Vinyl Ethylene Carbonate as an Effective SEI-Forming Additive in Carbonate-Based Electrolyte for Lithium-Metal Anodes.

We report the use of vinyl ethylene carbonate as a new solid electrolyte interface (SEI)-forming additive for Li-metal anodes in carbonate-based electrolyte, which has the advantages of both good storage performance and low price. Compared to the SEI formed in vinyl ethylene carbonate-free electrolyte, the SEI film formed in 10% vinyl ethylene carbonate electrolyte contains a higher relative content of polycarbonate species and a greater amount of decomposition products of LiPF6 salt. Both components are expected to have positive effects on the passivation of Li-metal surface and the accommodation of volume changes of anode during cycling. Scanning electron microscopy images and COMSOL numerical simulation results further confirm that uniform Li deposition morphology can be achieved in the presence of vinyl ethylene carbonate additive. When cycling at the current density of 0.25 mA cm-2 with a cycling capacity of 1.0 mAh cm-2, the vinyl ethylene carbonate-contained Li-Cu cell exhibits a long life span of 816 h (100 cycles) and a relatively high Coulombic efficiency of 93.2%.

Electrochemical Degradation Mechanism and Thermal Behaviors of the Stored LiNi0.5Co0.2Mn0.3O2 Cathode Materials.

The degradation mechanism of the stored LiNi0.5Co0.2Mn0.3O2 (NCM523) electrode has been systematically investigated by combining physical and electrochemical tests. After stored at 55 °C and 80% relative humidity for 4 weeks, the NCM523 materials are coated with a layer of impurities containing adsorbed species, Li2CO3 and LiOH, resulting in both the weight gains of the materials and the electrochemical performance deterioration of the electrode. The impurities generated in air will react with the electrolyte and instantly turn into Li xPO yF z and other species containing the decomposition products of electrolyte when the stored NCM523 materials are soaked into the electrolyte, causing the charge potential plateau and the impedance to ascend. For the stored NCM523 electrodes, the huge and changeable impedance deteriorates the discharge capacity in the first 10 cycles and the discharge capacity will slowly recover and stabilize within 10 cycles when charging/discharging in 0.1 or 0.2 C. The thermal stability of the stored NCM523 materials get slightly better due to the relatively lower delithiated state after charged to 4.3 V.

Synergistic Effect between LiNi0.5Co0.2Mn0.3O2 and LiFe0.15Mn0.85PO4/C on Rate and Thermal Performance for Lithium Ion Batteries.

A blend cathode has been prepared by mixing both LiNi0.5Co0.2Mn0.3O2 (NCM523) of high energy density and high specific capacity and LiFe0.15Mn0.85PO4/C (LFMP/C) of excellent thermal stability via a low-speed ball-milling method. The lithium ion batteries using the blend cathode with LFMP/C of optimum percent exhibit better capacity retention after 100 cycles than those using only single NCM523 or LFMP/C. Both theoretical simulation and experimental rate performances demonstrate that the electrochemical property of blend cathode materials is predictable and economical. In addition, the thermal behaviors of blend cathodes are studied by using differential scanning calorimetry analysis. The thermal stability of blend cathode materials behaves better than that of the bare NCM523 accompanied with an electrolyte. It is found that the outstanding rate and thermal performance of the blend cathode is due to the prominent synergistic effect between NCM523 and LFMP/C, and 10% LFMP/C in the blend cathode materials is the most adaptable as considering both electrochemical and thermal properties simultaneously.

A Promising High-Voltage Cathode Material Based on Mesoporous Na3 V2 (PO4 )3 /C for Rechargeable Magnesium Batteries.

The lack of suitable high-voltage cathode materials has hindered the development of rechargeable magnesium batteries (RMBs). Here, mesoporous Na3 V2 (PO4 )3 /C (NVP/C) spheres have been synthesized through a facile spray-drying-annealing method, and their electrochemically desodiated phase NaV2 (PO4 )3 /C (ED-NVP/C) has been investigated as an intercalation host for Mg2+ ions. The obtained ED-NVP/C exhibits an average discharge voltage of around 2.5 V (vs. Mg2+ /Mg), higher than those of most previously reported cathode materials. In addition, it can deliver an initial discharge capacity of 88.8 mA h g-1 at 20 mA g-1 , with good cycling stability. Ex situ X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results demonstrate that the electrochemical reaction is based on an intercalation mechanism and shows good reversibility. Galvanostatic intermittent titration technique (GITT) data have revealed that the intercalation process involves a two-phase transition. The reported ED-NVP/C cathode material with high working voltage offers promising potential for application in RMBs.