All-solid-state batteries (SSBs) have recently attracted much attention due to their potential application in electric vehicles. One key issue that is central to improve the function of SSBs is to gain a better understanding of the interfaces between the material components toward enhancing the electrochemical performance. In this work, the interfacial properties of a carbon-containing cathode composite, employing LiGePS as the solid electrolyte, are investigated. A large interfacial charge-transfer resistance builds up upon the inclusion of carbon in the composite, which is detrimental to the resulting cycle life. Analysis by X-ray photoelectron spectroscopy reveals that carbon facilitates faster electrochemical decomposition of the thiophosphate solid electrolyte at the cathode/solid electrolyte interface-by transferring the low chemical potential of lithium in the charged state deeper into the solid electrolyte and extending the decomposition region. The occurring accumulation of highly oxidized sulfur species at the interface is likely responsible for the large interfacial resistances and aggravated capacity fading observed.

achieve high safety and competitive energy and power density. [1,2] The solid electrolyte (SE) is the key component in ASSBs and has been extensively explored for several decades. [3,4] Among the different types of solid electrolytes, lithium thiophosphates have attracted ever-increasing attention for ASSBs due to their very high ionic conductivity and facile processing at room temperature. [5,6] Recent theoretical simulations suggest that the ionic conductivity of SEs in ASSB cathodes needs to reach at least 10 -2 S cm -1 in order to obtain comparable performance with commercial lithium-ion batteries with liquid electrolytes-a target that may only be achieved with thiophosphate electrolytes. [7] Therefore, significant research effort is spent on improving the ionic conductivity of thiophosphate SEs. [8,9] Glasses in the quasi-binary system xLi 2 S•yP 2 S 5 prepared by mechanical ball milling exhibit a conductivity of up to 10 -4 S cm -1 (e.g., 75Li 2 S•25P 2 S 5 glass [7525-glass], 70Li 2 S•30P 2 S 5 glass [7030-glass]) at room temperature. [10] The conductivity is enhanced by the precipitation of metastable phases upon heating, forming glass-ceramic dispersions: crystalline phases in an amorphous matrix, in this work denoted as "gc". [11] Although very high ionic conductivities above 10 mS cm -1 have been achieved in some Solid electrolytes (SEs) largely define the properties of all-solid-state batteries (ASSBs) and are expected to improve their safety, stability, and performance. Their ionic conductivity has much improved in recent years, enabling higher power and energy density. However, more subtle parameters, such as crystallinity, may also influence the electrochemical performance of cells. In this work, the correlation between the performance of ASSBs and thiophosphate SEs having the same stoichiometry, but different crystallinity is investigated. In In/InLi | SE | LiCoO 2 @ LiNb 0.5 Ta 0.5 O 3 model cells, better cycling and rate performance is achieved when using glass/glass-ceramic SEs (e.g., 75Li 2 S•25P 2 S 5 glass, 70Li 2 S•30P 2 S 5 glass, and Li 6 PS 5 Cl glass-ceramic). This can be mostly attributed to the mitigation of contact loss by the glass/glass-ceramic SEs compared to their crystalline SE counterparts. Furthermore, the SE decomposition at typical cathode potentials is investigated by using SE and carbon composites as cathodes. Larger volume changes and more severe decomposition are observed with crystalline SEs in the SE/carbon composite cathode after cycling. The crystalline SEs show higher electronic partial conductivity which results in more degradation in the composite cathode. This work sheds light on optimized composite cathode design for ASSB by carefully choosing solid electrolytes with appropriate mechanical and (electro-)chemical properties.

We demonstrate an electrochromic device with self-bleaching ability that uses ethyl viologen- ([EV]) and ferrocene-based redox ionic liquids ([FcNTf]) as the electroactive species. These electroactive compounds are insensitive to atmospheric O and HO in both their oxidized and reduced states once dissolved in a typical ionic liquid electrolyte ([BMIm][NTf]), allowing for the device to be assembled outside a glovebox without any encapsulation. This device could generate a deep blue color by the application of a 2.0 V potential between two fluorine-doped tin oxide (FTO) substrates to oxidize the ferrocenyl centers to [FcNTf] while reducing viologen to [EV]. Self-bleaching occurs at OCP as [EV] and [FcNTf] undergo homogeneous electron transfer in the electrolyte. The mass transport of ethyl viologen and ferrocenylsulfonyl(trifluoromethylsulfonyl)imide ([FcNTf]) anion was evaluated by double potential step chronoamperometry to study the impact of the diffusion coefficient on the self-bleaching mechanism. The electrochromic device demonstrated here shows a contrast ΔT (610 nm) around 40% at 2.0 V as colored cell voltage, a switching time in the order of few seconds for coloration and bleaching, coloration efficiency of 105.4 to 146.2 cm C at 610 nm, and very high stability (94.8% ΔT after 1000 cycles) despite the presence of O and HO in the electrolyte.

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