CN116169356A - A kind of electrolytic solution containing nitrile additive and its preparation method and application - Google Patents

Abstract

The invention discloses an electrolyte containing nitrile additives, and a preparation method and application thereof. Relates to the technical field of electrolyte. The electrolyte comprises the following components: a lithium source, 1, 5-dicyanopentane and a solvent; the mass percentage of the 1, 5-dicyanopentane in the electrolyte is 0.1-5%. The electrolyte provided by the invention is added with 1, 5-dicyanopentane as a film forming additive, and has the effects of enhancing the stability and high-pressure cycle performance of the electrolyte. When the electrolyte provided by the invention is used for preparing a battery, the battery can be found to show remarkable high-voltage cycle performance.

Description

A kind of electrolyte solution containing nitrile additive and its preparation method and application

technical field

The invention relates to the technical field of electrolytes, in particular to an electrolyte containing nitrile additives and a preparation method and application thereof.

Background technique

Lithium-ion batteries are now considered a clean commercial energy system. Due to their high energy density and considerable cycle performance, Li-ion batteries have been widely used in many small electronic devices, electric vehicles (EV), hybrid electric vehicles (HEV), etc. But the fast update rate of these products is urgent for a superior battery system with higher specific capacity and longer cycle life.

Fluorinated solvents, nitrile compounds, sulfone compounds, and ionic liquids are new solvents or co-solvents to improve the high-voltage performance of lithium-ion batteries. Fluorinated organic solvents can bring various benefits to high-potential electrolytes by taking advantage of the high electronegativity and low polarity of fluorine atoms. A series of fluorinated carbonates have been reported as electrolytes in LIBs. Succinonitrile (SN) improves the thermal stability of Li _1.2 Ni _0.2 MnO. This is due to the formation of a homogeneous catholyte interfacial phase (CEI) by the interfacial reaction between the LNMO cathode electrode and the electrolyte. Adiponitrile is suitable as an electrolyte co-solvent for high-power lithium-ion batteries to improve thermal and electrochemical stability. In addition, many studies have found that 1,5-dicyanopentane additives can participate in the formation of dense and stable surface films, thereby improving the cycle stability and capacity retention of lithium-ion batteries. When the electrolyte contains water and acidic impurities, LiPF6 is prone to hydrolysis reaction with water, and the generated HF affects battery performance. Since ADN contains a nitrile functional group (-CN), this functional group can react not only with the acid in the electrolyte, but also with the water in the electrolyte, thereby reducing the content of free acid and water in the electrolyte, thus affecting the stability of the electrolyte improvement.

Relatively speaking, the LiNi _0.33 Co _0.33 Mn _0.33 O ₂ /graphite battery has the advantages of low cost, good reversible specific capacity and cycle stability. However, in the existing LiNi _0.33 Co _0.33 Mn _0.33 O ₂ /graphite battery, the performance of the electrolyte is not good enough, so that the high-voltage cycle performance of the battery is still not good enough.

Therefore, there is an urgent need for a new type of electrolyte to solve the above problems.

Contents of the invention

The first technical problem to be solved by the present invention is:

An electrolyte is provided.

The second technical problem to be solved by the present invention is:

A method for preparing the electrolyte is provided.

The third technical problem to be solved by the present invention is:

Application of the electrolyte.

In order to solve the first technical problem, the technical solution adopted in the present invention is:

An electrolyte comprising the following components:

Lithium source, 1,5-dicyanopentane and solvent;

The mass percentage of the 1,5-dicyanopentane in the electrolyte is 0.1-5%.

According to the embodiments of the present invention, one of the technical solutions has at least one of the following advantages or beneficial effects:

1. In the electrolytic solution of the present invention, 1,5-dicyanopentane is added as a film-forming additive, which has the effect of enhancing the stability and high-voltage cycle performance of the electrolytic solution. Make the electrolyte have a higher oxidation potential (>6.2V vs. Li/Li ⁺ ). Electrolyte solution of the present invention is used for preparing battery, and it can be found that battery shows remarkable high-voltage cycle performance, and this is attributed to 1,5-dicyanopentane can promote to generate stable SEI film, and the protective effect of SEI film prevents The further decomposition of the electrolyte and the dissolution of the transition metal ions are achieved, thereby stabilizing the electrode-electrolyte interface.

2. The 1,5-dicyanopentane of the present invention can react with H ₂ O or HF in the electrolyte, which can further improve the stability of the electrolyte. The reaction formula is as follows: C ₆ H ₁₀ N-CN+2H ₂ O+HF→C ₆ H ₁₀ N-COOH+NH ₄ F.

3. The 1,5-dicyanopentane is a colorless liquid, which can not only react with the acid in the electrolyte, but also react with water, thereby reducing the content of free acid and water in the electrolyte, thereby Improve the stability of the electrolyte.

4. The 1,5-dicyanopentane has a chain structure, and the valeronitrile additive not only has small side reactions, but also can form a dense and stable SEI film, thereby improving the cycle performance of lithium-ion batteries under high voltage.

According to one embodiment of the present invention, if the 1,5-dicyanopentane of the present invention is replaced by other nitrile additives, such as 1,2 dicyanoethane or 1,4 dicyanobutane, when After the electrolyte is assembled into a battery, it will be found that the cycle performance of the battery replaced by other nitrile additives will be greatly reduced. Further, when replaced with 1,2-dinitrile ethane, the capacity retention rate of the battery will decrease by at least 5% after 120 cycles, and the coulombic efficiency will decrease by at least 1% after 120 cycles; when replaced by 1,4-dinitrile After adding butane, the capacity retention rate of the battery will decrease by at least 12% after 120 cycles, and the Coulombic efficiency will decrease by at least 2% after 120 cycles.

According to one embodiment of the present invention, the mass percentage of the 1,5-dicyanopentane in the electrolyte is 0.1-5%.

According to one embodiment of the present invention, the mass percentage of the 1,5-dicyanopentane in the electrolyte is 0.1-2%.

According to an embodiment of the present invention, the lithium source includes at least one of lithium hexafluorophosphate, bistrifluoromethylsulfonimide and lithium bisfluorosulfonimide.

According to one embodiment of the present invention, the molar concentration of the lithium source is 1-5 mol/L.

According to one embodiment of the present invention, the molar concentration of the lithium source is 1-4 mol/L.

According to one embodiment of the present invention, the molar concentration of the lithium source is 2-5 mol/L.

According to one embodiment of the present invention, the solvent includes ethylene carbonate and ethyl methyl carbonate.

According to one embodiment of the present invention, the weight ratio of the ethylene carbonate to ethyl methyl carbonate is 1-2:1-2.

According to one embodiment of the present invention, the weight ratio of the ethylene carbonate to ethyl methyl carbonate is 1-2:1-1.5.

According to one embodiment of the present invention, the weight ratio of the ethylene carbonate to ethyl methyl carbonate is 1-1.5:1-2.

In order to solve the second technical problem, the technical solution adopted in the present invention is:

A method for preparing the electrolyte, comprising the steps of:

Mix the lithium source and 1,5-dicyanopentane in the solvent to obtain the electrolyte solution.

According to an embodiment of the present invention, a battery includes a positive electrode, a negative electrode, and the electrolyte.

According to an embodiment of the present invention, the negative electrode includes at least one of graphite, disodium terephthalate and NaTiOPO ₄ .

Another aspect of the present invention also relates to the application of the electrolyte in batteries. Including the nitrile-containing additive as described in the embodiment of the first aspect above. Since this application adopts all the technical solutions of the above-mentioned nitrile-containing additives, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments.

Another aspect of the present invention also relates to the application of the electrolyte in electrical equipment. Including the nitrile-containing additive as described in the embodiment of the first aspect above. Since this application adopts all the technical solutions of the above-mentioned nitrile-containing additives, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention.

Description of drawings

The above and/or additional aspects and advantages of the present invention will become apparent and understandable from the description of the embodiments in conjunction with the following drawings, wherein:

FIG. 1 is a test chart of the batteries of Example 2 and Comparative Example 1 subjected to linear sweep voltammetry.

FIG. 2 is a cycle performance test chart of the batteries of Comparative Example 1 and Examples 1-3.

Detailed ways

The embodiments of the present invention are described in detail below, and the same or similar symbols throughout the embodiments represent the same or similar elements or elements with the same or similar functions. The embodiments described below are exemplary only for explaining the present invention and should not be construed as limiting the present invention.

In the description of the present invention, if the first, second, etc. are described only for the purpose of distinguishing technical features, it cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or implying Indicates the sequence of the indicated technical features.

The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, not all of them. 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 scope of the present invention.

The reagents, methods and equipment used in the present invention are conventional reagents, methods and equipment in the technical field unless otherwise specified.

Example 1

An electrolyte comprising the following components:

Lithium hexafluorophosphate with a concentration of 1mol/L;

1,5-dicyanopentane with a mass percentage of 0.2%;

Ethylene carbonate and ethyl methyl carbonate in a weight ratio of 1:2;

The method for preparing electrolyte, comprises the following steps:

In a glove box filled with argon (oxygen and moisture<1ppm), lithium hexafluorophosphate and 1,5-dicyanopentane were mixed in a solvent to obtain the above electrolyte.

The above-mentioned electrolyte is prepared into a lithium-ion battery, wherein the positive electrode slurry is prepared from the following components in mass percentage:

96.8% LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , 1.2% polyvinylidene fluoride (PVDF) binder and 2% carbon black conductive agent (SP).

Negative electrode slurry is prepared with the following components in mass percentage:

95% graphite, 1.5% sodium carboxymethylcellulose (CMC), 1.5% carbon black conductive agent (SP) and 2% styrene-butadiene rubber (SBR).

Example 2

An electrolyte comprising the following components:

Lithium hexafluorophosphate with a concentration of 1mol/L;

1,5-dicyanopentane with a mass percentage of 0.5%;

Ethylene carbonate and ethyl methyl carbonate in a weight ratio of 1:2;

The method for preparing electrolyte, comprises the following steps:

In a glove box filled with argon (oxygen and moisture<1ppm), lithium hexafluorophosphate and 1,5-dicyanopentane were mixed in a solvent to obtain the above electrolyte.

The above-mentioned electrolyte is prepared into a lithium-ion battery, wherein the positive electrode slurry is prepared from the following components in mass percentage:

96.8% LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , 1.2% polyvinylidene fluoride (PVDF) binder and 2% carbon black conductive agent (SP).

The negative electrode slurry is prepared from the following components in mass percentage:

95% graphite, 1.5% sodium carboxymethylcellulose (CMC), 1.5% carbon black conductive agent (SP) and 2% styrene-butadiene rubber (SBR).

Example 3

An electrolyte comprising the following components:

Lithium hexafluorophosphate with a concentration of 1mol/L;

1,5-dicyanopentane with a mass percentage of 1%;

Ethylene carbonate and ethyl methyl carbonate in a weight ratio of 1:2;

The method for preparing electrolyte, comprises the following steps:

In a glove box filled with argon (oxygen and moisture<1ppm), lithium hexafluorophosphate and 1,5-dicyanopentane were mixed in a solvent to obtain the above electrolyte.

The above-mentioned electrolyte is prepared into a lithium-ion battery, wherein the positive electrode slurry is prepared from the following components in mass percentage:

96.8% LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , 1.2% polyvinylidene fluoride (PVDF) binder and 2% carbon black conductive agent (SP).

The negative electrode slurry is prepared from the following components in mass percentage:

95% graphite, 1.5% sodium carboxymethylcellulose (CMC), 1.5% carbon black conductive agent (SP) and 2% styrene-butadiene rubber (SBR).

Comparative example 1

The difference between Comparative Example 1 and Example 2 is that the electrolyte solution of Comparative Example 1 does not contain 1,5-dicyanopentane.

An electrolyte comprising the following components:

Lithium hexafluorophosphate with a concentration of 1mol/L;

Ethylene carbonate and ethyl methyl carbonate in a weight ratio of 1:2;

The method for preparing electrolyte, comprises the following steps:

In a glove box filled with argon (oxygen and moisture<1ppm), lithium hexafluorophosphate is mixed in a solvent to obtain the above electrolyte.

The above-mentioned electrolyte is prepared into a lithium-ion battery, wherein the positive electrode slurry is prepared from the following components in mass percentage:

96.8% LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , 1.2% polyvinylidene fluoride (PVDF) binder and 2% carbon black conductive agent (SP).

The negative electrode slurry is prepared from the following components in mass percentage:

95% graphite, 1.5% sodium carboxymethylcellulose (CMC), 1.5% carbon black conductive agent (SP) and 2% styrene-butadiene rubber (SBR).

Comparative example 2

The difference between Comparative Example 2 and Example 2 is that: the nitrile-containing additive in Comparative Example 2 is 1,2-dicyanoethane; the nitrile-containing additive in Example 3 is 1,5-dicyanopentane.

An electrolyte comprising the following components:

Lithium hexafluorophosphate with a concentration of 1mol/L;

The mass percentage is 0.5% of 1,2-dicyanoethane;

Ethylene carbonate and ethyl methyl carbonate in a weight ratio of 1:2;

The method for preparing electrolyte, comprises the following steps:

In a glove box filled with argon (oxygen and moisture<1ppm), lithium hexafluorophosphate and 1,2-dicyanoethane were mixed in a solvent to obtain the above electrolyte.

The above-mentioned electrolyte is prepared into a lithium-ion battery, wherein the positive electrode slurry is prepared from the following components in mass percentage:

96.8% LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , 1.2% polyvinylidene fluoride (PVDF) binder and 2% carbon black conductive agent (SP).

The negative electrode slurry is prepared from the following components in mass percentage:

95% graphite, 1.5% sodium carboxymethylcellulose (CMC), 1.5% carbon black conductive agent (SP) and 2% styrene-butadiene rubber (SBR).

Comparative example 3

The difference between Comparative Example 3 and Example 2 is that: the nitrile-containing additive in Comparative Example 2 is 1,4-dicyanobutane; the nitrile-containing additive in Example 3 is 1,5-dicyanopentane.

An electrolyte comprising the following components:

Lithium hexafluorophosphate with a concentration of 1mol/L;

1,4 dicyanobutane with a mass percentage of 0.5%;

Ethylene carbonate and ethyl methyl carbonate in a weight ratio of 1:2;

The method for preparing electrolyte, comprises the following steps:

In a glove box filled with argon (oxygen and moisture<1ppm), lithium hexafluorophosphate and 1,4 dicyanobutane were mixed in a solvent to obtain the above electrolyte.

The above-mentioned electrolyte is prepared into a lithium-ion battery, wherein the positive electrode slurry is prepared from the following components in mass percentage:

96.8% LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , 1.2% polyvinylidene fluoride (PVDF) binder and 2% carbon black conductive agent (SP).

The negative electrode slurry is prepared from the following components in mass percentage:

95% graphite, 1.5% sodium carboxymethylcellulose (CMC), 1.5% carbon black conductive agent (SP) and 2% styrene-butadiene rubber (SBR).

Performance Testing:

The electrochemical window of the electrolyte in the system with platinum as the working electrode and metal lithium as the reference electrode was studied by linear sweep voltammetry (LSV). The battery test was completed by an electrochemical workstation (PGSTAT 3302N). The normal temperature and high voltage performance of 120 cycles in the range of 2.75V-4.4V was tested on a multi-channel battery performance tester (CT-3008W-5V/6A).

The batteries of Examples 1-3 and Comparative Examples 1-3 were tested for capacity retention and coulombic efficiency, and the test results are shown in Table 1.

Table 1

group Capacity retention after 120 cycles Coulombic efficiency after 120 cycles Example 1 68.3% 97.3% Example 2 85.2% 99.31% Example 3 70.4% 97.63% Comparative example 1 67.96% 96.91% Comparative example 2 80.3% 98.3% Comparative example 3 73.3% 97.86%

The batteries of Example 2 and Comparative Example 1 were tested by linear sweep voltammetry, and the test results are shown in FIG. 1 . It can be known from Figure 1 that the electrolyte containing 1,5-dicyanopentane (ADN) has a wider electrochemical window than the electrolyte without ADN. It shows that ADN as an additive can improve the electrochemical stability of the electrolyte. For Comparative Example 1, the current density increased significantly when the scanning voltage was close to 5.7V. However, for Example 2, the current density increases slowly until the decomposition potential is greater than 6.2 V. The results further indicate that ADN can actually increase the decomposition potential of the electrolyte and improve the oxidation stability of the electrolyte.

In order to explore the influence of ADN on the cycle performance of LiNi _0.33 Co _0.33 Mn _0.33 O ₂ /graphite batteries under high voltage (4.4V), the batteries of Comparative Example 1 and Examples 1-3 were placed in room temperature and 4.4V environment for long-term Cyclic performance test, the test results are shown in Figure 2.

As can be seen from a in Figure 2, the cycle performance of Example 1 is worse, obviously, the addition of 0.2% ADN does not reach saturation; the cycle performance of Example 3 is worse, obviously, adding too much ADN will cause SEI The film becomes thicker, resulting in reduced cycle performance. In Comparative Example 1, because no ADN was added, the stability of the electrolyte deteriorated, causing the electrolyte to decompose and the cycle performance of the battery to decrease. Based on the electrochemical test and the above analysis, it is concluded that the optimum mass percentage of ADN is 0.5%. Further, the battery capacity of Example 2 decays more slowly, and there is no rapid decay process. After 120 cycles, the battery capacity (1747.3mAh) remained at 85.2% of its initial discharge capacity (2050.8mAh), which was 17.24% higher than that of the battery without ADN (corresponding to Comparative Example 1). Therefore, the improved cycle performance of the battery at high voltage can be attributed to the addition of ADN in the electrolyte.

It can be seen from b in FIG. 2 that the battery of Example 2 and the battery of Comparative Example 1 exhibited similar coulombic efficiencies during the first to 80 cycles, and the coulombic efficiency exceeded 99%. However, after 80 cycles, the Coulombic efficiency of the battery of Comparative Example 1 continued to decay due to the absence of ADN. It may be that the electrolyte decomposes during the long-term cycle, consumes Li ⁺ , and produces products such as alkyl lithium carbonate, resulting in the irreversible reduction of Li ⁺ , which is also consistent with the cycle performance diagram in Figure 1 above. As the cycle proceeds, the Coulombic efficiency of the battery of Example 2 is always maintained above 99%, and remains at 99.313% after 120 cycles. However, the Coulombic efficiency of the battery of Comparative Example 1 only decayed to 96.91% after 120 cycles, indicating that the battery suffered severe electrochemical decomposition during cycling. The results show that the addition of ADN in the electrolyte can form a more stable SEI film and significantly improve the cycle performance at high voltage.

The above are only examples of the present invention, and are not intended to limit the patent scope of the present invention. All equivalent transformations made by using the content of the description of the present invention, or directly or indirectly used in related technical fields, are equally included in the patent protection of the present invention. within range.

Claims (10)

1. An electrolyte, characterized in that: comprising the following components: Lithium source, 1,5-dicyanopentane and solvent; The mass percentage of the 1,5-dicyanopentane in the electrolyte is 0.1-5%. 2. The electrolytic solution according to claim 1, characterized in that: the mass percentage of the 1,5-dicyanopentane in the electrolytic solution is 1-2%. 3. The electrolyte solution according to claim 1, wherein the lithium source comprises at least one of lithium hexafluorophosphate, bistrifluoromethylsulfonimide and lithium bisfluorosulfonimide. 4. The electrolyte solution according to claim 1, characterized in that: the molar concentration of the lithium source is 1-5 mol/L. 5. The electrolytic solution according to claim 1, characterized in that: said solvent comprises ethylene carbonate and ethyl methyl carbonate. 6. The electrolytic solution according to claim 5, characterized in that: the weight ratio of the ethylene carbonate to ethyl methyl carbonate is 1-2:1-2. 7. A method for preparing the electrolytic solution according to any one of claims 1 to 6, characterized in that: comprising the following steps: Mix the lithium source and 1,5-dicyanopentane in the solvent to obtain the electrolyte solution. 8. A battery, characterized in that it comprises a positive electrode, a negative electrode and the electrolyte according to any one of claims 1 to 6. 9 . The battery according to claim 8 , wherein the negative electrode comprises at least one of graphite, disodium terephthalate and NaTiOPO ₄ . 10. The application of the electrolytic solution according to any one of claims 1 to 6 in batteries or electrical equipment.

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