Potential and Limitations of Research Battery Cell Types for Electrochemical Data Acquisition

Abstract

Developing new electrode materials and/or electrolytes for lithium‐ion batteries requires reliable electrochemical testing thereof. For this purpose, in academic research typically hand‐made coin‐type cells are assembled. Their advantage is a rather cheap and facile assembly, and possibility to prepare full‐cells as well as half‐cells, meaning cathode‐anode or electrode‐elemental lithium configurations. Critical parameters for testing data quality and the potential and limitations of cell tests in half‐cell configuration are discussed. Further, on the basis of a round robin test, using highly homogenous commercial electrodes, where graphite is used as anode and LiNi0.33Mn0.33Co0.33O2 (NMC111) as the cathode material, it is shown that data acquired is highly influenced by assembling parameters. Besides known variables such as the amount of electrolyte or electrode positioning, the proper height of the cell stack and the steel grade of the housing material are identified as decisive variables. Finally, it is demonstrated that under proper conditions coin cells can show a great cycle stability of >2200 cycles using 1 C as dis‐/charge rate while retaining a capacity of 80 %. This performance is close to pouch‐type cells containing the same electrodes and electrolyte, which were used as a benchmark system and showed >3500 cycles of lifetime.

Enabling Long‐term Cycling Stability of Na3V2(PO4)3/C vs. Hard Carbon Full‐cells

“…To calculate the precise N/P ratio later on, electrodes were weighted prior to their use. It has recently been shown that the steel grade of coin cell cases can have an enormous impact on the cycle life of alkali-ion batteries cycled vs. carbon-based anodes [23] and accordingly, coin cell parts made of S316L steel were chosen. After crimping, the cells were cleaned to remove any electrolyte deposits and possible salt bridges.…”

“…All results were achieved in coin cells, which are known to have reduced lifetimes compared to pouch cells. [23] It can therefore be assumed that the degradation can still be significantly reduced by changing the cell format and that an excellent cycling stability should be possible based on NVP/C vs. HC cells with NaPF 6 in EC/PC as electrolyte. Likewise, it becomes evident that FEC, which doubtlessly extends the lifetime of NVP vs. Na cells, [30] reduces the lifetime of NVP vs. HC cells and is therefore not a suitable additive in full-cells.…”

“…For the latter, a continuous increase of the RiDC values was consistently observed for very similar cell building parameters and with the same test method. [23]…”

“…It becomes obvious that numerous studies report quite different lifetimes for NVP/C vs. HC cells, which may be largely due to different electrolytes, loadings and C-rates, or possibly also due to external factors such as cell assembly, which -especially in the case of coin cells -has an enormous influence on the long term cycling stability. [23] The cause of the capacity decay in full-cells has been investigated previously. [10] Herein, loss of active sodium to the solid electrolyte interface (SEI) is reported to lead to a decrease of the overall capacity of the NVP/C vs. HC cells.…”

A Guide to Making Highly Reproducible Li-Ion Single-Layer Pouch Cells for Academic Researchers

“…Moreover, the quality of the assembly process and parts used in coin cell preparation can greatly affect the representativeness and reproducibility of the electrochemical results. [1][2][3] Thus, academic researchers have increasingly adopted highly reproducible, industrial-quality wound pouch cells for more accurate studies. [4][5][6][7] However, these wound pouch cells are not always practical, especially for novel active material evaluation because they require larger amounts of material than typically synthesized at laboratory-scale.…”