Browsing by Author "Chen, Jiajia"

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A polyoxometalate-based polymer electrolyte with an improved electrode interface and ion conductivity for high-safety all-solid-state batteries
(2019-07-14)
Yuan, Xiangfei
;
Sun, Cui
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Duan, Jia-Ning
;
Fan, Jingmin
;
Yuan, Ruming
Solid electrolytes have been considered as some of the most promising candidates for next generation lithium-based batteries because they eliminate the potential safety hazards of liquid organic electrolytes and further increase the energy density of batteries. However, inherent defects such as low conductivity and poor interface compatibility with electrodes critically hinder their extensive application. Polyoxometalate Li-7[V15O36(CO3)] (LVC) can dissociate Li+ in electrolyte and possesses a high diffusion coefficient, which constitute a pathway for Li+ transmission. Herein, a polyoxometalate-based polymer electrolyte (PPE) with an improved electrode interface and ion conductivity for high-safety all-solid-state batteries has been designed and synthesized to further enhance their electrochemistry behaviour. Compared with the routine PEO18LiTFSI electrolyte, the ionic conductivity was enhanced. Meanwhile, LVC can improve the interface compatibility between the electrode and electrolyte significantly, which promotes reaction kinetics and suppresses lithium dendrites against Li metal. When employed in LiFePO4|Li batteries, the specific discharge capacity after 180 cycles reached 148 mA h g(-1) with a high coulombic efficiency of around 99.9% at 0.5C. According to the result of ARC, LiFePO4|C batteries with PPEs are endowed with superior safety as the onset temperature of the self-heating process reaches up to 181.4 degrees C and the thermal runaway process does not occur within the range of 360 degrees C, indicating the potential of the PPE for high-safety all-solid-state batteries.
Coverage Probability of Small Cell Networks with Composite Fading and Shadowing
(2014)
Chen, Jiajia
;
Wang, Li-Chun
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Liu, Chun-Hung
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電機工程學系
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Department of Electrical and Computer Engineering
Coverage analysis of a small cell network is very crucial since small cell deployment will dominates the topology of a cellular in the future. The majority of prior work on the coverage probability is studied based on a simple and consistent Rayleigh fading models in a Poisson-distributed cellular network in order to avoid analytical intractability. In this paper, we study the coverage probability problem in a Poisson small cell network with much more general channel impairments. First a neat expression of the coverage probability with compose Rayleigh fading and log-normal shadowing is derived and it discloses two important facts the coverage performance is not improved by deploying more base stations and it is significantly weakened by shadowing. Then we find the coverage probability with low complexity for the case that a dual-slop path loss is used, the desired signal experiences Nakagami-m fading and interference signals undergo Rayleigh fading. It is able to more practically reflect the coverage performance of a user.
Performance Analysis of Small Cells Using Stochastic Geometry Approach in Nakagami Fading Channels
(2013)
Chen, Jiajia
;
Wang, Li-Chun
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電機資訊學士班
;
Undergraduate Honors Program of Electrical Engineering and Computer Science
Interference analysis of small cellular systems plays an important role in next generation cellular systems. Recently, several papers adopts stochastic geometry provide analytical framework with distributed for a multi-cellular system that interfering signals. However, most papers in this area only consider Rayleigh fading signal and one-slope path loss. In this paper, we present an analytical framework for small cells taking into account of Nakagami-m fading and two-slope path loss.