Lithium Phosphorus Oxynitride Films Research Articles

Conformal High-Aspect-Ratio Solid Electrolyte Thin Films for Li-Ion Batteries by Atomic Layer Deposition.

Lithium phosphorus oxynitride (LiPON) is a state-of-the-art solid electrolyte material for thin-film microbatteries. These applications require conformal thin films on challenging 3D surface structures, and among the advanced thin-film deposition techniques, atomic layer deposition (ALD) is believed to stand out in terms of producing appreciably conformal thin films. Here we quantify the conformality (i.e., the evenness of deposition) of thin ALD-grown LiPON films using lateral high-aspect-ratio test structures. Two different lithium precursors, lithium tert-butoxide (LiOtBu) and lithium bis(trimethylsilyl)amide (Li-HMDS), were investigated in combination with diethyl phosphoramidate as the source of oxygen, phosphorus, and nitrogen. The results indicate that the film growth proceeded significantly deeper into the 3D cavities for the films grown from LiOtBu, while the Li-HMDS-based films grew more evenly initially, right after the cavity entrances. These observations can be explained by differences in the precursor diffusion and reactivity. The results open possibilities for the use of LiPON as a solid electrolyte in batteries with high-surface-area electrodes. This could enable faster charging and discharging as well as the use of thin-film technology in fabricating thin-film electrodes of meaningful charge capacity.

Synthesis of LiPON Solid Electrolyte Films by Thermal Evaporation of Lithium Orthophosphate

Lithium phosphorus-oxynitride (LiPON) films were deposited by the method of anodic evaporation of Li3PO4 in the nitrogen plasma of a low-pressure arc. A method for adjusting the degree of decomposition of vapors is proposed based on a change in the frequency of interaction of electrons with vapors at a constant heating power of the anode-crucible. The conditions ensuring the formation of films with a homogeneous microstructure and ionic conductivity (1–2) × 10−6 S/cm at a deposition rate of 8 nm/min have been determined. It is shown that the degree of vapor dissociation critically affects the morphology of the films and the magnitude of their ionic conductivity. The results of cyclic tests of LiPON films deposited by anodic evaporation in a low-pressure arc are presented.

A free-standing lithium phosphorus oxynitride thin film electrolyte promotes uniformly dense lithium metal deposition with no external pressure.

Lithium phosphorus oxynitride (LiPON) is an amorphous solid electrolyte that has been extensively studied over the last three decades. Despite the promise of pairing it with various electrode materials, LiPON's rigidity and air sensitivity set limitations to understanding its intrinsic properties. Here we report a methodology to synthesize LiPON in a free-standing form that manifests remarkable flexibility and a Young's modulus of ∼33 GPa. We use solid-state nuclear magnetic resonance and differential scanning calorimetry to quantitatively reveal the chemistry of the Li/LiPON interface and the presence of a well-defined LiPON glass-transition temperature of 207 °C. Combining interfacial stress and a gold seeding layer, our free-standing LiPON shows a uniformly dense deposition of lithium metal without the aid of external pressure. This free-standing LiPON film offers opportunities to study fundamental properties of LiPON for interface engineering for solid-state batteries.

Robust Transport: An Artificial Solid Electrolyte Interphase Design for Anode-Free Lithium-Metal Batteries.

One of the most challenging issues in the practical implementation of high-energy-density anode-free lithium-metal batteries (AFLMBs) is the sharp capacity attenuation caused by the mechanical degradation of the solid electrolyte interphase (SEI). However, developing an artificial SEI to address this issue remains a challenge due to the trade-off between ionic conductivity and mechanical robustness for general ionic conducting films. In this study, a tenacious composite artificial SEI with integrated heterostructure of lithium fluoride (LiF) and lithium phosphorus oxynitride (LiPON) is prepared using a co-sputtering approach to achieve both high ionic conductivity and fracture toughness. The embedded LiF domain has an extremely high Young's modulus and surface energy compared with those of bulk LiPON film, enabling a significant increase in fracture toughness by an order of magnitude. Most importantly, the interface between LiPON and LiF in the integrated structure generates additional fast Li+ -transport pathways, providing the artificial SEI with a conductivity higher than 10-6 Scm-1 . Consequently, the artificial SEI implementation significantly increases the cycling lifetime of the corresponding AFLMBs by >250%. This study highlights the importance of fracture toughness for the structural integrity of batteries and provides suggestions for designing viable SEI materials for high-performance AFLMBs.

Preparation of highly ionic conductive lithium phosphorus oxynitride electrolyte particles using the polygonal barrel-plasma treatment method

Herein, lithium phosphorus oxynitride (LiPON) electrolyte particles with high ionic conductivity were prepared using the polygonal barrel-plasma treatment method. Results showed that the ionic conductivity of Li3PO4 (particle size: 77 nm) was improved via the N2-plasma treatment (treatment time: 60–180 min). The maximum ionic conductivity (8.8 × 10–6 S cm–1 at room temperature) was obtained for a treatment time of 90 min, and it approximates that of amorphous LiPON films in literature. X-ray photoelectron spectroscopy of the treated samples (particle size: 29 µm) revealed the formation of LiPON: the area ratio of triply coordinated nitrogen (P–N<P2) versus doubly coordinated nitrogen (P–NP) bonds, which compose LiPON, increased as the treatment time increased to 90 min, and then decreased. The particle surface morphology hardly changed during treatment, whereas the cross-sectional observation showed that at least 320-nm amorphous LiPON layer was formed near the particle surfaces. Based on the LiPON layer thickness, it was found that amorphous LiPON particles can be obtained through N2-plasma treatment of 77 nm Li3PO4 particles. However, the formed LiPON was partially crystallized under the 120 and 180 min treatments. Thus, a variation in the formation of P–N<P2 and P–NP bonds and partial crystallization of the formed amorphous LiPON cause the treatment time dependence of ionic conductivity of the treated samples.

Local Structure of Glassy Lithium Phosphorus Oxynitride Thin Films: A Combined Experimental and Ab Initio Approach.

Lithium phosphorus oxynitride (LiPON) is an amorphous solid-state lithium ion conductor displaying exemplary cyclability against lithium metal anodes. There is no definitive explanation for this stability due to the limited understanding of the structure of LiPON. Herein, we provide a structural model of RF-sputtered LiPON. Information about the short-range structure results from 1D and 2D solid-state NMR experiments. These results are compared with first principles chemical shielding calculations of Li-P-O/N crystals and ab initio molecular dynamics-generated amorphous LiPON models to unequivocally identify the glassy structure as primarily isolated phosphate monomers with N incorporated in both apical and as bridging sites in phosphate dimers. Structural results suggest LiPON's stability is a result of its glassy character. Free-standing LiPON films are produced that exhibit a high degree of flexibility, highlighting the unique mechanical properties of glassy materials.

All-Solid-State Rechargeable Lithium Metal Battery with a Prussian Blue Cathode Prepared by a Nonvacuum Coating Technology.

A Prussian blue LiFeFe(CN)6 thin-film cathode is fabricated by a nonvacuum coating technology without post-annealing process. The thin film of the solid electrolyte lithium phosphorus oxynitride (LiPON) is deposited onto the cathode by using radio-frequency magnetron sputtering. Then, the lithium metal anode is deposited on the LiPON film by the thermal evaporation method to fabricate the all-solid-state LiFeFe(CN)6/LiPON/Li battery with a thickness of 16 μm and a size of ∼10 cm2. Electrochemical properties of LiFeFe(CN)6/LiPON/Li battery are first investigated at various temperatures from −30 to 80 °C. Our results demonstrated that the all-solid-state LiFeFe(CN)6/LiPON/Li battery exhibits a discharge capacity of 82.5 mA h/g for the third cycle at 60 °C and shows stable cyclic performance within 200 cycles. These results provide the feasibility to assemble an all-solid-state lithium-ion battery by combining nonvacuum and vacuum techniques through an environmentally friendly process at low temperature.

Improvement of Power Characteristics of Thin Film Battery By Li3PO4-Li4SiO4 Electrolyte

Introduction Recently, all-solid-state thin-film rechargeable lithium batteries (TFBs) have expected to be used in various applications such as wireless sensor, smart device and other small devices for an auxiliary power supply. The TFBs are fabricated by forming each layers (i.e. cathode, electrolyte, anode and current collectors) mainly using physical vapor deposition process1,2). As a solid electrolyte, lithium phosphorus oxynitride (LiPON) thin film has been used commonly due to same advantages as no grain-boundary, isotropic property, less electronic conductivity and electrochemical stability. Ionic conductivity of LiPON thin film has been reported ~3.3 x 10-6 S/cm at 25 deg.C3), but it is lower compared with other solid electrolyte4). It is necessary to reduce the internal resistance of TFBs for applying to the device as described above. We tried to improve internal resistance used by Li3PO4-Li4SiO4 (LPO-LSO) electrolyte. Experimental LPO-LSO film was prepared by RF sputtering with 4 inch LPO-LSO target (Toshima manufacturing Co.). The LPO-LSO films were prepared by 0.1 Pa, 0.25 Pa and 0.6 Pa. LiPON film was prepared by RF magnetron reactive sputtering method with lithium phosphate (LPO; Li3PO4) target and N2 gas by 0.25 Pa. The substrate was glass wafer. The cathode film (LiCoO2) was prepared by RF and DC spattering method. The anode film (Metal Li) was prepared by vacuum evaporation method. Acrylic monomer was coated on the anode surface, covered with barrier lid, and cured by ultraviolet light for formation as an encapsulation. The LPO-LSO films quality were measured by FT-IR and SEM. The fabricated TFB cells were investigated by electrical and electrochemical properties at room temperature. Result and discussion Fig.1 shows the nyquist plot of Half-cell (Li/LPO-LSO/Pt, Li/LiPON/Pt) prepared by each pressure. The bulk resistance of LPO-LSO film prepared by 0.1 Pa and 0.25 Pa are lower than the bulk resistance of LiPON film. And the pressure condition of lowest bulk resistance was 0.25 Pa. Fig.2 shows the nyquist plot of TFB that electrolyte were LPO-LSO and LPO-LSO/LiPON . Two semi-circle were observed TFB that electrolyte is only LPO-LSO. We thought 1st semi-circle was the bulk resistance of LPO-LSO and 2nd semi-circle was the interfacial resistance between LPO-LSO and LiCoO2 because 2nd semi-circle was not observed in half-cell of LPO-LSO. We could improve the interfacial resistance by insertion of LiPON film (100nm) between LPO-LSO and LiCoO2. These results show LPO-LSO/LiPON electrolyte improved internal resistance of TFB. References J. B. Bates, N. J. Dudney, G. R. Gruzalski, R. A. Zuhr, A. Choudhury, C. F. Luck and J. D.Robertson, J. Power Sources, 43, 103 (1993).T. Jimbo, P. Kim and K. Suu, Energy Procedia, 14, 1574 (2012).Xiaohua Yu, J. B. Bates, G. E. Jellison, Jr., and F. X. Hart, J. Electrochem. Soc., 144, 524 (1997).N. Kamaya, K. Homma, Y. Yamakawa, M. Hirayama, R. Kanno, M. Yonemura, T. Kamiyama, Y.Kato, S. Hama, K. Kawamoto and A. Mitsui, Nature Materials, 10, 682 (2011). Figure 1

The role of interface between LiPON solid electrolyte and electrode in inorganic monolithic electrochromic devices

Transparent lithium phosphorus oxynitride (LiPON) thin films were deposited by RF sputtering at room temperature for electrochromic (EC) applications. We carried out a basic study from single layer, double layers, and eventually to devices. The interactions between LiPON and bottom EC electrode during sputtering were highlighted. The effects of N2 pressure on structural, morphological, chemical, and electrical properties of the LiPON films were investigated. The Li ionic conductivity of the films increased with decreasing N2 pressure. The results of Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy indicated a probable increase of nitrogen content in the films with decreasing N2 pressure. However, low pressure sputtering process induced the formation of a resistive layer between LiPON and bottom electrode. The electrochemical impedance measurements were conducted to evaluate the charge transfer processes across the interfaces. In the case of WO3 electrode, the charge transfer resistance at the WO3/LiPON interface could be considerably high up to 5100 Ω cm2. For the NiO/LiPON interface, the highest value was 1400 Ω cm2. The high charge transfer resistance significantly hindered the ion transport, thus leading to irreversible Li insertion/extraction processes and lowered charge capacity in the electrode layers. The cycling reversibility and optical contrast for the complete EC device were compromised accordingly. The device using a 130 nm-thick LiPON ion conductor showed an optical modulation of 40% at 550 nm driven by −1.5 V (coloration) and 1 V (bleaching) with switching time of 30 s.

Highly conformal and high-ionic conductivity thin-film electrolyte for 3D-structured micro batteries: Characterization of LiPON film deposited by MOCVD method

This paper reports a lithium phosphorus oxynitride (LiPON) thin-film electrolyte deposited using a metalorganic-chemical vapor deposition (MOCVD) method for 3D-structured micro batteries. It is shown that the MOCVD-LiPON film has both highly-conformal step coverage on a patterned substrate with line/space=2μm/2μm and aspect ratio=1 (51±3 nm) and high-ionic conductivity for very thin films deposited at 4.7 nm/min (5.9×10-6 S/cm for 190 nm and 5.3×10-6 S/cm for 95 nm). Detailed material characterization attributes the enhancement in ionic conductivity to a decrease in nanocrystallite size and improvement in chemical-composition uniformity in the film. In addition, electrochemical characterization of an all-solid-state thin-film battery fabricated with the 190 nm-thick LiPON film (Si substrate/Ti/Pt/LiCoO2/LiPON/a-Si:H/Cu) demonstrates that the LiPON film can successfully act as the electrolyte for lithium-ion batteries. Therefore, the MOCVD-LiPON film is a promising candidate material to realize 3D-structured micro batteries in the near future.

Effects of rough interface on impedance of solid LiPON in MIM cells

The influences of the rough interface on the impedance of solid lithium phosphorus oxynitride (LiPON) in its metal/insulator/metal (MIM) cells over a wide frequency are studied. Using magnetron sputtering method, Al/LiPON/Al cells with different rough interfaces are fabricated. With increasing the Al films electrode roughness, the deposited LiPON films on these electrodes are correspondingly roughened, which result the interface in MIM cell roughened. Rough LiPON films make their ionic resistance decreasing and the real contact area and the bulk capacitance of MIM cells increasing. These lead to the ionic conductivity of LiPON films improved from 1.09 to 2.70 μS/cm. Meanwhile, the bulk capacitance and the electrolyte resistance in MIM cells could be separated by changing the interface roughness. Rough interfaces in MIM cells contribute to the differences in the morphology of LiPON thin films, which result in the decrease of the activation energy of ionic conductivity E g from 0.45 to 0.38 eV. Without changing LiPON components ratio and sputtering conditions for the thin films deposition, or using any heat treatment, we demonstrate an effective way to improve the ionic conductivity by increasing the roughness of the contact electrode in MIM cells, corresponding roughening the LiPON films and decreasing its ionic impedance.

Precursor Chemistry of Lithium Phosphorus Oxynitride Film for Metalorganic Chemical Vapor Deposition

In this study, precursor chemistry of lithium phosphorus oxynitride (LiPON) film is investigated for metalorganic chemical vapor deposition (MOCVD). As a solid-electrolyte, LiPON film is widely used for all solid state thin film batteries. All solid state thin film batteries can provide as much power as conventional coin batteries, but is small enough to be used to provide power to semiconductor-related chips. The battery is safer, thinner and has faster charge and discharge current rate than conventional liquid batteries. It offers the prospect of supplying micro systems with long lasting, environmentally friendly and sustainable electrical power. In general, a sputtering method is applied to deposit LiPON film. LiPON film deposited by sputtering methods has some problems such as the generation of pin-holes, poor coverage and low deposition rates. These problems lead to higher cost and inferior properties of all solid state thin film batteries. In order to overcome these problems, we investigated the possibility of LiPON film deposited by MOCVD. A variety of Li precursors such as lithium tert-butoxide (LiOtBu), lithium hexamethyldisilazide (LiHMDS) and 2,2,6,6-tetramethyl-3,5-heptanedionato lithium (LiTMHD) shown in the table on the left below, were used in our experiments. Regarding P precursor, tris(dimethylamino)phosphine (TDMAP) was used in our experiments. We found the appropriate Li and P precursor chemistry for depositing LiPON films. In addition, as shown in the figure on the right below, it was confirmed that N atom concentration in all LiPON films is precisely controlled due to NH3 and O2 gas chemistry. In summary, we concluded that NH3 and O2 gas chemistry, and the combination of LiOtBu as Li precursor and TDMAP as P precursor, are critical factors for depositing LiPON film using MOCVD. Figure 1

Properties of Lithium Phosphorus Oxynitride Films Prepared By Metalorganic Chemical Vapor Deposition Method

3D-structured thin-film batteries draw attention to applications like IoT, wearable, and medical devices because of their having non-flammability, electrochemical stability, and flexibility; furthermore, their capacity density can be enhanced by designing the structure, e.g. the aspect ratio (AR) of trench and pillar structures. For realizing 3D-structured batteries with high-capacity density, the step coverage for high AR-patterned structures is a crucial process parameter. In the case of conventional physical vapor deposition (PVD) method, the coverage is not conformal enough to deposit onto a high AR-patterned surface. On the other hand, chemical vapor deposition (CVD) method is attractive to deposit much more conformal films than PVD. In this study, properties of lithium phosphorus oxynitride (LiPON), which is a promising thin-film electrolyte material due to high-chemical stability and nontoxicity, films deposited using metalorganic (MO) CVD are investigated in detail. In this experiment, utilized precursors were lithium tert-butoxide, tris(dimethylamino)phosphine, O2, and NH3. Chemical composition and microstructure of prepared films were evaluated by various analytical methods such as XPS, RBS/NRA, Raman spectroscopy, and XRD. In addition, electrochemical properties of the film were evaluated by AC impedance (Nyquist plot) and cyclic voltammetry methods. Using this MOCVD system, Li4.1PO4.2N0.7 film with 7.5 nm of crystallite size and 5.0 nm/min of deposition rate shows 5.9x10-6 S/cm at 200 nm and 3.3x10-6 S/cm at 50 nm of ionic conductivity, and an excellent step coverage on a patterned substrate is also shown by SEM and EDX (Fig. 1). These results demonstrate the LiPON film deposited by MOCVD would be successfully available for 3D-structured thin-film batteries. Figure 1

Spectroscopic ellipsometry and optical transmission study of LiPON thin films prepared by RF sputtering

Lithium phosphorus oxynitride (LiPON) film with high ionic conductivity, low electronic conductivity and high transparency in UV–VIS range offers the possible applications as electrolyte for optical devices, e.g. electrochromic device. In this work, the optical properties of LiPON are investigated by means of variable-angle spectroscopic ellipsometry (VASE) and optical transmission spectra. LiPON thin films with composition of Li3.13PO1.69N1.39 and ionic conductivity of 4.9 × 10−6 S cm−1 at room temperature were prepared by RF magnetron sputtering. Optical constants have been derived on multiple samples with film thickness from 400 to 2000 nm in the energy range of 0.58–5.5 eV. The optical bandgap (Eg) of LiPON film is shown to be 3.07 eV by a Tauc plot. It is found that when E < Eg the Urbach exponential decay of absorption is observed. The Urbach tail width at room temperature is estimated to be 0.361 eV for the LiPON film.

Cathode Composite Films for Oxide-Based All-Solid-State Rechargeable Lithium Batteries Prepared By Aerosol Deposition at Room Temperature

Introduction Oxide-based all-solid-state rechargeable batteries (Ox-SSBs) have been expected as next generation energy storage devices with both high energy density and safety. Especially, thin-film type Ox-SSBs will be the most successful battery and are commercially available. In case of those thin-film Ox-SSBs, crystalline cathode electrodes are generally used, which have been prepared by RF magnetron sputtering, PLD, et al with heating process. On the other hand, aerosol deposition (AD) is a novel technique for preparing dense ceramics films at room temperature by jetting dry powders to the substrates. In addition, the deposition rate of the AD is much higher (5-50 μm min-1) than those in conventional deposition techniques such as RF magnetron sputtering (0.01-0.05 μm min-1)[1]. Hence, we focus on the AD to deposit thin films of composite cathode electrodes for thin-film type SSBs. In this work, we prepared composite electrode films composed of LiNi1/3Co1/3Mn1/3O2 (NMC) and Li1.4Ti2Si0.4P2.6O12-AlPO4(LATP) by the AD. These composite films were combined with LiPON and Si anode film, and electrochemical properties of the thin-film SSB of Si/LiPON/NMC-LATP were investigated. Experimental Composite powders of NMC (Nihon Kagaku Inc.) and LATP (Ohara Inc.) were prepared using a dry-powder mixer (NOB-MINI, Hosokawa Micron Co.). The mixing ratio of NMC to LATP was 100 : 5 in weight. Obtained composite powders were deposited onto a SUS substrate or a Si wafer by AD to fabricate a composite electrode. The resultant thin film was coated with a lithium phosphorus oxynitride (LiPON) glass electrolyte thin film by radio frequency (RF) magnetron sputtering. Subsequently, the Si anode thin film was deposited on the top of a LiPON film by RF magnetron sputtering. Cross-sections of a fabricated SSB (Si/LiPON/NMC-LATP) were observed by FE-SEM. Impedance measurements were performed in frequency ranges within 100 mHz to 200 kHz. Charge-discharge measurements were carried out for fabricated SSBs using 50 μA cm-2 (0.5C) for charging and 50-2000 μA cm-2for discharging. All electrochemical measurements were carried out at 100 °C in Ar-filled-glove boxes. Results and Discussion Figure 1 shows the cross-sectional FE-SEM image of a SSB (Si/LiPON/NMC-LATP) on a Si wafer substrate. A dense NMC-LATP composite film was successfully deposited on SUS by “one-scan” AD (ca. 6 second) as shown in Fig. 1. The thicknesses of NMC-LATP, LiPON, and Si anode layers were approximately 2.6 μm, 4.0 μm, and 300 nm, respectively. Figure 2 shows charge-discharge curves for a SSB on a SUS substrate. The discharge capacity for the first cycle at 50 μA cm-2 was 147 mAh g-1 where the cutt-off voltage was 3.0 V. This value corresponds to 98% of the capacity of a NMC-LATP composite film measured in liquid electrolyte cells. Moreover, 40 mAh g-1 was still obtained as the discharge capacity at 2.0 mA cm-2 (20C). Highly Li+-conductive-glass-ceramic LATP is supposed to promote the Li+ conduction and inhibit crack propagations associated with volume changes of NMC particles. These effects are likely to be the reason that this SSB provides higher rate capability than that in previous work[2]. We will further examine the effect of film thickness on the rate capabilities and stabilities. Reference 1. J. Akedo, S. Nakano, J. Park, S. Baba, and K. Ashida, Synthesiology 1, 130 (2008). 2. S. Iwasaki, T. Hamanaka, T. Yamakawa, W. C. West, K. Yamamoto, M. Motoyama, and Y. Iriyama, J. Power Sources, 272, 1086 (2014). Figure 1

Improvement of Internal Resistance of All-Solid-State Thin-Film Rechargeable Lithium Batteries

1. IntroductionRecently, all-solid-state thin-film rechargeable lithium batteries (TFBs) have expected to be used in various applications such as wireless sensor, smart device and other small devices for an auxiliary power supply. The TFBs are fabricated by forming each layers (i.e. cathode, electrolyte, anode and current collectors) mainly using physical vapor deposition process1,2). As a solid electrolyte, lithium phosphorus oxynitride (LiPON) thin film has been used commonly due to same advantages as no grain-boundary, isotropic property, less electronic conductivity and electrochemical stability. Ionic conductivity of LiPON thin film has been reported ~3.3 x 10-6 S/cm at 25 deg.C3), but it is lower compared with other solid electrolyte4). It is necessary to reduce the internal resistance of TFBs for applying to the device as described above. We improved this issue by reducing the thickness of LiPON film and reported in the previous meeting5). Internal resistance was successfully reduced. However, we had another issue that interfacial resistance between a cathode and an electrolyte was increased by planarization of a cathode surface. In this study, we investigated the mechanism of increasing of interfacial resistance and improved it with new surface modification material (LiCo0.9Al0.1O2). 2. ExperimentalLithium cobalt oxide (LCO) film as a cathode was prepared by RF and DC hybrid magnetron sputtering method on platinum film as a current collector. Ar was used as sputtering gas, and process pressure was kept at 1.6 Pa. New surface modification material, LiCo0.9Al0.1O2 (LCAO) film was prepared by RF magnetron sputtering method on LCO film. Sputtering gas and process pressure were same as LCO deposition. After deposition, LCO and LCAO were annealed at 600deg.C under atmospheric pressure by lamp heating system. Solid electrolyte (LiPON) film was prepared by RF magnetron reactive sputtering method with lithium phosphate (LPO; Li3PO4) target and N2 gas. Lithium film as an anode was prepared by vacuum evaporation method. Acrylic monomer was coated on the anode surface, covered with barrier lid, and cured by ultraviolet light for formation as an encapsulation. The fabricated TFB cells were investigated by electrical and electrochemical properties at room temperature. 3. Results and discussionFigure 1 shows the scanning electron microscopy (SEM) images of LCO films with and without LCAO film after annealing process. As result , it was confirmed that top of LCO columnar grain became sharp by coating with LCAO film. We think this result shows decomposition reaction was suppressed with LCAO film. Figure 2 shows the nyquist plot of TFB and each resistance with and without LCAO film. It was also confirmed that the resistance of 1st semicircle was not changed by LCAO film thickness and the resistance of 2nd semicircle is was decreased by it. These results show LCAO film improved interfacial resistance between a cathode and an electrolyte. Reference1) J. B. Bates, N. J. Dudney, G. R. Gruzalski, R. A. Zuhr, A. Choudhury, C. F. Luck and J. D.Robertson, J. Power Sources, 43, 103 (1993).2) T. Jimbo, P. Kim and K. Suu, Energy Procedia, 14, 1574 (2012).3) Xiaohua Yu, J. B. Bates, G. E. Jellison, Jr., and F. X. Hart, J. Electrochem. Soc., 144, 524 (1997).4) N. Kamaya, K. Homma, Y. Yamakawa, M. Hirayama, R. Kanno, M. Yonemura, T. Kamiyama, Y.Kato, S. Hama, K. Kawamoto and A. Mitsui, Nature Materials, 10, 682 (2011).5) A. Suzuki, S. Sasaki, I. Kimura and T. Jimbo, #449, 227th ECS Meeting (2015). Figure 1

Thermal Atomic Layer Deposition of Lithium Phosphorus Oxynitride as a Thin-Film Solid Electrolyte

In this study, thermal atomic-layer deposition (ALD) is utilized to deposit a film of lithium phosphorus oxynitride (LiPON) to improve the solid-electrolyte performance of thin-film lithium batteries, increasing their viability for high-energy-storage applications. This technique enabled the successful fabrication of a carbon-free LIPON film using a deposition sequence constructed on the basis of a phosphate backbone and film deposition temperatures of 400–500°C. The obtained film has an ionic activity of 3.2 × 10−7 S cm−1 and an activation energy of 0.57 eV, values that are largely equivalent to those of sputtered LiPON films. Characterization of the film revealed that the thermal ALD-based film deposition is highly conformal, as the LiPON film is deposited deep (several hundreds of nanometers) into the grain boundaries of the lithium cobalt dioxide and the pores in this film are several tens of nanometers in diameter. These findings suggest that the use of thermal ALD to deposit LiPON films has a wide range of potential applications in battery technologies.

LiPON thin films with high nitrogen content for application in lithium batteries and electrochromic devices prepared by RF magnetron sputtering

Transparent amorphous lithium phosphorus oxynitride (LiPON) thin films with different thickness have been prepared by RF magnetron sputtering at a growth rate of 14nm/min. The mean ionic conductivity of as-deposited LiPON films determined by impedance spectroscopy was 4.9 μS/cm at 22°C with the activation energy of 0.55eV. The electronic partial conductivity was measured to be 1.6×10−6 μS/cm by recording the current–time curves at a constant voltage. The optical transmission of LiPON films were measured by UV–Vis/IR spectroscopy. The prepared LiPON films on silica glass substrate showed transmission higher than 80% in the visible light range. The complex refractive index and bandgap (~2.94eV) were estimated by fitting the transmission data with the Tauc–Lorentz dielectric function model. The local structure of the film was investigated by X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. Both methods confirmed the incorporation of nitrogen in the matrix. Nitrogen is present in two different chemical environments, corresponding to P−N<PP and PNP. Inductively coupled plasma-optical emission spectrometry (ICP-OES) and Rutherford backscattering spectrometry (RBS) measurements showed that the composition of the LiPON film was Li3.13PO1.69N1.39. The high nitrogen content and low oxygen content appears to be responsible for the specific electrical and optical properties of the LiPON films.

Improvement of Power Characteristics of All-Solid-State Thin-Film Rechargeable Lithium Batteries

1. Introduction Recently, all-solid-state thin-film rechargeable lithium batteries (TFBs) has expected in various applications such as wireless sensor, smart device and other small devices for an auxiliary power supply. The TFBs are fabricated by forming each layers (i.e. cathode, electrolyte, anode and current collector) using physical vapor deposition process1,2). As a solid electrolyte, lithium phosphorus oxynitride (LiPON) thin film has been used commonly due to no grain-boundary, isotropic property, less electronic conductivity and electrochemical stability. Ionic conductivity of LiPON thin film has been reported ~3.3 x 10-6 S/cm at 25 deg.C3), but it is lower compared with other solid electrolyte4). It is necessary to reduce the internal resistance of TFBs for applying to the device as described above. In order to improve this, it has to be thinner LiPON film or change the electrolyte material having higher ionic conductivity. However, there is a limited to the thickness of electrolyte film without short- circuit because the surface of cathode film is rougher with thicker cathode film5). In this study, we investigated the planarization of cathode film for thinner electrolyte film. 2. Experimental Lithium cobalt oxide (LCO) film was prepared by RF and DC hybrid power magnetron sputtering method on platinum film as current collector. Ar was used as sputtering gas, and process pressure was kept at 1.6 Pa. Furthermore, LCO was deposited with applying each bias power to the substrate for investigating the planarization. After deposition, LCO was annealed at 600 deg.C under atmospheric pressure by lamp heating system. Solid electrolyte (LiPON) film was prepared by RF magnetron reactive sputtering method with only N2gas. Lithium film as an anode was prepared by vacuum evaporation method. Acrylic monomer as a sealant was coating on the anode surface, covered with barrier lid, and cured by ultraviolet light for encapsulation. The fabricated TFB cells were investigated by electrical and electrochemical properties at room temperature. 3. Results and discussion Figure 1 shows the scanning electron microscopy (SEM) image of 3-μm-thick LCO film under different bias power condition. As the result of this, it was confirmed that surface of LCO becomes smoother with higher bias power and surface morphology changes from pyramid-like to dome-like by re-sputtering. TFB cell was fabricated with 2-μm-thick LiPON and 2-μm-thick lithium and discharge capacity was also checked. The charge method is CCCVmode (current density: 0.21 mA/cm2, cut-off: >4.2 V and <0.021 mA/cm2) and the discharge method is CC mode (current density: 0.21 mA/cm2, cut-off: <3.0 V). Figure 2 shows the discharge curve of TFB cells. It was confirmed that discharge capacity of TFB cell is higher with increasing bias power. It is thought that film density of LCO becomes high due to ion peening effect. The improvement of thinner LiPON film and the other are on evaluating. Reference 1) J. B. Bates, N. J. Dudney, G. R. Gruzalski, R. A. Zuhr, A. Choudhury, C. F. Luck and J. D. Robertson, J. Power Sources, 43, 103 (1993).2) T. Jimbo, P. Kim and K. Suu, Energy Procedia, 14, 1574 (2012).3) Xiaohua Yu, J. B. Bates, G. E. Jellison, Jr., and F. X. Hart, J. Electrochem. Soc., 144, 524 (1997).4) N. Kamaya, K. Homma, Y. Yamakawa, M. Hirayama, R. Kanno, M. Yonemura, T. Kamiyama, Y. Kato, S. Hama, K. Kawamoto and A. Mitsui, Nature Materials, 10, 682 (2011).5) T. Jimbo, S. Sasaki, A. Suzuki, I. Kimura and K. Suu, #1235, 224th ECS Meeting (2013) Figure 1

マグネトロンスパッタ法により作製したリン酸リチウムオキシナイトライド固体電解質薄膜のイオン伝導性に及ぼす導入ガス中窒素濃度の影響

Amorphous lithium phosphorus oxynitride (LiPON) thin films were deposited on SUS plates from a Li3PO4 target using RF magnetron sputtering with induction gas having various N2 concentrations. The ionic conductivity of the amorphous LiPON films was approximately 7.6×10－6 S･cm－1 at 75% N2 concentration, at which both doubly and triply phosphorus-coordinated nitrogen units would be linked to the Li3PO4 structure.