Coordination-Assisted Precise Construction of Metal Oxide Nanofilms for High-Performance Solid-State Batteries.

The application of solid-state batteries (SSBs) is challenged by the inherently poor interfacial contact between the solid-state electrolyte (SSE) and the electrodes, typically a metallic lithium anode. Building artificial intermediate nanofilms is effective in tackling this roadblock, but their implementation largely relies on vapor-based techniques such as atomic layer deposition, which are expensive, energy-intensive, and time-consuming due to the monolayer deposited per cycle. Herein, an easy and low-cost wet-chemistry fabrication process is used to engineer the anode/solid electrolyte interface in SSBs with nanoscale precision. This coordination-assisted deposition is initiated with polyacrylate acid as a functional polymer to control the surface reaction, which modulates the distribution and decomposition of metal precursors to reliably form a uniform crack-free and flexible nanofilm of a large variety of metal oxides. For demonstration, artificial Al2O3 interfacial nanofilms were deposited on a ceramic SSE, typically garnet-structured Li6.5La3Zr1.5Ta0.5O12 (LLZT), that led to a significant decrease in the Li/LLZT interfacial resistance (from 2079.5 to 8.4 Ω cm2) as well as extraordinarily long cycle life of the assembled SSBs. This strategy enables the use of a nickel-rich LiNi0.83Co0.07Mn0.1O2 cathode to deliver a reversible capacity of 201.5 mAh g-1 at a considerable loading of 4.8 mg cm-2, featuring performance metrics for an SSB that is competitive with those of traditional Li-ion systems. Our study demonstrates the potential of solution-based routes as an affordable and scalable manufacturing alternative to vapor-based deposition techniques that can accelerate the development of SSBs for practical applications.

Co4 N-Decorated 3D Wood-Derived Carbon Host Enables Enhanced Cathodic Electrocatalysis and Homogeneous Lithium Deposition for Lithium-Sulfur Full Cells.

The sluggish kinetics of sulfur conversion in the cathode and the nonuniform deposition of lithium metal at the anode result in severe capacity decay and poor cycle life for lithium-sulfur (Li-S) batteries. Resolving these deficiencies is the most direct route toward achieving practical cells of this chemistry. Herein, a vertically aligned wood-derived carbon plate decorated with Co4 N nanoparticles host (Co4 N/WCP) is proposed that can serve as a host for both the sulfur cathode and the metallic lithium anode. This Co4 N/WCP electrode host drastically enhances the reaction kinetics in the sulfur cathode and homogenizes the electric field at the anode for the uniform lithium plating. Density functional theory calculations confirm the experimental observations that Co4 N/WCP provides a lower energy barrier for the polysulfide redox reaction in the cathode and a low adsorption energy for lithium deposition at the anode. Employing the Co4 N/WCP host at both electrodes in a S@Co4 N/WCP||Li@Co4 N/WCP full cell delivers a specific capacity of 807.9 mAh g-1 after 500 cycles at a 1 C rate. Additional experiments are performed with high areal sulfur loading of 4 mg cm-2 to demonstrate the viability of this strategy for producing practical Li-S cells.

Li2 S6 -Integrated PEO-Based Polymer Electrolytes for All-Solid-State Lithium-Metal Batteries.

The integration of Li2 S6 within a poly(ethylene oxide) (PEO)-based polymer electrolyte is demonstrated to improve the polymer electrolyte's ionic conductivity because the strong interplay between O2- (PEO) and Li+ from Li2 S6 reduces the crystalline volume within the PEO. The Li/electrolyte interface is stabilized by the in situ formation of an ultra-thin Li2 S/Li2 S2 layer via the reaction between Li2 S6 and lithium metal, which increases the ionic transport at the interface and suppresses lithium dendrite growth. A symmetric Li/Li cell with the Li2 S6 -integrated composite electrolyte has excellent cyclability and a high critical current density of 0.9 mA cm-2 at 40 °C. Impressive electrochemical performance is demonstrated with all-solid-state Li/LiFePO4 and high-voltage Li/LiNi0.8 Mn0.1 Co0.1 O2 cells at 40 °C.

Ionic Liquid (IL) Laden Metal-Organic Framework (IL-MOF) Electrolyte for Quasi-Solid-State Sodium Batteries.

An ionic liquid (IL) laden metal-organic framework (MOF) sodium-ion electrolyte has been developed for ambient-temperature quasi-solid-state sodium batteries. The MOF skeleton is designed according to a UIO-66 (Universitetet i Oslo) structure. A sodium sulfonic (-SO3Na) group grafted to the UIO-based MOF ligand improves the Na+-ion conductivity. Upon lading with a sodium-based ionic liquid (Na-IL), sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) in 1-n-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Bmpyr-TFSI), the Na-IL laden sulfonated UIO-66 (UIOSNa) quasi-solid electrolyte exhibits a Na+-ion conductivity of 3.6 × 10-4 S cm-1 at ambient temperature. Quasi-solid-state sodium batteries with the Na-IL/UIOSNa electrolyte are demonstrated with a layered Na3Ni1.5TeO6 cathode and sodium-metal anode. The quasi-solid-state Na∥Na-IL/UIOSNa∥Na3Ni1.5TeO6 cells show remarkable cycling performance.

Interfacial Chemistry Enables Stable Cycling of All-Solid-State Li Metal Batteries at High Current Densities.

The application of flexible, robust, and low-cost solid polymer electrolytes in next-generation all-solid-state lithium metal batteries has been hindered by the low room-temperature ionic conductivity of these electrolytes and the small critical current density of the batteries. Both issues stem from the low mobility of Li+ ions in the polymer and the fast lithium dendrite growth at the Li metal/electrolyte interface. Herein, Mg(ClO4)2 is demonstrated to be an effective additive in the poly(ethylene oxide) (PEO)-based composite electrolyte to regulate Li+ ion transport and manipulate the Li metal/electrolyte interfacial performance. By combining experimental and computational studies, we show that Mg2+ ions are immobile in a PEO host due to coordination with ether oxygen and anions of lithium salts, which enhances the mobility of Li+ ions; more importantly, an in-situ formed Li+-conducting Li2MgCl4/LiF interfacial layer homogenizes the Li+ flux during plating and increases the critical current density up to a record 2 mA cm-2. Each of these factors contributes to the assembly of competitive all-solid-state Li/Li, LiFePO4/Li, and LiNi0.8Mn0.1Co0.1O2/Li cells, demonstrating the importance of surface chemistry and interfacial engineering in the design of all-solid-state Li metal batteries for high-current-density applications.

General Strategy for Synthesis of Ordered Pt3 M Intermetallics with Ultrasmall Particle Size.

Controllable synthesis of atomically ordered intermetallic nanoparticles (NPs) is crucial to obtain superior electrocatalytic performance for fuel cell reactions, but still remains arduous. Herein, we demonstrate a novel and general hydrogel-freeze drying strategy for the synthesis of reduced graphene oxide (rGO) supported Pt3 M (M=Mn, Cr, Fe, Co, etc.) intermetallic NPs (Pt3 M/rGO-HF) with ultrasmall particle size (about 3 nm) and dramatic monodispersity. The formation of hydrogel prevents the aggregation of graphene oxide and significantly promotes their excellent dispersion, while a freeze-drying can retain the hydrogel derived three-dimensionally (3D) porous structure and immobilize the metal precursors with defined atomic ratio on GO support during solvent sublimation, which is not afforded by traditional oven drying. The subsequent annealing process produces rGO supported ultrasmall ordered Pt3 M intermetallic NPs (≈3 nm) due to confinement effect of 3D porous structure. Such Pt3 M intermetallic NPs exhibit the smallest particle size among the reported ordered Pt-based intermetallic catalysts. A detailed study of the synthesis of ordered intermetallic Pt3 Mn/rGO catalyst is provided as an example of a generally applicable method. This study provides an economical and scalable route for the controlled synthesis of Pt-based intermetallic catalysts, which can pave a way for the commercialization of fuel cell technologies.

Fast Li+ Conduction Mechanism and Interfacial Chemistry of a NASICON/Polymer Composite Electrolyte.

The unclear Li+ local environment and Li+ conduction mechanism in solid polymer electrolytes, especially in a ceramic/polymer composite electrolyte, hinder the design and development of a new composite electrolyte. Moreover, both the low room-temperature Li+ conductivity and large interfacial resistance with a metallic lithium anode of a polymer membrane limit its application below a relatively high temperature. Here we have identified the Li+ distribution and Li+ transport mechanism in a composite polymer electrolyte by investigating a new solid poly(ethylene oxide) (PEO)-based NASICON-LiZr2(PO4)3 composite with 7Li relaxation time and 6Li → 7Li trace-exchange NMR measurements. The Li+ population of the two local environments in the composite electrolytes depends on the Li-salt concentration and the amount of ceramic filler. A composite electrolyte with a [EO]/[Li+] ratio n = 10 and 25 wt % LZP filler has a high Li+ conductivity of 1.2 × 10-4 S cm-1 at 30 °C and a low activation energy owing to the additional Li+ in the mobile A2 environment. Moreover, an in situ formed solid electrolyte interphase layer from the reaction between LiZr2(PO4)3 and a metallic lithium anode stabilized the Li/composite-electrolyte interface and reduced the interfacial resistance, which provided a symmetric Li/Li cell and all-solid-state Li/LiFePO4 and Li/LiNi0.8Co0.1Mn0.1O2 cells a good cycling performance at 40 °C.

Enhanced Surface Interactions Enable Fast Li+ Conduction in Oxide/Polymer Composite Electrolyte.

Li+ -conducting oxides are considered better ceramic fillers than Li+ -insulating oxides for improving Li+ conductivity in composite polymer electrolytes owing to their ability to conduct Li+ through the ceramic oxide as well as across the oxide/polymer interface. Here we use two Li+ -insulating oxides (fluorite Gd0.1 Ce0.9 O1.95 and perovskite La0.8 Sr0.2 Ga0.8 Mg0.2 O2.55 ) with a high concentration of oxygen vacancies to demonstrate two oxide/poly(ethylene oxide) (PEO)-based polymer composite electrolytes, each with a Li+ conductivity above 10-4  S cm-1 at 30 °C. Li solid-state NMR results show an increase in Li+ ions (>10 %) occupying the more mobile A2 environment in the composite electrolytes. This increase in A2-site occupancy originates from the strong interaction between the O2- of Li-salt anion and the surface oxygen vacancies of each oxide and contributes to the more facile Li+ transport. All-solid-state Li-metal cells with these composite electrolytes demonstrate a small interfacial resistance with good cycling performance at 35 °C.

A New Type of Electrolyte System To Suppress Polysulfide Dissolution for Lithium-Sulfur Battery.

Lithium-sulfur (Li-S) batteries have been explored extensively for high-capacity electric-power storage, but their practical application has been prevented by severe issues stemming from the use of a lithium anode and an organic-liquid electrolyte in which Li2Sx intermediates of the cell discharge reaction are soluble and shuttle to the anode. Both problems are addressed using bis(4-nitrophenyl) carbonate as an additive in the organic-liquid electrolyte. The soluble Li2Sx polysulfides react with the additive to create insoluble polysulfides with a lithium byproduct; this byproduct reacts with the Li-metal anode to create an anode passivation layer that is a good Li+ conductor, which allows for safe and rapid plating/stripping of lithium metal with a low impedance.