박막 리튬 금속 분말 음극의 전기전도성 네트워크 및 계면 설계

Li metal powder; Li metal batteries; Li dendrites; Dead Li; Solid electrolyte interphase; Conductive networks; Lithium nitrideI. Introduction 1 1.1 Introduction to lithium metal batteries 1 1.2 Challenges of lithium metal batteries 3 1.2.1 Lithium dendrites and dead Li 3 1.2.2 Volume expansion 4 1.3 Strategies to solve the challenging issues of the Li metal anode 5 1.3.1 Solid electrolyte interphase (SEI) 5 1.3.2 Increasing the surface area of the anode 5 1.4 Research objectives and outline 7 1.5 References 9 II. Screening of conductive agents for Li powder composite anode 14 2.1 Background of research 14 2.2 Experimental section 15 2.2.1 Materials 15 2.2.2 Electrode preparation 15 2.2.3 Cell assembly 16 2.2.4 Electrochemical analysis and characterization 16 2.3 Results and discussion 17 2.4 Conclusion 24 2.5 References 25 III. Bifunctional role of carbon nanotubes within Li powder composite anode 28 3.1 Introduction 28 3.2 Experimental section 30 3.2.1 Materials 30 3.2.2 Electrode preparation 30 3.2.3 Cell assembly 30 3.2.4 Electrochemical analysis 31 3.2.5 Characterization and post-mortem analysis 31 3.3 Results and discussion 33 3.4 Conclusion 46 3.5 References 47 IV. Artificial Li3N SEI for stable cycling of Li powder anode in carbonate electrolytes 51 4.1 Introduction 51 4.2 Experimental section 54 4.2.1 Materials 54 4.2.2 Copper hydroxide/nitride nanowires preparation 54 4.2.3 Electrode preparation 55 4.2.4 Copper nitride nanowires-printed LMP preparation 55 4.2.5 Materials characterization and post-mortem analysis 55 4.2.6 Cell assembly 56 4.2.7 Electrochemical analysis 56 4.3 Results and discussion 58 4.4 Conclusion 74 4.5 References 75 Summary in Korean 81DoctordCollectio

A Review on Ultrathin Ceramic-Coated Separators for Lithium Secondary Batteries using Deposition Processes

리튬이온전지의 에너지밀도가 지속적으로 높아지고 사용환경이 가혹해지고 있지만, 전지의 안전성은 타협할 수 있는 특성이 아니다. 특히, 더 높은 에너지밀도 확보를 위해 고용량 전극 소재개발과 함께 분리막 원단 뿐만 아니라 세라믹 코팅층의 두께 및 무게의 박막화와 경량화가 동시에 요구되고 있다. 그 중, 기존 슬러리 코팅 방식을 증착 방식으로 대체하는 기술이 주목받고있으며, 분리막의 내열성 확보를 위해 도입된 수 μm 수준의 세라믹 코팅층을 nm 수준으로 박막/경량화 하면서도 동등의 내열성을 확보하는 시도가 진행되고 있다. 증착법으로 제조된 세라믹코팅 분리막은 리튬이온전지 에너지밀도를 크게 증가시킬 수 있는 효율적인 방법이지만, 균일한물성의 세라믹 코팅 분리막을 제작하기 위해서는 증착 공정 중 온도를 제어해야 하며, 생산속도와 공정비용을 기존 슬러리 코팅 수준으로 떨어뜨려야 하는 현실적 문제가 존재한다. 그럼에도불구하고, 분리막 원단 대비 두께 및 무게 증가가 거의 없다는 점에서는 전지의 고에너지밀도달성에 필요한 매력적인 접근법임은 분명하다. 본 총설에서는 세라믹 증착 코팅에 사용되고 있는세 가지 방법인 1) 화학적 기상 증착법, 2) 원자층 증착법, 그리고 3) 물리적 기상 증착법으로제조된 세라믹 코팅 분리막을 소개하고자 한다. 각 증착법의 원리와 장/단점을 설명하고, 제조된세라믹 코팅 분리막의 물리적, 전기화학적 특성 및 전지의 성능 변화를 비교 분석하였다. 또한, 소재 관점에서 금속 또는 유기물질이 코팅된 초박막 코팅 분리막의 기술 동향도 소개하였다. Regardless of a trade-off relationship between energy density and safety, it is essential to improve both properties for future lithium secondary batteries. Especially, to improve the energy density of batteries further, not only thickness but also weight of separators including ceramic coating layers should be reduced continuously apart from the development of high-capacity electrode active materials. For this purpose, an attempt to replace conventional slurry coating methods with a deposition one has attracted much attention for securing comparable thermal stability while minimizing the thickness and weight of ceramic coating layer in the separator. This review introduces state-of-the-art technology on ceramic-coated separators (CCSs) manufactured by the deposition method. There are three representative processesto form a ceramic coating layer as follows: chemical vapor deposition (CVD), atomic layer deposition (ALD), and physical vapor deposition (PVD). Herein, we summarized the principle and advantages/disadvantages of each deposition method. Furthermore, each CCS was analyzed and compared in terms of its mechanicaland thermal properties, air permeability, ionic conductivity, and electrochemical performance.FALS

Effect of electrolyte concentration on electrochromic performance of sputtered tungsten oxide film:Experiments and simulation

Tungsten oxide (WO3) thin films are of critical importance in electrochromic devices as positive electrodes. However, the effect of electrolyte properties on the electrochromic properties of these films is not well ascertained. Herein, we demonstrate the effect of various LiClO4 salt concentrations in propylene carbonate (PC) on the switching speed and coloration efficiency of RF sputtered tungsten oxide film via experiments and simulation. The model developed for simulating the electrochromic performance of the WO3 thin films is based on dilute solution theory. The model is flexible enough to account for variable physical properties: lithium salt concentrations, film thickness and thickness of electrolyte diffusion layer. Relevant model parameters are obtained by fitting the model predicted cyclic voltammogram to experimental data obtained from a three-electrode cell composed of sputtered tungsten oxide, platinum, and Ag/AgCl. The switching time strongly depends on thickness of WO3 thin film and the electrolyte diffusion layer while the depth of coloration depends on concentration of the salt and operating voltage. Our simulated and experimental results provide an insight into the design of electrochromic devices with excellent switching speed and coloration efficiency. © 20201

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

A Bis(2-fluoroethyl) Carbonate as a New Electrolyte Additive for Enhancing the Long-Term Cycle Performance of Li-Metal Batteries

To meet the demand for high energy density, Li metal is considered a next-generation anode material owing to its high theoretical specific capacity and low electrode potential. However, conventional LiPF6-based electrolytes form a thick and porous solid electrolyte interphase (SEI) on Li metal, resulting in poor cycle performance. One of attempts to resolve these is to optimize the electrolyte composition because the Li metal reacts most actively with electrolyte. Here, bis(2-fluoroethyl) carbonate (B-FC), as a new fluorine-based linear carbonate, was added to a LiTFSI-LiBOB-based dual-salt electrolyte. To confirm the effect of B-FC on the electrochemical properties, Li || Li symmetric cells and LiNi0.6Co0.2Mn0.2O2 (NMC622) || Li metal full cells with or without B-FC were evaluated. The addition of B-FC forms LiF-rich SEI and significantly reduced Li dendrite growth, leading to the thin dead Li layer formation. Furthermore, high-voltage performances of NMC622 || Li metal full cells with B-FC were effectively improved compared to the pure DSL (capacity retention of 73.1% vs 62.4% after 300 cycles and a capacity of 117 mAh g−1 vs 87 mAh g−1 at 21 mA cm−2). Consequently, herein, we demonstrated that the dual-salts with B-FC can stabilize the SEI even under the 4.5 V cut-off condition. © 2023 The Electrochemical Society (“ECS”). Published on behalf of ECS by IOP Publishing Limited.FALS

Thin and porous polymer membrane-based electrochromic devices

An electrochromic (EC) device based on a thin and porous polymer membrane was newly fabricated for large-area applications such as smart windows. The pore structure of the poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) membrane was generated by extracting the pore generation material, dibutyl phthalate (DBP), from the cast film consisting of PVdF-HFP and DBP. The thickness of the porous polymer membrane was controlled to be very thin (approximately 30 μm), and the membrane was used to assemble WO3/W-NiO EC devices with 1 M LiClO4 in propylene carbonate as liquid electrolyte. Since the porous polymer membrane has a higher ionic conductivity than the non-porous one, the EC device with the porous polymer membrane showed a much higher current density in cyclic voltammetry even at a high scanning rate, faster color changing speed, and better stability after 500 cycles. © 2019 The Royal Society of Chemistry.1

Bifunctional role of carbon nanofibrils within Li powder composite anode: More Li nucleation but less Li isolation

Enlarging the surface area in the Li metal electrode is practically attractive for increasing long-term cycle life. In this regard, Li metal powders (LMPs) have a larger surface area, which is very beneficial for controlling dendrites and fast charging compared to planar Li metal foil. However, there is the need to increase nucleation sites in LMP electrodes for faster charging and suppress unavoidable dead Li formation caused by an electrical disconnection between individual LMPs and current collector for their commercial application. Herein, we present a 40 μm-thick, carbon nanotube-embedded LMP (CNT-LMP) electrode. The CNTs improve the LMP inter-particle contact and the contact with the Cu current collector and provide additional Li nucleation sites. As a result, the Li/Li symmetric cell with the CNT-LMP electrode exhibited a stable cycling and a longer cycle life (over 1000 h) than the bare LMP electrode (680 h). Furthermore, a full cell of LiNi0.6Mn0.2Co0.2O2/CNT-LMP could achieve a longer and more stable cycle performance of up to 600 cycles under practical current conditions (0.5 C/2 C, Charge/Discharge). In comparison, the bare cell without CNT decayed suddenly after 300 cycles. © 2022FALS

Electrode Alignment: Ignored but Important Design Parameter in Assembling Coin-Type Full Lithium-Ion Cells

Electrode alignment is one of design parameters that must be carefully controlled for reliable full cells with limited lithium ion inventory. Especially, since punched disk-type cathodes and anodes are movable during assembling coin-type cells, the misalignment of electrodes cannot be completely prevented. Furthermore, this misalignment is not only mixed with other defects but also sometimes leads to better electrochemical characteristics. To systematically unveil this ignored but important parameter, herein, we fabricate coin-type LiNi0.6Mn0.2Co0.2O2/graphite full cells with different electrode alignments and evaluate them to figure out any noticeable changes in their electrochemical properties. As frequently reported, the misaligned cell shows lower specific discharge capacity and initial coulombic efficiency than the well-aligned one due to an irreversible Li plating on the coin cell bottom during the first charging process. However, we have not recognized the misaligned cell can exhibit a smaller low-frequency semicircle in the AC impedance spectra and lower DC-IRs at lowly charged states than those of the well-aligned cell because of the less lithiated state of the misaligned cathode. Thus, to exclude data from misaligned full cells, it is necessary to verify the electrode alignment even after the cell evaluation process. © 2022 The Electrochemical Society ("ECS"). Published on behalf of ECS by IOP Publishing Limited.TRU

Digital‐twin‐driven structural and electrochemical analysis of Li+ single‐ion conducting polymer electrolyte for all‐solid‐state batteries

Abstract The electrode structure is a crucial factor for all‐solid‐state batteries (ASSBs) since it affects the electronic and ionic transport properties and determines the electrochemical performance. In terms of electrode structure design, a single‐ion conducting solid polymer electrolyte (SIC‐SPE) is an attractive solid electrolyte (SE) for the composite electrode among various SEs. Although the ionic conductivity of SIC‐SPE is lower than other inorganic SEs, the SIC‐SPE has a relatively lower density and can form an intimate contact between the SE and active materials (AM), resulting in an excellent electrode structure. The electrochemical performance of the cell with SIC‐SPE was comparable with the cell with Li6PS5Cl (LPSCl), which has 10 times higher intrinsic ionic conductivity than SIC‐SPE (SIC‐SPE: 0.2 × 10−3 S cm−1, LPSCl: 2.2 = 10−3 S cm−1 at 25°C). 3D digital‐twin‐driven simulation showed that the electrode with SIC‐SPE has a higher SE volume fraction, a lower tortuosity, and a larger AM/SE contact area than the LPSCl electrode. The favorable structure of the SIC‐SPE electrode leads to lower overpotential than the LPSCl electrode during operation. Our results suggest that the SIC‐SPE is a promising SE for making a good electrode structure in ASSBs

Degradation behavior of 21700 cylindrical lithium-ion battery cells during overdischarge cycling at low temperatures

Lithium-ion battery (LIB) cells are prone to overdischarge or overcharge when connected in series or parallel as a module or pack for large-format applications, such as electric vehicles (EVs) because of variations in battery capacities and difficulty in maintaining similar state-of-charge (SOC) of every single battery. However, the thermo-electrochemical behavior of LIBs during overdischarge has not been investigated at low temperatures. This study unveils the thermo-electrochemical behavior of overdischarged 21700 cylindrical LIB cells at −20 °C and 25 °C. Also, a thermo-electrochemical model was built to explain the heat generation within the cells and correlate them with the observed electrochemical characteristics. It was found that contrary to the severe cell degradation observed in the overdischarged cell compared to the standard cell at 25 °C, both cells show similar degradation behavior under low temperature cycling conditions. Thus, at low temperatures, overdischarge does not adversely affect cell degradation as observed at room temperature. This was attributed to the significant increase in the internal temperature, which results in improved electrochemical characteristics of the cell. © 2023FALS