Pedro L. Moss

An Electrical Circuit for Modeling the Dynamic Response of Li-Ion Polymer Batteries

An equivalent electrical circuit model based on parameters taken from ac impedance measurements obtained from a Li-ion polymer battery is simulated in a Matlab/Simulink environment. The model representation contains relevant parameters, including ohmic resistance, slow migration of Li-ions through the surface layers, faradaic charge transfer process, solid-state diffusion of Li-ions, and charge accumulation (intercalation capacitance) within the host material. The model also takes into account the non-homogeneous distribution properties (e.g, particle size, pore geometry) of the electrode which account for deviation from the ideal finite space Warburg behavior. The simulated and experimental results are compared and demonstrate that the impedance model can accurately predict the discharge power performance and transient and dynamic behavior of the Li-ion polymer batteries.

Study of Capacity Fade of Lithium-Ion Polymer Rechargeable Batteries with Continuous Cycling

A cycle life study was done on commercial lithium-ion polymer batteries to quantify contributions to capacity fade with continuous charge-discharge cycling. The cell consists of graphite (meso-carbon microbeads) as an anode material and lithium cobalt oxide (Li x CoO 2 ) as a cathode material. Analyses were done using ac impedance spectroscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The results show that contributions to capacity fade with continuous charge/discharge cycling included solvent―salt deposition on the anode surface; however, instability and cation disorder in the cathode electrode were identified as the main reasons for capacity fade with continuous charge/discharge cycling.

Investigation of cycle life of Li–LixV2O5 rechargeable batteries

Abstract Li rechargeable cells made with structural the arrangement Li/membrane/Li x V 2 O 5 were examined under different charge states using AC impedance, environmental scanning electron microscope (ESEM) and transmission electron microscope (TEM). These states include charged, discharged, and over-cycled. The lowest internal resistance was obtained from the cell in the charged state; the resistance increased when the cell was discharged; and the highest resistance was obtained from the cell in the over-cycled state. From the ESEM and TEM studies, it was found that the surface of the cathode was porous initially; however, it was coated with an amorphous film and porous features had also disappeared from the cell in the over-cycled state. In addition, higher concentration of aluminum was found on the surface of the cathode in over-cycled cells. The mechanisms for capacity degradation are discussed.

Transmission Line Model for Describing Power Performance of Electrochemical Capacitors

A simple equivalent circuit model for electrochemical (EC) capacitors can be established based on electrochemical impedance spectroscopy. The circuit consists of an ohmic resistor and a finite-length Warburg element in series. The EC capacitors performance including the transient/pulse response and energy density as a function of power density (Ragone plot) can be stimulated by the equivalent circuit model with three useful parameters including an ohmic resistance, total ionic resistance, and total capacitance of the electrodes.

Analysis of the Separator Thickness and Porosity on the Performance of Lithium-Ion Batteries

In this paper, investigation on the effect of separator thickness and porosity on the performance of Lithium Iron Phosphate batteries are analyzed. In recent years there have been intensive efforts to improve the performance of the lithium-ion batteries. Separators are important component of lithium-ion batteries since they isolate the electrodes and prevent electrical short-circuits. Separators are also used as an electrolyte reservoir which is used as a medium for ions transfer during charge and discharge. Electrochemical performance of the batteries is highly dependent on the material, structure, and separators used. This paper compares the effects of material properties and the porosity of the separator on the performance of lithium-ion batteries. Four different separators, polypropylene (PP) monolayer and polypropylene/polyethylene/polypropylene (PP/PE/PP) trilayer, with the thickness of 20 μm and 25 μm and porosities of 41%, 45%, 48%, and 50% were used for testing. It was found that PP separator with porosity of 41% and PP/PE/PP separator of 45% porosity perform better compared to other separators.

Analyses of the Calendaring Process for Performance Optimization of Li-Ion Battery Cathode

Olivine structure LiFePO4 (LFP) was synthesized via solid state processes, using Li2CO3, NH4H2PO4, and FeC2O4·H2O and C12H22O11 as precursor materials. The effects of calendaring are analyzed in terms of electrochemical performance, cycle life, surface morphology, and ac impedance analysis. The resulting LFP electrode was divided into calendared and uncalendared samples. Under electrochemical impedance testing, the calendared and uncalendared electrodes exhibited a charge transfer resistance of 157.8 Ω and 182.4 Ω, respectively. The calendared electrode also exhibited a higher discharge capacity of about 130 mAh/g at compared to a discharge capacity of 120 mAh/g at for the uncalendared electrode.

Fifth-order sigma delta modulator with decimation

This paper describes the use of very high precision noise shaping sigma delta modulation techniques for high fidelity audio applications that require a signal-to-noise ratio (SNR) of at least +80 dB. This paper discusses the implementation of a fifth-order sigma delta modulator with an oversampling frequency of 5.68 MHz. Specifically this paper is a comparative study of Matlab and Pspice implementations of our fifth order sigma delta modulator with a VHDL-based finite impulse response (FIR) filter.