Operando Analysis of Gas Evolution in TiNb2O7 (TNO)-Based Anodes for Advanced High-Energy Lithium-Ion Batteries under Fast Charging.

TiNb2O7 (TNO) is regarded as one of the promising next-generation anode materials for lithium-ion batteries (LIBs) due to its high rate capabilities, higher theoretical capacity, and higher lithiation voltage. This enables the cycling of TNO-based anodes under extreme fast charging (XFC) conditions with a minimal risk of lithium plating compared to that of graphite anodes. Here, the gas evolution in real time with TNO-based pouch cells is first reported via operando mass spectrometry. The main gases are identified to be CO2, C2H4, and O2. A solid-electrolyte interphase is detected on TNO, which continues evolving, forming, and dissolving with the lithiation and delithiation of TNO. The gas evolution can be significantly reduced when a protective coating is applied on the TNO particles, reducing the CO2 and C2H4 evolution by ∼2 and 5 times, respectively, at 0.1C in a half-cell configuration. The reduction on gas generation in full cells is even more pronounced. The surface coating also enables 20% improvement in capacity under XFC conditions.

Probing the Li4 Ti5 O12 Interface Upon Lithium Uptake by Operando Small Angle Neutron Scattering.

The formation of a solid-electrolyte interphase (SEI) on the surface of Li4 Ti5 O12 (LTO) has become a highly controversial topic, with arguments for it and against it. However, prior studies supporting the formation of an SEI layer have typically suggested that a layer forms upon cycling of a cell, although the layer is probed after disassembling. In this study, cubic mesostructured LTO is synthesized with crystallite domain sizes between 3 and 4 nm and uniform pores with diameters ≤8 nm. The mean pore size is controlled between 4-8 nm through the use of a triblock amphipathic copolymer with a tunable hydrophobic block as template and by thermal treatment. The LTO morphology obtained is spherical and evolves upon heat treatment. These materials show excellent electrochemical performance, including high rate capability and capacity retention. The LTO material is subjected to operando small-angle neutron scattering and X-ray photoelectron spectroscopy experiments, which reveal that the highly debated SEI forms at potentials as high as 2.2 V, first as a LiF-rich layer and subsequently by the growth of a carbonaceous layer. These SEI products form first on the smaller pores before forming on the mesopores.

Evaluation of Gas Formation and Consumption Driven by Crossover Effect in High-Voltage Lithium-Ion Batteries with Ni-Rich NMC Cathodes.

Gas formation during lithium-ion battery (LIB) cycling impacts the stability and safety of these batteries, especially for those containing Ni-rich NMC cathodes. In this paper, the cycling performance and gassing behavior of NMC811/graphite full cells with 4.2 and 4.4 V upper cutoff voltages were first compared. Cells with a 4.2 V upper cutoff voltage had good cycling stability, exhibiting a capacity retention of 96.8% after 100 cycles and generated little gas. On the other hand, cells with a 4.4 V upper cutoff voltage lost over 25% of initial capacity after 100 cycles and generated large amounts of gas in the first 10 cycles. Electrochemical cycling of anode and cathode symmetric cells was implemented to isolate gases formed at the electrode. Gas chromatography-mass spectrometry, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning transmission electron microscopy were used to characterize the gas formation and associated material surfaces and structural properties. It was found that CO2 and fluorinated alkanes were the dominant gases evolved on the cathode side during cycling to 4.4 V. Gas crossover to the anode led to the depletion of gaseous products, which stabilized the cell performance to some extent. However, the growing surface reconstruction layer at the cathode, the thickening of the solid electrolyte interphase layer at the anode, and the gradual depletion of lithium inventory collectively contributed to the continuous capacity loss of full cells cycled to 4.4 V.

Colloidal Synthesis of Silicon-Carbon Composite Material for Lithium-Ion Batteries.

We report colloidal routes to synthesize silicon@carbon composites for the first time. Surface-functionalized Si nanoparticles (SiNPs) dissolved in styrene and hexadecane are used as the dispersed phase in oil-in-water emulsions, from which yolk-shell and dual-shell hollow SiNPs@C composites are produced via polymerization and subsequent carbonization. As anode materials for Li-ion batteries, the SiNPs@C composites demonstrate excellent cycling stability and rate performance, which is ascribed to the uniform distribution of SiNPs within the carbon hosts. The Li-ion anodes composed of 46 wt % of dual-shell SiNPs@C, 46 wt % of graphite, 5 wt % of acetylene black, and 3 wt % of carboxymethyl cellulose with an areal loading higher than 3 mg cm-2 achieve an overall specific capacity higher than 600 mAh g-1 , which is an improvement of more than 100 % compared to the pure graphite anode. These new colloidal routes present a promising general method to produce viable Si-C composites for Li-ion batteries.

Titanium Sulfides as Intercalation-Type Cathode Materials for Rechargeable Aluminum Batteries.

We report the electrochemical intercalation-extraction of aluminum (Al) in the layered TiS2 and spinel-based cubic Cu0.31Ti2S4 as the potential cathode materials for rechargeable Al-ion batteries. The electrochemical characterizations demonstrate the feasibility of reversible Al intercalation in both titanium sulfides with layered TiS2 showing better properties. The crystallographic study sheds light on the possible Al intercalation sites in the titanium sulfides, while the results from galvanostatic intermittent titration indicate that the low Al3+ diffusion coefficients in the sulfide crystal structures are the primary obstacle to facile Al intercalation-extraction.

Below the 12-vertex: 10-vertex carborane anions as non-corrosive, halide free, electrolytes for rechargeable Mg batteries.

The development of practical Mg based batteries is limited by the lack of a library of suitable electrolytes. Recently a 12-vertex closo-carborane anion based electrolyte has been shown to be the first electrolyte for Mg based batteries, which is both non-corrosive and has high electrochemical stability (+3.5 V vs. Mg0/2+). Herein we show that smaller 10-vertex closo-carborane anions also enable electrolytes for Mg batteries. Reduction of the trimethylammonium cation of [HNMe31+][HCB9H91-] with elemental Mg yields the novel magnesium electrolyte [Mg2+][HCB9H91-]2. The electrolyte displays excellent electrochemical stability, is non-nucleophilic, reversibly deposits and strips Mg, and is halide free. This discovery paves the way for the development of libraries of Mg electrolytes based on more cost effective 10-vertex closo-carborane anions.