Surface modification effects of [Li,La]TiO<Subscript>3</Subscript> on the electrochemical performance of Li[Ni<Subscript>0.35</Subscript>Co<Subscript>0.3</Subscript>Mn<Subscript>0.35</Subscript>]O<Subscript>2</Subscript> cathode material for lithium–ion batteries

Surface modification of Li[Ni_0.35Co_0.3Mn_0.35]O₂ as a cathode material of lithium–ion batteries was carried out by hydrothermal treatment using lithium lanthanum titanate ([Li,La]TiO₃). The modified surfaces were analyzed by morphology observation using transmission electron microscopy and by element investigation using X-ray photoelectron spectroscopy. It was thereupon found that the [Li,La]TiO₃-coated layer formed by the surface modification played a definitive role in suppressing the solid electrolyte interface during repeated charge and discharge cycles. In addition, the thermal stability was enhanced by coated layer, resulting in an increase of the onset temperature to occur an exothermic reaction during thermal runaway.     

Preparation and electrochemical characterization of LiNi<Subscript>0.8</Subscript>Co<Subscript>0.2</Subscript>O<Subscript>2</Subscript> cathode material by a modified sol–gel method

LiNi_0.8Co_0.2O₂ cathode powders for lithium-ion batteries were prepared by a modified sol–gel method with citric acid as chelating agent and a small amount of hydroxypropyl cellulose as dispersant agent. The structure and morphology of LiNi_0.8Co_0.2O₂ powders calcined at various temperatures for 4 h in air were characterized by means of powder X-ray diffraction analyzer, scanning electron microscope, thermogravimetric analyzer and differential thermal analyzer, and Brunauer–Emmett–Teller specific surface area analyzer. The results show that LiNi_0.8Co_0.2O₂ powders calcined at 800 °C exhibit the best layered structure ordering and appear to have monodispersed particulates surface. In addition, the electrochemical properties of LiNi_0.8Co_0.2O₂ powders as cathode material were investigated by the charge–discharge and cyclic voltammetry studies in a three-electrode test cell. The initial charge–discharge studies indicate that LiNi_0.8Co_0.2O₂ cathode material obtained from the powders calcined at 800 °C shows the largest charge capacity of 231 mAh g⁻¹ and the largest discharge capacity of 191 mAh g⁻¹. And, the cyclic voltammetry studies indicate that Li⁺ insertion and extraction in LiNi_0.8Co_0.2O₂ powders is reversible except for the first cycle.     

Fe-doping effects on the structural and electrochemical properties of 0.5Li<Subscript>2</Subscript>MnO<Subscript>3</Subscript>·0.5LiMn<Subscript>0.5</Subscript>Ni<Subscript>0.5</Subscript>O<Subscript>2</Subscript> electrode material

With the aim of achieving a high-performance 0.5Li₂MnO₃·0.5LiMn_0.5Ni_0.5O₂ material, a series of 0.5Li₂MnO₃·0.5LiMn _x Ni _y Fe_(1−x−y)O₂ (0.3 ≤ x ≤ 0.5, 0.4 ≤ y ≤ 0.5) samples with low Fe content was synthesized via coprecipitation of carbonates. Its crystal structure and electrochemical performance were characterized by means of powder X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, galvanostatic charge/discharge testing, cyclic voltammetry, and electrochemical impedance spectra. Rietveld refinements with a model integrating R [`3] \overline{3} m and Fm [`3] \overline{3} m indicate that a low concentration of Fe incorporated in 0.5Li₂MnO₃·0.5LiMn_0.5Ni_0.5O₂ decrease a disordered cubic domain of the composite structure. The preferential distribution of Fe in cubic rock-salt contributes to an unimaginable decrease of c-axis parameter of the predominant layered structure as the Fe content increases. Moreover, including Fe as a dopant can kinetically improve crystallization and also change the ratio of Mn³⁺/Mn⁴⁺ and Ni³⁺/Ni²⁺. As a result, 0.5Li₂MnO₃·0.5LiMn_0.4Ni_0.5Fe_0.1O₂ exhibits lower Warburg impedance and higher reversible capacity than the undoped material.     

Notable Reactivity of Acetonitrile Towards Li<Subscript>2</Subscript>O<Subscript>2</Subscript>/LiO<Subscript>2</Subscript> Probed by NAP XPS During Li–O<Subscript>2</Subscript> Battery Discharge

One of the key factors responsible for the poor cycleability of Li–O₂ batteries is a formation of byproducts from irreversible reactions between electrolyte and discharge product Li₂O₂ and/or intermediate LiO₂. Among many solvents that are used as electrolyte component for Li–O₂ batteries, acetonitrile (MeCN) is believed to be relatively stable towards oxidation. Using near ambient pressure X-ray photoemission spectroscopy (NAP XPS), we characterized the reactivity of MeCN in the Li–O₂ battery. For this purpose, we designed the model electrochemical cell assembled with solid electrolyte. We discharged it first in O₂ and then exposed to MeCN vapor. Further, the discharge was carried out in O₂?+?MeCN mixture. We have demonstrated that being in contact with Li–O₂ discharge products, MeCN oxidizes. This yields species that are weakly bonded to the surface and can be easily desorbed. That’s why they cannot be detected by the conventional XPS. Our results suggest that the respective chemical process most probably does not give rise to electrode passivation but can decrease considerably the Coulombic efficiency of the battery.     

Polyindole–CuO composite polymer electrolyte containing LiClO<Subscript>4</Subscript> for lithium ion polymer batteries

This study presents the preparation of a composite polymer electrolyte (CPE), polyindole-based CuO dispersed CPE containing lithium perchlorate by sol–gel method. Morphology and the structural studies were conducted by scanning electron microscopy and X-ray diffraction. The ionic conductivity of CPE was measured for different concentration of the monomer by impedance spectroscopy. CPE containing CuO/indole (2:1 w/w ratio) (CPE3) exhibited enhanced conductivity of 1.9498 × 10⁻⁵ S/cm at RT. This CPE showed a linear relationship between the ionic conductivity and the reciprocal of the temperature, indicative of the system decoupled from the segmental motion of the polymer.     

Synthesis and electrochemical performance of LiVOPO4–Li3V2(PO4)3 cathode materials for lithium ion batteries

Lithium-ion batteries (LIBs) present the advantages of long cycle life, high voltage, and energy density and are widely made in the field of energy storage. LiVOPO₄ (LVOP), a cathode material used in LIBs, has a high conceptual capacity of 159 mAh g⁻¹ and high operating voltage of 3.9 V. However, its low electrical conductivity and cycle performance limit its commercial applications. According to the X-ray diffraction results, orthogonal crystal LVOP and monoclinic crystal Li₃V₂(PO₄)₃ (LVP) coexisted in the synthesised composite material. The transmission electron microscopy results also indicated that the LVOP and LVP phases coexist, which were coated by carbon layer of about 2.5 nm. The discharge of LVOP–LVP composite material initially was 143.2 mAh g⁻¹, and that after 120 cycles was 132.2 mAh g⁻¹ (at 0.1 C and 3–4.5 V). Thus, the electronic conductivity and first discharge specific capacity of the material enhanced due to the introduction of fast ion conductor LVP into LVOP. Electrochemical performance improved because the introduction of LVP led to an increase in Li⁺ pervasion channels in the original material and the acceleration of the Li⁺ transmission speed.     

Synthesis and properties of Na<Subscript>0.55</Subscript>Co<Subscript>0.9</Subscript>M<Subscript>0.1</Subscript>O<Subscript>2</Subscript> (M = Sc,Ti, Cr–Zn,Mo, W,Pb, Bi) solid solutions

Ceramic samples of Na_0.55Co_0.9M_0.1O₂ (M = Sc, Ti, Cr–Zn, Mo, W, Pb, Bi) solid solutions are synthesized using the solid-phase method; their crystal structure parameters are determined; their microstructure, thermal expansion, thermal and electrical conductivity, and thermal e.m.f. are studied; and the values of their power factor and thermoelectric figure of merit are calculated. It is revealed that Na_0.55Co_0.9M_0.1O₂ cobaltites are p type conductors with the linear thermal expansion coefficient (LTEC) changed within limits of (12.2–16.2) × 10^–6 K^–1. The effect of the substitution of other metal cations for cobalt cations in Na_0.55CoO₂ on the parameters of the crystal structure, as well as the physicochemical and functional properties of Na_0.55Co_0.9M_0.1O₂ solid solutions, which are formed, is analyzed. It is shown that ceramic samples of the Na_0.55Co_0.9Cr_0.1O₂ and Na_0.55Co_0.9Bi_0.1O₂ compositions have the maximal power factor values among those studied at 0.917 and 1.018 mW/(m K²), respectively, at a temperature of 1100 K.     

The effects of N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide–based electrolyte on the electrochemical performance of high capacity cathode material Li[Li0.2Mn0.54Ni0.13Co0.13]O2

The effects of ionic liquid (IL) N-methyl-N-butylpyrrolidinium bis(trifluoromethylsulfonyl)imide (Py₁₄TFSI) based electrolyte on the electrochemical performance of cathode material Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ have been investigated. The results of thermogravimetric analysis (TGA), flammability and differential scanning calorimetry (DSC) tests indicate that Py₁₄TFSI addition enhances thermal stability of the electrolyte and reduces the safety concern of Li-ion battery. Electrochemical measurements demonstrate that the cathode material shows good electrochemical performance in Py₁₄TFSI-added electrolyte. The cathode material is able to deliver high initial discharge capacity of 250 mAh g^?1 in electrolyte with Py₁₄TFSI content up to 80% at 0.1 C. In addition, the cathode material delivers less initial irreversible capacity loss and higher initial coulombic efficiency in electrolyte with higher Py₁₄TFSI content. However, increasing Py₁₄TFSI content in the electrolyte affects rate capability of the cathode material distinctively. With 60% Py₁₄TFSI-added electrolyte, Li[Li_0.2Mn_0.54Ni_0.13Co_0.13]O₂ shows better cycling stability with a capacity retention of 84.4% after 150 cycles at 1.0 C than that in IL free electrolyte. The superior cycling performance of the cathode material cycled in Py₁₄TFSI-added electrolyte is mainly ascribed to the formation of stable electrode/electrolyte interfaces, based on the results of scanning electron microscopy (SEM), X-ray photoelectron spectra (XPS) and electrochemical impedance spectroscopy (EIS) investigations.