Nina V. Kosova

Mechanochemical synthesis of LiMn2O4 cathode material for lithium batteries

Abstract The mechanochemical method was used for the synthesis of highly dispersed stoichiometric and nonstoichiometric LixMn2O4 spinel starting from different manganese (MnO2, Mn2O3, MnO) and lithium (LiOH, LiOH·H2O, Li2CO3) compounds. It is shown that the oxidation state of manganese greatly influences on the kinetics of mechanochemical reactions. On the other hand, different crystal structure and mechanical properties of initial lithium compounds result in different mechanisms of mechanochemical action on the activated mixtures. A strong effect of temperature and lithium content on the composition and lattice constant of the final products was found. Conductivity of LixMn2O4 spinels, measured by complex impedance spectroscopy, is likely caused by intergrain resistance. The activation energy of conductivity does not depend on x, the phase transition at 290±10 K, observed for stoichiometric spinel, is accompanied by a conductivity decrease. Test experiments in the electrochemical cell Li/LiPF6, EC/LiMn2O4,C demonstrate that lithium–manganese oxide obtained by the mechanochemical method is a promising cathode material for 4 V lithium batteries.

Effect of Fe2+ substitution on the structure and electrochemistry of LiCoPO4 prepared by mechanochemically assisted carbothermal reduction

LiCo1−yFeyPO4 solid solutions (0 ≤ y ≤ 1) were prepared by the mechanochemically assisted carbothermal reduction of Co3O4 and Fe2O3. Mechanical activation was performed using a high-energy planetary mill AGO-2. The samples were characterized in detail by X-ray powder diffraction (XRD) using a Rietveld refinement, Fourier transform infrared spectroscopy (FTIR), Mossbauer spectroscopy, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), galvanostatic cycling, and galvanostatic intermittent titration technique (GITT). According to XRD, all the samples are single-phase solid solutions, crystallized in an orthorhombic structure (S.G. Pnma). The cell volume of LiCo1−yFeyPO4 linearly increases vs. the Fe content. All the Fe ions are in the 2+ oxidation state and are octahedrally coordinated. The LiCo1−yFeyPO4 solid solutions show improved electrochemical performance, compared with LiCoPO4. Based on the data from XRD and GITT, the improvement is attributed to the enhanced Li+ diffusion, due to the enlargement of the 1D diffusion channels in the polyanion structure of LiCoPO4 and the reduced cell volume change in the material during the Li extraction/insertion process. Moreover, a systematic decrease in the average potential of the Co2+/Co3+ redox pair is observed with the increased Fe content, leading to the reaction termination in the electrochemical window of conventionally available electrolytes. In situ synchrotron diffraction shows that upon charging LiCo0.5Fe0.5PO4, the two-phase mechanism of Li (de)intercalation at the Fe2+/Fe3+ and Co2+/Co3+ redox stages changes to a solid solution-like mechanism, contrary to the pristine LiFePO4 and LiCoPO4 materials.

Hydrothermal reactions under mechanochemical treating

The mechanochemical treating of solids containing some amount of free or chemically bound water in high-energetic activators enable the hydrothermal processes (as in autoclaves). Estimations of the optimal value of the water content were carried out. The data on the investigation of the mechanochemical reaction between calcium hydroxide and hydrated silica are presented as the experimental confirmation of the hydrothermal regime being realized.

Synthesis of nanosized materials for lithium-ion batteries by mechanical activation. Studies of their structure and properties

This short review reports on the synthesis of nanosized electrode materials for lithium-ion batteries by mechanical activation (MA) and studies of their properties. Different structural types of compounds were considered, namely, compounds with a layered (LiNi1 − x − yCoxMnyO2), spinel (LiMn2O4, Li4Ti5O12), and framework (LiFePO4, LiTi2(PO4)3) structures. The compounds also differed in electronegativity, which varied from 10−4 S cm−1 for LiCoO2 to 10−9 S cm−1 for LiFePO4. The preliminary MA of mixtures of reagents in energy intensive mechanoactivators led to the formation of highly reactive precursors, and annealing of the latter formed nanosized products (the mean particle size is 50–200 nm). The local structure of the synthesized compounds and the composition of their surface were studied by spectral methods. An increase in the dispersity and defect concentration, especially in the region of the surface, improved some electrochemical characteristics. It increased the stability during cycling (LiMn2O4, at 3 V) and the regions of the formation of solid solutions during cycling (Li4Ti5O12, LiFePO4), led to growth of surface Li-ion conductivity (LiTi2(PO4)3), etc. The mechanochemical approach was also used for the synthesis of core-shell type composite materials (LiFePO4/C, LiCoO2/MeOx) and materials based on two active electrode components (LiCoO2/LiMn2O4).

Fast and Low Cost Synthesis of LiFePO4 Using Fe3 + Precursor

Submicrometer and phase-pure LiFeP0 4 was prepared by carbothermal reduction of Fe 2 O 3 using a preliminary mechanical activation. The reaction mechanism, particle size, and electrochemical performance of as-prepared LiFeP0 4 were studied and compared with LiFeP0 4 obtained from the Fe 2+ precursor (FeC 2 O 4 ·2H 2 O) using thermal analysis, X-ray diffraction, Mossbauer spectroscopy, scanning electron microscopy, and galvanostatic cycling. The carbothermal synthesis of LiFeP0 4 from Fe 2 O 3 in inert atmosphere is a multistep process, including first the formation of Li-Fe 3+ phosphates, mainly pyrophosphate LiFeP 2 O 7 . A single-phase high crystalline LiFePO 4 is formed at temperatures ≥ 700°C. The preliminary mechanical activation accelerates the reaction due to a very fine grinding and an intimate mixing of the reactants. The specific discharge capacity of LiFeP0 4 prepared from iron oxide is comparable with that of LiFeP0 4 prepared from iron oxalate (~155 mAh/g).

LiMn2O4 and LiCoO2 composite cathode materials obtained by mechanical activation

New composite cathode materials xLiMn2O4/(1 − x) LiCoO2(x = 0.7, 0.6, 0.5 и 0.4) were obtained by mechanical activation. According to scanning electron microscopy data, the process was accompanied by pronounced dispersion and fine mixing of the initial components. In the course of the preparation and electrochemical cycling of the composites, LiMn2O4 and LiCoO2 partially reacted, leading to the replacement of manganese with cobalt in the structure of spinel, which was detected by powder X-ray diffraction (XRD), IR and X-ray photoelectron spectroscopy (XPS), and cyclic chronopotentiometry. The specific discharge capacity of composites was ∼100 mAh/g.

Effect of electronic state of ions on the electrochemical properties of layered cathode materials LiNi1−2xCoxMnxO2

The cathode materials of the composition LiNi1 − 2xCoxMnxO2 (x = 0.1, 0.2. 0.33) synthesized from the Ni, Co, Mn mixed hydroxides and LiOH by using mechanical activation method are studied. It is shown that all synthesized compounds have layered structure described by the space group R-3m. With the decreasing of the nickel content the cell volume and the degree of structure disordering decrease. According to XPS data, the electronic main state of d-ions at the prepared samples’ surfaces corresponds to Ni2+, Co3+, and Mn4+. An increase in the nickel content leads to the increase of the Ni2p3/2 and Co2p3/2 binding energy, which points to the change in the Me-O bond covalence. According to magnetic susceptibility measurements data, the nickel ions in LiNi0.6Co0.2Mn0.2O2 exist in the two oxidation states: Ni2+ and Ni3+. It is shown that this sample has the highest specific discharge capacity (∼170 mAh/g). The positions of redox peaks in the differential capacitance curves depend on the sample composition: with the increasing of nickel content they are shifted toward lower voltages.

Soft mechanochemical synthesis: Preparation of cathode materials for rechargeable lithium batteries

Abstract To prepare intercalation lithium — transition metal oxide cathode materials for rechargeable lithium batteries, the reactions in the mixtures of the correspondent hydroxides in highly energetic planetary activators, so called ‘soft mechanochemical synthesis’ were studied. The method can be used for direct preparation of final products in a high dispersed and disordered state, as well as for obtaining high reactive precursors yielding final products by the subsequent brief heating at considerably lower temperatures as compared to conventional ceramic method. The as prepared products were analyzed using X-ray diffraction, TG, IRS, XPS, 7 Li NMR, EPR, diffuse reflectance spectroscopy, electron microscopy, BET, and electrochemical measurements. The peculiarities of crystal structure, electronic state of transition metal ions and cycling behaviour of materials are discussed. The method as proposed is concluded to be economically effective and ecologically clean.

LiNi1 − x − yCoxMnyO2 (x = y = 0.1, 0.2, 0.33) cathode materials prepared using mechanical activation: Structure, state of ions, and electrochemical performance

AbstractWe have investigated LiNi1 − x − yCoxMnyO2 (x = y = 0.1, 0.2, 0.33) cathode materials synthesized from mechanically activated mixtures of lithium hydroxide and nickel cobalt manganese hydroxide. The materials have a layered structure (sp. gr.