Isophorone Diisocyanate: An Effective Additive to Form Cathode-Protective-Interlayer and Its Influence on LiNi_0.5Co_0.2Mn_0.3O₂ at High Potential

In this work, we propose a novel electrolyte additive, isophorone diisocyanate (IPDI), to construct the surface protective interlayer. This membrane is produced via nucleophilic addition between the IPDI’s diisocyanate groups and the free-radical-onium ion oxidative intermediate of propylene carbonate (PC). In the electrolyte with IPDI added between 10–20 mM, LiNi_0.5Co_0.2Mn_0.3O₂ presents the excellent performance, demonstrating the relative wide operational window to form the optimal protective membrane. This protective membrane ameliorates the cyclic stability. Although all systems deliver ∼185 mAh g^–1 under 1 C between 2.5–4.6 V (vs Li⁺/Li), the cells in the suitable electrolyte maintain 90.4% in the 50 cycles and 83.2% in the 200 cycles, whereas the control cells are seriously dropped to 73.4% and 69.8%. The cells in the electrolyte with the appropriate IPDI also present the good rate capability, attaining ∼143 mAh g^–1 under 5 C, much higher than the cells in the control electrolyte­(92.4 mAh g^–1). The additive proposed in this work is helpful to augment the energy density of lithium ion battery and prolong the one-drive distance of electric vehicles

Controlled Synthesis of Mesoporous Carbon Nanostructures via a “Silica-Assisted” Strategy

We have established a facile and generalizable “silica-assisted” synthesis for diverse carbon spheresa category that covers mesoporous carbon nanospheres, hollow mesoporous carbon nanospheres, and yolk-shell mesoporous carbon nanospheresby using phenolic resols as a polymer precursor, silicate oligomers as an inorganic precursor, and hexadecyl trimethylammoniumchloride as a template. The particle sizes of the carbon nanospheres are uniform and easily controlled in a wide range of 180–850 nm by simply varying the ethanol concentrations. All three types of mesoporous carbon nanospheres have high surface areas and large pore volumes and exhibit promising properties for supercapacitors with high capacitance and favorable capacitance retention

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

Synthesis and Lithium Storage Mechanism of Ultrafine MoO₂ Nanorods

Ultrafine MoO₂ nanorods with a diameter of ∼5 nm were successfully synthesized by a nanocasting method using mesoporous silica SBA-15 as hard template. This material demonstrates high reversible capacity, excellent cycling performance, and good rate capacity as an anode electrode material for Li ion batteries. The significant enhancement in the electrochemical Li storage performance in ultrafine MoO₂ nanorods is attributed to the nanorod structure with small diameter and efficient one-dimensional electron transport pathways. Moreover, density functional theory calculations were performed to elucidate the Li uptake/removal mechanism in the MoO₂ electrodes, which can help us understand the unique cycling behavior of MoO₂ material

Removal of Interstitial H₂O in Hexacyanometallates for a Superior Cathode of a Sodium-Ion Battery

Sodium is globally available, which makes a sodium-ion rechargeable battery preferable to a lithium-ion battery for large-scale storage of electrical energy, provided a host cathode for Na can be found that provides the necessary capacity, voltage, and cycle life at the prescribed charge/discharge rate. Low-cost hexacyanometallates are promising cathodes because of their ease of synthesis and rigid open framework that enables fast Na⁺ insertion and extraction. Here we report an intriguing effect of interstitial H₂O on the structure and electrochemical properties of sodium manganese­(II) hexacyanoferrates­(II) with the nominal composition Na₂MnFe­(CN)₆·<i>z</i>H₂O (Na_2−δMnHFC). The newly discovered dehydrated Na_2−δMnHFC phase exhibits superior electrochemical performance compared to other reported Na-ion cathode materials; it delivers at 3.5 V a reversible capacity of 150 mAh g^–1 in a sodium half cell and 140 mAh g^–1 in a full cell with a hard-carbon anode. At a charge/discharge rate of 20 C, the half-cell capacity is 120 mAh g^–1, and at 0.7 C, the cell exhibits 75% capacity retention after 500 cycles

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