Electrochemical Windows of Sulfone-Based Electrolytes for High-Voltage Li-Ion Batteries

Further development of high-voltage lithium-ion batteries requires electrolytes with electrochemical windows greater than 5 V. Sulfone-based electrolytes are promising for such a purpose. Here we compute the electrochemical windows for experimentally tested sulfone electrolytes by different levels of theory in combination with various solvation models. The MP2 method combined with the polarizable continuum model is shown to be the most accurate method to predict oxidation potentials of sulfone-based electrolytes with mean deviation less than 0.29 V. Mulliken charge analysis shows that the oxidation happens on the sulfone group for ethylmethyl sulfone and tetramethylene sulfone, and on the ether group for ether functionalized sulfones. Large electrochemical windows of sulfone-based electrolytes are mainly contributed by the sulfone group in the molecules which helps lower the HOMO level. This study can help understand the voltage limits imposed by the sulfone-based electrolytes and aid in designing new electrolytes with greater electrochemical windows

In Situ Observation of Solid Electrolyte Interphase Formation in Ordered Mesoporous Hard Carbon by Small-Angle Neutron Scattering

The aim of this work was to better understand the electrochemical processes occurring during the cycling of a lithium half-cell based on ordered mesoporous hard carbon with time-resolved in situ small-angle neutron scattering (SANS). Utilizing electrolytes containing mixtures of deuterated (²H) and nondeuterated (¹H) carbonates, we have addressed the challenging task of monitoring the formation and evolution of the solid–electrolyte interphase (SEI) layer. An evolution occurs in the SEI layer during discharge from a composition dominated by a higher scattering length density (SLD) lithium salt to a lower SLD lithium salt for the ethylene carbonate/dimethyl carbonate (EC/DMC) mixture employed. By comparing half-cells containing different solvent deuteration levels, we show that it is possible to observe both SEI formation and lithium intercalation occurring concurrently at the low voltage region in which lithium intercalates into the hard carbon. These results demonstrate that SANS can be employed to better understand complicated electrochemical processes occurring in rechargeable batteries, in a manner that simultaneously provides information on the composition and microstructure of the electrode

Observing Framework Expansion of Ordered Mesoporous Hard Carbon Anodes with Ionic Liquid Electrolytes via in Situ Small-Angle Neutron Scattering

The reversible capacity of materials for energy storage, such as battery electrodes, is deeply connected with their microstructure. Here, we address the fundamental mechanism by which hard mesoporous carbons, which exhibit high capacities versus Li, achieve stable cycling during the initial “break-in” cycles with ionic liquid electrolytes. Using in situ small-angle neutron scattering we show that hard carbon anodes that exhibit reversible Li⁺ cycling typically expand in volume up to 15% during the first discharge cycle, with only relatively minor expansion and contraction in subsequent cycles after a suitable solid electrolyte interphase (SEI) has formed. While a largely irreversible framework expansion is observed in the first cycle for the 1-methyl-1-propypyrrolidinium bis­(trifluoromethanesulfonyl)­imide (MPPY.TFSI) electrolyte, reversible expansion is observed in the electrolyte lithium bis­(trifluoro-methanesulfonyl)­imide (LiTFSI)/1-ethyl-3-methyl-imidazolium bis­(trifluoromethanesulf-onyl)­imide (EMIM.TFSI) related to EMIM⁺ intercalation and deintercalation before a stable SEI is formed. We find that irreversible framework expansion in conjunction with SEI formation is essential for the stable cycling of hard carbon electrodes

Insights into the Chemistry of the Cathodic Electrolyte Interphase for PTFE-Based Dry-Processed Cathodes

Dry processing is a promising method for high-performance and low-cost lithium-ion battery manufacturing which uses polytetrafluoroethylene (PTFE) as a binder. However, the electrochemical stability of the PTFE binder in the cathodes and the generated chemistry of the cathode electrolyte interphase (CEI) layers are rarely reported. Herein, the CEI properties and PTFE electrochemical stability are studied via cycling the high-loading dry-processed electrodes in electrolytes with LiPF6 or LiClO4 salt. Using LiClO4 salt can eliminate other possible F sources, allowing the decomposition of PTFE to be studied. The detection of LiF in cells with the LiClO4 salt confirms that PTFE undergoes side reaction(s) in the cathodes. When compared with LiClO4, the CEI layer is much thicker when LiPF6 is used as the electrolyte salt. These results provide insights into the CEI layer and may potentially enlighten the development of binders and electrolytes for the high efficiency and long durability of DP-based LIBs

Superior Conductive Solid-like Electrolytes: Nanoconfining Liquids within the Hollow Structures

The growth and proliferation of lithium (Li) dendrites during cell recharge are currently unavoidable, which seriously hinders the development and application of rechargeable Li metal batteries. Solid electrolytes with robust mechanical modulus are regarded as a promising approach to overcome the dendrite problems. However, their room-temperature ionic conductivities are usually too low to reach the level required for normal battery operation. Here, a class of novel solid electrolytes with liquid-like room-temperature ionic conductivities (>1 mS cm^–1) has been successfully synthesized by taking advantage of the unique nanoarchitectures of hollow silica (HS) spheres to confine liquid electrolytes in hollow space to afford high conductivities (2.5 mS cm^–1). In a symmetric lithium/lithium cell, the solid-like electrolytes demonstrate a robust performance against the Li dendrite problem, preventing the cell from short circuiting at current densities ranging from 0.16 to 0.32 mA cm^–2 over an extended period of time. Moreover, the high flexibility and compatibility of HS nanoarchitectures, in principle, enables broad tunability to choose desired liquids for the fabrication of other kinds of solid-like electrolytes, such as those containing Na⁺, Mg²⁺, or Al³⁺ as conductive media, providing a useful alternative strategy for the development of next generation rechargeable batteries