KR101663026B1

KR101663026B1 - Capacity restoration method of lithium secondary battery

Info

Publication number: KR101663026B1
Application number: KR1020150079295A
Authority: KR
Inventors: 정철수; 이충호; 박범준; 이영주; 김주영
Original assignee: 서울시립대학교 산학협력단
Priority date: 2015-06-04
Filing date: 2015-06-04
Publication date: 2016-10-06

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for restoring the capacity of a lithium secondary battery, and more particularly, to a method for restoring a capacity of a lithium secondary battery by discharging the battery at a voltage lower than a conventional operating voltage.
The method for recovering the capacity of an electrochemical device according to the present invention is a simple method of discharging at a voltage lower than a discharge voltage at which an electrochemical device is used without discarding or decomposing the electrochemical device, The effect of reducing the amount of waste of the electrochemical device is exhibited.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery,

The present invention relates to a method of restoring a capacity of a lithium secondary battery, and more particularly, to a method of restoring a capacity of a lithium secondary battery by discharging the battery to a voltage lower than a conventional use voltage, And a method of restoring the capacity of the lithium secondary battery.

BACKGROUND ART [0002] As a material for providing a predetermined power to such an electric / electronic device, for example, an electric / electronic device such as a portable computer, a portable communication terminal, etc., A secondary battery which can be charged and used is widely used. Currently, various kinds of secondary batteries are being researched and developed, but the most widely commercialized product is lithium secondary battery.

Since the lithium secondary battery is not a consumable product that can be charged and discharged indefinitely but is a consumable product having a durability that can not achieve its original intended function when the number of times exceeds a predetermined number of times of several hundreds to several thousands of limited charge and discharge cycles, Discharge amount of lithium secondary battery is also increasing in proportion to expansion. However, it is preferable that the lithium secondary battery, which is discarded due to the original purpose of the lithium secondary battery or is discarded due to the cause of failure in the manufacturing process, is left in a natural state due to the harmfulness of various chemical substances contained therein Can not do it. Usage Organic materials such as organic electrolytes among the chemicals contained in the disposed lithium secondary batteries can greatly reduce the harmfulness to the environment and human body through a simple heat treatment. However, inorganic substances such as lithium cobalt oxide constituting the electrode of the battery Simple heat treatment alone has technical limitations to reduce the environmental and human hazards. Purpose Lithium cobalt oxide, such as lithium cobalt oxide (LiCoO ₂ ), contained in waste lithium secondary batteries, gives pathological stimulation to eyes and skin through respiratory or skin contact with animals and animals, especially humans. Especially, It is a substance that is recognized as a harmful substance to the environment and human body that causes vomiting when inhaled through.

As described above, the disused lithium secondary battery includes a positive electrode made of a lithium cobalt oxide, a conductive carbon, a binder and an aluminum current collector with reduced electrical activity, an electrolyte composed of ethylene carbonate and dimethyl carbonate, a separator impregnated with an electrolyte, The conventional recovery process known so far includes a complicated step because it includes an active material, a conductive carbon, a binder, and a cathode collector made of a copper current collector, and the like. Therefore, only the lithium cobalt oxide is mechanically sorted It is almost impossible to do so, and thus it is a reality that the technology has not been adopted and used as a commercialized technology to date.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a new method for recovering the capacity of an electrochemical device for reusing an electrochemical device including a lithium secondary battery.

The present invention has been made to solve the above problems

A first step of measuring a resistance of the electrochemical device; And

A second step of discharging by applying a voltage of 2 V to 3 V or less; The present invention also provides a method for restoring the capacitance of an electrochemical device.

The method for recovering the capacity of an electrochemical device according to the present invention increases the amount of lithium desorption from the negative electrode by discharging to a voltage of 2V to 3V or less, which is lower than the discharge voltage of 3.3V to 3.5V of the conventional lithium ion secondary battery, Thereby increasing the lithium insertion amount and consequently reducing the inactive amount of the lithium secondary battery, thereby restoring the capacity.

In the method for restoring capacitance of an electrochemical device according to the present invention, the resistance of the electrochemical device and the resistance of the electrochemical device can be measured by any method known to those skilled in the art. In the present invention, the impedance is measured by the method disclosed in Korean Patent No. 10-0388314, and a method of deriving the resistance value using the impedance is used.

Specifically, the first step

A first step of testing and measuring a complex impedance for a plurality of frequencies in a preset frequency range;

A first step of separating a plurality of parameters into a resistance component and a power storage component by fitting the impedance spectrum curve measured in the step 1-1 to the defined impedance function of the power source equivalent circuit model; And

(1-3) of deriving one or more total resistance values (DC approximation resistances as real part values of impedance data at a frequency of 0 Hz) corresponding to the resistance components detected in the step 1-2; And a control unit.

In the method of restoring capacitance of an electrochemical device according to the present invention, in the first step, the resistance is specifically i) charged to a full-charge voltage condition (4.2 V in the case of the present invention) C = constant voltage of each cell), ii) constant voltage charging at full voltage (charge current up to 0.01C), iii) complex impedance test measurement for multiple frequencies in full charge state, iv) Detecting the separation of the resistance component and the charge component, and v) deriving the value of the component corresponding to the second semi- circle in the complex plane.

In the method of restoring capacitance of an electrochemical device according to the present invention, the second step is performed when the resistance of the electrochemical device measured in the first step is 200% or more of the initial value. That is, the capacity recovery method of the electrochemical device according to the present invention can efficiently restore the capacity when the capacity is decreased due to an increase in the resistance value.

In the method of restoring the capacity of an electrochemical device according to the present invention, the second step is performed a plurality of times, specifically, repeatedly at least five times.

In the method for restoring the capacity of an electrochemical device according to the present invention, the electrochemical device is a lithium ion secondary battery or a lithium ion polymer secondary battery. In addition to a unit cell such as a cylindrical battery, The present invention is also applicable to a battery pack including a plurality of batteries.

The method for recovering the capacity of an electrochemical device according to the present invention is a simple method of discharging at a voltage lower than a discharge voltage at which an electrochemical device is used without discarding or decomposing the electrochemical device, The effect of reducing the amount of waste of the electrochemical device is exhibited.

FIG. 1 shows a result of measurement of charge / discharge curves of a lithium ion battery according to an embodiment of the present invention.
FIG. 2 and FIG. 3 show the results of measurement of the charging / discharging curve of the lithium ion battery according to the comparative example of the present invention.

Hereinafter, the present invention will be described in more detail by way of examples. However, the present invention is not limited by the following examples.

&Lt; Example 1 >

A rectangular lithium ion secondary battery was prepared and charged / discharged five times. The result is shown in Fig. The measurement conditions were 0.5C filling rate and 1.0C discharge rate. After 5 cycles of charging and discharging, the cell voltage was maintained at 4.2 V as a charging condition to make the same SOC state. Then, the impedance spectrum of these cells was measured and analyzed for internal resistance comparison. Impedance measurements were carried out in the frequency range between 200 kHz and 10 mHz using the IM6 ex of Zhahner and the resistance was calculated to be more than 200% of the initial value.

FIG. 1 shows the result of measuring the battery capacity and voltage before and after the low-voltage discharge by discharging five times at a low voltage of 2.8 V for the battery. In FIG. 1, the discharge capacity after the low-voltage discharge is increased by 34 mAh, and the capacity is increased by 5.0%.

&Lt; Comparative Example 1 &

A new lithium ion secondary battery that was not used was discharged five times at a low voltage of 2.8 V as in Example 1 without measuring impedance, and the results of measuring the battery capacity and voltage before and after the low voltage discharge are shown in FIG.

In FIG. 2, it can be seen that the discharge capacity does not increase even after the low voltage discharge in the case of the novel lithium ion secondary battery.

&Lt; Comparative Example 2 &

As a result of measuring the battery capacity and voltage before and after the low-voltage discharge, discharging was performed at a low voltage of 2.8 V five times, as in the case of Example 1, with respect to a battery whose resistance increase value through impedance measurement was within 200% 3.

In FIG. 3, it can be seen that the discharge capacity does not increase even after the low voltage discharge when the resistance increase value is within 200% of the initial value.

Claims

Electrochemical device A first step of measuring the resistance when the resistance is 200% or more of the initial value; And
A second step of discharging by applying a voltage of 2 V to 3 V or less; Containing
A method for restoring capacity of an electrochemical device.

The method according to claim 1,
The first step
A first step of testing and measuring a complex impedance for a plurality of frequencies in a preset frequency range;
A first step of separating a plurality of parameters into a resistance component and a power storage component by fitting the impedance spectrum curve measured in the step 1-1 to the defined impedance function of the power source equivalent circuit model; And
(1-3) of deriving one or more total resistance values (DC approximation resistances as real part values of impedance data at a frequency of 0 Hz) corresponding to the resistance components detected in the step 1-2; &Lt; / RTI >
A method for restoring capacity of an electrochemical device.

delete

The method according to claim 1,
Wherein the second step is performed a plurality of times
A method for restoring capacity of an electrochemical device.

The method according to claim 1,
The electrochemical device may be a lithium ion secondary battery or a lithium ion polymer secondary battery.
A method for restoring capacity of an electrochemical device.