Work in warehouses, mines, and simply in enclosed spaces is often impossible without electric transport, since air quality requirements do not allow the use of vehicles on internal combustion engines. An integral part of any electric vehicle, which determines its autonomy, power and cost of operation, is the battery as an energy source. There are several different battery systems on the market, differing in the nominal voltage of the battery cell, the amount of allowable discharge and charging current, so even at the stage of purchasing equipment, it is necessary to make a balanced choice that determines significant capital costs. The most common problem is choosing between alkaline and lead batteries,
In order to determine the advantages and disadvantages of these systems, it is necessary to consider the processes occurring in them. In this article, we have discussed in detail the difference between alkaline battery and lead acid battery.
Lead Acid Battery
The positive electrode of a charged battery contains lead dioxide PbO2, and the negative electrode contains spongy lead. The electrolyte is a sulfuric acid solution. The process that occurs when the battery is discharged can be described by the equation
PbO 2 + Pb + 2 H 2 SO 4 \u003d 2 PbSO 4 + 2 H 2 O.
This process works in opposite direction while charging.
2 PbSO 4 + 2 H 2 O \u003d PbO 2 + Pb + 2 H 2 SO 4,
and at the end of the charge on the electrodes, in addition to the main reactions of the formation of active substances, side reactions begin to occur – the release of hydrogen on the negative electrode and oxygen on the positive one. The voltage of a fully charged battery is 2.07…2.11 V.
As can be seen from the equations describing the chemical processes of charge/discharge, the acid electrolyte concentration decreases during the discharge process, and vice versa, when charging, it increases. From this it follows that when the temperature drops, the electrolyte of a discharged battery can freeze, which will lead to the destruction of the battery.
A decrease in concentration and a corresponding increase in the resistance of the electrolyte during discharge leads to a decrease in the energy efficiency of the battery at the end of the discharge. It is also worth noting that the end product of the discharge of both electrodes is non-conductive lead sulfate, which means that when discharged by a capacity greater than a certain value, the likelihood of exfoliation of sulfate crystals and an irreversible decrease in battery capacity increases. Increased temperature can lead to an increase in the size of the crystal and their shedding from the electrodes; increased rate of formation, which is observed when the value of the permissible discharge current is exceeded; recrystallization as a result of prolonged contact of lead sulfate with a solution of sulfuric acid, which occurs during storage of even partially discharged batteries.
Alkaline Batteries
Nickel-cadmium and nickel-iron cells are the most widely used as traction among alkaline batteries. In both types, the positive electrode contains non-stoichiometric nickel oxide-hydroxide NiOOH. The negative electrode contains either a mixture of cadmium and iron, or sponge iron. The electrolyte is an alkali solution – sodium or potassium hydroxide. The discharge of the battery is accompanied by reactions
2 Ni(OOH) + Cd + 2 H 2 O = 2 Ni(OH) 2 + Cd(OH) 2
Or
2 Ni (OOH) + Fe + 2 H 2 O \u003d 2 Ni (OH) 2 + Fe (OH) 2.
When charging, the processes in the opposite direction take place on the electrodes. In addition, a side process of oxygen evolution occurs at the positive electrode during charging. On the negative electrode, the side process of hydrogen evolution begins to proceed after gaining: on iron – 50% of the capacity, and on cadmium – 80% of the capacity. The voltage of freshly charged batteries is 1.25 … 1.45 V.
Since the electrolyte is not consumed in the charge / discharge processes, its concentration does not change, which leads to greater frost resistance of alkaline batteries. However, a greater decomposition of water compared to an acid battery requires the implementation of recombination cycles with the participation of evolved gases and regular topping up of water. Moreover, the alkali absorbs carbon dioxide heavily from the environment. This absorption lead to decrease in electrolyte’s electrical conductivity due to carbonization. In addition, the alkaline electrolyte has lower electrical conductivity and higher cost.
The substances formed during the discharge of electrodes have a sufficiently high conductivity, therefore alkaline batteries are less sensitive to excess charge / discharge currents and are not prone to shedding from the electrodes, as a result of which the batteries have a long service life and withstand up to 2000 … 3000 discharge / charge cycles (for lead acid traction batteries – about 1500 cycles). Such alkaline batteries can withstand even short-term short circuits, while a lead battery is almost guaranteed to fail. At the same time, nickel hydroxide tends to go into other modifications, which leads to the appearance of such a factor as the “memory effect” – after interruptions in the discharge process or incomplete discharge, the battery capacity decreases, therefore, such batteries require a complete “additional discharge” first.
In addition to an increased resource, alkaline batteries have greater mechanical strength. While lead is a fairly soft and brittle material, and the case of lead batteries is made of polymer materials due to the aggressiveness of sulfuric acid, which makes it brittle and sensitive to shock and vibration, in alkaline batteries, the electrodes are installed in steel frames, and the cases are made from steel sheet.
After learning about both batteries, here are the advantages of both:
Acid Batteries:
- Have a higher rated voltage;
- Characterized by low self-discharge;
- Do not have a “memory effect”;
- Have a lower cost of all components;
- Simple structurally;
- Easy to operate.
Alkaline Batteries:
- Have higher specific energy characteristics (due to the lower weight of the components);
- Little sensitive to short circuits and over-current;
- Allow the possibility of storage in a discharged state;
- Have high mechanical strength and vibration resistance;
- Less sensitive to low temperatures.