Rational design and evaluation of UV curable nano-silver ink applied in highly conductive textile-based electrodes and flexible silver-zinc batteries

doi:10.1016/j.jmst.2021.04.061

Abstract

Abstract:

The possibility of printing conductive ink on textiles is progressively researched due to its potential benefits in manufacturing functional wearable electronics and improving wearing comfort. However, few studies have reported the effect of conductive ink formulation on electrodes directly screen-printed on flexible substrates, especially printing UV curable conductive ink on common textiles. In this work, a novel UV curable nano-silver ink with short-time curing and low temperature features was developed to manufacture the fully flexible and washable textile-based electrodes by screen printing. The aim of this study was to determine the influence of ink formulation on UV-curing speed, degree of conversion, morphology and electrical properties of printed electrodes. Besides, the application demonstration was highlighted. The curing speed and adhesion of ink was found depending dominantly on the type of prepolymer and the functionality of monomer, and the type of photoinitiator had a decisive effect on the curing speed, degree of double bond conversion and morphology of printed patterns. The nano-silver content is key to guarantee the suitable screen-printability of conductive ink and therefore the uniformity and high conductivity of textile-based electrodes. Optimally, an ink formulation with 60 wt% nano-silver meets the potential application requirements. The electrode with 1.0 mm width showed significantly high electrical conductivity of 2.47 × 10 ⁶ S/m, outstanding mechanical durability and satisfactory washability. The high-performance of electrodes screen-printed on different fabrics proved the feasibility and utility of UV curable nano-silver ink. In addition, the application potential of the conductive ink in fabricating electronic textiles (e-textiles) was confirmed by using the textile-based electrodes as the cathodes of silver-zinc batteries. We anticipate the developed UV curable conductive ink for screen-printing on textiles can provide a novel design opportunity for flexible and wearable e-textile applications.

Key words: Nano-silver ink formulation, UV curing, Textile-based electrodes, High conductivity, Mechanical durability, Washability

Hong Hong, Lihong Jiang, Huating Tu, Jiyong Hu, Kyoung-Sik Moon, Xiong Yan, Ching-ping Wong. Rational design and evaluation of UV curable nano-silver ink applied in highly conductive textile-based electrodes and flexible silver-zinc batteries[J]. J. Mater. Sci. Technol., 2022, 101: 294-307.

Figures/Tables 18

Fig. 1. (a) Size distribution of nano-silver by intensity. (b) The UV-vis spectrum of nano-silver.

Fig. 2. (a) Optical microscopy image of conductive pattern printed on fabric with UV curable conductive ink (Defoamer-free). (b) Optical microscopy image of conductive pattern printed using UV curable conductive ink prepared with additives.

Table 1 Formulation of UV curable inks with different monomers.

Ingredients (wt%)	Ink-IBTP	Ink-IBPE	Ink-TPPE	Ink-TMTP	Ink-TMPE
PUA	60	60	60	60	60
IBOMA + TPGDA	27	0	0	0	0
IBOMA + PEG200DA	0	27	0	0	0
TPGDA + PEG200DA	0	0	27	0	0
TMPTA + TPGDA	0	0	0	27	0
TMPTA + PEG200DA	0	0	0	0	27
1173	10	10	10	10	10
KH-560	2.2	2.2	2.2	2.2	2.2
BYK-A555	0.5	0.5	0.5	0.5	0.5
BYK-333	0.3	0.3	0.3	0.3	0.3

Table 2 Formulation of UV curable inks with different prepolymers.

Ingredients (wt%)	Ink-HR93	Ink- HR96	Ink- R93R96	Ink- ER93	Ink- ER96
HPU + PUA (R93)	60	0	0	0	0
HPU + PUA (R96)	0	60	0	0	0
PUA (R93) + PUA (R96)	0	0	60	0	0
EA + PUA (R93)	0	0	0	60	0
EA + PUA (R96)	0	0	0	0	60
TPGDA	13.5	13.5	13.5	13.5	13.5
TMPTA	13.5	13.5	13.5	13.5	13.5
1173	10	10	10	10	10
KH-560	2.2	2.2	2.2	2.2	2.2
BYK-A555	0.5	0.5	0.5	0.5	0.5
BYK-333	0.3	0.3	0.3	0.3	0.3

Table 3 Formulation of UV curable inks with different photoinitiators.

Ingredients (wt%)	Ink-184	Ink-907	Ink-1173	Ink-ITX	Ink-TPO
PUA	60	60	60	60	60
TPGDA	13.5	13.5	13.5	13.5	13.5
TMPTA	13.5	13.5	13.5	13.5	13.5
184	10	0	0	0	0
907	0	10	0	0	0
1173	0	0	10	0	0
ITX	0	0	0	10	0
TPO	0	0	0	0	10
KH-560	2.2	2.2	2.2	2.2	2.2
BYK-A555	0.5	0.5	0.5	0.5	0.5
BYK-333	0.3	0.3	0.3	0.3	0.3

Table 4 Formulation of UV curable conductive inks with different silver content.

Ingredients (wt%)	CI-30 wt%	CI-40 wt%	CI-50 wt%	CI-60 wt%	CI-70 wt%	CI-80 wt%
PUA	42	36	30	24	18	12
TPGDA	9.45	8.1	6.75	5.4	4.05	2.7
TMPTA	9.45	8.1	6.75	5.4	4.05	2.7
1173	7	6	5	4	3	2
KH-560	1.54	1.32	1.1	0.88	0.66	0.44
BYK-555	0.35	0.3	0.25	0.2	0.15	0.1
BYK-333	0.21	0.18	0.15	0.12	0.09	0.06
Nano-silver	30	40	50	60	70	80

Table 5 Adhesion rating scale.

Grade	Evaluation criteria
5B	The edges of the cuts are completely smooth, none of the squares of the lattice is detached.
4B	Small flakes of the coating are detached at intersections, less than 5% of the area is affected.
3B	Small flakes of the coating are detached along edges and at intersections of cuts. The area affected is 5 to 15% of the lattice.
2B	The coating has flaked along the edges and on parts of the squares. The area affected is 15 to 35% of the lattice.
1B	The coating has flaked along the edges of cuts in large ribbons and whole squares have detached. The area affected is 35 to 65% of the lattice.
0B	Flaking and detachment worse than Grade 1B.

Fig. 3. (a) Influence of different monomers on curing speed. (b) Influence of different monomers on the adhesion between UV-curing ink and fabric substrate.

Fig. 4. (a) Influence of different prepolymers on curing speed. b) Influence of different prepolymers on the adhesion between UV-curing ink and fabric substrate.

Fig. 5. (a) Influence of different photoinitiators on curing speed. (b) FT-IR spectra of UV curable ink with 1173 before and after UV curing. (c) FT-IR spectra of UV curable inks with different photoinitiators after UV curing. (d) The effect of different photoinitiators on the conversion of double bond.

Fig. 6. (a-d, g and h) SEM images of textile-based electrodes printed with different UV curable nano-silver inks. (a) CI-30 wt%, (b) CI-40 wt%, (c) CI-50 wt%, (d) CI-60 wt%, (g) CI-70 wt%, and (h) CI-80 wt%, (e) SEM image of the edge of electrode printed with CI-60 wt%, (f) Local SEM image electrode printed with CI-60 wt%.

Fig. 7. (a) Electrical resistance of the textile-based electrodes as a function of silver content. (b) Change of a particle-particle contact resistance due to the more contact between two silver flakes caused by shrinkage of the polymeric matrix. (RAg, RCr and Rt are bulk resistance of silver, constriction resistance and tunneling resistance). (c) Cross-sectional SEM image of the electrode printed with CI-60 wt%. (d) Electrical conductivity of the electrodes printed with different conductive inks.

Fig. 8. (a) Resistance of textile-based electrode printed using CI-60 wt% with variable degrees of bending. (b) Relative electrical resistance of electrode during 3000 bending cycles. (c) SEM image of electrode before bending. (d) SEM image of electrode after 3000 bending cycles.

Fig. 9. (a) Relative electrical resistance of textile-based electrode printed using CI-60 wt% during 20 washing cycles. (b) SEM images of electrodes before washing. c) SEM images of electrodes after 20 washing cycles.

Fig. 10. (a-d) SEM images of the electrodes on different fabrics. (a) carbonate-coated fabric, (b) plain fabric, (c) twill fabric, and (d) knitted fabric.

Fig. 11. Electrical resistance of the electrodes printed on different fabrics.

Fig. 12. (a-d) The corresponding elemental mapping images of Ag, C, and O: (a) carbonate-coated fabric, (b) plain fabric, (c) twill fabric, and (d) knitted fabric.

Fig. 13. (a) Schematic diagram of a two-electrode system for the characterization of flexible nano-silver electrode. (b) CV curve of the nano-silver electrode. (c) GCD curves at 1 mA/cm2 between 1.0 and 1.8 V. (d) Cyclic stability of the flexible electrodes at 1 mA/cm2 for 300 cycles.

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