CN103094614A - Lithium ion battery electrolyte and lithium ion battery containing same - Google Patents

Abstract

其中，R₁、R₂、R₃、R₄、R₅以及R₆任一为氢原子、烷基、苯基、联苯基、苯醚基、卤代烷基、卤代苯基、卤代联苯基中的一种，其中，所述烷基为C₁-C₂₀的直链或支链烷基，所述卤素为F、Br、Cl、I。The invention discloses a lithium-ion battery electrolyte and a lithium-ion battery containing the electrolyte, relates to the field of batteries, can effectively control the acidity of the electrolyte, and further significantly improve the cycle performance and high-temperature storage performance of the lithium-ion battery. The lithium ion battery electrolyte includes: lithium salt, non-aqueous organic solvent, and stabilizing additive, and the stabilizing additive is a silazane derivative, and the structure of the silazane derivative is:

Among them, any of R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ is a hydrogen atom, alkyl, phenyl, biphenyl, phenyl ether group, haloalkyl, halophenyl, halobi One of phenyl groups, wherein the alkyl group is a C ₁ -C ₂₀ linear or branched chain alkyl group, and the halogen is F, Br, Cl, I.

Description

A kind of lithium ion battery electrolyte and lithium ion battery containing the electrolyte

technical field

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

Background technique

Lithium-ion batteries are mainly composed of four parts: positive electrode material, negative electrode material, electrolyte, and separator. Among them, the electrolyte is an ion conductor that conducts electricity between the positive and negative electrodes of the battery, and generally consists of two parts: electrolyte lithium salt and organic solvent. The electrolyte lithium salt widely used in commercial lithium-ion batteries is generally LIPF ₆ , and the organic solvent is generally a mixture of two or more organic solvents, mainly ethylene carbonate ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and other chain and cyclic carbonates.

The performance of the electrolyte greatly affects the performance of the battery, and there are two main factors that affect the performance of the electrolyte: the composition of the electrolyte and the content of impurities in the electrolyte. Among them, the HF contained in the electrolyte has a great influence on the stability of the electrolyte and the performance of the battery.

The impact of HF on the stability of the electrolyte itself is mainly manifested in two aspects: catalyzing the hydrolysis of lithium salts such as LiPF ₆ , thereby accelerating the deterioration of the electrolyte; catalyzing the polymerization of organic solvents, resulting in an increase in the viscosity of the electrolyte and a decrease in conductivity.

The impact of HF on battery performance is mainly manifested in three aspects:

First, HF undergoes the following electrochemical reduction reaction on the carbon negative electrode during the first charge and discharge of the battery:

HF+e ^- +Li ⁺ →LiF↓+1/2H ₂

The above reaction will not only consume the limited lithium ions in the battery and increase the internal pressure of the battery, but also the generated LiF has poor conductivity, and the LiF content in the solid electrolyte interface (SEI) film component on the surface of the carbon negative electrode will increase, resulting in an electrode/electrolyte interface impedance. increases, thereby increasing the internal resistance of the battery.

Secondly, HF will react with the SEI film on the surface of the electrolysis to generate water or alcohol, etc. Aurbach et al. believed that in the EC-based electrolyte, the HF and SEI membranes mainly reacted as follows:

Li ₂ CO ₃ +2HF→2LiF+H ₂ O+CO ₂

The LiF generated in the above reaction will also lead to an increase in the electrode/electrolyte interface impedance. In addition, the water and ethylene glycol generated in the reaction will react with LiPF ₆ to generate HF. Decrease continuously until the entire battery is destroyed.

Finally, HF will react with positive electrode active materials such as LiMn ₂ O ₄ to cause the dissolution of part of manganese, which is one of the main reasons for the capacity fading of LiMn ₂ O ₄ . The reaction principle is as follows:

LiMn ₂ O ₄ +H ⁺ →Li ⁺ +λ-MnO ₂ +Mn ²⁺ +2H ₂ O

In view of the influence of HF on the electrolyte and battery performance, in the prior art, one or more mixtures of oxides of zinc, aluminum, magnesium, and calcium, or magnesium or aluminum are added to the electrolyte as additives, and they are compatible with the electrolytic A small amount of HF in the liquid reacts, reduces the content of HF, prevents its damage to the electrode and catalyzes the decomposition of lithium salts such as LiPF ₆ , improves the stability of the electrolyte, and improves battery performance.

However, the above method for removing HF is slow, and treating the electrolyte with metal or metal oxide is easy to introduce metal impurities.

In addition, in the prior art, hexamethyldisilazane (chemical formula (CH ₃ ) ₃ SiNHSi(CH ₃ ) ₃ ) can also be added to the electrolyte as an additive, and its mechanism of action is as follows:

(CH ₃ ) ₃ SiNHSi(CH ₃ ) ₃ +H ₂ O→(CH ₃ ) ₃ SiOSi(CH ₃ ) ₃ +NH ₃

NH ₃ +HF→NH ₄ F

Hexamethyldisilazane reacts with water to generate NH ₃ , and then NH ₃ reacts with HF to generate NH ₄ F, thereby reducing the content of HF in the electrolyte and improving the cycle performance of lithium-ion batteries. However, in this method, hexamethyldisiloxane itself is unstable, easily decomposed in the air, and difficult to store; and the NH ₄ F produced by the reaction of NH ₃ and HF is unstable, especially at high temperatures, it is easy to decompose, and it is difficult to achieve The purpose of improving the high temperature performance of lithium-ion batteries.

Contents of the invention

Embodiments of the present invention provide a lithium-ion battery electrolyte and a lithium-ion battery containing the electrolyte, which can effectively control the acidity of the electrolyte and improve the cycle life and high-temperature storage performance of the lithium-ion battery.

The above object of the embodiments of the present invention is achieved through the following technical solutions:

An electrolyte solution for a lithium-ion battery, the electrolyte comprising: a solute, a solvent, and a stabilizing additive, the stabilizing additive silazane derivative, the structure of the silazane derivative being:

In the above formula, any of R ₁ , R ₂ , R ₃ , R ₄ , R ₅ and R ₆ is H, alkyl, phenyl, biphenyl, phenyl ether, haloalkyl, halophenyl, halo One of biphenyl groups, wherein the alkyl group is a C ₁ -C ₂₀ straight chain or branched chain alkyl group, and the halogen is F, Br, Cl, I.

Preferably, the content of the silazane derivative is 0.1%-50% of the total weight of the electrolyte.

In the lithium ion battery electrolyte provided in the embodiment of the present invention, the solute is a lithium salt, and the lithium salt can be various lithium salts commonly used in the art, preferably LiPF ₆ , LiBF ₄ , LiClO ₄ , LiPF ₃ (CF One or more of ₂ CF ₃ ) ₃ , LiCF ₃ SO ₃ and LiBOB.

In the lithium-ion battery electrolyte provided in the embodiment of the present invention, the solvent is a non-aqueous organic solvent, and the non-aqueous organic solvent can be various non-aqueous organic solvents commonly used in the art, preferably carbonate and its halogenated derivatives One or more of compounds, esters, ethers and ketones.

The lithium-ion battery electrolyte provided in the embodiment of the present invention also includes a film-forming additive, and the film-forming additive can be various film-forming additives commonly used in the art, preferably vinylene carbonate, ethylene carbonate, 1 , one or more of 3-propiolactone sulfonate and 1,4-butyrolactone sulfonate. Preferably, the content of the film-forming additive is 0.1%-50% of the total weight of the electrolyte.

A lithium ion battery, comprising: an electrolyte, a positive electrode, and a negative electrode. The positive electrode and the negative electrode are commonly used in the field. The electrolyte is the electrolyte provided by the embodiment of the present invention.

The lithium-ion battery electrolyte provided in the embodiments of the present invention and the lithium-ion battery containing the electrolyte can react with the hydrogen ions generated by the hydrolysis of lithium salt in the electrolyte to form stable compounds by adding a silazane derivative as a stabilizing additive, thereby Effectively control the acidity of the electrolyte, improve the cycle life and high temperature storage performance of lithium-ion batteries.

Detailed ways

In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be further described in detail below in conjunction with the embodiments. Here, the schematic embodiments of the present invention and their descriptions are used to explain the present invention, but not as a limitation 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 creative efforts fall within the protection scope of the present invention.

The lithium-ion battery electrolyte provided in the embodiment of the present invention includes: a solute, a solvent, and a stabilizing additive, the silazane derivative of the stabilizing additive, and the structure of the silazane derivative is:

In the above formula, R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , and R ₆ are hydrogen, alkyl, phenyl, biphenyl, phenyl ether, haloalkyl, halophenyl, halobiphenyl One or more of the groups, wherein the alkyl group is a C ₁ -C ₂₀ straight chain or branched chain alkyl group, and the halogen includes F, Cl, Br, I.

As we all know, in lithium-ion batteries, the lithium salt in the electrolyte undergoes a hydrolysis reaction with water to generate hydrogen ions. As mentioned above, hydrogen ions have a huge impact on the stability of the electrolyte itself and the performance of the battery. Adding the above-mentioned stable additive silazane derivatives to the electrolyte can react with hydrogen ions in the electrolyte to form stable compounds, thereby effectively controlling the acidity of the electrolyte and improving the cycle life and high-temperature storage performance of lithium-ion batteries. The reaction principle is as follows Formula 1):

Formula 1)

The salt compound formed by the reaction has strong stability at high temperature, and it is difficult to decompose to generate hydrogen ions. Therefore, the acidity of the electrolyte can be well controlled, thereby improving the cycle life and high-temperature storage performance of the lithium-ion battery. In addition, the above-mentioned silazane derivative additive has a fast acid removal _speed , and 1 mol of the silazane derivative can remove ₂ mol of hydrogen ions. ₃ ) ₃ ) 2 times the acid removal speed, so the acidity of the electrolyte can be better controlled.

Preferably, the content of the silazane derivative is 0.1%-50% of the total weight of the electrolyte. Obviously, those skilled in the art can adjust the content of the silazane derivatives according to common knowledge and common technical means in the field to determine the appropriate content of the silazane derivatives, which is not limited in the embodiments of the present invention.

In the lithium ion battery electrolyte provided in the embodiment of the present invention, the lithium salt can be various lithium salts commonly used in the art, preferably LiPF ₆ , LiBF ₄ , LiClO ₄ , LiPF ₃ (CF ₂ CF ₃ ) ₃ , LiCF One or more of ₃ SO ₃ and LiBOB. Of course, those skilled in the art can select one or several other suitable lithium salts according to common knowledge in the field, which is not limited in the embodiments of the present invention.

In the lithium-ion battery electrolyte provided in the embodiments of the present invention, the non-aqueous organic solvent can be various non-aqueous solvents commonly used in the art, preferably one of carbonates and their halogenated derivatives, esters, ethers and ketones. species or several. Of course, those skilled in the art can choose one or several other suitable non-aqueous organic solvents, which is not limited in the embodiments of the present invention.

It can be understood that those skilled in the art can select the content of lithium salt, non-aqueous organic solvent and other components in the electrolyte solution of the embodiment of the present invention according to the common knowledge and common technical means in this field. Not limited.

In the lithium-ion battery electrolyte provided in the embodiments of the present invention, the film-forming additives can be various film-forming additives commonly used in the art, preferably vinylene carbonate, vinylethylene carbonate, 1,3-propanesulfonic acid Of course, one or more of lactone and 1,4-sulfonic acid butyrolactone, other suitable film-forming additives can also be selected by those skilled in the art according to the common knowledge and common technical means in the art, and the embodiments of the present invention to this No limit.

Preferably, the content of the film-forming additive is 0.1%-50% of the total weight of the electrolyte. Certainly, the appropriate content of the film-forming additive can also be determined by those skilled in the art, which is not limited in the embodiment of the present invention.

It should be noted that the lithium-ion battery electrolyte provided in the embodiments of the present invention can be prepared by methods known in the art for preparing lithium-ion electrolytes. For example, the lithium salt, the non-aqueous organic solvent, the film-forming additive and the silazane derivative of the stabilizing additive are mixed and stirred uniformly according to a selected content range.

An embodiment of the present invention also provides a lithium-ion battery, including an electrolyte, and the electrolyte is the above-mentioned electrolyte for the lithium-ion battery.

Since the present invention only involves the improvement of the prior art lithium-ion battery electrolyte, there is no special limitation on other compositions and structures of the lithium-ion battery.

The lithium-ion battery provided in the embodiments of the present invention can be prepared by methods known in the art for preparing lithium-ion batteries.

The lithium-ion battery electrolyte provided in the embodiments of the present invention and the lithium-ion battery containing the electrolyte can react with the hydrogen ions generated by the hydrolysis of lithium salt in the electrolyte to form stable compounds by adding a silazane derivative as a stabilizing additive, thereby Effectively control the acidity of the electrolyte, improve the cycle life and high temperature storage performance of lithium-ion batteries.

In order to better illustrate the lithium-ion battery electrolyte provided in the embodiments of the present invention, specific examples will be described in detail below.

Preparation of lithium-ion battery electrolyte:

Adding a certain amount of lithium salt into a non-aqueous organic solvent to obtain a solution;

By adding a certain proportion of film-forming additives and stabilizing additives, the lithium-ion battery electrolyte can be obtained.

comparative example

Preparation of lithium-ion battery electrolyte:

Dissolve 1M lithium salt LiPF ₆ in a mixed solvent of ethylene carbonate (EC)/ethyl methyl carbonate (EMC)/dimethyl carbonate (DMC) = 1:1:1 (wt%) to obtain a solution, and then add electrolytic The total weight of 2% ethylene carbonate (VC) was used to prepare the comparative electrolyte, which was recorded as sample A.

The preparation of the lithium-ion battery containing lithium-ion battery electrolyte A:

A lithium-ion battery is prepared by a method known in the art for preparing a lithium-ion battery, which is denoted as B.

Example 1

Preparation of lithium-ion battery electrolyte:

Dissolve 1M lithium salt LiPF ₆ in a mixed solvent of ethylene carbonate (EC)/ethyl methyl carbonate (EMC)/dimethyl carbonate (DMC) = 1:1:1 (wt%) to obtain a solution, and then add electrolytic 2% of the total weight of ethylene carbonate (VC), and 0.5% of the total weight of the electrolyte is added to the silazane derivative I shown in formula (2), that is, the desired electrolyte is prepared, which is recorded as A1.

Formula (2)

The preparation of the lithium-ion battery containing lithium-ion battery electrolyte A1:

Using the same method as the comparative example, a lithium-ion battery was prepared, which was denoted as B1.

Example 2

Preparation of lithium-ion battery electrolyte:

Dissolve 1M lithium salt LiPF ₆ in a mixed solvent of ethylene carbonate (EC)/ethyl methyl carbonate (EMC)/dimethyl carbonate (DMC) = 1:1:1 (wt%) to obtain a solution, and then add electrolytic 2% of the total weight of ethylene carbonate (VC) and 0.5% of the total weight of the electrolyte is added to the silazane derivative II shown in formula (3), that is, the desired electrolyte is prepared, which is recorded as A2 sample.

Formula (3)

The preparation of the lithium-ion battery containing lithium-ion battery electrolyte A2:

Using the same method as the comparative example, a lithium-ion battery was prepared, which was denoted as B2.

Example 3

Dissolve 1M lithium salt LiPF ₆ in a mixed solvent of ethylene carbonate (EC)/ethyl methyl carbonate (EMC)/dimethyl carbonate (DMC) = 1:1:1 (wt%) to obtain a solution, and then add electrolytic 2% ethylene carbonate (VC) in the total weight of the electrolyte, and 0.5% of the silazane derivative III shown in formula (4) in the total weight of the electrolyte is added to prepare the required electrolyte, which is recorded as sample A3.

Formula (4)

The preparation of the lithium-ion battery containing lithium-ion battery electrolyte A3:

Using the same method as the comparative example, a lithium-ion battery was prepared, which was denoted as B3.

Embodiment one to three performance test

In order to strongly support the beneficial effects brought by the technical solutions of the embodiments of the present invention, the following performance tests for the embodiments of the present invention and comparative examples are provided:

(1) Lithium-ion battery electrolyte acid removal performance test

The lithium-ion battery electrolyte A in the comparative example and the lithium-ion battery electrolytes A1, A2, and A3 in Examples 1 to 3 were tested for acid removal performance. The test method is as follows:

Add 1 drop of distilled water to the electrolyte samples A, A1, A2, and A3 respectively, then test the water (H ₂ O) content in the electrolyte by the Coulomb Karst method, and test the acidity in the electrolyte by the acid-base titration method to determine Characterize the content of HF. At this time, the content of H ₂ O and HF is recorded as the content before storage, as shown in Table 1, where ppm is parts per million.

The lithium-ion battery electrolyte samples A, A1, A2, and A3 added with water were left at room temperature for a week, and the water content in the electrolyte was tested by the Coulomb Karst method, and the acidity in the electrolyte was tested by the acid-base titration method. The contents of H ₂ O and HF were recorded as the contents after storage, as shown in Table 1.

Table 1

The test results show that, compared with the comparative electrolyte solution without adding silazane derivatives, the free acid content of the electrolyte solution added with silazane derivatives provided by the embodiment of the present invention after shelving is significantly reduced, that is, the HF content is significantly reduced; and As the alkyl chain in the substituent grows, the free acid concentration decreases more.

(2) Lithium-ion battery cycle performance test

The lithium-ion battery B in the comparative example and the lithium-ion batteries B1, B2, and B3 in Examples 1 to 3 were subjected to a cycle performance test. Record the initial capacity of the battery and the capacity of the battery after 100, 200, 300, 400 and 500 cycles of charging and discharging. The unit of measurement is mAh (milliampere hours). See Table 2 for the specific test results.

Table 2

The test results show that, compared with the battery containing the electrolyte solution without adding silazane derivatives in the comparative example, the cycle performance of the battery containing the electrolyte solution added with nitrogen silane derivatives provided by the embodiment of the present invention is significantly improved; and the battery The cycle performance of B1, B2, and B3 increases gradually with the growth of the alkyl chain in the substituent of the silazane derivative added to the electrolyte, that is, the longer the alkyl chain in the substituent of the silazane derivative, the longer the battery cycle. The better the performance.

(3) Lithium-ion battery high temperature storage performance test

The lithium-ion battery B of the comparative example and the lithium-ion batteries B1, B2, and B3 in Examples 1 to 3 were subjected to a high-temperature storage performance test, and the following method was used for testing:

Lithium-ion batteries B, B1, B2, and B3 were placed at 55°C for 10 days, and the high-temperature storage data were recorded as shown in Table 3.

table 3

The test results show that, compared with the battery in the comparative example without adding the electrolyte of the silazane derivative, the high-temperature storage performance of the battery containing the electrolyte added with the silazane derivative provided by the embodiment of the present invention is significantly improved; and The high-temperature storage performance of batteries B1, B2, and B3 gradually improves with the growth of the alkyl chain in the substituent of the silazane derivative added to the electrolyte, that is, the longer the alkyl chain in the substituent of the silazane derivative, The better the high temperature storage performance of the battery.

Through the above performance comparison test with the comparative example, it can be seen that the lithium ion battery electrolyte in the specific examples provided by the invention and the lithium ion battery containing the electrolyte can effectively control the acidity of the electrolyte, improve the cycle life and high temperature of the lithium ion battery storage performance. And the longer the alkyl chain of the substituent added to the silazane derivative in the electrolyte, the better the corresponding acid removal performance, cycle performance and high-temperature storage performance.

The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Anyone skilled in the art can easily think of changes or substitutions within the technical scope disclosed in the present invention, and all should be included in the scope of the present invention. within the protection scope of the present invention. Therefore, the protection scope of the present invention should be determined by the protection scope of the claims.

Claims (8)

1. lithium-ion battery electrolytes comprises: solute, solvent, stabilization additives, it is characterized in that, and described stabilization additives is the silazane derivative, described silazane derivant structure is:

Wherein, R ₁, R ₂, R ₃, R ₄, R ₅And R ₆Arbitrary is a kind of in hydrogen atom, alkyl, phenyl, xenyl, phenylate base, haloalkyl, halogenophenyl and halogenated biphenyl base.

2. lithium-ion battery electrolytes according to claim 1, described alkyl is C ₁-C ₂₀The straight or branched alkyl, in described haloalkyl, halogenophenyl and halogenated biphenyl base, halogen comprises F, Br, Cl, I.

3. lithium-ion battery electrolytes according to claim 1, is characterized in that, described silazane derivative is the 0.1%-50% of electrolyte total weight.

4. lithium-ion battery electrolytes according to claim 1, is characterized in that, described solute is lithium salts, and described lithium salts is selected from LiPF ₆, LiBF ₄, LiClO ₄, LiPF ₃(CF ₂CF ₃) ₃, LiCF ₃SO ₃With one or more in LiBOB.

5. lithium-ion battery electrolytes according to claim 1, is characterized in that, described solvent is non-aqueous organic solvent, and described non-aqueous organic solvent is one or more the mixed solvent in carbonic ester, carbonic ester halo derivatives, ester, ether and ketone.

6. lithium-ion battery electrolytes according to claim 1, it is characterized in that, described lithium-ion battery electrolytes also comprises film for additive, and described film for additive is vinylene carbonate, vinylethylene carbonate, 1, one or more in 3-sulfonic acid propiolactone and Isosorbide-5-Nitrae-sulfonic acid butyrolactone.

7. lithium-ion battery electrolytes according to claim 6, is characterized in that, described film for additive content is the 0.1%-50% of electrolyte total weight.

8. a lithium ion battery, comprise positive pole, negative pole and electrolyte, it is characterized in that, described electrolyte is the described lithium-ion battery electrolytes of claim 1 to 7 any one.