Consumer-Based Evaluation of Commercially Available Protected 18650 Cells

Abstract

Over the past few years, the use of 18650 form factor lithium-ion (Li-ion) cells have transitioned from primarily commercial applications to consumer/residential use. An evaluation of eight commercially available, circuit protected, 18650 form factor Li-ion cells were performed, with analysis focusing on a residential consumer evaluation of performance. As typical consumer cell usage occurs at a relatively low discharge rate, cells were evaluated between 4.2 V and 2.7 V at C/10, C/5, and C/2 discharge rates. The evaluated cells ranged from “high-cost” Panasonic, Hixon, Orbtronic, and EastValley cells to “low-cost” UltraFire (UF) and Eilong cells. Initial discharge comparisons revealed that no cells delivered their nameplate capacity, with a large overstatement of cell capacity occurring for low-cost cells. On average, high-cost cells delivered 92.5% of their advertised capacity, with low-cost cells delivering 20.6% at a C/10 rate. Basing consumer evaluation on a cost per unit capacity and/or cost per unit energy, even with this large overstatement in capacity, low-cost cells still offer an advantage over higher-cost alternatives. The average cost per amp-hour for each cell group ranged from $1.65 to $3.38 for the low-cost and high-cost cell groupings, respectively. Analysis of voltage profiles highlighted two chemistries used in cell production, coinciding with each cell grouping.

An Impedance Behavior Study of Commercial NCA Cylindrical Battery Cells at Different SOCs

“…The classic 18650 format cylindrical Li-ion battery has been widely used today by electric vehicles (EVs), which has a wound jelly-roll structure in a form of an Archimedean spiral. 1,2 Comparing to the stacked electrodes, such wound electrodes can be produced faster and provide a relatively higher energy density in the limited given space on the electric vehicles. 3,4 With the help of numerous research activities by battery makers, an optimized manufacturing procedure from the material selection through electrode production to cell fabrication and quality control has been well established, which gives these commercial cylindrical cells a stable structure and cycling performance.…”