CN103825048B - Lithium rechargeable battery and electrolyte thereof - Google Patents

Abstract

The invention provides a lithium ion secondary battery and its electrolytic solution. The electrolyte solution of the lithium ion secondary battery includes: a non-aqueous organic solvent; a lithium salt dissolved in the non-aqueous organic solvent; and an additive dissolved in the non-aqueous organic solvent. The additive includes a butenyl ester compound having a structure of formula I, formula II or formula III, and the mass of the butenyl ester compound is 0.5% to 3% of the total mass of the non-aqueous organic solvent, wherein R ₁ and R are independently selected from one of haloalkyl, haloalkenyl, halophenyl, _halobiphenyl , the halogen is F, Cl or Br, and the halo is monosubstituted, partially Replace or replace all. The lithium ion secondary battery of the present invention includes the electrolyte solution of the lithium ion secondary battery described above. The lithium ion secondary battery of the invention can effectively improve its initial discharge capacity and storage performance under high temperature and high voltage.

Description

Lithium-ion secondary battery and its electrolyte

technical field

The invention relates to the field of batteries, in particular to a lithium-ion secondary battery and its electrolyte.

Background technique

As notebook computers, mobile phones, handheld game consoles, tablet computers and other electronic mobile devices can achieve more and more functions, people's requirements for lithium-ion secondary batteries as their main driving energy are also getting higher and higher. The application technology of lithium-ion secondary batteries in electric vehicles, smart grids, etc. is also becoming more and more mature. Prolonging the service life of lithium-ion secondary batteries and improving their safety performance have become one of the hot research topics in the industry.

When we increase the energy density of the lithium-ion secondary battery, especially the voltage of the lithium-ion secondary battery, it is equivalent to increasing the activity of the electrochemical reaction of the electrolyte. At this time, the electrolyte will be violently oxidized on the positive and negative electrodes. The reduction reaction, accompanied by a large number of side reactions, will have a very negative impact on the performance of the lithium-ion secondary battery. In actual use, electronic products are also faced with continuous use of heat or an increase in the ambient temperature of the lithium-ion secondary battery, which may cause the lithium-ion secondary battery to be in a high temperature state, and at high temperature, the electrolyte will be subject to stricter conditions. In severe cases, due to the expansion and deformation of the lithium-ion secondary battery, a short circuit occurs inside the lithium-ion secondary battery or the packaging of the lithium-ion secondary battery bursts, resulting in the leakage of flammable electrolyte, causing fire and other safety accidents. Therefore, an effective technology is needed to solve the problems of electrolyte decomposition and flatulence of lithium-ion secondary batteries.

Contents of the invention

The object of the present invention is to provide a lithium ion secondary battery and its electrolyte, which can effectively improve the initial discharge capacity and storage performance of the lithium ion secondary battery under high temperature and high voltage.

In order to achieve the above object, in the first aspect of the present invention, the present invention provides an electrolyte solution for a lithium-ion secondary battery, comprising: a non-aqueous organic solvent; a lithium salt dissolved in a non-aqueous organic solvent; and an additive dissolved in in non-aqueous organic solvents. The additive includes a butenyl ester compound having a structure of formula I, formula II or formula III, and the mass of the butenyl ester compound is 0.5% to 3% of the total mass of the non-aqueous organic solvent, wherein R ₁ and R are independently selected from one of haloalkyl, haloalkenyl, halophenyl, _halobiphenyl , the halogen is F, Cl or Br, and the halo is monosubstituted, partially replace or fully replace,

In the second aspect of the present invention, the present invention provides a lithium ion secondary battery, comprising: a positive electrode sheet; a negative electrode sheet; a separator spaced between adjacent positive electrode sheets and negative electrode sheets; and an electrolyte. Wherein, the electrolyte is the electrolyte of the lithium ion secondary battery according to the first aspect of the present invention.

The beneficial effects of the present invention are as follows:

The lithium ion secondary battery and its electrolyte solution of the present invention have good initial discharge capacity and storage performance under high temperature and high voltage.

detailed description

The lithium ion secondary battery according to the present invention and its electrolyte, comparative examples and examples are described in detail below.

First, the electrolyte solution of the lithium ion secondary battery according to the first aspect of the present invention will be described.

The electrolyte solution of the lithium ion secondary battery according to the first aspect of the present invention includes: a non-aqueous organic solvent; a lithium salt dissolved in the non-aqueous organic solvent; and an additive dissolved in the non-aqueous organic solvent. The additive includes a butenyl ester compound having a structure of formula I, formula II or formula III, and the mass of the butenyl ester compound is 0.5% to 3% of the total mass of the non-aqueous organic solvent, wherein R ₁ and R are independently selected from one of haloalkyl, haloalkenyl, halophenyl, _halobiphenyl , the halogen is F, Cl or Br, and the halo is monosubstituted, partially Replace or replace all.

Due to the large molecular weight of the maleic ester compound, it has a great influence on the viscosity of the electrolyte. When the mass percentage of the maleic ester compound is less than 0.5%, a stable SEI film cannot be formed on the negative electrode. The impact on the high-temperature storage performance and initial discharge capacity of lithium-ion secondary batteries is not obvious; when the mass percentage of maleic esters is greater than 3%, the viscosity of the electrolyte increases, which affects the conductivity of lithium ions. The deintercalation speed of lithium ions is negatively affected, which deteriorates the first discharge capacity of the lithium ion secondary battery.

Compounds containing a double bond structure are usually easily reduced on the surface of the negative electrode and oxidized on the surface of the positive electrode, thereby electrochemically polymerizing to form a polymer passivation film, such as vinylene carbonate (VC) has a good negative electrode passivation effect, However, under the action of high pressure, due to its low oxidation potential, it will be oxidized and decomposed on the surface of the positive electrode, which makes the high-temperature storage performance of lithium-ion secondary batteries deteriorate significantly. For the maleic butene ester compound, the oxidation potential of the compound and the oxidation resistance of the positive electrode under high voltage are improved by introducing electron-withdrawing groups at both ends of the maleic butene. The structures of carbonate and sulfonate at both ends of the maleic butene molecule may participate in the formation of the SEI film when the negative electrode participates in the formation of chain-like alkyl lithium hemicarbonate or chain-like lithium hemisulfonate. Moreover, the double bond in the butene molecule ensures that it has similar film-forming efficiency to VC. In addition, this intramolecular butene structure can improve the initial discharge capacity of lithium-ion secondary batteries and achieve a film-forming effect similar to that of VC. Carbonate and sulfonate compounds themselves have high compatibility with the electrolyte system, and because the R1 and R2 substituents are electron _- withdrawing groups, the oxidation resistance of these _compounds can be greatly improved, and the halogen substitution The group, especially the fluorinated functional group, may also generate LiF at the negative electrode to participate in the formation of the SEI film, further increasing the stability of the film formation.

In the electrolyte solution of the lithium ion secondary battery according to the first aspect of the present invention, the mass of the maleic ester compound may be 1% to 2% of the total mass of the non-aqueous organic solvent.

In the electrolyte solution of the lithium-ion secondary battery according to the first aspect of the present invention, the maleic ester compound may be selected from one or more of structures C-1 to C-9.

In the electrolyte solution of the lithium ion secondary battery according to the first aspect of the present invention, the non-aqueous organic solvent can be ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate, diethyl carbonate ( DEC), Dipropyl Carbonate, Methyl Ethyl Carbonate (MEC), Methyl Propyl Carbonate, Methyl Formate, Ethyl Acetate, Methyl Butyrate, Methyl Acrylate, Dimethyl Sulfite, Diethyl Sulfite , anhydride, N-methylpyrrolidone, N-methylformamide, N-methylacetamide, acetonitrile, N,N-dimethylformamide, sulfolane, dimethylsulfoxide, methyl sulfide, γ-butyrol One or more of esters, tetrahydrofuran, fluorine-containing cyclic organic esters, sulfur-containing cyclic organic esters, and unsaturated bond-containing cyclic organic esters.

In the electrolyte solution of the lithium ion secondary battery according to the first aspect of the present invention, the additives may further include vinylene carbonate (VC), fluoroethylene carbonate, ethylene sulfite, propylene sulfite, 1, One or more of 3-propane sultone (PS).

In the electrolyte solution of the lithium ion secondary battery according to the first aspect of the present invention, the lithium salt may be LiPF ₆ , LiBF ₄ , LiBOB, LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , Li(CF ₃ SO ₂ ) One or more of ₂ N.

Next, a lithium ion secondary battery according to the second aspect of the present invention will be described.

The lithium ion secondary battery according to the second aspect of the present invention comprises: a positive electrode sheet; a negative electrode sheet; a separator spaced between adjacent positive electrode sheets and negative electrode sheets; and an electrolyte. The electrolyte is the electrolyte of the lithium ion secondary battery according to the first aspect of the present invention.

In the lithium ion secondary battery according to the second aspect of the present invention, the positive electrode sheet may include a positive electrode active material capable of deintercalating and intercalating lithium ions. The positive active material may be a lithium transition metal composite oxide. The lithium transition metal oxide can be selected from one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide kind.

In the lithium ion secondary battery according to the second aspect of the present invention, the negative electrode sheet may include a negative electrode active material capable of intercalating and deintercalating lithium ions. The negative electrode active material can be selected from one or more of soft carbon, hard carbon, artificial graphite, natural graphite, silicon, silicon oxide compound, silicon carbon composite, lithium titanate or metals capable of forming alloys with lithium.

Next, the lithium ion secondary battery according to the present invention and its electrolytic solution as well as examples and comparative examples will be described.

Comparative example 1

(1) Preparation of positive electrode sheets for lithium-ion secondary batteries

The active material lithium cobalt oxide, the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are fully stirred and mixed uniformly in the solvent N-methylpyrrolidone according to the mass ratio of 96:2:2, and then coated on The current collector is dried on Al foil and cold-pressed to obtain the positive electrode sheet of the lithium-ion secondary battery.

(2) Preparation of negative electrode sheet for lithium-ion secondary battery

The active material graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), thickener sodium carboxymethylcellulose (CMC) are fully stirred in the solvent deionized water according to the mass ratio of 95:2:2:1 After being mixed evenly, it is coated on the Cu foil of the current collector, dried, and cold-pressed to obtain the negative electrode sheet of the lithium ion secondary battery.

(3) Preparation of electrolyte solution for lithium ion secondary battery

Mix ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) at a mass ratio of 30:5:65 (as a non-aqueous organic solvent), and dissolve 1MLiPF ₆ lithium salt to obtain lithium ions Electrolyte for secondary batteries.

(4) Preparation of lithium-ion secondary battery

Stack the positive electrode sheet, the separator PE porous polymer film, and the negative electrode sheet in order, so that the PE porous polymer film is in the middle of the positive electrode sheet and the negative electrode sheet to play the role of isolation, and wind up to obtain a bare cell, and place the bare cell in the In the outer packaging, the prepared electrolyte solution is injected and packaged to obtain a lithium ion secondary battery.

Comparative example 2

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 2% vinylene carbonate (VC) in the total mass of water organic solvent.

Comparative example 3

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not Maleic lactone carbonate (C-10) with 2% of the total mass of the water organic solvent.

Comparative example 4

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not Propylene methyl carbonate (C-11) with 2% total mass of water organic solvent.

Comparative example 5

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 2% cis-butene-1,4-diacetate (C-12) of the total mass of the water-organic solvent.

Comparative example 6

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not Maleic acid ester (C-13) with 2% of the total mass of water organic solvent.

Comparative example 7

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 0.1% of C-2 in the total mass of water organic solvent.

Comparative example 8

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 4% of C-2 in the total mass of water organic solvent.

Comparative example 9

(1) Preparation of positive electrode sheets for lithium-ion secondary batteries

The active material LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , the conductive agent acetylene black, and the binder polyvinylidene fluoride (PVDF) are fully stirred in the solvent N-methylpyrrolidone at a mass ratio of 96:2:2 and mixed evenly Finally, it is coated on the current collector Al foil, dried, and cold-pressed to obtain the positive electrode sheet of the lithium ion secondary battery.

(2) Preparation of negative electrode sheet for lithium-ion secondary battery

The active material graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), thickener sodium carboxymethylcellulose (CMC) are fully stirred in the solvent deionized water according to the mass ratio of 95:2:2:1 After being mixed evenly, it is coated on the Cu foil of the current collector, dried, and cold-pressed to obtain the negative electrode sheet of the lithium ion secondary battery.

(3) Preparation of electrolyte solution for lithium ion secondary battery

Mix ethylene carbonate (EC), methyl ethyl carbonate (MEC), and diethyl carbonate (DEC) at a mass ratio of 30:35:35 (as a non-aqueous organic solvent), and dissolve 0.95MLiPF ₆ and 0.05MLiBF ₄ Lithium salt, to obtain the electrolyte solution of the lithium ion secondary battery.

(4) Preparation of lithium-ion secondary battery

Stack the positive electrode sheet, the separator PE porous polymer film, and the negative electrode sheet in order, so that the PE porous polymer film is in the middle of the positive electrode sheet and the negative electrode sheet to play the role of isolation, and wind up to obtain a bare cell, and place the bare cell The prepared electrolyte solution is injected into the outer package and packaged to obtain a lithium ion secondary battery.

Example 1

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not The total mass of water organic solvent is 0.5% of C-2.

Example 2

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 1% of C-2 in the total mass of water organic solvent.

Example 3

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 2% of C-2 in the total mass of water organic solvent.

Example 4

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not The total mass of water organic solvent is 3% of C-2.

Example 5

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 2% of C-1 in the total mass of water organic solvent.

Example 6

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 2% of C-3 in the total mass of water organic solvent.

Example 7

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 0.5% of C-1 in the total mass of water organic solvent.

Example 8

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not The total mass of water organic solvent is 1.0% of C-1.

Example 9

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not The total mass of water organic solvent is 3.0% of C-1.

Example 10

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not The total mass of water organic solvent is 1.0% of C-3.

Example 11

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 2% of C-4 in the total mass of water organic solvent.

Example 12

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 2% C-5 in the total mass of water organic solvent.

Example 13

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 1% C-5 in the total mass of water organic solvent.

Example 14

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 0.5% of C-5 in the total mass of water organic solvent.

Example 15

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 2% C-6 in the total mass of water organic solvent.

Example 16

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 1% C-6 in the total mass of water organic solvent.

Example 17

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 1% of C-7 in the total mass of water organic solvent.

Example 18

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 2% of C-8 in the total mass of water organic solvent.

Example 19

The lithium-ion secondary battery was prepared according to the method of Comparative Example 1, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 1% C-9 in the total mass of water organic solvent.

Example 20

A lithium-ion secondary battery was prepared according to the method of Comparative Example 9, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), an additive was added to the electrolyte solution, and the additive was 0.5% by mass. % of C-3.

Example 21

A lithium-ion secondary battery was prepared according to the method of Comparative Example 9, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie step (3)), the lithium salt was 0.95MLiPF ₆ and 0.05MLi(CF ₃ SO2) ₂ N (LiTFSI), an additive is added to the electrolyte, and the additive is C-3 with a mass percentage of 0.5% of the total mass of the non-aqueous organic solvent.

Example 22

The lithium-ion secondary battery was prepared according to the method of Comparative Example 9, except that in the preparation of the electrolyte solution of the lithium-ion secondary battery (ie, step (3)), additives were added to the electrolyte solution, and the additives were not 0.5% of the total mass of the water organic solvent and 0.5% of the mass percentage of C-3 in the total mass of the non-aqueous organic solvent are 1,3-propane sultone (PS).

Finally, the test process and test results of the lithium ion secondary battery of the present invention will be described.

(1) Relative first discharge capacity test

Under the condition of 45°C, first charge the lithium-ion secondary battery to 4.4V with a constant current of 0.7C, and then charge it at a constant voltage of 4.4V until the current is less than 0.05C, and then charge the lithium-ion secondary battery with a constant current of 0.5C The battery is discharged to 3.0V. Record the discharge capacity of this time as the first discharge capacity (T) of the lithium-ion secondary battery, and use the first discharge capacity (T ₀ ) of Comparative Example 1 as a reference to obtain the results of Examples 1-19 and Comparative Examples 1-9 Relative initial discharge capacity r=T/T ₀ ; taking the initial discharge capacity (T ₀ ) of Comparative Example 9 as a reference, the relative initial discharge capacity r=T/T ₀ of Examples 20-22 and Comparative Example 9 was obtained.

(2) High temperature storage test

Each lithium-ion secondary battery is charged at a constant current of 0.5C at room temperature to a voltage higher than 4.4V, and further charged at a constant voltage of 4.4V to a current lower than 0.05C, so that it is in a fully charged state of 4.4V. Test the thickness of the fully charged lithium-ion secondary battery before storage and record it as D ₀ , then place the fully charged lithium-ion secondary battery in an oven at 60°C. After 14 days, take out the lithium-ion secondary battery and test it immediately Its thickness after storage is denoted as D ₁ . Thickness expansion rate ε=(D ₁ -D ₀ )/D ₀ ×100% of lithium-ion secondary battery before and after storage

Table 1 shows the relevant parameters and test results of the lithium ion secondary batteries of Comparative Examples 1-9 and Examples 1-22.

(1) Analysis of relative initial discharge capacity test results

From the comparison of Comparative Example 1 and Examples 1-22, it can be seen that the carbonate and sulfonate compounds of maleic butene have an improving effect on the relative initial discharge capacity of the lithium-ion secondary battery, which may be due to the The combination of the double bond of the butene structure in the molecule and the carbonate and/or sulfonate functional group can form a better SEI film on the surface of the negative electrode, and consume less lithium ions in the process, thus improving the lithium ion density. The relative initial discharge capacity of the secondary battery.

From the comparison of Comparative Examples 2-5, it can be seen that the relative initial discharge capacity of the lithium-ion secondary battery is poor with the addition of non-maleic carbonate and sulfonate compounds. This is because the oxidation potential of VC in Comparative Example 2 is low, and the effect of improving the relative initial discharge capacity of the lithium-ion secondary battery is not obvious; High, consumes a lot of lithium ions, which may be related to its large ring structure; the "bare" double bond structure in methyl propylene carbonate (C-11) in Comparative Example 4 cannot form a good SEI film , which has a large film-forming resistance and a low oxidation potential, which will deteriorate the relative initial discharge capacity of the lithium-ion secondary battery; in comparative example 5, maleic-1,4-diacetate (C-12) is easier to The surface of the positive electrode is oxidized, and the film-forming effect on the surface of the negative electrode is not particularly good, which easily deteriorates the performance of the lithium-ion secondary battery.

In comparative example 6, although maleic dimesylate (C-13) is a sulfonic ester compound of maleic acid, its substituent is an alkyl group, and the relative initial discharge capacity of the lithium-ion secondary battery has not been significantly improved. improve. However, the carbonate and sulfonate compounds of maleic butene in Examples 1-22 significantly improved the relative initial discharge capacity of the lithium-ion secondary battery. This may be due to the fact that the halogen-containing R ₁ and R ₂ functional groups in the maleic ester compounds with formula I, formula II or formula III can participate in the film-forming process during the first charge and discharge process, especially the fluorine-containing R The ₁ and R ₂ functional groups can generate LiF and form a stable SEI film, which improves the stability and efficiency of film formation, thereby improving the relative initial discharge capacity of Li-ion secondary batteries.

As can be seen from the comparison of Comparative Examples 7-8 and Examples 1-4, when the mass percentage of C-2 was less than 0.5%, the relative initial discharge capacity of the lithium-ion secondary battery did not change; As the mass percentage of 2 continues to increase, the relative initial discharge capacity of the lithium-ion secondary battery also increases; when the mass percentage of C-2 exceeds 3%, the relative initial discharge capacity of the lithium-ion secondary battery begins to decline. This is because when the mass percentage content of C-2 is too high, it will increase its impedance at the time of negative electrode film formation, and then affect the relative initial discharge capacity of the lithium-ion secondary battery; and when the mass percentage content of C-2 The influence of too small a value on the relative initial discharge capacity of the lithium-ion secondary battery is not obvious. Likewise, the same trend can also be seen from the comparison between Example 5 and Examples 7-9.

From the comparison of Example 6, Example 11 and Example 12, it can be seen that the chain length of the substituent increases, and the relative initial discharge capacity of the lithium-ion secondary battery decreases, which may be due to the increase in the chain length leading to the electrolyte solution Viscosity increases and the formed SEI film structure is not stable enough, thereby affecting the relative initial discharge capacity of lithium-ion secondary batteries.

From the comparison of Example 2, Example 8 and Example 10, it can be seen that the relative initial discharge capacity of the butene ester compound with the structure of formula II is higher than that of the butene ester compound with the structure of formula I and formula III Both are poor, that is, the relative initial discharge capacity of the butene ester compound with at least one carbonate is better than that of the butene ester compound (formula II) with sulfonate esters at both ends, which may be related to the butene structure and The impedance of the SEI film formed by the combination of carbonate is related to the lower resistance. The compound with sulfonate structure will generally be reduced to form a film on the negative electrode before the compound with carbonate structure, and the film-forming activity is higher, so the film-forming resistance may be larger. , thus negatively affecting the relative initial discharge capacity of the lithium-ion secondary battery. Comparative Example 3, Example 5 and Example 6, Comparative Example 1 and Example 7, Comparative Example 4 and Example 9, also find the same trend, that is, the butene ester compound with at least one carbonate It is better than the relative initial discharge capacity of the butene ester compound (formula II) with sulfonate at both ends.

From the comparison of Comparative Example 9 and Examples 20-22, it can be seen that when the electrolyte contains dilithium salts and the maleic esters of carbonates and sulfonates, than using dilithium salts alone (comparative example 9) The relative initial discharge capacity of the lithium-ion secondary battery is higher, which is because one of the lithium salts LiBF ₄ or LiTFSI as an additive can have a synergistic effect with the butene ester compound, so the relative capacity of the lithium-ion secondary battery The first discharge capacity should be high.

(2) Analysis of high temperature storage test results

As can be seen from the comparison of Comparative Example 1 and Examples 1-22, the carbonate and sulfonate compounds of maleic acid have obvious improvement on the high-temperature thickness expansion rate of lithium-ion secondary batteries, which may be due to the The combination of the double bond of the butene-like structure in the molecule and the carbonate and/or sulfonate functional groups can form a stable SEI film on the surface of the negative electrode, and the halogen _- containing R1 and R2 functional groups can participate in the film _- forming process and consolidate the SEI The stability of the membrane can isolate the further reaction of the electrolyte; in addition, the oxidation resistance of the maleic ester compound with electron-withdrawing groups on both sides is further improved, thereby improving the high-temperature storage performance of the lithium-ion secondary battery.

From the comparison of Comparative Examples 2-5, it can be seen that with the addition of non-maleic ester carbonate and sulfonate compounds, the high-temperature thickness expansion rate of the lithium-ion secondary battery is high, and the high-temperature storage performance is poor. This is due to the low oxidation potential of VC in Comparative Example 2, which will deteriorate the storage performance of lithium-ion secondary batteries under high temperature and high pressure; maleic lactone carbonate (C-10) in Comparative Example 3 also has a lower oxidation potential. Potential, and can not form a good SEI film on the surface of the negative electrode, the deterioration of the high-temperature storage performance of the lithium-ion secondary battery is also more obvious. The "bare" double bond structure in methyl propylene carbonate (C-11) in Comparative Example 4 cannot form a good SEI film, and its film-forming resistance is large and its oxidation potential is low, which is not suitable for the high temperature of lithium-ion secondary batteries. There is no improvement in storage performance; in Comparative Example 5, maleic-1,4-diacetate (C-12) is easier to oxidize on the surface of the positive electrode, and the film-forming performance on the surface of the negative electrode is not particularly good, and it is easy to deteriorate lithium High-temperature storage performance of ion secondary batteries.

In Comparative Example 6, although the maleic acid ester (C-13) is a sulfonic ester compound of maleic acid, its substituent is an alkyl group, and the thickness expansion rate of the lithium-ion secondary battery has an absorption capacity compared with other materials. Lithium-ion secondary batteries with electron group substituent structures have a high thickness expansion rate and poor high-temperature storage performance. This is because when the maleic ester compound contains an electron-withdrawing group, its oxidation resistance is further improved, especially when the substituent is a fluorinated functional group, which can form LiF on the surface of the negative electrode to form a stable The SEI film prevents the further reduction of the electrolyte, and its relatively high oxidation potential improves the oxidation resistance on the surface of the positive electrode, thereby improving the high-temperature storage performance of the lithium-ion secondary battery.

As can be seen from the comparison of Comparative Examples 7-8 and Examples 1-4, when the mass percentage of C-2 was 0.1%, the high-temperature thickness expansion rate of the lithium-ion secondary battery was higher, reaching 50.8%; When the mass percentage of C-2 reaches 0.5%, the high-temperature thickness expansion rate of the lithium-ion secondary battery is significantly improved, which is reduced to 30.2%; as the mass percentage of C-2 continues to increase, the lithium-ion secondary battery The high-temperature thickness expansion rate of ion secondary batteries decreases continuously; when the mass percentage of C-2 exceeds 3%, the high-temperature thickness expansion rate of lithium-ion secondary batteries begins to increase again. This is because when the mass percentage of C-2 is too high, its impedance at the time of negative electrode film formation will increase, and the viscosity of the electrolyte will also increase significantly. Although the high-temperature storage performance of lithium ion secondary batteries is still There is improvement, but it will obviously affect other properties of lithium-ion secondary batteries; when the mass percentage of C-2 is too small, there are fewer components involved in film formation, and the stability of film formation cannot be significantly improved, so it cannot be effectively improved High-temperature storage performance of lithium-ion secondary batteries. Likewise, the same trend can also be seen from the comparison between Example 5 and Examples 7-9.

From the comparison of Example 6, Example 11 and Example 12, it can be seen that changing the chain length of the substituent has a great influence on the high-temperature thickness expansion rate of the lithium-ion secondary battery. With the increase of the chain length of the substituent, lithium The high-temperature thickness expansion rate of the ion secondary battery increases, and the high-temperature storage performance deteriorates, so the chain length of the substituent should not be too long. This may be due to the fact that the structure of the protective film formed by the long-chain substituents is not stable enough to effectively protect the electrolyte from decomposing due to side reactions on the positive and negative electrodes, resulting in increased gas production. Therefore, high-temperature storage of lithium-ion secondary batteries Performance deteriorates.

From the comparison of Example 2, Example 8 and Example 10, it can be seen that the butene ester compounds with the structure of formula I and formula III are more than the lithium ion of the butene ester compound with the structure of formula II. The high-temperature thickness expansion rate of the secondary battery is better, that is, the high-temperature storage performance of the maleic ester compound with at least one carbonate is better than that of the maleic ester compound with sulfonate at both ends, which may be due to the The structure of butene can produce a synergistic effect, forming a stable SEI film without causing large film resistance; in addition, compared with sulfonate, carbonate is less sensitive to the pH of the chemical system. Comparative Example 3, Example 5 and Example 6, Comparative Example 1 and Example 7, Comparative Example 4 and Example 9 also all find the same trend, that is, there is at least one maleic acid ester of carbonate The high-temperature storage performance of the compound is better than that of the butene ester compound (formula II) whose both ends are sulfonate esters.

From the comparison of Comparative Example 9 and Examples 20-22, it can be seen that when the electrolyte contains dilithium salts and the maleic esters of carbonates and sulfonates, than using dilithium salts alone (comparative example 9) The high-temperature thickness expansion rate of the lithium-ion secondary battery is better, because one of the lithium salts LiBF ₄ or LiTFSI as an additive can have a synergistic effect with the butene ester compound, thus improving the lithium-ion secondary battery. High temperature storage performance.

As mentioned above, add 0.5% to 3% of non-aqueous organic solvents, especially 1% to 2% of cis-organic solvents with the structure of formula I, formula II or formula III in the electrolyte solution of lithium ion secondary batteries. Butylene ester compounds, lithium-ion secondary batteries have good initial discharge capacity and storage performance under high temperature and high pressure.

Relevant parameters and test results of Table 1 Comparative Examples 1-9 and Embodiment 1-22

Claims (10)

1. an electrolyte for lithium rechargeable battery, comprising:

Non-aqueous organic solvent;

Lithium salts, is dissolved in non-aqueous organic solvent; And

Additive, is dissolved in non-aqueous organic solvent;

It is characterized in that,

Described additive comprises the maleic ester compounds with formula I, formula II or formula III structure, described suitableButene esters compound quality is 0.5%～3% of described non-aqueous organic solvent gross mass, wherein, and R₁And R₂Respectively independently selected from the one in haloalkyl, haloalkene alkyl, halogenophenyl, halogenated biphenyl base,Described halogen is F, Cl or Br, and described halo is monosubstituted, partly replacement or replacement entirely,

2. the electrolyte of lithium rechargeable battery according to claim 1, is characterized in that, described inMaleic ester compounds quality is 1%～2% of described non-aqueous organic solvent gross mass.

3. the electrolyte of lithium rechargeable battery according to claim 1, is characterized in that, described inMaleic ester compounds is selected from one or more in C-1 to C-9 structure,

4. the electrolyte of lithium rechargeable battery according to claim 1, is characterized in that, described inNon-aqueous organic solvent is ethylene carbonate, propene carbonate, dimethyl carbonate, diethyl carbonate, carbonic acidDipropyl, methyl ethyl carbonate, methyl propyl carbonate, methyl formate, ethyl acetate, methyl butyrate, propyleneAcid methyl esters, dimethyl sulfite, diethyl sulfite, 1-METHYLPYRROLIDONE, N-METHYLFORMAMIDE,N-methylacetamide, acetonitrile, DMF, sulfolane, methyl-sulfoxide, methyl sulfide, γ-One or more in butyrolactone, oxolane.

5. the electrolyte of lithium rechargeable battery according to claim 1, is characterized in that, described inAdditive also comprises vinylene carbonate, fluorinated ethylene carbonate, ethene sulfite, propylene sulfurous acidOne or more in ester, PS.

6. the electrolyte of lithium rechargeable battery according to claim 1, is characterized in that, described inLithium salts is LiPF₆、LiBF₄、LiBOB、LiClO₄、LiAsF₆、LiCF₃SO₃、Li(CF₃SO₂)₂NIn one or more.

7. a lithium rechargeable battery, comprising:

Positive plate;

Negative plate;

Barrier film, is interval between adjacent positive sheet and negative plate; And

Electrolyte;

It is characterized in that,

Described electrolyte is according to the electrolysis of the lithium rechargeable battery described in any one in claim 1-6Liquid.

8. lithium rechargeable battery according to claim 7, is characterized in that, described positive plate bagContaining positive electrode active materials, described positive electrode active materials is lithium-transition metal composite oxide.

9. lithium rechargeable battery according to claim 8, is characterized in that, described lithium transition goldBelong to composite oxides be selected from lithium and cobalt oxides, lithium nickel oxide, lithium manganese oxide, Li, Ni, Mn oxide,One or more in lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide.

10. lithium rechargeable battery according to claim 7, is characterized in that, described negative plate bagDraw together negative active core-shell material, described negative active core-shell material be selected from soft carbon, hard carbon, Delanium, native graphite,Silicon, silicon oxide compound, silicon-carbon compound, lithium titanate or can with lithium form a kind of in the metal of alloy orSeveral.