KR100322450B1 - A electrolyte containing a monomer of conductive polymer and a lithium secondary battery made thereof - Google Patents

Abstract

In the electrolyte solution for a lithium secondary battery according to the present invention, a monomer of a conductive polymer selected from the group consisting of pyrrole, aniline, thiophene, and derivatives thereof is added to the water-insoluble organic solvent in an amount of less than 2.0 wt%. It is manufactured by. As the non-aqueous solvent, an organic solvent such as cyclic or chain carbonate may be used, or two or more may be mixed. The lithium secondary battery containing the electrolyte solution uses a resin binder as a negative electrode plate and a graphitic carbonaceous material capable of occluding / discharging lithium ions as a negative electrode active material and occludes lithium ions as a positive electrode plate. Use a lithium composite oxide that can be released. The non-aqueous electrolyte containing the monomer of the conductive polymer of the present invention forms a conductive polymer film on the surface of the positive electrode active material during charging to block the flow of a large current to improve the safety of the battery. In addition, the conductive polymer film formed on the surface of the anode may allow lithium ions to enter and exit more reversibly, thereby extending the life of the battery.

Description

Electrolytic solution containing a monomer of a conductive polymer and a lithium secondary battery comprising the same {A ELECTROLYTE CONTAINING A MONOMER OF CONDUCTIVE POLYMER AND A LITHIUM SECONDARY BATTERY MADE THEREOF}

Field of invention

The present invention relates to an electrolyte solution containing a monomer of a conductive polymer and a lithium secondary battery comprising the same, and more particularly, an electrolyte solution containing a monomer of a conductive polymer capable of blocking the flow of overcurrent by forming a conductive polymer film on a surface of a cathode. It relates to a lithium secondary battery comprising the same.

Prior art

Recently, with the development of the high-tech electronic industry, it is possible to reduce the weight and weight of electronic equipment, and thus the use of portable electronic devices is increasing. As a power source for such portable electronic devices, the necessity of a battery having a high energy density has been increased, and research on lithium secondary batteries has been actively conducted. Li-metal or carbon material is used as a negative electrode material of a lithium secondary battery, and Li-metal oxide is used as a positive electrode material. When Li-metal is used as a negative electrode material, there is a risk of explosion due to short-circuit due to the formation of dendrite (dentrite), which is being replaced by carbon material instead of Li-metal as negative electrode material. Composite metal oxides such as LiMn ₂ O ₄ , LiMnO ₂ , LiCoO ₂ , LiNiO ₂ , LiNi _1-x Co _x O ₂ (0 <x <1) are used as the anode material. Mn-based electrode materials, such as LiMn ₂ O ₄ , LiMnO ₂ , are easy to synthesize, relatively inexpensive, and have low environmental pollution but have a small capacity. In particular, LiMn ₂ O ₄ has a lower discharge capacity than other active materials such as LiCoO ₂ and LiNiO ₂ , a rapid decrease in discharge capacity at high rates of charge and discharge, and battery life due to elution of manganese during continuous charge and discharge at high temperatures. There is a problem of this deterioration rapidly. LiCoO ₂ has good electrical conductivity, high battery voltage, and excellent electrode characteristics, and is a representative anode electrode material commercialized and sold by SONY, and has a disadvantage of being expensive. LiNiO ₂ is relatively inexpensive among the above-mentioned positive electrode materials and exhibits the highest discharge capacity. However, LiNiO ₂ is difficult to synthesize and has high discharge capacity.

In addition, since a battery is characterized by a complex reaction such as an anode / electrolyte and a cathode / electrolyte, the use of an appropriate electrolyte is also one of the important variables for improving the performance of the battery. Conventional electrolyte systems have expected and only acted as the mediators to move lithium ions. When using a conventional electrolyte, there is no way to block it when a large current flows, such as penetration and overcharging, which causes thermal runaway and can turn into a dangerous situation. Therefore, recently, in order to solve such a problem, a method of using an additive to form a thin passivation film on the surface of an anode by an initial reaction with a cathode in an existing electrolyte solution is known.

However, there is no known electrolyte solution that forms a conductive polymer film on the surface of the anode to block a large current such as overcharge or penetration.

An object of the present invention is to provide a non-aqueous electrolyte solution containing a monomer of the conductive polymer that can improve the safety of the battery by blocking the overcurrent flow by forming a conductive polymer film on the positive electrode surface.

Another object of the present invention is to provide a lithium secondary battery with improved safety and battery life.

The above and other objects can be achieved by the present invention described below.

1 is a graph showing the cycle life and capacity according to the pyrrole content of the lithium secondary battery.

In order to achieve the above object of the present invention, the present invention is applied to a lithium secondary battery by preparing a non-aqueous electrolyte by adding a monomer of the conductive polymer to the water-insoluble organic solvent.

Hereinafter, the present invention will be described in more detail.

The electrolyte solution for a lithium secondary battery according to the present invention is prepared by adding a monomer of a conductive polymer to a water-insoluble solvent. Monomers of the conductive polymer that can be used in the present invention include pyrrole, aniline, thiophene or derivatives thereof that can be electrochemically polymerized at about 4.0V with respect to lithium potential. It is preferable to use these compounds in amounts less than 2.0 weight. When more than 2.0 weight is added, the discharge capacity and the irreversible capacity increase, which causes a problem of degrading the performance of the battery. As the non-aqueous solvent, an organic solvent such as cyclic or chain carbonate may be used, or two or more may be mixed. Specific examples thereof include ethylene carbonate (EC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), and the like.

In the present invention, the lithium secondary battery is composed of a negative electrode plate, an electrolyte, and a positive electrode plate. The negative electrode plate is made of a graphite binder and a graphite carbonaceous material capable of occluding / discharging lithium ions as a negative electrode active material. The anode active material has a dOO2 interplanar distance of 3.35 to 3.38, an Lc (crystallite size) by X-ray diffraction at least 20 nm, and an exothermic peak at 700 ° C or higher. The negative electrode active material used in the present invention is a carbon material prepared by using a mesophase spherical particle, by a carbonizing step and a graphitizing step process. In addition, fibrous graphite prepared by a carbonization step and a graphitization step using a fibrous mesophase pitch (mesophase pitch fiber) can also be used as a negative electrode active material, both artificial graphite or natural graphite can be used.

As the positive electrode plate, a lithium composite oxide capable of occluding / discharging lithium ions is used. Specific examples thereof include LiCoO ₂ , LiNi _1-xy Co _x M _y O ₂ (0 <x <1, 0 <y <1, 0 <x + y <1, M is Al, Sr, Mg, La, etc.). Metal), LiMnO ₂ , LiMn ₂ O _4, and the like. As supporting electrolyte salts that can be used in the electrolyte of the lithium secondary battery of the present invention, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium trifluoromethanesulfonate and mixtures of two or more thereof may be used. Can be.

When the non-aqueous electrolyte solution containing the monomer of the conductive polymer is applied between the positive electrode and the negative electrode plate, a conductive polymer film is formed on the surface of the positive electrode active material during charging. The conductive polymer film thus formed is not involved in the movement of lithium ions in normal charging and discharging, but loses its conductivity at high potentials of 4.3V or higher generated during overcharging or penetration, thereby having the characteristics of the non-conducting membrane. This can block the flow of large currents to prevent thermal runaway due to overcharge or penetration. In addition, the conductive polymer film is formed on the surface of the positive electrode to help the lithium ions in and out more reversible to extend the life of the battery.

The following presents a preferred embodiment to aid the understanding of the present invention. However, the following examples are merely provided to more easily understand the present invention, and the present invention is not limited to the following examples.

Examples and Comparative Examples

An electrolyte was prepared while changing the content of pyrrole in a non-aqueous organic solvent in which ethylene carbonate / ethylmethyl carbonate / diethyl carbonate (EC / EMC / DEC) was mixed at 3/3/1. LiNi _1-xy Co _x Sr _y O ₂ (0 <x <1, 0 <y <1, 0 <x + y <1) The anode is composed of an active material and the cathode is composed of graphite (KMFC: manufactured by Kawasaki Steel). And 18650 lithium secondary battery was prepared by applying an electrolyte having a composition ratio shown in Table 1. The cycle life, capacity (initial discharge capacity and irreversible capacity), and safety of the battery were measured and evaluated using the lithium secondary battery prepared above, and are shown in Table 1 below.

Pyrrole content (weight) Lifespan, 1C (100 Times) Volume Safety evaluation Initial discharge capacity (mAh) Irreversible capacity () Overcharge, 1C Penetrate Example One 0.1 92 1780 91 L0 L1 2 0.5 90 1585 89 L0 L1 Comparative example One 0 90 1800 92 L3 L5 2 2.0 85 1347 85 L0 L1 3 5.0 65 1037 77 L0 L1

In Table 1, the safety criteria are as follows:

L0: good, L1: leakage, L2: flash, L2: flame, L3: smoke, L4: ignition, L5: burst.

As shown in Table 1, when pyrrole, which is a monomer of the conductive polymer, was added, both of the overcharging and the penetration showed good results. However, in Comparative Examples 2 and 3 having a pyrrole content of 2.0 or more, the initial discharge capacity and the irreversible capacity were increased, indicating that the battery performance decreased. On the other hand, in the case of Examples 1 and 2 according to the present invention added in an amount of less than 2.0 wt%, both the initial discharge capacity and the irreversible capacity increase as well as safety were improved and cycle life was also excellent. Cycle life and capacity according to the content of the pyrrole in the results of Table 1 are shown in FIG. Using a lithium secondary battery containing an electrolyte solution of Example 2 having a pyrrole content of 0.5 wt%, the safety was evaluated under various test conditions, and the results are shown in Table 2 below.

Test Items Before test OVC (V) ^* Leakage (L1) Flash (L2) Flame (L2) Smoke (L3) Ignition (L4) Rupture (L5) Temperature (℃) Evaluation level ^** Overcharge 1C 4.157 × × × × × × 107 L0 4.157 × × × × × × 104 L0 4.156 × × × × × × 106 L0 4.157 × × × × × × 98 L0 4.156 × × × × × × 109 L0 Overcharge 3C 4.157 × × × × × × 158 L0 4.157 × × × × × × 134 L0 4.157 ○ × × × × × 158 L1 4.157 ○ × × × × × 148 L1 4.157 × × × × × × 150 L0 Penetrate 4.158 ○ × × × × × 85 L1 4.149 ○ × × × × × 106 L1 4.152 ○ × × × × × 92 L1 4.159 ○ × × × × × 104 L1 4.156 ○ × × × × × 97 L1 Overcharge Penetration 4.211 ○ × × × × × 96 L1 4.210 ○ × × × × × 91 L1 4.212 ○ × × × × × 84 L1 4.198 ○ × × × × × 88 L1 4.193 ○ × × × × × 105 L1 Compressed species 4.154 ○ × × × × × 24 L1 4.154 ○ × × × × × 24 L1 4.154 ○ × × × × × 26 L1 4.156 ○ × × × × × 26 L1 4.154 ○ × × × × × 31 L1 Compression side 4.156 ○ × × × × × 27 L1 4.154 ○ × × × × × 27 L1 4.153 ○ × × × × × 28 L1 1.153 ○ × × × × × 29 L1 1.154 ○ × × × × × 28 L1

Note) * OCV: Open Cell Voltage before charging

** Evaluation level: L0 (good), L1 (leakage)

○: Occurrence X: No occurrence

As shown in Table 2, all showed good results even under poor conditions such as penetration and overcharge. Therefore, it can be seen that the lithium secondary battery manufactured according to the present invention has excellent safety.

Electrolyte solution containing the monomer of the conductive polymer prepared according to the present invention has the effect of forming a conductive polymer film on the surface of the anode during charging to block the over-current, such as overcharge or penetration, thereby improving the safety of the battery. The lithium secondary battery including the electrolyte according to the present invention has the characteristics of the non-conductor membrane by losing the conductivity at the high potential generated during overcharging or penetrating, and also has the effect of preventing the thermal runaway phenomenon due to overcharging or penetrating. . In addition, the conductive polymer film formed on the surface of the positive electrode may allow lithium ions to enter and exit more reversibly, thereby improving battery life.

Simple modifications or changes of the present invention can be easily carried out by those skilled in the art, and all such modifications or changes can be seen to be included in the scope of the present invention.

Claims (7)

(Corrected) water-insoluble organic solvent; And Monomers of conductive polymers selected from the group consisting of pyrrole, aniline, thiophene and derivatives thereof (The monomers can be electrochemically polymerized around 4.0V for lithium potential.) Electrolyte for lithium secondary battery comprising a. The electrolyte for a lithium secondary battery according to claim 1, wherein the monomer of the conductive polymer is added in an amount of less than 2.0 wt%. The method according to claim 1, wherein the electrolyte further comprises a supporting electrolytic salt selected from the group consisting of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium trifluoromethanesulfonate and mixtures of two or more thereof. An electrolytic solution for a lithium secondary battery, comprising: (Correction) The electrolyte according to claim 1; A negative electrode plate comprising a resin binder, a graphite carbonaceous material capable of occluding / discharging lithium ions as a negative electrode active material; And Anode plate containing lithium composite oxide that can occlude / discharge lithium ions Lithium secondary battery, characterized in that consisting of. The negative active material has a dOO2 interplanar distance of 3.35 to 3.38, an Lc (crystallite size) by X-ray diffraction of at least 20 nm and an exothermic peak at 700 ° C. or more. Lithium secondary battery. The lithium secondary battery of claim 4, wherein the anode active material is a carbon material manufactured from a mesophase spherical particle through a carbonizing step and a graphitizing step. The lithium secondary battery according to claim 4, wherein the negative active material is fibrous graphite prepared through a carbonization step and a graphitization step from a fibrous mesophase pitch fiber. 6.