CN102832408B - Electrolyte with high flame retardation performance and electrochemical performance and lithium ion battery - Google Patents

Abstract

The invention discloses an electrolyte solution for a lithium ion battery with high flame retardancy and electrochemical performance. The electrolyte contains a solvent, a lithium salt, a flame retardant and an additive, and the additive is a halogenated organic compound containing unsaturated one or more of cyclic carbonate compounds containing unsaturated bonds or asymmetric chain carbonate compounds containing unsaturated bonds, the amount of lithium salt is 0.6-1.5mol/L, and the amount of 1-70% of the total mass of the electrolyte, and the amount of the additive accounts for 0.1-15% of the total mass of the electrolyte. In the present invention, by adding a flame retardant to the electrolyte solution for lithium-ion batteries, and adding an additive capable of inhibiting the degradation of the electrochemical performance of the electrolyte solution by the flame retardant, the electrolyte solution has flame retardancy or non-combustibility, improving the safety of the battery, and The influence of the flame retardant on the electrochemical performance of the battery is overcome, and the performance of the battery is excellent.

Description

Electrolyte and lithium-ion battery with high flame retardancy and electrochemical performance

technical field

The invention relates to the technical field of lithium ion batteries, in particular to an electrolyte with high flame retardancy and electrochemical performance and a lithium ion battery using the electrolyte.

Background technique

Due to the advantages of high energy density, high output voltage, long cycle life, and low environmental pollution, lithium-ion batteries have extremely important applications in the fields of electronic products, electric vehicles, aerospace, and energy storage. However, in recent years, there have been frequent reports of fires and even explosions caused by lithium-ion batteries, and the safety of lithium-ion batteries has attracted widespread attention. At the same time, safety issues are also a bottleneck restricting the development of lithium-ion batteries in the direction of large-scale and high-energy.

The most important components of a lithium-ion battery are the positive and negative electrode materials and the electrolyte. The current lithium-ion battery electrolyte mainly uses organic carbonate compounds as solvents, and these solvents have very low flash points, which makes the electrolyte extremely flammable. When the battery is in a harsh environment or abused, it is easy to cause thermal runaway and cause an explosion and fire.

Adding flame retardants to the electrolyte is one of the important ways to reduce or solve battery fires. US patents US 6,589,697, US 6,924,061, and US 6,589,697 report adding flame retardants such as trimethyl phosphate (TMP), tributyl phosphate (TBP), triphenyl phosphate (TPP), and trifluoroethyl phosphate to the electrolyte , but these additives cannot be used alone as a solvent in large quantities due to their shortcomings such as high viscosity and high freezing point. Even when used as an additive in a small amount, the amount should be controlled within a certain limit. When its dosage is large, although it has a good flame retardant effect on the flame retardant performance of the electrolyte, it will cause a large negative impact on the electrochemical performance of the electrolyte; US Patent US 6,455,200 uses hexamethoxyphosphazene as the Liquid flame retardant, but its flame retardant efficiency is low; Chinese patents CN 101017917A, CN 101079504B and CN 101079505B use dimethyl methyl phosphate (DMMP) as a flame retardant or solvent. When the mass percentage of DMMP is greater than 10%, It can make the electrolyte non-flammable, but it will obviously deteriorate the electrochemical performance of the battery (such as rate performance, cycle performance, etc.).

None of the above reports take into account both the flame retardancy of the electrolyte and its damage to the electrochemical performance.

Contents of the invention

Based on this, the object of the present invention is to provide an electrolyte solution with high flame retardancy and electrochemical performance.

The specific technical scheme is as follows:

An electrolyte solution for a lithium-ion battery with high flame retardancy and electrochemical performance, the electrolyte contains a solvent, a lithium salt, a flame retardant and an additive, and the additive is a halogenated organic compound, a cyclic compound containing an unsaturated bond One or more of carbonate compounds or asymmetric chain carbonate compounds containing unsaturated bonds, the amount of the lithium salt is 0.6-1.5mol/L, and the amount of the flame retardant accounts for the total mass of the electrolyte 1-70% of the total mass of the electrolyte, and the amount of the additive accounts for 0.1-15% of the total mass of the electrolyte.

In some of these embodiments, the halogenated organic compound is selected from the following compounds:

(a) A fluorine-substituted cyclic carbonate having the following general formula (1):

Formula 1)

Among them, R ₁ , R ₂ , R ₃ , and R ₄ are selected from H, Cl, C1-C3 alkyl or fluorine-containing alkyl, and the following conditions are met at the same time: R ₁ and R ₂ are not simultaneously alkyl or fluorine-containing Alkyl group; R ₃ and R ₄ are not both alkyl groups or fluorine-containing alkyl groups; at least one of R ₁ , R ₂ , R ₃ , and R ₄ is a fluorine-containing alkyl group;

(b) A linear carbonate containing a fluoroether bond with the following general formula (2) or (3)

Formula (2)

Wherein, R ₅ and R ₆ are C1-C7 alkyl groups or C1-C7 fluorine-containing ether groups, and at least one of R ₅ and R ₆ is C1-C7 fluorine-containing ether groups;

Formula (3)

Wherein, _Rf is a C1~C7 fluorine-containing ether group in which at least one H atom on the terminal carbon atom is replaced by F, and _R7 is a C1~C7 alkyl group;

(c) a fluorine-substituted linear carboxylate having the following general formula (4):

Formula (4)

Among them, R ₈ is a C1-C7 alkyl group with at least one H atom on the terminal carbon atom replaced by F; R ₉ is a C1-C7 alkyl group;

(d) Halogenated lactones having the following general formula (5):

Formula (5)

Wherein, R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ , R ₁₄ , and R ₁₅ are respectively selected from H, F, C1-C7 fluorine-containing alkyl groups or C6-C12 fluorine-containing aromatic groups, 0≤m≤8, and R ₁₀ , R ₁₁ , R ₁₂ , R ₁₃ , R ₁₄ , and R ₁₅ are not all H;

(e) Fluorine-substituted ether compounds having the following general formula (6):

R ₁₆ -OR ₁₇ formula (6)

Among them, R ₁₆ and R ₁₇ are C1-C7 alkyl or C1-C7 fluorine-containing alkyl, and at least one of them is C1-C7 fluorine-containing alkyl;

(f) Fluorine-substituted sulfone compounds having the following general formula (7):

Formula (7)

Wherein, _R18 is a C1-C7 fluorine-containing alkyl group, a C2-C7 fluorine-containing alkenyl group, a C2-C7 fluorine-containing ether group or a C6-C9 fluorine-containing aromatic group.

In some of these embodiments, the general formula of the unsaturated bond-containing cyclic carbonate compound is (8) or (9)

Formula (8)

Among them, R ₁₉ , R ₂₀ , R ₂₁ , and R ₂₂ are respectively selected from H, F, C1-C7 fluorine-containing alkyl groups, C2-C7 fluorine-containing alkenyl groups, and R ₁₉ and R ₂₀ are not simultaneously fluorine-containing alkyl groups or Fluorine-containing alkenyl, R ₂₁ and R ₂₂ are not simultaneously fluorine-containing alkyl or fluorine-containing alkenyl, and only one of R ₁₉ , R ₂₀ , R ₂₁ , and R ₂₂ is a fluorine-containing alkenyl;

Formula (9)

Wherein, R ₂₃ and R ₂₄ are selected from H, F, C1-C5 alkyl or C2-C5 alkenyl, and both are not H.

In some of these embodiments, the asymmetric chain carbonate compound containing unsaturated bonds has the general formula (10)

Formula (10)

Among them, R ₂₅ is different from R ₂₆ , and R ₂₅ is selected from: C1-C7 fluorine-containing alkyl or C 3-C7 fluorine-containing alkenyl; R ₂₆ is selected from: C1-C7 fluorine-containing alkyl or general formula (11) represented group.

Formula (11)

Among them, 0≤p≤5.

In some of these embodiments, the additives are: difluoropropylene carbonate, difluoroethylene carbonate, methyl monofluoroacetate, ethyl trifluoroacetate, ethyl monofluoroacetate, 3,3, Ethyl 3-trifluoropropionate, 4-fluoromethyl butyl ether, 4,5 dimethyl vinylene carbonate, phenyl vinylene carbonate, 4,5-diphenyl vinylene carbonate, difluoro Propylene carbonate, difluoroethylene carbonate, methyl monofluoroacetate, ethyl trifluoroacetate, ethyl monofluoroacetate, ethyl 3,3,3-trifluoropropionate, 4-fluoromethyl Butyl ether, 4,5-dimethyl vinylene carbonate, phenyl vinylene carbonate or 4,5-diphenyl vinylene carbonate.

In some of these embodiments, the flame retardant is used in an amount of 3-50% of the total mass of the electrolyte.

In some of these embodiments, the flame retardant is selected from trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, trioctyl phosphate, dimethyl cyanomethyl phosphate, cyanomethyl Diethyl phosphate, dipropyl cyanomethyl phosphate, dibutyl cyanomethyl phosphate, tricresyl phosphate, diethyl vinyl phosphate, dimethyl phthalic diimide methyl phosphate, phthalic diimide methyl diethyl phosphonate, dimethyl methyl phosphonate, diethyl methyl phosphonate, ethyl methyl phosphonate, diethyl ethyl phosphonate, dimethyl ethyl phosphonate, ethyl phosphonic acid Methyl ethyl ester, diethyl (cyanomethyl) phosphonate, trimethyl phosphite, methyl phenyl methyl phosphonate, ethyl phenyl methyl phosphonate, methyl ethyl phosphonate Phenyl ester, ethyl phenyl ethyl phosphonate, methyl phenyl butyl phosphonate, ethyl phenyl butyl phosphonate, methyl diphenyl phosphonate, diphenyl cresyl phosphonate, phosphoric acid Tributyl, dimethyl phenyl phosphonate, dimethyl benzyl phosphonate, diphenyloctyl phosphate, tris (2-chloroethyl) phosphate, tris (2-chloropropyl) phosphate, tris - one or more of (2,2,2-trifluoroethyl)phosphite, tris(fluorooxyethyl)phosphate or difluorophosphate compounds represented by formula (12),

Formula (12)

Among them, R ₂₇ is a C1-C7 fluorine-containing alkyl group, a C2-C8 fluorine-containing alkenyl group, or a C6-C12 fluorine-containing aromatic group.

In some of these embodiments, the solvent is one or more of carbonates, carboxylates, ethers, fluorocarbonates, fluorocarboxylates, and fluoroethers.

In some of these embodiments, the lithium salt is one of LiPF ₆ , LiBF ₄ , LiBOB, LiODFB, LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) ₂ or Several kinds.

Another object of the present invention is to provide the application of the above electrolytic solution.

The specific technical scheme is as follows:

Application of the electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance in lithium ion batteries.

Another object of the present invention is to provide a lithium ion battery.

The specific technical scheme is as follows:

A lithium ion battery using the above electrolyte with high flame retardancy and electrochemical performance.

The advantages of the present invention and the positive effects brought by it: by adding a flame retardant in the electrolyte for lithium ion batteries, and adding an additive or additive composition that can inhibit the flame retardant from deteriorating the electrochemical performance of the electrolyte (the additive is: halogen One or any combination of organic compounds, cyclic carbonate compounds containing unsaturated bonds, and asymmetric chain carbonate compounds containing unsaturated bonds), which makes the electrolyte flame-retardant or non-flammable, and improves the battery life. Safety, and overcome the influence of flame retardants on the electrochemical performance of the battery, so that the battery performance is excellent.

Generally, flame retardants have the characteristics of high viscosity, difficult to dissolve lithium salts, strong corrosion and destructiveness on the contact surface (such as SEI film, etc.) Low, battery performance is far from ideal. The anti-inferiority principle of the additive or additive composition that can inhibit the electrochemical performance of the electrolyte from being deteriorated by the flame retardant of the present invention is that these anti-inferior additives have at least one of the following advantages: 1) The viscosity is relatively low, and it is resistant to lithium salts. The dissolution and the solvation of lithium ions are strong, so the conductivity is high, which can make up for the negative impact of the decrease in conductivity caused by the addition of flame retardants; 2) It can form a dense and stable battery on the contact surface between the positive and negative electrodes of the battery and the electrolyte. The advanced SEI film is highly resistant to the damage of flame retardants, thus ensuring the stable performance of the battery.

Detailed ways

The present invention will be further elaborated below by specific examples.

Comparative example 1

Mix the solvent ethylene carbonate (EC) and diethyl carbonate (DEC) at a mass ratio of 1:2 (there are no special instructions below, all are mass ratios), and then dissolve 1mol/L LiPF ₆ in the mixed solvent, Shake well to obtain the electrolyte solution of Comparative Example 1. The whole process of electrolyte preparation was carried out in an argon atmosphere glove box (the same under the preparation environment).

Comparative example 2

Taking 1mol/L LiPF ₆ /(EC+DEC (1:2) as the standard electrolyte, add 10% (mass fraction, the same below) flame retardant dimethyl methylphosphonate to it. Comparative example 2 of electrolyte.

Comparative example 3

Taking 1mol/L LiPF ₆ /(EC+DEC (1:2) as the reference electrolyte, 5% difluoropropylene carbonate was added to it. The electrolyte of Comparative Example 3 was obtained.

Example 1

An electrolyte solution for lithium-ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte solution includes solvent (EC+DEC (1:2 mass ratio), lithium salt (Li PF ₆ ), resistor Flame agent and additive, the consumption of described lithium salt is 1mol/L, the consumption of described flame retardant methyl methyl phosphonate accounts for 10% of the total mass of electrolyte, the consumption of described additive difluoropropylene carbonate Accounting for 5% of the total mass of the electrolyte.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 2

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant Agent and additive, the consumption of described lithium salt is 1mol/L, the consumption of described flame retardant ethyl dimethyl phosphate accounts for 15% of the total mass of electrolyte, the consumption of described additive difluoroethylene carbonate accounts for 4% of the total mass of the electrolyte.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 3

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant agent and additives, the consumption of the lithium salt is 0.8mol/L, the consumption of the flame retardant tributyl phosphate accounts for 20% of the total mass of the electrolyte, and the consumption of the additive methyl monofluoroacetate accounts for 20% of the total mass of the electrolytic solution. 10% of the total mass of liquid.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 4

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant agent and additives, the amount of the lithium salt is 1mol/L, the amount of the flame retardant diethyl (cyanomethyl) phosphonate accounts for 5% of the total mass of the electrolyte, the additive trifluoroacetic acid The amount of ethyl ester accounts for 15% of the total mass of the electrolyte.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 5

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant agent and additives, the consumption of the lithium salt is 1mol/L, the consumption of the flame retardant diphenyl cresyl phosphonate accounts for 3% of the total mass of the electrolyte, and the consumption of the additive ethyl monofluoroacetate accounts for 3% of the total mass of the electrolytic solution. 4% of the total mass of liquid.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 6

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant agent and additives, the amount of the lithium salt is 1.2mol/L, the amount of the flame retardant dimethyl difluorophosphate accounts for 70% of the total mass of the electrolyte, the additive 3,3,3-trifluoropropane The amount of ethyl acetate accounts for 8% of the total mass of the electrolyte.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 7

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant agent and additives, the consumption of the lithium salt is 1mol/L, the consumption of the flame retardant tricresyl phosphate accounts for 12% of the total mass of the electrolyte, and the consumption of the additive 4-fluoromethyl butyl ether accounts for 1% of the total mass of the electrolyte. 15% of the total mass.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 8

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant agent and additives, the consumption of the lithium salt is 1mol/L, the consumption of the flame retardant vinyl diethyl phosphate accounts for 8% of the total mass of the electrolyte, and the additive 4,5 dimethyl vinylene carbonate The dosage accounts for 3% of the total mass of the electrolyte.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 9

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant agent and additives, the consumption of the lithium salt is 1mol/L, the consumption of the flame retardant tricresyl phosphate accounts for 7% of the total mass of the electrolyte, and the consumption of the additive phenyl vinylene carbonate accounts for the total mass of the electrolyte 6%.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 10

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant agent and additives, the amount of the lithium salt is 1mol/L, the amount of the flame retardant methyl ethyl phosphonate accounts for 10% of the total mass of the electrolyte, the additive 4,5-diphenyl carbonate The amount of vinyl ester accounts for 3% of the total mass of the electrolyte.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 11

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant agent and additives, the consumption of the lithium salt is 1mol/L, the consumption of the flame retardant trimethyl phosphite accounts for 9% of the total mass of the electrolyte, and the consumption of the additive difluoropropylene carbonate accounts for 9% of the total mass of the electrolyte. 12% of the total mass.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 12

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant Agent and additive, the consumption of described lithium salt is 1mol/L, and the consumption of described flame retardant methyl phenyl methyl phosphonate accounts for 16% of the total mass of electrolyte, the content of described additive difluoroethylene carbonate The dosage accounts for 11% of the total mass of the electrolyte.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 13

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant Agent and additive, the consumption of described lithium salt is 1mol/L, and the consumption of described flame retardant methyl phenyl methyl phosphonate accounts for 7% of the total mass of electrolyte, and the consumption of described additive methyl monofluoroacetate The dosage accounts for 8% of the total mass of the electrolyte.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 14

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant agent and additives, the amount of the lithium salt is 1mol/L, the amount of the flame retardant tris (2-chloroethyl) phosphate accounts for 14% of the total mass of the electrolyte, the additive ethyl trifluoroacetate The amount of the electrolyte accounts for 7% of the total mass of the electrolyte.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 15

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant agent and additives, the amount of the lithium salt is 1mol/L, the amount of the flame retardant tris(2-chloropropyl) phosphate accounts for 4% of the total mass of the electrolyte, and the additive monofluoroacetate ethyl The amount accounts for 4% of the total mass of the electrolyte.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 16

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant agent and additives, the amount of the lithium salt is 1mol/L, the amount of the flame retardant phosphorus tris (fluorooxyethyl) phosphate accounts for 8% of the total mass of the electrolyte, the additive 3,3,3- The amount of ethyl trifluoropropionate accounted for 6% of the total mass of the electrolyte.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 17

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant agent and additives, the consumption of the lithium salt is 1mol/L, the consumption of the flame retardant diethyl methylphosphonate accounts for 9% of the total mass of the electrolyte, the additive 4-fluoromethyl butyl ether The dosage accounts for 8% of the total mass of the electrolyte.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 18

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant Agent and additive, the consumption of described lithium salt is 1mol/L, the consumption of described flame retardant methyl ethyl phosphonate accounts for 4% of the total mass of electrolyte, and described additive 4,5 dimethyl vinylene carbonate The amount of ester accounts for 0.5% of the total mass of the electrolyte.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 19

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant agent and additive, the consumption of the lithium salt is 1mol/L, the consumption of the flame retardant triphenyl phosphate accounts for 5% of the total mass of the electrolyte, and the consumption of the additive phenyl vinylene carbonate accounts for the total mass of the electrolyte. 1% of mass.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Example 20

An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in this embodiment, the electrolyte contains solvent (EC+DEC (1:2 mass ratio), lithium salt (LiPF ₆ ), flame retardant Agent and additive, the consumption of described lithium salt is 1mol/L, and the consumption of described flame retardant ethyl phosphonic acid methyl phenyl ester accounts for 7% of the total mass of electrolyte, and described additive 4,5-diphenyl The amount of vinylene carbonate accounts for 0.5% of the total mass of the electrolyte.

Lithium-ion batteries were prepared using the above electrolytic solutions by conventional methods.

Comparative example and electrolyte evaluation method of the present invention are as follows:

Flame retardant performance evaluation

Defined according to the method specified in UL94HB, immerse non-combustible quartz fiber (glass fiber) in 1.0mL of electrolyte, prepare a 127mm×12.7mm test piece, ignite the test piece in the atmosphere, if the flame after ignition does not If it reaches the 25mm line of the device, and it is not confirmed that the falling objects from the net are ignited, it is defined as having flammability; if no ignition is found (flame length 0mm), it is defined as being non-combustible.

In the present invention, the self-extinguishing time (Self-extinguishing time, SET for short) is used to evaluate the flame retardancy of the electrolyte.

Self-extinguishing time test: weigh a glass wool ball with a diameter of 5mm, place it on a thin iron wire folded into an O shape, inject a certain quality of electrolyte into the glass wool with a syringe, and then ignite it quickly with an ignition device. Record the time from when the ignition device is removed to when the flame is automatically extinguished, and this time is the self-extinguishing time. The flame retardant properties of different electrolytes were compared based on the self-extinguishing time per unit mass of electrolyte.

How to measure electrical conductivity

The conductivity of the electrolyte at 25°C was measured using a conductivity meter (DDS-307A conductivity meter from Shanghai Leici).

Comparative example and the lithium-ion battery evaluation method of electrolyte assembly of the present invention are as follows:

Cycle Performance Evaluation

Charging procedure: 1C constant current charging to 4.2V, then constant voltage charging until the current is 0.02C, stop charging;

Discharge procedure: 1C constant current discharge to 2.75V;

After the charge and discharge cut off, both rest for 5 minutes, so cycle 800 cycles. Investigate the initial discharge capacity of the battery and the capacity retention rate of the battery after cycling.

Rate Performance Evaluation

Charge the battery with a charging current of 1C, and then discharge it with a discharge current of 1C-10C, and investigate the discharge capacity retention rate of the battery under different discharge rate conditions.

Safety Performance Evaluation

Battery 3C10V overcharge, short circuit, acupuncture and other safety test methods are carried out in accordance with industry standards.

The conductivity and self-extinguishing time of the comparative example and the electrolyte of the present invention are shown in Table 1 below, and the performance of the lithium-ion battery assembled by the comparative example and the electrolyte of the present invention is shown in Table 2 below. Compared with the electrolyte of Comparative Example 1, Comparative Example 2 Only flame retardant additives are added without adding additives that inhibit flame retardants from deteriorating the electrochemical performance of the electrolyte. Although the flame retardant effect is good, the conductivity of the electrolyte drops significantly, and the capacity, cycle, and rate of the assembled battery are significantly reduced. The various performances declined significantly or even destroyed; Comparative Example 3 did not add a flame retardant and only added an additive that could inhibit the flame retardant from deteriorating the electrochemical performance of the electrolyte, which had no negative impact on the electrical conductivity of the electrolyte and the related performance of the battery. However, the lack of flame retardancy cannot solve the safety of the battery; and the electrolytic solution of the present invention has very little conductivity drop, and has obvious flame retardancy or non-combustibility, and the battery assembled by it can meet the safety performance, and the capacity is exerted, There is almost no effect on performance such as cycle and magnification.

Table 1

Table 2

Note: The battery design capacity is 10000mAh

The above-mentioned embodiments only express several implementation modes of the present invention, and the description thereof is relatively specific and detailed, but should not be construed as limiting the patent scope of the present invention. It should be pointed out that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent for the present invention should be based on the appended claims.

Claims (5)

1. An electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance, characterized in that the electrolyte comprises solvent, lithium salt, flame retardant and additive, and the consumption of the lithium salt is 0.6 to 1.5 mol/L, the amount of the flame retardant accounts for 1 to 70% of the total mass of the electrolyte, and the amount of the additive accounts for 0.1 to 15% of the total mass of the electrolyte; the additive is selected from difluoropropylene carbonate, difluoropropylene Fluoroethylene carbonate, methyl monofluoroacetate, ethyl trifluoroacetate, ethyl monofluoroacetate, ethyl 3,3,3-trifluoropropionate, 4-fluoromethylbutyl ether one or several; The flame retardant is selected from diethyl vinyl phosphate, diethyl methyl phosphonate, ethyl methyl phosphonate, ethyl methyl ethyl phosphonate, diethyl (cyanomethyl) phosphonate , methyl phenyl methyl phosphonate, ethyl phenyl methyl phosphonate, methyl phenyl ethyl phosphonate, diphenyl cresyl phosphonate, dimethyl benzyl phosphonate, tri(phosphonate One or more of 2-chloroethyl) ester, tris (2-chloropropyl) phosphate, and tris (fluorooxyethyl) phosphate. 2. The electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance according to claim 1, wherein the amount of the flame retardant accounts for 3-50% of the total mass of the electrolyte. 3. The electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance according to claim 1, wherein the solvent is carbonate, carboxylate, ether, fluorocarbonate, fluorinated One or more of carboxylic acid esters and fluoroethers; the lithium salts are LiPF ₆ , LiBF ₄ , LiBOB, LiODFB, LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ , LiN(C ₂ F ₅ SO ₂ ) One or more of ₂ . 4. The application of the electrolyte solution for lithium ion batteries with high flame retardancy and electrochemical performance described in any one of claims 1 to 3 in lithium ion batteries. 5. A lithium-ion battery, characterized in that the electrolyte used in the lithium-ion battery is the electrolyte for lithium-ion batteries with high flame retardancy and electrochemical performance according to any one of claims 1 to 3.