Tetrazole tethered polyacrylonitrile for high performance lithium-ion battery

Yoon, Jeonghoon Sungkyunkwan University 2022 국내박사

Today's globally growing efforts toward renewable and clean energy drive an urgent need for major breakthroughs in energy storage technology. Lithium-ion batteries, first commercialized in 1991 and with high energy density, have led to a boom in portable electronic devices in the past few decades. However, lithium-ion batteries with high energy density for future EVs and high-end IT devices have not evolved rapidly due to not only the limitation in active materials with low specific/volumetric capacity but also a safety issue. Therefore, high-capacity anode material should be adopted to replace conventional graphite anode along with the development of cathode materials. In this respect, Si has emerged as the most prominent anode material due to its high theoretical capacity (3579 mAh/g). However, it suffers from a huge capacity decay resulting from the multiscale fractures in the Si electrode owing to the enormous volume variation (~300%) during cycles. The modification of Si surface with polymeric materials has attracted considerable attention since the highly stable Si anode can be utilized with little morphological and interfacial change of Si. In addition, safe and high ionic conductivity electrolytes should be developed to replace conventional liquid electrolytes, which have leakage and safety problems. In this respect, the solid polymer electrolyte has been proposed to overcome the safety issue, but it is difficult to use at ambient temperature due to its low ionic conductivity. Thus, gel polymer electrolyte (GPE) was suggested, which combined liquid and solid electrolytes advantages. Especially, crosslinked GPE has high mechanical strength, flexibility, and ionic conductivity even after uptake of liquid electrolytes, thus it can be applied to flexible electronic devices. In this dissertation, self-cross-linkable tetrazole tethered polyacrylonitrile (PANVDAC) was designed and synthesized. The synthesized PANVDAC was coated on the silicon nanoparticles, which was next-generation high energy density anode materials. Si NPs@PANVDAC has highly stable cycle retention even 50 C. In addition, PANVDAC based gel polymer electrolytes were prepared and applied to lithium metal batteries. Finally, single-ion conducting gel polymer electrolytes was fabricated by converting tetrazole to tetrazolium TFSI, which has high lithium-ion conductivity possible to apply next-generation lithium-ion batteries. 오늘날 전 세계적으로 신재생 에너지 및 청정 에너지 개발이 증가함에 따라 에너지 저장 기술 혁신이 긴급하게 요구되고 있다. 특히, 화석 연료 자동차에서 전기 자동차(EV)로의 전환은 고에너지 충전식 배터리의 개발에 크게 의존하고 있다. 1991년에 처음 상용화된 높은 에너지 밀도를 지닌 리튬 이온 전지는 지난 20년 동안 휴대용 전자 장치의 붐을 이끌었다. 그러나 미래형 전기차 (EV)와 첨단 IT기기를 위한 고에너지 밀도의 리튬 이온 전지는 비/체적 용량이 낮은 활물질의 한계와 안전성 문제로 인해 빠르게 발전하지 못하고 있다. 따라서, 양극재 개발과 함께 기존 흑연계 음극재를 대체할 고용량 음극재의 개발도 필요하다. 실리콘은 높은 이론적 용량(3579mAh/g)으로 인해 차세대 음극 재료로 부상했으나 충방전시에 엄청난 부피변화(~300%)로 인해 실리콘 기반 전극에 심각한 균열이 생겨 용량이 크게 저하된다. 그러나, 고분자 물질로 실리콘 입자 표면을 개질 하는 것은 실리콘의 형태 및 계면 변화가 거의 없이 매우 안정적으로 실리콘 음극재를 사용할 수 있기 때문에 상당한 주목을 받고 있다. 또한, 액체 전해질 누출로 인한 안전성 문제가 있는 기존의 액체 전해질을 대체하기 위해 차세대 전해질이 개발되어야 한다. 안전성 문제를 극복하기 위해 고체 고분자 전해질이 제안되었으나, 상온에서 낮은 이온전도도 때문에 실제 리튬 이온 전지에 적용하는데 한계가 있다. 따라서 액체 전해질과 고체 전해질의 장점을 결합한 겔 고분자 전해질이 제안되었다. 특히 가교구조가 도입된 젤 고분자 전해질은 액체 전해질을 흡수한 후에도 충분한 기계적 강도, 유연성 및 이온 전도성을 가지므로 리튬 이온 전지에 광범위하게 적용할 수 있다. 본 논문에서는 테트라졸 형태로 자가 가교 가능한 폴리아크릴로니트릴 고분자를 설계 및 합성하였고, 이를 차세대 고 에너지 음극 활물질인 실리콘 나노 입자 표면에 코팅하여 높은 율속 특성과 높은 용량을 유지하며 안정적인 수명 특성을 가지는 실리콘 음극 기반 리튬 이온 전지를 제작하였다. 또한 합성된 고분자를 이용하여 젤 고분자 전해질을 제작 후 높은 에너지밀도를 가지는 리튬 금속 음극 기반 리튬 금속 전지에 적용하여 안정적인 수명특성을 확인하였다. 마지막으로는 테트라졸 형태의 가교 구조를 이온성 액체 형태로 치환하여 단일 이온 수송체 고분자 젤 전해질을 제작하여 높은 리튬 이온 전도 효율을 가지는 차세대 고분자 전해질을 제작하여 리튬 이차 전지에 적용하였다.

리튬이온이차전지 음극활물질로써 탄소와 금속산화물의 전기화학적 특성 연구

마리아사바크리 전북대학교 2010 국내박사

Energy and the environment are closely interlinked since energy comes via the environment and can have a strong effect on it. An increasing awareness of the effect of human activity on the natural environment has led to the use of sustainable energy and, in an increasingly populated world, the need for energy conservation, , energy storage and energy efficiency. In the past two decades, with the prevalence of portable consumer electronics, the demand for rechargeable energy storage sources of high energy density and low weight has been rapidly growing. Lithium secondary batteries are very promising fulfillment for such demands because of its outstanding characteristics such as light weight, high energy density, intrinsic discharge voltage and environmental friendly. From the first introduction into the market, in the last two decades, lithium secondary batteries has become dominant from small rechargeable battery application like cell phones, note book computers, personal digital assistance etc. to large applications such as satellites and electric vehicles. This growing demand has attracted researchers to develop lithium secondary batteries with high voltage and capacity and low cost and safety. Extensive researches are underway an alternative electrode materials and electrolytes for these batteries. This present thesis details the study of electrochemical characterization of carbon and metal oxide anode materials for lithium ion secondary batteries. Various materials like boron doped diamond, Pyrolytic Carbon, Tin oxide and transition metal oxides are studied as anode materials for lithium ion secondary batteries. Their synthesis, physical characterization and electrochemical properties are discussed. For many years, nickel-cadmium had been the only suitable battery for portable equipment from wireless communications to mobile computing. Nickel-metal-hydride and lithium-ion emerged in the early 1990s, fighting nose-to-nose to gain customer's acceptance. Today, lithium-ion is the fastest growing and most promising battery chemistry. Lithium-ion is a low maintenance battery, an advantage that most other chemistries cannot claim. There is no memory and no scheduled cycling is required to prolong the battery's life. In addition, the self-discharge is less than half compared to nickel-cadmium, making lithium-ion well suited for modern fuel gauge applications. Lithium-ion cells cause little harm when disposed. Chapter 1 gives a brief review on the back ground and basic concepts of lithium ion secondary batteries, their structure, mechanism, development and application and highlights the motivation of this work. The experimental details of all the works undergone are discussed in chapter 2. The synthesis processes involved including Chemical vapour deposition and simple Pyrolysis and all physical characterization techniques such as spectroscopic and microscopic studies are discussed in detail. Cyclic Voltammetry, Impedance measurements and Charge discharge studies of battery systems were also explained in detail. Boron doped diamond synthesis and characterizations are discussed in chapter 3. Boron doped diamond was prepared by hot filament chemical vapor deposition method. The prepared samples were subjected to X- ray diffraction, scanning electron microscopy and Raman spectroscopy studies. The BDD composite electrode/Li cell has been assembled and its cycling behavior is detailed. Pyrolytic carbons were synthesized from sorona polymer and its characteristics both physical and electrochemical are discussed in chapter 4. Carbonaceous materials were derived by the simple pyrolysis of sorona at 800?C and 900?C. The structure and morphology of the materials analyzed by Scanning Electron Microscopy, Thermal gravimetric analysis, and X-Ray diffraction studies are explained. The prepared porogen sorona carbons are used as the anode materials for Li ion battery and electrochemical behavior investigated with Cyclic Voltammetry studies and cycling studies are detailed in the chapter. Chapter 5 explains the tin oxide based anode materials for lithium ion batteries. Zinc oxide and Tin oxide mixture was synthesized by usual chemical method and the precursors for the compounds were synthesized via Solvothermal method. The structure and electrochemical properties are studied in detail with characterization techniques and cycling data and discussed clearly. Zinc oxide anodes with large irreversible capacity and Tin oxide anodes with volume change, different combinations of both oxides may sooner replace the graphitic anode materials with further investigations. The synthesis, characterization and electrochemical properties of Co3O4 are discussed in chapter 6. The Cobalt oxide was synthesized by simple template method which is very interesting and inexpensive. Avian egg shells were used as templates and their characteristics and electrochemical properties are studied. The final chapter includes an overall view of this thesis work. It gives a summary of all the works included and conclusion for carbon based anode materials and metal oxide based anode materials. The future scope for further development of the study is also presented. It is worth mentioning that all the research reports in this thesis has been published and submitted in different international journals and conferences. The details of publications are mentioned at the end of the thesis.

Electrochemical Characterization of All Solid-like Lithium Rechargeable Cells Comprising of Modified Electrodes and Polymeric Electrolytes

조성규 부산대학교 대학원 2019 국내박사

Currently, commercially available Li ion batteries applied to electric motor vehicles possess typical disadvantages such as low energy density and short movement distance, which magnifies the safety issues and limits broad applications. As the total energy is expanded these become more serious to overcome. The next-generation batteries are designed to solve these problems, possessing higher energy density and safety than current commercial products. All-solid-state Li ion battery is one of the next-generation batteries by removing typical risk factors of liquid-based batteries including leakages and explosion. All-solid-state Li ion batteries are physically and chemically stable at high voltage. It displays optimized characteristics for high energy density. The high-voltage applicable cathode materials are working at higher than 4.3 V in which liquid electrolytes are usually disabled by decomposition. In this point, all-solid-state Li ion battery is one of the best solutions. However, for the solid-state Li ion battery, ion conductivity corresponding to that of liquid (>1mS/cm) is hardly obtained. The solid-state electrolytes composed of polyethylene oxide (PEO) display relatively high ion conductivity but cannot be optimized due to high crystallinity which limits ion movement. In this study, hybrid solid electrolyte (HSE) system are designed using Li_(1.3)Al_(0.3)Ti)(0.7)(PO₄)₃ (LATP), PEO, and Lithium bis(trifluoromethanesulfonyl) imide (LITFSI). HSC are composed of LATP, PEO and Lithium cobalt oxide (LiCoO₂, LCO) – Lithium manganese oxide (LiMn₂O₄, LMO). This HSE system works without additionally introduced separation membranes and displays electrochemical stability as of 6.0V and ion conductivity as of 2.0×10^(-4) S/cm (23℃) and 1.6×10^(-3) S/cm (55℃). In this system a plasticizer Succinonitrile (SN) is incorporated to reduce the crystallinity of PEO and develop commercially useful all-solid-state Li ion battery. The HSC/HSE/Li all-solid-state Li ion battery designed in this study plays a role under the broken condition without any leakage or shortage. The designed HSC/HSE/Li all-solid-state Li ion battery shows initial charging-discharging capacity as of 82/62 mAh/g (23℃) and 123.4/102.7 mAh/g (55℃). The developed system overcomes the disadvantageous internal resistance increase due to lost Ti ions in LATP by prohibiting the physical contact between the Li metal and LATP. Therefore, this study contributes to new technology development for commercial all-solid-state Li ion battery. Second, by investigating stable materials under the high voltage condition, mass-production of cathode material, LiNi_(0.5)Mn_(1.5)O₄ (LNMO) becomes possible. LNMO is applicable to high-voltage condition and synthesized by modified solid-state synthesis process by utilizing variety of raw materials such as NiO, Ni₂O₃, MnO₂ and Mn₃O₄. The results of XRD and SEM verifies the successful synthesis of 1st and 2nd particles by this modified solid-state synthesis process. Among the designed materials LNMO synthesized from Li₂CO₃, NiO and Mn₃O₄ displays optimized charge-discharge capacity at 25°C as of 124mAh/g by 1C charge/1C discharge and 111mAh/g by 1C charge /10C discharge. In terms of the calcination condition, LNMO shows excellent initial capacity at 750℃ where the size of the 1st particle is small. By this, specific surface area increases while diffusion pathways of Li ions decreases. Meanwhile, at a highly controlled discharge condition, Mn^(3+) ions increase by the temperature increase. Therefore, LNMO calcined at 850℃ exhibits excellent rate-controlled efficiency by 1C charge/10C discharge. However, at the temperatures higher than 900℃ it shows low electrochemical efficiency due to Li volatilization. In this study, general solid-state synthesis process advantageous for commercial products is modified and the whole process is simplified to synthesize LNMO from optimally selected raw materials. In addition, commercial usefulness of LNMO is increased by investigating the morphology and electrochemical properties modulated by calcination temperature. Third, to resolve disadvantages inapplicability of LNMO and reduced cyclelife due to side-reaction of LNMO surface with electrolytes, commercially useful drying coating is applied using MgCO₃, Al₂O₃, SiO₂ and TiO₂. The structure of the bare LNMO and coated LNMO has been analyzed by XRD, SEM, SEM-EDS, TEM and ICP. The results of XRD, SEM, SEM-EDS, TEM and ICP confirm that without structural change, LNMO surface are coated by MgCO₃, Al₂O₃, SiO₂ and TiO₂ in 8.8 ~ 10.4 nm thickness. Compared with bare LNMO, the coated LNMO displays significantly reduced side-reaction with electrolytes at the first cycle. In addition, compared with bare one, coated LNMO is thermally stable at the condition of 25°C and 55°C and at high rates. Especially, the coating layer of SiO₂ inhibits side-reaction with electrolytes at the initial moisture generation condition and keeps 90.2% of capacity under the 50 and 100 cycles compared with sudden death LNMO. This is the same results obtained by electrochemical impedance spectroscopy (EIS). In this study drying coating method has been utilized to evaluate variety of coating materials for LNMO and sheds new light on possibility to develop new high energy density electrode materials. In this study, solid-state electrolytes and cathode materials applicable to high voltage condition have been investigated. This study can contribute to overcoming typical disadvantages of Li ion batteries and to new possibility to develop commercially available safe and high-energy-density Li ion batteries.

Ion conduction, mechanical, and thermal stability enhancement of poly(ethylene glycol)-based polymer electrolytes for Li metal battery

Tian, Zhenchuan Sungkyunkwan University 2023 국내박사

A solid polymer electrolyte (SPE) membrane based on poly(ethylene glycol) (PEG) has been designed to replace the conventional liquid electrolyte because of its feasible ion conduction and high chemical, thermal, mechanical, dimensional stability, interfacial compatibility, various functionalization, and simple fabrication process. PEG is applied for ion-conduction material to modify with other flexible polymers such as poly(arylene ether sulfone) (PAES) and poly(vinyl alcohol) (PVA) under grafting copolymer and semi-interpenetrating network (semi-IPN) for SPE application in lithium metal battery via constructing (i) copolymer electrolyte membrane based on poly(arylene ether sulfone)-grafting-poly(ethylene glycol) (PAES-g-PEG) with various functional end groups; (ii) semi-IPN structured electrolyte membrane based on poly(vinyl alcohol)/ poly(ethylene glycol) (PVA/PEG); and (iii) in-situ polymerized electrolyte membrane based on poly(vinyl alcohol)/poly(ethylene glycol)-poly(vinyl ethylene carbonate) (PVA/PEG-PVEC); and (iv) composite electrolyte membrane based on semi-IPN structured PVA/PEG matrix and halloysite nanoclay systems. Firstly, the copolymer electrolyte membranes were prepared by grafting 2000 molecular weight PEG with various functional end groups into the PAES backbone. Among them, the nitrile (-CN) end group modified PAES-g-PEG showed the highest ion conductivity and enhanced thermal, mechanical, and chemical stability. The semi-IPN structured electrolyte membrane synthesized by crosslinking poly(ethylene glycol) diacrylate (PEGDA) in the presence of PVA exhibited an enhancement in both lithium ion conductivity and mechanical and thermal stability. Besides, the in-situ polymerized electrolyte membrane prepared from PVA/PEG-PVEC showed a high lithium ion transfer number, improved lithium ion conductivity, and optimized interface contact between the cathode and SPE. Additionally, the composite electrolyte membranes combined both superiorities of SPE and inorganic electrolyte, showed excellent Li+ conducting capability and promising potential for the application of lithium metal batteries. Poly(ethylene glycol) (PEG) 기반의 고체 고분자 전해질(solid polymer electrolyte, SPE) 막은 실현 가능한 이온 전도와 높은 화학적, 열적, 기계적, 치수 안정성, 계면 호환성, 다양한 기능화 및 간단한 제조 공정으로 인해 기존의 액체 전해질을 대체 하도록 설계되었다. PEG는 이온 전도 물질에 적용되어 리튬 금속 전지에서 SPE 적용을 위한 반상호 침입 네트워크(semi-IPN) 및 그라프트 공중합체 하에서 poly(arylene ether sulfone) (PAES) 및 poly(vinyl alcohol) (PVA)와 같은 다른 유연한 중합 체와 개질된다: (i) 다양한 기능성 말단기를 갖는 poly(arylene ether sulfone)-graftingpoly(ethylene glycol) (PAES-g-PEG) 기반의 공중합체 전해질 막; (ii) 폴리pol (vinylalcohol)/poly(ethylene glycol) (PVA/PEG) 기반의 반 IPN 구조 전해질 막; (iii) poly(vinyl alcohol)/poly(ethylene glycol)-poly(vinyl ethylene carbonate) (PVA/PEG-PVEC) 기반의 insitu 중합 전해질막; (iv) 반 IPN 구조의 PVA/PEG 매트릭스 및 halloysite nanoclay 시스템에 기반한 복합 전해질 막. 먼저, 다양한 기능성 말단기를 갖는 2000분자량의 PEG를 PAES 골격에 접목시켜 공중합체 전해질막을 제조하였다. 그 중 니트릴(-CN) 말단기 개질 PAES-g-PEG가 가장 높은 이온전도도와 향상된 열적, 기계적, 화학적 안정성을 보였다. PVA의 존재 하에서 poly(ethylene glycol) diacrylate (PEGDA)를 가교시켜 합성한 반 IPN 구조 전해 질막은 리튬 이온 전도도와 기계적 및 열적 안정성 모두 향상된 결과를 나타내었다. 이외에도 PVA/PEG-PVEC로부터 제조된 in-situ 중합 전해질막은 높은 리튬 이온 전달수와 향상된 리튬 이온 전도도 및 양극과 SPE의 계면 접촉이 최적화된 것으로 나타났다. 또한, 복합 전해질막은 SPE와 무기 전해질의 우수성이 모두 결합되어 우수한 Li+ 전도 능력과 리튬 금속 전지의 적용에 유망한 잠재력을 보였다.

Modeling, state estimation and control of lithium-ion battery for hybrid energy system

조성우 서울대학교 대학원 2012 국내박사

최근 휴대용 기기와 친환경 자동차의 에너지 저장 시스템이 큰 관심을 받으며, 특히 전압과 출력 면에서 높은 성능을 보이는 리튬 이온 전지가 가장 각광을 받고 있다. 이러한 리튬 이온 전지는 친환경 자동차와 같은 하이브리드 에너지 시스템의 주요 출력 공급원 또는 보조 출력 공급원으로 쓰인다. 친환경 자동차 내에 탑재되는 리튬 이온 전지의 경우 자동차에 출력을 공급하는 동시에 여분의 출력이 남는 경우 이를 저장하는 역할을 수행한다. 따라서 리튬 이온 전지의 성능이 친환경 자동차의 성능을 대표할 수 있는 중요한 요소 중 하나라고 할 수 있다. 리튬 이온 전지의 성능을 대표하여 나타낼 수 있는 것으로 가용 잔존 용량과 건전 상태를 들 수 있다. 이러한 두 종류의 상태는 센서를 통해 직접 측정이 불가능하기 때문에 이를 추정하기 위해 동적 상세 모델의 개발이 필요하다. 따라서 본 논문에서는 리튬 이온 전지에 대한 동적 상세 모델을 개발하였다. 그리고 이를 바탕으로 하여 전지의 가용 잔존 용량과 건전 상태를 추정하는 방법론을 개발하였다. 최종적으로 본 논문에서 개발한 모델 및 추정 방법론을 연료 전지 하이브리드 자동차의 최적 제어 방법론에 적용하였다. 우선, 친환경 자동차에 쓰이는 리튬 이온 전지의 가용 잔존 용량 추정 알고리즘을 제안하고자 한다. 제안된 방법론은 다양한 온도, 운전 상태 및 출력 부하에 따른 운전 조건에 부합할 수 있는 강건한 가용 잔존 용량 추정을 기본적인 목표로 한다. 이러한 방법론은 전기화학적 모델에 기반을 둔 등가 회로 모델과 재귀 추정자를 포함하고 있다. 등가 회로 모델에 필요한 각 파라미터들은 다양한 온도 및 전류 조건에 따른 실험에 의해 추정하였다. 이러한 모델에 기반을 둔 가용 잔존 용량 추정 방법론과 전류 적산에 의한 추정 방법론의 결합을 통해 가용 잔존 용량의 추정 알고리즘을 개발하였다. 제안된 방법론은 저온 및 상온, 고온 상태에서의 다양한 운전 범위 하에서 실시된 리튬 이온 전지 팩에 대한 실험을 통해 검증하였다. 또한 각종 센서의 이상으로 인한 경우에 대해서도 검증하여 신뢰성을 입증하였다. 그 결과 제안된 방법론은 가용 잔존 용량의 추정에 적당하다는 것을 알 수 있으며 다양한 조건에 적합하고 센서 오류에 대한 문제에도 신뢰성을 가지고 있으며 계산 부하가 작기 때문에 온라인으로 적용 가능하다는 사실 또한 입증하였다. 또한 건전 상태로 대표되는 리튬 이온 전지의 실제 성능에 대한 온라인 감시를 위한 알고리즘을 개발하였다. 여러 변수 중 전지의 충전 용량이 건전 상태를 나타낼 수 있는 대표적인 변수로 선정되었다. 이러한 충전 용량의 추정을 위해 주요 알고리즘, 보조 알고리즘, 두 알고리즘을 결합한 통합 알고리즘의 세 가지 알고리즘을 개발하였다. 주요 알고리즘은 간략화한 등가 회로 모델과 소프트 센서 기술을 결합하여 개발하였다. 소프트 센서 기술은 시스템 인지 방법론과 이동 지평선 추정 방법론에 기반을 둔 방법론으로 파라미터 추정 방법에 주로 사용하였다. 그리고 주요 알고리즘의 계산 부하 문제를 해결하기 위해 보조 방법론을 개발하였다. 그리고 이 두 알고리즘의 단점을 상쇄하고 장점을 극대화하기 위해 두 알고리즘을 결합하여 통합 알고리즘을 개발하였다. 개발된 알고리즘의 적합성을 평가하기 위해 새로운 상태의 전지와 열화된 전지에 대해 다양한 온라인 추정 시험을 거쳤다. 다양한 하이브리드 자동차 및 플러그인 하이브리드 자동차용 리튬 이온 전지에 대한 실험 결과, 개발한 알고리즘은 정확도, 신뢰성, 강건성 및 계산 부하에 대해 강점을 가지고 있어 적합하다는 결론을 내릴 수 있었다. 즉, 개발한 통합 알고리즘은 충전 용량 및 가용 출력에 대해 실시간으로 정량적인 값을 온라인 형태로 추정할 수 있어 실제 하이브리드 자동차 계열 리튬 이차 전지 시스템에 대한 응용에 적합하다는 것을 알 수 있다. 마지막으로 퍼지 제어 논리를 이용하여 고분자 전해질 연료 전지/리튬 이온 전지 하이브리드 에너지 시스템의 최적 제어 논리를 설계하였다. 이를 위해 우선적으로 앞에서 개발된 리튬 이온 전지 모델과 고분자전해질연료전지 시스템에 대해 모사를 하였다. 특히 고분자 전해질 연료 전지의 경우 수소 재활용과 공기극의 가습을 고려하여 모사하였다. 최적 제어기는 퍼지 논리 알고리즘을 활용하여 개발하였다. 이 제어기는 세 가지의 입력 변수가 있다. 그 중 첫 번째 변수인 연료 전지 하이브리드 자동차에서 요구하는 출력을 통해 연료 전지에서 생산해야 하는 출력을 계산하였다. 또한, 앞에서 개발한 방법론을 통해 추정이 가능한 가용 잔존 용량과 건전 상태 역시 제어기의 입력 값으로 사용되었다. 이렇게 개발한 퍼지 제어기를 친환경 자동차의 다양한 운전 조건 및 리튬 이온 전지의 상태에 대해 검증하였다. 검증 결과 제안된 퍼지 논리 제어기를 통해 친환경 자동차의 운전 및 부품 교환 비용을 줄일 수 있으며 최적으로 운전을 할 수 있어 실제 이러한 시스템의 운영에 적합하다는 것을 알 수 있었다. 이러한 연구는 하이브리드 에너지 시스템을 위한 리튬 이온 전지에 대한 상태 추정 및 제어를 온라인으로 가능하게 할 수 있다. 본 논문에서 소개한 모델, 상태 추정 방법론과 제어 논리는 친환경 자동차와 같은 하이브리드 에너지 시스템에 대해 온라인으로 적용할 수 있을 것으로 보인다. In recent years, energy storage systems have been highlighted in portable electronics and eco-friendly vehicle applications. In particular, lithium-ion batteries are used as principal or auxiliary power supply devices for the eco-friendly vehicle applications as hybrid energy systems due to high performance of voltage and power. The batteries in the eco-friendly vehicles either store excess power from the vehicle or supply insufficient power to vehicle motive power generator. Therefore, the performance of the lithium-ion battery is a key variable for the performance evaluation of eco-friendly cars. The key variables of the lithium-ion battery are state-of-charge and state-of-health. Rigorous dynamic model is required to estimate the key variables as state. Therefore, the lithium-ion battery model for hybrid energy system is presented in this thesis. The estimation methodologies for state-of-charge and state-of-health are suggested based on the developed model. Finally, the developed model and estimation methodologies are applied to the optimal control logic of fuel cell hybrid electric vehicle as the hybrid energy system. This thesis describes a state-of-charge estimation methodology for lithium-ion batteries in eco-friendly vehicles. The proposed methodology is intended for state-of-charge estimation under various operating conditions including changes in temperature, driving mode and power duty. The suggested methodology consists of a recursive estimator and employs an equivalent circuit as the electrochemical cell model. Model parameters are estimated by parameter map on experimental cell data with various temperatures and current conditions. The parameter map is developed by a least sum square error estimation method based on nonlinear programming. An adaptive estimator is employed and is based on the combination of current integration and battery model based estimation. The proposed state-of-charge estimation methodology is validated with experimental lithium-ion battery pack data under various driving schedules with low and ambient temperatures and sensor fault cases. The presented results show that the proposed model and methodology are appropriate for estimating state-of-charge under various conditions; power duty, temperature and sensor fault situations. State-of-health estimation algorithms for the actual performance of a lithium-ion battery as state-of-health are presented for on-line monitoring. The capacity is selected as the representative variable, which indicates the performance of the battery. Three algorithms are suggested to estimate the degree of capacity fading: principal algorithm, supplementary algorithm, and hybridized algorithm. The principal algorithm is based on a simplified equivalent circuit model and soft sensor technique. The soft sensor technique is based on a system identification methodology with variance inhibition based approach. The second algorithm is developed to compensate for the problem of computational load. Finally, both of the algorithms are combined in a hybridized algorithm to complement each other. The suitability of algorithms is demonstrated with on-line monitoring of fresh and aged cells using cyclic experiments. The results from diverse experiments for hybrid electric vehicle and plug-in hybrid electric vehicle applications demonstrate the appropriateness of the accuracy, reliability against the inaccurate previous estimated values and computational load. Consequently, the developed hybridized algorithm was appropriate for on-line estimation of the actual battery performance as quantitative values of capacity and power in real time. The optimal control logic for lithium-ion battery / proton exchange membrane fuel cell hybrid energy system is developed using fuzzy logic controller. The developed lithium-ion battery model is applied to design of the control logic. The proton exchange membrane fuel cell system model with hydrogen recirculation and cathode humidifier is developed. The optimal controller is suggested by fuzzy logic control algorithm. Demanded power of the fuel cell hybrid electric vehicle is used with the fuzzy logic controller to calculate the output power from the fuel cell system. In addition, estimated state-of-charge and state-of-health are used as input variables of the fuzzy logic controller. The fuzzy controller is validated with various operations for the eco-friendly vehicles as the hybrid energy system. The suggested control logic is appropriate for application in commercialization and practical usage of the eco-friendly vehicles. This work could contribute to state estimation and control of the lithium-ion battery for the hybrid energy system. The developed models, state estimation methodologies and control logic could be implemented to on-line application for practical usage of the eco-friendly vehicle.

Safety and performance improvement by post-treatment of electrospinning separator and estimation of internal temperature of lithium-ion battery

Leng, Xiaolong 영남대학교 대학원 2023 국내박사

First, a preparation method for a lithium-ion battery separator was developed based on the dual hybridizing of materials and processes. This method aimed to prepare a new composite separator by electrospinning various polymer materials with different properties. In addition to the characteristics of each material, multiple corresponding processes were used for post-treatment of the composite separator to enhance the comprehensive performance of the separator. The prepared composite separator PAN/PVDF-HFP/PVP allows the use of various raw materials. PAN with high thermal stability is suitable as a framework to support the separator structure. PVDF-HFP are binders that can crosslink the fibers after heat treatment (HT), thereby increasing the tensile strength of the separator threefold. PVP, easily soluble in water, was used as a pore-forming agent. After hydrolysis (HD), the fiber of the separator formed a porous structure with high porosity, high electrolyte absorption, and high ionic conductivity. After a heat treatment combined with hydrolysis (HT-HD) to improve the mechanical strength and porosity, the composite separator showed excellent thermal dimensional stability. Its profile integrity was maintained, even at 200 °C. The HT-HD separator produced outstanding electrochemical performance. Hence, the HT-HD separator with all-around performance has potential applications in lithium-ion batteries. Additionally, an online estimation method of the internal temperature of lithium-ion batteries is proposed based on the imaginary part of Electrochemical impedance spectroscopy (EIS). EIS is a classical and advanced sensing technique. Herein, an online prediction method of the internal temperature of lithium-ion batteries is proposed based on the imaginary part of EIS. The effects of different battery states of charge (SOCs), states of health (SOHs), and temperature on the EIS are studied. The relationship between the real & imaginary part & amplitude & phase shift and frequency were explored under different SOC and SOH. The results showed that the SOC and SOH influence the real part& amplitude & phase shift over the entire excitation frequency. However, the imaginary part of EIS was not disturbed by different SOC and SOH in the specific frequency range of 0 – 5×104 Hz. The imaginary part corresponding to the excitation frequency unaffected by SOC and SOH was selected to estimate the internal temperature of a battery. The imaginary part value is sensitive to the temperature and has a good mapping relationship with the internal temperature of a battery. An internal temperature prediction mathematical model based on the imaginary part is established. The temperature evaluation model can control the temperature error within 0.8 ℃ through experimental verification. Meanwhile, a real-time battery internal temperature estimation strategy based on EIS is presented. The prediction method has excellent application prospects in the real-time predictions of the internal temperature of lithium-ion batteries.

A Study on Physics-Based Numerical Models to Assess the Lifespan of Lithium-Ion Batteries for Energy Storage Systems

류성택 서울대학교 대학원 2024 국내박사

A Study on Physics-Based Numerical Models to Assess the Lifespan of Lithium-Ion Batteries for Energy Storage Systems Seong Taek Ryu Department of Mechanical Engineering The Graduate School Seoul National University The current energy landscape is experiencing a significant transformation, propelled by the imperative to lessen reliance on fossil fuels for the sake of environmental conservation. Lithium-ion batteries (LIBs) have surfaced as a viable substitute in the realms of energy storage and transport, attracting considerable interest. To establish lithium-ion batteries as a viable energy solution, paramount importance lies in ensuring their reliability and longevity. A fundamental challenge in this context revolves around comprehending the performance and degradation of battery systems over time. Given the constraints of time and costs associated with traditional battery life experiments, solely relying on experimental data to predict long-term battery life is impractical. Consequently, there is a need for an integrated approach that fuses empirical testing with computational modeling, offering a consolidated perspective. Within the realm of battery modeling, numerous methods exist, and physics-based models stand out as potent tools, albeit computationally intensive. These models meticulously examine the intricate physical procedures occurring at the electrode's scale. This document presents a physics-oriented model designed to forecast the efficiency and longevity of lithium- ion batteries. Integrating the LER and GH-MSMD models with the P2D model could significantly enhance the computational effectiveness of battery examination. This integrated approach unveils the core behavior of LIBs, which emerges from intricate electrical, chemical, and thermal interactions. Furthermore, it establishes a coherent framework for comprehending complex systems by modeling the pivotal physical phenomena influencing battery performance and longevity. With this integrated model, we embark on the following investigations. First, we deviate from conventional empirical approaches by amalgamating cycle and calendar life testing with physics-based models. This synergistic approach yields a more holistic grasp of the multifaceted factors influencing lithium-ion battery performance and lifespan. The model's precision is confirmed using data from calendar tests and 1,800 cycle tests carried out over a six-month period, verifying its alignment with actual battery behavior in real-world scenarios. Second, in the domain of pack models, we introduce a perspective on energy storage system (ESS) pack performance and longevity. By reducing a multifaceted multi-cell system to a solitary representative cell and utilizing authentic power frequencies, we highlight the non-linear correlation between the number of battery cells and the overall reaction of the battery. This approach provides understanding into the principal factors impacting battery performance and lifespan. It also investigates how the state-of-charge (SOC) operating scope affects battery conduct. In conclusion, it is essential to comprehend the battery life path by concentrating on the distinct traits of the ultra-long usage duration, which displays a non-linear deterioration pattern that differs from the initial usage stage. In this chapter, we propose an electrolyte depletion mechanism to explain the nonlinearity of ultra-long life. While it is still difficult to measure electrolyte depletion in real-time, we model it by intentionally depleting the electrolyte in a new battery. This modeling approach helps explain the phenomena of undershooting and sudden battery discharge during operation. In conclusion, our study integrates the augmented computational efficiency of physics-based models with hands-on trials, providing a more profound understanding of the performance and longevity of lithium-ion batteries. It comprehensively analyzes battery behavior at the pack level and elucidates the abrupt performance degradation stemming from electrolyte depletion. These findings hold significant implications for future research endeavors in this domain, presenting a physical modeling approach that informs battery design, management, and utilization. Keywords: Lithium-ion battery, physics-based model, cycle, calendar, pack system, electrolyte dry-out. Student Number: 2016-20682 환경 보존을 위해 화석 연료에 대한 의존도를 낮춰야 한다는 요구로 인해 역동적인 에너지 환경은 현재 중추적인 변화를 겪고 있습니다. 리튬이온 배터리(LIB)는 에너지 저장 및 운송 분야에서 유망한 대안으로 떠오르며 상당한 탄력을 받고 있습니다. 리튬이온 배터리가 실행 가능한 에너지 솔루션으로 자리 잡기 위해서는 무엇보다도 신뢰성과 수명을 보장하는 것이 중요합니다. 이러한 맥락에서 근본적인 과제는 시간이 지남에 따라 배터리 시스템의 성능 및 성능 저하를 이해하는 것입니다. 기존의 배터리 수명 실험과 관련된 시간과 비용의 제약을 고려할 때, 실험 데이터에만 의존하여 장기적인 배터리 수명을 예측하는 것은 비현실적입니다. 따라서 경험적 실험과 컴퓨팅 모델링을 결합하여 시너지 효과를 낼 수 있는 통합적인 접근 방식이 필요합니다. 배터리 모델링의 영역에는 다양한 방법이 존재하며, 물리 기반 모델은 계산 집약적이기는 하지만 강력한 도구로 각광받고 있습니다. 이러한 모델은 전극 규모에서 발생하는 복잡한 물리적 현상을 깊이 있게 탐구합니다. 이 백서에서는 리튬 이온 배터리의 성능과 수명을 예측하기 위해 설계된 물리 기반 모델을 소개합니다. LER 및 GH-MSMD 모델과 P2D 모델을 융합하면 배터리 분석의 계산 효율을 크게 향상시킬 수 있습니다. 이러한 통합 접근 방식은 복잡한 전기적, 화학적, 열적 상호 작용에서 나타나는 리튬 이온 전지의 핵심 거동을 밝혀냅니다. 또한 배터리 성능과 수명에 영향을 미치는 핵심적인 물리적 현상을 모델링하여 복잡한 시스템을 이해하기 위한 일관된 프레임워크를 구축합니다. 이 통합 모델을 통해 다음과 같은 연구를 진행합니다. 첫째, 기존의 경험적 접근 방식에서 벗어나 주기 및 달력 수명 테스트와 물리 기반 모델을 통합합니다. 이러한 시너지 효과를 내는 접근 방식을 통해 리튬 이온 배터리의 성능과 수명에 영향을 미치는 다각적인 요인을 보다 총체적으로 파악할 수 있습니다. 모델의 정확성은 캘린더 테스트와 6개월에 걸쳐 수행된 1,800회 사이클 테스트의 데이터를 통해 검증되어 실제 배터리 역학과 일치하는지 확인합니다. 둘째, 팩 모델 영역에서는 에너지 저장 시스템(ESS) 팩 성능과 수명에 대한 관점을 소개합니다. 복잡한 다중 셀 시스템을 하나의 대표 셀로 단순화하고 현실적인 전력 주파수를 적용함으로써 배터리 셀 수와 전체 배터리 응답 간의 비선형 관계를 조명합니다. 이 접근 방식은 배터리 성능과 수명에 영향을 미치는 중요한 요소를 조명합니다. 또한 충전 상태(SOC) 작동 범위가 배터리 동작에 미치는 영향에 대해서도 자세히 살펴봅니다. 마지막으로, 초기 사용 단계와 다른 비선형 성능 저하 패턴을 보이는 초 장기 사용 기간의 고유한 특성에 초점을 맞춰 배터리 수명 궤적을 이해하는 것이 중요합니다. 이 장에서는 초장수명의 비선형성을 설명할 수 있는 전해질 고갈 메커니즘을 제안합니다. 전해질 고갈을 실시간으로 측정하는 것은 여전히 어렵지만, 새 배터리의 전해질을 의도적으로 고갈시켜 모델링합니다. 이러한 모델링 접근 방식은 작동 중 회복 현상과 갑작스러운 배터리 방전 현상을 설명하는 데 도움이 됩니다. 요약하자면, 물리 기반 모델의 향상된 계산 효율성과 실증적 테스트를 결합하여 리튬 이온 배터리의 성능과 수명에 대한 심층적인 분석을 제공합니다. 팩 수준에서 배터리 거동을 종합적으로 분석하며, 전해질 고갈로 인한 갑작스러운 성능 저하를 규명합니다. 이러한 연구 결과는 배터리 설계, 관리 및 활용에 정보를 제공하는 물리적 모델링 접근법을 제시함으로써 향후 이 분야의 연구 노력에 중요한 시사점을 제공합니다. 주 요 어: 리튬이온 배터리, 물리 기반 모델, 사이클, 캘린더, 팩 시스템, 전해질 고갈. 학 번: 2016-20682

충전 특성에 의한 리튬이온 배터리의 건강상태 추정

필계개 계명대학원 대학원 2022 국내박사

최근 리튬이온 배터리는 주요 에너지 저장장치로서 지능형 전자기기, 친환경 자동차, 항공우주 등에 널리 사용되고 있다. 리튬이온 배터리는 사용 과정에서 비가역적인 용량 감쇠를 발생시켜 배터리의 건강 상태(SOH)는 점차적으로 악화될 것이다. 리튬이온 배터리가 수명 종료 상태에 도달하고 제때 교체하지 않으면 안전상의 잠재적 위험을 가진다. 배터리의 SOH를 정확하게 추정하는 것은 안전상 매우 중요하다. 이러한 배경을 바탕으로, 본 논문은 전류, 전압, 내부 저항을 포함한 리튬이온 배터리의 충전특성을 연구하여 리튬이온 배터리 SOH와 관련된 예측 특징을 추출하고 리튬이온 배터리 SOH 예측을 목적으로 한다. 이 연구는 주로 네 부분으로 나뉜다. 첫째, 노화된 리튬이온 배터리의 충전특성을 연구하여 예측 특징을 추출한다. 둘째, 공개된 리튬이온 배터리 실험 데이터베이스를 통해 추출된 특징에 의한 SOH 예측 가능성을 확인한다. 셋째, 리튬이온 배터리 노화 실험을 설계하여 실험 데이터를 얻어 추출한 특징으로 SOH의 정확성을 검증한다. 넷째, LSTM (Long Short-Term Memory) 및 TCN (Temporal Convolution Network) 알고리즘의 성능을 비교한다. 구체적인 내용은 다음과 같다. 먼저, 리튬이온 배터리의 정상적인 충전, 방전 데이터만을 사용하여 SOH를 예측할 수 있도록 리튬이온 배터리를 끊임없는 충전, 방전을 통해 노화 시 나타나는 전류, 전압 및 내부 저항 변화를 연구하였다. 그리고 특징 추출을 통해 리튬이온 배터리 SOH 관련 특징 3개를 추출했다. 다음으로, 이미 공개되어 많은 연구자들이 사용하고 있는 NASA 배터리 데이터세트의 리튬이온 배터리 충전 특성에 대한 이론과 실험 검증을 연구하였다. 리튬이온 배터리의 SOH는 물리적 모델 기반 예측 방법 및 데이터에 따라서 처리하는 예측 방법 중 다양한 알고리즘을 사용하여 예측되고 검증하였다. 마지막으로, 배터리 노화 테스트 시스템을 설계하고 구축하였다. 배터리 노화 테스트 시스템은 하드웨어 설계와 LabVIEW를 이용한 모니터링 및 시스템을 제어하는 프로그래밍을 개발하였으며 또한, 실제 실험으로 리튬이온 배터리의 노화 데이터를 얻었다. 실제 실험 데이터를 통해 각각 Nonlinear Least Square (NLS), Bayesian Method (BM), Particle Filter (PF), LSTM, TCN 알고리즘을 사용하여 제안된 3가지 리튬이온 배터리의 예측 특징을 이용하여 리튬이온 배터리의 SOH를 예측하였다. LSTM과 TCN은 각각 순환 신경망(RNN)과 컨볼루션 신경망(CNN)을 기반으로 하는 시계열 딥러닝 네트워크이며, LSTM과 TCN의 서로 다른 두 가지의 딥러닝을 이용해 리튬이온 배터리 SOH 예측 결과의 성능 비교를 수행하였다. 그 결과는 제안된 방법이 예측 정확도가 높다는 것을 보여주었으며, 리튬이온 배터리의 SOH 예측에서 평균 최대 상대오차는 LSTM보다 TCN의 성능이 우수하였다. Lithium-ion batteries have become the primary energy storage devices in intelligent electronic gadgets, new energy vehicles, aircraft, and for other applications in recent years. The lithium-ion battery produces irreversible capacity attenuation during usage. Hence, its state of health (SOH) will deteriorate gradually, which may cause potential safety hazards if the lithium ions approach their end-of-life conditions without timely replacement of the battery. Therefore, it is critical to precisely estimate the battery's SOH for safety reasons. Accordingly, the objective of this work is to investigate the charging properties of lithium-ion batteries, such as current, voltage, and internal resistance, and to extract prediction features related to the battery SOH without direct or difficult measurements of the battery capacity. This research primarily involves four parts: extracting predicted features by studying the charging properties of lithium-ion batteries with degradation, verifying the possibility of SOH prediction from the extracted features through a public experimental database, designing a lithium-ion battery degradation test system to obtain battery degradation data to verify the accuracy of the extracted features in predicting SOH, and comparing the performance of long short-term memory (LSTM) and temporal convolution network (TCN) algorithms. First, the study investigates changes in current, voltage, and internal resistance of a lithium-ion battery with continuous degradation. Through feature extraction, three features that can reflect the SOH of the lithium-ion battery are extracted. The SOH of the battery can then be predicted using only the normal charge and discharge data. Second, theoretical and experimental verifications are performed for the three proposed charging features using the lithium-ion battery charging and discharging experimental data from the NASA battery dataset, which has been investigated and used by many battery researchers. The SOH of the lithium-ion battery is then predicted and validated using algorithms for both physical model based and data-driven approaches. Finally, a battery degradation test system is designed and built, including hardware design and programming using LabVIEW, to control and monitor the system. The lithium-ion battery degradation data are obtained by practical experiments. Then, the nonlinear least-squares (NLS), Bayesian method (BM), particle filter (PF), LSTM, and TCN algorithms are used to estimate the SOH of the battery using the three charging features. Moreover, two separate time-series deep-learning architectures are used to predict the SOH and compare the estimated results. These results demonstrate that the suggested method has high predictability and that the TCN outperforms the LSTM in terms of the average maximum relative error for lithium-ion battery SOH estimation.

Design, Synthesis, and Electrochemical Study of Novel Fluorosulfonyl Imide Based Electrolytes for Lithium-Ion Batteries

Ahmed, Faiz 건국대학교 대학원 2020 국내박사

The researches conducted during this Ph.D. thesis aimed to develop a wide range of imide-based electrolytes for aqueous, non-aqueous, and solid state Li-ion batteries. In the chapter 1, we described the fundamentals of different electrolyte materials and their performaneces in Li-ion battery applications. Novel electrolytes with wide electrochemical potential window and high thermal stability have great potential for aqueous rechargeable lithium-ion batteries (ARLBs). In the chapter 2, we report the synthesis of two ionic salts of lithium sulfonylbis(fluorosulfonyl)imide (LiSFSI) and lithium carbonylbis(fluorosulfonyl)imide (LiCFSI) with divalent Li+ for ARLBs. These ionic compounds are the derivatives of monovalent lithium bis(fluorosulfonyl)imide (LiFSI). The LiSFSI and LiCFSI exhibit the kinetic electrochemical stability window of ca. 3.78 and 3.52 V, respectively, which can be further expanded due to the formation of a stable solid electrolyte interface (SEI) layer. While LiFSI exhibits the kinetic electrochemical stability window of ca. 2.22 V without the formation of an SEI layer. Full ARLBs based on LiSFSI and LiCFSI electrolytes with a LiCoO2 cathode and graphite anode can deliver the specific discharge capacity of ca. 113.50 and 95.0 mAh/g, respectively, at 0.1 C rate. Whereas, it is ca. 52.53 mAh/g for LiFSI at 0.1 C rate. The capacity retention for LiSFSI, LiCFSI, and LiFSI based ARLBs are ca. 97.3, 89.6, and 67.8%, respectively, after 500 cycles. Furthermore, both LiSFSI and LiCFSI reveal much higher thermal stability compared to LiFSI. Thus, the derivatization of conventional ionic compounds is an effective strategy to enhance the battery performance and its lifetime. Imide-based electrolyte salts are crucial in lithium-ion battery (LIB) research, due to their high oxidative capacity, thermal performance, and cycling stability. LIBs with imide electrolytes exhibit slow charge-discharge (CD) capacity and high efficiency, even though most of these electrolytes show low ionic conductivity (). In the chapter 3, we synthesize two highly conductive and pure divalent imide electrolytes, lithium sulfonylbis(fluorosulfonyl)imide (LiSFSI) and lithium (1,3-phenylenedisulfonyl)bis(fluoro sulfonyl)imide (LiPDSFSI), for LIBs application. Compared to LiPDSFSI electrolyte, the LiSFSI imide electrolyte with mixed solvent ethylene carbonate (EC) and dimethyl sulfoxide (DMSO) (75:25 v/v) exhibits better electrochemical stability, , transference number (tL+), cycling stability, and high specific capacity of 142 mAhg-1 with the full cell battery configuration of LiFePO4/electrolytes/graphite at 0.1 C. Additionally, lithium bis(fluoro-sulfonyl)imide (LiFSI) (20%), as additive, improve their performance substantially. The results demonstrate that the LiSFSI electrolyte with LiFSI additive shows maximum  (8.9 mS/cm at 30 ºC), tL+ (0.64), and anodic stability (5.47 V), which concurrently delivers high efficiency and improves specific capacity to 156 mAhg-1 with excellent capacity retention (99.93%) after 500 CD cycles with the full cell LiFePO4/electrolytes/graphite battery system. In the chapter 4, we report the synthesis of a novel imidazolium-based ionic salt, lithium (fluorosulfonyl)((3-(1-methyl-1H-imidazol-3-ium-3-yl)propyl)sulfonyl) bis(fluorosulfonyl)imide (LiFSMIPFSI) as an electrolyte for the application in lithium-ion battery (LIB). The as-synthesized LiFSMIPFSI exhibited high purity and yield, which was characterized by various spectroscopic techniques. The LiFSMIPFSI electrolyte with a mixed solvent of ethylene carbonate (EC) and dimethyl sulfoxide (DMSO) (75:25 v/v) showed a high oxidative stability (ca. 4.6 V vs. Li/Li+) and high thermal stability (240 ºC), good Li+ conductivity (ca. 8.02 mS/cm at 30 ºC), and low viscosity, which concurrently delivered a specific discharge capacity of ca. 125 mAhg-1 at 0.1 C with the full LIB configuration of LiFePO4/electrolytes/graphite. The performance of this LiFSMIPFSI electrolyte was enhanced further by the addition of conventional lithium bis(fluoro-sulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) ionic salts (20% each) as additives with the discharge specific of ca. 147 and 139 mAhg-1, respectively, at 0.1 C. This is mainly due to the additional enhancement of Li+ conductivity and transference number induced by the additives. The LiFSMIPFSI electrolyte with LiFSI additive based LIB showed the highest cycling stability (capacity retention ca. 97%) among the electrolytes after 500 charge-discharge cycles. Thus, the present work contributes to the development of new ionic salt and its effects upon the addition of additives on LIB performance. In the chapter 5, this research demonstrates the synthesis of an imidazolium functionalized imide based electrolyte salt, lithium (fluorosulfonyl)((3-(1-methyl-1H-imidazol-3-ium-3-yl)propyl)sulfonyl)imide) bis(trifluorosulfonyl)imide (LiFSMIPTFSI) for the development of lithium-ion battery (LIB). The LiFSMIPTFSI electrolyte with a mix-solvent of ethylene carbonate (EC) and dimethyl sulfoxide (DMSO) (75:25 v/v) shows high electrochemical oxidative stability (up to 5.3 V vs. Li/Li+), good Li+ conductivity (ca. 6.10 mS/cm at 30 ºC) and transference number (ca. 0.55), and low viscosity, which concurrently provide a specific capacity of ca. 141 mAhg-1 at 0.1 C with a full LIB structure of LiFePO4/LiFSMIPTFSI/graphite. The electrochemical performance of this electrolyte is enhancing additionally by adding conventional imide salts (lithium bis(fluoro-sulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI)) (20% each) as additives with the specific capacity of ca. 160 and 150 mAhg-1, respectively, at 0.1 C. This is mainly due to the additional enhancement of Li+ conductivity and transference number of the LiFSMIPTFSI electrolyte induce by the additives. The LiFSMIPTFSI electrolyte with LiFSI additive based LIB shows the maximum capacity retention of ca. 95.50% among the electrolytes after 500 charge-discharge cycles, along with high coulombic efficiency (98.50%). Single-ion conducting polymer electrolyte (SICPE) is a safer alternative to the conventional high-performance liquid electrolyte for Li-ion batteries. The performance of SICPEs based Li-ion batteries is limited due to the low Li+ conductivities of SICPEs at room temperature. In the chapter 6, we demonstrated the synthesis of a novel SICPE, poly (ethylene-co-acrylic lithium (fluoro sulfonyl)imide) (PEALiFSI) with acrylic (fluoro sulfonyl)imide) anion (AFSI). The solvent and plasticizer-free PEALiFSI electrolyte, which was assembled at 90 ºC under pressure, exhibited self-healing properties with remarkably high Li+ conductivity (5.84×10-4 S/cm at 25 ºC). This is mainly due to the self-healing behavior of this electrolyte, which induced to increase the proportion of the amorphous phase. Additionally, the weak interaction of Li+ with the resonance stabilized AFSI anion is also responsible for high Li+ conductivity. This self-healed SICPE showed high Li+ transference number (ca. 0.91), flame and heat retardancy, and good thermal stability, which concurrently delivered ca. 88.25% (150 mAh/g at 0.1 C) of the theoretical capacitance of LiFePO4 cathode material at 25 ºC with the full cell configuration of LiFePO4/PEALiFSI/graphite. Furthermore, the self-healed PEALiFSI based all-solid-state Li-battery showed high electrochemical cycling stability with the capacity retention of 95% after 500 charge-discharge cycles. Finally, in chapter 7, we briefly described the conclusions together with the outlooks. 박사과정 졸업 논문에 수록된 연구들은 이미드구조를 기반으로 리튬이온 전지의 수계, 비수계 및 고체 고분자 전해질의 개발을 목표로 하였다. 제 1장에서는 리튬이온 배터리응용 분야에서 다양한 전해질 재료의 기초와 성능에 대해 설명하였다. 넓은 범위의 전위창과 높은 열적안정성을 갖춘 새로운 전해질은 수계 충전식 리튬배터리용으로 큰 잠재적 가치를 갖고 있다. 제 2장에서는 두개의 리튬이온을 가진 LiSFSI 와 LiCFSI의 두 이온염의 합성에 대해 수행하였다. 이 이온 화합물들은 단일 LiFSI염에서 온 파생물이다. LiSFSI와 LiCFSI는 안정적인 SEI층 형성에 의해 더욱 높은 안정성을 가질 수 있어 약 3.78, 3.52 V의 산화-환원 전압 범위를 보였다. 반면 LiFSI는 SEI층이 없기 때문에 약 2.2 V의 산화-환원 전압 범위를 보였다. LiCoO2 음극, Graphite양극, LiSFSI와 LiCFSI 전해질을 기반으로 한 ARLBs Full cell은 0.1 C에서 약 113.50, 95.0 mAh/g의 방전 용량을 가졌다. 반면, LiFSI의 경우 0.1C에서 약 52.53 mAh/g의 방전 용량을 가졌다. LiFSI, LiCFSI, LiFSI을 기반으로 한 ARLBs는 500번 충방전 이후 잔류용량은 약 97.3, 89.6, 67.8%였다. 또한, LiSFSI와 LiCFSI는 LiFSI에 비해 훨씬 높은 열적 안정성을 보였다. 따라서 LiSFSI와 LiCFSI는 배터리의 성능과 수명을 향상시키기 위한 효과적인 방법이다. 이미드 기반 전해질 염은 높은 충방전 용량, 열적 안정성, 사이클 안정성 때문에 lithium-ion battery (LIB)연구에서 매우 중요하다. 이미드기반 전해질은 대부분 이온 전도성(σ)이 낮지만 방전이 천천히 진행되고 높은 효율을 나타낸다. 제 3장에서는 LIBs에 적용할 전도도가 높고 두개의 리튬염을 가진 고순도의 LiSFSI와 LiPDSFSI 두가지를 합성했다. LiPDSFSI 전해질에 비해 EC와 DMSO(75:25 v/v)혼합 용매에 포함된 LiSFSI 이미드 전해질은 LiFPO4/electrolytes/graphite로 구성된 Full cell에서 0.1 C조건하에 전기화학적 안정성, 전도도, transference number(tL+), 사이클 안정성, 142 mAhg-1의 높은 방전 용량을 보여준다. 또한 첨가제로서 LiFSI(20%)를 사용하면 성능을 매우 향상시킨다. LiFPO4/electrolytes/graphite로 구성된 Full cell에서 LiFSI가 첨가된 LiSFSI전해질은 전도도가 최대 30 ºC에서 8.9 mS/cm, tL+의 경우 0.64, 5.47 V의 산화 안정성을 입증하고, 동시에 156 mAhg-1 의 용량 향상과 500싸이클 이후 99.93%의 충방전용량 유지율을 보여준다. 제 4장에서는 리튬이온 배터리용 새로운 이미다졸륨계 이온염인 LiFSMIPFSI 전해질의 합성을 보여준다. 합성된 LiFSMIPFSI는 높은 순도와 수율을 보였으며, 이는 다양한 분광기법으로 분석되었다. EC와 DMSO(75:25 v/v)의 혼합용액을 용매로 사용한 LiFSMIPFSI 전해질은 높은 산화 안정성(약 4.6 V vs. Li/Li+), 높은 열적 안정성(240 ºC), 좋은 이온전도도(30 ºC에서 약 8.02 mS/cm), 낮은 점도를 보였다. LiFPO4/electrolytes/graphite로 구성된 Full cell에서 0.1 C에서 약 125 mAhg-1의 방전용량을 나타냈다. 이 LiFSMIPFSI 전해질에 LiFSI와 LiTFSI 이온염을(각 20%) 첨가해 0.1 C에서 약 147, 139 mAhg-1으로 성능이 향상되었다. 이는 주로 첨가제에 의해 나타나는 이온 전도도와 transference number 향상 때문이다. LiFSI 첨가한 LiFSMIPFSI 전해질은 500회 충방전 후 가장 높은 사이클링 안정성을 보여준다(용량 유지율 약 97%). 따라서 이 연구는 새로운 이온염의 개발과 LIB 성능에서 첨가제의 효과에 대해 기여한다. 제 5장에서는, 이 연구는 리튬 이온 배터리의 개발을 위해 이미드 작용기를 가진 이미다졸륨 기반 전해질 LiFSMIPTFSI의 합성을 입증한다. EC와 DMSO(75:25 v/v)의 혼합 용액을 용매로 사용한 LiFSMIPTFSI 전해질은 높은 산화 안정성 (최대 5.3 V vs. Li/Li+), 좋은 이온 전도도 (30 ºC에서 약 6.10 mS/cm) 및 transference number (약 0.55) 및 낮은 점도를 보이고 동시에 LiFPO4/electrolytes/graphite로 구성된 Full cell에서 0.1 C에서 약 141 mAhg-1의 방전용량을 나타냈다. LiFSI와 LiTFSI(각각 20%)를 첨가하여 이 전해질의 전기화학적 성능은 0.1 C에서 약 160, 150 mAhg-1로 향상되었다. 이는 주로 첨가제에 의해 나타나는 LiFSMIPTFSI 전해질의 이온 전도도와 transference number가 향상되었기 때문이다. LiFSI를 첨가한 LiFSMIPTFSI 전해질은 500번 충방전 후 최대 약 95.50%의 용량 유지율과 높은 쿨롱효율 (약 98.50%)을 보여준다. Single Ion Conducting Polymer Electrolyte(SICPE)는 Li-ion 배터리에서 액체 전해질에 대한 안전한 대안이지만, 상온에서 이온전도도가 낮기 때문에 제한적이다. 제 6장에서는, 새로운 SICPE인 AFSI음이온을 가지는 PEALiFSI의 합성에 대해 입증하였다. 압력하에 90 ºC 조건에서 만들어진 용매와 가소제가 없는 PEALiFSI 전해질은 현저하게 높은 이온 전도도(25 ºC에서 5.84×10-4 S/cm)와 자가치유 특성을보였다. 이는 비정질의 비율을 증가시키는 전해질의 자가치유능력 때문이다. 또한 공명으로 안정화된 AFSI 음이온과 Li+ 의 약한 상호작용 또한 이온 전도도를 높여줍니다. 이 자가치유 SICPE는 LiFePO4/PEALiFSI/graphite로 구성된 Full cell은 25 ºC에서 0.1 C일 때 약 150 mAhg-1를 가지면서 높은 Li+ transference number (약 0.91), 난연성과 내열성, 좋은 열적안정성을 보여주었다. 또한 자가치유 SICPE는 500번 충방전 사이클 후 95%의 용량 유지율과 높은 산화-환원 안정성을 보였다. 마지막으로 제 7장에서는 그 결론에 대해 전망과 함께 간략하게 설명하였다.

고분자 전해질연료전지 및 리튬이온 전지 하이브리드 파워시스템 성능 향상을 위한 모델링 및 제어 연구

왕아웅 전남대학교 2015 국내박사

Hybrid polymer electrolyte membrane (PEMFC)/lithium-ion battery power systems have recently attracted attentions from both academia and industry. These systems have maintained the benefit of each PEMFC and battery advantages, and at the same time, have eliminated independent system disadvantage. In the hybrid structure, PEMFC serves as a main power source, and lithium-ion battery functions as an energy storage (ES) system. However, PEMFC is an opening system which needs balance-of-plant (BOP) such as air blower, cooling fan, and humidifier, to provide normal operation condition. Meanwhile, a PEMFC-based hybrid system power management also requires control proper energy distributions from each power source. In order to efficiently use the hybrid PEMFC/lithium-ion battery power system, the following components are needed, PEMFC independent system BOP electrical control unit (ECU), and power control unit (PCU) for hybrid PEMFC/lithium-ion battery system. To develop ECU and PCU of a hybrid PEMFC-based system, control-oriented models of PEMFC are primarily required. A PEMFC system model is composed of three parts: static characteristics, dynamics response model, and BOP auxiliary system model. In this study, static characteristics of the PEMFC model are obtained based on the empirical identification methods. The developed dynamics model is based on two main approaches: two-phase reactants thermodynamics principles, and simplified electrical equivalent circuit with varied double layer capacitor effects, where the first method is used for PEMFC independent system control, and the second one is for hybrid system regulations. Subsequently, PEMFC BOP, which consists of air supply system, cooling system, hydrogen feeding system, and humidifier, is controlled. Among the mentioned subsystems, air flow regulation is considered in this study, since the oxygen excess ratio is the most crucial factor for protecting PEMFC and improving efficiency, i.e., preventing PEMFC from oxygen starvation that may cause PEMFC performance degradation, or even damaging. In addition, optimizing the oxygen excess ratio can obtain maximum net power as it affects stack power and parasitic power consumed by BOP. Control methods including conventional proportional-integral (PI) control, model predictive control (MPC), and time delay control (TDC), are developed, and their performance compared in terms of regulating air flow. The experimental validation shows that MPC and TDC are suitable to manipulate air blower. Furthermore, voltage and/or current regulation and power management are extremely important in operating the hybrid system with high efficiency and in providing satisfactory power delivery for subsequent motor systems (e.g., feeding inverter with constant bus voltage). This study develops a new methodology of voltage and/or current control and power management based on TDC for hybrid PEMFC/battery power systems. First, PEMFC-fed DC?DC boost converter system, lithium-ion battery-supplied bidirectional DC?DC converter, and hybrid PEMFC/lithium-ion battery power system are designed and controlled in simulations and experiments. Moreover, three control methods of dual-voltage control, coordinated current-voltage control, and fast current-voltage control, are introduced based on TDC to implement and maintain constant bus voltage and current. The effects are compared with energy management rules by considering PEMFC efficiency, PEMFC and battery currents stresses. Finally, a hybrid PEMFC/lithium-ion battery power system prototype is constructed and tested to validate the proposed power management approaches.