Ab initio study on the Li deintercalation in ternary lithium nitridocuprate Li2.5Cu0.5N

Using the first-principles method within the density functional theory and the generalized gradient approximation, the properties of lithium deintercalation were studied in the ternary lithium transition metal nitride Li_2.5Cu_0.5N. The lithium deintercalation formation energies per lithium atom were found to be between −2.72 and −4.08 eV for various amounts of Li extraction. The changes in the crystal volume, the electronic structures and the changes in charge densities of the Li_xCu_0.5N due to Li extractions are also presented. This study demonstrates that the extraction of lithium ions from the [Li₂N] layer is easier than that from the [Li_0.5Cu_0.5] layer. The change in unit cell volume was less than 5% for extractions of less than 30% of the Li ions in the unit cell. However, for a higher percentage of Li extractions, the system could shrink much more remarkably. The sequence of Li deintercalation, which was based on the calculated formation energies and the ratio of volume change, also gave some insight into the amorphization phenomenon after the first charge.     

The role of structural and electronic alterations on the lithium diffusion in LixCo0.5Ni0.5O2

The mechanisms for lithium diffusion in Li_xCo_0.5Ni_0.5O₂ were investigated using the galvanostatic intermittent titration technique (GITT). Membrane electrodes prepared with poly(vinylidene fluoride) and carbon black were employed in this study. The measured Brunauer-Emmett-Teller (BET) area of the Li_xCo_0.5Ni_0.5O₂ powder was combined with the GITT data to obtain the lithium chemical diffusion coefficient (), the lithium self-diffusion coefficient (D_Li⁺) and the thermodynamic factor (Φ) as a function of Li concentration (x). All three parameters vary non-monotonically with x. A minimum in and D_Li⁺ at x=0.5, along with structural changes, suggests the formation of a lithium superlattice at that concentration. The behavior of is complex but for x<0.34 it eventually undergoes a continuous decrease due to the metallic character of Li_xCo_0.5Ni_0.5O₂. We attribute the limitation of the specific reversible capacity of Li_xCo_0.5Ni_0.5O₂ to this decrease in and to elevated electrode voltages. Li transport in Li_xCo_0.5Ni_0.5O₂ is analyzed taking the variations in the cell parameters and the oxidation states of the Ni, Co and O ions into account.     

Electrochemical reactivity of Co-Li2S nanocomposite for lithium-ion batteries

The fabrication of Co-Li₂S nanocomposite thin film is reported by pulsed laser deposition (PLD) for the first time. Li₂S-Co nanocomposite thin film is used as storing Li electrodes that have led to promising electrochemical activity and good electrochemical performance. The releasing Li process from the as-deposited Li₂S-Co nanocomposite thin films is confirmed by the ex situ high resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction (SAED) measurements and may come from the decomposition of Li₂S with and without the interaction of metal Co into CoS₂ and S. The electrochemical reaction mechanism of Co-Li₂S nanocomposite film electrode involving both the formation and decomposition of Li₂S and the lithium extraction/insertion of CoS₂ after the initial charging process is proposed. Our results demonstrate the advantages of using Co-Li₂S nanocomposite in storage lithium materials.     

Sulfur–carbon composite electrode for all-solid-state Li/S battery with Li2S–P2S5 solid electrolyte

All-solid-state Li/S batteries with Li₂S–P₂S₅ glass–ceramic electrolytes were fabricated and their electrochemical performance was examined. Sulfur–carbon composite electrodes were prepared by grinding with a mortar and milling with a planetary ball-mill apparatus. Milling of a mixture of sulfur, acetylene black and the Li₂S–P₂S₅ glass–ceramic electrolyte resulted in the amorphization of sulfur and a reduction in the particle size of the mixture. The charge–discharge properties of all-solid-state cells with the composite electrode were investigated at temperatures from −20 °C to 80 °C. The cells retained a reversible capacity higher than 850 mAh g⁻¹ for 200 cycles under 1.3 mA cm⁻² (333 mA g⁻¹) at 25 °C. The cell performance was influenced by the crystallinity of sulfur and the particle size of the electrode material, whereby improved contact among the electrode components achieved by milling contributed to enhancement of the capacity of an all-solid-state Li/S cell.     

Measurement of concentration profile during charging of Li battery anode materials in LiClO4-PC electrolyte

Li metal was galvanostatically electrodeposited on a horizontally positioned, downward-facing Li metal cathode in 0.5 M LiClO₄-PC electrolyte. The refractive index profile corresponding to the transient Li⁺ ion concentration profile formed in the electrolyte solution upon applying a current step was measured in-situ by holographic interferometry. The configuration of the electrolytic cell was such that mass transfer was governed only by transient diffusion and migration, in the absence of convection. Between the moment of closing the current circuit and the time at which the interference fringes started to shift, an incubation period was observed. Such an incubation period had earlier been observed in lithium electrodeposition at a vertical planar Li metal cathode. The incubation period for the horizontal Li cathode was roughly half that for a vertical one. To study the effect of the electrode material on the incubation period, interferometry measurements were also made at an electrodeposited Ni-Sn alloy electrode. The concentration profile formed near the Ni-Sn alloy electrode during lithiation (alloying or intercalation of Li⁺ into the electrode) agrees well with predictions made by means of the one-dimensional diffusion equation. Only very short incubation period was detected, but the magnitude was negligibly smaller than that of Li metal electrodeposition. The incubation period therefore appears to be characteristic for Li metal electrode only.     

Cycling-induced stress in lithium ion negative electrodes: LiAl/LiFePO4 and Li4Ti5O12/LiFePO4 cells

In this work, we examined the electrochemical behaviour of lithium ion batteries containing lithium iron phosphate as the positive electrode and systems based on Li-Al or Li-Ti-O as the negative electrode. These two systems differ in their potential versus the redox couple Li⁺/Li and in their morphological changes upon lithium insertion/deinsertion. Under relatively slow charge/discharge regimes, the lithium-aluminium alloys were found to deliver energies as high as 438 Wh kg⁻¹ but could withstand only a few cycles before crumbling, which precludes their use as negative electrodes. Negative electrodes consisting solely of aluminium performed even worse. However, an electrode made from a material with zero-strain associated to lithium introduction/removal such as a lithium titanate spinel exhibited good performance that was slightly dependent on the current rate used. The Li₄Ti₅O₁₂/LiFePO₄ cell provided capacities as high as 150 mAh g⁻¹ under C-rate in the 100th cycle.     

Electrochemical reactions of lithium with Li2ZnGe and Li2ZnSi

Electrochemical reactions of lithium with cubic α-Li₂ZnGe and with hexagonal Li₂ZnSi have been studied. Charging a Li/α-Li₂ZnGe battery results in lithium extraction to yield a Li_1.2ZnGe composition, through a first step at ca. 0.9 V that involves a phase transition from cubic to hexagonal, and a second step at ca. 1.1 V where Ge and Zn segregation is observed. By discharge of the Li/α-Li₂ZnGe battery, the composition Li₃ZnGe is reached at 0.2 V while the cubic structure is maintained. Lithium insertion into Li₂ZnSi preserves the hexagonal structure, but lithium extraction modifies the X-ray diffraction pattern.     

The effect of quaternary ammonium on discharge characteristic of a non-aqueous electrolyte Li/O2 battery

The effect of quaternary ammonium on discharge characteristic of Li/O₂ cells was studied by using Super-P carbon as air cathode, a 0.2 mol kg⁻¹ LiSO₃CF₃ 1:3 (wt.) PC/DME solution as baseline electrolyte, and tetrabutylammonium triflate (NBu₄SO₃CF₃) as an electrolyte additive or a co-salt. Results show that Li/O₂ cells can run normally in an electrolyte with NBu₄SO₃CF₃ as the sole conductive salt. However, such cells suffer lower voltage and capacity as compared with those using the lithium ionic baseline electrolyte. This is due to the larger molar volume of quaternary ammonium cation, which results in less deposition of oxygen reduction products on the surface of carbon. When used as an electrolyte additive or a co-salt, the ammonium is shown to increase capacity of Li/O₂ cells. The plot of differential capacity versus cell voltage shows that the Li/O₂ cell with ammonium added has broad and scatted differential capacity peaks between the voltages of two reactions of “2Li + O₂ → Li₂O₂” and “2Li + Li₂O₂ → 2Li₂O”. This phenomenon can be attributed to the phase transfer catalysis (PTC) property of quaternary ammonium on the second reaction. Due to inverse effects of the cation geometric volume and the PTC property of ammonium ions on the discharge capacity, there is an optimum range for the concentration of ammonium. It is shown that the addition of NBu₄SO₃CF₃ increases discharge capacity of Li/O₂ cell only when its concentration is in a range from 5 mol% to 50 mol% vs. the total of Li/ammonium mixed salt, and that the optimum concentration is about 5 mol%. In this work we show that the addition of 5 mol% NBu₄SO₃CF₃ into the baseline electrolyte can increase discharge capacity of a Li/O₂ cell from 732 mAh g⁻¹ to 1068 mAh g⁻¹ (in reference to the weight of Super-P carbon) when the cell is discharged at 0.2 mA cm⁻².     

Preparation and characterization of ramsdellite Li2Ti3O7 as an anode material for asymmetric supercapacitors

Ramsdellite Li₂Ti₃O₇ was first synthesized via sol-gel process with good crystallity of an average particle size of 0.175 μm. The product was thoroughly investigated as a lithium intercalation compound, and as an active anode material in asymmetric supercapacitors coupling with activated carbon as cathode. Lithium intercalation reactions were found occurring at 1.32 and 1.62 V versus Li/Li⁺, respectively. A reversible specific capacity of 150 mA h g⁻¹ at 1C was obtained on Li₂Ti₃O₇ electrode in a nonaqueous electrolyte. The charge current was found to strongly influence the anodic discharge capacity in the asymmetric cell. The capacity retention at 10C charge-discharge rate was found to be 75.9% in comparison with that at 1C.     

Influence of precursors of Li2O and MgO on surface and catalytic properties of Li‐promoted MgO in oxidative coupling of methane

The influence of the catalyst precursors (for Li₂O and MgO) used in the preparation of Li‐doped MgO (Li/Mg = 0.1) on its surface properties (viz basicity, CO₂ content and surface area) and activity/selectivity in the oxidative coupling of methane (OCM) process at 650–750 °C (CH₄/O₂ feed ratio = 3.0–8.0 and space velocity = 5140–20550 cm³ g⁻¹ h⁻¹) has been investigated. The surface and catalytic properties are found to be strongly affected by the precursor for Li₂O (viz lithium nitrate, lithium ethanoate and lithium carbonate) and MgO (viz magnesium nitrate, magnesium hydroxide prepared by different methods, magnesium carbonate, magnesium oxide and magnesium ethanoate). Among the Li–MgO (Li/MgO = 0.1) catalysts, the Li–MgO catalyst prepared using lithium carbonate and magnesium hydroxide (prepared by the precipitation from magnesium sulfate by ammonia solution) and lithium ethanoate and magnesium acetate shows high surface area and basicity, respectively. The catalysts prepared using lithium ethanoate and magnesium ethanoate, and lithium nitrate and magnesium nitrate have very high and almost no CO₂ contents, respectively. The catalysts prepared using lithium ethanoate or carbonate as precursor for Li₂O, and magnesium carbonate or ethanoate, as precursor for MgO, showed a good and comparable performance in the OCM process. The performance of the other catalysts was inferior. No direct relationship between the basicity of Li‐doped MgO or surface area and its catalytic activity/selectivity in the OCM process was, however, observed. © 2000 Society of Chemical Industry     

Preparation of micro-dot electrodes of LiCoO2 and Li4Ti5O12 for lithium micro-batteries

Fabrications of micro-dot electrodes of LiCoO₂ and Li₄Ti₅O₁₂ on Au substrates were demonstrated using a sol-gel process combined with a micro-injection technology. A typical size of prepared dots was about 100 μm in diameter, and the dot population on the substrate was 2400 dots cm⁻². The prepared LiCoO₂ and Li₄Ti₅O₁₂ micro-dot electrodes were characterized with scanning electron microscopy, X-ray diffraction, micro-Raman spectroscopy, and cyclic voltammetry. The prepared LiCoO₂ and Li₄Ti₅O₁₂ micro-dot electrodes were evaluated in an organic electrolyte as cathode and anode for lithium micro-battery, respectively. The LiCoO₂ micro-dot electrode exhibited reversible electrochemical behavior in a potential range from 3.8 to 4.2 V versus Li/Li⁺, and the Li₄Ti₅O₁₂ micro-dot electrode showed sharp redox peaks at 1.5 V.     

Hydrogen storage mechanism and lithium dynamics in Li12C60 investigated by μSR

The lithium cluster intercalated fulleride Li₁₂C₆₀ was investigated by means of Muon Spin Relaxation (μSR) spectroscopy with the intent of unveil its hydrogen storage mechanism. Thanks to the well-known propensity of positive muons to form Muonium, a light isotope of the hydrogen atom, the final stages of the absorption process can be probed. The appearance of a slow oscillating signal in the time evolution of the muon polarization indicates the presence of Li–Mu covalent pair, never observed before in lower doped Li fullerides, which mimics the formation of LiH at the first stage of hydrogen chemisorption in the material. In addition, the μSR signal shows a clear transition above 150 K, compatible with a thermally activated Li cluster rearrangement. The combined Inelastic Neutron Scattering analysis suggests that tetrahedral Li clusters may undergo a progressive melting upon heating, which could favour room temperature ionic diffusion.     

Electrochemical properties of mixed cathode consisting of μm-sized LiCoO2 and nm-sized Li[Co0.1Ni0.15Li0.2Mn0.55]O2 in lithium rechargeable batteries

In order to enhance the utilization of active cathode material in lithium rechargeable batteries, physical mixtures of μm-sized LiCoO₂ (LCO) and nm-sized Li[Co_0.1Ni_0.15Li_0.2Mn_0.55]O₂ (LCMNO) were prepared by varying the LCO content, and the physical and electrochemical properties of lithium half-cells utilizing the mixed cathodes were characterized. Our main concern is the packing state between the microparticles and nanoparticles within the electrode, which influences the determination of the electrode density. We found that the electrode composed of 80 wt.% LCO and 20 wt.% LCMNO shows the best performance in capacity retention ratio and high-rate capability, which are comparable to those of LCMNO, due to the superior density in the electrode’s packing state over other samples.     

A novel layered Li [Li0.12NizMg0.32−zMn0.56]O2 cathode material for lithium-ion batteries

Layered Li[Li_0.12Ni_zMg_0.32−zMn_0.56]O₂ oxide cathodes containing lithium atoms in the transition metal layers were synthesized and characterized using X-ray diffraction (XRD), galvanostatic cycling, and differential scanning calorimetry (DSC). The Li[Li_0.12Ni_zMg_0.32−zMn_0.56]O₂ cathodes deliver a specific discharge capacity of about 190 mAh/g at room temperature and 236 mAh/g at 55 °C when cycled between 2.7 and 4.6 V versus Li/Li⁺. Excellent capacity retention and smooth potential profiles at room and elevated temperatures over extended cycles suggest that this material does not convert into a spinel structure.     

Fabrication of all-solid-state battery using Li5La3Ta2O12 ceramic electrolyte

The chemical and electrochemical properties of Li₅La₃Ta₂O₁₂ (LLTa) solid electrolyte were extensively investigated to determine its compatibility with an all-solid-state battery. A well-sintered LLTa pellet with a garnet-like structure was obtained after sintering at 1200 °C for 24 h. Li ion conductivity of the LLTa pellet was estimated to be 1.3×10⁻⁴ S cm⁻¹. The LLTa pellet was stable when in contact with lithium metal. This indicates that Li metal anode, which is the best anode material, can be applied with the LLTa system. A full cell composed of LiCoO₂/LLTa/Li configuration was constructed, and its electrochemical properties were tested. In the resulting cyclic voltammogram, a clear redox couple of LiCoO₂ was observed, implying that the all-solid-state battery with the Li metal anode was successfully operated at room temperature. The redox peaks of the battery were still observed even after one year of storage in an Ar-filled glove-box. It can be concluded that the LLTa electrolyte is a promising candidate for the all-solid-state battery because of its relatively high Li ion conductivity and good stability when in contact with Li metal anode and LiCoO₂ cathode.     

EIS study of the influence of BrCl on the behavior of electrodes in Li/SOCl<Subscript>2</Subscript> cells

The influence of BrCl on the impedance response of both the lithium anode and the carbon cathode in Li/SOCl₂ cells was studied. The impedance of the lithium anode increases with storage time while the addition of BrCl to Li/SOCl₂ cells decreases the impedance. However, the porous carbon cathode shows a small film resistance before discharge. The addition of BrCl to Li/SOCl₂ cells also decreases the impedance, especially for that part of the interface reaction resistance R₂. As a rule, the film resistance of the lithium anode decreases sharply during the early period of discharge, while that of the porous carbon cathode rises rapidly. It follows that the porous carbon cathode is the rate controlling electrode during discharge.     

Mechanism transition of cell-impedance-controlled lithium transport through Li1−δMn2O4 composite electrode caused by surface-modification and temperature variation

The mechanism transition of lithium transport through a Li_1−δMn₂O₄ composite electrode caused by the surface-modification and temperature variation was investigated using the galvanostatic intermittent titration technique (GITT), electrochemical impedance spectroscopy (EIS) and the potentiostatic current transient technique. From the analyses of the ac-impedance spectra, experimentally measured from unmodified Li_1−δMn₂O₄ and surface-modified Li_1−δMn₂O₄ with MgO composite electrodes, the internal cell resistance of the MgO-modified Li_1−δMn₂O₄ electrode was determined to be much smaller in value than that of the unmodified electrode over the whole potential range. Moreover, from the analysis of the anodic current transients measured on the MgO-modified Li_1−δMn₂O₄ electrode, it was found that the cell-impedance-controlled constraint at the electrode surface is changed to a diffusion-controlled constraint, which is characterised by a large potential step and simultaneously by a small amount of lithium transferred during lithium transport. This strongly suggests that the internal cell resistance plays a significant role in determining the cell-impedance-controlled lithium transport through the MgO-modified Li_1−δMn₂O₄ electrode. Furthermore, from the temperature dependence of the internal cell resistance and diffusion resistance in the unmodified Li_1−δMn₂O₄ composite electrode measured by GITT and EIS, it was concluded that which mechanism of lithium transport will be operative strongly depends on the diffusion resistance as well as on the internal cell resistance.     

Li6V10O28, a novel cathode material for Li-ion battery

A novel cathode material, lithium decavanadate Li₆V₁₀O₂₈ with a large tunnel within the framework structure for lithium ion battery has been prepared by hydrothermal synthesis and annealing dehydration treatment. The structure and electrochemical properties of the sample have been investigated. The novel material shows good reversibility for Li⁺ insertion/extraction and long cycle life. High discharge capacity (132 mAh/g) is obtained at 0.2 mA/cm² discharge current and potential range between 2.0 and 4.2 V versus Li⁺/Li. AC impedance of the Li/Li₆V₁₀O₂₈ cell reveals that the cathode process is controlled mainly by Li⁺ diffusion in the active material. The novel material would be a promising cathode material for Li-ion batteries.     

Influence of electrode microstructure on the reactivity of Cu2Sb with lithium

The reactivity of lithium with Cu₂Sb was recently described to be governed by displacement reactions of Cu similar to those occurring in Cu_2.33V₄O₁₁. In order to complement the earlier work of Fransson et al., we have revisited the electrochemical reactivity of Cu₂Sb with Li. Through a different arsenal of characterization techniques, we have emphasized the role of the particle size, electrode preparation and temperature on the reversibility of the electrochemical reaction. We have demonstrated that the structural reversibility of the Cu₂Sb electrode can be obtained in two special cases: (1) when the particle size of Cu₂Sb is small and when the powders are ball milled with carbon and (2) when Li₂CuSb is used as the starting material and some Sb is lost from the electrode during charge.     

Electrochemical performance of the carbon coated Li3V2(PO4)3 cathode material synthesized by a sol-gel method

A carbon coated Li₃V₂(PO₄)₃ cathode material for lithium ion batteries was synthesized by a sol-gel method using V₂O₅, H₂O₂, NH₄H₂PO₄, LiOH and citric acid as starting materials, and its physicochemical properties were investigated using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDAX), transmission electron microscope (TEM), and electrochemical methods. The sample prepared displays a monoclinic structure with a space group of P2₁/n, and its surface is covered with a rough and porous carbon layer. In the voltage range of 3.0-4.3 V, the Li₃V₂(PO₄)₃ electrode displays a large reversible capacity, good rate capability and excellent cyclic stability at both 25 and 55 °C. The largest reversible capacity of 130 mAh g⁻¹ was obtained at 0.1C and 55 °C, nearly equivalent to the reversible cycling of two lithium ions per Li₃V₂(PO₄)₃ formula unit (133 mAh g⁻¹). It was found that the increase in total carbon content can improve the discharge performance of the Li₃V₂(PO₄)₃ electrode. In the voltage range of 3.0-4.8 V, the extraction and reinsertion of the third lithium ion in the carbon coated Li₃V₂(PO₄)₃ host are almost reversible, exhibiting a reversible capacity of 177 mAh g⁻¹ and good cyclic performance. The reasons for the excellent electrochemical performance of the carbon coated Li₃V₂(PO₄)₃ cathode material were also discussed.