Charge-clustering induced fast ion conduction in 2LiX-GaF3: A strategy for electrolyte design.

2LiX-GaF3 (X = Cl, Br, I) electrolytes offer favorable features for solid-state batteries: mechanical pliability and high conductivities. However, understanding the origin of fast ion transport in 2LiX-GaF3 has been challenging. The ionic conductivity order of 2LiCl-GaF3 (3.20 mS/cm) > 2LiBr-GaF3 (0.84 mS/cm) > 2LiI-GaF3 (0.03 mS/cm) contradicts binary LiCl (10-12 S/cm) < LiBr (10-10 S/cm) < LiI (10-7 S/cm). Using multinuclear 7Li, 71Ga, 19F solid-state nuclear magnetic resonance and density functional theory simulations, we found that Ga(F,X)n polyanions boost Li+-ion transport by weakening Li+-X- interactions via charge clustering. In 2LiBr-GaF3 and 2LiI-GaF3, Ga-X coordination is reduced with decreased F participation, compared to 2LiCl-GaF3. These insights will inform electrolyte design based on charge clustering, applicable to various ion conductors. This strategy could prove effective for producing highly conductive multivalent cation conductors such as Ca2+ and Mg2+, as charge clustering of carboxylates in proteins is found to decrease their binding to Ca2+ and Mg2+.

Nanoscale Encapsulation of Hybrid Perovskites Using Hybrid Atomic Layer Deposition.

Organic-inorganic hybrid perovskites have shown tremendous potential for optoelectronic applications. Ion migration within the crystal and across heterointerfaces, however, imposed severe problems with material degradation and performance loss in devices. Encapsulating hybrid perovskite with a thin physical barrier can be essential for suppressing the undesirable interfacial reactions without inhibiting the desirable transport of charge carriers. Here, we demonstrated that nanoscale, pinhole-free Al2O3 layer can be coated directly on the perovskite CH3NH3PbI3 using atomic layer deposition (ALD). The success can be attributed to a multitude of strategies including surface molecular modification and hybrid ALD processing combining the thermal and plasma-enhanced modes. The Al2O3 films provided remarkable protection to the underlying perovskite films, surviving by hours in solvents without noticeable decays in either structural or optical properties. The results advanced the understanding of applying ALD directly on hybrid perovskite and provided new opportunities to implement stable and high-performance devices based on the perovskites.

Multifunctional Electrolyte Additive Stabilizes Electrode-Electrolyte Interface Layers for High-Voltage Lithium Metal Batteries.

A lithium metal anode and high nickel ternary cathode are considered viable candidates for high energy density lithium metal batteries (LMBs). However, unstable electrode-electrolyte interfaces and structure degradation of high nickel ternary cathode materials lead to serious capacity decay, consequently hindering their practical applications in LMBs. Herein, we introduced N,O-bis(trimethylsilyl) trifluoro acetamide (BTA) as a multifunctional additive for removing trace water and hydrofluoric acid (HF) from the electrolyte and inhibiting corrosive HF from disrupting the electrode-electrolyte interface layers. Furthermore, the BTA additive containing multiple functional groups (C-F, Si-O, Si-N, and C═N) promotes the formation of LiF-rich, Si- and N-containing solid electrolyte interfacial films on a lithium metal anode and LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode surfaces, thereby improving the electrode-electrolytes interfacial stability and mitigating the capacity decay caused by structural degradation of the layered cathode. Using the BTA additive had tremendous benefits through modification of both anode and cathode surface layers. This was demonstrated using a Li||NMC811 metal battery with the BTA electrolyte, which exhibits remarkable cycling and rate performances (122.9 mA h g-1 at 10 C) and delivers a discharge capacity of 162 mA h g-1 after 100 cycles at 45 °C. Likewise, this study establishes a cost-effective approach of using a single additive to improve the electrochemical performance of LMBs.

Structure and Properties of Cs7(H4PO4)(H2PO4)8: A New Superprotonic Solid Acid Featuring the Unusual Polycation (H4PO4).

We report the discovery of a new superprotonic compound, Cs7(H4PO4)(H2PO4)8, or CPP, which forms at elevated temperatures from the reaction of CsH2PO4 and CsH5(PO4)2. The structure, solved using high-temperature single-crystal X-ray diffraction and confirmed by high-temperature 31P NMR spectroscopy, crystallizes in space group Pm3̅n and has a lattice constant of 20.1994(9) Å at 130 °C. The unit cell resembles a 4 × 4 × 4 superstructure of superprotonic CsH2PO4, but features an extraordinary chemical moiety, rotationally disordered H4PO4+ cations, which periodically occupy one of every eight cation sites. The influence of this remarkable cation on the structure, thermodynamics, and proton transport properties of the CPP phase is discussed. Notably, CPP forms at a temperature of 90 °C, much lower than the superprotonic transition temperature of 228 °C of CsH2PO4, and the compound does not appear to have an ordered, low-temperature form. Under nominally dry conditions, the material is stable against dehydration to ∼151 °C, and this results in a particularly wide region of stability of a superprotonic material in the absence of active humidification. The conductivity of Cs7(H4PO4)(H2PO4)8 is moderate, 5.8 × 10-4 S cm-1 at 140 °C, but appears nevertheless facilitated by polyanion (H2PO4-) group reorientation.