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.