The exfoliation of tridimensional crystal structures has recently been considered a new source of bidimensional materials. The new approach offers the possibility of dramatically enlarging the library of bidimensional materials, but the number of nanolayers produced so far is still limited. Here, we report for the first time the use of a new type of material, α-germanium nanolayers (2D α-Ge). The 2D α-Ge is obtained by exfoliating crystals of α-germanium in a simple one-step procedure assisted by wet ball-milling (gram-scale fabrication). The α-germanium nanolayers have been tested as anode material for high-performance LIBs. The results show excellent performance in semi-cell configuration with a high specific capacity of 1630 mAh g⁻¹ for mass loading of 1 mg cm⁻² at 0.1 C. The semi-cell was characterized by a constant current rate of 0.5 C during 400 cycles and different scan rates (0.1 C, 0.5 C, and 1 C). Interestingly, the structural characterization, including Raman spectroscopy, XRPD, and XPS, concludes that 2D α-Ge largely retains its crystallinity after continuous cycling. These results can be used to potentially apply these novel 2D germanium nanolayers to high-performance Li-ion batteries.

Li6PS5Cl has attracted much attention due to its high Li-ion conductivity and ease in processibility, which allows large-scale applications of solid-state batteries. However, when combined with high-voltage cathodes, Li6PS5Cl suffers from detrimental side reactions. Due to the stability towards high voltages combined with a relatively high Li-ion conductivity Li3InCl6 has been considered as catholyte with the potential to compensate Li6PS5Cl shortcomings. Despite previous claims about its (electro)chemical instability, we hypothesize that Li3InCl6 remains a promising choice when (i) triple junctions between Li3InCl6, Li6PS5Cl, and Ni-rich cathodes are avoided and (ii) the cut-off voltage is below 3.6 V (vs Li/In). Therefore, a core-shell-structured cathode, i.e., LiNi0.8Co0.15Al0.05O₂ particles with a 100 nm thick pin-hole-free Li3InCl6 layer, has been developed using mechanofusion. When employed in a solid-state battery with a cut-off voltage of 3.58V (vs Li/In) a specific capacity enhancement of about 80 mAh/g at any C-rate (0.1 to 1C) was achieved. The stability of Li3InCl6 as well as its functionality to prevent Li6PS5Cl from decomposition and cathode particles from mechanical degradation has been demonstrated, by synchrotron operando XRD and, e.g., post-mortem analysis using Plasma FIB SEM and XPS. This study shows that Li3InCl6 can be used as catholyte when applied appropriately.

Interdiffusion of transition metals across the cathode-electrolyte interface is identified as a key challenge for the practical realization of solid-state batteries. This is related to the formation of highly resistive interphases impeding the charge transport across the materials thus limiting the battery performance. Herein, we investigate the hypothesis that formation of interphases is associated with the incorporation of Co into the LLZO lattice representing the starting point of a cascade of degradation processes. It is shown that Co incorporates into the garnet structure preferably four-fold coordinated as Co2+ or Co3+ depending on oxygen fugacity. The solubility limit of Co is determined to be around 0.16 pfu, whereby concentrations beyond this limit causes a cubic-to-tetragonal phase transition. Moreover, the temperature-dependent Co diffusion coefficient is determined, e.g., D700 °C = 9.46 × 10-14 cm2/s and an activation energy Ea = 1.65 eV, suggesting that detrimental cross diffusion will take place at any relevant process condition. Additionally, the optimal protective Al2O3 coating thickness for relevant temperatures is studied, which allows to create a process diagram to mitigate any degradation with a minimum compromise on electrochemical performance. This study provides a tool to optimize processing conditions toward developing high energy density solid-state batteries.