Sol–gel synthesis of Li1.5Al0.5Ge1.5(PO4)3 solid electrolyte

The effect of calcination on Li ion conductivity of Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) solid electrolyte prepared by a sol–gel method is examined. The Li ion conductivity of LAGP increases with calcination temperature. After reaching maximum conductivity at 850 °C, the conductivity decreases with increase of the calcination temperature. The calcination holding time also strongly affects Li ion conductivity of LAGP. The conductivity increases with holding time until 12 h and then decreases. It is found that the control of crystallization rate is critical to obtain bulk LAGP with high Li ion conductivity. The highest bulk and total conductivities at 30 °C are 9.5×10⁻⁴ and 1.8×10⁻⁴ S cm⁻¹, respectively, obtained for the bulk LAGP calcined at 850 °C for 12 h.     

Phase formation of Na+-beta-aluminas synthesized by double zeta process

Na⁺-beta-aluminas in the Na₂O–Al₂O₃–Li₂O ternary system were synthesized by double zeta process and the dependence of the crystal phase formation on the composition and the calcination temperature was studied. For the synthesis of Na⁺-β/β″-alumina, sodium aluminate varying compositions of [Na₂O]:[Al₂O₃] = 1:4–1:6 and lithium aluminate in the forms of Li₂O·5Al₂O₃ with different amounts of Li₂O (0.35–0.45 wt%) were well-mixed and calcined at temperatures ranging between 1300 and 1600 °C for 2 h. The β″-alumina fraction appeared to be approximately 10% higher compared to the conventional solid state reaction, showing around 70% of β″-alumina fraction. These values increased about 10–15% by additional heating near the binary eutectic temperature for a short time.     

A review on integrating nano-carbons into polyanion phosphates and silicates for rechargeable lithium batteries

Lithium metal phosphate (Li₂MPO₄) and silicates (Li₂MSiO₄) (where M = Fe, Mn, and Co) are promising polyanion cathodes for rechargeable lithium batteries, owing to the inherent merits such as low cost, decent electrochemical property, and high stability. However, these merits have often been undermined by insufficient energy and power delivery due to poor Li extraction/insertion kinetics. It is generally believed that the extremely low conductivity, i.e. ∼10⁻⁹ s cm⁻¹ for phosphates and 10⁻¹²–10⁻¹⁶ s cm⁻¹ for silicates at room temperature, in combination with slow Li ion diffusion could account for such sluggish Li cycling kinetics. To address this critical issue, it is essential to integrate well-defined nano-carbons such as one-dimensional (1D) carbon nanotube (CNT), two-dimensional (2D) graphene, and their three-dimensional (3D) assembly into polyanion materials. By constructing hybrid architectures, integrated composites could afford much improved activity towards Li storage versus the bare ones. In this short review, we summarize recent advance in integrating CNT, graphene, and their 3D assemblies into LiMPO₄ and Li₂MSiO₄ cathodes, with particular emphasis on how the cathodes interact with carbon materials and their mechanism. We also conclude some general rules to engineer such integration structures to maximize their utilization towards Li storage.     

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.     

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.     

Synthesis of p-sulfonated calix[4]arene-intercalated layered double hydroxides and their adsorption properties for organic molecules

Calixarenes are macrocyclic organo anions, which cavity is capable of molecular recognition, while layered double hydroxides (LDHs) are widely known as hydrotalcite-like compounds, anion exchangers and host–guest materials. In this study, the intercalation of water-soluble p-sulfonated calix[4]arene (CS4) in the interlayer of the Mg–Al and Zn–Al LDHs (M²⁺/Al ratio = 3) by the coprecipitation method has been investigated as well as the adsorption property of the resulting CS4/LDHs for benzyl alcohol (BA) and p-nitrophenol (NP). It was found that the CS4/LDHs with the molar ratio of CS4/Al = 0.25 (Mg–Al LDH) and 0.12 (Zn–Al LDH) were obtained as a single phase. The arrangement of CS4 in the LDH interlayer was different by the kind of the host metal ions as CS4 cavity axis perpendicular (Mg–Al LDH) and parallel (Zn–Al LDH) to the basal layer, influencing strongly on the BET surface area, N₂ adsorbed volume and adsorption property for BA and NP.     

Layered particle-based polymer composites for coatings: Part I. Evaluation of layered double hydroxides

Layered double hydroxides (LDH) suitable as fillers for the formulation of waterborne polyurethane (WPU) nanocomposites in coating applications are designed and characterized. Their elaboration follows a simple and reproducible process leading to samples without impurity. The attention is paid to the impact of the LDH nature (M_xAl/CO₃^2?, M = Mg and/or Zn, and x = 2, 3 and 4) on the structure characteristics, i.e. cell parameters and coherent domain dimensions. Focusing on two end-member phases M₂Al/CO₃^2?, M = Mg or Zn, the microstructural characterization performed from X-ray diffraction peak profile analyses permits to point out larger coherent domain sizes for Zn₂Al species than for Mg₂Al ones, and then to correlate with the “macroscopic” crystallinity of the samples. The evolution of LDH slurries over time is tentatively considered in a prediction interest. The stability of a chosen organic–inorganic hybrid, taken Mg₂Al as inorganic host structure with anions of the 4-aminobenzene sulfonic acid (4-ABSA), is studied as function of its carbonate contamination in time. Finally, the dispersion of LDH fillers in WPU is scrutinized in terms of WPU/LDH structure revealed by indirect and direct observations, XRD and TEM, respectively.     

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.     

New insight into the modification of Li-rich cathode material by stannum treatment

In this work, Sn is used to dope the Li-rich cathode material to improve the electrochemical performance of Li ion battery. After Sn treatment, the lattice parameters a, c and lattice volume V become larger. Compared with the pristine sample, the Sn-contained samples show longer plateaux at about 4.5 V in the first charging process, which means that Sn can activate the Li₂MnO₃ component. Meanwhile, with appropriate content of Sn doping, the sample exhibits enhanced rate capability and cycling stability. Especially, the sample S10 shows the best electrochemical performance, with a capacity retention of 88.66% after 100 cycles at 1 C (1 C=250 mA g⁻¹). The mechanisms of Sn doping have also been investigated. The increased activation of Li₂MnO₃ is due to the improved conductivity of Li₂MnO₃ phase by Sn doping, and the enhanced electrochemical performance is mainly ascribed to the increased ability of Li ion diffusing into bulk phase and the improved structure stability during the prolonged charge-discharge cycles. It is suggested that Sn doping is an effective way to improve the electrochemical performance of Li-rich cathode material.     

The effect of AlF3 modification on the physicochemical and electrochemical properties of Li-rich layered oxide

Lithium (Li)-rich layered oxides are considered promising cathode materials for Li-ion batteries because of their favorable properties. Here, we report our recent finding in the novel oxide, aluminum fluoride (AlF₃)-modified Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (LMNCAF), which was synthesized via a facile, cost-effective and readily scalable solid-state reaction. LMNCAF possess an F and Al co-doped core structure with a LiF nano-coating on its surface which leads to considerably enhancement in the electrochemical performance of the oxide. The initial discharge capacity (at 0.05 C) increased from 212 mA h g⁻¹ for Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ to 291 mA h g⁻¹ for LMNCAF. A much higher discharge capacity of 211 mA h g⁻¹ was obtained for LMNCAF after 99 charge/discharge cycles at 0.2 C compared with that of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ (160 mA h g⁻¹). Our preliminary results suggest that AlF₃ modification is an effective strategy to tailor the physicochemical and electrochemical properties of Li-rich layered oxides.     

Preparation of Li4Ti5O12 spherical particles for rechargeable lithium batteries

Spherical Li₄Ti₅O₁₂ particles were prepared via an emulsion-gel process. The preparation of spherical Li₄Ti₅O₁₂ such as the concentrations of the starting materials and heat treatment were optimized. The particle size distribution of the Li₄Ti₅O₁₂ prepared under optimized condition was very narrow, and the particle size was 0.45 μm. It was found that a short heat treatment in an infrared furnace was useful to crystallize amorphous LiTiO powders without aggregation of particles or morphology change. The obtained Li₄Ti₅O₁₂ had the spinel structure, and was phase pure. The prepared Li₄Ti₅O₁₂ exhibited a high discharge capacity of 160 mA h g⁻¹ at the potential of 1.5 V versus Li/Li⁺, and the charge–discharge cycle stability was excellent.     

Robust growth of herringbone carbon nanofibers on layered double hydroxide derived catalysts and their applications as anodes for Li-ion batteries

Herringbone carbon nanofibers (CNFs) were efficiently produced by chemical vapor deposition on Ni nanoparticles derived from layered double hydroxide (LDH) precursors. The as-obtained CNFs with a diameter ranging from 40 to 60 nm demonstrated herringbone morphologies when they grew on Ni/Al LDH derived catalysts both in the fixed-bed and fluidized-bed reactor. The Ni/Mg/Al, Ni/Cu/Al, as well as Ni/Mo/Mg/Al catalysts were also effective to grow herringbone CNFs. The diameter and specific surface area of the as-obtained CNFs highly depended on the catalyst composition and the growth temperature. When CNFs were grown at 550 °C on Ni/Al catalyst, the as-obtained products had an outer diameter of ca. 50 nm and a specific surface area of 242 m² g⁻¹, possessed a discharge capacity of 330 mAh g⁻¹ as the electrode in a two-electrode coin-type cell. With the increase of the surface area, the discharge capacity increased at a rate of 0.90 mAh cm⁻², while the initial coulombic efficiency decreased gradually on nanocarbon anodes. This is attributed to the fact that CNFs with higher surface area afford smaller sp² carbon layer that facilitated more Li ions to extract from the anodes.     

Influence of different lithium sources on the morphology,structure and electrochemical performances of lithium-rich layered oxides

Lithium-rich layered oxides were synthesized via co-precipitation by using different lithium sources (LiOH, Li₂CO₃ and CH₃COOLi). Scanning electron microscope (SEM), Thermo gravimetric analysis (TGA), Brunauer-Emmett-Teller (BET), Inductively coupled plasma atomic emission spectrometry (ICP-AES), X-ray diffraction (XRD) and electrochemical measurements were used to investigate the morphology, reaction process, specific surface area, composition, structure and electrochemical performance of the lithium-rich oxides, respectively. The use of different lithium sources mainly affects the primary particle size and secondary particle morphology of the final product. Using LiOH as the lithium source, the maximum discharge capacity of sample can reach to 272.1 mA h g^–1 in the voltage range of 2.0–4.6 V at room temperature, even after 50 cycles, the retention rate is still reach 91.4%. The electrochemical impedance spectroscopy (EIS) results show that lithium-rich oxides using LiOH as the lithium source have the minimum value of impedance after 50 cycles. Therefore, the choice of appropriate lithium source is an effective way to improve the electrochemical properties of lithium-rich layered oxides.     

Thermal,optical and dielectric properties of Zn–Al layered double hydroxide

Zn–Al–NO₃–layered double hydroxide (Zn–Al–NO₃–LDH) was prepared by the co-precipitation method at a constant pH of 7 and a ratio of Zn/Al = 4. A thermal treatment was performed for LDH at various temperatures. Powder XRD patterns showed that the layered structure of the LDH samples was stable below 200 °C, which was also confirmed by thermogravimetric (TGA) and differential thermal (DTA) analyses. Infrared spectra of the samples showed the characteristic peaks of LDH, and changes of these peaks were observed when thermal treatment was performed above 150 °C. Diffuse reflectance spectroscopy of the samples showed more than one energy gap at calcination temperatures below200 °C. In samples calcined at 200 °C and above only one energy gap was observed at approximately 3.3 eV. The photocatalytic activity was found to increase with the increase of the ZnO crystal size, which can be achieved by increasing the calcination temperature of the samples. Because of the presence of water molecules and anionic NO₃⁻ in the interlayer of the LDH, the dielectric response of the calcined LDH can be described by an anomalous low frequency dispersion using the second type of Universal Power Law for calcination temperatures below 200 °C. The dielectric response of the calcined LDH above 150 °C displays the dielectric relaxation behaviour of ZnO because of the formation of a ZnO phase in the LDH within this temperature range.     

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.     

From hydrated layered-spinel lithium manganate composite to high-performance spinel LiMn2O4: A novel synthesis tuned by the concentration of LiOH

To obtain high-performance spinel LiMn₂O₄, various types of hydrated layered-spinel lithium manganate composites have been controllably synthesized through the hydrothermal process. It is found that the composition and morphology of these intermediate products can be tuned by the concentration of LiOH: Li⁺ act as the template and OH^- provide the required alkaline environment. In particular, the nanostructure varies from nanowires to nanosheets at different levels, depending on the phase ratio of the spinel phase ranging from 0% to 100%. Phase purity and the corresponding electrochemical properties of the as-prepared LiMn₂O₄ products are further tailored through the subsequent heat treatment. With the optimized LiOH concentration of 0.08 M, the resulting LiMn₂O₄ cathode material exhibits the best electrochemical performance with the initial discharge capacity of 121.7 mA h g⁻¹ at 1 C and 117.8 mA h g⁻¹ at 30 C, while a retention over 90% can be achieved after 1500 cycles. This study will help deepen understanding of the function mechanisms and further direct the novel synthesis from hydrated layered-spinel lithium manganate composites to high-performance spinel LiMn₂O₄ cathode materials.     

Synthesis and electrochemical performance of Li4Ti5O12 submicrospheres coated with TiN as anode materials for lithium-ion battery

The TiN coated Li₄Ti₅O₁₂ (LTO) submicrospheres with high electrochemical performance as anode materials for lithium-ion battery were synthesized successfully by solvothermal method and subsequent nitridation process in the presence of ammonia. The XRD results revealed that the crystal structure of LTO did not change after thermal nitridation process. The submicrospheres morphology of LTO and TiN film on the surface of LTO submicrospheres were characterized by FESEM and HRTEM, respectively. XPS result confirmed that a small amount of Ti changed from Ti⁴⁺ to Ti³⁺ after nitridation process, which will increase the electronic conductivity of LTO. Electrochemical results showed that electrochemical performance of TiN coated LTO anode materials compared favorably with that of pure LTO. Also its rate capability and cycling performance were apparently superior to those of pure LTO. The reversible capacity of TiN-LTO is 105.2 mA h g⁻¹ at a current density of 10 C after 100 cycles and maintain 92.9% of its initial discharge capacity, while that of pure LTO is only 83.6 mA h g⁻¹ with a capacity retention of 90.3%. Even at 20 C, the discharge capacity of TiN coated LTO sample is 101.3 mA h g⁻¹, compared with 77.3 mA h g⁻¹ for pristine LTO in the potential range 1.0–2.5 V (vs. Li/Li⁺).     

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.     

Incorporation of lithium and nitrogen into CVD diamond thin films

High concentrations of lithium (~ 5 × 10¹⁹ cm^− 3) and nitrogen (~ 3 × 10²⁰ cm^− 3) have been simultaneously incorporated into single-crystal and microcrystalline diamond films using Li₃N and gaseous ammonia as the sources of Li and N, respectively. Using sequential deposition methods, well-defined localised layers of Li:N-doped diamond with a depth spread of less than ± 200 nm have been created within the diamond. The variation in Li:N content and amount of diffusion within the various types of diamond suggests a model whereby these atoms can migrate readily through the grain-boundary network, but do not migrate much within the grains themselves where the diffusion rate is much slower. However, the high electrical resistivity of the doped films, despite the high Li and N concentrations, suggests that much of the Li and N are trapped as electrically inactive species.     

Raman spectra and ferromagnetism of nanocrystalline Fe-doped Li0.43Nb0.57O3+δ

Nanocrystalline undoped LiNbO₃ and LiNbO₃ doped with x% Fe (x=0.5, 1, 2, 3, 5) were synthesized via a combustion method. Fe-doped LiNbO₃ with a 1 mol% doping concentration exhibited a room-temperature ferromagnetism of 0.06 emu/g. There was an abrupt change in properties when the doping concentration of Fe reached 2 mol%, where the lattice contracted obviously and the saturation magnetization (M_s) increased an order of magnitude to 0.275 emu/g; M_s slightly increased to its maximum value of 1.18 emu/g when the doping concentration was further increased to 5 mol%. Raman spectra showed that the substitution of Li by Fe occurred at small doping concentrations and the substitution of Nb at the Nb site occurred at higher doping concentrations. The results suggest that Fe³⁺ replaced Nb_Li⁴⁺ first and the weaker ferromagnetism is due to the minor fraction of Nb_Li⁴⁺ in LiNbO₃. Then, Fe³⁺ substituted Li⁺, resulting in large lattice distortion and much stronger spin coupling of Fe–Nb. Finally, the excess Fe³⁺ started to replace Nb⁵⁺at the Nb sites, where the spin coupling of Fe–Nb is weaker than that at the Li site. An analysis of the experimental results suggests that the congruent Fe-doped LiNbO₃ is a promising room-temperature single-phase multiferroic material.