Lithium-ion
batteries are core components of flexible electronic
devices. However, deformation types, such as impinging, bending, stretching,
folding, and twisting, can cause internal cracks and, eventually,
damage these batteries. The cracks separate the active particles from
the conductive particles and the binder, as well as the electrode
from the collector. Self-healing binders can alleviate this mechanical
damage and improve the stress response of active material particles
during high rates of charging and discharging of these batteries and
the operation at a high voltage, thereby enhancing their cycle performance.
In the present study, a thermoplastic intrinsic self-healing polymer
(TISP) binder is proposed. The TISP is obtained by polymerization
of butanediol (2,3-BDO), propylene glycol (1,3-PDO), succinic acid
(SuA), sebacic acid (SeA), and iconic acid (IA). The hydroxyl and
ester groups in its structure can form diverse bonds including the
hydrogen and ion-dipole with active particles and the current collector,
thereby producing elevated adhesion. Its properties, including a low
glass transition temperature (−60 °C), amorphous structure,
and low cross-link density, improve the mobility of polymer chains
at 40 °C, and this facilitates structural recovery and the maintenance
of strong adhesions. Owing to its higher occupied molecular orbital
(HOMO) level than the electrolyte solvent, the TISP is likely oxidized
before the main component of the electrolyte during charging. This
decomposition produces a chemical passivation interphase on the cathode
which reduces side reactions of LiCoO2 and the electrolyte
under high-voltage conditions. Tests reveal that a LiCoO2 electrode battery using the TISP as a binder retains 162.4 mAh g–1 after 349 cycles at 4.5 V, and this represents an
86.5% capacity retention. In addition, heating (40 °C, 1 h) of
a scratch-damaged electrode can recover a specific capacity of 156.6
mAh g–1 after 349 cycles at 4.5 V. Relative to a
battery without any mechanical scratch, this capacity recovery represents
approximately 96%, and this demonstrates the importance of the TISP
to the high-voltage damaged electrode.
