Nickel dioxide polymorphs as lithium insertion electrodes

Five kinds of nickel dioxide polymorphs, Li_xNiO₂ with x≈0, were prepared by treating LiNiO₂ with sulfuric acid solutions, occasionally followed by low-temperature heating. Here we report their structure and properties as lithium insertion electrodes. Acid-treated Li_0.10NiO₂ with two layered phases turned into a single-layered compound at 160 °C and then to a spinel-related compound at 170 °C. Acid-treated Li_0.04NiO₂ contained a phase with a cadmium iodide structure, which was not observed with Li_0.10NiO₂. Heating this Li_0.04NiO₂ yielded a spinel-related compound on heating. The NiO distances in these compounds suggested that the nickel oxidation state was kept approximately +4. These ‘nickel dioxide’ polymorphs exhibited varied characteristics as lithium insertion electrodes. We discuss the electrode behavior together with the structural changes that occur during lithium insertion. We also examined the effect of the electrode drying condition on the cycling performance.     

Electrochemical Recovery of Lithium Ions in the Aqueous Phase

Abstract

The electrochemical insertion of lithium ions into a Pt/λ-MnO₂ electrode was investigated in various metal chloride solutions. The Li⁺ insertion occurred effectively in LiCl solutions with higher concentration than 10 mmol/dm³, but it could hardly occur in a 0.1 mmol/dm³ LiCl solution. Alkaline earth metal ions showed a stronger inhibition effect against the Li⁺ insertion into the Pt/λ-MnO₂ electrode than alkali metal ions. However, since only Li⁺ ions were taken up from a mixed solution of lithium and alkaline earth metal chlorides, a high selectivity of the electrode for lithium ions was shown.

It was possible to recover lithium ions from geothermal water by this electrochemical method using the Pt/λ-MnO₂ electrode; the lithium uptake was 11 mg/g-MnO₂.     

A novel lithium intercalation compound based on the layered structure of lithium nitridonickelates Li3−2xNixN

New lithium nickel nitrides Li_3−2xNi_xN (0.20 ≤ x ≤ 0.60) have been prepared and investigated as negative electrode in the 0.85/0.02 V potential window. These materials are prepared from a Ni/Li₃N mixture at 700 °C under a nitrogen flow. Their structural characteristics as well as their electrochemical behaviour are investigated as a function of the nickel content. For the first time are reported here the electrochemical properties of a lithium intercalation compound based on a layered nitride structure. The Li_3−2xNi_xN compounds can be reversibly reduced and oxidized around 0.5 V versus Li/Li⁺ leading to specific capacities in the range 120-160 mAh/g depending on the nickel content and the C rate. Due to a large number of lithium vacancies, the structural stability provides an excellent capacity retention of the specific capacity upon cycling.     

MnO2 cathode in an aqueous Li2SO4 solution for battery applications

A manganese dioxide (MnO₂) cathode with zinc (Zn) as the anode has been investigated using lithium sulphate (Li₂SO₄) as an electrolyte. Previously we demonstrated that cells comprising MnO₂ and lithium hydroxide (LiOH) as an electrolyte can be made rechargeable to over one-electron capacity with a discharge capacity of 150 mAh g⁻¹. Here we have extended our work to assess Li₂SO₄ as an electrolyte and have found that the battery is not rechargeable. Based on the electrochemical (discharge/charge) performance and the products formed following discharge and charge, the mechanism proposed for the sulphate-based media is one of proton insertion into the MnO₂ cathode, rather than the lithium ion insertion observed for the LiOH electrolyte. The addition of bismuth species to the Li₂SO₄-based cell results in a transition to rechargeable behaviour. This is believed to be due to the influence of Bi ions on the formation of soluble Mn³⁺ soluble intermediates. However, the coulombic efficiency of the cell diminishes rapidly with repeated charge/discharge cycles. This confirms that the nature of the Li-containing electrolyte has a marked influence on the electrochemistry of the cell.     

Electrochemical insertion of lithium ions into disordered carbons derived from reduced graphite fluoride

Both covalent (obtained by direct fluorination at high temperature) and semi-ionic carbon fluorides (synthesized at room temperature) were reduced in order to obtain disordered carbons containing very small content of fluorine and different physical properties according to the reduction treatment (chemical, thermal or electrochemical). After a physical characterization (X-ray diffraction, electron spin resonance and FT-IR spectroscopies), the electrochemical behaviours of the pristine carbon fluorides and of the treated samples were investigated during the insertion of lithium using liquid carbonate-based electrolytes (LiClO₄-EC/PC, 50:50%, v/v). Both galvanostatic and voltammetric modes were performed and revealed that the voltage profiles and the capacities differed according to the starting material and the reduction treatment. Semi-ionic carbon fluoride treated in F₂ atmosphere for 2 h at 150 °C and then chemically reduced in KOH exhibits high reversible capacities (the reversible capacity is 530 mAh g⁻¹ in the second cycle); in this case, the voltage profiles show a large flat portion at potentials lower than 0.3 V which is attributed to the insertion/deinsertion of lithium ions between the small graphene sheets and/or the absorption of pseudo metallic lithium into the microporosity of the sample. Nevertheless, a part of the lithium ions are removed at potentials higher than 0.5 V versus Li⁺/Li limiting the useful capacity.     

Effect of synthesis condition on the structural and electrochemical properties of Li[Ni1/3Mn1/3Co1/3]O2 prepared by the metal acetates decomposition method

In order to get homogeneous layered oxide Li[Ni_1/3Mn_1/3Co_1/3]O₂ as a lithium insertion positive electrode material, we applied the metal acetates decomposition method. The oxide compounds were calcined at various temperatures, which results in greater difference in morphological (shape, particle size and specific surface area) and the electrochemical (first charge profile, reversible capacity and rate capability) differences. The Li[Ni_1/3Mn_1/3Co_1/3]O₂ powders were characterized by means of X-ray diffraction (XRD), charge/discharge cycling, cyclic voltammetry and SEM. XRD experiment revealed that the layered Li[Ni_1/3Mn_1/3Co_1/3]O₂ material can be best synthesized at temperature of 800 °C. In that synthesized temperature, the sample showed high discharge capacity of 190 mAh g⁻¹ as well as stable cycling performance at a current density of 0.2 mA cm⁻² in the voltage range 2.3-4.6 V. The reversible capacity after 100 cycles is more than 190 mAh g⁻¹ at room temperature.     

The study of lithium ion de-insertion/insertion in LiMn2O4 and determination of kinetic parameters in aqueous Li2SO4 solution using electrochemical impedance spectroscopy

In this work, we report a basic study on the mechanism of lithium ion de-insertion/insertion process from/into LiMn₂O₄ cathode material in aqueous Li₂SO₄ solution using electrochemical impedance spectroscopy (EIS). An equivalent circuit distinguishing the kinetic parameters of lithium ion de-insertion/insertion is used to simulate the experimental impedance data. The fitting results are in good agreement with the experimental results and the parameters of the kinetic process of Li⁺ de-insertion and insertion in LiMn₂O₄ at different potentials during charge and discharge are obtained using the same circuit. The results indicate that the de-insertion/insertion behavior of lithium ions at LiMn₂O₄ cathode in Li₂SO₄ aqueous solution is similar to that reported in the organic electrolytes. The charge transfer resistance (R_ct), warburg resistance, double layer capacitance and chemical diffusion coefficient (DLi+) vary with potentials during de-insertion/insertion processes. R_ct is lowest at the CV peak potentials and the important kinetic parameter, DLi+ exhibits two distinct minima at potentials corresponding to CV peaks during de-insertion–insertion and it was found to be between 10⁻⁸ and 10⁻¹⁰ cm² s⁻¹during lithium de-insertion/insertion processes.     

Synthesis of lithium rich layered oxides with controllable structures through a MnO2 template strategy as advanced cathode materials for lithium ion batteries

The electrochemical performance of lithium ion batteries depend largely on the structural properties of electrode materials. In this work, we propose an approach to synthesize lithium-rich layered oxides (LLOs) materials using a manganese dioxide (MnO₂) template strategy, which could control the structure and particle size of final products via choosing different MnO₂ templates. Through precisely optimizing, we successfully prepare cross-linked nanorods (CLNs) and agglomerate microrods (AMs) Li_1.2Ni_0.15Co_0.1Mn_0.55O₂ cathode materials by using carbon-decorated MnO₂ nanowires and MnO₂ nanorods as templates, respectively. The lithium ion battery based on the CLNs exhibits excellent performance, delivering a high capacity of 286.2 mAh g⁻¹ at 0.1 C and 237.5 mAh g⁻¹ at 1 C. In addition, the device remains 98% and 89% of its initial capacity after 50 cycles at 0.1 C and 100 cycles at 1 C, respectively. The remarkable electrochemical performance can be mainly attributed to the cross-linked nanorods structure which can provide relatively shorter lithium ion diffusion length, larger reaction surface and more internal cavity. This universal structure engineering strategy may shed light on new material structures for high performance lithium-rich layered oxide cathode materials.     

Electrochemical behaviour of some transition metal oxides in molten dimethylsulphone at 150°C

In view of the possible application in non-aqueous líthium cells operating at relatively high temperatures, molten dimethylsulphone (DMSO₂) has been used as the electrolyte solvent in lithium cells at 150°C. The stability of lithium in molten DMSO₂ has been found to be good as compared with that observed in organic solvents such as propylene carbonate, thus indicating that the Li⁺/Li system can be used as a suitable reference electrode in this medium.The electrochemical behaviour of some transition metal oxides has been investigated in LIClO₄ solutions in molten DMSO₂. The results obtained from voltammetric and chronopotentiometric measurements have shown a satisfactory behaviour for all the cathodic materials tested. Moreover, electrochemical insertion of Li⁺ ions into the crystal lattice of these oxides is a very fast process. Thus molten DMSO₂ appears to be a very interesting organic solvent usable in high energy density non-aqueous lithium cells.     

Synthesis of hollandite-type LixMnO2 by Li ion-exchange in molten salt and lithium insertion characteristics

The Li⁺ ion-exchange reaction of K⁺-type α-K_0.14MnO_1.93·nH₂O containing different amounts of water molecules (n = 0-0.15) with a large (2 × 2) tunnel structure has been investigated in a LiNO₃-LiCl molten salt at 300 °C. The Li⁺ ion-exchanged products were examined by chemical analysis, X-ray diffraction, and transmission electron microscopy measurements. The K⁺ ions and the hydrogens of the water molecules in the (2 × 2) tunnels of α-MnO₂ were exchanged by Li⁺ ions in the molten salt, resulting in the Li⁺-type α-MnO₂ containing different amounts of Li⁺ ions and lithium oxide (Li₂O) in the (2 × 2) tunnels with maintaining the original hollandite structure.The electrochemical properties and structural variation with initial discharge and charge-discharge cycling of the Li⁺ ion-exchanged α-MnO₂ samples have been investigated as insertion compounds in the search for new cathode materials for rechargeable lithium batteries. The Li⁺ ion-exchanged α-MnO₂ samples provided higher capacities and higher Li⁺ ion diffusivity than the parent K⁺-type materials on initial discharge and charge-discharge cyclings, probably due to the structural stabilization with the existence of Li₂O in the (2 × 2) tunnels.     

Characterization of structure and electrochemical properties of lithium manganese oxides for lithium secondary batteries hydrothermally synthesized from δ-KxMnO2

Lithium manganese oxides have attracted much attention as cathode materials for lithium secondary batteries in view of their high capacity and low toxicity. In this study, layered manganese oxide (δ-K_xMnO₂) has been synthesized by thermal decomposition of KMnO₄, and four lithium manganese oxide phases have been synthesized for the first time by mild hydrothermal reactions of this material with different lithium compounds. The lithium manganese oxides were characterized by powder X-ray diffraction (XRD), inductively coupled plasma emission (ICPE) spectroscopy, and chemical redox titration. The four materials obtained are rock salt structure Li₂MnO₃, hollandite (BaMn₈O₁₆) structure α-MnO₂, spinel structure LiMn₂O₄, and birnessite structure Li_xMnO₂. Their electrochemical properties used as cathode material for secondary lithium batteries have been investigated. Of the four lithium manganese oxides, birnessite structure Li_xMnO₂ demonstrated the most stable cycling behavior with high Coulombic efficiency. Its reversible capacity reaches 155 mAh g⁻¹, indicating that it is a viable cathode material for lithium secondary batteries.     

Electrochemical performance and local cationic distribution in layered LiNi1/2Mn1/2O2 electrodes for lithium ion batteries

LiNi_1/2Mn_1/2O₂ electrodes with layered structure were synthesized by solid-state reaction between lithium hydroxide and mixed Ni,Mn oxides obtained from co-precipitated Ni,Mn carbonates and hydroxides and freeze-dried Ni,Mn citrates. The temperature of the solid-state reaction was varied between 800 and 950 °C. This method of synthesis allows obtaining oxides characterized with well-crystallized nanometric primary particles bounded in micrometric aggregates. The extent of particle agglomeration is lower for oxides obtained from freeze-dried Ni,Mn citrates. The local Mn⁴⁺ surrounding in the transition metal layers was determined by X-band electron paramagnetic resonance (EPR) spectroscopy. It has been found that local cationic distribution is consistent with α,β-type cationic order with some extent of disordering that depends mainly on the precursors used. The electrochemical extraction and insertion of lithium was tested in lithium cells using Step Potential Electrochemical Spectroscopy. The electrochemical performance of LiNi_1/2Mn_1/2O₂ oxides depends on the precursors used, the synthesis temperature and the potential range. The best electrochemical response was established for LiNi_1/2Mn_1/2O₂ prepared from the carbonate precursor at 900 °C. The changes in local environment of Mn⁴⁺ ions during electrochemical reaction in both limited and extended potential ranges were discussed on the basis of ex situ EPR experiments.     

Electrochemical and structural study on cycling performance of γ-LiV2O5 cathode

Electrochemical and structural properties of LiV₂O₅ cathode were investigated. Obtained by solid state reaction at high temperature the material crystallized as gamma polymorph phase, γ-LiV₂O₅. The gamma structure provides two crystallographic sites to accommodate lithium ions, Li1 and Li2 position. Lithium insertion at these two sites occurs at two respective voltages versus lithium metal: ~3.6 V (Li1) and ~2.4 V (Li2). Intercalation at Li1 position is reversible in both organic and aqueous electrolyte and provides stable cycling performance at the high voltage. On the contrary, sluggish insertion/removal of Li⁺ at Li2 sites causes unstable performance and significant storage capacity fade at lower voltages. Lithium diffusion 3d landscape was determined by bond valence calculations applied on the γ-LiV₂O₅ phase, as well as on the metastable phases of γ′-V₂O₅ and ζ-Li₂V₂O₅ that exist at high and low voltages respectively. The model was proposed based on inactivity of Li2 position of the metastable ζ-Li₂V₂O₅ phase which provides explanation for the observed storage capacity loss at low voltages.     

Synthesis of octacalcium phosphate with incorporated succinate and suberate ions

Octacalcium phosphate (OCP) has a layered structure composed of apatitic and hydrated layers. HPO₄^2? in the hydrated layer can be substituted by dicarboxylate ions. The synthesis of octacalcium phosphate with incorporated dicarboxylate ions (octacalcium phosphate carboxylate, OCPC), was investigated through the effects of the initial concentration of dicarboxylic acid on the formation of OCPC. Succinic acid (Suc) and suberic acid (Sub) were used as dicarboxylic acids for preparing OCPC, and crystalline phases of the products were characterized by powder X-ray diffraction (XRD). When the amount of added dicarboxylic acid was 1–5 times the amount corresponding to the stoichiometric composition of OCPC, incorporation of dicarboxylate ions progressed with increasing amount of added dicarboxylic acids, although OCP without incorporated dicarboxylate ions was also present. When the amounts of added Suc and Sub were larger than 10 times the stoichiometric amount in OCPC, a single OCPC phase was detected in the powder XRD patterns. Amounts of Suc and Sub greater than 10 times the stoichiometric amounts facilitated formation of the OCPCs and inhibited formation of OCP. The incorporation of dicarboxylate ions into OCP competes with incorporation of HPO₄^2?. Hence a high concentration of dicarboxylic acids is required for complete incorporation of dicarboxylate ions in OCP.     

Hollow tremella-like graphene sphere/SnO2 composite for high performance Li-ion battery anodes

A hollow tremella-like graphene sphere/tin dioxide (HTGS/SnO₂) composite was successfully prepared by simple emulsification and impregnation followed by calcination. In this material, tin dioxide adheres to the folds on the surface of the hollow tremella-like graphene spheres. Hollow tremella-like graphene spheres as the matrix of SnO₂ not only provide a space of volumetric expansion for the tin oxide particles, relieve the internal stress of the tin dioxide, but also effectively avoid aggregation of the tin dioxide and increase the electrical conductivity. As an anode electrode material for batteries, the initial discharge/charge capacities of HTGS/SnO₂ are 1762.4 mAh g^-1 and 1169.4 mAh g^-1, and the Coulomb efficiency is 96.9%. After 50 cycles, capacity remains 80.4% of reversible capacity. The excellent electrochemical stability is attributed to the extraordinary structure of HTGS/SnO₂. The hollow structure of graphene sphere allows simultaneous insertion of lithium ions from the inner and outer surfaces. Meanwhile, the tin dioxide particles are uniformly dispersed by the wrinkles on the surface of the graphene, thereby enlarging the space for the volume expansion of tin dioxide in order to avoid contact with the electrolyte.     

Electrochemical evaluation of the a carbon-paste electrode modified with spinel manganese(IV) oxide under flow conditions for amperometric determination of lithium

The participation of cations in redox reactions of manganese oxides provides an opportunity for development of chemical sensors for non-electroactive ions. This paper describes the amperometric determination of lithium ions using carbon-paste electrode modified with spinel manganese(IV) oxide under flow conditions. Systematic investigations were made to optimize the experimental parameters for lithium sensor by flow injection analysis. The detection was based on the measurement of anodic current generated by oxidation of Mn(III) to Mn(IV) at the surface of the electrode and consequently the lithium ions extraction into the spinel structure. An operating potential of 0.50 V (vs. Ag/AgCl/3 KCl mol/L) was exploited for amperometric monitoring. The amperometric signal was linearly dependent on the lithium ions concentration over the range 4.0 × 10⁻⁵ to 1.0 × 10⁻³ mol L⁻¹. The equilibrium constant of insertion/extraction of the lithium ion in the spinel structure, apparent Gibbs energy of insertion, and surface coverage of the electrode with manganese oxide, were calculated by peak charge (Q) in different concentration under flow conditions. Considering selectivity, the peak charge of the sensor was found to be linearly dependent on the ionic radius of the alkaline and earth-alkaline cations.     

Lithium ion conductivity of molecularly compatibilized chitosan-poly(aminopropyltriethoxysilane)-poly(ethylene oxide) nanocomposites

Films of composites of chitosan/poly(aminopropyltriethoxysilane)/poly(ethylene oxide) (CHI/pAPS/PEO) containing a fixed amount of lithium salt are studied. The ternary composition diagram of the composites, reporting information on the mechanic stability, the transparence and the electrical conductivity of the films, shows there is a window in which the molecular compatibility of the components is optimal. In this window, defined by the components ratios CHI/PEO 3:2, pAPS/PEO 2:3 and CHI/PEO 1:2, there is a particular composition Li_x(CHI)₁(PEO)₂(pAPS)_1.2 for which the conductivity reaches a value of 1.7 × 10⁻⁵ S cm⁻¹ at near room temperature. Considering the balance between the Lewis acid and basic sites available in the component and the observed stoichiometry limits of formed polymer complexes, the conductivity values of these products may be understood by the formation of a layered structure in which the lithium ions, stabilized by the donors, poly(ethylene oxide) and/or poly(aminopropyltriethoxysilane), are intercalated in a chitosan matrix.     

Synthesis of 1D-MoS2/graphene nanotubes aided with sodium chloride for reversible lithium storage

A novel negative material consisting of graphene nanotubes and ultrathin MoS₂ is synthesized by a simple one-step hydrothermal method assisted with Sodium chloride. The MoS₂/Graphene electrodes deliver a specific capacity of 1350 mAh g^?1 under 0.1 A g^?1 and high rate capability (retaining 85.5% capacity from 0.1 A g^?1 to 0.8 A g^?1). A high remarkable capacity of 820 mAh g^?1 can still be recovered at 0.5 A g^?1 after 500 cycles, and the average coulombic efficiency was as high as 99.98% during the additional 500 cycles. The excellent Li-ion storage performance of MoS₂/Graphene nanotubes may be attributed to the ultra-thin MoS₂ flakes and curled graphene nanotubes. This structural feature has a strong adsorption capacity for lithium ions, which can provide a broad space for ion storage. A large number of active sites dispersed in the layered molybdenum disulfide promote the kinetics of the electrochemical reaction, empowering the ultra-thin layered molybdenum disulfide to get a higher theoretical capacity. In addition, the existence of the tubular structure alleviates volume expansion and provides a way for the rapid movement of electrons and diffusion of Li⁺ during repeated cycles.     

Crystal structure of cubic Li7-3xGaxLa3Zr2O12 with space group of I-43d

Cubic Li_7-3xGa_xLa₃Zr₂O₁₂ is a cubic phase with a space group of I-43d instead of Ia-3d. This structure is more conducive to the migration of lithium ions. However, the effect of Ga on the size and environment of lithium ion transport channels has not been researched. In this work, Li_7-3xGa_xLa₃Zr₂O₁₂ (x = 0–0.25) was formulated, and the crystal structure was obtained by neutron diffraction. The results indicated that the minimum channel size to control Li⁺ migration in LLZO was the bottleneck size between the Li2 and Li3 sites (bottleneck size 2), and compared with lanthanum ions, the zirconium ions were closer to lithium ions. As the Ga content increased, bottleneck size 2 levelled off, while the lithium concentration and the distance between skeleton ions and lithium ions decreased. As a result, the lithium ionic conductivity primarily increased and then decreased. When doping 0.2 pfu of Ga, LLZO exhibited the highest lithium ionic conductivity of 1.45 mS/cm at 25 °C due to the coordinated regulation of Li⁺ concentration, bottleneck size, and the distance between skeleton ions and lithium ions.     

Nuclear microanalysis: An efficient tool to study intercalation compounds containing lithium

Lithium can intercalate easily into graphite leading to the LiC₆ compound but the synthesis of a ternary compound associating lithium with a second element seems to be difficult. Recently, graphite-lithium-calcium compounds were obtained by reaction of a pyrographite platelet in a molten Ca-Li alloy at 350 °C. Chemical analyses, electron microprobe, SEM and TEM give the C/Ca ratio but do not allow to determine the lithium concentration and its distribution in these compounds. Therefore, the nuclear microprobe was used to characterise more precisely these ternary intercalation compounds. Using a 3.1 MeV proton beam, the three elements can be quantified simultaneously from the ⁷Li(p,α)⁴He nuclear reaction for lithium and from elastic scattering for calcium and carbon. Among the three synthesised compounds, one of them (α phase) opposes great heterogeneities in lithium and the amount of lithium in the β phase is very high (C/Li ratio approaches 2).