We have prepared the Li-rich layered NMC composite cathode material of the composition 0.3Li 2 MnO 3 0.7LiMn 0.33 Ni 0.33 Co 0.33 O 2 , (NMC) with 5 wt% Na doping. The latter material with composition of 0.3Li 2 MnO 3 .0.7Li 0.97 Na 0.03 Mn 0.33 Ni 0.33 Co 0.33 O 2 , synthesized as 200-300 nm size particles, was compared to its counterpart without Na. The discharge rate capability of the Li-rich NMC was greatly improved at both room temperature and 50 • C with the Na doping. The Na doped material exhibited significantly higher conductivity than its un-doped analog as evidenced by dc electronic conductivity data and impedance of Li cells. Charge/discharge cycling results of Li cells at 50 • C indicated that the voltage decay of Li-rich NMC accompanied by a layer to spinel structural conversion was mitigated with Na doping. XRD analysis revealed that ionic exchange of Na occurs upon contact of the cathode material with the electrolyte and produces a volume expansion of the crystal lattice which triggers a favorable metal (probably Ni) migration to Li depleted regions during oxidation of Li 2 MnO 3 in the first cycle. XANES data showed that Na doped NMC has better Ni reduction efficiency to provide higher rate capability. EXAFS data supported this conclusion by showing that in the case of Na doped NMC, the structure has larger crystal cage allowing for better metal migration into the Li depleted regions located in the layered unit cell of C2/m space group. XANES of Mn K-edge supported by pre-edge analysis also revealed that during charging of the electrode, the Na doped NMC was oxidized to a higher Mn valence state compared to its undoped counterpart.

A new lithium rich composite positive electrode material of the composition 0.3Li 2 MnO 3 .0.7LiNi 0.5 Co 0.5 O 2 (LLNC) was synthesized using the conventional co-precipitation method. Its crystal structure and electrochemistry in Li cells have been compared to that of the previously known material, 0.3Li 2 MnO 3 .0.7LiMn 0.33 Ni 0.33 Co 0.33 O 2 (LLNMC). The removal of Mn from the LiMO 2 (M = transition metal) segment of the composite cathode material allowed us to determine the location of the manganese oxide moiety in its structure that triggers the layered to spinel conversion during cycling. The new material resists the layered to spinel structural transformation under conditions in which LLNMC does. X-ray diffraction patterns revealed that both compounds, synthesized as approximately 300 nm crystals, have identical super lattice ordering attributed to Li 2 MnO 3 existence. Using X-ray absorption spectroscopy we elucidated the oxidation states of the K edges of Ni and Mn in the two materials with respect to different charge and discharge states. The XAS data along with electrochemical results revealed that Mn atoms are not present in the LiMO 2 structural segment of LLNC. Electrochemical cycling data from Li cells further revealed that the absence of Mn in the LiMO 2 segment significantly improves the rate capabilities of LLNC with good capacity maintenance during long term cycling. Removing the Mn from the LiMO 2 segment of lithium rich layered metal oxides appears to be a good strategy for improving the structural robustness and rate capabilities of these high capacity cathode materials for Li-ion batteries.The lithium rich layered metal oxide cathode materials of the formula (1-x)Li 2 MnO 3 .xLiMnO 2 for Li-ion batteries have spurred great interest due to their exceptionally high discharge capacities, reaching almost 300 mAh/g, 1,2 or one electron transfer per transition metal. These materials, also known as layered metal oxide composite cathodes, offer the greatest promise to meet the energy and power demands of batteries for hybrid electric vehicles (HEVs) and electric vehicles (EVs). The myriad investigations reported to further advance these cathode materials include substitution of some of the Mn in the LiMnO 2 segment of parent structure with other transition metals, 3-6 special surface treatments using (NH 4 ) 2 HPO 4 solution 7 and ZnO, 8 and coating with the Li + -conducting solid electrolyte LiPON 9 aiming to improve the surface chemistry of (1-x)Li 2 MnO 3 .xLiMnO 2 during Li 2 O removal. Other modifications of these composite cathode materials attempted include suppression of possible oxygen vacancies created during Li 2 MnO 3 activation and development of new preparation methods. Among the alternative syntheses methods, there is a microsphere particle driven method, 10 molten salt technique, 11 and synthesis directly from Li 2 MnO 3 to incorporate NiO rock-salt regions 12 to enhance rate capability. During the first charge of (1-x)Li 2 MnO 3 . xLiMO 2 , (where M = Mn, Ni and Co) Li extraction...

We report a high rate Li-rich layered manganese nickel cobalt (MNC) oxide cathode material of the composition 0.5Li 2 MnO 3 $0.5LiMn 0.5 Ni 0.35 Co 0.15 O 2 , termed Li-rich MNC cathode material, with discharge capacities of 200, 250, and 290 mA h g À1 at C, C/4 and C/20 rates, respectively, for Li-ion batteries. This high rate discharge performance combined with little capacity fade during long term cycling is unprecedented for this class of lithium ion (Li-ion) cathode materials. The exceptional electrochemistry of the Li-rich MNC in Li-ion cells is attributed to its open porous morphology and high electronic conductivity. The structure of the material investigated by means of X-ray diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM) and X-ray Absorption Spectroscopy (XAS)combined with electrochemical data revealed that the porous morphology was effective in allowing electrolyte penetration through the particle grains in tandem with its high electronic conductivity to provide high Li + transport for high rate discharge. Extended cycling behavior and structural phase transition of the new material were further examined through Field Emission Scanning Electron Microscopy (FESEM), XRD, XAS and HRTEM. The new Li-rich MNC cathode material could provide the next generation Li-ion batteries with specific energy exceeding 400 W h kg À1 or energy density over 1000 W h l À1 .

Intercalation provides to the host materials a means for controlled variation of many physical/chemical properties and dominates the reactions in metal-ion batteries. Of particular interest is the graphite intercalation compounds with intriguing staging structures, which however are still unclear, especially in their nanostructure and dynamic transition mechanism. Herein, the nature of the staging structure and evolution of the lithium (Li)-intercalated graphite was revealed by cryogenic-transmission electron microscopy and other methods at the nanoscale. The intercalated Li-ions distribute unevenly, generating local stress and dislocations in the graphitic structure. Each staging compound is found macroscopically ordered but microscopically inhomogeneous, exhibiting a localized-domains structural model. Our findings uncover the correlation between the long-range ordered structure and short-range domains, refresh the insights on the staging structure and transition of Li-intercalated/deintercalated graphite, and provide effective ways to enhance the reaction kinetic in rechargeable batteries by defect engineering.

The redox behavior and kinetic parameters of five ferrocene derivatives were investigated in 1M LiPF 6 in 50:50 volume percent EC:EMC, a typical electrolyte used in lithium-ion batteries. Using cyclic voltammetry (CV) and rotating disk electrode voltammetry (RDE) techniques, the effect of electron donating and withdrawing substituents on each derivative was evaluated from the view point of the Hammett substituent constant. We found that electrochemical rate constants of the ferrocene derivatives can be related to the Hammett equation which gives an accurate approximation for predicting the oxidation potential of redox shuttles when changes are desired in their electron donating and electron withdrawing properties by means of functional group substitution. Our results show that the exchange current density and reaction rate for oxidation decrease as the electron withdrawing property of the substituent increases. It is also shown that electron donating and electron withdrawing property of a substituent affect the exchange current density and electrochemical oxidation reaction rate obeying a trend opposite to that of the Hammett substituent constants (σ). The correlations found here are expected to improve the ability to systematically design chemical overcharge protection reagents through judicious substitution of functional groups on redox shuttles.

We report the results of a comprehensive study of the relationship between electrochemical performance in Li cells and chemical composition of a series of Li rich layered metal oxides of the general formula xLi2MnO3 · (1-x)LiMn0.33Ni0.33Co0.33O2 in which x = 0,1, 0.2, 0,3, 0.5 or 0.7, synthesized using the same method. In order to identify the cathode material having the optimum Li cell performance we first varied the ratio between Li2MnO3 and LiMO2 segments of the composite oxides while maintaining the same metal ratio residing within their LiMO2 portions. The materials with the overall composition 0.5Li2MnO3 · 0.5LiMO2 containing 0.5 mole of Li2MnO3 per mole of the composite metal oxide were found to be the optimum in terms of electrochemical performance. The electrochemical properties of these materials were further tuned by changing the relative amounts of Mn, Ni and Co in the LiMO2 segment to produce xLi2MnO3 · (1-x)LiMn0.50Ni0.35Co0.15O2 with enhanced capacities and rate capabilities. The rate capability of the lithium rich compound in which x = 0.3 was further increased by preparing electrodes with about 2 weight-percent multiwall carbon nanotube in the electrode. Lithium cells prepared with such electrodes were cycled at the 4C rate with little fade in capacity for over one hundred cycles.

Solid-phase catalysts prepared by pyrolysis of Iron(II) phthalocyanine (FePC) embedded in high-surface carbons were evaluated for the catalysis of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) in Li +-conducting non-aqueous electrolytes. The ORR mechanism in high donor number (DN) dimethyl sulfoxide (DMSO)-based electrolytes is markedly different from that occurs in low DN acetonitrile(MeCN)-based electrolytes. The ORR is catalyzed by the reduced Fe(I) state of Fe(II)PC. Consequently, the Fe(II)PC/Fe(I)PC redox potential relative to O 2 reduction potential in each electrolyte is important for ORR catalysis. In MeCNbased electrolytes, the Fe(I)PC catalyst is formed at a higher potential than the ORR potential. Hence the catalyzed ORR occurs at the inner-Helmholtz plane of the electrode, stabilizing the superoxide ion (O 2 −) formed by one-electron reduction of O 2 , as Fe(I)PC-O 2 −. Indeed, LiO 2 was identified in the Raman spectra of cathodes from discharged Li-O 2 battery cells. In DMSO-based electrolytes, the Fe(I)PC formation potential occurs below the ORR potential and accordingly LiO 2 is more stable in its solvated state in the electrolyte solution as the Li(DMSO) nO 2 − ion pair. This drives the ORR at the outer-Helmholtz plane of both catalyzed and uncatalyzed electrodes in DMSO-based electrolytes. The FePC embedded carbon electrode doubled the cycle life of Li-O 2 cells utilizing low DN electrolytes.

Here we report the fabrication of a carbon-nanotube (CNT) based lithium ion electrode architecture, consisting of alternating layers of multi-walled carbon nanotubes (MWNT) and lithium ion active material, to significantly increase the aerial power and energy density of lithium ion battery cathodes. The CNT-based architecture aims to address engineering limitations of nanoscale active materials such as poor packing density, electrolyte reactivity, and costly fabrication. The alternating layers create a highly porous and highly conductive scaffolding to enhance ionic and electronic transport pathways within the electrode. The results show that the presented CNT-based architecture yielded excellent rate capability and highly stable cycling of lithium manganese oxide (LiMn 2 O 4 ) active materials and lithium (Li) rich layered (xLi 2 MnO 3 • (1-x)LiMO 2 ) materials. For LiMn 2 O 4 materials, the CNT-based architecture demonstrates 14-20x higher aerial capacity over standard fabrication electrodes at discharge rates of 10C. For Li-rich layered materials, the CNT-based architecture demonstrates 70% higher aerial capacity over standard fabrication electrodes at discharge rates of C/2. Highly stable cycling for 100 cycles at 15C for LiMn 2 O 4 and 500 cycles at 1C for Li-rich layered materials is also observed using the CNT-based architecture. The effect of the number of layers, layer thickness, and composition of the active material is investigated.