Drawing a Soft Interface: An Effective Interfacial Modification Strategy for Garnet-type Solid-state Li Batteries

Transcription

1 Drawing a Soft Interface: An Effective Interfacial Modification Strategy for Garnet-type Solid-state Li Batteries Yuanjun Shao 1,2,#,Hongchun Wang 2,#,Zhengliang Gong 2,*,Dawei Wang 3, Bizhu Zheng 3, Jianping Zhu 3, Yaxiang Lu 1,*, Yong-Sheng Hu 1, Xiangxin Guo 4, Hong Li 1, Xuejie Huang 1, Yong Yang 2,3,*, Ce-Wen Nan 5 and Liquan Chen 1 AUTHOR ADDRESS 1.Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Institute of Physics, Chinese Academy of Sciences, School of Physical Sciences, University of Chinese Academy of Sciences, Beijing , China 2. College of Energy, Xiamen University, Xiamen , China 3. State Key Laboratory for Physical Chemistry of Solid Surfaces and Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen , China 4. State Key Laboratory of High Performance Ceramics and Superfine Microstructure, Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, , China

2 5. School of Materials Science and Engineering, State Key Lab of New Ceramics and Fine Processing, Tsinghua University, Beijing , China # These authors contributed equally Experimental Preparation of garnet LALZWO pellet Cubic garnet-type solid electrolyte Li 5.9 Al 0.2 La 3 Zr 1.75 W 0.25 O 12 (LALZWO) was synthesized and sintered into ceramic pellets following the previous work with traditional solid phase method. Briefly, LiOH H 2 O (95%, Sinopharm), La 2 O 3 (99.99%, Sinopharm), ZrO 2 (99.99%, Aladdin), and WO 3 (99.8%, Aladdin) were well mixed in a stoichiometric ratio with 15 wt% excess of LiOH H 2 O, then pressed and calcined at 900 C for 10 h in air. The pellets were then crushed and ground sufficiently, and the obtained mixture powder was pressed into pellets again which were fully covered with parent powder and followed by a high-temperature sintering process at 1150 C for 10 h in Al 2 O 3 crucible. As alumina crucibles were used during the high-temperature sintering process, it is reasonable that Al element exists in the samples. 1-3 The as-prepared LALZWO pellets were polished and stored in an Ar-filled glove box. The final ceramic pellets are about 1.0 mm thick and 11.0 mm in diameter. Characterizations of material properties The crystal structure and phase purity of the as-prepared garnet pellets were identified by using a Rigaku Ultima IV X-ray Diffractometer (Rigaku Corporation, Japan) equipped with Cu Ka radiation (λ= Å) and operated at 40 kv and 30 ma with a scanning rate of 5 per min over the range

3 of 10~70 (2Ɵ). A Hitachi S-4800 scanning electron microscope (SEM) coupled with an energy-dispersive X-ray (EDX) spectrometer was used to check the morphology and element distribution of samples. Surface morphology images were acquired with a Bruker Multimode8 Atomic Force Microscope (AFM). Electrochemical impedance spectroscopy (EIS) measurements were conducted at a Solartron electrochemical station with the frequency range from 10 6 to 0.01 Hz and an Alternating Current (AC) amplitude of 10 mv. Ionic conductivity measurements were performed by sputtering a thin gold layer on both surfaces of ceramic pellet to form a good contact and the coated layer is acted as electrode. The temperature dependence conductivity was measured in the same way at several specific temperatures ranging from 15 to 85 C. For conductivity test at each temperature, the samples were allowed to equilibrate for 2 h prior to measurements. The total mass changes of graphite-coated garnet with the painting number were recorded by XS3DU Mettler Toledo microbalance, and this experiment has been operated for 5 times and all of them share the similar trends. Symmetric cell fabrication In order to prepare the symmetric Li cells for electrochemical deposition experiments, the surfaces of SSE pellets were polished by 400 grit size sandpaper. The graphite-based symmetric cells were constructed as follows: first, the graphite layer was coated on both surfaces of garnet pellets by pencil painting. Then, the coated pellets were sandwiched between two pieces of Li metal (the thickness is 1 mm) to assemble the symmetric cells. After that, all cells were heated at 210 for 30 min under Ar atmosphere with a good sealing mold, a 0.05 MPa pressure were exerted by a spring to keep a close contact. Li metal/bare

4 LALZWO/Li metal symmetric cells were also fabricated under the same procedure as a comparison. Preparation of the toothpaste-like cathode composite The toothpaste-like cathode was prepared according to previous work: 0.3 M LiTFSI (99%, Aldrich) was dissolved in ionic liquid (IL) PY14TFSI (Moni Chem. Eng. Sci. & Tech. Co., Ltd.) to obtain an homogeneous solution (0.3M-IL, the density is about 1.47 mg µl -1 ), then the prepared IL solution (145 µl) was added into an thorough mixture of ternary LNCM materials LiNi 0.5 Co 0.2 Mn 0.3 O 2 (240 mg, NCM523, Beijing WeLion New Energy Technology Co., Ltd.) and Super-P (80 mg) and ground thoroughly to obtain the toothpaste-like cathode 4. The cathode materials are placed in an oven at 60 under vacuum for 24 h before being moved to the glove-box. The percent of the active material was 45 wt % and the cathode material loading is about 2.0 mg. Assembly of batteries First, the Li metal and one-side graphite-painted LALZWO pellets with good contact were achieved through the above-mentioned method. Then, the prepared toothpaste-like cathode was pasted on the other side of LALZWO, and stainless steel sheet was attached on it as current collector. The as-prepared sandwich batteries were well sealed in a battery shell. The whole processes were operated in an argon filled glove-box. Electrochemical performance test Electrochemical measurements of the symmetric cells and solid-state batteries were carried out with a Land CT-2001A (Wuhan,China) battery test system. Galvanostatic charge/discharge tests were carried out at different current rates (1 C corresponding to 200 ma g -1 ) at room temperature and 60

5 between 3.0 and 4.3 V. Electrochemical stripping/plating experiments were carried out to evaluate the stability and Li-ion transport capability across the interface at room temperature. Theoretical calculations First-principles calculations were carried out within density functional theory (DFT) using projector-augmented wave method, as implemented in the VASP code. The Li(1s,2s) and C(2s,2p) orbital are treated as valence states. The cutoff energy was 520 ev. The calculations for electronic structures and ground state energy were performed with (a b c) supercells including 42 atoms total for LiC 6. The k-mesh with the density of one point per~0.02 Å -3 was generated using the Monkhorst Pack method to sample the Brillouin zone. The energy and force convergence criterion were 10-6 ev and 0.01eVÅ -1 respectively.

6 Figure S1. XRD pattern comparison of the sintered LALZWO ceramic pellet and standard Li 7 La 3 Zr 2 O 12 with cubic garnet phase. Figure S2. The photo of Garnet SSEs with Li metal. From left to right are bare LALZWO ceramics contacted with molten metal Li, graphite-based interface modified LALZWO ceramics, lithiated graphite-based interface modified LALZWO ceramics and molten metal Li contacted with the graphite-based interface modified LALZWO ceramics, respectively.

7 Figure S3. SEM image of bare garnet ceramics with molten metallic lithium Figure S4. Raman spectrum of the sintered LALZWO ceramic pellet covered with graphite-based interface layer.

8 Figure S5. SEM images of the lithiated graphite layer on LALZWO ceramic surface Figure S6. AFM image and 3D image for top view of the graphite-based interface modified LALZWO ceramic pellet.

9 Figure S7. SEM image and EDX analysis of the interface of graphite coated LALZWO ceramic pellet with molten metallic lithium. Figure S8. The images of graphite-based interface modified LALZWO ceramics contacted with molten metal Li for different time(conducted at a heating platform, 210 ).

10 Figure S9. The structure of a) graphite ( ) and b) LiC 6 ( ) Figure S10. EIS spectra of Li/ drawing-interface-treated garnet/li symmetric cell at various cycling states

11 Figure S11. SEM images of the interface of Li/ graphite coated garnet after plating-stripping for different cycling time. a, b and c are the samples after plating-stripping for 2h first plating, 3h first stripping and 1003h 500th cycled respectively, and d is the partial enlargement of c.

12 Figure S12. a. Galvanostatic cycling of Li/ graphite-interface-treated garnet/li cell at a current density of 0.5 ma/cm 2 and 80 (The previous three cycle test time was 4 hours and with 6 h running per process latter cycle.)b. SEM images of the Li/ drawing-interface-treated garnet interface with large amount of Li plating-stripping. Figure S13. EIS spectra of the solid-state battery before and after cycling

13 Figure S14. The 10 th -20 th cycles of charge-discharge curves of NCM523/LALZWO/Li battery at 0.2 C Figure S15. Cycling performance of the solid-state battery at a rate of 0.2 C at RT with first 3 cycles tested at 0.1C.

14 Figure S16. Cycling performance of the solid-state battery at a rate of 2 C at 60 with first 3 cycles tested at 0.1C. REFERENCES (1) Wang, D.; Zhong, G.; Dolotko, O.; Li, Y.; McDonald, M. J.; Mi, J.; Fu, R.; Yang, Y. The synergistic effects of Al and Te on the structure and Li+-mobility of garnet-type solid electrolytes. J. Mater. Chem. A. 2014, 2, (2) Wang, D.; Zhong, G.; Pang, W. K.; Guo, Z.; Li, Y.; McDonald, M. J.; Fu, R.; Mi, J.-X.; Yang, Y. Toward Understanding the Lithium Transport Mechanism in Garnet-type Solid Electrolytes: Li+ Ion Exchanges and Their Mobility at Octahedral/Tetrahedral Sites. Chem. Mater. 2015, 27, (3) Rangasamy, E.; Wolfenstine, J.; Sakamoto, J. The role of Al and Li concentration on the formation of cubic garnet solid electrolyte of nominal composition Li 7 La 3 Zr 2 O 12. Solid State Ionics 2012, 206, (4) Liu, L.; Qi, X.; Ma, Q.; Rong, X.; Hu, Y. S.; Zhou, Z.; Li, H.; Huang, X.; Chen, L. Toothpaste-like Electrode: A Novel Approach to Optimize the Interface for Solid-State Sodium-Ion Batteries with Ultralong Cycle Life. ACS Appl. Mater. Interfaces 2016, 8,