Searching for new electrode materials with high capacity and energy density for use in Li-ion batteries is currently an important research topic. However, there is an urgent demand for more compact batteries for large-scale applications. We fabricated Si-Ti-Ni (STN) alloys by melt spinning and analyzed their crystal structure by X-ray diffraction and transmission electron and scanning electron microscopy. During Li insertion into the alloy electrodes, Si crystallites (active material) reacted with Li to form Li x Si alloys. The STN phase was the inactive matrix. To improve the electrochemical performance (initial efficiency, cycle life, etc.), the structure and composition of the STN anode were optimized. With 65 at% Si, the initial efficiency dramatically improved to 76%, and after 100 cycles, the charge/discharge efficiency was very high, 80%. In terms of cycle performance, the carbon coating and the electrolyte matching will be expected to reach the graphite level.Graphite is a representative anode material; however, it has reached its limit in energy density. 1 The lithiation mechanism proves that although Si alloys have higher capacity than does graphite, they suffer from large volumetric expansion. 2 Researchers have tried to solve this problem in various ways, for example, by using SiO x -based anodes. 3 Another method involves the use of Si/SiO x consisting of multiple nanosized domains of amorphous Si and SiO x . 4 Recently, researchers have stated that growing Si nanowires (SiNWs) on metal current collectors by chemical vapor deposition (CVD) is challenging because of the competing metal silicide formation duringthe growth process. 5 The aforementioned methods still involve critical issues such as volumetric expansion. We prepared Si-Ti-Ni (STN) alloys by using a rapid solidification process called melt spinning and tested Si contents ranging from 60 to 68 at% in order to determine the optimum Si content for the alloys. Electrochemical characteristics revealed the capacity retention rate (CRR) and charge/discharge (C/D) efficiency of the STN alloy containing 65 at% Si. We also determined the trade-off between the capacity and the cycle life for various Si contents in order to study the electrochemical characteristics of the STN alloys. ExperimentalSynthesis of Si-Ti-Ni alloy.-The experimental equipment for preparing the STN alloy primarily composed of an arc-melting chamber and a collecting powder after ball mill. Bulk STN ingots were prepared from Si (purity >99.9%), Ti (purity >99.9%), and Ni (purity >99.9%) by arc melting in argon atmosphere. Fig. 1 depicts the Si alloy manufacturing process. The left-hand side of the figure shows a simple diagram depicting the typical method to manufacture the alloys. Using this process, we first obtained the mother alloy, which on melting gave the molten alloy. Finally, we obtained alloy ribbons by rapid solidification using a quenching wheel. However, with lithium ion battery (LIB) anode, we used the ball mill to grind the ribbon which range <10 μm. Figs. 2a and 2...
This paper performs a dynamic analysis of a 10-kW solid oxide fuel cell/combined heat and power (SOFC-CHP) system with a multi-stack module via numerical simulations. The performance of stacks, tail gas burners, heat exchangers, and fuel reformers are modeled by the MATLAB/Simulink module. The effects of fuel and air maldistribution on SOFC-CHP systems are addressed in this work. A two-stack module for 10-kW power generation is adopted to represent the multi-stack module with high power modulation. The air flow rate and operating current, which are related to the fuel use rate of an SOFC system, should be optimally regulated to perform with maximum power generation and efficiency. The proposed dynamic analysis shows that the operating temperatures of the two stacks have a difference of 33 K, which results in a reduced total power generation of 9.77 kW, with inconsistent fuel use (FU) rates of 78.3% and 56.8% for the two stacks. With the optimal control strategy, the output power is increased to 10.6 kW, an increment of 8.5%, and the FU rates of the two stacks are improved to 79% and 70%, respectively. As a potential distributed power generator, the long-term effects of the studied SOFC-CHP systems are also investigated. The dynamic analysis of the long-term operating SOFC-CHP system shows that the total daily output power can be increased 7.34% by using the optimal control strategy.
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