KR100530350B1 - The lithium ion secondary battery comprising 2-side coating type of separator - Google Patents

Abstract

The present invention provides a separator coated with a polymer electrolyte, a lithium ion secondary battery wound the positive electrode and the negative electrode. The battery according to the present invention ensures the safety of the battery.

Description

Lithium ion secondary battery including a double-sided coating separator {TH L LITHIUM ION SECONDARY BATTERY COMPRISING 2-SIDE COATING TYPE OF SEPARATOR}

The present invention relates to a separator coated with a polymer electrolyte, a lithium ion secondary battery wound the positive electrode and the negative electrode.

In order to secure safety of a lithium ion secondary battery, a technique of coating a polymer electrolyte on an electrode when manufacturing a wound battery has been generalized. Coating the electrode with a polymer electrolyte prevents leakage of the electrolyte and the polymer electrolyte acts as an additional separator to reduce the probability of short generation.

However, the method of coating the electrode remains to secure the safety by coating the polymer electrolyte on the surface of one of the positive electrode and the negative electrode. When applying this method, the adhesiveness of the polymer electrolyte should be taken into account in the storage and manufacturing process of the electrode coated with the polymer electrolyte, resulting in the complexity of the process.

Accordingly, the present inventors recognize the above problems when the electrode is coated with a polymer electrolyte, and attempt to achieve improved battery safety by constructing a wound battery such that both the positive electrode and the negative electrode contact the polymer electrolyte by double-coating the separator with the polymer electrolyte.

The present invention provides a lithium ion secondary battery in which a cathode, a membrane coated on both sides with a polymer electrolyte, a cathode, a membrane coated on both sides with a polymer electrolyte, and laminated.

The present invention is characterized by using a separator coated on both sides with a polymer electrolyte in a wound lithium ion secondary battery. Here, the polymer electrolyte is integral with the separator. In addition, the separator coated with a polymer electrolyte according to the present invention may be impregnated with the electrolyte.

Unlike the prior art in which the electrode is coated with a polymer electrolyte, the present invention, in which the separator is coated with a polymer electrolyte, does not cause a problem of adhesion of the separator due to the polymer electrolyte. On the other hand, contamination of the core in the process may be concerned, but the problem can be solved by the core surface treatment. In addition, since the polymer electrolyte and the separator exist in two phases in the manufacturing process, the ideal case exists in one phase, so there is no problem of membrane contamination by the polymer electrolyte.

The membrane coated with a polymer electrolyte may be prepared by applying a polymer electrolyte solution to the separator and then removing the solvent by drying. The coating amount of the polymer electrolyte is preferably 0.1 to 10 g per 1 m * 1 m area.

As the separator, a material used in a general purpose or a combination thereof may be used, and a separator of a polyolefin series may be preferably used.

The polymer electrolyte may be a lithium ion polymer battery or a lithium polymer battery such as polyvinylidene fluoride (PVdF), polymethyl methacrylate (PMMA), polyethylene glycol (PEG), polyvinylidene fluoride-chlorotrifluoroethylene copolymer All general purpose polymer electrolytes used in the present invention and combinations thereof can be used. The polymer electrolyte solution is obtained by dissolving the polymer electrolyte in a solvent. Examples of the solvent include alcohols and ketones (eg, acetone), and a general electrolyte may be used as a solvent. Non-limiting examples of usable electrolytes include solvents such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), or mixtures thereof.

As a coating method, the separator may be coated with a polymer electrolyte dissolved in a solvent using a die coater.

When the polymer electrolyte is coated on the separator, a pattern may be given as necessary to partially remove the polymer electrolyte coated on the separator, thereby controlling the area and amount of the polymer electrolyte. Moreover, the reason for giving a pattern is to make electrolyte solution impregnation easy. The pattern can be provided by controlling the detachment of the die during coating.

The wound lithium ion secondary battery according to the present invention is a positive electrode, a separator coated on both sides with a polymer electrolyte, a negative electrode, and laminated by winding the separator, both of the positive electrode and the negative electrode may be in contact with the polymer electrolyte may improve battery safety. Here, the polymer electrolyte coated on the separator can contain the electrolyte solution to prevent leakage of the electrolyte, and the polymer electrolyte acts as an additional separator to reduce the probability of short generation.

As the positive electrode, a positive electrode active material, a conductive material, a coating layer made of a binder and an electrode plate made of aluminum foil may be used, and the negative electrode active material, a conductive layer, a coating layer made of a binder and a electrode plate made of copper foil may be used.

As the electrode active material, the conductive material, and the binder material, a material used in general or a combination thereof may be used.

Non-limiting examples of the positive electrode active material include a general-purpose active material such as lithium cobalt oxide, lithium manganese oxide, lithium nickel oxide, lithium vanadium oxide and mixtures thereof. Non-limiting examples of the negative electrode active material is lithium metal, artificial graphite-based graphite, natural graphite, etc. There is a substance and its mixture. Non-limiting examples of the binder include polyvinylidene fluoride (PVdF) homopolymer and styrene butadiene rubber (SBR) and mixtures thereof, and polar solvents such as NMP and water may be used as the active material solvent.

Before winding, during winding, or the rolled roll, the thickness can be adjusted by applying heat and pressure external forces. As more heat is applied within the range where the separator is not damaged, the adhesion between the coated polymer electrolyte and the electrode may be uniformly improved by controlling the thickness by adjusting the pressure and time within the range where the short does not occur. The temperature for the thickness control is 50 ~ 200 ℃, the pressure is 50 ~ 500kgf, the time is determined in consideration of mass productivity within 30 minutes. The temperature, pressure, and time range are for preventing electrode and separator damage.

Table 1 and 2 show the discharge characteristics of a battery prepared by coating the separator with a polymer electrolyte and changing the thickness by applying an external force at 70 ° C., 200 kgf for 1 minute.

Thickness test results at 70 ℃ Initial thickness (mm) Thickness of roll wound after 1 minute crimp (mm) 6.547 3.354 6.641 3.378 6.596 3.411 6.744 3.381 6.469 3.385 6.599 3.382

Discharge Efficiency Characteristics According to Thickness Control Before initial thickness adjustment After adjusting the thickness of the rolled roll 95% 97% 96% 98% 95% 97% 95% 97% 94% 98% 95% 97%

Discharge Efficiency: Percentage of Discharge Capacity in One Hour at 100 Nominal Capacity

As can be seen in Tables 1 and 2, the closer the electrode and the polymer layer are in contact with each other, the thinner the thickness becomes, and the closer the internal structure of the battery is, the better the discharge efficiency is.

The present invention will be described in more detail with reference to the following examples. However, the examples are for illustrating the present invention and the present invention is not limited by the following examples.

EXAMPLE

Example 1

(Anode manufacturing)

Lithium cobalt oxide (LiCoO ₂ ): Carbon black: Polyvinylidene fluoride (PVDF) is dispersed in 1-methyl-2-pyrrolidone (NMP) to prepare a slurry, and the slurry is coated on both sides of the aluminum foil. And sufficiently dried, followed by pressing to prepare a positive electrode.

(Cathode production)

Graphite: Acetylene Black: PVDF was dispersed in NMP to prepare a slurry, and the slurry was coated on both sides of the copper foil, sufficiently dried, and then pressed to prepare a negative electrode.

(Production of Polymer Electrolyte Coating Separator)

Using polyethylene as a separator and polyvinylidene fluoride-chlorotrifluoroethylene copolymer as a gelling polymer electrolyte layer, the polymer electrolyte dissolved in acetone was coated on both sides of the separator with a die coater, and then dried to obtain a solvent. It was removed to form a gelling polymer layer on the separator. At this time, in order to prevent core contamination, the membrane was coated with a pattern so that the portion contacting the core was free of the polymer electrolyte layer. At this time, the polymer coating amount is 0.1g in the area of 1m * 1m.

(Battery manufacturing)

The electrode and the separator prepared above were aligned with a cathode (cathode) / a double coated membrane / a cathode (anode) / a double coated membrane and then wound. After the winding was carried out, a roll was applied to improve the adhesion between the electrode and the coated polymer layer by applying an external force of 70 ° C. and a pressure of 200 kgf for 5 minutes.

The prepared roll was put in an aluminum laminate packaging material, and EC / PC = 1/1, 1M LiPF ₆ was injected into the liquid electrolyte and packed.

Example 2

As in Example 1, the polymer electrolyte coating amount was 1g per 1m * 1m.

Example 3

As in Example 1, the polymer electrolyte coating amount was 10g per 1m * 1m.

Comparative Example 1

A battery was manufactured in the same manner as in Example 1, except that a separator not coated with a polymer electrolyte was used.

<Stability Experiment>

Table 3 shows the results of experiments on the safety of the batteries of Examples 1 to 3 and the batteries of Comparative Example 1. A nail test was performed to check the occurrence of ignition and smoke by passing a nail having a diameter of 4 mm through the battery.

Experiment Fever Acting Judgment Example 1 × × pass Example 2 × × pass Example 3 × × pass Comparative Example 1 ○ ○ fail

O: Occurrence, X: Non Occurrence

As can be seen in Table 3, it can be seen that the safety of the test results when the polymer electrolyte is coated on the separator so that both the positive electrode and the negative electrode contact the polymer electrolyte layer.

In the conventional method of coating and winding the polymer electrolyte on the electrode, the polymer electrolyte layer must be coated on the electrode. Therefore, the coating error of the electrode and the coating error of the polymer electrolyte layer are combined to restrict the process of manufacturing in order to secure the uniformity of the battery. This follows.

However, the present invention has a high mass productivity since it is possible to ensure the simplicity in the process configuration by the manufacturing method of coating the polymer electrolyte on the separator to make an integral separator and then wound up. In addition, the polymer electrolyte is present in both the positive electrode and the negative electrode to ensure safety.

Claims (4)

A lithium ion secondary battery obtained by stacking and winding a separator coated on both sides with a cathode, a polymer electrolyte, a cathode, and a membrane coated with a polymer electrolyte, wherein the polymer electrolyte layer coated on both sides of the separator is wound in contact with the anode and the cathode. A portion in contact with the core is patterned so that the polymer electrolyte layer does not exist. delete delete The lithium ion secondary battery according to claim 1, wherein heat and pressure are applied before winding, during winding, or after winding to enhance adhesion between the electrode surface and the polymer layer.