Multi-layered Graphene embedded 2D-Molybdenum Dichalcogenides: Application to energy storage systems

Abstract

이 논문에서는, 에너지 저장 시스템과 관련하여 사용된 다중층 그래핀 물질을 사용하여 연구를 하였다. 저렴한 재료로 에너지 저장 시스템을 만드는 것은 에너지 사용에 있어서 매우 중요하며, 높은 용량을 가진 물질과 전해질을 찾아서 연구하는 것은 전기자동차나 모바일 기기 등에서 상당히 크게 다룰 수 있다. 소듐 전지의 경우 리튬보다 저렴한 가격으로 배터리를 제작할 수 있다는 점에서 차세대 배터리로서 역할을 할 수 있다. 그리고 전해질을 이용하여 용량을 안정하게 하면 배터리를 오래 쓸 수 있는 장점이 있다. 1장에서는, 우리는 Li-S battery와 Na-S battery, electrolyte에 대해 설명을 진행하였다. 이를 통해 Li-S battery와 Na-S battery에서 cathode와 anode 사이에 충전과 방전이 일어날 때 작동하는 원리에 대해 알아볼 것이다. Cathode에서 Sulfur가 충전과 방전 과정에서 어떻게 Lithium ion이나 Sodium ion과 반응을 하는지, Anode에서 Lithium ion이나 Sodium ion이 어떻게 반응을 하는지 알아볼 것이다. Electrolyte에 대해서는 Li-S battery와 Na-S battery에서 쓰이는 solvent와 solid들의 특징들에 대해 알아볼 것이다. 2장에서는 리튬-황 배터리, 소듐-황 배터리에서 사용될 물질인 Ethylene glycol, Diethylene glycol, Poly(propyl viologen)을 각각 assist한 MoS2 물질들에 대해 물리적 성질과 characterization에 대해 살펴볼 것이다. 그래서, 각각의 물질들에 대해 graphene이 존재하는지 살펴보았는데, 라만에서 모두 graphene이 존재하는 것이 확인되었으며, XPS에서도 graphene이 존재하는데, graphene의 양이 많아질수록 peak의 세기도 커지는 것을 확인할 수 있다. 그래서 MoS2 물질 사이에 graphene이 존재하는 것을 확인하였으며, graphene이 도체의 성질을 가지고 있는 것을 고려해보면, Sulfur의 단점인 conductivity를 보완할 수 있는 역할을 할 수 있는 것으로 보인다. 3장에서는 리튬-황 배터리에서 사용되는 Ethylene glycol, Diethylene glycol, Poly(propyl viologen)을 각각 assist한 MoS2 물질들에 대한 Electrochemical 성질과 performance에 대해 알아보았다. 먼저, 층으로 이루어진 MoS2 물질이 Lithium ion이 MoS2 층 사이로 들어가면서 물질이 형성되었고, 그 이후 최종적으로 Li2S와 Mo가 형성되는 것을 XRD를 통해 확인하였다. Electrochemical properties에서, calcination을 하면서 Poly(propyl viologen)이 Multilayer graphene으로 바뀌는데 Poly(propyl viologen)를 assist한 MoS2 물질이 가장 높게 나왔으며, Cyclic performance도 Poly(propyl viologen)를 assist한 MoS2 물질이 가장 높게 나오는 것으로 확인되었다. 4장에서는, 소듐-황 배터리에서 Poly(propyl viologen)을 assist한 MoS2 물질에 대해 Vinylene carbonate를 넣었을 때 나타난 결과에 대해 분석할 것이다. 그 결과에서 Cyclic Voltammetry의 경우 calcination을 하면서 Poly(propyl viologen)이 Multilayer graphene으로 바뀌는데, 남은 MoS2 물질이 반응에 관여하게 된다. MoS2 물질이 Sodium과 반응이 일어나면서 중간체가 형성되고 Na2S와 Mo로 분리되게 된다. 5장에서는, Sodium-Sulfur Selenium hybrid batery에서 Poly(propyl viologen)을 assist한 MoSSe 물질에 대해 Vinylene carbonate를 넣었을 때 나타난 결과에 대해 분석할 것이다. 비율로 볼 때 Sulfur와 Selenium은 2:1이랑 1:3으로 구성하였다. 그 결과에서 Sulfur와 Selenium의 비율에 따라서 결과가 다르게 나왔는데, Selenium의 함량이 높은 1:3의 물질의 경우 초기에는 Sulfur보다 높은 conductivity에 의해 specific capacity가 높게 나오나, capacity fading이 일어나면서 cyclic performance가 감소하게 된다. 그러나, Selenium의 함량이 상대적으로 낮은 2:1의 물질의 경우 500 cycle까지 측정하면서 cyclic performance가 일정하게 유지되는 것을 확인하였다.; therefore, SSBs are promising next-generation alternatives. Recently, sodiated layer transition metal sulfides, phosphates and organic compounds have been introduced as cathode materials above batteries. Simultaneously, recent developments have been facilitated by the use of select carbonaceous materials, transition metal sulfides, and intermetallic and organic compounds as anodes for SSBs. Apart from electrode materials, suitable electrolytes, additives (Vinylene carbonate (VC)), and binders are equally important for the development of practical these batteries. Despite developments in electrode materials and other components, there remain several challenges, including cell design and electrode balancing, in the application of sodium Sulphur cells. In this Thesis, we growth, characterization and discuss current research on materials and propose future directions for SSBs. This will provide important insights into scientific and practical issues in the development of SSBs. In this study, the multilayered graphene is produce by metal chalcogenide (MoS2 and MoSSe) materials supported of ethylene glycol, diethylene glycol, and poly (propyl viologen) depending on the selected amount percentage of carbon for the applications of laboratory production of Li-S battery, Na-S battery, and Na-hybrid battery. The important electrochemical studies were emphasized on electrolyte (LiPF6 and NaPF6) additives with different concentrations (0%, 3%, 5% and 7%) of Vinylene carbonate (VC) for the long cycle life stability of these batteries. In the 1st chapter, we discussed Li-S battery, Room Temperature Na-S battery, and electrolyte. This will look at how Li-S and Room Temperature Na-S batteries work when charging and discharging occur between the cathode and anode. In cathode, we will see how Sulfur reacts with lithium ion or sodium ion during charging and discharging, and how lithium ion or sodium ion reacts with anode. About electrolyte, we will show about the characteristics of solvents and solids used in Li-S batteries and Room Temperature Na-S batteries. In the 2nd chapter, physical properties and characterization of MoS2 materials assisted with Ethylene glycol, Diethylene glycol, and Poly (propyl viologen), which are materials to be used in Li-S batteries and Room Temperature Na-S batteries, will be examined. So, it was checked whether graphene exists for each substance, and it was confirmed that graphene exists in Raman, and graphene exists in XPS. As the amount of graphene increases, the intensity of peak increases. So, it was confirmed that graphene exists between MoS2 materials, and considering that graphene has the properties of a conductor, it seems that it can play a role in supplementing the conductivity of sulfur. In the 3rd chapter, the electrochemical properties and performance of Ethylene glycol, Diethylene glycol, and Poly (propyl viologen) assisted MoS2 materials used in Li-S batteries were investigated. First, it was confirmed through XRD that the MoS2 material composed of layers was formed as the Lithium ion entered between the MoS2 layers, and finally, Li2S and Mo were formed. In electrochemical properties, poly(propyl viologen) is converted to multi-layer graphene during calcination. The current of the calcinated MoS2 material is the highest, and the cyclic performance is the highest in the graphene content, that is, the highest carbon content of the MoS2 material was confirmed. In the 4th chapter, we will analyze the results of adding vinylene carbonate to poly(propyl viologen) assisted MoS2 materials in a sodium-sulfur battery. As a result, poly(propyl viologen) is converted to multilayer graphene during calcination, and the remaining MoS2 material is involved in the reaction. As the MoS2 material reacts with sodium in the reduction region of the cyclic voltammetry, an intermediate is formed and separated into Na2S and Mo. MoS¬2 and Sulfur are formed in the oxidation region of cyclic voltammetry. It shows the most stable cyclic performance when 3 wt% vinylene carbonate is added when vinylene carbonate is added depending on the various concentration of additive electrolyte. In the 5th chapter, we will analyze the results of adding vinylene carbonate to MoSSe materials assisted with poly (propyl viologen) in the Sodium-Sulfur Selenium hybrid batery. In terms of ratio of MoSSe, Sulfur and Selenium were composed of MoSSe (2: 1) and MoSSe (1: 3). In the results, the results were different depending on the ratio of sulfur and selenium. In the case of a 1: 3 materials with a high selenium content, specific capacity is higher due to higher conductivity than sulfur, but cyclic performance decreases as capacity fading occurs. However, in the case of a MoSSe (2: 1) material have a relatively low selenium content, it was confirmed that the cyclic performance was kept constant while measuring up to 500 cycles.; Energy storage technologies have attracted a great deal of attention for day-to-day applications. In recent decades, advances in lithium-ion battery (LIB) technology have improved living conditions around the globe. LIBs are used in most mobile electronic devices as well as in zero-emission electronic vehicles. However, there are increasing concerns regarding load leveling of renewable energy sources and the smart grid as well as the sustainability of lithium sources due to their limited availability and consequent expected price increase. Therefore, whether LIBs alone can satisfy the rising demand for small- and/or mid-to-large-format energy storage applications remains unclear. To mitigate these issues, present research work of thesis has focused on alternative energy storage systems. Li-S battery, Sodium-Sulphur batteries (SSBs) and hybrid Sodium-Sulphur Selenium (SSSBs) batteries are considered as the best candidates power sources because sodium also is widely available and exhibits similar chemistry to that of LIBs