Isobel J. Davidson

High capacity anode materials for Li-ion batteries based on spinel metal oxides AMn2O4 (A = Co, Ni, and Zn)

Manganites of transition and/or post-transition metals, AMn2O4 (where A was Co, Ni or Zn), were synthesized by a simple and easily scalable co-precipitation route and were evaluated as anode materials for Li-ion batteries. The obtained powders were characterized by SEM, TEM, and XRD techniques. Battery cycling showed that ZnMn2O4 exhibited the best performance (discharge capacity, cycling, and rate capability) compared to the two other manganites and their corresponding simple oxides. Further studies on the effect of different sintering temperatures (from 400 to 1000 °C) on particle size were performed, and it is found that the size of the particles had a significant effect on the performance of the batteries. The optimum particle size for ZnMn2O4 is found to be 75–150 nm. In addition, the use of water-soluble and environmentally friendly binders, such as lithium and sodium salts of carboxymethlycellulose, greatly improved the performance of the batteries compared to the conventional binder, PVDF. Finally, ZnMn2O4 powder sintered at 800 °C (<150 nm) and the use of the in-house synthesized lithium salt of carboxymethlycellulose (LiCMC) binder gave the best battery performance: a capacity of 690 mA h g−1 (3450 mA h mL−1) at C/10, along with good rate capability and excellent capacity retention (88%).

High-Voltage Electrolytes Based on Adiponitrile for Li-Ion Batteries

Adiponitrile, CN CH2 4CN, ADN, was evaluated as both a solvent and cosolvent in safer and more electrochemically stable electrolytes suitable for high energy and power density Li-ion batteries. An electrochemical investigation of its electrolyte solution with the Li CF3SO2 2N, LiTFSI, salt showed a wide electrochemical window of 6 V vs Li+/Li. The high melting point and the incompatibility of ADN with graphite anode required the use of ethylene carbonate EC as a cosolvent. The resultant EC:ADN electrolyte solutions showed ionic conductivities reaching 3.4 mS/cm, viscosities of 9.2 cP, and an improved resistance to aluminum corrosion up to 4.4 V, all at 20°C. Li-ion batteries incorporating graphite/LiCoO2 electrodes were assembled using EC:ADN electrolyte mixture containing 1 M LiTFSI and 0.1 M LiBOB as a cosalt, and discharge capacities of 108 mAh/g with very good capacity retention were obtained. AC impedance spectra of the batteries recorded as a function of charging and cycling indicated the presence of a stable solid electrolyte interface.

Local Structure and First Cycle Redox Mechanism of Layered Li 1.2 Cr 0.4 Mn 0.4 O 2 Cathode Material

Electrochemical, X-ray diffraction, and K and L edge X-ray absorption data are reported for the layered cathode material Li1.2Mn0.4Cr0.4O2 . The structural data show that this material can be understood as a solid solution of the layered phases Li 2MnO3 and LiCrO2 , comprising tretravalent Mn and trivalent Cr, with approximately 0.2 lithium incorporated in the transition metal layers. According to the analysis of the K edge extended X-ray absorption fine structure, lithium ions in the transition metal layers are clustered around Mn ions. L edge X-ray absorption near edge spectra show that in the first charge-discharge cycle chromium is the electrochemically active species, cycling between Cr 31 and Cr 61 . Manganese remains as Mn 41 throughout charge and discharge.

Study of the Cathode–Electrolyte Interface of LiMn1.5Ni0.5O4 Synthesized by a Sol–Gel Method for Li-Ion Batteries

High voltage spinel LiMn 1.5 Ni 0.5 O 4 has been synthesized by a modified Pechini sol-gel method and has been characterized by transmission electron microscopy, X-ray diffraction (XRD), and electrochemical methods. The synthesized materials are porous structures of nanosized crystallites ranging in size from 21 to over 400 nm depending on the sintering temperature used. The XRD patterns of the materials were assigned to the disordered spinel structure of the space group Fd3m. The Li-ion batteries assembled using the synthesized cathode materials showed significant capacity fade for samples sintered at 500°C, while for those sintered at 800°C the capacity fade was low. Impedance spectroscopy, Fourier transform IR spectroscopy, and X-ray photoelectron spectroscopy were used to determine the compositions of the cathode electrolyte interphase (CEI). Impedance spectroscopy confirmed the spontaneous formation of the CEI on LiMn 1.5 Ni 0.5 O 4 and that its thickness grows on cycling. After more than 100 cycles, it is found that the CEI film is composed of polycarbonates, polyether, LiF, and Li x PO y F z salts. The composition of the organic layer was the same regardless of the capacity fade.

In Situ X-Ray Absorption Study of a Layered Manganese-Chromium Oxide-Based Cathode Material

We have investigated the electronic and atomic structure of a manganese-chromium-based layered oxide material Li@Li0.2Cr0.4Mn0.4#O2 during electrochemical cycling using in situ X-ray absorption spectroscopy. Our results indicate that charge compensation in the cathode material is achieved by the oxidation/reduction of octahedral Cr~III! ions to tetrahedral Cr~VI! ions during delithiation/lithiation. Manganese ions are present predominantly in the Mn~IV! oxidation state and do not appear to actively participate in the charge compensation process. To accommodate the large changes in coordination symmetry of the Cr~III! and Cr~VI! ions, the chromium ions have to move between the regular octahedral sites in the R3 m-like lattice to interstitial tetrahedral sites during the charge/discharge process. The highly reversible ~at least after the first charge! three-electron oxidation/ reductions and the easy mobility of the chromium between octahedral and tetrahedral sites are very unusual and interesting. Equally interesting is the fact that chromium is the active metal undergoing oxidation/reduction rather than manganese. Our results also suggest that in the local scale manganese and chromium ions are not evenly distributed in the as-prepared material, but are present in separate domains of Mn and Cr-rich regions.

Study of the LiMn1.5Ni0.5O4/Electrolyte Interface at Room Temperature and 60°C

The surface layer (Cathode-Electrolyte Interface; CEI) on LiMn 1.5 Ni 0.5 O 4 , a promising, high voltage positive electrode for Li-ion batteries, was studied by XPS, AC impedance spectroscopy and FTIR spectroscopy. Half cells and full cells with LiMn 1.5 Ni 0.5 O 4 as positive electrode material and Li 4 Ti 5 O 12 as a negative electrode material were assembled in conventional carbonate-based electrolytes with LiPF 6 or LiBF 4 as the salt, and the effect of cycling at different operating conditions (short and long storage time, state of charge and temperature) on the surface layer composition was assessed. Capacities reaching near the theoretical value of 140 mAh g -1 were obtained in half cells cycled at C/2 and room temperature, with 85% of the capacity being retained after 100 cycles. Cycling at 60°C leads to a decrease in capacity and coulombic efficiency. The surface analysis by XPS revealed that the CEI is composed of inorganic species such as LiF and Li x PFyO z or Li x BF y O z as well as organic species such as polyethers and carbonates. Generally, it was found that cycling or storing the material at 60°C with an electrolyte using LiPF 6 as a salt yield more organic species and less LiF at the surface than the one with LiBF 4 .

Lithium-ion cell based on orthorhombic LiMnO2

Abstract This paper will demonstrate that cathodes based on the high temperature form of orthorhombic LiMnO 2 , with the structure described by Hoppe, Brachtel and Jansen, have good capacity and cycle life. X-ray diffraction studies have revealed that cathodes prepared from orthorhombic LiMnO 2 undergo a structural change on being charged beyond a certain potential in which the original structure is converted to spinel Li 1− x Mn 2 O 4 . Orthorhombic LiMnO 2 has been found to have long-term stability in ambient conditions and is easily prepared in a one-step reaction.

Use of Chloroethylene Carbonate as an Electrolyte Solvent for a Graphite Anode in a Lithium‐Ion Battery

The electrolyte decomposition during the first lithiation of graphite is reduced to 90 mAh/g in an electrolyte containing equal volumes of chloroethylene carbonate and a cosolvent of propylene carbonate, dimethyl carbonate, or diethyl carbonate. The volume fraction of chloroethylene carbonate can be further reduced to 0.05 in a trisolvent system with a cosolvent containing equal volumes of ethylene carbonate and propylene carbonate. A lithium-ion cell containing chloroethylene carbonate and propylene carbonate shows a long cycle life. The capacity decreases by 20% from the initial value in over 800 cycles. The charging efficiency is 80 to 90%, is rate dependent, and is accompanied by a self-discharge mechanism. A hypothesis of a chemical shuttle is suggested to explain the low charge efficiency and self-discharge.

Use of Chloroethylene Carbonate as an Electrolyte Solvent for a Lithium Ion Battery Containing a Graphitic Anode

An electrolyte system which consists of chloroethylene carbonate and propylene carbonate has been developed for lithium ion batteries containing a graphitic anode. The electrolyte decomposition during the first lithium intercalation into graphite in a propylene carbonate based electrolyte is significantly reduced in the presence of chloroethylene carbonate. Formation of a stable passivation film on the graphite surface is believed to be the reason for the improved cell performance.

Rechargeable cathodes based on Li2CrxMn2−xO4

Abstract Phases in the solid-state solution series Li 2 Cr x Mn 2− x O 4 were prepared as single-phase compounds over the range 0 x 3+ , with a smaller ionic radius, is substituted for Mn 3+ . The X-ray powder diffraction patterns of phases in the range 1.5≤ x 2 , while the diffraction patterns of Li 2 Cr x Mn 2− x O 4 phases over the range 0 x ≤1.25 resemble that of λ-Li 2 Mn 2 O 4 . Selected phases of Li 2 Cr x Mn 2− x O 4 were formed into cathodes and evaluated in lithium-ion cells with petroleum coke-based anodes.