Electrochemical preparation of a lithium–graphite-intercalation compound in a dimethyl sulfoxide-based electrolyte containing calcium ions

Electrochemical preparation of lithium–graphite-intercalation compound in dimethyl sulfoxide (DMSO)-based electrolytes containing calcium salt was studied. Intercalation of DMSO-solvated cation took place in 1.0 mol dm⁻³ lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) + 1.5 mol dm⁻³ calcium bis(trifluoromethanesulfonyl)amide (Ca(TFSA)₂)/DMSO, whereas intercalation of Li⁺ ions without solvent took place in 1.0 mol dm⁻³ LiTFSA + 2.5 mol dm⁻³ Ca(TFSA)₂/DMSO. Raman spectroscopic study suggests absence of free DMSO in 1.0 mol dm⁻³ LiTFSA + 2.5 mol dm⁻³ Ca(TFSA)₂/DMSO, which can lead to different solvation structure of Li⁺ from the one in 1.0 mol dm⁻³ LiTFSA + 1.5 mol dm⁻³ Ca(TFSA)₂/DMSO. Factors that are responsible for co-intercalation and only Li⁺ ion intercalation are discussed based on the Li⁺ ion solvation structures.     

Micromechanisms of solid electrolyte interphase formation on electrochemically cycled graphite electrodes in lithium-ion cells

The microstructural and compositional changes that occurred in the solid electrolyte interphase (SEI) formed on graphite electrodes subjected to voltammetry tests (vs. Li/Li⁺) at different voltage scan rates were investigated. The microstructure of the SEI layer, characterized using high-resolution transmission electron microscopy, consisted of an amorphous structure incorporating crystalline domains of ～5–20 nm in size. Evidence of lithium compounds, namely Li₂CO₃ and Li₂O₂, and nano-sized graphite fragments was found within these crystalline domains. The morphology and thickness of the SEI depended on the applied voltage scan rate (dV/dt). The variations in the Li⁺ diffusion coefficient (D_Li⁺) at the electrode/electrolyte interface during the SEI formation process were measured and two regimes were identified depending on the scan rate; for dV/dt ≥ 3.00 mV s^?1, D_Li⁺ was 3.13 × 10^?8 cm² s^?1. At lower scan rates where D_Li⁺ was low, 0.57 × 10^?8 cm² s^?1, a uniform and continuous SEI layer with a tubular morphology was formed whereas at high dV/dt, the SEI formed had a columnar morphology and did not provide a uniform coverage.     

Temperature stability and high-Qf of low temperature firing Mg2SiO4–Li2TiO3 microwave dielectric ceramics

In this work, a series of low-temperature-firing (1−x)Mg₂SiO₄–xLi₂TiO₃–8 wt% LiF (x = 35–85 wt%) microwave dielectric ceramics was prepared through conventional solid state reaction. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analyses showed that the Li₂TiO₃ phase was transformed into cubic phase LiTiO₂ phase and secondary phase Li₂TiSiO₅. Partial substitution of Mg²⁺ ions for Ti³⁺ ions or Li⁺Ti³⁺ ions increased the cell volume of the LiTiO₂ phase. The dense microstructures were obtained in low Li₂TiO₃ content (x ≤ 65 wt%) samples sintered at 900 °C, whereas the small quantity of pores presented in high Li₂TiO₃ content (x ≥ 75 wt%) samples sintered at 900 °C and low Li₂TiO₃ content (x = 45 wt%) sintered at 850 and 950 °C. Samples at x = 45 wt% under sintering at 900 °C for 4 h showed excellent microwave dielectric properties of ε_r = 10.7, high Q × f = 237,400 GHz and near-zero τ_f = − 3.0 ppm/°C. The ceramic also exhibited excellent chemical compatibility with Ag. Thus, the fabricated material could be a possible candidate for low temperature co-fired ceramic (LTCC) applications.     

An unusual emissive and colorimetric copper (II) detection by a selective probe based on a pseudo-crown cysteine dye: Solution and gas phase studies

An off-on-off emissive and colorimetric probe L, based on a Pseudo-Crown cysteine dye was designed for Copper (II). Compound L was studied in solution and in gas-phase (MALDI-MS) over alkaline, alkaline, earth-alkaline and transition metal ions (Li⁺, Na⁺, K⁺, Ca^2 +, Mg^2 +, Zn^2 +, Cu^2 +, Co^2 +, Ni^2 +, Pb^2 +, and Hg^2 +) in organic media. The recognition of Cu^2 + by L lead to red/dark red colored complexes, one emissive L₂Cu and another LCu, less emissive. In regards to fluorescent quantum yield in both cases an increase respective to L was visualized (2 fold for LCu and 7 fold for L₂Cu). The paramagnetic nature of both complexes was proved by the synthesis of both complex species, as well as, through ¹H NMR and FTIR. Compound L demonstrate to be able to detect and quantify the minimal amounts of 1.3 μM/3.3 μM of Cu^2 +.     

Electrochemical cycling behaviour of lithium carbonate (Li2CO3) pre-treated graphite anodes – SEI formation and graphite damage mechanisms

Graphite electrode surfaces were treated using a simple process of sedimentation in aqueous solutions containing 0.5 and 1.0 wt.% Li₂CO₃ with particle sizes of ∼1–2 μm. During the first cycle of voltammetry tests (vs. Li/Li⁺), the graphite surface was subjected to electrochemical degradation as a result of fracture and removal of near-surface graphite particles. Surface degradation was accompanied by a 0.4% strain in the graphite lattice as determined by in situ Raman spectroscopy. Pre-treated electrodes experienced a capacity drop of 3% in the first cycle, compared to a 40% drop observed in case of untreated graphite electrodes. After testing for 100 cycles, a capacity of 0.54 mAh cm⁻² was recorded for the pre-treated electrodes as opposed to a significant drop to 0.11 mAh cm⁻² for the untreated graphite. Cross-sectional HR-TEM indicated that the SEI formed on the pre-treated electrodes primarily consisted of Li₂CO₃ crystals of 14.6 ± 6.9 nm in size distributed within an amorphous matrix. The results suggested that the Li₂CO₃ enriched SEI formed on the pre-treated electrodes reduced the intensity of solvent co-intercalation induced surface damage. It is proposed that the Li₂CO₃ enriched SEI facilitated Li⁺ diffusion and hence improved the capacity retention during long-term cycling.     

Selective detection of mercury ions using benzothiazole based colorimetric chemosensor

Three new receptors L1, L2 and L3 were designed and synthesized in a single pot synthesis. The synthesized receptors were characterized by ¹H NMR, FT-IR and Mass spectrometry. The cation binding affinity was studied using colorimetric and UV–Vis spectral methods for the three receptors. Receptor L1 showed high selectivity with a significant color change from yellow to colorless (turn-off response) in the presence of Hg^2 + ions over the other cations such as, Ni^2 +, Cr^3 +, Pb^2 +, Cu^2 +, Cd^2 +, Co^2 +, Zn^2 + and Fe^2 + and the receptor L2, L3 did not show any color change or change in the absorption in UV–Vis spectral studies with Hg^2 + ions and other tested metal ions, this may be due to lack of –OH group in receptor L2 and L3. The B-H Plot shown 1:1 complex between L1and Hg^2 + ions.     

Polymer microsphere-assisted synthesis of lithium-rich cathode with improved electrochemical performance

The Li-rich layered cathode material Li_1.165Mn_0.501Ni_0.167Co_0.167O₂ with porous structure has been successfully synthesized through a facile co-precipitation approach followed with a high-temperature calcination treatment, adopting polymer microsphere (PSA) as a template and conductive agent. The PSA-assisted Li_1.165Mn_0.501Ni_0.167Co_0.167O₂ composite exhibits remarkably improved cycling stability and rate capability compared with the bare composite. It delivers a high initial discharge capacity of 267.0 mA h g⁻¹ at 0.1 C (1 C=250 mA g⁻¹) between 2.0 V and 4.65 V. A discharge capacity of 214.9 mA h g ⁻¹ is still obtained after 100 cycles. Furthermore, the diffusion coefficients of Li⁺ investigated by the cyclic voltammetry technique are approximately 10⁻¹⁵–10⁻¹⁴ cm² s⁻¹. Such outstanding performance is mainly ascribed to: on one hand, the carbon residue of PSA after being calcined at high temperature contributes to enhance the electronic conductivity of the electrode and alleviates the volume changes during the Li⁺-insertion/extraction, leading to an improved rate capability; on the other hand, the unique porous structure and small particle size are conductive to increase the exposed electrochemical active surface, shorten Li⁺ diffusion distance and thus enhance the lithium storage capacity.     

Deep-red emission of Mn4+ and Cr3+ in (Li1−xAx)2MgTiO4 (A=Na and K) phosphor: Potential application as W-LED and compact spectrometer

Mn⁴⁺ doped and Mn⁴⁺/Cr³⁺ co-doped alkali metal titanate phosphors have been prepared by solid state reaction method. A part of Li⁺ ions in the Li₂MgTiO₄: Mn⁴⁺ are substituted with Na⁺ and K⁺ ions and consequently the intensity of Mn⁴⁺ emission at 678 nm is enhanced by 1.7 and 2.5 times, respectively. In the Mn⁴⁺/Cr³⁺ co-doped (Li_0.95K_0.05)₂MgTi_0.999O₄, both emission of Cr³⁺at 726 nm and emission of Mn⁴⁺ at 678 nm of Mn⁴⁺ are observed. It is interesting to find that the intensity ratio of 726–678 nm emissions in the Mn⁴⁺/Cr³⁺ phosphor continually increases with excitation wavelength increasing from 290 nm to 455 nm, which means that the intensity ratio in turn can be used to identify the excitation light wavelength. This refers a possible approach to design novel compact light-wavelength detector or spectrometer based on the phosphor. The mechanism of Na⁺ or K⁺ substitution induced luminescence enhancement in the Mn⁴⁺ phosphor and the competition between the Cr³⁺ and Mn⁴⁺ emissions in the Mn⁴⁺/Cr³⁺ co-doped has been discussed.     

Effect of prior C,Si and Sn implantation on the etch rate of CVD diamond

Diamond films were implanted with C⁺, Si⁺ or Sn⁺ ions at multiple energies in order to generate a uniform layer of implantation-induced disorder. The implant energies of 60, 180, 330 and 525 keV for C⁺ ions, 200, 500 and 950 keV for Si⁺ ions and 750 and 2000 keV for Sn⁺ ions were selected to give an approximately constant vacancy concentration at depths over the range ∼ 0–0.5 μm. An analysis of the C⁺ implanted surfaces by Raman spectroscopy has shown an increase in non-diamond or sp²-bonded carbon at doses in the range 5 × 10¹³ to 5 × 10¹⁵ cm^− 2. In comparison, a completely non-diamond structure was evident after implantation with either Si⁺ ions at a dose of 5 × 10¹⁵ ions/cm² or Sn⁺ ions at ≥ 5 × 10¹⁴ cm^− 2. For a given dose, the etch rate of the diamond film was shown to increase with the mass of the implanted species in the order of C⁺, Si⁺ and Sn⁺. For a given implant species, the etch rate increased with the implant dose and the ion-induced vacancy concentration. The etch rate of the implanted diamond in various gases decreased in the order of O₂, CF₄/O₂ and CHF₃/O₂ plasmas.     

Electrochemical characterization of P2-type layered Na2/3Ni1/4Mn3/4O2 cathode in aqueous hybrid sodium/lithium ion electrolyte

P2-type layered Na_2/3Ni_1/4Mn_3/4O₂ has been synthesized by a solid-state method and its electrochemical behavior has been investigated as a potential cathode material in aqueous hybrid sodium/lithium ion electrolyte by adopting activated carbon as the counter electrode. The results indicate that the Na⁺/Li⁺ ratio in aqueous electrolyte has a strong influence on the capacity and cyclic stability of the Na_2/3Ni_1/4Mn_3/4O₂ electrode. Increase on the Li⁺ content leads to a shift of the redox potential towards a high value, which is favorable for the improvement of the working voltage of the layered material as cathode. It is found that the coexistence of Na⁺ and Li⁺ in aqueous electrolyte can improve the cyclic stability for the Na_2/3Ni_1/4Mn_3/4O₂ electrode. A reversible capacity of 54 mAh g⁻¹ was obtained with a high cyclability as the Na⁺/Li⁺ ratio was 2:2. Furthermore, an aqueous hybrid ion cell was assembled with the as-proposed Na_2/3Ni_1/4Mn_3/4O₂ as cathode and NaTi₂(PO₄)₃/graphite synthesized in this work as anode in 1 M Na₂SO₄/Li₂SO₄ (mole ratio as 2:2) mixed electrolyte. The cell shows an average discharge voltage at 1.2 V, delivering an energy density of 36 Wh kg⁻¹ at a power density of 16 W kg⁻¹ based on the total mass of the active materials.     

Fluorescence of Kryptofix 5 metal complexes

Kryptofix 5 forms complexes with a variety of metal cations. The coordination with the crown ether moiety affects only slightly the emission wavelength of the free Kryptofix 5 ligand (λ_max = 425 nm) in a buffer (pH = 9) solution, but the emission intensity of this blue fluorescence can increase strongly upon complex formation, probably owing to the rigidity of the complex. This applies e.g. to Ba^2 +, Zn^2 +, Cd^2 +, Hg^2 +, Ag⁺ and La^3 +. A second group of metal ions such as Al^3 +, Pb^2 +, Sb^3 +, Bi^3 +, Te^4 +, Gd^3 + and Th^4 + causes a large red shift of the fluorescence of free Kryptofix 5 to approximately λ_max = 500 nm. This green fluorescence resembles that of Kryptofix 5 in acidic solution. It is suggested, that the second group of metal ions is also coordinated to the pyridine nitrogen atoms of the quinoline substituents.     

Thermal cycling induced capacity enhancement of graphite anodes in lithium-ion cells

Graphite electrodes were electrochemically cycled in Li-ion cells at 50 and 60 °C in order to determine the changes in their surface properties in comparison to the electrodes tested at 25 °C. A 17% drop in planar capacity occurred during the first cycle at 60 °C compared to a 40% at 25 °C and reduced the amount of damage that occurred to graphite due to a rapidly formed solid electrolyte interphase (SEI). During the following cycles, a planar capacity of 3.11 ± 0.12 mAh cm⁻² was attained at 60 °C rather than 0.53 ± 0.03 mAh cm⁻² at 25 °C. The SEI layer formed at 60 °C predominantly consisted of Li₂CO₃ and was devoid of residual LiClO₄ detected at 25 °C. At 25 °C, the diffusion coefficient of Li⁺ (D_Li⁺) was calculated as 1.07 × 10⁻⁸ cm² s⁻¹, whereas at 60 °C, D_Li⁺ increased to 3.25 × 10⁻⁸ cm² s⁻¹. A pre-treatment conducted at 60 °C enhanced the cyclic performance of graphite subsequently cycled at 25 °C; a Li₂CO₃-enriched SEI, generated during the 60 °C pre-treatment, covered the graphite surface uniformly and resulted in a 28% increase in battery capacity at 25 °C.     

Highly selective recognition of mercury ions through the “naked-eye”

A new sensor 2-((E)-(3-(1H-imidazol-1-yl)propylimino)methyl)-5-(diethylamino)phenol (1) based on the combination of diethylaminosalicylaldehyde and imidazole groups was designed and synthesized as a Hg^2 + selective colorimetric chemosensor. Upon treatment of 1 with mercury ions, sensor 1 showed a color-change from colorless to yellow in a mixture of H₂O/DMF (5:95), while many other ions such as Al^3 +, Zn^2 +, Cd^2 +, Cu^2 +, Fe^2 +, Mg^2 +, Cr^3 +, Ag⁺, Co^2 +, Ni^2 +, Na⁺, K⁺, Ca^2 +, Mn^2 + and Pb^2 + had no influence. Notably, this chemosensor could distinguish clearly Hg^2 + from Cu^2 +, Ag⁺, Fe^2 + and Pb^2 +. The underlying signaling mechanism is a ligand-to-metal charge-transfer (LMCT) process. Compound 1 showed the serial formation of the 1:1 and the 1:2 complexation between 1 and Hg^2 +. This two-step binding mode was proposed based on the UV titration, ¹H NMR titration and ESI-mass studies.     

Visible green upconversion luminescence of Er3+/Yb3+/Li+ co-doped CaWO4 particles

The upconversion (UC) luminescence of Li⁺/Er³⁺/Yb³⁺ co-doped CaWO₄ phosphors is investigated in detail. Single crystallized CaWO₄:Li⁺/Er³⁺/Yb³⁺ phosphor can be obtained, co-doped up to 25.0/5.0/20.0 mol% (Li⁺/Er³⁺/Yb³⁺) by solid-state reaction. Under 980 nm excitation, CaWO₄:Li⁺/Er³⁺/Yb³⁺ phosphor exhibited strong green UC emissions visible to the naked eye at 530 and 550 nm induced by the intra-4f transitions of Er³⁺ (²H_11/2,⁴S_3/2→⁴I_15/2). The optimum doping concentrations of Yb³⁺/Li⁺ for the highest UC luminescence were verified to be 10/15 mol%, and a possible UC mechanism that depends on the pumping power is discussed in detail.     

Investigations on pure and Ag doped lithium lanthanum titanate (LLTO) nanocrystalline ceramic electrolytes for rechargeable lithium-ion batteries

The nano-crystalline Li_0.5La_0.5TiO₃ (LLTO) was prepared as an electrolyte material for lithium-ion batteries. The effect of Ag⁺ ion doping in three different concentrations were investigated: Ag_0.1Li_0.4La_0.5TiO₃, Ag_0.3Li_0.2La_0.5TiO₃, and Ag_0.5La_0.5TiO₃ along with Li_0.5La_0.5TiO₃. The prepared pure and Ag⁺ doped LLTO were subjected for structural, morphological, electrical and optical characterizations. The cubic superlattice structure of LLTO nano-powder was altered due to the Ag⁺ substitution tending towards a tetragonal phase. Increasing Ag⁺ substitution a complete tetragonal phase occurs in Ag_0.5La_0.5TiO₃. The average particle size of the prepared ceramic electrolyte ranged between 80 nm and 120 nm. The photoluminescence study reveals that the LLTO and Ag doped LLTO gives a blue emission peak. The size effect on grain and grain boundary resistance was observed and reported. With Ag⁺ substitution, the conductivity got decreased due to the impedance caused by Ag⁺ ions in the conducting path of Li⁺ ion. Among all the samples, Ag_0.5La_0.5TiO₃ shows maximum conductivity of the order of 10^?3 S cm^?1.     

A fluorescein derivative FLTC as a chemosensor for Hg2 + and Ag+ and its application in living-cell imaging

FLTC was synthesized and used as a fluorescent chemosensor to detect Hg^2 +. It showed high selectivity toward Hg^2 + over many heavy metal ions in an ethanol–H₂O (3:2, v/v, HEPES buffer, 0.5 mM, pH 7.15) solution with a detection limit of 0.21 μM. After complexation with Hg^2 +, FLTC showed extremely high selectivity toward Ag⁺ with a detection limit of 0.009 μM. Therefore, detection of Hg^2 + and Ag⁺ could be realized using FLTC and the FLTC–Hg^2 + complex, respectively. Cytotoxicity assays and fluorescence microscopy analysis showed that FLTC could be used as a fluorescent probe to detect Hg^2 + and Ag⁺ in L-02 human liver cells.     

Effective production of fluorescent nanodiamonds containing negatively-charged nitrogen-vacancy centers by ion irradiation

Fluorescence from negatively-charged nitrogen-vacancy centers (NV⁻s) in diamonds has unique optical properties with none of the undesirable effects such as photo-bleaching and photo-blinking. In addition, the spin-dependent fluorescence intensity of NV⁻s allows us to perform optically detected magnetic resonance (ODMR) investigation for evaluating the presence of NV⁻s and for the electronic local environment. In this work, we irradiated H⁺, He⁺, Li⁺ and N⁺ ions to nanodiamonds with a median size of 26 nm at various irradiation energies and doses for improving the NV⁻ concentration. ODMR observations of the nanodiamonds showed that ion irradiation increased the number of nanodiamonds containing NV⁻s up to 200 ppm, whereas without ion irradiation, only few NV⁻s were found. The number of nanodiamonds containing NV⁻s at various ion irradiation doses was not monotonous, but had maxima at certain irradiation doses. These results suggest a competition in two opponent roles of vacancies, effective for pairing with nitrogen atoms and as defects for developing damage in crystalline. We also found that sharp and strong ODMR signals were obtained from nanodiamonds irradiated at the optimal condition for the highest yield of NV⁻s. We concluded that He⁺ ion irradiations with 60 or 80 keV at a dose of 1 × 10¹³ ions cm^–2 are the conditions required for the most efficient production of a high quantity of nanodiamonds containing NV⁻s.     

Lanthanide complexes with a biphosphonate ester ligand and their fluorescent properties

A bi-phosphonate ligand 4,4′-bis(diethylphosphonomethyl)biphenyl has been designed and synthesized. The ligand reacted with lanthanide nitrates forming three different types of coordination complexes: interwoven net polymer (type I), linear polymer (type II), and ladder polymer (type III). The photophysical properties of Sm^3 +, Eu^3 +, Tb^3 + and Dy^3 + complexes were investigated. The Sm^3 +, Eu^3 + and Dy^3 + complexes displayed the characteristic spectrum of the lanthanide ions. The Tb^3 + complex exhibited a prominent strong fluorescence by excitation of 300 nm, which indicated that there may be a luminescence sensitization effect of the complex via excitation of the ligand.     

Red,green and blue-violet emission coexistence in white-light-emitting Ca3SiO4Cl2:Bi3+, Li+, Eu2+, Eu3+ phosphor

A series of emission-tunable Ca₃SiO₄Cl₂:Bi³⁺, Li⁺, Euⁿ⁺(n =2, 3) (CSC:Bi³⁺, Li⁺, Euⁿ⁺) phosphors have been synthesized via sol-gel method. The X-ray diffraction results indicate that the as-synthesized phosphors crystallize in a low temperature phase with the space group of P21/c. Energy transfer from Bi³⁺ to Eu³⁺/Eu²⁺ exists in CSC:Bi³⁺, Li⁺, Euⁿ⁺ phosphors. Under the excitation of 327 or 365 nm, the Ca_2.98−ySiO₄Cl₂:0.01Bi³⁺, 0.01Li⁺, yEuⁿ⁺(y=0.0001–0.002) phosphors show an intense green emission band around 505 nm, while under the excitation of 264 nm, three emission bands centered around 396 nm (Bi³⁺), 505 nm (Eu²⁺) and 614 nm (Eu³⁺) are observed and tunable colors from blue-violet to green or white are achieved in these phosphors by varying the content of Eu. White-light emission with the color coordinate (0.312, 0.328) is obtained in Ca_2.978SiO₄Cl₂:0.01Bi³⁺, 0.01Li⁺, 0.002Euⁿ⁺(n =2, 3). Based on these results, the as-prepared CSC:Bi³⁺, Li⁺, Eu²⁺, Eu³⁺ phosphors can act as color-tunable and single-phase white emission phosphors for potential applications in UV-excited white LEDs.     

Photoluminescence and structural characteristics of double tungstates A(M1−X PrX)W2O8 (A = Li,Cs, M = Al,Sc, La)

In this article, photoluminescence of Pr³⁺ ions in the double tungstate A(M_1?X Pr_X)W₂O₈ (A = Li, Cs, M = Al, Sc, La; 0.0 ≤ X ≤ 0.1) are characterised. By varying ion radius in A and M sites the crystal structure was modified and even in crystals with similar structural characteristics three distinctive types of luminescence are observed. When the substitution ions in both A and M sites are relatively small the host lattice exhibits luminescence dominantly. With the small A site ion (Li⁺) and the large M site ion (La³⁺, 1.03 Å) the Pr³⁺ ion exhibits prominent luminescence. With the very large A site ion (Cs⁺, 1.67 Å) and relatively small M site ion (Sc³⁺, 0.75 Å) the Pr³⁺ exhibits both the 4f²–4f5d excitation and the ³P_J manifold excitations in the absorption spectrum. These excitation levels lead to two strong emissions from the Pr³⁺. PL characteristics are discussed with respect to crystal structural criteria.