Li[Lil/zTi~/3]O ~ having a defect spinel-framework structure (Fd3m; a = 8.36 A) was prepared and examined in nonaqueous lithium cells. Li[Li~/~Ti~/3]O 4 (white in color) was reduced to Li2[Lil/~Tij/3104 (dark blue) at a voltage of 1.55 V and the reaction was highly reversible. X-ray diffraction measurements indicated that the lattice dimension did not change during the reaction Li[Lil/~Tis/3]O4 + Li + + e .... L12[Lll/3Ti5 3]O4 8(a) 16(d) 32(e) ~16(c) 16(d)/32(e)Since the reaction consists of lithium ion and electron insertion into/extraction from the solid matrix without a noticeable change in lattice dimension, called a zero-strain insertion reaction, capacity failure due to the damage to the solid matrix was not observed even after 100 cycles. Feasibility of zero-strain insertion materials for advanced batteries is discussed based on the experimental results.

The synthesis and characterization of LiNiO2 for a 4 V secondary lithium cell was done. The LiNiO2 was prepared by ten different methods and characterized by x-ray diffraction and electrochemical methods. LiNiO8 prepared from LiNO3 and NiCO3 [or Ni(OH)2] exhibited more than 150 mAh 9 g-1 of rechargeable capacity in the voltage range between 2.5 and 4.2 V in 1M LiC104 propylene carbonate solution. The reaction mechanism was also examined and explained in terms of to~otactic reaction. Lithium nickelate(III) (R3m; a = 2.88 A, c = 14.18 A in hexagonal setting) was oxidized to nickel dioxide (R3m; a = 2.81/~, c = 13.47 A) via Lil_=NiO2 (0.25(2) _-< x _-< 0.55(2)) having a monoclinic lattice (C2/m). The nickel dioxide could be reversibly reduced to lithium nickelate(III). Factors affecting the electrochemical reactivity of LiNiO2 are given and the possibility of using LiNiO2 for 4 V secondary lithium cells is described.

Layered LiCo1/3Ni1/3Mn1/3O2 was prepared by a solid state reaction at 1000 °C in air and examined in nonaqueous lithium cells. LiCo1/3Ni1/3Mn1/3O2 showed a rechargeable capacity of 150 mAh g−1 in 3.5–4.2 V or 200 mAh g−1 in 3.5–5.0 V. Operating voltage of Li / LiCo1/3Ni1/3Mn1/3O2 was by 0.2–0.25 V lower than that of a cell with LiCoO2 or LiMn2O4 and by 0.15–0.3 V higher than that with LiNiO2 or LiCo1/2Ni1/2O2 due to a complex solid solution mechanism.

Electrochemical reduction of natural graphite was carried out in 1M LiClO4 ethylene carbonate (EC)/1,2‐dimethoxyethane (DME) (1:1 by volume) solution at 30°C. Natural graphite was reduced stepwise to LiC6 (golden yellow in color). The staging phenomenon was observed by x‐ray diffraction (XRD). The first stage ( LiC6 ; cL=3.70true3_Å ) and the second stage ( LiC12 ; d2=7.06Å ) compounds were identified as a commensurate structure in which lithium atoms form a close‐packed two‐dimensional array. A second‐stage compound false(LiC18false) with a different in‐plane lithium ordering based on a LiC9 two‐dimensional packing in lithium intercalated sheets also was observed; also third ( LiC27 ; d3=10.4Å ), fourth‐( LiC36 ; d4=13.8Å ), and eighth‐( LiC72 ; d8=27.2Å ) stage compounds were identified. The electrochemical oxidation of the first‐stage compound false(LiC6false) was examined and shown to be reversible over the entire range, i.e., □C6+xnormalLi⇄LixC6 . The reaction mechanism for the reduction of graphite and the oxidation of the first‐stage compound are discussed in relation to the staging phenomenon from the detailed open‐circuit voltage and XRD data. The chemical potential of LiC6 was estimated to be −3.6 kcal · mol−1 from the observed reversible potential. The feasibility of using a lithium‐graphite intercalation compound in lithium ion (shuttlecock) cells is described, and the innovative secondary systems, □C6/LiCoO2 and □C6/LiNiO2 fabricated in discharged states, are demonstrated.

LiCoO2 (R3m; a = 2.82 A, c = 14.1/~ in hexagonal setting) was prepared and examined in nenaqueous lithium cells using IM LiCIQ propylene carbonate solution at 30~The oxidation of LiCoO2 and the reduction of Li~_xCoO~ proceeded reversibly in the voltage region above 3.9 V. X-ray diffraction (XRD) examinations indicated the reaction proceeded in a topotactic manner, i.e., two-phase reactions (0 < x< 1/4 and 3/4 < x < 1 in Li~_=CoO~) and a single-phase reaction (1/4 < x < 3/4). A monoclinic phase (a~ 4.91 A, bo= 2.82 A, c= 5.02 A, and ~ = 111.4 ~ was observed in 3/4 < x < 1 in addition to that at about x = 0.45 (a = 4.90 A, b = 2.81 A, c = 5.05 A, and ~ = 108.3~ Detailed open-circuit voltage measurements were carried out. The open-circuit voltage are invariable at 3.92 V for 0 < x < 1/4 and at 4.50 V for 3/4 < x < 1. The two straight lines are connected smoothly by a composition-dependent curve for 1/4 < x < 3/4, which was consistent with the XRD observations. The differences and similarities between the solid-state redox reactions of LiCoO~ and LiNiO~ were discussed by comparing the structural and electrochemical data. Possible lithium ordering at x = 1/4 and 3/4 for this type of material is described in terms of a [2 • 2] superlattice in a triangular lattice of sites.Lithium-ion cells consisting of LiMeO2 (Me; 3d-transition metal element) and carbon materials 1-~ have been of interest because of their capability for operating thousands of cycles safely while retaining a high-energy density lithium technology. Candidate materials extensively examined for positive electrodes have been LiCoO2, ~' 6' 7 LiNiO2, 2,s,9 LiNizC01_~O2 (0 < z < 1), l~ LiMn204, 3,13,14 and LiMnO2.15.~ Of these, the research on LiCoQ is more advanced than the other materials and a lithium-ion cell consisting of LiCoO2 and a nongraphitized carbon material has been fabricated and used as power sources for electronic devices. ~The reaction of LiCoO2 in a lithium-ion cell is well known to be lithium-ion extraction from and insertion into a layered cobalt dioxide matrix by varying the interlayer distance. When the Li/LiCoO2 cell is cycled over the limited composition range 0 < x < 1/2, rechargeability and capacity retention are good. 7 However, the rechargeable capacity fades rapidly for deep charge/discharge cycles (x > 1/2). A critical composition in terms of cycle life failure seems to be at about x = 1/2 in Li~ =C002, at which a monoclinic phase is observed by some researchers, 17'18 but not by others. 6'19-2~ Coexistence of two phases ~7'~s'2~ is also a debatable subject in understanding the electrochemical reactions of Li1_=CoO.~.Here we describe electrochemical charge and discharge, open-circuit voltage, and detailed XRD measurements of Li~_~CoO~. We show a reaction mechanism of Li~_~CoO2 (0 _-< x < I) and discuss a one-phase/two-phase problem in solid-state electrochemistry.