Constructing Dual Interfacial Modification by

Synergetic Electronic and Ionic Conductors:

Toward High-Performance LAGP-Based Li-S

Batteries

KEYWORDS: interfacial modification, graphite layer, all-solid-state, LAGP

electrolyte, Li-S batteries

Contents

1. The morphology characterizations of the LAGP electrolyte

2. AFM image for top view of the (1) raw LAGP ceramic pellet and (2) graphite

modified LAGP.

3. Magnified cross-section SEM images of the graphite modified LAGP.

4. Raman spectrum of the LAGP ceramic pellet covered with graphite layer.

5. Electrochemical performance of CPE modified electrolyte.

6. The critical current density of the CPE-LAGP/Li symmetric cell

7. Cycling performance and EIS spectrums of Li-LAGP-Li cell.

8. SEM images of LAGP ceramic after cycles for naked LAGP and modified

LAGP.

9. The cycling performance of LiNi1/3Mn1/3Co1/3O2/Li cell based on CPE

modified LAGP.

10. The voltage profiles of Li-S batteries for unmodified electrolytes at 60 °C.

11. Cross-section SEM images of interface of the S/C cathode/LAGP.

12. SEM images of LAGP ceramics after 200 cycles.

13. The S 2p XPS spectra of the S/C cathodes.

14. Electrochemical performance comparison among modified LAGP and

reported solid electrolytes for Li-S cell.

Experimental

Preparation of LAGP ceramics

The LAGP ceramic electrolyte was synthesized by the solid-state reaction method

according to previous report.1 Stoichiometric amounts of LiOH•H2O, Al2O3 (γ-phase),

GeO2, and (NH4) H2PO4 were mixed and ground for 8 h in a planetary ball mill. The

ground materials were heated at 700 °C for 4 h, followed by a second ball milling and

heating at 800 °C for 6 h to obtain pure LAGP powder. The powder was ball-milled

for 12 h to obtain the fine ceramic precursor powders. Then the powders were pressed

into plate and sintered at 820 °C for 2 h. All of the above heat treatments were

conducted in the ambient atmosphere. The final LAGP pellets are about 700 μm thick

and 14.5 mm in diameter.

Preparation of graphite and CPE modified LAGP electrolytes

The graphite layer was covered on one side on the LAGP pellet completely by 6B

pencil painting. The CPE slurry was prepared according to previous report and stirred

for 24 h in an argon-filled glove box.2 The CPE slurry was spin-coated on the other

side on LAGP, and then dried for 24 h in 60 °C under vacuum.

Electrodes preparation, batteries assembly and electrochemical measurements

The cathode slurry was prepared by mixing 80 wt% S/KB (Ketjen Black)

composites (w/w= 6: 4), 10 wt% acetylene black, 5 wt% carboxymethyl cellulose, and

5 wt% styrene–butadiene rubber by ball milling. Then the slurry was cast onto an

aluminum foil substrate. After evaporation of the solvent water, the as-prepared

cathode was cut into circular disks with 12 mm in diameter and dried for 12 h at 60

°C under vacuum. The sulfur loading was about 1 mg cm-2. The LiFePO4 cathodes are

fabricated by similar procedure and the active material loading was 4 mg cm -2. Before

assembled in Li-S and LFP-Li cells, 20 μL as-prepared CPE slurry was coated on the

cathodes and dried completely. The cathode and anode are pasted to graphite side and

the CPE modified side of LAGP respectively, then assembled in CR2025-type

coin cells. The large-scale Li-S batteries with same configuration were sealed using a

plastic film in an argon-filled glove box. The CPE modified pellets were

sandwiched between two pieces of lithium metal to assemble the

symmetric cell. All cells were heated at 70 °C for 8 h to wetting the

interfaces before electrochemical measurements.

Electrochemical measurements of the symmetric cells and all-solid-state batteries

were carried out on a LAND CT2001A battery test system (Wuhan, China) at 60 °C.

The voltage range of Li-S and LFP-Li batteries are 1 V-3 V and 2.5 V-4 V

respectively. The electrochemical impedance spectroscopy (EIS) measurements were

performed on an Autolab PGSTAT302N Electrochemical Workstation (ECO CHEMIE

B.V, Netherlands) from 1 MHz to 0.1 Hz with an amplitude of 10 mV. And the linear

sweep voltammograms (LSV) measurement between 2.6 V and 6 V at a scan rate of 5

mV s-1 was also tested on Autolab workstation. The Li+ transference number of

electrolytes was obtained by direct-current (DC) polarization measurements and

combining alternating current (AC) impedance using a symmetric Li/electrolyte/Li

battery. The ionic conductivities of electrolytes were obtained by AC impedance

analysis using a symmetric battery with stainless steel as reference electrodes.

Characterizations methods

Powder X-ray diffraction (Rigaku) was employed to determine the phase component

of ceramics at room temperature. SEM microscopy (Hitachi S-4800) coupled with

energy-dispersive X-ray (EDX) spectrometer were used to study the

morphology and element distribution of electrolytes and electrodes. Surface

morphology images were acquired with a Bruker Multimode8 Atomic Force

Microscope (AFM). Raman spectra are tested to characterize the graphite properties

on the ceramic. X-ray photoelectron spectroscopy (XPS) analyses were performed

(Thermo scientific ESCALAB 250) to confirm the sulfur environment of cathodes

and the valence states of solid electrolyte.

Figure S1. (a) XRD characterization of the LAGP ceramic powder and LAGP plate. (b) Cross-section SEM image of the sintered LAGP ceramic. (c) EIS spectra of the LAGP

electrolyte at 60 °C. (d) Arrhenius plots for the ionic conductivities of the LAGP electrolyte from 0 °C to 80 °C.

Figure S2. AFM image for top view of the (1) raw LAGP ceramic pellet and (2) graphite modified LAGP.

Figure S3. Magnified cross-section SEM images of the graphite modified LAGP.

Figure S4. Raman spectrum of the LAGP ceramic pellet covered with graphite layer.

Figure S5. EIS spectrum of (a) LAGP pellet and (b) CPE-LAGP at various temperatures between 10 to 60 °C. (c) Chronoamperometry curve of the symmetric lithium metal cells based on CPE-LAGP at 10 mV and a duration time of 3600 s at 60 °C. insert: AC impedance spectra of the cells before and after the polarization. (d) Linear sweep voltammetry curves of SS/electrolyte/Li cells based on SPE (blue) and LAGP electrolyte (yellow) at 60 °C.

Figure S6. Galvanostatic cycling of CPE-LAGP lithium symmetric cell, stepping the current density from 100 to 1000 µA cm-2 at room temperature

Figure S7. (a) Li plating/striping curves of Li-LAGP-Li symmetric cells at 0.1 mA cm-

2 at 60 °C. (b) EIS impedance spectra of symmetric cell before and after cycles. (c) Time evolution resistance for Li-LAGP-Li symmetric cell after different storage time at 60 °C.

Figure S8. (a)-(c) SEM images of LAGP ceramic after 1000 cycles for lithium metal symmetric cell based on CPE-LAGP. (d)-(f) SEM images of LAGP after 100 cycles for lithium metal symmetric cell based on naked LAGP.

Figure S9. The cycling performance of LiNi1/3Mn1/3Co1/3O2-Li battery using CPE-LAGP at the 0.1 C, respectively.

Figure S10. The voltage profiles of Li-S batteries for unmodified electrolytes at 60 °C.

Figure S11. Cross-section SEM images of interface of the S/C cathode/LAGP.

Figure S12. SEM images of LAGP ceramics after 200 cycles. (a) Close to S/C cathode side. (b) Close to Li anode side.

Figure S13. The S 2p XPS spectra of the S/C cathodes before cycling.

Table S1. Electrochemical performance comparison between modified LAGP and reported solid electrolytes for Li-S batteries.

Electrolytes Battery type Capacity retention (0.1 C) cycles Ref.

Porous LLZN Semi-solid-state 1100 mAh g-1 50 3

LLZTO- DOL/DME Semi-solid-state 800 mAh g-1 20 4

PEO-Li-Zr All-solid-state 980 mAh g-1 40 5

Li7P2.9S10.85Mo0.01 All-solid-state 570 mAh g-1 30 6

3D bilayer LLZO All-solid-state 580 mAh g-1 30 7

Graphite and CPE modified LAGP All-solid-state 1150 mAh g-1 150 This

Study

Reference

(1) Gu, S.; Huang, X.; Wang, Q.; Jin, J.; Wang, Q.; Wen, Z.; Qian, R. A hybrid electrolyte for long-life semi-solid-state lithium sulfur batteries. J. Mater. Chem. A 2017, 5 (27), 13971-13975.(2) Li, W.; Zhang, S.; Wang, B.; Gu, S.; Xu, D.; Wang, J.; Chen, C.; Wen, Z. Nanoporous adsorption effect on altering Li+ diffusion pathway by a highly ordered porous electrolyte additive for high rate all-solid-state lithium metal batteries. ACS Appl. Mater. Interfaces 2018.(3) Liu, B.; Zhang, L.; Xu, S.; McOwen, D. W.; Gong, Y.; Yang, C.; Pastel, G. R.; Xie, H.; Fu, K.; Dai, J.; Chen, C.; Wachsman, E. D.; Hu, L. 3D Lithium Metal Anodes Hosted in Asymmetric Garnet Frameworks toward High Energy Density Batteries. Energy Storage Mater. 2018.(4) Huang, X.; Lu, Y.; Jin, J.; Gu, S.; Xiu, T.; Song, Z.; Badding, M. E.; Wen, Z. Method Using Water-Based Solvent to Prepare Li7La3Zr2O12 Solid Electrolytes. ACS Appl. Mater. Interfaces 2018, 10 (20), 17147-17155.(5) Sheng, O.; Jin, C.; Luo, J.; Yuan, H.; Fang, C.; Huang, H.; Gan, Y.; Zhang, J.; Xia, Y.; Liang, C.; Zhang, W.; Tao, X. Ionic Conductivity Promotion of Polymer Electrolyte with Ionic Liquid Grafted Oxides for All-Solid-State Lithium-Sulfur Batteries. J. Mater. Chem. A 2017.(6) Xu, R.-c.; Xia, X.-h.; Wang, X.-l.; Xia, Y.; Tu, J.-p. Tailored Li 2 S–P 2 S 5 glass-ceramic electrolyte by MoS 2 doping, possessing high ionic conductivity for all-solid-state lithium-sulfur batteries. J. Mater. Chem. A 2017, 5 (6), 2829-2834.(7) Fu, K.; Gong, Y.; Li, Y.; Xu, S.; Wen, Y.; Zhang, L.; Wang, C.; Pastel, G.; Dai, J.; Liu, B.; Xie, H.; yao, Y.; Wachsman, E.; Hu, L. Three-Dimensional Bilayer Garnet Solid Electrolyte Based High Energy Density Lithium Metal-Sulfur Batteries. Energy Environ. Sci. 2017.