X-ray and neutron diffraction studies were carried out on highly ordered (2−3% Li/Ni exchange) layered Li1 - x Co1/3Ni1/3Mn1/3O2 [(1 − x) = 1.0; 0.8, 0.6, 0.45, 0.30, 0.04] prepared by chemical delithiation and relithiation. The studies reveal that the initial R3̄m phase (O3) is maintained up to extraction of 0.70−0.75 Li and exhibits only ∼1% change in volume over the range of composition. Additional extraction of Li results in the appearance of the O1 phase (trigonal; P3̄m1), which displays a strong contraction in the c axis by 5.3% and a volume decrease of 7.2%. Oxygen vacancies were not evident in the completely delithiated material. Re-intercalation of lithium in this phase was relatively irreversible, however, resulting in poorly defined mixtures of the O3 and O1 structures that exhibited a large fraction of stacking faults. In contrast, materials that were not delithiated beyond x = 0.30 resulted in fully reversible reformation of the original crystalline O3 phase on re-intercalation. Electrochemical cycling under different cutoff voltages were in accord with these observations and suggest an optimum upper cutoff voltage of 4.3−4.4 V.

LiFePO 4 is a promising cathode material for lithium-ion batteries despite its low intrinsic electronic conductivity. We show, using a combination of Mössbauer, X-ray diffraction, and X-ray photoelectron spectroscopy ͑XPS͒, that conductive metal phosphides which enhance its electrochemical performance ͑FeP, and metallic Fe 2 P͒, are generated on the surface of the parent LiFePO 4 by reaction with in situ carbon from iron citrate and reducing gases such as hydrogen. Their relative fraction, nature, and location was quantified. Under the most mild reducing conditions, nanosized FeP is formed on the surface along with Li 3 PO 4 , and carbon resulting from the precursor. Under more aggressive reducing conditions, FeP is still present, but thermodynamics now favor the formation of Fe 2 P, with fractions varying from 4 to 18 wt % depending on the temperature and atmosphere used for treatment. Both large ͑0.5 m͒ crystallites, and amorphous or nanodimensioned particles are present. XPS studies reveal that the amorphous or nanodimensioned Fe 2 P lies on the inner surface adjacent to the LiFePO 4 , and the residual carbon lies on the outer surface. The resulting LiFePO 4 "composites" show significantly enhanced electrochemical rate properties as well as outstanding cyclability, which allows a high discharge capacity of ϳ105 mAh g −1 at a 14.8C rate ͑2500 mA g −1 ͒.

Lithium metal phosphates are amongst the most promising cathode materials for high capacity lithium-ion batteries. Owing to their inherently low electronic conductivity, it is essential to optimize their properties to minimize defect concentration and crystallite size (down to the submicron level), control morphology, and to decorate the crystallite surfaces with conductive nanostructures that act as conduits to deliver electrons to the bulk lattice. Here, we discuss factors relating to doping and defects in olivine phosphates LiMPO4 (M = Fe, Mn, Co, Ni) and describe methods by which in situ nanophase composites with conductivities ranging from 10(-4)-10(-2) S cm(-1) can be prepared. These utilize surface reactivity to produce intergranular nitrides, phosphides, and/or phosphocarbides at temperatures as low as 600 degrees C that maximize the accessibility of the bulk for Li de/insertion. Surface modification can only address the transport problem in part, however. A key issue in these materials is also to unravel the factors governing ion and electron transport within the lattice. Lithium de/insertion in the phosphates is accompanied by two-phase transitions owing to poor solubility of the single phase compositions, where low mobility of the phase boundary limits the rate characteristics. Here we discuss concerted mobility of the charge carriers. Using Mössbauer spectroscopy to pinpoint the temperature at which the solid solution forms, we directly probe small polaron hopping in the solid solution Li(x)FePO4 phases formed at elevated temperature, and give evidence for a strong correlation between electron and lithium delocalization events that suggests they are coupled.

Ordered mesoporous carbon materials with a semi-graphitized structure have been synthesized by directly employing a tri-block copolymer as a structure directing agent and carbon source to form mesoporous carbon. Poly(ethylene oxide)20-poly(propylene oxide)70-poly(ethylene oxide)20 (EO20PPO70EO20), or “P123”, was cross-linked in the channels of mesoporous silicate, carbonized, and graphitized. Extraction of the silica produces a mesoporous graphitic carbon replica. The graphitization of carbon was realized by employing transition metals (Fe, Co, Ni) as a catalyst in a reducing atmosphere. Of the three transition metal catalysts, nickel was found to be the best candidate in terms of preserving structural order. All three nanoporous carbon materials have 3 orders higher conductivity and better thermal stability than non-graphitic carbon. A composite of ordered mesostructured carbon/metallic MoO2 (63.7 wt % MoO2) was prepared and examined as a negative electrode in a lithium rechargeable battery. The material exhibited a reversible capacity of 760 mA·h/g in the voltage window 3.0−0.0 V.

Amongst solid solutions of the Li-Ni-Mn-Co-O series, LiNi1/3Mn1/3Co1/3O2 has received much attention owing to its high capacity and thermal stability. A major issue in these ordered rock salt structures is the irreversibility on the first cycle, and degree of Li+/Ni2+ cation disorder which inhibits the rate capability. To examine these factors, different synthesis methods were employed which led to LiNi1/3Mn1/3Co1/3O2 that exhibited varying degrees of cation disorder. Neutron diffraction studies were carried out on samples (LixNi1/3Mn1/3Co1/3O2, x = 1.00 → 0.04) prepared by chemical oxidation. The studies reveal that the extent of Ni2+/Li+ disorder between the 3b and 3a sites was preserved on Li extraction and re-insertion. Complete extraction of lithium to form the O1 phase was achieved in some materials. However, reformation of the O3 phase on chemical relithiation does not occur in these cases, whereas materials that only partly convert to the Ol phase exhibit complete conversion back to the O3 phase on relithiation. The differences are attributed to lithium site occupancy/stoichiometry and crystallite size effects.