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Li-ion batteries using the Li[Ni0.8Co0.15Al0.05]O2 (NCA) electrode containing an aqueous binder have been fabricated by a pressurized CO2 gas treatment (PCT). With the PCT, the pH of the NCA slurry containing an aqueous binder significantly decreased from 12.2 to 8.3 in 3 minutes. The cyclability and coulombic efficiency were greatly improved and the retention rate of the discharge capacity at the 50th cycle with respect to that at the 1st cycle achieved 82%. A Li2CO3 layer may be formed on the NCA electrode surfaces during the PCT and the corrosion reaction on the Al foil collector was significantly suppressed. The Li2CO3 layer is electronically insulating and prevents decomposition of the electrolyte during the cycling, resulting in a decreased film resistance (Rf ) between the 25th and 50th cycles. On the other hand, without the PCT, the discharge capacity drastically decreased during the cycling. The aqueous binder may be degraded, the corrosion reaction on the Al foil collector occurred and Al compound layers were formed on an Al foil collector. However, these layers didn't protect the NCA particle surfaces. Therefore, the electrolyte was decomposed during the cycling. These results caused an increase in the charge transfer resistance and Rf . [ABSTRACT FROM AUTHOR]

A layered compound, NaxMn2/3Co1/6N1/6O2 (NMCN), prepared by a solid-state reaction, served as a high capacity positive electrode material with the reversible capacity of ca. 200 mA ⋅ h ⋅ g-1 using a Na foil as the counter electrode. A high-resolution synchrotron X-ray diffraction (XRD) analysis revealed that, whereas the NMCN sample had the P3 structure (R3m) when the precursor was heated below 700°C, the P2 structure (P63/mmc) was obtained when heated above 800°C. The latter excels over the former in both capacity and cycle stability; i.e., the initial discharge capacities and potentials of the P2 and P3-NMCN were 216 mA ⋅ h ⋅ g-1, 2.87 V vs. Na+/Na and 206 mA ⋅ h ⋅ g-1, 2.78 V vs. Na+/Na, respectively. The P2-MNCN retained 80% of its initial discharge capacity while the P3-NMCN dropped to 69% after 30 cycles in the potential range of 1.0-4.5 V vs. Na+/Na. An in-situ XRD analysis revealed that the lattice volume of the P2-NMCN contracts and expands by 20% during the charge and discharge (i.e., Na extraction and insertion) without drastically changing its crystallographic structure. [ABSTRACT FROM AUTHOR]

The electrochemical properties of SnC2O4-coated Si materials with various compositions were investigated. Among them, the Si-70 wt%SnC2O4 composite maintained a high capacity of greater than 1000 mAhg-1 after more than 30 cycles. A synchrotron XRD analysis revealed that the SnC2O4 decomposed into Sn and an irreversible product during the first lithiation process. Subsequently, Sn and Si were independently lithiated/de-lithiated to Li17Sn4 and Li15Si4, respectively, during the Li insertion and de-insertion process. A full-cell using LiFePO4 as the positive electrode material was assembled, and the cell exhibited a good cycle performance in which it maintained almost 100% of the initial capacity after 100 cycles in the temperature range of -20-60°C. The 1-Ah class cell showed a high safety during a nail penetration test and an overcharge test; no smoke and flames were observed during these safety tests. [ABSTRACT FROM AUTHOR]

The cycling stability at 80°C for the LiNi1/3Co1/3Mn1/3O2 (LNCMO) electrodes was improved by using a carboxymethyl cellulose (CMC) binder and then Li4Ti5O12 (LTO)-coating on the particle surface. The detailed structural analysis was done for the LTO-coated LNCMO(CMC) electrode after 100 charge-discharge cycles at 80°C by high-energy synchrotron X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS) analyzes. The number of exchanged electrons (NEE) for the nickel ions in the electrode was lower at 100 cycles than at the first cycle and in a good relation with the capacity of the LTO-coated LNCMO(CMC)/SiO cell. The 1.7 Ah LTO-coated LNCMO(CMC)/SiO laminate cells were prepared in order to evaluate their safety, showing a higher safety for the nail penetration test. [ABSTRACT FROM AUTHOR]