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LiMnPO 4 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 Ͼ4 V vs Li/Li + , with a reasonable capacity retention during prolonged charge/discharge cycling. The rate capability of the LiMnPO 4 electrodes studied herein was higher than that of LiNi 0.5 Mn 0.5 O 2 and LiNi 0.8 Co 0.15 Al 0.05 O 2 ͑NCA͒ in similar experiments and measurements. The active mass studied herein seems to be the least surface reactive in alkyl carbonate/LiPF 6 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 LiMnPO 4 material in solutions ͑measured by differential scanning calorimetry͒ is much higher compared to that of transition-metal oxide cathodes. This is demonstrated herein by a comparison with NCA electrodes. 2 Among them, LiMnPO 4 is of particular interest as it offers the advantages of a flat discharge voltage profile at 4.1 V vs Li/Li + , the expected safety features, and an abundance of the relevant elements in the earth's crust.1-6 Hence, LiMnPO 4 can be an ideal substitute for the commonly used cathode material, LiCoO 2 , which is expensive, toxic, and demonstrates problematic safety features. The three-dimensional framework of the olivine structure is stabilized by the strong covalent bonds between the oxygen and the P 5+ ions, resulting in PO 4 3− tetrahedral polyanions. As a result, lithium metal phosphate materials do not undergo a structural rearrangement during lithiation and delithiation. This indicates that LiMPO 4 electrodes may demonstrate better stability and capacity retention during prolonged cycling as compared to lithiated transition-metal oxide cathode materials such as LiCoO 2 , LiNiO 2 , LiMnO 2 , and LiMn 2 O 4 . However, LiMPO 4 compounds and LiMnPO 4 , in particular, suffer from poor electronic and ionic ͑Li + ͒ conductivity, which means a limited rate capability ͑especially at low temperatures͒.

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Li 4 Ti 5 O 12 ͑spinel͒ materials were prepared with Brunauer-Emmett-Teller surface areas ranging from 1.3 to 196 m 2 /g. The corresponding average particle sizes varied from ca. 1 m to ca. 9 nm. Twenty-five different materials were tested as Li insertion hosts in thin-film electrodes ͑2-4 m͒ made from a pure spinel. Trace amounts of anatase in Li 4 Ti 5 O 12 were conveniently determined by cyclic voltammetry of Li insertion. Electrodes from nanocrystalline Li 4 Ti 5 O 12 exhibited excellent activity towards Li insertion, even at charging rates as high as 250C. The charge capability at 50-250C was proportional to the logarithm of surface area for coarse particles ͑surface areas smaller than ca. 20 m 2 /g͒. With increasing charge/discharge rates, a narrowing plateau in performance was observed for materials with surface areas between ca. 20 to 100 m 2 /g. These materials can be charged/discharged nearly to the nominal capacity of Li 4 Ti 5 O 12 ͑175 mAh/g͒ within a wide range of the rates. Very small particles (surface areas Ͼ 100 m 2 /g) exhibit a growing decrease of charge capability at 50-250C. The Li-diffusion coefficients, calculated from chronoamperometry, decrease by orders of magnitude if the average particle size drops from ca. 1 m to ca. 9 nm. However, the sluggish Li ϩ transport in small particles is compensated by the increase in active electrode area. Materials having surface areas larger than ca. 100 m 2 /g also tend to show increased charge irreversibility. This could be caused by parasitic cathodic reactions, due to enhanced adsorption of reducible impurities ͑humidity͒ or the quality of the spinel crystalline lattice itself. The optimum performance of thin-film Li 4 Ti 5 O 12 electrodes is achieved, if the parent materials have surface areas between ca. 20 to 110 m 2 /g, with the maximum peak at 100 m 2 /g. Spinel oxides Li 1ϩx Ti 2Ϫx O 4 ; 0 р x р 1/3 were introduced in the early 1990s as promising zero-strain Li-insertion hosts. 1-3 The cubic lattice constant, a ͑space group Fd3m) scales with composition ͑x͒ according to Eq. 1 ͑for a in nm͒ 4The relations between composition ͑x͒ and Li-insertion thermodynamics were not studied very systematically, but the end members of the series, i.e., LiTi 2 O 4 and Li 4/3 Ti 5/3 O 4 (Li 4 Ti 5 O 12 ) exhibited the formal potential of Li insertion 1.36-1.338 V and 1.55-1.562 V, respectively. 1,5 The Li 1ϩx Ti 2Ϫx O 4 ͑spinels͒ are usually prepared by solid-state reactions of suitable Li-and Ti-containing precursors during 12-24 h at 800-1000°C. 1,2,4-11 The particle size was not systematically addressed in most cited works, but Abraham et al. 11 have reported that the solid-state reaction of TiO 2 with Li 2 CO 3 or LiOH gave at 800°C micrometer-sized product. Amatucci et al. 12,13 have recently reported on nanocrystalline Li 4 Ti 5 O 12 resulting from a hightemperature solid-state reaction of TiO 2 and Li 2 CO 3 , 12 but neither the particle size nor preparative details were specified in their works. 12,13 Alternatively, the lithium titanate spinels can also ...