No abstract

Batteries & Supercaps www.batteries-supercaps.org Review doi.org/10.1002/batt.202200097 Lithium-sulfur (LiÀ S) batteries are recognized as one of the most promising technologies with the potential to become the next-generation batteries. However, to ensure LiÀ S batteries reach commercialization, complex challenges remain, among which the tailoring of an appropriate electrolyte is the most important. This review discusses the role of electrolytes in LiÀ S batteries, focusing on the main issues and solutions for the shuttle mechanism of polysulfides and the instability of the interface with lithium metal. Herein, we present a background on LiÀ S chemistry followed by the state-of-the-art electrolytes highlighting the different strategies undertaken with liquid and solid electrolytes.

Solid‐state batteries (SSBs) are promising candidates to significantly exceed the energy densities of today's state‐of‐the‐art technology, lithium‐ion batteries (LIBs). To enable this advancement, optimizing the solid electrolyte (SE) is the key. β‐Li3PS4 (β‐LPS) is the most studied member of the Li2S‐P2S5 family, offering promising properties for implementation in electric vehicles. In this work, the microstructure of this SE and how it influences the electrochemical performance are systematically investigated. To figure this out, four batches of β‐LPS electrolyte with different particle size, shape, and porosity are investigated in detail. It is found that differences in pellet porosities mostly originate from single‐particle intrinsic features and less from interparticle voids. Surprisingly, the β‐LPS electrolyte pellets with the highest porosity and larger particle size not only show the highest ionic conductivity (up to 0.049 mS cm–1 at RT), but also the most stable cycling performance in symmetrical Li cells. This behavior is traced back to the grain boundary resistance. Larger SE particles seem to be more attractive, as their grain boundary contribution is lower than that of denser pellets prepared using smaller β‐LPS particles.

For many years, composite electrolytes (CEs) consisting of a mixture of inorganic solid electrolytes (ISEs) and polymer electrolytes (PEs) have been investigated as promising materials for the scalable production of solid-state batteries. It is believed that CEs can overcome limitations of the single components, namely the low room-temperature conductivity and lithium ion transference number of PEs and the poor mechanical properties and high temperature processing necessary for ISE ceramics. To facilitate ion transport in the CE between the electrodes a low and stable charge transfer resistance between PEs and ISEs is required. In this study, we investigate by means of electrochemical impedance spectroscopy how polymer crystallinity influences the charge-transfer resistance of hetero-ionic interfaces between polyethylene oxide (PEO)-based electrolytes and Li1.5Al0.5Ti1.5(PO4)3 (LATP) as well as Li6.25Al0.25La3Zr2O12 (LLZO) as ISEs. Crystallization of PEO based electrolytes below their melting temperature leads to an increased charge-transfer resistance. On the other hand, electrolytes based on the amorphous poly[2-(2-(2-methoxyethoxy)ethoxy)ethyl glycidyl ether (PTG) do not show an increased charge transfer resistance. Finally, the conductivity of ISE-rich CEs is measured as a function of their temperature and composition for elucidating how the interface resistance influences charge transport in ISE-rich composite electrolytes.

Solid-state lithium batteries are considered one of the most promising candidates for future electrochemical energy storage. However, both inorganic solid electrolytes (such as oxide-based or sulfide-based materials) and polymer electrolytes still have to overcome several challenges to replace the currently used liquid organic electrolytes. An increasingly adopted approach to overcome these challenges relies on the combination of different electrolyte systems. Herein, we report the synthesis and characterization of a novel sulfur-doped single-ion conducting multi-block copolymer (SIC-BCE) system. This SIC-BCE may serve as interlayer between the electrodes and the sulfidic electrolyte such as Li6PS5Cl, thus benefitting of the high ionic conductivity of the latter and the favorable interfacial contact and electrochemical stability of the polymer. The polymer shows excellent ionic conductivity when swollen with ethylene carbonate and allows for stable stripping/plating of lithium, accompanied by a suitable electrochemical stability towards reduction and oxidation. First tests in symmetric Cu|SIC-BCE|Li6PS5Cl|SIC-BCE|Cu cells confirm the general suitability of the polymer to stabilize the electrode|electrolyte interface by preventing the direct contact of the sulfidic electrolyte with, e.g., metallic copper foils.

A novel fluorine-free ionic liquid electrolyte comprising lithium dicyanamide (LiDCA) and trimethyl(isobutyl)phosphonium tricyanomethanide (P 111i4 TCM) in a 1:9 molar ratio is studied as an electrolyte for lithium metal batteries. At room temperature, it demonstrates high ionic conductivity and viscosity of about 4.5 mS cm −1 and 64.9 mPa s, respectively, as well as a 4 V electrochemical stability window (ESW). Li stripping/ plating tests prove the excellent electrolyte compatibility with Li metal, evidenced by the remarkable cycling stability over 800 cycles. The evolution of the Li−electrolyte interface upon cycling was investigated via electrochemical impedance spectroscopy, displaying a relatively low impedance increase after the initial formation cycles. Finally, the solid electrolyte interphase (SEI) formed on Li metal appeared to have a bilayer structure mostly consisting of DCA and TCM reduction products. Additionally, decomposition products of the phosphonium cation were also detected, despite prior studies reporting its stability against Li metal.

The distribution of degradation products, before and after cycling, within common sulfide based solid electrolytes (β-Li3PS4, Li6PS5Cl and Li10GeP2S12) were mapped using Raman microscopy. All composite electrodes displayed appearance of...