Low Molecular Weight Spandex as a Promising Polymeric Binder for LiFePO₄ Electrodes

Abstract

can deliver superior rate performance despite its inherently low electric conductivity. Especially, modifications of the intrinsic phase via doping [17] with aliovalent elements and incorporating off-stoichiometry [18] improved the rate performance remarkably. Also, the formation of metastable structures that allows the nucleation of a second phase to bypass was revealed [19,20] as the origin of the exceptional rate capability of LFP.Besides the tuning of active material, various polymeric binders were lately investigated [21][22][23][24][25] for LFP electrodes in both organic and aqueous media. Aqueous binders were particularly highlighted because of their conspicuous advantages, including low cost and easy disposal of waste solvents after processing. [21,22,24,26] In spite of these advantages, currently, LFP electrodes are mostly manufactured via N-methyl-2pyrrolidone (NMP)-based slurry process because the use of aqueous media causes Li ion extraction from active powder and corrosion of aluminum (Al) current collector. [27][28][29] As in most LIB cathodes, polyvinylidene difluoride (PVDF) dispersed in NMP has been mainly used for LFP electrodes, to take advantages of the properties of PVDF, such as high electrochemical stability, high specific dielectric constant, and decent Li ion conductivity. However, PVDF binders operate mainly based on van der Waals interaction, leading to weak adhesion of the electrode to the current collector. Also, PVDF used for most commercial LIBs has high molecular weights (MWs) of around 1 000 000 and therefore often suffers from binder aggregation during slurry preparation as well as in the final electrode film. Herein, we introduce an unconventional binder, namely spandex, with relatively low molecular weight of around 300 000. Compared to the commercial PVDF binders with both high and low MWs, the spandex binder exhibited superiority in uniformness of electrode morphology, adhesion of electrode to an Al current collector, conservation of solvent during slurry preparation, and rate capability in battery operation. Furthermore, the enhanced adhesion of electrode renders the spandex binder suitable for 3D porous electrodes that are considered for future flexible battery applications. Moreover, we can take advantage of the long research and industrial experience of spandex; spandex is usually produced by step-growth polymerization and used for various applications, including clothes, daily supplies, biomedical devices, etc. [30,31] This investigation conveys a useful lesson that although occupying a small content in the electrode, binder can considerably improve the performance of established commercial LIB electrodes, and unexplored polymers can be good candidates for such opportunities. Figure 1 schematically illustrates the electrode morphologies when high MW PVDF (H-PVDF) and low MW spandex (L-spandex) are adopted as binders. H-PVDF often causes Lithium-ion batteries (LIBs) have been successfully developed as power sources for mobile information technology (IT) devices and hybrid...

Graphite-Embedded Lithium Iron Phosphate for High-Power–Energy Cathodes

“…The LFP/graphite electrodes can supply higher discharge capacity, discharge current, and middle discharge voltage, indicating the ability to deliver higher energy (capacity × voltage) and power density (voltage × current), which are essential characteristics for the applications of power tools and electric vehicles. Meanwhile, Figure e compares the capacity and cycling number at different C-rates for various LFP-based cathodes reported, ,,− including carbon-coated LFP, conductive polymer-coated LFP, graphene-modified LFP, and LFP/carbon-nanotube composites. The LFP/graphite electrode can provide a capacity over 100 mA h g –1 when charging and discharging under 60 C rate, which is the best-known value for previously reported LFP cathodes. ,,− …”

“…Meanwhile, Figure e compares the capacity and cycling number at different C-rates for various LFP-based cathodes reported, ,,− including carbon-coated LFP, conductive polymer-coated LFP, graphene-modified LFP, and LFP/carbon-nanotube composites. The LFP/graphite electrode can provide a capacity over 100 mA h g –1 when charging and discharging under 60 C rate, which is the best-known value for previously reported LFP cathodes. ,,− …”

Moving to Aqueous Binder: A Valid Approach to Achieving High‐Rate Capability and Long‐Term Durability for Sodium‐Ion Battery

“…3. A solid permeable interface (SPI) is known to usually form on a cathode surface due to oxidation of the electrolyte, which can strongly affect the long‐term cycling stability . To further understand the effect of the binder on the SPI layer, an X‐ray photoelectron spectroscopy (XPS) analysis was carried out.…”

Exploiting Materials to Their Full Potential, a Li-Ion Battery Electrode Formulation Optimization Study

“…To put these results in perspective, in the literature, new materials or architectures are often initially tried in formulations with 80% w AM and 10% w of both a carbon additive and a binder and compared to known materials. − Figure shows the power capabilities of such a formulation with LFP- and LTO-based TPE-bound electrodes compared to the optimal formulation drawn from our DoE. The best, unoptimized PVDF-bound electrode from each DoE is also displayed, LFP-RUN04 and LTO-RUN29 for comparison’s sake.…”