Room-Temperature Solid-State Polymer Electrolyte in Li-LiFePO4 , Li-S and Li-O2 Batteries.

A solid polymer electrolyte has been developed and employed in lithium-metal batteries of relevant interest. The material includes crystalline poly(ethylene glycol)dimethyl ether (PEGDME), LiTFSI and LiNO3 salts, and a SiO2 ceramic filler. The electrolyte shows ionic conductivity more than 10-4  S cm-1 at room temperature and approaching 10-3  S cm-1 at 60 °C, a Li+ -transference number exceeding 0.3, electrochemical stability from 0 to 4.4 V vs. Li+ /Li, lithium stripping/deposition overvoltage below 0.08 V, and electrode/electrolyte interphase resistance of 400 Ω. Thermogravimetry indicates that the electrolyte stands up to 200 °C without significant weight loss, while FTIR spectroscopy suggests that the LiTFSI conducting salt dissolves in the polymer. The electrolyte is used in solid-state cells with various cathodes, including LiFePO4 olivine exploiting the Li-insertion, sulfur-carbon composite operating through Li conversion, and an oxygen electrode in which reduction and evolution reactions (i. e., ORR/OER) evolve on a carbon-coated gas diffusion layer (GDL). The cells operate reversibly at room temperature with a capacity of 140 mA h g-1 at 3.4 V for LiFePO4 , 400 mA h g-1 at 2 V for sulfur electrode, and 500 mA h g-1 at 2.5 V for oxygen. The results suggest that the electrolyte could be applied in room-temperature solid polymer cells.

Structural and Interfacial Characterization of a Sustainable Si/Hard Carbon Composite Anode for Lithium-Ion Batteries.

The effects of a biomass-derived hard carbon matrix and a sustainable cross-linked binder are investigated as electrode components for a silicon-based anode in lithium-ion half-cells, in order to reduce the capacity fade due to volume expansion and shrinkage upon cycling. Ex situ Raman spectroscopy and impedance spectroscopy are used to deeply investigate the structural and interfacial properties of the material within a single cycle and upon cycling. An effective buffering of the volume changes of the composite electrode is evidenced, even at a high Si content up to 30% in the formulation, resulting in the retention of structural and interfacial integrity. As a result, a high capacity performance and a very good rate capability are displayed even at high current densities, with a stable cycling behavior and low polarization effects.

Lithium-Metal Batteries Using Sustainable Electrolyte Media and Various Cathode Chemistries.

Lithium-metal batteries employing concentrated glyme-based electrolytes and two different cathode chemistries are herein evaluated in view of a safe use of the highly energetic alkali-metal anode. Indeed, diethylene-glycol dimethyl-ether (DEGDME) and triethylene-glycol dimethyl-ether (TREGDME) dissolving lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrate (LiNO3) in concentration approaching the solvents saturation limit are used in lithium batteries employing either a conversion sulfur-tin composite (S:Sn 80:20 w/w) or a Li+ (de)insertion LiFePO4 cathode. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) clearly show the suitability of the concentrated electrolytes in terms of process reversibility and low interphase resistance, particularly upon a favorable activation. Galvanostatic measurements performed on lithium-sulfur (Li/S) batteries reveal promising capacities at room temperature (25 °C) and a value as high as 1300 mAh gS -1 for the cell exploiting the DEGDME-based electrolyte at 35 °C. On the other hand, the lithium-LiFePO4 (Li/LFP) cells exhibit satisfactory cycling behavior, in particular when employing an additional reduction step at low voltage cutoff (i.e., 1.2 V) during the first discharge to consolidate the solid electrolyte interphase (SEI). This procedure allows a Coulombic efficiency near 100%, a capacity approaching 160 mAh g-1, and relevant retention particularly for the cell using the TREGDME-based electrolyte. Therefore, this work suggests the use of concentrated glyme-based electrolytes, the fine-tuning of the operative conditions, and the careful selection of active materials chemistry as significant steps to achieve practical and safe lithium-metal batteries.