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Internal short circuit of a lithium polymer battery (4.6 Ah capacity and 4.30 V charging voltage) with a ceramic-coated separator has been investigated by infrared measurement during nail penetration. The surface temperatures at nail penetration area and battery body were simultaneously measured by infrared camera and, as a result, three different failure modes have been proposed. The battery with 100% of SOC experiences thermal runaway phenomenon by means of the second internal short circuit. The batteries with low SOC (0% and 50% of SOC) were also investigated to identify the phenomena occurred in SOC 100% battery (the second internal short circuit), but neither fire nor explosion in the battery with low SOC was observed. The analysis of burr status after nail penetration demonstrates that it is quite important factor related to the failure modes. The results of this study can be applied to the design of safe battery.

The degradation of cathode materials due to the so-called ‘NiO dissolution’ problem, is one of the most critical issues restricting the long-term operation of molten carbonate fuel cells (MCFCs). To overcome this problem, a modified NiO powder is prepared by the annealing of a pre-mixed powder consisting of Ni powder and Co 3 O 4 nano-particles ( n -Co 3 O 4 ) at 650 °C. Annealing above 300 °C plays an important role in converting the physically bound mixed oxide system to a chemically bound system and, therefore, the separation of n -Co 3 O 4 from Ni is prevented. This modification leads to the formation of a Ni 0.9 Co 0.1 O solid solution, and the lithiated Ni 0.9 Co 0.1 O has a core–shell structure that consists of different Li contents. Whereas the core phase has a low concentration of lithium, the outer layer is a highly lithiated phase. Since the highly lithiated outer phase, acting as a barrier, minimizes the dissolution of NiO, the modified cathode demonstrates good electrochemical properties and chemical stability under actual operating conditions. This study can provide an effective way to mass produce MCFC cathode materials.

LiMn 1.5 Ni 0.5 O 4 materials coated with AlPO 4 are prepared by a sol–gel method with citric acid to improve their electrochemical performance; the physical and electrochemical properties are characterized by various analytical techniques. The coated AlPO 4 layer completely covers the surfaces of the LiMn 1.5 Ni 0.5 O 4 particles and the thickness of the coated layer is ∼15 nm. 1 wt.% AlPO 4 -coated LiMn 1.5 Ni 0.5 O 4 has much lower surface and charge-transfer resistances and shows a higher lithium diffusion rate in comparison with the pristine sample. The modified material demonstrates dramatically enhanced electrochemical reversibility and stability under elevated temperature conditions. This is because the coated AlPO 4 layer reduces the contact area between the electrode and electrolyte and suppresses the formation of undesirable solid electrolyte interface films.

Nafion®–silica nanocomposite membranes are successfully prepared by adding hydrophobic silica nanoparticles to a Nafion® solution. To distribute these nanoparticles evenly in the Nafion® matrix, various fluorosurfactants of different ionic character are employed. Fluorosurfactants with acid groups such as phosphonic acid and sulfonic acid play an important role in simultaneously increasing the homogeneous dispersion of silica nanoparticles, enhancing proton conductivity, and reducing the methanol permeability of the nanocomposite membranes. Therefore, the dispersion properties of inorganic fillers such as silica can significantly affect nanocomposite performance in direct methanol fuel cell (DMFC) applications, whereas surfactants, if used properly, can improve the nanocomposite membrane properties. In particular, a commercial fluorosurfactant containing a sulfonic acid group (Zonyl® TBS) at the end of the surfactant chain exhibits better miscibility with the Nafion® ionomer. This feature results in a reduction in the dimensional change of the nanocomposite membrane due to relatively lower water swelling and significantly reduced methanol permeability through the membrane. A membrane–electrode assembly (MEA) prepared from a Nafion®–silica nanocomposite membrane with TBS shows the highest DMFC performance in terms of voltage vs. current density (V–I) and power density vs. current density (P–I). The current densities at 0.4 V and 90 °C are 342, 508, and 538 mA cm−2 with 1, 3 and 5 M methanol being fed at the anode side, respectively.

Nafion is modified by incorporating poly(1-vinylimidazole)/Pd composites into the ion cluster channels of the membrane. The poly(1-vinylimidazole)/Pd-impregnated (PVI/Pd-impregnated) membranes is characterized by means of X-ray photoelectron spectroscopy (XPS), proton conductivity and methanol permeability measurements and compared with those of the untreated Nafion. The dependence of the membrane proton conductivity and methanol permeability on the poly(1-vinylimidazole) (PVI) and palladium contents in the PVI/Pd-impregnated Nafion is studied. The performance of the cells employing the PVI/Pd-impregnated Nafion is evaluated using a direct methanol fuel cell (DMFC) unit cell. It is found that the best cell performance is obtained when Nafion is impregnated with the PVI/Pd composite solution for 20 h. This result suggests that there exists an optimum content of palladium and PVI in the modified membrane to obtain a high-proton conductivity and low-methanol permeability that result in a high-cell performance.

We prepared a novel phosphoric acid-doped sulfonated poly(fluorinated arylene ether)s/poly(N-vinylimidazole) blend polymer and poly(tetrafluoroethylene) (PTFE) layered membrane. The thermal and electrochemical properties of the new layered membrane were investigated by thermogravimetric analysis (TGA), electrochemical impedance spectroscopy (EIS), as well as the performance of its membrane electrode assembly (MEA). The morphology of membrane was observed with field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). The fabricated membrane shows good mechanical property comparable to PBI membrane. The conductivity of new layered membrane was similar to that of polybenzimidazole (PBI) at high temperature. The single cell test showed that new PTFE layered membrane had a good performance over 150 °C. The PTFE layered membrane can be an alternative approach for PEMFC applications at high temperature.

The surface of Nafion was modified by applying palladium nanoparticles as methanol barrier materials to decrease methanol crossover and improve the performance of fuel cells. The properties of the Pd-modified membrane, in terms of conductivity, methanol permeability, percentage of liquid uptake as well as the performance of its membrane electrode assembly (MEA) in the direct methanol fuel cell, were analyzed and compared with those using bare Nafion. The modified membrane showed considerable improvement on reducing methanol loss without decreasing proton conductivity. The DMFC performance of modified membrane was superior to that of bare Nafion both at a typical fuel state of 2 M and at high concentration of 5 M, implying that the palladium-modified Nafion can be a good alternative approach for DMFC applications.

LiNi 1− x Ti x O 2 (0 ≤ x ≤ 0.1) compounds have been synthesized by a direct molten-salt method that uses a eutectic mixture of LiNO 3 and LiOH salts. According to X-ray diffraction analysis, these materials have a well-developed layered structure (R3-m) and are an isostructure of LiNiO 2 . The LiNi 1− x Ti x O 2 (0 ≤ x ≤ 0.1) compounds have average particle sizes of 1–5 μm depending on the amount of Ti salt. Charge–discharge tests show that a LiNi 1− x Ti x O 2 (0 ≤ x ≤ 0.1) cathode prepared at 700 °C has an initial discharge capacity as high as 171 mA h g −1 and excellent capacity retention in the range 4.3–2.8 V at a current density of 0.2 mA cm −2 .

Olivine structure LiFePO 4 /C composite powders are synthesized as cathode materials for Li-ion batteries via a conventional solid-state reaction. Improvement in electrochemical performance has been achieved by using poly(vinyl alcohol) as the carbon sources for the as-prepared materials. The influence of the heat treatment on the physical and the electrochemical properties of LiFePO 4 /C materials is investigated. To examine the effect of added carbon content on the properties of materials, a one-step heat treatment has been employed with control of the PVA content in the precursor. Six samples were prepared with 0, 1, 3, 5, 10 and 30 wt.% PVA added to the raw materials. The particle size of LiFePO 4 decreases as the carbon content increases. Materials with medium carbon contents have a small charge-transfer resistance and thus exhibit superior electrochemical performance. Interestingly, for a LiFePO 4 /C composite with a low PVA content, an unusual plateau at 4.3 V is observed. It is considered that this is due to the Fe 3+ /Fe 4+ redox reaction of Fe 3+ compounds that are present as an impurity. For samples with a high PVA amount, a thicker carbon coating provides an obstacle to improve the electrochemical properties.

The properties of a new cathode material of nano-sized TiO 2 -coated Ni powder for application in molten carbonate fuel cells (MCFCs) are investigated. The material is prepared by a sol–gel method. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM) with energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM) and Raman spectroscopy are employed to characterize the cathode material. The nano-sized TiO 2 particles are homogenously coated on the surface of the Ni powder. A stable LiTi 1− x Ni x O 2 phase is formed on the surface of the Ni powder during immersion in molten carbonate at 650 °C. The solubility of the TiO 2 -coated Ni cathode is about 50% lower compare with that of a pure Ni cathode.

Co/Mg solid solution coated Ni powder, where Mg-doped LiCoO2 is coated on NiO in molten carbonate, has been used as a new cathode material to reduce the solubility of NiO and to maintain the advantages of NiO cathode. The (Co/Mg)-coated NiO cathode was prepared by a coating Co/Mg solid solution on the surface of the Ni powder using a PVA assisted sol–gel method. The phase changes of the (Co/Mg)-coated Ni powder after immersed into Li/K eutectic carbonate mixtures at 550 °C ∼ 850 °C for 48 h was performed by XRD and Raman. SEM was used to study the particle morphologies. Co/Mg solid solution was coated on the surface of the Ni powder and Li(NiCoMg)O2 is formed on NiO in molten carbonate. It is expected that the Li(NiCoMg)O2 phase will reduce the solubility of NiO cathode in molten carbonate.

Iodine-containing, cation-deficient, lithium manganese oxides (ICCD-LMO) are prepared by reaction of MnO2 with LiI. The MnO2 is completely transformed into spinel-structured compounds with a nominal composition of Li1−δMn2−2δO4Ix. A sample prepared at 800 °C, viz. Li0.99Mn1.98O4I0.02, exhibits an initial discharge capacity of 113 mA h g−1 with good cycleability and rate capability in the 4-V region. Iodine-containing, lithium-rich lithium manganese oxides (ICLR-LMO) are also prepared by reaction of LiMn2O4 with LiI, which results in a nominal composition of Li1+xMn2−xO4Ix. Li1.01Mn1.99O4I0.02 shows a discharge capacity of 124 mA h g−1 on the first cycle and 119 mA h g−1 a on the 20th cycle. Both results indicate that a small amount of iodine species helps to maintain cycle performance.

To elucidate the mechanism of gas generation during charge–discharge cycling of a lithium-ion cell, the generated gases and passive films on the carbon electrode are examined by means of gas chromatography (GC) and Fourier transform infrared (FTIR) spectroscopy. In ethyl carbonate/dimethyl carbonate and ethyl carbonate/diethyl carbonate 1 M LiPF 6 electrolytes, the detected gaseous products are CO 2 , CO, CH 4 , C 2 H 4 , C 2 H 6 , etc. The FTIR spectrum of the surface of the carbon electrode shows bands which correspond to Li 2 CO 3 , ROCO 2 Li, (ROCO 2 Li) 2 , and RCO 2 Li. These results suggest that gas evolution is caused by electrode decomposition, reactive trace impurities, and electrolyte reduction. The surface of the electrode is composed of electrolyte reduction products. When 0.05 M Li 2 CO 3 is added as an electrolyte additive, the total volume of generated gases is reduced, and the discharge capacity and the conductivity of lithium-ions are increased. These results can be explained by a more compact and thin ‘solid electrolyte interface’ film on the carbon electrode formed by Li 2 CO 3 , which effectively prevents solvent co-intercalation and carbon exfoliation.

Lithium cobalt oxide powders have been successfully prepared by a molten-salt synthesis (MSS) method using a eutectic mixture of LiCl and Li 2 CO 3 salts. The physico-chemical properties of the lithium cobalt oxide powders are investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), particle-size analysis and charge–discharge cycling. A lower temperature and a shorter time (∼700°C and 1 h) in the Li:Co=7 system are sufficient to prepare single-phase HT-LiCoO 2 powders by the MSS method, compared with the solid-state reaction method. Charge–discharge tests show that the lithium cobalt oxide prepared at 800°C has an initial discharge capacity as high as 140 mA h g −1 , and 100 mA h g −1 after 40 cycles. The dependence of the synthetic conditions of HT-LiCoO 2 on the reaction temperature, time and amount of flux with respect to starting oxides is extensively investigated.

The prepolymers of polyether urethane acrylate (PEUA) were synthesized from polyether polyol (polyethylene glycol (PEG) or polypropylene glycol (PPG)), diisocyanate (hexamethylene diisocyanate (HMDI) or toluene 2,4-diisocyanate (TDI)), and the caprolactone-modified hydroxyethyl acrylate (FA2D) using the catalyst (dibutyltin dilaurate (DBTDL)) by stepwise addition reaction. Lithium triflate (LiCF3SO3) was dissolved in PEUA prepolymers, and plasticizer (propylene carbonate (PC)) was added into prepolymer and salt mixtures. Then photoinitiator (Irgacure 184) was also dissolved in the mixtures. Thin films were prepared by casting on the glass plate, and then by curing the plasticized prepolymer and salt mixtures under UV radiation. Electrochemical and electrical properties of PEUA–LiCF3SO3-based polymer electrolytes were evaluated and discussed to be used in lithium batteries.

The solubility of a nickel oxide cathode in molten carbonate fuel cell (MCFC) electrolyte is one of the major technical obstacles to the commercialization of such fuel cells. Lithium cobalt oxide, LiCoO 2 , has been selected as a candidate material for MCFC cathodes because its solubility is small and the rate of dissolution into the melt is slower than that for nickel oxide. On the other hand, the electrical conductivity of LiCoO 2 is lower than that of nickel oxide. Thus, nickel oxide has been coated with stable LiCoO 2 in carbonate by a PVA-assisted sol–gel method to give a LiCoO 2 -coated NiO (LC-NiO) cathode. Raman spectra show that the structure of LC-NiO is different from that of nickel oxide, and that a LiCo 1− y Ni y O 2 phase is formed during heat-treatment of the LC-NiO cathode. The coating of LiCoO 2 on NiO electrode increases with increase in the dipping and heating times. The performance of unit cells show that the mean voltage of the cells is 0.80 V using a NiO cathode and 0.85 V with a LC-NiO cathode at a current density of 150 mA cm −2 . The solubility of the LC-NiO cathode in molten carbonate electrolyte is half that of NiO cathode after 300 h at 650°C.

The corrosion of chromium species in molten (Li/K) 2 CO 3 and (Li/Na/K) 2 CO 3 are investigated by spectrophotometry. A strong charge-transfer absorption band is observed in the ultraviolet region with λ max =372 nm, and the molar absorptivity of CrO 4 2− in molten (Li/K) 2 CO 3 is calculated. The corrosion rates are investigated by means of increasing the concentration of CrO 4 2− in the melts. Under an air atmosphere, the corrosion rate is slower in molten (Li/K) 2 CO 3 than in molten (Li/Na/K) 2 CO 3 and Cr 2 O 3 corrodes more easily in molten (Li/K) 2 CO 3 than Cr. With an atmosphere of CO 2 =1 atm, there is no increase in the CrO 4 2− concentration in the solution phase during a period of 5 h.

In order to determine the burnt-out condition of polyvinyl butyral as a binder in the fuel cell, thermal gravimetric analysis, gas chromatography and gas chromatography/mass spectrometry are used to analyse decomposed products during the thermal decomposition process in the matrix-green sheet and electrolyte-green sheet. Most of thermal degradation takes place under 400 °C, but degradation-resistant structures still remain up to 700 °C. Adding water vapour to the atmosphere gas could be one method to promote thermal degradation. Butyraldehyde and butene peaks among the released gases show characteristic decomposition behaviour. Thus, the butyraldehyde and butene peaks can be used as an index to check the extent of decomposition in the thermal decomposition process.

The aluminium pack cementation (pack aluminization) process on a porous nickel anode for molten carbonate fuel cells has been studied to improve anode creep resistance. The porous nickel substrates used in this study were fabricated by doctor blade equipment followed by sintering (850 °C). Packs surrounding the Ni anode were made by mixing Al2O3 powder, Al powder, and NaCl as activator. The pack aluminization was performed at 700 to 850 °C for 0.5–5.0 h. After pack aluminization, the principal NiAl intermetallic compounds detected were Ni3Al at 700 °C, NiAl at 750 °C and Ni3Al2 at 800 °C. The aluminum content in the aluminized Ni anode was proportional to the square root of pack aluminizing time. With increasing the Al content in the anode, the creep of the anode decreased. It was nearly constant (2.0%) when the Al content was above 5.0%. Although the exchange current density (24 mA/cm2) for the aluminized (2.5 wt.%) Ni anode was somewhat lower than that of the pure Ni anode (40 mA/cm2), the performance of a single cell using an aluminized Ni anode was similar to that of the one with pure Ni anode.