Supporting Information Robust Pitaya-Structured Pyrite as High Energy Density Cathode for High Rate Lithium Batteries Xijun Xu,, Jun Liu,,,* Zhengbo Liu,, Jiadong Shen,, Renzong Hu,, Jiangwen Liu,, Liuzhang Ouyang,, Lei Zhang, and Min Zhu,,* School of Materials Science and Engineering and Guangdong Provincial Key Laboratory of Advanced Energy Storage Materials, South China University of Technology, Guangzhou, 510641, PR China China-Australia Joint Laboratory for Energy & Environmental Materials, South China University of Technology, Guangzhou, 510641, PR China Email: msjliu@scut.edu.cn; memzhu@scut.edu.cn School of Chemistry and Chemical Engineering, South China University of Technology, Guangzhou, 510640, China 1
Figure S1. The XPS spectra of Fe 3 O 4 @C (a) survey; (b) Fe 2p; (c) O 1s; (d) C 1s. 2
Figure S2. The XPS spectra of FeS 2 @C (a) survey; (b) Fe 2p; (c) S 2p; (d) C 1s. 3
Figure S3. Low- and high-magnification TEM images of porous vesica-like carbon frameworks obtained via etching the inner FeS 2 nanoparticles in pitaya-structured FeS 2 @C nanospheres. 4
Figure S4. N 2 adsorption/desorption isotherms (a) of the pitaya-structured FeS 2 @C and the corresponding pore-size distribution (b) calculated using the BJH method. 5
Intensity (a.u.) C-3.0 V C-2.0 V C-1.5 V D-1.5 V D-1.0 V FeS 2 Li 2 S Fe 7 S 8 Li 2 FeS 2 Cu foil 20 30 40 50 60 70 80 2-Theta (degree) Figure S5. The ex-situ XRD patterns of pitaya-structured pyrite at different voltages during discharge/charge processes. 6
Figure S6. The Fe 2p XPS spectra of FeS 2 @C electrode at different discharge/charge stages: (a) before cycles; (b) discharged to 1.0 V; (c) discharged to 1.5 V; (d) charged to1.5 V; (e) charged to 2.0 V; (f) charged to 3.0 V. 7
Figure S7. The S 2p XPS spectra of FeS 2 @C electrode at different discharge/charge stages: (a) before cycles; (b) discharged to 1.5 V; (c) discharged to 1.0 V; (d) charged to1.5 V; (e) charged to 2.0 V; (f) charged to 3.0 V. 8
Figure S8. Different magnification SEM images of pitaya-structured FeS 2 @C cathode after 100 cycles at 0.3 A g -1 showing the encapsulated framework of particles. 9
1000 100 Specific capacity (ma h g -1 ) 800 600 400 300 ma g -1 FeS 2 nanoparticles 200 Charge 20 Discharge 0 0 0 10 20 30 40 50 Cycle number 80 60 40 Coulombic efficiency (%) Figure S9. The electrochemical performance of pure FeS 2 nanoparticles at 300 ma g -1. 10
The calculation method of energy density and power density: Energy density = Voltage Capacity (eq. S1) Power density = Voltage Current density (eq. S2) According to the eq. S1 and S2, the energy density and power density can be calculated, respectively. In the current work of FeS 2 @C electrode, the average voltage was used to replace the voltage for determining the result, and it could be got from the charge/discharge profiles. 11
Table S1. A comparison of rate performance between the pitaya-structured pyrite (FeS 2 ) and other reported FeS 2 -cathodes for Li-ion storage. Materials Rate (A g 1 ) Capacity (mah g 1 ) PAN-FeS 2 1 0.0894 470 (after 50 cycles) Al 2 O 3 -coated 0.2 FeS 2 @carbon fiber 2 530 (after 100 cycles) FeS 2 nanocrystals 3 0.2 630 (after 100 cycles) 1.0 600 (after 50 cycles) 0.0894 FeS 2 nanowires 4 350 (after 50 cycles) 0.5 FeS 2 @N-graphene 5 401.7 (after 400 cycles) 1.0 FeS 2 /graphene 6 435 (after 200 cycles) 0.1 FeS2@C nanowires 7 570 (after 100 cycles) This work 0.3 614 (after 100 cycles) 1.5 455 (after 100 cycles) 12
Figure S10. Na-ion storage performance of pitaya-structured FeS 2 @C nanospheres: (a) CV curves at a scanning rate of 0.1 mv s 1 in the voltage range of 0.5 2.5 V; (b) voltage-capacity curves of pitaya-structured FeS 2 @C nanospheres at 0.6 A g -1. 13
800 -Z"(ohm) 600 400 200 SIB LIB 0 0 200 400 600 800 Z'(ohm) Figure S11. The EIS spectra of pitaya-structured FeS 2 @C nanospheres for Na-ion (the black line) and Li-ion (the red line) storage. 14
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