KR20020014152A - A lithium ion cell having increased reversible capacity and a manufacturing method there of - Google Patents

A lithium ion cell having increased reversible capacity and a manufacturing method there of Download PDF

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KR20020014152A
KR20020014152A KR1020000047264A KR20000047264A KR20020014152A KR 20020014152 A KR20020014152 A KR 20020014152A KR 1020000047264 A KR1020000047264 A KR 1020000047264A KR 20000047264 A KR20000047264 A KR 20000047264A KR 20020014152 A KR20020014152 A KR 20020014152A
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South Korea
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lithium ion
ion battery
electrolyte solution
carbon electrode
additive
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KR1020000047264A
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Korean (ko)
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최용국
정명우
남형표
김우성
성영은
김신국
정광일
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최용국
임영우
주식회사 애니셀
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Priority to KR1020000047264A priority Critical patent/KR20020014152A/en
Publication of KR20020014152A publication Critical patent/KR20020014152A/en

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
    • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
    • H01M10/0566—Liquid materials
    • H01M10/0567—Liquid materials characterised by the additives
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/058—Construction or manufacture
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
    • Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
    • Y02P70/50—Manufacturing or production processes characterised by the final manufactured product

Abstract

PURPOSE: A lithium ion battery and its preparation method are provided, to inhibit the degradation of a solvent producing the irreversible capacity, to improve the reversible capacity and to enhance the charging/discharging cycle efficiency. CONSTITUTION: The lithium ion battery is prepared by adding an additive whose constituent is the same to that of a passive membrane, into an electrolyte solution in advance, for producing a passive membrane with a small resistance onto the surface of a carbon electrode before the electrode reaction, thereby inhibiting the degradation of a solvent producing the initial irreversible capacity. Preferably the additive is Li2CO3.

Description

가역용량을 증대시킨 리튬이온전지 및 그 제조방법 {A lithium ion cell having increased reversible capacity and a manufacturing method there of}A lithium ion cell having increased reversible capacity and a manufacturing method there of}

본 발명은 가역용량을 증대시킨 리튬이온전지 및 그 제조방법에 관한 것으로, 전극에 저항이 큰 부동태막이 형성되는 것을 억제하고 용매의 분해를 억제함으로써, 가역용량을 증대시킬 수 있는 가역용량을 증대시킨 리튬이온전지 및 그 제조방법에 관한 것이다.BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium ion battery having an increased reversible capacity, and a method for manufacturing the same. The present invention relates to a method for manufacturing a lithium ion battery having a high resistance to an electrode, and to suppressing the decomposition of a solvent, thereby increasing the reversible capacity. A lithium ion battery and a method of manufacturing the same.

일반적으로, 리튬 이온(Li-Ion) 2차 전지의 성능은 용량과 수명시험 결과로 평가한다. 대개 리튬이온 전지의 음전극(陰電極)으로는 탄소가 사용되는데, 이 탄소전극은 초기 충전시 표면에 부동태 막을 형성한다. 이와 같이 탄소전극에 부동태 막이 형성되는 주요원인은 충전시에 용매가 분해될 때 생성되는 리튬 염들이 탄소 전극에 흡착되어 막을 형성하기 때문이다.In general, the performance of lithium ion (Li-Ion) secondary batteries is evaluated by the capacity and life test results. Usually, carbon is used as a negative electrode of a lithium ion battery, which forms a passivation film on its surface during initial charging. The main reason why the passivation film is formed on the carbon electrode is because lithium salts generated when the solvent is decomposed during charging are adsorbed on the carbon electrode to form the film.

이러한 부동태 막은 충전시에 전극을 통해 이루어지는 가역작용을 방해하며 특히, 충전 초기의 비가역용량을 증대시키기 때문에, 전지의 성능을 저하시키는 직접적인 원인이 된다.Such a passivation film prevents the reversible action made through the electrode during charging and, in particular, increases the irreversible capacity at the beginning of charging, which is a direct cause of deterioration of the performance of the battery.

상기와 같은 부동태 막의 형성을 제한하는 방법으로 다음의 2가지 방법에 대한 연구가 진행되고 있다. 첫째는 탄소 표면에 Ni이나 Sn 등의 코팅처리를 통해 부동태 막의 형성을 방지하는 방법, 둘째는 용매 분해를 억제하기 위해 첨가제를 넣는 방법이 있다.As a method of limiting the formation of the passivation film as described above, studies on the following two methods are being conducted. First, there is a method of preventing the formation of a passivation film through coating treatment such as Ni or Sn on the carbon surface, and second, a method of adding an additive to suppress solvent decomposition.

그러나, 상기 표면 코팅법은 코팅 제조 공정이 추가되어 전체 제조공정이 복잡해지고 제조에 장시간이 소요되는 문제점이 있고, 아울러 코팅제를 첨가함으로 인해 그만큼 활물질의 양이 감소하여 전지의 셀 용량이 감소하는 문제점이 있다. 일예로, 탄소 표면 코팅을 위해서는 대략 150℃에서 12시간 이상의 전처리공정을 수행해야만 한다.However, the surface coating method has a problem in that the entire manufacturing process is complicated due to the addition of the coating manufacturing process and takes a long time to manufacture, and the amount of the active material is reduced by the addition of the coating agent, thereby reducing the cell capacity of the battery. There is this. For example, the carbon surface coating requires a pretreatment of at least 12 hours at approximately 150 ° C.

상기 첨가제를 첨가하는 방법에는, 전해질 용액속에 CO2기체를 포화시켜 용매분해가 형성되기 전에 Li2CO3부동태 막을 형성시키는 방법이 있으나 이와 같이 CO2기체를 용액속에 포화시키는 방법은 제조공정상 장시간이 소요되므로 생산성을 저하시킬 수 있는 문제점이 있고, 또, 전해질 용액속에 HF를 첨가하여 LiF 부동태 막을 형성시키는 방법이 있으나, 이와 같은 방법으로 형성된 LiF 부동태 막은 오히려 전극의 저항을 증가시켜 가역용량을 감소시키는 문제점이 있었다.In the method of adding the additive, there is a method of saturating CO 2 gas in the electrolyte solution to form a Li 2 CO 3 passivation film before the solvent decomposition is formed, but the method of saturating the CO 2 gas in the solution is a long time in the manufacturing process. There is a problem that the productivity can be reduced, and there is also a method of forming a LiF passivation film by adding HF to the electrolyte solution, but the LiF passivation film formed in this way rather increases the resistance of the electrode to reduce the reversible capacity There was a problem.

이에 본 발명은 상기한 바와 같은 종래기술의 문제점을 해결하기 위해 안출한 것으로서, 제조공정이 복잡하거나 장시간이 소요되지 않음은 물론 전지의 셀 용량을 감소시키는 역작용을 유발되지 않으면서 전극에 저항값이 큰 부동태 막이 형성되는 것을 방지함으로써, 충전 초기의 비가역 용량을 억제하여 가역용량을 증대시킨 리튬이온전지 및 리튬이온전지의 가역용량을 증대시키는 방법을 제공하는 데에 그 목적이 있다.Accordingly, the present invention has been made to solve the problems of the prior art as described above, the manufacturing process is not complicated or takes a long time, as well as the resistance value of the electrode does not cause the adverse effect of reducing the cell capacity of the battery It is an object of the present invention to provide a method of increasing the reversible capacity of a lithium ion battery and a lithium ion battery by preventing the formation of a large passivation film, thereby suppressing the irreversible capacity in the initial stage of charging.

도 1a는 전해질 용액으로 1 M LiPF6/EC:DEC (1:1, 부피비)을 이용한 종래 리튬이온전지의 탄소전극에 대한 전형적인 초기 충방전곡선을 나타낸 그래프,1A is a graph showing a typical initial charge / discharge curve of a carbon electrode of a conventional lithium ion battery using 1 M LiPF 6 / EC: DEC (1: 1, volume ratio) as an electrolyte solution,

도 1b는 본 발명의 바람직한 실시예에 따라 1 M LiPF6/EC:DEC (1:1, 부피비) 전해질 용액에 첨가제로써 Li2CO3를 첨가하여 Li2CO3로 포화된 전해질 용액에 대한 초기 충방전곡선을 나타낸 그래프,Figure 1b is a preferred embodiment according to the example 1 M LiPF 6 / EC of the present invention: the initial for the addition of Li 2 CO 3 as an additive to: (1, volume ratio: 1) electrolyte solution saturated with Li 2 CO 3 electrolyte solution DEC Graph showing charge and discharge curve,

도 2a는 종래 리튬이온전지에 사용되는 1 M LiPF6/EC:DEC (1:1, 부피비) 전해질 용액에 대한 순환-전압 전류도,FIG. 2A is a cyclic-voltage current diagram for a 1 M LiPF 6 / EC: DEC (1: 1, volume ratio) electrolyte solution used in a conventional lithium ion battery,

도 2b는 본 발명의 바람직한 실시예에 따라 1 M LiPF6/EC:DEC (1:1, 부피비)과 Li2CO3로 포화된 전해질 용액의 순환-전압 전류도,FIG. 2B is a cyclic-voltage current diagram of an electrolyte solution saturated with 1 M LiPF 6 / EC: DEC (1: 1, by volume) and Li 2 CO 3 according to a preferred embodiment of the present invention.

도 3a는 충방전되기 이전의 탄소전극에 대한 표면 형상을 나타낸 도면,Figure 3a is a view showing the surface shape for the carbon electrode before charging and discharging,

도 3b는 종래의 리튬이온전지에서 초기 충전이 완료된 후 1 M LiPF6/EC:DEC (1:1, 부피비) 전해질 용액 내에 있는 탄소전극의 표면 형상을 나타낸 도면,3b is a view showing the surface shape of the carbon electrode in the 1 M LiPF 6 / EC: DEC (1: 1, volume ratio) electrolyte solution after the initial charge is completed in a conventional lithium ion battery,

도 3c는 본 발명의 바람직한 실시예에 따라 Li2CO3가 포화된 1 M LiPF6/EC:DEC(1:1, 부피비) 전해질 용액 속에서 초기 충전을 수행한 후 탄소전극의 표면 형상을 나타낸 도면,3c illustrates the surface shape of a carbon electrode after initial charging in a 1 M LiPF 6 / EC: DEC (1: 1, volume ratio) electrolyte solution in which Li 2 CO 3 is saturated according to a preferred embodiment of the present invention. drawing,

도 4는 일반 전해용액으로 이루어진 종래 리튬이온전지의 탄소전극 및 본 발명에 따라 전해용액에 Li2CO3를 첨가한 리튬이온전지의 탄소전극의 임피던스를 측정한 결과를 나타낸 그래프.Figure 4 is a graph showing the results of measuring the impedance of the carbon electrode of a conventional lithium ion battery made of a general electrolytic solution and the lithium ion battery added Li 2 CO 3 to the electrolytic solution according to the present invention.

상기 목적을 달성하기 위한 본 발명에 따른 가역용량을 증대시킨 리튬이온전지는, 용매분해에 의해 발생되는 부동태 막의 원인성분과 동일한 성분의 첨가제를 전해질용액속에 미리 첨가하여 제조한 것을 특징으로 하며, 상기 첨가제는 Li2CO3일 수 있다.Lithium ion battery with an increased reversible capacity according to the present invention for achieving the above object is prepared by adding an additive of the same component as the causative component of the passivation membrane generated by solvent decomposition in the electrolyte solution in advance, The additive may be Li 2 CO 3 .

상기 목적을 달성하기 위한 본 발명에 따른 가역용량을 증대시킨 리튬이온전지의 제조방법은, 리튬이온전지를 제조할 때 용매분해에 의해 발생되는 부동태 막의 원인성분과 동일한 성분의 첨가제를 전해질용액속에 미리 첨가하는 것을 특징으로 하며, 상기 첨가제는 Li2CO3일 수 있다.In order to achieve the above object, a method of manufacturing a lithium ion battery having an increased reversible capacity according to the present invention, in the preparation of a lithium ion battery, adds an additive having the same component as the causative component of the passivation membrane generated by solvent decomposition in an electrolyte solution. It is characterized in that the addition, the additive may be Li 2 CO 3 .

이하, 본 발명의 바람직한 실시예를 첨부된 도면을 참조하여 상세히 설명하기로 한다.Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

본 발명은, 리튬 이온 전지의 전해질 용액속에 Li2CO3를 첨가한다. 이와 같이 리튬 이온 전지의 전해질 용액속에 첨가된 Li2CO3는 리튬 이온 전지용으로 사용되는 유기 용매에 잘 녹지 않는 난용성 물질이다. 이런 Li2CO3를 전해질 용액에 포화시키면 르샤틀리에 원리에 의해 낮은 농도 쪽으로 반응이 진행되므로 용매 분해가 억제된다.In the present invention, Li 2 CO 3 is added to an electrolyte solution of a lithium ion battery. As described above, Li 2 CO 3 added to the electrolyte solution of the lithium ion battery is a poorly soluble substance that is insoluble in an organic solvent used for the lithium ion battery. When such Li 2 CO 3 is saturated in the electrolyte solution, the reaction proceeds to a lower concentration according to the LeChatlie principle, thereby suppressing solvent decomposition.

리튬 이온 전지에 사용되는 용매는 모두 카르보닐기를 포함하고 있기 때문에, 이들 용매가 분해될 경우 CO3 2-를 다량 생성하게 되며, 이로 인해, 종래의 리튬이온전지는 CO3 2-와 전해질 용액속에 포화되어 있는 Li+들이 충전시에 반응하여 탄소전극의 표면에 비전자전도성의 Li2CO3막을 형성하게 되는데, 이와 같이 충전시에 전해질 용액속에 포화되어 있는 Li+와 CO3 2-들이 반응하여 형성되는 Li2CO3막은 비교적 두꺼워서 전기적 저항이 크기 때문에 충전시에 초기 비가역 용량이 증가되었던 것이다.Since all the solvents used in the lithium ion battery contain carbonyl groups, when these solvents are decomposed, a large amount of CO 3 2- is generated. Thus, conventional lithium ion batteries are saturated in CO 3 2- and electrolyte solutions. Li + reacts at the time of charging to form a non-electroconductive Li 2 CO 3 film on the surface of the carbon electrode. In this way, Li + formed by reacting saturated Li + and CO 3 2- in the electrolyte solution is formed. The 2 CO 3 membranes were relatively thick, with high electrical resistance, which increased the initial irreversible capacity upon charging.

이에 반해, 본 발명은, 용매분해에 의해 생성되는 Li2CO3를 전극 반응 전에 미리 첨가하여 용매분해를 억제함으로써, 전극 반응으로 인해 Li2CO3막이 전극에 생성되는 것을 방지하여 충전 초기의 비가역 용량을 감소시킬 뿐 아니라, 전극의 막 저항을 감소시켜 전지의 가역용량을 증가시키고, 싸이클 수명도 증가시킨 것이다.In contrast, the present invention, by adding Li 2 CO 3 generated by the solvent decomposition in advance before the electrode reaction to suppress the solvent decomposition, thereby preventing the formation of Li 2 CO 3 film on the electrode due to the electrode reaction irreversible in the initial stage of charging In addition to reducing the capacity, the membrane resistance of the electrode is reduced to increase the reversible capacity of the battery and increase the cycle life.

이하에서는, 상기한 바와 같은 본 발명의 보다 실제적인 작용 효과에 대해 첨부된 도면을 참조하여 종래의 일반적인 리튬이온전지와 대비하여 설명하기로 한다.Hereinafter, with reference to the accompanying drawings for a more practical effect of the present invention as described above will be described in contrast to the conventional general lithium ion battery.

도 1a는 전해질 용액으로 1 M LiPF6/EC:DEC (1:1, 부피비)을 이용한 종래 리튬이온전지의 탄소전극에 대한 전형적인 초기 충방전곡선을 나타낸 그래프이다. 동도면에 도시된 바와 같이, 초기 비가역 용량이 80 mAh/g 이 존재한다. 이와 같이 초기 비가역 용량이 발생되는 주요 원인은 크게 2가지인데, 이중 하나는 용매분해에 의하여 탄소 표면에 피막이 형성되는 반응에 의한 것이고, 다른 하나는 탄소속에 들어간 리튬이 가역적으로 다시 나오지 못한 양 때문이다. 용매분해에 의한 반응으로 형성된 부동태 막으로 인한 비가역 용량은 O [V]에서 0.5 [V] 까지 흐른 전류량으로 계산할 수 있다. 이렇게 계산된 용매분해에 의한 비가역 용량은 30 mAh/g 이다.1A is a graph showing a typical initial charge / discharge curve of a carbon electrode of a conventional lithium ion battery using 1 M LiPF 6 / EC: DEC (1: 1, volume ratio) as an electrolyte solution. As shown in the figure, the initial irreversible capacity is 80 mAh / g. There are two main causes of the initial irreversible capacity, one of which is due to the reaction of the film formation on the surface of the carbon by solvent decomposition, and the other is due to the amount of lithium that has entered the carbon reversibly. . The irreversible capacity due to the passivation film formed by the reaction by solvent decomposition can be calculated as the amount of current flowing from 0 [V] to 0.5 [V]. The irreversible capacity by solvation calculated in this way is 30 mAh / g.

도 1b는 본 발명의 바람직한 실시예에 따라 1 M LiPF6/EC:DEC (1:1, 부피비) 전해질 용액에 첨가제로써 Li2CO3를 첨가하여 Li2CO3로 포화된 전해질 용액에 대한 초기 충방전곡선을 나타낸 그래프이다. 동도면을 참조하면 알 수 있듯이, 초기 비가역 용량은 50 mAh/g 이었다. 도 1a의 종래 리튬이온전의 충방전곡선과 경우와 비교해 볼 때, 초기 비가역 용량이 30 mAh/g 이 줄어들었다. 이것은 용매분해에 의한 부동태 막형성 반응이 억제되었기 때문이다.Figure 1b is a preferred embodiment according to the example 1 M LiPF 6 / EC of the present invention: the initial for the addition of Li 2 CO 3 as an additive to: (1, volume ratio: 1) electrolyte solution saturated with Li 2 CO 3 electrolyte solution DEC A graph showing charge and discharge curves. As can be seen from the figure, the initial irreversible capacity was 50 mAh / g. Compared with the charging / discharging curve of the conventional lithium ion battery of FIG. 1A, the initial irreversible capacity is reduced by 30 mAh / g. This is because the passivation film formation reaction by solvent decomposition was suppressed.

도 2a는 종래 리튬이온전지에 사용되는 1 M LiPF6/EC:DEC (1:1, 부피비) 전해질 용액에 대한 순환-전압 전류도이다. 동도면에 도시된 바와 같이, 초기 충방전에 해당하는 1st Cycle에서 용매분해 반응에 의한 전류치의 맥동구간이 2.2 [V]구간과, 2.0 [V} 구간 그리고, 0.7 [V] 구간에서 관찰된다. 이와 같이 1st Cycle에서 용매분해에서 생성된 생성물들은 탄소 표면에 부동태 막을 형성하게 되는 데, 이러한 용매분해에 의해 형성된 부동태 막의 특징은 더 이상의 용매가 분해되는 반응을억제하는 보호막 역할을 하게 된다. 이런 이유로 2nd Cycle 에서는 더 이상의 용매분해 반응이 관찰되지 않음을 알 수 있다.FIG. 2A is a cyclic-voltage current diagram for a 1 M LiPF 6 / EC: DEC (1: 1, volume ratio) electrolyte solution used in a conventional lithium ion battery. FIG. As shown in the figure, the pulsation interval of the current value by the solvent decomposition reaction in the 1st cycle corresponding to the initial charge and discharge is observed in the 2.2 [V] section, the 2.0 [V] section, and the 0.7 [V] section. As described above, the products generated by the solubilization in the 1st cycle form a passivation film on the carbon surface, and the characteristic of the passivation film formed by the solubility serves as a protective film to suppress the reaction in which the solvent is further degraded. For this reason, it can be seen that no further solvation reaction is observed in the 2nd Cycle.

도 2b는 본 발명의 바람직한 실시예에 따라 1 M LiPF6/EC:DEC (1:1, 부피비)과 Li2CO3로 포화된 전해질 용액의 순환-전압 전류도이다. 동도면에 도시된 바와 같이, 본 발명의 바람직한 실시예에 따라 Li2CO3가 첨가된 전해일 용액은 1st Cycle에서 용매분해 반응에 의한 전류치의 맥동이 관찰되지 않고 있다. 이는 초기 충전이전에 전해질 용액에 첨가된 Li2CO3가 1st Cycle에서 용매분해 반응을 억제하였기 때문이다.FIG. 2B is a cyclic voltammogram of an electrolyte solution saturated with 1 M LiPF 6 / EC: DEC (1: 1, volume ratio) and Li 2 CO 3 according to a preferred embodiment of the present invention. As shown in the figure, in the electrolytic solution of Li 2 CO 3 is added according to a preferred embodiment of the present invention, the pulsation of the current value due to the solvent decomposition reaction in the 1st Cycle is not observed. This is because Li 2 CO 3 added to the electrolyte solution before the initial charging inhibited the solubility reaction in the 1st cycle.

즉, 본 발명은 도 2a에서 설명한 바 있듯이 이미 전극에 생성된 부동태 막은 그 이후의 용매분해 반응을 억제하는 작용원리를 이용한 것이다.That is, the present invention utilizes the principle of action that inhibits the solubilization reaction after the passivation membrane is already formed in the electrode as described in Figure 2a.

도 3a는 충방전되기 이전의 탄소전극에 대한 표면 형상을 나타낸 도면으로, 동도면에 도시된 바와 같이, 충방전을 수행하기 전에는 탄소전극은 일반적인 섬유형태를 나타내며 그 표면이 매우 깨끗한 상태임을 알 수 있다.Figure 3a is a view showing the surface shape of the carbon electrode before charging and discharging, as shown in the figure, before performing the charging and discharging, the carbon electrode shows a general fiber shape and the surface is very clean state have.

도 3b는 종래의 리튬이온전지에서 초기 충전이 완료된 후 1 M LiPF6/EC:DEC (1:1, 부피비) 전해질 용액 내에 있는 탄소전극의 표면 형상을 나타낸 도면으로, 동도면에 도시된 바와 같이, 탄소전극의 표면에 부동화된 부동태 막이 뒤덮여 있음을 알 수 있다. 이것은 용매분해 반응의 생성물들이 부동태 막 형태로 탄소전극의 표면을 덮고 있음을 보여주는 증거이다.3b is a view showing the surface shape of the carbon electrode in the 1 M LiPF 6 / EC: DEC (1: 1, volume ratio) electrolyte solution after the initial charge is completed in a conventional lithium ion battery, as shown in the figure It can be seen that the passivation film is immobilized on the surface of the carbon electrode. This is evidence that the products of the solubilization reaction cover the surface of the carbon electrode in the form of a passivation film.

도 3c는 본 발명의 바람직한 실시예에 따라 Li2CO3가 포화된 1 M LiPF6/EC:DEC (1:1, 부피비) 전해질 용액 속에서 초기 충전을 수행한 후 탄소전극의 표면 형상을 나타낸 도면이다. 상기 도 2b에서 설명된 바와 같이 본 발명의 리튬이온전지에서는 용매분해 반응이 일어나지 않았음에도 불구하고 탄소 전극의 표면은 얇고 고른 부동태 막으로 덮여져 있음을 볼 수 있는데, 이것은 전극 반응 이전에 미리 전해질용액속에 포화되어 있던 불용성 물질인 Li2CO3가 탄소전극의 표면에서 침전이 일어나 그 표면을 덮고 있어서 나타난 결과이다.3c illustrates the surface shape of a carbon electrode after initial charging in a 1 M LiPF 6 / EC: DEC (1: 1, volume ratio) electrolyte solution in which Li 2 CO 3 is saturated according to a preferred embodiment of the present invention. Drawing. In the lithium ion battery of the present invention, as described in FIG. 2B, the surface of the carbon electrode is covered with a thin and even passivation membrane, although no solvent decomposition reaction occurs. It is the result that Li 2 CO 3 , an insoluble substance saturated inside, precipitates on the surface of the carbon electrode and covers the surface.

이와 같이 전해질용액속에 첨가한 Li2CO3에 의해 생성된 부동태 막은 탄소전극의 표면에 얇고 고르게 덮여있어 용매가 직접 탄소전극으로부터 전자를 받아 분해되는 반응을 억제하는 보호막으로 작용한다.Thus, the passivation film formed by Li 2 CO 3 added to the electrolyte solution is thin and evenly coated on the surface of the carbon electrode, acting as a protective film to suppress the reaction in which the solvent directly receives electrons from the carbon electrode and decomposes.

도 4는 일반 전해용액으로 이루어진 종래 리튬이온전지의 탄소전극 및 본 발명에 따라 전해용액에 Li2CO3를 첨가한 리튬이온전지의 탄소전극의 임피던스를 측정한 결과를 나타낸 그래프이다. 도 4에서, 일반 전해용액으로 이루어진 종래 리튬이온전지의 탄소전극의 임피던스는 "·"으로 나타내었으며, 본 발명에 따라 전해용액에 Li2CO3를 첨가한 리튬이온전지의 탄소전극의 임피던스는 "˚"으로 나타내었다.Figure 4 is a graph showing the result of measuring the impedance of the carbon electrode of a conventional lithium ion battery made of a general electrolytic solution and the lithium electrode of Li-ion battery added Li 2 CO 3 to the electrolytic solution according to the present invention. In Figure 4, the impedance of the carbon electrode of the conventional lithium ion battery made of a general electrolytic solution is represented by "·", the impedance of the carbon electrode of the lithium ion battery added Li 2 CO 3 to the electrolyte solution according to the present invention " ˚ ".

동도면에 도시된 바와 같이, 본 발명의 바람직한 실시예에 따라 Li2CO3가 첨가된 1 M LiPF6/EC:DEC (1:1, 부피비) 전해용액 속에서 충전된 탄소 전극의 임피던스(˚)는 종래 리튬이온전지의 1 M LiPF6/EC:DEC (1:1, 부피비) 전해용액 속에서 충전된 탄소 전극의 임피던스(·)보다 더 작게 나왔다. 이것은 전해액 속에 Li2CO3로 첨가로 인해 탄소 전극 표면에 형성된 부동태 막의 성질이 개선되어 전체 셀 저항이 감소되었음을 나타내는 것이다.As shown in the figure, the impedance of the carbon electrode charged in 1 M LiPF 6 / EC: DEC (1: 1, volume ratio) electrolyte solution to which Li 2 CO 3 was added according to a preferred embodiment of the present invention ) Is smaller than the impedance (·) of the carbon electrode charged in the 1 M LiPF 6 / EC: DEC (1: 1, volume ratio) electrolyte solution of the conventional lithium ion battery. This indicates that the addition of Li 2 CO 3 into the electrolyte improved the properties of the passivation film formed on the surface of the carbon electrode, thereby reducing the overall cell resistance.

상술한 바와 같이 본 발명은, 전해질 용액속에 Li2CO3를 첨가하여 전극 반응 이전에 미리 탄소전극의 표면에 저항이 작은 부동태 막을 형성시킴으로써, 초기 비가역용량의 발생 원인인 용매분해를 억제시킬 수 있으며, 탄소전극에 얇고 고르게 형성된 부동태 막으로 인하여 탄소전극의 가역용량을 증대시킬 수 있고 충방전 싸이클 효율도 향상시킬 수 있는 효과가 있다.As described above, in the present invention, by adding Li 2 CO 3 to the electrolyte solution to form a passivation film having a low resistance on the surface of the carbon electrode before the electrode reaction, it is possible to suppress the solvent decomposition which is the cause of the initial irreversible capacity. Due to the thin and even passivation film formed on the carbon electrode, the reversible capacity of the carbon electrode can be increased and the charge / discharge cycle efficiency can be improved.

또한, 상기와 같이 탄소전극에 얇고 고르게 형성된 부동태 막은 자가방전을 막는 역할을 함으로써, 충전된 전지의 저장수명도 늘릴 수 있는 효과가 있다.In addition, as described above, the passivation film thinly and evenly formed on the carbon electrode serves to prevent self-discharge, thereby increasing the shelf life of the charged battery.

본 발명은, 단지 전해질 용액에 Li2CO3를 첨가하는 것만으로 부동태 막의 저항을 획기적으로 감소시킬 수 있는 것으로, 별도의 추가 공정이 필요없으며, Li2CO3는 난용성 염이므로 극소량만 첨가해도 되기 때문에, 첨가제의 과다한 첨가로 인해 오히려 전지의 셀용량이 감소하는 역작용이 없다.The present invention can dramatically reduce the resistance of the passivation membrane by simply adding Li 2 CO 3 to the electrolyte solution, and does not require any additional process. Since Li 2 CO 3 is a poorly soluble salt, even if only a very small amount is added, Therefore, there is no adverse effect of reducing the cell capacity of the battery due to excessive addition of the additive.

Claims (4)

리튬이온전지에 있어서,In a lithium ion battery, 용매분해에 의해 발생되는 부동태 막의 원인성분과 동일한 성분의 첨가제를 전해질용액속에 미리 첨가하여 제조한 것을 특징으로 하는 가역용량을 증대시킨 리튬이온전지.A lithium ion battery with an increased reversible capacity, characterized in that it is prepared by adding an additive of the same component as the causative component of the passivation membrane generated by solvent decomposition to an electrolyte solution in advance. 제 1 항에 있어서, 상기 첨가제는, Li2CO3인 것을 특징으로 하는 가역용량을 증대시킨 리튬이온전지.The lithium ion battery according to claim 1, wherein the additive is Li 2 CO 3 . 리튬이온전지의 제조방법에 있어서,In the manufacturing method of a lithium ion battery, 리튬이온전지를 제조할 때 용매분해에 의해 발생되는 부동태 막의 원인성분과 동일한 성분의 첨가제를 전해질용액속에 미리 첨가하는 것을 특징으로 하는 가역용량을 증대시킨 리튬이온전지의 제조방법.A method of manufacturing a lithium ion battery with increased reversible capacity, wherein an additive of the same component as the causative component of the passivation film generated by solvent decomposition when the lithium ion battery is manufactured is added in advance to the electrolyte solution. 제 3 항에 있어서, Li2CO3성분의 첨가제를 전해질용액속에 첨가하는 것을 특징으로 하는 가역용량을 증대시킨 리튬이온전지의 제조방법.4. The method of manufacturing a lithium ion battery according to claim 3, wherein an additive of a Li 2 CO 3 component is added to the electrolyte solution.
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