Kazuyuki Adachi

Layered Polyaniline Composites with Cation‐Exchanging Properties for Positive Electrodes of Rechargeable Lithium Batteries

Layered polyaniline/polyaniline-polyanion composite films (PAn-X/PAn-PA) were synthesized by electrochemical oxidation of aniline in aqueous acid solutions (HCl, HClO[sub 4]) followed by polymerization in poly(styrene-4-sulfonic acid) (PSSH) solutions. The films consist of inner polyaniline (PAn) layers doped with smaller size anions (X) and outer PSS-doped PAn layers. The resulting films showed high redox activities with cation-transfer properties in organic electrolyte solutions. The improved charge/discharge characteristics of the composite films gave an expectation of higher energy density for the full cell with lithium negative electrode.

Charge/discharge characteristics of polyaniline-based polymer composite positives for rechargeable lithium batteries

The structure of a polyaniline-poly(styrene-4-sulfonate) (PAn-PSS) composite film was optimized as the positive electrode for rechargeable lithium batteries to improve the charge/discharge characteristics in organic electrolyte solutions. The composite films prepared in aqueous poly(styrene-4-sulfonic acid) (PSSH) solutions containing small amounts of HClO4 showed higher charge/discharge capacities than those prepared in PSSH without HClO4. However, the utilization of Li+-ion transport in the redox process decreased with an increase in the HClO4 concentration. A stacked PAn-ClO4/PAn-PSS film, which consists of an inner PAn layer doped with smaller size anion (ClO4−) and an outer PAn-PSS composite layer, was prepared by the electrolysis of aniline in aqueous HClO4 followed by the polymerization in a PSSH solution. The resulting films gave improved charge/discharge characteristics in organic electrolyte solutions and lead to higher energy density of the full cell with lithium negative electrode.

Multi-step constant-current charging method for electric vehicle, valve-regulated, lead/acid batteries during night time for load-levelling

For the popularization of electric vehicles (EVs), the conditions for charging EV batteries with available current patterns should allow complete charging in a short time, i.e., less than 5 to 8 h. Therefore, in this study, a new charging condition is investigated for the EV valve-regulated lead/acid battery system, which should allow complete charging of EV battery systems with multi-step constant currents in a much shorter time with longer cycle life and higher energy efficiency compared with two-step constant-current charging. Although a high magnitude of the first current in the two-step constant-current method prolongs cycle life by suppressing the softening of positive active material, too large a charging current magnitude degrades cells due to excess internal evolution of heat. A charging current magnitude of approximately 0.5 C is expected to prolong cycle life further. Three-step charging could also increase the magnitude of charging current in the first step without shortening cycle life. Four-or six-step constant-current methods could shorten the charging time to less than 5 h, as well as yield higher energy efficiency and enhanced cycle life of over 400 cycles compared with two-step charging with the first step current of 0.5 C. Investigation of the degradation mechanism of the batteries revealed that the conditions of multi-step constant-current charging suppressed softening of positive active material and sulfation of negative active material, but, unfortunately, advanced the corrosion of the grids in the positive plates. By adopting improved grids and cooling of the battery system, the multistep constant-current method may enhance the cycle life.

Charging operation with high energy efficiency for electric vehicle valve-regulated lead-acid battery system

A new, high-energy-efficiency charging operation with as little amount of overcharge as possible is proposed to improve the energy efficiency and the cycle life for an EV valve-regulated lead–acid battery. Under this operation, the EV battery system is charged with 105% of amount of the preceding discharge five out of six times and once with 115% in order that it is fully charged. The cycle lives were estimated using a valve-regulated lead–acid battery system of 12 modules connected in series, by SFUDS79 pattern discharging and measurement of the amount of discharge every 50 cycles. Three-step constant current charging with 115% of amount of the preceding discharge required more than 5 h with the final charging step of more than 210 min, with coulomb efficiency of only 87% and energy efficiency of 74%. On the other hand, under the high-energy-efficiency charging operation, three-step charging with 105% shortens the final charging time to 132 min. It was completed in less than 4 h with coulomb and energy efficiency of 95% and 84%, respectively. This operation increased the energy efficiency from 74% to 83% on average in six chargings, and extended the cycle life by about 30% to more than 400 cycles. Decreasing the amount of charge by as much as possible suppressed the corrosion of the grids in the positive plate and the heat evolution in batteries due to shortening of the final charging step. Although the high-energy-efficiency charging operation led to the accumulation of inactive PbSO4 at the upper part of the negative plate, possibly due to the decreasing amount of overcharge, this operation could prolong the cycle life. Full charging once every six times is though to be effective in suppressing degradation caused by the accumulation of inactive PbSO4 in the negative plate due to the shortage of charge.

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.