18. Which batteries provide high discharge current, nickel cadmium or lithium? Give examples.
Discharge characteristics of accumulators in case of different current densities are defined by the features of accumulators influencing value of their internal resistance. To such features first of all thickness of electrodes and their structural characteristics, density of assembly of a packet of electrodes, thickness and structure of a separator, quantity of an electrolyte and separate parameters of construction of the accumulator belong. The modern cylindrical Ni-cds accumulators with rolled electrodes allow higher discharge currents: for some types of accumulators the maximum long-time current makes 7-10C.
Fig 1. The discharge characteristic of the nickel - cadmium accumulator. From a figure it is visible how essential factor of external influence on electrical characteristics of accumulators is ambient temperature. Capacity, which can be received from the accumulator in case of 20 °C, the greatest. It almost doesn't decrease also in case of discharge in case of more high temperature. But at a temperature below 0 °C bit capacity decreases, and the it is more, than more discharge current. All lithium accumulators are characterized by rather good safety. Loss of capacity at the expense of a self-discharge of 5-10% a year. The self-discharge of Li-ion of accumulators constitutes 4-6% for the first month, then - it is significantly less: in 12 months accumulators lose 10-20% of the stocked reservoir. Li-ion of accumulators several times has less loss of reservoir, than at nickel - cadmium accumulators, both in case of 20 °C, and in case of 40 °C. Resource-500-1000 of cycles.
19. Draw the diagram of the apparatus of a cylindrical lithium-ion battery.
A lithium-ion battery or Li-ion battery is a type of rechargeable battery in which lithium ions move from the negative electrode to the positive electrode during discharge and back when charging. Li-ion batteries use an intercalated lithium compound as one electrode material, compared to the metallic lithium used in a non-rechargeable lithium battery. The electrolyte, which allows for ionic movement, and the two electrodes are the constituent components of a lithium-ion battery cell.
They are one of the most popular types of rechargeable batteries for portable electronics, with a high energy density, tiny memory effect and low self-discharge.
20. Draw the diagram of the apparatus of a Lead batteries.
The first working sample was created by Gaston Plante (France) in 1859. The two lead sheets separated by separator linen, coiled and inserted into a jar of sulfuric acid. Current-producing half reaction: on the positive electrode(+) PbO2 + 3H+ + HSO4- +2e « PbSO4¯ + 2H2O; on the negative electrode(–) Pb + HSO4- « PbSO4¯ + H+ +2e; total current-producing reaction: discharge PbO2 + Pb + H2SO4 « 2 PbSO4 + 2H2O, EMF = 2.047 V at 250 ° C. When discharging spent sulfuric acid, the electrolyte is diluted with water. Electrodes formed on both the slightly soluble lead sulfate (II). Open circuit voltage and the discharge/charge curves: ( - ) Pb | H2SO4 | PbO2 (+).
The capacity is quite depending of the current and the temperature.
The main application area of these batteries is Accumulators for cars. Nominal voltage produced by such a battery is 2 volts. Single batteries are connected in series to obtain higher voltage values. For example to create car 12 V accumulator it is necessary to connect 6 batteries.
Advantages: reliability; durability; low production cost; the possibility of repeated recycling. Disadvantages: Lead - metal, dangerous for the environment; long charging process; low productivity at low temperature. Care and maintenance: Keep only in the charged state (Deep discharge of the lead battery is very harmful for him); Regularly topped up with distilled water. When corrosion of lead and recharging the water is decomposed. In recent years, issued sealed maintenance-free SA. The room in which the charge is made, should be well ventilated (releases toxic Stibine SbH3 and arsine AsH3).