Page 336 - Polymer-based Nanocomposites for Energy and Environmental Applications

304 Polymer-based Nanocomposites for Energy and Environmental Applications

was soluble; complexes formed between PVP and polysulfide helped in improving the
capacity retention showing the benefits of composite materials.
The enhancement in capacity retention in Li-S batteries has been the focus of much
research. Another approach to reduce the shuttle effect was by using TiO 2
nanoparticles within a solid PEO nanocomposite electrolyte [107]. TiO 2 showed a
good affinity and interaction with polysulfide, improving at the same time the ionic
conductivity of PEO.
Environmentally friendly materials for Li-S batteries have also seen some recent
progress. A green composite polymer electrolyte based on methacrylic oligomers
and reinforced with raw nanoscale cellulose fibers [108] demonstrated synergistic
effect of excellent ionic conductivity and thermal stability and led to an overall
improvement of the cycling performance (Fig. 10.13).
Chitosan has numerous hydroxyl groups and amine groups, which make it an
attracting candidate as electrode binder for Li-S batteries [109]. In fact, the hydro-
philic dOH and dNH 2 groups are efficient in immobilizing polysulfide, thus
minimizing their dissolution in the electrolyte. Chitosan was used to fabricate a sulfur
cathode and a carbon-/chitosan-coated Celgard polypropylene separator facing the
cathode [110]. The cycling performance of both the cathode and the complete cell
was improved; the latter exhibited a stable capacity of 830 mAh g 1 at C/2 after
100 cycles and 675 mAh g 1 at 1C after 200 cycles.
Chitosan was also exploited in cathode with high sulfur loading. The modified high
sulfur-loading electrode (MHSE) was made of three components: (i) the scaffold’s
uniform mixture of N-doped acetylene black and N-doped multiwalled carbon nano-
tube (MWCNT), (ii) chitosan binder, and (iii) N-doped MWCNT of netting carbon
film [111]. A sulfur loading of 10 mg cm 2 with a homogeneous distribution in the
conducting agent was achieved together with an improved structural strength of
the cathode. This is a relevant result considering that the gravimetric energy density
of a sulfur battery is dependent on S loading although it is challenging due to the
insulating nature of S.
Although at a very early stage, the research in the field of secondary batteries based
on multivalent ions has made significant progress. In the Mg field, an essential
requirement is to avoid SEI formation on Mg in order to enable highly reversible
Mg plating/stripping. Reports on solid polymer electrolytes for this system are still
limited [112,113]; recently, a new nanocomposite electrolyte based on PEO-Mg
(BH 4 ) 2 and MgO nanoparticles for reversible Mg plating/stripping with a high cou-
lomb efficiency and stable cycling was reported [114]. The electrochemical test
was carried out at 100°C, and a coulomb efficiency of 98% was achieved with a good
Mg plating and stripping reversibility.

10.5 Conclusions and outlook

The continued growth of portable electronics market, increased electrification of
transport, and improvement of grid stability demands cheaper, longer life, and safer
batteries with much higher energy densities. Polymer nanocomposites show