KR100706714B1 - Hybrid battery - Google Patents

Abstract

A hybrid cell is provided. The hybrid battery is filled in an electrode space consisting of a positive electrode and a negative electrode, a separator for electrically separating the positive electrode and the negative electrode, and a space between the positive electrode and the negative electrode so that an electric double layer is formed on the surface of the positive electrode and the negative electrode when a predetermined voltage is applied. An electrolyte solution in which a solvent containing propylene carbonate and ethylene carbonate and a solute containing lithium salt, imide salt and ammonium salt are mixed.

Hybrid, battery, capacitor, imide salt

Description

Hybrid battery

The present invention relates to a hybrid battery, and more particularly, in a hybrid battery using a metal oxide as a positive electrode and activated carbon as a negative electrode, a hybrid battery capable of improving high temperature characteristics and lifetime by specifying a solvent and a solute of an electrolyte. It is about.

Supercapacitors can be classified into Electric Double Layer Capacitors (EDLC) and Pseudocapacitors according to the type of electrode used.

An electric double layer capacitor refers to a capacitor which stores energy in the storage due to the formation of an electric double layer at both electrodes using activated carbon in both the positive electrode and the negative electrode.

The pseudocapacitor uses a metal oxide such as nickel oxide (NiO), ruthenium dioxide (RuO ₂ ), cobalt oxide (Co ₃ O ₄ ), and manganese dioxide (MnO ₂ ) as a positive electrode. The term "capacitor" refers to a capacitor using activated carbon used in an electric double layer capacitor, which is also referred to as a hybrid capacitor.

In the case of the electric double layer capacitor, since the electrical storage and discharge are caused by the physical desorption and adsorption of ions according to the potential, the reaction rate is considerably fast and the charge and discharge life is very long, but the storage capacity is low. .

In comparison, the hybrid capacitor uses the electrode material used in the secondary battery as the positive electrode and the material capable of forming the electric double layer at the negative electrode. Thus, the electric double layer capacitor with low storage capacity, cycle life and power density are used. It is an energy storage device that attempts to overcome the weaknesses of secondary batteries with limitations.

The technology level up to now is about 2 times the storage capacity and 10,000 cycles longer than the electric double layer capacitor in the form of a hybrid capacitor.

Such a hybrid capacitor has a capacity more than twice that of a conventional electric double layer capacitor. For this purpose, it is necessary to control the concentration of an appropriate electrolyte.

In particular, since the capacity of the hybrid capacitor is realized by the insertion and desorption of lithium, and the capacity of the cathode is implemented according to the degree of formation of the electric double layer, the smooth movement of lithium ions used as the solute of the electrolyte and Proper concentration control of the cations is necessary.

In particular, lithium ions have a low dissociation degree due to the low dissociation rate between cations and anions, compared to ammonium ions. Therefore, in order to reduce resistance and increase high current characteristics, control is very important in relation to other ions.

The cycle characteristics improve only when the solubility and mobility of the lithium salt are excellent, but the solubility and mobility of the lithium salt are closely related to the paired anions.

In general, hexafluorophosphate is often used as a counter ion of a lithium salt in a capacitor. Hexafluorophosphate can increase the solubility and mobility of lithium salts and has a high dissociation degree, which is very advantageous for increasing power characteristics.

However, there is a problem in using hexafluorophosphate anion in the hybrid capacitor, because the hybrid capacitor uses activated carbon as the negative electrode, so that the water has a high adsorption amount, because the hexafluorophosphate anion is particularly sensitive to water.

In addition, when the life test for 1000 hours or more at high temperature, the use of hexafluorophosphate anion is restricted due to the problem of being vulnerable to the reaction with impurities such as moisture. Therefore, tetrafluoroborate anions are often used in place of hexafluorophosphate, which has excellent solubility and mobility when paired with tetraalkylammonium cations, but weak solubility and mobility when paired with lithium ions. Has

In particular, in order to improve the cycle characteristics and low temperature characteristics, the dissociation degree of lithium ions must be high, so that ions excellent in solubility and mobility must be added.

The technical problem to be achieved by the present invention is to propose a hybrid battery having an electrolyte composition excellent in cycle characteristics, excellent electrolyte composition, and a cathode material and a cathode material, which are not only toxic but also have a low capacity and excellent stability at high and low temperatures.

Technical problems to be achieved by the present invention are not limited to the above-mentioned technical problems, and other technical problems not mentioned will be clearly understood by those skilled in the art from the following description.

The hybrid battery according to the embodiment of the present invention for solving the above technical problem, a separator for electrically separating the positive electrode and the negative electrode, a separator for electrically separating the positive electrode and the negative electrode, and when a predetermined voltage is applied on the surface of the positive electrode and the negative electrode Filled in the separation space between the positive electrode and the negative electrode to form an electric double layer, and includes an electrolyte solution containing a solvent containing propylene carbonate, ethylene carbonate and a solute containing lithium salt, imide salt, ammonium salt.

Specific details of other embodiments are included in the detailed description and the accompanying drawings.

Advantages and features of the present invention and methods for achieving them will be apparent with reference to the embodiments described below in detail with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, only the present embodiments to make the disclosure of the present invention complete, and common knowledge in the art to which the present invention pertains. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

The electrolyte proposed in the present patent adds a salt capable of generating an imide-based anion in order to enhance high voltage stability to lithium salt and ammonium salt, which are conventionally used in hybrid batteries.

The imide salt represented by N (C _n F _{2n +1} SO ₂ ) ₂ ⁻ is very stable because of the large degree of delocalizing of negative charges, and is very stable in the electrolyte and excellent in fluidity.

Such imide salt is very advantageous when added to a hybrid battery because of the following characteristics.

First, by forming an excellent film on the surface of the anode, the stability at high temperatures is increased, the breakdown voltage characteristics are improved, and the self-discharge rate is reduced.

Second, since the solubility is high in the solvent and the dissociation degree is excellent enough to form an ionic liquid together with tetraalkyl ammonium, there is an advantage to increase the solubility in the electrolyte. In addition, when LiBF4 is used as lithium ion when present with lithium ions, the bonding force between Li + and BF 4-ions is not so strong that it dissociates well in a solvent. However, the dissociation degree of lithium ions is considerably high.

Therefore, by adding an appropriate amount of an imide salt as the solute of the electrolyte, the stability and power characteristics of the electrolyte can be improved.

The reason for dissolving manganese oxide, which is mainly used as a positive electrode in a hybrid battery, is due to the reaction by hydrogen fluoride (HF) formed by side reaction of water and salts on the surface, and because the imide salt inhibits this reaction, LiMnO ₄ or LiMn It is more effective when _x M _{1 - x} O ₂ (M = Co, Ni, Li) is used as the positive electrode active material.

When an imide anion is added, an appropriate amount should be added, because when adding an imide salt, for example, LiN (CF ₃ SO ₂ ) ₂ salt, the aluminum current collector at the positive electrode is corroded to a maximum of 0.1 M. The amount must not be exceeded. In addition, if a large amount of imide salt is added, a lot of gases are generated due to side reactions on the surface of the anode, so the total concentration should not exceed 0.1M.

As a solvent, propylene carbonate (PC) which is excellent in stability and nontoxic is mainly used, and ethylene carbonate may be further added to increase solubility and dissociation ability of Li ⁺ or to increase high temperature and low temperature stability.

However, propylene carbonate and ethylene carbonate are added in an amount of 8: 2 based on the volume.

As the lithium salt used as the solute of the electrolyte of the hybrid battery of the present invention, a lithium salt generally used in a hybrid battery or an electric double layer capacitor may be used, but lithium tetrafluoroborate (LiBF ₄ ) is preferably used. All. In addition, ammonium salts may be generally used ammonium salts used in hybrid batteries or electric double layer capacitors, but tetraethylammonium tetrafluoroborate ((C ₂ H ₅ ) ₄ NBF ₄ ) is preferably used.

The mixing ratio of lithium salt, ammonium salt and imide salt as the solute used in the present invention is preferably added in a ratio of 7: 7: 1 based on the molar concentration. In addition, the concentration of the total electrolyte is preferably set to 1.0 ~ 2.5 mol / L.

As the active material used for the positive electrode, LiMO 2 (M = Li, Co, Mn, Ni, where Co is 0.33 or less) may be used as a material having a layered structure, and preferably LiMn ₂ O ₄ is used. As the active material used for the negative electrode, activated carbon having a storage capacity of 100 to 300 F / g is used. However, as the positive electrode active material, a metal oxide generally used in a hybrid battery may be used.

Hereinafter, specific embodiments will be described that reliability is improved, such as high temperature load characteristics and cycle characteristics, according to the addition of the imide salt in the hybrid battery. Details not described herein are omitted because they can be sufficiently inferred by those skilled in the art.

< Example  1 ~ 3>

Examples 1 to 3 are examples for checking the initial characteristics of the case where the positive electrode active material is different. Example 1 is a LiMn ₂ O _4, the second embodiment has a positive electrode active material in the positive electrode active material _{Li (Ni 0.37 Co 0.16 Mn 0.37} Li 0.1) O 2, in Example 3, _{Li (Ni 1/3 Co 1} /3 as a cathode active material using Mn _1/3) O _2, and, as a negative electrode active material was prepared in the capacitor using the activated carbon of the capacity 140F / g, a specific surface area of 2,000m ² / g. The positive electrode was made of 75% of an active material, 15% of carbon black, 10% of CMC (Carboxy Methyl Cellulose) and 10% of Polytetrafluoroethylene (PTFE) binder, and coated on 20 μm aluminum foil.

The positive electrode and the negative electrode were coated 50 μm each so that the total thickness including the foil was 120 μm, and the negative electrode was coated on both sides with 100 μm each so that the total thickness was 220 μm.

As the solute of the electrolyte, 0.7 mol of lithium tetrafluoroborate (LiBF ₄ ), 0.1 mol of lithium trifluoroethylsulfonimide (LiN (CF ₃ SO ₂ ) ₂ ), and tetraethylammonium tetrafluoroborate ((C ₂ H ₅ ) ₄ NBF ₄ ) 0.7 moles.

As the solvent of the electrolyte, a solvent in which propylene carbonate (PC) and ethylene carbonate (EC) are mixed at a ratio of 8: 2 is used.

Each electrode was cut to a size of 30mm * 400mm, wound into a cylindrical shape and placed in a can of 18mm in diameter and 40mm in height. Capacitance was measured based on 2.3V applied voltage and 1mA / F, resistance was measured at 1kHz, and the results of initial characteristic measurement under the above conditions are shown in Table 1.

<Examples 4-6>

Examples 4 to 6 were prepared by fixing the positive electrode to LiMn2O4 and the negative electrode to activated carbon as a characteristic of the addition of the onium salt, the solvent is 80 mol% propylene carbonate and 20 mol% ethylene carbonate, solute LiBF After fixing to ₄ 0.7M, in Example 4 tetraethylammonium tetrafluoroborate ((C ₂ H ₅ ) ₄ NBF ₄ ), in Example 5 butylmethylpyrrolidiniumtetrafluoroborate ((CH ₃ ) (C ₄ H ₉ ) (cyc-C ₄ H ₈ N) BF ₄ ), in Example 6 ethylmethylimidazoliumtetrafluoroborate ((C ₂ H ₅ ) (CH ₃ ) (cyc-C ₃ H ₃ N ₂ ) BF ₄ ) A cell was prepared under the same conditions as in Example 1 using 0.7 M of onium salt.

Capacity was measured based on 2.3V voltage and 1mA / F, and resistance was measured at 1kHz. As measurement items, initial characteristics, high temperature load (1000 hours), and cycle characteristics (20,000 times) were measured, and the measurement results are shown in Table 2.

< Example  7-9

Examples 7 to 9 are for explaining the results of the improved reliability according to the addition of the imide salt, the cells were prepared in the same manner as in Examples 4 to 6, and the change in properties by adding 0.1M imide salt was confirmed. It was. In this case, the imide salt used was lithium trifluoromethylsulfonimide (LiN (SO ₂ CF ₃ ) ₂ ) (HQ-115 manufactured by 3M), and a cell was prepared under the same conditions as in Example 1.

Capacity was measured based on 2.3V applied voltage and 1mA / F, and resistance was measured at 1kHz. Initial characteristics, high temperature load (1000 hours), and cycle characteristics (20,000 cycles) were measured. The results are shown in Table 3.

As shown in Table 3, it can be seen that when the imide salt is added as the solute of the electrolyte, the overall high temperature load characteristics and the cycle characteristics are improved.

< Example  10 to 11

Example 10 and Example 11 were to investigate the characteristics of the addition of each imide salt, the electrode was prepared by using the positive electrode as LiMn ₂ O ₄ and the negative electrode as the active carbon active material, the solvent is propylene carbonate 80mol% and ethylene carbonate 20 mol%, the solute was fixed with LiBF ₄ 0.7M, tetraethylammonium tetrafluoroborate (Et ₄ NBF ₄ ) 0.7M, and then 0.1M imide salt was used to prepare a cell under the same conditions as in Example 1. In this case, the imide salt used was LiN (CF ₃ SO ₂ ) ₂ in Example 10, and LiN (C ₂ F ₅ SO ₂ ) ₂ (3M FC-130) was used in Example 11. .

Capacity was measured based on 2.3V applied voltage and 1mA / F, and resistance was measured at 1kHz. As the measurement items, initial characteristics, high temperature load (1,000 hours), and cycle characteristics (20,000 times) were measured, and the results are shown in Table 4.

As shown in Table 4, when the imide salt is used, the capacity change rate at a high temperature is good, but since the size of the molecule is increased and mobility is reduced, the resistance is increased and the improvement of cycle characteristics is slightly decreased.

Although the embodiments of the present invention have been described, the present invention is not limited to the above embodiments and can be manufactured in various forms, and a person of ordinary skill in the art to which the present invention belongs may have It will be understood that other specific forms may be practiced without changing the essential features. Therefore, it should be understood that the embodiments described above are exemplary in all respects and not restrictive.

According to the hybrid battery according to the embodiment of the present invention, one or more of the following effects exist.

First, since the anode material is stable charging and discharging even at a high voltage of 4.3V or more, the use voltage can be further increased, thereby increasing the energy density.

Second, the use of the imide salt has an effect of improving the cycle characteristics.

Third, the use of the imide salt has an effect of improving the high temperature characteristics.

Claims (7)

An electrode unit consisting of a positive electrode and a negative electrode; A separator electrically separating the positive electrode and the negative electrode; And Lithium salt and a solvent containing propylene carbonate and ethylene carbonate in a volume ratio of 8: 2, filled in a space between the positive electrode and the negative electrode so that an electric double layer is formed on the surfaces of the positive electrode and the negative electrode when a predetermined voltage is applied. And an electrolyte solution in which a solute containing an imide salt and an ammonium salt is mixed. delete The method of claim 1, The lithium salt is lithium tetrafluoroborate (LiBF ₄ ), the imide salt is lithium trifluoroethylsulfonimide (LiN (CF ₃ SO ₂ ) ₂ ) or lithium hexafluoroethylsulfonimide (LiN (C ₂ F ₅ SO) ₂ ) ₂ ), The ammonium salt is a hybrid battery, characterized in that using tetraethylammonium tetrafluoroborate ((C ₂ H ₅ ) ₄ NBF ₄ ). The method according to claim 1 or 3, The mixing ratio of the lithium salt: imide salt: ammonium salt is a hybrid battery, characterized in that the mixing ratio of 7: 1: 7 based on the molar concentration. The method of claim 1, The concentration of the electrolyte is a hybrid battery, characterized in that 1.0 ~ 2.5 mol / L. The method of claim 1, The positive electrode is a hybrid battery, characterized in that the lithium manganate (LiMn ₂ O ₄ ) as an active material. The method of claim 1, The negative electrode is a hybrid battery, characterized in that formed using activated carbon having a storage capacity of 100 ~ 300 F / g as an active material.