Design, Properties, and Manufacturing of Cylindrical Li-Ion Battery Cells—A Generic Overview

Abstract

Battery cells are the main components of a battery system for electric vehicle batteries. Depending on the manufacturer, three different cell formats are used in the automotive sector (pouch, prismatic, and cylindrical). In the last 3 years, cylindrical cells have gained strong relevance and popularity among automotive manufacturers, mainly driven by innovative cell designs, such as the Tesla tabless design. This paper investigates 19 Li-ion cylindrical battery cells from four cell manufacturers in four formats (18650, 20700, 21700, and 4680). We aim to systematically capture the design features, such as tab design and quality parameters, such as manufacturing tolerances and generically describe cylindrical cells. We identified the basic designs and assigned example cells to them. In addition, we show a comprehensive definition of a tabless design considering the current and heat transport paths. Our findings show that the Tesla 4680 design is quasi-tabless. In addition, we found that 25% of the cathode and 30% of the anode are not notched, resulting in long electrical and thermal transport paths. Based on CT and post-mortem analyses, we show that jelly rolls can be approximated very well with the Archimedean spiral. Furthermore, we compare the gravimetric and volumetric energy density, the impedance, and the heating behavior at the surface and in the center of the jelly rolls. From the generic description, we present and discuss production processes focusing on format and design flexible manufacturing of jelly rolls.

Lithium-Ion Cells in Automotive Applications: Tesla 4680 Cylindrical Cell Teardown and Characterization

“…For the internal connection of the cell poles a disk tab design with notched and folded electrode tabs is utilized. 8 The cathode disk is made out of aluminum and the anode disk out of copper with both having a thickness of 0.2 mm. The dimensions of the two disks are depicted in Fig.…”

“…After each pulse, a pause of 300 s was added, before the charge was reset using coulomb counting and the cell was relaxed for 1 h before the next pulse. For all test procedures at cell level a lower cutoff voltage of 2.5 V was selected, with 4.2 V as the upper limit (voltage range based on Baazouzi et al 8 and publicly available battery characteristics 31 ). A high precision battery cycler (BCS-815, Bio-Logic SAS, France) was used to perform the electrical capacity characterization procedures and the galvanostatic EIS measurements, with cell holders model KSR-150-OS (Voltavision, Germany) to constrain and connect the cells using a 4-wire-measurement.…”

“…Compared to a 21700 cell, the new format increases volume by a factor of 5.5. 8 Large-format cylindrical cells are expected to reduce production costs in pack assembly, as fewer individual cells need to be assembled and interconnected to achieve the same battery pack characteristics. In addition to Tesla, the manufacturer BMW announced the launch of its new electric vehicle platform called "Neue Klasse", also utilizing cylindrical cells with a diameter of 46 mm (with two different axial lengths).…”

“…9 Battery cell manufacturers usually only provide limited information about cell characteristics and do not disclose their highly complex, interdependent manufacturing processes. 8,[10][11][12] In addition, cell chemistry and cell design vary depending on the cell and original equipment manufacturers as well as customer requirements, which leads to manufacturer-specific production chains. 13,14 In contrast, academic lithium-ion battery (LIB) research is typically conducted on a laboratory scale or utilizing pilot production lines using smaller cell formats, easy-to-make cell designs, and manual or semi-manual production processes.…”

“…Shen et al 25 used a distributed 3D coupled electro-thermal equivalent circuit network model of a 4680 cell to study different thermal management options and demonstrate that there does not need to be a trade-off between cell size and thermal performance, as long as cylindrical cells are designed tabless. To the best of the authors' knowledge, the first academic article with actual 4680 cells from Tesla was presented by Baazouzi et al, 8 in which the authors investigated 19 cylindrical lithium-ion battery cells from four cell manufacturers in four formats (18650, 20700, 21700, 4680) with respect to their design features, such as tab design and quality parameters. The results show that the Tesla 4680 cell architecture is not fully tabless since only the jelly roll design is engineered in a tabless manner.…”