Yangxing Li

Inhibition of Lithium Dendrites by Fumed Silica-Based Composite Electrolytes

Lithium dendrite formation is investigated via in situ microscopy in a liquid electrolyte containing polyethylene glycol dimethyl ether 1 lithium bis~trifluoromethylsulfonyl !imide and composite gel-like electrolytes formed by dispersing nanometer-size fumed silica into the liquid. Fumed silicas with either hydrophilic silanol surface groups or hydrophobic octyl surface groups were employed. Dendrites with current density-dependent morphology are formed in liquid electrolyte but addition of fumed silica inhibits their formation, with hydrophilic fumed silica having a more pronounced effect than hydrophobic silica. The dendrite inhibition effect of fumed silica is attributed to its abilities to form a continuous network with elastic-like properties and scavenge impurities from the electrolyte.

Lithium/V6O13 cells using silica nanoparticle-based composite electrolyte

The electrochemical behavior of Li/V6O13 cells is investigated at room temperature (22 8C) both in liquid electrolyte consisting of oligomeric poly(ethyleneglycol)dimethylether� /lithium bis(trifluoromethylsulfonylimide) and composite electrolytes formed by blending the liquid electrolyte with silica nanoparticles (fumed silica). The addition of fumed silica yields a gel-like electrolyte that demonstrates the desirable property of suppressing lithium dendrite growth due to the rigidity and immobility of the electrolyte structure. The lithium/electrolyte interfacial resistance for composite gel electrolytes is less than that for the corresponding baseliquid electrolyte, and the charge � /discharge cycle performance and electrochemical efficiency for the Li/V6O13 cell is significantly improved. The effect of fumed silica surface group on the electrochemical performance is discussed; the native hydrophilic silanol surface group appears better than fumed silica that is modified with a hydrophobic octyl surface moiety. # 2002 Elsevier Science Ltd. All rights reserved.

Attenuation of Aluminum Current Collector Corrosion in LiTFSI Electrolytes Using Fumed Silica Nanoparticles

Linear sweep voltammetry and electrochemical impedance spectroscopy were used to investigate the corrosion behavior of an aluminum current collector in contact with polymer solvent containing lithium bis(trifluoromethanesulfonyl)imide [LiN(CF 3 SO 2 ) 2 , LiTFSI] at room temperature. The electrolytes were liquid poly(ethylene glycol) dimethyl ether (Mw 250) + LiTFSI (Li:O ratio of 1:20), and composite gel electrolytes consisting of the baseline liquid electrolyte + 10 wt% fumed silica nanoparticles. Such electrolytes have potential utility in lithium-based rechargeable cells, although LiTFSI is known to affect corrosion of the commonly employed aluminum current collector. The electrochemical data indicate that aluminum corrosion is attenuated in the Presence of fumed silica nanoparticles. Possible mechanisms are discussed.

Nanocomposite Gel Electrolytes Based on Fumed Silica for Lithium-Ion Batteries

Nanocomposite gel electrolytes based on silica particles dispersed in lithium bis(perfluoroethylsulfonyl)imide (LiBETI) salt + mixed-carbonate solvent are examined as an electrolyte system for a lithium-ion battery. Gel behavior is observed with both hydrophilic (A200) and hydrophobic (R805) fumed silicas. The silica nanoparticles affect a small decrease in conductivity but increase mechanical strength significantly (elastic modulus ∼10 5 Pa). Chronoamperometry and linear sweep voltammetry results show that an Al current collector is stable in 1 M LiBETI carbonates up to ∼5 V. Cycling Li(Ni)/electrolyte/Li cells shows that silica nanoparticles improve the coulombic efficiency and interfacial stability in the order: 10% R805 LiBETI gel > LiBETI liquid > LiPF 6 liquid. Cycling Li/LiFePO 4 cells shows that both liquid and 10% R805 gel electrolytes provide good capacity and cycle performance, but the average charge/discharge voltages for the latter are more stable. Both Li/LiMn 2 O 4 and Li/graphite cells have less capacity fade using LiBETI than LiPF 6 electrolyte. The gel electrolyte provides better cycle performance than its liquid counterpart because of its increased interfacial stability due to improved rheology and ability to scavenge residual moisture. Silica-based LiBETI carbonate nanocomposite gel electrolytes appear to be a promising candidate for lithium-ion batteries.

Rate Capabilities of Composite Gel Electrolytes Containing Fumed Silica Nanoparticles

Rate capabilities are reported of Li/V 6 O 13 cells at room temperature (22°C) using composite gel electrolytes. The performance of cells containing base liquid electrolyte are compared with composite gel electrolytes that are formed by adding fumed silica nanoparticles to a solution of poly(ethylene glycol)dimethylether + lithium bis(trifluoromethylsulfonylimide). The discharge-charge rate capabilities are improved with addition of fumed silica. The average Coulombic efficiencies using gel electrolytes containing 10% A200, which have a native silanol surface, and 10% R805, which have an octyl-modified surface, remain at approximately 99% up to a C/2 rate, while the average Coulombic efficiency for the base liquid electrolyte decreases with increasing C rate. The improved rate capabilities for composite gel electrolytes are suggested to be related to their ability to inhibit lithium dendrite formation and form stable interfaces between electrolyte and electrodes.