May/June_AMP_Digital

A D V A N C E D M A T E R I A L S & P R O C E S S E S | M A Y / J U N E 2 0 2 0 1 8 self-healable electrodes [13] . Magnetical- ly self-healable electrochemical devices can be also fabricated using conduc- tive inks containing ferromagnetic par- ticles, which can find applications in a wide range of printed-electronic de- vices. By loading permanent magnetic microparticle into graphitic inks, mul- tiple time self-healing of printed con- ductive materials can be fabricated by printing on electrochemical devic- es [14] . Instead of a laminar structure su- percapacitor, flexible and stretchable self-healable supercapacitors with all- in-one configurations largely simplify stretchable and self-healing properties became an essential requirement in the fabrication process of supercapacitors. In response to these demands, high- ly stretchable and omni-self-healable supercapacitors were developed using sandwich construction of polypyrrole‐ incorporated gold nanoparticle/car- bon nanotube (CNT)/poly(acrylamide) (GCP@PPy) hydrogel as electrodes, and CNT‐free GCP (GP) hydrogel as electrolytes [15] . EXTENDING THE LIFECYCLE Lithium-ion batteries with high en- ergy capacity and long cycle life are of vital importance to meet increasing de- mands of powering advanced portable devices, medical implants, and electric vehicles. In order to enhance capacity, significant efforts have been made in developing new electrodes. However, the major issue is that these electrodes suffer from poor cycle lifetime attribut- ed to mechanical damage, which large- ly shortens their lifespan. Thus, new self-healing materials will be essen- tial for longer lasting applications and rechargeability. One example is the self-healing layered GeP anode pre- pared by a mechano-chemical meth- od and low-temperature annealing. In this case, self-healing is achieved by a reversible construction of layered crys- tal structures during the charging and discharge cycle [16] . Although considered as a promising material for Li-ion bat- teries, the main drawback of Ge is slow Li-ion diffusion. On the other hand, the use of silicon as one electrode mate- rial in Li-ion batteries may be prom- ising, but fractures of silicon particles and polymer binders may cause insuf- ficient electrical contacts, thus causing the loss of capacity. One example of the development of high-capacity silicon anodes are cross-linked polymer bind- ers obtained by dynamic host–guest interactions between hyperbranched β-cyclodextrin polymer and a dendrit- ic gallic acid cross-linker. This approach improved cycling performance [17] . Inspi- red by a millipede’s strong adhesion and double helical superstructure, a xanthan gum with a series of trisaccha- ride side chain and ion-dipole inter- the device assembly process and min- imize the displacement and delami- nation of multilayered configurations due to deformations. All-in-one self- healable supercapacitors can be pro- duced using in-situ polymerization and deposition of nanocomposites elec- trode materials onto double-sided fac- es of self-healing hydrogel electro- lyte separators. In this process, self- healing hydrogel films were prepared via crosslinked hydrogels with mul- tiple hydrogen-bonds (Fig. 2) [12] . Due to the increasing demands for porta- ble and wearable electronics, highly (a) (b) (c) (d) (e) (f) Fig. 2 — (a,b) Flexible healable hydrogel films fabricated by crosslinking of poly(vinyl alcohol). (c,d) The preparation of the flexible healable all-in-one configured supercapacitors by in-situ polymerization and deposition of nanocomposites electrode materials onto the two-sided faces of self-healing hydrogel electrolyte separator. (e,f) The flexible healable all-in-one configured supercapacitor. Figure used with permission from Ref. 12.