Starch-Based Polymer Electrolytes

Starch is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. It is a polysaccharide and produced by most green plants for energy storage. It is the most common carbohydrate in human diets and is contained in large amounts in staple foods, such as potatoes, wheat, maize (corn), rice, and cassava.

Starch is white in color and forms a tasteless and odorless powder. It is insoluble in cold water or ethanol. It consists of two types of molecules: the linear and helical amylose and the branched amylopectin. Depending on the plant, starch generally contains 20 to 25% amylose and 75 to 80% amylopectin by weight.

Starch has attractive processing characteristics, which include (i) considerable abundance in nature, (ii) biocompatibility, (iii) cost effectiveness, and (iv) high mechanical integrity. Both amylopectin and amylose have hydroxyl (-OH) groups. Hence, the lone pair of electrons in the oxygen atom favors the solvation of the charge carriers within the polymer network and forms transient coordination bonds. A vacant site is created when the coordination bond is broken. As a consequence, the neighboring ions from the adjacent site occupy this vacant site, resulting in the transportation of ions via the hopping process [31]. Table 12.2 lists some of the lithium ion and ammonium salts added to polymer electrolytes based on starch.

Carrageenan-Based Polymer Electrolytes

Carrageenans can be obtained from the red seaweeds of the class Rhodophyceae. Carrageenans are a group of l inear galactans with an ester sulfate content of 15-40% (w/w) and containing alternating ot-(l->3)-D and (3-(l->4)-D-galactopyranosyl (or 3,6-anhydro-a-D-galactopyranosyl) linkages. It dissolves in hot water at room temperature, but in solvents, such as dimethylsulfoxide (DMSO), the solubility temperature is between 40 and 70°C. It is insoluble in ethanol, aceton, and some other organic solvents [52]. Kappa, iota and lambda are the three main commercial classes of carrageenan. The primary differences that influence the properties of kappa-, iota-, and lambda-carrageenan are the number and position of the ester sulfate groups on the repeating galactose units. Higher levels of ester sulfate lower the solubility temperature of the carrageenan and produce lower strength gels or contribute to gel inhibition (in lambda-carrageenan). Figure 12.2 shows the electrochemical characteristics of iota-carrageenan with ammonium nitrate [53]. Table 12.3 describes the polymer electrolytes composed of lithium and proton salts based on carrageenan.

Electrochemical performance of EDLC with chitosan-based electrolytes sandwiched between activated carbon cloth electrodes

FIGURE 12.1 Electrochemical performance of EDLC with chitosan-based electrolytes sandwiched between activated carbon cloth electrodes: (a) Typical discharge characteristics of EDLC studied; (b) Variation in the discharge capacitance with cycle numbers for EDLC (iota- carrageenan/chitosan). Adapted and reproduced with permission from Ref. [18]. Copyright © 2011 Taylor and Francis.

TABLE 12.2

Room-Temperature (RT) Ionic Conductivity of Various Starch-Based Polymer Electrolytes

Materials

Optimized

Composition

Conductivity (S cm-’) (RT)

References

Corn starch (CS), lithium hexafluorophosphate (LiPF6), l-butyl-3- methylimidazolium hexafluorophosphate (BmImPF6)

50 wt.% BmImPF6

1.47x1 O'2

[32]

Corn starch (CS), lithium hexafluorophosphate (LiPF6), l-butyl-3-methyl imidazolium trifluoromethanesulfonate (BmlmTf)

80 wt.% of CS-20 wt.% of LiPF6-80 wt.% BmlmTf

3.21X10-4

[33]

Corn starch (CS), lithium perchlorate (LiC104)

60 wt.% CS-40 wt.% LiC104

1.28x10-*

[34]

Corn starch (CS), lithium bis(trifluoro methane sulfonyDimide (LITFSI), deep eutectic solvent (DES)

14 wt.% CS-6 wt.% LiTFSI-80 wt.% DES

4.56x10-’

[35]

Corn starch (CS), lithium iodide, glycerol

49 wt.% starch-21 wt.% LiI-30 wt.% glycerol

9.56x10-1

[36]

Corn starch (CS), chitosan, ammonium iodide

40 wt.% NH,I

3.04x10-1

[37]

Corn starch, lithium perchlorate, nano silica

96 wt.%(CS- LiC104)-4 wt.% SiO,

1.23X10-4

[38]

Corn starch, ammonium bromide, glycerol

49 wt.% starch- 21 wt.% NH4Br-30 wt.% glycerol

1.80x10-’

[39]

Corn starch (CS), lithium bis(trifluoro methane sulfonyDimide (LITFSI),

1 -allyl-3-methylimidazolium chloride,[Amim] Cl

14 wt.% CS- 6 wt.% LiTFSI- 80 wt.% [Amim] Cl

4.18x1 O'2

[40]

Corn starch (CS), l-allyl-3- methylimidazolium chloride [Amim] Cl

5 g (CS)-30 wt.% [Amim] Cl-

10-16

[41]

Corn starch (CS), lithium chloride, N,N- dimethyl acetamide (DMAc)

18 wt.% LiCl

К)415

[42]

Rice starch (RS), lithium iodide (LI)

65 wt.% RS-35 wt.%LiI

4.68x10-’

[43]

Rice starch (RS), lithium iodide (LI),

1 -methyl-3-propylimidazolium iodide (MPII), titania (Ti02)

44.2 wt.% RS-23.8 wt.%LiI-30.2 wt.%

3.63x10-4

[44]

Potato starch (PS), ammonium iodide

-

2.4x10-4

[45]

Potato starch (PS), chitosan, lithium trifluoromethanesulfonate (LiCF,S03), glycerol

50 wt.% PS-50 wt.% chitosan-45 wt.% LiCF,SO,-30 wt.% glycerol

1.32x10-’

[46]

TABLE 12.2 (CONTINUED)

Room-Temperature (RT) Ionic Conductivity of Various Starch-Based Polymer Electrolytes

Materials

Optimized

Composition

Conductivity (S cm-') (RT)

References

Potato starch (PS), methylcellulose (MC), ammonium nitrate, glycerol

25 wt.% MC-17 wt.% PS-18 wt.% NH4NO,^t() wt.% glycerol

~io-j

[47]

Potato starch (PS), graphene oxide (GO), lithium trifluoromethanesulfonate (LiCF,S03), 1 -butyl-3-methylimidazolium chloride ([Bmim][Cl])

PS-GO (80-20 wt.%)/0.333g LiCF,SO,/30wt.% [Bmim|[Cl]

4.8 x 10-4

[48]

Poly(vinyl alcohol) (PVA), starch, ammonium thiocyanate, glutaraldehyde

PVA:starch (50:50) + 0.4 ml of

glutaraldehyde + 30% NH4SCN

1.311 x 10-4

[49]

Potato starch (PS), glycerol,

sago starch (SS), lithium chloride, glycerol

PS/Gly-0.5 80 wt.% SS- 20 wt.% glycerol-8 wt.% LiCI.

5.2 x 10-'

~io-j

[50]

[51]

 
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