CN111668546B - Nonaqueous electrolyte solution and lithium ion battery using same - Google Patents

Nonaqueous electrolyte solution and lithium ion battery using same Download PDF

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CN111668546B
CN111668546B CN202010586182.0A CN202010586182A CN111668546B CN 111668546 B CN111668546 B CN 111668546B CN 202010586182 A CN202010586182 A CN 202010586182A CN 111668546 B CN111668546 B CN 111668546B
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lithium ion
nonaqueous electrolyte
ion battery
compound
lithium
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CN111668546A (en
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肖培涛
李轶
陈石穿
陶亮
林玉春
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Vision Power Technology Hubei Co ltd
Envision Power Technology Jiangsu 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
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • 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
    • 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
    • H01M2300/00—Electrolytes
    • H01M2300/0017—Non-aqueous electrolytes
    • H01M2300/0025—Organic electrolyte
    • 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

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Abstract

The invention provides a non-aqueous electrolyte and a lithium ion battery using the same, and particularly discloses a lithium ion battery non-aqueous electrolyte containing various additives. The service life of the lithium ion battery using the non-aqueous electrolyte is remarkably prolonged, and the gas generation amount is greatly reduced.

Description

Nonaqueous electrolyte solution and lithium ion battery using same
Technical Field
The invention belongs to the field of lithium ion batteries, and relates to a non-aqueous electrolyte and a lithium ion battery using the same.
Background
The lithium ion battery is a secondary battery, and mainly realizes charging and discharging work by moving lithium ions between a positive electrode and a negative electrode. During charging and discharging, Li+Intercalation and deintercalation to and from two electrodes: upon charging, Li+The lithium ion battery is extracted from the positive electrode and is inserted into the negative electrode through the electrolyte, and the negative electrode is in a lithium-rich state; the opposite is true during discharge. Lithium ion batteries have been widely used because of their high energy density, no memory effect, high operating voltage, and environmental friendliness. With the expansion of the market demand of electronic products and the development of power and energy storage devices, power lithium batteries are beginning to be applied to electric tools and electric vehicles, and therefore, the requirements on the performance of lithium batteries are higher and higher.
A negative electrode material of a lithium secondary battery may undergo reductive decomposition in a large amount of a solvent because lithium and electrons are stored and desorbed at an extremely low potential equivalent to that of lithium metal, and a part of the solvent in an electrolyte on the negative electrode is reductively decomposed regardless of the kind of the negative electrode material, and the movement of lithium ions is inhibited by deposition of decomposed products, gas generation, and swelling of an electrode, thereby deteriorating battery characteristics and deforming the battery when the battery is used at high temperature and high voltage. In addition, when lithium metal or its alloy, a simple metal such as tin or silicon, or a metal oxide is used as a negative electrode material in a lithium secondary battery, although the initial capacity is high, the reductive decomposition of a nonaqueous solvent is accelerated compared with a negative electrode made of a carbon material, and the battery capacity, cycle characteristics, and other properties are greatly deteriorated, and the swelling of an electrode is caused, and the battery is deformed.
When the positive electrode material is LiCoO2、LiMn2O4、LiNiO2、LiFePO4For example, when a battery is used under a high-temperature and high-voltage environment (lithium and electrons are stored and desorbed at a high voltage of 3.5V or more based on lithium), a large amount of solvent undergoes oxidative decomposition, the deposition of decomposed products increases the resistance, and the decomposition of the solvent generates gas to swell the battery.
In a thin electronic device such as a tablet terminal or a super notebook, a laminate type battery or a square type battery is often used. Since these batteries are thin, a problem of deformation due to swelling is likely to occur. In the field of electric automobiles, as the demand for cruising ability increases, an electric storage device having high energy density, long cycle, and high safety becomes important. However, in the current electricity storage device, especially a lithium ion battery, gas generation is serious, the battery capacity can be continuously attenuated, and the gas generation can also cause the battery capacity to be attenuated and even cause the phenomenon of 'water jump'.
Therefore, those skilled in the art have made efforts to develop a nonaqueous electrolytic solution and a secondary battery device that can achieve both of a longer battery life and suppression of gas generation.
Disclosure of Invention
The invention aims to provide a nonaqueous electrolyte and a lithium ion battery using the same.
In a first aspect of the invention, a lithium ion battery nonaqueous electrolyte is provided, which comprises a first compound and a second compound, wherein the structure of the first compound is shown as formula I, and the structure of the second compound is shown as formula II:
Figure BDA0002554725370000021
wherein R is1、R2、R3、R4、R5、R6Each independently selected from: H. and C with or without substituents1-8An alkyl group (a straight or branched chain alkyl group having 1 to 8 carbon atoms, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, or the like).
In another preferred embodiment, R1、R2、R3、R4、R5、R6Each independently is H.
In another preferred example, in the lithium ion battery nonaqueous electrolyte, the mass percentage content of the first compound is 0.1% to 10.0%. And the total mass of the lithium ion battery nonaqueous electrolyte is 100%. Preferably, the mass percentage content of the first compound is 0.2-5%. Most preferably, the mass percentage of the first compound is about 0.5% to 2%.
In another preferable example, in the lithium ion battery nonaqueous electrolyte, the mass percentage of the second compound is 0.1% to 1.0%. And the total mass of the lithium ion battery nonaqueous electrolyte is 100%. Preferably, the mass percentage of the second compound is 0.2-0.8%. Most preferably, the mass percentage of the first compound is about 0.5%.
In another preferred embodiment, the nonaqueous electrolytic solution further contains one or more compounds selected from the group consisting of: unsaturated cyclic carbonates, fluorinated cyclic carbonates, and cyclic sultones.
In another preferred embodiment, the unsaturated cyclic carbonate is Vinylene Carbonate (VC), Vinyl Ethylene Carbonate (VEC), or a combination thereof.
In another preferable example, in the lithium ion battery nonaqueous electrolyte, the unsaturated cyclic carbonate is contained in an amount of 0 to 10% by mass. And the total mass of the lithium ion battery nonaqueous electrolyte is 100%. Preferably, the unsaturated cyclic carbonate accounts for 0.2 to 5 percent by weight. Most preferably, the unsaturated cyclic carbonate is present in an amount of about 0.5% to about 2% by weight.
In another preferred embodiment, the fluorocyclic carbonate is fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), or a combination thereof.
In another preferable example, in the lithium ion battery nonaqueous electrolyte, the fluorinated cyclic carbonate is contained in an amount of 0 to 10% by mass. And the total mass of the lithium ion battery nonaqueous electrolyte is 100%. Preferably, the fluorinated cyclic carbonate accounts for 0.2 to 5 percent by weight. Most preferably, the fluorinated cyclic carbonate is present in an amount of about 0.5% to about 2% by weight.
In another preferred embodiment, the cyclic sultone is 1, 3-Propane Sultone (PS), 1, 4-butane sultone, propenyl-1, 3-sultone, or a combination thereof.
In another preferable example, in the lithium ion battery nonaqueous electrolyte, the content of the cyclic sultone in the nonaqueous electrolyte is 0 to 10% by mass. And the total mass of the lithium ion battery nonaqueous electrolyte is 100%. Preferably, the content of the cyclic sultone is 0.2-5% by mass. Most preferably, the content of the cyclic sultone is about 0.5 to 2 percent by mass.
In another preferred example, the solvent in the lithium ion battery nonaqueous electrolyte comprises Ethylene Carbonate (EC) and diethyl carbonate (DEC); preferably, the mass ratio of Ethylene Carbonate (EC) to diethyl carbonate (DEC) in the solvent is 20-50: 50-100 parts of; more preferably, the mass ratio of Ethylene Carbonate (EC) to diethyl carbonate (DEC) in the solvent is 20-40: 60-80.
In another preferred example, the electrolyte in the nonaqueous electrolyte solution of the lithium ion battery is LiPF6(ii) a Preferably, the electrolyte concentration in the lithium ion battery nonaqueous electrolyte is 0.1-3 mol/L; more preferably, the electrolyte concentration in the lithium ion battery nonaqueous electrolyte solution is 0.5-1.5 mol/L.
In another preferable example, the conductivity of the non-aqueous electrolyte of the lithium ion battery is 7.5-9.0 mS/cm.
In another preferred example, the density of the nonaqueous electrolyte of the lithium ion battery is 1.2-1.22g/cm3。
In another preferred example, the water content of the lithium ion battery nonaqueous electrolyte is less than or equal to 15 ppm.
In a second aspect of the present invention, there is provided a lithium ion battery, including a positive electrode, a negative electrode, a separator and an electrolyte, wherein the separator is configured to separate the positive electrode from the negative electrode, and the electrolyte is the lithium ion battery non-aqueous electrolyte according to the first aspect of the present invention.
In another preferred example, the positive electrode includes a positive electrode active material, and the positive electrode active material may be a lithium-containing composite oxide. Specific examples of the lithium-containing composite oxide include LiMnO2、LiFeO2、LiMn2O4、Li2FeSiO4LiNi1/3Co1/3Mn1/3O2、LiNi5CO2Mn3O2、LizNi(1-x-y)CoxMyO2(x, y and z are values satisfying 0.01. ltoreq. x.ltoreq.0.20, 0. ltoreq. y.ltoreq.0.20, and 0.97. ltoreq. z.ltoreq.1.20, M represents at least one element selected from the group consisting of Mn, V, Mg, Mo, Nb and Al), LiFePO4 and LizCO(1-x)MxO2(x and z are values satisfying 0. ltoreq. x.ltoreq.0.1 and 0.97. ltoreq. z.ltoreq.1.20, M represents at least one element selected from the group consisting of Mn, Ni, V, Mg, Mo, Nb, and Al).
Since the additive for nonaqueous electrolytic solution of the present embodiment can effectively cover the surface, the positive electrode active material may be LizNi(1-x-y)CoxMyO2(x, y and z are values satisfying 0.01. ltoreq. x.ltoreq.0.15, 0. ltoreq. y.ltoreq.0.15, and 0.97. ltoreq. z.ltoreq.1.20, M represents at least one element selected from the group consisting of Mn, Ni, V, Mg, Mo, Nb and Al) or LizCO(1-x)MxO2(x and z are values satisfying 0. ltoreq. x.ltoreq.0.1 and 0.97. ltoreq. z.ltoreq.1.20, and M represents at least one element selected from Mn, V, Mg, Mo, Nb, and Al). Especially in the use of e.g. LizNi(1-x-y)CoxMyO2(x, y and z are values satisfying 0.01. ltoreq. x.ltoreq.0.15, 0. ltoreq. y.ltoreq.0.15 and 0.97. ltoreq. z.ltoreq.1.20, M represents a group selected fromAt least one element selected from the group consisting of Mn, Ni, V, Mg, Mo, Nb, and Al) has a high Ni content, gas generation tends to be facilitated, but even in this case, gas generation can be effectively suppressed by the combination of the above-described electrolyte components.
In another preferred example, the negative electrode contains a negative electrode active material. The negative electrode active material is a material capable of inserting and extracting lithium. Including, but not limited to, carbon materials such as crystalline carbon (natural graphite, artificial graphite, and the like), amorphous carbon, carbon-coated graphite, and resin-coated graphite, and oxide materials such as indium oxide, silicon oxide, tin oxide, lithium titanate, zinc oxide, and lithium oxide. The negative electrode active material may also be lithium metal or a metal material that can form an alloy with lithium. Specific examples of metals that can be alloyed with lithium include Cu, Sn, Si, Co, Mn, Fe, Sb, and Ag. Binary or ternary alloys containing these metals and lithium may also be used as the negative electrode active material. These negative electrode active materials may be used alone, or two or more of them may be used in combination. From the viewpoint of high energy density, a carbon material such as graphite and an Si-based active material such as Si, an Si alloy, and an Si oxide may be combined as the negative electrode active material. From the viewpoint of both cycle characteristics and high energy density, graphite and an Si-based active material may be combined as the negative electrode active material. In the combination, the ratio of the mass of the Si-based active material to the total mass of the carbon material and the Si-based active material may be 0.5% to 95%, 1% to 50%, or 2% to 40%.
It is to be understood that within the scope of the present invention, the above-described features of the present invention and those specifically described below (e.g., in the examples) may be combined with each other to form new or preferred embodiments. Not to be reiterated herein, but to the extent of space.
Detailed Description
The inventors of the present invention have conducted extensive and intensive studies to obtain a nonaqueous electrolyte for a lithium ion battery, which contains a compound of formula I and a compound of formula I I, and as a result, the compound of formula I and the compound of formula I I, which are added to the nonaqueous electrolyte at the same time, show a remarkable synergistic effect. The service life of the lithium ion battery using the non-aqueous electrolyte is remarkably prolonged, and the gas generation amount is greatly reduced, thereby completing the invention
Before the present invention is described, it is to be understood that this invention is not limited to the particular methodology and experimental conditions described, as such methodologies and conditions may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. As used herein, the term "about" when used in reference to a specifically recited value means that the value may vary by no more than 1% from the recited value. For example, as used herein, the expression "about 100" includes 99 and 101 and all values in between (e.g., 99.1, 99.2, 99.3, 99.4, etc.).
Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods and materials are now exemplified.
Non-aqueous electrolyte
Since the metal lithium and water can have violent chemical reaction, the electrolyte of the common lithium battery adopts non-aqueous solvent.
The nonaqueous electrolytic solution is composed of a lithium salt, a nonaqueous solvent and an additive. As the nonaqueous solvent, carbonates such as Ethylene Carbonate (EC), Propylene Carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) are used. Lithium salts include, but are not limited to, LiPF6、LiBF4、LiClO4、LiAsO4LiTFSI, LiFSI, etc. Additives include VC, FEC, MMDS, LiBOB, LiODFB, LiODFP, PS, PST, and the like. The content of the lithium salt can vary within a wide range, and preferably, the content of the lithium salt in the lithium ion battery nonaqueous electrolyte is 0.1-15%.
The addition of various additives to the electrolyte solution can suppress the decrease in battery capacity accompanying the progress of charge-discharge cycles. The additive is decomposed during initial charge and discharge, and forms a coating called a Solid Electrolyte Interface (SEI) on the electrode surface. Since the SEI is formed in the initial cycle of the charge-discharge cycle, decomposition of a solvent or the like in the electrolyte consumes no power, and lithium ions can pass back and forth through the SEI in the electrode. That is, the formation of SEI is considered to play a large role in preventing deterioration of an electric storage device such as a nonaqueous electrolyte secondary battery when charge and discharge cycles are repeated, and improving battery characteristics, storage characteristics, load characteristics, and the like.
In a preferred embodiment of the present invention, the present invention provides a nonaqueous electrolytic solution comprising a first compound and a second compound, wherein the structure of the first compound is represented by formula I ', and the structure of the second compound is represented by formula II':
Figure BDA0002554725370000061
in another preferred example, in the lithium ion battery nonaqueous electrolyte, the mass percentage content of the first compound is 0.1% to 10.0%. And the total mass of the lithium ion battery nonaqueous electrolyte is 100%. Preferably, the mass percentage content of the first compound is 0.2-5%. Most preferably, the mass percentage of the first compound is about 0.5% to 2%.
In another preferable example, in the lithium ion battery nonaqueous electrolyte, the mass percentage of the second compound is 0.1% to 1.0%. And the total mass of the lithium ion battery nonaqueous electrolyte is 100%. Preferably, the mass percentage of the second compound is 0.2-0.8%. Most preferably, the mass percentage of the first compound is about 0.5%.
In another preferred embodiment, the nonaqueous electrolytic solution further contains one or more compounds selected from the group consisting of: unsaturated cyclic carbonates, fluorinated cyclic carbonates, and cyclic sultones.
In another preferred embodiment, the unsaturated cyclic carbonate is Vinylene Carbonate (VC), Vinyl Ethylene Carbonate (VEC), or a combination thereof.
In another preferable example, in the lithium ion battery nonaqueous electrolyte, the unsaturated cyclic carbonate is contained in an amount of 0 to 10% by mass. And the total mass of the lithium ion battery nonaqueous electrolyte is 100%. Preferably, the unsaturated cyclic carbonate accounts for 0.2 to 5 percent by weight. Most preferably, the unsaturated cyclic carbonate is present in an amount of about 0.5% to about 2% by weight.
In another preferred embodiment, the fluorocyclic carbonate is fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), or a combination thereof.
In another preferable example, in the lithium ion battery nonaqueous electrolyte, the fluorinated cyclic carbonate is contained in an amount of 0 to 10% by mass. And the total mass of the lithium ion battery nonaqueous electrolyte is 100%. Preferably, the fluorinated cyclic carbonate accounts for 0.2 to 5 percent by weight. Most preferably, the fluorinated cyclic carbonate is present in an amount of about 0.5% to about 2% by weight.
In another preferred embodiment, the cyclic sultone is 1, 3-Propane Sultone (PS), 1, 4-butane sultone, propenyl-1, 3-sultone, or a combination thereof.
In another preferable example, in the lithium ion battery nonaqueous electrolyte, the content of the cyclic sultone in the nonaqueous electrolyte is 0 to 10% by mass. And the total mass of the lithium ion battery nonaqueous electrolyte is 100%. Preferably, the content of the cyclic sultone is 0.2-5% by mass. Most preferably, the content of the cyclic sultone is about 0.5 to 2 percent by mass.
In another preferred example, the solvent in the lithium ion battery nonaqueous electrolyte comprises Ethylene Carbonate (EC) and diethyl carbonate (DEC); preferably, the mass ratio of Ethylene Carbonate (EC) to diethyl carbonate (DEC) in the solvent is 20-50: 50-100 parts of; more preferably, the mass ratio of Ethylene Carbonate (EC) to diethyl carbonate (DEC) in the solvent is 20-40: 60-80.
In another preferred embodimentIn the embodiment, the electrolyte in the non-aqueous electrolyte of the lithium ion battery is LiPF6(ii) a Preferably, the electrolyte concentration in the lithium ion battery nonaqueous electrolyte is 0.1-3 mol/L; more preferably, the electrolyte concentration in the lithium ion battery nonaqueous electrolyte solution is 0.5-1.5 mol/L.
In another preferable example, the conductivity of the non-aqueous electrolyte of the lithium ion battery is 7.5-9.0 mS/cm.
In another preferred example, the density of the nonaqueous electrolyte of the lithium ion battery is 1.2-1.22g/cm3。
In another preferred example, the water content of the lithium ion battery nonaqueous electrolyte is less than or equal to 15 ppm.
Lithium ion battery
The lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm for separating the positive electrode and the negative electrode, and a lithium ion battery non-aqueous electrolyte.
The positive electrode contains a positive electrode active material. The positive electrode active material may be a lithium-containing composite oxide. Specific examples of the lithium-containing composite oxide include LiMnO2、LiFeO2、LiMn2O4、Li2FeSiO4LiNi1/3Co1/3Mn1/3O2、LiNi5CO2Mn3O2、LizNi(1-x-y)CoxMyO2(x, y and z are values satisfying 0.01. ltoreq. x.ltoreq.0.20, 0. ltoreq. y.ltoreq.0.20, and 0.97. ltoreq. z.ltoreq.1.20, M represents at least one element selected from the group consisting of Mn, V, Mg, Mo, Nb and Al), LiFePO4 and LizCO(1-x)MxO2(x and z are values satisfying 0. ltoreq. x.ltoreq.0.1 and 0.97. ltoreq. z.ltoreq.1.20, M represents at least one element selected from the group consisting of Mn, Ni, V, Mg, Mo, Nb, and Al). Since the additive for nonaqueous electrolytic solution of the present embodiment can effectively cover the surface, the positive electrode active material may be LizNi(1-x-y)CoxMyO2(x, y and z are values satisfying 0.01. ltoreq. x.ltoreq.0.15, 0. ltoreq. y.ltoreq.0.15, and 0.97. ltoreq. z.ltoreq.1.20, M represents at least one element selected from the group consisting of Mn, Ni, V, Mg, Mo, Nb and Al) or LizCO(1-x)MxO2(x and z are values satisfying 0. ltoreq. x.ltoreq.0.1 and 0.97. ltoreq. z.ltoreq.1.20, and M represents at least one element selected from Mn, V, Mg, Mo, Nb, and Al). Especially in the use of e.g. LizNi(1-x-y)CoxMyO2In the case of a positive electrode active material having a high Ni content (where x, y, and z are values satisfying 0.01. ltoreq. x.ltoreq.0.15, 0. ltoreq. y.ltoreq.0.15, and 0.97. ltoreq. z.ltoreq.1.20, and M represents at least one element selected from the group consisting of Mn, Ni, V, Mg, Mo, Nb, and Al), gas generation tends to be easily caused, but even in this case, gas generation can be effectively suppressed by the combination of the above electrolyte components.
The negative electrode active material contains a negative electrode active material. Examples of the negative electrode active material include materials capable of inserting and extracting lithium. Such materials include crystalline carbon (natural graphite, artificial graphite, and the like), amorphous carbon, carbon-coated graphite, resin-coated graphite, and other carbon materials, and oxide materials such as indium oxide, silicon oxide, tin oxide, lithium titanate, zinc oxide, and lithium oxide. The negative electrode active material may also be lithium metal or a metal material that can form an alloy with lithium. Specific examples of metals that can be alloyed with lithium include Cu, Sn, Si, Co, Mn, Fe, Sb, and Ag. Binary or ternary alloys containing these metals and lithium may also be used as the negative electrode active material. These negative electrode active materials may be used alone, or two or more of them may be used in combination. From the viewpoint of high energy density, a carbon material such as graphite and an Si-based active material such as Si, an Si alloy, and an Si oxide may be combined as the negative electrode active material. From the viewpoint of both cycle characteristics and high energy density, graphite and an Si-based active material may be combined as the negative electrode active material. In the combination, the ratio of the mass of the Si-based active material to the total mass of the carbon material and the Si-based active material may be 0.5% to 95%, 1% to 50%, or 2% to 40%.
The separator is conventional in the field of lithium ion batteries, and the invention will not be discussed in detail here.
The lithium ion battery provided by the invention contains the nonaqueous electrolyte, so that the lithium ion battery has good high-temperature cycle performance and high-temperature storage performance.
In a preferred embodiment of the present invention, the present invention provides an additive for a nonaqueous electrolytic solution for obtaining an electric storage device having a long life and suppressing gas generation, the additive for a nonaqueous electrolytic solution comprising a specific compound of formula I (carbonate compound), a compound of formula II (vinyl sulfate, DTD), an ethylene carbonate compound (VC), a vinyl ethylene carbonate compound (VEC), fluoroethylene carbonate (FEC), and 1, 3-Propane Sultone (PS). The use of the additive, a nonaqueous electrolytic solution comprising a lithium salt and a solvent makes it possible to achieve a long life and suppress gas generation in an electric storage device, and the present invention has been completed.
In the nonaqueous electrolytic solution, the mass fraction of the formula 1 is 0.1 to 10%, the mass fraction of an ethylene carbonate compound (VC) is 0 to 10%, the mass fraction of a vinyl ethylene carbonate compound (VEC) is 0 to 10%, the mass fraction of fluoroethylene carbonate (FEC) is 0 to 10%, the mass fraction of 1, 3-Propane Sultone (PS) is 0 to 10%, the mass fraction of vinyl sulfate (DTD) is 0 to 10%, the mass fraction of lithium salt is 0.1 to 50%, the solvent ratio is 50 to 99%, and the sum of the mass fractions of all components is 100%. And the physical property index of the nonaqueous electrolyte is in the following range:
conductivity (mS/cm) Density (g/cm3) Water content (ppm)
Characteristic value 8.3 1.213 5.2
Range 7.5-9.0 1.2-1.22 ≤15
Battery performance testing
Each of the obtained nonaqueous electrolyte secondary batteries was charged to 4.2V at 25 ℃ with a current corresponding to 0.33C, and then aged while being kept at 45 ℃ for 24 hours. Then, at 25 ℃, the discharge was carried out to 2.8V with a current corresponding to 0.33C. Then, the battery was charged to 4.2V with a current corresponding to 0.23C and further discharged to 2.8V with a current corresponding to 0.33C, and this operation was repeated for 3 cycles to perform initial charge and discharge, thereby stabilizing the battery. Then, initial charge and discharge were performed by charging and discharging at a current corresponding to 1C, and the discharge capacity was measured. The obtained value is set as "initial capacity". Further, after the initial charge and discharge, the ac impedance was measured at 25 ℃ for the nonaqueous electrolyte secondary battery charged with a capacity of 50% of the initial capacity, and the obtained value was referred to as "initial resistance (Ω)".
Measurement of discharge Capacity conservation Rate and resistance increase Rate
Each nonaqueous electrolyte secondary battery after initial charge and discharge was subjected to a charge-discharge cycle test, and 200 cycles were performed with a charge rate of 1C, a discharge rate of 1C, a charge termination voltage of 4.2V, and a discharge termination voltage of 2.8V. Then, the discharge capacity was measured by charging and discharging at 1C, and the obtained value was defined as "capacity after cycle". Further, after the cycle test, the ac impedance was measured in an environment at 25 ℃ for a nonaqueous electrolyte secondary battery charged to a capacity of 50% of the capacity after the cycle, and the obtained value was referred to as "resistance (Ω) after the cycle". "discharge capacity retention rate" is represented by the formula: a value calculated by (capacity after cycle)/(initial capacity), "resistance increase rate" is represented by the formula: (resistance after cycle)/(initial resistance).
Measurement of gas generation amount
Unlike the batteries used for the evaluation of initial resistance, the evaluation of discharge capacity retention rate, and the evaluation of resistance increase rate, nonaqueous electrolyte secondary batteries of the same composition including each electrolyte of examples and comparative examples were prepared. The nonaqueous electrolyte secondary battery was charged to 4.2V at 25 ℃ with a current corresponding to 0.33C, and then aged while being kept at 45 ℃ for 24 hours. Then, at 25 ℃, the discharge was carried out to 2.8V with a current corresponding to 0.33C. Then, the battery was charged to 4.2V with a current corresponding to 0.33C, and further discharged to 2.8V with a current corresponding to 0.33C, and this operation was repeated for 3 cycles to perform initial charge and discharge, thereby stabilizing the battery. The volume of the nonaqueous electrolyte secondary battery after initial charge and discharge was measured by the archimedes method, and the obtained value was defined as "initial volume (cm) of the battery3)". Further, the nonaqueous electrolyte secondary battery after initial charge and discharge was charged to 4.2V at 1C at 25 ℃ and then held at 60 ℃ for 168 hours. Then, it was cooled to 25 ℃ and discharged to 2.8V at 1C. Then, the volume of the nonaqueous electrolyte secondary battery was measured by the archimedes method, and the obtained value was defined as "the volume (cm) of the battery after storage at high temperature3)". The "gas generation amount" of each cell is shown. "gas generation amount" is represented by the formula: (volume after high-temperature storage) - (initial volume).
The main advantages of the invention are:
(1) the non-aqueous electrolyte has good chemical and electrochemical stability;
(2) the non-aqueous electrolyte has high discharge capacity maintenance rate, low resistance increase rate and remarkably reduced gas production.
The present invention will be described in further detail with reference to the following examples. It should be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the present invention. Experimental procedures in the following examples, where no detailed conditions are indicated, are generally carried out according to conventional conditions, or according to conditions recommended by the manufacturer. Unless otherwise indicated, percentages and parts are by weight. The test materials and reagents used in the following examples are commercially available without specific reference.
Example 1
Ethylene Carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of EC: DEC of 30:70 to obtain a mixed nonaqueous solvent.
LiPF is added to a concentration of 1.0mol/L6As an electrolyte, is dissolved in the mixed nonaqueous solvent.
The compound of formula I ', the compound of formula II', the ethylene carbonate compound (VC), fluoroethylene carbonate (FEC), and 1, 3-Propane Sultone (PS) were added to the obtained solution as additives for nonaqueous electrolytic solution to prepare a nonaqueous electrolytic solution. Based on the total weight of the nonaqueous electrolytic solution, the mass content of the compound of formula I is 1.0%, the mass content of the compound of formula I I is 0.5%, the mass content of the ethylene carbonate compound (VC) is 0.2%, the mass content of the fluoroethylene carbonate (FEC) is 1%, and the mass content of 1, 3-Propane Sultone (PS) is 1%.
The positive electrode active material is LiNi0.8Co0.1Mn0.1O2And the negative electrode material is artificial graphite for preparing the lithium ion battery.
In other examples and comparative examples, a nonaqueous electrolytic solution and a lithium ion battery were prepared in the same manner as in example 1, except that the additives used were different, as specifically shown in the following table 1:
TABLE 1
Figure BDA0002554725370000111
The test results of each example and comparative example are as follows:
TABLE 2
Figure BDA0002554725370000112
Figure BDA0002554725370000121
The detection results show that the compound shown in the formula I, the compound shown in the formula II, the ethylene carbonate compound (VC), the fluoroethylene carbonate (FEC) and the 1, 3-Propane Sultone (PS) are added simultaneously as additives in the non-aqueous electrolyte of the invention, so that an obvious synergistic effect is shown. The service life of the lithium ion battery using the non-aqueous electrolyte is remarkably prolonged, and the gas generation amount is greatly reduced.
Example 2 selection of solvent
The inventors have found in their studies that the addition of different types of additives to different solvents results in significantly different chemical and electrochemical stability of the battery system.
Thus, in the present invention, a large number of solvent and additive combinations were investigated and screened, and some of the screening results are as follows:
TABLE 3
Figure BDA0002554725370000122
Figure BDA0002554725370000131
The test results of each example and comparative example are as follows:
TABLE 4
Group of Discharge capacity maintenance rate (%) Rate of increase in resistance (%) Gas production (cm)3)
Group 1 92 1.2 0.15
Group 2 91 1.2 0.20
Group 3 91 1.2 0.36
Group 4 93 1.3 0.45
Group 5 88 1.3 0.48
Group 6 86 1.4 0.36
Group 7 87 1.2 0.43
Group 8 88 1.2 0.39
The test results show that the additive composed of the compound of formula I, the compound of formula II, the ethylene carbonate compound (VC), the fluoroethylene carbonate (FEC), and the 1, 3-Propane Sultone (PS), and the solvent combination composed of the Ethylene Carbonate (EC) and the diethyl carbonate (DEC) have the optimal electrochemical performance.
All documents referred to herein are incorporated by reference into this application as if each were individually incorporated by reference. Furthermore, it should be understood that various changes and modifications of the present invention can be made by those skilled in the art after reading the above teachings of the present invention, and these equivalents also fall within the scope of the present invention as defined by the appended claims.

Claims (7)

1. The non-aqueous electrolyte of the lithium ion battery is characterized by comprising a lithium salt, a non-aqueous solvent and an additive, wherein the additive consists of a first compound, a second compound, ethylene carbonate, fluoroethylene carbonate and 1, 3-propane sultone, the structure of the first compound is shown as a formula I, and the structure of the second compound is shown as a formula II:
Figure FDA0003325879580000011
wherein R is1、R2、R3、R4、R5、R6Each independently selected from: H. and C with or without substituents1-8An alkyl group;
the mass percentage content of the first compound is 1%; and the mass percentage content of the second compound is 0.5 percent;
the ethylene carbonate accounts for 0.2 percent by mass, the fluoroethylene carbonate accounts for 1 percent by mass, and the 1, 3-propane sultone accounts for 1 percent by mass;
the conductivity of the non-aqueous electrolyte of the lithium ion battery is 7.5-9.0 mS/cm; and/or
The density of the lithium ion battery nonaqueous electrolyte is 1.2-1.22g/cm 3; and/or
The water content of the lithium ion battery non-aqueous electrolyte is less than or equal to 15 ppm.
2. The nonaqueous electrolyte solution for lithium ion batteries according to claim 1, wherein C is1-8Alkyl is methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl or tert-butyl.
3. The nonaqueous electrolyte solution for lithium ion batteries according to claim 1, wherein the solvent in the nonaqueous electrolyte solution for lithium ion batteries comprises ethylene carbonate and diethyl carbonate.
4. The nonaqueous electrolyte solution for lithium ion batteries according to claim 1, wherein the lithium salt in the nonaqueous electrolyte solution for lithium ion batteries is LiPF6。
5. The nonaqueous electrolyte for lithium ion batteries according to claim 3, wherein the mass ratio of Ethylene Carbonate (EC) to diethyl carbonate (DEC) in the solvent is 20-50: 50-100.
6. The nonaqueous electrolyte solution for lithium ion batteries according to claim 4, wherein the concentration of the lithium salt in the nonaqueous electrolyte solution for lithium ion batteries is 0.1 to 3 mol/L.
7. A lithium ion battery comprising a positive electrode, a negative electrode, a separator and the electrolyte of any one of claims 1-6, the separator being configured to separate the positive electrode and the negative electrode.
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