Improving lithium-ion cells by replacing polyethylene terephthalate jellyroll tape

Abstract

Polyethylene terephthalate (PET) tape is widely used by well-known lithium-ion battery manufacturers to prevent electrode stacks from unwinding during assembly. PET tape is selected since it has suitable mechanical and electrical properties, but its chemical stability has been largely overlooked. In the absence of effective electrolyte additives, PET can depolymerize into its monomer dimethyl terephthalate (DMT), which is an unwanted redox shuttle that induces significant self-discharge in a lithium-ion cell. This study presents a chemical screening experiment to probe the PET decomposition mechanism involving in situ generated methanol and lithium methoxide from dimethyl carbonate, one of the most common electrolyte solvents in lithium-ion cells. By screening other polymers, it is found that polypropylene (PP) and polyimide (Kapton) are stable in the electrolyte. Finally, it is demonstrated that reversible self-discharge of LiFePO4/graphite cells can be virtually eliminated by replacing PET jellyroll tape with chemically stable PP tape.

A Multifunctional Amino Acid Enables Direct Recycling of Spent LiFePO4 Cathode Material

“…After the hydrothermal regeneration process, the main binding energy peaks of R‐LFP shift lower to 724.1 and 710.9 eV, which corresponds to Fe(II) of Fe 2 p 1/2 and Fe 2 p 3/2 . [ 19,30 ] The presence of Fe(III) is not detected in the R‐LFP sample, which agrees well with the XRD data. This demonstrates that the chemical composition and crystal structure of S‐LFP are restored after one‐step hydrothermal process.…”

“…[16,27,28] By fitting the XPS spectra of C 1s Figure 4i, the S-LFP sample shows no C─N bond but an apparent 𝜋-𝜋* bond at 290.8 eV which is associated with the presence of carbon nanotubes due to incomplete removal of the binders (Figure S14, Supporting Information). [30,42] For R-LFP, the hydrothermal regeneration process removes binders, enabling the formation of C─N bond. The peak value of C─N bond is at 285.6 eV, which is supported by the previous reports in the literatures.…”

Correlating Mn Dissolution and Capacity Fade in LiMn0.8Fe0.2PO4/Graphite Cells During Cycling and Storage at Elevated Temperature

“…In the absence of effective electrolyte additives, cells with polyethylene terephthalate jellyroll tape (like the cells used here) can have high rates of self-discharge due to the in situ formation of a redox shuttle. [39][40][41][42][43] This and other self-discharge mechanisms would decrease the voltage of the cells during the storage period and change the transition metal oxidations states, which is undesirable for this experiment; hence the voltage hold protocol was selected. Cells completed a total of 500 h of storage, which corresponds to a total of 600 h of test time to account for the time required for the C/10 check-up cycles every 100 h (see Fig.…”

“…The parasitic current is worse for CTRL cells than 2VC cells, which matches the trend of the capacity fade being more severe for the cells filled with CTRL electrolyte. This parasitic current could be due to the formation of a redox shuttle 40,43 or electrolyte oxidation. This is discussed further in the SI.…”

Impact of Salts and Linear Carbonates on the Performance of Layered Oxide/Hard Carbon Sodium-Ion Pouch Cells with Alkyl Carbonate Electrolytes

“…In addition, the jellyroll tape found in commercial cells has been shown to be of concern for cell performance with certain salt/solvent combinations. [6][7][8][9][10] In our previous work, we used 1 M NaPF 6 in EC:DEC (50:50 wt%) as the electrolyte in layered oxide/hard carbon sodium-ion pouch cells. This electrolyte formulation led to 95% capacity retention after 500 cycles at C/5 and 40 °C in the presence of 2 wt% vinylene carbonate (VC).…”