The thermal stability of pristine and electrochemically delithiated LiMPO(4) (Carbon coated-LiMnPO(4), Carbon coated-LiMn(0.8) Fe(0.2)PO(4), and Carbon coated-LiFePO(4)), LiCoO(2) and LiNi(0.8)Co(0.15)Al(0.05)O(2) (NCA) composite electrodes with LiPF(6) solutions in ethylene carbonate (EC)/dimethyl carbonate (DMC) and EC/propylene carbonate (PC), was investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis, coupled with mass spectrometry. The thermal reactions products were measured by XRD and electron microscopy. The LiFePO(4) and LiMnPO(4) cathode materials were found to have comparable thermal stability in their pristine and fully delithiated states. The onset temperatures of the thermal reactions are lower in EC/DMC than in EC/PC solutions but the specific heat evolution of all the thermal reactions are higher with EC-PC solutions. No evidence was found that delithiated LiMnPO(4) or Li[MnFe]PO(4) have lower thermal stability than delithiated LiFePO(4). The thermal reactivity of the layered LiCoO(2) and LiNi(0.8)Co(0.15)Al(0.05)O(2) cathode materials was found to be comparable to that of the LiMPO(4) materials. Oxygen release was detected from the layered compounds upon their heating around 200 degrees C. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3622849] All rights reserved.

A new type of lithium-ion cell based on the combination of spinel Li4Ti5O12 anode with a high voltage olivine LiMnPO4 cathode, which can be promising for load leveling applications, is demonstrated for the first time. The power and safety characteristics of this battery system were found to meet the requirement for this application. The structure, surface morphology, and the performance were characterized by X-ray diffraction (XRD), high-resolution scanning electron microscopy (HRSEM) and standard electrochemical techniques. A stable reversible capacity up to 125 mAh g(-1) of the cathode in full cell could be measured at discharge potentials > 2.5 V with a reasonable capacity retention during prolonged charge/discharge cycling. The thermal stability of pristine and electrochemically delithiated LiMnPO4-Li4Ti5O12 composite cathodes and anodes in contact with the electrolyte solution was investigated by differential scanning calorimetry (DSC). The electrodes were also studied by thermogravimetric analysis, coupled with mass spectrometry. We did not found appreciable changes in the thermal stability of the electrodes in their pristine and charged states, in contact with LiPF6 solution in mixtures of ethylene carbonate (EC) and dimethyl carbonate (DMC). (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3585837] All rights reserved.

Introduction Since the pioneering work of Goodenough and coworkers, [1] LiMPO4 compounds (M = Fe, Mn, Co or Ni, theoretical capacity around 170 mAhg) have been investigated as promising cathode materials for rechargeable lithium-ion batteries. The use of LiFePO4 as carbon coated nano-particles enables this compound to serve as high rate cathode material in Li ion batteries. LiMnPO4 is a much more promising cathode material for Li ion batteries than LiFePO4 due to its higher red-ox voltage, 4.2 V vs. Li/ Li, compared to 3.5 V of the latter one. We demonstrated recently [2] that carbon-coated nano-particles of LiMnPO4 can be used indeed as a practical cathode material with capacity around 145 mAhg, acceptable rate capabilities excellent cyclability and impressive stability. But LiMnPO4 has comparatively less specific capacity (its theoretical capacity of 170 mAhg) and rate capability than Li[MnNiCo]O2 (layered) cathode materials. So, it is important to find ways to improve the practical capacity and rate capability of LiMnPO4. This can be achieved by a partial substitution of Mn with Fe ions and an appropriate carbon coating. Since the red-ox potential of the Fe ions in the olivine compounds is lower by 600-700 mV than that of Mn ions, it is important to maximize the Mn/Fe ratio in Li[MnFe]PO4 in order to obtain most of the capacity at the high voltage domain. We report herein on the study of carbon-coated nano LiMn0.8Fe0.2PO4 (C-LiMn0.8Fe0.2PO4) as a superb cathode material for advanced Li ion batteries. We found that replacement of 20% (optimal percentage) Mn by Fe atoms in the olivine compound, thus giving up part of the high red-ox potential profile of this compound (compared to LiMnPO4) led to improved capacity and highly impressive rate capability and energy density. Highly important is also to discuss safety features and the thermal stability of LiMnPO4 and its derivatives.

HPL SA report the modification of the electrochemical performance of lithium manganese phosphate (LiMnPO4) via Mn-site bivalent substitution. Manganese (10%) is substituted with iron, nickel, magnesium, or zinc. These substituents are shown via an X-ray to form solid solutions. The choice of substituent is demonstrated to have a strong influence on the electrochemical performance. The optimum performance improvement was achieved when 10% of Fe is substituted. This is ascribed to a smaller crystallite and a higher electronic conductivity observed in this material: Presumably Fe plays a role in hindering the crystallite growth and in increasing the carrier's transportation. Electronic structures were calculated by density function theory to understand the different influences of substitute cations.

LiMnPO4 (olivine) was surface-modified by two different complexes: Ru-bis(4,4'-diethoxycarbonyl-2,2'-bipyridine)(4,4'-dicarboxylate-2,2'-bipyridine) and Ru-bis(4-carboxylic acid-4'-carboxylate-2,2'-bipyridine)(4,4'-dinonyl-2,2'bipyridine). These complexes have redox potentials of 4.45 and 4.25 V vs. Li/Li+, respectively, and are both active for molecular wiring of LiMnPO4. The surface-confined Ru(II)/Ru(III) redox reaction propagates across the monolayer via hole-hopping, allowing a subsequent chemical delithiation of the underneath olivine towards MnPO4. The activity of LiMnPO4 is about half of that of LiFePO4 (olivine) at similar experimental conditions. (C) 2009 Elsevier B.V. All rights reserved.

LiMnPO4 nanoparticles synthesized by the polyol method were examined as a cathode material for advanced Li-ion batteries. The structure, surface morphology, and performance were characterized by X-ray diffraction, high resolution scanning electron microscopy, high resolution transmission electron microscopy, Raman, Fourier transform IR, and photoelectron spectroscopies, and standard electrochemical techniques. A stable reversible capacity up to 145 mAh g(-1) could be measured at discharge potentials > 4 V vs Li/Li+, with a reasonable capacity retention during prolonged charge/discharge cycling. The rate capability of the LiMnPO4 electrodes studied herein was higher than that of LiNi0.5Mn0.5O2 and LiNi0.8Co0.15Al0.05O2 (NCA) in similar experiments and measurements. The active mass studied herein seems to be the least surface reactive in alkyl carbonate/LiPF6 solutions. We attribute the low surface activity of this material, compared to the lithiated transition-metal oxides that are examined and used as cathode materials for Li-ion batteries, to the relatively low basicity and nucleophilicity of the oxygen atoms in the olivine compounds. The thermal stability of the LiMnPO4 material in solutions (measured by differential scanning calorimetry) is much higher compared to that of transition-metal oxide cathodes. This is demonstrated herein by a comparison with NCA electrodes. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3125765] All rights reserved.

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The supramolecular assembly of Ru-bipyridine complex, coded Z-907Na, with single-walled carbon nanotube (SWNT) exhibits unique redox behavior, which is applicable for the nanotube wiring of LiFePO4 (olivine). Cyclic voltammograms of thin films of Z-907Na/SWNT reveal two pairs of peaks labeled C-1 and C-2 with formal redox potentials of ca. 3.6 and 3.8 V vs Li/Li+, respectively, indicating two surface-confined redox couples. The same behavior was also found for the Z-907Na adsorbed on carbon black, but not for the Z-907Na adsorbed on Al2O3 or dissolved in the electrolyte solution. In these cases, a single diffusion-controlled voltammogram is observed, with one redox couple at ca. 3.6 V vs Li/Li+. The diffusion coefficients equal 7.8x10(-10) cm(2)/s (for Z-907Na adsorbed on Al2O3) or 1.5x10(-6) cm(2)/s (for Z-907Na in solution). An interpretation is suggested that the C-1 peak is for a hydrophilic interaction, that is anchoring of Z-907Na to the carbon surface via carboxylic groups, and the C-2 peak is for a hydrophobic anchoring, that is interaction with the carboxyl-free bipyridine ligand with the carbon surface. The existence of C-1/C-2 peaks provides further insight into the nanotube wiring of LiFePO4 (olivine) using various nanotubes.

The poor electronic conductivity of LiFePO4 has been one of the major issues impeding it from achieving high power and energy density lithium-ion batteries. In this communication, a novel polymer-wiring concept was proposed to improve the conduction of the insulating electrode material. By using a polymer with tethered “swing” redox active molecules (S) attached on a polymer chain, as the standard redox potential of S matches closely the Fermi level of LiFePO4, electronic communication between the redox molecule and LiFePO4 is established. Upon charging, S is oxidized at the current collector to S+, which then delivers the charge (holes) to the LiFePO4 particles by intermolecular hopping assisted by a “swing” – type motion of the shuttle molecule. And Li+ is extracted. Upon discharging, the above process is just reversed. Preliminary studies with redox polymer consisting of poly (4-vinylpyridine) and phenoxazine moiety tethered with a C12 alkyl chain have shown promising result with carbon-free LiFePO4, where effective electron exchange between the shuttle molecule and LiFePO4 has been observed. In addition, as the redox polymer itself could act as binder, we anticipate that the polymer-wiring concept would provide a viable approach to conducting-additive and binder free electrode for high energy density batteries.

Mit Kohlenstoff beschichtete LiMn0.8Fe0.2PO4-Nanopartikel (siehe TEM-Bild) aus einer Festkörpersynthese erwiesen sich als hervorragendes Kathodenmaterial für Lithiumionenbatterien: Neben einer stabilen reversiblen Kapazität von 165 mA h g−1 wurden ein hervorragendes Zyklusverhalten, schnelles Ansprechverhalten, eine hohe Temperaturbeständigkeit und sehr geringe Oberflächenreaktivität beobachtet.

We review herein several important aspects of surface chemistry in Li-ion batteries, and discuss the use of ionic liquids (ILs) for rechargeable Li batteries. We explored the suitability of ILs for 5V cathodes and Li-graphite anodes. Some advantages of the use of ILs to attenuate the thermal behavior of delithiated cathode materials are demonstrated. We also report briefly on a comparative study of the following cathode materials: LiNi0.5Mn0.5O2; LiNi0.33Mn0.33Co0.33O2; LiNi0.4Mn0.4Co0.2O2; LiNi0.8Co0.15Al0.05O2 and LiMnPO4, in standard electrolyte solutions based on mixtures of alkyl carbonates and LiPF6. We also discuss aging, rate capability, cycle life and surface chemistry of these cathode materials. The techniques applied included electrochemical measurements, e.g., XRD, HRTEM, Raman spectroscopy, XPS and FTIR spectroscopy. We found that ILs based on cyclic quaternary alkyl ammonium cations may provide much better electrolyte solutions for 5V cathodes than standard electrolyte solutions, while being quite suitable for Li-graphite electrodes. All the lithiated transition metal oxides studied (as mentioned above) develop unique surface chemistry during aging and cycling due to the acid-base and nucleophilic reactions of their surface oxygen anions. LiMn0.33Ni0.33Co0.33O2 has the highest rate capability compared to all the other above-mentioned cathode materials. Cathodes comprising nanometric size carbon-coated LiMnPO4 produced by HPL demonstrate a better rate capability than LiNi0.5Mn0.5O2 and LiNi0.8Co0.15Al0.05O2 cathodes. The former material seems to be the least surface reactive with alkyl carbonates/LiPF6 solutions, among all the cathode materials explored herein.

A novel polyol synthesis was adopted to synthesize nano-structured LiMnPO4. This route yields well-crystallized nanoparticles with platelet morphology that are only ∼30 nm thick oriented in the b direction. The obtained material presented a good rate behavior and a very long cyclic life both at room temperature (RT) and 50 °C. The sample exhibited a specific capacity of 145 mAh g−1 at C/20, 141 mAh g−1 at C/10 rate and 113 mAh g−1 1C rate. This represents is the highest performance results reported to date for this material. The high rate performance is ascribed to the platelet shape of the LiMnPO4 as it minimizes the paths for Li diffusion. At elevated temperature (50 °C) this material demonstrated improved reversible capacity of 159 mAh g−1 at C/10 and 138 at 1C. The electrode retained 95% of its capacity, over 200 cycles, both at RT and 50 °C. This electrochemical stability is ascribed to the structural strength of the P–O bond and the stability of the electrolyte–LiMnPO4 interface. It allows us to conclude that the impact of a possible Jahn–Teller distortion is not critical. These excellent results clarified some ambiguities on LiMnPO4 as cathode materials, and demonstrate its promise for its practical application.

The amphiphilic Ru-bipyridine complex, Z-907Na acts as a surfactant for solubilization of single walled carbon nanotubes (SWNTs) in acetonitrile+t-butanol. The supramolecular assembly Z-907Na/SWNT was characterized by optical and Raman spectro/electrochemistry. Its redox potential of 3.5 V vs. Li/Li is matching almost exactly the formal potential of LiFePO4/FePO4 couple. The Z907Na/SWNT assembly is adsorbed on the surface of LiFePO4 (olivine) via the free carboxylic groups at the bipyridine ligand. This provides a composite material with roughly monolayer coverage by Z-907Na. Electrodes fabricated from Z-907Na/SWNT/LiFePO4 composite exhibited greatly enhanced activity for electrochemical Li extraction/insertion compared to the performance of electrodes made from pure LiFePO4.