Kingo Ariyoshi

Topotactic Two-Phase Reactions of Li [ Ni1 / 2Mn3 / 2 ] O 4 ( P4332 ) in Nonaqueous Lithium Cells

Li[Ni 1/2 Mn 3/2 ]O 4 was prepared by a two-step solid state reaction and characterized by X-ray diffraction (XRD) infrared (IR)-Raman, and electron diffraction (ED). Li[Ni 1/2 Mn 3/2 ]O 4 having characteristic eight absorption bands in 400-800 cm -1 in IR spectrum, extra lines in XRD, and extra spots in ED was analyzed in terms of a superlattice structure. Analytical results on the structural data indicated that Li[Ni 1/2 Mn 3/2 ]O 4 (cubic: a = 8.167 A) was a superlattice structure based on a spinel framework structure having a space group of P4 3 32 (or P4 1 32) in which nickel ions were located at the octahedral 4(b) sites, manganese ions were at the octahedral 12(d) sites, and lithium ions were at the 8(c) sites in a cubic-close packed oxygen array consisting of the 8(c) and 24(e) sites. Well-defined Li[Ni 1/2 Mn 3/2 ]O 4 was examined in nonaqueous lithium cells and showed that the cell exhibited extremely flat operating voltage of about 4.7 V with rechargeable capacity of 135 mAh/g based on the sample weight. The reaction mechanism of Li[Ni 1/2 Mn 3/2 ]O 4 was examined and shown that the reaction at ca. 4.7 V consisted of two cubic/cubic two-phase reactions, i.e., □[Ni 1/2 Mn 3/2 ]O 4 (a = 8.00 A) was reduced to Li[Ni 1/2 Mn 3/2 ]O 4 (a = 8.17 A) via □ 1/2 Li 1/2 [Ni 1/2 Mn 3/2 ]O 4 (a = 8.09 A). Results on the detailed reversible potential measurements indicated that the flat voltage at ca. 4.7 V consisted of two voltages of 4.718 and 4.739 V. The reaction of Li[Ni 1/2 Mn 3/2 ]O 4 to Li 2 [Ni 1/2 Mn 3/2 ]O 4 is also examined and showed that the reaction proceeded in a cubic (a = 8.17 A)/tetragonal (a = 5.74 A, c = 8.69 A) two-phase reaction with the reversible potential of 2.795 V. From these results, characteristic features of topotactic two-phase reactions of Li[Ni 1/2 Mn 3/2 ]O 4 (P4 3 32) were discussed by comparing with the results on LiMn 2 O 4 (Fd3m).

High-capacity lithium insertion materials of lithium nickel manganese oxides for advanced lithium-ion batteries: toward rechargeable capacity more than 300 mA h g−1

Lithium nickel manganese oxides Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 (x = 1/2, 2/7, and 1/5) are prepared and characterized by XRD and FT-IR, and the samples are examined in non-aqueous lithium cells at room temperature and 55 °C. Among these materials LiNi1/2Mn1/2O2 (x = 1/2) shows the highest operating voltage and the smallest polarization with a rechargeable capacity of ca. 230 mA h g−1 and Li[Li1/5Ni1/5Mn3/5]O2 (x = 1/5) shows the lowest operating voltage and the largest polarization with a rechargeable capacity more than 300 mA h g−1. Extraordinarily large rechargeable capacity of Li[Li1/5Ni1/5Mn3/5]O2 together with an anomalously long voltage plateau at 4.5 V only observed at first charging process is examined by window-opening charge and discharge, continuous charge and discharge combined with differential chronopotentiometry at room temperature and at 55 °C, and possible mechanisms are discussed in terms of lithium insertion scheme.

Synthesis and characterization of 5 V insertion material of Li[FeyMn2−y]O4 for lithium-ion batteries

LiFeyMn2−yO4 (0≤y<1) is prepared and examined by electrochemical, X-ray diffractional (XRD), and Mossbauer-spectral methods. Li[FeyMn2−y]O4(Fdm) having a normal spinel-framework structure can be prepared with 0≤y<0.6 and an intermediate between a normal and inverse spinel for 0.6<y. Li[FeyMn2−y]O4 shows discrete operating voltages at 3, 4, and 5 V versus Li. When the iron concentration y is increased from 0 to 0.5, the capacity at 5 V increases while the capacity at 4 V decreases. The operating voltage at 3 V is not affected so much by the iron concentration. The XRD examinations for the oxidation and reduction of Li[Fe0.5Mn1.5]O4 show that the reaction proceeds in a topotactic manner over an entire range, i.e. the cubic phase at voltages above 3 V, the cubic/tetragonal phases in the range 2–3 V, and the tetragonal phase below 2 V. Reversible capacity observed below 2 V is not explained in terms of a topotactic reaction from □[Fe0.5Mn1.5]O4(cubic) to Li2[Fe0.5Mn1.5]O4(tetragonal) via Li[Fe0.5Mn1.5]O4(cubic). Mossbauer spectra indicate that Fe4+ is formed above 4.5 V and Fe3+ (high spin state) below 4.5 V. From these results the reaction mechanism is discussed in terms of the solid-state redox reaction.

Effect of Primary Particle Size upon Polarization and Cycling Stability of 5-V Lithium Insertion Material of Li [ Ni1 ∕ 2Mn3 ∕ 2 ] O4

The 5-V lithium insertion materials of Li[Ni 1/2 Mn 3/2 ]O 4 having different primary particle sizes were prepared by the two-step solid-state reaction at several temperatures and characterized by Fourier transform infrared, X-ray diffraction, and scanning electron microscopy. The primary particle size of Li[Ni 1/2 Mn 3/2 ]O 4 depends on the heating temperature. High temperature synthesis gives highly crystallized Li[Ni 1/2 Mn 3/2 ]O 4 having large particle sizes with smooth {111} facets of octahedra characteristic of spinel. The steady-state polarization measurements were carried out by applying the sinusoidal voltage of peak amplitude of 1 V at 0.1 Hz to the cell consisting of Li[Ni 1/2 Mn 3/2 ]O 4 and Li[Li 1/3 Ti 5/3 ]O 4 . The well-developed primary particles prepared at 1000°C were superior to the small primary particles prepared at temperatures lower than that value in terms of polarization together with cycling stability.

Lithium Aluminum Manganese Oxide Having Spinel-Framework Structure for Long-Life Lithium-Ion Batteries

Lithium aluminum manganese oxide (LAMO) having a spinel-framework structure (a = 8.211 A) was prepared and examined in lithium nonaqueous cells. LAMO shows extremely small irreversible capacity with rechargeable capacity of ca. 105 mAh g -1 in lithium cells operated in voltage of 3 to 5 V. To show durability for long-life applications, a 2.5 V lithium-ion cell of Li[Li 1/3 Ti 5/3 ]O 4 and LAMO was fabricated and accelerated cycle tests were done at room temperature in voltage of 2 to 3 V for 3600 cycles, and an empirical relation between capacity (Q) and number of cycle (n) was obtained to be Q = 102.7 - 0.144 n 1/2 .

In situ 57Fe Mössbauer Investigation of Solid-State Redox Reactions of Lithium Insertion Electrodes for Advanced Batteries

A novel in situ electrochemical cell for 57Fe Mossbauer measurements was developed in order to clarify the mechanisms of solid-state redox reactions in lithium insertion materials containing iron. Our in situ Mossbauer technique was successfully applied to the determination as to which transition metal ion was a redox center in the insertion electrodes, such as LiFe0.5Mn1.5O4, LiFeTiO4, or LiFe0.25Ni0.75O2, for the lithium-ion batteries.