KR102544272B1 - Anode for lithium ion battery and manufacturing method for the same - Google Patents

Abstract

As a negative electrode for a lithium ion battery, a negative electrode for a lithium ion battery is provided, characterized in that it includes a two-dimensional silicon material (2DSi) as an active material and a polyimide (PI)-based binder.

Description

Anode for lithium ion battery and manufacturing method for the same}

The present invention relates to a negative electrode for a lithium ion battery and a method for manufacturing the same, and more particularly, to a negative electrode for a lithium ion battery having an extended lifespan by forming stable chemical and structural bonds between electrode materials and a method for manufacturing the same.

Lithium-ion batteries have a light weight, small volume and high energy density. These are widely used in mobile conventional devices, digital cameras, laptops, and the like. Graphite (~372 mAh/g) is widely used as the anode of these lithium ion batteries, but silicon anode material is promising as a next-generation anode material with a high theoretical capacity of 4200 mAh/g (see Korean Patent No. 10-2006-0061064, etc.) ).

However, there is a problem in that it is difficult to induce charge and discharge stability of the electrode because the volume expansion of silicon is very severe during lithium storage.

Therefore, the problem to be solved by the present invention is to provide a lithium ion battery negative electrode with increased battery life and chemical and structural stability and a manufacturing method thereof.

In order to solve the above problems, the present invention provides a negative electrode for a lithium ion battery comprising a two-dimensional silicon material (2DSi) as an active material and a polyimide (PI)-based binder.

In addition, the two-dimensional silicon material is siloxene (Si ₆ H ₃ (OH) ₃ ) to provide a negative electrode for a lithium ion battery, characterized in that.

In addition, the two-dimensional silicon material (2DSi) provides a negative electrode for a lithium ion battery, characterized in that it has a two-dimensional crystal structure, but loses the two-dimensional crystal structure after two cycles and becomes amorphous.

In addition, the polyimide provides a negative electrode for a lithium ion battery, characterized in that imidized by heat treatment of polyamic acid (PAA).

In addition, a lithium ion battery including the negative electrode is provided.

In addition, the negative electrode provides a lithium ion battery, characterized in that laminated on the metal current collector.

In addition, preparing a two-dimensional silicon slurry by mixing a two-dimensional silicon material (2DSi) as an active material and a polyimide (PI)-based binder, applying the slurry on a current collector, and firing the coated current collector It provides a method for manufacturing a negative electrode for a lithium ion battery, characterized in that it comprises the step.

In addition, the polyimide (PI)-based binder is polyamic acid (PAA), and the polyamic acid is imidized in the firing step so that the polyimide (PI) is bonded to the two-dimensional silicon material (2DSi). It provides a method for manufacturing a negative electrode for a lithium ion battery.

In addition, it provides a method for manufacturing a negative electrode for a lithium ion battery, characterized in that the temperature of the firing step is greater than 120 ℃ and less than 500 ℃.

In addition, the two-dimensional silicon material provides a method for manufacturing a negative electrode for a lithium ion battery, characterized in that siloxene.

In addition, a negative electrode for a lithium ion battery manufactured by the above manufacturing method is provided.

According to the present invention, a lithium ion battery negative electrode is manufactured using a two-dimensional silicon active material and a polyimide-based binder. In particular, in one embodiment of the present invention, heat treatment of polyamic acid as a binder induces imidation, which forms a stable chemical and structural bond between electrode materials. In addition, it is possible to improve the lifespan and cycle characteristics of the 2D silicon anode by increasing the contact between materials due to the sintering effect caused by high-temperature firing.

1 is a schematic diagram of manufacturing a negative electrode for a lithium ion battery according to an embodiment of the present invention, and FIG. 2 is a step diagram of a method for manufacturing a negative electrode for a lithium ion battery.
3 is a view showing the crystalline material before and after firing the electrode.
4 is an IR spectroscopy analysis result of an electrode according to an embodiment of the present invention.
5 is a charge and discharge test result of a battery including an electrode according to the present invention.
6 is a cycle test result of a battery including an electrode according to the present invention.
7 is an XRD analysis result of the electrode after the second charge and discharge cycle of the electrode according to an embodiment of the present invention.
8 is a schematic diagram of an electrode casting process in the case of using PAA (or PI-based binder), the case of using the binder, and the case of using the PVdF binder.

Hereinafter, a preferred embodiment of a negative electrode for a lithium ion battery and a manufacturing method thereof according to the present invention will be described in detail based on the accompanying drawings. For reference, the terms and words used in this specification and claims should not be construed as being limited to their ordinary or dictionary meanings, and the inventors use the concept of terms appropriately to describe their invention in the best way. It should be interpreted as meaning and concept consistent with the technical idea of the present invention based on the principle that it can be defined.

In addition, the embodiments described in this specification and the configurations shown in the drawings are only one of the most preferred embodiments of the present invention, and do not represent all of the technical ideas of the present invention. It should be understood that there may be equivalents and variations.

In order to solve the above problems, the present invention provides a negative electrode for a lithium ion battery comprising a two-dimensional silicon material (2DSi) as an active material and a polyimide (PI)-based binder. Although materials such as Super P or NMP are used in one embodiment of the present invention, the scope of the present invention is not limited thereto, and at least as long as two-dimensional silicon such as siloxene and polyimide are combined, they all fall within the scope of the present invention. .

In the present specification, the polyimide-based binder includes not only a compound having a polyimide structure but also all polymeric binders having an imide structure in a final negative electrode after heat treatment.

In the present invention, in particular, polyimide having an excellent heat resistance temperature is used as a binder produced by high-temperature heat treatment, and loss of a two-dimensional silicon anode due to volume expansion during lithium storage can be minimized and battery life stability can be secured. In addition, polyimide (PI) formed by high-temperature firing according to the present invention forms a covalent bond with a silicon negative electrode or a current collector and minimizes contact resistance between electrode material particles, which will be described in more detail in the following experimental examples.

1 is a schematic diagram of manufacturing a negative electrode for a lithium ion battery according to an embodiment of the present invention, and FIG. 2 is a step diagram of a method for manufacturing a negative electrode for a lithium ion battery.

1 and 2, a negative electrode for a lithium ion battery according to an embodiment of the present invention is prepared by mixing a two-dimensional silicon material (2DSi) and a polyimide (PI)-based binder as an active material to prepare a two-dimensional silicon slurry. step; applying the slurry on a current collector; and firing the coated current collector. In one embodiment of the present invention, the firing step is a process of imidizing a binder such as poly(amic acid) (PAA), so that the final manufactured electrode is already with a two-dimensional silicon compound (2DSi) such as siloxene. It has a structure in which a polymer compound containing a group is bonded.

The present invention will be described in more detail through the following examples and experimental examples.

Example

Two-dimensional silicon (2DSi) synthesis

CaSi ₂ (20 g) was added to 37 wt.% hydrochloric acid (67 ml) and reacted for 12 hours or longer to remove Ca ions. The remaining material (2DSi) after removal of Ca ions was recovered using a filter, sufficiently washed with acetone, and dried in a vacuum oven at 100° C. for 24 hours before recovery.

PAA synthesis

30 g of 4,4'-oxydianiline (ODA) was put in a reactor, and 564 g of methyl pyrrolidone used as a solvent was added and stirred. Thereafter, the temperature of the reactor was set to 0° C., and 32.7 g of pyromellitic acid dianhydride (PMDA) was added, followed by stirring for 1 hour to react. Next, the reaction was carried out by raising the temperature to room temperature and stirring for 4 hours to synthesize polyamic acid (PAA) having a solid content of 10 wt.%.

2DSi slurry synthesis

A slurry was prepared by mixing the above-described 2DSi with PAA, Super P, and NMP. At this time, PAA, which is a binder, is dissolved in NMP solvent at a concentration of 10 wt.%, and in one embodiment of the present invention, 2DSi (350 mg), PAA (500 mg), and Super P (100 mg) are dissolved in 2.5 ml NMP. At this time, the mass ratio of 2DSi: PAA: Super P was 7: 1: 2, respectively, but the scope of the present invention is not limited thereto. belongs to the range of If the amount of the binder is greater than the above range, battery characteristics are deteriorated, and if the amount is less than the above range, the physical and chemical bonding strength of the electrode is weakened.

2DSI cathode fabrication

The above slurry was applied on a copper foil (7.5 cm x 14.5 cm) using a doctor blade method. The copper foil (2DSi-PAA-Cu) to which the 2DSi slurry was uniformly coated was dried in a vacuum oven at 120° C. for 24 hours, and the 2DSi-PAA-Cu foil was prepared by cutting to a diameter of 14 mm in accordance with the coin cell standard.

half cell manufacturing

In order to compare the firing temperatures, the working electrodes were classified according to three firing temperatures: 1) non-fired electrode (as) 2) electrode fired at 350 ° C (-350 ° C) 3) electrode fired at 500 ° C (as) -500 ° C) was prepared. Other cell elements were used as follows. 1) cell case (CR-2032, MTI KOREA Co.) 2) Li-metal (counter electrode, diameter: 10 mm, thickness: 0.75 mm, Alfa Aesar Co.), 3) separator (GF/C, diameter 19 mm) , thickness: 0.26 mm, Whatman Co.), 4) electrolyte (1M LiPF6 dissolved in EC:DMC 1:1 vol.%, Sigma Aldrich Co.)

Electrochemical performance evaluation

For electrochemical performance evaluation, an automatic battery cycler (WonAtech Co., WBCS 3000 model) was used. Voltage range 0.05 to 2.0 V vs. Li/Li ⁺ , current density of 0.375 mA/cm ² was operated, and after a sufficient rest time for 6 hours to reduce contact resistance due to contact between electrodes, the experimental conditions were set to repeat the discharge-charge cycle. designed.

Experimental example

3 is a view showing the crystalline material before and after firing the electrode.

Referring to FIG. 3, 2D siloxene (Si ₆ H ₃ (OH) ₃ ), which is 2DSi of an electrode material according to an embodiment of the present invention, has 17 It can be seen that the two-dimensional structure is maintained more stably as the ° peak is maintained even after heat treatment. Therefore, it can be seen that 2D siloxene stably maintaining a two-dimensional structure is suitable as an anode active material in the present invention undergoing a heat treatment process for conversion to polyimide. In addition, the strong peaks appearing at 43 °, 50.2 °, and 74 ° are peaks of the current collector copper foil, which suggests that the crystallinity of the current collector Cu foil is maintained as it is even after heat treatment.

4 is an IR spectroscopy analysis result of an electrode according to an embodiment of the present invention.

Referring to Figure 4, after vacuum drying (120 ℃) and high temperature (350 ℃, 500 ℃) heat treatment, -NH and COOH functional groups (3200 ~ 4000 cm ^-1 ) of PAA form an imide group and disappear. can That is, the peaks found at 1350 to 1780 cm ^-1 refer to carbonyl (C=O) bonds generated after covalent bond formation, and were most frequently found in electrodes subjected to vacuum drying only, followed by high-temperature firing. It appears that some of the carbonyl (C=O) bonds may be lost.

5 is a charge/discharge test result of a battery including an electrode according to the present invention.

Referring to FIG. 5, when the charge and discharge test is performed at a current density of 3: 375 mA/g (0.375 mA/cm ² ), 2DSi-PI'Cu ('Cu is a state in which the active material is applied to copper foil), 2DSi -PI'Cu-350 (2DSi-PI'Cu calcined at 350 °C) and 2DSi-PI'Cu-500 (2DSi-PI'Cu calcined at 500 °C) batteries were all 0.2 V vs. A plateau was formed below Li/Li+ and discharge capacity was generated. The lithiation potential of typical silicon materials, 0.1-0.2 V vs. It is the same position as Li/Li ⁺ , indicating that 2DSi is acting as an active material.

6 is a cycle test result of a battery including an electrode according to the present invention.

Referring to FIG. 6, at a current density of 3: 375 mA/g (0.375 mA/cm ² ), 2DSi-PI'Cu, 2DSi-PI'Cu-350, and 2DSi-PI'Cu-500 samples were charged and discharged 20 times. After cycles, discharge capacities of 410, 514, and 461 mAh/g were shown, respectively, and 2 V vs. When charging up to Li/Li ⁺ , it was possible to recover all stored lithium ions (Coulombic efficiency ~100%).

In addition, during 200 charge and discharge cycles, 2DSi-PI'Cu, 2DSi-PI'Cu-350, and 2DSi-PI'Cu-500 had a capacity loss per cycle of 0.23, 0.03, and 0.14%, respectively. The samples calcined at high temperature, especially at 350°C, showed the most stable characteristics. In the case of vacuum drying at a low temperature (120 ° C), the strength of the covalent bond is expected to be low, and in the case of 500 ° C, it is considered that the thermal decomposition of polyimide (PI) is intensified. Therefore, the sintering temperature of 2DSi-PAA according to an embodiment of the present invention is preferably greater than 120°C and less than 500°C, more preferably more than 300°C and less than 500°C.

7 is an XRD analysis result of the electrode after the second charge and discharge cycle of the electrode according to an embodiment of the present invention.

Typically, silicon cathodes have 0.1 to 0.2 V vs. It is known that Li/Li ⁺ reacts by breaking bonds when storing lithium ions. Referring to FIG. 7, as a result of analyzing the electrode according to the discharge voltage in the second charge and discharge cycle, the Si ₆ ring of the 2DSi-PI'Cu, 2DSi-PI'Cu-350, and 2DSi-PI'Cu-500 samples It can be seen that the 27˚ peak corresponding to the two-dimensional array 100 has disappeared. Therefore, it is expected that the Si-Si bond in the initially prepared two-dimensional siloxene disappears by lithiation, and then the crystal structure remains in an amorphous state without recovery, leading to lithiation/delithiation of the electrode.

8 is a schematic diagram of an electrode casting process in the case of using PAA (or PI-based binder), the case of using the binder, and the case of using the PVdF binder.

Referring to FIG. 8 , in the case of using a PI binder, it is determined that the contact force between electrode materials is enhanced due to physical and chemical bonding through heat treatment.

Claims (11)

As a negative electrode for lithium ion batteries,
It is characterized by including a two-dimensional silicon material (2DSi) and a polyimide (PI)-based binder as an active material,
The polyimide (PI)-based binder is characterized in that polyamic acid (PAA),
A slurry in which the two-dimensional silicon material (2DSi) and the polyimide (PI)-based binder are mixed is applied and fired on the current collector, and the polyamic acid is imidized to form the polyimide (PI) into the two-dimensional silicon material (2DSi) A negative electrode for a lithium ion battery, characterized in that coupled to. According to claim 1,
The two-dimensional silicon material is a negative electrode for a lithium ion battery, characterized in that siloxene (Si ₆ H ₃ (OH) ₃ ). According to claim 1,
The anode for a lithium ion battery, characterized in that the two-dimensional silicon material (2DSi) has a two-dimensional crystal structure, but loses the two-dimensional crystal structure after two cycles and becomes amorphous. delete A lithium ion battery comprising the negative electrode according to claim 1 . delete As a method for manufacturing a negative electrode for a lithium ion battery,
preparing a two-dimensional silicon slurry by mixing a two-dimensional silicon material (2DSi) as an active material and a polyimide (PI)-based binder;
applying the slurry on a current collector; and
Characterized in that it comprises the step of firing the coated current collector,
The polyimide (PI)-based binder is polyamic acid (PAA), and the polyamic acid is imidized in the firing step so that the polyimide (PI) bonds to the two-dimensional silicon material (2DSi) Lithium, characterized in that Method for manufacturing negative electrode for ion battery. delete According to claim 7,
A negative electrode manufacturing method for a lithium ion battery, characterized in that the temperature of the firing step is more than 120 ℃ and less than 500 ℃. According to claim 7,
The method of manufacturing a negative electrode for a lithium ion battery, characterized in that the two-dimensional silicon material is siloxene. An anode for a lithium ion battery manufactured by the method according to claim 7.

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