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Lithium iron silicate (Li 2 FeSiO 4) has high theoretical capacity of 332 mAh∙g-1 upon full extraction of two lithium ions, which is accompanied by high delithiation potential and large volume change. Sulfur modification could be an effective approach for stabilizing Li 2 FeSiO 4 cathodes. A series of carbon-coated Li 2 FeSiO 4 samples were prepared through a hydrothermal and solid-state reaction route at a fixed sucrose content (14 wt% carbon) with varying amounts of sublimed sulfur at 5, 10, 15, 20 and 25 at%. The crystal structures, chemical compositions, microstructures and electrochemical performances of the differently sulfur-modified Li 2 FeSiO 4 /C were systematically investigated. The sulfur-carbon co-modifications and possible existing chemical states of sulfur are discussed in terms of the surface and near-bulk modifications. It was found that all the samples exhibited a monoclinic P 2 1 structural Li 2 FeSiO 4 , while the sulfur contents over 10 at% formed impure phases such as iron sulfides (Fe 1-x S) and lithium metasilicate (Li 2 SiO 3). Furthermore, three types of sulfur states could be found when sulfur and carbon were added simultaneously into Li 2 FeSiO 4. The surfaces were predominated by S–C and S–O–C, indicating the sulfur-carbon co-modification, which would reduce the resistance at the solid/electrode interface (SEI) but increase the charge transfer resistance. Near the bulk, the enhanced interactions between sulfur and iron S–Fe(−S) or sulfur and silicon S–Si(−O) may lead to the formation of possible impurities or oxygen substitution by sulfur. The former is detrimental as the effective sulfur amount is reduced, while the latter is beneficial to improve specific capacity and cycle stability. The overall performance of sulfur-carbon co-modified sample is influenced complicatedly by the sulfur content. The best initial discharge capacity of 152.3 mAh∙g-1 was obtained with 5 at% sulfur modification, while the best overall performance, showing a typical warm-up response and good cycle stability, was observed with 15 at% sulfur modification. [ABSTRACT FROM AUTHOR]

As a typical transition-metal dichalcogenide (TMD), vanadium disulfide (VS 2) is an excellent candidate for cathode material in lithium-ion batteries due to its metallic properties and large interlayer spacing. But they often suffer from low intercalation capacity and sluggish kinetics processes, significantly limiting their practical application. Herein, the cetyltrimethylammonium bromide (CTAB) is employed in the synthesis process to construct the sulfur (S) vacancy in VS 2. The sulfur vacancy could improve its intercalation capacity and kinetics performance. In this structure, the interlayer vacancy defects could provide extra intercalation sites to improve intercalation capacity. It could induce multiple migration paths for lithium-ion (Li+) and electron (e–), enabling fast Li + migration and rapid charge transfer. It also presents favorable rate performance with a high pseudocapacitance contribution during a typical intercalation reaction. The above positive behaviors significantly promote the kinetics performance of VS 2-x as a cathode material for lithium-ion batteries (smaller charge transfer resistance and high Li+ diffusion rate). Finally, this material could provide a high storage capacity of 140 mAh g−1 after 180th and favorable rate performance (55.5 mAh g−1 at 1A g−1). This work could provide a reference for improving TMD's electrochemical performance and expanding their applications. [ABSTRACT FROM AUTHOR]

LiNi 0.5 Mn 1.5 O 4 (LNMO) is a promising next-generation cathode material for high energy density lithium-ion batteries, but the application of LNMO is blocked because of its inherent side effects with electrolytes at high voltages, namely, serious Mn dissolution and capacity attenuation. A novel LiNi 0.5 Mn 1.5-x Sr x O 4 material (x = 0, 0.05, 0.1, 0.15, and 0.2) was successfully prepared using the sol-gel method, and the effect of varying in situ Sr2+-doping on the crystal structure, morphology, and electrochemical performance was researched. A series of characterizations showed that the Sr-doped LNMO structure contains less Mn3+, which enhances its cycling stability. In addition, Sr doping promotes morphological changes more remarkably. Accompanied by the appearance of (100) surfaces, the morphology of LNMO changes from an octahedron to a truncated octahedron. The (100) surface can effectively inhibit side reactions with the electrolyte and steady the structure at the working voltage, which also helps support Li+ transport kinetics. The Sr-doped LiNi 0.5 Mn 1.4 Sr 0.1 O 4 (expressed as LNMO-Sr0.1) cathode exhibits preeminent cycling stability, after 500 cycles at 1C, the capacity retention is 86.63 %. CV and EIS results show that the right amount of Sr doping efficiently reduces electrode polarization and charge transfer resistance and increases the Li+ diffusion coefficient. [Display omitted] [ABSTRACT FROM AUTHOR]

Li 2 ZnTi 3 O 8 @ α -Fe 2 O 3 composites have been successfully prepared by a facile hydrothermal process. Li 2 ZnTi 3 O 8 /α-Fe 2 O 3 composites show similar irregular spherical morphologies like Li 2 ZnTi 3 O 8 and relatively smaller particle sizes than pristine Li 2 ZnTi 3 O 8. Among all Li 2 ZnTi 3 O 8 /α-Fe 2 O 3 composites, Li 2 ZnTi 3 O 8 /α-Fe 2 O 3 composite (5 wt%) exhibits the best electrochemical properties. Li 2 ZnTi 3 O 8 /α-Fe 2 O 3 composite (5 wt%) delivers a reversible charge capacity of 184.8 mAh g−1 even at 1000 mA g−1 after 500 cycles, while pristine Li 2 ZnTi 3 O 8 only delivers a reversible charge capacity of 110.7 mAh g−1. The strong covalent bonds between Li 2 ZnTi 3 O 8 and α-Fe 2 O 3 will be formed, which is beneficial for the reduction of interfacial energy and thus helpful for the stabilization of the composite. Because of the special synergistic effect of the multi-phase interface, Li 2 ZnTi 3 O 8 /α-Fe 2 O 3 composites not only possess the advantages of single components but also show novel and attractive performances, such as the enhanced ionic conductivity, reduced interfacial charge transfer impedance, improved migration rate of lithium ions, and the enhancement of the rate performance and reversible capacity. The as-prepared Li 2 ZnTi 3 O 8 /α-Fe 2 O 3 composites reveal important potentials as anode materials for next-generation rechargeable Li-ion batteries, and this work also offers an effective strategy to design high performance lithium storage materials for advanced lithium-ion batteries. [ABSTRACT FROM AUTHOR]