Sui Gu

Sulfonic Groups Originated Dual-Functional Interlayer for High Performance Lithium–Sulfur Battery

The lithium-sulfur battery is one of the most prospective chemistries in secondary energy storage field due to its high energy density and high theoretical capacity. However, the dissolution of polysulfides in liquid electrolytes causes the shuttle effect, and the rapid decay of lithium sulfur battery has greatly hindered its practical application. Herein, combination of sulfonated reduced graphene oxide (SRGO) interlayer on the separator is adopted to suppress the shuttle effect. We speculate that this SRGO layer plays two roles: physically blocking the migration of polysulfide as ion selective layer and anchoring lithium polysulfide by the electronegative sulfonic group. Lewis acid-base theory and density functional theory (DFT) calculations indicate that sulfonic groups have a strong tendency to interact with lithium ions in the lithium polysulfide. Hence, the synergic effect involved by the sulfonic group contributes to the enhancement of the battery performance. Furthermore, the uniformly distributed sulfonic groups working as active sites which could induce the uniform distribution of sulfur, alleviating the excessive growth of sulfur and enhancing the utilization of active sulfur. With this interlayer, the prototype battery exhibits a high reversible discharge capacity of more than 1300 mAh g-1 and good capacity retention of 802 mAh g-1 after 250 cycles at 0.5 C rate. After 60 cycles at different rates from 0.2 to 4 C, the cell with this functional separator still recovered a high specific capacity of 1100 mAh g-1 at 0.2 C. The results demonstrate a promising interlayer design toward high performance lithium-sulfur battery with longer cycling life, high specific capacity, and rate capability.

Suppressing the dissolution of polysulfides with cosolvent fluorinated diether towards high-performance lithium sulfur batteries.

The dissolution and shuttle of polysulfides in electrolytes cause severe anode corrosion, low coulombic efficiency, and a rapid fading of the capacity of lithium-sulfur batteries. Fluorinated diether (FDE) was selected as a cosolvent in traditional ether electrolytes to suppress the dissolution of polysulfides. The modified electrolytes lead to a negligible solubility of polysulfides, as well as decreased corrosion of the lithium anode. In an optimal system, the cells show improved cycling performance with an average coulombic efficiency of above 99% and a highly stable reversible discharge capacity of 701 mA h g-1 after 200 cycles at a 0.5C rate. A combination of electrochemical studies and X-ray photoelectron spectroscopy demonstrates the sulfur reduction mechanism with three voltage plateaus.

Carbon Disulfide Cosolvent Electrolytes for High-Performance Lithium Sulfur Batteries

Development of lithium sulfur (Li-S) batteries with high Coulombic efficiency and long cycle stability remains challenging due to the dissolution and shuttle of polysulfides in electrolyte. Here, a novel additive, carbon disulfide (CS2), to the organic electrolyte is reported to improve the cycling performance of Li-S batteries. The cells with the CS2-additive electrolyte exhibit high Coulombic efficiency and long cycle stability, showing average Coulombic efficiency >99% and a capacity retention of 88% over the entire 300 cycles. The function of the CS2 additive is 2-fold: (1) it inhibits the migration of long-chain polysulfides to the anode by forming complexes with polysulfides and (2) it passivates electrode surfaces by inducing the protective coatings on both the anode and the cathode.

Facile synthesis of the sandwich-structured germanium/reduced graphene oxide hybrid: an advanced anode material for high-performance lithium ion batteries

A sandwich-structured reduced graphene oxide/germanium/reduced graphene oxide hybrid (denoted as rGO/Ge/rGO) is successfully synthesized through a facile thermal reduction method for the first time. The rGO/Ge/rGO hybrid, with submicron Ge crystals (200–600 nm) uniformly encapsulated in a conductive rGO matrix, offers several favorable features: enough void space to accommodate the volume change, fast electrons and lithium ions transport, and superior structural stability. When acting as the anode in lithium ion batteries (LIBs), rGO/Ge/rGO exhibits significantly improved electrochemical performance compared to that of pure Ge, owing to the sufficient wrapping of Ge by rGO and strong chemical interaction between Ge and rGO. Enhanced reversible specific capacity of 1085 mA h g−1 after 500 cycles can be achieved at 1C rate (1C = 1600 mA g−1) with the capacity loss of ∼0.017% per cycle. Furthermore, the coin-type full cell composed of the rGO/Ge/rGO anode and the LiNi0.5Co0.2Mn0.3O2 cathode delivers a high specific capacity of 940 mA h g−1 with a capacity retention of 93.6% after 100 cycles at 1C rate. Such a sandwich-type rGO/Ge/rGO hybrid, which presents excellent cycle life and remarkably high capacity, is expected to be a promising anode material candidate for further application in next-generation high energy density LIBs and other electrochemical devices.

A hybrid electrolyte for long-life semi-solid-state lithium sulfur batteries

A novel hybrid electrolyte prepared using NASICON-type oxide ceramics and fluorinated electrolytes has been employed in semi-solid-state Li–S batteries. A high stability of over 1200 cycles and superior tolerance to low temperature were attained. Meanwhile, the hybrid electrolyte configurations have been demonstrated to be applicable to other oxide electrolytes, like garnet-type ceramics.

Method Using Water-Based Solvent to Prepare Li7La3Zr2O12 Solid Electrolytes

Li-garnet Li7La3Zr2O12 (LLZO) is a promising candidate of solid electrolytes for high-safety solid-state Li+ ion batteries. However, because of its high reactivity to water, the preparation of LLZO powders and ceramics is not easy for large-scale amounts. Herein, a method applying water-based solvent is proposed to demonstrate a possible solution. Ta-doped LLZO, that is, Li6.4La3Zr1.4Ta0.6O12 (LLZTO), and its LLZTO/MgO composite ceramics are made by attrition milling, followed by a spray-drying process using water-based slurries. The impacts of parameters of the method on the structure and properties of green and sintered pellets are studied. A relative density of ∼95%, a Li-ion conductivity of ∼3.5 × 10-4 S/cm, and uniform grain size LLZTO/MgO garnet composite ceramics are obtained with an attrition-milled LLZTO/MgO slurry that contains 40 wt % solids and 2 wt % polyvinyl alcohol binder. Li-sulfur batteries based on these ceramics are fabricated and work under 25 °C for 20 cycles with a Coulombic efficiency of 100%. This research demonstrates a promising mass production method for the preparation of Li-garnet ceramics.

Nanoporous Adsorption Effect on Alteration of the Li+ Diffusion Pathway by a Highly Ordered Porous Electrolyte Additive for High-Rate All-Solid-State Lithium Metal Batteries

Solid polymer electrolytes (SPEs) have shown extraordinary promise for all-solid-state lithium metal batteries with high energy density and flexibility but are mainly limited by low ionic conductivity and their poor stability with lithium metal anodes. In this work, we propose a highly ordered porous electrolyte additive derived from SSZ-13 for high-rate all-solid-state lithium metal batteries. The nanoporous adsorption effect provided by the highly ordered porous nanoparticles in the poly(ethylene oxide) (PEO) electrolyte is found to significantly improve the Li+ conductivity (1.91 × 10-3 S cm-1 at 60 °C, 4.43 × 10-5 S cm-1 at 20 °C) and widen the electrochemical stability window to 4.7 V vs Li+/Li. Meanwhile, the designed PEO-based electrolyte demonstrates enhanced stability with the lithium metal anode. Through systematically increasing Li+ diffusion, widening the electrochemical stability window, and enhancing the interfacial stability of the SSZ-composite electrolyte (CPE) electrolyte, the LiFePO4/SSZ-CPE/Li cell is optimized to deliver high rate capability and stable cycling performance, which demonstrates great potential for all-solid-state energy storage application.

High-Strength Internal Cross-Linking Bacterial Cellulose-Network-Based Gel Polymer Electrolyte for Dendrite-Suppressing and High-Rate Lithium Batteries

Lithium is a promising anode material for high energy density batteries. However, the growth of lithium dendrite causes serious safety issues, which inhibits the application of lithium anode. Herein, a novel gel polymer electrolyte based on high-strength internal cross-linking bacterial cellulose network was prepared via an environmentally friendly and simple fast freeze-drying method. The as-obtained gel polymer electrolyte demonstrates an excellent lithium ion conductivity of 4.04 × 10-3 S cm-1 with an exceptional lithium ion transference number of 0.514 at 25 °C. The lithium metal battery with this gel polymer electrolyte shows an initial reversible capacity of 141.2 mA h g-1 with a capacity retention of 104.2% (compared with the initial reversible capacity) after 150 cycles at 0.5 C. An average reversible capacity of 75.2 mA h g-1 is maintained at high rate of 9 C. Moreover, this gel polymer electrolyte possesses superior mechanical strength of 49.9 MPa with a maximum strain of 56.33%. Therefore, the vertical growth of lithium dendrite is effectively suppressed. This research indicates the potential of applying low cost bacterial cellulose into high performance energy storage devices.