No abstract

Surface impurity species, most notably Li 2 CO 3 , that develop on layered oxide positive electrode materials with atmospheric aging have been reported to be highly detrimental to the subsequent electrochemical performance. LiNi 0.8 Co 0.15 Al 0.05 O 2 (NCA) was used as a model layered oxide compound to evaluate the growth and subsequent electrochemical impact of H 2 O, LiHCO 3 , LiOH and Li 2 CO 3 . Methodical high temperature annealing enabled the systematic removal of each impurity specie, thus permitting the determination of each specie's individual effect on the host material's electrochemical performance. Extensive cycling of exposed and annealed materials emphasized the cycle life degradation and capacity loss induced by each impurity, while rate capability measurements correlated the electrode impedance to the impurity species present. Based on these characterization results, this work attempts to clarify decades of ambiguity over the growth mechanisms and the electrochemical impact of the specific surface impurity species formed during powder storage in various environments.

The electrochemical reactivity of cations such as Ca 2ϩ , Mg 2ϩ , and Y 3ϩ into crystalline V 2 O 5 materials was investigated. The ionic diffusion constant of Li ϩ and Y 3ϩ into microcrystalline and nanocrystalline V 2 O 5 was measured by the galvanostatic intermittent titration technique. The Y 3ϩ ion diffusion constant into a 500 nm crystalline V 2 O 5 was found to be approximately two orders of magnitude lower than for the Li ϩ ion. In order to enable practical intercalation of Y 3ϩ , a nanocrystalline V 2 O 5 was fabricated through a combustion flame synthesis technique. For the first time, reversible electrochemical intercalation of Y 3ϩ into a host structure was shown to be feasible. An asymmetric hybrid cell configuration was utilized in order to provide a reversible counter electrode during intercalation. Preliminary data indicates Y 3ϩ can be reversibly intercalated into V 2 O 5 with apparent gravimetric capacities exceeding that of Ca 2ϩ , Mg 2ϩ , or Li ϩ over the limited voltage range of 2.5 to 4.2 V (Li/Li ϩ ). The concept of polyvalent intercalation is discussed relative to intercalation, pseudocapacitance, apparent specific capacity, and practical energy storage systems.High energy density electrochemically rechargeable energy storage systems are the key to the future realization of a myriad of next generation applications ranging from biomedical to electric vehicles. Currently, there exist two commercialized single-ion room temperature secondary battery technologies utilizing at least one intercalation electrode, NiMeH ͑proton͒ and Li ion ͑lithium͒. NiMeH batteries utilize the reversible intercalation of a H ϩ guest cation into NiOOH and alloying reactions with rare earth or misch metal counter electrodes. The basic Li-ion battery utilizes intercalation reactions of Li ϩ into transition metal positive electrodes or carbonbased negative electrodes. Presently, the Li-ion battery is the highest energy density commercialized rechargeable battery technology. This technology has the future potential to far exceed the theoretical energy densities of the aqueous NiMeH technology. Although much research has focused on the improvement of the host electrodes for Li-ion guest cation intercalation, little work has focused on alternative guest cation species to replace the Li ϩ cation.The use of Na ϩ as a low cost, potentially less reactive cation for rocking chair intercalation batteries is the most prevalent of the reported research on alternative guest cation intercalation. 1-7 Na ϩ cells have seen little commercial success because of the lack of suitable electroactive negative electrode materials. Fewer papers have focused on polyvalent cation intercalation reactions in order to develop alternative rocking chair cells using guest cations with valences greater than one. 8 Of these, the development of Mg 2ϩ -based batteries and related electrolytes 9-12 are the most widely discussed. Electrochemical intercalation of Mg 2ϩ into a number of metal oxides and sulfides were investigated, 13 however, electrochemica...

Near-theoretical utilization of high-energy-density CuF 2 positive electrode materials for lithium batteries was enabled through the use of nanocomposites consisting of 2-30 nm domains of CuF 2 within a mixed ionic + electronic conducting matrix of a metal oxide. Small but significant crystallographic changes to the core crystal of the CuF 2 were found to occur in all oxide-based matrices. These modifications to the core crystal and the surrounding matrix were investigated through a host of characterization methods, including XRD, XPS, and XAS. This new approach to the enablement of the anhydrous CuF 2 is distinctly superior in performance to that of macro CuF 2 or CuF 2 nanocomposites utilizing carbon as a matrix, the latter of which is also introduced herein for the first time.