고에너지 밀도 리튬이온전지의 신뢰성 및 안전성 확보를 위한 다기능 세라믹 코팅 분리막

Lithium secondary battery; Separator; Ceramic-coated separator; High energy density; Safety; Thermal stability; Functional separatorLithium-ion batteries (LIBs) are used in everyday applications such as portable electronics and electric vehicles (EVs) in our daily life. Securing battery safety becomes extremely challenging as densifying the cell energy and increasing the battery. The safety of batteries must be guaranteed from the cell to the module, the pack, and the system, and it must not be ignored at every step. The separator is highlighted at the cell level as it plays an essential part in safety. To guarantee the safety of large-scale LIBs, it is essential to employ a ceramic-coated separator (CCS). However, an additional ceramic coating layer (CCL) inevitably leads to energy density loss and electrochemical performance degradation. This thesis reports multi-functional ceramic-coated separator for securing the reliability and safety of higher-energy-density LIBs. The first part of thesis refers to the research on ceramic materials used in CCS. This is a basic research that can help select ceramic materials with the purpose. Second, I treated the surface of ceramic particles with a polydopamine (PD) nanolayer using a simple solution polymerization method. Then, a poly(acrylic acid) binder can react with the amine group in the PD and is selected as an aqueous ceramic-coated slurry, which creates many crosslinking points within the CCL, thereby leading to higher adhesion within the CCL even after electrolyte impregnation. As a result, the cross-linked PD ceramic-coated separator can maintain its original dimension even at 160 °C for 1 h with a 9-μm polyethylene base film. Finally, I developed a functional flame-retardant and ceramic-coated separator (F-CCS) that enhances safety features while maintaining optimal performance. The F-CCS incorporates an encapsulated flame retardant and a hydroxide ceramic, namely AlOOH, to achieve flame retardancy. These findings present a promising solution for enhancing the safety and reliability of LIBs, particularly in high-energy-density applications, thereby paving the way for their wider implementation. |Lithium ion battery(LIB)에 사용되는 분리막 소재인 polyethylene(PE)은 낮은 내열성을 갖고 있어 이를 보완하고자 원단 표면에 ceramic coating layer (CCL)을 도입한 ceramic coated separator(CCS)가 개발되었다. CCS는 고온에 노출되어도 높은 내열성을 갖는 CCL가 내부 원단의 열수축을 억제하여 전지의 안전성 확보에 기여한다. 그러나, 원단에 부가적으로 도입된 CCL은 LIB의 에너지 밀도 손실과 CCL 내 포함된 바인더가 저항체로 작용하여 전지 성능 저하를 불러온다. 최근 LIB의 적용 분야가 넓어진 만큼 전지의 안전성은 소비자의 보호를 위해 필수적이며, 분리막 개발에 있어서 안전성과 고에너지밀도를 모두 확보해야만 한다. 하지만, 우수한 내열성을 만족하는 동시에 고에너지밀도를 위한 얇은 두께를 만족하기는 매우 어려우며, 이를 만족하더라도 높은 소재 단가 및 복잡한 공정으로 인한 양산불가의 문제로 인해 상용화에 난항을 겪고 있다. 본 논문에서는 LIB에 적합하며 상용화 가능성을 고려한 기능성 세라믹 코팅 분리막에 대한 연구를 제안한다. 첫째, 세라믹 소재의 특징에 따른 세라믹 코팅 분리막의 물성 변화를 분석하고, 난연성을 갖는 수산화계 세라믹의 자기소화 특성에 대하여 소개한다. 이에 따라 전지의 목적에 따른 세라믹 입자 선택에 대한 방향성을 제공한다. 둘째, 세라믹 코팅층의 내열성을 상승시킬 수 있는 방법으로 세라믹 표면을 화학적으로 개질하여, 건조 공정 중 세라믹 표면과 바인더와 화학적 가교 반응을 일으켰다. 가교된 CCS는 코팅층 내부 물성이 향상되었으며, 가교되지 않은 CCS에 비하여 동일한 무게, 두께에서 높은 고온에서도 열 안정성이 우수함을 보여준다. 이 연구는 CCL 내부의 가교를 통하여 에너지밀도를 감소시키지 않으며 전지의 안전성을 향상시킬 수 있는 방안을 제안한다. 마지막으로 난연제를 캡슐화하여 세라믹과 함께 분리막에 코팅, 기능성 코팅 분리막을 제조했다. 캡슐화된 난연제는 LIB 구동환경에서 분해되지 않으며, 특정 온도에서 내부의 난연제가 용출되어 화재를 진압했다. 기능성 코팅 분리막은 기존 CCS와 동등한 이온전도 특성 및 출력특성을 보이며, 실제 점화실험을 통해 기능성 분리막이 자기소화특성을 갖고, 점화 이후 난연 보호막을 형성하는 것을 확인했다. 이 연구는 화재 시 연소되지 않는 난연 분리막을 통해 전지의 안전성을 극대화할 수 있는 방안을 제시하였다.Ⅰ. Introduction 1 1.1 Introduction to separators for lithium-ion batteries 1 1.2 Challenge issues of ceramic-coated separators 2 1.3 Research goals 4 1.4 Reference 6 Ⅱ. Physical and Electrochemical Properties of Ceramic-Coated Separators with Different Ceramic Types for Lithium-Ion Batteries 8 2.1 Introduction 8 2.2 Experimental Section 10 2.2.1 Separator and cell assembly 10 2.2.2 Separator characterization 11 2.2.3 Electrochemical characterization 12 2.3 Results and discussion 14 2.4 Conclusion 20 2.5 Reference 21 Ⅲ. Highly improved thermal stability of the ceramic coating layer on the polyethylene separator via chemical crosslinking between ceramic particles and polymeric binders 23 3.1 Introduction 23 3.2 Experimental Section/Methods 26 3.2.1 Materials 26 3.2.2 Fabrication and characterization of the PD-treated ceramic particles 26 3.2.3 Preparation and characterization of the ceramic-coated PE separators 26 3.2.4. Adhesion measurements using a peel tester and a SAICAS 27 3.2.5. Cell assembly and electrochemical analysis 27 3.3 Results & discussion 29 3.4 Conclusion 41 3.5 Reference 42 Ⅳ. Enhanced safety of lithium ion batteries through a novel functional separator with encapsulated flame retardant and hydroxide ceramics 44 4.1 Introduction 44 4.2 Experimental Section 46 4.2.1 Materials 46 4.2.2 Preparation of Microcapsules 46 4.2.3 Fabrication of functional flame retardant and ceramic-coated separator (F-CCS) 46 4.2.4. Characterization of F-CCS 47 4.2.5. Electrode preparation 47 4.2.6. Electrochemical analysis 48 4.2.7. Flame retardant test 48 4.3 Results and discussion 49 4.4 Conclusion 61 4.5 Reference 62 Summary in Korean 65DoctordCollectio

Toward understanding the real mechanical robustness of composite electrode impregnated with a liquid electrolyte

The mechanical robustness of highly loaded composite electrodes is important for ensuring the long-term reliability of high-energy-density secondary batteries. Considering that in real state, the electrodes in batteries are completely impregnated with electrolyte, the swelling of the polymeric binder must be carefully observed and controlled to maintain the electric connectivity within the electrode. However, the decrease in the cohesion/adhesion of electrodes caused by electrolyte impregnation has not been directly measured due to the absence of appropriate tools. Here, the surface and interfacial cutting analysis system and a specifically designed sample holder are well combined to realize this breakthrough measurement. When electrode is impregnated with a liquid electrolyte, not only the 12% increase in electrode thickness but also the greater than 74% decrease in cohesion/adhesion, which is caused by the swelling of the amorphous phase of the polymeric binders, is clearly observed. The large decrease in cohesion/adhesion can be greatly ameliorated by controlling both the degree of crystallinity and crystallite size of the polymeric binder through a simple annealing process. Thus, it believes that the measurement of the real cohesion and adhesion of composite electrodes can provide an innovative and practical way to secure the reliability of high-energy-density batteries. © 2020 Elsevier Ltd1

Robust Cycling of Ultrathin Li Metal Enabled by Nitrate-Preplanted Li Powder Composite

Making Li metal batteries (LMBs) with thinner Li is necessary to improve the cell energy density in practice. Li metal powders (LMPs) are beneficial for the facile manufacturing of thin Li, flexible cell design, and the 3D control of Li plating/stripping. However, the inhomogeneous surfaces of commercial LMPs limit their practical use in LMBs. Herein, a 20 mu m-thick, LiNO3 preplanted LMP (LN-LMP) composite electrode, rationally designed for LMP surface stabilization, is presented. The addition of LiNO3 into the slurry uniformly modified the LMP surface by N-rich solid-electrolyte interphase (SEI). Preplanted LiNO3 further acts as a reservoir for the sustainable release into the electrolyte, thereby repairing the SEI upon cycling. The LMBs with LN-LMP exhibited excellent cycling performances (450 cycles at 87.3% retention) compared to the control cells, and even outperformed the cells with LiNO3-containing electrolytes. Further verification with high loading of a LiNixMnyCo1-x-yO2 (NMC) cathode demonstrated the feasibility of the practical cells and the versatility of the thin, LN-LMP anode combined with advanced electrolytes.1

Mechanical robustness of composite electrode for lithium ion battery: Insight into entanglement & crystallinity of polymeric binder

To investigate the correlation between the molecular weight of the polymeric binder in Li-ion battery electrodes and their adhesion properties, polyvinylidene fluoride (PVdF) with three different molecular weights of 500,000, 630,000, and 1,000,000 are selected for LiCoO2 electrode fabrication. Using a surface and interfacial cutting analysis system, it is observed that, as the molecular weight of the PVdF increases, the adhesion strength not only in the electrode composite, but also at the electrode/current collector interface increases. This enhancement can be attributed to the increased polymeric chain entanglement and higher crystallinity of PVdF with higher molecular weight, which is confirmed using a microfluidic viscometer and differential scanning calorimeter, respectively. In summary, regardless of slightly higher electrode resistance, the LiCoO2 electrode with a PVdF binder of high molecular weight shows better electrochemical performance during cycling test even at 60 °C due to its stable mechanical integrity. © 2019 Elsevier Ltd1

Design of Thin-Film Interlayer between Silicon Electrode and Current Collector Using a Chemo-Mechanical Degradation Model

To enhance delamination limitations in silicon electrode, a thin-film interlayer between silicon electrode and copper current collector is designed using a chemo-mechanical degradation model. The chemo-mechanical degradation model considers the formation of the solid electrolyte interphase on the surface and within the cracks of the silicon electrode, the physical isolation of active materials and the resistance due to loss of contact between the silicon composite electrode and the copper foil as the main capacity fading mechanisms. The model is validated with experimental data collected from coin cells made of silicon electrode with a bare and an adhesive thin film laminated copper foil. The reduction in the delamination limitations depends on the interplay of the adhesion strength, conductivity, coverage and thickness of adhesive thin film on the surface of the copper foil. © 2020 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.1

Time‐Effective Accelerated Cyclic Aging Analysis of Lithium‐Ion Batteries

We propose a time-effective framework for accelerated cyclic aging analysis of lithium-ion batteries. The proposed framework involves the coupling of a physico-chemical capacity-fade model that considers the cyclic aging mechanisms of the LiMn2O4/graphite cell, with a physics-based porous-composite electrode model to predict cycling performance at different temperatures. A one-dimensional simple empirical life model is then developed from the coupled physico-chemical capacity-fade model and the physics-based porous-composite electrode model predictions. An accelerated cyclic aging analysis based on the principle of time-temperature superposition is performed using the developed one-dimensional simple life empirical model. The proposed framework is used to predict the maximum number of cycles and the highest temperature required for accelerated cyclic aging analysis of LiMn2O4/graphite cells. The efficacy of the proposed framework is validated with experimental cycle-performance data obtained from LiMn2O4/graphite coin cells at 25 and 60 °C. © 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim1

Ultra-thin ceramic coated separator for high energy density lithium-ion battery:In-depth analysis on Al2O3 nano particles penetration into the structure pore

The energy density and power of lithium-ion batteries (LIBs) are undoubtedly essential to fuel the satisfying pursuit of next-generation energy storage systems. However, to ensure the safety of LIBs, a micrometer-thick ceramic coating layer (CCL) is coated on the separator by a conventional slurry process, which reduces the energy density and performance of LIBs. For this purpose, a ceramic-coated separator (CCS) fabricated by sputtering has attracted attention because it can secure thermal stability and performance while minimizing the CCL thickness to nanometers. Nevertheless, the analysis of why a CCL with only nanometer thickness could improve the properties of the separator still needs to be investigated. Theoretically, it could be suggested that sputtered nano ceramic particles could penetrate the internal micropore structure of the separator, but no experiments were conducted to identify this. In this study, depth profiling using time-of-flight secondary ion mass spectrometry was conducted to confirm the distribution of sputtered nano ceramic particles in the internal structure of the separator depending on the porosity. The surface composition of the separator changed by the plasma generated during the sputtering process was observed by X-ray photoelectron spectroscopy. In addition, to investigate the effect of the nm-CCL on the properties and electrochemical performance of the separator, we compared it with commercial slurry CCS and single/double-sided ceramic sputtering samples. © 2023 The Korean Society of Industrial and Engineering ChemistryFALS

Crosslinkable polyhedral silsesquioxane-based ceramic-coated separators for Li-ion batteries

Inorganic polyhedral oligomeric silsesquioxane with epoxy functional groups (ePOSS) is newly presented as a co-binder for the ceramic-coated separator (CCS) for safe Li-ion batteries. The ePOSS-incorporated coating layer significantly improved the dimensional stability of the CCS at 140 °C and maintained the original form even after an ignition test. Although the permeability of the CCS was slightly decreased due to the crosslinked structure of the silsesquioxane coating layer, it showed high electrochemical stability up to 5 V. Moreover, the improved liquid electrolyte wettability by ePOSS co-binder enhanced the ionic conductivity and showed 93% of cycle capacity at 0.5C rate in Li-ion batteries. © 2018 The Korean Society of Industrial and Engineering Chemistry1

Separator Dependency on Cycling Stability of Lithium Metal Batteries Under Practical Conditions

Development of practical lithium (Li) metal batteries (LMBs) remains challenging despite promises of Li metal anodes (LMAs), owing to Li dendrite formation and highly reactive surface nature. Polyolefin separators used in LMBs may undergo severe mechanical and chemical deterioration when contacting with LMAs. To identify the best polyolefin separator for LMBs, this study investigated the separator-deterministic cycling stability of LMBs under practical conditions, and redefined the key influencing factors, including pore structure, mechanical stability, and chemical affinity, using 12 different commercial separators, including polyethylene (PE), polypropylene (PP), and coated separators. At extreme compression triggered by LMA swelling, isotropic stress release by balancing the machine direction and transverse direction tensile strengths was found to be crucial for mitigating cell short-circuiting. Instead of PP separators, a PE separator that possesses a high elastic modulus and a highly connected pore structure can uniformly regulate LMA swelling. The ceramic coating reinforced short-circuiting resistance, while the cycling efficiency degraded rapidly owing to the detrimental interactions between ceramics and LMAs. This study identified the design principle of separators for practical LMBs with respect to mechanical stability and chemical affinity toward LMAs by elucidating the impacts of separator modification on the cycling performance.FALS

Highly improved thermal stability of the ceramic coating layer on the polyethylene separator via chemical crosslinking between ceramic particles and polymeric binders

The ceramic coating layer (CCL) on a polyolefin separator plays a pivotal role in securing the safety of lithium-ion batteries (LIBs) by suppressing the thermal shrinkage of the separator even under abnormal circumstances. However, an additional CCL inevitably leads to energy density loss and electrochemical performance degradation. To mitigate these weaknesses, we designed a new chemical crosslinking between ceramic particles and polymeric binders to minimize the thickness of the CCL while maintaining its thermal stability. For this purpose, a polydopamine (PD) nanolayer is preliminarily introduced on the surface of ceramic particles using a simple solution polymerization method. Then, a poly(acrylic acid) binder, which can react with the amine groups in the PD, is chosen for the aqueous ceramic coating slurry. Thus, this combination can create a number of crosslinking points within the CCL, which leads to higher adhesion within the CCL after electrolyte impregnation. As a result, the crosslinked PD ceramic-coated separator (xPD-CCS) can maintain its original dimension even at 160 °C for 1 h with a 9-μm polyethylene base film. In addition, a full cell (LiNi0.8Co0.1Mn0.1O2/graphite) with the xPD-CCS can show a comparable cycle performance (capacity retention of 89.2% after 400 cycles) to those of bare polyethylene and non-crosslinked PD-CCS cases. © 2022 Elsevier B.V.1