Preparation method of positive electrode lithium supplement additive and application thereof and positive electrode of lithium ion battery

Abstract

The invention discloses a preparation method of a positive electrode lithium supplement additive and its application and a positive electrode of a lithium ion battery, belonging to the technical field of lithium ion batteries. The preparation method thereof is as follows: 1) silicon tetrafluoride gas is absorbed by water to obtain a fluosilicic acid solution containing silicon dioxide precipitates, and the fluosilicic acid solution and silicon dioxide solid are obtained by filtration; 2) the fluosilicic acid solution and lithium hydroxide are subjected to alkaline hydrolysis reaction to generate a slurry solution containing a mixed precipitate of lithium fluoride and silicon dioxide, and a lithium fluoride mixed filter cake containing silicon dioxide is obtained after aging, filtering and washing; 3) the lithium fluoride mixed filter cake containing silicon dioxide is vacuum dried and sintered to obtain the positive electrode lithium supplement additive. The preparation method is simple and the conditions are mild. The obtained lithium supplement additive is applied to the positive electrode of a lithium ion battery, which can improve the short board problem of low initial efficiency of the positive electrode of the lithium ion battery, further improve the battery energy density and extend the cycle life, and lay the foundation for the preparation of high-capacity lithium ion batteries.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and specifically relates to a preparation method of a positive electrode lithium supplement additive and an application thereof and a positive electrode of a lithium ion battery. Background Art

[0002] As market demand increases, the energy density of lithium-ion batteries is required to increase, and the search for cathode materials with larger battery capacity has become one of the hottest topics in the battery field today. With the continuous development of lithium-ion batteries, cathode materials with high battery capacity are gradually being used in lithium-ion batteries. + Due to the positive electrode material, during the first charging of the battery, the positive electrode surface of the lithium-ion battery consumes Li + A layer of SEI film is formed, resulting in the initial charge and discharge capacity loss (Initial Capacity Loss, ICL), which in turn causes problems such as low first-cycle efficiency and poor cycle life.

[0003] Lithium replenishment additives can optimize the efficiency and cycle life of the first cycle of the battery. Lithium replenishment additives actually pre-lithiate the electrode material, and improve the first cycle efficiency and life by replenishing the lithium loss during the first cycle. By replenishing lithium to the electrode material, the irreversible lithium loss caused by the formation of the SEI film is offset to increase the total capacity and energy density of the battery. Therefore, the development of simple and efficient lithium replenishment technology is extremely important for promoting the application of positive electrode materials in lithium-ion batteries. Summary of the invention

[0004] The purpose of the present invention is to provide a method for preparing a positive electrode lithium supplement additive and its application and a lithium ion battery positive electrode. The method is simple to operate. The obtained lithium supplement additive is applied to the lithium ion battery positive electrode, which can improve the shortcoming of the low initial efficiency of the lithium ion battery positive electrode, further improve the battery capacity and extend the cycle life, laying a foundation for the preparation of high-capacity lithium ion batteries.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] A method for preparing a positive electrode lithium supplement additive is provided, comprising the following steps:

[0007] S1: absorbing silicon tetrafluoride gas with water to obtain a fluorosilicic acid solution containing silicon dioxide precipitate, and filtering to obtain a fluorosilicic acid solution and silicon dioxide solid;

[0008] S2: subjecting the fluorosilicic acid solution obtained in step S1 and lithium hydroxide to an alkaline hydrolysis reaction to generate a slurry solution containing a mixed precipitate of lithium fluoride and silicon dioxide, and subjecting the slurry solution to aging, filtering and washing to obtain a lithium fluoride mixed filter cake containing silicon dioxide;

[0009] S3: The lithium fluoride mixed filter cake containing silicon dioxide obtained in step S2 is vacuum dried and sintered to obtain a positive electrode lithium supplement additive.

[0010] According to the above scheme, in step S1, silicon tetrafluoride gas is obtained by thermal decomposition and purification of fluorosilicate.

[0011] According to the above scheme, in the step S1, silicon tetrafluoride gas is introduced into the water for 60-120 minutes. After the ventilation is completed, the reaction is continued for another 8-15 minutes.

[0012] According to the above scheme, in the step S1, the ratio of the flow rate of silicon tetrafluoride gas to the volume of water is 10-20 L / min: 100 mL of water.

[0013] According to the above scheme, in the step S2, the mass ratio of pure fluorosilicic acid to lithium hydroxide is (1.0-1.5):1.0.

[0014] According to the above scheme, in the step S2, the alkaline hydrolysis temperature is 40-60°C; and the alkaline hydrolysis time is 0.8-1.5h.

[0015] According to the above scheme, in the step S2, the reaction process needs to be stirred at a speed of 60 to 100 r / min.

[0016] According to the above scheme, in the step S2, the aging time is 0.5 to 1.5 hours.

[0017] According to the above scheme, in step S2, the filtrate is a saturated solution of lithium fluoride, which can be used in step S1 to replace ultrapure water for recycling.

[0018] According to the above scheme, in the step S3, during vacuum drying: the vacuum degree is 0-0.05MPa, the temperature is 100°C-120°C, and the drying time is 3-5h.

[0019] According to the above scheme, in the step S3, the sintering temperature is 300-350°C and the sintering time is 4-6h.

[0020] Provided is an application of the lithium supplement additive prepared by the above preparation method in a positive electrode of a lithium ion battery.

[0021] Provided is a lithium ion battery positive electrode, comprising a lithium supplement additive prepared by the above preparation method.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] 1. The present invention provides a method for preparing a positive electrode lithium supplement additive, which uses silicon tetrafluoride gas as a raw material, absorbs with water to obtain fluorosilicic acid, further reacts with lithium hydroxide for alkaline hydrolysis, and then sinters to obtain the lithium supplement additive, wherein lithium fluoride is uniformly embedded in the silicon dioxide gap to form a stable supporting structure; the obtained lithium supplement additive is applied to the positive electrode of a lithium ion battery, which can improve the shortcoming of the low first efficiency of the positive electrode of the lithium ion battery, further improve the battery energy density and extend the cycle life; at the same time, the lithium supplement additive does not react with solvents, binders, etc. during the production of the electrode sheet, has no adverse side reactions with the electrolyte during the cycle, and its decomposition products after the first effect cycle do not affect the battery cycle, and has important application prospects.

[0024] 2. The process for preparing the positive electrode lithium replenishing additive of the present invention is simple, the raw materials are easily available, the conditions are mild, the obtained positive electrode lithium replenishing additive has good stability and good lithium replenishing effect, and is suitable for industrial promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a curve of the capacity retention rate of the lithium-ion battery obtained in Example 5 of the present invention after 100 cycles. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] Example 1

[0028] A method for preparing a positive electrode lithium supplement additive is provided, comprising the following steps:

[0029] 1) introducing silicon tetrafluoride gas into 46 g of water at a rate of 8.6 L / min for 60 min, reacting for 10 min after the completion of the ventilation, filtering to obtain a fluorosilicic acid solution and a silica gel (wet product) filter cake; wherein the silica gel filter cake is washed with water, filtered, and dried to obtain a silicon dioxide byproduct, and the washing water obtained after washing the silica gel can be reused to react with silicon tetrafluoride gas to obtain a fluorosilicic acid solution.

[0030] 2) taking lithium hydroxide solid, adding lithium hydroxide to the fluosilicic acid solution obtained in step 1) at 50° C. and a stirring rate of 85 r / min, wherein the mass ratio of pure fluosilicic acid to lithium hydroxide is 1.1:1.0, reacting for 1 hour, then aging for 1 hour, separating, washing, and filtering to obtain a solid, and the filtrate can be reused in step 1) to react with silicon tetrafluoride gas;

[0031] 3) The solid obtained by filtration in step 2) is dried at a vacuum degree of 0.02 MPa and a temperature of 110° C. for 4 h, and finally sintered at 320° C. for 5 h to obtain a lithium fluoride composite material.

[0032] In this embodiment, the recovery rate of the main product of the lithium fluoride composite material is 95%.

[0033] Example 2

[0034] A method for preparing a positive electrode lithium supplement additive is provided, comprising the following steps:

[0035] 1) introducing silicon tetrafluoride gas into 58 g of water at a rate of 8.9 L / min for 108 min, reacting for 12 min after the completion of the ventilation, filtering to obtain a fluorosilicic acid solution and a silica gel (wet product) filter cake; wherein the silica gel filter cake is washed with water, filtered, and dried to obtain a silicon dioxide byproduct, and the washing water obtained after washing the silica gel can be reused to react with silicon tetrafluoride gas to obtain a fluorosilicic acid solution.

[0036] 2) lithium hydroxide is placed in a reactor, and added to the fluorosilicic acid solution obtained in step 1) at 55°C and a stirring rate of 80 r / min, wherein the mass ratio of pure fluorosilicic acid to lithium hydroxide is 1.2:1.0, and the reaction is carried out for 1.2 hours, and then aged for 1.5 hours, and the solid is separated, washed, and filtered to obtain a solid. The filtrate can be reused in step 1) to react with silicon tetrafluoride gas;

[0037] 3) The solid obtained by filtration in step 2) is dried at a vacuum degree of 0.04 MPa and a temperature of 120° C. for 3 h, and finally sintered at 300° C. for 6 h to obtain a lithium fluoride composite material.

[0038] In this embodiment, the recovery rate of the main product of the lithium fluoride composite material is 94%.

[0039] Example 3

[0040] A method for preparing a positive electrode lithium supplement additive is provided, comprising the following steps:

[0041] 1) introducing silicon tetrafluoride gas into 46 g of water at a rate of 8.6 L / min for 90 min, reacting for 10 min after the completion of the ventilation, filtering to obtain a fluorosilicic acid solution and a silica gel (wet product) filter cake; wherein the silica gel filter cake is washed with water, filtered, and dried to obtain a silicon dioxide byproduct, and the washing water obtained after washing the silica gel can be reused to react with silicon tetrafluoride gas to obtain a fluorosilicic acid solution.

[0042] 2) Lithium hydroxide is placed in a reactor, and added to the fluorosilicic acid solution obtained in step 1) at 55° C. and a stirring rate of 90 r / min, wherein the mass ratio of pure fluorosilicic acid to lithium hydroxide is 1.1:1.0, and the reaction is carried out for 1.5 hours, and then aged for 1 hour, and the solid is separated, washed, and filtered to obtain a solid. The filtrate can be reused in step 1) to react with silicon tetrafluoride gas.

[0043] 3) The solid obtained by filtration in step 2) is dried at a vacuum degree of 0.03 MPa and a temperature of 115° C. for 3.5 h, and finally sintered at 330° C. for 5 h to obtain a lithium fluoride composite material.

[0044] In this embodiment, the recovery rate of the main product of the lithium fluoride composite material is 96%.

[0045] Example 4

[0046] A method for preparing a positive electrode lithium supplement additive is provided, comprising the following steps:

[0047] 1) introducing silicon tetrafluoride gas into 58 g of water at a rate of 8.6 L / min for 90 min, reacting for 12 min after the completion of the ventilation, filtering to obtain a fluorosilicic acid solution and a silica gel (wet product) filter cake; wherein the silica gel filter cake is washed with water, filtered, and dried to obtain a silicon dioxide byproduct, and the washing water obtained after washing the silica gel can be reused to react with silicon tetrafluoride gas to obtain a fluorosilicic acid solution.

[0048] 2) Lithium hydroxide is placed in a reactor, and added to the fluosilicic acid solution at 55° C. and a stirring rate of 75 r / min, wherein the mass ratio of pure fluosilicic acid to lithium hydroxide is 1.1:1.0, and the reaction is carried out for 1 hour, and then aged for 1 hour, and the solid is separated, washed, and filtered to obtain the solid. The filtrate can be reused in step 1) to react with silicon tetrafluoride gas.

[0049] 3) The solid obtained by filtration in step 2) is vacuum dried at a vacuum degree of 0.04 MPa and a temperature of 120° C. for 3 h, and finally sintered at 310° C. for 4 h to obtain a lithium fluoride composite material.

[0050] In this embodiment, the recovery rate of the main product of the lithium fluoride composite material is 93%.

[0051] Example 5

[0052] A lithium-ion battery is provided, comprising a positive electrode, a negative electrode, a separator and an electrolyte; wherein:

[0053] The positive electrode is prepared by adding positive electrode active material lithium iron phosphate, the lithium supplement additive obtained in Example 3, adhesive polyvinylidene fluoride and conductive agent Super-P into N-methylpyrrolidone in a weight ratio of 93:3:2:2, stirring and homogenizing to prepare positive electrode slurry; and then coating it on both sides on the positive electrode current collector.

[0054] The negative electrode is a graphite negative electrode;

[0055] The diaphragm is a high-strength thin-film polyolefin porous membrane;

[0056] The electrolyte is a 1 mol / L lithium hexafluorophosphate (LiPF6) solution, and the solvent and additive are ethylene carbonate (EC) and vinylene carbonate (VC) in a volume ratio of 1:1.

[0057] The lithium ion battery obtained in this example was compared with a lithium ion battery with lithium fluoride directly added to the positive electrode (control group 1) and a lithium ion battery without lithium supplementation additive added to the positive electrode (control group 2). After calculation (first coulomb efficiency = first charge specific capacity / first discharge specific capacity; capacity retention rate = discharge capacity after 100 cycles / first cycle discharge capacity), the comparison results are shown in Table 1 below.

[0058] Table 1. Comparison of battery coulombic efficiency

[0059]

[0060] Figure 1 This is a curve of the capacity retention rate of the battery with the positive electrode lithium supplement additive added in Example 5 after 100 cycles. It can be seen from the curve that the capacity of the battery after the cycle is relatively stable, and the capacity retention rate reaches 95.62%.

[0061] The lithium-ion battery to which the lithium-supplement additive material in this embodiment is added and the lithium-ion battery without the lithium-supplement additive material (control group 2) are subjected to charge and discharge experiments under the same conditions of normal temperature and pressure, and the number of charge and discharge times of the battery is recorded to verify the stable performance of the lithium-ion battery with the lithium-supplement additive. The results are shown in Table 2 below.

[0062] Table 2. Comparison of battery charge and discharge cycle times

[0063] serial number Cycle times (times) Example 5 3000 Control group 2 2500

[0064] The data in Table 2 show that the number of cycles of lithium iron phosphate lithium-ion batteries with added lithium supplement additives is significantly higher than that of lithium iron phosphate lithium-ion batteries without added lithium supplement additives under the same conditions. The results show that lithium iron phosphate lithium-ion batteries with added lithium supplement additives are more stable and have better performance.

[0065] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a positive electrode lithium supplement additive, characterized in that: The following steps are involved: S1: absorbing silicon tetrafluoride gas with water to obtain a fluorosilicic acid solution containing silicon dioxide precipitate, and filtering to obtain a fluorosilicic acid solution and silicon dioxide solid; S2: subjecting the fluorosilicic acid solution obtained in step S1 and lithium hydroxide to an alkaline hydrolysis reaction to generate a slurry solution containing a mixed precipitate of lithium fluoride and silicon dioxide, and subjecting the slurry solution to aging, filtering and washing to obtain a lithium fluoride mixed filter cake containing silicon dioxide; S3: The lithium fluoride mixed filter cake containing silicon dioxide obtained in step S2 is vacuum dried and sintered to obtain a positive electrode lithium supplement additive.

2. The preparation method according to claim 1, characterized in that: In the step S1, silicon tetrafluoride gas is introduced into water for 60-120 minutes. After the ventilation is completed, the water is reacted for another 8-15 minutes.

3. The preparation method according to claim 1, characterized in that: In the step S1, the ratio of the flow rate of silicon tetrafluoride gas to the volume of water is 10-20 L / min:100 mL.

4. The preparation method according to claim 1, characterized in that: In the step S2, the mass ratio of fluorosilicic acid to lithium hydroxide is 1.0-1.5:1.

0.

5. The preparation method according to claim 1, characterized in that: In the step S2, the alkaline hydrolysis temperature is 40-60° C.; the alkaline hydrolysis time is 0.8-1.5 h; stirring is performed during the alkaline hydrolysis reaction at a stirring speed of 60-100 r / min.

6. The preparation method according to claim 1, characterized in that: In the step S2, the aging time is 0.5 to 1.5 hours.

7. The preparation method according to claim 1, characterized in that: In the step S3, during vacuum drying: the vacuum degree is 0-0.05 MPa, the temperature is 100° C.-120° C., and the drying time is 3-5 hours.

8. The preparation method according to claim 1, characterized in that: In the step S3, the sintering temperature is 300-350° C. and the sintering time is 4-6 hours.

9. Use of the lithium supplement additive prepared by the preparation method according to any one of claims 1 to 8 in a positive electrode of a lithium ion battery.

10. A positive electrode for a lithium ion battery, characterized in that: The lithium supplement additive is prepared by the preparation method according to any one of claims 1 to 8.

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