Cellulose-based carbon—A potential anode material for lithium-ion battery

A series of hard carbons was produced by the carbonization of microcrystalline cellulose powder in the temperature range of 950–1100 °C. The properties of the carbons were characterized using elemental analysis, X-ray diffraction and N₂ and CO₂ adsorption. The effect of heat-treatment temperature (HTT), pyrolytic carbon (PC) coating and discharging mode on the lithium insertion/deinsertion behavior of the carbons was assessed in a coin-type half-cell with metal lithium cathode. Increasing cellulose HTT modifies mostly carbon porosity, the surface area (S_DFT) decreases from about 500 to 167 m² g⁻¹. It is associated with lowering the reversible C_rev and irreversible C_irr capacities, but without improving relatively low (0.72) 1st cycle coulombic efficiency. Applying constant current (CC)+constant voltage (CV) discharging mode instead of conventional CC enhances the reversible capacity by 15–18%. PC coating is effective in reducing C_irr by ∼20% with a little change of C_rev. The best capacity parameters, C_rev of 458 mA h g⁻¹ and C_irr of 139 mA h g⁻¹, were measured for PC coated 1000 °C carbon. The prolonged cycling of full-cell assembled with anode of the carbon and commercial cathode revealed that after initial 20 cycles the capacity decay (0.029 mA h/cycle) is comparable to that of commercial cell with graphite-based anode.     

Synthesis and characterization of layered Li1−x(Ni0.5Co0.5)1−yFeyO2(0 ≤ (1 − x) ≤ 1 and 0 ≤ y ≤ 0.2) cathodes

Layered Li(Ni_0.5Co_0.5)_1−yFe_yO₂ cathodes with 0 ≤ y ≤ 0.2 have been synthesized by firing the coprecipitated hydroxides of the transition metals and lithium hydroxide at 700 °C and characterized as cathode materials for lithium ion batteries to various cutoff charge voltages (up to 4.5 V). While the y = 0.05 sample shows an improvement in capacity, cyclability, and rate capability, those with y = 0.1 and 0.2 exhibit a decline in electrochemical performance compared to the y = 0 sample. Structural characterization of the chemically delithiated Li_1−x(Ni_0.5Co_0.5)_1−yFe_yO₂ samples indicates that the initial O3 structure is maintained down to a lithium content (1 − x) ≈ 0.3. For (1 − x) < 0.3, while a P3 type phase is formed for the y = 0 sample, an O1 type phase is formed for the y = 0.05, 0.1 and 0.2 samples. Monitoring the average oxidation state of the transition metal ions with lithium contents (1 − x) reveals that the system is chemically more stable down to a lower lithium content (1 − x) ≈ 0.3 compared to the Li_1−xCoO₂ system. The improved structural and chemical stabilities appear to lead to better cyclability to higher cutoff charge voltages compared to that found before with the LiCoO₂ system.     

Structural and electrochemical properties of layered lithium nitridocuprates Li3 − xCuxN

We report a systematic study of the layered lithium nitridocuprates Li_3 ? xCu_xN with 0.1 ≤ x ≤ 0.39. The structural data obtained from experimental XRD patterns, Rietveld refinements and unit cell parameters calculation vs x, indicate that copper (I) substitute interlayer lithium ions in the parent nitride Li₃N to form the Li_3 ? xCu_xN compound without any Li vacancy in the Li₂N^? layer. Electrochemical results report Li insertion into the corresponding layered structures cannot take place in the 1.2/0.02 V voltage range as in the case of lithium into nitridonickelates and nitridocobaltates. However, in the initial charge process of Li_3 ? xCu_xN at 1.4 V leading to a specific capacity higher than 1000 mA h/g, the oxidation of copper and nitride ions is probably involved inducing a strong structural disordering process. As a consequence a new rechargeable electrochemical system characterized by discharge–charge potential of ≈ 0.3 V/1.2 V appears from the second cycle. Cycling experiments 0.02 V voltage/0.02 V range induce a complete destruction of the layered host lattice and the presence of Cu₃N in the charge state suggests a conversion reaction. The capacity recovered in the 1.4/0.02 V range practically stabilizes around 500 mA h/g after 20 cycles.     

Structural and electrochemical properties of 20-micron Li(Co1−xLix)O2−δ (x>0) agglomerates with layered structures: Identification of tetravalent cobalt

The increasing demand for the high energy density of lithium-ion batteries gives rise to the development of larger particle sizes of the active electrode materials. 20 μm-sized Li(Co_1−xLi_x)O_2−δ agglomerates are synthesized via solid-state reactions with different nominal compositions (Li/Co=1.00, 1.02, and 1.05) at 1000 °C for 5 h in ambient air while suppressing the lithium vaporization. Careful inductively coupled plasma and iodometric measurements indicate the existence of tetravalent cobalt in the solid solutions (x>0). The decreasing ideal capacity with the increasing x value could cause the resulting initial capacities at under a quasi-equilibrium condition. The defect structure is also discussed in terms of the structural parameters calculated from Rietveld refinements of the high-energy synchrotron-radiation powder-diffraction data.     

Preparation of carbon nanoparticles from electrolysis of molten carbonates and use as anode materials in lithium-ion batteries

The electrochemical reduction of molten Li–Na–K carbonates at 450 °C provides “quasi-spherical” carbon nanoparticles with size comprised between 40 and 80 nm (deduced from AFM measurements). XRD analyses performed after washing and heat-treatment at various temperatures have revealed the presence of graphitised and amorphous phases. The d₀₀₂ values were close to the ideal one obtained for pure graphite. Raman spectroscopy has pointed out surface disordering which increases with increasing temperature of the heat-treatment. The presence of Na and Li on the surface of the carbon powder has been evidenced by SIMS. The maximum Na and Li contents were observed for carbon samples heat-treated at 400 °C. Their electrochemical performances vs. the insertion/deinsertion of lithium cations were studied in 1 M LiPF₆–EC : DEC : DMC (2 : 1 : 2). The first charge–discharge cycle is characterised by a high irreversible capacity as in the case of hard-disordered carbon materials. However, the potential profile in galvanostatic mode is intermediate between that usually observed for graphite and amorphous carbon: rather continuous charge–discharge curves sloping between 1.5 and 0.3 V vs. Li / Li⁺, and successive phase transformations between 0.3 and 0.02 V vs. Li / Li⁺. The best electrochemical performances were obtained with carbon powders heat-treated at 400 °C which exhibits a reversible capacity value of 1080 mAh g^− 1 (composition of Li_2.9C₆). This sample has also both the lowest surface disordering (deduced from Raman spectroscopy), and the highest Na and Li surface contents (deduced from SIMS).     

Carbon and transition metal containing titanium phosphates as electrodes for lithium ion batteries

We prepared transition metal containing titanium phosphates obtained from mesoporous titanium phosphate treated with cobalt and copper acetates and subsequently heated at 573 K under either air or nitrogen atmospheres. The first treatment with acetates incorporates the metal and acetate ions in the system. Moreover, it partially extracts the director agent. Total extraction of the surfactant can be reached in the copper samples after heating twice. However, the surfactant is not removed from the cobalt samples under the thermal conditions therein used. The composition of the heated materials is close to NASICON structures with a formula close to M_1.5Ti_1.5(PO₄)₃ (M = Co,Cu). A certain content in elemental carbon is observed in the samples obtained under nitrogen atmosphere, which are also more conductive than those prepared under air. The first discharge of lithium cells based in these mesoporous materials show electrochemical activity of Ti⁴⁺/Ti³⁺, Co²⁺/Co⁰ and Cu²⁺/Cu⁰ couples in the OCV–1.0 V region. Below this voltage, the discharge profiles are typical of phosphate systems where Li₃PO₄ is a product of the electrochemical reaction with lithium and, moreover, electrolyte solvent is reduced. Electrolyte is more degraded when the samples contain carbon. Capacities as high as 1600 mA h g^− 1 can be obtained at deep discharge. However, there is an irreversible capacity loss in the four systems due to the occurrence of insulating products as Li₃PO₄ and a solid electrolyte interface.     

Effects of Ca doping on the electrochemical properties of LiNi0.8Co0.2O2 cathode material

LiNi_0.8Co_0.2O₂ and Ca-doped LiNi_0.8Co_0.2O₂ cathode materials were synthesized via a rheological phase reaction method. It is found that the Ca doping significantly improves reversible capacity, cycling performance, thermal stability and rate capability. The Ca-doped LiNi_0.8Co_0.2O₂ cathode material maintains nearly its initial discharge capacity up to 100 cycles at room temperature. It also delivers an initial discharge capacity of 183 mA h g^− 1 and still keeps 131 mA h g^− 1 even after 120 cycles at 60 °C. These results, together with the X-ray diffraction and electrochemical impedance spectroscopy analysis, reveal that Ca²⁺ ions occupy Li⁺ ion sites to form Ca_Li defects and lithium vacancies (V_Li′), which reduce the resistance and increases conductivity of LiNi_0.8Co_0.2O₂.     

Effect of composition change of metals in transition metal sites on electrochemical behavior of layered Li[Co1 −2x(Li1 / 3Mn2 / 3)x(Ni1 / 2Mn1 / 2)x]O2 solid solutions

Five compositions of Li[Co_1 −2x(Li_1 / 3Mn_2 / 3)_x(Ni_1 / 2Mn_1 / 2)_x]O₂ solid solutions ( x = 0.1, 0.2, 0.3, 0.4, and 0.5) were synthesized using a sol–gel method with three end members of LiCoO₂, Li₂MnO₃(Li[Li_1 / 3Mn_2 / 3]O₂), and Li[Ni_0.5Mn_0.5]O₂. The compositions of metals in transition metal sites were changed to see the effect of them on electrochemical behavior of the solid solutions. All the samples were nano-sized semi-spherical shaped particles with a layered structure. The reduction of cobalt content (the increase of other metals) in the sites increases the lattice parameters, a and c, resulting in the shift of Raman and XRD peak positions. The discharge capacity fading turned serious at higher Co contents, but it was significantly diminished with the decrease of Co content. At lower Co contents, the capacity increased with cycle numbers. The most stable voltage profile was obtained from the composition of Li[Li_1 / 15Co_3 / 5Ni_1 / 10Mn_7 / 30]O₂ (x = 0.2).     

The study of novel multi-doped spinel Li1.15Mn1.96Co0.03Gd0.01O4 + δ as cathode material for Li-ion rechargeable batteries

Novel spinel Li_1.15Mn_1.96Co_0.03Gd_0.01O_4 + δ was synthesized by high temperature solid-state reaction method. The product was identified as well-defined spinel phase by X-ray diffraction (XRD); the SEM images illustrated that the particle distribution was well-proportioned. The initial special capacity was 126.5 and 128.1 mAh g^? 1 at 25 and 50 °C. The fading rate was 0.017% and 0.098% per cycle under 0.5 °C at 25 and 50 °C, respectively. The results showed that Li_1.15Mn_1.96Co_0.03Gd_0.01O_4 + δ displayed excellent capacity and cycleability.     

Effects of Li2CO3 as a secondary lithium source on the LiFePO4/C composites prepared via solid-state method

Li₂CO₃ was used as the secondary lithium source for the synthesis of LiFePO₄/C composites via a solid-state reaction method by adopting Li₃PO₄ as the main lithium source. The main purpose of using Li₂CO₃ is to compensate for the partial lithium loss during the sintering while reducing the usage of excess Li₃PO₄. In this study, the effects of Li₂CO₃ amount on the phase, structural and electrochemical properties of LiFePO₄/C material were systematically investigated. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), constant-current charge–discharge test and cyclic voltammetry (CV). The results showed that by adding an appropriate amount of Li₂CO₃, the impurities, e.g. Li₃PO₄, normally appearing in the final product, could be excluded. It was found that LiFePO₄/C with Li₂CO₃ in 6% excess (vs. stoichiometric LiFePO₄) exhibited the best electrochemical performance, which delivered initial discharge capacities of 141.7, 125.2, 119.9 and 108.9 mAh g^?1, respectively, at 0.5, 1, 2 and 5C rates. The capacity was reduced to 113.4 mAh g^?1 after 50 cycles at 2C rate, with capacity retention rate of 94.6%.     

The studies on structural and thermal properties of delithiated LixNi1/3Co1/3Mn1/3O2 (0 < x ≤ 1) as a cathode material in lithium ion batteries

The structural and thermal properties of the delithiated Li_xNi_1/3Co_1/3Mn_1/3O₂ (0 < x ≤ 1) material have been investigated by using diffraction and thermoanalytical techniques such as XRD and TG-DSC methods. XRD result shows that the delithiated materials maintain the O3-type structure with defined stoichiometric number at the range of 0.24 < x ≤ 1, exhibiting good crystal structural stability. The cobalt and nickel ions in the delithiated materials change their valence state (i.e. Co³⁺ to Co⁴⁺ and Ni³⁺ to Ni⁴⁺) when x < 0.49; the irreversible changes of the transformation may affect the first cycle of charge–discharge efficiency of the materials. A comparison of the results of TG-DSC with TPD-MS shows that the irreversible change of oxygen species during the delithiation process of Li_xNi_1/3Co_1/3Mn_1/3O₂ have great influence on the structural and thermal stability and reversibility of the materials.     

Thermodynamic analysis and experimental research on Li intercalation reactions of the intermetallic compound Al2Cu

The lithiation mechanism of the intermetallic compound Al₂Cu as anode materials for lithium-ion batteries during lithium intercalation/deintercalation was studied in this paper. The Gibbs free energy changes for five possible electrochemical reactions of Li intercalated into Al₂Cu electrode have been calculated based on the first-principles plane-wave pseudopotential method in conjunction with thermodynamic principles. The reaction Li + Al₂Cu → LiAl + AlCu that possesses the most negative value of the Gibbs free energy change per unit lithium on average among all the five reactions was claimed to be the lithiation mechanism of Al₂Cu electrode. In order to warrant the speculation, the 2032-type coin cells with Al₂Cu and lithium metal as the testing and the counter electrode, respectively, was assembled. The electrochemical performance of the cells and the phase changes in Al₂Cu electrode were examined. Finally, it is found that the experimental results were consistent with the calculated ones, indicating that the first-principles calculations can be used to investigate the lithiation mechanism of the intermetallic compounds.     

UV–visible absorption spectrum determination of optical energy gaps of α and β lithium nitrides

It is well known that a high pressure can induce α–β phase transformation of lithium nitride (Li₃N). However, this work demonstrated that a reverse phase transformation of Li₃N from β to α could occur when it was subjected to heat-treatment at 500 °C in vacuum. Furthermore, the optical properties of α and β lithium nitrides were evaluated by UV–visible spectra. The optical energy gaps (E_g) of α and β lithium nitrides, which were determined from the derivative UV–visible spectra, are 1.81±0.01 and 2.14±0.01 eV, respectively.     

Li4Ti5O12/Ag composite as electrode materials for lithium-ion battery

The Li₄Ti₅O₁₂/Ag composites were prepared by thermal decomposition of AgNO₃ added to Li₄Ti₅O₁₂ powders. The influence of the Ag contents and the mixing media on the particle size, morphology and electrochemical performance of Li₄Ti₅O₁₂/Ag composites were investigated. The highest discharge capacity of the Li₄Ti₅O₁₂/Ag composite reached at the 5 wt.% of Ag content. Compared with alcohol medium, distilled water as mixing medium presented the Li₄Ti₅O₁₂/Ag composite with higher specific capacity and better cycling performance, leading to a reversible capacity after 50 cycles of 184.2 mAh/g with a capacity degradation of 3.31% compared to the second cycle at 2 C rate.     

Correlation between Li+ adsorption capacity and the preparation conditions of spinel lithium manganese precursor

Spinel lithium manganese oxides can be used as Li⁺ adsorbent with topotactical extraction of lithium. In this paper, the solid state methods were introduced to prepare spinel lithium manganese precursors with Li₂CO₃ and LiOH·H₂O as different Li sources. The Li⁺ uptake was studied to clarify the correction between Li⁺ adsorption capacity and the preparation conditions of precursors, including different Li sources, Li/Mn mole ratios and heating time. The results indicated that the Li⁺-extracted materials prepared with LiOH·H₂O and MnCO₃ usually have higher Li⁺ adsorption capacity than Li₂CO₃ and MnCO₃, and an ascending trend was found in Li⁺ uptake with increasing Li/Mn mole ratio in the preparation of the precursor, but it is not proportional. The Mn₂O₃ impurities could be the primary reason for decreasing Li⁺ adsorption capacity. Furthermore, it is concluded that the Li⁺-extracted materials obtained from spinel manganese oxides synthesized with Li/Mn = 1.0 can serve as selective Li⁺ absorbents due to its high selectivity and large adsorption capacity.     

Development and application of combinatorial electrostatic atomization system “M-ist Combi”: High-throughput preparation of electrode materials

We introduce a newly developed combinatorial electrostatic atomization system, “M-ist Combi,” and demonstrate the effectiveness of the system by establishing a pseudo-ternary Li–Ni–Co oxide phase diagram. After heating the starting materials with compositions in the range of 0.4 ≤ Li / (Li + Ni + Co) ≤ 0.6 at 973 K for 3 h, the diffraction of all of the products was indexed as single-phase with layer-type hexagonal structures such as LiCoO₂ and LiNiO₂. As the substitution quantity of Co to the Ni site increased, the value of 2θ shifted to a high-angle. By combining the M-ist Combi system with combinatorial XRD apparatus, we successfully completed the high-throughput sample preparation and phase identification of over 150 samples in one day.     

Lithium-ionic diffusion and electrical conduction in the Li7La3Ta2O13 compounds

The electrical properties and the mechanism of lithium ionic diffusion in the Li₇La₃Ta₂O₁₃ compounds were investigated. The bulk and total conductivity at 300 K of the Li₇La₃Ta₂O₁₃ compound are about 3.3 × 10^? 6 S/cm and 2.6 × 10^? 6 S/cm, respectively. The activation energy of bulk and total conductivity is in the range of 0.38–0.4 eV. A prominent internal friction peak in Li₇La₃Ta₂O₁₃ compounds was observed around 280 K at 0.5 Hz, which is actually composed of two subpeaks (P₁ peak at lower temperature and P₂ peak at higher temperature). From the shift of peak position with frequency, the activation energy of 1.0 eV and the pre-exponential factor of relaxation time in the order of 10^? 18–10^? 21 s were obtained if one assumes Debye relaxation processes. These values of relaxation parameters strongly suggest the existence of interaction between the relaxation species (here lithium ions or vacancies). Based on the coupling model, the relaxation activation energies are deduced as 0.45 eV and the pre-exponential factor of relaxation time as 10^? 15 s. Judging from these relaxation parameters and the similarity of structure between Li₇La₃Ta₂O₁₃ and Li₅La₃Ta₂O₁₂ compounds, the P₁ and P₂ peaks are suggested to be related with the lithium ionic diffusion between 48g?48g and 24d?48g.     

First-principles study of C3N nanoribbons as anode materials for Li-ion batteries

The potential of C₃N nanoribbons used as anode material for lithium-ion batteries has been systematically investigated through first-principles calculations. The results suggest that C₃N nanoribbons have excellent mechanical properties (stiffness ranging from 286.28 to 412.69 N m⁻¹) and good electronic conductivity (with a bandgap of 0-0.31 eV). Further studies reveal that the H-passivated C₃N nanoribbons have high Li insertion capacity (708.60 mA h g⁻¹) and significantly enhanced Li binding strength (0.21-2.11 eV) without the sacrifice of Li mobility. The high stiffness, superior cycle performance, good electronic conductivity, and excellent Li migration capability indicate the great potential of C₃N nanoribbons to be an anode material. The calculated results provide the valuable insights for the development of high-performance C₃N nanoribbons electrode materials in lithium-ion batteries.     

Studies on the percolation limit of Ce0.9Gd0.1O1.95 in La0.6Sr0.4Co0.2Fe0.8O3−δ–Ce0.9Gd0.1O1.95 nanocomposites for solid oxide fuel cells application

A large difference in thermal expansion coefficient of electrode and electrolyte leads to imperfect electrode/electrolyte interface and hence significant polarization losses in solid oxide fuel cells. To overcome the difficulties associated with electrode and electrode/electrolyte interface, there is need to fabricate the composite cathode. Thus the present paper deals with study of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ(LSCF)–Ce_0.9Gd_0.1O_1.95(GDC) nanocomposite with different fractions of GDC obtained by physical mixing of combustion synthesized nanopowders. No secondary phases were observed upon sintering at 1100 °C for 2 h affirming the chemical compatibility between LSCF and GDC. The composites with relatively high GDC% have higher density as a consequence of rapid grain growth and less conductivity. The nanocomposite with 50% of GDC showed electric conductivity of 30 Scm⁻¹ at 500 °C and low area specific resistance of 106 Ω cm² with 10 μs relaxation time at 200 °C.     

Determination of the diffusion coefficient of lithium ions in nano-Si

The diffusion coefficients of lithium ions (D_Li⁺) in nano-Si were determined by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT). D_Li⁺ values are estimated to be ~ 10^? 12 cm² s^? 1 and exhibit a “W” type varying with the lithium concentration in silicon. Two minimum regions of D_Li⁺ (at Li_2.1 ± 0.2Si and Li_3.2 ± 0.2Si) are found, which probably result from two amorphous compositions (a-Li₇Si₃ and a-Li₁₃Si₄). Besides the two minimum regions, one maximum D_Li⁺ is observed at Li₁₅Si₄, corresponding to the crystallization of highly lithiated amorphous Li_xSi.