Toshio Matsushima

Development of a rack-mounted DC-power-supply system utilizing lithium-ion batteries for backup

This paper describes the characteristics on a rack-mounted DC-power-supply system utilizing lithium-ion batteries, which have higher energy density than conventional secondary batteries. The entire system is compact and light-weight so it is ideal as a high-energy-density backup power-supply. We report on functions, system configuration and characteristics of a rack-mounted DC-power-supply system utilizing lithium-ion batteries.

Fundamental characteristics of stationary lithium-ion secondary cells and a cell-voltage-management system

This paper describes the results of several performance tests evaluating lithium-ion cells developed for stationary use, such as stand-by sources in power systems. The effect of a cell-voltage-management system developed for batteries of cells is also shown. The tested cells were suitable for being charged by using the constant-current and constant-voltage (CCCV) method and could be charged efficiently over a wide range of temperatures. They also showed good discharge performances that were scarcely influenced by the discharge current and temperature. The cell-voltage-management system was revealed to be useful for the suppression of deviation of cell voltage and capacity loss.

Construction of three-dimensional thermal simulation model of lithium-ion secondary battery

We are developing a large-capacity lithium-ion secondary battery as a backup power supply for next generation communications. The lithium-ion secondary battery has the advantage of very high energy density. However, the temperature of the battery rises when overcharge or internal short-circuit occurs. If the temperature of the battery exceeds a constant value, there is a danger that the positive electrodepsilas active material may decompose, oxygen may be discharged, the electrolysis liquid may burn, and rapid ignition (thermal runaway) may occur. In general, lithium-ion secondary batteries come in three shapes (cylinder, flat, and accumulating). A structural examination of the temperature increase is indispensable to develop a large-capacity lithium-ion secondary battery. We developed a highly accurate three-dimensional thermal simulation model using the finite-element method.

Rack-Mounted DC Power Supply System Utilizing Li-Ion Batteries for Backup

A rack-mounted DC power-supply system utilizing Li-ion batteries, which have higher energy density than conventional VRLA batteries, was developed. The system was designed to have the management functions of Li-ion batteries, such as overcharge protection, over-discharge protection, and cell-voltage equalization, by taking operational requirements into consideration. The volume and weight of the entire system were decreased to one-fourth and three-fifths, respectively, of the volume and weight of a conventional system, making the proposed system ideal as a high-energy-density backup power supply. The functions, system configuration, and characteristics of this rack-mounted DC power supply system utilizing Li-ion batteries are described.

Large-Capacity and Long-Life Sealed Lead-Acid Batteries for Telecommunications Systems

Lead-acid batteries used in telecommunications systems as a standby power sources play an important role in providing power in the event of commercial power failures. However, these batteries require numerous inspections and a great deal of manpower to maintain them. Therefore, reduction of labor involved in those maintenance has been requested. Sealed lead-acid batteries with a large capacity and a long life have been developed for telecommunications applications. They are safe and easily maintained. They have a maximum capacity of 3,000 Ah and are designed to have a life of over 10 years. Parameters such as plate thickness and electrolyte specific gravity were determined to attain the specified performance and life. Adhesives and rubber valves are made of reliable materials. Flame-retardant resin is applied to the battery container. Performance tests in laboratory and in telephone offices have confirmed that the sealed lead-acid batteries exhibit satisfactory characteristics and are sufficiently suited to telecommunications applications.

Field trials on DC-power-supply system equipped with 80-ah stationary lithium-ion secondary batteries

A DC-power-supply system with a maximum output current of 30 A was developed using stationary 80-Ah lithium-ion batteries and performance tests were carried out in laboratories and a base transceiver station offering actual services. The system was designed for an outdoor setting. The lithium-ion batteries had recharge characteristics evaluated by a method of constant-current and constant-voltage charge and delivered almost equal discharge at current rates that ranged between and 1-10 hr. Their cell voltage was over 3.6 V per cell during discharge at the same current rates. The weight of the batteries was reduced to about a quarter and the volume of the system was reduced to about a third by applying the lithium-ion batteries, compared to a conventional system with VRLA batteries. The composition, fundamental characteristics, and field-test results for the DC-power-supply system are also described.

Fundamental Characteristics of Stationary Lithium-Ion Secondary Cells and a Cell-Voltage-Equalizing Circuit

This paper describes the characteristics of lithium-ion cells developed for stationary use, as in the case of stand-by sources in power systems. The effect of a cell-voltage-equalizing circuit developed for batteries of cells is also demonstrated. The tested lithium-ion cells were suitable to be charged by the constant-current, constant-voltage (CCCV) method and could be charged efficiently over a wide range of temperatures. They also showed good discharge performance with little dependence on the discharge current and temperature. Total capacity reduction of over 60% can be expected in batteries of lithium-ion cells. The cell-voltage-equalizing circuit was shown to be useful and necessary for batteries of lithium-ion cells in order to suppress deviations in the cell voltage and capacity loss.

Residual Capacity Estimation of Stationary Lithium-ion Secondary Cells in Telecommunications Systems Using a Brief Discharge

Lithium-ion batteries are expected to contribute to miniaturizing power systems and prolonging backup times in telecommunications systems. From the viewpoint of maintenance, checking battery conditions automatically is desirable after the deployment of lithium-ion batteries to telecommunications systems. Estimating the residual capacity of backup batteries is one of our major concerns in maintaining them. To do this, we propose discharging lithium-ion batteries to an actual load for a short duration, measuring the voltages in this discharge, and estimating the capacity using the correlations between the voltages and residual capacities. We studied the fundamental correlations between the voltages during discharge and the residual capacities using trickle-charged single cells and a float-charged 14-cell series-connected battery in high-temperature acceleration tests. We found good correlations between the voltages and residual capacities in both the single cells and the battery. These correlations may be useful for estimating the residual capacities of float-charged lithium-ion batteries using brief discharges into actual loads

VRLA battery remote management system

NTT has used VRLA batteries as a backup power supply for over 17 years, and the use of VRLA batteries has reduced the battery maintenance cost. NTT Facilities must ensure that a reliable telecommunications power supply is maintained, and we need to be able to determine the degree of battery deterioration to prevent unexpected power failures. In addition, as our maintenance bases have been consolidated in recent years, maintenance workers are often no longer assigned to a particular site and they now have to maintain several types of equipment at different sites. Therefore, a remote management system for VRLA batteries has become necessary. We have developed a VRLA battery management system that automatically measures the voltage and ambient temperature of each cell and reports the appropriate time for battery replacement. These data can be monitored at an operating center located elsewhere. Furthermore, to help ensure a highly reliable telecommunications power supply, we have developed an electrolyte leakage detection function and an internal resistance measurement function. These functions have been added to the VRLA battery remote management system.

439 Investigation into technical factors related to stationary lithium-ion battery used in telecommunications applications

Today, lead-acid batteries are the most common choice for battery backup of communication equipment power systems. In recent years, however, a demand for a more compact power supply is growing amid expectations for spreading use of the NGN. Lithium ion batteries, which feature high energy density, are expected to greatly contribute to such reduction of power supply size. Improved safety and longer lifetime are indispensable for use of lithium ion batteries in power supply facilities for communication equipment. When manganese-based active material is used for the positive material, manganese eluted from the positive electrode migrates to the negative electrode surface, where it reacts with lithium ions to deactivate the lithium. That phenomenon has been confirmed to decrease battery capacity. Therefore, to extend battery life, we investigated the elution characteristics of manganese ions from the positive electrode by using test samples in which the elemental manganese of the positive material is partially replaced with some other metal element. The results show that there is least elution of manganese from the positive electrodes of lithium ion batteries that use manganese-based pasitive materials when the manganese is replaced by magnesium. With the objective of higher battery safety, we also investigated the elution characteristics of manganese ions from the positive electrode for when a phosphazene-based flame retardant has added to the electrolyte solution. The results show that the flame retardant in electrolyte decomposes during long-term storage to generate fluorine compounds, which have been confirmed to accelerate the elution of manganese ions. We also learned that decomposition of the flame retardant is related to the stability of the electrolyte, so elution of the manganese ion can be controlled by using a stable electrolyte.