A Study on Lead-based Anode Materials for Li/Na-ion Batteries

Jehee Park Ulsan National Institute of Science and Technology 2022 국내박사

With the growing demand of electric transportation and stationary storage applications, Li-ion batteries are widely used because of their high energy density and long lifetime compared to other battery systems. As these batteries become commercialized, Li-containing oxide cathodes and graphite-based materials serve as a practical anode. Although the graphite in these conventional anodes offers low operating voltage, acceptable specific capacity and good electric conductivity, its limited capacity—372 mAh/g, 856 mAh/cm3—cannot satisfy the growing demands of advanced performance for electric applications. Accordingly, a variety of alloying and conversion-type materials have been considered as candidates with the potential of higher energy density. For example, Group IV metals (e.g., Si, Ge, Sn)-based materials can provide a significantly higher capacity, and Lead (Pb) is abundant, cheap and has a high volumetric capacity for Li storage (550 mAh/g, 1906 mAh/cm3). Its toxicity, however, has prevented it from being considered a serious contender as new anode material. The toxicity of Pb-based materials can be addressed with well-established closed recycling systems based on the current lead-acid industry. Furthermore, from the degeneration of lead-acid batteries by replacement with Li-ion batteries, reused Pb-based materials can be used in advanced Li-ion batteries. Herein, we demonstrate that Pb-based material are suitable candidates for Li-ion and Na-ion battery anodes and elucidate a unique energy-storage mechanism that challenges conventional alloying reactions. Based on these findings, the development strategies through simple material engineering for Pb-based anodes are proposed to improve electrochemical performance. The dissertation can be summarized as follows: In Chapter II, we demonstrate Pb anode using commercial powder was for Li-ion batteries and investigate electrochemical Li-alloying reaction by ex-situ XRD analysis. Electrochemical Li alloying reaction of Pb anode forms crystalline Li-Pb alloy compounds as intermediate phases and is different from other alloy-based anodes. A comparative study of Pb and other alloy-based anodes in Group IV provides a new understanding of the fundamental alloying reaction by material properties and emphasizes the advantages of Pb anode, resulting in improved performance with less volume change, faster Li diffusion and enhanced reversibility. In Chapter III, a new high-performance Pb-based nanocomposite anode material was developed for lithium-ion batteries. Pb@PbO-C nanocomposite was synthesized by facile high energy ball milling. Electrochemical performance tests showed excellent reversible capacity (600 mAh/g) and cycle stability (92% retention at 100th cycle). The carbon matrix buffers the large volume changes, and the nanoscale particle size can alleviate the stress. We monitored the detailed lithium storage mechanism with the wide reversible Pb redox (between Pb2+ and Pb4-) and the evolution of extended Zintl-type LiyPb structures during the electrochemical reaction through advanced characterization using synchrotron X-ray diffraction and absorption analysis. In Chapter IV, the Pb@PbO-C nanocomposite was used for Na-ion batteries with advantages of low-cost, easy fabrication process and high capacity. These batteries exhibit decent performance compared to previous works. However, their storage performance is poorer than that of Li cell even using the same materials. Compared to Li-Pb alloying phase transition, the Na storage mechanism was elucidated to the formation of Zintl clusters in the electrochemical Na-Pb alloying reaction by experiment, resulting in a limited sodiation kinetic and reversible capacity due to its ionic character and high electrical resistivity. These findings provide new insights for future research directions through understanding and development of the unique Na storage mechanism of Pb-based anodes. In Chapter V, further development strategies for Pb@PbO-C nanocomposite were suggested according to our new understanding. Although the carbon nanocomposite design resolves the issues on large volume change of Pb-based anodes, the Li/Na diffusion kinetics are still limited by the formation of ionic Zintl compounds as an intermediate phase. Therefore, Pb-based multi-metallic compounds (Pb-M-O/C) were introduced by adding other metallic elements during synthesis and obtained improved cycling performance for Li/Na-ion batteries. Furthermore, the alloy-type anodes suffer irreversible capacity loss especially at the initial cycle due to large volume change and solid electrolyte interphase (SEI) formation, which limits the commercial use by decreasing energy density of full cell. Chemical prelithiation/presodiation technique using biphenyl-based reagents was applied to compensate the Li/Na loss of Pb anode resulting in improved the coulombic efficiency. These results suggest the possibility of overcoming the limitations of high capacity Pb-based anodes and practical use in the future. Based on these promising results, this study provides an understanding of Pb-based anodes in terms of their unique Li/Na storage mechanism beyond the conventional alloying reaction and presents a new perspective of developing high-performance anode materials for Li/Na-ion batteries.

Structural fading of Ni-rich layered cathode materials in high temperature environment

Lee, Eunkang Sungkyunkwan University 2022 국내박사

The technological advances in electronic devices, electric vehicles, and smart grids have exploded the ever-growing demand for rechargeable Li-ion batteries with high power and energy density. As a result, the use of Ni-rich layered cathode materials has emerged as an efficient candidate to boost the power and energy density of Li-ion batteries. The Ni-rich layered cathode materials have the advantages of high power and energy density, low cost, high reversible capacity, and good rate capability. However, the Ni-rich layered cathode materials have a decisive problem that they are unstable in high-temperature environments. The critical drawback for Li-ion batteries using Ni-rich layered cathode materials induces serious safety and durability issues of Li-ion batteries in a high-temperature environment, threatening the safe and convenient use of Li-ion batteries for humankind. Furthermore, the safety and durability issues are gradually approaching as a major priority because the Li-ion batteries are easily exposed to high temperatures as the use environment is diversified by technological development. In chapter 2, the underlying cause of thermal instability of Li0.33Ni0.5+xCo0.2Mn0.3-xO2 (x=0, 0.1, 0.2) cathode materials are systematically found using the in situ XRD during the heating process, HRPD, and XAS analysis for non-heated and heated cathode samples. Our accurate investigations show that before starting temperature of layered to spinel phase transition, the thermal expansion of Li slab becomes larger as the increase of Ni content in the cathode material. In addition, the oxygen vacancies are formed and accumulated around only Ni ions before the starting temperature of phase transition, and the number of oxygen vacancies decreases during the transformation to a spinel phase. Thermal expansion and the presence of oxygen vacancies decrease the energy barrier for cation migration and facilitate the phase transitions in charged cathode materials during the heating process, affecting the thermal stability of charged Ni-rich layered cathode materials. In chapter 3, the specific thermal decomposition reactions and their causes of Ni-rich layered cathode material as the SOC changes are investigated using the in situ XRD during the heating process, HRPD, and XAS analysis. The intermediate within the cation migration pathway is contracted as the SOC of Ni-rich layered cathode material increases. Small intermediate causes a large energy barrier for phase transition from layered to disordered spinel phase. Thus, the phase transition of Ni-rich layered cathode material into the disordered spinel phase begins at a higher temperature as the SOC increases. In addition, the Li-ion adjacent to the migrating cations increases the energy barrier for cation migration. Thus, as SOC in Ni-rich layered cathode material increases, many transition metal cations that are less affected by Li-ion can simultaneously participate in the thermal phase transition, inducing the quick completion of thermal phase transition of Ni-rich layered cathode material with high SOC. Furthermore, the thermal reduction of Ni ion and weakening of Ni-O bond strength occur rapidly at the temperature where the non-linear increase of lattice parameter starts. These rapid changes in the local environment induce the non-linear increase of lattice parameter in Ni-rich layered cathode material with low Li content during the heating process. In chapter 4, the structural changes of NCA cathode before and after the 60 ℃ storage process were investigated through synchrotron-based X-ray techniques and electrochemical analysis. The bulk crystal structure of fresh NCA cathode is maintained at each SOC even after the 60 ℃ storage process. However, it was observed that during the 60 ℃ storage process, the NiO-like rock salt phase grows at the particle surface, and the fracture of particles is deepened. These structural degradations disrupt the transport of Li-ions and electrons, which lowers the kinetic property of Li-ion and electron and increases the less active cathode region. Based on the X-ray & imaging techniques, we found that the heterogeneity in bulk structure change and redox reaction during electrochemical cycling is further intensified after the 60 ℃ storage process, aggravating the electrochemical performance degradation of the 60 ℃ storage NCA cathode. The findings of this research provide a better understanding of thermal instability and the electrochemical degradation of Ni-rich layered cathode materials in a high-temperature environment. Thereby, this dissertation is anticipated to play an important role in further improving the safety and durability of rechargeable Li-ion batteries with high power and energy density. 전자 장치, 전기 자동차 및 스마트 그리드의 기술 발전으로 인해 전력 및 에너지 밀도가 높은 충전식 리튬 이온 배터리에 대한 수요가 계속 증가하고 있다. 그 결과, 리튬 이온 배터리의 전력 및 에너지 밀도를 높이기 위한 효율적인 후보로 니켈함량이 높은 양극 재료의 사용이 부각되었다. 니켈 함량이 높은 양극 재료는 높은 전력 및 에너지 밀도, 저렴한 비용, 높은 가역 용량 및 우수한 속도 성능의 장점이 있다. 그러나 니켈 함량이 높은 양극재는 고온 환경에서 불안정하다는 결정적인 문제가 있다. 니켈 함량이 높은 양극재를 사용하는 리튬이온 배터리의 치명적인 단점은 고온 환경에서 리튬이온 배터리의 안전성과 내구성 문제를 야기하여 인류의 안전하고 편리한 리튬이온 배터리 사용을 위협하고 있다. 또한 기술 발전으로 사용 환경이 다양해짐에 따라 리튬이온 전지는 고온에 쉽게 노출되기 때문에 안전성과 내구성 문제가 점차 최우선 과제로 대두되고 있다. 2장에서 가열 과정 중 in situ XRD, 비가열 및 가열된 양극 샘플에 대한 HRPD 및 XAS 분석을 사용하여 Li0.33Ni0.5+xCo0.2Mn0.3-xO2(x=0, 0.1, 0.2) 양극 재료의 열적 불안정성의 근본 원인을 체계적으로 조사하였다. 우리의 정밀한 연구는 층상구조에서 스피넬 상으로의 상전이 시작 온도 이전에, 양극 재료의 Ni 함량이 증가함에 따라 리튬층의 열팽창이 커짐을 보여준다. 또한 상전이 시작 온도 이전에는, 니켈 이온 주위에만 산소 결손이 형성되어 축적되며, 스피넬 상으로 전이하는 동안 산소 결손의 수는 감소한다. 열팽창과 산소 결손의 존재는 양이온 이동을 위한 에너지 장벽을 감소시킴으로써, 가열 과정에서 충전된 양극 활물질의 상전이를 촉진하여 충전된 니켈함량이 높은 양극 물질의 열 안정성에 영향을 준다. 3장에서는 가열과정 중 in situ XRD, HRPD, XAS 분석을 이용하여 충전 깊이 변화에 따른 니켈함량이 높은 양극재의 특정 열분해 반응과 그 원인을 조사하였다. 양이온 이동 경로 내의 중간체는 니켈함량이 높은 양극 물질의 충전 깊이가 깊어짐에 따라 수축된다. 작은 중간체는 층상구조에서 무질서한 스피넬 상으로의 상 전이에 필요한 큰 에너지 장벽을 유발한다. 따라서, 니켈함량이 높은 층상 캐소드 물질의 무질서한 스피넬 상으로의 상전이는 충전 깊이가 깊어짐에 따라 더 높은 온도에서 시작된다. 또한 이동하는 양이온에 인접한 리튬 이온은 양이온 이동에 필요한 에너지 장벽을 증가시킨다. 따라서 니켈함량이 높은 양극재의 충전 깊이가 깊어짐에 따라 리튬 이온의 영향을 덜 받는 많은 전이금속 양이온이 동시에 열상전이에 참여할 수 있으며, 이는 충전깊이가 깊은 니켈함량이 높은 양극재의 빠른 열상전이를 유발한다. 추가적으로, 격자 파라미터의 비선형 증가가 시작되는 온도에서 니켈 이온의 열적 환원과 Ni-O 결합 강도의 약화가 급격히 발생한다. 이러한 국부 환경의 급격한 변화는 가열 과정에서 리튬 함량이 낮은 니켈함량이 높은 양극 재료 내 격자상수의 비선형 증가를 유도한다. 4장에서는 방사광 기반의 X-선 기법들과 전기화학적 분석을 통해 60℃ 저장 공정 전후의 고함량 니켈계 양극의 구조적 변화를 조사하였다. 프레쉬한 고함량 니켈계 양극의 벌크 결정 구조는 60 ℃ 저장 공정 후에도 각 충전 깊이에서 동일하게 유지된다. 그러나, 60 ℃ 저장과정에서 입자표면에 니켈옥사이드와 같은 암염상의 성장과 입자의 파단이 깊어지는 것을 관찰하였다. 이러한 구조적 열화는 리튬 이온과 전자의 수송을 방해하여 리튬 이온과 전자의 운동 특성을 낮추고 전기화학적 활성이 낮은 양극 영역을 증가시킨다. X-선 이미징 기술을 기반으로, 60 ℃ 저장 공정 이후에 전기화학적 반응 중 벌크 구조 변화 및 산화환원 반응의 이질성이 더욱 강화되고, 이 이질성이 60 ℃ 저장 고함량 니켈계 양극의 전기화학적 성능 저하를 악화시키는 것을 발견하였다. 또한, 입자 표면에서 니켈옥사이드와 같은 암염상의 성장은 충전 과정에서 용량 손실을 의미하는 전하 페이딩의 비대칭 용량 손실과 관련이 있음을 발견했다. 이 연구의 결과는 고온 환경에서 고함량 니켈계 양극 재료의 열적 불안정성과 전기화학적 열화에 대한 더 나은 이해를 제공한다. 따라서 본 논문은 고출력 및 에너지 밀도를 갖는 리튬이온배터리의 안전성과 내구성을 더욱 향상시키는 데 중요한 역할을 할 것으로 기대된다.

Surface Modified Silicon Electrode for Li-ion Batteries

Yoon Hwa 서울대학교 대학원 2013 국내박사

Nowadays, energy storage and retrieve system are important issues to solve energy problems. There are many energy storage systems such as Pb-acid, Ni-Cd, Li-S and Li-ion batteries. Among them, Li-ion battery is one of the most viable candidates for energy storage due to its high energy and high power density. At present, conventional Li-ion batteries employ a carbonaceous material for anode material. But, it is not suitable for the new large unit applications due to due to its low specific capacity and poor rate capability. For this reason, it is necessary to develop advance anode materials for Li-ion batteries. To overcome the limitations of carbonaceous materials, many researchers are paying attention to find other candidates replacing the graphite. Most of all, Si based systems are definitely attractive candidate for replacing the carbonaceous electrode due to the large theoretical specific capacity at room temperature (Li15Si4 : 3600 mAh g-1) and low operating voltage (near 0.1 V vs. Li/Li+). However, in general, most Si based electrodes suffer from a large volume change during cycling and have a poor rate capability. The stress induced by a large volume change during the cycling cause pulverization of Si which leads to loss of electrical contact with current collector and formation of solid electrolyte interphase (SEI) layer on the electrode surface repetitively. In this work, conducting carbon and SnO2 were coated on Si nanoparticles for enhance the electrochemical properties of Si electrode, respectively. Conformal conducting carbon is one of the most famous coating material for enhance the electrochemical properties of electrode, and SnO2 is a one of the promising candidate as anode materials for Li-ion batteries due to its excellent electrochemical performance. By combining those materials with Si, respectively, Si based electrode can be utilized fully in the anodes of Li-ion batteries. As a result of electrochemical test, each electrodes showed excellent electrochemical behaviors. And also reaction mechanism of each electrodes was confirmed by various analyses. These core-shell nanostructured electrodes could be a strong candidate as an anode materials for Li-ion batteries.

Electrolyte and Interfacial Engineering for Lithium-Ion and Lithium-Sulfur Batteries

백민성 서울대학교 대학원 2021 국내박사

The advent of lithium ion batteries has changed the paradigm of our lives, bringing about the proliferation of a variety of portable electronics and vehicles. One of the leading players in the successful paradigm shift is the development of a superior electrolytes and interfaces which have contributed to the achievement of high energy density. With an adequate electrolytes and interfaces, most battery performance criteria such as high voltage, high capacity, and stable cyclability are to be met beyond the expectations. However, with the demand of much superior performance from the ever-growing battery industry, innovative electrolyte and interfacial engineering technologies is constantly being highlighted. For this purpose, sophisticated electrolyte design for Li-S batteries and delicate ex-situ interface manipulating techniques for Li-ion batteries are covered in this text. In chapter 1, a high donor electrolyte strategy to achieve high energy density in lithium-sulfur (Li-S) batteries is covered. Li-S batteries continue to be considered promising post-lithium-ion batteries owing to their high theoretical energy density. In pursuit of a Li-S cell with long-term cyclability, most studies thus far have relied on using ether-based electrolytes. However, their limited ability to dissolve polysulfides requires a high electrolyte-to-sulfur ratio, which impairs the achievable specific energy. Recently, the battery community found high donor electrolytes to be a potential solution to this shortcoming because their high solubility towards polysulfides enables a cell to operate under lean electrolyte conditions. Despite the increasing number of promising outcomes with high donor electrolytes, a critical hurdle related to stability of the lithium-metal counter electrode needs to be overcome. As a solution to the above problem, Chapter 2 deals with an elaborately designed high donor electrolyte. Specifically, 1,3-dimethyl-2-imidazolidinone (DMI) is introduced as a new high donor electrolyte for Li-S batteries. The high solubility of polysulfides in DMI as well as its activation of a new reaction route, which engages the sulfur radical (S3•–), enables the efficient utilization of sulfur as reflected in the specific capacity under lean electrolyte conditions. Moreover, the addition of LiNO3 stabilizes the lithium metal interface, thereby elevating the cycling performance to one of the highest known for high donor electrolytes in Li-S cells. These engineered high donor electrolytes are expected to advance Li-S batteries to cover a wide range of practical applications, particularly by incorporating established strategies to realize the reversibility of lithium metal electrodes. Chapter 3 deals with delicate ex-situ interface engineering for high-speed charging lithium-ion batteries. Extremely fast charging (i.e., 80% of storage capacity within 15 minutes) is a pressing requirement for current lithium-ion battery technology and also affects the planning of charging infrastructure. Accelerating lithium ion transport through the solid-electrolyte interphase (SEI) is a major bottleneck in boosting charging; limited kinetics at the SEI layer, in turn, negatively affect the cycle life and battery safety as a result of lithium metal plating on the electrode surface. Here, we report a γ-ray-driven SEI layer that allows a battery cell to be charged to 80% capacity in 10.8 minutes as determined for a graphite full-cell with a capacity of 2.6 mAh cm−2. This exceptional charging performance is attributed to the lithium fluoride-rich SEI induced by salt-dominant decomposition via γ-ray irradiation. This study highlights the potential of non-electrochemical approaches to adjust the SEI composition toward fast charging and long-term stability, two parameters that are difficult to improve simultaneously in typical electrochemical processes owing to the trade-off relation. 리튬 이온 배터리의 개발은 우리 삶의 패러다임을 바꾸어 다양한 휴대용 전자 제품 및 전기차량의 보급화를 가능하게 했다. 이런 성공적인 패러다임 전환의 가장 중요한 역할을 하는 것은 높은 에너지 밀도의 배터리를 가능하게 한 우수한 전해질 및 인터페이스의 개발이다. 우수한 전해질과 인터페이스를 도입한 덕분에 현재까지 고전압, 고용량 및 안정적인 사이클등 높은 배터리 성능들을 보여왔다. 그러나 계속 성장하는 배터리 산업에서는 계속해서 훨씬 우수한 성능에 대한 요구를 하고 있고 이를 위해서는 혁신적인 전해질 및 계면 엔지니어링 기술이 지속적으로 강조되고 있다. 이를 위해 이 학위 논문에서는 리튬-황 배터리를 위한 정교한 전해질 설계와 리튬 이온 배터리를 위한 정교한 계면 기술을 다룬다. 1 장에서는 리튬-황 배터리에서 높은 에너지 밀도를 달성하기위한 전략 중 하나인 하이 도너 전해질 전략에 대해 다룬다. 리튬-황 배터리는 높은 이론적 에너지 밀도로 인해 유망한 차세대 리튬 이온 배터리로 간주되고 있다. 높은 가역성의 리튬-황 전지를 달성하기 위해 지금까지 대부분의 연구는 에테르 기반 전해질 사용에 의존했었다. 그러나 이런 전해질은 폴리 설파이드를 용해하는 데 한계가 있기 때문에 많은 양의 전해질을 요구하여 달성 가능한 에너지 밀도가 제한적이다. 최근 배터리 커뮤니티는 폴리 설파이드에 대한 높은 용해도를 통해 전지가 작은 양의 전해질 조건에서도 잘 작동할 수 있는 하이 도너 전해질이 이러한 단점에 대한 해결책이 될 수 있다는 것을 발견했다. 하이 도너 전해질에 대한 유망한 용해도에도 불구하고 이 전해질들은 음극으로 사용되는 리튬 금속 전극과 크게 불안정하여 이것이 극복해야할 큰 장애물로 여겨지고 있다. 위의 문제에 대한 해결책으로 2 장에서는 정교하게 설계된 새로운하이도너 전해질을 다룬다. 구체적으로 1,3-다이메틸-2-이미다졸리돈 (DMI)을 새로운 하이도너넘버 전해질로써 도입한다. DMI는 폴리 설파이드에 대한 높은 용해도와 다양한 황의 화학종을 안정화시켜 황의 활용도를 높일 수 있어 희박 전해질 조건에서 황의 효율적인 이용을 가능하게한다. 더 나아가 리튬나이트레이트를 첨가제로 사용하여 하이도너넘버 전해질의 근본적인 문제점이었던 리튬 메탈과의 심각한 부반응을 억제할 수 있는 방안을 제시한다. 이러한 전해질 엔지니어링을 통한 안정한 하이도너 전해질을 도입하는 근본적인 해결 전략은 리튬-황 배터리의 발전에 크게 도움이 될 수 있을 것으로 예상된다. 3 장에서는 고속 충전 리튬 이온 배터리를 위한 섬세한 계면 조절 기술에 대해 다룬다. 초고속 충전 (15 분 이내에 저장 용량의 80 %)은 현재 리튬 이온 배터리 기술의 시급한 요구 사항으로 여겨지고 있다. 현재의 충전 속도에 있어서 SEI라 불리는 전극의 계면층은 리튬 이온 수송이 가장 힘들게 일어나는 층으로 알려져 있다. 이를 해결하는 것이 결과적으로 SEI 층에서 제한된 충전 속도를 극복하는 것이고 이를 통해 전극 표면에 리튬 금속 전착과 같은 부반응으로 인한 사이클 수명 감소를 방지할 수 있다. 여기에서는 2.6 mAh cm-2 용량의 흑연 기반 리튬이온 전지를 이용하여 10.8 분 안에 80 % 용량까지 충전할 수 있는 γ-선을 이용해 형성한 광화학 SEI층을 보고한다. 이 뛰어난 충전 성능은 γ-선 조사를 통한 리튬염의 분해로 유도된 LiF 기반 SEI층 형성으로 부터 기인합니다. 이 연구는 일반적인 전기 화학 공정으로 동시에 개선하기 어려운 두 가지 매개 변수 인 고속 충전 및 장기 안정성을 새로운 광화학 계면 처리기술을 통해 동시에 가능하게 함으로써 광화학이라는 비 전기화학 접근법이 고속 충전 문제를 해결하는데 새로운 근본적인 해결책이 될 수 있음을 제시한다.

(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.

Studies on Materials Synthesis and Characterization of Electrode Active Materials for Lithum and Sodium Ion Batteries

강형섭 경희대학교 대학원 2020 국내석사

Nowadays, a variety of green energy is being developed to protect environmental pollution. Among them, rechargeable batteries are the most representative energy sources and are widely used in various IT appliances and electric vehicles (EVs). However, EVs sill have problems both low mileage and safety. Accordingly, researchers need to develop batteries for EVs with high energy density and stabilities. We explain the basic principles of lithium and sodium-ion batteries in Chapter I. In Chapter II, Ni-rich layered structure of LiNi0.8Co0.1Mn0.1O2(NCM811) is promising cathode active material for EVs applications. The high amount of Ni in active material can make high capacity for lithium ion batteries. However, as the amount of Ni increasing makes instability of layered structure. It leads to side reactions like the dissolution of cathode into electrolyte and results degradation of batteries. The side reactions of cathode active materials accelerate at high temperature. To improve the electrochemical properties and stabilities of NCM811 cathode active material, lithium diborate (Li2O-2B2O3) has been used as a coated material to protect the side reactions and thermal stability. In Chapter III, Sodium-ion batteries have attracted significant attention nowadays. Sodium is abundant resource, low cost and safe which makes attractive materials for alternative to lithium. However, there are some obstacles to develop sodium-ion batteries. Na+ ion are larger than Li+ ions which affect the transport properties. Also sodium is heavier than lithium and higher standard electrode potential. To solve this problems, we try to make anode materials. Because graphite which already commercialized in LIBs does not intercalate sodium ions properly. In this study, to make high capacity anode material for sodium-ion batteries, we tried to make nitrogen-doped carbon coated tin-iron oxide nanocomposite (Sn-Fe2O3@NC) and check electrochemical properties. 오늘날 환경 오염을 보호하기 위해 다양한 녹색 에너지가 개발되고 있습니다. 그 중에서 충전 가능한 배터리가 가장 대표적인 에너지 원이며 다양한 IT 기기 및 전기 자동차 (EV)에 널리 사용됩니다. 그러나, EV는 주행 거리와 안전에 모두 문제가 있습니다. 따라서 연구자들은 에너지 밀도와 안정성이 높은 전기 자동차 용 배터리를 개발해야 합니다. 이에 관한 리튬 및 나트륨 이온 배터리의 기본 원리는 1 장에서 설명합니다. 2 장에서는 LiNi0.8Co0.1Mn0.1O2 (NCM811)의 하이 니켈 층상 구조는 EV와 같은 응용 분야에 유망한 양극활물질입니다. 활물질에 함유 된 많은 양의 니켈은 리튬 이온 배터리에 고용량을 만들 수 있습니다. 그러나, 니켈의 양이 증가함에 따라 층상 구조는 불안정해집니다. 특히, 양극활물질을 전해질로 용해시키는 것과 같은 부반응을 일으켜 배터리의 성능을 저하시킵니다. 특히, 양극활물질의 부반응은 고온에서 가속화된다. NCM811 양극활물질의 전기화학적 특성 및 안정성을 개선하기 위해, Li2O-2B2O3가 부반응 및 열 안정성을 보호하기 위해 코팅 된 물질로서 사용되었습니다. 3 장에서는 요즘 주목 받고 있는 나트륨 이온 배터리를 소개합니다. 나트륨은 풍부한 자원, 저비용 및 안전성으로 리튬을 대체 할 수 있는 매력적인 재료입니다. 그러나 나트륨 이온 배터리를 개발하는 데에는 몇 가지 장애물이 있습니다. Na+ 이온은 운송 특성에 영향을 주는 장애요소들이 Li+ 이온보다 큽니다. 또한 나트륨은 리튬보다 무겁고 표준 전극 전위가 높습니다. 이 문제를 해결하기 위해 음극 재료를 만들려고 했습니다. 왜냐하면 이미 리튬 이차 배터리에서 상용화 된 흑연은 나트륨 이온의 삽탈입을 진행 하지 못하기 때문입니다. 본 연구에서는 나트륨 이온 배터리의 고용량 음극재를 만들기 위해 질소 도핑 된 탄소 코팅된 주석 산화철 나노 복합체 (Sn-Fe2O3@NC)를 만들고 전기 화학적 특성을 확인하고자 하였습니다.

Effect of Surface Oxide Layer to Si-based Materials for Li-ion Batteries : 리튬 이온전지용 실리콘계 물질들의 표면 산화층의 영향

유병철 서울대학교 대학원 2014 국내박사

The global energy demand is continually increasing, and it has been accelerated recently by the depletion of fossil fuels and by climate change caused by human activities. Hence, energy devices such as solar cells, fuel cells, rechargeable batteries, and supercapacitors have become increasingly important for energy harvesting, conversion and storage. Among them, Li-ion batteries have been the leading rechargeable battery and with the rapid development of mobile devices and EVs, their market has continued to expand. Currently, graphite (LiC6: 372 mAh g-1) is used as an anode material in rechargeable Li-ion batteries. To meet the requirements such as high capacity, high power, and stable cycle performance, many researchers have focused their attention on Si-based materials (Si,SiO and SiO2). However, the main problem associated with the use of Li-alloys in rechargeable batteries is the large volume change during alloying-dealloying with Li, resulting in cracking and fracturing of active materials, causing deterioration of the anodes. Also another important factor is silicon oxide layer on surface of Si-based materials because a thick oxide layer hindered the Li–ion diffusion, reacting with active material. In this work, we investigated the oxide layer effect to Si-based materials (Si and SiO) for Li-ion batteries. The oxide layer of Si and SiO material was confirmed using HRTEM and XPS, respectively. And the oxide layer was etched by NaOH solution and etched samples were tested as an anode. As the oxide layer of Si and SiO reduced, the electrochemical performance was also significantly enhanced. Also, the self-limiting reaction behavior of nano-Si with oxide layer and a new mechanism of SiO with Li during first cycle were proposed. Finally, a new concept for the preparation of porous SiOx was suggested adopting Si as a pore generating agent and Si oxides as template using NaOH solution. The porous SiOx was tested as an anode for Li-ion batteries, and it showed excellent electrochemical performance without any carbon coating. These studies of oxide layer could provide basic information when the Si-based materials were used as an anode for Li-ion batteries.

Carrier ion diffusion and phase transition in anode materials and their effects on electrochemical properties of batteries

최용석 Graduate School, Korea University 2020 국내박사

Despite their wide applicability for portable electronic devices such as smart phones and laptop computers, Li-ion batteries (LIBs) lack high power density and suffer from safety hazard that are critical for emerging electric transportation systems. To this end, there has been much interest on finding alternative materials with higher specific capacity than traditional materials, while maintaining the required cycle life. One major attempt is to change the carrier ions from conventional Li to Na. This is because, Na not only exhibits electrochemical properties similar to those of Li but also is earth-abundant resources and thus, can be obtained with much lower prices. The other attempt to discover alternative battery materials is to use of alloying anodes. Alloying anodes react with carrier ions via an alloying mechanism: carrier ions diffuse into anodes by breaking the atomic bonds between host atoms to alloy with anode materials. This diffusion process is not constrained by the atomic framework of anodes and thus, can promote the insertion/extrusion of a large number of carrier ions to anodes, resulting in the high specific capacity of alloying anodes. Above previous studies suggest that the proper selection of carrier ions (Li or Na) and alloying anodes can enable the development of batteries for future electric vehicles. Generally, the electrochemical properties of batteries are directly related to the diffusion behaviors and phase transitions occurring at anode materials. In this regard, by understanding these behaviors in alloying anodes can pave the way for selecting proper carrier ions and alloying anodes. In this study, we first address the effect of diffusion of carrier ions on the various electrochemical performances of energy efficiency, rate performance, and cycle life. In the following section, we interpret the relationship between the phase transition behaviors in alloying anodes and energy loss at anodes, or equivalently, energy efficiency of batteries. Based on above results, the present thesis suggests crude yet effective design criteria for developing future batteries with superior electrochemical performances.

Li-ion battery health diagnosis based on electrochemical model

김정수 포항공과대학교 일반대학원 2022 국내박사

Secondary batteries are widely leveraged in the rapidly growing electric vehicle (EV) and energy-storage system (ESS) markets. Among the battery types, Li-ion batteries are extensively used, owing to their advantages of high energy and power densities, low self-discharge rate, and lack of memory effect. However, they tend to be susceptible to thermal runaways caused by undesirable operations, because their thermal stability is inherently lower than other batteries. Moreover, as Li-ion batteries become more widespread, the number of associated accidents also increases significantly. To use such delicate batteries safely and efficiently, it is essential to accurately estimate their health states. This thesis deals with several methods for diagnosing the health states of Li-ion batteries from various angles based on an electrochemical model, especially a pseudo-2-dimensional (P2D) model, which precisely expresses the dynamics of a Li-ion battery. First, a data-driven state-of-health (SOH) estimation scheme for Li-ion batteries with reference performance test (RPT)-reduced experimental data is proposed. In this work, it is proved that the capacity of a Li-ion battery can be effectively estimated using only scarce data acquired through minimal number of RPT performing, unlike most of existing studies have employed abundant reference data. Second, some parameters of the P2D model for effective and practical diagnosis of Li-ion batteries are selected as aging parameters and identified. In this study, some major parameters of the P2D model were identified through a genetic algorithm (GA). Based on the results, the parameters suitable for diagnosing the battery health state were selected as aging parameters, and their physical meanings were considered. Lastly, a novel P2D model parameter identification method, genetic algorithm and neural network cooperative optimization (GANCO), is proposed. Many existing studies that employ meta-heuristic methods to identify model parameters did not efficiently utilize data generated during optimization. In this work, an 1-dimensional convolutional neural network (1D CNN) periodically trains the sample data obtained from previous iterations to learn thedynamics between the known input current and the corresponding simulated voltage. Then the trained network recommends highly probable parameter candidates to the GA. In such manner, an 1D CNN and a GA cooperate and complement each other in GANCO.

The Role of Functional Electrolytes for Superior Power Performance in Li-ion Batteries and Electrolyte Additive for Enhanced Thermal Stability of Na-ion Batteries

Dong-Hui Kim DGIST 2019 국내박사

본 논문은 리튬 이온 배터리의 전력 성능에 대한 전해질의 영향과 나트륨 이온 배터리 용 전해질 고온 첨가제 개발에 대한 연구이다. 아크릴레이트계 잴 고분자를 리튬 이온 배터리에 적용하여, 안전성과 고출력 성능을 개선하였고 글라임 계열 보조 전해액을 적용하여 내부 저항에 따른 리튬 이온 배터리의 성능을 평가 분석했다. 이를 통하여 리튬 이온 배터리의 고출력 성능에 대한 전해질의 영향을 연구했다. 또한 나트륨 이온 배터리의 고온 성능을 위한 첨가제들을 비교 분석했다. 이를 정리하면 다음과 같다. (1) 내부 열 중합으로 제조된 아크릴레이트계 잴 고분자 전해질 (A-GPE) 을 리튬 이온 배터리 (LIB) 에 적용했다. 잴 고분자 전해질은 다른 유형의 고체 전해질과 비교하여 간단한 공정, 낮은 재료비, 전극과의 낮은 접촉저항으로 상업적으로 장점을 가지고 있어 다양한 차세대 배터리에 적용이 가능하다. 아크릴레이트계 잴 고분자 전해질은 일반적인 액체 전해질과 비교하여 다양한 조건에서 향상된 안전성과 고출력 성능을 보여주었다. 심층적인 전기화학 및 분광학 분석을 통하여 아크릴레이트계 잴 고분자 전해액의 우수한 고출력 성능은 고율 방전 동안 리튬이온의 활동도 (aLi) 를 낮추는 독특한 용매화 구조로 인한 낮은 농도 과전압 (ηcon) 에 기인한다. 이 연구는 배터리의 출력 성능에 농도 과전압 영향의 중요성을 밝혀냈다. (2) 글라임 보조 용매를 사용하여 서로 다른 두께의 LCO 전극의 출력 특성에 영향을 주는 내부 저항을 체계적으로 조사하여 속도 성능과 내부 저항 사이의 관계를 이해했다. 글라임 보조 용매를 사용하여 이온전도도가 향상 되었지만 이온 전도도의 경향과 일치하지 않는 속도 성능을 확인하였다. 전기화학적 임피던스 측정을 통하여 전체 내부저항에 대한 공극 내부의 이온 이동 저항 (Rion) 과 계면 전하 이동 저항 (Rct) 이 전극 두께와 전해질에 따라 상대적으로 변함을 확인했다. 이를 통하여 출력 성능은 전극 두께와 전해질의 영향으로 결정된 Rion과 Rct로 인한 전체 내부 저항에 의해 결정되는 것을 확인했다. (3) 나트륨 이온 배터리 음극 용 경질 탄소의 고온 수명 성능향상을 위해 fluoroethylene carbonate (FEC) 및 succinic anhydride (SA) 첨가제의 역할을 조사하였다. 경질 탄소와 나트륨 금속 전극에 대한 첨가제의 영향을 구분하기 위해 경질 탄소/나트륨 금속 반쪽 전지와 경질 탄소 대칭 전지를 사용하여 체계적으로 조사하였다. 경질 탄소/나트륨 금속 반쪽 전지에서 경질 탄소의 열화는 나트륨 금속에서 유도된 부산물에 기인한다. 이 결과를 바탕으로 나트륨 금속 전극의 영향을 제외하기 위해 경질 탄소 대칭 전지를 사용하여 고온 수명 실험을 진행했다. FEC는 수명 성능에 영향을 주지 않지만, SA는 고온 수명 성능을 크게 향상 시키는 것을 확인했다. SA의 고온 수명 성능 향상은 전기 화학 임피던스 (EIS) 와 X-선 광전자 분광법 (XPS) 을 통해 열적으로 안정한 solid electrolyte interphase (SEI) 층 형성에 기인한 것으로 밝혀졌다. Despite two decades of commercial history, enhanced secondary-ion batteries performance is required to satisfy the evolving electric vehicles (EVs) and energy storage system (ESS) market requirements which is essential for thermal stability, long-term cycle, safety, and power performance. Here, we resolve these chal-lenges using a gel polymer electrolytes (GPEs) and glyme co-solvent electrolyte for Li-ion batteries, and additive of hard-carbon for Na ion batteries. (1) To date, solid and semi-solid electrolytes have not been adopted in Li-ion batteries despite the for-midable safety advantage because of their poor power performance compared to that of liquid electrolytes. We herein report that an acrylate-based gel polymer electrolyte (A-GPE) prepared by in situ thermal polymer-ization displays a rate capability superior to that of its liquid counterpart. LiCoO2/graphite pouch cells (720 mAh) employing A-GPE exhibit a capacity more than 30 % higher than practical cells using a liquid electro-lyte at a high-rate discharge ( ≥ 3 C), while retaining far better stability in overcharging and high-temperature (90 oC and 150 oC) storage tests. Electrochemical and spectroscopic evidence confirms that the unexpected superior power performance of A-GPE is ascribed to the unique solvation structure surrounding the Li-ions. The solvation structure lowers the effective concentration (i.e., the mean ionic activity) of Li-ions and thus mitigates the concentration polarization during high-rate discharge. This study demonstrates a breakthrough strategy to simultaneously enhance both the safety and high-power performance of Li-ion batteries. (2) To improve the total electrochemical reaction of lithium ion battery, we have focused on the phe-nomenon of the interfacial reaction at thick and thin electrodes using glyme-mixed electrolyte (1,2-dimethoxyethane (1G), 1-methoxy-2-(2-methoxyethoxy)ethane (2G) as co-solvent) which raises the ionic conductivity due to low viscosity of glyme. The results of coin cell test indicate that 1G-mixed electrolyte shows much better rate performance with both electrodes. However, 2G-mixed electrolyte despite its higher ionic conductivity than the base electrolyte exhibits negligible improvement with thick electrode and even diminished rate performance with thin electrode. To examine the internal resistance, the electrochemical im-pedance spectroscopy (EIS) is employed using symmetric cell at SOC of 0% and 50%. Then, the ionic re-sistance in pores (Rion) and charge transfer resistance (Rct) are determined. As the result, 1G-mixed electrolyte shows the lowest Rion and Rct among the electrolytes. Otherwise, 2G-mixed electrolyte has lower Rion and larger Rct than that of base electrolyte. The total resistance (Rtotal), which is the sum of Rion and Rct, at the thick electrode shows the smallest in 1G-mixed electrolyte, and shows similar value is observed base electrolyte and 2G-mixed electrolyte. In thin electrode, the Rtotal increases in the following order: 1G-mixed electrolyte < base electrolyte < 2G-mixed electrolyte. These results suggest that the rate performance is greatly affected by the Rtotal. (3) Hard carbon (HC) is the most popular anode material for Na-ion batteries (NIBs), but its long-term reliability has to be still further improved. To improve the cycle performance of HC anodes, we herein exam-ine fluoroethylene carbonate (FEC) and succinic anhydride (SA) as an electrolyte additive. It is revealed that FEC hardly affects the cyclability of HC symmetric cells, but it enables far better cycle behavior of Na metal, and thus improving the cycle performance of HC/Na metal half cells by suppressing the formation of by-products derived from Na metal that accelerates the degradation of HC anodes. In contrast, SA markedly im-proves the performance of HC symmetric cells in the cycle and storage tests at 60 oC. The superior thermal stability of SA additive is attributed to the formation of an inorganic-rich solid electrolyte interphase (SEI) layer on HC surface as evidenced by X-ray photoelectron spectroscopy (XPS) measurements.