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Abstract Magnesium silicide (Mg2Si) is a new anode material candidate for Mg‐ion batteries due to the Earth‐abundance of Mg and Si and its high theoretical specific capacity of 1398 mAh/g. However, to date, no one reported its reversible Mg‐storage ability. Herein, we demonstrate for the first time the experimental visualization of a reversible electrochemical demagnesiation and magnasiation of Mg2Si film model electrode in a half‐cell with the electrolyte of PhMgCl/THF at room temperature. The Mg2+‐diffusivity, 1.3 × 10–18 cm2/s, of Mg2Si film model electrode determined with cyclic voltammetry is four orders of magnitude lower than that of Li+‐diffusivity of Mg2Si film electrode in a lithium cell, indicating a sluggish diffusion kinetics. Surface chemistry studies of the 1st discharged (demagnesiated) and the 1st cycled (re‐magnesiated) electrodes utilizing X‐ray photoelectron spectroscopy reveal that the surface of pristine Mg2Si is highly covered by various silicon oxides, and Mg2Si undergoes segregation and phase separation partly to Mg and Si along with the surface coverage of electrolyte decomposition products. Those events lower the homogeneity and connectivity of electrode composition, which limits the reaction reversibility. The data give insight into a new material design for Mg‐ion batteries.

Lithium-ion batteries (LIBs) are ubiquitous power sources and demand for higher energy and higher performance LIBs than state-of-the-art ones continues to increase for longer range use of electric mobility and energy-storage systems. Performance of conventional LIBs is often limited or failed in tough working environments, particularly, subzero-temperatures because of reduced ionic conductivity of electrolyte and diffusion kinetics of both anode and cathode, causing lithium metal plating and dendrite growth and finally safety issue and death of LIBs. Herein, for the first time we report a lithium metal plating-free and unprecedented high-performance graphite∥LiNi0.8Co0.1Mn0.1O2 (NCM811) full-cell under subzero-temperature of -10 °C and high-voltage of 4.45 V through the construction of robust solid electrolyte interphase (SEI) layers at both anode and cathode and their structural stabilization in 1 M LiPF6 and nonflammable electrolyte. Subzero-temperature operation of commercial electrolytebased full-cell however results in a drastic performance failure in early cycles and shows distinguishing marks such as lithium metal plating at graphite anode and irreversible phase transformation of NCM811 to disordered H3 phase with a large volume contraction. The strong correlation between anode-electrolyte and cathode-electrolyte interfacial stabilization, bulk structural stabilization of both anode and cathode, and highly reversible cycling performance under subzero-temperature is clearly demonstrated. [ABSTRACT FROM AUTHOR]

Artificial graphite anode materials are promising for high-performance Li-ion batteries for electric vehicles. Battery cycle-life and performance are known to rely on the formation and stability of solid electrolyte interphase (SEI) layer, particularly, of the anode. Herein, we report the investigation of material characteristics-dependent SEI formation behavior and stability of model artificial graphite anodes in conventional electrolyte with vinylene carbonate additive, and their correlation to performance. Surface analysis results reveal that artificial graphite composite of Cokes and binder pitch in a relatively smaller particle size at 100% graphitization degree and with higher surface area of edges provides promoted interfacial reactivity and formation of more stable, thinner and softer SEI layer that includes plenty of organic compounds, leading to high structural robustness and improved cycling performance. By contrast, aggregated larger particles and/or lower graphitization degree results in inferior performance. A full-cell with the optimized artificial graphite anode and LiCoO2 cathode delivers initial discharge capacity of 161 mAhg-1 at 0.2C, respectively, and initial coulombic efficiency of 89%, and capacity retention of 91% at the 100th cycle. The data give an insight into the principles of material design, the SEI layer stabilization and performance enhancement of artificial graphite anode for high-energy Li-ion batteries. [ABSTRACT FROM AUTHOR]

Designing and controlling the anode-electrolyte interfacial chemistry of a micron Sn-Ni/graphite composite battery anode led to the formation of a stable solid electrolyte interphase (SEI) layer. We utilized fluoroethylene carbonate (FEC)-based electrolyte that is more interfacially compatible than an EC-based electrolyte, trimethyl phosphite electrolyte additive that reduces the attack of LiPF6-derived acidic species in the electrolyte, and the addition of a low fraction of SnF2 to anode for capturing the F anions of HF present in the electrolyte. Mechanistic surface chemistry studies using ATR FTIR and X-ray photoelectron spectroscopy revealed that the SnF2 transforms to SnF4 by capturing F anions, while FEC and phosphite provide a surface protective and robust SEI. The interfacially controlled composite anode with a tuned content of graphite exhibits good cycling stability (90% retention at the 50th cycle) with high discharge capacity of ~800 mAhg-1 of tin, in contrast to a rapid capacity fade in the conventional electrolyte. [ABSTRACT FROM AUTHOR]

Film model electrodes of silicon oxide (SiOx) with various oxygen content (x = 0.4, 0.85, 1.0 and 1.3) have been studied for the effects of oxygen content and interfacial reaction behavior on cycling ability. IR and XPS analyses on the origin of initial charge plateau in 1M LiPF6/EC:DEC indicate that the contribution of electrolyte reduction to the plateau is far larger than the formation of lithium silicates, lithium oxide and silicon. Higher oxygen content of SiOx induces to decrease initial electrolyte reduction, whereas larger fraction of oxides is subjected to dissolution by acid (e.g., HF)-etching. Cycling ability at higher oxygen content however is remarkably improved when constructing a surface protective siloxane network at the electrodes using silane electrolyte additive. The SiO1.0 electrode exhibits superior capacity retention of 84% at the 200th cycle delivering discharge capacity of 1206-1017 mAh/g. The SEI layer formed over surface siloxane network consists of a plenty of organic compounds and lithium carbonate, in contrast to mainly inorganic salts and organic phosphorus fluoride compounds upon cycling without silane adidtive. A better protection and passivation of electrode surface should be of the effects of siloxane network, and in that fashion cycling ability is greatly stabilized. [ABSTRACT FROM AUTHOR]

The Mn4+-abundant surface of the Li- and Al-substituted spinel cathode materials is found to provide electrochemical and interfacial stabilities in the voltage region of 3.3-4.3 V vs. Li/Li+ in the room temperature electrolyte of 1M LiPF6/EC:DEC. Surface characterization using ex situ X-ray photoelectron spectroscopy reveals that surface Mn4+-abundance induces the formation of aplenty of new surface components and the passivation of cathode surface before being reduced to Mn3+ to Mn2+, leading to capacity retention 90% with discharge capacities 102-90 mAh/g over 50 cycles. FTIR spectroscopic analysis results and scanning electron microscopic imaging ensure that the Mn4+-abundant surface is better passivated by solid electrolyte interphase (SEI) layer that is composed of mixed organic and inorganic compounds, resulting in somewhat preserved particle morphology. On the contrary, the cathodes with equal amounted surface Mn4+/Mn3+ and Mn3+-abundant surface are readily subjected to severe interfacial reaction and particle morphology change accompanied by inferior surface coverage by surface species, which are responsible for a rapid capacity fade. The data contribute to a basic understanding of importance of surface control and its impact on the cycling performance of spinel-based cathode materials for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

Well crystallized, shape-formed, and electrochemically active lithium cobalt oxide (LiCoO[sub 2]) films are electroplated directly on an electron-conducting substrate in an aqueous solution using a soft solution processing that is economical, consumes less energy consuming, and is environmentally friendly. Although LiCoO[sub 2] films are easily and economically prepared without any post-synthesis heat treatment, the estimated film properties show a possibility of using the deposited films as a cathode film for lithium rechargeable microbatteries. In addition, the soft solution processing reveals that an exact understanding of chemical reactions and the proper combination of the chemical reactions can create an advanced synthetic procedure. [ABSTRACT FROM AUTHOR]

The article discusses a study on the crystal structure of the inorganic compound strontium magnesium phosphate Sr2+xMg3-xP4O15 (x ~ 0.36), refined from the findings of a laboratory powder X-ray diffraction. The research noted that the findings of synthesis, which revealed that magnesium phosphates were impurity phases, matched with a nonstoichiometry model that has greater strontium and fewer magnesium ions. Also explained is the procedure of synthesizing such compound.