Qinxing Xie1 Peng Zhao2 Shihua Wu2 Yufeng Zhang1

Supporting Information

Flexible carbon@graphene composite cloth for advanced lithium- sulfur batteries and supercapacitors with enhanced energy storage capability

1 Tianjin Key Laboratory of Advanced Fibers and Energy Storage, School of Materials Science and

Engineering, Tianjin Polytechnic University, Tianjin 300387, China

2 Department of Chemistry, Nankai University, Tianjin 300017, China

Corresponding author: Qinxing Xie, [email protected] Preparation of graphite oxide

Graphite oxide was prepared by a modified Hummers method [1]. Typically, 2.0 g of natural graphite was dispersed in 50 mL of concentrated H2SO4 (98%), and 1.0 g of sodium nitrate was added. The mixture was further stirred for 1 h in an ice-water bath, and then 6.0 g of KMnO4 was added slowly under vigorous stirring so that the temperature was kept below 20 C. After that, the resultant mixture was stirred for 3 h at 35 C. The suspension was diluted with 100 mL of distilled water, and stirred for 15 min at 98 C. 280 mL of distilled water was then added to terminate the reaction. 30 mL of 30% H2O2 solution was added under constant stirring till the solution color turned into bright-yellow. The mixture was filtered, and the brown solid was rinsed with 5% hydrochloric acid and distilled water for several times until no sulfate in filtrate could be detected.

The product was freeze-dried finally.

Electrochemical measurements

-1 The gravimetric specific capacitance of the materials (Cm, F g ) can be calculated according to the CV and GCD curves by using the eqs. S1,2 [2,3]:

(S2) where I is the response current or applied current (A), S is the potential scan rate (V s-1), m is the mass (g) of active material on the electrode, Δt is the discharge time (s), and V is the potential

-3 window (V). The volumetric specific capacitance (Cv, F cm ) can be calculated by using the eqs.

(S3,4) [4,5]:

Cv =   Cm (S3) (S4)

-3 3 -1 where  is the particle density (g cm ) of carbon, Vt is the total pore volume (cm g ), ρT is the true density of carbon (2 g cm-3 ).

-1 -1 The gravimetric specific energy density (Eg, Wh kg ) and power density (Pg, W kg ) of the two- electrode supercapacitors were evaluated by using the eqs. (S5,6) [3,6,7], and the volumetric energy

-1 -1 density Ev (Wh L ) and power density Pv (W L ) were determined based on the eqs. (S7,8) [5]:

Ev = Eg (S7)

Pv = Pg (S8)

-1 where Cs represents the gravimetric specific capacitance of the supercapacitor (Cm/4, F g ),ΔV is the voltage change after the deduction of IR drop (V) during the discharge process, Δt is the discharge time (s).

Fig. S1 (a-b) CV curves of CGC at varied scan rates from 5 to 400 mV s-1, and (c) the calculated specific capacitances at 5 mV s-1 and 200 mV s-1 for CC and CGC, respectively. Fig. S2 GCD curves of CGC composite at varied current densities from 0.05 to 20 A g-1. References

1. Hummers WS, Offeman RE(1958) Preparation of Graphitic Oxide. J Am Chem Soc 80:1339-

2. Xie Q, Zhou S, Zheng A, Xie C, Yin C, Wu S, Zhang Y, Zhao P (2016) Sandwich-like nitrogen- enriched porous carbon/graphene composites as electrodes for aqueous symmetric supercapacitors with high energy density.Electrochim Acta 189:22-31.

3. Conway BE (1999) Electrochemical supercapacitors: scientific fundamentals and technological applications, Plenum Press, New York.

4. Long C, Chen X, Jiang L, Zhi L, Fan Z (2015), Porous layer-stacking carbon derived from in- built template in biomass for high volumetric performance supercapacitors. Nano Energy 12: 141-

5. Li Y, Zhao D (2015) Preparation of reduced graphite oxide with high volumetric capacitance in supercapacitors. Chem Commun 51:5598-5601.

6. Xu C, Xu B, Gu Y, Xiong Z, Sun J, Zhao XS (2013) Graphene-based electrodes for electrochemical energy storage. Energ Environ Sci 6:1388-1414.

7. Lang JW, Yan XB, Liu WW, Wang RT, Xue QJ (2012) Influence of nitric acid modification of ordered mesoporous carbon materials on their capacitive performances in different aqueous electrolytes. J Power Sources 204:220-229.