Organic lithium supplement agent and preparation method and application thereof

Abstract

The invention relates to an organic lithium supplement agent and a preparation method and application thereof. The preparation method comprises the following steps: mixing an aromatic compound with a lithium source to obtain a mixture, and sintering the mixture in a protective gas atmosphere at 220-300 DEG C to obtain the organic lithium supplement agent. According to the preparation method provided by the invention, the cyanophenyl compound and the lithium source are mixed and then sintered in a protective gas atmosphere at a specific temperature, so that the organic lithium supplementing agent can be prepared, and the preparation method is simple and does not need a solvent. The preparation method is not only suitable for cyanophenyl compounds, but also suitable for biphenyl nitrile compounds and naphthyl nitrile compounds. When the organic lithium supplement agent prepared by the preparation method is used for preparing the lithium ion battery, the specific capacity, the first coulombic efficiency and the cycle retention performance of the lithium ion battery can be improved, and the electrochemical impedance of the lithium ion battery can be reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and more specifically, to an organic lithium supplement agent and a preparation method and application thereof. Background Art

[0002] With the increasing depletion of fossil energy and the enhancement of global environmental awareness, new energy electric vehicles are seen as the best choice to replace traditional fuel vehicles in the future. With the popularization of new energy electric vehicles, the requirements for lithium-ion battery performance continue to increase, especially in terms of long driving range, which has driven the market demand for and resource investment in the research and development of high specific capacity batteries. While meeting the requirements of battery safety, rate performance and cycle life, improving specific capacity has become a key factor in the future large-scale market promotion of new energy electric vehicles and replacing traditional fuel vehicles.

[0003] During the initial charge and discharge process of lithium-ion batteries, the electrolyte decomposes on the surface of the negative electrode to form a solid electrolyte interface (SEI) film. This process permanently consumes a large amount of lithium in the positive electrode, resulting in a low initial coulombic efficiency (ICE), which reduces the capacity and energy density of the battery. Existing graphite negative electrode materials will cause 5-10% irreversible lithium loss, and for silicon-based and tin-based alloy negative electrodes with high specific capacity, the irreversible lithium loss is even as high as 10-20%. The technology to supplement the lithium loss in the above process is lithium-ion battery lithium replenishment technology, which is an important means to improve the specific capacity of the battery.

[0004] At present, lithium replenishment technology for lithium-ion batteries can be divided into two categories according to the technical route: negative electrode replenishment and positive electrode replenishment. Among them, positive electrode replenishment technology has the advantages of being relatively stable, easy to implement, and having high lithium replenishment capacity. Positive electrode replenishment agent refers to the lithium in the first charge and discharge process within the operating voltage range of the battery. + Can be removed without reinsertion, used to compensate for the active Li consumed by SEI formation + High-capacity lithium-containing materials. Compared with inorganic lithium supplements, the decomposition products of organic lithium supplements after lithium supplementation do not produce additional impurities such as gas or moisture under high voltage. 3,4-dihydroxybenzonitrile lithium is one of the organic lithium supplements. The existing preparation method is usually a liquid phase synthesis method (see document: DOI:10.1149 / ma2020-0113mtgabs). The synthesis steps are: first dissolve 3,4-dihydroxybenzonitrile in anhydrous tetrahydrofuran and stir evenly, then add lithium hydride and stir for 15 hours to carry out lithiation reaction, and finally purify and dry to obtain the target compound. This method has strict requirements on solvents (for example, it is necessary to control anhydrous), and the use of solvents will bring post-processing steps such as waste liquid treatment.

[0005] The existing methods for preparing organic lithium supplements have high solvent requirements and complex post-processing, which greatly restricts the application of organic lithium supplements in large-scale industrial production of lithium-ion batteries. Therefore, new technologies need to be developed to solve the current problems. Summary of the invention

[0006] The primary purpose of the present invention is to overcome the problems of high solvent requirements and complex post-processing in the above-mentioned existing methods for preparing organic lithium supplements, and to provide a method for preparing an organic lithium supplement. In the preparation method provided by the present invention, a benzonitrile compound is mixed with a lithium source, and then sintered under a protective gas atmosphere and a specific temperature to prepare an organic lithium supplement. The preparation method is simple and does not require a solvent. The preparation method is not only applicable to benzonitrile compounds, but also to diphenylnitrile compounds and naphthalene nitrile compounds. The organic lithium supplement prepared by the preparation method is used to prepare lithium-ion batteries, which can improve the specific capacity, first coulomb efficiency, cycle retention performance of lithium-ion batteries, and reduce the electrochemical impedance of lithium-ion batteries.

[0007] A further object of the present invention is to provide an organic lithium supplement prepared by the above preparation method.

[0008] Another object of the present invention is to provide a positive electrode mixed material added with the organic lithium supplement agent.

[0009] Another object of the present invention is to provide a lithium ion battery having the positive electrode mixed material added thereto.

[0010] The above-mentioned object of the present invention is achieved by the following technical solutions:

[0011] A method for preparing an organic lithium supplement comprises the following steps:

[0012] The aromatic compound is mixed with a lithium source to obtain a mixture, and the mixture is sintered under a protective gas atmosphere at 220-300° C. to obtain the organic lithium supplement;

[0013] The aromatic compound is a structure represented by any one of formula (I) to formula (III):

[0014]

[0015] In formula (I) and formula (II), R 1 , R 2 are independently H, OH or COOH, and R 1 and R 2 At least one of them is OH or COOH;

[0016] In formula (III), R 3 , R 4 , R 5 , R 6are independently H, OH or COOH, and R 3 , R 4 , R 5 and R 6 At least one of them is OH or COOH.

[0017] In the preparation method provided by the present invention, a benzonitrile compound (formula (I)) is mixed with a lithium source, and then sintered under a protective gas atmosphere and a specific temperature to prepare an organic lithium supplement. The preparation method is simple and does not require a solvent.

[0018] The inventors of the present invention have also found that the preparation method is not only applicable to benzonitrile compounds, but also to biphenylnitrile compounds and naphthalenenitrile compounds.

[0019] The organic lithium supplement prepared by the preparation method is used to prepare lithium-ion batteries, which can improve the specific capacity, first coulomb efficiency, and cycle retention performance of lithium-ion batteries, and reduce the electrochemical impedance of lithium-ion batteries.

[0020] Preferably, the aromatic compound is any of the following structures:

[0021]

[0022] More preferably, the aromatic compound is any of the following structures:

[0023] When the aromatic compound has these structures, the electron cloud density at the hydroxyl or carboxyl position in the aromatic compound is smaller, so that the potential at this position is lower and it is easier to remove lithium, thereby making the prepared organic lithium supplement The lithium-ion battery has better electrochemical performance.

[0024] Preferably, the ratio of the sum of the amounts of hydroxyl and carboxyl groups in the aromatic compound to the amount of lithium in the lithium source is 1:0.8-1.6.

[0025] More preferably, the ratio of the sum of the amounts of hydroxyl and carboxyl groups in the aromatic compound to the amount of lithium in the lithium source is 1:0.9-1.45.

[0026] Further preferably, the ratio of the sum of the amount of hydroxyl and carboxyl groups in the aromatic compound to the amount of lithium in the lithium source is 1:0.9-1.1. Under the same other conditions, when the ratio of the sum of the amount of hydroxyl and carboxyl groups in the aromatic compound to the amount of lithium in the lithium source is regulated within this range, the prepared organic lithium supplement can improve the specific capacity, first coulomb efficiency, cycle retention performance of the lithium-ion battery, and reduce the electrochemical impedance of the lithium-ion battery.

[0027] Preferably, the average particle size of the mixture before sintering is less than 25 μm.

[0028] The inventors of the present invention have found through research that by controlling the average particle size of the mixture obtained by mixing the aromatic compound with the lithium source to below 25 μm, the contact area between the aromatic compound and the lithium source can be increased, which is conducive to a more complete reaction and thus shortens the reaction time.

[0029] Preferably, the sintering time is 4 to 12 hours.

[0030] The preparation method of the invention can prepare the organic lithium supplement agent within 4 to 12 hours, and the reaction time is greatly shortened compared with the liquid phase synthesis method.

[0031] Preferably, the lithium source is one or both of an inorganic lithium source and an organic lithium source.

[0032] More preferably, the inorganic lithium source is one or both of lithium hydroxide and inorganic lithium salt.

[0033] More preferably, the lithium hydroxide is lithium hydroxide.

[0034] More preferably, the inorganic lithium salt is lithium carbonate.

[0035] More preferably, the organic lithium source is lithium oxalate.

[0036] Preferably, the protective gas is at least one of nitrogen or argon.

[0037] Preferably, the temperature is raised from room temperature to the sintering temperature (220-300° C.) at a heating rate of 2-10° C. / min. Specifically, the heating rate may be 2° C. / min, 4° C. / min, 6° C. / min, 8° C. / min, or 10° C. / min.

[0038] Preferably, the step of sanding is further included after sintering.

[0039] More preferably, the sand grinding process is: sand grinding the sintered product to an average particle size of 4 to 10 μm.

[0040] The present invention also protects an organic lithium supplement agent prepared by the above preparation method.

[0041] The present invention also protects a lithium ion battery positive electrode material, wherein the lithium ion battery positive electrode material contains the above organic lithium supplement agent.

[0042] The use of the above organic lithium supplement in the preparation of positive electrode materials for lithium-ion batteries is also within the protection scope of the present invention.

[0043] The present invention also protects a lithium ion battery, which includes a positive electrode, and the material of the positive electrode is the above-mentioned lithium ion battery positive electrode material.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] In the preparation method provided by the present invention, a benzonitrile compound is mixed with a lithium source, and then sintered in a protective gas atmosphere at a specific temperature to prepare an organic lithium supplement. The preparation method is simple and does not require a solvent. The preparation method is not only applicable to benzonitrile compounds, but also to biphenylnitrile compounds and naphthalene nitrile compounds. The organic lithium supplement prepared by the preparation method is used to prepare lithium-ion batteries, which can improve the specific capacity, first coulomb efficiency, cycle retention performance of lithium-ion batteries, and reduce the electrochemical impedance of lithium-ion batteries. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is the infrared spectrum of 3,4-dihydroxybenzonitrile of Example 1.

[0047] Figure 2 This is the infrared spectrum of the organic lithium supplement agent prepared in Example 1. DETAILED DESCRIPTION

[0048] In order to more clearly and completely describe the technical solution of the present invention, the present invention is further described in detail through specific embodiments below. It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention. Various changes can be made within the scope of the rights of the present invention.

[0049] Example 1

[0050] This embodiment provides a method for preparing an organic lithium supplement agent, comprising the following steps:

[0051] 1) Mixing an aromatic compound with a lithium source to obtain a mixture; the aromatic compound is 3,4-dihydroxybenzonitrile, and its structure is as follows:

[0052]

[0053] The lithium source is lithium carbonate; the ratio of the amount of hydroxyl in the aromatic compound to the amount of lithium in the lithium source is 1:1.

[0054] 2) The mixture obtained in step 1) is sand-milled to make the average particle size of the mixture after sand-milling be less than 20 μm.

[0055] 3) placing the mixture treated in step 2) in an argon atmosphere for sintering, the sintering process is: heating to 260° C. at a heating rate of 5° C. / min, and then keeping the temperature for 10 hours; then sand grinding the sintered product to make the average particle size of the sintered product less than 6 μm, thereby obtaining the organic lithium supplement agent.

[0056] Example 2

[0057] This embodiment provides a method for preparing an organic lithium supplement. The difference from Embodiment 1 is that the aromatic compound is p-hydroxybenzonitrile, and its structure is as follows:

[0058]

[0059] The ratio of the amount of substance of the hydroxyl group in the aromatic compound to the amount of substance of the lithium in the lithium source is 1:1.2.

[0060] Example 3

[0061] This embodiment provides a method for preparing an organic lithium supplement. The difference from Embodiment 2 is that the ratio of the amount of hydroxyl groups in the aromatic compound to the amount of lithium in the lithium source is 1:0.9.

[0062] Example 4

[0063] This embodiment provides a method for preparing an organic lithium supplement. The difference from Embodiment 1 is that the aromatic compound is 5-cyano-2-hydroxybenzoic acid, and its structure is as follows:

[0064]

[0065] The lithium source is lithium hydroxide; the ratio of the sum of the amounts of hydroxyl and carboxyl groups in the aromatic compound to the amount of lithium in the lithium source is 1:1.3.

[0066] Example 5

[0067] This embodiment provides a method for preparing an organic lithium supplement. The difference from Embodiment 4 is that the ratio of the sum of the amounts of hydroxyl and carboxyl groups in the aromatic compound to the amount of lithium in the lithium source is 1:1.05.

[0068] Example 6

[0069] This embodiment provides a method for preparing an organic lithium supplement. The difference from Embodiment 1 is that the aromatic compound is 4-(3-hydroxyphenyl)benzonitrile, and its structure is as follows:

[0070]

[0071] The lithium source is obtained by mixing lithium hydroxide and lithium carbonate in a molar ratio of 1:1; the molar ratio of the hydroxyl group in the aromatic compound to the molar ratio of the lithium in the lithium source is 1:1.4.

[0072] Example 7

[0073] This embodiment provides a method for preparing an organic lithium supplement. The difference from Embodiment 6 is that the ratio of the amount of hydroxyl groups in the aromatic compound to the amount of lithium in the lithium source is 1:1.2.

[0074] Example 8

[0075] This embodiment provides a method for preparing an organic lithium supplement. The difference from Embodiment 1 is that the aromatic compound is 4-hydroxy-4-biphenylcarbonitrile, and its structure is as follows:

[0076]

[0077] The lithium source is obtained by mixing lithium hydroxide and lithium carbonate in a molar ratio of 8:2; the molar ratio of the hydroxyl group in the aromatic compound to the molar ratio of the lithium in the lithium source is 1:1.

[0078] Example 9

[0079] This embodiment provides a method for preparing an organic lithium supplement. The difference from Embodiment 8 is that the ratio of the amount of hydroxyl groups in the aromatic compound to the amount of lithium in the lithium source is 1:1.2.

[0080] Example 10

[0081] This embodiment provides a method for preparing an organic lithium supplement agent, comprising the following steps:

[0082] 1) Mixing an aromatic compound with a lithium source to obtain a mixture; the aromatic compound is p-cyanobenzoic acid, and its structure is as follows:

[0083]

[0084] The lithium source is obtained by mixing lithium hydroxide and lithium carbonate in a molar ratio of 7:3; the molar ratio of the carboxyl group in the aromatic compound to the lithium in the lithium source is 1:1.

[0085] 2) The mixture obtained in step 1) is sand-milled to make the average particle size of the mixture after sand-milling be less than 15 μm.

[0086] 3) placing the mixture treated in step 2) in an argon atmosphere for sintering, the sintering process is: heating to 300° C. at a heating rate of 10° C. / min, and then keeping the temperature for 4 hours; then sand-milling the sintered product to make the average particle size of the sintered product less than 10 μm, thereby obtaining the organic lithium supplement agent.

[0087] Embodiment 11

[0088] This embodiment provides a method for preparing an organic lithium supplement agent, comprising the following steps:

[0089] 1) Mixing an aromatic compound with a lithium source to obtain a mixture; the aromatic compound is 3-hydroxy-1-naphthonitrile, and its structure is as follows:

[0090]

[0091] The lithium source is lithium hydroxide; the ratio of the amount of hydroxyl in the aromatic compound to the amount of lithium in the lithium source is 1:1.05.

[0092] 2) The mixture obtained in step 1) is sand-milled to make the average particle size of the mixture after sand-milling be less than 25 μm.

[0093] 3) placing the mixture treated in step 2) in an argon atmosphere for sintering, the sintering process is: heating to 220° C. at a heating rate of 2° C. / min, and then keeping the temperature for 12 hours; then sand-milling the sintered product to make the average particle size of the sintered product less than 4 μm, thereby obtaining the organic lithium supplement agent.

[0094] Comparative Example 1

[0095] This comparative example provides a method for preparing an organic lithium supplement agent, which is different from Example 1 in that the temperature in step 3) is 120°C.

[0096] Comparative Example 2

[0097] This comparative example provides a method for preparing an organic lithium supplement agent, which is different from Example 1 in that the temperature in step 3) is 400°C.

[0098] Comparative Example 3

[0099] The present comparative example provides a method for preparing an organic lithium supplement, comprising the following steps: adding 3,4-dihydroxybenzonitrile to 15 mL of anhydrous tetrahydrofuran, stirring until the 3,4-dihydroxybenzonitrile is completely dissolved, then adding a lithium source, the lithium source is lithium carbonate, the ratio of the sum of the amounts of hydroxyl and carboxyl groups in the 3,4-dihydroxybenzonitrile to the amount of lithium in the lithium source is 1:1, stirring for 15 hours, filtering to obtain a solid, and vacuum drying at 150° C. for 5 hours to obtain an organic lithium supplement.

[0100] Performance Testing

[0101] 1. Infrared spectroscopy characterization

[0102] The aromatic compound and the organic lithium supplement agent of Example 1 were subjected to infrared spectroscopy measurement. The measurement results were as follows: Figure 1 and Figure 2 As shown. Figure 1 and Figure 2 It can be seen that the hydroxyl peak (3400cm -1The peak intensity of the aromatic compound before the reaction is significantly weakened, indicating that the hydroxyl group of the aromatic compound reacts with the lithium source, indicating the successful synthesis of the organic lithium supplement. The infrared spectra of the aromatic compound and the organic lithium supplement of other examples are similar to those of Example 1, indicating that the preparation method of the present invention successfully prepares the organic lithium supplement.

[0103] 2. Determination of the electrochemical performance of the battery

[0104] Preparation of positive electrode materials: Weigh 1g of the organic lithium supplement prepared in Examples 1 to 11 and Comparative Examples 1 to 3, 8g of the positive electrode active material LiNi 0.5 Mn 4 O 4 , 1.5 g of conductive agent SP (carbon black), 0.5 g of binder polyvinylidene fluoride, grind evenly, add 7 g of NMP and mix to obtain a positive electrode material.

[0105] Preparation of negative electrode material: Weigh 8 g of silicon-carbon material, 1 g of conductive agent SP (carbon black), and 0.5 g of carboxymethyl cellulose powder, grind them evenly, add 9 g of deionized water and mix them to obtain the negative electrode material.

[0106] Preparation of button batteries: The positive electrode material and the negative electrode material are coated on aluminum foil and copper foil respectively, and then vacuum dried at 120°C for 2 hours to form electrodes with a diameter of 12 mm, which are then transferred to a glove box and assembled into button batteries with a specification of 2032.

[0107] In addition, a comparative button cell is also provided, in which the positive electrode material does not contain the organic lithium supplement agent prepared by the present invention.

[0108] The button-type battery / comparison button-type battery prepared as above was subjected to the measurement of the first discharge capacity, the first coulombic efficiency, the capacity retention rate after 500 cycles of charge and discharge, and the electrochemical impedance. The measurement results are shown in Table 1.

[0109] Table 1 Electrochemical performance test results

[0110]

[0111] As shown in Table 1, the first discharge capacity of the lithium-ion battery prepared with the organic lithium supplement agent in Examples 1 to 11 is above 975 mAh / g, the first coulomb efficiency is higher than 85%, the capacity retention rate after 500 cycles of charge and discharge is higher than 85%, and the electrochemical impedance is less than or equal to 83π / cm 2, indicating that the organic lithium supplement prepared by the present invention can achieve lithium removal in lithium-ion batteries, and the lithium-ion batteries containing the organic lithium supplement have good electrochemical performance. Among them, the organic lithium supplement prepared in Example 1 has the best electrochemical comprehensive performance, with the highest first discharge capacity of 1070mAh / g, the highest first coulombic efficiency of 93.3%, the highest capacity retention rate after 500 cycles of charge and discharge of 94.1%, and the lowest electrochemical impedance of 25π / cm 2 .

[0112] It can be seen from Examples 2 to 9 that, under the same other conditions, the closer the ratio of the sum of the amounts of hydroxyl and carboxyl groups in the aromatic compound to the amount of lithium in the lithium source is to 1:1, the better the electrochemical performance of the lithium ion battery of the prepared organic lithium supplement.

[0113] The electrochemical performance of the lithium ion battery of the organic lithium supplement prepared in Example 5 is better than that in Example 11. The reason is that the aromatic compound selected in Example 5 has fewer benzene rings, which makes the electron cloud density of the hydroxyl position in the aromatic compound small, which makes the potential of this position lower and easier to remove lithium.

[0114] Comparative Example 1 and Comparative Example 2 are respectively the cases where the temperature is too low and too high. A temperature that is too low may make it difficult for the raw materials to react, and a temperature that is too high may cause the raw materials to decompose at high temperature to form other substances. Both of these cases are equivalent to introducing impurities into the positive electrode of the battery, which deteriorates the electrochemical performance of the lithium-ion battery prepared with the organic lithium supplement.

[0115] Comparative Example 3 is a liquid phase synthesis method of the prior art (see document: DOI: 10.1149 / ma2020-0113mtgabs). The organic lithium supplement prepared in Example 1 has similar electrochemical properties to that of Comparative Example 3, but the preparation method of the present invention is simple, does not require a solvent, and shortens the reaction time, which is conducive to application in large-scale industrial production of lithium-ion batteries.

[0116] Obviously, the above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the embodiments here. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing an organic lithium supplement, characterized in that: The steps include: The aromatic compound is mixed with a lithium source to obtain a mixture, and the mixture is sintered under a protective gas atmosphere at 220-300° C. to obtain the organic lithium supplement; The aromatic compound is a structure represented by any one of formula (I) to formula (III): In formula (I) and formula (II), R1 and R2 are independently H, OH or COOH, and at least one of R1 and R2 is OH or COOH; In formula (III), R3, R4, R5, and R6 are independently H, OH, or COOH, and at least one of R3, R4, R5, and R6 is OH or COOH.

2. The preparation method according to claim 1, characterized in that: The aromatic compound is any of the following structures:

3. The preparation method according to claim 1, characterized in that: The ratio of the sum of the amounts of hydroxyl and carboxyl groups in the aromatic compound to the amount of lithium in the lithium source is 1:0.8-1.

6.

4. The preparation method according to claim 1, characterized in that: The average particle size of the mixture before sintering is less than 25 μm.

5. The preparation method according to claim 1, characterized in that: The lithium source is one or both of an inorganic lithium source and an organic lithium source.

6. The preparation method according to claim 1, characterized in that: The sintering time is 4 to 12 hours.

7. An organic lithium supplement, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 6.

8. A positive electrode material for a lithium ion battery, characterized in that: The lithium-ion battery positive electrode material contains the organic lithium supplement agent according to claim 7.

9. Use of the organic lithium supplement agent according to claim 7 in preparing positive electrode materials for lithium-ion batteries.

10. A lithium ion battery, characterized in that: The lithium-ion battery comprises a positive electrode, and the material of the positive electrode is the lithium-ion battery positive electrode material according to claim 9.

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