No abstract

All-solid-state batteries are promising candidates for safe energy-storage systems due to nonflammable solid electrolytes and the possibility to use metallic lithium as an anode. Thus, there is a challenge to design new solid electrolytes and to understand the principles of ion conduction on an atomic scale. We report on a new concept for compounds with high lithium ion mobility based on a rigid open-framework boron structure. The host-guest structure Li 6 B 18 (Li 3 N) comprises large hexagonal pores filled with ∞ 1 ½Li 7 N] strands that represent a perfect cutout from the structure of α-Li 3 N. Variable-temperature 7 Li NMR spectroscopy reveals a very high Li mobility in the template phase with a remarkably low activation energy below 19 kJ mol À 1 and thus much lower than pristine Li 3 N. The formation of the solid solution of Li 6 B 18 (Li 3 N) and Li 6 B 18 (Li 2 O) over the complete compositional range allows the tuning of lithium defects in the template structure that is not possible for pristine Li 3 N and Li 2 O.

Magnesium Ion based Solid State Batteries (MIBs) are subject of intensive studies due to abundance of magnesium, its advantages in volumetric capacity, and the reduced dendrite growth. Here we report on a true solid polymer electrolyte system without liquid additives or plasticizers that reaches conductivities above 10 À 5 S cm À 1 at room temperature and above 10 À 4 S cm À 1 at 50 °C. An electrospun polymer electrolyte membrane fabricated from a polymer electrolyte featuring a composition of PEO : Mg(TFSI) 2 36 : 1 [where PEO stands for poly(ethyleneoxide) and Mg(TFSI) 2 for magnesium bis(trifluoromethanesulfonyl) imide] was identified as the best performing system. Magnesium transport was substantiated by different methods, and the electrochemical properties including solid electrolyte interface (SEI) formation were investigated. Electrospinning as a preparation method has been identified as a powerful tool to enhance the electrochemical properties beyond conventional polymer membrane fabrication techniques.

Solid lithium-ion conductors are important components for allsolid-state batteries and the knowledge of the mechanism of Li diffusion is an important step in improving known materials and developing new materials. For the Li-ion conductor α-Li 3 N, the lithium diffusion process has been intensively investigated. We report here on the Li-ion diffusion in the open-framework structure Li 6 B 18 (Li 3 N) 1−x (Li 2 O) in which Li 3 N and/or Li 2 O serve as a guest. Whereas vacancy formation for α-Li 3 N is not possible by forming a solid solution with Li 2 O, the solid solution of Li 6 B 18 (Li 3 N) 1−x (Li 2 O) x exists over the whole composition range with an increasing number of Li vacancies with x and samples for x = 0, 0.25, 0.5, 0.75, and 1 are investigated. A variety of solid-state NMR approaches, including 7 Li T 1 relaxation NMR, temperature-dependent 6 Li-magic angle spinning (MAS)-NMR, and 6 Li-{ 7 Li}-cross-polarization (CP)-MAS 2Dexchange NMR, and a detailed 7 Li line shape analysis are combined with quantum chemical calculations of Li migration pathways to unravel the mechanism of Li diffusion in the open-framework structures Li 6 B 18 (Li 3 N) 1−x (Li 2 O) x , hosting three different Li sites. The combined results indicate an anisotropic Li diffusion process, in which the motion along the crystallographic c-direction seems to be strongly hindered (Li2 ↔ Li3). On the other hand, the diffusion pathway in the ab-plane is characterized by a two-step motional process that combines Li1 ↔ Li2 and Li2 ↔ Li2 jumps with very low activation energies in the range of 30−40 kJ/mol for Li1 ↔ Li2 and 5�15 kJ/mol for Li2 ↔ Li2. Thus, lithium migration within the title compound bears strong similarities to the Li diffusion processes present in the well-known Li-ion conductor α-Li 3 N.

All‐solid‐state batteries are promising candidates for safe energy‐storage systems due to non‐flammable solid electrolytes and the possibility to use metallic lithium as an anode. Thus, there is a challenge to design new solid electrolytes and to understand the principles of ion conduction on an atomic scale. We report on a new concept for compounds with high lithium ion mobility based on a rigid open‐framework boron structure. The host–guest structure Li6B18(Li3N) comprises large hexagonal pores filled with ∞1[ ${{}_{{\rm { \infty }}}{}^{{\rm { 1}}}{\rm { [}}}$ Li7N] strands that represent a perfect cutout from the structure of α‐Li3N. Variable‐temperature 7Li NMR spectroscopy reveals a very high Li mobility in the template phase with a remarkably low activation energy below 19 kJ mol−1 and thus much lower than pristine Li3N. The formation of the solid solution of Li6B18(Li3N) and Li6B18(Li2O) over the complete compositional range allows the tuning of lithium defects in the template structure that is not possible for pristine Li3N and Li2O.