Rechargeable lithium (Li)-metal batteries (LMBs) stand out as a top contender for nextgeneration high-energy-density storage solutions, originating from the high theoretical specific capacity and low redox potential of metallic Li. However, developing LMBs is hindered by safety issues arising from dendrite growth as well as electrolyte decomposition reactions during Li plating/stripping. These dendrites can cause short-circuits that may start thermal runaway, greatly amplifying fire hazards. The rapid reaction between the electrolyte and Li-metal leads to the formation of the solid electrolyte interphase (SEI), whose structure and Li-ion conduction properties are crucial for the uniformity of Li deposition. This affects dendrite formation and cycling efficiency, which in turn influences battery life. Yet very little is known about the Li-ion kinetics through the SEI and how these correlate with the structure and composition of the SEI...@en

An all-solid-state battery represents a promising solution for overcoming current lithium-ion batteries ’technological and safety limitations. However, the individual limitations of both inorganic and organic solid electrolytes hinder technological progression. Hybrid solid electrolytes hold the potential to surpass these limitations by integrating both the inorganic and organic phases. A comparative assessment was conducted between hybrid solid electrolytes produced via solvent and dry synthesis, to address potential solvent interactions during hybrid solid electrolyte production and prioritise sustainability.

At 30°C, the comparative analysis demonstrates that the dry-processed PEO13LPSC10 hybrid solid electrolyte achieves a higher ionic conductivity of 1.61×10−5 S/cm, exceeding that of its solvent pro-cessed counterpart, which exhibits a conductivity of 1.51×10−5 S/cm. Conversely, for the PEO18LPSC10 hybrid solid electrolytes, the solvent processing method leads to a higher ionic conductivity, measured at 8.37×10−6 S/cm, in contrast to 7.61×10−6 S/cm observed for the dry-processed method. Thermal analysis indicates that heating above the polymer’s melting transition temperature leads to slow crystallisation in hybrid solid electrolytes using the dry method, resulting in two crystalline phases, as opposed to the single crystalline phase, which was observed using the solvent method. Both processing methods demonstrate homogeneity when comparing the top and bottom surfaces; however, an analysis of surface compositions between the two synthesis methods reveals distinct differences, as identified through. X-ray photoelectron spectroscopy. Moreover, decomposition is observed in both synthesis approaches but is more significant in solvent synthesis. The chemical stability of hybrid solid electrolytes produced by dry synthesis surpasses the solvent-based method.

Further analysis through the dry method investigation reveals that an ethylene oxide to Li+ ratio of 10:1, and a Li6PS5Cl ratio of 10 wt%, yield the highest ionic conductivity among all studied hybrid solid electrolytes. This combination achieves an ionic conductivity of 3.35×10−5 S/cm at 30° C. Additionally, adding Li6PS5Cl and the alkali salt lithium bis(trifluoromethanesulfonyl)imide enhances the amorphous nature and mobility of the polymer, due to a plasticising effect on the organic matrix.

Solid state lithium ion batteries are generally safer than liquid electrolytes. Li6PS5Cl is a promising electrolyte with an instability in the active material and electrolyte interphase which causes an increase in impedance and capacity loss.
Doping with stable salts of LiCl and LiF could affect the stability. It is found that doping LiCl reduces the specific capacity retention despite having higher ionic conductivity from EIS. With the ex-situ XRD analysis, it is found that the decomposition is less than of pristine argyrodite. This could be due to poor interphase contact. In the case of dopant LiF, small doping of the argyrodite decreases the specific capacity retention of the active material which may be due to lowered ionic conductivity. The higher amount of LiF doped argyrodite improves the specific capacity retention despite the lower ionic conductivities. This could be due high decomposition rate. Alternatively, another doping method was used, but it was found to have higher chemical decomposition despite having good specific capacity retention. To improve the quality of this research, better synthesis of the argyrodite is preferred as this research has side phases. Further analysis that could be included are: TEM, XRD in-operando mode, and EDS.

Lithium ion batteries are currently the most attractive choice for mobile energy storage and power sources [4] in terms of energy density. However, it is unlikely that current battery chemistries will reach the energy density desired for future applications [8]. Li-metal, which has the highest reduction potential of all metals and the highest achievable capacity per weight unit, could significantly increase the energy density when used as an Anode. Unfortunately, the dendritic growth of Li-metal is a safety hazard, and the low electrochemical potential of Li-metal
is outside the stability window of many electrolytes leading to capacity degradation.
It has been suggested that safe Li-metal Anodes may be possible in combination with solid electrolytes, as the higher shear modulo of solid over liquid electrolytes may be able to suppress dendrite formation [21].
To study the stability of the interface between Li-metal and the solid electrolyte Li6PS5Cl, electrochemical measurements of the cells, ex-situ x-ray diffraction, and solid state Nuclear Magnetic Resonance measurements were made. It was not possible to confirm the decomposition products that were proposed in literature by density functional theory calculations and in-situ XPS. The XRD-pattern of the cycled electrolyte did not show additional phases. The NMR spectra developed broader peaks and one additional phosphorous environment upon cycling. As a tool to study dendritic growth through Li-ion concentration profiles, a cell for in-situ neutron depth profiling (NDP) was developed. The electrochemical performance is comparable to regular cells, except for a voltage drop due to contact problems during the break after Li-metal stripping. A thin layer of Li-metal between the window and the electrolyte pellet, as well as a collimator plate to put some pressure on the window, could be the solution
to go towards operando measurements.
The current standard data analysis method was implemented and its sensitivity towards gaussian broadening, due to energy straggling (from small angle scattering in the material and the stochastic nature of energy loss), was
investigated. It is shown that the standard deviation of energy straggling is larger than that of energy broadening due to the detector resolution, and that the error on the depth scale is in the order of micrometers.