7 results on '"areal capacity"'
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2. Inter-Bonded Carbon Nanofibers Based Anode for High Areal Capacity Lithium-Ion Battery
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Jonghyun Park, Hiep Pham, Tazdik Patwary Plateau, and Susmita Sarkar
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Materials science ,Chemical engineering ,Carbon nanofiber ,Lithium-ion battery ,Anode ,Areal capacity - Abstract
Improving anode electrode conductivity and boosting mechanical strength of carbon nanofibers (CNFs) is beneficial to fabricate binder-free anode for high areal capacity in Lithium-ion Batteries (LIBs). A typical way to improve CNFs conductivity is adding high conductive transition metals to CNFs precursors. In this work, several ideas are incorporated together to enhance LIB performance. First, CNFs with 3% and 5% nickel is introduced by using electrospinning technique for improving electrical conductivity and capacity, because nickel has high theoretical capacity (718mAh/g) and enhanced electrical conductivity (1.43x107 S/m). Small addition of Nickel was done because higher usage of nickel metal fillers cause volume expansion during cycling which results in poor cell performance. Second, development of strong mechanical connections, enhancement of electron transport by better inter-bonding network among the CNFs is also addressed here. In this study, polyvinylpyrrolidone (PVP)/ polyacrylonitrile (PAN) polymers are used to fabricate the CNFs where the semi-interpenetrating polymer PVP assists in creating inter-bonded morphologies in the nanofibers. Thus, well inter-bonded CNFs showed not only the better areal capacity but also the higher specific capacity. Further an optimum stabilization and carbonization heat-treatment process was also observed. The synergetic effect of adding high conductive Nickel and well-inter-bonded CNFs network represents a favorable anode material with an areal capacity as high as 792.7 μAh/cm2 after 300 cycles at a current density of 1.16 mA/cm2 and excellent cycling stability. more...
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- 2021
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3. Degradation Mechanism of Lithium-Oxygen Batteries with High Areal Capacity and Lean Electrolyte
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Shoichi Matsuda and Hitoshi Asahina
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Materials science ,chemistry ,Chemical engineering ,Degradation (geology) ,chemistry.chemical_element ,Lithium ,Electrolyte ,Oxygen ,Mechanism (sociology) ,Areal capacity - Abstract
Because the nonaqueous Li–O2 batteries are still in their infancy due to numerous problems, there is no report, which actually attained the energy density of 500 Wh/kg in a complete cell level as a rechargeable battery. Except a few works[ref.1-3], almost all studies reported so far included too much excess weight of electrolytes, which results in much lower energy densities than those of LIBs. When the electrolyte amount is decreased to fulfill the energy density of 500 Wh/kg, the cell cannot be cycled. Therefore, it is especially important to quantify the decomposition reactions in Li–O2 batteries under more practical conditions of less electrolyte amount and high areal capacity[ref.4]. In previous studies, less attention have been payed about the amounts of Li metal electrode and liquid electrolyte, when they determined cycle life of Li–O2 cells, even though these amounts are the important factors to determine not only energy density but also cycle life. Almost all studies so far have been carried out using a thick Li foil (100–500 μm thick). Because the equivalent weight of Li and graphite are 3860 and 372 mAh/g, respectively, the capacity ratio of negative to positive electrodes (N/P ratio) should be at least less than 3860/372 ≒ 10 to keep the advantage over graphite electrodes. When the areal capacity of the Li metal anode is set to 4 mAh/cm2, the thickness of the Li metal is calculated to be about 20 μm. On the other hand, the electrolyte amount has a more significant influence on the energy density than the Li metal thickness owing to the larger mass density of the electrolyte (1.16 g/cm3) than that of Li metal (0.53 g/cm3). The ratio of the electrolyte volume to the total pore volume of cell components is an important parameter, however, the ratio of electrolyte weight to cell capacity (E/C, gA/h) is empirically used to represent the electrolyte amount in LIBs.10 The E/C ratio in our experiments is 10 gA/h, which is much smaller than those of previous studies (E/C ≥ 50 gA/h). In the present study, we have examined reaction products in a porous carbon positive electrode by using a two-compartment cell design, where anode and cathode compartments were separated by a solid-state Li+ conductor to eliminate possible interference from the reactions at Li metal negative electrode. Because the monitoring the gas consumed/produced during the operation is nearly the only way to determine the CE of the O2 electrode, we used on-line gas analysis as well as pressure change measurements for understanding parasitic reactions coming from electrolyte decomposition. As a result, we clarified that the ratio of electrolyte weight to cell capacity is a good parameter to correlate with cycle life. Only 5 cycles were obtained at an areal capacity of 4 mAh/cm2. When the areal capacity was decreased to half, the cycle life was extended to 18 cycles. However, the total electric charge consumed for parasitic reactions was 35 and 59% at the first and the third cycle, respectively. This surprisingly large amount of parasitic reactions was suppressed by half using redox mediators while keeping a similar cycle life. Based on by-product distribution, we will propose possible mechanisms of TEGDME decomposition. References 1. H. Lee , D. J. Lee , M. Kim , H. Kim , Y. S. Cho , H. J. Kwon , H. C. Lee , C. R. Park and D. Im , ACS Appl. Mater. Interfaces, 2020, 12 , 17385 2. J. O. Park , M. Kim , J.-H. Kim , K. H. Choi , H. C. Lee , W. Choi , S. B. Ma and D. Im , J. Power Sources, 2019, 419 , 112 3. S. Zhao , L. Zhang , G. Zhang , H. Sun and J. Yang , J. Energy Chem., 2020, 45 , 74 4. M. Ue, H. Asahina, S. Matsuda and K. Uosaki, RSC Adv., 2020,10, 42971 more...
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- 2021
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4. A Rational Design of a Porous Copper Current Collector for Alkali Metal Anodes with a High Areal Capacity
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Ki-Yeop Cho, KwangSup Eom, Subin Kim, and Hayong Song
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Materials science ,chemistry ,Metallurgy ,Rational design ,chemistry.chemical_element ,Current collector ,Alkali metal ,Porosity ,Copper ,Anode ,Areal capacity - Abstract
Alkali metals are the ideal anode materials for improving the specific energy of secondary ion batteries because of the lowest redox potentials (3.04 and 2.71 VSHE for lithium and sodium, respectively) and the highest capacities (3860 and 1166 mAh g-1 for lithium and sodium, respectively). Nevertheless, using alkali metal anode is still challenging, because the dendritic growth and large volume changes of alkali metal anode cause many problems such as cell shorting, dead lithium, excessive SEI formation, and so on. Among the previously suggested solutions, the strategy to accommodate the Li or Na metal in the porous electrode has a great potential to address the aforementioned issues. [1] Particularly, the volume changes in the deposition and stripping processes of alkali metal can be minimized by adopting a porous electrode, and therefore increase the areal capacity of the anode. Furthermore, it is expected to increase the nucleation sites and impede the ununiform growth of specific position on the alkali metal by increasing the exposed surface area (that is, reducing the current density). In designing an alkali metal anode using a porous electrode, the required characteristics of the electrodes to improve the electrochemical performances such as coulombic efficiency and specific energy of full-cell are considered as follows. Firstly, the weight of the porous electrode should not be too heavy. In the case of porous Cu electrode, the porosity determines the specific capacity, as shown in Figure 1(a), thus the porous electrode having low porosity rather reduces a specific capacity. [2] Therefore, in the case of porous Cu electrode, the specific capacity of the electrode including the mass of current collector is improved when the porosity is more than 85%. Secondly, the conductivity of the thickened porous electrode should be high and uniform to achieve less voltage hysteresis, because the larger voltage hysteresis (high overpotential) of anode reduces the specific energy and energy efficiency of full-cell. [3] In this context, we focused on the control of structural characteristics of the porous Cu electrode including porosity, thickness, and surface area. As shown in Figure 1(b), the self-standing porous Cu sheet was fabricated by calendaring of the Cu/SiO2 mixture, and then followed by sintering of Cu and etching of SiO2.. Namely, the amount of SiO2 in the Cu/SiO2 mixture determines the porosity of the porous Cu electrode, leading to a facile control of the porosity of Cu. The fabricated porous Cu current collector with 15 mg cm-2 could deliver a high areal capacity of 40 mA h cm-2 at a current density of 10 mA cm-2 with high coulombic efficiency (99.98%) and low voltage hysteresis (~20 mV), as shown in Figure 1(c). The required weight of the porous Cu electrode (Cu:SiO2=1:2) for storing 4 mAh cm-2 was only 1.5 mg, whereas the porous Cu electrode (Cu:SiO2=1:0) required 3.6 mg. Furthermore, the number of cycle for reaching maximum coulombic efficiency was shorter in high porosity (90%) compared to the lower porosity (30%~80%). Therefore, the outstanding performance would be due to the high porosity and conductivity of the porous Cu electrode providing multiple nucleation sites, as well as enough space for the growth of alkali metal. This work will provide insights into the rational design of the alkali metal anode with high areal capacity and low voltage hysteresis, by providing a facile method to control of structural characteristics of the Cu current collector. References [1] R. Zhang, N.-W. Li, X.-B. Cheng, Y.-X. Y Tin, Q. Zhang, and Y.-G. Guo, Adv. Sci., 2017, 4, 1600445 [2] D. Zhang, A. Dai, M. Wu, K. Shen, T. Xiao, G. Hou, J. Lu, and Y. Tang, ACS Energy Lett., 2020, 5, 180-186 [3] X. Gao, X Yang, K. Adair, X. Li, J. Liang, Q. Sun, Y. Zhao, R. Li, T.-K. Sham, and X. Sun, Adv. Energy Mater., 2020, 10, 1903753 Figure 1 more...
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- 2020
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5. (Invited) Ultrahigh Areal Capacity Holey Graphene Air Cathodes for Li-O2 and Li-CO2 Batteries
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John W. Connell and Yi Lin
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Materials science ,business.industry ,Graphene ,law ,Optoelectronics ,business ,Cathode ,law.invention ,Areal capacity - Abstract
Advanced lithium (Li) batteries using gaseous cathode reactants such as oxygen (O2) and carbon dioxide (CO2) are attractive energy storage platforms because the gases are obtained externally and thus not accounted for in the total battery weight when fully charged. The discharge products at the cathode, typically Li2O2 for Li-O2 batteries and Li2CO3for Li-CO2 batteries, are insoluble in the electrolyte. Therefore, in order for such batteries to function properly, an “air cathode”, which is a conductive scaffold within the battery cell, is required as a physical location for cathode electrochemical reactions to occur. Prior research has identified many carbon nanomaterials such as carbon nanotubes and graphene as viable choices for air cathode scaffold, while various metallic and metal-free catalytic systems integrated onto carbon-based air cathodes have been developed to improve the sluggish discharge and charge reactions. For future practical applications, the air cathode must exhibit a usable capacity per unit electrode area, or areal capacity, a critical parameter that has been largely overlooked so far in this field. In order to achieve high areal capacity, the air cathode must exhibit a sufficient amount of accessible void volume per unit electrode area while maintaining the conductive scaffold integrity during the entire electrochemical process. Here we present an ultrathick, holey graphene-based air cathode platform fabricated from a facile dry compression process that exhibits remarkable areal capacity values. Holey graphene is a carbon nanomaterial derived from graphene, but with nanometer sized holes through the nanosheet thickness. The holes are generated in a controlled air oxidation process in which the defective carbon on the graphene surface are selectively oxidized and removed. The presence of these holes enhances mass transport through electrode thickness and also enables the unique dry-press fabrication process that is not achievable using other carbon scaffold materials. The dry-pressed holey graphene air cathode platform is compatible with catalyst incorporation to improve battery reaction kinetics. This platform also allows for novel engineering of electrode architectures not achievable using conventional electrode fabrication approaches. The applications of such highly versatile, ultrahigh areal capacity air cathode platforms to both Li-O2 and Li-CO2 battery chemistries will be discussed. more...
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- 2020
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6. Silicon-Graphite Anode with High-Areal Capacity for Li-Ion Battery
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Geumjae Han, Yang-Kook Sun, and Peng Li
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Battery (electricity) ,Materials science ,Graphite anode ,Silicon ,chemistry ,chemistry.chemical_element ,Composite material ,Ion ,Areal capacity - Abstract
Nowadays, researchers are increasingly interested in silicon active material for lithium-ion batteries, which could meet the ever-increasing demand for high energy density owing to their satisfactory theoretical capacity (~4200 mAh g-1). Nevertheless, replacing the commercial graphite totally with silicon is still insurmountable due to bottlenecks such as low loading level and unsatisfactory areal capacity. Therefore, in this work, we turned eyes back on improved graphite anode with modified silicon cooperation through a facile blending process. The nano/microporous silicon active mateiral with boron doping and carbon nanotube wedging (B-Si/CNT) exhibits stable electrochemical performance (88.2% retention after 200 cycles at 2000 mA g-1) and high reversible capacity (ca. 2400 mAh g-1). After graphite cooperation, the resultant B-Si/CNT-graphite composite could illustrate an areal capacity of 5.2 mAh cm-2 with a high mass loading (11.2 mg cm-2). Besides, the enhanced anode also demonstrates acceptable utilization in lithium ion full battery with 2 mol% Al-doped full concentration gradient Li[Ni0.76Co0.09Mn0.15]O2 as cathode, showing a good energy density of ca. 8.0 mWh cm-2. Furthermore, considering that low initial coulombic efficiency (ICE) of silicon is another drawback for its industrial application, tough graphite framework and optimized lithium polyacrylate binder could be applied to increase the ICE effectively. Reference s 1. U.-H. Kim, S.-T. Myung, C. S. Yoon and Y.-K. Sun, ACS Energy Lett. 2017, 2, 196. 2. J. H. Lee, C. S. Yoon, J.-Y. Hwang, S.-J. Kim, F. Maglia, P. Lamp, S.-T. Myung and Y.-K. Sun, Energy Environ. Sci., 2016, 9, 2152. 3. P. Li, J.-Y. Hwang and Y.-K. Sun, ACS Nano, 2019, 13, 2624. Figure 1 more...
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- 2020
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7. Toward High Areal Capacity Lithium Batteries Via 3D Printing: From Liquid to Solid
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Xuejie Gao and Xueliang Sun
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Materials science ,chemistry ,Chemical engineering ,business.industry ,3D printing ,chemistry.chemical_element ,Lithium ,business ,Areal capacity - Abstract
3D-printing has found wide applications in numerous research fields, ranging from mechanical engineering, medicine, and material science to chemistry. Among them, it is capable of fabricating electrodes with high active material loading and improved ion/electron conductivity, and is thereby a promising method to improve the energy and power density of energy storage systems. And this technique offers a fresh viewpoint in designing high loading cathodes and will arise interest in other energy storage devices such as Li-ion batteries, Li-S batteries, and Li-Se batteries, etc. In this talk, I will talk about 3D-printed high active material loading cathode applied in batteries: from liquid to solid. In the first part of this talk, I will introduce 3D-printed high S loading cathode applied in liquid-based Li-S batteries. Compared with conventional cathode fabrication method, a 3D-printed S cathode with grid structure, which could facilitate Li+/e- transport at the macro, micro and nano scale in Li-S batteries. Moreover, a thickness-independent S cathode structure is also proposed via converting thick electrode into thousands of vertically aligned thin electrode by 3D printing. And each thin electrode delivers a constant thickness of around 20 μm, which is not affected by the intrinsic thickness of electrode as well as sulfur loading. Compared with other high S loading Li-S batteries performace, this work demonstrate a similar electrochemical kinetics in spite of the total sulfur loading or thickness of the electrode. [1-2] In the second part of this talk, I will talk about 3D-printed ultra-high Se loading cathode applied in solid-state Li-Se batteries. Compared with other Li-Se work, this work exhibits excellent cycling stability and remarkable rate performance with the highest reported Se loadings of 20 mg cm-2, and also delivers the highest reported areal capacity of 12.99 mA h cm-2 under a current density of 3 mA cm-2. The 3D-printed Se cathodes with grid structure provide large spaces for polymer electrolyte impregnation to further build interconnected Li+ transport channels in thick electrodes, enabling fast Li+ transport in solid-state Li-Se batteries. [3] References [1] X. Gao, X. Sun* et al, Nano Energy , 2019, 56, 595-603. [2] X. Gao, X. Sun* et al, Energy Storage Mater. Doi.org/10.1016/j.ensm.2019.08.001. [3] X. Gao, X. Sun* et al, J. Mater. Chem. A , under revision. Figure 1 more...
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- 2020
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