posted on 2021-04-21, 09:14authored byJunho Ahn, Byeongho Park, Jongsoon Kim, Moon-Kwang Um, Jin Woo Yi, Jung-Keun Yoo
Cylindrical-type
cells have been widely adopted by major battery
and electric vehicle manufacturers owing to their price competitiveness,
safety, and easy expandability. However, placement of electrodes at
the core of cylindrical cells is currently restricted because of high
electrode curvature and the lack of specialized electrodes and electrode
materials. Here, we report the realization of highly flexible high-energy-density
electrodes (active material loading of >98.4%) that can be used
at
the cores of cylindrical cells. The improved properties result from
the introduction of a multifunctional poly(melamine-co-formaldehyde) (MF copolymer) additive, which yields a relatively
more fluidic and well-dispersed slurry using only 0.08 wt %. MF copolymer-mediated
formation of completely wrapped CNT/PVDF networks on LiCoO2 (LCO) and accompanying contact enhancement between LCO and carbon
nanotubes (CNTs) resulted in an increase of electrical and mechanical
properties of the two types (composites with or without collectors)
of electrodes compared with those of additive-free electrodes. Flexibility
tests were carried out by rolling electrodes onto cylinder substrates
(diameters of ca. 1 and 10 mm); this process resulted in relatively
lower resistance changes of the MF copolymer-containing electrodes
than for the reference electrodes. In addition, capacity retention
after 100 cycles for cells with and without MF copolymers was approximately
10–20% better for the samples with the MF copolymer than for
those without. CNT/PVDF networks with MF copolymers were proven to
induce a relatively thin and stable cathode electrolyte interface
layer accompanying the chemical bond formation during cycling.