CN116315091A - A kind of electrolyte and lithium-ion battery containing it - Google Patents

Abstract

The invention discloses an electrolyte and a lithium ion battery comprising the same, wherein the electrolyte comprises lithium salt, an organic solvent and a multifunctional six-membered heterocyclic compound additive shown in the following formula:

Description

A kind of electrolyte and lithium-ion battery containing it

technical field

The invention relates to the technical field of lithium ion batteries, in particular to an electrolyte and a lithium ion battery containing the same.

Background technique

Lithium-ion batteries are widely used because of their high working voltage, large specific energy, long cycle life and no memory effect. For example, lithium-ion batteries have been widely used in the field of 3C consumer electronics products, and with the new With the development of energy vehicles, lithium-ion batteries are also widely used in the field of power and energy storage. Therefore, higher requirements are placed on the performance of lithium-ion batteries.

Lithium-ion battery electrolyte is one of the four main materials of lithium-ion batteries. It exists between the positive and negative electrode materials and in the pores of the diaphragm to play the role of lithium ion transmission. All performances have an important impact. The current commercially used electrolyte is composed of lithium salt, solvent and additives. Although the amount of additives added is relatively small, because it can form a solid electrolyte interface film on the surface of the electrode material, it can suppress the continuous side reactions between the electrode material and the electrolyte and It plays an important role in helping lithium ions desolvate and other processes. There are many kinds of electrolyte additives currently being researched, including phosphorus-containing phosphates, boron-containing borates, sulfur-containing sulfates, etc. In order to improve the overall performance of lithium-ion batteries, it is usually necessary to add Adding various additives with different functional groups, the cost of using additives is high, the optimization, screening and optimization work is cumbersome, and it is difficult to play a coordinated role between different functional groups. The synergistic effect can improve the screening efficiency of additive combination, and then improve the comprehensive electrochemical performance of lithium-ion batteries.

Contents of the invention

Based on the technical problems existing in the background technology, the object of the present invention is to provide an electrolyte and a lithium ion battery comprising it, the electrolyte uses a multifunctional six-membered heterocyclic compound as an electrolyte additive for a lithium ion battery, which can improve the electrolyte additive Combining and optimizing efficiency to achieve comprehensive electrochemical performance improvement such as constant and high cycle and low temperature discharge performance of lithium-ion batteries.

The purpose of the present invention is achieved through the following technical solutions:

A kind of electrolytic solution, described electrolytic solution comprises lithium salt, organic solvent and polyfunctional group six-membered heterocyclic compound additive, the chemical structural formula of described multifunctional group six-membered heterocyclic compound additive is as follows:

Where: R1 and R2 are independently selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkenyl, substituted or unsubstituted C1-C10 alkynyl, substituted or unsubstituted phenyl , a substituted or unsubstituted carbonyl group, a substituted or unsubstituted carboxylate group, a substituted or unsubstituted alkylsilyl group, a cyano group, an isocyano group or an isothiocyano group.

In a further scheme, the multifunctional six-membered heterocyclic compound additive includes at least one of the compounds shown in the following formula (1) to formula (6):

Preferably, the organic solvent is at least one selected from cyclic or chain carbonates, cyclic or linear carboxylates, and cyclic or linear ethers. Further preferably, the organic solvent is selected from dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, ethyl propionate, butyric acid One or more of methyl acetate, butyl acetate, methyl propionate, propyl butyrate, tetrahydrofuran, 2-methyltetrahydrofuran, and 1,3-dioxolane.

Preferably, the lithium salt is selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium bisfluorosulfonimide and lithium bistrifluoromethanesulfonylimide one or more of.

Preferably, the lithium salt content in the electrolyte is 5 to 30 wt%; the content of the multifunctional six-membered heterocyclic compound additive in the electrolyte is 0.5 to 20%; the content of the organic solvent in the electrolyte is 60 to 30 wt%. 85%.

The present invention also discloses a lithium-ion battery, comprising a positive electrode sheet, a negative electrode sheet, a diaphragm and an electrolyte, and the electrolyte is the above-mentioned electrolyte

Compared with the prior art, the beneficial effects of the present invention are:

1) The multifunctional six-membered heterocyclic compound additive proposed by the present invention can participate in the film-forming reaction on the surface of lithium-ion battery electrode materials, decompose and produce various film-forming products containing silicon, sulfur and phosphorus, and promote the formation of dense, stable and low-density Impedance solid electrolyte interfacial film, thereby improving the constant, high cycle and low temperature discharge performance of lithium-ion batteries at the same time.

2) The multifunctional six-membered heterocyclic compound additive proposed by the present invention contains multiple functional groups such as phosphate ester, borate ester and sulfonate ester at the same time, which avoids the cumbersome screening work of combining and optimizing multiple additives containing a single functional group, and can be more Good coordination between different functional groups.

Detailed ways

Below in conjunction with embodiment the present invention will be further described. Apparently, the described embodiments are some, but not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention. The raw materials, reagents, etc. used in the following examples and comparative examples are all commercially available products, and are commercially available.

Example 1

An electrolyte solution for a lithium ion battery, comprising a lithium salt, an organic solvent and an additive, wherein the additive is a polyfunctional six-membered heterocyclic compound of compound 1 shown in the following formula (1).

The preparation method of this electrolytic solution: in the inert atmosphere glove box of water/oxygen index all＜0.1ppm, LiPF ₆ is dissolved in organic solvent ethylene carbonate (EC), dimethyl carbonate (DMC), ethyl methyl carbonate ( EMC) in the mixed solvent, the mass ratio of different solvents is 3:2:5, and the concentration of LiPF ₆ is 1.0mol/L. After LiPF ₆ is completely dissolved, compound 1 with 4% of the total mass of the electrolyte is added as an additive, and mixed and stirred evenly to obtain Lithium-ion battery electrolyte samples

A lithium ion battery comprises a positive electrode sheet, a negative electrode sheet, a diaphragm and an electrolyte, and the electrolyte is the lithium ion battery electrolyte sample prepared above.

The preparation method of the lithium-ion battery: the negative electrode material artificial graphite, conductive base SP, binder CMC, dispersant SBR according to the mass ratio of 96:1:1.5:1.5, add an appropriate amount of deionized water, and mix into a uniform paste uniformly coated on a copper foil serving as a 12 μm negative electrode collector, and baked at 100° C. for 12 hours to obtain a negative electrode sheet. The positive electrode material LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , the conductive agent SP, and the binder PVDF according to the mass ratio of 96:2:2, add an appropriate amount of NMP solvent, mix into a uniform paste, and evenly coat it on the positive electrode On the 15 μm aluminum foil of the current collector, bake at 110° C. for 12 hours to obtain the positive electrode sheet. The positive electrode sheet, separator, and negative electrode sheet are stacked in sequence to obtain a lithium-ion battery cell. The battery prepared in this experiment is a 2Ah soft-pack battery. After drying the cell, inject 8g of electrolyte sample to obtain the corresponding battery sample.

Example 2

A lithium-ion battery electrolyte and battery, the production method and steps are the same as in Example 1, the only difference is that Compound 1 is replaced by Compound 2 as shown in the following formula (2), and the rest are the same as in Example 1, and will not be repeated. .

Example 3

A lithium-ion battery electrolyte and battery, the production method and steps are the same as in Example 1, the only difference is that the compound 3 shown in the following formula (3) is used to replace the compound 1, and the rest are the same as in Example 1, and will not be repeated. .

Example 4

A lithium-ion battery electrolyte and battery, the production method and steps of which are the same as in Example 1, the only difference is that compound 4 shown in the following formula (4) is used to replace compound 1, and the rest are the same as in Example 1, and will not be repeated. .

Example 5

A lithium-ion battery electrolyte and battery, the production method and steps are the same as in Example 1, the only difference is that compound 5 shown in the following formula (5) is used to replace compound 1, and the rest are the same as in Example 1, and will not be repeated. .

Example 6

A lithium-ion battery electrolyte and battery, the production method and steps are the same as in Example 1, the only difference is that compound 6 shown in the following formula (6) is used to replace compound 1, and the rest are the same as in Example 1, and will not be repeated. .

Example 7

A lithium-ion battery electrolyte and battery, the production method and steps are the same as in Example 1, the only difference is that 2% of Compound 1 and 2% of Compound 2 are used to replace 4% of Compound 1, and the rest are the same as in Example 1, except Let me repeat.

Comparative example 1

A lithium-ion battery electrolyte and battery, the production method and steps are the same as in Example 1, the only difference is that the additive only contains 4% vinylene carbonate, and the rest are the same as in Example 1, and will not be repeated.

Comparative example 2

A lithium-ion battery electrolyte and battery, the production method and steps are the same as in Example 1, the only difference is that 4% of compound 1 in Example 1 is replaced by 1% vinylene carbonate, 1% sulfuric acid A mixture of vinyl ester, 1% tris(trimethylsilyl) phosphate and 1% tris(trimethylsilyl) borate, and the rest are the same as in Example 1, and will not be repeated.

Test method: The batteries prepared in the above examples and comparative examples were subjected to normal temperature cycle test, high temperature cycle test and low temperature discharge performance test respectively.

(1) Normal temperature cycle test

At 25°C, the batteries of Examples 1-7 and Comparative Examples 1-2 were charged to 4.2V with 0.2C constant current and constant voltage, and the cut-off current was 0.05C; then discharged to 2.5V with 0.2C constant current, and the discharge was recorded The capacity Q ₀ is initially regarded as the discharge initial capacity. Keep the ambient temperature constant and cycle 100 times according to the same charge-discharge system, record the discharge capacity Q ₃₀₀ of the 300th cycle, then the discharge capacity retention rate at room temperature = Q ₃₀₀ /Q ₀ *100%.

(2) High temperature cycle performance test

The high temperature cycle performance test method is the same as the normal temperature cycle test method, the only difference is that the cycle test environment temperature is set to 45°C

(3) -20℃ low temperature discharge performance test

At 25°C, the lithium-ion batteries of Examples 1-7 and Comparative Examples 1-2 were charged to 4.2V with a 0.2C constant current and constant voltage, and the cut-off current was 0.05C; then discharged to 2.0V with a 0.2C constant current, and recorded Its discharge capacity Q ₀ is used as the discharge initial capacity. The battery was charged to 4.2V with 0.2C constant current and constant voltage, and the cut-off current was 0.05C; then the sample was placed at -20°C for 3 hours to achieve temperature equilibrium, and then the experimental cell was discharged to 2.0V with 0.2C constant current , record its discharge capacity Q ₁ , and take the average value of three experimental batteries tested in parallel, then the low-temperature discharge capacity retention rate = Q ₁ /Q ₀ *100%.

The above test results are shown in Table 1.

Table 1 Example and Comparative Example Battery Sample Test Results

From the test data of Comparative Example 1-2, it can be seen that only vinylene carbonate additive is used, the low-temperature performance of the electrolyte is very poor, and the low-temperature discharge capacity retention rate at -20°C is less than 60%, even though vinyl sulfate is used in combination in Comparative Example 2 ester, tri(trimethylsilyl) phosphate, tri(trimethylsilyl) borate and other additives, and the electrochemical properties are improved compared with the multifunctional six-membered heterocyclic compound additives in the examples. Worse, the main reason is that the synergy of different additives cannot be brought into play, the stability of film formation is poor, and the side reactions between electrolyte and electrode materials are serious.

In contrast, the test data of Examples 1-7 show that using one or a combination of the multifunctional six-membered heterocyclic compounds of Compounds 1-7 as an additive can exert the synergistic effect of different functional groups and promote the formation of a dense and stable solid electrolyte The interfacial film significantly improves the cycle performance, the capacity retention rate of 300 cycles at room temperature is > 94%, and the capacity retention rate of 300 cycles at room temperature is > 85.9%. %. It can be seen that the multifunctional six-membered heterocyclic compound additive proposed by the present invention avoids the tedious screening work of combination optimization of various additives containing a single functional group, and can better realize the synergistic effect between different functional groups.

The above is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto, any person familiar with the technical field within the technical scope disclosed in the present invention, according to the technical solution of the present invention Any equivalent replacement or change of the inventive concepts thereof shall fall within the protection scope of the present invention.

Claims (9)

1. an electrolytic solution, it is characterized in that: described electrolytic solution comprises lithium salt, organic solvent and polyfunctional group six-membered heterocyclic compound additive, and the chemical structural formula of described multifunctional group six-membered heterocyclic compound additive is as follows:

Where: R1 and R2 are independently selected from substituted or unsubstituted C1-C10 alkyl, substituted or unsubstituted C1-C10 alkenyl, substituted or unsubstituted C1-C10 alkynyl, substituted or unsubstituted phenyl , a substituted or unsubstituted carbonyl group, a substituted or unsubstituted carboxylate group, a substituted or unsubstituted alkylsilyl group, a cyano group, an isocyano group or an isothiocyano group. 2. The electrolytic solution according to claim 1, characterized in that: the multifunctional six-membered heterocyclic compound additive comprises at least one of the compounds shown in the following formula (1) to formula (6):

3. The electrolytic solution according to claim 1, characterized in that: said organic solvent is selected from at least one of cyclic or chain carbonates, cyclic or linear carboxylates, cyclic or linear ethers kind. 4. electrolytic solution according to claim 3, is characterized in that: described organic solvent is selected from dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, propyl methyl carbonate, ethylene carbonate, propylene carbonate, One of γ-butyrolactone, ethyl propionate, methyl butyrate, butyl acetate, methyl propionate, propyl butyrate, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane one or more species. 5. The electrolyte solution according to claim 1, wherein the lithium salt is selected from lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium bisoxalate borate, lithium difluorooxalate borate, difluorosulfonyl One or more of lithium imide and lithium bistrifluoromethanesulfonylimide. 6. The electrolytic solution according to any one of claims 1 to 5, characterized in that: the lithium salt content in the electrolytic solution is 5-30 wt%. 7. The electrolytic solution according to any one of claims 1 to 5, characterized in that the content of the multifunctional six-membered heterocyclic compound additive in the electrolytic solution is 0.5-20%. 8. The electrolytic solution according to any one of claims 1 to 5, characterized in that: the organic solvent content in the electrolytic solution is 60-85%. 9. A lithium ion battery, characterized in that it comprises a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte, and the electrolyte is the electrolyte according to any one of claims 1 to 8.