Pier Paolo Prosini

Determination of the chemical diffusion coefficient of lithium in LiFePO4

Abstract The lithium insertion in the ordered olivine-type structure of LiFePO 4 was analyzed as an insertion process with a Frumkin-type sorption isotherm. A minimum in the chemical diffusion coefficient of lithium ( D Li ) was predicted by the model for strong attractive interactions between the intercalation species and the host matrix. The D Li in the material was measured as a function of the lithium content by using the galvanostatic intermittent titration technique (GITT). The diffusion coefficient was found 1.8×10 −14 and 2.2×10 −16 cm 2 s −1 for LiFePO 4 and FePO 4 , respectively, with a minimum in correspondence of the peak of the differential capacity. The D Li has also been measured by AC impedance method for various lithium contents. The calculated values are in very good agreement with the previous calculated ones.

Li4Ti5O12 as anode in all-solid-state, plastic, lithium-ion batteries for low-power applications

Abstract Spinel Li 4 Ti 5 O 12 was prepared and tested as alternative anode for lithium-ion batteries. The electrochemical performance of the material was evaluated in liquid electrolyte at C/25 rate. The material delivered 150 mA h g −1 with a very satisfactory capacity retention. The electrochemical performance of commercial LiMn 2 O 4 was also tested. These materials were used to prepare polymer electrodes on aluminium foil substrate by using a screen-printing deposition technique. The transport properties of symmetrical polymer-electrode/polymer-electrolyte cells were evaluated by AC impedance. All-solid-state, plastic, lithium-ion batteries were fabricated with the cell configuration Li 4 Ti 5 O 12 /polymer electrolyte/LiMn 2 O 4 . The electrochemical performance of such a cell was evaluated at various temperatures.

A New Synthetic Route for Preparing LiFePO4 with Enhanced Electrochemical Performance

Nanocrystalline LiFePO 4 was obtained by heating amorphous nanosized LiFePO 4 . The amorphous material was obtained by lithiation of FePO 4 synthesized by spontaneous precipitation from equimolar aqueous solutions of Fe(NH 4 ) 2 (SO 4 ) 2 .6H 2 O and NH 4 H 2 PO 4. using hydrogen peroxide as the oxidizing agent. The materials were characterized by chemical analysis, thermogravimetric and differential thermal analysis, X-ray powder diffraction, and scanning electron microscopy. The Brunauer- Emmett-Teller method was used to evaluate the specific surface area. Nanocrystalline LiFePO 4 showed very good electrochemical performance delivering about the full theoretical capacity (170 Ah kg -1 ) when cycled at the C/10 rate. A capacity fade of about 0.25% per cycle affected the material upon cycling.

Composite Polymer Electrolytes with Improved Lithium Metal Electrode Interfacial Properties I. Elechtrochemical Properties of Dry PEO‐LiX Systems

Several types of lithium ion conducting polymer electrolytes have been synthesized by hot-pressing homogeneous mixtures of the components, namely, poly(ethylene oxide) (PEO) as the polymer matrix, lithium trifluoromethane sulfonate (LiCF{sub 3}SO{sub 3}), and lithium tetrafluoroborate (LiBF{sub 4}), respectively, as the lithium salt, and lithium gamma-aluminate {gamma}-LiAlO{sub 2}, as a ceramic filler. This preparation procedure avoids any step including liquids so that plasticizer-free, composite polymer electrolytes can be obtained. These electrolyte have enhanced electrochemical properties, such as an ionic conductivity of the order of 10{sup {minus}4} S/cm at 80--90 C and an anodic breakdown voltage higher than 4 V vs. Li. In addition, and most importantly, the combination of the dry feature of the synthesis procedure with the dispersion of the ceramic powder, concurs to provide these composite electrolytes with an exceptionally high stability with the lithium metal electrode. In fact, this electrode cycles in these dry polymer electrolytes with a very high efficiency, i.e., approaching 99%. This in turn suggests the suitability of the electrolytes for the fabrication of improved rechargeable lithium polymer batteries.

Synthesis and Characterization of Amorphous Hydrated FePO4 and Its Electrode Performance in Lithium Batteries

Amorphous iron(III) phosphate was synthesized by spontaneous precipitation from equimolar aqueous solutions of Fe(NH 4 ) 2 (SO 4 ) 2 .6H 2 O and NH 4 H 2 PO 4 , using hydrogen peroxide as the oxidizing agent. The material was characterized by chemical analysis thermogravimetrical analysis, differential thermoanalysis, X-ray powder diffraction, and scanning electron microscopy. The material was tested as a cathode in nonaqueous lithium cells Galvanostatic intermittent titration technique was used to follow the lithium intercalation process The effect of firing on the specific capacity was also tested. The material lired at 400°C showed the best electrochemical performance, delivering about 0.108 Ah g -1 when cycled at C/10 rate. The capacity fade upon cycling was found as low as 0.075% per cycle.

Long-term cyclability of nanostructured LiFePO4

Amorphous LiFePO4 was obtained by lithiation of FePO4 synthesized by spontaneous precipitation from equimolar aqueous solutions of Fe(NH4)2(SO4)2·6H2O and NH4H2PO4, using hydrogen peroxide as oxidizing agent. Nano-crystalline LiFePO4 was obtained by heating amorphous nano-sized LiFePO4 for different periods of time. The materials were characterized by TG, DTA, X-ray powder diffraction, scanning electron microscopy (SEM) and BET. All materials showed very good electrochemical performance in terms of energy and power density. Upon cycling, a capacity fading affected the materials, thus reducing the electrochemical performance. Nevertheless, the fading decreased upon cycling and after the 200th cycle the cell was able to cycle for more than 500 cycles without further fading.

A novel intrinsically porous separator for self-standing lithium-ion batteries

γ-LiAlO2, Al2O3 and MgO were used as fillers in a PVdF-HFP polymer matrix to form self-standing, intrinsically porous separators for lithium-ion batteries. These separators can be hot-laminated onto the electrodes without losing their ability to adsorb liquid electrolyte. The electrochemical stability of the separators was tested by constructing half-cells with the configuration: Li/fibre-glass/filler-based separator/electrode. MgO-based separators were found to work well with both positive and negative electrodes. An ionic conductivity of about 4×10−4 S cm−1 was calculated for the MgO-based separator containing 40% 1 M solution of LiPF6 in an EC/DMC 1:1 solvent. Self-standing, lithium-ion cells were constructed using the MgO-based separator and the resulting battery performance evaluated in terms of cyclability, power and energy density.

Solid‐State Lithium‐Polymer Batteries Using Lithiated MnO2 Cathodes

We have used a lithiated MnO 2 , Li 0 33 MnO 2 , with ordered alternating one-dimensional [1 × 2] and [1 × 1] channels as a cathode material in solid-state lithium/polymer cells. An optimized cell can operate at moderate temperatures (40-80°C). Li 0.33 MnO 2 delivers a rechargeable capacity of 160 mAh/g with a flat potential plateau at ca. 3.0 V vs. Li/Li + at the C/3 rate and 65°C, corresponding to a specific energy of 450 Wh/kg of the pure oxide. Cells show good rate capability and excellent cyclability when cycled between 2.7 and 3.5 V at 80% depth of discharge, whereas a capacity decline was observed when cycled between 2.0 and 3.5 V. Capacity fading upon cycling is believed to be due to the formation of a thin layer of spinel phase (transformation to Li 0.5 MnO 2 from Li 0.33 MnO 2 ) on the particle surfaces, as well as to increased cell resistance during charge/discharge cycling. The cell self-discharge at high temperature and the thermal stability of Li 0.33 MnO 2 in contact with the polymer electrolyte are also discussed.

Versatile Synthesis of Carbon-Rich LiFePO4 Enhancing Its Electrochemical Properties

LiFePO 4 /C composites were prepared from thermal decomposition of Fe(II) organophosphonates Fe[(RPO 3 )(H 2 O)] (R = methyl or phenyl group) in the presence of Li 2 CO 3 at high temperature and under inert atmosphere. The compounds were characterized by chemical analysis, thermogravimetric analysis and differential scanning colorimetry, X-ray powder diffraction, and scanning electron microscopy. Electrodes were fabricated for the electrochemical characterization. The cathode material obtained from Fe[C 6 H 5 PO 3 (H 2 O)] showed a specific energy evaluated at C/10 rate of about 550 Wh kg - 1 . The specific power calculated at 30C rate in excess at 14,000 W kg - 1 , while the specific energy was about 28% of the theoretical one. No capacity fading was observed upon cycling.

Investigation on lithium–polymer electrolyte batteries

Abstract Lithium–polymer batteries using vanadium oxide-based composite electrodes and operating at moderate temperatures (∼90°C) have been investigated. The work was developed within the advanced lithium–polymer batteries for electric vehicles (ALPE) project, an Italian integrated project, devoted to the realization of lithium–polymer batteries for electric vehicle applications.