Characterisation of Ni carbonate-bearing minerals by UV–Vis–NIR spectroscopy

Four nickel carbonate-bearing minerals from Australia have been investigated to study the effect of Ni for Mg substitution. The spectra of nullaginite, zaratite, widgiemoolthalite and takovite show three main features in the range of 26,720–25,855 cm⁻¹ (ν₁-band), 15,230–14,740 cm⁻¹ (ν₂-band) and 9,200–9,145 cm⁻¹ (ν₃-band) which are characteristic of divalent nickel in six-fold coordination. The Crystal Field Stabilization Energy (CFSE) of Ni²⁺ in the four carbonates is calculated from the observed ³A_2g(³F) → ³T_2g(³F) transition. CFSE is dependent on mineralogy, crystallinity and chemical composition (Al/Mg-content). The splitting of the ν₁- and ν₃-bands and non-Gaussian shape of ν₃-band in the minerals are the effects of Ni-site distortion from regular octahedral. The effect of structural cation substitutions (Mg²⁺, Ni²⁺, Fe²⁺ and trivalent cations, Al³⁺, Fe³⁺) in the carbonate minerals is noticed on band shifts. Thus, electronic bands in the UV–Vis–NIR spectra and the overtones and combination bands of OH and carbonate ion in NIR show shifts to higher wavenumbers, particularly for widgiemoolthalite and takovite.     

Chromium(III) complexes ofd(−)tartaric andl(−) mandelic acids

The binary complexes of anhydrous chromium(III) chloride withd(−) tartaric acidl(−) mandelic acids have been characterized by elemental analyses, magnetic susceptibility, vibrational, electronic and circular dichroism spectra. The magnetic susceptibility data are close to the spin only value for a d³ chromium(III) ion. Three (Cr−Cl) vibrational modes in the region 420–290 cm⁻¹ are observed for the formed complexes indicatingC ₂ local symmetry of ligand atoms around the chromium(III) rather thanC ₃, which would allow two modes. In the visible spectra, two peaks in the 21052–22222 and 15384–16129 cm⁻¹ range are observed and are assigned to the⁴ A _2g → ⁴ T _1g (F) and⁴ A _2g → ⁴ T _2g transitions. The parameters (Dq, B,β ₃₅) place the ligands in the higher end of the spectrochemical series and provide reassurance that the hydroxy acid oxygen complexes to chromium(III) ion. The Cotton effects observed in the spin-forbidden band are assigned to the² E(² E _g ),² A ₂(² T _1g ) and² E(² T _1g ), while that in the spin-allowed band are a results of the splitting of the⁴ A _2g (⁴ T _2g ) to⁴ A ₁(⁴ T _2g) and⁴ E(⁴ T _2g ) transitions. The tartaric acid chelates are likely to befac in terms of ligand carboxylate and/or hydroxy groups since stronger and better defined Cotton effects are observed while mandelic acid chelates are weak suggesting formation of themer structure. TMC 2633     

Electrochemical study of Meldola's blue,methylene blue and toluidine blue immobilized on a SiO<Subscript>2</Subscript>/Sb<Subscript>2</Subscript>O3 binary oxide matrix obtained by the sol-gel processing method

SiO₂/Sb₂O₃ (SiSb), having a specific surface area, S _BET, of 788 m² g⁻¹, an average pore diameter of 1.9 nm and 4.7 wt% of Sb, was prepared by the sol-gel processing method. Meldola's blue (MeB), methylene blue (MB) and toluidine blue (TB) were immobilized on SiSb by an ion exchange reaction. The amounts of the dyes bonded to the substrate surface were 12.49, 14.26 and 22.78 μmol g⁻¹ for MeB, MB and TB, respectively. These materials were used to modify carbon paste electrodes. The midpoint potentials (E _m) of the immobilized dyes were −0.059, −0.17 and −0.18 V vs. SCE for SiSb/MeB, SiSb/MB and SiSb/TB modified carbon paste electrodes, respectively. A solution pH between 3 and 7 practically did not affect the midpoint potential of the immobilized dyes. The electrodes presented reproducible responses and were chemically stable under various oxidation-reduction cycles. Among the immobilized dyes, MeB was the most efficient to mediate the electron transfer for NADH oxidation in aqueous solution at pH 7. In this case, amperometric detection of NADH at an applied potential of 0 mV vs. SCE gives linear responses over the concentration range of 0.1–0.6 mmol L⁻¹, with a detection limit of 7 μmol L⁻¹.     

Electrochemical studies of LiCr x Fe x Mn2?2x O4 in an aqueous electrolyte

In this paper, LiCr _x Fe _x Mn_2−2x O₄ (x = 0, 0.05, 0.1) electrode materials were prepared by sol–gel technique and characterized by X-ray diffraction (XRD) and transmission electron microscopy or high-resolution transmission electron microscopy techniques. XRD results reveal that the Cr–Fe-co-doped LiCr _x Fe _x Mn_2−2x O₄ materials are phase-pure spinels. The electrochemical properties of the LiMn₂O₄, LiCr_0.05Fe_0.05Mn_1.9O₄, and LiCr_0.1Fe_0.1Mn_1.8O₄ electrodes in 5 M LiNO₃ aqueous electrolyte were investigated using cyclic voltammetry, AC impedance, and galvanostatic charge/discharge methods. In the current range of 0.5–2 A g⁻¹, the specific capacity of the LiCr_0.05Fe_0.05Mn_1.9O₄ electrode is close to that of the LiMn₂O₄ electrode, but the specific capacity of the LiCr_0.1Fe_0.1Mn_1.8O₄ electrode is obviously lower than that of the LiMn₂O₄ electrode. When the electrodes are charge/discharge-cycled at the high current rate of 2 A g⁻¹, the LiCr_0.05Fe_0.05Mn_1.9O₄ electrode exhibits an initial specific capacity close to that of the LiMn₂O₄ electrode, but its cycling stability is obviously prior to that of the LiMn₂O₄ electrode.     

Development of activated carbon from vine shoots by physical and?chemical activation methods. Some insight into activation mechanisms

Activated carbons (ACs) are prepared from vine shoots (VS) by the method of physical activation in air, CO₂ and steam atmospheres and by the method of chemical activation with H₃PO₄, ZnCl₂ and KOH aqueous solutions. The ACs were characterized texturally by N₂ adsorption at −196 °C, mercury porosimetry, and density measurements. The method of chemical activation has been proved to be more effective than the method of physical activation to prepare ACs with a well-developed porosity. ACs with high micro- and mesopore volumes are prepared with ZnCl₂ and H₃PO₄. Using ZnCl₂, the volume of micropores is 0.62 cm³ g⁻¹ and the volume of mesopores is 0.81 cm³ g⁻¹. A greater development of macroporosity is obtained by KOH activation. The volume of macropores is as high as 1.13 cm³ g⁻¹ for the resulting AC. Yield of the process of preparation of the ACs is low for the method of chemical activation. Some insights into the performance of the activating agents in the activation process are provided.     

Mechano-chemical synthesis K2MF6 (M = Mn,Ni) by cation-exchange reaction at room temperature

In order to establish the power of mechanochemistry to produce industrially important phosphors, synthesis of K₂MnF₆ has been attempted by the successive grinding reactions of manganese (II) acetate with ammonium fluoride and potassium fluoride. The progress of reaction was followed by ex-situ characterization after periodic intervals of time. Cubic symmetry of K₂MnF₆ was evident from its powder X-ray diffraction pattern which was refined successfully in cubic space group (Fm-3m) with a = 8.4658 (20) Å. Stretching and bending vibration modes of MnF₆²⁻ octahedral units appeared at 740 and 482 cm⁻¹ in the fourier transformed infrared spectrum. Bands at 405 and 652 cm⁻¹ appeared in the Raman spectrum and they were finger-print positions of cubic K₂MnF₆. Other than the ligand to metal charge transfer transition at 242 nm, transitions from ⁴A_2g to ⁴T_1g, ⁴T_2g and ²T_2g of Mn⁴⁺-ion appeared at 352, 429, 474 and 569 nm in the UV–visible diffuse reflectance spectrum of the sample. Red emission due to Mn⁴⁺ was observed in the photoluminescence spectrum with a decay time of 0.22 ms. Following the success in forming cubic K₂MnF₆, this approach has been extended to synthesize cubic K₂NiF₆ at room temperature. All these results confirmed the susceptibility of acetate salts of transition metals belonging to first-row of the periodic table to facile fluorination at room temperature aided by mechanical forces.     

Electrochemical behavior of spherical LiNi1/3Co1/3Mn1/3O2 as cathode material for aqueous rechargeable lithium batteries

Spherical LiNi_1/3Co_1/3Mn_1/3O₂ powders have been synthesized from co-precipitated spherical metal hydroxide. The electrochemical performances of the LiNi_1/3Co_1/3Mn_1/3O₂ electrodes in 1 M LiNO₃, 5 M LiNO₃, and saturated LiNO₃ aqueous electrolytes have been studied using cyclic voltammetry and ac impedance tests in this work. The results show that LiNi_1/3Co_1/3Mn_1/3O₂ electrode in saturated LiNO₃ electrolyte exhibits the best electrochemical performance. An aqueous rechargeable lithium battery containing LiNi_1/3Co_1/3Mn_1/3O₂ cathode, LiV_2.9Ni_0.050Mn_0.050O₈ anode, and saturated LiNO₃ electrolyte is fabricated. The battery delivers an initial capacity of 98.2 mAh g⁻¹ and keeps a capacity of 63.9 mAh g⁻¹ after 50 cycles at a rate of 0.5 C (278 mA g⁻¹ was assumed to be 1 C rate).     

An application of near-infrared and mid-infrared spectroscopy to the study of selected tellurite minerals: xocomecatlite,tlapallite and rodalquilarite

Near-infrared and mid-infrared spectra of three tellurite minerals have been investigated. The structures and spectral properties of copper bearing xocomecatlite and tlapallite are compared with an iron bearing rodalquilarite mineral. Two prominent bands observed at 9,855 and 9,015 cm⁻¹ are assigned to ²B_1g → ²B_2g and ²B_1g → ²A_1g transitions of Cu²⁺ ion in xocomecatlite. The cause of spectral distortion is the result of many cations of Ca, Pb, Cu and Zn in the tlapallite mineral structure. Rodalquilarite is characterised by ferric ion absorption in the range 12,300–8,800 cm⁻¹. Three water vibrational overtones are observed in xocomecatlite at 7,140, 7,075 and 6,935 cm⁻¹ whereas in tlapallite bands are shifted to lower wavenumbers at 7,135, 7,080 and 6,830 cm⁻¹. The complexity of rodalquilarite spectrum increases with the number of overlapping bands in the near-infrared. The observation of intense absorption feature near 7,200 cm⁻¹ confirms hydrogen bonding water molecules in xocomecatlite. Weak bands observed near 6,375 and 6,130 cm⁻¹ in tellurites are attributed to the hydrogen bonding between (TeO₃)²⁻ and H₂O. A number of overlapping bands at low wave numbers 4,800–4,000 cm⁻¹ are caused by combinational modes of tellurite ion. (TeO₃)²⁻ stretching vibrations are characterised by three main absorptions at ~1,070, 780 and 665 cm⁻¹. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Partially substituted lithium manganese oxides as 3 V cathode materials for secondary lithium batteries

Low temperature synthesis and electrochemical properties of partially substituted lithium manganese oxides are reported. We demonstrate various metallic cations (Cu²⁺, Ni²⁺, Fe³⁺, Co³⁺) can be incorporated in the 3 V layered cathodic material Li_0.45MnO_2.1. New compounds Li_0.45Mn_0.88Fe_0.12O_2.1, Li_0.45Mn_0.84Ni_0.16O_2.05, Li_0.45Mn_0.79Cu_0.21O_2.3, Li_0.45Mn_0.85Co_0.15O_2.3 are prepared. These 3 V cathode materials are characterized by the same shape of discharge-charge profiles but different values of the specific capacity, between 90 mAh g⁻¹ and 180 mAh g⁻¹. The best results in terms of capacity and cycle life are obtained with the selected content of 0.15 Co per mole of oxide, as the optimum composition. The high kinetics of Li⁺ transport in Li_0.45Mn_0.85Co_0.15O_2.3 compared to that in the Co-free material is consistent with a substitution of Mn(III) by Co(III) in MnO₂ sheets.     

State of manganese ions in the structure of corundum synthesized in supercritical water fluid

The kinetics and formation mechanism of doped corundum (α-Al₂O₃) from hydrargillite (γ-Al(OH)₃) in supercritical water fluid (SCWF) in the presence of manganese ions are studied. It was ascertained that due to the reversible dehydroxylation in an aqueous medium, solid-phase transformation of hydrargillite into boehmite (γ-AlOOH) and then into corundum occurs with the formation of well-faceted corundum micro-crystals that are uniformly doped with manganese. It was found that when Mn²⁺ or MnO₄⁻ ions are introduced into the reaction medium, Mn⁵⁺, Mn⁴⁺, Mn³⁺, and Mn²⁺ ions are observed in the synthesized corundum. Meanwhile, the manganese ions form a complex defect in the corundum structure, which comprises oxygen vacancies and hydroxyl groups. The defects in corundum that emerge upon doping with manganese in SCWF are different from those in corundum doped during high-temperature synthesis.     

XRD and UV-Vis diffuse reflectance analysis of CeO2-ZrO2 solid solutions synthesized by combustion method

A series of ceria-incorporated zirconia (Ce_1−xZr_xO₂,x = 0 to 1) solid solutions were prepared by employing the solution combustion synthesis route. The products were characterized by XRD and UV-Vis-NIR diffuse reflectance spectroscopy. The materials are crystalline in nature and the lattice parameters of the solid solution series follow Vegard’s law. Diffuse reflectance spectra of the solid solutions in the UV region show two intense bands at 250 and 297 nm which are assigned respectively to Ce³⁺ ← O²⁻and Ce⁴⁺ ← O²⁻ charge transfer transitions. The two vibrational bands in 6960 cm⁻¹ and 5168 cm⁻¹ in the NIR region indicate the presence of surface hydroxyl groups on these materials.     

Pressure Dependence of the Acid/Base Equilibria of Methyl Orange in Aqueous Solutions to 1000 bar at 20°C

The pressure dependence on the acid/base equilibria of methyl orange in aqueous solution was measured at 20 °C in the 1–1000 bar range with a newly designed flow-through spectrophotometric cell. Combined chemometric and thermodynamic analyses of the UV-Vis spectrophotometric data were used to extract the dissociation constants as well as the changes in molar volume and isothermal compressibility of methyl orange as a function of pressure. The results show that increasing the pressure promotes the deprotonation of methyl orange, with pK values ranging from 3.505 at 1 bar to 3.445 ± 0.002 at 1000 bar. Increasing the pressure also yields small negative changes in the molar volume ranging from –6.9 cm³·mol⁻¹ at 1 bar to −1.7 cm³·mol⁻¹ at 1000 bar. The isothermal compressibility of methyl orange in this pressure range was estimated using the second derivative of second and third order polynomial fits to the constants, and resulted in a constant value of –48.4 × 10⁻⁴ cm³·mol⁻¹·bar⁻¹ in the former case, but increasing values from –107 × 10⁻⁴ cm³·mol⁻¹·bar⁻¹ at 1 bar to 3.43 × 10⁻⁴ cm³·mol⁻¹·bar⁻¹ at 1000 bar in the latter case. Molar absorption coefficients for the protonated and deprotonated species were also shown to be only slightly effected by pressure changes and can be used to accurately predict the absorption spectra of methyl orange as a function of pressure.     

ESR spectra of spacered copper(II) dimers of 5-bromo-2-hydroxyacetophenone acyldihydrazones based on aliphatic dicarboxylic acids

Binuclear copper(II) complexes with 5-bromo-2-hydroxyacetophenone acyldihydrazones (H₄L) with the composition [Cu₂L·nPy] where the coordination polyhedra are linked by polymethylene chains with different lengths (from one to five units) have been synthesized and studied. The ESR spectrum of a polycrystalline sample of a complex based on malonyldihydrazone contains a major signal (g = 2.11) together with a weak signal corresponding to the forbidden transition (ΔM _S = 2, g = 4.18). At room temperature, ESR spectra of solutions of complexes of acyldihydrazones based on malonic, succinic, glutaric, and adipic acids contain seven HFS lines from two equivalent copper nuclei. These lines result from weak spin-spin exchange interaction between two unpaired electrons with the constant (36–38)·10⁻⁴ cm⁻¹. An increase in the polymethylene chain length to five units prevents the exchange interactions, and the ESR spectrum of a complex of the acyldihydrazone based on pimelic acid contains a signal of four HFS lines (a _Cu = 69.5·10⁻⁴ cm⁻¹), which is common to the monomeric copper(II) compounds. In the parallel orientation, the ESR spectrum of a frozen solution of the complex of malonyldihydrazone contained the superposition of signals due to fine and hyperfine structures with similar constants (D _∥ = 0.0074 cm⁻¹, A _∥ = 0.0070 cm⁻¹, g _∥ = 2.089, g _⊥ = 2.053). __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1752–1757, August, 2005.     

Thermally stimulated luminescence of a natural layered double hydroxide

Layered double hydroxides (LDHs) and many of the related hydrotalcite-like minerals have been well studied from the chemical and structural point of view; however, their luminescence properties have been scarcely studied. We herein report on the thermoluminescence (TL) behaviour of a natural LDH (Mg₆Cr₂CO₃(OH)₁₆·4H₂O), previously characterized by X-ray fluorescence, X-ray energy-dispersive spectrometry, electron probe microanalysis, thermogravimetry and differential thermal analysis, that exhibited a very complex green-IR spectral emission. The broad waveband peaked at ~?640 nm can be mainly linked to the ⁴T₁?→?⁶A₁ (at 570 nm), ⁴A_2g?→?²E_g (~?685 nm), ⁴T₁?→?⁶A₁ (~?700 nm), and ¹T_2g?→?³A_2g (green) and ¹T_2g?→?³T_2g (red) transitions due, respectively, to the presence of Mn²⁺, Cr³⁺, Fe²⁺ and Ni²⁺. The weak red-TL emission can likely be attributed to the quenching effect due to Fe (~?8–11%) ions substituting for Mg²⁺.     

Determination of diffusion coefficient of lithium in LiMyMn2 ? yO4 spinels using potentiostatic intermittent titration technique

The potentiostatic intermittent titration technique is used to study lithium transport in the LiM _yMn_{2 − y} O₄ compounds with a spinel structure intended for application as cathodic materials in lithiumion and lithium-polymer batteries. The materials are synthesized using the sol-gel method and the melt-impregnation method. Kinetic and diffusion characteristics of the Li _x Mn₂O₄ and Li _x Mn_1.95Cr_0.05O₄ compounds are determined at 25°C as dependent on lithium content 0 < x < 1. The diffusion coefficient of lithium varies significantly in the range of 10⁻¹⁰ to 10⁻¹³ cm²/s under variation of the electrode composition; the surface resistance depends weakly on the concentration of lithium and is 200–500 Ohm cm².     

Effects of complexants on [Ni1/3Co1/3Mn1/3]CO3 morphology and electrochemical performance of LiNi1/3Co1/3Mn1/3O2

LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials for the application of lithium ion batteries were synthesized by carbonate co-precipitation routine using different ammonium salt as a complexant. The structures and morphologies of the precursor [Ni_1/3Co_1/3Mn_1/3]CO₃ and LiNi_1/3Co_1/3Mn_1/3O₂ were investigated through X-ray diffraction, scanning electron microscope, and transmission electron microscopy. The electrochemical properties of LiNi_1/3Co_1/3Mn_1/3O₂ were examined using charge/discharge cycling and cyclic voltammogram tests. The results revealed that the microscopic structures, particle size distribution, and the morphology properties of the precursor and electrochemical performance of LiNi_1/3Co_1/3Mn_1/3O₂ were primarily dependent on the complexant. Among all as-prepared LiNi_1/3Co_1/3Mn_1/3O₂ cathode materials, the sample prepared from Na₂CO₃–NH₄HCO₃ routine using NH₄HCO₃ as the complexant showed the smallest irreversible capacity of 19.5 mAh g⁻¹ and highest discharge capacity of 178.4 mAh g⁻¹ at the first cycle as well as stable cycling performance (98.7% of the initial capacity was retained after 50 cycles) at 0.1 C (20 mA g⁻¹) in the voltage range of 2.5–4.4 V vs. Li⁺/Li. Moreover, it delivered high discharge capacity of over 135 mAh g⁻¹ at 5 C (1,000 mA g⁻¹).     

The X˜1A1, a˜3B1, a˜1B˜1, and B˜1A1 electronic states of SiH2

Four electronically low-lying states of silylene (SiH₂) have been studied systematically using high level ab initio electronic structure theory. Self-consistent field (SCF), two-configuration (TC) SCF, complete active space (CAS) SCF, configuration interaction with single and double excitations (CISD), and CASSCF second-order (SO) CI levels of theory were employed with eight distinct basis sets. The zeroth-order wave functions of the ground (X˜ ¹A₁ or 1 ¹A₁) and B˜ ¹A₁ (or 2 ¹A₁) excited states are appropriately described by the first and second eigenvectors of the TCSCF secular equations. The TCSCF-CISD, CASSCF, and CASSCF-SOCI wave functions for the B˜ ¹A₁ (or 2 ¹A₁) state were obtained by following the second root of the CISD, CASSCF, and SOCI Hamiltonian matrices. At the highest level of theory, the CASSCF-SOCI method with the triple zeta plus triple polarization augmented with two sets of higher angular momentum functions and two sets of diffuse functions basis set [TZ3P(2f,2d)+2diff], the energy separation (T₀) between the ground (X˜ ¹A₁) and first excited (a˜ ³B₁) states is determined to be 20.5 kcal/mol (0.890eV,7180cm⁻¹), which is in excellent agreement with the experimental T₀ value of 21.0 kcal/mol (0.910eV,7340cm⁻¹). With the same method the T₀ value for the a˜ ¹B₁−X˜ ¹A₁ separation is predicted to be 45.1 kcal/mol (1.957 eV,15780 cm⁻¹), which is also in fine agreement with the experimental value of 44.4 kcal/mol (1.925 eV,15530 cm⁻¹). The T₀ value for the B˜ ¹A₁−X˜ ¹A₁ separation is determined to be 79.6 kcal/mol (3.452 eV,27 840 cm⁻¹). After comparison of theoretical and experimental T₀ values for the a˜ ³B₁ and a˜ ¹B₁ states and previous studies, error bars for the B˜ ¹A₁ state are estimated to be ±1.5 kcal/mol (±525 cm⁻¹). The predicted geometry of the B˜ ¹A₁ state is r_e(SiH)=1.458 and θ_e=162.3^∘. The physical properties including harmonic vibrational frequencies of the B˜ ¹A₁ state are newly determined. Received: 10 March 1997 / Accepted: 2 April 1997     

Electrochemical properties of tetravalent Ti-doped spinel LiMn2O4

Ti-doped spinel LiMn₂O₄ is synthesized by solid-state reaction. The X-ray photoelectron spectroscopy and X-ray diffraction analysis indicate that the structure of the doped sample is Li( Mn^{3 +} Mn_{1 - x} ^{4 +} Ti_x^{4 +} )O₄ {\hbox{Li}}\left( {{\hbox{M}}{{\hbox{n}}^{3 + }}{\hbox{Mn}}_{1 - x\,}^{4 + }{\hbox{Ti}}_x^{4 + }} \right){\hbox{O}}{}_4 . The first principle-based calculation shows that the lattice energy increases as Ti doping content increases, which indicates that Ti doping reinforces the stability of the spinel structure. The galvanostatic charge–discharge results show that the doped sample LiMn_1.97Ti_0.03O₄ exhibits maximum discharge capacity of 135.7 mAh g⁻¹ (C/2 rate). Moreover, after 70 cycles, the capacity retention of LiMn_1.97Ti_0.03O₄ is 95.0% while the undoped sample LiMn₂O₄ shows only 84.6% retention under the same condition. Additionally, as charge–discharge rate increases to 12C, the doped sample delivers the capacity of 107 mAh g⁻¹, which is much higher than that of the undoped sample of only 82 mAh g⁻¹. The significantly enhanced capacity retention and rate capability are attributed to the more stable spinel structure, higher ion diffusion coefficient, and lower charge transfer resistance of the Ti-doped spinel.     

Determination of diffusion coefficient of lithium in LiMyMn2 ? yO4 spinels using galvanostatic intermittent titration technique

The galvanostatic intermittent titration technique is used to study lithium transport in the LiM _y Mn_{2 − y} O₄ compounds with a spinel structure intended for application as cathodic materials in lithium-ion and lithium-polymer batteries. Equilibrium intercalation isotherms of the Li _x Mn₂O₄ and Li _x Mn_1.95Cr_0.05O₄ compounds and also their diffusion characteristics are determined at 25°C as dependent on lithium content x, 0 < x < 1. The diffusion coefficient of lithium varies in a complex way in the range of 10⁻¹⁰ to 10⁻¹² cm²/s under variation of the electrode composition.