Failure Mechanisms of Nickel/Metal Hydride Batteries with Cobalt-Substituted Superlattice Hydrogen-Absorbing Alloy Anodes at 50 °C
The incorporation of a small amount of Co in the A2B7 superlattice hydrogen absorbing alloy (HAA) can benefit its electrochemical cycle life performance at both room temperature (RT) and 50 °C. The electrochemical properties of the Co-substituted A2B7 and the failure mechanisms of cells using such alloys cycled at RT have been reported previously. In this paper, the failure mechanisms of the same alloys cycled at 50 °C are reported. Compared to that at RT, the trend of the cycle life at 50 °C versus the Co content in the Co-substituted A2B7 HAAs is similar, but the cycle life is significantly shorter. Failure analysis of the cells at 50 °C was performed using X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDS), and inductively coupled plasma (ICP) analysis. It was found that the elevated temperature accelerates electrolyte dry-out and the deterioration (both pulverization and oxidation) of the A2B7 negative electrode, which are major causes of cell failure when cycling at 50 °C. Cells from HAA with higher Co-content also showed micro-shortage in the separator from the debris of the corrosion of the negative electrode.
Performance Comparison of Rechargeable Batteries for Stationary Applications (Ni/MH vs. Ni–Cd and VRLA)
The stationary power market, particularly telecommunications back-up (telecom) applications, is dominated by lead-acid batteries. A large percentage of telecom powerplants are housed in outdoor enclosures where valve-regulated lead-acid (VRLA) batteries are commonly used because of their low-maintenance design. Batteries in these enclosures can be exposed to temperatures which can exceed 70 °C, significantly reducing battery life. Nickel–cadmium (Ni–Cd) batteries have traditionally been deployed in hotter locations as a high-temperature alternative to VRLA. This paper compares the performances of nickel/metal hydride (Ni/MH), Ni–Cd, and VRLA batteries in a simulated telecom environment according to published testing standards. Among these three choices, Ni/MH batteries showed the best overall performance, suggesting substantially longer operating life in high temperature stationary use.
Failure analysis for poor solderability of Au surface of PCB
Nonwetting is one of the common problems and is always rejected in electronic assemblies. ENIG pads of a PCBA exhibited nonwetting after lead-free reflow soldering. With the aid of stereomicroscope, SEM&EDS and XRF, a series of analysis was performed. And after visual inspection, surface and cross section analysis, thickness measurement and solderability test, it can be inferred that oxidation of plating surface was the main reason for nonwetting, and corrosion in Ni plating caused an adverse impact on solderalibity.