Effect of Prelithiation Process for Hard Carbon Negative Electrode on the Rate and Cycling Behaviors of Lithium-Ion Batteries

Two prelithiation processes (shallow Li-ion insertion, and thrice-repeated deep Li-ion　insertion and extraction) were applied to the hard carbon (HC) negative electrode (NE) used in　lithium-ion batteries (LIBs). LIB full-cells were assembled using Li(Ni0.5Co0.2Mn0.3)O2 positive　electrodes (PEs) and the prelithiated HC NEs. The assembled full-cells were charged and discharged　under a low current density, increasing current densities in a stepwise manner, and then constant　under a high current density. The prelithiation process of shallow Li-ion insertion resulted in the　high Coulombic efficiency (CE) of the full-cell at the initial charge-discharge cycles as well as in a　superior rate capability. The prelithiation process of thrice-repeated Li-ion insertion and extraction　attained an even higher CE and a high charge-discharge specific capacity under a low current density.　However, both prelithiation processes decreased the capacity retention during charge-discharge　cycling under a high current density, ascertaining a trade-off relationship between the increased CE　and the cycling performance. Further elimination of the irreversible capacity of the HC NE was　responsible for the higher utilization of both the PE and NE, attaining higher initial performances,　but allowing the larger capacity to fade throughout charge-discharge cycling

Electrochemical Impedance Spectroscopy on the Performance Degradation of LiFePO4/Graphite Lithium-Ion Battery Due to Charge-Discharge Cycling under Different C-Rates

Lithium-ion batteries (LIBs) using a LiFePO4 cathode and graphite anode were assembled in　coin cell form and subjected to 1000 charge-discharge cycles at 1, 2, and 5 C at 25 C. The performance　degradation of the LIB cells under di erent C-rates was analyzed by electrochemical impedance　spectroscopy (EIS) and scanning electron microscopy. The most severe degradation occurred at 2 C　while degradation was mitigated at the highest C-rate of 5 C. EIS data of the equivalent circuit model　provided information on the changes in the internal resistance. The charge-transfer resistance within　all the cells increased after the cycle test, with the cell cycled at 2 C presenting the greatest increment　in the charge-transfer resistance. Agglomerates were observed on the graphite anodes of the cells　cycled at 2 and 5 C; these were more abundantly produced in the former cell. The lower degradation　of the cell cycled at 5 C was attributed to the lowered capacity utilization of the anode. The larger cell　voltage drop caused by the increased C-rate reduced the electrode potential variation allocated to the　net electrochemical reactions, contributing to the charge-discharge specific capacity of the cells

Structure and non-blocking properties of bidirectional unfolded two-stage switches

Two-stage switch networks are an emerging design option for relatively small-capacity space switches. They are classified into two categories: folded and unfolded. Although folded switches have been well studied, research on unfolded two-stage switch networks (UTSNs) remains limited. Here, non-blocking UTSNs are considered. First, a new UTSN design is presented that consists of input and output switch modules (ISMs and OSMs) using bidirectional switching techniques. The proposed UTSN is represented by B(n, m, r), where n, m, and r denote the number of input ports of the ISM, number of OSMs, and number of ISMs, respectively. Second, the maximum number of rearrangements for B(n, n, r) is proved to be L(r-1)/2(n-1) RIGHT FLOOR in general, whereas it is limited to two when n >= r. The strictly non-blocking condition for B(n, m, r) to be m >= n + 1 is also determined. Finally, it is shown that the switch hardware complexity becomes minimal at n=N/2 and saturates at N-2/2 as N -> infinity

Bayesian co-estimation of selfing rate and locus-specific mutation rates for a partially selfing population

We present a Bayesian method for characterizing the mating system of populations reproducing through a mixture of self-fertilization and random outcrossing. Our method uses patterns of genetic variation across the genome as a basis for inference about pure hermaphroditism, androdioecy, and gynodioecy. We extend the standard coalescence model to accommodate these mating systems, accounting explicitly for multilocus identity disequilibrium, inbreeding depression, and variation in fertility among mating types. We incorporate the Ewens Sampling Formula (ESF) under the infinite-alleles model of mutation to obtain a novel expression for the likelihood of mating system parameters. Our Markov chain Monte Carlo (MCMC) algorithm assigns locus-specific mutation rates, drawn from a common mutation rate distribution that is itself estimated from the data using a Dirichlet Process Prior (DPP) model. Among the parameters jointly inferred are the population-wide rate of self-fertilization, locus-specific mutation rates, and the number of generations since the most recent outcrossing event for each sampled individual

Design and optimization of a wideband impact mode piezoelectric power generator

This paper proposes a new design of an impact mode piezoelectric power generator that is able to operate in a wide frequency bandwidth by using a round piezoelectric ceramic as the energy converter. The evaluation results show that the output of the power generator can be optimized by implementing a so-called indirect impact configuration. To realize this type of configuration, a shim plate is placed between the piezoelectric ceramic and the hitting structure. At a certain base excitation frequency, the output efficiency of this configuration increases to about 4.3 times that of the direct impact configuration. Furthermore, it is demonstrated that the designated power generator is able to generate electric energy up to approximately 1.57 mJ within 120 s from the vibration of a moving vehicle

Role of SiOx in rice-husk-derived anodes for Li-ion batteries

The present study investigated the role of SiOx in a rice-husk-derived C/SiOx anode on the rate and cycling performance of a Li-ion battery. C/SiOx active materials with different SiOx contents (45, 24, and 5 mass%) were prepared from rice husk by heat treatment and immersion in NaOH solution. The C and SiOx specific capacities were 375 and 475 mAh g(-1), respectively. A stable anodic operation was achieved by pre-lithiating the C/SiOx anode. Full-cells consisting of this anode and a Li(Ni-0.5,Co-0.2,Mn-0.3) O-2 cathode displayed high initial Coulombic efficiency (similar to 85%) and high discharge specific capacity, indicating the maximum performance of the cathode (similar to 150 mAh g(-1)). At increased current density, the higher the SiOx content, the higher the specific capacity retention, suggesting that the time response of the reversible reaction of SiOx with Li ions is faster than that of the C component. The full-cell with the highest SiOx content exhibited the largest decrease in cell specific capacity during the cycle test. The structural decay caused by the volume expansion of SiOx during Li-ion uptake and release degraded the cycling performance. Based on its high production yield and electrochemical benefits, degree of cycling performance degradation, and disadvantages of its removal, SiOx is preferably retained for Li-ion battery anode applications