1905849 (1 of 7) © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.small-journal.com FULL PAPER Construction of 3D Electronic/Ionic Conduction Networks for All-Solid-State Lithium Batteries Hongli Wan, Liangting Cai, Fudong Han, Jean Pierre Mwizerwa, Chunsheng Wang,* and Xiayin Yao* H. Wan, L. Cai, J. P. Mwizerwa, Prof. X. Yao Ningbo Institute of Materials Technology and Engineering Chinese Academy of Sciences Ningbo 315201, P. R. China E-mail: yaoxy@nimte.ac.cn H. Wan, J. P. Mwizerwa, Prof. X. Yao Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of Sciences Beijing 100049, P. R. China Dr. F. Han, Prof. C. Wang Department of Chemical and Biomolecular Engineering University of Maryland College Park, MD 20742, USA E-mail: cswang@umd.edu The ORCID identification number(s) for the author(s) of this article can be found under https://doi.org/10.1002/smll.201905849. DOI: 10.1002/smll.201905849 are considered to be one of the most promising solid-state electrolytes due to high ionic conductivity and excel- lent processability as well as low elastic modulus. [5–9] The high ionic conductivi- ties of glass-ceramic sulfide electrolytes such as Li 10 GeP 2 S 12 (1.2 × 10 -2 S cm -1 ), [8] Li 7 P 3 S 11 (1.7 × 10 -2 S cm -1 ), [5] and Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.3 (2.5 × 10 -2 S cm -1 ) [9] are comparable with that of the liquid car- bonate electrolytes. However, the electro- chemical performance of all-solid-state lithium batteries using sulfide electrolytes is still inferior to that of commercial liquid electrolyte based lithium-ion batteries. The challenges are attributed to (1) poor elec- tronic/ionic conduction networks in cath- odes due to the limited triple solid–solid contact interface and the poor interface compatibility, and (2) high stress/strain due to volume change of active mate- rials and immobile/incompressible solid electrolytes. [10–12] Among all cathode materials, transi- tion-metal sulfides have been considered the most promising cathodes for high- performance all-solid-state lithium batteries because they (1) show better interface compatibility with sulfide electrolytes than lithium transition-metal oxides, (2) have higher energy density and higher chemical stability than lithium transition-metal oxides, [13–16] and (3) possess better electronic conductivity and electrochemical stability than Li 2 S and sulfur. [17–20] However, the poor electronic/ionic conduction network and continuously increased solid–solid contact interface resistance during charge/ discharge cycles are still challenges for solid-state transition- metal sulfide cathodes. One promising strategy is to coat nano- sized transition-metal sulfides onto highly conductive carbona- ceous materials to enhance the electronic conductivity. [21–23] The thickness of transition-metal sulfide should be less than few nanometers to reduce the stress/strain and interface resistance, and to allow the electrons conduction across the transition-metal sulfide nanolayer through tunnel effect to solid electrolyte for charge transfer reaction. The long cycle life of such active mate- rial/electron additive nanocmposite cathodes was demonstrated by us using nanolayer Cu 2 ZnSnS 4 (or sulfur) deposited gra- phene as model cathodes. [21,24] The Cu 2 ZnSnS 4 /graphene nano- composite prepared using hydrothermal approach shows a dis- charge capacity of 645.4 mAh g -1 after 50 cycles at 50 mA g -1 , [21] High and balanced electronic and ionic transportation networks with nanoscale distribution in solid-state cathodes are crucial to realize high- performance all-solid-state lithium batteries. Using Cu 2 SnS 3 as a model active material, such a kind of solid-state Cu 2 SnS 3 @graphene-Li 7 P 3 S 11 nanocomposite cathodes are synthesized, where 5–10 nm Cu 2 SnS 3 nanoparticles homogenously anchor on the graphene nanosheets, while the Li 7 P 3 S 11 electrolytes uniformly coat on the surface of Cu 2 SnS 3 @graphene composite forming nanoscaled electron/ion transportation networks. The large amount of nanoscaled triple-phase boundary in cathode ensures high power density due to high ionic/electronic conductions and long cycle life due to uniform and reduced volume change of nano-Cu 2 SnS 3. The Cu 2 SnS 3 @ graphene-Li 7 P 3 S 11 cathode layer with 2.0 mg cm -2 loading in all-solid-state lithium batteries demonstrates a high reversible discharge specific capacity of 813.2 mAh g -1 at 100 mA g -1 and retains 732.0 mAh g -1 after 60 cycles, corresponding to a high energy density of 410.4 Wh kg -1 based on the total mass of Cu 2 SnS 3 @graphene-Li 7 P 3 S 11 composite based cathode. Moreover, it exhibits excellent rate capability and high-rate cycling stability, showing reversible capacity of 363.5 mAh g -1 at 500 mA g -1 after 200 cycles. The study provides a new insight into constructing both electronic and ionic conduction networks for all-solid-state lithium batteries. 1. Introduction All-solid-state lithium batteries using nonflammable inor- ganic solid electrolytes have attracted increasing attention due to its high safety and reliability. [1–4] Sulfide electrolytes Small 2019, 15, 1905849