KR20040084117A - Method For Fabricating Lithium-Ion Polymer Battery With Interpenetrating Network Type Gel Polymer Electrolyte - Google Patents

Abstract

PURPOSE: Provided is a method for manufacturing a lithium ion polymer battery using a gel polymer electrolyte which has high voltage, high energy and excellent cycle characteristic, and can easily control the physical properties of gel. CONSTITUTION: The method for manufacturing a lithium ion polymer battery comprises injecting an electrolytic liquid-containing precursor into an electrode laminate and then, polymerizing it by heat to obtain a gel-phase electrolyte. The electrode laminate includes a cathode layer(2) comprising an active material capable of lithium ion-intercalation and deintercalation which is deposited on a cathode collector(1); an anode layer(4) comprising an active material capable of lithium ion-intercalation and deintercalation which is deposited on an anode collector(5); and a separator(3) interposed between the cathode layer(2) and the anode layer(4).

Description

Method for manufacturing lithium ion polymer battery using gel polymer electrolyte {Method For Fabricating Lithium-Ion Polymer Battery With Interpenetrating Network Type Gel Polymer Electrolyte}

The present invention relates to a method for producing a lithium ion polymer battery, and more particularly, to a method for producing a lithium ion polymer battery using a gel polymer electrolyte.

In recent years, there has been a demand for higher performance of batteries due to miniaturization and weight reduction of devices such as mobile phones and notebook computers. In particular, in order to cope with the miniaturization of the main body of the apparatus, miniaturization of the battery and securing of capacity at the same time, that is, high energy density are required. Lithium ion batteries have high energy density and have high voltage, so that research and development has been actively conducted. In particular, the gel polymer battery is a secondary battery having high energy density as well as no electrolyte leakage, and can be used as an energy source in various portable devices.

The lithium ion battery is composed of a positive electrode, a negative electrode, a lithium salt and a non-aqueous electrolyte capable of inserting and removing lithium ions. The reason why non-aqueous electrolyte is used is that lithium cannot be stably present because of its high reactivity with water. Therefore, a non-aqueous electrolyte is used for a lithium battery. However, most of the non-aqueous electrolytes are organic compound liquids, which are flammable and odorous, and have a risk of leakage and ignition. For this reason, in recent years, in order to improve safety, a battery in which a non-aqueous electrolyte is replaced with a gel electrolyte has been developed. In a gel electrolyte, fluidity | liquidity falls remarkably and maintains shape, maintaining electrolyte solution characteristics, such as ionic conductivity. In addition, the volatilization rate is also suppressed. Therefore, the risk of leakage or fire is lowered.

In general, in a lithium ion battery, a positive electrode or a negative electrode is prepared by applying a mixture containing a positive electrode active material or a negative electrode active material, an electrolyte, a conductive material, and a binder on a current collector such as aluminum foil (Al foil) or copper foil (Cu Foil). . As the gel electrolyte, a method in which a precursor in which a liquid electrolyte, a reactive monomer, and a polymerization initiator are mixed and then thermally polymerized is laminated after the electrode and the separator are laminated.

However, the problem with the prior art is that the physical properties of the gel polymer electrolyte are not easy to control. In other words, in order to control the mechanical and electrochemical properties of the gel polymer electrolyte, it is necessary to optimize the type and amount of the reactive monomer and to set appropriate polymerization conditions. However, since most monomers having excellent mechanical properties have low electrochemical properties, and reactive monomers having excellent electrochemical properties have low mechanical properties, their physical properties are not easily controlled.

The present invention has been made to solve the above-mentioned problems, to provide a method for producing a lithium ion polymer battery using a gel polymer electrolyte having a high voltage and high energy, excellent cycle characteristics and easy control of the physical properties of the gel The purpose is to.

The inventors of the present invention intensively studied to obtain a lithium ion polymer battery using a gel polymer electrolyte having the high voltage and high energy density described above, excellent cycle characteristics and minimizing leakage and other problems. It was found that various physical properties can be obtained by changing the mixing ratio by using a reactive monomer.

Specifically, the positive electrode and the negative electrode are coated and pressed on the collector with a layer containing an active material capable of inserting and removing lithium ions, and laminated in the order of the positive electrode, the separator, and the negative electrode, and then inserted into an aluminum laminate film. do. Thereafter, a precursor mixed with a liquid electrolyte solution, a polymerized polymer, a reactive monomer or macromonomer, a polymerization initiator, and the like is injected and vacuum-sealed. Thereafter, the mixture is maintained in a constant temperature chamber of 60 ° C. to 80 ° C. for up to 1 hour 30 minutes to prepare a gel polymer electrolyte.

In the present invention, a polymer polymerized in advance and a reactive monomer are mixed to use as a reactive mixture and injected into a battery to obtain a gel polymer having a network structure. It can be freely controlled according to the type and amount of the polymer and the reactive monomer, and the type and amount of the reactive modifier to be added later.

1A to 1C are cross-sectional views illustrating a manufacturing process of a lithium ion polymer battery according to the present invention;

2 is a view showing a state in which the laminated structure of Figure 1c is inserted into an aluminum laminate film,

3 is a view measuring the amount and viscosity of PMMA IPN (Polymethyle Methacrylate Interpenetrating Polymer Network) in the precursor,

4 is a diagram measuring the alternating impedance of the gel polymer electrolyte,

5 is a view measuring the ion conductivity of the gel polymer electrolyte at various temperatures,

6 is a diagram of an electrochemical potential window of a gel polymer electrolyte measured at a scanning rate of 5 mV / s.

7 is a diagram showing charge and discharge curves of a gel polymer electrolyte battery measured at a current density of 0.5 mA cm ⁻² ;

8 is a view showing a discharge curve according to a discharge rate of a LiCoO ₂ / GPE / graphite battery measured at 20 ° C.

9 is a graph showing a discharge curve according to temperature of a LiCoO ₂ / GPE / graphite battery measured at a current density of 1.1 mAcm ⁻² .

FIG. 10 shows the cycle characteristics of a LiCoO ₂ / GPE / graphite battery measured at a current density of 1.1 mAcm ⁻² .

<Description of Symbols for Major Parts of Drawings>

1: positive electrode current collector 2: positive electrode

3: separator 4: cathode

5: negative electrode current collector 6: exterior material (aluminum laminate film)

7: sealing part

Hereinafter, a method of manufacturing a lithium ion polymer battery according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

First, as shown in FIG. 1A, LiCoO ₂ as a cathode active material, Super P black as a conductive material, and PVDF (PolyVinyliDeneFluoride) as a dispersant are mixed at a ratio of 91: 6: 3 (wt%). Then, the positive electrode 2 was manufactured by coating on the positive electrode current collector 1 made of aluminum foil or copper foil, followed by drying and pressing. The positive electrode active material may be a transition metal oxide capable of inserting and deintercalating lithium ions, a composite oxide of lithium and a transition metal, and the like.

In addition, as shown in FIG. 1B, MCF (Milled Carbon Fiber) as a negative electrode active material, Super P black as a conductive material, and PVDF as a dispersant at a ratio of 90: 2: 8 (wt%). After mixing, after coating on the negative electrode current collector (5) made of a copper foil (Cu foil) was dried, pressed to prepare a negative electrode (4). As the negative electrode active material, graphite or carbon-based material capable of inserting and removing lithium ions is used.

After that, the positive electrode portions of the positive electrode current collector 1 and the positive electrode 2 prepared above, and the negative electrode portions of the negative electrode current collector 5 and the positive electrode 4 prepared above, are shown in FIG. 1C. After the cathode 4 and the cathode 4 face each other and are laminated in such a manner as to sandwich a separator (Polyethylene or Polypropylene) 3 therebetween, the laminated structure is used as an exterior material of a battery as shown in FIG. 2. Al laminate film) (6). Here, the aluminum laminate film 6 is composed of a plastic layer made of PET, Nylon, and the like, an aluminum layer, and an adhesive layer.

Precursors for preparing a gel polymer electrolyte were composed of a liquid electrolyte, a polymethyle methacrylate interpenetrating polymer network (PMMA IPN), a reactive modifier, and a polymerization initiator. PMMA IPN is prepared by dropping a small amount of MMA (methylmethacrylat) in PMMA (polymethylmethacrylat, Mw = 56,000) at 60 ℃, purge with nitrogen gas at room temperature for 24 hours to remove water and residual oxygen. 1M LiPF ₆ / EC + DEC (5 + 5 vol%) as the electrolyte, HDDA (Hexanediol diacrylate) as the reactive modifier, BPO (Benzoyl Peroxide) was used as the polymerization initiator. The mixing ratio of the liquid electrolyte and the curable mixture (IPN + reactive modifier + polymerization initiator) in the precursor was 95: 5 (vol%).

After the precursor is injected into the aluminum laminate film 6 into which the electrode is inserted, a predetermined pressure and heat are applied to the sealing portion 7 of the aluminum laminate film 6 under vacuum. After that, the mixture is stored at room temperature for about 3 days, and the polymerization is performed after the precursor is sufficiently impregnated into the separator and the electrode. The polymerization was performed using a constant temperature chamber in which the temperature was kept constant, and the temperature was performed at 80 ° C. for 60 minutes.

Figure 3 shows the results of measuring the amount and viscosity of PMMA IPN (Polymethyle Methacrylate Interpenetrating Polymer Network) in the precursor. The viscosity of the precursor containing 30 vol% of the reactive admixture was about 21 mPas, and the viscosity decreased as the amount of electrolyte increased. The precursor must be low in viscosity to be impregnated into the electrode and into the separator. The viscosity of the precursor containing 5 vol% of the reactive mixture was 5.6 mPas, which was almost equivalent to that of the liquid electrolyte.

Figure 4 shows the results of measuring the alternating impedance of the gel polymer electrolyte. Spectra is only a straight line, which means that the resistor and capacitor consist of an equivalent circuit connected in series. The real axis intersection means the resistance of the gel polymer electrolyte, and the ion conductivity obtained using the thickness and the cross-sectional area of the gel polymer electrolyte was 5.8 x 10 ^-3 S / cm.

5 shows the relationship between the ion conductivity and the temperature of the gel polymer electrolyte. The ion conductivity at 20 ° C was 5.8 x 10 ^-3 S / cm, and the higher the temperature, the higher the ion conductivity, and the lower the temperature, the lower the ion conductivity. However, even at -20 ° C., 1.4 × 10 ⁻³ S / cm showed considerably high ion conductivity. This value is higher than the conventional gel polymer electrolyte, and is expected to have excellent discharge characteristics at high and low temperatures.

FIG. 6 shows the results of cyclic voltammetry of the gel polymer electrolyte measured at a scanning speed of 5 mV / s. As can be seen from the figure, 4.5 V vs. No current peak is observed in the voltage range up to Li / Li ⁺ . This indicates that it is electrochemically stable.

FIG. 7 shows the charge and discharge curves of a gel polymer electrolyte-applied battery measured at a current density of 0.5 mAcm ⁻² . Charge was up to 4.2V, discharge was up to 3V, and current density was 1.5 mA / cm ² . In the super charge, irreversible capacity was generated due to the formation of the passivation film, but as shown in FIG. 7, the charge and discharge efficiency was almost 100%. In addition, only a slight voltage drop was observed during discharge, indicating that the internal resistance was low.

8 shows a discharge curve according to the discharge rate of a LiCoO ₂ / GPE / graphite battery measured at 20 ° C. The capacity at 0.2 C of a lithium ion polymer battery containing about 5 vol% of a reactive mixture is about 448 mAh. Based on this, the capacity at the 1.0C discharge rate was about 366mAh, representing about 82%.

Figure 9 shows the discharge curve according to the temperature of the LiCoO ₂ / GPE / graphite battery measured at a current density of 1.1 mAcm ^-2 . The capacity at 20 ° C. of a lithium secondary battery containing about 5 vol% of a reactive mixture is about 414 mAh. Based on this, the capacity at −10 ° C. was about 355 mAh, representing about 86%.

FIG. 10 shows cycle characteristics of a LiCoO ₂ / GPE / graphite battery measured at a current density of 1.1 mAcm ⁻² . The cycle characteristics are good so that the initial capacity is almost maintained even after 60 cycles have elapsed. This shows that gel polymer batteries employing PMMA IPN have superior properties than batteries using conventional gels.

On the other hand, the present invention is not limited to the above-described typical preferred embodiments, but can be carried out in various ways without departing from the gist of the present invention, various modifications, alterations, substitutions or additions are common in the art Those who have knowledge will easily understand. If the implementation by such improvement, change, replacement or addition falls within the scope of the appended claims, the technical idea should also be regarded as belonging to the present invention.

As described in detail above, according to the present invention, the ion conductivity of the gel polymer electrolyte is as high as about 10 ⁻³ S / cm, and the electrolyte solution is formed in a gel form, so that there is no fear of leakage. In addition, by adjusting the mixing ratio of the reactive macromer and the reactive modifier, physical properties such as ion conductivity and mechanical properties can be changed. In addition, the productivity is high due to the simplification of the production process.

Claims (6)

An electrolyte solution in an electrode laminated structure in which a positive electrode layer and a negative electrode layer containing an active material capable of inserting and removing lithium ions are placed on a positive electrode current collector and a negative electrode current collector, respectively, and a separator is interposed between the both side layers and the negative electrode layer. Method of producing a lithium ion polymer battery, characterized in that the injection into a precursor comprising a thermal electrolyte to make a gel electrolyte. The method of claim 1, Inserting the electrode laminated structure into an aluminum laminate film, injecting a precursor including an IPN (Interpenetrating Polymer Network) mixed with a polymer and a reactive monomer already polymerized and an electrolyte solution, followed by heating, polymerization to polymerize to make a gel polymer electrolyte. Method for producing a lithium ion polymer battery characterized by. The method of claim 2, IPN (Interpenetrating Polymer Network), and a reactive modifier is added to the precursor, the method of manufacturing a lithium ion polymer battery, characterized in that by changing their composition ratio to change the physical properties of the gel polymer electrolyte. The method of claim 3, wherein In the IPN (Interpenetrating Polymer Network), one or two or more acrylate (acrylate) monomers capable of reacting with a polymer having a polymerized acrylate group are used. The reactive modifiers include HDDA (Hexanediol diacrylate) and triethylene glycol di. A method for producing a lithium ion polymer battery, characterized in that at least one acrylate having two or more reactors is used, such as methacrylate (Triethyleneglycoldimehtacrylate) and tetraethyleneglycoldiacrylate. The method of claim 3, wherein The precursor is composed of a liquid electrolyte and a curable mixture, the ratio of the method of producing a lithium ion polymer battery, characterized in that in the range of 80:20 (vol%) to 99: 1 (vol%). The method of claim 5, The curable mixture is a method for producing a lithium ion polymer battery, characterized in that it comprises a polymer, a reactive monomer, a reactive modifier and a polymerization initiator.