This paper presents an extensive study concerning a lithium-ion battery system for constructing high-performance power source systems intended to make advanced environmental vehicles a practical reality. Battery performance must be predicted and designed with higher accuracy in order to achieve performance attributes suitable for such power source systems. For example, more quantitative approaches for improving battery power output are needed that are based on a thorough understanding of the fundamental processes which take place in a battery. In line with these perspectives, we constructed a simulation model of electrode reactions and charge transport processes and used it to examine the effects of different factors on battery performance. This approach is considered to be promising for the construction of a high-performance battery system for EV application. Higher battery performance can be expected from optimization of the electrode parameters. With regard to specific power in particular, the present study examined the possibility of improving battery power output during a short duration. This paper describes how the concept of short-duration power output might be derived from the electrode characteristics and discusses its potential effects on the overall battery system. It also presents the results of simulations that examined the battery system from the standpoint of thermal behavior.
We demonstrate a heterojunction diode (HJD) fabricated with p + -type polycrystalline silicon on an n --type epitaxial layer of 4H-SiC. The HJD achieved extremely low V on and high reverse blocking voltage compared with a SiC Schottky barrier diode (SBD). The HJD shows good diode characteristics for temperatures ranging up to 200°C. Measured switching characteristics of the HJD exhibit almost zero reverse recovery similar to that of the SBD.
Thin (~10nm) Si layers have been deposited using Rapid Thermal CVD at temperatures ranging 950°C-1050°C. RTCVD deposited Si layers have been oxidized using N2O at 1300°C during relatively short times (15min) to produce SiO2 layers of 20-30nm. The interfacial characteristics of N2O oxidized RTCVD layers have been studied using the conductance method, showing a reduced traps density and a low band bending fluctuation when compared with conventional N2O grown oxides on 4H-SiC substrates. The surface topology of these layers has also been analyzed evidencing an adequate topography with low roughness.
We demonstrate a new high-voltage p+ Si/n- 4H-SiC heterojunction diode (HJD) by numerical simulation and experimental results. This HJD is expected to display good reverse recovery because of unipolar action similar to that of a SiC Schottky barrier diode (SBD) when forward biased. The blocking voltage of the HJD is almost equal to the ideal level in the drift region of n- 4H-SiC. In addition, the HJD has the potential for a lower reverse leakage current compared with the SBD. A HJD was fabricated with p+-type polycrystalline silicon on an n--type epitaxial layer of 4H-SiC. Measured reverse blocking voltage was 1600 V with low leakage current. Switching characteristics of the fabricated HJD showed nearly zero reverse recovery with an inductive load circuit.
In the first stage of our research and development work on high-performance lithium-ion batteries from the early to the mid-1990s, a high-energy-capacity battery was investigated with the aim of applying it to electric vehicles (EVs). The second stage of our program concerned studies of a lithium-ion battery for application to series hybrid electric vehicles (SHEVs), and the third stage was mainly focused on a high- power lithium-ion battery for use on parallel hybrids (PHEVs). The results of those studies demonstrated that lithium-ion batteries are the best battery systems for use on these environmental vehicles. A battery simulation program was also constructed concurrently with those investigations for use as a tool in verifying the superiority of lithium-ion batteries. This simulation program takes into account the electrochemical phenomena that occur inside the battery, especially the effect of lithium-ion diffusion on power output characteristics. In the present study, battery simulations were performed to quantify the flow of ions inside the battery. This paper presents the results of sensitivity analyses concerning the electrode structural parameters influencing the long-duration power output characteristic that is required of batteries for use on EVs and SHEVs.
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