14. Define the characteristics, which allow to compare electrochemical cells with each other.

At the heart of any power source, and battery is not that other, as the source current on a simple circuit: anode and cathode and between the electrolyte. Due to the different nature of the material of the anode and cathode when immersed in electrolyte a potential difference – the voltage which an electric current. Chemical current sources are its name because of the nature of power: the chemical energy of active substances is converted directly into electrical energy. They are divided into two groups – primary and secondary. In the primary power sources (batteries), the process proceeds irreversibly. Secondary power sources include batteries that can be recharged after they are exhausted itself. Different devices work with different voltage, so the battery it should be different. In addition, the voltage different types of batteries depends on the used electrolyte. For example, lithium batteries have a nominal voltage of 3 V, alkaline is 1.5 V. the capacity of the battery is calculated from the volume of active elements placed in the housing of the battery. However, calculated in this way capacity can not be used to determine the health of batteries and has a title of "design capacity". Actual capacity depends on many factors: level of charging; mode of use; ambient temperature; cut-off current (Voltage at which the device does not work even though saved battery life. For example, a battery which no longer works in the camera often continues working in hours or control panels).

Each cell batteries produces 1.5 volts TOKK that a little compared to the 220-volt household voltage' the mains. So the batteries are not dangerous for the consumer. Any battery, the voltage which is higher than 1.5 volts (e.g., 6 volts) is, in essence, a set of batteries connected in series at 1.5 volts. Exceptions are the rechargeable Nickel-cadmium batteries, the voltage which is charged only 1.2 volts. Electric battery power. The quantity of electricity in batteries is measured in ampere or milliampere-hours. If for example, the battery would be 1.0 ampere-hour and an electrical device in which it operates, requires a current of 200 milliamps (i.e., 0.2 ampere), the validity of the battery is calculated according to the following formula: = validity period (in hours)

In the example, this period will be five hours (1,0 : 0,2 = 5). Self-discharge is a consequence of the non-working state of the battery, which leads to capacity loss. The storage mode can occur for two reasons. First, it concerns a new product since the release of before using. Second, if you use the resource of batteries with sufficiently long intervals-breaks. The reason lies in the self-discharge of the battery of the instability of the electrode, contamination of the electrolyte. Usually, the normal shelf life of the battery loses about 30% of its initial capacity. The most severely discharged battery at the beginning of storage. Also the self discharge rate increases with increasing temperature.

15. Define the charge\discharge curves of the batteries. Give examples.

The Charge/Discharge Curve. The measured terminal voltage of any battery will vary as it is charged and discharged. The MPV (mid-point voltage) is the nominal voltage of the cell during charge or discharge. The maximum and minimum voltage excursion from the nominal value is an important design consideration: a "flatter" discharge curve means less voltage variation that the design must tolerate. When peak charged, the actual cell voltage will be higher than the MPV. When nearing the EODV (end of discharge voltage) point, the cell voltage will be less than the MPV. The EODV is sometimes referred to as the EOL (end of life) voltage by manufacturers.

.

Lead-Acid Batteries: Discharging. Connection of an electrical load allows electrons to flow from negative to positive terminals. This reduces the charge and the voltages at the electrodes. The chemical reactions are able to proceed, generating new electrons and generating the power that is converted to electrical form to drive the external electrical load. As the battery is discharged, the electrodes become coated with lead sulfate and the acid electrolyte becomes weaker. Charging. Connection of an electrical power source forces electrons to flow from positive to negative terminals. This increases the charge and the voltages at the electrodes The chemical reactions are driven in the reverse direction, converting electrical energy into stored chemical energy. As the battery is charged, the lead sulfate coating on the electrodes is removed, and the acid electrolyte becomes stronger.