Lead-acid storage batteries with liquid electrolyte
Principle of lead-acid batteries’ operation is based on electrochemical reactions of lead and lead dioxide in sulfuric acid environment. During the discharge there occurs deoxidation on cathode and lead oxidation on anode. During the charge there arise back reactions and plus to that at the end of charge there occurs water electrolysis reaction by which oxygen releases on positive electrode and hydrogen releases on negative one.
Lead-acid battery’s cell comprises positive and negative electrodes, separators and electrolyte. Positive electrode is a lead grid, and the active mass is a lead oxide (PbO2). Negative electrodes are also lead grids, and active mass is a spongy lead (Pb). On practice the antimony is added to grid lead for higher grid strength. Electrodes are dipped into electrolyte that consists of diluted sulfuric acid (H2SO4).
Currently for motor and tractor internal-combustion engine start there are used lead-acid storage batteries with high specific electrochemical characteristics. Usually starter batteries are produced with grids made of lead-antimony alloy (Pb-Sb) where antimony content is (Sb) 5,0 to 7,0 %, and thin shunts which thickness is less than 1,5 mm are casted of alloy with higher antimony content.
There exist lots of ideas for benefit of lead-antimony alloys application:
- Pb-Sb alloy has good casting characteristics;
- Alloy provides clear founding (casting);
- Alloy can be used for active mass retention and it will not lose its strength because of formation process at battery operation, that is Sb availability furthers stronger electric contact of active mass and grid;
- There does not arise blocking effect in Pb-Sb alloys that is often present in Pb-Ca ones, which does not contain Sb (blocking effect means a formation of layer non-conductors (CaSO4) between positive grid and active mass;
- Antimony increases lead hardness and its yielding and breaking strength as well (see the Table).
|Antimony content in alloy, %||Alloy melting temperature, °С||Alloy density,
However, the application of traditional starter storage batteries results in some certain difficulties because of the following disadvantages and peculiarities::
- During operation interruption there arises battery self-discharge that leads to average daily capacity loss which is determined during 14 storage days, new batteries have to 1% capacity loss and at the end of service life it increases to 4%. As a result, during batteries’ (filled with electrolyte) storage it is necessary to charge them monthly over 8-10 h. Batteries are to be stored and charged in charging stations’ premised, thus there is a necessity of large areas, charging equipment and skilled personnel.
- During automobile exploitation electrolyte level decreases because of water electrolysis, that is why it is necessary to add distilled water to battery every 12-15 days and this increases maintenance volume.
- Water electrolysis is connected with active oxygen emission that leads to faster positive electrode corrosion. It is known that storage battery life time is limited mainly by grids corrosion. Electrolyses rate and correspondingly corrosion rate increases during recharge, higher temperature and battery ageing. That is why some limitation measures for ceiling voltage of motor and tractor generator are necessary to be done.
- Inspections and maintenance necessity complicates batteries’ installation in automobiles and tractors. It is required to ensure access to the battery for electrolyte level and density measuring, and for water filling-up.
- It is substantially that oxygen and hydrogen mixture released from batteries is highly explosive. It hampers batteries’ warmth keeping and heating, because to do this it is important to provide essential ventilation of compartment where the battery is located.
- Electrolyte gases and vapors released from the battery lead to corrosion of hardware, that is located near the battery and its pole terminals, they are also toxic (antimonous hydrogen).
The above mentioned peculiarities and disadvantages of up-to-date starter lead-acid batteries result in additional maintenance costs namely to service personnel, to materials, electro energy and amortization of premises and equipment. Violation of maintenance volume and periodicity leads to decrease of battery’s life time to 30%, and that is inadmissible.
The main reason for all mentioned peculiarities and disadvantages is availability of 5% of antimony in lead alloy from which the grids are produced. That is why maintenance-free batteries are being produced in such way in order to limit water electrolysis which results in gas emission.
Antimony presence in positive electrode’s grids leads on the one hand to increased oxygen release and on the other hand to electrochemical antimony transfer and its precipitation on negative electrode’s surface. It is antimony presence on negative electrode surface that leads to gas emission increase. On practice it means that at joint action of battery and automobile generator set gas emission begins long before battery is charged. Thus, the works to meet the need in decreased water loss, self-discharge and grids corrosion must further increased oxygen and hydrogen overstrain on the electrodes.
«Calcium Plus» (negative electrode made of lead-calcium alloy)
Currently, there are three main areas of work to create batteries with reduced volume of service:
- the use of lattices of electrodes made of lead-calcium-tin alloys instead of lead-antimony;
- the use of lattices of modified lead-antimony alloys with a reduced content of antimony;
- application of lattices of positive electrodes with low content of antimony and cadmium, negative electrodes from lead-calcium-tin alloys.
VLADAR was the first in Ukraine to start producing lead-calcium batteries “Vladar Calcium Plus” using its own original developments in this direction in January 2002.
In the batteries “Vladar Calcium Plus” a combined circuit is used: the positive electrode is made of a low-antimony (Sb content up to 2%) lead alloy, and the negative electrode is made of lead-calcium-tin alloy. The features of the battery manufactured using this technology provide important consumer properties. At an affordable price, these batteries have good technical qualities: the ability to restore the launch characteristics after deep discharges and, if properly operated, a sufficiently long service life.
Such a technological solution allows to lower the water flow rate to such a level that the need for a distillate top with proper battery operation does not occur more than once in 3-4 years. Also, it makes it possible to reduce self-discharge in such a way that the battery can be stored without recharging for a long time.
One of the important advantages of doping a positive calcium electrode is to reduce the corrosion of the gratings, thereby increasing the battery life by 30% compared to conventional batteries and at the same time increasing the battery life to recharge.
No less important quality of the “Vladar Calcium Plus” batteries is the increase of the starter current by more than 20% compared to conventional batteries.
Thus, the advantages of the “Vladar Calcium Plus” technology are:
- excellent performance at low and high temperatures;
- durability – the service life of starter batteries is 4-5 years;
- vibration resistance;
- increased corrosion resistance;
- resistance to reloading;
- extremely low losses of water during battery operation, and as a result, a reduction in costs associated with maintenance of the battery during operation;
- low battery self-discharge.
The area of primary use of “Vladar Calcium Plus” batteries is a starter battery for starting engines of cars and railway locomotives (especially in extreme climatic conditions).
It is also possible for stationary use of such batteries, but there are certain difficulties, primarily related to the need for proper ventilation in the room where the batteries are installed.
Sealed (VRLA) maintenance-free storage batteries with gel electrolyte
The technology, called “Vladar Calcium Plus”, is successfully used today. Of course, this research has not stopped. Hundreds of experiments were carried out, various versions of the electrolyte, the shape of the plates, and the separator brand were tested. As a result, in late 2004 a new type of battery was released. The first among manufacturers in Ukraine and CIS countries, the factory “Vladar” mastered the technology of production of battery with gel electrolyte!
In batteries, a recombination of gases in a closed cell is carried out with the formation of water due to the course of the chemical process. Due to the decomposition of water in the element, oxygen forms on the positive plate and hydrogen on the negative plate. Through cracks and channels in the gel and microporous separators, oxygen enters the negative plate, where it combines with hydrogen ions, again forming water. This water is absorbed by the gel. Special safety plugs ensure the maintenance of excessive pressure inside the battery, the decomposition and recombination process is of a closed nature, therefore, water loss in the cell does not occur. As a result, the battery absolutely does not need maintenance!
Advantages of gel batteries:
- Maintenance free for the whole service life;
- Absence of leakage of electrolyte even if the housing is damaged;
- Absence of acid vapors in the environment during battery operation;
- Does not require topping up water and checking the electrolyte level;
- Very low self-discharge. After a year of storage at a temperature of + 20 ° C, the batteries retain about 65% of the original capacity;
- Possibility of safe operation of batteries in the same room with other equipment and personnel;
- The possibility of compact installation of sections, the battery occupies a small area;
- Ability to quickly restore the nominal capacity;
- Excellent performance in high-current discharge;
- Do not belong to the category of dangerous goods for transportation by all modes of transport.
All of the above features of this technology determine the primary area of application of gel batteries and batteries: in premises with high ecological requirements (as stationary sources of current, as traction batteries for floor transport, for rolling stock of railway transport).