of an electrolyte of a lithium secondary battery comprises the following steps:
1. preparing a basic electrolyte: in an argon glove box environment, Ethylene Carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) are fully mixed by using magnetic stirring according to the volume ratio EC/DEC/DMC =1:1:1, lithium hexafluorophosphate is slowly introduced into the solution after uniform mixing, the concentration of the lithium hexafluorophosphate is controlled to be 1M (the formula is shown in table 1), and the basic electrolyte is obtained after uniform stirring again for later use.
2. Electrolyte preparation: taking 2ml of basic electrolyte in an argon glove box environment, adding lithium nitrate into the basic electrolyte to enable the concentration of the basic electrolyte to be 0.05M, and fully stirring until lithium nitrate crystals are dispersed to be white; boron trifluoride etherate was then introduced so that its concentration was 0.05M, and stirred uniformly again until the solution was clear. To be injected with NCM811 Li battery.
Example 2
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: the lithium nitrate crystal is changed into a sodium nitrate crystal. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Example 3
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: the lithium nitrate crystal is changed into silver nitrate crystal. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Example 4
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: so that the concentrations of lithium nitrate crystals and boron trifluoride etherate were 0.1M. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Example 5
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: the lithium nitrate crystal was changed to a sodium nitrate crystal, and the concentration of boron trifluoride ether complex was made 0.1M. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Example 6
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: the lithium nitrate crystal was changed to a silver nitrate crystal, and the concentration of boron trifluoride ether complex was made 0.1M. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Example 7
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: the boron trifluoride diethyl etherate complex is changed to boron trifluoride dimethyl carbonate complex. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Example 8
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: the boron trifluoride diethyl etherate complex was changed to boron trifluoride dimethyl carbonate complex, and the lithium nitrate crystal was changed to sodium nitrate crystal. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Example 9
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: the boron trifluoride diethyl etherate complex was changed to boron trifluoride dimethyl carbonate complex, and the lithium nitrate crystal was changed to silver nitrate crystal. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Example 10
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: the boron trifluoride diethyl etherate complex was changed to boron trifluoride dimethyl carbonate complex, and the concentration of lithium nitrate crystals and boron trifluoride dimethyl carbonate complex was made 0.1M. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Example 11
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: the boron trifluoride diethyl etherate complex was changed to boron trifluoride dimethyl carbonate complex, the lithium nitrate crystal was changed to sodium nitrate crystal, and the concentration of the sodium nitrate crystal and boron trifluoride dimethyl carbonate complex was made 0.1M. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Example 12
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: the boron trifluoride diethyl etherate complex was changed to boron trifluoride dimethyl carbonate complex, the lithium nitrate crystal was changed to silver nitrate crystal, and the concentration of the silver nitrate crystal and boron trifluoride dimethyl carbonate complex was made 0.1M. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Example 13
A preparation method of an electrolyte of a lithium secondary battery comprises the following steps:
1. preparing a basic electrolyte: in an argon glove box environment, Ethylene Carbonate (EC), diethyl carbonate (DEC) and dimethyl carbonate (DMC) are fully mixed by using magnetic stirring according to the volume ratio EC/DEC/DMC =1:1:1, lithium hexafluorophosphate is slowly introduced into the solution after uniform mixing, the concentration of the lithium hexafluorophosphate is controlled to be 1M (the formula is shown in table 1), and the basic electrolyte is obtained after uniform stirring again for later use.
2. Electrolyte preparation: in an argon glove box environment, 2ml of basic electrolyte is taken, silver nitrate is added into the basic electrolyte to enable the concentration of the basic electrolyte to be 0.1M, and the basic electrolyte is fully stirred until silver nitrate crystals are dispersed to be white; then, boron trifluoride dimethyl carbonate and methyl salicylate were introduced so that the concentrations of both dimethyl trifluoride carbonate and methyl salicylate were 0.05M, and the mixture was uniformly stirred again until the solution was clear. To be injected with NCM811 Li battery.
Example 14
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: the system finally injected by the electrolyte is a silicon-based negative electrode battery.
Example 15
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: and replacing the lithium nitrate crystal with a sodium nitrate crystal, wherein the system finally injected by the electrolyte is a silicon-based negative electrode battery.
Example 16
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: and replacing the lithium nitrate crystal with a silver nitrate crystal, wherein the system finally injected by the electrolyte is a silicon-based negative electrode battery.
Example 17
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 16, except that: the boron trifluoride diethyl etherate was exchanged for boron trifluoride diethyl etherate and methyl salicylate, and the concentrations of both boron trifluoride diethyl etherate and ethyl salicylate were 0.025M. Other steps were carried out in the same manner as in example 16 to prepare an electrolyte for a lithium secondary battery.
Example 18
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: so that the concentration of boron trifluoride diethyl etherate was 0.1M. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Comparative example 1
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: boron trifluoride diethyl etherate and lithium nitrate crystal are not introduced any more. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Comparative example 2
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: no boron trifluoride etherate complex was introduced. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Comparative example 3
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: boron trifluoride diethyl etherate is not introduced any more, and the lithium nitrate crystals are exchanged for sodium nitrate crystals. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Comparative example 4
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: boron trifluoride diethyl etherate is not introduced any more, and the lithium nitrate crystal is exchanged for a silver nitrate crystal. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Comparative example 5
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: no lithium nitrate crystals were introduced. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Comparative example 6
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: so that the concentration of boron trifluoride diethyl etherate was 0.1M, and no lithium nitrate crystals were introduced. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Comparative example 7
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: the boron trifluoride diethyl etherate complex is changed into boron trifluoride dimethyl carbonate complex, and lithium nitrate crystal is not introduced any more. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Comparative example 8
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: the boron trifluoride diethyl etherate complex is changed into boron trifluoride dimethyl carbonate complex, the concentration of the boron trifluoride dimethyl carbonate complex is changed into 0.1M, and lithium nitrate crystals are not introduced any more. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Comparative example 9
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: lithium nitrate crystals and boron trifluoride diethyl etherate complex are not introduced any more, and finally the silicon-based negative electrode system is injected. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Comparative example 10
A lithium secondary battery electrolyte according to the present invention was prepared in the same manner as in example 1, except that: no boron trifluoride diethyl etherate complex is introduced any more, and finally the silicon-based negative electrode system is injected. The other steps were the same as in example 1 to prepare an electrolyte for a lithium secondary battery.
Fig. 1 is an optical photograph of the electrolyte for a lithium secondary battery obtained in example 1, and it can be seen that the electrolyte is in a completely clear and transparent state, indicating that lithium nitrate crystals have been completely dissolved. Fig. 2 is an optical picture of the electrolyte for a lithium secondary battery obtained in comparative example 2, in contrast to the presence of a large amount of white lithium nitrate precipitate at the bottom of the glass bottle without the introduction of a co-solvent. The above demonstrates that boron trifluoride can aid in the dissolution of lithium nitrate. Further, fig. 3 and 4 are XPS spectra of SEI on the surface of lithium metal after cycling of NCM811 lithium metal batteries using the lithium secondary battery electrolytes obtained in example 1 and comparative example 1, respectively, and again demonstrate that lithium nitrate is dissolved with the aid of boron trifluoride and promotes Li dissolution3And (4) generating an N interface.
Application example 1
The electrochemical properties of the electrolytes for lithium secondary batteries prepared in the above examples and comparative examples were measured in the following manner:
the positive pole piece is prepared as follows: LiNi as active material with the specific weight of 80 percent0.8Co0.1Mn0.1O2The positive electrode plate is obtained by adding 10% of activated carbon as a conductive additive and 10% of polyvinylidene fluoride (PVdF) as a binder into N-methyl-2-pyrrolidone (NMP) as a solvent, sufficiently and uniformly mixing to form a slurry, coating the slurry on an aluminum foil with a thickness of about 20 μm as a positive electrode current collector, and sufficiently vacuum-drying for 12 hours.
The silicon-based negative pole piece is prepared as follows: SiO active material with the specific gravity of 80 percentwThe active carbon as the conductive additive in 10 percent and the polyacrylic acid (PAA) as the binder in 10 percent are fully and uniformly mixed to form slurry, the slurry is coated on copper foil with the thickness of about 10 mu m as a negative electrode current collector, and the negative electrode pole piece is obtained after full vacuum drying.
The cell was assembled as follows:
NCM811| | Li: and under the atmosphere of an argon glove box, injecting the prepared electrolytes by using a PP porous diaphragm and the positive plate and the metal lithium plate prepared by the method as negative plates to finish the preparation of the lithium ion battery.
SiOx[ C ] Li: and injecting the prepared electrolytes into a PP porous diaphragm and the positive plate and the silicon-based negative plate prepared by the method under the atmosphere of an argon glove box to finish the preparation of the lithium ion battery.
An electrolyte was prepared and a battery was assembled according to the method of each example and comparative example (table 1), and charge and discharge characteristics thereof were tested. Specifically, the above series of batteries were charged to 4.3V at a rate of 0.2C under a constant current, and then the ester was discharged at a rate of 0.2C for 3.0V to measure discharge capacity, followed by a charge and discharge experiment at 0.5C, the results of which are shown in table 2, wherein the detailed results of example 1 are shown in fig. 5. The method has the advantages that the capacity of the material is exerted to 183 mAh/g, the capacity retention rate is 93% after 100 cycles of circulation, the advantages are obvious compared with comparative examples, the idea that the circulation performance is improved by introducing the cosolvent to assist in dissolving the nitrate and promoting the generation of the nitriding interface is correct, and the implementation mode is verified. Similarly, fig. 6 shows that the charge-discharge performance test using the silicon-based negative electrode also proves that the specific capacity is higher and the cycling stability is good.
Figure DEST_PATH_IMAGE003
Figure 290945DEST_PATH_IMAGE004
Figure DEST_PATH_IMAGE005
It can be seen from table 2 that, by using the formulation of the present invention, firstly, nitrate represented by lithium nitrate can be dissolved, and simultaneously, the combined action of the cosolvent and the nitrate can make the metal lithium battery and the silicon-based negative electrode lithium ion battery show higher specific capacity performance, and the retention rate of the capacity of hundreds of cycles is correspondingly improved.
The present invention is illustrated in detail by the above examples, but the present invention is not limited to the above detailed preparation method, that is, it is not meant to imply that the present invention must be carried out by the above detailed preparation method. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims (4)

1. A lithium secondary battery electrolyte, characterized by comprising: a base electrolyte, a nitrate additive and a cosolvent; the basic electrolyte comprises lithium salt, ester solvent and basic electrolyte additive, wherein the lithium salt is LiPF6The nitrate additive is silver nitrate, the concentration of the silver nitrate in the electrolyte is 0.1M, and the ester solvents are ethylene carbonate, diethyl carbonate and dimethyl carbonate in a volume ratio of 1:1:1, the cosolvent comprises boron trifluoride dimethyl carbonate and methyl salicylate, and the concentrations of the boron trifluoride dimethyl carbonate and the methyl salicylate in the electrolyte are both 0.05M.
2. A method for preparing the electrolyte for a lithium secondary battery according to claim 1, comprising the steps of:
a) in an inert environment, introducing lithium salt and a basic electrolyte additive into an ester solvent, and fully mixing until the mixture is stable and clear to obtain a basic electrolyte for later use;
b) in an inert environment, introducing a nitrate additive into a basic electrolyte, fully mixing until the nitrate additive is fully dispersed, and then introducing a cosolvent, fully mixing until the nitrate additive is fully clarified, thereby obtaining the electrolyte of the lithium secondary battery.
3. A lithium secondary battery comprising the lithium secondary battery electrolyte according to claim 1.
4. Use of the lithium secondary battery of claim 3 in the field of 3C electronics or electric automobiles.
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