Exploration of anion effects in solvothermal synthesis using in situ X-ray diffraction

Solvothermal synthesis presents a facile and highly flexible approach to chemical processing and it is widely used for preparation of micro- and nanosized inorganic materials. The large number of synthesis parameters in combination with the richness of inorganic chemistry means that it is difficult to predict or design synthesis outcomes, and it is demanding to uncover the effect of different parameters due to the sealed and complex nature of solvothermal reactors along with the time demands related to reactor cleaning, sample purification, and characterization. This study explores the effect on formation of crystalline products of six common anions in solvothermal treatment of aqueous and ethanolic precursors. Three different cations are included in the study (Mn2+, Co2+, Cu2+) representing chemical affinities towards different regions of the periodic table with respect to the hard soft acid base (HSAB) classification and the Goldschmidt classification. They additionally belong to the commonly used 3d transition metals and display a suitable variety in solvothermal chemistry to highlight anion effects. The results of the solvothermal in situ experiments demonstrate a clear effect of the precursor anions, with respect to whether crystallization occurs or not and the characteristics of the formed phases. Additionally, some of the anions are shown to be redox active and to influence the formation temperature of certain phases which in turn relates to the observed average crystallite sizes.

Anisotropic alignments of hierarchical Li2SiO3/TiO2 @nano-C anode//LiMnPO4@nano-C cathode architectures for full-cell lithium-ion battery

We report on low-cost fabrication and high-energy density of full-cell lithium-ion battery (LIB) models. Super-hierarchical electrode architectures of Li2SiO3/TiO2@nano-carbon anode (LSO.TO@nano-C) and high-voltage olivine LiMnPO4@nano-carbon cathode (LMPO@nano-C) are designed for half- and full-system LIB-CR2032 coin cell models. On the basis of primary architecture-power-driven LIB geometrics, the structure keys including three-dimensional (3D) modeling superhierarchy, multiscale micro/nano architectures and anisotropic surface heterogeneity affect the buildup design of anode/cathode LIB electrodes. Such hierarchical electrode surface topologies enable continuous in-/out-flow rates and fast transport pathways of Li+-ions during charge/discharge cycles. The stacked layer configurations of pouch LIB-types lead to excellent charge/discharge rate, and energy density of 237.6 Wh kg-1. As the most promising LIB-configurations, the high specific energy density of hierarchical pouch battery systems may improve energy storage for long-driving range of electric vehicles. Indeed, the anisotropic alignments of hierarchical electrode architectures in the large-scale LIBs provide proof of excellent capacity storage and outstanding durability and cyclability. The full-system LIB-CR2032 coin cell models maintain high specific capacity of ∼89.8% within a long-term life period of 2000 cycles, and average Coulombic efficiency of 99.8% at 1C rate for future configuration of LIB manufacturing and commercialization challenges.

Density Functional Theory Investigation of Mixed Transition Metals in Olivine and Tavorite Cathode Materials for Li-Ion Batteries

Lithium-ion batteries (LIBs) are widely used in various electronic devices and have garnered a huge amount of attention. In addition, evaluation of the intrinsic properties of LIB cathode materials is of considerable interest for practical applications. Therefore, through first-principles calculations based on the density functional theory, we investigated the structural, electronic, electrochemical, and kinetic properties of mixed transition metals, that is, Ni-substituted LiMnPO₄ (LMP) and LiMnPO₄F (LMPF) cathode materials, that is, LiMn_0.5Ni_0.5PO₄ (LMNP) and LiMn_0.5Ni_0.5PO₄F (LMNPF), respectively, which have not been extensively studied. We also evaluated their delithiated phases, that is, Mn_0.5Ni_0.5PO₄ (MNP) and Mn_0.5Ni_0.5PO₄F (MNPF). Our calculations suggest that Ni substitution significantly affected the structural and electrochemical properties. After Li insertion, the MNPF unit-cell volume increased by about 8%, lower than that of pristine MnPO₄F. The Li intercalation voltage also increased in LMNP (4.27 V) and LMNPF (5.23 V). In addition, the migration barrier was calculated to be 0.4 eV for LMNPF, lower than that of LMPF. This study may provide insights for developing LMNP and LMNPF cathode materials in LIB applications.

Cathode Properties of Na3MnPO4CO3 Prepared by the Mechanical Ball Milling Method for Na-Ion Batteries

A novel carbonophosphate, Na3MnPO4CO3, was synthesized as a cathode material using a mechanical ball milling method with starting materials of MnCO3 and Na3PO4 without washing or drying. Duo to the formation of nano-size particles and good dispersion of the obtained Na3MnPO4CO3, the initial discharge capacity in an organic electrolyte of 1 M NaPF6/ethylene carbonate (EC): dimethyl carbonate (DMC) (1:1 v/v) was 135 mAh∙g−1 and 116 mAh∙g−1 at 1/30 C and 1/10 C, respectively. We also investigated the cathode properties of Na3MnPO4CO3 in an aqueous electrolyte of 17 m NaClO4. This is the first investigation of the electrochemical performance of Na3MnPO4CO3 with aqueous electrolyte. Na3MnPO4CO3 achieved a discharge capacity as large as 134 mAh g−1 even at a high current density of 2 mA cm−2 (0.5 C), because of the high ionic conductivity of the aqueous electrolyte of 17 m NaClO4.

Deep Eutectic Solvent Synthesis of LiMnPO₄/C Nanorods as a Cathode Material for Lithium Ion Batteries

Olivine-type LiMnPO₄/C nanorods were successfully synthesized in a chloride/ethylene glycol-based deep eutectic solvent (DES) at 130 °C for 4 h under atmospheric pressure. As-synthesized samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and electrochemical tests. The prepared LiMnPO₄/C nanorods were coated with a thin carbon layer (approximately 3 nm thick) on the surface and had a length of 100–150 nm and a diameter of 40–55 nm. The prepared rod-like LiMnPO₄/C delivered a discharge capacity of 128 mAh·g⁻¹ with a capacity retention ratio of approximately 93% after 100 cycles at 1 C. Even at 5 C, it still had a discharge capacity of 106 mAh·g⁻¹, thus exhibiting good rate performance and cycle stability. These results demonstrate that the chloride/ethylene glycol-based deep eutectic solvents (DES) can act as a new crystal-face inhibitor to adjust the oriented growth and morphology of LiMnPO₄. Furthermore, deep eutectic solvents provide a new approach in which to control the size and morphology of the particles, which has a wide application in the synthesis of electrode materials with special morphology.

Hierarchical Self-Assembly of Cu7Te5 Nanorods into Superstructures with Enhanced SERS Performance

This paper reports a strategy to get self-assembly of Cu₇Te₅ nanorods into hierarchical superstructures: the side-by-side self-assembly of nanorods into microscale one-dimensional (1D) nanowires (primary structure), the side-by-side alignments of the 1D nanowires into two-dimensional (2D) nanowire bundles (secondary structure), and the further rolling up of the 2D bundles into three-dimensional (3D) microtubes (tertiary structure). It was found that the oleylamine (OLA)/n-dodecanethiol (DDT) mixture as a binary capping agent was key to produce Cu₇Te₅ nanorods in the quantum size regime with high monodispersity, and this was a prerequisite for their hierarchical self-assembly based on elaborate control of the solvent evaporation process. The obtained Cu₇Te₅ microtube superstructures were used as SERS substrate and showed much stronger SERS enhancement than the as-prepared Cu₇Te₅ nanorods before assembly. This was probably ascribed to the remarkably enhanced local electromagnetic field arising from the plasmon coupling of Cu₇Te₅ nanorods in the well-assembled superstructures.

In-depth mesocrystal formation analysis of microwave-assisted synthesis of LiMnPO4 nanostructures in organic solution

Formation of LiMnPO₄ mesocrystals via self-assembled subunits employing microwave-assisted synthesis in rac-1-phenylethanol.

Recent progress in hybrid cathode materials for lithium ion batteries

Various binary composite cathode materials for lithium ion batteries are summarized and discussed.

Superior high rate capability of size-controlled LiMnPO4/C nanosheets with preferential orientation

Rectangular-shaped LiMnPO₄/C nanosheets prepared via a solvothermal process exhibited high discharge capacities near the theoretical value and stable cycling retentions.

Synthesis and Electrochemical Performance of LiMnPO4by Hydrothermal Method

LiMnPO4with olivinestructure which is the promising candidate for high voltage cathode material was synthesized by hydrothermal method. In order to synthesize high purity and well-defined LiMnPO4, several precursors for Li, Mn, and P sources and hydrothermal reaction parameters including temperature and [H2O]/[Mn] value are optimized. By analyzing the structure, Mn valence, morphology, and chemical ratio via XRD, XPS, Raman, SEM, and ICP LiMnPO4synthesized from manganese acetate tetrahydrate have single phase of LiMnPO4without impurity and showed charge and discharge reaction caused by Mn2+/Mn3+redox. Specific capacity of synthesized LiMnPO4grew up during cycling. Moreover, when hydrothermal temperature was set at 150°C and [H2O]/[Mn] value was set at 15, discharge capacity as high as 70 mAh/g was obtained at1/20  Crate.

P-type Cu7Te5 single-crystalline nanocuboids: size-controlled synthesis and large-scale self-assembly

The synthesis, shape evolution and large-scale self-assembly of p-type Cu₇Te₅ single-crystalline nanocuboids have been studied in this communication.