Here, we directly observe the interface lithium-ion accumulation resulting from the SCL by investigating the net-charge-density distribution across the electrode/electrolyte interface of a working sulfide-based ASSLIB using the in situ DPC-STEM technique. Recently, the segmented-detector differential phase contrast STEM (DPC-STEM) technique was used to reconstruct an electric field vector map and a charge-density map with higher spatial resolution than and without the restriction of specimen geometry imposed by EH-TEM 26, offering a new method to solve this challenging issue in ASSLIBs 23, 24, 27, 28, 29. However, to the best of our knowledge, an SCL visualization study related to sulfide SEs has not been reported because they are easily damaged by the electron beam, which, in turn, hinders the development of a rational interface design strategy to solve the SCL issue in promising sulfide-based ASSLIBs. Furthermore, it has been reported that the oxide/sulfide interface exhibits more severe SCL effects than the oxide/oxide interface 25. Although previous studies have tried to visualize the ionic and potential profiles in the SCL via in situ electron-holography transmission electron microscopy (EH-TEM) 20, spatially resolved electron energy-loss spectroscopy (SR-EELS) 21, and Kelvin probe force microscopy (KPFM) 22, the SCL effect on interfacial lithium-ion transport is still unclear due to the lack of direct experimental evidence of the interfacial charge distribution and accumulation 23, 24. Unfortunately, inspiring solutions for the SCL issue still remain to be explored owing to the unclear action mechanism of the SCL on interfacial lithium-ion transport in ASSLIBs. Recently, important progress has been achieved in solving the interface reaction and physical contact issues by coating, thermal soldering, or forming epitaxial interfaces 17, 18, 19. The sluggish lithium-ion transport across the solid electrode/electrolyte interface mainly results from three aspects: the space charge layer (SCL), interface reaction generating ionically resistive products, and poor physical contact. Nevertheless, the performance of ASSLIBs based on these electrolytes is still inferior to that of commercially available LIBs 12 because fast solid electrode/electrolyte interfacial lithium-ion transport remains a vital challenge in ASSLIBs 13, 14, 15, 16. As an essential component of ASSLIBs, several state-of-the-art sulfide solid-state electrolytes (SEs) have achieved a high room-temperature ion conductivity of 10 −2 S cm −1 6, 7, 8, 9, 10, 11, which is close to or even exceeds that of liquid electrolytes (LEs).
![sulfide charge sulfide charge](https://d3i71xaburhd42.cloudfront.net/b95b91195b8c085f976d0a250c37ba2de584ae38/1-Figure1-1.png)
Our findings will strikingly advance the fundamental scientific understanding of the SCL mechanism in ASSLIBs and shed light on rational electrode/electrolyte interface design for high-rate performance ASSLIBs.Īll-solid-state lithium-ion batteries (ASSLIBs) have been considered one of the most promising alternatives to conventional LIBs in terms of their superior safety and great potential to meet the requirements of high energy and power density 1, 2, 3, 4, 5.
![sulfide charge sulfide charge](https://showme0-9071.kxcdn.com/files/1000081730/pictures/thumbs/1943976/last_thumb1426109117.jpg)
Moreover, we further demonstrate a built-in electric field and chemical potential coupling strategy to reduce the SCL formation and boost lithium-ion transport across the electrode/electrolyte interface by the in-situ DPC-STEM technique and finite element method simulations.
![sulfide charge sulfide charge](https://1.bp.blogspot.com/-i-iA2jirhUg/Xc2RZukfVqI/AAAAAAAAf8A/zwJ0b7uZSaUaBy9LFssKAfACVUk5gyigwCLcBGAsYHQ/s1600/20191114_233703.jpg)
Here, we directly observe the electrode/electrolyte interface lithium-ion accumulation resulting from the SCL by investigating the net-charge-density distribution across the high-voltage LiCoO 2/argyrodite Li 6PS 5Cl interface using the in-situ differential phase contrast scanning transmission electron microscopy (DPC-STEM) technique. However, in-situ visualization of the SCL effect on the interfacial lithium-ion transport in sulfide-based ASSLIBs is still a great challenge. The space charge layer (SCL) is generally considered one of the origins of the sluggish interfacial lithium-ion transport in all-solid-state lithium-ion batteries (ASSLIBs).