The mechanical flexibility of a cable‐type battery reaches levels far beyond what is possible with conventional designs. The hollow‐spiral (helical) multi‐helix anode architecture is critical to the robustness under mechanical stress and facilitates electrolyte wetting of the battery components. This design enables the battery to reliably power an LED screen or an MP3 player even under severe mechanical twisting and bending.

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The interfacial origin of performance improvement and fade of high-voltage cathodes of LiNi 0.5 Co 0.2 Mn 0.3 O 2 for high-energy lithium-ion batteries has been investigated. Performance improvement was achieved through interfacial stabilization using 5 wt % methyl (2,2,2-trifluoroethyl) carbonate (FEMC) of fluorinated linear carbonate as a new electrolyte additive. Cycling with the FEMC additive at 3.0−4.6 V versus Li/Li + results in the formation of a stable solid electrolyte interface (SEI) layer and effective passivation of cathode surface, leading to improved cycling performance delivering enhanced discharge capacities to 205−182 mAhg −1 and capacity retention of 84% over 50 cycles. The SEI layer notably includes plenty of metal fluorides and −CF-containing species formed by additive decomposition. On the contrary, the origin of performance fade in electrolyte only was ineffective surface passivation and dissolution of metal elements, which leads to oxygen loss, surface structural degradation and crack formation at the LiNi 0.5 Co 0.2 Mn 0.3 O 2 particles. The data provide a basic understanding of the interfacial stabilization mechanism on high-voltage layered oxide cathodes.

Systematic Mn 2p XPS and Mn K-edge XAS analyses together with the electrochemical measurement have been carried out for the spinel LiMn 2 O 4 prepared at various sintering temperatures in order to elucidate an origin of the dependence of electrochemical properties on synthetic conditions. From the comparative experiments, it becomes clear that a lowering of synthetic temperature gives rise to an increase of structural disorder and of the average oxidation state of manganese, which is more prominent on the surface than in the bulk. Such results suggest that the modification of surface property induced by a decrease of particle size is closely related to the electrochemical performance. The nanocrystalline LiMn 2 O 4 prepared at 250 °C shows excellent cyclability at the 3 V region compared to that of microcrystalline LiMn 2 O 4 prepared at 700 °C. For the purpose of examining the evolution of the chemical bonding nature of inserted lithium, 7 Li MAS NMR studies have been performed for both the spinel compounds before and after Li + intercalation. While the intercalation of 0.2 mol Li + does not induce any remarkable spectral change for the microcrystalline LiMn 2 O 4 , it leads to a dramatic suppression of the NMR signal for the nanocrystalline LiMn 2 O 4 , indicating that the process of grafting Li into the latter phase results in significant modifications of the chemical environment of lithium. On the basis of present experimental findings, it can be concluded that the lowering of synthetic temperature modifies the surface properties, which facilitates the grafting process of Li + ion and, thereby, enhances the electrochemical properties for the 3 V region corresponding to the Li insertion.

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The surface films formed on commercial LiNi 0.8 Co 0.15 Al 0.05 O 2 cathodes ͑ATD Gen2͒ charged from 3.75 to 4.2 V vs. Li/Li ϩ in ethylene carbonate:diethyl carbonate-1 M LiPF 6 were analyzed using ex situ Fourier transform IR spectroscopy with the attenuated total reflection technique. A surface layer of Li 2 CO 3 is present on the virgin cathode, probably from reaction of the active material with air during the cathode preparation procedure. The Li 2 CO 3 layer disappeared even after soaking in the electrolyte, indicating that the layer dissolved into the electrolyte possibly even before potential cycling of the electrode. IR features only from the binder ͑poly͑vinylidene difluoride͒͒ and a trace of polyamide from the Al current collector were observed on the surfaces of cathodes charged to below 4.2 V, i.e., no surface species from electrolyte oxidation. However, some new IR features were found on the cathode charged to 4.2 V and higher. An electrolyte oxidation product was observed that appeared to contain dicarbonyl anhydride and ͑poly͒ester functionalities. The reaction appears to be an indirect electrochemical oxidation with overcharging ͑removal of Ͼ0.6 Li ion͒ destabilizing oxygen in the oxide lattice, resulting in oxygen transfer to the solvent molecules.Lithium-ion cells generally exhibit a relatively large ͑ca. 15-20%͒ irreversible loss of capacity during the initial few cycles. Research in the last decade has established that most of this irreversible capacity loss is due to the formation of a solid electrolyte interface ͑SEI͒ layer on graphite and other carbon-based negative electrodes. 1-11 These irreversible reactions consist of electrochemical reductions of the electrolyte below the potential ca. 1.5 V vs. Li/Li ϩ , but the specific reactions occurring and specific composition of the SEI layer in commercial cells is difficult to establish and complicated by adventitious impurities introduced during processing and assembly. 11 There have also been reports of irreversible capacity loss on the first few cycles with LiCoO 2 and LiMn 2 O 4 cathodes. [12][13][14][15][16][17] There have been several reports that an SEI layer also forms on cathodes such as LiCoO 2 , LiMn 2 O 4 , and LiNi 1Ϫx Co x O 2 from electrolyte oxidation, 18-25 although the nature of the reactions is unclear. More recently, Abraham and co-workers 26 proposed formation of an oxygen-deficient surface layer on a LiNi 1Ϫx Co x O 2 cathode as a result of oxygen-transfer reactions with the electrolyte. Various spectroscopic methods have been applied ex situ to analyze surface films formed on Ni-, Co-and Mn-based cathodes harvested from cells, including NMR, 22 X-ray photoelectron spectroscopy ͑XPS͒, 23 and X-ray absorption spectroscopy ͑XAS͒, 21,24,26 but the results were only suggestive, not conclusive.Recently, ab initio density functional theory ͑DFT͒ 27 was used to examine the energetics of electrochemical oxidation of common battery solvents, including ethylene carbonate ͑EC͒, diethyl carbonate ͑DEC͒, and dimethyl carbonate ͑DMC͒. T...

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.