In situ lithiation of TiS2 enabled by spontaneous decomposition of Li3N

We report on a novel method for in situ lithiation of lithium free TiS₂ using Li₃N in an all-solid-state battery configuration. This method was tested using a Li₃N-TiS₂-80Li₂S:20P₂S₅ composite positive electrode and an indium metal negative electrode. It is shown that approximately 37% of Li₃N spontaneously decomposes during composite preparation regardless of the composition. Solid-state battery cells built with a 3:1 stoichiometric ratio of Li:Ti demonstrated a high 1st cycle charge capacity of 287 mAh g⁻¹, 20% greater than the theoretical capacity of TiS₂ at 239 mAh g⁻¹. The difference provides an excess capacity in the indium metal negative electrode.     

Gallium (III) sulfide as an active material in lithium secondary batteries

In an attempt to identify an active material for use in lithium secondary batteries with high energy density, we investigated the electrochemical properties of gallium (III) sulfide (Ga₂S₃) at 30 °C. Ga₂S₃ shows two sloping plateaus in the potential range between 0.01 V and 2.0 V vs. (Li/Li⁺). The specific capacity of the Ga₂S₃ electrode in the first delithiation is ca. 920 mAh g⁻¹, which corresponds to 81% of the theoretical capacity (assuming a 10-electron reaction). The capacity in the 10th cycle is 63% of the initial capacity. Ex situ X-ray diffraction and X-ray absorption fine structure analyses revealed that the reaction of the Ga₂S₃ electrode proceeds in two steps: Ga₂S₃ + 6Li⁺ + 6e⁻ ? 2Ga + 3Li₂S and Ga + xLi⁺ + xe⁻ ? Li_xGa.     

Formation of the high lithium ion conducting phase from mechanically milled amorphous Li2S-P2S5 system

The fast ionic conducting structure similar to thio-Lithium Super Ionic Conductor (LISICON) phase is synthesized in the Li₂S-P₂S₅ system. The Li₂S-P₂S₅ glass-ceramics with the composition of xLi₂S·(100−x)P₂S₅ (75 ≤ x ≤ 80) are prepared by the heat-treatment of mechanically milled amorphous sulfide powders. In the binary Li₂S-P₂S₅ system, 78.3Li₂S·21.7P₂S₅ glass ceramic prepared by mechanical milling and subsequent heat-treatment at 260 °C for 3 h shows the highest conductivity of 6.3 × 10⁻⁴ S cm⁻¹ at room temperature and the lowest activation energy for conduction of 30.5 kJ mol⁻¹. The enhancement of conductivity with increasing x up to 78.3 is probably caused by the introduction of interstitial lithium ions at the Li sites which affects the Li ion distribution. The prepared electrolyte exhibits the lithium ion transport number of almost unity and voltage stability of 5 V vs. Li at room temperature.     

Mechanism of lithium storage in Si-O-C composite anodes

A Si-O-C composite material is prepared by pyrolyzing a copolymer of phenyl-substituted polysiloxane and divinylbenzene at 800 °C under a hydrogen atmosphere. The material has a high delithiation capacity about 965.3 mA h g⁻¹ in the first cycle and retains 660 mA h g⁻¹ after 40 cycles at 50 mA g⁻¹. The differential capacity curves of the anode show that there are several reduction peaks between 0.2 and 0.6 V existing all the time during repeated cycles. By comparing ²⁹Si nuclear magnetic resonance (²⁹Si MAS NMR), Si (2p) X-ray photoelectron spectroscopy (XPS) of the anode in the original, fully lithiated, and fully delithiated state, the reduction peaks are related to lithium reversible insertion into SiO₂C₂, SiO₃C, and SiO₄ units, respectively. The corresponding ²⁹Si MAS NMR resonances shift to high field and their binding energies of the Si (2p) XPS peak increase in the fully lithiated state, and then both turn to the opposite direction in the fully delithiated state. The SiO₄ units decrease during repeated cycles. The remaining ones can reversibly transform to Li-silicate (Li₂SiO₃) when lithium is inserted, while the lost ones irreversibly transform to Li-silicate (Li₄SiO₄). However, the SiOC₃ units of the material are totally irreversible with lithium because they nearly disappear in the first discharge process, and lead to the formation SiC₄ units.     

Preparation of electrochemically active lithium sulfide-carbon composites using spark-plasma-sintering process

Electrochemically active lithium sulfide-carbon (Li₂S-C) composite positive electrodes, applicable for rechargeable lithium-ion batteries, were prepared using spark-plasma-sintering (SPS) process. The electrochemical tests demonstrated that the SPS-treated Li₂S-C composites showed the initial charge and discharge capacities of ca. 1200 and 200 mAh g⁻¹, respectively, though Li₂S has been reported to show no significant charge capacities when conventionally mixed with carbon powder. Such activation of Li₂S was attributed principally to strong bindings between Li₂S and carbon powders, formed by the SPS treatment. The ex situ XRD measurements showed that some amounts of Li₂S were still remained unchanged and any elemental sulfur was not detected even at fully charged state, which was similar to Li/S cells.     

NiSb2 as negative electrode for Li-ion batteries: An original conversion reaction

The study of the electrochemical reaction mechanism of lithium with NiSb₂ intermetallic material is reported here. The nickel diantimonide prepared by classic ceramic route is proposed as possible candidate for anodic applications in Li-ion batteries. The electrochemical characterisation of NiSb₂ versus Li⁺/Li⁰ shows a reversible uptake of 5 lithium per formula unit, which leads to reversible capacities of 500 mAh g⁻¹ at an average potential of 0.9 V. From ex situ XRD and ¹²¹Sb Mössbauer measurements it was shown that during the first discharge the orthorhombic NiSb₂ phase undergoes a pure conversion process (NiSb₂ + 6 Li⁺ + 6e⁻ → Ni⁰ + 2Li₃Sb). During the charge process that follows, the lithium extraction from the composite electrode takes place through an original conversion process, leading to the formation of the high pressure NiSb₂ polymorph. This highly reversible mechanism makes it possible to sustain 100% of the specific capacity after 15 cycles.     

Electrochemical characteristics of aluminum sulfide for use in lithium secondary batteries

In our effect to develop a lithium secondary battery with high energy density, aluminum sulfide (Al₂S₃) was studied for use as an active material. The measured initial discharge capacity of Al₂S₃ was ca. 1170 mAh g⁻¹ at 100 mA g⁻¹. This corresponds to 62% of the theoretical capacity for the sulfide. Al₂S₃ exhibited poor capacity retention in the potential range between 0.01 V and 2.0 V, mainly due to the structural irreversibility of the charge process or Li extraction. XRD and Al and S K-XANES analyses indicated that the surface of Al₂S₃ reacts reversibly during charge and discharge processes, while the core of Al₂S₃ showed structural irreversibility because LiAl and Li₂S were formed from Al₂S₃ at the initial discharge and remained as they were afterward.     

Al-doped Li7La3Zr2O12 synthesized by a polymerized complex method

Li₇La₃Zr₂O₁₂ electrolytes doped with different amounts of Al (0, 0.2, 0.7, 1.2, and 2.5 wt.%) were prepared by a polymerized complex (Pechini) method. The influence of aluminum on the structure and conductivity of Li₇La₃Zr₂O₁₂ were investigated by X-ray diffraction (XRD), impedance spectroscopy, scanning electron microscopy (SEM), and thermal dilatometry. It was found that even a small amount of Al (e.g. 0.2 wt.%) added to Li₇La₃Zr₂O₁₂ can greatly accelerate densification during the sintering process. SEM micrographs showed the existence of a liquid phase introduced by Al additions which led to the enhanced sintering rate. The addition of Al also stabilized the higher conductivity cubic form of Li₇La₃Zr₂O₁₂ rather than the less conductive tetragonal form. The combination of these two beneficial effects of Al enabled greatly reduced sintering times for preparation of highly conductive Li₇La₃Zr₂O₁₂ electrolyte. With optimal additions of Al (e.g. 1.2 wt.%), Li₇La₃Zr₂O₁₂ electrolyte sintered at 1200 °C for only 6 h showed an ionic conductivity of 2.0 × 10⁻⁴ S cm⁻¹ at room temperature.     

Rechargeable lithium sulfide electrode for a polymer tin/sulfur lithium-ion battery

In this work we investigate the electrochemical behavior of a new type of carbon-lithium sulfide composite electrode. Results based on cyclic voltammetry, charge (lithium removal)-discharge (lithium acceptance) demonstrate that this electrode has a good performance in terms of reversibility, cycle life and coulombic efficiency. XRD analysis performed in situ in a lithium cell shows that lithium sulfide can be converted into sulfur during charge and re-converted back into sulfide during the following discharge process. We also show that this electrochemical process can be efficiently carried out in polymer electrolyte lithium cells and thus, that the Li₂S-C composite can be successfully used as cathode for the development of novel types of rechargeable lithium-ion sulfur batteries where the reactive and unsafe lithium metal anode is replaced by a reliable, high capacity tin-carbon composite and the unstable organic electrolyte solution is replaced by a composite gel polymer membrane that is safe, highly conductive and able to control dendrite growth across the cell. This new Sn-C/Li₂S polymer battery operates with a capacity of 600 mAh g⁻¹ and with an average voltage of 2 V, this leading to a value of energy density amounting to 1200 Wh kg⁻¹.     

The reactions in LiBH4-NaNH2 hydrogen storage system

Stepwise reactions were observed in the ball milling and heating process of the LiBH₄-NaNH₂ system by means of X-ray diffraction (XRD) and Fourier transform infrared spectrometry (FT-IR). During the ball milling process, two concurrent reactions take place in the mixture: 3LiBH₄ + 4NaNH₂ → Li₃Na(NH₂)₄ + 3NaBH₄ and LiBH₄ + NaNH₂ → LiNH₂ + NaBH₄. The heating process from 50 °C to 400 °C is mainly the concurrent reactions of Li₃Na(NH₂)₄ + 3LiBH₄ → 2Li₃BN₂ + NaBH₄ + 8H₂ and 2LiNH₂ + LiBH₄ → Li₃BN₂H₈ → Li₃BN₂ + 4H₂, where the intermediate phases Li₃Na(NH₂)₄ and LiNH₂ serve as the reagents to decompose LiBH₄. The merged equations for the mechanochemical and the heating reactions below 400 °C can be denoted as 3LiBH₄ + 2NaNH₂ → Li₃BN₂ + 2NaBH₄ + 4H₂. The maximum dehydrogenation capacity in closed system below 400 °C is 5.1 wt.% H₂, which agrees well with the theoretical capacity (5.5 wt.% H₂) of the merged equation and thus demonstrates the suggested pathway. The subsequent step consists of the decompositions of NaBH₄ and Li₃Na(NH₂)₄ within the temperature range of 400 °C-600 °C. The apparent activation energies of the two steps are 114.8 and 123.5 kJ/mol, respectively. They are all lower than that of our previously obtained bulk LiBH₄.     

Mixed-metal Li3N-based systems for hydrogen storage: Li3AlN2 and Li3FeN2

The hydrogen storage systems Li₃AlN₂ and Li₃FeN₂ were synthesized mechanochemically by two different routes. In each case an intermediate material formed after milling, which transformed into Li₃MN₂ (M = Al or Fe) upon annealing. The synthesis route had a measurable effect on the hydrogen storage properties of the material: Li₃AlN₂ prepared from hydrogenous starting materials (LiNH₂ and LiAlH₄) performed better than that synthesized from non-hydrogenous materials (Li₃N and AlN). For both Li₃AlN₂ materials, the hydrogen storage capacity and the absorption kinetics improved significantly upon cycling. Ti-doped Li₃AlN₂ synthesized from LiNH₂ and LiAlH₄ showed the best hydrogen storage characteristics of all, with the best kinetics for hydrogen uptake and release, and the highest hydrogen storage capacity of 3.2 wt.%, of which about half was reversible. Meanwhile, Li₃FeN₂ synthesized from Li₃N and Fe displayed similar kinetics to that synthesized from Li₃N and Fe_xN (2 ≤ x ≤ 4), but demonstrated lower gravimetric hydrogen storage capacities. Li₃FeN₂ displayed a hydrogen uptake capacity of 2.7 wt.%, of which about 1.5 wt.% was reversible. For both Li₃AlN₂ and Li₃FeN₂, doping with TiCl₃ resulted in enhancement of hydrogen absorption kinetics. This represents the first study of a ternary lithium-transition metal nitride system for hydrogen storage.     

High-rate cathodes based on Li3V2(PO4)3 nanobelts prepared via surfactant-assisted fabrication

In this work, we have synthesized monoclinic Li₃V₂(PO₄)₃ nanobelts via a single-step, solid-state reaction process in a molten hydrocarbon. The as-prepared Li₃V₂(PO₄)₃ nanoparticles have a unique nanobelt shape and are ∼50-nm thick. When cycled in a voltage range between 3.0 V and 4.3 V at a 1C rate, these unique Li₃V₂(PO₄)₃ nanobelts demonstrate a specific discharge capacity of 131 mAh g⁻¹ (which is close to the theoretical capacity of 132 mAh g⁻¹) and stable cycling characteristics.     

Synthesis and electrochemical properties of Li1−xFe0.8Ni0.2O2–LixMnO2 (Mn/(Fe + Ni + Mn) = 0.8) material

A new type of Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ (Mn/(Fe + Ni + Mn) = 0.8) material was synthesized at 350 °C in air atmosphere using a solid-state reaction. The material had an XRD pattern that closely resembled that of the original Li_1−xFeO₂–Li_xMnO₂ (Mn/(Fe + Mn) = 0.8) with much reduced impurity peaks. The Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell showed a high initial discharge capacity above 192 mAh g⁻¹, which was higher than that of the parent Li/Li_1−xFeO₂–Li_xMnO₂ (186 mAh g⁻¹). We expected that the increase of initial discharge capacity and the change of shape of discharge curve for the Li/Li_1−xFe_0.8Ni_0.2O₂–Li_xMnO₂ cell is the result from the redox reaction from Ni²⁺ to Ni³⁺ during charge/discharge process. This cell exhibited not only a typical voltage plateau in the 2.8 V region, but also an excellent cycle retention rate (96%) up to 45 cycles.     

Li2MSiO4 (M = Fe and/or Mn) cathode materials

Two iso-structural end members of the family of orthosilicates, i.e. Li₂MSiO₄ (M = Mn and Fe) and their solid solutions, were prepared and electrochemically characterized for potential use in Li-ion batteries. Due to the low specific conductivity (∼5 × 10⁻¹⁶ S cm⁻¹ for Li₂MnSiO₄ and ∼6 × 10⁻¹⁴ S cm⁻¹ for Li₂FeSiO₄ at room temperature), small particles in an intimate contact with a conducting phase (i.e. carbon) are needed. Li₂MSiO₄/C composites (M = Mn and/or Fe) prepared by the Pechini synthesis generally leads to 30–50 nm large particles embedded in a carbon matrix. The amount of carbon in the composite is close to 10 wt.% for the Li₂FeSiO₄/C composite and slightly more than 5 wt.% for the Li₂MnSiO₄/C composite. In situ XRD experiment confirms a structural collapse of Li₂MnSiO₄ and the observed structural stability is completely different for Li₂FeSiO₄, which undergoes a fully reversible two-phase transition. Solid solutions between Li₂MnSiO₄ and Li₂FeSiO₄ in principle lead to higher capacities (>1e⁻ per transition metal is feasible). For a long-term operation the cut-off voltage should be properly chosen. Electrochemical characterisation and in situ XRD experiments suggest the use of cut-off voltage close to 4.2 V.     

Synthesis and characterization of Li3V(2 − 2x/3)Mgx(PO4)3/C cathode material for lithium-ion batteries

Li₃V_{(2 − 2x/3)}Mg_x(PO₄)₃/C (x = 0, 0.15, 0.30, 0.45) composites have been synthesized by the sol-gel assisted solid state method, using adipic acid C₆H₁₀O₄ (hexanedioic acid) as carbon source. The particle size of the composites is ∼1 μm. During the pyrolysis process, Li₃V_{(2 − 2x/3)}Mg_x(PO₄)₃/C network structure is formed. The effect of Mg²⁺ doped on the electrochemical properties of Li₃V₂(PO₄)₃/C positive materials has been studied. Li₃V_1.8Mg_0.30(PO₄)₃/C as the cathode materials of Li-ion batteries, the retention rate of discharge capacity is 91.4% (1 C) after 100 cycles. Compared with Li₃V₂(PO₄)₃/C, Li₃V_{(2 − 2x/3)}Mg_x(PO₄)₃/C composites have shown enhanced capacity and retention rate capability. The long-term cycles and ex situ XRD tests disclose that Li₃V_1.8Mg_0.30(PO₄)₃ exhibits higher structural stability than the undoped system.     

First-principles modelling of lithium iron oxides as battery cathode materials

Starting from published charge/discharge curves and X-ray data on Pmmn-LiFeO₂ and LiFe₅O₈ as cathode materials vs. Li anode, a scheme of electrochemical reactions is proposed to explain the unclear electrode functionality of the ‘corrugated layer’ LiFeO₂ phase. The scheme was validated by quantum-mechanical calculations (CRYSTAL09 code, hybrid B3LYP Hamiltonian) on a number of structural models for Li_1−xFeO₂, LiFe₅O₈, and Li₃Fe₅O₈. Magnetic interactions were taken into account, finding antiferromagnetic (Li_1−xFeO₂) and ferrimagnetic (LiFe₅O₈ and Li₃Fe₅O₈) orderings as stable states. At variance with spinel-like LiFe₅O₈, Li₃Fe₅O₈ displays a rocksalt-type superstructure. The computed energies for reactions (I) 4LiFeO₂ → 4Li_0.75FeO₂ + Li, (II) 4Li_0.75FeO₂ + Li → 4/5LiFe₅O₈ + 8/5Li₂O, and (III) 1/2LiFe₅O₈ + Li ↔ 1/2Li₃Fe₅O₈ are 4.44, −3.62, and −2.10 eV, respectively. Such values compare satisfactorily with the average charge/discharge voltages observed for positive electrodes made up of Pmmn-LiFeO₂ and of LiFe₅O₈.     

Hybrid microwave synthesis and characterization of the compounds in the Li–Ti–O system

Hybrid microwave synthesis has been applied for preparation of Li₄Ti₅O₁₂, Li₂Ti₃O₇, Li₂TiO₃ and LiTiO₂ for the first time. Stepwise heating was used for avoiding the instantaneous release of gas by-product and obtaining well-shaped samples. The samples were characterized by powder X-ray diffraction, energy-dispersive X-ray analysis and scanning electron microscopy. The obtained samples have relatively uniform particle sizes. The electrochemical performance of Li₄Ti₅O₁₂ and Li₂Ti₃O₇ were investigated. The first discharge capacity of Li₄Ti₅O₁₂ was 150 mAh g⁻¹ and 141 mAh g⁻¹ after 27 cycles and a very flat discharge and charge curve of Li₄Ti₅O₁₂ was shown at about 1.56 V. Similarly, Li₂Ti₃O₇ exhibits good cycle performance. The initial discharge capacity is 118 mAh g⁻¹ and 30th cycle is still 112 mAh g⁻¹.     

Synthesis and electrochemical performances of Li3V2(PO4)3/(Ag + C) composite cathode

Li₃V₂(PO₄)₃, Li₃V₂(PO₄)₃/C and Li₃V₂(PO₄)₃/(Ag + C) composites as cathodes for Li ion batteries are synthesized by carbon-thermal reduction (CTR) method and chemical plating reactions. The microstructure and morphology of the compounds are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Li₃V₂(PO₄)₃/(Ag + C) particles are 0.5-1 μm in diameters. As compared to Li₃V₂(PO₄)₃, Li₃V₂(PO₄)₃/C, the Li₃V₂(PO₄)₃/(Ag + C) composite cathode exhibits high discharge capacity, good cycle performance (140.5 mAh g⁻¹ at 50th cycle at 1 C, 97.3% of initial discharge capacity) and rate behavior (120.5 mAh g⁻¹ for initial discharge at 5 C) for the fully delithiated (3.0-4.8 V) state. Electrochemical impedance spectroscopy (EIS) measurements show that the carbon and silver co-modification decreases the charge transfer resistance of Li₃V₂(PO₄)₃/(Ag + C) cathode, and improves the conductivity and boosts the electrochemical performance of the electrode.     

Electrochemical properties of the soluble reduction products in rechargeable Li/S battery

In this paper, the electrochemical behavior of the reduction products in solution for Li/S cell is studied by UV-visual spectroscopy and electrochemical impedance spectroscopy (EIS). The results tell that the redox process of the polysulfide intermediate contains five charge-transfer steps in the practical Li/S cell. The formation of final reduction product of Li₂S and the final re-oxidation product of S₈ is completely irreversible. The transform between polysulfide and Li₂S₂ is electrochemical sluggish. The peaks corresponding to transformation Li₂S_x ↔ Li₂S_y (2 < x < y ≤ 6) are still symmetrical in spite of an increasing polarization with the proceeding of CV scan. While the redox process corresponding to Li₂S_m ↔ Li₂S_n (4 < m < n ≤ 8) is reversible. The dissolution long-chain polysulfide and deposition of short-chain polysulfide contribute mostly to the electrode deterioration even electrode blockage. Therefore, homogeneous mixing element sulfur with conductive components and alleviating the polysulfide dissolution are equally important to improving the active material utilization and rechargeability for rechargeable Li/S battery.     

Synthesis and hydriding properties of Li2Mg(NH)2

The phase pure Li₂Mg(NH)₂ has been synthesized via a dehydriding treatment of a ball milled 2LiNH₂ + MgH₂ mixture. This phase pure Li₂Mg(NH)₂ has been utilized to investigate its hydriding kinetics at the temperature range 180-220 °C. It is found that the hydriding process of Li₂Mg(NH)₂ is very sluggish even though it has favorable thermodynamic properties for near the ambient temperature operation. Holding at 200 °C for 10 h only results in 3.75 wt.% H₂ uptake. The detailed kinetic analysis reveals that the hydriding process of Li₂Mg(NH)₂ is diffusion-controlled. Thus, this study unambiguously indicates that the future direction to enhance the hydriding kinetics of this promising hydrogen storage material system should be to minimize the diffusion distance and increase the diffusion rate.