A stable electrolyte system at a charge voltage over 4.5 V is the key to successfully obtaining higher energy density by raising the charging cutoff voltage. We demonstrate a fluorinated electrolyte (1 M LiPF 6 fluoroethylene carbonate (FEC) and methyl (2,2,2-trifluoroethyl) carbonate (FEMC) (FEC/FEMC = 1/9, v/v)) for a high-voltage LiNi 0.5 Mn 0.3 Co 0.2 O 2 /graphite system. The stability of the fluorinated electrolyte for the LiNi 0.5 Mn 0.3 Co 0.2 O 2 (NMC532) cathode was investigated using scanning electron microscopy, X-ray photoelectron spectroscopy, and electrochemical impedance spectroscopy. The charge-discharge performance of the fluorinated electrolyte was superior to the corresponding non-fluorinated electrolyte system at a charging cutoff voltage of 4. Considerable efforts have been made for developing high-charge voltage platforms that provide large capacities, thereby helping improve the energy density of lithium-ion batteries (LIB). Because electrical energy is the product of the discharge capacity and the average discharge voltage, it is important to search for cathode materials with a high discharge voltage.1 To this end, many studies have been devoted to improving cathode materials for high-voltage applications, such as polyanion oxides (LiCoPO 4 ), spinel-type oxides (LiMn 2 O 4 ), and layered oxides (LiNi x Mn y Co 1-x-y O 2 ). Among cathode materials, LiNi 0.5 Mn 0.3 Co 0.2 O 2 (NMC532) is one of the most promising for its potential practical application in high-voltage lithium-ion battery. 2-4However, there remains a critical obstacle that should be overcome for high-voltage lithium-ion batteries. Oxidative instability of the conventional non-aqueous electrolyte takes place at a charging voltage beyond 4.5 V, leading to severe decay of cycling performances.5 Per research, practical approaches to improving performance for highvoltage operation include use of a new solvent or introducing functional additives to the electrolyte. [6][7][8] Recently, incorporation of the fluorinated compound either as solvent or as additive have been investigated for high-voltage LIB and positive effects have been reported. [9][10][11][12][13] Especially, utilization of fluoroethylene carbonate (FEC), which is well known to form solid-electrolyte interphase (SEI) on the anode surface with the small amounts addition, in high-voltage LIB has gathered attention. Based on 1 M LiPF 6 ethylene carbonate (EC) and ethyl methyl carbonate (EMC) (EC/EMC = 3/7, wt/wt) electrolyte, FEC was used as a fluorinated solvent (20∼50%) to replace EC or as a fluorinated additive (>5%) in a base electrolyte solution. However, there are a few studies reported on the electrolyte system consisting of wholly fluorinated solvents and additive. Here, we demonstrate a fully fluorinated electrolyte system composed of FEC and methyl (2,2,2-trifluoroethyl) carbonate (FEMC) at a volume ratio of 1:9 for high-voltage lithium-ion batteries. Amount of FEC is selected slightly higher than the case of FEC as additive in base solvent and much lower th...

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Initial reversibility and excellent capacity retention are the key requirements for the success of high‐capacity electrode materials in high‐performance Li‐ion batteries and pose a number of challenges to development. Silicon has been regarded as a promising anode material because of its outstanding theoretical capacity. However, it suffers from colossal volume change and continuous formation of unstable solid electrolyte interphases during lithiation/delithiation processes, which eventually result in low initial Coulombic efficiency (ICE) and severe capacity decay. To circumvent these challenges, a new sandwich Si anode (SiOx/Si/SiOx) free from prelithiation is designed and fabricated using a combination of P‐doping and SiOx layers. This new anode exhibits high conductivity and specific capacity compared to other Si thin‐film electrodes. Cells with SiOx/Si/SiOx anodes deliver the highest presently known ICE value among Si thin‐film anodes of 90.4% with a charge capacity of 3534 mA h g−1. In addition, the SiOx layer has sufficient mechanical stability to accommodate the large volume change of the intervening Si layer during charge‐discharge cycling, exhibiting high potential for practical applications of Si thin‐film anodes.

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This study demonstrates the wrinkle formation on biodegradable polymer‐blend microparticles prepared from an emulsion‐solvent evaporation method and investigates the formed patterns. A labyrinthine pattern is obtained for uniform‐sized microparticles, owing to the considerable size reduction during solvent evaporation. Changing the radius of the organic droplets dispersed in the aqueous solution switches the wrinkle pattern from labyrinth to bi‐phase. For the first time, the dual wrinkling structure is prepared; both labyrinthine texture and hexagonal dimple structures are spontaneously formed on the same microparticle surface. The former pattern is due to the surface instability from blends of hydrophobic polymer and amphiphilic block copolymer, while the latter is due to a mechanism similar that of the breath figure formed with organic phase change materials during solidification of microparticles. The general applicability of this approach is demonstrated on other pairs of polymer blends.