The electrochemical and optical properties of lithium phosphorous oxynitride (Lipon) thin films have been studied with an emphasis on the stability window vs. lithium metal and the behavior of the Li/Lipon interface. Impedance measurements made between -26 and 140°C show that Lipon exhibits a single, Lit-ion conducting phase with an average conductivity of 2.3 (±07) X 10' S/cm at 25°C and an average activation energy of E, = 0.55 0.02 eV. No detectable reaction or degradation was evident at the Li/Lipon interface, and linear sweep voltammetry measurements on three-electrode cells indicated that Lipon is stable from 0 to about 5.5 V with respect to a Li7Li reference. The complex refractive index of Lipon was measured by spectroscopic ellipsometry. Optical bandgaps of 3.45 and 3.75 eV were obtained from the ellipsometry data and from optical absorption measurements, respectively.

Research over the last decade at Oak Ridge National Laboratory has led to the development of solid-state thin-film lithium and lithium-ion batteries. The batteries, which are less than 15 mm thick, have important applications in a variety of consumer and medical products, and they are useful research tools in characterizing the properties of lithium intercalation compounds in thin-film form. The batteries consist of cathodes that are crystalline or nanocrystalline oxide-based lithium intercalation compounds such as LiCoO and LiMn O , and anodes of lithium metal, inorganic compounds such as can deliver up to 30% of their maximum capacity between 4.2 and 3 V at discharge currents of 10 mA / cm , and at more moderate discharge-charge rates, the capacity decreases by negligible amounts over thousands of cycles. Thin films of crystalline lithium manganese oxide with the general composition Li Mn O exhibit on the initial charge significant 11x 22y 4 capacity at 5 V and, depending on the deposition process, at 4.6 V as well, as a consequence of the manganese deficiency-lithium excess. The 5-V plateau is believed to be due to oxidation Mn of ions to valence states higher than 1 4 accompanied by a rearrangement of the lattice. The gap between the discharge-charge curves of cells with as-deposited nanocrystalline Li Mn O cathodes is due to a true hysteresis as opposed to a kinetically hindered relaxation observed 11x 22y 4with the highly crystalline films. This behavior was confirmed by observing classic scanning curves on charge and discharge 1 at intermediate stages of insertion and extraction of Li ions. Extended cycling of lithium cells with these cathodes at 25 and 1008C leads to grain growth and evolution of the charge-discharge profiles toward those characteristic of well crystallized films.

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It is an old concept to fabricate lithium batteries in the discharged state with only an appropriate current collector as the negative electrode (anode). On the initial charge, metallic Li is electroplated at this anode current collector, and so, during electrochemical cycling, the battery operates as a Li battery which contains only the amount of lithium that is supplied by the positive electrode (cathode).Despite some improvements, 1 the manufacture of a practical, rechargeable Li battery that operates exclusively with an in situ plated Li anode has been prevented by the formation of mossy, dendritic, and granular metallic lithium deposits on metal foils. 2 In this paper, we report on the feasibility and electrochemical properties of a Cu/solid lithium electrolyte/LiCoO 2 thin-film battery, where Cu represents an anode current collector that does not form intermetallic compounds with lithium. Prior to the initial charge, all of the battery components are stable in air for several hours, which facilitates handling and processing of this "Li-free" lithium battery.During operation, this Li-free battery shows the maximum potential and high rate capability inherent in a Li battery but avoids the major drawbacks of a battery fabricated with a Li metal anode. The vapor deposition of a metallic lithium film is more complicated than the deposition of other metal films that are less air sensitive, and due to the low melting point of lithium (181ЊC) a Li battery does not survive the 250ЊC solder reflow process commonly used to assemble electronic circuit boards. 3 In this paper, we demonstrate that the Li free battery with an in situ plated Li anode shows no signs of degradation after being heated at 250ЊC in air for 10 min in the Li-free state. Furthermore, complete stripping of the electroplated Li anode is reversible, and since no excess Li is present, the Li-free battery cannot be destroyed by overdischarging the LiCoO 2 cathode, in contrast to a conventional Li-LiCoO 2 battery.The Li-free battery prior to operation resembles a Li-ion battery, which is also assembled in its fully discharged state. However, the Li-free battery avoids the capacity problem inherent to tin oxide-and oxynitride-based insertion materials 3-7 which have recently been proposed as anodes for Li-ion cells. These anodes are known to consume, irreversibly, between 40 and 60% of the lithium inserted during their electrochemical activation in the initial cycle due to the formation of an amorphous matrix containing Li 2 O or Li 3 N. [3][4][5]8 Despite the technically high capacity of these anodes, between 600 and 700 mAh/g, the unsatisfactory ratio of reversible to irreversible capacity severely limits the utilization of the cathode, which serves as the Li-ion cell's initial lithium source. Recently, we showed that the cathode utilization could be improved by fabricating cathodeheavy cells in which a good deal of the total reversible cell capacity was obtained by electrochemical plating and stripping of metallic lithium from the overlithiated anode ...

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Polycrystalline films of LiCoO 2 deposited by radio frequency magnetron sputtering exhibited a strong preferred orientation or texturing after annealing at 700ЊC. For films thicker than about 1 m, more than 90% of the grains were oriented with their (101) and (104) planes parallel to the substrate and less than 10% with their (003) planes parallel to the substrate. As the film thickness decreased below 1 m, the percentage of (003)-oriented grains increased until at a thickness of about 0.05 m, 100% of the grains were (003) oriented. These extremes in texturing were caused by the tendency to minimize volume strain energy for the thicker films or the surface energy for the very thin films. Films were deposited using different process gas mixtures and pressures, deposition rates, substrate temperatures, and substrate bias. Of these variables, only changes in substrate temperature could cause large changes in texturing of thick films from predominately ( 101)-( 104) to (003). Although lithium ion diffusion should be much faster through cathodes with a high percentage of (101)-and (104)-oriented grains than through cathodes with predominately (003)-oriented grains, it was not possible to verify this expectation because the resistance of most cells was dominated by the electrolyte and electrolyte-cathode interface. Nonetheless, cells with cathodes thicker than about 2 m could deliver more than 50% of their maximum energies at discharge rates of 5 mA/cm 2 or higher.

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Thin-film rechargeable lithium batteries with amorphous and crystafline LiCoO2 cathodes were investigated, The lithium cobalt oxide films were deposited by radio-frequency (RF) magnetron sputtering of an LiCoO2 target in a 3:1 Ar/02 mixture gas. From proton-induced -y-ray emission analysis (PIGE) and Rutherford backscatterung spectrometry (RBS), the average composition of these films was determined to be Li115CoO216 or, within experimental uncertainty, LiCoO2 + 0.08 Li20. The x-ray powder diffraction patterns of films annealed in air at 500 to 7 00°C were consistent with the regular hexagonal structure observed for crystalline LiCoO2. The discharge curves of the cells with amorphous LiCoO2 cathodes showed no obvious structural transition between 4.2 and 2.0 V, while the discharge curves of the cells with polycrystalline cathodes were consistent with a two-phase potential plateau at -3.9 V with a relatively large capacity. Two lower capacity plateaus were observed at ---4.2 and 4.1 V with the 600 and 700°C annealed cathodes; the -dq/dV peaks were broader and weaker for the 600°C annealed cathodes and were not present at all with the 500°C annealed films. The chemical diffusion coefficients of Li in the cathodes obtained from ac impedance measurements at cell potentials of -4 V ranged from ,1012 cm2/s for the as-deposited amorphous cathodes to --10 cm2/s for the films annealed at 700°C. The capacity loss on extended cycling of the thin-film cells varied with the crystallinity and thickness of the cathodes and with temperature. With the highly crystalline, 700°C annealed material, losses on cycling between 4.2 and 3.8 V at 25°C ranged from 0.0001%/cycle (>1O cycles) to 0.002%/cycle for cells with cathodes from 0.05 to 0.5 m thick.