Preparation method and application of composite electrolyte based on film-forming additive modification

Abstract

The invention discloses a preparation method of a composite electrolyte based on film-forming additive modification, the composite electrolyte comprises an electrolyte additive LiDFOB, a lithium salt and a solvent, the preparation method comprises the following steps: (1) adding a basic electrolyte comprising the lithium salt and the solvent into the electrolyte additive LiDFOB; (2) adding a solvent to balance the concentration of lithium ions; and (3) performing magnetic stirring to fully dissolve the electrolyte additive LiDFOB and homogenize the electrolyte to obtain the composite electrolyte. The invention also discloses an application of the composite electrolyte obtained by the preparation method in a lithium ion battery. The uniform modified electrolyte is formed by accurately regulating and controlling the concentration of LiDFOB in the electrolyte and magnetically stirring, and the ion mobility and the interface stability of the electrolyte are optimized, so that the cycling stability and the safety of the battery are remarkably improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of energy storage and conversion, and in particular relates to a preparation method and application of a composite electrolyte modified by a film-forming additive. Background Art

[0002] As one of the most competitive energy storage devices, lithium-ion batteries have been widely used in human life and production. So far, the development trend of lithium-ion batteries is to have higher energy density and more reliable safety to meet the needs of energy storage and safety. For example, a Chinese patent with publication number CN118367200A discloses a lithium-ion battery, including a positive electrode, a negative electrode and a composite electrolyte membrane located between the positive electrode and the negative electrode. Among them, the composite electrolyte membrane includes a first electrolyte layer close to the positive electrode and a second electrolyte layer close to the negative electrode, the first electrolyte layer includes a first solid electrolyte, the second electrolyte layer includes a first polymer electrolyte, and the Young's modulus of the first solid electrolyte is less than 50GPa. And a Chinese patent with publication number CN115413376A discloses lithium-ion batteries, which include anodes including 30 to 85wt.% of silicon, thereby promoting the high energy density and high N:P ratio of these lithium-ion batteries. The high N:P ratio further enables the fast charging and low-temperature charging performance of these lithium-ion batteries.

[0003] However, lithium-ion batteries still have some shortcomings, such as high internal resistance - usually more than 10 times that of nickel-cadmium and nickel-metal hydride batteries; wide operating voltage range, when the battery is discharged to more than 80%, the voltage change of lithium-ion batteries can almost reach 40%, which is about twice that of nickel-cadmium batteries; the capacity decreases greatly during high-rate discharge, especially when the discharge rate is greater than 1C, the capacity is severely attenuated. Lithium-ion battery electrolytes usually use a mixed system with LiPF6 as lithium salt and carbonate as organic solvent. Therefore, how to significantly improve the cycle stability and safety of batteries by modifying lithium-ion battery electrolytes is a research hotspot in this field. Summary of the invention

[0004] The present invention provides a method for preparing a composite electrolyte modified by a film-forming additive, which optimizes the ion mobility and interface stability of the electrolyte by precisely controlling the concentration of LiDFOB in the electrolyte and magnetic stirring to form a uniform modified electrolyte, thereby significantly improving the cycle stability and safety of the battery.

[0005] A method for preparing a composite electrolyte modified by a film-forming additive, wherein the composite electrolyte comprises a LiDFOB electrolyte additive, a lithium salt and a solvent, and the preparation method comprises:

[0006] (1) adding a basic electrolyte including a lithium salt and a solvent to an electrolyte additive LiDFOB;

[0007] (2) adding solvent to balance the lithium ion concentration;

[0008] (3) Magnetic stirring is used to fully dissolve the electrolyte additive LiDFOB and homogenize the electrolyte to obtain a composite electrolyte.

[0009] The LiDFOB additive is a film-forming additive used to improve the performance of the electrolyte.

[0010] The solvents in step (1) and step (2) are selected from one or more of carbonate solvents or ether solvents.

[0011] Preferably, the solvent comprises ethylene carbonate and dimethyl carbonate.

[0012] The lithium salt is composed of LiPF6.

[0013] More preferably, the solvent is a combination of EC (ethylene carbonate) and DMC (dimethyl carbonate) in a volume ratio of 3:7.

[0014] In step (3), the molar concentration of LiDFOB in the composite electrolyte is 1-3%.

[0015] In step (3), the dissolution temperature should be controlled at 25-27°C, and the magnetic stirring speed should be controlled at 150-250 r / min.

[0016] Preferably, the preparation method comprises: the lithium salt (LiPF6) concentration of the basic electrolyte is 1 mol / L, 2% of lithium difluorooxalate borate (LiDFOB) is added, that is, the LiDFOB concentration is 0.02 mol / L, the amount of the substance is calculated according to the volume of the electrolyte to be configured, and then the required mass is obtained by multiplying the molar mass; in addition, in order to keep the overall lithium ion concentration of the electrolyte at 1 mol / L, EC and DMC are added to dilute the lithium ion concentration; the volume of the required solvent is calculated according to the amount of LiDFOB substance added, and a certain volume of EC and DMC are calculated and measured according to the ratio of 3:7 in the original electrolyte, and then magnetic stirring is performed to completely dissolve the LiDFOB and homogenize the electrolyte.

[0017] The present invention also provides an application of the composite electrolyte obtained by the above preparation method in a lithium ion battery. The lithium ion battery comprises a nickel-cobalt-manganese ternary positive electrode material NCM811, a composite electrolyte and a lithium metal negative electrode.

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] The invention mixes a certain mass of lithium salt LiDFOB with a basic electrolyte, balances the lithium salt concentration with an organic solvent, and then performs magnetic stirring. The obtained electrolyte has good uniformity, simple process steps, and high preparation efficiency. Moreover, the lithium battery prepared by the prepared modified composite electrolyte has higher cycle efficiency than the lithium battery prepared by the basic electrolyte, and its specific capacity can be maintained stable without a downward trend within a certain number of cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings are only used for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used to represent the same components throughout the accompanying drawings. In the accompanying drawings:

[0021] Figure 1 A flow chart for preparing a modified composite electrolyte provided in an embodiment of the present invention;

[0022] Figure 2 A measurement diagram of cycle specific capacity of batteries using unmodified basic electrolyte and composite electrolyte provided in an embodiment of the present invention;

[0023] Figure 3 A graph showing the coulombic efficiency of a battery using an unmodified basic electrolyte and a composite electrolyte provided in an embodiment of the present invention;

[0024] Figure 4 The charge and discharge voltage-capacity curve of the battery using the unmodified basic electrolyte and the composite electrolyte provided in the embodiment of the present invention at the 16th cycle;

[0025] Figure 5 The XRD characterization result diagram of the positive electrode after cycling in the composite electrolyte provided by the embodiment of the present invention;

[0026] Figure 6 This is a SEM characterization result diagram of the positive electrode surface after cycling in the composite electrolyte provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] Various additional advantages and benefits will become apparent to those of ordinary skill in the art from a reading of the following detailed description of the preferred embodiments.

[0028] Specifically, the method for preparing the composite electrolyte modified by the film-forming additive provided in the embodiment of the present invention comprises:

[0029] like Figure 1As shown, the required mass of LiDFOB (2% addition, i.e., LiDFOB concentration is 0.02 mol / L, the amount of substance is calculated according to the volume of the electrolyte to be configured, and then multiplied by the molar mass to obtain the required mass) is weighed with an electronic balance, placed in an aluminum bottle containing electrolyte and transferred to a glove box, and a basic electrolyte is added (lithium salt LiPF6 concentration is 1 mol / L, solvent EC: DMC = 3:7). In order to keep the overall lithium ion concentration of the electrolyte at 1 mol / L, the volume of the required solvent is calculated by the amount of LiDFOB substance added, and then a certain volume of EC and DMC is calculated and measured with a pipette according to the ratio of 3:7 in the original electrolyte, and then the electrolyte bottle mouth is wrapped with parafilm and transferred out of the glove box, followed by magnetic stirring to completely dissolve LiDFOB and homogenize the electrolyte.

[0030] Application Examples

[0031] The positive electrode of the battery uses 80wt% NCM811 material (Lingbao Rongbei New Energy Technology Co., Ltd., China), 10wt% Ketjen Black (Lion Co., Ltd, China), 10wt% Ketjen Black (Lion Co., Japan) and 10wt% polyvinylidene fluoride (PVDF, Arkema, France). Before being dissolved in NMP (99.5%, Rhawn, China) solvent, all ingredients were ground in an agate mortar for 10 minutes to ensure adequate mixing, and then stirred for 5 hours using a magnetic rotor at a speed of about 800 rpm to form a uniform slurry. It was then cast on a carbon-coated aluminum foil and vacuum dried at 80°C for 12 hours. The positive electrode was then wrapped into a circular positive electrode sheet with a radius of 15 mm, rolled at a pressure of 20 MPa, and dried in a vacuum at 80°C for another 4 hours to further remove residual NMP solvent. Standard button cells were then assembled in an argon-filled glove box. The electrolyte is assembled using multiple groups of modified electrolytes and their control groups, lithium metal negative electrodes, and diaphragms.

[0032] Perform cycle tests on the assembled batteries: Use a cycle test station in a 25°C constant temperature box. For long-term cycle tests, the first cycle is tested at 0.1C, followed by a cycle test at 1C:

[0033] Figure 2 The graphs for measuring the cycle specific capacity of the battery using the unmodified basic electrolyte and the composite electrolyte prepared in the example show that the discharge specific capacity of the battery modified with 2% LiDFOB after the second cycle is greatly improved compared with the unmodified battery; Figure 3The graphs for measuring the cycle coulombic efficiency of the battery using the unmodified basic electrolyte and the composite electrolyte prepared in the embodiment show that the coulombic efficiency of the battery modified with 2% LiDFOB is slightly higher than that of the unmodified battery after the second cycle; Figure 4 The charge and discharge voltage-capacity curves of the composite electrolyte battery prepared using the unmodified basic electrolyte and the embodiment at the 16th cycle show that the voltage of the modified battery is lower than that of the unmodified battery at the same specific capacity, which is beneficial to the safety protection of the battery. Figure 5 The XRD characterization result diagram of the positive electrode after cycling in the composite electrolyte provided in the embodiment shows that lithium nickel oxide is generated at the positive electrode of the battery and the reaction proceeds smoothly; Figure 6 The SEM characterization result diagram of the positive electrode surface after cycling in the composite electrolyte provided in the embodiment shows that the surface condition of the positive electrode of the battery is good and no cracking or the like occurs.

[0034] In summary, the present invention provides a composite electrolyte prepared by adding a LiDFOB electrolyte additive with a molar concentration of 2%. Experimental results show that the lithium battery prepared by the modified composite electrolyte has a higher cycle efficiency than the lithium battery prepared by the basic electrolyte, and its specific capacity can remain stable without a downward trend within a certain number of cycles.

[0035] The present invention adopts the nickel-cobalt-manganese ternary positive electrode material NCM811 as the positive electrode of the lithium-ion battery, regulates the chemical composition of the electrolyte, and prepares a new lithium-ion battery with high efficiency and excellent charge retention ability by controlling the composition ratio of the lithium salt.

[0036] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, and thus, the scope of the present invention should not be limited to the above embodiments.

Claims

1. A method for preparing a composite electrolyte modified by a film-forming additive, characterized in that: The composite electrolyte comprises an electrolyte additive LiDFOB, a lithium salt and a solvent, and the preparation method comprises: (1) adding a basic electrolyte including a lithium salt and a solvent to an electrolyte additive LiDFOB; (2) adding solvent to balance the lithium ion concentration; (3) Magnetic stirring is used to fully dissolve the electrolyte additive LiDFOB and homogenize the electrolyte to obtain a composite electrolyte.

2. The method for preparing a composite electrolyte modified by a film-forming additive according to claim 1, characterized in that: The solvents in step (1) and step (2) are selected from one or more of carbonate solvents or ether solvents.

3. The method for preparing a composite electrolyte modified by a film-forming additive according to claim 2, characterized in that: The solvents include ethylene carbonate and dimethyl carbonate.

4. The method for preparing a composite electrolyte modified by a film-forming additive according to claim 1, characterized in that: In step (3), the molar concentration of LiDFOB in the composite electrolyte is 1-3%.

5. The method for preparing a composite electrolyte modified by a film-forming additive according to claim 1, characterized in that: In step (3), the dissolving temperature is 25-27° C. and the magnetic stirring speed is 150-250 r / min.

6. Use of the composite electrolyte obtained by the preparation method according to any one of claims 1 to 5 in a lithium ion battery.

7. The use according to claim 6, characterized in that: The lithium-ion battery comprises a nickel-cobalt-manganese ternary positive electrode material NCM811, a composite electrolyte and a lithium metal negative electrode.

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