Mechanistic design and structural integration of MOF-based composite solid-state electrolytes for CFRP structural batteries

Li, Shuang 영남대학교 대학원 2026 국내박사

Structural batteries, which integrate mechanical load-bearing and electrochemical energy storage into a single multifunctional system, show great promise for next-generation lightweight devices in aerospace, automotive, and robotics. However, their development is limited by the inherently sluggish ion transport in structural electrolytes, severe lithium dendrite growth, poor electrode/electrolyte interfacial stability, and the conflict between mechanical stiffness and ionic conductivity. In addition, scalable manufacturing and free-form integration remain critical challenges that hinder practical deployment. This dissertation aims to resolve these coupled electrochemical – mechanical conflicts by establishing a mechanistic understanding of lithium-ion transport and dendrite suppression, designing bimetallic MOF- based high-performance composite solid electrolytes, and validating their integration into carbon-fiber-reinforced polymer (CFRP) structural batteries capable of real mechanical service conditions and scalable free- form manufacturing. First, the lithium dendrite formation mechanism was analyzed based on the Chazalviel space-charge model and interfacial electrochemical theory, revealing the role of anion depletion and Li+ concentration polarization. Zn –Co bimetallic MOFs (ZNB) were designed with dual- metal Lewis acid sites to anchor anions and enhance Li+ mobility. DFT and AIMD simulations were employed to explore the adsorption energetics and dynamic ion-transport behavior. Electrochemical tests in liquid electrolytes experimentally verified the ion-sieving effect of ZNB. To extend these findings to structural systems, a dual-channel composite solid electrolyte (BMOF@HF/H-ZIF-8) was fabricated using hollow- fiber-supported 3D bimetallic MOF architectures to achieve simultaneous mechanical reinforcement and continuous Li+ transport. The optimized electrolyte was further incorporated into a CFRP structural battery laminate manufactured via vacuum-infusion curing. The coupled electrochemical-mechanical performance and deformation tolerance were evaluated under operando bending, drilling, and cutting conditions. Finally, free-form scalable manufacturing and robotic conformal deposition pathways were analyzed to guide future industrial application. ZNB-modified electrolytes exhibited superior ionic conductivity (7.5867×10-4 S cm-1) and high Li+ transference number (0.72), enabling dense dendrite-free lithium deposition and stable cycling over 1600–2000 h in symmetric cells. The BMOF@HF/H-ZIF-8 composite solid electrolyte achieved 6.09× 10-4 S cm-1 conductivity, a tLi+ of 0.74, high tensile strength (15.89 MPa), and strong thermal stability (>300 °C). The assembled CFRP structural battery delivered 144.82 mAh g-1 at 0.1C and maintained 92.5% capacity retention after 100 cycles while preserving mechanical integrity (tensile strength 365 MPa; bending strength 342 MPa). Under 4-mm bending deformation, reversible capacity retention reached 94.7%. Even after drilling and cutting damage, the structural battery safely powered devices without short-circuiting and successfully drove an electric vehicle chassis for ~12 minutes. 구조용 배터리는 기계적 하중 지지와 전기화학적 에너지 저장을 하나의 시스템으로 합치는 기술이다. 그리고 이 기술은 차세대 경량 항공우주, 자동차, 로봇 장치 분야에서 큰 잠재력을 가진다. 하지만 구조용 전해질에서는 이온 이동이 느리고, 리튬 수지상이 쉽게 생기고, 전극과 전해질 계면 안정성이 낮다. 그래서 기계적 강성과 이온 전도도 사이에 상충 문제가 생기며 개발이 제한된다. 또한 확장 가능한 제조와 자유형 통합도 여전히 중요한 과제로 남아 있다. 본 학위논문은 리튬 이온 이동과 수지상 억제 메커니즘을 이해하고자 하였다. 그리고 고성능 bimetallic MOF 기반 복합 고체 전해질을 설계하였다. 또한 이 전해질을 실제 기계적 조건과 자유형 제조가 가능한 CFRP 구조 배터리에 통합하는 것을 목표로 하였다. 우선 Chazalviel 공간 전하 모델과 계면 전기화학 이론을 사용하여 리튬 수지상 형성 메커니즘을 분석하였다. 그리고 Zn과 Co로 구성된 bimetallic MOF인 ZNB를 설계하여 음이온 고정과 Li⁺ 이동성을 향상시켰다. DFT와 AIMD 시뮬레이션을 통해 흡착 에너지와 이온 이동 거동을 조사하였다. 또한 액체 전해질 환경에서 전기화학 실험을 진행하여 ZNB의 이온 체거림 효과를 확인하였다. 그리고 중공 섬유 기반 3차원 bimetallic MOF 구조를 제작하였다. 이 구조는 연속적인 Li+ 이동 경로와 기계적 보강을 동시에 제공하는 이중 채널 복합 고체 전해질 BMOF@HF/H-ZIF-8이다. 이 전해질을 진공 인퓨전 경화 공정을 이용해 CFRP 구조 배터리 적층체에 넣었다. 그리고 굽힘 변형, 드릴링, 절단 조건에서 전기화학·기계적 성능과 변형 내성을 평가하였다. 마지막으로 확장 가능한 제조와 로봇 기반 자유형 적층 기술의 방향도 분석하였다. ZNB가 포함된 전해질은 7.5867×10-4 S cm-1의 높은 이온 전도도를 보였다. 그리고 0.72의 Li+ 전달 수를 나타냈다. 대칭 셀에서는 1600~2000시간 동안 안정적인 사이클링을 유지하였고 수지상 없이 리튬 침전을 이루었다. BMOF@HF/H-ZIF-8 복합 고체 전해질은 6.09×10-4 S cm-1의 전도도를 보였다. 그리고 0.74의 Li+ 전달 수, 15.89 MPa의 인장 강도, 300 ℃ 이상의 열 안정성을 확보하였다. 제작된 CFRP 구조 배터리는 0.1C에서 144.82 mAh -1의 용량을 보였다. 그리고 100회 후 92.5%의 용량을 유지했다. 인장 강도는 365 MPa, 굽힘 강도는 342 MPa이었다. 4 mm 굽힘 변형 후에도 용량 회복률은 94.7%였다. 또한 드릴링과 절단 이후에도 단락이나 열폭주 없이 안전하게 작동하였다. 약 2 mm 두께의 구조 배터리는 소형 전기차를 약 12분 동안 구동하였다. 본 연구는 이온 이동 제어 메커니즘, 복합 고체 전해질 구조 설계, 구조용 배터리 통합과 실증, 그리고 확장 가능한 자유형 제조 기술 분석을 포함한 연구 체계를 제시한다. 그리고 고강도와 고안전성을 가진 CFRP 구조 배터리의 실용화 가능성을 보여준다. 또한 확장 제조와 자유형 표면 통합에 대한 통찰은 향후 항공우주, 자동차, 로보틱스 산업에서의 실제 적용을 위한 중요한 기술 기반을 제공한다.

High-Throughput Computational Search for Li-Free Li-Ion Battery Cathodes

Li, Haoming Howard University of California, Berkeley ProQuest Disser 2025 해외박사(DDOD)

As Li-metal anodes become more readily available, next-gen Li-ion battery cathodes are no longer required to contain Li in their as-synthesized state, vastly expanding the materials search space. In order to identify potential cathode materials that do not necessarily contain Li in their native state, I here present a series of tools and guidelines to carry out computational screening in this search space.Firstly, a pipeline for rapid cathode discovery has been established. This pipeline operates on any database of inorganic materials without a priori information on Li sites and performs screening based on computed voltage, capacity from sequential insertions of Li ions and most importantly, mobility built upon the graph-based migration network obtained through site connectivity. A preliminary application of the pipeline was carried out on a subset of the Materials Project database, and one particular polymorph of MnP2O7 is shown here as an an example of a new candidate compound which completed the pipeline and was selected for further, detailed analysis. The compound is shown to present a 2D ion migration topology, consisting of two separate intercalation pathways where the corresponding energy landscapes are calculated with the nudged-elastic band formalism. Acceptable energy barriers are found in the dilute (highly charged) limit, however the material is expected to exhibit slower kinetics in the vacancy (highly discharged) limit.Furthermore, a set of design principles are derived from data mining on voltage information from two classes of Li-ion battery cathodes. Most of Li-free cathodes are natively found in their charged state, in contrast to today's commercial lithium-ion battery cathodes, which are more stable in their discharged state. In this work, calculated cathode voltage information from both categories of cathode materials are combined, covering 5577 and 2423 total unique structure pairs, respectively. The resulting voltage distributions with respect to the redox pairs and anion types for both classes of compounds emphasize design principles for high-voltage cathodes, which favor later Period 4 transition metals in their higher oxidation states and more electronegative anions like fluorine or polyanion groups. Generally, cathodes that are found in their charged, delithiated state are shown to exhibit voltages lower than those that are most stable in their lithiated state, in agreement with thermodynamic expectations. Deviations from this trend are found to originate from different anion distributions between redox pairs.Lastly, a machine learning model for voltage prediction based on chemical formulae is trained on the data set obtained from the voltage distribution. This model displays sound connections to physical characteristics that impact cathode voltage and shows state-of-the-art performance when compared to two established composition-based ML models for materials properties predictions, Roost and CrabNet. The screening workflow, chemical design principles and the machine learning voltage model together compose a data-driven methodology for effectively executing high throughput materials discovery for practical and high-performance next-gen non-Li-containing cathodes.

Luminescent properties of hydrothermally prepared zinc silicate phosphors

Li, Qinghua The Pennsylvania State University 2004 해외박사(DDOD)

Mn substituted willemite Zn2SiO4:Mn2+ phosphor is traditionally used in low refresh rate display technology. This phosphor shows high quantum efficiency, high luminance and purer green color than other green phosphors such as Tb3+-activated phosphates and aluminates. The long lifetime of the phosphor limits its use in the display that needs a rapid change in its image. In this research, the decay properties of Zn silicate phosphor were investigated by a new experimental technique. Hydrothermal reactions were carried out at high temperatures to synthesize pure and dopant-containing Zn2SiO 4:Mn2+ phosphors. The dopants include the ion pairs of Ga3+ + Li+ and Al3+ + Li +. High emission intensity was obtained at 700°C under hydrothermal conditions for the pure and dopant-containing phosphors. For the pure Zn2SiO4:Mn2+ phosphor, the decay properties at low Mn contents were investigated. The intrinsic decay time t1/e (the decay time to the 1/e emission point) is about 13 ms at room temperature. The influence of the Mn content on the decay time t10 was studied. The Mn distribution in each single particle and among particles was adjusted by the solid/water ratio and the reactivity of ZnO. Mode emission wavelength was measured to determine the Mn concentration in the emission layer of phosphor particles. The results show that the decay time t10 of an isolated Mn2+ ion pair is not less than 15 ms. Fast decay rate is attributed to the formation of Mn clusters in willemite structure. For the phosphors with dopants, the dopants (Ga + Li; Al + Li) do not influence the decay time t10 at 11 ms or below. The solubility of (Ga + Li) in Zn silicate willemite phase at 700°C is estimated to be 1.5--2atm% of the Zn couples, or 3--4atm% of the Zn sites can be occupied by the Ga + Li ion couples. About 4--5atm% of Zn sites can be occupied by Al + Li ion couples at 700°C. The addition of the Al + Li ion couples promotes the quantum efficiency in the VUV range, that is, from 120 to 200 nm.

Synthesis and physical properties of impurity doped ZnO materials

Li Guojie 부경대학교 대학원 2014 국내박사

ZnO is becoming more and more popular as third-generation semiconductor for its wide band gap (~3.4 eV) and large exciton binding energy (60meV) at room temperature, which permits efficient excitonic emission processes, therefore ZnO has gereat development potential in the field of optoelectronic devices. In addition, ZnO has a high melting point, high thermal and chemical stability. ZnO single crystal thin film can be obtained at the high temperature at certain condition, so it can greatly reduce the defects formed in ZnO. Furthermore, ZnO is abundant, cheap, innoxious, easy to be prepared and with potential commercial value. To realize the ZnO-based device applications, an imperative issue is to fabricate the high quality n- and p-type ZnO. While ZnO is naturally n-type conductivity due to the various native defects, which is the difficulty in achieving high-quality stable p-type ZnO. Powder, ceramic and thin film n- and p-type ZnO-based samples are made by various methods including sol-gel, solid phase and pulsed laser deposition (PLD) methods. The physical properties of the samples are characterized by X-ray diffraction (XRD), Field-Emission Scanning Electron Microscope (FE-SEM), Atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Hall test instruments. A special phenomenon is observed during the investigation that the Li-doped thin films show ferromagnetism at room temperature. The detailed contents and innovations would be introduced next. For n-type ZnO, Al is chosen as the dopant element in research. Ceramics and thin films are prepared to do the investigation with various doping compositions (Zn1−xAlxO, x = 0.02-0.2). The XRD patterns show the Al is well doped into the host material and higher reaction temperature may improve the composition. The good target ceramics also affect the quality of the thin films. Except the substrate peak, there is only the (002) c-axis direction peaks are observed from the XRD patterns of thin films. The flat surface and low roughness thin films are observed from FE-SEM and AFM images. The optical transmittance of the thin film is good, and the carrier concentration of electrons of Zn1-xAlxO film is as high as 4×1021 cm-3. Both the powder and ceramic Li-doped ZnO show no impurity peak from the XRD patterns. The reaction temperature and time would affect the morphology of the powder which is made by sol-gel method. pH value should be another considerable condition during the experiment. All of the samples show the signature dielectric property follow the changeable test conditions. For p-type Li doped ZnO thin film, conditions has been changed including different substrates, temperatures and various dopant concentration. Thin films are grown on the Al2O3(0001) substrate at 600 ℃ with the Li concentration from 2% to 18%. SEM and AFM images show the surface conditions of the thin films while the optical absorption studies in the wavelength range 200-900 nm revealed an increase in the band gap of the Li-doped ZnO films from 3.19 to 3.41 eV. And during the Zn1−xLixO thin films for x=0.01, 0.05 and 0.10 on Pt (111) /Ti/SiO2/Si substrate under 500 ℃, 5 at% and 10 at% Li doped ZnO thin films show p-type behavior by Hall effect testing results. The existence of defects such as Lii (interstitial Li) and LiZn (substitutional Li on the Zn site) should be considered in the host materials. The stabilization of p-type thin films is also discussed in defects theoretically. In further research, the structural, electric and magnetic properties of ZnO:Li thin films for 2%, 5%, 8% and 10% Li-doped thin films which are prepared on Pt(111)/TiO2/Si/SiO2 substrates by pulsed laser deposition are reported. Lattice parameters and Zn-O bond lengths are calculated from X-ray diffraction (XRD) results. The 8% ZnO:Li thin film show room temperature ferromagnetism and the hysteresis loop is observed. In particular, the native point defects in ZnO (such as Zni, Vo, Vzn) and Li-related defects (Lii and Lizn) are analyzed by X-ray photoelectron spectroscopy (XPS). Zni and Vo defects give indirect evidences, while the photoluminescence results show circumstantial proof of the existence of VZn, LiZn and VZn defects play a vital role in p-type films and ferromagnetism, respectively. Moreover, the Hall effect results also corroborate the formation and stabilization of efficiency factors and thus stabilizing the p-type ferromagnetism predicted for cation vacancy in ZnO thin film.

Applying nanoscale science to lithium-ion battery and membrane transport

Li, Naichao University of Florida 2003 해외박사(DDOD)

This dissertation provides background information on nanoscale science, the template synthesis of nanomaterials, and its application to Li-ion battery and membrane transport. My work has shown that compared with conventional thin-film electrodes with the same mass, the template-synthesized SnO 2 nanofibers and the nanoporous carbon-honeycomb have much higher rate capability and cycling performance as Li-ion battery anodes. This is because the high-rate capacity of Li-ion battery is limited by slow solid-state Li + diffusion in electrode materials, and the nanostructured electrodes decrease the distance that Li+ must diffuse in the solid state. Furthermore, the surface area of the nanostructured electrode was larger, making the effective current-density during discharge smaller than that for a conventional electrode. Better cycling performance was achieved because the spaces between the nanostructures of electrode materials could accommodate the volume changes due to Li+ insertion and extraction through the electrode materials. In an effort to combine the advantages of both nanostructured electrodes and all-solid-state Li-ion batteries, a nanostructured all-solid-state Li-ion battery was investigated. This battery was designed to use the carbon honeycomb as the anode and the substrate; the surface and the inner walls of the carbon honeycomb were then covered with an ultrathin electrochemically polymerized poly(phenylene oxide) (PPO) film, which was used as the solid electrolyte. The PPO film was very thin (0.5--1.9 nm) and could be easily deposited into the inner walls of the carbon honeycomb. PPO film was only conductive to cations (e.g., Li+) after sulfonation. My research also showed that O2 plasma etching could be used to prepare not only the carbon honeycomb anode but also nanostructured conical pores in polymeric membranes. Conical pore embedded membranes can be used for enhanced membrane transport and resistive-pulse sensing of particles such as molecules and ions. The plasma etch method provides a simple and convenient route for preparing conical-nanopore membranes.

Dielectric properties of Li-doped ZnO thin films prepared by pulsed laser deposition

Li Guojie 부경대학교 2010 국내석사

ZnO is becoming more and more popular third-generation semiconductor for its wide band gap and large exciton binding energy. But the pure ZnO gradually can?ft meet the people?fs demands in nowadays, then impurity doping and the using of the defects which can improve and enlarge the properties are hot spot in nowadays. This article introduces the way of Li doped into ZnO. Thin films of Li-doped ZnO with different compositions (Zn1−xLixO, x = 0.02-0.2) have been prepared on heavily doped Si substrates by a pulsed laser deposition technique, and we get the good quality transparent conducting oxides thin film with a ferroelectric nature. Through many substantial tests, theoretical studies and comparisons to the conclusions in hand, our mainly contents as following: 1. We choose the Li element doped into the ZnO and the impurities are well doped into the ZnO; the impurities affect little to the structure of the ZnO. 2. The thin films are made by the PLD method, and the structure of the crystal in the thin film grows well follow the c-axis. The ferroelectricity of the thin film Zn0.88Li0.12O is observed in the P-E hysteresis loop test ,and Ec is 5.53 KV/cm and Pr is 0.186 ??c/cm2 3. The permittivity of the Zn1-xLixO is involved with the temperature and the frequencies. And we also find a crest in the test around certain temperature, so we can call the change temperature Tc for short , for example, the Tc of the Zn0.85Li0.15O is about 95?? 4. The optical transmission of the .Zn1-xLixO thin films are good, most are over 75%; through the calculation with the test dates, we can roughly get the academic thickness of the thin film, which is coincide with the actual result.

(A) study on CuO conversion cathode based on LiAlCl4·3SO2 electrolyte system for lithium rechargeable batteries

Li, Siying Sungkyunkwan university 2021 국내박사

Due to the high energy density, long cycle life, and environmental friendliness features, lithium-ion batteries (LIBs) have been widely applied in portable electronic devices and have become a promising power source for electric vehicles. However, numerous safety accidents related to thermal runaways due to battery failures have occurred over the past decade, indicating that the fire hazard of LIBs can no longer be ignored. Among the strategies to improve the thermal stability of the battery system, the use of non-flammable electrolytes is an effective way to prevent battery ignition and explosion. SO2-in-salt electrolyte composed of LiAlCl4·3SO2, as one of the non-flammable inorganic ionic liquids with high conductivity and Li-ion transference number, has attracted increasing attention. This dissertation mainly focuses on a high-energy-density LiAlCl4·3SO2 electrolyte lithium rechargeable battery system based on CuO cathode. Chapter 2 presents a natural-activable CuO hollow nanocube (HNC) cathode material for dual-ion Li metal batteries using SO2-in-salt electrolyte. Natural activation is achieved via spontaneous chlorination of CuO HNCs into an electrochemically active CuCl2 phase upon immersed in the SO2-in-salt electrolyte. The on-site conversion reactions are proposed with the support of thermodynamic calculations; the phase transformations of active materials are confirmed through X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and field emission scanning electron microscopy (SEM). As a solution to alleviate the volume expansion after chlorination, the HNC structure of CuO allows the resulting CuCl2 cathode material to deliver a reversible capacity up to 262.2 mAh g-1 (894.2 Wh kgCuO-1) with stable cycle performance over 150 cycles. The Li-CuO battery system presented here demonstrates the feasibility of non-flammable, high-energy-density Li/Cl dual-ion Li metal batteries as a potential alternative to currently used lithium-ion batteries. Chapter 3 introduces the optimization of CuO cathode for the Li/Cl dual-ion Li metal batteries system with polyacrylonitrile (PAN). The multi-yolk-shell (MYS) CuO has been fabricated and used as the active material for the CuO cathode. The oxidative cyclization of PAN at different temperatures has been investigated through Fourier transform infrared spectroscopy (FTIR), Differential scanning calorimetry (DSC), and XPS. The effect of cyclized PAN on electrode performance has been studied by experiments on Cu ion adsorption and active material loss as well as electrochemical tests. The extent of cyclization increases with temperature leading to an increase in electrical conductivity owing to the formation of N-doped delocalized C-ring in cyclized-PAN. This oxidative process also leads to the formation of O-containing functional groups, which facilitates the transfer of Li ions and adsorbs Cu ions to slow the capacity decay. The MYS-CuO electrode with 280℃ cyclized-PAN achieves a significantly enhanced initial energy density of 1074.0 Wh kg-1 and maintains 866.2 Wh kg-1 at the 250th cycle with a retention rate of 80.7%. A unique flower-like morphology with a blooming-fading evolution during discharge and charge has been observed in the electrode with 280 ℃ cyclized-PAN, which is also related to the effect of cyclized PAN.

Taxonomic Study of Genus Bryoria(Lichenized Ascomycota, Parmeliaceae) from the Sino-Himalays : Sino-Himalaya 지역에서의 Bryoria 속 지의류의 분류학적 연구

Wang, Li-Song The Graduate School Sunchon Nation Universty 2006 국내박사

Sino-Himalaya 지역에서 Bryoria 속에 속하는 20종을 기록하여 보고하였다. 그 중에서 Bryoria fastigiata Li S. Wang과 B. flocculosa Li S. Wang를 신종으로 보고하며, B. himalayana var. sorediata Li S. Wang은 새로운 변종으로 보고하며, B. nadvornikiana, B. trichodes subsp. trichodes와 B. tenuis종은 중국에서 최초로 보고하며, B. trichodes subsp. americana와 B. furcellata는 Sino-Himalaya 지역에서 최초로 보고하며, B. asiatica, B. himalayana와 B. poeltii는 신장자치구 지역에서 B. divergescens, B. lactinea, B. nitidula와 B. variabilis는 사천성 지역에서, B. bicolor는 신장과 사천성 지역, B. furcellata는 사천성과 운남성 지역에서 최초로 보고한다. 각 종에 대한 이차대사산물을 분석한 결과, usnic acid와 lobaric acid를 본 속에서 최초로 보고 하였다. 각 종에 대한 분류키와 형태, 서식처 및 분포에 대하여 기술하였다. Twenty taxa of the genus Bryoria were recognized and recorded in the Sino-Himalayas. Among them, Bryoria fastigiata Li S. Wang and B. flocculosa Li S. Wang are new species, B. himalayana var. sorediata Li S. Wang is a new variety; Bryoria nadvornikiana, B. trichodes subsp. trichodes and B. tenuis are new to China; B. trichodes subsp. americana and B. furcellata are new to the Sino-Himalayas; B. asiatica, B. himalayana and B. poeltii are new to Xizang; B. divergescens, B. lactinea, B. nitidula and B. variabilis are new to Sichuan; B. bicolor is new to Sichuan and Xizang; B. furcellata is new to Sichuan and Yunnan. Secondary chemical products were studied for each taxon. Among them, usnic and lobaric acids were first reported in the genus. A key to the species and notes on morphology, habitat and distribution are given. One of specimen was collected from the type locality of B. divergescens (Li-S. Wang 04-23413, in KUN-L), which was selected as an epitype of this species, because of the fragmental nature of the holotype (H-Nyl. 35972).

Design and performance evaluation of DNA @ metal-organic framework (MOF) composites for next-generation electrochemical energy storage devices

Li, Man Gachon University 2022 국내박사

Based on the main problems existing in the current development of lithium-sulfur batteries (Li-S batteries), including low areal sulfur-loading (˂ 2.0 mg cm −2), poor polysulfides conversion kinetic, the "shuttle effect" of soluble intermediate polysulfides (Li2Sx, 4 ≤ x ≤ 8), growth of lithium dendrites and safety problems of liquid electrolytes, this thesis is mainly focusing on the modification of cathode/separator materials and designing solid-state electrolyte to enhance the performances of Li-S batteries. Deoxyribonucleic acid (DNA) decorated metal-organic framework (MOF)-derived cathode composites, and double-layer structured MOF/carbon nanotube (CNT)@DNA interlayer have been rationally designed and fabricated to enhance the performance of Li-S batteries. The morphology, microstructure, electrochemical storage mechanism, and theoretical computation were studied to investigate the roles of as-fabricated materials in enhancing the performance of L-S batteries.

Design, Syntheses, and Electrochemical Properties of FeF3·0.33H2O and FePO4 Cathode Materials for Metal-ion Battery

장, 리궈 부산대학교 대학원 2023 국내박사

To realize the large-scale application of energy storage batteries by reducing costs, it is very important and necessary to find an ideal cathode for alkali metal ion batteries (MIBs). Iron is a common, low-cost, and resource-rich element in nature. The development of iron-based fluorides and phosphates as battery cathode materials has attracted more and more researchers’ great interest due to their high theoretical specific capacity, high working potential, low costs, and environmental friendliness. In this paper, the application of FeF3·0.33H2O@C and FePO4 as cathodes for Li-ion and Na-ion batteries is investigated in detail. First part, the demand for energy storage applications in today's world is increasing, and obtaining charge storage devices with both energy and power advantages is the focus of energy materials research. Recently, compared with the research on pseudocapacitive anode materials, the research on pseudocapacitive cathode materials is rare. Herein, FeF3·0.33H2O@CNS (carbon nanosheets) composites were successfully prepared by solid-phase fluorination, in which nitrogen-doped carbon nanosheets tightly encapsulated ultrafine FeF3·0.33H2O particles. The pseudocapacitive properties of as-prepared FeF3·0.33H2O@CNS cathode are verified by the analysis of the Li+ storage kinetics of the electrode material, and the results show that the FeF3·0.33H2O@CNS cathode has a higher capacitance distribution than bare FeF3·0.33H2O cathode, resulting in higher rate capability and excellent cycling performance (capacity retention at 1C after 200 cycles of 97.2%). The excellent performance of FeF3·0.33H2O@CNS//LCNS full cells also shows its excellent application feasibility. In short, improving the electrochemical performance of cathode materials by tuning their pseudocapacitive contributions is an effective means to modify electrode materials, and this strategy will obtain ideal electrode materials with high energy and high power density. Second part, compared with the intercalation-reaction cathode materials, iron fluoride based on the conversion reaction is an excellent cathode material with high working voltage and ultra-high specific discharge capacity in alkali- MIBs. However, the iron fluoride material has the disadvantages of poor electrical conductivity, sluggish electrochemical kinetics and electrode pulverization and dissolution. A pomegranate-structured FeF3·0.33H2O@carbon nanocomposite (FeF3·0.33H2O@C) was successfully synthesized by hydrothermal synthesis and in situ solid-phase synthesis. Pomegranate-structured FeF3·0.33H2O@C cathodes can effectively reduce electrode polarization due to the unique hierarchical carbon coating structure, plus other structural advantages (coordinated volume expansion, reduced Fe dissolution, inhibited nanoparticle coarsening), the composite can obtain good reversibility and excellent battery rate performance. The FeF3·0.33H2O@C electrode achieved a capacity retention rate of 93% after 200 cycles in Li-ion battery tests. And the FeF3·0.33H2O@C electrode in SIBs achieved an ultra-high energy density of 1015 Wh kg-1. Third part, uniform amorphous FePO4 nanospheres were successfully synthesized by a simple one-step hydrothermal synthesis method. The SEM pictures show that the samples are uniform nanospheres with a diameter of 255 nm. X-ray diffraction (XRD) data confirmed the sample to be an amorphous structure. The data of XRD, energy spectrum analysis, and XPS analysis after the amorphous material annealing confirmed the nature of the sample as FePO4. The necessity of amorphous FePO4 cathodes as a replacement for olivine NaFePO4 cathodes was analyzed by the crystal phase structure diagram. The ex-situ XRD results at different charge-discharge potentials confirmed the transition between amorphous FePO4 and microcrystalline structures. The amorphous FePO4 cathodes achieves a reversible capacity of 152.5 mAh g-1 close to the theoretical specific capacity at low current density. Furthermore, the amorphous FePO4 cathodes exhibited excellent stable cycling performance after 200 cycles at a current density of 20 mA g-1. Therefore, amorphous FePO4 may be an ideal cathode material for a feasible and low-cost high-performance Na-ion battery. In summary, low-cost and environmentally friendly iron-based fluoride and iron-based phosphate cathode materials were successfully synthesized and studied, they both obtained excellent electrochemical performance in battery tests and showed good application feasibility. These studies will open up new avenues for large-scale commercial applications of energy storage batteries