Substandard? Lithium-ion cells available on online marketplaces

Summary:

Access to up-to-date information on lithium-ion cells is crucial for a wide range of academic research areas. However, researchers generally do not have access to the latest cells from large manufacturers and therefore have to rely cells available on online marketplaces.

To quantify the state of these cells, we collected data on 495 unique cells from seven online marketplaces and compared their characteristics to the 2019 status quo defined by the EUCAR consortium and measurements of a VW ID.3 cell. The majority of cells are cylindrical, with a nominal voltage of 3.6V or higher and a capacity of up to 6 Ah. An analysis of the data availability revealed that less than half the cells provided information regarding the cycle life or continuous discharging power. Only 4% of the cells contained information on all parameters that are considered in the EUCAR status quo.

A comparison with the EUCAR status quo revealed that the majority of cells match the status quo for energy density, discharging power and cycle life, but underperform in specific energy and charging rate. It should be noted that the charging rate specified by the EUCAR consortium is also not met by the VW ID.3 cell. An analysis of cell parameters versus their release date shows no clear progress in any of the parameters. The best performance for each cell parameter has been stagnant for a few years across all parameters. A regression analysis between the cell specific cost and the other parameters revealed that the lowest specific cost is achieved by cells with a high energy content. This is likely caused by the overhead involved in selling individual cells, which makes it impossible to identify cost-performance trade-offs.

We can conclude that the lithium-ion cells available on online marketplaces match the status quo in the automotive industry when it comes to energy density, discharging power and cycle life. However, only few cells match the status quo specific energy and charging rate. The largest observed deficiency is the quality of the available data, where only 4% of the cells listed the required parameters for a full comparison.