Grain Boundary Electronic Insulation for High-Performance All-Solid-State Lithium Batteries.

Sulfide electrolytes with high ionic conductivities are one of the most highly sought for all-solid-state lithium batteries (ASSLBs). However, the non-negligible electronic conductivities of sulfide electrolytes (≈10-8  S cm-1 ) lead to electron smooth transport through the sulfide electrolyte pellets, resulting in Li dendrite directly depositing at the grain boundaries (GBs) and serious self-discharge. Here, a grain-boundary electronic insulation (GBEI) strategy is proposed to block electron transport across the GBs, enabling Li-Li symmetric cells with 30 times longer cycling life and Li-LiCoO2 full cells with three times lower self-discharging rate than pristine sulfide electrolytes. The Li-LiCoO2 ASSLBs deliver high capacity retention of 80 % at 650 cycles and stable cycling performance for over 2600 cycles at 0.5 mA cm-2 . The innovation of the GBEI strategy provides a new direction to pursue high-performance ASSLBs via tailoring the electronic conductivity.

Highly Stable Halide-Electrolyte-Based All-Solid-State Li-Se Batteries.

Solid-state Li-S and Li-Se batteries are promising devices that can address the safety and electrochemical stability issues that arise from liquid-based systems. However, solid-state Li-Se/S batteries usually present poor cycling stability due to the high resistance interfaces and decomposition of solid electrolytes caused by their narrow electrochemical stability windows. Here, an integrated solid-state Li-Se battery based on a halide Li3 HoCl6 solid electrolyte with high ionic conductivity is presented. The intrinsic wide electrochemical stability window of the Li3 HoCl6 and its stability toward Se and the lithiated species effectively inhibit degeneration of the electrolyte and the Se cathode by suppressing side reactions. The inherent thermodynamic mechanism of the lithiation/delithiation process of the Se cathode in solid is also revealed and confirmed by theoretical calculations. The battery achieves a reversible capacity of 402 mAh g-1 after 750 cycles. The electrochemical performance, thermodynamic lithiation/delithiation mechanism, and stability of metal-halide-based Li-Se batteries confer theoretical study and practical applicability that extends to other energy-storage systems.

A universal wet-chemistry synthesis of solid-state halide electrolytes for all-solid-state lithium-metal batteries.

Solid-state halide electrolytes have gained revived research interests owing to their high ionic conductivity and high-voltage stability. However, synthesizing halide electrolytes from a liquid phase is extremely challenging because of the vulnerability of metal halides to hydrolysis. In this work, ammonium-assisted wet chemistry is reported to synthesize various solid-state halide electrolytes with an exceptional ionic conductivity (>1 microsiemens per centimeter). Microstrain-induced localized microstructure change is found to be beneficial to lithium ion transport in halide electrolytes. Furthermore, the interfacial incompatibility between halide electrolytes and lithium metal is alleviated by transforming the mixed electronic/ionic conductive interface into a lithium ion­conductive interface. Such all-solid-state lithium-metal batteries (ASSLMBs) demonstrate a high initial coulombic efficiency of 98.1% based on lithium cobalt oxide and a high discharge capacity of 166.9 microampere hours per gram based on single-crystal LiNi0.6Mn0.2Co0.2O2. This work provides universal approaches in both material synthesis and interface design for developing halide-based ASSLMBs.

Revealing the Local Cathodic Interfacial Chemism Inconsistency in a Practical Large-Sized Li-O2 Model Battery with High Energy Density to Underpin Its Key Cyclic Constraints.

Due to the theoretical ultrahigh energy density of the Li-O2 battery chemistry, it has been hailed as the ultimate battery technology. Yet, practical Li-O2 batteries usually need to be designed in a large-sized pattern to actualize a high specific energy density, and such batteries often cannot be cycled effectively. To understand the inherent reasons, we specially prepared large-sized (13 cm × 13 cm) Li-O2 model batteries with practical energy output (6.9 Ah and 667.4 Wh/kgcell) for investigations. By subregional and postmortem analysis, the cathode interface was found to have severe local inhomogeneity after discharge, which was highly associated with the electrolyte and O2 maldistribution. The quantitative results by X-ray photoelectron spectroscopy (XPS) evidenced that this local inhomogeneity can exacerbate the generation of lithium acetate during charge, where the locally higher ratio of unutilized carbon surface and less Li2O2 after discharge would result in increased lithium acetate formation for a subsequent local overcharge. Moreover, verification experiments proved that the byproduct lithium acetate, which had been of less concern, was recalcitrant and triggered much larger polarization compared with the commonly reported byproduct Li2CO3 during battery operations, further revealing the key limiting factors leading to the poor rechargeability of batteries by its accumulation at a pouch-type cell level.

An Air-Stable and Li-Metal-Compatible Glass-Ceramic Electrolyte enabling High-Performance All-Solid-State Li Metal Batteries.

The development of all-solid-state Li metal batteries (ASSLMBs) has attracted significant attention due to their potential to maximize energy density and improved safety compared to the conventional liquid-electrolyte-based Li-ion batteries. However, it is very challenging to fabricate an ideal solid-state electrolyte (SSE) that simultaneously possesses high ionic conductivity, excellent air-stability, and good Li metal compatibility. Herein, a new glass-ceramic Li3.2 P0.8 Sn0.2 S4 (gc-Li3.2 P0.8 Sn0.2 S4 ) SSE is synthesized to satisfy the aforementioned requirements, enabling high-performance ASSLMBs at room temperature (RT). Compared with the conventional Li3 PS4 glass-ceramics, the present gc-Li3.2 P0.8 Sn0.2 S4 SSE with 12% amorphous content has an enlarged unit cell and a high Li+ ion concentration, which leads to 6.2-times higher ionic conductivity (1.21 × 10-3 S cm-1 at RT) after a simple cold sintering process. The (P/Sn)S4 tetrahedron inside the gc-Li3.2 P0.8 Sn0.2 S4 SSE is verified to show a strong resistance toward reaction with H2 O in 5%-humidity air, demonstrating excellent air-stability. Moreover, the gc-Li3.2 P0.8 Sn0.2 S4 SSE triggers the formation of Li-Sn alloys at the Li/SSE interface, serving as an essential component to stabilize the interface and deliver good electrochemical performance in both symmetric and full cells. The discovery of this gc-Li3.2 P0.8 Sn0.2 S4 superionic conductor enriches the choice of advanced SSEs and accelerates the commercialization of ASSLMBs.

Transition of the Reaction from Three-Phase to Two-Phase by Using a Hybrid Conductor for High-Energy-Density High-Rate Solid-State Li-O2 Batteries.

Solid-state Li-O2 batteries possess the ability to deliver high energy density with enhanced safety. However, designing a highly functional solid-state air electrode is the main bottleneck for its further development. Herein, we adopt a hybrid electronic and ionic conductor to build solid-state air electrode that makes the transition of Li-O2 battery electrochemical mechanism from a three-phase process to a two-phase process. The solid-state Li-O2 battery with this hybrid conductor solid-state air electrode shows decreased interfacial resistance and enhanced reaction kinetics. The Coulombic efficiency of Li-O2 battery is also significantly improved, benefiting from the good contact between discharge products and electrode materials. In situ environmental transmission electron microscopy under oxygen was used to illustrate the reversible deposition and decomposition of discharge products on the surface of this hybrid conductor, visually verifying the two-phase reaction.

Origin of Superionic Li3Y1-xInxCl6 Halide Solid Electrolytes with High Humidity Tolerance.

The high ionic conductivity, air/humidity tolerance, and related chemistry of Li3MX6 solid-state electrolytes (SSEs, M is a metal element, and X is a halogen) has recently gained significant interest. However, most of the halide SSEs suffer from irreversible chemical degradation when exposed to a humid atmosphere, which originates from hydrolysis. Herein, the function of the M atom in Li3MX6 was clarified by a series of Li3Y1-xInxCl6 (0 ≤ x < 1). When the ratio of In3+ was increased, a gradual structural conversion from the hexagonal-closed-packed (hcp) anion arrangement to cubic-closed-packed (ccp) anion arrangement has been traced. Compared to hcp anion sublattice, the Li3MX6 with ccp anion sublattice reveals faster Li+ migration. The tolerance of Li3Y1-xInxCl6 towards humidity is highly improved when the In3+ content is high enough due to the formation of hydrated intermediates. The correlations among composition, structure, Li+ migration, and humidity stability presented in this work provide insights for designing new halide-based SSEs.

Site-Occupation-Tuned Superionic LixScCl3+xHalide Solid Electrolytes for All-Solid-State Batteries.

The enabling of high energy density of all-solid-state lithium batteries (ASSLBs) requires the development of highly Li+-conductive solid-state electrolytes (SSEs) with good chemical and electrochemical stability. Recently, halide SSEs based on different material design principles have opened new opportunities for ASSLBs. Here, we discovered a series of LixScCl3+x SSEs (x = 2.5, 3, 3.5, and 4) based on the cubic close-packed anion sublattice with room-temperature ionic conductivities up to 3 × 10-3 S cm-1. Owing to the low eutectic temperature between LiCl and ScCl3, LixScCl3+x SSEs can be synthesized by a simple co-melting strategy. Preferred orientation is observed for all the samples. The influence of the value of x in LixScCl3+x on the structure and Li+ diffusivity were systematically explored. With increasing x value, higher Li+, lower vacancy concentration, and less blocking effects from Sc ions are achieved, enabling the ability to tune the Li+ migration. The electrochemical performance shows that Li3ScCl6 possesses a wide electrochemical window of 0.9-4.3 V vs Li+/Li, stable electrochemical plating/stripping of Li for over 2500 h, as well as good compatibility with LiCoO2. LiCoO2/Li3ScCl6/In ASSLB exhibits a reversible capacity of 104.5 mAh g-1 with good cycle life retention for 160 cycles. The observed changes in the ionic conductivity and tuning of the site occupations provide an additional approach toward the design of better SSEs.

Principle understanding towards synthesizing Fe/N decorated carbon catalysts with pyridinic-N enriched and agglomeration-free features for lithium-oxygen batteries.

Metal-N-decorated carbon catalysts are cheap and effective alternatives for replacing the high-priced Pt-based ones in activating the reduction of oxygen for metal-air or fuel cells. The preparation of such heterogeneous catalysts often requires complex synthesis processes, including harsh acid treatment, secondary pyrolysis processes, etching, etc., to make the heteroatoms evenly dispersed in the carbon substrates to obtain enhanced activities. Through combined experimental characterizations, we found that by precise control of the precursors added, a Fe/N uniformly distributed, agglomeration-free Fe/N decorated Super-P carbon material (FNDSP) can be easily obtained by a one-pot synthesis process with distinctly higher pyridinic-N content and elevated catalytic activity. An insight into this phenomenon was carefully demonstrated and also verified in Li-O2 batteries, which delivered a high discharging platform of 2.85 V and can be fully discharged with a capacity of 5811.5 mA h gcarbon+catalyst -1 at the cut-off voltage of 2.5 V by the low-cost Super-P modified catalyst.

Water-Mediated Synthesis of a Superionic Halide Solid Electrolyte.

To promote the development of solid-state batteries, polymer-, oxide-, and sulfide-based solid-state electrolytes (SSEs) have been extensively investigated. However, the disadvantages of these SSEs, such as high-temperature sintering of oxides, air instability of sulfides, and narrow electrochemical windows of polymers electrolytes, significantly hinder their practical application. Therefore, developing SSEs that have a high ionic conductivity (>10-3  S cm-1 ), good air stability, wide electrochemical window, excellent electrode interface stability, low-cost mass production is required. Herein we report a halide Li+ superionic conductor, Li3 InCl6 , that can be synthesized in water. Most importantly, the as-synthesized Li3 InCl6 shows a high ionic conductivity of 2.04×10-3  S cm-1 at 25 °C. Furthermore, the ionic conductivity can be recovered after dissolution in water. Combined with a LiNi0.8 Co0.1 Mn0.1 O2 cathode, the solid-state Li battery shows good cycling stability.