1.  Field of the Invention
The present invention relates to a storage battery system suitable for, for example, vehicles, bicycles, trams, elevators, aerogenerators and emergency power supplies, etc.,  which aim to enhance energy efficiency, and also relates to an on-vehicle power supply system and vehicle provided with such a storage battery system. 
2.  Description of the Related Art
In recent years, hybrid vehicles, bicycles, trams, elevators and aerogenerators, etc.,  which are provided with a battery, have been proposed, and some of them have been put into practice, to effectively use energy, in particular, regenerative energy as environmental measures.  Secondary batteries, which have been proposed as backup power supplies for an emergency, such as a blackout, and have been put to into practice and installed in vehicles so far, include, for example, lead storage batteries and nickel hydride batteries. 
However, nickel hydride batteries installed in hybrid vehicles, for example, have the problem that they suddenly generate heat during high-power outputting or fast charging (regenerative charging), and their thermal degradation is very conspicuous.  Furthermore, lead storage batteries used as emergency power supplies have a low weight energy density and hence heavy weight, therefore, involve constraints on their installation place. 
Hybrid vehicles using a large-capacity capacitor have now been developed.  Compared to secondary batteries, capacitors can accumulate high power instantly, but have a very small electric capacity and hence cannot be made compact. 
To solve the above problems, JPA KOKAI No.  2003-134689, for example, has proposed a high-power lithium ion battery.  While lithium ion batteries can generate high voltage and be made light, and hence have a high energy density, they use a carbon material as the material of their negative electrodes.  Accordingly, their cycle lives will degrade if fast charging, such as energy regeneration, is performed.  This being so, when low power is input to the batteries, they cannot efficiently accumulate regenerative energy.  Further, if lithium ion batteries are made into high-power ones, their inherent high energy density is significantly reduced to thereby reduce their discharge capacity.  Accordingly, the travel distance of, for example, electric vehicles is inevitably shortened.  Furthermore, for hybrid vehicles, there is a demand for enhancing the energy regenerative performance during braking and the acceleration performance, and also a demand for increasing the travel distance during motor driving (EV driving).  However, it is difficult to satisfy both the enhancement of energy regenerative performance and acceleration performance, and the traveling performance during motor driving (EV driving). 
JP-A 2004-289892(Kokai) has proposed a hybrid vehicle with a storage battery system as an on-vehicle power supply.  The storage battery system includes main and sub battery modules.  The sub battery module accumulates regenerative current supplied by a motor or dynamo, and the main battery module is charged with the power accumulated by the sub battery module.  However, in this storage battery system, the active material of the negative electrode is low in the rate of occluding and discharging ions, and hence efficient charging cannot be achieved during fast charging, such as regenerative charging.