Mathematical Models for the Performance Degradation of Lithium-Ion Batteries with Different Status of Charge (SOC) in Long-Term High Temperature Storage

Mathematical models to evaluate and predict the performance degradation of lithium-ion batteries (LIBs) with different status of charge (SOC) in long-term high-temperature storage which are also applicable for setting rational storage conditions (temperature, SOC, and time) of LIBs were established. Parameters including voltage drop (Delta V), reversible capacity (RC) loss, and internal impedance (IMP) increase of LIBs under different temperature (60, 45, and 25°C) are used to allow the model to clarify its function. According to the results obtained from commercial 18650 cylindrical batteries with LiNi0.33Co0.33Mn0.33O2 cathode, the mathematical relationship between Delta V and storage days (x) is fitted into a simple formula: Delta V =m.In(x)-n, and similarly, RC loss = m'.exp (n'.x) and IMP increase = m''.xn'' can also be acquired. In these formulas, m, n, m', n', m'' and n'' are constants when temperature and SOC are fixed. If only the temperature is fixed, the value of these constants can be derived into a function with SOC (y), respectively, while further plugging the function into the calculation formula of Delta V, RC loss, and IMP increase, respectively, allows the mathematical models to be set up.

Solderability and Reliability of Sintered Nano-Ag Bond Pads of Printed Re-Distribution Layer (RDL)

Re-distribution layer (RDL) is one key enabling technology for advance packaging. RDL is usually fabricated in wafer level by photolithography process. An alternative approach for implementing RDL by additive manufacturing (AM) method is proposed in this study. This allows RDL to be fabricated on singulation chip. Nano-silver (nano-Ag) ink is printed on the silicon chip to form routing traces and bond pads. However, the Ag pad may be consumed by solder quickly if the process is not properly controlled. This paper studied the effect of nano-Ag ink sintering condition on the solderability of Ag pad. The solder joint mechanical integrity was evaluated by solder ball shear test. High temperature storage test was also carried out to evaluate the solder joint reliability. Experiment results showed that Ag pad fabricated by AM is SMT compatible. High temperature storage did not cause early failure to the samples. There was not significant change in the Ag3Sn IMC layer thickness and mechanical strength. The finding of the present study will serve as a very useful reference for future practice of forming solder joints on sintered nano-Ag pads.