Toru Iwahori

All-solid-state lithium secondary battery with ceramic/polymer composite electrolyte

Abstract Dense lithium lanthanum titanate, (Li,La)TiO 3 , pellets were prepared using a spark-plasma sintering (SPS) method. The obtained (Li,La)TiO 3 pellets showed relatively high lithium ion conductivity, typically 10 −3 S cm −1 at 22 °C, with an activation energy of 30.1 kJ mol −1 . Lithium manganese oxide, LiMn 2 O 4 , was deposited on (Li,La)TiO 3 pellets by an electrostatic spray deposition (ESD) method at 400 °C without significant formation of by-products at the interface (Li,La)TiO 3 /LiMn 2 O 4 . An all-solid-state battery system, LiMn 2 O 4 /(Li,La)TiO 3 /SPE/Li, where a solid polymer electrolyte (SPE) was sandwiched between (Li,La)TiO 3 and Li, showed good charge/discharge characteristics over 100 cycles at 60 °C.

5 V Class All-Solid-State Composite Lithium Battery with Li3 PO 4 Coated LiNi0.5Mn1.5 O 4

A 5 V class ceramic/polymer composite all-solid-state lithium battery was prepared. The cell configuration was [Li 3 PO 4 coated LiNi 0.5 Mn 1.5 O 4 |solid polymer electrolyte| Li]. The total cell impedance was 4 kΩ at 333 K and the discharge capacity was 100 mAh g -1 with a discharge voltage plateau in both 4.7 and 4.1 V regions. X-ray absorption near-edge structure results indicated that both transition metal ions, Ni and Mn, involved in the oxidation/reduction processes. The cell without Li 3 PO 4 showed a lower discharge voltage plateau (<3.5 V) than the composite one. Although the Li 3 PO 4 film was so thin that it could be nearly removed with only 2 min of Ar etching in X-ray photoelectron spectroscopy, Li 3 PO 4 is thought to have a function as a solid electrolyte interface between LiNi 0.5 Mn 1.5 O 4 and SPE to prevent the degradation of solid polymer electrolyte.

Precise Electrochemical Calorimetry of LiCoO2/Graphite Lithium-Ion Cell Understanding Thermal Behavior and Estimation of Degradation Mechanism

The thermal behavior of a lithium-ion cell during charge and discharge was determined using an isothermal calorimeter. In order to assign the thermal characteristics of the lithium-ion cell to the cathode (LiCoO 2 ) and the anode (graphite) material, a LiCoO 2 /Li cell and a graphite/Li cell were prepared. The thermal behaviors were compared with that of a lithium-ion (LiCoO 2 /graphite) cell. The notable thermal characteristics could be attributed to the individual electrode materials. In particular, the discontinuous thermal profiles showed good agreement with the phase change of the host structure of each electrode material. The degradation factor of commercially available lithium-ion cells was determined using these discontinuous thermal profiles as an indicator of the electrode reactions. We found that the decrease in the effective active material of the graphite is the main cause of capacity fading after cycling.

An X-ray photoelectron spectroscopy study on the surface film on carbon black anode in lithium secondary cells

Abstract The property of the surface film formed on the carbon black anode of a lithium cell at the initial reduction stage was investigated. About 90% of the carbon black surface was covered with a smooth film about 10–15 A in thickness after five cyclic voltammetry cycles. The X-ray photoelectron spectroscopy analysis revealed that this film contained oxygen atom bonding directly to the carbon atoms and was formed by decomposition of the solvent. The inhibiting effect of the surface film against further solvent decomposition reaction disappeared after washing with ethanol or heat treatment above 200 °C. The surface film was confirmed to form also by chemical reduction using lithium naphthalide, where lithium insertion in the carbon black took place. The inhibiting effect of a chemically formed surface film against the solvent decomposition was less marked than that of an electrochemically formed film.

High-Performance Genuine Lithium Polymer Battery Obtained by Fine-Ceramic-Electrolyte Coating of LiCoO2

A lithium polymer battery with high-capacity (>180 mAh g - 1 ) LiCoO 2 was prepared by the fine-powder coating of highly lithium-ion-conductive ceramic electrolyte [Li 1 . 5 Al 0 . 5 Ge 1 . 5 (P04)3] on LiCoO 2 powder. The obtained cell (operated at 333 K) exhibited a good reversibility up to 4.4 V and a good sustainability of 105 mAh g - 1 at the 200th cycle. The oxidation of the polymer electrolyte was determined by alternating current (ac) impedance analysis, and it was observed that a suitable ceramic electrolyte coating is an effective oxidation barrier at the polymer/cathode interface.

Effects of the macroscopic structure of carbon black on its behaviour as the anode in a lithium secondary cell

Abstract The anodic behaviour of various carbon black (CB) samples prepared by the oil furnace method has been investigated in 1 M LiPF6 solution in ethylene carbonate-1,2-dimethoxyethane 50 50 (by volume). These CB samples had different macroscopic structures, though their microscopic parameters such as d002 and Lc remained constant substantially. The irreversible capacity at the initial reduction stage increased almost linearly with the BET surface area. The reversible capacity, on the other hand, showed no correlation with the BET area and was large for a highly aggregated coarse CB sample. The neck position connecting two primary CB particles was considered to be mainly active for the electrochemical insertion/extraction of lithium including effective electrolyte penetration on to the carbon surface.

Degradation mechanism due to decomposition of organic electrolyte in Li/MoS2 cells during long cycling

Abstract The degradation mechanism due to the decomposition of organic electrolytes during charge and discharge cycling of Li/MoS2 cells has been investigated. The gas products of the electrolyte decomposition during long cycling were measured by gas chromatography (GC), and the changes of electrolyte composition was measured by gas chromatography/mass spectrometry (GC/MS). The gases were produced through two types of electrolyte decomposition: the electrochemical reaction, which was dependent on the charge and discharge voltage, and the chemical reaction, which was independent of the discharge voltage. This decomposition of electrolytes occurred under a discharge voltage lower than 1.4 V. The operating conditions with a lower discharge rate and a deeper depth of discharge (D.O.D.) accelerated the electrochemical decomposition. The rate of gas production by chemical decomposition, which is independent of the discharge condition, was estimated to be about 0.1 ml/h.

Mechanical Process for Enhancing Metal Hydride for the Anode of a Ni‐MH Secondary Battery

This study attempted to find a simpler method for modifying hydrogen storage alloys that are used as anodes in Ni-MH batteries to prolong their cycle life. The alloy was modified by mechanical grinding with cobalt metal powder. A short grinding time yielded samples with a higher discharge capacity and longer cycle life than those of the alloy which was mixed with the cobalt powder without the mechanical treatment. However, prolonged grinding caused a decrease in the discharge capacity because of amorphization of the alloy by mechanical stress. The authors believed the formation of a cobalt compound on the alloy surface plus closer contact between particle enhanced the cyclic durability and discharge capacity of metal hydride anodes.

Deposition Rate of Suspended Hematite in a Boiling Water System under BWR Conditions

Abstract The state and rate of deposition of suspended hematite were studied on a boiling heat transfer surface under the heat flux, temperature, and pressure similar to those in BWR power plants. ...

Collaborative investigation on charging electic-vehicle battery systems for night-time load levelling by Japanese electric power companies

Abstract In 1995, ten Japanese electric power companies and CRIEPI started a three-year collaborative investigation of battery systems for electric vehicles (EVs). In the first year, the charging procedure for valve-regulated lead/acid (VRLA) batteries connected in series in EVs has been evaluated for both night-time load levelling and prolonging the cycle life. An EV battery system with VRLA batteries can be charged by both constant current and constant current (CC-CC) and constant current and constant voltage (CC-CV) in less than 8 h under night-time conditions. The charging method with CC-CC prolongs the cycle life further than that with CC-CV. Excess charging capacity on the part of CV in CC-CV charging degrades the positive electrode through softening of the active material. A higher rate of the first current in CC-CC charging prolongs the cycle life by suppressing the softening of the positive electrode due to active-material particle growth. On the other hand, control of the uniform environment in battery boxes during the charging with CC-CC and CC-CV is very important in order to prolong the cycle life. This is because cooled batteries tend to have insufficient charge capacity due to their greater energy consumption for the electrolysis of water than uncooled ones.