The main performance indicators of lead-acid battery
The main results of lead-acid batteries are as follows :(1) batteries with unqualified safety performance indexes are unacceptable, among which the most important is explosion and leakage. Explosion and leakage are mainly related to internal pressure, structure, process design (such as the failure of safety valve) and improper operation that should be prohibited.
(2) rated capacity refers to the rated capacity of lead-acid battery. The rated capacity is the minimum quantity of electricity that should be released when the battery is under certain discharge conditions and under different working conditions. The discharge capacity of the battery is also different.
The specified discharge conditions of the battery are as follows:
1, lead acid battery discharge current. Generally speaking, the discharge rate is the time rate and current rate of the discharge current of the battery. Discharge time rate refers to the time between discharge voltage and termination voltage under certain discharge conditions. According to IEC standard, discharge rates are 20 hours, 10 hours, 5 hours, 3 hours, 2 hours, 1 hour, 0.5 hour, etc. The rated capacity of the battery is expressed as C, and the battery capacity varies with different discharge rates.
2. Discharge termination voltage. The terminal voltage is different under different discharge currents. With the discharge, the voltage of lead-acid battery decreases gradually. Used in 25 ℃ lowest voltage is called discharge termination voltage charging. Discharge termination voltage varies with discharge rate. At 10-hour rate discharge, most terminal voltages are 1.8v/single gate, and the terminal voltages at 2-hour rate are 1.75v/single gate. Below this voltage, although can release a little more power, but it is easy to form a charge capacity drop, so unless special circumstances, do not discharge to the terminal voltage.
3. Discharge temperature. Lead-acid batteries have small discharge capacity at low temperature and large discharge capacity at high temperature.
(4) The actual capacity of storage battery. The actual capacity of the battery reflects the actual storage capacity of the battery, which is expressed in Ah per unit. Similarly, the larger the ampere hours, the larger the capacity of the battery and the longer the distance of the electric bicycle. The actual capacity of lead-acid batteries will gradually decrease in the course of use. The national standard stipulates that qualified batteries are those whose actual capacity of new batteries is larger than the rated capacity. For example, the battery of electric bicycle in the market now discharges more than 2 hours at a constant current of 5A, which is equivalent to the continuous driving of electric bicycle for more than 2 hours on a flat road. The factors affecting the capacity of batteries are plate structure, charge-discharge current, temperature and density of electrolyte, among which charge-discharge current and temperature are the most important. If the charge-discharge current is too large, the active substances on the plate will change on the surface, and the capacity will be reduced a lot. The discharge current of the battery is different, and the discharge capacity is different. The larger the discharge current is, the smaller the discharge capacity is. For example, the commonly used current of electric bicycle is 5A. The battery with the nominal 10Ah discharge rate is 2 hours. If the discharge rate is 10 hours, it can reach 1212 hours. In this way, if the battery is nominated as 10Ah according to the 2-hour rate and 12Ah according to the 10-hour rate, the evaluation of the capacity of the battery depends not only on the nominal capacity of the battery, but also on the discharge rate of the battery. Electric bicycle batteries are often labeled 10Ah, and the same batteries can also be labeled 12Ah and 144h. For example, a 14Ah Xu tram can also be marked 17Ah. Some batteries are marked as 20Ah, the nominal value of battery capacity is large, but its capacity has not changed significantly.
(3) The internal resistance of internal resistance battery refers to the resistance of current flowing through the battery. The internal resistance of lead-acid battery is very small, so it needs special instrument to get more accurate results. Generally speaking, the internal resistance of the battery is the internal resistance of the charging state, that is, the internal resistance of the battery when it is full of electricity. Corresponding to this is the internal resistance in the discharge state, which is not stable. The greater the internal resistance of the battery, the more energy the battery consumes, and the lower its efficiency. The battery with large internal resistance heats up badly when charging, which makes the temperature of the battery rise sharply, and has great influence on the battery and charger. With the increase of the number of batteries used, the internal resistance of the batteries will increase in varying degrees due to the consumption of electrolyte and the decrease of chemical activity in the batteries, and the faster the batteries with worse quality will increase. The internal impedance of batteries will increase with the increase of discharge amount, especially at the end of discharge. The main reason is that lead sulfate, a bad conductor in the plate, and the proportion of electrolyte will decrease as the discharge proceeds, so it is necessary to charge immediately after discharge. If it is discharged continuously, lead sulfate will form stable white crystals (i.e. sulfurization phenomenon). Even if charged, the active material of the plate can not be restored to its original state, which will shorten the service life of the battery. 温度的下降将导致电解液流动性变差，极板收缩，化学变化迟缓，蓄电池内阻增加。 Starting from 30 C, if the temperature drops by 1 C, the capacity will decrease by about 1%, and the internal resistance will also increase. Therefore, in cold areas, when the temperature is below - 20 C, the capacity has dropped to 60%, and the internal resistance has increased. It is often felt that the battery power is insufficient. Excessive discharge is prone to occur in cold regions, while excessive charging often occurs in temperate regions. Therefore, in order to use accumulator well, we must grasp the rule of its use according to the local climate conditions and the actual situation. In order to increase the capacity of storage battery and prolong its service life, proper charging methods and proper use of charging equipment must be selected according to different conditions. The internal resistance of lead-acid batteries is smaller than that of nickel-hydrogen batteries and lithium-ion batteries. That is to say, when the capacity of lead-acid batteries decreases by 2/3, they can still provide a larger current, while the supply voltage is basically stable and the fluctuation is small. Nickel-hydrogen batteries and lithium-ion batteries are different. Taking 36V/9Ah lithium-ion batteries as an example, when the capacity is reduced to 1/3 of the original capacity and the current output is 12A, the voltage will fluctuate 4-5V, that is, 31V with current output, and nearly 35V without current output. In this way, in the application of electric bicycle, there will be unstable running, sometimes there will be output, sometimes there will be no output.
(4) Cyclic life cycle life refers to the number of repeated charges and discharges that a battery can experience. The life and capacity of lead-acid batteries are inversely proportional. Cyclic life is also closely related to charging and discharging conditions. Generally, the larger the charging current (the faster the charging speed), the shorter the cycle life. Life is an index to indicate the decay rate of battery capacity. With the deepening of use, the decay of battery capacity is inevitable. When the capacity decays to a specified value, the end of life can be determined. According to the newly established battery standard for electric bicycle, the life of the battery can be expressed by 70% charge-discharge cycles of a certain capacity, and the qualified bottom line is 350 cycles. Therefore, for users whose daily traffic distance is less than 30_, if motors, controllers, chargers, etc. are all good and the use method is correct, the shortest service time of a group of better batteries should be guaranteed for more than one year. Capacity and life are the main indicators to measure the performance of batteries. Capacity generally takes Ah as a unit, indicating the capacity of storage energy of batteries. For example, a battery with a nominal capacity of 122h must discharge at 6A, and the time to terminate voltage 3105V (36V) should be no less than 2h. When the battery is used in electric bicycle with a load of 75kg and a working current of about 4A, the discharging time should be more than 3H and the speed should be 20_per hour, the theoretical range of the battery will reach 50_. Considering the factors such as braking and starting on the way, the mileage of the electric bicycle with this kind of battery can reach 40-50_. Generally speaking, the greater the discharge current, the shorter the life of the battery; the deeper the discharge depth, the shorter the life of the battery. Lead-acid batteries can cope with a short period of high current discharge, when the discharge depth is not deep. When the discharge current is small, even if the discharge depth is slightly deeper, it has little effect on the life of the battery. Batteries are most afraid of continuous high current deep discharge. The factors affecting the life of lead-acid batteries are the internal factors of the plates, such as the composition, crystal form, porosity, plate size, grid material and structure, etc. They also depend on a series of external factors, such as discharge current density, electrolyte concentration and temperature, discharge depth, maintenance status and storage time.
Discharge depth. Discharge depth is when the discharge starts to stop, and 100% depth refers to the discharge capacity. The life of lead-acid batteries is greatly affected by the discharge depth. Deep recycling, which should be considered in design and modeling, will lead-acid batteries fail quickly. Because the positive active material lead dioxide itself is not strong in combination with each other, lead sulfate is produced when discharging and recovered to lead dioxide when charging. The molar volume of lead sulfate is larger than that of lead oxide, and the volume of active material expands when discharging. When 1mo1 lead oxide is converted to 1mo1 lead sulfate, the volume increases by 95%. In this way, repeated shrinkage and expansion will make the interaction between lead dioxide particles gradually relaxed and easy to fall off. If only 2220% of the active material of 1mo1 lead dioxide is discharged, the shrinkage and expansion process will be greatly reduced, and the binding force damage will be slowed down. Therefore, the deeper the discharge depth, the shorter the cycle life.
②Overcharging degree When overcharging, a large number of gases are released. At this time, the active substance of the cathode plate is impacted by gases, which will promote the active substance to fall off. In addition, the positive grid alloy also suffers from serious anodic oxidation and corrosion, so the service life of lead-acid batteries will be shortened when the batteries are overcharged.
(3) The influence of temperature. The life of lead-acid batteries increases with temperature. In the range of 10 ~35 C, the temperature increases by 1 C and increases by 5 to 6 cycles; in the range of 35 ~45 C, the temperature increases by 1 C, the service life can be prolonged by more than 25 cycles; when the temperature is higher than 50 the service life is shortened The life of the battery increases with the increase of temperature in a certain temperature range, because the capacity increases with the increase of temperature. If the discharge capacity remains unchanged, the discharge depth decreases and the service life prolongs as the temperature rises.
(4) The influence of sulfuric acid concentration. The increase of sulfuric acid concentration is beneficial to the capacity of positive plate, but the self-discharge of lead-acid batteries accelerates the corrosion of grid, and also promotes the loose shedding of lead dioxide. With the increase of sulfuric acid concentration in the battery, the cycle life will be shortened.
_The influence of discharge current density. With the increase of discharge current density, the life of lead-acid batteries will be shortened, because the positive lead dioxide is easy to loose and fall off under the conditions of high current density and high sulfuric acid concentration.
