WO2018120792A1

WO2018120792A1 - Electrolyte and secondary battery

Info

Publication number: WO2018120792A1
Application number: PCT/CN2017/093862
Authority: WO
Inventors: 王小梅; 周晓崇; 付成华
Original assignee: 宁德时代新能源科技股份有限公司
Priority date: 2016-12-26
Filing date: 2017-07-21
Publication date: 2018-07-05
Also published as: CN108242557A; CN108242557B

Abstract

An electrolyte and a secondary battery. The electrolyte comprises an electrolyte salt, an organic solvent and an additive. The additive comprises: silyl sulfate and cyclic sulfate and/or cyclic sulfonate. After the electrolyte is applied to the secondary battery, the secondary battery may have a low internal resistance, a good low-temperature discharge performance, a good high-temperature storage performance and a high-temperature cycle performance under the synergistic action of the described substances.

Description

Electrolyte and secondary battery

Technical field

The present invention relates to the field of battery technologies, and in particular, to an electrolyte and a secondary battery.

Background technique

In the rapidly developing information age, the demand for electronic products such as mobile phones, notebooks, and cameras has increased year by year. Secondary batteries, especially lithium ion secondary batteries, are the working power source for electronic products. They have high energy density, no memory effect, high working voltage, etc., and are gradually replacing traditional Ni-Cd and MH-Ni batteries. However, with the expansion of the demand for electronic products and the development of power and energy storage equipment, the demand for lithium ion secondary batteries has been continuously improved. It has become a top priority to develop lithium ion secondary batteries with high energy density and satisfying rapid charge and discharge. At present, an effective method is to increase the voltage of the electrode material, the compaction density, and select a suitable electrolyte.

At present, the cycle performance and high temperature performance of lithium ion secondary batteries are affected by many factors. Among them, electrolytes, as an important component of lithium ion secondary batteries, have a significant impact on their performance. The electrolyte can improve the kinetic performance of the lithium ion secondary battery, and can also improve the stability of the interface between the positive and negative electrodes in the cycle and high temperature storage process, thereby achieving the purpose of improving the cycle performance and storage performance of the lithium ion secondary battery.

Summary of the invention

In view of the problems in the background art, an object of the present invention is to provide an electrolyte and a secondary battery which, when applied to a secondary battery, can provide a secondary battery with low internal resistance and good Low temperature discharge performance, as well as good high temperature storage performance and high temperature cycle performance.

In order to achieve the above object, in one aspect of the invention, the present invention provides an electrolyte comprising an electrolyte salt, an organic solvent, and an additive. The additives include silyl sulfates as well as cyclic sulfates and/or cyclic sulfonates.

In another aspect of the invention, the invention provides a secondary battery comprising an electrolyte according to an aspect of the invention.

Advantageous effects of the present invention include, but are not limited to: relative to the prior art:

The electrolyte of the present invention includes both a silyl sulfate and a cyclic sulfate and/or a cyclic sulfonate. When applied to a secondary battery, the secondary battery can be made more synergistically under the synergistic action of the above substances. Low internal resistance, good low temperature discharge performance, and good high temperature storage performance and high temperature cycle performance.

detailed description

Hereinafter, the electrolytic solution and the secondary battery according to the present invention will be described in detail.

First, the electrolytic solution according to the first aspect of the invention will be explained.

The electrolytic solution according to the first aspect of the invention includes an electrolyte salt, an organic solvent, and an additive. The additives include silyl sulfates as well as cyclic sulfates and/or cyclic sulfonates.

In the electrolytic solution according to the first aspect of the present invention, the silane-based sulfate has a high reduction potential, which can reduce the interface resistance of the negative electrode, thereby improving the cycle performance of the secondary battery and reducing the internal resistance of the secondary battery. It improves the low-temperature discharge performance and the high-temperature cycle performance, but it cannot suppress the high-temperature storage gas generation of the secondary battery. The cyclic sulfate and the cyclic sulfonate have a high reduction potential, and can preferentially form a film on the surface of the negative electrode at a high voltage, thereby effectively suppressing high-temperature storage gas generation of the secondary battery, but when the amount of addition is high, The internal resistance of the secondary battery is increased, and the low-temperature discharge performance and high-temperature cycle performance of the secondary battery are deteriorated. When the above substances are simultaneously included in the electrolyte, the secondary battery can have a low internal resistance, a good low-temperature discharge performance, and good high-temperature storage performance and cycle performance under the synergistic action of the above substances.

In the electrolytic solution according to the first aspect of the invention, the silyl sulfate is selected from one or more of the compounds represented by Formula 1. Wherein R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ are each independently selected from an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, and a carbon number of One of an alkynyl group of 2 to 5 and an alkoxy group having 1 to 5 carbon atoms, and an H atom of an alkyl group, an alkenyl group, an alkynyl group or an alkoxy group may be further represented by F, Cl, Br, I, One or more substitutions of a cyano group, a carboxyl group, or a sulfonic acid group.

In the electrolytic solution according to the first aspect of the invention, the silane-based sulfate is selected from the group consisting of Silicate, bis(triethylsilyl)sulfate, bis(tri-n-propylsilyl)sulfate, bis(triisopropylsilyl)sulfate, bis(tri-n-butylsilyl) Sulfate, bis(triisobutylsilyl)sulfate, bis(tri-tert-butylsilyl)sulfate, bis(trimethoxysilyl)sulfate, bis(triethoxysilyl)sulfate , bis(tri-n-propoxysilyl)sulfate, bis(triisopropoxysilyl)sulfate, bis(tri-n-butoxysilyl)sulfate, bis(tri-sec-butoxysilyl) Sulfate, bis(tri-tert-butoxysilyl) sulfate, bis(trifluoromethylsilyl)sulfate, trimethylsilyltriethylsilylsulfate, bis(trivinylsilyl)sulfate One or more of an ester or bis(triacetylenylsilyl) sulfate.

In the electrolytic solution according to the first aspect of the invention, the cyclic sulfate is selected from one or more of the compounds represented by Formula 2. In Formula 2, n is an integer within 1 to 3; and R ₂₁ , R ₂₂ , R ₂₃ and R ₂₄ are each independently selected from H, F, Cl, Br, I, an alkyl group having 1 to 10 carbon atoms. And an alkoxy group having 1 to 10 carbon atoms, wherein the H atom on the alkyl group or the alkoxy group may be substituted with one or more of F, Cl, Br, and I.

In the electrolytic solution according to the first aspect of the invention, the cyclic sulfate is selected from one or more of the following compounds:

In the electrolytic solution according to the first aspect of the invention, the cyclic sulfonate is selected from one or more of the compounds represented by Formula 3. In Formula 3, n is an integer within 1 to 3, and R ₃₁ , R ₃₂ , R ₃₃ , R ₃₄ , R ₃₅ and R ₃₆ are each independently selected from H, F, Cl, Br, I, and the number of carbon atoms is One of an alkyl group having 1 to 10 carbon atoms and an alkoxy group having 1 to 10 carbon atoms, and an alkyl group or an alkoxy group H may be substituted by one or more of F, Cl, Br, and I. .

In the electrolytic solution according to the first aspect of the invention, the cyclic sulfonate is selected from one or more of the following compounds:

In the electrolytic solution according to the first aspect of the present invention, the content of the silyl sulfate is 0.5% to 10% by weight based on the total weight of the electrolytic solution, and preferably, the content of the silyl sulfate is 1% to 5% of the total weight of the electrolyte.

In the electrolytic solution according to the first aspect of the invention, the total content of the cyclic sulfate and/or cyclic sulfonate is from 0.5% to 10% by weight based on the total weight of the electrolytic solution. Preferably, the total content of the cyclic sulfate and/or cyclic sulfonate is from 1% to 5% of the total weight of the electrolyte.

In the electrolytic solution according to the first aspect of the invention, the electrolyte salt may be selected from a lithium salt, a sodium salt or a zinc salt, which varies depending on the secondary battery to which the electrolyte is applied.

In the electrolytic solution according to the first aspect of the present invention, the content of the electrolyte salt is 6.2% to 25% of the total weight of the electrolytic solution, and preferably, the content of the electrolyte salt is the electrolytic solution. The total weight is from 6.25% to 18.8%, and further preferably, the content of the electrolyte salt is from 10% to 15% of the total weight of the electrolyte.

In the electrolytic solution according to the first aspect of the present invention, the specific kind of the organic solvent is not particularly limited and may be selected according to actual needs. Preferably, a non-aqueous organic solvent is used. The non-aqueous organic solvent may include any kind of carbonate, carboxylate. The carbonate may include a cyclic carbonate or a chain carbonate. The non-aqueous organic solvent may also include a halogenated compound of a carbonate. Specifically, the organic solvent may be selected from the group consisting of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, pentylene carbonate, fluoroethylene carbonate, dimethyl carbonate (DMC), Diethyl carbonate (DEC), dipropyl carbonate, ethyl methyl carbonate (EMC), methyl formate, ethyl formate, ethyl acetate, propyl propionate, ethyl propionate, γ-butyrolactone (BL One or more of tetrahydrofuran (THF).

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

A secondary battery according to a second aspect of the invention includes the electrolytic solution according to the first aspect of the invention.

In the secondary battery according to the second aspect of the present invention, in addition to the electrolytic solution, the secondary battery further includes: a positive electrode sheet, a negative electrode sheet, and a separator. The positive electrode sheet includes a positive electrode current collector and a positive electrode film disposed on the positive electrode current collector, the positive electrode film including a positive electrode active material, a binder, and a conductive material Agent. The negative electrode sheet includes a negative electrode current collector and an negative electrode film disposed on the negative electrode current collector, and the negative electrode film includes a negative electrode active material, a binder, and may also include a conductive agent. The separator is spaced between the positive electrode tab and the negative electrode tab.

In the secondary battery according to the second aspect of the invention, the separator may be any separator material used in the existing secondary battery, such as polyethylene, polypropylene, polyvinylidene fluoride, and multilayers thereof. Composite membranes, but are not limited to these.

In the secondary battery according to the second aspect of the invention, the secondary battery may be a lithium ion secondary battery, a sodium ion secondary battery, or a zinc ion secondary battery.

When the secondary battery is a lithium ion secondary battery, the electrolyte salt may be selected from a lithium salt, and the lithium salt may be selected from LiPF ₆ , LiBF ₄ , LiN(SO ₂ F) ₂ (abbreviated as LiFSI), LiN ( CF ₃ SO ₂ ) ₂ (abbreviated as LiTFSI), LiClO ₄ , LiAsF ₆ , LiB(C ₂ O ₄ ) ₂ (abbreviated as LiBOB), LiBF ₂ C ₂ O ₄ (abbreviated as LiDFOB), LiPO ₂ F ₂ , LiTFOP One or more of LiN(SO ₂ RF) ₂ and LiN(SO ₂ F)(SO ₂ RF), wherein RF=C _n F _2n+1 represents a saturated perfluoroalkyl group, and n is 1～ An integer within 10. Preferably, the lithium salt is LiPF ₆ .

When the secondary battery is a lithium ion secondary battery, the positive active material may be selected from one or more of lithium cobaltate (LiCoO ₂ ), lithium nickel manganese cobalt ternary material, lithium iron phosphate, lithium manganese oxide. Kind.

When the secondary battery is a lithium ion secondary battery, the anode active material may be selected from metallic lithium. The negative active material may also be selected from materials capable of intercalating lithium at <2 V (vs. Li/Li ⁺ ). Specifically, the negative active material may be selected from natural graphite, artificial graphite, mesophase micro carbon spheres ( MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO ₂ , spinel structure lithiated TiO ₂ -Li ₄ Ti ₅ One or more of O ₁₂ and Li-Al alloys.

When the secondary battery is a sodium ion secondary battery or a zinc ion secondary battery, it is only necessary to change the corresponding positive electrode active material, negative electrode active material, and electrolyte salt.

The present application is further illustrated below in conjunction with the embodiments. It is to be understood that the examples are not intended to limit the scope of the application. Only the case where the secondary battery is a lithium ion secondary battery is shown in the embodiment, but the invention is not limited thereto.

In the following examples, the materials, reagents, and instruments used were commercially available unless otherwise specified.

For ease of explanation, the additives used in the following examples are abbreviated as follows:

A1: bis(trifluoromethylsilyl) sulfate

A2: trimethylsilyltriethylsilyl sulfate

B1: Vinyl sulfate (Compound 1)

B2: 1,3-propane sultone (compound 15)

The lithium ion secondary batteries of Examples 1-10 and Comparative Examples 1-3 were all prepared in the following manner.

(1) Preparation of positive electrode sheets

The positive electrode active material lithium cobaltate (LiCoO ₂ ), the binder polyvinylidene fluoride, and the conductive agent acetylene black are mixed at a weight ratio of 96:2:2, and N-methylpyrrolidone (NMP) is added under the action of a vacuum mixer. Stir the system to a uniform transparency to obtain a positive electrode slurry; uniformly apply the positive electrode slurry to a positive electrode current collector aluminum foil having a thickness of 12 μm; dry the aluminum foil at room temperature, transfer it to an oven at 120 ° C for 1 hour, and then pass cold pressing. The positive electrode sheets were obtained by slitting.

(2) Preparation of negative electrode sheets

The negative electrode active material graphite, the conductive agent acetylene black, the binder styrene-butadiene rubber (SBR), and the thickener sodium carboxymethyl cellulose (CMC) are mixed at a weight ratio of 97:1:1:1, and deionized water is added. Obtaining a negative electrode slurry under the action of a vacuum mixer; uniformly coating the negative electrode slurry on a negative current collector copper foil having a thickness of 8 μm; drying the copper foil at room temperature, transferring it to an oven at 120 ° C for 1 hour, and then subjecting it to cold pressing The negative electrode sheet was obtained by slitting.

(3) Electrolyte preparation

In an argon atmosphere glove box with a water content of <10 ppm, EC, PC, and DEC were mixed at a volume ratio of EC:PC:DEC=1:1:1, and then the sufficiently dried lithium salt LiPF _{6 was} dissolved in the mixed organic In the solvent, a silyl sulfate, a cyclic sulfate, and a cyclic sulfonate are added, and the mixture is uniformly mixed to obtain an electrolytic solution. Wherein, the content of LiPF ₆ is 12.5% of the total weight of the electrolyte. The specific types and contents of the silyl sulfate, cyclic sulfate, and cyclic sulfonate used in the electrolytic solution are shown in Table 1. In Table 1, the content of the silyl sulfate, the cyclic sulfate, and the cyclic sulfonate is a weight percentage calculated based on the total weight of the electrolytic solution.

(4) Preparation of separator

A 16 μm thick polypropylene separator (model C210, supplied by Celgard) was used.

(5) Preparation of lithium ion secondary battery

The positive electrode sheet, the separator film and the negative electrode sheet are stacked in order, so that the separator is in a role of isolation between the positive and negative electrode sheets, and then wound to obtain a bare cell; the bare cell is placed in the outer package foil, and the electricity is placed in the outer package foil. After the core is allowed to stand at a high temperature of 75 ° C for 24 hours, the prepared electrolyte is injected into the dried bare cell, and after vacuum encapsulation, standing, formation, shaping, etc., a lithium ion secondary battery is obtained. .

Table 1 Additives and contents of Examples 1-10 and Comparative Examples 1-3

Note: "-" means not added.

Next, the test process of the lithium ion secondary battery will be described.

(1) Internal resistance (DCIR) test of lithium ion secondary battery

The lithium ion secondary battery was charged at a constant current of 1 C (nominal capacity) to a voltage of 4.45 V at 25 ° C. Further, the battery is charged at a constant voltage of 4.45 V until the current is ≤ 0.05 C, left for 5 min, discharged at a constant current of 1 C to a voltage of 3 V, and the actual discharge capacity is recorded, and the lithium ion secondary battery is based on the discharge capacity (100% SOC). Adjust to 50% SOC. After the adjustment is completed, the lithium ion secondary battery is allowed to stand at -25 ° C for more than 4 h, so that the temperature of the lithium ion secondary battery reaches -25 ° C, and the discharge is continued for 10 s at a current of 0.3 C, and the voltage before the discharge and the voltage at the end of the discharge are used. The difference is divided by the current to obtain the DCIR of the lithium ion secondary battery. 15 lithium ion secondary batteries were tested in each group and averaged.

(2) Low-temperature discharge performance test of lithium ion secondary battery

The lithium ion secondary battery was charged at a constant current of 1 C (nominal capacity) to a voltage of 4.45 V at 25 ° C, and then charged at a constant voltage of 4.45 V until the current was less than or equal to 0.05 C. After leaving for 5 minutes, the constant current was 0.5 C. The discharge to the cut-off voltage is 3V, at which time the actual discharge capacity is recorded as D0.

Then, the lithium ion secondary battery was allowed to stand at -15 ° C for 1 h, charged at a constant current of 1 C to a voltage of 4.45 V, and then charged at a constant voltage of 4.45 V until the current was less than or equal to 0.05 C. After being left for 10 min, the constant current was 0.5 C. The discharge was discharged to a voltage of 3 V, and the discharge capacity at this time was recorded as D1.

Capacity retention rate (%) of low-temperature discharge of lithium ion secondary battery = D1/D0 × 100%. 15 lithium ion secondary batteries were tested in each group and averaged.

(3) High temperature cycle performance test of lithium ion secondary battery

The lithium ion secondary battery was charged at a constant current of 1 C to a voltage of 4.45 V at 45 ° C, further charged at a constant voltage of 4.45 V until the current was 0.05 C, and then discharged at a constant current of 1 C to a voltage of 3.0 V, which is a During the charge and discharge cycle, this discharge capacity is the discharge capacity of the first cycle. The lithium ion secondary battery was subjected to 300 cycles of charge/discharge test in accordance with the above method, and the discharge capacity at the 300th cycle was detected.

The capacity retention ratio (%) of the lithium ion secondary battery after circulating at 45 ° C for 300 times = (discharge capacity of 300 cycles of lithium ion secondary battery discharge / discharge capacity of the first cycle of lithium ion secondary battery) × 100%. 15 lithium ion secondary batteries were tested in each group and averaged.

(4) High-temperature storage performance test of lithium ion secondary battery

The lithium ion secondary battery was charged at a constant current of 0.5 C to a voltage of 4.45 V at 25 ° C, and then charged at a constant voltage of 4.45 V to a current of 0.05 C to be fully charged at 4.45 V, at which time the lithium ion was tested. The thickness of the secondary battery was recorded as h ₀ ; thereafter, the lithium ion secondary battery was placed in an incubator at 60 ° C, and after 30 days of storage, it was taken out, and the thickness of the lithium ion secondary battery at this time was measured and recorded as h ₁ .

The thickness expansion ratio of the lithium ion secondary battery after storage at 60 ° C for 30 days = [(h ₁ -h ₀ ) / h ₀ ] × 100%. Each group was tested for 15 lithium ion secondary batteries and averaged.

Table 2 Test results of Examples 1-10 and Comparative Examples 1-3

From the correlation data analysis of Table 2, it can be known that the silane-based sulfate and the cyclic sulfate and/or the cyclic sulfonate are not added in the comparative example 1, and the internal resistance (DCIR) and the low temperature of the lithium ion secondary battery at low temperature. The capacity retention rate after high discharge, high temperature cycle performance, and high temperature storage performance are both poor. When only silane-based sulfate was added to the electrolyte (Comparative Example 2), the high-temperature cycle performance of the lithium ion secondary battery, the internal resistance at low temperature, and the capacity retention after low-temperature discharge were improved, but the lithium ion secondary battery The high-temperature storage gas production is still not inhibited; when only the cyclic sulfate is added to the electrolyte (Comparative Example 3), the high-temperature storage gas production of the lithium ion secondary battery is significantly suppressed, but the lithium ion secondary battery is low temperature. The internal resistance and the capacity retention rate after low temperature discharge are significantly deteriorated.

When the silyl sulfate and the cyclic sulfate and/or the cyclic sulfonate (Examples 1-10) are simultaneously added to the electrolyte, the lithium ion can be improved while reducing the internal resistance at the low temperature of the lithium ion secondary battery. Two The capacity retention rate, high temperature cycle performance and high temperature storage performance of the secondary battery after low temperature discharge.

Claims

An electrolyte comprising:

Electrolyte salt

Organic solvent;

additive;

It is characterized in that

The additive includes:

Silyl sulfate;

Cyclic sulfates and/or cyclic sulfonates.
The electrolyte according to claim 1, wherein the silane-based sulfate is selected from one or more of the compounds represented by Formula 1;

among them,

R 1 , R 2 , R 3 , R 4 , R 5 and R 6 are each independently selected from an alkyl group having 1 to 5 carbon atoms, an alkenyl group having 2 to 5 carbon atoms, and 2 to 2 carbon atoms. One of an alkynyl group of 5 and an alkoxy group having 1 to 5 carbon atoms, and an H atom of an alkyl group, an alkenyl group, an alkynyl group or an alkoxy group may be further represented by F, Cl, Br, I or a cyano group. One or several substitutions of a carboxyl group or a sulfonic acid group.
The electrolyte according to claim 2, wherein said silane-based sulfate is selected from the group consisting of bis(trimethylsilyl) sulfate, bis(triethylsilyl) sulfate, and bis(tri-n-propyl) Silicate, bis(triisopropylsilyl)sulfate, bis(tri-n-butylsilyl)sulfate, bis(triisobutylsilyl)sulfate, bis(tri-tert-butylsilyl) Sulfate, bis(trimethoxysilyl)sulfate, bis(triethoxysilyl)sulfate, bis(tri-n-propoxysilyl)sulfate, bis(triisopropoxysilyl) Sulfate, bis(tri-n-butoxysilyl) sulfate, bis(tri-sec-butoxysilyl) sulfate, bis(tri-tert-butoxysilyl) sulfate, bis(trifluoromethylsilyl) One or more of sulfate, trimethylsilyltriethylsilylsulfate, bis(trivinylsilyl)sulfate, bis(triethynylsilyl)sulfate.
The electrolyte according to claim 1, wherein

The cyclic sulfate is selected from one or more of the compounds represented by Formula 2:

In Formula 2, n is an integer within 1 to 3; and R 21 , R 22 , R 23 and R 24 are each independently selected from H, F, Cl, Br, I, an alkyl group having 1 to 10 carbon atoms. And one of alkoxy groups having 1 to 10 carbon atoms, wherein the H atom on the alkyl group or the alkoxy group may be substituted by one or more of F, Cl, Br, and I;

The cyclic sulfonate is selected from one or more of the compounds represented by Formula 3:

In Formula 3, n is an integer within 1 to 3, and R 31 , R 32 , R 33 , R 34 , R 35 and R 36 are each independently selected from H, F, Cl, Br, I, and the number of carbon atoms is One of an alkyl group having 1 to 10 carbon atoms and an alkoxy group having 1 to 10 carbon atoms, and an alkyl group or an alkoxy group H may be substituted by one or more of F, Cl, Br, and I. .
The electrolyte according to claim 4, wherein

The cyclic sulfate is selected from one or more of the following compounds:

The cyclic sulfonate is selected from one or more of the following compounds:
The electrolytic solution according to claim 1, wherein the content of the silyl sulfate is 0.5% to 10%, preferably 1% to 5%, based on the total mass of the electrolytic solution.
The electrolyte according to claim 1, wherein the total content of the cyclic sulfate and/or cyclic sulfonate is from 0.5% to 10%, preferably 1%, based on the total weight of the electrolyte. ~5%.
The electrolyte according to claim 1, wherein the organic solvent is selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, pentylene carbonate, fluoroethylene carbonate, and dimethyl carbonate. , one of diethyl carbonate, dipropyl carbonate, ethyl methyl carbonate, methyl formate, ethyl formate, ethyl acetate, propyl propionate, ethyl propionate, γ-butyrolactone, tetrahydrofuran or Several.
The electrolyte according to claim 1, wherein the content of the electrolyte salt is 6.2% to 25% of the total weight of the electrolyte, and preferably, the content of the electrolyte salt is the electrolyte. The total weight is from 6.25% to 18.8%, and further preferably, the content of the electrolyte salt is from 10% to 15% of the total weight of the electrolyte.
A secondary battery comprising the electrolytic solution according to any one of claims 1-9.