M. Nishijima

Sodium deintercalation from sodium iron oxide

Na ion deintercalation from α-NaFeO2 by charging a LiαNaFeO2 cell gives a new monoclinic phase, Na0.5FeO2. The room-temperature Mossbauer spectrum shows two kinds of doublet lines with almost same intensity. The isomer shifts are 0.33 and −0.07mm/s (relative to Fe metal), respectively, the former comes from Fe3+ state and the latter clearly originates in Fe4+ state. The trial of further deintercalation of Na ion brings the decomposition of the electrolyte and electrode. Discharge in LiNa0.5FeO2 cell is possible, but the Na ions remained hinders smooth lithium intercalation.

Synthesis and electrochemical studies of a new anode material, Li3 − xCoxN

Abstract Li 3 − x Co x N with hexagonal symmetry, P6 mmm , was prepared by heating a mixture of Li 3 N and metallic Co powder in a N 2 gas stream. A solid solution of Li 3 − x Co x N is formed in the range of 0 ≦ x ≦ 0.5. It is suggested that Li 3 − x Co x N has some Li defects written as Li 3 − x − y Co x N, which are probably produced because of the compensation of the Co 2+ state in the structure, and are filled in by Li-intercalation. Lithium ion is easily deintercalated and re-intercalated in a Li/Li 3 − x Co x N cell forming Li 3 − x − z Co x N over a wide range of 0 ≦ z ≦ 1.0, where the cell voltage ranges between 0 and 1.1 V. The specific capacity of the cell is about 480 mAh/g, which is larger than that of carbon materials and does not change during the proceeding cycles. Li 3 − x Co x N is thus suggested to be a good candidate for an anode in a lithium secondary battery.

Li Deintercalation‐Intercalation Reaction and Structural Change in Lithium Transition Metal Nitride, Li7MnN4

Li[sub 7]MnN[sub 4] which has cubic symmetry, P[bar 4]3n, a = 9.5453 is prepared by heating a mixture of Li[sub 3]N and Mn[sub 4]N in a 1%H[sub 2]-99%N[sub 2] gas stream. The li ion is easily deintercalated in a Li/Li[sub 7]MnN[sub 4] cell forming Li[sub 7[minus]x]MnN[sub 4] over a wide range of 0 [le] x [le] 1.25. The specific capacity of the cell is about 210 mAh/g. With an increase in x, a new phase which also has cubic symmetry but has a smaller lattice parameter appears. The original phase decreases with an increase in x, and disappears at x = 0.625. A two-phase reaction then occurs. In the range of 0.625 [le] x [le] 1.25, the lattice parameter of the second phase decreases with an increase in x. The Li/Li[sub 7]MnN[sub 4] cell shows a good reversibility under high current density (1,200 [mu]A/cm[sup 2]). Li[sub 7]MnN[sub 4] is thus suggested to be a good candidate for an electrode for a lithium secondary battery.

Lithium secondary batteries using a lithium cobalt nitride, Li2.6Co0.4N, as the anode

Abstract Lithium cobalt nitride, Li 2.6 Co 0.4 N, has a high capacity of 900 mAh/g with good cycle performance in lithium deintercalation and intercalation. The good reversibility and low potential in comparison to lithium metal (0.7 V on average) suggests that this nitride is a good candidate for an anode in a lithium secondary battery. In order to use Li 2.6 Co 0.4 N as the anode for lithium secondary batteries, possible combinations with cathode materials were considered: (1) Li 2.6 Co 0.4 N/Li 0.64 Mn 1.96 O 4 cell. Lithium ions were initially extracted from Li 1.05 Mn 1.96 O 4 by using Br 2 as an oxidant; (2) Li 2.6 Co 0.4 N/a-Cr 3 O 8 cell, using a Li-free material of amorphous Cr 3 O 8 , which has a high lithium insertion capacity of more than 300 mAh/g; (3) Li 1.37 Co 0.4 N/Li 1.10 Mn 1.90 O 4 cell. Li 1.37 Co 0.4 N was used as the anode with the lithium chemically extracted. These lithium secondary batteries showed very high capacity.

Electrochemical studies of a new anode material, Li3-xMxN (M = Co, Ni, Cu)

Li3 − xMxN (M = Co, Ni, Cu) with hexagonal symmetry, P6/mmm, was prepared by heating a mixture of Li3N and metallic powder in a nitrogen gas stream. Solid solutions of Li3 − xMxN are formed in the range of 0 ≤ x ≤ 0.5, 0 ≤ x ≤ 0.6, and 0 ≤ x ≤ 0.3 for M = Co, Ni and Cu, respectively. The cycle performance in an Li/Li3 − xMxN cell was studied in the cell voltage range between 0.01 and 1.5 V. The lithium ion is easily cycled over a wide range of 0.0 ≤ z ≤ 1.0 in Li3 − x − zCoxN and is also cycled fairly well Li3 − x − zCuxN with the cell voltage range between 0 and 1.1 V. It is characteristic that the charge and discharge curves of the second cycle differ from the first one. On the other hand, in the Li/Li3 − xNixN cell, the lithium ion is only cycled in a narrow range of 0.0 ≤ z ≤ 0.5 between 0.01 and 1.5 V, while the charge and discharge curves of the second cycle are almost similar to the first one.

Crystal chemistry and transport properties of Nd2-xAxNiO4 (A = Ca, Sr, or Ba, 0 ≤ x ≤ 1.4)

Structural and electrical properties of the system crystallizing in the K2NiF4 structure, Nd2−xAxNiO4 (A = Ca, Sr, or Ba, 0≤x≤1.4), were studied. The solid solution limits of alkaline earth were 0.6, 1.4, and 0.6 for Ca, Sr, and Ba, respectively. Oxygen content was controlled by annealing under various oxygen pressures below 150 atm. Powder X-ray diffraction data were analyzed by the Rietveld method to determine the bond lengths. In the case of the Sr-substituted system, tetragonality in the lattice parameters, c/a, shows a maximum at x = 0.6, while distortion of a NiO6 octahedron, Ni−O(2) (//c-axis)/Ni−O(1) (//a-axis), monotonically decreases from 1.13 (x=0) to 1.04 (x = 1.4). No Jahn-Teller distortion appears in a Ni3+ region. A metal-semiconductor transition is observed for O

Anti-fluorite type Li6CoO4, Li5FeO4, and Li6MnO4 as the cathode for lithium secondary batteries

Abstract The anti-fluorite type materials Li 6 CoO 4 , Li 5 FeO 4 and Li 6 MnO 4 were synthesized and studied as a cathode for lithium secondary batteries. One equivalent Li was deintercalated from Li 6 CoO 4 and reversibly intercalated, while only 0.5 Li extraction and insertion was possible for Li 5 FeO 4 and no Li was extracted from Li 6 MnO 4 . The cell performance of Li/Li 6 CoO 4 with 1 M LiClO 4 /EC-DME was relatively good in the shallow region 0≤ x ≤0.75 in Li 6− x CoO 4 and the large hysteresis with the charge and discharge curves showed a different mechanism between Li deintercalation and intercalation.