KR102639662B1 - A negative electrode for a lithium secondary battery formed with a ferroelectric polymer protective layer, method for preparing the same, and a lithium secondary battery including the negative electrode - Google Patents
A negative electrode for a lithium secondary battery formed with a ferroelectric polymer protective layer, method for preparing the same, and a lithium secondary battery including the negative electrode Download PDFInfo
- Publication number
- KR102639662B1 KR102639662B1 KR1020180094292A KR20180094292A KR102639662B1 KR 102639662 B1 KR102639662 B1 KR 102639662B1 KR 1020180094292 A KR1020180094292 A KR 1020180094292A KR 20180094292 A KR20180094292 A KR 20180094292A KR 102639662 B1 KR102639662 B1 KR 102639662B1
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- KR
- South Korea
- Prior art keywords
- ferroelectric polymer
- protective layer
- secondary battery
- polymer protective
- lithium secondary
- Prior art date
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- 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
- H01M4/134—Electrodes based on metals, Si or alloys
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- C08L27/02—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment
- C08L27/12—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by a halogen; Compositions of derivatives of such polymers not modified by chemical after-treatment containing fluorine atoms
- C08L27/16—Homopolymers or copolymers or vinylidene fluoride
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- D01D—MECHANICAL METHODS OR APPARATUS IN THE MANUFACTURE OF ARTIFICIAL FILAMENTS, THREADS, FIBRES, BRISTLES OR RIBBONS
- D01D5/00—Formation of filaments, threads, or the like
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- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Abstract
리튬 이온 이동도가 개선됨과 동시에 전기장이 균일하게 작용함으로써 리튬 덴드라이트의 성장을 억제할 수 있고, 이에 의해 전지의 단락 현상을 방지할 수 있는, 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극, 이의 제조 방법 및 상기 음극을 포함하는 리튬 이차전지가 개시된다. 상기 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극은, 집전체; 상기 집전체 상에 위치하는 리튬 메탈; 및 상기 집전체와 리튬 메탈의 사이 또는 상기 리튬 메탈의 상부에 위치하는 강유전성 고분자 보호층;을 포함한다.A negative electrode for a lithium secondary battery formed with a ferroelectric polymer protective layer, which can inhibit the growth of lithium dendrites by improving lithium ion mobility and acting uniformly on the electric field, thereby preventing short circuit of the battery, manufacturing the same. A lithium secondary battery including a method and the negative electrode is disclosed. The negative electrode for a lithium secondary battery on which the ferroelectric polymer protective layer is formed includes a current collector; Lithium metal located on the current collector; and a ferroelectric polymer protective layer located between the current collector and the lithium metal or on top of the lithium metal.
Description
본 발명은 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극 및 그 제조 방법에 관한 것으로서, 더욱 상세하게는, 리튬 이온 이동도가 개선됨과 동시에 전기장이 균일하게 작용함으로써 리튬 덴드라이트의 성장을 억제할 수 있고, 이에 의해 전지의 단락 현상을 방지할 수 있는, 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극, 이의 제조 방법 및 상기 음극을 포함하는 리튬 이차전지에 관한 것이다.The present invention relates to a negative electrode for a lithium secondary battery formed with a ferroelectric polymer protective layer and a method of manufacturing the same. More specifically, the present invention relates to an anode for a lithium secondary battery having a ferroelectric polymer protective layer formed thereon, and more specifically, to improve lithium ion mobility and to suppress the growth of lithium dendrites by applying an electric field uniformly. It relates to a negative electrode for a lithium secondary battery having a ferroelectric polymer protective layer formed thereon, which can prevent short-circuiting of the battery, a method of manufacturing the same, and a lithium secondary battery including the negative electrode.
모바일 기기에 대한 기술 개발과 수요가 증가함에 따라, 에너지원으로서의 이차전지에 대한 수요 또한 급격히 증가하고 있다. 최근에는 전기 자동차(EV), 하이브리드 전기 자동차(HEV) 등에 동력원으로서 이차전지의 사용이 실현화되고 있다. 이에 따라, 다양한 요구에 부응할 수 있는 이차전지에 대한 많은 연구가 진행되고 있고, 특히, 높은 에너지 밀도, 높은 방전 전압 및 출력 안정성의 리튬 이차전지에 대한 수요가 높아, 이에 대한 연구가 보다 활발히 진행되고 있다.As technology development and demand for mobile devices increase, demand for secondary batteries as an energy source is also rapidly increasing. Recently, the use of secondary batteries as a power source for electric vehicles (EV), hybrid electric vehicles (HEV), etc. has been realized. Accordingly, much research is being conducted on secondary batteries that can meet various needs. In particular, the demand for lithium secondary batteries with high energy density, high discharge voltage, and output stability is high, so research on these is being conducted more actively. It is becoming.
리튬 이차전지의 기술은 최근 현저한 발전을 통하여 다양한 분야에서 응용되고 있으나, 전지의 용량, 안전성, 출력, 대형화, 초소형화 등의 한계에 부딪혀, 이를 극복할 수 있는 방안이 연구되고 있다. 대표적으로, 현재의 리튬 이차전지 대비 용량 측면에서 이론 용량이 매우 큰 금속-공기 전지(Metal-air battery), 안전성 측면에서 폭발 위험이 없는 전고체 전지(All solid battery), 출력 측면에서 리튬 이차전지에 비해 출력 특성이 우수한 슈퍼 캐퍼시터(Supercapacitor), 대형화 측면에서는 나트륨-황(Na-S) 전지 혹은 레독스 플로우 전지(RFB: Rex flow battery), 초소형화 측면에서는 박막전지(Thin film battery) 등이 학계 및 산업계 전반에서 지속적인 연구가 진행되고 있다.Lithium secondary battery technology has recently made significant progress and is being applied in various fields. However, it has encountered limitations in battery capacity, safety, output, large size, and ultra-miniaturization, and ways to overcome these limitations are being studied. Representative examples include a metal-air battery with a very large theoretical capacity compared to current lithium secondary batteries, an all-solid battery with no risk of explosion in terms of safety, and a lithium secondary battery in terms of output. Compared to supercapacitors, which have excellent output characteristics, sodium-sulfur (Na-S) batteries or redox flow batteries (RFB) in terms of large size, and thin film batteries in terms of miniaturization. Continuous research is underway throughout academia and industry.
이와 관련하여, 현재 상용화된 탄소계 음극 활물질의 용량 한계 및 미흡한 출력 특성으로 인하여, 이차전지 시장의 수요에 상응하기 어려운 상황에 직면해 있다. 차세대 전지 소재로서 흑연 대비 약 10배의 용량을 가지는 리튬 금속이 큰 관심을 받고 있으나, 리튬 덴드라이트 성장으로 인하여 셀이 단락되는 문제가 있다. 이와 같은 리튬 덴드라이트의 성장을 방지하는 방안으로, 전극의 표면에 인공층을 형성하거나, 전해액 첨가제를 투입하거나, 구조체 내부에서 리튬을 성장시키는 등의 방법이 제안되었으나, 셀 단락을 지연시키는 것에 불과할 뿐 근본적으로 해결하지는 못하였다. 이에, 당 분야에서는, 리튬 덴드라이트의 성장을 억제하여 리튬 이차전지의 단락 현상을 근본적으로 방지할 수 있는 방안의 연구개발에 박차를 가하고 있다.In this regard, due to the capacity limitations and insufficient output characteristics of currently commercialized carbon-based anode active materials, we are facing a situation where it is difficult to meet the demand in the secondary battery market. Lithium metal, which has a capacity about 10 times that of graphite, is receiving great attention as a next-generation battery material, but there is a problem with cells short-circuiting due to lithium dendrite growth. As a way to prevent the growth of lithium dendrites, methods such as forming an artificial layer on the surface of the electrode, adding electrolyte additives, or growing lithium inside the structure have been proposed, but these only delay cell short circuiting. However, it was not fundamentally resolved. Accordingly, the field is accelerating the research and development of methods that can fundamentally prevent the short circuit phenomenon of lithium secondary batteries by suppressing the growth of lithium dendrites.
따라서, 본 발명의 목적은, 리튬 이온 이동도가 개선됨과 동시에 전기장이 균일하게 작용함으로써 리튬 덴드라이트의 성장을 억제할 수 있고, 이에 의해 전지의 단락 현상을 방지할 수 있는, 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극, 이의 제조 방법 및 상기 음극을 포함하는 리튬 이차전지를 제공하는 것이다.Therefore, the object of the present invention is to provide a ferroelectric polymer protective layer that can improve lithium ion mobility and suppress the growth of lithium dendrites by acting uniformly on the electric field, thereby preventing short circuits in the battery. The object is to provide a formed negative electrode for a lithium secondary battery, a manufacturing method thereof, and a lithium secondary battery including the negative electrode.
상기 목적을 달성하기 위하여, 본 발명은, 집전체; 상기 집전체 상에 위치하는 리튬 메탈; 및 상기 집전체와 리튬 메탈의 사이 또는 상기 리튬 메탈의 상부에 위치하는 강유전성 고분자 보호층;을 포함하는 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극을 제공한다.In order to achieve the above object, the present invention, a current collector; Lithium metal located on the current collector; and a ferroelectric polymer protective layer positioned between the current collector and the lithium metal or on top of the lithium metal. It provides a negative electrode for a lithium secondary battery having a ferroelectric polymer protective layer including.
또한, 본 발명은, (a) 강유전성 고분자 화합물을 용매에 용해시켜 강유전성 고분자 용액을 제조하는 단계; (b) 상기 제조된 강유전성 고분자 용액을 집전체 또는 이형필름 상에 전기방사하여, 상기 집전체 또는 이형필름 상에 강유전성 고분자 보호층을 형성시키는 단계; 및 (c) 상기 집전체 상에 형성된 강유전성 고분자 보호층에 리튬을 증착하거나, 이형필름 상에 형성된 강유전성 고분자 보호층을 집전체 상에 형성된 리튬 메탈의 표면에 전사시키는 단계;를 포함하는 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극의 제조 방법을 제공한다.In addition, the present invention includes the steps of (a) dissolving a ferroelectric polymer compound in a solvent to prepare a ferroelectric polymer solution; (b) electrospinning the prepared ferroelectric polymer solution onto a current collector or release film to form a ferroelectric polymer protective layer on the current collector or release film; and (c) depositing lithium on the ferroelectric polymer protective layer formed on the current collector or transferring the ferroelectric polymer protective layer formed on the release film to the surface of the lithium metal formed on the current collector. Ferroelectric polymer protection comprising a. A method for manufacturing a layered negative electrode for a lithium secondary battery is provided.
또한, 본 발명은, 상기 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극을 포함하는 리튬 이차전지를 제공한다.Additionally, the present invention provides a lithium secondary battery including a negative electrode for a lithium secondary battery on which the ferroelectric polymer protective layer is formed.
본 발명에 따른 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극, 이의 제조 방법 및 상기 음극을 포함하는 리튬 이차전지는, 리튬 이온 이동도가 개선됨과 동시에 전기장이 균일하게 작용함으로써 리튬 덴드라이트의 성장을 억제할 수 있고, 이에 의해 전지의 단락 현상을 방지할 수 있는 장점을 가진다.A negative electrode for a lithium secondary battery formed with a ferroelectric polymer protective layer according to the present invention, a method for manufacturing the same, and a lithium secondary battery including the negative electrode improve lithium ion mobility and suppress the growth of lithium dendrites by applying a uniform electric field. This has the advantage of preventing a short circuit in the battery.
도 1은 본 발명의 일 실시예 따라 음극 집전체의 표면에 강유전성 고분자 화합물을 전기 방사하는 모습이다.
도 2는 음극 집전체의 표면에 형성된 강유전성 고분자 보호층을 보여주는 도면이다.
도 3은 본 발명의 일 실시예에 따라 제조된 리튬 이차전지 하프-셀의 쿨롱 효율도를 보여주는 그래프이다.Figure 1 shows electrospinning a ferroelectric polymer compound on the surface of a negative electrode current collector according to an embodiment of the present invention.
Figure 2 is a diagram showing a ferroelectric polymer protective layer formed on the surface of a negative electrode current collector.
Figure 3 is a graph showing the coulombic efficiency of a lithium secondary battery half-cell manufactured according to an embodiment of the present invention.
이하, 본 발명을 상세히 설명한다.Hereinafter, the present invention will be described in detail.
본 발명에 따른 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극은, 집전체, 상기 집전체 상에 위치하는 리튬 메탈 및 상기 집전체와 리튬 메탈의 사이 또는 상기 리튬 메탈의 상부에 위치하는 강유전성 고분자 보호층을 포함한다.The negative electrode for a lithium secondary battery formed with a ferroelectric polymer protective layer according to the present invention includes a current collector, a lithium metal located on the current collector, and a ferroelectric polymer protective layer located between the current collector and the lithium metal or on top of the lithium metal. Includes.
전술한 바와 같이, 리튬 이차전지에 있어서 리튬 덴드라이트 성장으로 인하여 셀이 단락되는 현상이 나타나는데, 리튬 덴드라이트의 성장을 억제하기 위하여 전극 표면에 인공층을 형성시키는 등의 다양한 방법이 제안된 바 있다. 하지만, 이들 방법은 셀 단락을 지연시키는 것에 불과할 뿐, 셀 단락 현상을 근본적으로 해결하지는 못하고 있다. 이에 본 출원인은, 상기의 문제점을 해소시킬 수 있는 신규한 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극, 이의 제조 방법 및 상기 음극을 포함하는 리튬 이차전지를 발명해 낸 것이다.As mentioned above, in lithium secondary batteries, the cell short circuit occurs due to the growth of lithium dendrites. Various methods, such as forming an artificial layer on the electrode surface, have been proposed to suppress the growth of lithium dendrites. . However, these methods only delay cell short-circuiting and do not fundamentally solve the cell short-circuit phenomenon. Accordingly, the present applicant has invented a novel negative electrode for a lithium secondary battery formed with a ferroelectric polymer protective layer that can solve the above problems, a manufacturing method thereof, and a lithium secondary battery including the negative electrode.
상기 집전체는, 리튬(Li)계 이차전지에 적용되는 통상의 것으로서, 백금(Pt), 금(Au), 팔라듐(Pd), 이리듐(Ir), 은(Ag), 루테늄(Ru), 니켈(Ni), 스테인리스스틸(STS), 알루미늄(Al), 몰리브데늄(Mo), 크롬(Cr), 카본(C), 티타늄(Ti), 텅스텐(W), ITO(In doped SnO2), FTO(F doped SnO2), 및 이들의 합금과, 알루미늄(Al) 또는 스테인리스 스틸의 표면에 카본(C), 니켈(Ni), 티타늄(Ti) 또는 은(Ag)을 표면 처리한 것 등을 사용할 수 있으나, 반드시 이에 한정되는 것은 아니다. 또한, 상기 집전체는 호일, 필름, 시트, 펀칭된 것, 다공질체 또는 발포체 등의 형태일 수 있다.The current collector is a common one applied to lithium (Li)-based secondary batteries, and includes platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), and nickel. (Ni), stainless steel (STS), aluminum (Al), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO 2 ), FTO (F doped SnO 2 ) and its alloys, and aluminum (Al) or stainless steel surface treated with carbon (C), nickel (Ni), titanium (Ti) or silver (Ag), etc. It can be used, but is not necessarily limited to this. Additionally, the current collector may be in the form of foil, film, sheet, punched material, porous material, or foam.
상기 리튬 메탈은, 리튬 금속이나 리튬 합금(예를 들어, 리튬과 알루미늄, 아연, 비스무스, 카드뮴, 안티몬, 실리콘, 납, 주석, 갈륨 또는 인듐 등과 같은 금속과의 합금)을 포함하는 통상의 것일 수 있으며, 따라서, 이에 대한 구체적인 설명은 생략하기로 한다.The lithium metal may be a common material including lithium metal or lithium alloy (e.g., an alloy of lithium with metals such as aluminum, zinc, bismuth, cadmium, antimony, silicon, lead, tin, gallium, or indium). Therefore, detailed description thereof will be omitted.
상기 강유전성 고분자 보호층은, 상기 집전체와 리튬 메탈의 사이 또는 상기 리튬 메탈의 상부(즉, 리튬 메탈의 표면 또는 음극 표면)에 위치하는 보호막으로서, 이와 같은 강유전성 고분자 보호층이 형성된 음극을 리튬 이차전지에 적용할 경우, 리튬 이온 이동도가 개선됨과 동시에 전기장이 균일하게 작용함으로써 리튬 덴드라이트의 성장을 억제할 수 있고, 이에 의해 전지의 단락 현상을 방지할 수 있다.The ferroelectric polymer protective layer is a protective film located between the current collector and the lithium metal or on top of the lithium metal (i.e., the surface of the lithium metal or the cathode surface), and the cathode on which the ferroelectric polymer protective layer is formed is used as a lithium secondary. When applied to a battery, lithium ion mobility is improved and the electric field acts uniformly, thereby suppressing the growth of lithium dendrites and thereby preventing short circuits in the battery.
상기 강유전성 고분자 보호층을 구성하는 강유전성 고분자는 통상의 강유전체일 수 있으나, 상온 하에서의 유전상수(또는 유전율, Dielectric Constant)가 5 내지 100, 바람직하게는 10 내지 70, 더욱 바람직하게는 30 내지 60인 강유전체를 적용하는 것이 상기의 목적을 달성하는데 유리하다. 상기 강유전성 고분자의 유전상수가 5 미만이면, 쌍극자들이 정렬되지 않아 리튬 이온 이동도 향상 및 균일한 전기장을 효과를 기대하기 어려운 문제가 발생할 수 있다.The ferroelectric polymer constituting the ferroelectric polymer protective layer may be a conventional ferroelectric, but is a ferroelectric having a dielectric constant (or dielectric constant) of 5 to 100, preferably 10 to 70, and more preferably 30 to 60 at room temperature. It is advantageous to achieve the above purpose. If the dielectric constant of the ferroelectric polymer is less than 5, the dipoles may not be aligned, making it difficult to expect improved lithium ion mobility and a uniform electric field.
상기의 유전상수 값을 만족하는 강유전성 고분자로는, PVDF[유전상수: 7] 등의 단중합 강유전체, 그리고, P(VdF-TrFE)[유전상수: 12], P(VdF-HFP)[유전상수: 11], P(VdF-TrFE-CTFE)[유전상수: 40] 및 P(VdF-TrFE-CFE)[유전상수: 55] 등의 공중합 강유전체를 예시할 수 있으며, 단중합 강유전체보다는 공중합 강유전체를 사용하는 것이 바람직하고, 공중합 강유전체 중에서도 높은 유전상수 값을 가지는 것들, 예를 들어, P(VdF-TrFE-CTFE)나 P(VdF-TrFE-CFE)를 사용하는 것이 더욱 바람직하다.Ferroelectric polymers that satisfy the above dielectric constant values include monopolymerized ferroelectrics such as PVDF [dielectric constant: 7], and P(VdF-TrFE) [dielectric constant: 12] and P(VdF-HFP) [dielectric constant : 11], P(VdF-TrFE-CTFE) [dielectric constant: 40], and P(VdF-TrFE-CFE) [dielectric constant: 55]. Examples of copolymer ferroelectrics include copolymer ferroelectrics rather than monopolymer ferroelectrics. It is preferable to use, and among copolymerized ferroelectrics, it is more preferable to use those having a high dielectric constant value, for example, P(VdF-TrFE-CTFE) or P(VdF-TrFE-CFE).
한편, 상기 강유전성 고분자 보호층에는 다수의 기공이 형성되어 있다. 상기 기공은 리튬 이온의 이동도 또는 전도도를 향상시키기 위한 것으로서, 상기 강유전성 고분자 보호층의 공극률은 40 내지 90 %, 바람직하게는 45 내지 85 %, 더욱 바람직하게는 50 내지 80 %일 수 있다. 상기 강유전성 고분자 보호층의 공극률이 40 % 미만이면 리튬을 저장할 공간이 부족할 뿐만 아니라 저항이 커져 전지 성능이 떨어지는 문제가 발생할 수 있고, 90 %를 초과하는 경우에는 빈 공간이 너무 많아 리튬 덴드라이트 성장을 물리적으로 억제하지 못하는 문제가 발생할 수 있다.Meanwhile, multiple pores are formed in the ferroelectric polymer protective layer. The pores are intended to improve the mobility or conductivity of lithium ions, and the porosity of the ferroelectric polymer protective layer may be 40 to 90%, preferably 45 to 85%, and more preferably 50 to 80%. If the porosity of the ferroelectric polymer protective layer is less than 40%, not only is there not enough space to store lithium, but the resistance increases, which may cause a problem in battery performance, and if it exceeds 90%, there is too much empty space, preventing lithium dendrite growth. Problems may arise that cannot be physically suppressed.
또한, 상기 강유전성 고분자 보호층에 형성된 각 기공의 크기는 0.1 내지 10 ㎛, 바람직하게는 0.2 내지 5 ㎛, 더욱 바람직하게는 0.5 내지 3 ㎛로서, 상기 기공의 크기가 0.1 ㎛ 미만이면 리튬을 저장할 공간이 부족할 뿐만 아니라 저항이 커져 전지 성능이 떨어지는 문제가 발생할 수 있고, 10 ㎛를 초과하는 경우에는 기공의 크기가 너무 커 덴드라이트 성장을 물리적으로 억제하지 못하는 문제가 발생할 수 있다.In addition, the size of each pore formed in the ferroelectric polymer protective layer is 0.1 to 10 ㎛, preferably 0.2 to 5 ㎛, more preferably 0.5 to 3 ㎛, and if the pore size is less than 0.1 ㎛, there is a space for storing lithium. Not only is this insufficient, but battery performance may decrease due to increased resistance, and if it exceeds 10 ㎛, the pore size may be so large that dendrite growth cannot be physically suppressed.
상기 강유전성 고분자 보호층의 두께는 10 내지 100 ㎛, 바람직하게는 20 내지 90 ㎛, 더욱 바람직하게는 30 내지 80 ㎛일 수 있으며, 상기 강유전성 고분자 보호층의 두께가 10 ㎛ 미만인 경우, 리튬 저장공간이 부족하여 리튬 덴드라이트 성장을 억제하지 못하는 문제가 발생할 수 있고, 100 ㎛를 초과하는 경우에는, 고분자 보호층이 저항으로 작용하여 전지 성능이 하락하는 문제가 발생할 수 있다.The thickness of the ferroelectric polymer protective layer may be 10 to 100 ㎛, preferably 20 to 90 ㎛, more preferably 30 to 80 ㎛, and when the thickness of the ferroelectric polymer protective layer is less than 10 ㎛, the lithium storage space If it is insufficient, a problem may arise in which lithium dendrite growth cannot be suppressed, and if it exceeds 100 ㎛, the polymer protective layer may act as a resistance, which may cause a problem in which battery performance deteriorates.
그밖에, 상기 강유전성 고분자 보호층에 포함되는 강유전성 고분자의 중량평균분자량(weight average molecular weight, Mw)은 10,000 내지 3,000,000 g/mol, 바람직하게는 50,000 내지 2,000,000 g/mol, 더욱 바람직하게는 100,000 내지 1,000,000 g/mol일 수 있다. 또한, 상기 강유전성 고분자 보호층은 전기방사에 의해 나노섬유로 형성된 것일 수 있다.In addition, the weight average molecular weight (Mw) of the ferroelectric polymer included in the ferroelectric polymer protective layer is 10,000 to 3,000,000 g/mol, preferably 50,000 to 2,000,000 g/mol, more preferably 100,000 to 1,000,000 g. It can be /mol. Additionally, the ferroelectric polymer protective layer may be formed of nanofibers by electrospinning.
다음으로, 본 발명에 따른 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극의 제조 방법에 대하여 설명한다. 본 발명에 따른 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극의 제조 방법은, (a) 강유전성 고분자 화합물을 용매에 용해시켜 강유전성 고분자 용액을 제조하는 단계, (b) 상기 제조된 강유전성 고분자 용액을 집전체 또는 이형필름 상에 전기방사하여, 상기 집전체 또는 이형필름 상에 강유전성 고분자 보호층을 형성시키는 단계 및 (c) 상기 집전체 상에 형성된 강유전성 고분자 보호층에 리튬을 증착하거나, 이형필름 상에 형성된 강유전성 고분자 보호층을 집전체 상에 형성된 리튬 메탈의 표면에 전사시키는 단계를 포함한다.Next, a method for manufacturing a negative electrode for a lithium secondary battery formed with a ferroelectric polymer protective layer according to the present invention will be described. The method of manufacturing a negative electrode for a lithium secondary battery with a ferroelectric polymer protective layer according to the present invention includes the steps of (a) dissolving a ferroelectric polymer compound in a solvent to prepare a ferroelectric polymer solution, (b) applying the prepared ferroelectric polymer solution to a current collector. or electrospinning on a release film to form a ferroelectric polymer protective layer on the current collector or the release film; and (c) depositing lithium on the ferroelectric polymer protective layer formed on the current collector or forming a ferroelectric polymer protective layer on the release film. It includes transferring the ferroelectric polymer protective layer to the surface of the lithium metal formed on the current collector.
상기한 바와 같이, 강유전성 고분자 보호층은 강유전성 고분자 화합물을 용매에 녹인 후 전기방사를 실시함으로써 형성된다. 하지만, 전기방사 공정 환경이 대기 중에 노출이 되어 있고, 사용하는 용매가 리튬 금속과 반응성이 있는 것이 대부분이어서 리튬 금속 위에 직접 방사하는 데에 어려움이 있다(즉, 대기중 산화/용매와 반응). 이에 본 출원인은, 집전체 또는 이형필름 위에 강유전성 고분자 보호층을 전기방사시키는 방안을 발명해 낸 것이다. 한편, 상기 이형필름은, PET 또는 이와 유사한 성질을 가지는 고분자 필름 위에 박리력이 낮은 이형물질이 코팅된 것으로서, 코팅 시 제막한 필름을 쉽게 떼어낼 수 있다는 장점을 가진다.As described above, the ferroelectric polymer protective layer is formed by dissolving a ferroelectric polymer compound in a solvent and then electrospinning it. However, since the electrospinning process environment is exposed to the air and most of the solvents used are reactive with lithium metal, it is difficult to spin directly on lithium metal (i.e., oxidation/reaction with solvent in the air). Accordingly, the present applicant has invented a method of electrospinning a ferroelectric polymer protective layer on a current collector or release film. Meanwhile, the release film is a release material with low peeling force coated on PET or a polymer film with similar properties, and has the advantage that the film formed during coating can be easily removed.
상기 강유전성 고분자 화합물은 유전상수(또는, 유전율)가 5 내지 100, 바람직하게는 10 내지 70, 더욱 바람직하게는 30 내지 60인 강유전체로서, 상기의 유전상수 값을 만족하는 강유전성 고분자 화합물로는, PVDF[유전상수: 7] 등의 단중합 강유전체, 그리고, P(VdF-TrFE)[유전상수: 12], P(VdF-HFP)[유전상수: 11], P(VdF-TrFE-CTFE)[유전상수: 40] 및 P(VdF-TrFE-CFE)[유전상수: 55] 등의 공중합 강유전체를 예시할 수 있으며, 단중합 강유전체보다는 공중합 강유전체를 사용하는 것이 바람직하고, 공중합 강유전체 중에서도 높은 유전상수 값을 가지는 것들, 예를 들어, P(VdF-TrFE-CTFE)나 P(VdF-TrFE-CFE)를 사용하는 것이 더욱 바람직하다.The ferroelectric polymer compound is a ferroelectric having a dielectric constant (or dielectric constant) of 5 to 100, preferably 10 to 70, and more preferably 30 to 60. Examples of the ferroelectric polymer compound satisfying the above dielectric constant value include PVDF. Monopolymer ferroelectrics such as [dielectric constant: 7], and P(VdF-TrFE) [dielectric constant: 12], P(VdF-HFP) [dielectric constant: 11], P(VdF-TrFE-CTFE) [dielectric constant Constant: 40] and P(VdF-TrFE-CFE) [dielectric constant: 55] can be used as examples of copolymerized ferroelectrics. It is preferable to use copolymerized ferroelectrics rather than monopolymerized ferroelectrics, and among copolymerized ferroelectrics, they have higher dielectric constant values. It is more preferable to use those that have, for example, P(VdF-TrFE-CTFE) or P(VdF-TrFE-CFE).
상기 용매는 통상의 유기용매일 수 있고, 구체적으로는 디메틸포름아미드(dimethylformamide, DMF), 아세톤, 톨루엔, 테트라하이드로푸란(tetrahydrofuran, THF), 메틸피롤리돈(N-methyl-2-pyrrolidone, NMP), 메탄올, 에탄올, 1-프로판올, 2-프로판올(IPA) 및 이들의 혼합물을 예시할 수 있다. 이때, 2종 이상의 유기용매를 혼합 사용하는 경우, 그 혼합 비율에 있어서는 특별한 제한이 없다.The solvent may be a common organic solvent, and specifically, dimethylformamide (DMF), acetone, toluene, tetrahydrofuran (THF), and methylpyrrolidone (N-methyl-2-pyrrolidone, NMP). ), methanol, ethanol, 1-propanol, 2-propanol (IPA), and mixtures thereof. At this time, when two or more types of organic solvents are mixed and used, there is no particular limitation on the mixing ratio.
상기 (a) 단계에 있어서, 상기 강유전성 고분자 화합물의 사용 함량은, 상기 용매의 총 중량 100 중량부에 대하여 1 내지 70 중량부, 바람직하게는 5 내지 50 중량부, 더욱 바람직하게는 10 내지 30 중량부일 수 있다. 상기 강유전성 고분자 화합물의 사용 함량이 상기 용매의 총 중량 100 중량부에 대하여 1 중량부 미만인 경우, 용액이 너무 묽어 전기 방사 시 섬유가 아닌 입자의 형태로 합성되는 문제점이 발생할 수 있고, 70 중량부를 초과하는 경우에는, 용액의 점도가 너무 높아 전기 방사 시 노즐이 막히거나 섬유 직경이 과다하게 커지는 문제점이 발생할 수 있다. 그밖에, 상기 (a) 단계에서 강유전성 고분자 화합물을 용매에 용해시키는 과정은, 25 내지 100 ℃의 온도 하에서 1 내지 12 시간 동안 수행될 수 있다.In step (a), the amount of the ferroelectric polymer compound used is 1 to 70 parts by weight, preferably 5 to 50 parts by weight, more preferably 10 to 30 parts by weight, based on 100 parts by weight of the total weight of the solvent. It could be wealth. If the amount of the ferroelectric polymer compound used is less than 1 part by weight based on 100 parts by weight of the total weight of the solvent, the solution may be too dilute and a problem may occur in that it is synthesized in the form of particles rather than fibers during electrospinning, and if it exceeds 70 parts by weight In this case, the viscosity of the solution is too high, which may cause problems such as clogging of the nozzle or excessively large fiber diameter during electrospinning. In addition, the process of dissolving the ferroelectric polymer compound in the solvent in step (a) may be performed at a temperature of 25 to 100° C. for 1 to 12 hours.
상기 (a) 단계를 통하여 강유전성 고분자 용액이 제조되면, 상기 제조된 강유전성 고분자 용액을 집전체 또는 이형필름 상에 전기 방사시켜야 한다(step b). 도 1은 본 발명의 일 실시예 따라 음극 집전체의 표면에 강유전성 고분자 화합물을 전기 방사하는 모습이고, 도 2는 음극 집전체의 표면에 형성된 강유전성 고분자 보호층을 보여주는 도면이다. 도 2에 도시된 분자식에 대하여 간략히 설명하면, 전기장이 가해지는 경우, 강유전성 고분자 보호층이 양전하 및 음전하를 띠는 부분끼리 정렬이 된다. 따라서, 양전하를 띠는 리튬 이온이 음전하를 띠는 고분자 보호층 전반에 걸쳐 고르게 분포할 수 있고, 정전기적 인력을 통해 빠르게 이동하는 것이 가능하다.When the ferroelectric polymer solution is prepared through step (a), the prepared ferroelectric polymer solution must be electrospun on a current collector or release film (step b). FIG. 1 is a view showing electrospinning a ferroelectric polymer compound on the surface of a negative electrode current collector according to an embodiment of the present invention, and FIG. 2 is a view showing a ferroelectric polymer protective layer formed on the surface of a negative electrode current collector. Briefly explaining the molecular formula shown in FIG. 2, when an electric field is applied, the positively and negatively charged portions of the ferroelectric polymer protective layer are aligned. Therefore, positively charged lithium ions can be evenly distributed throughout the negatively charged polymer protective layer and can move quickly through electrostatic attraction.
여기서, 전기 방사 메커니즘에 대하여 간략하게 설명하면, 먼저, 전기 방사장치의 노즐에서 강유전성 고분자 용액이 분사되는 팁과, 이로부터 제조되어 강유전성 고분자 보호층(보호막)이 모아지는 집전체나 이형필름의 표면에 각각 양전하와 음전하를 침지시켜야 하며, 이때, 전위차를 만들기 위해 고전압 발생 장치로 전압을 공급하여야 한다. 이와 같이 노즐 팁과 집전체나 이형필름의 표면에 각각 양전하 및 음전하를 형성시킨 후에는, 상기 제조된 강유전성 고분자 용액을 전기 방사 장치의 노즐에 일정 속도로 공급하고 팁을 통하여 방사함으로써, 도 1 및 2에 도시된 바와 같이, 집전체나 이형필름의 표면에 강유전성 고분자 보호층을 형성시킬 수 있다.Here, to briefly explain the electrospinning mechanism, first, the tip from which the ferroelectric polymer solution is sprayed from the nozzle of the electrospinning device, and the surface of the current collector or release film on which the ferroelectric polymer protective layer (protective film) is collected. Positive and negative charges must be immersed in each, and at this time, voltage must be supplied to the high voltage generator to create a potential difference. After forming positive and negative charges on the nozzle tip and the surface of the current collector or release film, respectively, the prepared ferroelectric polymer solution is supplied to the nozzle of the electrospinning device at a constant speed and spun through the tip, as shown in Figures 1 and 1. As shown in Figure 2, a ferroelectric polymer protective layer can be formed on the surface of the current collector or release film.
상기 전기 방사(electrospinning) 장치로는 통상의 것을 특별한 제한 없이 사용할 수 있다. 인가되는 전압, 방사 거리 및 방사 속도 또한 목적으로 하는 강유전성 고분자 보호층의 두께 등에 따라 상이해질 수 있으며, 예를 들어, 인가 전압은 5 내지 30 kV, 바람직하게는 10 내지 20 kV, 방사 거리는 5 내지 30 cm, 바람직하게는 10 내지 20 cm, 그리고, 방사 속도는 0.1 내지 2 ml/h, 바람직하게는 0.3 내지 1 ml/h일 수 있다.As the electrospinning device, a conventional electrospinning device can be used without any particular restrictions. The applied voltage, radiation distance, and radiation speed may also vary depending on the thickness of the intended ferroelectric polymer protective layer, etc., for example, the applied voltage is 5 to 30 kV, preferably 10 to 20 kV, and the radiation distance is 5 to 20 kV. 30 cm, preferably 10 to 20 cm, and the spinning speed may be 0.1 to 2 ml/h, preferably 0.3 to 1 ml/h.
한편, 본 발명은, 이상에서 설명한 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극을 포함하는 리튬 이차전지를 제공한다. 여기서, 리튬 이차전지란, 리튬 덴드라이트 성장의 문제점을 내포하고 있는 모든 리튬계 이차전지를 의미한다. 이하, 본 발명의 리튬 이차전지에 대하여 보다 상세히 설명한다.Meanwhile, the present invention provides a lithium secondary battery including a negative electrode for a lithium secondary battery on which the ferroelectric polymer protective layer described above is formed. Here, lithium secondary batteries refer to all lithium-based secondary batteries that contain problems with lithium dendrite growth. Hereinafter, the lithium secondary battery of the present invention will be described in more detail.
양극anode
양극은 양극 활물질, 바인더 및 도전재 등을 포함한다. 상기 바인더는 양극 활물질과 도전재 등의 결합 및 집전체에 대한 결합에 조력하는 성분으로서, 예컨대, 폴리비닐리덴플루오라이드(PVdF),폴리비닐리덴플루오라이드-폴리헥사플루오로프로필렌 공중합체(PVdF/HFP), 폴리비닐아세테이트, 폴리비닐알코올, 폴리비닐에테르, 폴리에틸렌, 폴리에틸렌옥사이드, 알킬화 폴리에틸렌옥사이드, 폴리프로필렌, 폴리메틸(메트)아크릴레이트, 폴리에틸(메트)아크릴레이트, 폴리테트라플루오로에틸렌(PTFE), 폴리비닐클로라이드, 폴리아크릴로니트릴, 폴리비닐피리딘, 폴리비닐피롤리돈, 스티렌-부타디엔 고무, 아크릴로니트릴-부타디엔 고무, 에틸렌-프로필렌-디엔 모노머(EPDM) 고무, 술폰화 EPDM 고무, 스틸렌-부틸렌 고무, 불소 고무, 카르복시메틸셀룰로우즈(CMC), 전분, 히드록시프로필셀룰로우즈, 재생 셀룰로우즈, 및 이들의 혼합물로 이루어진 군에서 선택되는 1종 이상을 사용할 수 있으나, 반드시 이에 한정되는 것은 아니다.The positive electrode includes a positive electrode active material, a binder, and a conductive material. The binder is a component that assists the bonding of the positive electrode active material and the conductive material and the bonding to the current collector, for example, polyvinylidene fluoride (PVdF), polyvinylidene fluoride-polyhexafluoropropylene copolymer (PVdF/ HFP), polyvinyl acetate, polyvinyl alcohol, polyvinyl ether, polyethylene, polyethylene oxide, alkylated polyethylene oxide, polypropylene, polymethyl (meth)acrylate, polyethyl (meth)acrylate, polytetrafluoroethylene (PTFE) ), polyvinyl chloride, polyacrylonitrile, polyvinylpyridine, polyvinylpyrrolidone, styrene-butadiene rubber, acrylonitrile-butadiene rubber, ethylene-propylene-diene monomer (EPDM) rubber, sulfonated EPDM rubber, styrene -One or more selected from the group consisting of butylene rubber, fluororubber, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, and mixtures thereof can be used, but must be used. It is not limited to this.
상기 바인더는 통상적으로 양극 총 중량 100 중량부를 기준으로 1 내지 50 중량부, 바람직하게는 3 내지 15 중량부 첨가된다. 상기 바인더의 함량이 1 중량부 미만이면 양극 활물질과 집전체와의 접착력이 불충분해질 수 있고, 50 중량부를 초과하면 접착력은 향상되지만 그만큼 양극 활물질의 함량이 감소하여 전지 용량이 낮아질 수 있다.The binder is typically added in an amount of 1 to 50 parts by weight, preferably 3 to 15 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. If the content of the binder is less than 1 part by weight, the adhesion between the positive electrode active material and the current collector may become insufficient. If it exceeds 50 parts by weight, the adhesion is improved, but the content of the positive electrode active material is reduced, which may lower battery capacity.
상기 양극에 포함되는 도전재는 전지의 내부 환경에서 부반응을 유발하지 않고 당해 전지에 화학적 변화를 유발하지 않으면서 우수한 전기전도성을 가지는 것이라면 특별히 제한되지 않으며, 대표적으로는 흑연 또는 도전성 탄소를 사용할 수 있으며, 예컨대, 천연 흑연, 인조 흑연 등의 흑연; 카본 블랙, 아세틸렌 블랙, 케첸 블랙, 뎅카 블랙, 써멀 블랙, 채널 블랙, 퍼네이스 블랙, 램프 블랙, 서머 블랙 등의 카본블랙; 결정구조가 그라펜이나 그라파이트인 탄소계 물질; 탄소 섬유, 금속 섬유 등의 도전성 섬유; 불화 카본; 알루미늄, 니켈 분말 등의 금속 분말; 산화 아연, 티탄산 칼륨 등의 도전성 위스키; 산화 티탄 등의 도전성 산화물; 및 폴리페닐렌 유도체 등의 도전성 고분자;를 단독으로 또는 2종 이상 혼합하여 사용할 수 있으나, 반드시 이에 한정되는 것은 아니다.The conductive material included in the positive electrode is not particularly limited as long as it has excellent electrical conductivity without causing side reactions in the internal environment of the battery and without causing chemical changes in the battery. Representative examples include graphite or conductive carbon. For example, graphite such as natural graphite and artificial graphite; Carbon black such as carbon black, acetylene black, Ketjen black, Denka black, thermal black, channel black, furnace black, lamp black, and thermal black; Carbon-based materials with a crystal structure of graphene or graphite; Conductive fibers such as carbon fiber and metal fiber; fluorinated carbon; Metal powders such as aluminum and nickel powder; Conductive whiskeys such as zinc oxide and potassium titanate; Conductive oxides such as titanium oxide; and conductive polymers such as polyphenylene derivatives; may be used alone or in a mixture of two or more types, but are not necessarily limited thereto.
상기 도전재는 통상적으로 양극 전체 중량 100 중량부를 기준으로 0.5 내지 50 중량부, 바람직하게는 1 내지 30 중량부로 첨가된다. 도전재의 함량이 0.5 중량부 미만으로 너무 적으면 전기전도성 향상 효과를 기대하기 어렵거나 전지의 전기화학적 특성이 저하될 수 있으며, 도전재의 함량이 50 중량부를 초과하여 너무 많으면 상대적으로 양극 활물질의 양이 적어져 용량 및 에너지 밀도가 저하될 수 있다. 양극에 도전재를 포함시키는 방법은 크게 제한되지 않으며, 양극 활물질에의 코팅 등 당분야에 공지된 통상적인 방법을 사용할 수 있다. 또한, 필요에 따라, 양극 활물질에 도전성의 제2 피복층이 부가됨으로 인해 상기와 같은 도전재의 첨가를 대신할 수도 있다.The conductive material is usually added in an amount of 0.5 to 50 parts by weight, preferably 1 to 30 parts by weight, based on 100 parts by weight of the total weight of the positive electrode. If the content of the conductive material is too small (less than 0.5 parts by weight), it may be difficult to expect an improvement in electrical conductivity or the electrochemical properties of the battery may deteriorate. If the content of the conductive material is too high (more than 50 parts by weight), the relative amount of the positive electrode active material may decrease. As it decreases, capacity and energy density may decrease. The method of including the conductive material in the positive electrode is not greatly limited, and conventional methods known in the art, such as coating the positive electrode active material, can be used. Additionally, if necessary, a conductive second coating layer may be added to the positive electrode active material to replace the addition of the above-described conductive material.
또한, 본 발명의 양극에는 그 팽창을 억제하는 성분으로서 충진제가 선택적으로 첨가될 수 있다. 이러한 충진제는 당해 전지에 화학적 변화를 유발하지 않으면서 전극의 팽창을 억제할 수 있는 것이라면 특별히 제한되는 것은 아니며, 예컨대, 폴리에틸렌, 폴리프로필렌 등의 올리핀계 중합체; 유리섬유, 탄소 섬유 등의 섬유상 물질; 등을 사용할 수 있다.Additionally, a filler may be selectively added to the positive electrode of the present invention as a component to suppress its expansion. These fillers are not particularly limited as long as they can suppress the expansion of the electrode without causing chemical changes in the battery, and include, for example, olipine polymers such as polyethylene and polypropylene; Fibrous materials such as glass fiber and carbon fiber; etc. can be used.
상기 양극 활물질, 바인더 및 도전재 등을 분산매(용매)에 분산, 혼합시켜 슬러리를 만들고, 이를 양극 집전체 상에 도포한 후 건조 및 압연함으로써, 본 발명의 양극을 제조할 수 있다. 상기 분산매로는 NMP(N-methyl-2-pyrrolidone), DMF(Dimethyl formamide), DMSO(Dimethyl sulfoxide), 에탄올, 이소프로판올, 물 및 이들의 혼합물을 사용할 수 있으나, 반드시 이에 한정되는 것은 아니다.The positive electrode of the present invention can be manufactured by dispersing and mixing the positive electrode active material, binder, and conductive material in a dispersion medium (solvent) to make a slurry, applying it on a positive electrode current collector, and then drying and rolling it. The dispersion medium may be NMP (N-methyl-2-pyrrolidone), DMF (Dimethyl formamide), DMSO (Dimethyl sulfoxide), ethanol, isopropanol, water, and mixtures thereof, but is not necessarily limited thereto.
상기 양극 집전체로는 백금(Pt), 금(Au), 팔라듐(Pd), 이리듐(Ir), 은(Ag), 루테늄(Ru), 니켈(Ni), 스테인리스스틸(STS), 알루미늄(Al), 몰리브데늄(Mo), 크롬(Cr), 카본(C), 티타늄(Ti), 텅스텐(W), ITO(In doped SnO2), FTO(F doped SnO2), 및 이들의 합금과, 알루미늄(Al) 또는 스테인리스스틸의 표면에 카본(C), 니켈(Ni), 티타늄(Ti) 또는 은(Ag)을 표면 처리한 것 등을 사용할 수 있으나, 반드시 이에 한정되는 것은 아니다. 양극 집전체의 형태는 호일, 필름, 시트, 펀칭된 것, 다공질체, 발포체 등의 형태일 수 있다.The positive electrode current collector includes platinum (Pt), gold (Au), palladium (Pd), iridium (Ir), silver (Ag), ruthenium (Ru), nickel (Ni), stainless steel (STS), and aluminum (Al). ), molybdenum (Mo), chromium (Cr), carbon (C), titanium (Ti), tungsten (W), ITO (In doped SnO 2 ), FTO (F doped SnO 2 ), and alloys thereof , Aluminum (Al) or stainless steel surface treated with carbon (C), nickel (Ni), titanium (Ti), or silver (Ag) may be used, but are not necessarily limited thereto. The positive electrode current collector may be in the form of foil, film, sheet, punched material, porous material, foam, etc.
분리막separator
상기 분리막은 양극과 음극 사이에 개재되어 이들 사이의 단락을 방지하고 리튬이온의 이동 통로를 제공하는 역할을 한다. 상기 분리막으로는 폴리에틸렌, 폴리프로필렌과 같은 올레핀계 폴리머, 유리섬유 등을 시트, 다중막, 미세다공성 필름, 직포 및 부직포 등의 형태로 사용할 수 있으나, 반드시 이에 한정되는 것은 아니다. 한편 전해질로서 폴리머 등의 고체 전해질(예컨대, 유기 고체 전해질, 무기 고체 전해질 등)이 사용되는 경우에는 상기 고체 전해질이 분리막을 겸할 수도 있다. 구체적으로는, 높은 이온 투과도와 기계적 강도를 가지는 절연성의 얇은 박막을 사용한다. 분리막의 기공 직경은 일반적으로 0.01 내지 10 ㎛, 두께는 일반적으로 5 내지 300 ㎛ 범위일 수 있다.The separator is interposed between the anode and the cathode to prevent short circuit between them and to provide a passage for lithium ions. As the separator, olefinic polymers such as polyethylene and polypropylene, glass fiber, etc. may be used in the form of sheets, multilayers, microporous films, woven fabrics, and non-woven fabrics, but are not necessarily limited thereto. Meanwhile, when a solid electrolyte such as a polymer (eg, organic solid electrolyte, inorganic solid electrolyte, etc.) is used as the electrolyte, the solid electrolyte may also serve as a separator. Specifically, a thin insulating film with high ion permeability and mechanical strength is used. The pore diameter of the separator may generally range from 0.01 to 10 ㎛, and the thickness may generally range from 5 to 300 ㎛.
전해질electrolyte
상기 전해질 또는 전해액으로는 비수계 전해액(비수계 유기 용매)으로서 카보네이트, 에스테르, 에테르 또는 케톤을 단독으로 또는 2종 이상 혼합하여 사용할 수 있으나, 반드시 이에 한정되는 것은 아니다. 예를 들어, 디메틸 카보네이트, 디에틸 카보네이트, 디프로필 카보네이트, 메틸프로필 카보네이트, 에틸프로필 카보네이트, 메틸에틸 카보네이트, 에틸렌 카보네이트, 프로필렌 카보네이트, 부틸렌 카보네이트, γ-부틸로락톤, n-메틸 아세테이트, n-에틸 아세테이트, n-프로필 아세테이트, 인산 트리에스테르, 디부틸 에테르, N-메틸-2-피롤리디논, 1,2-디메톡시 에탄, 테트라히드록시 프랑(Franc), 2-메틸 테트라하이드로푸란과 같은 테트라하이드로푸란 유도체, 디메틸설폭시드, 포름아미드, 디메틸포름아미드, 디옥소런 및 그 유도체, 아세토니트릴, 니트로메탄, 포름산 메틸, 초산 메틸, 트리메톡시 메탄, 설포란, 메틸 설포란, 1,3-디메틸-2-이미다졸리디논, 프로피온산 메틸, 프로피온산 에틸 등의 비양자성 유기 용매가 사용될 수 있으나, 반드시 이에 한정되는 것은 아니다.The electrolyte or electrolyte solution is a non-aqueous electrolyte (non-aqueous organic solvent) and carbonate, ester, ether, or ketone can be used alone or in a mixture of two or more types, but is not necessarily limited thereto. For example, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methylpropyl carbonate, ethylpropyl carbonate, methylethyl carbonate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, n-methyl acetate, n- Such as ethyl acetate, n-propyl acetate, phosphoric acid triester, dibutyl ether, N-methyl-2-pyrrolidinone, 1,2-dimethoxy ethane, tetrahydroxy Franc, 2-methyl tetrahydrofuran. Tetrahydrofuran derivatives, dimethylsulfoxide, formamide, dimethylformamide, dioxoran and its derivatives, acetonitrile, nitromethane, methyl formate, methyl acetate, trimethoxy methane, sulfolane, methyl sulfolane, 1,3 Aprotic organic solvents such as -dimethyl-2-imidazolidinone, methyl propionate, and ethyl propionate may be used, but are not necessarily limited thereto.
상기 전해액에는 리튬염을 더 첨가하여 사용할 수 있으며(이른바, 리튬염 함유 비수계 전해액), 상기 리튬염으로는 비수계 전해액에 용해되기 좋은 공지의 것, 예를 들어 LiCl, LiBr, LiI, LiClO4, LiBF4, LiB10Cl10, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiPF3(CF2CF3)3, LiAlCl4, CH3SO3Li, CF3SO3Li, (CF3SO2)2NLi, 클로로 보란 리튬, 저급 지방족 카르본산 리튬, 4 페닐 붕산 리튬, 이미드 등을 들 수 있으나, 반드시 이에 한정되는 것은 아니다. 상기 (비수계) 전해액에는 충방전 특성, 난연성 등의 개선을 목적으로, 예를 들어 피리딘, 트리에틸포스파이트, 트리에탄올아민, 환상 에테르, 에틸렌 디아민, n-글라임(glyme), 헥사 인산 트리 아미드, 니트로벤젠 유도체, 유황, 퀴논 이민 염료, N-치환 옥사졸리디논, N,N-치환 이미다졸리딘, 에틸렌글리콜 디알킬 에테르, 암모늄염, 피롤, 2-메톡시 에탄올, 삼염화 알루미늄 등이 첨가될 수도 있다. 필요에 따라서는, 불연성을 부여하기 위해 사염화탄소, 삼불화에틸렌 등의 할로겐 함유 용매를 더 포함시킬 수도 있고, 고온보존 특성을 향상시키기 위해 이산화탄산 가스를 더 포함시킬 수도 있다.A lithium salt can be further added to the electrolyte solution (so-called lithium salt-containing non-aqueous electrolyte solution), and the lithium salt is a known lithium salt that is easily soluble in a non-aqueous electrolyte solution, such as LiCl, LiBr, LiI, LiClO 4 , LiBF 4 , LiB 10 Cl 10 , LiPF 6 , LiCF 3 SO 3 , LiCF 3 CO 2 , LiAsF 6 , LiSbF 6 , LiPF 3 (CF 2 CF 3 ) 3 , LiAlCl 4 , CH 3 SO 3 Li, CF 3 SO Examples include 3 Li, (CF 3 SO 2 ) 2 NLi, lithium chloroborane, lithium lower aliphatic carboxylate, lithium 4 phenyl borate, imide, etc., but are not necessarily limited thereto. The (non-aqueous) electrolyte solution includes, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylene diamine, n-glyme, and hexaphosphoric acid triamide for the purpose of improving charge/discharge characteristics, flame retardancy, etc. , nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salt, pyrrole, 2-methoxy ethanol, aluminum trichloride, etc. It may be possible. If necessary, a halogen-containing solvent such as carbon tetrachloride or ethylene trifluoride may be further included to provide incombustibility, and carbon dioxide gas may be further included to improve high-temperature preservation characteristics.
한편, 본 발명의 리튬 이차전지는 당 분야의 통상적인 방법에 따라 제조될 수 있다. 예를 들어, 양극과 음극 사이에 다공성의 분리막을 넣고, 비수 전해액을 투입함으로써 제조할 수 있다. 본 발명에 따른 리튬 이차전지는 소형 디바이스의 전원으로 사용되는 코인 셀 등의 전지 셀로 적용됨은 물론, 중대형 디바이스의 전원인 전지모듈의 단위 전지로 특히 적합하게 사용될 수 있다. 이러한 측면에서, 본 발명은 또한 상기 리튬 이차전지 2개 이상이 전기적으로 연결(직렬 또는 병렬)되어 포함된 전지모듈을 제공한다. 상기 전지모듈에 포함되는 전지의 수량은, 전지모듈의 용도 및 용량 등을 고려하여 다양하게 조절될 수 있음은 물론이다.Meanwhile, the lithium secondary battery of the present invention can be manufactured according to conventional methods in the art. For example, it can be manufactured by placing a porous separator between the anode and the cathode and adding a non-aqueous electrolyte solution. The lithium secondary battery according to the present invention is not only applied to battery cells such as coin cells used as a power source for small devices, but can also be particularly suitably used as a unit cell of a battery module that is a power source for medium to large devices. In this respect, the present invention also provides a battery module containing two or more lithium secondary batteries electrically connected (series or parallel). Of course, the quantity of batteries included in the battery module can be adjusted in various ways considering the use and capacity of the battery module.
나아가, 본 발명은 당 분야의 통상적인 기술에 따라 상기 전지모듈을 전기적으로 연결한 전지팩을 제공한다. 상기 전지모듈 및 전지팩은 파워 툴(Power Tool); 전기차(Electric Vehicle, EV), 하이브리드 전기차(Hybrid Electric Vehicle, HEV), 및 플러그인 하이브리드 전기차(Plug-in Hybrid Electric Vehicle, PHEV)를 포함하는 전기차; 전기 트럭; 전기 상용차; 또는 전력 저장용 시스템 중 어느 하나 이상의 중대형 디바이스 전원으로 이용 가능하나, 반드시 이에 한정되는 것은 아니다.Furthermore, the present invention provides a battery pack in which the battery modules are electrically connected according to common techniques in the art. The battery module and battery pack include Power Tool; Electric vehicles, including Electric Vehicle (EV), Hybrid Electric Vehicle (HEV), and Plug-in Hybrid Electric Vehicle (PHEV); electric truck; electric commercial vehicles; Alternatively, it can be used as a power source for any one or more mid- to large-sized devices among power storage systems, but is not necessarily limited to this.
이하 본 발명의 이해를 돕기 위하여 바람직한 실시예를 제시하나, 하기 실시예는 본 발명을 예시하는 것일 뿐, 본 발명의 범주 및 기술사상 범위 내에서 다양한 변경 및 수정이 가능함은 당업자에게 있어서 명백한 것이며, 이러한 변경 및 수정이 첨부된 특허청구범위에 속하는 것도 당연한 것이다.Preferred examples are presented below to aid understanding of the present invention. However, the following examples are merely illustrative of the present invention, and it is obvious to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention. It is natural that such changes and modifications fall within the scope of the attached patent claims.
[실시예 1] 강유전성 고분자 보호층이 형성된 음극의 제조 [Example 1] Manufacturing of a cathode with a ferroelectric polymer protective layer
먼저, 유전상수가 7인 강유전성 고분자 화합물 poly[vinylidenefluoride](PVdF) 2 g을 완전히 녹이기 위하여, 이를 DMF 7 g과 아세톤 3 g을 혼합한 용매에 투입하고, 80 ℃에서 3 시간 동안 교반하여 강유전성 고분자 용액을 제조하였다. 이어서, 상기 제조된 강유전성 고분자 용액을 전기 방사 장치의 노즐에 공급한 후, 노즐 팁을 통하여 구리 집전체 표면에 전기방사하여, 공극률 50 %의 강유전성 고분자 보호층이 형성된 음극을 제조하였다. 이때, 인가된 전압은 15 kV, 방사 거리는 10 cm, 방사 속도는 0.3 ml/h로 설정하였다.First, in order to completely dissolve 2 g of poly[vinylidenefluoride] (PVdF), a ferroelectric polymer compound with a dielectric constant of 7, it was added to a solvent mixed with 7 g of DMF and 3 g of acetone, and stirred at 80°C for 3 hours to dissolve the ferroelectric polymer. A solution was prepared. Next, the prepared ferroelectric polymer solution was supplied to the nozzle of the electrospinning device, and then electrospun on the surface of the copper current collector through the nozzle tip to prepare a cathode with a ferroelectric polymer protective layer with a porosity of 50%. At this time, the applied voltage was set to 15 kV, the spinning distance was set to 10 cm, and the spinning speed was set to 0.3 ml/h.
[실시예 2] 강유전성 고분자 보호층이 형성된 음극의 제조 [Example 2] Manufacturing of a cathode with a ferroelectric polymer protective layer
강유전성 고분자 화합물로서 PVdF를 유전상수가 12인 P(VdF-TrFE)로 변경한 것을 제외하고는 상기 실시예 1과 동일하게 수행하여, 공극률 50 %의 강유전성 고분자 보호층이 형성된 음극을 제조하였다.A cathode having a ferroelectric polymer protective layer with a porosity of 50% was manufactured in the same manner as in Example 1, except that PVdF as the ferroelectric polymer compound was changed to P(VdF-TrFE) with a dielectric constant of 12.
[실시예 3] 강유전성 고분자 보호층이 형성된 음극의 제조 [Example 3] Manufacturing of a cathode with a ferroelectric polymer protective layer
강유전성 고분자 화합물로서 PVdF를 유전상수가 40인 P(VdF-TrFE-CTFE)로 변경한 것을 제외하고는 상기 실시예 1과 동일하게 수행하여, 공극률 50 %의 강유전성 고분자 보호층이 형성된 음극을 제조하였다.A cathode having a ferroelectric polymer protective layer with a porosity of 50% was manufactured in the same manner as in Example 1, except that PVdF as a ferroelectric polymer compound was changed to P(VdF-TrFE-CTFE) with a dielectric constant of 40. .
[실시예 4] 강유전성 고분자 보호층이 형성된 음극의 제조 [Example 4] Manufacturing of a cathode with a ferroelectric polymer protective layer
먼저, 유전상수가 7인 강유전성 고분자 화합물 PVdF 2 g을 완전히 녹이기 위하여, 이를 DMF 7 g과 아세톤 3 g을 혼합한 용매에 투입하고, 80 ℃에서 3 시간 동안 교반하여 강유전성 고분자 용액을 제조하였다. 이어서, 상기 제조된 강유전성 고분자 용액을 전기 방사 장치의 노즐에 공급하고, 노즐 팁을 통하여 이형필름(PET 고분자 필름 + 유기 실리콘계 이형물질)에 전기방사한 후, 이형필름을 이용하여 집전체/20 um 리튬 샘플에 전사하여(정확하게는 리튬에 전사), 공극률 50 %의 강유전성 고분자 보호층이 형성된 집전체 / 20 um 리튬 / 고분자 보호층 구조의 음극을 제조하였다. 이때, 전기 방사 시 인가된 전압은 15 kV, 방사 거리는 10 cm, 방사 속도는 0.3 ml/h로 설정하였다.First, in order to completely dissolve 2 g of PVdF, a ferroelectric polymer compound with a dielectric constant of 7, it was added to a solvent mixed with 7 g of DMF and 3 g of acetone, and stirred at 80°C for 3 hours to prepare a ferroelectric polymer solution. Next, the prepared ferroelectric polymer solution is supplied to the nozzle of the electrospinning device, electrospun on a release film (PET polymer film + organic silicon-based release material) through the nozzle tip, and then used as a release film to create a current collector/20 um By transferring to the lithium sample (to be precise, transferring to lithium), a negative electrode with a current collector/20 um lithium/polymer protective layer structure formed with a ferroelectric polymer protective layer with a porosity of 50% was manufactured. At this time, the voltage applied during electrospinning was set at 15 kV, the spinning distance was set at 10 cm, and the spinning speed was set at 0.3 ml/h.
[실시예 5] 강유전성 고분자 보호층이 형성된 음극의 제조 [Example 5] Manufacturing of a cathode with a ferroelectric polymer protective layer
강유전성 고분자 화합물로서 PVdF를 유전상수가 12인 P(VdF-TrFE)로 변경한 것을 제외하고는 상기 실시예 4와 동일하게 수행하여, 공극률 50 %의 강유전성 고분자 보호층이 형성된 음극을 제조하였다.A cathode having a ferroelectric polymer protective layer with a porosity of 50% was manufactured in the same manner as in Example 4, except that PVdF as the ferroelectric polymer compound was changed to P(VdF-TrFE) with a dielectric constant of 12.
[실시예 6] 강유전성 고분자 보호층이 형성된 음극의 제조 [Example 6] Manufacturing of a cathode with a ferroelectric polymer protective layer
강유전성 고분자 화합물로서 PVdF를 유전상수가 40인 P(VdF-TrFE-CTFE)로 변경한 것을 제외하고는 상기 실시예 4와 동일하게 수행하여, 공극률 50 %의 강유전성 고분자 보호층이 형성된 음극을 제조하였다.A cathode having a ferroelectric polymer protective layer with a porosity of 50% was manufactured in the same manner as in Example 4, except that PVdF as the ferroelectric polymer compound was changed to P(VdF-TrFE-CTFE) with a dielectric constant of 40. .
[비교예 1] 고분자 층이 형성된 음극의 제조 [Comparative Example 1] Manufacturing of a cathode with a polymer layer formed
강유전성 고분자 화합물인 PVdF를 유전상수가 4인 폴리아크릴로니트릴(PAN)로 변경한 것을 제외하고는 상기 실시예 1과 동일하게 수행하여, 고분자 층이 형성된 음극을 제조하였다.A cathode with a polymer layer was manufactured in the same manner as in Example 1, except that PVdF, a ferroelectric polymer compound, was changed to polyacrylonitrile (PAN) with a dielectric constant of 4.
[비교예 2] 고분자 층이 형성된 음극의 제조 [Comparative Example 2] Manufacturing of a cathode with a polymer layer formed
강유전성 고분자 화합물인 PVdF를 유전상수가 4인 폴리아크릴로니트릴(PAN)로 변경한 것을 제외하고는 상기 실시예 4와 동일하게 수행하여, 고분자 층이 형성된 음극을 제조하였다.A cathode with a polymer layer was manufactured in the same manner as in Example 4, except that PVdF, a ferroelectric polymer compound, was changed to polyacrylonitrile (PAN) with a dielectric constant of 4.
[실시예 1~3, 비교예 1] 리튬 이차전지의 제조 - A [Examples 1 to 3, Comparative Example 1] Manufacturing of lithium secondary battery - A
상기 실시예 1 내지 3 및 비교예 1에서 제조된 음극을 리튬 금속을 대극으로 하여 리튬 이차전지 하프-셀(half-cell)을 제작하였다.A lithium secondary battery half-cell was manufactured using the negative electrodes prepared in Examples 1 to 3 and Comparative Example 1 with lithium metal as the counter electrode.
[실시예 1~3, 비교예 1] 리튬 이차전지의 제조 - B [Examples 1 to 3, Comparative Example 1] Manufacturing of lithium secondary battery - B
상기 실시예 1 내지 3 및 비교예 1에서 제조된 음극에 20 um 두께만큼 리튬 금속을 증착한 후, 양극재(LCO 등)와 조합하여 리튬 이차전지 풀-셀(full-cell)을 제작하였다.Lithium metal was deposited to a thickness of 20 um on the negative electrode prepared in Examples 1 to 3 and Comparative Example 1, and then combined with a positive electrode material (LCO, etc.) to produce a full-cell lithium secondary battery.
[실시예 4~6, 비교예 2] 리튬 이차전지의 제조 - C [Examples 4 to 6, Comparative Example 2] Manufacturing of lithium secondary battery - C
상기 실시예 4 내지 6 및 비교예 2에서 제조된 음극을 양극재(LCO 등)와 조합하여 리튬 이차전지 풀-셀을 제작하였다.A full-cell lithium secondary battery was manufactured by combining the negative electrodes prepared in Examples 4 to 6 and Comparative Example 2 with a positive electrode material (LCO, etc.).
[실험예 1] 리튬 이차전지의 쿨롱 효율도 평가 - A [Experimental Example 1] Evaluation of coulombic efficiency of lithium secondary battery - A
상기 '리튬 이차전지의 제조 - A'에서 제조된 리튬 이차전지 하프-셀을 50 사이클(cycle) 동안 충/방전(충전: 0.5C, 방전: 0.5C)하여 쿨롱 효율(Columbic efficiency)을 평가하였으며, 그 결과를 하기 표 1에 나타내었다.Coulombic efficiency was evaluated by charging/discharging the lithium secondary battery half-cell manufactured in 'Manufacture of lithium secondary battery - A' for 50 cycles (charge: 0.5C, discharge: 0.5C). , the results are shown in Table 1 below.
(PVdF)Example 1
(PVdF)
(P(VdF-TrFE))Example 2
(P(VdF-TrFE))
(P(VdF-TrFE-CTFE))Example 3
(P(VdF-TrFE-CTFE))
(PAN)Comparative Example 1
(PAN)
PVdF를 강유전성 고분자 화합물로 적용한 실시예 1의 경우, 상기 표 1에 나타낸 바와 같이, 94.9 %의 초기 쿨롱 효율 및 95.0 %의 평균 쿨롱 효율을 나타내었다. 또한, P(VdF-TrFE)를 강유전성 고분자 화합물로 적용한 실시예 2의 경우, 96.0 %의 초기 쿨롱 효율 및 95.8 %의 평균 쿨롱 효율을 나타내었으며, P(VdF-TrFE-CTFE)를 강유전성 고분자 화합물로 적용한 실시예 3의 경우에는, 97.3 %의 초기 쿨롱 효율 및 95.1 %의 평균 쿨롱 효율을 나타내었다. 도 3은 본 발명의 일 실시예에 따라 제조된 리튬 이차전지 하프-셀의 쿨롱 효율도를 보여주는 그래프로서, 상기와 같은 결과를 그래프로 나타내었다. 반면, 폴리아크릴로니트릴(PAN)을 강유전성 고분자 화합물로 적용한 비교예 1의 경우, 75.9 %의 초기 쿨롱 효율 및 91.2 %의 평균 쿨롱 효율을 나타내어, 실시예 1 내지 3에 비하여 쿨롱 효율도가 현저히 낮은 것을 확인할 수 있었다.In Example 1 in which PVdF was applied as a ferroelectric polymer compound, as shown in Table 1 above, the initial Coulombic efficiency was 94.9% and the average Coulombic efficiency was 95.0%. In addition, in Example 2 in which P(VdF-TrFE) was applied as a ferroelectric polymer compound, an initial coulombic efficiency of 96.0% and an average coulombic efficiency of 95.8% were shown, and P(VdF-TrFE-CTFE) was used as a ferroelectric polymer compound. In the case of Example 3 applied, the initial coulombic efficiency of 97.3% and the average coulombic efficiency of 95.1% were shown. Figure 3 is a graph showing the coulombic efficiency of a lithium secondary battery half-cell manufactured according to an embodiment of the present invention, and the above results are shown graphically. On the other hand, in the case of Comparative Example 1 in which polyacrylonitrile (PAN) was applied as a ferroelectric polymer compound, the initial coulombic efficiency of 75.9% and the average coulombic efficiency of 91.2% were shown, and the coulombic efficiency was significantly lower than that of Examples 1 to 3. could be confirmed.
[실험예 2] 리튬 이차전지의 쿨롱 효율도 평가 - B [Experimental Example 2] Evaluation of coulombic efficiency of lithium secondary battery - B
[실험예 3] 리튬 이차전지의 쿨롱 효율도 평가 - C [Experimental Example 3] Evaluation of coulombic efficiency of lithium secondary battery - C
Claims (14)
상기 집전체 상에 위치하는 리튬 메탈; 및
상기 집전체와 리튬 메탈의 사이 또는 상기 리튬 메탈의 상부에 위치하는 강유전성 고분자 보호층;을 포함하며,
상기 강유전성 고분자의 유전상수는 30 내지 60이고,
상기 강유전성 고분자 보호층의 두께는 20 내지 90 ㎛인 것을 특징으로 하는 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극.house collector;
Lithium metal located on the current collector; and
It includes a ferroelectric polymer protective layer located between the current collector and the lithium metal or on top of the lithium metal,
The dielectric constant of the ferroelectric polymer is 30 to 60,
A negative electrode for a lithium secondary battery having a ferroelectric polymer protective layer, characterized in that the thickness of the ferroelectric polymer protective layer is 20 to 90 ㎛.
(b) 상기 제조된 강유전성 고분자 용액을 집전체 또는 이형필름 상에 전기방사하여, 상기 집전체 또는 이형필름 상에 강유전성 고분자 보호층을 형성시키는 단계; 및
(c) 상기 집전체 상에 형성된 강유전성 고분자 보호층에 리튬을 증착하거나, 이형필름 상에 형성된 강유전성 고분자 보호층을 집전체 상에 형성된 리튬 메탈의 표면에 전사시키는 단계;를 포함하며,
상기 강유전성 고분자 화합물의 유전상수는 30 내지 60이고,
상기 강유전성 고분자 보호층의 두께는 20 내지 90 ㎛인 것을 특징으로 하는 강유전성 고분자 보호층이 형성된 리튬 이차전지용 음극의 제조 방법.(a) preparing a ferroelectric polymer solution by dissolving the ferroelectric polymer compound in a solvent;
(b) electrospinning the prepared ferroelectric polymer solution onto a current collector or release film to form a ferroelectric polymer protective layer on the current collector or release film; and
(c) depositing lithium on the ferroelectric polymer protective layer formed on the current collector, or transferring the ferroelectric polymer protective layer formed on the release film to the surface of the lithium metal formed on the current collector;
The dielectric constant of the ferroelectric polymer compound is 30 to 60,
A method of manufacturing a negative electrode for a lithium secondary battery having a ferroelectric polymer protective layer, characterized in that the thickness of the ferroelectric polymer protective layer is 20 to 90 ㎛.
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